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Sample records for surface si atom

  1. Interaction of Hg Atom with Bare Si(111) Surface

    Institute of Scientific and Technical Information of China (English)

    LIU Yong-Jun; LIU Ying

    2006-01-01

    To evaluate the interaction between Hg atom and bare Si(111) surface, three types of silicon cluster models of Si4H7, Si7H10 and Si16H20 together with their Hg complexes were studied by using hybrid (U)B3LYP density functional theory method. Optimized geometries and energies for Hg atom on different adsorption sites indicate that: 1) the binding energies at different adsorption sites are small (ranging from ~3 to 8 kJ/mol dependent on the adsorption sites), suggesting a weak interaction between Hg atom and silicon surface; 2) the most favorable adsorption site is the on top (T) site. By analyzing their natural bonding orbitals, the possible reason of this difference is suggested.

  2. Adsorption of oxygen atom on MoSi2 (110) surface

    Science.gov (United States)

    Sun, S. P.; Li, X. P.; Wang, H. J.; Jiang, Y.; Yi, D. Q.

    2016-09-01

    The adsorption energy, structural relaxation and electronic properties of oxygen atom on MoSi2 (110) surface have been investigated by first-principles calculations. The energetic stability of MoSi2 low-index surfaces was analyzed, and the results suggested that MoSi2 (110) surface had energetically stability. The site of oxygen atom adsorbed on MoSi2 (110) surface were discussed, and the results indicated that the preference adsorption site of MoSi2 (110) surface for oxygen atom was H site (hollow position). Our calculated work should help to understand further the interaction between oxygen atoms and MoSi2 surfaces.

  3. 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.

  4. Laser-induced emission of atoms and electrons from deposited Si atoms on the Si(100) 2x1 surface

    Energy Technology Data Exchange (ETDEWEB)

    Yu, In Keun; Kanasaki, Jun' ichi; Nakai, Yasuo; Itoh, Noriaki [Nagoya Univ., Nagoya (Japan)

    1998-07-01

    We have measured the emissions of electrons and Si atoms induced by laser irradiation on a Si(100) 2x1 surface with Si atoms deposited in a coverage range between 4.6 x 10{sup -4} and 1.67 x 10{sup -1} monolayers (ML) at room temperature. Two types of configurations, referred to as configuration R and S, of deposited atoms are differentiated.. The atom emission from configuration R occurs above a laser fluence of 310 mJ/cm{sup 2} for 28-ns laser pulses with a photon energy of 2.48 eV, while that from configuration S occurs only above a fluence of 540 mJ/cm{sup 2}. The electron emission from configuration R gives rise to a peak at a binding energy of 5.0 eV, while that from configuration S gives rise to a peak at 4.85 eV. Component R grows in proportion to the Si coverage in a coverage range below 4.0 x 10{sup -2} ML and then saturates, while component S grows in proportion to the square of the coverage at initial stage before saturation occurs. The yield of atom emitted from configuration S is reduced only for small coverages. Based on the number of atoms emitted by laser irradiation, the concentrations of configuration R and S after saturation were estimated to be 1.2 x 10{sup -4} ML and 1.94 x 10{sup -3} ML, respectively. It is suggested that configuration R is an adatom weakly bonded by the step edge or a defect and configuration S is an ad-dimer.

  5. Adsorption of oxygen atom on MoSi{sub 2} (110) surface

    Energy Technology Data Exchange (ETDEWEB)

    Sun, S.P., E-mail: sunshunping@jsut.edu.cn [School of Materials Engineering, Jiangsu University of Technology, Changzhou 213001 (China); Li, X.P.; Wang, H.J. [School of Materials Engineering, Jiangsu University of Technology, Changzhou 213001 (China); Jiang, Y., E-mail: yjiang@csu.edu.cn [School of Materials Science and Engineering, and Key Laboratory for Non-ferrous Materials of Ministry of Education, Central South University, Changsha 410083 (China); Yi, D.Q. [School of Materials Science and Engineering, and Key Laboratory for Non-ferrous Materials of Ministry of Education, Central South University, Changsha 410083 (China)

    2016-09-30

    Highlights: • The adsorption of oxygen atom on MoSi{sub 2} (110) surface was studied systematically. • The stability of MoSi{sub 2} low-index surfaces was also investigated. • The preference adsorption site of MoSi{sub 2} (110) surface for oxygen atom was H site. - Abstract: The adsorption energy, structural relaxation and electronic properties of oxygen atom on MoSi{sub 2} (110) surface have been investigated by first-principles calculations. The energetic stability of MoSi{sub 2} low-index surfaces was analyzed, and the results suggested that MoSi{sub 2} (110) surface had energetically stability. The site of oxygen atom adsorbed on MoSi{sub 2} (110) surface were discussed, and the results indicated that the preference adsorption site of MoSi{sub 2} (110) surface for oxygen atom was H site (hollow position). Our calculated work should help to understand further the interaction between oxygen atoms and MoSi{sub 2} surfaces.

  6. Low temperature diffusion of Li atoms into Si nanoparticles and surfaces

    Science.gov (United States)

    Nienhaus, Hermann; Karacuban, Hatice; Krix, David; Becker, Felix; Hagemann, Ulrich; Steeger, Doris; Bywalez, Robert; Schulz, Christof; Wiggers, Hartmut

    2013-07-01

    The diffusion of Li atoms deposited on hydrogen-passivated Si(001) surfaces, chemically oxidized Si(001) surfaces, Si nanoparticle films, and thick SiO2 layers is investigated with electron-beam induced Auger electron spectroscopy. The nanoparticles exhibit an average diameter of 24 nm. The Li metal film is evaporated at a sample temperature below 120 K. The reappearance of the Si substrate Auger signal as a function of time and temperature can be measured to study the Li diffusion into the bulk material. Values for the diffusion barrier of 0.5 eV for H:Si(001) and 0.3 eV for the ox-Si(001) and Si nanoparticle films are obtained. The diffusion of the Li atoms results in the disruption of the crystalline Si surfaces observed with atomic force microscopy. Contrasting to that, the Si nanoparticle films show less disruption by Li diffusion due to filling of the porous films detected with cross section electron microscopy. Silicon dioxide acts as a diffusion barrier for temperatures up to 300 K. However, the electron beam induces a reaction between Li and SiO2, leading to LiOx and elemental Si floating on the surface.

  7. Atomic dipole moment distribution of Si atoms on a Si111-(7 x 7) surface studied using noncontact scanning nonlinear dielectric microscopy.

    Science.gov (United States)

    Cho, Yasuo; Hirose, Ryusuke

    2007-11-02

    A local atomic electric dipole moment distribution of Si atoms on Si(111)-(7 x 7) surface is clearly resolved by using a new technique called noncontact scanning nonlinear dielectric microscopy. The dc-bias voltage dependence of the atomic dipole moment on the Si(111)-(7 x 7) surface is measured. At the weak applied voltage of -0.5 V, a positive dipole moment is detected on the Si adatom sites, whereas a negative dipole moment is observed at the interstitial sites of inter Si adatoms. Moreover, the quantitative dependence of the surface dipole moment as a function of the applied dc voltage is also revealed at a fixed point above the sample surface. This is the first successful demonstration of direct atomic dipole moment observation achieved in the field of capacitance measurement.

  8. Adsorption and migration behavior of Si atoms on the hydrogen-terminated diamond (001) surface: A first principles study

    Science.gov (United States)

    Liu, Xuejie; Qiao, Haimao; Kang, Congjie; Ren, Yuan; Tan, Xin; Sun, Shiyang

    2017-10-01

    The adsorption and migration activation energies of a silicon (Si) atom on a hydrogen-terminated diamond (001) surface were calculated using first principles methods based on density functional theory. On the fully hydrogen-terminated surface, the surface carbon atoms possess saturated bonds. The Si atom cannot bond with the surface carbon atoms; thus, the adsorption energy of the Si atom is low. However, on the hydrogen-terminated surface with one or two open radical sites (ORS), the adsorption energy of a Si atom increases to 3.1 eV and even up to 4.7 eV, thereby forming a stable configuration. Along the three ORS in the direction of dimer row or chain, a Si atom can migrate between two deep basins with migration activation energies at 1.5 or 1.3 eV. Given the relatively large energy barrier at approximately 3.8 or 4.7 eV, escaping from the deep basin is difficult for the Si atom. This investigation showed that the number and distribution of ORS, namely, the adsorption site of hydrogen atoms and the removal site of surface hydrogen atoms, can affect the adsorption and migration of Si atoms on the hydrogen-terminated diamond surface. Electron structure analysis further reveals that the reactivity of the surface C atoms and the charge transfer amount between the Si and surface C atoms affect the adsorption and migration of Si atoms.

  9. Molecular Dynamics Simulations of Atomic H Etching SiC Surface

    NARCIS (Netherlands)

    Sun, W.; Liu, H.; Lin, L.; Zhao, C. L.; Lu, X. D.; He, P. N.; Gou, F.

    2012-01-01

    In this paper, molecular dynamics simulations were performed to study interactions between atomic H and SiC, silicon carbon surfaces were continuously bombarded by atomic H with different energies. The Tersoff-Brenner potentials were implemented. The simulation results show that with increasing

  10. 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.

  11. Growth kinetics of indium metal atoms on Si(1 1 2) surface

    Energy Technology Data Exchange (ETDEWEB)

    Raj, Vidur; Chauhan, Amit Kumar Singh; Gupta, Govind, E-mail: govind@nplindia.org

    2015-12-15

    Graphical abstract: Controlled growth of indium atoms on Si(1 1 2) surface has been carried out systematically and the influence of substrate temperature on the kinetics is analysed under various growth conditions. Temperature induced anomalous layer-to-clusters transformation during thermal desorption has also been reported. - Highlights: • Controlled growth of indium atoms on Si(1 1 2) surface & their thermal stability. • Influence of substrate temperature on the kinetics under various growth conditions. • Temperature induced layer-to-clusters transformation during thermal desorption. - Abstract: The growth kinetics and desorption behavior of indium (In) atoms grown on high index Si(1 1 2) surface at different substrate temperatures has been studied. Auger electron spectroscopy analysis revealed that In growth at room temperature (RT) and high substrate temperature (HT) ∼250 °C follows Frank–van der Merve growth mode whereas at temperatures ≥450 °C, In growth evolves through Volmer–Weber growth mode. Thermal desorption studies of RT and 250 °C grown In/Si(1 1 2) systems show temperature induced rearrangement of In atoms over Si(1 1 2) surface leading to clusters to layer transformation. The monolayer and bilayer desorption energies for RT grown In/Si(1 1 2) system are calculated to be 2.5 eV and 1.52 eV, while for HT-250 °C the values are found to be 1.6 eV and 1.3 eV, respectively. This study demonstrates the effect of temperature on growth kinetics as well as on the multilayer/monolayer desorption pathway of In on Si(1 1 2) surface.

  12. 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.

  13. Surface Phenomena During Plasma-Assisted Atomic Layer Etching of SiO2.

    Science.gov (United States)

    Gasvoda, Ryan J; van de Steeg, Alex W; Bhowmick, Ranadeep; Hudson, Eric A; Agarwal, Sumit

    2017-09-13

    Surface phenomena during atomic layer etching (ALE) of SiO2 were studied during sequential half-cycles of plasma-assisted fluorocarbon (CFx) film deposition and Ar plasma activation of the CFx film using in situ surface infrared spectroscopy and ellipsometry. Infrared spectra of the surface after the CFx deposition half-cycle from a C4F8/Ar plasma show that an atomically thin mixing layer is formed between the deposited CFx layer and the underlying SiO2 film. Etching during the Ar plasma cycle is activated by Ar(+) bombardment of the CFx layer, which results in the simultaneous removal of surface CFx and the underlying SiO2 film. The interfacial mixing layer in ALE is atomically thin due to the low ion energy during CFx deposition, which combined with an ultrathin CFx layer ensures an etch rate of a few monolayers per cycle. In situ ellipsometry shows that for a ∼4 Å thick CFx film, ∼3-4 Å of SiO2 was etched per cycle. However, during the Ar plasma half-cycle, etching proceeds beyond complete removal of the surface CFx layer as F-containing radicals are slowly released into the plasma from the reactor walls. Buildup of CFx on reactor walls leads to a gradual increase in the etch per cycle.

  14. Fabrication and surface passivation of porous 6H-SiC by atomic layer deposited films

    DEFF Research Database (Denmark)

    Lu, Weifang; Ou, Yiyu; Petersen, Paul Michael

    2016-01-01

    photoluminescence was observed and the etching process was optimized in terms of etching time and thickness. Enormous enhancement as well as redshift and broadening of photoluminescence spectra were observed after the passivation by atomic layer deposited Al2O3 and TiO2 films. No obvious luminescence was observed...... above the 6H-SiC crystal band gap, which suggests that the strong photoluminescence is ascribed to surface state produced during the anodic etching....

  15. Quantum chemical modelling of Si sub-surface amorphisation due to incorporation of H atoms and its stabilisation by O atoms

    Energy Technology Data Exchange (ETDEWEB)

    Pushkarchuk, Alexander [Institute of Physical-Organic Chemistry NASB, Minsk (Belarus); Saad, Anis [Al-Balqa Applied University, Salt (Jordan); Pushkarchuk, Vadim [Belarusian State University of Informatics and Radioelectronics, Minsk (Belarus); Fedotov, Alexander; Mazanik, Alexander; Zinchuk, Olga [Belarusian State University, Minsk (Belarus); Turishchev, Sergey [Voronezh State University, Voronezh (Russian Federation)

    2010-04-15

    Here we present the results of systematic simulating studies of atomic configurations in silicon ''surface clusters'' with different numbers (per cluster) of interstitial H and O atoms as impurities, obtained by semi-empirical (PM3) and DFT quantum-chemical methods. The aim of modeling was to study the near-surface region Si amorphization caused by H-incorporation (from H-plasma, for example) and changes in the atomic structure of this amorphized sub-surface region by additionally incorporated O-atoms. A set of Si{sub x}H{sub y}[H{sub L}O{sub M}] clusters was used in order to reproduce a local atomic structure of H- or H-O-containing complexes with different numbers of impurity atoms per cluster for the corresponding Si(111) and Si(100) near-surface regions. Here x-number of Si atoms, y-number of H atoms which saturate dangling bonds at the cluster surface, L-number of incorporated H atoms which create hydrogen-containing defect complexes, M-number of O atoms incorporated in hydrogen-containing complexes. The optimization procedure, using the PM3 and DFT levels quantum chemical theory geometry optimisation of all Si clusters, allowed comparison of changes in the atomic structures of Si surface and sub-surface regions with different configurations of Si-H and Si-H-O impurity complexes (copyright 2010 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  16. Atomically flattening of Si surface of silicon on insulator and isolation-patterned wafers

    Science.gov (United States)

    Goto, Tetsuya; Kuroda, Rihito; Akagawa, Naoya; Suwa, Tomoyuki; Teramoto, Akinobu; Li, Xiang; Obara, Toshiki; Kimoto, Daiki; Sugawa, Shigetoshi; Ohmi, Tadahiro; Kamata, Yutaka; Kumagai, Yuki; Shibusawa, Katsuhiko

    2015-04-01

    By introducing high-purity and low-temperature Ar annealing at 850 °C, atomically flat Si surfaces of silicon-on-insulator (SOI) and shallow-trench-isolation (STI)-patterned wafers were obtained. In the case of the STI-patterned wafer, this low-temperature annealing and subsequent radical oxidation to form a gate oxide film were introduced into the complementary metal oxide semiconductor (CMOS) process with 0.22 µm technology. As a result, a test array circuit for evaluating the electrical characteristics of a very large number (>260,000) of metal oxide semiconductor field effect transistors (MOSFETs) having an atomically flat gate insulator/Si interface was successfully fabricated on a 200-mm-diameter wafer. By evaluating 262,144 nMOSFETs, it was found that not only the gate oxide reliability was improved, but also the noise amplitude of the gate-source voltage related to the random telegraph noise (RTN) was reduced owing to the introduction of the atomically flat gate insulator/Si interface.

  17. Excellent c-Si surface passivation by low-temperature atomic layer deposited titanium oxide

    Science.gov (United States)

    Liao, Baochen; Hoex, Bram; Aberle, Armin G.; Chi, Dongzhi; Bhatia, Charanjit S.

    2014-06-01

    In this work, we demonstrate that thermal atomic layer deposited (ALD) titanium oxide (TiOx) films are able to provide a—up to now unprecedented—level of surface passivation on undiffused low-resistivity crystalline silicon (c-Si). The surface passivation provided by the ALD TiOx films is activated by a post-deposition anneal and subsequent light soaking treatment. Ultralow effective surface recombination velocities down to 2.8 cm/s and 8.3 cm/s, respectively, are achieved on n-type and p-type float-zone c-Si wafers. Detailed analysis confirms that the TiOx films are nearly stoichiometric, have no significant level of contaminants, and are of amorphous nature. The passivation is found to be stable after storage in the dark for eight months. These results demonstrate that TiOx films are also capable of providing excellent passivation of undiffused c-Si surfaces on a comparable level to thermal silicon oxide, silicon nitride, and aluminum oxide. In addition, it is well known that TiOx has an optimal refractive index of 2.4 in the visible range for glass encapsulated solar cells, as well as a low extinction coefficient. Thus, the results presented in this work could facilitate the re-emergence of TiOx in the field of high-efficiency silicon wafer solar cells.

  18. Excellent c-Si surface passivation by low-temperature atomic layer deposited titanium oxide

    Energy Technology Data Exchange (ETDEWEB)

    Liao, Baochen, E-mail: liaobaochen@nus.edu.sg [Solar Energy Research Institute of Singapore, National University of Singapore, 7 Engineering Drive 1, Singapore 117574 (Singapore); Department of Electrical and Computer Engineering, National University of Singapore, 4 Engineering Drive 3, Singapore 117576 (Singapore); A*STAR Institute of Materials Research and Engineering (IMRE), 3 Research Link, Singapore 117602 (Singapore); Hoex, Bram [Solar Energy Research Institute of Singapore, National University of Singapore, 7 Engineering Drive 1, Singapore 117574 (Singapore); Aberle, Armin G.; Bhatia, Charanjit S., E-mail: elebcs@nus.edu.sg [Solar Energy Research Institute of Singapore, National University of Singapore, 7 Engineering Drive 1, Singapore 117574 (Singapore); Department of Electrical and Computer Engineering, National University of Singapore, 4 Engineering Drive 3, Singapore 117576 (Singapore); Chi, Dongzhi [A*STAR Institute of Materials Research and Engineering (IMRE), 3 Research Link, Singapore 117602 (Singapore)

    2014-06-23

    In this work, we demonstrate that thermal atomic layer deposited (ALD) titanium oxide (TiO{sub x}) films are able to provide a—up to now unprecedented—level of surface passivation on undiffused low-resistivity crystalline silicon (c-Si). The surface passivation provided by the ALD TiO{sub x} films is activated by a post-deposition anneal and subsequent light soaking treatment. Ultralow effective surface recombination velocities down to 2.8 cm/s and 8.3 cm/s, respectively, are achieved on n-type and p-type float-zone c-Si wafers. Detailed analysis confirms that the TiO{sub x} films are nearly stoichiometric, have no significant level of contaminants, and are of amorphous nature. The passivation is found to be stable after storage in the dark for eight months. These results demonstrate that TiO{sub x} films are also capable of providing excellent passivation of undiffused c-Si surfaces on a comparable level to thermal silicon oxide, silicon nitride, and aluminum oxide. In addition, it is well known that TiO{sub x} has an optimal refractive index of 2.4 in the visible range for glass encapsulated solar cells, as well as a low extinction coefficient. Thus, the results presented in this work could facilitate the re-emergence of TiO{sub x} in the field of high-efficiency silicon wafer solar cells.

  19. Correlation between morphology, electron band structure, and resistivity of Pb atomic chains on the Si(5 5 3)-Au surface.

    Science.gov (United States)

    Jałochowski, M; Kwapiński, T; Łukasik, P; Nita, P; Kopciuszyński, M

    2016-07-20

    Structural and electron transport properties of multiple Pb atomic chains fabricated on the Si(5 5 3)-Au surface are investigated using scanning tunneling spectroscopy, reflection high electron energy diffraction, angular resolved photoemission electron spectroscopy and in situ electrical resistance. The study shows that Pb atomic chains growth modulates the electron band structure of pristine Si(5 5 3)-Au surface and hence changes its sheet resistivity. Strong correlation between chains morphology, electron band structure and electron transport properties is found. To explain experimental findings a theoretical tight-binding model of multiple atomic chains interacting on effective substrate is proposed.

  20. Advacancy-mediated atomic steps kinetics and two-dimensional negative island nucleation on ultra-flat Si(111) surface

    Science.gov (United States)

    Sitnikov, S. V.; Latyshev, A. V.; Kosolobov, S. S.

    2017-01-01

    We have investigated Si(111) surface morphology transformations during high-temperature sublimation and oxygen treatments by means of in situ ultrahigh vacuum reflection electron microscopy. By analyzing atomic steps kinetics and two-dimensional negative (vacancy) islands nucleation on ultra-flat Si(111) surface with extremely wide (up to 120 μm in size) terraces we have estimated the activation energy associated with the surface-bulk vacancy exchange processes. We show that atomic steps motion and negative islands nucleation kinetics at temperatures above 1180 °C can be described by the step-flow model of Burton, Cabrera and Frank taking into account advacancies formation. By comparing experimental results with predictions of model we conclude that the surface mass transport at temperatures above 1180 °C is governed by surface vacancies nucleation and interaction with atomic steps rather than via adatoms surface diffusion.

  1. Single atom diffusion of Pb on a Si(1 1 1)-7 × 7 surface

    Science.gov (United States)

    Kuntová, Z.; Jelínek, P.; Cháb, V.; Chvoj, Z.

    2004-09-01

    Pb diffusion on the Si(1 1 1)-7 × 7 surface was studied with 16 different energy barriers. As a part of general problem of diffusion in the unit cell, some characteristics of diffusion (as frequency factor, effective energy barrier or differences in binding energy) was found analytically as a steady state solution of the master equation. The probability distribution of the occupation of particular sites was compared with the result of the Monte Carlo simulation and the STM experiment. Starting from the values obtained with the semi-empirical extended Hückel approximation, the diffusion barriers were adjusted to obtain a reasonable coherence with the experiment. The results of MC simulation and the analytical solution agree quite well and reproduce the dynamics of a Pb atom in the 7 × 7 unit cell.

  2. Topographical characterization of Ar-bombarded Si(1 1 1) surfaces by atomic force microscopy

    CERN Document Server

    Niebieskikwiat, D G; Pregliasco, G R; Gayone, J E; Grizzi, O; Sanchez, E A

    2002-01-01

    We used atomic force microscopy to study the topographical changes induced on Si(1 1 1) surfaces by 10-22 keV Ar sup + bombardment. The irradiation was carried on normal to the surface with doses in the 1-60x10 sup 1 sup 6 ions/cm sup 2 range. We observed a first generation of blisters at a critical dose around 3x10 sup 1 sup 6 ions/cm sup 2 , which flakes off at 19x10 sup 1 sup 6 ions/cm sup 2 , and a second generation of smaller blisters between 35 and 45x10 sup 1 sup 6 ions/cm sup 2. Measurements of the mean surface height show that at low irradiation doses the surface inflates because of voids produced by Ar sup + implantation. For doses greater than 20x10 sup 1 sup 6 Ar sup + /cm sup 2 the height decreases linearly because of sputtering, with a slope corresponding to a sputtering yield of 1.4. Finally, we present electron spectra produced during grazing proton bombardment of samples whose topography has been modified by Ar irradiation.

  3. One-dimensional diffusion of Sr atoms on Sr/Si(111)-3 × 2 reconstruction surface

    Science.gov (United States)

    Du, Wenhan; Yang, Jingjing

    2016-11-01

    The electronic and geometric structures of the Sr/Si(111)-3 × 2 surface were investigated by scanning tunnelling microscopy and scanning tunnelling spectroscopy. The honeycomb-chain (HCC) model may be used to describe the reconstruction structure of the Sr/Si(111)-3 × 2 surface. Furthermore, one-dimensional (1D) concerted motion of Sr atom chains on the Sr/Si(111)-3 × 2 surface was observed at room temperature. Three reasons contribute to this 1D self-diffusion: low metal coverage of the Sr/Si(111)-3 × 2 reconstruction surface, weak interaction between the Sr and Si substrate, and surface vacancies and thermal fluctuation energy at room temperature. From this study, the origin of the long-existing blurred low energy electron diffraction pattern of alkali-earth metal induced-Si(111)3 × 2 surface was clarified, and the self-diffusion of metal atoms at room temperature also explains the common phase transition phenomenon on these reconstructed surfaces.

  4. Formation of indium arsenide atomic wires on the In/Si(111)-4 × 1 surface

    Science.gov (United States)

    Guerrero-Sánchez, J.

    2017-03-01

    Density functional theory calculations have been applied to describe the formation of InAs atomic-size wires on the In/Si(111)-4 × 1 surface. Two different coverages, ¼ ML and ½ ML, were considered. We have taken in to consideration different high symmetry sites for As adsorption. At ¼ ML coverage, in the energetically stable configuration, As and In atoms form atomic wires. Upon increasing the coverage up to ½ ML of As, a pair of InAs atomic wires are formed. Surface formation energy calculations help to clarify the stability ranges of these structures: for arsenic poor conditions the stable configuration corresponds to the In/Si(111)-4 × 1 surface (with no As atoms). Increasing the arsenic content, for intermediate to rich As conditions, results in the formation of an InAs wire. At the arsenic rich limit, the formation of two InAs wires is favorable. The InAs wires are highly symmetric, and charge density distributions and projected density of states show the covalent character of the Insbnd As bonds of the wire. These results demonstrate that the In/Si(111)-4 × 1 surface may be used as a substrate to growth quasi-unidimensional InAs wires.

  5. Nanopatterning on silicon surface using atomic force microscopy with diamond-like carbon (DLC-coated Si probe

    Directory of Open Access Journals (Sweden)

    Zhou Jingfang

    2011-01-01

    Full Text Available Abstract Atomic force microscope (AFM equipped with diamond-like carbon (DLC-coated Si probe has been used for scratch nanolithography on Si surfaces. The effect of scratch direction, applied tip force, scratch speed, and number of scratches on the size of the scratched geometry has been investigated. The size of the groove differs with scratch direction, which increases with the applied tip force and number of scratches but decreases slightly with scratch speed. Complex nanostructures of arrays of parallel lines and square arrays are further fabricated uniformly and precisely on Si substrates at relatively high scratch speed. DLC-coated Si probe has the potential to be an alternative in AFM-based scratch nanofabrication on hard surfaces.

  6. Impact of surface morphology of Si substrate on performance of Si/ZnO heterojunction devices grown by atomic layer deposition technique

    Energy Technology Data Exchange (ETDEWEB)

    Hazra, Purnima; Singh, Satyendra Kumar [Department of Electronics and Communication Engineering, Motilal Neheru National Institute of Technology, Allahabad 211004 (India); Jit, Satyabrata, E-mail: sjit.ece@itbhu.ac.in [Department of Electronics Engineering, Indian Institute of Technology (BHU), Varanasi 221005 (India)

    2015-01-01

    In this paper, the authors have investigated the structural, optical, and electrical characteristics of silicon nanowire (SiNW)/zinc oxide (ZnO) core–shell nanostructure heterojunctions and compared their characteristics with Si/ZnO planar heterojunctions to investigate the effect of surface morphology of Si substrate in the characteristics of Si/ZnO heterojunction devices. In this work, ZnO thin film was conformally deposited on both p-type 〈100〉 planar Si substrate and substrate with vertically aligned SiNW arrays by atomic layer deposition (ALD) method. The x-ray diffraction spectra show that the crystalline structures of Si/ZnO heterojunctions are having (101) preferred orientation, whereas vertically oriented SiNW/ZnO core–shell heterojunctions are having (002)-oriented wurtzite crystalline structures. The photoluminescence (PL) spectra of Si/ZnO heterojunctions show a very sharp single peak at 377 nm, corresponding to the bandgap of ZnO material with no other defect peaks in visible region; hence, these devices can have applications only in UV region. On the other hand, SiNW/ZnO heterojunctions are having band-edge peak at 378 nm along with a broad emission band, spreading almost throughout the entire visible region with a peak around 550 nm. Therefore, ALD-grown SiNW/ZnO heterojunctions can emit green and red light simultaneously. Reflectivity measurement of the heterojunctions further confirms the enhancement of visible region peak in the PL spectra of SiNW/ZnO heterojunctions, as the surface of the SiNW/ZnO heterojunctions exhibits extremely low reflectance (<3%) in the visible wavelength region compared to Si/ZnO heterojunctions (>20%). The current–voltage characteristics of both Si/ZnO and SiNW/ZnO heterojunctions are measured with large area ohmic contacts on top and bottom of the structure to compare the electrical characteristics of the devices. Due to large surface to-volume ratio of SiNW/ZnO core–shell heterojunction devices, the

  7. Surface passivation of nano-textured fluorescent SiC by atomic layer deposited TiO2

    DEFF Research Database (Denmark)

    Lu, Weifang; Ou, Yiyu; Jokubavicius, Valdas

    2016-01-01

    Nano-textured surfaces have played a key role in optoelectronic materials to enhance the light extraction efficiency. In this work, morphology and optical properties of nano-textured SiC covered with atomic layer deposited (ALD) TiO2 were investigated. In order to obtain a high quality surface...... for TiO2 deposition, a three-step cleaning procedure was introduced after RIE etching. The morphology of anatase TiO2 indicates that the nano-textured substrate has a much higher surface nucleated grain density than a flat substrate at the beginning of the deposition process. The corresponding...... reflectance increases with TiO2 thickness due to increased surface diffuse reflection. The passivation effect of ALD TiO2 thin film on the nano-textured fluorescent 6H-SiC sample was also investigated and a PL intensity improvement of 8.05% was obtained due to the surface passivation....

  8. Molecular and atomic manipulation mediated by electronic excitation of the underlying Si(111)-7x7 surface

    Science.gov (United States)

    Rusimova, Kristina R.; Sloan, Peter A.

    2017-02-01

    We report the local atomic manipulation properties of chemisorbed toluene molecules on the Si(111)-7x7 surface and of the silicon adatoms of the surface. Charge injected directly into the molecule, or into its underlying bonding silicon adatom, can induce the molecule to change bonding site. The voltage dependence of the rates of these processes match closely with scanning tunnelling spectroscopy of the toluene and adatom species. The branching ratio between toluene molecules which are moved to a neighbouring site, or those that travel further is invariant to voltage, suggesting a common final manipulation step for both injection into the molecule and into the bonding adatom site. At low temperatures the rate of silicon adatom manipulation matches that of toluene manipulation, further suggesting that all these manipulation processes are driven by electronic excitation of the underlying silicon surface. Our results therefore suggest that a common non-adiabatic process mediates atomic and molecular manipulation induced by the STM on the Si(111)-7x7 surface and may also mediate similar manipulation induced by the laser irradiation of the Si(111)-7x7 surface.

  9. Aligning DNA on Si surface and cutting off by tips of atomic force microscope

    Institute of Scientific and Technical Information of China (English)

    2003-01-01

    DNA is a kind of promising molecule as nano-lead to build or connect nano-devices due to its stable linear structure and certain conductivity. Many methods have been applied to constructing nano-patterns by using DNA molecule. In this report it is presented that (-DNA was aligned on Si substrate by using the free-flowing method and then imaged by an atomic force microscope (AFM). After the second liquid flow, a catenary-like pattern and a crossed network of -DNA were formed. In addition, the aligned (-DNA was successfully cut off by tips of AFM.

  10. Theoretical investigation of the atomic and electronic structure of amino acids on Si(100) surfaces

    Science.gov (United States)

    Luo, Xuan; Qian, Gefei; Sagui, Celeste; Roland, Christopher

    2006-03-01

    There are currently considerable efforts underway to combine silicon-based device technology with myriad of organic molecules, thereby fabricating new structures that take advantage of the tunable electronic and optical properties of organic molecules. A key aspect of this integration process is binding of the organics to the silicon surfaces. As part of this effort, we have been investigating the binding of several amino acids -- the building blocks for proteins -- on the Si (100) surface with state-of-the art density functional theory methods. Specifically, the binding between the buckled Si(100) and the NH2, CH2, COOH, C=0 and NC entities at various surface sites have been investigated. We report and discuss on the resulting structures and their electronic properties.

  11. Role of surface fixed charge in the surface passivation of thermal atomic layer deposited Al2O3 on crystalline-Si

    Science.gov (United States)

    Dou, Y. N.; He, Y.; Huang, C. Y.; Zhou, C. L.; Ma, X. G.; Chen, R.; Chu, J. H.

    2012-11-01

    In this work, surface passivation of thermal atomic layer deposited (ALD) Al2O3 films on Si has been investigated. A quantitative analysis shows that field-effect passivation based on surface fixed charge combined with chemical passivation is assumed to contribute to the passivation performance and that a low defect density is critical to passivation quality. The surface fixed negative charge, which is exponentially modulated from ˜0 cm-2 to -2×1012 cm-2 by annealing, is proposed to have arisen from the reconstruction of the interfacial SiO x layer.

  12. Binary functionalization of H:Si(111) surfaces by alkyl monolayers with different linker atoms enhances monolayer stability and packing.

    Science.gov (United States)

    Arefi, Hadi H; Nolan, Michael; Fagas, Giorgos

    2016-05-14

    Alkyl monolayer modified Si forms a class of inorganic-organic hybrid materials with applications across many technologies such as thin-films, fuel/solar-cells and biosensors. Previous studies have shown that the linker atom, through which the monolayer binds to the Si substrate, and any tail group in the alkyl chain, can tune the monolayer stability and electronic properties. In this paper we study the H:Si(111) surface functionalized with binary SAMs: these are composed of alkyl chains that are linked to the surface by two different linker groups. Aiming to enhance SAM stability and increase coverage over singly functionalized Si, we examine with density functional theory simulations that incorporate vdW interactions, a range of linker groups which we denote as -X-(alkyl) with X = CH2, O(H), S(H) or NH(2) (alkyl = C6 and C12 chains). We show how the stability of the SAM can be enhanced by adsorbing alkyl chains with two different linkers, e.g. Si-[C, NH]-alkyl, through which the adsorption energy is increased compared to functionalization with the individual -X-alkyl chains. Our results show that it is possible to improve stability and optimum coverage of alkyl functionalized SAMs linked through a direct Si-C bond by incorporating alkyl chains linked to Si through a different linker group, while preserving the interface electronic structure that determines key electronic properties. This is important since any enhancement in stability and coverage to give more densely packed monolayers will result in fewer defects. We also show that the work function can be tuned within the interval of 3.65-4.94 eV (4.55 eV for bare H:Si(111)).

  13. Influence of the Localization of Ge Atoms within the Si(001(4 × 2 Surface Layer on Semicore One-Electron States

    Directory of Open Access Journals (Sweden)

    Olha I. Tkachuk

    2016-03-01

    Full Text Available Adsorption complexes of germanium on the reconstructed Si(001(4 × 2 surface have been simulated by the Si96Ge2Н84 cluster. For Ge atoms located on the surface layer, DFT calculations (B3LYP/6-31G** of their 3d semicore-level energies have shown a clear-cut correlation between the 3d5/2 chemical shifts and mutual arrangement of Ge atoms. Such a shift is positive when only one Ge atom penetrates into the crystalline substrate, while being negative for both penetrating Ge atoms. We interpret these results in terms of the charge distribution in clusters under consideration.

  14. Si surface passivation by Al2O3 thin films deposited using a low thermal budget atomic layer deposition process

    Energy Technology Data Exchange (ETDEWEB)

    Seguini, G.; Cianci, E.; Wiemer, C.; Perego, M. [Laboratorio MDM, IMM-CNR, Via C. Olivetti 2, 20864 Agrate Brianza MB (Italy); Saynova, D.; Van Roosmalen, J.A.M. [ECN Solar Energy, Westerduinweg 3, NL-1755 ZG Petten (Netherlands)

    2013-04-05

    High-quality surface passivation of crystalline Si is achieved using 10 nm thick Al2O3 films fabricated by thermal atomic layer deposition at 100C. After a 5 min post deposition annealing at 200C, the effective carrier lifetime is 1 ms, indicating a functional level of surface passivation. The interplay between the chemical and the field effect passivation is investigated monitoring the density of interface traps and the amount of fixed charges with conductance-voltage and capacitance-voltage techniques. The physical mechanisms underlying the surface passivation are described. The combination of low processing temperatures, thin layers, and good passivation properties facilitate a technology for low-temperature solar cells.

  15. Atomic layer deposition of ZnO on thermal SiO2 and Si surfaces using N2-diluted diethylzinc and H2O2 precursors

    Science.gov (United States)

    Qian, Ke-Jia; Chen, Sun; Zhu, Bao; Chen, Lin; Ding, Shi-Jin; Lu, Hong-Liang; Sun, Qing-Qing; Zhang, David Wei; Chen, Zhenyi

    2012-03-01

    ZnO nanodots are attracting more and more attention in various photoelectrical applications due to multiple excition generation. In this article, atomic layer deposition (ALD) growth of ZnO nanodots has been realized for the first time on both thermal SiO2 and Si surfaces using N2-diluted gaseous DEZn and H2O2 precursors. The experimental results indicate that the ALD ZnO exhibits a nano-crystalline film with corrugated surfaces in the case of the deposition temperature of 200 °C, likely due to concrescence among ZnO nanodots. When the deposition temperature is increased up to 300 °C, ZnO is grown in the form of well-discrete nanodots. This is due to increased desorption of the reacting molecules and a reduction of nucleation sites on the growing surfaces at 300 °C, thus leading to the reaction between DEZn and sbnd OH groups only on some favorable sites from thermodynamic and energy points of view. In terms of the thermal SiO2 surface, ZnO nanodots with a density of around 5 × 1010 cm-2 are obtained for 100 cycles. As for the Si surface, ZnO nanodots with a density as high as ˜1 × 1011 cm-2 are achieved for 50 cycles. Finally, the X-ray photoelectron spectroscopy and X-ray diffraction analyses reveal that the ALD ZnO at 300 °C is dominated by Znsbnd O bonds together with a small quantity of Znsbnd OH bonds, and the deposition temperature of 300 °C can result in preferential growth of ZnO (0 0 2) orientation and a bigger crystallite size.

  16. Tip-force induced surface deformation in the layered commensurate tellurides NbA xTe 2 (A = Si, Ge) during atomic force microscopy measurements

    Science.gov (United States)

    Bengel, H.; Cantow, H.-J.; Magonov, S. N.; Monconduit, L.; Evain, M.; Whangbo, M.-H.

    1994-12-01

    The Te-atom surfaces of commensurate layered tellurides NbA xTe 2 ( A = Si, x = {1}/{2}; A = Ge, x = {1}/{3}, {2}/{5}, {3}/{7}) were examined by atomic force microscopy (AFM) at different applied forces. Although the bulk crystal structures show a negligible height corrugation in the surface Te-atom sheets, the AFM images exhibit dark linear patterns that become strongly pronounced at high applied forces (several hundreds nN). This feature comes about because the tip-sample force interactions induce a surface corrugation according to the local hardness variation of the surface.

  17. Neutron Diffraction Studies of the Atomic Vibrations of Bulk and Surface Atoms of Nanocrystalline SiC

    Science.gov (United States)

    Stelmakh, S.; Grzanka, E.; Zhao, Y.; Palosz, W.; Palosz, B.

    2004-01-01

    Thermal atomic motions of nanocrystalline Sic were characterized by two temperature atomic factors B(sub core), and B(sub shell). With the use of wide angle neutron diffraction data it was shown that at the diffraction vector above 15A(exp -1) the Wilson plots gives directly the temperature factor of the grain interior (B(sub core)). At lower Q values the slope of the Wilson plot provides information on the relative amplitudes of vibrations of the core and shell atoms.

  18. Effects of Ga-induced reconstructed surfaces and atomic steps on the morphology of GaSb islands on Si(1 0 0)

    Energy Technology Data Exchange (ETDEWEB)

    Machida, Ryuto, E-mail: 8113703@ed.tus.ac.jp [Department of Applied Electronics, Graduate School of Industrial Science and Technology, Tokyo University of Science, 6-3-1 Niijuku, Katsushika-ku, Tokyo 125-8585 (Japan); Toda, Ryusuke; Fujikawa, Sachie [Department of Applied Electronics, Graduate School of Industrial Science and Technology, Tokyo University of Science, 6-3-1 Niijuku, Katsushika-ku, Tokyo 125-8585 (Japan); Hara, Shinsuke; Watanabe, Issei [National Institute of Information and Communications Technology (NICT), 4-2-1 Nukui-Kitamachi, Koganei, Tokyo 184-8795 (Japan); Fujishiro, Hiroki I., E-mail: fujisiro@te.noda.tus.ac.jp [Department of Applied Electronics, Graduate School of Industrial Science and Technology, Tokyo University of Science, 6-3-1 Niijuku, Katsushika-ku, Tokyo 125-8585 (Japan)

    2015-10-01

    Highlights: • The shape and morphology of GaSb islands were studied under various conditions. • The atomic step type affected the shape and morphology of the GaSb islands. • The reconstructed surface type affects the density and size of the islands. - Abstract: The effects of the Ga-induced reconstructed surface and atomic step type on the shape and morphology of GaSb islands on a Si(1 0 0) surface were studied using ultrahigh-vacuum scanning tunneling microscopy and atomic force microscopy. Though both anisotropic elongated islands and isotropic islands were formed on clean Si and Ga/Si(1 0 0)-2 × 3 substrates, isotropic islands were dominantly formed on Ga/Si(1 0 0)-2 × 2 substrates at 300 °C. The density and size of GaSb islands on 2 × 2-Ga at 300 °C were estimated to be 4.9 × 10{sup 10} cm{sup −2} and 29.1 nm, respectively. The difference in the GaSb island shapes could be caused by the terrace and step of the substrate surface being changed by step rearrangement due to the deposition of Ga atoms at high temperatures. Above 350 °C, the density and size of islands decreased to 2.7 × 10{sup 9} cm{sup −2} and increased to 62.0 nm, respectively. In the initial growth stage, scanning tunneling microscopy results revealed that a Sb/Si(1 0 0)-2 × 1 reconstructed surface was formed above 350 °C. The large islands were assumed to aggregate from the surface diffusion of each atom because the Sb-terminated Si surface is inactive against Ga and Sb atoms. The type of the reconstructed surface is also suggested to affect the density and size of the islands.

  19. Water wettability of Si(1 1 1) and (0 0 1) surfaces prepared to be reconstructed, atomic-hydrogen terminated and thinly oxidized in an ultrahigh vacuum chamber

    Energy Technology Data Exchange (ETDEWEB)

    Miyagi, Tomoaki; Sasahara, Akira; Tomitori, Masahiko, E-mail: tomitori@jaist.ac.jp

    2015-09-15

    Graphical abstract: - Highlights: • Clean and oxidized Si surfaces show super-hydrophilicity at WCAs less than 6°. • The most super-hydrophilic surface was the oxidized Si(1 1 1) surface. • H-terminated (1 1 1) and (0 0 1) surfaces exhibited different water contact angles. • Estimated the energetic contribution of OH-termination for WCA from the Young equation. • Discussed the water wettability based on density and angle of Si dangling bonds. - Abstract: Water contact angles on three types of Si(1 1 1) and (0 0 1) surfaces were measured in nitrogen gas atmosphere without exposing them to air; the surfaces were prepared to be (I) cleaned and reconstructed, subsequently (II) atomic hydrogen (H) terminated, or (III) thinly oxidized in an ultrahigh vacuum (UHV) chamber. The surfaces were characterized by Auger electron spectroscopy and atomic force microscopy. The H-terminated Si surfaces showed as less hydrophilic with a water contact angle of about 37° on the (1 1 1) and about 60° on the (0 0 1) surface, respectively. The clean and oxidized surfaces showed as super-hydrophilic with the angles less than 6°. To quantitatively evaluate the contact angles on the super-hydrophilic surfaces, an optical interference fringe method was used under an optical microscope in air. The most super-hydrophilic surface was the oxidized Si(1 1 1) surface. The reactivity of the Si surfaces and their degree of hydroxyl group termination to the Si surfaces responsible for water wettability were discussed.

  20. Atomic-Level Investigation of CHx and C2Hx Adsorption on β-SiC (111 Surface for CVD Diamond Growth from DFT Calculations

    Directory of Open Access Journals (Sweden)

    Naichao Chen

    2011-01-01

    Full Text Available The focus of this paper is on the adsorption of unsaturated hydrocarbon molecules on β-SiC (111 surfaces during diamond film growth. The CHx and C2Hx molecules have been investigated to obtain a specific insight into absorbing diamond processes on the atomic scale. Structural and electronic properties of CHx and C2Hx adsorption on the Si- and C-terminated surfaces have been studied by first-principles calculations based on density functional theory (DFT. From the calculated energetics and geometries, we find that C2Hx adsorption on the Si-terminated surfaces has six possible surface reconstructions. For the C-terminated surface, there exist eight possible surface reconstructions. Five surface reconstructions, including CH2 adsorption on the Si- and C-terminated surface, CH–CH2 and CH=CH2 adsorption on the C-terminated surface, and C2H5 adsorption on the Si-terminated surface, have the largest hydrogen adsorption energies and more stability of surface reconstructions. Calculations demonstrate that the Si-terminated surface is energetically more favorable for fabricating CVD diamond coatings than the C-terminated surface.

  1. Effect of Trimethyl Aluminium Surface Pretreatment on Atomic Layer Deposition Al2O3 Ultra-Thin Film on Si Substrate

    Institute of Scientific and Technical Information of China (English)

    XU Min; LU Hong-Liang; DING Shi-Jin; SUN Liang; ZHANG Wei; WANG Li-Kang

    2005-01-01

    @@ Ultra-thin Al2O3 dielectric films have been deposited on Si substrates by using trimethyl aluminium (TMA)and water as precursors in an atomic layer deposition (ALD) system. Growth of the interfacial layer between ultra-thin Al2O3 and the Si substrate is effectively suppressed by a long-time TMA surface pretreatment of the Si substrate prior to Al2O3 atomic layer deposition. High resolution transmission electron microscopy (TEM) images show that the thickness of the interfacial layer is reduced to be 0.5nm for the sample with TMA pretreatment lasting 3600s. The x-ray photoelectron spectroscopy results indicate that the Al2O3 film deposited on the TMApretreated Si surface exhibits very good thermal stability. However, a hysteresis of about 50mV is observed in the C-V curve of the samples with the TMA pretreatment.

  2. Energetics and kinetics of Cu atoms and clusters on the Si(111)-7 × 7 surface: first-principles calculations.

    Science.gov (United States)

    Ren, Xiao-Yan; Niu, Chun-Yao; Chen, Wei-Guang; Tang, Ming-Sheng; Cho, Jun-Hyung

    2016-07-21

    Exploring the properties of noble metal atoms and nano- or subnano-clusters on the semiconductor surface is of great importance in many surface catalytic reactions, self-assembly processes, crystal growth, and thin film epitaxy. Here, the energetics and kinetic properties of a single Cu atom and previously reported Cu magic clusters on the Si(111)-(7 × 7) surface are re-examined by the state-of-the-art first-principles calculations based on density functional theory. First of all, the diffusion path and high diffusion rate of a Cu atom on the Si(111)-(7 × 7) surface are identified by mapping out the total potential energy surface of the Cu atom as a function of its positions on the surface, supporting previous experimental hypothesis that the apparent triangular light spots observed by scanning tunneling microscopy (STM) are resulted from a single Cu atom frequently hopping among adjacent adsorption sites. Furthermore, our findings confirm that in the low coverage of 0.15 monolayer (ML) the previously proposed hexagonal ring-like Cu6 cluster configuration assigned to the STM pattern is considerably unstable. Importantly, the most stable Cu6/Si(111) complex also possesses a distinct simulated STM pattern with the experimentally observed ones. Instead, an energetically preferred solid-centered Cu7 structure exhibits a reasonable agreement between the simulated STM patterns and the experimental images. Therefore, the present findings convincingly rule out the tentative six-atom model and provide new insights into the understanding of the well-defined Cu nanocluster arrays on the Si(111)-(7 × 7) surface.

  3. Competition between surface modification and abrasive polishing: a method of controlling the surface atomic structure of 4H-SiC (0001).

    Science.gov (United States)

    Deng, Hui; Endo, Katsuyoshi; Yamamura, Kazuya

    2015-03-10

    The surface atomic step-terrace structure of 4H-SiC greatly affects its performance in power device applications. On the basis of the crystal structure of 4H-SiC, we propose the generation mechanism of the a-b-a*-b* type, a-b type and a-a type step-terrace structures. We demonstrate that the step-terrace structure of SiC can be controlled by adjusting the balance between chemical modification and physical removal in CeO2 slurry polishing. When chemical modification plays the main role in the polishing of SiC, the a-b-a*-b* type step-terrace structure can be generated. When the roles of physical removal and chemical modification have similar importance, the a-b-a*-b* type step-terrace structure changes to the a-b type. When physical removal is dominant, the uniform a-a type step-terrace structure can be generated.

  4. FY1995 study on the low energy reaction of Si surface with halogen atoms and positive and negative ions; 1995 nendo harogen genshi, sei/fu ion to Si hyomen hanno no teisonshoka kenkyu

    Energy Technology Data Exchange (ETDEWEB)

    NONE

    1997-03-01

    For the damageless fabrication of nanometer-electronics devices, low energy and damage-free surface reactions have been investigated as follows. (1) Negative ion etching of silicon has been investigated in SF{sub 6} and Cl{sub 2} plasma. (2) To establish the self-limiting reaction process which is necessary to realize the atomically layer-by-layer etching, the initial reaction of fluorine (F) atoms and F{sub 2} molecules with hydrogen (H)-terminated Si (111) has been studied. In both SF{sub 6} and Cl{sub 2} plasma etching, the etching reactivity of negative ions was proved to be higher than those of positive ions, since negative ions are atomical like the radical. A notch-free etching of n+ poly-silicon with 0.3{mu}m L and S pattern was successfully obtained by an alternative irradiation of positive and negative ions in SF{sub 6} plasma. For SiO{sub 2} and other oxide etching with negative ions the high rate was observed but not with high selectivity. Negative ion-assisted Si oxidation was found to be one order faster than radical and thermal oxidations. Based on the ATR and XPS measurements, F atom/H-terminated Si(111) surface reaction has been revealed. First F radicals penetrates just underneath of the Si-H bond, generating the B{sub 2} peak. Further exposure appear the B{sub 3} peak which arises from the bonding of a F atom with a Si-H bond at the five-coordination state. However, more exposure of F atoms caused higher order SiF{sub x}(x=l,2,3) products. Hence, F{sub 2} gas which was less reactive than F atoms was investigated. It was found out that the exposure of 5 % F{sub 2}/He to H-terminated Si (111) reached a plateau value at 5{sub x}10{sup 5} L where terminated H atoms quite disappeared. The SiF monolayer corresponded exactly to an atomic layer of Si(111) was formed. This indicates that the self-limiting process for the Si/F system has been realized first. (NEDO)

  5. Oxidation precursor dependence of atomic layer deposited Al2O3 films in a-Si:H(i)/Al2O3 surface passivation stacks

    Science.gov (United States)

    Xiang, Yuren; Zhou, Chunlan; Jia, Endong; Wang, Wenjing

    2015-03-01

    In order to obtain a good passivation of a silicon surface, more and more stack passivation schemes have been used in high-efficiency silicon solar cell fabrication. In this work, we prepared a-Si:H(i)/Al2O3 stacks on KOH solution-polished n-type solar grade mono-silicon(100) wafers. For the Al2O3 film deposition, both thermal atomic layer deposition (T-ALD) and plasma enhanced atomic layer deposition (PE-ALD) were used. Interface trap density spectra were obtained for Si passivation with a-Si films and a-Si:H(i)/Al2O3 stacks by a non-contact corona C-V technique. After the fabrication of a-Si:H(i)/Al2O3 stacks, the minimum interface trap density was reduced from original 3 × 1012 to 1 × 1012 cm-2 eV-1, the surface total charge density increased by nearly one order of magnitude for PE-ALD samples and about 0.4 × 1012 cm-2 for a T-ALD sample, and the carrier lifetimes increased by a factor of three (from about 10 μs to about 30 μs). Combining these results with an X-ray photoelectron spectroscopy analysis, we discussed the influence of an oxidation precursor for ALD Al2O3 deposition on Al2O3 single layers and a-Si:H(i)/Al2O3 stack surface passivation from field-effect passivation and chemical passivation perspectives. In addition, the influence of the stack fabrication process on the a-Si film structure was also discussed in this study.

  6. Adsorption of atomic oxygen on the Si(110)5×1 surface via interaction with N2O

    NARCIS (Netherlands)

    Keim, E.G.; Silfhout, van A.; Wolterbeek, L.

    1987-01-01

    This paper describes the interaction of a clean Si(110) surface, showing a prominent 5×1 superstructure, with N2O at 300 K in UHV. Differential reflectometry in the photon energy range 1.5-4.5 eV, Auger electron spectroscopy, and low-energy electron diffraction have been used to monitor this solid-g

  7. 60 keV Ar{sup +}-ion induced pattern formation on Si surface: Roles of sputter erosion and atomic redistribution

    Energy Technology Data Exchange (ETDEWEB)

    Garg, S.K., E-mail: sandeep@iopb.res.in [Institute of Physics, Sachivalaya Marg, Bhubaneswar 751005 (India); Datta, D.P.; Kumar, M. [Institute of Physics, Sachivalaya Marg, Bhubaneswar 751005 (India); Kanjilal, D. [Inter-University Accelerator Centre, Aruna Asaf Ali Marg, New Delhi 110067 (India); Som, T., E-mail: tsom@iopb.res.in [Institute of Physics, Sachivalaya Marg, Bhubaneswar 751005 (India)

    2014-08-15

    Highlights: • AFM study of morphological evolution on Si surface under 60 keV Ar{sup +} ions irradiation as a function of angle of incidence and fluence. • Construction of parametric phase diagram of medium energy ion induced ripple formation on Si. • Observation of sticking similarities between medium and low energy ion-induced pattern. • Numerical estimation shows that simultaneous contribution of curvature dependent sputtering and ion induced atomic redistribution. - Abstract: We study the evolution of surface morphology on Si(1 0 0) surface due to 60 keV Ar{sup +}-ion irradiation at room temperature for a wide range of ion fluences (2–80 × 10{sup 17} ions cm{sup −2}) and angles of incidence (0°–75°). We have clearly distinguished linear and nonlinear regimes for the observed ripple patterns in our experiment. From our experimental results and those available in the literature, we have created a parametric phase diagram which summarizes an overview of pattern formation on silicon surface under medium energy ion irradiation. On the basis of this phase diagram, we demonstrate some striking similarities between medium and low energy ion-induced ripple patterns and infer that similar mechanisms may be responsible for pattern formation at both regimes. Comparison of our experimental results with numerical estimations reveals that both curvature dependent sputter erosion and ion induced atomic redistribution are responsible for the observed evolution of surface morphology.

  8. Lateral gas phase diffusion length of boron atoms over Si/B surfaces during CVD of pure boron layers

    NARCIS (Netherlands)

    Mohammadi, V.; Nihtianov, S.

    2016-01-01

    The lateral gas phase diffusion length of boron atoms, LB, along silicon and boron surfaces during chemical vapor deposition(CVD) using diborane (B2H6) is reported. The value of LB is critical for reliable and uniform boron layer coverage. The presented information was obtained experimentally and co

  9. Lateral gas phase diffusion length of boron atoms over Si/B surfaces during CVD of pure boron layers

    NARCIS (Netherlands)

    Mohammadi, V.; Nihtianov, S.

    2016-01-01

    The lateral gas phase diffusion length of boron atoms, LB, along silicon and boron surfaces during chemical vapor deposition(CVD) using diborane (B2H6) is reported. The value of LB is critical for reliable and uniform boron layer coverage. The presented information was obtained experimentally and co

  10. One-dimensional Si-in-Si(001) template for single-atom wire growth

    Science.gov (United States)

    Owen, J. H. G.; Bianco, F.; Köster, S. A.; Mazur, D.; Bowler, D. R.; Renner, Ch.

    2010-08-01

    Single atom metallic wires of arbitrary length are of immense technological and scientific interest. We present atomic-resolution scanning tunneling microscope data of a silicon-only template, which modeling predicts to enable the self-organized growth of isolated micrometer long surface and subsurface single-atom chains. It consists of a one-dimensional, defect-free Si reconstruction four dimers wide—the Haiku core—formed by hydrogenation of self-assembled Bi-nanolines on Si(001) terraces, independent of any step edges. We discuss the potential of this Si-in-Si template as an appealing alternative to vicinal surfaces for nanoscale patterning.

  11. Surface functionalized SiO2 nanoparticles with cationic polymers via the combination of mussel inspired chemistry and surface initiated atom transfer radical polymerization: Characterization and enhanced removal of organic dye.

    Science.gov (United States)

    Huang, Qiang; Liu, Meiying; Mao, Liucheng; Xu, Dazhuang; Zeng, Guangjian; Huang, Hongye; Jiang, Ruming; Deng, Fengjie; Zhang, Xiaoyong; Wei, Yen

    2017-03-28

    Monodispersed SiO2 particles functionalized with cationic polymers poly-((3-acrylamidopropyl)trimethylammonium chloride) (PAPTCl) were prepared using mussel inspired surface modification strategy and surface initiated atom transfer radical polymerization (SI-ATRP). Fourier transform infrared spectroscopy, transmission electron microscope, thermogravimetric analysis, X-ray photoelectron spectroscopy, and zeta potential were employed to characterize these SiO2 samples. The adsorption performance of the functionalized SiO2 (donated as SiO2-PDA-PAPTCl) towards anionic organic dye Congo red (CR) was investigated to evaluate their potential environmental applications. We demonstrated that the surface of SiO2 particles can be successfully functionalized with cationic PAPTCl. The adsorption capability of as-prepared SiO2 was found to increases from 28.70 and 106.65mg/g after surface grafted with cationic polymers. The significant enhancement in the adsorption capability of SiO2-PDA-PAPTCl is mainly attributed to the introduction of cationic polymers. More importantly, this strategy is expected to be promising for fabrication of many other functional polymer nanocomposites for environmental applications due to the universality of mussel inspired chemistry and well designability and good monomer adaptability of SI-ATRP.

  12. Chemisorption of Au on Si(001) surface

    Institute of Scientific and Technical Information of China (English)

    Wei Shu-Yi; Wang Jian-Guang; Ma Li

    2004-01-01

    @@ The chemisorption of one monolayer of Au atoms on an ideal Si(001) surface is studied by using the self-consistent tight binding linear muffin-tin orbital method. Energies of the adsorption system of a Au atom on different sites are calculated. It is found that the most stable position is A site (top site) for the adsorbed Au atoms above the Si(001)surface. It is possible for the adsorbed Au atoms to sit below the Si(001) surface at the B1 site(bridge site), resulting in a Au-Si mixed layer. This is in agreement with the experiment results. The layer projected density of states is calculated and compared with that of the clean surface. The charge transfer is also investigated.

  13. Diffraction Studies of the Atomic Vibrations of Bulk and Surface Atoms in the Reciprocal and Real Spaces of Nanocrystalline SiC

    Science.gov (United States)

    Stelmakh, S.; Grzanka, E.; Weber, H.-P.; Vogel, S.; Palosz, B.; Palosz, B.

    2004-01-01

    To describe and evaluate the vibrational properties of nanoparticles it is necessary to distinguish between the surface and the core of the particles. Theoretical calculations show that vibrational density of states of the inner atoms of nanograins is similar to bulk material but shifted to higher energies which can be explained by the fact that the gain core is stressed (hardened) due to the presence of internal pressure. Theoretical calculations also show that there is a difference between vibrational properties of a crystal lattice of the grain interior in isolated particles and in a dense (sintered) nanocrystalline material. This is probably due to a coupling of the modes inside the grains via the grain boundaries in dense nanocrystalline bodies. We examined strains present in the surface shell based on examination of diamond and Sic nanocrystals in reciprocal (Bragg-type scattering) and real (PDF analysis) space analysis of neutron diffraction data. Recently we examined the atomic thermal motions in nanocrystalline Sic based on the assumption of a simple Einstein model for uncorrelated atomic notions. According to this model, the Bragg intensity is attenuated as a function of scattering angle by the Debye-Waller factor. Based on this assumption overall temperature factors were determined from the Wilson plots.

  14. Role of field-effect on c-Si surface passivation by ultrathin (2-20 nm) atomic layer deposited Al2O3

    Science.gov (United States)

    Terlinden, N. M.; Dingemans, G.; van de Sanden, M. C. M.; Kessels, W. M. M.

    2010-03-01

    Al2O3 synthesized by plasma-assisted atomic layer deposition yields excellent surface passivation of crystalline silicon (c-Si) for films down to ˜5 nm in thickness. Optical second-harmonic generation was employed to distinguish between the influence of field-effect passivation and chemical passivation through the measurement of the electric field in the c-Si space-charge region. It is demonstrated that this electric field—and hence the negative fixed charge density—is virtually unaffected by the Al2O3 thickness between 2 and 20 nm indicating that a decrease in chemical passivation causes the reduced passivation performance for <5 nm thick Al2O3 films.

  15. Scanning tunneling microscopy and spectroscopy of ion-bombarded Si(111) and Si(100) surfaces

    NARCIS (Netherlands)

    Zandvliet, H.J.W.; Elswijk, H.B.; Loenen, van E.J.; Tsong, I.S.T.

    1992-01-01

    Surfaces of Si(111)-(7×7) and Si(100)-(2×1) were bombarded by 3-keV Ar+ ions at doses of ≤1012 ions cm-2 to study the effect of individual ion impacts on the atomic structure of surfaces. Atom-resolved images show damaged regions of missing and displaced atoms. Current-imaging tunneling spectroscop

  16. Lateral gas phase diffusion length of boron atoms over Si/B surfaces during CVD of pure boron layers

    Energy Technology Data Exchange (ETDEWEB)

    Mohammadi, V., E-mail: V.Mohammadi@tudelft.nl; Nihtianov, S. [Department of Microelectronics, Delft University of Technology, Mekelweg 4, 2628 CD, Delft (Netherlands)

    2016-02-15

    The lateral gas phase diffusion length of boron atoms, L{sub B}, along silicon and boron surfaces during chemical vapor deposition (CVD) using diborane (B{sub 2}H{sub 6}) is reported. The value of L{sub B} is critical for reliable and uniform boron layer coverage. The presented information was obtained experimentally and confirmed analytically in the boron deposition temperature range from 700 °C down to 400 °C. For this temperature range the local loading effect of the boron deposition is investigated on the micro scale. A L{sub B} = 2.2 mm was determined for boron deposition at 700 °C, while a L{sub B} of less than 1 mm was observed at temperatures lower than 500 °C.

  17. Ternary hybrid polymeric nanocomposites through grafting of polystyrene on graphene oxide-TiO{sub 2} by surface initiated atom transfer radical polymerization (SI-ATRP)

    Energy Technology Data Exchange (ETDEWEB)

    Kumar, Arvind; Bansal, Ankushi; Behera, Babita; Jain, Suman L.; Ray, Siddharth S., E-mail: ssray@iip.res.in

    2016-04-01

    A ternary hybrid of graphene oxide-titania-polystyrene (GO-TiO{sub 2}-PS) nanocomposite is developed where polystyrene composition is regulated by controlling growth of polymer chains and nanoarchitectonics is discussed. Graphene Oxide-TiO{sub 2} (GO-TiO{sub 2}) nanocomposite is prepared by in-situ hydrothermal method and the surface is anchored with α-bromoisobutyryl bromide to activate GO-TiO{sub 2} as initiator for polymerization. In-situ grafting of polystyrene through surface initiated atom transfer radical polymerization (SI- ATRP) on this Br-functionalized nano-composite initiator yields GO-TiO{sub 2}-PS ternary hybrid. Varying the monomer amount and keeping the concentration of initiator constant, polystyrene chain growth is regulated with narrow poly-dispersivity to achieve desired composition. This composite is well characterized by various analytical techniques like FTIR, XRD, DSC, SEM, TEM, and TGA. - Highlights: • Nanocomposite of ternary hybrid of GO-TiO{sub 2} with polystyrene. • PS is surface grafted on GO-TiO{sub 2}. • Polymer chain lengths are well regulated by SI-ATRP living polymerization. • Thermal stability of this hybrid is relatively high.

  18. The atomic structure of the cleaved Si(111)-(2x1) surface refined by dynamical LEED

    Energy Technology Data Exchange (ETDEWEB)

    Xu, Geng; Deng, Bingcheng; Yu, Zhaoxian; Tong, S.Y.; Van Hove, M.A.; Jona, F.; Zasada, I.

    2004-03-01

    New or modified models have been proposed for the much-studied Si(111)-(2x1) surface structure, including: a reverse-tilted p-bonded chain model (by Zitzlsperger et al); a three-bond scission model (by Haneman et al); and a p-bonded chain model with enhanced vibrations (present work). These models are compared here to the generally accepted modified p-bonded chain model (by Himpsel et al, 1984), by analyzing low-energy electron diffraction (LEED) I-V curves measured earlier. Using the efficient automated tensor LEED technique, the models can be refined to a much greater degree than with earlier methods of LEED analysis. This study distinctly favors the earlier modified p-bonded chain model, but with strongly enhanced vibrations. To compare models that have different numbers of adjustable free parameters a Hamilton ratio test is used: it can distinguish between improvement due to a better model and improvement due only to more parameters.

  19. RHEED studies of the nucleation, growth, and mobility of Ag atoms on the Si(111)7 x 7 surface

    Energy Technology Data Exchange (ETDEWEB)

    Roos, K.R.

    1993-07-01

    The low temperature and flux dependent growth of ultrathin Ag films on the Si(111)7x7 surface is studied with Reflection High-Energy Electron Diffraction (RHEED). The grazing incidence geometry of RHEED allows for an incident molecular beam normal to the surface, and makes it an ideal surface probe for studying ultrathin film growth in real time. Short-lived oscillations in the diffracted intensity are observed during Ag deposition at 150 K, indicating quasi-layer-by-layer growth mediated by adatom mobility. When the 150 K growth is performed over a wide range of deposition rates F, the peak intensity is observed to scale, i.e. I(Ft) depends only on the total amount deposited, which implies thermally activated diffusion is absent at 150 K. Scaling is not obeyed at higher temperatures (T{ge}473 K) for the growth of the {radical}3{times}{radical}3 R30{degrees} ({radical}3) superstructure. Testing for scaling of the diffracted intensity constitutes a new experimental method which can be applied generally to determine if thermal diffusion is active at a particular temperature. Scaling is consistent with a constant diffusion length R{sub 0}, independent of substrate temperature and deposition rate. The presence of a non-thermal diffusion mechanism (responsible for the constant diffusion length R{sub 0}) is confirmed by monitoring the flux dependence of the {radical}3 superstructure growth during deposition at T{ge}473 K. At these temperatures the total diffusion length R is given by R=R{sub 0}+(4Dt){sup 1/2}, where (4Dt){sup 1/2} is the thermal component. A non-zero intercept R{sub 0} is found by plotting the peak intensity I{sub p}{sup 1/2} (a measure of the average domain size) vs. deposition rate F{sup {minus}1/2} (F{sup {minus}1} is proportional to the available diffusion time.) From the FWHM of a low coverage (0.2 ML) {radical}3 spot, an estimation of 50 {angstrom} is made for a lower bound of the magnitude of R{sub 0}.

  20. Nanoline templates for single atom wires on Si(001)

    Energy Technology Data Exchange (ETDEWEB)

    Koester, Sigrun A.; Owen, James H.G.; Bianco, Francois; Mazur, Daniel; Renner, Chrisoph [Universite de Geneve, Section Physique/DPMC, Geneve (Switzerland); Rodriguez-Prieto, Alvaro; Bowler, David R. [London Centre for Nanotechnology (LCN), University College London (United Kingdom)

    2010-07-01

    Low dimensional structures are of wide scientific and technological interest. The physics of single atom metallic wires is already described in detail by theory, but a more systematic experimental verification is still desirable. The experimental problems are mainly caused by the difficulties of growing electronically isolated wires which is necessary to test the expected properties from existing theories. Here we introduce templates on a Si(001) surface which enable the growth of self-assembled single atom wires on top of them. The main template consists of a Si reconstruction called the Haiku structure which develops underneath self-assembled Bi nanowires. By hydrogenation the Si surface can be passivated and additionally the Bi dimers are stripped off while the underlying reconstruction of the Si surface remains intact. In addition the Bi nanowire by itself can be considered as a template.

  1. Introduction of atomic H into Si3N4/SiO2/Si stacks

    Institute of Scientific and Technical Information of China (English)

    JIN Hao; WEBER K.J.; LI Weitang; BLAKERS A.W.

    2006-01-01

    Atomic H generated by a plasma NH3 source at 400 ℃ was demonstrated to passivate dehydrogenated Si3N4/SiO2/Si stacks effectively by bonding with defectsin the Si3N4 film and at the Si-SiO2 interface. A subsequent anneal in N2 after atomic H reintroduction was demonstrated to further improve passivation of the Si-SiO2 interface. Isothermal and isochronal anneals in N2 were carried out in order to determine the optimized annealing conditions.

  2. Adsorption of Si on Gu(100) and (111) Surfaces

    Institute of Scientific and Technical Information of China (English)

    HE Guo-Min

    2004-01-01

    @@ Employing the density-functional theory within the generalized gradient approximation, we investigate the interaction between atomic Si and the Cu(100) and (111) surfaces. Various structures of on-surface adsorption as well as surface-substitutional adsorption for a wide range of Si coverage are considered. Our results show that both Cu(100) and (111) surfaces are active for adsorption of Si. The c(2 × 2)-Si/Cu(100) surface alloy is energetically favourable for a large range of Si chemical potential while c(2 × 2)-Si/Cu(111) is energetically favourable only under Si rich conditions.

  3. Multimillion-atom molecular dynamics simulation of atomic level stresses in Si(111)/Si3N4(0001) nanopixels

    Science.gov (United States)

    Bachlechner, Martina E.; Omeltchenko, Andrey; Nakano, Aiichiro; Kalia, Rajiv K.; Vashishta, Priya; Ebbsjö, Ingvar; Madhukar, Anupam; Messina, Paul

    1998-04-01

    Ten million atom multiresolution molecular-dynamics simulations are performed on parallel computers to determine atomic-level stress distributions in a 54 nm nanopixel on a 0.1 μm silicon substrate. Effects of surfaces, edges, and lattice mismatch at the Si(111)/Si3N4(0001) interface on the stress distributions are investigated. Stresses are found to be highly inhomogeneous in the nanopixel. The top surface of silicon nitride has a compressive stress of +3 GPa and the stress is tensile, -1 GPa, in silicon below the interface.

  4. Atomically resolved graphitic surfaces in air by atomic force microscopy.

    Science.gov (United States)

    Wastl, Daniel S; Weymouth, Alfred J; Giessibl, Franz J

    2014-05-27

    Imaging at the atomic scale using atomic force microscopy in biocompatible environments is an ongoing challenge. We demonstrate atomic resolution of graphite and hydrogen-intercalated graphene on SiC in air. The main challenges arise from the overall surface cleanliness and the water layers which form on almost all surfaces. To further investigate the influence of the water layers, we compare data taken with a hydrophilic bulk-silicon tip to a hydrophobic bulk-sapphire tip. While atomic resolution can be achieved with both tip materials at moderate interaction forces, there are strong differences in force versus distance spectra which relate to the water layers on the tips and samples. Imaging at very low tip-sample interaction forces results in the observation of large terraces of a naturally occurring stripe structure on the hydrogen-intercalated graphene. This structure has been previously reported on graphitic surfaces that are not covered with disordered adsorbates in ambient conditions (i.e., on graphite and bilayer graphene on SiC, but not on monolayer graphene on SiC). Both these observations indicate that hydrogen-intercalated graphene is close to an ideal graphene sample in ambient environments.

  5. The surface characteristics of Al-7%Si aluminum alloy manufactured by thixo/rheoforming process through nanoindentation/atomic force microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Cho, S.H. [School of Mechanical Engineering, Pusan National University, Pusan 609-735 (Korea, Republic of); Kang, C.G. [School of Mechanical Engineering, Pusan National University, Pusan 609-735 (Korea, Republic of)], E-mail: cgkang@pusan.ac.kr; Lee, S.M. [Engineering Research Center for Net Shape and Die Manufacturing, Pusan National University, Pusan 609-735 (Korea, Republic of)], E-mail: smlee@pnu.edu

    2008-08-15

    This study investigated nano/microsturcture and mechanical/tribological properties in the thixo/rheoformed A356 alloy parts using nano/microindentation and nanoscratch, incorporated with optical microscopy and atomic force microscopy (AFM). As a result, thixo-cast sample exhibited higher mechanical properties than rheo-cast, irrespective of grain size. The reason that mechanical properties of thixo-cast part was higher than that of rheo-cast, was interpreted by the effect of the eutectic region surrounded by the primary {alpha} phase on the hardness. It was also observed that shape and distribution of Si particles in the adjacent eutectic region to the primary {alpha}-Al phase of the thixo/rheo-cast products were different. By scratching surface of thixo/rheo-cast parts using a nanoindentor, friction forces and coefficients for the primary {alpha}-Al and eutectic phases in thixo-cast products were resulted to be higher than those in the rheo-cast. Nanoscratch for the thixo-cast product also revealed a rough and irregular surface compared to that for the rheo-cast, providing the evidence for the effect of eutectic entrapped by primary {alpha}-Al phase on mechanical properties.

  6. Atomic displacement free interfaces and atomic registry in SiO2/(1×1) Si(100)

    Science.gov (United States)

    Shaw, Justin M.; Herbots, N.; Hurst, Q. B.; Bradley, D.; Culbertson, R. J.; Atluri, V.; Queeney, K. T.

    2006-11-01

    We use ion beam analysis to probe the structure and interface of ultrathin thermal oxide films grown on (1×1) Si(100) surfaces prepared using the Herbots-Atluri [U.S. patent No. 6,613,677 (Sept. 2, 2003)] wet chemical clean. We discover that these oxide layers are structurally registered with the substrate lattice with no interfacial structural disorder. Registry of Si atoms is most pronounced along ⟨111⟩ directions relative to the Si substrate, consistent with a β-cristobalite epitaxial phase. This structurally registered phase transitions to an amorphous structure approximately 2nm from the interface.

  7. Fabrication of atomic wires on H-terminated Si (001)

    Science.gov (United States)

    Hashizume, Tomihiro

    2000-03-01

    Atomic-scale one-dimensional structures on a hydrogen-terminated Si(100)-2x1-H surface are studied by scanning tunneling microscopy/spectroscopy and the first-principles calculations. The Jahn-Teller distortion resulting from the pairing of the second-layer Si atoms of the dangling-bond (DB) linear-chain structures is observed. In a short even-numbered DB structures, an unpaired second-layer Si atom exists and behaves as a soliton accompanied by the flip-flop motion of the structure. A Ga atom on the Si(100)-2x1-H surface migrates in a linear potential well confined by adjacent dimer rows and local dihydride defects, and is observed as a continuous linear protrusion ( a Ga-bar structure) at a narrow range of temperatures near 100 K. The height of the Ga-bar structure maps out the local variation in potential energy at individual adsorption sites. [1] T. Hitosugi, S. Heike, T. Onogi, T. Hashizume, S. Watanabe, Z. -Q. Li, K. Ohno, Y. Kawazoe, T. Hasegawa, and K. Kitazawa, PRL 82, 4034 (1999). [2] T. Hitosugi, Y. Suwa, S. Matsuura, S. Heike, T. Onogi, S. Watanabe, T. Hasegawa, K. Kitazawa, and T. Hashizume, PRL 83, 4116 (1999).

  8. Cold atoms close to surfaces

    DEFF Research Database (Denmark)

    Krüger, Peter; Wildermuth, Stephan; Hofferberth, Sebastian

    2005-01-01

    Microscopic atom optical devices integrated on atom chips allow to precisely control and manipulate ultra-cold (T atoms and Bose-Einstein condensates (BECs) close to surfaces. The relevant energy scale of a BEC is extremely small (down to ... be utilized as a sensor for variations of the potential energy of the atoms close to the surface. Here we describe how to use trapped atoms as a measurement device and analyze the performance and flexibility of the field sensor. We demonstrate microscopic magnetic imaging with simultaneous high spatial...

  9. Atomic Layer Deposition of Al2O3 on H-Passivated GeSi: Initial Surface Reaction Pathways with H/GeSi(100)-2 × 1

    Institute of Scientific and Technical Information of China (English)

    SHI Yu; SUN Qing-Qing; DONG Lin; LIU Han; DING Shi-Jin; ZHANG Wei

    2009-01-01

    The reaction mechanisms of Al(CH3 )3 (TMA ) adsorption on H-passivated GeSi(l O0)-2 × 1 surface are investigated with density functional theory. The Si-Ge and Ge-Ge one-dimer duster models are employed to represent the GeSi(100)-2 × 1 surface with different Ge compositions. For a Si-Ge dimer of a H-passivated SiGe surface, TMA adsorption on both Si-H* and Ge-H* sites is considered. The activation barrier of TMA with the Si-H* site (1.2eV) is higher than that of TMA with the Ge-H* site (0.91 eV), which indicates that the reaction proceeds more slowly on the Si-H* site than on the Ge-H* site. In addition, adsorption of TMA is more energetically favorable on the Ge-Ge dimer than on the Si-Ge dimer of H-passivated SiGe.

  10. Quantitative analysis of hydrogen in SiO2/SiN/SiO2 stacks using atom probe tomography

    Directory of Open Access Journals (Sweden)

    Yorinobu Kunimune

    2016-04-01

    Full Text Available We have demonstrated that it is possible to reproducibly quantify hydrogen concentration in the SiN layer of a SiO2/SiN/SiO2 (ONO stack structure using ultraviolet laser-assisted atom probe tomography (APT. The concentration of hydrogen atoms detected using APT increased gradually during the analysis, which could be explained by the effect of hydrogen adsorption from residual gas in the vacuum chamber onto the specimen surface. The amount of adsorbed hydrogen in the SiN layer was estimated by analyzing another SiN layer with an extremely low hydrogen concentration (<0.2 at. %. Thus, by subtracting the concentration of adsorbed hydrogen, the actual hydrogen concentration in the SiN layer was quantified as approximately 1.0 at. %. This result was consistent with that obtained by elastic recoil detection analysis (ERDA, which confirmed the accuracy of the APT quantification. The present results indicate that APT enables the imaging of the three-dimensional distribution of hydrogen atoms in actual devices at a sub-nanometer scale.

  11. Kinetics and thermodynamics of Si(111) surface nitridation in ammonia

    Science.gov (United States)

    Mansurov, Vladimir G.; Malin, Timur V.; Galitsyn, Yurij G.; Shklyaev, Alexander A.; Zhuravlev, Konstantin S.

    2016-05-01

    Kinetics and thermodynamics of Si(111) surface nitridation under an ammonia flux at different substrate temperatures are investigated by reflection high-energy electron diffraction. Two different stages of the nitridation process were revealed. The initial stage is the fast (within few seconds) formation of ordered two-dimensional SiN phase, occuring due to the topmost active surface Si atom (Sisurf) interaction with ammonia molecules. It is followed by the late stage consisting in the slow (within few minutes) amorphous Si3N4 phase formation as a result of the interaction of Si atoms in the lattice site (Siinc) with chemisorbed ammonia molecules. It was found that the ordered SiN phase formation rate decreases, as the temperature increases. The kinetic model of the initial stage was developed, in which the ordered SiN phase formation is the two-dimensional phase transition in the lattice gas with SiN cells. The enthalpy of the active surface Si atom generation on the clean Si(111) surface was estimated to be about 1.5 eV. In contrast, the amorphous Si3N4 phase formation is the normal (thermally activated) chemical process with the first-order kinetics, whose activation energy and pre-exponential factor are 2.4 eV and 108 1/s, respectively.

  12. Surface and Step Conductivities on Si(111) Surfaces.

    Science.gov (United States)

    Just, Sven; Blab, Marcus; Korte, Stefan; Cherepanov, Vasily; Soltner, Helmut; Voigtländer, Bert

    2015-08-07

    Four-point measurements using a multitip scanning tunneling microscope are carried out in order to determine surface and step conductivities on Si(111) surfaces. In a first step, distance-dependent four-point measurements in the linear configuration are used in combination with an analytical three-layer model for charge transport to disentangle the 2D surface conductivity from nonsurface contributions. A termination of the Si(111) surface with either Bi or H results in the two limiting cases of a pure 2D or 3D conductance, respectively. In order to further disentangle the surface conductivity of the step-free surface from the contribution due to atomic steps, a square four-probe configuration is applied as a function of the rotation angle. In total, this combined approach leads to an atomic step conductivity of σ(step)=(29±9)  Ω(-1) m(-1) and to a step-free surface conductivity of σ(surf)=(9±2)×10(-6)  Ω(-1)/□ for the Si(111)-(7×7) surface.

  13. Very low surface recombination velocities on p- and n-type c-Si by ultrafast spatial atomic layer deposition of aluminum oxide

    NARCIS (Netherlands)

    Werner, F.; Veith, B.; Tiba, V.; Poodt, P.W.G.; Roozeboom, F.; Brendel, R.; Schmidt, J.

    2010-01-01

    Using aluminum oxide (Al2 O3) films deposited by high-rate spatial atomic layer deposition (ALD), we achieve very low surface recombination velocities of 6.5 cm/s on p -type and 8.1 cm/s on n -type crystalline silicon wafers. Using spatially separated reaction zones instead of

  14. Nonspherical atomic effective pseudopotentials for surface passivation

    Science.gov (United States)

    Karpulevich, Anastasia; Bui, Hanh; Antonov, Denis; Han, Peng; Bester, Gabriel

    2016-11-01

    We present a method to extract accurate pseudopotentials for surface passivants, within the framework of the atomic effective pseudopotential method. We retain the imaginary part of the pseudopotential in the construction procedure. This imaginary component in reciprocal space translates into a nonspherical component in real space. This asphericity allows to model surface dipoles and their ensuing band offsets. We show that these surface effects need to be taken into account to model electronic properties of quantum dots accurately—which requires to go beyond the spherical potential approximation for the passivant/surface atoms. The good level of transferability, without additional computational costs, is demonstrated for Si, CdSe, and InP nanostructures. The results are directly compared to large-scale density functional theory calculations.

  15. Experimental surface charge density of the Si (100)-2x1H surface

    DEFF Research Database (Denmark)

    Ciston, J.; Marks, L.D.; Feidenhans'l, R.;

    2006-01-01

    We report a three-dimensional charge density refinement from x-ray diffraction intensities of the Si (100) 2x1H surface. By paying careful attention to parameterizing the bulk Si bonding, we are able to locate the hydrogen atoms at the surface, which could not be done previously. In addition, we...... are able to partially refine the local charge density at the surface. We find experimentally an increased, slightly localized bond density of approximately 0.31 electrons between each Si atom pair at the surface. Both the atomic positions and the charge density are in remarkably good agreement with density...

  16. Experimental surface charge density of the Si (100)-2x1H surface

    DEFF Research Database (Denmark)

    Ciston, J.; Marks, L.D.; Feidenhans'l, R.

    2006-01-01

    We report a three-dimensional charge density refinement from x-ray diffraction intensities of the Si (100) 2x1H surface. By paying careful attention to parameterizing the bulk Si bonding, we are able to locate the hydrogen atoms at the surface, which could not be done previously. In addition, we...... are able to partially refine the local charge density at the surface. We find experimentally an increased, slightly localized bond density of approximately 0.31 electrons between each Si atom pair at the surface. Both the atomic positions and the charge density are in remarkably good agreement with density...

  17. Atomically precise self-organization of perfectly ordered gadolinium–silicide nanomeshes controlled by anisotropic electromigration-induced growth on Si(1 1 0)-16 × 2 surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Hong, Ie-Hong, E-mail: ihhong@mail.ncyu.edu.tw [Department of Electrophysics, National Chiayi University, Chiayi 60004, Taiwan (China); Institute of Optoelectronics and Solid State Electronics, National Chiayi University, Chiayi 60004, Taiwan (China); Chen, Tsung-Ming; Tsai, Yung-Feng [Institute of Optoelectronics and Solid State Electronics, National Chiayi University, Chiayi 60004, Taiwan (China)

    2015-09-15

    Highlights: • This work provides a clear understanding of the template-directed self-organization mechanism of a perfectly ordered Gd-silicide nanomesh on a double-domain Si(1 1 0)-16 × 2 and identifies that the anisotropic electromigration is the driving force governing the two-dimensional self-ordering of the atomically precise silicide nanomesh. • The ability to self-organize a variety of the perfectly ordered silicide nanomeshes on Si(1 1 0) with atomic precision represents a promising route for the optimal bottom-up fabrication of well-defined crossbar nanocircuits, which opens the possibility for their utilizations in crossbar nanoarchitectures and Si-based magnetoelectronic nanodevices. - Abstract: Detailed scanning tunneling microscopy and spectroscopy (STM and STS) studies for the effects of thermal migration and electromigration on the growth of gadolinium–silicide nanomeshes on double-domain Si(1 1 0)-16 × 2 surfaces are presented to identify the driving force for the self-organization of a perfectly ordered silicide nanomesh on Si(1 1 0). STM results clearly show that the anisotropic electromigration effect is crucial for the control of the spatial uniformity of a self-ordered silicide nanomesh on Si(1 1 0). This two-dimensional self-ordering driven by the anisotropic-electromigration-induced growth allows the sizes and positions of crossed nanowires to be precisely controlled within a variation of ±0.2 nm over a mesoscopic area, and it can be straightforwardly applied to other metals (e.g., Au and Ce) to grow a variety of highly regular silicide nanomeshes for the applications as nanoscale interconnects. Moreover, the STS results show that the anisotropic electromigration-induced growth causes the metallic horizontal nanowires to cross over the semiconducting oblique nanowires, which opens the possibility for the atomically precise bottom-up fabrication of well-defined crossbar nanoarchitectures.

  18. A low-temperature synthesis of electrochemical active Pt nanoparticles and thin films by atomic layer deposition on Si(111) and glassy carbon surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Rui [Joint Center for Artificial Photosynthesis, California Institute of Technology, Pasadena, CA 91125 (United States); Han, Lihao [Joint Center for Artificial Photosynthesis, California Institute of Technology, Pasadena, CA 91125 (United States); Photovoltaic Materials and Devices (PVMD) Laboratory, Delft University of Technology, P.O. Box 5031, GA Delft 2600 (Netherlands); Huang, Zhuangqun; Ferrer, Ivonne M. [Joint Center for Artificial Photosynthesis, California Institute of Technology, Pasadena, CA 91125 (United States); Division of Chemistry and Chemical Engineering, California Institute of Technology, 210 Noyes Laboratory 127-72, Pasadena, CA 91125 (United States); Smets, Arno H.M.; Zeman, Miro [Photovoltaic Materials and Devices (PVMD) Laboratory, Delft University of Technology, P.O. Box 5031, GA Delft 2600 (Netherlands); Brunschwig, Bruce S., E-mail: bsb@caltech.edu [Beckman Institute, California Institute of Technology, Pasadena, CA 91125 (United States); Lewis, Nathan S., E-mail: nslewis@caltech.edu [Joint Center for Artificial Photosynthesis, California Institute of Technology, Pasadena, CA 91125 (United States); Beckman Institute, California Institute of Technology, Pasadena, CA 91125 (United States); Division of Chemistry and Chemical Engineering, California Institute of Technology, 210 Noyes Laboratory 127-72, Pasadena, CA 91125 (United States); Kavli Nanoscience Institute, California Institute of Technology, Pasadena, CA 91125 (United States)

    2015-07-01

    Atomic layer deposition (ALD) was used to deposit nanoparticles and thin films of Pt onto etched p-type Si(111) wafers and glassy carbon discs. Using precursors of MeCpPtMe{sub 3} and ozone and a temperature window of 200–300 °C, the growth rate was 80–110 pm/cycle. X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and scanning electron microscopy (SEM) were used to analyze the composition, structure, morphology, and thickness of the ALD-grown Pt nanoparticle films. The catalytic activity of the ALD-grown Pt for the hydrogen evolution reaction was shown to be equivalent to that of e-beam evaporated Pt on glassy carbon electrode. - Highlights: • Pure Pt films were grown by atomic layer deposition (ALD) using MeCpPtMe3 and ozone. • ALD-grown Pt thin films had high growth rates of 110 pm/cycle. • ALD-grown Pt films were electrocatalytic for hydrogen evolution from water. • Electrocatalytic activity of the ALD Pt films was equivalent to e-beam deposited Pt. • No carbon species were detected in the ALD-grown Pt films.

  19. Helium atom scattering from surfaces

    CERN Document Server

    1992-01-01

    High resolution helium atom scattering can be applied to study a number of interesting properties of solid surfaces with great sensitivity and accuracy. This book treats in detail experimental and theoretical aspects ofthis method as well as all current applications in surface science. The individual chapters - all written by experts in the field - are devoted to the investigation of surface structure, defect shapes and concentrations, the interaction potential, collective and localized surface vibrations at low energies, phase transitions and surface diffusion. Over the past decade helium atom scattering has gained widespread recognitionwithin the surface science community. Points in its favour are comprehensiveunderstanding of the scattering theory and the availability of well-tested approximation to the rigorous theory. This book will be invaluable to surface scientists wishing to make an informed judgement on the actual and potential capabilities of this technique and its results.

  20. Half-flat vs. atomically flat: Alkyl monolayers on morphologically controlled Si(100) and Si(111) have very similar structure, density, and chemical stability.

    Science.gov (United States)

    DeBenedetti, William J I; Li, Thomas L; Hines, Melissa A

    2017-02-07

    Chemists have long preferred the Si(111) surface for chemical functionalization, as a simple aqueous etch can be used to produce ideal, atomically flat H/Si(111) surfaces for subsequent reactions. In contrast, industry-standard etches produce rough H/Si(100) surfaces terminated by nanohillocks. The recent discovery of an aqueous etch that produces morphologically controlled H/Si(100) surfaces with a near atomically flat or "half-flat" morphology challenges the assumption that Si(111) is an inherently preferable starting point for chemical functionalization. This study shows that alkyl functionalization of morphologically controlled, "half-flat" Si(100) surfaces by terminal alkenes produces dense, tightly packed monolayers that are essentially identical to those on atomically flat Si(111). The striking similarity between the infrared spectra on these two surfaces - in terms of absolute absorbance, line shape and position, and polarization dependence - strongly suggests that alkyl monolayers on morphologically controlled Si(111) and Si(100) have essentially identical structures. The principle difference between the two surfaces is the amount of residual H at the Si/organic interface, a difference that is dictated by the structure of the Si(100) surface. Alkyl monolayers on morphologically controlled Si(111) and Si(100) surfaces were shown to be equally resistant to harsh oxidants. As a result, there appears to be no chemical reason to prefer one surface over the other, at least for functionalization with terminal alkenes.

  1. Half-flat vs. atomically flat: Alkyl monolayers on morphologically controlled Si(100) and Si(111) have very similar structure, density, and chemical stability

    Science.gov (United States)

    DeBenedetti, William J. I.; Li, Thomas L.; Hines, Melissa A.

    2017-02-01

    Chemists have long preferred the Si(111) surface for chemical functionalization, as a simple aqueous etch can be used to produce ideal, atomically flat H/Si(111) surfaces for subsequent reactions. In contrast, industry-standard etches produce rough H/Si(100) surfaces terminated by nanohillocks. The recent discovery of an aqueous etch that produces morphologically controlled H/Si(100) surfaces with a near atomically flat or "half-flat" morphology challenges the assumption that Si(111) is an inherently preferable starting point for chemical functionalization. This study shows that alkyl functionalization of morphologically controlled, "half-flat" Si(100) surfaces by terminal alkenes produces dense, tightly packed monolayers that are essentially identical to those on atomically flat Si(111). The striking similarity between the infrared spectra on these two surfaces — in terms of absolute absorbance, line shape and position, and polarization dependence — strongly suggests that alkyl monolayers on morphologically controlled Si(111) and Si(100) have essentially identical structures. The principle difference between the two surfaces is the amount of residual H at the Si/organic interface, a difference that is dictated by the structure of the Si(100) surface. Alkyl monolayers on morphologically controlled Si(111) and Si(100) surfaces were shown to be equally resistant to harsh oxidants. As a result, there appears to be no chemical reason to prefer one surface over the other, at least for functionalization with terminal alkenes.

  2. 3C-SiC nanocrystal growth on 10° miscut Si(001) surface

    Energy Technology Data Exchange (ETDEWEB)

    Deokar, Geetanjali, E-mail: gitudeo@gmail.com [INSP, UPMC, CNRS UMR 7588, 4 place Jussieu, Paris F-75005 (France); D' Angelo, Marie; Demaille, Dominique [INSP, UPMC, CNRS UMR 7588, 4 place Jussieu, Paris F-75005 (France); Cavellin, Catherine Deville [INSP, UPMC, CNRS UMR 7588, 4 place Jussieu, Paris F-75005 (France); Faculté des Sciences et Technologie UPEC, 61 av. De Gaulle, Créteil F-94010 (France)

    2014-04-01

    The growth of 3C-SiC nano-crystal (NC) on 10° miscut Si(001) substrate by CO{sub 2} thermal treatment is investigated by scanning and high resolution transmission electron microscopies. The vicinal Si(001) surface was thermally oxidized prior to the annealing at 1100 °C under CO{sub 2} atmosphere. The influence of the atomic steps at the vicinal SiO{sub 2}/Si interface on the SiC NC growth is studied by comparison with the results obtained for fundamental Si(001) substrates in the same conditions. For Si miscut substrate, a substantial enhancement in the density of the SiC NCs and a tendency of preferential alignment of them along the atomic step edges is observed. The SiC/Si interface is abrupt, without any steps and epitaxial growth with full relaxation of 3C-SiC occurs by domain matching epitaxy. The CO{sub 2} pressure and annealing time effect on NC growth is analyzed. The as-prepared SiC NCs can be engineered further for potential application in optoelectronic devices and/or as a seed for homoepitaxial SiC or heteroepitaxial GaN film growth. - Highlights: • Synthesis of 3C-SiC nanocrystals epitaxied on miscut-Si using a simple technique • Evidence of domain matching epitaxy at the SiC/Si interface • SiC growth proceeds along the (001) plane of host Si. • Substantial enhancement of the SiC nanocrystal density due to the miscut • Effect of the process parameters (CO{sub 2} pressure and annealing duration)

  3. CMOS-compatible dense arrays of Ge quantum dots on the Si(001) surface: hut cluster nucleation, atomic structure and array life cycle during UHV MBE growth.

    Science.gov (United States)

    Arapkina, Larisa V; Yuryev, Vladimir A

    2011-04-15

    We report a direct observation of Ge hut nucleation on Si(001) during UHV molecular beam epitaxy at 360°C. Nuclei of pyramids and wedges were observed on the wetting layer (WL) (M × N) patches starting from the coverage of 5.1 Å and found to have different structures. Atomic models of nuclei of both hut species have been built as well as models of the growing clusters. The growth of huts of each species has been demonstrated to follow generic scenarios. The formation of the second atomic layer of a wedge results in rearrangement of its first layer. Its ridge structure does not repeat the nucleus. A pyramid grows without phase transitions. A structure of its vertex copies the nucleus. Transitions between hut species turned out to be impossible. The wedges contain point defects in the upper corners of the triangular faces and have preferential growth directions along the ridges. The derived structure of the {105} facet follows the paired dimer model. Further growth of hut arrays results in domination of wedges, and the density of pyramids exponentially drops. The second generation of huts arises at coverages >10 Å; new huts occupy the whole WL at coverages ~14 Å. Nanocrystalline Ge 2D layer begins forming at coverages >14 Å.

  4. CMOS-compatible dense arrays of Ge quantum dots on the Si(001 surface: hut cluster nucleation, atomic structure and array life cycle during UHV MBE growth

    Directory of Open Access Journals (Sweden)

    Arapkina Larisa

    2011-01-01

    Full Text Available Abstract We report a direct observation of Ge hut nucleation on Si(001 during UHV molecular beam epitaxy at 360°C. Nuclei of pyramids and wedges were observed on the wetting layer (WL (M × N patches starting from the coverage of 5.1 Å and found to have different structures. Atomic models of nuclei of both hut species have been built as well as models of the growing clusters. The growth of huts of each species has been demonstrated to follow generic scenarios. The formation of the second atomic layer of a wedge results in rearrangement of its first layer. Its ridge structure does not repeat the nucleus. A pyramid grows without phase transitions. A structure of its vertex copies the nucleus. Transitions between hut species turned out to be impossible. The wedges contain point defects in the upper corners of the triangular faces and have preferential growth directions along the ridges. The derived structure of the {105} facet follows the paired dimer model. Further growth of hut arrays results in domination of wedges, and the density of pyramids exponentially drops. The second generation of huts arises at coverages >10 Å; new huts occupy the whole WL at coverages ~14 Å. Nanocrystalline Ge 2D layer begins forming at coverages >14 Å.

  5. Stability of Ta-encapsulating Si clusters on Si(111)-(7x7) surfaces

    CERN Document Server

    Uchida, N; Miyazaki, T; Kanayama, T

    2003-01-01

    Tantalum containing Si cluster ions TaSi sub 1 sub 0 sub - sub 1 sub 3 H sub x sup + were synthesized in an ion trap and deposited onto Si(111)-(7x7) surfaces with a kinetic energy of 18 eV. Scanning tunnelling microscope observations revealed that the clusters adsorbed on the surface without decomposition, consistent with ab initio calculation results, that predicted the clusters would have stable Si-cage structures with a Ta atom at the centre. (rapid communication)

  6. Atomic Manipulation on Metal Surfaces

    Science.gov (United States)

    Ternes, Markus; Lutz, Christopher P.; Heinrich, Andreas J.

    Half a century ago, Nobel Laureate Richard Feynman asked in a now-famous lecture what would happen if we could precisely position individual atoms at will [R.P. Feynman, Eng. Sci. 23, 22 (1960)]. This dream became a reality some 30 years later when Eigler and Schweizer were the first to position individual Xe atoms at will with the probe tip of a low-temperature scanning tunneling microscope (STM) on a Ni surface [D.M. Eigler, E.K. Schweizer, Nature 344, 524 (1990)].

  7. Multimillion-atom molecular dynamics simulation of atomic level stresses in Si(111)/Si{sub 3}N{sub 4}(0001) nanopixels

    Energy Technology Data Exchange (ETDEWEB)

    Bachlechner, M.E.; Omeltchenko, A.; Nakano, A.; Kalia, R.K.; Vashishta, P. [Concurrent Computing Laboratory for Materials Simulations, Department of Physics Astronomy and Department of Computer Science, Louisiana State University, Baton Rouge, Louisiana70803-4001 (United States); Ebbsjoe, I. [Studsvik Neutron Research Laboratory, University of Uppsala, S-611 82Nykoeping (Sweden); Madhukar, A. [Department of Materials Science and Engineering, University of Southern California, Los Angeles, California90089-0241 (United States); Messina, P. [Center for Advanced Computing Research, California Institute of Technology, Pasadena, California91125 (United States)

    1998-04-01

    Ten million atom multiresolution molecular-dynamics simulations are performed on parallel computers to determine atomic-level stress distributions in a 54 nm nanopixel on a 0.1 {mu}m silicon substrate. Effects of surfaces, edges, and lattice mismatch at the Si(111)/Si{sub 3}N{sub 4}(0001) interface on the stress distributions are investigated. Stresses are found to be highly inhomogeneous in the nanopixel. The top surface of silicon nitride has a compressive stress of +3GPa and the stress is tensile, {minus}1GPa, in silicon below the interface. {copyright} {ital 1998 American Institute of Physics.}

  8. Interfacial reaction of eutectic AuSi solder with Si (100) and Si (111) surfaces

    Science.gov (United States)

    Jang, Jin-Wook; Hayes, Scott; Lin, Jong-Kai; Frear, Darrel R.

    2004-06-01

    The dissolution behavior of Si (100) and (111) dies by eutectic AuSi solder was investigated. On the Si (100) surface, the dissolution primarily occurred by the formation of craters resulting in a rough surface. The dissolution of the Si (111) resulted in a relatively smooth surface. The morphology of the Si (100) surface during a AuSi soldering reaction exhibited more time-dependent behavior and the etching craters on a Si (100) surface grew larger with time whereas Si (111) did not significantly change. This difference was ascribed to the surface energy differences between Si (111) and (100) surfaces that resulted in the two- and three-dimensional dissolution behaviors, respectively. This difference plays an important role in the formation of voids during the AuSi die bonding. The etching craters on Si (100) act as a AuSi solder sink and the regions surrounded by etch pits tend to become voids. For Si (111), flat surfaces were observed in the voided regions. Cross section analysis showed that no solder reaction occurred in the voided region of the Si (111) surface. This suggests the possibility of the formation of a thin inert layer in a potentially voided region prior to assembly. To achieve void-free die bonding, different parameters must be adjusted to the Si (100) and Si (111) surfaces with the AuSi alloy.

  9. Defect-initiated atomic emissions from semiconductor surfaces induced by laser irradiation: Electronic cleaning of defects on surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Kanasaki, Jun' ichi; Okano, Akiko; Nakai, Yasuo; Itoh, Noriaki (Dept. of Physics, Nagoya Univ., Furo-cho, Chikusa, Nagoya (Japan))

    1994-05-15

    We compare the emission of Si atoms from Si (100) surfaces and of Ga atoms from GaAs (110) and GaP (110) surfaces induced by irradiation with low-fluence laser pulses, each of which emits atoms of about 10[sup -6] monolayers, and found a strong correlation between the laser fluence that can cause emission and the strength of the bond by which the emitted atoms are bound

  10. Friction of atomically stepped surfaces

    Science.gov (United States)

    Dikken, R. J.; Thijsse, B. J.; Nicola, L.

    2017-03-01

    The friction behavior of atomically stepped metal surfaces under contact loading is studied using molecular dynamics simulations. While real rough metal surfaces involve roughness at multiple length scales, the focus of this paper is on understanding friction of the smallest scale of roughness: atomic steps. To this end, periodic stepped Al surfaces with different step geometry are brought into contact and sheared at room temperature. Contact stress that continuously tries to build up during loading, is released with fluctuating stress drops during sliding, according to the typical stick-slip behavior. Stress release occurs not only through local slip, but also by means of step motion. The steps move along the contact, concurrently resulting in normal migration of the contact. The direction of migration depends on the sign of the step, i.e., its orientation with respect to the shearing direction. If the steps are of equal sign, there is a net migration of the entire contact accompanied by significant vacancy generation at room temperature. The stick-slip behavior of the stepped contacts is found to have all the characteristic of a self-organized critical state, with statistics dictated by step density. For the studied step geometries, frictional sliding is found to involve significant atomic rearrangement through which the contact roughness is drastically changed. This leads for certain step configurations to a marked transition from jerky sliding motion to smooth sliding, making the final friction stress approximately similar to that of a flat contact.

  11. Study of GaN adsorption on the Si surface

    Energy Technology Data Exchange (ETDEWEB)

    Li Wei, E-mail: tolwwt@163.com [Laboratory of Quantum Information Technology, School of Physics and Telecommunication Engineering, South China Normal University, 510006 Guangzhou (China); Chen Junfang [Laboratory of Quantum Information Technology, School of Physics and Telecommunication Engineering, South China Normal University, 510006 Guangzhou (China); Wang Teng [School of Computer, South China Normal University, 510006 Guangzhou (China)

    2009-10-15

    The adsorption energy, the band structures and DOS (density of states) of GaN on surface of Si(1 0 0) and Si(1 1 1) are calculated by the first-principle using plane-wave pseudo-potentials method based on the density functional theory in order to know the adsorption between the surface of Si and GaN. The calculation results show that GaN is easier adsorbed on the surface of Si(1 0 0) than the surface of Si(1 1 1) under the same experimental condition. There are strong charge distributions between N and Si atom. The bandgap of GaN on surface of Si(1 0 0) becomes a little narrower than that of pure GaN. On the other hand, GaN film is deposited on the surface of Si(1 0 0) by ECR-MOPECVD (electron cyclotron resonance-plasma enhanced chemical vapor deposition) at low temperature. For substrate of Si(1 1 1), no film is obtained under the same experimental condition.

  12. Optical properties of Si nanoclusters with passivated surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Dinh, L.N. [Univ. of California, Davis, CA (United States). Dept. of Applied Science]|[Lawrence Livermore National Lab., CA (United States). Chemistry and Materials Science Dept.; Chase, L.L.; Balooch, M.; Siekhaus, W.J. [Lawrence Livermore National Lab., CA (United States). Chemistry and Material Science Dept.; Wooten, F. [Univ. of California, Davis, CA (United States). Dept. of Applied Science

    1996-12-31

    Si nanoclusters with average size of a few nanometers have been synthesized by thermal vaporization of Si in an Ar buffer gas, and passivated with oxygen or atomic hydrogen. High resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD) revealed that these nanoclusters were crystalline. All samples showed strong infrared and/or visible photoluminescence (PL) with varying decay times form nanoseconds to microseconds depending on synthesis conditions. Absorption mainly in the Si cores was observed by photoluminescence excitation (PLE) spectroscopy. The visible components of PL spectra were noted to blue shift and broaden as the size of the Si nanocrystals (nc-Si) was reduced, and there were differences in PL spectra for hydrogen and oxygen passivated nc-Si. This data can be explained best by a model involving absorption between quantum confined states in the Si cores and emission by surface/interface states.

  13. Atomic mechanisms governing the elastic limit and the incipient plasticity of bending Si nanowires.

    Science.gov (United States)

    Zheng, Kun; Han, Xiaodong; Wang, Lihua; Zhang, Yuefei; Yue, Yonghai; Qin, Yan; Zhang, Xiaona; Zhang, Ze

    2009-06-01

    Individual single-crystalline Si nanowires (NWs) were bent by forming loops or arcs with different radius. Positional-resolved atomic level strain distribution (PRALSD) along both of the radial and axial directions were calculated and mapped directly from the atomic-resolution strained high-resolution electron microscopy (HREM) images of the bent Si NWs. For the first time, the neutral-strain axis shifted from the compressive zone to the tensile region was directly demonstrated from the PRALSD along the radial direction. Bending-induced ripple-buckling of the bent Si NW was observed and a significant strain variation along the bending axial direction in the compressive region was revealed. The tensile surface atomic steps and the compressive buckling are the physical origin of the asymmetric tensile-compressive properties of postelastic instabilities and the incipient plasticity. Both of the tensile surface atomic-steps and the compressive buckling initiated versatile ductile plastic dislocation events.

  14. Deposition temperature dependence of material and Si surface passivation properties of O{sub 3}-based atomic layer deposited Al{sub 2}O{sub 3}-based films and stacks

    Energy Technology Data Exchange (ETDEWEB)

    Bordihn, Stefan, E-mail: s.bordihn2@q-cells.com [Department of Applied Physics, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands and Hanwha Q CELLS GmbH, Sonnenallee 17-21, 06766 Bitterfeld-Wolfen (Germany); Mertens, Verena; Müller, Jörg W. [Hanwha Q CELLS GmbH, Sonnenallee 17-21, 06766 Bitterfeld-Wolfen (Germany); Kessels, W. M. M., E-mail: w.m.m.kessels@tue.nl [Department of Applied Physics, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven (Netherlands)

    2014-01-15

    The material composition and the Si surface passivation of aluminum oxide (Al{sub 2}O{sub 3}) films prepared by atomic layer deposition using Al(CH{sub 3}){sub 3} and O{sub 3} as precursors were investigated for deposition temperatures (T{sub Dep}) between 200 °C and 500 °C. The growth per cycle decreased with increasing deposition temperature due to a lower Al deposition rate. In contrast the material composition was hardly affected except for the hydrogen concentration, which decreased from [H] = 3 at. % at 200 °C to [H] < 0.5 at. % at 400 °C and 500 °C. The surface passivation performance was investigated after annealing at 300 °C–450 °C and also after firing steps in the typical temperature range of 800 °C–925 °C. A similar high level of the surface passivation performance, i.e., surface recombination velocity values <10 cm/s, was obtained after annealing and firing. Investigations of Al{sub 2}O{sub 3}/SiN{sub x} stacks complemented the work and revealed similar levels of surface passivation as single-layer Al{sub 2}O{sub 3} films, both for the chemical and field-effect passivation. The fixed charge density in the Al{sub 2}O{sub 3}/SiN{sub x} stacks, reflecting the field-effect passivation, was reduced by one order of magnitude from 3·10{sup 12} cm{sup −2} to 3·10{sup 11} cm{sup −2} when T{sub Dep} was increased from 300 °C to 500 °C. The level of the chemical passivation changed as well, but the total level of the surface passivation was hardly affected by the value of T{sub Dep}. When firing films prepared at of low T{sub Dep}, blistering of the films occurred and this strongly reduced the surface passivation. These results presented in this work demonstrate that a high level of surface passivation can be achieved for Al{sub 2}O{sub 3}-based films and stacks over a wide range of conditions when the combination of deposition temperature and annealing or firing temperature is carefully chosen.

  15. Strain-induced morphology manipulations of Si and Ge-based heterostructures on Si(0 0 1) surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Dentel, D.; Aiet-Mansour, K.; Bischoff, J.L.; Kubler, L.; Bolmont, D

    2004-07-31

    By using reflection high energy electron diffraction (RHEED), atomic force microscopy (AFM), high-resolution transmission electron microscopy (HRTEM) analyses, we show that the well-known Stranski-Krastanov growth mode of Ge/Si(0 0 1) can be modified in a Volmer-Weber one by C pre-deposition on the Si(0 0 1) surface or in a Frank-Van der Merve one by supplying atomic hydrogen during the Ge growth. By tuning the growth conditions and acting on the interplay of surface diffusion, strain and surface energy, morphology manipulations by the growth process control are therefore possible. The Si capping of these Ge self-assembled nanostructures also allows us to point out a correlation between the nucleation mechanism of the Ge or SiGe islands and their associated embedding process. On bare Si surfaces, the final morphology of the embedded Ge film is strongly dependent on the kinetic parameters of the capping layer. Indeed oriented migrations of both Si and Ge atoms are able to smooth or to maintain the islands on the surface. Si diffusions also contribute in a rapid restoration of a planar morphology. On Si(0 0 1)-c(4 x 4) the adatom migrations and consequently the covering mechanism of the Ge islands seems to be governed by the strain mapping related to the C pre-deposited surface. The first stages of the Si capping process have revealed the preservation of the Ge islands associated to an increase of the surface roughness.

  16. Can atom-surface potential measurements test atomic structure models?

    Science.gov (United States)

    Lonij, Vincent P A; Klauss, Catherine E; Holmgren, William F; Cronin, Alexander D

    2011-06-30

    van der Waals (vdW) atom-surface potentials can be excellent benchmarks for atomic structure calculations. This is especially true if measurements are made with two different types of atoms interacting with the same surface sample. Here we show theoretically how ratios of vdW potential strengths (e.g., C₃(K)/C₃(Na)) depend sensitively on the properties of each atom, yet these ratios are relatively insensitive to properties of the surface. We discuss how C₃ ratios depend on atomic core electrons by using a two-oscillator model to represent the contribution from atomic valence electrons and core electrons separately. We explain why certain pairs of atoms are preferable to study for future experimental tests of atomic structure calculations. A well chosen pair of atoms (e.g., K and Na) will have a C₃ ratio that is insensitive to the permittivity of the surface, whereas a poorly chosen pair (e.g., K and He) will have a ratio of C₃ values that depends more strongly on the permittivity of the surface.

  17. Atomic arrangements and electronic properties of semiconductor surfaces and interfaces

    Science.gov (United States)

    Chadi, D. J.; Martin, R. M.

    1982-05-01

    The areas of research during the past 12 months have included: step-formation energies and domain orientation at Si(111) surfaces; the electronic structure of the Al-GaAs(110) surface chemisorption system; density-functional calculations of bulk properties of GaAs and of (100)GaAs-Ge interfaces; demonstration of the importance of correlation effects on the atomic and electronic structure of Si(111) surfaces; and derivation of an exact scaling law for the resistance of a thin wire for the one dimensional Anderson model containing Loth diagonal and off-diagonal disorder.

  18. Modeling noncontact atomic force microscopy resolution on corrugated surfaces

    Directory of Open Access Journals (Sweden)

    Kristen M. Burson

    2012-03-01

    Full Text Available Key developments in NC-AFM have generally involved atomically flat crystalline surfaces. However, many surfaces of technological interest are not atomically flat. We discuss the experimental difficulties in obtaining high-resolution images of rough surfaces, with amorphous SiO2 as a specific case. We develop a quasi-1-D minimal model for noncontact atomic force microscopy, based on van der Waals interactions between a spherical tip and the surface, explicitly accounting for the corrugated substrate (modeled as a sinusoid. The model results show an attenuation of the topographic contours by ~30% for tip distances within 5 Å of the surface. Results also indicate a deviation from the Hamaker force law for a sphere interacting with a flat surface.

  19. Surface Acoustic Wave Atomizer and Electrostatic Deposition

    Science.gov (United States)

    Yamagata, Yutaka

    A new methodology for fabricating thin film or micro patters of organic/bio material using surface acoustic wave (SAW) atomizer and electrostatic deposition is proposed and characteristics of atomization techniques are discussed in terms of drop size and atomization speed. Various types of SAW atomizer are compared with electrospray and conventional ultrasonic atomizers. It has been proved that SAW atomizers generate drops as small as electrospray and have very fast atomization speed. This technique is applied to fabrication of micro patterns of proteins. According to the result of immunoassay, the specific activity of immunoglobulin was preserved after deposition process.

  20. Equilibrium Geometries, Reaction Pathways, and Electronic Structures of Ethanol Adsorbed on the Si (111) Surface

    CERN Document Server

    Gavrilenko, A V; Gavrilenko, V I

    2008-01-01

    Equilibrium atomic configurations and electron energy structure of ethanol adsorbed on the Si (111) surface are studied by the first-principles density functional theory. Geometry optimization is performed by the total energy minimization method. Several equilibrium atomic configurations of ethanol, both undissociated and dissociated, on the Si (111) surface are found. Reaction pathways and predicted transition states are discussed in comparison with available experimental data in terms of the feasibility of the reactions occurring. Analysis of atom and orbital resolved projected density of states indicate substantial modifications of the Si surface valence and conduction bands due to the adsorption of ethanol affecting the electrical properties of the surface.

  1. PREFACE: Atom-surface scattering Atom-surface scattering

    Science.gov (United States)

    Miret-Artés, Salvador

    2010-08-01

    It has been a privilege and a real pleasure to organize this special issue or festschrift in the general field of atom-surface scattering (and its interaction) in honor of J R Manson. This is a good opportunity and an ideal place to express our deep gratitude to one of the leaders in this field for his fundamental and outstanding scientific contributions. J R Manson, or Dick to his friends and colleagues, is one of the founding fathers, together with N Cabrera and V Celli, of the 'Theory of surface scattering and detection of surface phonons'. This is the title of the very well-known first theoretical paper by Dick published in Physical Review Letters in 1969. My first meeting with Dick was around twenty years ago in Saclay. J Lapujoulade organized a small group seminar about selective adsorption resonances in metal vicinal surfaces. We discussed this important issue in surface physics and many other things as if we had always known each other. This familiarity and warm welcome struck me from the very beginning. During the coming years, I found this to be a very attractive aspect of his personality. During my stays in Göttingen, we had the opportunity to talk widely about science and life at lunch or dinner time, walking or cycling. During these nice meetings, he showed, with humility, an impressive cultural background. It is quite clear that his personal opinions about history, religion, politics, music, etc, come from considering and analyzing them as 'open dynamical systems'. In particular, with good food and better wine in a restaurant or at home, a happy cheerful soirée is guaranteed with him, or even with only a good beer or espresso, and an interesting conversation arises naturally. He likes to listen before speaking. Probably not many people know his interest in tractors. He has an incredible collection of very old tractors at home. In one of my visits to Clemson, he showed me the collection, explaining to me in great detail, their technical properties

  2. Depth Profiling of Melting and Metallization in Si(111) and Si(001) Surfaces

    Science.gov (United States)

    Gunnella, R.; Ali, M.; Abbas, M.; D'Amico, F.; Principi, E.; di Cicco, A.

    2011-10-01

    An original approach for measuring the depth profile of melting and metallization of the Si(111) and Si(001) surfaces is proposed and applied. The different probing depths of the Auger electron and electron energy loss (EELS) spectroscopies are exploited to study the number of molten and metallic layers within 5-30 Å from the surface up to about 1650 K. Melting is limited to 3 atomic layers in Si(001) in the range 1400-1650 K while the number of molten layers grows much faster (5 layers at about 1500 K) in Si(111) as also indicated by the L3-edge shift observed by EELS. The relationship between melting and metallization is briefly discussed.

  3. Structural Features of Boron-Doped Si(113) Surfaces Simulated by ab initio Calculations

    Institute of Scientific and Technical Information of China (English)

    LIAO Long-Zhong; LIU Zheng-Hui; ZHANG Zhao-Hui

    2008-01-01

    Based on ab initio calculations, boron-doped Si(113) surfaces have been simulated and atomic structures of the surfaces have been proposed. It has been determined that surface features of empty and filled states that are separately localized at pentamers and adatoms indicates a low surface density of B atoms, while it is attributed to heavy doping of B atoms at the second layer that pentamers and adatoms are both present in an image of scanning tunnelling microscopy. B doping at the second layer should be balanced by adsorbed B or Si atoms beside the adatoms and inserted B interstitials below the adatoms.

  4. Controlling the fixed charge and passivation properties of Si(100)/Al(2)O(3) interfaces using ultrathin SiO(2) interlayers synthesized by atomic layer deposition

    NARCIS (Netherlands)

    Dingemans, G.; Terlinden, N. M.; Verheijen, M. A.; M. C. M. van de Sanden,; Kessels, W. M. M.

    2011-01-01

    Al(2)O(3) synthesized by atomic layer deposition (ALD) on H-terminated Si(100) exhibits a very thin (similar to 1 nm) interfacial SiO(x) layer. At this interface, a high fixed negative charge density, Q(f), is present after annealing which contributes to ultralow surface recombination velocities sim

  5. Atomic Processes on Mineral Surfaces

    Science.gov (United States)

    Hillner, Paul Everett

    This thesis describes research using atomic force microscopy (AFM) to observe the growth and dissolution mechanisms of crystals. Chapter 1 starts with an overview of crystal growth theory and then outlines the impact of AFM on the field. Chapter 2 introduces the techniques of real-time AFM imaging of crystal growth and shows the strong preferential dissolution of material at defects. Chapter 3 expands the importance of crystal defects, showing the importance of spiral defects to the aqueous growth of calcite. Chapter 4 presents a rigorous analysis of step kinetics on calcite and shows that surface diffusion is not the controlling factor of growth rate. Chapter 5 examines the effect of solvent modifications on the growth morphology of spiral hillocks on calcite and also determines the mechanisms by which manmade and natural poisons stop crystal growth. Chapter 6 presents quantitative calcite spiral rotation rates and step velocities vs. supersaturation as well as contrasting the layer-spiral growth mechanism of calcite with the poly -nucleation growth mechanism of fluorite.

  6. Thermal compatibility studies of U 3Si 2 dispersion fuels prepared with centrifugally atomized powder

    Science.gov (United States)

    Kim, Ki-Hwan; Park, Jong-Man; Kim, Chang-Kyu; Hofman, Gerard L.; Paik, Kyung-Wook

    The interaction between atomized U 3Si 2 and aluminum in dispersion fuel samples has been characterized and compared with that of comminuted U 3Si 2. Fuel samples with atomized powder showed a smaller volume increase compared to those with the comminuted powder, irrespective of heat treatment, and volume fraction of U 3Si 2 powder. The possible reasons for this seem to be as follows: (1) the smaller specific surface area of the atomized spherical powder compared to the irregular comminuted powder translating in a smaller U 3Si 2-Al interface area for the former affecting what appears to be a diffusion-controlled interaction process, (2) the atomized fuel samples also contain lower fraction of as-fabricated porosity than the comminuted fuel samples, which may enhance the restraint force in the swelling fuel meat, (3) the comminuted powder particles have distinctive aluminum penetration paths in the form of deformation zones that originated from the comminution process. There appear to be two pronounced penetration paths of aluminum into atomized U 3Si 2 powder; (1) through the phase interface, leaving a central unreacted island, (2) along grain boundaries, leaving several unreacted islands.

  7. Polymer coating comprising 2-methoxyethyl acrylate units synthesized by surface-initiated atom transfer radical polymerization

    DEFF Research Database (Denmark)

    2011-01-01

    Source: US2012184029A The present invention relates to preparation of a polymer coating comprising or consisting of polymer chains comprising or consisting of units of 2-methoxyethyl acrylate synthesized by Surface-Initiated Atom Transfer Radical Polymerization (SI ATRP) such as ARGET SI ATRP...... or AGET SI ATRP and uses of said polymer coating....

  8. Fluorinated saccharides on the Si(0 0 1) surface

    Energy Technology Data Exchange (ETDEWEB)

    Szwajca, Anna, E-mail: Anna.Szwajca@amu.edu.pl [Faculty of Chemistry, A. Mickiewicz University, Poznan (Poland); Rapp, Magdalena; Bilska, Monika [Faculty of Chemistry, A. Mickiewicz University, Poznan (Poland); Krzywiecki, Maciej [Institute of Physics, Silesian University of Technology, Gliwice (Poland); Koroniak, Henryk [Faculty of Chemistry, A. Mickiewicz University, Poznan (Poland)

    2013-06-01

    The attachment of saccharide molecules directly to silicon surface has been for the first time. Oxygen free silicon surface was functionalized with monosacharides thanks to UV irradiation in acetonitryl solution (254 nm). Selected derivatives of pentofuranose were protected at the C-1 and C-2 position. The remaining hydroxyl group at C-3 or C-5 was suitable for direct attachment to H-terminated Si(0 0 1) surface via Si-O-C bonds. The binding energy of the saccharide to the Si surface was investigated by quantum mechanical calculations method. The Parametric Method 5 (PM5) calculations confirmed that the formation of Si-O-C bonds was chemically possible. Synthesis of new fluorinated carbohydrates has been described. The resulting monolayers were characterized by Atomic Force Microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and Attenuated Total Reflection (ATR) infrared spectroscopy. The effect of incorporating fluorine atom or CF{sub 3} group into self-assembled monosaccharide monolayers was studied using a water contact angle measurements. The resulting surface wettability of different fluorinated components on one kind of planar substrate enables an answer which of derivative is required for the preparation of the hydrophobic monolayer.

  9. 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.

  10. Probing Co/Si interface behaviour by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM)

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    In this work, we investigate the Co-Si reaction, the Co growth mode at room temperature, diffusion behaviour as well as morphology evolution during annealing on both H-terminated and clean Si(001) and Si(111) surfaces. From in-situ X-ray photoelectron spectroscopy (XPS) investigation, "Co-Si" reaction appears to occur on both H-terminated and clean surfaces at room temperature (RT) and the silicide crystallinity is improved upon annealing.Co growth mode on H-terminated Si surfaces occurs in a pseudo layer-by-layer manner while small close-packed island growth mode is observed on the clean Si surface. Upon annealing at different temperatures, Co atom concentration decreases versus annealing time, which in part is attributed to Co atoms inward diffusion. The diffusion behaviour on both types of surfaces demonstrates a similar trend. Morphology study using ex-situ atomic force microscopy (AFM) shows that the islands formed on Si(001) surface after annealing at 700 ℃ are elongated with growth directions alternate between the two perpendicular [(-1)10] and [110] directions. Triangular islands are observed on Si(111) surface.

  11. On the structure of Si(100) surface

    DEFF Research Database (Denmark)

    Back, Seoin; Schmidt, Johan Albrecht; Ji, Hyunjun;

    2013-01-01

    We revisit a dangling theoretical question of whether the surface reconstruction of the Si(100) surface would energetically favor the symmetric or buckled dimers on the intrinsic potential energy surfaces at 0 K. This seemingly simple question is still unanswered definitively since all existing...

  12. Bi covered Si(111) surface revisited

    CERN Document Server

    Miwa, R H; Srivastava, G P

    2003-01-01

    We have performed an ab initio study of the stability, atomic geometry and electronic structure of the Bi-covered (sq root 3 x sq root 3) reconstructed Si(111) surface. We find that the energetically stable structure changes from the milkstool model (for 1 monolayer (ML) coverage) to the T sub 4 model (for 1/3 ML coverage), without going through a stable structure for the honeycomb model (2/3 ML coverage). Our theoretical scanning tunnelling microscopy (STM) simulation for the 1 ML coverage reveals the formation of Bi trimers for occupied states, and a honeycomb image for empty states. This result, together with the energetically unstable structure for 2/3 ML coverage, suggests that the experimentally observed STM image in the form of the honeycomb structure does not mean that the minimum energy configuration corresponds to Bi coverage of 2/3 ML, but rather represents current tunnelling into the empty states localized between Bi trimers for the milkstool model with 1 ML coverage.

  13. Hydrophilization of poly(ether ether ketone) films by surface-initiated atom transfer radical polymerization

    DEFF Research Database (Denmark)

    Fristrup, Charlotte Juel; Jankova Atanasova, Katja; Hvilsted, Søren

    2010-01-01

    Surface-Initiated Atom Transfer Radical Polymerization (SI-ATRP) has been exploited to hydrophilize PEEK. The ketone groups on the PEEK surface were reduced to hydroxyl groups which were converted to bromoisobutyrate initiating sites for SI-ATRP. The modification steps were followed by contact...

  14. Investigation of Si(001) stable surfaces in alternating current heating

    Science.gov (United States)

    Doi, T.; Koguchi, M.

    2016-11-01

    The topography of a Si(001) vicinal surface is investigated using reflection electron microscopy (REM) during alternating current (AC) heating of the surface in ultra-high vacuum. The normal direction of the surface is slightly tilted from the [001] direction at θx or θy on the x or y axis (they are orthogonal directions in the Si(001) surface), and the average widths of the terraces (a or b in x or y axis) are determined by θx or θy; the direction perpendicular to the incidence electron beam on the surface is selected as the x (horizontal) axis in each REM image. Alternating current heating changes each initial surface from stable to double-domain (DD), in which 2 × 1 and 1 × 2 terraces are arranged regularly with approximately equal width, at its transition temperature Tc; the dimer rows are parallel to the x or y axis in the 1 × 2 or 2 × 1 terraces. There are two types of stable surfaces in the vicinal surface. At temperatures below its Tc, the surface with horizontally (vertically) long terraces, where b a), changes to a 2 × 1 (1 × 2) surface with wide 2 × 1 (1 × 2) and narrow 1 × 2 (2 × 1) terraces. The terrace, the short side of which is parallel to its dimer row direction, grows to create a stable surface by thermal diffusion of Si atoms at temperatures below Tc. During AC heating, thermal diffusion plays a key role in analyzing the kinetics of the atoms on the surface because the thermal effect acts as the driving force for the atoms that have not yet evaporated from the surface. Then, by evaporating atoms from the vicinal surface, AC heating creates a DD surface at temperatures between its Tc and 1100 °C and a rugged surface consisting of small 2 × 1 and 1 × 2 terraces at temperatures above 1100 °C.

  15. A computational study on the adsorption configurations and reactions of SiHx(x = 1-4) on clean and H-covered Si(100) surfaces

    Science.gov (United States)

    Le, Thong N.-M.; Raghunath, P.; Huynh, Lam K.; Lin, M. C.

    2016-11-01

    Possible adsorption configurations of H and SiHx (x = 1 - 4) on clean and H-covered Si(100) surfaces are determined by using spin-polarized DFT calculations. The results show that, on the clean surface, the gas-phase hydrogen atom and SiH3 radicals effectively adsorb on the top sites, while SiH and SiH2 prefer the bridge sites of the first layer. Another possibility for SiH is to reside on the hollow sites with a triple-bond configuration. For a partially H-coverd Si(100) surface, the mechanism is similar but with higher adsorption energies in most cases. This suggests that the surface species become more stable in the presence of surface hydrogens. The minimum energy paths for the adsorption/migration and reactions of H/SiHx species on the surfaces are explored using the climbing image-nudged elastic band method. The competitive surface processes for Si thin-film formation from SiHx precursors are also predicted. The study reveals that the migration of hydrogen adatom is unimportant with respect to leaving open surface sites because of its high barriers (>29.0 kcal/mol). Alternatively, the abstraction of hydrogen adatoms by H/SiHx radicals is more favorable. Moreover, the removal of hydrogen atoms from adsorbed SiHx, an essential step for forming Si layers, is dominated by abstraction rather than the decomposition processes.

  16. Oxidation of silicon surface with atomic oxygen radical anions

    Institute of Scientific and Technical Information of China (English)

    Wang Lian; Song Chong-Fu; Sun Jian-Qiu; Hou Ying; Li Xiao-Guang; Li Quan-Xin

    2008-01-01

    The surface oxidation of silicon (Si) wafers by atomic oxygen radical anions (O- anions) and the preparation of metal-oxide-semiconductor (MOS) capacitors on the O--oxidized Si substrates have been examined for the first time. The O- anions are generated from a recently developed O- storage-emission material of [Ca24Al28O64]4+.4O- (C12A7-O- for short). After it has been irradiated by an O- anion beam (0.5 μA/cm2) at 300℃ for 1-10 hours, the Si wafer achieves an oxide layer with a thickness ranging from 8 to 32 nm. X-ray photoelectron spectroscopy (XPS) results reveal that the oxide layer is of a mixture of SiO2, Si2O3, and Si2O distributed in different oxidation depths. The features of the MOS capacitor of are investigated by measuring capacitance-voltage (C - V) and current-voltage (Ⅰ - Ⅴ) curves. The oxide charge density is about 6.0×1011 cm-2 derived from the C - V curves. The leakage current density is in the order of 10-6 A/cm2 below 4 MV/cm, obtained from the Ⅰ - Ⅴ curves. The Oanions formed by present method would have potential applications to the oxidation and the surface-modification of materials together with the preparation of semiconductor devices.

  17. 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.

  18. Atomic structure of the adsorption of transition metals on silicon surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Cocoletzi, G.H. [IF-BUAP, 72000 Puebla (Mexico); Takeuchi, N. [CCMC-UNAM, Ensenada, BCN (Mexico)

    2007-07-01

    Full text: Solid state devices are useful for their high sensitivity in a small volume. Applications of such devices as dose materials include semi-conducting dose-rate, and dose-reading measuring devices. Transition metals (TM) have electronic and atomic properties similar to those of rare earth elements when they are adsorbed on silicon surfaces. The interfaces of transition metals silicides with Si (111) have very small lattice mismatches, sharp interfaces, and low Schottky barrier, making them ideal in electronic devices, such as infrared detectors and rectifying contacts. In this work we shall describe our first principles total energy calculations to investigate structural properties of bulk ScSi and YSi, the two dimensional arrangement of ScSi{sub 2} and YSi{sub 2} on the Si(111) surface, and the growth of a few layers of ScSi{sub 1.7} and YSi{sub 1.7} on the Si(111) surface. Our calculated bulk structural parameters are in excellent agreement with experimental values. It will be shown that one monolayer of a TM on Si( l l 1) yields a two dimensional phase with (lxl) periodicity consisting of a layer of TM atoms on T4 sites and a Si bilayer on top. This double layer of Si atoms is very close to ideal Si(111)-(1x1) surface, but rotated 180 with respect to the rest of the crystal. More layers of TM silicide epitaxially grown on Si(l 11) result in a hexagonal structure similar to bulk ScSi2 and YSi2: graphite-like Si planes (with vacancies) intercalated with TM planes, and forming a ({radical}3x{radical}3) arrangement with a ScSi{sub 1.7} and YSi{sub 1.7} stoichiometry. The top Si layer does not contain vacancies and it does not present a graphite-like structure, but forms a bilayer arrangement as in bulk Si. (Author)

  19. Structure of the Co/Si(111) √{13}×√{13} surface revisited

    Science.gov (United States)

    Olyanich, D. A.; Utas, T. V.; Alekseev, A. A.; Kotlyar, V. G.; Zotov, A. V.; Saranin, A. A.

    2014-07-01

    The Si(111) √{13}×√{13}-R 13.9°-Co surface reconstruction shows up in the scanning tunneling microscopy images as an array of clusters. Two types of clusters coexist appearing as dark and bright in the images. P. Wetzel with co-workers (Surf. Sci. 604 (2010) 513 and Surf. Sci. 607 (2013) 111) have recently proposed a structural model of the dark cluster containing three Co atoms located in substitutional sites of the Si(111) surface with overlying triangle of six Si adatoms. The bright clusters have been suggested to contain three additional Si atoms on top of the six Si atoms terminating the dark cluster. The proposed models assume that the Si(111) √{13}×√{13}-R 13.9°-Co surface contains 3/13-0.23 ML Co. Our thorough experimental evaluations of the surface composition confirm that the bright cluster adopts three additional Si atoms but unambiguously demonstrate that the actual Co coverage at the Si(111) √{13}×√{13}-R 13.9°-Co surface is 1.4 ± 0.2 ML. To reconcile the reported structural models with the newly determined Co coverage, we suggest that the clusters reside not at the bare Si(111) surface (as suggested previously), but on the silicide Si-Co-Si triple layer on Si(111) substrate. Among about forty models with various types of completed and uncompleted silicide interfaces, the two models (with A8- and B8-type interfaces) have been proven to represent the most stable configurations.

  20. Formation of hollow atoms above a surface

    Science.gov (United States)

    Briand, Jean Pierre; Phaneuf, Ronald; Terracol, Stephane; Xie, Zuqi

    2012-06-01

    Slow highly stripped ions approaching or penetrating surfaces are known to capture electrons into outer shells of the ions, leaving the innermost shells empty, and forming hollow atoms. Electron capture occurs above and below the surfaces. The existence of hollow atoms below surfaces e.g. Ar atoms whose K and L shells are empty, with all electrons lying in the M and N shells, was demonstrated in 1990 [1]. At nm above surfaces, the excited ions may not have enough time to decay before hitting the surfaces, and the formation of hollow atoms above surfaces has even been questioned [2]. To observe it, one must increase the time above the surface by decelerating the ions. We have for the first time decelerated O^7+ ions to energies as low as 1 eV/q, below the minimum energy gained by the ions due to the acceleration by their image charge. As expected, no ion backscattering (trampoline effect) above dielectric (Ge) was observed and at the lowest ion kinetic energies, most of the observed x-rays were found to be emitted by the ions after surface contact. [4pt] [1] J. P. Briand et al., Phys.Rev.Lett. 65(1990)159.[0pt] [2] J.P. Briand, AIP Conference Proceedings 215 (1990) 513.

  1. Passivation of surface-nanostructured f-SiC and porous SiC

    DEFF Research Database (Denmark)

    Ou, Haiyan; Lu, Weifang; Ou, Yiyu

    The further enhancement of photoluminescence from nanostructured fluorescent silicon carbide (f-SiC) and porous SiC by using atomic layer deposited (ALD) Al2O3 is studied in this paper.......The further enhancement of photoluminescence from nanostructured fluorescent silicon carbide (f-SiC) and porous SiC by using atomic layer deposited (ALD) Al2O3 is studied in this paper....

  2. Semiconducting Electronic Property of Graphene Adsorbed on (0001) Surfaces of SiO2

    OpenAIRE

    Cuong, Nguyen Thanh; Otani, Minoru; Okada, Susumu

    2011-01-01

    First-principles total energy calculations are performed to investigate the energetics and electronic structures of graphene adsorbed on both an oxygen-terminated SiO2 (0001) surface and a fully hydroxylated SiO2 (0001) surface. We find that there are several stable adsorption sites for graphene on both O-terminated and hydroxylated SiO2 surfaces. The binding energy in the most stable geometry is found to be 15 meV per C atom, indicating a weak interaction between graphene and SiO2 (0001) sur...

  3. Electronic and Quantum Transport Properties of Atomically Identified Si Point Defects in Graphene.

    Science.gov (United States)

    Lopez-Bezanilla, Alejandro; Zhou, Wu; Idrobo, Juan-Carlos

    2014-05-15

    We report high-resolution scanning transmission electron microscopy images displaying a range of inclusions of isolated silicon atoms at the edges and inner zones of graphene layers. Whereas the incorporation of Si atoms to a graphene armchair edge involves no reconstruction of the neighboring carbon atoms, the inclusion of a Si atom to a zigzag graphene edge entails the formation of five-membered carbon rings. In all the observed atomic edge terminations, a Si atom is found bridging two C atoms in a 2-fold coordinated configuration. The atomic-scale observations are underpinned by first-principles calculations of the electronic and quantum transport properties of the structural anomalies. Experimental estimations of Si-doped graphene band gaps realized by means of transport measurements may be affected by a low doping rate of 2-fold coordinated Si atoms at the graphene edges, and 4-fold coordinated at inner zones due to the apparition of mobility gaps.

  4. Fluorinated saccharides on the Si(0 0 1) surface

    Science.gov (United States)

    Szwajca, Anna; Rapp, Magdalena; Bilska, Monika; Krzywiecki, Maciej; Koroniak, Henryk

    2013-06-01

    The attachment of saccharide molecules directly to silicon surface has been for the first time. Oxygen free silicon surface was functionalized with monosacharides thanks to UV irradiation in acetonitryl solution (254 nm). Selected derivatives of pentofuranose were protected at the C-1 and C-2 position. The remaining hydroxyl group at C-3 or C-5 was suitable for direct attachment to H-terminated Si(0 0 1) surface via Sisbnd Osbnd C bonds. The binding energy of the saccharide to the Si surface was investigated by quantum mechanical calculations method. The Parametric Method 5 (PM5) calculations confirmed that the formation of Sisbnd Osbnd C bonds was chemically possible. Synthesis of new fluorinated carbohydrates has been described. The resulting monolayers were characterized by Atomic Force Microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and Attenuated Total Reflection (ATR) infrared spectroscopy. The effect of incorporating fluorine atom or CF3 group into self-assembled monosaccharide monolayers was studied using a water contact angle measurements. The resulting surface wettability of different fluorinated components on one kind of planar substrate enables an answer which of derivative is required for the preparation of the hydrophobic monolayer.

  5. Cold atom microtraps above a videotape surface

    CERN Document Server

    Retter, J A

    2002-01-01

    Much progress has been made in the last two years towards miniaturizing magnetic traps for cold atoms. This will enable manipulation of coherent samples of atoms, such as Bose-Einstein condensates, or single atoms, on the scale of the atomic de Broglie wavelength. This thesis concerns an array of microscopic magnetic potentials formed close to the surface of magnetized videotape, when a uniform bias field is applied. The recorded magnetization is a 100 mu m sine wave, which covers a 12.5mm x 22mm piece of commercial videotape. This videotape is glued flat onto a thin glass substrate and is gold coated by evaporation so that atoms can be trapped close to the surface in a mirror-MOT. An 'atom chip' has been developed, incorporating the videotape and current-carrying wires located below the magnetized surface. A single wire and bias field create a magnetic tube potential, oriented parallel with the microtraps and with a quadrupole radial field. This allows the mirror-MOT to be compressed and distorted in order t...

  6. In situ measurement of adsorbed nitrogen atoms for PA-MBE growth of group III nitrides on Si

    Energy Technology Data Exchange (ETDEWEB)

    Ohachi, Tadashi; Yamabe, Nobuhiko; Yamamoto, Yuka; Wada, Motoi [Department of Electrical Engineering, Doshisha University, Kyotababe, Kyoto (Japan); Ariyada, Osamu [Arios Inc. Akishima, Tokyo (Japan)

    2011-05-15

    An atom probe of two parallel electrodes is proposed to monitor adsorbed (ADS) nitrogen atoms in situ during growth of {beta}-Si{sub 3}N{sub 4} using indirect exposure of effusing active nitrogen beam from the radio frequency induction coupled plasma cell. The {beta}-Si{sub 3}N{sub 4} film is a component of a double buffer layer (DBL) AlN(0001)/{beta}-Si{sub 3}N{sub 4}/Si(111) to grow high quality the group III nitrides and their alloys on Si. Atom current between the parallel electrodes corresponds to flux of the ADS nitrogen atoms on the inside surface at the atom potential, V{sub A}. The ADS atom current received influence of wall and shutter of the cell, because adsorption of nitrogen atom depended wall condition such as temperature and the concentration of adatoms on the wall (copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  7. Atomic scale control and understanding of cubic silicon carbide surface reconstructions, nanostructures and nanochemistry

    Science.gov (United States)

    Soukiassian, Patrick G.; Enriquez, Hanna B.

    2004-05-01

    The atomic scale ordering and properties of cubic silicon carbide (bgr-SiC) surfaces and nanostructures are investigated by atom-resolved room and high-temperature scanning tunnelling microscopy (STM) and spectroscopy (STS), synchrotron radiation-based valence band and core level photoelectron spectroscopy (VB-PES, CL-PES) and grazing incidence x-ray diffraction (GIXRD). In this paper, we review the latest results on the atomic scale understanding of (i) the structure of bgr-SiC(100) surface reconstructions, (ii) temperature-induced metallic surface phase transition, (iii) one dimensional Si(C) self-organized nanostructures having unprecedented characteristics, and on (iv) nanochemistry at SiC surfaces with hydrogen. The organization of these surface reconstructions as well as the 1D nanostructures' self-organization are primarily driven by surface stress. In this paper, we address such important issues as (i) the structure of the Si-rich 3 × 2, the Si-terminated c (4 × 2), the C-terminated c (2 × 2) reconstructions of the bgr-SiC(100) surface, (ii) the temperature-induced reversible {\\mathrm {c}}(4\\times 2) \\Leftrightarrow 2\\times 1 metallic phase transition, (iii) the formation of highly stable (up to 900 °C) Si atomic and vacancy lines, (iv) the temperature-induced sp to sp3 diamond like surface transformation, and (v) the first example of H-induced semiconductor surface metallization on the bgr-SiC (100) 3 × 2 surface. The results are discussed and compared to other experimental and theoretical investigations.

  8. Evaporative cooling of cold atoms at surfaces

    CERN Document Server

    Märkle, J; Federsel, P; Jetter, B; Günther, A; Fortágh, J; Proukakis, N P; Judd, T E

    2014-01-01

    We theoretically investigate the evaporative cooling of cold rubidium atoms that are brought close to a solid surface. The dynamics of the atom cloud are described by coupling a dissipative Gross-Pitaevskii equation for the condensate with a quantum Boltzmann description of the thermal cloud (the Zaremba-Nikuni-Griffin method). We have also performed experiments to allow for a detailed comparison with this model and find that it can capture the key physics of this system provided the full collisional dynamics of the thermal cloud are included. In addition, we suggest how to optimize surface cooling to obtain the purest and largest condensates.

  9. Alane adsorption and dissociation on the Si(0 0 1) surface

    Science.gov (United States)

    Smith, R. L.; Bowler, D. R.

    2017-10-01

    We used DFT to study the energetics of the decomposition of alane, AlH3, on the Si(0 0 1) surface, as the acceptor complement to PH3. Alane forms a dative bond with the raised atoms of silicon surface dimers, via the Si atom lone pair. We calculated the energies of various structures along the pathway of successive dehydrogenation events following adsorption: AlH2, AlH and Al, finding a gradual, significant decrease in energy. For each stage, we analyse the structure and bonding, and present simulated STM images of the lowest energy structures. Finally, we find that the energy of Al atoms incorporated into the surface, ejecting a Si atom, is comparable to Al adatoms. These findings show that Al incorporation is likely to be as precisely controlled as P incorporation, if slightly less easy to achieve.

  10. In-induced stable ordering of stepped Si(553) surface

    Energy Technology Data Exchange (ETDEWEB)

    Chauhan, Amit Kumar Singh [Physics of Energy Harvesting, (CSIR-NPL) , Dr. K.S. KrishnanRoad, New Delhi -110012 (India); Department of Physics, JMI, New Delhi 110025 (India); Niazi, Asad; Nair, Lekha [Department of Physics, JMI, New Delhi 110025 (India); Gupta, Govind, E-mail: govind@nplindia.org [Physics of Energy Harvesting, (CSIR-NPL) , Dr. K.S. KrishnanRoad, New Delhi -110012 (India)

    2015-05-15

    Highlights: • Control growth of In on step Si(553) & thermal stability of novel superstructure. • Influence of temperature on growth modes (SK,VB) under different growth conditions. • In-induced superstructure: (8 × 2), (8 × 4), mixed (553)-7 × 1 + (111)√3 × √3R30° phases. - Abstract: The growth mechanism and adsorbate-induced surface morphology of metal atoms on semiconducting surfaces crucially determines the electronic and physicochemical properties of these metal/semiconductor systems. In this study, we investigate the kinetically controlled growth of indium (In) atoms on the high index stepped Si(553)-7 × 7 surface and the thermal stability of various novel In-induced superstructural phases formed during adsorption/desorption process. Auger electron spectroscopy analysis reveals that In adsorption at room temperature (RT) and at 350 °C, with a controlled incident flux of 0.0016 ML/s, proceeds in the Stranski–Krastanov growth mode where two dimensional (2D)/three dimensional (3D) islands are formed on top of two complete monolayers. At higher substrate temperature up to 450 °C, the growth of In atoms occurs in the form of islands on the bare Si(553) surface, and In coverage is limited to the sub-monolayer regime. During the thermal desorption of the RT grown In/Si(553) system, the In clusters rearrange themselves and an unusual “cluster to layer” transformation occurs on top of the stable monolayer. In situ low energy electron diffraction analysis during adsorption and desorption shows the development of various coverage and temperature dependent In-induced superstructural phases on Si(553) surface, such as: (8 × 2) after annealing at 520 °C with coverage 0.5 ML, (8 × 4) after annealing at 580 °C (∼1 ML coverage) and (553)-7 × 1 + (111)-√3 × √3-R30° at 0.3 ML (630 °C). These adsorbate-induced superstructural phases could potentially be utilized as templates for pattern assisted growth of various exotic 1D/2D structures for

  11. Buckling of reconstruction elements of the edges of triple steps on vicinal Si(111) surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Zhachuk, R. A., E-mail: zhachuk@gmail.com [Russian Academy of Sciences, Rzhanov Institute of Semiconductor Physics, Siberian Branch (Russian Federation); Coutinho, J. [University of Aveiro, Campus Santiago, I3N, Department of Physics (Portugal); Rayson, M. J. [University of Surrey, Department of Chemistry (United Kingdom); Briddon, P. R. [Newcastle University, School of Electrical, Electronic and Computer Engineering (United Kingdom)

    2015-04-15

    The structure of steps with a height of three (111) interplanar distances on vicinal Si(111) surfaces has been analyzed through density functional theory calculations. It has been shown that several stable atomic configurations are possible depending on the buckling of the reconstruction elements of edges of the steps on the surface. It has been found that the direction of the buckling of reconstruction elements in the ground state of the surface is determined by the Coulomb interaction with their nearest atomic environment.

  12. Atomically flat single terminated oxide substrate surfaces

    Science.gov (United States)

    Biswas, Abhijit; Yang, Chan-Ho; Ramesh, Ramamoorthy; Jeong, Yoon H.

    2017-05-01

    Scientific interest in atomically controlled layer-by-layer fabrication of transition metal oxide thin films and heterostructures has increased intensely in recent decades for basic physics reasons as well as for technological applications. This trend has to do, in part, with the coming post-Moore era, and functional oxide electronics could be regarded as a viable alternative for the current semiconductor electronics. Furthermore, the interface of transition metal oxides is exposing many new emergent phenomena and is increasingly becoming a playground for testing new ideas in condensed matter physics. To achieve high quality epitaxial thin films and heterostructures of transition metal oxides with atomically controlled interfaces, one critical requirement is the use of atomically flat single terminated oxide substrates since the atomic arrangements and the reaction chemistry of the topmost surface layer of substrates determine the growth and consequent properties of the overlying films. Achieving the atomically flat and chemically single terminated surface state of commercially available substrates, however, requires judicious efforts because the surface of as-received substrates is of chemically mixed nature and also often polar. In this review, we summarize the surface treatment procedures to accomplish atomically flat surfaces with single terminating layer for various metal oxide substrates. We particularly focus on the substrates with lattice constant ranging from 4.00 Å to 3.70 Å, as the lattice constant of most perovskite materials falls into this range. For materials outside the range, one can utilize the substrates to induce compressive or tensile strain on the films and explore new states not available in bulk. The substrates covered in this review, which have been chosen with commercial availability and, most importantly, experimental practicality as a criterion, are KTaO3, REScO3 (RE = Rare-earth elements), SrTiO3, La0.18Sr0.82Al0.59Ta0.41O3 (LSAT), Nd

  13. 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.

  14. Semiconducting electronic property of graphene adsorbed on (0001) surfaces of SiO2.

    Science.gov (United States)

    Nguyen, Thanh Cuong; Otani, Minoru; Okada, Susumu

    2011-03-11

    First-principles total energy calculations are performed to investigate the energetics and electronic structures of graphene adsorbed on both an oxygen-terminated SiO2 (0001) surface and a fully hydroxylated SiO2 (0001) surface. We find that there are several stable adsorption sites for graphene on both O-terminated and hydroxylated SiO2 surfaces. The binding energy in the most stable geometry is found to be 15 meV per C atom, indicating a weak interaction between graphene and SiO2 (0001) surfaces. We also find that the graphene adsorbed on SiO2 is a semiconductor irrespective of the adsorption arrangement due to the variation of on-site energy induced by the SiO2 substrate.

  15. SiO adsorption on a p(2 × 2) reconstructed Si(1 0 0) surface

    NARCIS (Netherlands)

    Violanda, M.; Rudolph, H.

    2009-01-01

    We have investigated the adsorption mechanism of SiO molecule incident on a clean Si(1 0 0) p(2 × 2) reconstructed surface using density functional theory based methods. Stable adsorption geometries of SiO on Si surface, as well as their corresponding activation and adsorption energies are identifie

  16. Hollow-atom probing of surfaces

    NARCIS (Netherlands)

    Limburg, J.

    1997-01-01

    This paper discusses the mechanisms governing the formation and decay of hollow atoms in front of (semi) conducting and insulating surfaces. First, the primary neutralization of the highly charged ions is treated in terms of the classical overbarrier model. Different views are presented. Then the mo

  17. Surface Plasmon Polaritons Probed with Cold Atoms

    DEFF Research Database (Denmark)

    Kawalec, Tomasz; Sierant, Aleksandra; Panas, Roman

    2017-01-01

    We report on an optical mirror for cold rubidium atoms based on a repulsive dipole potential created by means of a modified recordable digital versatile disc. Using the mirror, we have determined the absolute value of the surface plasmon polariton (SPP) intensity, reaching 90 times the intensity...

  18. Controlling the fixed charge and passivation properties of Si(100)/Al2O3 interfaces using ultrathin SiO2 interlayers synthesized by atomic layer deposition

    Science.gov (United States)

    Dingemans, G.; Terlinden, N. M.; Verheijen, M. A.; van de Sanden, M. C. M.; Kessels, W. M. M.

    2011-11-01

    Al2O3 synthesized by atomic layer deposition (ALD) on H-terminated Si(100) exhibits a very thin (˜1 nm) interfacial SiOx layer. At this interface, a high fixed negative charge density, Qf, is present after annealing which contributes to ultralow surface recombination velocities ˜5 nm), the polarity of the effective charge density changed from negative to positive. The observed changes in Qf and the associated field-effect passivation had a significant influence on the injection-level-dependent minority carrier lifetime of Si.

  19. Atomic structure and electronic properties of the two-dimensional (Au ,Al )/Si (111 )2 ×2 compound

    Science.gov (United States)

    Gruznev, D. V.; Bondarenko, L. V.; Matetskiy, A. V.; Tupchaya, A. Y.; Chukurov, E. N.; Hsing, C. R.; Wei, C. M.; Eremeev, S. V.; Zotov, A. V.; Saranin, A. A.

    2015-12-01

    A combination of scanning tunneling microscopy, angle-resolved photoelectron spectroscopy, ab initio random structure searching, and density functional theory electronic structure calculations was applied to elucidate the atomic arrangement and electron band structure of the (Au ,Al )/Si (111 )2 ×2 two-dimensional compound formed upon Al deposition onto the mixed 5 ×2 /√{3 }×√{3 } Au/Si(111) surface. It was found that the most stable 2 ×2 -(Au, Al) compound incorporates four Au atoms, three Al atoms, and two Si atoms per 2 ×2 unit cell. Its atomic arrangement can be visualized as an array of meandering Au atomic chains with two-thirds of the Al atoms incorporated into the chains and one-third of the Al atoms interconnecting the chains. The compound is metallic and its electronic properties can be controlled by appropriate Al dosing since energetic location of the bands varies by ˜0.5 eV during increasing of Al contents. The 2 ×2 -(Au, Al) structure appears to be lacking the C3 v symmetry typical for the hexagonal lattices. The consequence of the peculiar atomic structure of the two-dimensional alloy is spin splitting of the metallic states, which should lead to anisotropy of the current-induced in-plane spin polarization.

  20. Spatially separated atomic layer deposition of Al2O3, a new option for high-throughput Si solar cell passivation

    NARCIS (Netherlands)

    Vermang, B.; Werner, F.; Stals, W; Lorenz, A.; Rothschild, A.; Racz, A.; John, J.; Poortmans, J.; Mertens, R.; Gortzen, R.M.W.; Poodt, P.W.G.; Tiba, V.; Roozeboom, F.; Schmidt, J.

    2011-01-01

    A next generation material for surface passivation of crystalline Si is Al2O3. It has been shown that both thermal and plasma-assisted (PA) atomic layer deposition (ALD) A l2O3 provide an adequate level of surface passivation for both p- and n-type Si substrates. However, conventional time-resolved

  1. First-principles study of the charge transfer and evolution of Si doping 2N2Ta islands adsorption on TaN (001) surfaces

    Science.gov (United States)

    Ren, Yuan; Zhang, Honglv; Zhang, Chao; Zeng, Haiqing; Liu, Xuejie

    2017-01-01

    The separation and aggregation of Si atoms around TaN grains during deposition of Ta-Si-N nanocomposite films were studied, and the adsorption energies, charge transfer and atomic partial density of state of Si-2N2Ta islands on the TaN (001) surface and diffusion energy of the islands during their evolution were evaluated using the first-principles method based on density functional theory (DFT). In the lowest total energy stable configuration, N and Ta atoms tended to combine to form 2N2Ta islands, whereas Si atoms tended to stay at a position diagonal to the Ta atom outside of the island. Si atoms entered the position of the missing N atom of the TaN island and formed a substitute solid solution during Ta-Si-N growth. The Si atoms of the solid solution in the island could be easily extruded by Ta- or N-rich island during the deposition process. The process of Si atom extrusion by a N atom which was the configuration of N-by-2Ta1N1Si island evolved into Si-by-2N2Ta island in rich N-atom. The process of Si atom was extruded by the Ta atom which was the configuration of Ta-by-2N1Ta1Si island evolved into Si-of-2Ta2N island, that reduced the total energy of island. The diffusion energies of these evolutions were 0.974 and 1.712 eV, respectively. The Si atoms and TaN grain phase tended to separate during the deposition process. Si atoms could give way to Ta and N atoms during the Ta-Si-N nanocomposite film deposition process.

  2. Direct methods determination of the Si(111)-(6x6)Au surface structure

    DEFF Research Database (Denmark)

    Grozea, D.; Landree, E.; Marks, L.D.;

    1998-01-01

    The atomic structure of the Au 6 x 6 on Si(111) phase has been determined using direct methods and surface X-ray diffraction data. This surface structure is very complicated, with 14 independent gold atoms, relaxations in 24 independent silicon sites and three partially occupied gold sites. In on...... the gold structures in the coverage range 0.8-1.5 monolayers as pseudo-glasses with strong short-range order but varying degrees of long-range order. (C) 1998 Elsevier Science B.V. All rights reserved.......The atomic structure of the Au 6 x 6 on Si(111) phase has been determined using direct methods and surface X-ray diffraction data. This surface structure is very complicated, with 14 independent gold atoms, relaxations in 24 independent silicon sites and three partially occupied gold sites. In one...

  3. Observation by conductive-probe atomic force microscopy of strongly inverted surface layers at the hydrogenated amorphous silicon/crystalline silicon heterojunctions

    Science.gov (United States)

    Maslova, O. A.; Alvarez, J.; Gushina, E. V.; Favre, W.; Gueunier-Farret, M. E.; Gudovskikh, A. S.; Ankudinov, A. V.; Terukov, E. I.; Kleider, J. P.

    2010-12-01

    Heterojunctions made of hydrogenated amorphous silicon (a-Si:H) and crystalline silicon (c-Si) are examined by conducting probe atomic force microscopy. Conductive channels at both (n )a-Si:H/(p)c-Si and (p)a-Si:H/(n)c-Si interfaces are clearly revealed. These are attributed to two-dimension electron and hole gases due to strong inversion layers at the c-Si surface in agreement with previous planar conductance measurements. The presence of a hole gas in (p )a-Si:H/(n)c-Si structures implies a quite large valence band offset (EVc-Si-EVa-Si:H>0.25 eV).

  4. Microstructure of as-fabricated UMo/Al(Si) plates prepared with ground and atomized powder

    Science.gov (United States)

    Jungwirth, R.; Palancher, H.; Bonnin, A.; Bertrand-Drira, C.; Borca, C.; Honkimäki, V.; Jarousse, C.; Stepnik, B.; Park, S.-H.; Iltis, X.; Schmahl, W. W.; Petry, W.

    2013-07-01

    UMo-Al based fuel plates prepared with ground U8wt%Mo, ground U8wt%MoX (X = 1 wt%Pt, 1 wt%Ti, 1.5 wt%Nb or 3 wt%Nb) and atomized U7wt%Mo have been examined. The first finding is that that during the fuel plate production the metastable γ-UMo phases partly decomposed into two different γ-UMo phases, U2Mo and α'-U in ground powder or α″-U in atomized powder. Alloying small amounts of a third element to the UMo had no measurable effect on the stability of the γ-UMo phase. Second, the addition of some Si inside the Al matrix and the presence of oxide layers in ground and atomized samples is studied. In the case with at least 2 wt%Si inside the matrix a Silicon rich layer (SiRL) forms at the interface between the UMo and the Al during the fuel plate production. The SiRL forms more easily when an Al-Si alloy matrix - which is characterized by Si precipitates with a diameter ⩽1 μm - is used than when an Al-Si mixed powder matrix - which is characterized by Si particles with some μm diameter - is used. The presence of an oxide layer on the surface of the UMo particles hinders the formation of the SiRL. Addition of some Si into the Al matrix [7-11]. Application of a protective barrier at the UMo/Al interface by oxidizing the UMo powder [7,12]. Increase of the Mo content or use of UMo alloys with ternary element addition X (e.g. X = Nb, Ti, Pt) to stabilize the γ-UMo with respect to α-U or to control the UMo-Al interaction layer kinetics [9,12-24]. Use of ground UMo powder instead of atomized UMo powder [10,25] The points 1-3 are to limit the formation of the undesired UMo/Al layer. Especially the addition of Si into the matrix has been suggested [3,7,8,10,11,26,27]. It has been often mentioned that Silicon is efficient in reducing the Uranium-Aluminum diffusion kinetics since Si shows a higher chemical affinity to U than Al to U. Si suppresses the formation of brittle UAl4 which causes a huge swelling during the irradiation. Furthermore it enhances the

  5. Photoluminescence of phosphorus atomic layer doped Ge grown on Si

    Science.gov (United States)

    Yamamoto, Yuji; Nien, Li-Wei; Capellini, Giovanni; Virgilio, Michele; Costina, Ioan; Schubert, Markus Andreas; Seifert, Winfried; Srinivasan, Ashwyn; Loo, Roger; Scappucci, Giordano; Sabbagh, Diego; Hesse, Anne; Murota, Junichi; Schroeder, Thomas; Tillack, Bernd

    2017-10-01

    Improvement of the photoluminescence (PL) of Phosphorus (P) doped Ge by P atomic layer doping (ALD) is investigated. Fifty P delta layers of 8 × 1013 cm‑2 separated by 4 nm Ge spacer are selectively deposited at 300 °C on a 700 nm thick P-doped Ge buffer layer of 1.4 × 1019 cm‑3 on SiO2 structured Si (100) substrate. A high P concentration region of 1.6 × 1020 cm‑3 with abrupt P delta profiles is formed by the P-ALD process. Compared to the P-doped Ge buffer layer, a reduced PL intensity is observed, which might be caused by a higher density of point defects in the P delta doped Ge layer. The peak position is shifted by ∼0.1 eV towards lower energy, indicating an increased active carrier concentration in the P-delta doped Ge layer. By introducing annealing at 400 °C to 500 °C after each Ge spacer deposition, P desorption and diffusion is observed resulting in relatively uniform P profiles of ∼2 × 1019 cm‑3. Increased PL intensity and red shift of the PL peak are observed due to improved crystallinity and higher active P concentration.

  6. One-atom-layer 4×4 compound in (Tl, Pb)/Si(111) system

    Science.gov (United States)

    Mihalyuk, A. N.; Hsing, C. R.; Wei, C. M.; Gruznev, D. V.; Bondarenko, L. V.; Tupchaya, A. Y.; Zotov, A. V.; Saranin, A. A.

    2017-03-01

    An ordered 4×4-periodicity 2D compound has been found in the (Tl, Pb)/Si(111) system and its composition, structure and electronic properties have been characterized using low-energy electron diffraction, scanning tunneling microscopy observations and density-functional-theory calculations. The compound has been concluded to contain 9 Tl atoms and 12 Pb atoms per 4×4 unit cell, i.e., 0.56 ML of Tl and 0.75 ML of Pb. Structural model was proposed for the 4×4-(Tl, Pb) compound where building blocks are a hexagonal array of 12 Pb atoms, a triangular array of 6 Tl atoms and a Tl trimer. The proposed structure has a C3 symmetry and occurs in the two equivalent orientations. The electron band structure of the compound contains two metallic spin-split surface-state bands. Bearing in mind the advanced properties of the known √{ 3 } ×√{ 3 } 2D compound in the same (Tl, Pb)/Si(111) system (i.e., combination of giant Rashba effect and superconductivity), the found 4×4-(Tl, Pb) compound is believed to be a promising object for exploration of its superconductive properties.

  7. On the interplay between Si(110) epilayer atomic roughness and subsequent 3C-SiC growth direction

    Science.gov (United States)

    Khazaka, Rami; Michaud, Jean-François; Vennéguès, Philippe; Nguyen, Luan; Alquier, Daniel; Portail, Marc

    2016-11-01

    In this contribution, we performed the growth of a 3C-SiC/Si/3C-SiC layer stack on a Si(001) substrate by means of chemical vapor deposition. We show that, by tuning the growth conditions, the 3C-SiC epilayer can be grown along either the [111] direction or the [110] direction. The key parameter for the growth of the desired 3C-SiC orientation on the Si(110)/3C-SiC(001)/Si(001) heterostructure is highlighted and is linked to the Si epilayer surface morphology. The epitaxial relation between the layers has been identified using X-ray diffraction and transmission electron microscopy (TEM). We showed that, regardless of the top 3C-SiC epilayer orientation, domains rotated by 90° around the growth direction are present in the epilayer. Furthermore, the difference between the two 3C-SiC orientations was investigated by means of high magnification TEM. The results indicate that the faceted Si(110) epilayer surface morphology results in a (110)-oriented 3C-SiC epilayer, whereas a flat hetero-interface has been observed between 3C-SiC(111) and Si(110). The control of the top 3C-SiC growth direction can be advantageous for the development of new micro-electro-mechanical systems.

  8. Effective passivation of Si surfaces by plasma deposited SiOx/a-SiNx:H stacks

    Science.gov (United States)

    Dingemans, G.; Mandoc, M. M.; Bordihn, S.; van de Sanden, M. C. M.; Kessels, W. M. M.

    2011-05-01

    Very low surface recombination velocities field-effect passivation was absent for a reference stack comprising thermally grown SiO2. The results indicate that hydrogenation of interface states played a key role in the passivation and remained effective up to annealing temperatures >800 °C.

  9. Interface orbital engineering of large-gap topological states: Decorating gold on a Si(111) surface

    Science.gov (United States)

    Huang, Bing; Jin, Kyung-Hwan; Zhuang, Houlong L.; Zhang, Lizhi; Liu, Feng

    2016-03-01

    Intensive effort has recently been made in search of topological insulators (TIs) that have great potential in spintronics applications. In this paper, a novel concept of overlayer induced interfacial TI phase in conventional semiconductor surface is proposed. The first-principles calculations demonstrate that a p -band-element X (X =In , Bi, and Pb) decorated d -band surface, such as Au/Si(111) surface [X /Au/Si(111)] of an existing experimental system, offers a promising prototype for TIs. Specifically, Bi/Au/Si(111) and Pb/Au/Si(111) are identified to be large-gap TIs. A p -d band inversion mechanism induced by growth of X in the Au/Si(111) surface is revealed to function at different coverage of X with different lattice symmetries, suggesting a general approach of interface orbital engineering of large-gap TIs via tuning the interfacial atomic orbital position of X relative to Au.

  10. What a difference a bond makes: the structural, chemical, and physical properties of methyl-terminated Si(111) surfaces.

    Science.gov (United States)

    Wong, Keith T; Lewis, Nathan S

    2014-10-21

    The chemical, electronic, and structural properties of surfaces are affected by the chemical termination of the surface. Two-step halogenation/alkylation of silicon provides a scalable, wet-chemical method for grafting molecules onto the silicon surface. Unlike other commonly studied wet-chemical methods of surface modification, such as self-assembly of monolayers on metals or hydrosilylation on silicon, the two-step method enables attachment of small alkyl chains, even methyl groups, to a silicon surface with high surface coverage and homogeneity. The methyl-terminated Si(111) surface, by comparison to hydrogen-terminated Si(111), offers a unique opportunity to study the effects of the first surface bond connecting the overlayer to the surface. This Account describes studies of methyl-terminated Si(111), which have shown that the H-Si(111) and CH3-Si(111) surfaces are structurally nearly identical, yet impart significantly different chemical and electronic properties to the resulting Si surface. The structure of methyl-terminated Si(111) formed by a two-step halogenation/methylation process has been studied by a variety of spectroscopic methods. A covalent Si-C bond is oriented normal to the surface, with the methyl group situated directly atop a surface Si atom. Multiple spectroscopic methods have shown that methyl groups achieve essentially complete coverage of the surface atoms while maintaining the atomically flat, terraced structure of the original H-Si(111) surface. Thus, the H-Si(111) and CH3-Si(111) surface share essentially identical structures aside from the replacement of a Si-H bond with a Si-C bond. Despite their structural similarity, hydrogen and methyl termination exhibit markedly different chemical passivation. Specifically, CH3-Si(111) exhibits significantly greater oxidation resistance than H-Si(111) in air and in aqueous electrolyte under photoanodic current flow. Both surfaces exhibit similar thermal stability in vacuum, and the Si-H and Si

  11. Potential Energy Surfaces for Reactions of X Metal Atoms (X = Cu, Zn, Cd, Ga, Al, Au, or Hg with YH4 Molecules (Y = C, Si, or Ge and Transition Probabilities at Avoided Crossings in Some Cases

    Directory of Open Access Journals (Sweden)

    Octavio Novaro

    2012-01-01

    Full Text Available We review ab initio studies based on quantum mechanics on the most important mechanisms of reaction leading to the C–H, Si–H, and Ge–H bond breaking of methane, silane, and germane, respectively, by a metal atom in the lowest states in Cs symmetry: X(2nd excited state, 1st excited state and ground state + YH4→ H3XYH → H + XYH3 and XH + YH3. with X = Au, Zn, Cd, Hg, Al, and G, and Y = C, Si, and Ge. Important issues considered here are (a the role that the occupation of the d-, s-, or p-shells of the metal atom plays in the interactions with a methane or silane or germane molecule, (b the role of either singlet or doublet excited states of metals on the reaction barriers, and (c the role of transition probabilities for different families of reacting metals with these gases, using the H–X–Y angle as a reaction coordinate. The breaking of the Y–H bond of YH4 is useful in the production of amorphous hydrogenated films, necessary in several fields of industry.

  12. First-principles study on initial stage of oxidation on Si(110) surface

    Energy Technology Data Exchange (ETDEWEB)

    Nagasawa, Takahiro; Shiba, Seiji; Sueoka, Koji [Department of System Engineering, Okayama Prefectural University, 111 Kuboki, Soja, Okayama 719-1197 (Japan)

    2011-03-15

    There is a great deal of engineering interest in Si (110) wafers as the substrates of large scale integrations (LSIs) in the next generation. However, few studies on Si (110) surface have been reported in comparison with those on other low-index surfaces, still less the mechanism of surface oxidation. We analyzed the surface structure and the initial stage of oxidation on the Si (110)-(16 x 2) clean surface with first-principles calculation. The results of our calculations showed that first, the stable structure of the Si (110) clean surface was the adatom-tetramer-interstitial (ATI) reconstruction. Second, pairs of pentagon (PPs) were preferentially oxidized in the initial stage of the oxidation. Third, the oxidation growth should progress with the clustering of O atoms. (copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  13. Organising Atoms, Clusters and Proteins on Surfaces

    Science.gov (United States)

    Palmer, Richard E.

    2008-10-01

    This talk will discuss new developments in the creation of nanoscale surface features and their applications in biomedicine. Electron-surface interactions and plasma methods play a crucial role in both the production and analysis of these ``atomic architectures.'' At the extreme limit, electron injection from the tip of a scanning tunnelling microscope (STM) enables bond-selective manipulation of individual polyatomic molecules [1]. On a more practical level, the controlled deposition of size-selected clusters [2], generated by magnetron sputtering and gas condensation followed by mass selection, represents a surprisingly efficient route to the fabrication of surface features of size 1-10 nm, the size scale of biological molecules such as proteins. STM and AFM measurements show the clusters can act as binding sites for individual protein molecules. For example, the pinning of size-selected AuN clusters (N = 1--2000) to the (hydrophobic) graphite surface presents bindings site for sulphur atoms and thus for the cysteine residues in protein molecules. Systematic studies of different proteins [3] provide ``ground rules'' for residue-specific protein immobilisation by clusters and have led to the development of a novel biochip for protein screening by a spin-off company. The 3D atomic structure of the clusters is highly relevant to such applications. We show that measurement of the scattered electron beam intensity - specifically, the high angle annular dark field (HAADF) signal - in the scanning transmission electron microscope (STEM) allows us (a) to count the number of atoms in a cluster on the surface and (b) to determine a 3D atom-density map of the cluster when an aberration-corrected STEM is used [4]. 1. P.A. Sloan and R.E. Palmer, Nature 434 367 (2005). 2. S. Pratontep, P. Preece, C. Xirouchaki, R.E. Palmer, C.F. Sanz-Navarro, S.D. Kenny and R. Smith, Phys. Rev. Lett. 90 055503 (2003). 3. R.E. Palmer, S. Pratontep and H.-G. Boyen, Nature Materials 2 443 (2003

  14. The atomic structure of the Si(111) (2 root 3x2 root 3)R30 degrees-Sn reconstruction

    DEFF Research Database (Denmark)

    Levermann, A.H.; Howes, P.B.; Edwards, K.A.

    1996-01-01

    are in contradiction with existing models in the literature and we conclude the need for a new surface atomic structure model. We have been able to determine a number of properties of an appropriate surface model to allow a better fit to the experimental structure factors.......We have studied the atomic structure of the (2 root 3x2 root)R30 degrees reconstruction induced by adsorption of about 1.1 monolayers of Sn on Si(lll) using surface X-ray diffraction (SXRD) and scanning tunnelling microscopy (STM). The experimentally obtained structure factors in SXRD...

  15. Influence of SiC surface polarity on the wettability and reactivity in an Al/SiC system

    Science.gov (United States)

    Shen, Ping; Wang, Yi; Ren, Lihua; Li, Shixin; Liu, Yuhua; Jiang, Qichuan

    2015-11-01

    The wetting of (0 0 0 1) 6H-SiC single crystals by molten Al was investigated using a dispensed sessile drop method in a high vacuum at 973-1173 K. The wettability and reactivity in this system are sensitive to the surface polarity of SiC. The interfacial reaction on the Si-terminated surface is rapid. The formation of a continuous Al4C3 product layer at the interface leads to an equilibrium contact angle of 56 ± 1° at 1173 K. In comparison, the interfacial reaction on the C-terminated surface is sluggish. The interface is only partially covered by discrete Al4C3 platelets even after dwelling at 1173 K for 2 h. The final wettability, however, is much better (θF = 41 ± 1°) than that of the Si-terminated surface which was covered by a dense Al4C3 layer, suggesting that the formation of Al4C3 should not always contribute to the wetting in the Al/SiC system. A plausible explanation is that the clean (i.e., deoxidized) C-terminated surface should be well wetted by molten Al in nature, owing to the strong chemical interactions between liquid Al and the surface atoms of the C-terminated SiC. It is likely that the presence of the oxide film at the surface of the molten Al drop or the SiC substrate and the rapid formation of Al4C3, which prevent the establishment of a real Al/SiC interface, conceal the intrinsic wettability of this system.

  16. Atomic Diffusion in Cu/Si (111) and Cu/SiO2/Si (111) Systems by Neutral Cluster Beam Deposition

    Institute of Scientific and Technical Information of China (English)

    CAO Bo; LI Gong-Ping; CHEN Xi-Meng; CHO Seong-Jin; KIM Hee

    2008-01-01

    @@ The Cu films are deposited on two kinds of p-type Si (111) substrates by ionized cluster beam (ICB) technique.The interface reaction and atomic diffusion of Cu/Si (111) and Cu/SiO2/Si (111) systems are studied at different annealing temperatures by x-ray diffraction (XRD) and Rutherford backscattering spectrometry (RBS). Some significant results are obtained: For the Cu/Si (111) samples prepared by neutral clusters, the interdiffusion of Cu and Si atoms occurs when annealed at 230℃. The diffusion coefficients of the samples annealed at 230℃and 500℃ are 8.5 × 10-15 cm2.s-1 and 3.0 × 10-14 cm2.s-1, respectively. The formation of the copper-silicide phase is observed by XRD, and its intensity becomes stronger with the increase of annealing temperature. For the Cu/SiO2/Si (111) samples prepared by neutral clusters, the interdiffusion of Cu and Si atoms occurs and copper silicides are formed when annealed at 450℃. The diffusion coefficients of Cu in Si are calculated to be 6.0 × 10-16 cm2.s-1 at 450℃, due to the fact that the existence of the SiO2 layer suppresses the interdiffusion of Cu and Si.

  17. Adsorption and reaction of silver on an oxidized Si(0 0 1) surface

    Energy Technology Data Exchange (ETDEWEB)

    Ohno, S., E-mail: sohno@ynu.ac.jp [Faculty of Engineering, Yokohama National University, 79-5 Tokiwadai, Hodogaya-ku, Yokohama 240-8501 (Japan); Tanaka, H. [Faculty of Engineering, Yokohama National University, 79-5 Tokiwadai, Hodogaya-ku, Yokohama 240-8501 (Japan); Takahashi, K.; Kamada, M. [Synchrotron Light Application Center, Saga University, Honjo 1, Saga 840-8502 (Japan); Tanaka, M. [Faculty of Engineering, Yokohama National University, 79-5 Tokiwadai, Hodogaya-ku, Yokohama 240-8501 (Japan)

    2015-08-15

    Highlights: • Electronic states associated with silver adsorption processes on oxidized silicon surfaces were investigated. • Characterization of oxide thin films on Si surfaces was performed using photoelectron spectroscopy with synchrotron radiation. • The changes in the Si 2p oxide components upon silver adsorption are ascribed to charge transfer rather than a conformation change. - Abstract: The adsorption and reaction of silver on an oxidized Si(0 0 1) surface were investigated on the basis of Si 2p, Ag 3d and O 1s core-level photoemission measurements at room temperature (RT). We compared the present results with those obtained in the case of titanium in our previous study. We found that silver on an oxidized Si(0 0 1) surface at RT causes a reduction in the intensity of the Si{sup 1+} and Si{sup 2+} states and an increase in the intensity of the Si{sup 3+} and Si{sup 4+} states. Based on an analysis of the Ag 3d and O 1s states, we concluded that the change in the Si 2p oxidized states upon silver adsorption is due to charge transfer rather than conformation change, although the applicability of the charge transfer scheme may be dependent on the thickness of the silver layer. We also deduced that penetration of silver atoms through a thin silicon oxide film occurs.

  18. Measurements of SiO2 glass surface parameters by methods of microscopy

    Science.gov (United States)

    Gavars, Eduards; Svagere, Anda; Skudra, Atis; Zorina, Natalia; Poplausks, Raimonds

    2012-08-01

    In this research we compare chemical and plasma treatment methods for surface of SiO2 glass. For chemical treatment of surface tequila and alcohol were used but for plasma treatment - Ar+As and Ar+Se plasmas. Surface topography was analyzed using atomic force microscope. Comparison of chemical and plasma treatment methods shows that surface treated with plasma is smoother. Because of their various chemical compositions tequila and alcohol show different results.

  19. Laser-assisted atom probe tomography of four paired poly-Si/SiO2 multiple-stacks with each thickness of 10 nm

    Science.gov (United States)

    Kwak, C.-M.; Seol, J.-B.; Kim, Y.-T.; Park, C.-G.

    2017-02-01

    For the past 10 years, laser-assisted atom probe tomography (APT) analysis has been performed to quantify the near-atomic scale distribution of elements and their local chemical compositions within interfaces that determine the design, processing, and properties of virtually all materials. However, the nature of the occurring laser-induced emission at the surface of needle-shaped sample is highly complex and it has been an ongoing challenge to understand the surface-related interactions between laser-sources and tips containing non-conductive oxides for a robust and reliable analysis of multiple-stacked devices. Here, we find that the APT analysis of four paired poly-Si/SiO2 (conductive/non-conductive) multiple stacks with each thickness of 10 nm is governed by experimentally monitoring three experimental conditions, such as laser-beam energies ranged from 30 to 200 nJ, analysis temperatures varying with 30-100 K, and the inclination of aligned interfaces within a given tip toward analysis direction. Varying with laser-energy and analysis temperature, a drastic compositional ratio of doubly charged Si ions to single charged Si ions within conductive poly-Si layers is modified, as compared with ones detected in the non-conductive layers. Severe distorted APT images of multiple stacks are also inevitable, especially at the conductive layers, and leading to a lowering of the successful analysis yields. This lower throughput has been overcome though changing the inclination of interfaces within a given tip to analysis direction (planar interfaces parallel to the tip axis), but significant deviations in chemical compositions of a conductive layer counted from those of tips containing planar interfaces perpendicular to the tip axis are unavoidable owing to the Si2, SiH2O, and Si2O ions detected, for the first time, within poly-Si layers.

  20. Characteristics and Microstructure of a Hypereutectic Al-Si Alloy Powder by Ultrasonic Gas Atomization Process

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    A hypereutectic Al-Si alloy powder was prepared by ultrasonic gas atomization process. The morphologies, microstructure and phase constituent of the alloy powder were studied. The results showed that powder of the alloy was very fine and its rnicrostructure was mainly consisted of Si crystals plus intermetallic compound Al9FeSi3, which were. very fine and uniformly distributed.

  1. NiO/SiC nanocomposite prepared by atomic layer deposition used as a novel electrocatalyst for nonenzymatic glucose sensing.

    Science.gov (United States)

    Yang, Peng; Tong, Xili; Wang, Guizhen; Gao, Zhe; Guo, Xiangyun; Qin, Yong

    2015-03-04

    NiO nanoparticles are deposited onto SiC particles by atomic layer deposition (ALD). The structure of the NiO/SiC hybrid material is investigated by inductively coupled plasma atomic emission spectrometry (ICP-AES), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). The size of the NiO nanoparticles is flexible and can be adjusted by altering the cycle number of the NiO ALD. Electrochemical measurements illustrate that NiO/SiC prepared with 600 cycles for NiO ALD exhibits the highest glucose sensing ability in alkaline electrolytes with a low detection limit of 0.32 μM (S/N = 3), high sensitivity of 2.037 mA mM(-1) cm(-2), a linear detection range from approximately 4 μM to 7.5 mM, and good stability. Its sensitivity is about 6 times of that for commercial NiO nanoparticles and NiO/SiC nanocomposites prepared by a traditional incipient wetness impregnation method. It is revealed that the superior electrochemical ability of ALD NiO/SiC is ascribed to the strong interaction between NiO and the SiC substrate and the high dispersity of NiO nanoparticles on the SiC surface. These results suggest that ALD is an effective way to deposit NiO on SiC for nonenzymatic glucose sensing.

  2. Nanoscopic oxidation of p-type and un-doped Si (100) surfaces using un-externally biased atomic force microscope tips (AFM) in the presence of selected organic solvents

    Science.gov (United States)

    McCausland, Jeffrey; Withanage, Sajeevi; Mallik, Robert; Lyuksyutov, Sergei

    A conductive un-biased AFM tip oscillating above p-type or un-doped Si (100) treated with toluene, butan-2-ol, and propan-2-ol creates nanostructures ranging in height from 1-100 nm. The tip was oscillated in ambient conditions (30-70% Rel. Humidity) at frequencies in the 102 kHz range. It was repeatable with various concentrations of solvent in aqueous solution. It is suggested that mechanical oscillations of the AFM tip polarizes the solvent molecules deposited on the surface resulting in electron transfer from the tip to the surface followed by feature formation. This process effectively creates an electrochemical cell at the microscopic level and the miscibility of the solvents is the key to enabling the process. Species which ionize during the process may be consumed in irreversible reactions whereas the alcohols act as catalysts and are not consumed. The influence of boron defects in the Si substrates is also discussed. It appears that the observed oxidation is different from all other similar reported phenomena including local anodic oxidation, and chemo-mechanical lithographic techniques utilizing AFM.

  3. Oxidation of atomically thin MoS2 on SiO2

    Science.gov (United States)

    Yamamoto, Mahito; Cullen, William; Einstein, Theodore; Fuhrer, Michael

    2013-03-01

    Surface oxidation of MoS2 markedly affects its electronic, optical, and tribological properties. However, oxidative reactivity of atomically thin MoS2 has yet to be addressed. Here, we investigate oxidation of atomic layers of MoS2 using atomic force microscopy and Raman spectroscopy. MoS2 is mechanically exfoliated onto SiO2 and oxidized in Ar/O2 or Ar/O3 (ozone) at 100-450 °C. MoS2 is much more reactive to O2 than an analogous atomic membrane of graphene and monolayer MoS2 is completely etched very rapidly upon O2 treatment above 300 °C. Thicker MoS2 (> 15 nm) transforms into MoO3 after oxidation at 400 °C, which is confirmed by a Raman peak at 820 cm-1. However, few-layer MoS2 oxidized below 400 °C exhibits no MoO3 Raman mode but etch pits are formed, similar to graphene. We find atomic layers of MoS2 shows larger reactivity to O3 than to O2 and monolayer MoS2 transforms chemically upon O3 treatment even below 100 °C. Work supported by the U. of Maryland NSF-MRSEC under Grant No. DMR 05-20741.

  4. Formation of oxides and segregation of mobile atoms during SIMS profiling of Si with oxygen ions

    Energy Technology Data Exchange (ETDEWEB)

    Petravic, M.; Williams, J.S.; Svensson, B.G.; Conway, M. [Australian National Univ., Canberra, ACT (Australia). Research School of Physical Sciences

    1993-12-31

    An oxygen beam is commonly used in secondary ion mass spectroscopy (SIMS) analysis to enhance the ionization probability for positive secondary ions. It has been observed, however, that this technique produces in some cases a great degradation of depth resolution. The most pronounced effects have been found for impurities in silicon under oxygen bombardment at angles of incidence smaller than {approx} 30 deg from the surface normal. A new approach is described which involved broadening of SIMS profiles for some mobile atoms, such as Cu, Ni and Au, implanted into silicon. The anomalously large broadening is explained in terms of segregation at a SiO{sub 2}/Si interface formed during bombardment with oxygen at impact angles less than 30 deg. 2 refs., 1 tab., 4 figs.

  5. Initial stages of Zr-Fe-Si alloy formation on Zr(0001) surface

    Science.gov (United States)

    Horáková, Kateřina; Cichoň, Stanislav; Lančok, Ján; Sajdl, Petr; Cháb, Vladimír

    2017-03-01

    We studied initial stages of Fe and Si atoms interaction with the Zr(0001) surface. Fe and Si were deposited in-situ on the clean Zr surface up to coverage of one monolayer. Chemical state of Zr as a function of annealing temperature and the surface composition was investigated. Characteristic (1×1) LEED (Low Energy Electron Diffraction) pattern of the clean Zr surface becomes significantly modified when Fe and Si are deposited and annealed at 400 °C. The arrangement of new spots of the pattern corresponds to the (2√3×2√3)R30° structure, stable up to annealing at 750 °C. Changes in the electronic structure were identified from the images of equi-energy cuts of the k-space covering the entire Brillouin zone. The results imply that hydrogen, typically present in the clean surface, was eliminated either by annealing or upon the deposition of Fe and Si.

  6. Low-temperature atomic layer deposition of MgO thin films on Si

    Science.gov (United States)

    Vangelista, S.; Mantovan, R.; Lamperti, A.; Tallarida, G.; Kutrzeba-Kotowska, B.; Spiga, S.; Fanciulli, M.

    2013-12-01

    Magnesium oxide (MgO) films have been grown by atomic layer deposition in the wide deposition temperature window of 80-350 °C by using bis(cyclopentadienyl)magnesium and H2O precursors. MgO thin films are deposited on both HF-last Si(1 0 0) and SiO2/Si substrates at a constant growth rate of ˜0.12 nm cycle-1. The structural, morphological and chemical properties of the synthesized MgO thin films are investigated by x-ray reflectivity, grazing incidence x-ray diffraction, time-of-flight secondary ion mass spectrometry and atomic force microscopy measurements. MgO layers are characterized by sharp interface with the substrate and limited surface roughness, besides good chemical uniformity and polycrystalline structure for thickness above 7 nm. C-V measurements performed on Al/MgO/Si MOS capacitors, with MgO in the 4.6-11 nm thickness range, allow determining a dielectric constant (κ) ˜ 11. Co layers are grown by chemical vapour deposition in direct contact with MgO without vacuum-break (base pressure 10-5-10-6 Pa). The as-grown Co/MgO stacks show sharp interfaces and no elements interdiffusion among layers. C-V and I-V measurements have been conducted on Co/MgO/Si MOS capacitors. The dielectric properties of MgO are not influenced by the further process of Co deposition.

  7. Surface defects and temperature on atomic friction

    Energy Technology Data Exchange (ETDEWEB)

    Fajardo, O Y; Mazo, J J, E-mail: yovany@unizar.es [Departamento de Fisica de la Materia Condensada and Instituto de Ciencia de Materiales de Aragon, CSIC-Universidad de Zaragoza, 50009 Zaragoza (Spain)

    2011-09-07

    We present a theoretical study of the effect of surface defects on atomic friction in the stick-slip dynamical regime of a minimalistic model. We focus on how the presence of defects and temperature change the average properties of the system. We have identified two main mechanisms which modify the mean friction force of the system when defects are considered. As expected, defects change the potential profile locally and thus affect the friction force. But the presence of defects also changes the probability distribution function of the tip slip length and thus the mean friction force. We corroborated both effects for different values of temperature, external load, dragging velocity and damping. We also show a comparison of the effects of surface defects and surface disorder on the dynamics of the system. (paper)

  8. Surface Acidity and Properties of TiO2/SiO2 Catalysts Prepared by Atomic Layer Deposition: UV-visible Diffuse Reflectance, DRIFTS, and Visible Raman Spectroscopy Studies

    Science.gov (United States)

    2009-06-15

    commercial anatase titania was also measured. The edge energy (Eg) for allowed transitions was determined by finding the intercept of the straight...150 °C (xTS-150C, where x is the number of cycles (1, 4, 10, and 20)) are depicted in Figure 1, where silica gel and anatase titania were also measured...titanium (atoms/nm2) BET surface area (m2/g) pore diameter (Å) chlorine (wt %, XRF) Eg (eV) silica powder 91.6 301.5 anatase TiO2 3.47 1TS-TTIP-150C 1.92

  9. First-principles Study on Adsorption of Au Atom on Hydroxylated SiO2 Surfaee

    Institute of Scientific and Technical Information of China (English)

    WAN Miao; HE Kaihua; CHEN QiH; HONG Hanlie

    2011-01-01

    Adsorption of single gold (Au) atom at three kinds of sites (hollow,bridge and top) on the hydroxylated β-cristobalite SiO2 (111) surface was studied using the first-principles calculations with general gradient approximation (GGA).The results of adsorption energies and density of electronic states (DOS)suggest that the hollow and bridge sites have the basically equal capability of binding Au,while the ability of the Top site is weaker.Two new energy levels emerge after the adsorption at all sites; in DOS of the Hollow configuration,one locates at -0.15 eV,composed of Au 5d and O 2p electronic states,another just crosses through the Fermi level,consisting of Au 6s,H 1s and O 2p.In addition,Mulliken population analyses indicate that electron transfer takes place between the Au atom and the surface H and O atoms in the Hollow and Bridge configurations,which can be used to interpret the adsorption of Au onto the positions.However,neither H nor O chemically bonds with Au atom.

  10. Influence of SiC surface polarity on the wettability and reactivity in an Al/SiC system

    Energy Technology Data Exchange (ETDEWEB)

    Shen, Ping, E-mail: shenping@jlu.edu.cn [Key Laboratory of Automobile Materials (Ministry of Education), School of Materials Science and Engineering, Jilin University, No. 5988 Renmin Street, Changchun 130025 (China); Wang, Yi [Key Laboratory of Automobile Materials (Ministry of Education), School of Materials Science and Engineering, Jilin University, No. 5988 Renmin Street, Changchun 130025 (China); Ren, Lihua; Li, Shixin [Nuclear and radiation safety center, No. 54 Hongliannancun, Haidian District, Beijing 100082 (China); Liu, Yuhua; Jiang, Qichuan [Key Laboratory of Automobile Materials (Ministry of Education), School of Materials Science and Engineering, Jilin University, No. 5988 Renmin Street, Changchun 130025 (China)

    2015-11-15

    Graphical abstract: - Highlights: • The wettability and reactivity are sensitive to the surface polarity of SiC. • In comparison, the reaction at the Si-terminated surface is much stronger and faster. • The intrinsic wettability between clean Al and clean SiC could be fairly good. • The formation of Al{sub 4}C{sub 3} might not essentially promote the wettability. - Abstract: The wetting of (0 0 0 1) 6H-SiC single crystals by molten Al was investigated using a dispensed sessile drop method in a high vacuum at 973–1173 K. The wettability and reactivity in this system are sensitive to the surface polarity of SiC. The interfacial reaction on the Si-terminated surface is rapid. The formation of a continuous Al{sub 4}C{sub 3} product layer at the interface leads to an equilibrium contact angle of 56 ± 1° at 1173 K. In comparison, the interfacial reaction on the C-terminated surface is sluggish. The interface is only partially covered by discrete Al{sub 4}C{sub 3} platelets even after dwelling at 1173 K for 2 h. The final wettability, however, is much better (θ{sub F} = 41 ± 1°) than that of the Si-terminated surface which was covered by a dense Al{sub 4}C{sub 3} layer, suggesting that the formation of Al{sub 4}C{sub 3} should not always contribute to the wetting in the Al/SiC system. A plausible explanation is that the clean (i.e., deoxidized) C-terminated surface should be well wetted by molten Al in nature, owing to the strong chemical interactions between liquid Al and the surface atoms of the C-terminated SiC. It is likely that the presence of the oxide film at the surface of the molten Al drop or the SiC substrate and the rapid formation of Al{sub 4}C{sub 3}, which prevent the establishment of a real Al/SiC interface, conceal the intrinsic wettability of this system.

  11. Study of the Adsorption of Atoms and Molecules on Silicon Surfaces Crystallographics and Electronic Structure

    CERN Document Server

    Bengio, S

    2003-01-01

    This thesis work has been concerned with adsorption properties of silicon surfaces.The atomic and electronic structure of molecules and atoms adsorbed on Si has been investigated by means of photoemission experiments combined with synchrotron radiation.The quantitative atomic structure determination was held applying the photoelectron diffraction technique.This technique is sensible to the local structure of a reference atomic specie and has elemental and chemical-state specificity.This approach has been applied to three quite different systems with different degrees of complexity, Sb/Si(111) sq root 3x sq root 3R30 sup 0 , H sub 2 O/Si(100)2x1 and NH sub 3 /Si(111)7x7.Our results show that Sb which forms a ( sq root 3 sq root 3)R30 sup 0 phase produces a bulklike-terminated Si(111)1x1 substrate free of stacking faults.Regarding the atomic structure of its interface, this study strongly favours the T4-site milkstool model over the H3 one.An important aspect regarding the H sub 2 O/Si(100)(2x1) system was esta...

  12. Impacts of light illumination on monocrystalline silicon surfaces passivated by atomic layer deposited Al2O3 capped with plasma-enhanced chemical vapor deposited SiN x

    Science.gov (United States)

    Lin, Fen; Toh, Mei Gi; Thway, Maung; Li, Xinhang; Nandakumar, Naomi; Gay, Xavier; Dielissen, Bas; Raj, Samuel; Aberle, Armin G.

    2017-08-01

    In this work, we investigate the impact of light illumination on crystalline silicon surfaces passivated with inline atomic layer deposited aluminum oxide capped with plasma-enhanced chemical vapor deposited silicon nitride. It is found that, for dedicated n-type lifetime samples under illumination, there is no light induced degradation (LID) but enhanced passivation. The lifetime increase happened with a much faster speed compared to the lifetime decay during dark storage, resulting in the overall lifetime enhancement for actual field application scenarios (sunshine during the day and darkness during the night). In addition, it was found that the lifetime enhancement is spectrally dependent and mainly associated with the visible part of the solar spectrum. Hence, it has negligible impact for such interfaces applied on the rear of the solar cells, for example p-type aluminum local back surface field (Al-LBSF) cells.

  13. Disilicon complexes with two hexacoordinate Si atoms: paddlewheel-shaped isomers with (ClN4 )Si-Si(S4 Cl) and (ClN2 S2 )Si-Si(S2 N2 Cl) skeletons.

    Science.gov (United States)

    Wagler, Jörg; Brendler, Erica; Heine, Thomas; Zhechkov, Lyuben

    2013-10-11

    The reaction of 1-methyl-3-trimethylsilylimidazoline-2-thione with hexachlorodisilane proceeds toward substitution of four of the disilane Cl atoms during the formation of disilicon complexes with two neighboring hexacoordinate Si atoms. The N,S-bidentate methimazolide moieties adopt a buttressing role, thus forming paddlewheel-shaped complexes of the type ClSi(μ-mt)4 SiCl (mt=methimazolyl). Most interestingly, three isomers (i.e., with (ClN4 )SiSi(S4 Cl), (ClN3 S)SiSi(S3 NCl), and (ClN2 S2 )SiSi(S2 N2 Cl) skeletons as so-called (4,0), (3,1), and cis-(2,2) paddlewheels) were detected in solution by using (29) Si NMR spectroscopic analysis. Two of these isomers could be isolated as crystalline solids, thus allowing their molecular structures to be analyzed by using X-ray diffraction studies. In accord with time-dependent NMR spectroscopy, computational analyses proved the cis-(2,2) isomer with a (ClN2 S2 )SiSi(S2 N2 Cl) skeleton to be the most stable. The compounds presented herein are the first examples of crystallographically evidenced disilicon complexes with two SiSi-bonded octahedrally coordinated Si atoms and representatives of the still scarcely explored class of Si coordination compounds with sulfur donor atoms.

  14. Near-interface Si substrate 3d metal contamination during atomic layer deposition processing detected by electron spin resonance

    Science.gov (United States)

    Nguyen, A. P. D.; Stesmans, A.; Hiller, D.; Zacharias, M.

    2012-06-01

    A K- and Q-band electron spin resonance (ESR) study has been carried out on (100)Si/SiO2 entities manufactured by low temperature (150 °C) atomic layer deposition (ALD) of a high-quality SiO2 layer on Si using 3-aminopropyltriethoxysilane, H2O, and ozone in a three-step process. Whereas previous work has demonstrated the high quality of the deposited SiO2 layer, the current ESR analysis reports on the tracing of growth-related contamination of near interface Si substrate layers by two transition metals. This includes, first, detection of the signal of interstitial Cr+ (S = 5/2) impurities in c-Si, characterized by an isotropic central g value of 1.9980 ± 0.0002, an isotropic 53Cr (I = 3/2) hyperfine interaction of splitting Aiso = 11.8 G, and cubic crystal field splitting parameter a = +32.2 G, well in agreement with the known bulk c-Si case; A small anisotropic contribution to the hyperfine interaction has additionally been revealed. The total Cr+ defect density is inferred as ˜5 × 1011 cm-2. Second, a single signal is observed at isotropic g = 2.070 ± 0.001, corresponding to interstitial Fe impurities (Fei)0 (S = 1) positioned in a c-Si matrix. Defect density depth profiling reveals the impurities to be confined to a few μm thick Si substrate top layer, the density decaying exponential-like from the Si/SiO2 interface inward the Si substrate. The total of the results points to a contamination of reactor-environment origin, connected with the layer deposition process. It concerns a weak contamination, in which detection the ESR technique emerges as a powerful technique able to unveil very low levels of contamination of near-surface Si substrate layers.

  15. Model, First-Principle Calculation of Ammonia Dissociation on Si(100 Surface. Importance of Proton Tunneling

    Directory of Open Access Journals (Sweden)

    Marek Z. Zgierski

    2003-06-01

    Full Text Available Abstract: The dissociation of an ammonia molecule on a cluster of Si atoms simulating the 100 silicon crystal structure with two Si dimers has been investigated by means of the DFT and an approximate instanton methods. The model corresponds to the low coverage limit of the surface. Absolute rate constants of two different dissociation paths are evaluated together with deuterium isotope effects. It is demonstrated that, even at room temperatures, the process is dominated by tunneling and that dissociation to a silicon atom of the adjacent dimer, rather than a silicon within the same dimer, is the prevailing mechanism. This leads to creation of a metastable structure which will slowly decay through a two-step hydrogen atom migration towards the absolute minimum on the potential energy surface corresponding to the NH2 group and the hydrogen atom residing in the same dimer.

  16. The surface potential of the Si nanostructure on a Si (1 1 1) 7x7 surface generated by contact of a cantilever tip

    Energy Technology Data Exchange (ETDEWEB)

    Shiota, T.; Nakayama, K

    2002-12-30

    A Si microstructure on a Si (1 1 1) 7x7 surface was investigated by a noncontact atomic force microscopy (ncAFM) and a scanning Kelvin probe microscopy (SKPM) in ultra high vacuum. The Si microstructure was generated by intermittent contact of a cantilever tip. It was found by the ncAFM and SKPM observations that the Si mound with a height of 1 A and a width of 30 nm was generated, and the surface potential of the small mound was 0.1 V lower than that of the 7x7 domain. A quenched Si (1 1 1) surface was also observed by the ncAFM and SKPM. The differences in height and potential between the reconstructed 7x7 and the disordered 1x1 domains were about 1 A and 0.1 V, respectively. Therefore, it was concluded that there appeared the disordered 1x1 structure on the surface of the Si small mound, lowering the surface potential by 0.1 V.

  17. Formation mechanisms of nano and microcones by laser radiation on surfaces of Si, Ge, and SiGe crystals.

    Science.gov (United States)

    Medvid, Artur; Onufrijevs, Pavels; Jarimaviciute-Gudaitiene, Renata; Dauksta, Edvins; Prosycevas, Igoris

    2013-06-04

    In this work we study the mechanisms of laser radiation interaction with elementary semiconductors such as Si and Ge and their solid solution SiGe. As a result of this investigation, the mechanisms of nanocones and microcones formation on a surface of semiconductor were proposed. We have shown the possibility to control the size and the shape of cones both by the laser. The main reason for the formation of nanocones is the mechanical compressive stresses due to the atoms' redistribution caused by the gradient of temperature induced by strongly absorbed laser radiation. According to our investigation, the nanocone formation mechanism in semiconductors is characterized by two stages. The first stage is characterized by formation of a p-n junction for elementary semiconductors or of a Ge/Si heterojunction for SiGe solid solution. The generation and redistribution of intrinsic point defects in elementary semiconductors and Ge atoms concentration on the irradiated surface of SiGe solid solution in temperature gradient field take place at this stage due to the thermogradient effect which is caused by strongly absorbed laser radiation. The second stage is characterized by formation of nanocones due to mechanical plastic deformation of the compressed Ge layer on Si. Moreover, a new 1D-graded band gap structure in elementary semiconductors due to quantum confinement effect was formed. For the formation of microcones Ni/Si structure was used. The mechanism of the formation of microcones is characterized by two stages as well. The first stage is the melting of Ni film after irradiation by laser beam and formation of Ni islands due to surface tension force. The second step is the melting of Ni and subsequent manifestations of Marangoni effect with the growth of microcones.

  18. Oxidation of the Si(100) surface promoted by Sr overlayer - An X-ray photoemission study. [high temperature superconductors

    Science.gov (United States)

    Mesarwi, A.; Fan, W. C.; Ignatiev, A.

    1990-01-01

    The interaction of strontium films with the underlaying Si (100) surface and the Sr-promoted low-temperature oxidation of Si were investigated, using XPS, at three different Sr coverages (theta): theta = 0.55 monolayer (ML), theta = 1 ML, and theta = 1.85 ML. Oxygen adsorption was studied both at room temperature and at 500 C, and at oxygen exposures up to 2 x 10 to the 6th L (1 L = 10 to the -6th torr) and 2 x 10 to the 5th L, respectively. The XPS spectra of the Si2p, O1s, and Sr3d core levels were measured for the atomically clean Si, the Sr-covered Si, and for the Sr-covered Si after each oxygen exposure. Results indicate that Sr interacts with the Si(100) surface forming a strong ionic bond, and that Sr promotes the oxidation of the Si (100) surface.

  19. Self-excitation of Rydberg atoms at a metal surface

    Science.gov (United States)

    Bordo, V. G.

    2017-08-01

    The novel effect of self-excitation of an atomic beam propagating above a metal surface is predicted and a theory is developed. Its underlying mechanism is positive feedback provided by the reflective surface for the atomic polarization. Under certain conditions the atomic beam flying in the near field of the metal surface acts as an active device that supports sustained atomic dipole oscillations, which generate, in their turn, an electromagnetic field. This phenomenon does not exploit stimulated emission and therefore does not require population inversion in atoms. An experiment with Rydberg atoms in which this effect should be most pronounced is proposed and the necessary estimates are given.

  20. Self-excitation of Rydberg atoms at a metal surface

    DEFF Research Database (Denmark)

    Bordo, Vladimir

    2017-01-01

    The novel effect of self-excitation of an atomic beam propagating above a metal surface is predicted and a theory is developed. Its underlying mechanism is positive feedback provided by the reflective surface for the atomic polarization. Under certain conditions the atomic beam flying in the near...... field of the metal surface acts as an active device that supports sustained atomic dipole oscillations, which generate, in their turn, an electromagnetic field. This phenomenon does not exploit stimulated emission and therefore does not require population inversion in atoms. An experiment with Rydberg...... atoms in which this effect should be most pronounced is proposed and the necessary estimates are given....

  1. Growing extremely thin bulklike metal film on a semiconductor surface: Monolayer Al(111) on Si(111)

    Energy Technology Data Exchange (ETDEWEB)

    Jiang, Ying; Kim, Yong-Hyun; Zhang, S. B.; Ebert, Philipp; Yang, Shenyuan; Tang, Zhe; Wu, Kehui; Wang, E. G.

    2007-10-29

    We report combined scanning tunneling microscopy, x-ray photoelectron emission spectroscopy, electron energy loss spectroscopy, and theoretical study of the growth of ultrathin Al film on the Si(111) substrate. We show that by (i) a modification of the substrate reconstruction with a √3×√3 surface and (ii) a choice of materials with commensurate lattices, atomically flat film can be obtained even at the ultimate one monolayer limit, while maintaining a bulklike atomic structure. Detailed analysis shows that this monolayer Al(111)-1×1Al(111)-1×1 film is electronically decoupled from the Si substrate, and it shows metallic characteristics.

  2. Interaction between graphene and SiO2 surface

    OpenAIRE

    Fan, X. F.; W. T. Zheng; Shen, Z. X.; Kuo, Jer-Lai

    2011-01-01

    With first-principles DFT calculations, the interaction between graphene and SiO2 surface has been analyzed by constructing the different configurations based on {\\alpha}-quartz and cristobalite structures. The single layer graphene can stay stably on SiO2 surface is explained based on the general consideration of configuration structures of SiO2 surface. It is also found that the oxygen defect in SiO2 surface can shift the Fermi level of graphene down which opens out the mechanism of hole-do...

  3. Density Functional Theory Study on the Surface Reaction Mechanism of Atomic Layer Deposited Ta_2O_5 on Si(100) Surfaces%Ta_2O_5在Si(100)表面原子层沉积反应机理的密度泛函研究

    Institute of Scientific and Technical Information of China (English)

    任杰; 周广芬; 郭子成; 张卫

    2009-01-01

    The surface reaction mechanism of atomic layer deposited (ALD) Ta_2O_5 on silicon surfaces was studied via density functional theory. The ALD process is designed into two sequential half-reactions, i. e. , TaCl_5 and H_2O half-reactions. Both of them proceed through an analogous trapping-mediated mechanism. By comparing with the reactions of TaCl_5 on the H-terminated silicon surfaces, we find that it is both kinetically and thermodynamically more favorable for the reactions of TaCl_5 on the hydroxylated silicon surfaces. In addition, we also find that it is energetically unfavorable for the H_2O half-reactions.%采用密度泛函方法研究了以TaCl_5和H_2O作为前驱体在硅表面原子层沉积(ALD) Ta_2O_5的初始反应机理. Ta_2O_5的原子层沉积过程包括两个连续的"半反应", 即TaCl_5和H_2O"半反应". 两个"半反应"都经历了一个相似的吸附中间体反应路径. 通过H钝化和羟基预处理硅表面反应能量的比较发现, TaCl_5在羟基预处理硅的表面反应是热力学和动力学都更加有利的反应. 另外, 从能量上看, H_2O的"半反应"不容易向生成产物的方向进行.

  4. Surface-Initiated Atom Transfer Radical Polymerization from Electrospun Mats: An Alternative to Nafion

    DEFF Research Database (Denmark)

    Javakhishvili, Irakli; Dimitrov, Ivaylo; Tynelius, Oskar

    2017-01-01

    Proton exchange membranes for fuel cell applications are synthesized by surface-initiated(SI) atom transfer radical polymerization (ATRP). Poly(vinylidene fluoride-co-chlorotrifluoroethylene)is electrospun into 50 μm thick mat, which is then employed as multifunctionalinitiator for copper...

  5. Protein repellent hydrophilic grafts prepared by surface-initiated atom transfer radical polymerization from polypropylene

    DEFF Research Database (Denmark)

    Fristrup, Charlotte Juel; Jankova Atanasova, Katja; Eskimergen, Rüya

    2012-01-01

    Grafting of poly(ethylene glycol)methacrylate (PEGMA) and N,N-dimethylacrylamide (DMAAm) from UV-initiator modified polypropylene (PP) was performed by Surface-Initiated Atom Transfer Radical Polymerization (SI-ATRP). The modification and hydrophilization of the PP substrates were confirmed...

  6. Photoionization microscopy of hydrogen atom near a metal surface

    Institute of Scientific and Technical Information of China (English)

    Yang Hai-Feng; Wang Lei; Liu Xiao-Jun; Liu Hong-Ping

    2011-01-01

    We have studied the ionization of Rydberg hydrogen atom near a metal surface with a semiclassical analysis of photoionization microscopy. Interference patterus of the electron radial distribution are calculated at different scaled energies above the classical saddle point and at various atom-surface distances. We find that different types of trajectories contribute predominantly to different manifolds in a certain interference pattern. As the scaled energy increases, the structure of the interference pattern evolves smoothly and more types of trajectories emerge. As the atom approaches the metal surface closer, there are more types of trajectories contributing to the interference pattern as well. When the Rydberg atom comes very close to the metal surface or the scaled energy approaches the zero field ionization energy,the potential induced by the metal surface will make atomic system chaotic. The results also show that atoms near a metal surface exhibit similar properties like the atoms in the parallel electric and magnetic fields.

  7. Using Atom-Probe Tomography to Understand Zn O ∶Al /SiO 2/Si Schottky Diodes

    Science.gov (United States)

    Jaramillo, R.; Youssef, Amanda; Akey, Austin; Schoofs, Frank; Ramanathan, Shriram; Buonassisi, Tonio

    2016-09-01

    We use electronic transport and atom-probe tomography to study Zn O ∶Al /SiO 2/Si Schottky diodes on lightly doped n - and p -type Si. We vary the carrier concentration in the ZnO ∶Al films by 2 orders of magnitude, but the Schottky barrier height remains nearly constant. Atom-probe tomography shows that Al segregates to the interface, so that the ZnO ∶Al at the junction is likely to be metallic even when the bulk of the ZnO ∶Al film is semiconducting. We hypothesize that the observed Fermi-level pinning is connected to the insulator-metal transition in doped ZnO. This implies that tuning the band alignment at oxide/Si interfaces may be achieved by controlling the transition between localized and extended states in the oxide, thereby changing the orbital hybridization across the interface.

  8. Influence of the step properties on submonolayer growth of Ge and Si at the Si(111) surface

    Energy Technology Data Exchange (ETDEWEB)

    Romanyuk, Konstantin

    2009-10-21

    preferred steps direction resulting into different islands shapes. The symmetry of the properties of the different step directions can determine the symmetry of the 2D islands. The growth shape of reconstructed 2D islands (nanostructures) on reconstructed surfaces can deviate from the internal symmetry of the substrate and the island. An analysis of the symmetry of the combined system of reconstructed substrate and island can deduce predictions for the island growth shape. It was found experimentally that the shape of two-dimensional (2D) Si or Ge islands has a lower symmetry than the threefold symmetry of the underlying Si(111) substrate if Bi is used as a surfactant during growth. Arrow-shaped or rhomb-shaped 2D islands were observed by scanning tunneling microscopy. This symmetry breaking was explained by a mutual shift between the surface reconstructions present on the substrate and on the islands. The mutual shift results into different step structure for initially symmetry related step directions. Using the kinematic Wulff construction the growth velocities of the steps could be determined from the island shape if the nucleation center had been located by a marker technique. The structural stability of 2D SiGe nanostructures was studied by scanning tunneling microscopy (STM). The formation of pits with a diameter of 2 - 30 nm in one atomic layer thick Ge stripes was observed. The unanticipated pit formation occurs due to an energetically driven motion of the Ge atoms out of the Ge stripe towards the Si terminated step edge followed by an entropy driven GeSi intermixing at the step edge. The pit formation can be also used for nanostructuring. Using conditions at which pit formation is enhanced the fabrication of freestanding GeSi stipes with single digit nanometer width is possible. Continuous {proportional_to} 8 nm wide freestanding GeSi wires have been fabricated by pit coalescence. (orig.)

  9. Atomic-level imaging, processing and characterization of semiconductor surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Kazmerski, L.L.

    1995-08-22

    A method for selecting and removing single specific atoms from a solid material surface uses photon biasing to break down bonds that hold the selected atom in the lattice and to reduce barrier effects that hold the atom from transferring to a probe. The photon bias is preferably light or other electromagnetic radiation with a wavelength and frequency that approximately matches the wave function of the target atom species to be removed to induce high energy, selective thermionic-like vibration. An electric field potential is then applied between the probe and the surface of the solid material to pull the atom out of the lattice and to transfer the atom to the probe. Different extrinsic atoms can be installed in the lattice sites that are vacated by the removed atoms by using a photon bias that resonates the extrinsic atom species, reversing polarity of the electric field, and blowing gas comprising the extrinsic atoms through a hollow catheter probe. 8 figs.

  10. Atomic-level imaging, processing and characterization of semiconductor surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Kazmerski, Lawrence L. (Lakewood, CO)

    1995-01-01

    A method for selecting and removing single specific atoms from a solid material surface uses photon biasing to break down bonds that hold the selected atom in the lattice and to reduce barrier effects that hold the atom from transferring to a probe. The photon bias is preferably light or other electromagnetic radiation with a wavelength and frequency that approximately matches the wave function of the target atom species to be removed to induce high energy, selective thermionic-like vibration. An electric field potential is then applied between the probe and the surface of the solid material to pull the atom out of the lattice and to transfer the atom to the probe. Different extrinsic atoms can be installed in the lattice sites that are vacated by the removed atoms by using a photon bias that resonates the extrinsic atom species, reversing polarity of the electric field, and blowing gas comprising the extrinsic atoms through a hollow catheter probe.

  11. Analysis of the Si(111) surface prepared in chemical vapor ambient for subsequent III-V heteroepitaxy

    Science.gov (United States)

    Zhao, W.; Steidl, M.; Paszuk, A.; Brückner, S.; Dobrich, A.; Supplie, O.; Kleinschmidt, P.; Hannappel, T.

    2017-01-01

    For well-defined heteroepitaxial growth of III-V epilayers on Si(111) substrates the atomic structure of the silicon surface is an essential element. Here, we study the preparation of the Si(111) surface in H2-based chemical vapor ambient as well as its atomic structure after contamination-free transfer to ultrahigh vacuum (UHV). Applying complementary UHV-based techniques, we derive a complete picture of the atomic surface structure and its chemical composition. X-ray photoelectron spectroscopy measurements after high-temperature annealing confirm a Si surface free of any traces of oxygen or other impurities. The annealing in H2 ambient leads to a monohydride surface termination, as verified by Fourier-transform infrared spectroscopy. Scanning tunneling microscopy confirms a well ordered, atomically smooth surface, which is (1 × 1) reconstructed, in agreement with low energy electron diffraction patterns. Atomic force microscopy reveals a significant influence of homoepitaxy and wet-chemical pretreatment on the surface morphology. Our findings show that wet-chemical pretreatment followed by high-temperature annealing leads to contamination-free, atomically flat Si(111) surfaces, which are ideally suited for subsequent III-V heteroepitaxy.

  12. Self-organized arrays of Cd nanocluster on Si (111)-7×7 surface

    Science.gov (United States)

    Hao, Shao-Jie; Xiao, Hua-Fang; Ye, Juan; Sun, Kai; Tao, Min-Long; Tu, Yu-Bing; Wang, Ya-Li; Xie, Zheng-Bo; Wang, Jun-Zhong

    2017-02-01

    We studied the self-organization of Cd clusters on Si(111)-7×7 surface with an ultrahigh vacuum scanning tunneling microcopy (STM). Highly-ordered arrays of Cd nanoclusters have been fabricated by elevating the substrate temperature. The Cd clusters occupy equally the faulted and unfaulted half-unit cells of Si(111)-7×7 without obvious preference to either of them, forming Cd cluster pairs or hexamers. Furthermore, high-resolution STM images demonstrate that the charge transfer between Cd and Si atoms is responsible for cluster-cluster attractions, which in turn drive the self-organization of Cd nanoclusters into highly ordered arrays.

  13. Pt-Si Bifunctional Surfaces for CO and Methanol Electro-Oxidation

    DEFF Research Database (Denmark)

    Permyakova, Anastasia A.; Han, Binghong; Jensen, Jens Oluf

    2015-01-01

    Bimetallic surfaces offer activity benefits derived from synergistic effects among active sites with uniquely different functions, which is particularly important for the development of highly effective heterogeneous catalysts for specific technological applications, such as energy conversion...... and storage. Here we report on Pt-Si bulk samples prepared by arc-melting, for the first time, with high activities toward the electro-oxidation of CO and methanol. Increasing the Si concentration on the surface was correlated with the shifts of onset oxidation potentials to lower values and higher activities...... for CO and methanol electro-oxidation. It is proposed that the reaction on the Pt-Si catalyst could follow a Langmuir-Hinshelwood type of mechanism, where substantially enhanced catalytic activity is attributed to the fine-tuning of the surface Pt-Si atomic structure....

  14. Surface alloy formation of noble adatoms adsorbed on Si(111)-{radical}3x{radical}3-Pb surface: a first-principles study

    Energy Technology Data Exchange (ETDEWEB)

    Li Chong; Wang Fei; Sun, Q; Jia Yu, E-mail: jiayu@zzu.edu.cn [Center for Clean Energy and Quantum Structures, and School of Physics and Engineering, Zhengzhou University, Zhengzhou 450052 (China)

    2011-07-06

    The geometric structures, stability and electronic properties of initial stages of surface alloy formation for noble atoms adsorbed on Si(111)-{radical}3x{radical}3-Pb surfaces have been comparatively and extensively studied by using first-principles calculations within density functional theory. Our results revealed that an Au trimer rather than a tetramer adsorption induces a surface alloy by combining with Pb atoms in covalent bonds, exhibiting semiconducting characteristics due to the localization of surface states. The stability of the two-dimensional (2D) surface alloy obeys the Hume-Rothery rule. The electronic structures of the 2D surface alloy are sensitive to the number of Au adatoms and can be modulated by the quantity of Au adatoms. Unlike the Au atoms, our further calculations indicated that adsorption of Ag or Cu atoms on the surface cannot form a surface alloy with Pb atoms in the surface layer due to a weaker interaction or smaller radius.

  15. Effect of Si interface surface roughness to the tunneling current of the Si/Si{sub 1-x}Ge{sub x}/Si heterojunction bipolar transistor

    Energy Technology Data Exchange (ETDEWEB)

    Hasanah, Lilik, E-mail: lilikhasanah@upi.edu; Suhendi, Endi; Tayubi, Yuyu Rahmat; Yuwono, Heru [Department of Physics Education, Universitas Pendidikan Indonesia, Jl. Setiabudhi 229 Bandung 40154 (Indonesia); Nandiyanto, Asep Bayu Dani [Department Kimia, Universitas Pendidikan Indonesia, Jl. Setiabudhi 229 Bandung 40154 (Indonesia); Murakami, Hideki [Graduate School of Advanced Sciences of Matter, Hiroshima University, Higashi-Hiroshima 739-8527 (Japan); Khairrurijal [Physics of Electronic Materials Research Division, Institut Teknologi Bandung, Bandung 40132 (Indonesia)

    2016-02-08

    In this work we discuss the surface roughness of Si interface impact to the tunneling current of the Si/Si{sub 1-x}Ge{sub x}/Si heterojunction bipolar transistor. The Si interface surface roughness can be analyzed from electrical characteristics through the transversal electron velocity obtained as fitting parameter factor. The results showed that surface roughness increase as Ge content of virtual substrate increase This model can be used to investigate the effect of Ge content of the virtual substrate to the interface surface condition through current-voltage characteristic.

  16. Structure determination of the indium induced Si(001)-(4X3) reconstruction by surface x-ray diffraction and scanning tunneling microscopy

    DEFF Research Database (Denmark)

    Bunk, O.; Falkenberg, G.; Seehofer, L.;

    1998-01-01

    The indium-induced Si(001)-(4 X 3) reconstruction has been investigated by surface X-ray diffraction (SXRD) measurements with synchrotron radiation and scanning tunneling microscopy (STM). The Patterson function analysis enables us to exclude In dimers as a structural element in this reconstruction....... We present a new structural model which includes 6 In atoms threefold coordinated to Si atoms and 5 displaced Si atoms per unit cell. Relaxations down to the sixth layer were determined. 'Trimers' made up of In-Si-In atoms are a key structural element. (C) 1998 Elsevier Science B.V....

  17. Evolution of kinetically controlled In-induced surface structure on Si(5 5 7) surface

    Energy Technology Data Exchange (ETDEWEB)

    Chauhan, Amit Kumar Singh [Physics of Energy Harvesting, (CSIR-NPL), Dr. K.S. Krishnan Road, New Delhi 110012 (India); Department of Physics, JMI, New Delhi 110025 (India); Eldose, Nirosh M.; Mishra, Monu [Physics of Energy Harvesting, (CSIR-NPL), Dr. K.S. Krishnan Road, New Delhi 110012 (India); Niazi, Asad; Nair, Lekha [Department of Physics, JMI, New Delhi 110025 (India); Gupta, Govind, E-mail: govind@nplindia.org [Physics of Energy Harvesting, (CSIR-NPL), Dr. K.S. Krishnan Road, New Delhi 110012 (India)

    2014-09-30

    Highlights: • Evolution of In induced superstructures on Si(5 5 7) surface during RT and HT adsorption/desorption process. • Kinetics is governed by substrate temperature which exhibits various growth modes (FM, SK, VB) under different conditions. • Strain relaxation play significant role in the commencement of desorption/rearrangement of atoms. • A consolidated phase diagram of In/Si(5 5 7) interface has been reported with new √3 × √3-R30° and 4 × 1 phases. - Abstract: This paper introduces issue of kinetically controlled and temperature driven superstructural phase transition of Indium (In) on atomically clean high index Si(5 5 7)-7 × 1 surface. Auger electron spectroscopy analysis reveals that at room-temperature (RT) with a controlled incident flux of 0.002 ML/s; In overlayers evolve through the Frank-van der Merwe growth mode and yield a (1 × 1) diffraction pattern for coverage ≥1 ML. For substrate temperature <500°C, growth of In follows Stranski–Krastanov growth mode while for temperature >500°C island growth is observed. On annealing the In/Si(5 5 7) interface in the temperature range 250–340°C, clusters to two dimensional (2D) layer transformation on top of a stable monolayer is predominated. In-situ RT and HT adsorption and thermal desorption phenomena revealed the formation of coverage and temperature dependent thermally stable In induced superstructural phases such as (4 × 1) at 0.5 ML (520°C), (√3 × √3-R30°) at 0.3 ML (560°C) and (7 × 7) at 0.1 ML (580°C). These indium induced superstructures could be utilized as potential substrate for the growth of various exotic 1D/2D structures.

  18. Hydrophilization of Poly(ether ether ketone) Films by Surface-initiated Atom Transfer Radical Polymerization

    DEFF Research Database (Denmark)

    Fristrup, Charlotte Juel; Eskimergen, Rüya; Burkrinsky, J.T.

    2008-01-01

    -modified PEEK using Surface-Initiated Atom Transfer Radical Polymerization (SI ATRP). Surface reduction of PEEK to form hydroxyl groups [1, 2, 3] was .performed prior to the attachment of 2-bromoisobutyrate initiating groups. Each modification step of PEEK as well as the polymer grafting was followed...... and confirmed by ATR FTIR, water contact ang;le, and Thermal Gravimetric Analysis (TGA). The surface topography was evaluated by "Atomic Force Microscopy (AFM). X-ray Photoelectron Spectroscopy (XPS) has been used to investigate the degree of functionalization. The performed modification allowed for successful...

  19. Hydrophilization of Poly(ether ether ketone) Films by Surface-initiated Atom Transfer Radical Polymerization

    DEFF Research Database (Denmark)

    Fristrup, Charlotte Juel; Eskimergen, Rüya; Burkrinsky, J.T.

    2008-01-01

    -modified PEEK using Surface-Initiated Atom Transfer Radical Polymerization (SI ATRP). Surface reduction of PEEK to form hydroxyl groups [1, 2, 3] was .performed prior to the attachment of 2-bromoisobutyrate initiating groups. Each modification step of PEEK as well as the polymer grafting was followed...... and confirmed by ATR FTIR, water contact ang;le, and Thermal Gravimetric Analysis (TGA). The surface topography was evaluated by "Atomic Force Microscopy (AFM). X-ray Photoelectron Spectroscopy (XPS) has been used to investigate the degree of functionalization. The performed modification allowed for successful...

  20. On the atomic structure of liquid Ni-Si alloys: a neutron diffraction study

    Energy Technology Data Exchange (ETDEWEB)

    Gruner, S; Marczinke, J; Hoyer, W [Institute of Physics, Chemnitz University of Technology, D-09107 Chemnitz (Germany); Hennet, L [CNRS-CEMHTI, University of Orleans, F-45071 Orleans (France); Cuello, G J, E-mail: sascha.gruner@physik.tu-chemnitz.d [Institute Laue-Langevin, PO Box 156, F-38042 Grenoble (France)

    2009-09-23

    The atomic structure of the liquid NiSi and NiSi{sub 2} alloys is investigated by means of neutron diffraction experiments with isotopic substitution. From experimental data-sets obtained using four Ni isotopes, partial structure factors and pair correlation functions are obtained by applying a reverse Monte Carlo modelling approach. Both alloys were found to exhibit a strong tendency to hetero-coordination within the first coordination shell. In particular, covalent Si-Si bonds with somewhat greater distances seem to influence the structure of the liquid NiSi alloy.

  1. Reactions between monolayer Fe and Si(001) surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Hasegawa, M.; Kobayashi, N.; Hayashi, N. [Electrotechnical Lab., Tsukuba, Ibaraki (Japan)

    1997-03-01

    Reactions between 1.5 monolayer(ML) Fe deposited on Si(001)-2x1 and -dihydride surfaces were studied in situ by reflection high-energy electron diffraction and time-of-flight ion scattering spectrometry with the use of 25 keV H ions. The reactions between Fe and Si which were successively deposited on Si(001)-dihydride surface were also studied. After the room temperature deposition Fe reacted with Si(001)-2x1 substrate resulting in the formation of polycrystalline Fe5Si3. By annealing to 560-650degC composite heteroepitaxial layer of both type A and type B {beta}-FeSi2 was formed. On the dihydride surface polycrystalline Fe was observed after 1.5ML Fe deposition at room temperature, and reaction between Fe and Si(001)-dihydride surface is not likely at room temperature. We observed 3D rough surface when we deposited only Fe layer on the dihydride surface and annealed above 700degC. The hydrogen termination of Si(001) surface prevents the deposited Fe from diffusing into the substrate below 500degC, however the annealing above 710degC leads to the diffusion. We obtained 2D ordered surface, which showed 3x3 RHEED pattern as referenced to the primitive unreconstructed Si(001) surface net, when we deposited 2.5ML Fe and 5.8ML Si successively onto Si(001)-dihydride surface and annealed to 470degC. (author)

  2. Deposition of size-selected atomic clusters on surfaces

    CERN Document Server

    Carroll, S J

    1999-01-01

    implant into the surface. For Ag sub 2 sub 0 -Ag sub 2 sub 0 sub 0 clusters, the implantation depth is found to scale linearly with the impact energy and inversely with the cross-sectional area of the cluster, with an offset due to energy lost to the elastic compression of the surface (Paper VI). For smaller (Ag sub 3) clusters the orientation of the cluster with respect to the surface and the precise impact site play an important role; the impact energy has to be 'focused' in order for cluster implantation to occur (Paper VII). The application of deposited clusters for the creation of Si nanostructures by plasma etching is explored in Paper VIII. This dissertation presents technical developments and experimental and computational investigations concerned with the deposition of atomic clusters onto surfaces. It consists of a collection of papers, in which the main body of results are contained, and four chapters presenting a subject review, computational and experimental techniques and a summary of the result...

  3. Incorporation of Si and SiO(x) into diamond-like carbon films: impact on surface properties and osteoblast adhesion.

    Science.gov (United States)

    Randeniya, L K; Bendavid, A; Martin, P J; Amin, Md S; Preston, E W; Magdon Ismail, F S; Coe, S

    2009-06-01

    The interaction of human osteoblast cells with diamond-like carbon films incorporating silicon and silicon oxide (SiO(x), 1 activated chemical vapour deposition method was investigated. Cell culture studies were performed for films with Si contents ranging from approximately 4 at.% to 15 at.%. Substantial differences between Si-incorporated and SiO(x)-incorporated films were found for the bonding environments of Si atoms and the hybridization of underlying carbon structures. However, osteoblast-attachment studies did not show statistically significant trends in properties of cell growth (count, area and morphology) that can be attributed either to the Si content of the films or to the chemical structure of the films. The surface energy decreased by 40% as the Si content of the SiO(x) incorporated DLC films increased to 13 at.%. The cell adhesion properties however did not change in response to lowering of the surface energy. The incorporation of both Si and SiO(x) leads to a beneficial reduction in the residual stress of the films. The average roughness of the films increases and the hardness decreases when Si and SiO(x) are added to DLC films. The impact of these changes for load-bearing biomedical applications can be determined only by carefully controlled experiments using anatomic simulators.

  4. Characterization of a SiC/SiC composite by X-ray diffraction, atomic force microscopy and positron spectroscopies

    Energy Technology Data Exchange (ETDEWEB)

    Brauer, G. [Institut fuer Ionenstrahlphysik und Materialforschung, Forschungszentrum Rossendorf e.V., PF 510119, D-01314 Dresden (Germany)]. E-mail: g.brauer@fz-rossendorf.de; Anwand, W. [Institut fuer Ionenstrahlphysik und Materialforschung, Forschungszentrum Rossendorf e.V., PF 510119, D-01314 Dresden (Germany); Eichhorn, F. [Institut fuer Ionenstrahlphysik und Materialforschung, Forschungszentrum Rossendorf e.V., PF 510119, D-01314 Dresden (Germany); Skorupa, W. [Institut fuer Ionenstrahlphysik und Materialforschung, Forschungszentrum Rossendorf e.V., PF 510119, D-01314 Dresden (Germany); Hofer, C. [Institut fuer Physik, Montanuniversitaet Leoben, Franz Josef Str. 18, A-8700 Leoben (Austria); Teichert, C. [Institut fuer Physik, Montanuniversitaet Leoben, Franz Josef Str. 18, A-8700 Leoben (Austria); Kuriplach, J. [Department of Low Temperature Physics, Faculty of Mathematics and Physics, Charles University, V Holesovickach 2, CZ-180 00 Prague (Czech Republic); Cizek, J. [Department of Low Temperature Physics, Faculty of Mathematics and Physics, Charles University, V Holesovickach 2, CZ-180 00 Prague (Czech Republic); Prochazka, I. [Department of Low Temperature Physics, Faculty of Mathematics and Physics, Charles University, V Holesovickach 2, CZ-180 00 Prague (Czech Republic); Coleman, P.G. [Department of Physics, University of Bath, Bath BA2 7 AY (United Kingdom); Nozawa, T. [Metals and Ceramics Division, Oak Ridge National Laboratory, P.O. Box 2008, MS6151, Oak Ridge, TN 37831-6151 (United States); Kohyama, A. [Institute of Advanced Energy, Kyoto University, Gokasho, Uji, Kyoto 611-0011 (Japan)

    2006-02-28

    A SiC/SiC composite is characterized by X-ray diffraction, atomic force microscopy and various positron spectroscopies (slow positron implantation, positron lifetime and re-emission). It is found that besides its main constituent 3C-SiC the composite still must contain some graphite. In order to better interpret the experimental findings of the composite, a pyrolytic graphite sample was also investigated by slow positron implantation and positron lifetime spectroscopies. In addition, theoretical calculations of positron properties of graphite are presented.

  5. Density-functional study of Mn monosilicide on the Si(111) surface: Film formation versus island nucleation

    Science.gov (United States)

    Hortamani, Mahbube; Kratzer, Peter; Scheffler, Matthias

    2007-12-01

    The stability of thin films and of small crystallites of Mn monosilicide (MnSi) on the Si(111) surface is investigated by density-functional theory calculations. Extending previous studies of MnSi/Si(001) , our calculations indicate that MnSi films on Si(111) have similar electronic and magnetic properties, i.e., large magnetic moments at the Mn atoms near the surfaces and interfaces and a high degree of spin polarization at the Fermi level. Hence, such MnSi films could be interesting as a spintronics material compatible with silicon. Moreover, from our calculated total energies we conclude that the Si(111) substrate should be more suitable to grow MnSi layers than the Si(001) substrate. This result is obtained by analyzing the conditions for the formation of three-dimensional (3D) MnSi islands, either in the B20 crystal structure or as pseudomorphic islands in the B2 structure: On Si(001), 3D islands, even if they are just a few lattice constants wide, are found to be already more stable than a homogeneous MnSi film. A bipyramidal “iceberg” island consisting of MnSi in the B20 structure on the Si(001) substrate is found to be most stable among the structures investigated. For MnSi on Si(111), however, our calculations show that the nucleus for forming a 3D island is larger. Therefore, Mn deposition initially leads to the formation of flat 2D islands. On Si(111), the lowest-energy structure for such islands is found to be similar to the B20 structure of bulk MnSi, whereas on Si(001) this structure is incompatible with the substrate lattice. Our results are in agreement with the experimental observations, formation of an almost closed film with (3×3) structure on Si(111), and 3D island formation on Si(001).

  6. Mixing of Cr and Si atoms induced by noble gas ions irradiation of Cr/Si bilayers

    Energy Technology Data Exchange (ETDEWEB)

    Tobbeche, S., E-mail: said_tobbeche@yahoo.com [Faculte des Sciences, Universite El-Hadj Lakhdar, Batna 05000 (Algeria); Boukhari, A. [Faculte des Sciences, Universite El-Hadj Lakhdar, Batna 05000 (Algeria); Khalfaoui, R. [Faculte des Sciences, Universite M. Bougara, Boumerdes 35000 (Algeria); Amokrane, A. [Faculte de Physique, USTHB, B.P. 32 El-Alia, Bab-Ezzouar 16111 (Algeria); Ecole Nationale Preparatoire aux Etudes d' Ingeniorat, Route Nationale, Rouiba (Algeria); Benazzouz, C.; Guittoum, A. [Centre de Recherche Nucleaire d' Alger, 02, Boulevard Frantz Fanon, B.P. 399 Alger-Gare (Algeria)

    2011-12-15

    Cr/Si bilayers were irradiated at room temperature with 120 keV Ar, 140 keV Kr and 350 keV Xe ions to fluences ranging from 10{sup 15} to 2 Multiplication-Sign 10{sup 16} ions/cm{sup 2}. The thickness of Cr layer evaporated on Si substrate was about 400 A. Rutherford backscattering spectrometry (RBS) was used to investigate the atomic mixing induced at the Cr-Si interface as function of the incident ion mass and fluence. We observed that for the samples irradiated with Ar ions, RBS yields from both Cr layer and Si substrate are the same as before the irradiation. There is no mixing of Cr and Si atoms, even at the fluence of 2 Multiplication-Sign 10{sup 16} ions/cm{sup 2}. For the samples irradiated with Kr ions, a slight broadening of the Cr and Si interfacial edges was produced from the fluence of 5 Multiplication-Sign 10{sup 15} ions/cm{sup 2}. The broadening of the Cr and Si interfacial edges is more pronounced with Xe ions particularly to the fluence of 10{sup 16} ions/cm{sup 2}. The interface broadening was found to depend linearly on the ion fluence and suggests that the mixing is like a diffusion controlled process. The experimental mixing rates were determined and compared with values predicted by ballistic and thermal spike models. Our experimental data were well reproduced by the thermal spikes model.

  7. Atomic Scale Understanding of Poly-Si/SiO2/c-Si Passivated Contacts: Passivation Degradation Due to Metallization

    Energy Technology Data Exchange (ETDEWEB)

    Aguiar, Jeffery A.; Young, David; Lee, Benjamin; Nemeth, William; Harvey, Steve; Aoki, Toshihiro; Al-Jassim, Mowafak; Stradins, Paul

    2016-11-21

    The key attributes for achieving high efficiency crystalline silicon solar cells include class leading developments in the ability to approach the theoretical limits of silicon solar technology (29.4% efficiency). The push for high efficiency devices is further compounded with the clear need for passivation to reduce recombination at the metal contacts. At the same time there is stringent requirement to retain the same material device quality, surface passivation, and performance characteristics following subsequent processing. The development of passivated silicon cell structures that retain active front and rear surface passivation and overall material cell quality is therefore a relevant and active area of development. To address the potential outcomes of metallization on passivated silicon stack, we report on some common microstructural features of degradation due to metallization for a series of silicon device stacks. A fundamental materials understanding of the metallization process on retaining high-efficiency passivated Si devices is therefore gained over these series of results.

  8. Investigation of the 6H-SiC (0001) surface by AFM

    Institute of Scientific and Technical Information of China (English)

    Shouzhen Jiang; Guangwei Yu; Yingmin Wang; Xiaobo Hu; Xiangang Xu; Minhua Jiang

    2008-01-01

    Micropipe and step structures on 6H-SiC (0001) surface were investigated by an atomic force microscopy (AFM). On the facet, all micropipes examined are the origins of spiral steps, indicating that dislocations intersect the surface at these points. Micro-pipes are empty-core super-dislocations as originally described by Frank. The micropipe radius increases with the square of the dis-location Burgers vector. From the center to the periphery, step structures change with different surface inehnations. Regular step is observed within the central faceted area. Step bunching and atomically rough surfaces are observed within the peripheral convex area.If the inclination with respect to the (0001) plane is large enough, step bunching of 15R-SiC can be observed.

  9. High-efficiency si/polymer hybrid solar cells based on synergistic surface texturing of Si nanowires on pyramids.

    Science.gov (United States)

    He, Lining; Lai, Donny; Wang, Hao; Jiang, Changyun; Rusli

    2012-06-11

    An efficient Si/PEDOT:PSS hybrid solar cell using synergistic surface texturing of Si nanowires (SiNWs) on pyramids is demonstrated. A power conversion efficiency (PCE) of 9.9% is achieved from the cells using the SiNW/pyramid binary structure, which is much higher than similar cells based on planar Si, pyramid-textured Si, and SiNWs. The PCE is the highest reported to-date for hybrid cells based on Si nanostructures and PEDOT.

  10. Methods for growth of relatively large step-free SiC crystal surfaces

    Science.gov (United States)

    Neudeck, Philip G. (Inventor); Powell, J. Anthony (Inventor)

    2002-01-01

    A method for growing arrays of large-area device-size films of step-free (i.e., atomically flat) SiC surfaces for semiconductor electronic device applications is disclosed. This method utilizes a lateral growth process that better overcomes the effect of extended defects in the seed crystal substrate that limited the obtainable step-free area achievable by prior art processes. The step-free SiC surface is particularly suited for the heteroepitaxial growth of 3C (cubic) SiC, AlN, and GaN films used for the fabrication of both surface-sensitive devices (i.e., surface channel field effect transistors such as HEMT's and MOSFET's) as well as high-electric field devices (pn diodes and other solid-state power switching devices) that are sensitive to extended crystal defects.

  11. Graphene on SiC(0001 inspected by dynamic atomic force microscopy at room temperature

    Directory of Open Access Journals (Sweden)

    Mykola Telychko

    2015-04-01

    Full Text Available We investigated single-layer graphene on SiC(0001 by atomic force and tunneling current microscopy, to separate the topographic and electronic contributions from the overall landscape. The analysis revealed that the roughness evaluated from the atomic force maps is very low, in accord with theoretical simulations. We also observed that characteristic electron scattering effects on graphene edges and defects are not accompanied by any out-of-plane relaxations of carbon atoms.

  12. The adsorption and reaction of fluorine on the Si(100) surface

    Science.gov (United States)

    Engstrom, J. R.; Nelson, Mark M.; Engel, Thomas

    1989-05-01

    The adsorption and reaction of both molecular and atomic flourine with the Si(100) surface has been examined under ultraligh vacuum conditions with supersonic molecular beam techniques, X-ray photoelectron spectroscopy (XPS), quadrupole mass spectrometry and low-energy ion scattering spectroscopy. Molecular flourine adsorbs dissociatively on the clean Si(100) surface with an initial (zero-coverage) probability of the adsorption of 0.46±0.02, which is essentially independent of both the incident beam energy (flouride adlayers, produced by exposing the clean Si(100) surface a 120 K to a beam of flourine, yielded SiF 2(g) and SiF 4(g) as the only gas phase reaction products. The relative yield to these two gas phase reaction products dependes strongly on the initial coverage of the flourine adatoms-below ˜ ML, SiF 2(g) in the major reaction product, whereas above ˜3 ML, the yield of SiF 2(g) remains constant while that of SiF 2(g) increases continuously. Above initial coverages of 2 ML, the thermal decomposition is terminated near 800 K by the removal of one monolayer of the silicon substrate in the form of SiF 2(g). A detailed analysis of the decomposition for coverages of 3 ML revealed complex behavior, the kinetics depending sensitively on the initial coverage of flourin adatome. For example, for initial coverages of 1-1.3 ML, zero-order kinetics were found to apply as the coverage decreases from 1.0 to 0.3 ML. A qualitative assessment of the adlayer configuration following partial decomposition suggests that the thermal decomposition in the zero-order regime proceeds inhomogenously, leaving separate domains where the local coverage of flourine is either near saturation or zero. We suggest that the spatially inhomogenous decomposition is a manifestation of preferential reactivity at surface defects such as atomic steps. Investigation of the steady-state reaction of preferential reactivity at surface defects such as atomic steps. Investigation of the steady

  13. Molecular simulation of alkyl monolayers on the Si(111)surface

    Institute of Scientific and Technical Information of China (English)

    YUAN; Shiling; (苑世领); CAI; Zhengting; (蔡政亭); XIAO; Li; (肖莉); XU; Guiying; (徐桂英); LIU; Yongjun; (刘永军)

    2003-01-01

    The structure of twelve-carbon monolayers on the H-terminated Si(111) surface is investigated by molecular simulation method. The best substitution percent on Si(111) surface obtained via molecular mechanics calculation is equal to 50%, and the (8×8) simulated cell can be used to depict the structure of alkyl monolayer on Si surface. After two-dimensional cell containing alkyl chains and four-layer Si(111) crystal at the substitution 50% is constructed, the densely packed and well-ordered monolayer on Si(111) surface can be shown through energy minimization in the suitable-size simulation cell. These simulation results are in good agreement with the experiments. These conclusions show that molecular simulation can provide otherwise inaccessible mesoscopic information at the molecular level, and can be considered as an adjunct to experiments.

  14. Mechanical properties of In/Si(111)-(8×2) investigated by atomic force microscopy

    Science.gov (United States)

    Iwata, Kota; Yamazaki, Shiro; Shiotari, Akitoshi; Sugimoto, Yoshiaki

    2017-01-01

    We use noncontact atomic force microscopy (AFM) as well as scanning tunneling microscopy (STM) to investigate the mechanical properties of quasi-one-dimensional indium chains on an In/Si(111) surface. The system shows phase transition from the 4×1 to 8×2 periodicity at temperatures near 120 K. AFM could not detect ×2 modulation along the chains near point defects at room temperature, but STM could. In contrast, the 8×2 phase at 80 K could be observed by AFM in phase with the STM image. High-resolution AFM images show that the 8×2 phase is not perturbed by mechanical interaction with the AFM tip because of misalignment between the reaction coordinates of the phase transition and the direction of the vertical force of the tip.

  15. Low-temperature one-atom-layer √{ 7} ×√{ 7}-In phase on Si(111)

    Science.gov (United States)

    Mihalyuk, A. N.; Alekseev, A. A.; Hsing, C. R.; Wei, C. M.; Gruznev, D. V.; Bondarenko, L. V.; Matetskiy, A. V.; Tupchaya, A. Y.; Zotov, A. V.; Saranin, A. A.

    2016-07-01

    The Si(111)-hex-√{ 7} ×√{ 3}-In reconstruction has been attracted considerable attention due to its superconducting properties occurring in the one-atom-layer metal film. However, the √{ 7} ×√{ 3} periodicity is a characteristic feature of this surface only at room temperature. Upon cooling to low temperatures the √{ 7} ×√{ 3} structure transforms reversibly to the √{ 7} ×√{ 7} one that should not be ignored while considering superconductivity in this system. In the present study, atomic structure of the low-temperature one-atom-layer Si(111)√{ 7} ×√{ 7}-In phase has been evaluated using scanning tunneling microscopy (STM), low-energy electron diffraction (LEED) and ab initio random structure searching (AIRSS) technique. Basing on the LEED observations, it has been found that the √{ 7} ×√{ 7}-In surface incorporates plausibly eight In atoms per √{ 7} ×√{ 7} unit cell (i.e., 1.14 ML In). AIRSS demonstrates occurrence of a set of various surface structures with very close formation energies. Some of their counterparts can be found in the experimental STM images.

  16. Evaluation of electric field intensity on atom diffusion of Cu/Ta/Si stacks during annealing

    Energy Technology Data Exchange (ETDEWEB)

    Wang, L. [Jiangsu University of Science and Technology, Key Laboratory of Advanced Welding Technology of Jiangsu Province, Zhenjiang (China); Nanjing University, Stomatology Department, Nanjing General Hospital of Nanjing Command, Medical School, Nanjing (China); Jin, L. [Nanjing University, Stomatology Department, Nanjing General Hospital of Nanjing Command, Medical School, Nanjing (China); Yu, L.H.; Dong, S.T.; Chen, J.; Xu, J.H. [Jiangsu University of Science and Technology, Key Laboratory of Advanced Welding Technology of Jiangsu Province, Zhenjiang (China)

    2016-01-15

    Cu/Ta/Si stacks were prepared and, subsequently, annealed at 650 C with different electric field intensity (0-4.0 kV/cm). The effect of electric field intensity on atomic diffusion was determined from cross-sectional TEM micrographs of Cu/Ta/Si stacks. The atomic diffusion as well as the growth of amorphous layer at Ta/Si interface tended to enhance with the increased electric field intensity at 650 C. The growth of amorphous layer obeyed a logarithmic law. The reduction in diffusion activation energy Q by increased electric field intensity will accelerate the atom diffusion, leading to significant barrier failure of Cu/Ta/Si stacks. (orig.)

  17. Experimental demonstration of single electron transistors featuring SiO{sub 2} plasma-enhanced atomic layer deposition in Ni-SiO{sub 2}-Ni tunnel junctions

    Energy Technology Data Exchange (ETDEWEB)

    Karbasian, Golnaz, E-mail: Golnaz.Karbasian.1@nd.edu; McConnell, Michael S.; Orlov, Alexei O.; Rouvimov, Sergei; Snider, Gregory L. [Electrical Engineering Department, University of Notre Dame, Indiana 46556 (United States)

    2016-01-15

    The authors report the use of plasma-enhanced atomic layer deposition (PEALD) to fabricate single-electron transistors (SETs) featuring ultrathin (≈1 nm) tunnel-transparent SiO{sub 2} in Ni-SiO{sub 2}-Ni tunnel junctions. They show that, as a result of the O{sub 2} plasma steps in PEALD of SiO{sub 2}, the top surface of the underlying Ni electrode is oxidized. Additionally, the bottom surface of the upper Ni layer is also oxidized where it is in contact with the deposited SiO{sub 2}, most likely as a result of oxygen-containing species on the surface of the SiO{sub 2}. Due to the presence of these surface parasitic layers of NiO, which exhibit features typical of thermally activated transport, the resistance of Ni-SiO{sub 2}-Ni tunnel junctions is drastically increased. Moreover, the transport mechanism is changed from quantum tunneling through the dielectric barrier to one consistent with thermally activated resistors in series with tunnel junctions. The reduction of NiO to Ni is therefore required to restore the metal-insulator-metal (MIM) structure of the junctions. Rapid thermal annealing in a forming gas ambient at elevated temperatures is presented as a technique to reduce both parasitic oxide layers. This method is of great interest for devices that rely on MIM tunnel junctions with ultrathin barriers. Using this technique, the authors successfully fabricated MIM SETs with minimal trace of parasitic NiO component. They demonstrate that the properties of the tunnel barrier in nanoscale tunnel junctions (with <10{sup −15} m{sup 2} in area) can be evaluated by electrical characterization of SETs.

  18. Electrical charge trapping at defects on the Si(111)7×7 surface

    Science.gov (United States)

    Jiang, C.-S.; Moutinho, H. R.; Romero, M. J.; Al-Jassim, M. M.; Kazmerski, L. L.

    2006-02-01

    We report on a direct measurement of electron trapping at defects on the Si(111)7×7 surface, by combining Kelvin probe force microscopy (KPFM) and scanning tunneling microscopy (STM) measurements. One-dimensional defects of atomic steps and two-dimensional defects of disordered domains were found on the surface. STM reveals that the disordered domain is located in the intersection area between three 7×7 domains. KPFM measurement shows that electrons are trapped at both the atomic steps and the disordered domains, and this electron trapping gives rise to a larger local work function on the defect region than on the defect-free 7×7 regions.

  19. Electronic transport through Si nanowires: Role of bulk and surface disorder

    DEFF Research Database (Denmark)

    Markussen, Troels; Rurali, R.; Brandbyge, Mads

    2006-01-01

    on the situation a preferable method can be identified. Several numerical results are presented to illustrate the relative merits of the two methods. Our calculations of relaxed atomic structures and their conductance properties are based on density functional theory without introducing adjustable parameters. Two...... specific models of disorder are considered: Unpassivated, surface reconstructed SiNW's are perturbed by random on-site (Anderson) disorder whereas defects in hydrogen passivated wires are introduced by randomly removed H atoms. The unpassivated wires are very sensitive to disorder in the surface whereas...

  20. Interactions between solute atoms in Fe-Si-Al-C alloys as studied by mechanical spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Sinning, H.-R., E-mail: hr.sinning@tu-bs.de [Institut fuer Werkstoffe, Technische Universitaet Braunschweig, Braunschweig (Germany); Golovin, I.S. [Physics of Metals Department, Moscow Institute of Steel and Alloys, Moscow (Russian Federation); Physics of Metals and Materials Science Department, Tula State University, Tula (Russian Federation); Strahl, A. [Institut fuer Fachdidaktik der Naturwissenschaften, TU Braunschweig (Germany); Sokolova, O.A. [Physics of Metals and Materials Science Department, Tula State University, Tula (Russian Federation); Sazonova, T. [Institut fuer Werkstoffe, Technische Universitaet Braunschweig, Braunschweig (Germany)

    2009-09-15

    In Fe-Si-Al-C alloys, point-defect relaxation includes both the interstitial carbon Snoek-type relaxation, split into a 'pure iron' (Fe-C-Fe) Snoek peak and an 'interstitial-substitutional' (Fe-C-Me; Me = Al, Si) peak, and the substitutional Zener relaxation. The influence of Al and Si, with varying Al/Si ratio, on these effects is used to study the qualitative characteristics of substitutional-interstitial (Si-C, Al-C) and substitutional-substitutional (Al-Al, Si-Si, Al-Si) interactions in these alloys. Concerning the latter, there is a mutual compensation of the elastic distortion fields, produced in the Fe matrix by the relatively bigger Al and smaller Si atoms, respectively, which largely suppresses the Zener relaxation in the ternary Fe-Si-Al alloys, probably without affecting the elastic dipole strength of interstitial carbon. From the kinetic behavior of the two components of the Snoek-type relaxation, it is concluded that the substitutional-interstitial interaction is generally attractive and sufficient for modifying the distribution of the C atoms, but not for trapping to become dominant.

  1. Atomic scale fabrication of dangling bond structures on hydrogen passivated Si(0 0 1) wafers processed and nanopackaged in a clean room environment

    Science.gov (United States)

    Kolmer, Marek; Godlewski, Szymon; Zuzak, Rafal; Wojtaszek, Mateusz; Rauer, Caroline; Thuaire, Aurélie; Hartmann, Jean-Michel; Moriceau, Hubert; Joachim, Christian; Szymonski, Marek

    2014-01-01

    Specific surfaces allowing the ultra-high vacuum (UHV) creation of electronic interconnects and atomic nanostructures are required for the successful development of novel nanoscale electronic devices. Atomically flat and reconstructed Si(0 0 1):H surfaces are serious candidates for that role. In this work such Si:H surfaces were prepared in a cleanroom environment on 200 mm silicon wafers with a hydrogen bake and were subsequently bonded together to ensure the surface protection, and allow their transportation and storage for several months in air. Given the nature of the bonding, which was hydrophobic with weak van der Waals forces, we were then able to de-bond them in UHV. We show that the quality of the de-bonded Si:H surface enables the "at will" construction of sophisticated and complex dangling bond (DB) nanostructures by atomically precise scanning tunneling microscope (STM) tip induced desorption of hydrogen atoms. The DB structures created on slightly doped Si:H samples were characterized by scanning tunneling microscopy and spectroscopy (STM/STS) performed at 4 K. Our results demonstrate that DB nanostructures fabricated on UHV de-bonded Si(0 0 1):H wafers could be directly incorporated in future electronics as interconnects and parts of nanoscale logic circuits.

  2. Atomic scale fabrication of dangling bond structures on hydrogen passivated Si(0 0 1) wafers processed and nanopackaged in a clean room environment

    Energy Technology Data Exchange (ETDEWEB)

    Kolmer, Marek; Godlewski, Szymon; Zuzak, Rafal; Wojtaszek, Mateusz [Centre for Nanometer-Scale Science and Advanced Materials, NANOSAM, Faculty of Physics, Astronomy and Applied Computer Science, Jagiellonian University, Reymonta Str. 4, PL 30-059 Krakow (Poland); Rauer, Caroline; Thuaire, Aurélie; Hartmann, Jean-Michel; Moriceau, Hubert [CEA, LETI, Minatec Campus, 17, Avenue des Martyrs, 38 054 Grenoble Cedex 9 (France); Joachim, Christian [Nanosciences Group and MANA Satellite, CEMES-CNRS, 29 rue Jeanne Marvig, F-31055 Toulouse (France); Szymonski, Marek, E-mail: marek.szymonski@uj.edu.pl [Centre for Nanometer-Scale Science and Advanced Materials, NANOSAM, Faculty of Physics, Astronomy and Applied Computer Science, Jagiellonian University, Reymonta Str. 4, PL 30-059 Krakow (Poland)

    2014-01-01

    Specific surfaces allowing the ultra-high vacuum (UHV) creation of electronic interconnects and atomic nanostructures are required for the successful development of novel nanoscale electronic devices. Atomically flat and reconstructed Si(0 0 1):H surfaces are serious candidates for that role. In this work such Si:H surfaces were prepared in a cleanroom environment on 200 mm silicon wafers with a hydrogen bake and were subsequently bonded together to ensure the surface protection, and allow their transportation and storage for several months in air. Given the nature of the bonding, which was hydrophobic with weak van der Waals forces, we were then able to de-bond them in UHV. We show that the quality of the de-bonded Si:H surface enables the “at will” construction of sophisticated and complex dangling bond (DB) nanostructures by atomically precise scanning tunneling microscope (STM) tip induced desorption of hydrogen atoms. The DB structures created on slightly doped Si:H samples were characterized by scanning tunneling microscopy and spectroscopy (STM/STS) performed at 4 K. Our results demonstrate that DB nanostructures fabricated on UHV de-bonded Si(0 0 1):H wafers could be directly incorporated in future electronics as interconnects and parts of nanoscale logic circuits.

  3. Metastability of a-SiOx:H thin films for c-Si surface passivation

    Science.gov (United States)

    Serenelli, L.; Martini, L.; Imbimbo, L.; Asquini, R.; Menchini, F.; Izzi, M.; Tucci, M.

    2017-01-01

    The adoption of a-SiOx:H films obtained by PECVD in heterojunction solar cells is a key to further increase their efficiency, because of its transparency in the UV with respect to the commonly used a-Si:H. At the same time this layer must guarantee high surface passivation of the c-Si to be suitable in high efficiency solar cell manufacturing. On the other hand the application of amorphous materials like a-Si:H and SiNx on the cell frontside expose them to the mostly energetic part of the sun spectrum, leading to a metastability of their passivation properties. Moreover as for amorphous silicon, thermal annealing procedures are considered as valuable steps to enhance and stabilize thin film properties, when performed at opportune temperature. In this work we explored the reliability of a-SiOx:H thin film layers surface passivation on c-Si substrates under UV exposition, in combination with thermal annealing steps. Both p- and n-type doped c-Si substrates were considered. To understand the effect of UV light soaking we monitored the minority carriers lifetime and Sisbnd H and Sisbnd O bonding, by FTIR spectra, after different exposure times to light coming from a deuterium lamp, filtered to UV-A region, and focused on the sample to obtain a power density of 50 μW/cm2. We found a certain lifetime decrease after UV light soaking in both p- and n-type c-Si passivated wafers according to a a-SiOx:H/c-Si/a-SiOx:H structure. The role of a thermal annealing, which usually enhances the as-deposited SiOx passivation properties, was furthermore considered. In particular we monitored the UV light soaking effect on c-Si wafers after a-SiOx:H coating by PECVD and after a thermal annealing treatment at 300 °C for 30 min, having selected these conditions on the basis of the study of the effect due to different temperatures and durations. We correlated the lifetime evolution and the metastability effect of thermal annealing to the a-SiOx:H/c-Si interface considering the evolution

  4. Atomic structure of graphene on SiO2.

    Science.gov (United States)

    Ishigami, Masa; Chen, J H; Cullen, W G; Fuhrer, M S; Williams, E D

    2007-06-01

    We employ scanning probe microscopy to reveal atomic structures and nanoscale morphology of graphene-based electronic devices (i.e., a graphene sheet supported by an insulating silicon dioxide substrate) for the first time. Atomic resolution scanning tunneling microscopy images reveal the presence of a strong spatially dependent perturbation, which breaks the hexagonal lattice symmetry of the graphitic lattice. Structural corrugations of the graphene sheet partially conform to the underlying silicon oxide substrate. These effects are obscured or modified on graphene devices processed with normal lithographic methods, as they are covered with a layer of photoresist residue. We enable our experiments by a novel cleaning process to produce atomically clean graphene sheets.

  5. Fluorocarbon based atomic layer etching of Si{sub 3}N{sub 4} and etching selectivity of SiO{sub 2} over Si{sub 3}N{sub 4}

    Energy Technology Data Exchange (ETDEWEB)

    Li, Chen [Department of Physics, and Institute for Research in Electronics and Applied Physics, University of Maryland, College Park, Maryland 20742 (United States); Metzler, Dominik; Oehrlein, Gottlieb S., E-mail: oehrlein@umd.edu [Department of Materials Science and Engineering, and Institute for Research in Electronics and Applied Physics, University of Maryland, College Park, Maryland 20742 (United States); Lai, Chiukin Steven; Hudson, Eric A. [Lam Research Corporation, 4400 Cushing Parkway, Fremont, California 94538 (United States)

    2016-07-15

    Angstrom-level plasma etching precision is required for semiconductor manufacturing of sub-10 nm critical dimension features. Atomic layer etching (ALE), achieved by a series of self-limited cycles, can precisely control etching depths by limiting the amount of chemical reactant available at the surface. Recently, SiO{sub 2} ALE has been achieved by deposition of a thin (several Angstroms) reactive fluorocarbon (FC) layer on the material surface using controlled FC precursor flow and subsequent low energy Ar{sup +} ion bombardment in a cyclic fashion. Low energy ion bombardment is used to remove the FC layer along with a limited amount of SiO{sub 2} from the surface. In the present article, the authors describe controlled etching of Si{sub 3}N{sub 4} and SiO{sub 2} layers of one to several Angstroms using this cyclic ALE approach. Si{sub 3}N{sub 4} etching and etching selectivity of SiO{sub 2} over Si{sub 3}N{sub 4} were studied and evaluated with regard to the dependence on maximum ion energy, etching step length (ESL), FC surface coverage, and precursor selection. Surface chemistries of Si{sub 3}N{sub 4} were investigated by x-ray photoelectron spectroscopy (XPS) after vacuum transfer at each stage of the ALE process. Since Si{sub 3}N{sub 4} has a lower physical sputtering energy threshold than SiO{sub 2}, Si{sub 3}N{sub 4} physical sputtering can take place after removal of chemical etchant at the end of each cycle for relatively high ion energies. Si{sub 3}N{sub 4} to SiO{sub 2} ALE etching selectivity was observed for these FC depleted conditions. By optimization of the ALE process parameters, e.g., low ion energies, short ESLs, and/or high FC film deposition per cycle, highly selective SiO{sub 2} to Si{sub 3}N{sub 4} etching can be achieved for FC accumulation conditions, where FC can be selectively accumulated on Si{sub 3}N{sub 4} surfaces. This highly selective etching is explained by a lower carbon consumption of Si{sub 3}N{sub 4} as compared to Si

  6. Comparison of thermal compatibility between atomized and comminuted U{sub 3}Si dispersion fuels

    Energy Technology Data Exchange (ETDEWEB)

    Ryu, Woo-Seog; Park, Jong-Man; Kim, Chang-Kyu; Kuk, II-Hyun [Korea Atomic Research Institute, Taejon (Korea, Republic of)

    1997-08-01

    Thermal compatibility of atomized U{sub 3}Si dispersion fuels were evaluated up to 2600 hours in the temperature range from 250 to 500{degrees}C, and compared with that of comminuted U{sub 3}Si. Atomized U{sub 3}Si showed better performance in terms of volume expansion of fuel meats. The reaction zone of U{sub 3}Si and Al occurred along the grain boundaries and deformation bands in U{sub 3}Si particles. Pores around fuel particles appeared at high temperature or after long-term annealing tests to remain diffusion paths over the trench of the pores. The constraint effects of cladding on fuel rod suppressed the fuel meat, and reduced the volume expansion.

  7. DFT Study of the Electronic Structure of Cubic-SiC Nanopores with a C-Terminated Surface

    Directory of Open Access Journals (Sweden)

    M. Calvino

    2014-01-01

    Full Text Available A study of the dependence of the electronic structure and energetic stability on the chemical surface passivation of cubic porous silicon carbide (pSiC was performed using density functional theory (DFT and the supercell technique. The pores were modeled by removing atoms in the [001] direction to produce a surface chemistry composed of only carbon atoms (C-phase. Changes in the electronic states of the porous structures were studied by using different passivation schemes: one with hydrogen (H atoms and the others gradually replacing pairs of H atoms with oxygen (O atoms, fluorine (F atoms, and hydroxide (OH radicals. The results indicate that the band gap behavior of the C-phase pSiC depends on the number of passivation agents (other than H per supercell. The band gap decreased with an increasing number of F, O, or OH radical groups. Furthermore, the influence of the passivation of the pSiC on its surface relaxation and the differences in such parameters as bond lengths, bond angles, and cell volume are compared between all surfaces. The results indicate the possibility of nanostructure band gap engineering based on SiC via surface passivation agents.

  8. Ammonia modification of oxide-free Si(111) surfaces

    Science.gov (United States)

    Chopra, Tatiana Peixoto; Longo, Roberto C.; Cho, Kyeongjae; Chabal, Yves J.

    2016-08-01

    Amination of surfaces is useful in a variety of fields, ranging from device manufacturing to biological applications. Previous studies of ammonia reaction on silicon surfaces have concentrated on vapor phase rather than wet chemical processes, and mostly on clean Si surfaces. In this work, the interaction of liquid and vapor-phase ammonia is examined on three types of oxide-free surfaces - passivated by hydrogen, fluorine (1/3 monolayer) or chlorine - combining infrared absorption spectroscopy, X-ray photoelectron spectroscopy, and first-principles calculations. The resulting chemical composition highly depends on the starting surface; there is a stronger reaction on both F- and Cl-terminated than on the H-terminated Si surfaces, as evidenced by the formation of Si-NH2. Side reactions can also occur, such as solvent reaction with surfaces, formation of ammonium salt by-products (in the case of 0.2 M ammonia in dioxane solution), and nitridation of silicon (in the case of neat and gas-phase ammonia reactions for instance). Unexpectedly, there is formation of Si-H bonds on hydrogen-free Cl-terminated Si(111) surfaces in all cases, whether vapor phase of neat liquid ammonia is used. The first-principles modeling of this complex system suggests that step-edge surface defects may play a key role in enabling the reaction under certain circumstances, despite the endothermic nature for Si-H bond formation.

  9. Transport Properties and Surface Morphology Correlated Studies on Graphene Formed by Si Desorption of 6H-SiC

    Science.gov (United States)

    Roach, William; Beringer, Douglas; Skuza, Jonathan; Clavero, Cesar; Lukaszew, Rosa Alejandra

    2009-11-01

    Interest in graphene, a single layer of carbon atoms arranged in a hexagonal lattice, has increased in recent years due to exciting characteristics such as its predicted high mobility [1]. However, developing a method to produce graphene that is easily integrated into existing fabrication processes has proved difficult thus far. One promising method is high temperature annealing of 6H-SiC such that Si desorption occurs [2], although this method leads to graphene that exhibits lower mobility than predicted [3]. Thus, we have investigated the relationship between different growth conditions (i.e. annealing time and temperature), the resulting surface morphology and the transport properties of graphene films produced using this method. Raman spectroscopy, atomic force microscopy, and Van der Pauw Hall mobility measurements have been used to correlate the surface morphology to transport properties of graphene formed on SiC. Understanding the effect of growth conditions on the resulting transport properties will help optimize the fabrication of graphene for use in the next generation of electronic devices and other applications. [1] Novoselov et al., Science 306, 666 (2004). [2] C. Berger et al., J. Phys. Chem. B 108, 19912 (2004). [3] G. Gu et al., Appl. Phys. Lett. 90, 253507 (2007).

  10. Formation and local electronic structure of Ge clusters on Si(111)-7×7 surfaces

    Institute of Scientific and Technical Information of China (English)

    Ma Hai-Feng; Xu Ming-Chun; Yang Bing; Shi Dong-Xia; Guo Hai-Ming; Pang Shi-Jin; Gao Hong-Jun

    2007-01-01

    We report the formation and local electronic structure of Ge clusters on the Si(111)-7×7 surface studied by using variable temperature scanning tunnelling microscopy (VT-STM) and low-temperature scanning tunnelling spectroscopy (STS). Atom-resolved STM images reveal that the Ge atoms are prone to forming clusters with 1.0 nm in diameter for coverage up to 0.12 ML. Such Ge clusters preferentially nucleate at the centre of the faulted-half unit cells, leading to the 'dark sites' of Si centre adatoms from the surrounding three unfaulted-half unit cells in filled-state images. Biasdependent STM images show the charge transfer from the neighbouring Si adatoms to Ge clusters. Low-temperature STS of the Ge clusters reveals that there is a band gap on the Ge cluster and the large voltage threshold is about 0.9 V.

  11. 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.

  12. Immunogold labels: cell-surface markers in atomic force microscopy

    NARCIS (Netherlands)

    Putman, Constant A.J.; Grooth, de Bart G.; Hansma, Paul K.; Hulst, van Niek F.; Greve, Jan

    1993-01-01

    The feasibility of using immunogold labels as cell-surface markers in atomic force microscopy is shown in this paper. The atomic force microscope (AFM) was used to image the surface of immunogold-labeled human lymphocytes. The lymphocytes were isolated from whole blood and labeled by an indirect imm

  13. Surface engineering of SiC via sublimation etching

    Science.gov (United States)

    Jokubavicius, Valdas; Yazdi, Gholam R.; Ivanov, Ivan G.; Niu, Yuran; Zakharov, Alexei; Iakimov, Tihomir; Syväjärvi, Mikael; Yakimova, Rositsa

    2016-12-01

    We present a technique for etching of SiC which is based on sublimation and can be used to modify the morphology and reconstruction of silicon carbide surface for subsequent epitaxial growth of various materials, for example graphene. The sublimation etching of 6H-, 4H- and 3C-SiC was explored in vacuum (10-5 mbar) and Ar (700 mbar) ambient using two different etching arrangements which can be considered as Si-C and Si-C-Ta chemical systems exhibiting different vapor phase stoichiometry at a given temperature. The surfaces of different polytypes etched under similar conditions are compared and the etching mechanism is discussed with an emphasis on the role of tantalum as a carbon getter. To demonstrate applicability of such etching process graphene nanoribbons were grown on a 4H-SiC surface that was pre-patterned using the thermal etching technique presented in this study.

  14. Adsorption of CO molecules on the Si(111)-(7×7) surface

    Science.gov (United States)

    Seo, Eonmi; Eom, Daejin; Hyun, Jung-Min; Kim, Hanchul; Koo, Ja-Yong

    2017-02-01

    Adsorption of CO molecules on Si(111)-(7×7) is investigated by using scanning tunneling microscopy (STM) and density-functional theory calculations. The most reactive site on the Si(111)-(7×7) surface is the corner adatom in the faulted half unit (FHU), followed by the center adatom in the FHU. The initial sticking probability of CO molecules on Si(111)-(7×7) at room temperature (RT) is estimated to be ∼ 4 ×1010 molecules/(cm2·Langmuir), which is comparable with that on Si(001)-(2×1). From the experiments and theoretical calculations, the adsorption of CO molecules are found to occur on Si adatoms either in the upright on-top configuration or in the back-bond inserted configuration, while the adsorption on the rest and the corner hole atoms (which are theoretically probable) are not observable using STM due to their low-lying geometries. Though the sticking probability is very low, every surface dangling bond on the surface can bind strongly with the C atom of a CO molecule even at temperatures higher than RT.

  15. Self-assembled C60 layers on incommensurate Cu/Si(111)'pseudo-5 × 5' surface

    Science.gov (United States)

    Olyanich, D. A.; Mararov, V. V.; Utas, T. V.; Zotov, A. V.; Saranin, A. A.

    2015-12-01

    Self-assembled growth of C60 monolayers on the pristine and Ge-modified Cu/Si(111)'pseudo-5 × 5' surfaces was studied using scanning tunneling microscopy observations. The pristine Cu/Si(111)'pseudo-5 × 5' surface shows up as an incommensurate reconstruction on Si(111) substrate, while Ge-modified surface shows up as an array of Ge atomic clusters grown on the Cu/Si(111)'pseudo-5 × 5' template. It has been found that C60 fullerenes are highly mobile on the both surfaces, hence at the early growth stages fullerenes are accumulated along the atomic steps forming their quasi-one-dimensional molecular stripes. With further C60 deposition, almost ideal two-dimensional close-packed molecular monolayers are formed. The layers are modulated as evidenced by developing quasi-periodic pattern of dim and bright fullerenes displaying 2 × 2 periodicity. Contrast difference between dim and bright fullerenes is supposed to have a topographical origin, namely, bright fullerenes reside higher than dim fullerenes. Dim fullerenes were concluded to occupy centers of hexagons which constitute honeycomb-like structure of the Cu/Si(111)'pseudo-5 × 5' surface. For the Ge-modified surface, this means that adsorbing C60 fullerenes displace Ge atoms from their original positions to the interstitial sites in the molecular monolayer. Ge atoms were found to terminate rotational motion of selected fullerenes in the layer.

  16. Carrier Mobility Enhancement of Tensile Strained Si and SiGe Nanowires via Surface Defect Engineering.

    Science.gov (United States)

    Ma, J W; Lee, W J; Bae, J M; Jeong, K S; Oh, S H; Kim, J H; Kim, S-H; Seo, J-H; Ahn, J-P; Kim, H; Cho, M-H

    2015-11-11

    Changes in the carrier mobility of tensile strained Si and SiGe nanowires (NWs) were examined using an electrical push-to-pull device (E-PTP, Hysitron). The changes were found to be closely related to the chemical structure at the surface, likely defect states. As tensile strain is increased, the resistivity of SiGe NWs deceases in a linear manner. However, the corresponding values for Si NWs increased with increasing tensile strain, which is closely related to broken bonds induced by defects at the NW surface. Broken bonds at the surface, which communicate with the defect state of Si are critically altered when Ge is incorporated in Si NW. In addition, the number of defects could be significantly decreased in Si NWs by incorporating a surface passivated Al2O3 layer, which removes broken bonds, resulting in a proportional decrease in the resistivity of Si NWs with increasing strain. Moreover, the presence of a passivation layer dramatically increases the extent of fracture strain in NWs, and a significant enhancement in mobility of about 2.6 times was observed for a tensile strain of 5.7%.

  17. Influence of helium atoms on the shear behavior of the fiber/matrix interphase of SiC/SiC composite

    Science.gov (United States)

    Jin, Enze; Du, Shiyu; Li, Mian; Liu, Chen; He, Shihong; He, Jian; He, Heming

    2016-10-01

    Silicon carbide has many attractive properties and the SiC/SiC composite has been considered as a promising candidate for nuclear structural materials. Up to now, a computational investigation on the properties of SiC/SiC composite varying in the presence of nuclear fission products is still missing. In this work, the influence of He atoms on the shear behavior of the SiC/SiC interphase is investigated via Molecular Dynamics simulation following our recent paper. Calculations are carried out on three dimensional models of graphite-like PyC/SiC interphase and amorphous PyC/SiC interphase with He atoms in different regions (the SiC region, the interface region and the PyC region). In the graphite-like PyC/SiC interphase, He atoms in the SiC region have little influence on the shear strength of the material, while both the shear strength and friction strength may be enhanced when they are in the PyC region. Low concentration of He atoms in the interface region of the graphite-like PyC/SiC interphase increases the shear strength, while there is a reduction of shear strength when the He concentration is high due to the switch of sliding plane. In the amorphous PyC/SiC interphase, He atoms can cause the reduction of the shear strength regardless of the regions that He atoms are located. The presence of He atoms may significantly alter the structure of SiC/SiC in the interface region. The influence of He atoms in the interface region is the most significant, leading to evident shear strength reduction of the amorphous PyC/SiC interphase with increasing He concentration. The behaviors of the interphases at different temperatures are studied as well. The dependence of the shear strengths of the two types of interphases on temperatures is studied as well. For the graphite-like PyC/SiC interphase, it is found strongly related to the regions He atoms are located. Combining these results with our previous study on pure SiC/SiC system, we expect this work may provide new insight

  18. Structural origin of Si-2p core-level shifts from Si(100)-c[4x2] surface: A spectral x-ray photoelectron diffraction study

    Energy Technology Data Exchange (ETDEWEB)

    Chen, X.; Tonner, B.P. [Univ. of Wisconsin, Milwaukee, WI (United States); Denlinger, J. [Univ. of Wisconsin, Milwaukee, WI (United States)][Ernest Orlando Lawrence Berkeley National Lab., CA (United States)] [and others

    1997-04-01

    The authors have performed angle-resolved x-ray photoelectron diffraction (XPD) from a Si(100)-c(4x2) surface to study the structural origin of Si-2p core-level shifts. In the experiment, the highly resolved surface Si-2p core-level spectra were measured as a fine grid of hemisphere and photon energies, using the SpectroMicroscopy Facility {open_quotes}ultraESCA{close_quotes} instrument. By carefully decomposing the spectra into several surface peaks, the authors are able to obtain surface-atom resolved XPD patterns. Using a multiple scattering analysis, they derived a detailed atomic model for the Si(100)-c(4x2) surface. In this model, the asymmetric dimers were found tilted by 11.5 plus/minus 2.0 degrees with bond length of 2.32 plus/minus 0.05{angstrom}. By matching model XPD patterns to experiment, the authors can identify which atoms in the reconstructed surface are responsible for specific photoemission lines in the 2p spectrum.

  19. Second harmonic generation spectroscopy on Si surfaces and interfaces

    DEFF Research Database (Denmark)

    Pedersen, Kjeld

    2010-01-01

    Optical second harmonic generation (SHG) spectroscopy studies of Si(111) surfaces and interfaces are reviewed for two types of systems: (1) clean 7 x 7 and root 3 x root 3-Ag reconstructed surfaces prepared under ultra-high vacuum conditions where surface states are excited and (2) interfaces......-like interband transitions that can be referred to excitations of dangling bond surface states. Adsorption of oxygen leads to formation of a new surface resonance. Such resonances appearing in the region between the bulk critical points E-1 and E-2 are also shown to be important for Si/oxide interfaces in SOI...

  20. Atomic Layer Deposition TiO2 Films and TiO2/SiNx Stacks Applied for Silicon Solar Cells

    Directory of Open Access Journals (Sweden)

    Zu-Po Yang

    2016-08-01

    Full Text Available Titanium oxide (TiO2 films and TiO2/SiNx stacks have potential in surface passivation, anti-reflection coatings and carrier-selective contact layers for crystalline Si solar cells. A Si wafer, deposited with 8-nm-thick TiO2 film by atomic layer deposition, has a surface recombination velocity as low as 14.93 cm/s at the injection level of 1.0 × 1015 cm−3. However, the performance of silicon surface passivation of the deposited TiO2 film declines as its thickness increases, probably because of the stress effects, phase transformation, atomic hydrogen and thermal stability of amorphous TiO2 films. For the characterization of 66-nm-thick TiO2 film, the results of transmission electron microscopy show that the anatase TiO2 crystallinity forms close to the surface of the Si. Secondary ion mass spectrometry shows the atomic hydrogen at the interface of TiO2 and Si which serves for chemical passivation. The crystal size of anatase TiO2 and the homogeneity of TiO2 film can be deduced by the measurements of Raman spectroscopy and spectroscopic ellipsometry, respectively. For the passivating contacts of solar cells, in addition, a stack composed of 8-nm-thick TiO2 film and a plasma-enhanced chemical-vapor-deposited 72-nm-thick SiNx layer has been investigated. From the results of the measurement of the reflectivity and effective carrier lifetime, TiO2/SiNx stacks on Si wafers perform with low reflectivity and some degree of surface passivation for the Si wafer.

  1. 200 nm-1000 nm spectra of light emitted in the impact of 40Ar10+ upon Al and Si solid surfaces

    Institute of Scientific and Technical Information of China (English)

    ZHANG; Xiaoan; (张小安); ZHAO; Yongtao; (赵永涛); LI; Fuli; (李福利); YANG; Zhihu(杨治虎); XIAO; Guoqing(肖国青); ZHAN; Wenlong(詹文龙)

    2003-01-01

    This paper reports the measured results of the 200 nm-1000 nm characteristic spectral lines of Al, Si and Ar atoms when highly charged ions 40Ar10+ are incident upon Al and P-type Si surfaces. The ion 40Ar10+ is provided by the ECR ion source of the National Laboratory of the Heavy Ion Accelerator in Lanzhou. The results show that when the low-speed ions in the highly charged state interact with the solid surfaces, the characteristic spectral lines of the target atoms and ions spurted from the surfaces can be effectively excited. Moreover, because of the competition of the non-radiation de-excitation of the hollow atom by emitting secondary electrons with the de-excitation process by radiating photons, the spectral intensity of the characteristic spectral lines of Ar atoms on the P-type Si surface is, as a whole, greater than that of Ar atoms on the Al surface.

  2. Electric field sensing near the surface microstructure of an atom chip using cold Rydberg atoms

    CERN Document Server

    Carter, J D; Martin, J D D

    2012-01-01

    The electric fields near the heterogeneous metal/dielectric surface of an atom chip were measured using cold atoms. The atomic sensitivity to electric fields was enhanced by exciting the atoms to Rydberg states that are 10^8 times more polarizable than the ground state. We attribute the measured fields to charging of the insulators between the atom chip wires. Surprisingly, it is observed that these fields may be dramatically lowered with appropriate voltage biasing, suggesting configurations for the future development of hybrid quantum systems.

  3. Growth behavior and properties of nano Pb quantum islands on Si(111) surfaces at low temperatures

    Science.gov (United States)

    Tsong, Tien T.

    2004-03-01

    Quantum effects can affect the dynamic properties of surface atoms and the growth behavior of nanometer size islands. Using scanning tunneling microscopy (STM), we have studied: 1) Dynamics of atoms and silicon magic clusters on clean Si(111)-7x7 surfaces. 2) How the electronic property affects the growth behavior of Pb ultra-thin quantum-islands on the Si(111) surface. We find the low temperature growth of Pb quantum-islands on the Si(111)-7x7 surface is affected by the electronic standing wave states formed in the normal direction of these islands. The scaling behavior in the growth of these multilayer flat-top quantum islands can be described by a scaling theory of growth of single layer 2D islands with a minor modification. 3) Observed the vertical Friedel oscillation of the electronic Morie patterns formed at the Pb-Si interface and found the decay of the amplitude to follow the inverse square of the distance to the interface. 4) Observed the dynamics of a structure phase transition of monolayer quasi two dimensional Pb islands and its size effect. These and other recent interesting observations of ours will be presented. Coworkers: C-S Chang, I-S Hwang, W-B Su, M-S Ho, W-B Jian, and S-H Chang etc. Work supported by NSC of Taiwan and Academia Sinica (Taiwan).

  4. Behind the Nature of Titanium Oxide Excellent Surface Passivation and Carrier Selectivity of c-Si

    DEFF Research Database (Denmark)

    Plakhotnyuk, Maksym; Crovetto, Andrea; Hansen, Ole

    We present an expanded study of the passivation properties of titanium dioxide (TiO2) on p-type crystalline silicon (c-Si). We report a low surface recombination velocity (16 cm/s) for TiO2 passivation layers with a thin tunnelling oxide interlayer (SiO2 or Al2O3) on p-type crystalline silicon (c......-Si). The TiO2 films were deposited by thermal atomic layer deposition (ALD) at temperatures in the range of 80-300  ̊C using titanium tetrachloride (TiCl4) as Ti precursor and water as the oxidant. The influence of TiO2 thickness (5, 10, 20 nm), presence of additional tunneling interlayer (SiO2 or Al2O3...

  5. Multiple atomic scale solid surface interconnects for atom circuits and molecule logic gates.

    Science.gov (United States)

    Joachim, C; Martrou, D; Rezeq, M; Troadec, C; Jie, Deng; Chandrasekhar, N; Gauthier, S

    2010-03-05

    The scientific and technical challenges involved in building the planar electrical connection of an atomic scale circuit to N electrodes (N > 2) are discussed. The practical, laboratory scale approach explored today to assemble a multi-access atomic scale precision interconnection machine is presented. Depending on the surface electronic properties of the targeted substrates, two types of machines are considered: on moderate surface band gap materials, scanning tunneling microscopy can be combined with scanning electron microscopy to provide an efficient navigation system, while on wide surface band gap materials, atomic force microscopy can be used in conjunction with optical microscopy. The size of the planar part of the circuit should be minimized on moderate band gap surfaces to avoid current leakage, while this requirement does not apply to wide band gap surfaces. These constraints impose different methods of connection, which are thoroughly discussed, in particular regarding the recent progress in single atom and molecule manipulations on a surface.

  6. A computational study on the adsorption configurations and reactions of SiH{sub x}(x = 1-4) on clean and H-covered Si(100) surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Le, Thong N-M [Molecular Science and Nano-Materials Laboratory, Institute for Computational Science and Technology, Quang Trung Software Park, Dist. 12, Ho Chi Minh City (Viet Nam); Raghunath, P. [Center for Interdisciplinary Molecular Science, Department of Applied Chemistry, National Chiao Tung University, Hsinchu 300, Taiwan (China); Huynh, Lam K., E-mail: lamhuynh.us@gmail.com [Department of Applied Chemistry, School of Biotechnology,International University, VNU-HCMC, Quarter 6, Linh Trung, Thu Duc District, Ho Chi Minh City (Viet Nam); Lin, M.C., E-mail: chemmcl@emory.edu [Center for Interdisciplinary Molecular Science, Department of Applied Chemistry, National Chiao Tung University, Hsinchu 300, Taiwan (China)

    2016-11-30

    Highlights: • Possible adsorption configurations of all adsorbates on Si(100) surface are systematically explored. • The mechanisms leading to the formation of silicon adatoms on the surface are proposed. • The barriers for hydrogen abstractions from the surface are negligible comparing to the barriers for the hydrogen migrations. • The barriers for hydrogen abstractions from the adsorbed speices are negligible comparing to the barriers for the decompositions. - Abstract: Possible adsorption configurations of H and SiH{sub x} (x = 1 − 4) on clean and H-covered Si(100) surfaces are determined by using spin-polarized DFT calculations. The results show that, on the clean surface, the gas-phase hydrogen atom and SiH{sub 3} radicals effectively adsorb on the top sites, while SiH and SiH{sub 2} prefer the bridge sites of the first layer. Another possibility for SiH is to reside on the hollow sites with a triple-bond configuration. For a partially H-coverd Si(100) surface, the mechanism is similar but with higher adsorption energies in most cases. This suggests that the surface species become more stable in the presence of surface hydrogens. The minimum energy paths for the adsorption/migration and reactions of H/SiH{sub x} species on the surfaces are explored using the climbing image-nudged elastic band method. The competitive surface processes for Si thin-film formation from SiH{sub x} precursors are also predicted. The study reveals that the migration of hydrogen adatom is unimportant with respect to leaving open surface sites because of its high barriers (>29.0 kcal/mol). Alternatively, the abstraction of hydrogen adatoms by H/SiH{sub x} radicals is more favorable. Moreover, the removal of hydrogen atoms from adsorbed SiH{sub x}, an essential step for forming Si layers, is dominated by abstraction rather than the decomposition processes.

  7. Ab initio study of subsurface diffusion of Cu on the H-passivated Si(001) surface

    Science.gov (United States)

    Rodriguez-Prieto, A.; Bowler, D. R.

    2009-10-01

    In this paper we use density-functional theory calculations to analyze both the stability and diffusion of Cu adatoms near and on the H-passivated Si(001) surface. Two different Cu sources are considered: depositing Cu from vacuum, and contaminating Cu outdiffusing from bulk Si. Deposited Cu from vacuum quickly moves subsurface to an interstitial site in the third Si layer (T2). Once there, Cu adatoms enter a subsurface zigzag migration route between T2 and another subsurface site, T2→HSL→T2 , along the dimer row direction. Contaminating Cu outdiffusing from bulk is found to be a fast diffuser along both parallel and perpendicular directions to the dimer row when far from the surface. It is attracted to the layers close to the surface and becomes trapped at an interstitial site located at the sixth Si layer (T3). As the outdiffusing Cu atoms get closer to the surface, a channeling zigzag diffusion along the dimer row direction, similar to that one followed by deposited Cu from vacuum, is favoured over diffusion along the perpendicular direction. These results are consistent with previous experimental work done on similar systems and will motivate further experiments on the interesting interaction between Cu and Si surfaces.

  8. Extended study of the atomic step-terrace structure on hexagonal SiC (0 0 0 1) by chemical-mechanical planarization

    Energy Technology Data Exchange (ETDEWEB)

    Shi, Xiaolei [The State Key Laboratory of Tribology, Tsinghua University, Beijing 100084 (China); Shenzhen Key Laboratory of Micro/Nano Manufacturing, Research Institute of Tsinghua University in Shenzhen, Shenzhen 518057 (China); Pan, Guoshun, E-mail: pangs@tsinghua.edu.cn [The State Key Laboratory of Tribology, Tsinghua University, Beijing 100084 (China); Shenzhen Key Laboratory of Micro/Nano Manufacturing, Research Institute of Tsinghua University in Shenzhen, Shenzhen 518057 (China); Zhou, Yan; Zou, Chunli; Gong, Hua [The State Key Laboratory of Tribology, Tsinghua University, Beijing 100084 (China); Shenzhen Key Laboratory of Micro/Nano Manufacturing, Research Institute of Tsinghua University in Shenzhen, Shenzhen 518057 (China)

    2013-11-01

    The atomic step-terrace structure on hexagonal silicon carbide (0 0 0 1) surface is significant in that it guides the improvement of chemical-mechanical planarization (CMP) and epitaxial technique. The final state of atomic step-terrace structure can be used as a feedback for improving the CMP process, the formula of slurry and the epitaxial technique. In this paper an extended study of the atomic step-terrace structure on 4H- and 6H-SiC (0 0 0 1) planarized by CMP is presented. Surface topography of the (0 0 0 1) facet plane of 4H- and 6H-SiC wafers during CMP process was studied by atomic force microscopy (AFM). The results demonstrate that high-definition atomic step-terrace structure of the (0 0 0 1) facet plane of both 4H- and 6H-SiC can be obtained by appropriate CMP process, and during CMP process, the formation of step-terrace structure had a certain rule. We studied the relationship between the CMP process and the characteristics of the atomic step-terrace structure, and analyzed the possible impact of the CMP process on the status of terraces. We studied the distribution of terraces in different areas of the wafer, and the origin of this distribution was discussed briefly. We also describe the formation of dislocations in hexagonal SiC. The results of this paper may provide some ideas and suggestions for CMP, crystal growth and epitaxy research.

  9. Damage effects of {ion}/{atom} beam milling on MNOS (Al/Si 3N 4/SiO 2/Si) capacitors

    Science.gov (United States)

    Bangert, U.; Belson, J.; Wilson, I. H.

    1984-02-01

    Low energy argon ion and atom beams produced by saddle field sources have been used to study changes in CVD Si 3N 4/SiO 2/Si structures after bombardment of the bare nitride at a particle energy of 2.9 keV. Interface state densities Nst and flatband voltages VFB were extracted from high frequency (1.3 MHz) and quasi-static C- V curves. Bombardment was found to induce an increase in Nst and positive and negative charge storage associated with the nitride (or the nitride/oxide interface). The effect was more pronounced under ion bombardment. On the supposition that displacement damage is similar for ion and atom bombardments the differences in charge storage are interpreted in terms of enhanced trapping under the field associated with ion bombardment.

  10. Ab initio study of the epitaxial growth of Ge on Si(100) surface

    Energy Technology Data Exchange (ETDEWEB)

    Milman, V.; Pennycook, S.J.; Jesson, D.E. [Oak Ridge National Lab., TN (United States); Payne, M.C.; Stich, I. [Cambridge Univ. (United Kingdom). Dept. of Physics

    1993-11-01

    We identify the binding sites for adsorption of a single Ge atom on the Si(100) surface using ab initio total energy calculations. The calculated diffusion barriers are in excellent agreement with experimental estimates. Using a large supercell we resolve the controversy regarding the binding geometry and migration path for the adatom, and investigate the influence of the adatom on the buckling of Si dimers. The adatom induces a buckling defect that is frequently observed using scanning tunneling microscopy (STM); therefore the study of single adatoms may be experimentally accessible.

  11. Effect of PECVD SiNx/SiOyNx-Si interface property on surface passivation of silicon wafer

    Science.gov (United States)

    Jia, Xiao-Jie; Zhou, Chun-Lan; Zhu, Jun-Jie; Zhou, Su; Wang, Wen-Jing

    2016-12-01

    It is studied in this paper that the electrical characteristics of the interface between SiOyNx/SiNx stack and silicon wafer affect silicon surface passivation. The effects of precursor flow ratio and deposition temperature of the SiOyNx layer on interface parameters, such as interface state density Dit and fixed charge Qf, and the surface passivation quality of silicon are observed. Capacitance-voltage measurements reveal that inserting a thin SiOyNx layer between the SiNx and the silicon wafer can suppress Qf in the film and Dit at the interface. The positive Qf and Dit and a high surface recombination velocity in stacks are observed to increase with the introduced oxygen and minimal hydrogen in the SiOyNx film increasing. Prepared by deposition at a low temperature and a low ratio of N2O/SiH4 flow rate, the SiOyNx/SiNx stacks result in a low effective surface recombination velocity (Seff) of 6 cm/s on a p-type 1 Ω·cm-5 Ω·cm FZ silicon wafer. The positive relationship between Seff and Dit suggests that the saturation of the interface defect is the main passivation mechanism although the field-effect passivation provided by the fixed charges also make a contribution to it. Project supported by the National High Technology Research and Development Program of China (Grant No. 2015AA050302) and the National Natural Science Foundation of China (Grant No. 61306076).

  12. 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<Si> and W1-xNx , where x= 15- 22 at%, thin films were grown using the ALD (Atomic Layer Deposition) principle. Growth rate of W<Si> 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%

  13. Effects of hydrogen atoms on surface conductivity of diamond film

    Directory of Open Access Journals (Sweden)

    Fengbin Liu

    2015-04-01

    Full Text Available To investigate the effects of surface chemisorbed hydrogen atoms and hydrogen atoms in the subsurface region of diamond on surface conductivity, models of hydrogen atoms chemisorbed on diamond with (100 orientation and various concentrations of hydrogen atoms in the subsurface layer of the diamond were built. By using the first-principles method based on density functional theory, the equilibrium geometries and densities of states of the models were studied. The results showed that the surface chemisorbed hydrogen alone could not induce high surface conductivity. In addition, isolated hydrogen atoms in the subsurface layer of the diamond prefer to exist at the bond centre site of the C-C bond. However, such a structure would induce deep localized states, which could not improve the surface conductivity. When the hydrogen concentration increases, the C-H-C-H structure and C-3Hbc-C structure in the subsurface region are more stable than other configurations. The former is not beneficial to the increase of the surface conductivity. However, the latter would induce strong surface states near the Fermi level, which would give rise to high surface conductivity. Thus, a high concentration of subsurface hydrogen atoms in diamond would make significant contributions to surface conductivity.

  14. Laser Surface Hardening of 9CrSi Steel

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    The effects of laser hardening parameters such as beam power, beam diameter and scanning rate on microstructureand hardness of 9CrSi steel were investigated. The microstructure of the surface layer of 9CrSi steel was changed frompearlite to martensite, retained austenite and carbide by laser hardening. The depth of the hardened layer increasedwith increasing laser energy density and the surface hardeness increased by 3~5 times as high as the untreated steel.The laser hardened surface had good wear resistance due to martensite and carbide in the surface layer. The wearmode at Iow speed was abrasive, while the wear mode at high speed was adhesive.

  15. Surface structure of thin pseudomorphous GeSi layers

    Science.gov (United States)

    Nikiforov, A. I.; Timofeev, V. F.; Pchelyakov, O. P.

    2015-11-01

    Reflection high-energy electron diffraction (RHEED) was used to study the evolution of thin GexSi1-x film surface superstructures s in the course of molecular beam epitaxy. The (2 × N) superstructure of the epitaxial film surface at periodicity N from 14 to 8, the latter being characteristic of pure germanium at the Si(1 0 0) surface. The epitaxial film thickness that is required for the formation of the (2 × 8) superstructure depends on the deposition temperature and germanium content in the solid solution. The germanium segregation on the growing film surface is shown to be responsible for the observed superstructural changes.

  16. Systematic Investigation of Gettering Effects on 4th Row Element Impurities in Si by Dopant Atoms

    Directory of Open Access Journals (Sweden)

    Koji Sueoka

    2009-01-01

    Full Text Available The gettering of 4th row element impurities (K, Ca, 3d transition metals, and Zn in Si crystals by dopant atoms was systematically investigated by first-principles calculation through evaluation of the diffusion barrier and the binding energy. The dopant atoms considered include p-type dopants (B, n-type dopants (P, As, Sb, or light elements (C, O. It was found that (1 the diffusion barrier of impurity atoms decreases with an increase in their atomic number up to Ni, (2 B atom becomes an efficient gettering center for metals except for Ni, (3 most of the metals except for Fe and Co cannot be gettered by n-type dopants, and (4 C and O atoms alone do not become efficient gettering centers for the metals used in actual LSI processes. The vacancy and n-type dopant complexes (P, As, Sb can be efficient gettering centers for Cu in n/n+ epitaxial wafers.

  17. Adsorption of atomic S and C on Mg(0001) surface

    Institute of Scientific and Technical Information of China (English)

    HU Yu-lin; ZHANG Wei-bing; TANG Bi-yu; DING Wen-jiang; ZENG Xiao-qin

    2006-01-01

    First-principle calculations based on density functional theory were used to study the adsorption of atomic sulfur and carbon on the Mg(0001) surface in a wide range of coverages from 1/4 ML(monolayer) to 1 ML. It is found that the adsorption of atomic S and C on the high coordinate hollow site is more energetically favorable than that on other adsorption sites. S atom is favorable to be adsorbed at on-surface site and C atom is favorable to be adsorbed at subsurface site. The results suggest that when the coverage increases,the binding energy for S and C atoms will decrease and the interaction between adsorbed atoms tends to be stronger. It indicates that as coverage increases,S-Mg and C-Mg interaction weakens.

  18. Effect of annealing on atomic ordering of amorphous ZrTaTiNbSi alloy

    Science.gov (United States)

    Yang, Tsung-Han; Huang, Rong-Tang; Wu, Cheng-An; Chen, Fu-Rong; Gan, Jon-Yiew; Yeh, Jien-Wei; Narayan, Jagdish

    2009-12-01

    In this letter, we have reported on initial stages of atomic ordering in ZrTaTiNbSi amorphous films during annealing. The atomic ordering and structure evolution were studied in Zr17Ta16Ti19Nb22Si26 amorphous films as a function of annealing temperature in the temperature range from 473 to 1173 K. Up to annealing temperature of 1173 K, the films retained amorphous structure, but the degree of disorder is increased with the increase in temperature. The formation of Si-M covalent bonds, which contributed to the local atomic arrangement, occurred in the initial stages of ordering. The bonding reactions between Si and other metal species explain the anomalous structural changes which were observed in x-ray diffraction and transmission electron microscopy. We discuss the stages of phase transformation for amorphous films as a function of annealing temperature. From these results, we propose that annealing leads to formation of random Si-M4 tetrahedron, and two observed rings, a first and second in the electron diffraction patterns compared to M-M and Si-M bond length, respectively.

  19. Static and dynamic buckling of reconstructions at triple steps on Si(111) surfaces

    Science.gov (United States)

    Zhachuk, R.; Teys, S.; Coutinho, J.; Rayson, M. J.; Briddon, P. R.

    2014-10-01

    Triple steps on Si(111) surfaces are popular building blocks for bottom-up nanostructure assembly, conferring size uniformity and precise positioning of growing nanostructures. In this work, we employ the Si(7 7 10) regular stepped surface as model system to study the triple steps by scanning tunneling microscopy (STM) and large-scale first-principles calculations. We find a surprising cohabitation of reconstruction elements at the step edge that either buckles statically or dynamically at room temperature. The driving force for the observed sequence of buckling patterns is traced back to Coulomb interactions involving charged adatoms and rest-atoms lying on a mini-terrace. These results reconcile the Si(111) triple step model with the experimental STM data.

  20. Static and dynamic buckling of reconstructions at triple steps on Si(111) surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Zhachuk, R., E-mail: zhachuk@gmail.com; Teys, S. [Institute of Semiconductor Physics, pr. Lavrentyeva 13, Novosibirsk 630090 (Russian Federation); Coutinho, J. [Department of Physics and I3N, University of Aveiro, Campus Santiago, 3810-193 Aveiro (Portugal); Rayson, M. J. [Department of Chemistry, University of Surrey, Guildford GU2 7XH (United Kingdom); Briddon, P. R. [School of Electrical, Electronic and Computer Engineering, Newcastle University, Newcastle Upon Tyne NE1 7RU (United Kingdom)

    2014-10-27

    Triple steps on Si(111) surfaces are popular building blocks for bottom-up nanostructure assembly, conferring size uniformity and precise positioning of growing nanostructures. In this work, we employ the Si(7 7 10) regular stepped surface as model system to study the triple steps by scanning tunneling microscopy (STM) and large-scale first-principles calculations. We find a surprising cohabitation of reconstruction elements at the step edge that either buckles statically or dynamically at room temperature. The driving force for the observed sequence of buckling patterns is traced back to Coulomb interactions involving charged adatoms and rest-atoms lying on a mini-terrace. These results reconcile the Si(111) triple step model with the experimental STM data.

  1. Connolly Surface on an Atomic Structure via Voronoi Diagram of Atoms

    Institute of Scientific and Technical Information of China (English)

    Joonghyun Ryu; Rhohun Park; Deok-Soo Kim

    2006-01-01

    One of the most important geometric structures of a protein is the Connolly surface of protein since a Connolly surface plays an important role in protein folding, docking, interactions between proteins, amongst other things. This paper presents an algorithm for precisely and efficiently computing the Connolly surface of a protein using a proposed geometric construct called β-shape based on the Voronoi diagram of atoms in the protein. Given the Voronoi diagram of atoms based on the Euclidean distance from the atom surfaces, the proposed algorithm first computes a β-shape with an appropriate probe. Then, the Connolly surface is computed by employing the blending operation on the atomic complex of the protein by the given probe.

  2. Interaction of cationic hydrophobic surfactants at negatively charged surfaces investigated by atomic force microscopy.

    Science.gov (United States)

    McNamee, Cathy E; Butt, Hans-Jürgen; Higashitani, Ko; Vakarelski, Ivan U; Kappl, Michael

    2009-10-06

    Atomic force microscopy was used to study the adsorption of the surfactant octadecyl trimethyl ammonium chloride (C18TAC) at a low concentration (0.03 mM) to negatively charged surfaces in water. Atomic force microscopy tips were functionalized with dimethyloctadecyl(3-tripropyl)ammonium chloride (C18TAC-si) or N-trimethoxysilylpropyl-N,N,N-trimethylammomium chloride (hydrophilpos-si) to facilitate imaging of the adsorbed surfactant without artifacts. Tapping mode images and force measurements revealed C18TAC patches, identified as partial surfactant bilayers or hemimicelles. The forces controlling the adsorption process of the C18TAC to a negatively charged surface were investigated by measuring the forces between a C18TAC-si or a hydrophilpos-si tip and a silica surface in the presence of varying concentrations of either NaCl or NaNO3. Screening of forces with an increasing NaCl concentration was observed for the C18TAC-si and hydrophilpos-si tips, proving an electrostatic contribution. Screening was also observed for the hydrophilpos-si tip in NaNO3, whereas a long-range attraction was observed for the C18TAC-si tip for all NaNO3 concentrations. These results indicate that screening of the forces for the C18TAC-si tip depended on the type and/or size of the anion, possibly due to a different probability of the anions to enter the silane layers. The interaction of C18TAC patches with C18TAC-si tips in the presence of NaCl and the interaction of the patches with hydrophilpos-si tips in either NaCl or NaNO3 were repulsive and independent of the number of force curves measured, indicating a stable, positively charged C18TAC patch. However, the forces measured between the patches and a C18TAC-si tip in NaNO3 depended on the number of force curves measured, indicating a change in patch structure induced by the first interaction.

  3. 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.

  4. Evolution of interfacial intercalation chemistry on epitaxial graphene/SiC by surface enhanced Raman spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Ferralis, Nicola, E-mail: ferralis@mit.edu [Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139 (United States); Carraro, Carlo [Department of Chemical and Biomolecular Engineering, University of California, Berkeley, CA 94720 (United States)

    2014-11-30

    Highlights: • H-intercalated epitaxial graphene–SiC interface studied with surface enhanced Raman. • Evolution of graphene and H–Si interface with UV-ozone, annealing and O-exposure. • H–Si interface and quasi-freestanding graphene are retained after UV-ozone treatment. • Enhanced ozonolytic reactivity at the edges of H-intercalated defected graphene. • Novel SERS method for characterizing near-surface graphene–substrate interfaces. - Abstract: A rapid and facile evaluation of the effects of physical and chemical processes on the interfacial layer between epitaxial graphene monolayers on SiC(0 0 0 1) surfaces is essential for applications in electronics, photonics, and optoelectronics. Here, the evolution of the atomic scale epitaxial graphene-buffer-layer–SiC interface through hydrogen intercalation, thermal annealings, UV-ozone etching and oxygen exposure is studied by means of single microparticle mediated surface enhanced Raman spectroscopy (smSERS). The evolution of the interfacial chemistry in the buffer layer is monitored through the Raman band at 2132 cm{sup −1} corresponding to the Si-H stretch mode. Graphene quality is monitored directly by the selectively enhanced Raman signal of graphene compared to the SiC substrate signal. Through smSERS, a simultaneous correlation between optimized hydrogen intercalation in epitaxial graphene/SiC and an increase in graphene quality is uncovered. Following UV-ozone treatment, a fully hydrogen passivated interface is retained, while a moderate degradation in the quality of the hydrogen intercalated quasi-freestanding graphene is observed. While hydrogen intercalated defect free quasi-freestanding graphene is expected to be robust upon UV-ozone, thermal annealing, and oxygen exposure, ozonolytic reactivity at the edges of H-intercalated defected graphene results in enhanced amorphization of the quasi-freestanding (compared to non-intercalated) graphene, leading ultimately to its complete etching.

  5. A surface extended X-ray absorption fine structure study of tellurium adsorbed onto Si(100)

    Science.gov (United States)

    Burgess, S. R.; Cowie, B. C. C.; Wilks, S. P.; Dunstan, P. R.; Dunscombe, C. J.; Williams, R. H.

    1996-09-01

    The adsorption of tellurium on Si(100) has been studied using surface extended X-ray adsorption fine structure (SEXAFS) and X-ray standing wave spectroscopy (XSW). This particular system is of interest due to its potential applicability in the surfactant aided growth of CdHgTeCdTeSi(100) based infra-red detectors. The Te/Si(100) structure was generated by depositing a thick layer (˜ 100 Å) of CdTe onto a clean Si (2 × 1) double domain surface, and annealing the sample to 350°C. This resulted is a ˜ 1 ML Te terminated surface where the (2 × 1) reconstruction was lost in favour of a (1 × 1) symmetry. X-ray absorption of the Te L 3 edge ( E = 4341 eV), with a photon energy range of 4440-4700 eV, was probed using a total yield detection scheme. The SEXAFS results indicated that the Te atoms sat in 2-fold bridge sites directly above a fourth layer Si atom. The corresponding bond length was measured to be 2.52 ± 0.05 Å. The XSW measurements of the (400) reflection gave a coherent position of 1.63 ± 0.03 Å and a coherent fraction of 0.65. This is consistent with the breaking of the SiSi dimers and thus could be an example of the phenomena of adsorbate-induced dereconstruction of the surface. These results are compared with those of Bennet et al. who examined a similar system using soft X-ray photoemission (SXPS) and the STM study of Yoshikawa et al.

  6. Influence of surface preparation on atomic layer deposition of Pt films

    Institute of Scientific and Technical Information of China (English)

    Ge Liang; Hu Cheng; Zhu Zhiwei; Zhang Wei; Wu Dongping; Zhang Shili

    2012-01-01

    We report Pt deposition on a Si substrate by means of atomic layer deposition (ALD) using (methylcyclopentadienyl) trimethylplatinum (CH3CsH4Pt(CH3)3) and O2.Silicon substrates with both HF-last and oxidelast surface treatments are employed to investigate the influence of surface preparation on Pt-ALD.A significantlylonger incubation time and less homogeneity are observed for Pt growth on the HF-last substrate compared to the oxide-last substrate.An interfacial oxide layer at the Pt-Si interface is found inevitable even with HF treatment of the Si substrate immediately prior to ALD processing.A plausible explanation to the observed difference of Pt-ALD is discussed.

  7. Atomic layer deposition of HfO{sub 2} onto SiO{sub 2} substrates investigated in-situ by non-contact UHV/AFM

    Energy Technology Data Exchange (ETDEWEB)

    Kolanek, Krzysztof; Karavaev, Konstantin; Tallarida, Massimo; Schmeisser, Dieter [Brandenburgische Technische Universitaet, LS Angewandte Physik-Sensorik, Cottbus (Germany)

    2010-07-01

    We investigated in-situ the atomic layer deposition (ALD) of HfO{sub 2} onto SiO{sub 2} substrates with ultra high vacuum (UHV) non-contact atomic force microscope (NC-AFM). The ALD process was started after detailed analysis of the initial Si(001)/SiO{sub 2} substrate. The ALD cycles, made by using tetrakis-di-methyl-amido-Hf (TDMAHf) and water as precursors, were performed on the SiO{sub 2} substrate maintained at 230 C. We studied the relation between the film growth and the root mean square surface roughness, surface skewness, kurtosis, fractal dimension and correlation length. In the initial stages of the ALD process with our analysis of the surface height histograms we were capable of determination: HfO{sub 2} layer thickness, surface coverage and surface roughness of a substrate and deposited material. Observation of the surface height histograms evolution during deposition allowed us to verify conformal and effective ALD growth on SiO{sub 2} substrate. With this detailed analysis of the surface topography we confirmed the completion of the first HfO{sub 2} layer after four ALD cycles.

  8. Atomic forces between noble gas atoms, alkali ions, and halogen ions for surface interactions

    Science.gov (United States)

    Wilson, J. W.; Outlaw, R. A.; Heinbockel, J. H.

    1988-01-01

    The components of the physical forces between noble gas atoms, alkali ions, and halogen ions are analyzed and a data base developed from analysis of the two-body potential data, the alkali-halide molecular data, and the noble gas crystal and salt crystal data. A satisfactory global fit to this molecular and crystal data is then reproduced by the model to within several percent. Surface potentials are evaluated for noble gas atoms on noble gas surfaces and salt crystal surfaces with surface tension neglected. Within this context, the noble gas surface potentials on noble gas and salt crystals are considered to be accurate to within several percent.

  9. Nanochemistry at the atomic scale revealed in hydrogen-induced semiconductor surface metallization

    Science.gov (United States)

    Derycke, Vincent; Soukiassian, Patrick G.; Amy, Fabrice; Chabal, Yves J.; D'Angelo, Marie D.; Enriquez, Hanna B.; Silly, Mathieu G.

    2003-04-01

    Passivation of semiconductor surfaces against chemical attack can be achieved by terminating the surface-dangling bonds with a monovalent atom such as hydrogen. Such passivation invariably leads to the removal of all surface states in the bandgap, and thus to the termination of non-metallic surfaces. Here we report the first observation of semiconductor surface metallization induced by atomic hydrogen. This result, established by using photo-electron and photo-absorption spectroscopies and scanning tunnelling techniques, is achieved on a Si-terminated cubic silicon carbide (SiC) surface. It results from competition between hydrogen termination of surface-dangling bonds and hydrogen-generated steric hindrance below the surface. Understanding the ingredient for hydrogen-stabilized metallization directly impacts the ability to eliminate electronic defects at semiconductor interfaces critical for microelectronics, provides a means to develop electrical contacts on high-bandgap chemically passive materials, particularly for interfacing with biological systems, and gives control of surfaces for lubrication, for example of nanomechanical devices.

  10. Two-Dimensional Superconductor with a Giant Rashba Effect: One-Atom-Layer Tl-Pb Compound on Si(111)

    Science.gov (United States)

    Matetskiy, A. V.; Ichinokura, S.; Bondarenko, L. V.; Tupchaya, A. Y.; Gruznev, D. V.; Zotov, A. V.; Saranin, A. A.; Hobara, R.; Takayama, A.; Hasegawa, S.

    2015-10-01

    A one-atom-layer compound made of one monolayer of Tl and one-third monolayer of Pb on a Si(111) surface having √{3 }×√{3 } periodicity was found to exhibit a giant Rashba-type spin splitting of metallic surface-state bands together with two-dimensional superconducting transport properties. Temperature-dependent angle-resolved photoelectron spectroscopy revealed an enhanced electron-phonon coupling for one of the spin-split bands. In situ micro-four-point-probe conductivity measurements with and without magnetic field demonstrated that the (Tl, Pb)/Si(111) system transformed into the superconducting state at 2.25 K, followed by the Berezinskii-Kosterlitz-Thouless mechanism. The 2D Tl-Pb compound on Si(111) is believed to be the prototypical object for prospective studies of intriguing properties of the superconducting 2D system with lifted spin degeneracy, bearing in mind that its composition, atomic and electron band structures, and spin texture are already well established.

  11. On the wettability diversity of C/SiC surface: Comparison of the ground C/SiC surface and ablated C/SiC surface from three aspects

    Science.gov (United States)

    Wu, M. L.; Ren, C. Z.; Xu, H. Z.

    2016-11-01

    The coefficient of thermal conductivity was influenced by the wetting state of material. The wetting state usually depends on the surface wettability. C/SiC is a promising ceramic composites with multi-components. The wettability of C/SiC composites is hard to resort to the classical wetting theory directly. So far, few investigations focused on C/SiC surface wettability diversity after different material removal processes. In this investigation, comparative studies of surface wettability of ground C/SiC surface and laser-ablated C/SiC surface were carried out through apparent contact angle (APCA) measurements. The results showed that water droplets easily reached stable state on ground C/SiC surface; while the water droplets rappidly penetrated into the laser-ablated C/SiC surface. In order to find out the reason for wettability distinctions between the ground C/SiC surface and the laser-ablated C/SiC surface, comparative studies on the surface micro-structure, surface C-O-Si distribution, and surface C-O-Si weight percentage were carried out. The results showed that (1) A large number of micro cracks in the fuzzy pattern layer over laser-ablated C/SiC surfaces easily destoried the surface tension of water droplets, while only a few cracks existed over the ground C/SiC surfaces. (2) Chemical components (C, O, Si) were non-uniformly distributed on ground C/SiC surfaces, while the chemical components (C, O, Si) were uniformly distributed on laser-ablated C/SiC surfaces. (3) The carbon weight percentage on ground C/SiC surfaces were higher than that on laser-ablated C/SiC surfaces. All these made an essential contribution to the surface wettability diversity of C/SiC surface. Although more investigations about the quantitative influence of surface topography and surface chemical composition on composites wettability are still needed, the conslusion can be used in application: the wettability of C/SiC surface can be controlled by different material removal process

  12. Preparation of polystyrene/SiO2 nanocomposites by surface-initiated nitroxide-mediated radical polymerization

    Institute of Scientific and Technical Information of China (English)

    NI Gang; YANG Wu; BO Lili; GUO Hao; ZHANG Wenhao; GAO Jinzhang

    2006-01-01

    Polystyrene/SiO2 composite nanoparticles (PS-g-Silica) were prepared by an in-situ surface-initiated nitroxide-mediated radical polymerization. After SiO2 nanoparticles were treated by thionyl chloride (SOCl2), peroxide initiation groups were immobilized on their surfaces through a reaction with tertiary butyl hydroperoxide (TBHP). Then surface nitroxide-mediated radical polymerization was initiated and polystyrene was grafted on the surface of SiO2 particles. Composite nanoparticles were characterized by IR spectra, transmission electron microscopy (TEM), atomic force microscopy (AFM) and thermogravimetry (TGA) and the results indicated that the surface-initiated nitroxide-mediated radical polymerization could be successfully used to synthesize well-dispersive PS/SiO2 nanocomposites.

  13. Simulation of Nano Si and Al Wires Growth on Si(1O0) Surface

    Institute of Scientific and Technical Information of China (English)

    吴锋民; 黄辉; 吴自勤

    2000-01-01

    Growth of nano Si and Al wires on the Si(100) surfaces is investigated by computer simulation, including the anisotropic diffusion and the anisotropic sticking. The diffusion rates along and across the substrate dimer rows are different, so are the sticking probabilities of an adatom, at the end sites of existing islands or the side sites. Both one-dimensional wires of Si and Al are perpendicular to the dimer rows of the substrate, though the diffusion of Si adatoms is contrary to that of Al adatoms, i.e. Si adatoms diffuse faster along the dimer rows while Al adatoms faster across the dimer rows. The simulation results also show that the shape anisotropy of islands is due to the sticking anisotropy rather than the diffusion anisotropy,which is in agreement with the experiments.

  14. Stripping scattering of fast atoms on surfaces of metal-oxide crystals and ultrathin films; Streifende Streuung schneller Atome an Oberflaechen von Metalloxid-Kristallen und ultraduennen Filmen

    Energy Technology Data Exchange (ETDEWEB)

    Blauth, David

    2010-03-11

    In the framework of the present dissertation the interactions of fast atoms with surfaces of bulk oxides, metals and thin films on metals were studied. The experiments were performed in the regime of grazing incidence of atoms with energies of some keV. The advantage of this scattering geometry is the high surface sensibility and thus the possibility to determine the crystallographic and electronic characteristics of the topmost surface layer. In addition to these experiments, the energy loss and the electron emission induced by scattered projectiles was investigated. The energy for electron emission and exciton excitation on Alumina/NiAl(110) and SiO{sub 2}/Mo(112) are determined. By detection of the number of projectile induced emitted electrons as function of azimuthal angle for the rotation of the target surface, the geometrical structure of atoms forming the topmost layer of different adsorbate films on metal surfaces where determined via ion beam triangulation. (orig.)

  15. Surface Selective Oxidation of Sn-Added CMnSi TRIP Steel

    Science.gov (United States)

    Cho, Lawrence; Seo, Eun Jung; Jung, Geun Su; Suh, Dong Woo; De Cooman, Bruno C.

    2016-04-01

    The influence of the addition of Sn on the selective oxidation and the reactive wetting of CMnSi transformation-induced plasticity (TRIP) steels was studied by means of galvanizing simulator tests. A reference TRIP steel and TRIP steels containing Sn in the range of 0.05 to 1 wt pct were intercritically annealed at 1093 K (820 °C) in an N2+ 5 pct H2 gas atmosphere with a dew point of -60 °C. The thin-film oxides formed on the surface of the Sn-added CMnSi TRIP steel were investigated using transmission electron microscopy and 3-dimensional atom probe tomography. The addition of Sn (≥0.05 wt pct) changed the morphology of the xMnO·SiO2 surface oxides from a continuous film morphology to a lens-shaped island morphology. It also suppressed the formation of the Mn-rich oxides of MnO and 2MnO·SiO2. The changes in the morphology and chemistry of the surface oxides were clearly related to the surface segregation of Sn, which appeared to result in a decrease of the oxygen permeability at the surface. The formation of lens-shaped oxides improved the wettability of the CMnSi TRIP steel surface by the molten Zn. The improved wetting effect was attributed to an increased area fraction of the surface where the oxide layer was thinner. This enabled a direct, unhindered reaction between Fe and the Al in the liquid Zn and the formation of the inhibition layer in the initial stages of the hot dipping. The addition of a small amount of Sn was also found to decrease significantly the density of Zn-coating defects on CMnSi TRIP steel.

  16. Low-temperature SiON films deposited by plasma-enhanced atomic layer deposition method using activated silicon precursor

    Energy Technology Data Exchange (ETDEWEB)

    Suh, Sungin; Kim, Jun-Rae; Kim, Seongkyung; Hwang, Cheol Seong; Kim, Hyeong Joon, E-mail: thinfilm@snu.ac.kr [Department of Materials Science and Engineering with Inter-University Semiconductor Research Center (ISRC), Seoul National University, 599 Gwanak-ro, Gwanak-gu, Seoul 08826 (Korea, Republic of); Ryu, Seung Wook, E-mail: tazryu78@gmail.com [Department of Electrical Engineering, Stanford University, Stanford, California 94305-2311 (United States); Cho, Seongjae [Department of Electronic Engineering and New Technology Component & Material Research Center (NCMRC), Gachon University, Seongnam-si, Gyeonggi-do 13120 (Korea, Republic of)

    2016-01-15

    It has not been an easy task to deposit SiN at low temperature by conventional plasma-enhanced atomic layer deposition (PE-ALD) since Si organic precursors generally have high activation energy for adsorption of the Si atoms on the Si-N networks. In this work, in order to achieve successful deposition of SiN film at low temperature, the plasma processing steps in the PE-ALD have been modified for easier activation of Si precursors. In this modification, the efficiency of chemisorption of Si precursor has been improved by additional plasma steps after purging of the Si precursor. As the result, the SiN films prepared by the modified PE-ALD processes demonstrated higher purity of Si and N atoms with unwanted impurities such as C and O having below 10 at. % and Si-rich films could be formed consequently. Also, a very high step coverage ratio of 97% was obtained. Furthermore, the process-optimized SiN film showed a permissible charge-trapping capability with a wide memory window of 3.1 V when a capacitor structure was fabricated and measured with an insertion of the SiN film as the charge-trap layer. The modified PE-ALD process using the activated Si precursor would be one of the most practical and promising solutions for SiN deposition with lower thermal budget and higher cost-effectiveness.

  17. Silane activation by laser-ablated Be atoms: Formation of HBeSiH3 and HBe(μ-H)3Si molecules

    Science.gov (United States)

    Zhao, Jie; Yu, Wenjie; Xu, Bing; Huang, Tengfei; Wang, Xuefeng

    2017-03-01

    Laser-ablated beryllium atoms have been reacted with silane molecules during condensation in excess neon and argon at 4 K. Absorptions due to HBeSiH3 and HBe(μ-H)3Si were observed and identified on the basis of isotopic IR spectroscopy, deuterium substitution with SiD4, and quantum chemical frequency calculations. The observed results show excited Be atom (1P1:2s12p1) can insert into Sisbnd H bond spontaneously and the insertion product rearranges to HBe(μ-H)3Si upon photolysis. The electron localization function (ELF) analysis suggests that 3c-2e hydrogen bridge bond (Besbnd Hsbnd Si) was formed by the donation of electrons for Sisbnd H σ bond to the empty p orbital of Be atom for HBe(μ-H)3Si molecule, which shows much difference from Csbnd H bond complexes.

  18. Surface Damage Mechanism of Monocrystalline Si Under Mechanical Loading

    Science.gov (United States)

    Zhao, Qingliang; Zhang, Quanli; To, Suet; Guo, Bing

    2017-03-01

    Single-point diamond scratching and nanoindentation on monocrystalline silicon wafer were performed to investigate the surface damage mechanism of Si under the contact loading. The results showed that three typical stages of material removal appeared during dynamic scratching, and a chemical reaction of Si with the diamond indenter and oxygen occurred under the high temperature. In addition, the Raman spectra of the various points in the scratching groove indicated that the Si-I to β-Sn structure (Si-II) and the following β-Sn structure (Si-II) to amorphous Si transformation appeared under the rapid loading/unloading condition of the diamond grit, and the volume change induced by the phase transformation resulted in a critical depth (ductile-brittle transition) of cut (˜60 nm ± 15 nm) much lower than the theoretical calculated results (˜387 nm). Moreover, it also led to abnormal load-displacement curves in the nanoindentation tests, resulting in the appearance of elbow and pop-out effects (˜270 nm at 20 s, 50 mN), which were highly dependent on the loading/unloading conditions. In summary, phase transformation of Si promoted surface deformation and fracture under both static and dynamic mechanical loading.

  19. Simulation analysis of the effects of a back surface field on a p-a-Si:H/n-c-Si/n+-a-Si:H heterojunction solar cell

    Institute of Scientific and Technical Information of China (English)

    Hu Yuehui; Zhang Xiangwen; Qu Minghao; Wang Lifu; Zeng Tao; Xie Yaojiang

    2009-01-01

    In order to investigate the effects of a back surface field (BSF) on the performance of a p-doped amorphous silicon (p-a-Si:H)/n-doped crystalline silicon (n-c-Si) solar cell, a heterojunction solar cell with a p-a-Si:H/nc-Si/n+-a-Si:H structure was designed. An n+-a-Si:H film was deposited on the back of an n-c-Si wafer as the BSF.The photovoltaic performance of p-a-Si:H/n-c-Si/n+-a-Si:H solar cells were simulated. It was shown that the BSF of the p-a-Si:H/n-c-Si/n+-a-Si:H solar cells could effectively inhibit the decrease of the cell performance caused by interface states.

  20. Surface passivation and optical characterization of Al2O3/a-SiCx stacks on c-Si substrates.

    Science.gov (United States)

    López, Gema; Ortega, Pablo R; Voz, Cristóbal; Martín, Isidro; Colina, Mónica; Morales, Anna B; Orpella, Albert; Alcubilla, Ramón

    2013-01-01

    The aim of this work is to study the surface passivation of aluminum oxide/amorphous silicon carbide (Al2O3/a-SiCx) stacks on both p-type and n-type crystalline silicon (c-Si) substrates as well as the optical characterization of these stacks. Al2O3 films of different thicknesses were deposited by thermal atomic layer deposition (ALD) at 200 °C and were complemented with a layer of a-SiCx deposited by plasma-enhanced chemical vapor deposition (PECVD) to form anti-reflection coating (ARC) stacks with a total thickness of 75 nm. A comparative study has been carried out on polished and randomly textured wafers. We have experimentally determined the optimum thickness of the stack for photovoltaic applications by minimizing the reflection losses over a wide wavelength range (300-1200 nm) without compromising the outstanding passivation properties of the Al2O3 films. The upper limit of the surface recombination velocity (S eff,max) was evaluated at a carrier injection level corresponding to 1-sun illumination, which led to values below 10 cm/s. Reflectance values below 2% were measured on textured samples over the wavelength range of 450-1000 nm.

  1. Surface passivation and optical characterization of Al2O3/a-SiCx stacks on c-Si substrates

    Directory of Open Access Journals (Sweden)

    Gema López

    2013-11-01

    Full Text Available The aim of this work is to study the surface passivation of aluminum oxide/amorphous silicon carbide (Al2O3/a-SiCx stacks on both p-type and n-type crystalline silicon (c-Si substrates as well as the optical characterization of these stacks. Al2O3 films of different thicknesses were deposited by thermal atomic layer deposition (ALD at 200 °C and were complemented with a layer of a-SiCx deposited by plasma-enhanced chemical vapor deposition (PECVD to form anti-reflection coating (ARC stacks with a total thickness of 75 nm. A comparative study has been carried out on polished and randomly textured wafers. We have experimentally determined the optimum thickness of the stack for photovoltaic applications by minimizing the reflection losses over a wide wavelength range (300–1200 nm without compromising the outstanding passivation properties of the Al2O3 films. The upper limit of the surface recombination velocity (Seff,max was evaluated at a carrier injection level corresponding to 1-sun illumination, which led to values below 10 cm/s. Reflectance values below 2% were measured on textured samples over the wavelength range of 450–1000 nm.

  2. Scanning Tunneling Spectroscopy Study of Single Layer Step Edges on Si (100) Surfaces

    Science.gov (United States)

    Wang, Xiqiao; Namboodiri, Pradeep; Li, Kai; Deng, Xiao; Silver, Richard

    Advanced Hydrogen lithography enables the fabrication of atomically precise donor-based quantum devices on Si(100) surfaces. Understanding the defect and step edge interaction with local electronic and geometric structures is needed to properly interpret device measurement results. Low temperature Si epitaxy, used to encapsulate devices, introduces island growth and step edges near/above buried donor nanostructures, presenting a real challenge in relocating and characterizing buried donor devices using Scanning Tunneling Microscopy/Spectroscopy (STM/STS). We present spatially resolved STS results across single layer steps on Si(100) surfaces. While the electronic properties across SA steps were found to be very similar to that on flat terraces, we observed an edge induced gap state on rebonded SB step edges, which was assigned to the unpaired dangling bond state at the lower edge atom of the rebonded SB steps. In addition, we used computational simulation within Bardeen's formalism to probe the influence of subsurface doping density profiles on the observed STS features over step edges and other defects. This study will help to elucidate the role played by surface step edges and subsurface doping densities in characterizing surface and subsurface nanostructures using STS/STM.

  3. Microwave absorbing performance enhancement of Fe75Si15Al10 composites by selective surface oxidation

    Science.gov (United States)

    Zhang, Nan; Wang, Xin; Liu, Tao; Xie, Jianliang; Deng, Longjiang

    2017-09-01

    An excessively large dielectric constant is a challenge to improve the performances of the Fe-based absorbing material. Here, we propose a selective surface oxidation method to reduce the permittivity without sacrificing the permeability, by annealing under 5%H2—95%N2 (H2/N2). It is found that a thin layer of aluminum and silicon oxides formed on the surface of Fe75Si15Al10 particles during annealing in the range of 500-780 °C under H2/N2, thereby leading to an obvious decrease of permittivity of the Fe75Si15Al10 composite. According to Gibbs free energy, aluminum and silicon oxides are formed and iron oxides are reduced during annealing under H2/N2 at above 500 °C. Interestingly, the XPS result shows that the atomic ratio of Fe decreases significantly on the particle surface, which infers that the reduced Fe atoms diffuse to the interior of the particles. The surface oxide layer can protect the inner part of the alloy from further oxidation, which contributes to a high permeability. Meanwhile, the XRD result shows the formation of DO3-type ordering, which leads to the promotion of permeability. The two reasons lead to the improvement of permeability of the Fe75Si15Al10 composite after annealing. The composite is confirmed to have high permeability and low permittivity, exhibiting better electromagnetic wave absorption properties.

  4. Evolution of kinetically controlled In-induced surface structure on Si(5 5 7) surface

    Science.gov (United States)

    Chauhan, Amit Kumar Singh; Eldose, Nirosh M.; Mishra, Monu; Niazi, Asad; Nair, Lekha; Gupta, Govind

    2014-09-01

    This paper introduces issue of kinetically controlled and temperature driven superstructural phase transition of Indium (In) on atomically clean high index Si(5 5 7)-7 × 1 surface. Auger electron spectroscopy analysis reveals that at room-temperature (RT) with a controlled incident flux of 0.002 ML/s; In overlayers evolve through the Frank-van der Merwe growth mode and yield a (1 × 1) diffraction pattern for coverage ≥1 ML. For substrate temperature 500 °C island growth is observed. On annealing the In/Si(5 5 7) interface in the temperature range 250-340 °C, clusters to two dimensional (2D) layer transformation on top of a stable monolayer is predominated. In-situ RT and HT adsorption and thermal desorption phenomena revealed the formation of coverage and temperature dependent thermally stable In induced superstructural phases such as (4 × 1) at 0.5 ML (520 °C), (√3 × √3-R30°) at 0.3 ML (560 °C) and (7 × 7) at 0.1 ML (580 °C). These indium induced superstructures could be utilized as potential substrate for the growth of various exotic 1D/2D structures.

  5. Molecular dynamics simulations of dotriacontane films supported on a SiO2 surface

    Science.gov (United States)

    Gutierrez, Sebastian; Araya, Raul; Perez-Acle, Tomas; Retamal, Maria Jose; Volkmann, Ulrich G.

    2011-03-01

    Dotriacontane (C32 H66 , C32) films supported on Si O2 surfaces were studied using very high-resolution ellipsometry, atomic force microscopy (AFM) and x-ray reflectivity techniques. For almost complete layers a model was proposed in which the C32/ Si O2 interfacial region is characterized by a parallel bilayer and perpendicular layers on top. Recent AFM measurements performed on samples forming sea-weed like structures, showed that for these particular perpendicular ``fractal like'' layers the heights are lower than the all-trans length of dotriacontane (42.5 AA). To gain insights on the internal molecular ordering and layering of C32 supported on Si O2 surfaces, we used all-atom molecular dynamics to simulate C32 films at different temperatures. Our results confirm the presence of the parallel bilayer suggesting the existence of a mixed layer on top, formed by molecules with both parallel and perpendicular segments. These findings suggest a different molecular architecture for sea-weed like structures of dotriacontane supported on Si O2 .

  6. Process of Energetic Carbon Atom Deposition on Si (001) Substrate by Molecular Dynamics Simulation

    Institute of Scientific and Technical Information of China (English)

    于威; 滕晓云; 李晓苇; 傅广生

    2002-01-01

    The process of energetic C atom deposition on Si (001)-(2×1) is studied by the molecular dynamics method using the semi-empirical many-bond Tersoff potential. It is found that the incident energy of the carbon atom has an important effect on the collision process and its diffusion process on the substrate. Most of the incident energy of the carbon atom is transferred to the substrate atoms within the initial two vibration periods of substrate atoms and its value increases with the incident energy. The spreading distance and penetration depth of the incident atom increasing with the incident energy are also identified. The simulated results imply that an important effect of energy of incident carbon on the film growth at Iow substrate temperature provides activation energy for silicon carbide formation through the vibration enhancement of local substrate atoms. In addition, suppressing carbon atom inhomogeneous collection and dispensing with the silicon diffusion process may be effectively promoted by the spreading and penetration of the energetic carbon atom in the silicon substrate.

  7. 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.

  8. Impact of organic overlayers on a-Si:H/c-Si surface potential

    KAUST Repository

    Seif, Johannes P.

    2017-04-11

    Bilayers of intrinsic and doped hydrogenated amorphous silicon, deposited on crystalline silicon (c-Si) surfaces, simultaneously provide contact passivation and carrier collection in silicon heterojunction solar cells. Recently, we have shown that the presence of overlaying transparent conductive oxides can significantly affect the c-Si surface potential induced by these amorphous silicon stacks. Specifically, deposition on the hole-collecting bilayers can result in an undesired weakening of contact passivation, thereby lowering the achievable fill factor in a finished device. We test here a variety of organic semiconductors of different doping levels, overlaying hydrogenated amorphous silicon layers and silicon-based hole collectors, to mitigate this effect. We find that these materials enhance the c-Si surface potential, leading to increased implied fill factors. This opens opportunities for improved device performance.

  9. Dynamics of interstitial atoms and vacancies during the crystallization of amorphous Si and Ge films by flash lamp annealing

    Science.gov (United States)

    Matsuo, Naoto; Yoshioka, Naoki; Heya, Akira

    2017-08-01

    We examined the dynamics of interstitial atoms and vacancies in amorphous Si (a-Si) and a-Ge films crystallized by flash lamp annealing in consideration of the self-diffusion coefficients of Si and Ge. We found that the interstitial atoms play an important role in the liquid-phase crystallization (LPC) of a-Si films, whereas the vacancies are more important for the solid-phase crystallization (SPC) of a-Si films along with the LPC and SPC of a-Ge films. For Si, the crystal defect density of the film crystallized by LPC was higher than that of the film crystallized by SPC; the opposite result was achieved for Ge. This phenomenon is considered to be attributed to the existence of interstitial atoms introduced in Si. The thermodynamic calculated results related to the relationship between the point defect and SPC or LPC supported the crystallization mechanism.

  10. Ab initio study of the adsorption of antimony and arsenic on the Si(110) surface

    Energy Technology Data Exchange (ETDEWEB)

    Huitzil-Tepanecatl, Arely [Postgrado en Fisica Aplicada, Facultad de Ciencias Fisico-Matematicas, BUAP, Apartado Postal 52, Puebla 72000 (Mexico); Cocoletzi, Gregorio H., E-mail: cocoletz@sirio.ifuap.buap.m [Centro de Investigacion Cientifica y de Educacion Superior de Ensenada, Km. 107 Carretera Tijuana-Ensenada, Codigo Postal 22860, Apartado Postal 2732 Ensenada, Baja California (Mexico); Centro de Nanociencia y Nanotecnologia, Universidad Nacional Autonoma de Mexico, Apartado Postal 2681, Ensenada, Baja California, 22800 (Mexico); Instituto de Fisica, Universidad Autonoma de Puebla, Apartado Postal J-48, Puebla 72570 (Mexico); Takeuchi, Noboru [Centro de Nanociencia y Nanotecnologia, Universidad Nacional Autonoma de Mexico, Apartado Postal 2681, Ensenada, Baja California, 22800 (Mexico)

    2010-10-29

    We have performed first principles total energy calculations to investigate the adsorption of Sb and As adatoms on the Si(110) surface using a (2 x 3) supercell. The energetics and atomic structures have been investigated in four atomic configurations. One structure is obtained by placing 1/3 of a monolayer (ML) of Sb (As) atoms on the Si(110) surface. The other three geometries are obtained by depositing 1 ML of Sb (As) atoms on the surface. In the first case the structure is formed by four trimers, in the second case the geometry is formed by zigzag atomic chains and in the third case the structure contains 'microfacets'. The energetics results of the Sb adsorption show that for low coverage the tetrahedrons formed by the adsorption of 1/3 ML is the most stable configuration, while in the monolayer region the zigzag atomic chain is the most stable structure. However, the total energies of the trimer and microfacet structures are slightly higher, indicating that under some conditions, they may be formed. In an experimental report it has been suggested that the adsorption of 1/3 and 1 ML of Sb corresponds to the low and high coverage in the experiments of Zotov et al. [A. V. Zotov, V. G. Lifshifts, and A. N. Demidchik, Surf. Sci. 274, L583 (1992)]. On the other hand, our results of the As adsorption show that for low coverage, the tetrahedrons in the adsorption of 1/3 ML also give the most stable configuration. However, at the 1 ML coverage, a structure formed by microfacets is the most stable structure, in agreement with previous results.

  11. The resistance of single atomic steps in ultrathin Pb nanowires on Si(557)

    Energy Technology Data Exchange (ETDEWEB)

    Roenspies, J.P.; Wiessell, S.; Pfnuer, H. [Leibniz Universitaet Hannover, Institut fuer Festkoerperphysik, Abteilung ATMOS, Hannover (Germany)

    2010-09-15

    We studied the local electronic transport properties of a monolayer thick Pb wire by local potentiometry with the tip of a tunneling microscope. 50-nm-wide wires on bare Si(557) were generated by direct writing with an electron beam in an ultrathin film of SiO{sub 2} using the process of electron-beam-induced selective stimulated thermal desorption of oxygen (EBSTD) in combination with a shadow-mask technique and macroscopic TiSi{sub 2} contacts. The resistivity of this wire agrees well with expectations derived from anisotropic monolayer thick Pb films on Si(557). Although small Pb clusters nucleated during annealing and desorption of excess Pb, they had a negligible effect on the local resistive properties of the wire. Steps in the substrate of atomic height apparently do not interrupt the conducting path, but due to local scattering at step edge states increase the local resistivity by more than one order of magnitude. (orig.)

  12. Adsorption and diffusion of Si adatom near single-layer steps on Si surface

    Institute of Scientific and Technical Information of China (English)

    Zhu Xiao-Yan; Huang Yan

    2005-01-01

    By use of the empirical tight-binding (ETB) method, the adsorption and diffusion behaviours of single silicon adatom on the reconstructed Si(100) surface with single-layer steps are simulated. The adsorption energies around the SA step, nonrebonded SB step, rebonded SB step, and rough SB step with a kink structure are specially mapped out in this paper, from which the favourable binding sites and several possible diffusion paths are achieved. Because of the rebonded and kink structures, the SB step is more suitable for the attachment of Si adatom than the SA step or defective surface.

  13. Plasmonic properties of Ag nanoparticles embedded in GeO2-SiO2 matrix by atom beam sputtering.

    Science.gov (United States)

    Mohapatra, Satyabrata

    2016-02-01

    Nanocomposite thin films containing Ag nanoparticles embedded in the GeO2-SiO2 matrix were synthesized by the atom beam co-sputtering technique. The structural, optical and plasmonic properties and the chemical composition of the nanocomposite thin films were studied by transmission electron microscopy (TEM) with energy dispersive X-ray spectroscopy (EDX), UV-visible absorption spectroscopy and X-ray photoelectron spectroscopy (XPS). UV-visible absorption studies on Ag-SiO2 nanocomposites revealed the presence of a strong localized surface plasmon resonance (LSPR) peak characteristic of Ag nanoparticles at 413 nm, which showed a blue shift of 26 nm (413 to 387 nm) along with a significant broadening and drastic decrease in intensity with the incorporation of 16 at% of Ge into the SiO2 matrix. TEM studies on Ag-GeO2-SiO2 nanocomposite thin films confirmed the presence of Ag nanoparticles with an average size of 3.8 nm in addition to their aggregates with an average size of 16.2 nm. Thermal annealing in air resulted in strong enhancement in the intensity of the LSPR peak, which showed a regular red shift of 51 nm (from 387 to 438 nm) with the increase in annealing temperature up to 500 °C. XPS studies showed that annealing in air resulted in oxidation of excess Ge atoms in the nanocomposite into GeO2. Our work demonstrates the possibility of controllably tuning the LSPR of Ag nanoparticles embedded in the GeO2-SiO2 matrix by single-step thermal annealing, which is interesting for optical applications.

  14. Theory of noncontact friction for atom-surface interactions

    CERN Document Server

    Jentschura, U D; DeKieviet, M

    2016-01-01

    The noncontact (van der Waals) friction is an interesting physical effect which has been the subject of controversial scientific discussion. The "direct" friction term due to the thermal fluctuations of the electromagnetic field leads to a friction force proportional to 1/Z^5 where Z is the atom-wall distance). The "backaction" friction term takes into account the feedback of thermal fluctuations of the atomic dipole moment onto the motion of the atom and scales as 1/Z^8. We investigate noncontact friction effects for the interactions of hydrogen, ground-state helium and metastable helium atoms with alpha-quartz (SiO_2), gold (Au) and calcium difluorite (CaF_2). We find that the backaction term dominates over the direct term induced by the thermal electromagnetic fluctuations inside the material, over wide distance ranges. The friction coefficients obtained for gold are smaller than those for SiO_2 and CaF_2 by several orders of magnitude.

  15. An Atomically-Resolved STM Study of the Thermal Decomposition of Disilane on Si(001)

    Science.gov (United States)

    1994-05-27

    K for 5 min, showing how the surface appears more ordered when imaged at high bias voltages. (a): Vs = -1.5 V, It = 0.5 nA, 162A X 162A ; (b): Vs...2.5 V, It = 0.5 nA, 162A X 162A . Fig. 18: Si(001) surface after exposure to 0.2 L Si2H6 at 300 K, then annealed at 540K for 5min. Anisotropic Si "dimer

  16. Effect of nano-Si3N4 surface treatment on the tribological performance of epoxy composite

    Directory of Open Access Journals (Sweden)

    2010-03-01

    Full Text Available To overcome the disadvantages generated by the loose nano-partilce agglomerates dispersed in polymer composites, a chemical grafting method was applied to modify nano-Si3N4 by covalently bonding glycidyl methacrylate (GMA onto the particles. The tribological behavior of the epoxy composite filled with nano-Si3N4 or GMA treated Si3N4 (Si3N4-g-PGMA was studied using a ring-on-block wear tester under dry sliding, and the worn surface of the filled epoxy composite and the surface roughness of the composites after the sliding wear test were investigated by SEM (scanning electron microscopy and AFM (atomic force microscopy, respectively. In comparison to the composites filled with untreated nano-Si3N4 particles, the composites with the grafted Sinano-3N4 exhibit improved sliding wear resistance and reduced friction coefficient owing to the chemical bonding at the filler/matrix interface.

  17. Controlled amino-functionalization by electrochemical reduction of bromo and nitro azobenzene layers bound to Si(111) surfaces

    NARCIS (Netherlands)

    Ullien, D.; Thüne, P.C.; Jager, W.F.; Sudhölter, E.J.R.; De Smet, L.C.P.M.

    2014-01-01

    4-Nitrobenzenediazonium (4-NBD) and 4-bromobenzenediazonium (4-BBD) salts were grafted electrochemically onto H-terminated, p-doped silicon (Si) surfaces. Atomic force microscopy (AFM) and ellipsometry experiments clearly showed layer thicknesses of 2–7 nm, which indicate multilayer formation. Decre

  18. Simple method for coating Si (1 0 0) surfaces with ferritin monolayers-Iron oxide quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Papadopoulos, Georgios, E-mail: geopap@bio.uth.gr [University of Thessaly, Department of Biochemistry and Biotechnology, Ploutonos 26 and Aeolou, 41221 Larisa (Greece); Anetakis, Constantine, E-mail: kanetaki@physics.auth.gr [Aristotle University of Thessaloniki, Department of Physics, Laboratory for Thin Films - Nanosystems and Nanometrology and Laboratory of Electronic Microscopy, 54124 Thessaloniki (Greece); Gravalidis, Christoforos, E-mail: cgrava@physics.auth.gr [Aristotle University of Thessaloniki, Department of Physics, Laboratory for Thin Films - Nanosystems and Nanometrology and Laboratory of Electronic Microscopy, 54124 Thessaloniki (Greece); Kassavetis, Spiros, E-mail: skasa@physics.auth.gr [Aristotle University of Thessaloniki, Department of Physics, Laboratory for Thin Films - Nanosystems and Nanometrology and Laboratory of Electronic Microscopy, 54124 Thessaloniki (Greece); Vouroutzis, Nikolaos, E-mail: nikosv@auth.gr [Aristotle University of Thessaloniki, Department of Physics, Laboratory for Thin Films - Nanosystems and Nanometrology and Laboratory of Electronic Microscopy, 54124 Thessaloniki (Greece); Frangis, Nikolaos, E-mail: frangis@auth.gr [Aristotle University of Thessaloniki, Department of Physics, Laboratory for Thin Films - Nanosystems and Nanometrology and Laboratory of Electronic Microscopy, 54124 Thessaloniki (Greece); Logothetidis, Stergios, E-mail: logot@auth.gr [Aristotle University of Thessaloniki, Department of Physics, Laboratory for Thin Films - Nanosystems and Nanometrology and Laboratory of Electronic Microscopy, 54124 Thessaloniki (Greece)

    2011-04-15

    With the goal to develop iron oxide quantum dots we developed a simple method to spread horse spleen ferritin monolayers on a Si (1 0 0) surface. Application of atomic force microscopy and spectroscopic ellipsometry showed the existence of regions with dense ferritin monolayers. Application of transmission electron microscopy identified the core of the spread ferritin as FeO nanocrystals.

  19. Surface morphology and structure of ultra-thin magnesium oxide grown on (100) silicon by atomic layer deposition oxidation

    Energy Technology Data Exchange (ETDEWEB)

    Rochdi, N., E-mail: rochdi.nabil@gmail.com [Centre Interdisciplinaire de Nanoscience de Marseille (CINaM), CNRS UPR 3118, Aix-Marseille Universite, Case 913, Campus de Luminy, 13288 Marseille cedex 9 (France); Liudvikouskaya, K. [Belarusian State University of Informatics and Radioelectronics, P. Browka 6, 220013 Minsk (Belarus); Descoins, M.; Raissi, M.; Coudreau, C.; Lazzari, J.-L. [Centre Interdisciplinaire de Nanoscience de Marseille (CINaM), CNRS UPR 3118, Aix-Marseille Universite, Case 913, Campus de Luminy, 13288 Marseille cedex 9 (France); Oughaddou, H. [Commissariat a l' Energie Atomique, DSM-IRAMIS-SPCSI, Bat. 462, Saclay, 91191, Gif-sur-Yvette cedex (France); Universite de Cergy-Pontoise, LAMAp, 95000 Cergy-Pontoise cedex (France); D' Avitaya, F. Arnaud [Centre Interdisciplinaire de Nanoscience de Marseille (CINaM), CNRS UPR 3118, Aix-Marseille Universite, Case 913, Campus de Luminy, 13288 Marseille cedex 9 (France)

    2011-07-29

    Ultra-thin magnesium oxide layers were elaborated by atomic layer deposition and oxidation process on silicon (100) starting from (2 x 1) thermally-reconstructed or hydrogen-terminated Si surfaces. Low-energy electron diffraction experiments show (2 x 3) and (3 x 3) reconstructions while depositing a magnesium monolayer on Si clean surfaces, and a 3-dimentional growth of the oxide as confirmed by ex-situ atomic force microscopy. For hydrogen-terminated or clean surfaces previously physisorbed by oxygen, uniform cobalt/magnesium-oxide/silicon stacks of layers are observed by transmission electron microscopy. Annealing above 150 deg. C leads to MgO dissolution and formation of an interfacial complex compound by inter-diffusion of Si and Co.

  20. New bonding configuration on Si(111) and Ge(111) surfaces induced by the adsorption of alkali metals

    DEFF Research Database (Denmark)

    Lottermoser, L.; Landemark, E.; Smilgies, D.M.;

    1998-01-01

    The structure of the (3×1) reconstructions of the Si(111) and Ge(111) surfaces induced by adsorption of alkali metals has been determined on the basis of surface x-ray diffraction and low-energy electron diffraction measurements and density functional theory. The (3×1) surface results primarily f...... from the substrate reconstruction and shows a new bonding configuration consisting of consecutive fivefold and sixfold Si (Ge) rings in 〈11̅ 0〉 projection separated by channels containing the alkali metal atoms. © 1998 The American Physical Society......The structure of the (3×1) reconstructions of the Si(111) and Ge(111) surfaces induced by adsorption of alkali metals has been determined on the basis of surface x-ray diffraction and low-energy electron diffraction measurements and density functional theory. The (3×1) surface results primarily...

  1. Gradient induced liquid motion on laser structured black Si surfaces

    Science.gov (United States)

    Paradisanos, I.; Fotakis, C.; Anastasiadis, S. H.; Stratakis, E.

    2015-09-01

    This letter reports on the femtosecond laser fabrication of gradient-wettability micro/nano-patterns on Si surfaces. The dynamics of directional droplet spreading on the surface tension gradients developed is systematically investigated and discussed. It is shown that microdroplets on the patterned surfaces spread at a maximum speed of 505 mm/s, which is the highest velocity demonstrated so far for liquid spreading on a surface tension gradient in ambient conditions. The application of the proposed laser patterning technique for the precise fabrication of surface tension gradients for open microfluidic systems, liquid management in fuel cells, and drug delivery is envisaged.

  2. Gradient induced liquid motion on laser structured black Si surfaces

    CERN Document Server

    Paradisanos, I; Anastasiadis, S H; Stratakis, E

    2015-01-01

    This letter reports on the femtosecond laser fabrication of gradient-wettability micro/nano- patterns on Si surfaces. The dynamics of directional droplet spreading on the surface tension gradients developed is systematically investigated and discussed. It is shown that microdroplets on the patterned surfaces spread at a maximum speed of 505 mm/sec, that is the highest velocity demonstrated so far for liquid spreading on a surface tension gradient in ambient conditions. The application of the proposed laser patterning technique for the precise fabrication of surface tension gradients for open microfluidic systems, liquid management in fuel cells and drug delivery is envisaged.

  3. 具有SiC缓冲层的Si衬底上直接沉积碳原子生长石墨烯%Direct Graphene Growth by Depositing Carbon Atoms on Si Substrate Covered by SiC Buffer Layers

    Institute of Scientific and Technical Information of China (English)

    唐军; 康朝阳; 李利民; 徐彭寿

    2011-01-01

    improves. However, a very high temperature decreases the quality of graphene. The best graphene films were obtained at a substrate temperature of 1000 °C. This is due to the low substrate temperature resulting in a too low carbon atom activity for the formation of an ordered six-member ring of C-sp2. When the substrate temperature was too high the silicon atoms in the substrate became so active that silicon atoms diffused to the surface of the sample through SiC buffer defects and they bonded to the depositing carbon atoms, which resulted in a lower crystallization quality of the carbon layers.

  4. Measuring Forces between Oxide Surfaces Using the Atomic Force Microscope

    DEFF Research Database (Denmark)

    Pedersen, Henrik Guldberg; Høj, Jakob Weiland

    1996-01-01

    The interactions between colloidal particles play a major role in processing of ceramics, especially in casting processes. With the Atomic Force Microscope (AFM) it is possible to measure the inter-action force between a small oxide particle (a few micron) and a surface as function of surface sep...

  5. Measuring Forces between Oxide Surfaces Using the Atomic Force Microscope

    DEFF Research Database (Denmark)

    Pedersen, Henrik Guldberg; Høj, Jakob Weiland

    1996-01-01

    The interactions between colloidal particles play a major role in processing of ceramics, especially in casting processes. With the Atomic Force Microscope (AFM) it is possible to measure the inter-action force between a small oxide particle (a few micron) and a surface as function of surface...

  6. A Novel Gravito-Optical Surface Trap for Neutral Atoms

    Institute of Scientific and Technical Information of China (English)

    XIE Chun-Xia; WANG Zhengling; YIN Jian-Ping

    2006-01-01

    @@ We propose a novel gravito-optical surface trap (GOST) for neutral atoms based on one-dimensional intensity gradient cooling. The surface optical trap is composed of a blue-detuned reduced semi-Gaussian laser beam (SGB), a far-blue-detuned dark hollow beam and the gravity field.

  7. Determination of Surface Exciton Energies by Velocity Resolved Atomic Desorption

    Energy Technology Data Exchange (ETDEWEB)

    Hess, Wayne P.; Joly, Alan G.; Beck, Kenneth M.; Sushko, Petr V.; Shluger, Alexander L.

    2004-08-20

    We have developed a new method for determining surface exciton band energies in alkali halides based on velocity-resolved atomic desorption (VRAD). Using this new method, we predict the surface exciton energies for K1, KBr, KC1, and NaC1 within +0.15 eV. Our data, combined with the available EELS data for alkali fluorides, demonstrate a universal linear correlation with the inverse inter-atomic distance in these materials. The results suggest that surface excitons exist in all alkali halides and their excitation energies can be predicted from the known bulk exciton energies and the obtained correlation plot.

  8. Early stages of plasma induced nitridation of Si (111) surface and study of interfacial band alignment

    Energy Technology Data Exchange (ETDEWEB)

    Shetty, Satish; Shivaprasad, S. M., E-mail: smsprasad@jncasr.ac.in [International Centre for Materials Science, Jawaharlal Nehru Centre for Advanced Scientific Research, Bangalore 560064 (India)

    2016-02-07

    We report here a systematic study of the nitridation of the Si (111) surface by nitrogen plasma exposure. The surface and interface chemical composition and surface morphology are investigated by using RHEED, X-ray photoelectron spectroscopy, and atomic force microscopy (AFM). At the initial stage of nitridation two superstructures—“8 × 8” and “8/3 × 8/3”—form, and further nitridation leads to 1 × 1 stoichiometric silicon nitride. The interface is seen to have the Si{sup 1+} and Si{sup 3+} states of silicon bonding with nitrogen, which suggests an atomically abrupt and defect-free interface. The initial single crystalline silicon nitride layers are seen to become amorphous at higher thicknesses. The AFM image shows that the nitride nucleates at interfacial dislocations that are connected by sub-stoichiometric 2D-nitride layers, which agglomerate to form thick overlayers. The electrical properties of the interface yield a valence band offset that saturates at 1.9 eV and conduction band offset at 2.3 eV due to the evolution of the sub-stoichiometric interface and band bending.

  9. Examination of Short- and Long-Range Atomic Order Nanocrystalline SiC and Diamond by Powder Diffraction Methods

    Science.gov (United States)

    Palosz, B.; Grzanka, E.; Stelmakh, S.; Gierlotka, S.; Weber, H.-P.; Proffen, T.; Palosz, W.

    2002-01-01

    The real atomic structure of nanocrystals determines unique, key properties of the materials. Determination of the structure presents a challenge due to inherent limitations of standard powder diffraction techniques when applied to nanocrystals. Alternate methodology of the structural analysis of nanocrystals (several nanometers in size) based on Bragg-like scattering and called the "apparent lattice parameter" (alp) is proposed. Application of the alp methodology to examination of the core-shell model of nanocrystals will be presented. The results of application of the alp method to structural analysis of several nanopowders were complemented by those obtained by determination of the Atomic Pair Distribution Function, PDF. Based on synchrotron and neutron diffraction data measured in a large diffraction vector of up to Q = 25 Angstroms(exp -1), the surface stresses in nanocrystalline diamond and SiC were evaluated.

  10. The atomic structure of ternary amorphous TixSi1-xO2 hybrid oxides.

    Science.gov (United States)

    Landmann, M; Köhler, T; Rauls, E; Frauenheim, T; Schmidt, W G

    2014-06-25

    Atomic length-scale order characteristics of binary and ternary amorphous oxides are presented within the framework of ab initio theory. A combined numerically efficient density functional based tight-binding molecular dynamics and density functional theory approach is applied to model the amorphous (a) phases of SiO2 and TiO2 as well as the amorphous phase of atomically mixed TixSi1-xO2 hybrid-oxide alloys over the entire composition range. Short and mid-range order in the disordered material phases are characterized by bond length and bond-angle statistics, pair distribution function analysis, coordination number and coordination polyhedra statistics, as well as ring statistics. The present study provides fundamental insights into the order characteristics of the amorphous hybrid-oxide frameworks formed by versatile types of TiOn and SiOm coordination polyhedra. In a-SiO2 the fourfold crystal coordination of Si ions is almost completely preserved and the atomic structure is widely dominated by ring-like mid-range order characteristics. In contrast, the structural disorder of a-TiO2 arises from short-range disorder in the local coordination environment of the Ti ion. The coordination number analysis indicates a large amount of over and under-coordinated Ti ions (coordination defects) in a-TiO2. Aside from the ubiquitous distortions of the crystal-like coordinated polyhedra, even the basic coordination-polyhedra geometry type changes for a significant fraction of TiO6 units (geometry defects). The combined effects of topological and chemical disorder in a-TixSi1-xO2 alloys lead to a continuos increase in both the Si as well as the Ti coordination number with the chemical composition x. The important roles of intermediate fivefold coordination states of Ti and Si cations are highlighted for ternary a-TixSi1-xO2 as well as for binary a-TiO2. The continuous decrease in ring size with increasing Ti content reflects the progressive loss of mid-range order structure

  11. Surface chemistry of a Cu(I) beta-diketonate precursor and the atomic layer deposition of Cu2O on SiO2 studied by x-ray photoelectron spectroscopy

    OpenAIRE

    Dhakal, Dileep; Waechtler, Thomas; E. Schulz, Stefan; Gessner, Thomas; Lang, Heinrich; Mothes, Robert; Tuchscherer, Andre

    2014-01-01

    This article has been published online on 21st May 2014, in Journal of Vacuum Science & Technology A: Vac (Vol.32, Issue 4): http://scitation.aip.org/content/avs/journal/jvsta/32/4/10.1116/1.4878815?aemail=author DOI: 10.1116/1.4878815 This article may be accessed via the issue's table of contents at this link: http://scitation.aip.org/content/avs/journal/jvsta/32/4?aemail=author The surface chemistry of the bis(tri-n-butylphosphane) copper(I) acetylacetonate, [(nBu3P)2Cu(a...

  12. Atomic force microscopy of lead iodide crystal surfaces

    Science.gov (United States)

    George, M. A.; Azoulay, M.; Jayatirtha, H. N.; Biao, Y.; Burger, A.; Collins, W. E.; Silberman, E.

    1994-03-01

    Atomic force microscopy (AFM) was used to characterize the surface of lead iodide crystals. The high vapor pressure of lead iodide prohibits the use of traditional high resolution surface study techniques that require high vacuum conditions. AFM was used to image numerous insulating surface in various ambients, with very little sample preparation techniques needed. Freshly cleaved and modified surfaces, including, chemical and vacuum etched, and air aged surfaces, were examined. Both intrinsic and induced defects were imaged with high resolution. The results were compared to a similar AFM study of mercuric iodide surfaces and it was found that, at ambient conditions, lead iodide is significantly more stable than mercuric iodide.

  13. Restoring the lattice of Si-based atom probe reconstructions for enhanced information on dopant positioning.

    Science.gov (United States)

    Breen, Andrew J; Moody, Michael P; Ceguerra, Anna V; Gault, Baptiste; Araullo-Peters, Vicente J; Ringer, Simon P

    2015-12-01

    The following manuscript presents a novel approach for creating lattice based models of Sb-doped Si directly from atom probe reconstructions for the purposes of improving information on dopant positioning and directly informing quantum mechanics based materials modeling approaches. Sophisticated crystallographic analysis techniques are used to detect latent crystal structure within the atom probe reconstructions with unprecedented accuracy. A distortion correction algorithm is then developed to precisely calibrate the detected crystal structure to the theoretically known diamond cubic lattice. The reconstructed atoms are then positioned on their most likely lattice positions. Simulations are then used to determine the accuracy of such an approach and show that improvements to short-range order measurements are possible for noise levels and detector efficiencies comparable with experimentally collected atom probe data.

  14. Stress Domains in Si\\(111\\)/a-Si3N4 Nanopixel: Ten-Million-Atom Molecular Dynamics Simulations on Parallel Computers

    Science.gov (United States)

    Omeltchenko, Andrey; Bachlechner, Martina E.; Nakano, Aiichiro; Kalia, Rajiv K.; Vashishta, Priya; Ebbsjö, Ingvar; Madhukar, Anupam; Messina, Paul

    2000-01-01

    Parallel molecular dynamics simulations are performed to determine atomic-level stresses in Si\\(111\\)/Si3N4\\(0001\\) and Si\\(111\\)/a-Si3N4 nanopixels. Compared to the crystalline case, the stresses in amorphous Si3N4 are highly inhomogeneous in the plane of the interface. In silicon below the interface, for a 25 nm square mesa stress domains with triangular symmetry are observed, whereas for a rectangular, 54 nm×33 nm, mesa tensile stress domains \\(~300 Å\\) are separated by Y-shaped compressive domain wall. Maximum stresses in the domains and domain walls are -2 GPa and +2 GPa, respectively.

  15. Stress domains in Si(111)/a-Si3N4 nanopixel: ten-million-atom molecular dynamics simulations on parallel computers

    Science.gov (United States)

    Omeltchenko; Bachlechner; Nakano; Kalia; Vashishta; Ebbsjo; Madhukar; Messina

    2000-01-10

    Parallel molecular dynamics simulations are performed to determine atomic-level stresses in Si(111)/Si(3)N4(0001) and Si(111)/a-Si3N4 nanopixels. Compared to the crystalline case, the stresses in amorphous Si3N4 are highly inhomogeneous in the plane of the interface. In silicon below the interface, for a 25 nm square mesa stress domains with triangular symmetry are observed, whereas for a rectangular, 54 nmx33 nm, mesa tensile stress domains ( approximately 300 A) are separated by Y-shaped compressive domain wall. Maximum stresses in the domains and domain walls are -2 GPa and +2 GPa, respectively.

  16. Kinetically controlled growth of gallium on stepped Si (553) surface

    Energy Technology Data Exchange (ETDEWEB)

    Kumar, Mukesh; Pasha, Syed Khalid; Govind,, E-mail: govind@nplindia.org

    2013-10-15

    Kinetically controlled growth of gallium (Ga) metal has been reported on high index stepped Si (553) surface and its thermal stability with various novel superstructural phases has been analyzed. Auger electron spectroscopy studies revealed that the adsorption of Ga at room temperature (RT) follows Frank–van der Merwe (FM) growth mode while for higher substrate temperature, Ga adsorption remains within the submonolayer range. Thermal desorption and low energy electron diffraction studies investigated the formation of thermally stable Ga-islands and the various Ga induced superstructural phase on Si (553). During room temperature adsorption, (1 1 1)7 × 7 facet of Si (553) reconstructed into (1 1 1)6 × 6 facet while during desorption process, stable (1 1 1)6 × 6 and (1 1 1)√3 × √3-R30° surface reconstructions has been observed.

  17. Kinetically controlled growth of gallium on stepped Si (553) surface

    Science.gov (United States)

    Kumar, Mukesh; Pasha, Syed Khalid; Govind

    2013-10-01

    Kinetically controlled growth of gallium (Ga) metal has been reported on high index stepped Si (553) surface and its thermal stability with various novel superstructural phases has been analyzed. Auger electron spectroscopy studies revealed that the adsorption of Ga at room temperature (RT) follows Frank-van der Merwe (FM) growth mode while for higher substrate temperature, Ga adsorption remains within the submonolayer range. Thermal desorption and low energy electron diffraction studies investigated the formation of thermally stable Ga-islands and the various Ga induced superstructural phase on Si (553). During room temperature adsorption, (1 1 1)7 × 7 facet of Si (553) reconstructed into (1 1 1)6 × 6 facet while during desorption process, stable (1 1 1)6 × 6 and (1 1 1)√3 × √3-R30° surface reconstructions has been observed.

  18. Second harmonic generation spectroscopy on Si surfaces and interfaces

    Energy Technology Data Exchange (ETDEWEB)

    Pedersen, Kjeld [Department of Physics and Nanotechnology, Aalborg University, Skjernvej 4A, 9220 Aalborg Oest (Denmark)

    2010-08-15

    Optical second harmonic generation (SHG) spectroscopy studies of Si(111) surfaces and interfaces are reviewed for two types of systems: (1) clean 7 x 7 and {radical}(3) x {radical}(3)-Ag reconstructed surfaces prepared under ultra-high vacuum conditions where surface states are excited and (2) interfaces in silicon-on-insulator (SOI) structures and thin metal films on Si surfaces where several interfaces contribute to the SHG. In all the systems resonances are seen at interband transitions near the bulk critical points E{sub 1} and E{sub 2}. On the clean surfaces a number of resonances appear below the onset of bulk-like interband transitions that can be referred to excitations of dangling bond surface states. Adsorption of oxygen leads to formation of a new surface resonance. Such resonances appearing in the region between the bulk critical points E{sub 1} and E{sub 2} are also shown to be important for Si/oxide interfaces in SOI structures. Finally, examples of spectroscopy on layers buried below thin Ag and Au films are given. (Abstract Copyright [2010], Wiley Periodicals, Inc.)

  19. Atom probe tomography of a Ti-Si-Al-C-N coating grown on a cemented carbide substrate.

    Science.gov (United States)

    Thuvander, M; Östberg, G; Ahlgren, M; Falk, L K L

    2015-12-01

    The elemental distribution within a Ti-Si-Al-C-N coating grown by physical vapour deposition on a Cr-doped WC-Co cemented carbide substrate has been investigated by atom probe tomography. Special attention was paid to the coating/substrate interface region. The results indicated a diffusion of substrate binder phase elements into the Ti-N adhesion layer. The composition of this layer, and the Ti-Al-N interlayer present between the adhesion layer and the main Ti-Si-Al-C-N layer, appeared to be sub-stoichiometric. The analysis of the interlayer showed the presence of internal surfaces, possibly grain boundaries, depleted in Al. The composition of the main Ti-Al-Si-C-N layer varied periodically in the growth direction; layers enriched in Ti appeared with a periodicity of around 30 nm. Laser pulsing resulted in a good mass resolution that made it possible to distinguish between N(+) and Si(2+) at 14 Da.

  20. Surface Recombination Investigation in Thin 4H-SiC Layers

    Directory of Open Access Journals (Sweden)

    Karolis GULBINAS

    2011-07-01

    Full Text Available n- and p-type 4H-SiC epilayers were grown on heavily doped SiC substrates. The thickness of the p-type layer was 7 µm and the doping level around 1017 cm 3, while the n-type epilayers were 15 µm thick and had a doping concentration of 3 - 5*1015 cm 3. Several different surface treatments were then applied on the epilayers for surface passivation: SiO2 growth, Al2O3 deposited by atomic layer deposition, and Ar-ion implantation. Using collinear pump - probe technique the effective carrier lifetimes were measured from various places and statistical lifetime distributions were obtained. For surface recombination evaluation, two models are presented. One states that surface recombination velocity (SRV is equal on both the passivation/epi layer interface (S2 and the deeper interface between the epilayer and the SiC substrate i. e. (S1 = S2. The other model is simulated assuming that SRV in the epilayer/substrate (S1 interface is constant while in the passivation layer/epilayer (S2 interface SRV can be varied S2 < S1. Empirical nomograms are presented with various parameters sets to evaluate S2 values. We found that on the investigated 4H-SiC surfaces S2 ranges from 3x104 to 5x104 assuming that the bulk lifetime is 4 (µs. In Ar+ implanted surfaces S2 is between (105 - 106 cm/s.http://dx.doi.org/10.5755/j01.ms.17.2.479

  1. Formation of Si{sup 1+} in the early stages of the oxidation of the Si[001] 2 × 1 surface

    Energy Technology Data Exchange (ETDEWEB)

    Herrera-Gomez, Alberto, E-mail: aherrerag@cinvestav.mx [CINVESTAV-Unidad Queretaro, Queretaro 76230 (Mexico); Aguirre-Tostado, Francisco-Servando [Centro de Investigación en Materiales Avanzados, Monterrey, Nuevo Leon, 66600 (Mexico); Pianetta, Piero [SLAC National Accelerator Center, Menlo Park, California 94025 (United States)

    2016-03-15

    The early stages of the oxidation of the Si[001] 2 × 1 surface were studied with synchrotron radiation photoelectron spectroscopy. The analysis was based on the block approach, which is a refinement of spectra-subtraction that accounts for changes on the background signal and for band-bending shifts. By this method, it was possible to robustly show that the formation of Si{sup 1+} is due to oxygen bonding to the upper dimer atoms. Our results contrast with ab initio calculation, which indicates that the most favorable bonding site is the back-bond of the down-dimer.

  2. Direct Observations of Correlation between Si-2p Components and Surface States on Si(110)-16 × 2 Single-Domain Surface Using Si-L23VV Auger-Electron and Si-2p Photoelectron Coincidence Measurements

    Science.gov (United States)

    Kakiuchi, Takuhiro; Yoshizaki, Yuya; Kubota, Hiroyuki; Sato, Yuki; Nagaoka, Shin-ichi; Mase, Kazuhiko

    2017-05-01

    A Si(110)-16 × 2 single-domain (SD) surface is investigated in a site-selective way using Si L23VV Auger-electron Si-2p photoelectron coincidence spectroscopy (Si-L23VV-Si-2p APECS) and Si-2p photoelectron Si-L23VV Auger-electron coincidence spectroscopy (Si-2p-Si-L23VV PEACS). The Si(110)-16 × 2 SD consists of five Si-2p surface components (SC1-SC5) and has four semiconducting surface states (S1-S4). The Si-L2VV-Si-2p1/2 APECS spectrum of the Si(110)-16 × 2 SD measured in coincidence with Si-2p1/2 photoelectrons of SC3, SC4, and SC5 shows two small shoulders in the higher Auger electron kinetic energy (AeKE) region. These shoulders suggest Auger processes involving the surface states S1 and S3. The spectral weights of SC3, SC4, and SC5 Si-2p components are greatly enhanced in the Si-2p-Si-L23VV PEACS spectrum measured at Auger electrons with an AeKE of +5.0 eV relative to the Si L23VV peak. On the other hand, the spectral weights of SC1 and SC2 Si-2p components in the Si-2p-Si-L23VV PEACS spectrum show a maximum peak at a relative AeKE of +3 eV. These results directly support the correlations between the five surface components (SC1-SC5) and four surface states (S1-S4) in the adatom-buckling model for the Si(110)-16 × 2 SD proposed by Sakamoto et al. [https://doi.org/10.1103/PhysRevB.79.045304" xlink:type="simple">Phys. Rev. B 79, 045304 (2009)].

  3. Visible Light-Induced Metal Free Surface Initiated Atom Transfer Radical Polymerization of Methyl Methacrylate on SBA-15

    Directory of Open Access Journals (Sweden)

    Liang Ma

    2017-02-01

    Full Text Available Surface-initiated atom transfer radical polymerization (SI-ATRP is one of the most versatile techniques to modify the surface properties of materials. Recent developed metal-free SI-ATRP makes such techniques more widely applicable. Herein photo-induced metal-free SI-ATRP of methacrylates, such as methyl methacrylate, N-isopropanyl acrylamide, and N,N-dimethylaminoethyl methacrylate, on the surface of SBA-15 was reported to fabricate organic-inorganic hybrid materials. A SBA-15-based polymeric composite with an adjustable graft ratio was obtained. The structure evolution during the SI-ATRP modification of SBA-15 was monitored and verified by FT-IR, XPS, TGA, BET, and TEM. The obtained polymeric composite showed enhanced adsorption ability for the model compound toluene in aqueous conditions. This procedure provides a low-cost, readily available, and easy modification method to synthesize polymeric composites without the contamination of metal.

  4. Stepwise mechanism and H2O-assisted hydrolysis in atomic layer deposition of SiO2 without a catalyst.

    Science.gov (United States)

    Fang, Guo-Yong; Xu, Li-Na; Wang, Lai-Guo; Cao, Yan-Qiang; Wu, Di; Li, Ai-Dong

    2015-01-01

    Atomic layer deposition (ALD) is a powerful deposition technique for constructing uniform, conformal, and ultrathin films in microelectronics, photovoltaics, catalysis, energy storage, and conversion. The possible pathways for silicon dioxide (SiO2) ALD using silicon tetrachloride (SiCl4) and water (H2O) without a catalyst have been investigated by means of density functional theory calculations. The results show that the SiCl4 half-reaction is a rate-determining step of SiO2 ALD. It may proceed through a stepwise pathway, first forming a Si-O bond and then breaking Si-Cl/O-H bonds and forming a H-Cl bond. The H2O half-reaction may undergo hydrolysis and condensation processes, which are similar to conventional SiO2 chemical vapor deposition (CVD). In the H2O half-reaction, there are massive H2O molecules adsorbed on the surface, which can result in H2O-assisted hydrolysis of the Cl-terminated surface and accelerate the H2O half-reaction. These findings may be used to improve methods for the preparation of SiO2 ALD and H2O-based ALD of other oxides, such as Al2O3, TiO2, ZrO2, and HfO2.

  5. Scattering approach to dispersive atom-surface interactions

    Energy Technology Data Exchange (ETDEWEB)

    Dalvit, Diego [Los Alamos National Laboratory; Messina, Riccardo [LAB KASTLER BROSSEL; Maia Neto, Paulo [INSTITUTO DE FISICA UFRJ; Lambrecht, Astrid [LAB KASTLER BROSSEL; Reynaud, Serge [LAB KASTLER BROSSEL

    2009-01-01

    We develop the scattering approach for the dispersive force on a ground state atom on top of a corrugated surface. We present explicit results to first order in the corrugation amplitude. A variety of analytical results are derived in different limiting cases, including the van der Waals and Casimir-Polder regimes. We compute numerically the exact first-order dispersive potential for arbitrary separation distances and corrugation wavelengths, for a Rubidium atom on top of a silicon or gold corrugated surface. We consider in detail the correction to the proximity force approximation, and present a very simple approximation algorithm for computing the potential.

  6. Scanning tunneling microscopic and spectroscopic studies on a crystalline silica monolayer epitaxially formed on hexagonal SiC(0001¯) surfaces

    Science.gov (United States)

    Tochihara, Hiroshi; Shirasawa, Tetsuroh; Suzuki, Takayuki; Miyamachi, Toshio; Kajiwara, Takashi; Yagyu, Kazuma; Yoshizawa, Shunsuke; Takahashi, Toshio; Tanaka, Satoru; Komori, Fumio

    2014-02-01

    An epitaxial silicon-oxide monolayer of chemical composition of Si2O3 (the Si2O3 layer) formed on hexagonal SiC(0001¯) surfaces has been observed by scanning tunneling microscopy (STM). Filled- and empty-state STM images with atomic resolution support the previously reported model. Typical structural defects in the Si2O3 layer are found to be missing SiOn (n = 1, 2, 3) molecules. The band gap of the Si2O3 layer obtained by point tunneling spectroscopy is 5.5±0.5 eV, exhibiting considerable narrowing from that of bulk SiO2, 8.9 eV. It is proposed that the Si2O3 layer is suitable as a relevant interface material for formation of SiC-based metal-oxide-semiconductor devices.

  7. Phospholipid bilayer formation at a bare Si surface

    DEFF Research Database (Denmark)

    Gutberlet, T.; Steitz, R.; Fragneto, G.;

    2004-01-01

    Neutron reflectivity was applied to monitor in situ the adsorption of small unilamellar phospholipid vesicles on a solid bare hydrophilic Si interface. The obtained reflectivity curves are consistent with the rupture and fusion model for the adsorption of phosphatidylcholine vesicles to solid...... interfaces. The results show details of the adsorbed bilayer system at ångström resolution and indicate the presence of a thin ∼6 Å thick water leaflet that separates the bilayer from the Si surface. The resolved structural details provide the basis for further investigation of processes such as adsorption...

  8. Thermal Diffusion of Si Atoms at the Interface of Mo/Si Bilayers Studied with a Soft X-ray Emission Microscope

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    Thermal diffusion of Si atoms at the interface in Mo/Si multilayers was observed with an imaging-type soft-X-ray emission microscope developed by us. It was possible to observe the diffusion with 0.2nm depth resolution in the direction normal to the interface by comparing the emission intensity for exactly the same position. The diffusion coefficient of Si atoms in Mo at 600℃ was roughly estimated to be 6.0×10-17cm2/s.

  9. Ethers on Si(001): A prime example for the common ground between surface science and molecular organic chemistry

    KAUST Repository

    Pecher, Lisa

    2017-09-15

    Using computational chemistry, we show that the adsorption of ether molecules on Si(001) under ultra-high vacuum conditions can be understood with textbook organic chemistry. The two-step reaction mechanism of (1) dative bond formation between the ether oxygen and a Lewis acidic surface atom and (2) a nucleophilic attack of a nearby Lewis basic surface atom is analysed in detail and found to mirror the acid-catalysed ether cleavage in solution. The O-Si dative bond is found to be the strongest of its kind and reactivity from this state defies the Bell-Evans-Polanyi principle. Electron rearrangement during the C-O bond cleavage is visualized using a newly developed bonding analysis method, which shows that the mechanism of nucleophilic substitutions on semiconductor surfaces is identical to molecular chemistry SN2 reactions. Our findings thus illustrate how the fields of surface science and molecular chemistry can mutually benefit and unexpected insight can be gained.

  10. Haemocompatibility evaluation of DLC- and SiC-coated surfaces

    Directory of Open Access Journals (Sweden)

    Nurdin N.

    2003-06-01

    Full Text Available Diamond-like carbon (DLC and silicon carbide (SiC coatings are attractive because of low friction coefficient, high hardness, chemical inertness and smooth finish, which they provide to biomedical devices. Silicon wafers (Siwaf and silicone rubber (Sirub plates were coated using plasma-enhanced chemical vapour deposition (PE-CVD techniques. This article describes: 1- the characterization of modified surfaces using attenuated total reflection-Fourier transform infrared spectroscopy (ATR/FTIR and contact angle measurements, 2- the results of three in-vitro haemocompatibility assays. Coated surfaces were compared to uncoated materials and various substrates such as polymethylmethacrylate (PMMA, polyethylene (LDPE, polydimethylsiloxane (PDMS and medical steel (MS. Thrombin generation, blood platelet adhesion and complement convertase activity tests revealed the following classification, from the most to the least heamocompatible surface: Sirub/ DLC-Sirub/ DLC-Siwaf/ LDPE/ PDMS/ SiC-Siwaf/ Siwaf/ PMMA/ MS. The DLC coating surfaces delayed the clotting time, tended to inhibit the platelet and complement convertase activation, whereas SiC-coated silicon wafer can be considered as thrombogenic. This study has taken into account three events of the blood activation: coagulation, platelet activation and inflammation. The response to those events is an indicator of the in vitro haemocompatibility of the different surfaces and it allows us to select biomaterials for further in vivo blood contacting investigations.

  11. Effect of Na adsorption on the structural and electronic properties of Si(111)√3 × √3-Au surface.

    Science.gov (United States)

    Bondarenko, L V; Matetskiy, A V; Yakovlev, A A; Tupchaya, A Y; Gruznev, D V; Ryzhkova, M V; Tsukanov, D A; Borisenko, E A; Chukurov, E N; Denisov, N V; Vilkov, O; Vyalikh, D V; Zotov, A V; Saranin, A A

    2014-02-05

    Adsorption of ∼0.1 ML of Na onto the Si(111)√3 × √3-Au surface held at 300 °C has been found to induce pronounced changes in its structural and electronic properties. Domain wall networks, characteristic of the pristine surface, are removed completely, leading to the formation of a highly ordered homogeneous surface. The original atomic arrangement of the Si(111)√3 × √3-Au is preserved and Na atoms occupy T4 adsorption sites at the centers of surface Si trimers. Upon Na adsorption, a pronounced metallic S1 surface-state band develops. It is characterized by a large spin splitting (momentum splitting at the Fermi level Δk∥ = 0.027 Å(-1) and consequent energy splitting ΔEF = 110 meV), large electron filling (on the order of 0.5 electrons per √3 × √3 unit cell) and small effective electron mass of (0.028 ± 0.006)me. The natural consequence of the latter properties is a high surface conductivity of the Si(111)√3 × √3-(Au, Na) surface.

  12. Orbital Calculations of Kaolinite Surface:on Substitution of Al3+ for Si4+ in the Tetrahedral Sites

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    The surface properties of kaolinite were determined using density functional theory discrete variational method (DFT-DVM) and Gaussian 03 program. A SiO4 tetrahedral hexagonal ring with two Al octahedra was chosen to model the kaolinite crystal. The total density of states of the kaolinite cluster are located near the Fermi level at both sides of the Fermi level. Both the highest occupied molecular orbit(HOMO) and the lowest unoccupied molecular orbit (LUMO) of kaolinite indicate that kaolinite system can not only readily interact with electron-acceptor species, but also readily interact with electron-donor species on the edge surface and the gibbsite layer surface, and thus, shows amphoteric behavior. Substitution of Al3+ for Si4+ in the tetrahedral site linking the vacant Al3+ octahedra does not increase the surface chemical reactivity of kaolinite, while substitution of Al3+ for Si4+ in the tetrahedral site with the apex O linking Al3+ octahedra increase the surface chemical reactivity of the siloxane surface of kaolinite, especially acting as electron donors.Additionally, substitution of Al3+ for Si4+ in the tetrahedral site results in the re-balance of charges, leading to the increase of negative charge of the coordinated O atoms of the AlO4 tetrahedra, and therefore favoring the formation of ionic bonds between cations and the surface O atoms in the basal plane.

  13. Probing atomic structure and Majorana wavefunctions in mono-atomic Fe chains on superconducting Pb surface

    Science.gov (United States)

    Pawlak, Rémy; Kisiel, Marcin; Klinovaja, Jelena; Meier, Tobias; Kawai, Shigeki; Glatzel, Thilo; Loss, Daniel; Meyer, Ernst

    2016-11-01

    Motivated by the striking promise of quantum computation, Majorana bound states (MBSs) in solid-state systems have attracted wide attention in recent years. In particular, the wavefunction localisation of MBSs is a key feature and is crucial for their future implementation as qubits. Here we investigate the spatial and electronic characteristics of topological superconducting chains of iron atoms on the surface of Pb(110) by combining scanning tunnelling microscopy and atomic force microscopy. We demonstrate that the Fe chains are mono-atomic, structured in a linear manner and exhibit zero-bias conductance peaks at their ends, which we interpret as signature for a MBS. Spatially resolved conductance maps of the atomic chains reveal that the MBSs are well localised at the chain ends (≲25 nm), with two localisation lengths as predicted by theory. Our observation lends strong support to use MBSs in Fe chains as qubits for quantum-computing devices.

  14. Growth of Co Nanoclusters on Si3N4 Surface Formed on Si(111)

    Institute of Scientific and Technical Information of China (English)

    刘熙; 贾金锋; 王俊忠; 薛其坤

    2003-01-01

    We have grown high density Co dusters with a narrow-sized distribution on the Si3N4(0001)-(8 × 8) surface. In the submonolayer regime, Co clusters tend to keep a certain size (~ 1.45 nm in diameter) irrespective of coverage.With increasing coverage above 0.92 ML, two new clusters with certain but larger sizes are formed. This novel growth behaviour can be explained by the quantum size effect [Phys. Rev. Lett. 90 (2003) 185506]. It is found that the Co cluster size distribution can be improved by post annealing. Even at high temperature (700℃ ), no reaction of Co with Si3N4 is observed, indicating that Si3N4(0001)-(8 × 8) is a promising substrate for growth of magnetic nanostructures.

  15. Capillary-force measurement on SiC surfaces

    NARCIS (Netherlands)

    Sedighi, M.; Svetovoy, V. B.; Palasantzas, G.

    2016-01-01

    Capillary forces have been measured by atomic force microscopy in the sphere-plate geometry, in a controlled humidity environment, between smooth silicon carbide and borosilicate glass spheres. The force measurements were performed as a function of the rms surface roughness similar to 4-14 nm mainly

  16. Si-rich W silicide films composed of W-atom-encapsulated Si clusters deposited using gas-phase reactions of WF6 with SiH4.

    Science.gov (United States)

    Okada, Naoya; Uchida, Noriyuki; Kanayama, Toshihiko

    2016-02-28

    We formed Si-rich W silicide films composed of Sin clusters, each of which encapsulates a W atom (WSi(n) clusters with 8 composed of WSi(n) clusters with a uniform n, which was determined by the gas temperature. The formed films were amorphous semiconductors with an optical gap of ∼0.8-1.5 eV and an electrical mobility gap of ∼0.05-0.12 eV, both of which increased as n increased from 8 to 12. We attribute this dependence to the reduction of randomness in the Si network as n increased, which decreased the densities of band tail states and localized states.

  17. Mechanistic study of atomic layer deposition of Al{sub x}Si{sub y}O thin film via in-situ FTIR spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Cho, Jea; Kim, Taeseung; Seegmiller, Trevor; Chang, Jane P., E-mail: jpchang@ucla.edu [Department of Chemical and Biomolecular Engineering, UCLA, Los Angeles, California 90095 (United States)

    2015-09-15

    A study of surface reaction mechanism on atomic layer deposition (ALD) of aluminum silicate (Al{sub x}Si{sub y}O) was conducted with trimethylaluminum (TMA) and tetraethoxysilane (TEOS) as precursors and H{sub 2}O as the oxidant. In-situ Fourier transform infrared spectroscopy (FTIR) was utilized to elucidate the underlying surface mechanism that enables the deposition of Al{sub x}Si{sub y}O by ALD. In-situ FTIR study revealed that ineffective hydroxylation of the surface ethoxy (–OCH{sub 2}CH{sub 3}) groups prohibits ALD of SiO{sub 2} by TEOS/H{sub 2}O. In contrast, effective desorption of the surface ethoxy group was observed in TEOS/H{sub 2}O/TMA/H{sub 2}O chemistry. The presence of Al-OH* group in vicinity of partially hydroxylated ethoxy (–OCH{sub 2}CH{sub 3}) group was found to propagate disproportionation reaction, which results in ALD of Al{sub x}Si{sub y}O. The maximum thickness from incorporation of SiO{sub x} from alternating exposures of TEOS/H{sub 2}O chemistry in Al{sub x}Si{sub y}O was found to be ∼2 Å, confirmed by high resolution transmission electron microscopy measurements.

  18. Influence of Group-III-metal and Ag adsorption on the Ge growth on Si(111) and its vicinal surface

    Energy Technology Data Exchange (ETDEWEB)

    Speckmann, Moritz

    2011-12-15

    In the framework of this thesis the surfactant-mediated heteroepitaxial growth of Ge on different Si surfaces has been investigated by means of low-energy electron microscopy, low-energy electron diffraction, spot-profile analysing low-energy electron diffraction, X-ray standing waves, grazing-incidence X-ray diffraction, x-ray photoemission electron microscopy, X-ray photoemission spectroscopy, scanning tunneling microscopy, scanning electron microscopy, transmission electron microscopy, and density functional theory calculations. As surfactants gallium, indium, and silver were used. The adsorption of Ga or In on the intrinsically faceted Si(112) surface leads to a smoothing of the surface and the formation of (N x 1) reconstructions, where a mixture of building blocks of different sizes is always present. For both adsorbates the overall periodicity on the surface is strongly dependent on the deposition temperature and the coverage. For the experimental conditions chosen here, the periodicities are in the range of 5.2{<=}N{<=}6.5 and 3.4{<=}N{<=}3.7 for Ga and In, respectively. The (N x 1) unit cells of Ga/Si(112) and In/Si(112) are found to consist of adsorbate atoms on terrace and step-edge sites, forming two atomic chains along the [110] direction. In the Ga-induced structures two Ga-vacancies per unit cell (one in the terrace and one in the step-edge site) are found and a continuous vacancy line on the surface is formed. In the In/Si(112) structure only one vacancy per unit cell in the step-edge site exists and, thus, a continuous adsorbate chain on the terrace sites is present. The adsorption of Ga or In on Si(112) strongly influences the subsequent Ge growth. Ge deposition on the Ga-terminated Si(112) surface leads to the formation of Ge nanowires, which are elongated along the Ga chains and reach lengths of up to 2000 nm for a growth temperature of 600 C. On In-covered Si(112), both small dash-like Ge islands and triangularly shaped islands are found, where

  19. Atomic simulations for surface-initiated melting of Nb(111)

    Institute of Scientific and Technical Information of China (English)

    YANG Xi-yuan; WU Dan

    2009-01-01

    A modified analytic embedded-atom model(MAEAM) was applied to investigate surface premelting and melting behaviors of Nb(111) plane by molecular dynamics(MD) simulations. First the relaxation of surface interface space at 300 K was studied. Then a number N of the disordered atoms per unit area was determined at the given temperatures to investigate the surface premelting and melting evolution. The obtained results indicated that the premelting phenomena occurred at about 1 100 K and a liquid-like layer emerged on (111) plane simultaneously. As temperature increased up to 2 200 K, the number N grew logarithmically for short-range metallic interactions. Upon 2 350 K surface melting generated originally and the number N increased exponentially with the incremental temperature.

  20. Surface morphology of ultrathin graphene oxide films obtained by the SAW atomization

    Science.gov (United States)

    Balachova, Olga V.; Balashov, Sergey M.; Costa, Carlos A. R.; Pavani Filho, A.

    2015-08-01

    Lately, graphene oxide (GO) thin films have attracted much attention: they can be used as humidity-sensitive coatings in the surface acoustic wave (SAW) sensors; being functionalized, they can be used in optoelectronic or biodevices, etc. In this research we study surface morphology of small-area thin GO films obtained on Si and quartz substrates by deposition of very small amounts of H2O-GO aerosols produced by the SAW atomizer. An important feature of this method is the ability to work with submicrovolumes of liquids during deposition that provides relatively good control over the film thickness and quality, in particular, minimization of the coffee ring effect. The obtained films were examined using AFM and electron microscopy. Image analysis showed that the films consist of GO sheets of different geometry and sizes and may form discrete or continuous coatings at the surface of the substrates with the minimum thickness of 1.0-1.8 nm which corresponds to one or two monolayers of GO. The thickness and quality of the deposited films depend on the parameters of the SAW atomization (number of atomized droplets, a volume of the initial droplet, etc.) and on sample surface preparation (activation in oxygen plasma). We discuss the structure of the obtained films, uniformity and the surface coverage as a function of parameters of the film deposition process and sample preparation. Qualitative analysis of adhesion of GO films is made by rinsing the samples in DI water and subsequent evaluation of morphology of the remained films.

  1. A surface-mediated siRNA delivery system developed with chitosan/hyaluronic acid-siRNA multilayer films through layer-by-layer self-assembly

    Science.gov (United States)

    Wu, Lijuan; Wu, Changlin; Liu, Guangwan; Liao, Nannan; Zhao, Fang; Yang, Xuxia; Qu, Hongyuan; Peng, Bo; Chen, Li; Yang, Guang

    2016-12-01

    siRNA delivery remains highly challenging because of its hydrophilic and anionic nature and its sensitivity to nuclease degradation. Effective siRNA loading and improved transfection efficiency into cells represents a key problem. In our study, we prepared Chitosan/Hyaluronic acid-siRNA multilayer films through layer-by-layer self-assembly, in which siRNAs can be effectively loaded and protected. The construction process was characterized by FTIR, 13C NMR (CP/MAS), UV-vis spectroscopy, and atomic force microscopy (AFM). We presented the controlled-release performance of the films during incubation in 1 M NaCl solution for several days through UV-vis spectroscopy and polyacrylamide gel electrophoresis (PAGE). Additionally, we verified the stability and integrity of the siRNA loaded on multilayer films. Finally, the biological efficacy of the siRNA delivery system was evaluated via cells adhesion and gene silencing analyses in eGFP-HEK 293T cells. This new type of surface-mediated non-viral multilayer films may have considerable potential in the localized and controlled-release delivery of siRNA in mucosal tissues, and tissue engineering application.

  2. Layer uniformity in glucose oxidase immobilization on SiO{sub 2} surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Libertino, Sebania [CNR - IMM unita Catania, Stradale Primosole 50, 95121 Catania (Italy)], E-mail: sebania.libertino@imm.cnr.it; Scandurra, Antonino [Laboratorio Superfici e Interfasi (SUPERLAB), Consorzio Catania Ricerche, Stradale Primosole 50, 95121 Catania (Italy); Aiello, Venera [CNR - IMM unita Catania, Stradale Primosole 50, 95121 Catania (Italy); Universita degli Studi di Catania, Dipartimento di Chimica Biologica, Chimica Medica e Biologia Molecolare, Viale A.Doria, 6, 95125 Catania (Italy); Giannazzo, Filippo [CNR - IMM unita Catania, Stradale Primosole 50, 95121 Catania (Italy); Sinatra, Fulvia [Universita degli Studi di Catania, Dipartimento di Scienze Biomediche, Via S. Sofia, 87, 95100 Catania (Italy); Renis, Marcella [Universita degli Studi di Catania, Dipartimento di Chimica Biologica, Chimica Medica e Biologia Molecolare, Viale A.Doria, 6, 95125 Catania (Italy); Fichera, Manuela [CNR - IMM unita Catania, Stradale Primosole 50, 95121 Catania (Italy)

    2007-09-30

    The goal of this work was the characterization, step by step, of the enzyme glucose oxidase (GOx) immobilization on silicon oxide surfaces, mainly by means of X-Ray photoelectron spectroscopy (XPS). The immobilization protocol consists of four steps: oxide activation, silanization, linker molecule deposition and GOx immobilization. The linker molecule, glutaraldehyde (GA) in this study, must be able to form a uniform layer on the sample surface in order to maximize the sites available for enzyme bonding and achieve the best enzyme deposition. Using a thin SiO{sub 2} layer grown on Si wafers and following the XPS Si2p signal of the Si substrate during the immobilization steps, we demonstrated both the glutaraldehyde layer uniformity and the possibility to use XPS to monitor thin layer uniformity. In fact, the XPS substrate signal, not shielded by the oxide, is suppressed only when a uniform layer is deposited. The enzyme correct immobilization was monitored using the XPS C1s and N1s signals. Atomic force microscopy (AFM) measurements carried out on the same samples confirmed the results.

  3. Interaction of tetraethoxysilane with OH-terminated SiO2 (0 0 1) surface: A first principles study

    Science.gov (United States)

    Deng, Xiaodi; Song, Yixu; Li, Jinchun; Pu, Yikang

    2014-06-01

    First principles calculates have been performed to investigate the surface reaction mechanism of tetraethoxysilane (TEOS) with fully hydroxylated SiO2(0 0 1) substrate. In semiconductor industry, this is the key step to understand and control the SiO2 film growth in chemical vapor deposition (CVD) and atomic layer deposition (ALD) processes. During the calculation, we proposed a model which breaks the surface dissociative chemisorption into two steps and we calculated the activation barriers and thermochemical energies for each step. Our calculation result for step one shows that the first half reaction is thermodynamically favorable. For the second half reaction, we systematically studied the two potential reaction pathways. The comparing result indicates that the pathway which is more energetically favorable will lead to formation of crystalline SiO2 films while the other will lead to formation of disordered SiO2 films.

  4. On the structural and electronic properties of Ir-silicide nanowires on Si(001) surface

    Science.gov (United States)

    Fatima, Can Oguz, Ismail; ćakır, Deniz; Hossain, Sehtab; Mohottige, Rasika; Gulseren, Oguz; Oncel, Nuri

    2016-09-01

    Iridium (Ir) modified Silicon (Si) (001) surface is studied with Scanning Tunneling Microscopy/Spectroscopy (STM/STS) and Density Functional Theory (DFT). A model for Ir-silicide nanowires based on STM images and ab-initio calculations is proposed. According to our model, the Ir adatom is on the top of the substrate dimer row and directly binds to the dimer atoms. I-V curves measured at 77 K shows that the nanowires are metallic. DFT calculations confirm strong metallic nature of the nanowires.

  5. The Si/Si_3N4 Interface and Si/Si_3N4 Submicron Mesa: A Multi-million Atom Molecular Dynamics Study

    Science.gov (United States)

    Bachlechner, Martina E.; Omeltchenko, Andrey; Nakano, Aiichiro; Kalia, Rajiv K.; Vashishta, Priya; Ebbsjö, Ingvar; Madhukar, Anupam

    1998-03-01

    Using molecular dynamics simulations on parallel computers, the interface structure, stress distribution, crack propagation and fracture in a Si_3N4 film on Si substrate are studied. Bulk Si is described by Stillinger-Weber potential and Si_3N4 is represented by a combination of two- and three-body covalent interactions. At the interface, the charge transfer is taken from LCAO electronic structure calculations (G.-L. Zhao and M.E. Bachlechner, Europhys. Lett. 36, 287 (1997)). Results for structural correlations at the interface and 3D stress distribution for the submicron mesa are presented.

  6. Surface Roughness and Dislocation Distribution in Compositionally Graded Relaxed SiGe Buffer Layer with Inserted Strained Si Layers

    Science.gov (United States)

    Yoon, Tae-Sik

    2005-03-01

    We report the experimental investigation of surface roughness and dislocation distribution of 1 μm-thick, compositionally graded, relaxed SiGe buffer layer with a final Ge surface content of 30%. Tensile-strained Si layers are inserted at various locations in the graded buffer during SiGe epitaxial growths. Slight reduction in surface roughness from about 10.3 nm to about 7.8 nm by inserting two 20 nm thick tensile-strained Si layers followed by SiGe growths. It turns out that majority of the residual surface roughness is developed during the SiGe growths on top of the topmost strain Si layer. The surface immediately after the growth of tensile strained Si is very flat with about 1.1 nm RMS roughness and without crosshatch morphology. Cross-sectional TEM shows clear signs of increased interaction between dislocation half-loops at the top surface of the strained Si layers. Our observation shows that although thin Si layers under tensile-strain are effective in reducing cross-hatch, they could in the meantime impede dislocation propagation leading to higher threading dislocation density. Considerations for an optimized scheme exploiting the flattening function of tensile-strained layers will be discussed.

  7. Plasmas and atom beam activation of the surface of polymers

    Energy Technology Data Exchange (ETDEWEB)

    Lopez-Santos, C; Yubero, F; Cotrino, J; Barranco, A; Gonzalez-Elipe, A R [Instituto de Ciencia de Materiales de Sevilla (CSIC-Univ. Sevilla), Avda Americo Vespucio 49, E-41092 Sevilla (Spain)], E-mail: arge@icmse.csic.es

    2008-11-21

    Wetting properties of polyethylene terephthalate (PET) and low-density polyethylene polymers have been investigated after treatment with a microwave (MW) plasma discharge at low pressure and a dielectric barrier discharge at atmospheric pressure. Experiments have also been carried out in situ with an atom source installed in an x-ray photoemission spectrometer (XPS). The water contact angle measured on both polymers experienced a significant decrease after activation, but a progressive recovery up to different values after ageing. Standard chemical analysis by XPS showed that the plasma and oxygen beam treatments produced an increase in the concentration of -C(O){sub x} functional groups at the outermost surface layers of the treated polymers. Besides, the oxygen distribution between the topmost surface layer and the bulk has been obtained by non-destructive XPS peak shape analysis. Atomic force microscopy analysis of the surface topography showed that, except for PET treated with the MW plasma and the atom beam, the surface roughness increased after the plasma treatments. Wetting angle variations, oxygen content and distribution, surface roughness and evolution of these properties with time are comparatively discussed by taking into account the basic processes that each type of activation procedure induces in the outmost surface layers of the treated polymers.

  8. Surface-Initiated Atom Transfer Radical Polymerization and Electrografting Technique as a Means For Attaining Tailor-Made Polymer Coatings

    DEFF Research Database (Denmark)

    Chernyy, Sergey

    2012-01-01

    Atom transfer radical polymerization initiated from a surface of various substrates (SI-ATRP) has become a progressively popular technique for obtaining thin polymer films with predetermined properties. The present work addresses the main features of SI-ATRP with respect to the controllability......, the kinetics of polymerization was analyzed in-situ and in real time by QCM. For the first time the specific adsorption of monovalent copper to the surface tethered initiator was detected by observation of an activation period preceding the onset of polymerization. The driving force for high affinity of copper...

  9. Microstructural investigation of Sr-modified Al-15 wt%Si alloys in the range from micrometer to atomic scale.

    Science.gov (United States)

    Timpel, M; Wanderka, N; Vinod Kumar, G S; Banhart, J

    2011-05-01

    Strontium-modified Al-15 wt%Si casting alloys were investigated after 5 and 60 min of melt holding. The eutectic microstructures were studied using complementary methods at different length scales: focused ion beam-energy selective backscattered tomography, transmission electron microscopy and 3D atom probe. Whereas the samples after 5 min of melt holding show that the structure of eutectic Si changes into a fine fibrous morphology, the increase of prolonged melt holding (60 min) leads to the loss of Sr within the alloy with an evolution of an unmodified eutectic microstructure displaying coarse interconnected Si plates. Strontium was found at the Al/Si eutectic interfaces on the side of the eutectic Al region, measured by 3D atom probe. The new results obtained using 3D atom probe shed light on the location of Sr within the Al-Si eutectic microstructure.

  10. Influences of high-temperature annealing on atomic layer deposited Al2O3/4H-SiC

    Institute of Scientific and Technical Information of China (English)

    Wang Yi-Yu; Shen Hua-Jun; Bai Yun; Tang Yi-Dan; Liu Ke-An; Li Cheng-Zhan; Liu Xin-Yu

    2013-01-01

    High-temperature annealing of the atomic layer deposition (ALD) of Al2O3 films on 4H-SiC in O2 atmosphere is studied with temperature ranging from 800 ℃ to 1000 ℃.It is observed that the surface morphology of Al2O3 films annealed at 800 ℃ and 900 ℃ is pretty good,while the surface of the sample annealed at 1000 ℃ becomes bumpy.Grazing incidence X-ray diffraction (GIXRD) measurements demonstrate that the as-grown films are amorphous and begin to crystallize at 900 ℃.Furthermore,C-V measurements exhibit improved interface characterization after annealing,especially for samples annealed at 900 ℃ and 1000 ℃.It is indicated that high-temperature annealing in O2 atmosphere can improve the interface of Al2O3/SiC and annealing at 900 ℃ would be an optimum condition for surface morphology,dielectric quality,and interface states.

  11. Conditioning of Si-interfaces by wet-chemical oxidation: Electronic interface properties study by surface photovoltage measurements

    Science.gov (United States)

    Angermann, Heike

    2014-09-01

    The field-modulated surface photovoltage (SPV) method, a very surface sensitive technique, was utilized to determine electronic interface properties on wet-chemically oxidized and etched silicon (Si) interfaces. The influence of preparation-induced surface micro-roughness and un-stoichiometric oxides on the resulting the surface charge, energetic distribution Dit(E), and density Dit,min of rechargeable states was studied by simultaneous, spectroscopic ellipsometry (SE) measurements on polished Si(111) and Si(100) substrates. Based on previous findings and new research, a study of conventional and newly developed wet-chemical oxidation methods was established, correlating the interactions between involved oxidizing and etching solutions and the initial substrate morphology to the final surface conditioning. It is shown, which sequences of wet-chemical oxidation and oxide removal, have to be combined in order to achieve atomically smooth, hydrogen terminated surfaces, as well as ultra-thin oxide layers with low densities of rechargeable states on flat, saw damage etched, and textured Si substrates, as commonly applied in silicon device and solar cell manufacturing. These conventional strategies for wet-chemical pre-treatment are mainly based on concentrated solutions. Therefore, special attention was put on the development of more environmentally acceptable processes, utilizing e.g. hot pure water with low contents of oxygen or hydrochloric acid, and of ozone, working at ambient temperatures. According to our results, these methods could be a high quality and low cost alternative to current approaches with liquid chemicals for the preparation of hydrophobic Si substrate surfaces and ultra-thin passivating oxide layers. As demonstrated for selected examples, the effect of optimized wet-chemical pre-treatments can be preserved during subsequent soft plasma enhanced chemical vapor depositions of Si oxides (SiOx), or amorphous materials such as Si (a-Si:H), Si nitride (a-Si

  12. Self-activated, self-limiting reactions on Si surfaces

    DEFF Research Database (Denmark)

    Morgen, Per; Hvam, Jeanette; Bahari, Ali

    mechanism for the direct growth of ultrathin films (0-3 nm) of oxides and nitrides under ultrahigh vacuum conditions. Neutral oxygen and a microwave excited nitrogen plasma interact directly with Si surfaces kept at different temperatures during the reaction. The gas pressures are around 10-6 Torr......The direct thermally activated reactions of oxygen and ammonia with Si surfaces in furnaces have been used for a very long time in the semiconductor industry for the growth of thick oxides and nitride layers respectively. The oxidation mechanism was described in the Deal-Grove model as a diffusion......, and the temperatures vary from room temperature to 10000C.The growth is in these cases self-limiting, with the optimal oxide thickness around 0.7-0.8 nm, at 5000C, and up to a few nm for nitride. The self-limiting oxide case was recently predicted by Alex Demkov in a structural optimization to minimise the total...

  13. 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.

  14. An all-atom simulation study of the ordering of liquid squalane near a solid surface

    Science.gov (United States)

    Tsige, Mesfin; Patnaik, Soumya S.

    2008-05-01

    An all-atom molecular dynamics study using the OPLS force field has been carried out to obtain new insights in to the orientation and ordering of liquid squalane near a solid surface. As observed in previous experiments, the squalane molecules closest to a SiO 2 substrate are found to be tightly bound with their molecular axis preferentially parallel to the interface. Unlike linear alkanes, the squalane molecules are also found to lie preferentially parallel to the liquid/vapor interface. The simulation results predict that the molecular plane orientation of the squalane molecules changes from mainly parallel to perpendicular to the substrate in going further away from the substrate.

  15. Electron collisions with atoms, ions, molecules, and surfaces: Fundamental science empowering advances in technology

    Science.gov (United States)

    Bartschat, Klaus; Kushner, Mark J.

    2016-06-01

    Electron collisions with atoms, ions, molecules, and surfaces are critically important to the understanding and modeling of low-temperature plasmas (LTPs), and so in the development of technologies based on LTPs. Recent progress in obtaining experimental benchmark data and the development of highly sophisticated computational methods is highlighted. With the cesium-based diode-pumped alkali laser and remote plasma etching of Si3N4 as examples, we demonstrate how accurate and comprehensive datasets for electron collisions enable complex modeling of plasma-using technologies that empower our high-technology-based society.

  16. First-principles study of electronic properties and stability of Nb5SiB2 (001) surface

    Institute of Scientific and Technical Information of China (English)

    Xu Yu-Jiang-Zi; Shang Jia-Xiang; Wang Fu-He

    2011-01-01

    The density functional calculations are performed to study the electronic structure and stability of Nb5SiB2 (001) surface with different terminations. The calculated cleavage energies along the (001) planes in Nb5SiB2 are 5.015 J ? m-2 and 6.593 J ? m-2 with the break of Nb-Si and Nb-NbB bonds, respectively. There exists a close correlation between the surface relaxation including surface ripple and the cleavage energy: the larger the cleavage energy, the larger the surface relaxation. Moreover, the surface stability of the Nb5SiB2 (001) with different terminations has been investigated by the chemical potential phase diagram. From a thermodynamics point of view, the four terminations can be stabilized under different conditions. In chemical potential space, NbB (Nb) and Nb (Si) terminations are just stable in a small area, whereas Si (Nb) and Nb (NbB) terminations are stable in a large area (the letters in brackets represent the subsurface atoms).

  17. Ionization of Rydberg H atoms at band-gap metal surfaces via surface and image states

    CERN Document Server

    So, E; Softley, T P

    2015-01-01

    Wavepacket propagation calculations are reported for the interaction of a Rydberg hydrogen atom ($n=2-8)$ with Cu(111) and Cu(100) surfaces (represented by a Chulkov potential), in comparison with a Jellium surface. Both copper surfaces have a projected band gap at the surface in the energy range degenerate with some or all of the Rydberg energies. The charge transfer of the Rydberg electron to the surface is found to be enhanced for $n$ values at which there is a near-degeneracy between the Rydberg energy level and an image state or a surface state of the surface. The enhancement is facilitated by the strong overlap of the surface image-state orbital lying outside the surface and the orbital of the incoming Rydberg atom. These calculations point to the possibility of using Rydberg-surface collisions as a probe of surface electronic structure.

  18. Surface modification of glycidyl-containing poly(methyl methacrylate) microchips using surface-initiated atom-transfer radical polymerization.

    Science.gov (United States)

    Sun, Xuefei; Liu, Jikun; Lee, Milton L

    2008-02-01

    Fabrication of microfluidic systems from polymeric materials is attractive because of simplicity and low cost. Unfortunately, the surfaces of many polymeric materials can adsorb biological samples. Therefore, it is necessary to modify their surfaces before these polymeric materials can be used for separation and analysis. Oftentimes it is difficult to modify polymeric surfaces because of their resistance to chemical reaction. Recently, we introduced a surface-reactive acrylic polymer, poly(glycidyl methacrylate-co-methyl methacrylate) (PGMAMMA), which can be modified easily and is suitable for fabrication of microfluidic devices. Epoxy groups on the surface can be activated by air plasma treatment, hydrolysis, or aminolysis. In this work, the resulting hydroxyl or amino groups were reacted with 2-bromoisobutylryl bromide to introduce an initiator for surface-initiated atom-transfer radical polymerization (SI-ATRP). Polyethylene glycol (PEG) layers grown on the surface using this method were uniform, hydrophilic, stable, and resistant to protein adsorption. Contact angle measurement and X-ray photoelectron spectroscopy (XPS) were used to characterize activated polymer surfaces, initiator-bound surfaces, and PEG-grafted surfaces. We obtained excellent capillary electrophoresis (CE) separations of proteins and peptides with the PEG-modified microchips. A separation efficiency of 4.4 x 10(4) plates for a 3.5 cm long separation channel was obtained.

  19. Atomic-layer chemical-vapor-deposition of TiN thin films on Si(100) and Si(111)

    CERN Document Server

    Kim, Y S; Kim, Y D; Kim, W M

    2000-01-01

    An atomic-layer chemical vapor deposition (AL-CVD) system was used to deposit TiN thin films on Si(100) and Si(111) substrates by cyclic exposures of TiCl sub 4 and NH sub 3. The growth rate was measured by using the number of deposition cycles, and the physical properties were compared with those of TiN films grown by using conventional deposition methods. To investigate the growth mechanism, we suggest a growth model for TiN n order to calculate the growth rate per cycle with a Cerius program. The results of the calculation with the model were compared with the experimental values for the TiN film deposited using the AL-CVD method. The stoichiometry of the TiN film was examined by using Auger electron spectroscopy, and the chlorine and the oxygen impurities were examined. The x-ray diffraction and the transmission electron microscopy results for the TiN film exhibited a strong (200) peak and a randomly oriented columnar microstructure. The electrical resistivity was found to decrease with increasing deposit...

  20. Theory of the temperature dependent dielectric function of semiconductors: from bulk to surfaces. Application to GaAs and Si

    Energy Technology Data Exchange (ETDEWEB)

    Shkrebtii, Anatoli I.; Teatro, Timothy; Henderson, Laura [Faculty of Science, University of Ontario Institute of Technology, Simcoe Street North 2000, L1H 7K4 Oshawa (Canada); Ibrahim, Zahraa A. [Faculty of Science, University of Ontario Institute of Technology, Simcoe Street North 2000, L1H 7K4 Oshawa (Canada); Department of Physics, University of Toronto, M5S 1A7, Toronto (Canada); Richter, Wolfgang [Dipartimento di Fisica, Universita di Roma Tor Vergata, 00133 Rome (Italy); Institut fuer Festkoerperphysik, Technische Universitaet Berlin, 10623 Berlin (Germany); Lee, Martin J.G. [Department of Physics, University of Toronto, M5S 1A7, Toronto (Canada)

    2010-08-15

    A novel, efficient method for calculating the temperature dependencies of the linear dielectric functions of semiconductor systems and its application are presented. The method follows an intuitive and natural path with ab-initio finite temperature molecular dynamics providing the thermally perturbed atomic configurations, which are used as structural inputs for calculating the dielectric function. The effect of lattice dynamics, including quantum zero point vibration, on the electronic bands and dielectric function of crystalline (c-) GaAs and Si as well as hydrogenated amorphous Si (a-Si:H) is discussed. Our theoretical results for bulk c-GaAs and c-Si in the range from 0 to 1000 K are in good overall agreement with highly accurate ellipsometric measurements. The implementation of the method resolves a serious discrepancy in energy and line shape between experiment and the latest optical models, all of which neglect lattice dynamics, and provides information on the indirect gap and indirect optical transitions in c-Si. For a-Si:H, the calculated temperature dependent optical response combined with the vibrational spectroscopy provides detailed insight into electronic, dynamical properties, and stability of this important prototypical amorphous semiconductor material. At semiconductor surfaces, dynamical effects are expected to be even more pronounced due to reduced atom coordination and reconstruction. This is demonstrated for C(111) 2 x 1, an intensively studied but controversial surface of the quantum diamond crystal. (Abstract Copyright [2010], Wiley Periodicals, Inc.)

  1. Atomic scale deformation in the solid surface induced by nanoparticle impacts

    Science.gov (United States)

    Xu, J.; Luo, J. B.; Lu, X. C.; Wang, L. L.; Pan, G. S.; Wen, S. Z.

    2005-06-01

    Nanoparticle impacts on an ultra-smooth surface always occur in nano-machining processes, such as polishing of a monocrystalline silicon wafer, which is an important process in the manufacture of semiconductors. A fundamental understanding of nanoparticle impacts on a solid surface is important to control and prevent the deformation of the surface. In this study, a cylindrical liquid jet containing de-ionized water and SiO2 nanoparticles impacts obliquely on a single crystal silicon surface at a speed of 50 m s-1. The microstructure of the impacted surface was examined using a high resolution transmission electron microscope, an atomic force microscope, etc. Some crystal defects, lattice distortion, grain refinement and rotation of grains in the surface layer of the silicon wafer after exposure for 30 s have been observed. However, when the exposure time is extended to 10 min, an amorphous layer containing crystal grains is exhibited in the subsurface, and many craters, scratches and atom pileups can be found in the surface.

  2. AES and LEED study of the zinc blende SiC(100) surface

    Science.gov (United States)

    Dayan, M.

    1985-01-01

    Auger and LEED measurements have been carried out on the (100) surface of zinc blende SiC. Two different phases of the clean surface, in addition to two kinds of oxygen-covered surfaces, have been obtained, identified, and discussed. In the oxygen-covered surface, the oxygen is bonded to the Si. The carbon-rich phase is reconstructed (2 x 1), similar to the (100) clean surfaces of Si, Ge, and diamond. The Si-topped surface is reconstructed. A model of alternating Si dimers is suggested for this surface.

  3. 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.

  4. Can Point Defects in Surfaces in Solution be Atomically Resolved by Atomic Force Microscopy?

    Science.gov (United States)

    Reischl, Bernhard; Raiteri, Paolo; Gale, Julian D.; Rohl, Andrew L.

    2016-11-01

    While the atomic force microscope (AFM) is able to image mineral surfaces in solution with atomic resolution, so far, it has been a matter of debate whether imaging point defects is also possible under these conditions. The difficulties stem from the limited knowledge of what types of defects may be stable in the presence of an AFM tip, as well as from the complicated imaging mechanism involving interactions between hydration layers over the surface and around the tip apex. Here, we present atomistic molecular dynamics and free energy calculations of the AFM imaging of vacancies and ionic substitutions in the calcite (10 1 ¯ 4 ) surface in water, using a new silica AFM tip model. Our results indicate that both calcium and carbonate vacancies, as well as a magnesium substitution, could be resolved in an AFM experiment, albeit with different imaging mechanisms.

  5. Characterizing fluorocarbon assisted atomic layer etching of Si using cyclic Ar/C4F8 and Ar/CHF3 plasma

    Science.gov (United States)

    Metzler, Dominik; Li, Chen; Engelmann, Sebastian; Bruce, Robert L.; Joseph, Eric A.; Oehrlein, Gottlieb S.

    2017-02-01

    With the increasing interest in establishing directional etching methods capable of atomic scale resolution for fabricating highly scaled electronic devices, the need for development and characterization of atomic layer etching processes, or generally etch processes with atomic layer precision, is growing. In this work, a flux-controlled cyclic plasma process is used for etching of SiO2 and Si at the Angstrom-level. This is based on steady-state Ar plasma, with periodic, precise injection of a fluorocarbon (FC) precursor (C4F8 and CHF3) and synchronized, plasma-based Ar+ ion bombardment [D. Metzler et al., J. Vac. Sci. Technol., A 32, 020603 (2014) and D. Metzler et al., J. Vac. Sci. Technol., A 34, 01B101 (2016)]. For low energy Ar+ ion bombardment conditions, physical sputter rates are minimized, whereas material can be etched when FC reactants are present at the surface. This cyclic approach offers a large parameter space for process optimization. Etch depth per cycle, removal rates, and self-limitation of removal, along with material dependence of these aspects, were examined as a function of FC surface coverage, ion energy, and etch step length using in situ real time ellipsometry. The deposited FC thickness per cycle is found to have a strong impact on etch depth per cycle of SiO2 and Si but is limited with regard to control over material etching selectivity. Ion energy over the 20-30 eV range strongly impacts material selectivity. The choice of precursor can have a significant impact on the surface chemistry and chemically enhanced etching. CHF3 has a lower FC deposition yield for both SiO2 and Si and also exhibits a strong substrate dependence of FC deposition yield, in contrast to C4F8. The thickness of deposited FC layers using CHF3 is found to be greater for Si than for SiO2. X-ray photoelectron spectroscopy was used to study surface chemistry. When thicker FC films of 11 Å are employed, strong changes of FC film chemistry during a cycle are seen

  6. Characterizing fluorocarbon assisted atomic layer etching of Si using cyclic Ar/C4F8 and Ar/CHF3 plasma.

    Science.gov (United States)

    Metzler, Dominik; Li, Chen; Engelmann, Sebastian; Bruce, Robert L; Joseph, Eric A; Oehrlein, Gottlieb S

    2017-02-07

    With the increasing interest in establishing directional etching methods capable of atomic scale resolution for fabricating highly scaled electronic devices, the need for development and characterization of atomic layer etching processes, or generally etch processes with atomic layer precision, is growing. In this work, a flux-controlled cyclic plasma process is used for etching of SiO2 and Si at the Angstrom-level. This is based on steady-state Ar plasma, with periodic, precise injection of a fluorocarbon (FC) precursor (C4F8 and CHF3) and synchronized, plasma-based Ar(+) ion bombardment [D. Metzler et al., J. Vac. Sci. Technol., A 32, 020603 (2014) and D. Metzler et al., J. Vac. Sci. Technol., A 34, 01B101 (2016)]. For low energy Ar(+) ion bombardment conditions, physical sputter rates are minimized, whereas material can be etched when FC reactants are present at the surface. This cyclic approach offers a large parameter space for process optimization. Etch depth per cycle, removal rates, and self-limitation of removal, along with material dependence of these aspects, were examined as a function of FC surface coverage, ion energy, and etch step length using in situ real time ellipsometry. The deposited FC thickness per cycle is found to have a strong impact on etch depth per cycle of SiO2 and Si but is limited with regard to control over material etching selectivity. Ion energy over the 20-30 eV range strongly impacts material selectivity. The choice of precursor can have a significant impact on the surface chemistry and chemically enhanced etching. CHF3 has a lower FC deposition yield for both SiO2 and Si and also exhibits a strong substrate dependence of FC deposition yield, in contrast to C4F8. The thickness of deposited FC layers using CHF3 is found to be greater for Si than for SiO2. X-ray photoelectron spectroscopy was used to study surface chemistry. When thicker FC films of 11 Å are employed, strong changes of FC film chemistry during a cycle are seen

  7. Formation of atomically ordered and chemically selective Si-O-Ti monolayer on Si0.5Ge0.5(110) for a MIS structure via H2O2(g) functionalization.

    Science.gov (United States)

    Park, Sang Wook; Choi, Jong Youn; Siddiqui, Shariq; Sahu, Bhagawan; Galatage, Rohit; Yoshida, Naomi; Kachian, Jessica; Kummel, Andrew C

    2017-02-07

    Si0.5Ge0.5(110) surfaces were passivated and functionalized using atomic H, hydrogen peroxide (H2O2), and either tetrakis(dimethylamino)titanium (TDMAT) or titanium tetrachloride (TiCl4) and studied in situ with multiple spectroscopic techniques. To passivate the dangling bonds, atomic H and H2O2(g) were utilized and scanning tunneling spectroscopy (STS) demonstrated unpinning of the surface Fermi level. The H2O2(g) could also be used to functionalize the surface for metal atomic layer deposition. After subsequent TDMAT or TiCl4 dosing followed by a post-deposition annealing, scanning tunneling microscopy demonstrated that a thermally stable and well-ordered monolayer of TiOx was deposited on Si0.5Ge0.5(110), and X-ray photoelectron spectroscopy verified that the interfaces only contained Si-O-Ti bonds and a complete absence of GeOx. STS measurements confirmed a TiOx monolayer without mid-gap and conduction band edge states, which should be an ideal ultrathin insulating layer in a metal-insulator-semiconductor structure. Regardless of the Ti precursors, the final Ti density and electronic structure were identical since the Ti bonding is limited by the high coordination of Ti to O.

  8. Fabrication of Co/Si nanowires by ultrahigh-vacuum scanning tunneling microscopy on hydrogen-passivated Si(100) surfaces

    NARCIS (Netherlands)

    Palasantzas, G; Ilge, B; De Nijs, J

    1999-01-01

    We have fabricated nanometer width Co/Si metal lines on Si(100) surfaces by ultrahigh-vacuum scanning tunneling microscopy (UHVSTM) based nanolithography on the hydrogen-passivated surface, combined with vapor deposition of Co at room temperature and subsequent annealing. The STM tip was used to def

  9. Influence of multi-hit capability on quantitative measurement of NiPtSi thin film with laser-assisted atom probe tomography

    Energy Technology Data Exchange (ETDEWEB)

    Kinno, T., E-mail: teruyuki.kinno@toshiba.co.jp [Corporate Research and Development Center, Toshiba Corporation, 8 Shinsugita-cho, Isogo-ku, Yokohama 235-8522 (Japan); Akutsu, H.; Tomita, M. [Corporate Research and Development Center, Toshiba Corporation, 8 Shinsugita-cho, Isogo-ku, Yokohama 235-8522 (Japan); Kawanaka, S. [Center for Semiconductor Research and Development, Toshiba Corporation Semiconductor and Storage Products Company, 8 Shinsugita-cho, Isogo-ku, Yokohama 235-8522 (Japan); Sonehara, T. [Advanced Memory Development Center, Toshiba Corporation Semiconductor and Storage Products Company, 800 Yamano-Isshiki-cho, Yokkaichi, Mie 512-8550 (Japan); Hokazono, A. [Center for Semiconductor Research and Development, Toshiba Corporation Semiconductor and Storage Products Company, 8 Shinsugita-cho, Isogo-ku, Yokohama 235-8522 (Japan); Renaud, L.; Martin, I.; Benbalagh, R.; Salle, B. [Cameca SAS, 29 Quai des Gresillons, 92622 Gennevilliers Cedex (France); Takeno, S. [Corporate Research and Development Center, Toshiba Corporation, 8 Shinsugita-cho, Isogo-ku, Yokohama 235-8522 (Japan)

    2012-10-15

    Highlights: Black-Right-Pointing-Pointer Laser-assisted atom probe tomography was applied to NiPtSi films on Si substrates. Black-Right-Pointing-Pointer Comparison of depth profiles of single-hit events and those of multi-hit events. Black-Right-Pointing-Pointer {approx}80% of Pt atoms were detected in multi-hit events. Black-Right-Pointing-Pointer Multiple-ion detection is important for Laser-assisted atom probe tomography. - Abstract: Laser-assisted atom probe tomography (LA-APT) was applied to NiPtSi (0, 30, and 50% Pt contents) thin films on Si substrates. Consistent results with those of high-resolution Rutherford backscattering spectrometry (HR-RBS) were obtained. Based on the obtained data sets, the composition profiles from only the signals of single-hit events, meaning detection of one ion by one laser pulse, were compiled. The profiles from only the signals of multi-hit events, meaning detection of multiple ions by one laser pulse, were also compiled. There were large discrepancies with respect to Ni and Pt concentrations among the compiled profiles and the original profiles including the signals of both types of detection events. Additionally, the profiles compiled from single-hit events showed that Si concentration in NiPtSi layer became smaller toward the surface, differing from the original profiles and the multi-hit profiles. These results suggest that capability of simultaneous multiple-ion detection is important for appropriate LA-APT analyses.

  10. Low energy ion beam modification of Cu/Ni/Si(100) surface

    Indian Academy of Sciences (India)

    S K Parida; V R Rmedicherla; D K Mishra; S Choudhary; V Solanki; Shikha Varma

    2014-12-01

    Cu/Ni bilayer has been prepared by thermal evaporation of pure Cu and Ni metals onto Si(100) surface in high vacuum; it was sputtered using argon ion beam in ultra-high vacuum. The ion beam-induced surface and interface modification was investigated using X-ray photoelectron spectroscopy and atomic force microscopy techniques. The deposited sample exhibits the formation of CuO nano-structures of size 40 nm on Cu surface and after sputtering with argon ion beam at a fluence of 5 × 1015 ions/cm2, the surface exhibits a mound structure with an average size of about 100 nm. Interestingly, with sputtering at higher fluence of 2.4 × 1016 ions/cm2, the surface exhibits broad pits of sizes ranging from 100 to 300 nm with an average depth of 10 nm. Bottom surface of these pits contains Ni atoms. The Cu 23/2 peak exhibits a shift of 0.3 eV towards high binding energy and also a large asymmetry of 0.11 after sputtering at high fluence compared with pure copper. These changes are attributed to Cu–Ni interactions at the interface.

  11. Atomic-level structures and physical properties of magnetic CoSiB metallic glasses

    Energy Technology Data Exchange (ETDEWEB)

    Shan, Guangcun, E-mail: gshan2-c@my.cityu.edu.hk [Department of Physics and Materials Science, City University of Hong Kong, Kowloon Tong, Hong Kong (China); Liang Zhang, Ji [Department of Physics and Materials Science, City University of Hong Kong, Kowloon Tong, Hong Kong (China); Li, Jiong; Zhang, Shuo; Jiang, Zheng; Huang, Yuying [Shanghai Synchrotron Radiation Facility, Shanghai Institute of Applied Physics, Shanghai 200624 (China); Shek, Chan-Hung, E-mail: apchshek@cityu.edu.hk [Department of Physics and Materials Science, City University of Hong Kong, Kowloon Tong, Hong Kong (China)

    2014-02-15

    Two CoSiB metallic glasses of low Co contents, which consist of different clusters, have recently been developed by addition of solute atoms. In this work, the atomic structure and the magnetic properties of the two CoBSi metallic glasses were elucidated by state-of-the-art extended X-ray absorption fine structure spectroscopy (EXAFS) combining with ab initio molecular-dynamics (AIMD) computational techniques. Besides, the origin of these magnetic behaviors was discussed in view of the EXAFS results and atomic structures of the metallic glasses. - Graphical abstract: The atomic structure and the origins of the magnetic properties of two ternary CoBSi metallic glasses were elucidated by state-of-the-art extended X-ray absorption fine structure spectroscopy (EXAFS) combining with ab initio molecular-dynamics (AIMD) techniques. - Highlights: • The atomic structure and the origins of the magnetic properties of two ternary CoBSi metallic glasses were revealed. • The atomic structures were elucidated by state-of-the-art extended X-ray absorption fine structure spectroscopy (EXAFS) combining with ab initio molecular-dynamics (AIMD) techniques. • The experimental spectra were in good agreement with the predictions of ab initio full multiple scattering theory using the FEFF8.4 code. • The origin of these magnetic behaviors was discussed in view of the EXAFS results and atomic structures of the metallic glasses. • These two metallic glasses consist of different clusters, and hence different magnetic properties, which are dominated by short-range orders (SROs)

  12. Laser-assisted atom probe tomography of Ti/TiN films deposited on Si.

    Science.gov (United States)

    Sanford, N A; Blanchard, P T; White, R; Vissers, M R; Diercks, D R; Davydov, A V; Pappas, D P

    2017-03-01

    Laser-assisted atom probe tomography (L-APT) was used to examine superconducting TiN/Ti/TiN trilayer films with nominal respective thicknesses of 5/5/5 (nm). Such materials are of interest for applications that require large arrays of microwave kinetic inductance detectors. The trilayers were deposited on Si substrates by reactive sputtering. Electron energy loss microscopy performed in a scanning transmission electron microscope (STEM/EELS) was used to corroborate the L-APT results and establish the overall thicknesses of the trilayers. Three separate batches were studied where the first (bottom) TiN layer was deposited at 500°C (for all batches) and the subsequent TiN/Ti bilayer was deposited at ambient temperature, 250°C, and 500°C, respectively. L-APT rendered an approximately planar TiN/Si interface by making use of plausible mass-spectral assignments to N3(1+), SiN(1+), and SiO(1+). This was necessary since ambiguities associated with the likely simultaneous occurrence of Si(1+) and N2(1+) prevented their use in rendering the TiN/Si interface upon reconstruction. The non-superconducting Ti2N phase was also revealed by L-APT. Neither L-APT nor STEM/EELS rendered sharp Ti/TiN interfaces and the contrast between these layers diminished with increased film deposition temperature. L-APT also revealed that hydrogen was present in varying degrees in all samples including control samples that were composed of single layers of Ti or TiN.

  13. Surface modification of nanodiamond through metal free atom transfer radical polymerization

    Science.gov (United States)

    Zeng, Guangjian; Liu, Meiying; Shi, Kexin; Heng, Chunning; Mao, Liucheng; Wan, Qing; Huang, Hongye; Deng, Fengjie; Zhang, Xiaoyong; Wei, Yen

    2016-12-01

    Surface modification of nanodiamond (ND) with poly(2-methacryloyloxyethyl phosphorylcholine) [poly(MPC)] has been achieved by using metal free surface initiated atom transfer radical polymerization (SI-ATRP). The ATRP initiator was first immobilized on the surface of ND through direct esterification reaction between hydroxyl group of ND and 2-bromoisobutyryl bromide. The initiator could be employed to obtain ND-poly(MPC) nanocomposites through SI-ATRP using an organic catalyst. The final functional materials were characterized by 1H nuclear magnetic resonance, transmission electron microscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy and thermo gravimetric analysis in detailed. All of these characterization results demonstrated that ND-poly(MPC) have been successfully obtained via metal free photo-initiated SI-ATRP. The ND-poly(MPC) nanocomposites shown enhanced dispersibility in various solvents as well as excellent biocompatibility. As compared with traditional ATRP, the metal free ATRP is rather simple and effective. More importantly, this preparation method avoided the negative influence of metal catalysts. Therefore, the method described in this work should be a promising strategy for fabrication of polymeric nanocomposites with great potential for different applications especially in biomedical fields.

  14. In situ transmission infrared spectroscopy of high-kappa oxide atomic layer deposition onto silicon surfaces

    Science.gov (United States)

    Ho, Ming-Tsung

    Ultra-thin aluminum oxide (Al2O3) and hafnium oxide (HfO2) layers have been grown by atomic layer deposition (ALD) using tri-methyl-aluminum (TMA) and tetrakis-ethyl-methyl-amino-hafnium (TEMAH) respectively with heavy water (D2O) as the oxidizing agent. Several different silicon surfaces were used as substrates such as hydrogen terminated silicon (H/Si), SC2 (or RCA 2) cleaned native silicon oxide (SiO 2/Si), and silicon (oxy)nitride. In-situ transmission Fourier transform infrared spectroscopy (FTIR) has been adopted for the study of the growth mechanisms during ALD of these films. The vibrational spectra of gas phase TEMAH and its reaction byproducts with oxidants have also been investigated. Density functional theory (DFT) normal mode calculations show a good agreement with the experimental data when it is combined with linear wave-number scaling method and Fermi resonance mechanism. Ether (-C-O-C-) and tertiary alkylamine (N(R1R 2R3)) compounds are the two most dominant products of TEMAH reacting with oxygen gas and water. When ozone is used as the oxidant, gas phase CH2O, CH3NO2, CH3-N=C=O and other compounds containing -(C=O)- and --C-O-C- (or --O-C-) segments are observed. With substrate temperatures less than 400°C and 300°C for TMA and TEMAH respectively, Al oxide and Hf oxide ALD can be appropriately performed on silicon surfaces. Thin silicon (oxy)nitride thermally grown in ammonia on silicon substrate can significantly reduce silicon oxide interlayer formation during ALD and post-deposition annealing. The crystallization temperature of amorphous ALD grown HfO2 on nitridized silicon is 600°C, which is 100°C higher than on the other silicon surfaces. When HfO2 is grown on H/Si(111) at 100°C deposition temperature, minimum 5--10 ALD cycles are required for the full surface coverage. The steric effect can be seen by the evolution of the H-Si stretching mode at 2083 cm-1. The observed red shift of H-Si stretching to ˜ 2060 cm-1 can be caused by Si

  15. Molecular modeling of alkyl monolayers on the Si (100)-2 x 1 surface

    NARCIS (Netherlands)

    Lee, M.V.; Guo, D.; Linford, M.R.; Zuilhof, H.

    2004-01-01

    Molecular modeling was used to simulate various surfaces derived from the addition of 1-alkenes and 1-alkynes to Si=Si dimers on the Si(100)-2 × 1 surface. The primary aim was to better understand the interactions between adsorbates on the surface and distortions of the underlying silicon crystal du

  16. Surface diffusivity of atomic deuterium on Ni3(Al, Ti)(110) surface with and without boron

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    The electron-stimulated desorption was used to measure the surface diffusivity of at omic deuterium on clean and boron-modified Ni3(Al, Ti)(110) surfaces. Boron dosing was performed using a solid-state boronion source. Earlier studies showed that boron dissociates water readily at temperatures as low as 130 Kand that the resulting atomic hydrogen is bound to the surface strongly. The surface diffusi on coefficient of atomic D on 0.05 monolayer boron-modified surface was measured to be about 10 times smaller than that on the clean surface. This slower diffu sion of atomic hydrogen may explain why boron improves the ductility of polycrys talline Ni3Al in moist environments.

  17. The resistance of single atomic steps in ultrathin Pb nanowires on Si(557)

    Energy Technology Data Exchange (ETDEWEB)

    Roenspies, Jan; Kuehnemund, Lisa; Wiessell, Svend; Pfnuer, Herbert [Leibniz-Universitaet Hannover, Inst. f. Festkoerperphysik (Germany)

    2011-07-01

    We studied the local electronic transport properties of a monolayer thick Pb wire by local potentiometry with the tip of a tunneling microscope. 50-nm-wide wires on bare Si(557) were generated by direct writing with an electron beam in an ultrathin film of SiO{sub 2} using the process of electron-beam-induced selective stimulated thermal desorption of oxygen (EBSTD) in combination with a shadow mask technique and macroscopic TiSi{sub 2} contacts. The resistivity of this wire agrees well with expectations derived from anisotropic monolayer thick Pb films on Si(557). Although small Pb clusters nucleated during annealing and desorption of excess Pb, they had a negligible effect on the local resistive properties of the wire. Steps in the substrate of atomic height apparently do not interrupt the conducting path, but due to local scattering at step edge states increase the local resistivity by more than one order of magnitude. Furthermore, a systematic study of the resistance as a function of the lateral width of the wires revealed an effective conducting width, which is about 3 nm smaller on both sides than the geometrically determined width. In addition, we found deviations from Ohm's law at widths below 20 nm.

  18. Atomically precise gold nanocrystal molecules with surface plasmon resonance.

    Science.gov (United States)

    Qian, Huifeng; Zhu, Yan; Jin, Rongchao

    2012-01-17

    Since Faraday's pioneering work on gold colloids, tremendous scientific research on plasmonic gold nanoparticles has been carried out, but no atomically precise Au nanocrystals have been achieved. This work reports the first example of gold nanocrystal molecules. Mass spectrometry analysis has determined its formula to be Au(333)(SR)(79) (R = CH(2)CH(2)Ph). This magic sized nanocrystal molecule exhibits fcc-crystallinity and surface plasmon resonance at approximately 520 nm, hence, a metallic nanomolecule. Simulations have revealed that atomic shell closing largely contributes to the particular robustness of Au(333)(SR)(79), albeit the number of free electrons (i.e., 333 - 79 = 254) is also consistent with electron shell closing based on calculations using a confined free electron model. Guided by the atomic shell closing growth mode, we have also found the next larger size of extraordinarily stability to be Au(~530)(SR)(~100) after a size-focusing selection--which selects the robust size available in the starting polydisperse nanoparticles. This work clearly demonstrates that atomically precise nanocrystal molecules are achievable and that the factor of atomic shell closing contributes to their extraordinary stability compared to other sizes. Overall, this work opens up new opportunities for investigating many fundamental issues of nanocrystals, such as the formation of metallic state, and will have potential impact on condensed matter physics, nanochemistry, and catalysis as well.

  19. Equilibrium and kinetic Si isotope fractionation factors and their implications on Si isotope distributions in the Earth's surface environments

    Science.gov (United States)

    Tang, M.; Zhang, S.; Liu, Y.

    2015-12-01

    Several important equilibrium Si isotope fractionation factors among minerals, organic molecules and the H4SiO4 solution are complemented to facilitate explanation of distributions of Si isotope in the Earth's surface environments. The results reveal that heavy Si isotopes will be significantly enriched in the secondary silicate minerals in comparison to aqueous H4SiO4. On the contrary, quadra-coordinated organosilicon complexes are enriched in light silicon isotope relative to the solution. The extent of 28Si-enrichment in hyper-coordinated organosilicon complexes is found the largest. In addition, the large kinetic isotope effect associated with the polymerization of monosilicic acid and dimer is calculated and the result supports previous statement that highly 28Si-enrichment in the formation of amorphous quartz precursor contributes to the discrepancy between theoretical calculations and field observations. With equilibrium Si isotope fractionation factors provided here, Si isotope distributions in many surface systems of the Earth can be explained. For example, the change of bulk soil δ30Si can be predicted as a concave pattern with respect to weathering degree, with the minimum value where allophane completely dissolves and the total amount of sesqui-oxides and poorly crystalline minerals reaches its maximum. When well-crystallized clays start to precipitate from pore solutions under equilibrium conditions, the bulk soil δ30Si will increase again and reach a constant value. Similarly, the precipitation of crystalline smectite and the dissolution of poorly crystalline kaolinite may explain δ30Si variations in the ground water profile. Equilibrium Si isotope fractionations among quadra-coordinated organosilicon complexes and the H4SiO4 solution may also shed the light on the Si isotope distributions in Si-accumulating plants.

  20. Electrothermally driven high-frequency piezoresistive SiC cantilevers for dynamic atomic force microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Boubekri, R.; Cambril, E.; Couraud, L.; Bernardi, L.; Madouri, A. [LPN, CNRS-UPR20, route de Nozay, 91460 Marcoussis (France); Portail, M. [Centre de Recherche sur l' Hetero-Epitaxie et ses Applications CNRS, Rue Bernard Gregory, 06560 Valhonne (France); Chassagne, T.; Moisson, C.; Zielinski, M. [NOVASiC, Savoie Technolac, Arche bât 4, BP 267, 73375 Le Bourget du Lac Cedex (France); Jiao, S.; Michaud, J.-F.; Alquier, D. [Université François Rabelais, Tours, GREMAN, CNRS-UMR7347, 16 rue Pierre et Marie Curie, BP 7155, 37071 Tours Cedex 2 (France); Bouloc, J.; Nony, L.; Bocquet, F.; Loppacher, C. [IM2NP-CNRS/Aix-Marseille University, 38 rue Frédéric Joliot-Curie, 13451 Marseille (France); Martrou, D.; Gauthier, S., E-mail: gauthier@cemes.fr [CEMES, CNRS UPR 8011 et Université de Toulouse, 29 rue Jeanne Marvig, 31055 Toulouse (France)

    2014-08-07

    Cantilevers with resonance frequency ranging from 1 MHz to 100 MHz have been developed for dynamic atomic force microscopy. These sensors are fabricated from 3C-SiC epilayers grown on Si(100) substrates by low pressure chemical vapor deposition. They use an on-chip method both for driving and sensing the displacement of the cantilever. A first gold metallic loop deposited on top of the cantilever is used to drive its oscillation by electrothermal actuation. The sensing of this oscillation is performed by monitoring the resistance of a second Au loop. This metallic piezoresistive detection method has distinct advantages relative to more common semiconductor-based schemes. The optimization, design, fabrication, and characteristics of these cantilevers are discussed.

  1. Nonlinear simulation of free surfaces and atomization in pressure swirl atomizers

    Science.gov (United States)

    Park, Hongbok; Heister, Stephen D.

    2006-05-01

    A fully nonlinear boundary element method (BEM) model has been developed to simulate the pressure swirl or simplex atomizer. The free surface inside the vortex chamber and within the hollow-cone/primary atomization zone is simulated with a fourth order scheme thereby permitting investigation of highly distorted surfaces up to the point where atomization occurs. For the axisymmetric calculations, annular rings of fluid are pinched from the main liquid domain. Swirling flow is simulated via a superposition of a potential vortex with the base axial flow emanating from the nozzle in a BEM formulation. Results show good comparison to film thicknesses from test data as well as from linear one-dimensional theory. Parametric studies are conducted to assess the influence of injector geometry and flow characteristics on film thickness and spray angle produced by the atomizer. Limited results are also provided to compare droplet sizes with experimental data. In this regard, the linear stability analysis of Ponstein is used to predict the number of droplets created from each ring of fluid shed by the axisymmetric calculation.

  2. The surface morphologies of (Pb, Sr) TiO3 thin film fabricated on Si-buffered Pt/Ti/SiO2/Si substrate

    Institute of Scientific and Technical Information of China (English)

    2005-01-01

    (Pb, Sr)TiO3 (PST) thin film are fabricated by RF magnetron sputtering on Si-buffered Pt/Ti/SiO2/Si substrates with different buffer layer deposition time. Surface morphologies of the buffer layer indicate an improving surface roughness and larger grains with the prolongation of sputtering time. Deposition of PST thin films shows excellent surface fluctuation filling ability to improve the surface roughness of substrates. PST surface morphologies exhibit apparently different grain forms according to the preparation time durance of buffer layer.

  3. Transverse electric surface mode in atomically thin Boron-Nitride

    CERN Document Server

    Merano, Michele

    2016-01-01

    The spatial confinement and the propagation length of surface waves in a single-layer two-dimensional atomic crystal are analysed in term of its surface susceptibility and its surface conductivity. Based on the values of these macroscopic parameters, extracted from experimental observations, it is confirmed that graphene supports a transverse magnetic non-radiating surface mode in the ultraviolet spectral region while a single-layer hexagonal Boron-Nitride is predicted to support a transverse electric non-radiating surface mode in the visible spectrum. This last mode, at a vacuum wavelength of 633 nm, has a spatial confinement of 15 microns and an intensity-propagation distance greater than 2 cm.

  4. Early stage oxynitridation process of Si(001) surface by NO gas: Reactive molecular dynamics simulation study

    Energy Technology Data Exchange (ETDEWEB)

    Cao, Haining; Kim, Seungchul; Lee, Kwang-Ryeol, E-mail: krlee@kist.re.kr [Computational Science Research Center, Korea Institute of Science and Technology, 5, Hwarangno 14-gil, Seongbuk-gu, Seoul 02792 (Korea, Republic of); Department of Nanomaterial Science and Technology, Korea University of Science and Technology, 217 Gajeong-ro, Yuseong-gu, Daejeon 34113 (Korea, Republic of); Srivastava, Pooja; Choi, Keunsu [Computational Science Research Center, Korea Institute of Science and Technology, 5, Hwarangno 14-gil, Seongbuk-gu, Seoul 02792 (Korea, Republic of)

    2016-03-28

    Initial stage of oxynitridation process of Si substrate is of crucial importance in fabricating the ultrathin gate dielectric layer of high quality in advanced MOSFET devices. The oxynitridation reaction on a relaxed Si(001) surface is investigated via reactive molecular dynamics (MD) simulation. A total of 1120 events of a single nitric oxide (NO) molecule reaction at temperatures ranging from 300 to 1000 K are statistically analyzed. The observed reaction kinetics are consistent with the previous experimental or calculation results, which show the viability of the reactive MD technique to study the NO dissociation reaction on Si. We suggest the reaction pathway for NO dissociation that is characterized by the inter-dimer bridge of a NO molecule as the intermediate state prior to NO dissociation. Although the energy of the inter-dimer bridge is higher than that of the intra-dimer one, our suggestion is supported by the ab initio nudged elastic band calculations showing that the energy barrier for the inter-dimer bridge formation is much lower. The growth mechanism of an ultrathin Si oxynitride layer is also investigated via consecutive NO reactions simulation. The simulation reveals the mechanism of self-limiting reaction at low temperature and the time evolution of the depth profile of N and O atoms depending on the process temperature, which would guide to optimize the oxynitridation process condition.

  5. Nanoscale triboactivity of functionalized c-Si surfaces by Fe+ ion implantation

    Science.gov (United States)

    Nunes, B.; Alves, E.; Colaço, R.

    2016-04-01

    In the present work, we present a study of the effect of Fe+ ion implantation on the tribological response at nanoscale contact lengths of crystalline silicon (c-Si) surfaces. (1 0 0) silicon wafers were implanted with Fe+ at a fluence of 2  ×  1017 cm-2, followed by annealing treatments at temperatures of 800 °C and 1000 °C. After microstructural characterization, nanoabrasive wear tests were performed with an atomic force microscope (AFM) using an AFM diamond tip with a stiff steel cantilever that enables the application of loads between 1 μN and 8 μN. After the nanowear tests, the same AFM was used to visualize and measure the worn craters. It was observed that the as-implanted samples present the poorest nanowear response, i.e. the highest wear rate, even higher than that of the unimplanted Si wafers used as a reference. Nevertheless, annealing treatments result in a measurable increase in the nanowear resistance. In this way we show that Fe+ ion implantation of c-Si, followed by the proper post-heat treatment, results in the formation of FeSi2 nanoprecipitates finely dispersed in a recrystallized matrix. This can be a valuable way of optimizing the nanotribological behavior of silicon.

  6. Atomic oxidation of large area epitaxial graphene on 4H-SiC(0001)

    Energy Technology Data Exchange (ETDEWEB)

    Velez-Fort, E. [Laboratoire de Photonique et de Nanostructures (CNRS-LPN), Route de Nozay, 91460 Marcoussis (France); Institut de Minéralogie et de Physique des Milieux Condensés, CNRS–UMR7590, Sorbonne Universités-Pierre et Marie Curie, 4 Pl. Jussieu, 75005 Paris (France); Ouerghi, A. [Laboratoire de Photonique et de Nanostructures (CNRS-LPN), Route de Nozay, 91460 Marcoussis (France); Silly, M. G.; Sirtti, F. [Synchrotron-SOLEIL, Saint-Aubin, BP48, F91192 Gif sur Yvette Cedex (France); Eddrief, M.; Marangolo, M. [CNRS, UMR 7588, Institut des NanoSciences de Paris (INSP), F-75005 Paris (France); Sorbonne Universités, UPMC Univ. Paris 06, UMR 7588, INSP, F-75005 Paris (France); Shukla, A. [Institut de Minéralogie et de Physique des Milieux Condensés, CNRS–UMR7590, Sorbonne Universités-Pierre et Marie Curie, 4 Pl. Jussieu, 75005 Paris (France)

    2014-03-03

    Structural and electronic properties of epitaxial graphene on 4H-SiC were studied before and after an atomic oxidation process. X-ray photoemission spectroscopy indicates that oxygen penetrates into the substrate and decouples a part of the interface layer. Raman spectroscopy demonstrates the increase of defects due to the presence of oxygen. Interestingly, we observed on the near edge x-ray absorption fine structure spectra a splitting of the π* peak into two distinct resonances centered at 284.7 and 285.2 eV. This double structure smears out after the oxidation process and permits to probe the interface architecture between graphene and the substrate.

  7. The Correlation of the N{sub A} Measurements by Counting {sup 28}Si Atoms

    Energy Technology Data Exchange (ETDEWEB)

    Mana, G., E-mail: g.mana@inrim.it; Massa, E.; Sasso, C. P. [INRIM—Istituto Nazionale di Ricerca Metrologica, Str. delle Cacce 91, 10135 Torino (Italy); Stock, M. [BIPM—Bureau International des Poids et Mesures BIPM, Pavillon de Breteuil, 92312 Sèvres Cedex (France); Fujii, K.; Kuramoto, N.; Mizushima, S.; Narukawa, T. [NMIJ—National Metrology Institute of Japan, 1-1-1 Umezono, Tsukuba, Ibaraki 305-8563 (Japan); Borys, M.; Busch, I.; Nicolaus, A.; Pramann, A. [PTB—Physikalisch-Technische Bundesanstalt, Bundesallee 100, 38116 Braunschweig (Germany)

    2015-09-15

    An additional value of the Avogadro constant was obtained by counting the atoms in isotopically enriched Si spheres. With respect to the previous determination, the spheres were etched and repolished to eliminate metal contaminations and to improve the roundness. In addition, all the input quantities—molar mass, lattice parameter, mass, and volume—were remeasured aiming at a smaller uncertainty. In order to make the values given in Andreas et al. [Metrologia 48, S1 (2011)] and Azuma et al. [Metrologia 52, 360 (2015)] usable for a least squares adjustment, we report about the estimate of their correlation.

  8. An accurate determination of the Avogadro constant by counting the atoms in a 28Si crystal

    CERN Document Server

    Andreas, B; Bartl, G; Becker, P; Bettin, H; Borys, M; Busch, I; Gray, M; Fuchs, P; Fujii, K; Fujimoto, H; Kessler, E; Krumrey, M; Kuetgens, U; Kuramoto, N; Mana, G; Manson, P; Massa, E; Mizushima, S; Nicolaus, A; Picard, A; Pramann, A; Rienitz, O; Schiel, D; Valkiers, S; Waseda, A

    2010-01-01

    The Avogadro constant links the atomic and the macroscopic properties of matter. Since the molar Planck constant is well known via the measurement of the Rydberg constant, it is also closely related to the Planck constant. In addition, its accurate determination is of paramount importance for a definition of the kilogram in terms of a fundamental constant. We describe a new approach for its determination by "counting" the atoms in 1 kg single-crystal spheres, which are highly enriched with the 28Si isotope. It enabled isotope dilution mass spectroscopy to determine the molar mass of the silicon crystal with unprecedented accuracy. The value obtained, 6.02214084(18) x 10^23 mol^-1, is the most accurate input datum for a new definition of the kilogram.

  9. Fabrication of DNA nanowires by orthogonal self-assembly and DNA intercalation on a Au patterned Si/SiO2 surface.

    Science.gov (United States)

    Kobayashi, Katsuaki; Tonegawa, Naoya; Fujii, Sho; Hikida, Jiro; Nozoye, Hisakazu; Tsutsui, Ken; Wada, Yasuo; Chikira, Makoto; Haga, Masa-Aki

    2008-11-18

    A novel Ru complex bearing both an acridine group and anchoring phosphonate groups was immobilized on a surface in order to capture double-stranded DNAs (dsDNAs) from solution. At low surface coverage, the atomic force microscopy (AFM) image revealed the "molecular dot" morphology with the height of the Ru complex ( approximately 2.5 nm) on a mica surface, indicating that four phosphonate anchor groups keep the Ru complex in an upright orientation on the surface. Using a dynamic molecular combing method, the DNA capture efficiency of the Ru complex on a mica surface was examined in terms of the effects of the number of molecular dots and surface hydrophobicity. The immobilized surface could capture DNAs; however, the optimal number of molecular dots on the surface as well as the optimal pull-up speed exist to obtain the extended dsDNAs on the surface. Applying this optimal condition to a Au-patterned Si/SiO 2 (Au/SiO 2) surface, the Au electrode was selectively covered with the Ru complex by orthogonal self-assembly of 4-mercaptbutylphosphonic acid (MBPA), followed by the formation of a Zr (4+)-phosphonate layer and the Ru complex. At the same time, the remaining SiO 2 surface was covered with octylphosphonic acid (OPA) by self-assembly. The selective immobilization of the Ru complex only on the Au electrode was identified by time-of-flight secondary-ion mass spectrometry (TOF-SIMS) imaging on the chemically modified Au/SiO 2 surface. The construction of DNA nanowires on the Au/SiO 2 patterned surface was accomplished by the molecular combing method of the selective immobilized Ru complex on Au electrodes. These interconnected nanowires between Au electrodes were used as a scaffold for the modification of Pd nanoparticles on the DNA. Furthermore, Cu metallization was achieved by electroless plating of Cu metal on a priming of Pd nanoparticles on the Pd-covered DNA nanowires. The resulting Cu nanowires showed a metallic behavior with relatively high resistance.

  10. Characterization of Si(1 1 1){radical}(3) Multiplication-Sign {radical}(3)-(Au,In) surface by optical second-harmonic generation

    Energy Technology Data Exchange (ETDEWEB)

    Ignatovich, K.V. [Institute of Automation and Control Processes, 5 Radio Street, 690041 Vladivostok (Russian Federation); Zotov, A.V. [Institute of Automation and Control Processes, 5 Radio Street, 690041 Vladivostok (Russian Federation); School of Natural Sciences, Far Eastern Federal University, 690950 Vladivostok (Russian Federation); Department of Electronics, Vladivostok State University of Economics and Service, 690600 Vladivostok (Russian Federation); Saranin, A.A. [Institute of Automation and Control Processes, 5 Radio Street, 690041 Vladivostok (Russian Federation); School of Natural Sciences, Far Eastern Federal University, 690950 Vladivostok (Russian Federation)

    2012-03-01

    We investigated the change of optical second harmonic generation (SHG) intensity in the course of Si(1 1 1){radical}(3) Multiplication-Sign {radical}(3)-(Au,In) surface formation and during subsequent In island growth on this surface. The Si(1 1 1){radical}(3) Multiplication-Sign {radical}(3)-(Au,In) surface is essentially a modified Si(1 1 1)-{alpha}-{radical}(3) Multiplication-Sign {radical}(3)-Au surface in which the domain-wall network (characteristic of the original surface) is completely eliminated due to In adsorption. This surface shows up as the one having homogeneous highly ordered atomic structure. Its formation is accompanied by the extremely high (namely, tenfold) increase of the SHG signal. It was recognized that this increase is associated with an extraordinary high long-range atomic ordering of the Si(1 1 1){radical}(3) Multiplication-Sign {radical}(3)-(Au,In) surface, while its other peculiar features, developing the 2D electron gas system and occurrence of the 2D gas of mobile adatoms on it, produce minor effects. Growth of random In islands on Si(1 1 1){radical}(3) Multiplication-Sign {radical}(3)-(Au,In) at RT In deposition leads to the decrease of SHG signal indicating its sensitivity to the surface inhomogeneity not only in atomic scale but in the mesascopic scale also.

  11. The atomic structure of the Si(111)-Pb buried interface grown on the Si(111)-(#sq root#3 x #sq root#3)-Pb reconstruction

    DEFF Research Database (Denmark)

    Howes, P.B.; Edwards, K.A.; Macdonald, J.E.

    1998-01-01

    The Si(111)-Pb interface is a prototypical metal-semiconductor interface and has been the subject of a number of experimental studies. The Schottky barrier height is known to depend on the initial reconstruction formed by the first monolayer of Pb atoms and we have previously shown that there are......The Si(111)-Pb interface is a prototypical metal-semiconductor interface and has been the subject of a number of experimental studies. The Schottky barrier height is known to depend on the initial reconstruction formed by the first monolayer of Pb atoms and we have previously shown...

  12. Optically excited structural transition in atomic wires on surfaces at the quantum limit

    Science.gov (United States)

    Frigge, T.; Hafke, B.; Witte, T.; Krenzer, B.; Streubühr, C.; Samad Syed, A.; Mikšić Trontl, V.; Avigo, I.; Zhou, P.; Ligges, M.; von der Linde, D.; Bovensiepen, U.; Horn-von Hoegen, M.; Wippermann, S.; Lücke, A.; Sanna, S.; Gerstmann, U.; Schmidt, W. G.

    2017-03-01

    Transient control over the atomic potential-energy landscapes of solids could lead to new states of matter and to quantum control of nuclear motion on the timescale of lattice vibrations. Recently developed ultrafast time-resolved diffraction techniques combine ultrafast temporal manipulation with atomic-scale spatial resolution and femtosecond temporal resolution. These advances have enabled investigations of photo-induced structural changes in bulk solids that often occur on timescales as short as a few hundred femtoseconds. In contrast, experiments at surfaces and on single atomic layers such as graphene report timescales of structural changes that are orders of magnitude longer. This raises the question of whether the structural response of low-dimensional materials to femtosecond laser excitation is, in general, limited. Here we show that a photo-induced transition from the low- to high-symmetry state of a charge density wave in atomic indium (In) wires supported by a silicon (Si) surface takes place within 350 femtoseconds. The optical excitation breaks and creates In-In bonds, leading to the non-thermal excitation of soft phonon modes, and drives the structural transition in the limit of critically damped nuclear motion through coupling of these soft phonon modes to a manifold of surface and interface phonons that arise from the symmetry breaking at the silicon surface. This finding demonstrates that carefully tuned electronic excitations can create non-equilibrium potential energy surfaces that drive structural dynamics at interfaces in the quantum limit (that is, in a regime in which the nuclear motion is directed and deterministic). This technique could potentially be used to tune the dynamic response of a solid to optical excitation, and has widespread potential application, for example in ultrafast detectors.

  13. Optically excited structural transition in atomic wires on surfaces at the quantum limit.

    Science.gov (United States)

    Frigge, T; Hafke, B; Witte, T; Krenzer, B; Streubühr, C; Samad Syed, A; Mikšić Trontl, V; Avigo, I; Zhou, P; Ligges, M; von der Linde, D; Bovensiepen, U; Horn-von Hoegen, M; Wippermann, S; Lücke, A; Sanna, S; Gerstmann, U; Schmidt, W G

    2017-03-29

    Transient control over the atomic potential-energy landscapes of solids could lead to new states of matter and to quantum control of nuclear motion on the timescale of lattice vibrations. Recently developed ultrafast time-resolved diffraction techniques combine ultrafast temporal manipulation with atomic-scale spatial resolution and femtosecond temporal resolution. These advances have enabled investigations of photo-induced structural changes in bulk solids that often occur on timescales as short as a few hundred femtoseconds. In contrast, experiments at surfaces and on single atomic layers such as graphene report timescales of structural changes that are orders of magnitude longer. This raises the question of whether the structural response of low-dimensional materials to femtosecond laser excitation is, in general, limited. Here we show that a photo-induced transition from the low- to high-symmetry state of a charge density wave in atomic indium (In) wires supported by a silicon (Si) surface takes place within 350 femtoseconds. The optical excitation breaks and creates In-In bonds, leading to the non-thermal excitation of soft phonon modes, and drives the structural transition in the limit of critically damped nuclear motion through coupling of these soft phonon modes to a manifold of surface and interface phonons that arise from the symmetry breaking at the silicon surface. This finding demonstrates that carefully tuned electronic excitations can create non-equilibrium potential energy surfaces that drive structural dynamics at interfaces in the quantum limit (that is, in a regime in which the nuclear motion is directed and deterministic). This technique could potentially be used to tune the dynamic response of a solid to optical excitation, and has widespread potential application, for example in ultrafast detectors.

  14. Dinitrogen dissociation on an isolated surface tantalum atom.

    Science.gov (United States)

    Avenier, P; Taoufik, M; Lesage, A; Solans-Monfort, X; Baudouin, A; de Mallmann, A; Veyre, L; Basset, J-M; Eisenstein, O; Emsley, L; Quadrelli, E A

    2007-08-24

    Both industrial and biochemical ammonia syntheses are thought to rely on the cooperation of multiple metals in breaking the strong triple bond of dinitrogen. Such multimetallic cooperation for dinitrogen cleavage is also the general rule for dinitrogen reductive cleavage with molecular systems and surfaces. We have observed cleavage of dinitrogen at 250 degrees C and atmospheric pressure by dihydrogen on isolated silica surface-supported tantalum(III) and tantalum(V) hydride centers [(identical with Si-O)2Ta(III)-H] and [(identical with Si-O)2Ta(V)H3], leading to the Ta(V) amido imido product [(identical with SiO)2Ta(=NH)(NH2)]: We assigned the product structure based on extensive characterization by infrared and solid-state nuclear magnetic resonance spectroscopy, isotopic labeling studies, and supporting data from x-ray absorption and theoretical simulations. Reaction intermediates revealed by in situ monitoring of the reaction with infrared spectroscopy support a mechanism highly distinct from those previously observed in enzymatic, organometallic, and heterogeneous N2 activating systems.

  15. The microstructure of Si surface layers after plasma-immersion He+ ion implantation and subsequent thermal annealing1

    Science.gov (United States)

    Lomov, Andrey; Shcherbachev, Kirill; Chesnokov, Yurii

    2017-01-01

    The structural changes in the surface layer of p-type Cz-Si(001) samples after high-dose low-energy (2 keV) He+ plasma-immersion ion implantation and subsequent thermal annealing were studied using a set of complementary methods: high-resolution X-ray reflectometry, high-resolution X-ray diffraction, transmission electron microscopy and atomic force microscopy. The formation of a three-layer structure was observed (an amorphous a-SiOx layer at the surface, an amorphous a-Si layer and a heavily damaged tensile-strained crystalline c-Si layer), which remained after annealing. Helium-filled bubbles were observed in the as-implanted sample. The influence of annealing on the evolution of the three-layer structure and the bubbles is considered. The bubbles are shown to grow after annealing. Their characteristic size is determined to be in the range of 5–20 nm. Large helium-filled bubbles are located in the amorphous a-Si layer. Small bubbles form inside the damaged crystalline Si layer. These bubbles are a major source of tensile strain in the c-Si layer.

  16. Site-selective substitutional doping with atomic precision on stepped Al (111) surface by single-atom manipulation.

    Science.gov (United States)

    Chen, Chang; Zhang, Jinhu; Dong, Guofeng; Shao, Hezhu; Ning, Bo-Yuan; Zhao, Li; Ning, Xi-Jing; Zhuang, Jun

    2014-01-01

    In fabrication of nano- and quantum devices, it is sometimes critical to position individual dopants at certain sites precisely to obtain the specific or enhanced functionalities. With first-principles simulations, we propose a method for substitutional doping of individual atom at a certain position on a stepped metal surface by single-atom manipulation. A selected atom at the step of Al (111) surface could be extracted vertically with an Al trimer-apex tip, and then the dopant atom will be positioned to this site. The details of the entire process including potential energy curves are given, which suggests the reliability of the proposed single-atom doping method.

  17. Nanomechanical properties of SiC films grown from C{sub 60} precursors using atomic force microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Morse, K. [Colorado School of Mines, Golden, CO (United States); Balooch, M.; Hamza, A.V.; Belak, J. [Lawrence Livermore National Lab., CA (United States)

    1994-12-01

    The mechanical properties of SiC films grown via C{sub 60} precursors were determined using atomic force microscopy (AFM). Conventional silicon nitride and modified diamond cantilever AFM tips were employed to determine the film hardness, friction coefficient, and elastic modulus. The hardness is found to be between 26 and 40 GPa by nanoindentation of the film with the diamond tip. The friction coefficient for the silicon nitride tip on the SiC film is about one third that for silicon nitride sliding on a silicon substrate. By combining nanoindentation and AFM measurements an elastic modulus of {approximately}300 GPa is estimated for these SiC films. In order to better understand the atomic scale mechanisms that determine the hardness and friction of SiC, we simulated the molecular dynamics of a diamond indenting a crystalline SiC substrate.

  18. Compositional effects on Si3N4 fracture surfaces

    Science.gov (United States)

    Hench, L. L.; Ohuchi, F.; Vaidyanathan, P. N.; Dutta, S.

    1983-01-01

    Surface analysis techniques (X-ray, infrared reflection spectroscopy, Auger electron spectroscopy) applied to the same samples reveal that fracture surfaces of Si3N4 with Y2O3 densification aids possess a higher concentration of oxygen than the bulk. The oxide densification aids thus concentrate in the grain boundaries, and even low-temperature fracture is seen as occurring preferentially within the oxygen-enriched grain boundaries. It is found that increasing the concentrations of Y2O3 and Al2O3 increases the oxygen content of the fracture surface. A range of 13-15 percent Y2O3 + 6 percent Al2O3 gives an amorphous grain-boundary phase that is resistant to devitrification. Fracture occurs through the amorphous phase, and heat treatment at 1000 C has little effect on the amorphous phase.

  19. Atomic force microscopy of polymer and oligomer surfaces

    CERN Document Server

    Winkel, A K

    2001-01-01

    The surface of ultra-thin films of polyethylene, isotactic polypropylene, polybutene, isotactic polystyrene and polytetrafluoroethylene was studied using an atomic force microscope and resolution of individual molecules was achieved. Comparison of the images with Connolly surfaces enabled identification of which plane was observed in the AFM images, with greater accuracy than conclusions drawn on the basis of surface feature measurement alone. In particular, the results from the experiments with polybutene show that for samples aged sufficiently so that the stable phase is expected in the bulk, this phase is also stable on the surface. The samples were aged sufficiently to ensure that the bulk would be in the stable phase. It is found that this phase is also stable on the surface. Additionally, the annealing behaviour of once folded crystals of the long-chain alkane, C sub 1 sub 6 sub 2 H sub 3 sub 2 sub 6 , is examined in situ, in real time, by atomic force microscopy. Regions of thickening material can be c...

  20. Atomic Resolution Imaging and Quantification of Chemical Functionality of Surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Schwarz, Udo D. [Yale Univ., New Haven, CT (United States). Dept. of Mechanical Engineering and Materials Science; Altman, Eric I. [Yale Univ., New Haven, CT (United States). Dept. of Chemical and Environmental Engineering

    2014-12-10

    The work carried out from 2006-2014 under DoE support was targeted at developing new approaches to the atomic-scale characterization of surfaces that include species-selective imaging and an ability to quantify chemical surface interactions with site-specific accuracy. The newly established methods were subsequently applied to gain insight into the local chemical interactions that govern the catalytic properties of model catalysts of interest to DoE. The foundation of our work was the development of three-dimensional atomic force microscopy (3DAFM), a new measurement mode that allows the mapping of the complete surface force and energy fields with picometer resolution in space (x, y, and z) and piconewton/millielectron volts in force/energy. From this experimental platform, we further expanded by adding the simultaneous recording of tunneling current (3D-AFM/STM) using chemically well-defined tips. Through comparison with simulations, we were able to achieve precise quantification and assignment of local chemical interactions to exact positions within the lattice. During the course of the project, the novel techniques were applied to surface-oxidized copper, titanium dioxide, and silicon oxide. On these materials, defect-induced changes to the chemical surface reactivity and electronic charge density were characterized with site-specific accuracy.

  1. Atomic Resolution Imaging and Quantification of Chemical Functionality of Surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Schwarz, Udo [Yale University

    2014-12-10

    The work carried out from 2006-2014 under DoE support was targeted at developing new approaches to the atomic-scale characterization of surfaces that include species-selective imaging and an ability to quantify chemical surface interactions with site-specific accuracy. The newly established methods were subsequently applied to gain insight into the local chemical interactions that govern the catalytic properties of model catalysts of interest to DoE. The foundation of our work was the development of three-dimensional atomic force microscopy (3D-AFM), a new measurement mode that allows the mapping of the complete surface force and energy fields with picometer resolution in space (x, y, and z) and piconewton/millielectron volts in force/energy. From this experimental platform, we further expanded by adding the simultaneous recording of tunneling current (3D-AFM/STM) using chemically well-defined tips. Through comparison with simulations, we were able to achieve precise quantification and assignment of local chemical interactions to exact positions within the lattice. During the course of the project, the novel techniques were applied to surface-oxidized copper, titanium dioxide, and silicon oxide. On these materials, defect-induced changes to the chemical surface reactivity and electronic charge density were characterized with site-specific accuracy.

  2. The Si(100)-Sb 2{times}1 and Ge(100) 2{times}1 surfaces: A multi-technique study

    Energy Technology Data Exchange (ETDEWEB)

    Richter, M.

    1993-08-01

    The electronic and geometric structures of the clean and Sb terminated Si(100)2{times}1 and Ge(100)-2{times}1 surfaces have been investigated using a multi-technique approach. Low energy electron diffraction (LEED), scanning tunneling microscopy (STM), surface extended X-ray absorption fine structure (SEXAFS) spectroscopy and angle-integrated core-level photoemission electron spectroscopy (PES) were employed to measure the surface symmetry, defect structure, relevant bond lengths, atomic coordination and electronic structure. By employing a multi-technique approach, it is possible to correlate changes in the geometric structure to specific features of the core-level lineshape of the substrate. This allows for the assignment of components of the core-level lineshape to be assigned to specific surface and near-surface atoms.

  3. Some issues on atomic force microscopy based surface characterization

    Institute of Scientific and Technical Information of China (English)

    CHEN Yu-hang; HUANG Wen-hao

    2007-01-01

    Influences of tip radius and sampling interval on applying atomic force microscopy(AFM)in quantitative surface evaluations are investigated by numerical simulations and experiments. Several evaluation parameters of surfaces ranging from amplitude to functional parameters are studied. Numerical and experimental results are in good agreements. The accuracy of estimating tip radius on random rough surface with Gaussian distribution of heights using a blind reconstruction method is also discussed theoretically. It is found that the accuracy is greatly depending on the ratio of actual tip radius to rootmean-square (rms) radius of curvature. To obtain an accurate estimation of tip radius under Gaussian rough surface, the ratio has to be larger than 3/2.

  4. Co-adsorption of Cu and Pb on the Si(1 1 1)-(7 × 7) surface: interface formation

    Science.gov (United States)

    Shukrinov, Pavel; Mutombo, Pingo; Cháb, Vladimír.; Prince, K. C.

    2003-06-01

    The adsorption of Cu and Pb atoms on a Si(1 1 1)-7 × 7 surface was studied by means of scanning tunnelling microscopy (STM). After deposition of ⩽0.1 monolayer (ML) of copper on the Pb √3×√3 mosaic phase and a subsequent annealing up to ˜373 K, new objects of a hexagonal shape appear on a surface. They are scattered over the surface and localised next to the mosaic phase islands. The difference between atomically resolved images of filled and empty states suggests strong covalent bonding within a hexagon. Increasing the concentration of Cu atoms leads to an increasing number of hexagons and their agglomeration. Annealing of this surface at a higher temperature (>470 K) leads to the transformation of these hexagonal-like objects and their agglomeration into the pseudo-"5 × 5" structure, commonly observed for the Cu/Si(1 1 1)system. The absence of hexagons at very low Cu concentration demonstrates the presence of a long-range, attractive interaction among Cu atoms and their strong diffusion just above room temperature (RT).

  5. Infrared reflection absorption study of water interaction with H-terminated Si(100) surfaces

    Indian Academy of Sciences (India)

    G Ranga Rao

    2004-12-01

    Water adsorption on clean and hydrogenated Si(100) surfaces was studied under ultra high vacuum conditions using surface infrared spectroscopy. The study shows that H–Si–Si–OH and SiH2 species are formed on Si(100)–(2 × 1) and Si(100)–(2 × 1)–H surfaces, respectively. The reactivity behaviour of Si(100)–(3 × 1)–H and Si(100)–(1 × 1)–H is similar, both stabilizing oxygen inserted silicon dihydrides.

  6. Interaction of atomic oxygen with a graphite surface

    Science.gov (United States)

    Mateljevic, Natasa

    This project was a part of the Multi University Research Initiative (MURI) Center for Materials Chemistry in the Space Environment which seeks to develop a quantitative and predictive understanding of how materials degrade or become passivated in the space environment. This is a critical research area for the Department of Defense (DoD) and National Aeronautics and Space Administration (NASA) given the large and increasing dependence on satellites and manned spacecrafts that reside in, or pass through, the low-Earth orbit (LEO) space environment. In this work, we completed three separate projects. First, we carried out ab initio electronic structure studies of the interaction of oxygen atoms with graphite surfaces. The (O3 P) ground state of oxygen interacts weakly with the graphite surface while the excited (O1D) state interacts more strongly with a binding energy sufficient for a high coverage of oxygen to be maintained on the surface. Thus, it requires a transition from O(3P) to O(1D) in order for oxygen to strongly bind. Since graphite is a semi-metal, it requires a vanishingly small energy to remove an electron of up spin from just below the Fermi level, and replace it with a down spin electron just above the Fermi level; spin-orbit interaction is not required to switch the state of the oxygen atom. We have examined this complexity for the first time and developed guidelines for properly describing chemical reactivity on graphite surfaces. The second project is a kinetic Monte Carlo study of the erosion of graphite by energetic oxygen atoms in LEO and in the laboratory. These simulations, in conjunction with experiments by our MURI collaborators, reveal new insights about reaction pathways. Finally, we have developed a new model for accommodation of energy and momentum in collisions of gases with highly corrugated surfaces. This model promises to be valuable in simulating frictional heating and drag of objects moving through the atmosphere.

  7. Stress Domains in Si(111)/a-Si{sub 3}N{sub 4} Nanopixel: Ten-Million-Atom Molecular Dynamics Simulations on Parallel Computers

    Energy Technology Data Exchange (ETDEWEB)

    Omeltchenko, Andrey; Bachlechner, Martina E.; Nakano, Aiichiro; Kalia, Rajiv K.; Vashishta, Priya; Ebbsjoe, Ingvar; Madhukar, Anupam; Messina, Paul

    2000-01-10

    Parallel molecular dynamics simulations are performed to determine atomic-level stresses in Si(111)/Si {sub 3}N{sub 4}(0001) and Si(111)/a-Si {sub 3}N{sub 4} nanopixels. Compared to the crystalline case, the stresses in amorphous Si{sub 3}N {sub 4} are highly inhomogeneous in the plane of the interface. In silicon below the interface, for a 25 nm square mesa stress domains with triangular symmetry are observed, whereas for a rectangular, 54 nmx33 nm , mesa tensile stress domains ({approx}300 Angstrom) are separated by Y-shaped compressive domain wall. Maximum stresses in the domains and domain walls are -2 GPa and +2 GPa , respectively. (c) 2000 The American Physical Society.

  8. Critical Temperature Programs for Surface Carbonization of Si(111) and Their Effects on 3C-SiC Film Growth

    Science.gov (United States)

    Giang Nguyen, Nam; Liu, Chie-Sheng; Hu, Ming-Shien; Hong, Lu-Sheng

    2013-08-01

    We have studies of the changes in the surface states of carbonized Si(111) substrates treated under various temperature programs prior to high-temperature 3C-SiC film growth in a low pressure chemical vapor deposition system using SiH4, C2H2, and H2 as reactant gases. The carbonized Si surface underwent a change in bonding from SiC to disordered graphite, together with the formation of etch pits, when heated directly from the carbonization temperature of 1343 K to the growth temperature of 1523 K under a H2 flow over a period of 5 min; this transformation deteriorated the quality of the subsequent 3C-SiC growth. In contrast, a void-free stoichiometric SiC surface was preserved when we inserted a rapid cooling step, to near room temperature, under a H2 flow of 352 sccm within a period of 15 min after shutting off the C2H2 gas flow at the end of the surface carbonization process. The sharp temperature decrease in this program sealed off the carbonized substrate surface and, thus, led to a high film quality for subsequent 3C-SiC(111) growth.

  9. Self-activated, self-limiting reactions on Si surfaces

    DEFF Research Database (Denmark)

    Morgen, Per; Hvam, Jeanette; Bahari, Ali

    The direct thermally activated reactions of oxygen and ammonia with Si surfaces in furnaces have been used for a very long time in the semiconductor industry for the growth of thick oxides and nitride layers respectively. The oxidation mechanism was described in the Deal-Grove model as a diffusion...... limited transport of oxygen to the oxide/silicon interface. For thin oxides the deal-Grove growth rate is initially constant, but for ultrathin oxides (a couple of nm thick) this is not true and the Deal-Grove model does not explain the mechanism. In a series of recent reports we have found a new...

  10. Friction Consolidation of Gas-Atomized Fe-Si Powders for Soft Magnetic Applications

    Energy Technology Data Exchange (ETDEWEB)

    Jiang, Xiujuan; Whalen, Scott A.; Darsell, Jens T.; Mathaudhu, Suveen; Overman, Nicole R.

    2017-01-01

    Soft magnetic materials are often limited in scalability due to conventional processes that do not retain beneficial microstructures, and their associated physical properties, during densification. In this work, friction consolidation (FC) has been studied to fabricate Fe-Si soft magnetic materials from gas-atomized powder precursors. Fe-Si powder is consolidated using variable pressure and tool rotation speed in an effort to evaluate this unique densification approach for potential improvements in magnetic properties. FC, due to the high shear deformation involved, is shown to result in uniform gradual grain structure refinement across the consolidated workpiece from the center nearest the tool to the edge. Magnetic properties along different orientations indicate little, if any, textural orientation in the refined grain structure. The effect of annealing on the magnetic properties is evaluated and shown to decrease coercivity. FC processing was able to retain the magnetization of the original gas-atomized powders but further process optimization is needed to reach the optimal coercivity for the soft magnetic materials applications.

  11. Effect of Surface Charge on Surface-Initiated Atom Transfer Radical Polymerization from Cellulose Nanocrystals in Aqueous Media.

    Science.gov (United States)

    Zoppe, Justin O; Xu, Xingyu; Känel, Cindy; Orsolini, Paola; Siqueira, Gilberto; Tingaut, Philippe; Zimmermann, Tanja; Klok, Harm-Anton

    2016-04-11

    Cellulose nanocrystals (CNCs) with different charge densities were utilized to examine the role of electrostatic interactions on surface-initiated atom transfer radical polymerization (SI-ATRP) in aqueous media. To this end, growth of hydrophilic uncharged poly(N,N-dimethylacrylamide) (PDMAM) brushes was monitored by electrophoresis, (1)H NMR spectroscopy, and dynamic light scattering (DLS). Molecular weight and polydispersity of PDMAM brushes was determined by GPC analysis of hydrolytically cleaved polymers. Initiator and polymer brush grafting densities, and thus, initiator efficiencies were derived from elemental analysis. Higher initiator efficiency of polymer brush growth was observed for CNCs with higher anionic surface sulfate half-ester group density, but at the expense of high polydispersity caused by inefficient deactivation. PDMAM grafts with number-average molecular weights up to 530 kDa and polydispersity indices interfacial region at the onset of polymerization is proposed. The results presented here could have implications for other substrates that present surface charges and for the assumption that the kinetics of Cu-mediated SI-CRP are analogous to those conducted in solution.

  12. FTIR-ATR analysis of SiC(000 anti 1) and SiC(0001) surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Tsuchida, H.; Kamata, I.; Izumi, K. [Central Research Inst. of Electric Power Industry, Yokosuka (Japan)

    1998-06-01

    Recently developed SiC wafers with large diameter have been utilized to investigate the chemical state of the SiC surfaces by Fourier-transformed infrared attenuated total reflection (FTIR-ATR) spectroscopy with high sensitivity. The ex-situ ATR spectroscopy equipped with a Ge prism was used to study the chemisorbed species on 6H-SiC(000 anti 1) and (0001) surface after the chemical treatment and after the heat treatment in hydrogen. We obtained clear absorption bands attributable to hydrides on the surfaces. The polarity dependencies of Si-H and C-H stretch modes between the 6H-SiC(000 anti 1) and (0001) were discussed. (orig.) 10 refs.

  13. On new definitions of SI base units. Why is the "atomic" kilogram preferable

    CERN Document Server

    Bronnikov, K A; Kalinin, M I; Khruschov, V V; Kononogov, S A; Melnikov, V N

    2014-01-01

    We discuss the role of fundamental constants and measurement data for the Planck, Avogadro and Boltzmann constants and the elementary electric charge in connection with the planned transition to new definitions of four base SI units (the kilogram, mole, ampere and kelvin) in terms of fixed values of these constants. It is proposed to choose a new definition of any base SI unit in terms of a particular fundamental physical constant using a number of criteria, or principles, such as succession relative to the current SI, a sufficient stability of the new unit standards, and concordance between physical dimensions of the unit and the corresponding fundamental constant. It is argued that a redefinition of the kilogram and mole by fixing the values of the atomic mass unit and the Avogadro constant satisfies all these criteria and bears some more advantages against the version with fixed Planck constant: a well founded approach to definition of the ampere and the opportunity to preserve the current relationship bet...

  14. Self-assembly of conductive Cu nanowires on Si(111)'5 × 5 '-Cu surface.

    Science.gov (United States)

    Tsukanov, Dmitry A; Ryzhkova, Maria V; Gruznev, Dimitry V; Utas, Oleg A; Kotlyar, Vasily G; Zotov, Andrey V; Saranin, Alexander A

    2008-06-18

    Upon room-temperature deposition onto a Cu/Si(111)'5 × 5' surface in ultra-high vacuum, Cu atoms migrate over extended distances to become trapped at the step edges, where they form Cu nanowires (NWs). The formed NWs are 20-80 nm wide, 1-3 nm high and characterized by a resistivity of ∼8 µΩ cm. The surface conductance of the NW array is anisotropic, with the conductivity along the NWs being about three times greater than that in the perpendicular direction. Using a similar growth technique, not only the straight NWs but also other types of NW-based structures (e.g. nanorings) can be fabricated.

  15. Heterogeneous recombination of neutral oxygen atoms on niobium surface

    Energy Technology Data Exchange (ETDEWEB)

    Mozetic, Miran; Zalar, Anton; Cvelbar, Uros; Poberaj, Igor

    2003-04-30

    The recombination coefficient for the reaction O+O{yields}O{sub 2} on a polycrystalline niobium surface was measured at various experimental conditions. The source of O atoms was a low pressure weakly ionized highly dissociated oxygen plasma created in a RF discharge. The electron temperature in plasma was about 5 eV and the density of positive ions between 5 and 10x10{sup 15} m{sup -3}. The density of neutral oxygen atoms was measured in the afterglow with a nickel catalytic probe and was between 2.5 and 7x10{sup 21} m{sup -3}. The recombination coefficient was measured at different temperature between 420 and 620 K, and was found to be a constant within the limits of the experimental error at the value of 0.09{+-}0.018.

  16. The role of phase separation for self-organized surface pattern formation by ion beam erosion and metal atom co-deposition

    Energy Technology Data Exchange (ETDEWEB)

    Hofsaess, H.; Zhang, K.; Pape, A.; Bobes, O.; Broetzmann, M. [Georg-August University Goettingen, II. Institute of Physics, Goettingen (Germany)

    2013-05-15

    We investigate the ripple pattern formation on Si surfaces at room temperature during normal incidence ion beam erosion under simultaneous deposition of different metallic co-deposited surfactant atoms. The co-deposition of small amounts of metallic atoms, in particular Fe and Mo, is known to have a tremendous impact on the evolution of nanoscale surface patterns on Si. In previous work on ion erosion of Si during co-deposition of Fe atoms, we proposed that chemical interactions between Fe and Si atoms of the steady-state mixed Fe{sub x} Si surface layer formed during ion beam erosion is a dominant driving force for self-organized pattern formation. In particular, we provided experimental evidence for the formation of amorphous iron disilicide. To confirm and generalize such chemical effects on the pattern formation, in particular the tendency for phase separation, we have now irradiated Si surfaces with normal incidence 5 keV Xe ions under simultaneous gracing incidence co-deposition of Fe, Ni, Cu, Mo, W, Pt, and Au surfactant atoms. The selected metals in the two groups (Fe, Ni, Cu) and (W, Pt, Au) are very similar regarding their collision cascade behavior, but strongly differ regarding their tendency to silicide formation. We find pronounced ripple pattern formation only for those co deposited metals (Fe, Mo, Ni, W, and Pt), which are prone to the formation of mono and disilicides. In contrast, for Cu and Au co-deposition the surface remains very flat, even after irradiation at high ion fluence. Because of the very different behavior of Cu compared to Fe, Ni and Au compared to W, Pt, phase separation toward amorphous metal silicide phases is seen as the relevant process for the pattern formation on Si in the case of Fe, Mo, Ni, W, and Pt co-deposition. (orig.)

  17. Silicic acid (Si(OH)(4)) is a significant influence upon the atomic absorption signal of aluminium measured by graphite furnace atomic absorption spectrometry (GFAAS).

    Science.gov (United States)

    Schneider, C; Exley, C

    2001-11-01

    We have identified silicic acid (Si(OH)(4)) as an important modifier of the absorbance signal of aluminium measured by graphite furnace atomic absorption spectrometry (GFAAS). The presence of Si(OH)(4) enhanced the signal by as much as 50%. The extent of the enhancement was dependent upon both [Al] and [Si(OH)(4)] and was maximal when [Al] or =0.50 mmol dm(-3). The enhancement of the Al absorbance signal was not linearly related to [Si(OH)(4)] and the effect was, generally, saturated, for all [Al] tested, at [Si(OH)(4)]> or =0.50 mmol dm(-3). Si(OH)(4) was significantly more effective in enhancing the Al absorbance signal than Mg(NO(3))(2). However, the co-occurrence of 10 mmol dm(-3) Mg(NO(3))(2) and 2 mmol dm(-3) Si(OH)(4) in samples abolished the enhancement due to Si(OH)(4). The presence of Si(OH)(4) in samples could result in an overestimation of the Al content of those samples by as much as 50%. Errors in the measurement of Al in samples containing Si(OH)(4) could be prevented using matrix-matched calibration standards. Our observation could have serious implications for the determination of Al in aqueous samples of both geochemical and biological interest. It may also point towards the application of Si(OH)(4) as a novel and effective matrix modifier in the determination of Al by GFAAS since the inclusion of Si(OH)(4) in standards and samples improved the limit of detection of Al from ca 8 nmol dm(-3) to 3 nmol dm(-3).

  18. Single atom anisotropic magnetoresistance on a topological insulator surface

    KAUST Repository

    Narayan, Awadhesh

    2015-03-12

    © 2015 IOP Publishing Ltd and Deutsche Physikalische Gesellschaft. We demonstrate single atom anisotropic magnetoresistance on the surface of a topological insulator, arising from the interplay between the helical spin-momentum-locked surface electronic structure and the hybridization of the magnetic adatom states. Our first-principles quantum transport calculations based on density functional theory for Mn on Bi2Se3 elucidate the underlying mechanism. We complement our findings with a two dimensional model valid for both single adatoms and magnetic clusters, which leads to a proposed device setup for experimental realization. Our results provide an explanation for the conflicting scattering experiments on magnetic adatoms on topological insulator surfaces, and reveal the real space spin texture around the magnetic impurity.

  19. Atomic and electronic structure of surfaces theoretical foundations

    CERN Document Server

    Lannoo, Michel

    1991-01-01

    Surfaces and interfaces play an increasingly important role in today's solid state devices. In this book the reader is introduced, in a didactic manner, to the essential theoretical aspects of the atomic and electronic structure of surfaces and interfaces. The book does not pretend to give a complete overview of contemporary problems and methods. Instead, the authors strive to provide simple but qualitatively useful arguments that apply to a wide variety of cases. The emphasis of the book is on semiconductor surfaces and interfaces but it also includes a thorough treatment of transition metals, a general discussion of phonon dispersion curves, and examples of large computational calculations. The exercises accompanying every chapter will be of great benefit to the student.

  20. Oxygen Atom Adsorption and Diffusion on Pd Low-index Surfaces and (311) Stepped Surface

    Institute of Scientific and Technical Information of China (English)

    WANG, Ze-Xin(王泽新); JIA, Xiang-Feng(贾祥凤); TIAN, Feng-Hui(田凤惠); CHEN, Shou-Gang(陈守刚)

    2004-01-01

    The 5-parameter Morse potential (5-MP for short) of the interaction system between an oxygen atom and palladium surface clusters was constructed. The adsorption and diffusion of an oxygen atom on low index surfaces Pd (100), Pd (111), Pd (110) and Pd (311) stepped surface were investigated in detail with 5-MP. It is found that fcc and hcp sites on the (111) surface and (111) microfacets are equivalent. The calculation results show that O atom adsorbs in the three-fold hollow site, and the long-bridge site is a stable site both in regular Pd (110) surface and in the (1×2) missing-row reconstruction structure. Moreover, in the study of O-Pd (311) surface system, We conclude that there are two stable adsorption states (four-fold site: H4, three-fold site: Hh) on O-Pd (311) surface and the three-fold site (Hf) is the metastable adsorption. At low coverage oxygen atom favors the four-fold hollow site (H4).

  1. Facile synthesis of thermally stable poly(N-vinylpyrrolidone)-modified gold surfaces by surface-initiated atom transfer radical polymerization.

    Science.gov (United States)

    Liu, Xiaoli; Sun, Kai; Wu, Zhaoqiang; Lu, Jianhong; Song, Bo; Tong, Weifang; Shi, Xiujuan; Chen, Hong

    2012-06-26

    Well-controlled polymerization of N-vinylpyrrolidone (NVP) on Au surfaces by surface-initiated atom transfer radical polymerization (SI-ATRP) was carried out at room temperature by a silanization method. Initial attempts to graft poly(N-vinylpyrrolidone) (PVP) layers from initiators attached to alkanethiol monolayers yielded PVP films with thicknesses less than 5 nm. The combined factors of the difficulty in the controllable polymerization of NVP and the instability of alkanethiol monolayers led to the difficulty in the controlled polymerization of NVP on Au surfaces. Therefore, the silanization method was employed to form an adhesion layer for initiator attachment. This method allowed well-defined ATRP polymerization to occur on Au surfaces. Water contact angle, X-ray photoelectron spectroscopy (XPS), and reflectance Fourier transform infrared (reflectance FTIR) spectroscopy were used to characterize the modified surfaces. The PVP-modified gold surface remained stable at 130 °C for 3 h, showing excellent thermal stability. Thus, postfunctionalization of polymer brushes at elevated temperatures is made possible. The silanization method was also applied to modify SPR chips and showed potential applications in biosensors and biochips.

  2. Interaction between solute atoms and radiation defects in Fe-Ni-Si and Fe-Mn-Si alloys under irradiation with proton ions at low-temperature

    Science.gov (United States)

    Murakami, Kenta; Iwai, Takeo; Abe, Hiroaki; Sekimura, Naoto

    2016-12-01

    Isochronal annealing followed by residual resistivity measurements at 12 K was performed in Fe-0.6Ni-0.6Si and Fe-1.5Mn-0.6Si alloys irradiated with 1 MeV proton ions below 70 K, and recovery stages were compared with those of Fe-0.6Ni and Fe-1.5Mn. The effects of silicon addition in the Fe-Ni alloy was observed as the appearance of a new recovery stage at 282-372 K, presumably corresponding to clustering of solute atoms in matrix, and as a change in mixed dumbbell migration at 122-142 K. Silicon addition mitigated the manganese effect in Fe-Mn alloy that is obstructing the recovery of radiation defects. Reduction of resistivity in Fe-Mn-Si alloy also suggested formation of small solute atom clusters.

  3. SiC/SiO2界面的原子分辨率三维重构%Atomic resolution 3 D reconstruction of SiC/SiO2 interface

    Institute of Scientific and Technical Information of China (English)

    刘培植; 许并社; 郭俊杰

    2015-01-01

    Silicon carbide ( SiC) is widely used in high power electronics as a substitute of silicon. The key problem of SiC based metal⁃oxide⁃semiconductor field effect transistors ( MOSFET) is the relatively low channel electron mobility, and the transition layer of SiC/SiO2 interface is considered to be the main cause for the reduced electron mobility. However, the atomic structure of the transition layer is still unclear. In this paper, the transition layer was investigated with a 5th order spherical aberration corrected scanning transmission electron microscope. Depth sectioning images of SiC/SiO2 interface were obtained with the through⁃focal series technique, and an atomic resolution 3D structure of the interface was reconstructed with the through⁃focal series images. The clear 3D interface structure suggests that tshe interface has an atomic scale roughness, and the transition layer is a contrast of the roughness. The kinks, steps and microfacets increase the scattering probability of channel electrons, resulting in reducing the channel mobility of the MOSFET devices.%碳化硅( SiC)作为一种新型材料被广泛应用于高功率半导体器件中。目前的SiC基金属氧化物半导体场效应晶体管器件存在的主要问题是沟道电子迁移率低。 SiC/SiO2界面处的过渡层被认为是造成沟道电子迁移率低的主要原因,但是该过渡层的原子结构尚不清楚。本文利用球差矫正扫描透射电子显微镜深入研究了SiC/SiO2的界面。以变聚焦序列技术得到了界面过渡层不同深度的原子分辨率断层扫描图像,用变聚焦序列图像重构了界面的原子分辨率三维结构。精确的界面原子结构表明SiC/SiO2界面处的过渡区是由于邻晶界面上台阶突起和微刻面构成的。它是界面原子尺度的粗糙度的反映。邻晶界面上的台阶突起和微刻面增加了电子在界面传输过程中的散射几率,造成了沟道电子迁移率过低。

  4. Thermal chemistry of copper acetamidinate atomic layer deposition precursors on silicon oxide surfaces studied by XPS

    Energy Technology Data Exchange (ETDEWEB)

    Yao, Yunxi; Zaera, Francisco, E-mail: zaera@ucr.edu [Department of Chemistry, University of California, Riverside, California 92521 (United States)

    2016-01-15

    The thermal surface chemistry of copper(I)-N,N′-di-sec-butylacetamidinate, [Cu({sup s}Bu-amd)]{sub 2}, a metalorganic complex recently proposed for the chemical-based deposition of copper films, has been characterized on SiO{sub 2} films under ultrahigh vacuum conditions by x-ray photoelectron spectroscopy (XPS). Initial adsorption at cryogenic temperatures results in the oxidation of the copper centers with Cu 2p{sub 3/2} XPS binding energies close to those seen for a +2 oxidation state, an observation that the authors interpret as the result of the additional coordination of oxygen atoms from the surface to the Cu atoms of the molecular acetamidinate dimer. Either heating to 300 K or dosing the precursor directly at that temperature leads to the loss of one of its two ligands, presumably via hydrogenation/protonation with a hydrogen/proton from a silanol group, or following a similar reaction on a defect site. By approximately 500 K the Cu 2p{sub 3/2}, C 1s, and N 1s XPS data suggest that the remaining acetamidinate ligand is displaced from the copper center and bonds to the silicon oxide directly, after which temperatures above 900 K need to be reached to promote further (and only partial) decomposition of those organic moieties. It was also shown that the uptake of the Cu precursor is self-limiting at either 300 or 500 K, although the initial chemistry is somewhat different at the two temperatures, and that the nature of the substrate also defines reactivity, with the thin native silicon oxide layer always present on Si(100) surfaces being less reactive than thicker films grown by evaporation, presumably because of the lower density of surface nucleation sites.

  5. Fast atom diffraction for grazing scattering of Ne atoms from a LiF(0 0 1) surface

    Energy Technology Data Exchange (ETDEWEB)

    Gravielle, M.S., E-mail: msilvia@iafe.uba.ar [Instituto de Astronomia y Fisica del Espacio (CONICET-UBA), Casilla de correo 67, sucursal 28 C1428EGA, Buenos Aires (Argentina); Departamento de Fisica, Fac. de Ciencias Exactas y Naturales, Universidad de Buenos Aires (Argentina); Schueller, A.; Winter, H. [Institut fuer Physik, Humboldt Universitaet zu Berlin, Newtonstrasse 15, D-12489 Berlin-Adlershof (Germany); Miraglia, J.E. [Instituto de Astronomia y Fisica del Espacio (CONICET-UBA), Casilla de correo 67, sucursal 28 C1428EGA, Buenos Aires (Argentina); Departamento de Fisica, Fac. de Ciencias Exactas y Naturales, Universidad de Buenos Aires (Argentina)

    2011-06-01

    Angular distributions of fast Ne atoms after grazing collisions with a LiF(0 0 1) surface under axial surface channeling conditions are experimentally and theoretically studied. We use the surface eikonal approximation to describe the quantum interference of scattered projectiles, while the atom-surface interaction is represented by means of a pairwise additive potential, including the polarization of the projectile atom. Experimental data serve as a benchmark to investigate the performance of the proposed potential model, analyzing the role played by the projectile polarization.

  6. Surface chemical structure and doping characteristics of boron-doped Si nanowires fabricated by plasma doping

    Science.gov (United States)

    Oh, Seung-Hoon; Ma, Jin-Won; Bae, Jung Min; Kang, Yu-seon; Ahn, Jae-Pyung; Kang, Hang-Kyu; Chae, Jimin; Suh, Dongchan; Song, Woobin; Kim, Sunjung; Cho, Mann-Ho

    2017-10-01

    We investigated the conduction characteristics of plasma-doped Si nanowires (NWs) after various rapid thermal annealing (RTA) times. The plasma doping (PD) process developed a highly-deposited B layer at the NW surface. RTA process controls electrical conductivity by mediating the dopant diffusion from the surface layer. The surface chemical and substitutional states of the B plasma-doped Si NWs were analyzed by x-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. To elucidate the detailed structure of the NWs, we analyzed the change in the optical phonon mode caused by the incorporated B atoms. For this purpose, we examined Fano resonance by the investigation of the asymmetry, line-width, and phonon wavenumber in Raman spectra. The changes in symmetry level of the Raman peak, phonon lifetime, and internal strain were closely related to the number of electrically activated borons, which was drastically increased with RTA time. The change in electrical and optical characterizations related to the doping characteristics of the NWs was investigated using a 4-point probe and terahertz time-domain spectroscopy (THz-TDS). The resistivity of the NWs was 3000 times lower after the annealing process compared to that before the annealing process, which is well consistent with the optical conductivity data. The data provide the potential utility of PD in conformal doping for three-dimensional nanodevices.

  7. Atomic force microscopy analysis of different surface treatments of Ti dental implant surfaces

    Science.gov (United States)

    Bathomarco, Ti R. V.; Solorzano, G.; Elias, C. N.; Prioli, R.

    2004-06-01

    The surface of commercial unalloyed titanium, used in dental implants, was analyzed by atomic force microscopy. The morphology, roughness, and surface area of the samples, submitted to mechanically-induced erosion, chemical etching and a combination of both, were compared. The results show that surface treatments strongly influence the dental implant physical and chemical properties. An analysis of the length dependence of the implant surface roughness shows that, for scan sizes larger than 50 μm, the average surface roughness is independent of the scanning length and that the surface treatments lead to average surface roughness in the range of 0.37 up to 0.48 μm. It is shown that the implant surface energy is sensitive to the titanium surface area. As the area increases there is a decrease in the surface contact angle.

  8. Atomic force microscopy analysis of different surface treatments of Ti dental implant surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Bathomarco, R.V.; Solorzano, G.; Elias, C.N.; Prioli, R

    2004-06-30

    The surface of commercial unalloyed titanium, used in dental implants, was analyzed by atomic force microscopy. The morphology, roughness, and surface area of the samples, submitted to mechanically-induced erosion, chemical etching and a combination of both, were compared. The results show that surface treatments strongly influence the dental implant physical and chemical properties. An analysis of the length dependence of the implant surface roughness shows that, for scan sizes larger than 50 {mu}m, the average surface roughness is independent of the scanning length and that the surface treatments lead to average surface roughness in the range of 0.37 up to 0.48 {mu}m. It is shown that the implant surface energy is sensitive to the titanium surface area. As the area increases there is a decrease in the surface contact angle.

  9. Room temperature bonding of SiO2 and SiO2 by surface activated bonding method using Si ultrathin films

    Science.gov (United States)

    Utsumi, Jun; Ide, Kensuke; Ichiyanagi, Yuko

    2016-02-01

    The bonding of metal electrodes and insulator hybrid interfaces is one of the key techniques in three-dimensional integration technology. Metal materials such as Cu or Al are easily directly bonded by surface activated bonding at room temperature, but insulator materials such as SiO2 or SiN are not. Using only Si ultrathin films, we propose a new bonding technique for SiO2/SiO2 bonding at room temperature. Two SiO2 surfaces, on which Si thin films were deposited, were contacted in vacuum. We confirmed that the thickness of the layer was about 7 nm by transmission electron microscopy observation and that the layer was non crystalline by electron energy loss spectroscopy analysis. No metal material was found in the bonding interface by energy-dispersive X-ray spectroscopy analysis. The surface energy was about 1 J/m2, and the bonding strength was more than 25 MPa. This bonding technique was successfully realized to enable SiO2/SiO2 bonding without a metal adhesion layer.

  10. Effect of the tip state during qPlus noncontact atomic force microscopy of Si(100) at 5 K: Probing the probe.

    Science.gov (United States)

    Sweetman, Adam; Jarvis, Sam; Danza, Rosanna; Moriarty, Philip

    2012-01-01

    Noncontact atomic force microscopy (NC-AFM) now regularly produces atomic-resolution images on a wide range of surfaces, and has demonstrated the capability for atomic manipulation solely using chemical forces. Nonetheless, the role of the tip apex in both imaging and manipulation remains poorly understood and is an active area of research both experimentally and theoretically. Recent work employing specially functionalised tips has provided additional impetus to elucidating the role of the tip apex in the observed contrast. We present an analysis of the influence of the tip apex during imaging of the Si(100) substrate in ultra-high vacuum (UHV) at 5 K using a qPlus sensor for noncontact atomic force microscopy (NC-AFM). Data demonstrating stable imaging with a range of tip apexes, each with a characteristic imaging signature, have been acquired. By imaging at close to zero applied bias we eliminate the influence of tunnel current on the force between tip and surface, and also the tunnel-current-induced excitation of silicon dimers, which is a key issue in scanning probe studies of Si(100). A wide range of novel imaging mechanisms are demonstrated on the Si(100) surface, which can only be explained by variations in the precise structural configuration at the apex of the tip. Such images provide a valuable resource for theoreticians working on the development of realistic tip structures for NC-AFM simulations. Force spectroscopy measurements show that the tip termination critically affects both the short-range force and dissipated energy.

  11. Effect of the tip state during qPlus noncontact atomic force microscopy of Si(100 at 5 K: Probing the probe

    Directory of Open Access Journals (Sweden)

    Adam Sweetman

    2012-01-01

    Full Text Available Background: Noncontact atomic force microscopy (NC-AFM now regularly produces atomic-resolution images on a wide range of surfaces, and has demonstrated the capability for atomic manipulation solely using chemical forces. Nonetheless, the role of the tip apex in both imaging and manipulation remains poorly understood and is an active area of research both experimentally and theoretically. Recent work employing specially functionalised tips has provided additional impetus to elucidating the role of the tip apex in the observed contrast.Results: We present an analysis of the influence of the tip apex during imaging of the Si(100 substrate in ultra-high vacuum (UHV at 5 K using a qPlus sensor for noncontact atomic force microscopy (NC-AFM. Data demonstrating stable imaging with a range of tip apexes, each with a characteristic imaging signature, have been acquired. By imaging at close to zero applied bias we eliminate the influence of tunnel current on the force between tip and surface, and also the tunnel-current-induced excitation of silicon dimers, which is a key issue in scanning probe studies of Si(100.Conclusion: A wide range of novel imaging mechanisms are demonstrated on the Si(100 surface, which can only be explained by variations in the precise structural configuration at the apex of the tip. Such images provide a valuable resource for theoreticians working on the development of realistic tip structures for NC-AFM simulations. Force spectroscopy measurements show that the tip termination critically affects both the short-range force and dissipated energy.

  12. Effect of the nature of the substrate on the surface chemistry of atomic layer deposition precursors

    Science.gov (United States)

    Yao, Yunxi; Coyle, Jason P.; Barry, Seán T.; Zaera, Francisco

    2017-02-01

    The thermal chemistry of Cu(I)-sec-butyl-2-iminopyrrolidinate, a promising copper amidinate complex for atomic layer deposition (ALD) applications, was explored comparatively on several surfaces by using a combination of surface-sensitive techniques, specifically temperature-programmed desorption and x-ray photoelectron spectroscopy (XPS). The substrates explored include single crystals of transition metals (Ni(110) and Cu(110)), thin oxide films (NiO/Ni(110) and SiO2/Ta), and oxygen-treated metals (O/Cu(110)). Decomposition of the pyrrolidinate ligand leads to the desorption of several gas-phase products, including CH3CN, HCN and butene from the metals and CO and CO2 from the oxygen-containing surfaces. In all cases dehydrogenation of the organic moieties is accompanied by hydrogen removal from the surface, in the form of H2 on metals and mainly as water from the metal oxides, but the threshold for this chemistry varies wildly, from 270 K on Ni(110) to 430 K on O/Cu(110), 470 K on Cu(110), 500 K on NiO/Ni(110), and 570 K on SiO2/Ta. Copper reduction is also observed in both the Cu 2p3/2 XPS and the Cu L3 VV Auger (AES) spectra, reaching completion by 300 K on Ni(110) but occurring only between 500 and 600 K on Cu(110). On NiO/Ni(110), both Cu(I) and Cu(0) coexist between 200 and 500 K, and on SiO2/Ta a change happens between 500 and 600 K but the reduction is limited, with the copper atoms retaining a significant ionic character. Additional experiments to test adsorption at higher temperatures led to the identification of temperature windows for the self-limiting precursor uptake required for ALD between approximately 300 and 450 K on both Ni(110) and NiO/Ni(110); the range on SiO2 had been previously determined to be wider, reaching an upper limit at about 500 K. Finally, deposition of copper metal films via ALD cycles with O2 as the co-reactant was successfully accomplished on the Ni(110) substrate.

  13. STM observation of the surface structures formed on the initial stage of SiC growth using monomethylsilane

    CERN Document Server

    Harashima, M; Akahane, T

    2003-01-01

    A c(4x4) structure formed by exposing monomethylsilane (MMSi) to a Si(001)-(2x1) surface at substrate temperature of 700degC was measured using scanning tunneling microscopy (STM). At the stage that the spots originated from c(4x4) structure were brightly observed by reflection high energy electron diffraction (RHEED), both c(4x4) and (2x1) domains coexisted. From the evaluation of the c(4x4) and the (2x1) structures by lineprofile of STM images, the c(4x4) structure was revealed to be contracted, while the distance between the (2x1) dimer rows was expanded. Using X-ray photoelectron spectroscopy (XPS), we have confirmed that the carbon atoms included in MMSi diffused into Si substrate. It can therefore be assumed that the contraction of the c(4x4) surface was originated from the diffusion of carbon into Si subsurface. Because of small lattice constant of SiC compared to Si, the c(4x4) structure was predicted to become the site that enhances the nucleation of SiC islands. (author)

  14. Systematic STM and LEED investigation of the Si/Ag(110) surface.

    Science.gov (United States)

    Colonna, S; Serrano, G; Gori, P; Cricenti, A; Ronci, F

    2013-08-07

    Interest in the Si/Ag(110) system, which forms highly ordered linear nanostructures coined 'silicon nanoribbons', was recently boosted by the claim that such nanoribbons may be formed by silicon atoms arranged in a 2D honeycomb structure as in graphene, i.e. silicene. Despite such a revived interest, many discrepancies still exist in the recently reported results. This paper reports on a systematic investigation by scanning tunneling microscopy and low-energy electron diffraction of the Si/Ag(110) system as a function of the amount of deposited silicon and the deposition temperature. This reveals a complex interplay between these two factors, resulting in a rich array of possible self-assembled nanostructures and surface reconstructions. Several novel findings and clarification of the contradictory results reported in the literature are discussed in this work. In particular, the deposition temperature is demonstrated to be a key parameter to control the width of the Si nanoribbons produced. Recently, massive linear nanostructures were reported to be 'multilayer silicene', forming once the deposited silicon amount exceeds full coverage. However, we show that such nanostructures are also observed at low silicon coverage, demonstrating that their formation is exclusively determined by a deposition temperature higher than 460 K. On the other hand, for Si amounts higher than one monolayer the surface presents a novel c(8 × 4) reconstruction, which is responsible for the ×4 periodicity detected by LEED measurements, previously attributed to the 1.6 nm-wide nanoribbons overlayer or to 'multilayer silicene'. Finally, the large collection of acquired data also allowed us to single out image artifacts that may explain the contradictory results appearing in previous papers.

  15. Effects of Vacuum Ultraviolet Radiation on Atomic Oxygen Erosion of Polysiloxane/SiO2 Hybrid Coatings

    Institute of Scientific and Technical Information of China (English)

    Longfei Hu; Meishuan Li; Yanchun Zhou

    2009-01-01

    Polysiloxane/SiO2 hybrid coatings have been prepared on Kapton films by a sol-gel process. The erosion resistance of polysiloxane/SiO2 (20 wt pct) coating was evaluated by exposure tests of vacuum ultraviolet radiation (VUV) and atomic oxygen beam (AO) in a ground-based simulation facility. The experimental results indicate that this coating exhibits better AO resistance than pure polysiloxane coating. The erosion yield (Ey) of the polysiloxane/SiO2 (20 wt pct) hybrid coating is about 10-27 cm3/atom, being one or two orders of magnitude lower than that of polysiloxane. VUV radiation can affect the erosion process greatly. Under simultaneous AO and VUV exposure, the value of Ey of the polysiloxane/SiO2 (20 wt pct) hybrid coating increases by 39% compared with that under single AO exposure.

  16. Benchmarking surface signals when growing GaP on Si in CVD ambients

    Energy Technology Data Exchange (ETDEWEB)

    Doescher, Henning

    2010-10-26

    agree very well with InP(100) surface reconstructions, as well as the development of the corresponding RAS signatures, gained by benchmarking the optical in situ signals with STM and LEED results. APD quantification by RAS was greatly improved by an empirical correction of the in situ spectra taking thin film interferences into account. In addition, optical model calculations were developed to extract the anisotropy of the GaP/Si(100) heterointerface from the RAS signals by separation of surface, bulk and interface contributions. The quantitative in situ analysis concept was compared to and supported by low energy electron microscopy (LEEM) experiments, which were established for APD quantification and APD visualization on a mesoscopic length scale, as well as atomic force microscopy (AFM) and transmission electron microscopy (TEM). Benchmarking of all of these methods served to improve the MOVPE process consisting of Si substrate conditioning and GaP nucleation and growth. (orig.)

  17. Capillary-force measurement on SiC surfaces

    Science.gov (United States)

    Sedighi, M.; Svetovoy, V. B.; Palasantzas, G.

    2016-06-01

    Capillary forces have been measured by atomic force microscopy in the sphere-plate geometry, in a controlled humidity environment, between smooth silicon carbide and borosilicate glass spheres. The force measurements were performed as a function of the rms surface roughness ˜4-14 nm mainly due to sphere morphology, the relative humidity (RH) ˜0%-40%, the applied load on the cantilever, and the contact time. The pull-off force was found to decrease by nearly two orders of magnitude with increasing rms roughness from 8 to 14 nm due to formation of a few capillary menisci for the roughest surfaces, while it remained unchanged for rms roughness <8 nm implying fully wetted surface features leading to a single meniscus. The latter reached a steady state in less than 5 s for the smoothest surfaces, as force measurements versus contact time indicated for increased RH˜40%. Finally, the pull-off force increases and reaches a maximum with applied load, which is associated with plastic deformation of surface asperities, and decreases at higher loads.

  18. Simulating atomic-scale phenomena on surfaces of unconventional superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Kreisel, Andreas; Andersen, Brian [Niels Bohr Institute (Denmark); Choubey, Peayush; Hirschfeld, Peter [Univ. of Florida (United States); Berlijn, Tom [CNMS and CSMD, Oak Ridge National Laboratory (United States)

    2016-07-01

    Interest in atomic scale effects in superconductors has increased because of two general developments: First, the discovery of new materials as the cuprate superconductors, heavy fermion and Fe-based superconductors where the coherence length of the cooper pairs is as small to be comparable to the lattice constant, rendering small scale effects important. Second, the experimental ability to image sub-atomic features using scanning-tunneling microscopy which allows to unravel numerous physical properties of the homogeneous system such as the quasi particle excitation spectra or various types of competing order as well as properties of local disorder. On the theoretical side, the available methods are based on lattice models restricting the spatial resolution of such calculations. In the present project we combine lattice calculations using the Bogoliubov-de Gennes equations describing the superconductor with wave function information containing sub-atomic resolution obtained from ab initio approaches. This allows us to calculate phenomena on surfaces of superconductors as directly measured in scanning tunneling experiments and therefore opens the possibility to identify underlying properties of these materials and explain observed features of disorder. It will be shown how this method applies to the cuprate material Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8} and a Fe based superconductor.

  19. Influence of O 2 and oxide on Cl/Si surface reactions

    Science.gov (United States)

    Aoto, Nahomi; Ikawa, Eiji; Kikkawa, Takamaro; Kurogi, Yukinori

    1991-05-01

    Variation of Si(111) and Si(100) surface conditions under sequential Cl 2 exposure, O 2 exposure, and other O-related treatments are examined by Auger electron spectroscopy (AES) and low-energy electron energy loss spectroscopy (LEELS). Cl-adsorbed Si surfaces, particularly Cl-adsorbed Si(111) surfaces, have a passivation effect under dry O 2 atmosphere, where O adsorption and oxidation are suppressed. On the other hand, Cl desorption and oxidation take place immediately on Cl-adsorbed surfaces when exposed to wet environments: humid clean-room air or de-ionized water. When O 2-treated Si surfaces are exposed to Cl 2 atmospheres, Cl adsorption occurs on SiO x but not on SiO 2.

  20. Effects of surface oxide species and contents on SiC slurry viscosity

    Institute of Scientific and Technical Information of China (English)

    NING Shufan; LI Hongyan; CHEN Wei; LIU Bin; CHEN Shoutian

    2005-01-01

    The disadvantageous effects of colloidal SiO2 layer and micro-content of metal oxide adsorbed on SiC powder surface on SiC slurry stable dispersion were studied, and the novel method to avoid this disadvantage was proposed. By acidwashing, on the one hand, because the maximum Zeta potential of SiC powder increases to 72.49 mV with the decreasing content of metal oxide adsorbed on the SiC powder surface, the repulsion force between SiC powders that dispersed in slurry is enhanced, thus the SiC powder can be fully dispersed in slurry. On the other hand, after HF acidwashing, with the OH- group adsorbed on SiC powder surface destroyed and replaced by the F- ion, the hydrogen bond adsorbed on the OH-group is also destroyed. Therefore, the surface property of the SiC powder is changed from hydrophilic to hydrophobic;H2O that adsorbed on SiC powder surface is released and can flow freely, and it actually increases the content of the effective flow phase in the slurry. These changes of SiC powder surface property can be proved by XPS and FTIR analysis. Fivolume fraction of SiC powder in the slurry is maximized to 61.5 vol.%.

  1. Photoluminescence enhancement in porous SiC passivated by atomic layer deposited Al2O3 films

    DEFF Research Database (Denmark)

    Lu, Weifang; Iwasa, Yoshimi; Ou, Yiyu

    2016-01-01

    Porous SiC co-doped with B and N was passivated by atomic layer deposited (ALD) Al2O3 films to enhance the photoluminescence. After optimizing the deposition conditions, as high as 14.9 times photoluminescence enhancement has been achieved.......Porous SiC co-doped with B and N was passivated by atomic layer deposited (ALD) Al2O3 films to enhance the photoluminescence. After optimizing the deposition conditions, as high as 14.9 times photoluminescence enhancement has been achieved....

  2. Photoluminescence enhancement in porous SiC passivated by atomic layer deposited Al2O3 films

    DEFF Research Database (Denmark)

    Lu, Weifang; Iwasa, Yoshimi; Ou, Yiyu;

    2016-01-01

    Porous SiC co-doped with B and N was passivated by atomic layer deposited (ALD) Al2O3 films to enhance the photoluminescence. After optimizing the deposition conditions, as high as 14.9 times photoluminescence enhancement has been achieved.......Porous SiC co-doped with B and N was passivated by atomic layer deposited (ALD) Al2O3 films to enhance the photoluminescence. After optimizing the deposition conditions, as high as 14.9 times photoluminescence enhancement has been achieved....

  3. Dependence of Y sub 2 O sub 3 film growth on the state of the Si surface

    CERN Document Server

    Cho, M H; Jeong, K H; Whang, C N Y; Ko, D H; Choi, S C; Cho, S J

    1999-01-01

    Y sub 2 O sub 3 films were grown on Si substrates with various surface conditions by using ionized cluster beam deposition. The interface and the surface characteristics was investigated by reflection high energy electron diffraction, atomic force microscopy, and X-ray photoelectron spectroscopy. The dependence of the crystallinities of the films on the surface conditions was investigated using X-ray diffraction. The investigation showed that control of the silicide layer played a crucial role in the growth of Y sub 2 O sub 3 films during the initial stage of growth. The Y sub 2 O sub 3 film grown on a silicide layer formed on a clean Si surface was a polycrystal with a monoclinic structure. However, the film grown on a silicide layer formed on a SiO sub 2 -terminated surface turned out to be a single crystalline Y sub 2 O sub 3 with a cubic structure. A high-quality film in terms of crystallinity and stochiometry was obtained when the growth of the silicide layer was controlled by a SiO sub 2 layer which had...

  4. Inspecting the surface of implanted Si(111) during annealing by reflective second harmonic generation: The influence of chamber pressure

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Chung-Wei; Chang, Shoou-Jinn [Institute of Microelectronics and Department of Electrical Engineering and Center for Micro/Nano Science and Technology, National Cheng Kung University, Tainan 701, Taiwan (China); Advanced Optoelectronic Technology Center, National Cheng Kung University, Tainan 701, Taiwan (China); Liu, Chun-Chu [Department of Electrophysics, National Chia Yi University, Chia Yi 600, Taiwan (China); Lo, Kuang-Yao, E-mail: kuanglo@mail.ncyu.edu.tw [Department of Electrophysics, National Chia Yi University, Chia Yi 600, Taiwan (China); Advanced Optoelectronic Technology Center, National Cheng Kung University, Tainan 701, Taiwan (China)

    2013-02-01

    The present study used the reflective second harmonic generation (RSHG) method to analyze the quality of the surface layer of implanted Si(111) and to discuss the influence of chamber pressure during rapid thermal annealing. Under a lower chamber pressure, the recrystallization is better, and the defects are eliminated for a higher implanted dose because dopant phosphorus (P) atoms on the surface region more easily out-diffuse at lower chamber pressures. Thus, the occurrence of less out-diffusion makes more P atoms remain on the surface layer and causes larger defects, especially for higher implanted doses. Defects on the surface region are influenced by chamber pressure. In the current work, the RSHG results showed more detailed information by linking secondary ion mass spectrometry and sheet resistance measurement. - Highlights: ► Rapid thermal annealing (RTA) with different chamber pressures was performed. ► The quality of implanted Si was analyzed by reflective second harmonic generation. ► High-dose implanted Si is obviously influenced by the pressure in the RTA chamber. ► Pressure in the RTA chamber affects the generation of defects. ► Defect suppression is obvious at relatively low chamber pressure.

  5. Correlation between surface damage and micro-defects in Si covered with insulating layer by implantation of He and H ions

    Energy Technology Data Exchange (ETDEWEB)

    Liu, C.L., E-mail: liuchanglong@tju.edu.c [School of Science, Tianjin University, Tianjin 300072 (China); Tianjin Key Laboratory of Low Dimension Materials Physics and Preparing Technology, Institute of Advanced Materials Physics Faculty of Science, Tianjin 300072 (China); Li, M.K.; Wang, Z.; Gao, Y.J.; Liao, J.Q.; Zhang, D.C.; Zhang, X.L.; Shen, Y.Y. [School of Science, Tianjin University, Tianjin 300072 (China)

    2011-03-01

    Cz n-type Si (100) wafers covered with a 220 nm SiO{sub 2} layer or a 170 nm Si{sub 3}N{sub 4} layer were singly implanted with 160 keV He ions at a dose of 5 x 10{sup 16}/cm{sup 2} or successively implanted with 160 keV He ions at a dose of 5 x 10{sup 16}/cm{sup 2} and 110 keV H ions at a dose of 1 x 10{sup 16}/cm{sup 2}. Surface morphologies together with defect microstructures have been studied by means of several techniques, including optical microscopy, atomic force microscopy, and cross-sectional transmission electron microscopy (XTEM). Only surface blistering has been observed for He and H sequentially implanted SiO{sub 2}/Si samples after annealing in temperature range up to 1000 {sup o}C. However, as for the He and H implanted Si{sub 3}N{sub 4}/Si samples, surface features including blistering and the localized exfoliation of both the top Si{sub 3}N{sub 4} layer and the implanted Si layer have been well demonstrated during subsequent annealing. XTEM observations reveal quite different defect morphologies in two kinds of materials under the same implantation and annealing conditions. The possible mechanisms of surface damage in two kinds of materials have been discussed and presented based on the XTEM results.

  6. Surface etching, chemical modification and characterization of silicon nitride and silicon oxide—selective functionalization of Si3N4 and SiO2

    Science.gov (United States)

    Liu, Li-Hong; Michalak, David J.; Chopra, Tatiana P.; Pujari, Sidharam P.; Cabrera, Wilfredo; Dick, Don; Veyan, Jean-François; Hourani, Rami; Halls, Mathew D.; Zuilhof, Han; Chabal, Yves J.

    2016-03-01

    The ability to selectively chemically functionalize silicon nitride (Si3N4) or silicon dioxide (SiO2) surfaces after cleaning would open interesting technological applications. In order to achieve this goal, the chemical composition of surfaces needs to be carefully characterized so that target chemical reactions can proceed on only one surface at a time. While wet-chemically cleaned silicon dioxide surfaces have been shown to be terminated with surficial Si-OH sites, chemical composition of the HF-etched silicon nitride surfaces is more controversial. In this work, we removed the native oxide under various aqueous HF-etching conditions and studied the chemical nature of the resulting Si3N4 surfaces using infrared absorption spectroscopy (IRAS), x-ray photoelectron spectroscopy (XPS), low energy ion scattering (LEIS), and contact angle measurements. We find that HF-etched silicon nitride surfaces are terminated by surficial Si-F and Si-OH bonds, with slightly subsurface Si-OH, Si-O-Si, and Si-NH2 groups. The concentration of surficial Si-F sites is not dependent on HF concentration, but the distribution of oxygen and Si-NH2 displays a weak dependence. The Si-OH groups of the etched nitride surface are shown to react in a similar manner to the Si-OH sites on SiO2, and therefore no selectivity was found. Chemical selectivity was, however, demonstrated by first reacting the -NH2 groups on the etched nitride surface with aldehyde molecules, which do not react with the Si-OH sites on a SiO2 surface, and then using trichloro-organosilanes for selective reaction only on the SiO2 surface (no reactivity on the aldehyde-terminated Si3N4 surface).

  7. Surface etching, chemical modification and characterization of silicon nitride and silicon oxide--selective functionalization of Si3N4 and SiO2.

    Science.gov (United States)

    Liu, Li-Hong; Michalak, David J; Chopra, Tatiana P; Pujari, Sidharam P; Cabrera, Wilfredo; Dick, Don; Veyan, Jean-François; Hourani, Rami; Halls, Mathew D; Zuilhof, Han; Chabal, Yves J

    2016-03-09

    The ability to selectively chemically functionalize silicon nitride (Si3N4) or silicon dioxide (SiO2) surfaces after cleaning would open interesting technological applications. In order to achieve this goal, the chemical composition of surfaces needs to be carefully characterized so that target chemical reactions can proceed on only one surface at a time. While wet-chemically cleaned silicon dioxide surfaces have been shown to be terminated with surficial Si-OH sites, chemical composition of the HF-etched silicon nitride surfaces is more controversial. In this work, we removed the native oxide under various aqueous HF-etching conditions and studied the chemical nature of the resulting Si3N4 surfaces using infrared absorption spectroscopy (IRAS), x-ray photoelectron spectroscopy (XPS), low energy ion scattering (LEIS), and contact angle measurements. We find that HF-etched silicon nitride surfaces are terminated by surficial Si-F and Si-OH bonds, with slightly subsurface Si-OH, Si-O-Si, and Si-NH2 groups. The concentration of surficial Si-F sites is not dependent on HF concentration, but the distribution of oxygen and Si-NH2 displays a weak dependence. The Si-OH groups of the etched nitride surface are shown to react in a similar manner to the Si-OH sites on SiO2, and therefore no selectivity was found. Chemical selectivity was, however, demonstrated by first reacting the -NH2 groups on the etched nitride surface with aldehyde molecules, which do not react with the Si-OH sites on a SiO2 surface, and then using trichloro-organosilanes for selective reaction only on the SiO2 surface (no reactivity on the aldehyde-terminated Si3N4 surface).

  8. Electrical transport properties of graphene on SiO2 with specific surface structures

    OpenAIRE

    Nagashio, K.; Yamashita, T; Nishimura, T.; K. Kita; Toriumi, A.

    2011-01-01

    The mobility of graphene transferred on a SiO2/Si substrate is limited to ~10,000 cm2/Vs. Without understanding the graphene/SiO2 interaction, it is difficult to improve the electrical transport properties. Although surface structures on SiO2 such as silanol and siloxane groups are recognized, the relation between the surface treatment of SiO2 and graphene characteristics has not yet been elucidated. This paper discusses the electrical transport properties of graphene on specific surface stru...

  9. Analysis of intraocular lens surface adhesiveness by atomic force microscopy.

    Science.gov (United States)

    Lombardo, Marco; Carbone, Giovanni; Lombardo, Giuseppe; De Santo, Maria P; Barberi, Riccardo

    2009-07-01

    To analyze intraocular lens (IOL) optic surface adhesiveness using atomic force microscopy (AFM). LiCryL Laboratory, University of Calabria, Rende, Italy. The surface adhesive properties of poly(methyl methacrylate) (PMMA), silicone, hydrophilic acrylic, and hydrophobic acrylic IOLs were evaluated by AFM. Analysis was performed at room temperature (21 degrees C) in a liquid environment using the force-versus-distance mode of a commercial instrument (NanoScope III). Measurements were acquired with rectangular silicon cantilevers of a nominal elastic constant of 10 Newton/m. The nominal value of the tip's radius of curvature was 1 mum, and the scanning speed during the acquisitions ranged from 10 to 400 nm/s. The adhesion force measurements showed different characteristics for the various types of IOLs (Pdevelopment and the interface interactions between the IOL and capsule, the results in this study may bolster the theory of manufacturing more-adhesive materials to prevent PCO.

  10. Atomic force microscopic observation of surface-supported human erythrocytes

    Science.gov (United States)

    Ho, Mon-Shu; Kuo, Feng-Jia; Lee, Yu-Siang; Cheng, Chao-Min

    2007-07-01

    The nanomechanical characteristics of the membrane cytoskeleton of human erythrocytes were studied using atomic force microscopy (AFM). The self-assembly, fine structure, cell diameter, thickness, and reticulate cytoskeleton of erythrocytes on the mica surface were investigated. The adhesive forces that correspond to the membrane elasticity of various parts of the erythrocyte membrane surface were measured directly by AFM to be 0.64±0.14nN for cell indentation, 4.2±0.7nN for cell hump, and 11.5nN for side waist, respectively. The deformation of erythrocytes was discussed. Standing waves on the membrane that were set up by increased AFM amplitude were observed. The propagating velocity on the erythrocyte membrane was estimated to be ˜2.02×10-2m/s. Liquid physiological conditions were considered throughout.

  11. Helium atom scattering investigation of the Sb(111) surface.

    Science.gov (United States)

    Mayrhofer-Reinhartshuber, M; Tamtögl, A; Kraus, P; Ernst, W E

    2013-10-02

    The Sb(111) surface was studied with helium atom scattering (HAS). Elastic HAS at different energies of the incident helium beam (15.3, 21.9, 28.4 meV) was applied for structural investigations. The lattice constants derived from the positions of the observed diffraction peaks up to third order were found to be in perfect agreement with previous structure determinations of Sb(111). The observed diffraction patterns with clear peaks up to second order were used to model the electronic surface corrugation with the GR method. As an estimation for the attractive part of the interaction potential a well depth of (4.0 ± 0.5) meV was found. Best fit results were obtained with a corrugation height of 12-13% of the lattice constant, which is rather large compared to other surfaces with metallic character. Intensity measurements of the specular peak as a function of incident energy were analysed to determine the distribution of terraces on the surface. The results show a quite flat Sb(111) surface and a step height of 3.81 Å of the remaining terraces.

  12. Microstructural investigation of Sr-modified Al-15 wt%Si alloys in the range from micrometer to atomic scale

    Energy Technology Data Exchange (ETDEWEB)

    Timpel, M., E-mail: melanie.timpel@helmholtz-berlin.de [Helmholtz-Zentrum Berlin fuer Materialien und Energie GmbH, Hahn-Meitner-Platz 1, 14109 Berlin (Germany); Wanderka, N. [Helmholtz-Zentrum Berlin fuer Materialien und Energie GmbH, Hahn-Meitner-Platz 1, 14109 Berlin (Germany); Vinod Kumar, G.S.; Banhart, J. [Helmholtz-Zentrum Berlin fuer Materialien und Energie GmbH, Hahn-Meitner-Platz 1, 14109 Berlin (Germany); Technische Universitaet Berlin, Werkstoffwissenschaften und -Technologien, Hardenbergstr. 36, 10623 Berlin (Germany)

    2011-05-15

    Strontium-modified Al-15 wt%Si casting alloys were investigated after 5 and 60 min of melt holding. The eutectic microstructures were studied using complementary methods at different length scales: focused ion beam-energy selective backscattered tomography, transmission electron microscopy and 3D atom probe. Whereas the samples after 5 min of melt holding show that the structure of eutectic Si changes into a fine fibrous morphology, the increase of prolonged melt holding (60 min) leads to the loss of Sr within the alloy with an evolution of an unmodified eutectic microstructure displaying coarse interconnected Si plates. Strontium was found at the Al/Si eutectic interfaces on the side of the eutectic Al region, measured by 3D atom probe. The new results obtained using 3D atom probe shed light on the location of Sr within the Al-Si eutectic microstructure. -- Research highlights: {yields} Microstructural investigation of Sr-modified Al-15 wt%Si alloy after 5 and 60 min of melt holding using 3D microscopy techniques. {yields} FIB-EsB tomography: Fibrous eutectic modification of Si after 5 min of melt holding; unmodified eutectic microstructure after 60 min of melt holding. {yields} Structural and chemical analysis of Fe-rich intermetallic phases using TEM: Fe-rich {alpha}-phases are present in the eutectic microstructure after 60 min of melt holding; no Fe rich {alpha}-phases are observed within the modified fibrous network after 5 min of melt holding. {yields} 3D-AP analysis of specimens containing A/Si eutectic interfaces: enrichment of Sr is found at the Al/Si interface on the side of the eutectic Al region.

  13. Trace surface analysis with Pico-Coulomb ion fluences: direct detection of multiphoton ionized iron atoms from iron-doped silicon targets

    Energy Technology Data Exchange (ETDEWEB)

    Pellin, M.J.; Young, C.E.; Calaway, W.F.; Gruen, D.M.

    1984-01-01

    A system for surface analysis is described which has the objective of maximizing the probability of detection of atoms sputtered from the sample. Resonance ionization techniques have been combined with pulsed ion-induced erosion to detect and count Fe atoms sputtered from Fe and Fe in Si samples without the interposition of a mass spectrometer between the target and the detector (direct detection). At present, surface analysis by resonance ionization of sputtered atoms (SARISA) allows determination at the fifty parts per million (ppm) level of Fe doped into Si with removal of less than 10/sup -5/ of a monolayer. Separation of the Fe impurity from the isobaric Si/sub 2/ dimers is accomplished in the resonant photo-excitation step. Improvements in the method are suggested which, if successful, would bring the sensitivity into the parts per billion (ppb) range with primary ion currents remaining low enough to produce negligible surface damage. The quantitative and element specific nature of the SARISA technique is established by demonstrating that the ground state neutral fraction is essentially unchanged in two very different matrixes (Fe and Si). Also presented are measurements of the low-lying excited state fraction of Fe atoms sputtered both from an Fe and a Si matrix. 45 references, 5 figures, 2 tables.

  14. Effect of Annealing Temperature on the Formation of Silicides and the Surface Morphologies of PtSi Films

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    The effect of annealing temperature on the formation of the PtSi phase, distribution of silicides and the surface morphologies of silicides films is investigated by XPS, AFM. It is shown that the phase sequences of the films change from Pt-Pt2Si-PtSi-Si to Pt+Pt2Si+PtSi-PtSi-Si or Pt+Pt2Si+PtSi-PtSi-Si with an increase of annealing temperature and the reason for the formation of mixed layers is discussed.

  15. Si(111)-sq root 21 x sq root 21 -(Ag+Cs) surface studied by scanning tunneling microscopy and angle-resolved photoemission spectroscopy

    CERN Document Server

    Liu, C; Morikawa, H; Okino, H; Hasegawa, S; Okuda, T; Kinoshita, T

    2003-01-01

    Scanning tunneling microscopy (STM) and angle-resolved photoemission spectroscopy (ARPES) were used to study the atomic and electronic structures of the Si(111)-sq root 21 x sq root 21-(Ag + Cs) surface (sq root 21-Cs in short), which was induced by depositing caesium atoms on the Si(111)-sq root 3 x sq root 3-Ag surface at room temperature (RT). Compared with previously reported STM images of noble-metal induced sq root 21 x sq root 21 phases including the Si(111)-sq root 21 x sq root 21-(Ag+Ag) and Si(111)-sq root 21 x sq root 21-(Ag+Au) surfaces (sq root 21-Ag and sq root 21-Au, respectively), the sq root 21-Cs surface displayed quite different features in STM images. The ARPES data of the sq root 21-Cs surface revealed an intrinsic dispersive surface-state band, together with a non-dispersive one near the Fermi level, which was also different from those of the sq root 21-Ag and sq root 21-Au surfaces. These results strongly suggest different atomic arrangements between Cs- and noble-metal induced sq root ...

  16. ONE-DIMENSIONAL ORDERING OF IN ATOMS IN A CU(100) SURFACE

    NARCIS (Netherlands)

    BREEMAN, M; BARKEMA, GT; BOERMA, DO

    1994-01-01

    A Monte Carlo study of the ordering of In atoms embedded in the top layer of a Cu(100) surface is presented. The interaction energies between the In and Cu atoms were derived from atom-embedding calculations, with Finnis-Sinclair potentials. It was found that the interaction between In atoms in the

  17. Passivation of Si and a-Si:H surfaces by thin oxide and oxy-nitride layers

    Energy Technology Data Exchange (ETDEWEB)

    Pincik, E. [Institute of Physics of SAS, Dubravska Cesta 9, 845 11 Bratislava (Slovakia)]. E-mail: emil.pincik@savba.sk; Kobayashi, H. [Institute of Scientific and Industrial Research, Osaka University, and CREST, Japan Science and Technology Organizarion, 8-1 Mihogaoka, Ibaraki, Osaka 567-0047 (Japan); Rusnak, J. [Institute of Physics of SAS, Dubravska Cesta 9, 845 11 Bratislava (Slovakia); Takahashi, M. [Institute of Scientific and Industrial Research, Osaka University, and CREST, Japan Science and Technology Organizarion, 8-1 Mihogaoka, Ibaraki, Osaka 567-0047 (Japan); Brunner, R. [Institute of Physics of SAS, Dubravska Cesta 9, 845 11 Bratislava (Slovakia); Jergel, M. [Institute of Physics of SAS, Dubravska Cesta 9, 845 11 Bratislava (Slovakia); Morales-Acevedo, A. [CINVESTAV-IPN, Electrical Engineering Departmant, Avenida IPN No. 2508, 07360 Mexico, D.F. (Mexico); Ortega, L. [Laboratoire de Cristallographie du CNRS, BP 166, 38042 Grenoble Cedex 09 (France); Kakos, J. [Department of Ceramics, Glass and Cement of FCFT of SUT, Radlinskeho 9, 812 37 Bratislava (Slovakia)

    2006-08-31

    An aim of the contribution is focused predominantly on investigation of electrical interface properties of MIS structures consisting of silicon-based substrates, which were passivated by 1.5-12 nm silicon dioxide, silicon nitride and/or silicon oxy-nitride layers. Substrates of different structural properties were used-crystalline Si (c-Si), amorphous hydrogenated silicon (a-Si:H), and silicon layer deposited by plasma enhanced chemical vapor deposition (PECVD). A stress was laid upon structures prepared on n moderately doped c-Si. The paper presents also changes of structural properties of a-Si:H surface after Ar low energy beam impact. For the first time we are presenting important results concerning utilization of X-ray diffraction with {beta} filter in investigation of a-Si:H cluster structure. Considerable part of the contribution is devoted to investigation of electrical properties of Al/Si{sub 3}N{sub 4}/Si (2-3 nm)/GaAs structures with aim to clarify the particular effect of the ultrathin Si interlayer in the structure. Our observations indicate that the silicon interlayer can act as delta doping of GaAs and/or as quantum well. Therefore, the experimental results are compared and discussed with calculated ones obtained by application of our theoretical description of electron emission of quantum well.

  18. Short-range ordering of ion-implanted nitrogen atoms in SiC-graphene

    Energy Technology Data Exchange (ETDEWEB)

    Willke, P.; Druga, T.; Wenderoth, M. [IV. Physikalisches Institut der Universität Göttingen, Friedrich-Hund-Platz 1, D-37077 Göttingen (Germany); Amani, J. A.; Weikert, S.; Hofsäss, H. [II. Physikalisches Institut der Universität Göttingen, Friedrich-Hund-Platz 1, D-37077 Göttingen (Germany); Thakur, S.; Maiti, K. [Department of Condensed Matter Physics and Materials' Science, Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai 400 005 (India)

    2014-09-15

    We perform a structural analysis of nitrogen-doped graphene on SiC(0001) prepared by ultra low-energy ion bombardment. Using scanning tunneling microscopy, we show that nitrogen atoms are incorporated almost exclusively as graphitic substitution in the graphene honeycomb lattice. With an irradiation energy of 25 eV and a fluence of approximately 5 × 10{sup 14 }cm{sup −2}, we achieve a nitrogen content of around 1%. By quantitatively comparing the position of the N-atoms in the topography measurements with simulated random distributions, we find statistically significant short-range correlations. Consequently, we are able to show that the dopants arrange preferably at lattice sites given by the 6 × 6-reconstruction of the underlying substrate. This selective incorporation is most likely triggered by adsorbate layers present during the ion bombardment. This study identifies low-energy ion irradiation as a promising method for controlled doping in epitaxial graphene.

  19. Thermally induced anchoring of fullerene in copolymers with Si-bridging atom: Spectroscopic evidences

    Science.gov (United States)

    Marchiori, Cleber F. N.; Garcia-Basabe, Yunier; de A. Ribeiro, Fabio; Koehler, Marlus; Roman, Lucimara S.; Rocco, Maria Luiza M.

    2017-01-01

    We use X-ray photoelectron spectroscopy (XPS), Near-edge X-ray absorption fine structure (NEXAFS), resonant Auger spectroscopy (RAS), Attenuation Total Reflection Infrared (ATR-IR) and Atomic Force Microscopy (AFM) to study the blend between the copolymer poly[2,7-(9,9-bis(2-ethylhexyl)-dibenzosilole)-alt-4,7-bis(thiophen-2-yl)benzo-2,1,3-thiadiazole] (PSiF-DBT) and the fullerene derivative PC71BM submitted to different annealing temperatures. Those measurements indicate that there is an incidental anchoring of a fullerene derivative to the Si-bridging atoms of a copolymer induced by thermal annealing of the film. Insights about the physical properties of one possible PSiF-DBT/PC71BM anchored structure are obtained using Density Functional Theory calculations. Since the performance of organic photovoltaic based on polymer-fullerene blends depends on the chemical structure of the blend components, the anchoring effect might affect the photovoltaic properties of those devices.

  20. Dynamic Deposition of Nanocopper Film on the β-SiCp Surface by Magnetron Sputtering

    Directory of Open Access Journals (Sweden)

    Hu Ming

    2015-01-01

    Full Text Available The uniform nanocopper film was deposited on the surface of micron β-SiC particle by magnetron sputtering technology successfully. The surface morphology and phase constitution of the β-SiC particle with nanocopper film were analyzed and dynamic deposition behavior was investigated in detail. The concept of dynamic deposition was put forward to interpret formation mechanism of copper nanofilm on the surface of β-SiC particles.

  1. Characterization and fabrication of nano- and micron-sized structures on the Si surface using scanning probe microscopies

    Science.gov (United States)

    Fu, Elain Su-Eng

    The fabrication and stability of nanostructures on the Si surface were investigated using scanning tunneling microscopy (STM) and atomic force microscopy (AFM). We used direct current heating to fabricate step bunch structures, 30 to 50 angstroms in size, on the Si(111) surface. Using STM, we monitored their relaxation as a function of electron bombardment heating time at 930, made quantitative comparison with a step based theory of mass transport, and found good agreement with the size scaling predictions of a locally conserved mechanism of mass transport. We then monitored the relaxation of the step bunch structures as a function of direct current heating time, and found that the presence of the electric field significantly increased the rate of the relaxation relative to the zero field case. We made quantitative comparison with a step based model modified to include a surface diffusion bias and obtained an upper limit on the effective charge of an adatom on the surface. We also studied the step bunching effect in the temperature range 1155-1215. The step patterns on the surface were analyzed using STM and the model of Kandel and Weeks was used to calculate the anisotropy ratio on the surface. Assuming the operation of a surface diffusion bias, we calculated the effective charge of an adatom on the surface in this higher temperature range. We used AFM to fabricate and characterize micron-sized structures on the Si(100) surface. We couple the fabrication process of Snow and Campbell to anneals in ultra-high vacuum. We then present the results of a preliminary study of the thermal decay of two-dimensional structures fabricated on the Si(100) surface.

  2. Electronic band structure of a Tl/Sn atomic sandwich on Si(111)

    Science.gov (United States)

    Gruznev, D. V.; Bondarenko, L. V.; Matetskiy, A. V.; Tupchaya, A. Y.; Alekseev, A. A.; Hsing, C. R.; Wei, C. M.; Eremeev, S. V.; Zotov, A. V.; Saranin, A. A.

    2015-01-01

    A two-dimensional compound made of one monolayer of Tl and one monolayer of Sn on Si(111) has been found to have a sandwichlike structure in which the Sn layer (having the milk-stool arrangement) resides on the bulklike terminated Si(111) surface and the Tl layer (having the honeycomb-chained-trimer arrangement) is located above the Sn layer. The electronic band structure of the compound contains two spin-split surface-state bands, of which one is nonmetallic and the other is metallic. Near the Fermi level the metallic band is split with the momentum splitting Δ k∥=0.037 Å-1 and energy splitting Δ EF=167 meV. The steep dispersion of the band when crossing the Fermi level corresponds to an electron velocity of ≈8.5 ×105 m/s, which is comparable to the value reported for graphene. The 2D Fermi contours have almost circular shape with spin texture typical for hexagonal surfaces.

  3. Effect of fiber surface state on mechanical properties of C{sub f}/Si-O-C composites

    Energy Technology Data Exchange (ETDEWEB)

    Wang Song [Key Laboratory of Advanced Ceramic Fibres and Composites, College of Aerospace and Materials Engineering, National University of Defense Technology, Changsha 410073 (China)]. E-mail: wangsong0731@163.com; Chen Zhaohui [Key Laboratory of Advanced Ceramic Fibres and Composites, College of Aerospace and Materials Engineering, National University of Defense Technology, Changsha 410073 (China); Ma Qingsong [Key Laboratory of Advanced Ceramic Fibres and Composites, College of Aerospace and Materials Engineering, National University of Defense Technology, Changsha 410073 (China); Hu Haifeng [Key Laboratory of Advanced Ceramic Fibres and Composites, College of Aerospace and Materials Engineering, National University of Defense Technology, Changsha 410073 (China); Zheng Wenwei [Key Laboratory of Advanced Ceramic Fibres and Composites, College of Aerospace and Materials Engineering, National University of Defense Technology, Changsha 410073 (China)

    2005-10-25

    Three-dimensional braided carbon fiber reinforced silicon oxycarbide composites (3D-B C{sub f}/Si-O-C) were fabricated via a polysiloxane infiltration and pyrolysis route. The effects of fiber surface state on microstructure and mechanical properties of C{sub f}/Si-O-C composites were investigated. The change of carbon fiber surface state was achieved via heat treatment in vacuum. The results showed that heat treatment decreased carbon fiber surface activity due to the decrease of the amount of oxygen and nitrogen atoms. The C{sub f}/Si-O-C composites fabricated from the carbon fiber with low surface activity had excellent mechanical properties, which resulted from perfect interfacial bonding and good in situ fiber strength. The flexural strength and fracture toughness of the C{sub f}/Si-O-C composites from the treated fiber were 534 MPa and 23.4 MPa m{sup 1/2}, respectively, which were about 7 and 11 times more than those of the composites from the as-received carbon fiber, respectively.

  4. Excitonic effects in the nonlinear optical response of a Si(111) surface

    Energy Technology Data Exchange (ETDEWEB)

    Stamova, Maria; Rebentrost, Frank [Max-Planck-Institut fuer Quantenoptik, 85748 Garching (Germany)

    2010-08-15

    We discuss methods to calculate the linear and nonlinear optical spectra for cyclic cluster models of an ideal Si(111) surface. The cluster approach offers the possibility to implement the excitonic effects due to the Coulomb interaction between electron and hole in a relatively straight-forward way. In order to appproximate a situation resembling a surface we use clusters with several hundreds of Si atoms. The electronic structure is obtained from a tight-binding parametrization of the hamiltonian. A time-dependent density operator formalism is used to calculate the response functions S({tau}) and S({tau}{sub 1},{tau}{sub 2}) for the optical polarization, which also directly describe the response to ultrashort pulses. Their Fourier transforms are the frequency-dependent optical susceptibilities {chi}{sup (1)}(-{omega};{omega}) and {chi}{sup (2)} (-{omega}{sub 1}-{omega}{sub 2};{omega}{sub 1},{omega}{sub 2}) for second-harmonic ({omega}{sub 1} ={omega}{sub 2}) or sum-frequency generation from surfaces. The excitonic Coulomb interaction is treated in the time-dependent Hartree-Fock approximation, leading to large sets of differential equations that are integrated explicitly. The results on the linear susceptibility are in accord with earlier findings on the excitonic origin of the relative intensities of the E{sub 1} and E{sub 2} peaks near 3.4 and 4.3 eV. We present new results on excitonic effects in the nonlinear spectra and investigate in particular the surface-related peaks near 2{Dirac_h}{omega}= 1.3-1.5 and 2.4 eV that govern the strong enhancement observed in SHG of clean silicon surfaces. (Abstract Copyright [2010], Wiley Periodicals, Inc.)

  5. 2D Tl-Pb compounds on Ge(1 1 1) surface: atomic arrangement and electronic band structure.

    Science.gov (United States)

    Gruznev, D V; Bondarenko, L V; Tupchaya, A Y; Eremeev, S V; Mihalyuk, A N; Chou, J P; Wei, C M; Zotov, A V; Saranin, A A

    2017-01-25

    Structural transformations and evolution of the electron band structure in the (Tl, Pb)/Ge(1 1 1) system have been studied using low-energy electron diffraction, scanning tunneling microscopy, angle-resolved photoelectron spectroscopy and density functional theory calculations. The two 2D Tl-Pb compounds on Ge(1 1 1), [Formula: see text]-(Tl, Pb) and [Formula: see text]-(Tl, Pb), have been found and their composition, atomic arrangement and electron properties has been characterized. The (Tl, Pb)/Ge(1 1 1)[Formula: see text] compound is almost identical to the alike (Tl, Pb)/Si(1 1 1)[Formula: see text] system from the viewpoint of its atomic structure and electronic properties. They contain 1.0 ML of Tl atoms arranged into a honeycomb network of chained trimers and 1/3 ML of Pb atoms occupying the centers of the honeycomb units. The (Tl, Pb)/Ge(1 1 1)[Formula: see text] compound contains six Tl atoms and seven Pb atoms per [Formula: see text] unit cell (i.e.  ∼0.67 ML Tl and  ∼0.78 ML Pb). Its atomic structure can be visualized as consisting of Pb hexagons surrounded by Tl trimers. The (Tl, Pb)/Ge(1 1 1)[Formula: see text] and (Tl, Pb)/Ge(1 1 1)[Formula: see text] compounds are metallic and their band structures contain spin-split surface-state bands. By analogy with the (Tl, Pb)/Si(1 1 1)[Formula: see text], these (Tl, Pb)/Ge(1 1 1) compounds are believed to be promising objects for prospective studies of superconductivity in one-atom-layer systems.

  6. 2D Tl-Pb compounds on Ge(1 1 1) surface: atomic arrangement and electronic band structure

    Science.gov (United States)

    Gruznev, D. V.; Bondarenko, L. V.; Tupchaya, A. Y.; Eremeev, S. V.; Mihalyuk, A. N.; Chou, J. P.; Wei, C. M.; Zotov, A. V.; Saranin, A. A.

    2017-01-01

    Structural transformations and evolution of the electron band structure in the (Tl, Pb)/Ge(1 1 1) system have been studied using low-energy electron diffraction, scanning tunneling microscopy, angle-resolved photoelectron spectroscopy and density functional theory calculations. The two 2D Tl-Pb compounds on Ge(1 1 1), \\sqrt{3}× \\sqrt{3} -(Tl, Pb) and 3× 3 -(Tl, Pb), have been found and their composition, atomic arrangement and electron properties has been characterized. The (Tl, Pb)/Ge(1 1 1)\\sqrt{3}× \\sqrt{3} compound is almost identical to the alike (Tl, Pb)/Si(1 1 1)\\sqrt{3}× \\sqrt{3} system from the viewpoint of its atomic structure and electronic properties. They contain 1.0 ML of Tl atoms arranged into a honeycomb network of chained trimers and 1/3 ML of Pb atoms occupying the centers of the honeycomb units. The (Tl, Pb)/Ge(1 1 1)3× 3 compound contains six Tl atoms and seven Pb atoms per 3× 3 unit cell (i.e.  ˜0.67 ML Tl and  ˜0.78 ML Pb). Its atomic structure can be visualized as consisting of Pb hexagons surrounded by Tl trimers. The (Tl, Pb)/Ge(1 1 1)\\sqrt{3}× \\sqrt{3} and (Tl, Pb)/Ge(1 1 1)3× 3 compounds are metallic and their band structures contain spin-split surface-state bands. By analogy with the (Tl, Pb)/Si(1 1 1)\\sqrt{3}× \\sqrt{3} , these (Tl, Pb)/Ge(1 1 1) compounds are believed to be promising objects for prospective studies of superconductivity in one-atom-layer systems.

  7. DFT Investigations About Pyrazine Molecules on Si(100)-2×1 Surface

    Institute of Scientific and Technical Information of China (English)

    YU Ang-yang; QU Yong-quan; HAN Ke-li; HE Guo-zhong

    2007-01-01

    It is important to understand the interface of aromatic molecules on semiconductor surfaces because of the rich functionality of such molecules on semiconductor surfaces. The chemisorption of pyrazine molecules on the Si( 100)-2×1 surface has been investigated using the B3LYP density functional theory with Si9H12 one-dimer and Si15H16 twodimer cluster models. The calculated results predict that N-dative bonded-state, C2= C5 [ 4 + 2 ] and the tightbridge1, 2, 5,6 products may coexist on the Si(100)-2×1 surface.

  8. 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.

  9. Self-organization of bimetallic PdAu nanoparticles on SiO{sub 2} surface

    Energy Technology Data Exchange (ETDEWEB)

    Ruffino, F., E-mail: francesco.ruffino@ct.infn.it; Grimaldi, M. G. [Universita di Catania, Dipartimento di Fisica e Astronomia (Italy)

    2011-06-15

    Bimetallic PdAu nanoparticles on SiO{sub 2} substrate were produced by a sequential room-temperature sputtering deposition method. By the atomic force microscopy technique we studied the nanoparticles self-organization mechanisms in various conditions. First, Pd nucleation and growth proceeds at the substrate defects and the Pd nanoparticles density increase rapidly. During the second sputtering deposition, Au atoms adsorb on the SiO{sub 2} and diffuse toward Pd nanoparticles without forming new nuclei. The Au atoms are trapped by the preformed Pd nanoparticles, forming PdAu bimetallic nanoparticles which size increases. Furthermore, fixing the amount of deposited Pd and increasing the amount of deposited Au, we analyzed the evolution of the PdAu film surface morphology: we observe that the PdAu grows initially as three-dimensional islands; then the PdAu film morphology evolves from compact three-dimensional islands to partially coalesced worm-like structures, followed by a percolation morphology and finally to a continuous and rough film. The application of the interrupted coalescence model allowed us to evaluate the critical mean island diameter R{sub c} Almost-Equal-To 2.8 nm for the partial coalescence process. The application of the dynamic scaling theory of growing interfaces allowed us to evaluate the dynamic growth exponent {beta} = 0.21 {+-} 0.01 from the evolution of the film surface roughness. Finally, fixing the amount of deposited Pd and Au we studied the self-organization mechanism of the PdAu nanoparticles induced by thermal processes performed in the 973-1173 K temperature range. The observed kinetic growth mechanism is consistent with a surface diffusion-limited ripening of the nanoparticles with a temperature-dependent growth exponent. The dependence of the growth exponent on the temperature is supposed to be linked to the variation with the temperature of the characteristics of the PdAu alloy. The activation energy for the surface diffusion

  10. Fine tuning the ionic liquid-vacuum outer atomic surface using ion mixtures.

    Science.gov (United States)

    Villar-Garcia, Ignacio J; Fearn, Sarah; Ismail, Nur L; McIntosh, Alastair J S; Lovelock, Kevin R J

    2015-03-28

    Ionic liquid-vacuum outer atomic surfaces can be created that are remarkably different from the bulk composition. In this communication we demonstrate, using low-energy ion scattering (LEIS), that for ionic liquid mixtures the outer atomic surface shows significantly more atoms from anions with weaker cation-anion interactions (and vice versa).

  11. Thermosensitive Nanocables Prepared by Surface-Initiated Atom Transfer Radical Polymerization

    Directory of Open Access Journals (Sweden)

    Wei Qingshan

    2008-01-01

    Full Text Available Abstract Thermosensitive nanocables consisting of Au nanowire cores and poly(N-isopropylacrylamide sheaths (denoted as Au/PNIPAAm were synthesized by surface-initiated atom transfer radical polymerization (SI-ATRP. The formation of PNIPAAm sheath was verified by Fourier transform infrared (FTIR and hydrogen nuclear magnetic resonance (1H NMR spectroscopy. Transmission electron microscope (TEM results confirmed the core/shell structure of nanohybrids. The thickness and density of PNIPAAm sheaths can be adjusted by controlling the amount of cross-linker during the polymerization. Signature temperature response was observed from Au/cross-linked-PNIPAAm nanocables. Such smart nanocables show immense potentials as building blocks for novel thermosensitive nanodevices in future.

  12. Hydrogel brushes grafted from stainless steel via surface-initiated atom transfer radical polymerization for marine antifouling

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Jingjing, E-mail: jjwang1@hotmail.com; Wei, Jun

    2016-09-30

    Highlights: • Crosslinked hydrogel brushes were grafted from SS surfaces for marine antifouling. • All brush-coated SS surfaces could effectively reduce the adhesion of biofouling. • The antifouling efficacy increased with the crosslinking density of hydrogels. - Abstract: Crosslinked hydrogel brushes were grafted from stainless steel (SS) surfaces for marine antifouling. The brushes were prepared by surface-initiated atom transfer radical polymerization (SI-ATRP) of 2-methacryloyloxyethyl phosphorylcholine (MPC) and poly(ethylene glycol) methyl ether methacrylate (PEGMA) respectively with different fractions of crosslinker in the feed. The grafted layers prepared with different thickness were characterized by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), ellipsometry and water contact angle measurements. With the increase in the fraction of crosslinker in the feed, the thickness of the grafted layer increased and the surface became smooth. All the brush-coated SS surfaces could effectively reduce the adhesion of bacteria and microalgae and settlement of barnacle cyprids, as compared to the pristine SS surface. The antifouling efficacy of the PEGMA polymer (PPEGMA)-grafted surface was higher than that of the MPC polymer (PMPC)-grafted surfaces. Furthermore, the crosslinked hydrogel brush-grafted surfaces exhibited better fouling resistance than the non-crosslinked polymer brush-grafted surfaces, and the antifouling efficacy increased with the crosslinking density. These hydrogel coatings of low toxicity and excellent anti-adhesive characteristics suggested their useful applications as environmentally friendly antifouling coatings.

  13. Theoretical Investigation on the Adsorption of Ag+ and Hydrated Ag+ Cations on Clean Si(111)Surface

    Institute of Scientific and Technical Information of China (English)

    SHENG Yong-Li; LI Meng-Hua; WANG Zhi-Guo; LIU Yong-Jun

    2008-01-01

    In this paper,the adsorption of Ag+ and hydrated Ag+ cations on clean Si(111)surface were investigated by using cluster(Gaussian 03)and periodic(DMol3)ab initio calculations.Si(111)surface was described with cluster models(Si14H17 and Si22H21)and a four-silicon layer slab with periodic boundary conditions.The effect of basis set superposition error(BSSE)was taken into account by applying the counterpoise correction.The calculated results indicated that the binding energies between hydrated Ag+ cations and clean Si(111)surface are large,suggesting a strong interaction between hydrated Ag+ cations and the semiconductor surface.With the increase of number,water molecules form hydrogen bond network with one another and only one water molecule binds directly to the Ag+ cation.The Ag+ cation in aqueous solution will safely attach to the clean Si(111)surface.

  14. Comparative Investigation of Mo(CO)6 Adsorption on Clean and Oxidized Si(111) Surfaces

    Institute of Scientific and Technical Information of China (English)

    Zhi-quan Jiang; Wei-xin Huang

    2011-01-01

    Mo(CO)6 adsorption on the clean,oxygen-precovered and deeply oxidized Si(lll) surfaces was comparatively investigated by high-resolution electron energy loss spectroscopy.The downward vibrational frequency shift of the C-O stretching mode in adsorbed Mo(CO)6 illustrates that different interactions of adsorbed Mo(CO)6 occur on clean Si(lll) and SiO2/Si(lll) surfaces,weak on the former and strong on the latter.The strong interaction on SiO2/Si(111) might lead to the partial dissociation of Mo(CO)6,consequently the formation of molybdenum subcarbonyls.Therefore,employing Mo(CO)6 as the precursor,metallic molybdenum could be successfully deposited on the SiO2/Si(111) surface but not on the clean Si(111) surface.A portion of the deposited metallic molybdenum is transformed into the MoO3 on the SiO2/Si(111) surface upon heating,and the evolved MoO3 finally desorbs from the substrate upon annealing at elevated temperatures.

  15. Effects of A Top SiO2 Surface Layer on Cavity Formation and Helium Desorption in Silicon

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    Cz n-type Si (100) samples with and without a top SiO2 layer were implanted with 40 keV helium ions at the same dose of 5×1016 cm-2. Cross-sectional transmission electron microscopy (XTEM) and thermal desorption spectroscopy (THDS) were used to study the thermal evolution of cavities upon and helium thermal release, respectively. XTEM results show that the presence of the top SiO2 layer could suppress the thermal growth of cavities mainly formed in the region close to the SiO2/Si interface, which leads to the reduction in both the cavity band and cavity density. THDS results reveal that the top oxide layer could act as an effective barrier for the migration of helium atoms to the surface, and it thus gives rise to the formation of more overpresurrized bubbles and to the occurrence of a third release peak located at about 1100 K. The results were qualitively discussed by considering the role of the oxide surface layer in defect migration and evolution upon annealing.

  16. Atomic clocks as a tool to monitor vertical surface motion

    CERN Document Server

    Bondarescu, Ruxandra; Lundgren, Andrew; Hetényi, György; Houlié, Nicolas; Jetzer, Philippe; Bondarescu, Mihai

    2015-01-01

    Atomic clock technology is advancing rapidly, now reaching stabilities of $\\Delta f/f \\sim 10^{-18}$, which corresponds to resolving $1$ cm in equivalent geoid height over an integration timescale of about 7 hours. At this level of performance, ground-based atomic clock networks emerge as a tool for monitoring a variety of geophysical processes by directly measuring changes in the gravitational potential. Vertical changes of the clock's position due to magmatic, volcanic, post-seismic or tidal deformations can result in measurable variations in the clock tick rate. As an example, we discuss the geopotential change arising due to an inflating point source (Mogi model), and apply it to the Etna volcano. Its effect on an observer on the Earth's surface can be divided into two different terms: one purely due to uplift and one due to the redistribution of matter. Thus, with the centimetre-level precision of current clocks it is already possible to monitor volcanoes. The matter redistribution term is estimated to b...

  17. Functionalization of undoped and p-doped Si (100) using atomic force microscope tips in the presence of propan-2-ol, butan-2-ol and toluene

    Science.gov (United States)

    McCausland, Jeffrey A.; Withanage, Sajeevi; Mallik, Robert R.; Lyuksyutov, Sergei F.

    2017-07-01

    A technique, based on amplitude modulation of Atomic Force Microscope (AFM) tips, in the absence of an applied bias voltage, is reported in this study. Under ambient humidity conditions, ultra-sharp n-doped silicon tips (spike radius 1 nm) oscillating at 160-250 kHz generate raised nanostructures 50-200 nm wide and 2 nm high on undoped or p-doped Si (100) surfaces pretreated with certain neat organic solvents. The solvents in the present work are propan-2-ol, butan-2-ol, or toluene. AFM is used to characterize the nanostructures which are found to be stable for at least 96 h. It is suggested that mechanical stress associated with the oscillatory Hookean energy ( 5-15 eV) of the tip promotes cleavage of residual solvent bonds on the surface. This bond cleavage, and the presence of surface defects, which may be critical in the formation of surface-solvent bonds (specifically Si-O-C or Si-C) to create the observed nanostructures, is discussed. The process described here to create raised nanostructures is distinctly different from all other reported techniques to date.

  18. Atomic layer deposition precursor step repetition and surface plasma pretreatment influence on semiconductor–insulator–semiconductor heterojunction solar cell

    Energy Technology Data Exchange (ETDEWEB)

    Talkenberg, Florian, E-mail: florian.talkenberg@ipht-jena.de; Illhardt, Stefan; Schmidl, Gabriele; Schleusener, Alexander; Sivakov, Vladimir [Leibniz Institute of Photonic Technology, Albert-Einstein-Str. 9, D-07745 Jena (Germany); Radnóczi, György Zoltán; Pécz, Béla [Centre for Energy Research, Institute of Technical Physics and Materials Science, Konkoly-Thege Miklós u. 29-33, H-1121 Budapest (Hungary); Dikhanbayev, Kadyrjan; Mussabek, Gauhar [Department of Physics and Engineering, al-Farabi Kazakh National University, 71 al-Farabi Ave., 050040 Almaty (Kazakhstan); Gudovskikh, Alexander [Nanotechnology Research and Education Centre, St. Petersburg Academic University, Russian Academy of Sciences, Hlopina Str. 8/3, 194021 St. Petersburg (Russian Federation)

    2015-07-15

    Semiconductor–insulator–semiconductor heterojunction solar cells were prepared using atomic layer deposition (ALD) technique. The silicon surface was treated with oxygen and hydrogen plasma in different orders before dielectric layer deposition. A plasma-enhanced ALD process was applied to deposit dielectric Al{sub 2}O{sub 3} on the plasma pretreated n-type Si(100) substrate. Aluminum doped zinc oxide (Al:ZnO or AZO) was deposited by thermal ALD and serves as transparent conductive oxide. Based on transmission electron microscopy studies the presence of thin silicon oxide (SiO{sub x}) layer was detected at the Si/Al{sub 2}O{sub 3} interface. The SiO{sub x} formation depends on the initial growth behavior of Al{sub 2}O{sub 3} and has significant influence on solar cell parameters. The authors demonstrate that a hydrogen plasma pretreatment and a precursor dose step repetition of a single precursor improve the initial growth behavior of Al{sub 2}O{sub 3} and avoid the SiO{sub x} generation. Furthermore, it improves the solar cell performance, which indicates a change of the Si/Al{sub 2}O{sub 3} interface states.

  19. Evolution of the interfacial layer during the atomic layer deposition of HfO{sub 2} on Si/SiO{sub 2} substrates

    Energy Technology Data Exchange (ETDEWEB)

    Karavaev, Konstantin; Tallarida, Massimo; Schmeisser, Dieter [Brandenburgische Technische Universitaet, LS Angewandte Physik-Sensorik, Konrad-Wachsmann-Allee, 17, 03046, Cottbus (Germany)

    2009-07-01

    We studied the formation of the interfacial layer in the Si/SiO{sub 2}/HfO{sub 2} system using the in-situ Atomic Layer Deposition (ALD) reactor developed in our group. We measured the X-ray photoelectron and X-ray absorption spectra with synchrotron radiation at the beamline U49-2/PGM2-BESSY II. The ALD growth was obtained using different Hf-precursors (HfCl{sub 4},TEMAHf and TDMAHf) on various prepared substrates at different temperatures. The investigation was carried out in-situ giving the possibility to determine the properties of the grown film after every ALD cycle without breaking the vacuum. We observed the evolution of the Si/SiO{sub 2}/HfO{sub 2} system during the formation of first three Hf-oxide layers, detecting the interfacial growth of SiO{sub 2} during the initial ALD cycles from the XPS spectra of Si2p. We discuss how the interfacial layer growth depends on the various ALD parameters.

  20. Direct scattering, trapping, and desorption in atom-surface collisions.

    Science.gov (United States)

    Fan, Guoqing; Manson, J R

    2008-08-08

    Maxwell is credited as the first to invoke the assumption that an impinging gas beam scatters from a surface with a direct contribution exhibiting little change in state and a trapping-desorption fraction that desorbs in equilibrium [J. C. Maxwell, Phil. Trans. R. Soc. London 170, 231 (1879)]. Here a classical mechanical scattering theory is developed to describe direct scattering, trapping, and subsequent desorption of the incident beam. This theory allows a rigorous test of the Maxwell assumption and determines the conditions under which it is valid. The theory also gives quantitative explanations of important new experimental measurements [K. D. Gibson, N. Isa, and S. J. Sibener, J. Chem. Phys. 119, 13 083 (2003)] for direct and trapping-desorption scattering of Ar atoms by a self-assembled layer of 1-decanethiol on Au(111).

  1. Promotion Effect of Lantanum ions on Co/SiO2 Catalysts Prepared via Solvated Metal Atom Impregnation Method

    Institute of Scientific and Technical Information of China (English)

    吴世华; 张守民; 黄维平; 李保庆; 石娟

    2004-01-01

    In order to assess the promotional effects of La3+ on CO hydrogenation of Co/SiO2 catalyst, solvated metal atom impregnation (SMAI) method was used to prepare unpromoted 10% (mass fraction) Co/SiO2 and a series of La3+-promoted 10% (mass fraction) Co/SiO2 catalyst with different La/Co atomic ratios (0.1, 0.3, 0.5). X-ray diffraction (XRD), and CO chemisorption measurements show that the cobalt particle size decreases as the La/Co ratios increase. X-ray photoelectron spectrescopy indicates that cobalt is in zero-valent state for all the samples. Catalytic test shows that the catalytic activity of La3+-promoted Co/SiO2 in CO hydrogenation is higher than that of unpromoted Co/SiO2, and enhances with the La/Co ratios increase. La3+ promotion also causes the enhanced selectivity of Co/SiO2 catalyst for higher hydrocarbon products.

  2. Atomic structure and surface defects at mineral-water interfaces probed by in situ atomic force microscopy

    Science.gov (United States)

    Siretanu, Igor; van den Ende, Dirk; Mugele, Frieder

    2016-04-01

    Atomic scale details of surface structure play a crucial role for solid-liquid interfaces. While macroscopic characterization techniques provide averaged information about bulk and interfaces, high resolution real space imaging reveals unique insights into the role of defects that are believed to dominate many aspects of surface chemistry and physics. Here, we use high resolution dynamic Atomic Force Microscopy (AFM) to visualize and characterize in ambient water the morphology and atomic scale structure of a variety of nanoparticles of common clay minerals adsorbed to flat solid surfaces. Atomically resolved images of the (001) basal planes are obtained on all materials investigated, namely gibbsite, kaolinite, illite, and Na-montmorillonite of both natural and synthetic origin. Next to regions of perfect crystallinity, we routinely observe extended regions of various types of defects on the surfaces, including vacancies of one or few atoms, vacancy islands, atomic steps, apparently disordered regions, as well as strongly adsorbed seemingly organic and inorganic species. While their exact nature is frequently difficult to identify, our observations clearly highlight the ubiquity of such defects and their relevance for the overall physical and chemical properties of clay nanoparticle-water interfaces.Atomic scale details of surface structure play a crucial role for solid-liquid interfaces. While macroscopic characterization techniques provide averaged information about bulk and interfaces, high resolution real space imaging reveals unique insights into the role of defects that are believed to dominate many aspects of surface chemistry and physics. Here, we use high resolution dynamic Atomic Force Microscopy (AFM) to visualize and characterize in ambient water the morphology and atomic scale structure of a variety of nanoparticles of common clay minerals adsorbed to flat solid surfaces. Atomically resolved images of the (001) basal planes are obtained on all

  3. Relation of lifetime to surface passivation for atomic-layer-deposited Al{sub 2}O{sub 3} on crystalline silicon solar cell

    Energy Technology Data Exchange (ETDEWEB)

    Cho, Young Joon [Graduate School of Energy Science and Technology, Chungnam National University, Yuseong-gu, Daejeon 305-764 (Korea, Republic of); Song, Hee Eun, E-mail: hsong@kier.re.kr [Photovoltaic Center, Korea Institute of Energy Research, Yuseong-gu, Daejeon 305-343 (Korea, Republic of); Chang, Hyo Sik, E-mail: hschang@cnu.ac.kr [Graduate School of Energy Science and Technology, Chungnam National University, Yuseong-gu, Daejeon 305-764 (Korea, Republic of)

    2015-03-15

    Highlights: • We investigated the relation of potassium contamination on Si solar wafer to lifetime. • We deposited Al{sub 2}O{sub 3} layer by atomic layer deposition (ALD) on Si solar wafer after several cleaning process. • Potassium can be left on Si surface by incomplete cleaning process and degrade the Al{sub 2}O{sub 3} passivation quality. - Abstract: We investigated the relation of potassium contamination on a crystalline silicon (c-Si) surface after potassium hydroxide (KOH) etching to the lifetime of the c-Si solar cell. Alkaline solution was employed for saw damage removal (SDR), texturing, and planarization of a textured c-Si solar wafer prior to atomic layer deposition (ALD) Al{sub 2}O{sub 3} growth. In the solar-cell manufacturing process, ALD Al{sub 2}O{sub 3} passivation is utilized to obtain higher conversion efficiency. ALD Al{sub 2}O{sub 3} shows excellent surface passivation, though minority carrier lifetime varies with cleaning conditions. In the present study, we investigated the relation of potassium contamination to lifetime in solar-cell processing. The results showed that the potassium-contaminated samples, due to incomplete cleaning of KOH, had a short lifetime, thus establishing that residual potassium can degrade Al{sub 2}O{sub 3} surface passivation.