WorldWideScience

Sample records for atomic layer epitaxy

  1. Photoenhanced atomic layer epitaxy. Hikari reiki genshiso epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Mashita, M.; Kawakyu, Y. (Toshiba corp., Tokyo (Japan))

    1991-10-01

    The growth temperature range was greatly expanded of atomic layer epitaxy (ALE) expected as the growth process of ultra-thin stacks. Ga layers and As layers were formed one after the other on a GaAs substrate in the atmosphere of trimethylgallium (TMG) or AsH{sub 2} supplied alternately, by KrF excimer laser irradiation normal to the substrate. As a result, the growth temperature range was 460-540{degree}C nearly 10 times that of 500 {plus minus} several degrees centigrade in conventional thermal growth method. Based on the experimental result where light absorption of source molecules adsorbed on a substrate surface was larger than that under gaseous phase condition, new adsorbed layer enhancement model was proposed to explain above irradiation effect verifying it by experiments. As this photoenhancement technique is applied to other materials, possible fabrication of new crystal structures as a super lattice with ultra-thin stacks of single atomic layers is expected because of a larger freedom in material combination for hetero-ALE. 11 refs., 7 figs.

  2. Atomic layer epitaxy of 3-5 compounds

    Science.gov (United States)

    Dapkus, P. D.; Wittig, C.; Allen, S.

    1986-08-01

    This program is intended to develop a process for the growth of GaAs and related compounds by Atomic Layer Epitaxy (ALE). The program involves fundamental studies of gas phase kinetics of the organometallic and hydrides to be used in the process as well as surface reaction studies to determine the surface of various organometallics. We have chosen in this program to effect ALE growth in a dense H2 atmosphere. We believe that the reactivity of H2 is important to the removal, by hydrogenation, of the alkyl radicals from the growing surface. To better understand the process we are pursuing fundamental information in two areas. First, basic measurements of the reactivity band reaction products of organometallics and hydrides and of photogenerated species with compound semiconductor surfaces are being undertaken that will determine the feasibility of using photoactivation and in thermal catalytic reactions in the gas phase to accomplish ALE. Second, epitaxial growth experiments are being performed to determine the feasibility of an ALE process employing photodecomposition of surface absorbed species as well as thermal catalytic reactions.

  3. Low-temperature atomic layer epitaxy of AlN ultrathin films by layer-by-layer, in-situ atomic layer annealing.

    Science.gov (United States)

    Shih, Huan-Yu; Lee, Wei-Hao; Kao, Wei-Chung; Chuang, Yung-Chuan; Lin, Ray-Ming; Lin, Hsin-Chih; Shiojiri, Makoto; Chen, Miin-Jang

    2017-01-03

    Low-temperature epitaxial growth of AlN ultrathin films was realized by atomic layer deposition (ALD) together with the layer-by-layer, in-situ atomic layer annealing (ALA), instead of a high growth temperature which is needed in conventional epitaxial growth techniques. By applying the ALA with the Ar plasma treatment in each ALD cycle, the AlN thin film was converted dramatically from the amorphous phase to a single-crystalline epitaxial layer, at a low deposition temperature of 300 °C. The energy transferred from plasma not only provides the crystallization energy but also enhances the migration of adatoms and the removal of ligands, which significantly improve the crystallinity of the epitaxial layer. The X-ray diffraction reveals that the full width at half-maximum of the AlN (0002) rocking curve is only 144 arcsec in the AlN ultrathin epilayer with a thickness of only a few tens of nm. The high-resolution transmission electron microscopy also indicates the high-quality single-crystal hexagonal phase of the AlN epitaxial layer on the sapphire substrate. The result opens a window for further extension of the ALD applications from amorphous thin films to the high-quality low-temperature atomic layer epitaxy, which can be exploited in a variety of fields and applications in the near future.

  4. Deposition of O atomic layers on Si(100) substrates for epitaxial Si-O superlattices: investigation of the surface chemistry

    Energy Technology Data Exchange (ETDEWEB)

    Jayachandran, Suseendran, E-mail: suseendran.jayachandran@imec.be [KU Leuven, Department of Metallurgy and Materials, Castle Arenberg 44, B-3001 Leuven (Belgium); IMEC, Kapeldreef 75, 3001 Leuven (Belgium); Delabie, Annelies; Billen, Arne [KU Leuven, Department of Chemistry, Celestijnenlaan 200F, B-3001 Leuven (Belgium); IMEC, Kapeldreef 75, 3001 Leuven (Belgium); Dekkers, Harold; Douhard, Bastien; Conard, Thierry; Meersschaut, Johan; Caymax, Matty [IMEC, Kapeldreef 75, 3001 Leuven (Belgium); Vandervorst, Wilfried [KU Leuven, Department of Physics and Astronomy, Celestijnenlaan 200D, B-3001 Leuven (Belgium); IMEC, Kapeldreef 75, 3001 Leuven (Belgium); Heyns, Marc [KU Leuven, Department of Metallurgy and Materials, Castle Arenberg 44, B-3001 Leuven (Belgium); IMEC, Kapeldreef 75, 3001 Leuven (Belgium)

    2015-01-01

    Highlights: • Atomic layer is deposited by O{sub 3} chemisorption reaction on H-terminated Si(100). • O-content has critical impact on the epitaxial thickness of the above-deposited Si. • Oxygen atoms at dimer/back bond configurations enable epitaxial Si on O atomic layer. • Oxygen atoms at hydroxyl and more back bonds, disable epitaxial Si on O atomic layer. - Abstract: Epitaxial Si-O superlattices consist of alternating periods of crystalline Si layers and atomic layers of oxygen (O) with interesting electronic and optical properties. To understand the fundamentals of Si epitaxy on O atomic layers, we investigate the O surface species that can allow epitaxial Si chemical vapor deposition using silane. The surface reaction of ozone on H-terminated Si(100) is used for the O deposition. The oxygen content is controlled precisely at and near the atomic layer level and has a critical impact on the subsequent Si deposition. There exists only a small window of O-contents, i.e. 0.7–0.9 atomic layers, for which the epitaxial deposition of Si can be realized. At these low O-contents, the O atoms are incorporated in the Si-Si dimers or back bonds (-OSiH), with the surface Si atoms mainly in the 1+ oxidation state, as indicated by infrared spectroscopy. This surface enables epitaxial seeding of Si. For O-contents higher than one atomic layer, the additional O atoms are incorporated in the Si-Si back bonds as well as in the Si-H bonds, where hydroxyl groups (-Si-OH) are created. In this case, the Si deposition thereon becomes completely amorphous.

  5. Growth mechanisms for Si epitaxy on O atomic layers: Impact of O-content and surface structure

    Science.gov (United States)

    Jayachandran, Suseendran; Billen, Arne; Douhard, Bastien; Conard, Thierry; Meersschaut, Johan; Moussa, Alain; Caymax, Matty; Bender, Hugo; Vandervorst, Wilfried; Heyns, Marc; Delabie, Annelies

    2016-10-01

    The epitaxial growth of Si layers on Si substrates in the presence of O atoms is generally considered a challenge, as O atoms degrade the epitaxial quality by generating defects. Here, we investigate the growth mechanisms for Si epitaxy on O atomic layers (ALs) with different O-contents and structures. O ALs are deposited by ozone (O3) or oxygen (O2) exposure on H-terminated Si at 50 °C and 300 °C respectively. Epitaxial Si is deposited by chemical vapor deposition using silane (SiH4) at 500 °C. After O3 exposure, the O atoms are uniformly distributed in Si-Si dimer/back bonds. This O layer still allows epitaxial seeding of Si. The epitaxial quality is enhanced by lowering the surface distortions due to O atoms and by decreasing the arrival rate of SiH4 reactants, allowing more time for surface diffusion. After O2 exposure, the O atoms are present in the form of SiOx clusters. Regions of hydrogen-terminated Si remain present between the SiOx clusters. The epitaxial seeding of Si in these structures is realized on H-Si regions, and an epitaxial layer grows by a lateral overgrowth mechanism. A breakdown in the epitaxial ordering occurs at a critical Si thickness, presumably by accumulation of surface roughness.

  6. Atomic layer epitaxy of hematite on indium tin oxide for application in solar energy conversion

    Energy Technology Data Exchange (ETDEWEB)

    Martinson, Alex B.; Riha, Shannon; Guo, Peijun; Emery, Jonathan D.

    2016-07-12

    A method to provide an article of manufacture of iron oxide on indium tin oxide for solar energy conversion. An atomic layer epitaxy method is used to deposit an uncommon bixbytite-phase iron (III) oxide (.beta.-Fe.sub.2O.sub.3) which is deposited at low temperatures to provide 99% phase pure .beta.-Fe.sub.2O.sub.3 thin films on indium tin oxide. Subsequent annealing produces pure .alpha.-Fe.sub.2O.sub.3 with well-defined epitaxy via a topotactic transition. These highly crystalline films in the ultra thin film limit enable high efficiency photoelectrochemical chemical water splitting.

  7. Atomic layer deposition of epitaxial layers of anatase on strontium titanate single crystals: Morphological and photoelectrochemical characterization

    Energy Technology Data Exchange (ETDEWEB)

    Kraus, Theodore J.; Nepomnyashchii, Alexander B.; Parkinson, B. A., E-mail: bparkin1@uwyo.edu [Department of Chemistry, School of Energy Resources, University of Wyoming, Laramie, Wyoming 82071 (United States)

    2015-01-15

    Atomic layer deposition was used to grow epitaxial layers of anatase (001) TiO{sub 2} on the surface of SrTiO{sub 3} (100) crystals with a 3% lattice mismatch. The epilayers grow as anatase (001) as confirmed by x-ray diffraction. Atomic force microscope images of deposited films showed epitaxial layer-by-layer growth up to about 10 nm, whereas thicker films, of up to 32 nm, revealed the formation of 2–5 nm anatase nanocrystallites oriented in the (001) direction. The anatase epilayers were used as substrates for dye sensitization. The as received strontium titanate crystal was not sensitized with a ruthenium-based dye (N3) or a thiacyanine dye (G15); however, photocurrent from excited state electron injection from these dyes was observed when adsorbed on the anatase epilayers. These results show that highly ordered anatase surfaces can be grown on an easily obtained substrate crystal.

  8. Growth mechanisms for Si epitaxy on O atomic layers: Impact of O-content and surface structure

    Energy Technology Data Exchange (ETDEWEB)

    Jayachandran, Suseendran, E-mail: suseendran.jayachandran@imec.be [Imec, Kapeldreef 75, 3001 Leuven (Belgium); KU Leuven (University of Leuven), Department of Metallurgy and Materials, Castle Arenberg 44, B-3001 Leuven (Belgium); Billen, Arne [Imec, Kapeldreef 75, 3001 Leuven (Belgium); KU Leuven (University of Leuven), Department of Chemistry, Celestijnenlaan 200F, B-3001 Leuven (Belgium); Douhard, Bastien; Conard, Thierry; Meersschaut, Johan; Moussa, Alain; Caymax, Matty; Bender, Hugo [Imec, Kapeldreef 75, 3001 Leuven (Belgium); Vandervorst, Wilfried [Imec, Kapeldreef 75, 3001 Leuven (Belgium); KU Leuven (University of Leuven), Department of Physics and Astronomy, Celestijnenlaan 200D, B-3001 Leuven (Belgium); Heyns, Marc [Imec, Kapeldreef 75, 3001 Leuven (Belgium); KU Leuven (University of Leuven), Department of Metallurgy and Materials, Castle Arenberg 44, B-3001 Leuven (Belgium); Delabie, Annelies [Imec, Kapeldreef 75, 3001 Leuven (Belgium); KU Leuven (University of Leuven), Department of Chemistry, Celestijnenlaan 200F, B-3001 Leuven (Belgium)

    2016-10-30

    Highlights: • O{sub 3} or O{sub 2} exposures on H-Si(100) result in O ALs with different surface structures. • Si-EPI on O AL using O{sub 3} process is by direct epitaxial growth mechanism. • Si-EPI on O AL using O{sub 2} process is by epitaxial lateral overgrowth mechanism. • Distortions by O AL, SiH{sub 4} flux rate and Si thickness has an impact on Si-EPI quality. - Abstract: The epitaxial growth of Si layers on Si substrates in the presence of O atoms is generally considered a challenge, as O atoms degrade the epitaxial quality by generating defects. Here, we investigate the growth mechanisms for Si epitaxy on O atomic layers (ALs) with different O-contents and structures. O ALs are deposited by ozone (O{sub 3}) or oxygen (O{sub 2}) exposure on H-terminated Si at 50 °C and 300 °C respectively. Epitaxial Si is deposited by chemical vapor deposition using silane (SiH{sub 4}) at 500 °C. After O{sub 3} exposure, the O atoms are uniformly distributed in Si-Si dimer/back bonds. This O layer still allows epitaxial seeding of Si. The epitaxial quality is enhanced by lowering the surface distortions due to O atoms and by decreasing the arrival rate of SiH{sub 4} reactants, allowing more time for surface diffusion. After O{sub 2} exposure, the O atoms are present in the form of SiO{sub x} clusters. Regions of hydrogen-terminated Si remain present between the SiO{sub x} clusters. The epitaxial seeding of Si in these structures is realized on H-Si regions, and an epitaxial layer grows by a lateral overgrowth mechanism. A breakdown in the epitaxial ordering occurs at a critical Si thickness, presumably by accumulation of surface roughness.

  9. Atomic layer deposition of perovskite oxides and their epitaxial integration with Si, Ge, and other semiconductors

    Science.gov (United States)

    McDaniel, Martin D.; Ngo, Thong Q.; Hu, Shen; Posadas, Agham; Demkov, Alexander A.; Ekerdt, John G.

    2015-12-01

    Atomic layer deposition (ALD) is a proven technique for the conformal deposition of oxide thin films with nanoscale thickness control. Most successful industrial applications have been with binary oxides, such as Al2O3 and HfO2. However, there has been much effort to deposit ternary oxides, such as perovskites (ABO3), with desirable properties for advanced thin film applications. Distinct challenges are presented by the deposition of multi-component oxides using ALD. This review is intended to highlight the research of the many groups that have deposited perovskite oxides by ALD methods. Several commonalities between the studies are discussed. Special emphasis is put on precursor selection, deposition temperatures, and specific property performance (high-k, ferroelectric, ferromagnetic, etc.). Finally, the monolithic integration of perovskite oxides with semiconductors by ALD is reviewed. High-quality epitaxial growth of oxide thin films has traditionally been limited to physical vapor deposition techniques (e.g., molecular beam epitaxy). However, recent studies have demonstrated that epitaxial oxide thin films may be deposited on semiconductor substrates using ALD. This presents an exciting opportunity to integrate functional perovskite oxides for advanced semiconductor applications in a process that is economical and scalable.

  10. Atomic layer deposition of perovskite oxides and their epitaxial integration with Si, Ge, and other semiconductors

    Energy Technology Data Exchange (ETDEWEB)

    McDaniel, Martin D.; Ngo, Thong Q.; Hu, Shen; Ekerdt, John G., E-mail: ekerdt@utexas.edu [Department of Chemical Engineering, The University of Texas at Austin, Austin, Texas 78712 (United States); Posadas, Agham; Demkov, Alexander A. [Department of Physics, The University of Texas at Austin, Austin, Texas 78712 (United States)

    2015-12-15

    Atomic layer deposition (ALD) is a proven technique for the conformal deposition of oxide thin films with nanoscale thickness control. Most successful industrial applications have been with binary oxides, such as Al{sub 2}O{sub 3} and HfO{sub 2}. However, there has been much effort to deposit ternary oxides, such as perovskites (ABO{sub 3}), with desirable properties for advanced thin film applications. Distinct challenges are presented by the deposition of multi-component oxides using ALD. This review is intended to highlight the research of the many groups that have deposited perovskite oxides by ALD methods. Several commonalities between the studies are discussed. Special emphasis is put on precursor selection, deposition temperatures, and specific property performance (high-k, ferroelectric, ferromagnetic, etc.). Finally, the monolithic integration of perovskite oxides with semiconductors by ALD is reviewed. High-quality epitaxial growth of oxide thin films has traditionally been limited to physical vapor deposition techniques (e.g., molecular beam epitaxy). However, recent studies have demonstrated that epitaxial oxide thin films may be deposited on semiconductor substrates using ALD. This presents an exciting opportunity to integrate functional perovskite oxides for advanced semiconductor applications in a process that is economical and scalable.

  11. Atomic layer deposition of metastable β-Fe₂O₃ via isomorphic epitaxy for photoassisted water oxidation.

    Science.gov (United States)

    Emery, Jonathan D; Schlepütz, Christian M; Guo, Peijun; Riha, Shannon C; Chang, Robert P H; Martinson, Alex B F

    2014-12-24

    We report the growth and photoelectrochemical (PEC) characterization of the uncommon bibyite phase of iron(III) oxide (β-Fe2O3) epitaxially stabilized via atomic layer deposition on an conductive, transparent, and isomorphic template (Sn-doped In2O3). As a photoanode, unoptimized β-Fe2O3 ultrathin films perform similarly to their ubiquitous α-phase (hematite) counterpart, but reveal a more ideal bandgap (1.8 eV), a ∼0.1 V improved photocurrent onset potential, and longer wavelength (>600 nm) spectral response. Stable operation under basic water oxidation justifies further exploration of this atypical phase and motivates the investigation of other unexplored metastable phases as new PEC materials.

  12. Electrochemical removal of hydrogen atoms in Mg-doped GaN epitaxial layers

    Energy Technology Data Exchange (ETDEWEB)

    Lee, June Key, E-mail: junekey@jnu.ac.kr, E-mail: hskim7@jbnu.ac.kr; Hyeon, Gil Yong; Tawfik, Wael Z.; Choi, Hee Seok [Department of Materials Science and Engineering, and Optoelectronics Convergence Research Center, Chonnam National University, Gwangju 500-757 (Korea, Republic of); Ryu, Sang-Wan [Department of Physics and Optoelectronics Convergence Research Center, Chonnam National University, Gwangju 500-757 (Korea, Republic of); Jeong, Tak [Korea Photonics Technology Institute, Gwangju 500-460 (Korea, Republic of); Jung, Eunjin; Kim, Hyunsoo, E-mail: junekey@jnu.ac.kr, E-mail: hskim7@jbnu.ac.kr [School of Semiconductor and Chemical Engineering, Semiconductor Physics Research Center, Chonbuk National University, Jeonju 561-756 (Korea, Republic of)

    2015-05-14

    Hydrogen atoms inside of an Mg-doped GaN epitaxial layer were effectively removed by the electrochemical potentiostatic activation (EPA) method. The role of hydrogen was investigated in terms of the device performance of light-emitting diodes (LEDs). The effect of the main process parameters for EPA such as solution type, voltage, and time was studied and optimized for application to LED fabrication. In optimized conditions, the light output of 385-nm LEDs was improved by about 26% at 30 mA, which was caused by the reduction of the hydrogen concentration by ∼35%. Further removal of hydrogen seems to be involved in the breaking of Ga-H bonds that passivate the nitrogen vacancies. An EPA process with high voltage breaks not only Mg-H bonds that generate hole carriers but also Ga-H bonds that generate electron carriers, thus causing compensation that impedes the practical increase of hole concentration, regardless of the drastic removal of hydrogen atoms. A decrease in hydrogen concentration affects the current-voltage characteristics, reducing the reverse current by about one order and altering the forward current behavior in the low voltage region.

  13. Growth and characterization of III-N ternary thin films by plasma assisted atomic layer epitaxy at low temperatures

    Energy Technology Data Exchange (ETDEWEB)

    Nepal, Neeraj; Anderson, Virginia R.; Hite, Jennifer K.; Eddy, Charles R.

    2015-08-31

    We report the growth and characterization of III-nitride ternary thin films (Al{sub x}Ga{sub 1−x}N, In{sub x}Al{sub 1−x}N and In{sub x}Ga{sub 1−x}N) at ≤ 500 °C by plasma assisted atomic layer epitaxy (PA-ALE) over a wide stoichiometric range including the range where phase separation has been an issue for films grown by molecular beam epitaxy and metal organic chemical vapor deposition. The composition of these ternaries was intentionally varied through alterations in the cycle ratios of the III-nitride binary layers (AlN, GaN, and InN). By this digital alloy growth method, we are able to grow III-nitride ternaries by PA-ALE over nearly the entire stoichiometry range including in the spinodal decomposition region (x = 15–85%). These early efforts suggest great promise of PA-ALE at low temperatures for addressing miscibility gap challenges encountered with conventional growth methods and realizing high performance optoelectronic and electronic devices involving ternary/binary heterojunctions, which are not currently possible. - Highlights: • III-N ternaries grown at ≤ 500 °C by plasma assisted atomic layer epitaxy • Growth of InGaN and AlInN in the spinodal decomposition region (15–85%) • Epitaxial, smooth and uniform III-N film growth at low temperatures.

  14. Epitaxial growth of zinc oxide by the method of atomic layer deposition on SiC/Si substrates

    Science.gov (United States)

    Kukushkin, S. A.; Osipov, A. V.; Romanychev, A. I.

    2016-07-01

    For the first time, zinc oxide epitaxial films on silicon were grown by the method of atomic layer deposition at a temperature T = 250°C. In order to avoid a chemical reaction between silicon and zinc oxide (at the growth temperature, the rate constant of the reaction is of the order of 1022), a high-quality silicon carbide buffer layer with a thickness of ~50 nm was preliminarily synthesized by the chemical substitution of atoms on the silicon surface. The zinc oxide films were grown on n- and p-type Si(100) wafers. The ellipsometric, Raman, electron diffraction, and trace element analyses showed that the ZnO films are epitaxial.

  15. Determination of the types and densities of dislocations in GaN epitaxial layers of different thicknesses by optical and atomic force microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Kravchuk, K. S. [Moscow State Institute of Steel and Alloys (Russian Federation); Mezhennyi, M. V. [Institute of Chemical Problems for Microelectronics (Russian Federation); Yugova, T. G., E-mail: p_Yugov@mail.ru [Institute of Rare Metals (Russian Federation)

    2012-03-15

    The change in the dislocation density on the surface of GaN epitaxial layers, which were grown by hydride vapor-phase epitaxy on sapphire substrates with c and r orientations, has been investigated by optical and atomic force microscopy (AFM). It is shown that the observed decrease in the density of threading dislocations with an increase in the layer thickness is related to the annihilation of mixed dislocations. The experimental and theoretical data on the change in the density of mixed dislocations with an increase in the epitaxial-layer thickness are in good correspondence.

  16. Growth of bismuth telluride thin film on Pt by electrochemical atomic layer epitaxy

    Institute of Scientific and Technical Information of China (English)

    ZHU Wen; YANG Jun-you; GAO Xian-hui; HOU Jie; ZHANG Tong-jun; CUI Kun

    2005-01-01

    An automated thin-layer flow cell electrodeposition system was developed for growing Bi2 Te3 thin film by ECALE. The dependence of the Bi and Te deposition potentials on Pt electrode was studied. In the first attempt,this reductive Te underpotential deposition (UPD)/reductive Bi UPD cycle was performed to 100 layers. A better linearity of the stripping charge with the number of cycles has been shown and confirmed a layer-by-layer growth mode, which is consistent with an epitaxial growth. The 4: 3 stoichiometric ratio of Bi to Te suggests that the incomplete charge transfer in HTeO2+ reduction excludes the possibility of Bi2 Te3 formation. X-ray photoelectron spectroscopy (XPS) analysis also reveals that the incomplete charge transfer in HTeO2+ occurs in Te direct deposition. The effective way of depositing Bi2 Te3 on Pt consists in oxidative Te UPD and reductive Bi UPD. The thin film deposited by this procedure was characterized by X-ray diffraction(XRD), scanning electron microscopy(SEM) and X-ray photoelectron spectroscopy(XPS). A polycrystalline characteristic was confirmed by XRD. The 2 : 3 stoichiometric ratio was confirmed by XPS. The SEM image indicates that the deposit looks like a series of buttons about 0.3 - 0.4 μm in diameter, which is corresponding with calculated thickness of the epitaxial film. This suggests that the particle growth appears to be linear with the number of cycles, as it is consistent with a layer by layer growth mode.

  17. Epitaxial TiO 2/SnO 2 core-shell heterostructure by atomic layer deposition

    KAUST Repository

    Nie, Anmin

    2012-01-01

    Taking TiO 2/SnO 2 core-shell nanowires (NWs) as a model system, we systematically investigate the structure and the morphological evolution of this heterostructure synthesized by atomic layer deposition/epitaxy (ALD/ALE). All characterizations, by X-ray diffraction, high-resolution transmission electron microscopy, selected area electron diffraction and Raman spectra, reveal that single crystalline rutile TiO 2 shells can be epitaxially grown on SnO 2 NWs with an atomically sharp interface at low temperature (250 °C). The growth behavior of the TiO 2 shells highly depends on the surface orientations and the geometrical shape of the core SnO 2 NW cross-section. Atomically smooth surfaces are found for growth on the {110} surface. Rough surfaces develop on {100} surfaces due to (100) - (1 × 3) reconstruction, by introducing steps in the [010] direction as a continuation of {110} facets. Lattice mismatch induces superlattice structures in the TiO 2 shell and misfit dislocations along the interface. Conformal epitaxial growth has been observed for SnO 2 NW cores with an octagonal cross-section ({100} and {110} surfaces). However, for a rectangular core ({101} and {010} surfaces), the shell also derives an octagonal shape from the epitaxial growth, which was explained by a proposed model based on ALD kinetics. The surface steps and defects induced by the lattice mismatch likely lead to improved photoluminescence (PL) performance for the yellow emission. Compared to the pure SnO 2 NWs, the PL spectrum of the core-shell nanostructures exhibits a stronger emission peak, which suggests potential applications in optoelectronics. © The Royal Society of Chemistry 2012.

  18. Atomic Layer Epitaxy of h-BN(0001) Multilayers on Co(0001) and Molecular Beam Epitaxy Growth of Graphene on h-BN(0001)/Co(0001).

    Science.gov (United States)

    Driver, M Sky; Beatty, John D; Olanipekun, Opeyemi; Reid, Kimberly; Rath, Ashutosh; Voyles, Paul M; Kelber, Jeffry A

    2016-03-22

    The direct growth of hexagonal boron nitride (h-BN) by industrially scalable methods is of broad interest for spintronic and nanoelectronic device applications. Such applications often require atomically precise control of film thickness and azimuthal registry between layers and substrate. We report the formation, by atomic layer epitaxy (ALE), of multilayer h-BN(0001) films (up to 7 monolayers) on Co(0001). The ALE process employs BCl3/NH3 cycles at 600 K substrate temperature. X-ray photoelectron spectroscopy (XPS) and low energy electron diffraction (LEED) data show that this process yields an increase in h-BN average film thickness linearly proportional to the number of BCl3/NH3 cycles, with BN layers in azimuthal registry with each other and with the Co(0001) substrate. LEED diffraction spot profile data indicate an average BN domain size of at least 1900 Å. Optical microscopy data indicate the presence of some domains as large as ∼20 μm. Transmission electron microscopy (TEM) and ambient exposure studies demonstrate macroscopic and microscopic continuity of the h-BN film, with the h-BN film highly conformal to the Co substrate. Photoemission data show that the h-BN(0001) film is p-type, with band bending near the Co/h-BN interface. Growth of graphene by molecular beam epitaxy (MBE) is observed on the surface of multilayer h-BN(0001) at temperatures of 800 K. LEED data indicate azimuthal graphene alignment with the h-BN and Co(0001) lattices, with domain size similar to BN. The evidence of multilayer BN and graphene azimuthal alignment with the lattice of the Co(0001) substrate demonstrates that this procedure is suitable for scalable production of heterojunctions for spintronic applications.

  19. Photo-irradiation effects on GaAs atomic layer epitaxial growth. GaAs no genshiso epitaxial seicho ni okeru hikari reiki koka

    Energy Technology Data Exchange (ETDEWEB)

    Mashita, M.; Kawakyu, Y.; Sasaki, M.; Ishikawa, H. (Toshiba Corp., Kawasaki (Japan). Research and Development Center)

    1990-08-10

    Single atomic layer epitaxy (ALE) aims at controlling a growing film at a precision of single molecular layer. In this article, it is reported that the growth temperature range of ALE was expanded by the vertical irradiation of KrF exima laser (248 nm) onto the substrate for the ALE growth of GaAs using the metalorganic chemical vapor deposition (MOCVD) method. Thanks for the results of the above experiment, it was demonstrated that the irradiation effect was not thermal, but photochemical. In addition, this article studies the possibility of adsorption layer irradiation and surface irradiation as the photo-irradiation mechanism, and points out that coexistence of both irradiation mechanisms can be considered and, in case of exima laser, strong possibility of direct irradiation of the adsorption layer because of its high power density. Hereinafter, by using both optical growth ALE and thermal growth ALE jointly, the degree of freedom of combination of hetero ALE increases and its application to various material systems becomes possible. 16 refs., 6 figs.

  20. Surface structure and surface kinetics of InN grown by plasma-assisted atomic layer epitaxy: A HREELS study

    Energy Technology Data Exchange (ETDEWEB)

    Acharya, Ananta R., E-mail: aacharya@georgiasouthern.edu, E-mail: anantaach@gmail.com [Department of Physics, Georgia Southern University, Statesboro, Georgia 30460 (United States); Thoms, Brian D. [Department of Physics and Astronomy, Georgia State University, Atlanta, Georgia 30303 (United States); Nepal, Neeraj [American Association for Engineering Education, 1818 N Street NW, Washington, DC 20034 (United States); Eddy, Charles R. [Electronics Science and Technology Division, U.S. Naval Research Laboratory, 4555 Overlook Avenue SW, Washington, DC 20375 (United States)

    2015-03-15

    The surface bonding configuration and kinetics of hydrogen desorption from InN grown by plasma-assisted atomic layer epitaxy have been investigated. High resolution electron energy loss spectra exhibited loss peaks assigned to a Fuchs–Kliewer surface phonon, N-N and N-H surface species. The surface N-N vibrations are attributed to surface defects. The observation of N-H but no In-H surface species suggested N-terminated InN. Isothermal desorption data were best fit by the first-order desorption kinetics with an activation energy of (0.88 ± 0.06) eV and pre-exponential factor of (1.5 ± 0.5) × 10{sup 5 }s{sup −1}.

  1. Growth of nitrogen-doped p-type ZnO thin films prepared by atomic layer epitaxy

    Institute of Scientific and Technical Information of China (English)

    LEE Chongmu; LIM Jongmin; PARK Suyoung; KIM Hyounwoo

    2006-01-01

    Nitrogen-doped, p-type ZnO thin films were grown successfully on sapphire (0001) substrates by using atomic layer epitaxy (ALE). Zn(C2H5)2[Diethylzinc,DEZn], H2O and NH3 were used as a zinc precursor, an oxidant and a doping source gas, respectively. The lowest electrical resistivity of the p-type ZnO films grown by ALE and annealed at 1000 ℃ in an oxygen atmosphere for 1 h was 18.3 Ω·m with a hole concentration of 3.71×1017cm-3 . Low temperature-photoluminescence analysis and time-dependent Hall measurement results support that the nitrogen-doped ZnO after annealing is ap-type semiconductor.

  2. Epitaxial Growth of Perovskite Strontium Titanate on Germanium via Atomic Layer Deposition.

    Science.gov (United States)

    Lin, Edward L; Edmondson, Bryce I; Hu, Shen; Ekerdt, John G

    2016-07-26

    Atomic layer deposition (ALD) is a commercially utilized deposition method for electronic materials. ALD growth of thin films offers thickness control and conformality by taking advantage of self-limiting reactions between vapor-phase precursors and the growing film. Perovskite oxides present potential for next-generation electronic materials, but to-date have mostly been deposited by physical methods. This work outlines a method for depositing SrTiO3 (STO) on germanium using ALD. Germanium has higher carrier mobilities than silicon and therefore offers an alternative semiconductor material with faster device operation. This method takes advantage of the instability of germanium's native oxide by using thermal deoxidation to clean and reconstruct the Ge (001) surface to the 2×1 structure. 2-nm thick, amorphous STO is then deposited by ALD. The STO film is annealed under ultra-high vacuum and crystallizes on the reconstructed Ge surface. Reflection high-energy electron diffraction (RHEED) is used during this annealing step to monitor the STO crystallization. The thin, crystalline layer of STO acts as a template for subsequent growth of STO that is crystalline as-grown, as confirmed by RHEED. In situ X-ray photoelectron spectroscopy is used to verify film stoichiometry before and after the annealing step, as well as after subsequent STO growth. This procedure provides framework for additional perovskite oxides to be deposited on semiconductors via chemical methods in addition to the integration of more sophisticated heterostructures already achievable by physical methods.

  3. Single-Crystal Y2O3 Epitaxially on GaAs(001 and (111 Using Atomic Layer Deposition

    Directory of Open Access Journals (Sweden)

    Y. H. Lin

    2015-10-01

    Full Text Available Single-crystal atomic-layer-deposited (ALD Y\\(_{\\mathrm{2}}\\O\\(_{\\mathrm{3}}\\ films 2 nm thick were epitaxially grown on molecular beam epitaxy (MBE GaAs(001-4 \\(\\times\\ 6 and GaAs(111A-2 \\(\\times\\ 2 reconstructed surfaces. The in-plane epitaxy between the ALD-oxide films and GaAs was observed using \\textit{in-situ} reflection high-energy electron diffraction in our uniquely designed MBE/ALD multi-chamber system. More detailed studies on the crystallography of the hetero-structures were carried out using high-resolution synchrotron radiation X-ray diffraction. When deposited on GaAs(001, the Y\\(_{\\mathrm{2}}\\O\\(_{\\mathrm{3}}\\ films are of a cubic phase and have (110 as the film normal, with the orientation relationship being determined: Y\\(_{\\mathrm{2}}\\O\\(_{\\mathrm{3}}\\(\\(110\\[\\(001\\][\\(\\overline{1}10\\]//GaAs(\\(001\\[\\(110\\][\\(1\\overline{1}0\\]. On GaAs(\\(111\\A, the Y\\(_{\\mathrm{2}}\\O\\(_{\\mathrm{3}}\\ films are also of a cubic phase with (\\(111\\ as the film normal, having the orientation relationship of Y\\(_{\\mathrm{2}}\\O\\(_{\\mathrm{3}}\\(\\(111\\[\\(2\\overline{1}\\overline{1}\\] [\\(01\\overline{1}\\]//GaAs (\\(111\\ [\\(\\overline{2}11\\][\\(0\\overline{1}1\\]. The relevant orientation for the present/future integrated circuit platform is (\\(001\\. The ALD-Y\\(_{\\mathrm{2}}\\O\\(_{\\mathrm{3}}\\/GaAs(\\(001\\-4 \\(\\times\\ 6 has shown excellent electrical properties. These include small frequency dispersion in the capacitance-voltage CV curves at accumulation of ~7% and ~14% for the respective p- and n-type samples with the measured frequencies of 1 MHz to 100 Hz. The interfacial trap density (Dit is low of ~10\\(^{12}\\ cm\\(^{−2}\\eV\\(^{−1}\\ as extracted from measured quasi-static CVs. The frequency dispersion at accumulation and the D\\(_{it}\\ are the lowest ever achieved among all the ALD-oxides on GaAs(\\(001\\.

  4. Zinc sulfide and terbium-doped zinc sulfide films grown by traveling wave reactor atomic layer epitaxy

    CERN Document Server

    Yun, S J; Nam, K S

    1998-01-01

    Zinc sulfide (ZnS) and terbium-doped ZnS (ZnS:Tb) thin films were grown by traveling wave reactor atomic layer epitaxy (ALE). In the present work, ZnCl sub 2 , H sub 2 S, and tris (2,2,6,6-tetramethyl-3,5-heptandionato) terbium (Tb(tmhd) sub 3) were used as the precursors. The dependence of crystallinity and Cl content of ZnS films was investigated on the growth temperature. ZnS and ZnS:Tb films grown at temperatures ranging from 400 to 500 .deg. C showed a hexagonal-2H crystalline structure. The crystallinity of ZnS film was greatly enhanced as the temperature increased. At growth temperatures higher than 450.deg.C, the films showed preferred orientation with mainly (002) diffraction peak. The Cl content decreased from approximately 9 to 1 at.% with the increase in growth temperature from 400 to 500 .deg. C. The segregation of Cl near the surface region and the incorporation of O from Tb(tmhd) sub 3 during ALE process were also observed using Auger electron spectroscopy. The ALE-grown ZnS and ZnS:Tb films re...

  5. The Growth of Gallium Nitride Films via the Innovative Technique of Atomic Layer Epitaxy

    Science.gov (United States)

    1989-06-01

    6 3.2 Aluminum Nitride and AIN/GaN Layered Structures ............ 8 3.3 Boron Nitride and BGaN Graded...of tearing in lower left region, indirectly indicating the presence of multiple layers of BGaN ............................... 14 12. Auger electron...electron spectroscopy sputtered depth profile of a BN/ BGaN /GaN/P-SiC film. Note peak in nitrogen trace as interface of BN is passed

  6. Kinetic model of II-VI(001) semiconductor surfaces : Growth rates in atomic layer epitaxy

    NARCIS (Netherlands)

    Volkmann, T; Ahr, M; Biehl, M

    2004-01-01

    We present a zinc-blende lattice gas model of II-VI(001) surfaces, which is investigated by means of kinetic Monte Carlo simulations. Anisotropic effective interactions between surface metal atoms allow for the description of, e.g., the sublimation of CdTe(001), including the reconstruction of Cd-te

  7. Electrodeposition of a Pt monolayer film: using kinetic limitations for atomic layer epitaxy.

    Science.gov (United States)

    Brimaud, Sylvain; Behm, R Jürgen

    2013-08-14

    A new and facile one-step method to prepare a smooth Pt monolayer film on a metallic substrate in the absence of underpotential deposition-type stabilizations is presented as a general approach and applied to the growth of Pt monolayer films on Au. The strongly modified electronic properties of these films were demonstrated by in situ IR spectroscopy at the electrified solid-liquid interface with adsorbed carbon monoxide serving as a probe molecule. The Pt monolayer on Au is kinetically stabilized by adsorbed CO, inhibiting further Pt deposition in higher layers.

  8. Preparation of bismuth telluride thin film by electrochemical atomic layer epitaxy(ECALE)

    Institute of Scientific and Technical Information of China (English)

    ZHU Wen; YANG Junyou; GAO Xianhui; HOU Jie; BAO Siqian; FAN Xian

    2007-01-01

    Thin-layer electrochemical studies of the underpotential deposition(UPD)of Bi and Te on cold rolled silver substrate have been performed.The voltammetric analysis of underpotential shift demonstrates that the initial Te UPD on Bi-covered Ag and Bi UPD on Te-covered Ag fitted UPD dynamics mechanism.A thin film of bismuth telluride was formed by alternately depositing Te and Bi via an automated flow deposition system.X-ray diffraction indicated the deposits of Bi2Te3.Energy Dispersive X-ray Detector quantitative analysis gave a 2:3 stoichiornetric ratio of Bi to Te,which was consistent with X-ray Diffraction results.Electron probe microanalysis of the deposits showed a network structure that results from the surface defects of the cold rolled Ag substrate and the lattice mismatch between substrate and deposit.

  9. Investigation on the lattice site location of the excess arsenic atoms in GaAs layers grown by low temperature molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Yu, Kin Man; Liliental-Weber, Z.

    1991-11-01

    We have measured the excess As atoms present in gaze layers grown by molecular beam epitaxy at low substrate temperatures using particle induced x-ray emission technique. The amount of excess As atoms in layers grown by MBE at 200{degrees}C were found to be {approximately} 4 {times} 10{sup 20} cm{sup {minus}2}. Subsequent annealing of the layers under As overpressure at 600{degrees}C did not result in any substantial As loss. However, transmission electron microscopy revealed that As precipitates (2-5nm in diameter) were present in the annealed layers. The lattice location of the excess As atoms in the as grown layers was investigated by ion channeling methods. Angular scans were performed in the <110> axis of the crystal. Our results strongly suggest that a large fraction of these excess As atoms are located in an interstitial position close to an As row. These As intersitials'' are located at a site slightly displaced from the tetrahedral site in a diamond cubic lattice. No interstitial As signal is observed in the annealed layers.

  10. Investigation on the lattice site location of the excess arsenic atoms in GaAs layers grown by low temperature molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Yu, Kin Man; Liliental-Weber, Z.

    1991-11-01

    We have measured the excess As atoms present in gaze layers grown by molecular beam epitaxy at low substrate temperatures using particle induced x-ray emission technique. The amount of excess As atoms in layers grown by MBE at 200{degrees}C were found to be {approximately} 4 {times} 10{sup 20} cm{sup {minus}2}. Subsequent annealing of the layers under As overpressure at 600{degrees}C did not result in any substantial As loss. However, transmission electron microscopy revealed that As precipitates (2-5nm in diameter) were present in the annealed layers. The lattice location of the excess As atoms in the as grown layers was investigated by ion channeling methods. Angular scans were performed in the <110> axis of the crystal. Our results strongly suggest that a large fraction of these excess As atoms are located in an interstitial position close to an As row. These As ``intersitials`` are located at a site slightly displaced from the tetrahedral site in a diamond cubic lattice. No interstitial As signal is observed in the annealed layers.

  11. Incorporation of La in epitaxial SrTiO3 thin films grown by atomic layer deposition on SrTiO3-buffered Si (001) substrates

    Science.gov (United States)

    McDaniel, Martin D.; Posadas, Agham; Ngo, Thong Q.; Karako, Christine M.; Bruley, John; Frank, Martin M.; Narayanan, Vijay; Demkov, Alexander A.; Ekerdt, John G.

    2014-06-01

    Strontium titanate, SrTiO3 (STO), thin films incorporated with lanthanum are grown on Si (001) substrates at a thickness range of 5-25 nm. Atomic layer deposition (ALD) is used to grow the LaxSr1-xTiO3 (La:STO) films after buffering the Si (001) substrate with four-unit-cells of STO deposited by molecular beam epitaxy. The crystalline structure and orientation of the La:STO films are confirmed via reflection high-energy electron diffraction, X-ray diffraction, and cross-sectional transmission electron microscopy. The low temperature ALD growth (˜225 °C) and post-deposition annealing at 550 °C for 5 min maintains an abrupt interface between Si (001) and the crystalline oxide. Higher annealing temperatures (650 °C) show more complete La activation with film resistivities of ˜2.0 × 10-2 Ω cm for 20-nm-thick La:STO (x ˜ 0.15); however, the STO-Si interface is slightly degraded due to the increased annealing temperature. To demonstrate the selective incorporation of lanthanum by ALD, a layered heterostructure is grown with an undoped STO layer sandwiched between two conductive La:STO layers. Based on this work, an epitaxial oxide stack centered on La:STO and BaTiO3 integrated with Si is envisioned as a material candidate for a ferroelectric field-effect transistor.

  12. Dynamic atomic layer epitaxy of InN on/in +c-GaN matrix: Effect of “In+N” coverage and capping timing by GaN layer on effective InN thickness

    Energy Technology Data Exchange (ETDEWEB)

    Yoshikawa, Akihiko, E-mail: yoshi@faculty.chiba-u.jp [Center for SMART Green Innovation Research, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba 263-8522 (Japan); Graduate School of Engineering, Kogakuin University, Hachioji, Tokyo 192-0015 (Japan); Kusakabe, Kazuhide; Hashimoto, Naoki [Center for SMART Green Innovation Research, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba 263-8522 (Japan); Hwang, Eun-Sook; Itoi, Takaomi [Graduate School of Engineering, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba 263-8522 (Japan)

    2016-01-11

    The growth front in the self-organizing and self-limiting epitaxy of ∼1 monolayer (ML)-thick InN wells on/in +c-GaN matrix by molecular beam epitaxy (MBE) has been studied in detail, with special attention given to the behavior and role of the N atoms. The growth temperatures of interest are above 600 °C, far higher than the typical upper critical temperature of 500 °C in MBE. It was confirmed that 2 ML-thick InN wells can be frozen/inserted in GaN matrix at 620 °C, but it was found that N atoms at the growth front tend to selectively re-evaporate more quickly than In atoms at temperatures higher than 650 °C. As a result, the effective thickness of inserted InN wells in the GaN matrix at 660–670 °C were basically 1 ML or sub-ML, even though they were capped by a GaN barrier at the time of 2 ML “In+N” coverage. Furthermore, it was found that the N atoms located below In atoms in the dynamic atomic layer epitaxy growth front had remarkably weaker bonding to the +c-GaN surface.

  13. Growth and characterization of epitaxial anatase TiO{sub 2}(001) on SrTiO{sub 3}-buffered Si(001) using atomic layer deposition

    Energy Technology Data Exchange (ETDEWEB)

    McDaniel, M.D. [University of Texas at Austin, Department of Chemical Engineering, Austin, TX 78712 (United States); Posadas, A. [University of Texas at Austin, Department of Physics, Austin, TX 78712 (United States); Wang, T. [University of Texas at Austin, Department of Chemical Engineering, Austin, TX 78712 (United States); Demkov, A.A. [University of Texas at Austin, Department of Physics, Austin, TX 78712 (United States); Ekerdt, J.G., E-mail: ekerdt@che.utexas.edu [University of Texas at Austin, Department of Chemical Engineering, Austin, TX 78712 (United States)

    2012-08-31

    Epitaxial anatase titanium dioxide (TiO{sub 2}) films have been grown by atomic layer deposition (ALD) on Si(001) substrates using a strontium titanate (STO) buffer layer grown by molecular beam epitaxy (MBE) to serve as a surface template. The growth of TiO{sub 2} was achieved using titanium isopropoxide and water as the co-reactants at a substrate temperature of 225-250 Degree-Sign C. To preserve the quality of the MBE-grown STO, the samples were transferred in-situ from the MBE chamber to the ALD chamber. After ALD growth, the samples were annealed in-situ at 600 Degree-Sign C in vacuum (10{sup -7} Pa) for 1-2 h. Reflection high-energy electron diffraction was performed during the MBE growth of STO on Si(001), as well as after deposition of TiO{sub 2} by ALD. The ALD films were shown to be highly ordered with the substrate. At least four unit cells of STO must be present to create a stable template on the Si(001) substrate for epitaxial anatase TiO{sub 2} growth. X-ray diffraction revealed that the TiO{sub 2} films were anatase with only the (004) reflection present at 2{theta} = 38.2 Degree-Sign , indicating that the c-axis is slightly reduced from that of anatase powder (2{theta} = 37.9 Degree-Sign ). Anatase TiO{sub 2} films up to 100 nm thick have been grown that remain highly ordered in the (001) direction on STO-buffered Si(001) substrates. - Highlights: Black-Right-Pointing-Pointer Epitaxial anatase films are grown by atomic layer deposition (ALD) on Si(001). Black-Right-Pointing-Pointer Four unit cells of SrTiO{sub 3} on silicon create a stable template for ALD. Black-Right-Pointing-Pointer TiO{sub 2} thin films have a compressed c-axis and an expanded a-axis. Black-Right-Pointing-Pointer Up to 100 nm thick TiO{sub 2} films remain highly ordered in the (001) direction.

  14. Atomic layer epitaxy of Ruddlesden-Popper SrO(SrTiO{sub 3}){sub n} films by means of metalorganic aerosol deposition

    Energy Technology Data Exchange (ETDEWEB)

    Jungbauer, M.; Hühn, S.; Moshnyaga, V. [Erstes Physikalisches Institut, Universität Göttingen, Friedrich-Hund-Platz 1, 37077 Göttingen (Germany); Egoavil, R.; Tan, H.; Verbeeck, J.; Van Tendeloo, G. [EMAT, University of Antwerp, Groenenborgerlaan 171, 2020 Antwerp (Belgium)

    2014-12-22

    We report an atomic layer epitaxial growth of Ruddlesden-Popper (RP) thin films of SrO(SrTiO{sub 3}){sub n} (n = ∞, 2, 3, 4) by means of metalorganic aerosol deposition (MAD). The films are grown on SrTiO{sub 3}(001) substrates by means of a sequential deposition of Sr-O/Ti-O{sub 2} atomic monolayers, monitored in-situ by optical ellipsometry. X-ray diffraction and transmission electron microscopy (TEM) reveal the RP structure with n = 2–4 in accordance with the growth recipe. RP defects, observed by TEM in a good correlation with the in-situ ellipsometry, mainly result from the excess of SrO. Being maximal at the film/substrate interface, the SrO excess rapidly decreases and saturates after 5–6 repetitions of the SrO(SrTiO{sub 3}){sub 4} block at the level of 2.4%. This identifies the SrTiO{sub 3} substrate surface as a source of RP defects under oxidizing conditions within MAD. Advantages and limitations of MAD as a solution-based and vacuum-free chemical deposition route were discussed in comparison with molecular beam epitaxy.

  15. Atomic Layer Deposition of p-Type Epitaxial Thin Films of Undoped and N-Doped Anatase TiO2.

    Science.gov (United States)

    Vasu, K; Sreedhara, M B; Ghatak, J; Rao, C N R

    2016-03-01

    Employing atomic layer deposition, we have grown p-type epitaxial undoped and N-doped anatase TiO2(001) thin films on c-axis Al2O3 substrate. From X-ray diffraction and transmission electron microscopy studies, crystallographic relationships between the film and the substrate are found to be (001)TiO2//(0001)Al2O3 and [1̅10]TiO2//[011̅0]Al2O3. N-doping in TiO2 thin films enhances the hole concentration and mobility. The optical band gap of anatase TiO2 (3.23 eV) decreases to 3.07 eV upon N-doping. The epitaxial films exhibit room-temperature ferromagnetism and photoresponse. A TiO2-based homojunction diode was fabricated with rectification from the p-n junction formed between N-doped p-TiO2 and n-TiO2.

  16. Photoluminescence associated with basal stacking faults in c-plane ZnO epitaxial film grown by atomic layer deposition

    Energy Technology Data Exchange (ETDEWEB)

    Yang, S.; Kuo, C. C.; Hsieh, W. F. [Department of Photonics and Institute of Electro-Optical Engineering, National Chiao Tung University, Hsinchu 30010, Taiwan (China); Liu, W.-R. [Scientific Research Division, National Synchrotron Radiation Research Center, Hsinchu 30076, Taiwan (China); Lin, B. H. [Department of Photonics and Institute of Electro-Optical Engineering, National Chiao Tung University, Hsinchu 30010, Taiwan (China); Scientific Research Division, National Synchrotron Radiation Research Center, Hsinchu 30076, Taiwan (China); Hsu, H.-C. [Institute of Electro-Optical Science and Engineering and Advanced Optoelectronic Technology Center, National Cheng Kung University, Tainan 70101, Taiwan (China); Hsu, C.-H. [Scientific Research Division, National Synchrotron Radiation Research Center, Hsinchu 30076, Taiwan (China); Department of Photonics and Institute of Electro-Optical Engineering, National Chiao Tung University, Hsinchu 30010, Taiwan (China)

    2012-03-05

    Basal plane stacking faults (BSFs) with density of {approx}1 x 10{sup 6} cm{sup -1} are identified as the dominant defect in the annealed ZnO thin films grown on c-plane sapphire by atomic layer deposition. The dominant peak centered at 3.321 eV in low-temperature photoluminescence measurements is attributed to the emission from the BSFs. The emission mechanism is considered to be the confined indirect excitons in the region of quantum-well-like structure formed by the BSFs. The observed energy shift of 19 meV with respect to the BSF-bounded exciton at low temperature may be caused by the localization effect associated with the coupling between BSF quantum wells.

  17. Optical characterization of epitaxial semiconductor layers

    CERN Document Server

    Richter, Wolfgang

    1996-01-01

    The last decade has witnessed an explosive development in the growth of expitaxial layers and structures with atomic-scale dimensions. This progress has created new demands for the characterization of those stuctures. Various methods have been refined and new ones developed with the main emphasis on non-destructive in-situ characterization. Among those, methods which rely on the interaction of electromagnetic radiation with matter are particularly valuable. In this book standard methods such as far-infrared spectroscopy, ellipsometry, Raman scattering, and high-resolution X-ray diffraction are presented, as well as new advanced techniques which provide the potential for better in-situ characterization of epitaxial structures (such as reflection anistropy spectroscopy, infrared reflection-absorption spectroscopy, second-harmonic generation, and others). This volume is intended for researchers working at universities or in industry, as well as for graduate students who are interested in the characterization of ...

  18. Atomic scale structure investigations of epitaxial Fe/Cr multilayers

    Energy Technology Data Exchange (ETDEWEB)

    Kąc, M., E-mail: malgorzata.kac@ifj.edu.pl [The Henryk Niewodniczański Institute of Nuclear Physics PAN, ul. Radzikowskiego 152, 31-342 Kraków (Poland); Morgiel, J. [Institute of Metallurgy and Materials Science PAN, 25 Reymonta St., 30-059 Kraków (Poland); Polit, A.; Zabila, Y.; Marszałek, M. [The Henryk Niewodniczański Institute of Nuclear Physics PAN, ul. Radzikowskiego 152, 31-342 Kraków (Poland)

    2014-06-01

    Fe/Cr multilayers were deposited by molecular beam epitaxy on the MgO(1 0 0) substrate. Structural properties of the samples were analyzed by low energy electron diffraction, high resolution transmission electron microscopy (HRTEM), as well as by X-ray reflectivity, conversion electron Mössbauer spectroscopy (CEMS) and Auger electron spectroscopy. Investigations revealed multilayered system built of well-ordered Fe and Cr thin films with (1 0 0) orientation. A high geometrical perfection of the system, i.e. planar form of interfaces and reproducible thickness of layers, was also proven. Fe/Cr interface roughness was determined to be 2–3 atomic layers. CEMS studies allowed to analyze at atomic scale the structure of buried Fe/Cr interfaces, as well as to distinguish origin of interface roughness. Roughnesses resulting from interface corrugations and from the Fe–Cr interdiffusion at interfaces were observed. Fe/Cr multilayers showed strong antiferromagnetic coupling of Fe layers.

  19. Growth kinetics and structural perfection of (InN)1/(GaN)1-20 short-period superlattices on +c-GaN template in dynamic atomic layer epitaxy

    Science.gov (United States)

    Kusakabe, Kazuhide; Hashimoto, Naoki; Itoi, Takaomi; Wang, Ke; Imai, Daichi; Yoshikawa, Akihiko

    2016-04-01

    The growth kinetics and structural perfection of (InN)1/(GaN)1-20 short-period superlattices (SPSs) were investigated with their application to ordered alloys in mind. The SPSs were grown on +c-GaN template at 650 °C by dynamic atomic layer epitaxy in conventional plasma-assisted molecular beam epitaxy. It was found that coherent structured InN/GaN SPSs could be fabricated when the thickness of the GaN barrier was 4 ML or above. Below 3 ML, the formation of SPSs was quite difficult owing to the increased strain in the SPS structure caused by the use of GaN as a template. The effective or average In composition of the (InN)1/(GaN)4 SPSs was around 10%, and the corresponding InN coverage in the ˜1 ML-thick InN wells was 50%. It was found that the effective InN coverage in ˜1 ML-thick InN wells could be varied with the growth conditions. In fact, the effective In composition could be increased up to 13.5%, i.e., the corresponding effective InN coverage was about 68%, by improving the capping/freezing speed by increasing the growth rate of the GaN barrier layer.

  20. Atomic layer deposition of nanostructured materials

    CERN Document Server

    Pinna, Nicola

    2012-01-01

    Atomic layer deposition, formerly called atomic layer epitaxy, was developed in the 1970s to meet the needs of producing high-quality, large-area fl at displays with perfect structure and process controllability. Nowadays, creating nanomaterials and producing nanostructures with structural perfection is an important goal for many applications in nanotechnology. As ALD is one of the important techniques which offers good control over the surface structures created, it is more and more in the focus of scientists. The book is structured in such a way to fi t both the need of the expert reader (du

  1. Interface engineering in epitaxial growth of layered oxides via a conducting layer insertion

    Energy Technology Data Exchange (ETDEWEB)

    Yun, Yu; Meng, Dechao; Wang, Jianlin [Hefei National Laboratory for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei 230026, Anhui (China); Department of Materials Science and Engineering, University of Science and Technology of China, Hefei 230026, Anhui (China); Ma, Chao [Hefei National Laboratory for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei 230026, Anhui (China); Zhai, Xiaofang, E-mail: xfzhai@ustc.edu.cn [Hefei National Laboratory for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei 230026, Anhui (China); Synergetic Innovation Center of Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei 230026, Anhui (China); Huang, Haoliang; Fu, Zhengping; Peng, Ranran [Hefei National Laboratory for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei 230026, Anhui (China); Department of Materials Science and Engineering, University of Science and Technology of China, Hefei 230026, Anhui (China); Synergetic Innovation Center of Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei 230026, Anhui (China); Brown, Gail J. [Materials and Manufacturing Directorate, Air Force Research Laboratory, Wright-Patterson Air Force Base, Ohio 45433-7707 (United States); and others

    2015-07-06

    There is a long-standing challenge in the fabrication of layered oxide epitaxial films due to their thermodynamic phase-instability and the large stacking layer number. Recently, the demand for high-quality thin films is strongly pushed by their promising room-temperature multiferroic properties. Here, we find that by inserting a conducting and lattice matched LaNiO{sub 3} buffer layer, high quality m = 5 Bi{sub 6}FeCoTi{sub 3}O{sub 18} epitaxial films can be fabricated using the laser molecular beam epitaxy, in which the atomic-scale sharp interface between the film and the metallic buffer layer explains the enhanced quality. The magnetic and ferroelectric properties of the high quality Bi{sub 6}FeCoTi{sub 3}O{sub 18} films are studied. This study demonstrates that insertion of the conducting layer is a powerful method in achieving high quality layered oxide thin films, which opens the door to further understand the underline physics and to develop new devices.

  2. Epitaxy of an Al-Droplet-Free AlN Layer with Step-Flow Features by Molecular Beam Epitaxy

    Institute of Scientific and Technical Information of China (English)

    PAN Jian-Hai; WANG Xin-Qiang; CHEN Guang; LIU Shi-Tao; FENG Li; XU Fu-Jun; TANG Ning; SHEN Bo

    2011-01-01

    We investigate epitaxy of A1N layers on sapphire substrates by molecular beam epitaxy. It is found that an atomically Bat surface can be obtained under Al-rich conditions at growth temperature of 780°C. However, the growth window to obtain an Al-droplet-free surface is too narrow to be well-controlled. However, the growth window can be greatly broadened by increasing the growth temperature up to 950 "C, where an Al-droplet-free surface with a step-How feature is obtained due to the enhanced re-evaporization rate and migration ability of Al adatoms. The samples grown at the higher temperature also show a higher crystalline quality than those grown at lower temperatures.%@@ We investigate epitaxy of AlN layers on sapphire substrates by molecular beam epitaxy.It is found that an atomically fiat surface can be obtained under Al-rich conditions at growth temperature of 780℃.However, the growth window to obtain an Al-droplet-free surface is too narrow to be well-controlled.However, the growth window can be greatly broadened by increasing the growth temperature up to 950℃, where an Al-droplet-free surface with a step-flow feature is obtained due to the enhanced re-evaporization rate and migration ability of Al adatoms.The samples grown at the higher temperature also show a higher crystalline quality than those grown at lower temperatures.

  3. Effect of as Passivation on Vapor-Phase Epitaxial Growth of Ge on (211)Si as a Buffer Layer for CdTe Epitaxy

    Science.gov (United States)

    2011-04-07

    time periods of (a) 5 min and (b) 10 min. It can be seen that Ge grows layer-by- layer, resulting in a very thin Ge film . Fig. 4. SEM image of Ge...REPORT Effect Of As Passivation On Vapor-Phase Epitaxial Growth of Ge on (211)Si As A Buffer Layer For CdTe Epitaxy 14. ABSTRACT 16. SECURITY...The films were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), cross-sectional 1. REPORT DATE (DD-MM-YYYY) 4

  4. Growth of high purity semiconductor epitaxial layers by liquid phase epitaxy and their characterization

    Indian Academy of Sciences (India)

    S Dhar

    2005-07-01

    This paper briefly describes our work and the results on the growth of several III–V epitaxial semiconductor materials in high purity form by liquid phase epitaxy (LPE) technique. Various possible sources of impurities in such growth are listed and step-by-step procedures adopted to reduce them are discussed in particular reference to the growth of GaAs layers. The technique of growing very high purity layers by treating the melt with erbium is described for the growth of InGaAs and GaSb layers.

  5. Fast atom diffraction inside a molecular beam epitaxy chamber, a rich combination

    Science.gov (United States)

    Debiossac, M.; Atkinson, P.; Zugarramurdi, A.; Eddrief, M.; Finocchi, F.; Etgens, V. H.; Momeni, A.; Khemliche, H.; Borisov, A. G.; Roncin, P.

    2017-01-01

    Two aspects of the contribution of grazing incidence fast atom diffraction (GIFAD) to molecular beam epitaxy (MBE) are reviewed here: the ability of GIFAD to provide in-situ a precise description of the atomic-scale surface topology, and its ability to follow larger-scale changes in surface roughness during layer-by-layer growth. Recent experimental and theoretical results obtained for the He atom beam incident along the highly corrugated [ 1 1 bar 0 ] direction of the β2(2 × 4) reconstructed GaAs(001) surface are summarized. We also discuss the measurements and calculations for the beam incidence along the weakly corrugated [010] direction where a periodicity twice smaller than expected is observed. The combination of the experiment, quantum scattering matrix calculations, and semiclassical analysis allows structural characteristics of the surface to be revealed. For the in situ measurements of GIFAD during molecular beam epitaxy of GaAs on GaAs surface we analyze the change in elastic and inelastic contributions in the scattered beam, and the variation of the diffraction pattern in polar angle scattering. This analysis outlines the robustness, the simplicity and the richness of the GIFAD as a technique to monitor the layer-by-layer epitaxial growth.

  6. Stochastic growth theory of molecular beam epitaxy with atom correlation effects: A Monte-Carlo master equation method

    Science.gov (United States)

    Nakayama, Hiroshi; Furuichi, Akihisa; Kita, Takashi; Nishino, Taneo

    1997-04-01

    Structural phase transition of epitaxial growing layer is quite important to understand the atomic scale mechanism of molecular beam epitaxy (MBE). GaAs and related alloy semiconductors are typical systems which show variety of such structural transitions during MBE. Structural evolution of surface reconstruction phases and an order-disorder transition in III-V alloy semiconductors are typical cases where such phase transitions appear during epitaxial processes. In this work, a stochastic theory and the Monte-Carlo simulation have been presented to describe the structural evolution of epitaxial growth in binary system. This method, known here as the 'Monte-Carlo master equation (MCME) method', couples a master equation for epitaxial growth kinetics with an Ising Hamiltonian of growing surface. The Monte-Carlo (MC) simulation of binary growing surface with atom-correlation effects has successfully revealed the evolution of atomic structure and the formation of short-range ordering (SRO) during epitaxy. This demonstrates the usefulness of the MCME method in describing the atomic-structural dynamics as compared with a conventional theory of epitaxy based on a diffusion equation and standard nucleation theory.

  7. Epitaxial few-layer graphene: towards single crystal growth

    Energy Technology Data Exchange (ETDEWEB)

    Hibino, H; Kageshima, H; Nagase, M, E-mail: hibino@will.brl.ntt.co.j [NTT Basic Research Laboratories, NTT Corporation, Atsugi, Kanagawa 243-0198 (Japan)

    2010-09-22

    We review our research towards single-crystal growth of epitaxial few-layer graphene (FLG) on SiC substrates. We have established a method for evaluating the number of graphene layers microscopically using low-energy electron microscopy. Scanning probe microscopy in air is also useful for estimating the number-of-layers distribution in epitaxial FLG. The number-of-layers dependence of the work function and C1s binding energy is determined using photoelectron emission microscopy. We investigate the growth processes of epitaxial FLG on the basis of the microscopic observations of surface morphology and graphene distribution. To gain insights into the growth mechanism, we calculate the SiC surface structures with various C coverages using a first-principles scheme. Uniform bilayer graphene a few micrometres in size is obtained by annealing in UHV.

  8. Electric circuit model for strained-layer epitaxy

    Science.gov (United States)

    Kujofsa, Tedi; Ayers, John E.

    2016-11-01

    For the design and analysis of a strained-layer semiconductor device structure, the equilibrium strain profile may be determined numerically by energy minimization but this method is computationally intense and non-intuitive. Here we present an electric circuit model approach for the equilibrium analysis of an epitaxial stack, in which each sublayer may be represented by an analogous configuration involving a current source, a resistor, a voltage source, and an ideal diode. The resulting node voltages in the analogous electric circuit correspond to the equilibrium strains in the original epitaxial structure. This new approach enables analysis using widely accessible circuit simulators, and an intuitive understanding of electric circuits may be translated to the relaxation of strained-layer structures. In this paper, we describe the mathematical foundation of the electrical circuit model and demonstrate its application to epitaxial layers of Si1-x Ge x grown on a Si (001) substrate.

  9. Fabrication of atomically smooth SrRuO3 thin films by laser molecular beam epitaxy

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    High-quality SrRuO3 (SRO) thin films and SrTiO3/SRO bilayer were grown epitaxially on SrTiO3 (STO)(001) substrates by laser molecular beam epitaxy. The results of in situ observation of reflection high-energy electron diffraction and ex situ X-ray diffraction θ -2θ scan indicate that the SRO thin films have good crystallinity. The measurements of atomic force microscopy and scan tunneling microscopy reveal that the surface of the SRO thin film is atomically smooth. The resistivity of the SRO thin film is 300 μΩ·cm at room temperature. Furthermore, the transmission electron microscopy study shows that the interfaces of STO/SRO and SRO/STO are very clear and no interfacial reaction layer was observed. The experimental results show that the SRO thin film is an excellent electrode material for devices based on perovskite oxide materials.

  10. Epitaxy of layered semiconductor thin films

    Science.gov (United States)

    Brahim Otsmane, L.; Emery, J. Y.; Jouanne, M.; Balkanski, M.

    1993-03-01

    Epilayers of InSe on InSe(00.1) and GaSe(00.1) have been grown by the molecular beam epitaxy (MBE) technique. Raman spectroscopy was used for a characterization of the structure and crystallinity in InSe/InSe(00.1) (homoepitaxy) and InSe/GaSe(00.1) (heteroepitaxy). The Raman spectra of the InSe thin films are identical to those of polytype γ-InSe. An activation of the E(LO) mode at 211 cm -1 is observed in these films here. Scanning electron microscopy (SEM) is also used to investigate surfaces of these films.

  11. Seed layer technique for high quality epitaxial manganite films

    Science.gov (United States)

    Graziosi, P.; Gambardella, A.; Calbucci, M.; O’Shea, K.; MacLaren, D. A.; Bergenti, I.; Homonnay, N.; Schmidt, G.; Pullini, D.; Busquets-Mataix, D.; Dediu, V.

    2016-01-01

    We introduce an innovative approach to the simultaneous control of growth mode and magnetotransport properties of manganite thin films, based on an easy-to-implement film/substrate interface engineering. The deposition of a manganite seed layer and the optimization of the substrate temperature allows a persistent bi-dimensional epitaxy and robust ferromagnetic properties at the same time. Structural measurements confirm that in such interface-engineered films, the optimal properties are related to improved epitaxy. A new growth scenario is envisaged, compatible with a shift from heteroepitaxy towards pseudo-homoepitaxy. Relevant growth parameters such as formation energy, roughening temperature, strain profile and chemical states are derived. PMID:27648371

  12. Seed layer technique for high quality epitaxial manganite films

    Directory of Open Access Journals (Sweden)

    P. Graziosi

    2016-08-01

    Full Text Available We introduce an innovative approach to the simultaneous control of growth mode and magnetotransport properties of manganite thin films, based on an easy-to-implement film/substrate interface engineering. The deposition of a manganite seed layer and the optimization of the substrate temperature allows a persistent bi-dimensional epitaxy and robust ferromagnetic properties at the same time. Structural measurements confirm that in such interface-engineered films, the optimal properties are related to improved epitaxy. A new growth scenario is envisaged, compatible with a shift from heteroepitaxy towards pseudo-homoepitaxy. Relevant growth parameters such as formation energy, roughening temperature, strain profile and chemical states are derived.

  13. Laser Molecular Beam Epitaxy Growth of BaTiO3 in Seven Thousands of Unit-Cell Layers

    Institute of Scientific and Technical Information of China (English)

    HUANG Yan-Hong; YANG Guo-Zhen; HE Meng; ZHAO Kun; TIAN Huan-Fang; L(U) Hui-Bin; JIN Kui-Juan; CHEN Zheng-Hao; ZHOU Yue-Liang; LI Jian-Qi

    2005-01-01

    @@ BaTiO3 thin films in seven thousands of unit-cell layers have been successfully fabricated on SrTiO3 (001)substrates by laser molecular beam epitaxy. The fine streak pattern and the undamping intensity oscillation of reflection high-energy electron diffraction indicate that the BaTiO3 film was layer-by-layer epitaxial growth. The measurements of scanning electron microscopy and atomic force microscopy show that surfaces of the BaTiO3thin film are atomically smooth. The measurements of x-ray diffraction and transmission electron microscopy,as well as selected-area electron diffraction revealthat the BaTiO3 thin film is a c-oriented epitaxial crystalline structure.

  14. Dynamic layer rearrangement during growth of layered oxide films by molecular beam epitaxy.

    Science.gov (United States)

    Lee, J H; Luo, G; Tung, I C; Chang, S H; Luo, Z; Malshe, M; Gadre, M; Bhattacharya, A; Nakhmanson, S M; Eastman, J A; Hong, H; Jellinek, J; Morgan, D; Fong, D D; Freeland, J W

    2014-09-01

    The A(n+1)B(n)O(3n+1) Ruddlesden-Popper homologous series offers a wide variety of functionalities including dielectric, ferroelectric, magnetic and catalytic properties. Unfortunately, the synthesis of such layered oxides has been a major challenge owing to the occurrence of growth defects that result in poor materials behaviour in the higher-order members. To understand the fundamental physics of layered oxide growth, we have developed an oxide molecular beam epitaxy system with in situ synchrotron X-ray scattering capability. We present results demonstrating that layered oxide films can dynamically rearrange during growth, leading to structures that are highly unexpected on the basis of the intended layer sequencing. Theoretical calculations indicate that rearrangement can occur in many layered oxide systems and suggest a general approach that may be essential for the construction of metastable Ruddlesden-Popper phases. We demonstrate the utility of the new-found growth strategy by performing the first atomically controlled synthesis of single-crystalline La3Ni2O7.

  15. Towards precise defect control in layered oxide structures by using oxide molecular beam epitaxy

    Directory of Open Access Journals (Sweden)

    Federico Baiutti

    2014-05-01

    Full Text Available In this paper we present the atomic-layer-by-layer oxide molecular beam epitaxy (ALL-oxide MBE which has been recently installed in the Max-Planck Institute for Solid State Research and we report on its present status, providing some examples that demonstrate its successful application in the synthesis of different layered oxides, with particular reference to superconducting La2CuO4 and insulator-to-metal La2−xSrxNiO4. We briefly review the ALL-oxide MBE technique and its unique capabilities in the deposition of atomically smooth single-crystal thin films of various complex oxides, artificial compounds and heterostructures, introducing our goal of pursuing a deep investigation of such systems with particular emphasis on structural defects, with the aim of tailoring their functional properties by precise defects control.

  16. Towards precise defect control in layered oxide structures by using oxide molecular beam epitaxy.

    Science.gov (United States)

    Baiutti, Federico; Christiani, Georg; Logvenov, Gennady

    2014-01-01

    In this paper we present the atomic-layer-by-layer oxide molecular beam epitaxy (ALL-oxide MBE) which has been recently installed in the Max-Planck Institute for Solid State Research and we report on its present status, providing some examples that demonstrate its successful application in the synthesis of different layered oxides, with particular reference to superconducting La2CuO4 and insulator-to-metal La2- x Sr x NiO4. We briefly review the ALL-oxide MBE technique and its unique capabilities in the deposition of atomically smooth single-crystal thin films of various complex oxides, artificial compounds and heterostructures, introducing our goal of pursuing a deep investigation of such systems with particular emphasis on structural defects, with the aim of tailoring their functional properties by precise defects control.

  17. Improved radiation tolerance of MAPS using a depleted epitaxial layer

    Energy Technology Data Exchange (ETDEWEB)

    Dorokhov, A., E-mail: Andrei.Dorokhov@IReS.in2p3.f [Institut Pluridisciplinaire Hubert Curien (IPHC), 23 rue du loess, BP 28, 67037 Strasbourg (France); Bertolone, G.; Baudot, J.; Brogna, A.S.; Colledani, C.; Claus, G.; De Masi, R. [Institut Pluridisciplinaire Hubert Curien (IPHC), 23 rue du loess, BP 28, 67037 Strasbourg (France); Deveaux, M. [Goethe-Universitaet Frankfurt am Main, Senckenberganlage 31, 60325 Frankfurt am Main (Germany); Doziere, G.; Dulinski, W. [Institut Pluridisciplinaire Hubert Curien (IPHC), 23 rue du loess, BP 28, 67037 Strasbourg (France); Fontaine, J.-C. [Groupe de Recherche en Physique des Hautes Energies (GRPHE), Universite de Haute Alsace, 61, rue Albert Camus, 68093 Mulhouse (France); Goffe, M.; Himmi, A.; Hu-Guo, Ch.; Jaaskelainen, K.; Koziel, M.; Morel, F.; Santos, C.; Specht, M.; Valin, I. [Institut Pluridisciplinaire Hubert Curien (IPHC), 23 rue du loess, BP 28, 67037 Strasbourg (France)

    2010-12-11

    Tracking performance of Monolithic Active Pixel Sensors (MAPS) developed at IPHC (Turchetta, et al., 2001) have been extensively studied (Winter, et al., 2001; Gornushkin, et al., 2002) . Numerous sensor prototypes, called MIMOSA, were fabricated and tested since 1999 in order to optimise the charge collection efficiency and power dissipation, to minimise the noise and to increase the readout speed. The radiation tolerance was also investigated. The highest fluence tolerable for a 10{mu}m pitch device was found to be {approx}10{sup 13}n{sub eq}/cm{sup 2}, while it was only 2x10{sup 12}n{sub eq}/cm{sup 2} for a 20{mu}m pitch device. The purpose of this paper is to show that the tolerance to non-ionising radiation may be extended up to O(10{sup 14}) n{sub eq}/cm{sup 2}. This goal relies on a fabrication process featuring a 15{mu}m thin, high resistivity ({approx}1k{Omega}cm) epitaxial layer. A sensor prototype (MIMOSA-25) was fabricated in this process to explore its detection performance. The depletion depth of the epitaxial layer at standard CMOS voltages (<5V) is similar to the layer thickness. Measurements with m.i.p.s show that the charge collected in the seed pixel is at least twice larger for the depleted epitaxial layer than for the undepleted one, translating into a signal-to-noise ratio (SNR) of {approx}50. Tests after irradiation have shown that this excellent performance is maintained up to the highest fluence considered (3x10{sup 13}n{sub eq}/cm{sup 2}), making evidence of a significant extension of the radiation tolerance limits of MAPS.

  18. High quality GaN-based LED epitaxial layers grown in a homemade MOCVD system

    Institute of Scientific and Technical Information of China (English)

    Yin Haibo; Wang Xiaoliang; Ran Junxue; Hu Guoxin; Zhang Lu; Xiao Hongling; Li Jing; Li Jinmin

    2011-01-01

    A homemade 7 × 2 inch MOCVD system is presented.With this system,high quality GaN epitaxial layers,InGaN/GaN multi-quantum wells and blue LED structural epitaxial layers have been successfully grown.The non-uniformity of undoped GaN epitaxial layers is as low as 2.86%.Using the LED structural epitaxial layers,blue LED chips with area of 350 × 350μm2 were fabricated.Under 20 mA injection current,the optical output power of the blue LED is 8.62 mW.

  19. Epitaxially Grown Layered MFI–Bulk MFI Hybrid Zeolitic Materials

    KAUST Repository

    Kim, Wun-gwi

    2012-11-27

    The synthesis of hybrid zeolitic materials with complex micropore-mesopore structures and morphologies is an expanding area of recent interest for a number of applications. Here we report a new type of hybrid zeolite material, composed of a layered zeolite material grown epitaxially on the surface of a bulk zeolite material. Specifically, layered (2-D) MFI sheets were grown on the surface of bulk MFI crystals of different sizes (300 nm and 10 μm), thereby resulting in a hybrid material containing a unique morphology of interconnected micropores (∼0.55 nm) and mesopores (∼3 nm). The structure and morphology of this material, referred to as a "bulk MFI-layered MFI" (BMLM) material, was elucidated by a combination of XRD, TEM, HRTEM, SEM, TGA, and N2 physisorption techniques. It is conclusively shown that epitaxial growth of the 2-D layered MFI sheets occurs in at least two principal crystallographic directions of the bulk MFI crystal and possibly in the third direction as well. The BMLM material combines the properties of bulk MFI (micropore network and mechanical support) and 2-D layered MFI (large surface roughness, external surface area, and mesoporosity). As an example of the uses of the BMLM material, it was incorporated into a polyimide and fabricated into a composite membrane with enhanced permeability for CO2 and good CO2/CH4 selectivity for gas separations. SEM-EDX imaging and composition analysis showed that the polyimide and the BMLM interpenetrate into each other, thereby forming a well-adhered polymer/particle microstructure, in contrast with the defective interfacial microstructure obtained using bare MFI particles. Analysis of the gas permeation data with the modified Maxwell model also allows the estimation of the effective volume of the BMLM particles, as well as the CO2 and CH4 gas permeabilities of the interpenetrated layer at the BMLM/polyimide interface. © 2012 American Chemical Society.

  20. Epitaxial growth of cadmium telluride films on silicon with a buffer silicon carbide layer

    Science.gov (United States)

    Antipov, V. V.; Kukushkin, S. A.; Osipov, A. V.

    2017-02-01

    An epitaxial 1-3-μm-thick cadmium telluride film has been grown on silicon with a buffer silicon carbide layer using the method of open thermal evaporation and condensation in vacuum for the first time. The optimum substrate temperature was 500°C at an evaporator temperature of 580°C, and the growth time was 4 s. In order to provide more qualitative growth of cadmium telluride, a high-quality 100-nm-thick buffer silicon carbide layer was previously synthesized on the silicon surface using the method of topochemical substitution of atoms. The ellipsometric, Raman, X-ray diffraction, and electron-diffraction analyses showed a high structural perfection of the CdTe layer in the absence of a polycrystalline phase.

  1. Growth of uniform CaGe2 films by alternating layer molecular beam epitaxy

    Science.gov (United States)

    Xu, Jinsong; Katoch, Jyoti; Ahmed, Adam S.; Pinchuk, Igor V.; Young, Justin R.; Johnston-Halperin, Ezekiel; Pelz, Jonathan; Kawakami, Roland K.

    2017-02-01

    Layered Zintl phase van der Waals (vdW) materials are of interest due to their strong spin-orbit coupling and potential for high mobility. Here, we report the successful growth of large area CaGe2 films, as a model of layered Zintl phase materials, on atomically flat Ge(111) substrates by molecular beam epitaxy (MBE) using an alternating layer growth (ALG) protocol. Reflection high energy electron diffraction (RHEED) patterns of the Ge buffer layer and CaGe2 indicate high quality two dimensional surfaces, which is further confirmed by atomic force microscopy (AFM), showing atomically flat and uniform CaGe2 films. The appearance of Laue oscillations in X-ray diffraction (XRD) and Kiessig fringes in the X-ray reflectivity (XRR), which are absent in co-deposited CaGe2, confirms the uniformity of the CaGe2 film and the smoothness of the interface. These results demonstrate a novel method of deposition of CaGe2 that could be also applied to other layered Zintl phase vdW materials. Also, the high quality of the CaGe2 film is promising for the exploration of novel properties of germanane.

  2. Growth and characterization of epitaxial aluminum layers on gallium-arsenide substrates for superconducting quantum bits

    Science.gov (United States)

    Tournet, J.; Gosselink, D.; Miao, G.-X.; Jaikissoon, M.; Langenberg, D.; McConkey, T. G.; Mariantoni, M.; Wasilewski, Z. R.

    2016-06-01

    The quest for a universal quantum computer has renewed interest in the growth of superconducting materials on semiconductor substrates. High-quality superconducting thin films will make it possible to improve the coherence time of superconducting quantum bits (qubits), i.e., to extend the time a qubit can store the amplitude and phase of a quantum state. The electrical losses in superconducting qubits highly depend on the quality of the metal layers the qubits are made from. Here, we report on the epitaxy of single-crystal Al (011) layers on GaAs (001) substrates. Layers with 110 nm thickness were deposited by means of molecular beam epitaxy at low temperature and monitored by in situ reflection high-energy electron diffraction performed simultaneously at four azimuths. The single-crystal nature of the layers was confirmed by ex situ high-resolution x-ray diffraction. Differential interference contrast and atomic force microscopy analysis of the sample’s surface revealed a featureless surface with root mean square roughness of 0.55 nm. A detailed in situ study allowed us to gain insight into the nucleation mechanisms of Al layers on GaAs, highlighting the importance of GaAs surface reconstruction in determining the final Al layer crystallographic orientation and quality. A highly uniform and stable GaAs (001)-(2× 4) reconstruction reproducibly led to a pure Al (011) phase, while an arsenic-rich GaAs (001)-(4× 4) reconstruction yielded polycrystalline films with an Al (111) dominant orientation. The near-atomic smoothness and single-crystal character of Al films on GaAs, in combination with the ability to trench GaAs substrates, could set a new standard for the fabrication of superconducting qubits.

  3. Layer-by-layer epitaxial thin films of the pyrochlore Tb2Ti2O7

    Science.gov (United States)

    Bovo, Laura; Rouleau, Christopher M.; Prabhakaran, Dharmalingam; Bramwell, Steven T.

    2017-02-01

    Layer-by-layer epitaxial growth of the pyrochlore magnet Tb2Ti2O7 on the isostructural substrate Y2Ti2O7 results in high-quality single crystal films of up to 60 nm thickness. Substrate-induced strain is shown to act as a strong and controlled perturbation to the exotic magnetism of Tb2Ti2O7, opening up the general prospect of strain-engineering the diverse magnetic and electrical properties of pyrochlore oxides.

  4. Schottky barrier detection devices having a 4H-SiC n-type epitaxial layer

    Science.gov (United States)

    Mandal, Krishna C.; Terry, J. Russell

    2016-12-06

    A detection device, along with methods of its manufacture and use, is provided. The detection device can include: a SiC substrate defining a substrate surface cut from planar to about 12.degree.; a buffer epitaxial layer on the substrate surface; a n-type epitaxial layer on the buffer epitaxial layer; and a top contact on the n-type epitaxial layer. The buffer epitaxial layer can include a n-type 4H--SiC epitaxial layer doped at a concentration of about 1.times.10.sup.15 cm.sup.-3 to about 5.times.10.sup.18 cm.sup.-3 with nitrogen, boron, aluminum, or a mixture thereof. The n-type epitaxial layer can include a n-type 4H--SiC epitaxial layer doped at a concentration of about 1.times.10.sup.13 cm.sup.-3 to about 5.times.10.sup.15 cm.sup.-3 with nitrogen. The top contact can have a thickness of about 8 nm to about 15 nm.

  5. Influence of layer thickness on the structure and the magnetic properties of Co/Pd epitaxial multilayer films

    Energy Technology Data Exchange (ETDEWEB)

    Tobari, Kousuke, E-mail: tobari@futamoto.elect.chuo-u.ac.jp [Faculty of Science and Engineering, Chuo University, Bunkyo-ku, Tokyo 112-8551 (Japan); Ohtake, Mitsuru; Nagano, Katsumasa; Futamoto, Masaaki [Faculty of Science and Engineering, Chuo University, Bunkyo-ku, Tokyo 112-8551 (Japan)

    2012-03-15

    Co/Pd epitaxial multilayer films were prepared on Pd(111){sub fcc} underlayers hetero-epitaxially grown on MgO(111){sub B1} single-crystal substrates at room temperature by ultra-high vacuum RF magnetron sputtering. In-situ reflection high energy electron diffraction shows that the in-plane lattice spacing of Co on Pd layer gradually decreases with increasing the Co layer thickness, whereas that of Pd on Co layer remains unchanged during the Pd layer formation. The CoPd alloy phase formation is observed around the Co/Pd interface. The atomic mixing is enhanced for thinner Co and Pd layers in multilayer structure. With decreasing the Co and the Pd layer thicknesses and increasing the repetition number of Co/Pd multilayer film, stronger perpendicular magnetic anisotropy is observed. The relationships between the film structure and the magnetic properties are discussed. - Highlights: Black-Right-Pointing-Pointer Epitaxial Co/Pd multilayer films are prepared on Pd(111){sub fcc} underlayers. Black-Right-Pointing-Pointer Lattice strain in Co layer and CoPd-alloy formation are noted around the interface. Black-Right-Pointing-Pointer Magnetic property dependence on layer thickness is reported.

  6. Band Gap Opening Induced by the Structural Periodicity in Epitaxial Graphene Buffer Layer.

    Science.gov (United States)

    N Nair, Maya; Palacio, Irene; Celis, Arlensiú; Zobelli, Alberto; Gloter, Alexandre; Kubsky, Stefan; Turmaud, Jean-Philippe; Conrad, Matthew; Berger, Claire; de Heer, Walter; Conrad, Edward H; Taleb-Ibrahimi, Amina; Tejeda, Antonio

    2017-04-12

    The epitaxial graphene buffer layer on the Si face of hexagonal SiC shows a promising band gap, of which the precise origin remains to be understood. In this work, we correlate the electronic to the atomic structure of the buffer layer by combining angle resolved photoemission spectroscopy (ARPES), scanning tunneling microscopy (STM), and high-resolution scanning transmission electron microscopy (HR-STEM). We show that the band structure in the buffer has an electronic periodicity related to the structural periodicity observed in STM images and published X-ray diffraction. Our HR-STEM measurements show the bonding of the buffer layer to the SiC at specific locations separated by 1.5 nm. This is consistent with the quasi 6 × 6 periodic corrugation observed in the STM images. The distance between buffer C and SiC is 1.9 Å in the bonded regions and up to 2.8 Å in the decoupled regions, corresponding to a 0.9 Å corrugation of the buffer layer. The decoupled regions are sp(2) hybridized. Density functional tight binding (DFTB) calculations demonstrate the presence of a gap at the Dirac point everywhere in the buffer layer, even in the decoupled regions where the buffer layer has an atomic structure close to that of graphene. The surface periodicity also promotes band in the superperiodic Brillouin zone edges as seen by photoemission and confirmed by our calculations.

  7. Epitaxial Growth of High-Quality Silicon Films on Double-Layer Porous Silicon

    Institute of Scientific and Technical Information of China (English)

    黄宜平; 竺士炀; 李爱珍; 王瑾; 黄靖云; 叶志镇

    2001-01-01

    The epitaxial growth of a high-quality silicon layer on double-layer porous silicon by ultra-high vacuum/chemical vapour deposition has been reported. The two-step anodization process results in a double-layer porous silicon structure with a different porosity. This double-layer porous silicon structure and an extended low-temperature annealing in a vacuum system was found to be helpful in subsequent silicon epitaxial growth. X-ray diffraction,cross-sectional transmission electron microscopy and spreading resistance testing were used in this work to study the properties of epitaxial silicon layers grown on the double-layer porous silicon. The results show that the epitaxial silicon layer is of good crystallinity and the same orientation with the silicon substrate and the porous silicon layer.

  8. films using atomic layer deposition

    Science.gov (United States)

    Chervinskii, Semen; Matikainen, Antti; Dergachev, Alexey; Lipovskii, Andrey A.; Honkanen, Seppo

    2014-08-01

    We fabricated self-assembled silver nanoisland films using a recently developed technique based on out-diffusion of silver from an ion-exchanged glass substrate in reducing atmosphere. We demonstrate that the position of the surface plasmon resonance of the films depends on the conditions of the film growth. The resonance can be gradually shifted up to 100 nm towards longer wavelengths by using atomic layer deposition of titania, from 3 to 100 nm in thickness, upon the film. Examination of the nanoisland films in surface-enhanced Raman spectrometry showed that, in spite of a drop of the surface-enhanced Raman spectroscopy (SERS) signal after the titania spacer deposition, the Raman signal can be observed with spacers up to 7 nm in thickness. Denser nanoisland films show slower decay of the SERS signal with the increase in spacer thickness.

  9. Changing of micromorphology of silicon-on-sapphire epitaxial layer surface at irradiation by subthreshold energy X-radiation

    CERN Document Server

    Kiselev, A N; Skupov, V D; Filatov, D O

    2001-01-01

    The morphology of silicon-on-sapphire epitaxial layer surface after pulse irradiation by the X-rays with the energy of <= 140 keV is studied. The study on the irradiated material surface is carried out by the methods of the atomic force microscopy and ellipsometry. The average roughness value after irradiation constitutes 7 nm. The change in the films surface microrelief occurs due to reconstruction of their dislocation structure under the action of elastic waves, originating in the X radiation

  10. Thin film solar cells based on layered chalcogenides: Fundamentals and perspectives of van der Waals epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Jaegermann, W.; Pettenkofer, C.; Lang, O.; Schlaf, R.; Tiefenbacher, S.; Tomm, Y. [Hahn-Meitner-Inst., Berlin (Germany)

    1994-12-31

    The preparation of thin films of layered chalcogenide semiconductors as MX and MX{sub 2} (X = S, Se) based on the concept of van der Waals epitaxy (VDWE) is presented for different substrate/overlayer combinations as GaSe, InSe, SnSe{sub 2}, WS{sub 2} on WSe{sub 2}, GaSe, MoTe{sub 2}, graphite and mica. In all cases stoichiometric films are formed either as epitaxial layers or strongly textured films with the c-axis aligned in spite of strong lattice mismatch. The interfaces are non-reactive and atomically abrupt. The electronic properties of the interfaces are mostly ideal showing band offsets according to the electron affinity rule and no operative interface states. However, doping of the films is still a problem which limits the band bending and the attainable surface photovoltage. The perspectives and preconditions for the further development of layered semiconductor VDWE films for solar cells will be critically discussed.

  11. Substrate-induced magnetism in epitaxial graphene buffer layers.

    Science.gov (United States)

    Ramasubramaniam, A; Medhekar, N V; Shenoy, V B

    2009-07-08

    Magnetism in graphene is of fundamental as well as technological interest, with potential applications in molecular magnets and spintronic devices. While defects and/or adsorbates in freestanding graphene nanoribbons and graphene sheets have been shown to cause itinerant magnetism, controlling the density and distribution of defects and adsorbates is in general difficult. We show from first principles calculations that graphene buffer layers on SiC(0001) can also show intrinsic magnetism. The formation of graphene-substrate chemical bonds disrupts the graphene pi-bonds and causes localization of graphene states near the Fermi level. Exchange interactions between these states lead to itinerant magnetism in the graphene buffer layer. We demonstrate the occurrence of magnetism in graphene buffer layers on both bulk-terminated as well as more realistic adatom-terminated SiC(0001) surfaces. Our calculations show that adatom density has a profound effect on the spin distribution in the graphene buffer layer, thereby providing a means of engineering magnetism in epitaxial graphene.

  12. Synthesis of atomically thin hexagonal boron nitride films on nickel foils by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Nakhaie, S.; Wofford, J. M.; Schumann, T.; Jahn, U.; Ramsteiner, M.; Hanke, M.; Lopes, J. M. J., E-mail: lopes@pdi-berlin.de; Riechert, H. [Paul-Drude-Institut für Festkörperelektronik, Hausvogteiplatz 5-7, 10117 Berlin (Germany)

    2015-05-25

    Hexagonal boron nitride (h-BN) is a layered two-dimensional material with properties that make it promising as a dielectric in various applications. We report the growth of h-BN films on Ni foils from elemental B and N using molecular beam epitaxy. The presence of crystalline h-BN over the entire substrate is confirmed by Raman spectroscopy. Atomic force microscopy is used to examine the morphology and continuity of the synthesized films. A scanning electron microscopy study of films obtained using shorter depositions offers insight into the nucleation and growth behavior of h-BN on the Ni substrate. The morphology of h-BN was found to evolve from dendritic, star-shaped islands to larger, smooth triangular ones with increasing growth temperature.

  13. Triggering the atomic layers control of hexagonal boron nitride films

    Energy Technology Data Exchange (ETDEWEB)

    Song, Yangxi [State Key Laboratory of Advanced Ceramic Fibers and Composites, College of Aerospace Science and Engineering, National University of Defense Technology, Changsha 410073 (China); Zhang, Changrui, E-mail: crzhang12@gmail.com [State Key Laboratory of Advanced Ceramic Fibers and Composites, College of Aerospace Science and Engineering, National University of Defense Technology, Changsha 410073 (China); Li, Bin [State Key Laboratory of Advanced Ceramic Fibers and Composites, College of Aerospace Science and Engineering, National University of Defense Technology, Changsha 410073 (China); Jiang, Da; Ding, Guqiao; Wang, Haomin [State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, 865 Changning Road, Shanghai 200050 (China); Xie, Xiaoming, E-mail: xmxie@mail.sim.ac.cn [State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, 865 Changning Road, Shanghai 200050 (China)

    2014-09-15

    Highlights: • Thickness of h-BN films can be controlled from double atomic layers to over ten atomic layers by adjusting the CVD parameters, quite different from the reported thickness control of up to tens of nanometers. (The interlayer distance of h-BN is 0.333 nm.) • Growth mechanisms of h-BN are discussed, especially for bilayer h-BN films. • Both epitaxial growth and diffusion-segregation process are involved in the synthesis of bilayer h-BN films. - Abstract: In this work, we report the successful synthesis of large scale hexagonal boron nitride films with controllable atomic layers. The films are grown on thin nickel foils via ambient pressure chemical vapor deposition with borazine as the precursor. The atomic layers of h-BN films can be controlled in a narrow range by adjusting growth time and the cooling rates. Transmission electron microscope results shows the h-BN films exhibit high uniformity and good crystalline. X-ray photoelectron spectroscopy shows the B/N elemental ratio is about 1.01. The h-BN films exhibit a pronounced deep ultraviolet absorption at 203.0 nm with a large optical band gap of 6.02 ± 0.03 eV. The results suggest potential applications of h-BN films in deep ultraviolet and dielectric materials. Growth mechanisms of h-BN films with thickness control are discussed, especially when the synthesized h-BN films after a higher cooling rate show an in-plane rotation angle between bilayers. Both epitaxial growth and diffusion-segregation process are involved in the synthesis of bilayer h-BN films.

  14. Electron molecular beam epitaxy: Layer-by-layer growth of complex oxides via pulsed electron-beam deposition

    Energy Technology Data Exchange (ETDEWEB)

    Comes, Ryan; Liu Hongxue; Lu Jiwei [Department of Materials Science and Engineering, University of Virginia, Charlottesville, Virginia 22904 (United States); Gu, Man [Department of Physics, University of Virginia, Charlottesville, Virginia 22904 (United States); Khokhlov, Mikhail; Wolf, Stuart A. [Department of Materials Science and Engineering, University of Virginia, Charlottesville, Virginia 22904 (United States); Guilford College, Greensboro, North Carolina 27410 (United States)

    2013-01-14

    Complex oxide epitaxial film growth is a rich and exciting field, owing to the wide variety of physical properties present in oxides. These properties include ferroelectricity, ferromagnetism, spin-polarization, and a variety of other correlated phenomena. Traditionally, high quality epitaxial oxide films have been grown via oxide molecular beam epitaxy or pulsed laser deposition. Here, we present the growth of high quality epitaxial films using an alternative approach, the pulsed electron-beam deposition technique. We demonstrate all three epitaxial growth modes in different oxide systems: Frank-van der Merwe (layer-by-layer); Stranski-Krastanov (layer-then-island); and Volmer-Weber (island). Analysis of film quality and morphology is presented and techniques to optimize the morphology of films are discussed.

  15. Electron molecular beam epitaxy: Layer-by-layer growth of complex oxides via pulsed electron-beam deposition

    Science.gov (United States)

    Comes, Ryan; Gu, Man; Khokhlov, Mikhail; Liu, Hongxue; Lu, Jiwei; Wolf, Stuart A.

    2013-01-01

    Complex oxide epitaxial film growth is a rich and exciting field, owing to the wide variety of physical properties present in oxides. These properties include ferroelectricity, ferromagnetism, spin-polarization, and a variety of other correlated phenomena. Traditionally, high quality epitaxial oxide films have been grown via oxide molecular beam epitaxy or pulsed laser deposition. Here, we present the growth of high quality epitaxial films using an alternative approach, the pulsed electron-beam deposition technique. We demonstrate all three epitaxial growth modes in different oxide systems: Frank-van der Merwe (layer-by-layer); Stranski-Krastanov (layer-then-island); and Volmer-Weber (island). Analysis of film quality and morphology is presented and techniques to optimize the morphology of films are discussed.

  16. Zintl layer formation during perovskite atomic layer deposition on Ge (001)

    Science.gov (United States)

    Hu, Shen; Lin, Edward L.; Hamze, Ali K.; Posadas, Agham; Wu, HsinWei; Smith, David J.; Demkov, Alexander A.; Ekerdt, John G.

    2017-02-01

    Using in situ X-ray photoelectron spectroscopy, reflection high-energy electron diffraction, and density functional theory, we analyzed the surface core level shifts and surface structure during the initial growth of ABO3 perovskites on Ge (001) by atomic layer deposition, where A = Ba, Sr and B = Ti, Hf, Zr. We find that the initial dosing of the barium- or strontium-bis(triisopropylcyclopentadienyl) precursors on a clean Ge surface produces a surface phase that has the same chemical and structural properties as the 0.5-monolayer Ba Zintl layer formed when depositing Ba by molecular beam epitaxy. Similar binding energy shifts are found for Ba, Sr, and Ge when using either chemical or elemental metal sources. The observed germanium surface core level shifts are consistent with the flattening of the initially tilted Ge surface dimers using both molecular and atomic metal sources. Similar binding energy shifts and changes in dimer tilting with alkaline earth metal adsorption are found with density functional theory calculations. High angle angular dark field scanning transmission microscopy images of BaTiO3, SrZrO3, SrHfO3, and SrHf0.55Ti0.45O3 reveal the location of the Ba (or Sr) atomic columns between the Ge dimers. The results imply that the organic ligands dissociate from the precursor after precursor adsorption on the Ge surface, producing the same Zintl template critical for perovskite growth on Group IV semiconductors during molecular beam epitaxy.

  17. Lattice sites of diffused gold and platinum in epitaxial ZnSe layers

    Science.gov (United States)

    Seppälä, A.; Salonen, R.; Slotte, J.; Ahlgren, T.; Rauhala, E.; Räisänen, J.

    2000-03-01

    The lattice location of diffused gold and platinum in zinc selenide (ZnSe) epitaxial layers was studied using the Rutherford backscattering (RBS) channeling technique. Thin Au and Pt films were evaporated onto ZnSe samples. The Au/ZnSe samples were annealed at 525°C and the residual Au film was removed by etching. Channeling angular scan measurements showed that about 30% of Au atoms were close to substitutional site (displaced about 0.2 Å). In the case of the Pt/ZnSe samples the annealing temperatures ranged from 600°C to 800°C. The Pt minimum yields along direction were close to the random value, varying from 80% to 90%. The measured Pt angular scans along and directions indicated a random location.

  18. STM studies of GeSi thin layers epitaxially grown on Si(111)

    Science.gov (United States)

    Motta, N.; Sgarlata, A.; De Crescenzi, M.; Derrien, J.

    1996-08-01

    Ge/Si alloys were prepared in UHV by solid phase epitaxy on Si(111) substrates. The alloy formation, as a function of the evaporation rate and the Ge layer thickness has been followed in situ by RHEED and scanning tunneling microscopy. The 5 × 5 surface reconstruction appeared after annealing at 450°C Ge layers (up to 10 Å thick), obtained from a low rate Knudsen cell evaporator. In this case a nearly flat and uniform layer of reconstructed alloy was observed. When using an e-gun high rate evaporator we needed to anneal the Ge layer up to 780°C to obtain a 5 × 5 reconstruction. The grown layer was not flat, with many steps and Ge clusters; at high coverages (10 Å and more) large Ge islands appeared. Moreover, we then succeeded in visualizing at atomic resolution the top of some of these Ge islands which displayed a 2 × 1 reconstruction, probably induced from the high compressive strain due to the lattice mismatch with the substrate. We suggest that this unusual behavior could be connected to the high evaporation rate, which helped the direct formation of Ge microcrystals on the Si substrate during the deposition process.

  19. Atomic layer deposition of nanoporous biomaterials

    Directory of Open Access Journals (Sweden)

    Roger J Narayan

    2010-03-01

    Full Text Available Due to its chemical stability, uniform pore size, and high pore density, nanoporous alumina is being investigated for use in biosensing, drug delivery, hemodialysis, and other medical applications. In recent work, we have examined the use of atomic layer deposition for coating the surfaces of nanoporous alumina membranes. Zinc oxide coatings were deposited on nanoporous alumina membranes using atomic layer deposition. The zinc oxide-coated nanoporous alumina membranes demonstrated antimicrobial activity against Escherichia coli and Staphylococcus aureus bacteria. These results suggest that atomic layer deposition is an attractive technique for modifying the surfaces of nanoporous alumina membranes and other nanostructured biomaterials.

  20. Epitaxially grown polycrystalline silicon thin-film solar cells on solid-phase crystallised seed layers

    Energy Technology Data Exchange (ETDEWEB)

    Li, Wei, E-mail: weili.unsw@gmail.com; Varlamov, Sergey; Xue, Chaowei

    2014-09-30

    Highlights: • Crystallisation kinetic is used to analyse seed layer surface cleanliness. • Simplified RCA cleaning for the seed layer can shorten the epitaxy annealing duration. • RTA for the seed layer can improve the quality for both seed layer and epi-layer. • Epitaxial poly-Si solar cell performance is improved by RTA treated seed layer. - Abstract: This paper presents the fabrication of poly-Si thin film solar cells on glass substrates using seed layer approach. The solid-phase crystallised P-doped seed layer is not only used as the crystalline template for the epitaxial growth but also as the emitter for the solar cell structure. This paper investigates two important factors, surface cleaning and intragrain defects elimination for the seed layer, which can greatly influence the epitaxial grown solar cell performance. Shorter incubation and crystallisation time is observed using a simplified RCA cleaning than the other two wet chemical cleaning methods, indicating a cleaner seed layer surface is achieved. Cross sectional transmission microscope images confirm a crystallographic transferal of information from the simplified RCA cleaned seed layer into the epi-layer. RTA for the SPC seed layer can effectively eliminate the intragrain defects in the seed layer and improve structural quality of both of the seed layer and the epi-layer. Consequently, epitaxial grown poly-Si solar cell on the RTA treated seed layer shows better solar cell efficiency, V{sub oc} and J{sub sc} than the one on the seed layer without RTA treatment.

  1. Influence of the V/III ratio in the gas phase on thin epitaxial AlN layers grown on (0001) sapphire by high temperature hydride vapor phase epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Claudel, A., E-mail: arnaud.claudel@grenoble-inp.org [ACERDE, 354 Voie Magellan — Alpespace, 73800 Ste Hélène du Lac (France); Fellmann, V. [ACERDE, 354 Voie Magellan — Alpespace, 73800 Ste Hélène du Lac (France); Science et Ingénierie des Matériaux et des Procédés, Grenoble INP-CNRS-UJF, BP 75, 38402 Saint Martin d' Hères (France); Gélard, I. [ACERDE, 354 Voie Magellan — Alpespace, 73800 Ste Hélène du Lac (France); Coudurier, N. [ACERDE, 354 Voie Magellan — Alpespace, 73800 Ste Hélène du Lac (France); Science et Ingénierie des Matériaux et des Procédés, Grenoble INP-CNRS-UJF, BP 75, 38402 Saint Martin d' Hères (France); Sauvage, D. [ACERDE, 354 Voie Magellan — Alpespace, 73800 Ste Hélène du Lac (France); Balaji, M. [ACERDE, 354 Voie Magellan — Alpespace, 73800 Ste Hélène du Lac (France); Science et Ingénierie des Matériaux et des Procédés, Grenoble INP-CNRS-UJF, BP 75, 38402 Saint Martin d' Hères (France); Crystal Growth Center, Anna University, Chennai 600025 (India); and others

    2014-12-31

    Thin (0001) epitaxial aluminum nitride (AlN) layers were grown on c-plane sapphire using high temperature hydride vapor phase epitaxy. The experimental set-up consists of a vertical cold-wall quartz reactor working at low pressure in which the reactions take place on a susceptor heated by induction. The reactants used are ammonia and aluminum chlorides in situ formed via hydrogen chloride reaction with high purity aluminum pellets. As-grown AlN layers have been characterized by scanning electron microscopy, atomic force microscopy, X-ray diffraction, transmission electron microscopy, photoluminescence and Raman spectroscopies. The influence of the V/III ratio in the gas phase, from 1.5 to 15, on growth rate, surface morphology, roughness and crystalline quality is investigated in order to increase the quality of thin epitaxial AlN layers grown at high temperature. Typical growth rates of around 0.45 μm/h were obtained for such thin epitaxial AlN layers. The growth rate was unaffected by the V/III ratio. An optimum for roughness, crystalline quality and optical properties seems to exist at V/III = 7.5. As a matter of fact, for a V/III ratio of 7.5, best root mean square roughness and crystalline quality — measured on 0002 symmetric reflection — as low as 6.9 nm and 898 arcsec were obtained, respectively. - Highlights: • Growth of thin epitaxial AlN layers by high temperature hydride vapor phase epitaxy • Influence of V/III ratio on growth rate, morphology and crystalline quality • The effect of surface morphology on strain state and crystal quality is established.

  2. Atom probe tomography characterisation of a laser diode structure grown by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Bennett, Samantha E.; Humphreys, Colin J.; Oliver, Rachel A. [Department of Materials Science and Metallurgy, University of Cambridge, Pembroke Street, Cambridge, CB2 3QZ (United Kingdom); Smeeton, Tim M.; Hooper, Stewart E.; Heffernan, Jonathan [Sharp Laboratories of Europe Limited, Edmund Halley Road, Oxford Science Park, Oxford, OX4 4GB (United Kingdom); Saxey, David W.; Smith, George D. W. [Department of Materials, University of Oxford, Parks Road, Oxford, OX1 3PH (United Kingdom)

    2012-03-01

    Atom probe tomography (APT) has been used to achieve three-dimensional characterization of a III-nitride laser diode (LD) structure grown by molecular beam epitaxy (MBE). Four APT data sets have been obtained, with fields of view up to 400 nm in depth and 120 nm in diameter. These data sets contain material from the InGaN quantum well (QW) active region, as well as the surrounding p- and n-doped waveguide and cladding layers, enabling comprehensive study of the structure and composition of the LD structure. Two regions of the same sample, with different average indium contents (18% and 16%) in the QW region, were studied. The APT data are shown to provide easy access to the p-type dopant levels, and the composition of a thin AlGaN barrier layer. Next, the distribution of indium within the InGaN QW was analyzed, to assess any possible inhomogeneity of the distribution of indium (''indium clustering''). No evidence for a statistically significant deviation from a random distribution was found, indicating that these MBE-grown InGaN QWs do not require indium clusters for carrier localization. However, the APT data show steps in the QW interfaces, leading to well-width fluctuations, which may act to localize carriers. Additionally, the unexpected presence of a small amount (x = 0.005) of indium in a layer grown intentionally as GaN was revealed. Finally, the same statistical method applied to the QW was used to show that the indium distribution within a thick InGaN waveguide layer in the n-doped region did not show any deviation from randomness.

  3. Ultra-smooth epitaxial Ge grown on Si(001) utilizing a thin C-doped Ge buffer layer

    KAUST Repository

    Mantey, J.

    2013-01-01

    Here, we present work on epitaxial Ge films grown on a thin buffer layer of C doped Ge (Ge:C). The growth rate of Ge:C is found to slow over time and is thus unsuitable for thick (>20 nm) layers. We demonstrate Ge films from 10 nm to >150 nm are possible by growing pure Ge on a thin Ge:C buffer. It is shown that this stack yields exceedingly low roughness levels (comparable to bulk Si wafers) and contains fewer defects and higher Hall mobility compared to traditional heteroepitaxial Ge. The addition of C at the interface helps reduce strain by its smaller atomic radius and its ability to pin defects within the thin buffer layer that do not thread to the top Ge layer. © 2013 AIP Publishing LLC.

  4. Increasing the radiation resistance of single-crystal silicon epitaxial layers

    OpenAIRE

    Kurmashev Sh. D.; Kulinich O. A.; Brusenskaya G. I.; Verem’eva A. V.

    2014-01-01

    The authors investigate the possibility of increasing the radiation resistance of silicon epitaxial layers by creating radiation defects sinks in the form of dislocation networks of the density of 109—1012 m–2. Such networks are created before the epitaxial layer is applied on the front surface of the silicon substrate by its preliminary oxidation and subsequent etching of the oxide layer. The substrates were silicon wafers KEF-4.5 and KDB-10 with a diameter of about 40 mm, grown by the Czoch...

  5. Fabrication of magnetic tunnel junctions with epitaxial and textured ferromagnetic layers

    Science.gov (United States)

    Chang, Y. Austin; Yang, Jianhua Joshua

    2008-11-11

    This invention relates to magnetic tunnel junctions and methods for making the magnetic tunnel junctions. The magnetic tunnel junctions include a tunnel barrier oxide layer sandwiched between two ferromagnetic layers both of which are epitaxial or textured with respect to the underlying substrate upon which the magnetic tunnel junctions are grown. The magnetic tunnel junctions provide improved magnetic properties, sharper interfaces and few defects.

  6. Epitaxially grown polycrystalline silicon thin-film solar cells on solid-phase crystallised seed layers

    Science.gov (United States)

    Li, Wei; Varlamov, Sergey; Xue, Chaowei

    2014-09-01

    This paper presents the fabrication of poly-Si thin film solar cells on glass substrates using seed layer approach. The solid-phase crystallised P-doped seed layer is not only used as the crystalline template for the epitaxial growth but also as the emitter for the solar cell structure. This paper investigates two important factors, surface cleaning and intragrain defects elimination for the seed layer, which can greatly influence the epitaxial grown solar cell performance. Shorter incubation and crystallisation time is observed using a simplified RCA cleaning than the other two wet chemical cleaning methods, indicating a cleaner seed layer surface is achieved. Cross sectional transmission microscope images confirm a crystallographic transferal of information from the simplified RCA cleaned seed layer into the epi-layer. RTA for the SPC seed layer can effectively eliminate the intragrain defects in the seed layer and improve structural quality of both of the seed layer and the epi-layer. Consequently, epitaxial grown poly-Si solar cell on the RTA treated seed layer shows better solar cell efficiency, Voc and Jsc than the one on the seed layer without RTA treatment.

  7. Epitaxial growth of a monolayer WSe2-MoS2 lateral p-n junction with an atomically sharp interface

    Science.gov (United States)

    Li, Ming-Yang; Shi, Yumeng; Cheng, Chia-Chin; Lu, Li-Syuan; Lin, Yung-Chang; Tang, Hao-Lin; Tsai, Meng-Lin; Chu, Chih-Wei; Wei, Kung-Hwa; He-Hau, Jr.; Chang, Wen-Hao; Suenaga, Kazu; Li, Lain-Jong

    2015-07-01

    Two-dimensional transition metal dichalcogenides (TMDCs) such as molybdenum sulfide MoS2 and tungsten sulfide WSe2 have potential applications in electronics because they exhibit high on-off current ratios and distinctive electro-optical properties. Spatially connected TMDC lateral heterojunctions are key components for constructing monolayer p-n rectifying diodes, light-emitting diodes, photovoltaic devices, and bipolar junction transistors. However, such structures are not readily prepared via the layer-stacking techniques, and direct growth favors the thermodynamically preferred TMDC alloys. We report the two-step epitaxial growth of lateral WSe2-MoS2 heterojunction, where the edge of WSe2 induces the epitaxial MoS2 growth despite a large lattice mismatch. The epitaxial growth process offers a controllable method to obtain lateral heterojunction with an atomically sharp interface.

  8. Epitaxial growth of a monolayer WSe2-MoS2 lateral p-n junction with an atomically sharp interface

    KAUST Repository

    Li, Ming Yang

    2015-07-30

    Two-dimensional transition metal dichalcogenides (TMDCs) such as molybdenum sulfide MoS2 and tungsten sulfide WSe2 have potential applications in electronics because they exhibit high on-off current ratios and distinctive electro-optical properties. Spatially connected TMDC lateral heterojunctions are key components for constructing monolayer p-n rectifying diodes, light-emitting diodes, photovoltaic devices, and bipolar junction transistors. However, such structures are not readily prepared via the layer-stacking techniques, and direct growth favors the thermodynamically preferred TMDC alloys. We report the two-step epitaxial growth of lateral WSe2-MoS2 heterojunction, where the edge of WSe2 induces the epitaxial MoS2 growth despite a large lattice mismatch. The epitaxial growth process offers a controllable method to obtain lateral heterojunction with an atomically sharp interface.

  9. Complex Materials by Atomic Layer Deposition.

    Science.gov (United States)

    Schwartzberg, Adam M; Olynick, Deirdre

    2015-10-14

    Complex materials are defined as nanostructured materials with combinations of structure and/or composition that lead to performance surpassing the sum of their individual components. There are many methods that can create complex materials; however, atomic layer deposition (ALD) is uniquely suited to control composition and structural parameters at the atomic level. The use of ALD for creating complex insulators, semiconductors, and conductors is discussed, along with its use in novel structural applications.

  10. Perovskite Thin Films via Atomic Layer Deposition

    KAUST Repository

    Sutherland, Brandon R.

    2014-10-30

    © 2014 Wiley-VCH Verlag GmbH & Co. KGaA. (Graph Presented) A new method to deposit perovskite thin films that benefit from the thickness control and conformality of atomic layer deposition (ALD) is detailed. A seed layer of ALD PbS is place-exchanged with PbI2 and subsequently CH3NH3PbI3 perovskite. These films show promising optical properties, with gain coefficients of 3200 ± 830 cm-1.

  11. Perovskite thin films via atomic layer deposition.

    Science.gov (United States)

    Sutherland, Brandon R; Hoogland, Sjoerd; Adachi, Michael M; Kanjanaboos, Pongsakorn; Wong, Chris T O; McDowell, Jeffrey J; Xu, Jixian; Voznyy, Oleksandr; Ning, Zhijun; Houtepen, Arjan J; Sargent, Edward H

    2015-01-01

    A new method to deposit perovskite thin films that benefit from the thickness control and conformality of atomic layer deposition (ALD) is detailed. A seed layer of ALD PbS is place-exchanged with PbI2 and subsequently CH3 NH3 PbI3 perovskite. These films show promising optical properties, with gain coefficients of 3200 ± 830 cm(-1) .

  12. Laser Molecular Beam Epitaxy of Multilayer Heterostructure SrNb0.05 Ti0.95O3/La0.9Sr0.1MnO3 in 10000 Unit-Cell Layers

    Institute of Scientific and Technical Information of China (English)

    HUANG Yan-Hong; HE Meng; TIAN Huan-Fang; ZHAO Kun; L(U) Hui-Bin; JIN Kui-Juan; LI Jian-Qi; YANG Guo-Zhen

    2008-01-01

    Ten thousands of unit-cell multilayer heterosturctures, [SrNb0.05 Ti0.95 O3/La0.9Sr0.1MnO3]3 (SNTO/LSMO),have been epitaxial grown on SrTiO3 (001) substrates by laser molecular beam epitaxy. The monitor of insitu reflection high-energy electron diffraction demonstrates that the heterosturctures are layer-by-layer epitaxial growth. Atomic force microscope observation indicates that the surface of the heterosturcture is atomically smooth. The measurements of cross-sectional low magnification and high-resolution transmission electron microscopy as well as the corresponding selected area electron diffraction reveal that the interfaces are of perfect orientation, and the epitaxial crystalline structure shows the orientation relation of SNTO(001)//LSMO(001),and SNTO[100]//LSMO[100].

  13. Photoluminescence Characterization of Boron-doped Si Layers Grown by Molecular Beam Epitaxy

    Institute of Scientific and Technical Information of China (English)

    LI Cheng; LAI Hong-kai; CHEN Song-yan

    2005-01-01

    Photoluminescence spectra were used to characterize the boron-doped Si layers grown by molecular beam epitaxy using HBO2 as the doping source. The influence of boron doping concentration on the dislocation-related photoluminescence spectra of molecular beam epitaxy Si layers annealed at 900 ℃ was studied with different doping concentrations and growth temperature. The broad photoluminescence band(from 0.75 eV to 0.90 eV) including D1 and D2 bands was associated with high boron doping concentration in the samples, while D3 and D4 bands might be related to oxygen precipitates.

  14. Characterization of thick epitaxial GaAs layers for X-ray detection

    CERN Document Server

    Samic, H; Donchev, V; Nghia, N X; Gandouzi, M; Zazoui, M; Bourgoin, J C; El-Abbassi, H; Rath, S; Sellin, P J

    2002-01-01

    We have studied the current-voltage and capacitance-voltage characteristics of p/i/n structures made on non-intentionally doped epitaxial GaAs layers grown by the chemical reaction method. Deep level transient spectroscopy demonstrates that these layers contain a low defect concentration. X-ray photoconductivity shows that the diffusion length is large. The homogeneity of the properties of these layers, which has been evaluated over large area (cm sup 2), is confirmed by photoluminescence mapping.

  15. Layered Atom Arrangements in Complex Materials

    Energy Technology Data Exchange (ETDEWEB)

    K.E. Sikafus; R.W.Grimes; S.M.Corish; A.R. Cleave; M.Tang; C.R.Stanek; B.P. Uberuaga; J.A.Valdez

    2005-04-15

    In this report, we develop an atom layer stacking model to describe systematically the crystal structures of complex materials. To illustrate the concepts, we consider a sequence of oxide compounds in which the metal cations progress in oxidation state from monovalent (M{sup 1+}) to tetravalent (M{sup 4+}). We use concepts relating to geometric subdivisions of a triangular atom net to describe the layered atom patterns in these compounds (concepts originally proposed by Shuichi Iida). We demonstrate that as a function of increasing oxidation state (from M{sup 1+} to M{sup 4+}), the layer stacking motifs used to generate each successive structure (specifically, motifs along a 3 symmetry axis), progress through the following sequence: MMO, MO, M{sub r}O, MO{sub r/s}O{sub u/v}, MOO (where M and O represent fully dense triangular atom nets and r/s and u/v are fractions used to describe partially filled triangular atom nets). We also develop complete crystallographic descriptions for the compounds in our oxidation sequence using trigonal space group R{bar 3}.

  16. InGaN light emitting diodes with a nanopipe layer formed from the GaN epitaxial layer.

    Science.gov (United States)

    Hsu, Wei-Ju; Chen, Kuei-Ting; Huang, Wan-Chun; Wu, Chia-Jung; Dai, Jing-Jie; Chen, Sy-Hann; Lin, Chia-Feng

    2016-05-30

    A Si-heavy doped GaN:Si epitaxial layer is transformed into a directional nanopipe GaN layer through a laser-scribing process and a selectively electrochemical (EC) etching process. InGaN light-emitting diodes (LEDs) with an EC-treated nanopipe GaN layer have a high light extraction efficiency. The direction of the nanopipe structure was directed perpendicular to the laser scribing line and was guided by an external bias electric field. An InGaN LED structure with an embedded nanopipe GaN layer can enhance external quantum efficiency through a one-step epitaxial growth process and a selective EC etching process. A birefringence optical property and a low effective refractive index were observed in the directional-nanopipe GaN layer.

  17. Atomic-layer engineering of oxide superconductors

    Science.gov (United States)

    Bollinger, A. T.; Eckstein, J. N.; Dubuis, G.; Pavuna, D.; Božović, I.

    2012-02-01

    Molecular beam epitaxy technique has enabled synthesis of atomically smooth thin films, multilayers, and superlattices of cuprates and other complex oxides. Such heterostructures show high temperature superconductivity and enable novel experiments that probe the basic physics of this phenomenon. For example, it was established that high temperature superconductivity and anti-ferromagnetic phases separate on Ångström scale, while the pseudo-gap state apparently mixes with high temperature superconductivity over an anomalously large length scale (the "Giant Proximity Effect"). We review some recent experiments on such films and superlattices, including X-ray diffraction, atomic force microscopy, angle-resolved time of flight ion scattering and recoil spectroscopy, transport measurements, highresolution transmission electron microscopy, resonant X-ray scattering, low-energy muon spin resonance, and ultrafast photo-induced reflection high energy electron diffraction. The results include an unambiguous demonstration of strong coupling of in-plane charge excitations to out-of-plane lattice vibrations, a discovery of interface high temperature superconductivity that occurs in a single CuO2 plane, evidence for local pairs, and establishing tight limits on the temperature range of superconducting fluctuations.

  18. Atomic-Layer Engineering of Oxide Superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Bozovic I.; Bollinger, A.T.; Eckstein, J.N.; Dubuis, G.; Pavuna, D.

    2012-03-01

    Molecular beam epitaxy technique has enabled synthesis of atomically smooth thin films, multilayers, and superlattices of cuprates and other complex oxides. Such heterostructures show high temperature superconductivity and enable novel experiments that probe the basic physics of this phenomenon. For example, it was established that high temperature superconductivity and anti-ferromagnetic phases separate on Angstrom scale, while the pseudo-gap state apparently mixes with high temperature superconductivity over an anomalously large length scale (the 'Giant Proximity Effect'). We review some recent experiments on such films and superlattices, including X-ray diffraction, atomic force microscopy, angle-resolved time of flight ion scattering and recoil spectroscopy, transport measurements, high resolution transmission electron microscopy, resonant X-ray scattering, low-energy muon spin resonance, and ultrafast photo-induced reflection high energy electron diffraction. The results include an unambiguous demonstration of strong coupling of in-plane charge excitations to out-of-plane lattice vibrations, a discovery of interface high temperature superconductivity that occurs in a single CuO{sub 2} plane, evidence for local pairs, and establishing tight limits on the temperature range of superconducting fluctuations.

  19. Nano-soldering to single atomic layer

    Science.gov (United States)

    Girit, Caglar O.; Zettl, Alexander K.

    2011-10-11

    A simple technique to solder submicron sized, ohmic contacts to nanostructures has been disclosed. The technique has several advantages over standard electron beam lithography methods, which are complex, costly, and can contaminate samples. To demonstrate the soldering technique graphene, a single atomic layer of carbon, has been contacted, and low- and high-field electronic transport properties have been measured.

  20. DOE-EPSCoR. Exchange interactions in epitaxial intermetallic layered systems

    Energy Technology Data Exchange (ETDEWEB)

    LeClair, Patrick R. [Univ. of Alabama, Tuscaloosa, AL (United States); Gary, Mankey J. [Univ. of Alabama, Tuscaloosa, AL (United States)

    2015-05-25

    The goal of this research is to develop a fundamental understanding of the exchange interactions in epitaxial intermetallic alloy thin films and multilayers, including films and multilayers of Fe-Pt, Co-Pt and Fe-P-Rh alloys deposited on MgO and Al2O3 substrates. Our prior results have revealed that these materials have a rich variety of ferromagnetic, paramagnetic and antiferromagnetic phases which are sensitive functions of composition, substrate symmetry and layer thickness. Epitaxial antiferromagnetic films of FePt alloys exhibit a different phase diagram than bulk alloys. The antiferromagnetism of these materials has both spin ordering transitions and spin orienting transitions. The objectives include the study of exchange-inversion materials and the interface of these materials with ferromagnets. Our aim is to formulate a complete understanding of the magnetic ordering in these materials, as well as developing an understanding of how the spin structure is modified through contact with a ferromagnetic material at the interface. The ultimate goal is to develop the ability to tune the phase diagram of the materials to produce layered structures with tunable magnetic properties. The alloy systems that we will study have a degree of complexity and richness of magnetic phases that requires the use of the advanced tools offered by the DOE-operated national laboratory facilities, such as neutron and x-ray scattering to measure spin ordering, spin orientations, and element-specific magnetic moments. We plan to contribute to DOE’s mission of producing “Materials by Design” with properties determined by alloy composition and crystal structure. We have developed the methods for fabricating and have performed neutron diffraction experiments on some of the most interesting phases, and our work will serve to answer questions raised about the element-specific magnetizations using the magnetic x-ray dichroism techniques and interface magnetism in layered structures

  1. Spotting 2D atomic layers on aluminum nitride thin films.

    Science.gov (United States)

    Chandrasekar, Hareesh; Bharadwaj B, Krishna; Vaidyuala, Kranthi Kumar; Suran, Swathi; Bhat, Navakanta; Varma, Manoj; Srinivasan Raghavan

    2015-10-23

    Substrates for 2D materials are important for tailoring their fundamental properties and realizing device applications. Aluminum nitride (AIN) films on silicon are promising large-area substrates for such devices in view of their high surface phonon energies and reasonably large dielectric constants. In this paper epitaxial layers of AlN on 2″ Si wafers have been investigated as a necessary first step to realize devices from exfoliated or transferred atomic layers. Significant thickness dependent contrast enhancements are both predicted and observed for monolayers of graphene and MoS2 on AlN films as compared to the conventional SiO2 films on silicon, with calculated contrast values approaching 100% for graphene on AlN as compared to 8% for SiO2 at normal incidences. Quantitative estimates of experimentally measured contrast using reflectance spectroscopy show very good agreement with calculated values. Transistors of monolayer graphene on AlN films are demonstrated, indicating the feasibility of complete device fabrication on the identified layers.

  2. Growth and characterization of molecular beam epitaxial GaAs layers on porous silicon

    Science.gov (United States)

    Lin, T. L.; Liu, J. K.; Sadwick, L.; Wang, K. L.; Kao, Y. C.

    1987-01-01

    GaAs layers have been grown on porous silicon (PS) substrates with good crystallinity by molecular beam epitaxy. In spite of the surface irregularity of PS substrates, no surface morphology deterioration was observed on epitaxial GaAs overlayers. A 10-percent Rutherford backscattering spectroscopy minimum channeling yield for GaAs-on-PS layers as compared to 16 percent for GaAs-on-Si layers grown under the same condition indicates a possible improvement of crystallinity when GaAs is grown on PS. Transmission electron microscopy reveals that the dominant defects in the GaAs-on-PS layers are microtwins and stacking faults, which originate from the GaAs/PS interface. GaAs is found to penetrate into the PS layers. n-type GaAs/p-type PS heterojunction diodes were fabricated with good rectifying characteristics.

  3. Efficient Exciton Diffusion and Resonance-Energy Transfer in Multi-Layered Organic Epitaxial Nanofibers

    DEFF Research Database (Denmark)

    Tavares, Luciana; Cadelano, Michele; Quochi, Francesco;

    2015-01-01

    Multi-layered epitaxial nanofibers are exemplary model systems for the study of exciton dynamics and lasing in organic materials due to their well-defined morphology, high luminescence efficiencies, and color tunability. We resort to temperature-dependent cw and picosecond photoluminescence (PL) ...

  4. Atomic layer deposition of nanoporous biomaterials.

    Energy Technology Data Exchange (ETDEWEB)

    Narayan, R. J.; Adiga, S. P.; Pellin, M. J.; Curtiss, L. A.; Stafslien, S.; Chisholm, B.; Monteiro-Riviere, N. A.; Brigmon, R. L.; Elam, J. W.; Univ. of North Carolina; North Carolina State Univ.; Eastman Kodak Co.; North Dakota State Univ.; SRL

    2010-03-01

    Due to its chemical stability, uniform pore size, and high pore density, nanoporous alumina is being investigated for use in biosensing, drug delivery, hemodialysis, and other medical applications. In recent work, we have examined the use of atomic layer deposition for coating the surfaces of nanoporous alumina membranes. Zinc oxide coatings were deposited on nanoporous alumina membranes using atomic layer deposition. The zinc oxide-coated nanoporous alumina membranes demonstrated antimicrobial activity against Escherichia coli and Staphylococcus aureus bacteria. These results suggest that atomic layer deposition is an attractive technique for modifying the surfaces of nanoporous alumina membranes and other nanostructured biomaterials. Nanoporous alumina, also known as anodic aluminum oxide (AAO), is a nanomaterial that exhibits several unusual properties, including high pore densities, straight pores, small pore sizes, and uniform pore sizes. In 1953, Keller et al. showed that anodizing aluminum in acid electrolytes results in a thick layer of nearly cylindrical pores, which are arranged in a close-packed hexagonal cell structure. More recently, Matsuda & Fukuda demonstrated preparation of highly ordered platinum and gold nanohole arrays using a replication process. In this study, a negative structure of nanoporous alumina was initially fabricated and a positive structure of a nanoporous metal was subsequently fabricated. Over the past fifteen years, nanoporous alumina membranes have been used as templates for growth of a variety of nanostructured materials, including nanotubes, nanowires, nanorods, and nanoporous membranes.

  5. Spatial atomic layer deposition: a route towards further industrialization of atomic layer deposition

    NARCIS (Netherlands)

    Poodt, P.W.G.; Cameron, D.C.; Dickey, E.; George, S.M.; Kuznetsov, V.; Parsons, G.N.; Roozeboom, F.; Sundaram, G.; Vermeer, A.

    2012-01-01

    Atomic layer deposition (ALD) is a technique capable of producing ultrathin conformal films with atomic level control over thickness. A major drawback of ALD is its low deposition rate, making ALD less attractive for applications that require high throughput processing. An approach to overcome this

  6. The role of defects in fluorescent silicon carbide layers grown by sublimation epitaxy

    DEFF Research Database (Denmark)

    Schimmel, Saskia; Kaiser, Michl; Jokubavicius, Valdas;

    lifetimes, high nonradiative lifetimes are crucial for efficient light conversion. Despite the excellent crystalline quality that can generally be obtained by sublimation epitaxy according to XRD measurements, the role of defects in f-SiC is not yet well understood. Recent results from room temperature...... photoluminescence, charge carrier lifetime measurements by microwave detected photoconductivity and internal quantum efficiency measurements suggest that the internal quantum efficiency of f-SiC layers is significantly affected by the incorporation of defects during epitaxy. Defect formation seems to be related...

  7. Epitaxial composite layers of electron donors and acceptors from very large polycyclic aromatic hydrocarbons.

    Science.gov (United States)

    Samorí, Paolo; Severin, Nikolai; Simpson, Christopher D; Müllen, Klaus; Rabe, Jürgen P

    2002-08-14

    Large polycyclic aromatic hydrocarbons (PAHs) can be considered as nanographenes, whose electron donating or accepting properties are controlled by their size and shape as well as functionalities in their periphery. Epitaxial thin films of them are targets for optoelectronic applications; however, large PAHs are increasingly difficult to process. Here we show that epitaxial layers of very large unsubstituted PAHs (C(42)H(18) and C(132)H(34)), as well as a mixed layer of C(42)H(18) with an electron acceptor, can be obtained by self-assembly from solution. The C(132)H(34) is by far the largest nanographene that up to now has been processed into ordered thin films; due to its size it cannot be sublimed in a vacuum. Scanning tunneling microscopy (STM) studies reveal that the interaction with the substrate induces a strong perturbation of the electronic structure of the pure donor in the first epitaxial monolayer. In a second epitaxial layer with a donor acceptor stoichiometry of 2:1 the molecules are unperturbed.

  8. Characterization and growth of epitaxial layers of Gs exhibiting high resistivity for ionic implantation

    Science.gov (United States)

    1979-01-01

    Either classical or low temperature epitaxial growth techniques can be used to control the deposition of buffer layers of GaAs on semiconducting substrates and to obtain the resistivity and purity desired. Techniques developed to study, as a function of thickness, the evolution of mobilities by photoHall, and the spectroscopy of shallow and deep centers by cathodoluminescence and current transients reveal one very pure layer of medium resistivity and high mobility, and another "dead layer" of elevated resistivity far from the surface. The highly resistive layer remains pure over several microns, which appears interesting for implantation.

  9. Electronic and material characterization of silicon-germanium and silicon-germanium-carbon epitaxial layers

    Science.gov (United States)

    Peterson, Jeffrey John

    This dissertation presents results of material and electronic characterization of strained SiGe and SiGeC epitaxial layers grown on (100) silicon using Atmospheric Pressure Chemical Vapor Deposition and Reduced Pressure Chemical Vapor Deposition. Fabrication techniques for SiGe and SiGeC are also presented. Materials characterization of epitaxial SiGe and SiGeC was done to characterize crystallinity using visual, microscopic, and Rutherford Backscattering (RBS) characterization. Surface roughness was characterized and found to correspond roughly with epitaxial crystal quality. Spectroscopic ellipsometry was used to study epitaxial layer composition and thickness, requiring development of models for nSiGe and nSiGeC versus composition (the first published for nSiGeC) and generation of ellipsometric nomograms. X-ray diffraction (XRD) measurements of epitaxial strain and relaxation showed Ge composition dominates the stress, although strain compensation due to C was observed. XRD, Raman, and Fourier Transform Infrared (FTIR) characterization were done to characterize substitutional C in SiGeC epitaxial layers, finding that C incorporation into SiGeC saturates for C contents >1%. Fabrication techniques for SiGe and SiGeC were examined. Low thermal budget processing of strained layers were investigated as well as fabrication techniques using advantageous material properties of SiGe and SiGeC. Ti/Al contacts were developed and characterized for electrical contact to SiGe and SiGeC. Schottky contacts of Pt silicide on SiGe and SiGeC was done; formation and resistivity were characterized. Four separate resistivity characterization structures have been fabricated using mesa-etch and Si etch-stop techniques. A NPN Heterojunction Bipolar transistor has been fabricated using successive mesa-etches and SiGe (or SiGeC) etch-stops. Electronic characterization of in-situ doped SiGe and SiGeC epitaxial layers was done to determine resistivity, mobility, and bandgap. Resistivities

  10. Atomically Thin Heterostructures Based on Single-Layer Tungsten Diselenide and Graphene

    KAUST Repository

    Lin, Yu-Chuan

    2014-11-10

    Heterogeneous engineering of two-dimensional layered materials, including metallic graphene and semiconducting transition metal dichalcogenides, presents an exciting opportunity to produce highly tunable electronic and optoelectronic systems. In order to engineer pristine layers and their interfaces, epitaxial growth of such heterostructures is required. We report the direct growth of crystalline, monolayer tungsten diselenide (WSe2) on epitaxial graphene (EG) grown from silicon carbide. Raman spectroscopy, photoluminescence, and scanning tunneling microscopy confirm high-quality WSe2 monolayers, whereas transmission electron microscopy shows an atomically sharp interface, and low energy electron diffraction confirms near perfect orientation between WSe2 and EG. Vertical transport measurements across the WSe2/EG heterostructure provides evidence that an additional barrier to carrier transport beyond the expected WSe2/EG band offset exists due to the interlayer gap, which is supported by theoretical local density of states (LDOS) calculations using self-consistent density functional theory (DFT) and nonequilibrium Green\\'s function (NEGF).

  11. Lattice-matched HfN buffer layers for epitaxy of GaN on Si

    Energy Technology Data Exchange (ETDEWEB)

    Armitage, Robert; Yang, Qing; Feick, Henning; Gebauer, Joerg; Weber, Eicke R.; Shinkai, Satoko; Sasaki, Katsutaka

    2002-05-08

    Gallium nitride is grown by plasma-assisted molecular-beam epitaxy on (111) and (001) silicon substrates using sputter-deposited hafnium nitride buffer layers. Wurtzite GaN epitaxial layers are obtained on both the (111) and (001) HfN/Si surfaces, with crack-free thickness up to 1.2 (mu)m. Initial results for GaN grown on the (111) surface show a photoluminescence peak width of 17 meV at 11 K, and an asymmetric x-ray rocking curve width of 20 arcmin. Wurtzite GaN on HfN/Si(001) shows reduced structural quality and peculiar low-temperature luminescence features. However, growth on the (001) surface results in nearly stress-free films, suggesting that much thicker crack-free layers could be obtained.

  12. Epitaxial Growth of Hard Ferrimagnetic Mn3Ge Film on Rhodium Buffer Layer

    Directory of Open Access Journals (Sweden)

    Atsushi Sugihara

    2015-06-01

    Full Text Available Mn\\(_3\\Ge has a tetragonal Heusler-like D0\\(_{22}\\ crystal structure, exhibiting a large uniaxial magnetic anisotropy and small saturation magnetization due to its ferrimagnetic spin structure; thus, it is a hard ferrimagnet. In this report, epitaxial growth of a Mn\\(_3\\Ge film on a Rh buffer layer was investigated for comparison with that of a film on a Cr buffer layer in terms of the lattice mismatch between Mn\\(_3\\Ge and the buffer layer. The film grown on Rh had much better crystalline quality than that grown on Cr, which can be attributed to the small lattice mismatch. Epitaxial films of Mn\\(_3\\Ge on Rh show somewhat small coercivity (\\(H_{\\rm c}\\ = 12.6 kOe and a large perpendicular magnetic anisotropy (\\(K_{\\rm u}\\ = 11.6 Merg/cm\\(^3\\, comparable to that of the film grown on Cr.

  13. Sidewall GaAs tunnel junctions fabricated using molecular layer epitaxy

    Directory of Open Access Journals (Sweden)

    Takeo Ohno and Yutaka Oyama

    2012-01-01

    Full Text Available In this article we review the fundamental properties and applications of sidewall GaAs tunnel junctions. Heavily impurity-doped GaAs epitaxial layers were prepared using molecular layer epitaxy (MLE, in which intermittent injections of precursors in ultrahigh vacuum were applied, and sidewall tunnel junctions were fabricated using a combination of device mesa wet etching of the GaAs MLE layer and low-temperature area-selective regrowth. The fabricated tunnel junctions on the GaAs sidewall with normal mesa orientation showed a record peak current density of 35 000 A cm-2. They can potentially be used as terahertz devices such as a tunnel injection transit time effect diode or an ideal static induction transistor.

  14. Effect of the Ammonia Flow on the Formation of Microstructure Defects in GaN Layers Grown by High-Temperature Vapor Phase Epitaxy

    Science.gov (United States)

    Barchuk, M.; Lukin, G.; Zimmermann, F.; Röder, C.; Motylenko, M.; Pätzold, O.; Heitmann, J.; Kortus, J.; Rafaja, D.

    2016-12-01

    High-temperature vapor phase epitaxy (HTVPE) is a physical vapor transport technology for a deposition of gallium nitride (GaN) layers. However, little is known about the influence of the deposition parameters on the microstructure of the layers. In order to fill this gap, the influence of the ammonia (NH3) flow applied during the HTVPE growth on the microstructure of the deposited GaN layers is investigated in this work. Although the HTVPE technology is intended to grow GaN layers on foreign substrates, the GaN layers under study were grown on GaN templates produced by metal organic vapor phase epitaxy in order to be able to separate the growth defects from the defects induced by the lattice misfit between the foreign substrate and the GaN layer. The microstructure of the layers is characterized by means of high-resolution x-ray diffraction (XRD), transmission electron microscopy and photoluminescence. In samples deposited at low ammonia flow, planar defects were detected, along which the nitrogen atoms are found to be substituted by impurity atoms. The interplay between these planar defects and the threading dislocations is discussed. A combination of XRD and micro-Raman spectroscopy reveals the presence of compressive residual stress in the samples.

  15. Comparative study of single InGaN layers grown on Si(111) and GaN(0001) templates: The role of surface wetting and epitaxial constraint

    Science.gov (United States)

    Gómez, V. J.; Gačević, Ž.; Soto-Rodríguez, P. E. D.; Aseev, P.; Nötzel, R.; Calleja, E.; Sánchez-García, M. A.

    2016-08-01

    This work presents a comparative study, based mainly on X-ray diffraction analysis, of compact (~100 nm thick) and uniform single crystal InGaN layers (In content <35%) grown by plasma-assisted molecular beam epitaxy. InGaN layers have been grown directly on Si(111) substrates and on commercially available GaN(0001)-on-sapphire templates.. A high reactivity of atomic N with Si leads to a formation of amorphous SiN on Si substrate, i.e. an indirect crystal-to-crystal InGaN/SiN/Si contact; the weak InGaN interaction with the underlying substrate (weak epitaxial constraint) further leads to poor surface "wetting" and consequent 3D nucleation. The InGaN growth on GaN is, on the other hand, characterized by a direct crystal-to-crystal InGaN/GaN contact; the strong InGaN interaction with the underlying substrate (strong epitaxial constraint) leads to good surface "wetting" and consequent 2D nucleation. All studied InGaN layers show single epitaxial relationship to both Si(111) and GaN(0001)-on-sapphire substrates as well as a relatively good compositional uniformity (no trace of InGaN phase separation). However, layers grown on Si show significantly lower strain and inferior crystallographic uniformity i.e. higher disorder in crystallographic tilt and twist. The surface "wetting" (poor vs. good) and epitaxial constraint (weak vs. strong) are suggested as the main origins of these discrepancies.

  16. Self-corrected sensors based on atomic absorption spectroscopy for atom flux measurements in molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Du, Y., E-mail: yingge.du@pnnl.gov, E-mail: scott.chambers@pnnl.gov; Liyu, A. V. [Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, Washington 99352 (United States); Droubay, T. C.; Chambers, S. A., E-mail: yingge.du@pnnl.gov, E-mail: scott.chambers@pnnl.gov [Fundamental and Computational Sciences Directorate, Pacific Northwest National Laboratory, Richland, Washington 99352 (United States); Li, G. [Energy and Environment Directorate, Pacific Northwest National Laboratory, Richland, Washington 99352 (United States)

    2014-04-21

    A high sensitivity atom flux sensor based on atomic absorption spectroscopy has been designed and implemented to control electron beam evaporators and effusion cells in a molecular beam epitaxy system. Using a high-resolution spectrometer and a two-dimensional charge coupled device detector in a double-beam configuration, we employ either a non-resonant line or a resonant line with low cross section from the same hollow cathode lamp as the reference for nearly perfect background correction and baseline drift removal. This setup also significantly shortens the warm-up time needed compared to other sensor technologies and drastically reduces the noise coming from the surrounding environment. In addition, the high-resolution spectrometer allows the most sensitive resonant line to be isolated and used to provide excellent signal-to-noise ratio.

  17. Self-corrected Sensors Based On Atomic Absorption Spectroscopy For Atom Flux Measurements In Molecular Beam Epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Du, Yingge; Droubay, Timothy C.; Liyu, Andrey V.; Li, Guosheng; Chambers, Scott A.

    2014-04-24

    A high sensitivity atom flux sensor based on atomic absorption spectroscopy has been designed and implemented to control electron beam evaporators and effusion cells in a molecular beam epitaxy system. Using a high-resolution spectrometer and a two-dimensional charge coupled device (CCD) detector in a double-beam configuration, we employ a non-resonant line or a resonant line with lower absorbance from the same hollow cathode lamp as the reference for nearly perfect background correction and baseline drift removal. This setup also significantly shortens the warm-up time needed compared to other sensor technologies and drastically reduces the noise coming from the surrounding environment. In addition, the high-resolution spectrometer allows the most sensitive resonant line to be isolated and used to provide excellent signal-to-noise ratio.

  18. Self-corrected sensors based on atomic absorption spectroscopy for atom flux measurements in molecular beam epitaxy

    Science.gov (United States)

    Du, Y.; Droubay, T. C.; Liyu, A. V.; Li, G.; Chambers, S. A.

    2014-04-01

    A high sensitivity atom flux sensor based on atomic absorption spectroscopy has been designed and implemented to control electron beam evaporators and effusion cells in a molecular beam epitaxy system. Using a high-resolution spectrometer and a two-dimensional charge coupled device detector in a double-beam configuration, we employ either a non-resonant line or a resonant line with low cross section from the same hollow cathode lamp as the reference for nearly perfect background correction and baseline drift removal. This setup also significantly shortens the warm-up time needed compared to other sensor technologies and drastically reduces the noise coming from the surrounding environment. In addition, the high-resolution spectrometer allows the most sensitive resonant line to be isolated and used to provide excellent signal-to-noise ratio.

  19. High perpendicular hard magnetic properties of nanocomposite Co-rich Co-Pt/Pt double-layered films by epitaxial deposition without capped layer

    Energy Technology Data Exchange (ETDEWEB)

    Chen, S.C., E-mail: chensc@mail.mcut.edu.t [Department of Materials Engineering, MingChi University of Technology, Taipei 243, Taiwan (China); Kuo, P.C.; Shen, C.L.; Hsu, S.L.; Fang, Y.H.; Lin, G.P.; Huang, K.T. [Institute of Materials Science and Engineering, National Taiwan University, Taipei 106, Taiwan (China)

    2009-07-01

    The HRTEM cross-sectional lattice image shows that a well epitaxial growth of hcp Co-rich Co-Pt (002) on Pt (111) underlayer leads to good perpendicular magnetic anisotropy of Co-rich Co-Pt film. It is found that both the perpendicular coercivity (Hc{sub perpendicular}) and perpendicular squareness (S{sub perpendicular}) of Co-rich Co-Pt films without Pt capped layer are larger than that of Co-rich Co-Pt films with Pt capped layer. The cross-sectional TEM-EDS and AES analysis confirm that the oxygen atoms will diffuse from film surface into the Co-rich Co-Pt film without adding Pt capped layer, and it react with cobalt atoms to form CoO, which is detected by XPS analysis. The increase in perpendicular hard magnetic properties of Co-rich Co-Pt film without Pt capped layer is mainly due to form CoO in the Co-rich Co-Pt film.

  20. Growth of layered superconductor β-PdBi2 films using molecular beam epitaxy

    Science.gov (United States)

    Denisov, N. V.; Matetskiy, A. V.; Tupkalo, A. V.; Zotov, A. V.; Saranin, A. A.

    2017-04-01

    Bulk β-PdBi2 layered material exhibits advanced properties and is supposed to be probable topological superconductor. We present a method based on molecular beam epitaxy that allows us to grow β-PdBi2 films from a single β-PdBi2 triple layer up to the dozens of triple layers, using Bi(111) film on Si(111) as a template. The grown films demonstrate structural, electronic and superconducting properties similar to those of bulk β-PdBi2 crystals. Ability to grow the β-PdBi2 films of desired thickness opens the promising possibilities to explore fascinating properties of this advanced material.

  1. Atomic Layer Deposition from Dissolved Precursors.

    Science.gov (United States)

    Wu, Yanlin; Döhler, Dirk; Barr, Maïssa; Oks, Elina; Wolf, Marc; Santinacci, Lionel; Bachmann, Julien

    2015-10-14

    We establish a novel thin film deposition technique by transferring the principles of atomic layer deposition (ALD) known with gaseous precursors toward precursors dissolved in a liquid. An established ALD reaction behaves similarly when performed from solutions. "Solution ALD" (sALD) can coat deep pores in a conformal manner. sALD offers novel opportunities by overcoming the need for volatile and thermally robust precursors. We establish a MgO sALD procedure based on the hydrolysis of a Grignard reagent.

  2. Surface photovoltage method for the quality control of silicon epitaxial layers on sapphire

    Energy Technology Data Exchange (ETDEWEB)

    Yaremchuk, A. F.; Starkov, A. V.; Zaikin, A. V., E-mail: lynch0000@gmail.com [National Rsearch University MIET (Russian Federation); Alekseev, A. V. [ZAO “Telekom-STV” (Russian Federation); Sokolov, E. M. [ZAO “Epiel” (Russian Federation)

    2014-12-15

    The surface photovoltage method is used to study “silicon-on-sapphire” epitaxial layers with a thickness of 0.3–0.6 μm, which are used to fabricate p-channel MOS (metal—oxide-semiconductor) transistors with improved radiation hardness. It is shown that the manner in which the photoconductivity of the epitaxial layer decays after the end of a light pulse generated by a light-emitting diode (wavelength ∼400 nm) strongly depends on the density of structural defects in the bulk of the structure. This enables control over how a “silicon-on-sapphire” structure is formed to provide the manufacturing of MOS structures with optimal operating characteristics.

  3. Threading dislocations in GaAs epitaxial layers on various thickness Ge buffers on 300 mm Si substrates

    Science.gov (United States)

    Bogumilowicz, Y.; Hartmann, J. M.; Rochat, N.; Salaun, A.; Martin, M.; Bassani, F.; Baron, T.; David, S.; Bao, X.-Y.; Sanchez, E.

    2016-11-01

    We have grown GaAs epitaxial layers on Ge buffers, themselves on Si (001) substrates, using an Applied Materials 300 mm metal organic chemical vapor deposition tool. We varied the Ge buffer thickness between 0.36 and 1.38 μm and studied the properties of a 0.27 μm thick GaAs layer on top. We found that increasing the Ge buffer thickness yielded smoother GaAs films with an rms surface roughness as low as 0.5 nm obtained on a 5×5 μm2 area. The bow of the substrate increased following a linear law with the epitaxial stack thickness up to 240 μm for a 1.65 μm stack. We have also characterized the threading dislocations present in the GaAs layers using X-ray diffraction and cathodoluminescence. Increasing the Ge buffer thickness resulted in lower threading dislocation densities, enabling us to obtain anti-phase boundary - free GaAs films with a threading dislocation density as low as 3×107 cm-2. In addition, atomic force microscopy surface topology measurements showed the presence of pits in the GaAs layers whose density agreed well with other threading dislocation density assessments. It thus seems that threading dislocations can in certain cases induce some growth rate variations, making them visible in as-grown GaAs films. Using thicker Ge buffers results in smoother films with less threading dislocations, with the side effect of increasing the bow on the wafer. If bow is not an issue, this is a practical approach to improve the GaAs (on Ge buffer) on silicon quality.

  4. High quality InAlN single layers lattice-matched to GaN grown by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Gacevic, Z.; Fernandez-Garrido, S.; Calleja, E. [ISOM, Universidad Politecnica de Madrid, Avda. Complutense s/n, 28040 Madrid (Spain); Rebled, J. M.; Peiro, F. [LENS-MIND-IN2UB, Departament d' Electronica, Universitat de Barcelona, Marti i Franques 1, 08028 Barcelona (Spain); Estrade, S. [LENS-MIND-IN2UB, Departament d' Electronica, Universitat de Barcelona, Marti i Franques 1, 08028 Barcelona (Spain); TEM-MAT, CCiT-UB, Sole i Sabaris 1, 08028 Barcelona (Spain)

    2011-07-18

    We report on properties of high quality {approx}60 nm thick InAlN layers nearly in-plane lattice-matched to GaN, grown on c-plane GaN-on-sapphire templates by plasma-assisted molecular beam epitaxy. Excellent crystalline quality and low surface roughness are confirmed by X-ray diffraction, transmission electron microscopy, and atomic force microscopy. High annular dark field observations reveal a periodic in-plane indium content variation (8 nm period), whereas optical measurements evidence certain residual absorption below the band-gap. The indium fluctuation is estimated to be {+-} 1.2% around the nominal 17% indium content via plasmon energy oscillations assessed by electron energy loss spectroscopy with sub-nanometric spatial resolution.

  5. Analysis of the Band-Structure in (Ga, Mn)As Epitaxial Layers by Optical Methods

    OpenAIRE

    Yastrubchak, O.

    2012-01-01

    The ternary III-V semiconductor (Ga, Mn)As has recently drawn a lot of attention as the model diluted ferromagnetic semiconductor, combining semiconducting properties with magnetism. (Ga, Mn)As layers are usually gown by the low-temperature molecular-beam epitaxy (LT-MBE) technique. Below a magnetic transition temperature, TC, substitutional Mn2+ ions are ferromagnetically ordered owing to interaction with spin-polarized holes. However, the character of electronic states near the Fermi energy...

  6. Epitaxial thin film growth of LiH using a liquid-Li atomic template

    Energy Technology Data Exchange (ETDEWEB)

    Oguchi, Hiroyuki, E-mail: oguchi@nanosys.mech.tohoku.ac.jp [Department of Nanomechanics, Tohoku University, Sendai 980-8579 (Japan); Micro System Integration Center (muSIC), Tohoku University, Sendai 980-0845 (Japan); Ikeshoji, Tamio; Orimo, Shin-ichi [Institute for Materials Research, Tohoku University, Sendai 980-8577 (Japan); Advanced Institute for Materials Research (AIMR), Tohoku University, Sendai 980-8577 (Japan); Ohsawa, Takeo; Shiraki, Susumu; Hitosugi, Taro [Advanced Institute for Materials Research (AIMR), Tohoku University, Sendai 980-8577 (Japan); Kuwano, Hiroki [Department of Nanomechanics, Tohoku University, Sendai 980-8579 (Japan)

    2014-11-24

    We report on the synthesis of lithium hydride (LiH) epitaxial thin films through the hydrogenation of a Li melt, forming abrupt LiH/MgO interface. Experimental and first-principles molecular dynamics studies reveal a comprehensive microscopic picture of the crystallization processes, which sheds light on the fundamental atomistic growth processes that have remained unknown in the vapor-liquid-solid method. We found that the periodic structure that formed, because of the liquid-Li atoms at the film/MgO-substrate interface, serves as an atomic template for the epitaxial growth of LiH crystals. In contrast, films grown on the Al{sub 2}O{sub 3} substrates indicated polycrystalline films with a LiAlO{sub 2} secondary phase. These results and the proposed growth process provide insights into the preparation of other alkaline metal hydride thin films on oxides. Further, our investigations open the way to explore fundamental physics and chemistry of metal hydrides including possible phenomena that emerge at the heterointerfaces of metal hydrides.

  7. Epitaxial layers of 2122 BCSCO superconductor thin films having single crystalline structure

    Science.gov (United States)

    Pandey, Raghvendra K. (Inventor); Raina, Kanwal K. (Inventor); Solayappan, Narayanan (Inventor)

    1995-01-01

    A substantially single phase, single crystalline, highly epitaxial film of Bi.sub.2 CaSr.sub.2 Cu.sub.2 O.sub.8 superconductor which has a T.sub.c (zero resistance) of 83K is provided on a lattice-matched substrate with no intergrowth. This film is produced by a Liquid Phase Epitaxy method which includes the steps of forming a dilute supercooled molten solution of a single phase superconducting mixture of oxides of Bi, Ca, Sr, and Cu having an atomic ratio of about 2:1:2:2 in a nonreactive flux such as KCl, introducing the substrate, e.g., NdGaO.sub.3, into the molten solution at 850.degree. C., cooling the solution from 850.degree. C. to 830.degree. C. to grow the film and rapidly cooling the substrate to room temperature to maintain the desired single phase, single crystalline film structure.

  8. Defect Reduction in Epitaxial Growth Using Superlattice Buffer Layers

    Science.gov (United States)

    1988-07-01

    Katsuyama, Y. J. Yang and S. M. Bedair, Electron Dev. Lett., vol. 8, p. 240, 1987. 0 -15 -" Journal of (ryOstal (io iih 77 (108(,) ,xQ 9i4 S9 North-I...layer facilitat the csea of Gaosu 3 (5% in H2) + 500 sccm of H , and ed cross-sectional thickness measurements. trimethylgallium (TMG) + 500 sccm of H

  9. Effects of AIN nucleation layer thickness on crystal quality of AIN grown by plasma-assisted molecular beam epitaxy

    Institute of Scientific and Technical Information of China (English)

    Ren Fan; Hao Zhi-Biao; Hu Jian-Nan; Zhang Chen; Luo Yi

    2010-01-01

    In this paper,the effects of thickness of AIN nucleation layer grown at high temperature on AIN epi-layer crystalline quality are investigated.Crack-free AIN samples with various nucleation thicknesses are grown on sapphire substrates by plasma-assisted molecular beam epitaxy.The AIN crystalline quality is analysed by transmission electron microscope and x-ray diffraction(XRD)rocking curves in both(002)and(102)planes.The surface profiles of nucleation layer with different thicknesses after in-situ annealing are also analysed by atomic force microscope.A critical nucleation thickness for realising high quality AIN films is found.When the nucleation thickness is above a certain value,the(102)XRD full width at half maximum(FWHM)of AIN bulk increases with nucleation thickness increasing,whereas the(002)XRD FWHM shows an opposite trend.These phenomena can be attributed to the characteristics of nucleation islands and the evolution of crystal grains during AIN main layer growth.

  10. Influence of growth temperature on laser molecular beam epitaxy and properties of GaN layers grown on c-plane sapphire

    Science.gov (United States)

    Dixit, Ripudaman; Tyagi, Prashant; Kushvaha, Sunil Singh; Chockalingam, Sreekumar; Yadav, Brajesh Singh; Sharma, Nita Dilawar; Kumar, M. Senthil

    2017-04-01

    We have investigated the influence of growth temperature on the in-plane strain, structural, optical and mechanical properties of heteroepitaxially grown GaN layers on sapphire (0001) substrate by laser molecular beam epitaxy (LMBE) technique in the temperature range 500-700 °C. The GaN epitaxial layers are found to have a large in-plane compressive stress of about 1 GPa for low growth temperatures but the strain drastically reduced in the layer grown at 700 °C. The nature of the in-plane strain has been analyzed using high resolution x-ray diffraction, atomic force microscopy (AFM), Raman spectroscopy and photoluminescence (PL) measurements. From AFM, a change in GaN growth mode from grain to island is observed at the high growth temperature above 600 °C. A blue shift of 20-30 meV in near band edge PL emission line has been noticed for the GaN layers containing the large in-plane strain. These observations indicate that the in-plane strain in the GaN layers is dominated by a biaxial strain. Using nanoindentation, it is found that the indentation hardness and Young's modulus of the GaN layers increases with increasing growth temperature. The results disclose the critical role of growth mode in determining the in-plane strain and mechanical properties of the GaN layers grown by LMBE technique.

  11. Evaluation of methods for application of epitaxial layers of superconductor and buffer layers

    Energy Technology Data Exchange (ETDEWEB)

    NONE

    1997-06-01

    The recent achievements in a number of laboratories of critical currents in excess of 1.0x10{sup 6} amp/cm{sup 2} at 77K in YBCO deposited over suitably textured buffer/substrate composites have stimulated interest in the potential applications of coated conductors at high temperatures and high magnetic fields. As of today, two different approaches for obtaining the textured substrates have been identified. These are: Los Alamos National Laboratory`s (LANL) ion-beam assisted deposition called IBAD, to obtain a highly textured yttria-stabilized zirconia (YSZ) buffer on nickel alloy strips, and Oak Ridge National Laboratory`s (ORNL) rolling assisted, bi-axial texturized substrate option called RABiTS. Similarly, based on the published literature, the available options to form High Temperature Superconductor (HTS) films on metallic, semi-metallic or ceramic substrates can be divided into: physical methods, and non-physical or chemical methods. Under these two major groups, the schemes being proposed consist of: - Sputtering - Electron-Beam Evaporation - Flash Evaporation - Molecular Beam Epitaxy - Laser Ablation - Electrophoresis - Chemical Vapor Deposition (Including Metal-Organic Chemical Vapor Deposition) - Sol-Gel - Metal-Organic Decomposition - Electrodeposition, and - Aerosol/Spray Pyrolysis. In general, a spool- to-spool or reel-to-reel type of continuous manufacturing scheme developed out of any of the above techniques, would consist of: - Preparation of Substrate Material - Preparation and Application of the Buffer Layer(s) - Preparation and Application of the HTS Material and Required Post-Annealing, and - Preparation and Application of the External Protective Layer. These operations would be affected by various process parameters which can be classified into: Chemistry and Material Related Parameters; and Engineering and Environmental Based Parameters. Thus, one can see that for successful development of the coated conductors manufacturing process, an

  12. Epitaxial growth and characterization of InN nanorods and compact layers on silicon substrates

    Energy Technology Data Exchange (ETDEWEB)

    Sanchez-Garcia, M.A.; Grandal, J.; Calleja, E. [ISOM and Departamento de Ingenieria Electronica, ETSI Telecomunicacion, Universidad Politecnica de Madrid, Ciudad Universitaria, 28040 Madrid (Spain); Lazic, S.; Calleja, J.M. [Dpt. Fisica de Materiales, Universidad Autonoma de Madrid, Cantoblanco, 28049 Madrid (Spain); Trampert, A. [Paul-Drude-Institut fuer Festkoerperelektronik, Hausvogteiplatz 5-7, 10117 Berlin (Germany)

    2006-06-15

    This work reports on the morphology and optical properties of wurtzite InN layers grown by plasma assisted molecular beam epitaxy (PA-MBE) on Si(111) substrates. The layer morphology can be controlled by the effective indium to nitrogen molecular flux ratio, from N-rich conditions that lead to InN nanorods, to stoichiometric conditions leading to compact InN layers. The nanorods deliver a much higher intensity of the photoluminescence emission than compact layers, with a full width at half maximum down to 34 meV, indicative of a high crystal quality. Raman and X-ray measurements on the InN nanorods and compact layers confirm the practical full relaxation of both types of materials. TEM measurements reveal a perfect epitaxial alignment of Si substrate-AlN buffer and InN epilayer with clean AlN-InN interfaces when growth conditions are optimized. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  13. (abstract) All Epitaxial Edge-geometry SNS Devices with Doped PBCO and YBCO Normal Layers

    Science.gov (United States)

    Barner, J. B.; Hunt, B. D.; Foote, M. C.

    1995-01-01

    We will present our results on tapered-edge-geometry SNS weak link fabricated from c-axis oriented base-, counterelectrode and normal layers using a variety of processing conditions. To date, we have employed a variety of different normal materials (Co-doped YBCO, Y-doped PBCO, Ca-doped PBCO). We have been examining the junction fabrication process in detail and we will present our methods. In particular, we have been examining both epitaxial and non-epitaxial milling mask overlayers and we will present a comparison of both methods. These devices behave similar to the expectations of the resisively shunted junction model and conventional SNS proximity effect models but with some differences which will be discussed. We will present the detailed systematics of our junctions including device parameters versus temperature, rf and dc magnetic response for the various processing conditions.

  14. Unintentional gallium incorporation in InGaN layers during epitaxial growth

    Science.gov (United States)

    Zhou, Kun; Ren, Huaijin; Ikeda, Masao; Liu, Jianping; Ma, Yi; Gao, Songxin; Tang, Chun; Li, Deyao; Zhang, Liquan; Yang, Hui

    2017-01-01

    Unintentional gallium incorporation was observed and investigated in the epitaxial growth of InGaN by metalorganic vapor phase epitaxy. InGaN was grown without intentional gallium precursor and the gallium incorporation rate was found not dependent on TEGa source but was significantly influenced by temperature and TMIn source flow. The source of the unintentional gallium incorporation is confirmed to be from the flow distributor of the reactor. The incorporation mechanism was analyzed to be the diffusion of resultant of transmetalation reaction between TMIn or its decomposed products (for example DMIn) and residual gallium. Due to the unintentional gallium incorporation, the growth rate and indium content of InGaN layer are determined by indium source, gallium source and the growth temperature.

  15. Scanning proximal microscopy study of the thin layers of silicon carbide-aluminum nitride solid solution manufactured by fast sublimation epitaxy

    Directory of Open Access Journals (Sweden)

    Tománek P.

    2013-05-01

    Full Text Available The objective of the study is a growth of SiC/(SiC1−x(AlNx structures by fast sublimation epitaxy of the polycrystalline source of (SiC1−x(AlNx and their characterisation by proximal scanning electron microscopy and atomic force microscopy. For that purpose optimal conditions of sublimation process have been defined. Manufactured structures could be used as substrates for wide-band-gap semiconductor devices on the basis of nitrides, including gallium nitride, aluminum nitride and their alloys, as well as for the production of transistors with high mobility of electrons and also for creation of blue and ultraviolet light emitters (light-emitted diodes and laser diodes. The result of analysis shows that increasing of the growth temperature up to 2300 K allows carry out sublimation epitaxy of thin layers of aluminum nitride and its solid solution.

  16. Recent Results on Growth of (211)B CdTe on (211)Si with Intermediate Ge and ZnTe Buffer Layers by Metalorganic Vapor-Phase Epitaxy

    Science.gov (United States)

    Shintri, Shashidhar; Rao, Sunil; Wijewarnasuriya, Priyalal; Trivedi, Sudhir; Bhat, Ishwara

    2012-10-01

    We report on the investigation of epitaxial cadmium telluride grown by metalorganic vapor-phase epitaxy (MOVPE) on (211)Si, with particular emphasis on studying the effect of changing the reactor parameters and thermal annealing conditions on the epilayer quality. The CdTe films were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), and x-ray diffraction (XRD). The best CdTe films were observed when the Te/Cd precursor partial pressure ratio was close to 3.1. It was also observed that, though annealing improved the crystal quality, a slight increase in surface roughness was observed. Similar attempts were made to improve the growth conditions of ZnTe intermediate buffer layer, which showed similar trends with changes in precursor flows.

  17. Propagation of Structural Disorder in Epitaxially Connected Quantum Dot Solids from Atomic to Micron Scale.

    Science.gov (United States)

    Savitzky, Benjamin H; Hovden, Robert; Whitham, Kevin; Yang, Jun; Wise, Frank; Hanrath, Tobias; Kourkoutis, Lena F

    2016-09-14

    Epitaxially connected superlattices of self-assembled colloidal quantum dots present a promising route toward exquisite control of electronic structure through precise hierarchical structuring across multiple length scales. Here, we uncover propagation of disorder as an essential feature in these systems, which intimately connects order at the atomic, superlattice, and grain scales. Accessing theoretically predicted exotic electronic states and highly tunable minibands will therefore require detailed understanding of the subtle interplay between local and long-range structure. To that end, we developed analytical methods to quantitatively characterize the propagating disorder in terms of a real paracrystal model and directly observe the dramatic impact of angstrom scale translational disorder on structural correlations at hundreds of nanometers. Using this framework, we discover improved order accompanies increasing sample thickness and identify the substantial effect of small fractions of missing epitaxial bonds on statistical disorder. These results have significant experimental and theoretical implications for the elusive goals of long-range carrier delocalization and true miniband formation.

  18. Reduction in the crystal defect density of Zn Se layers grown by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Lopez L, M.; Perez C, A.; Luyo A, J.; Melendez L, M.; Tamura, M. [Departamento de Fisica, Centro de Investigacion y de Estudios Avanzados del instituto politecnico Nacional, A.P. 14-740, 07000 Mexico D.F. (Mexico); Mendez G, V.H.; Vidal, M.A. [Instituto de Investigacion en Comunicacion Optica, Universidad Autonoma de San Luis Potosi, Alvaro Obregon 64, 78000 San Luis Potosi (Mexico)

    2000-07-01

    We present a study of the molecular beam epitaxial (MBE) grown of Zn Se layers on Ga-As and Si substrates. For the growth on GaAs substrates we investigated the effects of introducing buffer layers of Al{sub x}Ga{sub 1-x} As and In{sub x}Ga{sub 1-x} As with x = 0.01. Moreover, an analysis by secondary ion mass spectroscopy revealed that the use of AlGaAs buffer layers effectively suppress the Ga segregation onto the Zn Se layers surface. On the other hand, for the growth of Zn Se on Si substrates, we achieved a significant improvement in the crystal quality of Zn Se by irradiating the Si substrates with plasma of nitrogen prior to the growth. (Author)

  19. Photoluminescence efficiency of BGaN epitaxial layers with high boron content

    Energy Technology Data Exchange (ETDEWEB)

    Jurkevičius, J.; Mickevičius, J., E-mail: juras.mickevicius@ff.vu.lt; Kadys, A.; Kolenda, M.; Tamulaitis, G.

    2016-07-01

    High-boron-content epitaxial layers of BGaN intended for lattice-matching with AlGaN in UV light emitters were grown on SiC substrate and GaN and AlN templates on sapphire. Photoluminescence (PL) of these layers was studied under quasi-steady-state conditions by varying temperature and excitation intensity. The PL spectra in the samples with different boron content and their dynamics evidence formation of boron-rich regions occupying a small fraction of the total layer volume and acting as the emission killers. The room-temperature PL efficiency of the BGaN epilayers was estimated and shown to drastically decrease at increasing boron content with no significant correlation with either the type of substrate/template or technological conditions of the layer deposition.

  20. Graphene oxide monolayers as atomically thin seeding layers for atomic layer deposition of metal oxides

    Science.gov (United States)

    Nourbakhsh, Amirhasan; Adelmann, Christoph; Song, Yi; Lee, Chang Seung; Asselberghs, Inge; Huyghebaert, Cedric; Brizzi, Simone; Tallarida, Massimo; Schmeißer, Dieter; van Elshocht, Sven; Heyns, Marc; Kong, Jing; Palacios, Tomás; de Gendt, Stefan

    2015-06-01

    Graphene oxide (GO) was explored as an atomically-thin transferable seed layer for the atomic layer deposition (ALD) of dielectric materials on any substrate of choice. This approach does not require specific chemical groups on the target surface to initiate ALD. This establishes GO as a unique interface which enables the growth of dielectric materials on a wide range of substrate materials and opens up numerous prospects for applications. In this work, a mild oxygen plasma treatment was used to oxidize graphene monolayers with well-controlled and tunable density of epoxide functional groups. This was confirmed by synchrotron-radiation photoelectron spectroscopy. In addition, density functional theory calculations were carried out on representative epoxidized graphene monolayer models to correlate the capacitive properties of GO with its electronic structure. Capacitance-voltage measurements showed that the capacitive behavior of Al2O3/GO depends on the oxidation level of GO. Finally, GO was successfully used as an ALD seed layer for the deposition of Al2O3 on chemically inert single layer graphene, resulting in high performance top-gated field-effect transistors.Graphene oxide (GO) was explored as an atomically-thin transferable seed layer for the atomic layer deposition (ALD) of dielectric materials on any substrate of choice. This approach does not require specific chemical groups on the target surface to initiate ALD. This establishes GO as a unique interface which enables the growth of dielectric materials on a wide range of substrate materials and opens up numerous prospects for applications. In this work, a mild oxygen plasma treatment was used to oxidize graphene monolayers with well-controlled and tunable density of epoxide functional groups. This was confirmed by synchrotron-radiation photoelectron spectroscopy. In addition, density functional theory calculations were carried out on representative epoxidized graphene monolayer models to correlate the

  1. Epitaxial strain induced atomic ordering in stoichiometric LaCoO3 thin films

    Science.gov (United States)

    Choi, Woo Seok; Kwon, Ji-Hwan; Jeen, Hyoungjeen; Sawatzky, George A.; Hinkov, Vladimir; Kim, Miyoung; Lee, Ho Nyung

    2015-03-01

    Heteroepitaxial strain imposed in complex transition metal oxide thin films is recognized as an effective tool for identifying and controlling emergent physical phenomena. Stoichiometric LaCoO3 is particularly interesting, since the thin film form of the material exhibits a robust macroscopic ferromagnetic ordering, while the bulk form of the material is a zero spin, nonmagnetic insulator. In this work, we show that the ferromagnetic ordering observed in LaCoO3 thin films is related to a lattice modulation in the atomic scale, originating from the epitaxial strain. The possibility of oxygen vacancies have been carefully ruled out using various macroscopic and microscopic spectroscopic techniques, and an unconventional strain relaxation behavior identified by strip-like lattice modulation pattern was responsible for the non-zero spin ground state of Co3+ ions. We further note that the unconventional strain relaxation did not involve any uncontrolled misfit dislocations.

  2. Epitaxial two-dimensional nitrogen atomic sheet in GaAs

    Energy Technology Data Exchange (ETDEWEB)

    Harada, Yukihiro, E-mail: y.harada@eedept.kobe-u.ac.jp; Yamamoto, Masuki; Baba, Takeshi; Kita, Takashi [Department of Electrical and Electronic Engineering, Graduate School of Engineering, Kobe University, 1-1 Rokkodai, Nada, Kobe 657-8501 (Japan)

    2014-01-27

    We have grown an epitaxial two-dimensional nitrogen (N) atomic sheet in GaAs by using the site-controlled N δ-doping technique. We observed a change of the electronic states in N δ-doped GaAs from the isolated impurity centers to the delocalized impurity band at 1.49 eV with increasing N-doping density. According to the excitation-power- and temperature-dependent photoluminescence (PL) spectra, the emission related to localized levels below the impurity band edge was dominant at low excitation power and temperature, whereas the effects of the localized levels can be neglected by increasing the excitation power and temperature. Furthermore, a clear Landau shift of the PL-peak energy was observed at several Tesla in the Faraday configuration, in contrast to the case in the impurity limit.

  3. Visualization of deuterium dead layer by atom probe tomography

    KAUST Repository

    Gemma, Ryota

    2012-12-01

    The first direct observation, by atom probe tomography, of a deuterium dead layer is reported for Fe/V multilayered film loaded with D solute atoms. The thickness of the dead layers was measured to be 0.4-0.5 nm. The dead layers could be distinguished from chemically intermixed layers. The results suggest that the dead layer effect occurs even near the interface of the mixing layers, supporting an interpretation that the dead layer effect cannot be explained solely by electronic charge transfer but also involves a modulation of rigidity. © 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

  4. Graphene oxide monolayers as atomically thin seeding layers for atomic layer deposition of metal oxides.

    Science.gov (United States)

    Nourbakhsh, Amirhasan; Adelmann, Christoph; Song, Yi; Lee, Chang Seung; Asselberghs, Inge; Huyghebaert, Cedric; Brizzi, Simone; Tallarida, Massimo; Schmeisser, Dieter; Van Elshocht, Sven; Heyns, Marc; Kong, Jing; Palacios, Tomás; De Gendt, Stefan

    2015-06-28

    Graphene oxide (GO) was explored as an atomically-thin transferable seed layer for the atomic layer deposition (ALD) of dielectric materials on any substrate of choice. This approach does not require specific chemical groups on the target surface to initiate ALD. This establishes GO as a unique interface which enables the growth of dielectric materials on a wide range of substrate materials and opens up numerous prospects for applications. In this work, a mild oxygen plasma treatment was used to oxidize graphene monolayers with well-controlled and tunable density of epoxide functional groups. This was confirmed by synchrotron-radiation photoelectron spectroscopy. In addition, density functional theory calculations were carried out on representative epoxidized graphene monolayer models to correlate the capacitive properties of GO with its electronic structure. Capacitance-voltage measurements showed that the capacitive behavior of Al2O3/GO depends on the oxidation level of GO. Finally, GO was successfully used as an ALD seed layer for the deposition of Al2O3 on chemically inert single layer graphene, resulting in high performance top-gated field-effect transistors.

  5. Terahertz absorption in GaN epitaxial layers under lateral electric field

    Science.gov (United States)

    Balagula, R. M.; Vinnichenko, M. Ya; Melentev, G. A.; Moldavskaya, M. D.; Shalygin, V. A.; Vorobjev, L. E.; Firsov, D. A.; Danilov, S. N.; Suihkonen, S.

    2016-08-01

    Variation of absorption of terahertz radiation in lateral electric field was investigated in GaN epitaxial layers. Different behaviour of the absorption modulation in electric field was observed for radiation polarized along electric field and perpendicular to it. Joint analysis of optical and transport measurements let us obtain field dependencies of mobility, electron concentration and absorption cross-section. For terahertz radiation polarized perpendicular to the electric field, results are in accordance with Drude model of free electron absorption. Another polarization demonstrates significant deviation that is yet to be studied more thoroughly.

  6. Investigation of InN layers grown by molecular beam epitaxy on GaN templates

    Energy Technology Data Exchange (ETDEWEB)

    Vilalta-Clemente, A.; Mutta, G.R.; Chauvat, M.P.; Morales, M.; Doualan, J.L.; Ruterana, P. [CIMAP UMR 6252 CNRS-ENSICAEN-CEA-UCBN, Caen (France); Grandal, J.; Sanchez-Garcia, M.A.; Calle, F. [ISOM y Department de Ingenieria Electronica, E.T.S.I. Telecomunicacion, Universidad Politecnica de Madrid, Ciudad Universitaria (Spain); Valcheva, E.; Kirilov, K. [Faculty of Physics, Sofia University (Bulgaria)

    2010-05-15

    An investigation of InN layers grown on GaN templates by molecular beam epitaxy (MBE) has been carried out by X-ray diffraction (XRD), Raman spectroscopy (RS) and photoluminescence (PL). A good correlation is noticed between their crystalline quality and optical properties. The best samples exhibit a PL emission between 0.6 and 0.7 eV. The surface structure was quite different from one sample to the other, pointing out to a critical role of the growth conditions, which probably need to be tightly optimized for a good reproducibility. (Abstract Copyright [2010], Wiley Periodicals, Inc.)

  7. Temperature-dependent efficiency droop in AlGaN epitaxial layers and quantum wells

    Directory of Open Access Journals (Sweden)

    J. Mickevičius

    2016-04-01

    Full Text Available Luminescence efficiency droop has been studied in AlGaN epitaxial layers and multiple quantum wells (MQWs with different strength of carrier localization in a wide range of temperatures. It is shown that the dominant mechanism leading to droop, i.e., the efficiency reduction at high carrier densities, is determined by the carrier thermalization conditions and the ratio between carrier thermal energy and localization depth. The droop mechanisms, such as the occupation-enhanced redistribution of nonthermalized carriers, the enhancement of nonradiative recombination due to carrier delocalization, and excitation-enhanced carrier transport to extended defects or stimulated emission, are discussed.

  8. Broadband electromagnetic response and ultrafast dynamics of few-layer epitaxial graphene

    Energy Technology Data Exchange (ETDEWEB)

    Choi, Hyunyong; Borondics, Ferenc; Siegel, David A.; Zhou, Shuyun Y.; Martin, Michael C.; Lanzara, Alessandra; Kaindl, Robert A.

    2009-03-26

    We study the broadband optical conductivity and ultrafast carrier dynamics of epitaxial graphene in the few-layer limit. Equilibrium spectra of nominally buffer, monolayer, and multilayer graphene exhibit significant terahertz and near-infrared absorption, consistent with a model of intra- and interband transitions in a dense Dirac electron plasma. Non-equilibrium terahertz transmission changes after photoexcitation are shown to be dominated by excess hole carriers, with a 1.2-ps mono-exponential decay that refects the minority-carrier recombination time.

  9. Above bandgap luminescence of p-type GaAs epitaxial layers

    Science.gov (United States)

    Sapriel, J.; Chavignon, J.; Alexandre, F.; Azoulay, R.; Sermage, B.; Rao, K.; Voos, M.

    1991-08-01

    New photoluminescence bands are observed in p-type GaAs epitaxial layers at 300 and 80 K, above the bandgap. These bands are independent of the nature of the dopant (Zn, Be, C) and of the growth technique (MBE or MOCVD). Their intensities increase as a function of the p doping (1 × 10 17 < p < 2 × 10 20cm-3) and peak at energies which correspond to transitions between the Γ 6, L 6 and X 6 minima of the conduction band and the Γ 8 and Γ 7 maxima of the valence band.

  10. Increasing the radiation resistance of single-crystal silicon epitaxial layers

    Directory of Open Access Journals (Sweden)

    Kurmashev Sh. D.

    2014-12-01

    Full Text Available The authors investigate the possibility of increasing the radiation resistance of silicon epitaxial layers by creating radiation defects sinks in the form of dislocation networks of the density of 109—1012 m–2. Such networks are created before the epitaxial layer is applied on the front surface of the silicon substrate by its preliminary oxidation and subsequent etching of the oxide layer. The substrates were silicon wafers KEF-4.5 and KDB-10 with a diameter of about 40 mm, grown by the Czochralski method. Irradiation of the samples was carried out using electron linear accelerator "Electronics" (ЭЛУ-4. Energy of the particles was 2,3—3,0 MeV, radiation dose 1015—1020 m–2, electron beam current 2 mA/m2. It is shown that in structures containing dislocation networks, irradiation results in reduction of the reverse currents by 5—8 times and of the density of defects by 5—10 times, while the mobility of the charge carriers is increased by 1,2 times. Wafer yield for operation under radiation exposure, when the semiconductor structures are formed in the optimal mode, is increased by 7—10% compared to the structures without dislocation networks. The results obtained can be used in manufacturing technology for radiation-resistant integrated circuits (bipolar, CMOS, BiCMOS, etc..

  11. Epitaxial TiN(001) wetting layer for growth of thin single-crystal Cu(001)

    Energy Technology Data Exchange (ETDEWEB)

    Chawla, J. S.; Zhang, X. Y.; Gall, D. [Department of Materials Science and Engineering, Rensselaer Polytechnic Institute, Troy, New York 12180 (United States)

    2011-08-15

    Single-crystal Cu(001) layers, 4-1400 nm thick, were deposited on MgO(001) with and without a 2.5-nm-thick TiN(001) buffer layer. X-ray diffraction and reflection indicate that the TiN(001) surface suppresses Cu-dewetting, yielding a 4 x lower defect density and a 9 x smaller surface roughness than if grown on MgO(001) at 25 deg. C. In situ and low temperature electron transport measurements indicate that ultra-thin (4 nm) Cu(001) remains continuous and exhibits partial specular scattering at the Cu-vacuum boundary with a Fuchs-Sondheimer specularity parameter p = 0.6 {+-} 0.2, suggesting that the use of epitaxial wetting layers is a promising approach to create low-resistivity single-crystal Cu nanoelectronic interconnects.

  12. Arsenic-Doped High-Resistivity-Silicon Epitaxial Layers for Integrating Low-Capacitance Diodes

    Directory of Open Access Journals (Sweden)

    Jaber Derakhshandeh

    2011-12-01

    Full Text Available An arsenic doping technique for depositing up to 40-μm-thick high-resistivity layers is presented for fabricating diodes with low RC constants that can be integrated in closely-packed configurations. The doping of the as-grown epi-layers is controlled down to 5 × 1011 cm−3, a value that is solely limited by the cleanness of the epitaxial reactor chamber. To ensure such a low doping concentration, first an As-doped Si seed layer is grown with a concentration of 1016 to 1017 cm−3, after which the dopant gas arsine is turned off and a thick lightly-doped epi-layer is deposited. The final doping in the thick epi-layer relies on the segregation and incorporation of As from the seed layer, and it also depends on the final thickness of the layer, and the exact growth cycles. The obtained epi-layers exhibit a low density of stacking faults, an over-the-wafer doping uniformity of 3.6%, and a lifetime of generated carriers of more than 2.5 ms. Furthermore, the implementation of a segmented photodiode electron detector is demonstrated, featuring a 30 pF capacitance and a 90 Ω series resistance for a 7.6 mm2 anode area.

  13. Atomic Layer Thermopile Materials: Physics and Application

    Directory of Open Access Journals (Sweden)

    P. X. Zhang

    2008-01-01

    Full Text Available New types of thermoelectric materials characterized by highly anisotropic Fermi surfaces and thus anisotropic Seebeck coefficients are reviewed. Early studies revealed that there is an induced voltage in high TC oxide superconductors when the surface of the films is exposed to short light pulses. Subsequent investigations proved that the effect is due to anisotropic components of the Seebeck tensor, and the type of materials is referred to atomic layer thermopile (ALT. Our recent studies indicate that multilayer thin films at the nanoscale demonstrate enhanced ALT properties. This is in agreement with the prediction in seeking the larger figure of merit (ZT thermoelectric materials in nanostructures. The study of ALT materials provides both deep insight of anisotropic transport property of these materials and at the same time potential materials for applications, such as light detector and microcooler. By measuring the ALT properties under various perturbations, it is found that the information on anisotropic transport properties can be provided. The information sometimes is not easily obtained by other tools due to the nanoscale phase coexistence in these materials. Also, some remained open questions and future development in this research direction have been well discussed.

  14. Hydrogen-surfactant-mediated epitaxy of Ge1- x Sn x layer and its effects on crystalline quality and photoluminescence property

    Science.gov (United States)

    Nakatsuka, Osamu; Fujinami, Shunsuke; Asano, Takanori; Koyama, Takeshi; Kurosawa, Masashi; Sakashita, Mitsuo; Kishida, Hideo; Zaima, Shigeaki

    2017-01-01

    The effect of hydrogen-surfactant-mediated molecular beam epitaxy (MBE) growth of Ge1- x Sn x layer on Ge(001) substrate on crystalline quality and photoluminescence (PL) property has been investigated. The effect of irradiation of atomic hydrogen (H) generated by dissociating molecular hydrogen (H2) were examined during the MBE growth. H irradiation significantly improves the surface morphology with the enhancement of the two-dimensional growth of the Ge1- x Sn x epitaxial layer. Enhanced diffuse scattering is observed in the X-ray diffraction profile, indicating a high density of point defects. In the PL spectrum of the H2-irradiated Ge1- x Sn x layer, two components are observed, suggesting the radiative recombination with both indirect and direct transitions, while one component related to the direct transition is observable in the H-irradiated sample. The postdeposition annealing in nitrogen ambient at as low as 220 °C decreases the PL intensity of the H-irradiated Ge1- x Sn x layer, although the intensity is recovered after annealing at 300 °C, suggesting the annihilation of point defects in the Ge1- x Sn x layer.

  15. Optimal Cu buffer layer thickness for growing epitaxial Co overlayers on Si(111)7 x 7

    Energy Technology Data Exchange (ETDEWEB)

    Ivanov, Yu. P.; Zotov, A. V. [School of Natural Science, Far Eastern Federal University, 690950 Vladivostok (Russian Federation); Institute of Automation and Control Processes, 690041 Vladivostok (Russian Federation); Ilin, A. I.; Davydenko, A. V. [School of Natural Science, Far Eastern Federal University, 690950 Vladivostok (Russian Federation)

    2011-10-15

    Using scanning tunneling microscopy, reflection high energy diffraction and magnetic optical Kerr effect measurements, growth mode and the magnetic properties of epitaxial Co films on Si(111) with epitaxial Cu(111) buffer layers of various thicknesses have been studied. The strained 3.5-monolayer-thick Cu/Si(111) film has been found to be an optimal buffer, in which case an almost ideal layer-by-layer like growth of Co is observed up to six Co monolayers, due to a negligible lattice mismatch. The coercivity of Co films grown in this layer-by-layer like fashion has been determined to be about 10 Oe, testifying to the high quality of the formed Co film and Co/Cu interface. Changeover of the Co film growth mode from layer-by-layer like to multilayer has been found to result in the transition of the film magnetic properties from isotropic to markedly uniaxially anisotropic.

  16. Growth of Few-Layer Graphene on Sapphire Substrates by Directly Depositing Carbon Atoms

    Institute of Scientific and Technical Information of China (English)

    KANG Chao-Yang; TANG Jun; LIU Zhong-Liang; LI Li-Min; YAN Wen-Sheng; WEI Shi-Qiang; XU Peng-Shou

    2011-01-01

    Few-layer graphene (FLG) is successfully grown on sapphire substrates by directly depositing carbon atoms at the substrate temperature of 1300℃ in a molecular beam epitaxy chamber.The reflection high energy diffraction,Raman spectroscopy and near-edge x-ray absorption fine structure are used to characterize the sample,which confirm the formation of graphene layers.The mean domain size of FLG is around 29.2 nm and the layer number is about 2-3.The results demonstrate that the grown FLG displays a turbostratic stacking structure similar to that of the FLG produced by annealing C-terminated a-SiC surface.Graphene,a monolayer of sp2-bonded carbon atoms,is a quasi two-dimensional (2D) material.It has attracted great interest because of its distinctive band structure and physical properties.[1] Graphene can now be obtained by several different approaches including micromechanical[1] and chemical[2] exfoliation of graphite,epitaxial growth on hexagonal SiC substrates by Si sublimation in vacuum,[3] and CVD growth on metal substrates.[4] However,these preparation methods need special substrates,otherwise,in order to design microelectronic devices,the prepared graphene should be transferred to other appropriate substrates.Thus the growth of graphene on the suitable substrates is motivated.%Few-layer graphene (FLG) is successfully grown on sapphire substrates by directly depositing carbon atoms at the substrate temperature of 1300℃ in a molecular beam epitaxy chamber. The reflection high energy diffraction, Raman spectroscopy and near-edge x-ray absorption fine structure are used to characterize the sample, which confirm the formation of graphene layers. The mean domain size of FLG is around 29.2nm and the layer number is about 2-3. The results demonstrate that the grown FLG displays a turbostratic stacking structure similar to that of the FLG produced by annealing C-terminated α-SiC surface.

  17. Molecular beam epitaxial growth of tungsten layers embedded in single crystal gallium arsenide

    Energy Technology Data Exchange (ETDEWEB)

    Harbison, J.P.; Hwang, D.M.; Levkoff, J.; Derkits G.E. Jr.

    1985-12-01

    We have been able to fabricate structures which consist of a thin (approx.10 nm) polycrystalline W film embedded in surrounding single crystalline GaAs by molecular beam epitaxy (MBE) using an electron beam evaporation source to deposit W metal in an ultrahigh vacuum MBE growth chamber. The entire deposition sequence can take place at elevated temperature (625--700 /sup 0/C) due to the nonreactive nature of W with respect to GaAs. Reflective high-energy diffraction and transmission electron microscopy indicate that the single crystal GaAs overgrowth proceeds by seeding from the GaAs layer beneath the W through spontaneously occurring perforations in the W layer.

  18. Columnar structured FePt films epitaxially grown on large lattice mismatched intermediate layer

    Science.gov (United States)

    Dong, K. F.; Deng, J. Y.; Peng, Y. G.; Ju, G.; Chow, G. M.; Chen, J. S.

    2016-09-01

    The microstructure and magnetic properties of the FePt films grown on large mismatched ZrN (15.7%) intermediate layer were investigated. With using ZrN intermediate layer, FePt 10 nm films exhibited (001) texture except for some weaker FePt (110) texture. Good epitaxial relationships of FePt (001) //ZrN (001) //TiN (001) among FePt and ZrN/TiN were revealed from the transmission electron microscopy (TEM) results. As compared with TiN intermediate layer, although FePt-SiO2-C films grown on ZrN/TiN intermediate layer showed isotropic magnetic properties, the large interfacial energy and lattice mismatch between FePt and ZrN would lead to form columnar structural FePt films with smaller grain size and improved isolation. By doping ZrN into the TiN layer, solid solution of ZrTiN was formed and the lattice constant is increased comparing with TiN and decreased comparing with ZrN. Moreover, FePt-SiO2-C films grown on TiN 2 nm-20 vol.% ZrN/TiN 3 nm intermediate layer showed an improved perpendicular magnetic anisotropy. Simultaneously, columnar structure with smaller grain size retained.

  19. Growth and characterization of GaAs layers on Si substrates by migration-enhanced molecular beam epitaxy

    Science.gov (United States)

    Kim, Jae-Hoon; Liu, John K.; Radhakrishnan, Gouri; Katz, Joseph; Sakai, Shiro

    1988-01-01

    Migration-enhanced molecular beam epitaxial (MEMBE) growth and characterization of the GaAs layer on Si substrates (GaAs/Si) are reported. The MEMBE growth method is described, and material properties are compared with those of normal two-step MBE-grown or in situ annealed layers. Micrographs of cross-section view transmission electron microscopy and scanning surface electron microscopy of MEMBE-grown GaAs/Si showed dislocation densities of 10 to the 7th/sq cm. AlGaAs/GaAs double heterostructures have been successfully grown on MEMBE GaAs/Si by both metalorganic chemical vapor deposition and liquid phase epitaxy.

  20. Planarization and Processing of Metamorphic Buffer Layers Grown by Hydride Vapor-Phase Epitaxy

    Science.gov (United States)

    Zutter, Brian T.; Schulte, Kevin L.; Kim, Tae Wan; Mawst, Luke J.; Kuech, T. F.; Foran, Brendan; Sin, Yongkun

    2014-04-01

    Hydride vapor-phase epitaxy (HVPE) is a high-growth-rate, cost-effective means to grow epitaxial semiconductor material. Thick HVPE-based metamorphic buffer layers (MBLs) can serve as "pseudosubstrates" with controllable lattice parameter. In our structures, the indium content in In x Ga1- x As is gradually increased from zero to the final composition corresponding to the desired lattice constant, and then a thick (˜10 μm) constant-composition capping layer is grown. This thick capping layer promotes maximum strain relaxation while permitting use of polishing procedures to achieve surface planarity. Lattice-mismatched growth of MBLs invariably results in rough, cross-hatched surface morphology exhibiting up to 200 nm peak-to-valley roughness. This roughness can be eliminated by chemical mechanical planarization, thus creating a suitable surface for subsequent regrowth. Polishing of In x Ga1- x As is complicated by the sensitivity of the surface layer to the polishing parameters, particularly the applied pressure. Polishing at high applied pressure (12 psi) results in the formation of circular asperities hundreds of nanometers high and tens of microns in diameter. When lower applied pressure (4 psi) was used, the cross-hatching height of MBLs was lowered from 200 nm to <10 nm over a 350 μm lateral scale. The successfully planarized In0.20Ga0.80As MBLs were used as a substrate for a superlattice (SL) structure such as that used in quantum cascade lasers. Use of planarization before regrowth of the SL resulted in a reduction of the high-resolution x-ray diffraction peak full-width at half-maximum from 389″ to 159″.

  1. Effects of AlN nucleation layers on the growth of AlN films using high temperature hydride vapor phase epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Balaji, M. [Science et Ingenierie des Materiaux et des Procedes, Grenoble INP-CNRS-UJF, BP 75, 38402 Saint Martin d' Heres (France); ACERDE, 452 rue des sources, 38920 Crolles (France); Crystal Growth Centre, Anna University-Chennai, Chennai 600025 (India); Claudel, A. [ACERDE, 452 rue des sources, 38920 Crolles (France); Fellmann, V. [Science et Ingenierie des Materiaux et des Procedes, Grenoble INP-CNRS-UJF, BP 75, 38402 Saint Martin d' Heres (France); Gelard, I. [ACERDE, 452 rue des sources, 38920 Crolles (France); Blanquet, E., E-mail: elisabeth.blanquet@simap.grenoble-inp.fr [Science et Ingenierie des Materiaux et des Procedes, Grenoble INP-CNRS-UJF, BP 75, 38402 Saint Martin d' Heres (France); Boichot, R. [Science et Ingenierie des Materiaux et des Procedes, Grenoble INP-CNRS-UJF, BP 75, 38402 Saint Martin d' Heres (France); Pierret, A. [Departement de Mesures Physiques, ONERA, Chemin de la Huniere, 91761 Palaiseau Cedex (France); CEA-CNRS Group ' NanoPhysique et SemiConducteurs' , INAC/SP2M/NPSC, CEA-Grenoble, 17 rue des Martyrs, 38054 Grenoble, Cedex 9 (France); and others

    2012-06-15

    Highlights: Black-Right-Pointing-Pointer Growth of AlN Nucleation layers and its effect on high temperature AlN films quality were investigated. Black-Right-Pointing-Pointer AlN nucleation layers stabilizes the epitaxial growth of AlN and improves the surface morphology of AlN films. Black-Right-Pointing-Pointer Increasing growth temperature of AlN NLs as well as AlN films improves the structural quality and limits the formation of cracks. - Abstract: AlN layers were grown on c-plane sapphire substrates with AlN nucleation layers (NLs) using high temperature hydride vapor phase epitaxy (HT-HVPE). Insertion of low temperature NLs, as those typically used in MOVPE process, prior to the high temperature AlN (HT-AlN) layers has been investigated. The NLs surface morphology was studied by atomic force microscopy (AFM) and NLs thickness was measured by X-ray reflectivity. Increasing nucleation layer deposition temperature from 650 to 850 Degree-Sign C has been found to promote the growth of c-oriented epitaxial HT-AlN layers instead of polycrystalline layers. The growth of polycrystalline layers has been related to the formation of dis-oriented crystallites. The density of such disoriented crystallites has been found to decrease while increasing NLs deposition temperature. The HT-AlN layers have been characterized by X-ray diffraction {theta} - 2{theta} scan and (0 0 0 2) rocking curve measurement, Raman and photoluminescence spectroscopies, AFM and field emission scanning electron microscopy. Increasing the growth temperature of HT-AlN layers from 1200 to 1400 Degree-Sign C using a NL grown at 850 Degree-Sign C improves the structural quality as well as the surface morphology. As a matter of fact, full-width at half-maximum (FWHM) of 0 0 0 2 reflections was improved from 1900 to 864 arcsec for 1200 Degree-Sign C and 1400 Degree-Sign C, respectively. Related RMS roughness also found to decrease from 10 to 5.6 nm.

  2. USE OF ATOMIC LAYER DEPOSITION OF FUNCTIONALIZATION OF NANOPOROUS BIOMATERIALS

    Energy Technology Data Exchange (ETDEWEB)

    Brigmon, R.; Narayan, R.; Adiga, S.; Pellin, M.; Curtiss, L.; Stafslien, S.; Chisholm, B.; Monteiro-Riviere, N.; Elam, J.

    2010-02-08

    Due to its chemical stability, uniform pore size, and high pore density, nanoporous alumina is being investigated for use in biosensing, drug delivery, hemodialysis, and other medical applications. In recent work, we have examined the use of atomic layer deposition for coating the surfaces of nanoporous alumina membranes. Zinc oxide coatings were deposited on nanoporous alumina membranes using atomic layer deposition. The zinc oxide-coated nanoporous alumina membranes demonstrated antimicrobial activity against Escherichia coli and Staphylococcus aureus bacteria. These results suggest that atomic layer deposition is an attractive technique for modifying the surfaces of nanoporous alumina membranes and other nanostructured biomaterials.

  3. Metalorganic vapor phase epitaxy of GaAs on Si using II a-flouride buffer layers

    Science.gov (United States)

    Tiwari, A. N.; Freundlich, A.; Beaumont, B.; Blunier, S.; Zogg, H.; Teodoropol, S.; Vèrié, C.

    1992-11-01

    Metalorganic vapor phase epitaxy has been used for the first time to grow epitaxial GaAs layers on (111) and (100) oriented Si either using CaF 2 or stacked (Ca,Sr)F 2/CaF 2 as a buffer. The GaAs layers show sharp and well resolved electron channeling patterns. The Rutherford backscattering (RBS) ion channeling minimum yield is 5% for (111) orientation and 6% for (100) orientation. The GaAs(111) layers are untwinned. The strain in the GaAs layer has been measured with RBS and X-ray diffraction and it is found that the thermal mismatch-induced strain in the GaAs layer is considerably lower than in similar GaAs films grown without flouride buffer.

  4. Characterization of GaN Buffer Layers and Its Epitaxial Layers Grown by MOCVD

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    Low-pressure MOCVD has been used to investigate the properties of low-temperature buffer layer deposition conditions and their influence on the properties of high-temperature GaN epilayers grown subsequently. It is found that the surface morphology of the as-grown buffer layer after thermal annealing at 1030℃ and 1050℃ depends strongly on the thickness of the buffer layer. In particular when a thick buffer layer is used, large trapezoidal nuclei are formed after annealing.

  5. Epitaxial growth of single-crystal C sub 60 on mica by helium-atom scattering

    Energy Technology Data Exchange (ETDEWEB)

    Schmicker, D.; Schmidt, S. (Max-Planck-Institut fuer Stroemungsforschung, Bunsenstrasse 10, W-3400 Goettingen (Germany)); Skofronick, J.G. (Department of Physics, Florida State University, Tallahassee, Florida 32306 (United States)); Toennies, J.P.; Vollmer, R. (Max-Planck-Institut fuer Stroemungsforschung, Bunsenstrasse 10, W-3400 Goettingen (Germany))

    1991-11-15

    We report on a helium-atom-scattering study of the growth, structure, and surface dynamics of a very thin film of C{sub 60} sublimed in ultrahigh vacuum onto a freshly cleaved mica substrate. The resulting diffraction pattern showed that the C{sub 60} forms a hexagonal crystal layer that is in registry with the mica substrate and at a spacing of 10.4 A. The dispersion results showed two Einstein modes.

  6. Nanoprocessing of layered crystalline materials by atomic force microscopy.

    Science.gov (United States)

    Miyake, Shojiro; Wang, Mei

    2015-01-01

    By taking advantage of the mechanical anisotropy of crystalline materials, processing at a single-layer level can be realized for layered crystalline materials with periodically weak bonds. Mica (muscovite), graphite, molybdenum disulfide (MoS2), and boron nitride have layered structures, and there is little interaction between the cleavage planes existing in the basal planes of these materials. Moreover, it is easy to image the atoms on the basal plane, where the processed shape can be observed on the atomic level. This study reviews research evaluating the nanometer-scale wear and friction as well as the nanometer-scale mechanical processing of muscovite using atomic force microscopy (AFM). It also summarizes recent AFM results obtained by our research group regarding the atomic-scale mechanical processing of layered materials including mica, graphite, MoS2, and highly oriented pyrolytic graphite.

  7. Synchrotron X-ray diffraction analysis of epitaxial GaN layer laterally overgrown

    CERN Document Server

    Feng Gan; Wang Yu Tian; Yang Hui; Liang Jun Wu; Zheng Wen Li; Jia Quan Jie

    2002-01-01

    The GaN layer grown by epitaxial lateral overgrowth on sapphire (0001) has been investigated by synchrotron X-ray diffraction. The results show that ELO GaN stripes bend towards the SiN sub x mask in directions perpendicular to the stripe direction. This lead to the GaN (0001) crystal planes in the 'wings' (overgrown GaN) exhibit crystallographic tilts away from those in the 'window' (seed) regions. The GaN (0002) diffraction was used to determine the grain sizes in the wing region and window region, respectively. It is found that the grain size in the wing region increases about three times comparing to those in window region

  8. Temperature Dependence of 1/f Noise in Gallium Nitride Epitaxial Layer

    Directory of Open Access Journals (Sweden)

    Ashutosh Kumar

    2011-01-01

    Full Text Available 1/f noise investigation was performed on n-GaN epitaxial layer grown on sapphire. The variation of spectral power density of voltage fluctuations density was observed as a function of frequency (100-50 Hz and it showed the 1/f spectra. This type of behavior was attributed to the presence of traps. The variation in spectral power density of voltage fluctuations with temperature was also observed with in the temperature range 80 K and 300 K and it was found to be slightly increasing with temperature. It was attributed to the trapping-detrapping process of charge carriers by the defects. Four probe configuration was used for noise measurement and contacts were made with indium. To check the stability and ohmic behavior of contacts, I-V measurements were performed with in the temperature range 80-325 K.

  9. Quantitative analysis of HOLZ line splitting in CBED patterns of epitaxially strained layers

    Energy Technology Data Exchange (ETDEWEB)

    Houdellier, F. [Centre d' Elaboration de Materiaux et d' Etudes Structurales, C.N.R.S., 29, Rue Jeanne Marvig, BP 94347 31055 Toulouse Cedex 4 (France)]. E-mail: florent@cemes.fr; Roucau, C. [Centre d' Elaboration de Materiaux et d' Etudes Structurales, C.N.R.S., 29, Rue Jeanne Marvig, BP 94347 31055 Toulouse Cedex 4 (France); Clement, L. [CEA, Departement de Recherche Fondamentale sur la Matiere Condensee, SP2M, 17, Rue des Martyrs, 38054 Grenoble (France); Rouviere, J.L. [CEA, Departement de Recherche Fondamentale sur la Matiere Condensee, SP2M, 17, Rue des Martyrs, 38054 Grenoble (France); Casanove, M.J. [Centre d' Elaboration de Materiaux et d' Etudes Structurales, C.N.R.S., 29, Rue Jeanne Marvig, BP 94347 31055 Toulouse Cedex 4 (France)

    2006-08-15

    A SiGe layer epitaxially grown on a silicon substrate is experimentally studied by convergent beam electron diffraction (CBED) experiments and used as a test sample to analyse the higher-order Laue zones (HOLZ) line splitting. The influence of surface strain relaxation on the broadening of HOLZ lines is confirmed. The quantitative fit of the observed HOLZ line profiles is successfully achieved using a formalism particularly well-adapted to the case of a z-dependent crystal potential (z being the zone axis). This formalism, based on a time-dependent perturbation theory approach, proves to be much more efficient than a classical Howie-Whelan approach, to reproduce the complex HOLZ lines profile in this heavily strained test sample.

  10. Real-time and in situ monitoring of sputter deposition with RHEED for atomic layer controlled growth

    Directory of Open Access Journals (Sweden)

    J. P. Podkaminer

    2016-08-01

    Full Text Available Sputter deposition is a widely used growth technique for a large range of important material systems. Epitaxial films of carbides, nitrides, metals, oxides and more can all be formed during the sputter process which offers the ability to deposit smooth and uniform films from the research level up to an industrial scale. This tunable kinematic deposition process excels in easily adapting for a large range of environments and growth procedures. Despite the vast advantages, there is a significant lack of in situ analysis options during sputtering. In particular, the area of real time atomic layer control is severely deficient. Atomic layer controlled growth of epitaxial thin films and artificially layered superlattices is critical for both understanding their emergent phenomena and engineering novel material systems and devices. Reflection high-energy electron diffraction (RHEED is one of the most common in situ analysis techniques during thin film deposition that is rarely used during sputtering due to the effect of the strong permanent magnets in magnetron sputter sources on the RHEED electron beam. In this work we have solved this problem and designed a novel way to deter the effect of the magnets for a wide range of growth geometries and demonstrate the ability for the first time to have layer-by-layer control during sputter deposition by in situ RHEED.

  11. Real-time and in situ monitoring of sputter deposition with RHEED for atomic layer controlled growth

    Science.gov (United States)

    Podkaminer, J. P.; Patzner, J. J.; Davidson, B. A.; Eom, C. B.

    2016-08-01

    Sputter deposition is a widely used growth technique for a large range of important material systems. Epitaxial films of carbides, nitrides, metals, oxides and more can all be formed during the sputter process which offers the ability to deposit smooth and uniform films from the research level up to an industrial scale. This tunable kinematic deposition process excels in easily adapting for a large range of environments and growth procedures. Despite the vast advantages, there is a significant lack of in situ analysis options during sputtering. In particular, the area of real time atomic layer control is severely deficient. Atomic layer controlled growth of epitaxial thin films and artificially layered superlattices is critical for both understanding their emergent phenomena and engineering novel material systems and devices. Reflection high-energy electron diffraction (RHEED) is one of the most common in situ analysis techniques during thin film deposition that is rarely used during sputtering due to the effect of the strong permanent magnets in magnetron sputter sources on the RHEED electron beam. In this work we have solved this problem and designed a novel way to deter the effect of the magnets for a wide range of growth geometries and demonstrate the ability for the first time to have layer-by-layer control during sputter deposition by in situ RHEED.

  12. Heat resistive dielectric multi-layer micro-mirror array in epitaxial lateral overgrowth gallium nitride.

    Science.gov (United States)

    Huang, Chen-Yang; Ku, Hao-Min; Liao, Wei-Tsai; Chao, Chu-Li; Tsay, Jenq-Dar; Chao, Shiuh

    2009-03-30

    Ta2O5 / SiO2 dielectric multi-layer micro-mirror array (MMA) with 3mm mirror size and 6mm array period was fabricated on c-plane sapphire substrate. The MMA was subjected to 1200 degrees C high temperature annealing and remained intact with high reflectance in contrast to the continuous multi-layer for which the layers have undergone severe damage by 1200 degrees C annealing. Epitaxial lateral overgrowth (ELO) of gallium nitride (GaN) was applied to the MMA that was deposited on both sapphire and sapphire with 2:56 mm GaN template. The MMA was fully embedded in the ELO GaN and remained intact. The result implies that our MMA is compatible to the high temperature growth environment of GaN and the MMA could be incorporated into the structure of the micro-LED array as a one to one micro backlight reflector, or as the patterned structure on the large area LED for controlling the output light.

  13. Temperature dependence of photoluminescence from ordered GaInP{sub 2} epitaxial layers

    Energy Technology Data Exchange (ETDEWEB)

    Prutskij, T. [Instituto de Ciencias, BUAP, Apartado Postal 207, 72000 Puebla, Pue. (Mexico); Pelosi, C. [IMEM/CNR, Parco Area delle Scienze 37/A, 43010 Parma (Italy)

    2010-01-15

    The temperature behavior of the integrated intensity of photoluminescence (PL) emission from ordered GaInP{sub 2} epitaxial layer was measured at temperatures of 10 - 300 K. Within this temperature range the PL emission is dominated by band-to-band radiative recombination. The PL intensity temperature dependence has two regions: at low temperatures it quenches rapidly as the temperature increases, and above 100 K it reduces slowly. This temperature behavior is compared with that of disordered GaInP{sub 2} layer. The specter of the PL emission of the disordered layer has two peaks, which are identified as due to donor-accepter (D-A) and band-to-band recombination. The PL intensity quenching of these spectral bands is very different: With increasing temperature, the D-A peak intensity remains almost unchanged at low temperatures and then decreases at a higher rate. The intensity of the band-to-band recombination peak decays gradually, having a higher rate at low temperatures than at higher temperatures. Comparing these temperature dependencies of these PL peaks of ordered and disordered alloys and the temperature behavior of their full width at half maximum (FWHM), we conclude that the different morphology of these alloys causes their different temperature behavior. (copyright 2010 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  14. Electrical transport in thin BeSeTe/Si epitaxial layers

    Science.gov (United States)

    Clark, Kevin; Maldonado, Eduardo; Basit, Nasir; Sandu, Titus; Bate, Robert; Kirk, Wiley

    2003-03-01

    Beryllium selenide telluride BeSe_0.41Te_0.59 is a II-VI semiconductor lattice-matched to silicon. For Si-based optoelectronic heterostructures, BeSeTe has planar epitaxial growth, covalent fault-resistant bonding, and thermal and chemical stability. BeSeTe has an indirect bandgap of 3.0eV, from a tight-binding model alloy of the indirect-gap constituents BeTe (2.7eV) and BeSe (4.5eV). Growth, fabrication, and vertical transport measurements were done for several thin ˜30-100ÅBeSeTe/Si structures in a range of compositions and thicknesses. I-V and I-T characteristics of the thinnest layers were modeled by direct tunneling while thicker layers were modeled by trap-assisted transport. Excess current was remarkably suppressed in composite films with a BeSeTe interface and a zinc chalcogenide (ZnS, ZnSe) cap layer. C-V measurements showed growth of low interface-state density BeSeTe/Si interfaces requires avoiding any excess Te flux at the interface.

  15. The Structural Quality of AlxGa1-xN Epitaxial Layers Grown by Digitally-AlloyedModulated Precursor Epitaxy Determined by Transmission Electron Microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Hawkridge, Michael E; Liliental-Weber, Zuzanna; Kim, Hee Jin; Choi, Suk; Yoo, Dongwon; Ryou, Jae-Hyun; Dupuis, Russell

    2008-10-13

    Al(x)Ga(1-x)N layers of varying composition (0.5epitaxial regime employing AlN and GaN binary sub-layers by metalorganic chemical vapor deposition on AlN templates were characterized by transmission electron microscopy techniques. Fine lamellae were observed in bright field images that indicate a possible variation in composition due to the modulated nature of growth. In higher Ga content samples (x(Al)<0.75), a compositional inhomogeniety associated with thicker island regions was observed, which is determined to be due to large Ga-rich areas formed at the base of the layer. Possible causes for the separation of Ga-rich material are discussed in the context of the growth regime used.

  16. Exposure of epitaxial graphene on SiC(0001) to atomic hydrogen.

    Science.gov (United States)

    Guisinger, Nathan P; Rutter, Gregory M; Crain, Jason N; First, Phillip N; Stroscio, Joseph A

    2009-04-01

    Graphene films on SiC exhibit coherent transport properties that suggest the potential for novel carbon-based nanoelectronics applications. Recent studies suggest that the role of the interface between single layer graphene and silicon-terminated SiC can strongly influence the electronic properties of the graphene overlayer. In this study, we have exposed the graphitized SiC to atomic hydrogen in an effort to passivate dangling bonds at the interface, while investigating the results utilizing room temperature scanning tunneling microscopy.

  17. Epitaxial growth of atomically flat gadolinia-doped ceria thin films by pulsed laser deposition

    DEFF Research Database (Denmark)

    Chen, Yunzhong; Pryds, Nini; Schou, Jørgen;

    Ceria-based thin films are often applied as key functional components in miniaturized electroceramic devices such as solid oxide fuel cells or gas sensors. Processing routes that prevent thermal degradation and yield access to the optimum microstructures are sought. Multi-step growth, involving......), to the growth of dense, gas impermeable 10 mol% gadolinia-doped ceria (CGO10) solid electrolyte can be overcome by the seeding process. In order to evaluate the seed layer preparation, the effects of different thermal annealing treatments on the morphology, microstructure and surface roughness of ultrathin CGO......10 layers with a thickness of 4 nm, 13 nm and 22 nm, respectively, grown on Mg(100), were studied by atomic force microscopy and X-ray reflectometry....

  18. Analysis of the Band-Structure in (Ga, MnAs Epitaxial Layers by Optical Methods

    Directory of Open Access Journals (Sweden)

    O. Yastrubchak

    2012-03-01

    Full Text Available The ternary III-V semiconductor (Ga, MnAs has recently drawn a lot of attention as the model diluted ferromagnetic semiconductor, combining semiconducting properties with magnetism. (Ga, MnAs layers are usually gown by the low-temperature molecular-beam epitaxy (LT-MBE technique. Below a magnetic transition temperature, TC, substitutional Mn2+ ions are ferromagnetically ordered owing to interaction with spin-polarized holes. However, the character of electronic states near the Fermi energy and the electronic structure in ferromagnetic (Ga, MnAs are still a matter of controversy. The photoreflectance (PR spectroscopy was applied to study the band-structure evolution in (Ga, MnAs layers with increasing Mn content. We have investigated thick (800-700 nm and 230-300 nm (Ga, MnAs layers with Mn content in the wide range from 0.001 % to 6 % and, as a reference, undoped GaAs layer, grown by LT-MBE on semi-insulating (001 GaAs substrates. Our findings were interpreted in terms of the model, which assumes that the mobile holes residing in the valence band of ferromagnetic (Ga, MnAs and the Fermi level position determined by the concentration of valence-band holes. The ternary III-V semiconductor (Ga, MnAs has recently drawn a lot of attention as the model diluted ferromagnetic semiconductor, combining semiconducting properties with magnetism. (Ga, MnAs layers are usually gown by the low-temperature molecular-beam epitaxy (LT-MBE technique. Below a magnetic transition temperature, TC, substitutional Mn2+ ions are ferromagnetically ordered owing to interaction with spin-polarized holes. However, the character of electronic states near the Fermi energy and the electronic structure in ferromagnetic (Ga, MnAs are still a matter of controversy. The photoreflectance (PR spectroscopy was applied to study the band-structure evolution in (Ga, MnAs layers with increasing Mn content. We have investigated thick (800-700 nm and 230-300 nm (Ga

  19. Spectroscopic detection of atom-surface interactions in an atomic vapour layer with nanoscale thickness

    CERN Document Server

    Whittaker, K A; Hughes, I G; Sargsyan, A; Sarkisyan, D; Adams, C S

    2015-01-01

    We measure the resonance line shape of atomic vapor layers with nanoscale thickness confined between two sapphire windows. The measurement is performed by scanning a probe laser through resonance and collecting the scattered light. The line shape is dominated by the effects of Dicke narrowing, self-broadening, and atom-surface interactions. By fitting the measured line shape to a simple model we discuss the possibility to extract information about the atom-surface interaction.

  20. Layer by layer three-dimensional tissue epitaxy by cell-laden hydrogel droplets.

    Science.gov (United States)

    Moon, SangJun; Hasan, Syed K; Song, Young S; Xu, Feng; Keles, Hasan Onur; Manzur, Fahim; Mikkilineni, Sohan; Hong, Jong Wook; Nagatomi, Jiro; Haeggstrom, Edward; Khademhosseini, Ali; Demirci, Utkan

    2010-02-01

    The ability to bioengineer three-dimensional (3D) tissues is a potentially powerful approach to treat diverse diseases such as cancer, loss of tissue function, or organ failure. Traditional tissue engineering methods, however, face challenges in fabricating 3D tissue constructs that resemble the native tissue microvasculature and microarchitectures. We have developed a bioprinter that can be used to print 3D patches of smooth muscle cells (5 mm x 5 mm x 81 microm) encapsulated within collagen. Current inkjet printing systems suffer from loss of cell viability and clogging. To overcome these limitations, we developed a system that uses mechanical valves to print high viscosity hydrogel precursors containing cells. The bioprinting platform that we developed enables (i) printing of multilayered 3D cell-laden hydrogel structures (16.2 microm thick per layer) with controlled spatial resolution (proximal axis: 18.0 +/- 7.0 microm and distal axis: 0.5 +/- 4.9 microm), (ii) high-throughput droplet generation (1 s per layer, 160 droplets/s), (iii) cell seeding uniformity (26 +/- 2 cells/mm(2) at 1 million cells/mL, 122 +/- 20 cells/mm(2) at 5 million cells/mL, and 216 +/- 38 cells/mm(2) at 10 million cells/mL), and (iv) long-term viability in culture (>90%, 14 days). This platform to print 3D tissue constructs may be beneficial for regenerative medicine applications by enabling the fabrication of printed replacement tissues.

  1. Layer-Controlled Chemical Vapor Deposition Growth of MoS2 Vertical Heterostructures via van der Waals Epitaxy.

    Science.gov (United States)

    Samad, Leith; Bladow, Sage M; Ding, Qi; Zhuo, Junqiao; Jacobberger, Robert M; Arnold, Michael S; Jin, Song

    2016-07-26

    The fascinating semiconducting and optical properties of monolayer and few-layer transition metal dichalcogenides, as exemplified by MoS2, have made them promising candidates for optoelectronic applications. Controllable growth of heterostructures based on these layered materials is critical for their successful device applications. Here, we report a direct low temperature chemical vapor deposition (CVD) synthesis of MoS2 monolayer/multilayer vertical heterostructures with layer-controlled growth on a variety of layered materials (SnS2, TaS2, and graphene) via van der Waals epitaxy. Through precise control of the partial pressures of the MoCl5 and elemental sulfur precursors, reaction temperatures, and careful tracking of the ambient humidity, we have successfully and reproducibly grown MoS2 vertical heterostructures from 1 to 6 layers over a large area. The monolayer MoS2 heterostructure was verified using cross-sectional high resolution transmission electron microscopy (HRTEM) while Raman and photoluminescence spectroscopy confirmed the layer-controlled MoS2 growth and heterostructure electronic interactions. Raman, photoluminescence, and energy dispersive X-ray spectroscopy (EDS) mappings verified the uniform coverage of the MoS2 layers. This reaction provides an ideal method for the scalable layer-controlled growth of transition metal dichalcogenide heterostructures via van der Waals epitaxy for a variety of optoelectronic applications.

  2. Spin transport in epitaxial magnetic manganite/ruthenate heterostructures with an LaMnO{sub 3} layer

    Energy Technology Data Exchange (ETDEWEB)

    Petrzhik, A. M., E-mail: petrzhik@hitech.cplire.ru; Ovsyannikov, G. A.; Shadrin, A. V. [Russian Academy of Sciences, Kotel’nikov Institute of Radio Engineering and Electronics (Russian Federation); Khaidukov, Yu. N.; Mustafa, L. [Max-Plank Institute for Solid State Research (Germany)

    2014-12-15

    Epitaxial La{sub 0.7}Sr{sub 0.3}MnO{sub 3}/LaMnO{sub 3}/SrRuO{sub 3} (LSMO/LMO/SRO) heterostructures with an LMO layer 0–35 nm thick are grown by laser ablation on an NdGaO{sub 3} substrate at a high temperature. X-ray diffraction and transmission electron microscopy demonstrate sharp interfaces and epitaxial growth of the LSMO and SRO layers in the heterostructures at an LMO layer thickness of 0–35 nm. SQUID measurements of the magnetic moment of the heterostructures with an LMO layer and the data obtained with reflectometry of polarized neutrons show that the manganite LMO layer is a ferromagnet at a temperature below 150 K and strongly affects the magnetic moment of the heterostructures at low temperatures. The magnetoresistance of the mesostructure created from the heterostructure using lithography and ion etching decreases with increasing LMO layer thickness and weakly depends on the direction of an applied magnetic field. If the LMP layer is absent, a negative magnetoresistance is detected; it is likely to be caused by a negative magnetization of the SRO layer.

  3. Atomic and molecular layer deposition for surface modification

    Science.gov (United States)

    Vähä-Nissi, Mika; Sievänen, Jenni; Salo, Erkki; Heikkilä, Pirjo; Kenttä, Eija; Johansson, Leena-Sisko; Koskinen, Jorma T.; Harlin, Ali

    2014-06-01

    Atomic and molecular layer deposition (ALD and MLD, respectively) techniques are based on repeated cycles of gas-solid surface reactions. A partial monolayer of atoms or molecules is deposited to the surface during a single deposition cycle, enabling tailored film composition in principle down to molecular resolution on ideal surfaces. Typically ALD/MLD has been used for applications where uniform and pinhole free thin film is a necessity even on 3D surfaces. However, thin - even non-uniform - atomic and molecular deposited layers can also be used to tailor the surface characteristics of different non-ideal substrates. For example, print quality of inkjet printing on polymer films and penetration of water into porous nonwovens can be adjusted with low-temperature deposited metal oxide. In addition, adhesion of extrusion coated biopolymer to inorganic oxides can be improved with a hybrid layer based on lactic acid.

  4. Interface morphology studies of liquid phase epitaxy grown HgCdTe films by atomic force microscopy

    Science.gov (United States)

    Azoulay, M.; George, M. A.; Burger, A.; Collins, W. E.; Silberman, E.

    1994-04-01

    In this paper we report an investigation of the morphology of the interfaces of liquid phase epitaxy (LPE) grown HgCdTe thin films on CdTe and CdZnTe substrates by atomic force microscopy (AFM) on freshly cleaved (110) crystallographic planes. An empirical observation which may be linked to lattice mismatch was indicated by an angle between the cleavage steps of the substrate to those of the film. The precipitates with size ranging from 5 nm to 20 nm were found to be most apparent near the interface.

  5. An Introduction to Atomic Layer Deposition with Thermal Applications

    Science.gov (United States)

    Dwivedi, Vivek H.

    2015-01-01

    Atomic Layer Deposition (ALD) is a cost effective nano-manufacturing technique that allows for the conformal coating of substrates with atomic control in a benign temperature and pressure environment. Through the introduction of paired precursor gases thin films can be deposited on a myriad of substrates ranging from glass, polymers, aerogels, and metals to high aspect ratio geometries. This talk will focus on the utilization of ALD for engineering applications.

  6. Bonding character of lithium atoms adsorbed on a graphene layer

    OpenAIRE

    Medeiros, P.V.C.; Mota,F.B.; Mascarenhas, A.J.S.; de Castilho, C. M. C.

    2011-01-01

    Acesso restrito: Texto completo. p. 529-531. This work uses first-principles calculations to investigate the aspects of the bonding character of lithium atoms adsorbed on a graphene layer. The presented results are in contradiction to other results that have recently appeared in the specialized literature, although they confirm some previous claims. In particular, a discussion of the characteristics of the bonding between lithium and carbon atoms and whether they interact via an sp2 ...

  7. Electrochemical atomic layer deposition of copper nanofilms on ruthenium

    Science.gov (United States)

    Gebregziabiher, Daniel K.; Kim, Youn-Geun; Thambidurai, Chandru; Ivanova, Valentina; Haumesser, Paul-Henri; Stickney, John L.

    2010-04-01

    As ULSI scales to smaller and smaller dimensions, it has become necessary to form layers of materials only a few nm thick. In addition, trenches are now being incorporated in ULSI formation which require conformal coating and will not be amenable to CMP. Atomic layer deposition (ALD) is being developed to address such issues. ALD is the formation of materials layer by layer using self-limiting reactions. This article describes the formation of Cu seed layers (for the Cu damascene process) on a Ru barrier layer. The deposit was formed by the electrochemical analog of ALD, using electrochemical self-limiting reactions which are referred to as underpotential deposition (UPD). Monolayer restricted galvanic displacement was used to form atomic layers of Cu. First Pb UPD was deposited, forming a sacrificial layer, and then a Cu +2 solution was flushed into the cell and Pb was exchanged for Cu. A linear dependence was shown for Cu growth over 8 ALD cycles, and STM showed a conformal deposition, as expected for an ALD process. Relative Cu coverages were determined using Auger electron spectroscopy, while absolute Cu coverages were obtained from coulometry during oxidative stripping of the deposits. Use of a Cl - containing electrolyte results in Cu deposits covered with an atomic layer of Cl atoms, which have been shown to protect the surfaced from oxidation during various stages of the deposition process. The 10 nm thick Ru substrates were formed on Si(1 0 0) wafers, and were partially oxidized upon receipt. Electrochemical reduction, prior to Cu deposition, removed the oxygen and some traces of carbon, the result of transport. Ion bombardment proved to clean all oxygen and carbon traces from the surface.

  8. Study of photoresponsivity in optoelectronic devices based on single crystal β-Ga2O3 epitaxial layers

    Science.gov (United States)

    Horng, Ray-Hua; Ravadgar, Parvaneh

    2013-03-01

    Single crystal β-Ga2O3 epitaxial layers have been prepared on c-axis (0001) sapphire substrates using metalorganic chemical vapor deposition technique at relatively low temperature. Post-annealing of β-Ga2O3 single crystals up to 800 °C does not affect the crystallinity, explored by x-ray diffraction, showing that β-Ga2O3 epitaxial layers are highly (-201) oriented. Metal-semiconductor-metal devices are fabricated on single crystals to study their photoresponsivity. A significant improvement in performance of post annealed-based devices is observed, attributed to point defect reduction. Annealing of as-grown samples results to a significant decrease in both oxygen and gallium vacancies, which are sources of current leakage.

  9. Real structure of the ZnO epitaxial films on (0001) leucosapphire substrates coated by ultrathin gold layers

    Energy Technology Data Exchange (ETDEWEB)

    Muslimov, A. E., E-mail: amuslimov@mail.ru; Butashin, A. V.; Kolymagin, A. B.; Vasilyev, A. L.; Kanevsky, V. M. [Russian Academy of Sciences, Shubnikov Institute of Crystallography (Russian Federation)

    2016-01-15

    The real structure of ZnO films formed by magnetron sputtering on (0001) leucosapphire substrates coated by an ultrathin (less than 0.7 nm) Au buffer layer has been studied by high-resolution microscopy. It is shown that modification of the leucosapphire substrate surface by depositing ultrathin Au layers does not lead to the formation of Au clusters at the film–substrate interface but significantly improves the structural quality of ZnO epitaxial films. It is demonstrated that the simplicity and scalability of the technique used to modify the substrate surface in combination with a high (above 2 nm/s) film growth rate under magnetron sputtering make it possible to obtain high-quality (0001) ZnO epitaxial films with an area of 5–6 cm{sup 2}.

  10. The influence of epitaxial Ti buffer layers for fabricating as-grown MgB{sub 2} films

    Energy Technology Data Exchange (ETDEWEB)

    Oba, T. [Graduate School of Engineering, Iwate University, 4-3-5 Ueda, Morioka, Iwate 020-8551 (Japan)]. E-mail: t3806005@iwate-u.ac.jp; Sun, P. [Graduate School of Engineering, Iwate University, 4-3-5 Ueda, Morioka, Iwate 020-8551 (Japan); Harada, Y. [JST Satellite Iwate, 3-35-2 Iioka-shinden, Morioka, Iwate 020-0852 (Japan); Takahashi, T. [Graduate School of Engineering, Iwate University, 4-3-5 Ueda, Morioka, Iwate 020-8551 (Japan); Iriuda, H. [Graduate School of Engineering, Iwate University, 4-3-5 Ueda, Morioka, Iwate 020-8551 (Japan); Seki, M. [Graduate School of Engineering, Iwate University, 4-3-5 Ueda, Morioka, Iwate 020-8551 (Japan); Nakanishi, Y. [Graduate School of Engineering, Iwate University, 4-3-5 Ueda, Morioka, Iwate 020-8551 (Japan); Noguchi, S. [Department of Physics and Electronics, Osaka Prefecture University, 1-1 Gakuen-cho, Naka-ku, Sakai, Osaka 599-8531 (Japan); JST-CREST, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012 (Japan); Ishida, T. [Department of Physics and Electronics, Osaka Prefecture University, 1-1 Gakuen-cho, Naka-ku, Sakai, Osaka 599-8531 (Japan); JST-CREST, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012 (Japan); Yoshizawa, M. [Graduate School of Engineering, Iwate University, 4-3-5 Ueda, Morioka, Iwate 020-8551 (Japan); JST Satellite Iwate, 3-35-2 Iioka-shinden, Morioka, Iwate 020-0852 (Japan)

    2007-03-15

    We have measured the magnetic field dependence of the resistivity using a 35T pulsed magnet for the as-grown MgB{sub 2} films fabricated on the epitaxial Ti buffer layer grown on c-plane ZnO and Al{sub 2}O{sub 3} substrates by molecular beam epitaxy (MBE). We will report the upper critical fields (H{sub c2}) along H||c-axis and H||ab-plane. The anisotropy ratio were obtained from these H{sub c2} values. The effects of Ti buffer layer on the H{sub c2} and the anisotropy of MgB{sub 2} film were discussed.

  11. Iridium wire grid polarizer fabricated using atomic layer deposition

    Directory of Open Access Journals (Sweden)

    Knez Mato

    2011-01-01

    Full Text Available Abstract In this work, an effective multistep process toward fabrication of an iridium wire grid polarizer for UV applications involving a frequency doubling process based on ultrafast electron beam lithography and atomic layer deposition is presented. The choice of iridium as grating material is based on its good optical properties and a superior oxidation resistance. Furthermore, atomic layer deposition of iridium allows a precise adjustment of the structural parameters of the grating much better than other deposition techniques like sputtering for example. At the target wavelength of 250 nm, a transmission of about 45% and an extinction ratio of 87 are achieved.

  12. Atomically thin semiconducting layers and nanomembranes: a review

    Science.gov (United States)

    Dragoman, Mircea; Dragoman, Daniela; Tiginyanu, Ion

    2017-03-01

    This article reviews the main physical properties of atomically thin semiconductors and the electronic devices based on them. We start with graphene, describing its physical properties and growth methods, followed by a discussion of its electronic device applications. Then, transition metal dichalcogenides (TMDs) are analyzed as a prototype of atomically thin semiconductors, their physical properties, growth methods, and electronic devices are discussed in detail. Finally, non-layered semiconducting membranes with thicknesses ranging from a few nanometers to about 50 nm, and considered as counterparts of atomically thin semiconductors, are analyzed, and their applications presented.

  13. Thermodynamic analysis of the deposition of GaAs epitaxial layers prepared by the MOCVD method

    Energy Technology Data Exchange (ETDEWEB)

    Leitner, J.; Mikulec, J. (Dept. of Materials for Electronics, Prague Inst. of Chemical Tech. (Czechoslovakia)); Vonka, P. (Dept. of Physical Chemistry, Prague Inst. of Chemical Tech. (Czechoslovakia)); Stejskal, J.; Hladina, R.; Klima, P. (TESLA Research Inst. of Radiocommunication, Prague (Czechoslovakia))

    1991-06-01

    On the basis of a detailed thermodynamic analysis of the Ga-As-C-H system, the initial conditions have been determined, under which the reaction of trimethylgallium (TMGa) and arsine in a hydrogen atmosphere produces a single condensed phase - solid GaAs. Liquid gallium with a small amount of dissolved arsenic is formed simultaneously when the initial ratio of the elements is B{sup V}/A{sup III}<1, whereas solid graphite is simultaneously deposited at a high initial concentration of TMGa, especially at an elevated temperature and a decreased pressure. The equilibrium concentrations of the gaseous substances are strongly influenced by the initial B{sup V}/A{sup III} ratio. As{sub 2}, As{sub 4}, and CH{sub 4} are the dominant species if B{sup V}/A{sup III}>1, while CH{sub 4}, GaCH{sub 3}, GaH and GaH{sub 2} are the most abundant if B{sup V}/A{sup III} < 1. The calculated deposition diagrams are in good qualitative agreement with experimental results published in the literature. A comparison of the calculated composition of the gaseous phase and the results of experiments under the conditions used for the deposition of GaAs epitaxial layers leads to the conclusion that the course and results of the deposition process are significantly affected by transport and kinetic phenomena. (orig.).

  14. Luminescence studies in InxGa1-xN epitaxial layers with different indium contents

    Science.gov (United States)

    Wu, T. Y.; Chang, C. C.; Tiong, K. K.; Lee, Y. C.; Hu, S. Y.; Lin, L. Y.; Lin, T. Y.; Feng, Z. C.

    2013-08-01

    The optical properties of InxGa1-xN epitaxial layers (x = 0.02, 0.04, 0.11, 0.15, 0.30 and 0.33) grown by metalorganic chemical vapor deposition (MOCVD) have been investigated by temperature-dependent photoluminescence (PL) measurement. The surface morphologies of InGaN samples are studied by scanning electron microscopy (SEM) images. The PL feature at 12 K has shown an increase in full-width at half-maximum (FWHM) with increasing In content. An anomalous S-shaped temperature dependence of the PL peak energy exhibited by InGaN films with higher In content enabled the evaluation of the exciton localization energy. The broadened FWHM and S-shaped emission shift are attributed to larger compositional fluctuation due to compositional inhomogeneity of In. Additionally, the luminescence mechanism relating to the phase separation has to be considered for the much larger FWHM value and the pronounced S-shaped behavior for the InGaN samples with In content of 0.30 and 0.33.

  15. Fabricating Buffer Layers for YBa2Cu3Oy Coated Conductor by Surface Oxidation Epitaxy

    Institute of Scientific and Technical Information of China (English)

    Yang Jian; Liu Huizhou; Gu Hongwei; Qu Fei; Fan Hongyan

    2005-01-01

    NiO buffer layers were formed on a tape of Ni for making YBCO coated conductor by surface-oxidation epitaxy (SOE) process. Different oxidizing conditions such as temperature and duration were studied for Ni tapes. It is found that the texture of NiO could be affected directly by the orientation and surface of substrate. X-ray diffraction (XRD) 2-2θ scan, φ-scan, and pole figure were employed to characterize the in-plane alignment and cube texture. X-ray φ-scan shows that NiO film is formed on Ni tape with high cube texture and a typical value at the full width at half maximum (FWHM) is ≤7.5°. Scanning electron microscopy was used to study the surface morphology of NiO films. No crack is found and the films appear dense. Such technique is simple and of low cost with perfect reproducibility, promising for developing long tapes.

  16. Epitaxial NbN/AlN/NbN tunnel junctions on Si substrates with TiN buffer layers

    Directory of Open Access Journals (Sweden)

    Rui Sun

    2016-06-01

    Full Text Available We have developed epitaxial NbN/AlN/NbN tunnel junctions on Si (100 substrates with a TiN buffer layer. A 50-nm-thick (200-oriented TiN thin film was introduced as the buffer layer for epitaxial growth of NbN/AlN/NbN trilayers on Si substrates. The fabricated NbN/AlN/NbN junctions demonstrated excellent tunneling properties with a high gap voltage of 5.5 mV, a large IcRN product of 3.8 mV, a sharp quasiparticle current rise with a ΔVg of 0.4 mV, and a small subgap leakage current. The junction quality factor Rsg/RN was about 23 for the junction with a Jc of 47 A/cm2 and was about 6 for the junction with a Jc of 3.0 kA/cm2. X-ray diffraction and transmission electron microscopy observations showed that the NbN/AlN/NbN trilayers were grown epitaxially on the (200-orientated TiN buffer layer and had a highly crystalline structure with the (200 orientation.

  17. Development of Production PVD-AIN Buffer Layer System and Processes to Reduce Epitaxy Costs and Increase LED Efficiency

    Energy Technology Data Exchange (ETDEWEB)

    Cerio, Frank

    2013-09-14

    The DOE has set aggressive goals for solid state lighting (SSL) adoption, which require manufacturing and quality improvements for virtually all process steps leading to an LED luminaire product. The goals pertinent to this proposed project are to reduce the cost and improve the quality of the epitaxial growth processes used to build LED structures. The objectives outlined in this proposal focus on achieving cost reduction and performance improvements over state-of-the-art, using technologies that are low in cost and amenable to high efficiency manufacturing. The objectives of the outlined proposal focus on cost reductions in epitaxial growth by reducing epitaxy layer thickness and hetero-epitaxial strain, and by enabling the use of larger, less expensive silicon substrates and would be accomplished through the introduction of a high productivity reactive sputtering system and an effective sputtered aluminum-nitride (AlN) buffer/nucleation layer process. Success of the proposed project could enable efficient adoption of GaN on-silicon (GaN/Si) epitaxial technology on 150mm silicon substrates. The reduction in epitaxy cost per cm{sup 2} using 150mm GaN-on-Si technology derives from (1) a reduction in cost of ownership and increase in throughput for the buffer deposition process via the elimination of MOCVD buffer layers and other throughput and CoO enhancements, (2) improvement in brightness through reductions in defect density, (3) reduction in substrate cost through the replacement of sapphire with silicon, and (4) reduction in non-ESD yield loss through reductions in wafer bow and temperature variation. The adoption of 150mm GaN/Si processing will also facilitate significant cost reductions in subsequent wafer fabrication manufacturing costs. There were three phases to this project. These three phases overlap in order to aggressively facilitate a commercially available production GaN/Si capability. In Phase I of the project, the repeatability of the performance

  18. Method and apparatus for depositing atomic layers on a substrate

    NARCIS (Netherlands)

    Vermeer, A.J.P.M.; Roozeboom, F.; Deelen, J. van

    2016-01-01

    Method of depositing an atomic layer on a substrate. The method comprises supplying a precursor gas from a precursor-gas supply of a deposition head that may be part of a rotatable drum. The precursor gas is provided from the precursor-gas supply towards the substrate. The method further comprises m

  19. Spatial atomic layer deposition of zinc oxide thin films

    NARCIS (Netherlands)

    Illiberi, A.; Roozeboom, F.; Poodt, P.W.G.

    2012-01-01

    Zinc oxide thin films have been deposited at high growth rates (up to ~1 nm/s) by spatial atomic layer deposition technique at atmospheric pressure. Water has been used as oxidant for diethylzinc (DEZ) at deposition temperatures between 75 and 250 °C. The electrical, structural (crystallinity and mo

  20. Method and system for continuous atomic layer deposition

    Energy Technology Data Exchange (ETDEWEB)

    Elam, Jeffrey W.; Yanguas-Gil, Angel; Libera, Joseph A.

    2017-03-21

    A system and method for continuous atomic layer deposition. The system and method includes a housing, a moving bed which passes through the housing, a plurality of precursor gases and associated input ports and the amount of precursor gases, position of the input ports, and relative velocity of the moving bed and carrier gases enabling exhaustion of the precursor gases at available reaction sites.

  1. Spatial Atomic Layer Deposition of transparent conductive oxides

    NARCIS (Netherlands)

    Illiberi, A.; Scherpenborg, R.; Poodt, P.; Roozeboom, F.

    2013-01-01

    Undoped and indium doped ZnO films have been grown by Spatial Atomic Layer Deposition at atmospheric pressure. The electrical properties of ZnO films are controlled by varying the indium content in the range from 0 to 15 %. A minimum resistivity value of 3 mΩ•cm is measured in 180 nm thick films for

  2. Cost-Effective Systems for Atomic Layer Deposition

    Science.gov (United States)

    Lubitz, Michael; Medina, Phillip A., IV; Antic, Aleks; Rosin, Joseph T.; Fahlman, Bradley D.

    2014-01-01

    Herein, we describe the design and testing of two different home-built atomic layer deposition (ALD) systems for the growth of thin films with sub-monolayer control over film thickness. The first reactor is a horizontally aligned hot-walled reactor with a vacuum purging system. The second reactor is a vertically aligned cold-walled reactor with a…

  3. Epitaxial growth of atomically flat gadolinia-doped ceria thin films by pulsed laser deposition

    DEFF Research Database (Denmark)

    Chen, Yunzhong; Pryds, Nini; Schou, Jørgen;

    2011-01-01

    Epitaxial growth of Ce0.8Gd0.2O2(CGO) films on (001) TiO2-terminated SrTiO3 substrates by pulsed laser deposition was investigated using in situ reflective high energy electron diffraction. The initial film growth shows a Stransky–Krastanov growth mode. However, this three-dimensional island...

  4. A Review of Atomic Layer Deposition for Nanoscale Devices

    Directory of Open Access Journals (Sweden)

    Edy Riyanto

    2012-12-01

    Full Text Available Atomic layer deposition (ALD is a thin film growth technique that utilizes alternating, self-saturation chemical reactions between gaseous precursors to achieve a deposited nanoscale layers. It has recently become a subject of great interest for ultrathin film deposition in many various applications such as microelectronics, photovoltaic, dynamic random access memory (DRAM, and microelectromechanic system (MEMS. By using ALD, the conformability and extreme uniformity of layers can be achieved in low temperature process. It facilitates to be deposited onto the surface in many variety substrates that have low melting temperature. Eventually it has advantages on the contribution to the wider nanodevices.

  5. Realization of high quality epitaxial current- perpendicular-to-plane giant magnetoresistive pseudo spin-valves on Si(001 wafer using NiAl buffer layer

    Directory of Open Access Journals (Sweden)

    Jiamin Chen

    2016-05-01

    Full Text Available In this letter, we report a NiAl buffer layer as a template for the integration of epitaxial current-perpendicular-plane-giant magnetoresistive (CPP-GMR devices on a Si(001 single crystalline substrate. By depositing NiAl on a Si wafer at an elevated temperature of 500 °C, a smooth and epitaxial B2-type NiAl(001 layer was obtained. The surface roughness was further improved by depositing Ag on the NiAl layer and applying subsequent annealing process. The epitaxial CPP-GMR devices grown on the buffered Si(001 substrate present a large magnetoresistive output comparable with that of the devices grown on an MgO(001 substrate, demonstrating the possibility of epitaxial spintronic devices with a NiAl templated Si wafer for practical applications.

  6. Structural Properties of Alternate Monatomic Layered [Fe/Co]n Epitaxial Films on MgO Substrate

    Science.gov (United States)

    Chu, In Chang; Saki, Yoshinobu; Kawasaki, Shohei; Doi, Masaaki; Sahashi, Masashi

    2008-06-01

    Body-centered-cubic (bcc) Fe50Co50 material is reported to show a high bulk spin scattering coefficient on current perpendicular to plane-giant magneto-resistance (CPP-GMR) system. But the origin of that phenomenon does not make sure yet. We prepared artificially alternate monatomic layered (AML) [Fe/Co] 41 MLs epitaxial films (Ts: 75, 250 °C) by monatomic deposition method and investigated the topology of AML [Fe/Co]n epitaxial films on MgO substrate with different orientation (001), (011) by the scanning tunnel microscopy (STM) and reflection high energy electron diffraction (RHEED), which we could confirm Frank-van der Merwe (FM) growth mode for AML [Fe/Co]n on MgO(001) and Volmer-Weber (VW) growth mode for that on Mg(011). The roughness of surface, Ra (0.20 nm) of AML [Fe/Co] 41 MLs epitaxial film grown at 75 °C on MgO(001) is smaller than that (0.46 nm) of AML [Fe/Co] grown at 250 °C on MgO(001), which has the large terraces of over 50 nm (Ra: 0.17 nm), even though there are some valleys between large terraces. Moreover we confirmed the structural properties of trilayered epitaxial films with AML [Fe/Co]n (Ra: 0.18 nm) and Fe50Co50 alloy epitaxial film on Au electrode by RHEED before confirming the characteristics of CPP-GMR devices.

  7. A DFT study of halogen atoms adsorbed on graphene layers

    Energy Technology Data Exchange (ETDEWEB)

    Medeiros, Paulo V C; De Brito Mota, F; De Castilho, Caio M C [Grupo de Fisica de Superfcies e Materiais, Instituto de Fisica, Universidade Federal da Bahia, Campus Universitario da Federacao/Ondina, 40170-115 Salvador, Bahia (Brazil); Mascarenhas, Artur J S, E-mail: caio@ufba.br [Instituto Nacional de Ciencia e Tecnologia em Energia e Ambiente-INCT-E and A, Universidade Federal da Bahia, 40170-280 Salvador, Bahia (Brazil)

    2010-12-03

    In this work, ab initio density functional theory calculations were performed in order to study the structural and electronic properties of halogens (X = fluorine, chlorine, bromine or iodine) that were deposited on both sides of graphene single layers (X-graphene). The adsorption of these atoms on only one side of the layer with hydrogen atoms adsorbed on the other was also considered (H,X-graphene). The results indicate that the F-C bond in the F-graphene system causes an sp{sup 2} to sp{sup 3} transition of the carbon orbitals, and similar effects seem to occur in the H,X-graphene systems. For the other cases, two configurations are found: bonded (B) and non-bonded (NB). For the B configuration, the structural arrangement of the atoms was similar to F-graphene and H-graphene (graphane), although the electronic structures present some differences. In the NB configuration, the interaction between the adsorbed atoms and the graphene layer seems to be essentially of the van der Waals type. In these cases, the original shape of the graphene layer presents only small deviations from the pristine form and the adsorbed atoms reach equilibrium far from the sheet. The F-graphene structure has a direct bandgap of approximately 3.16 eV at the {Gamma} point, which is a value that is close to the value of 3.50 eV that was found for graphane. The Cl-graphene (B configuration), H,F-graphene and H,Cl-graphene systems have smaller bandgap values. All of the other systems present metallic behaviours. Energy calculations indicate the possible stability of these X-graphene layers, although some considerations about the possibility of spontaneous formation have to be taken into account.

  8. Analysis for positions of Sn atoms in epitaxial Ge{sub 1−x}Sn{sub x} film in low temperature depositions

    Energy Technology Data Exchange (ETDEWEB)

    Kamiyama, Eiji, E-mail: ejkamiyama@aol.com [Dept. of Comm. Eng., Okayama Pref. Univ., 111 Kuboki, Soja, Okayama 719-1197 (Japan); Sueoka, Koji [Dept. of Comm. Eng., Okayama Pref. Univ., 111 Kuboki, Soja, Okayama 719-1197 (Japan); Nakatsuka, Osamu; Taoka, Noriyuki; Zaima, Shigeaki [Dept. of Cryst. Mat. Sci., Grad. School of Eng., Nagoya Univ., Furo-cho, Chikusa-ku, Nagoya 464-8603 (Japan); Izunome, Koji; Kashima, Kazuhiko [Technology, GlobalWafers Japan Corp. Ltd, 6-861-5 Higashiko, Seiro, Niigata 957-0197 (Japan)

    2014-04-30

    We investigated the position of Sn atoms in Ge{sub 1−x}Sn{sub x} film grown at a low temperature by using the Extended X-ray Absorption Fine Structure (EXAFS) method. Vacancies had been expected to be introduced near the growing surface vicinity of a Sn atom and located at a split-vacancy position due to the binding nature between a Sn atom and a vacancy, which was predicted by the calculation for a bulk model in the literature. However, the EXAFS showed that almost all Sn atoms were located at the substitutional position and did not form a split-vacancy. - Highlights: • Extended X-ray Absorption Fine Structure (EXAFS) study of epitaxial Ge{sub 1−x}Snx film • EXAFS shows that almost all Sn atoms are located at substitutional positions. • The amount of vacancies introduced in low-temperature epitaxial growth is small.

  9. Atomic and molecular layer deposition for surface modification

    Energy Technology Data Exchange (ETDEWEB)

    Vähä-Nissi, Mika, E-mail: mika.vaha-nissi@vtt.fi [VTT Technical Research Centre of Finland, PO Box 1000, FI‐02044 VTT (Finland); Sievänen, Jenni; Salo, Erkki; Heikkilä, Pirjo; Kenttä, Eija [VTT Technical Research Centre of Finland, PO Box 1000, FI‐02044 VTT (Finland); Johansson, Leena-Sisko, E-mail: leena-sisko.johansson@aalto.fi [Aalto University, School of Chemical Technology, Department of Forest Products Technology, PO Box 16100, FI‐00076 AALTO (Finland); Koskinen, Jorma T.; Harlin, Ali [VTT Technical Research Centre of Finland, PO Box 1000, FI‐02044 VTT (Finland)

    2014-06-01

    Atomic and molecular layer deposition (ALD and MLD, respectively) techniques are based on repeated cycles of gas–solid surface reactions. A partial monolayer of atoms or molecules is deposited to the surface during a single deposition cycle, enabling tailored film composition in principle down to molecular resolution on ideal surfaces. Typically ALD/MLD has been used for applications where uniform and pinhole free thin film is a necessity even on 3D surfaces. However, thin – even non-uniform – atomic and molecular deposited layers can also be used to tailor the surface characteristics of different non-ideal substrates. For example, print quality of inkjet printing on polymer films and penetration of water into porous nonwovens can be adjusted with low-temperature deposited metal oxide. In addition, adhesion of extrusion coated biopolymer to inorganic oxides can be improved with a hybrid layer based on lactic acid. - Graphical abstract: Print quality of a polylactide film surface modified with atomic layer deposition prior to inkjet printing (360 dpi) with an aqueous ink. Number of printed dots illustrated as a function of 0, 5, 15 and 25 deposition cycles of trimethylaluminum and water. - Highlights: • ALD/MLD can be used to adjust surface characteristics of films and fiber materials. • Hydrophobicity after few deposition cycles of Al{sub 2}O{sub 3} due to e.g. complex formation. • Same effect on cellulosic fabrics observed with low temperature deposited TiO{sub 2}. • Different film growth and oxidation potential with different precursors. • Hybrid layer on inorganic layer can be used to improve adhesion of polymer melt.

  10. Van der Waals epitaxial double heterostructure: InAs/single-layer graphene/InAs.

    Science.gov (United States)

    Hong, Young Joon; Yang, Jae Won; Lee, Wi Hyoung; Ruoff, Rodney S; Kim, Kwang S; Fukui, Takashi

    2013-12-17

    Van der Waals (vdW) epitaxial double heterostructures have been fabricated by vdW epitaxy of InAs nanostructures on both sides of graphene. InAs nanostructures diametrically form on/underneath graphene exclusively along As-polar direction, indicating polarity inversion of the double heterostructures. First-principles and density functional calculations demonstrate how and why InAs easily form to be double heterostructures with polarity inversion.

  11. Effects of Sb incorporation in GaAsSb-capping layer on the optical properties of InAs/GaAs QDs grown by Molecular Beam Epitaxy

    Science.gov (United States)

    Salhi, A.; Alshaibani, S.; Alhamdan, M.; Albrithen, H.; Alyamani, A.; El-Desouki, M.

    2017-01-01

    We have investigated the effect of antimony incorporation in GaAsSb as a capping layer on the optical properties of InAs quantum dots grown by Molecular Beam Epitaxy. Atomic Force Microscopy (AFM), High Resolution X-Ray Diffraction (HRXRD), photoluminescence (PL) and power dependent PL at 77 K and 300 K have been used for the characterization of the grown samples. Our analysis showed that the emission wavelength increases with Sb content and reaches ∼1.5 μm for Sb concentration of 22%. To achieve this wavelength, a reduction of the growth temperature of the GaAsSb layer from 500 °C to 440 °C was necessary. The wavelength increase is accompanied by a transition from a type I to type II band alignment and a broadening of the PL spectrum to a value of ∼237 nm for an excitation power of 100 mW. This broadening is attributed to the QD size inhomogeneity increase and Sb atoms redistribution during the in-situ annealing during the growth of the barriers at elevated temperature. Our results show the potential of the InAs/GaAsSb system in the development of broadband light sources and super-luminescent light emitting diodes in 1.2-1.5 μm wavelength range.

  12. Ge Implantation to Improve Crystallinity and Productivity for Solid Phase Epitaxy Prepared by Atomic Mass Unit Cross Contamination-Free Technique

    Science.gov (United States)

    Lee, Kong-Soo; Yoo, Dae-Han; Han, Jae-Jong; Son, Gil-Hwan; Lee, Chang-Hun; Noh, Ju-Hee; Kim, Seok-Jae; Kim, Yong-Kwon; You, Young-Sub; Hyung, Yong-Woo; Lee, Hyeon-Deok

    2006-11-01

    Germanium (Ge) ion implantation was investigated for crystallinity enhancement during solid phase epitaxial (SPE) regrowth. Electron back-scatter diffraction (EBSD) measurement showed numerical increase of 19% of (100) signal, which might be due to the effect of pre-amorphization implantation (PAI) on silicon layer. On the other hand, electrical property such as off-leakage current of n-channel metal oxide semiconductor (NMOS) transistor degraded in specific regions of wafers. It was confirmed that arsenic (As) atoms were incorporated into channel area during Ge ion implantation. Since the equipment for Ge PAI was using several source gases such as BF3 and AsH3, atomic mass unit (AMU) contamination during PAI of Ge with AMU 74 caused the incorporation of As with AMU 75 which resided in arc-chamber and other parts of the equipment. It was effective to use Ge isotope of AMU 72 to suppress AMU contamination. It was effective to use enriched Ge source gas with AMU 72 in order to improve productivity.

  13. Segregation of Sb in Ge epitaxial layers and its usage for the selective doping of Ge-based structures

    Energy Technology Data Exchange (ETDEWEB)

    Antonov, A. V.; Drozdov, M. N.; Novikov, A. V., E-mail: anov@ipmras.ru; Yurasov, D. V. [Institute for Physics of Microstructures of the Russian Academy of Sciences (Russian Federation)

    2015-11-15

    The segregation of Sb in Ge epitaxial layers grown by the method of molecular beam epitaxy on Ge (001) substrates is investigated. For a growth temperature range of 180–325°C, the temperature dependence is determined for the segregation ratio of Sb in Ge, which shows a sharp increase (by more than three orders of magnitude) with increasing temperature. The strong dependence of the segregation properties of Sb on the growth temperature makes it possible to adapt a method based on the controlled use of segregation developed previously for the doping of Si structures for the selective doping of Ge structures with a donor impurity. Using this method selectively doped Ge:Sb structures, in which the bulk impurity concentration varies by an order of magnitude at distances of 3–5 nm, are obtained.

  14. Structural properties of GaN(0001) epitaxial layers revealed by high resolution X-ray diffraction

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    High-resolution X-ray diffraction has been used to analyze GaN(0001) epitaxial layers on sapphire substrates. Several structural properties of GaN, including the lattice constants, strains, and dislocation densities are revealed by the technique of X-ray dffraction (XRD). Lattice constants calculated from the omega/2theta scan are c=0.5185 nm and a=0.3157 nm. Also, the in-plane strain is -1.003%, while out of the plane, the epitaxial film is almost relaxed. Several methods are used to deduce the mosaicity and dislocation density of GaN, showing that the edge type dislocations are the overwhelming majority.

  15. Atomic-Layer-Confined Doping for Atomic-Level Insights into Visible-Light Water Splitting.

    Science.gov (United States)

    Lei, Fengcai; Zhang, Lei; Sun, Yongfu; Liang, Liang; Liu, Katong; Xu, Jiaqi; Zhang, Qun; Pan, Bicai; Luo, Yi; Xie, Yi

    2015-08-03

    A model of doping confined in atomic layers is proposed for atomic-level insights into the effect of doping on photocatalysis. Co doping confined in three atomic layers of In2S3 was implemented with a lamellar hybrid intermediate strategy. Density functional calculations reveal that the introduction of Co ions brings about several new energy levels and increased density of states at the conduction band minimum, leading to sharply increased visible-light absorption and three times higher carrier concentration. Ultrafast transient absorption spectroscopy reveals that the electron transfer time of about 1.6 ps from the valence band to newly formed localized states is due to Co doping. The 25-fold increase in average recovery lifetime is believed to be responsible for the increased of electron-hole separation. The synthesized Co-doped In2S3 (three atomic layers) yield a photocurrent of 1.17 mA cm(-2) at 1.5 V vs. RHE, nearly 10 and 17 times higher than that of the perfect In2S3 (three atomic layers) and the bulk counterpart, respectively.

  16. Atom probe tomography study on Ge{sub 1−x−y}Sn{sub x}C{sub y} hetero-epitaxial film on Ge substrates

    Energy Technology Data Exchange (ETDEWEB)

    Kamiyama, Eiji, E-mail: ejkamiyama@aol.com [Technology, GlobalWafers Japan Corp. Ltd., 6-861-5 Higashiko, Seiro, Niigata 957-0197 (Japan); Department of Communication Engineering, Okayama Prefectural University, 111 Kuboki, Soja-shi, Okayama-ken 719-1197 (Japan); Sueoka, Koji [Department of Communication Engineering, Okayama Prefectural University, 111 Kuboki, Soja-shi, Okayama-ken 719-1197 (Japan); Terasawa, Kengo; Yamaha, Takashi; Nakatsuka, Osamu [Department of Crystalline Materials Science, Graduate School of Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603 (Japan); Zaima, Shigeaki [Department of Crystalline Materials Science, Graduate School of Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603 (Japan); EcoTopia Science Institute, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603 (Japan); Izunome, Koji; Kashima, Kazuhiko [Technology, GlobalWafers Japan Corp. Ltd., 6-861-5 Higashiko, Seiro, Niigata 957-0197 (Japan); Uchida, Hiroshi [Physical Analysis Technology Center, Toshiba Nanoanalysis Corporation, 8 Shinsugita-cho, Isogo-ku, Yokohama 235-8522 (Japan)

    2015-10-01

    We analyzed the incorporation of C atoms into a ternary alloy Ge{sub 1−x−y}Sn{sub x}C{sub y} epitaxial film on Ge substrates on a sub-nanometer scale by using atom probe tomography. Periodic atom distributions from individual (111) atomic planes were observed both in the Ge{sub 1−x−y}Sn{sub x}C{sub y} film and at the Ge substrates. Sn/C atoms had non-uniform distributions in the film. They also demonstrated a clear positive correlation in their distributions. Substitutional C atoms were only incorporated into the film when an Sn atom beam was applied onto the substrates under film growth conditions. - Highlights: • Incorporation of C atoms into epitaxial Ge{sub 1−x−y}Sn{sub x}C{sub y} film was studied. • Individual (111) atomic planes were observed by atom probe tomography. • Sn/C atoms had non-uniform distributions in the film. • Clear positive correlation in Sn/C atoms distributions was obtained.

  17. Interfacial Atomic Structure of Twisted Few-Layer Graphene.

    Science.gov (United States)

    Ishikawa, Ryo; Lugg, Nathan R; Inoue, Kazutoshi; Sawada, Hidetaka; Taniguchi, Takashi; Shibata, Naoya; Ikuhara, Yuichi

    2016-02-18

    A twist in bi- or few-layer graphene breaks the local symmetry, introducing a number of intriguing physical properties such as opening new bandgaps. Therefore, determining the twisted atomic structure is critical to understanding and controlling the functional properties of graphene. Combining low-angle annular dark-field electron microscopy with image simulations, we directly determine the atomic structure of twisted few-layer graphene in terms of a moiré superstructure which is parameterized by a single twist angle and lattice constant. This method is shown to be a powerful tool for accurately determining the atomic structure of two-dimensional materials such as graphene, even in the presence of experimental errors. Using coincidence-site-lattice and displacement-shift-complete theories, we show that the in-plane translation state between layers is not a significant structure parameter, explaining why the present method is adequate not only for bilayer graphene but also a few-layered twisted graphene.

  18. Interfacial Atomic Structure of Twisted Few-Layer Graphene

    Science.gov (United States)

    Ishikawa, Ryo; Lugg, Nathan R.; Inoue, Kazutoshi; Sawada, Hidetaka; Taniguchi, Takashi; Shibata, Naoya; Ikuhara, Yuichi

    2016-02-01

    A twist in bi- or few-layer graphene breaks the local symmetry, introducing a number of intriguing physical properties such as opening new bandgaps. Therefore, determining the twisted atomic structure is critical to understanding and controlling the functional properties of graphene. Combining low-angle annular dark-field electron microscopy with image simulations, we directly determine the atomic structure of twisted few-layer graphene in terms of a moiré superstructure which is parameterized by a single twist angle and lattice constant. This method is shown to be a powerful tool for accurately determining the atomic structure of two-dimensional materials such as graphene, even in the presence of experimental errors. Using coincidence-site-lattice and displacement-shift-complete theories, we show that the in-plane translation state between layers is not a significant structure parameter, explaining why the present method is adequate not only for bilayer graphene but also a few-layered twisted graphene.

  19. Electrical and Structural Characteristics of High-k Gate Dielectrics with Epitaxial Si3N4 Interfacial Layer on Si(111)

    Science.gov (United States)

    Sim, Hyunjun; Samantaray, Chandan B.; Lee, Taeho; Yeom, Hanwoong; Hwang, Hyunsang

    2004-12-01

    In this study, the electrical and structural characteristics of Gd2O3 gate dielectrics with an epitaxial Si3N4 interfacial layer grown on Si(111) were investigated. Compared with control Gd2O3 gate dielectrics deposited on HF-last treated Si (111), the Gd2O3 gate dielectrics with an epitaxial Si3N4 interfacial layer exhibited excellent electrical characteristics such as low leakage current density and low interface state density. These characteristics are due to a high-quality interfacial layer formation on Si. Transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) spectroscopy were employed to analyze the structures of the gate dielectrics and interfacial layer. High-k gate dielectrics with an epitaxial Si3N4 interfacial layer have considerable potential for future use in sub-0.1 μm metal oxide semiconductor field-effect transistors (MOSFETs).

  20. Applications of atomic layer deposition in solar cells.

    Science.gov (United States)

    Niu, Wenbin; Li, Xianglin; Karuturi, Siva Krishna; Fam, Derrick Wenhui; Fan, Hongjin; Shrestha, Santosh; Wong, Lydia Helena; Tok, Alfred Iing Yoong

    2015-02-13

    Atomic layer deposition (ALD) provides a unique tool for the growth of thin films with excellent conformity and thickness control down to atomic levels. The application of ALD in energy research has received increasing attention in recent years. In this review, the versatility of ALD in solar cells will be discussed. This is specifically focused on the fabrication of nanostructured photoelectrodes, surface passivation, surface sensitization, and band-structure engineering of solar cell materials. Challenges and future directions of ALD in the applications of solar cells are also discussed.

  1. Epitaxial ZnO/LiNbO{sub 3}/ZnO stacked layer waveguide for application to thin-film Pockels sensors

    Energy Technology Data Exchange (ETDEWEB)

    Akazawa, Housei, E-mail: akazawa.housei@lab.ntt.co.jp; Fukuda, Hiroshi [NTT Device Innovation Center, NTT Corporation 3-1 Morinosato Wakamiya, Atsugi, Kanagawa 243-0198 (Japan)

    2015-05-15

    We produced slab waveguides consisting of a LiNbO{sub 3} (LN) core layer that was sandwiched with Al-doped ZnO cladding layers. The ZnO/LN/ZnO stacked layers were grown on sapphire C-planes by electron cyclotron resonance (ECR) plasma sputtering and were subjected to structural, electrical, and optical characterizations. X-ray diffraction confirmed that the ZnO and LN layers were epitaxial without containing misoriented crystallites. The presence of 60°-rotational variants of ZnO and LN crystalline domains were identified from X-ray pole figures. Cross-sectional transmission electron microscopy images revealed a c-axis orientated columnar texture for LN crystals, which ensured operation as electro-optic sensors based on optical anisotropy along longitudinal and transversal directions. The interfacial roughness between the LN core and ZnO bottom layers as well as that between the ZnO top and the LN core layers was less than 20 nm, which agreed with surface images observed with atomic force microscopy. Outgrowth of triangular LN crystalline domains produced large roughness at the LN film surface. The RMS roughness of the LN film surface was twice that of the same structure grown on sapphire A-planes. Vertical optical transmittance of the stacked films was higher than 85% within the visible and infrared wavelength range. Following the approach adopted by Teng and Man [Appl. Phys. Lett. 56, 1734 (1990)], ac Pockels coefficients of r{sub 33} = 24-28 pm/V were derived for c-axis oriented LN films grown on low-resistive Si substrates. Light propagation within a ZnO/LN/ZnO slab waveguide as well as within a ZnO single layer waveguide was confirmed. The birefringence of these waveguides was 0.11 for the former and 0.05 for the latter.

  2. Buffer layer engineering on graphene via various oxidation methods for atomic layer deposition

    Science.gov (United States)

    Takahashi, Nobuaki; Nagashio, Kosuke

    2016-12-01

    The integration of a high-k oxide on graphene using atomic layer deposition requires an electrically reliable buffer layer. In this study, Y was selected as the buffer layer due to its highest oxidation ability among the rare-earth elements, and various oxidation methods (atmospheric, and high-pressure O2 and ozone annealing) were applied to the Y metal buffer layer. By optimizing the oxidation conditions of the top-gate insulator, we successfully improved the capacitance of the top gate Y2O3 insulator and demonstrated a large I on/I off ratio for bilayer graphene under an external electric field.

  3. Overview of atomic layer etching in the semiconductor industry

    Energy Technology Data Exchange (ETDEWEB)

    Kanarik, Keren J., E-mail: keren.kanarik@lamresearch.com; Lill, Thorsten; Hudson, Eric A.; Sriraman, Saravanapriyan; Tan, Samantha; Marks, Jeffrey; Vahedi, Vahid; Gottscho, Richard A. [Lam Research Corporation, 4400 Cushing Parkway, Fremont, California 94538 (United States)

    2015-03-15

    Atomic layer etching (ALE) is a technique for removing thin layers of material using sequential reaction steps that are self-limiting. ALE has been studied in the laboratory for more than 25 years. Today, it is being driven by the semiconductor industry as an alternative to continuous etching and is viewed as an essential counterpart to atomic layer deposition. As we enter the era of atomic-scale dimensions, there is need to unify the ALE field through increased effectiveness of collaboration between academia and industry, and to help enable the transition from lab to fab. With this in mind, this article provides defining criteria for ALE, along with clarification of some of the terminology and assumptions of this field. To increase understanding of the process, the mechanistic understanding is described for the silicon ALE case study, including the advantages of plasma-assisted processing. A historical overview spanning more than 25 years is provided for silicon, as well as ALE studies on oxides, III–V compounds, and other materials. Together, these processes encompass a variety of implementations, all following the same ALE principles. While the focus is on directional etching, isotropic ALE is also included. As part of this review, the authors also address the role of power pulsing as a predecessor to ALE and examine the outlook of ALE in the manufacturing of advanced semiconductor devices.

  4. Passivation effects of atomic-layer-deposited aluminum oxide

    Directory of Open Access Journals (Sweden)

    Kotipalli R.

    2013-09-01

    Full Text Available Atomic-layer-deposited (ALD aluminum oxide (Al2O3 has recently demonstrated an excellent surface passivation for both n- and p-type c-Si solar cells thanks to the presence of high negative fixed charges (Qf ~ 1012−1013 cm-2 in combination with a low density of interface states (Dit. This paper investigates the passivation quality of thin (15 nm Al2O3 films deposited by two different techniques: plasma-enhanced atomic layer deposition (PE-ALD and Thermal atomic layer deposition (T-ALD. Other dielectric materials taken into account for comparison include: thermally-grown silicon dioxide (SiO2 (20 nm, SiO2 (20 nm deposited by plasma-enhanced chemical vapour deposition (PECVD and hydrogenated amorphous silicon nitride (a-SiNx:H (20 nm also deposited by PECVD. With the above-mentioned dielectric layers, Metal Insulator Semiconductor (MIS capacitors were fabricated for Qf and Dit extraction through Capacitance-Voltage-Conductance (C-V-G measurements. In addition, lifetime measurements were carried out to evaluate the effective surface recombination velocity (SRV. The influence of extracted C-V-G parameters (Qf,Dit on the injection dependent lifetime measurements τ(Δn, and the dominant passivation mechanism involved have been discussed. Furthermore we have also studied the influence of the SiO2 interfacial layer thickness between the Al2O3 and silicon surface on the field-effect passivation mechanism. It is shown that the field effect passivation in accumulation mode is more predominant when compared to surface defect passivation.

  5. Passivation effects of atomic-layer-deposited aluminum oxide

    Science.gov (United States)

    Kotipalli, R.; Delamare, R.; Poncelet, O.; Tang, X.; Francis, L. A.; Flandre, D.

    2013-09-01

    Atomic-layer-deposited (ALD) aluminum oxide (Al2O3) has recently demonstrated an excellent surface passivation for both n- and p-type c-Si solar cells thanks to the presence of high negative fixed charges (Qf ~ 1012-1013 cm-2) in combination with a low density of interface states (Dit). This paper investigates the passivation quality of thin (15 nm) Al2O3 films deposited by two different techniques: plasma-enhanced atomic layer deposition (PE-ALD) and Thermal atomic layer deposition (T-ALD). Other dielectric materials taken into account for comparison include: thermally-grown silicon dioxide (SiO2) (20 nm), SiO2 (20 nm) deposited by plasma-enhanced chemical vapour deposition (PECVD) and hydrogenated amorphous silicon nitride (a-SiNx:H) (20 nm) also deposited by PECVD. With the above-mentioned dielectric layers, Metal Insulator Semiconductor (MIS) capacitors were fabricated for Qf and Dit extraction through Capacitance-Voltage-Conductance (C-V-G) measurements. In addition, lifetime measurements were carried out to evaluate the effective surface recombination velocity (SRV). The influence of extracted C-V-G parameters (Qf,Dit) on the injection dependent lifetime measurements τ(Δn), and the dominant passivation mechanism involved have been discussed. Furthermore we have also studied the influence of the SiO2 interfacial layer thickness between the Al2O3 and silicon surface on the field-effect passivation mechanism. It is shown that the field effect passivation in accumulation mode is more predominant when compared to surface defect passivation.

  6. Strain and crystalline defects in epitaxial GaN layers studied by high-resolution X-ray diffraction

    Energy Technology Data Exchange (ETDEWEB)

    Chierchia, Rosa

    2007-07-01

    This thesis treats strain and dislocations in MOVPE GaN layers. The mosaic structure of metalorganic vapour phase epitaxy (MOVPE)-grown GaN layers was studied in dependence on the grain diameter utilizing high-resolution XRD. Different models for the defect structure were analyzed, the edge type TD densities were calculated under the assumption that the dislocations are not randomly distributed but localized at the grain boundaries. Moreover, in situ measurements have shown that the layers are under tension in the c-plane when a nucleation layer is used. The second part of this thesis treats a particular approach to reduce dislocations in MOVPE GaN layers, i.e. maskless pendeo epitaxial growth of MOVPE GAN layers. FE simulations assuming the strain to be completely induced during cooling of the structures after growth agree only partly with experimental data. The strain state of single layers and stripes of GaN grown on SiC was studied to exploit the evolution of the strain in the different phases of the PE growth. The biaxial compressive stress, due to the lattice mismatch between the GaN layer and the AlN nucleation layer is plastically relieved before overgrowth. Temperature dependent measurements show a linear reduction of the wing tilt with increasing temperature varying from sample to sample. Bent TDs have been observed in TEM images of maskless PE samples. Stress induced from the mismatch between the AlN buffer layer and the GaN also contributes to the remaining part of the wing tilt not relieved thermally. It has to be noted that the rest tilt value varies from sample to sample at the growth temperature. In fact some of the data indicate that the wing tilt decreases with increasing V/III ratio. In the last Chapter the application of X-ray techniques for the analysis of strain and composition in layers of inhomogeneous composition is explored. In the first part of the Chapter the strain state and the Al content of AlGaN buffer layers grown directly on (0001

  7. Chemical order and selection of the mechanism for strain relaxation in epitaxial FePd(Pt) thin layers

    Science.gov (United States)

    Halley, D.; Marty, A.; Bayle-Guillemaud, P.; Gilles, B.; Attane, J. P.; Samson, Y.

    2004-11-01

    We observed that the relaxation mechanism of the epitaxial strain is dramatically dependent on the chemical ordering within the L10 structure in FePd(Pt) thin films. In disordered or weakly ordered layers, the relaxation takes place though perfect (1)/(2)[101] dislocations, whereas well-ordered films relax through the partial 1/6[112] Shockley dislocations, piled-up within microtwins, with a huge impact on both the morphology and the magnetic properties of the film. We show that the antiphase boundary energy is the key factor preventing the propagation of perfect dislocations in ordered alloys.

  8. ZnO layers grown by Atomic Layer Deposition: A new material for transparent conductive oxide

    Energy Technology Data Exchange (ETDEWEB)

    Godlewski, M., E-mail: godlew@ifpan.edu.p [Institute of Physics, Polish Academy of Sciences, Al. Lotnikow 32/46, Warsaw (Poland); Department of Mathematics and Natural Sciences, College of Science, Cardinal Stefan Wyszynski University, Warsaw (Poland); Guziewicz, E.; Luka, G.; Krajewski, T. [Institute of Physics, Polish Academy of Sciences, Al. Lotnikow 32/46, Warsaw (Poland); Lukasiewicz, M.; Wachnicki, L.; Wachnicka, A. [Institute of Physics, Polish Academy of Sciences, Al. Lotnikow 32/46, Warsaw (Poland); Department of Mathematics and Natural Sciences, College of Science, Cardinal Stefan Wyszynski University, Warsaw (Poland); Kopalko, K. [Institute of Physics, Polish Academy of Sciences, Al. Lotnikow 32/46, Warsaw (Poland); Sarem, A.; Dalati, B. [Department of Physics, Faculty of Science, Tishreen University, Latakia (Syrian Arab Republic)

    2009-12-15

    We demonstrate possibility of a control (by selection of zinc precursors and variation of a growth temperature) of electrical properties of ZnO films grown by Atomic Layer Deposition (ALD). ZnO films grown by ALD are used in test photovoltaic devices (solar cells) as transparent conductive oxides for upper, transparent layer in inorganic and organic solar cells, and as n-type partners of p-type CdTe.

  9. Epitaxial growth of mixed conducting layered Ruddlesden–Popper La{sub n+1}Ni{sub n}O{sub 3n+1} (n = 1, 2 and 3) phases by pulsed laser deposition

    Energy Technology Data Exchange (ETDEWEB)

    Wu, Kuan-Ting; Soh, Yeong-Ah; Skinner, Stephen J., E-mail: s.skinner@imperial.ac.uk

    2013-10-15

    Graphical abstract: - Highlights: • High quality epitaxial thin films of layered Ruddlesden–Popper nickelates were prepared. • For the first time this has been achieved by the PLD process. • n = 1, 2 and 3 films were successfully deposited on SrTiO{sub 3} and NdGaO{sub 3} substrates. • c-Axis oriented films were confirmed by XRD analysis. • In-plane and out-of-plane strain effects on lattice are discussed. - Abstract: Layered Ruddlesden–Popper phases of composition La{sub n+1}Ni{sub n}O{sub 3n+1} (n = 1, 2 and 3) have been epitaxially grown on SrTiO{sub 3} (0 0 1) or NdGaO{sub 3} (1 1 0) single crystal substrates using the pulsed laser deposition technique. X-ray diffraction analyses (θ/2θ, rocking curves, and φ-scans) and atomic force microscopy confirms the high-quality growth of the series of films with low surface roughness values (less than 1 nm). In particular, epitaxial growth of the higher order phases (n = 2 and 3) of lanthanum nickelate have been demonstrated for the first time.

  10. Epitaxial crystallization and nucleation during MeV-ion beam processing of amorphous GaAs surface layers

    Energy Technology Data Exchange (ETDEWEB)

    Bachmann, T. [Jena Univ. (Germany). Inst. fuer Festkoerperphysik; Glaser, E. [Jena Univ. (Germany). Inst. fuer Festkoerperphysik; Schulz, R. [Jena Univ. (Germany). Inst. fuer Festkoerperphysik; Kaiser, U. [Jena Univ. (Germany). Inst. fuer Festkoerperphysik; Safran, G. [Research Institute for Technical Physics, P.O. Box 76, H-1325 Budapest (Hungary)

    1996-06-01

    <100> -GaAs wafers were preamorphized in a thin surface layer using 50 keV {sup 14}N{sup +}-ions. Ion beam induced epitaxial crystallization (IBIEC) and interfacial amorphization (IBIIA) were studied as a function of the target temperature using MeV Ar{sup +}- or Kr{sup +}-ions. Backscattering experiments and electron microscopy show that the IBIEC process is stopped above a critical irradiation temperature due to enhanced ion beam induced nucleation and growth of crystallites. At a fixed dose an optimum irradiation temperature for IBIEC was found, at which the recrystallized layer thickness has a maximum and crystallite formation is negligible. This offers the possibility to crystallize much larger layer thicknesses than {approx}65 nm which stands for the maximum value reported up to now. (orig.).

  11. Elemental boron-doped p(+)-SiGe layers grown by molecular beam epitaxy for infrared detector applications

    Science.gov (United States)

    Lin, T. L.; George, T.; Jones, E. W.; Ksendzov, A.; Huberman, M. L.

    1992-01-01

    SiGe/Si heterojunction internal photoemission (HIP) detectors have been fabricated utilizing molecular beam epitaxy of p(+)-SiGe layers on p(-)-Si substrates. Elemental boron from a high-temperature effusion cell was used as the dopant source during MBE growth, and high doping concentrations have been achieved. Strong infrared absorption, mainly by free-carrier absorption, was observed for the degenerately doped SiGe layers. The use of elemental boron as the dopant source allows a low MBE growth temperature, resulting in improved crystalline quality and smooth surface morphology of the Si(0.7)Ge(0.3) layers. Nearly ideal thermionic emission dark current characteristics have been obtained. Photoresponse of the HIP detectors in the long-wavelength infrared regime has been demonstrated.

  12. Nanostructure templating using low temperature atomic layer deposition

    Science.gov (United States)

    Grubbs, Robert K.; Bogart, Gregory R.; Rogers, John A.

    2011-12-20

    Methods are described for making nanostructures that are mechanically, chemically and thermally stable at desired elevated temperatures, from nanostructure templates having a stability temperature that is less than the desired elevated temperature. The methods comprise depositing by atomic layer deposition (ALD) structural layers that are stable at the desired elevated temperatures, onto a template employing a graded temperature deposition scheme. At least one structural layer is deposited at an initial temperature that is less than or equal to the stability temperature of the template, and subsequent depositions made at incrementally increased deposition temperatures until the desired elevated temperature stability is achieved. Nanostructure templates include three dimensional (3D) polymeric templates having features on the order of 100 nm fabricated by proximity field nanopatterning (PnP) methods.

  13. The structural transition from epitaxial Fe/Pt multilayers to an ordered FePt film using low energy ion beam sputtering deposition with no buffer layer

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Chih-Hao, E-mail: chlee@mx.nthu.edu.tw [Department of Engineering and System Science, National Tsing Hua University, Hsinchu 30013, Taiwan (China); Chen, Yu-Sheng [Department of Engineering and System Science, National Tsing Hua University, Hsinchu 30013, Taiwan (China); Electronics and Optoelectronics Research Laboratories, Industrial Technology Research Institute, Hsinchu 31040, Taiwan (China); Liu, Li-Jung [Department of Engineering and System Science, National Tsing Hua University, Hsinchu 30013, Taiwan (China); Huang, J.C.A. [Department of Physics, National Cheng Kung University, Tainan 70101, Taiwan (China)

    2014-11-03

    An epitaxial L1{sub 0} FePt thin film grown from an [Fe(10 Å)/Pt(10 Å)]{sub 15} multilayer with the orientation of (001) was prepared by an ion beam sputtering deposition method without buffer layer. From the measurement data of X-ray diffraction and X-ray reflectivity, the multilayer structure was totally disappeared and a uniform FePt alloy thin film was formed at temperatures higher than 600 °C. For the as-deposited thin film grown at 100 °C, the multilayer already possesses an epitaxial structure. The epitaxial relation is FePt(001)[100]//MgO(001)[100] and this epitaxial relation persists after sequential high temperature annealing. An epitaxial L1{sub 0} ordered FePt(001) film with order parameter of 0.95 was obtained when the annealing temperature reached 650 °C. The ordered FePt(001) thin film has a perpendicular magnetic anisotropy with a squareness of 0.95 ± 0.03 on the magnetic hysteresis loop. This experiment demonstrates that the low energy ion beam sputtering deposition will preserve the epitaxial relation with no buffer layer between multilayer and substrate. - Highlights: • The Fe/Pt films using ion sputtering deposition with no buffer layer is epitaxial. • Multilayer structure was totally disappeared at temperatures higher than 600 °C. • Order parameter reach 0.95 after annealing at 650 °C. • Interfacial epitaxial FePt alloy already formed at 100 °C.

  14. Synthesis of Indium Nitride Epitaxial Layers on a Substrate of Porous Indium Phosphide

    Directory of Open Access Journals (Sweden)

    J.A. Suchikova

    2015-10-01

    Full Text Available The paper presents a technique to obtain InN films on porous InP substrates by radical-beam gettering epitaxy. According to the results of the Auger spectroscopy, InN film thickness ranged from 100 nm to 0.5 microns depending on the etching conditions.

  15. Atomically flat Ge buffer layers and alternating shutter growth of CaGe2 for large area germanane

    Science.gov (United States)

    Xu, Jinsong; Katoch, Jyoti; Ahmed, Adam; Pinchuk, Igor; Williams, Robert; McComb, David; Kawakami, Roland

    Germanane (GeH), which is converted from CaGe2 by soaking in HCl acid, has recently attracted interest because of its novel properties, such as large band gap (1.56eV), spin orbit coupling and predictions of high mobility (18000 cm2/Vs). Previously CaGe2 was successfully grown on Ge(111) substrates by molecular beam epitaxy (MBE) growth. But there were cracks between µm-sized islands, which is not desirable for scientific study and application, and limits the material quality. By growing atomically flat Ge buffer layers and using alternating shutter MBE growth, we are able to grow crack-free, large area films of CaGe2 films. Reflection high energy electron diffraction (RHEED) patterns of Ge buffer layer and CaGe2 indicates high quality two dimensional surfaces, which is further confirmed by atomic force microscopy (AFM), showing atomically flat and uniform Ge buffer layer and CaGe2. The appearance of Laue oscillation in X-ray diffraction (XRD) and Kiessig fringes in X-ray reflectivity (XRR) proves the uniformity of CaGe2 film and the smoothness of the interface. The high quality of CaGe2 film makes it promising to explore novel properties of GeH. Funded by NSF MRSEC DMR-1420451.

  16. Properties of Ultra-Thin Hafnium Oxide and Interfacial Layer Deposited by Atomic Layer Deposition

    Institute of Scientific and Technical Information of China (English)

    Taeho Lee; Young-Bae Kim; Kyung-Il Hong; Duck-Kyun Choi; Jinho Ahn

    2004-01-01

    Ultra-thin hafnium-oxide gate dielectric films deposited by atomic layer deposition technique using HfCl4 and H2O precursor on a hydrogen-terminated Si substrate were investigated. X-ray photoelectron spectroscopy indicates that the interface layer is Hf-silicate rather than phase separated Hf-silicide and silicon oxide structure. The Hf-silicate interfacial layer partially changes into SiOx after high temperature annealing, resulting in a complex HfO2-silicate-SiOx dielectric structure. Electrical measurements confirms that HfO2 on Si is stable up to 700 ℃ for 30 s under N2 ambient.

  17. Comparative study of polar and semipolar (112⁻2) InGaN layers grown by metalorganic vapour phase epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Dinh, Duc V., E-mail: vanduc.dinh@tyndall.ie, E-mail: peter.parbrook@tyndall.ie; Zubialevich, V. Z. [Tyndall National Institute, University College Cork, Lee Matltings, Dyke Parade, Cork (Ireland); Oehler, F.; Kappers, M. J.; Humphreys, C. J. [Department of Materials Science and Metallurgy University of Cambridge, Pembroke Street, Cambridge CB2 3QZ (United Kingdom); Alam, S. N.; Parbrook, P. J., E-mail: vanduc.dinh@tyndall.ie, E-mail: peter.parbrook@tyndall.ie [Tyndall National Institute, University College Cork, Lee Matltings, Dyke Parade, Cork (Ireland); School of Engineering, University College Cork, Cork (Ireland); Caliebe, M.; Scholtz, F. [Institute of Optoelectronics, Ulm University, Ulm 89069 (Germany)

    2014-10-21

    InGaN layers were grown simultaneously on (112⁻2) GaN and (0001) GaN templates by metalorganic vapour phase epitaxy. At higher growth temperature (≥750°C), the indium content (<15%) of the (112⁻2) and (0001) InGaN layers was similar. However, for temperatures less than 750°C, the indium content of the (112⁻2) InGaN layers (15%–26%) were generally lower than those with (0001) orientation (15%–32%). The compositional deviation was attributed to the different strain relaxations between the (112⁻2) and (0001) InGaN layers. Room temperature photoluminescence measurements of the (112⁻2) InGaN layers showed an emission wavelength that shifts gradually from 380 nm to 580 nm with decreasing growth temperature (or increasing indium composition). The peak emission wavelength of the (112⁻2) InGaN layers with an indium content of more than 10% blue-shifted a constant value of ≈(50–60) nm when using higher excitation power densities. This blue-shift was attributed to band filling effects in the layers.

  18. Atomic layer deposition of nanolaminate oxide films on Si

    Science.gov (United States)

    Tallarida, M.; Weisheit, M.; Kolanek, K.; Michling, M.; Engelmann, H. J.; Schmeisser, D.

    2011-11-01

    Among the methods for depositing thin films, atomic layer deposition is unique for its capability of growing conformal thin films of compounds with a control of composition and thickness at the atomic level. The conformal growth of thin films can be of particular interest for covering nanostructures since it assures the homogeneous growth of the ALD film in all directions, independent of the position of the sample with respect to the incoming precursor flow. Here we describe the technique for growing the HfO2/Al2O3 bilayer on Si substrate and our in situ approach for its investigation by means of synchrotron radiation photoemission. In particular, we study the interface interactions between the two oxides for various thickness compositions ranging from 0.4 to 2.7 nm. We find that the ALD of HfO2 on Si induces the increase of the interfacial SiO2 layer, and a change in the band bending of Si. On the contrary, the ALD of Al2O3 on HfO2 shows negligible interaction between layers as the binding energies of Hf4f, Si2p, and O1s core level peaks and the valence band maximum of HfO2 do not change and the interfacial SiO2 does not increase.

  19. Atomic Layer Deposition Films as Diffusion Barriers for Silver Artifacts

    Science.gov (United States)

    Marquardt, Amy; Breitung, Eric; Drayman-Weisser, Terry; Gates, Glenn; Rubloff, Gary W.; Phaneuf, Ray J.

    2012-02-01

    Atomic layer deposition (ALD) was investigated as a means to create transparent oxide diffusion barrier coatings to reduce the rate of tarnishing for silver objects in museum collections. Accelerated aging by heating various thicknesses (5 to 100nm) of ALD alumina (Al2O3) thin films on sterling and fine silver was used to determine the effectiveness of alumina as a barrier to silver oxidation. The effect of aging temperature on the thickness of the tarnish layer (Ag2S) created at the interface of the ALD coating and the bulk silver substrate was determined by reflectance spectroscopy and X-Ray Photoelectric Spectroscopy (XPS). Reflectance spectroscopy was an effective rapid screening tool to determine tarnishing rates and the coating's visual impact. X-Ray Photoelectric Spectroscopy (XPS), and Time of Flight Secondary Ion Mass Spectroscopy (ToF-SIMS) analysis showed a phase transformation in the Ag2S tarnish layer at 177 C and saturation in the thickness of the silver sulfide layer, indicating possible self-passivation of the tarnish layer.

  20. Triangular Black Phosphorus Atomic Layers by Liquid Exfoliation

    Science.gov (United States)

    Seo, Soonjoo; Lee, Hyun Uk; Lee, Soon Chang; Kim, Yooseok; Kim, Hyeran; Bang, Junhyeok; Won, Jonghan; Kim, Youngjun; Park, Byoungnam; Lee, Jouhahn

    2016-03-01

    Few-layer black phosphorus (BP) is the most promising material among the two-dimensional materials due to its layered structure and the excellent semiconductor properties. Currently, thin BP atomic layers are obtained mostly by mechanical exfoliation of bulk BP, which limits applications in thin-film based electronics due to a scaling process. Here we report highly crystalline few-layer black phosphorus thin films produced by liquid exfoliation. We demonstrate that the liquid-exfoliated BP forms a triangular crystalline structure on SiO2/Si (001) and amorphous carbon. The highly crystalline BP layers are faceted with a preferred orientation of the (010) plane on the sharp edge, which is an energetically most favorable facet according to the density functional theory calculations. Our results can be useful in understanding the triangular BP structure for large-area applications in electronic devices using two-dimensional materials. The sensitivity and selectivity of liquid-exfoliated BP to gas vapor demonstrate great potential for practical applications as sensors.

  1. Nanoscale Structuring of Surfaces by Using Atomic Layer Deposition.

    Science.gov (United States)

    Sobel, Nicolas; Hess, Christian

    2015-12-01

    Controlled structuring of surfaces is interesting for a wide variety of areas, including microelectronic device fabrication, optical devices, bio(sensing), (electro-, photo)catalysis, batteries, solar cells, fuel cells, and sorption. A unique feature of atomic layer deposition (ALD) is the possibility to form conformal uniform coatings on arbitrarily shaped materials with controlled atomic-scale thickness. In this Minireview, we discuss the potential of ALD for the nanoscale structuring of surfaces, highlighting its versatile application to structuring both planar substrates and powder materials. Recent progress in the application of ALD to porous substrates has even made the nanoscale structuring of high-surface-area materials now feasible, thereby enabling novel applications, such as those in the fields of catalysis and alternative energy.

  2. Current Transport Behaviour of Au/n-GaAs Schottky Diodes Grown on Ge Substrate With Different Epitaxial Layer Thickness Over a Wide Temperature Range

    Directory of Open Access Journals (Sweden)

    N. Padha

    2011-01-01

    Full Text Available The work presents temperature dependent forward and reverse current-voltage (I-V analyses of n-GaAs/Au Schottky Diodes grown on n+ Ge substrate with different epitaxial layer thicknesses. While some of the Schottky diodes follow TED mechanism, others exceed significantly from this theory due to existence of patches of reduced barrier height embedded in the Schottky interface. The zero bias barrier heights (φbo increase (0.649 to 0.809 eV while the ideality factors (η decrease (1.514 to 1.052 with increase in epitaxial layer thickness (1-4 μm, thus, indicating similar behaviour to that observed for the I-V characteristics of the undertaken Schottky diodes with decreasing temperature. It all indicated the existence of barrier inhomogenities over the M-S interface. The breakdown behaviour analysis of these diodes showed some interesting results; the breakdown voltage (VBR decreases with temperature and shows ‘Defect Assisted Tunneling’ phenomenon through surface or defect states in the 1 μm thick epitaxial layer Schottky diode while VBR increases with temperature in 3 μm and 4 μm thick epitaxial layer Schottky diodes which demonstrate ‘Avalanche Multiplication’ mechanism responsible for junction breakdown. The reverse breakdown voltage is also seen to increase (2.7-5.9 Volts with the increase in epitaxial layer thickness of the diodes. The undertaken diodes have been observed to follow TFE mechanism at low temperatures (below 200 K in which the tunneling current component increases with epitaxial layer thickness which has been ascribed as an impact of GaAs/Ge hetero-interface over the Au/n-GaAs Schottky barrier.

  3. Nanoporous SiO2 thin films made by atomic layer deposition and atomic etching

    Science.gov (United States)

    Ghazaryan, Lilit; Kley, E.-Bernhard; Tünnermann, Andreas; Szeghalmi, Adriana

    2016-06-01

    A new route to prepare nanoporous SiO2 films by mixing atomic-layer-deposited alumina and silica in an Å-scale is presented. The selective removal of Al2O3 from the composites using wet chemical etching with phosphoric acid resulted in nanoporous thin SiO2 layers. A diffusion-controlled dissolution mechanism is identified whereby an interesting reorganization of the residual SiO2 is observed. The atomic scale oxide mixing is decisive in attaining and tailoring the film porosity. The porosity and the refractive index of nanoporous silica films were tailored from 9% to 69% and from 1.40 to 1.13, respectively. The nanoporous silica was successfully employed as antireflection coatings and as diffusion membranes to encapsulate nanostructures.

  4. Results from Point Contact Tunnelling Spectroscopy and Atomic Layer Deposition

    Energy Technology Data Exchange (ETDEWEB)

    Proslier, Th. [Illinois Institute of Technology; Zasadzinski, J. [Illinois Institute of Technology; Ciovati, Gianluigi [JLAB; Kneisel, Peter K. [JLAB; Elam, J. W. [ANL; Norem, J. [ANL; Pellin, M. J. [ANL

    2009-11-01

    We have shown previously that magnetic niobium oxides can influence the superconducting density of states at the surface of cavity-grade niobium coupons. We will present recent results obtained by Point Contact Tunneling spectroscopy (PCT) on coupons removed from hot and cold spots in a niobium cavity, as well as a comparative study of magnetic oxides on mild baked/unbaked electropolished coupons. We will also describe recent results obtained from coated cavities, ALD films properties and new materials using Atomic Layer Deposition (ALD).

  5. Silicon protected with atomic layer deposited TiO2

    DEFF Research Database (Denmark)

    Seger, Brian; Tilley, David S.; Pedersen, Thomas

    2013-01-01

    The semiconducting materials used for photoelectrochemical (PEC) water splitting must withstand the corrosive nature of the aqueous electrolyte over long time scales in order to be a viable option for large scale solar energy conversion. Here we demonstrate that atomic layer deposited titanium...... dioxide (TiO2) overlayers on silicon-based photocathodes generate extremely stable electrodes. These electrodes can produce an onset potential of +0.510 V vs. RHE and a hydrogen evolution saturation current of 22 mA cm−2 using the red part of the AM1.5 solar spectrum (λ > 635 nm, 38.6 mW cm−2). A PEC...

  6. Effect of low-temperature annealing on the electronic- and band-structures of (Ga,Mn)As epitaxial layers

    Science.gov (United States)

    Yastrubchak, O.; Wosinski, T.; Gluba, L.; Andrearczyk, T.; Domagala, J. Z.; Żuk, J.; Sadowski, J.

    2014-01-01

    The effect of outdiffusion of Mn interstitials from (Ga,Mn)As epitaxial layers, caused by post-growth low-temperature annealing, on their electronic- and band-structure properties has been investigated by modulation photoreflectance (PR) spectroscopy. The annealing-induced changes in structural and magnetic properties of the layers were examined with high-resolution X-ray diffractometry and superconducting quantum interference device magnetometry, respectively. They confirmed an outdiffusion of Mn interstitials from the layers and an enhancement in their hole concentration, which were more efficient for the layer covered with a Sb cap acting as a sink for diffusing Mn interstitials. The PR results demonstrating a decrease in the band-gap-transition energy in the as-grown (Ga,Mn)As layers, with respect to that in the reference GaAs one, are interpreted by assuming a merging of the Mn-related impurity band with the GaAs valence band. Whereas an increase in the band-gap-transition energy caused by the annealing treatment of the (Ga,Mn)As layers is interpreted as a result of annealing-induced enhancement of the free-hole concentration and the Fermi level location within the valence band. The experimental results are consistent with the valence-band origin of itinerant holes mediating ferromagnetic ordering in (Ga,Mn)As, in agreement with the Zener model for ferromagnetic semiconductors.

  7. Morphology and optical properties of InN layers grown by molecular beam epitaxy on silicon substrates

    Energy Technology Data Exchange (ETDEWEB)

    Grandal, J.; Sanchez-Garcia, M.A.; Calle, F.; Calleja, E. [Universidad Politecnica de Madrid, Ciudad Universitaria, 28040 Madrid (Spain)

    2005-05-01

    This work reports on the morphology and photoluminescence (PL) properties of wurtzite InN layers grown by plasma assisted molecular beam epitaxy (PA-MBE) on AlN-buffered Si(111) substrates. The layer morphology can be controlled by the effective indium to nitrogen molecular flux ratio, from N-rich conditions that lead to columnar InN layers, to stoichiometric conditions leading to coalesced InN layers. X-Ray Diffraction (XRD) rocking curves around the InN (002) reflection yield a minimum value of 682 arcsec full width at half maximum (FWHM) for a coalesced InN layer. PL intensity from columnar InN samples is two orders of magnitude stronger than that corresponding to coalesced material, pointing to a much higher crystalline quality of the former. PL spectra in columnar InN layers reveal an emission at 0.75 eV (16 K) that follows the typical band-gap temperature dependence and shows a linear trend with the excitation power, suggesting a band-edge recombination that yields an estimate of the energy gap for InN around 0.72 eV at room temperature. No other emissions are observed at higher energies. (copyright 2005 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  8. Atomic-layer deposition of Lu2O3

    Science.gov (United States)

    Scarel, G.; Bonera, E.; Wiemer, C.; Tallarida, G.; Spiga, S.; Fanciulli, M.; Fedushkin, I. L.; Schumann, H.; Lebedinskii, Yu.; Zenkevich, A.

    2004-07-01

    Rare earth oxides could represent a valuable alternative to SiO2 in complementary metal-oxide-semiconductor devices. Lu2O3 is proposed because of its predicted thermodynamical stability on silicon and large conduction band offset. We report on the growth by atomic-layer deposition of lutetium oxide films using the dimeric {[C5H4(SiMe3)]2LuCl}2 complex, which has been synthesized for this purpose, and H2O. The films were found to be stoichiometric, with Lu2O3 composition, and amorphous. Annealing in nitrogen at 950°C leads to crystallization in the cubic bixbyite structure. The dielectric constant of the as-grown Lu2O3 layers is 12±1.

  9. Blistering during the atomic layer deposition of iridium

    Energy Technology Data Exchange (ETDEWEB)

    Genevée, Pascal, E-mail: pascal-genevee@chimie-paristech.fr, E-mail: a.szeghalmi@uni-jena.de; Ahiavi, Ernest; Janunts, Norik; Pertsch, Thomas; Kley, Ernst-Bernhard; Szeghalmi, Adriana, E-mail: pascal-genevee@chimie-paristech.fr, E-mail: a.szeghalmi@uni-jena.de [Institut für Angewandte Physik, Friedrich-Schiller-Universität Jena, Max-Wien-Platz 1, 07743 Jena (Germany); Oliva, Maria [Fraunhofer IOF, Albert-Einstein-Strasse 7, 07743 Jena (Germany)

    2016-01-15

    The authors report on the formation of blisters during the atomic layer deposition of iridium using iridium acetylacetonate and oxygen precursors. Films deposited on fused silica substrates led to sparsely distributed large blisters while in the case of silicon with native oxide additional small blisters with a high density was observed. It is found that the formation of blisters is favored by a higher deposition temperature and a larger layer thickness. Postdeposition annealing did not have a significant effect on the formation of blisters. Finally, changing purge duration during the film growth allowed us to avoid blistering and evidenced that impurities released from the film in gas phase were responsible for the formation of blisters.

  10. Volume production of high quality SiC substrates and epitaxial layers: Defect trends and device applications

    Science.gov (United States)

    Müller, St. G.; Sanchez, E. K.; Hansen, D. M.; Drachev, R. D.; Chung, G.; Thomas, B.; Zhang, J.; Loboda, M. J.; Dudley, M.; Wang, H.; Wu, F.; Byrappa, S.; Raghothamachar, B.; Choi, G.

    2012-08-01

    We review the progress of silicon carbide (SiC) bulk growth by the sublimation method, highlighting recent advances at Dow Corning, which resulted in the commercial release of 100 mm n-type 4H-SiC wafers with median micropipe densities (MPD) in production wafers screw dislocation densities reactor. The combined improvements in the epitaxy process, pre-epi wafer surface preparation and the underlying substrate quality itself have led to a reduction of the device killer defect density from 8 cm-2 to 1.5 cm-2 on a volume product like 100 mm 4° off-axis 6.5 μm epi-wafers. Dow Corning production epi-wafers routinely show Schottky diode yields above 90% at a die size of 2 mm×2 mm. Additionally, 50-100 μm thick epitaxy on 76 mm 4° off-axis wafers with morphological defect densities of 2-6 cm-2, a surface roughness (RMS) ≤1 nm as measured by atomic force microscopy (AFM), and carrier lifetimes consistently in the range of 2-3 μs has been demonstrated.

  11. Rational Design of Hyperbranched Nanowire Systems for Tunable Superomniphobic Surfaces Enabled by Atomic Layer Deposition

    Energy Technology Data Exchange (ETDEWEB)

    Bielinski, Ashley R.; Boban, Mathew; He, Yang; Kazyak, Eric; Lee, Duck Hyun; Wang, Chongmin; Tuteja, Anish; Dasgupta, Neil P.

    2017-01-24

    A method for tunable control of geometry in hyperbranched ZnO nanowire (NW) systems is reported, which enables the rational design and fabrication of superomniphobic surfaces. Branched NWs with tunable density and orientation were grown via a sequential hydrothermal process, in which atomic layer deposition (ALD) was used for NW seeding, disruption of epitaxy, and selective blocking of NW nucleation. This approach allows for the rational design and optimization of three-level hierarchical structures, in which the geometric parameters of each level of hierarchy can be individually controlled. We demonstrate the coupled relationships between geometry and contact angle for a variety of liquids, which is supported by mathematical models of structural superomniphobicity. The highest performing superomniphobic surface was designed with three levels of hierarchy and achieved the following advancing/receding contact angles, water: 172°/170°, hexadecane: 166°/156°, octane: 162°/145°, and heptane: 160°/130°. Low surface tension liquids were shown to bounce off the surface from a height of 7 cm without breaking through and wetting. This approach demonstrates the power of ALD as an enabling technique for hierarchical materials by design, spanning the macro, micro, and nano length scales.

  12. Atomic layer deposition of alternative glass microchannel plates

    Energy Technology Data Exchange (ETDEWEB)

    O' Mahony, Aileen, E-mail: aom@incomusa.com; Craven, Christopher A.; Minot, Michael J.; Popecki, Mark A.; Renaud, Joseph M.; Bennis, Daniel C.; Bond, Justin L.; Stochaj, Michael E.; Foley, Michael R.; Adams, Bernhard W. [Incom, Inc., 294 Southbridge Road, Charlton, Massachusetts 01507 (United States); Mane, Anil U.; Elam, Jeffrey W. [Argonne National Laboratory, 9700 S. Cass Ave., Argonne, Illinois 60439 (United States); Ertley, Camden; Siegmund, Oswald H. W. [Space Sciences Laboratory, University of California, 7 Gauss Way, Berkeley, California 94720 (United States)

    2016-01-15

    The technique of atomic layer deposition (ALD) has enabled the development of alternative glass microchannel plates (MCPs) with independently tunable resistive and emissive layers, resulting in excellent thickness uniformity across the large area (20 × 20 cm), high aspect ratio (60:1 L/d) glass substrates. Furthermore, the use of ALD to deposit functional layers allows the optimal substrate material to be selected, such as borosilicate glass, which has many benefits compared to the lead-oxide glass used in conventional MCPs, including increased stability and lifetime, low background noise, mechanical robustness, and larger area (at present up to 400 cm{sup 2}). Resistively stable, high gain MCPs are demonstrated due to the deposition of uniform ALD resistive and emissive layers on alternative glass microcapillary substrates. The MCP performance characteristics reported include increased stability and lifetime, low background noise (0.04 events cm{sup −2} s{sup −1}), and low gain variation (±5%)

  13. Atomic layer deposition ultrathin film origami using focused ion beams

    Science.gov (United States)

    Supekar, O. D.; Brown, J. J.; Eigenfeld, N. T.; Gertsch, J. C.; Bright, V. M.

    2016-12-01

    Focused ion beam (FIB) micromachining is a powerful tool for maskless lithography and in recent years FIB has been explored as a tool for strain engineering. Ion beam induced deformation can be utilized as a means for folding freestanding thin films into complex 3D structures. FIB of high energy gallium (Ga+) ions induces stress by generation of dislocations and ion implantation within material layers, which create creases or folds upon mechanical relaxation enabled by motion of the material layers. One limitation on such processing is the ability to fabricate flat freestanding thin film structures. This capability is limited by the residual stresses formed during processing and fabrication of the films, which can result in initial curvature and deformation of films upon release from a sacrificial fabrication layer. This paper demonstrates folding in freestanding ultrathin films (1:1000) by ion-induced stress relaxation. The ultrathin flat structures are fabricated using atomic layer deposition on sacrificial polyimide. We have demonstrated vertical folding with 30 keV Ga+ ions in structures with lateral dimensions varying from 10 to 50 μm.

  14. Plasma enhanced atomic layer deposition of silicon nitride using neopentasilane

    Energy Technology Data Exchange (ETDEWEB)

    Weeks, Stephen, E-mail: Stephen.Weeks@intermolecular.com; Nowling, Greg; Fuchigami, Nobi; Bowes, Michael; Littau, Karl [Intermolecular, 3011 North 1st Street, San Jose, California 95134 (United States)

    2016-01-15

    Progress in transistor scaling has increased the demands on the material properties of silicon nitride (SiN{sub x}) thin films used in device fabrication and at the same time placed stringent restrictions on the deposition conditions employed. Recently, low temperature plasma enhanced atomic layer deposition has emerged as a viable technique for depositing these films with a thermal budget compatible with semiconductor processing at sub-32 nm technology nodes. For these depositions, it is desirable to use precursors that are free from carbon and halogens that can incorporate into the film. Beyond this, it is necessary to develop processing schemes that minimize the wet etch rate of the film as it will be subjected to wet chemical processing in subsequent fabrication steps. In this work, the authors introduce low temperature deposition of SiN{sub x} using neopentasilane [NPS, (SiH{sub 3}){sub 4}Si] in a plasma enhanced atomic layer deposition process with a direct N{sub 2} plasma. The growth with NPS is compared to a more common precursor, trisilylamine [TSA, (SiH{sub 3}){sub 3 }N] at identical process conditions. The wet etch rates of the films deposited with NPS are characterized at different plasma conditions and the impact of ion energy is discussed.

  15. An Atomically Layered InSe Avalanche Photodetector.

    Science.gov (United States)

    Lei, Sidong; Wen, Fangfang; Ge, Liehui; Najmaei, Sina; George, Antony; Gong, Yongji; Gao, Weilu; Jin, Zehua; Li, Bo; Lou, Jun; Kono, Junichiro; Vajtai, Robert; Ajayan, Pulickel; Halas, Naomi J

    2015-05-13

    Atomically thin photodetectors based on 2D materials have attracted great interest due to their potential as highly energy-efficient integrated devices. However, photoinduced carrier generation in these media is relatively poor due to low optical absorption, limiting device performance. Current methods for overcoming this problem, such as reducing contact resistances or back gating, tend to increase dark current and suffer slow response times. Here, we realize the avalanche effect in a 2D material-based photodetector and show that avalanche multiplication can greatly enhance the device response of an ultrathin InSe-based photodetector. This is achieved by exploiting the large Schottky barrier formed between InSe and Al electrodes, enabling the application of a large bias voltage. Plasmonic enhancement of the photosensitivity, achieved by patterning arrays of Al nanodisks onto the InSe layer, further improves device efficiency. With an external quantum efficiency approaching 866%, a dark current in the picoamp range, and a fast response time of 87 μs, this atomic layer device exhibits multiple significant advances in overall performance for this class of devices.

  16. Photoconductivity of ultra-thin Ge(GeSn) layers grown in Si by low-temperature molecular beam epitaxy

    Science.gov (United States)

    Talochkin, A. B.; Chistokhin, I. B.; Mashanov, V. I.

    2016-04-01

    Photoconductivity (PC) spectra of Si/Ge(GeSn)/Si structures with the ultra-thin (1.0-2.3 nm) Ge and GeSn alloy layers grown by the low-temperature (T = 100 °C) molecular beam epitaxy are studied. Photoresponse in the range of 1.2-0.4 eV related to light absorption in the buried Ge(GeSn) layer is observed. It is shown that in case of lateral PC, a simple diffusion model can be used to determine the absorption coefficient of this layer α ˜ 105 cm-1. This value is 100 times larger than that of a single Ge quantum dot layer and is reached significantly above the band gap of most bulk semiconductors. The observed absorption is caused by optical transitions between electron and hole states localized at the interfaces. The anomalous high value of α can be explained by the unusual state of Ge(GeSn) layer with high concentration of dangling bonds, the optical properties of which have been predicted theoretically by Knief and von Niessen (Phys. Rev. B 59, 12940 (1999)).

  17. Bond-length variation in InxGa1-xAs/InP strained epitaxial layers

    Science.gov (United States)

    Romanato, F.; de Salvador, D.; Berti, M.; Drigo, A.; Natali, M.; Tormen, M.; Rossetto, G.; Pascarelli, S.; Boscherini, F.; Lamberti, C.; Mobilio, S.

    1998-06-01

    Tensile and compressive InxGa1-xAs epilayers grown on [001] InP substrates have been analyzed by fluorescence-detected x-ray-absorption fine structure in order to investigate the length variation suffered by Ga-As and In-As atomic bonds under epitaxial strain. A morphological and structural analysis had previously been performed in order to select only pseudomorphic samples with high lattice quality. A clear variation of the nearest-neighbor distances proportional to the tetragonal distortion of the film has been detected. We discuss the relationship between the long- and short-range descriptions of strain accommodation in the framework of an analytical model.

  18. Full compensation of oxygen vacancies in EuTiO3 (001) epitaxial thin film stabilized by a SrTiO3 surface protection layer

    Science.gov (United States)

    Shimamoto, K.; Hatabayashi, K.; Hirose, Y.; Nakao, S.; Fukumura, T.; Hasegawa, T.

    2013-01-01

    We fabricated highly insulating EuTiO3 (001) epitaxial thin films capped with SrTiO3 protection layers on SrTiO3 (001) substrates by combining pulsed laser deposition and post-annealing processes. The epitaxial SrTiO3 protection layer played a significant role in compensation of oxygen vacancies in the EuTiO3 thin films by preventing excess oxidation of the films and by "locking" the EuTiO3 perovskite structure in an epitaxial manner from the top during the air-annealing process. The obtained EuTiO3 thin films demonstrated an antiferromagnetic transition at 5.4 K, quantum paraelectricity down to ˜25 K, and a magnetoelectric coupling comparable to that of bulk EuTiO3.

  19. Effect of Buffer Layer on Epitaxial Growth of YSZ Deposited on Si Substrate by Slower Q-switched 266 nm YAG Laser

    Science.gov (United States)

    Kaneko, Satoru; Akiyama, Kensuke; Shimizu, Yoshitada; Ito, Takeshi; Yasaka, Shinji; Mitsuhashi, Masahiko; Ohya, Seishiro; Saito, Keisuke; Watanabe, Takayuki; Okamoto, Shoji; Funakubo, Hiroshi

    2004-04-01

    Yttria-stabilized zirconia (YSZ) was grown on Si(100) substrate by pulsed laser deposition (PLD). The laser used in this study was a 266 nm YAG laser with a second function generator modulating only the Q-switch while the primary generator modulated the flash lamp (slower Q-switch). Epitaxial growth was verified on YSZ film deposited without oxygen gas followed by primary deposition in oxygen atmosphere on Si substrate with a ˜0.4-nm-thin oxide layer. The crystallinity was strongly dependent on the thickness of the buffer layer deposited prior to the primary deposition of YSZ. The epitaxial growth was confirmed by φ scan, and ω scan (rocking curve) showed the full width at half maximum (FWHM) of 1.1 deg. The required oxygen pressure for epitaxial growth was quite high compared to that of excimer deposition.

  20. Homo and hetero epitaxy of Germanium using isobutylgermane

    Energy Technology Data Exchange (ETDEWEB)

    Attolini, G. [CNR-IMEM Institute, Parco Area delle Scienze 37/A, 43010 Fontanini, Parma (Italy); Bosi, M. [CNR-IMEM Institute, Parco Area delle Scienze 37/A, 43010 Fontanini, Parma (Italy)], E-mail: bosi@imem.cnr.it; Musayeva, N.; Pelosi, C.; Ferrari, C.; Arumainathan, S. [CNR-IMEM Institute, Parco Area delle Scienze 37/A, 43010 Fontanini, Parma (Italy); Timo, G. [CESI Ricerca S.P.A., Via Rubattino 54, 20134 Milano (Italy)], E-mail: Gianluca.Timo@cesiricerca.it

    2008-11-03

    Nominally undoped Ge epitaxial layers were deposited on Ge and GaAs substrates by means of Metal-Organic Vapor Phase (MOVPE) using a novel Germanium source, isobutylgermane (iBuGe), by Rohm and Haas Electronic Materials LLC (USA). High Resolution X-ray Diffraction, Atomic Force Microscopy and Raman spectroscopy were combined to characterize the layers. Ge layers were deposited using AsH{sub 3} as a surfactant and several growth procedures were tested. The use of arsine reduced the growth rate and also significantly improved the epitaxial quality and surface roughness.

  1. Atomic layer deposition of W - based layers on SiO2

    NARCIS (Netherlands)

    Bystrova, S.; Holleman, J.; Wolters, R.A.M.; Aarnink, A.A.I.

    2003-01-01

    W and W1-xNx , where x= 15- 22 at%, thin films were grown using the ALD (Atomic Layer Deposition) principle. Growth rate of W films is about 4- 5 monolayers/ cycle at 300- 350 ºC. Growth rate of W1-xNx is 0.5 monolayer/cycle at 325- 350 ºC. Standard Deviation (STDV) of thickness is about 2%

  2. Epitaxial AlN layers on sapphire and diamond; Epitaktische AlN-Schichten auf Saphir und Diamant

    Energy Technology Data Exchange (ETDEWEB)

    Hermann, Martin

    2009-04-27

    In this work, epitaxial AlN layers deposited by molecular beam epitaxy on sapphire and diamond substrates were investigated. Starting from this AlN, the dopant silicon was added. The influence of the silicon doping on the structural properties of the host AlN crystal was investigated using high resolution X-ray diffraction. Once the silicon concentration exceeds 1 x 10{sup 19} cm{sup -3}, a significant change of the AlN:Si crystal can be observed: increasing the silicon concentration up to 5 x 10{sup 20} cm{sup -3} results in a decrease of the a lattice parameter by approximately 1.2 pm and an increase of the c lattice parameter by about 1.0 pm. The crystal is stressed additionally by adding silicon resulting in a increase of the biaxial compressive stress of up to 2.0 GPa. Further increase of the silicon concentration leads to lattice relaxation. This result from X-ray diffraction was independently confirmed by Raman spectroscopy investigations. Further increase of the silicon concentration leads to the generation of polycrystalline phases within the epitaxial layer. XTEM measurements detected these polycrystalline phases. In addition, XTEM investigations confirmed also the increase of the lateral crystal size with increasing silicon concentration, as well as a great reduction of the screw dislocation density by more than one order of magnitude as found by X-ray diffraction: in undoped, nitrogen rich grown AlN layers the screw dislocation density is about 3 x 10{sup 8} cm{sup -2}, while AlN layers with a silicon concentration of 5 x 10{sup 20} cm{sup -3} show a screw dislocation density of only 1 x 10{sup 7} cm{sup -2}. In low-doped AlN:Si ([Si]{approx}2 x 10{sup 19} cm{sup -3}) the activation energy of the electronic conductivity is about 250 meV. Increasing the silicon concentration to about 1 x 10{sup 21} cm{sup -3} leads to an increase of the activation energy up to more than 500 meV in the now much more stressed AlN:Si epilayer. Studies of the absorption

  3. Epitaxial Cu{sub 2}ZnSnSe{sub 4} layers by annealing of Sn/Cu/ZnSe(001) precursors on GaAs(001)

    Energy Technology Data Exchange (ETDEWEB)

    Krämmer, Christoph, E-mail: Christoph.Kraemmer@kit.edu [Institute of Applied Physics, Karlsruhe Institute of Technology (KIT), 76131 Karlsruhe (Germany); Sachs, Johannes [Institute of Applied Physics, Karlsruhe Institute of Technology (KIT), 76131 Karlsruhe (Germany); Pfaffmann, Lukas [Laboratory for Electron Microscopy, KIT (Germany); Musiol, Timo; Lang, Mario; Gao, Chao [Institute of Applied Physics, Karlsruhe Institute of Technology (KIT), 76131 Karlsruhe (Germany); Gerthsen, Dagmar [Laboratory for Electron Microscopy, KIT (Germany); Kalt, Heinz [Institute of Applied Physics, Karlsruhe Institute of Technology (KIT), 76131 Karlsruhe (Germany); Powalla, Michael [Light Technology Institute, KIT (Germany); Zentrum für Sonnenenergie-und Wasserstoff-Forschung Baden-Württemberg (ZSW), 70565 Stuttgart (Germany); Hetterich, Michael [Institute of Applied Physics, Karlsruhe Institute of Technology (KIT), 76131 Karlsruhe (Germany)

    2015-05-01

    We report on the fabrication of epitaxial Cu{sub 2}ZnSnSe{sub 4} films by a two-step fabrication approach. An epitaxial ZnSe(001) layer on GaAs(001) is grown by molecular-beam epitaxy followed by sequential deposition of Cu and Sn. The Sn/Cu/ZnSe(001) precursor is then thermally annealed in a selenium atmosphere. Raman spectroscopy confirms the presence of the kesterite phase. Electron microscopy shows that the films exhibit monocrystalline regions of several micrometers in size with inclusions of smaller grains with a different chemical composition. The latter is confirmed by electron backscatter diffraction measurements which prove the conservation of the crystal orientation defined by the cubic ZnSe/GaAs(001) precursor structure throughout the whole CZTSe film. - Highlights: • Two-step fabrication approach to obtain epitaxial kesterite layers is presented. • Kesterite phase formation is confirmed by Raman spectroscopy. • SnSe{sub x} compounds are identified to be the main secondary phase. • Electron backscatter diffraction proves epitaxial orientation of the films.

  4. Atomic layer confined vacancies for atomic-level insights into carbon dioxide electroreduction

    Science.gov (United States)

    Gao, Shan; Sun, Zhongti; Liu, Wei; Jiao, Xingchen; Zu, Xiaolong; Hu, Qitao; Sun, Yongfu; Yao, Tao; Zhang, Wenhua; Wei, Shiqiang; Xie, Yi

    2017-01-01

    The role of oxygen vacancies in carbon dioxide electroreduction remains somewhat unclear. Here we construct a model of oxygen vacancies confined in atomic layer, taking the synthetic oxygen-deficient cobalt oxide single-unit-cell layers as an example. Density functional theory calculations demonstrate the main defect is the oxygen(II) vacancy, while X-ray absorption fine structure spectroscopy reveals their distinct oxygen vacancy concentrations. Proton transfer is theoretically/experimentally demonstrated to be a rate-limiting step, while energy calculations unveil that the presence of oxygen(II) vacancies lower the rate-limiting activation barrier from 0.51 to 0.40 eV via stabilizing the formate anion radical intermediate, confirmed by the lowered onset potential from 0.81 to 0.78 V and decreased Tafel slope from 48 to 37 mV dec−1. Hence, vacancy-rich cobalt oxide single-unit-cell layers exhibit current densities of 2.7 mA cm−2 with ca. 85% formate selectivity during 40-h tests. This work establishes a clear atomic-level correlation between oxygen vacancies and carbon dioxide electroreduction. PMID:28220847

  5. Atomic layer confined vacancies for atomic-level insights into carbon dioxide electroreduction

    Science.gov (United States)

    Gao, Shan; Sun, Zhongti; Liu, Wei; Jiao, Xingchen; Zu, Xiaolong; Hu, Qitao; Sun, Yongfu; Yao, Tao; Zhang, Wenhua; Wei, Shiqiang; Xie, Yi

    2017-02-01

    The role of oxygen vacancies in carbon dioxide electroreduction remains somewhat unclear. Here we construct a model of oxygen vacancies confined in atomic layer, taking the synthetic oxygen-deficient cobalt oxide single-unit-cell layers as an example. Density functional theory calculations demonstrate the main defect is the oxygen(II) vacancy, while X-ray absorption fine structure spectroscopy reveals their distinct oxygen vacancy concentrations. Proton transfer is theoretically/experimentally demonstrated to be a rate-limiting step, while energy calculations unveil that the presence of oxygen(II) vacancies lower the rate-limiting activation barrier from 0.51 to 0.40 eV via stabilizing the formate anion radical intermediate, confirmed by the lowered onset potential from 0.81 to 0.78 V and decreased Tafel slope from 48 to 37 mV dec-1. Hence, vacancy-rich cobalt oxide single-unit-cell layers exhibit current densities of 2.7 mA cm-2 with ca. 85% formate selectivity during 40-h tests. This work establishes a clear atomic-level correlation between oxygen vacancies and carbon dioxide electroreduction.

  6. Growth optimization and applicability of thick on-axis SiC layers using sublimation epitaxy in vacuum

    Science.gov (United States)

    Jokubavicius, Valdas; Sun, Jianwu; Liu, Xinyu; Yazdi, Gholamreza; Ivanov, Ivan. G.; Yakimova, Rositsa; Syväjärvi, Mikael

    2016-08-01

    We demonstrate growth of thick SiC layers (100-200 μm) on nominally on-axis hexagonal substrates using sublimation epitaxy in vacuum (10-5 mbar) at temperatures varying from 1700 to 1975 °C with growth rates up to 270 μm/h and 70 μm/h for 6H- and 4H-SiC, respectively. The stability of hexagonal polytypes are related to process growth parameters and temperature profile which can be engineered using different thermal insulation materials and adjustment of the induction coil position with respect to the graphite crucible. We show that there exists a range of growth rates for which single-hexagonal polytype free of foreign polytype inclusions can be maintained. Further on, foreign polytypes like 3C-SiC can be stabilized by moving out of the process window. The applicability of on-axis growth is demonstrated by growing a 200 μm thick homoepitaxial 6H-SiC layer co-doped with nitrogen and boron in a range of 1018 cm-3 at a growth rate of about 270 μm/h. Such layers are of interest as a near UV to visible light converters in a monolithic white light emitting diode concept, where subsequent nitride-stack growth benefits from the on-axis orientation of the SiC layer.

  7. Characterization and prevention of humidity related degradation of atomic layer deposited Al2O3

    Science.gov (United States)

    Rückerl, Andreas; Zeisel, Roland; Mandl, Martin; Costina, Ioan; Schroeder, Thomas; Zoellner, Marvin H.

    2017-01-01

    Atomic layer deposited aluminum oxide (ALD-Al2O3) is a dielectric material, which is widely used in organic light emitting diodes in order to prevent their organic layers from humidity related degradation. Unfortunately, there are strong hints that in some cases, ALD-Al2O3 itself is suffering from humidity related degradation. Especially, high temperature and high humidity seem to enhance ALD-Al2O3 degradation strongly. For this reason, the degradation behavior of ALD-Al2O3 films at high temperature and high humidity was investigated in detail and a way to prevent it from degradation was searched. The degradation behavior is analyzed in the first part of this paper. Using infrared absorbance measurements and X-ray diffraction, boehmite (γ-AlOOH) was identified as a degradation product. In the second part of the paper, it is shown that ALD-Al2O3 films can be effectively protected from degradation using a silicon oxide capping. The deposition of very small amounts of silicon in a molecular beam epitaxy system and an X-ray photoelectron spectroscopy investigation of the chemical bonding between the silicon and the ALD-Al2O3 surface led to the conclusion that a silicon termination of the ALD-Al2O3 surface (Al*-O-SiOx) is able to stop humidity related degradation of the underlying ALD-Al2O3 films. The third part of the paper shows that the protection mechanism of the silicon termination is probably due to the strong tendency of silicic acid to resilificate exposed ALD-Al2O3 surfaces. The protective effect of a simple silicon source on an ALD-Al2O3 surface is shown exemplary and the related chemical reactions are presented.

  8. Damage evaluation in graphene underlying atomic layer deposition dielectrics.

    Science.gov (United States)

    Tang, Xiaohui; Reckinger, Nicolas; Poncelet, Olivier; Louette, Pierre; Ureña, Ferran; Idrissi, Hosni; Turner, Stuart; Cabosart, Damien; Colomer, Jean-François; Raskin, Jean-Pierre; Hackens, Benoit; Francis, Laurent A

    2015-08-27

    Based on micro-Raman spectroscopy (μRS) and X-ray photoelectron spectroscopy (XPS), we study the structural damage incurred in monolayer (1L) and few-layer (FL) graphene subjected to atomic-layer deposition of HfO2 and Al2O3 upon different oxygen plasma power levels. We evaluate the damage level and the influence of the HfO2 thickness on graphene. The results indicate that in the case of Al2O3/graphene, whether 1L or FL graphene is strongly damaged under our process conditions. For the case of HfO2/graphene, μRS analysis clearly shows that FL graphene is less disordered than 1L graphene. In addition, the damage levels in FL graphene decrease with the number of layers. Moreover, the FL graphene damage is inversely proportional to the thickness of HfO2 film. Particularly, the bottom layer of twisted bilayer (t-2L) has the salient features of 1L graphene. Therefore, FL graphene allows for controlling/limiting the degree of defect during the PE-ALD HfO2 of dielectrics and could be a good starting material for building field effect transistors, sensors, touch screens and solar cells. Besides, the formation of Hf-C bonds may favor growing high-quality and uniform-coverage dielectric. HfO2 could be a suitable high-K gate dielectric with a scaling capability down to sub-5-nm for graphene-based transistors.

  9. GeSn p-i-n photodetectors with GeSn layer grown by magnetron sputtering epitaxy

    Science.gov (United States)

    Zheng, Jun; Wang, Suyuan; Liu, Zhi; Cong, Hui; Xue, Chunlai; Li, Chuanbo; Zuo, Yuhua; Cheng, Buwen; Wang, Qiming

    2016-01-01

    We report an investigation of normal-incidence GeSn-based p-i-n photodetectors (PDs) with a Ge0.94Sn0.06 active layer grown using sputter epitaxy on a Ge(100) substrate. A low dark current density of 0.24 A/cm2 was obtained at a reverse bias of 1 V. A high optical responsivity of the Ge0.94Sn0.06/Ge p-i-n PDs at zero bias was achieved, with an optical response wavelength extending to 1985 nm. The temperature-dependent optical-response measurement was performed, and a clear redshift absorption edge was observed. This work presents an approach for developing efficient and cost-effective GeSn-based infrared devices.

  10. Spreading resistance and C-DLTS spectra of proton-irradiated mesa diodes made on thick epitaxial Si layers

    Energy Technology Data Exchange (ETDEWEB)

    Nossarzewska-Orlowska, E. E-mail: nossar_e@sp.itme.edu.pl; Kozlowski, R.; Brzozowski, A

    1999-04-21

    High-resistivity, thick silicon epitaxial layers, deposited on Czochralski silicon (CZ Si) substrate were used as a material for test diodes. Resistivity profile as a function of depth and deep-level spectra were measured by spreading resistance method and deep-level transient spectroscopy (C-DLTS) on non-irradiated and proton irradiated mesa diodes. A deep level with activation energy E{sub c}-0.52 eV, attributed to V{sub 2}O defect, dominates in the non-irradiated diodes. After irradiation two levels, E{sub c}-0.38 and E{sub c}-0.45 eV, related to divacancies and the level E{sub c}-0.17 eV corresponding to VO complex are distinguished.

  11. Spreading resistance and C-DLTS spectra of proton-irradiated mesa diodes made on thick epitaxial Si layers

    CERN Document Server

    Nossarzhevska, E; Brzozowski, A

    1999-01-01

    High-resistivity, thick silicon epitaxial layers, deposited on Czochralski silicon (CZ Si) substrate were used as a material for test diodes. Resistivity profile as a function of depth and deep-level spectra were measured by spreading resistance method and deep-level transient spectroscopy (C-DLTS) on non-irradiated and proton irradiated mesa diodes. A deep level with activation energy E sub c -0.52 eV, attributed to V sub 2 O defect, dominates in the non-irradiated diodes. After irradiation two levels, E sub c -0.38 and E sub c -0.45 eV, related to divacancies and the level E sub c -0.17 eV corresponding to VO complex are distinguished.

  12. Spreading resistance and C-DLTS spectra of proton-irradiated mesa diodes made on thick epitaxial Si layers

    Science.gov (United States)

    Nossarzewska-Orłowska, E.; Kozłowski, R.; Brzozowski, A.

    1999-04-01

    High-resistivity, thick silicon epitaxial layers, deposited on Czochralski silicon (CZ Si) substrate were used as a material for test diodes. Resistivity profile as a function of depth and deep-level spectra were measured by spreading resistance method and deep-level transient spectroscopy (C-DLTS) on non-irradiated and proton irradiated mesa diodes. A deep level with activation energy E c-0.52 eV, attributed to V 2O defect, dominates in the non-irradiated diodes. After irradiation two levels, Ec-0.38 and Ec-0.45 eV, related to divacancies and the level Ec-0.17 eV corresponding to VO complex are distinguished.

  13. Atomic Layer Deposited Catalysts for Fuel Cell Applications

    DEFF Research Database (Denmark)

    Johansson, Anne-Charlotte Elisabeth Birgitta

    layer deposition (ALD), on the other hand, is a highly suitable and still relatively unexplored approach for the synthesis of noble metal catalysts. It is a vapor phase growth method, primarily used to deposit thin lms. ALD is based on self-limiting chemical reactions of alternately injected precursors...... for the realization of such tiny devices. It is a mature technology, suitable for mass production, where versatile structuring is available at the micro and nano regime. Carbon black supported catalysts synthesized by wet chemistry methods are not readily applicable for standard microfabrication techniques. Atomic...... on the sample surface. Its unique growth characteristic enables conformal and uniform lms of controlled thickness and composition. In certain conditions ALD commences by island growth, resulting in discrete nanoparticle formation, which is generally preferred for catalytic applications. Pt-Ru is the best...

  14. Oxygen-free atomic layer deposition of indium sulfide

    Energy Technology Data Exchange (ETDEWEB)

    Martinson, Alex B.; Hock, Adam S.; McCarthy, Robert; Weimer, Matthew S.

    2016-07-05

    A method for synthesizing an In(III) N,N'-diisopropylacetamidinate precursor including cooling a mixture comprised of diisopropylcarbodiimide and diethyl ether to approximately -30.degree. C., adding methyllithium drop-wise into the mixture, allowing the mixture to warm to room temperature, adding indium(III) chloride as a solid to the mixture to produce a white solid, dissolving the white solid in pentane to form a clear and colorless solution, filtering the mixture over a celite plug, and evaporating the solution under reduced pressure to obtain a solid In(III) N,N'-diisopropylacetamidinate precursor. This precursor has been further used to develop a novel atomic layer deposition technique for indium sulfide by dosing a reactor with the precursor, purging with nitrogen, dosing with dilute hydrogen sulfide, purging again with nitrogen, and repeating these steps to increase growth.

  15. Highly reflective polymeric substrates functionalized utilizing atomic layer deposition

    Science.gov (United States)

    Zuzuarregui, Ana; Coto, Borja; Rodríguez, Jorge; Gregorczyk, Keith E.; Ruiz de Gopegui, Unai; Barriga, Javier; Knez, Mato

    2015-08-01

    Reflective surfaces are one of the key elements of solar plants to concentrate energy in the receivers of solar thermal electricity plants. Polymeric substrates are being considered as an alternative to the widely used glass mirrors due to their intrinsic and processing advantages, but optimizing both the reflectance and the physical stability of polymeric mirrors still poses technological difficulties. In this work, polymeric surfaces have been functionalized with ceramic thin-films by atomic layer deposition. The characterization and optimization of the parameters involved in the process resulted in surfaces with a reflection index of 97%, turning polymers into a real alternative to glass substrates. The solution we present here can be easily applied in further technological areas where seemingly incompatible combinations of polymeric substrates and ceramic coatings occur.

  16. Protective silicon coating for nanodiamonds using atomic layer deposition

    Energy Technology Data Exchange (ETDEWEB)

    Lu, J. [State Key Laboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao, Hebei 066004 (China); College of Materials Science and Engineering, Yanshan University, Qinhuangdao, Hebei 066004 (China); Wang, Y.H. [State Key Laboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao, Hebei 066004 (China); College of Materials Science and Engineering, Yanshan University, Qinhuangdao, Hebei 066004 (China); Zang, J.B. [State Key Laboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao, Hebei 066004 (China) and College of Materials Science and Engineering, Yanshan University, Qinhuangdao, Hebei 066004 (China)]. E-mail: diamondzjb@163.com; Li, Y.N. [State Key Laboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao, Hebei 066004 (China); College of Materials Science and Engineering, Yanshan University, Qinhuangdao, Hebei 066004 (China)

    2007-01-30

    Ultrathin silicon coating was deposited on nanodiamonds using atomic layer deposition (ALD) from gaseous monosilane (SiH{sub 4}). The coating was performed by sequential reaction of SiH{sub 4} saturated adsorption and in situ decomposition. X-ray diffraction (XRD) and transmission electron microscopy (TEM) were utilized to investigate the structural and morphological properties of the coating. Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) were used to compare the thermal stability of nanodiamonds before and after silicon coating. The results confirmed that the deposited cubic phase silicon coating was even and continuous. The protective silicon coating could effectively improve the oxidation resistance of nanodiamonds in air flow, which facilitates the applications of nanodiamonds that are commonly hampered by their poor thermal stability.

  17. Highly reflective polymeric substrates functionalized utilizing atomic layer deposition

    Energy Technology Data Exchange (ETDEWEB)

    Zuzuarregui, Ana, E-mail: a.zuzuarregui@nanogune.eu; Gregorczyk, Keith E. [CIC Nanogune Consolider, de Tolosa Hiribidea 76, 20018 San Sebastián (Spain); Coto, Borja; Ruiz de Gopegui, Unai; Barriga, Javier [IK4-Tekniker, Iñaki Goenaga 5, 20600 Eibar (Spain); Rodríguez, Jorge [Torresol Energy (SENER Group), Avda. de Zugazarte 61, 48930 Las Arenas (Spain); Knez, Mato [CIC Nanogune Consolider, de Tolosa Hiribidea 76, 20018 San Sebastián (Spain); IKERBASQUE Basque Foundation for Science, Maria Diaz de Haro 3, 48013 Bilbao (Spain)

    2015-08-10

    Reflective surfaces are one of the key elements of solar plants to concentrate energy in the receivers of solar thermal electricity plants. Polymeric substrates are being considered as an alternative to the widely used glass mirrors due to their intrinsic and processing advantages, but optimizing both the reflectance and the physical stability of polymeric mirrors still poses technological difficulties. In this work, polymeric surfaces have been functionalized with ceramic thin-films by atomic layer deposition. The characterization and optimization of the parameters involved in the process resulted in surfaces with a reflection index of 97%, turning polymers into a real alternative to glass substrates. The solution we present here can be easily applied in further technological areas where seemingly incompatible combinations of polymeric substrates and ceramic coatings occur.

  18. Atomic layer deposition overcoating: tuning catalyst selectivity for biomass conversion.

    Science.gov (United States)

    Zhang, Hongbo; Gu, Xiang-Kui; Canlas, Christian; Kropf, A Jeremy; Aich, Payoli; Greeley, Jeffrey P; Elam, Jeffrey W; Meyers, Randall J; Dumesic, James A; Stair, Peter C; Marshall, Christopher L

    2014-11-01

    The terraces, edges, and facets of nanoparticles are all active sites for heterogeneous catalysis. These different active sites may cause the formation of various products during the catalytic reaction. Here we report that the step sites of Pd nanoparticles (NPs) can be covered precisely by the atomic layer deposition (ALD) method, whereas the terrace sites remain as active component for the hydrogenation of furfural. Increasing the thickness of the ALD-generated overcoats restricts the adsorption of furfural onto the step sites of Pd NPs and increases the selectivity to furan. Furan selectivities and furfural conversions are linearly correlated for samples with or without an overcoating, though the slopes differ. The ALD technique can tune the selectivity of furfural hydrogenation over Pd NPs and has improved our understanding of the reaction mechanism. The above conclusions are further supported by density functional theory (DFT) calculations.

  19. XRD and RBS studies of quasi-amorphous zinc oxide layers produced by Atomic Layer Deposition

    Energy Technology Data Exchange (ETDEWEB)

    Guziewicz, Elżbieta, E-mail: guzel@ifpan.edu.pl [Institute of Physics, Polish Academy of Sciences, Al. Lotników 32/46, 02-668 Warsaw (Poland); Turos, Andrzej [Institute of Electronic Materials Technology, Wólczyńska 133, 01-919 Warsaw (Poland); National Centre for Nuclear Research, Soltana 7, 04-500 Otwock (Poland); Stonert, Anna [National Centre for Nuclear Research, Soltana 7, 04-500 Otwock (Poland); Snigurenko, Dmytro; Witkowski, Bartłomiej S. [Institute of Physics, Polish Academy of Sciences, Al. Lotników 32/46, 02-668 Warsaw (Poland); Diduszko, Ryszard [Institute of Electronic Materials Technology, Wólczyńska 133, 01-919 Warsaw (Poland); Behar, Moni [Instituto de Fisica, Universidade do Rio Grande do Sul, 91501 Porto Alegre (Brazil)

    2016-08-01

    Although zinc oxide has been widely investigated for many important applications such as laser diodes, photovoltaics, and sensors, some basic properties of this material have not been established up to now. One of these are stopping power values which are crucial for the Rutherford Backscattering Spectrometry analysis. For this kind of measurements, amorphous materials should be used. In this paper we show the results of stopping power measurements for ZnO films grown by Atomic Layer Deposition. The films were grown on a silicon (100) substrate and parameters of the growth were chosen in a way that prevents crystallization of ZnO films. A series of ZnO films with thickness between 20 and 160 nm have been investigated. Extended film characterization has proven that the obtained nanopolycrystalline ZnO films can be considered as truly amorphous with respect to ion beam applications. ZnO films have been used for precise stopping power measurement of MeV He-ions in the energy range from 200 to 5000 keV. These results provide indispensable data for ion beam modification and analysis of ZnO. - Highlights: • Thin ZnO films of low crystallographic quality were obtained by Atomic Layer Deposition at 60 °C. • Nanopolycrystalline structure and atomically flat surface has been measured by X-ray diffraction. • Stopping power measurements show a very good agreement with the calculated values.

  20. Atomic Layer Deposition to Enable the Production, Optimization and Protection of Spaceflight Hardware Project

    Data.gov (United States)

    National Aeronautics and Space Administration — Atomic Layer Deposition (ALD) is a cost effective nano-manufacturing technique that allows for the conformal coating of substrates with atomic control in a benign...

  1. Atomic Layer Deposition of Bismuth Vanadates for Solar Energy Materials.

    Science.gov (United States)

    Stefik, Morgan

    2016-07-07

    The fabrication of porous nanocomposites is key to the advancement of energy conversion and storage devices that interface with electrolytes. Bismuth vanadate, BiVO4 , is a promising oxide for solar water splitting where the controlled fabrication of BiVO4 layers within porous, conducting scaffolds has remained a challenge. Here, the atomic layer deposition of bismuth vanadates is reported from BiPh3 , vanadium(V) oxytriisopropoxide, and water. The resulting films have tunable stoichiometry and may be crystallized to form the photoactive scheelite structure of BiVO4 . A selective etching process was used with vanadium-rich depositions to enable the synthesis of phase-pure BiVO4 after spinodal decomposition. BiVO4 thin films were measured for photoelectrochemical performance under AM 1.5 illumination. The average photocurrents were 1.17 mA cm(-2) at 1.23 V versus the reversible hydrogen electrode using a hole-scavenging sulfite electrolyte. The capability to deposit conformal bismuth vanadates will enable a new generation of nanocomposite architectures for solar water splitting.

  2. Oxygen-free atomic layer deposition of indium sulfide.

    Science.gov (United States)

    McCarthy, Robert F; Weimer, Matthew S; Emery, Jonathan D; Hock, Adam S; Martinson, Alex B F

    2014-08-13

    Atomic layer deposition (ALD) of indium sulfide (In2S3) films was achieved using a newly synthesized indium precursor and hydrogen sulfide. We obtain dense and adherent thin films free from halide and oxygen impurities. Self-limiting half-reactions are demonstrated at temperatures up to 225 °C, where oriented crystalline thin films are obtained without further annealing. Low-temperature growth of 0.89 Å/cycle is observed at 150 °C, while higher growth temperatures gradually reduce the per-cycle growth rate. Rutherford backscattering spectroscopy (RBS) together with depth-profiling Auger electron spectroscopy (AES) reveal a S/In ratio of 1.5 with no detectable carbon, nitrogen, halogen, or oxygen impurities. The resistivity of thin films prior to air exposure decreases with increasing deposition temperature, reaching In2S3 via ALD at temperatures up to 225 °C may allow high quality thin films to be leveraged in optoelectronic devices including photovoltaic absorbers, buffer layers, and intermediate band materials.

  3. Atomic layer deposition of TiO{sub 2}

    Energy Technology Data Exchange (ETDEWEB)

    Tallarida, Massimo; Dessmann, Nils; Staedter, Matthias; Friedrich, Daniel; Michling, Marcel; Schmeisser, Dieter [BTU-Cottbus, Konrad-Wachsmann-Allee 17, 03046 Cottbus (Germany)

    2011-07-01

    We present a study of the initial growth of TiO{sub 2} on Si(111) by atomic layer deposition (ALD). The Si substrate was etched with NH{sub 4}F before ALD to remove the native oxide film and to produce a Si-H termination. In-situ experiments by means of photoemission and X-ray absorption spectroscopy were conducted with synchrotron radiation on Ti-oxide films produced using Ti-tetra-iso-propoxide (TTIP) and water as precursors. O 1s, Ti 2p, C 1s, and S i2p core level, and O 1s and Ti 2p absorption edges show the transition of the Ti-oxide properties during the first layers. The growth starts with a very small growth rate (0.03 nm/cycle) due to the growth inhibition of the Si-H termination and proceeds with higher growth rate (0.1 nm/cycle) after 1.5 nm Ti-oxide has been deposited.

  4. Very high frequency plasma reactant for atomic layer deposition

    Science.gov (United States)

    Oh, Il-Kwon; Yoo, Gilsang; Yoon, Chang Mo; Kim, Tae Hyung; Yeom, Geun Young; Kim, Kangsik; Lee, Zonghoon; Jung, Hanearl; Lee, Chang Wan; Kim, Hyungjun; Lee, Han-Bo-Ram

    2016-11-01

    Although plasma-enhanced atomic layer deposition (PE-ALD) results in several benefits in the formation of high-k dielectrics, including a low processing temperature and improved film properties compared to conventional thermal ALD, energetic radicals and ions in the plasma cause damage to layer stacks, leading to the deterioration of electrical properties. In this study, the growth characteristics and film properties of PE-ALD Al2O3 were investigated using a very-high-frequency (VHF) plasma reactant. Because VHF plasma features a lower electron temperature and higher plasma density than conventional radio frequency (RF) plasma, it has a larger number of less energetic reaction species, such as radicals and ions. VHF PE-ALD Al2O3 shows superior physical and electrical properties over RF PE-ALD Al2O3, including high growth per cycle, excellent conformality, low roughness, high dielectric constant, low leakage current, and low interface trap density. In addition, interlayer-free Al2O3 on Si was achieved in VHF PE-ALD via a significant reduction in plasma damage. VHF PE-ALD will be an essential process to realize nanoscale devices that require precise control of interfaces and electrical properties.

  5. Kinetic limitation of chemical ordering in Bi2Te3-x Se x layers grown by molecular beam epitaxy.

    Science.gov (United States)

    Schreyeck, S; Brunner, K; Kirchner, A; Bass, U; Grauer, S; Schumacher, C; Gould, C; Karczewski, G; Geurts, J; Molenkamp, L W

    2016-04-13

    We study the chemical ordering in Bi2Te3-x Se x grown by molecular beam epitaxy on Si substrates. We produce films in the full composition range from x = 0 to 3, and determine their material properties using energy dispersive x-ray spectroscopy, x-ray diffraction and Raman spectroscopy. By fitting the parameters of a kinetic growth model to these results, we obtain a consistent description of growth at a microscopic level. Our main finding is that despite the incorporation of Se in the central layer being much more probable than that of Te, the formation of a fully ordered Te-Bi-Se-Bi-Te layer is prevented by kinetic of the growth process. Indeed, the Se concentration in the central layer of Bi2Te2Se1 reaches a maximum of only ≈ 75% even under ideal growth conditions. A second finding of our work is that the intensity ratio of the 0 0 12 and 0 0 6 x-ray reflections serves as an experimentally accessible quantitative measure of the degree of ordering in these films.

  6. Thermal stability of SrRuO{sub 3} epitaxial layers under forming-gas anneal

    Energy Technology Data Exchange (ETDEWEB)

    Halley, D.; Rossel, C.; Widmer, D.; Wolf, H.; Gariglio, S

    2004-06-15

    Perovskite SrRuO{sub 3} films are promising candidates as metallic electrodes in high-permittivity (high k) capacitors and possibly in fully epitaxial CMOS stacks. The thermal stability of SrRuO{sub 3} during forming-gas (FG) anneal is an important requirement and is investigated here by in situ X-ray diffraction (XRD) and electrical resistivity measurements. A weak and smooth increase of the resistivity is observed above 300 deg. C and is attributed to the effect of hydrogen diffusion. It is followed by a sharp transition at 500 deg. C into a highly resistive state due to the decomposition of the SrRuO{sub 3}. We found that the addition of about 1% O{sub 2} in the FG prevents both the onset of resistivity at 300 deg. C and the decomposition of the oxide.

  7. Structural properties of relaxed thin film germanium layers grown by low temperature RF-PECVD epitaxy on Si and Ge (100) substrates

    Energy Technology Data Exchange (ETDEWEB)

    Cariou, R., E-mail: romain.cariou@polytechnique.edu [LPICM-CNRS, Ecole Polytechnique, 91128, Palaiseau (France); III-V lab a joint laboratory between Alcatel-Lucent Bell Labs France, Thales Research and Technology and CEA-LETI, route de Nozay, 91460, Marcoussis, France. (France); Ruggeri, R. [LPICM-CNRS, Ecole Polytechnique, 91128, Palaiseau (France); CNR-IMM, strada VIII n°5, zona industriale, 95121, Catania (Italy); Tan, X.; Nassar, J.; Roca i Cabarrocas, P. [LPICM-CNRS, Ecole Polytechnique, 91128, Palaiseau (France); Mannino, Giovanni [CNR-IMM, strada VIII n°5, zona industriale, 95121, Catania (Italy)

    2014-07-15

    We report on unusual low temperature (175 °C) heteroepitaxial growth of germanium thin films using a standard radio-frequency plasma process. Spectroscopic ellipsometry and transmission electron microscopy (TEM) reveal a perfect crystalline quality of epitaxial germanium layers on (100) c-Ge wafers. In addition direct germanium crystal growth is achieved on (100) c-Si, despite 4.2% lattice mismatch. Defects rising from Ge/Si interface are mostly located within the first tens of nanometers, and threading dislocation density (TDD) values as low as 10{sup 6} cm{sup −2} are obtained. Misfit stress is released fast: residual strain of −0.4% is calculated from Moiré pattern analysis. Moreover we demonstrate a striking feature of low temperature plasma epitaxy, namely the fact that crystalline quality improves with thickness without epitaxy breakdown, as shown by TEM and depth profiling of surface TDD.

  8. Conductivity of epitaxial and CVD graphene with correlated line defects

    DEFF Research Database (Denmark)

    Radchenko, T. M.; Shylau, Artsem; Zozoulenko, I. V.

    2014-01-01

    Transport properties of single-layer graphene with correlated one-dimensional defects are studied theoretically using the computational model within the time-dependent real-space Kubo-Greenwood formalism. Such defects are present in epitaxial graphene, comprising atomic terraces and steps due to ...

  9. Characterization of hafnium oxide resistive memory layers deposited on copper by atomic layer deposition

    Energy Technology Data Exchange (ETDEWEB)

    Briggs, B.D.; Bishop, S.M. [SUNY College of Nanoscale Science and Engineering, 255 Fuller Road, Albany, NY 12203 (United States); Leedy, K.D. [Air Force Research Laboratory, 2241 Avionics Circle, Wright Patterson Air Force Base, Dayton, OH 45433 (United States); Cady, N.C., E-mail: ncady@albany.edu [SUNY College of Nanoscale Science and Engineering, 255 Fuller Road, Albany, NY 12203 (United States)

    2014-07-01

    Hafnium oxide-based resistive memory devices have been fabricated on copper bottom electrodes. The HfO{sub x} active layers in these devices were deposited by atomic layer deposition (ALD) at 250 °C with tetrakis(dimethylamido)hafnium(IV) as the metal precursor and an O{sub 2} plasma as the reactant. Depth profiles of the HfO{sub x} by X-ray photoelectron spectroscopy and secondary ion mass spectroscopy revealed a copper concentration on the order of five atomic percent throughout the HfO{sub x} film. In addition to the Cu doped HfO{sub x}, a thin layer (20 nm) of Cu{sub x}O is present at the surface. This surface layer is believed to have formed during the ALD process, and greatly complicates the analysis of the switching mechanism. The resistive memory structures fabricated from the ALD HfO{sub x} exhibited non-polar resistive switching, independent of the top metal electrode (Ni, Pt, Al, Au). Resistive switching current voltage (I–V) curves were analyzed using Schottky emission and ionic hopping models to gain insight into the physical mechanisms underpinning the device behavior. During the forming process it was determined that, at voltages in excess of 2.5 V, an ionic hopping model is in good agreement with the I–V data. The extracted ion hopping distance ∼ 4 Å was within the range of interatomic spacing of HfO{sub 2} during the forming process consistent with ionic motion of Cu{sup 2+} ions. Lastly the on state I–V data was dominated at larger voltages by Schottky emission with an estimated barrier height of ∼ 0.5 eV and a refractive index of 2.59. The consequence of the Schottky emission analysis indicates the on state resistance to be a product of a Pt/Cu{sub 2}O/Cu filament(s)/Cu{sub 2}O/Cu structure. - Highlights: • HfO{sub 2} was grown via atomic layer deposition at 250 and 100 °C on Cu substrates. • A Cu{sub 2}O surface layer and Cu doping were observed in post-deposition of HfO{sub 2}. • Resistive memory devices were fabricated and

  10. Room-temperature selective epitaxial growth of CoO (1 1 1) and Co{sub 3}O{sub 4} (1 1 1) thin films with atomic steps by pulsed laser deposition

    Energy Technology Data Exchange (ETDEWEB)

    Matsuda, Akifumi, E-mail: matsuda.a.aa@m.titech.ac.jp [Department of Innovative and Engineered Materials, Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology, 4259-J3-16 Nagatsuta, Midori, Yokohama 226-8502 (Japan); Yamauchi, Ryosuke; Shiojiri, Daishi; Tan, Geng [Department of Innovative and Engineered Materials, Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology, 4259-J3-16 Nagatsuta, Midori, Yokohama 226-8502 (Japan); Kaneko, Satoru [Department of Innovative and Engineered Materials, Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology, 4259-J3-16 Nagatsuta, Midori, Yokohama 226-8502 (Japan); Kanagawa Industrial Technology Center, 705-1 Shimoimaizumi, Ebina, Kanagawa 243-0435 (Japan); Yoshimoto, Mamoru [Department of Innovative and Engineered Materials, Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology, 4259-J3-16 Nagatsuta, Midori, Yokohama 226-8502 (Japan)

    2015-09-15

    Highlights: • Epitaxial CoO (1 1 1) and Co{sub 3}O{sub 4} (1 1 1) thin films were grown at room temperature (RT). • The CoO and Co{sub 3}O{sub 4} phases were selectively epitaxied by modifying the O{sub 2} atmosphere. • Ultra-smooth surfaces were obtained on the thin films suppressing grain coarsening. • Effect of RT-epitaxy on structures of the films such as lattice strain is presented. • Optical bandgaps consistent with past reports were obtained even by the growth at RT. - Abstract: Cobalt oxide epitaxial thin films of both rock-salt CoO and spinel Co{sub 3}O{sub 4} were selectively synthesized on atomically stepped α-Al{sub 2}O{sub 3} (0 0 0 1) substrates at room temperature under well-controlled oxygen pressures by pulsed laser deposition. X-ray diffraction and reflection high-energy electron diffraction analyses demonstrated that the CoO and Co{sub 3}O{sub 4} films were grown with phase control and good epitaxial quality at room temperature (20 °C). The CoO (1 1 1) film was obtained in ultra-high vacuum of 1 × 10{sup −8} Torr, while the Co{sub 3}O{sub 4} (1 1 1) film was grown in 1 × 10{sup −2} Torr of O{sub 2}. X-ray reciprocal space mapping results indicated that the in-plane mismatches of the {1 = 10} planes of CoO (1 1 1) and Co{sub 3}O{sub 4} (1 1 1) films with the substrate were 4.5% and 2.5%, respectively. The films were almost entirely relaxed with ratios of expansion less than ±2%; the films underwent slight elongation along the [1 1 1] axis and shrinkage in the (1 1 1) plane. The surfaces of the as-grown CoO and Co{sub 3}O{sub 4} thin films revealed atomic steps reflective of those on the substrates. Their root-mean-square roughness values were about 0.1 nm indicating suppressed grain growth on the substrates at room temperature. The optical bandgap of the epitaxial CoO (1 1 1) film was estimated to be 2.72 eV accompanied with a broad absorption attributable to non-stoichiometry or d-d transition. The bandgap of the Co{sub 3}O

  11. Characteristics of Spontaneous Emission of Polarized Atoms in Metal-Dielectric Multiple Layer Structures

    Institute of Scientific and Technical Information of China (English)

    ZHAO Li-Ming; GU Ben-Yuan; ZHOU Yun-Song

    2007-01-01

    The spontaneous emission (SE) progress of polarized atoms in a stratified structure ofair-dielectric(D0)-metal(M)-dielectric(D1)-air can be controlled effectively by changing the thickness of the D1 layer and rotating the polarized direction of atoms. It is found that the normalized SE rate of atoms located inside the D0 layer crucially depends on the atomic position and the thickness of the D1 layer. When the atom is located near the D0-M interface, the normalized atomic SE rate as a function of the atomic position is abruptly onset for the thin D1 layer. However, with the increasing thickness of the D1 layer, the corresponding curve profile exhibits plateau and stays nearly unchanged. The substantial change of the SE rate stems from the excitation of the surface plasmon polaritons in metal-dielectric interface, and the feature crucially depends on the thickness of D1 layer. If atoms are positioned near the D0-air interface, the substantial variation of the normalized SE rate appears when rotating the polarized direction of atoms. These findings manifest that the atomic SE processes can be flexibly controlled by altering the thickness of the dielectric layer D1 or rotating the orientation of the polarization of atoms.

  12. Strain-induced single-domain growth of epitaxial SrRuO3 layers on SrTiO3: A high-temperature x-ray diffraction study

    NARCIS (Netherlands)

    Vailionis, Arturas; Siemons, Wolter; Koster, Gertjan

    2007-01-01

    Temperature dependent structural phase transitions of SrRuO3 thin films epitaxially grown on SrTiO3(001) single crystal substrates have been studied using high-resolution x-ray diffraction. In contrast to bulk SrRuO3, coherently strained epitaxial layers do not display cubic symmetry up to ∼ 730 °C

  13. Si(111)衬底上多层石墨烯薄膜的外延生长%Epitaxial Growth of Multi-layer Graphene on the Substrate of Si(111)

    Institute of Scientific and Technical Information of China (English)

    李利民; 唐军; 康朝阳; 潘国强; 闫文盛; 韦世强; 徐彭寿

    2011-01-01

    Graphene thin films were epitaxial grown on Si(111) substrates by depositing carbon atoms with solid source molecular beam epitaxy (SSMBE). The structural properties of the samples deposited at different substrate temperature (400, 600, 700 and 800℃) were investigated by reflection high energy electron diffraction (RHEED),Fourier transform infrared spectroscope (FTIR), Raman spectroscope (RAMAN) and near-edge X-ray absorption fine-structure (NEXAFS). RAMAN and NEXAFS results indicated that the thin film deposited at 800℃ exhibited the characteristic of graphene, while the thin films deposited at 400℃, 600℃ and 700℃ were attributed to amorphous or polycrystalline carbon thin films. RHEED and FTIR results indicated that C atoms did not bond with Si atoms at the substrate temperature below 600℃, however, above 700℃, C atoms reacted with Si atoms and formed the SiC buffer layer. Furthermore, the better quality of SiC buffer layer could be obtained at 800℃. Thus, high substrate temperature and high-quality SiC buffer layers are essential to the formation of the graphene layers on the Si substrates.%利用固源分子束外延(SSMBE)技术,在Si(111)衬底上沉积碳原子外延生长石墨烯薄膜,通过反射式高能电子衍射(RHEED)、红外吸收谱(FTIR)、拉曼光谱(RAMAN)和X射线吸收精细结构谱(NEXAFS)等手段对不同衬底温度(400、600、700、800℃)生长的薄膜进行结构表征.RAMAN和NEXAFS结果表明:在800℃下制备的薄膜具有石墨烯的特征,而400、600和700℃生长的样品为非晶或多晶碳薄膜.RHEED和FTIR结果表明,沉积温度在600℃以下时C原子和衬底Si原子没有成键,而衬底温度提升到700℃以上,沉积的C原子会先和衬底Si原子反应形成SiC缓冲层,且在800℃沉积时缓冲层质量较好.因此在Si衬底上制备石墨烯薄膜需要较高的衬底温度和高质量的SiC缓冲层.

  14. Atomic structure of epitaxial graphene sidewall nanoribbons: flat graphene, miniribbons, and the confinement gap.

    Science.gov (United States)

    Palacio, Irene; Celis, Arlensiú; Nair, Maya N; Gloter, Alexandre; Zobelli, Alberto; Sicot, Muriel; Malterre, Daniel; Nevius, Meredith S; de Heer, Walt A; Berger, Claire; Conrad, Edward H; Taleb-Ibrahimi, Amina; Tejeda, Antonio

    2015-01-14

    Graphene nanoribbons grown on sidewall facets of SiC have demonstrated exceptional quantized ballistic transport up to 15 μm at room temperature. Angular-resolved photoemission spectroscopy (ARPES) has shown that the ribbons have the band structure of charge neutral graphene, while bent regions of the ribbon develop a bandgap. We present scanning tunneling microscopy and transmission electron microscopy of armchair nanoribbons grown on recrystallized sidewall trenches etched in SiC. We show that the nanoribbons consist of a single graphene layer essentially decoupled from the facet surface. The nanoribbons are bordered by 1-2 nm wide bent miniribbons at both the top and bottom edges of the nanoribbons. We establish that nanoscale confinement in the graphene miniribbons is the origin of the local large band gap observed in ARPES. The structural results presented here show how this gap is formed and provide a framework to help understand ballistic transport in sidewall graphene.

  15. Arsenic-doped high-resistivity-silicon epitaxial layers for integrating low-capacitance diodes

    NARCIS (Netherlands)

    Sakic, A.; Scholtes, T.L.M.; De Boer, W.B.; Golshani, N.; Derakhshandeh, J.; Nanver, L.K.

    2011-01-01

    An arsenic doping technique for depositing up to 40-μm-thick high-resistivity layers is presented for fabricating diodes with low RC constants that can be integrated in closely-packed configurations. The doping of the as-grown epi-layers is controlled down to 5 × 1011 cm−3, a value that is solely li

  16. Very high frequency plasma reactant for atomic layer deposition

    Energy Technology Data Exchange (ETDEWEB)

    Oh, Il-Kwon; Yoo, Gilsang; Yoon, Chang Mo [School of Electrical and Electronic Engineering, Yonsei University, Seoul 120-749 (Korea, Republic of); Kim, Tae Hyung; Yeom, Geun Young [Department of Advanced Materials Engineering, Sungkyunkwan University, Suwon 440-746 (Korea, Republic of); Kim, Kangsik; Lee, Zonghoon [School Materials Science and Engineering, Ulsan National Institute of Science and Technology (UNIST), Ulsan 44919 (Korea, Republic of); Jung, Hanearl; Lee, Chang Wan [School of Electrical and Electronic Engineering, Yonsei University, Seoul 120-749 (Korea, Republic of); Kim, Hyungjun, E-mail: hyungjun@yonsei.ac.kr [School of Electrical and Electronic Engineering, Yonsei University, Seoul 120-749 (Korea, Republic of); Lee, Han-Bo-Ram, E-mail: hbrlee@inu.ac.kr [Department of Materials Science and Engineering, Incheon National University, 406-840 Incheon (Korea, Republic of)

    2016-11-30

    Highlights: • Fundamental research plasma process for thin film deposition is presented. • VHF plasma source for PE-ALD Al{sub 2}O{sub 3} was employed to reduce plasma damage. • The use of VHF plasma improved all of the film qualities and growth characteristics. - Abstract: Although plasma-enhanced atomic layer deposition (PE-ALD) results in several benefits in the formation of high-k dielectrics, including a low processing temperature and improved film properties compared to conventional thermal ALD, energetic radicals and ions in the plasma cause damage to layer stacks, leading to the deterioration of electrical properties. In this study, the growth characteristics and film properties of PE-ALD Al{sub 2}O{sub 3} were investigated using a very-high-frequency (VHF) plasma reactant. Because VHF plasma features a lower electron temperature and higher plasma density than conventional radio frequency (RF) plasma, it has a larger number of less energetic reaction species, such as radicals and ions. VHF PE-ALD Al{sub 2}O{sub 3} shows superior physical and electrical properties over RF PE-ALD Al{sub 2}O{sub 3}, including high growth per cycle, excellent conformality, low roughness, high dielectric constant, low leakage current, and low interface trap density. In addition, interlayer-free Al{sub 2}O{sub 3} on Si was achieved in VHF PE-ALD via a significant reduction in plasma damage. VHF PE-ALD will be an essential process to realize nanoscale devices that require precise control of interfaces and electrical properties.

  17. Continuous production of nanostructured particles using spatial atomic layer deposition

    Energy Technology Data Exchange (ETDEWEB)

    Ommen, J. Ruud van, E-mail: j.r.vanommen@tudelft.nl; Kooijman, Dirkjan; Niet, Mark de; Talebi, Mojgan; Goulas, Aristeidis [Department of Chemical Engineering, Delft University of Technology, Julianalaan 136, 2628 BL Delft (Netherlands)

    2015-03-15

    In this paper, the authors demonstrate a novel spatial atomic layer deposition (ALD) process based on pneumatic transport of nanoparticle agglomerates. Nanoclusters of platinum (Pt) of ∼1 nm diameter are deposited onto titania (TiO{sub 2}) P25 nanoparticles resulting to a continuous production of an active photocatalyst (0.12–0.31 wt. % of Pt) at a rate of about 1 g min{sup −1}. Tuning the precursor injection velocity (10–40 m s{sup −1}) enhances the contact between the precursor and the pneumatically transported support flows. Decreasing the chemisorption temperature (from 250 to 100 °C) results in more uniform distribution of the Pt nanoclusters as it decreases the reaction rate as compared to the rate of diffusion into the nanoparticle agglomerates. Utilizing this photocatalyst in the oxidation reaction of Acid Blue 9 showed a factor of five increase of the photocatalytic activity compared to the native P25 nanoparticles. The use of spatial particle ALD can be further expanded to deposition of nanoclusters on porous, micron-sized particles and to the production of core–shell nanoparticles enabling the robust and scalable manufacturing of nanostructured powders for catalysis and other applications.

  18. High Gradient Accelerator Cavities Using Atomic Layer Deposition

    Energy Technology Data Exchange (ETDEWEB)

    Ives, Robert Lawrence [Calabazas Creek Research, Inc., San Mateo, CA (United States); Parsons, Gregory [North Carolina State Univ., Raleigh, NC (United States); Williams, Philip [North Carolina State Univ., Raleigh, NC (United States); Oldham, Christopher [North Carolina State Univ., Raleigh, NC (United States); Mundy, Zach [North Carolina State Univ., Raleigh, NC (United States); Dolgashev, Valery [SLAC National Accelerator Lab., Menlo Park, CA (United States)

    2014-12-09

    In the Phase I program, Calabazas Creek Research, Inc. (CCR), in collaboration with North Carolina State University (NCSU), fabricated copper accelerator cavities and used Atomic Layer Deposition (ALD) to apply thin metal coatings of tungsten and platinum. It was hypothesized that a tungsten coating would provide a robust surface more resistant to arcing and arc damage. The platinum coating was predicted to reduce processing time by inhibiting oxides that form on copper surfaces soon after machining. Two sets of cavity parts were fabricated. One was coated with 35 nm of tungsten, and the other with approximately 10 nm of platinum. Only the platinum cavity parts could be high power tested during the Phase I program due to schedule and funding constraints. The platinum coated cavity exhibit poor performance when compared with pure copper cavities. Not only did arcing occur at lower power levels, but the processing time was actually longer. There were several issues that contributed to the poor performance. First, machining of the base copper cavity parts failed to achieve the quality and cleanliness standards specified to SLAC National Accelerator Center. Secondly, the ALD facilities were not configured to provide the high levels of cleanliness required. Finally, the nanometer coating applied was likely far too thin to provide the performance required. The coating was ablated or peeled from the surface in regions of high fields. It was concluded that the current ALD process could not provide improved performance over cavities produced at national laboratories using dedicated facilities.

  19. Synthesis of platinum nanoparticle electrocatalysts by atomic layer deposition

    Science.gov (United States)

    Lubers, Alia Marie

    Demand for energy continues to increase, and without alternatives to fossil fuel combustion the effects on our environment will become increasingly severe. Fuel cells offer a promising improvement on current methods of energy generation; they are able to convert hydrogen fuel into electricity with a theoretical efficiency of up to 83% and interface smoothly with renewable hydrogen production. Fuel cells can replace internal combustion engines in vehicles and are used in stationary applications to power homes and businesses. The efficiency of a fuel cell is maximized by its catalyst, which is often composed of platinum nanoparticles supported on carbon. Economical production of fuel cell catalysts will promote adoption of this technology. Atomic layer deposition (ALD) is a possible method for producing catalysts at a large scale when employed in a fluidized bed. ALD relies on sequential dosing of gas-phase precursors to grow a material layer by layer. We have synthesized platinum nanoparticles on a carbon particle support (Pt/C) by ALD for use in proton exchange membrane fuel cells (PEMFCs) and electrochemical hydrogen pumps. Platinum nanoparticles with different characteristics were deposited by changing two chemistries: the carbon substrate through functionalization; and the deposition process by use of either oxygen or hydrogen as ligand removing reactants. The metal depositing reactant was trimethyl(methylcyclopentadienyl)platinum(IV). Functionalizing the carbon substrate increased nucleation during deposition resulting in smaller and more dispersed nanoparticles. Use of hydrogen produced smaller nanoparticles than oxygen, due to a gentler hydrogenation reaction compared to using oxygen's destructive combustion reaction. Synthesized Pt/C materials were used as catalysts in an electrochemical hydrogen pump, a device used to separate hydrogen fuel from contaminants. Catalysts deposited by ALD on functionalized carbon using a hydrogen chemistry were the most

  20. The mechanical robustness of atomic-layer- and molecular-layer-deposited coatings on polymer substrates

    Science.gov (United States)

    Miller, David C.; Foster, Ross R.; Zhang, Yadong; Jen, Shih-Hui; Bertrand, Jacob A.; Lu, Zhixing; Seghete, Dragos; O'Patchen, Jennifer L.; Yang, Ronggui; Lee, Yung-Cheng; George, Steven M.; Dunn, Martin L.

    2009-05-01

    The mechanical robustness of atomic layer deposited alumina and recently developed molecular layer deposited aluminum alkoxide ("alucone") films, as well as laminated composite films composed of both materials, was characterized using mechanical tensile tests along with a recently developed fluorescent tag to visualize channel cracks in the transparent films. All coatings were deposited on polyethylene naphthalate substrates and demonstrated a similar evolution of damage morphology according to applied strain, including channel crack initiation, crack propagation at the critical strain, crack densification up to saturation, and transverse crack formation associated with buckling and delamination. From measurements of crack density versus applied tensile strain coupled with a fracture mechanics model, the mode I fracture toughness of alumina and alucone films was determined to be KIC=1.89±0.10 and 0.17±0.02 MPa m0.5, respectively. From measurements of the saturated crack density, the critical interfacial shear stress was estimated to be τc=39.5±8.3 and 66.6±6.1 MPa, respectively. The toughness of nanometer-scale alumina was comparable to that of alumina thin films grown using other techniques, whereas alucone was quite brittle. The use of alucone as a spacer layer between alumina films was not found to increase the critical strain at fracture for the composite films. This performance is attributed to the low toughness of alucone. The experimental results were supported by companion simulations using fracture mechanics formalism for multilayer films. To aid future development, the modeling method was used to study the increase in the toughness and elastic modulus of the spacer layer required to render improved critical strain at fracture. These results may be applied to a broad variety of multilayer material systems composed of ceramic and spacer layers to yield robust coatings for use in chemical barrier and other applications.

  1. Properties of boron-doped epitaxial diamond layers grown on (110) oriented single crystal substrates

    OpenAIRE

    Mortet, Vincent; Pernot, J.; Jomard, F.; Soltani, A; Remes, Zdenek; Barjon, Julien; D'Haen, J; Haenen, Ken

    2015-01-01

    Boron doped diamond layers have been grown on (110) single crystal diamond substrates with B/C ratios up to 20 ppm in the gas phase. The surface of the diamond layers observed by scanning electron microscopy consists of (100) and (113) micro-facets. Fourier Transform Photocurrent Spectroscopy indicates substitutional boron incorporation. Electrical properties were measured using Hall effect from 150 to 1000 K. Secondary ion mass spectrometry analyses are consistent with the high incorporation...

  2. Atomic layer deposition of photoactive CoO/SrTiO3 and CoO/TiO2 on Si(001) for visible light driven photoelectrochemical water oxidation

    Science.gov (United States)

    Ngo, Thong Q.; Posadas, Agham; Seo, Hosung; Hoang, Son; McDaniel, Martin D.; Utess, Dirk; Triyoso, Dina H.; Buddie Mullins, C.; Demkov, Alexander A.; Ekerdt, John G.

    2013-08-01

    Cobalt oxide (CoO) films are grown epitaxially on Si(001) by atomic layer deposition (ALD) using a thin (1.6 nm) buffer layer of strontium titanate (STO) grown by molecular beam epitaxy. The ALD growth of CoO films is done at low temperature (170-180 °C), using cobalt bis(diisopropylacetamidinate) and water as co-reactants. Reflection high-energy electron diffraction, X-ray diffraction, and cross-sectional scanning transmission electron microscopy are performed to characterize the crystalline structure of the films. The CoO films are found to be crystalline as-deposited even at the low growth temperature with no evidence of Co diffusion into Si. The STO-buffered Si (001) is used as a template for ALD growth of relatively thicker epitaxial STO and TiO2 films. Epitaxial and polycrystalline CoO films are then grown by ALD on the STO and TiO2 layers, respectively, creating thin-film heterostructures for photoelectrochemical testing. Both types of heterostructures, CoO/STO/Si and CoO/TiO2/STO/Si, demonstrate water photooxidation activity under visible light illumination. In-situ X-ray photoelectron spectroscopy is used to measure the band alignment of the two heterojunctions, CoO/STO and CoO/TiO2. The experimental band alignment is compared to electronic structure calculations using density functional theory.

  3. Fabrication and Properties of Organic-Inorganic Nanolaminates Using Molecular and Atomic Layer Deposition Techniques

    Science.gov (United States)

    2012-02-01

    55, 1030-1039 (2009).* 2. B.B. Burton, D.N. Goldstein and S.M. George, "Atomic Layer Deposition of MgO Using Bis(ethylcyclopentadienyl) magnesium ...Atomic Layer Deposition Using Tin 2,4-Pentanedionate and Hydrogen Sulfide , J. Phys. Chem. C 114, 17597-17603 (2010).* 28. L.A. Riley, A.S

  4. Aqueous phase synthesis of upconversion nanocrystals through layer-by-layer epitaxial growth for in vivo X-ray computed tomography

    KAUST Repository

    Li, Feifei

    2013-05-21

    Lanthanide-doped core-shell upconversion nanocrystals (UCNCs) have tremendous potential for applications in many fields, especially in bio-imaging and medical therapy. As core-shell UCNCs are mostly synthesized in organic solvents, tedious organic-aqueous phase transfer processes are usually needed for their use in bio-applications. Herein, we demonstrate the first example of one-step synthesis of highly luminescent core-shell UCNCs in the "aqueous" phase under mild conditions using innocuous reagents. A microwave-assisted approach allowed for layer-by-layer epitaxial growth of a hydrophilic NaGdF4 shell on NaYF4:Yb, Er cores. During this process, surface defects of the nanocrystals could be gradually passivated by the homogeneous shell deposition, resulting in obvious enhancement in the overall upconversion emission efficiency. In addition, the up-down conversion dual-mode luminescent NaYF4:Yb, Er@NaGdF4:Ce, Ln (Eu, Tb, Sm, Dy) nanocrystals were also synthesized to further validate the successful formation of the core-shell structure. More significantly, based on their superior solubility and stability in water solution, high upconversion efficiency and Gd-doped predominant X-ray absorption, the as-prepared NaYF4:Yb, Er@NaGdF4 core-shell UCNCs exhibited high contrast in in vitro cell imaging and in vivo X-ray computed tomography (CT) imaging, demonstrating great potential as multiplexed luminescent biolabels and CT contrast agents.

  5. Atomic layer deposition of copper and copper silver films using an electrochemical process

    Energy Technology Data Exchange (ETDEWEB)

    Fang, J.S., E-mail: jsfang@nfu.edu.tw [Department of Materials Science and Engineering, National Formosa University, Huwei 63201, Taiwan (China); Liu, Y.S. [Department of Materials Science and Engineering, National Formosa University, Huwei 63201, Taiwan (China); Chin, T.S. [Department of Materials Science and Engineering, Feng Chia University, Taichung 40724, Taiwan (China)

    2015-04-01

    This paper describes the formation and properties of Cu and Cu(Ag) films on a Ru/Si substrate using electrochemical atomic layer deposition. The process was performed layer-by-layer using underpotential deposition (UPD) and surface-limited redox reactions. The first Cu atomic layer was deposited on the Ru/Si substrate via UPD. Using UPD, atomic layered of Pb, which acts as a sacrificial layer, was applied on the Cu layer. Then, a Cu{sup 2+} solution was flushed into the cell at an open-circuit potential, and the Pb layer was exchanged for Cu via redox replacements. The above sequences were repeated 500 times to form a Cu film. The Cu(Ag) alloy films were formed using Cu–UPD and Ag–UPD in predetermined sequences. The lowest electrical resistivity achieved was 3.6 and 2.2 μΩ cm for the Cu film and Cu(Ag) film, respectively, after annealing at 400 °C. Due to the self-limiting reactions, the process has the ability to deposit atomic layers to meet the requirement of Cu interconnects. - Highlights: • Layer-by-layer growth of Cu and Cu(Ag) films are prepared using electrochemical atomic layer deposition. • Cu coverage is from 0.33 to 0.51 ML for each deposition cycle in different NaCl concentrations. • The process can be applied in Cu interconnections.

  6. GaAs Solar Cells Grown by Hydride Vapor-Phase Epitaxy and the Development of GaInP Cladding Layers

    Energy Technology Data Exchange (ETDEWEB)

    Simon, John; Schulte, Kevin L.; Young, David L.; Haegel, Nancy M.; Ptak, Aaron J.

    2016-01-01

    The high cost of high-efficiency III-V photovoltaic devices currently limits them to niche markets. Hydride vapor-phase epitaxy (HVPE) growth of III-V materials recently reemerged as a low-cost, high-throughput alternative to conventional metal- organic vapor-phase epitaxy (MOVPE) growth of high-efficiency solar cells. Previously, we demonstrated unpassivated HVPEgrown GaAs p-n junctions with good quantum efficiency and high open-circuit voltage (Voc). In this work, we demonstrate the growth of GaInPby HVPE for use as a high-quality surface passivation layer to GaAs solar cells. Solar cells grown with GaInP window layers show significantly improved quantum efficiency compared with unpassivated cells, increasing the short-circuit current (JSC) of these low-cost devices. These results show the potential of low-cost HVPE for the growth of high-quality III-V devices.

  7. Microscopic potential fluctuations in Si-doped AlGaN epitaxial layers with various AlN molar fractions and Si concentrations

    Energy Technology Data Exchange (ETDEWEB)

    Kurai, Satoshi, E-mail: kurai@yamaguchi-u.ac.jp; Yamada, Yoichi [Department of Material Science and Engineering, Yamaguchi University, 2-16-1 Tokiwadai, Ube, Yamaguchi 755-8611 (Japan); Miyake, Hideto; Hiramatsu, Kazumasa [Department of Electrical and Electronic Engineering, Mie University, 1577 Kurimamachiya, Tsu, Mie 514-8507 (Japan)

    2016-01-14

    Nanoscopic potential fluctuations of Si-doped AlGaN epitaxial layers with the AlN molar fraction varying from 0.42 to 0.95 and Si-doped Al{sub 0.61}Ga{sub 0.39}N epitaxial layers with Si concentrations of 3.0–37 × 10{sup 17 }cm{sup −3} were investigated by cathodoluminescence (CL) imaging combined with scanning electron microscopy. The spot CL linewidths of AlGaN epitaxial layers broadened as the AlN molar fraction was increased to 0.7, and then narrowed at higher AlN molar fractions. The experimental linewidths were compared with the theoretical prediction from the alloy broadening model. The trends displayed by our spot CL linewidths were consistent with calculated results at AlN molar fractions of less than about 0.60, but the spot CL linewidths were markedly broader than the calculated linewidths at higher AlN molar fractions. The dependence of the difference between the spot CL linewidth and calculated line broadening on AlN molar fraction was found to be similar to the dependence of reported S values, indicating that the vacancy clusters acted as the origin of additional line broadening at high AlN molar fractions. The spot CL linewidths of Al{sub 0.61}Ga{sub 0.39}N epitaxial layers with the same Al concentration and different Si concentrations were nearly constant in the entire Si concentration range tested. From the comparison of reported S values, the increase of V{sub Al} did not contribute to the linewidth broadening, unlike the case of the V{sub Al} clusters.

  8. Low-temperature liquid-phase epitaxy and optical waveguiding of rare-earth-ion-doped $KY(WO_{4})_{2}$ thin layers

    NARCIS (Netherlands)

    Romanyuk, Y.E.; Utke, I.; Ehrentraut, D.; Apostolopoulos, V.; Pollnau, M.; Garcia-Revilla, S.; Valiente, B.

    2004-01-01

    Crystalline $KY(WO_{4})_{2}$ thin layers doped with different rare-earth ions were grown on b-oriented, undoped $KY(WO_{4})_{2}$ substrates by liquid-phase epitaxy employing a low-temperature flux. The ternary chloride mixture of NaCl, KCl, and CsCl with a melting point of 480°C was used as a solven

  9. Growth of Y3Fe5O12/GaN layers by laser molecular-beam epitaxy and characterization of their structural and magnetic properties

    Science.gov (United States)

    Kaveev, A. K.; Bursian, V. E.; Gastev, S. V.; Krichevtsov, B. B.; Suturin, S. M.; Volkov, M. P.; Sokolov, N. S.

    2016-12-01

    Laser molecular-beam epitaxy has been employed to obtain layers of yttrium-iron garnet (YIG) Y3Fe5O12 on gallium nitride substrates. It was found that there exists a polycrystalline YIG phase without admixtures of other structural phases. A magnetic anisotropy of films of the "easy-magnetic plane" type was found. The gyromagnetic ratio and the demagnetizing field 4π M S were calculated.

  10. Recombination-current suppression in GaAs p-n junctions grown on AlGaAs buffer layers by molecular-beam epitaxy

    Science.gov (United States)

    Rancour, D. P.; Melloch, M. R.; Pierret, R. F.; Lundstrom, M. S.; Klausmeier-Brown, M. E.; Kyono, C. S.

    1987-08-01

    n+pp+GaAs and n+pP+ GaAs/GaAs/Al0.3Ga0.7As mesa diodes have been fabricated from films grown by molecular-beam epitaxy. The diodes made from films employing an AlGaAs buffer layer show marked improvements (a factor of 5 reduction) in recombination current densities. Deep level transient spectroscopy measurements moreover indicate that deep level concentrations are reduced by the AlGaAs buffer.

  11. Resonant Raman Study Of ZnSe Epitaxial Layers Grown On GaAs Substrates

    Science.gov (United States)

    Djibladze, Merab I.; Dorosh, I. I.; Zlenko, A. A.; Kekelidze, George N.; Pashinin, Vladimir P.; Prokhorov, Kirill A.

    1989-05-01

    Quantitative difference between Raman and resonant Raman scattering spectra of thin ZnSe layers on GaAs substrates is presented. The dynamics of changing of Raman scattering properties while shortenning the exciting light wavelength for ZnSe/GaAs heterojunction is given. The difference in polarization spectra is demonstrated.

  12. Anelasticity of GaN Epitaxial Layer in GaN LED

    Science.gov (United States)

    Chung, C. C.; Yang, C. T.; Liu, C. Y.

    2016-10-01

    In this work, the anelasticity of the GaN layer in the GaN light-emitting-diode device was studied. The present results show that the forward-voltage of GaN LED increases with time, as the GaN light-emitting-diode was maintained at a constant temperature of 100 °C. We found that the increase of the forward-voltage with time attributes to the delay-response of the piezoelectric fields (internal electrical fields in GaN LED device). And, the delay-response of the internal electrical fields with time is caused by the anelasticity (time-dependent strain) of the GaN layer. Therefore, using the correlation of strain-piezoelectric-forward voltage, a plot of thermal strain of the GaN layer against time can be obtained by measuring the forward-voltage of the studied GaN LED against time. With the curves of the thermal strain of GaN epi-layers versus time, the anelasticity of the GaN compound can be studied. The key anelasticity parameter, characteristic relaxation time, of the GaN is defined to be 2623.76 min in this work.

  13. GaN layers with different polarities prepared by radio frequency molecular beam epitaxy and characterized by Raman scattering

    Institute of Scientific and Technical Information of China (English)

    Zhong Fei; Li Xin-Hua; Qiu Kai; Yin Zhi-Jun; Ji Chang-Jian; Cao Xian-Cun; Han Qi-Feng; Chen Jia-Rong; Wang Yu-Qi

    2007-01-01

    GaN layers with different polarities have been prepared by radio-frequency molecular beam epitaxy (RF-MBE) and characterized by Raman scattering. Polarity control are realized by controlling Al/N flux ratio during high temperature AlN buffer growth. The Raman results illustrate that the N-polarity GaN films have frequency shifts at A1(LO) mode because of their high carrier density; the forbidden A1 (TO) mode occurs for mixed-polarity GaN films due to the destroyed translation symmetry by inversion domain boundaries (IDBS); Raman spectra for Ga-polarity GaN films show that they have neither frequency shifts mode nor forbidden mode. These results indicate that Ga-polarity GaN films have a better quality, and they are in good agreement with the results obtained from the room temperature Hall mobility. The best values of Ga-polarity GaN films are 1042 cm2/Vs with a carrier density of 1.0×1017 cm-3.

  14. Schottky barrier detectors on 4H-SiC n-type epitaxial layer for alpha particles

    Energy Technology Data Exchange (ETDEWEB)

    Chaudhuri, S.K.; Krishna, R.M.; Zavalla, K.J. [Department of Electrical Engineering, University of South Carolina, Columbia, SC 29208 (United States); Mandal, K.C., E-mail: mandalk@cec.sc.edu [Department of Electrical Engineering, University of South Carolina, Columbia, SC 29208 (United States)

    2013-02-11

    Schottky barrier detectors have been fabricated on 50 μm n-type 4H-SiC epitaxial layers grown on 360 μm SiC substrates by depositing ∼10 nm nickel contact. Current–voltage (I–V) and capacitance–voltage (C–V) measurements were carried out to investigate the Schottky barrier properties. The detectors were evaluated for alpha particle detection using a {sup 241}Am alpha source. An energy resolution of ∼2.7% was obtained with a reverse bias of 100 V for 5.48 MeV alpha particles. The measured charge collection efficiency (CCE) was seen to vary as a function of bias voltage following a minority carrier diffusion model. Using this model, a diffusion length of∼3.5 μm for holes was numerically calculated from the CCE vs. bias voltage plot. Rise-time measurements of digitally recorded charge pulses for the 5.48 MeV alpha particles showed a presence of two sets of events having different rise-times at a higher bias of 200 V. A biparametric correlation scheme was successfully implemented for the first time to visualize the correlated pulse-height distribution of the events with different rise-times. Using the rise-time measurements and the biparametric plots, the observed variation of energy resolution with applied bias was explained.

  15. Epitaxial Growth of MOF Thin Film for Modifying the Dielectric Layer in Organic Field-Effect Transistors.

    Science.gov (United States)

    Gu, Zhi-Gang; Chen, Shan-Ci; Fu, Wen-Qiang; Zheng, Qingdong; Zhang, Jian

    2017-03-01

    Metal-organic framework (MOF) thin films are important in the application of sensors and devices. However, the application of MOF thin films in organic field effect transistors (OFETs) is still a challenge to date. Here, we first use the MOF thin film prepared by a liquid-phase epitaxial (LPE) approach (also called SURMOFs) to modify the SiO2 dielectric layer in the OFETs. After the semiconductive polymer of PTB7-Th (poly[4,8-bis(5-(2-ethylhexyl)thiophene-2-yl)benzo[1,2-b:4,5-b']dithiophene-co-3-fluorothieno[3,4-b]thiophene-2-carboxylate]) was coated on MOF/SiO2 and two electrodes on the semiconducting film were deposited sequentially, MOF-based OFETs were fabricated successfully. By controlling the LPE cycles of SURMOF HKUST-1 (also named Cu3(BTC)2, BTC = 1,3,5-benzenetricarboxylate), the performance of the HKUST-1/SiO2-based OFETs showed high charge mobility and low threshold voltage. This first report on the application of MOF thin film in OFETs will offer an effective approach for designing a new kind of materials for the OFET application.

  16. Multilayer epitaxial growth of lead phthalocyanine and C(70) using CuBr as a templating layer for enhancing the efficiency of organic photovoltaic cells.

    Science.gov (United States)

    Kim, Tae-Min; Shim, Hyun-Sub; Choi, Min-Soo; Kim, Hyo Jung; Kim, Jang-Joo

    2014-03-26

    The molecular orientation and crystallinity of donor and acceptor molecules are important for high-efficiency organic photovoltaic cells (OPVs) because they significantly influence both the absorption of light and charge-transport characteristics. We report that the templating effect extends to multilayers to increase the crystallinity and to modify the orientation of the crystals of lead phthalocyanine (PbPc) and C70 layers at the same time by adopting CuBr as a new templating layer on indium tin oxide (ITO). The formation of a monoclinic phase with a preferred orientation of (320) for PbPc and a fcc phase with a preferred orientation of (220) for C70 on the PbPc layer is revealed by X-ray diffraction (XRD) patterns. The multilayer epitaxy results in an increase of the exciton diffusion lengths from 5.6 to 8.8 nm for PbPc and from 6.9 to 13.8 nm for C70 to enhance the power conversion efficiency (PCE) of the planar heterojunction OPVs composed of PbPc and C70 from 1.4 to 2.3%. The quasi-epitaxy model is proposed to explain the multilayer epitaxy.

  17. Spatially Correlated Disorder in Epitaxial van der Waals Heterostructures

    Science.gov (United States)

    Laanait, Nouamane; Zhang, Zhan; Schleputz, Christian; Liu, Ying; Wojcik, Michael; Myers-Ward, Rachael; Gaskill, D. Kurt; Fenter, Paul; Li, Lian

    The structural cohesion of van der Waals (vdW) heterostructures relies upon a cooperative balance between strong intra-layer bonded interactions and weak inter-layer coupling. The confinement of extended defects to within a single vdW layer and competing interactions introduced by epitaxial constraints could generate fundamentally new structural disorders. Here we report on the presence of spatially correlated and localized disorder states that coexist with the near perfect crystallographic order along the growth direction of epitaxial vdW heterostructure of Bi2Se3/graphene/SiC grown by molecular beam epitaxy. With the depth penetration of hard X-ray diffraction microscopy and high-resolution surface scattering, we imaged local structural configurations from the atomic to mesoscopic length scales, and found that these disorder states result as a confluence of atomic scale modulations in the strength of vdW layer-layer interactions and nanoscale boundary conditions imposed by the substrate. These findings reveal a vast landscape of novel disorder states that can be manifested in epitaxial vdW heterostructures. Supported by the Wigner Fellowship program at Oak Ridge Nat'l Lab.

  18. Comparison of Epitaxial Growth Techniques for III-V Layer Structures

    Science.gov (United States)

    1992-05-22

    FOR Ill-V LAYER STRUCTURES DTIC byS ELECTE G. B. STRINGFELLOW MAY 2 819S2 A Prepared for Publication in the Proceedings of croissance de cristaux et de...overall process. This very area, that has retarded the development of OMVPE, now provides a significant advantage relative to other, competing...having miscibility gaps, as discussed in the last paper.[22] Another major factor retarding the development of OMVPE has been the inability to escape

  19. A new approach to grow C-doped GaN thick epitaxial layers

    Energy Technology Data Exchange (ETDEWEB)

    Gogova, D.; Siche, D.; Albrecht, M.; Irmscher, K.; Rost, H.J.; Fornari, R. [Leibniz Institute for Crystal Growth, Max-Born-Strasse 2, 12489 Berlin (Germany); Rudko, G.Yu. [V. Lashkarev Institute of Semiconductors Physics, 03028 Kiev (Ukraine)

    2011-07-15

    In this study we employ a new method for growth of carbon-doped wurtzite crystalline GaN (GaN:C) based on vapour phase transport of Ga by the pseudohalide hydrogen cyanide HCN. GaN:C layers with a thicknesses from 10 to 100 {mu}m and up to 19 mm in size were grown from gallium melt and ammonia as feeding materials in a carbon-containing equipment. The properties of the GaN:C layers were characterized by low-temperature photoluminescence (LTPL), High-Resolution X-ray Diffraction (HRXRD), Secondary Ion Mass Spectrometry (SIMS) and room-temperature Hall effect and Raman spectroscopy measurements. HRXRD studies demonstrated good crystalline quality of the thick GaN layers (the Rocking curve FWHMs are 570 arcsec for the (0004) reflection and 561 arcsec for the (10-14) reflection for 10 {mu}m thick samples). The LTPL and Raman spectroscopy confirmed the good optical and structural quality of the material. The carbon concentration measured by SIMS was 6x10{sup 18} cm{sup -3}, however, the room-temperature Hall effect experiments showed n-type conductivity. Carbon acceptor incorporation into GaN (from the transport agent) as well as the reason of its electrical overcompensation by unintentional impurities like oxygen and silicon is discussed. Ways of technological process improvement are proposed. (copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  20. Epitaxial growth of an antireflective, conductive, graded index ITO nanowire layer

    Directory of Open Access Journals (Sweden)

    Colm eO'Dwyer

    2013-10-01

    Full Text Available Nanoporous and nanostructured films, assemblies and arrangements are important from an applied point of view in microelectronics, photonics and optical materials. The ability to minimize reflection, control light output and use contrast and variation of the refractive index to modify photonic characteristics can provide routes to enhanced photonic crystal devices, omnidirectional reflectors, antireflection coatings and broadband absorbing materials. This work shows how multiscale branching of defect-free ITO NWs grown as a layer with a graded refractive index improves antireflection properties and shifts the transparency window into the near-infrared (NIR. The measurements confirm the structural quality and growth mechanism of the NW layer without any heterogeneous seeding for NW growth. Optical reflectance measurements confirm broadband antireflection down to <5% between 1.3-1.6 um which is tunable with the NW density. The work also outlines how the suppression of the Burstein-Moss shifts using refractive index variation allows transparency in a conductive NW layer into NIR range.

  1. Integration of atomic layer deposited high-k dielectrics on GaSb via hydrogen plasma exposure

    Directory of Open Access Journals (Sweden)

    Laura B. Ruppalt

    2014-12-01

    Full Text Available In this letter we report the efficacy of a hydrogen plasma pretreatment for integrating atomic layer deposited (ALD high-k dielectric stacks with device-quality p-type GaSb(001 epitaxial layers. Molecular beam eptiaxy-grown GaSb surfaces were subjected to a 30 minute H2/Ar plasma treatment and subsequently removed to air. High-k HfO2 and Al2O3/HfO2 bilayer insulating films were then deposited via ALD and samples were processed into standard metal-oxide-semiconductor (MOS capacitors. The quality of the semiconductor/dielectric interface was probed by current-voltage and variable-frequency admittance measurements. Measurement results indicate that the H2-plamsa pretreatment leads to a low density of interface states nearly independent of the deposited dielectric material, suggesting that pre-deposition H2-plasma exposure, coupled with ALD of high-k dielectrics, may provide an effective means for achieving high-quality GaSb MOS structures for advanced Sb-based digital and analog electronics.

  2. Two-Dimensional Electron Gas at SrTiO3-Based Oxide Heterostructures via Atomic Layer Deposition

    Directory of Open Access Journals (Sweden)

    Sang Woon Lee

    2016-01-01

    Full Text Available Two-dimensional electron gas (2DEG at an oxide interface has been attracting considerable attention for physics research and nanoelectronic applications. Early studies reported the formation of 2DEG at semiconductor interfaces (e.g., AlGaAs/GaAs heterostructures with interesting electrical properties such as high electron mobility. Besides 2DEG formation at semiconductor junctions, 2DEG was realized at the interface of an oxide heterostructure such as the LaAlO3/SrTiO3 (LAO/STO heterojunction. The origin of 2DEG was attributed to the well-known “polar catastrophe” mechanism in oxide heterostructures, which consist of an epitaxial LAO layer on a single crystalline STO substrate among proposed mechanisms. Recently, it was reported that the creation of 2DEG was achieved using the atomic layer deposition (ALD technique, which opens new functionality of ALD in emerging nanoelectronics. This review is focused on the origin of 2DEG at oxide heterostructures using the ALD process. In particular, it addresses the origin of 2DEG at oxide interfaces based on an alternative mechanism (i.e., oxygen vacancies.

  3. Structure and morphology of Ru films grown by atomic layer deposition from 1-ethyl-1’-methyl-ruthenocene

    Science.gov (United States)

    Kukli, Kaupo; Aarik, Jaan; Aidla, Aleks; Uustare, Teet; Jõgi, Indrek; Lu, Jun; Tallarida, Massimo; Kemell, Marianna; Kiisler, Alma-Asta; Ritala, Mikko; Leskelä, Markku

    2010-06-01

    Ru thin films were grown on TiO 2, Al 2O 3, HfO 2, and ZrO 2 films as well as on HF-etched silicon and SiO 2-covered silicon by atomic layer deposition from 1-ethyl-1'-methyl-ruthenocene, (CH 3C 5H 4)(C 2H 5C 5H 4)Ru, and oxygen. The growth of Ru was obtained and characterized at temperatures ranging from 250 to 325 °C. On epitaxial rutile, highly oriented growth of Ru with hexagonal structure was achieved, while on other substrates the films possessed nonoriented hexagonal structure. Ruthenium oxide was not detected in the films. The lowest resistivity value obtained for 5.0-6.6 nm thick films was 26 μΩ cm. The conductivity of the films depended somewhat on the deposition cycle time parameters and, expectedly, more strongly on the amount of deposition cycles. Increase in the deposition temperature of underlying metal oxide films increased the conductivity of Ru layers.

  4. Vertically Oriented Growth of GaN Nanorods on Si Using Graphene as an Atomically Thin Buffer Layer.

    Science.gov (United States)

    Heilmann, Martin; Munshi, A Mazid; Sarau, George; Göbelt, Manuela; Tessarek, Christian; Fauske, Vidar T; van Helvoort, Antonius T J; Yang, Jianfeng; Latzel, Michael; Hoffmann, Björn; Conibeer, Gavin; Weman, Helge; Christiansen, Silke

    2016-06-01

    The monolithic integration of wurtzite GaN on Si via metal-organic vapor phase epitaxy is strongly hampered by lattice and thermal mismatch as well as meltback etching. This study presents single-layer graphene as an atomically thin buffer layer for c-axis-oriented growth of vertically aligned GaN nanorods mediated by nanometer-sized AlGaN nucleation islands. Nanostructures of similar morphology are demonstrated on graphene-covered Si(111) as well as Si(100). High crystal and optical quality of the nanorods are evidenced through scanning transmission electron microscopy, micro-Raman, and cathodoluminescence measurements supported by finite-difference time-domain simulations. Current-voltage characteristics revealed high vertical conduction of the as-grown GaN nanorods through the Si substrates. These findings are substantial to advance the integration of GaN-based devices on any substrates of choice that sustains the GaN growth temperatures, thereby permitting novel designs of GaN-based heterojunction device concepts.

  5. Atomic layer deposition of NiO hole-transporting layers for polymer solar cells.

    Science.gov (United States)

    Hsu, Che-Chen; Su, Heng-Wei; Hou, Cheng-Hung; Shyue, Jing-Jong; Tsai, Feng-Yu

    2015-09-25

    NiO is an attractive hole-transporting material for polymer solar cells (PSCs) owing to its excellent stability and electrical/optical properties. This study demonstrates, for the first time, fabrication of uniform, defect-free, and conformal NiO ultra-thin films for use as hole-transporting layers (HTLs) in PSCs by atomic layer deposition (ALD) through optimization of the ALD processing parameters. The morphological, optical, and electrical properties of ALD NiO films were determined to be favorable for their HTL application. As a result, PSCs containing an ALD NiO HTL with an optimized thickness of 4 nm achieved a power conversion efficiency (PCE) of 3.4%, which was comparable to that of a control device with a poly(3,4-ethylenedioxy-thiophene):poly(styrene-sulfonate) HTL. The high quality and manufacturing scalability of ALD NiO films demonstrated here will facilitate the adoption of NiO HTLs in PSCs.

  6. Atomic layer deposition of NiO hole-transporting layers for polymer solar cells

    Science.gov (United States)

    Hsu, Che-Chen; Su, Heng-Wei; Hou, Cheng-Hung; Shyue, Jing-Jong; Tsai, Feng-Yu

    2015-09-01

    NiO is an attractive hole-transporting material for polymer solar cells (PSCs) owing to its excellent stability and electrical/optical properties. This study demonstrates, for the first time, fabrication of uniform, defect-free, and conformal NiO ultra-thin films for use as hole-transporting layers (HTLs) in PSCs by atomic layer deposition (ALD) through optimization of the ALD processing parameters. The morphological, optical, and electrical properties of ALD NiO films were determined to be favorable for their HTL application. As a result, PSCs containing an ALD NiO HTL with an optimized thickness of 4 nm achieved a power conversion efficiency (PCE) of 3.4%, which was comparable to that of a control device with a poly(3,4-ethylenedioxy-thiophene):poly(styrene-sulfonate) HTL. The high quality and manufacturing scalability of ALD NiO films demonstrated here will facilitate the adoption of NiO HTLs in PSCs.

  7. Atomic Layer Deposition for Coating of High Aspect Ratio TiO2 Nanotube Layers

    Science.gov (United States)

    2016-01-01

    We present an optimized approach for the deposition of Al2O3 (as a model secondary material) coating into high aspect ratio (≈180) anodic TiO2 nanotube layers using the atomic layer deposition (ALD) process. In order to study the influence of the diffusion of the Al2O3 precursors on the resulting coating thickness, ALD processes with different exposure times (i.e., 0.5, 2, 5, and 10 s) of the trimethylaluminum (TMA) precursor were performed. Uniform coating of the nanotube interiors was achieved with longer exposure times (5 and 10 s), as verified by detailed scanning electron microscopy analysis. Quartz crystal microbalance measurements were used to monitor the deposition process and its particular features due to the tube diameter gradient. Finally, theoretical calculations were performed to calculate the minimum precursor exposure time to attain uniform coating. Theoretical values on the diffusion regime matched with the experimental results and helped to obtain valuable information for further optimization of ALD coating processes. The presented approach provides a straightforward solution toward the development of many novel devices, based on a high surface area interface between TiO2 nanotubes and a secondary material (such as Al2O3). PMID:27643411

  8. Characterization of GaN/AlGaN epitaxial layers grown by metalorganic chemical vapour deposition for high electron mobility transistor applications

    Indian Academy of Sciences (India)

    Bhubesh Chander Joshi; Manish Mathew; B C Joshi; D Kumar; C Dhanavantri

    2010-01-01

    GaN and AlGaN epitaxial layers are grown by a metalorganic chemical vapour deposition (MOCVD) system. The crystalline quality of these epitaxially grown layers is studied by different characterization techniques. PL measurements indicate band edge emission peak at 363.8 nm and 312 nm for GaN and AlGaN layers respectively. High resolution XRD (HRXRD) peaks show FWHM of 272 and 296 arcsec for the (0 0 0 2) plane of GaN and GaN in GaN/AlGaN respectively. For GaN buffer layer, the Hall mobility is 346 cm2/V-s and carrier concentration is 4.5 × 1016 /cm3. AFM studies on GaN buffer layer show a dislocation density of 2 × 108/cm2 by wet etching in hot phosphoric acid. The refractive indices of GaN buffer layer on sapphire at 633 nm are 2.3544 and 2.1515 for TE and TM modes respectively.

  9. Impact of LT-GaAs layers on crystalline properties of the epitaxial GaAs films grown by MBE on Si substrates

    Science.gov (United States)

    Petrushkov, M. O.; Putyato, M. A.; Gutakovsky, A. K.; Preobrazhenskii, V. V.; Loshkarev, I. D.; Emelyanov, E. A.; Semyagin, B. R.; Vasev, A. V.

    2016-08-01

    GaAs films with low-temperature GaAs (LT-GaAs) layers were grown by molecular beam epitaxy (MBE) method on vicinal (001) Si substrates oriented 6° off towards [110]. The grown structures were different with the thickness of LT-GaAs layers and its arrangement in the film. The processes of epitaxial layers nucleation and growth were controlled by reflection high energy electron diffraction (RHEED) method. Investigations of crystalline properties of the grown structures were carried out by the methods of X-ray diffraction (XRD) and transmission electron microscopy (TEM). The crystalline perfection of the GaAs films with LT-GaAs layers and the GaAs films without ones was comparable. It was found that in the LT- GaAs/Si layers the arsenic clusters are formed, as it occurs in the LT-GaAs/GaAs system without dislocation. It is shown that large clusters are formed mainly on the dislocations. However, the clusters have practically no effect on the density and the propagation path of threading dislocations. With increasing thickness of LT-GaAs layer the dislocations are partly bent along the LT-GaAs/GaAs interface due to the presence of stresses.

  10. Characterization and modeling of atomic layer deposited high-density trench capacitors in silicon

    NARCIS (Netherlands)

    Matters-Kammerer, M.K.; Jinesh, K.B.; Rijks, T.G.S.M.; Roozeboom, F.; Klootwijk, J.H.

    2012-01-01

    A detailed electrical analysis of multiple layer trench capacitors fabricated in silicon with atomic-layer-deposited Al 2O 3 and TiN is presented. It is shown that in situ ozone annealing of the Al 2O 3 layers prior to the TiN electrode deposition significantly improves the electric properties of th

  11. Low-Temperature Plasma-Assisted Atomic Layer Deposition of Silicon Nitride Moisture Permeation Barrier Layers.

    Science.gov (United States)

    Andringa, Anne-Marije; Perrotta, Alberto; de Peuter, Koen; Knoops, Harm C M; Kessels, Wilhelmus M M; Creatore, Mariadriana

    2015-10-14

    Encapsulation of organic (opto-)electronic devices, such as organic light-emitting diodes (OLEDs), photovoltaic cells, and field-effect transistors, is required to minimize device degradation induced by moisture and oxygen ingress. SiNx moisture permeation barriers have been fabricated using a very recently developed low-temperature plasma-assisted atomic layer deposition (ALD) approach, consisting of half-reactions of the substrate with the precursor SiH2(NH(t)Bu)2 and with N2-fed plasma. The deposited films have been characterized in terms of their refractive index and chemical composition by spectroscopic ellipsometry (SE), X-ray photoelectron spectroscopy (XPS), and Fourier-transform infrared spectroscopy (FTIR). The SiNx thin-film refractive index ranges from 1.80 to 1.90 for films deposited at 80 °C up to 200 °C, respectively, and the C, O, and H impurity levels decrease when the deposition temperature increases. The relative open porosity content of the layers has been studied by means of multisolvent ellipsometric porosimetry (EP), adopting three solvents with different kinetic diameters: water (∼0.3 nm), ethanol (∼0.4 nm), and toluene (∼0.6 nm). Irrespective of the deposition temperature, and hence the impurity content in the SiNx films, no uptake of any adsorptive has been observed, pointing to the absence of open pores larger than 0.3 nm in diameter. Instead, multilayer development has been observed, leading to type II isotherms that, according to the IUPAC classification, are characteristic of nonporous layers. The calcium test has been performed in a climate chamber at 20 °C and 50% relative humidity to determine the intrinsic water vapor transmission rate (WVTR) of SiNx barriers deposited at 120 °C. Intrinsic WVTR values in the range of 10(-6) g/m2/day indicate excellent barrier properties for ALD SiNx layers as thin as 10 nm, competing with that of state-of-the-art plasma-enhanced chemical vapor-deposited SiNx layers of a few hundred

  12. Multidirectional channeling analysis of epitaxial CdTe layers using an automatic RBS/channeling system

    Energy Technology Data Exchange (ETDEWEB)

    Wielunski, L.S.; Kenny, M.J. [CSIRO, Lindfield, NSW (Australia). Applied Physics Div.

    1993-12-31

    Rutherford Backscattering Spectrometry (RBS) is an ion beam analysis technique used in many fields. The high depth and mass resolution of RBS make this technique very useful in semiconductor material analysis [1]. The use of ion channeling in combination with RBS creates a powerful technique which can provide information about crystal quality and structure in addition to mass and depth resolution [2]. The presence of crystal defects such as interstitial atoms, dislocations or dislocation loops can be detected and profiled [3,4]. Semiconductor materials such as CdTe, HgTe and Hg+xCd{sub 1-x}Te generate considerable interest due to applications as infrared detectors in many technological areas. The present paper demonstrates how automatic RBS and multidirectional channeling analysis can be used to evaluate crystal quality and near surface defects. 6 refs., 1 fig.

  13. Extremely deep profiling analysis of the atomic composition of thick (>100 μm) GaAs layers within power PIN diodes by secondary ion mass spectrometry

    Science.gov (United States)

    Drozdov, M. N.; Drozdov, Yu. N.; Yunin, P. A.; Folomin, P. I.; Gritsenko, A. B.; Kryukov, V. L.; Kryukov, E. V.

    2016-08-01

    A new opportunity to analyze the atomic composition of thick (>100 μm) epitaxial GaAs layers by SIMS with lateral imaging of the cross section of a structure is demonstrated. The standard geometry of ldepth analysis turns out to be less informative owing to material redeposition from the walls of a crater to its floor occurring when the crater depth reaches several micrometers. The profiles of concentration of doping impurities Te and Zn and concentrations of Al and major impurities in PIN diode layers are determined down to a depth of 130 μm. The element sensitivity is at the level of 1016 at/cm3 (typical for depth analysis at a TOF.SIMS-5 setup), and the resolution is twice the diameter of the probing beam of Bi ions. The possibility of enhancing the depth resolution and the element sensitivity of the proposed analysis method is discussed.

  14. Reducing interface recombination for Cu(In,Ga)Se{sub 2} by atomic layer deposited buffer layers

    Energy Technology Data Exchange (ETDEWEB)

    Hultqvist, Adam; Bent, Stacey F. [Department of Chemical Engineering, Stanford University, Stanford, California 94305 (United States); Li, Jian V.; Kuciauskas, Darius; Dippo, Patricia; Contreras, Miguel A.; Levi, Dean H. [National Renewable Energy Laboratory, Golden, Colorado 80401 (United States)

    2015-07-20

    Partial CuInGaSe{sub 2} (CIGS) solar cell stacks with different atomic layer deposited buffer layers and pretreatments were analyzed by photoluminescence (PL) and capacitance voltage (CV) measurements to investigate the buffer layer/CIGS interface. Atomic layer deposited ZnS, ZnO, and SnO{sub x} buffer layers were compared with chemical bath deposited CdS buffer layers. Band bending, charge density, and interface state density were extracted from the CV measurement using an analysis technique new to CIGS. The surface recombination velocity calculated from the density of interface traps for a ZnS/CIGS stack shows a remarkably low value of 810 cm/s, approaching the range of single crystalline II–VI systems. Both the PL spectra and its lifetime depend on the buffer layer; thus, these measurements are not only sensitive to the absorber but also to the absorber/buffer layer system. Pretreatment of the CIGS prior to the buffer layer deposition plays a significant role on the electrical properties for the same buffer layer/CIGS stack, further illuminating the importance of good interface formation. Finally, ZnS is found to be the best performing buffer layer in this study, especially if the CIGS surface is pretreated with potassium cyanide.

  15. Strain relaxation during solid-phase epitaxial crystallisation of Ge{sub x}Si{sub 1-x} alloy layers with depth dependent G{sub e} compositions

    Energy Technology Data Exchange (ETDEWEB)

    Wong, Wahchung; Elliman, R.G.; Kringhoj, P. [Australian National Univ., Canberra, ACT (Australia). Research School of Physical Sciences

    1993-12-31

    The solid-phase epitaxial crystallisation of depth dependent Ge{sub x}Si{sub lx} alloy layers produced by implanting Ge into Si substrates was studied. In-situ monitoring was done using time-resolved reflectivity (TRR) whilst post-anneal defect structures were characterised by Rutherford backscattering and channeling spectrometry (RBS-C) and transmission electron microscopy (TEM). Particular attention was directed at Ge concentrations above the critical concentration for the growth of fully strained layers. Strain relief is shown to be correlated with a sudden reduction in crystallisation velocity caused by roughening of the crystalline/amorphous interface. 11 refs., 1 tab., 2 figs.

  16. Visualization of arrangements of carbon atoms in graphene layers by Raman mapping and atomic-resolution TEM

    KAUST Repository

    Cong, Chunxiao

    2013-02-01

    In-plane and out-of-plane arrangements of carbon atoms in graphene layers play critical roles in the fundamental physics and practical applications of these novel two-dimensional materials. Here, we report initial results on the edge/crystal orientations and stacking orders of bi-and tri-layer graphene (BLG and TLG) from Raman spectroscopy and transmission electron microscopy (TEM) experiments performed on the same sample. We introduce a new method of transferring graphene flakes onto a normal TEM grid. Using this novel method, we probed the BLG and TLG flakes that had been previously investigated by Raman scattering with high-resolution (atomic) TEM.

  17. GaN Growth with Low-Temperature GaN Buffer Layers Directly on Si(111) by Hydride Vapour Phase Epitaxy

    Institute of Scientific and Technical Information of China (English)

    俞慧强; 陈琳; 张荣; 修向前; 谢自力; 叶宇达; 顾书林; 沈波; 施毅; 郑有蚪

    2004-01-01

    GaN films are grown on Si(111) with low-temperature GaN (LT-GaN) layers as buffer layers by hydride vapour phase epitaxy (HVPE). The deposition temperature of the LT-GaN layers is changed from 400 to 900 ℃. When the LT-GaN layer is deposited at 600 ℃, GaN films show only c-oriented GaN (0002) and have the band edge emission at 365 nm with no yellow luminescence bands. The results indicate that the LT-GaN layer can effectively block the unexpected Si etching by reactive gas during the GaN growth. However, the surface roughness of these GaN films grown on Si(111) is larger than that of GaN films on c-plane sapphire.

  18. Atomic-Scale Tuning of Layered Binary Metal Oxides for High Temperature Moving Assemblies

    Science.gov (United States)

    2015-06-01

    AFRL-OSR-VA-TR-2015-0166 Atomic -Scale Tuning of Layered Binary Metal OxideS ASHLIE MARTINI UNIVERSITY OF CALIFORNIA MERCED Final Report 06/01/2015...COVERED (From - To)      01-05-2012 to 30-04-2015 4.  TITLE AND SUBTITLE Atomic -Scale Tuning of Layered Binary Metal Oxides for High Temperature Moving...understand, at an atomic level, the material properties that influence the thermal, mechanical and tribological behavior of intrinsically layered binary

  19. High-barrier Schottky contact on n-type 4H-SiC epitaxial layer and studies of defect levels by deep level transient spectroscopy (DLTS)

    Science.gov (United States)

    Nguyen, Khai V.; Pak, Rahmi O.; Oner, Cihan; Mannan, Mohammad A.; Mandal, Krishna C.

    2015-08-01

    High barrier Schottky contact has been fabricated on 50 μm n-type 4H-SiC epitaxial layers grown on 350 μm thick substrate 8° off-cut towards the [11̅20] direction. The 4H-SiC epitaxial wafer was diced into 10 x 10 mm2 samples. The metal-semiconductor junctions were fabricated by photolithography and dc sputtering with ruthenium (Ru). The junction properties were characterized through current-voltage (I-V) and capacitance-voltage (C-V) measurements. Detectors were characterized by alpha spectroscopy measurements in terms of energy resolution and charge collection efficiency using a 0.1 μCi 241Am radiation source. It was found that detectors fabricated from high work function rare transition metal Ru demonstrated very low leakage current and significant improvement of detector performance. Defect characterization of the epitaxial layers was conducted by deep level transient spectroscopy (DLTS) to thoroughly investigate the defect levels in the active region. The presence of a new defect level induced by this rare transition metal-semiconductor interface has been identified and characterized.

  20. Perspective: Oxide molecular-beam epitaxy rocks!

    Directory of Open Access Journals (Sweden)

    Darrell G. Schlom

    2015-06-01

    Full Text Available Molecular-beam epitaxy (MBE is the “gold standard” synthesis technique for preparing semiconductor heterostructures with high purity, high mobility, and exquisite control of layer thickness at the atomic-layer level. Its use for the growth of multicomponent oxides got off to a rocky start 30 yr ago, but in the ensuing decades, it has become the definitive method for the preparation of oxide heterostructures too, particularly when it is desired to explore their intrinsic properties. Examples illustrating the unparalleled achievements of oxide MBE are given; these motivate its expanding use for exploring the potentially revolutionary states of matter possessed by oxide systems.

  1. Perspective: Oxide molecular-beam epitaxy rocks!

    Energy Technology Data Exchange (ETDEWEB)

    Schlom, Darrell G., E-mail: schlom@cornell.edu [Department of Materials Science and Engineering, Cornell University, Ithaca, New York 14853, USA and Kavli Institute at Cornell for Nanoscale Science, Ithaca, New York 14853 (United States)

    2015-06-01

    Molecular-beam epitaxy (MBE) is the “gold standard” synthesis technique for preparing semiconductor heterostructures with high purity, high mobility, and exquisite control of layer thickness at the atomic-layer level. Its use for the growth of multicomponent oxides got off to a rocky start 30 yr ago, but in the ensuing decades, it has become the definitive method for the preparation of oxide heterostructures too, particularly when it is desired to explore their intrinsic properties. Examples illustrating the unparalleled achievements of oxide MBE are given; these motivate its expanding use for exploring the potentially revolutionary states of matter possessed by oxide systems.

  2. Conduction mechanisms in thin atomic layer deposited Al{sub 2}O{sub 3} layers

    Energy Technology Data Exchange (ETDEWEB)

    Spahr, Holger; Montzka, Sebastian; Reinker, Johannes; Hirschberg, Felix; Kowalsky, Wolfgang; Johannes, Hans-Hermann, E-mail: h2.johannes@ihf.tu-bs.de [Institut für Hochfrequenztechnik, Technische Universität Braunschweig, Schleinitzstraße 22, 38106 Braunschweig (Germany)

    2013-11-14

    Thin Al{sub 2}O{sub 3} layers of 2–135 nm thickness deposited by thermal atomic layer deposition at 80 °C were characterized regarding the current limiting mechanisms by increasing voltage ramp stress. By analyzing the j(U)-characteristics regarding ohmic injection, space charge limited current (SCLC), Schottky-emission, Fowler-Nordheim-tunneling, and Poole-Frenkel-emission, the limiting mechanisms were identified. This was performed by rearranging and plotting the data in a linear scale, such as Schottky-plot, Poole-Frenkel-plot, and Fowler-Nordheim-plot. Linear regression then was applied to the data to extract the values of relative permittivity from Schottky-plot slope and Poole-Frenkel-plot slope. From Fowler-Nordheim-plot slope, the Fowler-Nordheim-energy-barrier was extracted. Example measurements in addition to a statistical overview of the results of all investigated samples are provided. Linear regression was applied to the region of the data that matches the realistic values most. It is concluded that ohmic injection and therefore SCLC only occurs at thicknesses below 12 nm and that the Poole-Frenkel-effect is no significant current limiting process. The extracted Fowler-Nordheim-barriers vary in the range of up to approximately 4 eV but do not show a specific trend. It is discussed whether the negative slope in the Fowler-Nordheim-plot could in some cases be a misinterpreted trap filled limit in the case of space charge limited current.

  3. Atomic Layer Deposition on Carbon Nanotubes and their Assemblies

    Science.gov (United States)

    Stano, Kelly Lynn

    Global issues related to energy and the environment have motivated development of advanced material solutions outside of traditional metals ceramics, and polymers. Taking inspiration from composites, where the combination of two or more materials often yields superior properties, the field of organic-inorganic hybrids has recently emerged. Carbon nanotube (CNT)-inorganic hybrids have drawn widespread and increasing interest in recent years due to their multifunctionality and potential impact across several technologically important application areas. Before the impacts of CNT-inorganic hybrids can be realized however, processing techniques must be developed for their scalable production. Optimization in chemical vapor deposition (CVD) methods for synthesis of CNTs and vertically aligned CNT arrays has created production routes both high throughput and economically feasible. Additionally, control of CVD parameters has allowed for growth of CNT arrays that are able to be drawn into aligned sheets and further processed to form a variety of aligned 1, 2, and 3-dimensional bulk assemblies including ribbons, yarns, and foams. To date, there have only been a few studies on utilizing these bulk assemblies for the production of CNT-inorganic hybrids. Wet chemical methods traditionally used for fabricating CNT-inorganic hybrids are largely incompatible with CNT assemblies, since wetting and drying the delicate structures with solvents can destroy their structure. It is therefore necessary to investigate alternative processing strategies in order to advance the field of CNT-inorganic hybrids. In this dissertation, atomic layer deposition (ALD) is evaluated as a synthetic route for the production of large-scale CNT-metal oxide hybrids as well as pure metal oxide architectures utilizing CNT arrays, ribbons, and ultralow density foams as deposition templates. Nucleation and growth behavior of alumina was evaluated as a function of CNT surface chemistry. While highly graphitic

  4. Layer-by-layer epitaxial growth of a Bi sub 2 Sr sub 2 CuO sub 6 thin film on a Bi sub 2 Sr sub 2 CaCu sub 2 O sub 8 single crystal

    Energy Technology Data Exchange (ETDEWEB)

    Matsumoto, T.; Kawai, T.; Kitahama, K.; Kawai, S. (The Institute of Scientific and Industrial Research, Osaka University, Mihogaoka, Ibaraki, Osaka 567, Japan (JP)); Shigaki, I.; Kawate, Y. (Superconducting Cryogenic Technology Center, Kobe Steel, Ltd., Takatsukadai 1-chome, Nishi-ku, Kobe 651-22, (Japan))

    1991-05-06

    The epitaxial growth of a Bi{sub 2}Sr{sub 2}CuO{sub 6} (2201) thin film on a Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8} (2212) single crystal has been performed using computer-controlled laser molecular beam epitaxy. The surface of the 2212 single crystal used as the substrate is smooth and invariant under the growth condition at 640 {degree}C in NO{sub 2} pressure of 1{times}10{sup {minus}5} mbar. The growth process of the 2201 film has been observed by {ital in} {ital situ} reflection high-energy electron diffraction (RHEED), and the layer-by-layer growth of the 2201 phase is confirmed by the oscillation of RHEED intensities. During the growth, a modulated surface structure which is characteristic of the Bi cuprate crystals is always present.

  5. Effect of substrate composition on atomic layer deposition using self-assembled monolayers as blocking layers

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Wenyu; Engstrom, James R., E-mail: jre7@cornell.edu [School of Chemical and Biomolecular Engineering, Cornell University, Ithaca, New York 14853 (United States)

    2016-01-15

    The authors have examined the effect of two molecules that form self-assembled monolayers (SAMs) on the subsequent growth of TaN{sub x} by atomic layer deposition (ALD) on two substrate surfaces, SiO{sub 2} and Cu. The SAMs that the authors have investigated include two vapor phase deposited, fluorinated alkyl silanes: Cl{sub 3}Si(CH{sub 2}){sub 2}(CF{sub 2}){sub 5}CF{sub 3} (FOTS) and (C{sub 2}H{sub 5}O){sub 3}Si(CH{sub 2}){sub 2}(CF{sub 2}){sub 7}CF{sub 3} (HDFTEOS). Both the SAMs themselves and the TaN{sub x} thin films, grown using Ta[N(CH{sub 3}){sub 2}]{sub 5} and NH{sub 3}, were analyzed ex situ using contact angle, spectroscopic ellipsometry, x-ray photoelectron spectroscopy (XPS), and low energy ion-scattering spectroscopy (LEISS). First, the authors find that both SAMs on SiO{sub 2} are nominally stable at T{sub s} ∼ 300 °C, the substrate temperature used for ALD, while on Cu, the authors find that HDFTEOS thermally desorbs, while FOTS is retained on the surface. The latter result reflects the difference in the head groups of these two molecules. The authors find that both SAMs strongly attenuate the ALD growth of TaN{sub x} on SiO{sub 2}, by about a factor of 10, while on Cu, the SAMs have no effect on ALD growth. Results from LEISS and XPS are decisive in determining the nature of the mechanism of growth of TaN{sub x} on all surfaces. Growth on SiO{sub 2} is 2D and approximately layer-by-layer, while on the surfaces terminated by the SAMs, it nucleates at defect sites, is islanded, and is 3D. In the latter case, our results support growth of the TaN{sub x} thin film over the SAM, with a considerable delay in formation of a continuous thin film. Growth on Cu, with or without the SAMs, is also 3D and islanded, and there is also a delay in the formation of a continuous thin film as compared to growth on SiO{sub 2}. These results highlight the power of coupling measurements from both LEISS and XPS in examinations of ultrathin films formed by ALD.

  6. Impact of growth and annealing conditions on the parameters of Ge/Si(001) relaxed layers grown by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Yurasov, D. V., E-mail: Inquisitor@ipm.sci-nnov.ru [Russian Academy of Sciences, Institute for Physics of Microstructures (Russian Federation); Bobrov, A. I. [Lobachevsky State University of Nizhny Novgorod (Russian Federation); Daniltsev, V. M.; Novikov, A. V. [Russian Academy of Sciences, Institute for Physics of Microstructures (Russian Federation); Pavlov, D. A. [Lobachevsky State University of Nizhny Novgorod (Russian Federation); Skorokhodov, E. V.; Shaleev, M. V.; Yunin, P. A. [Russian Academy of Sciences, Institute for Physics of Microstructures (Russian Federation)

    2015-11-15

    Influence of the Ge layer thickness and annealing conditions on the parameters of relaxed Ge/Si(001) layers grown by molecular beam epitaxy via two-stage growth is investigated. The dependences of the threading dislocation density and surface roughness on the Ge layer thickness, annealing temperature and time, and the presence of a hydrogen atmosphere are obtained. As a result of optimization of the growth and annealing conditions, relaxed Ge/Si(001) layers which are thinner than 1 μm with a low threading dislocation density on the order of 10{sup 7} cm{sup –2} and a root mean square roughness of less than 1 nm are obtained.

  7. Two-dimensional superconductivity in the cuprates revealed by atomic-layer-by-layer molecular beam epitaxy

    Science.gov (United States)

    Bollinger, A. T.; Božović, I.

    2016-10-01

    Various electronic phases displayed by cuprates that exhibit high temperature superconductivity continue to attract much interest. We provide a short review of several experiments that we have performed aimed at investigating the superconducting state in these compounds. Measurements on single-phase films, bilayers, and superlattices all point to the conclusion that the high-temperature superconductivity (HTS) in these materials is an essentially quasi-two dimensional phenomenon. With proper control over the film growth, HTS can exist in a single copper oxide plane with the critical temperatures as high as that achieved in the bulk samples.

  8. Gigahertz Dielectric Polarization of Single-atom Niobium Substituted in Graphitic layers

    OpenAIRE

    2015-01-01

    We have synthesized two Nb@C composites with an order of magnitude difference in the density of single-atom niobium substituted into graphitic layers. The concentration and sites of single-atom Nb are identified using aberration-corrected scanning transmission electron microscopy and density functional theory. Comparing the complex permittivity spectra show that the representative dielectric resonance at ~16 GHz originates from the intrinsic polarization of single-atom Nb sites, confirmed by ...

  9. Integration of epitaxial Pb(Zr{sub 0.52}Ti{sub 0.48})O{sub 3} films on GaN/AlGaN/GaN/Si(111) substrates using rutile TiO{sub 2} buffer layers

    Energy Technology Data Exchange (ETDEWEB)

    Elibol, K. [MESA + Institute for Nanotechnology, University of Twente, P.O. Box 217, 7500AE Enschede (Netherlands); Nguyen, M.D. [MESA + Institute for Nanotechnology, University of Twente, P.O. Box 217, 7500AE Enschede (Netherlands); SolMateS B.V., Drienerlolaan 5, Building 6, 7522NB Enschede (Netherlands); International Training Institute for Materials Science, Hanoi University of Science and Technology, No.1 Dai Co Viet road, Hanoi 10000 (Viet Nam); Hueting, R.J.E. [MESA + Institute for Nanotechnology, University of Twente, P.O. Box 217, 7500AE Enschede (Netherlands); Gravesteijn, D.J. [MESA + Institute for Nanotechnology, University of Twente, P.O. Box 217, 7500AE Enschede (Netherlands); NXP Semiconductors Research, High Tech Campus 46, 5656AE Eindhoven (Netherlands); Koster, G., E-mail: g.koster@utwente.nl [MESA + Institute for Nanotechnology, University of Twente, P.O. Box 217, 7500AE Enschede (Netherlands); Rijnders, G. [MESA + Institute for Nanotechnology, University of Twente, P.O. Box 217, 7500AE Enschede (Netherlands)

    2015-09-30

    The integration of ferroelectric layers on gallium nitride (GaN) offers a great potential for various applications. Lead zirconate titanate (PZT), in particular Pb(Zr{sub 0.52}Ti{sub 0.48})O{sub 3}, is an interesting candidate. For that a suitable buffer layer should be grown on GaN in order to prevent the reaction between PZT and GaN, and to obtain PZT with a preferred orientation and phase. Here, we study pulsed laser deposited (100) rutile titanium oxide (R-TiO{sub 2}) as a potential buffer layer candidate for ferroelectric PZT. For this purpose, the growth, morphology and the surface chemical composition of R-TiO{sub 2} films were analyzed by reflection high-energy electron diffraction, atomic force microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. We find optimally (100) oriented R-TiO{sub 2} growth on GaN (0002) using a 675 °C growth temperature and 2 Pa O{sub 2} deposition pressure as process conditions. More importantly, the R-TiO{sub 2} buffer layer grown on GaN/Si substrates prevents the unwanted formation of the PZT pyrochlore phase. Finally, the remnant polarization and coercive voltage of the PZT film on TiO{sub 2}/GaN/Si with an interdigitated-electrode structure were found to be 25.6 μC/cm{sup 2} and 8.1 V, respectively. - Highlights: • Epitaxial rutile TiO{sub 2} films were grown on GaN layer buffered Si substrate using pulsed laser deposition. • The rutile-TiO{sub 2} layer suppresses the formation of the pyrochlore phase in the epitaxial PZT film grown on GaN/Si. • An epitaxial PZT film on GaN/Si substrate with rutile TiO{sub 2} buffer layer exhibits good ferroelectric properties.

  10. Elemental intermixing within an ultrathin SrRuO3 electrode layer in epitaxial heterostructure BaTiO3/SrRuO3/SrTiO3

    Directory of Open Access Journals (Sweden)

    H. B. Zhang

    2016-01-01

    Full Text Available Aberration corrected scanning transmission electron microscopy is used to directly observe atom columns in an epitaxial BaTiO3 thin film deposited on a 3.6 nm-thick SrRuO3 electrode layer above an SrTiO3 (001 substrate. Compositional gradients across the heterointerfaces were examined using electron energy-loss spectroscopy techniques. It was found that a small amount of Ba and Ti had diffused into the SrRuO3 layer, and that this layer contained a non-negligible concentration of oxygen vacancies. Such point defects are expected to degrade the electrode’s electronic conductivity drastically, resulting in a much longer screening length. This may explain the discrepancy between experimental measurements and theoretical estimates of the ferroelectric critical thickness of a BaTiO3 ferroelectric barrier sandwiched between metallic SrRuO3 electrodes, since theoretical calculations generally assume ideal (stoichiometric perovskite SrRuO3.

  11. Elemental intermixing within an ultrathin SrRuO{sub 3} electrode layer in epitaxial heterostructure BaTiO{sub 3}/SrRuO{sub 3}/SrTiO{sub 3}

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, H. B.; Qi, R. J.; Ding, N. F.; Sun, L. [Key Laboratory of Polar Materials and Devices, Ministry of Education, East China Normal University, Shanghai, 200062 (China); Huang, R., E-mail: rhuang@ee.ecnu.edu.cn [Key Laboratory of Polar Materials and Devices, Ministry of Education, East China Normal University, Shanghai, 200062 (China); Nanostructures Research Laboratory, Japan Fine Ceramics Center, Nagoya 456-8587 (Japan); Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan, Shanxi 030006 (China); Duan, C. G., E-mail: cgduan@clpm.ecnu.edu.cn; Chu, J. H. [Key Laboratory of Polar Materials and Devices, Ministry of Education, East China Normal University, Shanghai, 200062 (China); Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan, Shanxi 030006 (China); Fisher, Craig A. J. [Nanostructures Research Laboratory, Japan Fine Ceramics Center, Nagoya 456-8587 (Japan); Ikuhara, Y. [Nanostructures Research Laboratory, Japan Fine Ceramics Center, Nagoya 456-8587 (Japan); Institute of Engineering Innovation, The University of Tokyo, Tokyo 113-8656 (Japan)

    2016-01-15

    Aberration corrected scanning transmission electron microscopy is used to directly observe atom columns in an epitaxial BaTiO{sub 3} thin film deposited on a 3.6 nm-thick SrRuO{sub 3} electrode layer above an SrTiO{sub 3} (001) substrate. Compositional gradients across the heterointerfaces were examined using electron energy-loss spectroscopy techniques. It was found that a small amount of Ba and Ti had diffused into the SrRuO{sub 3} layer, and that this layer contained a non-negligible concentration of oxygen vacancies. Such point defects are expected to degrade the electrode’s electronic conductivity drastically, resulting in a much longer screening length. This may explain the discrepancy between experimental measurements and theoretical estimates of the ferroelectric critical thickness of a BaTiO{sub 3} ferroelectric barrier sandwiched between metallic SrRuO{sub 3} electrodes, since theoretical calculations generally assume ideal (stoichiometric) perovskite SrRuO{sub 3}.

  12. Photoluminescence studies of epitaxial Si 1- xGe x and Si 1- x-yGe xC y layers on Si formed by ion beam synthesis

    Science.gov (United States)

    Katsumata, H.; Kobayashi, N.; Makita, Y.; Hasegawa, M.; Hayashi, N.; Shibata, H.; Uekusa, S.

    1997-01-01

    Low temperature (2 K) photoluminescence (PL) properties of epitaxial Si 1- xGe x and Si 1- x-yGe xC y layers on Si ( x = 0.13 and y = 0.014 at peak concentration) formed by ion beam synthesis (IBS) have been investigated. Samples were prepared by a high-dose Ge with/without C ion implantation (I 2) at room temperature and by subsequent three different crystallization techniques: (i) furnace annealing (FA) process up to 840°C, (ii) ion beam-induced epitaxial crystallization (IBIEC) process with 400 keV Ge or Ar ions at 300-350°C, and (iii) IBIEC process followed by FA process up to 640°C (IBIEC + FA). Although FA-grown Si 1- x-yGe xC y samples showed G-line (C sSi iC s complex) emission at 0.969 eV, IBIEC-grown samples presented a sharp I 1 non-phonon emission at 1.0193 eV. This indicates that C atoms agglomeration is dominant for FA-grown samples, while a creation of trigonal tetravacancy cluster is dominant for IBIEC-grown samples. On the other hand, (IBIEC with Ge ions + FA)-grown Si 1- x-yGe xC y samples showed neither G-line nor I 1-related emissions, which indicates that good crystalline Si 1- x-yGe xC y layers without C agglomeration were formed by this process. In contrast, (IBIEC with Ar ions + FA)-grown samples exhibited novel successive PL vibronic sidebands at 0.98-1.03 eV. From their excitation power dependence measurements, they were found to be associated with exciton bound to defects levels created by Ar + bombardment.

  13. Fermi level de-pinning of aluminium contacts to n-type germanium using thin atomic layer deposited layers

    Energy Technology Data Exchange (ETDEWEB)

    Gajula, D. R., E-mail: dgajula01@qub.ac.uk; Baine, P.; Armstrong, B. M.; McNeill, D. W. [School of Electronics, Electrical Engineering and Computer Science, Queen' s University Belfast, Ashby Building, Stranmillis Road, Belfast BT9 5AH (United Kingdom); Modreanu, M.; Hurley, P. K. [Tyndall National Institute, University College Cork, Lee Maltings, Cork (Ireland)

    2014-01-06

    Fermi-level pinning of aluminium on n-type germanium (n-Ge) was reduced by insertion of a thin interfacial dielectric by atomic layer deposition. The barrier height for aluminium contacts on n-Ge was reduced from 0.7 eV to a value of 0.28 eV for a thin Al{sub 2}O{sub 3} interfacial layer (∼2.8 nm). For diodes with an Al{sub 2}O{sub 3} interfacial layer, the contact resistance started to increase for layer thicknesses above 2.8 nm. For diodes with a HfO{sub 2} interfacial layer, the barrier height was also reduced but the contact resistance increased dramatically for layer thicknesses above 1.5 nm.

  14. Layer-by-layer growth of high-optical-quality ZnO film on atomically smooth and lattice relaxed ZnO buffer layer

    OpenAIRE

    2003-01-01

    The growth mode of ZnO thin films can be well regulated in a molecular layer-by-layer growth by employing a ZnO buffer layer deposited on a lattice-matched ScAlMgO4 substrate and annealed at high temperature. The annealed buffer layer has atomically flat surface and relaxed (strain-free) crystal structure. The intensity oscillation of reflection high-energy electron diffraction persisted for more than a 100-nm film deposition under optimized conditions on such a buffer layer. Thus prepared th...

  15. Selective electrodesorption based atomic layer deposition (SEBALD): a novel electrochemical route to deposit metal clusters on Ag(111).

    Science.gov (United States)

    Innocenti, M; Bellandi, S; Lastraioli, E; Loglio, F; Foresti, M L

    2011-09-20

    The possibility of synergic effects of some metals on the catalytic activity of silver led us to study the way to perform controlled deposition on silver. In fact, many metals of technological interest such as Co, Ni, and Fe cannot be deposited at underpotential on silver, and any attempt to control the deposition at overpotential, even at potentials slightly negative of the Nernst value, did not allow an effective control. However, due to the favorable energy gain involved in the formation of the corresponding sulfides, these metals can be deposited at underpotential on sulfur covered silver. The deposition is surface limited and the successive electrodesorption of sulfur leaves confined clusters of metals. The method can also be used to obtain metal clusters of different size. In fact, the alternate underpotential deposition of elements that form a compound is the basis of the electrochemical atomic layer epitaxy (ECALE), and the reiteration of the basic cycle allows us to obtain sulfide deposits whose thickness increases with the number of cycles. Therefore, the successive selective desorption of sulfur leaves increasing amounts of metals.

  16. Quantitative measurements and modeling of electronic and atomic surface structure in epitaxial LaNiO3 thin films by ARPES, LEED-I(V), and DFT +DMFT

    Science.gov (United States)

    Ruf, Jacob; Nowadnick, Elizabeth; Park, Hyowon; King, Philip; Millis, Andrew; Schlom, Darrell; Shen, Kyle

    Careful exploration of the phase space available for artificially engineering emergent electronic properties in epitaxial thin films and superlattices of transition-metal oxides requires close feedback between materials synthesis, experimental characterization of both electronic and atomic structures, and modeling based on advanced computational methods. Here we apply this general strategy to the perovskite rare-earth nickelate LaNiO3, using molecular-beam epitaxy to synthesize thin films, performing in situangle-resolved photoemission spectroscopy (ARPES) and low-energy electron diffraction (LEED) measurements, and comparing our results with the predictions of density functional theory plus dynamical mean-field theory (DFT +DMFT). Our study establishes LaNiO3 as a moderately correlated metal in which the quasiparticle mass enhancement can be modeled with quantitative accuracy by DFT +DMFT. Finally, in view of efforts to produce eg orbital polarization in nickelate heterostructures as a means of mimicking single-band cuprate-like physics, we discuss the extent to which our ARPES and LEED results suggest that such effects are intrinsically present at film surfaces due to the existence of polar distortions, as reported by coherent Bragg rod analysis of surface x-ray diffraction.

  17. Buffer-layer enhanced crystal growth of BaB{sub 6} (1 0 0) thin films on MgO (1 0 0) substrates by laser molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Kato, Yushi; Yamauchi, Ryosuke; Arai, Hideki; Tan, Geng [Department of Innovative and Engineered Materials, Tokyo Institute of Technology, 4259-J2-46, Nagatsuta-cho, Midori-ku, Yokohama 226-8503 (Japan); Tsuchimine, Nobuo; Kobayashi, Susumu [Toshima Manufacturing Company Limited, 1414 Shimonomoto, Higashimatsuyama-shi, Saitama 355-0036 (Japan); Saeki, Kazuhiko; Takezawa, Nobutaka [Department of Materials Technology, Industrial Technology Center of Tochigi Prefecture, 367-1 Karinuma, Utsunomiya-shi, Tochigi 321-3224 (Japan); Mitsuhashi, Masahiko; Kaneko, Satoru [Kanagawa Industrial Technology Center, Kanagawa Prefectural Government, 705-1 Shimo-Imaizumi, Ebina, Kanagawa 243-0435 (Japan); Yoshimoto, Mamoru, E-mail: yoshimoto.m.aa@m.titech.ac.jp [Department of Innovative and Engineered Materials, Tokyo Institute of Technology, 4259-J2-46, Nagatsuta-cho, Midori-ku, Yokohama 226-8503 (Japan); Patent Attorney, Tokyo Institute of Technology, 4259-J2-46, Nagatsuta-cho, Midori-ku, Yokohama 226-8503 (Japan)

    2012-02-01

    Crystalline BaB{sub 6} (1 0 0) thin films can be fabricated on MgO (1 0 0) substrates by inserting a 2-3 nm-thick epitaxial SrB{sub 6} (1 0 0) buffer layer by pulsed laser deposition (PLD) in ultra-high vacuum (i.e., laser molecular beam epitaxy). Reflection high-energy electron diffraction and X-ray diffraction measurements indicated the heteroepitaxial structure of BaB{sub 6} (1 0 0)/SrB{sub 6} (1 0 0)/MgO (1 0 0) with the single domain of the epitaxial relationship. Conversely, BaB{sub 6} thin films without the buffer layer were not epitaxial instead they developed as polycrystalline films with a random in-plane configuration and some impurity phases. As a result, the buffer layer is considered to greatly affect the initial growth of epitaxial BaB{sub 6} thin films; therefore, in this study, buffering effects have been discussed. From the conventional four-probe measurement, it was observed that BaB{sub 6} epitaxial thin films exhibit n-type semiconducting behavior with a resistivity of 2.90 Multiplication-Sign 10{sup -1} {Omega} cm at room temperature.

  18. A visualization of threading dislocations formation and dynamics in mosaic growth of GaN-based light emitting diode epitaxial layers on (0001) sapphire

    Science.gov (United States)

    Ravadgar, P.; Horng, R. H.; Ou, S. L.

    2012-12-01

    A clear visualization of the origin and characteristics of threading dislocations (TDs) of GaN-based light emitting diode epitaxial layers on (0001) sapphire substrates have been carried out. Special experimental set up and chemical etchant along with field emission scanning electron microscopy are employed to study the dynamics of GaN TDs at different growth stages. Cross-sectional transmission electron microscopy analysis visualized the formation of edge TDs is arising from extension of coalescences at boundaries of different tilting-twining nucleation grains "mosaic growth." Etch pits as representatives of edge TDs are in agreement with previous theoretical models and analyses of TDs core position and characteristics.

  19. Dependence of electric and zonal parameters of (PbSe)sub(1-x)(SnTe)sub(x) epitaxial layers on their composition

    Energy Technology Data Exchange (ETDEWEB)

    Frenk, D.M.; Kostik, B.F.; Voropaj, V.A. (Ivano-Frankovskij Gosudarstvennyj Pedagogicheskij Inst. (Ukrainian SSR))

    1983-05-01

    Effect of composition on electric properties and zonal structure of (PbSe)sub(1-x)(SnTe)sub(x) epitaxial films of p-type conductivity, obtained by the method of thermal evaporation in double quasiclosed volume with BaF/sub 2/ substrates was established. The energy and density of states on Fermi level, the effective mass of state density near the zone edge, anisotropy factor of fermi surface were determined for the layers with 0 <= x <= 0.3 within the framework of Kane model.

  20. Atomic Layer Deposition of Titanium Oxide on Single-Layer Graphene: An Atomic-Scale Study toward Understanding Nucleation and Growth

    Science.gov (United States)

    2017-01-01

    Controlled synthesis of a hybrid nanomaterial based on titanium oxide and single-layer graphene (SLG) using atomic layer deposition (ALD) is reported here. The morphology and crystallinity of the oxide layer on SLG can be tuned mainly with the deposition temperature, achieving either a uniform amorphous layer at 60 °C or ∼2 nm individual nanocrystals on the SLG at 200 °C after only 20 ALD cycles. A continuous and uniform amorphous layer formed on the SLG after 180 cycles at 60 °C can be converted to a polycrystalline layer containing domains of anatase TiO2 after a postdeposition annealing at 400 °C under vacuum. Using aberration-corrected transmission electron microscopy (AC-TEM), characterization of the structure and chemistry was performed on an atomic scale and provided insight into understanding the nucleation and growth. AC-TEM imaging and electron energy loss spectroscopy revealed that rocksalt TiO nanocrystals were occasionally formed at the early stage of nucleation after only 20 ALD cycles. Understanding and controlling nucleation and growth of the hybrid nanomaterial are crucial to achieving novel properties and enhanced performance for a wide range of applications that exploit the synergetic functionalities of the ensemble.

  1. Atomic-scale imaging of few-layer black phosphorus and its reconstructed edge

    Science.gov (United States)

    Lee, Yangjin; Yoon, Jun-Yeong; Scullion, Declan; Jang, Jeongsu; Santos, Elton J. G.; Jeong, Hu Young; Kim, Kwanpyo

    2017-03-01

    Black phosphorus (BP) has recently emerged as an alternative 2D semiconductor owing to its fascinating electronic properties such as tunable bandgap and high charge carrier mobility. The structural investigation of few-layer BP, such as identification of layer thickness and atomic-scale edge structure, is of great importance to fully understand its electronic and optical properties. Here we report atomic-scale analysis of few-layered BP performed by aberration corrected transmission electron microscopy (TEM). We establish the layer-number-dependent atomic resolution imaging of few-layer BP via TEM imaging and image simulations. The structural modification induced by the electron beam leads to revelation of crystalline edge and formation of BP nanoribbons. Atomic resolution imaging of BP clearly shows the reconstructed zigzag (ZZ) edge structures, which is also corroborated by van der Waals first principles calculations on the edge stability. Our study on the precise identification of BP thickness and atomic-resolution imaging of edge structures will lay the groundwork for investigation of few-layer BP, especially BP in nanostructured forms.

  2. Temperature dependence of atomic vibrations in mono-layer graphene

    NARCIS (Netherlands)

    Allen, C.S.; Liberti, E.; Kim, J.S.; Xu, Q.; Fan, Y.; He, K.; Robertson, A.W.; Zandbergen, H.W.; Warner, J.H.; Kirkland, A.I.

    2015-01-01

    We have measured the mean square amplitude of both in- and out-of-plane lattice vibrations for mono-layer graphene at temperatures ranging from ∼100 K to 1300 K. The amplitude of lattice vibrations was calculated from data extracted from selected area electron diffraction patterns recorded across a

  3. Silicon protected with atomic layer deposited TiO2

    DEFF Research Database (Denmark)

    Seger, Brian; Tilley, S. David; Pedersen, Thomas

    2013-01-01

    The present work demonstrates that tuning the donor density of protective TiO2 layers on a photocathode has dramatic consequences for electronic conduction through TiO2 with implications for the stabilization of oxidation-sensitive catalysts on the surface. Vacuum annealing at 400 °C for 1 hour o...

  4. Effect of double AlN buffer layer on the qualities of GaN films grown by radio-frequency molecular beam epitaxy

    Institute of Scientific and Technical Information of China (English)

    Li Xin-Hua; Zhong Fei; Qiu Kai; Yin Zhi-Jun; Ji Chang-Jian

    2008-01-01

    This paper reports that the GaN thin films with Ga-polarity and high quality were grown by radio-frequency molecular beam epitaxy on sapphire (0001) substrate with a double A1N buffer layer. The buffer layer consists of a high-temperature (HT) AlN layer and a low-temperature (LT) AlN layer grown at 800℃ and 600℃, respectively. It is demonstrated that the HT-AlN layer can result in the growth of GaN epilayer in Ga-polarity and the LT-AlN layer is helpful for the improvement of the epilayer quality. It is observed that the carrier mobility of the GaN epilayer increases from 458 to 858cm2/V.s at room temperature when the thickness of LT-AlN layer varies from 0 to 20nm. The full width at half maximum of x-ray rocking curves also demonstrates a substantial improvement in the quality of GaN epilayers by the utilization of LT-AlN layer.

  5. The investigation of cobalt intercalation underneath epitaxial graphene on 6H-SiC(0 0 0 1)

    Science.gov (United States)

    Zhang, Yuxi; Zhang, Hanjie; Cai, Yiliang; Song, Junjie; He, Pimo

    2017-02-01

    The intercalation behaviour of cobalt underneath both epitaxial graphene monolayer and bilayer on 6H-SiC(0001) have been investigated by scanning tunneling microscopy (STM) and density functional theory (DFT). Upon deposition, cobalt atoms prefer to agglomerate into clusters on the epitaxial graphene. After annealing the sample to 850 °C, the intercalation of the adsorbed cobalt atoms into both monolayer and bilayer epitaxial graphene on SiC takes place, as observed by the atomically resolved STM images. Further studies based on DFT modeling and simulated STM images show that, resulting from the interplay between the intercalated cobalt atoms and the carbon layers sandwiching it, the most energetically favourable intercalation sites of cobalt atoms underneath monolayer and bilayer graphene differ. Furthermore, the results show energy barriers of 0.60 eV and 0.41 eV for cobalt penetration through mono-vacancy defects at monolayer and bilayer graphene.

  6. Impact of N-plasma and Ga-irradiation on MoS2 layer in molecular beam epitaxy

    KAUST Repository

    Mishra, Pawan

    2017-01-03

    Recent interest in two-dimensional materials has resulted in ultra-thin devices based on the transfer of transition metal dichalcogenides (TMDs) onto other TMDs or III-nitride materials. In this investigation, we realized p-type monolayer (ML) MoS2, and intrinsic GaN/p-type MoS2 heterojunction by the GaN overgrowth on ML-MoS2/c-sapphire using the plasma-assisted molecular beam epitaxy. A systematic nitrogen plasma (N∗2N2*) and gallium (Ga) irradiation studies are employed to understand the individual effect on the doping levels of ML-MoS2, which is evaluated by micro-Raman and high-resolution X-Ray photoelectron spectroscopy (HRXPS) measurements. With both methods, p-type doping was attained and was verified by softening and strengthening of characteristics phonon modes E12gE2g1 and A1gA1g from Raman spectroscopy. With adequate N∗2N2*-irradiation (3 min), respective shift of 1.79 cm−1 for A1gA1g and 1.11 cm−1 for E12gE2g1 are obtained while short term Ga-irradiated (30 s) exhibits the shift of 1.51 cm−1 for A1gA1g and 0.93 cm−1 for E12gE2g1. Moreover, in HRXPS valence band spectra analysis, the position of valence band maximum measured with respect to the Fermi level is determined to evaluate the type of doping levels in ML-MoS2. The observed values of valance band maximum are reduced to 0.5, and 0.2 eV from the intrinsic value of ≈1.0 eV for N∗2N2*- and Ga-irradiated MoS2 layers, which confirms the p-type doping of ML-MoS2. Further p-type doping is verified by Hall effect measurements. Thus, by GaN overgrowth, we attained the building block of intrinsic GaN/p-type MoS2 heterojunction. Through this work, we have provided the platform for the realization of dissimilar heterostructure via monolithic approach.

  7. Method of transferring a thin crystalline semiconductor layer

    Science.gov (United States)

    Nastasi, Michael A.; Shao, Lin; Theodore, N. David

    2006-12-26

    A method for transferring a thin semiconductor layer from one substrate to another substrate involves depositing a thin epitaxial monocrystalline semiconductor layer on a substrate having surface contaminants. An interface that includes the contaminants is formed in between the deposited layer and the substrate. Hydrogen atoms are introduced into the structure and allowed to diffuse to the interface. Afterward, the thin semiconductor layer is bonded to a second substrate and the thin layer is separated away at the interface, which results in transferring the thin epitaxial semiconductor layer from one substrate to the other substrate.

  8. Bi-layer Channel AZO/ZnO Thin Film Transistors Fabricated by Atomic Layer Deposition Technique.

    Science.gov (United States)

    Li, Huijin; Han, Dedong; Liu, Liqiao; Dong, Junchen; Cui, Guodong; Zhang, Shengdong; Zhang, Xing; Wang, Yi

    2017-12-01

    This letter demonstrates bi-layer channel Al-doped ZnO/ZnO thin film transistors (AZO/ZnO TFTs) via atomic layer deposition process at a relatively low temperature. The effects of annealing in oxygen atmosphere at different temperatures have also been investigated. The ALD bi-layer channel AZO/ZnO TFTs annealed in dry O2 at 300 °C exhibit a low leakage current of 2.5 × 10(-13)A, I on/I off ratio of 1.4 × 10(7), subthreshold swing (SS) of 0.23 V/decade, and high transmittance. The enhanced performance obtained from the bi-layer channel AZO/ZnO TFT devices is explained by the inserted AZO front channel layer playing the role of the mobility booster.

  9. Thermoelectric material including conformal oxide layers and method of making the same using atomic layer deposition

    Energy Technology Data Exchange (ETDEWEB)

    Cho, Jung Young; Ahn, Dongjoon; Salvador, James R.; Meisner, Gregory P.

    2016-06-07

    A thermoelectric material includes a substrate particle and a plurality of conformal oxide layers formed on the substrate particle. The plurality of conformal oxide layers has a total oxide layer thickness ranging from about 2 nm to about 20 nm. The thermoelectric material excludes oxide nanoparticles. A method of making the thermoelectric material is also disclosed herein.

  10. Vapour phase growth and grain boundary structure of molybdenum disulphide atomic layers.

    Science.gov (United States)

    Najmaei, Sina; Liu, Zheng; Zhou, Wu; Zou, Xiaolong; Shi, Gang; Lei, Sidong; Yakobson, Boris I; Idrobo, Juan-Carlos; Ajayan, Pulickel M; Lou, Jun

    2013-08-01

    Single-layered molybdenum disulphide with a direct bandgap is a promising two-dimensional material that goes beyond graphene for the next generation of nanoelectronics. Here, we report the controlled vapour phase synthesis of molybdenum disulphide atomic layers and elucidate a fundamental mechanism for the nucleation, growth, and grain boundary formation in its crystalline monolayers. Furthermore, a nucleation-controlled strategy is established to systematically promote the formation of large-area, single- and few-layered films. Using high-resolution electron microscopy imaging, the atomic structure and morphology of the grains and their boundaries in the polycrystalline molybdenum disulphide atomic layers are examined, and the primary mechanisms for grain boundary formation are evaluated. Grain boundaries consisting of 5- and 7- member rings are directly observed with atomic resolution, and their energy landscape is investigated via first-principles calculations. The uniformity in thickness, large grain sizes, and excellent electrical performance signify the high quality and scalable synthesis of the molybdenum disulphide atomic layers.

  11. Deep levels in a-plane, high Mg-content Mg{sub x}Zn{sub 1-x}O epitaxial layers grown by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Guer, Emre [Department of Physics, Faculty of Science, Atatuerk University, Erzurum 25240 (Turkey); 205 Dreese Laboratory, Department of Electrical and Computer Engineering, The Ohio State University, 2015 Neil Avenue, Columbus, Ohio 43210-1272 (United States); Tabares, G.; Hierro, A. [Dpto. Ingenieria Electronica and ISOM, Universidad Politecnica de Madrid, Ciudad Universitaria s/n, 28040 Madrid (Spain); Arehart, A.; Ringel, S. A. [205 Dreese Laboratory, Department of Electrical and Computer Engineering, Ohio State University, 2015 Neil Avenue, Columbus, Ohio 43210-1272 (United States); Chauveau, J. M. [CRHEA-CNRS, 06560 Valbonne (France); University of Nice Sophia Antipolis, ParcValrose, 06102 Nice Cedex 2 (France)

    2012-12-15

    Deep level defects in n-type unintentionally doped a-plane Mg{sub x}Zn{sub 1-x}O, grown by molecular beam epitaxy on r-plane sapphire were fully characterized using deep level optical spectroscopy (DLOS) and related methods. Four compositions of Mg{sub x}Zn{sub 1-x}O were examined with x = 0.31, 0.44, 0.52, and 0.56 together with a control ZnO sample. DLOS measurements revealed the presence of five deep levels in each Mg-containing sample, having energy levels of E{sub c} - 1.4 eV, 2.1 eV, 2.6 V, and E{sub v} + 0.3 eV and 0.6 eV. For all Mg compositions, the activation energies of the first three states were constant with respect to the conduction band edge, whereas the latter two revealed constant activation energies with respect to the valence band edge. In contrast to the ternary materials, only three levels, at E{sub c} - 2.1 eV, E{sub v} + 0.3 eV, and 0.6 eV, were observed for the ZnO control sample in this systematically grown series of samples. Substantially higher concentrations of the deep levels at E{sub v} + 0.3 eV and E{sub c} - 2.1 eV were observed in ZnO compared to the Mg alloyed samples. Moreover, there is a general invariance of trap concentration of the E{sub v} + 0.3 eV and 0.6 eV levels on Mg content, while at least and order of magnitude dependency of the E{sub c} - 1.4 eV and E{sub c} - 2.6 eV levels in Mg alloyed samples.

  12. Effect of Ⅲ/Ⅴ Ratio of HT-AlN Buffer Layer on Polarity Selection and Electrical Quality of GaN Films Grown by Radio Frequency Molecular Beam Epitaxy

    Institute of Scientific and Technical Information of China (English)

    ZHONG Fei; CHEN Jia-Rong; WANG Yu-Qi; QIU Kai; LI Xin-Hua; YIN Zhi-Jun; XIE Xin-Jian; WANG Yang; JI Chang-Jian; CAO Xian-Cun; HAN Qi-Feng

    2007-01-01

    @@ We investigate the effect of Al/N ratio of the high temperature (HT) AlN buffer layer on polarity selection and electrical quality of GaN films grown by radio frequency molecular beam epitaxy. The results show that low Al/N ratio results in N-polarity GaN films and intermediate Al/N ratio leads to mixed-polarity GaN films with poor electrical quality. GaN films tend to grow with Ga polarity on Al-rich AlN buffer layers. GaN films with different polarities are confirmed by in-situ reflection high-energy electron diffraction during the growth process.Wet chemical etching, together with atomic force microscopy, also proves the polarity assignments. The optimum value for room-temperature Hall mobility of the Ga-polarity GaN film is 703cm2/V.s, which is superior to the N-polarity and mixed-polarity GaN films.

  13. Solid phase epitaxial regrowth of (001) anatase titanium dioxide

    Energy Technology Data Exchange (ETDEWEB)

    Barlaz, David Eitan; Seebauer, Edmund G., E-mail: eseebaue@illinois.edu [Department of Chemical and Biomolecular Engineering, University of Illinois, 600 S Mathews Ave., Urbana, Illinois 61801 (United States)

    2016-03-15

    The growing interest in metal oxide based semiconductor technologies has driven the need to produce high quality epitaxial films of one metal oxide upon another. Largely unrecognized in synthetic efforts is that some metal oxides offer strongly polar surfaces and interfaces that require electrostatic stabilization to avoid a physically implausible divergence in the potential. The present work examines these issues for epitaxial growth of anatase TiO{sub 2} on strontium titanate (001). Solid phase epitaxial regrowth yields only the (001) facet, while direct crystalline growth by atomic layer deposition yields both the (112) and (001). The presence of amorphous TiO{sub 2} during regrowth may provide preferential stabilization for formation of the (001) facet.

  14. Large-area growth of multi-layer hexagonal boron nitride on polished cobalt foils by plasma-assisted molecular beam epitaxy

    Science.gov (United States)

    Xu, Zhongguang; Tian, Hao; Khanaki, Alireza; Zheng, Renjing; Suja, Mohammad; Liu, Jianlin

    2017-01-01

    Two-dimensional (2D) hexagonal boron nitride (h-BN), which has a similar honeycomb lattice structure to graphene, is promising as a dielectric material for a wide variety of potential applications based on 2D materials. Synthesis of high-quality, large-size and single-crystalline h-BN domains is of vital importance for fundamental research as well as practical applications. In this work, we report the growth of h-BN films on mechanically polished cobalt (Co) foils using plasma-assisted molecular beam epitaxy. Under appropriate growth conditions, the coverage of h-BN layers can be readily controlled by growth time. A large-area, multi-layer h-BN film with a thickness of 5~6 nm is confirmed by Raman spectroscopy, scanning electron microscopy, X-ray photoelectron spectroscopy and transmission electron microscopy. In addition, the size of h-BN single domains is 20~100 μm. Dielectric property of as-grown h-BN film is evaluated by characterization of Co(foil)/h-BN/Co(contact) capacitor devices. Breakdown electric field is in the range of 3.0~3.3 MV/cm, which indicates that the epitaxial h-BN film has good insulating characteristics. In addition, the effect of substrate morphology on h-BN growth is discussed regarding different domain density, lateral size, and thickness of the h-BN films grown on unpolished and polished Co foils. PMID:28230178

  15. Morphology Evolution of (331)A High-Index Surfaces During Atomic Hydrogen Assisted Molecular Beam Epitaxy (MBE)%原子氢辅助分子束外延GaAs(331)A表面形貌演化

    Institute of Scientific and Technical Information of China (English)

    牛智红; 任正伟; 贺振宏

    2008-01-01

    Step like morphology of (331)A high-index surfaces during atomic hydrogen assisted molecular beam epitaxy (MBE) growth has been investigated. Atomic Force Microscope (AFM) measurements show that in conventional MBE, the step heights and terrace widths of GaAs layers increase monotonically with increasing substrate temperatures. The terrace widths and step densities increase with increasing the GaAs layer thickness and then saturates. And, in atomic hydrogen assisted MBE, the terrace width reduces and density increases when depositing the same amount of GaAs. It attributes this to the reduced surface migration length of Ga adatoms with atomic hydrogen. Laterally ordered InAs self-aligned nano-wires were grown on GaAs (331)A surfaces and its optical polarization properties were revealed by photoluminescence measurements.%研究了GaAs高指数面(331)A在原子氢辅助下分子束外延形貌的演化.原子力显微镜测试表明:在常规分子束外延情况下,GaAs外延层台阶的厚度和台面的宽度随衬底温度的升高而增加,增加外延层厚度会导致台阶的密度和台面的宽度增加然后饱和.而在原子氢辅助分子束外延情况下,当GaAs淀积量相同时GaAs外延层台阶的密度增大宽度减小.认为这是由于原子氢的作用导致Ga原子迁移长度的减小.在GaAs(331)A台阶基底上生长出InAs自组织纳米线,用光荧光测试研究了其光学各项异性特征.

  16. Si衬底上热壁外延制备GaAs单晶薄膜材料%Growth of Monocrystalline GaAs Layer on Si by Hot Wall Epitaxy

    Institute of Scientific and Technical Information of China (English)

    刘翔; 谭红琳; 吴长树; 张鹏翔; 赵德锐; 陈庭金; 廖世坤; 吴刚; 杨家明

    2000-01-01

    This paper reports the growth of GaAs layer on Si substrate by hot wall epitaxy (HWE). Si surface prior to epitaxy of GaAs layer is activated. Then two - step epitaxy is used to achieve GaAs layer. Finally, intermittent multi - layer cycle annealing (IMCA) is implemented to improve morphology and quality of the epitaxial layer. Measurement and analysis by electron probe micro - analysis (EPMA), Raman spectrum, Hall measurement and photo - luminescence (PL) confirm that GaAs layer with thickness of approximately 4 μm has been obtained.%报道了采用热壁外延(HWE)技术,在Si表面生长GaAs薄膜。先通过活化剂活化Si表面,再采取两步生长法外延GaAs单晶薄膜,最后进行断续多层循环退火(IMCA)。经电子探针(EPMA)、Raman光谱、Hall测量和荧光(PL)光谱测试分析,证实在Si表面获得了近4μm厚的GaAs单晶薄膜。

  17. Epitaxial Growth of Graphene on 6H-SiC (0001) by Thermal Annealing

    Institute of Scientific and Technical Information of China (English)

    TANG Jun; LIU Zhong-Liang; KANG Chao-Yang; PAN Hai-Bin; WEI Shi-Qiang; XU Peng-Shou; GAO Yu-Qiang; XU Xian-Gang

    2009-01-01

    An epitaxial graphene (EG) layer is successfully grown on a Si-terminated 6H-SiC (0001) substrate by the method of thermal annealing in an ultrahigh vacuum molecular beam epitaxy chamber.The structure and morphology of the EG sample are characterized by reflection high energy diffraction (RHEED),Raman spectroscopy and atomic force microscopy (AFM).Graphene diffraction streaks can be seen in RHEED.The G and 2D peaks of graphene are clearly observed in the Raman spectrum.The AFM results show that the graphene nominal thickness is about 4-10 layers.

  18. Strain and Structure Heterogeneity in MoS2 Atomic Layers Grown by Chemical Vapour Deposition

    Science.gov (United States)

    2014-11-18

    with second-layer MoS2 stripes grown along the GBs, indicated by the white arrows. Scale bar, 5 mm. (e) Annular dark-field scanning TEM image of defect...lattice of monolayer MoS2 (Fig. 1e) can be seen from the annular dark field scanning TEM imaging. The brighter atomic sites are Mo atoms, while the...strains in MoS2 layer as a function of the applied strain on PDMS are shown in Fig. 4i, where a linear relationship is predicted within the range of 5

  19. Epitaxial growth of thick 4H?SiC layers in a vertical radiant-heating reactor

    Science.gov (United States)

    Tsuchida, H.; Kamata, I.; Jikimoto, T.; Izumi, K.

    2002-04-01

    A vertical radiant-heating reactor has been developed for thick silicon carbide (SiC) epitaxial growth, in which the susceptor and substrates are heated by radiation from the hot wall. The benefit of the heating and sample-holding method is demonstrated by improvements in the curvature of crystal bending and FWHM of X-ray ω-rocking curves followed by epitaxial growth. The typical growth rate is 13-16 μm/h at 1530-1550°C at the susceptor top under reduced pressure as low as 50-70 mbar. Low background doping at low 10 13 cm -3 ( Nd- Na) was achieved, and some of the 4H-SiC epilayers exhibited a high resistivity. We also succeeded in growing a 4H-SiC epilayer over 240 μm-thick with minimal surface roughness. Little sign of impurities was observed by low-temperature photoluminescence (LTPL), and no impurities (Al, B, Ti, V and Cr) exceeding 1×10 14 cm -3 were found by secondary ion mass spectroscopy (SIMS) for a 150 μm-thick 4H-SiC epilayer. Thickness and doping uniformity along the gas flow of ˜5% and ˜11%, respectively, were obtained for 2-in substrates. Molten KOH etching analysis revealed that some of the micropipes were dissociated into closed core screw dislocations during epitaxial growth. The electrical performance of high-voltage devices was also demonstrated.

  20. Experimental investigations of atomic ordering effects in the epitaxial GaxIn1-xP, coherently grown on GaAs (100) substrates

    Science.gov (United States)

    Seredin, P. V.; Goloshchapov, D. L.; Khudyakov, Yu. Yu.; Lenshin, A. S.; Lukin, A. N.; Arsentyev, I. N.; Prutskij, Tatiana

    2017-03-01

    A range of structural and spectroscopic techniques were used for the study of the properties of epitaxial GaxIn1-xP alloys with an ordered arrangement of atoms in a crystal lattice grown by MOCVD on single-crystalline substrates of GaAs (100). The appearance of atomic ordering in the coherent growth conditions of the ordered GaxIn1-xP alloy on GaAs (100) resulted in cardinal changes of the structural and optical properties of semiconductor in comparison to disordered alloys, including the change of the crystal lattice parameter and, consequently, reduced crystal symmetry, decreased band gap and formation of two different types of surface nanorelief. This is the first report of the calculation of parameters of the crystal lattice in GaxIn1-xP with ordering taking into account the elastic stresses dependent on long-range ordering. Based on the variance analysis data with regard to the IR-reflection spectra as well as the UV-spectroscopy data obtained in the transmission-reflection mode, the main optical characteristics of the ordered GaxIn1-xP alloys were determined for the first time, namely, refractive index dispersion and high-frequency dielectric constant. All of the experimental results were in good agreement with the previously developed theoretical beliefs.

  1. Atomic Layer Deposition of High-k Dielectrics Using Supercritical CO2

    Science.gov (United States)

    Shende, Rajesh

    2005-03-01

    Atomic layer deposition (ALD) of high-κdielectric was performed in supercritical CO2 (SCCO2), using a two-step reaction sequence. In step one, tetraethoxy silane (TEOS) precursor was injected in SCCO2 at 80-100 C and 50 MPa pressure to obtain a chemisorbed surface monolayer, which was then oxidized into SiO2 using peroxide entrained in SCCO2. ALD process was controlled by estimating precursor solubility and its mass transport with respect to the density of SCCO2, and correlating these parameters with precursor injection volume. In the ALD process, 7 pulses of precursor were used anticipating deposition of one atomic layer in each of the pulses. The thickness of the SiO2 atomic layers deposited using SCCO2 was measured by variable angle spectroscopic ellipsometry (VASE), and the C-V measurements were also performed. The result obtained using VASE indicates that there were 7 monolayers of SiO2 with total thickness of 35 å, and the dielectric constant of the deposited layers was 4.0±0.1. Our initial findings clearly demonstrate that SCCO2 is capable of atomic layer deposition of high quality dielectric films at very low process temperatures preventing interface reaction. More research is in progress to achieve ALD of HfO2 and TiO2 in SCCO2.

  2. Subharmonic excitation in amplitude modulation atomic force microscopy in the presence of adsorbed water layers

    Energy Technology Data Exchange (ETDEWEB)

    Santos, Sergio [Laboratory of Energy and Nanosciences, Masdar Institute of Science and Technology, P.O. BOX 54224, Abu Dhabi (United Arab Emirates); Barcons, Victor [Departament de Disseny i Programacio de Sistemes Electronics, UPC - Universitat Politecnica de Catalunya Av. Bases, 61, 08242 Manresa (Spain); Verdaguer, Albert [Centre d' Investigacio en Nanociencia i Nanotecnologia (CIN2) (CSIC-ICN), Esfera UAB, Campus de la UAB, Edifici CM-7, 08193-Bellaterra, Catalunya (Spain); Chiesa, Matteo [Laboratory of Energy and Nanosciences, Masdar Institute of Science and Technology, P.O. BOX 54224, Abu Dhabi (United Arab Emirates); Department of Mechanical Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139-4307 (United States)

    2011-12-01

    In ambient conditions, nanometric water layers form on hydrophilic surfaces covering them and significantly changing their properties and characteristics. Here we report the excitation of subharmonics in amplitude modulation atomic force microscopy induced by intermittent water contacts. Our simulations show that there are several regimes of operation depending on whether there is perturbation of water layers. Single period orbitals, where subharmonics are never induced, follow only when the tip is either in permanent contact with the water layers or in pure noncontact where the water layers are never perturbed. When the water layers are perturbed subharmonic excitation increases with decreasing oscillation amplitude. We derive an analytical expression which establishes whether water perturbations compromise harmonic motion and show that the predictions are in agreement with numerical simulations. Empirical validation of our interpretation is provided by the observation of a range of values for apparent height of water layers when subharmonic excitation is predicted.

  3. Dislocation blocking by AlGaN hot electron injecting layer in the epitaxial growth of GaN terahertz Gunn diode

    Science.gov (United States)

    Li, Liang; Yang, Lin'an; Zhang, Jincheng; Hao, Yue

    2013-09-01

    This paper reports an efficient method to improve the crystal quality of GaN Gunn diode with AlGaN hot electron injecting layer (HEI). An evident reduction of screw dislocation and edge dislocation densities is achieved by the strain management and the enhanced lateral growth in high temperature grown AlGaN HEI layer. Compared with the top hot electron injecting layer (THEI) structure, the bottom hot electron injecting layer (BHEI) structure enhances the crystal quality of transit region due to the growth sequence modulation of HEI layer. A high Hall mobility of 2934 cm2/Vs at 77 K, a nearly flat downtrend of Hall mobility at the temperature ranging from 300 to 573 K, a low intensity of ratio of yellow luminescence band to band edge emission, a narrow band edge emission line-width, and a smooth surface morphology are observed for the BHEI structural epitaxy of Gunn diode, which indicates that AlGaN BHEI structure is a promising candidate for fabrication of GaN Gunn diodes in terahertz regime.

  4. Surface segregation as a means of gettering Cu in liquid-phase-epitaxy silicon thin layers grown from Al-Cu-Si solutions

    Energy Technology Data Exchange (ETDEWEB)

    Wang, T.H.; Ciszek, T.F.; Reedy, R.; Asher, S.; King, D. [National Renewable Energy Lab., Golden, CO (United States)

    1996-05-01

    The authors demonstrate that, by using the natural surface segregation phenomenon, Cu can be gettered to the surface from the bulk of silicon layers so that its concentrations in the liquid-phase-epitaxy (LPE) layers are much lower than its solubility at the layer growth temperature and the reported 10{sup 17} cm{sup {minus}3} degradation threshold for solar-cell performance. Secondary-ion mass spectroscopy (SIMS) analysis indicates that, within a micron-deep sub-surface region, Cu accumulates even in as-grown LPE samples. Slower cooling after growth to room temperature enhances this Cu enrichment. X-ray photoelectron spectroscopy (XPS) measurement shows as much as 3.2% Cu in a surface region of about 50 {Angstrom}. More surface-sensitive, ion-scattering spectroscopy (ISS) analysis further reveals about 7% of Cu at the top surface. These results translate to an areal gettering capacity of about 1.0 x 10{sup 16} cm{sup {minus}2}, which is higher than the available total-area density of Cu in the layer and substrate (3.6 x 10{sup 15} cm{sup {minus}2} for a uniform 1.2 x 10{sup 17}cm{sup {minus}3} Cu throughout the layer and substrate with a total thickness of 300 {mu}m).

  5. Interlayer breathing and shear modes in NbSe2 atomic layers

    Science.gov (United States)

    He, Rui; van Baren, Jeremiah; Yan, Jia-An; Xi, Xiaoxiang; Ye, Zhipeng; Ye, Gaihua; Lu, I.-Hsi; Leong, S. M.; Lui, C. H.

    2016-09-01

    Atomically thin NbSe2 is a metallic layered transition metal dichalcogenide with novel charge-density-wave (CDW) and superconductive phases. Properties of NbSe2 atomic layers are sensitive to interlayer coupling. Here we investigate the interlayer phonons of few-layer NbSe2 by ultralow-frequency Raman spectroscopy. We observe both the interlayer breathing modes and shear modes at frequencies below 40 cm-1 for samples of 2-15 layers. Their frequency, Raman activity, and environmental instability depend systematically on the layer number. We account for these results by a combination of linear-chain model, group theory and first-principles calculations. We find that, although NbSe2 has different stacking order from MoS2, MoSe2, WS2 and WSe2, they share the same crystal symmetry groups and exhibit similar Raman selection rules for interlayer phonons. In addition, the interlayer phonon modes evolve smoothly from T = 300 to 8 K, with no observable response to the CDW formation in NbSe2. This finding indicates that the atomic registry between adjacent NbSe2 layers is well preserved in the CDW transition.

  6. Atomic-layer soft plasma etching of MoS2.

    Science.gov (United States)

    Xiao, Shaoqing; Xiao, Peng; Zhang, Xuecheng; Yan, Dawei; Gu, Xiaofeng; Qin, Fang; Ni, Zhenhua; Han, Zhao Jun; Ostrikov, Kostya Ken

    2016-01-01

    Transition from multi-layer to monolayer and sub-monolayer thickness leads to the many exotic properties and distinctive applications of two-dimensional (2D) MoS2. This transition requires atomic-layer-precision thinning of bulk MoS2 without damaging the remaining layers, which presently remains elusive. Here we report a soft, selective and high-throughput atomic-layer-precision etching of MoS2 in SF6 + N2 plasmas with low-energy (MoS2 layers are removed uniformly across domains with vastly different initial thickness, without affecting the underlying SiO2 substrate and the remaining MoS2 layers. The etching rates can be tuned to achieve complete MoS2 removal and any desired number of MoS2 layers including monolayer. Layer-dependent vibrational and photoluminescence spectra of the etched MoS2 are also demonstrated. This soft plasma etching technique is versatile, scalable, compatible with the semiconductor manufacturing processes, and may be applicable for a broader range of 2D materials and intended device applications.

  7. Large area growth and electrical properties of p-type WSe2 atomic layers.

    Science.gov (United States)

    Zhou, Hailong; Wang, Chen; Shaw, Jonathan C; Cheng, Rui; Chen, Yu; Huang, Xiaoqing; Liu, Yuan; Weiss, Nathan O; Lin, Zhaoyang; Huang, Yu; Duan, Xiangfeng

    2015-01-14

    Transition metal dichacogenides represent a unique class of two-dimensional layered materials that can be exfoliated into single or few atomic layers. Tungsten diselenide (WSe(2)) is one typical example with p-type semiconductor characteristics. Bulk WSe(2) has an indirect band gap (∼ 1.2 eV), which transits into a direct band gap (∼ 1.65 eV) in monolayers. Monolayer WSe(2), therefore, is of considerable interest as a new electronic material for functional electronics and optoelectronics. However, the controllable synthesis of large-area WSe(2) atomic layers remains a challenge. The studies on WSe(2) are largely limited by relatively small lateral size of exfoliated flakes and poor yield, which has significantly restricted the large-scale applications of the WSe(2) atomic layers. Here, we report a systematic study of chemical vapor deposition approach for large area growth of atomically thin WSe(2) film with the lateral dimensions up to ∼ 1 cm(2). Microphotoluminescence mapping indicates distinct layer dependent efficiency. The monolayer area exhibits much stronger light emission than bilayer or multilayers, consistent with the expected transition to direct band gap in the monolayer limit. The transmission electron microscopy studies demonstrate excellent crystalline quality of the atomically thin WSe(2). Electrical transport studies further show that the p-type WSe(2) field-effect transistors exhibit excellent electronic characteristics with effective hole carrier mobility up to 100 cm(2) V(-1) s(-1) for monolayer and up to 350 cm(2) V(-1) s(-1) for few-layer materials at room temperature, comparable or well above that of previously reported mobility values for the synthetic WSe(2) and comparable to the best exfoliated materials.

  8. Bismuth iron oxide thin films using atomic layer deposition of alternating bismuth oxide and iron oxide layers

    Energy Technology Data Exchange (ETDEWEB)

    Puttaswamy, Manjunath; Vehkamäki, Marko [University of Helsinki, Department of Chemistry, P.O. Box 55, FI-00014 Helsinki (Finland); Kukli, Kaupo, E-mail: kaupo.kukli@helsinki.fi [University of Helsinki, Department of Chemistry, P.O. Box 55, FI-00014 Helsinki (Finland); University of Tartu, Institute of Physics, W. Ostwald 1, EE-50411 Tartu (Estonia); Dimri, Mukesh Chandra [National Institute of Chemical Physics and Biophysics, Akadeemia tee 23, EE-12618 Tallinn (Estonia); Kemell, Marianna; Hatanpää, Timo; Heikkilä, Mikko J. [University of Helsinki, Department of Chemistry, P.O. Box 55, FI-00014 Helsinki (Finland); Mizohata, Kenichiro [University of Helsinki, Department of Physics, P.O. Box 64, FI-00014 Helsinki (Finland); Stern, Raivo [National Institute of Chemical Physics and Biophysics, Akadeemia tee 23, EE-12618 Tallinn (Estonia); Ritala, Mikko; Leskelä, Markku [University of Helsinki, Department of Chemistry, P.O. Box 55, FI-00014 Helsinki (Finland)

    2016-07-29

    Bismuth iron oxide films with varying contributions from Fe{sub 2}O{sub 3} or Bi{sub 2}O{sub 3} were prepared using atomic layer deposition. Bismuth (III) 2,3-dimethyl-2-butoxide, was used as the bismuth source, iron(III) tert-butoxide as the iron source and water vapor as the oxygen source. The films were deposited as stacks of alternate Bi{sub 2}O{sub 3} and Fe{sub 2}O{sub 3} layers. Films grown at 140 °C to the thickness of 200–220 nm were amorphous, but crystallized upon post-deposition annealing at 500 °C in nitrogen. Annealing of films with intermittent bismuth and iron oxide layers grown to different thicknesses influenced their surface morphology, crystal structure, composition, electrical and magnetic properties. Implications of multiferroic performance were recognized in the films with the remanent charge polarization varying from 1 to 5 μC/cm{sup 2} and magnetic coercivity varying from a few up to 8000 A/m. - Highlights: • Bismuth iron oxide thin films were grown by atomic layer deposition at 140 °C. • The major phase formed in the films upon annealing at 500 °C was BiFeO{sub 3}. • BiFeO{sub 3} films and films containing excess Bi favored electrical charge polarization. • Slight excess of iron oxide enhanced saturative magnetization behavior.

  9. Epitaxial Cu(001) films grown on a Cr/Ag/Fe/GaAs(001) buffer system

    Energy Technology Data Exchange (ETDEWEB)

    Gottlob, Daniel M., E-mail: d.gottlob@fz-juelich.de [Peter Grünberg Institut, Electronic Properties (PGI-6), Forschungszentrum Jülich, 52425 Jülich (Germany); Fakultät für Physik and Center for Nanointegration Duisburg-Essen (CeNIDE), Universität Duisburg-Essen, 47048 Duisburg (Germany); Jansen, Thomas [Peter Grünberg Institut, Electronic Properties (PGI-6), Forschungszentrum Jülich, 52425 Jülich (Germany); Jülich-Aachen Research Alliance, Fundamentals for Future Information Technology (JARA-FIT), Forschungszentrum Jülich, 52425 Jülich (Germany); Hoppe, Michael [Peter Grünberg Institut, Electronic Properties (PGI-6), Forschungszentrum Jülich, 52425 Jülich (Germany); Bürgler, Daniel E. [Peter Grünberg Institut, Electronic Properties (PGI-6), Forschungszentrum Jülich, 52425 Jülich (Germany); Jülich-Aachen Research Alliance, Fundamentals for Future Information Technology (JARA-FIT), Forschungszentrum Jülich, 52425 Jülich (Germany); and others

    2014-07-01

    We present a procedure to prepare single-crystalline, high-purity Cu(001) films (templates) suitable as substrates for subsequent epitaxial thin-film growth. The template films were grown in a dedicated molecular-beam epitaxy system on a Cr/Ag/Fe/GaAs(001) buffer layer system. Low-energy electron diffraction and X-ray diffraction were applied to determine the surface orientation and the epitaxial relationship between all layers of the stack. Post-annealing at moderate temperatures enhances the quality of the film as shown by low-energy electron diffraction and atomic force microscopy. X-ray photoemission and Auger electron spectroscopy confirm that no atoms of the buffer layers diffuse into the Cu film during the initial preparation and the post-annealing treatment. The completed Cu(001) template system can be exposed to air and afterwards refurbished by Ar{sup +}-ion bombardment and annealing, enabling the transfer between vacuum systems. The procedure provides suitable conductive thin film templates for studies of epitaxial thin films, e.g. on the magnetic and magnetotransport properties of Co and Ni based films and multilayers. - Highlights: • Preparation of epitaxial Cu(001) template films on an insulating substrate • Characterization of template structure, orientation, cleanness, and roughness • Template films can be exposed to air and refurbished in different vacuum system. • Template films are suitable for further thin film growth at up to 570 K.

  10. Magnetic and dielectric properties of layered perovskite Gd2Ti2O7 thin film epitaxially stabilized on a perovskite single crystal

    Science.gov (United States)

    Ukita, Takashi; Hirose, Yasushi; Ohno, Sawako; Hatabayashi, Kunitada; Fukumura, Tomoteru; Hasegawa, Tetsuya

    2012-04-01

    Layered perovskite (LP) titanates, Ln2Ti2O7 (Ln = lanthanoids), are ferroelectric materials containing magnetic Ln3+ ions at A-site. Metastable LP-Gd2Ti2O7 was fabricated in epitaxial thin film form on lattice-matched perovskite substrates and its dielectric and magnetic properties were investigated. The (100)-oriented LP-Gd2Ti2O7 films were epitaxially grown on (110) plane of (LaAlO3)0.3-(SrAl0.5Ta0.5O3)0.7 (LSAT) and Nb-doped SrTiO3 by using a pulsed laser deposition method. Piezoresponse force microscope measurements revealed that LP-Gd2Ti2O7 has spontaneous polarization along the b-axis at room temperature, strongly suggesting room temperature ferroelectricity. Magnetization measurements showed paramagnetic behavior with weak antiferromagnetic interaction around 2 K. Small positive magneto-dielectric effect (Δɛ/ɛ ˜ 10-5 order) was also confirmed at 10 K.

  11. Protection of Polymers from the Space Environment by Atomic Layer Deposition

    Science.gov (United States)

    Lindholm, Ned F.; Zhang, Jianming; Minton, Timothy K.; O'Patchen, Jennifer; George, Steven M.; Groner, Markus D.

    2009-01-01

    Polymers in space may be subjected to a barrage of incident atoms, photons, and/or ions. For example, oxygen atoms can etch and oxidize these materials. Photons may act either alone or in combination with oxygen atoms to degrade polymers and paints and thus limit their usefulness. Colors fade under the intense vacuum ultraviolet (VUV) solar radiation. Ions can lead to the build-up of static charge on polymers. Atomic layer deposition (ALD) techniques can provide coatings that could mitigate many challenges for polymers in space. ALD is a gas-phase technique based on two sequential, self-limiting surface reactions, and it can deposit very uniform, conformal, and pinhole-free films with atomic layer control. We have studied the efficacy of various ALD coatings to protect Kapton® polyimide, FEP Teflon®, and poly(methyl methacrylate) films from atomic-oxygen and VUV attack. Atomic-oxygen and VUV studies were conducted with the use of a laser-breakdown source for hyperthermal O atoms and a D2 lamp as a source of VUV light. These studies used a quartz crystal microbalance (QCM) to monitor mass loss in situ, as well as surface profilometry and scanning electron microscopy to study the surface recession and morphology changes ex situ. Al2O3 ALD coatings applied to polyimide and FEP Teflon® films protected the underlying substrates from O-atom attack, and ZnO coatings protected the poly(methyl methacrylate) substrate from VUV-induced damage.

  12. In-situ RHEED analysis of atomic layer deposition and characterization of AL203 gate dielectrics

    NARCIS (Netherlands)

    Bankras, R.G.; Aarnink, A.A.I.; Holleman, J.; Schmitz, J.

    2003-01-01

    A new custom designed reactor was realized at the MESA+ cleanroom to fabricate high-k dielectrics using atomic layer deposition (ALD). Key features of the reactor are: a small reactor volume, in-situ RHEED analysis and low background pressure. The effect of precursor and purge pulse times is discuss

  13. History of atomic layer deposition and its relationship with the American Vacuum Society

    NARCIS (Netherlands)

    Parsons, G.N.; Elam, J.W.; George, S.M.; Haukka, S.; Jeon, H.; Kessels, W.M.M.; Leskelä, M.; Poodt, P.; Ritala, M.; Rossnagel, S.M.

    2013-01-01

    This article explores the history of atomic layer deposition (ALD) and its relationship with the American Vacuum Society (AVS). The authors describe the origin and history of ALD science in the 1960s and 1970s. They also report on how the science and technology of ALD progressed through the 1990s an

  14. Atomic layer deposition of platinum clusters on titania nanoparticles at atmospheric pressure

    NARCIS (Netherlands)

    Goulas, A.; Van Ommen, J.R.

    2013-01-01

    We report the fabrication of platinum nanoclusters with a narrow size distribution on TiO2 nanoparticles using atomic layer deposition. With MeCpPtMe3 and ozone as reactants, the deposition can be carried out at a relatively low temperature of 250 degrees C. Our approach of working with suspended na

  15. Atmospheric spatial atomic layer deposition of in-doped ZnO

    NARCIS (Netherlands)

    Illiberi, A.; Scherpenborg, R.; Roozeboom, F.; Poodt, P.

    2014-01-01

    Indium-doped zinc oxide (ZnO:In) has been grown by spatial atomic layer deposition at atmospheric pressure (spatial-ALD). Trimethyl indium (TMIn), diethyl zinc (DEZ) and deionized water have been used as In, Zn and O precursor, respectively. The metal content of the films is controlled in the range

  16. On the environmental stability of ZnO thin films by spatial atomic layer deposition

    NARCIS (Netherlands)

    Illiberi, A.; Scherpenborg, R.; Theelen, M.; Poodt, P.; Roozeboom, F.

    2013-01-01

    Undoped and indium-doped ZnO films have been deposited by atmospheric spatial atomic-layer-deposition (spatial-ALD). The stability of their electrical, optical, and structural properties has been investigated by a damp-heat test in an environment with 85% relative humidity at 85 °C. The resistivity

  17. Modeling Mechanism and Growth Reactions for New Nanofabrication Processes by Atomic Layer Deposition.

    Science.gov (United States)

    Elliott, Simon D; Dey, Gangotri; Maimaiti, Yasheng; Ablat, Hayrensa; Filatova, Ekaterina A; Fomengia, Glen N

    2016-07-01

    Recent progress in the simulation of the chemistry of atomic layer deposition (ALD) is presented for technologically important materials such as alumina, silica, and copper metal. Self-limiting chemisorption of precursors onto substrates is studied using density functional theory so as to determine reaction pathways and aid process development. The main challenges for the future of ALD modeling are outlined.

  18. The kinetics of low-temperature spatial atomic layer deposition of aluminum oxide

    NARCIS (Netherlands)

    Poodt, P.W.G.; Illiberi, A.; Roozeboom, F.

    2013-01-01

    Spatial atomic layer deposition can be used as a high-throughput manufacturing technique in functional thin film deposition for applications such as flexible electronics. This, however, requires low-temperature deposition processes. We have investigated the kinetics of low-temperature (< 100 C) spat

  19. Role of atomic terraces and steps in the electron transport properties of epitaxial graphene grown on SiC

    Directory of Open Access Journals (Sweden)

    H. Kuramochi

    2012-03-01

    Full Text Available Thermal decomposition of vicinal SiC substrates with self-organized periodic nanofacets is a promising method to produce large graphene sheets toward the commercial exploitation of graphene's superior electronic properties. The epitaxial graphene films grown on vicinal SiC comprise two distinct regions of terrace and step; and typically exhibit anisotropic electron transport behavior, although limited areas in the graphene film showed ballistic transport. To evaluate the role of terraces and steps in electron transport properties, we compared graphene samples with terrace and step regions grown on 4H-SiC(0001. Arrays of field effect transistors were fabricated on comparable graphene samples with their channels parallel or perpendicular to the nanofacets to identify the source of measured reduced mobility. Minimum conductivity and electron mobility increased with the larger proportional terrace region area; therefore, the terrace region has superior transport properties to step regions. The measured electron mobility in the terrace region, ∼1000 cm2/Vs, is 10 times larger than that in the step region, ∼100 cm2/Vs. We conclusively determine that parasitic effects originate in regions of graphene that grow over step edges in 4H-SiC(0001.

  20. A novel controllable double-layer magnetic lattice with cold atoms

    Institute of Scientific and Technical Information of China (English)

    Min Yun; Jianping Yin

    2005-01-01

    We propose a novel array of controllable double-well magnetic microtraps for cold atoms by using an array of square current-carrying wires and two additional bias magnetic fields. Arrays of double layer magnetooptical traps (MOTs) and Ioffe traps can be constructed by using same wire configurations and different currents and bias fields. Furthermore, the array of double-well magnetic microtraps can be continuously evolved as an array of single-well magnetic microtraps by reducing the currents in the wires. Our study shows that our scheme can be used to realize a controllable double-layer magnetic lattice with cold atoms, to form array of Bose-Einstein condensations (BECs), or to study atom interference, and so on.

  1. Low temperature formation of higher-k cubic phase HfO{sub 2} by atomic layer deposition on GeO{sub x}/Ge structures fabricated by in-situ thermal oxidation

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, R., E-mail: zhang@mosfet.t.u-tokyo.ac.jp [School of Engineering, The University of Tokyo, 2-11-16 Yayoi, Bunkyo-ku, Tokyo 113-8656 (Japan); Department of Information Science and Electronic Engineering, Zhejiang University, 38 Zheda Road, Hangzhou 310027 (China); Huang, P.-C.; Taoka, N.; Yokoyama, M.; Takenaka, M.; Takagi, S. [School of Engineering, The University of Tokyo, 2-11-16 Yayoi, Bunkyo-ku, Tokyo 113-8656 (Japan)

    2016-02-01

    We have demonstrated a low temperature formation (300 °C) of higher-k HfO{sub 2} using atomic layer deposition (ALD) on an in-situ thermal oxidation GeO{sub x} interfacial layer. It is found that the cubic phase is dominant in the HfO{sub 2} film with an epitaxial-like growth behavior. The maximum permittivity of 42 is obtained for an ALD HfO{sub 2} film on a 1-nm-thick GeO{sub x} form by the in-situ thermal oxidation. It is suggested from physical analyses that the crystallization of cubic phase HfO{sub 2} can be induced by the formation of six-fold crystalline GeO{sub x} structures in the underlying GeO{sub x} interfacial layer.

  2. Semiconductors and semimetals epitaxial microstructures

    CERN Document Server

    Willardson, Robert K; Beer, Albert C; Gossard, Arthur C

    1994-01-01

    Newly developed semiconductor microstructures can now guide light and electrons resulting in important consequences for state-of-the-art electronic and photonic devices. This volume introduces a new generation of epitaxial microstructures. Special emphasis has been given to atomic control during growth and the interrelationship between the atomic arrangements and the properties of the structures.Key Features* Atomic-level control of semiconductor microstructures* Molecular beam epitaxy, metal-organic chemical vapor deposition* Quantum wells and quantum wires* Lasers, photon(IR)detectors, heterostructure transistors

  3. Direct observation of strain in InAs quantum dots and cap layer during molecular beam epitaxial growth using in situ X-ray diffraction

    Energy Technology Data Exchange (ETDEWEB)

    Shimomura, Kenichi; Ohshita, Yoshio; Kamiya, Itaru, E-mail: kamiya@toyota-ti.ac.jp [Toyota Technological Institute, 2-12-1 Hisakata, Tempaku, Nagoya 468-8511 (Japan); Suzuki, Hidetoshi [Faculty of Engineering, University of Miyazaki, 1-1 Gakuen Kibanadai-nishi, Miyazaki 889-2192 (Japan); Sasaki, Takuo; Takahasi, Masamitu [Quantum Beam Science Center, Japan Atomic Energy Agency, Koto 1-1-1, Sayo-cho, Hyogo 679-5148 (Japan)

    2015-11-14

    Direct measurements on the growth of InAs quantum dots (QDs) and various cap layers during molecular beam epitaxy are performed by in situ X-ray diffraction (XRD). The evolution of strain induced both in the QDs and cap layers during capping is discussed based on the XRD intensity transients obtained at various lattice constants. Transients with different features are observed from those obtained during InGaAs and GaAs capping. The difference observed is attributed to In-Ga intermixing between the QDs and the cap layer under limited supply of In. Photoluminescence (PL) wavelength can be tuned by controlling the intermixing, which affects both the strain induced in the QDs and the barrier heights. The PL wavelength also varies with the cap layer thickness. A large redshift occurs by reducing the cap thickness. The in situ XRD observation reveals that this is a result of reduced strain. We demonstrate how such information about strain can be applied for designing and preparing novel device structures.

  4. Structural and morphological properties of GaN buffer layers grown by ammonia molecular beam epitaxy on SiC substrates for AlGaN/GaN high electron mobility transistors

    Science.gov (United States)

    Corrion, A. L.; Poblenz, C.; Wu, F.; Speck, J. S.

    2008-05-01

    The impact of growth conditions on the surface morphology and structural properties of ammonia molecular beam epitaxy GaN buffers layers on SiC substrates was investigated. The threading dislocation (TD) density was found to decrease with decreasing NH3:Ga flux ratio, which corresponded to an increase in surface roughness and reduction in residual compressive lattice mismatch stress. Furthermore, the dislocation density and compressive stress decreased for increasing buffer thickness. TD inclination was proposed to account for these observations. Optimized surface morphologies were realized at high NH3:Ga flux ratios and were characterized by monolayer-high steps, spiral hillocks, and pyramidal mounds, with rms roughness of ˜1.0 nm over 2×2 μm2 atomic force microscopy images. Smooth surface morphologies were realized over a large range of growth temperatures and fluxes, and growth rates of up to 1 μm/h were achieved. TD densities in the buffers as low as 3×109 cm-2 were demonstrated. These buffers were highly insulating and were used in recently reported AlGaN/GaN HEMTs with power densities of >11 W/mm at 4 and 10 GHz.

  5. Design of step composition gradient thin film transistor channel layers grown by atomic layer deposition

    Science.gov (United States)

    Ahn, Cheol Hyoun; Hee Kim, So; Gu Yun, Myeong; Koun Cho, Hyung

    2014-12-01

    In this study, we proposed the artificially designed channel structure in oxide thin-film transistors (TFTs) called a "step-composition gradient channel." We demonstrated Al step-composition gradient Al-Zn-O (AZO) channel structures consisting of three AZO layers with different Al contents. The effects of stacking sequence in the step-composition gradient channel on performance and electrical stability of bottom-gate TFT devices were investigated with two channels of inverse stacking order (ascending/descending step-composition). The TFT with ascending step-composition channel structure (5 → 10 → 14 at. % Al composition) showed relatively negative threshold voltage (-3.7 V) and good instability characteristics with a reduced threshold voltage shift ( Δ 1.4 V), which was related to the alignment of the conduction band off-set within the channel layer depending on the Al contents. Finally, the reduced Al composition in the initial layer of ascending step-composition channel resulted in the best field effect mobility of 4.5 cm2/V s. We presented a unique active layer of the "step-composition gradient channel" in the oxide TFTs and explained the mechanism of adequate channel design.

  6. Epitaxial growth and characterization of Gd2O3-doped HfO2 film on Ge (001) substrates with zero interface layer

    Institute of Scientific and Technical Information of China (English)

    张心强; 屠海令; 魏峰; 熊玉华; 杨萌萌; 赵洪滨; 杜军; 王文武

    2013-01-01

    The GHO (Gd2O3-doped HfO2) films were epitaxially grown on Ge (001) substrates adopting cube-on-cube mode with zero interface layer using pulsed laser deposition (PLD). Reflection high-energy electron diffraction (RHEED) and high-resolution transmission electron microscopy (HRTEM) observation revealed a sharp interface of GHO/Ge and orientation relationship corre-sponding to (001)GHO//(001)Ge and [011] GHO//[011]Ge. The band offset for GHO/Ge stack was evaluated to be 3.92 eV for va-lence band and 1.38 eV for conduction band by X-ray photoelectron spectrum. Small equivalent oxide thickness (0.49 nm) and inter-face state density (7×1011 cm-2) were achieved from Au/Ti/GHO/Ge/Al capacitors.

  7. Study of the conduction-type conversion in Si-doped (631)A GaAs layers grown by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Cruz-Hernandez, E.; Vazquez-Cortes, D.; Mendez-Garcia, V.H. [Coordinacion para la Innovacion y Aplicacion de la Ciencia y Tecnologia, Universidad Autonoma de San Luis Potosi, Av. Sierra Leona 550, Col. Lomas 2a. Seccion, San Luis Potosi, S.L.P. 78210 (Mexico); Shimomura, S. [Graduate School of Science and Engineering, Ehime University, 3 Bukyo-cho, Matsuyama, Ehime 790-8577 (Japan); Lopez-Lopez, M. [Physics Department, Centro de Investigacion y de Estudios Avanzados del IPN, Apartado Postal 14-740, Mexico DF 07000 (Mexico)

    2011-02-15

    We report the Si-doping of GaAs (631)A layers grown by molecular beam epitaxy under different As overpressure. From Hall effect measurements, we have found that the increase of the As pressure induces conduction conversion from p- to n-type, which is presumably related to lattice site switching of Si occupying an As site (where Si is acceptor) to a Ga site (where Si acts as a donor). This conversion is also studied by photoluminescence (PL) spectroscopy. The sharp conductivity conversion, at a critical As pressure value of 1.4-1.7 x 10{sup -5} mbar is reflected in the optical properties of the samples by a change of As vacancy defects into pairs of Ga vacancy and Ga antisite defects. (copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  8. Antiferromagnetic coupling between spinel ferrite and {alpha}-Fe layers in Fe{sub 3-{delta}O4}/MgO/Fe(0 0 1) epitaxial films

    Energy Technology Data Exchange (ETDEWEB)

    Yanagihara, Hideto; Toyoda, Yuta; Kita, Eiji [Institute of Applied Physics, University of Tsukuba, Ibaraki 305-8573 (Japan)

    2011-02-16

    We have investigated interlayer exchange coupling (IEC) in epitaxial films of both Fe{sub 3}O{sub 4}/MgO/Fe(0 0 1) and {gamma}-Fe{sub 2}O{sub 3}/MgO/Fe(0 0 1). Depending on the thickness of the MgO spacer, both systems exhibit strong antiferromagnetic IEC of -1 to -2 erg cm{sup -2}. The {gamma}-Fe{sub 2}O{sub 3}/MgO/Fe(0 0 1) trilayer exhibits the strongest IEC when the thickness of the MgO spacer is approximately 7 A, whereas the Fe{sub 3}O{sub 4}/MgO/Fe(0 0 1) trilayer exhibits the strongest IEC when the thickness of the MgO spacer is zero. The results suggest that two different types of exchange coupling exist in the magnetic trilayers which consist of metallic iron and spinel ferrite layers.

  9. Analysis of layer-by-layer thin-film oxide growth using RHEED and Atomic Force Microscopy

    Science.gov (United States)

    Adler, Eli; Sullivan, M. C.; Gutierrez-Llorente, Araceli; Joress, H.; Woll, A.; Brock, J. D.

    2015-03-01

    Reflection high energy electron diffraction (RHEED) is commonly used as an in situ analysis tool for layer-by-layer thin-film growth. Atomic force microscopy is an equally common ex situ tool for analysis of the film surface, providing visual evidence of the surface morphology. During growth, the RHEED intensity oscillates as the film surface changes in roughness. It is often assumed that the maxima of the RHEED oscillations signify a complete layer, however, the oscillations in oxide systems can be misleading. Thus, using only the RHEED maxima is insufficient. X-ray reflectivity can also be used to analyze growth, as the intensity oscillates in phase with the smoothness of the surface. Using x-ray reflectivity to determine the thin film layer deposition, we grew three films where the x-ray and RHEED oscillations were nearly exactly out of phase and halted deposition at different points in the growth. Pre-growth and post-growth AFM images emphasize the fact that the maxima in RHEED are not a justification for determining layer completion. Work conducted at the Cornell High Energy Synchrotron Source (CHESS) supported by NSF Awards DMR-1332208 and DMR-0936384 and the Cornell Center for Materials Research Shared Facilities are supported through DMR-1120296.

  10. Epitaxial growth and properties of La{sub 0.7}Sr{sub 0.3}MnO{sub 3} thin films with micrometer wide atomic terraces

    Energy Technology Data Exchange (ETDEWEB)

    Yuan, Wei; Zhao, Yuelei; Su, Tang; Song, Qi [International Center for Quantum Materials, Peking University, Beijing 100871 (China); Tang, Chi; Shi, Jing, E-mail: jing.shi@ucr.edu [Department of Physics and Astronomy, University of California, Riverside, California 92521 (United States); Han, Wei, E-mail: weihan@pku.edu.cn [International Center for Quantum Materials, Peking University, Beijing 100871 (China); Collaborative Innovation Center of Quantum Matter, Beijing 100871 (China)

    2015-07-13

    La{sub 0.7}Sr{sub 0.3}MnO{sub 3} (LSMO) films with extraordinarily wide atomic terraces are epitaxially grown on SrTiO{sub 3} (100) substrates by pulsed laser deposition. Atomic force microscopy measurements on the LSMO films show that the atomic step is ∼4 Å and the atomic terrace width is more than 2 μm. For a 20 monolayers (MLs) LSMO film, the magnetization is determined to be 255 ± 15 emu/cm{sup 3} at room temperature, corresponding to 1.70 ± 0.11 μ{sub B} per Mn atom. As the thickness of LSMO increases from 8 MLs to 20 MLs, the critical thickness for the temperature dependent insulator-to-metal behavior transition is shown to be 9 MLs. Furthermore, post-annealing in oxygen environment improves the electron transport and magnetic properties of the LSMO films.

  11. Low temperature p-type doping of (Al)GaN layers using ammonia molecular beam epitaxy for InGaN laser diodes

    Energy Technology Data Exchange (ETDEWEB)

    Malinverni, M., E-mail: marco.malinverni@epfl.ch; Lamy, J.-M.; Martin, D.; Grandjean, N. [ICMP, École Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne (Switzerland); Feltin, E.; Dorsaz, J. [NOVAGAN AG, CH-1015 Lausanne (Switzerland); Castiglia, A.; Rossetti, M.; Duelk, M.; Vélez, C. [EXALOS AG, CH-8952 Schlieren (Switzerland)

    2014-12-15

    We demonstrate state-of-the-art p-type (Al)GaN layers deposited at low temperature (740 °C) by ammonia molecular beam epitaxy (NH{sub 3}-MBE) to be used as top cladding of laser diodes (LDs) with the aim of further reducing the thermal budget on the InGaN quantum well active region. Typical p-type GaN resistivities and contact resistances are 0.4 Ω cm and 5 × 10{sup −4} Ω cm{sup 2}, respectively. As a test bed, we fabricated a hybrid laser structure emitting at 400 nm combining n-type AlGaN cladding and InGaN active region grown by metal-organic vapor phase epitaxy, with the p-doped waveguide and cladding layers grown by NH{sub 3}-MBE. Single-mode ridge-waveguide LD exhibits a threshold voltage as low as 4.3 V for an 800 × 2 μm{sup 2} ridge dimension and a threshold current density of ∼5 kA cm{sup −2} in continuous wave operation. The series resistance of the device is 6 Ω and the resistivity is 1.5 Ω cm, confirming thereby the excellent electrical properties of p-type Al{sub 0.06}Ga{sub 0.94}N:Mg despite the low growth temperature.

  12. Interface energetics and atomic structure of epitaxial La1-xSrxCoO3 on Nb:SrTiO3

    Science.gov (United States)

    Van Overmeere, Quentin; Baniecki, John D.; Yamazaki, Takashi; Ricinschi, Dan; Aso, Hiroyuki; Miyata, Yusuke; Yamada, Hiroaki; Fujimura, Norifumi; Kataoka, Yuji; Imanaka, Yoshihiko

    2015-06-01

    The energetics at oxide semiconductor/La1-xSrxCoO3 heterojunctions, including the respective alignment of the valence and conduction bands, govern charge transfer and have to be determined for the design of future La1-xSrxCoO3-based devices. In this letter, the electronic and atomic structures of epitaxial La1-xSrxCoO3 on Nb-doped strontium titanate are revealed by scanning transmission electron microscopy, electron energy loss spectroscopy, and in situ x-ray and ultra violet photoelectron spectroscopies. For LaCoO3, a valence band (VB) offset of 2.8 ± 0.1 eV is deduced. The large offset is attributed to the orbital contributions of the Co 3d states to the VB maximum of the LaCoO3 thin films, with no evidence of interface dipole contributions. The sensitivity of the valence band orbital character to spin state ordering and oxygen vacancies is assessed using density functional theory.

  13. Preface: Special Topic on Atomic and Molecular Layer Processing: Deposition, Patterning, and Etching.

    Science.gov (United States)

    Engstrom, James R; Kummel, Andrew C

    2017-02-07

    Thin film processing technologies that promise atomic and molecular scale control have received increasing interest in the past several years, as traditional methods for fabrication begin to reach their fundamental limits. Many of these technologies involve at their heart phenomena occurring at or near surfaces, including adsorption, gas-surface reactions, diffusion, desorption, and re-organization of near-surface layers. Moreover many of these phenomena involve not just reactions occurring under conditions of local thermodynamic equilibrium but also the action of energetic species including electrons, ions, and hyperthermal neutrals. There is a rich landscape of atomic and molecular scale interactions occurring in these systems that is still not well understood. In this Special Topic Issue of The Journal of Chemical Physics, we have collected recent representative examples of work that is directed at unraveling the mechanistic details concerning atomic and molecular layer processing, which will provide an important framework from which these fields can continue to develop. These studies range from the application of theory and computation to these systems to the use of powerful experimental probes, such as X-ray synchrotron radiation, probe microscopies, and photoelectron and infrared spectroscopies. The work presented here helps in identifying some of the major challenges and direct future activities in this exciting area of research involving atomic and molecular layer manipulation and fabrication.

  14. Preface: Special Topic on Atomic and Molecular Layer Processing: Deposition, Patterning, and Etching

    Science.gov (United States)

    Engstrom, James R.; Kummel, Andrew C.

    2017-02-01

    Thin film processing technologies that promise atomic and molecular scale control have received increasing interest in the past several years, as traditional methods for fabrication begin to reach their fundamental limits. Many of these technologies involve at their heart phenomena occurring at or near surfaces, including adsorption, gas-surface reactions, diffusion, desorption, and re-organization of near-surface layers. Moreover many of these phenomena involve not just reactions occurring under conditions of local thermodynamic equilibrium but also the action of energetic species including electrons, ions, and hyperthermal neutrals. There is a rich landscape of atomic and molecular scale interactions occurring in these systems that is still not well understood. In this Special Topic Issue of The Journal of Chemical Physics, we have collected recent representative examples of work that is directed at unraveling the mechanistic details concerning atomic and molecular layer processing, which will provide an important framework from which these fields can continue to develop. These studies range from the application of theory and computation to these systems to the use of powerful experimental probes, such as X-ray synchrotron radiation, probe microscopies, and photoelectron and infrared spectroscopies. The work presented here helps in identifying some of the major challenges and direct future activities in this exciting area of research involving atomic and molecular layer manipulation and fabrication.

  15. Superior Stable and Long Life Sodium Metal Anodes Achieved by Atomic Layer Deposition.

    Science.gov (United States)

    Zhao, Yang; Goncharova, Lyudmila V; Lushington, Andrew; Sun, Qian; Yadegari, Hossein; Wang, Biqiong; Xiao, Wei; Li, Ruying; Sun, Xueliang

    2017-03-03

    Na-metal batteries are considered as the promising alternative candidate for Li-ion battery beneficial from the wide availability and low cost of sodium, high theoretical specific capacity, and high energy density based on the plating/stripping processes and lowest electrochemical potential. For Na-metal batteries, the crucial problem on metallic Na is one of the biggest challenges. Mossy or dendritic growth of Na occurs in the repetitive Na stripping/plating process with an unstable solid electrolyte interphase layer of nonuniform ionic flux, which can not only lead to the low Coulombic efficiency, but also can create short circuit risks, resulting in possible burning or explosion. In this communication, the atomic layer deposition of Al2 O3 coating is first demonstrated for the protection of metallic Na anode for Na-metal batteries. By protecting Na foil with ultrathin Al2 O3 layer, the dendrites and mossy Na formation have been effectively suppressed and lifetime has been significantly improved. Furthermore, the thickness of protective layer has been further optimized with 25 cycles of Al2 O3 layer presenting the best performance over 500 cycles. The novel design of atomic layer deposition protected metal Na anode may bring in new opportunities to the realization of the next-generation high energy-density Na metal batteries.

  16. Epitaxial Growth of Si(111)/Er2O3(111) Structure on Si(111) by Molecular Beam Epitaxy

    Institute of Scientific and Technical Information of China (English)

    XU Run; TANG Min-Yan; ZHU Yan-Yan; WANG Lin-Jun

    2011-01-01

    The Si overlayers are grown by molecular beam epitaxy on atomically smllth Er2O3(111) films prepared on Si(111) substrates. Single crystalline Si overlayers are achieved and are evident due to the spot-like reflective high energy electron diffraction(RHEED) patterns and x-ray diffraction patterns. The epitaxial relationship of the Si overlayer along the surface with respect to the orientation of EreO3 and the Si substrate is as follows:overgrown Si(111)//Er2O3(111)//Si(111).The rough surface of Si overlayers, as identified by both RHEED patterns and atomic force microscopy images, indicates a three-dimensional growth mode. The reason for this is based on the interfacial energy argument. Further growth of Er2O3 films on this rough Si overlayer leads to the polycrystalline nature of the topmost Er2O3 layer.

  17. Atomically thin layered NiFe double hydroxides assembled 3D microspheres with promoted electrochemical performances

    Science.gov (United States)

    Li, Xiaomin; Zai, Jiantao; Liu, Yuanyuan; He, Xiaobo; Xiang, Shijie; Ma, Zifeng; Qian, Xuefeng

    2016-09-01

    LDHs in atomic thickness (mono-/bi-layers) usually exhibit novel physicochemical properties, especially in surface-dependent energy storage and catalysis areas. However, the thickness of the commonly reported 2D LDHs is in nanoscale and the bottom-up synthesis of atomically thin LDHs is rarely reported. Herein, high-quality atomically thin layered NiFe-LDHs assembled 3D microspheres were synthesized via a rational designed reaction system, where the formation of atomically thin building blocks was controlled by the synergetic effects of released carbonate anions and butanol. Furthermore, the complexant and solvents played important effects on the process of coprecipitation and the assembling of LDHs. Due to the nature of atomically thin LDHs nanosheets and unique 3D hierarchical structures, the obtained microspheres exhibited excellent electrocatalytic oxygen evolution reaction (OER) activity in alkaline medium with an onset overpotential (0.435 V, which is lower than that of common LDHs) and good durability. The as-prepared 3D NiFe-LDHs microspheres were also firstly used as supercapacitor materials and displayed a high specific capacitance of 1061 F g-1 at the current density of 1 A g-1.

  18. Local atomic arrangements and lattice distortions in layered Ge-Sb-Te crystal structures

    Science.gov (United States)

    Lotnyk, Andriy; Ross, Ulrich; Bernütz, Sabine; Thelander, Erik; Rauschenbach, Bernd

    2016-05-01

    Insights into the local atomic arrangements of layered Ge-Sb-Te compounds are of particular importance from a fundamental point of view and for data storage applications. In this view, a detailed knowledge of the atomic structure in such alloys is central to understanding the functional properties both in the more commonly utilized amorphous-crystalline transition and in recently proposed interfacial phase change memory based on the transition between two crystalline structures. Aberration-corrected scanning transmission electron microscopy allows direct imaging of local arrangement in the crystalline lattice with atomic resolution. However, due to the non-trivial influence of thermal diffuse scattering on the high-angle scattering signal, a detailed examination of the image contrast requires comparison with theoretical image simulations. This work reveals the local atomic structure of trigonal Ge-Sb-Te thin films by using a combination of direct imaging of the atomic columns and theoretical image simulation approaches. The results show that the thin films are prone to the formation of stacking disorder with individual building blocks of the Ge2Sb2Te5, Ge1Sb2Te4 and Ge3Sb2Te6 crystal structures intercalated within randomly oriented grains. The comparison with image simulations based on various theoretical models reveals intermixed cation layers with pronounced local lattice distortions, exceeding those reported in literature.

  19. Decoupling of epitaxial graphene via gold intercalation probed by dispersive Raman spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Pillai, P. B., E-mail: p.pillai@sheffield.ac.uk, E-mail: m.desouza@sheffield.ac.uk; DeSouza, M., E-mail: p.pillai@sheffield.ac.uk, E-mail: m.desouza@sheffield.ac.uk [Semiconductor Materials and Device Group, Electronic and Electrical Engineering, University of Sheffield, Mappin Street, S1 3JD Sheffield (United Kingdom); Narula, R.; Reich, S. [Department of Physics, Freie Universität Berlin, Arnimallee 14, 14195 Berlin (Germany); Wong, L. Y.; Batten, T. [Renishaw, Old Town, Wotton-under-Edge, GL12 7DW Gloucestershire (United Kingdom); Pokorny, J. [Department of Materials Science and Engineering, Sir Robert Hadfield Building, Mappin Street, S1 3JD Sheffield (United Kingdom); Institute of Physics, Academy of Sciences of the Czech Republic, Na Slovance 2, 182 21 Praha 8 (Czech Republic)

    2015-05-14

    Signatures of a superlattice structure composed of a quasi periodic arrangement of atomic gold clusters below an epitaxied graphene (EG) layer are examined using dispersive Raman spectroscopy. The gold-graphene system exhibits a laser excitation energy dependant red shift of the 2D mode as compared to pristine epitaxial graphene. The phonon dispersions in both the systems are mapped using the experimentally observed Raman signatures and a third-nearest neighbour tight binding electronic band structure model. Our results reveal that the observed excitation dependent Raman red shift in gold EG primarily arise from the modifications of the phonon dispersion in gold-graphene and shows that the extent of decoupling of graphene from the underlying SiC substrate can be monitored from the dispersive nature of the Raman 2D modes. The intercalated gold atoms restore the phonon band structure of epitaxial graphene towards free standing graphene.

  20. Atomically thick bismuth selenide freestanding single layers achieving enhanced thermoelectric energy harvesting.

    Science.gov (United States)

    Sun, Yongfu; Cheng, Hao; Gao, Shan; Liu, Qinghua; Sun, Zhihu; Xiao, Chong; Wu, Changzheng; Wei, Shiqiang; Xie, Yi

    2012-12-19

    Thermoelectric materials can realize significant energy savings by generating electricity from untapped waste heat. However, the coupling of the thermoelectric parameters unfortunately limits their efficiency and practical applications. Here, a single-layer-based (SLB) composite fabricated from atomically thick single layers was proposed to optimize the thermoelectric parameters fully. Freestanding five-atom-thick Bi(2)Se(3) single layers were first synthesized via a scalable interaction/exfoliation strategy. As revealed by X-ray absorption fine structure spectroscopy and first-principles calculations, surface distortion gives them excellent structural stability and a much increased density of states, resulting in a 2-fold higher electrical conductivity relative to the bulk material. Also, the surface disorder and numerous interfaces in the Bi(2)Se(3) SLB composite allow for effective phonon scattering and decreased thermal conductivity, while the 2D electron gas and energy filtering effect increase the Seebeck coefficient, resulting in an 8-fold higher figure of merit (ZT) relative to the bulk material. This work develops a facile strategy for synthesizing atomically thick single layers and demonstrates their superior ability to optimize the thermoelectric energy harvesting.

  1. Atomic-scale structure of single-layer MoS2 nanoclusters

    DEFF Research Database (Denmark)

    Helveg, S.; Lauritsen, J. V.; Lægsgaard, E.

    2000-01-01

    We have studied using scanning tunneling microscopy (STM) the atomic-scale realm of molybdenum disulfide (MoS2) nanoclusters, which are of interest as a model system in hydrodesulfurization catalysis. The STM gives the first real space images of the shape and edge structure of single-layer MoS2...... nanoparticles synthesized on Au(lll), and establishes a new picture of the active edge sires of the nanoclusters. The results demonstrate a way to get detailed atomic-scale information on catalysts in general....

  2. Thin film encapsulation for organic light-emitting diodes using inorganic/organic hybrid layers by atomic layer deposition.

    Science.gov (United States)

    Zhang, Hao; Ding, He; Wei, Mengjie; Li, Chunya; Wei, Bin; Zhang, Jianhua

    2015-01-01

    A hybrid nanolaminates consisting of Al2O3/ZrO2/alucone (aluminum alkoxides with carbon-containing backbones) grown by atomic layer deposition (ALD) were reported for an encapsulation of organic light-emitting diodes (OLEDs). The electrical Ca test in this study was designed to measure the water vapor transmission rate (WVTR) of nanolaminates. We found that moisture barrier performance was improved with the increasing of the number of dyads (Al2O3/ZrO2/alucone) and the WVTR reached 8.5 × 10(-5) g/m(2)/day at 25°C, relative humidity (RH) 85%. The half lifetime of a green OLED with the initial luminance of 1,500 cd/m(2) reached 350 h using three pairs of the Al2O3 (15 nm)/ZrO2 (15 nm)/alucone (80 nm) as encapsulation layers.

  3. BARK-MIMETIC LAYER-BY-LAYER ASSEMBLED MONTMORILLONITE/POLY(p-AMINOSTYRENE) FLEXIBLE NANOCOMPOSITES SHIELDING ATOMIC OXYGEN EROSION

    Institute of Scientific and Technical Information of China (English)

    Min Gao; Bing-jun Liu; Long-cheng Gao; Peng-gang Yin; Lei Jiang

    2013-01-01

    Inspired by the birch bark,which has multilayered structures,we fabricated layer-by-layer (LbL) assembled montmorillonite (MMT) and poly(p-aminostyrene) (PPAS) nanocomposites on cotton fiber curved surfaces to provide protection from atomic oxygen (AO) erosion.The multilayer coated fibers had high flexibility,uniformity,defect free,ease of preparation and low cost.The AO erosion durability has been dramatically enhanced which was evidenced by testing in the ground-based AO effects simulation facility.And the dimension and surface morphologies of the fibers observed by SEM had few changes,indicating excellent AO erosion resistant ability of the coatings.These results provide us a new method to design fibrous materials exposed directly in low earth orbit environment.

  4. Nondestructive Characterization of Residual Threading Dislocation Density in HgCdTe Layers Grown on CdZnTe by Liquid-Phase Epitaxy

    Science.gov (United States)

    Fourreau, Y.; Pantzas, K.; Patriarche, G.; Destefanis, V.

    2016-09-01

    The performance of mercury cadmium telluride (MCT)-based infrared (IR) focal-plane arrays is closely related to the crystalline perfection of the HgCdTe thin film. In this work, Te-rich, (111)B-oriented HgCdTe epilayers grown by liquid-phase epitaxy on CdZnTe substrates have been studied. Surface atomic steps are shown on as-grown MCT materials using atomic force microscopy (AFM) and white-light interferometry (WLI), suggesting step-flow growth. Locally, quasiperfect surface spirals are also evidenced. A demonstration is given that these spirals are related to the emergence of almost pure screw threading dislocations. A nondestructive and quantitative technique to measure the threading dislocation density is proposed. The technique consists of counting the surface spirals on the as-grown MCT surface from images obtained by either AFM or WLI measurements. The benefits and drawbacks of both destructive—chemical etching of HgCdTe dislocations—and nondestructive surface imaging techniques are compared. The nature of defects is also discussed. Finally, state-of-the-art threading dislocation densities in the low 104 cm-2 range are evidenced by both etch pit density (EPD) and surface imaging measurements.

  5. Charged particle detection performances of CMOS pixel sensors produced in a 0.18 um process with a high resistivity epitaxial layer

    CERN Document Server

    Senyukov, Serhiy; Besson, Auguste; Claus, Gilles; Cousin, Loic; Dorokhov, Andrei; Dulinski, Wojciech; Goffe, Mathieu; Hu-Guo, Christine; Winter, Marc

    2013-01-01

    The apparatus of the ALICE experiment at CERN will be upgraded in 2017/18 during the second long shutdown of the LHC (LS2). A major motivation for this upgrade is to extend the physics reach for charmed and beauty particles down to low transverse momenta. This requires a substantial improvement of the spatial resolution and the data rate capability of the ALICE Inner Tracking System (ITS). To achieve this goal, the new ITS will be equipped with 50 um thin CMOS Pixel Sensors (CPS) covering either the 3 innermost layers or all the 7 layers of the detector. The CPS being developed for the ITS upgrade at IPHC (Strasbourg) is derived from the MIMOSA 28 sensor realised for the STAR-PXL at RHIC in a 0.35 um CMOS process. In order to satisfy the ITS upgrade requirements in terms of readout speed and radiation tolerance, a CMOS process with a reduced feature size and a high resistivity epitaxial layer should be exploited. In this respect, the charged particle detection performance and radiation hardness of the TowerJa...

  6. Three-dimensional spirals of atomic layered MoS2.

    Science.gov (United States)

    Zhang, Liming; Liu, Kaihui; Wong, Andrew Barnabas; Kim, Jonghwan; Hong, Xiaoping; Liu, Chong; Cao, Ting; Louie, Steven G; Wang, Feng; Yang, Peidong

    2014-11-12

    Atomically thin two-dimensional (2D) layered materials, including graphene, boron nitride, and transition metal dichalcogenides (TMDs), can exhibit novel phenomena distinct from their bulk counterparts and hold great promise for novel electronic and optoelectronic applications. Controlled growth of such 2D materials with different thickness, composition, and symmetry are of central importance to realize their potential. In particular, the ability to control the symmetry of TMD layers is highly desirable because breaking the inversion symmetry can lead to intriguing valley physics, nonlinear optical properties, and piezoelectric responses. Here we report the first chemical vapor deposition (CVD) growth of spirals of layered MoS2 with atomically thin helical periodicity, which exhibits a chiral structure and breaks the three-dimensional (3D) inversion symmetry explicitly. The spirals composed of tens of connected MoS2 layers with decreasing areas: each basal plane has a triangular shape and shrinks gradually to the summit when spiraling up. All the layers in the spiral assume an AA lattice stacking, which is in contrast to the centrosymmetric AB stacking in natural MoS2 crystals. We show that the noncentrosymmetric MoS2 spiral leads to a strong bulk second-order optical nonlinearity. In addition, we found that the growth of spirals involves a dislocation mechanism, which can be generally applicable to other 2D TMD materials.

  7. Morphology and atomic-scale structure of single-layer WS2 nanoclusters.

    Science.gov (United States)

    Füchtbauer, Henrik G; Tuxen, Anders K; Moses, Poul G; Topsøe, Henrik; Besenbacher, Flemming; Lauritsen, Jeppe V

    2013-10-14

    Two-dimensional sheets of transition metal (Mo and W) sulfides are attracting strong attention due to the unique electronic and optical properties associated with the material in its single-layer form. The single-layer MoS2 and WS2 are already in widespread commercial use in catalytic applications as both hydrotreating and hydrocracking catalysts. Consequently, characterization of the morphology and atomic structure of such particles is of utmost importance for the understanding of the catalytic active phase. However, in comparison with the related MoS2 system only little is known about the fundamental properties of single-layer WS2 (tungstenite). Here, we use an interplay of atom-resolved Scanning Tunneling Microscopy (STM) studies of Au(111)-supported WS2 nanoparticles and calculated edge structures using Density Functional Theory (DFT) to reveal the equilibrium morphology and prevalent edge structures of single-layer WS2. The STM results reveal that the single layer S-W-S sheets adopt a triangular equilibrium shape under the sulfiding conditions of the synthesis, with fully sulfided edges. The predominant edge structures are determined to be the (101[combining macron]0) W-edge, but for the smallest nanoclusters also the (1[combining macron]010) S-edges become important. DFT calculations are used to construct phase diagrams of the WS2 edges, and describe their sulfur and hydrogen coordination under different conditions, and in this way shed light on the catalytic role of WS2 edges.

  8. Synthesis of magnetic tunnel junctions with full in situ atomic layer and chemical vapor deposition processes

    Energy Technology Data Exchange (ETDEWEB)

    Mantovan, R., E-mail: roberto.mantovan@mdm.imm.cnr.it [Laboratorio MDM, IMM-CNR, Via C. Olivetti 2, 20864 Agrate Brianza (Italy); Vangelista, S.; Kutrzeba-Kotowska, B.; Cocco, S.; Lamperti, A.; Tallarida, G. [Laboratorio MDM, IMM-CNR, Via C. Olivetti 2, 20864 Agrate Brianza (MB) (Italy); Mameli, D. [Laboratorio MDM, IMM-CNR, Via C. Olivetti 2, 20864 Agrate Brianza (Italy); Dipartimento di Scienze Chimiche, Universita di Cagliari, Cittadella Universitaria, 09042 Monserrato, Cagliari (Italy); Fanciulli, M. [Laboratorio MDM, IMM-CNR, Via C. Olivetti 2, 20864 Agrate Brianza (Italy); Dipartimento di Scienza dei Materiali, Universita degli studi Milano-Bicocca, Via R Cozzi 53, 20125 Milano (Italy)

    2012-05-01

    Magnetic tunnel junctions, i.e. the combination of two ferromagnetic electrodes separated by an ultrathin tunnel oxide barrier, are core elements in a large variety of spin-based devices. We report on the use of combined chemical vapor and atomic layer deposition processes for the synthesis of magnetic tunnel junctions with no vacuum break. Structural, chemical and morphological characterizations of selected ferromagnetic and oxide layers are reported, together with the evidence of tunnel magnetoresistance effect in patterned Fe/MgO/Co junctions.

  9. Flat metallic surface gratings with sub-10 nm gaps controlled by atomic-layer deposition

    Science.gov (United States)

    Chen, Borui; Ji, Dengxin; Cheney, Alec; Zhang, Nan; Song, Haomin; Zeng, Xie; Thomay, Tim; Gan, Qiaoqiang; Cartwright, Alexander

    2016-09-01

    Atomic layer lithography is a recently reported new technology to fabricate deep-subwavelength features down to 1-2 nm, based on combinations of electron beam lithography (EBL) and atomic layer deposition (ALD). However, the patterning area is relatively small as limited by EBL, and the fabrication yield is not very high due to technical challenges. Here we report an improved procedure to fabricate flat metallic surfaces with sub-10 nm features based on ALD processes. To demonstrate the scalability of the new manufacturing method, we combine the ALD process with large area optical interference patterning, which is particularly promising for the development of practical applications for nanoelectronics and nanophotonics with extremely strong confinement of electromagnetic fields.

  10. CoFe2/Al2O3/PMNPT multiferroic heterostructures by atomic layer deposition

    Science.gov (United States)

    Zhou, Ziyao; Grocke, Garrett; Yanguas-Gil, Angel; Wang, Xinjun; Gao, Yuan; Sun, Nianxiang; Howe, Brandon; Chen, Xing

    2016-05-01

    Multiferroic materials and applications allow electric bias control of magnetism or magnetic bias control of polarization, enabling fast, compact, energy-efficient devices in RF/microwave communication systems such as filters, shifters, and antennas; electronics devices such as inductors and capacitors; and other magnetic material related applications including sensors and memories. In this manuscript, we utilize atomic layer deposition technology to grow magnetic CoFe metallic thin films onto PMNPT, with a ˜110 Oe electric field induced ferromagnetic resonance field shift in the CoFe/Al2O3/PMNPT multiferroic heterostructure. Our work demonstrates an atomic layer deposition fabricated multiferroic heterostructure with significant tunability and shows that the unique thin film growth mechanism will benefit integrated multiferroic application in near future.

  11. Evolution of microstructure and related optical properties of ZnO grown by atomic layer deposition

    Directory of Open Access Journals (Sweden)

    Adib Abou Chaaya

    2013-10-01

    Full Text Available A study of transmittance and photoluminescence spectra on the growth of oxygen-rich ultra-thin ZnO films prepared by atomic layer deposition is reported. The structural transition from an amorphous to a polycrystalline state is observed upon increasing the thickness. The unusual behavior of the energy gap with thickness reflected by optical properties is attributed to the improvement of the crystalline structure resulting from a decreasing concentration of point defects at the growth of grains. The spectra of UV and visible photoluminescence emissions correspond to transitions near the band-edge and defect-related transitions. Additional emissions were observed from band-tail states near the edge. A high oxygen ratio and variable optical properties could be attractive for an application of atomic layer deposition (ALD deposited ultrathin ZnO films in optical sensors and biosensors.

  12. Evolution of microstructure and related optical properties of ZnO grown by atomic layer deposition.

    Science.gov (United States)

    Abou Chaaya, Adib; Viter, Roman; Bechelany, Mikhael; Alute, Zanda; Erts, Donats; Zalesskaya, Anastasiya; Kovalevskis, Kristaps; Rouessac, Vincent; Smyntyna, Valentyn; Miele, Philippe

    2013-01-01

    A study of transmittance and photoluminescence spectra on the growth of oxygen-rich ultra-thin ZnO films prepared by atomic layer deposition is reported. The structural transition from an amorphous to a polycrystalline state is observed upon increasing the thickness. The unusual behavior of the energy gap with thickness reflected by optical properties is attributed to the improvement of the crystalline structure resulting from a decreasing concentration of point defects at the growth of grains. The spectra of UV and visible photoluminescence emissions correspond to transitions near the band-edge and defect-related transitions. Additional emissions were observed from band-tail states near the edge. A high oxygen ratio and variable optical properties could be attractive for an application of atomic layer deposition (ALD) deposited ultrathin ZnO films in optical sensors and biosensors.

  13. Fabrication of Nanolaminates with Ultrathin Nanolayers Using Atomic Layer Deposition: Nucleation & Growth Issues

    Science.gov (United States)

    2009-02-01

    microscopy ( FE -SEM). • Construction of new experimental apparatus based on ALD reactor, glovebox and physical vapor deposition (PVD) chamber all...left the research group, Shih-Hui continued the barrier research and also made the FE -SEM measurements of film cracking resulting from compressive...Colorado, September 21, 2007. 25. "Atomic Layer Deposition: Fundamentals and Applications" (Invited Short Course), Sociedad Mexicana de Ciencia y

  14. Atomic layer deposition of ZnO:Al on PAA substrates

    Science.gov (United States)

    Blagoev, B. S.; Vlakhov, E.; Videkov, V.; Tzaneva, B.; Łuka, G.; Witkowski, B. S.; Terziyska, P.; Leclercq, J.; Krajewski, T. A.; Guziewicz, E.; Dimitrov, D. Z.; Mehandzhiev, V. B.; Sveshtarov, P.

    2016-10-01

    In this work the ZnO:Al films of different thickness are grown on the Porous Anodic Alumina (PAA) and p-Si (100) substrates by Atomic Layer Deposition. The ZnO:Al films thicknesses are chosen appropriately in order to obtain complete filled pores as well as pores with a thin covering on the surface. The obtained structures are investigated with spectroscopic ellipsometry and Scanning Electron Microscopy (SEM) techniques.

  15. On model materials designed by atomic layer deposition for catalysis purposes

    OpenAIRE

    Diskus, Madeleine

    2011-01-01

    The aim of this work was to investigate the potential of model materials designed by atomic layer deposition toward applications in catalysis research. Molybdenum based catalysts promoted with cobalt were selected as target materials, considering their important roles in various industrial processes. Particular attention was paid to understand the growth dynamics of the ALD processes involved and further to characterize the obtained materials carefully. It was of main concern to verify the fe...

  16. Atomic layer deposition of TiO{sub 2} photonic crystal waveguide biosensors

    Energy Technology Data Exchange (ETDEWEB)

    Jardinier, E; French, P J [Electronic Instrumentation Laboratory, Delft University of Technology, 4 Mekelweg, 2628 CD Delft (Netherlands); Pandraud, G; Pham, M H; Sarro, P M [Electronic Components, Technology and Materials, Delft University of Technology, 17 Feldmannweg, 2628 CT Delft (Netherlands)], E-mail: g.pandraud@tudelft.nl

    2009-09-01

    A photonic crystal waveguide biosensor in the visible is presented for biosensing. The sensor is applied to Refractive Index (RI) measurements. The sensitivity at different wavelength is presented for both air holes and air core configurations of photonic crystal waveguide (PCW) made of TiO{sub 2}. It is shown that by using Atomic Layer Deposition (ALD) the expected sensitivity of the air core configuration outperforms the previously reported results.

  17. Indium-Free Fully Transparent Electronics Deposited Entirely by Atomic Layer Deposition.

    Science.gov (United States)

    Nayak, Pradipta K; Wang, Zhenwei; Alshareef, Husam N

    2016-09-01

    Indium-free, fully transparent thin-film transistors are fabricated entirely by the atomic layer deposition technique on rigid and flexible substrates at a low temperature of 160 °C. The transistors show high saturation mobility, large switching ratio, and small subthreshold swing value. The inverters and ring oscillators show large gain value and small propagation delay time, indicating the potential of this process in transparent electronic devices.

  18. Dispersion engineered high-Q silicon Nitride Ring-Resonators via Atomic Layer Deposition

    CERN Document Server

    Riemensberger, Johann; Herr, Tobias; Brasch, Victor; Holzwarth, Ronald; Kippenberg, Tobias J

    2012-01-01

    We demonstrate dispersion engineering of integrated silicon nitride based ring resonators through conformal coating with hafnium dioxide deposited on top of the structures via atomic layer deposition (ALD). Both, magnitude and bandwidth of anomalous dispersion can be significantly increased. All results are confirmed by high resolution frequency-comb-assisted-diode-laser spectroscopy and are in very good agreement with the simulated modification of the mode spectrum.

  19. Seeded epitaxy of Co/Au(1 1 1) multilayers on {alpha}-Al{sub 2}O{sub 3}(0 0 0 1): Influence of Co seed layer

    Energy Technology Data Exchange (ETDEWEB)

    Kamiko, Masao [Institute of Industrial Science, University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8505 (Japan)], E-mail: kamiko@iis.u-tokyo.ac.jp; Yamamoto, Ryoichi [Institute of Industrial Science, University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8505 (Japan)

    2007-06-25

    The influence of a Co seed layer on the structural and magnetic properties of Co/Au(1 1 1) multilayers grown onto {alpha}-Al{sub 2}O{sub 3}(0 0 0 1) single crystal substrates by molecular beam epitaxy has been studied by reflection high-energy electron diffraction (RHEED), X-ray diffraction (XRD), and vibrating a sample magnetometer (VSM). The initial deposition of the Co seed layer onto Al{sub 2}O{sub 3}(0 0 0 1) prior to the deposition of an Au buffer layer yielded high-quality fcc-Au(1 1 1) oriented epitaxial films and a well-known (23 x 1) surface reconstruction structure. The RHEED results proved that the Co seed layer enhanced the layer-by-layer growth of the Co/Au multilayer on Au(1 1 1). The Co seed layer also improved the crystalline quality of the consequent Co/Au(1 1 1) multilayer. The results of XRD revealed that interfaces of the Co/Au multilayers with the Co seed layer were sharper than those without a seed layer. The magnetic anisotropy energy of the Co/Au multilayers was increased by using the Co seed layer. This indicated that a high structural quality resulted in a greater perpendicular magnetic anisotropy. However, this structural control was the result of the decrease in the coercive force and remanent magnetization.

  20. Hexagonal Boron Nitride Tunnel Barriers Grown on Graphite by High Temperature Molecular Beam Epitaxy

    Science.gov (United States)

    Cho, Yong-Jin; Summerfield, Alex; Davies, Andrew; Cheng, Tin S.; Smith, Emily F.; Mellor, Christopher J.; Khlobystov, Andrei N.; Foxon, C. Thomas; Eaves, Laurence; Beton, Peter H.; Novikov, Sergei V.

    2016-01-01

    We demonstrate direct epitaxial growth of high-quality hexagonal boron nitride (hBN) layers on graphite using high-temperature plasma-assisted molecular beam epitaxy. Atomic force microscopy reveals mono- and few-layer island growth, while conducting atomic force microscopy shows that the grown hBN has a resistance which increases exponentially with the number of layers, and has electrical properties comparable to exfoliated hBN. X-ray photoelectron spectroscopy, Raman microscopy and spectroscopic ellipsometry measurements on hBN confirm the formation of sp2-bonded hBN and a band gap of 5.9 ± 0.1 eV with no chemical intermixing with graphite. We also observe hexagonal moiré patterns with a period of 15 nm, consistent with the alignment of the hBN lattice and the graphite substrate. PMID:27681943

  1. Ge/GeSn heterostructures grown on Si (100) by molecular-beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Sadofyev, Yu. G., E-mail: sadofyev@hotmail.com; Martovitsky, V. P.; Bazalevsky, M. A.; Klekovkin, A. V. [Russian Academy of Sciences, Lebedev Physical Institute (Russian Federation); Averyanov, D. V.; Vasil’evskii, I. S. [National Research Nuclear University MEPhI (Russian Federation)

    2015-01-15

    The growth of GeSn layers by molecular-beam epitaxy on Si (100) wafers coated with a germanium buffer layer is investigated. The properties of the fabricated structures are controlled by reflection high-energy electron diffraction, atomic-force microscopy, X-ray diffractometry, Rutherford backscattering, and Raman scattering. It is shown that GeSn layers with thicknesses up to 0.5 μm and Sn molar fractions up to 0.073 manifest no sign of plastic relaxation upon epitaxy. The lattice constant of the GeSn layers within the growth plane is precisely the same as that of Ge. The effect of rapid thermal annealing on the conversion of metastable elastically strained GeSn layers into a plastically relaxed state is examined. Ge/GeSn quantum wells with Sn molar fraction up to 0.11 are obtained.

  2. Interfacial engineering of two-dimensional nano-structured materials by atomic layer deposition

    Science.gov (United States)

    Zhuiykov, Serge; Kawaguchi, Toshikazu; Hai, Zhenyin; Karbalaei Akbari, Mohammad; Heynderickx, Philippe M.

    2017-01-01

    Atomic Layer Deposition (ALD) is an enabling technology which provides coating and material features with significant advantages compared to other existing techniques for depositing precise nanometer-thin two-dimensional (2D) nanostructures. It is a cyclic process which relies on sequential self-terminating reactions between gas phase precursor molecules and a solid surface. ALD is especially advantageous when the film quality or thickness is critical, offering ultra-high aspect ratios. ALD provides digital thickness control to the atomic level by depositing film one atomic layer at a time, as well as pinhole-free films even over a very large and complex areas. Digital control extends to sandwiches, hetero-structures, nano-laminates, metal oxides, graded index layers and doping, and it is perfect for conformal coating and challenging 2D electrodes for various functional devices. The technique's capabilities are presented on the example of ALD-developed ultra-thin 2D tungsten oxide (WO3) over the large area of standard 4" Si substrates. The discussed advantages of ALD enable and endorse the employment of this technique for the development of hetero-nanostructure 2D semiconductors with unique properties.

  3. Enhancing of catalytic properties of vanadia via surface doping with phosphorus using atomic layer deposition

    Energy Technology Data Exchange (ETDEWEB)

    Strempel, Verena E.; Naumann d' Alnoncourt, Raoul, E-mail: r.naumann@bascat.tu-berlin.de [BasCat - UniCat BASF JointLab, Technische Universität Berlin, Sekr. EW K 01, Hardenbergstraße 36, 10623 Berlin (Germany); Löffler, Daniel [Process Research and Chemical Engineering, BASF SE, Carl-Bosch-Straße 38, 67056 Ludwigshafen (Germany); Kröhnert, Jutta; Skorupska, Katarzyna; Johnson, Benjamin [Department of Inorganic Chemistry, Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195 Berlin (Germany); Driess, Matthias [BasCat - UniCat BASF JointLab, Technische Universität Berlin, Sekr. EW K 01, Hardenbergstraße 36, 10623 Berlin, Germany and Technische Universität Berlin, Institut für Chemie, Sekr. C2, Straße des 17. Juni 135, 10623 Berlin (Germany); Rosowski, Frank [BasCat - UniCat BASF JointLab, Technische Universität Berlin, Sekr. EW K 01, Hardenbergstraße 36, 10623 Berlin, Germany and Process Research and Chemical Engineering, BASF SE, Carl-Bosch-Straße 38, 67056 Ludwigshafen (Germany)

    2016-01-15

    Atomic layer deposition is mainly used to deposit thin films on flat substrates. Here, the authors deposit a submonolayer of phosphorus on V{sub 2}O{sub 5} in the form of catalyst powder. The goal is to prepare a model catalyst related to the vanadyl pyrophosphate catalyst (VO){sub 2}P{sub 2}O{sub 7} industrially used for the oxidation of n-butane to maleic anhydride. The oxidation state of vanadium in vanadyl pyrophosphate is 4+. In literature, it was shown that the surface of vanadyl pyrophosphate contains V{sup 5+} and is enriched in phosphorus under reaction conditions. On account of this, V{sub 2}O{sub 5} with the oxidation state of 5+ for vanadium partially covered with phosphorus can be regarded as a suitable model catalyst. The catalytic performance of the model catalyst prepared via atomic layer deposition was measured and compared to the performance of catalysts prepared via incipient wetness impregnation and the original V{sub 2}O{sub 5} substrate. It could be clearly shown that the dedicated deposition of phosphorus by atomic layer deposition enhances the catalytic performance of V{sub 2}O{sub 5} by suppression of total oxidation reactions, thereby increasing the selectivity to maleic anhydride.

  4. Effects of the oxygen precursor on the electrical and structural properties of HfO2 films grown by atomic layer deposition on Ge

    Science.gov (United States)

    Spiga, S.; Wiemer, C.; Tallarida, G.; Scarel, G.; Ferrari, S.; Seguini, G.; Fanciulli, M.

    2005-09-01

    We report on the growth by atomic layer deposition of HfO2 films on HF-last treated Ge(001) substrates using HfCl4 as a Hf source and either O3 or H2O as oxygen sources. The choice of the oxygen precursor strongly influences the structural, chemical, and electrical properties of the HfO2 films: Those grown using H2O exhibit local epitaxial growth, a large amount of contaminants such as chlorine and carbon, and a large frequency dispersion of the capacitance-voltage (C -V) characteristics. Films grown using O3 are good insulators and exhibit well-shaped C -V curves with a minimum frequency dispersion of the accumulation capacitance. Moreover, they are smoother, less crystallized, and with a lower contaminant content than those grown using H2O. However, the use of O3 leads to the formation of a 2nm thick layer, possibly GeOx, at the HfO2/Ge interface.

  5. Growth Interruption Effect on the Fabrication of GaAs Concentric Multiple Rings by Droplet Epitaxy

    Directory of Open Access Journals (Sweden)

    Fedorov A

    2010-01-01

    Full Text Available Abstract We present the molecular beam epitaxy fabrication and optical properties of complex GaAs nanostructures by droplet epitaxy: concentric triple quantum rings. A significant difference was found between the volumes of the original droplets and the final GaAs structures. By means of atomic force microscopy and photoluminescence spectroscopy, we found that a thin GaAs quantum well-like layer is developed all over the substrate during the growth interruption times, caused by the migration of Ga in a low As background.

  6. Sharp chemical interface in epitaxial Fe{sub 3}O{sub 4} thin films

    Energy Technology Data Exchange (ETDEWEB)

    Gálvez, S. [SpLine, Spanish CRG Beamline at the European Synchrotron Radiation Facility, B.P. 200, F-38043 Grenoble (France); Rubio-Zuazo, J., E-mail: rubio@esrf.fr; Salas-Colera, E.; Muñoz-Noval, A.; Castro, G. R. [SpLine, Spanish CRG Beamline at the European Synchrotron Radiation Facility, B.P. 200, F-38043 Grenoble (France); ICMM-CSIC Cantoblanco, E-28049 Madrid (Spain)

    2014-12-15

    Chemically sharp interface was obtained on single phase single oriented Fe{sub 3}O{sub 4} (001) thin film (7 nm) grown on NiO (001) substrate using oxygen assisted molecular beam epitaxy. Refinement of the atomic structure, stoichiometry, and oxygen vacancies were determined by soft and hard x-ray photoelectron spectroscopy, low energy electron diffraction and synchrotron based X-ray reflectivity, and X-ray diffraction. Our results demonstrate an epitaxial growth of the magnetite layer, perfect iron stoichiometry, absence of oxygen vacancies, and the existence of an intermixing free interface. Consistent magnetic and electrical characterizations are also shown.

  7. Effects of growth temperature on high-quality In0.2Ga0.8N layers by plasma-assisted molecular beam epitaxy

    Institute of Scientific and Technical Information of China (English)

    Zhang Dongyan; Zheng Xinhe; Li Xuefei; Wu Yuanyuan; Wang Jianfeng; Yang Hui

    2012-01-01

    High-quality In0.2Ga0.8N epilayers were grown on a GaN template at temperatures of 520 and 580 ℃ via plasma-assisted molecular beam epitaxy.The X-ray rocking curve full widths at half maximum (FWHM) of (10.2)reflections is 936 arcsec for the 50-nm-thick InGaN layers at the lower temperature.When the growth temperature increases to 580 ℃,the FWHM of (00.2) reflections for these samples is very narrow and keeps similar,while significant improvement of(10.2) reflections with an FWHM value of 612 arcsec has been observed.This improved quality in InGaN layers grown at 580 ℃ is also reflected by the much larger size of the crystalline column from the AFM results,stronger emission intensity as well as a decreased FWHM of room temperature PL from 136 to 93.9 meV.

  8. Peculiarities of strain relaxation in linearly graded InxGa1-xAs/GaAs(001) metamorphic buffer layers grown by molecular beam epitaxy

    Science.gov (United States)

    Sorokin, S. V.; Klimko, G. V.; Sedova, I. V.; Sitnikova, A. A.; Kirilenko, D. A.; Baidakova, M. V.; Yagovkina, M. A.; Komissarova, T. A.; Belyaev, K. G.; Ivanov, S. V.

    2016-12-01

    This paper presents a comprehensive study of structural, optical and electrical properties of heterostructures with linearly graded InxGa1-xAs metamorphic buffer layers (MBLs) grown by molecular beam epitaxy on GaAs (001) substrates. The low density of threading dislocations (well below 106 cm-2) in 1-μm-thick In0.3Ga0.7As layers grown atop of the linearly graded InxGa1-xAs/GaAs MBLs has been confirmed by using transmission electron microscopy (TEM). X-ray diffraction (XRD) data demonstrate good agreement between the experimentally measured In step-back and its calculations in the frames of existing models. Combining the XRD reciprocal space maps (RSM) of the structures and the spatially-resolved selective area electron diffraction measurements by cross-sectional TEM in depth-profiled RSM diagrams allowed direct visualization of the strain relaxation dynamics during the MBL growth. Strong effect of the azimuth angle and the value of an unintentional initial miscut of nominally (001) oriented GaAs substrate on the strain relaxation dynamics was observed.

  9. Epitaxy of Semiconductors Introduction to Physical Principles

    CERN Document Server

    Pohl, Udo W

    2013-01-01

    Introduction to Epitaxy provides the essential information for a comprehensive upper-level graduate course treating the crystalline growth of semiconductor heterostructures. Heteroepitaxy represents the basis of advanced electronic and optoelectronic devices today and is considered one of the top fields in materials research. The book covers the structural and electronic properties of strained epitaxial layers, the thermodynamics and kinetics of layer growth, and the description of the major growth techniques metalorganic vapor phase epitaxy, molecular beam epitaxy and liquid phase epitaxy. Cubic semiconductors, strain relaxation by misfit dislocations, strain and confinement effects on electronic states, surface structures and processes during nucleation and growth are treated in detail. The Introduction to Epitaxy requires only little knowledge on solid-state physics. Students of natural sciences, materials science and electrical engineering as well as their lecturers benefit from elementary introductions t...

  10. Atomic scale imaging of competing polar states in a Ruddlesden-Popper layered oxide

    Science.gov (United States)

    Stone, Greg; Ophus, Colin; Birol, Turan; Ciston, Jim; Lee, Che-Hui; Wang, Ke; Fennie, Craig J.; Schlom, Darrell G.; Alem, Nasim; Gopalan, Venkatraman

    2016-08-01

    Layered complex oxides offer an unusually rich materials platform for emergent phenomena through many built-in design knobs such as varied topologies, chemical ordering schemes and geometric tuning of the structure. A multitude of polar phases are predicted to compete in Ruddlesden-Popper (RP), An+1BnO3n+1, thin films by tuning layer dimension (n) and strain; however, direct atomic-scale evidence for such competing states is currently absent. Using aberration-corrected scanning transmission electron microscopy with sub-Ångstrom resolution in Srn+1TinO3n+1 thin films, we demonstrate the coexistence of antiferroelectric, ferroelectric and new ordered and low-symmetry phases. We also directly image the atomic rumpling of the rock salt layer, a critical feature in RP structures that is responsible for the competing phases; exceptional quantitative agreement between electron microscopy and density functional theory is demonstrated. The study shows that layered topologies can enable multifunctionality through highly competitive phases exhibiting diverse phenomena in a single structure.

  11. Atomic scale imaging of competing polar states in a Ruddlesden–Popper layered oxide

    Science.gov (United States)

    Stone, Greg; Ophus, Colin; Birol, Turan; Ciston, Jim; Lee, Che-Hui; Wang, Ke; Fennie, Craig J.; Schlom, Darrell G.; Alem, Nasim; Gopalan, Venkatraman

    2016-01-01

    Layered complex oxides offer an unusually rich materials platform for emergent phenomena through many built-in design knobs such as varied topologies, chemical ordering schemes and geometric tuning of the structure. A multitude of polar phases are predicted to compete in Ruddlesden–Popper (RP), An+1BnO3n+1, thin films by tuning layer dimension (n) and strain; however, direct atomic-scale evidence for such competing states is currently absent. Using aberration-corrected scanning transmission electron microscopy with sub-Ångstrom resolution in Srn+1TinO3n+1 thin films, we demonstrate the coexistence of antiferroelectric, ferroelectric and new ordered and low-symmetry phases. We also directly image the atomic rumpling of the rock salt layer, a critical feature in RP structures that is responsible for the competing phases; exceptional quantitative agreement between electron microscopy and density functional theory is demonstrated. The study shows that layered topologies can enable multifunctionality through highly competitive phases exhibiting diverse phenomena in a single structure. PMID:27578622

  12. Atomic layer deposition enhanced grafting of phosphorylcholine on stainless steel for intravascular stents.

    Science.gov (United States)

    Zhong, Qi; Yan, Jin; Qian, Xu; Zhang, Tao; Zhang, Zhuo; Li, Aidong

    2014-09-01

    In-stent restenosis (ISR) and re-endothelialization delay are two major issues of intravascular stent in terms of clinical safety and effects. Construction of mimetic cell membrane surface on stents using phosphorylcholine have been regarded as one of the most powerful strategies to resolve these two issues and improve the performance of stents. In this study, atomic layer deposition (ALD) technology, which is widely used in semiconductor industry, was utilized to fabricate ultra-thin layer (10nm) of alumina (Al2O3) on 316L stainless steel (SS), then the alumina covered surface was modified with 3-aminopropyltriethoxysilane (APS) and 2-methacryloyloxyethyl phosphorylcholine (MPC) sequentially in order to produce phosphorylcholine mimetic cell membrane surface. The pristine and modified surfaces were characterized using X-ray photoelectron spectroscopy, atomic force microscope and water contact angle measurement. Furthermore, the abilities of protein adsorption, platelet adhesion and cell proliferation on the surfaces were investigated. It was found that alumina layer can significantly enhance the surface grafting of APS and MPC on SS; and in turn efficiently inhibit protein adsorption and platelet adhesion, and promote the attachment and proliferation of human umbilical vein endothelial cells (HUVEC) on the surfaces. In association with the fact that the deposition of alumina layer is also beneficial to the improvement of adhesion and integrity of drug-carrying polymer coating on drug eluting stents, we expect that ALD technology can largely assist in the modifications on inert metallic surfaces and benefit implantable medical devices, especially intravascular stents.

  13. Heating rate and spin flip lifetime due to near field noise in layered superconducting atom chips

    CERN Document Server

    Fermani, Rachele; Zhang, Bo; Lim, Michael J; Dumke, Rainer

    2009-01-01

    We theoretically investigate the heating rate and spin flip lifetimes due to near field noise for atoms trapped close to layered superconducting structures. In particular, we compare the case of a gold layer deposited above a superconductor with the case of a bare superconductor. We study a niobium-based and a YBCO-based chip. For both niobium and YBCO chips at a temperature of 4.2 K, we find that the deposition of the gold layer can have a significant impact on the heating rate and spin flip lifetime, as a result of the increase of the near field noise. At a chip temperature of 77 K, this effect is less pronounced for the YBCO chip.

  14. Atomic and electronic structure of ultrathin fluoride barrier layers at the oxide/Si interface

    Energy Technology Data Exchange (ETDEWEB)

    Pasquali, L; Montecchi, M; Nannarone, S [Department of Materials and Environmental Engineering, University of Modena and Reggio Emilia, Via Vignolese 905, I-41125 Modena (Italy); Boscherini, F [Department of Physics, University of Bologna, Viale Berti Pichat 6/2, I-40127 Bologna (Italy)

    2011-09-07

    A SrF{sub 2} ultrathin barrier layer on Si(001) is used to form a sharp interface and block reactivity and intermixing between the semiconductor and a Yb{sub 2}O{sub 3} overlayer. Yb{sub 2}O{sub 3}/Si(001) and Yb{sub 2}O{sub 3}/SrF{sub 2}/Si(001) interfaces grown in ultra high vacuum by molecular beam epitaxy are studied by photoemission and x-ray absorption fine structure. Without the fluoride interlayer, Yb{sub 2}O{sub 3}/Si(001) presents an interface reacted region formed by SiO{sub x} and/or silicate compounds, which is about 9 A thick and increases up to 14-15 A after annealing at 500-700 {sup 0}C. A uniform single layer of SrF{sub 2} molecules blocks intermixing and reduces the oxidized Si region to 2.4 A after deposition and to 3.5 A after annealing at 500 {sup 0}C. In both cases we estimate a conduction band offset and a valence band offset of {approx} 1.7 eV and 2.4 eV between the oxide and Si, respectively. X-ray absorption fine structure measurements at the Yb L{sub III} edge suggest that the Yb oxide films exhibit a significant degree of static disorder with and without the fluoride barrier. Sr K edge measurements indicate that the ultrathin fluoride films are reacted, with the formation of bonds between Si and Sr; the Sr-Sr and Sr-F interatomic distances in the ultrathin fluoride barrier film are relaxed to the bulk value.

  15. Effect of growth temperature on defects in epitaxial GaN film grown by plasma assisted molecular beam epitaxy

    Directory of Open Access Journals (Sweden)

    S. S. Kushvaha

    2014-02-01

    Full Text Available We report the effect of growth temperature on defect states of GaN epitaxial layers grown on 3.5 μm thick GaN epi-layer on sapphire (0001 substrates using plasma assisted molecular beam epitaxy. The GaN samples grown at three different substrate temperatures at 730, 740 and 750 °C were characterized using atomic force microscopy and photoluminescence spectroscopy. The atomic force microscopy images of these samples show the presence of small surface and large hexagonal pits on the GaN film surfaces. The surface defect density of high temperature grown sample is smaller (4.0 × 108 cm−2 at 750 °C than that of the low temperature grown sample (1.1 × 109 cm−2 at 730 °C. A correlation between growth temperature and concentration of deep centre defect states from photoluminescence spectra is also presented. The GaN film grown at 750 °C exhibits the lowest defect concentration which confirms that the growth temperature strongly influences the surface morphology and affects the optical properties of the GaN epitaxial films.

  16. Effect of growth temperature on defects in epitaxial GaN film grown by plasma assisted molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Kushvaha, S. S., E-mail: kushvahas@nplindia.org; Pal, P.; Shukla, A. K.; Joshi, Amish G.; Gupta, Govind; Kumar, M.; Singh, S.; Gupta, Bipin K.; Haranath, D. [CSIR- National Physical Laboratory, Dr. K. S. Krishnan Road, New Delhi, India 110012 (India)

    2014-02-15

    We report the effect of growth temperature on defect states of GaN epitaxial layers grown on 3.5 μm thick GaN epi-layer on sapphire (0001) substrates using plasma assisted molecular beam epitaxy. The GaN samples grown at three different substrate temperatures at 730, 740 and 750 °C were characterized using atomic force microscopy and photoluminescence spectroscopy. The atomic force microscopy images of these samples show the presence of small surface and large hexagonal pits on the GaN film surfaces. The surface defect density of high temperature grown sample is smaller (4.0 × 10{sup 8} cm{sup −2} at 750 °C) than that of the low temperature grown sample (1.1 × 10{sup 9} cm{sup −2} at 730 °C). A correlation between growth temperature and concentration of deep centre defect states from photoluminescence spectra is also presented. The GaN film grown at 750 °C exhibits the lowest defect concentration which confirms that the growth temperature strongly influences the surface morphology and affects the optical properties of the GaN epitaxial films.

  17. High quality boron-doped epitaxial layers grown at 200°C from SiF4/H2/Ar gas mixtures for emitter formation in crystalline silicon solar cells

    Directory of Open Access Journals (Sweden)

    Ronan Léal

    2017-02-01

    Full Text Available Controlling the doping profile in solar cells emitter and front/back surface field is mandatory to reach high efficiencies. In the current state of the art, these doped layers are made by dopant diffusion at around 900°C, which implies potential temperature induced damages in the c-Si absorber and for which a precise control of doping is difficult. An alternative solution based on boron-doped epitaxial silicon layers grown by plasma-enhanced chemical vapor deposition (PECVD from 200°C using SiF4/H2/Ar/B2H6 chemistry is reported. The structural properties of the doped and undoped epitaxial layers were assessed by spectroscopic ellipsometry (SE, high resolution transmission electron microscopy (HR-TEM and X-ray diffraction (XRD. The incorporation of boron has been studied via plasma profiling time of flight mass spectrometry (PP-TOFMS and secondary ion mass spectrometry (SIMS measurements. The boron-doped epitaxial layers revealed excellent structural and electrical properties even for high carrier concentrations (>1019cm-3. Sheet resistances between 100 and 130 Ω/sq can been obtained depending on the thickness and the doping concentration, which is within the range of targeted values for emitters in c-Si solar cells. Electrochemical capacitance voltage (ECV revealed a uniform doping profile around 3.1019 cm-3 and by comparing with SIMS measurement a doping efficiency around 50% has been found.

  18. High quality boron-doped epitaxial layers grown at 200°C from SiF4/H2/Ar gas mixtures for emitter formation in crystalline silicon solar cells

    Science.gov (United States)

    Léal, Ronan; Haddad, Farah; Poulain, Gilles; Maurice, Jean-Luc; Roca i Cabarrocas, Pere

    2017-02-01

    Controlling the doping profile in solar cells emitter and front/back surface field is mandatory to reach high efficiencies. In the current state of the art, these doped layers are made by dopant diffusion at around 900°C, which implies potential temperature induced damages in the c-Si absorber and for which a precise control of doping is difficult. An alternative solution based on boron-doped epitaxial silicon layers grown by plasma-enhanced chemical vapor deposition (PECVD) from 200°C using SiF4/H2/Ar/B2H6 chemistry is reported. The structural properties of the doped and undoped epitaxial layers were assessed by spectroscopic ellipsometry (SE), high resolution transmission electron microscopy (HR-TEM) and X-ray diffraction (XRD). The incorporation of boron has been studied via plasma profiling time of flight mass spectrometry (PP-TOFMS) and secondary ion mass spectrometry (SIMS) measurements. The boron-doped epitaxial layers revealed excellent structural and electrical properties even for high carrier concentrations (>1019cm-3). Sheet resistances between 100 and 130 Ω/sq can been obtained depending on the thickness and the doping concentration, which is within the range of targeted values for emitters in c-Si solar cells. Electrochemical capacitance voltage (ECV) revealed a uniform doping profile around 3.1019 cm-3 and by comparing with SIMS measurement a doping efficiency around 50% has been found.

  19. Atmospheric spatial atomic layer deposition of Zn(O,S) buffer layer for Cu(In,Ga)Se2 solar cells

    NARCIS (Netherlands)

    Frijters, C.H.; Poodt, P.; Illeberi, A.

    2016-01-01

    Zinc oxysulfide has been grown by spatial atomic layer deposition (S-ALD) and successfully applied as buffer layer in Cu(In, Ga)Se2 (CIGS) solar cells. S-ALD combines high deposition rates (up to nm/s) with the advantages of conventional ALD, i.e. excellent control of film composition and superior u

  20. Al2O3 on Black Phosphorus by Atomic Layer Deposition: An in Situ Interface Study.

    Science.gov (United States)

    Zhu, Hui; McDonnell, Stephen; Qin, Xiaoye; Azcatl, Angelica; Cheng, Lanxia; Addou, Rafik; Kim, Jiyoung; Ye, Peide D; Wallace, Robert M

    2015-06-17

    In situ "half cycle" atomic layer deposition (ALD) of Al2O3 was carried out on black phosphorus ("black-P") surfaces with modified phosphorus oxide concentrations. X-ray photoelectron spectroscopy is employed to investigate the interfacial chemistry and the nucleation of the Al2O3 on black-P surfaces. This work suggests that exposing a sample that is initially free of phosphorus oxide to the ALD precursors does not result in detectable oxidation. However, when the phosphorus oxide is formed on the surface prior to deposition, the black-P can react with both the surface adventitious oxygen contamination and the H2O precursor at a deposition temperature of 200 °C. As a result, the concentration of the phosphorus oxide increases after both annealing and the atomic layer deposition process. The nucleation rate of Al2O3 on black-P is correlated with the amount of oxygen on samples prior to the deposition. The growth of Al2O3 follows a "substrate inhibited growth" behavior where an incubation period is required. Ex situ atomic force microscopy is also used to investigate the deposited Al2O3 morphologies on black-P where the Al2O3 tends to form islands on the exfoliated black-P samples. Therefore, surface functionalization may be needed to get a conformal coverage of Al2O3 on the phosphorus oxide free samples.

  1. Growth of free-standing bulk wurtzite AlxGa1-xN layers by molecular beam epitaxy using a highly efficient RF plasma source

    Science.gov (United States)

    Novikov, S. V.; Staddon, C. R.; Sahonta, S.-L.; Oliver, R. A.; Humphreys, C. J.; Foxon, C. T.

    2016-12-01

    The recent development of group III nitrides allows researchers world-wide to consider AlGaN based light emitting diodes as a possible new alternative deep ultra-violet light source for surface decontamination and water purification. In this paper we will describe our recent results on plasma-assisted molecular beam epitaxy (PA-MBE) growth of free-standing wurtzite AlxGa1-xN bulk crystals using the latest model of Riber's highly efficient nitrogen RF plasma source. We have achieved AlGaN growth rates up to 3 μm/h. Wurtzite AlxGa1-xN layers with thicknesses up to 100 μm were successfully grown by PA-MBE on 2-inch and 3-inch GaAs (111)B substrates. After growth the GaAs was subsequently removed using a chemical etch to achieve free-standing AlxGa1-xN wafers. Free-standing bulk AlxGa1-xN wafers with thicknesses in the range 30-100 μm may be used as substrates for further growth of AlxGa1-xN-based structures and devices. High Resolution Scanning Transmission Electron Microscopy (HR-STEM) and Convergent Beam Electron Diffraction (CBED) were employed for detailed structural analysis of AlGaN/GaAs (111)B interface and allowed us to determine the N-polarity of AlGaN layers grown on GaAs (111)B substrates. The novel, high efficiency RF plasma source allowed us to achieve free-standing AlxGa1-xN layers in a single day's growth, making this a commercially viable process.

  2. Atomic layer deposition of crystalline SrHfO{sub 3} directly on Ge (001) for high-k dielectric applications

    Energy Technology Data Exchange (ETDEWEB)

    McDaniel, Martin D.; Ngo, Thong Q.; Ekerdt, John G., E-mail: ekerdt@utexas.edu [Department of Chemical Engineering, The University of Texas at Austin, Austin, Texas 78712 (United States); Hu, Chengqing; Jiang, Aiting; Yu, Edward T. [Microelectronics Research Center, The University of Texas at Austin, Austin, Texas 78758 (United States); Lu, Sirong; Smith, David J. [Department of Physics, Arizona State University, Tempe, Arizona 85287 (United States); Posadas, Agham; Demkov, Alexander A. [Department of Physics, The University of Texas at Austin, Austin, Texas 78712 (United States)

    2015-02-07

    The current work explores the crystalline perovskite oxide, strontium hafnate, as a potential high-k gate dielectric for Ge-based transistors. SrHfO{sub 3} (SHO) is grown directly on Ge by atomic layer deposition and becomes crystalline with epitaxial registry after post-deposition vacuum annealing at ∼700 °C for 5 min. The 2 × 1 reconstructed, clean Ge (001) surface is a necessary template to achieve crystalline films upon annealing. The SHO films exhibit excellent crystallinity, as shown by x-ray diffraction and transmission electron microscopy. The SHO films have favorable electronic properties for consideration as a high-k gate dielectric on Ge, with satisfactory band offsets (>2 eV), low leakage current (<10{sup −5} A/cm{sup 2} at an applied field of 1 MV/cm) at an equivalent oxide thickness of 1 nm, and a reasonable dielectric constant (k ∼ 18). The interface trap density (D{sub it}) is estimated to be as low as ∼2 × 10{sup 12 }cm{sup −2 }eV{sup −1} under the current growth and anneal conditions. Some interfacial reaction is observed between SHO and Ge at temperatures above ∼650 °C, which may contribute to increased D{sub it} value. This study confirms the potential for crystalline oxides grown directly on Ge by atomic layer deposition for advanced electronic applications.

  3. Atomic layer deposition of an Al2O3 dielectric on ultrathin graphite by using electron beam irradiation

    Institute of Scientific and Technical Information of China (English)

    Jiang Ran; Meng Lingguo; Zhang Xijian; Hyung-Suk Jung; Cheol Seong Hwang

    2012-01-01

    Atomic layer deposition ofan Al2O3 dielectric on ultrathin graphite is studied in order to investigate the integration of a high k dielectric with graphite-based substrates.Electron beam irradiation on the graphite surface is followed by a standard atomic layer deposition of Al2O3.Improvement of the Al2O3 layer deposition morphology was observed when using this radiation exposure on graphite.This result may be attributed to the amorphous change of the graphite layers during electron beam irradiation.

  4. UV protective zinc oxide coating for biaxially oriented polypropylene packaging film by atomic layer deposition

    Energy Technology Data Exchange (ETDEWEB)

    Lahtinen, Kimmo, E-mail: kimmo.lahtinen@lut.fi [ASTRaL, Lappeenranta University of Technology, Sammonkatu 12, FI-50130 Mikkeli (Finland); Kääriäinen, Tommi, E-mail: tommi.kaariainen@colorado.edu [ASTRaL, Lappeenranta University of Technology, Sammonkatu 12, FI-50130 Mikkeli (Finland); Johansson, Petri, E-mail: petri.johansson@tut.fi [Paper Converting and Packaging Technology, Tampere University of Technology, P.O.Box 589, FI-33101 Tampere (Finland); Kotkamo, Sami, E-mail: sami.kotkamo@tut.fi [Paper Converting and Packaging Technology, Tampere University of Technology, P.O.Box 589, FI-33101 Tampere (Finland); Maydannik, Philipp, E-mail: philipp.maydannik@lut.fi [ASTRaL, Lappeenranta University of Technology, Sammonkatu 12, FI-50130 Mikkeli (Finland); Seppänen, Tarja, E-mail: tarja.seppanen@lut.fi [ASTRaL, Lappeenranta University of Technology, Sammonkatu 12, FI-50130 Mikkeli (Finland); Kuusipalo, Jurkka, E-mail: jurkka.kuusipalo@tut.fi [Paper Converting and Packaging Technology, Tampere University of Technology, P.O.Box 589, FI-33101 Tampere (Finland); Cameron, David C., E-mail: david.cameron@miktech.fi [ASTRaL, Lappeenranta University of Technology, Sammonkatu 12, FI-50130 Mikkeli (Finland)

    2014-11-03

    Biaxially oriented polypropylene (BOPP) packaging film was coated with zinc oxide (ZnO) coatings by atomic layer deposition (ALD) in order to protect the film from UV degradation. The coatings were made at a process temperature of 100 °C using diethylzinc and water as zinc and oxygen precursors, respectively. The UV protective properties of the coatings were tested by using UV–VIS and infrared spectrometry, differential scanning calorimetry (DSC) and a mechanical strength tester, which characterised the tensile and elastic properties of the film. The results obtained with 36 and 67 nm ZnO coatings showed that the ZnO UV protective layer is able to provide a significant decrease in photodegradation of the BOPP film under UV exposure. While the uncoated BOPP film suffered a complete degradation after a 4-week UV exposure, the 67 nm ZnO coated BOPP film was able to preserve half of its original tensile strength and 1/3 of its elongation at break after a 6-week exposure period. The infrared analysis and DSC measurements further proved the UV protection of the ZnO coatings. The results show that a nanometre scale ZnO coating deposited by ALD is a promising option when a transparent UV protection layer is sought for polymer substrates. - Highlights: • Atomic layer deposited zinc oxide coatings were used as UV protection layers. • Biaxially oriented polypropylene (BOPP) film was well protected against UV light. • Formation of UV degradation products in BOPP was significantly reduced. • Mechanical properties of the UV exposed BOPP film were significantly improved.

  5. Influence of the interface layer on the strain relaxation of ZnSe epitaxial layers grown by MBE on (001)GaAs

    Energy Technology Data Exchange (ETDEWEB)

    Giannini, C.; Carlino, E.; Sciacovelli, P.; Tapfer, L. [Centro Nazionale Ricerca e Sviluppo Materiali (PASTIS-CNRSM), Brindisi (Italy); Sauvage-Simkin, M.; Jedrecy, N. [Laboratoire pour l' Utilisation du Rayonnement Electromagnetique (LURE), Batiment 209D, Universite Paris-Sud, Orsay (France); Laboratoire de Mineralogie-Cristallographie, CNRS-Universites P et M Curie et D Diderot, Paris (France); Garreau, Y.; Veron, M.B. [Laboratoire pour l' Utilisation du Rayonnement Electromagnetique (LURE), Batiment 209D, Universite Paris-Sud, Orsay (France); Pinchaux, P. [Laboratoire pour l' Utilisation du Rayonnement Electromagnetique LURE, Batiment 209D, Universite Paris-Sud, Orsay (France); Universite P et M Curie, Paris (France)

    1999-05-21

    ZnSe epilayers grown by molecular beam epitaxy on GaAs(001) substrates are investigated by grazing incidence x-ray diffraction, reciprocal space mapping and transmission electron microscopy. Our data show that the Zn/Se beam pressure ratio employed during the early stages of the ZnSe growth (2 nm) strongly affects the structural properties of the overgrown stoichiometric epilayer. The different strain status of the interface (tensile and compressive for the Zn-rich and Se-rich interfaces, respectively) is directly involved in the defects evolution mechanism. While the same order of magnitude of 60 deg. dislocations was measured in all the specimens, three orders of magnitude more stacking-faults were measured in samples with a Zn-rich interface with respect to those with a Se-rich interface. In addition, a contraction of the lattice parameter towards the sample surface along the growth direction is observed only in the sample grown with an excess of Se at the interface. This lattice gradient can be explained by the presence of point defects within the II-VI epilayer thickness. The formation of point defects could be favoured by the presence of the Se-rich compressive strained interface. (author)

  6. A 3D Computational Study on the Air-Blast Atomization of a Planar Liquid Layer

    Science.gov (United States)

    Chiodi, Robert; Desjardins, Olivier

    2016-11-01

    The air-blast atomization of a planar liquid layer is a complex fluid phenomenon involving the destabilization of a low speed liquid layer by a high speed gas coflow. While progress has been made in recent years on understanding the instability of the liquid surface, it remains difficult to accurately predict using stability analysis and requires special expertise and equipment to perform thorough experiments. Simulations provide an excellent way to conduct parametric studies to determine the effect of splitter plate geometry and momentum flux ratio on the frequency and wavelengths of instability, however, they are extremely difficult due to the high density ratio and large range of length and time scales present in the flow. Using an accurate conservative level set method in conjunction with a newly reformulated reinitialization equation, we perform 3D simulations of the air-blast atomization of a planar liquid layer and compare them to experiments. We then go on to explore the role momentum flux ratio plays in the longitudinal and transverse wavelengths of instability.

  7. Synthesis of multiferroic Er-Fe-O thin films by atomic layer and chemical vapor deposition

    Energy Technology Data Exchange (ETDEWEB)

    Mantovan, R., E-mail: roberto.mantovan@mdm.imm.cnr.it; Vangelista, S.; Wiemer, C.; Lamperti, A.; Tallarida, G. [Laboratorio MDM IMM-CNR, I-20864 Agrate Brianza (MB) (Italy); Chikoidze, E.; Dumont, Y. [GEMaC, Université de Versailles St. Quentin en Yvelines-CNRS, Versailles (France); Fanciulli, M. [Laboratorio MDM IMM-CNR, I-20864 Agrate Brianza (MB) (Italy); Dipartimento di Scienza dei Materiali, Università di Milano Bicocca, Milano (Italy)

    2014-05-07

    R-Fe-O (R = rare earth) compounds have recently attracted high interest as potential new multiferroic materials. Here, we report a method based on the solid-state reaction between Er{sub 2}O{sub 3} and Fe layers, respectively grown by atomic layer deposition and chemical vapor deposition, to synthesize Er-Fe-O thin films. The reaction is induced by thermal annealing and evolution of the formed phases is followed by in situ grazing incidence X-ray diffraction. Dominant ErFeO{sub 3} and ErFe{sub 2}O{sub 4} phases develop following subsequent thermal annealing processes at 850 °C in air and N{sub 2}. Structural, chemical, and morphological characterization of the layers are conducted through X-ray diffraction and reflectivity, time-of-flight secondary ion-mass spectrometry, and atomic force microscopy. Magnetic properties are evaluated by magnetic force microscopy, conversion electron Mössbauer spectroscopy, and vibrating sample magnetometer, being consistent with the presence of the phases identified by X-ray diffraction. Our results constitute a first step toward the use of cost-effective chemical methods for the synthesis of this class of multiferroic thin films.

  8. Synthesis of multiferroic Er-Fe-O thin films by atomic layer and chemical vapor deposition

    Science.gov (United States)

    Mantovan, R.; Vangelista, S.; Wiemer, C.; Lamperti, A.; Tallarida, G.; Chikoidze, E.; Dumont, Y.; Fanciulli, M.

    2014-05-01

    R-Fe-O (R = rare earth) compounds have recently attracted high interest as potential new multiferroic materials. Here, we report a method based on the solid-state reaction between Er2O3 and Fe layers, respectively grown by atomic layer deposition and chemical vapor deposition, to synthesize Er-Fe-O thin films. The reaction is induced by thermal annealing and evolution of the formed phases is followed by in situ grazing incidence X-ray diffraction. Dominant ErFeO3 and ErFe2O4 phases develop following subsequent thermal annealing processes at 850 °C in air and N2. Structural, chemical, and morphological characterization of the layers are conducted through X-ray diffraction and reflectivity, time-of-flight secondary ion-mass spectrometry, and atomic force microscopy. Magnetic properties are evaluated by magnetic force microscopy, conversion electron Mössbauer spectroscopy, and vibrating sample magnetometer, being consistent with the presence of the phases identified by X-ray diffraction. Our results constitute a first step toward the use of cost-effective chemical methods for the synthesis of this class of multiferroic thin films.

  9. Atomic Layer Deposition of SnO2 on MXene for Li-Ion Battery Anodes

    KAUST Repository

    Ahmed, Bilal

    2017-02-24

    In this report, we show that oxide battery anodes can be grown on two-dimensional titanium carbide sheets (MXenes) by atomic layer deposition. Using this approach, we have fabricated a composite SnO2/MXene anode for Li-ion battery applications. The SnO2/MXene anode exploits the high Li-ion capacity offered by SnO2, while maintaining the structural and mechanical integrity by the conductive MXene platform. The atomic layer deposition (ALD) conditions used to deposit SnO2 on MXene terminated with oxygen, fluorine, and hydroxyl-groups were found to be critical for preventing MXene degradation during ALD. We demonstrate that SnO2/MXene electrodes exhibit excellent electrochemical performance as Li-ion battery anodes, where conductive MXene sheets act to buffer the volume changes associated with lithiation and delithiation of SnO2. The cyclic performance of the anodes is further improved by depositing a very thin passivation layer of HfO2, in the same ALD reactor, on the SnO2/MXene anode. This is shown by high-resolution transmission electron microscopy to also improve the structural integrity of SnO2 anode during cycling. The HfO2 coated SnO2/MXene electrodes demonstrate a stable specific capacity of 843 mAh/g when used as Li-ion battery anodes.

  10. Design and implementation of a novel portable atomic layer deposition/chemical vapor deposition hybrid reactor

    Science.gov (United States)

    Selvaraj, Sathees Kannan; Jursich, Gregory; Takoudis, Christos G.

    2013-09-01

    We report the development of a novel portable atomic layer deposition chemical vapor deposition (ALD/CVD) hybrid reactor setup. Unique feature of this reactor is the use of ALD/CVD mode in a single portable deposition system to fabricate multi-layer thin films over a broad range from "bulk-like" multi-micrometer to nanometer atomic dimensions. The precursor delivery system and control-architecture are designed so that continuous reactant flows for CVD and cyclic pulsating flows for ALD mode are facilitated. A custom-written LabVIEW program controls the valve sequencing to allow synthesis of different kinds of film structures under either ALD or CVD mode or both. The entire reactor setup weighs less than 40 lb and has a relatively small footprint of 8 × 9 in., making it compact and easy for transportation. The reactor is tested in the ALD mode with titanium oxide (TiO2) ALD using tetrakis(diethylamino)titanium and water vapor. The resulting growth rate of 0.04 nm/cycle and purity of the films are in good agreement with literature values. The ALD/CVD hybrid mode is demonstrated with ALD of TiO2 and CVD of tin oxide (SnOx). Transmission electron microscopy images of the resulting films confirm the formation of successive distinct TiO2-ALD and SnOx-CVD layers.

  11. Observation of anomalous Stokes versus anti-Stokes ratio in MoTe2 atomic layers

    Science.gov (United States)

    Goldstein, Thomas; Chen, Shao-Yu; Xiao, Di; Ramasubramaniam, Ashwin; Yan, Jun

    We grow hexagonal molybdenum ditelluride (MoTe2), a prototypical transition metal dichalcogenide (TMDC) semiconductor, with chemical vapor transport methods and investigate its atomic layers with Stokes and anti-Stokes Raman scattering. We report observation of all six types of zone center optical phonons. Quite remarkably, the anti-Stokes Raman intensity of the low energy layer-breathing mode becomes more intense than the Stokes peak under certain experimental conditions, creating an illusion of 'negative temperature'. This effect is tunable, and can be switched from anti-Stokes enhancement to suppression by varying the excitation wavelength. We interpret this observation to be a result of resonance effects arising from the C excitons in the vicinity of the Brillouin zone center, which are robust even for multiple layers of MoTe2. The intense anti-Stokes Raman scattering provides a cooling channel for the crystal and opens up opportunities for laser cooling of atomically thin TMDC semiconductor devices. Supported by the University of Massachusetts Amherst, the National Science Foundation Center for Hierarchical Manufacturing (CMMI-1025020) and Office of Emerging Frontiers in Research and Innovation (EFRI-1433496).

  12. Design and implementation of a novel portable atomic layer deposition/chemical vapor deposition hybrid reactor.

    Science.gov (United States)

    Selvaraj, Sathees Kannan; Jursich, Gregory; Takoudis, Christos G

    2013-09-01

    We report the development of a novel portable atomic layer deposition chemical vapor deposition (ALD/CVD) hybrid reactor setup. Unique feature of this reactor is the use of ALD/CVD mode in a single portable deposition system to fabricate multi-layer thin films over a broad range from "bulk-like" multi-micrometer to nanometer atomic dimensions. The precursor delivery system and control-architecture are designed so that continuous reactant flows for CVD and cyclic pulsating flows for ALD mode are facilitated. A custom-written LabVIEW program controls the valve sequencing to allow synthesis of different kinds of film structures under either ALD or CVD mode or both. The entire reactor setup weighs less than 40 lb and has a relatively small footprint of 8 × 9 in., making it compact and easy for transportation. The reactor is tested in the ALD mode with titanium oxide (TiO2) ALD using tetrakis(diethylamino)titanium and water vapor. The resulting growth rate of 0.04 nm/cycle and purity of the films are in good agreement with literature values. The ALD/CVD hybrid mode is demonstrated with ALD of TiO2 and CVD of tin oxide (SnOx). Transmission electron microscopy images of the resulting films confirm the formation of successive distinct TiO2-ALD and SnO(x)-CVD layers.

  13. Tuning the mechanical properties of vertical graphene sheets through atomic layer deposition.

    Science.gov (United States)

    Davami, Keivan; Jiang, Yijie; Cortes, John; Lin, Chen; Shaygan, Mehrdad; Turner, Kevin T; Bargatin, Igor

    2016-04-15

    We report the fabrication and characterization of graphene nanostructures with mechanical properties that are tuned by conformal deposition of alumina. Vertical graphene (VG) sheets, also called carbon nanowalls (CNWs), were grown on copper foil substrates using a radio-frequency plasma-enhanced chemical vapor deposition (RF-PECVD) technique and conformally coated with different thicknesses of alumina (Al2O3) using atomic layer deposition (ALD). Nanoindentation was used to characterize the mechanical properties of pristine and alumina-coated VG sheets. Results show a significant increase in the effective Young's modulus of the VG sheets with increasing thickness of deposited alumina. Deposition of only a 5 nm thick alumina layer on the VG sheets nearly triples the effective Young's modulus of the VG structures. Both energy absorption and strain recovery were lower in VG sheets coated with alumina than in pure VG sheets (for the same peak force). This may be attributed to the increase in bending stiffness of the VG sheets and the creation of connections between the sheets after ALD deposition. These results demonstrate that the mechanical properties of VG sheets can be tuned over a wide range through conformal atomic layer deposition, facilitating the use of VG sheets in applications where specific mechanical properties are needed.

  14. Surface passivation of efficient nanotextured black silicon solar cells using thermal atomic layer deposition.

    Science.gov (United States)

    Wang, Wei-Cheng; Lin, Che-Wei; Chen, Hsin-Jui; Chang, Che-Wei; Huang, Jhih-Jie; Yang, Ming-Jui; Tjahjono, Budi; Huang, Jian-Jia; Hsu, Wen-Ching; Chen, Miin-Jang

    2013-10-09

    Efficient nanotextured black silicon solar cells passivated by an Al2O3 layer are demonstrated. The broadband antireflection of the nanotextured black silicon solar cells was provided by fabricating vertically aligned silicon nanowire (SiNW) arrays on the n(+) emitter. A highly conformal Al2O3 layer was deposited upon the SiNW arrays by the thermal atomic layer deposition (ALD) based on the multiple pulses scheme. The nanotextured black silicon wafer covered with the Al2O3 layer exhibited a low total reflectance of ∼1.5% in a broad spectrum from 400 to 800 nm. The Al2O3 passivation layer also contributes to the suppressed surface recombination, which was explored in terms of the chemical and field-effect passivation effects. An 8% increment of short-circuit current density and 10.3% enhancement of efficiency were achieved due to the ALD Al2O3 surface passivation and forming gas annealing. A high efficiency up to 18.2% was realized in the ALD Al2O3-passivated nanotextured black silicon solar cells.

  15. Preparation of gallium nitride surfaces for atomic layer deposition of aluminum oxide.

    Science.gov (United States)

    Kerr, A J; Chagarov, E; Gu, S; Kaufman-Osborn, T; Madisetti, S; Wu, J; Asbeck, P M; Oktyabrsky, S; Kummel, A C

    2014-09-14

    A combined wet and dry cleaning process for GaN(0001) has been investigated with XPS and DFT-MD modeling to determine the molecular-level mechanisms for cleaning and the subsequent nucleation of gate oxide atomic layer deposition (ALD). In situ XPS studies show that for the wet sulfur treatment on GaN(0001), sulfur desorbs at room temperature in vacuum prior to gate oxide deposition. Angle resolved depth profiling XPS post-ALD deposition shows that the a-Al2O3 gate oxide bonds directly to the GaN substrate leaving both the gallium surface atoms and the oxide interfacial atoms with XPS chemical shifts consistent with bulk-like charge. These results are in agreement with DFT calculations that predict the oxide/GaN(0001) interface will have bulk-like charges and a low density of band gap states. This passivation is consistent with the oxide restoring the surface gallium atoms to tetrahedral bonding by eliminating the gallium empty dangling bonds on bulk terminated GaN(0001).

  16. Atomic Structure of a Spinel-like Transition Al2O3 (100) Surface

    DEFF Research Database (Denmark)

    Jensen, Thomas Nørregaard; Meinander, Kristoffer; Helveg, Stig

    2014-01-01

    We study a crystalline epitaxial alumina thin film with the characteristics of a spinel-type transition Al2O3(100) surface by using atom-resolved noncontact atomic force microscopy and density functional theory. It is shown that the films are terminated by an Al-O layer rich in Al vacancies...

  17. Tuning negative differential resistance in single-atomic layer boron-silicon sheets

    Energy Technology Data Exchange (ETDEWEB)

    Zhou, Ming-Yue; Liu, Chun-Sheng, E-mail: csliu@njupt.edu.cn, E-mail: yanxh@njupt.edu.cn [School of Electronic Science and Engineering, Nanjing University of Posts and Telecommunications, Nanjing 210046 (China); Key Laboratory of Radio Frequency and Micro-Nano Electronics of Jiangsu Province, Nanjing 210023, Jiangsu (China); Yan, Xiaohong, E-mail: csliu@njupt.edu.cn, E-mail: yanxh@njupt.edu.cn [School of Electronic Science and Engineering, Nanjing University of Posts and Telecommunications, Nanjing 210046 (China); Key Laboratory of Radio Frequency and Micro-Nano Electronics of Jiangsu Province, Nanjing 210023, Jiangsu (China); College of Science, Nanjing University of Aeronautics and Astronautics, Nanjing 211106 (China)

    2015-03-21

    Using density functional theory and nonequilibrium Green's function formalism for quantum transport calculation, we have quantified the ballistic transport properties along different directions in two-dimensional boron-silicon (B-Si) compounds, as well as the current response to bias voltage. The conductance of the most B-Si devices is higher than the conductance of one-atom-thick boron and silicene. Furthermore, the negative differential resistance phenomenon can be found at certain B-Si stoichiometric composition, and it occurs at various bias voltages. Also, the peak-to-valley ratio is sensitive to the B-Si composition and dependent of the direction considered for B-Si monolayers. The present findings could be helpful for applications of the single-atomic layer B-Si sheets in the field of semiconductor devices or low-dimensional electronic devices.

  18. Low-temperature atomic layer deposition of copper(II) oxide thin films

    Energy Technology Data Exchange (ETDEWEB)

    Iivonen, Tomi, E-mail: tomi.iivonen@helsinki.fi; Hämäläinen, Jani; Mattinen, Miika; Popov, Georgi; Leskelä, Markku [Laboratory of Inorganic Chemistry, Department of Chemistry, University of Helsinki, P.O. Box 55, FI-00014 Helsinki (Finland); Marchand, Benoît; Mizohata, Kenichiro [Division of Materials Physics, Department of Physics, University of Helsinki, P.O. Box 43, FI-00014 Helsinki (Finland); Kim, Jiyeon; Fischer, Roland A. [Chair of Inorganic Chemistry II, Ruhr-University Bochum, Universitätsstrasse 150, 44780 Bochum (Germany)

    2016-01-15

    Copper(II) oxide thin films were grown by atomic layer deposition (ALD) using bis-(dimethylamino-2-propoxide)copper [Cu(dmap){sub 2}] and ozone in a temperature window of 80–140 °C. A thorough characterization of the films was performed using x-ray diffraction, x-ray reflectivity, UV‐Vis spectrophotometry, atomic force microscopy, field emission scanning electron microscopy, x-ray photoelectron spectroscopy, and time-of-flight elastic recoil detection analysis techniques. The process was found to produce polycrystalline copper(II) oxide films with a growth rate of 0.2–0.3 Å per cycle. Impurity content in the films was relatively small for a low temperature ALD process.

  19. Controlled Synthesis of Atomically Layered Hexagonal Boron Nitride via Chemical Vapor Deposition

    Directory of Open Access Journals (Sweden)

    Juanjuan Liu

    2016-11-01

    Full Text Available Hexagonal boron nitrite (h-BN is an attractive material for many applications including electronics as a complement to graphene, anti-oxidation coatings, light emitters, etc. However, the synthesis of high-quality h-BN is still a great challenge. In this work, via controlled chemical vapor deposition, we demonstrate the synthesis of h-BN films with a controlled thickness down to atomic layers. The quality of as-grown h-BN is confirmed by complementary characterizations including high-resolution transition electron microscopy, atomic force microscopy, Raman spectroscopy and X-ray photo-electron spectroscopy. This work will pave the way for production of large-scale and high-quality h-BN and its applications as well.

  20. Crystallization engineering as a route to epitaxial strain control

    Directory of Open Access Journals (Sweden)

    Andrew R. Akbashev

    2015-10-01

    Full Text Available The controlled synthesis of epitaxial thin films offers opportunities for tuning their functional properties via enabling or suppressing strain relaxation. Examining differences in the epitaxial crystallization of amorphous oxide films, we report on an alternate, low-temperature route for strain engineering. Thin films of amorphous Bi–Fe–O were grown on (001SrTiO3 and (001LaAlO3 substrates via atomic layer deposition. In situ X-ray diffraction and X-ray photoelectron spectroscopy studies of the crystallization of the amorphous films into the epitaxial (001BiFeO3 phase reveal distinct evolution profiles of crystallinity with temperature. While growth on (001SrTiO3 results in a coherently strained film, the same films obtained on (001LaAlO3 showed an unstrained, dislocation-rich interface, with an even lower temperature onset of the perovskite phase crystallization than in the case of (001SrTiO3. Our results demonstrate how the strain control in an epitaxial film can be accomplished via its crystallization from the amorphous state.

  1. Formation of palladium nanofilms using electrochemical atomic layer deposition (E-ALD) with chloride complexation.

    Science.gov (United States)

    Sheridan, Leah B; Gebregziabiher, Daniel K; Stickney, John L; Robinson, David B

    2013-02-05

    Pd thin films were formed by electrochemical atomic layer deposition (E-ALD) using surface-limited redox replacement (SLRR) of Cu underpotential deposits (UPD) on polycrystalline Au substrates. An automated electrochemical flow deposition system was used to deposit Pd atomic layers using a sequence of steps referred to as a cycle. The initial step was Cu UPD, followed by its exchange for Pd ions at open circuit, and finishing with a blank rinse to complete the cycle. Deposits were formed with up to 75 cycles and displayed proportional deposit thicknesses. Previous reports by this group indicated excess Pd deposition at the flow cell ingress, from electron probe microanalysis (EPMA). Those results suggested that the SLRR mechanism did not involve direct transfer between a Cu(UPD) atom and a Pd(2+) ion that would take its position. Instead, it was proposed that electrons are transferred through the metallic surface to reduce Pd(2+) ions near the surface where their activity is highest. It was proposed that if the cell was filled completely before a significant fraction of the Cu(UPD) atoms had been oxidized then the deposit would be homogeneous. Previous work with EDTA indicated that the hypothesis had merit, but it proved to be very sensitive to the EDTA concentration. In the present study, chloride was used to complex Pd(2+) ions, forming PdCl(4)(2-), to slow the exchange rate. Both complexing agents led to a decrease in the rate of replacement, producing more homogeneous films. Although the use of EDTA improved the homogeneity, it also decreased the deposit thickness by a factor of 3 compared to the thickness obtained via the use of chloride.

  2. Imaging of oxide charges and contact potential difference fluctuations in Atomic Layer Deposited AL203 on Si

    NARCIS (Netherlands)

    Sturm, J.M.; Zinine, A.; Wormeester, H.; Poelsema, B.; Bankras, R.G.; Holleman, J.; Schmitz, J.

    2005-01-01

    Ultrathin 2.5 nm high-k aluminum oxide (Al2O3) films on p-type silicon (001) deposited by atomic layer deposition (ALD) were investigated with noncontact atomic force microscopy (NC-AFM) in ultrahigh vacuum, using a conductive tip. Constant force gradient images revealed the presence of oxide charge

  3. Selective etching and TEM study of inversion domains in Mg-doped GaN epitaxial layers

    NARCIS (Netherlands)

    Kamler, G.; Borysiuk, J.; Weyher, J.L.; Czernecki, R.; Leszczynski, M.; Grzegory, I.; Porowski, S.

    2005-01-01

    Two different etching techniques were used for the investigation of polarity inversion in the magnesium-doped MOVPE GaN layers deposited on GaN pressure grown substrates. Etching in KOH solution at 100 degrees C and in molten bases at 450 degrees C allowed us to determine precisely the regions of di

  4. (Invited) Atomic Layer Deposition for Novel Dye-Sensitized Solar Cells

    KAUST Repository

    Tétreault, Nicolas

    2011-01-01

    Herein we present the latest fabrication and characterization techniques for atomic layer deposition of Al 2O 3, ZnO, SnO 2, Nb 2O 5, HfO 2, Ga 2O 3 and TiO 2 for research on dye-sensitized solar cell. In particular, we review the fabrication of state-of-the-art 3D host-passivation-guest photoanodes and ZnO nanowires as well as characterize the deposited thin films using spectroscopic ellipsometry, X-ray diffraction, Hall effect, J-V curves and electrochemical impedance spectroscopy. ©The Electrochemical Society.

  5. Growth and characterization of titanium oxide by plasma enhanced atomic layer deposition

    KAUST Repository

    Zhao, Chao

    2013-09-01

    The growth of TiO2 films by plasma enhanced atomic layer deposition using Star-Ti as a precursor has been systematically studied. The conversion from amorphous to crystalline TiO2 was observed either during high temperature growth or annealing process of the films. The refractive index and bandgap of TiO2 films changed with the growth and annealing temperatures. The optimization of the annealing conditions for TiO2 films was also done by morphology and density studies. © 2013 Elsevier B.V. All rights reserved.

  6. Quantum size effects in TiO2 thin films grown by atomic layer deposition.

    Science.gov (United States)

    Tallarida, Massimo; Das, Chittaranjan; Schmeisser, Dieter

    2014-01-01

    We study the atomic layer deposition of TiO2 by means of X-ray absorption spectroscopy. The Ti precursor, titanium isopropoxide, was used in combination with H2O on Si/SiO2 substrates that were heated at 200 °C. The low growth rate (0.15 Å/cycle) and the in situ characterization permitted to follow changes in the electronic structure of TiO2 in the sub-nanometer range, which are influenced by quantum size effects. The modified electronic properties may play an important role in charge carrier transport and separation, and increase the efficiency of energy conversion systems.

  7. Quantum size effects in TiO2 thin films grown by atomic layer deposition

    OpenAIRE

    Tallarida, Massimo; Das, Chittaranjan; Schmeisser, Dieter

    2014-01-01

    We study the atomic layer deposition of TiO2 by means of X-ray absorption spectroscopy. The Ti precursor, titanium isopropoxide, was used in combination with H2O on Si/SiO2 substrates that were heated at 200 °C. The low growth rate (0.15 Å/cycle) and the in situ characterization permitted to follow changes in the electronic structure of TiO2 in the sub-nanometer range, which are influenced by quantum size effects. The modified electronic properties may play an important role in charge carrier...

  8. Mechanistic Details of Surface Reactions in Atomic Layer Deposition (ALD) Processes

    Institute of Scientific and Technical Information of China (English)

    Menno; Bouman; Christopher; Clark; Hugo; Tiznado; Francisco; Zaera

    2007-01-01

    1 Results The reaction mechanisms of the atomic layer deposition (ALD) processes used for thin-film growth have been characterized by a combination of surface sensitive techniques. Our early studies focused on the deposition of TiN films from TiCl4 and ammonia,starting with the independent characterization of each of the two half steps comprising the ALD process. It was found that exposure of the substrate to TiCl4 leads to the initial deposition of titanium in the +3 oxidation state; only at a later st...

  9. Atomic Layer Deposition of Pt Nanoparticles for Microengine with Promoted Catalytic Motion.

    Science.gov (United States)

    Jiang, Chi; Huang, Gaoshan; Ding, Shi-Jin; Dong, Hongliang; Men, Chuanling; Mei, Yongfeng

    2016-12-01

    Nanoparticle-decorated tubular microengines were synthesized by a combination of rolled-up nanotechnology and atomic layer deposition. The presence of Pt nanoparticles with different sizes and distributions on the walls of microengines fabricated from bilayer nanomembranes with different materials results in promoted catalytic reaction efficiency, which leads to an ultrafast speed (the highest speed 3200 μm/s). The motion speed of the decorated microengines fits the theoretical model very well, suggesting that the larger surface area is mainly responsible for the acceleration of the motion speed. The high-speed nanoparticle-decorated microengines hold considerable promise for a variety of applications.

  10. Surface engineering of nanoporous substrate for solid oxide fuel cells with atomic layer-deposited electrolyte

    Directory of Open Access Journals (Sweden)

    Sanghoon Ji

    2015-08-01

    Full Text Available Solid oxide fuel cells with atomic layer-deposited thin film electrolytes supported on anodic aluminum oxide (AAO are electrochemically characterized with varying thickness of bottom electrode catalyst (BEC; BECs which are 0.5 and 4 times thicker than the size of AAO pores are tested. The thicker BEC ensures far more active mass transport on the BEC side and resultantly the thicker BEC cell generates ≈11 times higher peak power density than the thinner BEC cell at 500 °C.

  11. Effect of a ZnO buffer layer on the properties of epitaxial ZnO:Ga films deposited on c-sapphire substrate

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Zhiyun, E-mail: zhangzhiyun01@163.com [School of Materials Science and Engineering, Xi’an University of Science and Technology, Xi’an, Shaanxi Province 710054 (China); Bao, Chonggao [State Key Laboratory for Mechanical Behaviour of Materials, School of Materials Science and Engineering, Xi’an Jiaotong University, Xi’an, Shaanxi Province 710049 (China); Yi, Dawei [School of Materials Science and Engineering, Xi’an University of Science and Technology, Xi’an, Shaanxi Province 710054 (China); Yang, Bo [No. 95 Binhai Road, Jiaojiang, Taizhou, Zhejiang Province 318000 (China); Li, Qun; Hou, Shuzeng [State Key Laboratory for Mechanical Behaviour of Materials, School of Materials Science and Engineering, Xi’an Jiaotong University, Xi’an, Shaanxi Province 710049 (China); Han, Z.H. [School of Materials Science and Engineering, Xi’an University of Technology, Xi’an, Shaanxi Province 710068 (China)

    2014-09-01

    Highlights: • The lowest resistivity of 1.2 × 10{sup –4} Ω cm was obtained at a ZnO buffered substrate. • The characteristic of c-axis oriented texture grows up at different substrates. • Two kinds of stacking faults were observed at Fourier-filtered images. • Origin and consequences of stacking faults were discussed. • Lower defect density of film has a benefit effect on the resistivity. - Abstract: Bi-layer ZnO films with 2 wt.% Al (AZO; ZnO:Al) and 4 wt.% Ga-doped (GZO; ZnO:Ga) were deposited on the non-buffered and buffered c(0 0 0 1)-sapphire(Al{sub 2}O{sub 3}) substrates respectively by Pulsed Laser Deposition (PLD). The effect of a ZnO buffer layer on the crystallinity and electrical properties of the GZO thin films was investigated. X-ray Diffraction (XRD) peaks and High Resolution Transmission Electron Microscopy (HRTEM) studies showed that the GZO thin film on a buffered substrate was epitaxially grown with an orientation relationship of (0 0 0 1) [112{sup ¯}0]{sub GZO}||(0001)[112{sup ¯}0]{sub Al{sub 2O{sub 3}}}. However, GZO thin film on a non-buffered substrate was grown as a monocrystalline hexagonal wurtzite phase with c-axis preferred, out-of-plane orientation, and random in-plane orientation. The electrical resistivity of the GZO thin films was improved by introducing a ZnO buffer layer from 2.2 × 10{sup -4} Ω cm to 1.2 × 10{sup -4} Ω cm, respectively. In a word, it was found in the films that more preferred c-axis orientation texture and reduction of the defects such as stacking faults and dislocations, with introducing a ZnO buffer layer. It was seen that the ZnO buffer layer had a great influence on the orientation and defect density of GZO thin films from X-ray Diffraction (XRD) peaks and High Resolution Transmission Electron Microscopy (HRTEM) images.

  12. On the role of secondary extinction in the measurement of the integrated intensity of X-ray diffraction peaks and in the determination of the thickness of damaged epitaxial layers

    Science.gov (United States)

    Kyutt, R. N.

    2016-06-01

    The integrated intensity of X-ray diffraction reflections has been measured for a series of epitaxial layers of AIII nitrides (GaN, AlN, AlGaN) grown on different substrates (sapphire, SiC) and characterized by different degrees of structural perfection. It has been shown that, despite a high density of dislocations and a significant broadening of the diffraction peaks, the obtained values are not described by the kinematic theory of X-ray diffraction and suggest the existence of extinction. The results have been analyzed on the basis of the Darwin and Zachariasen extinction models. The secondary extinction coefficients and the thicknesses of epitaxial layers have been determined using two orders of reflection both in the Bragg geometry (0002 and 0004) and in the Laue geometry (10bar 10) and 10bar 20). It has been demonstrated that the secondary extinction coefficient is the greater, the smaller is the broadening of the diffraction peaks and, consequently, the dislocation density. It has been found that, for epitaxial layers with a regular system of threading dislocations, the secondary extinction coefficient for the Laue reflections is substantially greater than that for the Bragg reflections.

  13. Metal-organic-vapor-phase-epitaxy and characterization of homoepitaxial ZnO-layers; Metallorganische Gasphasenepitaxie und Charakteriesierung homoepitaktischer ZnO-Schichten

    Energy Technology Data Exchange (ETDEWEB)

    Heinze, Soeren

    2009-03-30

    ZnO is a direct semiconductor with a band gap of 3.37 eV and an exciton binding energy of about 60 meV. By alloying with cadmium or magnesium the band gap can be varied between 2.9 eV and 4 eV, which makes the realization of for instance quantum pot structures. Therefore ZnO is a promising material for optoelectronic applications in the blue and near-ultraviolet spectral range. In spite of world-wide numerous research activities over the last years the realization of p-type ZnO could indeed not sufficiently (i.e. reproduceable and long-time stably) be solved. The ZnO layers of this thesis were fabricated by means of metalorganic gas-phase epitaxy. By means of the studies on heteroepitactically deposed, undoped layers I show the limits of the heteroepitaxy. Although in doping attempts no p-type ZnO could be fabricated. By introduction of a three-stage growth procedure physical properties (morphology, luminescence, crystallographic and electric properties) of the upper ZnO layer could be distinctly improved. On the other hand it was proved that during the fabrication process an electrically high-conductive intermediate layer in the neighbourhood of the substrate/ZnO interface is formed, the formation of which cannot be avoided in the heteroepitaxy. Since about three years ZnO substrates with very good quality are commercially available. Therefore the essential part of this thesis tracts my works on the homoepitaxy of ZnO. For a successful homoepitactical growth a thermal pre-treatment (annealing) of the substrate is necessary. Thereby the substrate is located in a surrounding of ZnO powder and an oxygen atmosphere. The optimal tempering conditions were determined and the influence of these pre-treatment on the physical properties of the substrated were detailedly studied. After the annealing the substrates are suited for the epitaxy. The experiences from the heteroepitaxy could not without more ado be transferred to the homoepitaxy. The quality of the homoepitactical

  14. Atomic layer deposited borosilicate glass microchannel plates for large area event counting detectors

    Science.gov (United States)

    Siegmund, O. H. W.; McPhate, J. B.; Tremsin, A. S.; Jelinsky, S. R.; Hemphill, R.; Frisch, H. J.; Elam, J.; Mane, A.; Lappd Collaboration

    2012-12-01

    Borosilicate glass micro-capillary array substrates with 20 μm and 40 μm pores have been deposited with resistive, and secondary electron emissive, layers by atomic layer deposition to produce functional microchannel plates. Device formats of 32.7 mm and 20 cm square have been fabricated and tested in analog and photon counting modes. The tests show amplification, imaging, background rate, pulse shape and lifetime characteristics that are comparable to standard glass microchannel plates. Large area microchannel plates of this type facilitate the construction of 20 cm format sealed tube sensors with strip-line readouts that are being developed for Cherenkov light detection. Complementary work has resulted in Na2KSb bialkali photocathodes with peak quantum efficiency of 25% being made on borosilicate glass. Additionally GaN (Mg) opaque photocathodes have been successfully made on borosilicate microchannel plates.

  15. Modeling and optimization of atomic layer deposition processes on vertically aligned carbon nanotubes

    Directory of Open Access Journals (Sweden)

    Nuri Yazdani

    2014-03-01

    Full Text Available Many energy conversion and storage devices exploit structured ceramics with large interfacial surface areas. Vertically aligned carbon nanotube (VACNT arrays have emerged as possible scaffolds to support large surface area ceramic layers. However, obtaining conformal and uniform coatings of ceramics on structures with high aspect ratio morphologies is non-trivial, even with atomic layer deposition (ALD. Here we implement a diffusion model to investigate the effect of the ALD parameters on coating kinetics and use it to develop a guideline for achieving conformal and uniform thickness coatings throughout the depth of ultra-high aspect ratio structures. We validate the model predictions with experimental data from ALD coatings of VACNT arrays. However, the approach can be applied to predict film conformality as a function of depth for any porous topology, including nanopores and nanowire arrays.

  16. The possibility of multi-layer nanofabrication via atomic force microscope-based pulse electrochemical nanopatterning.

    Science.gov (United States)

    Kim, Uksu; Morita, Noboru; Lee, Deug; Jun, Martin; Park, Jeong Woo

    2017-03-27

    Pulse electrochemical nanopatterning (PECN), a non-contact scanning probe lithography (NC-SPL) process using ultrashort voltage pulses, is based primarily on an electrochemical machining (ECM) process using localized electrochemical oxidation between a sharp tool tip and the sample surface. In this study, nanoscale oxide patterns were formed on silicon Si (100) wafer surfaces via electrochemical surface nanopatterning, by supplying external pulsed currents through non-contact atomic force microscopy. Nanoscale oxide width and height were controlled by modulating the applied pulse duration. Additionally, protruding nanoscale oxides were removed completely by simple chemical etching, showing a depressed pattern on the sample substrate surface. Nanoscale two-dimensional oxides, prepared by a localized electrochemical reaction, can be defined easily by controlling physical and electrical variables, before proceeding further to a layer-by-layer nanofabrication process.

  17. Characterization of 1064nm laser-induced damage on antireflection coatings grown by atomic layer deposition

    Science.gov (United States)

    Liu, Zhichao; Wei, Yaowei; Chen, Songlin; Luo, Jin; Ma, Ping

    2011-12-01

    Damage tests were carried out to measure the laser resistance of Al2O3/TiO2 and Al2O3/HfO2 antireflection coatings at 1064nm grown by atomic layer deposition (ALD). The S-on-1 and R-on-1 damage results are given. It's interesting to find that ALD coatings damage performance seems closed to those grown by conventional e-beam evaporation process. For Al2O3/TiO2 coatings, the grown temperature will impact the damage resistance of thin films. Crystallization of TiO2 layer at higher temperature could play an importance role as absorption defects that reduced the LIDT of coatings. In addition, it is found that using inorganic compound instead of organic compound as precursors for ALD process can effective prevent residual carbon in films and will increase the LIDT of coatings.

  18. Atomic layer deposited TiO{sub 2} for implantable brain-chip interfacing devices

    Energy Technology Data Exchange (ETDEWEB)

    Cianci, E., E-mail: elena.cianci@mdm.imm.cnr.it [Laboratorio MDM, IMM-CNR, 20864 Agrate Brianza (MB) (Italy); Lattanzio, S. [Istituto di Fisiologia, Dipartimento di Anatomia Umana e Fisiologia, Universita di Padova, 35131 Padova (Italy); Dipartimento di Ingegneria dell' Informazione, Universita di Padova, 35131 Padova (Italy); Seguini, G. [Laboratorio MDM, IMM-CNR, 20864 Agrate Brianza (Italy); Vassanelli, S. [Istituto di Fisiologia, Dipartimento di Anatomia Umana e Fisiologia, Universita di Padova, 35131 Padova (Italy); Fanciulli, M. [Laboratorio MDM, IMM-CNR, 20864 Agrate Brianza (Italy); Dipartimento di Scienza dei Materiali, Universita degli Studi di Milano-Bicocca, 20126 Milano (Italy)

    2012-05-01

    In this paper we investigated atomic layer deposition (ALD) TiO{sub 2} thin films deposited on implantable neuro-chips based on electrolyte-oxide-semiconductor (EOS) junctions, implementing both efficient capacitive neuron-silicon coupling and biocompatibility for long-term implantable functionality. The ALD process was performed at 295 Degree-Sign C using titanium tetraisopropoxide and ozone as precursors on needle-shaped silicon substrates. Engineering of the capacitance of the EOS junctions introducing a thin Al{sub 2}O{sub 3} buffer layer between TiO{sub 2} and silicon resulted in a further increase of the specific capacitance. Biocompatibility for long-term implantable neuroprosthetic systems was checked upon in-vitro treatment.

  19. Reactor concepts for atomic layer deposition on agitated particles: A review

    Energy Technology Data Exchange (ETDEWEB)

    Longrie, Delphine, E-mail: delphine.longrie@asm.com; Deduytsche, Davy; Detavernier, Christophe, E-mail: christophe.detavernier@ugent.be [Department of Solid State Sciences, Ghent University, Krijgslaan 281/S1, B-9000 Gent (Belgium)

    2014-01-15

    The number of possible applications for nanoparticles has strongly increased in the last decade. For many applications, nanoparticles with different surface and bulk properties are necessary. A popular surface modification technique is coating the particle surface with a nanometer thick layer. Atomic layer deposition (ALD) is known as a reliable method for depositing ultrathin and conformal coatings. In this article, agitation or fluidization of the particles is necessary for performing ALD on (nano)particles. The principles of gas fluidization of particles will be outlined, and a classification of the gas fluidization behavior of particles based on their size and density will be given. Following different reactor concepts that have been designed to conformally coat (nano)particles with ALD will be described, and a concise overview will be presented of the work that has been performed with each of them ending with a concept reactor for performing spatial ALD on fluidized particles.

  20. Silicon dioxide mask by plasma enhanced atomic layer deposition in focused ion beam lithography

    Science.gov (United States)

    Liu, Zhengjun; Shah, Ali; Alasaarela, Tapani; Chekurov, Nikolai; Savin, Hele; Tittonen, Ilkka

    2017-02-01

    In this work, focused ion beam (FIB) lithography was developed for plasma enhanced atomic layer deposited (PEALD) silicon dioxide SiO2 hard mask. The PEALD process greatly decreases the deposition temperature of the SiO2 hard mask. FIB Ga+ ion implantation on the deposited SiO2 layer increases the wet etch resistivity of the irradiated region. A programmed exposure in FIB followed by development in a wet etchant enables the precisely defined nanoscale patterning. The combination of FIB exposure parameters and the development time provides greater freedom for optimization. The developed process provides high pattern dimension accuracy over the tested range of 90–210 nm. Utilizing the SiO2 mask developed in this work, silicon nanopillars with 40 nm diameter were successfully fabricated with cryogenic deep reactive ion etching and the aspect ratio reached 16:1. The fabricated mask is suitable for sub-100 nm high aspect ratio silicon structure fabrication.