WorldWideScience

Sample records for surfaces si-si dimer

  1. The effect of surface conductance on lateral gated quantum devices in Si/SiGe heterostructures

    Science.gov (United States)

    Lin, Xi; Hu, Jingshi; Lai, Andrew P.; Zhang, Zhenning; MacLean, Kenneth; Dillard, Colin; Xie, Ya-Hong; Kastner, Marc A.

    2011-07-01

    Quantum dots in Si/SiGe heterostructures are expected to have relatively long electron spin decoherence times, because of the low density of nuclear spins and the weak coupling between nuclear and electron spins. We provide experimental evidence suggesting that electron motion in a conductive layer parallel to the two-dimensional electron gas, possibly resulting from the donors used to dope the Si quantum well, is responsible for the well-known difficulty in achieving well-controlled dots in this system. Charge motion in the conductive layer can cause depletion on large length scales, making electron confinement in the dot impossible, and can give rise to noise that can overwhelm the single-electron charging signal. Results of capacitance versus gate bias measurements to characterize this conductive layer are presented.

  2. Ultraclean Si/Si interface formation by surface preparation and direct bonding in ultrahigh vacuum

    DEFF Research Database (Denmark)

    Hermansson, Karin; Grey, Francois; Bengtsson, Stefan;

    1998-01-01

    Silicon surfaces have been cleaned and bonded in ultrahigh vacuum, at a pressure in the 10(-10) Torr range. The bonded interfaces show extremely low contamination levels as measured by secondary ion mass spectroscopy. Nevertheless, a potential barrier could be detected at the interface by spreading...

  3. Fabrication of Si/SiO2/GaN structure by surface-activated bonding for monolithic integration of optoelectronic devices

    Science.gov (United States)

    Tsuchiyama, Kazuaki; Yamane, Keisuke; Sekiguchi, Hiroto; Okada, Hiroshi; Wakahara, Akihiro

    2016-05-01

    A Si/SiO2/GaN-light-emitting-diode (LED) wafer is proposed as a new structure for the monolithic integration of both Si circuits and GaN-based optical devices. Surface-activated bonding was performed to transfer a Si layer from a silicon-on-insulator substrate to a SiO2/GaN-LED substrate. Transmission electron microscopy observation revealed that a defect-free Si layer was formed on the SiO2/GaN-LED substrate without interfacial voids. The crystalline quality of the Si layer, which is characterized by an X-ray rocking curve, was markedly improved by flattening the SiO2/GaN-LED substrate before bonding. Finally, a micro-LED array was successfully fabricated on the Si/SiO2/GaN-LED wafer without the delamination of the Si layer.

  4. 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.

  5. A semiempirical surface scattering model for quantum corrected Monte-Carlo simulation of unstrained Si and strained Si/SiGe PMOSFETs

    Energy Technology Data Exchange (ETDEWEB)

    Pham, A.T. [BST, TU Braunschweig, Postfach 33 29, 38023 Braunschweig (Germany)]. E-mail: pham@nst.ing.tu-bs.de; Jungemann, C. [EIT4, 85577 Neubiberg, Universitaet der Bundeswehr Muenchen (Germany); Nguyen, C.D. [BST, TU Braunschweig, Postfach 33 29, 38023 Braunschweig (Germany); Meinerzhagen, B. [BST, TU Braunschweig, Postfach 33 29, 38023 Braunschweig (Germany)

    2006-12-15

    A new hole surface scattering model for FBMC simulations is presented for unstrained Si and biaxially strained Si/SiGe PMOSFETs. The new scattering model was developed for quantum corrected spatial hole charge distributions at the Si/SiO{sub 2} interface, where the quantum correction is based on the improved modified local density approximation (IMLDA). To extract channel mobility efficiently, a new linear response (LR) MC method has been developed. The new LRMC method, which is faster than standard MC by about three orders of magnitude, allows to extract the parameters of the surface scattering model for holes from the available measurements in an efficient manner. The model has been calibrated and verified for a wide range of doping levels (7.8x10{sup 15} to 6.6x10{sup 17}cm{sup -3}), temperatures (223-443-bar K) and Ge-content up to 30% by comparison to experimental data. A 23-bar nm PMOSFET with and without a strained Si layer on top of the substrate has been simulated with our new FBMC model. Drain current enhancement due to biaxial strain is found to be reduced in comparison to the NMOSFET case.

  6. Sputtering of dimers off a silicon surface

    Energy Technology Data Exchange (ETDEWEB)

    Nietiadi, Maureen L. [Physics Department, University Kaiserslautern, Erwin-Schroedinger-Strasse, D-67663 Kaiserslautern (Germany); Research Center OPTIMAS, University Kaiserslautern, Erwin-Schroedinger-Strasse, D-67663 Kaiserslautern (Germany); Rosandi, Yudi [Physics Department, University Kaiserslautern, Erwin-Schroedinger-Strasse, D-67663 Kaiserslautern (Germany); Research Center OPTIMAS, University Kaiserslautern, Erwin-Schroedinger-Strasse, D-67663 Kaiserslautern (Germany); Department of Physics, Universitas Padjadjaran, Jatinangor, Sumedang 45363 (Indonesia); Kopnarski, Michael [Physics Department, University Kaiserslautern, Erwin-Schroedinger-Strasse, D-67663 Kaiserslautern (Germany); Research Center OPTIMAS, University Kaiserslautern, Erwin-Schroedinger-Strasse, D-67663 Kaiserslautern (Germany); Institut fuer Oberflaechen- und Schichtanalytik IFOS GmbH, Trippstadter Strasse 120, D-67663 Kaiserslautern (Germany); Urbassek, Herbert M., E-mail: urbassek@rhrk.uni-kl.de [Physics Department, University Kaiserslautern, Erwin-Schroedinger-Strasse, D-67663 Kaiserslautern (Germany); Research Center OPTIMAS, University Kaiserslautern, Erwin-Schroedinger-Strasse, D-67663 Kaiserslautern (Germany)

    2012-10-15

    We present experimental and molecular-dynamics simulation results of the sputtering of a Si surface by 2 keV Ar ions. Results on both the monomer and dimer distributions are presented. In simulation, these distributions follow a generalized Thompson law with power exponent n=2 and n=3, respectively. The experimental data, obtained via plasma post-ionization in an SNMS (secondary neutral mass spectrometry) apparatus, show good agreement with respect to the dimer fraction, and the relative energy distributions of dimers and monomers. The consequences for the dimer sputtering mechanism are discussed.

  7. 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.

  8. Highly sensitive NIR PtSi/Si-nanostructure detectors

    Science.gov (United States)

    Li, Hua-gao; Guo, Pei; Yuan, An-bo; Long, Fei; Li, Rui-zhi; Li, Ping; Li, Yi

    2016-10-01

    We report a high external quantum efficiency (EQE) photodiode detector with PtSi/Si-nanostructures. Black silicon nanostructures were fabricated by metal-assist chemical etching (MCE), a 2 nm Pt layer was subsequently deposited on black silicon surface by DC magnetron sputtering system, and PtSi/Si-nanostructures were formed in vacuum annealing at 450 oC for 5 min. As the PtSi/Si-nanostructures presented a spiky shape, the absorption of incident light was remarkably enhanced for the repeat reflection and absorption. The breakdown voltage, dark current, threshold voltage and responsivity of the device were investigated to evaluate the performance of the PtSi/Si-nanostructures detector. The threshold voltage and dark currents of the PtSi/Si-nanostructure photodiode tends to be slightly higher than those of the standard diodes. The breakdown voltage remarkably was reduced because of existing avalanche breakdown in PtSi/Si-nanostructures. However, the photodiodes had high response at room temperature in near infrared region. At -5 V reverse bias voltage, the responsivity was 0.72 A/W in 1064 nm wavelength, and the EQE was 83.9%. By increasing the reverse bias voltage, the responsivity increased. At -60 V reverse bias voltage, the responsivity was 3.5 A/W, and the EQE was 407.5%, which means the quantum efficiency of PtSi/Si-nanostructure photodiodes was about 10 times higher than that of a standard diode. Future research includes how to apply this technology to enhance the NIR sensitivity of image sensors, such as Charge Coupled Devices (CCD).

  9. Hybrid Monte Carlo-molecular dynamics algorithm for the study of islands and step edges on semiconductor surfaces: application to Si/Si (001).

    Science.gov (United States)

    Tavazza, F; Nurminen, L; Landau, D P; Kuronen, A; Kaski, K

    2004-09-01

    A classical, hybrid Monte Carlo-molecular dynamic (MC-MD) algorithm is introduced for the study of phenomena like two-dimensional (2D) island stability or step-edge evolution on semiconductor surfaces. This method presents the advantages of working off lattice and utilizing bulk-fitted potentials. It is based on the introduction of collective moves, such as dimer jumps, in the MC algorithm. MD-driven local relaxations are considered as trial moves for the MC. The algorithm is applied to the analysis of 2D Si islands on Si(001). Results on early stages of island formation, island stability versus temperature and system size, and step-edge evolution are presented. In all cases good qualitative agreement with experimental results is found.

  10. Subsurface dimerization in III-V semiconductor (001) surfaces

    DEFF Research Database (Denmark)

    Kumpf, C.; Marks, L.D.; Ellis, D.

    2001-01-01

    We present the atomic structure of the c(8 X 2) reconstructions of InSb-, InAs-, and GaAs-(001) surfaces as determined by surface x-ray diffraction using direct methods. Contrary to common belief, group III dimers are not prominent on the surface, instead subsurface dimerization of group m atoms ...... takes place in the second bilayer, accompanied by a major rearrangement of the surface atoms above the dimers to form linear arrays. By varying the occupancies of four surface sites the (001)-c(8 X 2) reconstructions of III-V semiconductors can be described in a unified model....

  11. Dimers on Surface Graphs and Spin Structures. I

    DEFF Research Database (Denmark)

    Cimasoni, David; Reshetikhin, Nicolai

    2007-01-01

    Partition functions for dimers on closed oriented surfaces are known to be alternating sums of Pfaffians of Kasteleyn matrices. In this paper, we obtain the formula for the coefficients in terms of discrete spin structures.......Partition functions for dimers on closed oriented surfaces are known to be alternating sums of Pfaffians of Kasteleyn matrices. In this paper, we obtain the formula for the coefficients in terms of discrete spin structures....

  12. Influence of size, shape and core-shell interface on surface plasmon resonance in Ag and Ag@MgO nanoparticle films deposited on Si/SiO x.

    Science.gov (United States)

    D'Addato, Sergio; Pinotti, Daniele; Spadaro, Maria Chiara; Paolicelli, Guido; Grillo, Vincenzo; Valeri, Sergio; Pasquali, Luca; Bergamini, Luca; Corni, Stefano

    2015-01-01

    Ag and Ag@MgO core-shell nanoparticles (NPs) with a diameter of d = 3-10 nm were obtained by physical synthesis methods and deposited on Si with its native ultrathin oxide layer SiO x (Si/SiO x ). Scanning electron microscopy and transmission electron microscopy (TEM) images of bare Ag NPs revealed the presence of small NP aggregates caused by diffusion on the surface and agglomeration. Atomic resolution TEM gave evidence of the presence of crystalline multidomains in the NPs, which were due to aggregation and multitwinning occurring during NP growth in the nanocluster source. Co-deposition of Ag NPs and Mg atoms in an oxygen atmosphere gave rise to formation of a MgO shell matrix surrounding the Ag NPs. The behaviour of the surface plasmon resonance (SPR) excitation in surface differential reflectivity (SDR) spectra with p-polarised light was investigated for bare Ag and Ag@MgO NPs. It was shown that the presence of MgO around the Ag NPs caused a red shift of the plasmon excitation, and served to preserve its existence after prolonged (five months) exposure to air, realizing the possibility of technological applications in plasmonic devices. The Ag NP and Ag@MgO NP film features in the SDR spectra could be reproduced by classical electrodynamics simulations by treating the NP-containing layer as an effective Maxwell Garnett medium. The simulations gave results in agreement with the experiments when accounting for the experimentally observed aggregation.

  13. A semiempirical surface scattering model for quantum corrected full-band Monte-Carlo simulation of biaxially strained Si/SiGe NMOSFETs

    Science.gov (United States)

    Pham, A. T.; Nguyen, C. D.; Jungemann, C.; Meinerzhagen, B.

    2006-04-01

    A new semiempirical surface scattering model for electrons in strained Si devices including a quantum correction has been developed and implemented into our FBMC simulator. The strain is assumed to be consistent with pseudomorphic growth on a relaxed SiGe buffer. By introducing a few additional terms into the physical scattering rates which depend on the Ge-content in the SiGe buffer, the new surface scattering model can excellently reproduce low-field inversion layer mobility measurements for a wide range of Ge-content (0-30%) and substrate doping levels (10 16-5.5 × 10 18 cm -3). As a device example, an NMOSFET with 23 nm gate length with and without a strained Si channel has been simulated by the new FBMC model.

  14. Dimers on surface graphs and spin structures. II

    DEFF Research Database (Denmark)

    Cimasoni, David; Reshetikhin, Nicolai

    2009-01-01

    In a previous paper [3], we showed how certain orientations of the edges of a graph Γ embedded in a closed oriented surface Σ can be understood as discrete spin structures on Σ. We then used this correspondence to give a geometric proof of the Pfaffian formula for the partition function of the di......In a previous paper [3], we showed how certain orientations of the edges of a graph Γ embedded in a closed oriented surface Σ can be understood as discrete spin structures on Σ. We then used this correspondence to give a geometric proof of the Pfaffian formula for the partition function...... of the dimer model on Γ. In the present article, we generalize these results to the case of compact oriented surfaces with boundary. We also show how the operations of cutting and gluing act on discrete spin structures and how they change the partition function. These operations allow to reformulate the dimer...

  15. Laser cladding of Al-Si/SiC composite coatings : Microstructure and abrasive wear behavior

    NARCIS (Netherlands)

    Anandkumar, R.; Almeida, A.; Vilar, R.; Ocelik, V.; De Hosson, J.Th.M.

    2007-01-01

    Surface coatings of an Al-Si-SiC composite were produced on UNS A03560 cast Al-alloy substrates by laser cladding using a mixture of powders of Al-12 wt.% Si alloy and SiC. The microstructure of the coatings depends considerably on the processing parameters. For a specific energy of 26 MJ/m2 the

  16. Microstructure and abrasive wear studies of laser clad Al-Si/SiC composite coatings

    NARCIS (Netherlands)

    Anandkumar, R.; Colaco, R.; Ocelik, V.; De Hosson, J. Th. M.; Vilar, R.; Gyulai, J; Szabo, PJ

    2007-01-01

    Surface coatings of Al-Si/SiC metal-matrix composites were deposited on Al-7 wt. % Si alloy substrates by laser cladding. The microstructure of the coatings was characterized by optical microscopy, scanning electron microscopy (SEM) and X-ray diffraction (XRD). The microstructure of the coating mate

  17. Laser cladding of Al-Si/SiC composite coatings : Microstructure and abrasive wear behavior

    NARCIS (Netherlands)

    Anandkumar, R.; Almeida, A.; Vilar, R.; Ocelik, V.; De Hosson, J.Th.M.

    2007-01-01

    Surface coatings of an Al-Si-SiC composite were produced on UNS A03560 cast Al-alloy substrates by laser cladding using a mixture of powders of Al-12 wt.% Si alloy and SiC. The microstructure of the coatings depends considerably on the processing parameters. For a specific energy of 26 MJ/m2 the mic

  18. Ionization dynamics of water dimer on ice surface

    Science.gov (United States)

    Tachikawa, Hiroto

    2016-05-01

    The solid surface provides an effective two-dimensional reaction field because the surface increases the encounter probability of bi-molecular collision reactions. Also, the solid surface stabilizes a reaction intermediate because the excess energy generated by the reaction dissipates into the bath modes of surface. The ice surface in the universe is one of the two dimensional reaction fields. However, it is still unknown how the ice surface affects to the reaction mechanism. In the present study, to elucidate the specific property of the ice surface reaction, ionization dynamics of water dimer adsorbed on the ice surface was theoretically investigated by means of direct ab-initio molecular dynamics (AIMD) method combined with ONIOM (our own n-layered integrated molecular orbital and molecular mechanics) technique, and the result was compared with that of gas phase reaction. It was found that a proton is transferred from H2O+ to H2O within the dimer and the intermediate complex H3O+(OH) is formed in both cases. However, the dynamic features were different from each other. The reaction rate of the proton transfer on the ice surface was three times faster than that in the gas phase. The intermediate complex H3O+(OH) was easily dissociated to H3O+ and OH radical on the ice surface, and the lifetime of the complex was significantly shorter than that of gas phase (100 fs vs. infinite). The reason why the ice surface accelerates the reaction was discussed in the present study.

  19. 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

  20. Optical investigations of AlSi-SiC composites subjected to laser CO 2 annealing

    Science.gov (United States)

    Jaglarz, Janusz; Grabowski, Andrzej

    2010-10-01

    The optical study of the AlSi/SiC composite materials before and after laser annealing has been performed. They concerned total and diffuse reflectance measurements obtained by the means of integrating sphere in the spectral range 250-2500 nm, measurements of intensity of scattered light as a function of scattering angle ( BRDF method) and ellipsometric measurements performed in the range 190-1700 nm. For determination of optical constants, the Kramers-Krönig dispersion relation has been applied. Obtained results had great differences of optical properties alloys before and after laser annealing. For investigated composites roughness and correlation lengths of studied surfaces have been determined. Moreover, optical measurements allowed concluding the light scattering being a result of interaction of light with surface topography and material scattering appeared due to variation of optical constants on surfaces of AlSi/SiC composites.

  1. Si/SiO2和Si/SiNx/SiO2超晶格的能带结构%Band structure of Si/SiO2 and Si/SiNx/SiO2 superlattices

    Institute of Scientific and Technical Information of China (English)

    魏屹; 董成军; 徐明

    2010-01-01

    利用Kronig-Penney模型从理论上计算了Si/SiO2和Si/Si/SiNx/SiO2多层膜结构中量子阱的能带结构,进一步分析了各亚层薄膜厚度对能带结构和有效质量的影响.结果发现,适当减少亚层的厚度都能使得纳米Si薄膜的带隙发生明显宽化.在Si/SiO2超晶格中,Si量子阱层带隙能量随着Si层厚度的变化符合EPLL(eV)=1.6+0.7/d2关系,与我们的计算结果十分吻合.在Si/SiNdSiO2超晶格系统中,可以通过控制各亚层厚度,尤其是Si和SiNx层厚度,均能够有效地控制发光.

  2. Biomorphous SiSiC/Al-Si ceramic composites manufactured by squeeze casting: microstructure and mechanical properties

    Energy Technology Data Exchange (ETDEWEB)

    Zollfrank, C.; Travitzky, N.; Sieber, H.; Greil, P. [Department of Materials Science, Glass and Ceramics, University of Erlangen-Nuernberg (Germany); Selchert, T. [Advanced Ceramics Group, Technical University of Hamburg-Harburg (Germany)

    2005-08-01

    SiSiC/Al-Si composites were fabricated by pressure-assisted infiltration of an Al-Si alloy into porous biocarbon preforms derived from the rattan palm. Al-Si alloy was found in the pore channels of the biomorphous SiSiC preform, whereas SiC and carbon were present in the struts. The formation of a detrimental Al{sub 4}C{sub 3}-phase was not observed in the composites. A bending strength of 200 MPa was measured. The fractured surfaces showed pull-out of the Al-alloy. (Abstract Copyright [2005], Wiley Periodicals, Inc.)

  3. Surface characterization and orientation interaction between diamond- like carbon layer structure and dimeric liquid crystals

    Science.gov (United States)

    Naradikian, H.; Petrov, M.; Katranchev, B.; Milenov, T.; Tinchev, S.

    2017-01-01

    Diamond-like carbon (DLC) and amorphous carbon films are very promising type of semiconductor materials. Depending on the hybridization sp2/sp3 ratio, the material’s band gap varies between 0.8 and 3 eV. Moreover carbon films possess different interesting for practice properties: comparable to the Silicon, Diamond like structure has 22-time better thermal conductivity etc. Here we present one type of implementation of such type nanostructure. That is one attempt for orientation of dimeric LC by using of pre-deposited DLC layer with different ratio of sp2/sp3 hybridized carbon content. It could be expected a pronounced π1-π2interaction between s and p orbital levels on the surface and the dimeric ring of LC. We present comparison of surface anchoring strengths of both orientation inter-surfaces DLC/dimeric LC and single wall carbon nanotubes (SWCNT)/dimeric LC. The mechanism of interaction of dimeric LC and activated surfaces with DLC or SWCNT will be discussed. In both cases we have π-π interaction, which in combination with hydrogen bonding, typical for the dimeric LCs, influence the LC alignment. The Raman spectroscopy data evidenced the presence of charge transfer between contacting hexagonal rings of DLC and the C = O groups of the LC molecules.

  4. Analysis of X-Ray Diffraction as a Probe of Interdiffusion in Si/SiGe Heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Brennan, Sean M

    2003-08-20

    We investigate numerical simulations that utilize a non-linear interdiffusion solver and dynamical x-ray diffraction calculations to predict the local composition evolution in low Ge concentration Si/SiGe superlattices and their diffraction patterns during annealing. Superlattice satellite peak decay rates are compared with experimentally measured values and simulated diffraction patterns are matched directly to data with good success. The simulations are used to test the sensitivity of x-ray diffraction to various uncertainties commonly encountered when measuring interdiffusion at Si/SiGe interfaces. It is found that the most serious errors result from variations in the Ge content across the surface of the wafer. For example, the resolution limit of most experimental techniques used to measure Ge concentration in a SiGe film is -1 at.%, for a film with 11% mean Ge concentration annealed for 5 hours at 870 C, this level of error will cause the observed interdiffusivity values to deviate by -25% or +50%. The simulations are further used to show that for Si/SiGe interdiffusion, superlattice diffraction produces valid measurements when applied to 004 superlattice satellite peaks and square wave composition modulations even though it is only exactly applicable to satellite peaks about 000 reflection and to sinusoidal composition modulations. Finally, we show that proper interpretation of x-ray scattering data to extract Si/SiGe interdiffusivity values must account for the strong dependence of the interdiffusivity on Ge concentration.

  5. Synthesis and characterization of laminated Si/SiC composites

    Directory of Open Access Journals (Sweden)

    Salma M. Naga

    2013-01-01

    Full Text Available Laminated Si/SiC ceramics were synthesized from porous preforms of biogenous carbon impregnated with Si slurry at a temperature of 1500 °C for 2 h. Due to the capillarity infiltration with Si, both intrinsic micro- and macrostructure in the carbon preform were retained within the final ceramics. The SEM micrographs indicate that the final material exhibits a distinguished laminar structure with successive Si/SiC layers. The produced composites show weight gain of ≈5% after heat treatment in air at 1300 °C for 50 h. The produced bodies could be used as high temperature gas filters as indicated from the permeability results.

  6. Study of New Way about Si/Si Bonding

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    A new set of technique was adopted in bonding Si-Si by using Ge (Ⅳ element),which is used as the substitute for the common hydrophilic method. The bond layer has no holes, and the edge bond-rate amounts to above 98%, and the bond strength is above 2156 Pa. By doping the same kind of dopant with low-resistance in Ge, the stress compensation was realized.

  7. MONTE CARLO SIMULATIONS OF THE ADSORPTION OF DIMERS ON STRUCTURED HETEROGENEOUS SURFACES

    Directory of Open Access Journals (Sweden)

    Abreu C.R.A.

    2001-01-01

    Full Text Available The effect of surface topography upon the adsorption of dimer molecules is analyzed by means of grand canonical ensemble Monte Carlo simulations. Heterogeneous surfaces were assumed to consist of a square lattice containing active sites with two different energies. These were distributed in three different configurations: a random distribution of isolated sites; a random distribution of grains with four high-energy sites; and a random distribution of grains with nine high-energy sites. For the random distribution of isolated sites, the results are in good agreement with the molecular simulations performed by Nitta et al. (1997. In general, the comparison with theoretical models shows that the Nitta et al. (1984 isotherm presents good predictions of dimer adsorption both on homogeneous and heterogeneous surfaces with sites having small differences in characteristic energies. The molecular simulation results also show that the energy topology of the solid surfaces plays an important role in the adsorption of dimers on solids with large differences in site energies. For these cases, the Nitta et al. model does not describe well the data on dimer adsorption on random heterogeneous surfaces (grains with one acid site, but does describe reasonably well the adsorption of dimers on more patchwise heterogeneous surfaces (grains with nine acid sites.

  8. Radiation-induced plasmons in Si-SiO2

    Institute of Scientific and Technical Information of China (English)

    1999-01-01

    The first level plasmons of Si in the pure Si state (corresponding to bonding energy (BE) of 116.95 eV) and in the SiO2 state (corresponding to BE of 122.0 eV) of Si-SiO2 prepared by irradiation hard and soft processing were studied with XPS before and after 60Co radiation.The experimental results indicate thatthere was an interface consisting of the two plasmons,this interface was extended by 60Co radiation, the fractions of the plasmon for Si in the Si-SiO2 werechanged with the variation of radiation dosage,the difference of the change in fraction of plasmonsfor the two kinds of samples was that the soft variedfaster than hard, the change of concentrations inplasmons for both hard and soft Si-SiO2 irradiatedin positive bias field were greater than that in bias-free field.The experimental results are explained from the view point of energy absorbed in form of quantization.

  9. Resonance Raman mapping as a tool to monitor and manipulate Si nanocrystals in Si-SiO{sub 2} nanocomposite

    Energy Technology Data Exchange (ETDEWEB)

    Rani, Ekta; Ingale, Alka A., E-mail: alka@rrcat.gov.in [Laser Physics Applications Section, Raja Ramanna Centre for Advanced Technology, Indore-452013 (India); Homi Bhabha National Institute, Raja Ramanna Centre for Advanced Technology, Indore-452013 (India); Chaturvedi, A. [Laser Material Processing Division, Raja Ramanna Centre for Advanced Technology, Indore-452013 (India); Joshi, M. P.; Kukreja, L. M. [Homi Bhabha National Institute, Raja Ramanna Centre for Advanced Technology, Indore-452013 (India); Laser Material Processing Division, Raja Ramanna Centre for Advanced Technology, Indore-452013 (India)

    2015-10-19

    Specially designed laser heating experiment along with Raman mapping on Si-SiO{sub 2} nanocomposites elucidates the contribution of core and surface/interface in the intermediate frequency range (511–514 cm{sup −1}) Si phonons. The contribution of core to surface/interface increases with the size of Si nanocrystal, which itself increases on laser irradiation. Further, it is found that resonance Raman is crucial to the observance of surface/interface phonons and wavelength dependent Raman mapping can be corroborated with band edges observed in absorption spectra. This understanding can be gainfully used to manipulate and characterize Si-SiO{sub 2} nanocomposite, simultaneously for photovoltaic device applications.

  10. 射频 Si/SiGe/Si HBT的研究%Studies on RF Si/SiGe/Si HBT

    Institute of Scientific and Technical Information of China (English)

    廖小平; 殷刚毅

    2003-01-01

    Si/SiGe/Si HBT与Si工艺兼容的研究基础上,对射频Si/SiGe/Si HBT的射频特性和制备工艺进行了研究,分析了与器件结构有关的关键参数寄生电容和寄生电阻与Si/SiGe/Si HBT的特征频率fT和最高振荡频率fmax的关系,成功地制备了fT为2.5 GHz、fmax为2.3 GHz的射频Si/SiGe/Si HBT,为具有更好的射频性能的Si/SiGe/Si HBT的研究建立了基础.

  11. Strained Si/SiGe MOS transistor model

    Directory of Open Access Journals (Sweden)

    Tatjana Pešić-Brđanin

    2009-06-01

    Full Text Available In this paper we describe a new model of surfacechannel strained-Si/SiGe MOSFET based on the extension of non-quasi-static (NQS circuit model previously derived for bulk-Si devices. Basic equations of the NQS model have been modified to account for the new physical parameters of strained-Si and relaxed-SiGe layers. From the comparisons with measurements, it is shown that a modified NQS MOS including steady-state self heating can accurately predict DC characteristics of Strained Silicon MOSFETs.

  12. Boron induced charge traps near the interface of Si/SiO{sub 2} probed by second harmonic generation

    Energy Technology Data Exchange (ETDEWEB)

    Park, Heungman; Varga, Kalman; Tolk, Norman [Department of Physics and Astronomy, Vanderbilt University, Nashville, Tennessee 37235 (United States); Qi, Jingbo [Department of Physics and Astronomy, Vanderbilt University, Nashville, Tennessee 37235 (United States); National High Magnetic Field Laboratory, Tallahassee, Florida 32310 (United States); Xu, Ying [Department of Physics and Astronomy, Vanderbilt University, Nashville, Tennessee 37235 (United States); Zomega Terahertz Corporation, Troy, New York 12180 (United States); Weiss, Sharon M. [Department of Physics and Astronomy, Vanderbilt University, Nashville, Tennessee 37235 (United States); Department of Electrical Engineering and Computer Science, Vanderbilt University, Nashville, Tennessee 37235 (United States); Rogers, Bridget R. [Department of Chemical and Biomolecular Engineering, Nashville, Vanderbilt University, Tennessee 37235 (United States); Luepke, Gunter [Department of Applied Science, College of William and Mary, Williamsburg, Virginia 23187 (United States)

    2010-08-15

    We review recent second harmonic generation (SHG) measurements for highly boron-doped Si/SiO{sub 2} systems. Using electric field sensitive time-dependent SHG (TD-SHG), we determined that the direction of the initial DC electric field at the interface induced by boron induced charge traps is from oxide to silicon thus demonstrating that the boron induced charge traps in the oxide are positively charged. For a thin oxide ({proportional_to}2 nm) both boron traps and O{sub 2} surface oxide traps contribute. However, for a highly boron-doped Si/SiO{sub 2} sample with a thick thermally grown oxide (thickness: 12 nm), the TD-SHG signal exhibits a monotonic decrease arising from filling only the boron charge traps. By fitting our data, we show that the interface effective susceptibility vertical stroke {chi}{sup (2)} vertical stroke is heavily dependent on doping concentration. (Abstract Copyright [2010], Wiley Periodicals, Inc.)

  13. Plasmonic Dimer-Like Nanoassemblies for Surface-Enhanced Raman Spectroscop

    Science.gov (United States)

    Rigo, Maria; Seo, Jaetae; Kim, Wan-Joong; Jung, Sungsoo; Hampton University Team; Etri Collaboration; Kriss Collaboration

    2011-05-01

    We report on the preparation of gold dimers in which the near-field coupling in their subwavelength gap is influenced by the individual gold nanoparticles size and the molecule's length used to assemble the dimers. The nano assemblies display plasmonic modes similar to those observed in rod-like nanoparticles. The longitudinal mode of the gold dimers shift as a function of gold nanoparticles size and concentration and it is influenced by the concentration of Rhodamine 6G (R6G), the molecule used as nanoparticle linker. We report large surface enhanced Raman scattering (SERS) enhancements for R6G when using linked-gold nano-assemblies as a SERS substrate. A discussion about the main origins for the large enhancement of molecular vibrational modes is presented. This work at Hampton University was supported by the National Science Foundation (HRD-0734635 and HRD-0630372).

  14. Simulation of dimer diffusion on metal fcc (001)surfaces by molecular dynamics

    Institute of Scientific and Technical Information of China (English)

    LIU; Qingwei; ZHUANG; Jun

    2004-01-01

    We study systematically the dimer diffusion on metal fcc (001) surfaces through molecular dynamics calculations based on embedded atom method. Besides the conventional hopping and exchange mechanisms, some other interesting diffusion mechanisms are observed, such as the exchange rotation mechanism, the cooperative hopping mechanism, and the cooperative exchange mechanism. On the different kinds of metal surfaces, we find that not only the dominant diffusion mechanism but also the physical model for the exchange mechanism is different.

  15. Materials and devices for quantum information processing in Si/SiGe

    Energy Technology Data Exchange (ETDEWEB)

    Sailer, Juergen

    2010-12-15

    , starting from Si/SiGe 2DES, further reduce the degree of freedom of the motion of the electrons. This is accomplished by nano-structured Palladium (Pd) Schottky top-gates on the sample surface with which it is possible to selectively and precisely adjust the 2D sheet carrier density in a leakage and hysteresis free manner. Using this technique, it was possible to realize an electrostatically defined double quantum dot (DQD) in Si/SiGe. By adjusting the gate bias, the DQD could be tuned from the many electron regime, in which directly measurable current transport was still possible, all the way down to the few electron regime. In this few electron regime, current flow became unmeasurable small, which made the application of a charge sensing technique necessary. As a highly sensitive charge-sensor, another quantum dot nearby was used. Changes in the charge occupancy of the DQD smaller than one tenth of an elementary charge could be resolved. Suitability of the device for more sophisticated future experiments in QIP could be shown by measuring charge-stability-diagrams free of any unwanted charge reconfiguration events. (orig.)

  16. 与Si工艺兼容的Si/SiGe/Si HBT研究%The Study of Si/SiGe/Si HBT and Its Compatibility with Si Process

    Institute of Scientific and Technical Information of China (English)

    廖小平

    2001-01-01

    我们对Si/SiGe/Si HBT及其Si兼容工艺进行了研究,在研究了一些关键的单项工艺的基础上,提出了五个高速Si/SiGe/Si HBT结构和一个低噪声Si/SiGe/Si HBT结构,并已研制成功台面结构Si/SiGe/Si HBT和低噪声Si/SiGe/Si HBT,为进一步高指标的Si/SiGe/Si HBT的研究建立了基础.

  17. Numerical analysis of surface plasmon resonance effects on a rotational silver nanorod/nanoshell dimer

    Science.gov (United States)

    Chou Chau, Yuan-Fong

    2013-06-01

    In this work, we numerically investigate the surface plasmon resonance (SPR) effects on a pair of rotational silver nanorod/nanoshell dimer with a finite height of 1000 nm by means of finite element method with three dimensional calculation. The rotational angles of the silver nanorod/nanoshell dimer are chosen θ=0°, θ=25°, θ=45° and θ=90°, respectively. The proposed structure exhibits a red-shifted localized SPR that can tuned over an extended wavelength range by varying the dielectric constant in metal nanoshell and the rotational angle of the silver nanorod/nanoshell dimer. The tunable optical properties on SPR phenomena are attributed to the rotational effect and a larger effective size of dielectric constant that is filled with a higher refractive medium of finite height of metal nanorod/nanoshell. This unique property of a pair of rotational nanorod/nanoshell dimer is highly attractive for serving as resonant center to hold and probe smaller nanostructures, such as biomolecules or quantum dots. Such structures also show significant promise for applications in nano-switch devices, sensing, and surface-enhanced spectroscopy, due to their strong and tunable plasmon resonances.

  18. DESIGN AND FABRICATION OF Si/SiGe PMOSFETs

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    Based on theoretical analysis and computer-aided simulation, optimized design prin-ciples for Si/SiGe PMOSFET are given in this paper, which include choice of gate materials, determination of germanium percentage and profile in SiGe channel, optimization of thickness of dioxide and silicon cap layer, and adjustment of threshold voltage.In the light of these principles, a SiGe PMOSFET is designed and fabricated successfully.Measurement indicates that the SiGe PMOSFET's(L=2μ同洒45 mS/mm(300K) and 92 mS/mm(77K) ,while that is 33mS/mm (300K) and 39mS/mm (77K) in Si PMOSFET with the same structure.

  19. DESIGN AND FABRICATION OF Si/SiGe PMOSFETs

    Institute of Scientific and Technical Information of China (English)

    Yang Peifeng; Zhang Jing; Yi Qiang; Fan Zerui; Li Jingchun; Yu Qi; Wang Xiangzhan; Yang Mohua; He Lin; Li Kaicheng; Tan Kaizhou; Liu Daoguang

    2002-01-01

    Based on theoretical analysis and computer-aided simulation, optimized design principles for Si/SiGe PMOSFET are given in this paper, which include choice of gate materials,determination of germanium percentage and profile in SiGe channel, optimization of thickness of dioxide and silicon cap layer, and adjustment of threshold voltage. In the light of these principles,a SiGe PMOSFET is designed and fabricated successfully. Measurement indicates that the SiGe PMOSFET's (L=2μm) transconductance is 45 mS/mm (300K) and 92mS/mm (77K), while that is 33 mS/mm (300K) and 39mS/mm (77K) in Si PMOSFET with the same structure.

  20. Accurate correlated calculation of the intermolecular potential surface in the coronene dimer

    Science.gov (United States)

    Janowski, Tomasz; Ford, Alan R.; Pulay, Peter

    2010-02-01

    The binding energy of the coronene dimer was determined by high level ab initio calculations. In the first step a potential energy surface was determined for the stacked dimer at the SCS-MP2/aTZ level. The energy of the stacked parallel dimer was scanned with respect to the lateral displacement of the two molecules at various interplane distances, and the minima and saddle points were determined. These results were refined by high level quadratic CI (QCISD(T)/aDZ) calculations. The aTZ and aDZ basis sets employed are derived from the aug-cc-pVDZ and aug-cc-pVTZ basis sets but diffuse functions are placed only at every second carbon atom, alleviating the severe numerical difficulties of the full augmented basis sets while retaining all important contributions. To estimate the QCISD(T) energies for larger basis set, we employed commonly used procedure of adding basis set correction values obtained at the MP2 level. This hybrid scheme was used to obtain the final optimised geometries and binding energies; these are believed to be close approximations to the basis set limit QCISD(T) values. A few calculations were also performed to the T-shaped conformer, although this is less important in the coronene dimer than in the benzene dimer. The high-level results were used as a benchmark to assess the performance of simpler and less expensive ab initio methods for these large rings with small HOMO-LUMO gaps, for instance the SCS-MP2 method, and modern DFT versions that are optimised for dispersion dominated systems.

  1. Sidewall damage in plasma etching of Si/SiGe heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Ding, R.; Klein, L. J.; Friesen, Mark G.; Eriksson, M. A.; Wendt, A. E. [Materials Science Program, University of Wisconsin-Madison, Madison, Wisconsin 53706 (United States); IBM TJ Watson Research Center, Yorktown Heights, New York 10598 (United States); Department of Physics, University of Wisconsin-Madison, Madison, Wisconsin 53706 (United States); Department of Electrical and Computer Engineering, University of Wisconsin-Madison, Madison, Wisconsin 53706 (United States)

    2009-07-15

    Plasma etching is a critical tool in the fabrication of Si/SiGe heterostructure quantum devices, but it also presents challenges, including damage to etched feature sidewalls that affects device performance. Chemical and structural changes in device feature sidewalls associated with plasma-surface interactions are considered damage, as they affect band structure and electrical conduction in the active region of the device. Here the authors report the results of experiments designed to better understand the mechanisms of plasma-induced sidewall damage in modulation-doped Si/SiGe heterostructures containing a two-dimensional electron gas. Damage to straight wires fabricated in the heterostructure using plasma etching was characterized both by measuring the width of the nonconductive ''sidewall depletion'' region at the device sidewall and by measuring the noise level factor {gamma}{sub H}/N determined from spectra of the low frequency noise. Observed increases in sidewall depletion width with increasing etch depth are tentatively attributed to the increase in total number of sidewall defects with increased plasma exposure time. Excess negative charge trapped on the feature sidewall could be another contributing factor. Defects at the bottom of etched features appear to contribute minimally. The noise level shows a minimum at an ion bombardment energy of {approx}100 eV, while the sidewall depletion width is independent of bias voltage, within experimental uncertainty. A proposed explanation of the noise trend involves two competing effects as ion energy increases: the increase in damage caused by each bombarding ion and the reduction in total number of incident ions due to shorter etch times.

  2. Hybrid Structures for Surface-Enhanced Raman Scattering: DNA Origami/Gold Nanoparticle Dimer/Graphene.

    Science.gov (United States)

    Prinz, Julia; Matković, Aleksandar; Pešić, Jelena; Gajić, Radoš; Bald, Ilko

    2016-10-01

    A combination of three innovative materials within one hybrid structure to explore the synergistic interaction of their individual properties is presented. The unique electronic, mechanical, and thermal properties of graphene are combined with the plasmonic properties of gold nanoparticle (AuNP) dimers, which are assembled using DNA origami nanostructures. This novel hybrid structure is characterized by means of correlated atomic force microscopy and surface-enhanced Raman scattering (SERS). It is demonstrated that strong interactions between graphene and AuNPs result in superior SERS performance of the hybrid structure compared to their individual components. This is particularly evident in efficient fluorescence quenching, reduced background, and a decrease of the photobleaching rate up to one order of magnitude. The versatility of DNA origami structures to serve as interface for complex and precise arrangements of nanoparticles and other functional entities provides the basis to further exploit the potential of the here presented DNA origami-AuNP dimer-graphene hybrid structures.

  3. Analysis of Si/SiGe Heterostructure Solar Cell

    Directory of Open Access Journals (Sweden)

    Ashish Kumar Singh

    2014-01-01

    Full Text Available Sunlight is the largest source of carbon-neutral energy. Large amount of energy, about 4.3 × 1020 J/hr (Lewis, 2005, is radiated because of nuclear fusion reaction by sun, but it is unfortunate that it is not exploited to its maximum level. Various photovoltaic researches are ongoing to find low cost, and highly efficient solar cell to fulfil looming energy crisis around the globe. Thin film solar cell along with enhanced absorption property will be the best, so combination of SiGe alloy is considered. The paper presented here consists of a numerical model of Si/Si1-xGex heterostructure solar cell. The research has investigated characteristics such as short circuit current density (Jsc, generation rate (G, absorption coefficient (α, and open circuit voltage (Voc with optimal Ge concentration. The addition of Ge content to Si layer will affect the property of material and can be calculated with the use of Vegard’s law. Due to this, short circuit current density increases.

  4. STEM-EELS analysis of multipole surface plasmon modes in symmetry-broken AuAg nanowire dimers

    Science.gov (United States)

    Schubert, Ina; Sigle, Wilfried; van Aken, Peter A.; Trautmann, Christina; Toimil-Molares, Maria Eugenia

    2015-03-01

    Surface plasmon coupling in nanowires separated by small gaps generates high field enhancements at the position of the gap and is thus of great interest for sensing applications. It is known that the nanowire dimensions and in particular the symmetry of the structures has strong influence on the plasmonic properties of the dimer structure. Here, we report on multipole surface plasmon coupling in symmetry-broken AuAg nanowire dimers. Our dimers, consisting of two nanowires with different lengths and separated by gaps of only 10 to 30 nm, were synthesized by pulsed electrochemical deposition in ion track-etched polymer templates. Electron energy-loss spectroscopy in scanning transmission electron microscopy allows us to resolve up to nine multipole order surface plasmon modes of these dimers spectrally separated from each other. The spectra evidence plasmon coupling between resonances of different multipole order, resulting in the generation of additional plasmonic modes. Since such complex structures require elaborated synthesis techniques, dimer structures with complex composition, morphology and shape are created. We demonstrate that finite element simulations on pure Au dimers can predict the generated resonances in the fabricated structures. The excellent agreement of our experiment on AuAg dimers with finite integration simulations using CST microwave studio manifests great potential to design complex structures for sensing applications.

  5. Si/SiO2/p-Si结构的电学特性

    Institute of Scientific and Technical Information of China (English)

    马自军; 马书懿

    2008-01-01

    用射频磁控溅射法在p-Si衬底上制备了Si/SiO2薄膜,利用Au/(Si/SiO2)/p-Si结构的I-V特性曲线对其电学特性进行了分析.结果表明,样品具有很好的整流作用,起整流作用的势垒存在于(Si/SiO2)/p-Si界面附近.

  6. Electroluminescence from Si/SiO2 films deposited on p-Si substrates

    Institute of Scientific and Technical Information of China (English)

    马书懿; 萧勇; 陈辉

    2002-01-01

    The structure of Au/Si/SiO2/p-Si has been fabricated using the magnetron sputtering technique. It has a verygood rectifying behaviour. Visible electroluminescence (EL) has been observed from the Au/Si/SiO2/p-Si structureat a forward bias of 5V or larger. A broad band with one peak around 650-660 nm appears in all the EL spectra ofthe structure. The effects of the thickness of the Si layer in the Si/SiO2 films and of the input electrical power on ELspectra are studied systematically.

  7. Explicit correlation treatment of the potential energy surface of CO{sub 2} dimer

    Energy Technology Data Exchange (ETDEWEB)

    Kalugina, Yulia N., E-mail: kalugina@phys.tsu.ru [Tomsk State University, 36 Lenin Ave., Tomsk 634050 (Russian Federation); Buryak, Ilya A. [Obukhov Institute of Atmospheric Physics, Russian Academy of Sciences, Moscow (Russian Federation); Chemistry Department, Lomonosov Moscow State University, Moscow (Russian Federation); Ajili, Yosra [Université Paris-Est, Laboratoire Modélisation et Simulation Multi Echelle, MSME UMR 8208 CNRS, 5 Bd Descartes, 77454 Marne-La-Vallée (France); Laboratoire de Spectroscopie Atomique, Moléculaire et Applications - LSAMA Université de Tunis El Manar (Tunisia); Vigasin, Andrei A. [Obukhov Institute of Atmospheric Physics, Russian Academy of Sciences, Moscow (Russian Federation); Jaidane, Nejm Eddine [Laboratoire de Spectroscopie Atomique, Moléculaire et Applications - LSAMA Université de Tunis El Manar (Tunisia); Hochlaf, Majdi [Université Paris-Est, Laboratoire Modélisation et Simulation Multi Echelle, MSME UMR 8208 CNRS, 5 Bd Descartes, 77454 Marne-La-Vallée (France)

    2014-06-21

    We present an extensive study of the four-dimensional potential energy surface (4D-PES) of the carbon dioxide dimer, (CO{sub 2}){sub 2}. This PES is developed over the set of intermolecular coordinates. The electronic computations are carried out at the explicitly correlated coupled cluster method with single, double, and perturbative triple excitations [CCSD(T)-F12] level of theory in connection with the augmented correlation-consistent aug-cc-pVTZ basis set. An analytic representation of the 4D-PES is derived. Our extensive calculations confirm that “Slipped Parallel” is the most stable form and that the T-shaped structure corresponds to a transition state. Later on, this PES is employed for the calculations of the vibrational energy levels of the dimer. Moreover, the temperature dependence of the dimer second virial coefficient and of the first spectral moment of rototranslational collision-induced absorption spectrum is derived. For both quantities, a good agreement is found between our values and the experimental data for a wide range of temperatures. This attests to the high quality of our PES. Generally, our PES and results can be used for modeling CO{sub 2} supercritical fluidity and examination of its role in planetary atmospheres. It can be also incorporated into dynamical computations of CO{sub 2} capture and sequestration. This allows deep understanding, at the microscopic level, of these processes.

  8. Theoretic Study on Band Structure of Si/SiNx Multilayer Film%Si/SiNx多层膜能带结构的理论研究

    Institute of Scientific and Technical Information of China (English)

    徐明; 魏屹; 何贤模; 芦伟

    2010-01-01

    利用Kronig-Penney模型计算了Si/SiNx多层膜结构中Si亚层的能带结构.结果表明,无论是减少Si或Si/SiNx亚层的厚度都将导致Si层的带隙发生宽化,计算结果与实验值符合较好.进而还发现,当Si层厚度减小时,Si/SiNx多层膜结构中载流子(电子和空穴)的有效质量均减小,有利于对载流子复合发光的控制.计算结果对实验上研究发光可控的Si/SiNx多层膜结构有重要指导意义.

  9. Polymerization or Cyclic Dimerization: Solvent Dependent Homo-Coupling of Terminal Alkynes at HOPG Surface

    Science.gov (United States)

    Zhang, Xuemei; Liao, Lingyan; Wang, Shuai; Hu, Fangyun; Wang, Chen; Zeng, Qingdao

    2014-01-01

    Surface reactivity has become one of the most important issues in surface chemistry over the past few years. In this work, we, for the first time, have investigated the homo-coupling of a special terminal alkyne derivative on the highly oriented pyrolitic graphite (HOPG) surface. Using scanning tunneling microscopy (STM) technique, we have found that such coupling reaction seriously depends on the supramolecular assembly of the monomer on the studied substrate, whereas the latter appears an obvious solvent effect. As a result, the reaction in our system undergoes polymerization and cyclic dimerization process in 1-phenyloctane and 1,2,4-trichlorobenzene, respectively. That is to say, the solvent effect can be extended from the two-dimensional (2D) supramolecular self-assembly to surface chemical reactions, and the selective homo-coupling has been successfully achieved at the solid/liquid interface.

  10. Experimental and Theoretical Study of the Rotation of Si Ad-dimers on the Si(100) Surface

    DEFF Research Database (Denmark)

    Swartzentruber, B. S.; Smith, A. P.; Jonsson, Hannes

    1996-01-01

    Scanning tunneling microscopy measurements and first principles density functional theory calculations are used to study the rate of the rotational transition of Si ad-dimers on top of the surface dimer rows of Si(100). The rotation rate and the relative population of the two stable orientations ...... of the ad-dimers are measured as a function of the applied electric field to extract the zero-field behavior. The measured relative stability of the two configurations is used to test the accuracy of various functionals for density functional theory calculations....

  11. Structural transformation of Ge dimers on Ge(001) surfaces induced by bias voltage

    Institute of Scientific and Technical Information of China (English)

    Qin Zhi-Hui; Shi Dong-Xia; Gao Hong-Jun

    2008-01-01

    Scanning tunnelling microscopy is utilized to investigate the local bias voltage tunnelling dependent transformation between (2×1) and c(4×2) structures on Ge(001) surfaces, which is reversibly observed at room temperature and a critical bias voltage of -0.80 V. Similar transformation is also found on an epitaxial Ge islands but at a slightly different critical bias voltage of -1.00V. It is found that the interaction between the topmost atoms on the STM tip and the atoms of the dimers, and the pinning effect induced by Sb atoms, the vacancies or the epitaxial clusters, can drive the structural transformation at the critical bias voltage.

  12. Optimization of Waveguide Structure for Tunable Optical Switch in Si/SiGe System

    Institute of Scientific and Technical Information of China (English)

    Seongjae Boo; Won-Taek Han

    2003-01-01

    A new electro-optical device using Si/SiGe-system with two parallel ridge waveguides is proposed for optical switching and the optimization of the structure for a single mode operation is investigated.

  13. Quantum wells based on Si/SiO{sub x} stacks for nanostructured absorbers

    Energy Technology Data Exchange (ETDEWEB)

    Berghoff, B.; Suckow, S.; Roelver, R.; Spangenberg, B.; Kurz, H. [Institute of Semiconductor Electronics, RWTH Aachen University, Sommerfeldstr. 24, 52074 Aachen (Germany); Sologubenko, A.; Mayer, J. [Central Facility for Electron Microscopy, RWTH Aachen University, Ahornstr. 55, 52074 Aachen (Germany); Ernst Ruska Centre for Microscopy and Spectroscopy with Electrons, Research Centre Juelich, 52426 Juelich (Germany)

    2010-11-15

    We report on electrical transport and quantum confinement in thermally annealed Si/SiO{sub x} multiple quantum well (QW) stacks. Results are correlated with the morphology of the stacks. High temperature annealing of Si/SiO{sub x} stacks leads to precipitation of excess Si from the SiO{sub x} layers, which enhances the degree of crystallization and increases the grain sizes in the Si QWs compared to the conventional Si/SiO{sub 2} system. Moreover, the excess Si forms highly conductive pathways between adjacent Si QWs that are separated by ultrathin silicon oxide barriers. This results in an increase of conductivity by up to 10 orders of magnitude compared to the tunneling dominated transport in Si/SiO{sub 2} stacks. The stacks exhibit a distinct quantum confinement as confirmed by photoluminescence measurements. (author)

  14. C-V and DLTS studies of radiation induced Si-SiO2 interface defects

    Science.gov (United States)

    Capan, I.; Janicki, V.; Jacimovic, R.; Pivac, B.

    2012-07-01

    Interface traps at the Si-SiO2 interface have been and will be an important performance limit in many (future) semiconductor devices. In this paper, we present a study of fast neutron radiation induced changes in the density of Si-SiO2 interface-related defects. Interface related defects (Pb centers) are detected before and upon the irradiation. The density of interface-related defects is increasing with the fast neutron fluence.

  15. On the c-Si/SiO2 interface recombination parameters from photo-conductance decay measurements

    Science.gov (United States)

    Bonilla, Ruy S.; Wilshaw, Peter R.

    2017-04-01

    The recombination of electric charge carriers at semiconductor surfaces continues to be a limiting factor in achieving high performance optoelectronic devices, including solar cells, laser diodes, and photodetectors. The theoretical model and a solution algorithm for surface recombination have been previously reported. However, their successful application to experimental data for a wide range of both minority excess carrier concentrations and dielectric fixed charge densities has not previously been shown. Here, a parametrisation for the semiconductor-dielectric interface charge Q i t is used in a Shockley-Read-Hall extended formalism to describe recombination at the c-Si/SiO2 interface, and estimate the physical parameters relating to the interface trap density D i t , and the electron and hole capture cross-sections σ n and σ p . This approach gives an excellent description of the experimental data without the need to invoke a surface damage region in the c-Si/SiO2 system. Band-gap tail states have been observed to limit strongly the effectiveness of field effect passivation. This approach provides a methodology to determine interface recombination parameters in any semiconductor-insulator system using macro scale measuring techniques.

  16. Constrained Broyden Dimer Method with Bias Potential for Exploring Potential Energy Surface of Multistep Reaction Process.

    Science.gov (United States)

    Shang, Cheng; Liu, Zhi-Pan

    2012-07-10

    To predict the chemical activity of new matter is an ultimate goal in chemistry. The identification of reaction pathways using modern quantum mechanics calculations, however, often requires a high demand in computational power and good chemical intuition on the reaction. Here, a new reaction path searching method is developed by combining our recently developed transition state (TS) location method, namely, the constrained Broyden dimer method, with a basin-filling method via bias potentials, which allows the system to walk out from the energy traps at a given reaction direction. In the new method, the reaction path searching starts from an initial state without the need for preguessing the TS-like or final state structure and can proceed iteratively to the final state by locating all related TSs and intermediates. In each elementary reaction step, a reaction direction, such as a bond breaking, needs to be specified, the information of which is refined and preserved as a normal mode through biased dimer rotation. The method is tested successfully on the Baker reaction system (50 elementary reactions) with good efficiency and stability and is also applied to the potential energy surface exploration of multistep reaction processes in the gas phase and on the surface. The new method can be applied for the computational screening of new catalytic materials with a minimum requirement of chemical intuition.

  17. Si/SiGe/Si HBT的直流特性和低频噪声%Si/SiGe/Si HBT's DC Characterization and Its Low-frequency Noise

    Institute of Scientific and Technical Information of China (English)

    廖小平; 张中平

    2003-01-01

    在对Si/SiGe/Si HBT及其Si兼容工艺的研究基础上,研制成功低噪声Si/SiGe/Si HBT,测试和分析了它的直流特性和低频噪声特性,为具有更好的低噪声性能的Si/SiGe/Si HBT的研究建立了基础.

  18. Scattering mechanisms in shallow undoped Si/SiGe quantum wells

    Directory of Open Access Journals (Sweden)

    D. Laroche

    2015-10-01

    Full Text Available We report the magneto-transport study and scattering mechanism analysis of a series of increasingly shallow Si/SiGe quantum wells with depth ranging from ∼ 100 nm to ∼ 10 nm away from the heterostructure surface. The peak mobility increases with depth, suggesting that charge centers near the oxide/semiconductor interface are the dominant scattering source. The power-law exponent of the electron mobility versus density curve, μ ∝ nα, is extracted as a function of the depth of the Si quantum well. At intermediate densities, the power-law dependence is characterized by α ∼ 2.3. At the highest achievable densities in the quantum wells buried at intermediate depth, an exponent α ∼ 5 is observed. We propose and show by simulations that this increase in the mobility dependence on the density can be explained by a non-equilibrium model where trapped electrons smooth out the potential landscape seen by the two-dimensional electron gas.

  19. Fabrication and measurement of devices in Si/SiGe nanomembranes

    Science.gov (United States)

    Mohr, Robert

    Silicon/silicon-germanium (Si/SiGe) heterostructures are useful as hosts for gated quantum dots. The quality of the as-grown Si/SiGe heterostructure has a large impact on the final quality of the quantum dot as a qubit host. For many years, quantum dots have been fab- ricated on strain-graded heterostructures. Commonly used strain-graded heterostructures inevitably develop plastic defects that lead to interface roughness, crosshatch, and mosaic tilt. All of these factors are sources of disorder in Si/SiGe quantum electronics. In this dissertation, I report the fabrication of Hall bars and gated quantum dots on heterostructures grown on fully elastically relaxed SiGe nanomembranes, rather than strain-graded heterostructures. I report measurements of Hall bars demonstrating the creation of two-dimensional electron gases in these structures. I report the fabrication procedures used to create pairs of Hall bars and quantum dots on individual membranes. In addition, I explain a general process flow for the creation of Si/SiGe quantum devices. I focus especially on an ion-implantation technique I implemented for the fabrication of Hall bars and quantum dots in Si/SiGe heterostructures without modulation doping layers.

  20. Identification of Dimeric Methylalumina Surface Species during Atomic Layer Deposition Using Operando Surface-Enhanced Raman Spectroscopy.

    Science.gov (United States)

    Hackler, Ryan A; McAnally, Michael O; Schatz, George C; Stair, Peter C; Van Duyne, Richard P

    2017-02-15

    Operando surface-enhanced Raman spectroscopy (SERS) was used to successfully identify hitherto unknown dimeric methylalumina surface species during atomic layer deposition (ALD) on a silver surface. Vibrational modes associated with the bridging moieties of both trimethylaluminum (TMA) and dimethylaluminum chloride (DMACl) surface species were found during ALD. The appropriate monomer vibrational modes were found to be absent as a result of the selective nature of SERS. Density functional theory (DFT) calculations were also performed to locate and identify the expected vibrational modes. An operando localized surface plasmon resonance (LSPR) spectrometer was utilized to account for changes in SER signal as a function of the number of ALD cycles. DMACl surface species were unable to be measured after multiple ALD cycles as a result of a loss in SERS enhancement and shift in LSPR. This work highlights how operando optical spectroscopy by SERS and LSPR scattering are useful for probing the identity and structure of the surface species involved in ALD and, ultimately, catalytic reactions on these support materials.

  1. High performance amorphous-Si@SiOx/C composite anode materials for Li-ion batteries derived from ball-milling and in situ carbonization

    Science.gov (United States)

    Wang, Dingsheng; Gao, Mingxia; Pan, Hongge; Wang, Junhua; Liu, Yongfeng

    2014-06-01

    Amorphous-Si@SiOx/C composites with amorphous Si particles as core and coated with a double layer of SiOx and carbon are prepared by ball-milling crystal micron-sized silicon powders and carbonization of the citric acid intruded in the ball-milled Si. Different ratios of Si to citric acid are used in order to optimize the electrochemical performance. It is found that SiOx exists naturally at the surfaces of raw Si particles and its content increases to ca. 24 wt.% after ball-milling. With an optimized Si to citric acid weight ratio of 1/2.5, corresponding to 8.4 wt.% C in the composite, a thin carbon layer is coated on the surfaces of a-Si@SiOx particles, moreover, floc-like carbon also forms and connects the carbon coated a-Si@SiOx particles. The composite provides a capacity of 1450 mA h g-1 after 100 cycles at a current density of 100 mA g1, and a capacity of 1230 mA h g-1 after 100 cycles at 500 mA g1 as anode material for lithium-ion batteries. Effects of ball-milling and the addition of citric acid on the microstructure and electrochemical properties of the composites are revealed and the mechanism of the improvement in electrochemical properties is discussed.

  2. W-Mo-Si/SiC Oxidation Protective Coating for Carbon/Carbon Composites

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    A W-Mo-Si/SiC double-layer oxidation protective coating for carbon/carbon (C/C) composites was prepared by a two-step pack cementation technique. XRD (X-ray diffraction) and SEM (scanning electron microscopy)results show that the coating obtained by the first step pack cementation was a thin inner buffer layer of SiC with some cracks and pores, and a new phase of (WxMo1-x)Si2 appeared after the second step pack cementation. Oxidation test shows that, after oxidation in air at 1773 K for 175 h and thermal cycling between 1773 K and room temperature for 18 times, the weight loss of the W-Mo-Si/SiC coated C/C composites was only 2.06%. The oxidation protective failure of the W-Mo-Si/SiC coating was attributed to the formation of some penetrable cracks in the coating.

  3. The origin of blue photoluminescence from nc-Si/SiO2 multilayers

    Institute of Scientific and Technical Information of China (English)

    Ma Zhong-Yuan; Xu Ling; Huang Xin-Fan; Chen Kun-Ji; Feng Duan; Guo Si-Hua; Chen De-Yuan; Wei De-Yuan; Yao Yao; Zhou Jiang; Huang Rui; Li Wei; Xu Jun

    2008-01-01

    Intensive blue photoluminescence (PL) was observed at room temperature from the nanocrystalline-Si/SiO2 (ncSi/SiO2) multilayers (MLs) obtained by thermal annealing of SiO/SiO2 MLs for the first time.By controlling the size of nc-Si formed in SiO sublayer from 3.5 to 1.5 nm,the PL peak blueshifts from 457 to 411 nm.Combining the analysis of TEM,Raman and absorption measurement,this paper attributes the blue PL to multiple luminescent centres at the interface of nc-Si and SiO2.

  4. Fabrication of Si/SiO2 Superlattice Microwire Array Solar Cells Using Microsphere Lithography

    Directory of Open Access Journals (Sweden)

    Shigeru Yamada

    2016-01-01

    Full Text Available A fabrication process for silicon/silicon dioxide (Si/SiO2 superlattice microwire array solar cells was developed. The Si/SiO2 superlattice microwire array was fabricated using a microsphere lithography process with polystyrene particles. The solar cell shows a photovoltaic effect and an open-circuit voltage of 128 mV was obtained. The limiting factors of the solar cell performance were investigated from the careful observations of the solar cell structures. We also investigated the influence of the microwire array structure on light trapping in the solar cells.

  5. Hydrogen Passivation Effect on Enhanced Luminescence from Nanocrystalline Si/SiO2 Multilayers

    Institute of Scientific and Technical Information of China (English)

    XIA Zheng-Yue; HAN Pei-Gao; XU Jun; CHEN De-Yuan; WEI De-Yuan; MA Zhong-Yuan; CHEN Kun-Ji; XU Ling; HUANG Xin-Fan

    2007-01-01

    Nanocrystalline Si/SiO2 multilayers are prepared by thermally annealing amorphous Si/SiO2 stacked structures.The photoluminescence intensity is obviously enhanced after hydrogen passivation at various temperatures. It is suggested that the hydrogen trapping and detrapping processes at different temperatures strongly influence the passivation effect. Direct experimental evidence is given by electron spin resonance spectra that hydrogen effectively reduces the nonradiative defect states existing in the Si nanocrystas/SiO2 system which enhances the radiative recombination probability. The luminescence characteristic shows its stability after hydrogen passivation even after aging eight months.

  6. Design and Manufacture of GeSi/Si Superlattice Nanocrystalline Photodetector

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    According to Maxwell's theory, the optical transmission characteristics in GeSi/Si superlattice nanocrystalline layer have been analyzed and calculated. The calculated result shows that when the total thickness L is 340nm, the single mode lightwave can be transmitted only at periodic number M≥15.5. In addition, at the direction of transmission, when the transmission distance is larger than 500μm, the lightwave intensity is decreased greatly. Based on the above parameters, the design and manufacture of GeSi/Si superlattice nanocrystalline photodetector are carried out.

  7. 3D nanostar dimers with a sub-10-nm gap for single-/few-molecule surface-enhanced raman scattering

    KAUST Repository

    Chirumamilla, Manohar

    2014-01-22

    Plasmonic nanostar-dimers, decoupled from the substrate, have been fabricated by combining electron-beam lithography and reactive-ion etching techniques. The 3D architecture, the sharp tips of the nanostars and the sub-10 nm gap size promote the formation of giant electric-field in highly localized hot-spots. The single/few molecule detection capability of the 3D nanostar-dimers has been demonstrated by Surface-Enhanced Raman Scattering. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  8. Interface properties of Si-SiO{sub 2}-Ta{sub 2}O{sub 5} structure by cathodoluminescence spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Baraban, A. P.; Dmitriev, V. A.; Drozd, V. E.; Prokofiev, V. A.; Filatova, E. O. [St. Petersburg State University, St. Petersburg 198504 (Russian Federation); Samarin, S. N. [St. Petersburg State University, St. Petersburg 198504 (Russian Federation); School of Physics, The University of Western Australia, Perth, Western Australia 6009 (Australia)

    2016-02-07

    We studied formation of the SiO{sub 2}-T{sub 2}O{sub 5} interface in the Si-SiO{sub 2}-Ta{sub 2}O{sub 5} structure using Cathodoluminescence Spectroscopy (CLS). Analyzing the evolution of CLS spectrum of the Si-SiO{sub 2} structure while depositing the Ta{sub 2}O{sub 5} layer allowed to estimate an optical transmittance of the Ta{sub 2}O{sub 5} layer and its band gap. Spectral features related to the formation of the SiO{sub 2}-Ta{sub 2}O{sub 5} interface were identified by comparison of the experimental CL spectrum of the Si-SiO{sub 2}-Ta{sub 2}O{sub 5} structure and its simulated counterpart. This formation involves a decomposition of silanol groups at the outer surface of the SO{sub 2} layer and creation of the Si{sub x}Ta{sub y}O-type layer containing luminescence centers with the emission band centered at 3 eV photon energy.

  9. Oxidation of dimers at the Si(100) surface studied by first-principles simulation of high-resolution EELS

    Energy Technology Data Exchange (ETDEWEB)

    Caramella, Lucia; Onida, Giovanni [Dipartimento di Fisica dell' Universita' degli Studi di Milano (Italy); European Theoretical Spectroscopy Facility (ETSF), Milano (Italy); Hogan, Conor; Del Sole, Rodolfo [Dipartimento di Fisica, Universita di Roma ' ' Tor Vergata' ' , Roma (Italy); ETSF and CNR-INFM-SMC, Roma (Italy)

    2010-08-15

    Electron energy loss spectra of the Si(100) and Si(100):O surfaces are investigated using ab initio methods based on density functional theory. Computed spectra for the clean surface are found to be in good agreement with published experimental data, providing further confirmation that reconstructions of higher order than (2 x 1) are present on Si(100). The origins of the main spectral structures are analyzed and their relation to the surface bandstructure is illustrated. Oxygen adsorption on the surface dimers is found to cause strong modifications to the calculated spectra, thereby partially explaining the results of surface differential reflectivity experiments. (Abstract Copyright [2010], Wiley Periodicals, Inc.)

  10. Toward 17µm pitch heterogeneously integrated Si/SiGe quantum well bolometer focal plane arrays

    Science.gov (United States)

    Ericsson, Per; Fischer, Andreas C.; Forsberg, Fredrik; Roxhed, Niclas; Samel, Björn; Savage, Susan; Stemme, Göran; Wissmar, Stanley; Öberg, Olof; Niklaus, Frank

    2011-06-01

    Most of today's commercial solutions for un-cooled IR imaging sensors are based on resistive bolometers using either Vanadium oxide (VOx) or amorphous Silicon (a-Si) as the thermistor material. Despite the long history for both concepts, market penetration outside high-end applications is still limited. By allowing actors in adjacent fields, such as those from the MEMS industry, to enter the market, this situation could change. This requires, however, that technologies fitting their tools and processes are developed. Heterogeneous integration of Si/SiGe quantum well bolometers on standard CMOS read out circuits is one approach that could easily be adopted by the MEMS industry. Due to its mono crystalline nature, the Si/SiGe thermistor material has excellent noise properties that result in a state-ofthe- art signal-to-noise ratio. The material is also stable at temperatures well above 450°C which offers great flexibility for both sensor integration and novel vacuum packaging concepts. We have previously reported on heterogeneous integration of Si/SiGe quantum well bolometers with pitches of 40μm x 40μm and 25μm x 25μm. The technology scales well to smaller pixel pitches and in this paper, we will report on our work on developing heterogeneous integration for Si/SiGe QW bolometers with a pixel pitch of 17μm x 17μm.

  11. Fluorescence enhancement of single DNA molecules confined in Si/SiO2 nanochannels

    DEFF Research Database (Denmark)

    Westerlund, F.; Persson, Karl Fredrik; Kristensen, Anders;

    2010-01-01

    We demonstrate that the detected emission intensity from YOYO-labeled DNA molecules confined in 180 nm deep Si/SiO2 nano-funnels changes significantly and not monotonically with the width of the funnel. This effect may be of importance for quantitative fluorescence microscopy and for experiments ...

  12. Electron transport in n-doped Si/SiGe quantum cascade structures

    NARCIS (Netherlands)

    Lazic, I.; Ikonic, Z.; Milanovic, V.; Kelsall, R.W.; Indjin, D.; Harrison, P.

    2007-01-01

    An electron transport model in n-Si/SiGe quantum cascade or superlattice structures is described. The model uses the electronic structure calculated within the effective-mass complex-energy framework, separately for perpendicular (Xz) and in-plane (Xxy) valleys, the degeneracy of which is lifted by

  13. Electron transport in n-doped Si/SiGe quantum cascade structures

    NARCIS (Netherlands)

    Lazic, I.; Ikonic, Z.; Milanovic, V.; Kelsall, R.W.; Indjin, D.; Harrison, P.

    2007-01-01

    An electron transport model in n-Si/SiGe quantum cascade or superlattice structures is described. The model uses the electronic structure calculated within the effective-mass complex-energy framework, separately for perpendicular (Xz) and in-plane (Xxy) valleys, the degeneracy of which is lifted by

  14. Influence of Thermal Shock on the Mechanical Behavior of Si-SiC Coated Carbon/Carbon Composites

    Institute of Scientific and Technical Information of China (English)

    Qiangang Fu; Hejun Li; Yongjie Wang; Kezhi Li; Lu Wei

    2009-01-01

    Si-SiC coating was prepared on the surface of carbon/carbon (C/C) composites by a two-step technique of pack cementation, and the influences of thermal shock between 1773 K and room temperature in air on the mechanical property and fracture behavior of the coated C/C were studied. The results show that, after thermal shock between 1773 K and room temperature for 5, 10 and 15 times, the flexural strength of coated composites increases by 4.29%, 15.00% and 24.20%, respectively. The toughness of the coated C/C enhances gradually during the thermal shock test. The improvement of the mechanical property after the thermal shock test is primarily caused by the weakening of the fiber-matrix interface and the reduction of residual thermal stresses by thermal shock.

  15. Scaling of the Surface Plasmon Resonance in Gold and Silver Dimers Probed by EELS

    DEFF Research Database (Denmark)

    Kadkhodazadeh, Shima; de Lasson, Jakob Rosenkrantz; Beleggia, Marco

    2014-01-01

    with distance. Here, we have applied electron energy-loss spectroscopy (EELS) and scanning transmission electron microscopy (STEM) imaging to investigate the relationship between the SPR wavelength of gold and silver nanosphere dimers (radius R) and interparticle distance (d) in the range 0.1R .... Instead, within the range 0.1R gold and silver dimers. Despite this common power dependence, consistently larger SPR wavelength shifts are registered for silver for a given change in d, implying...... silver dimers to be more sensitive plasmon rulers than their gold counterparts....

  16. Growth and photoluminescence of Si-SiOx nanowires by catalyst-free chemical vapor deposition technique

    Energy Technology Data Exchange (ETDEWEB)

    Yu, Yue [School of Physics and Nuclear Energy Engineering, Beihang University, Beijing 100191 (China); Luo, Ruiying, E-mail: ryluo@buaa.edu.cn [School of Physics and Nuclear Energy Engineering, Beihang University, Beijing 100191 (China); School of Materials Science and Engineering, Shanxi University of Technology, Hanzhong 723000 (China); Shang, Haidong [School of Physics and Nuclear Energy Engineering, Beihang University, Beijing 100191 (China)

    2016-04-15

    Graphical abstract: - Highlights: • The Si-SiOx NWs were successfully synthesized via a one-step catalyst-free CVD method using TEOS as the precursor. • The Si-SiOx NWs had a core–shell structure with Si as the inner crystalline cores and SiOx as the outer amorphous layer. • The formation of Si-SiOx NWs was implemented by the non-classical crystallization mechanism. • The Si-SiOx NWs spontaneously self-assembled from the building block of charged nanoparticles. • The Si-SiOx NWs showed their potential applications in UV emission and visible light emission devices. - Abstract: We developed a one-step catalyst-free chemical vapor deposition process to synthesize Si-SiOx nanowires using tetraethoxysilane as the precursor. Observations using scanning electron microscopy showed that the Si-SiOx nanowires were 20–50 nm in diameter and tens of microns in length. The high-resolution transmission electron microscope analysis and X-ray diffraction demonstrated that the nanowires consisted of crystal silicon and amorphous SiOx. The Si and O with an atomic ratio of the Si-SiOx NWs were 1:1.2 according to the energy dispersion X-ray spectroscope. A systematic study on the effect of the growth conditions, such as reaction temperature, the reaction time, and the TEOS vapor flow rate was performed. The formation of Si-SiOx nanowires was implemented by the non-classical crystallization mechanism. The charged nanoparticles acting as building blocks self-assembled into nanowires. The photoluminescence measurements were carried out and showed that the Si-SiOx nanowires emitted stable ultraviolet and green luminescence excited by ultraviolet light.

  17. A comparative study of electroluminescence from Ge/SiO2 and Si/SiO2 films

    Institute of Scientific and Technical Information of China (English)

    Ma Shu-Yi; Chen Hui; Xiao Yong; Ma Zi-Jun; Sun Ai-Min

    2004-01-01

    Ge/SiO2 and Si/SiO2 films were deposited using the two-target alternation magnetron sputtering technique. The Au/Ge/SiO2/p-Si and Au/Si/SiO2/p-Si structures were fabricated and their electroluminescence (EL) characteristics were comparatively studied. Both Au/Ge/SiO2/p-Si and Au/Si/SiO2/p-Si structures have rectifying property. All the EL spectra from the two types of the structure have peak positions around 650-660 nm. The EL mechanisms of the structures are discussed.

  18. Oxide layer dissolution in Si/SiO{sub x}/Si wafer bonded structures

    Energy Technology Data Exchange (ETDEWEB)

    Pippel, E.; Werner, P.; Goesele, U. [Max-Planck-Institut fuer Mikrostrukturphysik, Halle (Germany); Vdovin, V. [Institute for Chemical Problems of Microelectronics, Moscow (Russian Federation); Institute of Rare Metals Giredmet, Moscow (Russian Federation); Zakharov, N.

    2009-10-15

    The evolution of the interfaces of hydrophilic-bonded Si wafers and the corresponding low-angle twist boundary have been analysed in relation to thermal annealing and their relative crystallographic orientation. Two orientation relationships were investigated: Si<001>/Si<001> and Si<001>/Si<110>, where the interfaces are separated by thin native SiO2 layers. The interfaces were analysed by TEM and STEM/EELS. It is found that the decomposition rate of the intermediate oxide layer and the formation of a Si-Si bonded interface depend very much on the lattice mismatch and on the twist angle. The velocity of the dissolution of the thin oxide layers and the formation of Si-Si bonds at the bonding interface depend on the orientation relations of the corresponding wafers. The processes of interface fusion and the dissolution of oxide layer are discussed. (copyright 2009 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  19. Nature of visible luminescence of co-sputtered Si-SiO{sub x} systems

    Energy Technology Data Exchange (ETDEWEB)

    Torchynska, T.; Becerril Espinoza, F.G.; Goldstein, Y.; Savir, E.; Jedrzejewski, J.; Khomenkova, L.; Korsunska, N.; Yukhimchuk, V

    2003-12-31

    Photoluminescence (PL) spectra and Raman scattering spectra of Si-SiO{sub x} systems, prepared by radio frequency magnetron sputtering method and thermal annealed at 1150 deg. C for creation of Si nano-crystallites, were investigated as a function of Si content and Si nano-crystallite sizes. It was shown that the PL spectrum of such systems consists of several bands with peak positions at 1.32-1.34, 1.42-1.58, 1.77, 2.05 and 2.30 eV. The dependencies of these PL band parameters on concentration and size of Si nano-crystallites in the Si-SiO{sub x} system have been investigated and analyzed. The nature of radiative optical transitions for all PL bands is discussed.

  20. Si/SiGe bound-to-continuum quantum cascade terahertz emitters

    Science.gov (United States)

    Paul, D. J.; Matmon, G.; Lever, L.; Ikonić, Z.; Kelsall, R. W.; Chrastina, D.; Isella, G.; von Känel, H.

    2008-04-01

    A review will be presented of recent work on Si/SiGe heavy-hole to heavy-hole quantum cascade emitters showing progress towards a laser using the bound-to-continuum design for the active region. The sample was grown by low energy plasma enhanced chemical vapour deposition in significantly less time than comparable structures and designs in III-V or Si/SiGe technology using molecular beam epitaxy or more standard chemical vapour deposition techniques. Clear intersubband electroluminescence is demonstrated at 4.2 K between 6.7 and 10.1 THz. This is inside the III-V restrahlung band where III-V materials cannot lase, unlike Group IV materials. A review of waveguide losses will also be presented and some ideas of how to design an active region with gain higher than the waveguide losses will be discussed.

  1. The property of Si/SiGe/Si heterostructure during thermal budget characterized by HRXRD

    Institute of Scientific and Technical Information of China (English)

    CHEN Chang-Chun; LIU Zhi-Hong; HUANG Wen-Tao; DOU Wei-Zhi; ZHANG Wei; TSIEN Pei-Hsin; ZHU De-Zhang

    2003-01-01

    Si/SiGe/Si heterostructures grown by ultra-high-vacuum chemical vapor deposition (UHVCVD) werecharacterized by Rutherford backscattering/Channeling (RBS/C) together with high resolution X ray diffraction(HRXRD). High quality SiGe base layer was obtained. The Si/SiGe/Si heterostructures were subject to conventionalfurnace annealing and rapid thermal annealing with temperature between 750 ℃ and 910 ℃. Both strain and its re-laxation degree in SiGe layer are calculated by HRXRD combined with elastic theory, which are never reported inother literatures. The rapid thermal annealing at elevated temperature between 880 ℃ and 910 ℃ for very short timehad almost no influence on the strain in Si0.84Ge0. 16 epilayer. However, high temperature (900℃) furnace annealingfor 1h prompted the strain in Si0.84Ge0.16 layer to relax.

  2. Long Spin Relaxation and Coherence Times of Electrons In Gated Si/SiGe Quantum Dots

    Science.gov (United States)

    He, Jianhua; Tyryshkin, A. M.; Lyon, S. A.; Lee, C.-H.; Huang, S.-H.; Liu, C. W.

    2012-02-01

    Single electron spin states in semiconductor quantum dots are promising candidate qubits. We report the measurement of 250 μs relaxation (T1) and coherence (T2) times of electron spins in gated Si/SiGe quantum dots at 350 mK. The experiments used conventional X-band (10 GHz) pulsed electron spin resonance (pESR), on a large area (3.5 x 20 mm^2) dual-gate undoped high mobility Si/SiGe heterostructure sample, which was patterned with 2 x 10^8 quantum dots using e-beam lithography. Dots having 150 nm radii with a 700 nm period are induced in a natural Si quantum well by the gates. The measured T1 and T2 at 350 mK are much longer than those of free 2D electrons, for which we measured T1 to be 10 μs and T2 to be 6.5 μs in this gated sample. The results provide direct proof that the effects of a fluctuating Rashba field have been greatly suppressed by confining the electrons in quantum dots. From 0.35 K to 0.8 K, T1 of the electron spins in the quantum dots shows little temperature dependence, while their T2 decreased to about 150 μs at 0.8 K. The measured 350 mK spin coherence time is 10 times longer than previously reported for any silicon 2D electron-based structures, including electron spins confined in ``natural quantum dots'' formed by potential disorder at the Si/SiO2ootnotetextS. Shankar et al., Phys. Rev. B 82, 195323 (2010) or Si/SiGe interface, where the decoherence appears to be controlled by spin exchange.

  3. Waveguide design for mid- and far-infrared p-Si/SiGe quantum cascade lasers

    Science.gov (United States)

    Ikonic, Z.; Kelsall, R. W.; Harrison, P.

    2004-01-01

    Design considerations are presented for waveguides to be used in p-Si/SiGe based quantum cascade lasers operating in the mid- and far-infrared wavelength ranges. Modal losses and confinement factors are calculated for both TM and TE modes in conventional double metal clad structures, metal-highly doped semiconductor layer structures and also in novel metal-metal silicide structures. Guidelines for choosing the confinement and contact layer parameters are given.

  4. Si/SiO2 quantum dots cause cytotoxicity in lung cells through redox homeostasis imbalance.

    Science.gov (United States)

    Stan, Miruna S; Memet, Indira; Sima, Cornelia; Popescu, Traian; Teodorescu, Valentin S; Hermenean, Anca; Dinischiotu, Anca

    2014-09-05

    Si/SiO2 quantum dots (QDs) are novel particles with unique physicochemical properties that promote them as potential candidates for biomedical applications. Although their interaction with human cells has been poorly investigated, oxidative stress appears to be the main factor involved in the cytotoxicity of these nanoparticles. In this study, we show for the first time the influence of Si/SiO2 QDs on cellular redox homeostasis and glutathione distribution in human lung fibroblasts. The nanoparticles morphology, composition and structure have been investigated using high resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), energy-dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD) analysis. MRC-5 cells (human lung fibroblasts) were incubated with various concentrations of Si/SiO2 QDs ranging between 25 and 200 μg/mL for up to 72 h. The results of the MTT and sulforhodamine B assays showed that exposure to QDs led to a time-dependent decrease in cell viability and biomass. The increase in reactive oxygen species (ROS) and malondialdehyde (MDA) levels together with the lower glutathione content suggested that the cellular redox homeostasis was altered. Regarding GSH distribution, the first two days of treatment resulted in a localization of GSH mainly in the cytoplasm, while at longer incubation time the nuclear/cytoplasmic ratio indicated a nuclear localization. These modifications of cell redox state also affected the redox status of proteins, which was demonstrated by the accumulation of oxidized proteins and actin S-glutathionylation. In addition, the externalization of phosphatidylserine provided evidence that apoptosis might be responsible for cell death, but necrosis was also revealed. Our results suggest that Si/SiO2 quantum dots exerted cytotoxicity on MRC-5 cells by disturbing cellular homeostasis which had an effect upon protein redox status.

  5. Thermal oxidation of Si/SiGe heterostructures for use in quantum dot qubits

    Science.gov (United States)

    Neyens, Samuel F.; Foote, Ryan H.; Knapp, T. J.; McJunkin, Thomas; Savage, D. E.; Lagally, M. G.; Coppersmith, S. N.; Eriksson, M. A.

    Here we demonstrate dry thermal oxidation of a Si/SiGe heterostructure at 700°C and use a Hall bar device to measure the mobility after oxidation to be 43,000 cm2V-1s-1 at a carrier density of 4.1 ×1011 cm-2. Surprisingly, we find no significant reduction in mobility compared with an Al2O3 device made with atomic layer deposition on the same heterostructure, indicating thermal oxidation can be used to process Si/SiGe quantum dot devices. This result provides a path for investigating improvements to the gate oxide in Si/SiGe qubit devices, whose performance is believed to be limited by charge noise in the oxide layer. This work was supported in part by ARO (W911NF-12-0607) and NSF (DMR-1206915 and PHY-1104660). Development and maintenance of the growth facilities used for fabricating samples is supported by DOE (DE-FG02-03ER46028). This research utilized NSF-supported shared facilities at the University of Wisconsin-Madison.

  6. The effect of donors on lateral gated quantum-devices in Si/SiGe heterostructures

    Science.gov (United States)

    Lin, Xi; Hu, Jingshi; Lai, A.; Zhang, Z.; Maclean, K.; Xie, Y. H.; Kastner, M. A.

    2011-03-01

    Much activity has focused on the development of quantum dots in Si/SiGe because of its potentially very long decoherence times (T2). However, to fabricate well-controlled quantum dots in Si/SiGe heterostructures, one must overcome complications that do not arise in GaAs/AlGaAs heterostructures. We demonstrate that switching charge noise and donor-layer conduction can lead to instability and cross-coupling among the tunnel barriers, thus making it difficult to achieve highly stable and tunable quantum devices in a Si/SiGe heterostructure. In particular, we have used an integrated charge-sensing quantum point contact to investigate the charge motion that originates from the excess donors, and present a systematic capacitance measurement to show how the donor layer affects device function in devices with large (~ 100 μ m 2) gates as well as nanometer-size ones. This work has been supported by the Nanoscale Science and Engineering Center program of NSF (PHY-0117795), NSF (DMR-0701386).

  7. Superconducting single electron transistor for charge sensing in Si/SiGe-based quantum dots

    Science.gov (United States)

    Yang, Zhen

    Si-based quantum devices, including Si/SiGe quantum dots (QD), are promising candidates for spin-based quantum bits (quits), which are a potential platform for quantum information processing. Meanwhile, qubit readout remains a challenging task related to semiconductor-based quantum computation. This thesis describes two readout devices for Si/SiGe QDs and the techniques for developing them from a traditional single electron transistor (SET). By embedding an SET in a tank circuit and operating it in the radio-frequency (RF) regime, a superconducting RF-SET has quick response as well as ultra high charge sensitivity and can be an excellent charge sensor for the QDs. We demonstrate such RF-SETs for QDs in a Si/SiGe heterostructure. Characterization of the SET in magnetic fields is studied for future exploration of advanced techniques such as spin detection and spin state manipulation. By replacing the tank circuit with a high-quality-factor microwave cavity, the embedded SET will be operated in the supercurrent regime as a single Cooper pair transistor (CPT) to further increase the charge sensitivity and reduce any dissipation. The operating principle and implementation of the cavity-embedded CPT (cCPT) will be introduced.

  8. Carrier recombination in tailored multilayer Si/Si{sub 1−x}Ge{sub x} nanostructures

    Energy Technology Data Exchange (ETDEWEB)

    Mala, S.A. [Department of Electrical and Computer Engineering, New Jersey Institute of Technology, Newark, NJ 07102 (United States); Tsybeskov, L., E-mail: tsybesko@njit.edu [Department of Electrical and Computer Engineering, New Jersey Institute of Technology, Newark, NJ 07102 (United States); Lockwood, D.J.; Wu, X.; Baribeau, J.-M. [National Research Council, Ottawa, ON, Canada KIA 0R6 (Canada)

    2014-11-15

    Photoluminescence (PL) measurements were performed in Si/Si{sub 1−x}Ge{sub x} nanostructures with a single Si{sub 0.92}Ge{sub 0.08} nanometer-thick layer incorporated into Si/Si{sub 0.6}Ge{sub 0.4} cluster multilayers. Under pulsed laser excitation, the PL decay associated with the Si{sub 0.92}Ge{sub 0.08} nano-layer is found to be nearly a 1000 times faster compared to that in Si/Si{sub 0.6}Ge{sub 0.4} cluster multilayers. A model considering Si/SiGe hetero-interface composition and explaining the fast and slow time-dependent recombination rates is proposed.

  9. C-V and DLTS studies of radiation induced Si-SiO{sub 2} interface defects

    Energy Technology Data Exchange (ETDEWEB)

    Capan, I., E-mail: capan@irb.hr [Rudjer Boskovic Institute, 10000 Zagreb (Croatia); Janicki, V. [Rudjer Boskovic Institute, 10000 Zagreb (Croatia); Jacimovic, R. [Jozef Stefan Institute, 1000 Ljubljana (Slovenia); Pivac, B. [Rudjer Boskovic Institute, 10000 Zagreb (Croatia)

    2012-07-01

    Interface traps at the Si-SiO{sub 2} interface have been and will be an important performance limit in many (future) semiconductor devices. In this paper, we present a study of fast neutron radiation induced changes in the density of Si-SiO{sub 2} interface-related defects. Interface related defects (P{sub b} centers) are detected before and upon the irradiation. The density of interface-related defects is increasing with the fast neutron fluence.

  10. Rational design of carbon network cross-linked Si-SiC hollow nanosphere as anode of lithium-ion batteries

    Science.gov (United States)

    Wen, Zhenhai; Lu, Ganhua; Cui, Shumao; Kim, Haejune; Ci, Suqin; Jiang, Junwei; Hurley, Patrick T.; Chen, Junhong

    2013-12-01

    This study aims to realize controllable synthesis of Si-based nanostructures from common and easily accessible silica nanoparticles and to study their component/structure-dependent electrochemical performance as an anode of lithium-ion batteries (LIBs). To this end, a controllable route based on deliberate design has been developed to prepare hollow Si-based nanospheres with tunable composition and crystal structure at the nanoscale. The synthesis process started with coating silica nanoparticles with a carbonaceous polymer with a controllable thickness followed by magnesiothermic reduction. An Si-SiC-C composite was finally produced with a unique hollow sphere structure featuring Si-SiC nanoparticles encapsulated by a cross-linked carbon film network. In addition to the scalability of the synthetic route, the resulting composite exhibits a number of advantageous properties, including excellent electrical conductivity, highly accessible surfaces, structural coherence, and a favorable structure for the formation of a stable solid-electrolyte interphase, which makes it attractive and promising for advanced anode materials of LIBs.This study aims to realize controllable synthesis of Si-based nanostructures from common and easily accessible silica nanoparticles and to study their component/structure-dependent electrochemical performance as an anode of lithium-ion batteries (LIBs). To this end, a controllable route based on deliberate design has been developed to prepare hollow Si-based nanospheres with tunable composition and crystal structure at the nanoscale. The synthesis process started with coating silica nanoparticles with a carbonaceous polymer with a controllable thickness followed by magnesiothermic reduction. An Si-SiC-C composite was finally produced with a unique hollow sphere structure featuring Si-SiC nanoparticles encapsulated by a cross-linked carbon film network. In addition to the scalability of the synthetic route, the resulting composite exhibits a

  11. Tribology of Si/SiO2 in humid air: transition from severe chemical wear to wearless behavior at nanoscale.

    Science.gov (United States)

    Chen, Lei; He, Hongtu; Wang, Xiaodong; Kim, Seong H; Qian, Linmao

    2015-01-13

    Wear at sliding interfaces of silicon is a main cause for material loss in nanomanufacturing and device failure in microelectromechanical system (MEMS) applications. However, a comprehensive understanding of the nanoscale wear mechanisms of silicon in ambient conditions is still lacking. Here, we report the chemical wear of single crystalline silicon, a material used for micro/nanoscale devices, in humid air under the contact pressure lower than the material hardness. A transmission electron microscopy (TEM) analysis of the wear track confirmed that the wear of silicon in humid conditions originates from surface reactions without significant subsurface damages such as plastic deformation or fracture. When rubbed with a SiO2 ball, the single crystalline silicon surface exhibited transitions from severe wear in intermediate humidity to nearly wearless states at two opposite extremes: (a) low humidity and high sliding speed conditions and (b) high humidity and low speed conditions. These transitions suggested that at the sliding interfaces of Si/SiO2 at least two different tribochemical reactions play important roles. One would be the formation of a strong "hydrogen bonding bridge" between hydroxyl groups of two sliding interfaces and the other the removal of hydroxyl groups from the SiO2 surface. The experimental data indicated that the dominance of each reaction varies with the ambient humidity and sliding speed.

  12. Delicate Structural Control of Si-SiOx-C Composite via High-Speed Spray Pyrolysis for Li-Ion Battery Anodes.

    Science.gov (United States)

    Lee, Seung Jong; Kim, Hye Jin; Hwang, Tae Hoon; Choi, Sunghun; Park, Sung Hyeon; Deniz, Erhan; Jung, Dae Soo; Choi, Jang Wook

    2017-03-08

    Despite the high theoretical capacity, silicon (Si) anodes in lithium-ion batteries have difficulty in meeting the commercial standards in various aspects. In particular, the huge volume change of Si makes it very challenging to simultaneously achieve high initial Coulombic efficiency (ICE) and long-term cycle life. Herein, we report spray pyrolysis to prepare Si-SiOx composite using an aqueous precursor solution containing Si nanoparticles, citric acid, and sodium hydroxide (NaOH). In the precursor solution, Si nanoparticles are etched by NaOH with the production of [SiO4](4-). During the dynamic course of spray pyrolysis, [SiO4](4-) transforms to SiOx matrix and citric acid decomposes to carbon surface layer with the assistance of NaOH that serves as a decomposition catalyst. As a result, a Si-SiOx composite, in which Si nanodomains are homogeneously embedded in the SiOx matrix with carbon surface layer, is generated by a one-pot process with a residence time of only 3.5 s in a flow reactor. The optimal composite structure in terms of Si domain size and Si-to-O ratio exhibited excellent electrochemical performance, such as reversible capacity of 1561.9 mAh g(-1) at 0.06C rate and ICE of 80.2% and 87.9% capacity retention after 100 cycles at 1C rate.

  13. Charge Losses in Silicon Sensors and Electric-Field Studies at the Si-SiO$_2$ Interface

    CERN Document Server

    Poehlsen, Thomas

    Electric fields and charge losses in silicon sensors before and after irradiation with x-rays, protons, neutrons or mixed irradiation are studied in charge-collection measurements. Electron-hole pairs ($eh$ pairs) are generated at different positions in the sensor using sub-ns pulsed laser light of different wavelengths. Light of 1063 nm, 830 nm and 660 nm wavelength is used to generate $eh$ pairs along the whole sensor depth, a few $\\mu$m below the surface and very close to the surface, respectively. Segmented p$^+$n silicon strip sensors are used to study the electric field below the SiO$_2$ separating the strip implants. The sensors are investigated before and after irradiation with 12 keV x-rays to a dose of 1 MGy. It is found that the electric field close to the Si-SiO$_2$ interface depends on both the irradiation dose and the biasing history. For the non-irradiated sensors the observed dependence of the electric field on biasing history and humidity is qualitatively as expected from simulations of the...

  14. p-n Junction Diodes Fabricated on Si-Si/Ge Heteroepitaxial Films

    Science.gov (United States)

    Das, K.; Mazumder, M. D. A.; Hall, H.; Alterovitz, Samuel A. (Technical Monitor)

    2000-01-01

    A set of photolithographic masks was designed for the fabrication of diodes in the Si-Si/Ge material system. Fabrication was performed on samples obtained from two different wafers: (1) a complete HBT structure with an n (Si emitter), p (Si/Ge base), and an n/n+ (Si collector/sub-collector) deposited epitaxially (MBE) on a high resistivity p-Si substrate, (2) an HBT structure where epitaxial growth was terminated after the p-type base (Si/Ge) layer deposition. Two different process runs were attempted for the fabrication of Si-Si/Ge (n-p) and Si/Ge-Si (p-n) junction diodes formed between the emitter-base and base-collector layers, respectively, of the Si-Si/Ge-Si HBT structure. One of the processes employed a plasma etching step to expose the p-layer in the structure (1) and to expose the e-layer in structure (2). The Contact metallization used for these diodes was a Cu-based metallization scheme that was developed during the first year of the grant. The plasma-etched base-collector diodes on structure (2) exhibited well-behaved diode-like characteristics. However, the plasma-etched emitter-base diodes demonstrated back-to-back diode characteristics. These back-to back characteristics were probably due to complete etching of the base-layer, yielding a p-n-p diode. The deep implantation process yielded rectifying diodes with asymmetric forward and reverse characteristics. The ideality factor of these diodes were between 1.6 -2.1, indicating that the quality of the MBE grown epitaxial films was not sufficiently high, and also incomplete annealing of the implantation damage. Further study will be conducted on CVD grown films, which are expected to have higher epitaxial quality.

  15. Efficient injection-type ballistic rectification in Si/SiGe cross junctions

    Science.gov (United States)

    Salloch, D.; Wieser, U.; Kunze, U.; Hackbarth, T.

    2010-09-01

    Tunable inertial-ballistic rectification is studied in a nanoscale injection-type Si/SiGe rectifier in the hot-electron regime. The rectifier consists of a cascade of two nanoscale cross junctions in series. Two pairs of opposing current injectors merge under 30∘ into a straight central voltage stem. The electron densities in the injectors and the stem can be adjusted separately by two local top-gates. The measurements reveal a substantial efficiency increase for a nearly depleted stem. The efficiency of ballistic rectifiers can be expressed by the transfer resistance RT (output voltage divided by input current), the best value we achieve is 800 Ω.

  16. Flash-lamp annealing of Si-SiO/sub 2/ transition layer defects

    Energy Technology Data Exchange (ETDEWEB)

    Lysenko, V.S.; Zimenko, V.I.; Tyagulskii, I.P.; Osiyuk, I.N.; Snitko, O.V.; Sytenko, T.N. (AN Ukrainskoj SSR, Kiev. Inst. Poluprovodnikov)

    1985-02-16

    The rearrangement of ion implanted Si-SiO/sub 2/ interface resulting from flash-lamp annealing is studied by the method of C(U) characteristics at 300 K and 1 MHz and by the method of thermostimulated charge release (TSCR) which being applied in a temperature range of 4.2 to 80 K provides information about energy spectrum and concentration of local centers in the Si-to-SiO/sub 2/ transition layer of 1 to 10 nm thickness. The analysis of TSCR current curves enabled one to determine the activation energy of shallow traps and their integrated density.

  17. Band offsets at the Si/SiO2 interface from many-body perturbation theory.

    Science.gov (United States)

    Shaltaf, R; Rignanese, G-M; Gonze, X; Giustino, Feliciano; Pasquarello, Alfredo

    2008-05-09

    We use many-body perturbation theory, the state-of-the-art method for band-gap calculations, to compute the band offsets at the Si/SiO2 interface. We examine the adequacy of the usual approximations in this context. We show that (i) the separate treatment of band structure and potential lineup contributions, the latter being evaluated within density-functional theory, is justified, (ii) most plasmon-pole models lead to inaccuracies in the absolute quasiparticle corrections, (iii) vertex corrections can be neglected, and (iv) eigenenergy self-consistency is adequate. Our theoretical offsets agree with the experimental ones within 0.3 eV.

  18. Intersubband carrier scattering in n - and p-Si/SiGe quantum wells with diffuse interfaces

    Science.gov (United States)

    Valavanis, A.; Ikonić, Z.; Kelsall, R. W.

    2008-02-01

    Scattering rate calculations in two-dimensional Si/Si1-xGex systems have typically been restricted to rectangular Ge profiles at interfaces between layers. Real interfaces, however, may exhibit diffuse Ge profiles either by design or as a limitation of the growth process. It is shown here that alloy disorder scattering dramatically increases with Ge interdiffusion in (100) and (111) n -type quantum wells, but remains almost constant in (100) p -type heterostructures. It is also shown that smoothing of the confining potential leads to large changes in subband energies and scattering rates, and a method is presented for calculating growth process tolerances.

  19. Simulation of Domain Formation in p-Si/SiGe Quantum Cascade Structures

    Science.gov (United States)

    Ikonic, Z.; Harrison, P.; Kelsall, R. W.

    Domain formation in p-doped Si/SiGe quantum cascades is considered using a carrier scattering transport framework. The hole flow along the cascade is described via scattering between quantized states belonging to neighbouring periods, caused by phonons, alloy disorder, and carrier-carrier interactions. The generation of either periodic or of nonperiodic domains is studied in uniformly or modulationally doped cascades, and criteria for their appearance are found. The domains in modulationally doped cascades have a relatively smaller effect on the energy structure than in uniformly doped ones.

  20. Theory and design of quantum cascade lasers in (111) n -type Si/SiGe

    Science.gov (United States)

    Valavanis, A.; Lever, L.; Evans, C. A.; Ikonić, Z.; Kelsall, R. W.

    2008-07-01

    Although most work toward the realization of group IV quantum cascade lasers (QCLs) has focused on valence-band transitions, there are many desirable properties associated with the conduction band. We show that the commonly cited shortcomings of n -type Si/SiGe heterostructures can be overcome by moving to the (111) growth direction. Specifically, a large band offset and low effective mass are achievable and subband degeneracy is preserved. We predict net gain up to lattice temperatures of 90 K in a bound-to-continuum QCL with a double-metal waveguide, and show that a Ge interdiffusion length of at least 8Å across interfaces is tolerable.

  1. Technology computer aided design for Si, SiGe and GaAs integrated circuits

    CERN Document Server

    Armstrong, GA

    2007-01-01

    The first book to deal with a broad spectrum of process and device design, and modelling issues related to semiconductor devices, bridging the gap between device modelling and process design using TCAD. Examples for types of Si-, SiGe-, GaAs- and InP-based heterostructure MOS and bipolar transistors are compared with experimental data from state-of-the-art devices. With various aspects of silicon heterostructures, this book presents a comprehensive perspective of emerging fields and covers topics ranging from materials to fabrication, devices, modelling and applications. Aimed at research-and-

  2. Transport and electroluminescence mechanism in Au/(Si/SiO2)/P-Si film

    Institute of Scientific and Technical Information of China (English)

    ZHANG Kai-biao; MA Shu-yi; MA Zi-jun; CHEN Hai-xia

    2006-01-01

    The samples of Au/(Si/SiO2)/p-Si structure were fabricated by using the R.F magnetron sputtering technique.Its carrier transport and electroluminescence mechanism were studied from the I-V curves and EL spectra by using the Configuration Coordinate as a theoretical model.The result indicates that there are two defect centers in SiO2 films.The electron in Au and the hole in p-Si went into SiO2 film by the Fowler-Nordheim tunneling model at a high bias voltage and recombined through these defect centers in SiO2 film.

  3. Photoreflectance Spectroscopy for Study of Si/SiGe/Si Heterostructure

    Institute of Scientific and Technical Information of China (English)

    Liu Zhihong; Chen Changchun; Lin Huiwang; Xiong Xiaoyi; Dou Weizhi; Tsien Pei-Hsin

    2004-01-01

    UHVCVD-grown Si/Si1- xGex/Si heterostructure was investigated by Photoreflectance spectroscopy (PR). The principle of PR used in semiconductor film was thoroughly described. According to the E1 transition energy in the Si1- xGex alloy, the Ge content in SiGe film with constant composition can be accurately characterized. In this study, determine the composition uniformity of larger diameter SiGe epiwafer by PR mapping technique was determined. These results show PR is very promising for Si1- xGex epilayer characterization with constant Ge content and can provide film measurements for production-worthy line monitor.

  4. Data supporting beta-amyloid dimer structural transitions and protein–lipid interactions on asymmetric lipid bilayer surfaces using MD simulations on experimentally derived NMR protein structures

    Directory of Open Access Journals (Sweden)

    Sara Y. Cheng

    2016-06-01

    Full Text Available This data article supports the research article entitled “Maximally Asymmetric Transbilayer Distribution of Anionic Lipids Alters the Structure and interaction with Lipids of an Amyloidogenic Protein Dimer Bound to the Membrane Surface” [1]. We describe supporting data on the binding kinetics, time evolution of secondary structure, and residue-contact maps of a surface-absorbed beta-amyloid dimer protein on different membrane surfaces. We further demonstrate the sorting of annular and non-annular regions of the protein/lipid bilayer simulation systems, and the correlation of lipid-number mismatch and surface area per lipid mismatch of asymmetric lipid membranes.

  5. Strain and defect microstructure in ion-irradiated GeSi/Si strained layers as a function of annealing temperature

    Energy Technology Data Exchange (ETDEWEB)

    Glasko, J.M.; Elliman, R.G. [Australian National University, Canberra, ACT, (Australia). Department of Electronic Materials Engineering; Zou, J.; Cockayne, D.J.H. [Sydney University, Sydney, NSW (Australia). Australian Key Centre for Microscopy and Microanalysis and Electron Microscope Unit; Fitz Gerald, J.D. [Australian National University, Canberra, ACT (Australia). Research School of Earth Sciences

    1998-06-01

    High energy (1 MeV), ion irradiation of GeSi/Si strained layers at elevated temperatures can cause strain relaxation. In this study, the effect of subsequent thermal annealing was investigated. Three distinct annealing stages were identified and correlated with the evolution of the defect microstructure. In the temperature range from 350 to 600 deg C, a gradual recovery of strain is observed. This is believed to result from the annealing of small defect clusters and the growth of voids. The voids are visible at annealing temperatures in excess of 600 deg C, consistent with an excess vacancy concentration in the irradiated alloy layer. The 600 to 750 deg C range is marked by pronounced maximal recovery of strain, and is correlated with the dissolution of faulted loops in the substrate. At temperatures in the range 750-1000 deg C, strain relaxation is observed and is correlated with the growth of intrinsic dislocations within the alloy layer. These dislocations nucleate at the alloy-substrate interface and grow within the alloy layer, towards the surface. (authors). Extended abstract. 13 refs., 2 figs.

  6. Effect of thin Mo2C layer on thermal stability of Si/SiO2/Ti/Cu system

    Indian Academy of Sciences (India)

    C C Tripathi; Mukesh Kumar; Dinesh Kumar

    2011-12-01

    The effect of introducing a thin Mo2C (30 nm) layer between Ti and Cu on the thermal stability of Si/SiO2/Ti/Cu system was studied using four-point probe (FPP), scanning electron microscopy (SEM), energydispersive X-ray spectroscopy (EDAX) and X-ray diffraction (XRD) techniques. The measured value of the sheet resistance in the bi-layered diffusion barrier structure does not show any change up to an annealing temperature of 750°C. The sheet resistance when measured after annealing at 800°C marginally increases but less than twice its value at room temperature. The XRD analysis indicated no copper diffusion and the formation of Cu3Si phase up to 800°C. The bi-layered barrier structure annealed at elevated temperature shows copper-depleted and agglomerated regions. The sheet resistance measurement, study of surface morphology and the XRD analysis confirm that the insertion of thin Mo2C layer increases the thermal stability of the system from 400°C to 750°C. The increased thermal stability of the system is ascribed to longer diffusion path length in the bi-layered system probably because of grain boundaries mismatch at Ti–Mo2C interface.

  7. Polarization memory effect in the photoluminescence of nc-Si-SiOx light-emitting structures.

    Science.gov (United States)

    Michailovska, Katerina; Indutnyi, Ivan; Shepeliavyi, Petro; Sopinskyy, Mykola

    2016-12-01

    The polarization memory (PM) effect in the photoluminescence (PL) of the porous nc-Si-SiOx light-emitting structures, containing nanoparticles of silicon (nc-Si) in the oxide matrix and passivated in a solution of hydrofluoric acid (HF), has been investigated. The studied nc-Si-SiOx structures were produced by evaporation of Si monoxide (SiO) powder in vacuum and oblique deposition on Si wafer, and then the deposited silicon oxide (SiOx) films were annealed in the vacuum at 975 °C to grow nc-Si. It was found that the PM effect in the PL is observed only after passivation of nanostructures: during etching in HF solution, the initial symmetric nc-Si becomes asymmetric elongated. It was also found that in investigated nanostructures, there is a defined orientational dependence of the PL polarization degree (ρ) in the sample plane which correlates with the orientation of SiOx nanocolumns, forming the structure of the porous layer. The increase of the ρ values in the long-wavelength spectral range with time of HF treatment can be associated with increasing of the anisotropy of large Si nanoparticles. The PM effect for this spectral interval can be described by the dielectric model. In the short-wavelength spectral range, the dependence of the ρ values agrees qualitatively with the quantum confinement effect.

  8. Characterization of a gate-defined double quantum dot in a Si/SiGe nanomembrane

    Science.gov (United States)

    Knapp, T. J.; Mohr, R. T.; Li, Yize Stephanie; Thorgrimsson, Brandur; Foote, Ryan H.; Wu, Xian; Ward, Daniel R.; Savage, D. E.; Lagally, M. G.; Friesen, Mark; Coppersmith, S. N.; Eriksson, M. A.

    2016-04-01

    We report the fabrication and characterization of a gate-defined double quantum dot formed in a Si/SiGe nanomembrane. In the past, all gate-defined quantum dots in Si/SiGe heterostructures were formed on top of strain-graded virtual substrates. The strain grading process necessarily introduces misfit dislocations into a heterostructure, and these defects introduce lateral strain inhomogeneities, mosaic tilt, and threading dislocations. The use of a SiGe nanomembrane as the virtual substrate enables the strain relaxation to be entirely elastic, eliminating the need for misfit dislocations. However, in this approach the formation of the heterostructure is more complicated, involving two separate epitaxial growth procedures separated by a wet-transfer process that results in a buried non-epitaxial interface 625 nm from the quantum dot. We demonstrate that in spite of this buried interface in close proximity to the device, a double quantum dot can be formed that is controllable enough to enable tuning of the inter-dot tunnel coupling, the identification of spin states, and the measurement of a singlet-to-triplet transition as a function of an applied magnetic field.

  9. Polarization memory effect in the photoluminescence of nc-Si-SiOx light-emitting structures

    Science.gov (United States)

    Michailovska, Katerina; Indutnyi, Ivan; Shepeliavyi, Petro; Sopinskyy, Mykola

    2016-06-01

    The polarization memory (PM) effect in the photoluminescence (PL) of the porous nc-Si-SiOx light-emitting structures, containing nanoparticles of silicon (nc-Si) in the oxide matrix and passivated in a solution of hydrofluoric acid (HF), has been investigated. The studied nc-Si-SiOx structures were produced by evaporation of Si monoxide (SiO) powder in vacuum and oblique deposition on Si wafer, and then the deposited silicon oxide (SiOx) films were annealed in the vacuum at 975 °C to grow nc-Si. It was found that the PM effect in the PL is observed only after passivation of nanostructures: during etching in HF solution, the initial symmetric nc-Si becomes asymmetric elongated. It was also found that in investigated nanostructures, there is a defined orientational dependence of the PL polarization degree ( ρ) in the sample plane which correlates with the orientation of SiOx nanocolumns, forming the structure of the porous layer. The increase of the ρ values in the long-wavelength spectral range with time of HF treatment can be associated with increasing of the anisotropy of large Si nanoparticles. The PM effect for this spectral interval can be described by the dielectric model. In the short-wavelength spectral range, the dependence of the ρ values agrees qualitatively with the quantum confinement effect.

  10. Optimization of spectrally selective Si/SiO2 based filters for thermophotovoltaic devices

    Science.gov (United States)

    Khosroshahi, Farhad Kazemi; Ertürk, Hakan; Pınar Mengüç, M.

    2017-08-01

    Design of a spectrally selective filter based on one-dimensional Si/SiO2 layers is considered for improved performance of thermo-photovoltaic devices. Spectrally selective filters transmit only the convertible radiation from the emitter as non-convertible radiation leads to a reduction in cell efficiency due to heating. The presented Si/SiO2 based filter concept reflects the major part of the undesired range back to the emitter to minimize energy required for the process and it is adaptable to different types of cells and emitters with different temperatures since its cut-off wavelength can be tuned. While this study mainly focuses on InGaSb based thermo-photovoltaic cell, Si, GaSb, and Ga0.78In0.22As0.19Sb0.81 based cells are also examined. Transmittance of the structure is predicted by rigorous coupled wave approach. Genetic algorithm, which is a global optimization method, is used to find the best possible filter structure by considering the overall efficiency as an objective function that is maximized. The simulations show that significant enhancement in the overall system and device efficiency is possible by using such filters with TPV devices. The methodology described in this paper allows for an improved filter design procedure for selected applications.

  11. Photoluminescence and structural properties of Si/SiC core–shell nanowires growth by HWCVD

    Energy Technology Data Exchange (ETDEWEB)

    Nazarudin, Nur Fatin Farhanah Binti; Mohd Noor, Nurul Jannah Binti; Rahman, Saadah Abdul; Goh, Boon Tong, E-mail: boontong77@yahoo.com

    2015-01-15

    Si/SiC core–shell nanowires grown by hot-wire chemical vapor deposition were studied. Ni nanoparticles act as metal nano-templates to catalyze the growth of these core–shell nanowires. These nanowires were grown at different deposition pressures of 0.5 and 1 mbar. The nanowires showed a tapered-like morphology at deposition pressure 0.5 mbar. Increase in pressure to 1 mbar leads to a formation of agglomerated grains at the root of the nanowires. The results show that these nanowires consisted of crystalline Si core and amorphous SiC shell nanowires. Increase in pressure enhanced the formation of SiC phase in the shell of the nanowires. On the other hand, the formation of the agglomerated grains attributed to an increasing of the SiC phase at higher deposition pressure. The presence of Si and SiC nano-crystallites embedded within an amorphous matrix exhibited a room temperature PL emission in the range of 400–1000 nm. The effects of the deposition pressure on the optical and structural properties of the nanowires are also discussed. - Highlights: • Growth of Si/SiC core–shell nanowires by HWCVD. • The nanowires consisted of crystalline Si core and amorphous SiC shell. • Metal nano-templates catalyzed the growth of Si core nanowires. • Increase in deposition pressure enhanced the SiC phase. • The presence of nano-crystallites exhibited a room temperature PL.

  12. Photoluminescence from SiO sub 2 /Si/SiO sub 2 structures

    CERN Document Server

    Photopoulos, P

    2003-01-01

    Si layers were developed on pre-oxidized Si wafers by decomposition of silane in a low pressure chemical vapour deposition reactor. By keeping the deposition time constant (2 min) three sets of samples were fabricated at deposition temperatures equal to 580, 610 and 625 deg C. The deposited Si layers were thinned by high temperature dry oxidation thus forming SiO sub 2 /Si/SiO sub 2 structures. Room temperature photoluminescence (PL) measurements showed that for those samples in which the thickness of the remaining Si layer was greater than approx 6 nm, the spectra exhibited a peak at approx 650 nm. Prolonged oxidations led to the formation of SiO sub 2 /nanocrystalline-Si/SiO sub 2 structures in which the thickness of the remaining nanocrystalline Si (nc-Si) layer was smaller than 3 nm. The PL spectra obtained from these structures were at least ten times stronger compared to the previous ones. The PL peak wavelength exhibited a weak dependence on the nc-Si layer thickness shifting from 800 to 720 nm for nc-...

  13. Theoretical investigation of potential energy surface and bound states for the van der Waals complex Ar–BrCl dimer

    Energy Technology Data Exchange (ETDEWEB)

    Zheng, Rui [School of Mathematics and Information Science, North China University of Water Resources and Electric Power, Zhengzhou (China); Key Laboratory of Magnetic Resonance in Biological Systems, State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Wuhan Centre for Magnetic Resonance, Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan (China); Li, Song, E-mail: lsong@yangtzeu.edu.cn [School of Physics and Optoelectronic Engineering, Yangtze University, Jingzhou (China); Chen, Shan-Jun; Chen, Yan [School of Physics and Optoelectronic Engineering, Yangtze University, Jingzhou (China); Zheng, Li-Min [Key Laboratory of Magnetic Resonance in Biological Systems, State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Wuhan Centre for Magnetic Resonance, Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan (China)

    2015-09-08

    Highlights: • A two-dimensional potential for Ar–BrCl is constructed at the CCSD(T) level. • The PES is characterized by three minima and two saddle points between them. • Bound state calculations were carried out for the complex. - Abstract: The intermolecular potential energy surface (PES) of the ground electronic state for the Ar–BrCl dimer is constructed at the CCSD(T) level with the aug-cc-pVQZ basis set and mid-bond functions. The PES is characterized by three minima and two saddle points. The global minimum corresponding to a collinear Ar–BrCl configuration, which has been observed experimentally, is located at R = 4.10 Å and θ = 2.5° with a well depth of −285.207 cm{sup −1}. A nearly T-shaped structure and an anti-linear Ar–ClBr geometry is also predicted. The bound state calculations are preformed to study intermolecular vibrational modes, rotational levels and average structures for the complex. Our transition frequencies, spectroscopic constants and average structures for all isotopomers of the collinear isomer agree well with experimental data. We have also provided pure rotational transitional frequencies for both nearly T-shaped and anti-linear isomers. These results are significant for further experimental investigations of the Ar–BrCl dimer.

  14. Characterization method for relative Raman enhancement for surface-enhanced Raman spectroscopy using gold nanoparticle dimer array

    Science.gov (United States)

    Sugano, Koji; Ikegami, Kohei; Isono, Yoshitada

    2017-06-01

    In this paper, a characterization method for Raman enhancement for highly sensitive and quantitative surface-enhanced Raman spectroscopy (SERS) is reported. A particle dimer shows a marked electromagnetic enhancement when the particle connection direction is matched to the polarization direction of incident light. In this study, dimers were arrayed by nanotrench-guided self-assembly for a marked total Raman enhancement. By measuring acetonedicarboxylic acid, the fabricated structures were characterized for SERS depending on the polarization angle against the particle connection direction. This indicates that the fabricated structures cause an effective SERS enhancement, which is dominated by the electromagnetic enhancement. Then, we measured 4,4‧-bipyridine, which is a pesticide material, for quantitative analysis. In advance, we evaluated the enhancement of the particle structure by the Raman measurement of acetonedicarboxylic acid. Finally, we compared the Raman intensities of acetonedicarboxylic acid and 4,4‧-bipyridine. Their intensities showed good correlation. The advantage of this method for previously evaluating the enhancement of the substrate was demonstrated. This developed SERS characterization method is expected to be applied to various quantitative trace analyses of molecules with high sensitivity.

  15. Structure determination of the Si(001)-(2 x 1)-H reconstruction by surface X-ray diffraction: Weakening of the dimer bond by the addition of hydrogen

    DEFF Research Database (Denmark)

    Lauridsen, E.M.; Baker, J.; Nielsen, M.;

    2000-01-01

    The atomic structure of the monohydride Si(001)-(2 x 1)-H reconstruction has been investigated by surface X-ray diffraction. Atomic relaxations down to the eighth layer have been determined. The bond length of the hydrogenated silicon dimers was found to be 2.47 +/- 0.02 Angstrom. which is longer...... than the dimer bond of the clean (2 x 1)-reconstructed Si(001) surface and also 5% longer than the bulk bond length of 2.35 Angstrom. The differences to the (2 x 1) structure of the clean surface are discussed in terms of the elimination of the weak pi-bond character of the dimer bond by the addition...

  16. Application of variational reduced-density-matrix theory to the potential energy surfaces of the nitrogen and carbon dimers.

    Science.gov (United States)

    Gidofalvi, Gergely; Mazziotti, David A

    2005-05-15

    The acceleration of the variational two-electron reduced-density-matrix (2-RDM) method, using a new first-order algorithm [D. A. Mazziotti, Phys. Rev. Lett. 93, 213001 (2004)], has shown its usefulness in the accurate description of potential energy surfaces in nontrivial basis sets. Here we apply the first-order 2-RDM method to the potential energy surfaces of the nitrogen and carbon dimers in polarized valence double-zeta basis sets for which benchmark full-configuration-interaction calculations exist. In a wave function formalism accurately stretching the triple bond of the nitrogen dimer requires at least six-particle excitations from the Hartree-Fock reference. Furthermore, cleaving the double bond of C2 should produce a "non-Morse"-like potential curve because the ground state near equilibrium (X 1sigma(g)+) has an avoided crossing with the second excited state (B' 1sigma(g)+) and a level crossing with the first excited state (B 1delta(g)). Because the 2-RDM method variationally optimizes the energy over correlated 2-RDMs on the two-electron space without parametrization of the many-electron wave function, it captures multireference correlations that are difficult to describe with approximate wave functions. The 2-RDM method yields for N2 a potential energy surface with features and spectroscopic constants that are more accurate than those from single-reference methods and similar in accuracy to multireference techniques, and it describes the non-Morse-like behavior of C2 which is not captured by single-reference methods.

  17. On-Demand Fabrication of Si/SiO2 Nanowire Arrays by Nanosphere Lithography and Subsequent Thermal Oxidation.

    Science.gov (United States)

    Cao, Huaxiang; Li, Xinhua; Zhou, Bukang; Chen, Tao; Shi, Tongfei; Zheng, Jianqiang; Liu, Guangqiang; Wang, Yuqi

    2017-12-01

    We demonstrate the fabrication of the large-area arrays of vertically aligned Si/SiO2 nanowires with full tunability of the geometry of the single nanowires by the metal-assisted chemical etching technique and the following thermal oxidation process. To fabricate the geometry controllable Si/SiO2 nanowire (NW) arrays, two critical issues relating with the size control of polystyrene reduction and oxide thickness evolution are investigated. Through analyzing the morphology evolutions of polystyrene particles, we give a quantitative description on the diameter variations of polystyrene particles with the etching time of plasma etching. Based on this, pure Si NW arrays with controllable geometry are generated. Then the oxide dynamic of Si NW is analyzed by the extended Deal-Grove model. By control, the initial Si NWs and the thermal oxidation time, the well-aligned Si/SiO2 composite NW arrays with controllable geometry are obtained.

  18. Correlation between Light Emissions from Amorphous-Si:H/SiO2 and nc-Si/SiO2 Multilayers

    Institute of Scientific and Technical Information of China (English)

    MA Zhong-Yuan; HUANG Xin-Fan; CHEN Kun-Ji; FENG Duan; HAN Pei-Gao; LI Wei; CHEN De-Yuan; WEI De-Yuan; QIAN Bo; LI Wei; XU Jun; XU Ling

    2007-01-01

    We investigate the properties of light emission from amorphous-Si:H/SiO2 and nc-Si/SiO2 multilayers (MLs). The size dependence of light emission is well exhibited when the a-Si:H sublayer thickness is thinner than 4nm and the interface states are well passivated by hydrogen. For the nc-Si/SiO2 MLs, the oxygen modified interface states and nanocrystalline silicon play a predominant role in the properties of light emission. It is found that the light emission from nc-Si/SiO2 is in agreement with the model of interface state combining with quantum confinement when the size of nc-Si is smaller than 4 nm. The role of hydrogen and oxygen is discussed in detail.

  19. On-Demand Fabrication of Si/SiO2 Nanowire Arrays by Nanosphere Lithography and Subsequent Thermal Oxidation

    Science.gov (United States)

    Cao, Huaxiang; Li, Xinhua; Zhou, Bukang; Chen, Tao; Shi, Tongfei; Zheng, Jianqiang; Liu, Guangqiang; Wang, Yuqi

    2017-02-01

    We demonstrate the fabrication of the large-area arrays of vertically aligned Si/SiO2 nanowires with full tunability of the geometry of the single nanowires by the metal-assisted chemical etching technique and the following thermal oxidation process. To fabricate the geometry controllable Si/SiO2 nanowire (NW) arrays, two critical issues relating with the size control of polystyrene reduction and oxide thickness evolution are investigated. Through analyzing the morphology evolutions of polystyrene particles, we give a quantitative description on the diameter variations of polystyrene particles with the etching time of plasma etching. Based on this, pure Si NW arrays with controllable geometry are generated. Then the oxide dynamic of Si NW is analyzed by the extended Deal-Grove model. By control, the initial Si NWs and the thermal oxidation time, the well-aligned Si/SiO2 composite NW arrays with controllable geometry are obtained.

  20. Separation of Joule Heating and Peltier Cooling via Time-Resolved X-Ray Di?raction in Si/SiGe Superlattice

    Science.gov (United States)

    Kozina, Michael; Fuchs, Matthias; Chen, Jian; Jiang, Mason; Chen, Pice; Evans, Paul; Vermeersch, Bjorn; Bahk, Je-Hyeong; Shakouri, Ali; Brewe, Dale; Reis, David

    2012-02-01

    We present detailed measurements of the thermal pro?le in a pulsed current SiGe-based thermoelectric micro-cooler. The evolution of heat ?ow in thermoelectric materials has been previously studied using time-domain thermore?ectance imaging; however, such methods are typically only sensitive to the surface temperature of the device, and the heat ?ow into the material remains hidden. Using time-resolved x-ray di?raction, we probe the transient temperature change in both the surface gold electrode and the underlying Si/SiGe superlattice using the shift in diffraction pattern caused by thermal expansion. We are also able to resolve Joule heating vs. Peltier cooling taking place in the gold through separation of timescales made possible by the relatively short duration (100ps) of the Advanced Photon Source.

  1. Microwave based nanogenerator using the ratchet effect in Si/SiGe heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Bisotto, I; Kannan, E S; Sassine, S; Portal, J-C [LNCMI, UPR 3228, CNRS-INSA-UJF-UPS, BP 166, 38042 Grenoble, Cedex 9 (France); Murali, R; Beck, T J [Microelectronics Research Center Georgia Institute of Technology, 791 Atlantic Drive NW, Atlanta, GA 30332 (United States); Jalabert, L [LIMMS/CNRS-IIS, Institute of Industrial Science, University of Tokyo, 4-6-1 Komaba, Meguro-ku, 153-8505, Tokyo (Japan)

    2011-06-17

    Ratchet based microwave current generators and detectors were developed in Si/SiGe heterostructures for wireless communication with the possibility of extending the detection limit to the terahertz range. A microwave induced ratchet current was generated in the two-dimensional electron gas by patterning an array of semicircular antidots in hexagonal geometry. The spatial asymmetry created by the semicircular antidots forces the electrons under the influence of the microwave electric field to move preferentially towards the direction of the semidisc axis. A photovoltage of the order of few millivolts was observed. Such a photovoltage was completely absent in a symmetric system consisting of circular antidots. The induced photovoltage increased monotonically with microwave power and was found to be independent of the microwave polarization. This device opens the possibility of employing silicon based heterostructures for nanogenerators and other wireless communication devices using microwaves.

  2. Observation of ballistic conductance and Aharonov-Bohm oscillations in Si/SiGe heterostructures

    Science.gov (United States)

    Gao, W. X.; Ismail, K.; Lee, K. Y.; Chu, J. O.; Washburn, S.

    1994-12-01

    We have fabricated quantum devices from remotely doped Si/SiGe heterostructures. The devices are interferometers (loops) similar in plan to those used in experiments on ballistic GaAs/AlxGa1-xAs devices. The loops are approximately 2r=0.8 μm in diameter with linewidths of w=0.4 μm. We have observed clear Aharonov-Bohm (AB) oscillations that vanish systematically as the carrier temperature increases. Response of up to the second harmonic of the fundamental AB frequency e/h implies a phase coherence length of around Lφ=1.2 μm. In some samples, we see steps in conductance G(Vg) as a function of gate voltage similar to the ballistic mode steps seen in GaAs/AlxGa1-xAs point contacts.

  3. Electron transport in n-doped Si/SiGe quantum cascade structures

    Science.gov (United States)

    Lazic, I.; Ikonic, Z.; Milanovic, V.; Kelsall, R. W.; Indjin, D.; Harrison, P.

    2007-05-01

    An electron transport model in n-Si/SiGe quantum cascade or superlattice structures is described. The model uses the electronic structure calculated within the effective-mass complex-energy framework, separately for perpendicular (Xz) and in-plane (Xxy) valleys, the degeneracy of which is lifted by strain, and additionally by size quantization. The transport is then described via scattering between quantized states, using a rate equations approach and tight-binding expansion, taking the coupling with two nearest-neighbor periods. Acoustic phonon, optical phonon, alloy disorder, and interface roughness scattering are taken into account. The calculated current/voltage dependence and gain profiles are presented for two simple superlattice structures.

  4. n-Si/SiGe quantum cascade structures for THz emission

    Energy Technology Data Exchange (ETDEWEB)

    Ikonic, Z. [School of Electronic and Electrical Engineering, University of Leeds, Leeds LS2 9JT (United Kingdom)]. E-mail: z.ikonic@ee.leeds.ac.uk; Lazic, I. [School of Electrical Engineering, University of Belgrade, Belgrade (Yugoslavia); Department of Materials Science, Delft University of Technology, 2628 AL Delft (Netherlands); Milanovic, V. [School of Electrical Engineering, University of Belgrade, Belgrade (Yugoslavia); Kelsall, R.W. [School of Electronic and Electrical Engineering, University of Leeds, Leeds LS2 9JT (United Kingdom); Indjin, D. [School of Electronic and Electrical Engineering, University of Leeds, Leeds LS2 9JT (United Kingdom); Harrison, P. [School of Electronic and Electrical Engineering, University of Leeds, Leeds LS2 9JT (United Kingdom)

    2006-12-15

    In this work we report on modeling the electron transport in n-Si/SiGe structures. The electronic structure is calculated within the effective-mass complex-energy framework, separately for perpendicular (X {sub z} ) and in-plane (X {sub xy} ) valleys, the degeneracy of which is lifted by strain, and additionally by size quantization. The transport is described via scattering between quantized states, using the rate equations approach and tight-binding expansion, taking the coupling with two nearest-neighbour periods. The acoustic phonon, optical phonon, alloy and interface roughness scattering are taken in the model. The calculated U/I dependence and gain profiles are presented for a couple of QC structures.

  5. Hollow Bragg waveguides fabricated by controlled buckling of Si/SiO2 multilayers.

    Science.gov (United States)

    Epp, E; Ponnampalam, N; Newman, W; Drobot, B; McMullin, J N; Meldrum, A F; DeCorby, R G

    2010-11-22

    We describe integrated air-core waveguides with Bragg reflector claddings, fabricated by controlled delamination and buckling of sputtered Si/SiO2 multilayers. Thin film deposition parameters were tailored to produce a desired amount of compressive stress, and a patterned, embedded fluorocarbon layer was used to define regions of reduced adhesion. Self-assembled air channels formed either spontaneously or upon heating-induced decomposition of the patterned film. Preliminary optical experiments confirmed that light is confined to the air channels by a photonic band-gap guidance mechanism, with loss ~5 dB/cm in the 1550 nm wavelength region. The waveguides employ standard silicon processes and have potential applications in MEMS and lab-on-chip systems.

  6. Synthesis of nickel catalyzed Si/SiC core-shell nanowires by HWCVD

    Science.gov (United States)

    Tong Goh, Boon; Abdul Rahman, Saadah

    2014-12-01

    Si/SiC core-shell nanowires grown on glass substrates by hot-wire chemical vapor deposition were studied. Nickel was used as a catalyst to initiate the growth of these core-shell nanowires and the nanowires were grown at different deposition pressures of 0.5 and 1 mbar. The core of the nanowire was found to be a single crystalline Si. The shell of the nanowire consisted of Si nano-crystallites embedded within an amorphous SiC matrix which was attributed to a radial growth of columnar structures. The Si and SiC nano-crystallites embedded within an amorphous matrix exhibited room-temperature photoluminescence emissions in the range of 400 nm-1 μm. A vapor-solid-solid growth mechanism of these core-shell nanowires is proposed. The effects of the deposition pressure on the properties of the core-shell nanowires are also discussed.

  7. Resonant tunnelling in nc-Si/SiO2 multilayers at room temperature

    Institute of Scientific and Technical Information of China (English)

    Chen Deyuan

    2011-01-01

    Nc-Si/SiO2 multilayers were fabricated on silicon wafers in a plasma enhanced chemical vapour deposition system using in situ oxidation technology,followed by three-step thermal treatments.Carrier transportation at room temperature is characterized by current voltage measurement,and negative different conductances can be observed both under forward and negative biases,which is explained by resonant tunnelling.The resonant tunnelling peak voltage is related to the thicknesses of the nc-Si and SiO2 sublayers.And the resonant tunnelling peak voltage under negative bias is larger than that under forward bias.An energy band diagram and an equivalent circuit diagram were constructed to analyze and explain the above transportation process and properties.

  8. Effect of spatial inhomogeneities on the membrane surface on receptor dimerization and signal initiation

    Directory of Open Access Journals (Sweden)

    Romica Kerketta

    2016-08-01

    Full Text Available Important signal transduction pathways originate on the plasma membrane, where microdomains may transiently entrap diffusing receptors. This results in a non-random distribution of receptors even in the resting state, which can be visualized as clusters by high resolution imaging methods. Here, we explore how spatial in-homogeneities in the plasma membrane might influence the dimerization and phosphorylation status of ErbB2 and ErbB3, two receptor tyrosine kinases that preferentially heterodimerize and are often co-expressed in cancer. This theoretical study is based upon spatial stochastic simulations of the two-dimensional membrane landscape, where variables include differential distributions and overlap of transient confinement zones (domains for the two receptor species. The in silico model is parameterized and validated using data from single particle tracking experiments. We report key differences in signaling output based on the degree of overlap between domains and the relative retention of receptors in such domains, expressed as escape probability. Results predict that a high overlap of domains, which favors transient co-confinement of both receptor species, will enhance the rate of hetero-interactions. Where domains do not overlap, simulations confirm expectations that homo-interactions are favored. Since ErbB3 is uniquely dependent on ErbB2 interactions for activation of its catalytic activity, variations in domain overlap or escape probability markedly alter the predicted patterns and time course of ErbB3 and ErbB2 phosphorylation. Taken together, these results implicate membrane domain organization as an important modulator of signal initiation, motivating the design of novel experimental approaches to measure these important parameters across a wider range of receptor systems.

  9. Electron Spin Resonance on Mobile and Confined States in Gated Modulation Doped Si/SiGe Heterostructures

    Science.gov (United States)

    He, Jianhua; Malissa, H.; Lu, Tzu-Ming; Shankar, S.; Tyryshkin, A. M.; Lyon, S. A.; Chen, Hung-Ming; Kuan, Chieh-Hsiung

    2010-03-01

    Electron spins in quantum dots in Si/SiGe heterostructures are promising qubits but controlling and measuring spins in gated dots is challenging. Fortunately, electrons confined into natural quantum dots by interface disorder can capture the spin physics with minimal processing, exhibiting long T1 and T2 at the Si/SiO2 interface^1. Natural quantum dots in the Si/SiGe system may be similarly useful. As a first step, we have fabricated a 2.2 x 13mm^2 Hall bar on a Si/SiGe substrate gated with an Al gate above an Al2O3 insulator, and performed electron spin resonance (ESR) at gate voltages above and below threshold. The ESR signal arising from the Si quantum well evolves with gate voltage, and its intensity (spin susceptibility) is measured as a function of temperature down to 0.4K. The susceptibility follows a Pauli dependence when the gate is biased above threshold, while it is Curie-like below threshold, indicating an evolution from a mobile 2D system towards localized states confined in natural dots by the intrinsic disorder in the quantum well. This work is supported by LPS and ARO. [1] S. Shankar, et al., Physica E, 40, 1659-1661 (2008).

  10. Synthesis and characterization of Fe{sub 3}Si/SiO{sub 2} structures for spintronics

    Energy Technology Data Exchange (ETDEWEB)

    Mantovan, R.; Georgieva, M.; Fanciulli, M. [Laboratorio Nazionale MDM CNR-INFM, Agrate Brianza (Italy); Goikhman, A.; Barantcev, N.; Lebedinskii, Yu.; Zenkevich, A. [Moscow Engineering Physics Institute, Moscow (Russian Federation)

    2008-08-15

    The Fe{sub 3}Si thin film is a good candidate as ferromagnetic electrode in spintronics devices due to its high spin polarization and high Curie temperature. The use of Fe{sub 3}Si in contact with a thin SiO{sub 2} barrier can have various applications in practical devices, such as magnetic tunnel junctions. We report on the synthesis of Fe{sub 3}Si/SiO{sub 2} structures, in one vacuum cycle, by pulsed laser deposition and glow-discharge plasma oxidation followed by vacuum annealing. The structural and morphological characterization of the Fe{sub 3}Si/SiO{sub 2} stacks is performed by in-situ X-ray photoelectron spectroscopy and with atomic force microscopy. Using a {sup 57}Fe tracer layer, conversion electron Moessbauer spectroscopy is performed at the Fe{sub 3}Si/SiO{sub 2} interface, proving the formation of a ferromagnetic phase with no paramagnetic inclusions. Our experimental results indicate that the Fe{sub 3}Si/SiO{sub 2} stack is a promising system for application in spintronics devices. (copyright 2008 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  11. DLTS investigations of Si-SiO/sub 2/ interface states of electron-beam irradiated MOS structures

    Energy Technology Data Exchange (ETDEWEB)

    Huebner, K.; Koester, H.; Derlich, B. (Rostock Univ. (German Democratic Republic). Sektion Physik); Ecke, W. (Akademie der Wissenschaften der DDR, Jena. Physikalisch-Technisches Inst.)

    1983-08-01

    Results of CC-DLTS (constant-capacitance-deep-level-transient-spectroscopy) investigations of MOS structures are presented, which show the influence of electron-beam irradiation on the spectrum of interface states in the silicon gap at the Si-SiO/sub 2/ interface. They lead to a clear identification of a special interface state as a radiation induced one.

  12. The collision frequency model of the solid state plasma for Si/Si1-xGex/Si SPiN device

    Science.gov (United States)

    Kang, H. Y.; Hu, H. Y.; Wang, B.; Zhang, H. M.; Su, H.; Hao, M. R.

    2017-01-01

    A two dimensional(2D) collision frequency model is developed based on the 2D solid state plasma concentration distribution model and mobility model for a heterogeneous Si/Si1-xGex/Si structure SPiN(Surface PiN) devices, which are the basic radiating elements in the reconfigurable solid state plasma antenna. The lower collision frequency can be achieved when the Ge mole fraction x and applied voltage increase at the temperature T=300 K, and that the basically uniform distribution of collision frequency can be obtained for Ge mole fraction x=0.3. Moreover, radiation efficiency and the maximum gain of the antenna for the different collision frequency have also been studied. The proposed model can be a handful for the designing of the solid state plasma antenna.

  13. Effect of Surface Plasmon Coupling to Optical Cavity Modes on the Field Enhancement and Spectral Response of Dimer-Based sensors

    KAUST Repository

    Alrasheed, Salma

    2017-09-05

    We present a theoretical approach to narrow the plasmon linewidth and enhance the near-field intensity at a plasmonic dimer gap (hot spot) through coupling the electric localized surface plasmon (LSP) resonance of a silver hemispherical dimer with the resonant modes of a Fabry-Perot (FP) cavity. The strong coupling is demonstrated by the large anticrossing in the reflection spectra and a Rabi splitting of 76 meV. Up to 2-fold enhancement increase can be achieved compared to that without using the cavity. Such high field enhancement has potential applications in optics, including sensors and high resolution imaging devices. In addition, the resonance splitting allows for greater flexibility in using the same array at different wavelengths. We then further propose a practical design to realize such a device and include dimers of different shapes and materials.

  14. Universality in bosonic dimer-dimer scattering

    Energy Technology Data Exchange (ETDEWEB)

    Deltuva, A. [Centro de Fisica Nuclear, Universidade de Lisboa, P-1649-003 Lisboa (Portugal)

    2011-08-15

    Bosonic dimer-dimer scattering is studied near the unitary limit using momentum-space equations for the four-particle transition operators. The impact of the Efimov effect on the dimer-dimer scattering observables is explored, and a number of universal relations is established with high accuracy. The rate for the creation of Efimov trimers via dimer-dimer collisions is calculated.

  15. Gold nanoparticle dimer plasmonics: finite element method calculations of the electromagnetic enhancement to surface-enhanced Raman spectroscopy.

    Science.gov (United States)

    McMahon, Jeffrey M; Henry, Anne-Isabelle; Wustholz, Kristin L; Natan, Michael J; Freeman, R Griffith; Van Duyne, Richard P; Schatz, George C

    2009-08-01

    Finite element method calculations were carried out to determine extinction spectra and the electromagnetic (EM) contributions to surface-enhanced Raman spectroscopy (SERS) for 90-nm Au nanoparticle dimers modeled after experimental nanotags. The calculations revealed that the EM properties depend significantly on the junction region, specifically the distance between the nanoparticles for spacings of less than 1 nm. For extinction spectra, spacings below 1 nm lead to maxima that are strongly red-shifted from the 600-nm plasmon maximum associated with an isolated nanoparticle. This result agrees qualitatively well with experimental transmission electron microscopy images and localized surface plasmon resonance spectra that are also presented. The calculations further revealed that spacings below 0.5 nm, and especially a slight fusing of the nanoparticles to give tiny crevices, leads to EM enhancements of 10(10) or greater. Assuming a uniform coating of SERS molecules around both nanoparticles, we determined that regardless of the separation, the highest EM fields always dominate the SERS signal. In addition, we determined that for small separations less than 3% of the molecules always contribute to greater than 90% of the signal.

  16. Fabrication and ferromagnetism of Si-SiGe/MnGe core-shell nanopillars

    Science.gov (United States)

    Wang, Liming; Liu, Tao; Wang, Shuguang; Zhong, Zhenyang; Jia, Quanjie; Jiang, Zuimin

    2016-10-01

    Si-Si0.5Ge0.5/Mn0.08Ge0.92 core-shell nanopillar samples were fabricated on ordered Si nanopillar patterned substrates by molecular beam epitaxy at low temperatures. The magnetic properties of the samples are found to depend heavily on the growth temperature of the MnGe layer. The sample grown at a moderate temperature of 300 °C has the highest Curie temperature of 240 K as well as the strongest ferromagnetic signals. On the basis of the microstructural results, the ferromagnetic properties of the samples are believed to come from the intrinsic Mn-doped amorphous or crystalline Ge ferromagnetic phase rather than any intermetallic ferromagnetic compounds of Mn and Ge. After being annealed at a temperature of 500 °C, all the samples exhibit the same Curie temperature of 220 K, which is in sharp contrast to the different Curie temperature for the as-grown samples, and the ferromagnetism for the annealed samples comes from Mn5GeSi2 compounds which are formed during the annealing.

  17. Localization of Si/SiO2 Interface States: Properties and Physical Implications

    Science.gov (United States)

    Koiller, Belita; Dusko, Amintor; Saraiva, Andre

    2013-03-01

    Interface states (IS) form spontaneously at some semiconductor-barrier interfaces and they may improve or hinder electronic control and coherence for semiconductor-based qubits. Intrinsic Si/SiO2 IS and its hybridization to the Si bulk states were recently investigated within tight binding (TB) models. From the simplest model (1D), new insights emerge regarding the IS's energy and hybridization with the band states. In this work the 1D TB Hamiltonian is further explored, here within a Green's function formalism. The problem is solved exactly via a decimation technique based on renormalization group ideas. The IS thus obtained are strictly related to the junction of two semi-infinite chains modeling the Si material and the SiO2 barrier, excluding possible contributions from parameters (e.g. chain length) previously invoked. We obtain the energy of IS as well as the exponential longer (shorter) localization lengths into the Si (barrier) material. The IS may be probed experimentally by an external electric field, which modulates the capacitance of the system, or by the spacing between the two lowest levels, related to the valley splitting. Work partially supported by FAPERJ, CNPq, CAPES.

  18. Three-dimensional crossbar arrays of self-rectifying Si/SiO2/Si memristors

    Science.gov (United States)

    Li, Can; Han, Lili; Jiang, Hao; Jang, Moon-Hyung; Lin, Peng; Wu, Qing; Barnell, Mark; Yang, J. Joshua; Xin, Huolin L.; Xia, Qiangfei

    2017-06-01

    Memristors are promising building blocks for the next-generation memory and neuromorphic computing systems. Most memristors use materials that are incompatible with the silicon dominant complementary metal-oxide-semiconductor technology, and require external selectors in order for large memristor arrays to function properly. Here we demonstrate a fully foundry-compatible, all-silicon-based and self-rectifying memristor that negates the need for external selectors in large arrays. With a p-Si/SiO2/n-Si structure, our memristor exhibits repeatable unipolar resistance switching behaviour (105 rectifying ratio, 104 ON/OFF) and excellent retention at 300 °C. We further build three-dimensinal crossbar arrays (up to five layers of 100 nm memristors) using fluid-supported silicon membranes, and experimentally confirm the successful suppression of both intra- and inter-layer sneak path currents through the built-in diodes. The current work opens up opportunities for low-cost mass production of three-dimensional memristor arrays on large silicon and flexible substrates without increasing circuit complexity.

  19. Characterization of a gate-defined double quantum dot in a Si/SiGe nanomembrane

    Science.gov (United States)

    Knapp, T. J.; Mohr, R. T.; Li, Yize Stephanie; Thorgrimsson, Brandur; Foote, Ryan H.; Wu, Xian; Ward, Daniel R.; Savage, D. E.; Lagally, M. G.; Friesen, Mark; Coppersmith, S. N.; Eriksson, M. A.

    We report the characterization of a gate-defined double quantum dot formed in a Si/SiGe nanomembrane. Previously, all heterostructures used to form quantum dots were created using the strain-grading method of strain relaxation, a method that necessarily introduces misfit dislocations into a heterostructure and thereby degrades the reproducibility of quantum devices. Using a SiGe nanomembrane as a virtual substrate eliminates the need for misfit dislocations but requires a wet-transfer process that results in a non-epitaxial interface in close proximity to the quantum dots. We show that this interface does not prevent the formation of quantum dots, and is compatible with a tunable inter-dot tunnel coupling, the identification of spin states, and the measurement of a singlet-to-triplet transition as a function of the applied magnetic field. This work was supported in part by ARO (W911NF-12-0607), NSF (DMR-1206915, PHY-1104660), and the United States Department of Defense. The views and conclusions contained in this document are those of the author and should not be interpreted as representing the official policies, either expressly or implied, of the US Government. T.J. Knapp et al. (2015). arXiv:1510.08888 [cond-mat.mes-hall].

  20. Ballistic rectification in an asymmetric Si/SiGe cross junction with modulated electron density

    Energy Technology Data Exchange (ETDEWEB)

    Salloch, Daniel; Wieser, Ulrich; Kunze, Ulrich [Werkstoffe und Nanoelektronik, Ruhr-Universitaet Bochum (Germany); Hackbarth, Thomas [DaimlerChrysler Forschungszentrum Ulm (Germany)

    2010-07-01

    We demonstrate a substantial efficiency increase in an injection-type ballistic rectifier due to a modulated electron density in its active region. The rectifier is a nanoscale four-terminal {psi}-shaped cross junction fabricated from a high-mobility Si/SiGe heterostructure. Two nanoscale Schottky gates are locally deposited on top of the central stem above and below the cross junction. In addition to the inertial-ballistic rectified voltage, which will develop between the upper and lower end of the central stem if a current is injected between the branches, a hot-electron thermopower voltage establishes across the saddle-point potential formed below the local gate for negative gate-voltages. At T=4.2 K we observe an increase of the rectified signal due to the superposed hot-electron thermopower for negative gate voltages. Depending on the position of the constriction in the stem, a sign reversal of the output signal is also demonstrated. Both signals are experimentally separated in a modified device geometry.

  1. Si-Si0.7Ge0.3-Si结构的电阻特性%Resistance Characteristics of Si-Si0.7Ge0.3-Si Structure

    Institute of Scientific and Technical Information of China (English)

    王昱为; 黄非; 熊峰; 朱鹏飞; 祝昆

    2016-01-01

    Si-Si0.7Ge0.3-Si结构在激光的照射下,电阻值会随激光照射点位置的改变而改变.通过实验测量获得激光扫描Si-Si0.7Ge0.3-Si结构样品表面的二维数据分布图,并对水平方向与垂直方向进行分析,得到的电阻灵敏度最高为8.59 MΩ/mm.当激光在器件表面上的扫描线偏离X轴时,灵敏度会逐渐降低为7.72、3.98和1.50 MΩ/mm.研究表明,作为一种新型的位移传感器,Si-Si0.7Ge0.3-Si结构的电阻—位置关系曲线具有灵敏度高和线性关系好的特点.

  2. Energy band design for p-type tensile strained Si/SiGe multi-quantum well infrared photodetector

    Institute of Scientific and Technical Information of China (English)

    LI Jin-tao; CHEN Song-yan; QI Dong-feng; HUANG Wei; LI Cheng; LAI Hong-kai

    2011-01-01

    The band structure of the confined states is calculated for Si/SiGe multi-quantum well infrared photodetector (M-QWIP). The influence of the Ge component in pseudosubstrate on the energy band structure of Si/Si0.54Ce0.46 multi-quantum wells (MQWs) is investigated. It is found that the high energy levels in the MQWs move up while the low energy levels move down as the Ge component in psendosubstrate increases. The influence of the barrier width on the energy band structure of MQWs is also studied based on the 6 × 6 k-p method. The results show that the Si barrier between 5 nm and 10 nm is optimized to enhance the intersubband absorption in the MQWs.

  3. Optical Properties of Single-Wall Carbon Nanotube Films Deposited on Si/SiO2 Wafers

    OpenAIRE

    Soetedjo, Hariyadi; Mora, Maria F.; Garcia, Carlos D.

    2010-01-01

    The paper describes a set of simple experiments performed to develop an optical model to describe Si/SiO2 substrates coated with two transparent films of carbon nanotubes. The final goal is to use such optical model to investigate the interaction of proteins with carbon nanotubes. Experiments were performed to assess light reflection as a function of the wavelength or angle of incidence using two substrates (same material, different amounts) composed of oxidized carbon nanotubes. The experime...

  4. Ab initio 3D potential energy and dipole moment surfaces for the CH4-Ar complex: Collision-induced intensity and dimer content.

    Science.gov (United States)

    Kalugina, Yulia N; Lokshtanov, Sergei E; Cherepanov, Victor N; Vigasin, Andrey A

    2016-02-07

    We present new three-dimensional potential energy surface (PES) and dipole moment surfaces (DMSs) for the CH4-Ar van der Waals system. Ab initio calculations of the PES and DMS were carried out using the closed-shell single- and double-excitation coupled cluster approach with non-iterative perturbative treatment of triple excitations. The augmented correlation-consistent aug-cc-pVXZ (X = D,T,Q) basis sets were employed, and the energies obtained were then extrapolated to the complete basis set limit. The dipole moment surface was obtained using aug-cc-pVTZ basis set augmented with mid-bond functions for better description of exchange interactions. The second mixed virial coefficient was calculated and compared to available experimental data. The equilibrium constant for true dimer formation was calculated using classical partition function based on the knowledge of ab initio PES. Temperature variations of the zeroth spectral moment of the rototranslational collision-induced band as well as its true dimer constituent were traced with the use of the Boltzmann-weighted squared induced dipole properly integrated over respective phase space domains. Height profiles for N2-N2, N2-H2, CH4-N2, (CH4)2, and CH4-Ar true bound dimers in Titan's atmosphere were calculated with the use of reliable ab initio  PESs.

  5. Quantization and anomalous structures in the conductance of Si/SiGe quantum point contacts

    Science.gov (United States)

    von Pock, J. F.; Salloch, D.; Qiao, G.; Wieser, U.; Hackbarth, T.; Kunze, U.

    2016-04-01

    Quantum point contacts (QPCs) are fabricated on modulation-doped Si/SiGe heterostructures and ballistic transport is studied at low temperatures. We observe quantized conductance with subband separations up to 4 meV and anomalies in the first conductance plateau at 4e2/h. At a temperature of T = 22 mK in the linear transport regime, a weak anomalous kink structure arises close to 0.5(4e2/h), which develops into a distinct plateau-like structure as temperature is raised up to T = 4 K. Under magnetic field parallel to the wire up to B = 14 T, the anomaly evolves into the Zeeman spin-split level at 0.5(4e2/h), resembling the "0.7 anomaly" in GaAs/AlGaAs QPCs. Additionally, a zero-bias anomaly (ZBA) is observed in nonlinear transport spectroscopy. At T = 22 mK, a parallel magnetic field splits the ZBA peak up into two peaks. At B = 0, elevated temperatures lead to similar splitting, which differs from the behavior of ZBAs in GaAs/AlGaAs QPCs. Under finite dc bias, the differential resistance exhibits additional plateaus approximately at 0.8(4e2/h) and 0.2(4e2/h) known as "0.85 anomaly" and "0.25 anomaly" in GaAs/AlGaAs QPCs. Unlike the first regular plateau at 4e2/h, the 0.2(4e2/h) plateau is insensitive to dc bias voltage up to at least VDS = 80 mV, in-plane magnetic fields up to B = 15 T, and to elevated temperatures up to T = 25 K. We interpret this effect as due to pinching off one of the reservoirs close to the QPC. We do not see any indication of lifting of the valley degeneracy in our samples.

  6. Spin Dependent Transport in Si/SiGe Few-Electron Quantum Dots

    Science.gov (United States)

    Simmons, Christie

    2008-03-01

    Si/SiGe quantum dots are of interest for quantum information processing due in large part to the existence of spin zero isotopes of both Si and Ge. We present the results of transport measurements and integrated charge sensing in silicon double and single quantum dots.[1,2] We observe two effects arising from spin dependent transport in a double quantum dot. First, and as expected, for one direction of current flow we observe spin blockade -- the canonical example of spin-to-charge conversion in transport. In addition, when current flow is reversed, we observe a second effect: strong tails of current extend from the sharp triangular regions in which current conventionally is observed. The presence of these tails is explained by a combination of long spin relaxation times and preferential loading of an excited spin state. We also present charge-sensing measurements of single and double quantum dots using an integrated quantum point contact. The charge sensor signal from single electron tunneling is well correlated with conventional transport through the system. When the tunnel barriers are large and transport through the dot is not measurable, charge sensing remains a viable means to track charge transitions and is used to confirm individual-electron occupation in a single quantum dot. Work performed in collaboration with Nakul Shaji, Madhu Thalakulam, Levente J. Klein, H. Luo, Hua Qin, R. H. Blick, D. E. Savage, M. G. Lagally, A. J. Rimberg, R. Joynt, M. Friesen, S. N. Coppersmith, M. A. Eriksson. Work supported by ARO, LPS, NSF and DOE. (1) Shaji, N. et al. e-print arXiv:0708.0794 (2) Simmons, C. B. et al. Appl. Phys. Lett. 91, 213103 (2007).

  7. Microstructure and electrochemical performance of Si-SiO{sub 2}-C composites as the negative material for Li-ion batteries

    Energy Technology Data Exchange (ETDEWEB)

    Lu, Zhiwei; Zhang, Lianqi; Liu, Xingjiang [National Key Laboratory of Power Source, Tianjin Institute of Power Sources, No. 18 Lingzhuangzi Road, Tianjin 300381 (China)

    2010-07-01

    Si-SiO{sub 2}-C composites are synthesized by ball milling the mixture of SiO, graphite and coal pitch, and subsequent heat treatment at 900 C in inert atmosphere. The electrochemical performance and microstructure of the composites are investigated. XRD and TEM tests indicate that the carbon-coating structure of Si-SiO{sub 2}-C composites form in pyrolysis process, which can remarkably improve the electrochemical cycling performance. The coal pitch as carbon precursor and graphite demonstrate the same important effect on the Li-alloying/de-alloying property of the Si-SiO{sub 2}-C composites. The Si-SiO{sub 2}-C composites exhibit the electrochemical reversible Li-alloying/de-alloying capacity of 700 mAh g{sup -1} and excellent cyclic stability even at about the 90th cycle. (author)

  8. Charge losses in silicon sensors and electric-field studies at the Si-SiO{sub 2} interface

    Energy Technology Data Exchange (ETDEWEB)

    Poehlsen, Thomas

    2013-07-15

    Electric fields and charge losses in silicon sensors before and after irradiation with x-rays, protons, neutrons or mixed irradiation are studied in charge-collection measurements. Electron-hole pairs (eh pairs) are generated at different positions in the sensor using sub-ns pulsed laser light of different wavelengths. Light of 1063 nm, 830 nm and 660 nm wavelength is used to generate eh pairs along the whole sensor depth, a few {mu}m below the surface and very close to the surface, respectively. Segmented p{sup +}n silicon strip sensors are used to study the electric field below the SiO{sub 2} separating the strip implants. The sensors are investigated before and after irradiation with 12 keV X-rays to a dose of 1 MGy. It is found that the electric field close to the Si-SiO{sub 2} interface depends on both the irradiation dose and the biasing history. For the non-irradiated sensors the observed dependence of the electric field on biasing history and humidity is qualitatively as expected from simulations of the electrostatic potential for different boundary conditions at the surface. Depending on the biasing history incomplete collection of electrons, full charge collection or incomplete collection of holes is observed. After the bias voltage is changed, the amount of observed charge losses is time dependent with time constants being a function of humidity. For the irradiated sensors an increased effective oxide charge density and more electron losses are observed compared to the non-irradiated sensors. Due to positive oxide charges which are always present at the Si-SiO{sub 2} interface an electronaccumulation layer forms, if the oxide charge is not compensated by charges on top of the passivation. If negative charges overcompensate the oxide charge, a hole-accumulation layer forms. In both cases the number of accumulated charges can be temporarily increased by incomplete charge collection of either electrons or holes. How many additional charge carriers can be

  9. Spontaneous dimerization, critical lines, and short-range correlations in a frustrated spin-1 chain

    Science.gov (United States)

    Chepiga, Natalia; Affleck, Ian; Mila, Frédéric

    2016-11-01

    We report on a detailed investigation of the spin-1 J1-J2-J3 Heisenberg model, a frustrated model with nearest-neighbor coupling J1, next-nearest neighbor coupling J2, and a three-site interaction J3[(Si -1.Si) (Si.Si +1) +H .c . ] previously studied in [Phys. Rev. B 93, 241108(R) (2016), 10.1103/PhysRevB.93.241108]. Using density matrix renormalization group (DMRG) and exact diagonalizations, we show that the phase boundaries between the Haldane phase, the next-nearest neighbor Haldane phase, and the dimerized phase can be very accurately determined by combining the information deduced from the dimerization, the ground-state energy, the entanglement spectrum and the Berry phase. By a careful investigation of the finite-size spectrum, we also show that the transition between the next-nearest neighbor Haldane phase and the dimerized phase is in the Ising universality class all along the critical line. Furthermore, we justify the conformal embedding of the SU (2) 2 Wess-Zumino-Witten conformal field theory in terms of a boson and an Ising field, and we explicitly derive a number of consequences of this embedding for the spectrum along the SU (2) 2 transition line between the Haldane phase and the dimerized phase. We also show that the solitons along the first-order transition line between the Haldane phase and the dimerized phase carry a spin-1/2, while the domain walls between different dimerization domains inside the dimerized phase carry a spin 1. Finally, we show that short-range correlations change character in the Haldane and dimerized phases through disorder and Lifshitz lines, as well as through the development of short-range dimer correlations in the Haldane phase, leading to a remarkably rich phase diagram.

  10. Different strain relaxation mechanisms in strained Si/Si sub 1 sub - sub x Ge sub x /Si heterostructures by high dose B sup + and BF sub 2 sup + doping

    CERN Document Server

    Chen, C C; Zhang, S L; Zhu, D Z; Vantomme, A

    2002-01-01

    Strained Si/Si sub 0 sub . sub 8 Ge sub 0 sub . sub 2 /Si heterostructures are implanted at room temperature with 7.5 keV B sup + and 33 keV BF sub 2 sup + ions to a high dose of 2x10 sup 1 sup 5 ions/cm sup 2 , respectively. The samples are subsequently subjected to three-step anneals (spacer anneal, oxidation anneal and rapid thermal anneal), which are used to simulate a real fabrication process of SiGe-based MOSFET devices. The damage induced by implantation and its recovery are characterized by 2 MeV sup 4 He sup + RBS/channeling spectrometry. A damage layer on the surface is induced by B sup + implantation, but BF sup + sub 2 ion implantation amorphizes the surface of Si/Si sub 0 sub . sub 8 Ge sub 0 sub . sub 2 /Si heterostructure. Channeling angular scans along the axial direction demonstrate that the strain stored in the SiGe layer could be nearly completely retained for the B sup + implanted and subsequently annealed sample. However, the strain in the BF sub 2 sup + implanted/annealed SiGe layer has...

  11. Robust design of Si/Si3N4 high contrast grating mirror for mid-infrared VCSEL application

    CERN Document Server

    Chevallier, Christyves; Genty, Frédéric; Jacquet, Joel

    2012-01-01

    A Si/Si3N4 high contrast grating mirror has been designed for a VCSEL integration in mid-infrared ({\\lambda} = 2.65 $\\mu$m). The use of an optimization algorithm which maximizes a VCSEL mirror quality factor allowed the adjustment of the grating parameters while keeping large and shallow grating pattern. The robustness with respect to fabrication error has been enhanced thanks to a precise study of the grating dimension tolerances. The final mirror exhibits large high reflectivity bandwidth with a polarization selectivity and several percent of tolerance on the grating dimensions.

  12. Integration of complementary circuits and two-dimensional electron gas in a Si/SiGe heterostructure

    Science.gov (United States)

    Lu, T. M.; Lee, C.-H.; Tsui, D. C.; Liu, C. W.

    2010-06-01

    We have realized complementary devices on an undoped Si/SiGe substrate where both two-dimensional electrons and holes can be induced capacitively. The design of the heterostructure and the fabrication process are reported. Magnetotransport measurements show that the induced two-dimensional electron gas exhibits the quantum Hall effect characteristics. A p-channel field-effect transistor is characterized and the operation of an inverter is demonstrated. The proof-of-principle experiment shows the feasibility of integrating complementary logic circuits with quantum devices.

  13. Charge noise analysis of metal oxide semiconductor dual-gate Si/SiGe quantum point contacts

    Energy Technology Data Exchange (ETDEWEB)

    Kamioka, J.; Oda, S. [Quantum Nanoelectronics Research Center, Tokyo Institute of Technology, 2-12-1-S9-11, Ookayama, Meguro-ku, Tokyo, 152-8552 (Japan); Kodera, T., E-mail: kodera.t.ac@m.titech.ac.jp [Quantum Nanoelectronics Research Center, Tokyo Institute of Technology, 2-12-1-S9-11, Ookayama, Meguro-ku, Tokyo, 152-8552 (Japan); Department of Physical Electronics, Tokyo Institute of Technology, 2-12-1-NE-25, Ookayama, Meguro-ku, Tokyo, 152-8552 (Japan); PRESTO, Japan Science and Technology Agency (JST), 4-1-8 Honcho, Kawaguchi, Saitama 332-0012 (Japan); Takeda, K.; Obata, T. [Department of Applied Physics, School of Engineering, The University of Tokyo, 7-3-1, Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan); Tarucha, S. [Department of Applied Physics, School of Engineering, The University of Tokyo, 7-3-1, Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan); RIKEN, Center for Emergent Matter Science (CEMS), 2-1, Hirosawa, Wako, Saitama 351-0198 (Japan)

    2014-05-28

    The frequency dependence of conductance noise through a gate-defined quantum point contact fabricated on a Si/SiGe modulation doped wafer is characterized. The 1/f{sup 2} noise, which is characteristic of random telegraph noise, is reduced by application of a negative bias on the global top gate to reduce the local gate voltage. Direct leakage from the large global gate voltage also causes random telegraph noise, and therefore, there is a suitable point to operate quantum dot measurement.

  14. Si/Si1- xGex HEMT结构设计的研究%Study of Si/Si1- xGex HEMT structure design

    Institute of Scientific and Technical Information of China (English)

    胡英; 周晓华; 徐毓龙; 赵祖军

    2001-01-01

    从晶格匹配及能带阶跃角度讨论了 n沟 Si /Si1- xGex HEMT结构的设计原理及方法,对 Ismail器件进行了分析和计算,所得二维电子气 (2DEG)的 ns与实验结果基本相符,并利用该设计 理论对 Ismail器件的异质结结构进行了优化改进,提高了器件 2DEG的 ns。%The principle and methed of n- Si/Si1- xGex HEMT structure design has been discussed from the lattice match and the energy band discontinuity points. 2DEG density ns of the HEMT Ismail reported is essentially according with the experiment data. Final the design of the heterojunction of Ismail's HEMT is improved with higher 2DEG density ns.

  15. STM characterization of MOVPE-prepared silicon surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Kleinschmidt, Peter; Brueckner, Sebastian; Luczak, Johannes; Supplie, Oliver; Dobrich, Anja; Doescher, Henning; Hannappel, Thomas [Helmholtz-Zentrum Berlin fuer Materialien und Energie, Hahn-Meitner-Platz 1, 14109 Berlin (Germany)

    2011-07-01

    The clean Si(100) surface reconstructs by forming dimers, thus reducing the number of dangling bonds at the surface. In the MOVPE environment hydrogen is commonly used as process gas, which leads to a monohydride silicon surface with a 2 x 1 unit cell consisting of H-Si-Si-H dimers. Even so, the quality of the surface can vary dramatically depending on process conditions. In general, annealing in hydrogen leads to a two-domain surface structure with monoatomic steps, where the resulting structure also strongly depends on misorientation. We find process conditions for preparation of Si(100) surfaces with 0.1 , 2 and 6 offcut where a strong preference for one domain is obtained, making the resulting surfaces ideal substrates for III-V-on-Si epitaxy. A process consisting of deoxidation, homoepitaxial buffer layer growth and annealing is found to result in D{sub A}-type double layer steps for 0.1 , and D{sub B}-type double layer steps for 6 offcut. The identical process leads to single layer steps for 2 offcut. Here, we obtain D{sub A}-type double layer steps by a modified process which includes a slow cooling phase after the annealing step. Our results, verified by scanning tunneling microscopy, low energy electron diffraction and Fourier-transform infrared spectroscopy, are in sharp contrast to the clean and the hydrogenated Si(100) surface prepared in UHV.

  16. Gate fidelity and coherence of an electron spin in an Si/SiGe quantum dot with micromagnet.

    Science.gov (United States)

    Kawakami, Erika; Jullien, Thibaut; Scarlino, Pasquale; Ward, Daniel R; Savage, Donald E; Lagally, Max G; Dobrovitski, Viatcheslav V; Friesen, Mark; Coppersmith, Susan N; Eriksson, Mark A; Vandersypen, Lieven M K

    2016-10-18

    The gate fidelity and the coherence time of a quantum bit (qubit) are important benchmarks for quantum computation. We construct a qubit using a single electron spin in an Si/SiGe quantum dot and control it electrically via an artificial spin-orbit field from a micromagnet. We measure an average single-qubit gate fidelity of ∼99% using randomized benchmarking, which is consistent with dephasing from the slowly evolving nuclear spins in the substrate. The coherence time measured using dynamical decoupling extends up to ∼400 μs for 128 decoupling pulses, with no sign of saturation. We find evidence that the coherence time is limited by noise in the 10-kHz to 1-MHz range, possibly because charge noise affects the spin via the micromagnet gradient. This work shows that an electron spin in an Si/SiGe quantum dot is a good candidate for quantum information processing as well as for a quantum memory, even without isotopic purification.

  17. Transport properties of double-gate SiO{sub 2}-Si-SiO{sub 2} quantum well

    Energy Technology Data Exchange (ETDEWEB)

    Prunnila, Mika; Ahopelto, Jouni [VTT Information Technology, Microelectronics, P.O. Box 1208, 02044 VTT (Finland); Sakaki, Hiroyuki [University of Tokyo, Institute of Industrial Science, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8503 (Japan)

    2005-05-01

    We report on fabrication and low temperature transport properties of double-gate SiO{sub 2}-Si-SiO{sub 2} quantum well with a 16.5 nm thick Si layer. The device is fabricated on a silicon-on-insulator substrate utilizing wafer bonding, which enables us to use heavily doped back gate. Transport properties of the device are characterized by low field Hall and high field magnetotransport measurements at 4.2 K and at 0.38 K, respectively. Top (back) Si-SiO{sub 2} interface peak mobility of 1.9 m{sup 2}/Vs (1.0 m{sup 2}/Vs) is measured at 4.2 K. When both gates have a (large) positive bias the Hall carrier density is observed to fall below the value of the expected total carrier density, which is interpreted to arise from the occupancy of the second sub-band in the Si well. This is confirmed by the high field magnetotransport measurements. In quantizing magnetic fields the longitudinal resistivity minima show Landau level filling factor behavior which is typical for weakly coupled bi-layers. (copyright 2005 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  18. Large area and depth-profiling dislocation imaging and strain analysis in Si/SiGe/Si heterostructures.

    Science.gov (United States)

    Chen, Xin; Zuo, Daniel; Kim, Seongwon; Mabon, James; Sardela, Mauro; Wen, Jianguo; Zuo, Jian-Min

    2014-10-01

    We demonstrate the combined use of large area depth-profiling dislocation imaging and quantitative composition and strain measurement for a strained Si/SiGe/Si sample based on nondestructive techniques of electron beam-induced current (EBIC) and X-ray diffraction reciprocal space mapping (XRD RSM). Depth and improved spatial resolution is achieved for dislocation imaging in EBIC by using different electron beam energies at a low temperature of ~7 K. Images recorded clearly show dislocations distributed in three regions of the sample: deep dislocation networks concentrated in the "strained" SiGe region, shallow misfit dislocations at the top Si/SiGe interface, and threading dislocations connecting the two regions. Dislocation densities at the top of the sample can be measured directly from the EBIC results. XRD RSM reveals separated peaks, allowing a quantitative measurement of composition and strain corresponding to different layers of different composition ratios. High-resolution scanning transmission electron microscopy cross-section analysis clearly shows the individual composition layers and the dislocation lines in the layers, which supports the EBIC and XRD RSM results.

  19. Analyses of the As doping of SiO{sub 2}/Si/SiO{sub 2} nanostructures

    Energy Technology Data Exchange (ETDEWEB)

    Ruffino, Francesco; Miritello, Maria [CNR-IMM MATIS, via S. Sofia 64, 95123 Catania (Italy); Tomasello, Mario Vincenzo [Scuola Superiore di Catania, via San Nullo 5/i, 95123 Catania (Italy); De Bastiani, Riccardo; Grimaldi, Maria Grazia [Dipartimento di Fisica ed Astronomia, Universita di Catania, via S. Sofia 64, 95123 Catania (Italy); CNR-IMM MATIS, via S. Sofia 64, 95123 Catania (Italy); Nicotra, Giuseppe; Spinella, Corrado [Consiglio Nazionale delle Ricerche-Istituto per la Microelettronica e Microsistemi (CNR-IMM), VIII Strada 5, 95121 Catania (Italy)

    2011-03-15

    We illustrate the behaviour of As when it is confined, by the implantation technique, in a SiO{sub 2}(70nm)/Si(30nm)/SiO{sub 2}(70nm) multilayer and its spatial redistribution when annealing processes are performed. By Rutherford backscattering spectrometry and Z-contrast transmission electron microscopy we found an As accumulation at the Si/SiO{sub 2} interfaces and at the Si grain boundaries with no segregation of the As in the Si layer. Such an effect is in agreement with a model that assumes a traps distribution in the Si in the first 2-3 nm above the SiO{sub 2}/Si interfaces and along the Si grain boundaries. The traps concentration at the Si/SiO{sub 2} interfaces was estimated in 10{sup 14} traps/cm{sup 2}. The outlined results can open perspectives on the doping properties of As in Si nanocrystals, whose applications in nanoelectronics and optoelectronics are widely investigated (copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  20. Identification of photoluminescence P line in indium doped silicon as In{sub Si}-Si{sub i} defect

    Energy Technology Data Exchange (ETDEWEB)

    Lauer, Kevin, E-mail: klauer@cismst.de; Möller, Christian [CiS Forschungsinstitut für Mikrosensorik und Photovoltaik GmbH, Konrad-Zuse-Str. 14, 99099 Erfurt (Germany); Schulze, Dirk [TU Ilmenau, Institut für Physik, Weimarer Str. 32, 98693 Ilmenau (Germany); Ahrens, Carsten [Infineon Technologies AG, Am Campeon 1-12, 85579 Neubiberg (Germany)

    2015-01-15

    Indium and carbon co-implanted silicon was investigated by low-temperature photoluminescence spectroscopy. A photoluminescence peak in indium doped silicon (P line) was found to depend on the position of a silicon interstitial rich region, the existence of a SiN{sub x}:H/SiO{sub x} stack and on characteristic illumination and annealing steps. These results led to the conclusion that silicon interstitials are involved in the defect and that hydrogen impacts the defect responsible for the P line. By applying an unique illumination and annealing cycle we were able to link the P line defect with a defect responsible for degradation of charge carrier lifetime in indium as well as boron doped silicon. We deduced a defect model consisting of one acceptor and one silicon interstitial atom denoted by A{sub Si}-Si{sub i}, which is able to explain the experimental data of the P line as well as the light-induced degradation in indium and boron doped silicon. Using this model we identified the defect responsible for the P line as In{sub Si}-Si{sub i} in neutral charge state and C{sub 2v} configuration.

  1. Theoretically predicted and experimentally determined effects of the Si/(Si + C) gas phase ratio on the growth and character of monocrystalline beta silicon carbide films

    Science.gov (United States)

    Kim, H. J.; Davis, R. F.

    1986-10-01

    The effects of the Si/(Si + C) ratio in the reaction gas stream on the growth and properties of monocrystalline beta-SiC films grown on Si(100) substrates via chemical vapor deposition have been theoretically and experimentally studied. The amounts of condensed phases of beta-SiC and Si, and the partial pressures of the remaining Si and C-containing gases as a function of the Si/(Si + C) ratio in the source gases have been initially obtained from thermodynamic calculations using the 'SOLGASMIX-PV' computer program. Complementary and comparative experimental growth studies have shown that inclusion-free films having maximum values in growth rate and carrier concentration and a minimum value of resistivity were obtained near Si/(Si + C) = 0.5.

  2. In vitro evaluation of diamond-like carbon coatings with a Si/SiC {sub x} interlayer on surgical NiTi alloy

    Energy Technology Data Exchange (ETDEWEB)

    Liu, C.L. [Department of Physics and Materials Science, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong (China); State Key Laboratory of Materials Modification by Laser, Ion and Electron Beams, Dalian University of Technology, Dalian 116024 (China); Chu, Paul K. [Department of Physics and Materials Science, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong (China)]. E-mail: paul.chu@cityu.edu.hk; Yang, D.Z. [State Key Laboratory of Materials Modification by Laser, Ion and Electron Beams, Dalian University of Technology, Dalian 116024 (China)

    2007-04-15

    Diamond-like carbon (DLC) coatings were produced with a Si/SiC {sub x} interlayer by a hybrid plasma immersion ion implantation and deposition process to improve the adhesion between the carbon layer and surgical NiTi alloy substrate. The structure, mechanical properties, corrosion resistance and biocompatibility of the coatings were evaluated in vitro by Raman spectroscopy, pin-on-disk tests, potentiodynamic polarization tests and simulated fluid immersion tests. The DLC coatings with a Si/SiC {sub x} interlayer of a suitable thickness have better adhesion, lower friction coefficients and enhanced corrosion resistance. In the simulated body fluid tests, the coatings exhibit effective corrosion protection and good biocompatibility as indicated by PC12 cell cultures. DLC films fabricated on a Si/SiC {sub x} interlayer have high potential as protective coatings for biomedical NiTi materials.

  3. Toward chemical accuracy in the description of ion-water interactions through many-body representations. Alkali-water dimer potential energy surfaces

    Science.gov (United States)

    Riera, Marc; Mardirossian, Narbe; Bajaj, Pushp; Götz, Andreas W.; Paesani, Francesco

    2017-10-01

    This study presents the extension of the MB-nrg (Many-Body energy) theoretical/computational framework of transferable potential energy functions (PEFs) for molecular simulations of alkali metal ion-water systems. The MB-nrg PEFs are built upon the many-body expansion of the total energy and include the explicit treatment of one-body, two-body, and three-body interactions, with all higher-order contributions described by classical induction. This study focuses on the MB-nrg two-body terms describing the full-dimensional potential energy surfaces of the M+(H2O) dimers, where M+ = Li+, Na+, K+, Rb+, and Cs+. The MB-nrg PEFs are derived entirely from "first principles" calculations carried out at the explicitly correlated coupled-cluster level including single, double, and perturbative triple excitations [CCSD(T)-F12b] for Li+ and Na+ and at the CCSD(T) level for K+, Rb+, and Cs+. The accuracy of the MB-nrg PEFs is systematically assessed through an extensive analysis of interaction energies, structures, and harmonic frequencies for all five M+(H2O) dimers. In all cases, the MB-nrg PEFs are shown to be superior to both polarizable force fields and ab initio models based on density functional theory. As previously demonstrated for halide-water dimers, the MB-nrg PEFs achieve higher accuracy by correctly describing short-range quantum-mechanical effects associated with electron density overlap as well as long-range electrostatic many-body interactions.

  4. Ionic S(N)i-Si Nucleophilic Substitution in N-Methylaniline-Induced Si-Si Bond Cleavages of Si2Cl6.

    Science.gov (United States)

    Zhang, Jie; Xie, Ju; Lee, Myong Euy; Zhang, Lin; Zuo, Yujing; Feng, Shengyu

    2016-03-24

    N-Methylaniline-induced Si-Si bond cleavage of Si2Cl6 has been theoretically studied. All calculations were performed by using DFT at the MPWB1K/6-311++G(3df,2p)//MPWB1K/6-31+G(d,p) levels. An ionic SN i-Si nucleophilic substitution mechanism, which is a newly found nucleophilic substitution in silicon-containing compounds, is proposed in the N-methylaniline-induced Si-Si bond cleavage in Si2Cl6. Unlike general S(N)i-Si nucleophilic substitutions that go through a pentacoordinated silicon transition state, ionic nucleophilic substitution goes through a tetracoordinated silicon transition state, in which the Si-Si bond is broken and siliconium ions are formed. Special cleavage of the Si-Si bond is presumably due to the good bonding strength between Si and N atoms, which leads to polarization of the Si-Si bond and eventually to heterolytic cleavage. Calculation results show that, in excess N-methylaniline, the final products of the reaction, including (NMePh)(3-n) SiHCl(n) (n=0-2) and (NMePh)(4-n) SiCl(n) (n=2-3), are the Si-Si cleavage products of Si2Cl6 and the corresponding amination products of the former. The ionic S(N)i-Si nucleophilic substitution mechanism can also be employed to describe the amination of chlorosilane by N-methylaniline. The suggested mechanisms are consistent with experimental data.

  5. Relaxed SiGe-on-insulator fabricated by dry oxidation of sandwiched Si/SiGe/Si structure

    Energy Technology Data Exchange (ETDEWEB)

    Di Zengfeng [Research Center of Semiconductor Functional Film Engineering Technology and State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem and Information Technology (SIMIT), Chinese Academy of Sciences (CAS), Shanghai 200050 (China); Department of Physics and Material Science, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong (China); Zhang Miao [Research Center of Semiconductor Functional Film Engineering Technology and State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem and Information Technology (SIMIT), Chinese Academy of Sciences (CAS), Shanghai 200050 (China); Liu Weili [Research Center of Semiconductor Functional Film Engineering Technology and State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem and Information Technology (SIMIT), Chinese Academy of Sciences (CAS), Shanghai 200050 (China); Zhu Ming [Research Center of Semiconductor Functional Film Engineering Technology and State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem and Information Technology (SIMIT), Chinese Academy of Sciences (CAS), Shanghai 200050 (China); Department of Physics and Material Science, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong (China); Lin Chenglu [Research Center of Semiconductor Functional Film Engineering Technology and State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem and Information Technology (SIMIT), Chinese Academy of Sciences (CAS), Shanghai 200050 (China); Chu, Paul K. [Department of Physics and Material Science, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong (China)]. E-mail: paul.chu@cityu.edu.hk

    2005-12-05

    An improved technique is demonstrated to fabricate silicon-germanium on insulator (SGOI) starting with a sandwiched structure of Si/SiGe/Si. After oxidation of the sandwiched structure and successive annealing, a relaxed SiGe-on-insulator (SGOI) structure is produced. Our results indicate that the added Si cap layer is advantageous in suppressing Ge loss at the initial stage of SiGe oxidation and the subsequent annealing process homogenizes the Ge fraction. Raman measurements reveal that the strain in the SiGe layer is fully relaxed at high oxidation temperature ({approx}1150 deg. C) without generating any threading dislocations and crosshatch patterns, which generally exist in the relaxed SiGe layer on bulk Si substrate.

  6. Temporal correlation of blinking events in CdSe/ZnS and Si/SiO{sub 2} nanocrystals

    Energy Technology Data Exchange (ETDEWEB)

    Bruhn, Benjamin, E-mail: b.bruhn@uva.nl [Materials and Nanophysics, KTH Royal Institute of Technology, 164 40 Kista (Sweden); Van der Waals-Zeeman Institute, University of Amsterdam, Science Park 904, 1098 XH Amsterdam (Netherlands); Qejvanaj, Fatjon [Materials and Nanophysics, KTH Royal Institute of Technology, 164 40 Kista (Sweden); Gregorkiewicz, Tom [Van der Waals-Zeeman Institute, University of Amsterdam, Science Park 904, 1098 XH Amsterdam (Netherlands); Linnros, Jan [Materials and Nanophysics, KTH Royal Institute of Technology, 164 40 Kista (Sweden)

    2014-11-15

    Well passivated single Si/SiO{sub 2} nanoparticles obey mono-exponential blinking statistics, whereas CdSe/ZnS quantum dots follow an apparent (truncated) power-law. Log-normal distributions are found to describe the interval length histograms at least as well as power-laws, while at the same time being more physically feasible and significantly easing the determination of the exponential cutoff in the ON-time distribution. The correlation of an ON- (OFF-)interval with its temporally displaced ON (OFF) neighbors, as well as that of intermixed intervals (ON with OFF and OFF with ON neighbors) has been studied. As expected from purely random processes, the correlation coefficients for events in silicon nanocrystals equal zero, whereas positive correlations between the pure and negative correlations between the mixed states in CdSe quantum dots hint at a switching process between two distinct blinking regimes that are slower than the blinking itself.

  7. High-finesse cavities fabricated by buckling self-assembly of a-Si/SiO2 multilayers.

    Science.gov (United States)

    Allen, T W; Silverstone, J; Ponnampalam, N; Olsen, T; Meldrum, A; DeCorby, R G

    2011-09-26

    Arrays of half-symmetric Fabry-Perot micro-cavities were fabricated by controlled formation of circular delamination buckles within a-Si/SiO(2) multilayers. Cavity height scales approximately linearly with diameter, in reasonable agreement with predictions based on elastic buckling theory. The measured finesse (F > 10(3)) and quality factors (Q > 10(4) in the 1550 nm range) are close to reflectance limited predictions, indicating that the cavities have low roughness and few defects. Degenerate Hermite-Gaussian and Laguerre-Gaussian modes were observed, suggesting a high degree of cylindrical symmetry. Given their silicon-based fabrication, these cavities hold promise as building blocks for integrated optical sensing systems.

  8. Gate-defined quantum dot devices in undoped Si/SiGe heterostructures for spin qubit applications

    Science.gov (United States)

    Volk, Christian; Martins, Frederico; Marcus, Charles M.; Kuemmeth, Ferdinand

    Spin qubits based on few electron quantum dots in semiconductor heterostructures are among the most promising systems for realizing quantum computation. Due to its low concentration of nuclear-spin-carrying isotopes, silicon is of special interest as a host material. We characterize gate-defined double and triple quantum dot devices fabricated from undoped Si/Si0.7Ge0.3 heterostructures. Our device architecture is based on integrating all accumulation and depletion mode gates in a single gate layer. This allows us to omit the commonly used global accumulation gate in order to achieve a more local control of the potential landscape in the device. We present our recent progress towards implementing spin qubits in these structures. Support through the EC FP7- ICT project SiSPIN no. 323841, and the Danish National Research Foundation is acknowledged.

  9. 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.

  10. Reactive diffusion bonding of SiCp/Al composites by insert layers of mixed Al-Si and Al-Si-SiC powders

    Institute of Scientific and Technical Information of China (English)

    Jihua Huang; Yueling Dong; Yun Wan; Jiangang Zhang; Hua Zhang

    2005-01-01

    Mixed Al-Si and Al-Si-SiC powders were employed as insert layers to reactive diffusion bond SiCp/6063 MMC (metal matrix composites). The results show that SiCp/6063 MMC joints bonded by the insert layer of the mixed Al-Si powder have a dense joining layer with a typical hypoeutectic microstructure. Using the mixed Al-Si-SiC powder as the insert layer, SiCp/6063 MMC can be reactive diffusion bonded by a composite joint. Because of the SiC segregation, however, there are a number of porous zones in the joining layer, which results in the bad shear strength of the joints reactive diffusion bonded by the insert layer of the mixed Al-SiSiC powder, even lower than that of the joints reactive diffusion bonded by the insert layer of the mixed Al-Si powder. Ti and Mg added in the insert layers obviously improve the strength of the joints reactive diffusion bonded by the insert layer of the mixed AlSi-SiC powder, especially, Mg has a more obvious effect.

  11. Effect of Si/Si1-yCy/Si Barriers on the Characteristics of Si1-xGex/Si Resonant Tunneling Structures

    Institute of Scientific and Technical Information of China (English)

    HAN Ping; CHENG Xue-Mei; Masao Sakuraba; YoungCheon Jeong; Takashi Matsuura; Junichi Murota

    2000-01-01

    P-type double barrier resonant tunneling diodes (RTD) with the single Si0.6Ge0.4 quantum well and double Si0.6 Ge0.4 spacer have been realized by using an ultra clean low-pressure chemical vapor deposition system. The effect of Si1-yCy layer on the characteristics of the devices was shown by comparing the current-voltage (Ⅰ-Ⅴ) characteristics of RTD's of the barriers of Si layers with that of Si/Si1-yCy/Si structures. The peak voltage was gradually increased and the resonant current decreased obviously with increasing C content in the Si/Si1-yCy/Si barriers. The origin of the phenomena above can be attributed to the C related deep acceptor levels in the Si/Si1-yCy/Si barriers. The possible mechanism for the observed Ⅰ-Ⅴcharacteristics was shown more clearly by increasing C content to 3% and changing the thicknesses of Si and Si1-yCy layers in the Si/Si1-yCy/Si barriers.

  12. Electrically active interface defects in the (100)Si/SiOx/HfO2/TiN system: Origin, instabilities and passivation

    NARCIS (Netherlands)

    Hurley, P.K.; Cherkaoui, K.; Groenland, A.W.

    2006-01-01

    An analysis of the origin and passivation of interface states in (100)Si/SiOx/HfO2/TiN capacitor structures is presented. For high-k gate/metal gate capacitors which exhibit relatively high interface state densities (> 1x1011cm-2) the dominant interfacial defects are silicon dangling bond (Pbo) cent

  13. Si/SiGe heterointerfaces in one-, two-, and three-dimensional nanostructures: their impact on SiGe light emission

    Science.gov (United States)

    Lockwood, David; Wu, Xiaohua; Baribeau, Jean-Marc; Mala, Selina; Wang, Xialou; Tsybeskov, Leonid

    2016-03-01

    Fast optical interconnects together with an associated light emitter that are both compatible with conventional Si-based complementary metal-oxide- semiconductor (CMOS) integrated circuit technology is an unavoidable requirement for the next-generation microprocessors and computers. Self-assembled Si/Si1-xGex nanostructures, which can emit light at wavelengths within the important optical communication wavelength range of 1.3 - 1.55 μm, are already compatible with standard CMOS practices. However, the expected long carrier radiative lifetimes observed to date in Si and Si/Si1-xGex nanostructures have prevented the attainment of efficient light-emitting devices including the desired lasers. Thus, the engineering of Si/Si1-xGex heterostructures having a controlled composition and sharp interfaces is crucial for producing the requisite fast and efficient photoluminescence (PL) at energies in the range 0.8-0.9 eV. In this paper we assess how the nature of the interfaces between SiGe nanostructures and Si in heterostructures strongly affects carrier mobility and recombination for physical confinement in three dimensions (corresponding to the case of quantum dots), two dimensions (corresponding to quantum wires), and one dimension (corresponding to quantum wells). The interface sharpness is influenced by many factors such as growth conditions, strain, and thermal processing, which in practice can make it difficult to attain the ideal structures required. This is certainly the case for nanostructure confinement in one dimension. However, we demonstrate that axial Si/Ge nanowire (NW) heterojunctions (HJs) with a Si/Ge NW diameter in the range 50 - 120 nm produce a clear PL signal associated with band-to-band electron-hole recombination at the NW HJ that is attributed to a specific interfacial SiGe alloy composition. For three-dimensional confinement, the experiments outlined here show that two quite different Si1-xGex nanostructures incorporated into a Si0.6Ge0.4 wavy

  14. Si/SiGe heterointerfaces in one-, two-, and three-dimensional nanostructures: their impact on SiGe light emission

    Directory of Open Access Journals (Sweden)

    David J. Lockwood

    2016-03-01

    Full Text Available Fast optical interconnects together with an associated light emitter that are both compatible with conventional Si-based complementary metal-oxide- semiconductor (CMOS integrated circuit technology is an unavoidable requirement for the next-generation microprocessors and computers. Self-assembled Si/Si1-xGex nanostructures, which can emit light at wavelengths within the important optical communication wavelength range of 1.3 – 1.55 μm, are already compatible with standard CMOS practices. However, the expected long carrier radiative lifetimes observed to date in Si and Si/Si1-xGex nanostructures have prevented the attainment of efficient light-emitting devices including the desired lasers. Thus, the engineering of Si/Si1-xGex heterostructures having a controlled composition and sharp interfaces is crucial for producing the requisite fast and efficient photoluminescence (PL at energies in the range 0.8-0.9 eV. In this paper we assess how the nature of the interfaces between SiGe nanostructures and Si in heterostructures strongly affects carrier mobility and recombination for physical confinement in three dimensions (corresponding to the case of quantum dots, two dimensions (corresponding to quantum wires, and one dimension (corresponding to quantum wells. The interface sharpness is influenced by many factors such as growth conditions, strain, and thermal processing, which in practice can make it difficult to attain the ideal structures required. This is certainly the case for nanostructure confinement in one dimension. However, we demonstrate that axial Si/Ge nanowire (NW heterojunctions (HJs with a Si/Ge NW diameter in the range 50 – 120 nm produce a clear PL signal associated with band-to-band electron-hole recombination at the NW HJ that is attributed to a specific interfacial SiGe alloy composition. For three-dimensional confinement, the experiments outlined here show that two quite different Si1-xGex nanostructures incorporated into a Si

  15. 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.

  16. FEM for modelling 193 nm excimer laser treatment of SiO{sub 2}/Si/Si{sub (1-x)}Ge{sub x} heterostructures on SOI substrates

    Energy Technology Data Exchange (ETDEWEB)

    Conde, J.C.; Chiussi, S.; Gontad, F.; Gonzalez, P. [Dpto. Fisica Aplicada, E.T.S.I.I. University of Vigo, Campus Universitario, Rua Maxwell s/n, 36310 Vigo (Spain); Martin, E. [Dpto. de Mecanica, Maquinas, Motores Termicos y Fluidos, E.T.S.I.I. University of Vigo, Campus Universitario, Rua Maxwell s/n, 36310 Vigo (Spain)

    2011-03-15

    Research on epitaxial crystalline silicon (c-Si) and silicon-germanium (Si{sub 1-x}Ge{sub x}) alloys growth and annealing for microelectronic purposes, such as Micro- or Nano-Electro-Mechanical Systems (MEMS or NEMS) and Silicon-On-Nothing (SON) devices is continuously in progress. Laser assisted annealing techniques using commercial ArF Excimer Laser sources are based on ultra-rapid heating and cooling cycles induced by the 193 nm pulses of 20 ns, which are absorbed in the near surface region of the heterostructures. During and after the absorption of these laser pulses, complex physical processes appear that strongly depend on sample structure and applied laser pulse energy densities. The control of the experimental parameters is therefore a key task for obtaining high quality alloys. The Finite ElementsMethod (FEM) is a powerful tool for the optimization of such treatments, because it provides the spatial and temporal temperature fields that are produced by the laser pulses. In this work, we have used a FEM commercial software, to predict the temperatures gradients induced by ArF excimer laser over a wide energy densities range, 0.1<{phi}<0.4 J/cm{sup 2}, on different SiO{sub 2}/Si/Si{sub (1-x)}Ge{sub (x)} thin films deposited on SOI substrate. These numerical results allow us to predict the threshold energies needed to reach the melting point (MP) of the Si and SiGe alloy without oxidation of the thin films system. Therefore, it is possible to optimize the conditions to achieve high quality epitaxy films. (copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  17. The effect of oxide shell thickness on the structural, electronic, and optical properties of Si-SiO2 core-shell nano-crystals: A (time dependent)density functional theory study

    Science.gov (United States)

    Nazemi, Sanaz; Pourfath, Mahdi; Soleimani, Ebrahim Asl; Kosina, Hans

    2016-04-01

    Due to their tunable properties, silicon nano-crystals (NC) are currently being investigated. Quantum confinement can generally be employed for size-dependent band-gap tuning at dimensions smaller than the Bohr radius (˜5 nm for silicon). At the nano-meter scale, however, increased surface-to-volume ratio makes the surface effects dominant. Specifically, in Si-SiO2 core-shell semiconductor NCs the interfacial transition layer causes peculiar electronic and optical properties, because of the co-existence of intermediate oxidation states of silicon (Sin+, n = 0-4). Due to the presence of the many factors involved, a comprehensive understanding of the optical properties of these NCs has not yet been achieved. In this work, Si-SiO2 NCs with a diameter of 1.1 nm and covered by amorphous oxide shells with thicknesses between 2.5 and 4.75 Å are comprehensively studied, employing density functional theory calculations. It is shown that with increased oxide shell thickness, the low-energy part of the optical transition spectrum of the NC is red shifted and attenuated. Moreover, the absorption coefficient is increased in the high-energy part of the spectrum which corresponds to SiO2 transitions. Structural examinations indicate a larger compressive stress on the central silicon cluster with a thicker oxide shell. Examination of the local density of states reveals the migration of frontier molecular orbitals from the oxide shell into the silicon core with the increase of silica shell thickness. The optical and electrical properties are explained through the analysis of the density of states and the spatial distribution of silicon sub-oxide species.

  18. Si衬底和Si-SiO2-Si柔性衬底上的GaN生长%GaN Growth on Si and Si-SiO2-Si Compliant Substrates

    Institute of Scientific and Technical Information of China (English)

    王军喜; 王晓亮; 刘宏新; 胡国新; 李建平; 李晋闽; 曾一平

    2004-01-01

    使用MBE方法在Si(111)衬底和Si-SiO2-Si柔性衬底上生长了GaN外延层,并对在两种衬底上生长的样品进行了对比分析.在柔性衬底上获得了无裂纹的外延层,其表面粗糙度为0.6nm.研究了GaN外延层中的应力及其光学性质,光致发光测试结果表明柔性衬底上生长的外延层中应力和杂质浓度明显低于直接生长在Si衬底上的样品的值.研究结果显示了所用柔性衬底有助于改善GaN外延膜的质量.

  19. Neutron scattering in dimers

    DEFF Research Database (Denmark)

    Gudel, H. U.; Furrer, A.; Kjems, Jørgen

    1986-01-01

    Insulating compounds containing dimers of transition metal and rare earth ions have been studied by inelastic neutron scattering (INS). Energy splittings can be directly determined, and the corresponding parameters are easily extracted from the experimental data. The intensities of dimer excitati......Insulating compounds containing dimers of transition metal and rare earth ions have been studied by inelastic neutron scattering (INS). Energy splittings can be directly determined, and the corresponding parameters are easily extracted from the experimental data. The intensities of dimer...

  20. Adventures in Holographic Dimer Models

    Energy Technology Data Exchange (ETDEWEB)

    Kachru, Shamit; /Stanford U., Phys. Dept. /SLAC; Karch, Andreas; /Washington U., Seattle; Yaida, Sho; /Stanford U., Phys. Dept.

    2011-08-12

    We abstract the essential features of holographic dimer models, and develop several new applications of these models. Firstly, semi-holographically coupling free band fermions to holographic dimers, we uncover novel phase transitions between conventional Fermi liquids and non-Fermi liquids, accompanied by a change in the structure of the Fermi surface. Secondly, we make dimer vibrations propagate through the whole crystal by way of double trace deformations, obtaining nontrivial band structure. In a simple toy model, the topology of the band structure experiences an interesting reorganization as we vary the strength of the double trace deformations. Finally, we develop tools that would allow one to build, in a bottom-up fashion, a holographic avatar of the Hubbard model.

  1. The oxidant and laser power-dependent plasmon-driven surface photocatalysis reaction of p-aminothiophenol dimerizing into p,p‧-dimercaptoazobenzene on Au nanoparticles

    Science.gov (United States)

    Tan, Enzhong; Yin, Penggang; Yu, Chunna; Yu, Ge; Zhao, Chang

    2016-09-01

    Recently, plasmon-driven surface photocatalysis (PDSPC) reactions have attracted more and more attention by means of surface-enhanced Raman scattering (SERS) because we can in situ monitor the reaction process and determine the final products and their quantities by the real-time SERS spectrum. In this work, self-assembly AuNPs with both high catalytic activity and strong SERS effect were used as a bifunctional platform for in situ monitoring of PDSPC reactions. p-Aminothiophenol (PATP), a famous model molecule, was selected as a probe molecule and FeCl3 and NaClO were selected as oxidants. In this way, oxidation reaction of PATP dimerizing into p,p‧-dimercaptoazobenzene (DMAB) has been investigated by SERS, and the results show that oxidant and laser power can alter the conversion rate of the reaction. This work provides a novel approach for controlling PDSPC reaction rate, which may be useful for understanding the mechanism of PDSPC reactions.

  2. The oxidant and laser power-dependent plasmon-driven surface photocatalysis reaction of p-aminothiophenol dimerizing into p,p'-dimercaptoazobenzene on Au nanoparticles.

    Science.gov (United States)

    Tan, Enzhong; Yin, Penggang; Yu, Chunna; Yu, Ge; Zhao, Chang

    2016-09-05

    Recently, plasmon-driven surface photocatalysis (PDSPC) reactions have attracted more and more attention by means of surface-enhanced Raman scattering (SERS) because we can in situ monitor the reaction process and determine the final products and their quantities by the real-time SERS spectrum. In this work, self-assembly AuNPs with both high catalytic activity and strong SERS effect were used as a bifunctional platform for in situ monitoring of PDSPC reactions. p-Aminothiophenol (PATP), a famous model molecule, was selected as a probe molecule and FeCl3 and NaClO were selected as oxidants. In this way, oxidation reaction of PATP dimerizing into p,p'-dimercaptoazobenzene (DMAB) has been investigated by SERS, and the results show that oxidant and laser power can alter the conversion rate of the reaction. This work provides a novel approach for controlling PDSPC reaction rate, which may be useful for understanding the mechanism of PDSPC reactions.

  3. X-ray scattering studies of the Si-SiO2 interface

    Science.gov (United States)

    Fuoss, P. H.; Norton, L. J.; Brennan, S.; Fischer-Colbrie, A.

    1988-02-01

    We report observation of microcrystalline interface phases at the SiO2-Si(001) interface. The crystallites have varying degrees of orientational order with respect to the substrate depending on preparation techniques. Most of the diffraction peaks from these phases can be indexed as due to the α-cristobalite structure. Data are presented for oxides prepared on Si(001) surfaces by thermal oxidation, by electron beam evaporation, and by native oxide formation.

  4. Eu-doped Si-SiO2 core-shell nanowires for Si-compatible red emission

    Science.gov (United States)

    Xu, Jinyou; Guo, Pengfei; Zou, Zhijun; Lu, Yang; Yan, Hailong; Luo, Yongsong

    2016-09-01

    The indirect bandgap of single-crystalline silicon has so far precluded the full integration of silicon microelectronics with photonics—which is expected to allow the realization of low-cost, high-speed optical information processing and communication in the future. Here we report the growth of europium (Eu)-doped Si-SiO2 core-shell nanowires by an oxide-assisted chemical vapor deposition method. The Eu concentration in these nanowires is effectively improved by intentionally increasing the thickness of SiO2 shells. As a result, a strong Si-compatible red emission from Eu3+ ions was observed under laser illumination. The effect of Eu3+ concentration on the emission efficiency was comprehensively studied, with the highest efficiency at Eu content about 0.8 at%. The relaxation mechanism of this concentration dependent luminescence was further explored through lifetime measurements. In light of the strong characteristic red emission and nanoscale footprint, these nanowires are promising Si-compatible light emission materials for future integrated nanophotonics.

  5. Combining experiment and optical simulation in coherent X-ray nanobeam characterization of Si/SiGe semiconductor heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Tilka, J. A.; Park, J.; Ahn, Y.; Pateras, A.; Sampson, K. C.; Savage, D. E.; Lagally, M. G.; Evans, P. G., E-mail: pgevans@wisc.edu [Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, Wisconsin 53706 (United States); Prance, J. R.; Simmons, C. B.; Coppersmith, S. N.; Eriksson, M. A. [Department of Physics, University of Wisconsin-Madison, Madison, Wisconsin 53706 (United States); Holt, M. V. [Center for Nanoscale Materials, Argonne National Laboratory, Argonne, Illinois 60439 (United States)

    2016-07-07

    The highly coherent and tightly focused x-ray beams produced by hard x-ray light sources enable the nanoscale characterization of the structure of electronic materials but are accompanied by significant challenges in the interpretation of diffraction and scattering patterns. X-ray nanobeams exhibit optical coherence combined with a large angular divergence introduced by the x-ray focusing optics. The scattering of nanofocused x-ray beams from intricate semiconductor heterostructures produces a complex distribution of scattered intensity. We report here an extension of coherent x-ray optical simulations of convergent x-ray beam diffraction patterns to arbitrary x-ray incident angles to allow the nanobeam diffraction patterns of complex heterostructures to be simulated faithfully. These methods are used to extract the misorientation of lattice planes and the strain of individual layers from synchrotron x-ray nanobeam diffraction patterns of Si/SiGe heterostructures relevant to applications in quantum electronic devices. The systematic interpretation of nanobeam diffraction patterns from semiconductor heterostructures presents a new opportunity in characterizing and ultimately designing electronic materials.

  6. Combining experiment and optical simulation in coherent X-ray nanobeam characterization of Si/SiGe semiconductor heterostructures

    Science.gov (United States)

    Tilka, J. A.; Park, J.; Ahn, Y.; Pateras, A.; Sampson, K. C.; Savage, D. E.; Prance, J. R.; Simmons, C. B.; Coppersmith, S. N.; Eriksson, M. A.; Lagally, M. G.; Holt, M. V.; Evans, P. G.

    2016-07-01

    The highly coherent and tightly focused x-ray beams produced by hard x-ray light sources enable the nanoscale characterization of the structure of electronic materials but are accompanied by significant challenges in the interpretation of diffraction and scattering patterns. X-ray nanobeams exhibit optical coherence combined with a large angular divergence introduced by the x-ray focusing optics. The scattering of nanofocused x-ray beams from intricate semiconductor heterostructures produces a complex distribution of scattered intensity. We report here an extension of coherent x-ray optical simulations of convergent x-ray beam diffraction patterns to arbitrary x-ray incident angles to allow the nanobeam diffraction patterns of complex heterostructures to be simulated faithfully. These methods are used to extract the misorientation of lattice planes and the strain of individual layers from synchrotron x-ray nanobeam diffraction patterns of Si/SiGe heterostructures relevant to applications in quantum electronic devices. The systematic interpretation of nanobeam diffraction patterns from semiconductor heterostructures presents a new opportunity in characterizing and ultimately designing electronic materials.

  7. Intervalley splitting and intersubband transitions in n -type Si/SiGe quantum wells: Pseudopotential vs. effective mass calculation

    Science.gov (United States)

    Valavanis, A.; Ikonić, Z.; Kelsall, R. W.

    2007-05-01

    Intervalley mixing between conduction-band states in low-dimensional Si/SiGe heterostructures induces splitting between nominally degenerate energy levels. The symmetric double-valley effective mass approximation and the empirical pseudopotential method are used to find the electronic states in different types of quantum wells. A reasonably good agreement between the two methods is found, with the former being much faster computationally. Aside from being an oscillatory function of well width, the splitting is found to be almost independent of in-plane wave vector, and an increasing function of the magnitude of interface gradient. While the model is defined for symmetric envelope potentials, it is shown to remain reasonably accurate for slightly asymmetric structures such as a double quantum well, making it acceptable for simulation of multilayer intersubband optical devices. Intersubband optical transitions are investigated under both approximations and it is shown that in most cases valley splitting causes linewidth broadening, although under extreme conditions, transition line doublets may result.

  8. Growth of carbon nanotubes on Si/SiO{sub 2} wafer etched by hydrofluoric acid under different etching durations

    Energy Technology Data Exchange (ETDEWEB)

    Tan, Lling-Lling [Chemical Engineering Discipline, School of Engineering, Monash University, Jalan Lagoon Selatan, 46150 Bandar Sunway, Selangor (Malaysia); Chai, Siang-Piao, E-mail: chai.siang.piao@monash.edu [Chemical Engineering Discipline, School of Engineering, Monash University, Jalan Lagoon Selatan, 46150 Bandar Sunway, Selangor (Malaysia); Mohamed, Abdul Rahman [School of Chemical Engineering, Universiti Sains Malaysia, Engineering Campus, Seri Ampangan, 14300 NibongTebal, Pulau Pinang (Malaysia)

    2012-05-15

    The preparation of SiO{sub 2} nanoparticles for the metal-free catalyst growth of carbon nanotubes (CNTs) was investigated. SiO{sub 2} nanoparticles were generated by etching Si/SiO{sub 2} wafers with 48-50% hydrofluoric acid. Etching duration was varied to study its effects on the generation of the SiO{sub 2} nanoparticles. Atomic force microscopy characterization showed that etching at 1 min was the most effective considering the significant numbers of SiO{sub 2} nanoparticles obtained under this condition. The wafer etched at 1 min after chemical vapor deposition at 900 Degree-Sign C for 1 h demonstrated a low I{sub D}/I{sub G} from Raman analysis which establishes that CNTs with highly ordered graphitic structures were grown. Raman analysis also showed a strong radial breathing mode peak in the low-frequency range for the substrate following the 1 min etching process after the reaction.

  9. An Isotope Study of Hydrogenation of poly-Si/SiOx Passivated Contacts for Si Solar Cells: Preprint

    Energy Technology Data Exchange (ETDEWEB)

    Schnabel, Manuel; Nemeth, William; van de Loo, Bas, W.H.; Macco, Bart; Kessels, Wilhelmus, M.M.; Stradins, Paul; Young, David, L.

    2017-06-26

    For many years, the record Si solar cell efficiency stood at 25.0%. Only recently have several companies and institutes managed to produce more efficient cells, using passivated contacts of made doped poly-Si or a-Si:H and a passivating intrinsic interlayer in all cases. Common to these designs is the need to passivate the layer stack with hydrogen. In this contribution, we perform a systematic study of passivated contact passivation by hydrogen, using poly-Si/SiOx passivated contacts on n-Cz-Si, and ALD Al2O3 followed by a forming gas anneal (FGA) as the hydrogen source. We study p-type and n-type passivated contacts with implied Voc exceeding 690 and 720 mV, respectively, and perform either the ALD step or the FGA with deuterium instead of hydrogen in order to separate the two processes via SIMS. By examining the deuterium concentration at the SiOx in both types of samples, we demonstrate that the FGA supplies negligible hydrogen species to the SiOx, regardless of whether the FGA is hydrogenated or deuterated. Instead, it supplies the thermal energy needed for hydrogen species in the Al2O3 to diffuse there. Furthermore, the concentration of hydrogen species at the SiOx can saturate while implied Voc continues to increase, showing that the energy from the FGA is also required for hydrogen species already at the SiOx to find recombination-active defects to passivate.

  10. Ratchet effect study in Si/SiGe heterostructures in the presence of asymmetrical antidots for different polarizations of microwaves

    Science.gov (United States)

    Bisotto, Isabelle; Kannan, Ethirajulu S.; Portal, Jean-Claude; Brown, Devin; Beck, Thomas J.; Krupko, Yuriy; Jalabert, Laurent; Fujita, Hiroyuki; Hoshi, Yusuke; Shiraki, Yasuhiro; Saraya, Takura

    2014-08-01

    In this work, we studied the photovoltage response of an antidot lattice to microwave radiation for different antidot parameters. The study was carried out in a Si/SiGe heterostructure by illuminating the antidot lattice with linearly polarized microwaves and recording the polarity of induced photovoltage for different angles of incidence. Our study revealed that with increased antidot density and etching depth, the polarity of induced photovoltage changed when the angle of incidence was rotated 90 degrees. In samples with large antidot density and/or a deeply etched antidot lattice, scattering was dominated by electron interaction with the asymmetrical potential created by semicircular antidots. The strong electron-electron interaction prevailed in other cases. Our study provides insight into the mechanism of interaction between microwaves and electrons in an antidot lattice, which is the key for developing an innovative ratchet-based device. Moreover, we present an original and fundamental example of antidot lattice etching through the use of a two-dimensional electron gas. This system deals with a hole lattice instead of an electron depletion in the antidot lattice region.

  11. Local electric field enhancement at the heterojunction of Si/SiGe axially heterostructured nanowires under laser illumination

    Science.gov (United States)

    Pura, Jose Luis; Anaya, Julián; Souto, Jorge; Carmelo Prieto, Ángel; Rodríguez, Andrés; Rodríguez, Tomás; Jiménez, Juan

    2016-11-01

    We present a phenomenon concerning electromagnetic enhancement at the heterojunction region of axially heterostructured Si/SiGe nanowires when the nanowire is illuminated by a focused laser beam. The local electric field is sensed by micro Raman spectroscopy, which allows the enhancement of the Raman signal arising from the heterojunction region to be revealed; the Raman signal per unit volume increases at least ten times with respect to the homogeneous Si and SiGe nanowire segments. In order to explore the physical meaning of this phenomenon, a three-dimensional solution of the Maxwell equations of the interaction between the focused laser beam and the nanowire was carried out by finite element methods. A local enhancement of the electric field at the heterojunction was deduced. However, the magnitude of the electromagnetic field enhancement only approaches the experimental one when the free carriers are considered, showing enhanced absorption at the carrier depleted heterojunction region. The existence of this effect promises a way of improving photon harvesting using axially heterostructured semiconductor nanowires.

  12. Optical Absorption Measurement at 1550 nm on a Highly-Reflective Si/SiO$_2$ Coating Stack

    CERN Document Server

    Steinlechner, Jessica; Schnabel, Roman

    2014-01-01

    Future laser-interferometric gravitational wave detectors (GWDs) will potentially employ test mass mirrors from crystalline silicon and a laser wavelength of $1550\\,\\rm{nm}$, which corresponds to a photon energy below the silicon bandgap. Silicon might also be an attractive high-refractive index material for the dielectric mirror coatings. Films of amorphous silicon (a-Si), however, have been found to be significantly more absorptive at $1550\\,\\rm{nm}$ than crystalline silicon (c-Si). Here, we investigate the optical absorption of a Si/SiO$_2$ dielectric coating produced with the ion plating technique. The ion plating technique is distinct from the standard state-of-the-art ion beam sputtering technique since it uses a higher processing temperature of about 250$^\\circ$C, higher particle energies, and generally results in higher refractive indices of the deposited films. Our coating stack was fabricated for a reflectivity of $R=99.95\\,\\%$ for s-polarized light at $1550\\,\\rm{nm}$ and for an angle of incidence o...

  13. Quantum dimer model for the pseudogap metal

    Science.gov (United States)

    Punk, Matthias; Allais, Andrea; Sachdev, Subir

    2015-01-01

    We propose a quantum dimer model for the metallic state of the hole-doped cuprates at low hole density, p. The Hilbert space is spanned by spinless, neutral, bosonic dimers and spin S=1/2, charge +e fermionic dimers. The model realizes a “fractionalized Fermi liquid” with no symmetry breaking and small hole pocket Fermi surfaces enclosing a total area determined by p. Exact diagonalization, on lattices of sizes up to 8×8, shows anisotropic quasiparticle residue around the pocket Fermi surfaces. We discuss the relationship to experiments. PMID:26195771

  14. Quantum dimer model for the pseudogap metal.

    Science.gov (United States)

    Punk, Matthias; Allais, Andrea; Sachdev, Subir

    2015-08-04

    We propose a quantum dimer model for the metallic state of the hole-doped cuprates at low hole density, p. The Hilbert space is spanned by spinless, neutral, bosonic dimers and spin S = 1/2, charge +e fermionic dimers. The model realizes a "fractionalized Fermi liquid" with no symmetry breaking and small hole pocket Fermi surfaces enclosing a total area determined by p. Exact diagonalization, on lattices of sizes up to 8 × 8, shows anisotropic quasiparticle residue around the pocket Fermi surfaces. We discuss the relationship to experiments.

  15. Investigation of Coulomb scattering on sSi/Si0.5Ge0.5/sSOI quantum-well p-MOSFETs

    Science.gov (United States)

    Jiao, Wen; Qiang, Liu; Chang, Liu; Yize, Wang; Bo, Zhang; Zhongying, Xue; Zengfeng, Di; Wenjie, Yu; Qingtai, Zhao

    2016-09-01

    sSi/Si0.5Ge0.5/sSOI quantum-well (QW) p-MOSFETs with HfO2/TiN gate stack were fabricated and characterized. According to the low temperature experimental results, carrier mobility of the strained Si0.5Ge0.5 QW p-MOSFET was mainly governed by phonon scattering from 300 to 150 K and Coulomb scattering below 150 K, respectively. Coulomb scattering was intensified by the accumulated inversion charges in the Si cap layer of this Si/SiGe heterostructure, which led to a degradation of carrier mobility in the SiGe channel, especially at low temperature. Project supported by the National Natural Science Foundation of China (Nos. 61306126, 61306127, 61106015) and the CAS International Collaboration and Innovation Program on High Mobility Materials Engineering.

  16. Annealing effects on capacitance-voltage characteristics of a-Si/SiN(x) multilayer prepared using hot-wire chemical vapour deposition.

    Science.gov (United States)

    Panchal, A K; Rai, D K; Solanki, C S

    2011-04-01

    Post-deposition annealing of a-Si/SiN(x) multilayer films at different temperature shows varying shift in high frequency (1 MHz) capacitance-voltage (HFCV) characteristics. Various a-Si/SiN(x) multilayer films were deposited using hot wire chemical vapor deposition (HWCVD) and annealed in the temperature range of 800 to 900 degrees C to precipitate Si quantum dots (Si-QD) in a-Si layers. HFCV measurements of the as-deposited and annealed films in metal-insulator-semiconductor (MIS) structures show hysterisis in C-V curves. The hysteresis in the as-deposited films and annealed films is attributed to charge trapping in Si-dangling bonds in a-Si layer and in Si-QD respectively. The charge trapping density in Si-QD increases with temperature while the interface defects density (D(it)) remains constant.

  17. Characterization of Si/SiGe/Si Deposited on SIMOX SOI by Synchrotron Radiation X-Ray Double-crystal Topography

    Institute of Scientific and Technical Information of China (English)

    Ma Tongda; Tu Hailing; Hu Guangyong; Wang Jing

    2004-01-01

    The synchrotron X-ray double-crystal topography was employed to investigate the structure of Si/SiGe/Si deposited on SIMOX SOI. Rocking curves with three diffraction peaks were acquired before and after 180° rotation of samples. Double-crystal topographs taken at the full width at half maximum (FWHM) of the three peaks differ from each other. Many defects appear in the Si layers that are likely related to the tilt between SOI and epitaxial layers.

  18. Wear mechanism for spray deposited Al-Si/SiCp composites under dry sliding condition

    Institute of Scientific and Technical Information of China (English)

    滕杰; 李华培; 陈刚

    2015-01-01

    Al-Si/15%SiCp (volume fraction) composites with different silicon contents were fabricated by spray deposition technique, and typical microstructures of these composites were studied by optical microscopy (OM). Dry sliding wear tests were carried out using a block-on-ring wear machine to investigate the effect of applied load range of 10−220 N on the wear and friction behavior of these composites sliding against SAE 52100 grade bearing steel. Scanning electron microscopy (SEM) and energy-dispersive X-ray microanalysis (EDAX) were utilized to examine the morphologies of the worn surfaces in order to observe the wear characteristics and investigate the wear mechanism. The results show that the wear behavior of these composites is dependent on the silicon content in the matrix alloy and the applied load. Al-Si/15%SiCp composites with higher silicon content exhibit better wear resistance in the applied load range. Under lower loads, the major wear mechanisms are oxidation wear and abrasive wear for all tested composites. Under higher loads, severe adhesive wear becomes the main wear mechanisms for Al-7Si/15%SiCp and Al-13Si/15%SiCp composites, while Al-20Si/15%SiCp presents a compound wear mechanism, consisting of oxidation, abrasive wear and adhesion wear.

  19. Building-up novel coordination polymer with Zn(II) porphyrin dimer: Synthesis, structures, surface morphology and effect of axial ligands

    Indian Academy of Sciences (India)

    Sk Asif Ikbal; Sanfaori Brahma; Avinash Dhamija; Sankar Prasad Rath

    2014-09-01

    Highly flexible Zn(II)1,2-bis(meso-octaethylporphyrin)ethane (1) has been used as host in which two porphyrin rings are found to be face-to-face in non-coordinating solvents. Upon addition of one relatively smaller 4,4′-dipyridine (L1) and one extended N,N′-bispyridine-4-yl-methylene ethylenediamine (L2) guest ligands, the syn conformation of 1 is switched to the anti complexes 1·(L1)2 and 1·L2, respectively. Single crystal X-ray structures of all the complexes are reported in which a stable one-dimensional coordination polymer is produced only in 1·L2 that is, to the best of our knowledge, the first structural report of 1D-coordination polymer with porphyrin dimer. Solution structures of the complexes along with binding studies in solution between 1 and L have also been investigated. The morphology of the polymeric complex 1·L2 on silicon wafer surface was examined by Atomic Force Microscopy (AFM) in which the crystalline islands of well defined facets of size ranging from 200-550 nm perimeter and a height of 20-40 nm have been observed.

  20. Reactions with a Metalloid Tin Cluster {Sn10[Si(SiMe3)3]4}(2-): Ligand Elimination versus Coordination Chemistry.

    Science.gov (United States)

    Schrenk, Claudio; Gerke, Birgit; Pöttgen, Rainer; Clayborne, Andre; Schnepf, Andreas

    2015-05-26

    Chemistry that uses metalloid tin clusters as a starting material is of fundamental interest towards understanding the reactivity of such compounds. Since we identified {Sn10[Si(SiMe3)3]4}(2-) 7 as an ideal candidate for such reactions, we present a further step in the understanding of metalloid tin cluster chemistry. In contrast to germanium chemistry, ligand elimination seems to be a major reaction channel, which leads to the more open metalloid cluster {Sn10[Si(SiMe3)3]3}(-) 9, in which the Sn core is only shielded by three Si(SiMe3)3 ligands. Compound 9 is obtained through different routes and is crystallised together with two different countercations. Besides the structural characterisation of this novel metalloid tin cluster, the electronic structure is analysed by (119)Sn Mössbauer spectroscopy. Additionally, possible reaction pathways are discussed. The presented first step into the chemistry of metalloid tin clusters thus indicates that, with respect to metalloid germanium clusters, more reaction channels are accessible, thereby leading to a more complex reaction system.

  1. Fabrication of quantum dots in undoped Si/Si0.8Ge0.2 heterostructures using a single metal-gate layer

    Science.gov (United States)

    Lu, T. M.; Gamble, J. K.; Muller, R. P.; Nielsen, E.; Bethke, D.; Ten Eyck, G. A.; Pluym, T.; Wendt, J. R.; Dominguez, J.; Lilly, M. P.; Carroll, M. S.; Wanke, M. C.

    2016-08-01

    Enhancement-mode Si/SiGe electron quantum dots have been pursued extensively by many groups for their potential in quantum computing. Most of the reported dot designs utilize multiple metal-gate layers and use Si/SiGe heterostructures with Ge concentration close to 30%. Here, we report the fabrication and low-temperature characterization of quantum dots in the Si/Si0.8Ge0.2 heterostructures using only one metal-gate layer. We find that the threshold voltage of a channel narrower than 1 μm increases as the width decreases. The higher threshold can be attributed to the combination of quantum confinement and disorder. We also find that the lower Ge ratio used here leads to a narrower operational gate bias range. The higher threshold combined with the limited gate bias range constrains the device design of lithographic quantum dots. We incorporate such considerations in our device design and demonstrate a quantum dot that can be tuned from a single dot to a double dot. The device uses only a single metal-gate layer, greatly simplifying device design and fabrication.

  2. Physical studies of strained Si/SiGe heterostructures. From virtual substrates to nanodevices

    Energy Technology Data Exchange (ETDEWEB)

    Minamisawa, Renato Amaral

    2011-10-21

    During the past two decades, the decrease in intrinsic delay of MOSFETs has been driven by the scaling of the device dimensions. The performance improvement has relied mostly in the increase of source velocity with gate scaling, while the transport properties of the channel have remained constant, i.e., those of conventional Si. Starting at the 90 nm node, uniaxial strain has been introduced in the transistor channel in order to further increase the source velocity. Beyond the 32 nm node, novel channel materials, with superior carrier velocities, and novel device architectures are required in order to continue the performance enhancement of MOSFETs while preserving the electrostatic control. In this Thesis, different physical aspects of strained Si and SiGe materials are investigated as a mean to increase carrier velocity in MOSFET channels. Novel approaches for the fabrication of strained Si based on ion implantation and anneal induced relaxation of virtual substrates are developed. The strain relaxation of SiGe layers is improved using a buried thin Si:C layer in the Si(100) substrate. Further, a Si{sup +} ion implantation and annealing method is investigated for relaxing virtual substrates using lower implantation dose. Finally, the uniaxial relaxation of {l_brace}110{r_brace} surface oriented substrates is demonstrated using a He ion implantation and anneal technique. Apart of channel material studies, the fundamental and technological challenges involved in the integration of strained Si and SiGe into MOSFETs are assessed. The impact of source and drain formation on the elastic strain and electrical properties of strained Si layers and nanowires is examined. Also, the formation of ultra-shallow junction in strained Si/strained Si{sub 0.5}Ge{sub 0.5}/SSOI heterostructures is investigated using different types of ion implanted specie and annealing. The results show that BF{sup +}{sub 2} implantation and low temperature annealing are suitable approaches for

  3. Combined analysis of chemical bonding in a Cu(II) dimer using QTAIM, Voronoi tessellation and Hirshfeld surface approaches.

    Science.gov (United States)

    Vologzhanina, Anna V; Kats, Svitlana V; Penkova, Larisa V; Pavlenko, Vadim A; Efimov, Nikolay N; Minin, Vadim V; Eremenko, Igor L

    2015-10-01

    Interaction of 1-(1H-pyrazol-5-yl)ethanone oxime (H2PzOx) with copper(II) chloride in the presence of pyridine afforded a binuclear discrete [Cu2(HPzOx)2Cl2py2] complex, which was characterized by Fourier transform-IR and electron paramagnetic resonance (EPR) spectra, magnetochemistry and high-resolution X-ray diffraction experiments. Multipole refinement of X-ray diffraction data and density-functional theory (DFT) calculations of an isolated molecule allowed charge and spin distributions to be obtained for this compound. Magnetochemistry data, EPR spectra and DFT calculations of an isolated molecule show antiferromagnetic coupling between copper(II) ions. The spin distribution suggests an exchange pathway via the bridging pyrazole ring in the equatorial plane of the CuN4Cl coordination polyhedron, thus providing support for the classical superexchange mechanism; the calculated value of the magnetic coupling constant -2J is equal to 220 cm(-1), which compares well with the experimental value of 203 ± 2 cm(-1). Chemical connectivity was derived by Bader's 'quantum theory of atoms in molecules' and compared with Voronoi tessellation and Hirshfeld surface representations of crystal space. All methodologies gave a similar qualitative and semi-quantitative description of intra- and intermolecular connectivity.

  4. Molecular modeling of alkyl monolayers on the Si(100)-2 x 1 surface.

    Science.gov (United States)

    Lee, Michael V; Guo, Dawei; Linford, Matthew R; Zuilhof, Han

    2004-10-12

    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 x 1 surface. The primary aim was to better understand the interactions between adsorbates on the surface and distortions of the underlying silicon crystal due to functionalization. Random addition of ethylene and acetylene was used to determine how the addition of an adduct molecule affects subsequent additions for coverages up to one molecule per silicon dimer, that is, 100% coverage. Randomization subdues the effect that the relative positions of the adsorbates have on the enthalpy of the system. For ethylene and acetylene, the enthalpy of reaction changes less than 3 and 5 kcal/mol, respectively, from the first reacted species up to 100% coverage. As a result, a (near-)complete coverage is predicted, which is in line with experimental data. When 1-alkenes and 1-alkynes add by [2 + 2] addition, the hydrocarbon chains interact differently depending on the direction they project from the surface. These effects were investigated for four-carbon chains: 1-butene and 1-butyne. As expected, the chains that would otherwise intersect bend to avoid each other, raising the enthalpy of the system. For alkyl chains longer than four carbons, the chains are able to reorient themselves in a favorable manner, thus, resulting in a steady reduction in reaction enthalpy of about 2 kcal/mol for each additional methylene unit.

  5. Studies of diamond-like carbon (DLC) films deposited on stainless steel substrate with Si/SiC intermediate layers

    Institute of Scientific and Technical Information of China (English)

    Wang Jing; Liu Gui-Chang; Wang Li-Da; Deng Xin-Lü; Xu Jun

    2008-01-01

    In this work, diamond-like carbon (DLC) films were deposited on stainless steel substrates with Si/SiC intermediate layers by combining plasma enhanced sputtering physical vapour deposition (PEUMS-PVD) and microwave electron cyclotron resonance plasma enhanced chemical vapour deposition (MW-ECRPECVD) techniques. The influence of substrate negative self-bias voltage and Si target power on the structure and nano-mechanical behaviour of the DLC films were investigated by Raman spectroscopy, nano-indentation, and the film structural morphology by atomic force microscopy (AFM). With the increase of deposition bias voltage, the G band shifted to higher wave-number and the integrated intensity ratio ID/IG increased. We considered these as evidences for the development of graphitization in the films. As the substrate negative self-bias voltage increased, particle bombardment function was enhanced and thesp3-bond carbon density reducing, resulted in the peak values of hardness (H) and elastic modulus (E). Silicon addition promoted the formation of sp3 bonding and reduced the hardness. The incorporated Si atoms substituted sp2- bond carbon atoms in ring structures, which promoted the formation of sp3-bond. The structural transition from C-C to C-Si bonds resulted in relaxation of the residual stress which led to the decrease of internal stress and hardness. The results of AFM indicated that the films was dense and homogeneous, the roughness of the films was decreased due to the increase of substrate negative self-bias voltage and the Si target power.

  6. Liquid crystal dimers

    CERN Document Server

    Kumar Pal, Santanu

    2017-01-01

    This book covers in-depth discussion of design principles, synthesis and thermal behavior of all types of liquid crystal (LC) dimers. The text presents recent advances in the field of LC dimers consisting of different mesogenic units such as calamitic, discotic and bent-core molecules. It starts with a chapter on the introduction of liquid crystal dimers, including their odd-even behavior, basic classification of dimers and common mesophases in dimers. The text shows how the molecular architectures are being used to develop new materials to study a range of interesting phenomena such as the biaxial nematic phase containing rod-like and disc-like mesogenic units. Finally, the text presents perspectives related to technological relevance of these dimers such as dopants in LC display mixtures exhibiting faster relaxation time, strong flexoelectric coupling and others to effect control over the properties of these materials.

  7. A first principles analysis of the effect of hydrogen concentration in hydrogenated amorphous silicon on the formation of strained Si-Si bonds and the optical and mobility gaps

    Energy Technology Data Exchange (ETDEWEB)

    Legesse, Merid; Nolan, Michael, E-mail: Michael.nolan@tyndall.ie; Fagas, Giorgos, E-mail: Georgios.fagas@tyndall.ie [Tyndall National Institute, University College Cork, Lee Maltings, Dyke Parade, Cork (Ireland)

    2014-05-28

    In this paper, we use a model of hydrogenated amorphous silicon generated from molecular dynamics with density functional theory calculations to examine how the atomic geometry and the optical and mobility gaps are influenced by mild hydrogen oversaturation. The optical and mobility gaps show a volcano curve as the hydrogen content varies from undersaturation to mild oversaturation, with largest gaps obtained at the saturation hydrogen concentration. At the same time, mid-gap states associated with dangling bonds and strained Si-Si bonds disappear at saturation but reappear at mild oversaturation, which is consistent with the evolution of optical gap. The distribution of Si-Si bond distances provides the key to the change in electronic properties. In the undersaturation regime, the new electronic states in the gap arise from the presence of dangling bonds and strained Si-Si bonds, which are longer than the equilibrium Si-Si distance. Increasing hydrogen concentration up to saturation reduces the strained bonds and removes dangling bonds. In the case of mild oversaturation, the mid-gap states arise exclusively from an increase in the density of strained Si-Si bonds. Analysis of our structure shows that the extra hydrogen atoms form a bridge between neighbouring silicon atoms, thus increasing the Si-Si distance and increasing disorder in the sample.

  8. Dual Core-Shell Structured Si@SiOx@C Nanocomposite Synthesized via a One-Step Pyrolysis Method as a Highly Stable Anode Material for Lithium-Ion Batteries.

    Science.gov (United States)

    Jiang, Bolun; Zeng, Shi; Wang, Hui; Liu, Daotan; Qian, Jiangfeng; Cao, Yuliang; Yang, Hanxi; Ai, Xinping

    2016-11-23

    Silicon (Si) has been regarded as a promising high-capacity anode material for developing advanced lithium-ion batteries (LIBs), but the practical application of Si anodes is still unsuccessful mainly due to the insufficient cyclability. To deal with this issue, we propose a new route to construct a dual core-shell structured Si@SiOx@C nanocomposite by direct pyrolysis of poly(methyl methacrylate) (PMMA) polymer on the surface of Si nanoparticles. Since the PMMA polymers can be chemically bonded on the nano-Si surface through the interaction between ester group and Si surface group, and thermally decomposed in the subsequent pyrolysis process with their alkyl chains converted to carbon and the residue oxygen recombining with Si to form SiOx, the dual core-shell structure can be conveniently formed in a one-step procedure. Benefiting from the strong buffering effect of the SiOx interlayer and the efficient blocking action of dense outer carbon layer in preventing electrolyte permeation, the obtained nanocomposite demonstrates a high capacity of 1972 mA h g(-1), a stable cycling performance with a capacity retention of >1030 mA h g(-1) over 500 cycles, and particularly a superiorly high Coulombic efficiency of >99.5% upon extended cycling, exhibiting a great promise for practical uses. More importantly, the synthetic method proposed in this work is facile and low cost, making it more suitable for large-scale production of high capacity anode for advanced LIBs.

  9. 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.

  10. Fabrication and evaluation of propagation loss of Si/SiGe/Si photonic-wire waveguides for Si based optical modulator

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Younghyun, E-mail: yhkim@mosfet.t.u-tokyo.ac.jp [Department of Electrical Engineering and Information Systems, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan); Takenaka, Mitsuru [Department of Electrical Engineering and Information Systems, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan); Osada, Takenori; Hata, Masahiko [Sumitomo Chemical Co. Ltd., 6 Kitahara, Tsukuba, Ibaraki 300-3294 (Japan); Takagi, Shinichi [Department of Electrical Engineering and Information Systems, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan)

    2014-04-30

    We have characterized photonic-wire waveguides with Si/SiGe/Si heterostructure ribs for Si-based optical modulators. The Si (80 nm)/Si{sub 0.72}Ge{sub 0.28} (40 nm) layers grown on Si-on-insulator by molecular beam epitaxy for optical modulators were evaluated by in-situ reflection high-energy electron diffraction, atomic force microscope, X-ray diffraction and Raman spectroscopy, exhibiting that the fully-strained highly-crystalline SiGe layer was obtained. We have evaluated the propagation loss of the Si/strained SiGe/Si photonic-wire waveguides. The wavelength dependence of the propagation loss exhibits the bandgap narrowing of the strained Si{sub 0.72}Ge{sub 0.28}, while the optical absorption of the strained Si{sub 0.72}Ge{sub 0.28} is not significant for the optical modulator application at 1.55-μm wavelength. - Highlights: • We have characterized photonic-wire waveguides with Si/SiGe/Si heterostructure ribs. • The Si/Si{sub 0.72}Ge{sub 0.28} grown on Si-on-insulator were evaluated to be fully strained. • We have fabricated and evaluated the Si/strained SiGe/Si photonic-wire waveguides. • The wavelength dependence exhibits bandgap narrowing of the strained Si{sub 0.72}Ge{sub 0.28}. • Optical absorption of the SiGe is not significant for optical modulators at 1.55 μm.

  11. Interconnected sandwich structure carbon/Si-SiO2/carbon nanospheres composite as high performance anode material for lithium-ion batteries

    Institute of Scientific and Technical Information of China (English)

    Yuanjin Du; Mengyan Hou; Dandan Zhou; Yonggang Wang; Congxiao Wang; Yongyao Xia

    2014-01-01

    In the present work, an interconnected sandwich carbon/Si-SiO2/carbon nanospheres composite was prepared by template method and carbon thermal vapor deposition (TVD). The carbon conductive layer can not only efficiently improve the electronic conductivity of Si-based anode, but also play a key role in alleviating the negative effect from huge volume expansion over discharge/charge of Si-based anode. The resulting material delivered a reversible capacity of 1094 mAh/g, and exhibited excellent cycling stability. It kept a reversible capacity of 1050 mAh/g over 200 cycles with a capacity retention of 96%.

  12. The properties of dimers confined between two charged plates.

    Science.gov (United States)

    Hatlo, Marius M; Bohinc, Klemen; Lue, Leo

    2010-03-21

    We consider two like-charged planar surfaces immersed in solution of oppositely charged dimer counterions with a bond length l. To analyze this system, we extend and employ a self-consistent field theory that has been shown to be accurate from the weak to the intermediate through to the strong coupling regimes. In the limit of very short dimers, the results converge to the results for pointlike divalent ions. Near the surfaces, the dimers lie parallel to the charged plates. In the intermediate coupling regime, the dimers are aligned perpendicularly to the surface when they are a distance l from a surface. In the weak coupling regime, the interactions are only repulsive. At slightly higher couplings, there is a minimum in the variation of the free energy with distance at approximately the bond length of the dimers, which arises from bridging conformations of the dimers. In the intermediate coupling regime, an additional minimum in the free energy is observed at much smaller distances, which is due to the correlations between the dimers. For large dimer bond lengths, this minimum is metastable with respect to the previous minimum. However, as the bond length decreases, this minimum becomes the stable, while the minimum associated with the dimer bond length becomes metastable and eventually disappears. For shorter dimer bond length the attractive interaction is the result of correlations between counterions and charges on the surfaces. We find that dimers can mediate attractive interaction between like-charged surfaces in the intermediate coupling regime. The analysis of orientations confirms the bridging mechanism for sufficiently long dimers, whereas at high electrostatic couplings charge correlations contribute to the attraction.

  13. Protein dimerization. Inside job.

    Science.gov (United States)

    Metzger, H

    1994-04-01

    In a sophisticated combination of genetic engineering and organic synthesis, a general method for dimerizing recombinant intracellular proteins has been devised; the usefulness of the method should now be testable.

  14. Basics of the atomic layer deposition of HfO{sub 2} onto Si/SiO{sub 2} substrates: in-situ investigations with XPS, XAS and UHV-AFM

    Energy Technology Data Exchange (ETDEWEB)

    Tallarida, Massimo; Karavaev, Konstantin; Kolanek, Krzysztof; Schmeisser, Dieter [Brandenburgische Technische Universitaet, LS Angewandte Physik-Sensorik, Konrad-Wachsmann-Allee, 17, 03046, Cottbus (Germany)

    2009-07-01

    We developed a reactor for investigating in-situ the atomic layer deposition (ALD) of HfO{sub 2}. X-ray photoelectron and X-ray absorption spectra were collected after each ALD cycle using synchrotron radiation at the beamline U49-2/PGM2 - BESSY II, Berlin. The morphology of the substrate and thin film surfaces was investigated after each ALD cycle with an UHV-AFM microscopy attached to the ALD reactor. We studied the ALD on differently prepared substrates, at different substrate temperatures, and using different Hf-precursors (HfCl{sub 4}, TEMAHf, TDMAHf). We observed the evolution of the Si/SiO{sub 2}/HfO{sub 2} system during the formation of the first three Hf-oxide layers; we detected the incorporation of Cl into the Hf-oxide films and proposed a mechanism responsible for the Cl contamination; we found evidence of the interfacial-SiO{sub 2} growth during the initial ALD cycles and of dipole formation at the HfO{sub 2}/SiO{sub 2} interface. In this contribution we illustrate the basics of the technique used, and discuss the physical-chemical properties of ALD on the basis of the experimental results.

  15. Nanostructures based in boro nitride thin films deposited by PLD onto Si/Si{sub 3}N{sub 4}/DLC substrate

    Energy Technology Data Exchange (ETDEWEB)

    Roman, W S; Riascos, H [Grupo Plasma, Laser y Aplicaciones, Universidad Tecnologica de Pereira (Colombia); Caicedo, J C [Grupo de PelIculas Delgadas, Universidad del Valle, Cali (Colombia); Ospina, R [Laboratorio de Plasma, Universidad Nacional de Colombia, sede Manizales (Colombia); Tirado-MejIa, L, E-mail: hriascos@utp.edu.c [Laboratorio de Optoelectronica, Universidad del Quindio (Colombia)

    2009-05-01

    Diamond-like carbon and boron nitride were deposited like nanostructered bilayer on Si/Si{sub 3}N{sub 4} substrate, both with (100) crystallographic orientation, these films were deposited through pulsed laser technique (Nd: YAG: 8 Jcm{sup -2}, 9ns). Graphite (99.99%) and boron nitride (99.99%) targets used to growth the films in argon atmosphere. The thicknesses of bilayer were determined with a perfilometer, active vibration modes were analyzed using infrared spectroscopy (FTIR), finding bands associated around 1400 cm{sup -1} for B - N bonding and bands around 1700 cm{sup -1} associated with C=C stretching vibrations of non-conjugated alkenes and azometinic groups, respectively. The crystallites of thin films were analyzed using X-ray diffraction (XRD) and determinated the h-BN (0002), alpha-Si{sub 3}N{sub 4} (101) phases. The aim of this study is to relate the dependence on physical and chemical characteristics of the system Si/Si{sub 3}N{sub 4}/DLC/BN with gas pressure adjusted at the 1.33, 2.67 and 5.33 Pa values.

  16. Synthesis of biogenic silicon/silica (Si/SiO2) nanocomposites from rice husks and wheat bran through various microorganisms

    Science.gov (United States)

    Kaur, Taranjot; Pal Singh, Gurwinder; Kaur, Gurneet; Kaur, Sukhvir; Gill, Prabhjot Kaur

    2016-08-01

    Biosilification is an economically viable, energy saving and green approach for the commercial scale synthesis of oxide nanomaterials. The room temperature synthesis of oxide nanocomposites from cost effective agro-based waste is a particular example of biosilification. In this study, synthesis of Si/SiO2 nanocomposites from inexpensive agro-based waste material i.e. rice husks (RH) and wheat bran (WB) has been carried out by means of various eukaryotic microorganisms, i.e. Actinomycete, Fusarium oxysporum, Aspergillus niger, Trichoderma sp. and Penicillium sp., under ambient conditions. The XRD diffrectrograms represents that the synthesized nanomaterials exhibits silicon, amorphous silica and other crystal arrays such as cristobalite, trydimite and quartz, depending upon the type microorganism and time period used for extraction. All of the aforesaid microorganism bio transformed the naturally occurring amorphous silica to crystalline structures within the period of 24 h. However, the Actinomycete and Trichoderma sp. took 48 h in case of rice husks for biotransformation of naturally occurring plant silica to crystalline nanocomposite. While in case of wheat bran, Actinomycete and Trichoderma sp. took 24 h for biotransformation. The extracted nanocomposites exhibits band edge in the range 230-250 nm and blue emission. The procedure described in study can be used for commercial level production of Si/SiO2 nanocomposites from agro based waste materials.

  17. 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.

  18. Coupling atomistic and continuum length scales in heteroepitaxial systems: Multiscale molecular-dynamics/finite-element simulations of strain relaxation in Si/ Si3 N4 nanopixels

    Science.gov (United States)

    Lidorikis, Elefterios; Bachlechner, Martina E.; Kalia, Rajiv K.; Nakano, Aiichiro; Vashishta, Priya

    2005-09-01

    A hybrid atomistic-continuum simulation approach has been implemented to study strain relaxation in lattice-mismatched Si/Si3N4 nanopixels on a Si(111) substrate. We couple the molecular-dynamics (MD) and finite-element simulation approaches to provide an atomistic description near the interface and a continuum description deep into the substrate, increasing the accessible length scales and greatly reducing the computational cost. The results of the hybrid simulation are validated against full multimillion-atom MD simulations. We find that strain relaxation in Si/Si3N4 nanopixels may occur through the formation of a network of interfacial domain boundaries reminiscent of interfacial misfit dislocations. They result from the nucleation of domains of different interfacial bonding at the free edges and corners of the nanopixel, and subsequent to their creation they propagate inwards. We follow the motion of the domain boundaries and estimate a propagation speed of about ˜2.5×103m/s . The effects of temperature, nanopixel architecture, and film structure on strain relaxation are also investigated. We find: (i) elevated temperature increases the interfacial domain nucleation rates; (ii) a thin compliant Si layer between the film and the substrate plays a beneficial role in partially suppressing strain relaxation; and (iii) additional control over the interface morphology may be achieved by varying the film structure.

  19. High-Performance Si/SiOx Nanosphere Anode Material by Multipurpose Interfacial Engineering with Black TiO(2-x).

    Science.gov (United States)

    Bae, Juhye; Kim, Dae Sik; Yoo, Hyundong; Park, Eunjun; Lim, Young-Geun; Park, Min-Sik; Kim, Young-Jun; Kim, Hansu

    2016-02-01

    Silicon oxides (SiOx) have attracted recent attention for their great potential as promising anode materials for lithium ion batteries as a result of their high energy density and excellent cycle performance. Despite these advantages, the commercial use of these materials is still impeded by low initial Coulombic efficiency and high production cost associated with a complicated synthesis process. Here, we demonstrate that Si/SiOx nanosphere anode materials show much improved performance enabled by electroconductive black TiO(2-x) coating in terms of reversible capacity, Coulombic efficiency, and thermal reliability. The resulting anode material exhibits a high reversible capacity of 1200 mAh g(-1) with an excellent cycle performance of up to 100 cycles. The introduction of a TiO(2-x) layer induces further reduction of the Si species in the SiOx matrix phase, thereby increasing the reversible capacity and initial Coulombic efficiency. Besides the improved electrochemical performance, the TiO(2-x) coating layer plays a key role in improving the thermal reliability of the Si/SiOx nanosphere anode material at the same time. We believe that this multipurpose interfacial engineering approach provides another route toward high-performance Si-based anode materials on a commercial scale.

  20. Adsorption of dimeric surfactants in lamellar silicates

    Energy Technology Data Exchange (ETDEWEB)

    Balcerzak, Mateusz; Pietralik, Zuzanna [Department of Macromolecular Physics, Faculty of Physics, A. Mickiewicz University, Umultowska 85, 61-614 Poznań (Poland); Domka, Ludwik [Department of Metalorganic Chemistry, Faculty of Chemistry, A. Mickiewicz University, Grunwaldzka 6, 60-780 Poznań (Poland); Skrzypczak, Andrzej [Institute of Chemical Technology, Poznań University of Technology, Berdychowo 4, 60-965 Poznań (Poland); Kozak, Maciej, E-mail: mkozak@amu.edu.pl [Department of Macromolecular Physics, Faculty of Physics, A. Mickiewicz University, Umultowska 85, 61-614 Poznań (Poland)

    2015-12-01

    Highlights: • The intercalation of dimeric surfactants changed the morphology of MMT samples. • XRD indicated structures formed by surfactant molecules in interlayer space. • The four-step thermal decomposition of dimeric surfactant, confirms intercalation. - Abstract: The adsorption of different types of cationic surfactants in lamellar silicates changes their surface character from hydrophilic to hydrophobic. This study was undertaken to obtain lamellar silicates modified by a series of novel dimeric (gemini) surfactants of different length alkyl chains and to characterise these organophilised materials. Synthetic sodium montmorillonite SOMASIF® ME 100 (M) and enriched bentonite of natural origin (Nanoclay – hydrophilic bentonite®) were organophilised with dimeric (gemini) surfactants (1,1′-(1,4-butanediyl)bis(alkoxymethyl)imidazolium dichlorides). As a result of surfactant molecule adsorption in interlamellar space, the d-spacing (d{sub 001}) increased from 0.97 nm (for the anhydrous structure) to 2.04 nm. A Fourier transform infrared spectroscopy (FTIR) analysis of the modified systems reveals bands assigned to the stretching vibrations of the CH{sub 2} and CH{sub 3} groups and the scissoring vibrations of the NH group from the structure of the dimeric surfactants. Thermogravimetric (TG) and derivative thermogravimetric (DTG) studies imply a four-stage process of surfactant decomposition. Scanning electron microscopy (SEM) images provide information on the influence of dimeric surfactant intercalation into the silicate structures. Particles of the modified systems show a tendency toward the formation of irregularly shaped agglomerates.

  1. Superbackscattering nanoparticle dimers.

    Science.gov (United States)

    Liberal, Iñigo; Ederra, Iñigo; Gonzalo, Ramón; Ziolkowski, Richard W

    2015-07-10

    The theory and design of superbackscattering nanoparticle dimers are presented. We analytically derive the optimal configurations and the upper bound of their backscattering cross-sections. In particular, it is demonstrated that electrically small nanoparticle dimers can enhance the backscattering by a factor of 6.25 with respect to single dipolar particles. We demonstrate that optimal designs approaching this theoretical limit can be found by using a simple circuit model. The study of practical implementations based on plasmonic and high-permittivity particles has been also addressed. Moreover, the numerical examples reveal that the dimers can attain close to a fourfold enhancement of the single nanoparticle response even in the presence of high losses.

  2. Superbackscattering Nanoparticle Dimers

    CERN Document Server

    Liberal, Iñigo; Gonzalo, Ramón; Ziolkoski, Richard W

    2015-01-01

    The theory and design of superbackscattering nanoparticle dimers are presented. We analytically derive the optimal configurations and the upper bound of their backscattering cross-sections. In particular, it is demonstrated that electrically small nanoparticle dimers can enhance the backscattering by a factor of 6.25 with respect to single dipolar particles. We demonstrate that optimal designs approaching this theoretical limit can be found by using a simple circuit model. The study of practical implementations based on plasmonic and high-permittivity particles reveal that fourfold enhancement factors might be attainable even with realistic losses.

  3. A Monte Carlo Simulation of a Monomer Dimer CO-O2 Catalytic Reaction on the Surface and Subsurface of a Face-centered Cubic Lattice

    Institute of Scientific and Technical Information of China (English)

    K.Iqbal; A.Basit

    2011-01-01

    @@ The presence of oxygen in the subsurface in monomer-dimer reactions(CO-O2 and NO-CO)is observed experimentally.The effect of subsurface oxygen on a CO-O2 catalytic reaction on a face-centered cubic(FCC)lattice is studied using Monte Carlo simulation.The effect of adding subsurface neighbours on the phase diagram is also extensively explored.It is observed that the subsurface oxygen totally eliminates the typical second order phase transition.It is also shown that the introduction of the diffusion of O atoms and the subsurface of the FCC lattice shifts the single transition point towards the stoichiometric ratio.%The presence of oxygen in the subsurface in monomer-dimer reactions (CO-O2 and NO-CO) is observed experimentally. The effect of subsurface oxygen on a CO-O2 catalytic reaction on a face-centered cubic (FCC) lattice is studied using Monte Carlo simulation. The effect of adding subsurface neighbours on the phase diagram is also extensively explored. It is observed that the subsurface oxygen totally eliminates the typical second order phase transition. It is also shown that the introduction of the diffusion of O atoms and the subsurface of the FCC lattice shifts the single transition point towards the stoichiometric ratio.

  4. Ab initio Intermolecular Potential Energy Surface and Calculation of Second Virial Coefficients for the Cl2–Cl2 Dimer

    Directory of Open Access Journals (Sweden)

    Nguyen Thanh Duoc

    2015-12-01

    Full Text Available The results presented in this paper are the ab initio intermolecular potentials and the second virial coefficient, B2 (T of the dimer Cl2-Cl2. These ab initio potentials were proposed by the quantum chemical calculations at high level of theory CCSD (T with basis sets of Dunning’s valence correlation-consistent aug-cc-pVmZ (m = 2, 3; these results were extrapolated to complete basis set limit aug-cc-pV23Z. The ab initio energies of complete basis set limit aug-cc-pV23Z resulted from the exponential extrapolation were used to construct the 5-site pair potential functions. The second virial coefficients for this dimer were predicted from those with four-dimensional integration. The second virial coefficients were also corrected to first-order quantum effects. The results turn out to be in good agreement with experimental data, if available, or with those from empirical correlation. The quality of ab initio 5-site potentials proved the reliability for prediction of molecular thermodynamic properties.

  5. Diffusion thermopower of a p-type Si/Si{sub 1-x}Ge{sub x} heterostructure at zero magnetic field

    Energy Technology Data Exchange (ETDEWEB)

    Huan, Tran Doan [Institute of Engineering Physics, Hanoi University of Technology, 1 Dai Co Viet Rd., Hanoi (Viet Nam); Hai, Nguyen Phuc [Faculty of Engineering, Katholieke University of Leuven, Kasteelpark Arenberg 44, 3001 Heverlee (Leuven) (Belgium)

    2007-06-15

    We calculate the diffusion thermopower of the degenerate two-dimensional hole gas in a p-type Si/Si{sub 1-x}Ge{sub x} lattice mismatched heterostructure at low temperatures and zero magnetic field. The effects of possible scatterings, e.g. remote impurity, alloy disorder, interface roughness, deformation potential, and random piezoelectric on the hole mobility and the diffusion thermopower are examined. Calculated results are well fitted to the experimental data recently reported. In addition, we predict a possibility for the diffusion thermopower to change its sign as the SiGe layer thickness changes, the effect has not been discussed yet. (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  6. High quality-factor Si/SiO(2)-InP hybrid micropillar cavities with submicrometer diameter for 1.55-μm telecommunication band.

    Science.gov (United States)

    Song, Hai-Zhi; Takemoto, Kazuya; Miyazawa, Toshiyuki; Takatsu, Motomu; Iwamoto, Satoshi; Ekawa, Mitsuru; Yamamoto, Tsuyoshi; Arakawa, Yasuhiko

    2015-06-15

    We theoretically demonstrate high quality(Q)-factor micropillar cavities at 1.55-μm wavelength based on Si/SiO(2)-InP hybrid structure. An adiabatic design in distributed Bragg reflectors (DBRs) improves Q-factor for upto 3 orders of magnitude, while reducing the diameter to sub-micrometer. A moderate Q-factor of ~3000 and a Purcell factor of ~200 are realized by only 2 taper segments and fewer conventional DBR pairs, enabling single photon generation at GHz rate. As the taper segment number is increased, Q-factor can be boosted to ~10(5)-10(6), enabling coherent exchange between the emitter and the optical mode at 1.55 μm, which is applicable in quantum information networks.

  7. Giant electric field control of magnetism and narrow ferromagnetic resonance linewidth in FeCoSiB/Si/SiO2/PMN-PT multiferroic heterostructures

    Science.gov (United States)

    Gao, Y.; Wang, X.; Xie, L.; Hu, Z.; Lin, H.; Zhou, Z.; Nan, T.; Yang, X.; Howe, B. M.; Jones, J. G.; Brown, G. J.; Sun, N. X.

    2016-06-01

    It has been challenging to achieve combined strong magnetoelectric coupling and narrow ferromagnetic resonance (FMR) linewidth in multiferroic heterostructures. Electric field induced large effective field of 175 Oe and narrow FMR linewidth of 40 Oe were observed in FeCoSiB/Si/SiO2/PMN-PT heterostructures with substrate clamping effect minimized through removing the Si substrate. As a comparison, FeCoSiB/PMN-PT heterostructures with FeCoSiB film directly deposited on PMN-PT showed a comparable voltage induced effective magnetic field but a significantly larger FMR linewidth of 283 Oe. These multiferroic heterostructures exhibiting combined giant magnetoelectric coupling and narrow ferromagnetic resonance linewidth offer great opportunities for integrated voltage tunable RF magnetic devices.

  8. Graphene-enhanced, internal-magnetic-field-generated Rabi oscillations in metal-coated Si-SiO2 photoconductive detectors

    CERN Document Server

    Nalla, Venkatram; Loh, Kian Ping; Ji, Wei

    2013-01-01

    We report our demonstration of Rabi oscillations in Si-SiO2-Al photoconductive devices with nanosecond laser pulses of a few nJ at room temperature without external magnetic fields. Zeeman splitting of spin quantum states of dopants in silicon is achieved with internal magnetic fields produced by the Al film under excitation of laser pulses. Rabi oscillation frequency is 15 MHz and 25 MHz when photocurrent direction is perpendicular and parallel, respectively, to the propagation direction of linearly-polarized, 532-nm, 7-ns laser pulses. Insertion of graphene buffer layer between Al and SiO2 provides a three-fold enhancement in Rabi oscillation amplitude. This simple-structured, low-cost device operated at room temperature should open a new avenue for future spin-based electronics and optoelectronics.

  9. Capture, storage, and emission of holes in Si/Si 1- xGe x/Si QW's for the determination of the valence band offset by DLTS

    Science.gov (United States)

    Chretien, O.; Apetz, R.; Vescan, L.; Souifi, A.; Lüth, H.

    1996-08-01

    We report on the problem of the determination of the valence band offset between strained Si 1- xGe x and unstrained Si layers by deep level transient spectroscopy (DLTS) on Si/Si 1- xGe x/Si quantum well (QW) structures. To observe a DLTS signal, the holes must be stored long enough (>1 ms) in the QW so that the thermal emission is the dominating process. We achieved sufficiently long storage times by using two different structures. The first one was obtained by selective growth which leads to a lateral limitation of the QW-layer, where the holes are localized. For the second ones, the localization of holes is due to the presence of Si 1- xGe x-islands.

  10. Alkane dimers interaction

    DEFF Research Database (Denmark)

    Ferrighi, Lara; Madsen, Georg Kent Hellerup; Hammer, Bjørk

    2010-01-01

    The interaction energies of a series of n-alkane dimers, from methane to decane, have been investigated with Density Functional Theory (DFT), using the MGGA-M06-L density functional. The results are compared both to the available wavefunction-based values as well as to dispersion corrected DFT...

  11. Dimeric Surfactants: Promising Ingredients of Cosmetics and Toiletries

    Directory of Open Access Journals (Sweden)

    Naveen Kumar

    2013-11-01

    Full Text Available Surfactants are an essential ingredient for cosmetic, toiletries and personal care products for enhancing their performance. Dimeric surfactants demonstrate superiority compared to conventional surfactants in all areas of application. Dimeric surfactants are extremely promising for utilization in various cosmetic formulations viz. shampoo, lotions, creams, conditioners etc. These surfactants possess extremely unique surface properties viz. lower surface tension, unique micellization, low critical micelle concentration (CMC and antimicrobial activity, higher solubilization etc. Dimerics enhance the performances of cosmetics in an extraordinary manner and provide eco-friendly preparations for human epidermis.

  12. Comprehensive investigation of sequential plasma activated Si/Si bonded interfaces for nano-integration on the wafer scale.

    Science.gov (United States)

    Kibria, M G; Zhang, F; Lee, T H; Kim, M J; Howlader, M M R

    2010-04-02

    The sequentially plasma activated bonding of silicon wafers has been investigated to facilitate the development of chemical free, room temperature and spontaneous bonding required for nanostructure integration on the wafer scale. The contact angle of the surface and the electrical and nanostructural behavior of the interface have been studied. The contact angle measurements show that the sequentially plasma (reactive ion etching plasma followed by microwave radicals) treated surfaces offer highly reactive and hydrophilic surfaces. These highly reactive surfaces allow spontaneous integration at the nanometer scale without any chemicals, external pressure or heating. Electrical characteristics show that the current transportation across the nanobonded interface is dependent on the plasma parameters. High resolution transmission electron microscopy results confirm nanometer scale bonding which is needed for the integration of nanostructures. The findings can be applied in spontaneous integration of nanostructures such as nanowires/nanotubes/quantum dots on the wafer scale.

  13. 月桂酸二聚甘油酯硫酸酯钠盐的制备与表面性能%Preparation and surface properties of sodium lauric dimerized glyceryl sulfate

    Institute of Scientific and Technical Information of China (English)

    史鸿鑫; 张辉; 武宏科; 陈立军; 项菊萍

    2012-01-01

    Lauric dimerized glycerol ester was synthesized from lauric acid and glycerol dimer,and then the intermediate ester was sulfated by chlorosulfonic acid and neutralized by NaOH solution to get the product sodium lauric dimerized glyceryl sulfate (SLDGS). The intermediate and product were characterized by FTIR. The surface chemical properties were investigated at 298 K. The surface tensions of SLDGS aqueous solution increase with the increasing esterification degree of glycerol dimmer with lauric acid. When its esterification degree is 25% ,the cmc is 1.15 mmol · L-1 and γcwc is 28. 5 mN · m-1. When esterification degree is 30% , emulsifying property of SLDGS aqueous solution with kerosene and benzene is the best,and the emulsification time is 168 s. Foaming performance of SLPGS is not good.%以二聚甘油和月桂酸为原料进行酯化反应得到月桂酸二聚甘油酯,再与氯磺酸反应,经氢氧化钠中和制得月桂酸二聚甘油酯硫酸酯钠盐(SLDGS).对中问体和产物进行了红外光谱分析,测定了产物在298 K下的表面化学性能.发现SLDGS水溶液的表面张力随着月桂酸酯化度的升高而增大,酯化度为25%时,最低表面张力为28.5 mN·m-1,临界胶束浓度为1.15 mmol·L-1;在煤油和苯中,当酯化度为30%时,SLDGS水溶液的乳化性能达到最大值,乳化时间为168 s;SLDGS水溶液的泡沫性能不佳.

  14. Three types of couplings between asymmetric plasmonic dimers.

    Science.gov (United States)

    Chao, Yen-Chun; Tseng, Hsuan-Chi; Chang, Kao-Der; Chang, Chih-Wei

    2012-01-30

    We report extensive numerical studies on plasmonic dimers of different configurations and find that their coupling effects can be categorized into three types of phenomena. First, like ordinary mechanical systems, the plasmonic dimers can exhibit positive couplings that show anti-crossing behavior. Second, they can also be arranged to exhibit negative couplings that display opposite trends in resonant frequency shifts. Third, when there are surface currents in proximity to each other, the resonance frequencies of the dimers exhibit unusual redshifts that do not have any analogies in conventional systems. Our work suggests that in addition to the well-known electric and magnetic dipolar interactions, contributions from the inductance of displacement currents in the near field cannot be ignored. Overall, asymmetric plasmonic dimers exhibit better sensitivities than the symmetric counterparts and our extensive studies also enable us to identify the plasmonic dimer with the highest sensing capabilities.

  15. Synthesis of Si/SiO2/ZnO nanoporous materials using chemical and electrochemical deposition techniques

    Science.gov (United States)

    Dauletbekova, A. K.; Alzhanova, A. Ye.; Akilbekov, A. T.; Mashentseva, A. A.; Zdorovets, M. V.; Balabekov, K. N.

    2016-09-01

    The work represents the results of forming Zn-based nanoprecipitates in nanoporous amorphous silicon dioxide on silicon substrate by the template synthesis method. SEM and AFM images of the surface after chemical and electrochemical deposition of zinc were obtained. The analysis of photoluminescence of the precipitated samples resulted in the assumption of formation of nanoclusters of zinc oxide.

  16. 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.

  17. The acrylonitrile dimer ion

    Science.gov (United States)

    Ervasti, Henri K.; Jobst, Karl J.; Burgers, Peter C.; Ruttink, Paul J. Ae; Terlouw, Johan K.

    2007-04-01

    Large energy barriers prohibit the rearrangement of solitary acrylonitrile ions, CH2CHCN+, into their more stable hydrogen-shift isomers CH2CCNH+ or CHCH-CNH+. This prompted us to examine if these isomerizations occur by self-catalysis in acrylonitrile dimer ions. Such ions, generated by chemical ionization experiments of acrylonitrile with an excess of carbon dioxide, undergo five dissociations in the [mu]s time frame, as witnessed by peaks at m/z 53, 54, 79, 80 and 105 in their metastable ion mass spectrum. Collision experiments on these product ions, deuterium labeling, and a detailed computational analysis using the CBS-QB3 model chemistry lead to the following conclusions: (i) the m/z 54 ions are ions CH2CHCNH+ generated by self-protonation in ion-dipole stabilized hydrogen-bridged dimer ions [CH2CHCN...H-C(CN)CH2]+ and [CH2CHCN...H-C(H)C(H)CN]+; the proton shifts in these ions are associated with a small reverse barrier; (ii) dissociation of the H-bridged ions into CH2CCNH+ or CHCH-CNH+ by self-catalysis is energetically feasible but kinetically improbable: experiment shows that the m/z 53 ions are CH2CHCN+ ions, generated by back dissociation; (iii) the peaks at m/z 79, 80 and 105 correspond with the losses of HCN, C2H2 and H, respectively. The calculations indicate that these ions are generated from dimer ions that have adopted the (much more stable) covalently bound "head-to-tail" structure [CH2CHCN-C(H2)C(H)CN]+; experiments indicate that the m/z 79 (C5H5N) and m/z 105 (C6H6N2) ions have linear structures but the m/z 80 (C4H4N2) ions consist of ionized pyrimidine in admixture with its stable pyrimidine-2-ylidene isomer. Acrylonitrile is a confirmed species in interstellar space and our study provides experimental and computational evidence that its dimer radical cation yields the ionized prebiotic pyrimidine molecule.

  18. Calcium-dependent Dimerization of Human Soluble Calcium Activated Nucleotidase: Characterization of the Dimer Interface

    Energy Technology Data Exchange (ETDEWEB)

    Yang,M.; Horii, K.; Herr, A.; Kirley, T.

    2006-01-01

    Mammals express a protein homologous to soluble nucleotidases used by blood-sucking insects to inhibit host blood clotting. These vertebrate nucleotidases may play a role in protein glycosylation. The activity of this enzyme family is strictly dependent on calcium, which induces a conformational change in the secreted, soluble human nucleotidase. The crystal structure of this human enzyme was recently solved; however, the mechanism of calcium activation and the basis for the calcium-induced changes remain unclear. In this study, using analytical ultracentrifugation and chemical cross-linking, we show that calcium or strontium induce noncovalent dimerization of the soluble human enzyme. The location and nature of the dimer interface was elucidated using a combination of site-directed mutagenesis and chemical cross-linking, coupled with crystallographic analyses. Replacement of Ile{sup 170}, Ser{sup 172}, and Ser{sup 226} with cysteine residues resulted in calcium-dependent, sulfhydryl-specific intermolecular cross-linking, which was not observed after cysteine introduction at other surface locations. Analysis of a super-active mutant, E130Y, revealed that this mutant dimerized more readily than the wild-type enzyme. The crystal structure of the E130Y mutant revealed that the mutated residue is found in the dimer interface. In addition, expression of the full-length nucleotidase revealed that this membrane-bound form can also dimerize and that these dimers are stabilized by spontaneous oxidative cross-linking of Cys{sup 30}, located between the single transmembrane helix and the start of the soluble sequence. Thus, calcium-mediated dimerization may also represent a mechanism for regulation of the activity of this nucleotidase in the physiological setting of the endoplasmic reticulum or Golgi.

  19. The Effect of Plasma Spraying on the Microstructure and Aging Kinetics of the Al-Si Matrix Alloy and Al-Si/SiC Composites

    Science.gov (United States)

    Altunpak, Yahya; Akbulut, Hatem; Üstel, Fatih

    2010-02-01

    The Al-Si (LM 13)-based matrix alloy reinforced with SiC particles containing 10, 20, and 30 vol.% SiC particles were spray-formed onto Al-Si substrates. The sprayed samples were directly subjected to a standard aging treatment (T551). From the experiments, it was observed that the high rate of solidification resulted in very fine silicon particles which were observed as continuous islands in the matrix and each island exhibited several very fine silicon crystals. Analysis showed that plasma-spraying caused an increased solid solubility of the silicon in the aluminum matrix. DSC measurements in the permanent mold-cast Al-Si matrix alloy and plasma-sprayed Al-Si matrix alloy showed that plasma-spraying causes an increase in the amount of GP-zone formation owing to the very high rate solidification after plasma-spraying. In the plasma-sprayed Al-Si/SiC composites GP zones were suppressed, since particle-matrix interfaces act as a sink for vacancies during quenching from high plasma process temperature. Introduction of SiC particles to the Al-Si age-hardenable alloy resulted in a decrease in the time required to reach plateau matrix hardness owing to acceleration of aging kinetics by ceramic SiC particles.

  20. Enhanced Giant Piezoresistance Performance of Sandwiched ZnS/Si/SiO2 Radial Heterostructure Nanotubes for Nonvolatile Stress Memory with Repeatable Writing and Erasing.

    Science.gov (United States)

    Cheng, Baochang; Xiong, Li; Cai, Qiangsheng; Shi, Haiping; Zhao, Jie; Su, Xiaohui; Xiao, Yanhe; Lei, Shuijin

    2016-12-21

    It is a challenge to realize nonvolatile stress-writing memory. Herein, we propose a strategy to construct rewritable stress information storage devices, consisting of deliberately designing individual sandwiched ZnS/Si/SiO2 radial heterostructure nanotubes synthesized by one-step thermal evaporation method. A bulk trap-related Poole-Frenkel hopping mechanism is proposed. Carriers are localized in a narrow bandgap Si intermediate layer; moreover, incorporated impurities and heterointerface defects can serve as charge trap centers or storage mediators. Compressive strain can induce trap barrier height to decrease at relatively low operation bias voltage, whereas tensile strain can induce it to increase, resulting in a giant piezoresistance effect. After both loading compressive and tensile strains at low bias voltage, additionally, the emptying of trap states results in a high resistance state. However, the emptied trap states can be filled by applying a relatively high bias voltage without strains and, correspondingly, the memories return to low resistance state. The emptying and filling of trap states, respectively applied by strains and high electric field, result in a repeatable writing/erasing nonvolatile memory effect. The results indicate that the creation and modification of trap states in multiscale nanostructures can give an avenue to the development of novel nanodevices for rewritable nonvolatile stress sensor and memory.

  1. High-efficiency and wideband interlayer grating couplers in multilayer Si/SiO2/SiN platform for 3D integration of optical functionalities.

    Science.gov (United States)

    Sodagar, Majid; Pourabolghasem, Reza; Eftekhar, Ali A; Adibi, Ali

    2014-07-14

    We have designed interlayer grating couplers with single/double metallic reflectors for Si/SiO(2)/SiN multilayer material platform. Out-of-plane diffractive grating couplers separated by 1.6 μm thick buffer SiO(2) layer are vertically stacked against each other in Si and SiN layers. Geometrical optimization using genetic algorithm coupled with electromagnetic simulations using two-dimensional (2D) finite element method (FEM) results in coupler designs with high peak coupling efficiency of up to 89% for double- mirror and 64% for single-mirror structures at telecom wavelength. Also, 3-dB bandwidths of 40 nm and 50 nm are theoretically predicted for the two designs, respectively. We have fabricated the grating coupler structure with single mirror. Measured values for insertion loss and 3-dB bandwidth in the fabricated single-mirror coupler confirms the theoretical results. This opens up the possibility of low-loss 3D dense integration of optical functionalities in hybrid material platforms.

  2. Nanocrystalline Si/SiO{sub 2} core-shell network with intense white light emission fabricated by hot-wire chemical vapor deposition

    Energy Technology Data Exchange (ETDEWEB)

    Matsumoto, Y., E-mail: ymatsumo@cinvestav.mx; Dutt, A. [SEES, Electrical Engineering Department, Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional, Cinvestav-IPN, Mexico, D.F. 07360 (Mexico); Santana-Rodríguez, G. [Institute of Material Research, Universidad Nacional Autónoma de México, Coyoacán 04510 (Mexico); Santoyo-Salazar, J. [Department of Physics, Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional, Cinvestav-IPN, Mexico, D.F. 07360 (Mexico); Aceves-Mijares, M. [Departament of Electronics, Instituto Nacional de Astrofísica Óptica y Electrónica, Tonantzintla, Puebla 72000 (Mexico)

    2015-04-27

    We report the fabrication of a stable Si/SiO{sub 2} core-shell network using hot-wire chemical vapor deposition on a silicon substrate at a relatively low substrate temperature of 200 °C. Structural investigations using transmission electron microscopy and X-ray diffraction confirm the presence of nanocrystalline silicon and silicon dioxide quantum dots in the form of a core-shell network embedded in the amorphous SiO{sub x} matrix, while selected area electron diffraction confirms the formation of a core-shell structure. The core-shell structure exhibits a bright white emission that can be seen with the unaided eye at room temperature without any post-annealing treatments, and the observed photoemission does not alter in color or intensity after prolonged laser exposure. Additional measurements are performed while varying the laser power and optical gain is found in the as-deposited material. Intense stable white luminescence is observed and shows the prospective for various optical and biological applications in the future.

  3. Nanocrystalline Si/SiO2 core-shell network with intense white light emission fabricated by hot-wire chemical vapor deposition

    Science.gov (United States)

    Matsumoto, Y.; Dutt, A.; Santana-Rodríguez, G.; Santoyo-Salazar, J.; Aceves-Mijares, M.

    2015-04-01

    We report the fabrication of a stable Si/SiO2 core-shell network using hot-wire chemical vapor deposition on a silicon substrate at a relatively low substrate temperature of 200 °C. Structural investigations using transmission electron microscopy and X-ray diffraction confirm the presence of nanocrystalline silicon and silicon dioxide quantum dots in the form of a core-shell network embedded in the amorphous SiOx matrix, while selected area electron diffraction confirms the formation of a core-shell structure. The core-shell structure exhibits a bright white emission that can be seen with the unaided eye at room temperature without any post-annealing treatments, and the observed photoemission does not alter in color or intensity after prolonged laser exposure. Additional measurements are performed while varying the laser power and optical gain is found in the as-deposited material. Intense stable white luminescence is observed and shows the prospective for various optical and biological applications in the future.

  4. Effects of substrate temperature on the growth, structural and optical properties of NiSi/SiC core-shell nanowires

    Science.gov (United States)

    Hamzan, Najwa Binti; Nordin, Farah Nadiah Binti; Rahman, Saadah Abdul; Huang, Nay Ming; Goh, Boon Tong

    2015-07-01

    In this paper we attempt to study the growth of NiSi/SiC core-shell nanowires on Ni-coated glass substrates by hot-wire chemical vapor deposition. The samples were prepared at different substrate temperatures of between 350 and 527 °C to investigate the growth of the nanowires. Ni nanoparticles were used as templates for initially inducing the growth of these core-shell nanowires at substrate temperature as low as 350 °C. The high density of the nanowires was clearly demonstrated at higher substrate temperatures of 450 and 527 °C. These core-shell nanowires were structured by single crystalline NiSi and amorphous SiC as the core and shell of the nanowires respectively. The amorphous SiC shell consisted of SiC nanocolumns within an amorphous matrix. The formation of these high density nanowires showed a noticeable suppression in photoluminescence emissions from the oxygen-related defects and superior optical absorption in visible and limited near infrared regions. The effects of substrate temperatures on growth, optical and structural properties of the nanowires are presented and discussed.

  5. Low frequency noise and electrical transport properties of pseudomorphic Si/Si sub 1 sub - xGe sub x heterostructures

    CERN Document Server

    Prest, M J

    2001-01-01

    Growth of high germanium content (x=0.44) pseudomorphic Si/Si sub 1 sub - sub x Ge sub x structures at low temperature, followed by a high temperature anneal, was optimised for low temperature mobility. The optimum was found for growth at 380 deg C with an ex-situ anneal at 800 deg C which gave a 10K mobility of 1030cm sup 2 V sup - sup 1 s sup - sup 1 with a sheet density of 1.2x10 sup 1 sup 2 cm sup - sup 2. A sample grown at 380 deg C with an in-situ anneal at 800 deg C gave an even higher 10K mobility of 1985cm sup 2 V sup - sup 1 s sup - sup 1 with a sheet density of 1.0x10 sup 1 sup 2 cm sup - sup 2. Chemical etching was used to fully deplete the dopant supply layer so that a room temperature Hall mobility of 255cm sup 2 V sup - sup 1 s sup - sup 1 was measured. Variation of the Hall coefficient was used to determine the room temperature Hall scattering factor as 0.58 which gave a Drift mobility of 440cm sup 2 V sup - sup 1 s sup - sup 1 (about twice that of a conventional Si pMOS device at the same ver...

  6. Reactivity of [Ge9 {Si(SiMe3 )3 }3 ](-) Towards Transition-Metal M(2+) Cations: Coordination and Redox Chemistry.

    Science.gov (United States)

    Kysliak, Oleksandr; Schrenk, Claudio; Schnepf, Andreas

    2016-12-23

    Recently the metalloid cluster compound [Ge9 Hyp3 ](-) (1; Hyp=Si(SiMe3 )3 ) was oxidatively coupled by an iron(II) salt to give the largest metalloid Group 14 cluster [Ge18 Hyp6 ]. Such redox chemistry is also possible with different transition metal (TM) salts TM(2+) (TM=Fe, Co, Ni) to give the TM(+) complexes [Fe(dppe)2 ][Ge9 Hyp3 ] (3; dppe=1,2-bis(diphenylphosphino)ethane), [Co(dppe)2 ][Ge9 Hyp3 ] (4), [Ni(dppe)(Ge9 Hyp3 )] (5) and [Ni(dppe)2 (Ge9 Hyp3 )](+) (6). Such a redox reaction does not proceed for Mn, for which a salt metathesis gives the first open shell [Hyp3 Ge9 -M-Ge9 Hyp3 ] cluster (2; M=Mn). The bonding of the transition metal atom to 1 is also possible for Ni (e.g., compound 6), in which one or even two nickel atoms can bind to 1. In contrast to this in case of the Fe and Co compounds 3 and 4, respectively, the transition-metal atom is not bound to the Ge9 core of 1. The synthesis and the experimentally determined structures of 2-6 are presented. Additionally the bonding within 2-6 is analyzed and discussed with the aid of EPR measurements and quantum chemical calculations. © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  7. A Fractional Factorial Design Study of Reciprocating Wear Behavior of Al-Si-SiCp Composites at Lubricated Contacts

    Science.gov (United States)

    Rajeev, V. R.; Dwivedi, D. K.; Jain, S. C.

    2011-04-01

    The lubricated reciprocating wear behavior of two composites A319/15%SiCp and A390/15%SiCp produced by the liquid metallurgy route was investigated by means of an indigenously developed reciprocating friction wear test rig using a fractional factorial-design approach. The main purpose was to study the influence of wear and friction test parameters such as applied load, sliding distance, reciprocating velocity, counter surface temperature and silicon content in composites, as well as their interactions on the wear and friction characteristics of these composites. Two output responses (wear loss and coefficient of friction) were measured. The input parameter levels were fixed through pilot experiment conducted in the newly developed reciprocating friction and wear test rig. The counter surface material used for the wear study was cast iron having Vickers hardness of 244 HVN. It had been demonstrated through established equations that A390/15%SiCp composite is subjected to low wear compared to the A319/15%SiCp composite. The experimental results indicate that the proposed mathematical models suggested could adequately describe the performance indicators within the limits of the factors that are being investigated. The applied load, sliding distance, reciprocating velocity, counter surface temperature, and silicon content in composite are the five important factors controlling the friction and wear characteristics of the composite in lubricated condition. Moreover, the two factor interactions have a strong effect on the wear of composites. The results give a comprehensive insight into the wear of the composites.

  8. Asymmetric monometallic nanorod nanoparticle dimer and related compositions and methods

    KAUST Repository

    Han, Yu

    2016-03-31

    The fabrication of asymmetric monometallic nanocrystals with novel properties for plasmonics, nanophotonics and nanoelectronics. Asymmetric monometallic plasmonic nanocrystals are of both fundamental synthetic challenge and practical significance. In an example, a thiol-ligand mediated growth strategy that enables the synthesis of unprecedented Au Nanorod-Au Nanoparticle (AuNR-AuNP) dimers from pre-synthesized AuNR seeds. Using high-resolution electron microscopy and tomography, crystal structure and three-dimensional morphology of the dimer, as well as the growth pathway of the AuNP on the AuNR seed, was investigated for this example. The dimer exhibits an extraordinary broadband optical extinction spectrum spanning the UV, visible, and near infrared regions (300 - 1300 nm). This unexpected property makes the AuNR-AuNP dimer example useful for many nanophotonic applications. In two experiments, the dimer example was tested as a surface- enhanced Raman scattering (SERS) substrate and a solar light harvester for photothermal conversion, in comparison with the mixture of AuNR and AuNP. In the SERS experiment, the dimer example showed an enhancement factor about 10 times higher than that of the mixture, when the excitation wavelength (660 nm) was off the two surface plasmon resonance (SPR) bands of the mixture. In the photothermal conversion experiment under simulated sunlight illumination, the dimer example exhibited an energy conversion efficiency about 1.4 times as high as that of the mixture.

  9. 用气态源分子束外延生长法制备Si/SiGe/Si nPn异质结双极晶体管%Growth of Si/SiGe/Si Heterojunction Bipolar Transistors by Gas-Source Molecular Beam Epitaxy

    Institute of Scientific and Technical Information of China (English)

    刘学锋; 李晋闽; 孔梅影; 黄大定; 李建平; 林兰英

    2000-01-01

    用气态源分子束外延法制备了Si/SiGe/Si npn异质结双极晶体管.晶体管基区Ge组分为0.12,B掺杂浓度为1.5×101 9cm-3, SiGe合金厚度约45nm.直流特性测试表明,共发射极直流放大倍数约50,击穿电压VCE约9V;射频特性测试结果表明,晶体管的截止频率为7GHz,最高振荡频率为2.5GHz.

  10. The adsorption of 2,5-dimer- capto-1,3,4-thiadiazole (DMTD) on copper surface and its binding behavior

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    The interaction mechanism of 2,5-dimercapto- 1,3,4-thiadiazole (DMTD) on copper surface was studied by surface-enhanced Raman scattering (SERS), infrared (IR) and X-ray photoelectron spectroscopy (XPS) techniques. The SERS spectra were obtained. We found that DMTD bound with the copper via its two-excocyclic mercapto groups. The monosulphide salt was formed. At the same time, DMTD coordinated with the Cu+ ion through the excocyclic mercap-to groups and polymerized via the Cu+ ion into a one- dimen-sional polymer chain on the copper surface.

  11. Family C 7TM receptor dimerization and activation

    DEFF Research Database (Denmark)

    Bonde, Marie Mi; Sheikh, Søren P; Hansen, Jakob Lerche

    2006-01-01

    The family C seven transmembrane (7TM) receptors constitutes a small and especially well characterized subfamily of the large 7TM receptor superfamily. Approximately 50% of current prescription drugs target 7TM receptors, this biologically important family represents the largest class of drug......-targets today. It is well established that family C 7TM receptors form homo- or hetero-dimers on the cell surface of living cells. The large extra-cellular domains (ECD) have been crystallized as a dimer in the presence and absence of agonist. Upon agonist binding, the dimeric ECD undergoes large conformational...... to be fully defined. This review presents the biochemical support for family C 7TM receptor dimerization and discusses its importance for receptor biosynthesis, surface expression, ligand binding and activation, since lessons learnt here may well be applicable to the whole superfamily of 7TM receptors....

  12. 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.

  13. Giant Electric Field Control of Magnetism and Narrow Ferromagnetic Resonance Linewidth in FeCoSiB/Si/SiO2/PMN PT Multiferroic Heterostructures (Open Access Author’s Manuscript)

    Science.gov (United States)

    2016-06-06

    1 Giant electric field control of magnetism and narrow ferromagnetic resonance linewidth in FeCoSiB/Si/SiO2/PMN-PT multiferroic heterostructures...coupling and narrow ferromagnetic resonance (FMR) linewidth in multiferroic heterostructures. Electric field induced large effective field of 175Oe...in which the electric field applied to the piezoelectric layer produces a mechanical deformation that couples to the magnetic film, and hence induces

  14. Improved electrical properties of n-n and p-n Si/SiC junctions with thermal annealing treatment

    Science.gov (United States)

    Liang, J.; Nishida, S.; Arai, M.; Shigekawa, N.

    2016-07-01

    The effects of annealing process on the electrical properties of n+-Si/n-SiC and p+-Si/n-SiC junctions fabricated by using surface-activated bonding are investigated. It is found by measuring the current-voltage (I-V) characteristics of n+-Si/n-SiC junctions that the reverse-bias current and the ideality factor decreased to 2.0 × 10-5 mA/cm2 and 1.10, respectively, after the junctions annealing at 700 °C. The flat band voltages of n+-Si/n-SiC and p+-Si/n-SiC junctions obtained from capacitance-voltage (C-V) measurements decreased with increasing annealing temperature. Furthermore, their flat band voltages are very close to each other irrespective of the annealing temperature change, which suggests that the Fermi level is still pinned at the bonding interface even for the junctions annealing at high temperature and the interface state density causing Fermi level pinning varies with the junctions annealing. The reverse characteristics of n+-Si/n-SiC junctions are in good agreement with the calculations based on thermionic field emission. In addition, the calculated donor concentration of 4H-SiC epi-layers and flat band voltage is consistent with the values obtained from C-V measurements.

  15. Formation of bismuth oxide nanowires by simultaneous templating and electrochemical adhesion of DNA on Si/SiO{sub 2}

    Energy Technology Data Exchange (ETDEWEB)

    Hale, Michael G. [School of Chemistry, Newcastle University, Newcastle upon Tyne, NE1 7RU (United Kingdom); Little, Ross; Salem, Mohamed Ali [School of Chemical Engineering and Advanced Materials, Newcastle University, Newcastle upon Tyne, NE1 7RU (United Kingdom); Hedley, Joseph H.; Horrocks, Benjamin R. [School of Chemistry, Newcastle University, Newcastle upon Tyne, NE1 7RU (United Kingdom); Siller, Lidija, E-mail: Lidija.Siller@ncl.ac.uk [School of Chemical Engineering and Advanced Materials, Newcastle University, Newcastle upon Tyne, NE1 7RU (United Kingdom)

    2012-10-01

    Deoxyribonucleic acid (DNA)-templated growth of Bi/Bi{sub 2}O{sub 3} nanowires attached to the Si surface was obtained by electrochemical reduction of Bi(III) at an n-type Si electrode in aqueous Bi(NO{sub 3}){sub 3}/HNO{sub 3} at pH 2.5 with calf thymus DNA. The nanowires had a mean diameter of 5 nm and a range of lengths from 1.4 {mu}m to 6.1 {mu}m. The composition and structure of the wires were determined by atomic force microscopy, Fourier transform infrared spectroscopy, Raman spectroscopy and X-ray photoemission spectroscopy. The dominant component of the material is Bi{sub 2}O{sub 3} owing to the rapid re-oxidation of nanoscale Bi in the presence of air and water. Our method has the potential to construct complex architectures of Bi/Bi{sub 2}O{sub 3} nanostrucures on high quality Si substrates. - Highlights: Black-Right-Pointing-Pointer We have developed an electrochemical method to grow Bi/Bi{sub 2}O{sub 3} nanowires on silicon. Black-Right-Pointing-Pointer Bi/Bi{sub 2}O{sub 3} nanowires are templated by deoxyribonucleic acid molecules. Black-Right-Pointing-Pointer The procedure also adheres the nanowires to the electrode for characterization.

  16. Chlorodiethylaluminum supported on silica: A dinuclear aluminum surface species with bridging μ2-Cl-ligand as a highly efficient co-catalyst for the Ni-catalyzed dimerization of ethene

    KAUST Repository

    Kermagoret, Anthony

    2014-05-01

    Silica-supported chloro alkyl aluminum co-catalysts (DEAC@support) were prepared via Surface Organometallic Chemistry by contacting diethylaluminum chloride (DEAC) and high specific surface silica materials, i.e. SBA-15, MCM-41, and Aerosil SiO2. Such systems efficiently activate NiCl 2(PBu3)2 for catalytic ethene dimerization, with turnover frequency (TOF) reaching up to 498,000 molC2H4/ (molNi h) for DEAC@MCM-41. A detailed analysis of the DEAC@SBA-15 co-catalyst structure by solid-state aluminum-27 NMR at high-field (17.6 T and 20.0 T) and ultrafast spinning rates allows to detect six sites, characterized by a distribution of quadrupolar interaction principal values CQ and isotropic chemical shifts δiso. Identification of the corresponding Al-grafted structures was possible by comparison of the experimental NMR signatures with these calculated by DFT on a wide range of models for the aluminum species (mono- versus di-nuclear, mono- versus bis-grafted with bridging Cl or ethyl). Most of the sites were identified as dinuclear species with retention of the structure of DEAC, namely with the presence of μ2-Cl-ligands between two aluminum, and this probably explains the high catalytic performance of this silica-supported co-catalysts. © 2014 Elsevier Inc. All rights reserved.

  17. The effect of Na concentration on the kinetic phase transitions of a monomer-dimer reaction system on Na-promoted surface

    Energy Technology Data Exchange (ETDEWEB)

    Khan, K.M.; Basit, A. [Nuclear Physics Division, Pakistan Institute of Nuclear Science and Technology (PINSTECH), Islamabad (Pakistan); Albano, E.V. [Research Institute of Theoretical and Applied Physical Chemistry (INIFTA), CONICET, UNLP, CIC, La Plata (Argentina)

    2002-05-03

    A simple lattice-gas model for the reaction of CO and NO on an Na-modified surface of a square lattice is studied. The crucial property of the model is Na-induced dissociation of NO, which triggers the catalytic reaction. Some interesting features are added to the phase diagram when the range of Na-induced NO dissociation is studied in the nearest and the next-nearest neighbourhood. The moment CO partial pressure (y{sub CO}) departs from zero, the continuous production of CO{sub 2} and N{sub 2} starts. This production remains continuous until a point where the catalytic activity stops and the surface is poisoned with a combination of CO, N and O. The value of poisoning point depends upon the value of Na concentration on the surface. (author)

  18. Dynamics of a bouncing dimer

    CERN Document Server

    Dorbolo, S; Tsimring, L S; Kudrolli, A

    2005-01-01

    We investigate the dynamics of a dimer bouncing on a vertically oscillated plate. The dimer, composed of two spheres rigidly connected by a light rod, exhibits several modes depending on initial and driving conditions. The first excited mode has a novel horizontal drift in which one end of the dimer stays on the plate during most of the cycle, while the other end bounces in phase with the plate. The speed and direction of the drift depend on the aspect ratio of the dimer. We employ event-driven simulations based on a detailed treatment of frictional interactions between the dimer and the plate in order to elucidate the nature of the transport mechanism in the drift mode.

  19. Computer simulation of CaSiO3 glass under compression: correlation between Si-Si pair radial distribution function and intermediate range order structure

    Science.gov (United States)

    Lan, Mai Thi; Thuy Duong, Tran; Iitaka, Toshiaki; Van Hong, Nguyen

    2017-06-01

    The structural organization of CaSiO3 glass at 600 K and under pressure of 0-100 GPa is investigated by molecular dynamics simulation (MDS). Results show that the atomic structure of CaSiO3 comprises SiO n and CaO m units considered as basic structural polyhedra. At low pressure, most of the basic structural polyhedra are SiO4, CaO5, CaO6 and CaO7. At high pressure most of the basic structural polyhedra are SiO5, SiO6 and CaO9, CaO10 and CaO11. The distribution of basic structural polyhedra is not uniform resulting in formation of Ca-rich and Si-rich regions. The distribution of SiO4, SiO5 and SiO6 polyhedra is also not uniform, but it tends to form SiO4-, SiO5-, and SiO6-clusters. For the Si-O network, under compression there is a gradual transition from the tetrahedral network (SiO4) to the octahedral network (SiO6) via SiO5 polyhedra. The SiO5-clusters are the same as immediate-phase in the transformation process. The size and shape of SiO4 tetrahedra change strongly under compression. While the size of SiO5 and SiO6 has also changed significantly, but the shape is almost unchanged under compression. The SiO n polyhedra can connect to each other via one common oxygen ion (corner-sharing bond), two common oxygen ions (edge-sharing bond) or three common oxygen ions (face-sharing bond). The Si-Si bond length in corner-sharing bonds is much longer than the ones in edge-sharing and face-sharing bonds. The change of intermediate range order (IRO) structure under compression relating to edge- and face-sharing bonds amongst SiO n at high pressure is the origin of the first peak splitting of the radial distribution functions of Si-Si pair. Under compression, the number of non-bridging oxygen (NBO) decreases. This makes the Si-O network more polymerized. At low pressure, most of the Ca2+ ions incorporate into the Si-O network via NBOs. At high pressure, the amount of NBO decreases, Ca2+ ions mainly incorporate into the Si-O network via bridging oxygen (BO) that

  20. What's on the Surface? Physics and Chemistry of Delta-Doped Surfaces

    Science.gov (United States)

    Hoenk, Michael

    2011-01-01

    Outline of presentation: 1. Detector surfaces and the problem of stability 2. Delta-doped detectors 3. Physics of Delta-doped Silicon 4. Chemistry of the Si-SiO2 Interface 5. Physics and Chemistry of Delta-doped Surfaces a. Compensation b. Inversion c. Quantum exclusion. Conclusions: 1. Quantum confinement of electrons and holes dominates the behavior of delta-doped surfaces. 2. Stability of delta-doped detectors: Delta-layer creates an approx 1 eV tunnel barrier between bulk and surface. 3. At high surface charge densities, Tamm-Shockley states form at the surface. 4. Surface passivation by quantum exclusion: Near-surface delta-layer suppresses T-S trapping of minority carriers. 5. The Si-SiO2 interface compensates the surface 6. For delta-layers at intermediate depth, surface inversion layer forms 7. Density of Si-SiO2 interface charge can be extremely high (>10(exp 14)/sq cm)

  1. Universal dimer-dimer scattering in lattice effective field theory

    CERN Document Server

    Elhatisari, Serdar; Lee, Dean; Meißner, Ulf-G; Rupak, Gautam

    2016-01-01

    We consider two-component fermions with short-range interactions and large scattering length. This system has universal properties that are realized in many different fields including atomic, nuclear and particle physics. In the limit of large fermion-fermion scattering length $a_\\mathrm{ff}$ and zero range interaction, all properties of the system scale proportionally with the only length scale $a_\\mathrm{ff}$. We consider the case where there are bound dimers and calculate the scattering phase shifts for the two-dimer system near threshold using lattice effective field theory. From the scattering phase shifts, we extract the universal dimer-dimer scattering length $a_\\mathrm{dd}/a_\\mathrm{ff}=0.645(89)$ and effective range $r_\\mathrm{dd}/a_\\mathrm{ff}=-0.413(79)$.

  2. An ab initio potential energy surface for the formic acid dimer: zero-point energy, selected anharmonic fundamental energies, and ground-state tunneling splitting calculated in relaxed 1-4-mode subspaces.

    Science.gov (United States)

    Qu, Chen; Bowman, Joel M

    2016-09-14

    We report a full-dimensional, permutationally invariant potential energy surface (PES) for the cyclic formic acid dimer. This PES is a least-squares fit to 13475 CCSD(T)-F12a/haTZ (VTZ for H and aVTZ for C and O) energies. The energy-weighted, root-mean-square fitting error is 11 cm(-1) and the barrier for the double-proton transfer on the PES is 2848 cm(-1), in good agreement with the directly-calculated ab initio value of 2853 cm(-1). The zero-point vibrational energy of 15 337 ± 7 cm(-1) is obtained from diffusion Monte Carlo calculations. Energies of fundamentals of fifteen modes are calculated using the vibrational self-consistent field and virtual-state configuration interaction method. The ground-state tunneling splitting is computed using a reduced-dimensional Hamiltonian with relaxed potentials. The highest-level, four-mode coupled calculation gives a tunneling splitting of 0.037 cm(-1), which is roughly twice the experimental value. The tunneling splittings of (DCOOH)2 and (DCOOD)2 from one to three mode calculations are, as expected, smaller than that for (HCOOH)2 and consistent with experiment.

  3. Si/SiGe MMIC's

    Science.gov (United States)

    Luy, Johann-Friedrich; Strohm, Karl M.; Sasse, Hans-Eckard; Schueppen, Andreas; Buechler, Josef; Wollitzer, Michael; Gruhle, Andreas; Schaeffler, Friedrich; Guettich, Ulrich; Klaassen, Andreas

    1995-04-01

    Silicon-based millimeter-wave integrated circuits (SIMMWIC's) can provide new solutions for near range sensor and communication applications in the frequency range above 50 GHz. This paper gives a survey on the state-of-the-art performance of this technology and on first applications. The key devices are IMPATT diodes for mm-wave power generation and detection in the self-oscillating mixer mode, p-i-n diodes for use in switches and phase shifters, and Schottky diodes in detector and mixer circuits. The silicon/silicon germanium heterobipolar transistor (SiGe HBT) with f(sub max) values of more than 90 GHz is now used for low-noise oscillators at Ka-band frequencies. First system applications are discussed.

  4. 应用镁金属化学还原法制备多孔 Si/Si-O-C 负极材料机理研究%Mechanism of porous Si/Si-O-C anode material prepared by chemical reduction with magnesium

    Institute of Scientific and Technical Information of China (English)

    郑春满; 刘相; 谢凯; 韩喻

    2016-01-01

    以二乙烯基苯和聚硅氧烷为原料经先驱体转化法制备 Si-O-C 材料,利用镁金属在惰性气氛保护下高温还原制备多孔的 Si /Si-O-C 负极材料。利用 X 射线衍射、能谱分析、元素分析和场发射扫描电镜分析多孔 Si /Si-O-C 负极材料的组成、结构、形貌,从而研究利用镁金属化学还原法制备多孔 Si /Si-O-C 负极材料的机理。结果表明,镁金属在还原过程中生成 MgO 和 Mg2 SiO4等产物,经 HCl 洗涤后可形成多孔的 Si /Si-O-C 负极材料。Si /Si-O-C 材料中的单质硅分布于多孔的 Si-O-C 相中,一定程度上可缓解 Si 在循环过程中产生的体积效应。利用镁金属还原 Si-O-C 材料制备多孔 Si /Si-O-C 材料是一种可行的制备方法。%Si-O-C material was prepared by a polymer-derived method using copolymer of phenyl-substituted polysiloxane and divinylbenzene as raw materials.The porous Si /Si-O-C anode material was prepared with the chemical reduction of Si-O-C material by magnesium at high temperature under argon atmosphere.The composition,structure,morphology,and formation process of porous Si /Si-O-C anode material were investigated by X-ray diffraction, energy spectrum analysis, elemental analysis and field emission scanning electron microscope. The electrochemical properties of the material were characterized by using the electrochemical test instrument.The research results show that the magnesium will react with oxygen of Si-O-C material and turn into MgO and Mg2 SiO4 during the reduction process.When washed with HCl,MgO and Mg2 SiO4 react with HCl and turn into MgCl2 ,which can dissolve in the solution.Then,the porous Si /Si-O-C anode materials are formed.The silicon distribute in the porous Si-O-C material,which can improve the cycle performance of silicon.It can confirms that the material prepared by using magnesium reduction method is a potential material for the lithium-ion battery.

  5. Collisional properties of weakly bound heteronuclear dimers

    NARCIS (Netherlands)

    Marcelis, B.; Kokkelmans, S.J.J.M.F.; Shlyapnikov, G.V.; Petrov, D.S.

    2008-01-01

    We consider collisional properties of weakly bound heteronuclear molecules (dimers) formed in a two-species mixture of atoms with a large mass difference. We focus on dimers containing light fermionic atoms as they manifest collisional stability due to an effective dimer-dimer repulsion originating

  6. Luminescence of Strain Compensated Si/Si0.62 Ge0.38 Quantum Well Grown on Si0.75 Ge0.25 Virtual Substrate%Si0.75Ge0.25虚衬底上应变补偿Si/Si0.61Ge0.38量子阱发光

    Institute of Scientific and Technical Information of China (English)

    廖凌宏; 周志文; 李成; 陈松岩; 赖虹凯; 余金中; 王启明

    2009-01-01

    由于Si/SiGe异质结构的带阶差主要发生在价带,为实现高效率的发光,本文从理论上设计了在硅基Si1-x Gex虚衬底上外延应变补偿的Si/S1-y Ge,(y>x)量子阱的能带结构,将量子阱对电子的限制势垒提高到100meV以上.在实验上,采用300℃生长的Ge量子点插入层,制备出薄的SiGe驰豫缓冲层(虚衬底),表面Ge组份达到0.25,表面粗糙度小于2nm,驰豫度接近100%.在我们制备的SiGe缓冲层上外延了应变补偿SiGe/Si多量子阱结构,并初步研究了其发光特性.

  7. Small thermal fatigue crack propagation behavior of sprayed Al-Si/SiCp composite for brake disc%喷射沉积Al-Si/SiCp制动盘材料的热疲劳微裂纹扩展行为

    Institute of Scientific and Technical Information of China (English)

    李微; 陈鼎; 陈振华; 滕杰; 范沧

    2009-01-01

    采用V形缺口试样,研究喷射沉积Al-Si/SiCp复合材料制动盘在25(450 ℃热循环下的热疲劳行为.通过金相显微镜和扫描电镜观察了复合材料的组织和热疲劳裂纹形貌,研究热疲劳裂纹形成与扩展机制.结果表明:热疲劳主裂纹主要从V形缺口处萌生;在同样的热循环次数下,热处理前的试样要比热处理后的试样先出现裂纹,且裂纹扩展的速率较快;裂纹绕过Si颗粒向前扩展以及裂纹穿过Si颗粒向前扩展是裂纹与Si颗粒相互作用的主要机制;SiC颗粒与热疲劳裂纹有明显的交互作用.因此,改善Si相的形态和分布以及加强Al/SiC颗粒间的界面结合有利于提高热疲劳裂纹扩展的抗力.

  8. Synthesis and Applications of Non-spherical Dimer Colloids

    Science.gov (United States)

    Yoon, Kisun

    Colloids are promising building blocks in material synthesis because of their controllability of size and surface properties. The synthesis of chemically and/or geometrically anisotropic colloidal particles has received attentions with the expectation of building blocks for complex structures. However, the synthesis of anisotropic colloidal particles is by far more difficult than the synthesis of spherical colloidal particles. Lack of monodispersity and productivity of many anisotropic particles often limits their applications as a building block for complex structures. Thus, it is highly desirable to develop methods which can produce a large amount of monodisperse non-spherical particles with controllable asymmetric surface properties. This dissertation details the work for developing such a method. The major result of this dissertation is a synthetic method to produce monodisperse non-spherical colloids with anisotropic surface property in a large quantity. The anisotropic colloid, which we call it as Dimer particle, has two fused lobes like a dumbbell and each lobe's size can be independently controlled. We present a novel method to synthesize sub-micron size Dimer particles. This method can produce a large amount of submicron-sized Dimer particles with good monodispersity and well-controlled shape. Submicron-sized Dimer particles have been highly desired since they can be used as a building block for self assembly using Brownian motion, colloidal surfactant for Pickering emulsion, and photonic materials. To fully take advantage of the anisotropy of the particles, we develop a facile method to tailor the surface property of each lobe independently by asymmetrically coating the particles with gold nanoparticles. This method doesn't need the arrangement of particles onto any type of interfaces. Asymmetric coating of gold nanoparticles can be carried out simply by mixing Dimer particles with gold nanoparticles. The formation mechanism of the submicron-sized Dimer

  9. Inequivalent models of irreversible dimer filling: ``Transition state'' dependence

    Science.gov (United States)

    Nord, R. S.; Evans, J. W.

    1990-12-01

    Irreversible adsorption of diatomics on crystalline surfaces is sometimes modeled as random dimer filling of adjacent pairs of sites on a lattice. We note that this process can be implemented in two distinct ways: (i) randomly pick adjacent pairs of sites, jj', and fill jj' only if both are empty (horizontal transition state); or (ii) randomly pick a single site, j, and if j and at least one neighbor are empty, then fill j and a randomly chosen empty neighbor (vertical transition state). Here it is instructive to consider processes which also include competitive random monomer filling of single sites. We find that although saturation (partial) coverages differ little between the models for pure dimer filling, there is a significant difference for comparable monomer and dimer filling rates. We present exact results for saturation coverage behavior for a linear lattice, and estimates for a square lattice. Ramifications for simple models of CO oxidation on surfaces are indicated.

  10. Cleavage of the Fe—Fe Bond of (Me2SiSiMe2) [η5-C5H4Fe(CO)2]2 with Na/Hg and Molecular Structure of the Ring-Opened Complex

    Institute of Scientific and Technical Information of China (English)

    周秀中; 张怀林; 张振生

    2003-01-01

    The reaction of the rifle cyclic complex (1) with sodium amalgam in THF resulted in the expected cleavage of the Fe-Fe bond to afford his-sodium salt ( Me2SiSiMe2 ) [η5-C5H4Fe(CO)2]2 (4). The latter was not isolated and was used directly to react with MeI, PhCH2Cl, CH3C(O)Cl, PhC(O)Cl,Cy3SnCl (Cy= cyclohexyl) or Ph3SnCl to afford corresponding ring-opened derivatives (Me2SiSiMe2) [η5-C5H4Fe(CO)2]2 [5, R=Me; 6, R=PhCH2; 7, R=CH3C(O); 8, R=PhC(O); 9, R = Cy3Sn or 10, R = Ph3Sn ]. The crystal and molecular structures of 10 were determined by X-ray diffraction analysis. The molecule took the desired ant/ conformation around the Si-Si bond. The length of the Si--Si bond is 0.2343(3)nm, which is essentially identical to that in the cyclic structure of 1[0.2346(4) tun]. This result unambiguously demonstrates that the Si--Si bond in the cyclic structure of 1 is not subject to obvious strain.

  11. Kinetics of DNA tile dimerization.

    Science.gov (United States)

    Jiang, Shuoxing; Yan, Hao; Liu, Yan

    2014-06-24

    Investigating how individual molecular components interact with one another within DNA nanoarchitectures, both in terms of their spatial and temporal interactions, is fundamentally important for a better understanding of their physical behaviors. This will provide researchers with valuable insight for designing more complex higher-order structures that can be assembled more efficiently. In this report, we examined several spatial factors that affect the kinetics of bivalent, double-helical (DH) tile dimerization, including the orientation and number of sticky ends (SEs), the flexibility of the double helical domains, and the size of the tiles. The rate constants we obtained confirm our hypothesis that increased nucleation opportunities and well-aligned SEs accelerate tile-tile dimerization. Increased flexibility in the tiles causes slower dimerization rates, an effect that can be reversed by introducing restrictions to the tile flexibility. The higher dimerization rates of more rigid tiles results from the opposing effects of higher activation energies and higher pre-exponential factors from the Arrhenius equation, where the pre-exponential factor dominates. We believe that the results presented here will assist in improved implementation of DNA tile based algorithmic self-assembly, DNA based molecular robotics, and other specific nucleic acid systems, and will provide guidance to design and assembly processes to improve overall yield and efficiency.

  12. NMR Structural Studies on Alamethicin Dimers

    Institute of Scientific and Technical Information of China (English)

    李星

    2003-01-01

    15N labeled alamethicin dimer was synthesized. The structure and dynamics of alamethicin dimers were studied with nuclear magnetic resonance (NMR) spectroscopy. The data from 15N-labeled alamethicin dimer suggest little differences in conformation between the dimer and monomer in the Aib1-Pro14 region. Significant difference in the conformation of the C-terminus are manifest in the NH chemical shifts in the Val15-Pho20 region.

  13. Rubidium dimers in paraffin-coated cells

    CERN Document Server

    Acosta, V M; Windes, D; Corsini, E; Ledbetter, M P; Karaulanov, T; Auzinsh, M; Rangwala, S A; Kimball, D F Jackson; Budker, D

    2010-01-01

    Measurements were made to determine the density of rubidium dimer vapor in paraffin-coated cells. The number density of dimers and atoms in similar paraffin-coated and uncoated cells was measured by optical spectroscopy. Due to the relatively low melting point of paraffin, a limited temperature range of 43-80 deg C was explored, with the lower end corresponding to a dimer density of less than 10^7 cm^(-3). With one-minute integration time, a sensitivity to dimer number density of better than 10^6 cm^(-3) was achieved. No significant difference in dimer density was observed between the cells.

  14. Fiber optic D dimer biosensor

    Science.gov (United States)

    Glass, Robert S.; Grant, Sheila A.

    1999-01-01

    A fiber optic sensor for D dimer (a fibrinolytic product) can be used in vivo (e.g., in catheter-based procedures) for the diagnosis and treatment of stroke-related conditions in humans. Stroke is the third leading cause of death in the United States. It has been estimated that strokes and stroke-related disorders cost Americans between $15-30 billion annually. Relatively recently, new medical procedures have been developed for the treatment of stroke. These endovascular procedures rely upon the use of microcatheters. These procedures could be facilitated with this sensor for D dimer integrated with a microcatheter for the diagnosis of clot type, and as an indicator of the effectiveness, or end-point of thrombolytic therapy.

  15. Mechanism of FGF receptor dimerization and activation

    Science.gov (United States)

    Sarabipour, Sarvenaz; Hristova, Kalina

    2016-01-01

    Fibroblast growth factors (fgfs) are widely believed to activate their receptors by mediating receptor dimerization. Here we show, however, that the FGF receptors form dimers in the absence of ligand, and that these unliganded dimers are phosphorylated. We further show that ligand binding triggers structural changes in the FGFR dimers, which increase FGFR phosphorylation. The observed effects due to the ligands fgf1 and fgf2 are very different. The fgf2-bound dimer structure ensures the smallest separation between the transmembrane (TM) domains and the highest possible phosphorylation, a conclusion that is supported by a strong correlation between TM helix separation in the dimer and kinase phosphorylation. The pathogenic A391E mutation in FGFR3 TM domain emulates the action of fgf2, trapping the FGFR3 dimer in its most active state. This study establishes the existence of multiple active ligand-bound states, and uncovers a novel molecular mechanism through which FGFR-linked pathologies can arise.

  16. Formation and diffusion of water dimers on rutile TiO2(110).

    Science.gov (United States)

    Matthiesen, J; Hansen, J O; Wendt, S; Lira, E; Schaub, R; Laegsgaard, E; Besenbacher, F; Hammer, B

    2009-06-05

    From an interplay of time-lapsed high resolution scanning tunneling microscopy and density functional theory calculations we reveal the formation and diffusion of water dimers on hydrated rutile TiO2(110)-(1x1) surfaces, i.e., surfaces containing OH_{br} groups. At temperatures between approximately 150 and approximately 210 K water monomers diffusing along the Ti troughs were found to form stable water dimers that diffuse faster than the water monomers. An H bond mediated rollover mechanism operating for the water dimers explains the experimental findings.

  17. Design of Si/SiO2 micropillar cavities for Purcell-enhanced single photon emission at 1.55 μm from InAs/InP quantum dots.

    Science.gov (United States)

    Song, Hai-Zhi; Takemoto, Kazuya; Miyazawa, Toshiyuki; Takatsu, Motomu; Iwamoto, Satoshi; Yamamoto, Tsuyoshi; Arakawa, Yasuhiko

    2013-09-01

    Numerical simulations were carried out on micropillar cavities consisting of Si/SiO2 distributed Bragg reflectors (DBRs) with an InP spacer layer. Owing to a large refractive index contrast of ~2 in DBRs, cavities with just 4/6.5 top/bottom DBR pairs that give a low pillar height (~4.5 μm), have noticeable Purcell-enhancement effect in the 1.55-μm band. With careful designs on cavities with diameters of ~2.30 μm, a quality factor of up to 3300, a nominal Purcell factor of up to 110, and an output efficiency of ~60% are obtainable. These results ensure improvement of operation frequency and enhancement of photon indistinguishability for 1.55-μm single photon sources based on InAs/InP quantum dots.

  18. Induced electrostatic confinement of electron gas in W-designed strain-compensated Si/Si{sub 1-} {sub x} Ge {sub x} /Si type-II quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    Sfina, N. [Unite de Physique des Solides, Departement de Physique, Faculte des Sciences de Monastir, Avenue de l' Environnement, 5019 Monastir (Tunisia)]. E-mail: sfina_fsm@yahoo.fr; Lazzari, J.-L. [Centre de Recherche en Matiere Condensee et Nanosciences, CRMC-N, UPR-CNRS 7251, Laboratory associated with the Universite de la Mediterranee and the Universite Paul Cezanne, Campus de Luminy, Case 913, 13288 Marseille cedex 9 (France); Christol, P. [Centre d' Electronique et de Micro-optoelectronique de Montpellier, CEM2, UMR-CNRS 5507, Universite Montpellier 2-Sciences et Techniques du Languedoc, CC 067, Place Eugene Bataillon, 34095 Montpellier cedex 5 (France); Cuminal, Y. [Centre d' Electronique et de Micro-optoelectronique de Montpellier, CEM2, UMR-CNRS 5507, Universite Montpellier 2-Sciences et Techniques du Languedoc, CC 067, Place Eugene Bataillon, 34095 Montpellier cedex 5 (France); Said, M. [Unite de Physique des Solides, Departement de Physique, Faculte des Sciences de Monastir, Avenue de l' Environnement, 5019 Monastir (Tunisia)

    2006-12-15

    We present a numerical modeling of the conduction- and the valence-band diagrams of W designed Si/Si{sub 0.4}Ge{sub 0.6}/Si type II quantum wells. These W structures, strain-compensated on relaxed Si{sub 0.75}Ge{sub 0.25} pseudo-substrates, are potentially interesting for emission and photo-detection around a 1.55{mu}m wavelength. Two main features have been extrapolated by solving self-consistently Schroedinger and Poisson equations, taking into account the electrostatic attraction induced by carrier injection: (i) Coulomb attraction strongly modifies the band profiles and increases the electron probability density at the quantum well interfaces. (ii) The injected carrier concentration enhances the in-plane oscillator strength and the electron-hole wave-function overlap.

  19. 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.

  20. Synthesis of steroidal dimers: Selective amine catalysed steroidal dimerization

    Indian Academy of Sciences (India)

    Shamsuzzaman; Mohd Gulfam Aalam; Tabassum Siddiqui

    2011-07-01

    Some new dimeric steroids namely cholest-5-en-3-spiro-[6',5'-oxa]-5'-cholest-3'-one (2), cholest-5-en-7-spiro-[4',5'-oxa]-5'-cholest-7'-one (4a) and 3-substitutedcholest-5-en-7-spiro-[4',5'-oxa]-3'-substituted-5'-cholestan-7'-ones (4b, c) are synthesized starting from cholest-5-en-3-one (1), cholest-5-en-7-one (3a) and 3-substituted-cholest-5-en-7-ones (3b, c) respectively by using DMAP and xylene. All the synthesized compounds were characterized by using IR, MS and 1H, 13C NMR spectral and elemental analysis.

  1. Micellisation and immunoreactivities of dimeric beta-caseins.

    Science.gov (United States)

    Yousefi, Reza; Gaudin, Jean-Charles; Chobert, Jean-Marc; Pourpak, Zahra; Moin, Mostafa; Moosavi-Movahedi, Ali Akbar; Haertle, Thomas

    2009-12-01

    Bovine beta-casein (beta-CN) is a highly amphiphilic micellising phospho-protein showing chaperone-like activity in vitro. Recently, existence of multiple sequential epitopes on beta-CN polypeptide chain in both hydrophilic-polar (psi) and hydrophobic-apolar domains (phi) has been evidenced. In order to clarify specific contribution of polar and apolar domains in micellisation process and in shaping immunoreactivity of beta-CN, its dimeric/bi-amphiphilic "quasi palindromic" forms covalently connected by a disulfide bond linking either N-terminal (C4 beta-CND) or C-terminal domain (C208 beta-CND) were produced and studied. Depending on the C- or N-terminal position of inserted cysteine, each dimeric beta-CN contains one polar/apolar region at the centre and two external hydrophobic/hydrophilic ends. Consequently, such casein dimers have radically different polarities/hydrophobicities on their outside surfaces. Dynamic light scattering (DLS) measurements indicate that these dimeric casein molecules form micelles of different sizes depending on arrangement of polar fragments of the beta-CN mutants in their constrained dimers. Non-aggregated dimers have different hydrodynamic diameters that could be explained by their different geometries. Measurements of fluorescence showed more hydrophobic environment of Trp residues of C208 beta-CND, while in similar experimental conditions Trp residues of C4 beta-CND and native beta-CN were more exposed to the polar medium. Both fluorescence and DLS studies showed greater propensity for micellisation of the dimeric beta-CNs, suggesting that the factors inducing the formation of micelles are stronger in the bi-amphiphilic dimers. 1-anilino-naphthalene-8-sulfonate (ANS) binding studies showed different binding of ANS by these dimers as well as different exposition of ANS binding (hydrophobic) regions in the micellar states. The differences in fluorescence resonance energy transfer (FRET) profiles of C4 beta-CND and C208 beta-CND can

  2. A Model for Dimerization of the SOX Group E Transcription Factor Family.

    Science.gov (United States)

    Ramsook, Sarah N; Ni, Joyce; Shahangian, Shokofeh; Vakiloroayaei, Ana; Khan, Naveen; Kwan, Jamie J; Donaldson, Logan W

    2016-01-01

    Group E members of the SOX transcription factor family include SOX8, SOX9, and SOX10. Preceding the high mobility group (HMG) domain in each of these proteins is a thirty-eight amino acid region that supports the formation of dimers on promoters containing tandemly inverted sites. The purpose of this study was to obtain new structural insights into how the dimerization region functions with the HMG domain. From a mutagenic scan of the dimerization region, the most essential amino acids of the dimerization region were clustered on the hydrophobic face of a single, predicted amphipathic helix. Consistent with our hypothesis that the dimerization region directly contacts the HMG domain, a peptide corresponding to the dimerization region bound a preassembled HMG-DNA complex. Sequence conservation among Group E members served as a basis to identify two surface exposed amino acids in the HMG domain of SOX9 that were necessary for dimerization. These data were combined to make a molecular model that places the dimerization region of one SOX9 protein onto the HMG domain of another SOX9 protein situated at the opposing site of a tandem promoter. The model provides a detailed foundation for assessing the impact of mutations on SOX Group E transcription factors.

  3. Evidence for the dimerization-mediated catalysis of methionine sulfoxide reductase A from Clostridium oremlandii.

    Science.gov (United States)

    Lee, Eun Hye; Lee, Kitaik; Kwak, Geun-Hee; Park, Yeon Seung; Lee, Kong-Joo; Hwang, Kwang Yeon; Kim, Hwa-Young

    2015-01-01

    Clostridium oremlandii MsrA (CoMsrA) is a natively selenocysteine-containing methionine-S-sulfoxide reductase and classified into a 1-Cys type MsrA. CoMsrA exists as a monomer in solution. Herein, we report evidence that CoMsrA can undergo homodimerization during catalysis. The monomeric CoMsrA dimerizes in the presence of its substrate methionine sulfoxide via an intermolecular disulfide bond between catalytic Cys16 residues. The dimeric CoMsrA is resolved by the reductant glutaredoxin, suggesting the relevance of dimerization in catalysis. The dimerization reaction occurs in a concentration- and time-dependent manner. In addition, the occurrence of homodimer formation in the native selenoprotein CoMsrA is confirmed. We also determine the crystal structure of the dimeric CoMsrA, having the dimer interface around the two catalytic Cys16 residues. A central cone-shaped hole is present in the surface model of dimeric structure, and the two Cys16 residues constitute the base of the hole. Collectively, our biochemical and structural analyses suggest a novel dimerization-mediated mechanism for CoMsrA catalysis that is additionally involved in CoMsrA regeneration by glutaredoxin.

  4. Self-assembly of Asymmetric Dimer Particles in Supported Copolymer Bilayer

    Institute of Scientific and Technical Information of China (English)

    Xiao-chun Qin; Chun-lai Ren

    2011-01-01

    Using self-consistent field and density functional theories, we investigate the self-assembly behavior of asymmetric dimer particles in a supported AB block copolymer bilayer. Asymmetric dimer particles are amphiphilic molecules composed by two different spheres. One prefers to A block of copolymers and the other likes B block when they are introduced into the copolymer bilayer. The two layer structure of the dimer particles is formed within the bilayer.Due to the presence of the substrate surface, the symmetry of the two leaflets of the bilayer is broken, which may lead to two different layer structures of dimer particles within each leaflet of the bilayer. With the increasing concentration of the asymmetric dimer particles,in-plane structure of the dimer particles undergoes sparse square, hexagonal, dense square, and cylindrical structures. In a further condensed packing, a bending cylindrical structure comes into being. Here we verify that the entropic effect of copolymers, the enthalpy of the system and the steric repulsion of the dimer particles are three important factors determing the self-assembly of dimer particles within the supported copolymer bilayer.

  5. Scanning tunneling microscopy characterization of the geometric and electronic structure of hydrogen-terminated silicon surfaces

    Science.gov (United States)

    Kaiser, W. J.; Bell, L. D.; Hecht, M. H.; Grunthaner, F. J.

    1988-01-01

    Scanning tunneling microscopy (STM) methods are used to characterize hydrogen-terminated Si surfaces prepared by a novel method. The surface preparation method is used to expose the Si-SiO2 interface. STM images directly reveal the topographic structure of the Si-SiO2 interface. The dependence of interface topography on oxide preparation conditions observed by STM is compared to the results of conventional surface characterization methods. Also, the electronic structure of the hydrogen-terminated surface is studied by STM spectroscopy. The near-ideal electronic structure of this surface enables direct tunnel spectroscopy measurements of Schottky barrier phenomena. In addition, this method enables probing of semiconductor subsurface properties by STM.

  6. Dimerization of Human Growth Hormone by Zinc

    Science.gov (United States)

    Cunningham, Brian C.; Mulkerrin, Michael G.; Wells, James A.

    1991-08-01

    Size-exclusion chromatography and sedimentation equilibrium studies demonstrated that zinc ion (Zn2+) induced the dimerization of human growth hormone (hGH). Scatchard analysis of 65Zn2+ binding to hGH showed that two Zn2+ ions associate per dimer of hGH in a cooperative fashion. Cobalt (II) can substitute for Zn2+ in the hormone dimer and gives a visible spectrum characteristic of cobalt coordinated in a tetrahedral fashion by oxygen- and nitrogen-containing ligands. Replacement of potential Zn2+ ligands (His18, His21, and Glu174) in hGH with alanine weakened both Zn2+ binding and hGH dimer formation. The Zn2+-hGH dimer was more stable than monomeric hGH to denaturation in guanidine-HCl. Formation of a Zn2+-hGH dimeric complex may be important for storage of hGH in secretory granules.

  7. Dimer models and Calabi-Yau algebras

    CERN Document Server

    Broomhead, Nathan

    2008-01-01

    In this thesis we study dimer models, as introduced in string theory, which give a way of writing down a class of non-commutative `superpotential' algebras. Some examples are 3-dimensional Calabi-Yau algebras, as defined by Ginzburg, and some are not. We consider two types of `consistency' condition on dimer models, and show that a `geometrically consistent' model is `algebraically consistent'. Finally we prove that the algebras obtained from algebraically consistent dimer models are 3-dimensional Calabi-Yau algebras.

  8. On Dimer Models and Closed String Theories

    OpenAIRE

    Sarkar, Tapobrata

    2007-01-01

    We study some aspects of the recently discovered connection between dimer models and D-brane gauge theories. We argue that dimer models are also naturally related to closed string theories on non compact orbifolds of $\\BC^2$ and $\\BC^3$, via their twisted sector R charges, and show that perfect matchings in dimer models correspond to twisted sector states in the closed string theory. We also use this formalism to study the combinatorics of some unstable orbifolds of $\\BC^2$.

  9. Dimerization of norbornene on zeolite catalysts

    Institute of Scientific and Technical Information of China (English)

    N. G. Grigor’eva; S. V. Bubennov; L. M. Khalilov; B. I. Kutepov

    2015-01-01

    The high activity and selectivity of H‐Beta and H‐ZSM‐12 zeolites in the dimerization of norbornene was established. The norbornene conversion reached 100%in chlorinated paraffin and argon gas medium, with a selectivity of dimer formation of 88%–98%. Four stereo‐isomers of the bis‐2,2’‐norbornylidene structure were identified in the dimer fraction, with the (Z)‐anti‐bis‐2,2’‐norbornylidene prevailing over the others.

  10. Enhanced Chiral Recognition by Cyclodextrin Dimers

    Directory of Open Access Journals (Sweden)

    Bart Jan Ravoo

    2011-07-01

    Full Text Available In this article we investigate the effect of multivalency in chiral recognition. To this end, we measured the host-guest interaction of a β-cyclodextrin dimer with divalent chiral guests. We report the synthesis of carbohydrate-based water soluble chiral guests functionalized with two borneol, menthol, or isopinocampheol units in either (+ or (– configuration. We determined the interaction of these divalent guests with a β-cyclodextrin dimer using isothermal titration calorimetry. It was found that—in spite of a highly unfavorable conformation—the cyclodextrin dimer binds to guest dimers with an increased enantioselectivity, which clearly reflects the effect of multivalency.

  11. The Dimer Interface of the Membrane Type 1 Matrix Metalloproteinase Hemopexin Domain

    Science.gov (United States)

    Tochowicz, Anna; Goettig, Peter; Evans, Richard; Visse, Robert; Shitomi, Yasuyuki; Palmisano, Ralf; Ito, Noriko; Richter, Klaus; Maskos, Klaus; Franke, Daniel; Svergun, Dmitri; Nagase, Hideaki; Bode, Wolfram; Itoh, Yoshifumi

    2011-01-01

    Homodimerization is an essential step for membrane type 1 matrix metalloproteinase (MT1-MMP) to activate proMMP-2 and to degrade collagen on the cell surface. To uncover the molecular basis of the hemopexin (Hpx) domain-driven dimerization of MT1-MMP, a crystal structure of the Hpx domain was solved at 1.7 Å resolution. Two interactions were identified as potential biological dimer interfaces in the crystal structure, and mutagenesis studies revealed that the biological dimer possesses a symmetrical interaction where blades II and III of molecule A interact with blades III and II of molecule B. The mutations of amino acids involved in the interaction weakened the dimer interaction of Hpx domains in solution, and incorporation of these mutations into the full-length enzyme significantly inhibited dimer-dependent functions on the cell surface, including proMMP-2 activation, collagen degradation, and invasion into the three-dimensional collagen matrix, whereas dimer-independent functions, including gelatin film degradation and two-dimensional cell migration, were not affected. These results shed light on the structural basis of MT1-MMP dimerization that is crucial to promote cellular invasion. PMID:21193411

  12. Glycine transporter dimers: evidence for occurrence in the plasma membrane

    DEFF Research Database (Denmark)

    Bartholomäus, Ingo; Milan-Lobo, Laura; Nicke, Annette

    2008-01-01

    membrane based on hydrodynamic and native gel electrophoretic studies. Here, we used cysteine substitution and oxidative cross-linking to show that of GlyT1 and GlyT2 also form dimeric complexes within the plasma membrane. GlyT oligomerization at the cell surface was confirmed for both GlyT1 and GlyT2......Different Na(+)/Cl(-)-dependent neurotransmitter transporters of the SLC6a family have been shown to form dimers or oligomers in both intracellular compartments and at the cell surface. In contrast, the glycine transporters (GlyTs) GlyT1 and -2 have been reported to exist as monomers in the plasma...

  13. Role of the Chlorophyll Dimer in Bacterial Photosynthesis

    Science.gov (United States)

    Warshel, Arieh

    1980-06-01

    The role of a special dimer (D) of bacterio-chlorophyll molecules in bacterial photosynthesis was examined by calculations of the rates of electron transfer reactions in a system of the dimer and a bacteriopheophytin (BPh) molecule. It was found that the dependence of the potential surfaces of D on the distance between the monomers allows a fast light-induced electron transfer from D to BPh but only a slow back reaction (reduction of D+ by BPh-). The same potential surfaces allow efficient reduction of D+ by cytochrome c. Possible advantages of greatly different values of the electronic matrix elements for the forward and back reactions are pointed out. It is suggested that the electrostatic interaction between D+ and an ionized group of the protein might play an important role in the photosynthetic reaction.

  14. Structural and Thermodynamic Properties of the Argon Dimer: A Computational Chemistry Exercise in Quantum and Statistical Mechanics

    Science.gov (United States)

    Halpern, Arthur M.

    2010-01-01

    Using readily available computational applications and resources, students can construct a high-level ab initio potential energy surface (PES) for the argon dimer. From this information, they can obtain detailed molecular constants of the dimer, including its dissociation energy, which compare well with experimental determinations. Using both…

  15. Benzene and Pyridine on Silicon (001)

    DEFF Research Database (Denmark)

    Warschkow, Oliver; Bennett, J.M.; Miwa, J. A.

    2017-01-01

    The adsorption chemistry of benzene and pyridine on the silicon (001) surface is characterized by two prominent adsorbate configurations: a precursor structure bonded to a single Si Si dimer and a "tight-bridge" configuration that connects two adjacent dimers. We examine here the performance of 2...

  16. Mahler Measure, Eisenstein Series and Dimers

    NARCIS (Netherlands)

    Stienstra, J.

    2007-01-01

    This note reveals a mysterious link between the partition function of certain dimer models on 2-dimensional tori and the L-function of their spectral curves. It also relates the partition function in certain families of dimer models to Eisenstein series. http://www.arxiv.org/abs/math.NT/0502197

  17. Dimeric assembly of enterocyte brush border enzymes

    DEFF Research Database (Denmark)

    Danielsen, E M

    1994-01-01

    temperature (20 degrees C) reduced the rate of, but did not prevent, dimerization. Maltase-glucoamylase (EC 3.2.1.20) only appeared as a dimer when extracted and analyzed under low salt conditions, suggesting a weak association between the two subunits. This finding is consistent with the electronmicroscopic...

  18. Potassium Hexacyanoferrate (III-Catalyzed Dimerization of Hydroxystilbene: Biomimetic Synthesis of Indane Stilbene Dimers

    Directory of Open Access Journals (Sweden)

    Jing-Shan Xie

    2015-12-01

    Full Text Available Using potassium hexacyanoferrate (III–sodium acetate as oxidant, the oxidative coupling reaction of isorhapontigenin and resveratrol in aqueous acetone resulted in the isolation of three new indane dimers 4, 6, and 7, together with six known stilbene dimers. Indane dimer 5 was obtained for the first time by direct transformation from isorhapontigenin. The structures and relative configurations of the dimers were elucidated using spectral analysis, and their possible formation mechanisms were discussed. The results indicate that this reaction could be used as a convenient method for the semi-synthesis of indane dimers because of the mild conditions and simple reaction products.

  19. Statistical transmutation in doped quantum dimer models.

    Science.gov (United States)

    Lamas, C A; Ralko, A; Cabra, D C; Poilblanc, D; Pujol, P

    2012-07-06

    We prove a "statistical transmutation" symmetry of doped quantum dimer models on the square, triangular, and kagome lattices: the energy spectrum is invariant under a simultaneous change of statistics (i.e., bosonic into fermionic or vice versa) of the holes and of the signs of all the dimer resonance loops. This exact transformation enables us to define the duality equivalence between doped quantum dimer Hamiltonians and provides the analytic framework to analyze dynamical statistical transmutations. We investigate numerically the doping of the triangular quantum dimer model with special focus on the topological Z(2) dimer liquid. Doping leads to four (instead of two for the square lattice) inequivalent families of Hamiltonians. Competition between phase separation, superfluidity, supersolidity, and fermionic phases is investigated in the four families.

  20. Origin of Symmetric Dimer Images of Si(001) Observed by Low-Temperature Scanning Tunneling Microscopy

    Science.gov (United States)

    Ren, Xiao-Yan; Kim, Hyun-Jung; Niu, Chun-Yao; Jia, Yu; Cho, Jun-Hyung

    2016-06-01

    It has been a long-standing puzzle why buckled dimers of the Si(001) surface appeared symmetric below ~20 K in scanning tunneling microscopy (STM) experiments. Although such symmetric dimer images were concluded to be due to an artifact induced by STM measurements, its underlying mechanism is still veiled. Here, we demonstrate, based on a first-principles density-functional theory calculation, that the symmetric dimer images are originated from the flip-flop motion of buckled dimers, driven by quantum tunneling (QT). It is revealed that at low temperature the tunneling-induced surface charging with holes reduces the energy barrier for the flipping of buckled dimers, thereby giving rise to a sizable QT-driven frequency of the flip-flop motion. However, such a QT phenomenon becomes marginal in the tunneling-induced surface charging with electrons. Our findings provide an explanation for low-temperature STM data that exhibits apparent symmetric (buckled) dimer structure in the filled-state (empty-state) images.

  1. Universal four-Boson states in ultracold molecular gases: resonant effects in dimer-dimer collisions.

    Science.gov (United States)

    D'Incao, J P; von Stecher, J; Greene, Chris H

    2009-07-17

    We study the manifestations of universal four-body physics in ultracold dimer-dimer collisions. We show that resonant features associated with three-body Efimov physics and dimer-dimer scattering lengths are universally related. The emergence of universal four-boson states allows for the tunability of the dimer-dimer interaction, thus enabling the future study of ultracold molecular gases with both attractive and repulsive interactions. Moreover, our study of the interconversion between dimers and Efimov trimers shows that B2+B2-->B3+B rearrangement reactions can provide an efficient trimer formation mechanism. Our analysis of the temperature dependence of this reaction provides an interpretation of the available experimental data and sheds light on the possible experimental realization of rearrangement processes in ultracold gases.

  2. Novel covalently linked insulin dimer engineered to investigate the function of insulin dimerization

    DEFF Research Database (Denmark)

    Vinther, Tine N.; Norrman, Mathias; Strauss, Holger M.;

    2012-01-01

    An ingenious system evolved to facilitate insulin binding to the insulin receptor as a monomer and at the same time ensure sufficient stability of insulin during storage. Insulin dimer is the cornerstone of this system. Insulin dimer is relatively weak, which ensures dissociation into monomers...... in the circulation, and it is stabilized by hexamer formation in the presence of zinc ions during storage in the pancreatic ß-cell. Due to the transient nature of insulin dimer, direct investigation of this important form is inherently difficult. To address the relationship between insulin oligomerization...... and insulin stability and function, we engineered a covalently linked insulin dimer in which two monomers were linked by a disulfide bond. The structure of this covalent dimer was identical to the self-association dimer of human insulin. Importantly, this covalent dimer was capable of further oligomerization...

  3. Nanocrystalline-diamond thin films with high pH and penicillin sensitivity prepared on a capacitive Si-SiO{sub 2} structure

    Energy Technology Data Exchange (ETDEWEB)

    Poghossian, A. [Institute of Nano- and Biotechnologies (INB), Aachen University of Applied Sciences, Campus Juelich, Juelich (Germany); Institute of Bio- and Nanosystems (IBN-2), Research Centre Juelich GmbH, Juelich (Germany)], E-mail: a.poghossian@fz-juelich.de; Abouzar, M.H.; Razavi, A.; Baecker, M. [Institute of Nano- and Biotechnologies (INB), Aachen University of Applied Sciences, Campus Juelich, Juelich (Germany); Institute of Bio- and Nanosystems (IBN-2), Research Centre Juelich GmbH, Juelich (Germany); Bijnens, N. [Institute for Materials Research, Hasselt University, Diepenbeek (Belgium); Williams, O.A.; Haenen, K. [Institute for Materials Research, Hasselt University, Diepenbeek (Belgium); Division IMOMEC, IMEC vzw., Diepenbeek (Belgium); Moritz, W. [Humboldt University Berlin, Berlin (Germany); Wagner, P. [Institute for Materials Research, Hasselt University, Diepenbeek (Belgium); Schoening, M.J. [Institute of Nano- and Biotechnologies (INB), Aachen University of Applied Sciences, Campus Juelich, Juelich (Germany); Institute of Bio- and Nanosystems (IBN-2), Research Centre Juelich GmbH, Juelich (Germany)

    2009-10-30

    A capacitive field-effect EDIS (electrolyte-diamond-insulator-semiconductor) sensor with improved pH and penicillin sensitivity has been realised using a nanocrystalline-diamond (NCD) film as sensitive gate material. The NCD growth process on SiO{sub 2} as well as an additional surface treatment in oxidising medium have been optimised to provide high pH-sensitive, non-porous O-terminated films without damage of the underlying SiO{sub 2} layer. The surface morphology of O-terminated NCD thin films and the layer structure of EDIS sensors have been studied by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) methods. To establish the relative coverage of the surface functional groups generated by the oxidation of NCD surfaces, X-ray photoelectron spectroscopy analysis was carried out. The hydrophilicity of NCD thin films has been studied by water contact-angle measurements. A nearly Nernstian pH sensitivity of 54-57 mV/pH has been observed for O-terminated NCD films treated in an oxidising boiling mixture for 80 min and in oxygen plasma. The high pH-sensitive properties of O-terminated NCD have been used to develop an EDIS-based penicillin biosensor. A freshly prepared penicillin biosensor possesses a high sensitivity of 85 mV/decade in the concentration range of 0.1-2.5 mM penicillin G. The lower detection limit is 5 {mu}M.

  4. Influence of annealing and Al2O3 properties on the hydrogen-induced passivation of the Si/SiO2 interface

    NARCIS (Netherlands)

    Dingemans, G.; Einsele, F.; Beyer, W.; M. C. M. van de Sanden,; Kessels, W. M. M.

    2012-01-01

    Annealing at moderate temperatures is required to activate the silicon surface passivation by Al2O3 thin films while also the thermal stability at higher temperatures is important when Al2O3 is implemented in solar cells with screenprinted metallization. In this paper, the relationship between the m

  5. The E2 Domains of APP and APLP1 Share a Conserved Mode of Dimerization

    Energy Technology Data Exchange (ETDEWEB)

    S Lee; Y Xue; J Hulbert; Y Wang; X Liu; B Demeler; Y Ha

    2011-12-31

    Amyloid precursor protein (APP) is genetically linked to Alzheimer's disease. APP is a type I membrane protein, and its oligomeric structure is potentially important because this property may play a role in its function or affect the processing of the precursor by the secretases to generate amyloid {beta}-peptide. Several independent studies have shown that APP can form dimers in the cell, but how it dimerizes remains controversial. At least three regions of the precursor, including a centrally located and conserved domain called E2, have been proposed to contribute to dimerization. Here we report two new crystal structures of E2, one from APP and the other from APLP1, a mammalian APP homologue. Comparison with an earlier APP structure, which was determined in a different space group, shows that the E2 domains share a conserved and antiparallel mode of dimerization. Biophysical measurements in solution show that heparin binding induces E2 dimerization. The 2.1 {angstrom} resolution electron density map also reveals phosphate ions that are bound to the protein surface. Mutational analysis shows that protein residues interacting with the phosphate ions are also involved in heparin binding. The locations of two of these residues, Arg-369 and His-433, at the dimeric interface suggest a mechanism for heparin-induced protein dimerization.

  6. Trans-dimerization of JAM-A regulates Rap2 and is mediated by a domain that is distinct from the cis-dimerization interface.

    Science.gov (United States)

    Monteiro, Ana C; Luissint, Anny-Claude; Sumagin, Ronen; Lai, Caroline; Vielmuth, Franziska; Wolf, Mattie F; Laur, Oskar; Reiss, Kerstin; Spindler, Volker; Stehle, Thilo; Dermody, Terence S; Nusrat, Asma; Parkos, Charles A

    2014-05-01

    Junctional adhesion molecule-A (JAM-A) is a tight junction-associated signaling protein that regulates epithelial cell proliferation, migration, and barrier function. JAM-A dimerization on a common cell surface (in cis) has been shown to regulate cell migration, and evidence suggests that JAM-A may form homodimers between cells (in trans). Indeed, transfection experiments revealed accumulation of JAM-A at sites between transfected cells, which was lost in cells expressing cis- or predicted trans-dimerization null mutants. Of importance, microspheres coated with JAM-A containing alanine substitutions to residues 43NNP45 (NNP-JAM-A) within the predicted trans-dimerization site did not aggregate. In contrast, beads coated with cis-null JAM-A demonstrated enhanced clustering similar to that observed with wild-type (WT) JAM-A. In addition, atomic force microscopy revealed decreased association forces in NNP-JAM-A compared with WT and cis-null JAM-A. Assessment of effects of JAM-A dimerization on cell signaling revealed that expression of trans- but not cis-null JAM-A mutants decreased Rap2 activity. Furthermore, confluent cells, which enable trans-dimerization, had enhanced Rap2 activity. Taken together, these results suggest that trans-dimerization of JAM-A occurs at a unique site and with different affinity compared with dimerization in cis. Trans-dimerization of JAM-A may thus act as a barrier-inducing molecular switch that is activated when cells become confluent.

  7. Solution structure of the dimeric cytoplasmic domain of syndecan-4

    DEFF Research Database (Denmark)

    Shin, J; Lee, W; Lee, D

    2001-01-01

    The syndecans, transmembrane proteoglycans which are involved in the organization of cytoskeleton and/or actin microfilaments, have important roles as cell surface receptors during cell-cell and/or cell-matrix interactions. Since previous studies indicate that the function of the syndecan-4...... between peptides at physiological pH. Commensurately, the NMR structures demonstrate that syndecan-4L is a compact intertwined dimer with a symmetric clamp shape in the central variable V region with a root-mean-square deviation between backbone atom coordinates of 0.95 A for residues Leu(186)-Ala(195...... in the center of the dimeric twist similar to our previously reported 4V structure. The overall topology of the central variable region within the 4L structure is very similar to that of 4V complexed with the phosphatidylinositol 4,5-bisphosphate; however, the intersubunit interaction mode is affected...

  8. GLYCOLALDEHYDE FORMATION VIA THE DIMERIZATION OF THE FORMYL RADICAL

    Energy Technology Data Exchange (ETDEWEB)

    Woods, Paul M.; Viti, Serena [Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT (United Kingdom); Slater, Ben; Raza, Zamaan; Brown, Wendy A.; Burke, Daren J., E-mail: p.woods@qub.ac.uk [Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ (United Kingdom)

    2013-11-10

    Glycolaldehyde, the simplest monosaccharide sugar, has recently been detected in low- and high-mass star-forming cores. Following our previous investigation into glycolaldehyde formation, we now consider a further mechanism for the formation of glycolaldehyde that involves the dimerization of the formyl radical, HCO. Quantum mechanical investigation of the HCO dimerization process upon an ice surface is predicted to be barrierless and therefore fast. In an astrophysical context, we show that this mechanism can be very efficient in star-forming cores. It is limited by the availability of the formyl radical, but models suggest that only very small amounts of CO are required to be converted to HCO to meet the observational constraints.

  9. Glycolaldehyde Formation via the Dimerization of the Formyl Radical

    Science.gov (United States)

    Woods, Paul M.; Slater, Ben; Raza, Zamaan; Viti, Serena; Brown, Wendy A.; Burke, Daren J.

    2013-11-01

    Glycolaldehyde, the simplest monosaccharide sugar, has recently been detected in low- and high-mass star-forming cores. Following our previous investigation into glycolaldehyde formation, we now consider a further mechanism for the formation of glycolaldehyde that involves the dimerization of the formyl radical, HCO. Quantum mechanical investigation of the HCO dimerization process upon an ice surface is predicted to be barrierless and therefore fast. In an astrophysical context, we show that this mechanism can be very efficient in star-forming cores. It is limited by the availability of the formyl radical, but models suggest that only very small amounts of CO are required to be converted to HCO to meet the observational constraints.

  10. Intramolecular hydrophobic interactions are critical mediators of STAT5 dimerization

    Science.gov (United States)

    Fahrenkamp, Dirk; Li, Jinyu; Ernst, Sabrina; Schmitz-van de Leur, Hildegard; Chatain, Nicolas; Küster, Andrea; Koschmieder, Steffen; Lüscher, Bernhard; Rossetti, Giulia; Müller-Newen, Gerhard

    2016-10-01

    STAT5 is an essential transcription factor in hematopoiesis, which is activated through tyrosine phosphorylation in response to cytokine stimulation. Constitutive activation of STAT5 is a hallmark of myeloid and lymphoblastic leukemia. Using homology modeling and molecular dynamics simulations, a model of the STAT5 phosphotyrosine-SH2 domain interface was generated providing first structural information on the activated STAT5 dimer including a sequence, for which no structural information is available for any of the STAT proteins. We identified a novel intramolecular interaction mediated through F706, adjacent to the phosphotyrosine motif, and a unique hydrophobic interface on the surface of the SH2 domain. Analysis of corresponding STAT5 mutants revealed that this interaction is dispensable for Epo receptor-mediated phosphorylation of STAT5 but essential for dimer formation and subsequent nuclear accumulation. Moreover, the herein presented model clarifies molecular mechanisms of recently discovered leukemic STAT5 mutants and will help to guide future drug development.

  11. 2.3-MW Medium-Voltage, Three-Level Wind Energy Inverter Applying a Unique Bus Structure and 4.5-kV Si/SiC Hybrid Isolated Power Modules: Preprint

    Energy Technology Data Exchange (ETDEWEB)

    Erdman, W.; Keller, J.; Grider, D.; VanBrunt, E.

    2014-11-01

    A high-efficiency, 2.3-MW, medium-voltage, three-level inverter utilizing 4.5-kV Si/SiC (silicon carbide) hybrid modules for wind energy applications is discussed. The inverter addresses recent trends in siting the inverter within the base of multimegawatt turbine towers. A simplified split, three-layer laminated bus structure that maintains low parasitic inductances is introduced along with a low-voltage, high-current test method for determining these inductances. Feed-thru bushings, edge fill methods, and other design features of the laminated bus structure provide voltage isolation that is consistent with the 10.4-kV module isolation levels. Inverter efficiency improvement is a result of the (essential) elimination of the reverse recovery charge present in 4.5-kV Si PIN diodes, which can produce a significant reduction in diode turn-off losses as well as insulated-gate bipolar transistor (IGBT) turn-on losses. The hybrid modules are supplied in industry-standard 140 mm x 130 mm and 190 mm x 130 mm packages to demonstrate direct module substitution into existing inverter designs. A focus on laminated bus/capacitor-bank/module subassembly level switching performance is presented.

  12. Coupling-of-length-scale approach for multiscale atomistic-continuum simulations: Atomistically-induced stress distributions in Si/Si_3N4 nanopixels

    Science.gov (United States)

    Lidorikis, Elefterios; Bachlechner, Martina E.; Kalia, Rajiv K.; Nakano, Aiichiro; Vashishta, Priya; Voyiadjis, George; Madhukar, Anupam

    2001-03-01

    A hybrid molecular-dynamics and finite-element simulation approach has been used to investigate stress distributions in Si(111) nanopixels covered with both crystalline and amorphous Si_3N4 thin films. Surfaces, lattice-mismatched interfaces, edges, and corners create stress fields on the order of 1 GPa inside the Si substrate with patterns that cannot be reproduced by a continuum approach alone. For these atomistically-induced inhomogeneouse stresses, the hybrid simulation approach provides an excellent agreement with the standard molecular dynamics, with considerably less computational costs.

  13. Theoretical Studies on Intermolecular Interactions of 4-Amino-5-nitro-1,2,3-triazole Dimers

    Institute of Scientific and Technical Information of China (English)

    LU Ya-Lin; GONG Xue-Dong; JU Xue-Hai; MA Xiu-Fang; XIAO He-Ming

    2006-01-01

    Seven optimized configurations and their electronic structures of 4-amino-5-nitro-1,2,3-triazole dimers on their potential energy surface have been obtained by using density functional theory (DFT) method at the B3LYP/6-311++G** level. The maximum intermolecular interaction energy is -35.42 kJ/mol via the basis set superposition error-correction (BSSE) and zero point energy-correction (ZPE). Charge transfers between the two subsystems are small. The vibration analysis of optimized configurations was performed, and the thermodynamic property changes from monomer to dimer have been obtained with the temperature ranging from 200 to 800 K on the basis of statistical thermodynamics. It is found that the hydrogen bonds contribute to the dimers dominantly, and the extent of intermolecular interaction is mainly determined by the hydrogen bonds' strength rather than their number. The dimerization processes of Ⅳ, Ⅴ and Ⅵ can occur spontaneously at 200 K.

  14. Dimerization of tetherin is not essential for its antiviral activity against Lassa and Marburg viruses.

    Directory of Open Access Journals (Sweden)

    Toshie Sakuma

    Full Text Available Tetherin (also known as BST2, CD317 or HM1.24 has recently been reported to inhibit a wide range of viruses. However, the antiviral mechanism of action of tetherin has not been determined. Both ends of the tetherin molecule are associated with the plasma membrane and it forms a homodimer. Therefore, a model in which progeny virions are retained on the cell surface by dimer formation between tetherin molecules on the viral envelope and plasma membrane has been proposed as the antiviral mechanism of action of this molecule. To investigate this possibility, we examined the correlation between dimerization and antiviral activity of tetherin in Lassa and Marburg virus-like particle production systems using tetherin mutants deficient in dimer formation. However, the tetherin mutant with complete loss of dimerization activity still showed apparent antiviral activity, indicating that dimerization of tetherin is not essential for its antiviral activity. This suggests that tetherin retains progeny virions on the cell surface by a mechanism other than dimerization.

  15. Pocked surface neutron detector

    Energy Technology Data Exchange (ETDEWEB)

    McGregor, Douglas (Whitmore Lake, MI); Klann, Raymond (Bolingbrook, IL)

    2003-04-08

    The detection efficiency, or sensitivity, of a neutron detector material such as of Si, SiC, amorphous Si, GaAs, or diamond is substantially increased by forming one or more cavities, or holes, in its surface. A neutron reactive material such as of elemental, or any compound of, .sup.10 B, .sup.6 Li, .sup.6 LiF, U, or Gd is deposited on the surface of the detector material so as to be disposed within the cavities therein. The portions of the neutron reactive material extending into the detector material substantially increase the probability of an energetic neutron reaction product in the form of a charged particle being directed into and detected by the neutron detector material.

  16. Quantum Yields of Decomposition and Homo-Dimerization of Solid L-Alanine Induced by 7.2 eV Vacuum Ultraviolet Light Irradiation: An Estimate of the Half-Life of L-Alanine on the Surface of Space Objects

    Science.gov (United States)

    Izumi, Yudai; Nakagawa, Kazumichi

    2011-08-01

    One of the leading hypotheses regarding the origin of prebiotic molecules on primitive Earth is that they formed from inorganic molecules in extraterrestrial environments and were delivered by meteorites, space dust and comets. To evaluate the availability of extraterrestrial amino acids, it is necessary to examine their decomposition and oligomerization rates as induced by extraterrestrial energy sources, such as vacuum ultraviolet (VUV) and X-ray photons and high energy particles. This paper reports the quantum yields of decomposition ((8.2 ± 0.7) × 10-2 photon-1) and homo-dimerization ((1.2 ± 0.3) × 10-3 photon-1) and decomposition of the dimer (0.24 ± 0.06 photon-1) of solid l-alanine (Ala) induced by VUV light with an energy of 7.2 eV. Using these quantum yields, the half-life of l-Ala on the surface of a space object in the present earth orbit was estimated to be about 52 days, even when only photons with an energy of 7.2 eV emitted from the present Sun were considered. The actual half-life of solid l-Ala on the surface of a space object orbit around the present day Earth would certainly be much shorter than our estimate, because of the added effect of photons and particles of other energies. Thus, we propose that l-Ala needs to be shielded from solar VUV in protected environments, such as the interior of a meteorite, within a time scale of days after synthesis to ensure its arrival on the primitive Earth.

  17. Vibrations of the carbon dioxide dimer

    Science.gov (United States)

    Chen, Hua; Light, J. C.

    2000-03-01

    Fully coupled four-dimensional quantum-mechanical calculations are presented for intermolecular vibrational states of rigid carbon dioxide dimer for J=0. The Hamiltonian operator is given in collision coordinates. The Hamiltonian matrix elements are evaluated using symmetrized products of spherical harmonics for angles and a potential optimized discrete variable representation (PO-DVR) for the intermolecular distance. The lowest ten or so states of each symmetry are reported for the potential energy surface (PES) given by Bukowski et al. [J. Chem. Phys. 110, 3785 (1999)]. Due to symmetries, there is no interconversion tunneling splitting for the ground state. Our calculations show that there is no tunneling shift of the ground state within our computation precision (0.01 cm-1). Analysis of the wave functions shows that only the ground states of each symmetry are nearly harmonic. The van der Waals frequencies and symmetry adapted force constants are found and compared to available experimental values. Strong coupling between the stretching coordinates and the bending coordinates are found for vibrationally excited states. The interconversion tunneling shifts are discussed for the vibrationally excited states.

  18. Electrostatic effects of Au nanoparticles on near-infrared photoluminescence from Si/SiGe due to nanoscale metal/semiconductor contact.

    Science.gov (United States)

    Yin, Yefei; Wang, Ze; Wang, Shuguang; Bai, Yujie; Jiang, Zuimin; Zhong, Zhenyang

    2017-02-21

    The photoluminescence from the Si and the SiGe is comprehensively modified by the Au NPs under the excitation without the surface plasmon resonance. Moreover, it sensitively depends on the size of the Au NPs, the excitation power and the thickness of Si between the Au NPs and the SiGe. A model is proposed in terms of the electrostatic effects of the naturally charged Au NPs due to the electron transferring through the nanoscale metal/semiconductor Schottky junction without an external bias and an external injection of carriers. It well accounts for all those unique PL features. It also reveals that Au NPs can substantially modify the energy band structures, the distribution and the transition of carriers in the nanoscale region below the Au NPs. Our results demonstrate that the Au NPs on semiconductor can efficiently modulate the light-matter interaction from the fundamental aspect of the matter as well as the light.

  19. Design and simulation of a smart optically controlled high-power switch based on a Si/SiC hybrid device structure

    Science.gov (United States)

    Bhadri, Prashant; Sukumaran, Deepti; Dasgupta, Samhita; Beyette, Fred R., Jr.

    2001-11-01

    In avionic systems, data integrity and high data rates are necessary for stable flight control. Unfortunately, conventional electronic control systems are susceptible to electromagnetic interference (EMI) that can reduce the clarity of flight control signals. Fly-by-Light systems that use optical signals to actuate the flight control surfaces of an aircraft have been suggested as a solution to the EMI problem in avionic systems. Fly-by-Light in avionic systems reduces electromagnetic interference hence improving the clarity of the control signals. A hybrid approach combining a silicon photoreceiver module with a SiC power transistor is proposed. The resulting device uses a 5 mW optical control signal to produce a 150 A current suitable for driving an electric motor.

  20. Quantitative analysis of cyclic dimer fatty acid content in the dimerization product by proton NMR spectroscopy.

    Science.gov (United States)

    Park, Kyun Joo; Kim, Minyoung; Seok, Seunghwan; Kim, Young-Wun; Kim, Do Hyun

    2015-01-01

    In this work, (1)H NMR is utilized for the quantitative analysis of a specific cyclic dimer fatty acid in a dimer acid mixture using the pseudo-standard material of mesitylene on the basis of its structural similarity. Mesitylene and cyclic dimer acid levels were determined using the signal of the proton on the cyclic ring (δ=6.8) referenced to the signal of maleic acid (δ=6.2). The content of the cyclic dimer fatty acid was successfully determined through the standard curve of mesitylene and the reported equation. Using the linearity of the mesitylene curve, the cyclic dimer fatty acid in the oil mixture was quantified. The results suggest that the proposed method can be used to quantify cyclic compounds in mixtures to optimize the dimerization process.

  1. Formation of cystine slipknots in dimeric proteins.

    Directory of Open Access Journals (Sweden)

    Mateusz Sikora

    Full Text Available We consider mechanical stability of dimeric and monomeric proteins with the cystine knot motif. A structure based dynamical model is used to demonstrate that all dimeric and some monomeric proteins of this kind should have considerable resistance to stretching that is significantly larger than that of titin. The mechanisms of the large mechanostability are elucidated. In most cases, it originates from the induced formation of one or two cystine slipknots. Since there are four termini in a dimer, there are several ways of selecting two of them to pull by. We show that in the cystine knot systems, there is strong anisotropy in mechanostability and force patterns related to the selection. We show that the thermodynamic stability of the dimers is enhanced compared to the constituting monomers whereas machanostability is either lower or higher.

  2. A New Dimeric Phthalide from Angelica sinensis

    Institute of Scientific and Technical Information of China (English)

    Ling YI; Ping LI; Zhi Ming BI

    2006-01-01

    A new dimeric phthalide named Z, Z'-3.3'a, 7.7'a-diligustilide was isolated from the roots of Angelica sinensis. Its structure was determined using spectroscopic methods and X-ray crystallographic diffraction analysis.

  3. Designing Stable Antiparallel Coiled Coil Dimers

    Institute of Scientific and Technical Information of China (English)

    曾宪纲; 周海梦

    2001-01-01

    The history of antiparallel coiled coil dimer design is briefly reviewed and the main principles governing the successful designs are explained. They include analysis of the inter-subunit electrostatic repulsion for determining partners for dimerization and of the buried polar interaction for determining the relative orientation of the partners. A theory is proposed to explain the lack of antiparallel coiled coil homodimers in nature.

  4. Formation of Cystine Slipknots in Dimeric Proteins

    OpenAIRE

    Mateusz Sikora; Marek Cieplak

    2013-01-01

    We consider mechanical stability of dimeric and monomeric proteins with the cystine knot motif. A structure based dynamical model is used to demonstrate that all dimeric and some monomeric proteins of this kind should have considerable resistance to stretching that is significantly larger than that of titin. The mechanisms of the large mechanostability are elucidated. In most cases, it originates from the induced formation of one or two cystine slipknots. Since there are four termini in a dim...

  5. Role of Rydberg states in the photostability of heterocyclic dimers: the case of pyrazole dimer.

    Science.gov (United States)

    Zilberg, Shmuel; Haas, Yehuda

    2012-11-26

    A new route for the nonradiative decay of photoexcited, H-bonded, nitrogen-containing, heterocyclic dimers is offered and exemplified by a study of the pyrazole dimer. In some of these systems the N(3s) Rydberg state is the lowest excited singlet state. This state is formed by direct light absorption or by nonradiative transition from the allowed ππ* state. An isomer of this Rydberg state is formed by H atom transfer to the other component of the dimer. The newly formed H-bonded radical pair is composed of two radicals (a H-adduct of pyrazole, a heterocyclic analogue of the NH(4) radical) and the pyrazolium π-radical. It is calculated to have a shallow local minimum and is the lowest point on the PES of the H-pyrazole/pyrazolium radical pair. This species can cross back to the ground state of the original dimer through a relatively small energy gap and compete with the H-atom loss channel, known for the monomer. In both Rydberg dimers, an electron occupies a Rydberg orbital centered mostly on one of the two components of the dimer. This Rydberg Center Shift (RCS) mechanism, proposed earlier (Zilberg, S.; Kahan, A.; Haas, Y. Phys. Chem. Chem. Phys. 2012, 14, 8836), leads to deactivation of the electronically excited dimer while keeping it intact. It, thus, may explain the high photostability of the pyrazole dimer as well as other heterocyclic dimers.

  6. Dynamic interplay between adhesive and lateral E-cadherin dimers

    DEFF Research Database (Denmark)

    Klingelhöfer, Jörg; Laur, Oscar Y; Troyanovsky, Regina B;

    2002-01-01

    M. The disappearance of adhesive dimers was counterbalanced by an increase in Trp156-dependent lateral dimers. Increasing the calcium concentration to a normal level rapidly restored the original balance between adhesive and lateral dimers. We also present evidence that E-cadherin dimers in vivo have a short lifetime...

  7. A DFT study of substituent effects in corannulene dimers.

    Science.gov (United States)

    Josa, Daniela; Rodríguez Otero, Jesús; Cabaleiro Lago, Enrique M

    2011-12-21

    Corannulene dimers made up of corannulene monomers with different curvature and substituents were studied using M06-2X, B97D and ωB97XD functionals and 6-31+G* basis set. Corannulene molecules were substituted with five alternating Br, Cl, CH(3), C(2)H or CN units. Geometric results showed that substituents gave rise to small changes in the curvature of corannulene bowls. So, there was not a clear relationship between the curvature of bowls and the changes on interaction energy generated by addition of substituents in the bowl. Electron withdrawing substituents gave rise to a more positive molecular electrostatic potential (MEP) of the bowl, which was able to get a strong interaction with the negative MEP at the surface of a fullerene. Substitution with CN caused the largest effect, giving rise to the most positive MEP and to a large interaction energy of -24.64 kcal mol(-1), at the ωB97XD/6-31+G* level. Dispersive effects must be taken into account to explain the catching ability of the different substituted corannulenes. For unsubstituted dimers, calculations with DFT-D methods employing ωB97XD and B97D functionals led to similar results to those previously reported at the SCS-MP2/cc-pVTZ level for corannulene dimers (A. Sygula and S. Saebø, Int. J. Quant. Chem., 2009, 109, 65). In particular, the ωB97XD functional led to a difference of only 0.35 kcal mol(-1), regarding MP2 interaction energy for corannulene dimers. On the other hand, the M06-2X functional showed a general considerable underestimation of interaction energies. This functional worked quite well to study trends, but not to obtain absolute interaction energies.

  8. Microwave Measurements of the Tropolone-Formic Acid Doubly Hydrogen Bonded DIMER*

    Science.gov (United States)

    Pejlovas, Aaron M.; Serrato, Agapito, III; Lin, Wei; Kukolich, Stephen G.

    2016-06-01

    The microwave spectrum was measured for the tropolone-formic acid doubly hydrogen bonded dimer using a pulsed-beam Fourier transform microwave spectrometer in order to search for the concerted double proton tunneling motion. The tunneling motion was expected for the dimer, as the transition state of this motion exhibits C_2_V symmetry, which has been thought to be a requirement to observe the concerted double proton tunneling. The tunneling motion was not observed for this dimer, as the transitions measured did not show observable splittings into doublets. The barrier height calculated of the dimer using B3LYP/aug-cc-pVTZ was about 15000 cm^-^1, significantly larger than the value determined for the propiolic acid-formic acid dimer (3800 cm^-^1),^a which showed the tunneling motion. The estimated separation of the minima in the potential energy surface is estimated to be very similar to that of propiolic acid-formic acid (about 0.8 Å),^a so the large barrier height may be why the tunneling process was not observed. ^aDaly, A. M.; Bunker, P. R.; Kukolich, S. G. Communications: Evidence for Proton Tunneling from the Microwave Spectrum of the Formic Acid-Propiolic Acid Dimer. J. Chem. Phys. 132, 2010, 201101/1. *Supported by the NSF CHE-1057796

  9. 甘氨酸二聚体在银团簇表面吸附的结构和表面增强拉曼光谱%Structure and surface-enhanced Raman spectra of glycine dimer adsorbed on surface of silver clusters

    Institute of Scientific and Technical Information of China (English)

    李小军

    2016-01-01

    Using the B3LYP/6 -31++G** level of DFT theory, we have studied the structures , electronic properties and Raman spectra of glycine dimer and its compounds .The calculated results show that the strong binding position mainly happens at O -Ag bond for Gly2-Ag2 , leading the structure to be stable .The analysis of HOMO-LUMO gap also indicates that the Ag 2 cluster affects the electronic properties of Gly 2 , and rearranges the electronic structure.We compared the Raman spectra of Gly 2 and Gly2-Ag2 , and assigned main vibrational contributions for each peak , obviously some peaks appear more red -shifted wavelength.In addition, the Ag2 cluster enhances the Raman intensities of some vibrations because of the inducement of silver metal .These re-sults will provide significantly theoretical reference for explaining some experiments and mechanism of surface -enhanced Raman scattering .%利用密度泛函理论DFT-B3LYP方法和6-31++G**基组优化了甘氨酸二聚体( Gly2)的结构及其银复合物,并对它们的电子性质和拉曼振动光谱进行了理论研究。计算结果表明,复合物Gly2-Ag2中的O-Ag键表现了较强的吸附键位,致使结构上更为稳定。通过计算的HOMO-LUMO能隙研究也发现,银金属团簇影响了Gly2的电子特性,使得电子结构发生重排。我们对Gly2及其复合物的拉曼光谱特性进行了比较,并对主要振动模式进行了归属,其中一些特征峰位置发生了明显红移;由于银金属表面的诱导,致使复合物中某些特征拉曼峰被增强。这些研究对解释一些实验现象和SERS增强机理提供了理论参考。

  10. Substrate-Induced Dimerization of Engineered Monomeric Variants of Triosephosphate Isomerase from Trichomonas vaginalis.

    Directory of Open Access Journals (Sweden)

    Samuel Lara-Gonzalez

    Full Text Available The dimeric nature of triosephosphate isomerases (TIMs is maintained by an extensive surface area interface of more than 1600 Å2. TIMs from Trichomonas vaginalis (TvTIM are held in their dimeric state by two mechanisms: a ball and socket interaction of residue 45 of one subunit that fits into the hydrophobic pocket of the complementary subunit and by swapping of loop 3 between subunits. TvTIMs differ from other TIMs in their unfolding energetics. In TvTIMs the energy necessary to unfold a monomer is greater than the energy necessary to dissociate the dimer. Herein we found that the character of residue I45 controls the dimer-monomer equilibrium in TvTIMs. Unfolding experiments employing monomeric and dimeric mutants led us to conclude that dimeric TvTIMs unfold following a four state model denaturation process whereas monomeric TvTIMs follow a three state model. In contrast to other monomeric TIMs, monomeric variants of TvTIM1 are stable and unexpectedly one of them (I45A is only 29-fold less active than wild-type TvTIM1. The high enzymatic activity of monomeric TvTIMs contrast with the marginal catalytic activity of diverse monomeric TIMs variants. The stability of the monomeric variants of TvTIM1 and the use of cross-linking and analytical ultracentrifugation experiments permit us to understand the differences between the catalytic activities of TvTIMs and other marginally active monomeric TIMs. As TvTIMs do not unfold upon dimer dissociation, herein we found that the high enzymatic activity of monomeric TvTIM variants is explained by the formation of catalytic dimeric competent species assisted by substrate binding.

  11. Novel covalently linked insulin dimer engineered to investigate the function of insulin dimerization

    DEFF Research Database (Denmark)

    Vinther, Tine N.; Norrman, Mathias; Strauss, Holger M.

    2012-01-01

    An ingenious system evolved to facilitate insulin binding to the insulin receptor as a monomer and at the same time ensure sufficient stability of insulin during storage. Insulin dimer is the cornerstone of this system. Insulin dimer is relatively weak, which ensures dissociation into monomers...

  12. Calix[4]arene supported clusters: a dimer of [Mn(III)Mn(II)] dimers

    DEFF Research Database (Denmark)

    Taylor, Stephanie M; McIntosh, Ruaraidh D; Beavers, Christine M;

    2011-01-01

    Phosphinate ligands allow for the transformation of a calix[4]arene supported [Mn(III)(2)Mn(II)(2)] tetramer cluster motif into an unusual [Mn(III)Mn(II)](2) dimer of dimers; the clusters self-assemble in the crystal to form bi-layer arrays reminiscent of the typical packing of calixarene solvates....

  13. Novel covalently linked insulin dimer engineered to investigate the function of insulin dimerization.

    Directory of Open Access Journals (Sweden)

    Tine N Vinther

    Full Text Available An ingenious system evolved to facilitate insulin binding to the insulin receptor as a monomer and at the same time ensure sufficient stability of insulin during storage. Insulin dimer is the cornerstone of this system. Insulin dimer is relatively weak, which ensures dissociation into monomers in the circulation, and it is stabilized by hexamer formation in the presence of zinc ions during storage in the pancreatic β-cell. Due to the transient nature of insulin dimer, direct investigation of this important form is inherently difficult. To address the relationship between insulin oligomerization and insulin stability and function, we engineered a covalently linked insulin dimer in which two monomers were linked by a disulfide bond. The structure of this covalent dimer was identical to the self-association dimer of human insulin. Importantly, this covalent dimer was capable of further oligomerization to form the structural equivalent of the classical hexamer. The covalently linked dimer neither bound to the insulin receptor, nor induced a metabolic response in vitro. However, it was extremely thermodynamically stable and did not form amyloid fibrils when subjected to mechanical stress, underlining the importance of oligomerization for insulin stability.

  14. Moessbauer-spectroscopic study of structure and magnetism of the exchange-coupled layer systems Fe/FeSn{sub 2}, and Fe/FeSi/Si and the ion-implanted diluted magnetic semiconductor SiC(Fe); Moessbauerspektroskopische Untersuchung von Struktur und Magnetismus der austauschgekoppelten Schichtsysteme Fe/FeSn{sub 2} und Fe/FeSi/Si und des ionenimplantierten verduennten magnetischen Halbleiters SiC(Fe)

    Energy Technology Data Exchange (ETDEWEB)

    Stromberg, Frank

    2009-07-07

    In line with this work the structural and magnetic properties of the exchange coupled layered systems Fe/FeSn{sub 2} and Fe/FeSi/Si and of the Fe ion implanted diluted magnetic semiconductor (DMS) SiC(Fe) were investigated. The main measuring method was the isotope selective {sup 57}Fe conversion electron Moessbauer spectroscopy (CEMS), mostly in connection with the {sup 57}Fe tracer layer technique, in a temperature range from 4.2 K to 340 K. Further measurement techniques were X-ray diffraction (XRD), electron diffraction (LEED, RHEED), SQUID magnetometry and FMR (Ferromagnetic Resonance). In the first part of this work the properties of thin AF FeSn{sub 2}(001) films and of the exchange-bias system Fe/FeSn{sub 2}(001) on InSb(001) were investigated. With the application of {sup 57}Fe-tracer layers and CEMS both the Fe-spin structure and the temperature dependence of the magnetic hyperfine field (B{sub hf}) of FeSn{sub 2} could be examined. The evaporation of Fe films on the FeSn{sub 2} films produced in the latter ones a high perpendicular spin component at the Fe/FeSn{sub 2} interface. In some distance from the interface the Fe spins rotate back into the sample plane. Furthermore {sup 57}Fe-CEMS provided a correlation between the absolute value of the exchange field vertical stroke He vertical stroke and the amount of magnetic defects within the FeSn{sub 2}. Temperature dependent CEMS-measurements yielded informations about the spin dynamics within the AF. The transition temperatures T{sub B}{sup *}, which were interpreted as superparamagnetic blocking temperatures, obtain higher values compared to the temperatures T{sub B} of the exchange-bias effect, obtained with magnetometry measurements. The second part of this work deals with the indirect exchange coupling within Fe/FeSi/Si/FeSi/Fe multilayers and FeSi diffusion barriers. The goal was to achieve Fe free Si interlayers. The CEMS results show that starting from a thickness of t{sub FeSi}=10-12 A of the

  15. Gold dimer nanoantenna with slanted gap for tunable LSPR and improved SERS

    KAUST Repository

    Kessentini, Sameh

    2014-02-13

    We focus on improving the surface-enhanced Raman scattering (SERS) of dimer nanoantenna by tailoring the shape of the coupled nanoantennas extremities from rounded to straight or slanted ones. A numerical model based on the discrete dipole approximation method-taking into account periodicity, adhesion layer, and roughness-is first validated by comparison with localized surface plasmon resonance (LSPR) and SERS experiments on round-edged dimer nanoantennas and then used to investigate the effect of the straight or slanted gap in the dimer antenna. Simulations show that both LSPR and SERS can be tuned by changing the gap slanting angle. The SERS enhancement factor can also be improved by 2 orders of magnitude compared to the one reached using a rounded gap. Therefore, the slanting angle can be used as a new control parameter in the design of SERS substrates to guarantee stronger field confinement and higher sensitivity, especially as its feasibility is demonstrated. © 2014 American Chemical Society.

  16. The dimer interface of the membrane type 1 matrix metalloproteinase hemopexin domain: crystal structure and biological functions.

    Science.gov (United States)

    Tochowicz, Anna; Goettig, Peter; Evans, Richard; Visse, Robert; Shitomi, Yasuyuki; Palmisano, Ralf; Ito, Noriko; Richter, Klaus; Maskos, Klaus; Franke, Daniel; Svergun, Dmitri; Nagase, Hideaki; Bode, Wolfram; Itoh, Yoshifumi

    2011-03-04

    Homodimerization is an essential step for membrane type 1 matrix metalloproteinase (MT1-MMP) to activate proMMP-2 and to degrade collagen on the cell surface. To uncover the molecular basis of the hemopexin (Hpx) domain-driven dimerization of MT1-MMP, a crystal structure of the Hpx domain was solved at 1.7 Å resolution. Two interactions were identified as potential biological dimer interfaces in the crystal structure, and mutagenesis studies revealed that the biological dimer possesses a symmetrical interaction where blades II and III of molecule A interact with blades III and II of molecule B. The mutations of amino acids involved in the interaction weakened the dimer interaction of Hpx domains in solution, and incorporation of these mutations into the full-length enzyme significantly inhibited dimer-dependent functions on the cell surface, including proMMP-2 activation, collagen degradation, and invasion into the three-dimensional collagen matrix, whereas dimer-independent functions, including gelatin film degradation and two-dimensional cell migration, were not affected. These results shed light on the structural basis of MT1-MMP dimerization that is crucial to promote cellular invasion.

  17. Copper dimer interactions on a thermomechanical superfluid {sup 4}He fountain

    Energy Technology Data Exchange (ETDEWEB)

    Popov, Evgeny; Eloranta, Jussi, E-mail: Jussi.Eloranta@csun.edu [Department of Chemistry and Biochemistry, California State University at Northridge, 18111 Nordhoff St., Northridge, California 91330 (United States)

    2015-05-28

    Laser induced fluorescence imaging and frequency domain excitation spectroscopy of the copper dimer (B{sup 1}Σ{sub g}{sup +}←X{sup 1}Σ{sub u}{sup +}) in thermomechanical helium fountain at 1.7 K are demonstrated. The dimers penetrate into the fountain provided that their average propagation velocity is ca. 15 m/s. This energy threshold is interpreted in terms of an imperfect fountain liquid-gas interface, which acts as a trap for low velocity dimers. Orsay-Trento density functional theory calculations for superfluid {sup 4}He are used to characterize the dynamics of the dimer solvation process into the fountain. The dimers first accelerate towards the fountain surface and once the surface layer is crossed, they penetrate into the liquid and further slow down to Landau critical velocity by creating a vortex ring. Theoretical lineshape calculations support the assignment of the experimentally observed bands to Cu{sub 2} solvated in the bulk liquid. The vibronic progressions are decomposed of a zero-phonon line and two types of phonon bands, which correlate with solvent cavity interface compression (t < 200 fs) and expansion (200 < t < 500 fs) driven by the electronic excitation. The presented experimental method allows to perform molecular spectroscopy in bulk superfluid helium where the temperature and pressure can be varied.

  18. Geometric Reid's recipe for dimer models

    CERN Document Server

    Bocklandt, Raf; Velez, Alexander Quintero

    2013-01-01

    Crepant resolutions of three-dimensional toric Gorenstein singularities are derived equivalent to noncommutative algebras arising from consistent dimer models. By choosing a special stability parameter and hence a distinguished crepant resolution $Y$, this derived equivalence generalises the Fourier-Mukai transform relating the $G$-Hilbert scheme and the skew group algebra $\\CC[x,y,z]\\ast G$ for a finite abelian subgroup of $\\SL(3,\\CC)$. We show that this equivalence sends the vertex simples to pure sheaves, except for the zero vertex which is mapped to the dualising complex of the compact exceptional locus. This generalises results of Cautis-Logvinenko and Cautis-Craw-Logvinenko to the dimer setting, though our approach is different in each case. We also describe some of these pure sheaves explicitly and compute the support of the remainder, providing a dimer model analogue of results from Logvinenko.

  19. Partition-DFT on the Water Dimer

    CERN Document Server

    Gómez, Sara; Restrepo, Albeiro; Wasserman, Adam

    2016-01-01

    As is well known, the ground-state symmetry group of the water dimer switches from its equilibrium $C_{s}$-character to $C_{2h}$-character as the distance between the two oxygen atoms of the dimer decreases below $R_{\\rm O-O}\\sim 2.5$ \\AA{}. For a range of $R_{\\rm O-O}$ between 1 and 5 \\AA{}, and for both symmetries, we apply Partition Density Functional Theory (PDFT) to find the unique monomer densities that sum to the correct dimer densities while minimizing the sum of the monomer energies. We calculate the work involved in deforming the isolated monomer densities and find that it is slightly larger for the $C_s$ geometry for all $R_{\\rm O-O}$. We discuss how the PDFT densities and the corresponding partition potentials support the orbital-interaction picture of hydrogen-bond formation.

  20. Photoionization of helium dimers; Photoionisation von Heliumdimeren

    Energy Technology Data Exchange (ETDEWEB)

    Havermeier, Tilo

    2010-06-09

    The helium dimer is one of the most weakly bound systems in the universe. This makes it an interesting quantum mechanical object for investigation. These Van der Waals Clusters can be produced in an expansion of a cryogenic gas jet through a small nozzle into vacuum. In the present experiment we examine the interaction of He dimers with synchrotron radiation at an energy range from 64 to 78 eV. We observed different pathways leading to single ionization of both He atoms of the dimer compound. This two close standing ions begin now to dissociate in cause of their coulomb potential. All charged fragments were detected in coincidence with a COLTRIMS system. Especially Interatomic Coulombic Decay (ICD) and the two step process (TS1) were clearly identified. Furthermore a distribution of the internuclear distance was obtained from the measured Kinetic Energy Release (KER). (orig.)

  1. Kosterlitz Thouless Universality in Dimer Models

    CERN Document Server

    Chandrasekharan, S; Chandrasekharan, Shailesh; Strouthos, Costas G.

    2003-01-01

    Using the monomer-dimer representation of strongly coupled U(N) lattice gauge theories with staggered fermions, we study finite temperature chiral phase transitions in (2+1) dimensions. A new cluster algorithm allows us to compute monomer-monomer and dimer-dimer correlations at zero monomer density (chiral limit) accurately on large lattices. This makes it possible to show convincingly, for the first time, that these models undergo a finite temperature phase transition which belongs to the Kosterlitz-Thouless universality class. We find that this universality class is unaffected even in the large N limit. This shows that the mean field analysis often used in this limit breaks down in the critical region.

  2. A Novel Dimer of α-Tocopherol

    Directory of Open Access Journals (Sweden)

    Anjan Patel

    2008-01-01

    Full Text Available Decomposition of the complex 4, formed between the α-tocopherol ortho-quinone methide (2 and NMMO, by fast heating from −78∘C to 70∘C in inert solvents produces a novel α-tocopherol dimer with 6H,12H-dibenzo[b,f][1,5]dioxocine structure (5 which—in contrast to the well-known spiro-dimer of α-tocopherol (3—is symmetrical. This is the first example of a direct reaction of the highly transient zwitterionic, aromatic precursor 2a in the formation of the ortho-quinone methide 2.

  3. Synthesis of Methoxyethyl Nucleoside Dimer Phosphoramidates

    Energy Technology Data Exchange (ETDEWEB)

    Yu, Gi Weon; Kang, Yong Han [Hanyang University, Ansan (Korea, Republic of)

    2016-05-15

    Four types of methoxyethyl (MOE) nucleoside phosphoramidites, which are categorized as second-generation building blocks of antisense oligonucleotide drugs, were synthesized. Also, three types of MOE nucleoside dimer phosphoramidites were synthesized to increase the efficiency and oligomer purity in solid phase synthesis. The block-like dimer phosphoramidites can prevent or minimize the formation of the (N-1) mer impurity, thereby affording the fabrication of pure oligonucleotides and reducing the synthesis time by performing coupling reactions in the order of 2 + 2 + 2.

  4. Photon Propagation through Linearly Active Dimers

    Directory of Open Access Journals (Sweden)

    José Delfino Huerta Morales

    2017-06-01

    Full Text Available We provide an analytic propagator for non-Hermitian dimers showing linear gain or losses in the quantum regime. In particular, we focus on experimentally feasible realizations of the PT -symmetric dimer and provide their mean photon number and second order two-point correlation. We study the propagation of vacuum, single photon spatially-separable, and two-photon spatially-entangled states. We show that each configuration produces a particular signature that might signal their possible uses as photon switches, semi-classical intensity-tunable sources, or spatially entangled sources to mention a few possible applications.

  5. Refined conformal spectra in the dimer model

    CERN Document Server

    Rasmussen, Jorgen

    2012-01-01

    Working with Lieb's transfer matrix for the dimer model, we point out that the full set of dimer configurations may be partitioned into disjoint subsets (sectors) closed under the action of the transfer matrix. These sectors are labelled by an integer or half-integer quantum number we call the variation index. In the continuum scaling limit, each sector gives rise to a representation of the Virasoro algebra. We determine the corresponding conformal partition functions and their finitizations, and observe an intriguing link to the Ramond and Neveu-Schwarz sectors of the critical dense polymer model as described by a conformal field theory with central charge c=-2.

  6. Probing the roles of the two different dimers mediated by the receiver domain of the response regulator PhoB.

    Science.gov (United States)

    Mack, Timothy R; Gao, Rong; Stock, Ann M

    2009-06-05

    Structural analysis of the Escherichia coli response regulator transcription factor PhoB indicates that the protein dimerizes in two different orientations that are both mediated by the receiver domain. The two dimers exhibit 2-fold rotational symmetry: one involves the alpha 4-beta 5-alpha 5 surface and the other involves the alpha1/alpha 5 surface. The alpha 4-beta 5-alpha 5 dimer is observed when the protein is crystallized in the presence of the phosphoryl analog BeF(3)(-), while the alpha1/alpha 5 dimer is observed in its absence. From these studies, a model of the inactive and active states of PhoB has been proposed that involves the formation of two distinct dimers. In order to gain further insight into the roles of these dimers, we have engineered a series of mutations in PhoB intended to perturb each of them selectively. Our results indicate that perturbation of the alpha 4-beta 5-alpha 5 surface disrupts phosphorylation-dependent dimerization and DNA binding as well as PhoB-mediated transcriptional activation of phoA, while perturbations to the alpha1/alpha 5 surface do not. Furthermore, experiments with a GCN4 leucine zipper/PhoB chimera protein indicate that PhoB is activated through an intermolecular mechanism. Together, these results support a model of activation of PhoB in which phosphorylation promotes dimerization via the alpha 4-beta 5-alpha 5 face, which enhances DNA binding and thus the ability of PhoB to regulate transcription.

  7. A p-quinodimethane-bridged porphyrin dimer.

    Science.gov (United States)

    Zeng, Wangdong; Ishida, Masatoshi; Lee, Sangsu; Sung, Young Mo; Zeng, Zebing; Ni, Yong; Chi, Chunyan; Kim, Dongho; Wu, Jishan

    2013-12-01

    A p-quinodimethane (p-QDM)-bridged porphyrin dimer 1 has been prepared for the first time. An unexpected Michael addition reaction took place when we attempted to synthesize compound 1 by reaction of the cross-conjugated keto-linked porphyrin dimers 8a and 8b with alkynyl/aryl Grignard reagents. Alternatively, compound 1 could be successfully prepared by intramolecular Friedel-Crafts alkylation of the diol-linked porphyrin dimer 14 with concomitant oxidation in air. Compound 1 shows intense one-photon absorption (OPA, λ(max)=955 nm, ε=45400 M(-1) cm(-1)) and a large two-photon absorption (TPA) cross-section (σ((2))(max)=2080 GM at 1800 nm) in the near-infrared (NIR) region due to its extended π-conjugation and quinoidal character. It also exhibits a short singlet excited-state lifetime of 25 ps. The cyclic voltammogram of 1 displays multiple redox waves with a small electrochemical energy gap of 0.86 eV. The ground-state geometry, electronic structure, and optical properties of 1 have been further studied by density functional theory (DFT) calculations and compared with those of the keto-linked dimer 8b. This research has revealed that incorporation of a p-QDM unit into the porphyrin framework had a significant impact on its optical and electronic properties, leading to a novel NIR OPA and TPA chromophore.

  8. Geometric Reid's recipe for dimer models

    NARCIS (Netherlands)

    Bocklandt, R.; Craw, A.; Quintero Vélez, A.

    2015-01-01

    Crepant resolutions of three-dimensional toric Gorenstein singularities are derived equivalent to noncommutative algebras arising from consistent dimer models. By choosing a special stability parameter and hence a distinguished crepant resolution Y, this derived equivalence generalises the Fourier-M

  9. The Diamagnetic Susceptibility of the Tubulin Dimer

    Directory of Open Access Journals (Sweden)

    Wim Bras

    2014-01-01

    Full Text Available An approximate value of the diamagnetic anisotropy of the tubulin dimer, Δχdimer, has been determined assuming axial symmetry and that only the α-helices and β-sheets contribute to the anisotropy. Two approaches have been utilized: (a using the value for the Δχα for an α-helical peptide bond given by Pauling (1979 and (b using the previously determined anisotropy of fibrinogen as a calibration standard. The Δχdimer≈4×10-27 JT−2 obtained from these measurements are similar to within 20%. Although Cotton-Mouton measurements alone cannot be used to estimate Δχ directly, the value we measured, CMdimer=1.41±0.03×10-8 T−2cm2mg−1, is consistent with the above estimate for Δχdimer. The method utilized for the determination of the tubulin dimer diamagnetic susceptibility is applicable to other proteins and macromolecular assemblies as well.

  10. A new lignan dimer from Mallotus philippensis.

    Science.gov (United States)

    Mai, Nguyen Thi; Cuong, Nguyen Xuan; Thao, Nguyen Phuong; Nam, Nguyen Hoai; Khoi, Nguyen Huu; Minh, Chau Van; Heyden, Yvan Vander; Thuan, Ngo Thi; Tuyen, Nguyen Van; Quetin-Leclercq, Joëlle; Kiem, Phan Van

    2010-03-01

    A new lignan dimer, bilariciresinol (1), was isolated from the leaves of Mallotus philippensis, along with platanoside (2), isovitexin (3), dihydromyricetin (4), bergenin (5), 4-O-galloylbergenin (6), and pachysandiol A (7). Their structures were elucidated by spectroscopic experiments including 1D and 2D NMR and FTICR-MS.

  11. Biological consequences of cyclobutane pyrimidine dimers

    NARCIS (Netherlands)

    Vink, A.A.; Roza, L.

    2001-01-01

    In the skin many molecules may absorb ultraviolet (UV) radiation upon exposure. In particular, cellular DNA strongly absorbs shorter wavelength solar UV radiation, resulting in various types of DNA damage. Among the DNA photoproducts produced the cyclobutane pyrimidine dimers (CPDs) are predominant.

  12. Synthesis of novel 15-membered macrolide dimers

    Institute of Scientific and Technical Information of China (English)

    Shu Tao Ma; Rui Xin Ma; Rui Qing Xian; Bo Jiao

    2009-01-01

    A series of novel dimers of 15-memhered macrolides was synthesized and evaluated. The directs exhibited excellent activity against erythromycin-susceptible S. pneumonia, but did not show any improved activity against erythromycin-resistant S. pneumoniae encoded by erm gene.

  13. Amplitude enhancement by a gold dimer

    Science.gov (United States)

    Hong, Xin; Wang, Jingxin; Jin, Zheng

    2016-10-01

    The unique optical properties such as brightness, non-bleaching, good bio-compatibility make gold particles ideal label candidates for molecular probes. Due to the strongly enhanced field, aggregation of gold nanoparticles finds themselves plenty of applications in bio-imaging. But limited by its small cross-section associated with nanometer sized particle, it is a big challenge to employ it in a single molecular detection. The field enhancement results from the effect of plasmonic coupling between two closely attached gold nanoparticle under the right excitation condition. With the aim to apply the gold dimer probe to find the molecules in our recently established optical detection method, we compared of the amplitude enhancement by the dimer relative to a single particle. The amplitude distribution under a highly focused illumination objective was calculated, whose results suggest that at the optimized excitation condition, the local field can be enhanced 190 fold. In consequence, experimental detection was carried out. Gold dimers were linked together by the hybridization of two single chain DNAs. Dimer and single particle probes were mixed together in one detection. Overwhelming contrast between these two kinds of probes were clearly exhibited in the experimental detection image. This method can provide a way to a high specific detection in early diagnosis.

  14. Dimerization of HCN in the gas phase: A theoretical mechanistic study

    Science.gov (United States)

    Yim, Min Kyoung; Choe, Joong Chul

    2012-06-01

    Potential energy surfaces for the formation of covalently bound HCN dimers from two molecules of HCN or HNC were determined from CBS-QB3/APNO calculations. Several novel pathways, with and without the aid of protons, were found for the formation of iminoacetonitrile (HNdbnd CHCN), an intermediate in adenine synthesis from HCN by oligomerization. Covalent C-C or C-N bonds between the two monomers were formed after rearrangement of bimolecular complex intermediates. Energetic and kinetic analyses suggest that the proton-catalyzed dimerizations substantially lower reaction barriers but cannot occur efficiently under interstellar conditions.

  15. Unravelling Thiol’s Role in Directing Asymmetric Growth of Au Nanorod–Au Nanoparticle Dimers

    KAUST Repository

    Huang, Jianfeng

    2015-12-15

    Asymmetric nanocrystals have practical significance in nanotechnologies but present fundamental synthetic challenges. Thiol ligands have proven effective in breaking the symmetric growth of metallic nanocrystals but their exact roles in the synthesis remain elusive. Here, we synthesized an unprecedented Au nanorod-Au nanoparticle (AuNR-AuNP) dimer structure with the assistance of a thiol ligand. On the basis of our experimental observations, we unraveled for the first time that the thiol could cause an inhomogeneous distribution of surface strains on the seed crystals as well as a modulated reduction rate of metal precursors, which jointly induced the asymmetric growth of monometallic dimers. © 2015 American Chemical Society.

  16. Ligand-induced type II interleukin-4 receptor dimers are sustained by rapid re-association within plasma membrane microcompartments

    Science.gov (United States)

    Richter, David; Moraga, Ignacio; Winkelmann, Hauke; Birkholz, Oliver; Wilmes, Stephan; Schulte, Markos; Kraich, Michael; Kenneweg, Hella; Beutel, Oliver; Selenschik, Philipp; Paterok, Dirk; Gavutis, Martynas; Schmidt, Thomas; Garcia, K. Christopher; Müller, Thomas D.; Piehler, Jacob

    2017-07-01

    The spatiotemporal organization of cytokine receptors in the plasma membrane is still debated with models ranging from ligand-independent receptor pre-dimerization to ligand-induced receptor dimerization occurring only after receptor uptake into endosomes. Here, we explore the molecular and cellular determinants governing the assembly of the type II interleukin-4 receptor, taking advantage of various agonists binding the receptor subunits with different affinities and rate constants. Quantitative kinetic studies using artificial membranes confirm that receptor dimerization is governed by the two-dimensional ligand-receptor interactions and identify a critical role of the transmembrane domain in receptor dimerization. Single molecule localization microscopy at physiological cell surface expression levels, however, reveals efficient ligand-induced receptor dimerization by all ligands, largely independent of receptor binding affinities, in line with the similar STAT6 activation potencies observed for all IL-4 variants. Detailed spatiotemporal analyses suggest that kinetic trapping of receptor dimers in actin-dependent microcompartments sustains robust receptor dimerization and signalling.

  17. Universal bosonic tetramers of dimer-atom-atom structure

    OpenAIRE

    Deltuva, A.

    2012-01-01

    Unstable four-boson states having an approximate dimer-atom-atom structure are studied using momentum-space integral equations for the four-particle transition operators. For a given Efimov trimer the universal properties of the lowest associated tetramer are determined. The impact of this tetramer on the atom-trimer and dimer-dimer collisions is analyzed. The reliability of the three-body dimer-atom-atom model is studied.

  18. Pharmaceutical aspects of the recombinant human serum albumin dimer: structural characteristics, biological properties, and medical applications.

    Science.gov (United States)

    Taguchi, Kazuaki; Chuang, Victor Tuan Giam; Maruyama, Toru; Otagiri, Masaki

    2012-09-01

    Human serum albumin is the most abundant protein in the blood. It is clinically used in the treatment of severe hypoalbuminemia and as a plasma expander. The use of albumins as a carrier for drugs is currently being developed, and some are now in the preclinical and clinical trial stages. The main technologies for utilizing an albumin as a drug carrier are protein fusion, polymerization and surface modification, and so on. Among these technologies, albumin dimerization has wide clinical applications as a plasma expander as well as a drug carrier. Despite the fact that many reports have appeared on drugs using an albumin dimer as a carrier, our knowledge of the characteristics of the albumin dimer itself is incomplete. In this review, we summarize the structural characteristics of recombinant albumin dimers produced by two methods, namely, chemical linkage with 1,6-bis(maleimido)hexane and genetically linked with an amino acid linker, and the physicochemical characteristics and biological properties of these preparations. Finally, the potential for pharmaceutical applications of albumin dimers in clinical situations is discussed.

  19. Viscosity and sedimentation behaviors of the magnetorheological suspensions with oleic acid/dimer acid as surfactants

    Science.gov (United States)

    Yang, Jianjian; Yan, Hua; Hu, Zhide; Ding, Ding

    2016-11-01

    This work deals with the role of polar interactions on the viscosity and sedimentation behaviors of magnetorheological suspensions with micro-sized magnetic particles dispersed in oil carriers. The oleic acid and dimer acid were employed to make an adjustment of the hydrophobicity of iron particles, in the interest of performing a comparative evaluation of the contributions of the surface polarity. The viscosity tests show that the adsorbed surfactant layer may impose a hindrance to the movement of iron particles in the oil medium. The polar attractions between dimer acid covered particles gave rise to a considerable increase in viscosity, indicating flocculation structure developed in the suspensions. The observed plateau-like region in the vicinity of 0.1 s-1 for MRF containing dimer acid is possibly due to the flocculation provoked by the carboxylic polar attraction, in which the structure is stable against fragmentation. Moreover, a quick recovery of the viscosity and a higher viscosity-temperature index also suggest the existence of particle-particle polar interaction in the suspensions containing dimer acid. The sedimentation measurements reveal that the steric repulsion of oleic acid plays a limited role in the stability of suspensions only if a large quantity of surfactant was used. The sedimentation results observed in the dimer acid covered particles confirm that loose and open flocculation was formed and enhanced sedimentation stability.

  20. Using Dimers to Measure Biosignatures and Atmospheric Pressure for Terrestrial Exoplanets

    CERN Document Server

    Misra, Amit; Claire, Mark; Crisp, Dave

    2013-01-01

    We present a new method to probe atmospheric pressure on Earthlike planets using (O2-O2) dimers in the near-infrared. We also show that dimer features could be the most readily detectable biosignatures for Earthlike atmospheres, and may even be detectable in transit transmission with the James Webb Space Telescope (JWST). The absorption by dimers changes more rapidly with pressure and density than that of monomers, and can therefore provide additional information about atmospheric pressures. By comparing the absorption strengths of rotational and vibrational features to the absorption strengths of dimer features, we show that in some cases it may be possible to estimate the pressure at the reflecting surface of a planet. This method is demonstrated by using the O2 A band and the 1.06 $\\mu$m dimer feature, either in transmission or reflected spectra. It works best for planets around M dwarfs with atmospheric pressures between 0.1 and 10 bars, and for O2 volume mixing ratios above 50% of Earth's present day lev...

  1. Activation of NF-κB signalling by fusicoccin-induced dimerization.

    Science.gov (United States)

    Skwarczynska, Malgorzata; Molzan, Manuela; Ottmann, Christian

    2013-01-29

    Chemically induced dimerization is an important tool in chemical biology for the analysis of protein function in cells. Here we report the use of the natural product fusicoccin (FC) to induce dimerization of 14-3-3-fused target proteins with proteins tagged to the C terminus (CT) of the H(+)-ATPase PMA2. To prevent nonproductive or detrimental interactions of the 14-3-3 proteins and CT fusions with endogenous cell proteins, their interaction surface was engineered to facilitate FC-induced dimerization exclusively between the introduced protein constructs. Live-cell imaging documented the reversible FC-induced translocation of 14-3-3 and CT to different cell compartments depending on localization sequences fused to their dimerization partner protein. The functionality of this system was demonstrated by the FC-induced importation of the NF-κB-CT into the nucleus. In HeLa cells, FC-mediated dimerization of the NF-κB-CT with a constitutively nuclear-localized 14-3-3 protein led to an NF-κB-specific cellular response by inducing IL-8 secretion.

  2. Kinetic analysis of histamine release due to covalently linked IgE dimers

    Energy Technology Data Exchange (ETDEWEB)

    Dembo, M. (Los Alamos Scientific Lab., NM); Kagey-Sobotka, A.; Lichtenstein, L.M.; Goldstein, B.

    1982-01-01

    We present a kinetic model of histamine release from human basophils due to covalently linked IgE dimers. Comparison of theory with experiment shows that the model gives a good description of histamine release by IgE dimers and allows a number of the parameters of the model to be determined. Comparison with previous models of release by conventional antigens indicates that despite their covalent structure, IgE dimers are subject to the same laws governing inactivation as are antigen produced crosslinks. In addition, the kinetic equation which relates the rate of histamine release to the number of crosslinked Fc/sub e/ receptors per cell is the same for crosslinks formed by IgE dimers as for antigen induced crosslinks. Quantitative fitting of histamine release data also yields a value for the rate constant for crosslink formation by IgE dimer on the cell surface (r/sub x/ approx. = to 5 x 10/sup -10/ cm/sup 2//sec). This rate constant is remarkably high and indicates that the reaction is diffusion controlled.

  3. Resonance hybridization and near field properties of strongly coupled plasmonic ring dimer-rod nanosystem

    Energy Technology Data Exchange (ETDEWEB)

    Koya, Alemayehu Nana; Ji, Boyu; Hao, Zuoqiang; Lin, Jingquan, E-mail: linjingquan@cust.edu.cn [School of Science, Changchun University of Science and Technology, Changchun 130022 (China)

    2015-09-21

    Combined effects of polarization, split gap, and rod width on the resonance hybridization and near field properties of strongly coupled gold dimer-rod nanosystem are comparatively investigated in the light of the constituent nanostructures. By aligning polarization of the incident light parallel to the long axis of the nanorod, introducing small split gaps to the dimer walls, and varying width of the nanorod, we have simultaneously achieved resonance mode coupling, huge near field enhancement, and prolonged plasmon lifetime. As a result of strong coupling between the nanostructures and due to an intense confinement of near fields at the split and dimer-rod gaps, the extinction spectrum of the coupled nanosystem shows an increase in intensity and blueshift in wavelength. Consequently, the near field lifespan of the split-nanosystem is prolonged in contrast to the constituent nanostructures and unsplit-nanosystem. On the other hand, for polarization of the light perpendicular to the long axis of the nanorod, the effect of split gap on the optical responses of the coupled nanosystem is found to be insignificant compared to the parallel polarization. These findings and such geometries suggest that coupling an array of metallic split-ring dimer with long nanorod can resolve the huge radiative loss problem of plasmonic waveguide. In addition, the Fano-like resonances and immense near field enhancements at the split and dimer-rod gaps imply the potentials of the nanosystem for practical applications in localized surface plasmon resonance spectroscopy and sensing.

  4. Structural and Vibrational Study on Monomer and Dimer Forms and Water Clusters of Acetazolamide

    Directory of Open Access Journals (Sweden)

    Aysen E. Ozel

    2013-01-01

    Full Text Available Experimental IR and Raman spectra of solid acetazolamide have been analysed by computing the molecular structures and vibrational spectra of monomer and dimer forms and water clusters of acetazolamide. The possible stable conformers of free acetazolamide molecule in the ground state were obtained by scanning the potential energy surface through the dihedral angles, D1 (1S-2C-6S-9N, D2 (4N-5C-12N-14C, and D3 (5C-12N-14C-16C. The final geometry parameters for the obtained stable conformers were determined by means of geometry optimization, carried out at DFT/B3LYP/6-31G++(d,p theory level. Afterwards the possible dimer forms of the molecule and acetazolamide-H2O clusters were formed and their energetically preferred conformations were investigated using the same method and the same level of theory. The effect of BSSE on the structure and energy of acetazolamide dimer has been investigated. The assignment of the vibrational modes was performed based on the potential energy distribution of the vibrational modes, calculated by using GAR2PED program. The experimental vibrational wavenumbers of solid acetazolamide are found to be in better agreement with the calculated wavenumbers of dimer form of acetazolamide than those of its monomeric form. NBO analysis has been performed on both monomer and dimer geometries.

  5. Mapping key interactions in the dimerization process of HBHA from Mycobacterium tuberculosis, insights into bacterial agglutination.

    Science.gov (United States)

    Esposito, Carla; Cantisani, Marco; D'Auria, Gabriella; Falcigno, Lucia; Pedone, Emilia; Galdiero, Stefania; Berisio, Rita

    2012-03-23

    HBHA is a cell-surface protein implicated in the dissemination of Mycobacterium tuberculosis (Mtb) from the site of primary infection. Its N-terminal coiled-coil region is also involved in bacterial agglutination. However, despite the importance of HBHA dimerization in agglutination, protein regions involved in dimerization are hitherto not known. Here, we mapped these regions by coupling peptide synthesis, biochemical and computational analyses, and identified structural determinants for HBHA monomer-monomer recognition. Importantly, we obtained the first molecule able to induce HBHA dimer disaggregation at 37°C, the typical growth temperature of Mtb. This result provides new opportunities towards the development of Mtb anti-aggregation molecules with therapeutic interest.

  6. Structure of isothiocyanic acid dimers. Theoretical and FTIR matrix isolation studies

    Science.gov (United States)

    Krupa, Justyna; Wierzejewska, Maria

    2016-05-01

    A quantum mechanical study of the potential energy surface for the HNCS dimer is reported. The calculations were performed using DFT and ab initio MP2 methods. The most stable is a cyclic form with a double N-H⋯S interaction and the interaction energy in the range of 16.91-18.92 kJ mol-1. An open HNCS dimer bound by the N-H⋯N hydrogen bond is by ca 3.3-5.1 kJ mol-1 less stable. Experimental FTIR matrix isolation studies of HNCS/N2 system show that exclusively less stable open dimer is formed in solid nitrogen. Possible reasons for the observed discrepancy between theory and experiment are discussed.

  7. Finite size effects on the electromagnetic field enhancement from low-dimensional silver nanoshell dimer arrays

    Energy Technology Data Exchange (ETDEWEB)

    Song, Youlin [Zhengzhou University, China; Zhao, Ke [ORNL; Jia, Yu [Zhengzhou University, China; Hu, Xing [Zhengzhou University, China; Zhang, Zhenyu [ORNL

    2008-01-01

    Finite size effects on the optical properties of one-dimensional 1D and two-dimensional 2D nanoshell dimer arrays are investigated using generalized Mie theory and coupled dipole approximation within the context of surface-enhanced Raman spectroscopy SERS. It is shown that the huge enhancement in the electromagnetic EM field at the center of a given dimer oscillates with the length of the 1D array. For an array of fixed length, the EM enhancement also oscillates along the array, but with a different period. Both types of oscillations can be attributed to the interference of the dynamic dipole fields from different dimers in the array. When generalized to 2D arrays, EM enhancement higher than that of the 1D arrays can be gained with a constant magnitude, a salient feature advantageous to experimental realization of single-molecule SERS. 2008 American Institute of Physics. DOI: 10.1063/1.3009293

  8. Finite Size Effects on the Electromagnetic Field Enhancement from Low-dimensional Silver Nanoshell Dimer Arrays

    Science.gov (United States)

    Song, Youlin; Zhao, Ke; Jia, Yu; Hu, Xing; Zhang, Zhenyu

    2009-03-01

    Finite size effects on the optical properties of one-dimensional (1D) and 2D nanoshell dimer arrays are investigated using generalized Mie theory and coupled dipole approximation within the context of surface-enhanced Raman spectroscopy (SERS). It is shown that the huge enhancement in the electromagnetic (EM) field at the center of a given dimer oscillates with the length of the 1D array. For an array of fixed length, the EM enhancement also oscillates along the array, but with a different period. Both types of oscillations can be attributed to the interference of the dynamic dipole fields from different dimers in the array. When generalized to 2D arrays, EM enhancement higher than that of the 1D arrays can be gained with a constant magnitude, a salient feature advantageous to experimental realization of single-molecule SERS. [K. Zhao et al, J. Chem. Phys. 125, 081102 (2005); Y. L. Song et al, accepted by J. Chem. Phys.

  9. Ultraviolet Spectrum And Chemical Reactivity Of CIO Dimer

    Science.gov (United States)

    Demore, William B.; Tschuikow-Roux, E.

    1992-01-01

    Report describes experimental study of ultraviolet spectrum and chemical reactivity of dimer of chlorine monoxide (CIO). Objectives are to measure absorption cross sections of dimer at near-ultraviolet wavelengths; determine whether asymmetrical isomer (CIOCIO) exists at temperatures relevant to Antarctic stratosphere; and test for certain chemical reactions of dimer. Important in photochemistry of Antarctic stratosphere.

  10. A Nove Asymmetric ent—Kauranoid Dimer from Isodon enanderianus

    Institute of Scientific and Technical Information of China (English)

    纳智; 黎胜红; 等

    2002-01-01

    Further investigation on the aerial parts of Isodon enanderianus afforded a novel asymmetric ent-kauranoid dimer,enanderi-nanin J(1).The structure of the dimer was elucidated by means of spectroscopic methods (including 2D NMR tecniques ),Enanderinanin J was a dimer of xerophilusin A and probably formed by [4+2] cycloaddition.

  11. A Novel Asymmetric ent-Kauranoid Dimer from Isodon enanderianus

    Institute of Scientific and Technical Information of China (English)

    NA,Zhi(纳智); LI,Sheng-Hong(黎胜红); XIANG,Wei(项伟); ZHAO,Ai-Hua(赵爱华); LI,Chao-Ming(李朝明); SUN,Han-Dong(孙汉董)

    2002-01-01

    Further investigation on the aerial parts of Isodon enanderianus afforded a novel asymmetric ent-kauranoid dimer, enanuderinaninJ (1). The structure of the dimer was elucidated by means of spectroscopic methods (including 2D NMR techniques ). Enanderinanin J was a dimer of xerophilusin A and probably formed by [ 4 + 2] cycloaddition.

  12. Dimer monomer transition and dimer re-formation play important role for ATM cellular function during DNA repair.

    Science.gov (United States)

    Du, Fengxia; Zhang, Minjie; Li, Xiaohua; Yang, Caiyun; Meng, Hao; Wang, Dong; Chang, Shuang; Xu, Ye; Price, Brendan; Sun, Yingli

    2014-10-03

    The ATM protein kinase, is a serine/threonine protein kinase that is recruited and activated by DNA double-strand breaks, mediates responses to ionizing radiation in mammalian cells. Here we show that ATM is held inactive in unirradiated cells as a dimer and phosphorylates the opposite strand of the dimer in response to DNA damage. Cellular irradiation induces rapid intermolecular autophosphorylation of serine 1981 that causes dimer dissociation and initiates cellular ATM kinase activity. ATM cannot phosphorylate the substrates when it could not undergo dimer monomer transition. After DNA repair, the active monomer will undergo dephosphorylation to form dimer again and dephosphorylation is critical for dimer re-formation. Our work reveals novel function of ATM dimer monomer transition and explains why ATM dimer monomer transition plays such important role for ATM cellular activity during DNA repair.

  13. Novel dimeric β-helical model of an ice nucleation protein with bridged active sites

    Directory of Open Access Journals (Sweden)

    Walker Virginia K

    2011-09-01

    Full Text Available Abstract Background Ice nucleation proteins (INPs allow water to freeze at high subzero temperatures. Due to their large size (>120 kDa, membrane association, and tendency to aggregate, an experimentally-determined tertiary structure of an INP has yet to be reported. How they function at the molecular level therefore remains unknown. Results Here we have predicted a novel β-helical fold for the INP produced by the bacterium Pseudomonas borealis. The protein uses internal serine and glutamine ladders for stabilization and is predicted to dimerize via the burying of a solvent-exposed tyrosine ladder to make an intimate hydrophobic contact along the dimerization interface. The manner in which PbINP dimerizes also allows for its multimerization, which could explain the aggregation-dependence of INP activity. Both sides of the PbINP structure have tandem arrays of amino acids that can organize waters into the ice-like clathrate structures seen on antifreeze proteins. Conclusions Dimerization dramatically increases the 'ice-active' surface area of the protein by doubling its width, increasing its length, and presenting identical ice-forming surfaces on both sides of the protein. We suggest that this allows sufficient anchored clathrate waters to align on the INP surface to nucleate freezing. As PbINP is highly similar to all known bacterial INPs, we predict its fold and mechanism of action will apply to these other INPs.

  14. Effect of Ballistic-Type Hot Atom Adsorption Mechanism on the Phase Diagram of Monomer-Dimer CO-O2 Surface Catalytic Reaction:A Monte Carlo Simulation

    Institute of Scientific and Technical Information of China (English)

    M. Khalid; K. M. Khan; A. U. Qaisrani; Q. N. Malik

    2004-01-01

    @@ We investigate the effect of the ballistic mechanism on the phase diagram using a square surface. While using this mechanism whenever an O2 molecule hits a randomly vacant selected site, the molecule breaks up into atomic form and then executes a ballistic flight. The paths of the two oxygen atoms are taken exactly to be opposite to each other, i.e. anti-parallel, and the ranges of the atoms are taken to be equal, i.e. they may fly up to 1 or 1.414 or 2 of the atomic spacing from the site of impact. Four cases have been studied on the basis of the range of hot atoms. The range of the hot oxygen atoms executing a ballistic flight might be up to the first nearest neighbourhood (1 atomic spacing from the site of impact), the second nearest neighbourhood (1.414 atomic spacing from the site of impact), the third nearest neighbourhood (2 atomic spacing from the site of impact),known as cases a, b, and c, respectively, while for case d the range of the oxygen atoms executing the ballistic flight might be up to 1 atomic spacing or 1.414 atomic spacing or 2 atomic spacing from the site of impact. The steady reactive window is observed and the continuous transition disappears. As soon as the CO partial pressure departs from zero, the production of CO2 is observed, which clearly verifies the experimental observation.

  15. Analytic Morse/long-range potential energy surfaces and predicted infrared spectra for CO-H2 dimer and frequency shifts of CO in (para-H2)N N = 1-20 clusters

    Science.gov (United States)

    Li, Hui; Zhang, Xiao-Long; Le Roy, Robert J.; Roy, Pierre-Nicholas

    2013-10-01

    A five-dimensional ab initio potential energy surface (PES) for CO-H2 that explicitly incorporates dependence on the stretch coordinate of the CO monomer has been calculated. Analytic four-dimensional PESs are obtained by least-squares fitting vibrationally averaged interaction energies for vCO = 0 and 1 to the Morse/long-range potential function form. These fits to 30 206 points have root-mean-square (RMS) deviations of 0.087 and 0.082 cm-1, and require only 196 parameters. The resulting vibrationally averaged PESs provide good representations of the experimental infrared data: for infrared transitions of para H2-CO and ortho H2-CO, the RMS discrepancies are only 0.007 and 0.023 cm-1, which are almost in the same accuracy as those values of 0.010 and 0.018 cm-1 obtained from full six-dimensional ab initio PESs of V12 [P. Jankowski, A. R. W. McKellar, and K. Szalewicz, Science 336, 1147 (2012)]. The calculated infrared band origin shift associated with the fundamental of CO is -0.179 cm-1 for para H2-CO, which is the same value as that extrapolated experimental value, and slightly better than the value of -0.176 cm-1 obtained from V12 PESs. With these potentials, the path integral Monte Carlo algorithm and a first order perturbation theory estimate are used to simulate the CO vibrational band origin frequency shifts of CO in (para H2)N-CO clusters for N = 1-20. The predicted vibrational frequency shifts are in excellent agreement with available experimental observations. Comparisons are also made between these model potentials.

  16. Construction of a ferritin dimer by breaking its symmetry

    Energy Technology Data Exchange (ETDEWEB)

    Zheng, B; Uenuma, M; Uraoka, Y; Yamashita, I [Graduate School of Materials Science, Nara Institute of Science and Technology, 8916-5 Takayama, Ikoma, Nara 630-0192 (Japan); CREST, Japan Science and Technology Agency, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012 (Japan)

    2010-11-05

    Ferritin has a mono-dispersed structure and biomineralization properties that allow it to form various kinds of nanoparticles and play an important role in modern nanotechnology. Independent nanoparticles synthesized in ferritin are valuable, but moreover a pair of nanoparticles can bring new properties different from those of the independent nanoparticles. In this study, by breaking ferritin's symmetry, we successfully produced ferritin dimers which provide real protein frameworks for nanoparticle dimer formation. Identical nickel hydro-oxide nanoparticle dimers were produced by simply biomineralizing ferritin dimers. The method presented here can produce multi-functional ferritin dimers with different kinds of nanoparticles.

  17. Large D-Dimer Fluctuation in Normal Pregnancy

    DEFF Research Database (Denmark)

    Hedengran, Katrine K; Andersen, Malene R; Stender, Steen

    2016-01-01

    pregnancies were recruited. D-dimer was repeatedly measured during pregnancy, at active labor, and on the first and second postpartum days. Percentiles for each gestational week were calculated. Each individual D-dimer was normalized by transformation into percentiles for the relevant gestational age......Introduction. D-dimer levels increase throughout pregnancy, hampering the usefulness of the conventional threshold for dismissing thromboembolism. This study investigates the biological fluctuation of D-dimer in normal pregnancy. Methods. A total of 801 healthy women with expected normal...... normal pregnancy, repeated D-dimer measurements are of no clinical use in the evaluation of thromboembolic events during pregnancy....

  18. Plasmonic rod dimers as elementary planar chiral meta-atoms

    CERN Document Server

    Zhukovsky, Sergei V; Chigrin, Dmitry N

    2011-01-01

    Electromagnetic response of metallic rod dimers is theoretically calculated for arbitrary planar arrangement of rods in the dimer. It is shown that dimers without an in-plane symmetry axis exhibit elliptical dichroism and act as "atoms" in planar chiral metamaterials. Due to a very simple geometry of the rod dimer, such planar metamaterials are much easier in fabrication than conventional split-ring or gammadion-type structures, and lend themselves to a simple analytical treatment based on coupled dipole model. Dependencies of metamaterial's directional asymmetry on the dimer's geometry are established analytically and confirmed in numerical simulations.

  19. Revisiting the Optical PT-Symmetric Dimer

    Directory of Open Access Journals (Sweden)

    José Delfino Huerta Morales

    2016-08-01

    Full Text Available Optics has proved a fertile ground for the experimental simulation of quantum mechanics. Most recently, optical realizations of PT -symmetric quantum mechanics have been shown, both theoretically and experimentally, opening the door to international efforts aiming at the design of practical optical devices exploiting this symmetry. Here, we focus on the optical PT -symmetric dimer, a two-waveguide coupler where the materials show symmetric effective gain and loss, and provide a review of the linear and nonlinear optical realizations from a symmetry-based point of view. We go beyond a simple review of the literature and show that the dimer is just the smallest of a class of planar N-waveguide couplers that are the optical realization of the Lorentz group in 2 + 1 dimensions. Furthermore, we provide a formulation to describe light propagation through waveguide couplers described by non-Hermitian mode coupling matrices based on a non-Hermitian generalization of the Ehrenfest theorem.

  20. Revisiting the optical $PT$-symmetric dimer

    CERN Document Server

    Morales, J D Huerta; López-Aguayo, S; Rodríguez-Lara, B M

    2016-01-01

    Optics has proved a fertile ground for the experimental simulation of quantum mechanics. Most recently, optical realizations of $\\mathcal{PT}$-symmetric quantum mechanics have been shown, both theoretically and experimentally, opening the door to international efforts aiming at the design of practical optical devices exploiting this symmetry. Here, we focus on the optical $\\mathcal{PT}$-symmetric dimer, a two-waveguide coupler were the materials show symmetric effective gain and loss, and provide a review of the linear and nonlinear optical realizations from a symmetry based point of view. We go beyond a simple review of the literature and show that the dimer is just the smallest of a class of planar $N$-waveguide couplers that are the optical realization of Lorentz group in 2+1 dimensions. Furthermore, we provide a formulation to describe light propagation through waveguide couplers described by non-Hermitian mode coupling matrices based on a non-Hermitian generalization of Ehrenfest theorem.

  1. Fibrillar dimer formation of islet amyloid polypeptides

    Energy Technology Data Exchange (ETDEWEB)

    Chiu, Chi-cheng [Univ. of Chicago, IL (United States); Argonne National Lab. (ANL), Argonne, IL (United States); de Pablo, Juan J. [Univ. of Chicago, IL (United States); Argonne National Lab. (ANL), Argonne, IL (United States)

    2015-05-08

    Amyloid deposits of human islet amyloid polypeptide (hIAPP), a 37-residue hormone co-produced with insulin, have been implicated in the development of type 2 diabetes. Residues 20 – 29 of hIAPP have been proposed to constitute the amyloidogenic core for the aggregation process, yet the segment is mostly unstructured in the mature fibril, according to solid-state NMR data. Here we use molecular simulations combined with bias-exchange metadynamics to characterize the conformational free energies of hIAPP fibrillar dimer and its derivative, pramlintide. We show that residues 20 – 29 are involved in an intermediate that exhibits transient β-sheets, consistent with recent experimental and simulation results. By comparing the aggregation of hIAPP and pramlintide, we illustrate the effects of proline residues on inhibition of the dimerization of IAPP. The mechanistic insights presented here could be useful for development of therapeutic inhibitors of hIAPP amyloid formation.

  2. Immunoglobulin Free Light Chain Dimers in Human Diseases

    Directory of Open Access Journals (Sweden)

    Batia Kaplan

    2011-01-01

    Full Text Available Immunoglobulin free light chain (FLC kappa (κ and lambda (λ isotypes exist mainly in monomeric and dimeric forms. Under pathological conditions, the level of FLCs as well as the structure of monomeric and dimeric FLCs and their dimerization properties might be significantly altered. The abnormally high fractions of dimeric FLCs were demonstrated in the serum of patients with multiple myeloma (MM and primary systemic amyloidosis (AL, as well as in the serum of anephric patients. The presence of tetra- and trimolecular complexes formed due to dimer-dimer and dimer-monomer interactions was detected in the myeloma serum. Analysis of the amyloidogenic light chains demonstrated mutations within the dimer interface, thus raising the possibility that these mutations are responsible for amyloidogenicity. Increased κ monomer and dimer levels, as well as a high κ/λ monomer ratio, were typically found in the cerebrospinal fluid from patients with multiple sclerosis (MS. In many MS cases, the elevation of κ FLCs was accompanied by an abnormally high proportion of λ dimers. This review focuses on the disease-related changes of the structure and level of dimeric FLCs, and raises the questions regarding their formation, function, and role in the pathogenesis and diagnosis of human diseases.

  3. Entanglement and decoherence in a quantum dimer

    Institute of Scientific and Technical Information of China (English)

    Hou Xi-Wen; Hui Zi; Ding Rui-Min; Chen Xiao-Yang; Gao Yu

    2006-01-01

    The dynamical properties of quantum entanglement in an integrable quantum dimer are studied in terms of the reduced-density linear entropy with various coupling parameters and total boson numbers. The characteristic time of decoherence process in the early-time evolution of the linear entropy is obtained, indicating that the characteristic time and the corresponding entropy exhibit a maximum near the position of the corresponding classical separatrix energy.

  4. Path integrals for dimerized quantum spin systems

    Energy Technology Data Exchange (ETDEWEB)

    Foussats, Adriana, E-mail: afoussats@gmail.co [Facultad de Ciencias Exactas, Ingenieria y Agrimensura and Instituto de Fisica Rosario (UNR-CONICET), Av. Pellegrini 250, 2000 Rosario (Argentina); Greco, Andres [Facultad de Ciencias Exactas, Ingenieria y Agrimensura and Instituto de Fisica Rosario (UNR-CONICET), Av. Pellegrini 250, 2000 Rosario (Argentina); Muramatsu, Alejandro [Institut fuer Theoretische Physik III, Universitaet Stuttgart, Pfaffenwaldring 57, D-70550 Stuttgart (Germany)

    2011-01-11

    Dimerized quantum spin systems may appear under several circumstances, e.g. by a modulation of the antiferromagnetic exchange coupling in space, or in frustrated quantum antiferromagnets. In general, such systems display a quantum phase transition to a Neel state as a function of a suitable coupling constant. We present here two path-integral formulations appropriate for spin S=1/2 dimerized systems. The first one deals with a description of the dimers degrees of freedom in an SO(4) manifold, while the second one provides a path-integral for the bond-operators introduced by Sachdev and Bhatt. The path-integral quantization is performed using the Faddeev-Jackiw symplectic formalism for constrained systems, such that the measures and constraints that result from the algebra of the operators is provided in both cases. As an example we consider a spin-Peierls chain, and show how to arrive at the corresponding field-theory, starting with both an SO(4) formulation and bond-operators.

  5. Regulation of PrP(C) signaling and processing by dimerization.

    Science.gov (United States)

    Roucou, Xavier

    2014-01-01

    The cellular prion protein (PrP(C)) is a glycosylphosphatidylinositol (GPI)-anchored protein present at the cell surface. PrP(C) N-terminal moiety is intrinsically disordered and is able to interact with a variety of ligands. Physiological ligands have neurotrophic activity, whilst others, including protein toxic oligomers, have neurotoxic functions. These two opposite activities involve different interacting partners and result from different PrP(C)-activated signaling pathways. Remarkably, PrP(C) may be inactivated either by physiological endoproteolysis and release of the N-terminal domain, or by ectodomain shedding. Ligand-induced PrP(C) dimerization or enforced dimerization of PrP(C) indicate that PrP(C) dimerization represents an important molecular switch for both intracellular signaling and inactivation by the release of PrP(C) N-terminal domain or shedding. In this review, we summarize evidence that cell surface receptor activity of PrP(C) is finely regulated by dimerization.

  6. Dimer monomer transition and dimer re-formation play important role for ATM cellular function during DNA repair

    Energy Technology Data Exchange (ETDEWEB)

    Du, Fengxia [Laboratory of Genome Variations and Precision Bio-Medicine, Beijing Institute of Genomics, Chinese Academy of Sciences, Beijing 100101 (China); Zhang, Minjie [Laboratory of Genome Variations and Precision Bio-Medicine, Beijing Institute of Genomics, Chinese Academy of Sciences, Beijing 100101 (China); University of Chinese Academy of Sciences, Beijing 100049 (China); Li, Xiaohua; Yang, Caiyun [Laboratory of Genome Variations and Precision Bio-Medicine, Beijing Institute of Genomics, Chinese Academy of Sciences, Beijing 100101 (China); Meng, Hao; Wang, Dong; Chang, Shuang [Laboratory of Genome Variations and Precision Bio-Medicine, Beijing Institute of Genomics, Chinese Academy of Sciences, Beijing 100101 (China); University of Chinese Academy of Sciences, Beijing 100049 (China); Xu, Ye [Department of Radiation Oncology, Division of Genomic Stability, Dana Farber Cancer Institute, Harvard Medical School, MA 02134 (United States); Price, Brendan, E-mail: Brendan_Price@dfci.harvard.edu [Department of Radiation Oncology, Division of Genomic Stability, Dana Farber Cancer Institute, Harvard Medical School, MA 02134 (United States); Sun, Yingli, E-mail: sunyl@big.ac.cn [Laboratory of Genome Variations and Precision Bio-Medicine, Beijing Institute of Genomics, Chinese Academy of Sciences, Beijing 100101 (China)

    2014-10-03

    Highlights: • ATM phosphorylates the opposite strand of the dimer in response to DNA damage. • The PETPVFRLT box of ATM plays a key role in its dimer dissociation in DNA repair. • The dephosphorylation of ATM is critical for dimer re-formation after DNA repair. - Abstract: The ATM protein kinase, is a serine/threonine protein kinase that is recruited and activated by DNA double-strand breaks, mediates responses to ionizing radiation in mammalian cells. Here we show that ATM is held inactive in unirradiated cells as a dimer and phosphorylates the opposite strand of the dimer in response to DNA damage. Cellular irradiation induces rapid intermolecular autophosphorylation of serine 1981 that causes dimer dissociation and initiates cellular ATM kinase activity. ATM cannot phosphorylate the substrates when it could not undergo dimer monomer transition. After DNA repair, the active monomer will undergo dephosphorylation to form dimer again and dephosphorylation is critical for dimer re-formation. Our work reveals novel function of ATM dimer monomer transition and explains why ATM dimer monomer transition plays such important role for ATM cellular activity during DNA repair.

  7. MspA nanopores from subunit dimers.

    Directory of Open Access Journals (Sweden)

    Mikhail Pavlenok

    Full Text Available Mycobacterium smegmatis porin A (MspA forms an octameric channel and represents the founding member of a new family of pore proteins. Control of subunit stoichiometry is important to tailor MspA for nanotechnological applications. In this study, two MspA monomers were connected by linkers ranging from 17 to 62 amino acids in length. The oligomeric pore proteins were purified from M. smegmatis and were shown to form functional channels in lipid bilayer experiments. These results indicated that the peptide linkers did not prohibit correct folding and localization of MspA. However, expression levels were reduced by 10-fold compared to wild-type MspA. MspA is ideal for nanopore sequencing due to its unique pore geometry and its robustness. To assess the usefulness of MspA made from dimeric subunits for DNA sequencing, we linked two M1-MspA monomers, whose constriction zones were modified to enable DNA translocation. Lipid bilayer experiments demonstrated that this construct also formed functional channels. Voltage gating of MspA pores made from M1 monomers and M1-M1 dimers was identical indicating similar structural and dynamic channel properties. Glucose uptake in M. smegmatis cells lacking porins was restored by expressing the dimeric mspA M1 gene indicating correct folding and localization of M1-M1 pores in their native membrane. Single-stranded DNA hairpins produced identical ionic current blockades in pores made from monomers and subunit dimers demonstrating that M1-M1 pores are suitable for DNA sequencing. This study provides the proof of principle that production of single-chain MspA pores in M. smegmatis is feasible and paves the way for generating MspA pores with altered stoichiometries. Subunit dimers enable better control of the chemical and physical properties of the constriction zone of MspA. This approach will be valuable both in understanding transport across the outer membrane in mycobacteria and in tailoring MspA for nanopore

  8. Sensing Properties of a Fabry-Perot Dielectric Structure and Dimer Nanoparticles

    Directory of Open Access Journals (Sweden)

    A. Polemi

    2012-01-01

    Full Text Available We investigate the use of a Fabry-Perot dielectric structure combined with differently shaped nanoparticles for Surface Enhanced Raman Scattering. In particular, we show how an ideal two-layer Fabry-Perot configuration enhances the local surface field of silver nanoparticles positioned on the surface of the structure. We develop the concept using disc dimers and then extend the discussion to bowtie nanoparticles. The structure is excited by a single emitter, which couples to the nanoparticles through the dielectric layers, producing a wide aperture field that can be used to excite multiple dimers. We show how an array of nanoparticles can be properly arranged in order to increase the total scattering signal generated from the structure. The layered geometry produces robust field properties in between nanoparticles, making the overall sensing characteristics less sensitive to the interparticle seperation distance and incident polarization.

  9. Multi-Instrument Characterization of the Surfaces and Materials in Microfabricated, Carbon Nanotube-Templated Thin Layer Chromatography Plates. An Analogy to ‘The Blind Men and the Elephant’

    Energy Technology Data Exchange (ETDEWEB)

    Jensen, David S.; Kanyal, Supriya S.; Madaan, Nitesh; Hancock, Jared M.; Dadson, Andrew; Vail, Michael A.; Vanfleet, Richard; Shutthanandan, V.; Zhu, Zihua; Engelhard, Mark H.; Linford, Matthew R.

    2013-08-08

    Herein we apply a suite of surface/materials analytical tools to characterize some of the materials created in the production of microfabricated thin layer chromatography plates. Techniques used include X-ray photoelectron spectroscopy (XPS), valence band spectroscopy, static time-of-flight secondary ion spectrometry (ToF-SIMS) in both positive and negative ion modes, Rutherford backscattering spectroscopy (RBS), and helium ion microscopy (HIM). Materials characterized include: the Si(100) substrate with native oxide: Si/SiO2, alumina (35 nm) deposited as a diffusion barrier on the Si/SiO2: Si/SiO2/Al2O3, iron (6 nm) thermally evaporated on the Al2O3: Si/SiO2/Al2O3/Fe, the iron film annealed in H2 to make Fe catalyst nanoparticles: Si/SiO2/Al2O3/Fe(NP), and carbon nanotubes (CNTs) grown from the Fe nanoparticles: Si/SiO2/Al2O3/Fe(NP)/CNT. The Fe thin films and nanoparticles are found in an oxidized state. Some of the analyses of the CNTs/CNT forests reported appear to be unique: the CNT forest appears to exhibit an interesting ‘channeling’ phenomenon by RBS, we observe an odd-even effect in the ToF-SIMS spectra of Cn- species for n = 1 – 6, with ions at even n showing greater intensity than the neighboring signals, and ions with n ≥ 6 showing a steady decrease in intensity, and valence band characterization of CNTs using X-radiation is reported. The information obtained from the combination of the different analytical tools provides a more complete understanding of our materials than a single technique, which is analogous to the story of ‘The Blind Men and the Elephant’. (Of course there is increasing emphasis on the use of multiple characterization tools in surface and materials analysis.) The raw XPS and ToF-SIMS spectra from this study will be submitted to Surface Science Spectra for archiving.

  10. Amorphous Silica-Promoted Lysine Dimerization: a Thermodynamic Prediction

    Science.gov (United States)

    Kitadai, Norio; Nishiuchi, Kumiko; Nishii, Akari; Fukushi, Keisuke

    2017-08-01

    It has long been suggested that mineral surfaces played a crucial role in the abiotic polymerization of amino acids that preceded the origin of life. Nevertheless, it remains unclear where the prebiotic process took place on the primitive Earth, because the amino acid-mineral interaction and its dependence on environmental conditions have yet to be understood adequately. Here we examined experimentally the adsorption of L-lysine (Lys) and its dimer (LysLys) on amorphous silica over a wide range of pH, ionic strength, adsorbate concentration, and the solid/water ratio, and determined the reaction stoichiometries and the equilibrium constants based on the extended triple-layer model (ETLM). The retrieved ETLM parameters were then used, in combination with the equilibrium constant for the peptide bond formation in bulk water, to calculate the Lys-LysLys equilibrium in the presence of amorphous silica under various aqueous conditions. Results showed that the silica surface favors Lys dimerization, and the influence varies greatly with changing environmental parameters. At slightly alkaline pH (pH 9) in the presence of a dilute NaCl (1 mM), the thermodynamically attainable LysLys from 0.1 mM Lys reached a concentration around 50 times larger than that calculated without silica. Because of the versatility of the ETLM, which has been applied to describe a wide variety of biomolecule-mineral interactions, future experiments with the reported methodology are expected to provide a significant constraint on the plausible geological settings for the condensation of monomers to polymers, and the subsequent chemical evolution of life.

  11. Speciation of potentially mobile Si in Yangtze Estuary surface sediments: estimates using a modified sequential extraction technique.

    Science.gov (United States)

    Zhu, Huagang; Wang, Chao; Wang, Peifang; Hou, Jun; Qian, Jin; Ao, Yanhui; Liu, Cui

    2016-09-01

    To improve our understanding of the Si-related biogeochemical processes that occur in estuarine ecosystems with large subaqueous deltas (e.g., the Yangtze Estuary; YE), the speciation of Si in the surface sediments of the YE was investigated. The relationships between the different Si species and sediment bulk parameters were also discussed. Based on modified sequential extraction method, we can successfully estimate the following five sedimentary potentially mobile Si pools: weak acid leachable Si (W-Si); Si bound to organic matter (H-Si); Si coprecipitated with amorphous Fe/Al oxides (O-Si); Si coprecipitated with crystalline Fe/Al oxides (Ouv-Si), and biogenic silica (B-Si). The total potentially mobile Si pool (T-Si) ranged between 1689.31 and 5487.10 μg/g, with high values observed in deltaic mud deposits. The Si fractions were closely correlated with grain size compositions, except for O-Si. In deltaic mud deposits, efficient loss of organic matters and recycling of Fe oxides probably resulted in the amorphous or poorly crystalline Fe oxides uncoupled with the clay fractions, and thus leading to the lack of correlation between O-Si and grain size. As compared with Ouv-Si, the O-Si should possess stronger mobility, which highlights the importance of quantifying the O-Si pool in deltaic sediments.

  12. The Structure of the Poxvirus A33 Protein Reveals a Dimer of Unique C-Type Lectin-Like Domains

    Energy Technology Data Exchange (ETDEWEB)

    Su, Hua-Poo; Singh, Kavita; Gittis, Apostolos G.; Garboczi, David N. (NIH)

    2010-11-03

    The current vaccine against smallpox is an infectious form of vaccinia virus that has significant side effects. Alternative vaccine approaches using recombinant viral proteins are being developed. A target of subunit vaccine strategies is the poxvirus protein A33, a conserved protein in the Chordopoxvirinae subfamily of Poxviridae that is expressed on the outer viral envelope. Here we have determined the structure of the A33 ectodomain of vaccinia virus. The structure revealed C-type lectin-like domains (CTLDs) that occur as dimers in A33 crystals with five different crystal lattices. Comparison of the A33 dimer models shows that the A33 monomers have a degree of flexibility in position within the dimer. Structural comparisons show that the A33 monomer is a close match to the Link module class of CTLDs but that the A33 dimer is most similar to the natural killer (NK)-cell receptor class of CTLDs. Structural data on Link modules and NK-cell receptor-ligand complexes suggest a surface of A33 that could interact with viral or host ligands. The dimer interface is well conserved in all known A33 sequences, indicating an important role for the A33 dimer. The structure indicates how previously described A33 mutations disrupt protein folding and locates the positions of N-linked glycosylations and the epitope of a protective antibody.

  13. Dimerization and heme binding are conserved in amphibian and starfish homologues of the microRNA processing protein DGCR8.

    Directory of Open Access Journals (Sweden)

    Rachel Senturia

    Full Text Available Human DiGeorge Critical Region 8 (DGCR8 is an essential microRNA (miRNA processing factor that is activated via direct interaction with Fe(III heme. In order for DGCR8 to bind heme, it must dimerize using a dimerization domain embedded within its heme-binding domain (HBD. We previously reported a crystal structure of the dimerization domain from human DGCR8, which demonstrated how dimerization results in the formation of a surface important for association with heme. Here, in an attempt to crystallize the HBD, we search for DGCR8 homologues and show that DGCR8 from Patiria miniata (bat star also binds heme. The extinction coefficients (ε of DGCR8-heme complexes are determined; these values are useful for biochemical analyses and allow us to estimate the heme occupancy of DGCR8 proteins. Additionally, we present the crystal structure of the Xenopus laevis dimerization domain. The structure is very similar to that of human DGCR8. Our results indicate that dimerization and heme binding are evolutionarily conserved properties of DGCR8 homologues not only in vertebrates, but also in at least some invertebrates.

  14. Atomic resolution crystal structure of VcLMWPTP-1 from Vibrio cholerae O395: Insights into a novel mode of dimerization in the low molecular weight protein tyrosine phosphatase family

    Energy Technology Data Exchange (ETDEWEB)

    Nath, Seema; Banerjee, Ramanuj; Sen, Udayaditya, E-mail: udayaditya.sen@saha.ac.in

    2014-07-18

    Highlights: • VcLMWPTP-1 forms dimer in solution. • The dimer is catalytically active unlike other reported dimeric LMWPTPs. • The formation of extended dimeric surface excludes the active site pocket. • The surface bears closer resemblance to eukaryotic LMWPTPs. - Abstract: Low molecular weight protein tyrosine phosphatase (LMWPTP) is a group of phosphotyrosine phosphatase ubiquitously found in a wide range of organisms ranging from bacteria to mammals. Dimerization in the LMWPTP family has been reported earlier which follows a common mechanism involving active site residues leading to an enzymatically inactive species. Here we report a novel form of dimerization in a LMWPTP from Vibrio cholera 0395 (VcLMWPTP-1). Studies in solution reveal the existence of the dimer in solution while kinetic study depicts the active form of the enzyme. This indicates that the mode of dimerization in VcLMWPTP-1 is different from others where active site residues are not involved in the process. A high resolution (1.45 Å) crystal structure of VcLMWPTP-1 confirms a different mode of dimerization where the active site is catalytically accessible as evident by a tightly bound substrate mimicking ligand, MOPS at the active site pocket. Although being a member of a prokaryotic protein family, VcLMWPTP-1 structure resembles very closely to LMWPTP from a eukaryote, Entamoeba histolytica. It also delineates the diverse surface properties around the active site of the enzyme.

  15. Metal enhanced fluorescence of Ag-nanoshell dimer

    Science.gov (United States)

    Liaw, Jiunn-Woei; Chen, Huang-Chih; Chen, Bae-Renn; Kuo, Mao-Kuen

    2014-04-01

    The plasmon modes of Ag-nanoshell dimer on metal enhanced fluorescence (MEF) are studied theoretically. The amplified excitation rate of a dimer (two identical Ag nanoshells) illuminated by a plane wave for exciting a molecule located at the gap center is calculated. Subsequently, the apparent quantum yield of the emission of the excited molecule affected by the dimer is investigated. The multiple multipole method is used for the both simulations. Finally, the enhancement factor of the dimer on the overall photoluminescence of the molecule in terms of the two parameters is evaluated. Our results show that Ag-nanoshell dimer is a dual-band photoluminescence enhancer for MEF at the bonding dipole and quadrupole modes. The former is broadband, and the latter narrowband. Both bands depend on the gap size. Moreover, the average enhancement factor of Ag-nanoshell dimer for MEF with a Stokes shift is discussed.

  16. Cytochrome P450 as dimerization catalyst in diketopiperazine alkaloid biosynthesis.

    Science.gov (United States)

    Saruwatari, Takayoshi; Yagishita, Fumitoshi; Mino, Takashi; Noguchi, Hiroshi; Hotta, Kinya; Watanabe, Kenji

    2014-03-21

    As dimeric natural products frequently exhibit useful biological activities, identifying and understanding their mechanisms of dimerization is of great interest. One such compound is (−)-ditryptophenaline, isolated from Aspergillus flavus, which inhibits substance P receptor for potential analgesic and anti-inflammatory activity. Through targeted gene knockout in A. flavus and heterologous yeast gene expression, we determined for the first time the gene cluster and pathway for the biosynthesis of a dimeric diketopiperazine alkaloid. We also determined that a single cytochrome P450, DtpC, is responsible not only for pyrroloindole ring formation but also for concurrent dimerization of N-methylphenylalanyltryptophanyl diketopiperazine monomers into a homodimeric product. Furthermore, DtpC exhibits relaxed substrate specificity, allowing the formation of two new dimeric compounds from a non-native monomeric precursor, brevianamide F. A radical-mediated mechanism of dimerization is proposed.

  17. Thermodynamic properties for the sodium dimer

    Science.gov (United States)

    Song, Xiao-Qin; Wang, Chao-Wen; Jia, Chun-Sheng

    2017-04-01

    We present a closed-form expression of the classical vibrational partition function for the improved Rosen-Morse potential energy model. We give explicit expressions for the vibrational mean energy, vibrational specific heat, vibrational free energy, and vibrational entropy for diatomic molecule systems. The properties of these thermodynamic functions for the Na2 dimer are discussed in detail. We find that the improved Rosen-Morse potential model is superior to the harmonic oscillator in calculating the heat capacity for the Na2 molecules.

  18. Thermodynamics of acetylene van der Waals dimerization

    Science.gov (United States)

    Colussi, A. J.; Sander, S. P.; Friedl, R. R.

    1991-01-01

    Integrated band intensities of the 620/cm absorption in (C2H2)2 are measured by FTIR spectroscopy at constant acetylene pressure between 198 and 273 K. These data, in conjunction with ab initio results for (C2H2)2, are used for the statistical evaluation of the equilibrium constant Kp(T) for acetylene-cluster dimerization. The present results are used to clarify the role of molecular clusters in chemical systems at or near equilibrium, in particular in Titan's stratosphere.

  19. Rotational spectra of propargyl alcohol dimer: A dimer bound with three different types of hydrogen bonds

    Energy Technology Data Exchange (ETDEWEB)

    Mani, Devendra; Arunan, E., E-mail: arunan@ipc.iisc.ernet.in [Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore 560012 (India)

    2014-10-28

    Pure rotational spectra of the propargyl alcohol dimer and its three deuterium isotopologues have been observed in the 4 to 13 GHz range using a pulsed-nozzle Fourier transform microwave spectrometer. For the parent dimer, a total of 51 transitions could be observed and fitted within experimental uncertainty. For two mono-substituted and one bi-substituted deuterium isotopologues, a total of 14, 17, and 19 transitions were observed, respectively. The observed rotational constants for the parent dimer [A = 2321.8335(4) MHz, B = 1150.4774(2) MHz, and C = 1124.8898(2) MHz] are close to those of the most stable structure predicted by ab initio calculations. Spectra of the three deuterated isotopologues and Kraitchman analysis positively confirm this structure. Geometrical parameters and “Atoms in Molecules” analysis on the observed structure reveal that the two propargyl alcohol units in the dimer are bound by three different types of hydrogen bonds: O–H⋯O, O–H⋯π, and C–H⋯π. To the best of our knowledge, propargyl alcohol seems to be the smallest molecule forming a homodimer with three different points of contact.

  20. Synthesis of Symmetrical Biaryls via Rhodium Catalyzed Dimerization of Arylmercurials and Mechanism of the Dimerization

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    A series of symmetrical biaryls was synthesized from arylmercuric chlorides and biarylmercurials in the presence of [ClRh(CO)2]2 in hexamethylphosphoramide(HMPA). The mechanism of the [ClRh(CO)2]2 catalyzed dimerization of biarylmercurials was studied, and shown to be mainly intermolecular reaction.

  1. Interaction of the LILRB1 inhibitory receptor with HLA class Ia dimers.

    Science.gov (United States)

    Baía, Diogo; Pou, Jordi; Jones, Des; Mandelboim, Ofer; Trowsdale, John; Muntasell, Aura; López-Botet, Miguel

    2016-07-01

    Leukocyte immunoglobulin-like receptor subfamily B member 1 (LILRB1) has been reported to interact with a wide spectrum of HLA class I (HLA-I) molecules, albeit with different affinities determined by allelic polymorphisms and conformational features. HLA-G dimerization and the presence of intracellular Cys residues in HLA-B7 have been shown to be critical for their recognition by LILRB1. We hypothesized that dimerization of classical HLA class Ia molecules, previously detected in exosomes, might enhance their interaction with LILRB1. A soluble LILRB1-Fc fusion protein and a sensitive cellular reporter system expressing a LILRB1-ζ chimera were employed to assess receptor interaction with different HLA class Ia molecules transfected in the human lymphoblastoid 721.221 cell line. Under these conditions, intracellular Cys residues and HLA-I dimerization appeared associated with increased LILRB1 recognition. On the other hand, a marginal interaction of LILRB1 with primary monocytic cells, irrespective of their high HLA-I expression, was enhanced by type I interferon (IFN). This effect appeared disproportionate to the cytokine-induced increase of surface HLA-I expression and was accompanied by detection of HLA class Ia dimers. Altogether, the results support that a regulated assembly of these noncanonical HLA-I conformers during the immune response may enhance the avidity of their interaction with LILRB1.

  2. Structural features for the mechanism of antitumor action of a dimeric human pancreatic ribonuclease variant

    Science.gov (United States)

    Merlino, Antonello; Avella, Giovanna; Di Gaetano, Sonia; Arciello, Angela; Piccoli, Renata; Mazzarella, Lelio; Sica, Filomena

    2009-01-01

    A specialized class of RNases shows a high cytotoxicity toward tumor cell lines, which is critically dependent on their ability to reach the cytosol and to evade the action of the ribonuclease inhibitor (RI). The cytotoxicity and antitumor activity of bovine seminal ribonuclease (BSRNase), which exists in the native state as an equilibrium mixture of a swapped and an unswapped dimer, are peculiar properties of the swapped form. A dimeric variant (HHP2-RNase) of human pancreatic RNase, in which the enzyme has been engineered to reproduce the sequence of BSRNase helix-II (Gln28→Leu, Arg31→Cys, Arg32→Cys, and Asn34→Lys) and to eliminate a negative charge on the surface (Glu111→Gly), is also extremely cytotoxic. Surprisingly, this activity is associated also to the unswapped form of the protein. The crystal structure reveals that on this molecule the hinge regions, which are highly disordered in the unswapped form of BSRNase, adopt a very well-defined conformation in both subunits. The results suggest that the two hinge peptides and the two Leu28 side chains may provide an anchorage to a transient noncovalent dimer, which maintains Cys31 and Cys32 of the two subunits in proximity, thus stabilizing a quaternary structure, similar to that found for the noncovalent swapped dimer of BSRNase, that allows the molecule to escape RI and/or to enhance the formation of the interchain disulfides. PMID:19177350

  3. Structural and biochemical studies on Vibrio cholerae Hsp31 reveals a novel dimeric form and Glutathione-independent Glyoxalase activity

    Science.gov (United States)

    Dey, Sanjay

    2017-01-01

    Vibrio cholerae experiences a highly hostile environment at human intestine which triggers the induction of various heat shock genes. The hchA gene product of V. cholerae O395, referred to a hypothetical intracellular protease/amidase VcHsp31, is one such stress-inducible homodimeric protein. Our current study demonstrates that VcHsp31 is endowed with molecular chaperone, amidopeptidase and robust methylglyoxalase activities. Through site directed mutagenesis coupled with biochemical assays on VcHsp31, we have confirmed the role of residues in the vicinity of the active site towards amidopeptidase and methylglyoxalase activities. VcHsp31 suppresses the aggregation of insulin in vitro in a dose dependent manner. Through crystal structures of VcHsp31 and its mutants, grown at various temperatures, we demonstrate that VcHsp31 acquires two (Type-I and Type-II) dimeric forms. Type-I dimer is similar to EcHsp31 where two VcHsp31 monomers associate in eclipsed manner through several intersubunit hydrogen bonds involving their P-domains. Type-II dimer is a novel dimeric organization, where some of the intersubunit hydrogen bonds are abrogated and each monomer swings out in the opposite directions centering at their P-domains, like twisting of wet cloth. Normal mode analysis (NMA) of Type-I dimer shows similar movement of the individual monomers. Upon swinging, a dimeric surface of ~400Å2, mostly hydrophobic in nature, is uncovered which might bind partially unfolded protein substrates. We propose that, in solution, VcHsp31 remains as an equilibrium mixture of both the dimers. With increase in temperature, transformation to Type-II form having more exposed hydrophobic surface, occurs progressively accounting for the temperature dependent increase of chaperone activity of VcHsp31. PMID:28235098

  4. Assembly of Drosophila centromeric nucleosomes requires CID dimerization.

    Science.gov (United States)

    Zhang, Weiguo; Colmenares, Serafin U; Karpen, Gary H

    2012-01-27

    Centromeres are essential chromosomal regions required for kinetochore assembly and chromosome segregation. The composition and organization of centromeric nucleosomes containing the essential histone H3 variant CENP-A (CID in Drosophila) is a fundamental, unresolved issue. Using immunoprecipitation of CID mononucleosomes and cysteine crosslinking, we demonstrate that centromeric nucleosomes contain CID dimers in vivo. Furthermore, CID dimerization and centromeric targeting require a residue implicated in formation of the four-helix bundle, which mediates intranucleosomal H3 dimerization and nucleosome integrity. Taken together, our findings suggest that CID nucleosomes are octameric in vivo and that CID dimerization is essential for correct centromere assembly.

  5. Disordered clusters of Bak dimers rupture mitochondria during apoptosis

    Science.gov (United States)

    Uren, Rachel T; O’Hely, Martin; Iyer, Sweta; Bartolo, Ray; Shi, Melissa X; Brouwer, Jason M; Alsop, Amber E; Dewson, Grant; Kluck, Ruth M

    2017-01-01

    During apoptosis, Bak and Bax undergo major conformational change and form symmetric dimers that coalesce to perforate the mitochondrial outer membrane via an unknown mechanism. We have employed cysteine labelling and linkage analysis to the full length of Bak in mitochondria. This comprehensive survey showed that in each Bak dimer the N-termini are fully solvent-exposed and mobile, the core is highly structured, and the C-termini are flexible but restrained by their contact with the membrane. Dimer-dimer interactions were more labile than the BH3:groove interaction within dimers, suggesting there is no extensive protein interface between dimers. In addition, linkage in the mobile Bak N-terminus (V61C) specifically quantified association between dimers, allowing mathematical simulations of dimer arrangement. Together, our data show that Bak dimers form disordered clusters to generate lipidic pores. These findings provide a molecular explanation for the observed structural heterogeneity of the apoptotic pore. DOI: http://dx.doi.org/10.7554/eLife.19944.001 PMID:28182867

  6. Pathogenic Cysteine Removal Mutations in FGFR Extracellular Domains Stabilize Receptor Dimers and Perturb the TM Dimer Structure.

    Science.gov (United States)

    Sarabipour, Sarvenaz; Hristova, Kalina

    2016-10-09

    Missense mutations that introduce or remove cysteine residues in receptor tyrosine kinases are believed to cause pathologies by stabilizing the active receptor tyrosine kinase dimers. However, the magnitude of this stabilizing effect has not been measured for full-length receptors. Here, we characterize the dimer stabilities of three full-length fibroblast growth factor receptor (FGFR) mutants harboring pathogenic cysteine substitutions: the C178S FGFR1 mutant, the C342R FGFR2 mutant, and the C228R FGFR3 mutant. We find that the three mutations stabilize the FGFR dimers. We further see that the mutations alter the configuration of the FGFR transmembrane dimers. Thus, both aberrant dimerization and perturbed dimer structure likely contribute to the pathological phenotypes arising due to these mutations.

  7. Polarons in endohedral Li+@C60- dimers and in 1D and 2D crystals

    Science.gov (United States)

    Kawazoe, Yoshiyuki; Belosludov, Vladimir R.; Zhdanov, Ravil K.; Belosludov, Rodion V.

    2017-10-01

    The electron charge distribution and polaron formation on the carbon sites of dimer clusters Li+@C60- and of 1D or 2D Li+@C60- periodic systems are studied with the use of the generalized Su-Schrieffer-Heeger model with respect to the intermolecular and intramolecular degrees of freedom. The charge distributions over the molecular surface and Jahn-Teller bond distortions of carbon atoms are calculated using the self-consistent iterative methods. Polarons formed in periodic 1D and 2D systems (chains and planar layers) as well as in dimer cluster system are examined. In the periodic systems polaron formation may be described by the cooperative Jahn-Teller effect. Orientation of the polarons on the molecule surface depends on the doping of the system, moreover, electron doping changes the energy levels in the system.

  8. Dimeric Labdane Diterpenes: Synthesis and Antiproliferative Effects

    Directory of Open Access Journals (Sweden)

    Guillermo Schmeda-Hirschmann

    2013-05-01

    Full Text Available Several diterpenes with the labdane skeleton show biological activity, including antiproliferative effects. Most of the research work on bioactive labdanes has been carried out on naturally occurring diterpenes and semisynthetic derivatives, but much less is known on the effects of diterpene dimers. The aim of the present work was to synthesize dimeric diterpenes from the labdane imbricatolic acid using esters, ethers and the triazole ring as linkers. Some 18 new derivatives were prepared and the compounds were evaluated for antiproliferative activity on human normal fibroblasts (MRC-5 and the following human tumor cell lines: AGS, SK-MES-1, J82 and HL-60. The diethers 8–10, differing in the number of CH2 units in the linker, presented better antiproliferative activity with a maximum effect for the derivative 9. The best antiproliferative effect against HL-60 cells was found for compounds 3 and 17, with IC50 values of 22.3 and 23.2 μM, lower than that found for the reference compound etoposide (2.23 μM. The compounds 9, 17 and 11 were the most active derivatives towards AGS cells with IC50 values of 17.8, 23.4 and 26.1 μM. A free carboxylic acid function seems relevant for the effect as several of the compounds showed less antiproliferative effect after methylation.

  9. Water dimer absorption of visible light

    Directory of Open Access Journals (Sweden)

    J. Hargrove

    2007-07-01

    Full Text Available Laboratory measurements of water vapor absorption using cavity ring-down spectroscopy revealed a broad absorption at 405 nm with a quadratic dependence on water monomer concentration, a similar absorption with a linear component at 532 nm, and only linear absorption at 570 nm in the vicinity of water monomer peaks. D2O absorption is weaker and linear at 405 nm. Van't Hoff plots constructed at 405.26 nm suggest that for dimerization, Keq=0.056±0.02 atm−1, ΔH°301 K=−16.6±2 kJ mol−1 and ΔS°301 K=−80±10 J mol−1 K−1. This transition peaks at 409.5 nm, could be attributed to the 8th overtone of water dimer and the 532 nm absorption to the 6th overtone. It is possible that some lower overtones previously searched for are less enhanced. These absorptions could increase water vapor feed back calculations leading to higher global temperature projections with currently projected greenhouse gas levels or greater cooling from greenhouse gas reductions.

  10. Modelling study of dimerization in mammalian defensins

    Directory of Open Access Journals (Sweden)

    Verma Chandra

    2006-12-01

    Full Text Available Abstract Background Defensins are antimicrobial peptides of innate immunity functioning by non-specific binding to anionic phospholipids in bacterial membranes. Their cationicity, amphipathicity and ability to oligomerize are considered key factors for their action. Based on structural information on human β-defensin 2, we examine homologous defensins from various mammalian species for conserved functional physico-chemical characteristics. Results Based on homology greater than 40%, structural models of 8 homologs of HBD-2 were constructed. A conserved pattern of electrostatics and dynamics was observed across 6 of the examined defensins; models backed by energetics suggest that the defensins in these 6 organisms are characterized by dimerization-linked enhanced functional potentials. In contrast, dimerization is not energetically favoured in the sheep, goat and mouse defensins, suggesting that they function efficiently as monomers. Conclusion β-defensin 2 from some mammals may work as monomers while those in others, including humans, work as oligomers. This could potentially be used to design human defensins that may be effective at lower concentrations and hence have therapeutic benefits.

  11. Viscosity and sedimentation behaviors of the magnetorheological suspensions with oleic acid/dimer acid as surfactants

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Jianjian; Yan, Hua; Hu, Zhide; Ding, Ding

    2016-11-01

    This work deals with the role of polar interactions on the viscosity and sedimentation behaviors of magnetorheological suspensions with micro-sized magnetic particles dispersed in oil carriers. The oleic acid and dimer acid were employed to make an adjustment of the hydrophobicity of iron particles, in the interest of performing a comparative evaluation of the contributions of the surface polarity. The viscosity tests show that the adsorbed surfactant layer may impose a hindrance to the movement of iron particles in the oil medium. The polar attractions between dimer acid covered particles gave rise to a considerable increase in viscosity, indicating flocculation structure developed in the suspensions. The observed plateau-like region in the vicinity of 0.1 s{sup −1} for MRF containing dimer acid is possibly due to the flocculation provoked by the carboxylic polar attraction, in which the structure is stable against fragmentation. Moreover, a quick recovery of the viscosity and a higher viscosity-temperature index also suggest the existence of particle-particle polar interaction in the suspensions containing dimer acid. The sedimentation measurements reveal that the steric repulsion of oleic acid plays a limited role in the stability of suspensions only if a large quantity of surfactant was used. The sedimentation results observed in the dimer acid covered particles confirm that loose and open flocculation was formed and enhanced sedimentation stability. - Highlights: • Surfactants were employed to make adjustments of the hydrophobicity of particles. • Polar attractions between particles increased the viscosity considerably. • Loose and open flocculation was formed in CI/DA suspension. • The steric repulsion of oleic acid played a limited role in the stability.

  12. Positioning of cysteine residues within the N-terminal portion of the BST-2/tetherin ectodomain is important for functional dimerization of BST-2.

    Science.gov (United States)

    Welbourn, Sarah; Kao, Sandra; Du Pont, Kelly E; Andrew, Amy J; Berndsen, Christopher E; Strebel, Klaus

    2015-02-06

    BST-2/tetherin is a cellular host factor capable of restricting the release of a variety of enveloped viruses, including HIV-1. Structurally, BST-2 consists of an N-terminal cytoplasmic domain, a transmembrane domain, an ectodomain, and a C-terminal membrane anchor. The BST-2 ectodomain encodes three cysteine residues in its N-terminal half, each of which can contribute to the formation of cysteine-linked dimers. We previously reported that any one of the three cysteine residues is sufficient to produce functional BST-2 dimers. Here we investigated the importance of cysteine positioning on the ectodomain for functional dimerization of BST-2. Starting with a cysteine-free monomeric form of BST-2, individual cysteine residues were reintroduced at various locations throughout the ectodomain. The resulting BST-2 variants were tested for expression, dimerization, surface presentation, and inhibition of HIV-1 virus release. We found significant flexibility in the positioning of cysteine residues, although the propensity to form cysteine-linked dimers generally decreased with increasing distance from the N terminus. Interestingly, all BST-2 variants, including the one lacking all three ectodomain cysteines, retained the ability to form non-covalent dimers, and all of the BST-2 variants were efficiently expressed at the cell surface. Importantly, not all BST-2 variants capable of forming cysteine-linked dimers were functional, suggesting that cysteine-linked dimerization of BST-2 is necessary but not sufficient for inhibiting virus release. Our results expose new structural constraints governing the functional dimerization of BST-2, a property essential to its role as a restriction factor tethering viruses to the host cell.

  13. Using dimers to measure biosignatures and atmospheric pressure for terrestrial exoplanets.

    Science.gov (United States)

    Misra, Amit; Meadows, Victoria; Claire, Mark; Crisp, Dave

    2014-02-01

    We present a new method to probe atmospheric pressure on Earth-like planets using (O2-O2) dimers in the near-infrared. We also show that dimer features could be the most readily detectable biosignatures for Earth-like atmospheres and may even be detectable in transit transmission with the James Webb Space Telescope (JWST). The absorption by dimers changes more rapidly with pressure and density than that of monomers and can therefore provide additional information about atmospheric pressures. By comparing the absorption strengths of rotational and vibrational features to the absorption strengths of dimer features, we show that in some cases it may be possible to estimate the pressure at the reflecting surface of a planet. This method is demonstrated by using the O2 A band and the 1.06 μm dimer feature, either in transmission or reflected spectra. It works best for planets around M dwarfs with atmospheric pressures between 0.1 and 10 bar and for O2 volume mixing ratios above 50% of Earth's present-day level. Furthermore, unlike observations of Rayleigh scattering, this method can be used at wavelengths longer than 0.6 μm and is therefore potentially applicable, although challenging, to near-term planet characterization missions such as JWST. We also performed detectability studies for JWST transit transmission spectroscopy and found that the 1.06 and 1.27 μm dimer features could be detectable (SNR>3) for an Earth analogue orbiting an M5V star at a distance of 5 pc. The detection of these features could provide a constraint on the atmospheric pressure of an exoplanet and serve as biosignatures for oxygenic photosynthesis. We calculated the required signal-to-noise ratios to detect and characterize O2 monomer and dimer features in direct imaging-reflected spectra and found that signal-to-noise ratios greater than 10 at a spectral resolving power of R=100 would be required.

  14. Small molecule and peptide-mediated inhibition of Epstein-Barr virus nuclear antigen 1 dimerization

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Sun Young; Song, Kyung-A [Samsung Advanced Institute for Health Sciences and Technology (SAIHST), Sungkyunkwan University School of Medicine, Seoul (Korea, Republic of); Samsung Biomedical Research Institute (SBRI), Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul (Korea, Republic of); Kieff, Elliott [Department of Medicine, Brigham and Women' s Hospital and Harvard Medical School, Boston, MA 02115 (United States); Kang, Myung-Soo, E-mail: mkang@skku.edu [Samsung Advanced Institute for Health Sciences and Technology (SAIHST), Sungkyunkwan University School of Medicine, Seoul (Korea, Republic of); Samsung Biomedical Research Institute (SBRI), Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul (Korea, Republic of); Department of Medicine, Brigham and Women' s Hospital and Harvard Medical School, Boston, MA 02115 (United States)

    2012-07-27

    Highlights: Black-Right-Pointing-Pointer Evidence that targeting EBNA1 dimer, an EBV onco-antigen, can be achievable. Black-Right-Pointing-Pointer A small molecule and a peptide as EBNA1 dimerization inhibitors identified. Black-Right-Pointing-Pointer Both inhibitors associated with EBNA1 and blocked EBNA1 DNA binding activity. Black-Right-Pointing-Pointer Also, prevented its dimerization, and repressed viral gene transcription. -- Abstract: Latent Epstein-Barr virus (EBV) infection is associated with human B cell lymphomas and certain carcinomas. EBV episome persistence, replication, and gene expression are dependent on EBV-encoded nuclear antigen 1 (EBNA1)'s DNA binding domain (DBD)/dimerization domain (DD)-mediated sequence-specific DNA binding activity. Homodimerization of EBNA1 is essential for EBNA1 DNA binding and transactivation. In this study, we characterized a novel small molecule EBNA1 inhibitor EiK1, screened from the previous high throughput screening (HTS). The EiK1 compound specifically inhibited the EBNA1-dependent, OriP-enhanced transcription, but not EBNA1-independent transcription. A Surface Plasmon Resonance Biacore assay revealed that EiK1 associates with EBNA1 amino acid 459-607 DBD/DD. Consistent with the SPR data, in vitro gel shift assays showed that EiK1 suppressed the activity of EBNA1 binding to the cognate familial repeats (FR) sequence, but not control RBP-J{kappa} binding to the J{kappa} site. Subsequently, a cross-linker-mediated in vitro multimerization assay and EBNA1 homodimerization-dependent yeast two-hybrid assay showed that EiK1 significantly inhibited EBNA1 dimerization. In an attempt to identify more highly specific peptide inhibitors, small peptides encompassing the EBNA1 DBD/DD were screened for inhibition of EBNA1 DBD-mediated DNA binding function. The small peptide P85, covering EBNA1 a.a. 560-574, significantly blocked EBNA1 DNA binding activity in vitro, prevented dimerization in vitro and in vivo, associated

  15. Exact Solution of a Generalized Nonlinear Schrodinger Equation Dimer

    DEFF Research Database (Denmark)

    Christiansen, Peter Leth; Maniadis, P.; Tsironis, G.P.

    1998-01-01

    We present exact solutions for a nonlinear dimer system defined throught a discrete nonlinear Schrodinger equation that contains also an integrable Ablowitz-Ladik term. The solutions are obtained throught a transformation that maps the dimer into a double Sine-Gordon like ordinary nonlinear...... differential equation....

  16. Synthesis of novel organo-phosphorus C60 dimers

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    Carbon bridged organophosphorus C60 dimers were obtained by the reaction of aminome- thylenebisphosphonate anion with C60 and fully characterized by 1HNMR, 31PNMR, 13CNMR, FT- MALDI-MS, FT-IR, UV-Vis, DEPT and HMBC, and the dimeric compounds undergo hydrolysis by using TMSI.

  17. Local field enhancement: comparing self-similar and dimer nanoantennas

    CERN Document Server

    Pellegrini, Giovanni; Finazzi, Marco; Biagioni, Paolo

    2016-01-01

    We study the local field enhancement properties of self-similar nanolenses and compare the obtained results with the performance of standard dimer nanoantennas. We report that, despite the additional structural complexity, self-similar nanolenses are unable to provide significant improvements over the field enhancement performance of standard plasmonic dimers.

  18. Synthesis,Characterization,and Electrochemical Property of Nanometer Porphyrin Dimer

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    A nanometer porphyrin dimer was synthesized with fumaryl chloride as a bridge-linked reagent. The characterization was carried out with elemental analyses, 1H NMR, UV-Vis, and IR spectrometries, and then the electrochemical properties of the porphyrins were studied. The authors found that there was moderate electronic communication between the two porphyrin rings in the nanometer porphyrin dimer.

  19. LRP1 Modulates APP Intraneuronal Transport and Processing in Its Monomeric and Dimeric State

    Directory of Open Access Journals (Sweden)

    Claus U. Pietrzik

    2017-04-01

    Full Text Available The low-density lipoprotein receptor-related protein 1, LRP1, interacts with APP and affects its processing. This is assumed to be mostly caused by the impact of LRP1 on APP endocytosis. More recently, also an interaction of APP and LRP1 early in the secretory pathway was reported whereat retention of LRP1 in the ER leads to decreased APP cell surface levels and in turn, to reduced Aβ secretion. Here, we extended the biochemical and immunocytochemical analyses by showing via live cell imaging analyses in primary neurons that LRP1 and APP are transported only partly in common (one third but to a higher degree in distinct fast axonal transport vesicles. Interestingly, co-expression of LRP1 and APP caused a change of APP transport velocities, indicating that LRP1 recruits APP to a specific type of fast axonal transport vesicles. In contrast lowered levels of LRP1 facilitated APP transport. We further show that monomeric and dimeric APP exhibit similar transport characteristics and that both are affected by LRP1 in a similar way, by slowing down APP anterograde transport and increasing its endocytosis rate. In line with this, a knockout of LRP1 in CHO cells and in primary neurons caused an increase of monomeric and dimeric APP surface localization and in turn accelerated shedding by meprin β and ADAM10. Notably, a choroid plexus specific LRP1 knockout caused a much higher secretion of sAPP dimers into the cerebrospinal fluid compared to sAPP monomers. Together, our data show that LRP1 functions as a sorting receptor for APP, regulating its cell surface localization and thereby its processing by ADAM10 and meprin β, with the latter exhibiting a preference for APP in its dimeric state.

  20. LRP1 Modulates APP Intraneuronal Transport and Processing in Its Monomeric and Dimeric State.

    Science.gov (United States)

    Herr, Uta-Mareike; Strecker, Paul; Storck, Steffen E; Thomas, Carolin; Rabiej, Verena; Junker, Anne; Schilling, Sandra; Schmidt, Nadine; Dowds, C Marie; Eggert, Simone; Pietrzik, Claus U; Kins, Stefan

    2017-01-01

    The low-density lipoprotein receptor-related protein 1, LRP1, interacts with APP and affects its processing. This is assumed to be mostly caused by the impact of LRP1 on APP endocytosis. More recently, also an interaction of APP and LRP1 early in the secretory pathway was reported whereat retention of LRP1 in the ER leads to decreased APP cell surface levels and in turn, to reduced Aβ secretion. Here, we extended the biochemical and immunocytochemical analyses by showing via live cell imaging analyses in primary neurons that LRP1 and APP are transported only partly in common (one third) but to a higher degree in distinct fast axonal transport vesicles. Interestingly, co-expression of LRP1 and APP caused a change of APP transport velocities, indicating that LRP1 recruits APP to a specific type of fast axonal transport vesicles. In contrast lowered levels of LRP1 facilitated APP transport. We further show that monomeric and dimeric APP exhibit similar transport characteristics and that both are affected by LRP1 in a similar way, by slowing down APP anterograde transport and increasing its endocytosis rate. In line with this, a knockout of LRP1 in CHO cells and in primary neurons caused an increase of monomeric and dimeric APP surface localization and in turn accelerated shedding by meprin β and ADAM10. Notably, a choroid plexus specific LRP1 knockout caused a much higher secretion of sAPP dimers into the cerebrospinal fluid compared to sAPP monomers. Together, our data show that LRP1 functions as a sorting receptor for APP, regulating its cell surface localization and thereby its processing by ADAM10 and meprin β, with the latter exhibiting a preference for APP in its dimeric state.

  1. Loop groups, Clusters, Dimers and Integrable systems

    CERN Document Server

    Fock, V V

    2014-01-01

    We describe a class of integrable systems on Poisson submanifolds of the affine Poisson-Lie groups $\\widehat{PGL}(N)$, which can be enumerated by cyclically irreducible elements the co-extended affine Weyl groups $(\\widehat{W}\\times \\widehat{W})^\\sharp$. Their phase spaces admit cluster coordinates, whereas the integrals of motion are cluster functions. We show, that this class of integrable systems coincides with the constructed by Goncharov and Kenyon out of dimer models on a two-dimensional torus and classified by the Newton polygons. We construct the correspondence between the Weyl group elements and polygons, demonstrating that each particular integrable model admits infinitely many realisations on the Poisson-Lie groups. We also discuss the particular examples, including the relativistic Toda chains and the Schwartz-Ovsienko-Tabachnikov pentagram map.

  2. Pseudo-two-dimensional random dimer lattices

    Energy Technology Data Exchange (ETDEWEB)

    Naether, U., E-mail: naether@unizar.es [Instituto de Ciencia de Materiales de Aragón and Departamento de Física de la Materia Condensada, CSIC – Universidad de Zaragoza, 50009 Zaragoza (Spain); Mejía-Cortés, C.; Vicencio, R.A. [Departamento de Física and MSI – Nucleus for Advanced Optics, Center for Optics and Photonics (CEFOP), Facultad de Ciencias, Universidad de Chile, Santiago (Chile)

    2015-06-05

    We study the long-time wave transport in correlated and uncorrelated disordered 2D arrays. When a separation of dimensions is applied to the model, we find that the previously predicted 1D random dimer phenomenology also appears in so-called pseudo-2D arrays. Therefore, a threshold behavior is observed in terms of the effective size for eigenmodes, as well as in long-time dynamics. A minimum system size is required to observe this threshold, which is very important when considering a possible experimental realization. For the long-time evolution, we find that for correlated lattices a super-diffusive long-range transport is observed. For completely uncorrelated disorder 2D transport becomes sub-diffusive within the localization length and for random binary pseudo-2D arrays localization is observed.

  3. Dimerization and oligomerization of the chaperone calreticulin

    DEFF Research Database (Denmark)

    Jørgensen, Charlotte S; Ryder, L Rebekka; Steinø, Anne;

    2003-01-01

    protein. Using PAGE, urea gradient gel electrophoresis, capillary electrophoresis and MS, we show that dimerization through the SH group can be induced by lowering the pH to 5-6, heating, or under conditions that favour partial unfolding such as urea concentrations above 2.6 m or SDS concentrations above...... 0.025%. Moreover, we show that calreticulin also has the ability to self-oligomerize through noncovalent interactions at urea concentrations above 2.6 m at pH below 4.6 or above pH 10, at temperatures above 40 degrees C, or in the presence of high concentrations of organic solvents (25%), conditions...... urea or 1% SDS, and heat-induced oligomerization could be inhibited by 8 m urea or 1% SDS when present during heating. Comparison of the binding properties of monomeric and oligomeric calreticulin in solid-phase assays showed increased binding to peptides and denatured proteins when calreticulin...

  4. Edge Magnon Excitation in Spin Dimer Systems

    Science.gov (United States)

    Sakaguchi, Ryo; Matsumoto, Masashige

    2016-10-01

    Magnetic excitation in a spin dimer system on a bilayer honeycomb lattice is investigated in the presence of a zigzag edge, where disordered and ordered phases can be controlled by a quantum phase transition. In analogy with the case of graphene with a zigzag edge, a flat edge magnon mode appears in the disordered phase. In an ordered phase, a finite magnetic moment generates a mean-field potential to the magnon. Since the potential is nonuniform on the edge and bulk sites, it affects the excitation, and the dispersion of the edge mode deviates from the flat shape. We investigate how the edge magnon mode evolves when the phase changes through the quantum phase transition and discuss the similarities to ordered spin systems on a monolayer honeycomb lattice.

  5. The EBNA-2 N-Terminal Transactivation Domain Folds into a Dimeric Structure Required for Target Gene Activation.

    Directory of Open Access Journals (Sweden)

    Anders Friberg

    2015-05-01

    Full Text Available Epstein-Barr virus (EBV is a γ-herpesvirus that may cause infectious mononucleosis in young adults. In addition, epidemiological and molecular evidence links EBV to the pathogenesis of lymphoid and epithelial malignancies. EBV has the unique ability to transform resting B cells into permanently proliferating, latently infected lymphoblastoid cell lines. Epstein-Barr virus nuclear antigen 2 (EBNA-2 is a key regulator of viral and cellular gene expression for this transformation process. The N-terminal region of EBNA-2 comprising residues 1-58 appears to mediate multiple molecular functions including self-association and transactivation. However, it remains to be determined if the N-terminus of EBNA-2 directly provides these functions or if these activities merely depend on the dimerization involving the N-terminal domain. To address this issue, we determined the three-dimensional structure of the EBNA-2 N-terminal dimerization (END domain by heteronuclear NMR-spectroscopy. The END domain monomer comprises a small fold of four β-strands and an α-helix which form a parallel dimer by interaction of two β-strands from each protomer. A structure-guided mutational analysis showed that hydrophobic residues in the dimer interface are required for self-association in vitro. Importantly, these interface mutants also displayed severely impaired self-association and transactivation in vivo. Moreover, mutations of solvent-exposed residues or deletion of the α-helix do not impair dimerization but strongly affect the functional activity, suggesting that the EBNA-2 dimer presents a surface that mediates functionally important intra- and/or intermolecular interactions. Our study shows that the END domain is a novel dimerization fold that is essential for functional activity. Since this specific fold is a unique feature of EBNA-2 it might provide a novel target for anti-viral therapeutics.

  6. Acoustic Type-II Weyl Nodes from Stacking Dimerized Chains

    Science.gov (United States)

    Yang, Zhaoju; Zhang, Baile

    2016-11-01

    Lorentz-violating type-II Weyl fermions, which were missed in Weyl's prediction of nowadays classified type-I Weyl fermions in quantum field theory, have recently been proposed in condensed matter systems. The semimetals hosting type-II Weyl fermions offer a rare platform for realizing many exotic physical phenomena that are different from type-I Weyl systems. Here we construct the acoustic version of a type-II Weyl Hamiltonian by stacking one-dimensional dimerized chains of acoustic resonators. This acoustic type-II Weyl system exhibits distinct features in a finite density of states and unique transport properties of Fermi-arc-like surface states. In a certain momentum space direction, the velocity of these surface states is determined by the tilting direction of the type-II Weyl nodes rather than the chirality dictated by the Chern number. Our study also provides an approach of constructing acoustic topological phases at different dimensions with the same building blocks.

  7. Preparation of gold nanoparticle dimers via streptavidin-induced interlinking

    Energy Technology Data Exchange (ETDEWEB)

    Zon, Vera B.; Sachsenhauser, Matthias; Rant, Ulrich, E-mail: rant@wsi.tum.de [Technische Universitaet Muenchen, Walter Schottky Institut (Germany)

    2013-10-15

    There is great interest in establishing efficient means of organizing nanoparticles into complex structures, especially in fields like nano-optical devices. One of the demonstrated routes uses biomolecular scaffolds, like the streptavidin-biotin system, to deterministically separate and structure particle complexes. However, controlled formation of streptavidin-linked nanoparticle dimers or trimers is challenging, and large aggregates are often formed under conditions that are difficult to regulate. Here, we studied the aggregates and interlinking kinetics of biotin-functionalized 20 nm gold nanoparticles in the presence of the interlinking protein, streptavidin. We found two different protein-linker concentration regions where small stable particle aggregates are formed: when the protein and nanoparticle concentrations are similar and when the protein to nanoparticle concentration ratio exceeds intermediate concentrations (10:1-100:1) that promote precipitation of large aggregates. We attribute this behavior to the limited availability of free-linker molecules and the limited availability of free ligand (biotin) on the particle surface for low and high protein concentrations, respectively. Furthermore, we show that the product can be additionally enriched up to 25 % through either centrifugation in sucrose or size-exclusion chromatography. These results provide additional understanding into the assembly of ligand-functionalized nanoparticles with water-soluble linkers and provide a facile way to produce well-defined small aggregates for potential use in, for instance, surface-enhanced spectroscopy.

  8. Roughness effect on the efficiency of dimer antenna based biosensor

    Directory of Open Access Journals (Sweden)

    Dominique Barchiesi

    2012-08-01

    Full Text Available The fabrication process of nanodevices is continually improved. However, most of the nanodevices, such as biosensors present rough surfaces with mean roughness of some nanometers even if the deposition rate of material is more controlled. The effect of roughness on performance of biosensors was fully addressed for plane biosensors and gratings, but rarely addressed for biosensors based on Local Plasmon Resonance. The purpose of this paper is to evaluate numerically the influence of nanometric roughness on the efficiency of a dimer nano-biosensor (two levels of roughness are considered. Therefore, we propose a general numerical method, that can be applied to any other nanometric shape, to take into account the roughness in a three dimensional model. The study focuses on both the far-field, which corresponds to the experimental detected data, and the near-field, responsible for exciting and then detecting biological molecules. The results suggest that the biosensor efficiency is highly sensitive to the surface roughness. The roughness can produce important shifts of the extinction efficiency peak and a decrease of its amplitude resulting from changes in the distribution of near-field and absorbed electric field intensities.

  9. Molecular Dynamics Simulation of Amyloid Beta Dimer Formation

    CERN Document Server

    Urbanc, B; Ding, F; Sammond, D; Khare, S; Buldyrev, S V; Stanley, H E; Dokholyan, N V

    2004-01-01

    Recent experiments with amyloid-beta (Abeta) peptide suggest that formation of toxic oligomers may be an important contribution to the onset of Alzheimer's disease. The toxicity of Abeta oligomers depends on their structure, which is governed by assembly dynamics. Due to limitations of current experimental techniques, a detailed knowledge of oligomer structure at the atomic level is missing. We introduce a molecular dynamics approach to study Abeta dimer formation: (1) we use discrete molecular dynamics simulations of a coarse-grained model to identify a variety of dimer conformations, and (2) we employ all-atom molecular mechanics simulations to estimate the thermodynamic stability of all dimer conformations. Our simulations of a coarse-grained Abeta peptide model predicts ten different planar beta-strand dimer conformations. We then estimate the free energies of all dimer conformations in all-atom molecular mechanics simulations with explicit water. We compare the free energies of Abeta(1-42) and Abeta(1-40...

  10. Metal membrane with dimer slots as a universal polarizer

    DEFF Research Database (Denmark)

    Zhukovsky, Sergei; Zalkovskij, Maksim; Malureanu, Radu

    2014-01-01

    In this work, we show theoretically and confirm experimentally that thin metal membranes patterned with an array of slot dimers (or their Babinet analogue with metal rods) can function as a versatile spectral and polarization filter. We present a detailed covariant multipole theory...... for the electromagnetic response of an arbitrary dimer based on the Green functions approach. The theory confirms that a great variety of polarization properties, such as birefringence, chirality and elliptical dichroism, can be achieved in a metal layer with such slot-dimer patterning (i.e. in a metasurface). Optical...... properties of the metasurface can be extensively tuned by varying the geometry (shape and dimensions) of the dimer, for example, by adjusting the sizes and mutual placement of the slots (e.g. inter-slot distance and alignment angle). Three basic shapes of dimers are analyzed: II-shaped (parallel slots), V...

  11. Dehydrogenative silane coupling on silicon surfaces via early transition metal catalysis.

    Science.gov (United States)

    Li, Yun-Hui; Buriak, Jillian M

    2006-02-01

    Derivatization of silicon surfaces is an area of intense interest due to the centrality of silicon in the microelectronics industry and because of potential promise for a myriad of other applications. In this paper, we investigate the feasibility of Si-Si bond formation directly on the surface to contrast with the more widely studied Si-C and Si-O bond forming reactions. Functionalization of hydride-terminated silicon surfaces with silanes is carried out via early transition metal mediated dehydrogenative silane coupling reactions. Zirconocene and titanocene catalyst systems were evaluated for heterocoupling of a molecular silane, RSiH3, with a surface Si-H group on Si(s). The zirconocene catalysts proved to be much more reactive than the titanium system, and so the former was examined exclusively. The silanes, aromatic or aliphatic, are bonded to the silicon surface through direct Si-Si bonds, although the level of incorporation of the trihydroarylsilanes was substantially higher than that of the aliphatic silanes. The reaction proceeds on nanocrystalline hydride-terminated porous silicon surfaces, as well as flat Si(100)-H(x) and Si(111)-H interfaces. The reactions were studied by a variety of techniques, including FTIR, SIMS, and XPS.

  12. Inequivalent models of irreversible dimer filling: Transition state'' dependence

    Energy Technology Data Exchange (ETDEWEB)

    Nord, R.S. (Department of Chemistry, Eastern Michigan University, Ypsilanti, MI (USA)); Evans, J.W. (Ames Laboratory, Ames IA (USA) Department of Physics, Iowa State Univ., Ames, IA (USA) Department of Mathematics, Iowa State Univ., Ames, IA (USA))

    1990-12-01

    Irreversible adsorption of diatomics on crystalline surfaces is sometimes modeled as random dimer filling of adjacent pairs of sites on a lattice. We note that this process can be implemented in two distinct ways: (i) randomly pick adjacent pairs of sites, {ital jj}{prime}, and fill {ital jj}{prime} only if both are empty (horizontal transition state); or (ii) randomly pick a single site, {ital j}, and if {ital j} and at least one neighbor are empty, then fill {ital j} and a randomly chosen empty neighbor (vertical transition state). Here it is instructive to consider processes which also include competitive random monomer filling of single sites. We find that although saturation (partial) coverages differ little between the models for pure dimer filling, there is a significant difference for comparable monomer and dimer filling rates. We present exact results for saturation coverage behavior for a linear lattice, and estimates for a square lattice. Ramifications for simple models of CO oxidation on surfaces are indicated.

  13. Theoretical analysis of the S{sub 2}←S{sub 0} vibronic spectrum of the 2-pyridone dimer

    Energy Technology Data Exchange (ETDEWEB)

    Kopec, Sabine; Köppel, Horst [Theoretische Chemie, Physikalisch-Chemisches Institut, Universität Heidelberg, Im Neuenheimer Feld 229, D-69120 Heidelberg (Germany)

    2016-01-14

    The interplay between excitonic and vibronic coupling in hydrogen-bonded molecular dimers leads to complex spectral structures and other intriguing phenomena such as a quenching of the excitonic energy splitting. We recently extended our analysis from that of the quenching mechanism to the theoretical investigation of the complete vibronic spectrum for the ortho-cyanophenol dimer. We now apply the same approach to the vibronic spectrum of the 2-pyridone dimer and discuss the assignment of vibronic lines to gain insight into the underlying coupling mechanism. This is based on potential energy surfaces obtained at the RI-CC2/aug-cc-pVTZ level. They are used for the dynamical analysis in the framework of a multi-mode vibronic coupling approach. The theoretical results based on the quadratic vibronic coupling model are found to be in good agreement with the experimental resonant two-photon ionization spectrum.

  14. Properties and metathesis activity of monomeric and dimeric Mo centres variously located on γ-alumina A DFT study

    Science.gov (United States)

    Handzlik, Jarosław

    2007-05-01

    Ethene metathesis proceeding on monomeric and dimeric Mo species on the (1 0 0) and (1 1 0) γ-alumina is investigated by density functional theory, applying the cluster approach. The calculated vibrational frequencies of the surface OH groups are assigned to the experimental IR bands. It is shown that both monomeric and dimeric Mo forms can be the active sites of olefin metathesis. Metathesis activity and stability of the Mo-methylidene centres depend on their location on alumina. The differences in the sites reactivity are explained on the basis of their geometrical and electronic structure parameters. For the monomeric centres, isomerisation of the trigonal bipyramidal intermediate to the stable square pyramidal molybdacyclobutane is kinetically favoured over the cycloreversal step. The situation is opposite in the case of the dimeric species.

  15. Electronic structure of alloxan and its dimers: QM/QD simulations and quantum chemical topology analysis.

    Science.gov (United States)

    Allehyani, Basmah H; Elroby, Shaaban A; Aziz, Saadalluh G; Hilal, Rifaat H

    2015-01-01

    This study aims to identify the origin of the extra stability of alloxan, a biologically active pyrimidine. To achieve this goal, detailed DFT computations and quantum dynamics simulations have been performed to establish the most stable conformation and the global minimum structure on the alloxan potential energy surface. The effects of the solvent, basis set, and DFT method have been examined to validate the theoretical model adopted throughout the work. Two non-covalent intermolecular dimers of alloxan, the H-bonded and dipolar dimers, have been investigated at the ωB97X-D and M06-2X levels of theory using the triple zeta 6-311++G** to establish their relative stability. Quantum chemical topology features and natural bond orbital analysis (NBO) have been performed to identify and characterize the forces that govern the structures and underlie the extra stability of alloxan.

  16. An asymmetric dimer in a periodic potential: a minimal model for friction of graphene flakes

    Science.gov (United States)

    Hens, Remco; Fasolino, Annalisa

    2016-07-01

    We discuss the friction and motion of a model of a dimer with asymmetric interactions with a substrate potential. Starting from the consideration that a rigid dimer with spacing equal to half of the period of the potential has exactly zero static friction like the infinite incommensurate Frenkel Kontorova model, we show how stick-slip behaviour and friction arise as a function of asymmetry. We argue that this model can yield a simple yet insightful description of the frictional behaviour of graphene flakes on graphite and of superlubricity. The results can also be of interest for diatomic molecules on surfaces. Supplementary material in the form of three mp4 files available from the Journal web page at http://dx.doi.org/10.1140/epjb/e2016-70273-5

  17. Threshold electron attachment and electron impact ionization involving oxygen dimers

    Science.gov (United States)

    Kreil, J.; Ruf, M.-W.; Hotop, H.; Ettischer, I.; Buck, U.

    1998-12-01

    Using two different crossed-beams machines we have carried out the first quantitative study of threshold electron attachment and electron impact-induced ionization and fragmentation involving oxygen dimers (O 2) 2. In the electron attachment experiment we study electron transfer from state-selected Ar **(20d) Rydberg atoms to O 2 molecules and dimers in a skimmed supersonic beam at variable nozzle temperatures ( T0) and stagnation pressures ( p0). The relative dimer density is determined through measurements of Penning ionization by metastable Ne *(3s 3P2,0) atoms and used to estimate the absolute cross-section for O 2- formation in collisions of Ar **(20d) Rydberg atoms with O 2 dimers to be nearly 10 -17 m 2, almost four orders of magnitude larger than that for O 2- formation in collisions of Ar **(20d) Rydberg atoms with O 2 monomers. The fragmentation of the oxygen cluster beam is quantitatively characterized by the transverse helium beam scattering method which allows us to spatially separate different clusters. It is shown that in 70 eV electron impact of (O 2) 2 only 3.6(4)% of the dimers are detected as dimer ions (O 2) 2+. In additional experiments involving SF 6 clusters we show that SF 6 dimers fragment nearly completely upon 70 eV electron impact, yielding SF 5+ ions (probability for (SF 6)·SF 5+ production at most 0.3%).

  18. Stochastic optimization-based study of dimerization kinetics

    Indian Academy of Sciences (India)

    Srijeeta Talukder; Shrabani Sen; Ralf Metzler; Suman K Banik; Pinaki Chaudhury

    2013-11-01

    We investigate the potential of numerical algorithms to decipher the kinetic parameters involved in multi-step chemical reactions. To this end, we study dimerization kinetics of protein as a model system. We follow the dimerization kinetics using a stochastic simulation algorithm and combine it with three different optimization techniques (genetic algorithm, simulated annealing and parallel tempering) to obtain the rate constants involved in each reaction step. We find good convergence of the numerical scheme to the rate constants of the process. We also perform a sensitivity test on the reaction kinetic parameters to see the relative effects of the parameters for the associated profile of the monomer/dimer distribution.

  19. Circular dimers of lambda DNA in infected, nonlysogenic Escherichia coli

    Energy Technology Data Exchange (ETDEWEB)

    Freifelder, D.; Baran, N.; Folkmanis, A.; Freifelder, D.L.R.

    1977-09-01

    Covalently closed circular dimerss of phage lambda DNA have been found in Escherichia coli infected with lambda. These dimers can be formed by either the lambda Red or Int systems, by a nonrecombinational replicative mechanism requiring the activity of the lambda O and P genes or by joining of the cohesive ends. Dimers mediated by the E. coli Rec system have not been observed. Those formed by the Int system often result from recombination between different DNA molecules; however, the Red-mediated dimer may be a result of replicative extension of a single DNA molecule. Trimers have also been observed but studied only briefly.

  20. Time resolved structural dynamics of butadiyne-linked porphyrin dimers.

    Science.gov (United States)

    Camargo, Franco V A; Hall, Christopher R; Anderson, Harry L; Meech, Stephen R; Heisler, Ismael A

    2016-03-01

    In this work, the timescales and mechanisms associated with the structural dynamics of butadiyne-linked porphyrin dimers are investigated through time resolved narrowband pump/broadband probe transient absorption spectroscopy. Our results confirm previous findings that the broadening is partly due to a distribution of structures with different (dihedral) angular conformations. Comparison of measurements with excitations on the red and blue sides of the Q-band unravel the ground and excited state conformational re-equilibration timescales. Further comparison to a planarized dimer, through the addition of a ligand, provides conclusive evidence for the twisting motion performed by the porphyrin dimer in solution.

  1. Time resolved structural dynamics of butadiyne-linked porphyrin dimers

    Directory of Open Access Journals (Sweden)

    Franco V. A. Camargo

    2016-03-01

    Full Text Available In this work, the timescales and mechanisms associated with the structural dynamics of butadiyne-linked porphyrin dimers are investigated through time resolved narrowband pump/broadband probe transient absorption spectroscopy. Our results confirm previous findings that the broadening is partly due to a distribution of structures with different (dihedral angular conformations. Comparison of measurements with excitations on the red and blue sides of the Q-band unravel the ground and excited state conformational re-equilibration timescales. Further comparison to a planarized dimer, through the addition of a ligand, provides conclusive evidence for the twisting motion performed by the porphyrin dimer in solution.

  2. Multicritical tensor models and hard dimers on spherical random lattices

    CERN Document Server

    Bonzom, Valentin

    2012-01-01

    Random tensor models which display multicritical behaviors in a remarkably simple fashion are presented. They come with entropy exponents \\gamma = (m-1)/m, similarly to multicritical random branched polymers. Moreover, they are interpreted as models of hard dimers on a set of random lattices for the sphere in dimension three and higher. Dimers with their exclusion rules are generated by the different interactions between tensors, whose coupling constants are dimer activities. As an illustration, we describe one multicritical point, which is interpreted as a transition between the dilute phase and a crystallized phase, though with negative activities.

  3. How to use D-dimer in acute cardiovascular care

    DEFF Research Database (Denmark)

    Giannitsis, Evangelos; Mair, Johannes; Christersson, Christina

    2015-01-01

    D-dimer testing is important to aid in the exclusion of venous thromboembolic events (VTEs), including deep venous thrombosis and pulmonary embolism, and it may be used to evaluate suspected aortic dissection. D-dimer is produced upon activation of the coagulation system with the generation and s...... testing. For the exclusion of pulmonary embolism/deep vein thrombosis, age-adjusted cut-offs are recommend. Clinicians must be aware of the validated use of their hospital's D-dimer assay to avoid inappropriate use of this biomarker in routine care....

  4. Third-Order Optical Nonlinearity in Novel Porphyrin Dimers

    Institute of Scientific and Technical Information of China (English)

    PEI Song-Hao; ZHAO Da-Peng; ZHANG Wei; ZHENG Wen-Qi; WANG Xing-Qiao; PENG Wei-Xian; SHI Guang; SONG Ying-Lin

    2008-01-01

    @@ We investigate the third-order optical nonlinearities in four novel porphyrin dimers (directs A to I)) and a monomeric porphyrin H2 CPTPP measured by using the single-beam z-scan technique with a pulsed Q-switched Nd:YAG nanosecond laser at 532nm.All the samples show strong excited state absorption (ESA) and high value of X(3) in the ns domain at this wavelength.We perform a comparison between dimer A and its monomer H2 CPTPP in their third-order optical nonlinearity, and discuss the relationships between the values of X(3) and the different bridging groups for all the dimers.

  5. Smectic Phase Formed by DNA Dimers

    Science.gov (United States)

    Salamonczyk, Miroslaw; Gleeson, James; Jakli, Antal; Sprunt, Samuel; Dhont, Jan; Stiakakis, Emmanuel

    The rapidly expanding bio market is driving the development and characterization of new multifunctional materials. In particular, nucleic acids are under intense study for gene therapy, drug delivery and other bio-safe applications [1,2,3]. DNA is well-known to form a cholesteric nematic liquid crystal in its native form; however, much recent research has focused on self-assembly and mesomorphic behavior in concentrated solutions of short DNA helices [4]. Our work focuses on DNA dimers, consisting of 48 base-pair double-stranded helices connected by a 5 to 20 base flexible single strand, and suspended in a natural buffer. Depending on temperature, concentration and length of the flexible spacer, polarizing optical microscopy and small angle x-ray scattering reveal cholesteric nematic and, remarkably, smectic liquid crystalline phases. A model for smectic phase formation in this system will be presented. 1] J.-L. Lim et al., Int. J. of. Pharm. 490 (2015) 2652] D.-H. Kim et al., Nature Biotech. 23 (2005) 2223] K. Liu et al., Chem. Eur. J. 21 (2015) 48984] M. Nakata et al., Science 318 (2007) 1276 NSF DMR 1307674.

  6. Solution structure of the dimerization domain of the eukaryotic stalk P1/P2 complex reveals the structural organization of eukaryotic stalk complex.

    Science.gov (United States)

    Lee, Ka-Ming; Yu, Conny Wing-Heng; Chiu, Teddy Yu-Hin; Sze, Kong-Hung; Shaw, Pang-Chui; Wong, Kam-Bo

    2012-04-01

    The lateral ribosomal stalk is responsible for the kingdom-specific binding of translation factors and activation of GTP hydrolysis during protein synthesis. The eukaryotic stalk is composed of three acidic ribosomal proteins P0, P1 and P2. P0 binds two copies of P1/P2 hetero-dimers to form a pentameric P-complex. The structure of the eukaryotic stalk is currently not known. To provide a better understanding on the structural organization of eukaryotic stalk, we have determined the solution structure of the N-terminal dimerization domain (NTD) of P1/P2 hetero-dimer. Helix-1, -2 and -4 from each of the NTD-P1 and NTD-P2 form the dimeric interface that buries 2200 A(2) of solvent accessible surface area. In contrast to the symmetric P2 homo-dimer, P1/P2 hetero-dimer is asymmetric. Three conserved hydrophobic residues on the surface of NTD-P1 are replaced by charged residues in NTD-P2. Moreover, NTD-P1 has an extra turn in helix-1, which forms extensive intermolecular interactions with helix-1 and -4 of NTD-P2. Truncation of this extra turn of P1 abolished the formation of P1/P2 hetero-dimer. Systematic truncation studies suggest that P0 contains two spine-helices that each binds one copy of P1/P2 hetero-dimer. Modeling studies suggest that a large hydrophobic cavity, which can accommodate the loop between the spine-helices of P0, can be found on NTD-P1 but not on NTD-P2 when the helix-4 adopts an 'open' conformation. Based on the asymmetric properties of NTD-P1/NTD-P2, a structural model of the eukaryotic P-complex with P2/P1:P1/P2 topology is proposed.

  7. Metallothionein dimers studied by nano-spray mass spectrometry.

    Science.gov (United States)

    Hathout, Yetrib; Reynolds, Kristy J; Szilagyi, Zoltan; Fenselau, Catherine

    2002-01-15

    Both transient and stable dimers of metallothionein have been characterized, based on earlier studies using NMR, circular dichroism and size-exclusion chromatography. Here additional characterization is provided by nanospray mass spectrometry. Rapid redistribution of metal ions between monomeric Cd7- and Zn7-metallothionein 2a is monitored by nanospray. An experiment in which theses two forms of the monomeric protein are separated by a dialysis membrane, which will pass metal ions but not proteins, confirms that a transient dimer must form for metal ions to be redistributed. On the other hand, size-exclusion chromatography of reconstituted Zn7- or Cd7-metallothionein revealed the presence of monomeric and dimeric species. These dimers do not equilibrate readily to form monomers and they are shown to be covalent.

  8. 21 CFR 176.120 - Alkyl ketene dimers.

    Science.gov (United States)

    2010-04-01

    ... derived from the fatty acids of animal or vegetable fats and oils. (b) The alkyl ketene dimers are used as... HUMAN CONSUMPTION (CONTINUED) INDIRECT FOOD ADDITIVES: PAPER AND PAPERBOARD COMPONENTS Substances...

  9. [Antioxidant and antibacterial activities of dimeric phenol compounds].

    Science.gov (United States)

    Ogata, Masahiro

    2008-08-01

    We studied the antioxidant and antibacterial activities of monomeric and dimeric phenol compounds. Dimeric compounds had higher antioxidant activities than monomeric compounds. Electron spin resonance spin-trapping experiments showed that phenol compounds with an allyl substituent on their aromatic rings directly scavenged superoxide, and that only eugenol trapped hydroxyl radicals. We developed a generation system of the hydroxyl radical without using any metals by adding L-DOPA and DMPO to PBS or MiliQ water in vitro. We found that eugenol trapped hydroxyl radicals directly and is metabolized to a dimer. On the other hand, dipropofol, a dimer of propofol, has strong antibacterial activity against Gram-positive bacteria. However, it lacks solubility in water and this property is assumed to limit its efficacy. We tried to improve the solubility and found a new solubilization method of dipropofol in water with the addition of a monosaccharide or ascorbic acid.

  10. Gnetuhainin S, a New Resveratrol Dimer from Gnetum hainanense

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    Gnetuhainin S, a new resveratrol dimer, was isolated from the lianas of Gnetum hainanense C. Y. Cheng. Its structure and relative configuration were established on the basis of spectroscopic evidence.

  11. UV spectra of benzene isotopomers and dimers in helium nanodroplets

    Science.gov (United States)

    Schmied, Roman; ćarçabal, Pierre; Dokter, Adriaan M.; Lonij, Vincent P. A.; Lehmann, Kevin K.; Scoles, Giacinto

    2004-08-01

    We report spectra of various benzene isotopomers and their dimers in helium nanodroplets in the region of the first Herzberg-Teller allowed vibronic transition 601 1B2u←1A1g (the A00 transition) at ˜260 nm. Excitation spectra have been recorded using both beam depletion detection and laser-induced fluorescence. Unlike for many larger aromatic molecules, the monomer spectra consist of a single "zero-phonon" line, blueshifted by ˜30 cm-1 from the gas phase position. Rotational band simulations show that the moments of inertia of C6H6 in the nanodroplets are at least six-times larger than in the gas phase. The dimer spectra present the same vibronic fine structure (though modestly compressed) as previously observed in the gas phase. The fluorescence lifetime and quantum yield of the dimer are found to be equal to those of the monomer, implying substantial inhibition of excimer formation in the dimer in helium.

  12. DLTS study of the oxygen dimer formation kinetics in silicon

    Science.gov (United States)

    Yarykin, Nikolai; Weber, Jörg

    2009-12-01

    The introduction rates of radiation defects, in particular the X- and M-centers for which the oxygen dimer is a precursor, are investigated as a function of duration of the pre-irradiation heat treatment at 480∘ C in Czochralski-grown silicon both of n- and p-types. The characteristic annealing time to grow the X-center concentration in the n-type crystal is found to be about 1 h in accordance with the model which implies no significant barrier for the dimer formation. The M-center concentration in the p-type crystal is found to be nearly independent of duration of the pre-irradiation annealing after a few minutes transient period. This behavior is ascribed to the stabilization of dimer concentration due to an effective dimer trapping in these samples.

  13. DLTS study of the oxygen dimer formation kinetics in silicon

    Energy Technology Data Exchange (ETDEWEB)

    Yarykin, Nikolai, E-mail: nay@iptm.r [Institute of Microelectronics Technology RAS, 142432 Chernogolovka, Moscow Region (Russian Federation); Weber, Joerg [Technische Universitaet Dresden, 01062 Dresden (Germany)

    2009-12-15

    The introduction rates of radiation defects, in particular the X- and M-centers for which the oxygen dimer is a precursor, are investigated as a function of duration of the pre-irradiation heat treatment at 480 deg. C in Czochralski-grown silicon both of n- and p-types. The characteristic annealing time to grow the X-center concentration in the n-type crystal is found to be about 1 h in accordance with the model which implies no significant barrier for the dimer formation. The M-center concentration in the p-type crystal is found to be nearly independent of duration of the pre-irradiation annealing after a few minutes transient period. This behavior is ascribed to the stabilization of dimer concentration due to an effective dimer trapping in these samples.

  14. Ion-scattering spectroscopy of III-V semiconductor surfaces

    CERN Document Server

    Kaijaks, N S

    2000-01-01

    data was consistent with a bilayer model based on antiphase Sb dimers. However, MEIS results suggested significant staggering of the surface Sb dimers. Structural parameters for the dimerization of these reconstructions have been determined. Models for the c(6x4) reconstruction were considered, and a closer fit found for a model based on Sb dimer chains with staggered antiphase second layer Sb dimers. A (4x2) reconstruction of the (001) surface of indium arsenide was prepared by AHC and analysed by MEIS, LEED and AES. Three previously proposed models have been compared and evaluated. It was found that a model based on In dimer pairs separated by second layer dimers was relatively inconsistent with the MEIS data recorded. A model based on single In dimers separated by second layer two-dimer chains was consistent with MEIS results, but structural parameters determined were nonphysical. A model without dimerization in the second layer was found to be in best agreement with the experimental results, as well as be...

  15. Exact solution of the 2d dimer model: Corner free energy, correlation functions and combinatorics

    Energy Technology Data Exchange (ETDEWEB)

    Allegra, Nicolas, E-mail: nicolas.allegra@univ-lorraine.fr

    2015-05-15

    In this work, some classical results of the pfaffian theory of the dimer model based on the work of Kasteleyn, Fisher and Temperley are introduced in a fermionic framework. Then we shall detail the bosonic formulation of the model via the so-called height mapping and the nature of boundary conditions is unravelled. The complete and detailed fermionic solution of the dimer model on the square lattice with an arbitrary number of monomers is presented, and finite size effect analysis is performed to study surface and corner effects, leading to the extrapolation of the central charge of the model. The solution allows for exact calculations of monomer and dimer correlation functions in the discrete level and the scaling behavior can be inferred in order to find the set of scaling dimensions and compare to the bosonic theory which predicts particular features concerning corner behaviors. Finally, some combinatorial and numerical properties of partition functions with boundary monomers are discussed, proved and checked with enumeration algorithms.

  16. In vivo regulation of erythropoiesis by chemically inducible dimerization of the erythropoietin receptor intracellular domain.

    Directory of Open Access Journals (Sweden)

    Norio Suzuki

    Full Text Available Erythropoietin (Epo and its receptor (EpoR are required for the regulation of erythropoiesis. Epo binds to the EpoR homodimer on the surface of erythroid progenitors and erythroblasts, and positions the intracellular domains of the homodimer to be in close proximity with each other. This conformational change is sufficient for the initiation of Epo-EpoR signal transduction. Here, we established a system of chemically regulated erythropoiesis in transgenic mice expressing a modified EpoR intracellular domain (amino acids 247-406 in which dimerization is induced using a specific compound (chemical inducer of dimerization, CID. Erythropoiesis is reversibly induced by oral administration of the CID to the transgenic mice. Because transgene expression is limited to hematopoietic cells by the Gata1 gene regulatory region, the effect of the CID is limited to erythropoiesis without adverse effects. Additionally, we show that the 160 amino acid sequence is the minimal essential domain of EpoR for intracellular signaling of chemically inducible erythropoiesis in vivo. We propose that the CID-dependent dimerization system combined with the EpoR intracellular domain and the Gata1 gene regulatory region generates a novel peroral strategy for the treatment of anemia.

  17. Interactions of univalent counterions with headgroups of monomers and dimers of an anionic surfactant.

    Science.gov (United States)

    Jakubowska, Anna

    2015-03-24

    Specific ion effects in solution are related to the hydrated ion size and ion hydration, electrostatic interactions, dispersion forces, ion effects on water structure, and ion modification of surface tension. In this study, we tried to identify which factor determines the ion specificity observed. The preference and energy of metal cations binding with the headgroups of dodecylsulfate (DS) monomers and dimers were determined by mass spectrometry. In the gas phase, cation binding to DS dimer headgroups depends strongly on the cation radius. On the other hand, the interactions between DS monomer headgroups and chaotropic ions depend on the cation polarizability, and the binding of kosmotropic cations to DS monomer headgroups strongly depends on the Gibbs free energies of ion hydration. DS dimers are related to surfactants having doubly charged headgroups, and DS monomers are related to surfactants with singly charged headgroups. Our spectrometric study of the strength of counterion binding to free monomers of a surfactant provides insight into surfactant-counterion interactions at micellar interfaces in bulk solution.

  18. Dimer representations of the Temperley-Lieb algebra

    CERN Document Server

    Morin-Duchesne, Alexi; Ruelle, Philippe

    2014-01-01

    A new spin-chain representation of the Temperley-Lieb algebra $TL_n(\\beta=0)$ is introduced and related to the dimer model. Unlike the usual XXZ spin-chain representations of dimension $2^n$, this dimer representation is of dimension $2^{n-1}$. A detailed analysis of its structure is presented and found to yield indecomposable zigzag modules not appearing in traditional spin-chain scenarios.

  19. Theoretical Study on the Intermolecular Interactions of Tetrazole Dimers

    Institute of Scientific and Technical Information of China (English)

    2005-01-01

    Tetrazole monomers (Ⅰ,Ⅱ) and all of their possible stable dimers (1, 2, 3, 4, 5, 6, 7and 8) were fully optimized by DFT method at the B3LYP/6-311++G** level. Among the eight dimers, there were two 1H-tetrazole dimers, three 2H-tetrazole dimers and three hetero dimers of 1H-tetrazole and 2H-tetrazole. Vibrational frequencies were calculated to ascertain that each structure was stable (no imaginary frequencies). The basis set superposition errors (BSSE) are 2.78,2.28, 2.97, 2.75, 2.74, 2.18, 1.23 and 3.10 kJ/mol, and the zero point energy (ZPE) corrections for the interaction energies are 4.88, 4.18, 3.87, 3.65, 3.54, 3.22, 2.87 and 4.34 kJ/mol for 1, 2, 3, 4, 5, 6,7 and 8, respectively. After BSSE and ZPE corrections, the greatest corrected intermolecular interaction energy ofthe dimers is -43.71 kJ/mol. The charge redistribution mainly occurs on the very small. Natural bond orbital (NBO) analysis was performed to reveal the origin of the interaction. Based on the statistical thermodynamic method, the standard thermodynamic functions, heat capacities (C0p), entropies (S0T) and thermal corrections to enthalpy (H0T), and the changes of thermodynamic properties from monomer to dimer in the temperature range of 200.00 K to 700 K have been obtained. 1H-tetrazole monomer can spontaneously tum into two stable dimers at 298.15 K.

  20. Quantum Phase Transitions and Dimerized Phases in Frustrated Spin Ladder

    Institute of Scientific and Technical Information of China (English)

    WEN Rui; LIU Guang-Hua; TIAN Guang-Shan

    2011-01-01

    In this paper, we study the phase diagram of a frustrated spin ladder model by applying the bosonization technique and the density-matrix renormalization-group (DMRG) algorithm. Effect of the intra-chain next-nearestneighbor (NNN) super-exchange interaction is investigated in detail and the order parameters are calculated to detect the emergence of the dimerized phases. We find that the intra-chain NNN interaction plays a key role in inducing dimerized phases.

  1. Dimer representations of the Temperley–Lieb algebra

    Energy Technology Data Exchange (ETDEWEB)

    Morin-Duchesne, Alexi, E-mail: alexi.morin-duchesne@uclouvain.be [Institut de Recherche en Mathématique et Physique, Université Catholique de Louvain, Louvain-la-Neuve, B-1348 (Belgium); Rasmussen, Jørgen, E-mail: j.rasmussen@uq.edu.au [School of Mathematics and Physics, University of Queensland St Lucia, Brisbane, Queensland 4072 (Australia); Ruelle, Philippe, E-mail: philippe.ruelle@uclouvain.be [Institut de Recherche en Mathématique et Physique, Université Catholique de Louvain, Louvain-la-Neuve, B-1348 (Belgium)

    2015-01-15

    A new spin-chain representation of the Temperley–Lieb algebra TL{sub n}(β=0) is introduced and related to the dimer model. Unlike the usual XXZ spin-chain representations of dimension 2{sup n}, this dimer representation is of dimension 2{sup n−1}. A detailed analysis of its structure is presented and found to yield indecomposable zigzag modules.

  2. Asymmetric light reflectance from metal nanoparticle arrays on dielectric surfaces

    Science.gov (United States)

    Huang, K.; Pan, W.; Zhu, J. F.; Li, J. C.; Gao, N.; Liu, C.; Ji, L.; Yu, E. T.; Kang, J.Y.

    2015-01-01

    Asymmetric light reflectance associated with localized surface plasmons excited in metal nanoparticles on a quartz substrate is observed and analyzed. This phenomenon is explained by the superposition of two waves, the wave reflected by the air/quartz interface and that reflected by the metal nanoparticles, and the resulting interference effects. Far field behavior investigation suggests that zero reflection can be achieved by optimizing the density of metal nanoparticles. Near field behavior investigation suggests that the coupling efficiency of localized surface plasmon can be additionally enhanced by separating the metal NPs from substrates using a thin film with refractive index smaller than the substrate. The latter behavior is confirmed via surface-enhanced Raman spectroscopy studies using metal nanoparticles on Si/SiO2 substrates. PMID:26679353

  3. Sulfur dimers adsorbed on Au(111) as building blocks for sulfur octomers formation: A density functional study

    Energy Technology Data Exchange (ETDEWEB)

    Hernandez-Tamargo, Carlos E.; Montero-Alejo, Ana Lilian [Laboratory of Computational and Theoretical Chemistry (LQCT), Faculty of Chemistry, Havana University, Havana 10400 (Cuba); Pujals, Daniel Codorniu [Higher Institute of Technologies and Applied Sciences (InSTEC), Havana 10400 (Cuba); Mikosch, Hans [Institute of Chemical Technologies and Analytics, Vienna University of Technology, Getreidemarkt 9/E164-EC, 1060 Vienna (Austria); Hernández, Mayra P., E-mail: mayrap@imre.oc.uh.cu [Instituto de Ciencias y Tecnologías de Materiales (IMRE), Havana 10400 (Cuba)

    2014-07-28

    Experimental scanning tunneling microscopy (STM) studies have shown for more than two decades rectangular formations when sulfur atoms are deposited on Au(111) surfaces. The precursors have ranged from simple molecules or ions, such as SO{sub 2} gas or sulfide anions, to more complex organosulfur compounds. We investigated, within the framework of the Density Functional Theory, the structure of these rectangular patterns assuming them entirely composed of sulfur atoms as the experimental evidence suggests. The sulfur coverage at which the simulations were carried out (0.67 ML or higher) provoked that the sulfur-sulfur association had to be taken into account for achieving a good agreement between the sets of simulated and experimental STM images. A combination of four sulfur dimers per rectangular formation properly explained the trends obtained by the experimental STM analysis which were related with the rectangles' size and shape fluctuations together with sulfur-sulfur distances within these rectangles. Finally, a projected density of states analysis showed that the dimers were capable of altering the Au(5d) electronic states at the same level as atomic sulfur adsorbed at low coverage. Besides, sulfur dimers states were perfectly distinguished, whose presence near and above the Fermi level can explain both: sulfur-sulfur bond elongation and dimers stability when they stayed adsorbed on the surface at high coverage.

  4. Non-Covalent Interactions and Impact of Charge Penetration Effects in Linear Oligoacene Dimers and Single Crystals

    KAUST Repository

    Ryno, Sean M

    2016-05-18

    Non-covalent interactions determine in large part the thermodynamic aspects of molecular packing in organic crystals. Using a combination of symmetry-adapted perturbation theory (SAPT) and classical multipole electrostatics, we describe the interaction potential energy surfaces for dimers of the oligoacene family, from benzene to hexacene. An analysis of these surfaces and a thorough assessment of dimers extracted from the reported crystal structures underline that high-order interactions (i.e., three-body non-additive interactions) must be considered in order to rationalize the details of the crystal structures. A comparison of the SAPT electrostatic energy with the multipole interaction energy demonstrates the importance of the contribution of charge penetration, which is shown to account for up to 50% of the total interaction energy in dimers extracted from the experimental single crystals; in the case of the most stable co-facial model dimers, this contribution is even larger than the total interaction energy. Our results highlight the importance of taking account of charge penetration in studies of the larger oligoacenes.

  5. DEFORMATION OF COPOLYMER MICELLES INDUCED BY AMPHIPHILIC DIMER PARTICLES

    Institute of Scientific and Technical Information of China (English)

    Xiao-chun Qin; Chun-lai Ren

    2012-01-01

    Combining self-consistent-field theory and density-functional theory,we systematically study the deformation of copolymer micelles induced by the presence of amphiphilic dimer particles.Due to the amphiphilic nature,dimer particles tend to accumulate onto the interface of the copolymer micelle.With increasing concentration of the symmetric dimer particles,which are made of two identical spherical particles,the micelle deforms from the initial sphere to ellipse,dumbbell,and finally separates into two micelles.Furthermore,asymmetric dimer particles,composed by two particles with different sizes,are considered to investigate the influence of geometry of dimer particles on the deformation of the micelle.It is found that the micelle inclines to deform into dumbbell due to the additional curvature originating in the gathering of asymmetric dimer particles onto the interface of the micelle.The present study on the deformation of micelles is useful to understand the possible shape variation in the course of cell division/fusion.

  6. Tetramerization reinforces the dimer interface of MnSOD.

    Directory of Open Access Journals (Sweden)

    Yuewei Sheng

    Full Text Available Two yeast manganese superoxide dismutases (MnSOD, one from Saccharomyces cerevisiae mitochondria (ScMnSOD and the other from Candida albicans cytosol (CaMnSODc, have most biochemical and biophysical properties in common, yet ScMnSOD is a tetramer and CaMnSODc is a dimer or "loose tetramer" in solution. Although CaMnSODc was found to crystallize as a tetramer, there is no indication from the solution properties that the functionality of CaMnSODc in vivo depends upon the formation of the tetrameric structure. To elucidate further the functional significance of MnSOD quaternary structure, wild-type and mutant forms of ScMnSOD (K182R, A183P mutant and CaMnSODc (K184R, L185P mutant with the substitutions at dimer interfaces were analyzed with respect to their oligomeric states and resistance to pH, heat, and denaturant. Dimeric CaMnSODc was found to be significantly more subject to thermal or denaturant-induced unfolding than tetrameric ScMnSOD. The residue substitutions at dimer interfaces caused dimeric CaMnSODc but not tetrameric ScMnSOD to dissociate into monomers. We conclude that the tetrameric assembly strongly reinforces the dimer interface, which is critical for MnSOD activity.

  7. Dimeric interactions and complex formation using direct coevolutionary couplings.

    Science.gov (United States)

    dos Santos, Ricardo N; Morcos, Faruck; Jana, Biman; Andricopulo, Adriano D; Onuchic, José N

    2015-09-04

    We develop a procedure to characterize the association of protein structures into homodimers using coevolutionary couplings extracted from Direct Coupling Analysis (DCA) in combination with Structure Based Models (SBM). Identification of dimerization contacts using DCA is more challenging than intradomain contacts since direct couplings are mixed with monomeric contacts. Therefore a systematic way to extract dimerization signals has been elusive. We provide evidence that the prediction of homodimeric complexes is possible with high accuracy for all the cases we studied which have rich sequence information. For the most accurate conformations of the structurally diverse dimeric complexes studied the mean and interfacial RMSDs are 1.95Å and 1.44Å, respectively. This methodology is also able to identify distinct dimerization conformations as for the case of the family of response regulators, which dimerize upon activation. The identification of dimeric complexes can provide interesting molecular insights in the construction of large oligomeric complexes and be useful in the study of aggregation related diseases like Alzheimer's or Parkinson's.

  8. Determining equilibrium constants for dimerization reactions from molecular dynamics simulations.

    Science.gov (United States)

    De Jong, Djurre H; Schäfer, Lars V; De Vries, Alex H; Marrink, Siewert J; Berendsen, Herman J C; Grubmüller, Helmut

    2011-07-15

    With today's available computer power, free energy calculations from equilibrium molecular dynamics simulations "via counting" become feasible for an increasing number of reactions. An example is the dimerization reaction of transmembrane alpha-helices. If an extended simulation of the two helices covers sufficiently many dimerization and dissociation events, their binding free energy is readily derived from the fraction of time during which the two helices are observed in dimeric form. Exactly how the correct value for the free energy is to be calculated, however, is unclear, and indeed several different and contradictory approaches have been used. In particular, results obtained via Boltzmann statistics differ from those determined via the law of mass action. Here, we develop a theory that resolves this discrepancy. We show that for simulation systems containing two molecules, the dimerization free energy is given by a formula of the form ΔG ∝ ln(P(1) /P(0) ). Our theory is also applicable to high concentrations that typically have to be used in molecular dynamics simulations to keep the simulation system small, where the textbook dilute approximations fail. It also covers simulations with an arbitrary number of monomers and dimers and provides rigorous error estimates. Comparison with test simulations of a simple Lennard Jones system with various particle numbers as well as with reference free energy values obtained from radial distribution functions show full agreement for both binding free energies and dimerization statistics.

  9. Fourier transform infrared phase-modulated ellipsometry for in situ diagnostics of plasma-surface interactions

    Energy Technology Data Exchange (ETDEWEB)

    Shirafuji, T [International Innovation Center, Kyoto University, Sakyo-ku, Kyoto 606-8501 (Japan); Motomura, H [Department of Electronics, Kyoto University, Nishikyo-ku, Katsura 615-8510 (Japan); Tachibana, K [Department of Electronics, Kyoto University, Nishikyo-ku, Katsura 615-8510 (Japan)

    2004-03-21

    Applicability of Fourier transform infrared (FTIR) spectroscopy to an in situ diagnostics tool of plasma-surface interactions is described. After a brief review of conventional reflection absorption spectroscopy (RAS) and phase-modulated RAS (PMRAS), our FTIR phase-modulated spectroscopic ellipsometry (PMSE) is described in detail. The FTIR PMSE is constructed by insertion of a grid polarizer as an analyser in front of an infrared detector in addition to the conventional set-up of PMRAS. This simple change brings about a higher sensitivity than that of conventional PMRAS, which enables us to detect chemical species generated on (or removed from) the top surface layer during plasma processing. This feature is demonstrated by the fact that our FTIR PMSE can be applied to surface diagnostics during reactive ion etching processes such as for Si, SiO{sub 2}/Si, SiO{sub 2}/Si{sub 3}N{sub 4}, SiO{sub 2}/photo-resist and low-dielectric-constant films. (topical review)

  10. Products and mechanism of acene dimerization. A computational study.

    Science.gov (United States)

    Zade, Sanjio S; Zamoshchik, Natalia; Reddy, A Ravikumar; Fridman-Marueli, Galit; Sheberla, Dennis; Bendikov, Michael

    2011-07-20

    The high reactivity of acenes can reduce their potential applications in the field of molecular electronics. Although pentacene is an important material for use in organic field-effect transistors because of its high charge mobility, its reactivity is a major disadvantage hindering the development of pentacene applications. In this study, several reaction pathways for the thermal dimerization of acenes were considered computationally. The formation of acene dimers via a central benzene ring and the formation of acene-based polymers were found to be the preferred pathways, depending on the length of the monomer. Interestingly, starting from hexacene, acene dimers are thermodynamically disfavored products, and the reaction pathway is predicted to proceed instead via a double cycloaddition reaction (polymerization) to yield acene-based polymers. A concerted asynchronous reaction mechanism was found for benzene and naphthalene dimerization, while a stepwise biradical mechanism was predicted for the dimerization of anthracene, pentacene, and heptacene. The biradical mechanism for dimerization of anthracene and pentacene proceeds via syn or anti transition states and biradical minima through stepwise biradical pathways, while dimerization of heptacene proceeds via asynchronous ring closure of the complex formed by two heptacene molecules. The activation barriers for thermal dimerization decrease rapidly with increasing acene chain length and are calculated (at M06-2X/6-31G(d)+ZPVE) to be 77.9, 57.1, 33.3, -0.3, and -12.1 kcal/mol vs two isolated acene molecules for benzene, naphthalene, anthracene, pentacene, and heptacene, respectively. If activation energy is calculated vs the initially formed complex of two acene molecules, then the calculated barriers are 80.5, 63.2, 43.7, 16.7, and 12.3 kcal/mol. Dimerization is exothermic from anthracene onward, but it is endothermic at the terminal rings, even for heptacene. Phenyl substitution at the most reactive meso

  11. Dimer-atom-atom recombination in the universal four-boson system

    OpenAIRE

    Deltuva, A.

    2012-01-01

    The dimer-atom-atom recombination process in the system of four identical bosons with resonant interactions is studied. The description uses the exact Alt, Grassberger and Sandhas equations for the four-particle transition operators that are solved in the momentum-space framework. The dimer-dimer and atom-trimer channel contributions to the ultracold dimer-atom-atom recombination rate are calculated. The dimer-atom-atom recombination rate greatly exceeds the three-atom recombination rate.

  12. Immobilization and surface functionalization of gold nanoparticles monitored via streaming current/potential measurements.

    Science.gov (United States)

    Greben, Kyrylo; Li, Pinggui; Mayer, Dirk; Offenhäusser, Andreas; Wördenweber, Roger

    2015-05-14

    A streaming current/potential method is optimized and used for the analysis of the variation of the surface potential upon chemical modifications of a complex interface consisting of different organic molecules and gold nanoparticles (AuNPs). The surfaces of Si/SiO2 substrates modified with 3-aminopropyltriethoxysilane (APTES), AuNPs, and 11-amino-1-undecanethiol (aminothiols) are analyzed via pH and time dependent ζ potential measurements that reveal the stability and modification of the surface and identify crucial parameters for each individual preparation step. For instance, surface activation and especially molecular adsorbate layers tend not to be stable in time, whereas the substrate and the AuNPs provide a stable surface potential as long as impurities are avoided. It is shown that the streaming potential/current technique represents an ideal tool to analyze and monitor the complex surfaces and their modification.

  13. Binding of dengue virus particles and dengue proteins onto solid surfaces.

    Science.gov (United States)

    Pereira, Edla M A; Dario, Aline F; França, Rafael F O; Fonseca, Benedito A L; Petri, Denise F S

    2010-09-01

    The interaction between dengue virus particles (DENV), sedimentation hemagglutinin particles (SHA), dengue virus envelope protein (Eprot), and solid surfaces was investigated by means of ellipsometry and atomic force microscopy (AFM). The surfaces chosen are bare Si/SiO2 wafers and Si/SiO2 wafers covered with concanavalin A (ConA), jacalin (Jac), polystyrene (PS), or poly(styrene sulfonate) (PSS) films. Adsorption experiments at pH 7.2 and pH 3 onto all surfaces revealed that (i) adsorption of DENV particles took place only onto ConA under pH 7.2, because of specific recognition between glycans on DENV surface and ConA binding site; (ii) DENV particles did not attach to any of the surfaces at pH 3, suggesting the presence of positive charges on DENV surface at this pH, which repel the positively charged lectin surfaces; (iii) SHA particles are positively charged at pH 7.2 and pH 3 because they adhered to negatively charged surfaces at pH 7.2 and repelled positively charged layers at pH 3; and (iv) SHA particles carry polar groups on the surface because they attached to silanol surfaces at pH 3 and avoided hydrophobic PS films at pH 3 and pH 7.2. The adsorption behavior of Eprot at pH 7.2 revealed affinity for ConA>Jac>PSS>PS≈bare Si/SiO2 layers. These findings indicate that selectivity of the Eprot adsorption is higher when it is part of virus structure than when it is free in solution. The correlation between surface energy values determined by means of contact angle measurements and DENV, SHA, or Eprot adsorption behavior was used to understand the intermolecular forces at the interfaces. A direct correlation was not found because the contributions from surface energy were probably surpassed by specific contributions.

  14. Intermolecular disulfide bond influences unphosphorylated STAT3 dimerization and function.

    Science.gov (United States)

    Butturini, Elena; Gotte, Giovanni; Dell'Orco, Daniele; Chiavegato, Giulia; Marino, Valerio; Canetti, Diana; Cozzolino, Flora; Monti, Maria; Pucci, Piero; Mariotto, Sofia

    2016-10-01

    Signal transducer and activator of transcription 3 (STAT3) is a transcription factor activated by the phosphorylation of tyrosine 705 in response to many cytokines and growth factors. Recently, the roles for unphosphorylated STAT3 (U-STAT3) have been described in response to cytokine stimulation, in cancers, and in the maintenance of heterochromatin stability. It has been reported that U-STAT3 dimerizes, shuttles between the cytoplasm and nucleus, and binds to DNA, thereby driving genes transcription. Although many reports describe the active role of U-STAT3 in oncogenesis in addition to phosphorylated STAT3, the U-STAT3 functional pathway remains elusive.In this report, we describe the molecular mechanism of U-STAT3 dimerization, and we identify the presence of two intermolecular disulfide bridges between Cys367 and Cys542 and Cys418 and Cys426, respectively. Recently, we reported that the same cysteines contribute to the redox regulation of STAT3 signaling pathway both in vitro and in vivo The presence of these disulfides is here demonstrated to largely contribute to the structure and the stability of U-STAT3 dimer as the dimeric form rapidly dissociates upon reduction in the S-S bonds. In particular, the Cys367-Cys542 disulfide bridge is shown to be critical for U-STAT3 DNA-binding activity. Mutation of the two Cys residues completely abolishes the DNA-binding capability of U-STAT3. Spectroscopic investigations confirm that the noncovalent interactions are sufficient for proper folding and dimer formation, but that the interchain disulfide bonds are crucial to preserve the functional dimer. Finally, we propose a reaction scheme of U-STAT3 dimerization with a first common step followed by stabilization through the formation of interchain disulfide bonds. © 2016 The Author(s); published by Portland Press Limited on behalf of the Biochemical Society.

  15. Threshold electron attachment and electron impact ionization involving oxygen dimers

    Energy Technology Data Exchange (ETDEWEB)

    Kreil, J.; Ruf, M.-W.; Hotop, H. [Fachbereich Physik, Universitaet Kaiserslautern, D-67653 Kaiserslautern (Germany); Ettischer, I.; Buck, U. [Max-Planck-Institut fuer Stroemungsforschung, Bunsenstrasse 10, D-37073 Goettingen (Germany)

    1998-12-15

    Using two different crossed-beams machines we have carried out the first quantitative study of threshold electron attachment and electron impact-induced ionization and fragmentation involving oxygen dimers (O{sub 2}){sub 2}. In the electron attachment experiment we study electron transfer from state-selected Ar{sup **}(20d) Rydberg atoms to O{sub 2} molecules and dimers in a skimmed supersonic beam at variable nozzle temperatures (T{sub 0}) and stagnation pressures (p{sub 0}). The relative dimer density is determined through measurements of Penning ionization by metastable Ne{sup *}(3s {sup 3}P{sub 2,0}) atoms and used to estimate the absolute cross-section for O{sub 2}{sup -} formation in collisions of Ar{sup **}(20d) Rydberg atoms with O{sub 2} dimers to be nearly 10{sup -17} m{sup 2}, almost four orders of magnitude larger than that for O{sub 2}{sup -} formation in collisions of Ar{sup **}(20d) Rydberg atoms with O{sub 2} monomers. The fragmentation of the oxygen cluster beam is quantitatively characterized by the transverse helium beam scattering method which allows us to spatially separate different clusters. It is shown that in 70 eV electron impact of (O{sub 2}){sub 2} only 3.6(4)% of the dimers are detected as dimer ions (O{sub 2}){sub 2}{sup +}. In additional experiments involving SF{sub 6} clusters we show that SF{sub 6} dimers fragment nearly completely upon 70 eV electron impact, yielding SF{sub 5}{sup +} ions (probability for (SF{sub 6}){center_dot}SF{sub 5}{sup +} production at most 0.3%). (Copyright (c) 1998 Elsevier Science B.V., Amsterdam. All rights reserved.)

  16. Integrability and conformal data of the dimer model

    Science.gov (United States)

    Morin-Duchesne, Alexi; Rasmussen, Jørgen; Ruelle, Philippe

    2016-04-01

    The central charge of the dimer model on the square lattice is still being debated in the literature. In this paper, we provide evidence supporting the consistency of a c=-2 description. Using Lieb’s transfer matrix and its description in terms of the Temperley-Lieb algebra {{TL}}n at β =0, we provide a new solution of the dimer model in terms of the model of critical dense polymers on a tilted lattice and offer an understanding of the lattice integrability of the dimer model. The dimer transfer matrix is analyzed in the scaling limit, and the result for {L}0-\\frac{c}{24} is expressed in terms of fermions. Higher Virasoro modes are likewise constructed as limits of elements of {{TL}}n and are found to yield a c=-2 realization of the Virasoro algebra, familiar from fermionic bc ghost systems. In this realization, the dimer Fock spaces are shown to decompose, as Virasoro modules, into direct sums of Feigin-Fuchs modules, themselves exhibiting reducible yet indecomposable structures. In the scaling limit, the eigenvalues of the lattice integrals of motion are found to agree exactly with those of the c=-2 conformal integrals of motion. Consistent with the expression for {L}0-\\frac{c}{24} obtained from the transfer matrix, we also construct higher Virasoro modes with c = 1 and find that the dimer Fock space is completely reducible under their action. However, the transfer matrix is found not to be a generating function for the c = 1 integrals of motion. Although this indicates that Lieb’s transfer matrix description is incompatible with the c = 1 interpretation, it does not rule out the existence of an alternative, c = 1 compatible, transfer matrix description of the dimer model.

  17. Monitoring of receptor dimerization using plasmonic coupling of gold nanoparticles.

    Science.gov (United States)

    Crow, Matthew J; Seekell, Kevin; Ostrander, Julie H; Wax, Adam

    2011-11-22

    The dimerization of receptors on the cell membrane is an important step in the activation of cell signaling pathways. Several methods exist for observing receptor dimerization, including coimmunoprecipitation, chemical cross-linking, and fluorescence resonance energy transfer (FRET). These techniques are limited in that only FRET is appropriate for live cells, but even that method suffers from photobleaching and bleed-through effects. In this study, we implement an alternative method for the targeting of HER-2 homodimer formation based on the plasmonic coupling of gold nanoparticles functionalized with HER-2 Ab. In the presented studies, SK-BR-3 cells, known to overexpress HER-2, are labeled with these nanoparticles and receptor colocalization is observed using plasmonic coupling. HER-2 targeted nanoparticles bound to these cells exhibit a peak resonance that is significantly red-shifted relative to those bound to similar receptors on A549 cells, which have significantly lower levels of HER-2 expression. This significant red shift indicates plasmonic coupling is occurring and points to a new avenue for assessing dimerization by monitoring their colocalization. To determine that dimerization is occurring, the refractive index of the nanoenvironment of the labels is assessed using a theoretical analysis based on the Mie coated sphere model. The results indicate scattering by single, isolated nanoparticles for the low HER-2 expressing A549 cell line, but the scattering observed for the HER-2 overexpressing SK-BR-3 cell line may only be explained by plasmonic-coupling of proximal nanoparticle pairs. To validate the conformation of nanoparticles bound to HER-2 receptors undergoing dimerization, discrete dipole approximation (DDA) models are used to assess spectra of scattering by coupled nanoparticles. Comparison of the experimental results with theoretical models indicates that NP dimers are formed for the labeling of SK-BR-3 cells, suggesting that receptor

  18. Dimerization in Highly Concentrated Solutions of Phosphoimidazolide Activated Monomucleotides

    Science.gov (United States)

    Kanavarioti, Anastassia

    1997-08-01

    Phosphoimidazolide activated ribomononucleotides (*pN) are useful substrates for the non-enzymatic synthesis of polynucleotides. However, dilute neutral aqueous solutions of *pN typically yield small amounts of dimers and traces of polymers; most of *pN hydrolyzes to yield nucleoside 5'-monophosphate. Here we report the self-condensation of nucleoside 5'-phosphate 2-methylimidazolide (2-MeImpN with N = cytidine, uridine or guanosine) in the presence of Mg2+ in concentrated solutions, such as might have been found in an evaporating lagoon on prebiotic Earth. The product distribution indicates that oligomerization is favored at the expense of hydrolysis. At 1.0 M, 2-MeImpU and 2-MeImpC produce about 65% of oligomers including 4% of the 3',5'-linked dimer. Examination of the product distribution of the three isomeric dimers in a self-condensation allows identification of reaction pathways that lead to dimer formation. Condensations in a concentrated mixture of all three nucleotides (U,C,G mixtures) is made possible by the enhanced solubility of 2-MeImpG in such mixtures. Although percent yield of internucleotide linked dimers is enhanced as a function of initial monomer concentration, pyrophosphate dimer yields remain practically unchanged at about 20% for 2-MeImpU, 16% for 2-MeImpC and 25% of the total pyrophosphate in the U,C,G mixtures. The efficiency by which oligomers are produced in these concentrated solutions makes the evaporating lagoon scenario a potentially interesting medium for the prebiotic synthesis of dimers and short RNAs.

  19. Basis set effects on the energy and hardness profiles of the hydrogen fluoride dimer

    Indian Academy of Sciences (India)

    Miquel Torrent-Sucarrat; Miquel Duran; Josep M Luis; Miquel Solà

    2005-09-01

    In earlier work, the present authors have shown that hardness profiles are less dependent on the level of calculation than energy profiles for potential energy surfaces (PESs) having pathological behaviors. At variance with energy profiles, hardness profiles always show the correct number of stationary points. This characteristic has been used to indicate the existence of spurious stationary points on the PESs. In the present work, we apply this methodology to the hydrogen fluoride dimer, a classical difficult case for the density functional theory methods.

  20. Modification of Chinese fir with alkyl ketene dimer (AKD: Processing and characterization

    Directory of Open Access Journals (Sweden)

    Zengqian Shi

    2013-02-01

    Full Text Available A process for the chemical modification of Chinese fir with alkyl ketene dimer (AKD was studied. The hydrophobicity of the resulting products was evaluated by characterization of the equilibrium moisture content, water-surface contact angle, water absorption coefficient, and anti-swelling efficiency. The results indicated that when 5% AKD solution was used, the modified wood generally showed good hydrophobicity and improved dimensional stability. The result of boiling water and hexane extraction tests showed that the modified fir possessed very stable hydrophobicity.

  1. Crystal structure of the dimeric protein core of decorin, the archetypal small leucine-rich repeat proteoglycan.

    Science.gov (United States)

    Scott, Paul G; McEwan, Paul A; Dodd, Carole M; Bergmann, Ernst M; Bishop, Paul N; Bella, Jordi

    2004-11-02

    Decorin is a ubiquitous extracellular matrix proteoglycan with a variety of important biological functions that are mediated by its interactions with extracellular matrix proteins, cytokines, and cell surface receptors. Decorin is the prototype of the family of small leucine-rich repeat proteoglycans and proteins (SLRPs), characterized by a protein core composed of leucine-rich repeats (LRRs), flanked by two cysteine-rich regions. We report here the crystal structure of the dimeric protein core of decorin, the best characterized member of the SLRP family. Each monomer adopts the curved solenoid fold characteristic of LRR domains, with a parallel beta-sheet on the inside interwoven with loops containing short segments of beta-strands, 3(10) helices, and polyproline II helices on the outside. Two main features are unique to this structure. First, decorin dimerizes through the concave surfaces of the LRR domains, which have been implicated previously in protein-ligand interactions. The amount of surface buried in this dimer rivals the buried surfaces of some of the highest-affinity macromolecular complexes reported to date. Second, the C-terminal region adopts an unusual capping motif that involves a laterally extended LRR and a disulfide bond. This motif seems to be unique to SLRPs and has not been observed in any other LRR protein structure to date. Possible implications of these features for decorin ligand binding and SLRP function are discussed.

  2. The Ge(0 0 1) surface

    NARCIS (Netherlands)

    Zandvliet, Henricus J.W.

    2003-01-01

    Although germanium (Ge) (0 0 1) has a relatively small surface unit cell, this surface displays a wealth of fascinating phenomena. The Ge(0 0 1) surface is a prototypical example of a system possessing both a strong short-range interaction due to dimerization of the surface atoms, as well as an

  3. Reaction dynamics of molecular hydrogen on silicon surfaces

    DEFF Research Database (Denmark)

    Bratu, P.; Brenig, W.; Gross, A.

    1996-01-01

    between the two surfaces. These results indicate that tunneling, molecular vibrations, and the structural details of the surface play only a minor role for the adsorption dynamics. Instead, they appear to be governed by the localized H-Si bonding and Si-Si lattice vibrations. Theoretically, an effective...... of the preexponential factor by about one order of magnitude per lateral degree of freedom. Molecular vibrations have practically no effect on the adsorption/desorption dynamics itself, but lead to vibrational heating in desorption with a strong isotope effect. Ab initio calculations for the H-2 interaction......Experimental and theoretical results on the dynamics of dissociative adsorption and recombinative desorption of hydrogen on silicon are presented. Using optical second-harmonic generation, extremely small sticking probabilities in the range 10(-9)-10(-5) could be measured for H-2 and D-2 on Si(111...

  4. Mechanism of ubiquitylation by dimeric RING ligase RNF4

    Science.gov (United States)

    Plechanovová, Anna; Jaffray, Ellis G.; McMahon, Stephen A.; Johnson, Kenneth A.; Navrátilová, Iva; Naismith, James H.; Hay, Ronald T.

    2012-01-01

    Mammalian RNF4 is a dimeric RING ubiquitin E3 ligase that ubiquitylates poly-SUMOylated proteins. We found that RNF4 bound ubiquitin-charged UbcH5a tightly but free UbcH5a weakly. To provide insight into the mechanism of RING-mediated ubiquitylation we docked the UbcH5~ubiquitin thioester onto the RNF4 RING structure. This revealed that with E2 bound to one monomer of RNF4, the thioester-linked ubiquitin could reach across the dimer to engage the other monomer. In this model the “Ile44 hydrophobic patch” of ubiquitin is predicted to engage a conserved tyrosine located at the dimer interface of the RING and mutation of these residues blocked ubiquitylation activity. Thus, dimeric RING ligases are not simply inert scaffolds that bring substrate and E2-loaded ubiquitin into close proximity. Instead, they facilitate ubiquitin transfer by preferentially binding the E2~ubiquitin thioester across the dimer and activating the thioester bond for catalysis. PMID:21857666

  5. Synthesis of a distinct water dimer inside fullerene C70

    Science.gov (United States)

    Zhang, Rui; Murata, Michihisa; Aharen, Tomoko; Wakamiya, Atsushi; Shimoaka, Takafumi; Hasegawa, Takeshi; Murata, Yasujiro

    2016-05-01

    The water dimer is an ideal chemical species with which to study hydrogen bonds. Owing to the equilibrium between the monomer and oligomer structure, however, selective generation and separation of a genuine water dimer has not yet been achieved. Here, we report a synthetic strategy that leads to the successful encapsulation of one or two water molecules inside fullerene C70. These endohedral C70 compounds offer the opportunity to study the intrinsic properties of a single water molecule without any hydrogen bonding, as well as an isolated water dimer with a single hydrogen bond between the two molecules. The unambiguously determined off-centre position of water in (H2O)2@C70 by X-ray diffraction provides insights into the formation of (H2O)2@C70. Subsequently, the 1H NMR spectroscopic measurements for (H2O)2@C70 confirmed the formation of a single hydrogen bond rapidly interchanging between the encapsulated water dimer. Our theoretical calculations revealed a peculiar cis-linear conformation of the dimer resulting from confinement effects inside C70.

  6. Integrability and conformal data of the dimer model

    CERN Document Server

    Morin-Duchesne, Alexi; Ruelle, Philippe

    2015-01-01

    The central charge of the dimer model on the square lattice is still being debated in the literature. In this paper, we provide evidence supporting the consistency of a $c=-2$ description. Using Lieb's transfer matrix and its description in terms of the Temperley-Lieb algebra $TL_n$ at $\\beta = 0$, we provide a new solution of the dimer model in terms of the model of critical dense polymers on a tilted lattice and offer an understanding of the lattice integrability of the dimer model. The dimer transfer matrix is analysed in the scaling limit and the result for $L_0-\\frac c{24}$ is expressed in terms of fermions. Higher Virasoro modes are likewise constructed as limits of elements of $TL_n$ and are found to yield a $c=-2$ realisation of the Virasoro algebra, familiar from fermionic $bc$ ghost systems. In this realisation, the dimer Fock spaces are shown to decompose, as Virasoro modules, into direct sums of Feigin-Fuchs modules, themselves exhibiting reducible yet indecomposable structures. In the scaling lim...

  7. Recognition of HIV TAR RNA by triazole linked neomycin dimers.

    Science.gov (United States)

    Kumar, Sunil; Arya, Dev P

    2011-08-15

    A series of neomycin dimers have been synthesized using 'click chemistry' with varying linker functionality and length to target the TAR RNA region of HIV virus. TAR (trans activation response) RNA region, a 59 base pair stem loop structure located at 5'-end of all nascent HIV-1 transcripts interacts with a key regulatory protein, Tat, and necessitates the replication of HIV-1 virus. Neomycin, an aminosugar, has been shown to exhibit more than one binding site with HIV TAR RNA. Multiple TAR binding sites of neomycin prompted us to design and synthesize a small library of neomycin dimers using click chemistry. The binding between neomycin dimers and HIV TAR RNA was characterized using spectroscopic techniques including FID (Fluorescent Intercalator Displacement) titration and UV-thermal denaturation. UV thermal denaturation studies demonstrate that neomycin dimer binding increase the melting temperature (T(m)) of the HIV TAR RNA up to 10°C. Ethidium bromide displacement titrations revealed nanomolar IC(50) between neomycin dimers and HIV TAR RNA, whereas with neomycin, a much higher IC(50) in the micromolar range is observed.

  8. Regulation of primate lentiviral RNA dimerization by structural entrapment

    Directory of Open Access Journals (Sweden)

    Lodmell J Stephen

    2008-07-01

    Full Text Available Abstract Background Genomic RNA dimerization is an important process in the formation of an infectious lentiviral particle. One of the signals involved is the stem-loop 1 (SL1 element located in the leader region of lentiviral genomic RNAs which also plays a role in encapsidation and reverse transcription. Recent studies revealed that HIV types 1 and 2 leader RNAs adopt different conformations that influence the presentation of RNA signals such as SL1. To determine whether common mechanisms of SL1 regulation exist among divergent lentiviral leader RNAs, here we compare the dimerization properties of SIVmac239, HIV-1, and HIV-2 leader RNA fragments using homologous constructs and experimental conditions. Prior studies from several groups have employed a variety of constructs and experimental conditions. Results Although some idiosyncratic differences in the dimerization details were observed, we find unifying principles in the regulation strategies of the three viral RNAs through long- and short-range base pairing interactions. Presentation and efficacy of dimerization through SL1 depends strongly upon the formation or dissolution of the lower stem of SL1 called stem B. SL1 usage may also be down-regulated by long-range interactions involving sequences between SL1 and the first codons of the gag gene. Conclusion Despite their sequence differences, all three lentiviral RNAs tested in this study showed a local regulation of dimerization through the stabilization of SL1.

  9. Dimer-tetramer transition controls RUNX1/ETO leukemogenic activity.

    Science.gov (United States)

    Wichmann, Christian; Becker, Yvonne; Chen-Wichmann, Linping; Vogel, Vitali; Vojtkova, Anna; Herglotz, Julia; Moore, Sandra; Koch, Joachim; Lausen, Jörn; Mäntele, Werner; Gohlke, Holger; Grez, Manuel

    2010-07-29

    RUNX1/ETO, the fusion protein resulting from the chromosomal translocation t(8;21), is one of the most frequent translocation products in acute myeloid leukemia. Several in vitro and in vivo studies have shown that the homo-tetramerization domain of ETO, the nervy homology region 2 (NHR2), is essential for RUNX1/ETO oncogenic activity. We analyzed the energetic contribution of individual amino acids within the NHR2 to RUNX1/ETO dimer-tetramer transition and found a clustered area of 5 distinct amino acids with strong contribution to the stability of tetramers. Substitution of these amino acids abolishes tetramer formation without affecting dimer formation. Similar to RUNX1/ETO monomers, dimers failed to bind efficiently to DNA and to alter expression of RUNX1-dependent genes. RUNX1/ETO dimers do not block myeloid differentiation, are unable to enhance the self-renewal capacity of hematopoietic progenitors, and fail to induce leukemia in a murine transplantation model. Our data reveal the existence of an essential structural motif (hot spot) at the NHR2 dimer-tetramer interface, suitable for a molecular intervention in t(8;21) leukemias.

  10. Effects of Dimerization of Serratia marcescens Endonuclease on Water Dynamics.

    Energy Technology Data Exchange (ETDEWEB)

    Chen, Chuanying; Beck, Brian W.; Krause, Kurt; Weksberg, Tiffany E.; Pettitt, Bernard M.

    2007-02-15

    The research described in this product was performed in part in the Environmental Molecular Sciences Laboratory, a national scientific user facility sponsored by the Department of Energy's Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory. The dynamics and structure of Serratia marcescens endonuclease and its neighboring solvent are investigated by molecular dynamics (MD). Comparisons are made with structural and biochemical experiments. The dimer form is physiologic and functions more processively than the monomer. We previously found a channel formed by connected clusters of waters from the active site to the dimer interface. Here, we show that dimerization clearly changes correlations in the water structure and dynamics in the active site not seen in the monomer. Our results indicate that water at the active sites of the dimer is less affected compared with bulk solvent than in the monomer where it has much slower characteristic relaxation times. Given that water is a required participant in the reaction, this gives a clear advantage to dimerization in the absence of an apparent ability to use both active sites simultaneously.

  11. Non-destructive quantum reflection of helium dimers and trimers from a plane ruled grating

    Science.gov (United States)

    Zhao, Bum Suk; Zhang, Weiqing; Schöllkopf, Wieland

    2013-07-01

    We report on the non-destructive scattering and diffraction of He, He2 and He3 from a plane ruled reflection grating. At grazing incidence the normal component of the particle's wave-vector is sufficiently small to allow for quantum reflection at the attractive Casimir-van der Waals particle-surface interaction potential. Quantum reflection occurs tens of nanometres in front of the surface, before the dimers and trimers reach the region where the surface-induced forces would inevitably cause the breakup of the fragile bonds. The reflected particles are identified via their mass-dependent diffraction angles and by mass spectrometry. The intensity distributions of the observed diffraction patterns are discussed in terms of the grating's blaze angle.

  12. Photodissociation pathways and lifetimes of protonated peptides and their dimers

    DEFF Research Database (Denmark)

    Gopalan, Aravind; Klærke, Benedikte; Rajput, Jyoti

    2012-01-01

    Photodissociation lifetimes and fragment channels of gas-phase, protonated YAn (n = 1,2) peptides and their dimers were measured with 266 nm photons. The protonated monomers were found to have a fast dissociation channel with an exponential lifetime of ∼200 ns while the protonated dimers show...... rate constants also confirmed a statistical nature of the photodissociation processes in the dipeptide monomers and dimers. The classical RRKM expression gives a rate constant as an analytical function of the number of active vibrational modes in the system, estimated separately on the basis...... of the equipartition theorem. It demonstrates encouraging results in predicting fragmentation lifetimes of protonated peptides. Finally, we present the first experimental evidence for a photo-induced conversion of tyrosine-containing peptides into monocyclic aromatic hydrocarbon along with a formamide molecule both...

  13. Self-deactivation of water vapor - Role of the dimer

    Science.gov (United States)

    Zuckerwar, A. J.

    1984-01-01

    A phenomenological multiple-relaxation theory of the deactivation rate constant for the nu-2 (1 - 0) bending mode of water vapor is presented which incorporates the role not only of the excited monomer but also of the bound molecular complex, in particular the dimer. The deactivation takes place by means of three parallel processes: (1) collisional deexcitation of the excited monomer, (2) a two-step reaction involving association and spontaneous redissociation of an H2O collision complex, and (3) spontaneous dissociation of the stably bound H2O dimer. Oxygen, but not nitrogen or argon, serves as an effective chaperon for the formation of the activated complex. This observation explains the impurity dependence of the self-deactivation rate constant of water vapor. Analysis of an ultrasonic absorption peak based on the third process yields values for the standard entropy and enthalpy of dissociation of the stably bound H2O dimer.

  14. Characterization of oxygen dimer-enriched silicon detectors

    CERN Document Server

    Boisvert, V; Moll, M; Murin, L I; Pintilie, I

    2005-01-01

    Various types of silicon material and silicon p+n diodes have been treated to increase the concentration of the oxygen dimer (O2i) defect. This was done by exposing the bulk material and the diodes to 6 MeV electrons at a temperature of about 350 °C. FTIR spectroscopy has been performed on the processed material confirming the formation of oxygen dimer defects in Czochralski silicon pieces. We also show results from TSC characterization on processed diodes. Finally, we investigated the influence of the dimer enrichment process on the depletion voltage of silicon diodes and performed 24 GeV/c proton irradiations to study the evolution of the macroscopic diode characteristics as a function of fluence.

  15. Dimer Models from Mirror Symmetry and Quivering Amoebae

    CERN Document Server

    Feng, B; Kennaway, K D; Vafa, C; Feng, Bo; He, Yang-Hui; Kennaway, Kristian D.; Vafa, Cumrun

    2005-01-01

    Dimer models are 2-dimensional combinatorial systems that have been shown to encode the gauge groups, matter content and tree-level superpotential of the world-volume quiver gauge theories obtained by placing D3-branes at the tip of a singular toric Calabi-Yau cone. In particular the dimer graph is dual to the quiver graph. However, the string theoretic explanation of this was unclear. In this paper we use mirror symmetry to shed light on this: the dimer models live on a T^2 subspace of the T^3 fiber that is involved in mirror symmetry and is wrapped by D6-branes. These D6-branes are mirror to the D3-branes at the singular point, and geometrically encode the same quiver theory on their world-volume.

  16. Intrinsic Kinetic Modeling of Thermal Dimerization of C5 Fraction

    Institute of Scientific and Technical Information of China (English)

    Guo Liang; Wang Tiefeng; Li Dongfeng; Wang Jinfu

    2016-01-01

    This work aims to investigate the intrinsic kinetics of thermal dimerization of C5 fraction in the reactive distilla-tion process. Experiments are conducted in an 1000-mL stainless steel autoclave under some selected design conditions. By means of the weighted least squares method, the intrinsic kinetics of thermal dimerization of C5 fraction is established, and the corresponding pre-exponential factor as well as the activation energy are determined. For example, the pre-exponential factor A is equal to 4.39×105 and the activation energy Ea is equal to 6.58×104 J/mol for the cyclopentadiene dimerization re-action. The comparison between the experimental and calculated results shows that the kinetics model derived in this work is accurate and reliable, which can be used in the design of reactive distillation columns.

  17. Ultrafast Dissociation of Metastable CO2 + in a Dimer

    Science.gov (United States)

    Ding, Xiaoyan; Haertelt, M.; Schlauderer, S.; Schuurman, M. S.; Naumov, A. Yu.; Villeneuve, D. M.; McKellar, A. R. W.; Corkum, P. B.; Staudte, A.

    2017-04-01

    We triply ionize the van der Waals bound carbon monoxide dimer with intense ultrashort pulses and study the breakup channel (CO )23 +→C++O++CO+ . The fragments are recorded in a cold target recoil ion momentum spectrometer. We observe a fast CO2 + dissociation channel in the dimer, which does not exist for the monomer. We found that a nearby charge breaks the symmetry of a X3Π state of CO2 + and induces an avoided crossing that allows a fast dissociation. Calculation on the full dimer complex shows the coupling of different charge states, as predicted from excimer theory, gives rise to electronic state components not present in the monomer, thereby enabling fast dissociation with higher kinetic energy release. These results demonstrate that the electronic structure of molecular cluster complexes can give rise to dynamics that is qualitatively different from that observed in the component monomers.

  18. Optofluidic taming of a colloidal dimer with a silicon nanocavity

    Energy Technology Data Exchange (ETDEWEB)

    Pin, C.; Renaut, C. [Groupe d' Optique de Champ Proche - LRC CEA n°DSM-08-36, Laboratoire Interdisciplinaire Carnot de Bourgogne, UMR CNRS n°6303- Université de Bourgogne, Dijon (France); University Grenoble Alpes, INAC-SP2M-SINAPS, F-38000 Grenoble, France and CEA, INAC-SP2M-SINAPS, F-38000 Grenoble (France); University Grenoble Alpes, CNRS, CEA-Leti Minatec, LTM, F-38054 Grenoble Cedex (France); Cluzel, B., E-mail: benoit.cluzel@u-bourgogne.fr; Fornel, F. de [Groupe d' Optique de Champ Proche - LRC CEA n°DSM-08-36, Laboratoire Interdisciplinaire Carnot de Bourgogne, UMR CNRS n°6303- Université de Bourgogne, Dijon (France); Peyrade, D. [University Grenoble Alpes, CNRS, CEA-Leti Minatec, LTM, F-38054 Grenoble Cedex (France); Picard, E.; Hadji, E. [University Grenoble Alpes, INAC-SP2M-SINAPS, F-38000 Grenoble, France and CEA, INAC-SP2M-SINAPS, F-38000 Grenoble (France)

    2014-10-27

    We report here the optical trapping of a heterogeneous colloidal dimer above a photonic crystal nanocavity used as an on-chip optical tweezer. The trapped dimer consists of a cluster of two dielectric microbeads of different sizes linked by van der Waals forces. The smallest bead, 1 μm in diameter, is observed to be preferentially trapped by the nanotweezer, leaving the second bead untrapped. The rotational nature of the trapped dimer Brownian motion is first evidenced. Then, in the presence of a fluid flow, control of its orientation and rotation is achieved. The whole system is found to show high rotational degrees of freedom, thereby acting as an effective flow-sensitive microscopic optical ball joint.

  19. Photodissociation pathways and lifetimes of protonated peptides and their dimers

    DEFF Research Database (Denmark)

    Gopalan, Aravind; Klærke, Benedikte; Rajput, Jyoti

    2012-01-01

    channel in the dimer was found to result in cleavage of the H-bonds after energy transfer through these H-bonds. In general, the dissociation of these protonated peptides is non-prompt and the decay time was found to increase with the size of the peptides. Quantum RRKM calculations of the microcanonical......Photodissociation lifetimes and fragment channels of gas-phase, protonated YAn (n = 1,2) peptides and their dimers were measured with 266 nm photons. The protonated monomers were found to have a fast dissociation channel with an exponential lifetime of ∼200 ns while the protonated dimers show...... of the equipartition theorem. It demonstrates encouraging results in predicting fragmentation lifetimes of protonated peptides. Finally, we present the first experimental evidence for a photo-induced conversion of tyrosine-containing peptides into monocyclic aromatic hydrocarbon along with a formamide molecule both...

  20. REVISITING THE PUTATIVE TCR Cα DIMERIZATION MODEL THROUGH STRUCTURAL ANALYSIS

    Directory of Open Access Journals (Sweden)

    Jia-huai eWang

    2013-01-01

    Full Text Available Despite major advances in T cell receptor (TCR biology and structure, how peptide-MHC complex (pMHC ligands trigger αβ TCR activation remains unresolved. Two views exist. One model postulates that monomeric TCR-pMHC ligation events are sufficient while a second proposes that TCR-TCR dimerization in cis via Cα domain interaction plus pMHC binding is critical. We scrutinized 22 known TCR/pMHC complex crystal structures, and did not find any predicted molecular Cα-Cα contacts in these crystals that would allow for physiological TCR dimerization. Moreover, the presence of conserved glycan adducts on the outer face of the Cα domain preclude the hypothesized TCR dimerization through the Cα domain. Observed functional consequences of Cα mutations are likely indirect, with TCR microclusters at the immunological synapse driven by TCR transmembrane/cytoplasmic interactions via signaling molecules, scaffold proteins and/or cytoskeletal elements.