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Sample records for adjoining si atom

  1. Atomic scale quantum circuits in Si

    NASA Astrophysics Data System (ADS)

    Dusko, A.; Korkusinski, M.; Saraiva, A.; Delgado, A.; Koiller, B.; Hawrylak, P.

    The atomic scale circuits in Si are now realized by manipulation of dangling bonds on Si surface or incorporating dopant atoms in Si by STM techniques. We describe the electronic properties of these atomic scale quantum dot circuits (QDC) by the extended Hubbard-Kanamori Hamiltonian (HK), including on site Coulomb repulsion (U) and interdot hopping (t) , direct interaction (V) and exchange (J) terms. The interdot terms strongly depend on dopant position (RD) in Si lattice--small changes in RD strongly impact t, Vand J. We study how disorder in RD impacts QDC electronic properties, in particular the interplay of disorder and interactions. With no disorder in RD the energy spectrum (ES) of quantum dot chain at half-filling as a function of U / t (V , J = 0) shows a transition from ES dominated by kinetic energy (U / t < < 1) to ES dominated by Coulomb interactions for U / t > > 1 . The excited states group by single particle energy spacing (Hubbard bands) for weak (strong) interactions. In the weak interaction regime, disorder leads to localization, which strongly affects the electronic properties. We explore the effect of interactions and disorder on HK atomic scale circuits and potential many-body localized phases using Lanczos and Density Matrix Renormalization Group approaches.

  2. Incremental Parsing with Adjoining Operation

    NASA Astrophysics Data System (ADS)

    Kato, Yoshihide; Matsubara, Shigeki

    This paper describes an incremental parser based on an adjoining operation. By using the operation, we can avoid the problem of infinite local ambiguity. This paper further proposes a restricted version of the adjoining operation, which preserves lexical dependencies of partial parse trees. Our experimental results showed that the restriction enhances the accuracy of the incremental parsing.

  3. Experimental estimation of oxidation-induced Si atoms emission on Si(001) surfaces

    NASA Astrophysics Data System (ADS)

    Ogawa, Shuichi; Tang, Jiayi; Takakuwa, Yuji

    2015-08-01

    Kinetics of Si atoms emission during the oxidation of Si(001) surfaces have been investigated using reflection high energy electron diffraction combined with Auger electron spectroscopy. The area ratio of the 1 × 2 and the 2 × 1 domains on a clean Si(001) surface changed with the oxidation of the surface by Langmuir-type adsorption. This change in the domain ratio is attributed to the emission of Si atoms. We can describe the changes in the domain ratio using the Si emission kinetics model, which states that (1) the emission rate is proportional to the oxide coverage, and (2) the emitted Si atoms migrate on the surface and are trapped at SB steps. Based on our model, we find experimentally that up to 0.4 ML of Si atoms are emitted during the oxidation of a Si(001) surface at 576 °C.

  4. Experimental estimation of oxidation-induced Si atoms emission on Si(001) surfaces

    SciTech Connect

    Ogawa, Shuichi Tang, Jiayi; Takakuwa, Yuji

    2015-08-15

    Kinetics of Si atoms emission during the oxidation of Si(001) surfaces have been investigated using reflection high energy electron diffraction combined with Auger electron spectroscopy. The area ratio of the 1 × 2 and the 2 × 1 domains on a clean Si(001) surface changed with the oxidation of the surface by Langmuir-type adsorption. This change in the domain ratio is attributed to the emission of Si atoms. We can describe the changes in the domain ratio using the Si emission kinetics model, which states that (1) the emission rate is proportional to the oxide coverage, and (2) the emitted Si atoms migrate on the surface and are trapped at S{sub B} steps. Based on our model, we find experimentally that up to 0.4 ML of Si atoms are emitted during the oxidation of a Si(001) surface at 576 °C.

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

    NASA Astrophysics Data System (ADS)

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

    2010-08-01

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

  6. Diffusional kinetics of SiGe Dimers on Si(100) using atom-tracking scanning tunneling microscopy

    SciTech Connect

    QIN,X.R.; SWARTZENTRUBER,BRIAN S.; LAGALLY,M.G.

    2000-06-14

    Quantitative measurements of the diffusion of adsorbed mixed Ge-Si dimers on the Si(100) surface have been made as a function of temperature using atom-tracking scanning tunneling microscopy. These mixed dimers are distinguishable from pure Si-Si dimers by their characteristic kinetics--a 180-degree rotation between two highly buckled configurations. At temperatures at which the mixed dimers diffuse, atomic-exchange events occur, in which the Ge atom in the adsorbed dimer exchanges with a substrate Si atom. Re-exchange can also occur when the diffusing Si-Si dimer revisits the original site of exchange.

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

    NASA Astrophysics Data System (ADS)

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

    1998-04-01

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

  8. Fluorine atom abstraction by Si(100). I. Experimental

    NASA Astrophysics Data System (ADS)

    Tate, M. R.; Gosalvez-Blanco, D.; Pullman, D. P.; Tsekouras, A. A.; Li, Y. L.; Yang, J. J.; Laughlin, K. B.; Eckman, S. C.; Bertino, M. F.; Ceyer, S. T.

    1999-08-01

    In the interaction of low energy F2 with Si(100) at 250 K, a dissociative chemisorption mechanism called atom abstraction is identified in which only one of the F atoms is adsorbed while the other F atom is scattered into the gas phase. The dynamics of atom abstraction are characterized via time-of-flight measurements of the scattered F atoms. The F atoms are translationally hyperthermal but only carry a small fraction (˜3%) of the tremendous exothermicity of the reaction. The angular distribution of F atoms is unusually broad for the product of an exothermic reaction. These results suggest an "attractive" interaction potential between F2 and the Si dangling bond with a transition state that is not constrained geometrically. These results are in disagreement with the results of theoretical investigations implying that the available potential energy surfaces are inadequate to describe the dynamics of this gas-surface interaction. In addition to single atom abstraction, two atom adsorption, a mechanism analogous to classic dissociative chemisorption in which both F atoms are adsorbed onto the surface, is also observed. The absolute probability of the three scattering channels (single atom abstraction, two atom adsorption, and unreactive scattering) for an incident F2 are determined as a function of F2 exposure. The fluorine coverage is determined by integrating the reaction probabilities over F2 exposure, and the reaction probabilities are recast as a function of fluorine coverage. Two atom adsorption is the dominant channel [P2=0.83±0.03(95%, N=9)] in the limit of zero coverage and decays monotonically to zero. Single atom abstraction is the minor channel (P1=0.13±0.03) at low coverage but increases to a maximum (P1=0.35±0.08) at about 0.5 monolayer (ML) coverage before decaying to zero. The reaction ceases at 0.94±0.11(95%, N=9) ML. Thermal desorption and helium diffraction confirm that the dangling bonds are the abstraction and adsorption sites. No Si lattice

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

    NASA Astrophysics Data System (ADS)

    Hashizume, Tomihiro

    2000-03-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2006-11-01

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

  11. Atomic displacement free interfaces and atomic registry in SiO{sub 2}/(1x1) Si(100)

    SciTech Connect

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

    2006-11-15

    We use ion beam analysis to probe the structure and interface of ultrathin thermal oxide films grown on (1x1) Si(100) surfaces prepared using the Herbots-Atluri [U.S. patent No. 6,613,677 (Sept. 2, 2003)] wet chemical clean. We discover that these oxide layers are structurally registered with the substrate lattice with no interfacial structural disorder. Registry of Si atoms is most pronounced along <111> directions relative to the Si substrate, consistent with a {beta}-cristobalite epitaxial phase. This structurally registered phase transitions to an amorphous structure approximately 2 nm from the interface.

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

    NASA Astrophysics Data System (ADS)

    Kunimune, Yorinobu; Shimada, Yasuhiro; Sakurai, Yusuke; Inoue, Masao; Nishida, Akio; Han, Bin; Tu, Yuan; Takamizawa, Hisashi; Shimizu, Yasuo; Inoue, Koji; Yano, Fumiko; Nagai, Yasuyoshi; Katayama, Toshiharu; Ide, Takashi

    2016-04-01

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

  13. In situ control of atomic-scale Si layer with huge strain in the nanoheterostructure NiSi/Si/NiSi through point contact reaction.

    PubMed

    Lu, Kuo-Chang; Wu, Wen-Wei; Wu, Han-Wei; Tanner, Carey M; Chang, Jane P; Chen, Lih J; Tu, K N

    2007-08-01

    Nanoheterostructures of NiSi/Si/NiSi in which the length of the Si region can be controlled down to 2 nm have been produced using in situ point contact reaction between Si and Ni nanowires in an ultrahigh vacuum transmission electron microscope. The Si region was found to be highly strained (more than 12%). The strain increases with the decreasing Si layer thickness and can be controlled by varying the heating temperature. It was observed that the Si nanowire is transformed into a bamboo-type grain of single-crystal NiSi from both ends following the path with low-activation energy. We propose the reaction is assisted by interstitial diffusion of Ni atoms within the Si nanowire and is limited by the rate of dissolution of Ni into Si at the point contact interface. The rate of incorporation of Ni atoms to support the growth of NiSi has been measured to be 7 x 10(-4) s per Ni atom. The nanoscale epitaxial growth rate of single-crystal NiSi has been measured using high-resolution lattice-imaging videos. On the basis of the rate, we can control the consumption of Si and, in turn, the dimensions of the nanoheterostructure down to less than 2 nm, thereby far exceeding the limit of conventional patterning process. The controlled huge strain in the controlled atomic scale Si region, potential gate of Si nanowire-based transistors, is expected to significantly impact the performance of electronic devices.

  14. Origin of metallicity in atomic Ag wires on Si(557)

    NASA Astrophysics Data System (ADS)

    Krieg, U.; Lichtenstein, T.; Brand, C.; Tegenkamp, C.; Pfnür, H.

    2015-04-01

    We investigated the metallicity of Ag-\\sqrt{3} ordered atomic wires close to one monolayer (ML) coverage, which are formed on Si(557) via self assembly. For this purpose we combined high resolution electron energy loss spectroscopy with tunneling microscopy. By extending the excess Ag coverage up to 0.6 ML on samples annealed at high temperatures where partial desorption occurs, we demonstrate that one-dimensional metallicity in the Ag-\\sqrt{3}× \\sqrt{3} R30° ordered atomic wires on the (111) mini-terraces originates only from Ag atoms in excess of (local) monolayer coverage, which are adsorbed and localized at the highly stepped parts of the Si(557) surface. Thus these Ag atoms act as extrinsic dopants on the atomic scale, causing coverage dependent subband filling and increasing localization as a function of doping concentration. The second layer lattice gas as well as Ag islands on the (111) terraces turn out not to be relevant as dopants. We simulated the peculiar saturation behavior within a modified lattice gas model and give evidence that the preparation dependent saturation of doping is due to changes of average terrace size and step morphology induced by high temperature treatment.

  15. Atomic state and characterization of nitrogen at the SiC/SiO{sub 2} interface

    SciTech Connect

    Xu, Y.; Garfunkel, E. L.; Zhu, X.; Lee, H. D.; Xu, C.; Shubeita, S. M.; Gustafsson, T.; Ahyi, A. C.; Sharma, Y.; Williams, J. R.; Lu, W.; Ceesay, S.; Tuttle, B. R.; Pantelides, S. T.; Wan, A.; Feldman, L. C.

    2014-01-21

    We report on the concentration, chemical bonding, and etching behavior of N at the SiC(0001)/SiO{sub 2} interface using photoemission, ion scattering, and computational modeling. For standard NO processing of a SiC MOSFET, a sub-monolayer of nitrogen is found in a thin inter-layer between the substrate and the gate oxide (SiO{sub 2}). Photoemission shows one main nitrogen related core-level peak with two broad, higher energy satellites. Comparison to theory indicates that the main peak is assigned to nitrogen bound with three silicon neighbors, with second nearest neighbors including carbon, nitrogen, and oxygen atoms. Surprisingly, N remains at the surface after the oxide was completely etched by a buffered HF solution. This is in striking contrast to the behavior of Si(100) undergoing the same etching process. We conclude that N is bound directly to the substrate SiC, or incorporated within the first layers of SiC, as opposed to bonding within the oxide network. These observations provide insights into the chemistry and function of N as an interface passivating additive in SiC MOSFETs.

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

    NASA Astrophysics Data System (ADS)

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

    2016-06-01

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

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

    PubMed

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

    2016-06-24

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-09-01

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

  19. Atomic dynamics of In nanoclusters on Si(100)

    NASA Astrophysics Data System (ADS)

    Saranin, A. A.; Zotov, A. V.; Kuyanov, I. A.; Kishida, M.; Murata, Y.; Honda, S.; Katayama, M.; Oura, K.; Wei, C. M.; Wang, Y. L.

    2006-09-01

    Using scanning-tunneling microscopy and first-principles total-energy calculations, we have considered the structural properties of the so-called doped clusters formed by depositing additional 0.05 monolayer of In onto the 4×3 -periodicity magic-cluster array in the In/Si(100) system. Low-temperature STM observations have revealed that most of the doped clusters have an asymmetric shape. According to the total-energy calculations, these clusters have plausibly Si6In8 composition. In such a cluster, one of the In atoms is mobile and can hop between four equivalent sites within a cluster. The hopping between sites, located in the different 2a×3a halves of the cluster, is characterized by the barrier of about 0.7eV, and this hopping becomes frozen at 55K . In contrast, the hopping between the neighboring sites within the same cluster half persists up to very low temperatures, as the barrier height here is an order of magnitude lower. Due to the above structural properties, the doped asymmetric Si6In8 cluster can be treated as a promising switch, logic gate, or memory cell of the atomic-scale size.

  20. Molecular orbital calculations on atomic structures of Si-based covalent amorphous ceramics

    SciTech Connect

    Matsunaga, K.; Matsubara, H.

    1999-07-01

    The authors have performed ab-initio Hartree-Fock molecular orbital calculations of local atomic structures and chemical bonding states in Si-N covalent amorphous ceramics. Solute elements such as boron, carbon and oxygen were considered in the Si-N network, and the bonding characteristics around the solute elements were analyzed. When a nitrogen atom is substituted by a carbon atom, it was found that Si-C bonds reinforce the Si-N network due to strong covalency.

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

    PubMed

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

    2014-05-15

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

  2. Slow Collisions of Si3+ with Atomic Hydrogen

    NASA Astrophysics Data System (ADS)

    Joseph, D. C.; Gu, J.-P.; Saha, B. C.; Liebermann, H. P.; Funke, P.; Buenker, R. J.

    2010-03-01

    Low energy electron capture from hydrogen atom by multi-charged ions continues to be of interest and applications include both magnetically confined fusion and astrophysical plasmas. The charge exchange process reported here, Si^3+ + H -> Si^2+ + H^+ is an important destruction mechanism of Si^3+ in photo-ionized gas. The soft X-ray emission from comets has been explained by charge transfer of solar wind ions, among them Si^3+, with neutrals in the cometary gas vapor. The state selective cross sections are evaluated using the full quantum [1] and semi-classical molecular orbital close coupling (MOCC) [2] methods. Adiabatic potentials and wave functions for a number of low-lying singlet and triplet states of and symmetry are calculated wing the MRD-CI package [3]. Details will be presented at the conference. [4pt] [1] L. B. Zhao, D. C. Joseph, B. C. Saha, H. P. Liebermann, P. Funke and R. J. Buenker, Phys. Rev A, 79, 034701 (1009).[0pt] [2] M. Kimura and N. F. Lane, At. Mol. Opt. Phys 26, 79 (1990).[0pt] [3] R. J. Buenker, ``Current Aspects of Quantum Chemistry 1981, Vol 21, edited by R. Carbo (Elsevier, Amsterdam) p 17.

  3. Interplay between Switching Driven by the Tunneling Current and Atomic Force of a Bistable Four-Atom Si Quantum Dot.

    PubMed

    Yamazaki, Shiro; Maeda, Keisuke; Sugimoto, Yoshiaki; Abe, Masayuki; Zobač, Vladimír; Pou, Pablo; Rodrigo, Lucia; Mutombo, Pingo; Pérez, Ruben; Jelínek, Pavel; Morita, Seizo

    2015-07-08

    We assemble bistable silicon quantum dots consisting of four buckled atoms (Si4-QD) using atom manipulation. We demonstrate two competing atom switching mechanisms, downward switching induced by tunneling current of scanning tunneling microscopy (STM) and opposite upward switching induced by atomic force of atomic force microscopy (AFM). Simultaneous application of competing current and force allows us to tune switching direction continuously. Assembly of the few-atom Si-QDs and controlling their states using versatile combined AFM/STM will contribute to further miniaturization of nanodevices.

  4. Selective silver atom interaction at β-SiC(100) surfaces: From anisotropic diffusion to metal atomic wires and stripes

    NASA Astrophysics Data System (ADS)

    D'Angelo, M.; Aristov, V. Yu.; Soukiassian, P.

    2007-07-01

    Silver (Ag) atom interaction on β-SiC(100) surface reconstructions is investigated by atom-resolved scanning tunneling microscopy. On the 3×2 (Si-rich) reconstruction, the adsorbate-adsorbate interaction is dominant with no surface wetting, leading to Ag cluster formation. In contrast, on the c(4×2) Si-terminated reconstruction, almost equivalent Ag-Ag and Ag-surface interactions allow selective one dimensional nano-object formation including Ag atomic wires and stripes following the substrate registry. Their orientation is mediated by anisotropic Ag atom diffusion occurring along Si-dimer rows at 25°C and perpendicularly to them at elevated temperatures, suggesting dimer flipping as diffusion barrier. These metal nanowires potentially open up cross-wiring capability in massively parallel Si atomic lines network.

  5. Atomic force microscope manipulation of Ag atom on the Si(111) surface

    NASA Astrophysics Data System (ADS)

    Enkhtaivan, Batnyam; Oshiyama, Atsushi

    2017-01-01

    We present first-principles total-energy electronic-structure calculations that provide the microscopic mechanism of Ag atom diffusion between the half unit cells (HUCs) on the Si(111)-(7 ×7 ) surface with and without the tip of the atomic force microscope (AFM). We find that, without the presence of the AFM tip, there are three pathways of inter-HUC diffusion. The pathway, in which the diffusing atom passes over the nanohole of the surface, has the lowest energy barrier. The diffusion along this pathway between the two HUCs is almost symmetric with the energy barrier of about 0.8 eV in both directions. In the other two pathways, the adatom diffuses along the edge of the nanohole. The diffusion along these two pathways have an energy barrier of about 1 eV. With the presence of the tip, we find that the reaction pathways are essentially the same, but the diffusion along the edge of the nanohole has a lower energy barrier than the diffusion over the nanohole. Thus the diffusion channel is changed by the presence of the tip. In the diffusion along the edge of the nanohole, the energy barrier in one direction is substantially reduced to be 0.2-0.4 eV by the tip, while that of the diffusion in the reverse direction remains larger than 1 eV. The Si tip reduces the energy barrier more than the Pt tip due to the flexibility of the tip apex structure. In addition to the reduction of the barrier, the tip traps the diffusing adatom preventing diffusion in the reverse direction. Also we find that the shape of the tip apex structure is important for the adatom's trapping ability. The bond formation between the AFM tip atom and the surface adatom is essential for atom manipulation using the AFM tip. Our results show that atom manipulation is possible with both the metallic and semiconducting AFM tips.

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

    PubMed

    Cho, Yasuo; Hirose, Ryusuke

    2007-11-02

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

  7. Atomic-scale dynamics of atoms and dimers on the Si(001) surface

    SciTech Connect

    Swartzentruber, B.S.

    1996-12-31

    The kinetics of adsorbed Si monomers and dimers, at submonolayer coverage, are measured using scanning tunneling microscopy (STM). Si monomers are observed in empty-state STM images acquired between room temperature and 115 C. The monomers are trapped at the ends of rebonded-SB type dimer rows. When monomers thermally escape from the traps, they rapidly diffuse along the substrate dimer row until they find another unoccupied trap or return to their original trap. The binding activation barrier at isolated traps is {approximately}1.0 eV. A slightly lower barrier exists for monomers to hop between the ends of neighboring dimer rows - a process facilitating diffusion along segments of SB type steps. In addition to monomers, the interactions of adsorbed Si dimers with steps and islands on Si(001) are quantified using atom-tracking STM. Diffusing dimers are reflected from steps, sides of islands, and certain surface defect structures. Site-specific free energies are extracted from measurements of lattice-site occupation probabilities of dimers trapped between these reflecting barriers. Relative to the free energy of isolated dimers on a terrace, dimers located at the first lattice site next to SA steps and the sides of islands are bound by {approximately}0.03-0.06 eV. The binding decreases to half that at the second lattice site, and is indistinguishable from the free-terrace value at a distance of three or more lattice sites.

  8. Reactions of SiCl2 and SiHCl with H and Cl Atoms

    NASA Technical Reports Server (NTRS)

    Walch, Stephen P.; Dateo, C. E.

    2001-01-01

    Calculations have been carried out for the reaction of SiCl2 and SiHCl with H and Cl atoms. In each case, the stationary point geometries and harmonic frequencies were characterized using CASSCF/derivative methods and the cc-pVDZ basis set. Accurate energetics were obtained by combining the CCSD(T) results using the a-cc-pVTZ basis set with an extrapolation to the basis set limit using the a-cc-pVDZ, a-cc-pVTZ, and a-cc-pVQZ basis sets at the MP2 level. The geometries, energetics, and harmonic frequencies were used to obtain rate constants using conventional transition state theory or a Gorin-like model. In each case we find direct abstraction pathways compete with an addition elimination pathway. In the case of SiClH + H the two direct pathways are H abstraction which is barrierless and Cl abstraction with a barrier of 13.5 kcal/mol, while the addition elimination process has a barrier of 26.9 kcal/mol. In the case of SiCl2 + H the direct pathway is Cl abstraction with a barrier of 16.4 kcal/mol, while the addition elimination pathway has a barrier of 29.6 kcal/mol. In the case of SiClH + Cl the direct pathway is H abstraction which is barrierless and the addition elimination pathway has a barrier of 2.0 kcal/mol.

  9. Structure of self-assembled Mn atom chains on Si(001)

    NASA Astrophysics Data System (ADS)

    Villarreal, Renan; Longobardi, Maria; Koester, Sigrun A.; Kirkham, Christopher J.; Bowler, David; Renner, Christoph

    Mn has been found to self-assemble into atomic chains running perpendicular to the surface dimer reconstruction on Si(001). They differ from other atomic chains by a striking asymmetric appearance in filled state scanning tunneling microscopy (STM) images. This has prompted complicated structural models involving up to three Mn atoms per chain unit. Combining STM, atomic force microscopy and density functional theory we find that a simple necklace-like chain of single Mn atoms reproduces all their prominent features, including their asymmetry not captured by current models. The upshot is a remarkably simpler structure for modelling the electronic and magnetic properties of Mn atom chains on Si(001).

  10. Structure of Self-Assembled Mn Atom Chains on Si(001)

    NASA Astrophysics Data System (ADS)

    Villarreal, R.; Longobardi, M.; Köster, S. A.; Kirkham, Ch. J.; Bowler, D.; Renner, Ch.

    2015-12-01

    Mn has been found to self-assemble into atomic chains running perpendicular to the surface dimer reconstruction on Si(001). They differ from other atomic chains by a striking asymmetric appearance in filled state scanning tunneling microscopy (STM) images. This has prompted complicated structural models involving up to three Mn atoms per chain unit. Combining STM, atomic force microscopy, and density functional theory we find that a simple necklacelike chain of single Mn atoms reproduces all their prominent features, including their asymmetry not captured by current models. The upshot is a remarkably simpler structure for modeling the electronic and magnetic properties of Mn atom chains on Si(001).

  11. Study of the interaction of 4H-SiC and 6H-SiC(0001)Si surfaces with atomic nitrogen

    NASA Astrophysics Data System (ADS)

    Losurdo, Maria; Giangregorio, Maria M.; Bruno, Giovanni; Brown, April; Kim, Tong-Ho

    2004-11-01

    The interaction of atomic nitrogen with 4H- and 6H-SiC(0001) Si-face surfaces is investigated. Clean and atomically smooth terraced surfaces obtained by in situ cleaning using atomic hydrogen have been exposed at 200°C and 750°C to atomic nitrogen produced by a rf remote N2 plasma. Spectroscopic ellipsometry is used for real-time monitoring of the kinetics of SiC surface modifications, and determining the thickness and properties of the nitrided layer. Surface potential measurements reveal the band bending of the nitrided SiC surface. An improvement in the heteroepitaxy of GaN on the low-temperature nitrided SiC surface is found.

  12. DFT calculations on atom-specific electronic properties of G/SiC(0001)

    NASA Astrophysics Data System (ADS)

    Kajihara, M.; Suzuki, T.; Shahed, S. M. F.; Komeda, T.; Minamitani, E.; Watanabe, S.

    2016-05-01

    We investigate the atom-specific interfacial electronic properties of the epitaxial graphene on Si-terminated SiC substrate using density functional theory (DFT) calculation with van der Waals interaction correction, focusing on the dependency of the local electronic state on the chemical environment. The band structure projected on the respective atomic orbitals of the carbon atoms in the buffer layer and uppermost Si atoms demonstrates that the dangling bonds of these atoms form band structures around the Fermi level. The contribution of each atom to the dangling bond states strongly depends on the chemical environment, i.e., the presence/absence of the interlayer Si-C covalent bond. This difference also affects the atom-specific local density of states of the top-layer graphene through its interaction with the substrate/buffer layer. We demonstrate that the bias voltage dependency of the scanning tunneling spectroscopy (STS) mapping image clearly reflects the presence of the dangling bonds of the buffer layer carbon or uppermost Si atom in the substrate, which would enable the detection of the buried dangling bond with an atomic spatial resolution via STS.

  13. Mapping and control of atomic force on Si(1 1 1)square root(3) x square root(3)-Ag surface using noncontact atomic force microscope.

    PubMed

    Morita, S; Sugawara, Y

    2002-05-01

    We demonstrated the possibility of measuring the three-dimensional force-related map with true atomic resolution between an Si tip and Si(1 1 1)square root(3) x square root(3)-Ag sample surface by measuring the tip-sample distance dependence of noncontact atomic force microscope (NC-AFM) image, i.e. atomically resolved atomic force spectroscopy. Furthermore, we demonstrated the possibility of controlling the interaction force between the atom on the tip apex and a sample atom of Si(1 1 1)square root(3) x square root(3)-Ag surface on an atomic scale by placing an Ag atom on the Si tip apex instead of Si atom.

  14. Structural, electronic, and magnetic properties of heterofullerene C(58)Si with odd number of atoms and a near planar tetracoordinate Si atom.

    PubMed

    Liu, Feng-Ling; Jalbout, Abraham F

    2008-06-01

    Density functional calculations and minimization techniques have been employed to characterize the structural and electronic properties of [5,6]-heterofullerene-C(58)Si-C(2v). Since it has odd number of atoms and a near planar tetracoordinate Si atom on the skeleton of the cage, it has odd number of atoms assembling a cage and is a novel molecule. Vibrational frequencies of the molecule have been calculated at the B3LYP/6-31G* level of theory. The absence of imaginary vibrational frequency confirms that the molecule corresponds to a true minimum on the potential energy hypersurface. Sixteen (13)C nuclear magnetic resonance (NMR) spectral signals of C(58)Si are characterized, and its heat of formation was estimated in this work.

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

    NASA Astrophysics Data System (ADS)

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

    2016-09-01

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

  16. Thermal stability of hydrogen and sulfur atoms in a-SiSx:H films

    NASA Astrophysics Data System (ADS)

    Itoh, Takashi; Nitta, Shoji; Wang, S. L.; Taylor, P. C.

    1996-11-01

    The thermal stability of hydrogen and sulfur atoms in a-SiSx:H films is studied using gas effusion spectra and electron spectroscopy for chemical analysis. Two evolution peaks of hydrogen are found above 400 °C in gas effusion spectra of a-SiSx:H films. Sulfur atoms are evolved only above 550 °C. The stability of sulfur and the relationship of dangling bonds to sulfur effusion are discussed.

  17. Oxidation studies on small atom doped TI*5*SI*3*

    SciTech Connect

    Thom, Andrew

    1995-09-26

    This report described the oxidation and oxidation resistance of Ti5Si3, along with a discussion on general material properties. Single crystal studies of Ti5Si3Zx are included.

  18. Interface Engineering for Atomic Layer Deposited Alumina Gate Dielectric on SiGe Substrates.

    PubMed

    Zhang, Liangliang; Guo, Yuzheng; Hassan, Vinayak Vishwanath; Tang, Kechao; Foad, Majeed A; Woicik, Joseph C; Pianetta, Piero; Robertson, John; McIntyre, Paul C

    2016-07-27

    Optimization of the interface between high-k dielectrics and SiGe substrates is a challenging topic due to the complexity arising from the coexistence of Si and Ge interfacial oxides. Defective high-k/SiGe interfaces limit future applications of SiGe as a channel material for electronic devices. In this paper, we identify the surface layer structure of as-received SiGe and Al2O3/SiGe structures based on soft and hard X-ray photoelectron spectroscopy. As-received SiGe substrates have native SiOx/GeOx surface layers, where the GeOx-rich layer is beneath a SiOx-rich surface. Silicon oxide regrows on the SiGe surface during Al2O3 atomic layer deposition, and both SiOx and GeOx regrow during forming gas anneal in the presence of a Pt gate metal. The resulting mixed SiOx-GeOx interface layer causes large interface trap densities (Dit) due to distorted Ge-O bonds across the interface. In contrast, we observe that oxygen-scavenging Al top gates decompose the underlying SiOx/GeOx, in a selective fashion, leaving an ultrathin SiOx interfacial layer that exhibits dramatically reduced Dit.

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

    NASA Astrophysics Data System (ADS)

    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.

  20. Chemical reactions of atomic hydrogen at SiC surface and heterogeneous chemiluminescence

    NASA Astrophysics Data System (ADS)

    Styrov, V. V.; Tyutyunnikov, V. I.; Sergeev, O. T.; Oya, Y.; Okuno, K.

    2005-02-01

    In studies of the surface properties of SiC polytypes and chemical reactions of hydrogen atoms at SiC surfaces the surface (chemi)luminescence of SiC has been applied excited in the reaction of hydrogen atoms due to chemical energy released (heterogeneous chemiluminescence, HCL). The bulk photoluminescence (PL) have also been used for comparison with surface HCL. All the samples showed HCL, but only α-SiC (6H, 15R), technologically or specially doped (predominantly by N, B, Al), exhibited PL (λex=365 nm). Cubic polycrystalline β-SiC (or 3C SiC) did not show PL. The general luminescence band of α-SiC (6H, 15R) and B and Al doped SiC (6H) was a broad yellow band with λmax ranged from 620 to 650 nm for PL (110 K). Another less intensive luminescence band is a blue one, which has been observed only at low temperatures for α-SiC (6H,15R) and B and Al doped SiC (6H) in PL spectra and as a shoulder in HCL spectra (λmax=477 nm at 110 K for 15R SiC). The green band near 540 nm was also observed sometimes in PL spectra for α-SiC. The heat of adsorption of hydrogen atoms at polycrystalline β-SiC estimated from HCL data was found to be in the range from 2 to 3 eV.

  1. Atomic arrangement of alkali adatoms on the Si(001)-2 × 1 surface

    NASA Astrophysics Data System (ADS)

    Kobayashi, K.; Blügel, S.; Ishida, H.; Terakura, K.

    1991-02-01

    Adsorption sites of Na and Li on the Si(001)-2 × 1 surface at the saturation coverage are determined theoretically by using the simulated annealing method proposed by Williams and Soler. For Na, the most stable configuration is the combination of the hollow site along the dimer chain and the trough site on top of the third layer Si atom in contradiction to an earlier calculation. The substrate relaxation is a crucial factor for stabilizing this configuration. On the other hand Li atoms are adsorbed at low symmetry positions. For both of Na and Li, we observe a significant movement of the substrate atoms towards the ideal surface configuration.

  2. Fabrication of Cu nanowires along atomic step edge lines on Si(1 1 1) substrates

    NASA Astrophysics Data System (ADS)

    Tokuda, Norio; Watanabe, Hidenobu; Hojo, Daisuke; Yamasaki, Satoshi; Miki, Kazushi; Yamabe, Kikuo

    2004-10-01

    We have succeeded in the fabrication of high-aspect-ratio (length to width) Cu nanowires along atomic step edge lines on Si(1 1 1) substrates. The fabrication procedure consisted of two wet process steps: (1) flattening of the surface roughness to an atomic level by immersing Si(1 1 1) wafers in ultralow-dissolved-oxygen water (LOW), and (2) Cu nanowire formation by immersion in LOW containing 10 ppm Cu ions for 1 s at room temperature. On the other hand, no Cu nanowires were formed on the Si(1 1 1) surfaces when the dissolved oxygen content was 8 ppm in alkaline solution during the Cu deposition stage, even though the Si etching with OH - was enhanced. We consider that it is due to the decrease in reduced Cu atom density by the existence of the dissolved oxygen as superoxide anion radicals.

  3. Atomic structure of graphene on SiO2.

    PubMed

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

    2007-06-01

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

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

    SciTech Connect

    Ryu, Woo-Seog; Park, Jong-Man; Kim, Chang-Kyu; Kuk, II-Hyun

    1997-08-01

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

  5. Atomic probe microscopy of 3C SiC films grown on 6H SiC substrates

    NASA Technical Reports Server (NTRS)

    Steckl, A. J.; Roth, M. D.; Powell, J. A.; Larkin, D. J.

    1993-01-01

    The surface of 3C SiC films grown on 6H SiC substrates has been studied by atomic probe microscopy in air. Atomic-scale images of the 3C SiC surface have been obtained by STM which confirm the 111 line type orientation of the cubic 3C layer grown on the 0001 plane type surface of the hexagonal 6H substrate. The nearest-neighbor atomic spacing for the 3C layer has been measured to be 3.29 +/- 0.2 A, which is within 7 percent of the bulk value. Shallow terraces in the 3C layer have been observed by STM to separate regions of very smooth growth in the vicinity of the 3C nucleation point from considerably rougher 3C surface regions. These terraces are oriented at right angles to the growth direction. Atomic force microscopy has been used to study etch pits present on the 6H substrate due to high temperature HCl cleaning prior to CVD growth of the 3C layer. The etch pits have hexagonal symmetry and vary in depth from 50 nm to 1 micron.

  6. 1. EXTERIOR, SIDE OF PICKLE BARREL RESTAURANT AND ADJOINING STORE ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    1. EXTERIOR, SIDE OF PICKLE BARREL RESTAURANT AND ADJOINING STORE - Silverton Historic District, East Thirteenth & Green Streets (Commercial Building), East Thirteenh & Green Streets, Silverton, San Juan County, CO

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

    NASA Astrophysics Data System (ADS)

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

    2016-10-01

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

  8. The mechanism of low-k SiOCH film modification by oxygen atoms

    SciTech Connect

    Braginsky, O. V.; Kovalev, A. S.; Lopaev, D. V.; Malykhin, E. M.; Mankelevich, Yu. A.; Rakhimova, T. V.; Rakhimov, A. T.; Vasilieva, A. N.; Zyryanov, S. M.; Baklanov, M. R.

    2010-10-15

    The interaction of oxygen atoms with three types of plasma enhanced chemical vapor deposition low-k SiOCH films is studied. The samples were treated by O atoms in the far plasma afterglow conditions in a special experimental system designed for this study. The experimental system allowed avoiding the effect of ions and vacuum ultraviolet (VUV) photons on surface reactions and controlling the oxygen atom concentration over the samples. Fourier-transform infrared spectroscopy, x-ray fluorescence, and atomic force microscopy techniques were used to analyze the changes occurring in low-k films. Monte Carlo model for O atom interaction with low-k material that includes penetration, recombination, and reactions with methyl groups was developed. It is shown that the surface recombination on the pore wall surface determines the profile and penetration depth of O atoms into the films. The reaction of O atoms with methyl groups has lower probability and therefore proceeds in the background mode.

  9. Surfactant role of Ag atoms in the growth of Si layers on Si(111)√3×√3-Ag substrates

    SciTech Connect

    Yamagami, Tsuyoshi; Sone, Junki; Nakatsuji, Kan; Hirayama, Hiroyuki

    2014-10-13

    The growth of Si layers on Si(111)√3×√3-Ag substrates was studied for coverages of up to a few mono-layers. Atomically flat islands were observed to nucleate in the growth at 570 K. The top surfaces of the islands were covered in Ag atoms and exhibited a √3×√3 reconstruction with the same surface state dispersions as Si(111)√3×√3-Ag substrates. These results indicate that the Ag atoms on the substrate always hop up to the top of the Si layers.

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

    NASA Astrophysics Data System (ADS)

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

    1984-02-01

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

  11. Investigation of the local density of states in self-assembled GeSi/Si(001) nanoislands by combined scanning tunneling and atomic-force microscopy

    SciTech Connect

    Borodin, P. A.; Bukharaev, A. A.; Filatov, D. O. Isakov, M. A.; Shengurov, V. G.; Chalkov, V. Yu.; Denisov, Yu. A.

    2011-03-15

    The local density of states in self-assembled GeSi/Si(001) nanoislands is investigated for the first time by combined tunneling and atomic-force scanning microscopy. Current images and tunneling spectra of individual GeSi/Si(001) islands are obtained. These measurements yield the spatial and energy distributions of the local density of states in GeSi islands, respectively. The tunneling spectroscopy data demonstrate that uncapped Ge{sub 0.3}Si{sub 0.7}/Si(001) islands behave as type-I heterostructures.

  12. Recrystallization of atomically balanced amorphous pockets in Si: A source of point defects

    SciTech Connect

    Marques, Luis A.; Pelaz, Lourdes; Lopez, Pedro; Santos, Ivan; Aboy, Maria

    2007-10-15

    We use classical molecular dynamics simulation techniques to study the regrowth behavior of amorphous pockets in Si. We demonstrate that crystallization depends on the morphology of the pocket-crystal interface. Although our simulated amorphous pockets had not any excess nor deficit of atoms with respect to perfect crystal, after regrowth we found residual defects. Most of them are single Si interstitials and vacancies, but also larger defects have been encountered. We have determined their atomic structures and calculated their formation energies. These complexes are more stable than amorphous pockets, and may trigger the formation of extended defects or favor damage accumulation.

  13. Design of atomic step networks on Si(111) through strain distribution control

    NASA Astrophysics Data System (ADS)

    Omi, Hiroo; Homma, Yoshikazu; Ogino, Toshio; Stoyanov, Stoyan; Tonchev, Vesselin

    2004-01-01

    We propose an alternative method to control atomic step networks on silicon for future wafer-scale integration of self-assembling nanostructures. The method is the strain-distribution-control method that we have recently proposed in [H. Omi, D. J. Bottomley, and T. Ogino, Appl. Phys. Lett. 80, 1073 (2002)], which we apply here to design atomic step networks on vicinal Si(111) wafer. Si(111) with its strain patterned by buried silicon oxide inclusions was annealed at 1230 °C in ultrahigh vacuum and observed by in situ secondary electron microscopy and ex situ atomic force microscopy. The images show that the method enables us to create the desired arrays of atomic step networks on an arbitrary area of planar silicon wafer. The arrays remain stable during the 1230 °C annealing.

  14. Peculiarities of FeSi phonon spectrum induced by a change of atomic volume

    NASA Astrophysics Data System (ADS)

    Parshin, P. P.; Chumakov, A. I.; Alekseev, P. A.; Nemkovski, K. S.; Dubrovinskii, L.; Kantor, A.; Perßon, J.; Rüffer, R.

    2016-12-01

    We analyze in detail the results of experimental investigations of the evolution of the thermal vibration spectra for iron atoms in iron monosilicide FeSi depending on two external parameters, viz., temperature T (in the range 46-297 K at pressure P = 0.1 MPa) and pressure P (in the range 0.1 MPa-43 GPa at temperature T = 297 K), obtained by nuclear inelastic scattering of synchrotron radiation. The decrease of the atomic volume is accompanied by a rearrangement of the phonon spectrum, which is manifested, in particular, in the splitting of the low-energy peak in the spectrum and in an increase of the energy for all phonons. The changes of the average energy of the iron atom vibrational spectrum and of the Debye energy with decreasing atomic volume are analyzed. Different versions of FeSi electron spectrum variation, which can be used to explain the observed phonon anomalies, are considered.

  15. Reversible vertical manipulation of Ag atoms on Si(111)-(74 ×7) at room temperature

    NASA Astrophysics Data System (ADS)

    Ming, Fangfei; Wang, Kedong; Pan, Shuan; Liu, Jiepeng; Zhang, Xieqiu; Yang, Jinlong; Xiao, Xudong; Department of Physics, Chinese University of Hong Kong, Shatin, New Territory, Hong Kong, China Team; Hefei National LaboratoryPhysical Sciences At Microscales, University of Science; Technolog Team

    2011-03-01

    We have demonstrated a technique to conduct reproducible and reversible vertical manipulation of Ag atoms on the Si(111)-(7 × 7) surface at room temperature using a scanning tunneling microscope tip. The direction of the transfer of Ag atoms between the sample surface and the tip is simply controlled by the polarity of the bias voltage. Using the 7 × 7 unit cell as a nanometer size template, complex Ag nano-clusters could be assembled or disassembled by adding or removing Ag atoms in an atom-by-atom manner. With controlled number of Ag atoms filled in a half unit cell, we can construct Ag clusters with up to 25 Ag atoms. The precise control of the number of Ag atoms in the Ag clusters can provide critical information for understanding their physical and chemical properties, and form a fundamental base for the relevant studies of the Ag/Si(111)-(7 × 7) system and for fabricating nano-devices.

  16. Density functional theory study of stable configurations of substitutional and interstitial C and Sn atoms in Si and Ge crystals

    NASA Astrophysics Data System (ADS)

    Koyama, Hiroki; Sueoka, Koji

    2017-04-01

    Group IV semiconductor compounds, e.g., Si and Ge containing substitutional C (Cs) and/or Sn (Sns) atoms (mono-doping and co-doping) with contents of several % are attracting attention for application to solar cells because they are good for the environment and have an affinity with Si materials. In this study, we evaluate the stable configurations of C and/or Sn atoms in Si (Ge) crystals with a focus on the formation of interstitial C (Ci) atoms by means of density functional theory calculations. The Hakoniwa method proposed by Kamiyama et al. (2016) is applied to a 64-atom supercell to obtain the thermal equilibrium ratio of Ci to the total C atoms. The results of the analysis are fourfold. First, the isolated Cs atom is stabler than the isolated Ci atom in both Si and Ge crystals, and it is stabler in Si than in Ge. The isolated Sns atom is much stabler that Sni as well, but it is stabler in Ge than Si. Second, a Ci atom is formed in a [0 0 1] oriented Ci-Cs pair in Ge crystals with the ratio of 7.7% to total C atoms at 450 °C when the concentration of uniformly distributed C atoms is about 3%. Third, the difference of the formation energy of Ci and Cs in Si decreases to about 0.3 eV with an increase in the concentration of uniformly distributed C atoms up to 6%. Fourth, the co-doping of C and Sn suppresses the formation of Ci atoms in Si and Ge crystals. The results obtained here are useful for the prediction of possible atomic configurations of C and/or Sn in Si and Ge for solar cell application.

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

    PubMed

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

    2017-02-07

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

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

    NASA Astrophysics Data System (ADS)

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

    2017-02-01

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

  19. Protection of Diamond-like Carbon Films from Energetic Atomic Oxygen Degradation Through Si-doping Technology

    SciTech Connect

    Yokota, Kumiko; Tagawa, Masahito; Kitamura, Akira; Matsumoto, Koji; Yoshigoe, Akitaka; Teraoka, Yuden; Fontaine, Julien; Belin, Michel

    2009-01-05

    The effect of hyperthermal atomic oxygen (AO) exposure on the surface properties of Si-doped diamond-like carbon (DLC) was investigated. Two types of DLC were tested that contain approximately 10 at% and 20 at% of Si atoms. Surface analytical results of high-resolution x-ray photoelectron spectroscopy using synchrotron radiation (synchrotron radiation photoemission spectroscopy; SR-PES) as well as Rutherford backscattering spectroscopy (RBS) have been used for characterization of the AO-exposed Si-doped DLC. It was identified by SR-PES that a SiO{sub 2} layer was formed by the hyperthermal AO exposure at the Si-doped DLC surface. RBS data indicates that AO exposure leads to severe thickness loss on the undopedd DLC. In contrast, a SiO{sub 2} layer formed by the hyperthermal atomic oxygen reaction of Si-doped DLC protects the DLC underneath the SiO{sub 2} layer.

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

    SciTech Connect

    Suh, Sungin; Kim, Jun-Rae; Kim, Seongkyung; Hwang, Cheol Seong; Kim, Hyeong Joon; Ryu, Seung Wook; Cho, Seongjae

    2016-01-15

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

  1. Atomic-Level Simulation of Epitaxial Recrystallization and Phase Transformation in SiC

    SciTech Connect

    Gao, Fei; Devanathan, Ram; Zhang, Yanwen; Posselt, Matthias; Weber, William J.

    2006-06-01

    A nano-sized amorphous layer embedded in a perfect crystal has been created to study the amorphous-to-crystalline (a-c) transition and subsequent phase transformation in 3C-SiC by means of classical molecular dynamics methods. The recovery of bond defects and the rearrangement of atoms at the interfaces are important processes driving the initial epitaxial recrystallization of the amorphous layer, which is eventually hindered by the nucleation and growth of a polycrystalline 2H-SiC phase. A spectrum of activation energies, ranging from about 0.8 eV to 2.0 eV, is associated with these processes. Following formation of the 2H phase, the kink sites and triple junctions formed at the interfaces between 2H- and 3C-SiC provide low-energy paths for 2H-SiC atoms to transform to 3C-SiC atoms, and complete recrystallization back to the 3C structure occurs at 2000 K with an activation energy on the order of 2.3 eV.

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

    NASA Astrophysics Data System (ADS)

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

    2017-03-01

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

  3. Electronic bond rupture of Si atoms on Si(111)-(2×1) induced by valence excitation

    NASA Astrophysics Data System (ADS)

    Inami, E.; Tanimura, K.

    2007-07-01

    Scanning tunneling microscopy study reveals the electronic local bond rupture of threefold-coordinated Si atoms at intrinsic sites on Si(111)-(2×1) under nanosecond-laser excitation at 1064nm . The rate of bond rupture leading to monovacancy formation on the surface depends superlinearly on the excitation intensity. This primary step of surface-structural change is followed by efficient formation of vacancy clusters with two distinctive morphologies: vacancy strings aligned along the Si-atom chain in one dimension and vacancy islands developed across the chains in two dimensions. Quantitative analysis of the vacancy clustering process shows that the bond-rupture rate at sites nearest to pre-existing surface defects is enhanced more than a factor of 1000 relative to perfect sites. We also studied effects of different excitation wavelength and of Fermi-level positions on the bond-rupture process. The laser-induced surface bond-rupture mechanism is discussed in terms of two-hole localization of optically generated nonequilibrated valence holes on the surface sites.

  4. The atomic arrangement of iimoriite-(Y), Y2(SiO4)(CO3)

    USGS Publications Warehouse

    Hughes, J.M.; Foord, E.E.; Jai-Nhuknan, J.; Bell, J.M.

    1996-01-01

    Iimoriite-(Y) from Bokan Mountain, Prince of Wales Island, Alaska has been studied using single-crystal X-ray-diffraction techniques. The mineral, ideally Y2(SiO4)(CO3), crystallizes in space group P1, with a 6.5495(13), b 6.6291(14), c 6.4395(11)A??, ?? 116.364(15), ?? 92.556(15) and ?? 95.506(17)??. The atomic arrangement has been solved and refined to an R value of 0.019. The arrangement of atoms consists of alternating (011) slabs of orthosilicate groups and carbonate groups, with no sharing of oxygen atoms between anionic complexes in adjacent slabs. Y1 atoms separate adjacent tetrahedra along [100] within the orthosilicate slab, and Y2 atoms separate adjacent carbonate groups along [100] within the carbonate slab. Adjacent orthosilicate and carbonate slabs are linked in (100) by bonding Y atoms from each slab to oxygen atoms of adjacent slabs, in the form of YO8 polyhedra. The Y1 atoms exist in Y12O14 dimers in the orthosilicate slab, and the Y2 atoms exist in continuous [011] ribbons of edge-sharing Y2O8 polyhedra in the carbonate slab.

  5. Atomic insight into tribochemical wear mechanism of silicon at the Si/SiO2 interface in aqueous environment: Molecular dynamics simulations using ReaxFF reactive force field

    NASA Astrophysics Data System (ADS)

    Wen, Jialin; Ma, Tianbao; Zhang, Weiwei; Psofogiannakis, George; van Duin, Adri C. T.; Chen, Lei; Qian, Linmao; Hu, Yuanzhong; Lu, Xinchun

    2016-12-01

    In this work, the atomic mechanism of tribochemical wear of silicon at the Si/SiO2 interface in aqueous environment was investigated using ReaxFF molecular dynamics (MD) simulations. Two types of Si atom removal pathways were detected in the wear process. The first is caused by the destruction of stretched Si-O-Si bonds on the Si substrate surface and is assisted by the attachment of H atoms on the bridging oxygen atoms of the bonds. The other is caused by the rupture of Si-Si bonds in the stretched Si-Si-O-Si bond chains at the interface. Both pathways effectively remove Si atoms from the silicon surface via interfacial Si-O-Si bridge bonds. Our simulations also demonstrate that higher pressures applied to the silica phase can cause more Si atoms to be removed due to the formation of increased numbers of interfacial Si-O-Si bridge bonds. Besides, water plays a dual role in the wear mechanism, by oxidizing the Si substrate surface as well as by preventing the close contact of the surfaces. This work shows that the removal of Si atoms from the substrate is a result of both chemical reaction and mechanical effects and contributes to the understanding of tribochemical wear behavior in the microelectromechanical systems (MEMS) and Si chemical mechanical polishing (CMP) process.

  6. Competitive diffusion of gold and copper atoms in Cu/Au/Si and Au/Cu/Si annealed systems

    NASA Astrophysics Data System (ADS)

    Benazzouz, C.; Benouattas, N.; Bouabellou, A.

    2005-04-01

    Thermal evaporation is used to deposit Au/Cu and Cu/Au bilayers on (1 1 1) monocrystalline silicon substrates. The layers composition and surface morphology are performed as function of annealing temperature at 200 and 400 °C using X-ray diffraction, Rutherford backscattering spectroscopy and scanning electron microscopy. Independently to the sequence of copper and gold deposition, Cu3Si and Cu4Si copper silicides result to the reaction and interdiffusion at the different interfaces. The 1000 and 1200 Å thickness of gold and copper diffusion barriers are insufficient to prevent the diffusion of copper and gold atoms respectively, after an annealing of only 200 °C. The fitting of concentration profiles of RBS spectra by using the RUMP software revealed a growth of silicides layers not uniform laterally and in depth.

  7. Atomic pillar-based nanoprecipitates strengthen AlMgSi alloys.

    PubMed

    Chen, J H; Costan, E; van Huis, M A; Xu, Q; Zandbergen, H W

    2006-04-21

    Atomic-resolution electron microscopy reveals that pillarlike silicon double columns exist in the hardening nanoprecipitates of AlMgSi alloys, which vary in structure and composition. Upon annealing, the Si2 pillars provide the skeleton for the nanoparticles to evolve in composition, structure, and morphology. We show that they begin as tiny nuclei with a composition close to Mg2Si2Al7 and a minimal mismatch with the aluminum matrix. They subsequently undergo a one-dimensional growth in association with compositional change, becoming elongated particles. During the evolution toward the final Mg5Si6 particles, the compositional change is accompanied by a characteristic structural change. Our study explains the nanoscopic reasons that the alloys make excellent automotive materials.

  8. Toward the Understanding of Selective Si Nano-Oxidation by Atomic Scale Simulations.

    PubMed

    Khalilov, Umedjon; Bogaerts, Annemie; Neyts, Erik C

    2017-03-01

    The continuous miniaturization of nanodevices, such as transistors, solar cells, and optical fibers, requires the controlled synthesis of (ultra)thin gate oxides (<10 nm), including Si gate-oxide (SiO2) with high quality at the atomic scale. Traditional thermal growth of SiO2 on planar Si surfaces, however, does not allow one to obtain such ultrathin oxide due to either the high oxygen diffusivity at high temperature or the very low sticking ability of incident oxygen at low temperature. Two recent techniques, both operative at low (room) temperature, have been put forward to overcome these obstacles: (i) hyperthermal oxidation of planar Si surfaces and (ii) thermal or plasma-assisted oxidation of nonplanar Si surfaces, including Si nanowires (SiNWs). These nano-oxidation processes are, however, often difficult to study experimentally, due to the key intermediate processes taking place on the nanosecond time scale. In this Account, these Si nano-oxidation techniques are discussed from a computational point of view and compared to both hyperthermal and thermal oxidation experiments, as well as to well-known models of thermal oxidation, including the Deal-Grove, Cabrera-Mott, and Kao models and several alternative mechanisms. In our studies, we use reactive molecular dynamics (MD) and hybrid MD/Monte Carlo simulation techniques, applying the Reax force field. The incident energy of oxygen species is chosen in the range of 1-5 eV in hyperthermal oxidation of planar Si surfaces in order to prevent energy-induced damage. It turns out that hyperthermal growth allows for two growth modes, where the ultrathin oxide thickness depends on either (1) only the kinetic energy of the incident oxygen species at a growth temperature below Ttrans = 600 K, or (2) both the incident energy and the growth temperature at a growth temperature above Ttrans. These modes are specific to such ultrathin oxides, and are not observed in traditional thermal oxidation, nor theoretically considered

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

    PubMed

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

    2015-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2013-07-01

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

  11. Dust and Sand Forecasting in Iraq and Adjoining Countries

    DTIC Science & Technology

    1991-11-01

    8217’Illllllllt AD-A247 588 AWS/TN--91/001 DUST AND SAND FORECASTING IN IRAQ AND ADJOINING COUNTRIES by MSGT WALTER D. WILKERSON AFGWC/DOF NOVEMBER 1991...Sand Forecasting in Iraq and Adjoining Countries 6. Author: MSgt Walter D. Wilkerson, AFGWC/DOF 7. Performiig Organization Name and Address: Air...weather forecasting , discusses airborne dust and sand in Iraq, Kuwait, Syria, eastern Jordan, western Iran, and the northern Arabian Peninsula. Describes

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

    NASA Astrophysics Data System (ADS)

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

    2000-01-01

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

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

    PubMed

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

    2000-01-10

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

  14. Si-rich W silicide films composed of W-atom-encapsulated Si clusters deposited using gas-phase reactions of WF6 with SiH4.

    PubMed

    Okada, Naoya; Uchida, Noriyuki; Kanayama, Toshihiko

    2016-02-28

    We formed Si-rich W silicide films composed of Sin clusters, each of which encapsulates a W atom (WSi(n) clusters with 8 < n ≤ ∼ 12), by using a gas-phase reaction between WF6 and SiH4 in a hot-wall reactor. The hydrogenated WSi(n)H(x) clusters with reduced F concentration were synthesized in a heated gas phase and subsequently deposited on a substrate heated to 350-420 °C, where they dehydrogenated and coalesced into the film. Under a gas pressure of SiH4 high enough for the WSi(n)H(x) reactant to collide a sufficient number of times with SiH4 molecules before reaching the substrate, the resulting film was composed of WSi(n) clusters with a uniform n, which was determined by the gas temperature. The formed films were amorphous semiconductors with an optical gap of ∼0.8-1.5 eV and an electrical mobility gap of ∼0.05-0.12 eV, both of which increased as n increased from 8 to 12. We attribute this dependence to the reduction of randomness in the Si network as n increased, which decreased the densities of band tail states and localized states.

  15. Atomic decoration of a random-cluster model for icosahedral-phase AlMnSi

    SciTech Connect

    Robertson, J.L.; Moss, S.C. )

    1991-01-21

    Preliminary results on the atomic decoration of a random-cluster model for icosahedral-phase alloys are presented. The calculated neutron and x-ray intensities compare quite favorably with experimental intensity data on {ital i}-AlMnSi. The origin of the peak at {ital Q}=1.62 A{sup {minus}1}, associated with the prepeak found in amorphous'' AlMnSi, as well as the ubiquitous diffuse'' scattering, seen experimentally under the groups of strong peaks in all icosahedral-phase alloys, are revealed selectively in the calculated partial intensities for Al-Al, Al-Mn, and Mn-Mn correlations.

  16. Rapid Fabrication of Lightweight SiC Optics using Reactive Atom Plasma (RAP) Processing

    NASA Technical Reports Server (NTRS)

    Fiske, Peter S.

    2006-01-01

    Reactive Atom Plasma (RAP) processing is a non-contact, plasma-based processing technology that can be used to generate damage-free optical surfaces. We have developed tools and processes using RAP that allow us to shape extremely lightweight mirror Surfaces made from extremely hard-to-machine materials (e.g. SiC). We will describe our latest results using RAP in combination with other technologies to produce finished lightweight SiC mirrors and also discuss applications for RAP in the rapid fabrication of mirror segments for reflective and grazing incidence telescopes.

  17. Diffusons, locons and propagons: character of atomic vibrations in amorphous Si

    NASA Astrophysics Data System (ADS)

    Allen, Philip B.; Feldman, Joseph L.; Fabian, Jaroslav; Wooten, Frederick

    1999-11-01

    Numerical studies of amorphous Si show that the lowest 4% of vibrational modes are plane wave like ('propagons') and the highest 3% of modes are localized ('locons'). The rest are neither plane wave like nor localized. We call them 'diffusons'. Since diffusons are by far the most numerous, we try to characterize them by calculating such properties as the wave-vector and polarization (which do not seem to be useful), 'phase quotient' (a measure of the change of vibrational phase between first-neighbour atoms), spatial polarization memory and diffusivity. Localized states are characterized by finding decay lengths, inverse participation ratios and coordination numbers of the participating atoms.

  18. Catalytic role of boron atoms in self-interstitial clustering in Si

    NASA Astrophysics Data System (ADS)

    Hwang, Gyeong S.; Goddard, William A.

    2003-08-01

    Using density functional theory (DFT) calculations and kinetic simulations, we have investigated the influence of boron atoms on self-interstitial clustering in Si. From DFT calculations of neutral interstitial clusters with a single B atom (BsIn, n⩽4), we find that the binding of B (BsIn→In-1+BsI) becomes substantially weaker than that of an interstitial (BsIn→BsIn-1+I) when n⩾4. This implies boron can be liberated while leaving an interstitial cluster behind. Our kinetic simulations including the boron liberation explain well experimental observations reported by J. L. Benton et al., J. Appl. Phys. 82, 120 (1997).

  19. DNA molecules sticking on a vicinal Si(111) surface observed by noncontact atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Arai, Toyoko; Tomitori, Masahiko; Saito, Masato; Tamiya, Eiichi

    2002-03-01

    The DNA molecules on a vicinal Si(111) substrate with steps of single and double bi-atomic layers are imaged by noncontact atomic force microscopy (nc-AFM) in ultrahigh vacuum. The water solution containing pBR322 plasmid DNA molecules digested by Cla I is dropped on the substrate in a pure nitrogen atmosphere in a glove box, which is connected to the introduction chamber of the AFM. The ends of DNA molecules are frequently folded and pinned at the steps on the substrate, and the DNA strings often lie along the step. The chemical and dipole interactions between the DNA and the semiconductor substrate seem to play an important role in folding, pinning and sticking on the Si(111) substrate.

  20. Photoactivated processes in optical fibers: generation and conversion mechanisms of twofold coordinated Si and Ge atoms.

    PubMed

    Giacomazzi, Luigi; Martin-Samos, Layla; Boukenter, Aziz; Ouerdane, Youcef; Girard, Sylvain; Alessi, Antonino; Richard, Nicolas; de Gironcoli, Stefano

    2017-03-27

    In this work we present an extensive investigation of nanoscale physical phenomena related to oxygen-deficient centers (ODC) in silica and Ge-doped silica by means of first-principles calculations, including nudged-elastic band (NEB), electron paramagnetic resonance (EPR) parameters calculations, and many-body perturbation theory (GW and Bethe-Salpeter Equation) techniques. We show that by neutralizing positively charged oxygen monovacancies we can obtain model structures of twofold Si and Ge defects of which the calculated absorption spectra and singlet-to-triplet transitions are in excellent agreement with the experimental optical absorption and photo-luminescence data. In particular we provide an exhaustive analysis of the main exciton peaks related to the presence of twofold defects including long-range correlation effects. By calculating the reaction pathways and energy barriers necessary for the interconversion, we advance a double precursory origin of the E'α and Ge(2) centers as due to the ionization of neutral oxygen monovacancies (Si-Si and Ge-Si dimers) and as due to the ionization of twofold Si and Ge defects. Furthermore two distinct structural conversion mechanisms are found to occur between the neutral oxygen monovacancy and the twofold Si (and Ge) atom configurations. Such conversion mechanisms allow to explain the radiation induced generation of the ODC(II) centers, their photobleaching, and also their generation during the drawing of optical fibers.

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

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

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

  2. Partitioning of aluminum atoms in crystallographically non-equivalent tetrahedral sites of the zeolite offretite by 29Si MAS NMR

    NASA Astrophysics Data System (ADS)

    Chen, T. H.; Wang, K. X.; Luo, W. L.; Yuan, Z. Y.; Wang, J. Z.; Ding, D. T.; Li, H. X.; Hu, C.

    1996-04-01

    For the zeolite offretite, a formula is proposed which includes the framework Si/Al ratio ( R), the partitioning ratio of Al over two crystallographically non-equivalent tetrahedral sites ( r) and intensities of the observed peaks in the 29Si MAS NMR spectrum. By this formula, the framework Si/Al ratio of offretite can be estimated from the 29Si MAS NMR spectrum. Combined with chemical analysis of the Si/Al ratio, Al partitioning in two kinds of T sites can also be deduced. It is concluded that the T B sites are favored by Al atoms in parent offretites and Al atoms at T B sites can more easily be substituted isomorphously by Si when treated with (NH 4) 2SiF 6. The formula proposed here is based only on experiments and may be used to testify some statistical models of Al distributions in offretites.

  3. Nature of point defects on SiO2/Mo(112) thin films and their interaction with Au atoms.

    PubMed

    Martinez, Umberto; Giordano, Livia; Pacchioni, Gianfranco

    2006-08-31

    We have studied by means of periodic DFT calculations the structure and properties of point defects at the surface of ultrathin silica films epitaxially grown on Mo(112) and their interaction with adsorbed Au atoms. For comparison, the same defects have been generated on an unsupported silica film with the same structure. Four defects have been considered: nonbridging oxygen (NBO, [triple bond]Si-O(*)), Si dangling bond (E' center, [triple bond]Si(*)), oxygen vacancy (V(O), [triple bond]Si-Si[triple bond]), and peroxo group ([triple bond]Si-O-O-Si[triple bond]), but only the NBO and the V(O) centers are likely to form on the SiO(2)/Mo(112) films under normal experimental conditions. The [triple bond]Si-O(*) center captures one electron from Mo forming a silanolate group, [triple bond]Si-O(-), sign of a direct interaction with the metal substrate. Apart from the peroxo group, which is unreactive, the other defects bind strongly the Au atom forming stable surface complexes, but their behavior may differ from that of the same centers generated on an unsupported silica film. This is true in particular for the two most likely defects considered, the nonbridging oxygen, [triple bond]Si-O(*), and the oxygen vacancy, [triple bond]Si-Si[triple bond].

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

    NASA Astrophysics Data System (ADS)

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

    2017-03-01

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

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

    SciTech Connect

    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.

  6. The Si/Si_3N4 Interface and Si/Si_3N4 Submicron Mesa: A Multi-million Atom Molecular Dynamics Study

    NASA Astrophysics Data System (ADS)

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

    1998-03-01

    Using molecular dynamics simulations on parallel computers, the interface structure, stress distribution, crack propagation and fracture in a Si_3N4 film on Si substrate are studied. Bulk Si is described by Stillinger-Weber potential and Si_3N4 is represented by a combination of two- and three-body covalent interactions. At the interface, the charge transfer is taken from LCAO electronic structure calculations (G.-L. Zhao and M.E. Bachlechner, Europhys. Lett. 36, 287 (1997)). Results for structural correlations at the interface and 3D stress distribution for the submicron mesa are presented.

  7. Electrical behavior of atomic layer deposited high quality SiO{sub 2} gate dielectric

    SciTech Connect

    Pradhan, Sangram K.; Tanyi, Ekembu K.; Skuza, Jonathan R.; Xiao, Bo; Pradhan, Aswini K.

    2015-01-01

    Comprehensive and systematic electrical studies were performed on fabrication of high quality SiO{sub 2} thin films MOS capacitor using the robust, novel, and simple atomic layer deposition (ALD) technique using highly reactive ozone and tris (dimethylamino) silane (TDMAS) precursors. Ideal capacitance–voltage curve exhibits a very small frequency dispersion and hysteresis behavior of the SiO{sub 2} MOS capacitor grown at 1 s TDMAS pulse, suggesting excellent interfacial quality and purity of the film as probed using x-ray photoelectron studies. The flat-band voltage of the device shifted from negative toward positive voltage axis with increase of TDMAS pulses from 0.2 to 2 s. Based on an equivalent oxide thickness point of view, all SiO{sub 2} films have gate leakage current density of (5.18 × 10{sup −8} A/cm{sup 2}) as well as high dielectric break down fields of more than (∼10 MV/cm), which is better and comparable to that of thermally grown SiO{sub 2} at temperatures above 800 °C. These appealing electrical properties of ALD grown SiO{sub 2} thin films enable its potential applications such as high-quality gate insulators for thin film MOS transistors, as well as insulators for sensor and nanostructures on nonsilicon substrates.

  8. Microstructural investigation of Sr-modified Al-15 wt%Si alloys in the range from micrometer to atomic scale.

    PubMed

    Timpel, M; Wanderka, N; Vinod Kumar, G S; Banhart, J

    2011-05-01

    Strontium-modified Al-15 wt%Si casting alloys were investigated after 5 and 60 min of melt holding. The eutectic microstructures were studied using complementary methods at different length scales: focused ion beam-energy selective backscattered tomography, transmission electron microscopy and 3D atom probe. Whereas the samples after 5 min of melt holding show that the structure of eutectic Si changes into a fine fibrous morphology, the increase of prolonged melt holding (60 min) leads to the loss of Sr within the alloy with an evolution of an unmodified eutectic microstructure displaying coarse interconnected Si plates. Strontium was found at the Al/Si eutectic interfaces on the side of the eutectic Al region, measured by 3D atom probe. The new results obtained using 3D atom probe shed light on the location of Sr within the Al-Si eutectic microstructure.

  9. Electrical properties of amorphous and epitaxial Si-rich silicide films composed of W-atom-encapsulated Si clusters

    SciTech Connect

    Okada, Naoya; Uchida, Noriyuki; Kanayama, Toshihiko

    2015-03-07

    We investigated the electrical properties and derived the energy band structures of amorphous Si-rich W silicide (a-WSi{sub n}) films and approximately 1-nm-thick crystalline WSi{sub n} epitaxial films (e-WSi{sub n}) on Si (100) substrates with composition n = 8–10, both composed of Si{sub n} clusters each of which encapsulates a W atom (WSi{sub n} clusters). The effect of annealing in the temperature range of 300–500 °C was also investigated. The Hall measurements at room temperature revealed that a-WSi{sub n} is a nearly intrinsic semiconductor, whereas e-WSi{sub n} is an n-type semiconductor with electron mobility of ∼8 cm{sup 2}/V s and high sheet electron density of ∼7 × 10{sup 12 }cm{sup −2}. According to the temperature dependence of the electrical properties, a-WSi{sub n} has a mobility gap of ∼0.1 eV and mid gap states in the region of 10{sup 19 }cm{sup −3} eV{sup −1} in an optical gap of ∼0.6 eV with considerable band tail states; e-WSi{sub n} has a donor level of ∼0.1 eV with sheet density in the region of 10{sup 12 }cm{sup −2} in a band gap of ∼0.3 eV. These semiconducting band structures are primarily attributed to the open band-gap properties of the constituting WSi{sub n} cluster. In a-WSi{sub n}, the random network of the clusters generates the band tail states, and the formation of Si dangling bonds results in the generation of mid gap states; in e-WSi{sub n}, the original cluster structure is highly distorted to accommodate the Si lattice, resulting in the formation of intrinsic defects responsible for the donor level.

  10. Identification of 6H-SiC polar faces with pull-off force of atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Gan, Di; Song, Youting; Yang, Junwei; Chen, Hongxiang; Guo, Liwei; Chen, Xiaolong

    2016-12-01

    Distinguishing SiC (0001) Si-face from SiC (000-1) C-face without any damages is extremely important because the two polar faces have different physical and chemical properties which seriously influence the quality of a homoepitaxy or heteroepitaxy thin film on it. Here, a convenient and nondestructive detection method is developed to distinguish the Si-face and C-face of a (0001) oriented SiC wafer by employing a pull-off force measurement using atomic force microscopy. It is found that the pull-off force from a Si-face of 6H-SiC is about two times of that from a C-face, no matter it is a two-face chemical mechanical polishing or etched 6H-SiC wafer. The method developed here is suitable to identify polar faces of materials only if the two polar faces having different surface energy.

  11. Monitoring Si growth on Ag(111) with scanning tunneling microscopy reveals that silicene structure involves silver atoms

    SciTech Connect

    Prévot, G.; Bernard, R.; Cruguel, H.; Borensztein, Y.

    2014-11-24

    Using scanning tunneling microscopy (STM), the elaboration of the so-called silicene layer on Ag(111) is monitored in real time during Si evaporation at different temperatures. It is shown that the growth of silicene is accompanied by the release of about 65% of the surface Ag atoms from the Si covered areas. We observe that Si islands develop on the Ag terraces and Si strips at the Ag step edges, progressively forming ordered (4×4), (√(13)×√(13)) R13.9°, and dotted phases. Meanwhile, displaced Ag atoms group to develop additional bare Ag terraces growing round the Si islands from the pristine Ag step edges. This indicates a strong interaction between Si and Ag atoms, with an important modification of the Ag substrate beneath the surface layer. This observation is in contradiction with the picture of a silicene layer weakly interacting with the unreconstructed Ag substrate, and strongly indicates that the structure of silicene on Ag(111) corresponds either to a Si-Ag surface alloy or to a Si plane covered with Ag atoms.

  12. Atomic Precision Donor Devices Fabricated on Strained Silicon on Insulator (sSOI) with SiGe

    NASA Astrophysics Data System (ADS)

    Yitamben, E.; Bussmann, E.; Scrymgeour, D. A.; Rudolph, M.; Carr, S. M.; Ward, D. R.; Carroll, M. S.

    Recently, Si:P donor spin qubits have achieved coherence times (nuclear & e-) that underscore their quantum computing potential. One next major challenge is to integrate donors into a gated structure where electrons can be moved between P, or drawn off of the P to interact, e.g. to an interface as in Kane's proposal. A key constraint is limited thermal budget, to limit P thermal segregation, which precludes typical gate oxidation of Si. We are developing an alternative materials stack utilizing an interfacial barrier layer of relaxed epitaxial SiGe, with donors placed in a strained Si-on-insulator (sSOI) substrate. We fabricate atomic precision donor structures in sSOI via STM hydrogen lithography. Utilizing Si microfabrication and STM in tandem with our Si and Ge molecular beam epitaxy (MBE), we fabricated devices to test our SiGe/sSOI stack concept and atomic-precision fab techniques. To establish our donor-doping capability, we made Hall and Van der Pauw devices in P:sSOI delta-doped layers exhibiting ne >1014/cm2 and mobilities of ~100 cm2/Vs (T =4K) similar to results reported relaxed Si reported elsewhere. Second, we have grown our concept epitaxial SiGe/sSOI stack, evaluated the morphology using STM, and fabricated Hall devices to evaluate low-T transport in our first SiGe/sSOI. Here, we report on these advances in atomic precision donor fab, along with STM analysis our MBE SiGe/sSOI. This work extends STM-based atom precision fab on strained Si toward a vertically gated architecture.

  13. Laser-assisted atom probe tomography of Ti/TiN films deposited on Si.

    PubMed

    Sanford, N A; Blanchard, P T; White, R; Vissers, M R; Diercks, D R; Davydov, A V; Pappas, D P

    2017-03-01

    Laser-assisted atom probe tomography (L-APT) was used to examine superconducting TiN/Ti/TiN trilayer films with nominal respective thicknesses of 5/5/5 (nm). Such materials are of interest for applications that require large arrays of microwave kinetic inductance detectors. The trilayers were deposited on Si substrates by reactive sputtering. Electron energy loss microscopy performed in a scanning transmission electron microscope (STEM/EELS) was used to corroborate the L-APT results and establish the overall thicknesses of the trilayers. Three separate batches were studied where the first (bottom) TiN layer was deposited at 500°C (for all batches) and the subsequent TiN/Ti bilayer was deposited at ambient temperature, 250°C, and 500°C, respectively. L-APT rendered an approximately planar TiN/Si interface by making use of plausible mass-spectral assignments to N3(1+), SiN(1+), and SiO(1+). This was necessary since ambiguities associated with the likely simultaneous occurrence of Si(1+) and N2(1+) prevented their use in rendering the TiN/Si interface upon reconstruction. The non-superconducting Ti2N phase was also revealed by L-APT. Neither L-APT nor STEM/EELS rendered sharp Ti/TiN interfaces and the contrast between these layers diminished with increased film deposition temperature. L-APT also revealed that hydrogen was present in varying degrees in all samples including control samples that were composed of single layers of Ti or TiN.

  14. Atomic scale oxidation of a complex system: O2/alpha-SiC(0001)-( 3 x 3).

    PubMed

    Amy, F; Enriquez, H; Soukiassian, P; Storino, P F; Chabal, Y J; Mayne, A J; Dujardin, G; Hwu, Y K; Brylinski, C

    2001-05-07

    The atomic scale oxidation of the alpha-SiC(0001)-(3 x 3) surface is investigated by atom-resolved scanning tunneling microscopy, core level synchrotron radiation based photoemission spectroscopy, and infrared absorption spectroscopy. The results reveal that the initial oxidation takes place through the relaxation of lower layers, away from the surface dangling bond, in sharp contrast to silicon oxidation.

  15. Electrothermally driven high-frequency piezoresistive SiC cantilevers for dynamic atomic force microscopy

    SciTech Connect

    Boubekri, R.; Cambril, E.; Couraud, L.; Bernardi, L.; Madouri, A.; Portail, M.; Chassagne, T.; Moisson, C.; Zielinski, M.; Jiao, S.; Michaud, J.-F.; Alquier, D.; Bouloc, J.; Nony, L.; Bocquet, F.; Loppacher, C.

    2014-08-07

    Cantilevers with resonance frequency ranging from 1 MHz to 100 MHz have been developed for dynamic atomic force microscopy. These sensors are fabricated from 3C-SiC epilayers grown on Si(100) substrates by low pressure chemical vapor deposition. They use an on-chip method both for driving and sensing the displacement of the cantilever. A first gold metallic loop deposited on top of the cantilever is used to drive its oscillation by electrothermal actuation. The sensing of this oscillation is performed by monitoring the resistance of a second Au loop. This metallic piezoresistive detection method has distinct advantages relative to more common semiconductor-based schemes. The optimization, design, fabrication, and characteristics of these cantilevers are discussed.

  16. Force-enhanced atomic refinement: Structural modeling with interatomic forces in a reverse Monte Carlo approach applied to amorphous Si and SiO2

    NASA Astrophysics Data System (ADS)

    Pandey, A.; Biswas, Parthapratim; Drabold, D. A.

    2015-10-01

    We introduce a structural modeling technique, called force-enhanced atomic refinement (FEAR). The technique incorporates interatomic forces in reverse Monte Carlo (RMC) simulations for structural refinement by fitting experimental diffraction data using the conventional RMC algorithm, and minimizes the total energy and forces from an interatomic potential. We illustrate the usefulness of the approach by studying a -SiO2 and a -Si . The structural and electronic properties of the FEAR models agree well with experimental neutron and x-ray diffraction data and the results obtained from previous molecular dynamics simulations of a -SiO2 and a -Si . We have shown that the method is more efficient than the conventional molecular dynamics simulations via "melt quench." The computational time in FEAR has been observed to scale quadratically with the number of atoms.

  17. The Correlation of the N{sub A} Measurements by Counting {sup 28}Si Atoms

    SciTech Connect

    Mana, G. Massa, E.; Sasso, C. P.; Stock, M.; Fujii, K.; Kuramoto, N.; Mizushima, S.; Narukawa, T.; Borys, M.; Busch, I.; Nicolaus, A.; Pramann, A.

    2015-09-15

    An additional value of the Avogadro constant was obtained by counting the atoms in isotopically enriched Si spheres. With respect to the previous determination, the spheres were etched and repolished to eliminate metal contaminations and to improve the roundness. In addition, all the input quantities—molar mass, lattice parameter, mass, and volume—were remeasured aiming at a smaller uncertainty. In order to make the values given in Andreas et al. [Metrologia 48, S1 (2011)] and Azuma et al. [Metrologia 52, 360 (2015)] usable for a least squares adjustment, we report about the estimate of their correlation.

  18. The Correlation of the NA Measurements by Counting 28Si Atoms

    NASA Astrophysics Data System (ADS)

    Mana, G.; Massa, E.; Sasso, C. P.; Stock, M.; Fujii, K.; Kuramoto, N.; Mizushima, S.; Narukawa, T.; Borys, M.; Busch, I.; Nicolaus, A.; Pramann, A.

    2015-09-01

    An additional value of the Avogadro constant was obtained by counting the atoms in isotopically enriched Si spheres. With respect to the previous determination, the spheres were etched and repolished to eliminate metal contaminations and to improve the roundness. In addition, all the input quantities—molar mass, lattice parameter, mass, and volume—were remeasured aiming at a smaller uncertainty. In order to make the values given in Andreas et al. [Metrologia 48, S1 (2011)] and Azuma et al. [Metrologia 52, 360 (2015)] usable for a least squares adjustment, we report about the estimate of their correlation.

  19. Atomic oxidation of large area epitaxial graphene on 4H-SiC(0001)

    SciTech Connect

    Velez-Fort, E.; Ouerghi, A.; Silly, M. G.; Sirtti, F.; Eddrief, M.; Marangolo, M.; Shukla, A.

    2014-03-03

    Structural and electronic properties of epitaxial graphene on 4H-SiC were studied before and after an atomic oxidation process. X-ray photoemission spectroscopy indicates that oxygen penetrates into the substrate and decouples a part of the interface layer. Raman spectroscopy demonstrates the increase of defects due to the presence of oxygen. Interestingly, we observed on the near edge x-ray absorption fine structure spectra a splitting of the π* peak into two distinct resonances centered at 284.7 and 285.2 eV. This double structure smears out after the oxidation process and permits to probe the interface architecture between graphene and the substrate.

  20. Determination of the Avogadro Constant by Counting the Atoms in a Si28 Crystal

    NASA Astrophysics Data System (ADS)

    Andreas, B.; Azuma, Y.; Bartl, G.; Becker, P.; Bettin, H.; Borys, M.; Busch, I.; Gray, M.; Fuchs, P.; Fujii, K.; Fujimoto, H.; Kessler, E.; Krumrey, M.; Kuetgens, U.; Kuramoto, N.; Mana, G.; Manson, P.; Massa, E.; Mizushima, S.; Nicolaus, A.; Picard, A.; Pramann, A.; Rienitz, O.; Schiel, D.; Valkiers, S.; Waseda, A.

    2011-01-01

    The Avogadro constant links the atomic and the macroscopic properties of matter. Since the molar Planck constant is well known via the measurement of the Rydberg constant, it is also closely related to the Planck constant. In addition, its accurate determination is of paramount importance for a definition of the kilogram in terms of a fundamental constant. We describe a new approach for its determination by counting the atoms in 1 kg single-crystal spheres, which are highly enriched with the Si28 isotope. It enabled isotope dilution mass spectroscopy to determine the molar mass of the silicon crystal with unprecedented accuracy. The value obtained, NA=6.02214078(18)×1023mol-1, is the most accurate input datum for a new definition of the kilogram.

  1. Influence of Atomic Layer Deposition Temperatures on TiO2/n-Si MOS Capacitor

    SciTech Connect

    Wei, Daming; Hossain, T; Garces, N. Y.; Nepal, N.; Meyer III, Harry M; Kirkham, Melanie J; Eddy, C.R., Jr.; Edgar, J H

    2013-01-01

    This paper reports on the influence of temperature on the structure, composition, and electrical properties of TiO2 thin films deposited on n-type silicon (100) by atomic layer deposition (ALD). TiO2 layers around 20nm thick, deposited at temperatures ranging from 100 to 300 C, were studied. Samples deposited at 250 C and 200 C had the most uniform coverage as determined by atomic force microscopy. The average carbon concentration throughout the oxide layer and at the TiO2/Si interface was lowest at 200 C. Metal oxide semiconductor capacitors (MOSCAPs) were fabricated, and profiled by capacitance-voltage techniques. Negligible hysteresis was observed from a capacitance-voltage plot and the capacitance in the accumulation region was constant for the sample prepared at a 200 C ALD growth temperature. The interface trap density was on the order of 1013 eV-1cm-2 regardless of the deposition temperature.

  2. Determination of the Avogadro constant by counting the atoms in a 28Si crystal.

    PubMed

    Andreas, B; Azuma, Y; Bartl, G; Becker, P; Bettin, H; Borys, M; Busch, I; Gray, M; Fuchs, P; Fujii, K; Fujimoto, H; Kessler, E; Krumrey, M; Kuetgens, U; Kuramoto, N; Mana, G; Manson, P; Massa, E; Mizushima, S; Nicolaus, A; Picard, A; Pramann, A; Rienitz, O; Schiel, D; Valkiers, S; Waseda, A

    2011-01-21

    The Avogadro constant links the atomic and the macroscopic properties of matter. Since the molar Planck constant is well known via the measurement of the Rydberg constant, it is also closely related to the Planck constant. In addition, its accurate determination is of paramount importance for a definition of the kilogram in terms of a fundamental constant. We describe a new approach for its determination by counting the atoms in 1 kg single-crystal spheres, which are highly enriched with the 28Si isotope. It enabled isotope dilution mass spectroscopy to determine the molar mass of the silicon crystal with unprecedented accuracy. The value obtained, NA = 6.022,140,78(18) × 10(23) mol(-1), is the most accurate input datum for a new definition of the kilogram.

  3. Long range ordered magnetic and atomic structures of the quasicrystal approximant in the Tb-Au-Si system

    NASA Astrophysics Data System (ADS)

    Gebresenbut, Girma; Svante Andersson, Mikael; Beran, Přemysl; Manuel, Pascal; Nordblad, Per; Sahlberg, Martin; Pay Gomez, Cesar

    2014-08-01

    The atomic and magnetic structure of the 1/1 Tb(14)Au(70)Si(16) quasicrystal approximant has been solved by combining x-ray and neutron diffraction data. The atomic structure is classified as a Tsai-type 1/1 approximant with certain structural deviations from the prototype structures; there are additional atomic positions in the so-called cubic interstices as well as in the cluster centers. The magnetic property and neutron diffraction measurements indicate the magnetic structure to be ferrimagnetic-like below 9 K in contrast to the related Gd(14)Au(70)Si(16) structure that is reported to be purely ferromagnetic.

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

    PubMed

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

    2016-07-20

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

  5. In situ x-ray photoelectron spectroscopic and density-functional studies of Si atoms adsorbed on a C60 film.

    PubMed

    Onoe, Jun; Nakao, Aiko; Hara, Toshiki

    2004-12-08

    The interaction between C(60) and Si atoms has been investigated for Si atoms adsorbed on a C(60) film using in situ x-ray photoelectron spectroscopy (XPS) and density-functional (DFT) calculations. Analysis of the Si 2p core peak identified three kinds of Si atoms adsorbed on the film: silicon suboxides (SiO(x)), bulk Si crystal, and silicon atoms bound to C(60). Based on the atomic percent ratio of silicon to carbon, we estimated that there was approximately one Si atom bound to each C(60) molecule. The Si 2p peak due to the Si-C(60) interaction demonstrated that a charge transfer from the Si atom to the C(60) molecule takes place at room temperature, which is much lower than the temperature of 670 K at which the charge transfer was observed for C(60) adsorbed on Si(001) and (111) clean surfaces [Sakamoto et al., Phys. Rev. B 60, 2579 (1999)]. The number of electrons transferred between the C(60) molecule and Si atom was estimated to be 0.59 based on XPS results, which is in good agreement with the DFT result of 0.63 for a C(60)Si with C(2v) symmetry used as a model cluster. Furthermore, the shift in binding energy of both the Si 2p and C 1s core peaks before and after Si-atom deposition was experimentally obtained to be +2.0 and -0.4 eV, respectively. The C(60)Si model cluster provides the shift of +2.13 eV for the Si 2p core peak and of -0.28 eV for the C 1s core peak, which are well corresponding to those experimental results. The covalency of the Si-C(60) interaction was also discussed in terms of Mulliken overlap population between them.

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

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

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

  7. Absolute density of precursor SiH3 radicals and H atoms in H2-diluted SiH4 gas plasma for deposition of microcrystalline silicon films

    NASA Astrophysics Data System (ADS)

    Abe, Yusuke; Ishikawa, Kenji; Takeda, Keigo; Tsutsumi, Takayoshi; Fukushima, Atsushi; Kondo, Hiroki; Sekine, Makoto; Hori, Masaru

    2017-01-01

    Microcrystalline hydrogenated silicon films were produced at a high deposition rate of about 2 nm/s by using a capacitively coupled plasma under a practical pressure of around 1 kPa. The SiH4 source gas was almost fully dissociated when highly diluted with H2 gas, and the dominant species in the gas phase were found to be SiH3 radicals, which are film-growth precursors, and H atoms. The absolute density of these species was measured as the partial pressure of SiH4 gas was varied. With the increasing SiH4 gas flow rate, the SiH3 radical density, which was on the order of 1012 cm-3, increased linearly, while the H-atom density remained constant at about 1012 cm-3. The film growth mechanism was described in terms of precursors, based on the measured flux of SiH3 radicals and H atoms, and the relative fraction of higher-order radicals.

  8. View to east of windows overlooking interior of adjoining loading ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    View to east of windows overlooking interior of adjoining loading dock section from mezzanine of American Railway Express Building. Windows have been boarded over on loading dock side - Southern Pacific Railroad Depot, Railroad Terminal Post Office & Express Building, Fifth & I Streets, Sacramento, Sacramento County, CA

  9. Nanomechanical properties of SiC films grown from C{sub 60} precursors using atomic force microscopy

    SciTech Connect

    Morse, K.; Balooch, M.; Hamza, A.V.; Belak, J.

    1994-12-01

    The mechanical properties of SiC films grown via C{sub 60} precursors were determined using atomic force microscopy (AFM). Conventional silicon nitride and modified diamond cantilever AFM tips were employed to determine the film hardness, friction coefficient, and elastic modulus. The hardness is found to be between 26 and 40 GPa by nanoindentation of the film with the diamond tip. The friction coefficient for the silicon nitride tip on the SiC film is about one third that for silicon nitride sliding on a silicon substrate. By combining nanoindentation and AFM measurements an elastic modulus of {approximately}300 GPa is estimated for these SiC films. In order to better understand the atomic scale mechanisms that determine the hardness and friction of SiC, we simulated the molecular dynamics of a diamond indenting a crystalline SiC substrate.

  10. Oxidation of Mg atomic monolayer onto silicon: A road toward MgOx/Mg2Si (11-1)/Si (100) heterostructure

    NASA Astrophysics Data System (ADS)

    Sarpi, B.; Rochdi, N.; Daineche, R.; Bertoglio, M.; Girardeaux, C.; Baronnet, A.; Perrin-Toinin, J.; Bocquet, M.; Djafari Rouhani, M.; Hemeryck, A.; Vizzini, S.

    2015-12-01

    Surface interfaces of thin magnesium oxide films elaborated onto Si(100)-(2 × 1) substrates were characterized using scanning tunneling microscopy and spectroscopy, Auger electron spectroscopy, atomic force microscopy, and high-resolution transmission electron microscopy. We report that a flat and highly homogeneous magnesium oxide with well-defined interfaces could be grown at room temperature (RT) by repeating alternate adsorption of Mg atomic monolayer and O2 on Si(100). RT oxidation process of the first Mg monolayer plays a crucial role as driving force allowing a partial decomposition of amorphous ultra-thin Mg2Si at the Mg/Si interface to form more magnesium oxide in the surface. This process induces crystallization of the interfacial Mg2Si thin film and then gives arise to an unexpected MgOx/Mg2Si(11-1)/Si(100) heterostructure. MgOx monolayer displays a band gap of about 6 eV and exhibits a weak RMS roughness on large areas.

  11. Scanning capacitance microscopy of atomically-precise donor devices in Si

    NASA Astrophysics Data System (ADS)

    Bussmann, Ezra; Rudolph, M.; Carr, S. M.; Subramania, G.; Ten Eyck, G.; Dominguez, J.; Lilly, M. P.; Carroll, M. S.; QIST Team

    2014-03-01

    Recently, a scanning tunneling microscopy (STM) technique to fabricate atomically-precise dopant-based nanoelectronics in Si has been developed. Phosphorus donors are placed via an atomic-precision template formed by STM H-depassivation lithography, then capped with epi-Si and lastly metal contacts are made to the buried donor layer using conventional microfabrication. New challenges are introduced with this approach that center around difficulties to locate and characterize the pattern of buried donors. In this talk, we show that scanning capacitance microscopy (SCM) can image these buried donor nanostructures with sub-100-nm tip-limited resolution. The technique is used to successfully locate and characterize buried donor nanostructures relative to surface alignment marks. This approach relaxes alignment requirements for the STM lithography step and can offer improved alignment of subsequent metallization steps. The SCM technique is also used to nondestructively image the shape of the electronic carrier distribution and characterize the relative doping levels. This work, performed in part at the Center for Integrated Nanotechnologies, a U.S. DOE Office of Basic Energy Sciences user facility, was supported by Sandia's Lab Directed Research and Development Program. Sandia is a multi-program lab operated by Sandia Corp, a Lockheed-Martin Company, for U. S. DOE under Contract DE-AC04-94AL85000.

  12. Friction Consolidation of Gas-Atomized Fe-Si Powders for Soft Magnetic Applications

    SciTech Connect

    Jiang, Xiujuan; Whalen, Scott A.; Darsell, Jens T.; Mathaudhu, Suveen; Overman, Nicole R.

    2017-01-01

    Soft magnetic materials are often limited in scalability due to conventional processes that do not retain beneficial microstructures, and their associated physical properties, during densification. In this work, friction consolidation (FC) has been studied to fabricate Fe-Si soft magnetic materials from gas-atomized powder precursors. Fe-Si powder is consolidated using variable pressure and tool rotation speed in an effort to evaluate this unique densification approach for potential improvements in magnetic properties. FC, due to the high shear deformation involved, is shown to result in uniform gradual grain structure refinement across the consolidated workpiece from the center nearest the tool to the edge. Magnetic properties along different orientations indicate little, if any, textural orientation in the refined grain structure. The effect of annealing on the magnetic properties is evaluated and shown to decrease coercivity. FC processing was able to retain the magnetization of the original gas-atomized powders but further process optimization is needed to reach the optimal coercivity for the soft magnetic materials applications.

  13. Influence of the Si(111)-7 Multiplication-Sign 7 surface reconstruction on the diffusion of strontium atoms

    SciTech Connect

    Zhachuk, R. A.; Teys, S. A.; Olshanetsky, B. Z.

    2011-12-15

    The diffusion of strontium atoms on the Si(111) surface at room temperature has been investigated using scanning tunnel microscopy and simulation carried out in terms of the density functional theory and the Monte Carlo method. It has been found that the reconstruction of a clean silicon surface with a 7 Multiplication-Sign 7 structure has a profound effect on the diffusion process. The average velocity of motion of a strontium atom in a unit cell of the 7 Multiplication-Sign 7 structure has been calculated. The main diffusion paths of a strontium atom and the corresponding activation energies have been determined. It has been demonstrated that the formation of scanning tunnel microscope images of the Si(111)-7 Multiplication-Sign 7 surface with adsorbed strontium atoms is significantly affected by the shift of the electron density from the strontium atom to the nearest neighbor silicon adatoms in the 7 Multiplication-Sign 7 structure.

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

    NASA Astrophysics Data System (ADS)

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

    2014-06-01

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

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

    SciTech Connect

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

    2014-06-23

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

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

    SciTech Connect

    Hazra, Purnima; Singh, Satyendra Kumar; Jit, Satyabrata

    2015-01-01

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

  17. Thermal expansion and structural complexity of Ba silicates with tetrahedrally coordinated Si atoms

    NASA Astrophysics Data System (ADS)

    Gorelova, Liudmila A.; Bubnova, Rimma S.; Krivovichev, Sergey V.; Krzhizhanovskaya, Maria G.; Filatov, Stanislav K.

    2016-03-01

    Thermal expansion of Ba silicates with tetrahedrally coordinated Si atoms in the temperature range of 25-1100 °C had been studied by high-temperature X-ray powder diffraction. The volume thermal expansion coefficients (TECs) are in the range 41-50×10-6 °C-1 with an average value of <αV > = 45 ×10-6 °C-1. In the structures with chain and layered silicate anions, thermal expansion is anisotropic: the direction of maximal TEC is parallel to the extension of the zweier chains of silicate tetrahedra, which are strained owing to the interactions with Ba2+. The strain is released during thermal expansion due to the increasing effective size of Ba2+ induced by thermal vibrations. Information-theoretic analysis of the structural and topological complexities of Ba silicates indicates that their structural complexity is a function of the topological complexity of their silicate anions. The latter displays a non-linear behaviour with increasing SiO2 content (=the increasing degree of polymerization and increasing dimensionality): it starts from simple topologies, reaches a maximum at topologies of intermediate complexity, and ends up at simple topologies again. The specificity of the interactions of Ba2+ with the silicate anions results in higher complexity of high-temperature α-BaSi2O5 compared to that of low-temperature β-BaSi2O5. This uncommon behaviour may be explained by the vibrational advantages provided by flatter and more complex silicate layers in the α-phase, which overcome negative differences in configurational entropies of the two modifications apparent in the differences of their structural Shannon information.

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

    NASA Astrophysics Data System (ADS)

    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.

  19. Atomic and electronic structures of rubidium adsorption on Si(001)(2 x 1) surface: Comparison with Cs/Si(001) surface

    SciTech Connect

    Xiao, H Y.; Zu, Xiaotao; Zhang, Yanfeng; Gao, Fei

    2006-04-21

    First-principles calculations based on DFT-GGA method have been performed on rubidium adsorption on Si(001)(2?1) surface. The atomic and electronic structures of Si(001)(2?1)-Rb have been calculated and compared with those of Cs adsorption (J.Chem. Phys.122 (2005) 174704). It turns out that the saturation coverage of Rb is one monolayer rather than half a monolayer, similar to that of Cs adsorption. Comparison of Rb on Si(001)(2?1) with Cs adsorption showed that at saturation coverage larger alkali metal (AM) atom leads to stronger AM-AM interaction and weaker AM-Si interaction. However, for low coverage of 0.25 and 0.5 ML the Rb-Si interaction is surprisingly weaker than Cs-Si interaction. Further detailed analysis suggested that this is a consequence of depolarization effect with decreasing AM size below 1 ML coverage. For the saturation coverage the dispersion curves show that the surface is of semi-conducting character. This result does not support the direct and inverse angle-resolved photoemission investigation where a metallization is observed at saturation coverage.

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

    PubMed

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

    2015-03-04

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

  1. Metal-induced crystallization of amorphous Si thin films assisted by atomic layer deposition of nickel oxide layers.

    PubMed

    So, Byung-Soo; Bae, Seung-Muk; You, Yil-Hwan; Jo, DaiHui; Lee, Sun Sook; Chung, Taek-Mo; Kim, Chang Gyoun; An, Ki-Seok; Hwang, Jin-Ha

    2011-08-01

    Atomic layer deposition (ALD) of nickel oxide was applied to the nickel-induced crystallization of amorphous Si thin films. The nickel-induced crystallization was monitored as a function of annealing temperature and time using Raman spectroscopy. Since Raman spectroscopy allows for the numerical quantification of structural components, the incubation time and the crystallization rates were estimated as functions of the annealing temperature. The spatial locations of a nickel-based species, probably NiSi2, were investigated using X-ray photoelectron spectrometry. The formed NiSi2 seeds appeared to accelerate the crystallization kinetics in amorphous Si thin films deposited onto glass substrates. The ramifications of the atomic layer deposition are discussed with regard to large-panel displays, with special emphasis on the sophisticated control of the catalytic elements, especially nickel.

  2. Nanocrystallized Cu2Se grown on electroless Cu coated p-type Si using electrochemical atomic layer deposition

    NASA Astrophysics Data System (ADS)

    Zhang, Lu; He, Wenya; Chen, Xiang-yu; Du, Yi; Zhang, Xin; Shen, Yehua; Yang, Fengchun

    2015-01-01

    Cuprous selenide (Cu2Se) nanocrystalline thin films are grown onto electroless Cu coating on p-Si (100) substrates using electrochemical atomic layer deposition (EC-ALD), which includes alternate electrodeposition of Cu and Se atomic layers. The obtained films were characterized by X-ray diffraction (XRD), field emission scanning electronic microscopy (FE-SEM), FTIR, and open-circuit potential (OCP) studies. The results show the higher quality and good photoelectric properties of the Cu2Se film, suggesting that the combination of electroless coating and EC-ALD is an ideal method for deposition of compound semiconductor films on p-Si.

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

    NASA Astrophysics Data System (ADS)

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

    2017-01-01

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

  4. Al- and Cu-doped BaSi2 films on Si(111) substrate by molecular beam epitaxy and evaluation of depth profiles of Al and Cu atoms

    NASA Astrophysics Data System (ADS)

    Ajmal Khan, M.; Takeishi, M.; Matsumoto, Y.; Saito, T.; Suemasu, T.

    The main objective of the present work is to evaluate and compare the depth profiles of Al and Cu atoms in in-situ doped BaSi2. Furthermore, it is also desired to investigate and compare the carrier concentration of Al-doped as well as Cu-doped BaSi2 films and qualify as a potential dopant-candidate for more efficient solar cells of BaSi2. During the experiment, reactive deposition epitaxy and molecular beam epitaxy were used to develop the samples. X-ray diffraction (XRD) measurements and secondary ion mass spectroscopy (SIMS), were used to determine the structure, depth profile and composition of the already grown films. The electrical properties were characterized by Hall measurement using the van der Pauw method. In case of Al-doped BaSi2 films, it was not encouraging result due to diffusion and segregation of Al in both the surface and BaSi2/ Si interface regions. On the other hand, those phenomena were not observed for Cu-doped BaS2 films. Heavily Cu-doped BaSi2 showed n+ conductivity, differently from our prediction.

  5. Short-range ordering of ion-implanted nitrogen atoms in SiC-graphene

    SciTech Connect

    Willke, P.; Druga, T.; Wenderoth, M.; Amani, J. A.; Weikert, S.; Hofsäss, H.; Thakur, S.; Maiti, K.

    2014-09-15

    We perform a structural analysis of nitrogen-doped graphene on SiC(0001) prepared by ultra low-energy ion bombardment. Using scanning tunneling microscopy, we show that nitrogen atoms are incorporated almost exclusively as graphitic substitution in the graphene honeycomb lattice. With an irradiation energy of 25 eV and a fluence of approximately 5 × 10{sup 14 }cm{sup −2}, we achieve a nitrogen content of around 1%. By quantitatively comparing the position of the N-atoms in the topography measurements with simulated random distributions, we find statistically significant short-range correlations. Consequently, we are able to show that the dopants arrange preferably at lattice sites given by the 6 × 6-reconstruction of the underlying substrate. This selective incorporation is most likely triggered by adsorbate layers present during the ion bombardment. This study identifies low-energy ion irradiation as a promising method for controlled doping in epitaxial graphene.

  6. Thermally induced anchoring of fullerene in copolymers with Si-bridging atom: Spectroscopic evidences

    NASA Astrophysics Data System (ADS)

    Marchiori, Cleber F. N.; Garcia-Basabe, Yunier; de A. Ribeiro, Fabio; Koehler, Marlus; Roman, Lucimara S.; Rocco, Maria Luiza M.

    2017-01-01

    We use X-ray photoelectron spectroscopy (XPS), Near-edge X-ray absorption fine structure (NEXAFS), resonant Auger spectroscopy (RAS), Attenuation Total Reflection Infrared (ATR-IR) and Atomic Force Microscopy (AFM) to study the blend between the copolymer poly[2,7-(9,9-bis(2-ethylhexyl)-dibenzosilole)-alt-4,7-bis(thiophen-2-yl)benzo-2,1,3-thiadiazole] (PSiF-DBT) and the fullerene derivative PC71BM submitted to different annealing temperatures. Those measurements indicate that there is an incidental anchoring of a fullerene derivative to the Si-bridging atoms of a copolymer induced by thermal annealing of the film. Insights about the physical properties of one possible PSiF-DBT/PC71BM anchored structure are obtained using Density Functional Theory calculations. Since the performance of organic photovoltaic based on polymer-fullerene blends depends on the chemical structure of the blend components, the anchoring effect might affect the photovoltaic properties of those devices.

  7. Scanning tunneling microscopy of atomically precise graphene nanoribbons exfoliated onto H:Si(100)

    NASA Astrophysics Data System (ADS)

    Radocea, Adrian; Mehdi Pour, Mohammad; Vo, Timothy; Shekhirev, Mikhail; Sinitskii, Alexander; Lyding, Joseph

    Atomically precise graphene nanoribbons (GNRs) are promising materials for next generation transistors due to their well-controlled bandgaps and the high thermal conductivity of graphene. The solution synthesis of graphene nanoribbons offers a pathway towards scalable manufacturing. While scanning tunneling microscopy (STM) can access size scales required for characterization, solvent residue increases experimental difficulty and precludes band-gap determination via scanning tunneling spectroscopy (STS). Our work addresses this challenge through a dry contact transfer method that cleanly transfers solution-synthesized GNRs onto H:Si(100) under UHV using a fiberglass applicator. The semiconducting silicon surface avoids problems with image charge screening enabling intrinsic bandgap measurements. We characterize the nanoribbons using STM and STS. For chevron GNRs, we find a 1.6 eV bandgap, in agreement with computational modeling, and map the electronic structure spatially with detailed spectra lines and current imaging tunneling spectroscopy. Mapping the electronic structure of graphene nanoribbons is an important step towards taking advantage of the ability to form atomically precise nanoribbons and finely tune their properties.

  8. Mechanism of charging of Au atoms and nanoclusters on Li doped SiO2/Mo(112) films.

    PubMed

    Martinez, Umberto; Giordano, Livia; Pacchioni, Gianfranco

    2010-02-01

    We present the results of supercell DFT calculations on the adsorption properties of Au atoms and small clusters (Au(n), n < or = 5) on a SiO(2)/Mo(112) thin film and on the same system modified by doping with Li atoms. The adsorbed Li atoms penetrate into the pores of the silica film and become stabilized at the interface where they donate one electron to the Mo metal. As a consequence, the work function of the Li-doped SiO(2)/Mo(112) film is reduced and results in modified adsorption properties. In fact, while on the undoped SiO(2)/Mo(112) film Au interacts only very weakly, on the Li-doped surface Au atoms and clusters bind with significant bond strengths. The calculations show that this is due to the occurrence of an electron transfer from the SiO(2)/Mo(112) interface to the adsorbed gold. The occurrence of the charge transfer is related to the work function of the support but also to the possibility for the silica film to undergo a strong polaronic distortion.

  9. Kinetics of the WF 6 and Si 2H 6 surface reactions during tungsten atomic layer deposition

    NASA Astrophysics Data System (ADS)

    Elam, J. W.; Nelson, C. E.; Grubbs, R. K.; George, S. M.

    2001-05-01

    The atomic layer deposition (ALD) of tungsten (W) films has been demonstrated using alternating exposures to tungsten hexafluoride (WF 6) and disilane (Si 2H 6). The present investigation explored the kinetics of the WF 6 and Si 2H 6 surface reactions during W ALD at 303-623 K using Auger electron spectroscopy techniques. The reaction of WF 6 with the Si 2H 6-saturated W surface proceeded to completion at 373-573 K. The WF 6 reaction displayed a reactive sticking coefficient of S=0.4 and required an exposure of 30 L (1 L=1×10 -6 Torr s) to achieve saturation at 573 K. The WF 6 exposures necessary to reach saturation increased with decreasing temperature. At surface temperatures <373 K, the WF 6 reaction did not consume all the silicon (Si) surface species remaining from the previous Si 2H 6 exposure. The reaction of Si 2H 6 with the WF 6-saturated W surface displayed three kinetic regimes. In the first region at low Si 2H 6 exposures⩽50 L, the Si 2H 6 reaction was independent of temperature and had a reactive sticking coefficient of S˜5×10 -2. In the second kinetic region at intermediate Si 2H 6 exposures of 50-300 L, the Si 2H 6 reaction showed an apparent saturation behavior with a Si thickness at saturation that increased with substrate temperature. At high Si 2H 6 exposures of 300-1×10 5 L, additional Si was deposited with an approximately logarithmic dependence on Si 2H 6 exposure. The Si 2H 6 reaction in this third kinetic region had an activation energy E=2.6 kcal/mol and the Si thickness deposited by a 1.6×10 5 L Si 2H 6 exposure increased with temperature from 3.0 Å at 303 K to 6.6 Å at 623 K. These kinetic results should help to explain W ALD growth rates observed at different reactant exposures and substrate temperatures.

  10. Triangular Spin-Orbit-Coupled Lattice with Strong Coulomb Correlations: Sn Atoms on a SiC(0001) Substrate.

    PubMed

    Glass, S; Li, G; Adler, F; Aulbach, J; Fleszar, A; Thomale, R; Hanke, W; Claessen, R; Schäfer, J

    2015-06-19

    Two-dimensional (2D) atom lattices provide model setups with Coulomb correlations that induce competing ground states. Here, SiC emerges as a wide-gap substrate with reduced screening. We report the first artificial high-Z atom lattice on SiC(0001) by Sn adatoms, based on experimental realization and theoretical modeling. Density-functional theory of our triangular structure model closely reproduces the scanning tunneling microscopy. Photoemission data show a deeply gapped state (∼2  eV gap), and, based on our calculations including dynamic mean-field theory, we argue that this reflects a pronounced Mott-insulating scenario. We also find indications that the system is susceptible to antiferromagnetic superstructures. Such artificial lattices on SiC(0001) thus offer a novel platform for coexisting Coulomb correlations and spin-orbit coupling, with bearing for unusual magnetic phases and proposed topological quantum states of matter.

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

    NASA Astrophysics Data System (ADS)

    Guerrero-Sánchez, J.

    2017-03-01

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

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

    NASA Astrophysics Data System (ADS)

    Du, Wenhan; Yang, Jingjing

    2016-11-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2017-01-01

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

  14. Improved film quality of plasma enhanced atomic layer deposition SiO{sub 2} using plasma treatment cycle

    SciTech Connect

    Kim, Haiwon; Chung, Ilsub; Kim, Seokyun; Shin, Seungwoo; Jung, Wooduck; Hwang, Ryong; Jeong, Choonsik; Hwang, Hanna

    2015-01-15

    Chemical, physical, and electrical characteristics of high quality silicon dioxide (SiO{sub 2}) films grown using low temperature plasma enhanced atomic layer deposition (PE-ALD) have been investigated as a buffer layer for three dimensional vertical NAND flash memory devices. The comparative angle resolved x-ray photoelectron spectroscopy studies show the plasma treatment cycle causes to shift the core level binding energy (chemical shifts) in the SiO{sub 2} film. The wet etch rates with respect to plasma treatment cycle times were varied due to curing of the SiO{sub 2} network defects by Ar{sup +} ions and oxygen radicals. It is assumed that the angle between the bonds linking SiO{sub 4} tetrahedra is a critical point understanding the variation in wet etch rate of SiO{sub 2}. The features of wet etch rate of low temperature high quality SiO{sub 2} demonstrated lower than high temperature low-pressure chemical vapor deposition (LP-CVD) SiO{sub 2} values. In addition, the better step-coverage compared to that of the LP-CVD SiO{sub 2} film was achieved from the deep trench structure having the 20:1 aspect ratio. PE-ALD SiO{sub 2} with plasma treatment cycle showed excellent I–V properties with higher breakdown voltage compared to LP-CVD SiO{sub 2} and similar to the thermal SiO{sub 2} carrier transport plot.

  15. BARN IN SETTING FROM ADJOINING FIELD, LOOKING NORTHEAST. The photograph ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    BARN IN SETTING FROM ADJOINING FIELD, LOOKING NORTHEAST. The photograph was taken from the east side of the hedgerow along Fort Casey Road. Also shown are the mechanic’s shop, to the west of the barn; the tractor shed, directly south of the shop; and the monitor-roofed hay and lambing barn to the east. The Hugh Crockett house sat between the tractor shed and the hay and lambing barn. Only its chimney remains. - Boyer Farm, 711 South Fort Casey Road, Coupeville, Island County, WA

  16. Distribution of Al atoms in the clathrate-I phase Ba8AlxSi46-x at x = 6.9.

    PubMed

    Bobnar, Matej; Böhme, Bodo; Wedel, Michael; Burkhardt, Ulrich; Ormeci, Alim; Prots, Yurii; Drathen, Christina; Liang, Ying; Nguyen, Hong Duong; Baitinger, Michael; Grin, Yuri

    2015-07-28

    The clathrate-I phase Ba8AlxSi46-x has been structurally characterized at the composition x = 6.9 (space group Pm3[combining macron]n, no. 223, a = 10.4645(2) Å). A crystal structure model comprising the distribution of aluminium and silicon atoms in the clathrate framework was established: 5.7 Al atoms and 0.3 Si atoms occupy the crystallographic site 6c, while 1.2 Al atoms and 22.8 Si atoms occupy site 24k. The atomic distribution was established based on a combination of (27)Al and (29)Si NMR experiments, X-ray single-crystal diffraction and wavelength-dispersive X-ray spectroscopy.

  17. The influence of a Si cantilever tip with/without tungsten coating on noncontact atomic force microscopy imaging of a Ge(001) surface.

    PubMed

    Naitoh, Yoshitaka; Kinoshita, Yukinori; Jun Li, Yan; Kageshima, Masami; Sugawara, Yasuhiro

    2009-07-01

    A sharp probe tip with atomic scale stability is essential and desirable for noncontact atomic force microscopy (NC-AFM) studies at the atomic scale. We observed a Ge(001) surface using both a Si cantilever and a tungsten coated Si cantilever at room temperature in order to investigate the influence of the tip apex structure on the NC-AFM images. By using the Si cantilever, we first obtained four types of image at the atomic scale which can be explained assuming a dimer structure on the tip apex. On the other hand, the home-made tungsten coated tip, which has atomic scale stability and high electric conductivity, imaged the so-called ordered c(4 x 2) structure without any artifacts. The tungsten coated cantilever was found to have significantly higher performance for NC-AFM studies at the atomic scale than the Si cantilever.

  18. Interaction transfer of silicon atoms forming Co silicide for Co/√(3)×√(3)R30°-Ag/Si(111) and related magnetic properties

    SciTech Connect

    Chang, Cheng-Hsun-Tony; Fu, Tsu-Yi; Tsay, Jyh-Shen

    2015-05-07

    Combined scanning tunneling microscopy, Auger electron spectroscopy, and surface magneto-optic Kerr effect studies were employed to study the microscopic structures and magnetic properties for ultrathin Co/√(3)×√(3)R30°-Ag/Si(111). As the annealing temperature increases, the upward diffusion of Si atoms and formation of Co silicides occurs at temperature above 400 K. Below 600 K, the √(3)×√(3)R30°-Ag/Si(111) surface structure persists. We propose an interaction transferring mechanism of Si atoms across the √(3)×√(3)R30°-Ag layer. The upward transferred Si atoms react with Co atoms to form Co silicide. The step height across the edge of the island, a separation of 0.75 nm from the analysis of the 2 × 2 structure, and the calculations of the normalized Auger signal serve as strong evidences for the formation of CoSi{sub 2} at the interface. The interaction transferring mechanism for Si atoms enhances the possibility of interactions between Co and Si atoms. The smoothness of the surface is advantage for that the easy axis of magnetization for Co/√(3)×√(3)R30°-Ag/Si(111) is in the surface plane. This provides a possible way of growing flat magnetic layers on silicon substrate with controllable silicide formation and shows potential applications in spintronics devices.

  19. Band alignment of atomic layer deposited (HfZrO4)1-x(SiO2)x gate dielectrics on Si (100)

    NASA Astrophysics Data System (ADS)

    Heo, Sung; Tahir, Dahlang; Chung, Jae Gwan; Lee, Jae Cheol; Kim, KiHong; Lee, Junho; Lee, Hyung-Ik; Park, Gyeong Su; Oh, Suhk Kun; Kang, Hee Jae; Choi, Pyungho; Choi, Byoung-Deog

    2015-11-01

    The band alignment of atomic layer deposited (HfZrO4)1-x(SiO2)x (x = 0, 0.10, 0.15, and 0.20) gate dielectric thin films grown on Si (100) was obtained by using X-ray photoelectron spectroscopy and reflection electron energy loss spectroscopy. The band gap, valence band offset, and conduction band offset values for HfZrO4 silicate increased from 5.4 eV to 5.8 eV, from 2.5 eV to 2.75 eV, and from 1.78 eV to 1.93 eV, respectively, as the mole fraction (x) of SiO2 increased from 0.1 to 0.2. This increase in the conduction band and valence band offsets, as a function of increasing SiO2 mole fraction, decreased the gate leakage current density. As a result, HfZrO4 silicate thin films were found to be better for advanced gate stack applications because they had adequate band gaps to ensure sufficient conduction band offsets and valence band offsets to Si.

  20. Band alignment of atomic layer deposited (HfZrO{sub 4}){sub 1−x}(SiO{sub 2}){sub x} gate dielectrics on Si (100)

    SciTech Connect

    Heo, Sung; Tahir, Dahlang; Chung, Jae Gwan; Lee, Jae Cheol; Kim, KiHong; Lee, Junho; Lee, Hyung-Ik; Park, Gyeong Su; Oh, Suhk Kun; Kang, Hee Jae; Choi, Pyungho; Choi, Byoung-Deog

    2015-11-02

    The band alignment of atomic layer deposited (HfZrO{sub 4}){sub 1−x}(SiO{sub 2}){sub x} (x = 0, 0.10, 0.15, and 0.20) gate dielectric thin films grown on Si (100) was obtained by using X-ray photoelectron spectroscopy and reflection electron energy loss spectroscopy. The band gap, valence band offset, and conduction band offset values for HfZrO{sub 4} silicate increased from 5.4 eV to 5.8 eV, from 2.5 eV to 2.75 eV, and from 1.78 eV to 1.93 eV, respectively, as the mole fraction (x) of SiO{sub 2} increased from 0.1 to 0.2. This increase in the conduction band and valence band offsets, as a function of increasing SiO{sub 2} mole fraction, decreased the gate leakage current density. As a result, HfZrO{sub 4} silicate thin films were found to be better for advanced gate stack applications because they had adequate band gaps to ensure sufficient conduction band offsets and valence band offsets to Si.

  1. Amphiphilic Comb-Shaped Diblock Polymer Brushes on Si(100) Substrates via Surface-Initiated Atom Transfer Radical Polymerization

    NASA Astrophysics Data System (ADS)

    Peng, Jin-Wen; Huang, Wei; Kang, En-Tang; Neoh, Koon Gee

    Amphiphilic comb-shaped 2-hydroxyethyl methacrylate-graft-poly(styrene)-block-poly(poly (ethylene glycol) monomethacrylate) (P(HEMA)-g-PS-b-P(PEGMA)) copolymer brushes, covalently tethered on Si(100) substrate, have been successfully prepared by (i) UV-induced hydrosilylation of 4-vinylbenzyl chloride (VBC) with the hydrogen-terminated Si(100) (Si-VBC surface), (ii) surface-initiated atom transfer radical polymerization (ATRP) of 2-hydroxyethyl methacrylate (HEMA) to give the Si-VBC-g-P(HEMA) surface, (iii) coupling of 2-bromoisobutyryl bromide with the HEMA units via esterification to provide the comb-shaped macroinitiators (Si-VBC-g-P(HEMA)-R3Br) for the subsequent ATRP, (iv) surface-initiated ATRP of styrene (St) to produce the Si-VBC-g-P(HEMA)-g-PS surface, and (v) the persisting of an active PS chain end can be used as the initiator for the subsequent ATRP of poly(ethylene glycol) monomethacrylate (PEGMA) to give the amphiphilic Si-VBC-g-P(HEMA)-g-PS-b-P(PEGMA) brush surface. The chemical composition and functionality of the silicon surface were tailored by the well-defined comb-shaped PS and P (PEGMA) brushes.

  2. Conductance decay of a surface hydrogen tunneling junction fabricated along a Si(001)- (2×1) -H atomic wire

    NASA Astrophysics Data System (ADS)

    Kawai, Hiroyo; Yeo, Yong Kiat; Saeys, Mark; Joachim, Christian

    2010-05-01

    On a Si(001)- (2×1) -H substrate, electrons tunneling through hydrogen atomic junctions fabricated between two surface dangling-bond (DB) wires are theoretically investigated using the elastic-scattering quantum-chemistry method. The surface states introduced in the Si band gap by removing H atoms from a Si(001)- (2×1) -H surface were calculated and also analyzed using a simple tight-binding model. The two-channel surface conductance of a DB wire results from a combination of through-space and through-lattice electronic couplings between DB states. The conductance of the DB wire-H-junction-DB wire structure decreases exponentially with the length of H junction with an inverse decay rate ranging from 0.20 to 0.23Å-1 , depending on the energy. When the DB wire-H-junction-DB wire structure is contacted by Au nanoelectrodes, the transmission resonances corresponding to the DB wire states split, demonstrating a coupling of the DB wires through short surface hydrogen atomic junctions. This splitting decreases with the length of H junction between the DB wires with an inverse decay length ranging from 0.22 to 0.44Å-1 , indicating that such an atomic scale surface tunneling junction is not a very good insulator.

  3. Arrays of widely spaced atomic steps on Si(1 1 1) mesas due to sublimation

    NASA Astrophysics Data System (ADS)

    Chang, Kee-Chul; Blakely, Jack M.

    2005-10-01

    Steps with spacings of microns form on top of mesas fabricated on Si(1 1 1) that is annealed at temperatures where sublimation becomes important. Upon annealing, mesas first develop ridges along their edges, effectively creating craters which then become step-free by a step flow process described in the literature [S. Tanaka, C.C. Umbach, J.M. Blakely, R.M. Tromp, M. Mankos, Appl. Phys. Lett. 69 (9) (1996) 1235; Y. Homma, N. Aizawa, T. Ogino, Jpn. J. Appl. Phys. 35 (2B) (1996) L241]. Due to the miscut of the average surface from (1 1 1), ridge breakdown occurs on one edge of each mesa as sublimation proceeds. The breakdown point then acts as a source of steps which spread out over the mesa surface. The distribution of steps in the resulting step train depends on the sublimation rate, direct step-step interaction and the diffusive exchange of atoms among the steps. Insight into the role of these processes on the self-organization of the wide terrace distributions is provided by computer simulations using BCF (Burton, Cabrera and Frank) theory. This shows that step spacing can be controlled by varying the annealing temperature and the deposition flux. Comparison of the experimental and predicted step distributions suggest that the dynamics of the widely spaced steps are sublimation limited.

  4. Human microvascular endothelial cellular interaction with atomic N-doped DLC compared with Si-doped DLC thin films.

    PubMed

    Okpalugo, T I T; Murphy, H; Ogwu, A A; Abbas, G; Ray, S C; Maguire, P D; McLaughlin, J; McCullough, R W

    2006-08-01

    This article reports results of endothelial cell interaction with atom beam source N-doped a-C:H (diamond-like carbon, DLC) as it compares with that of Si-doped DLC thin films. The RF plasma source exhibits up to 40% N-dissociation and N-atomic fluxes of approximately 0.85 x 10(18) atoms/s, which ensures better atomic nitrogen incorporation. Two different types of nitrogen species (with and without the use of sweep plates to remove charged ions) were employed for nitrogen doping. The number of attached endothelial cells is highest on Si-DLC, followed by the N-DLC (where the sweep plates were used to remove ions), the N-DLC (without the use of sweep plates), undoped DLC, and finally the uncoated sample. The contact angle values for these films suggest that water contact angle is higher in the atomic nitrogen neutral films and Si-DLC films compared to the ionized-nitrogen specie doped films and undoped DLC thin films, suggesting that the more hydrophobic films, semiconducting films, and film with relieved stress have better interaction with human microvascular endothelial cells. It seems evident that N-doping increases the Raman I(D)/I(G) ratios, whereas N-neutral doping decreases it slightly and Si-doping decreases it even further. In this study, lower Raman I(D)/I(G) ratios are associated with increased sp(3)/sp(2) ratio, an increased H concentration, photoluminescence intensity, and a higher endothelial cellular adhesion. These investigations could be relevant to biocompatibility assessment of nanostructured biomaterials and tissue engineering.

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

    NASA Technical Reports Server (NTRS)

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

    2004-01-01

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

  6. Determination of the atomic weight of 28Si-enriched silicon for a revised estimate of the Avogadro constant.

    PubMed

    Yang, Lu; Mester, Zoltán; Sturgeon, Ralph E; Meija, Juris

    2012-03-06

    The much anticipated overhaul of the International System of Units (SI) will result in new definitions of base units in terms of fundamental constants. However, redefinition of the kilogram in terms of the Planck constant (h) cannot proceed without consistency between the Avogadro and Planck constants, which are both related through the Rydberg constant. In this work, an independent assessment of the atomic weight of silicon in a highly enriched (28)Si crystal supplied by the International Avogadro Coordination (IAC) was performed. This recent analytical approach, based on dissolution with NaOH and its isotopic characterization by multicollector inductively coupled plasma mass spectrometry, is critically evaluated. The resultant atomic weight A(r)(Si) = 27.976 968 39(24)(k=1) differs significantly from the most recent value of A(r)(Si) = 27.976 970 27(23)(k=1). Using the results generated herein for A(r)(Si) along with other IAC measurement results for mass, volume, and the lattice spacing, the estimate of the Avogadro constant becomes N(A) = 6.022 140 40(19) × 10(23) mol(-1).

  7. Imaging of all dangling bonds and their potential on the Ge/Si105 surface by noncontact atomic force microscopy.

    PubMed

    Eguchi, T; Fujikawa, Y; Akiyama, K; An, T; Ono, M; Hashimoto, T; Morikawa, Y; Terakura, K; Sakurai, T; Lagally, M G; Hasegawa, Y

    2004-12-31

    High-resolution noncontact atomic force microscope (AFM) images were successfully taken on the Ge105-(1 x 2) structure formed on the Si105 substrate and revealed all dangling bonds of the surface regardless of their electronic situation, surpassing scanning tunneling microscopy, whose images strongly deviated from the atomic structure by the electronic states involved. An atomically resolved electrostatic potential profile by a Kelvin-probe method with AFM shows potential variations among the dangling bond states, directly observing a charge transfer between them. These results clearly demonstrate that high-resolution noncontact AFM with a Kelvin-probe method is an ideal tool for analysis of atomic structures and electronic properties of surfaces.

  8. Atomic layer deposition of Al2O3 on H-passivated Si. I. Initial surface reaction pathways with H/Si(100)-2×1

    NASA Astrophysics Data System (ADS)

    Halls, Mathew D.; Raghavachari, Krishnan

    2003-06-01

    Aluminum oxide (Al2O3) grown by atomic layer deposition (ALD) is currently under investigation for use as a high-κ gate dielectric alternative to SiO2. Cluster calculations employing hybrid density functional theory have been carried out to examine the chemical reaction pathways between the ALD precursors, trimethylaluminum (TMA) and H2O, with the H/Si(100)-2×1 surface. Results obtained using Si9H14 and Si15H20, dimer and double dimer clusters to represent the surface active site are in good agreement, providing a consistent view of reaction energetics on the H/Si(100)-2×1 surface. The adsorption energies for TMA and H2O on the surface are calculated to be 0.02 and 0.15 eV, respectively. For the reaction between H2O and the H/Si(100)-2×1 surface, hydroxylation of the surface accompanied by loss of H2 was found to be the preferred pathway having an activation energy and overall reaction enthalpy of 1.60 eV and -0.75 eV, both of which are ⩾0.70 eV lower than the corresponding values for the possible H/D exchange reaction. TMA exposure of the H/Si(100)-2×1 surface favors the deposition of -Al(CH3)2 with loss of CH4, having a barrier height of 1.30 eV and reaction enthalpy of -0.31 eV, which are 0.10 and 0.40 eV lower than the surface methylation pathway (H/CH3 exchange) and 2.64 and 0.45 eV lower in energy than the H2 loss reaction, that results in the deposition of -CH2-Al(CH3)2 to the surface. Therefore, the dominant reactions identified in this work are those with direct implication in the Al2O3 ALD growth mechanism, leading to the formation of Si-O and Si-Al species on the H/Si(100)-2×1 surface.

  9. Effects of substitutional impurity Au and Si atoms on antiphase boundary energies in Ti3Al: A first principles study

    NASA Astrophysics Data System (ADS)

    Koizumi, Yuichiro; Mizuno, Masataka; Sugihara, Atsushi; Minamino, Yoritoshi; Shirai, Yasuharu

    2010-10-01

    Effects of substitutional impurity atoms Au and Si on the energies of antiphase boundaries (APBs) on {1overline 1 00} and (0001) planes in a Ti3Al intermetallic compound were examined using first principles calculations. Au additions reduce the energies of APBs on both {1overline 1 00} and (0001) planes by up to more than 40%. The reduction tends to be more remarkable especially when the added Au atom has larger number of Al atoms on its second-nearest neighbor sites rather than on first-nearest neighbor ones. In addition, in the case of Si addition, a significant energy reduction was found only for APBs on (0001) planes, and no remarkable dependence of APB energies on the coordinating atoms was found even for APBs on (0001) planes. These results are crucial to both understanding of the effect of APBs on the impurity diffusivity and predicting the ability of impurity atoms to stabilize antiphase domain structure that increases the strength of Ti3Al dramatically.

  10. The stability and electronic structures of Si/O/Al/P atom doped (5,0)boron nitrogen nanotubes with Stone-Wales defects: Density functional theory studies

    NASA Astrophysics Data System (ADS)

    Li, KeJing; Ye, JinQian; Zhang, Juan; Wang, XiYuan; Shao, QingYi

    2017-03-01

    Using density functional theory, we have investigated Si/O/Al/P atoms doped (5,0)BNNTs with SW defects. We have mainly found that Si/O/Al/P have improved the stability of (5,0)BNNTs with SW defects. In view of Mulliken charge, we have thought Si/O/Al/P atoms have donated electrons (charge +e state or charge -e state) to nanotubes, contributing BNNTs with SW defects to stable. Meanwhile, from the aspect of energy band structure and DOS, we have further explained the reason. We have considerred that stability of doped structures has related to hybridization between doped atom and BNNTs. The stability has changed with changing the degree of hybridization. Moreover, B atom can play a crucial role in the insertion of Si/O/Al/P atom into (5,0)BNNTs with SW defects.

  11. Adsorption and spin-related properties of multi-Co atoms assembled in the half unit cells of Si(111)-(7 × 7)

    NASA Astrophysics Data System (ADS)

    Liu, Qin; Shao, Xiji; Ming, Fangfei; Wang, Kedong; Xiao, Xudong

    2017-02-01

    Multiple Co atoms were assembled in the half unit cells (HUCs) of a Si(111)-(7 × 7) surface via vertical atom manipulation at room temperature. Combining scanning tunneling microscopy and first-principles calculations, we have determined the adsorption sites and spin-related properties of six Co atoms assembled in both faulted HUCs (FHUCs) and unfaulted HUCs (UHUCs). These multi-Co atoms do not form metal clusters, which usually have a definite adsorption configuration, because of the strong interaction between Si and Co atoms. Both the adsorption properties and magnetic moments of six Co atoms show strong HUC dependence. The six Co atoms in UHUC retain the adsorption sites of isolated single Co atoms, whereas the Co atoms in FHUC indirectly interact with each other via the mediation of Si atoms, leading to a deviation from the adsorption sites of single Co atoms. Around the suggested U eff value, the six-Co-atom configuration in UHUC is calculated to have a large magnetic moment of 11.78 μB, while the six-Co-atom configuration in FHUC only has a magnetic moment of 1.02 μB because of the anti-ferromagnetic-like coupling between the Co spins.

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

    SciTech Connect

    Karbasian, Golnaz McConnell, Michael S.; Orlov, Alexei O.; Rouvimov, Sergei; Snider, Gregory L.

    2016-01-15

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

  13. Origin of p(2 x 1) phase on Si(001) by noncontact atomic force microscopy at 5 k.

    PubMed

    Li, Yan Jun; Nomura, Hikaru; Ozaki, Naoyuki; Naitoh, Yoshitaka; Kageshima, Masami; Sugawara, Yasuhiro; Hobbs, Chris; Kantorovich, Lev

    2006-03-17

    The controversial issue of the origin of the p(2 x 1) reconstruction of the Si(001) surface observed in recent low temperature scanning tunneling microscopy experiments is clarified here using 5 K noncontact atomic force microscopy. The c(4 x 2) phase is observed at separations corresponding to weak tip-surface interactions, confirming that it is the ground state of the surface. At larger frequency shifts the p(2 x 1) phase of symmetric dimers is observed. By studying the interaction of a reactive Si tip with the c(4 x 2) Si(001) surface using an ab initio method, we find that the observed change in the surface reconstruction is an apparent effect caused by tip induced dimer flipping resulting in a modification of the surface structure and appearance of the p(2 x 1) phase in the image. Using an appropriate scanning protocol, one can manipulate the surface reconstruction at will, which has significance in nanotechnology.

  14. Light-induced metastable defects or light-induced metastable H atoms in a-Si:H films?

    SciTech Connect

    Godet, C.

    1997-07-01

    In hydrogenated amorphous silicon (a-Si:H) films, the increase of the metastable defect density under high-intensity illumination is usually described by an empirical two-parameter stretched-exponential time dependence (characteristic time {tau}{sub SE} and dispersion parameter {beta}). In this study, a clearly different (one-parameter) analytic function is obtained from a microscopic model based on the formation of metastable H (MSH) atoms in a-Si:H films. Assuming that MSH atoms are the only mobile species, only three chemical reactions are significant: MSH are produced from doubly hydrogenated (SiH HSi) configurations and trapped either at broken bonds or Si-H bonds, corresponding respectively to light-induced annealing (LIA) and light-induced creation (LIC) of defects. Competition between trapping sites results in a saturation of N(t) at a steady-state value N{sub ss}. A one-parameter fit of this analytical function to experimental data is generally good, indicating that the use of a statistical distribution of trap energies is not necessary.

  15. Observation of the atomic structure of ß'-SiAlON using three generations of high resolution electron microscopes

    NASA Astrophysics Data System (ADS)

    Thorel, A.; Ciston, J.; Bartel, T.; Song, C.-Y.; Dahmen, U.

    2013-04-01

    The structure of a ß‧-SiAlON (Si5.6Al0.4O0.4N7.6) has been observed using three generations of unique high resolution microscopes spanning over three decades of development in instrumentation - the Atomic Resolution Microscope (ARM), the One Angstrom Microscope (OAM) and the Transmission Electron Aberration-corrected Microscope (TEAM). The information limits of these microscopes are 0.16, 0.08 and 0.05 nm respectively. Observations along ⟨0 0 0 1⟩ at Scherzer defocus for each microscope demonstrate a drastic increase in structural information. Images taken on TEAM show clearly resolved atomic columns whereas the ARM images were only indirectly related to the structure. Nevertheless, the loss of the six-fold symmetry associated with the O/N and Al/Si substitutions was already visible on images taken on the ARM, and an associated ∼25 pm displacement of the O substituting for N in some of the 2c Wyckoff positions of the SiN unit cell was measured on exit wave reconstructions obtained from through focal series on the OAM. This paper illustrates how progress in instrumentation impacts our analysis and understanding of materials.

  16. Core-shell Si@TiO2 nanosphere anode by atomic layer deposition for Li-ion batteries

    NASA Astrophysics Data System (ADS)

    Bai, Ying; Yan, Dong; Yu, Caiyan; Cao, Lina; Wang, Chunlei; Zhang, Jinshui; Zhu, Huiyuan; Hu, Yong-Sheng; Dai, Sheng; Lu, Junling; Zhang, Weifeng

    2016-03-01

    Silicon (Si) has been regarded as next-generation anode for high-energy lithium-ion batteries (LIBs) due to its high Li storage capacity (4200 mA h g-1). However, the mechanical degradation and resultant capacity fade critically hinder its practical application. In this regard, we demonstrate that nanocoating of Si spheres with a 3 nm titanium dioxide (TiO2) layer via atomic layer deposition (ALD) can utmostly balance the high conductivity and the good structural stability to improve the cycling stability of Si core material. The resultant sample, Si@TiO2-3 nm core-shell nanospheres, exhibits the best electrochemical performance of all with a highest initial Coulombic efficiency and specific charge capacity retention after 50 cycles at 0.1C (82.39% and 1580.3 mA h g-1). In addition to making full advantage of the ALD technique, we believe that our strategy and comprehension in coating the electrode and the active material could provide a useful pathway towards enhancing Si anode material itself and community of LIBs.

  17. Core-shell Si@TiO2 nanosphere anode by atomic layer deposition for Li-ion batteries

    DOE PAGES

    Dai, Sheng

    2016-01-28

    Silicon (Si) is regarded as next-generation anode for high-energy lithium-ion batteries (LIBs) due to its high Li storage capacity (4200 mA h g-1). However, the mechanical degradation and resultant capacity fade critically hinder its practical application. In this regard, we demonstrate that nanocoating of Si spheres with a 3 nm titanium dioxide (TiO2) layer via atomic layer deposition (ALD) can utmostly balance the high conductivity and the good structural stability to improve the cycling stability of Si core material. The resultant sample, Si@TiO2-3 nm core–shell nanospheres, exhibits the best electrochemical performance of all with a highest initial Coulombic efficiency andmore » specific charge capacity retention after 50 cycles at 0.1C (82.39% and 1580.3 mA h g-1). In addition to making full advantage of the ALD technique, we believe that our strategy and comprehension in coating the electrode and the active material could provide a useful pathway towards enhancing Si anode material itself and community of LIBs.« less

  18. Passivation of pigment-grade TiO2 particles by nanothick atomic layer deposited SiO2 films

    NASA Astrophysics Data System (ADS)

    King, David M.; Liang, Xinhua; Burton, Beau B.; Kamal Akhtar, M.; Weimer, Alan W.

    2008-06-01

    Pigment-grade TiO2 particles were passivated using nanothick insulating films fabricated by atomic layer deposition (ALD). Conformal SiO2 and Al2O3 layers were coated onto anatase and rutile powders in a fluidized bed reactor. SiO2 films were deposited using tris-dimethylaminosilane (TDMAS) and H2O2 at 500 °C. Trimethylaluminum and water were used as precursors for Al2O3 ALD at 177 °C. The photocatalytic activity of anatase pigment-grade TiO2 was decreased by 98% after the deposition of 2 nm SiO2 films. H2SO4 digest tests were performed to exhibit the pinhole-free nature of the coatings and the TiO2 digest rate was 40 times faster for uncoated TiO2 than SiO2 coated over a 24 h period. Mass spectrometry was used to monitor reaction progress and allowed for dosing time optimization. These results demonstrate that the TDMAS-H2O2 chemistry can deposit high quality, fully dense SiO2 films on high radius of curvature substrates. Particle ALD is a viable passivation method for pigment-grade TiO2 particles.

  19. An X-ray absorption spectroscopy investigation of the local atomic structure in Cu-Ni-Si alloy after severe plastic deformation and ageing

    NASA Astrophysics Data System (ADS)

    Azzeddine, H.; Harfouche, M.; Hennet, L.; Thiaudiere, D.; Kawasaki, M.; Bradai, D.; Langdon, T. G.

    2015-08-01

    The local atomic structure of Cu-Ni-Si alloy after severe plastic deformation (SPD) processing and the decomposition of supersaturated solid solution upon annealing were investigated by means of X-ray absorption spectroscopy. The coordination number and interatomic distances were obtained by analyzing experimental extend X-ray absorption fine structure data collected at the Ni K-edge. Results indicate that the environment of Ni atoms in Cu-Ni-Si alloy is strongly influenced by the deformation process. Moreover, ageing at 973 K affects strongly the atomic structure around the Ni atoms in Cu-Ni-Si deformed by equal channel angular pressing and high pressure torsion. This influence is discussed in terms of changes and decomposition features of the Cu-Ni-Si solid solution.

  20. Atomic Control Of Water Interaction With Biocompatible Surfaces: The Case Of SiC(001)

    SciTech Connect

    Cicero, G; Catellani, A; Galli, G

    2004-07-19

    The interaction of water with Si- and C- terminated {beta}-SiC(001) surfaces was investigated by means of ab initio molecular dynamics simulations. Irrespective of coverage, varied from 1/4 to 1 monolayer, we found that water dissociates on the Si-terminated surface, substantially modifying the clean surface reconstruction, while the C-terminated surface is nonreactive and hydrophobic. Based on our results, we propose that STM images and photoemission experiments may detect specific changes induced by water on both the structural and electronic properties of SiC(001) surfaces.

  1. Studies of Ultra High Temperature Ceramic Composite Components: Synthesis and Characterization of HfOxCy and Si Oxidation in Atomic Oxygen Containing Environments

    DTIC Science & Technology

    2008-08-01

    focused onto the target surface . How the beam then interacts, i.e. absorbed , transmitted or reflected, with the target depends on the frequency of the...and/or absorbs onto the surface . Density functional theory (DFT) studies show that more reactive species like O atoms have a 85-90 % probability of... absorbing onto a silica surface [7] and will only desorb upon further recombination. Once adsorbed, O atoms incorporate into a surface Si-Si bond to

  2. Atomic structure and dehydration mechanism of amorphous silica: Insights from 29Si and 1H solid-state MAS NMR study of SiO2 nanoparticles

    NASA Astrophysics Data System (ADS)

    Kim, Hyun Na; Lee, Sung Keun

    2013-11-01

    Detailed knowledge of the atomic structure of hydrous species on surface of amorphous silica and the effect of temperature and particle size on their atomic configurations are essential to understand the nature of fluids-amorphous silicates interactions and the dehydration processes in the amorphous oxides. Here, we report the 29Si, 1H MAS, and 1H-29Si heteronuclear correlation (HetCor) NMR spectra of 7 nm and 14 nm amorphous silica nanoparticles—a model system for natural amorphous silica—where previously unknown details of changes in their atomic structures with varying dehydration temperature and particle size are revealed. Diverse hydroxyl groups with varying atomic configurations and molecular water apparently show distinct dehydration trends. The dehydration (i.e., removal of water) of amorphous silica nanoparticles mostly results in the increase of isolated silanol by removing water molecules from hydrogen-bonded silanols associated water molecules. With further increase in dehydration temperature, the intensity of isolated silanol peak decreases above ˜873 K, suggesting that the condensation of isolated silanol may occur mainly above ˜873 K. The entire dehydration (and dehydroxylation) process completes at ˜1473 K. Both the water (i.e., physisorbed water and hydrogen-bonded water) and hydrogen-bonded silanol species show a dramatic change in the slope of intensity variation at ˜873 K, indicating that most of silanols is hydrogen-bonded to water rather than to other silanols. The fraction of hydrogen-bonded proton species is also much smaller in 14 nm amorphous silica nanoparticles than in 7 nm amorphous silica nanoparticles mainly due to the presences of larger fractions of water and hydrogen-bonded silanol species. 29Si NMR results show that with increasing dehydration temperature, the fraction of Q4 species apparently increases at the expense of Q2 and Q3 species. The fractions of Q2 and Q3 structures in 7 nm amorphous silica nanoparticles are

  3. Fluorocarbon assisted atomic layer etching of SiO2 and Si using cyclic Ar/C4F8 and Ar/CHF3 plasma

    DOE PAGES

    Metzler, Dominik; Li, Chen; Engelmann, Sebastian; ...

    2015-11-11

    The need for atomic layer etching (ALE) is steadily increasing as smaller critical dimensions and pitches are required in device patterning. A flux-control based cyclic Ar/C4F8 ALE based on steady-state Ar plasma in conjunction with periodic, precise C4F8 injection and synchronized plasma-based low energy Ar+ ion bombardment has been established for SiO2.1 In this work, the cyclic process is further characterized and extended to ALE of silicon under similar process conditions. The use of CHF3 as a precursor is examined and compared to C4F8. CHF3 is shown to enable selective SiO2/Si etching using a fluorocarbon (FC) film build up. Othermore » critical process parameters investigated are the FC film thickness deposited per cycle, the ion energy, and the etch step length. Etching behavior and mechanisms are studied using in situ real time ellipsometry and X-ray photoelectron spectroscopy. Silicon ALE shows less self-limitation than silicon oxide due to higher physical sputtering rates for the maximum ion energies used in this work, ranged from 20 to 30 eV. The surface chemistry is found to contain fluorinated silicon oxide during the etching of silicon. As a result, plasma parameters during ALE are studied using a Langmuir probe and establish the impact of precursor addition on plasma properties.« less

  4. Thermal transport across graphene/SiC interface: effects of atomic bond and crystallinity of substrate

    NASA Astrophysics Data System (ADS)

    Li, Man; Zhang, Jingchao; Hu, Xuejiao; Yue, Yanan

    2015-05-01

    The effect of interatomic interaction between graphene and 4H-SiC on their interfacial thermal transport is investigated by empirical molecular dynamics simulation. Two magnitudes of interfacial thermal conductance (ITC) improvement are observed for graphene/4H-SiC interface interacting through covalent bonds than through van der Waals interaction, which can be explained by the bond strength and the number of covalent bonds. Besides, it is found that the ITC of covalent graphene/C-terminated SiC is larger than that Si-terminated SiC, which is due to the stronger bond strength of C-C than that of C-Si. The effect of crystallinity of the substrate is studied, and the result shows that the ITC of graphene/a-SiC is higher than that of graphene/c-SiC. These results are crucial to the understanding of thermal transport across graphene interfaces, which are useful for thermal design in graphene-based transistors.

  5. Interfacial reactions of ultrahigh-vacuum-deposited Cu thin films on atomically cleaned (111)Si. I. Phase formation and interface structure

    NASA Astrophysics Data System (ADS)

    Liu, C. S.; Chen, L. J.

    1993-11-01

    Interfacial reactions of ultrahigh-vacuum-deposited Cu thin films on atomically cleaned (111)Si have been studied by transmission electron microscopy, x-ray diffractometry, and Auger electron spectroscopy. An interface compound, CuSix with x=11.2-14 at. %, was observed to be present at the Cu/Si interface. η`-Cu3Si was found to form in samples annealed at 200 °C for 1 h. Solid-phase-epitaxial growth of silicon on (111)Si through a transport media (Cu or Cu3Si) was observed to occur at a temperature as low as 200 °C. Preferentially oriented η`-Cu3Si is the only phase present in samples annealed at 200-800 °C. In samples annealed at or higher than 850 °C, a mixture of η'-Cu3Si and η`-Cu3Si was found to be present.

  6. Analysis conditions of an industrial Al-Mg-Si alloy by conventional and 3D atom probes.

    PubMed

    Danoix, F; Miller, M K; Bigot, A

    2001-10-01

    Industrial 6016 Al-Mg-Si(Cu) alloys are presently regarded as attractive candidates for heat treatable sheet materials. Their mechanical properties can be adjusted for a given application by age hardening of the alloys. The resulting microstructural evolution takes place at the nanometer scale, making the atom probe a well suited instrument to study it. Accuracy of atom probe analysis of these aluminium alloys is a key point for the understanding of the fine scale microstructural evolution. It is known to be strongly dependent on the analysis conditions (such as specimen temperature and pulse fraction) which have been widely studied for ID atom probes. The development of the 3D instruments, as well as the increase of the evaporation pulse repetition rate have led to different analysis conditions, in particular evaporation and detection rates. The influence of various experimental parameters on the accuracy of atom probe data, in particular with regard to hydride formation sensitivity, has been reinvestigated. It is shown that hydrogen contamination is strongly dependent on the electric field at the specimen surface, and that high evaporation rates are beneficial. Conversely, detection rate must be limited to smaller than 0.02 atoms/pulse in order to prevent drastic pile-up effect.

  7. Performance and retention characteristics of nanocrystalline Si floating gate memory with an Al2O3 tunnel layer fabricated by plasma-enhanced atomic layer deposition

    NASA Astrophysics Data System (ADS)

    Ma, Zhongyuan; Wang, Wen; Yang, Huafeng; Jiang, Xiaofan; Yu, Jie; Qin, Hua; Xu, Ling; Chen, Kunji; Huang, Xinfan; Li, Wei; Xu, Jun; Feng, Duan

    2016-02-01

    The down-scaling of nanocrystal Si (nc-Si) floating gate memory must overcome the challenge of leakage current induced by the conventional ultra-thin tunnel layer. We demonstrate that an improved memory performance based on the Al/SiNx/nc-Si/Al2O3/Si structure can be achieved by adopting the Al2O3 tunnel layer fabricated by plasma-enhanced atomic layer deposition. A larger memory window of 7.9 V and better retention characteristics of 4.7 V after 105 s can be obtained compared with the devices containing a conventional SiO2 tunnel layer of equivalent thickness. The capacitance-voltage characteristic reveals that the Al2O3 tunnel layer has a smaller electron barrier height, which ensures that more electrons are injected into the nc-Si dots through the Al2O3/Si interface. The analysis of the conductance-voltage and high-resolution cross-section transmission microscopy reveals that the smaller nc-Si dots dominate in the charge injection in the nc-Si floating gate MOS device with an Al2O3 tunnel layer. With an increase of the nc-Si size, both nc-Si and the interface contribute to the charge storage capacity and retention. The introduction of the Al2O3 tunnel layer in nc-Si floating gate memory provides a method to achieve an improved performance of nc-Si floating gate memory.

  8. Molecular dynamics modeling of atomic displacement cascades in 3C-SiC: Comparison of interatomic potentials

    NASA Astrophysics Data System (ADS)

    Samolyuk, G. D.; Osetsky, Y. N.; Stoller, R. E.

    2015-10-01

    We used molecular dynamics modeling of atomic displacement cascades to characterize the nature of primary radiation damage in 3C-SiC. We demonstrated that the most commonly used interatomic potentials are inconsistent with ab initio calculations of defect energetics. Both the Tersoff potential used in this work and a modified embedded-atom method potential reveal a barrier to recombination of the carbon interstitial and carbon vacancy which is much higher than the density functional theory (DFT) results. The barrier obtained with a newer potential by Gao and Weber is closer to the DFT result. This difference results in significant differences in the cascade production of point defects. We have completed both 10 keV and 50 keV cascade simulations in 3C-SiC at a range of temperatures. In contrast to the Tersoff potential, the Gao-Weber potential produces almost twice as many C vacancies and interstitials at the time of maximum disorder (∼0.2 ps) but only about 25% more stable defects at the end of the simulation. Only about 20% of the carbon defects produced with the Tersoff potential recombine during the in-cascade annealing phase, while about 60% recombine with the Gao-Weber potential. The Gao-Weber potential appears to give a more realistic description of cascade dynamics in SiC, but still has some shortcomings when the defect migration barriers are compared to the ab initio results.

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

    NASA Astrophysics Data System (ADS)

    Rusimova, Kristina R.; Sloan, Peter A.

    2017-02-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-10-01

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

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

    PubMed

    Rusimova, Kristina R; Sloan, Peter A

    2017-02-03

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

  12. Epitaxial ferromagnetic Fe{sub 3}Si on GaAs(111)A with atomically smooth surface and interface

    SciTech Connect

    Liu, Y. C.; Hung, H. Y.; Kwo, J. E-mail: raynien@phys.nthu.edu.tw; Chen, Y. W.; Lin, Y. H.; Cheng, C. K.; Hong, M. E-mail: raynien@phys.nthu.edu.tw; Tseng, S. C.; Hsu, C. H. E-mail: raynien@phys.nthu.edu.tw; Chang, M. T.; Lo, S. C.

    2015-09-21

    Single crystal ferromagnetic Fe{sub 3}Si(111) films were grown epitaxially on GaAs(111)A by molecular beam epitaxy. These hetero-structures possess extremely low surface roughness of 1.3 Å and interfacial roughness of 1.9 Å, measured by in-situ scanning tunneling microscope and X-ray reflectivity analyses, respectively, showing superior film quality, comparing to those attained on GaAs(001) in previous publications. The atomically smooth interface was revealed by the atomic-resolution Z (atomic number)-contrast scanning transmission electron microscopy (STEM) images using the correction of spherical aberration (Cs)-corrected electron probe. Excellent crystallinity and perfect lattice match were both confirmed by high resolution x-ray diffraction. Measurements of magnetic property for the Fe{sub 3}Si/GaAs(111) yielded a saturation moment of 990 emu/cm{sup 3} with a small coercive field ≤1 Oe at room temperature.

  13. Atom probe tomography of a Ti-Si-Al-C-N coating grown on a cemented carbide substrate.

    PubMed

    Thuvander, M; Östberg, G; Ahlgren, M; Falk, L K L

    2015-12-01

    The elemental distribution within a Ti-Si-Al-C-N coating grown by physical vapour deposition on a Cr-doped WC-Co cemented carbide substrate has been investigated by atom probe tomography. Special attention was paid to the coating/substrate interface region. The results indicated a diffusion of substrate binder phase elements into the Ti-N adhesion layer. The composition of this layer, and the Ti-Al-N interlayer present between the adhesion layer and the main Ti-Si-Al-C-N layer, appeared to be sub-stoichiometric. The analysis of the interlayer showed the presence of internal surfaces, possibly grain boundaries, depleted in Al. The composition of the main Ti-Al-Si-C-N layer varied periodically in the growth direction; layers enriched in Ti appeared with a periodicity of around 30 nm. Laser pulsing resulted in a good mass resolution that made it possible to distinguish between N(+) and Si(2+) at 14 Da.

  14. Stabilizing Nanosized Si Anodes with the Synergetic Usage of Atomic Layer Deposition and Electrolyte Additives for Li-Ion Batteries.

    PubMed

    Hy, Sunny; Chen, Yi-Hsiu; Cheng, Ho-Ming; Pan, Chun-Jern; Cheng, Ju-Hsiang; Rick, John; Hwang, Bing-Joe

    2015-07-01

    A substantial increase in charging capacity over long cycle periods was made possible by the formation of a flexible weblike network via the combination of Al2O3 atomic layer deposition (ALD) and the electrolyte additive vinylene carbonate (VC). Transmission electron microscopy shows that a weblike network forms after cycling when ALD and VC were used in combination that dramatically increases the cycle stability for the Si composite anode. The ALD-VC combination also showed reduced reactions with the lithium salt, forming a more stable solid electrolyte interface (SEI) absent of fluorinated silicon species, as evidenced by X-ray photoelectron spectroscopy. Although the bare Si composite anode showed only an improvement from a 56% to a 45% loss after 50 cycles, when VC was introduced, the ALD-coated Si anode showed an improvement from a 73% to a 11% capacity loss. Furthermore, the anode with the ALD coating and VC had a capacity of 630 mAh g(-1) after 200 cycles running at 200 mA g(-1), and the bare anode without VC showed a capacity of 400 mAh g(-1) after only 50 cycles. This approach can be extended to other Si systems, and the formation of this SEI is dependent on the thickness of the ALD that affects both capacity and stability.

  15. Fe-implanted 6H-SiC: Direct evidence of Fe{sub 3}Si nanoparticles observed by atom probe tomography and {sup 57}Fe Mössbauer spectroscopy

    SciTech Connect

    Diallo, M. L.; Fnidiki, A. Lardé, R.; Cuvilly, F.; Blum, I.; Lechevallier, L.; Debelle, A.; Thomé, L.; Viret, M.; Marteau, M.; Eyidi, D.; Declémy, A.

    2015-05-14

    In order to understand ferromagnetic ordering in SiC-based diluted magnetic semiconductors, Fe-implanted 6H-SiC subsequently annealed was studied by Atom Probe Tomography, {sup 57}Fe Mössbauer spectroscopy and SQUID magnetometry. Thanks to its 3D imaging capabilities at the atomic scale, Atom Probe Tomography appears as the most suitable technique to investigate the Fe distribution in the 6H-SiC host semiconductor and to evidence secondary phases. This study definitely evidences the formation of Fe{sub 3}Si nano-sized clusters after annealing. These clusters are unambiguously responsible for the main part of the magnetic properties observed in the annealed samples.

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

    NASA Astrophysics Data System (ADS)

    Lu, Weifang; Ou, Yiyu; Jokubavicius, Valdas; Fadil, Ahmed; Syväjärvi, Mikael; Petersen, Paul Michael; Ou, Haiyan

    2016-07-01

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

  17. Atomic and electronic structure of ultrathin fluoride barrier layers at the oxide/Si interface

    NASA Astrophysics Data System (ADS)

    Pasquali, L.; Montecchi, M.; Nannarone, S.; Boscherini, F.

    2011-09-01

    A SrF2 ultrathin barrier layer on Si(001) is used to form a sharp interface and block reactivity and intermixing between the semiconductor and a Yb2O3 overlayer. Yb2O3/Si(001) and Yb2O3/SrF2/Si(001) interfaces grown in ultra high vacuum by molecular beam epitaxy are studied by photoemission and x-ray absorption fine structure. Without the fluoride interlayer, Yb2O3/Si(001) presents an interface reacted region formed by SiOx and/or silicate compounds, which is about 9 Å thick and increases up to 14-15 Å after annealing at 500-700 °C. A uniform single layer of SrF2 molecules blocks intermixing and reduces the oxidized Si region to 2.4 Å after deposition and to 3.5 Å after annealing at 500 °C. In both cases we estimate a conduction band offset and a valence band offset of ~ 1.7 eV and 2.4 eV between the oxide and Si, respectively. X-ray absorption fine structure measurements at the Yb LIII edge suggest that the Yb oxide films exhibit a significant degree of static disorder with and without the fluoride barrier. Sr K edge measurements indicate that the ultrathin fluoride films are reacted, with the formation of bonds between Si and Sr; the Sr-Sr and Sr-F interatomic distances in the ultrathin fluoride barrier film are relaxed to the bulk value.

  18. Quantitative studies of electric field intensity on atom diffusion of Cu/Ta/Si stacks during annealing

    NASA Astrophysics Data System (ADS)

    Wang, Lei; Asempah, Isaac; Dong, Song-Tao; Yin, Pian-Pian; Jin, Lei

    2017-03-01

    It has been shown that enhanced electric field intensity (0-4.0 kV/cm) has an obvious effect on accelerating atom diffusion in Cu/Ta/Si interconnect stacks at 650 °C. The theoretical deduction proves that diffusion coefficient is accelerated proportional to an acceleration factor (1 + a·αE/0.8)2. The analysis indicates that the accelerating effect is mainly attributed to the perturbation of the electric state of the defects and enhanced vacancy and dislocation densities.

  19. Circuit-quantum electrodynamics with direct magnetic coupling to single-atom spin qubits in isotopically enriched {sup 28}Si

    SciTech Connect

    Tosi, Guilherme Mohiyaddin, Fahd A.; Morello, Andrea; Huebl, Hans

    2014-08-15

    Recent advances in silicon nanofabrication have allowed the manipulation of spin qubits that are extremely isolated from noise sources, being therefore the semiconductor equivalent of single atoms in vacuum. We investigate the possibility of directly coupling an electron spin qubit to a superconducting resonator magnetic vacuum field. By using resonators modified to increase the vacuum magnetic field at the qubit location, and isotopically purified {sup 28}Si substrates, it is possible to achieve coupling rates faster than the single spin dephasing. This opens up new avenues for circuit-quantum electrodynamics with spins, and provides a pathway for dispersive read-out of spin qubits via superconducting resonators.

  20. Photoionization of atoms and small molecules using synchrotron radiation. [SF/sub 6/, SiF/sub 4/

    SciTech Connect

    Ferrett, T.A.

    1986-11-01

    The combination of synchrotron radiation and time-of-flight electron spectroscopy has been used to study the photoionization dynamics of atoms (Li) and small molecules (SF/sub 6/, SiF/sub 4/, and SO/sub 2/). Partial cross sections and angular distribution asymmetry parameters have been measured for Auger electrons and photoelectrons as functions of photon energy. Emphasis is on the basic understanding of electron correlation and resonant effects as manifested in the photoemission spectra for these systems. 254 refs., 46 figs., 10 tabs.

  1. Surface-initiated reverse atom transfer radical polymerization (SI-RATRP) for blood-compatible polyurethane substrates

    NASA Astrophysics Data System (ADS)

    Lu, Chunyan; Zhou, Ninglin; Xu, Dong; Tang, Yida; Jin, Suxing; Wu, Yue; Shen, Jian

    2011-10-01

    A well-defined polymer brushes (2-(methacryloyloxy) ethyl phosphorylcholine, MPC) grafted from the polyurethane (PU) substrate by surface-initiated reverse atom transfer radical polymerization (SI-RATRP) was studied. In this work, a kind of silane coupling agent (3-chloropropyltrimethoxysilane, CPTM) was adopted to serve as a coupling agent as well as a ligand for the first time. Surface structure, wettability, morphology of the PU substrates before and after modification were characterized by Fourier transform infrared spectra (FTIR), X-ray photoelectron spectroscopy measurement (XPS), Atomic force microscope (AFM), Water contact angle measurement, respectively. The results showed that zwitterionic brushes were successfully fabricated on the PU surfaces, and the content of the grafted layer increased gradually with the polymerization time. The blood compatibility of the PU substrates was evaluated by protein adsorption tests and platelet adhesion tests in vitro. It was found that all the PU functionalized with zwitterionic brush showed improved resistance to nonspecific protein adsorption and platelet adhesion.

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

    NASA Technical Reports Server (NTRS)

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

    2002-01-01

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

  3. Room-temperature ferromagnetism in Cr-doped Si achieved by controlling atomic structure, Cr concentration, and carrier densities: A first-principles study

    SciTech Connect

    Wei, Xin-Yuan; Yang, Zhong-Qin; Zhu, Yan; Li, Yun

    2015-04-28

    By using first-principles calculations, we investigated how to achieve a strong ferromagnetism in Cr-doped Si by controlling the atomic structure and Cr concentration as well as carrier densities. We found that the configuration in which the Cr atom occupies the tetrahedral interstitial site can exist stably and the Cr atom has a large magnetic moment. Using this doping configuration, room-temperature ferromagnetism can be achieved in both n-type and p-type Si by tuning Cr concentration and carrier densities. The results indicate that the carrier density plays a crucial role in realizing strong ferromagnetism in diluted magnetic semiconductors.

  4. Atomic Computer Simulations of Defect Migration in 3C and 4H-SiC

    SciTech Connect

    Gao, Fei; Weber, William J.; Posselt, Matthias; Belko, V

    2004-05-19

    Knowledge of the migration of intrinsic point defects is crucial to understand defect recovery, various annealing stages and microstructural evolution after irradiation or ion implantation. Molecular dynamics (MD) and the nudged-elastic band method have been applied to investigate long-range migration of point defects in SiC over the temperature range from 0.36 to 0.95 Tm , and the defect diffusion coefficient, activation energy and defect correlation factor have been determined. The results show that the activation energies for C and Si interstitials in 3C-SiC are about 0.74 and 1.53 eV, respectively, while it is about 0.77 eV for a C interstitial in 4H-SiC. The minima energy paths reveal that the activation energies for C and Si vacancies are about 4.1 and 2.35 eV, respectively. Finally, the results are discussed and compared with experimental observations and available ab initio data.

  5. The difference of energies of Si atoms with single-crystalline, amorphous, free and nanoparticle configurations

    NASA Astrophysics Data System (ADS)

    Wang, Y. L.; Deng, Z. C.; Chu, L. Z.; Fu, G. S.; Peng, Y. C.

    2009-04-01

    Nanocrystalline silicon (nc-Si) films were systematically prepared via three ways: a) laser anneal or b) thermal anneal of the amorphous silicon (α-Si) films deposited by pulsed-laser ablation (PLA) in base vacuum, c) direct PLA in high-purity Ar gas with pressure of 10 Pa. The anneal-laser fluence, thermal-anneal temperature and ablation-laser fluence thresholds corresponding to the beginning of nanoparticles formation were respectively determined by using scanning electron microscopy (SEM), Raman and X-ray diffraction (XRD) techniques. Incorporated with crystallization mechanism, energies compensated for the formation of one Si nanoparticle in the three ways were calculated approximately. The result shows that for different crystallization ways, the potential barriers during the formation of one ~16 nm nanoparticle are on the order of 10-9 mJ.

  6. Probing the Role of an Atomically Thin SiNx Interlayer on the Structure of Ultrathin Carbon Films

    PubMed Central

    Dwivedi, Neeraj; Rismani-Yazdi, Ehsan; Yeo, Reuben J.; Goohpattader, Partho S.; Satyanarayana, Nalam; Srinivasan, Narasimhan; Druz, Boris; Tripathy, S.; Bhatia, C. S.

    2014-01-01

    Filtered cathodic vacuum arc (FCVA) processed carbon films are being considered as a promising protective media overcoat material for future hard disk drives (HDDs). However, at ultrathin film levels, FCVA-deposited carbon films show a dramatic change in their structure in terms of loss of sp3 bonding, density, wear resistance etc., compared to their bulk counterpart. We report for the first time how an atomically thin (0.4 nm) silicon nitride (SiNx) interlayer helps in maintaining/improving the sp3 carbon bonding, enhancing interfacial strength/bonding, improving oxidation/corrosion resistance, and strengthening the tribological properties of FCVA-deposited carbon films, even at ultrathin levels (1.2 nm). We propose the role of the SiNx interlayer in preventing the catalytic activity of Co and Pt in media, leading to enhanced sp3C bonding (relative enhancement ~40%). These findings are extremely important in view of the atomic level understanding of structural modification and the development of high density HDDs. PMID:24846506

  7. Molecular dynamics modeling of atomic displacement cascades in 3C-SiC: Comparison of interatomic potentials

    SciTech Connect

    Samolyuk, German D.; Osetskiy, Yury N.; Stoller, Roger E.

    2015-06-03

    We used molecular dynamics modeling of atomic displacement cascades to characterize the nature of primary radiation damage in 3C-SiC. We demonstrated that the most commonly used interatomic potentials are inconsistent with ab initio calculations of defect energetics. Both the Tersoff potential used in this work and a modified embedded-atom method potential reveal a barrier to recombination of the carbon interstitial and carbon vacancy which is much higher than the density functional theory (DFT) results. The barrier obtained with a newer potential by Gao and Weber is closer to the DFT result. This difference results in significant differences in the cascade production of point defects. We have completed both 10 keV and 50 keV cascade simulations in 3C-SiC at a range of temperatures. In contrast to the Tersoff potential, the Gao-Weber potential produces almost twice as many C vacancies and interstitials at the time of maximum disorder (~0.2 ps) but only about 25% more stable defects at the end of the simulation. Only about 20% of the carbon defects produced with the Tersoff potential recombine during the in-cascade annealing phase, while about 60% recombine with the Gao-Weber potential.

  8. Molecular dynamics modeling of atomic displacement cascades in 3C-SiC: Comparison of interatomic potentials

    DOE PAGES

    Samolyuk, German D.; Osetskiy, Yury N.; Stoller, Roger E.

    2015-06-03

    We used molecular dynamics modeling of atomic displacement cascades to characterize the nature of primary radiation damage in 3C-SiC. We demonstrated that the most commonly used interatomic potentials are inconsistent with ab initio calculations of defect energetics. Both the Tersoff potential used in this work and a modified embedded-atom method potential reveal a barrier to recombination of the carbon interstitial and carbon vacancy which is much higher than the density functional theory (DFT) results. The barrier obtained with a newer potential by Gao and Weber is closer to the DFT result. This difference results in significant differences in the cascademore » production of point defects. We have completed both 10 keV and 50 keV cascade simulations in 3C-SiC at a range of temperatures. In contrast to the Tersoff potential, the Gao-Weber potential produces almost twice as many C vacancies and interstitials at the time of maximum disorder (~0.2 ps) but only about 25% more stable defects at the end of the simulation. Only about 20% of the carbon defects produced with the Tersoff potential recombine during the in-cascade annealing phase, while about 60% recombine with the Gao-Weber potential.« less

  9. Probing the role of an atomically thin SiNx interlayer on the structure of ultrathin carbon films.

    PubMed

    Dwivedi, Neeraj; Rismani-Yazdi, Ehsan; Yeo, Reuben J; Goohpattader, Partho S; Satyanarayana, Nalam; Srinivasan, Narasimhan; Druz, Boris; Tripathy, S; Bhatia, C S

    2014-05-21

    Filtered cathodic vacuum arc (FCVA) processed carbon films are being considered as a promising protective media overcoat material for future hard disk drives (HDDs). However, at ultrathin film levels, FCVA-deposited carbon films show a dramatic change in their structure in terms of loss of sp3 bonding, density, wear resistance etc., compared to their bulk counterpart. We report for the first time how an atomically thin (0.4 nm) silicon nitride (SiNx) interlayer helps in maintaining/improving the sp3 carbon bonding, enhancing interfacial strength/bonding, improving oxidation/corrosion resistance, and strengthening the tribological properties of FCVA-deposited carbon films, even at ultrathin levels (1.2 nm). We propose the role of the SiNx interlayer in preventing the catalytic activity of Co and Pt in media, leading to enhanced sp3C bonding (relative enhancement~40%). These findings are extremely important in view of the atomic level understanding of structural modification and the development of high density HDDs.

  10. An angular-dependent embedded atom method (A-EAM) interatomic potential to model thermodynamic and mechanical behavior of Al/Si composite materials

    NASA Astrophysics Data System (ADS)

    Dongare, Avinash M.; LaMattina, Bruce; Irving, Douglas L.; Rajendran, Arunachalam M.; Zikry, Mohammed A.; Brenner, Donald W.

    2012-04-01

    A new interatomic potential is developed for the Al/Si system in the formulation of the recently developed angular-dependent embedded atom method (A-EAM). The A-EAM is formulated by combining the embedded atom method potential for Al with the Stillinger-Weber potential for Si. The parameters of the Al/Si cross-interactions are fitted to reproduce the structural energetics of Al/Si bulk alloys determined based on the results of density functional theory calculations and the experimentally observed mixing behavior of the AlSi liquid alloy at high temperatures. The ability to investigate the thermodynamic properties of the Al/Si system is demonstrated by computing the binary phase diagram of the Al-Si system as predicted by the A-EAM potential and comparing with that obtained using experiments. The ability to study the mechanical behavior of the Al/Si composite systems is demonstrated by investigating the micromechanisms related to dynamic failure of the Al/Si nanocomposites using MD simulations.

  11. Surface modification of Au/TiO2 catalysts by SiO2 via atomic layer deposition

    SciTech Connect

    Ma, Zhen; Brown, Suree; Howe, Jane Y; Overbury, Steven {Steve} H; Dai, Sheng

    2008-01-01

    Atomic layer deposition (ALD) was utilized for the surface engineering of metallic nanoparticles to tame their sintering problems and catalytic activities. We chose the surface modification of gold nanocatalysts as an example to demonstrate the concept of this ALD-based approach. Herein, an active Au/TiO{sub 2} catalyst was modified by amorphous SiO{sub 2} via ALD, and the samples were characterized by inductively coupled plasma-optical emission spectrometry (ICP-OES), scanning (SEM-EDX) and transmission electron microscope-energy-dispersive X-ray spectrometry (TEM-EDX), X-ray diffraction (XRD), and thermogravimetry/differential thermogravimetry (TG/DTG), and the catalytic activities in CO oxidation and H{sub 2} oxidation were tested with respect to the pretreatment temperature and SiO{sub 2} content. A significant sintering resistance and changes in catalytic activities were observed. The difference between the SiO{sub 2}/Au/TiO{sub 2} samples prepared by gas-phase ALD and solution-phase chemical grafting was discussed.

  12. Bias-dependent conductive characteristics of individual GeSi quantum dots studied by conductive atomic force microscopy.

    PubMed

    Wu, R; Zhang, S L; Lin, J H; Jiang, Z M; Yang, X J

    2011-03-04

    The bias-dependent electrical characteristics of individual self-assembled GeSi quantum dots (QDs) are investigated by conductive atomic force microscopy. The results reveal that the conductive characteristics of QDs are strongly influenced by the applied bias. At low (-0.5 to - 2.0 V) and high (-2.5 to - 4.0 V) biases, the current distributions of individual GeSi QDs exhibit ring-like and disc-like characteristics respectively. The current of the QD's central part increases more quickly than that of the other parts as the bias magnitude increases. Histograms of the magnitude of the current on a number of QDs exhibit the same single-peak feature at low biases, and double- or three-peak features at high biases, where additional peaks appear at large-current locations. On the other hand, histograms of the magnitude of the current on the wetting layers exhibit the same single-peak feature for all biases. This indicates the conductive mechanism is significantly different for QDs and wetting layers. While the small-current peak of QDs can be attributed to the Fowler-Nordheim tunneling model at low biases and the Schottky emission model at high biases respectively, the large-current peak(s) may be attributed to the discrete energy levels of QDs. The results suggest the conductive mechanisms of GeSi QDs can be regulated by the applied bias.

  13. Charge injection and discharging of Si nanocrystals and arrays by atomic force microscopy

    NASA Technical Reports Server (NTRS)

    Boer, E.; Ostraat, M.; Brongersma, M. L.; Flagan, R. C.; Atwater, H. A.

    2000-01-01

    Charge injection and storage in dense arrays of silicon nanocrystals in SiO(sub 2) is a critical aspect of the performance of potential nanocrystal flash memory structures. The ultimate goal for this class of devices is few-or single- electron storage in a small number of nanocrystal elements.

  14. Initial and secondary oxidation products on the Si(111)-(7 × 7) surface identified by atomic force microscopy and first principles calculations

    SciTech Connect

    Onoda, Jo Sugimoto, Yoshiaki; Ondráček, Martin; Jelínek, Pavel

    2014-03-31

    We investigate the initial and secondary oxidation products on the Si(111)-(7 × 7) surface at room-temperature using atomic force microscopy (AFM) and density functional theory calculations. At the initial oxidation stages, we find that there are two types of bright spots in AFM images. One of them is identified as a Si adatom with one O atom inserted into one of the backbonds, while the other is ascribed to a Si adatom with two inserted O atoms. We observe that the latter one turns into the secondary oxidation product by a further coming O{sub 2} molecule, which appears as a more protruded bright spot. The atomic configuration of this product is identified as Si adatom whose top and all three backbonds make bonds with O atoms. The appearances of initial and secondary oxidation products are imaged as bright and dark sites by scanning tunneling microscopy, respectively. It is revealed that AFM gives us the topographic information close to the real atomic corrugation of adsorbed structures on the semiconductor surfaces.

  15. Evaluation of Solute Clusters Associated with Bake-Hardening Response in Isothermal Aged Al-Mg-Si Alloys Using a Three-Dimensional Atom Probe

    NASA Astrophysics Data System (ADS)

    Aruga, Yasuhiro; Kozuka, Masaya; Takaki, Yasuo; Sato, Tatsuo

    2014-12-01

    Temporal changes in the number density, size distribution, and chemical composition of clusters formed during natural aging at room temperature and pre-aging at 363 K (90 °C) in an Al-0.62Mg-0.93Si (mass pct) alloy were evaluated using atom probe tomography. More than 10 million atoms were examined in the cluster analysis, in which about 1000 clusters were obtained for each material after various aging treatments. The statistically proven records show that both number density and the average radius of clusters in pre-aged materials are larger than in naturally aged materials. It was revealed that the fraction of clusters with a low Mg/Si ratio after natural aging for a short time is higher than with other aging treatments, regardless of cluster size. This indicates that Si-rich clusters form more easily after short-period natural aging, and that Mg atoms can diffuse into the clusters or possibly form another type of Mg-Si cluster after prolonged natural aging. The formation of large clusters with a uniform Mg/Si ratio is encouraged by pre-aging. It can be concluded that an increase of small clusters with various Mg/Si ratios does not promote the bake-hardening (BH) response, whereas large clusters with a uniform Mg/Si ratio play an important role in hardening during the BH treatment at 443 K (170 °C).

  16. Optimizing SFR transmutation performance through direct adjoining control theory

    NASA Astrophysics Data System (ADS)

    Davis, Jeffrey C.

    2007-12-01

    We have developed the CORTANA code to optimize the transmutation performance of sodium cooled fast reactors (SFRs). We obtain the necessary conditions for optimal fuel and burnable absorber loadings using Pontryagin's maximum principle with a direct adjoining approach to explicitly account for either a flat flux or a power peaking inequality constraint providing a set of coupled system, Euler-Lagrange (E-L), and optimality equations which are iteratively solved with the method of conjugate gradients until no further improvement in the objective function is achieved. To satisfy the inequality constraints throughout the operating cycle, we have implemented a backwards diffusion theory (BDT) to establish a relationship between fuel loading and the relative assembly power distribution during the cycle and systematically eliminate the constraint violations with each conjugate gradient iteration. The CORTANA SFR optimization code uses multi-group, three-dimensional neutron diffusion theory, with a microscopic depletion scheme. We solve the system equations in a quasi-static fashion forward in time from beginning-of-cycle (BOC) to end-of-cycle (EOC), while we solve the E-L equations backwards in time from EOC to BOC, reflecting the adjoint nature of the Lagrange multipliers. A two enrichment-zone SFR problem verifies our formulation, yielding a TRU enrichment distribution nearly identical to that of the reference SFR core in the Generation IV Roadmap. Using a full heavy metal recycling mode, we coupled our optimization methodology with the REBUS-3 equilibrium cycle methodology to optimize an SFR operating as a second tier transmuter. We model the system using a three-dimensional triangular-z finite differencing scheme with full core symmetry and a time-independent 33-group microscopic cross section library. Beginning from a uniform TRU distribution, our CORTANA improves the SFR performance by reducing the maximum relative assembly power from 1.7 to 1.25, minimizes

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

    NASA Astrophysics Data System (ADS)

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

    2006-03-01

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

  18. Carbene supported dimer of heavier ketenimine analogue with p and si atoms.

    PubMed

    Roy, Sudipta; Dittrich, Birger; Mondal, Totan; Koley, Debasis; Stückl, A Claudia; Schwederski, Brigitte; Kaim, Wolfgang; John, Michael; Vasa, Suresh Kumar; Linser, Rasmus; Roesky, Herbert W

    2015-05-20

    A cyclic alkyl(amino) carbene (cAAC) stabilized dimer [(cAAC)Si(P-Tip)]2 (2) (Tip = 2,4,6-triisopropylphenyl) is reported. 2 can be considered as a dimer of the heavier ketenimine (R2C═C═N-R) analogue. The dark-red rod-shaped crystals of 2 were synthesized by reduction of the precursor, cAAC-dichlorosilylene-stabilized phosphinidene (cAAC)SiCl2→P-Tip with sodium napthalenide. The crystals of 2 are storable at room temperature for several months and stable up to 215 °C under an inert atmosphere. X-ray single-crystal diffraction revealed that 2 contains a cyclic nonplanar four-membered SiPSiP ring. Magnetic susceptibility measurements confirmed the singlet spin ground state of 2. Cyclic voltammetry of 2 showed a quasi-reversible one-electron reduction indicating the formation of the corresponding radical anion 2(•-), which was further characterized by EPR measurements in solution. The electronic structure and bonding of 2 and 2(•-) were studied by theoretical calculations. The experimentally obtained data are in good agreement with the calculated values.

  19. Growth of Atomically Flat Ultra-Thin Ag Films on Si(111) by Introducing a √3 × √3-Ga Buffer Layer

    NASA Astrophysics Data System (ADS)

    He, Jie-Hui; Jiang, Li-Qun; Qiu, Jing-Lan; Chen, Lan; Wu, Ke-Hui

    2014-12-01

    It is known that, when Ag is deposited on Si(111)-7×7 substrates in a conventional growth procedure at room temperature, no atomically flat Ag film could be obtained. We use scanning tunneling microscopy and low-energy electron diffraction to investigate the growth of ultra-thin Ag films on the Si(111) substrates at room temperature. Our study reveals that, upon introducing a Si(111)-√3 × √3-Ga buffer layer, atomically flat Ag films can easily grow on Si(111) with a critical thickness of two monolayers. Moreover, Ag film growth follows a layer-by-layer mode with further deposition. This novel growth behavior of Ag can be explained in terms of a free electron model (i.e., particle in a box) and kinetic Monte Carlo simulations.

  20. Counting the atoms in a 28Si crystal for a new kilogram definition

    NASA Astrophysics Data System (ADS)

    Andreas, B.; Azuma, Y.; Bartl, G.; Becker, P.; Bettin, H.; Borys, M.; Busch, I.; Fuchs, P.; Fujii, K.; Fujimoto, H.; Kessler, E.; Krumrey, M.; Kuetgens, U.; Kuramoto, N.; Mana, G.; Massa, E.; Mizushima, S.; Nicolaus, A.; Picard, A.; Pramann, A.; Rienitz, O.; Schiel, D.; Valkiers, S.; Waseda, A.; Zakel, S.

    2011-04-01

    This paper concerns an international research project aimed at determining the Avogadro constant by counting the atoms in an isotopically enriched silicon crystal. The counting procedure was based on the measurement of the molar volume and the volume of an atom in two 1 kg crystal spheres. The novelty was the use of isotope dilution mass spectrometry as a new and very accurate method for the determination of the molar mass of enriched silicon. Because of an unexpected metallic contamination of the sphere surfaces, the relative measurement uncertainty, 3 × 10-8 NA, is larger by a factor 1.5 than that targeted. The measured value of the Avogadro constant, NA = 6.022 140 82(18) × 1023 mol-1, is the most accurate input datum for the kilogram redefinition and differs by 16 × 10-8 NA from the CODATA 2006 adjusted value. This value is midway between the NIST and NPL watt-balance values.

  1. New bonding modes of carbon and heavier group 14 atoms Si-Pb.

    PubMed

    Frenking, Gernot; Tonner, Ralf; Klein, Susanne; Takagi, Nozomi; Shimizu, Takayazu; Krapp, Andreas; Pandey, Krishna K; Parameswaran, Pattiyil

    2014-07-21

    Recent theoretical studies are reviewed which show that the naked group 14 atoms E = C-Pb in the singlet (1)D state behave as bidentate Lewis acids that strongly bind two σ donor ligands L in the donor-acceptor complexes L→E←L. Tetrylones EL2 are divalent E(0) compounds which possess two lone pairs at E. The unique electronic structure of tetrylones (carbones, silylones, germylones, stannylones, plumbylones) clearly distinguishes them from tetrylenes ER2 (carbenes, silylenes, germylenes, stannylenes, plumbylenes) which have electron-sharing bonds R-E-R and only one lone pair at atom E. The different electronic structures of tetrylones and tetrylenes are revealed by charge- and energy decomposition analyses and they become obvious experimentally by a distinctively different chemical reactivity. The unusual structures and chemical behaviour of tetrylones EL2 can be understood in terms of the donor-acceptor interactions L→E←L. Tetrylones are potential donor ligands in main group compounds and transition metal complexes which are experimentally not yet known. The review also introduces theoretical studies of transition metal complexes [TM]-E which carry naked tetrele atoms E = C-Sn as ligands. The bonding analyses suggest that the group-14 atoms bind in the (3)P reference state to the transition metal in a combination of σ and π∥ electron-sharing bonds TM-E and π⊥ backdonation TM→E. The unique bonding situation of the tetrele complexes [TM]-E makes them suitable ligands in adducts with Lewis acids. Theoretical studies of [TM]-E→W(CO)5 predict that such species may becomes synthesized.

  2. Tuning optical properties of magic number cluster (SiO2)4O2H4 by substitutional bonding with gold atoms.

    PubMed

    Cai, Xiulong; Zhang, Peng; Ma, Liuxue; Zhang, Wenxian; Ning, Xijing; Zhao, Li; Zhuang, Jun

    2009-04-30

    By bonding gold atoms to the magic number cluster (SiO(2))(4)O(2)H(4), two groups of Au-adsorbed shell-like clusters Au(n)(SiO(2))(4)O(2)H(4-n) (n = 1-4) and Au(n)(SiO(2))(4)O(2) (n = 5-8) were obtained, and their spectral properties were studied. The ground-state structures of these clusters were optimized by density functional theory, and the results show that in despite of the different numbers and types of the adsorbed Au atoms, the cluster core (SiO(2))(4)O(2) of T(d) point-group symmetry keeps almost unchanged. The absorption spectra were obtained by time-dependent density functional theory. From one group to the other, an extension of absorption wavelength from the UV-visible to the NIR region was observed, and in each group the absorption strengths vary linearly with the number of Au atoms. These features indicate their advantages for exploring novel materials with easily controlled tunable optical properties. Furthermore, due to the weak electronic charge transfer between the Au atoms, the clusters containing Au(2) dimers, especially Au(8)(SiO(2))(4)O(2), absorb strongly NIR light at 900 approximately 1200 nm. Such strong absorption suggests potential applications of these shell-like clusters in tumor cells thermal therapy, like the gold-coated silica nanoshells with larger sizes.

  3. Atomic-scale scanning tunneling microscopy and spectroscopy studies of nanometer-sized graphene on the Si(111)-7x7 surface.

    NASA Astrophysics Data System (ADS)

    Koepke, Justin; Lyding, Joseph

    2009-03-01

    We have used ultrahigh vacuum scanning tunneling microscopy to perform atomic-level studies of graphene on the Si(111)-7x7 surface. We used a dry contact transfer technique (DCT) developed by Albrecht and Lyding [1] to deposit mechanically exfoliated graphene in-situ [2] onto atomically clean Si(111)-7x7 surfaces. The DCT method deposits single, double, and thicker layers of atomically clean graphene. We observe varying degrees of transparency of the graphene monolayers and bilayers on the Si(111)-7x7 surface, where the substrate atomic structure is clearly seen through the graphene. We believe that the electronic structure of a graphene monolayer on the Si(111)-7x7 surface leads to the transparency of monolayers and bilayers, similar to the findings of Rutter, et al [3]. Room-temperature scanning tunneling spectroscopy (STS) measurements of the graphene monolayers and bilayers on the Si(111)-7x7 surface show predominantly metallic behavior. [1] P.M. Albrecht and J.W. Lyding, Appl. Phys. Lett. 83, 5029 (2003) [2] K.A. Ritter and J.W. Lyding, Nanotechnology 19, 015704 (2008) [3] G.M. Rutter, et al, Phys. Rev. B 76, 235416 (2007)

  4. CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES: First-Principles Calculations of Atomic and Electronic Properties of Tl and In on Si(111)

    NASA Astrophysics Data System (ADS)

    Dai, Xian-Qi; Zhao, Jian-Hua; Sun, Yong-Can; Wei, Shu-Yi; Wei, Guo-Hong

    2010-09-01

    The atomic and electronic structures of Tl and In on Si(111) surfaces are investigated using the first-principles total energy calculations. Total energy optimizations show that the energetically favored structure is 1/3 ML Tl adsorbed at the T4 sites on Si(111) surfaces. The adsorption energy difference of one Tl adatom between (√3 × √3) and (1 × 1) is less than that of each In adatom. The DOS indicates that Tl 6p and Si 3p electrons play a very important role in the formation of the surface states. It is concluded that the bonding of Tl adatoms on Si(111) surfaces is mainly polar covalent, which is weaker than that of In on Si(111). So Tl atom is more easy to be migrated than In atom in the same external electric field and the structures of Tl on Si(111) is prone to switch between (√3 × √3) and (1 × 1).

  5. SiNx Charge Trap Nonvolatile Memory Based on ZnO Thin Film Transistor Prepared by Atomic Layer Deposition

    NASA Astrophysics Data System (ADS)

    Kim, E.; Lee, K.; Kim, D.; Parsons, G. N.; Park, K.

    2011-12-01

    We fabricated a nonvolatile thin film transistor (TFT) memory with SiNx charge traps using a ZnO thin film as an active channel layer. The thin film of ZnO was deposited by using atomic layer deposition process at TALD = 125 °C. The ZnO films were investigated by X-ray diffraction and X-ray photoemission measurements. The electrical measurements of the nonvolatile TFT memory showed a field-effect mobility of 2.95 cm2 V-1 s-1, a threshold voltage of -7.24 V, a subthreshold swing of 1.7 V/dec, and an on/off ratio of 3.4×105. From the C-V measurement, the memory window of 2 V was obtained.

  6. Determination of the geometric corrugation of graphene on SiC(0001) by grazing incidence fast atom diffraction

    SciTech Connect

    Zugarramurdi, A.; Debiossac, M.; Lunca-Popa, P.; Mayne, A. J.; Borisov, A. G.; Mu, Z.; Roncin, P.; Khemliche, H.; Momeni, A.

    2015-03-09

    We present a grazing incidence fast atom diffraction (GIFAD) study of monolayer graphene on 6H-SiC(0001). This system shows a Moiré-like 13 × 13 superlattice above the reconstructed carbon buffer layer. The averaging property of GIFAD results in electronic and geometric corrugations that are well decoupled; the graphene honeycomb corrugation is only observed with the incident beam parallel to the zigzag direction while the geometric corrugation arising from the superlattice is revealed along the armchair direction. Full-quantum calculations of the diffraction patterns show the very high GIFAD sensitivity to the amplitude of the surface corrugation. The best agreement between the calculated and measured diffraction intensities yields a corrugation height of 0.27 ± 0.03 Å.

  7. Interplay between atomic disorder, lattice swelling and defect energy in ion-irradiation-induced amorphization of SiC

    SciTech Connect

    Debelle, Aurelien; Boulle, Alexandre; Chartier, Alain; Gao, Fei; Weber, William J

    2014-11-25

    We present a combination of experimental and computational evaluations of disorder level and lattice swelling in ion-irradiated materials. Information obtained from X-ray diffraction experiments is compared to X-ray diffraction data generated using atomic-scale simulations. The proposed methodology, which can be applied to a wide range of crystalline materials, is used to study the amorphization process in irradiated SiC. Results show that this process can be divided into two steps. In the first step, point defects and small defect clusters are produced and generate both large lattice swelling and high elastic energy. In the second step, enhanced coalescence of defects and defect clusters occurs to limit this increase in energy, which rapidly leads to complete amorphization.

  8. Fabrication of high-aspect ratio Si pillars for atom probe 'lift-out' and field ionization tips.

    PubMed

    Morris, R A; Martens, R L; Zana, I; Thompson, G B

    2009-04-01

    A process for fabricating high-aspect ratio ( approximately 1:20), micron-sized Si [001] pillars using mechanical and chemical size reduction is presented. A dicing saw was used for mechanically patterning an array of square pillars with side lengths of >20mum. These pillars were then reduced in size using an aqueous NaOH and KOH solution heated to 100 degrees C. The chemical etch reduces the pillar size within the time range amenable for focus ion beam milling and/or attachment for atom probe 'lift-out' specimens. The pillars can be formed with either a flat top surface or into <100nm tip points for direct field ionization.

  9. Atomically sharp 318 nm Gd:AlGaN ultraviolet light emitting diodes on Si with low threshold voltage

    NASA Astrophysics Data System (ADS)

    Kent, Thomas F.; Carnevale, Santino D.; Myers, Roberto C.

    2013-05-01

    Self-assembled AlxGa1-xN polarization-induced nanowire light emitting diodes (PINLEDs) with Gd-doped AlN active regions are prepared by plasma-assisted molecular beam epitaxy on Si substrates. Atomically sharp electroluminescence (EL) from Gd intra-f-shell electronic transitions at 313 nm and 318 nm is observed under forward biases above 5 V. The intensity of the Gd 4f EL scales linearly with current density and increases at lower temperature. The low field excitation of Gd 4f EL in PINLEDs is contrasted with high field excitation in metal/Gd:AlN/polarization-induced n-AlGaN devices; PINLED devices offer over a three fold enhancement in 4f EL intensity at a given device bias.

  10. Interplay between atomic disorder, lattice swelling and defect energy in ion-irradiation-induced amorphization of SiC

    DOE PAGES

    Debelle, Aurelien; Boulle, Alexandre; Chartier, Alain; ...

    2014-11-25

    We present a combination of experimental and computational evaluations of disorder level and lattice swelling in ion-irradiated materials. Information obtained from X-ray diffraction experiments is compared to X-ray diffraction data generated using atomic-scale simulations. The proposed methodology, which can be applied to a wide range of crystalline materials, is used to study the amorphization process in irradiated SiC. Results show that this process can be divided into two steps. In the first step, point defects and small defect clusters are produced and generate both large lattice swelling and high elastic energy. In the second step, enhanced coalescence of defects andmore » defect clusters occurs to limit this increase in energy, which rapidly leads to complete amorphization.« less

  11. Mechanistic aspects of gas-phase hydrogen-atom transfer from methane to [CO](·+) and [SiO](·+) : why do they differ?

    PubMed

    Dietl, Nicolas; Troiani, Anna; Schlangen, Maria; Ursini, Ornella; Angelini, Giancarlo; Apeloig, Yitzhak; de Petris, Giulia; Schwarz, Helmut

    2013-05-17

    The reactivity of the two diatomic congeneric systems [CO](·+) and [SiO](·+) towards methane has been investigated by means of mass spectrometry and quantum-chemical calculations. While [CO](·+) gives rise to three different reaction channels, [SiO](·+) reacts only by hydrogen-atom transfer (HAT) from methane under thermal conditions. A theoretical analysis of the respective HAT processes reveals two distinctly different mechanistic pathways for [CO](·+) and [SiO](·+), and a comparison to the higher metal oxides of Group 14 emphasizes the particular role of carbon as a second-row p element.

  12. Atomic layer deposition of SiO2 thin films using tetrakis(ethylamino)silane and ozone.

    PubMed

    Kim, Jae-Kyung; Jin, Kwangsun; Jung, Jongwan; Rha, Sa-Kyun; Lee, Won-Jun

    2012-04-01

    We examined the atomic layer deposition (ALD) of silicon dioxide thin films on a silicon wafer by alternating exposures to tetrakis(ethylamino)silane [Si(NHC2H5)4] and O3. The growth kinetics of silicon oxide films was examined at substrate temperatures ranging from 325 to 514 degrees C. The deposition was governed by a self-limiting surface reaction, and the growth rate at 478 degrees C was saturated at 0.17 nm/cycle for Si(NHC2H5)4 exposures of 2 x 10(6) L (1 L = 10(-6) Torr x s). The films deposited at 365-404 degrees C exhibited a higher deposition rate of 0.20-0.21 nm/cycle. However, they contained impurities, such as carbon and nitrogen, and showed poor film qualities. The concentration of impurities decreased with increasing substrate temperature. It was found that the films deposited in the high-temperature regime (478-514 degrees C) showed excellent physical and electrical properties equivalent to those of LPCVD films.

  13. Accurate analytical measurements in the atomic force microscope: a microfabricated spring constant standard potentially traceable to the SI

    NASA Astrophysics Data System (ADS)

    Cumpson, Peter J.; Hedley, John

    2003-12-01

    Calibration of atomic force microscope (AFM) cantilevers is necessary for the measurement of nanonewton and piconewton forces, which are critical to analytical applications of AFM in the analysis of polymer surfaces, biological structures and organic molecules at nanoscale lateral resolution. We have developed a compact and easy-to-use reference artefact for this calibration, using a method that allows traceability to the SI (Système International). Traceability is crucial to ensure that force measurements by AFM are comparable to those made by optical tweezers and other methods. The new non-contact calibration method measures the spring constant of these artefacts, by a combination of electrical measurements and Doppler velocimetry. The device was fabricated by silicon surface micromachining. The device allows AFM cantilevers to be calibrated quite easily by the 'cantilever-on-reference' method, with our reference device having a spring constant uncertainty of around ± 5% at one standard deviation. A simple substitution of the analogue velocimeter used in this work with a digital model should reduce this uncertainty to around ± 2%. Both are significant improvements on current practice, and allow traceability to the SI for the first time at these nanonewton levels.

  14. Atom-scale covalent electrochemical modification of single-layer graphene on SiC substrates by diaryliodonium salts

    DOE PAGES

    Gearba, Raluca I.; Mueller, Kory M.; Veneman, Peter A.; ...

    2015-05-09

    Owing to its high conductivity, graphene holds promise as an electrode for energy devices such as batteries and photovoltaics. However, to this end, the work function and doping levels in graphene need to be precisely tuned. One promising route for modifying graphene’s electronic properties is via controlled covalent electrochemical grafting of molecules. We show that by employing diaryliodonium salts instead of the commonly used diazonium salts, spontaneous functionalization is avoided. This then allows for precise tuning of the grafting density. Moreover, by employing bis(4-nitrophenyl)iodonium(III) tetrafluoroborate (DNP) salt calibration curves, the surface functionalization density (coverage) of glassy carbon was controlled usingmore » cyclic voltammetry in varying salt concentrations. These electro-grafting conditions and calibration curves translated directly over to modifying single layer epitaxial graphene substrates (grown on insulating 6H-SiC (0 0 0 1)). In addition to quantifying the functionalization densities using electrochemical methods, samples with low grafting densities were characterized by low-temperature scanning tunneling microscopy (LT-STM). We show that the use of buffer-layer free graphene substrates is required for clear observation of the nitrophenyl modifications. Furthermore, atomically-resolved STM images of single site modifications were obtained, showing no preferential grafting at defect sites or SiC step edges as supposed previously in the literature. Most of the grafts exhibit threefold symmetry, but occasional extended modifications (larger than 4 nm) were observed as well.« less

  15. Atom-scale covalent electrochemical modification of single-layer graphene on SiC substrates by diaryliodonium salts

    SciTech Connect

    Gearba, Raluca I.; Mueller, Kory M.; Veneman, Peter A.; Holliday, Bradley J.; Chan, Calvin K.; Stevenson, Keith J.

    2015-05-09

    Owing to its high conductivity, graphene holds promise as an electrode for energy devices such as batteries and photovoltaics. However, to this end, the work function and doping levels in graphene need to be precisely tuned. One promising route for modifying graphene’s electronic properties is via controlled covalent electrochemical grafting of molecules. We show that by employing diaryliodonium salts instead of the commonly used diazonium salts, spontaneous functionalization is avoided. This then allows for precise tuning of the grafting density. Moreover, by employing bis(4-nitrophenyl)iodonium(III) tetrafluoroborate (DNP) salt calibration curves, the surface functionalization density (coverage) of glassy carbon was controlled using cyclic voltammetry in varying salt concentrations. These electro-grafting conditions and calibration curves translated directly over to modifying single layer epitaxial graphene substrates (grown on insulating 6H-SiC (0 0 0 1)). In addition to quantifying the functionalization densities using electrochemical methods, samples with low grafting densities were characterized by low-temperature scanning tunneling microscopy (LT-STM). We show that the use of buffer-layer free graphene substrates is required for clear observation of the nitrophenyl modifications. Furthermore, atomically-resolved STM images of single site modifications were obtained, showing no preferential grafting at defect sites or SiC step edges as supposed previously in the literature. Most of the grafts exhibit threefold symmetry, but occasional extended modifications (larger than 4 nm) were observed as well.

  16. Interplay of atomic randomness and Kondo effect in disordered metallic conductor La2NiSi3

    NASA Astrophysics Data System (ADS)

    Gnida, Daniel; Szlawska, Maria; Swatek, Przemysław; Kaczorowski, Dariusz

    2016-11-01

    A polycrystalline sample of La2NiSi3 was investigated by means of heat capacity, magnetic susceptibility, magnetization, electrical resistivity and magnetoresistivity measurements. The compound was basically characterized as a Pauli paramagnet with metallic-like electrical conductivity, notably reduced in magnitude and weakly temperature dependent, as is usually observed for atomically disordered systems. Furthermore, the experimental data revealed the presence of a small amount of paramagnetic impurities. As a result, the low-temperature electrical resistivity in La2NiSi3 was found to be governed by both quantum corrections due to electron-electron interactions (ρ ˜ {{T}1/2} contribution) and spin-flip Kondo scattering (ρ ˜ log T contribution). The presence of paramagnetic impurities led to an increase in s-electron spin splitting due to the s-d interactions, manifested by a B 1/2 dependence of the magnetoresistivity, anomalously observed in the present study for thermal energy being larger than the Zeeman splitting energy {{k}\\text{B}}T>g{μ\\text{B}}B .

  17. Effects of Post Annealing Treatments on the Interfacial Chemical Properties and Band Alignment of AlN/Si Structure Prepared by Atomic Layer Deposition.

    PubMed

    Sun, Long; Lu, Hong-Liang; Chen, Hong-Yan; Wang, Tao; Ji, Xin-Ming; Liu, Wen-Jun; Zhao, Dongxu; Devi, Anjana; Ding, Shi-Jin; Zhang, David Wei

    2017-12-01

    The influences of annealing temperature in N2 atmosphere on interfacial chemical properties and band alignment of AlN/Si structure deposited by atomic layer deposition have been investigated based on x-ray photoelectron spectroscopy and spectroscopic ellipsometry. It is found that more oxygen incorporated into AlN film with the increasing annealing temperature, resulting from a little residual H2O in N2 atmosphere reacting with AlN film during the annealing treatment. Accordingly, the Si-N bonding at the interface gradually transforms to Si-O bonding with the increasing temperature due to the diffusion of oxygen from AlN film to the Si substrate. Specially, the Si-O-Al bonding state can be detected in the 900 °C-annealed sample. Furthermore, it is determined that the band gap and valence band offset increase with increasing annealing temperature.

  18. Effects of Post Annealing Treatments on the Interfacial Chemical Properties and Band Alignment of AlN/Si Structure Prepared by Atomic Layer Deposition

    NASA Astrophysics Data System (ADS)

    Sun, Long; Lu, Hong-Liang; Chen, Hong-Yan; Wang, Tao; Ji, Xin-Ming; Liu, Wen-Jun; Zhao, Dongxu; Devi, Anjana; Ding, Shi-Jin; Zhang, David Wei

    2017-02-01

    The influences of annealing temperature in N2 atmosphere on interfacial chemical properties and band alignment of AlN/Si structure deposited by atomic layer deposition have been investigated based on x-ray photoelectron spectroscopy and spectroscopic ellipsometry. It is found that more oxygen incorporated into AlN film with the increasing annealing temperature, resulting from a little residual H2O in N2 atmosphere reacting with AlN film during the annealing treatment. Accordingly, the Si-N bonding at the interface gradually transforms to Si-O bonding with the increasing temperature due to the diffusion of oxygen from AlN film to the Si substrate. Specially, the Si-O-Al bonding state can be detected in the 900 °C-annealed sample. Furthermore, it is determined that the band gap and valence band offset increase with increasing annealing temperature.

  19. Atomic structures and energies of grain boundaries in Mg2SiO4 forsterite from atomistic modeling

    NASA Astrophysics Data System (ADS)

    Adjaoud, Omar; Marquardt, Katharina; Jahn, Sandro

    2012-10-01

    Grain boundaries influence many physical and chemical properties of crystalline materials. Here, we perform molecular dynamics simulations to study the structure of a series of [100] symmetric tilt grain boundaries in Mg2SiO4 forsterite. The present results show that grain boundary energies depend significantly on misorientation angle. For small misorientation angles (up to 22°), grain boundary structures consist of an array of partial edge dislocations with Burgers vector 1/2[001] associated with stacking faults and their energies can be readily fit with a model which adds the Peach-Koehler equation to the Read-Shockley dislocation model for grain boundaries. The core radius of partial dislocations and the spacing between the partials derived from grain boundary energies show that the transition from low- to high-angle grain boundaries occurs for a misorientation angle between 22° and 32°. For high misorientation angles (32.1° and 60.8°), the cores of dislocations overlap and form repeated structural units. Finally, we use a low energy atomic configuration obtained by molecular dynamics for the misorientation of 12.18° as input to simulate a high-resolution transmission electron microscopy (HRTEM) image. The simulated image is in good agreement with an observed HRTEM image, which indicates the power of the present approach to predict realistic atomic structures of grain boundaries in complex silicates.

  20. The Avogadro constant: determining the number of atoms in a single-crystal ²⁸Si sphere.

    PubMed

    Becker, Peter; Bettin, Horst

    2011-10-28

    The Avogadro constant, the number of entities in an amount of substance of one mole, links the atomic and the macroscopic properties of matter. Since the molar Planck constant--the product of the Planck constant and the Avogadro constant--is very well known via the measurement of the Rydberg constant, the Avogadro constant is also closely related to the Planck constant. In addition, its accurate determination is of paramount importance for a new definition of the kilogram in terms of a fundamental constant. Here, we describe a new and unique approach to determine the Avogadro constant from the number of atoms in 1 kg single-crystal spheres that are highly enriched with the (28)Si isotope. This approach has enabled us to apply isotope dilution mass spectroscopy to determine the molar mass of the silicon crystal with unprecedented accuracy. The value obtained, N(A)=6.022 140 82(18)×10(23) mol(-1), is now the most accurate input datum for a new definition of the kilogram.

  1. Anisotropic plasticity of MgSiO3 post-perovskite from atomic scale modeling

    NASA Astrophysics Data System (ADS)

    Goryaeva, Alexandra; Carrez, Philippe; Cordier, Patrick

    2016-04-01

    In contrast to the lower mantle, the D″ layer exhibits significant seismic anisotropy both at the global and local scale [1]. Located right above the CMB, the D'' represents a very complex region and the causes of its pronounced anisotropy are still debated (CPO, oriented inclusions, layering, thermo-chemical heterogeneities etc). Among them, contribution of the post-perovskite rheology is commonly considered to be substantial. However, for this high-pressure phase, information about mechanical properties, probable slip systems, dislocations and their behavior under stress are still extremely challenging to obtain directly from experiments [3, 4]. Thus, we propose employing full atomistic modeling (based on the pairwise potential previously derived by [2]) to access the ability of MgSiO3 post-perovskite to deform by dislocation glide at 120 GPa. Lattice friction opposed to the dislocation glide in MgSiO3 post-perovskite is shown to be highly anisotropic. Thus, remarkably low values of Peierls stress (1 GPa) are found for the glide of [100] screw dislocations in (010), while glide in (001) requires almost 18 times larger stress values. In general, (010) plane is characterized by the lowest lattice friction which suggests (010) deformation textures. Comparison of our results with previous study of MgSiO3 perovskite (bridgmanite) [5], based on similar simulation approach, clearly shows that monotonous increase in Peierls stress of bridgmanite will be followed by a dramatic drop after the phase transition to the post-perovskite phase, which consequently suggests the D'' located at the CMB to be weaker than the overlying mantle. In addition to that, the observed evolution of CRSS with temperature clearly demonstrates that post-perovskite deforms in the athermal regime which backs up it to be a very weak phase and indicates its deformation by dislocation glide in contrast to high-lattice friction perovskite (bridgmanite) phase deformed by climb only. References [1

  2. The new kilogram definition based on counting the atoms in a 28Si crystal

    NASA Astrophysics Data System (ADS)

    Becker, Peter

    2012-11-01

    The kilogram is the only unit of measure still defined by a physical object. Now, a marathon effort to tie the kilogram to a constant of nature is nearing the finish line. This paper concerns an international research project aimed at determining the Avogadro constant by counting the atoms in an isotopically enriched silicon crystal. The counting procedure was based on the measurement of the molar volume and the volume of an atom in two 1 kg crystal spheres. The novelty was the use of isotope dilution mass spectrometry as a new and very accurate method for the determination of the molar mass of enriched silicon. Because of an unexpected metallic contamination of the sphere surfaces, the relative measurement uncertainty, ? , results were larger by a factor 1.5 than that targeted. The measured value of the Avogadro constant, ? mol-1 is the most accurate input datum for the kilogram redefinition and differs only by ? from the CODATA 2010 adjusted value. This value is midway between the watt-balance values.

  3. Preparations and properties of a tunable void with shell thickness SiO2@SiO2 core-shell structures via activators generated by electron transfer for atom transfer radical polymerization

    NASA Astrophysics Data System (ADS)

    Ren, Yi-xian; Zhou, Guo-wei; Cao, Pei

    2016-02-01

    Core-shell structure nanoparticles are attracting considerable attention because of their applications in drug delivery, catalysis carrier, and nanomedicine. In this study, SiO2@SiO2 core-shell structure with tunable void and shell thickness was successfully prepared for the first time using SiO2-poly(buty acrylate) (PBA)-poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) (SiO2-PBA-b-PDMAEMA) as the template and tetraethoxysilane (TEOS) as the silica source. An amphiphilic copolymer PBA-b-PDMAEMA was first grafted onto the SiO2 nanosphere surface through activators regenerated by electron transfer for atom transfer radical polymerization. TEOS was hydrolyzed along with the PDMAEMA chain through hydrogen bonding, and the core-shell structure of SiO2@SiO2 was obtained through calcination to remove the copolymer. The gradient hydrophilicity of the PBA-b-PDMAEMA copolymer template facilitated the hydrolysis of TEOS molecules along the PDMAEMA to PBA segments, thereby tuning the voids between the SiO2 core and SiO2 shell, as well as the SiO2 shell thickness. The voids were about 10-15 nm and the shell thicknesses were about 4-11 nm when adding different amounts of DMAEMA monomer. SiO2@SiO2 core-shell structures with tunable void and shell thickness were employed as supports for the loading and release of doxorubicin hydrochloride (DOX) in PBS (pH 4.0). The samples demonstrated good loading capacity and controlled release rate of DOX.

  4. Mechanism of Gap Opening in a Triple-Band Peierls System: In Atomic Wires on Si

    NASA Astrophysics Data System (ADS)

    Ahn, J. R.; Byun, J. H.; Koh, H.; Rotenberg, E.; Kevan, S. D.; Yeom, H. W.

    2004-08-01

    One dimensional (1D) metals are unstable at low temperature undergoing a metal-insulator transition coupled with a periodic lattice distortion, a Peierls transition. Angle-resolved photoemission study for the 1D metallic chains of In on Si(111), featuring a metal-insulator transition and triple metallic bands, clarifies in detail how the multiple band gaps are formed at low temperature. In addition to the gap opening for a half-filled ideal 1D band with a proper Fermi surface nesting, two other quasi-1D metallic bands are found to merge into a single band, opening a unique but k-dependent energy gap through an interband charge transfer. This result introduces a novel gap-opening mechanism for a multiband Peierls system where the interband interaction is important.

  5. Atomic structure of Sr-induced reconstructions on the Si(100) surface

    NASA Astrophysics Data System (ADS)

    He, Jiehui; Zhang, Guanhua; Guo, Jiandong; Guo, Qinlin; Wu, Kehui

    2011-04-01

    The Sr-induced reconstructions on Si(100) at elevated temperature were studied using scanning tunneling microscopy and reflection high energy electron diffraction. With the Sr coverage increasing from 0 to 0.5 monolayer, the surface exhibits phase transitions from 2×1-Sr to 2×3-Sr and then to 1×2-Sr. The bias-dependent, high resolution STM images unambiguously support a dimer-vacancy structural model for the 2×3-Sr phase. Furthermore, the coverage-dependent evolution of the surface from 2×3-Sr to 1×2-Sr can also be nicely explained by extending the 2×3-Sr model to the 1×2-Sr.

  6. Fe{sub 2-x}Co{sub x}MnSi (x = 0, 1 and 2) Heusler alloys: Structural, magnetic and atomic site disorder properties

    SciTech Connect

    Bhatt, Harsh; Mukadam, M. D.; Meena, S. S.; Yusuf, S. M.

    2015-06-24

    The Heusler alloy series Fe{sub 2-x}Co{sub x}MnSi (x = 0, 1 and 2) is theoretically predicted to be half metallic. We prepared the sample series and determined the structural and magnetic properties to check if these materials are suitable for spintronics applications. The Curie temperatures of two of the alloys have been found to be well above the room temperature. But the presence of elements with atoms of similar size leads to atomic site disorder in these alloys, which may destroy the half metallic nature. The atomic site disorder has been confirmed by Mössbauer spectroscopy.

  7. Diffusion of single Au, Ag and Cu atoms inside Si(111)-(7 × 7) half unit cells: A comparative study

    NASA Astrophysics Data System (ADS)

    Liu, Qin; Fu, Qiang; Shao, Xiji; Ma, Xuhang; Wu, Xuefeng; Wang, Kedong; Xiao, Xudong

    2017-04-01

    The diffusion behaviors of single Au, Ag and Cu atoms on Si(111)-(7 × 7) half unit cells have been investigated via combining scanning tunneling microscopy and first-principles calculations. Despite the similar adsorption sites between both half unit cells among these elements, the diffusion dynamics show obvious differences between Ag and the other two. Although obvious asymmetry has been found in the diffusion behaviors of Au and Cu atoms in two half unit cells of Si(111)-(7 × 7), the asymmetry behaves in a way different from that of Ag atoms and no dual-time character has been observed for the diffusions of Au and Cu in both half unit cells. Theoretical calculations suggest a different potential energy profile caused by the stronger hybridization between d states of Au (Cu) and Si states make the concept of basin useless for the diffusion of Au and Cu atoms inside the half unit cells of Si(111)-(7 × 7).

  8. Realisation of magnetically and atomically abrupt half-metal/semiconductor interface: Co2FeSi0.5Al0.5/Ge(111).

    PubMed

    Nedelkoski, Zlatko; Kuerbanjiang, Balati; Glover, Stephanie E; Sanchez, Ana M; Kepaptsoglou, Demie; Ghasemi, Arsham; Burrows, Christopher W; Yamada, Shinya; Hamaya, Kohei; Ramasse, Quentin M; Hasnip, Philip J; Hase, Thomas; Bell, Gavin R; Hirohata, Atsufumi; Lazarov, Vlado K

    2016-11-21

    Halfmetal-semiconductor interfaces are crucial for hybrid spintronic devices. Atomically sharp interfaces with high spin polarisation are required for efficient spin injection. In this work we show that thin film of half-metallic full Heusler alloy Co2FeSi0.5Al0.5 with uniform thickness and B2 ordering can form structurally abrupt interface with Ge(111). Atomic resolution energy dispersive X-ray spectroscopy reveals that there is a small outdiffusion of Ge into specific atomic planes of the Co2FeSi0.5Al0.5 film, limited to a very narrow 1 nm interface region. First-principles calculations show that this selective outdiffusion along the Fe-Si/Al atomic planes does not change the magnetic moment of the film up to the very interface. Polarized neutron reflectivity, x-ray reflectivity and aberration-corrected electron microscopy confirm that this interface is both magnetically and structurally abrupt. Finally, using first-principles calculations we show that this experimentally realised interface structure, terminated by Co-Ge bonds, preserves the high spin polarization at the Co2FeSi0.5Al0.5/Ge interface, hence can be used as a model to study spin injection from half-metals into semiconductors.

  9. Realisation of magnetically and atomically abrupt half-metal/semiconductor interface: Co2FeSi0.5Al0.5/Ge(111)

    NASA Astrophysics Data System (ADS)

    Nedelkoski, Zlatko; Kuerbanjiang, Balati; Glover, Stephanie E.; Sanchez, Ana M.; Kepaptsoglou, Demie; Ghasemi, Arsham; Burrows, Christopher W.; Yamada, Shinya; Hamaya, Kohei; Ramasse, Quentin M.; Hasnip, Philip J.; Hase, Thomas; Bell, Gavin R.; Hirohata, Atsufumi; Lazarov, Vlado K.

    2016-11-01

    Halfmetal-semiconductor interfaces are crucial for hybrid spintronic devices. Atomically sharp interfaces with high spin polarisation are required for efficient spin injection. In this work we show that thin film of half-metallic full Heusler alloy Co2FeSi0.5Al0.5 with uniform thickness and B2 ordering can form structurally abrupt interface with Ge(111). Atomic resolution energy dispersive X-ray spectroscopy reveals that there is a small outdiffusion of Ge into specific atomic planes of the Co2FeSi0.5Al0.5 film, limited to a very narrow 1 nm interface region. First-principles calculations show that this selective outdiffusion along the Fe-Si/Al atomic planes does not change the magnetic moment of the film up to the very interface. Polarized neutron reflectivity, x-ray reflectivity and aberration-corrected electron microscopy confirm that this interface is both magnetically and structurally abrupt. Finally, using first-principles calculations we show that this experimentally realised interface structure, terminated by Co-Ge bonds, preserves the high spin polarization at the Co2FeSi0.5Al0.5/Ge interface, hence can be used as a model to study spin injection from half-metals into semiconductors.

  10. Realisation of magnetically and atomically abrupt half-metal/semiconductor interface: Co2FeSi0.5Al0.5/Ge(111)

    PubMed Central

    Nedelkoski, Zlatko; Kuerbanjiang, Balati; Glover, Stephanie E.; Sanchez, Ana M.; Kepaptsoglou, Demie; Ghasemi, Arsham; Burrows, Christopher W.; Yamada, Shinya; Hamaya, Kohei; Ramasse, Quentin M.; Hasnip, Philip J.; Hase, Thomas; Bell, Gavin R.; Hirohata, Atsufumi; Lazarov, Vlado K.

    2016-01-01

    Halfmetal-semiconductor interfaces are crucial for hybrid spintronic devices. Atomically sharp interfaces with high spin polarisation are required for efficient spin injection. In this work we show that thin film of half-metallic full Heusler alloy Co2FeSi0.5Al0.5 with uniform thickness and B2 ordering can form structurally abrupt interface with Ge(111). Atomic resolution energy dispersive X-ray spectroscopy reveals that there is a small outdiffusion of Ge into specific atomic planes of the Co2FeSi0.5Al0.5 film, limited to a very narrow 1 nm interface region. First-principles calculations show that this selective outdiffusion along the Fe-Si/Al atomic planes does not change the magnetic moment of the film up to the very interface. Polarized neutron reflectivity, x-ray reflectivity and aberration-corrected electron microscopy confirm that this interface is both magnetically and structurally abrupt. Finally, using first-principles calculations we show that this experimentally realised interface structure, terminated by Co-Ge bonds, preserves the high spin polarization at the Co2FeSi0.5Al0.5/Ge interface, hence can be used as a model to study spin injection from half-metals into semiconductors. PMID:27869132

  11. ODPEVP: A program for computing eigenvalues and eigenfunctions and their first derivatives with respect to the parameter of the parametric self-adjoined Sturm-Liouville problem

    NASA Astrophysics Data System (ADS)

    Chuluunbaatar, O.; Gusev, A. A.; Vinitsky, S. I.; Abrashkevich, A. G.

    2009-08-01

    A FORTRAN 77 program is presented for calculating with the given accuracy eigenvalues, eigenfunctions and their first derivatives with respect to the parameter of the parametric self-adjoined Sturm-Liouville problem with the parametric third type boundary conditions on the finite interval. The program calculates also potential matrix elements - integrals of the eigenfunctions multiplied by their first derivatives with respect to the parameter. Eigenvalues and matrix elements computed by the ODPEVP program can be used for solving the bound state and multi-channel scattering problems for a system of the coupled second-order ordinary differential equations with the help of the KANTBP programs [O. Chuluunbaatar, A.A. Gusev, A.G. Abrashkevich, A. Amaya-Tapia, M.S. Kaschiev, S.Y. Larsen, S.I. Vinitsky, Comput. Phys. Commun. 177 (2007) 649-675; O. Chuluunbaatar, A.A. Gusev, S.I. Vinitsky, A.G. Abrashkevich, Comput. Phys. Commun. 179 (2008) 685-693]. As a test desk, the program is applied to the calculation of the potential matrix elements for an integrable 2D-model of three identical particles on a line with pair zero-range potentials, a 3D-model of a hydrogen atom in a homogeneous magnetic field and a hydrogen atom on a three-dimensional sphere. Program summaryProgram title: ODPEVP Catalogue identifier: AEDV_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEDV_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: Standard CPC license, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 3001 No. of bytes in distributed program, including test data, etc.: 24 195 Distribution format: tar.gz Programming language: FORTRAN 77 Computer: Intel Xeon EM64T, Alpha 21264A, AMD Athlon MP, Pentium IV Xeon, Opteron 248, Intel Pentium IV Operating system: OC Linux, Unix AIX 5.3, SunOS 5.8, Solaris, Windows XP RAM: depends on the number and order of finite

  12. Mitigating valley-driven localization in atomically thin dopant chains in Si

    NASA Astrophysics Data System (ADS)

    Dusko, Amintor; Saraiva, A. L.; Koiller, Belita

    2016-09-01

    A theoretical study of the localization properties of nanowires of dopants in silicon (Si) fabricated by ionic implantation or scanning tunnel microscope lithography is presented for a model incorporating the currently unavoidable imprecision in individual donor positioning. Experiments have shown that Ohm's law holds in some cases, in apparent defiance to the Anderson localization theory in one dimension. We investigate how valley interference affects the traditional theory of electronic structure of disordered systems. Each isolated donor orbital is realistically described by multivalley effective-mass theory. We extend this model to describe chains of donors as a linear combination of dopant orbitals. Disorder in donor positioning is taken into account, leading to an intricate disorder distribution of hoppings between nearest-neighbor donor sites (donor-donor tunnel coupling)—an effect of valley interference. A decay length, related to the usual localization length, is obtained for phosphorous (P) donor chains from a transfer-matrix approach and is further compared with the chain length. We quantitatively determine the impact of uncertainties δ R in the implantation position relative to a target and also compare our results with those obtained without valley interference. We analyze systematically the aimed interdonor separation dependence (R0) and show that fairly diluted donor chains (R0=7.7 nm) may be as long as 100 nm before the effective onset of Anderson localization, as long as the positioning error is under a lattice parameter (δ R <0.543 nm).

  13. On atomic structure of Ge huts growing on the Ge/Si(001) wetting layer

    SciTech Connect

    Arapkina, Larisa V.; Yuryev, Vladimir A.

    2013-09-14

    Structural models of growing Ge hut clusters—pyramids and wedges—are proposed on the basis of data of recent STM investigations of nucleation and growth of Ge huts on the Si(001) surface in the process of molecular beam epitaxy. It is shown that extension of a hut base along <110> directions goes non-uniformly during the cluster growth regardless of its shape. Growing pyramids, starting from the second monolayer, pass through cyclic formation of slightly asymmetrical and symmetrical clusters, with symmetrical ones appearing after addition of every fourth monolayer. We suppose that pyramids of symmetrical configurations composed by 2, 6, 10, etc., monolayers over the wetting layer are more stable than asymmetrical ones. This might explain less stability of pyramids in comparison with wedges in dense arrays forming at low temperatures of Ge deposition. Possible nucleation processes of pyramids and wedges on wetting layer patches from identical embryos composed by 8 dimers through formation of 1 monolayer high 16-dimer nuclei different only in their symmetry is discussed. Schematics of these processes are presented. It is concluded from precise STM measurements that top layers of wetting layer patches are relaxed when huts nucleate on them.

  14. Multiple doping structures of the rare-earth atoms in β-SiAlON:Ce phosphors and their effects on luminescence properties.

    PubMed

    Gan, Lin; Xu, Fang-Fang; Zeng, Xiong-Hui; Li, Zuo-Sheng; Mao, Zhi-Yong; Lu, Ping; Zhu, Ying-Chun; Liu, Xue-Jian; Zhang, Lin-Lin

    2015-07-14

    The critical doping structures of rare-earth atoms in the promising β-SiAlON phosphors have long been argued owing to the lack of direct evidence. Here, the exact locations and coordination of the Ce rare-earth atoms in the β-SiAlON structure have been examined using an atom-resolved Cs-corrected scanning transmission electron microscope. Three different occupation sites for the Ce atoms have been directly observed: two of them are in the structural channel coordinated with six and nine N(O) atoms, respectively; the other one is the unexpected substitution site for Si(Al). The chemical valences and stabilities of the doping Ce ions at the different occupation sites have been evaluated using density functional calculations. Correlation of the different doping structures with the luminescence properties has been investigated by the aid of cathodoluminescence (CL) microanalysis, which verifies the different contribution of the interstitial trivalent Ce ions to the light emission while no luminescence is observed for the substitutional doping of quadrivalent Ce.

  15. Template-directed atomically precise self-organization of perfectly ordered parallel cerium silicide nanowire arrays on Si(110)-16 × 2 surfaces

    PubMed Central

    2013-01-01

    The perfectly ordered parallel arrays of periodic Ce silicide nanowires can self-organize with atomic precision on single-domain Si(110)-16 × 2 surfaces. The growth evolution of self-ordered parallel Ce silicide nanowire arrays is investigated over a broad range of Ce coverages on single-domain Si(110)-16 × 2 surfaces by scanning tunneling microscopy (STM). Three different types of well-ordered parallel arrays, consisting of uniformly spaced and atomically identical Ce silicide nanowires, are self-organized through the heteroepitaxial growth of Ce silicides on a long-range grating-like 16 × 2 reconstruction at the deposition of various Ce coverages. Each atomically precise Ce silicide nanowire consists of a bundle of chains and rows with different atomic structures. The atomic-resolution dual-polarity STM images reveal that the interchain coupling leads to the formation of the registry-aligned chain bundles within individual Ce silicide nanowire. The nanowire width and the interchain coupling can be adjusted systematically by varying the Ce coverage on a Si(110) surface. This natural template-directed self-organization of perfectly regular parallel nanowire arrays allows for the precise control of the feature size and positions within ±0.2 nm over a large area. Thus, it is a promising route to produce parallel nanowire arrays in a straightforward, low-cost, high-throughput process. PMID:24188092

  16. The effect of atomic structure on interface spin-polarization of half-metallic spin valves: Co{sub 2}MnSi/Ag epitaxial interfaces

    SciTech Connect

    Nedelkoski, Zlatko; Hasnip, Philip J.; Kuerbanjiang, Balati; Higgins, Edward; Lazarov, Vlado K.; Sanchez, Ana M.; Bell, Gavin R.; Oogane, Mikihiko; Hirohata, Atsufumi

    2015-11-23

    Using density functional theory calculations motivated by aberration-corrected electron microscopy, we show how the atomic structure of a fully epitaxial Co{sub 2}MnSi/Ag interfaces controls the local spin-polarization. The calculations show clear difference in spin-polarization at Fermi level between the two main types: bulk-like terminated Co/Ag and Mn-Si/Ag interfaces. Co/Ag interface spin-polarization switches sign from positive to negative, while in the case of Mn-Si/Ag, it is still positive but reduced. Cross-sectional atomic structure analysis of Co{sub 2}MnSi/Ag interface, part of a spin-valve device, shows that the interface is determined by an additional layer of either Co or Mn. The presence of an additional Mn layer induces weak inverse spin-polarisation (−7%), while additional Co layer makes the interface region strongly inversely spin-polarized (−73%). In addition, we show that Ag diffusion from the spacer into the Co{sub 2}MnSi electrode does not have a significant effect on the overall Co{sub 2}MnSi /Ag performance.

  17. Fluorocarbon assisted atomic layer etching of SiO{sub 2} using cyclic Ar/C{sub 4}F{sub 8} plasma

    SciTech Connect

    Metzler, Dominik; Oehrlein, Gottlieb S.; Bruce, Robert L.; Engelmann, Sebastian; Joseph, Eric A.

    2014-03-15

    The authors demonstrate atomic layer etching of SiO{sub 2} using a steady-state Ar plasma, periodic injection of a defined number of C{sub 4}F{sub 8} molecules, and synchronized plasma-based Ar{sup +} ion bombardment. C{sub 4}F{sub 8} injection enables control of the deposited fluorocarbon (FC) layer thickness in the one to several Ångstrom range and chemical modification of the SiO{sub 2} surface. For low energy Ar{sup +} ion bombardment conditions, the physical sputter rate of SiO{sub 2} vanishes, whereas SiO{sub 2} can be etched when FC reactants are present at the surface. The authors have measured for the first time the temporal variation of the chemically enhanced etch rate of SiO{sub 2} for Ar{sup +} ion energies below 30 eV as a function of fluorocarbon surface coverage. This approach enables controlled removal of Ångstrom-thick SiO{sub 2} layers. Our results demonstrate that development of atomic layer etching processes even for complex materials is feasible.

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

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

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

  19. Optimal Ge/SiGe nanofin geometries for hole mobility enhancement: Technology limit from atomic simulations

    SciTech Connect

    Vedula, Ravi Pramod; Mehrotra, Saumitra; Kubis, Tillmann; Povolotskyi, Michael; Klimeck, Gerhard; Strachan, Alejandro

    2015-05-07

    We use first principles simulations to engineer Ge nanofins for maximum hole mobility by controlling strain tri-axially through nano-patterning. Large-scale molecular dynamics predict fully relaxed, atomic structures for experimentally achievable nanofins, and orthogonal tight binding is used to obtain the corresponding electronic structure. Hole transport properties are then obtained via a linearized Boltzmann formalism. This approach explicitly accounts for free surfaces and associated strain relaxation as well as strain gradients which are critical for quantitative predictions in nanoscale structures. We show that the transverse strain relaxation resulting from the reduction in the aspect ratio of the fins leads to a significant enhancement in phonon limited hole mobility (7× over unstrained, bulk Ge, and 3.5× over biaxially strained Ge). Maximum enhancement is achieved by reducing the width to be approximately 1.5 times the height and further reduction in width does not result in additional gains. These results indicate significant room for improvement over current-generation Ge nanofins, provide geometrical guidelines to design optimized geometries and insight into the physics behind the significant mobility enhancement.

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

    SciTech Connect

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

    2015-12-15

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

  1. Effect of passivation layer grown by atomic layer deposition and sputtering processes on Si quantum dot superlattice to generate high photocurrent for high-efficiency solar cells

    NASA Astrophysics Data System (ADS)

    Maksudur Rahman, Mohammad; Higo, Akio; Sekhar, Halubai; Erman Syazwan, Mohd; Hoshi, Yusuke; Usami, Noritaka; Samukawa, Seiji

    2016-03-01

    The effect of passivation films on a Si quantum dot superlattice (QDSL) was investigated to generate high photocurrent in solar-cell applications. Three types of passivation films, sputter-grown amorphous silicon carbide (a-SiC), hydrogenated a-SiC (a-SiC:H), and atomic-layer-deposited aluminum oxide (ALD-Al2O3), were used to passivate the Si QDSLs containing a stack of four 4 nm Si nanodisks (NDs) and 2 nm silicon carbide (SiC) films fabricated by neutral beam etching (NBE). Because of the high surface-to-volume ratio typically present in quantum Si-NDs formed in the top-down NBE process, there is a tendency to form larger surface dangling bonds on untreated Si-ND surfaces as well as to have short distance (<10 nm) between high-aspect-ratio nanopillars of stacked 4 nm Si-NDs/2 nm SiC films, which conventionally sputter SiC films cannot uniformly cover. Therefore, we optimized the passivation techniques with an ALD-Al2O3 film. Scanning electron microscopy (SEM) analysis helped to explain the surface morphology before and after the passivation of the QDSLs. After the completion of the passivation process, the quality of the top surface films of the QDSLs was analyzed from the surface roughness by atomic force microscopy (AFM) analysis, which revealed that ALD-Al2O3 passivated films had the smallest roughness (RMS) of 1.09 nm with respect to sputter-grown a-SiC (RMS: 1.75 nm) and a-SiC:H (RMS: 1.54 nm) films. Conductive atomic force microscopy (CAFM) revealed that ALD-Al2O3 passivation decreased the surface-leakage current as a result of proper passivation of side-wall surface defects in the QDSLs. The carrier transport characteristics were extracted from the QDSLs using the photovoltaic (PV) properties of p++/i/n+ solar cells, where the QDSLs consisted of different passivation layers acting as intermediate layers (i-layers) between the high-doping-density p++ Si (1 × 1020 cm-3) and n+ Si (1 × 1019 cm-3) substrates. High-doping-density p++ Si acted as a hole

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

    PubMed

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

    2016-07-21

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

  3. Atomic layer deposition of Al2O3 on H-passivated Si: Al(CH3)2OH surface reactions with H/Si(100)-2×1

    NASA Astrophysics Data System (ADS)

    Halls, Mathew D.; Raghavachari, Krishnan; Frank, Martin M.; Chabal, Yves J.

    2003-10-01

    Infrared absorption studies of Al(CH3)3 interacting with H-terminated Si reveal that O incorporation from gas-phase impurities may be a crucial factor in interface formation in atomic layer deposition. Hybrid density-functional calculations have therefore been carried out on silicon cluster models to investigate the possible pathways for reaction between the important atomic layer deposition side-reaction product Al(CH3)2OH (DMAOH) and the H/Si(100)-2×1 surface. Comparisons with the analogous surface reactions for Al(CH3)3 and H2O are made. In general, the DMAOH surface reaction pathways are characterized by an activation of reactions involving the OH groups and suppression of CH3 group reactions, compared to Al(CH3)3 and H2O. A unique reaction pathway for DMAOH and the H/Si(100)-2×1 surface is identified resulting in the deposition of -O-Al(CH3)2 on the surface, which is significant since it represents an atomic-layer interface between Si and Al2O3. This reaction has an energy barrier of 1.3 eV and is the most thermodynamically favored pathway with an exothermicity of 0.9 eV.

  4. Characterization of electrical properties in axial Si-Ge nanowire heterojunctions using off-axis electron holography and atom-probe tomography

    SciTech Connect

    Gan, Zhaofeng; Perea, Daniel E.; Yoo, Jinkyoung; He, Yang; Colby, Robert J.; Barker, Josh E.; Gu, Meng; Mao, Scott X.; Wang, Chongmin; Picraux, S. T.; Smith, David J.; McCartney, Martha R.

    2016-09-13

    Doped Si-Ge nanowire (NW) heterojunctions were grown using the vapor-liquid-solid method with AuGa and Au catalyst particles. Transmission electron microscopy and off-axis electron holography (EH) were used to characterize the nanostructure and to measure the electrostatic potential profile across the junction resulting from electrically active dopants, while atom-probe tomography (APT) was used to determine the Si, Ge and total (active and inactive) dopant concentration profiles. A comparison of the measured potential profile with simulations indicated that Ga dopants unintentionally introduced during AuGa catalyst growth were electronically inactive despite APT results that showed considerable amounts of Ga in the Si region. 10% P in Ge and 100% B in Si were estimated to be activated, which was corroborated by in situ electron-holography biasing experiments. This combination of EH, APT, in situ biasing and simulations allows a better knowledge and understanding of the electrically active dopant distributions in NWs.

  5. Specific features of the atomic structure of metallic layers of multilayered (CoFeZr/SiO2)32 and (CoFeZr/ a-Si)40 nanostructures with different interlayers

    NASA Astrophysics Data System (ADS)

    Domashevskaya, E. P.; Guda, A. A.; Chernyshev, A. V.; Sitnikov, V. G.

    2017-02-01

    Multilayered nanostructures (MN) were prepared by ion-beam successive sputtering from two targets, one of which was a metallic Co45Fe45Zr10 alloy plate and another target was a quartz (SiO2) or silicon plate on the surface of a rotating glass-ceramic substrate in an argon atmosphere. The Co and Fe K edges X-ray absorption fine structure of XANES in the (CoFeZr/SiO2)32 sample with oxide interlayers was similar to XANES of metallic Fe foil. This indicated the existence in metallic layers of multilayered CoFeZr nanocrystals with a local environment similar to the atomic environment in solid solutions on the base of bcc Fe structure, which is also confirmed by XRD data. XANES near the Co and Fe K edges absorption in another multilayered nanostructure with silicon interlayers (CoFeZr/ a-Si)40 differs from XANES of MN with dielectric SiO2 interlayer, which demonstrates a dominant influence of the Fe-Si and Co-Si bonds in the local environment of 3 d Co and Fe metals when they form CoFeSi-type silicide phases in thinner bilayers of this MN.

  6. Low viscosity and high attenuation in MgSiO3 post-perovskite inferred from atomic-scale calculations

    PubMed Central

    Goryaeva, Alexandra M.; Carrez, Philippe; Cordier, Patrick

    2016-01-01

    This work represents a numerical study of the thermal activation for dislocation glide of the [100](010) slip system in MgSiO3 post-perovskite (Mg-ppv) at 120 GPa. We propose an approach based on a one-dimensional line tension model in conjunction with atomic-scale calculations. In this model, the key parameters, namely, the line tension and the Peierls barrier, are obtained from density functional theory calculations. We find a Peierls stress σp = 2.1 GPa and a line tension Γ = 9.2 eV/Å, which lead to a kink-pair enthalpy (under zero stress) of 2.69 eV. These values confirm that this slip system bears a very low lattice friction because it vanishes for temperatures above approximately 500 K under mantle conditions. In the Earth’s mantle, high-pressure Mg-ppv silicate is thus expected to become as ductile as ferropericlase. These results confirm the hypothesis of a weak layer in the D″ layer where Mg-ppv is present. Easy glide along [100](010) suggests strong preferred orientations with (010) planes aligned. Highly mobile [100] dislocations are also likely to respond to stresses related to seismic waves, leading to energy dissipation and strong attenuation. PMID:27708386

  7. Excellent c-Si surface passivation by thermal atomic layer deposited aluminum oxide after industrial firing activation

    NASA Astrophysics Data System (ADS)

    Liao, B.; Stangl, R.; Ma, F.; Mueller, T.; Lin, F.; Aberle, A. G.; Bhatia, C. S.; Hoex, B.

    2013-09-01

    We demonstrate that by using a water (H2O)-based thermal atomic layer deposited (ALD) aluminum oxide (Al2O3) film, excellent surface passivation can be attained on planar low-resistivity silicon wafers. Effective carrier lifetime values of up to 12 ms and surface recombination velocities as low as 0.33 cm s-1 are achieved on float-zone wafers after a post-deposition thermal activation of the Al2O3 passivation layer. This post-deposition activation is achieved using an industrial high-temperature firing process which is commonly used for contact formation of standard screen-printed silicon solar cells. Neither a low-temperature post-deposition anneal nor a silicon nitride capping layer is required in this case. Deposition temperatures in the 100-400 °C range and peak firing temperatures of about 800 °C (set temperature) are investigated. Photoluminescence imaging shows that the surface passivation is laterally uniform. Corona charging and capacitance-voltage measurements reveal that the negative fixed charge density near the AlOx/c-Si interface increases from 1.4 × 1012 to 3.3 × 1012 cm-2 due to firing, while the midgap interface defect density reduces from 3.3 × 1011 to 0.8 × 1011 cm-2 eV-1. This work demonstrates that direct firing activation of thermal ALD Al2O3 is feasible, which could be beneficial for solar cell manufacturing.

  8. Low viscosity and high attenuation in MgSiO3 post-perovskite inferred from atomic-scale calculations.

    PubMed

    Goryaeva, Alexandra M; Carrez, Philippe; Cordier, Patrick

    2016-10-06

    This work represents a numerical study of the thermal activation for dislocation glide of the [100](010) slip system in MgSiO3 post-perovskite (Mg-ppv) at 120 GPa. We propose an approach based on a one-dimensional line tension model in conjunction with atomic-scale calculations. In this model, the key parameters, namely, the line tension and the Peierls barrier, are obtained from density functional theory calculations. We find a Peierls stress σp = 2.1 GPa and a line tension Γ = 9.2 eV/Å, which lead to a kink-pair enthalpy (under zero stress) of 2.69 eV. These values confirm that this slip system bears a very low lattice friction because it vanishes for temperatures above approximately 500 K under mantle conditions. In the Earth's mantle, high-pressure Mg-ppv silicate is thus expected to become as ductile as ferropericlase. These results confirm the hypothesis of a weak layer in the D″ layer where Mg-ppv is present. Easy glide along [100](010) suggests strong preferred orientations with (010) planes aligned. Highly mobile [100] dislocations are also likely to respond to stresses related to seismic waves, leading to energy dissipation and strong attenuation.

  9. Low viscosity and high attenuation in MgSiO3 post-perovskite inferred from atomic-scale calculations

    NASA Astrophysics Data System (ADS)

    Goryaeva, Alexandra M.; Carrez, Philippe; Cordier, Patrick

    2016-10-01

    This work represents a numerical study of the thermal activation for dislocation glide of the [100](010) slip system in MgSiO3 post-perovskite (Mg-ppv) at 120 GPa. We propose an approach based on a one-dimensional line tension model in conjunction with atomic-scale calculations. In this model, the key parameters, namely, the line tension and the Peierls barrier, are obtained from density functional theory calculations. We find a Peierls stress σp = 2.1 GPa and a line tension Γ = 9.2 eV/Å, which lead to a kink-pair enthalpy (under zero stress) of 2.69 eV. These values confirm that this slip system bears a very low lattice friction because it vanishes for temperatures above approximately 500 K under mantle conditions. In the Earth’s mantle, high-pressure Mg-ppv silicate is thus expected to become as ductile as ferropericlase. These results confirm the hypothesis of a weak layer in the D″ layer where Mg-ppv is present. Easy glide along [100](010) suggests strong preferred orientations with (010) planes aligned. Highly mobile [100] dislocations are also likely to respond to stresses related to seismic waves, leading to energy dissipation and strong attenuation.

  10. AERIAL SHOWING COMPLETED REMOTE ANALYTICAL FACILITY (CPP627) ADJOINING FUEL PROCESSING ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    AERIAL SHOWING COMPLETED REMOTE ANALYTICAL FACILITY (CPP-627) ADJOINING FUEL PROCESSING BUILDING AND EXCAVATION FOR HOT PILOT PLANT TO RIGHT (CPP-640). INL PHOTO NUMBER NRTS-60-1221. J. Anderson, Photographer, 3/22/1960 - Idaho National Engineering Laboratory, Idaho Chemical Processing Plant, Fuel Reprocessing Complex, Scoville, Butte County, ID

  11. Adjoined Piecewise Linear Approximations (APLAs) for Equating: Accuracy Evaluations of a Postsmoothing Equating Method

    ERIC Educational Resources Information Center

    Moses, Tim

    2013-01-01

    The purpose of this study was to evaluate the use of adjoined and piecewise linear approximations (APLAs) of raw equipercentile equating functions as a postsmoothing equating method. APLAs are less familiar than other postsmoothing equating methods (i.e., cubic splines), but their use has been described in historical equating practices of…

  12. TESTING OF INDOOR RADON REDUCTION TECHNIQUES IN BASEMENT HOUSES HAVING ADJOINING WINGS

    EPA Science Inventory

    The report gives results of tests of indoor radon reduction techniques in 12 existing Maryland houses, with the objective of determining when basement houses with adjoining wings require active soil depressurization (ASD) treatment of both wings, and when treatment of the basemen...

  13. Two Recent Developments in Tree Adjoining Grammars: Semantics and Efficient Processing

    DTIC Science & Technology

    1990-01-01

    Two Recent Developments in Tree Adjoining Grammars: Semantics and Efficient Processing Yves Schabes Aravind K. Joshi Department of Computer and...interpretation or automatic translation of natural lan- guage. A variant of TAGs, called synchronous TAGs, has been developed (Shieber and Schabes ...lexicalized TAGs with adjunction and substitution ( Schabes , Abeill6 and Joshi [1988]). Other bases (as Multiple Component TAGs) are needed for more

  14. Observation of electronic states on Si(111)-(7 x 7) through short-range attractive force with noncontact atomic force spectroscopy.

    PubMed

    Arai, T; Tomitori, M

    2004-12-17

    We experimentally reveal that the short-range attractive force between a Si tip and a Si(111)-(7 x 7) surface is enhanced at specified bias voltages; we conduct force spectroscopy based on noncontact atomic force microscopy with changing bias voltage at a fixed separation. The spectra exhibit prominent peaks and a broad peak, which are attributed to quantum mechanical resonance as the energy levels of sample surface states are tuned to those of the tip states by shifting the Fermi level through changing bias voltage, and to the resonating states over a lowered tunneling barrier, respectively.

  15. The effect of cyclic martensitic transformations on diffusion of cobalt atoms in Fe-18wt.%Mn-2wt.%Si alloy.

    PubMed

    Danilchenko, Vitaliy E; Mazanko, Vladimir F; Filatov, Alexander V; Iakovlev, Viktor E

    2015-01-01

    Diffusion characteristics of cobalt atoms were investigated using radioactive isotope method in phase-hardened Fe-18wt.%Mn-2wt.%Si alloy. The observed significant increase of diffusion coefficient of cobalt atoms under the cyclic γ-ε-γ martensitic transformations was due to the action of two independent mechanisms - an athermal one and a thermally activated one. The first one arose from the direct γ-ε and the reverse ε-γ transformations with corresponding direct and reverse lattice shears during alternating stresses and simultaneous lattice restructuring. Another mechanism arose under the diffusion annealing of the phase-hardened alloy.

  16. The effect of cyclic martensitic transformations on diffusion of cobalt atoms in Fe-18wt.%Mn-2wt.%Si alloy

    NASA Astrophysics Data System (ADS)

    Danilchenko, Vitaliy E.; Mazanko, Vladimir F.; Filatov, Alexander V.; Iakovlev, Viktor E.

    2015-04-01

    Diffusion characteristics of cobalt atoms were investigated using radioactive isotope method in phase-hardened Fe-18wt.%Mn-2wt.%Si alloy. The observed significant increase of diffusion coefficient of cobalt atoms under the cyclic γ-ɛ-γ martensitic transformations was due to the action of two independent mechanisms - an athermal one and a thermally activated one. The first one arose from the direct γ-ɛ and the reverse ɛ-γ transformations with corresponding direct and reverse lattice shears during alternating stresses and simultaneous lattice restructuring. Another mechanism arose under the diffusion annealing of the phase-hardened alloy.

  17. Synergic effect of atomic oxygen and outgassing phenomena on Carbon/SiC composites for space applications

    NASA Astrophysics Data System (ADS)

    Albano, Marta

    so that sublimation and ablation easily can take place. The key role played by carbon composites in re-entry environment is due to their high stability at high temperature, preserving their mechanical properties. However, most of these applications involve extended time periods in oxidizing environments where carbon reacts rapidly with oxygen at temperatures as low as 770K and the composites are subjected to oxidation degradation. For these reasons coated C/C and C/SiC composites are the most promising materials for the exposed surface of a thermal protection system. The modern approaches to a design of such materials assume broad application of mathematical and physical simulation methods. But mathematical simulation is impossible if there is no true information available on the characteristics (properties) of objects analyzed. In the majority of cases in practice the direct measurement of materials thermo physical properties, especially of complex composition, is impossible. There is only one way which permits to overcome these complexities - the indirect measurement. Mathematically, such an approach is usually formulated as a solution of the inverse problem: through direct measurements of system's state (temperature, component concentration, etc.) define the properties of a system analyzed, for example, the materials thermophysical characteristics. Violation of cause-and-effect relations in the statement of these problems results in their correctness in mathematical sense (i.e., the absence of existence and/or uniqueness and/or stability of the solution). Hence to solve such problems special methods are developed usually called regularized. In order to guarantee the success of a space structure there is the necessity to study the synergic effects of all the challenges that the harsh space environment place to the structure. For this reason here is presented a joint experimental study on synergic effects on C/SiC composites. Outgassing and atomic oxygen corrosion

  18. Formation of atomically ordered and chemically selective Si-O-Ti monolayer on Si0.5Ge0.5(110) for a MIS structure via H2O2(g) functionalization.

    PubMed

    Park, Sang Wook; Choi, Jong Youn; Siddiqui, Shariq; Sahu, Bhagawan; Galatage, Rohit; Yoshida, Naomi; Kachian, Jessica; Kummel, Andrew C

    2017-02-07

    Si0.5Ge0.5(110) surfaces were passivated and functionalized using atomic H, hydrogen peroxide (H2O2), and either tetrakis(dimethylamino)titanium (TDMAT) or titanium tetrachloride (TiCl4) and studied in situ with multiple spectroscopic techniques. To passivate the dangling bonds, atomic H and H2O2(g) were utilized and scanning tunneling spectroscopy (STS) demonstrated unpinning of the surface Fermi level. The H2O2(g) could also be used to functionalize the surface for metal atomic layer deposition. After subsequent TDMAT or TiCl4 dosing followed by a post-deposition annealing, scanning tunneling microscopy demonstrated that a thermally stable and well-ordered monolayer of TiOx was deposited on Si0.5Ge0.5(110), and X-ray photoelectron spectroscopy verified that the interfaces only contained Si-O-Ti bonds and a complete absence of GeOx. STS measurements confirmed a TiOx monolayer without mid-gap and conduction band edge states, which should be an ideal ultrathin insulating layer in a metal-insulator-semiconductor structure. Regardless of the Ti precursors, the final Ti density and electronic structure were identical since the Ti bonding is limited by the high coordination of Ti to O.

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

    NASA Astrophysics Data System (ADS)

    Shi, Yu; Sun, Qing-Qing; Dong, Lin; Liu, Han; Ding, Shi-Jin; Zhang, Wei

    2009-05-01

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

  20. Characterizing fluorocarbon assisted atomic layer etching of Si using cyclic Ar/C4F8 and Ar/CHF3 plasma.

    PubMed

    Metzler, Dominik; Li, Chen; Engelmann, Sebastian; Bruce, Robert L; Joseph, Eric A; Oehrlein, Gottlieb S

    2017-02-07

    With the increasing interest in establishing directional etching methods capable of atomic scale resolution for fabricating highly scaled electronic devices, the need for development and characterization of atomic layer etching processes, or generally etch processes with atomic layer precision, is growing. In this work, a flux-controlled cyclic plasma process is used for etching of SiO2 and Si at the Angstrom-level. This is based on steady-state Ar plasma, with periodic, precise injection of a fluorocarbon (FC) precursor (C4F8 and CHF3) and synchronized, plasma-based Ar(+) ion bombardment [D. Metzler et al., J. Vac. Sci. Technol., A 32, 020603 (2014) and D. Metzler et al., J. Vac. Sci. Technol., A 34, 01B101 (2016)]. For low energy Ar(+) ion bombardment conditions, physical sputter rates are minimized, whereas material can be etched when FC reactants are present at the surface. This cyclic approach offers a large parameter space for process optimization. Etch depth per cycle, removal rates, and self-limitation of removal, along with material dependence of these aspects, were examined as a function of FC surface coverage, ion energy, and etch step length using in situ real time ellipsometry. The deposited FC thickness per cycle is found to have a strong impact on etch depth per cycle of SiO2 and Si but is limited with regard to control over material etching selectivity. Ion energy over the 20-30 eV range strongly impacts material selectivity. The choice of precursor can have a significant impact on the surface chemistry and chemically enhanced etching. CHF3 has a lower FC deposition yield for both SiO2 and Si and also exhibits a strong substrate dependence of FC deposition yield, in contrast to C4F8. The thickness of deposited FC layers using CHF3 is found to be greater for Si than for SiO2. X-ray photoelectron spectroscopy was used to study surface chemistry. When thicker FC films of 11 Å are employed, strong changes of FC film chemistry during a cycle are seen

  1. Characterizing fluorocarbon assisted atomic layer etching of Si using cyclic Ar/C4F8 and Ar/CHF3 plasma

    NASA Astrophysics Data System (ADS)

    Metzler, Dominik; Li, Chen; Engelmann, Sebastian; Bruce, Robert L.; Joseph, Eric A.; Oehrlein, Gottlieb S.

    2017-02-01

    With the increasing interest in establishing directional etching methods capable of atomic scale resolution for fabricating highly scaled electronic devices, the need for development and characterization of atomic layer etching processes, or generally etch processes with atomic layer precision, is growing. In this work, a flux-controlled cyclic plasma process is used for etching of SiO2 and Si at the Angstrom-level. This is based on steady-state Ar plasma, with periodic, precise injection of a fluorocarbon (FC) precursor (C4F8 and CHF3) and synchronized, plasma-based Ar+ ion bombardment [D. Metzler et al., J. Vac. Sci. Technol., A 32, 020603 (2014) and D. Metzler et al., J. Vac. Sci. Technol., A 34, 01B101 (2016)]. For low energy Ar+ ion bombardment conditions, physical sputter rates are minimized, whereas material can be etched when FC reactants are present at the surface. This cyclic approach offers a large parameter space for process optimization. Etch depth per cycle, removal rates, and self-limitation of removal, along with material dependence of these aspects, were examined as a function of FC surface coverage, ion energy, and etch step length using in situ real time ellipsometry. The deposited FC thickness per cycle is found to have a strong impact on etch depth per cycle of SiO2 and Si but is limited with regard to control over material etching selectivity. Ion energy over the 20-30 eV range strongly impacts material selectivity. The choice of precursor can have a significant impact on the surface chemistry and chemically enhanced etching. CHF3 has a lower FC deposition yield for both SiO2 and Si and also exhibits a strong substrate dependence of FC deposition yield, in contrast to C4F8. The thickness of deposited FC layers using CHF3 is found to be greater for Si than for SiO2. X-ray photoelectron spectroscopy was used to study surface chemistry. When thicker FC films of 11 Å are employed, strong changes of FC film chemistry during a cycle are seen

  2. Characterizing Fluorocarbon Assisted Atomic Layer Etching of Si Using Cyclic Ar/C4F8 and Ar/CHF3 Plasma

    DOE PAGES

    Metzler, Dominik; Li, Chen; Engelmann, Sebastian; ...

    2016-09-08

    With the increasing interest in establishing directional etching methods capable of atomic scale resolution for fabricating highly scaled electronic devices, the need for development and characterization of atomic layer etching (ALE) processes, or generally etch processes with atomic layer precision, is growing. In this work, a flux-controlled cyclic plasma process is used for etching of SiO2 and Si at the Angstrom-level. This is based on steady-state Ar plasma, with periodic, precise injection of a fluorocarbon (FC) precursor (C4F8 and CHF3), and synchronized, plasma-based Ar+ ion bombardment [D. Metzler et al., J Vac Sci Technol A 32, 020603 (2014), and D.more » Metzler et al., J Vac Sci Technol A 34, 01B101 (2016)]. For low energy Ar+ ion bombardment conditions, physical sputter rates are minimized, whereas material can be etched when FC reactants are present at the surface. This cyclic approach offers a large parameter space for process optimization. Etch depth per cycle, removal rates, and self-limitation of removal, along with material dependence of these aspects, were examined as a function of FC surface coverage, ion energy, and etch step length using in situ real time ellipsometry. The deposited FC thickness per cycle is found to have a strong impact on etch depth per cycle of SiO2 and Si, but is limited with regard to control over material etching selectivity. Ion energy over the 20 to 30 eV range strongly impacts material selectivity. The choice of precursor can have a significant impact on the surface chemistry and chemically enhanced etching. CHF3 has a lower FC deposition yield for both SiO2 and Si, and also exhibits a strong substrate dependence of FC deposition yield, in contrast to C4F8. The thickness of deposited FC layers using CHF3 is found to be greater for Si than for SiO2. X-ray photoelectron spectroscopy was used to study surface chemistry. When thicker FC films of 11 Å are employed, strong changes of FC film chemistry during a cycle are

  3. Experimental and theoretical investigations of electronic and atomic structure of Si-nanocrystals formed in sapphire by ion implantation

    NASA Astrophysics Data System (ADS)

    Wainstein, D.; Kovalev, A.; Tetelbaum, D.; Mikhailov, A.; Bulutay, C.; Aydinli, A.

    2008-03-01

    The semiconductor nanocomposites based on Si nanocrystals in dielectric matrices attract a great amount of attention due to their ability for luminescence in visible and near-IR part of the electromagnetic spectrum. Si nanocrystals in sapphire matrix were formed by Si+ ion implantation with doses from 5×1016 to 3×1017 cm-2 at an accelerating voltage 100 kV and post-implantation annealing at 500 - 1100 °C for 2 hours. Depth distribution of lattice defects, impurities and Si nanocrystals, the peculiarities of interband electronic transitions were investigated by XPS and HREELS. The molecular orbitals and local electronic structure of the Al2O3 matrix with Si nanocrystals was calculated using an atomistic pseudopotential technique. The electronic structure of Si nanocrystals as determined from HREELS measurements is in good agreement with the theoretically calculated electronic structure for Si nanocrystals.

  4. Thermal Atomic Layer Etching of SiO2 by a "Conversion-Etch" Mechanism Using Sequential Reactions of Trimethylaluminum and Hydrogen Fluoride.

    PubMed

    DuMont, Jaime W; Marquardt, Amy E; Cano, Austin M; George, Steven M

    2017-03-22

    The thermal atomic layer etching (ALE) of SiO2 was performed using sequential reactions of trimethylaluminum (TMA) and hydrogen fluoride (HF) at 300 °C. Ex situ X-ray reflectivity (XRR) measurements revealed that the etch rate during SiO2 ALE was dependent on reactant pressure. SiO2 etch rates of 0.027, 0.15, 0.20, and 0.31 Å/cycle were observed at static reactant pressures of 0.1, 0.5, 1.0, and 4.0 Torr, respectively. Ex situ spectroscopic ellipsometry (SE) measurements were in agreement with these etch rates versus reactant pressure. In situ Fourier transform infrared (FTIR) spectroscopy investigations also observed SiO2 etching that was dependent on the static reactant pressures. The FTIR studies showed that the TMA and HF reactions displayed self-limiting behavior at the various reactant pressures. In addition, the FTIR spectra revealed that an Al2O3/aluminosilicate intermediate was present after the TMA exposures. The Al2O3/aluminosilicate intermediate is consistent with a "conversion-etch" mechanism where SiO2 is converted by TMA to Al2O3, aluminosilicates, and reduced silicon species following a family of reactions represented by 3SiO2 + 4Al(CH3)3 → 2Al2O3 + 3Si(CH3)4. Ex situ X-ray photoelectron spectroscopy (XPS) studies confirmed the reduction of silicon species after TMA exposures. Following the conversion reactions, HF can fluorinate the Al2O3 and aluminosilicates to species such as AlF3 and SiOxFy. Subsequently, TMA can remove the AlF3 and SiOxFy species by ligand-exchange transmetalation reactions and then convert additional SiO2 to Al2O3. The pressure-dependent conversion reaction of SiO2 to Al2O3 and aluminosilicates by TMA is critical for thermal SiO2 ALE. The "conversion-etch" mechanism may also provide pathways for additional materials to be etched using thermal ALE.

  5. High-pressure synthesis and structural characterization of the type II clathrate compound Na(30.5)Si(136) encapsulating two sodium atoms in the same silicon polyhedral cages.

    PubMed

    Yamanaka, Shoji; Komatsu, Masaya; Tanaka, Masashi; Sawa, Hiroshi; Inumaru, Kei

    2014-05-28

    Single crystals of sodium containing silicon clathrate compounds Na8Si46 (type I) and NaxSi136 (type II) were prepared from the mixtures of NaSi and Si under high-pressure and high-temperature conditions of 5 GPa at 600-1000 °C. The type II crystals were obtained at relatively low-temperature conditions of 700-800 °C, which were found to have a Na excess composition Na30.5Si136 in comparison with the compounds NaxSi136 (x ≤ 24) obtained by a thermal decomposition of NaSi under vacuum. The single crystal study revealed that the Na excess type II compound crystallizes in space group Fd3̅m with a lattice parameter of a = 14.796(1) Å, slightly larger than that of the ambient phase (Na24Si136), and the large silicon hexakaidecahedral cages (@Si28) are occupied by two sodium atoms disordered in the two 32e sites around the center of the @Si28 cages. At temperatures <90 K, the crystal symmetry of the compound changes from the face-centered to the primitive cell with space group P213, and the Na atoms in the @Si28 cages are aligned as Na2 pairs. The temperature dependence of the magnetic susceptibility of Na30.5Si136 suggests that the two Na ions (2 Na(+)) in the cage are changed to a Na2 molecule. The Na atoms of Na30.5Si136 can be deintercalated from the cages topochemically by evacuation at elevated temperatures. The single crystal study of the deintercalated phases NaxSi136 (x = 25.5 and 5.5) revealed that only excess Na atoms have disordered arrangements.

  6. High efficiency n-Si/ p-Cu2O core-shell nanowires photodiode prepared by atomic layer deposition of Cu2O on well-ordered Si nanowires array

    NASA Astrophysics Data System (ADS)

    Kim, Hangil; Kim, Soo-Hyun; Ko, Kyung Yong; Kim, Hyungjun; Kim, Jaehoon; Oh, Jihun; Lee, Han-Bo-Ram

    2016-05-01

    A highly efficient n-Si/ p-Cu2O core-shell (C-S) nanowire (NW) photodiode was fabricated using Cu2O grown by atomic layer deposition (ALD) on a well-ordered Si NW array. Ordered Si nanowires arrays were fabricated by nano-sphere lithography to pattern metal catalysts for the metal-assisted etching of silicon, resulting in a Si NW arrays with a good arrangement, smooth surface and small diameter distribution. The ALD-Cu2O thin films were grown using a new non-fluorinated Cu precursor, bis(1-dimethylamino-2-methyl-2-butoxy)copper (C14H32N2O2Cu), and water vapor (H2O) at 140°C. Transmission electron microscopy equipped with an energy dispersive spectrometer confirmed that p-Cu2O thin films had been coated over arrayed Si NWs with a diameter of 150 nm (aspect ratio of ˜7.6). The C-S NW photodiode exhibited more sensitive photodetection performance under ultraviolet illumination as well as an enhanced photocurrent density in the forward biasing region than the planar structure diode. The superior performance of C-S NWs photodiode was explained by the lower reflectance of light and the effective carrier separation and collection originating from the C-S NWs structure. [Figure not available: see fulltext.

  7. Composition, atomic transport, and chemical stability of ZrAlxOy ultrathin films deposited on Si(001)

    NASA Astrophysics Data System (ADS)

    Morais, J.; da Rosa, E. B. O.; Pezzi, R. P.; Miotti, L.; Baumvol, I. J. R.

    2001-09-01

    The stability of a ZrAlxOy film sputtered on Si upon thermal annealing in vacuum or in O2 was investigated. X-ray diffraction indicated that the as-deposited film was amorphous and remained so after annealing. Rutherford backscattering, narrow nuclear resonance profiling, and low-energy ion scattering provided the average composition of the film and the depth distributions of different elements. Chemical analysis of these elements was accessed by x-ray photoelectron spectroscopy. Annealing in vacuum produced thickness inhomogeneities and/or transport of very small amounts of Si from the substrate into the overlying film, with formation of Si precipitates. Annealing in O2 led to oxygen exchange throughout the film, as well as Si transport in slightly higher amounts than in vacuum. Differently from the observed upon annealing in vacuum, Si was either incorporated into the Zr,Al-O framework or oxidized in SiO2.

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

    NASA Astrophysics Data System (ADS)

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

    2014-06-01

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

  9. Core-shell Si@TiO2 nanosphere anode by atomic layer deposition for Li-ion batteries

    SciTech Connect

    Dai, Sheng

    2016-01-28

    Silicon (Si) is regarded as next-generation anode for high-energy lithium-ion batteries (LIBs) due to its high Li storage capacity (4200 mA h g-1). However, the mechanical degradation and resultant capacity fade critically hinder its practical application. In this regard, we demonstrate that nanocoating of Si spheres with a 3 nm titanium dioxide (TiO2) layer via atomic layer deposition (ALD) can utmostly balance the high conductivity and the good structural stability to improve the cycling stability of Si core material. The resultant sample, Si@TiO2-3 nm core–shell nanospheres, exhibits the best electrochemical performance of all with a highest initial Coulombic efficiency and specific charge capacity retention after 50 cycles at 0.1C (82.39% and 1580.3 mA h g-1). In addition to making full advantage of the ALD technique, we believe that our strategy and comprehension in coating the electrode and the active material could provide a useful pathway towards enhancing Si anode material itself and community of LIBs.

  10. Three-dimensional analysis of Eu dopant atoms in Ca-α-SiAlON via through-focus HAADF-STEM imaging.

    PubMed

    Saito, Genki; Yamaki, Fuuta; Kunisada, Yuji; Sakaguchi, Norihito; Akiyama, Tomohiro

    2017-01-31

    Three-dimensional (3D) distributional analysis of individual dopant atoms in materials is important to development of optical, electronic, and magnetic materials. In this study, we adopted through-focus high-angle annular dark-field (HAADF) imaging for 3D distributional analysis of Eu dopant atoms in Ca-α-SiAlON phosphors. In this context, the effects of convergence semi-angle and Eu z-position on the HAADF image contrast were investigated. Multi-slice image simulation revealed that the contrast of the dopant site was sensitive to change of the defocus level. When the defocus level matched the depth position of a Eu atom, the contrast intensity was significantly increased. The large convergence semi-angle greatly increased the depth resolution because the electron beam tends spread instead of channeling along the atomic columns. Through-focus HAADF-STEM imaging was used to analyze the Eu atom distribution surrounding 10nm cubes with defocus steps of 0.68nm each. The contrast depth profile recorded with a narrow step width clearly analyzed the possible depth positions of Eu atoms. The radial distribution function obtained for the Eu dopants was analyzed using an atomic distribution model that was based on the assumption of random distribution. The result suggested that the Ca concentration did not affect the Eu distribution. The decreased fraction of neighboring Eu atoms along z-direction might be caused by the enhanced short-range Coulomb-like repulsive forces along the z-direction.

  11. Effect of the tip state during qPlus noncontact atomic force microscopy of Si(100) at 5 K: Probing the probe

    PubMed Central

    Jarvis, Sam; Danza, Rosanna; Moriarty, Philip

    2012-01-01

    Summary Background: Noncontact atomic force microscopy (NC-AFM) now regularly produces atomic-resolution images on a wide range of surfaces, and has demonstrated the capability for atomic manipulation solely using chemical forces. Nonetheless, the role of the tip apex in both imaging and manipulation remains poorly understood and is an active area of research both experimentally and theoretically. Recent work employing specially functionalised tips has provided additional impetus to elucidating the role of the tip apex in the observed contrast. Results: We present an analysis of the influence of the tip apex during imaging of the Si(100) substrate in ultra-high vacuum (UHV) at 5 K using a qPlus sensor for noncontact atomic force microscopy (NC-AFM). Data demonstrating stable imaging with a range of tip apexes, each with a characteristic imaging signature, have been acquired. By imaging at close to zero applied bias we eliminate the influence of tunnel current on the force between tip and surface, and also the tunnel-current-induced excitation of silicon dimers, which is a key issue in scanning probe studies of Si(100). Conclusion: A wide range of novel imaging mechanisms are demonstrated on the Si(100) surface, which can only be explained by variations in the precise structural configuration at the apex of the tip. Such images provide a valuable resource for theoreticians working on the development of realistic tip structures for NC-AFM simulations. Force spectroscopy measurements show that the tip termination critically affects both the short-range force and dissipated energy. PMID:22428093

  12. Studies of Diffusion, Atomic Hopping Frequency and Site Residence Times in Molten SiO2 by Molecular Dynamics

    NASA Astrophysics Data System (ADS)

    Gemmell, A. L.; Fraser, D. G.; Refson, K.

    2004-12-01

    , as well as radial distribution function (rdf) and density data provides a picture of the structure and dynamics of SiO2 over a range of conditions. We have developed a method for analysing residence times and 'hop' distances under varying conditions. The plots found at the URL accompanying this abstract compare diffusion of an oxygen atom at 3000K and 4000K over a 106 step (1ns) run. Peaks represent 'hopping', troughs residence in 'sites'. At temperatures of 4000K and above the concept of a discreet 'rattle and hop' diffusion mechanism breaks down to be replaced with a plasma-style situation of more continuous random movement. (1) Fraser DG, Cagin T, Demiralp E, Goddard WA, III, "New transferable interatomic potentials for simulating melting of Mg silicates near the base of mantle," A.G.U. 1998. (2) Van Beest BWH, Kramer GJ, Van Santen RA (1990) Force fields for silicas and aluminophosphates based on ab-initio calculations. Phys Rev Lett 64: 1995. (3) Gemmell AL, Refson K, Fraser DG. Molecular Dynamics Simulations of Diffusion in a Silica Melt. EOS Trans AGU 84(46), Fall Meet. Suppl., Abstract V11D-0528, 2003.

  13. Spectral aspects of the determination of Si in organic and aqueous solutions using high-resolution continuum source or line source flame atomic absorption spectrometry

    NASA Astrophysics Data System (ADS)

    Kowalewska, Zofia; Pilarczyk, Janusz; Gościniak, Łukasz

    2016-06-01

    High-resolution continuum source flame atomic absorption spectrometry (HR-CS FAAS) was applied to reveal and investigate spectral interference in the determination of Si. An intensive structured background was observed in the analysis of both aqueous and xylene solutions containing S compounds. This background was attributed to absorption by the CS molecule formed in the N2O-C2H2 flame. The lines of the CS spectrum at least partially overlap all five of the most sensitive Si lines investigated. The 251.611 nm Si line was demonstrated to be the most advantageous. The intensity of the structured background caused by the CS molecule significantly depends on the chemical form of S in the solution and is the highest for the most-volatile CS2. The presence of O atoms in an initial S molecule can diminish the formation of CS. To overcome this S effect, various modes of baseline fitting and background correction were evaluated, including iterative background correction (IBC) and utilization of correction pixels (WRC). These modes were used either independently or in conjunction with least squares background correction (LSBC). The IBC + LSBC mode can correct the extremely strong interference caused by CS2 at an S concentration of 5% w:w in the investigated solution. However, the efficiency of this mode depends on the similarity of the processed spectra and the correction spectra in terms of intensity and in additional effects, such as a sloping baseline. In the vicinity of the Si line, three lines of V were recorded. These lines are well-separated in the HR-CS FAAS spectrum, but they could be a potential source of overcorrection when using line source flame atomic absorption spectrometry (LS FAAS). The expected signal for the 251.625 nm Fe line was not registered at 200 mg L- 1 Fe concentration in the solution, probably due to the diminished population of Fe atoms in the high-temperature flame used. The observations made using HR-CS FAAS helped to establish a "safe" level

  14. Influence of annealing in H atmosphere on the electrical properties of Al2O3 layers grown on p-type Si by the atomic layer deposition technique

    NASA Astrophysics Data System (ADS)

    Kolkovsky, Vl.; Stübner, R.; Langa, S.; Wende, U.; Kaiser, B.; Conrad, H.; Schenk, H.

    2016-09-01

    In the present study the electrical properties of 100 nm and 400 nm alumina films grown by the atomic layer deposition technique on p-type Si before and after a post-deposition annealing at 440 °C and after a dc H plasma treatment at different temperatures are investigated. We show that the density of interface states is below 2 × 1010 cm-2 in these samples and this value is significantly lower compared to that reported previously in thinner alumina layers (below 50 nm). The effective minority carrier lifetime τg,eff and the effective surface recombination velocity seff in untreated p-type Si samples with 100 nm and 400 nm aluminum oxide is comparable with those obtained after thermal oxidation of 90 nm SiO2. Both, a post-deposition annealing in forming gas (nitrogen/hydrogen) at elevated temperatures and a dc H-plasma treatment at temperatures close to room temperature lead to the introduction of negatively charged defects in alumina films. The results obtained in samples annealed in different atmospheres at different temperatures or subjected to a dc H plasma treatment allow us to correlate these centers with H-related defects. By comparing with theory we tentatively assign them to negatively charged interstitial H atoms.

  15. From atomic structure to excess entropy: a neutron diffraction and density functional theory study of CaO-Al₂O₃-SiO₂ melts.

    PubMed

    Liu, Maoyuan; Jacob, Aurélie; Schmetterer, Clemens; Masset, Patrick J; Hennet, Louis; Fischer, Henry E; Kozaily, Jad; Jahn, Sandro; Gray-Weale, Angus

    2016-04-06

    Calcium aluminosilicate CaO-Al2O3-SiO2 (CAS) melts with compositions (CaO-SiO2)(x)(Al2O3)(1-x) for x  <  0.5 and (Al2O3)(x)(SiO2)(1-x) for x ≥ 0.5 are studied using neutron diffraction with aerodynamic levitation and density functional theory molecular dynamics modelling. Simulated structure factors are found to be in good agreement with experimental structure factors. Local atomic structures from simulations reveal the role of calcium cations as a network modifier, and aluminium cations as a non-tetrahedral network former. Distributions of tetrahedral order show that an increasing concentration of the network former Al increases entropy, while an increasing concentration of the network modifier Ca decreases entropy. This trend is opposite to the conventional understanding that increasing amounts of network former should increase order in the network liquid, and so decrease entropy. The two-body correlation entropy S2 is found to not correlate with the excess entropy values obtained from thermochemical databases, while entropies including higher-order correlations such as tetrahedral order, O-M-O or M-O-M bond angles and Q(N) environments show a clear linear correlation between computed entropy and database excess entropy. The possible relationship between atomic structures and excess entropy is discussed.

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

    PubMed Central

    Deng, Hui; Endo, Katsuyoshi; Yamamura, Kazuya

    2015-01-01

    The surface atomic step-terrace structure of 4H-SiC greatly affects its performance in power device applications. On the basis of the crystal structure of 4H-SiC, we propose the generation mechanism of the a-b-a*-b* type, a-b type and a-a type step-terrace structures. We demonstrate that the step-terrace structure of SiC can be controlled by adjusting the balance between chemical modification and physical removal in CeO2 slurry polishing. When chemical modification plays the main role in the polishing of SiC, the a-b-a*-b* type step-terrace structure can be generated. When the roles of physical removal and chemical modification have similar importance, the a-b-a*-b* type step-terrace structure changes to the a-b type. When physical removal is dominant, the uniform a-a type step-terrace structure can be generated. PMID:25752524

  17. Tip induced mechanical deformation of epitaxial graphene grown on reconstructed 6H-SiC(0001) surface during scanning tunneling and atomic force microscopy studies

    NASA Astrophysics Data System (ADS)

    Morán Meza, José Antonio; Lubin, Christophe; Thoyer, François; Cousty, Jacques

    2015-06-01

    The structural and mechanical properties of an epitaxial graphene (EG) monolayer thermally grown on top of a 6H-SiC(0001) surface were studied by combined dynamic scanning tunneling microscopy (STM) and frequency modulation atomic force microscopy (FM-AFM). Experimental STM, dynamic STM and AFM images of EG on 6H-SiC(0001) show a lattice with a 1.9 nm period corresponding to the (6 × 6) quasi-cell of the SiC surface. The corrugation amplitude of this (6 × 6) quasi-cell, measured from AFM topographies, increases with the setpoint value of the frequency shift Δf (15-20 Hz, repulsive interaction). Excitation variations map obtained simultaneously with the AFM topography shows that larger dissipation values are measured in between the topographical bumps of the (6 × 6) quasi-cell. These results demonstrate that the AFM tip deforms the graphene monolayer. During recording in dynamic STM mode, a frequency shift (Δf) map is obtained in which Δf values range from 41 to 47 Hz (repulsive interaction). As a result, we deduced that the STM tip, also, provokes local mechanical distortions of the graphene monolayer. The origin of these tip-induced distortions is discussed in terms of electronic and mechanical properties of EG on 6H-SiC(0001).

  18. Tip induced mechanical deformation of epitaxial graphene grown on reconstructed 6H-SiC(0001) surface during scanning tunneling and atomic force microscopy studies.

    PubMed

    Meza, José Antonio Morán; Lubin, Christophe; Thoyer, François; Cousty, Jacques

    2015-01-26

    The structural and mechanical properties of an epitaxial graphene (EG) monolayer thermally grown on top of a 6H-SiC(0001) surface were studied by combined dynamic scanning tunneling microscopy (STM) and frequency modulation atomic force microscopy (FM-AFM). Experimental STM, dynamic STM and AFM images of EG on 6H-SiC(0001) show a lattice with a 1.9 nm period corresponding to the (6 × 6) quasi-cell of the SiC surface. The corrugation amplitude of this (6 × 6) quasi-cell, measured from AFM topographies, increases with the setpoint value of the frequency shift Δf (15-20 Hz, repulsive interaction). Excitation variations map obtained simultaneously with the AFM topography shows that larger dissipation values are measured in between the topographical bumps of the (6 × 6) quasi-cell. These results demonstrate that the AFM tip deforms the graphene monolayer. During recording in dynamic STM mode, a frequency shift (Δf) map is obtained in which Δf values range from 41 to 47 Hz (repulsive interaction). As a result, we deduced that the STM tip, also, provokes local mechanical distortions of the graphene monolayer. The origin of these tip-induced distortions is discussed in terms of electronic and mechanical properties of EG on 6H-SiC(0001).

  19. Conformal SiO2 coating of sub-100 nm diameter channels of polycarbonate etched ion-track channels by atomic layer deposition.

    PubMed

    Sobel, Nicolas; Hess, Christian; Lukas, Manuela; Spende, Anne; Stühn, Bernd; Toimil-Molares, M E; Trautmann, Christina

    2015-01-01

    Polycarbonate etched ion-track membranes with about 30 µm long and 50 nm wide cylindrical channels were conformally coated with SiO2 by atomic layer deposition (ALD). The process was performed at 50 °C to avoid thermal damage to the polymer membrane. Analysis of the coated membranes by small angle X-ray scattering (SAXS) reveals a homogeneous, conformal layer of SiO2 in the channels at a deposition rate of 1.7-1.8 Å per ALD cycle. Characterization by infrared and X-ray photoelectron spectroscopy (XPS) confirms the stoichiometric composition of the SiO2 films. Detailed XPS analysis reveals that the mechanism of SiO2 formation is based on subsurface crystal growth. By dissolving the polymer, the silica nanotubes are released from the ion-track membrane. The thickness of the tube wall is well controlled by the ALD process. Because the track-etched channels exhibited diameters in the range of nanometres and lengths in the range of micrometres, cylindrical tubes with an aspect ratio as large as 3000 have been produced.

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

    PubMed

    Deng, Hui; Endo, Katsuyoshi; Yamamura, Kazuya

    2015-03-10

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

  1. [Analysis the properties of Cr2O7(2-) adsorption onto functional organic reagent modified nano-SiO2 by flame atomic absorption spectroscopy].

    PubMed

    Zhang, Zu-Lei; Li, Lei

    2011-02-01

    A new type of functional organic reagent modified nano-SiO2 sorbent (Si/ (CH2)3-NH-CO-Ph-CH2-P(C6H5)3 Br) was synthesized by several reasonable organic combination reactions using nano-SiO2, gamma-Aminopropyl triethoxysilane (KH-550) and functional organic reagent (COOH-Ph-CH2-P(C6 H5)3 Br) as raw materials. The prepared new sorbent was characterized by using FTIR, particle diameter and TG. A batch of adsorption experiments was performed to evaluate its adsorption behavior of Cr2O7(2-) by flame atomic absorption spectroscopy (FAAS). The effects of solution pH, shaken time and sorbent amount on the extraction of Cr2O7(2-) from aqueous solutions were studied. Results showed that when under the optimum conditions the solution pH 1, sorbent amount = 0.1 g, and shaken time = 30 min, the adsorption efficiency can be more than 95%. It indicated that this novel sorbent (Si/ (CH2)3-NH-CO-Ph-CH2-P (C6 H5)3 Br) was a solid sorbent being efficient and low-cost, with convenient separation, and can remove trace Cr2 O7(2-) in environmental waste water.

  2. Effects of isoconcentration surface threshold values on the characteristics of needle-shaped precipitates in atom probe tomography data from an aged Al-Mg-Si alloy.

    PubMed

    Aruga, Yasuhiro; Kozuka, Masaya

    2016-04-01

    Needle-shaped precipitates in an aged Al-0.62Mg-0.93Si (mass%) alloy were identified using a compositional threshold method, an isoconcentration surface, in atom probe tomography (APT). The influence of thresholds on the morphological and compositional characteristics of the precipitates was investigated. Utilizing optimum parameters for the concentration space, a reliable number density of the precipitates is obtained without dependence on the elemental concentration threshold in comparison with evaluation by transmission electron microscopy (TEM). It is suggested that careful selection of the concentration space in APT can lead to a reasonable average Mg/Si ratio for the precipitates. It was found that the maximum length and maximum diameter of the precipitates are affected by the elemental concentration threshold. Adjustment of the concentration threshold gives better agreement with the precipitate dimensions measured by TEM.

  3. The antiphase boundary in half-metallic Heusler alloy Co2Fe(Al,Si): atomic structure, spin polarization reversal, and domain wall effects

    NASA Astrophysics Data System (ADS)

    Nedelkoski, Zlatko; Sanchez, Ana M.; Ghasemi, Arsham; Hamaya, Kohei; Evans, Richard F. L.; Bell, Gavin R.; Hirohata, Atsufumi; Lazarov, Vlado K.

    2016-11-01

    Atomic resolution scanning transmission electron microscopy reveals the presence of an antiphase boundary in the half-metallic Co2Fe(Al,Si) full Heusler alloy. By employing the density functional theory calculations, we show that this defect leads to reversal of the sign of the spin-polarization in the vicinity of the defect. In addition, we show that this defect reduces the strength of the exchange interactions, without changing the ferromagnetic ordering across the boundary. Atomistic spin calculations predict that this effect reduces the width of the magnetic domain wall compared to that in the bulk.

  4. Atomic structure determination of the 3C -SiC(001) c(4×2) surface reconstruction: Experiment and theory

    NASA Astrophysics Data System (ADS)

    Tejeda, A.; Wimmer, E.; Soukiassian, P.; Dunham, D.; Rotenberg, E.; Denlinger, J. D.; Michel, E. G.

    2007-05-01

    The structure of the Si-terminated 3C-SiC(001)-c(4×2) surface reconstruction is determined using synchrotron-radiation-based x-ray photoelectron diffraction from the Si2p and C1s core levels. Only the alternating up-and-down dimer (AUDD) model reproduces satisfactorily the experimental results. The refinement of the AUDD model leads to a height difference of (0.4±0.1)Å between the up and down Si-Si dimers. Also, the top and bottom dimers have alternating bond lengths at (2.5±0.2)Å and (2.2±0.2)Å , respectively. These results are in excellent agreement with ab initio density-functional calculations, which also further support the high sensitivity of this reconstruction on lateral strain and on the presence of defects. Finally, beyond well-established synchrotron-radiation-based core-level photoemission spectroscopy, an assignment is made on the structural origin of each Si2p surface and subsurface shifted component, based on their different photoelectron diffraction patterns.

  5. Relationships among equivalent oxide thickness, nanochemistry, and nanostructure in atomic layer chemical-vapor-deposited Hf-O films on Si

    NASA Astrophysics Data System (ADS)

    Dey, S. K.; Das, A.; Tsai, M.; Gu, D.; Floyd, M.; Carpenter, R. W.; De Waard, H.; Werkhoven, C.; Marcus, S.

    2004-05-01

    The relationships among the equivalent oxide thickness (EOT), nanochemistry, and nanostructure of atomic layer chemical-vapor-deposited (ALCVD) Hf-O-based films, with oxide and nitrided oxide interlayers on Si substrates, were studied using x-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (HRTEM), scanning transmission electron microscopy (STEM) in annular dark-field imaging (ADF), and parallel electron energy-loss spectroscopy (PEELS), capacitance-voltage, and leakage-current-voltage measurements. The XPS (Hf 4f binding energy shift) studies indicated the formation of Hf-O-Si bonds in as-deposited amorphous films, the amount of which was influenced by the interlayer composition and annealing conditions. After post-deposition annealing in N2 and O2, the Hf-O layers were nanocrystalline. Although HRTEM images showed a structurally sharp interface between the Hf-O layer and the interlayer, angle-resolved XPS, ADF imaging, and PEELS in the STEM revealed a chemically diffused HfSiOx region in between. This interdiffusion was observed by the detection of Si (using Si L edge) and Hf (using Hf O2,3 edge) in the Hf-O layer and the interlayer. For an annealed Hf-O/interlayer stack, with an ALCVD target thickness of 4.0 nm for the Hf-O layer on 1.2 nm of nitrided chemical oxide, the experimentally measured EOT and leakage current (at -1 V) were 1.52 nm and ˜10-8 A/cm2. A three-layer (1.2 nm interlayer of nitrided chemical oxide/compositionally graded, 2 nm region of HfSiOx/2 nm HfO2 layer) capacitor model was used to determine the respective contributions to the measured EOT, and the dielectric permittivity of the interlayer was found to be 6.06. These studies clearly indicate that a total EOT of 1 nm and below is attainable in the Hf-N-O-Si/Si-N-O system.

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

    NASA Technical Reports Server (NTRS)

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

    2004-01-01

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

  7. Self-catalysis by aminosilanes and strong surface oxidation by O2 plasma in plasma-enhanced atomic layer deposition of high-quality SiO2.

    PubMed

    Fang, Guo-Yong; Xu, Li-Na; Cao, Yan-Qiang; Wang, Lai-Guo; Wu, Di; Li, Ai-Dong

    2015-01-25

    Plasma-enhanced atomic layer deposition (PE-ALD) has been applied to prepare high-quality ultrathin films for microelectronics, catalysis, and energy applications. The possible pathways for SiO2 PE-ALD using aminosilanes and O2 plasma have been investigated by density functional theory calculations. The silane half-reaction between SiH4 and surface -OH is very difficult and requires a high activation free energy of 57.8 kcal mol(-1). The introduction of an aminosilane, such as BDMAS, can reduce the activation free energy to 11.0 kcal mol(-1) and the aminosilane plays the role of a self-catalyst in Si-O formation through the relevant half-reaction. Among the various species generated in O2 plasma, (3)O2 is inactive towards surface silane groups, similar to ordinary oxygen gas. The other three species, (1)O2, (1)O, and (3)O, can strongly oxidize surface silane groups through one-step or stepwise pathways. In the (3)O pathway, the triplet must be converted into the singlet and follow the (1)O pathway. Meanwhile, both (1)O and (3)O can decay to (1)O2 and enter into the relevant oxidation pathway. The concept of self-catalysis of aminosilanes may be invoked to design and prepare more effective Si precursors for SiO2 ALD. At the same time, the mechanism of strong surface oxidation by O2 plasma may be exploited in the PE-ALD preparation of other oxides, such as Al2O3, HfO2, ZrO2, and TiO2.

  8. The transformation of nitrogen in soil under Robinia Pseudacacia shelterbelt and in adjoining cultivated field

    NASA Astrophysics Data System (ADS)

    Szajdak, L.; Gaca, W.

    2009-04-01

    The shelterbelts perform more than twenty different functions favorable to the environment, human economy, health and culture. The most important for agricultural landscape is increase of water retention, purification of ground waters and prevent of pollution spread in the landscape, restriction of wind and water erosion effects, isolation of polluting elements in the landscape, preservation of biological diversity in agricultural areas and mitigation of effects of unfavorable climatic phenomena. Denitrification is defined as the reduction of nitrate or nitrite coupled to electron transport phosphorylation resulting in gaseous N either as molecular N2 or as an oxide of N. High content of moisture, low oxygen, neutral and basic pH favour the denitrification. Nitrate reductase is an important enzyme involved in the process of denitrification. The reduction of nitrate to nitrite is catalyzed by nitrate reductase. Nitrite reductase is catalyzed reduction nitrite to nitrous oxide. The conversion of N2O to N2 is catalyzed by nitrous oxide reductase. This process leads to the lost of nitrogen in soil mainly in the form of N2 and N2O. Nitrous oxide is a greenhouse gas which cause significant depletion of the Earth's stratospheric ozone layer. The investigations were carried out in Dezydery Chlapowski Agroecological Landscape Park in Turew (40 km South-West of Poznań, West Polish Lowland). Our investigations were focused on the soils under Robinia pseudacacia shelterbelt and in adjoining cultivated field. The afforestation was created 200 years ago and it is consist of mainly Robinia pseudacacia with admixture of Quercus petraea and Quercus robur. This shelterbelt and adjoining cultivated field are located on grey-brown podzolic soil. The aim of this study is to present information on the changes of nitrate reductase activity in soil with admixture urea (organic form of nitrogen) in two different concentrations 0,25% N and 0,5% N. Our results have shown that this process

  9. Local atomic and electronic structure of oxide/GaAs and SiO2/Si interfaces using high-resolution XPS

    NASA Technical Reports Server (NTRS)

    Grunthaner, F. J.; Grunthaner, P. J.; Vasquez, R. P.; Lewis, B. F.; Maserjian, J.; Madhukar, A.

    1979-01-01

    The chemical structures of thin SiO2 films, thin native oxides of GaAs (20-30 A), and the respective oxide-semiconductor interfaces, have been investigated using high-resolution X-ray photoelectron spectroscopy. Depth profiles of these structures have been obtained using argon ion bombardment and wet chemical etching techniques. The chemical destruction induced by the ion profiling method is shown by direct comparison of these methods for identical samples. Fourier transform data-reduction methods based on linear prediction with maximum entropy constraints are used to analyze the discrete structure in oxides and substrates. This discrete structure is interpreted by means of a structure-induced charge-transfer model.

  10. Effect of Thermal Budget on the Electrical Characterization of Atomic Layer Deposited HfSiO/TiN Gate Stack MOSCAP Structure.

    PubMed

    Khan, Z N; Ahmed, S; Ali, M

    2016-01-01

    Metal Oxide Semiconductor (MOS) capacitors (MOSCAP) have been instrumental in making CMOS nano-electronics realized for back-to-back technology nodes. High-k gate stacks including the desirable metal gate processing and its integration into CMOS technology remain an active research area projecting the solution to address the requirements of technology roadmaps. Screening, selection and deposition of high-k gate dielectrics, post-deposition thermal processing, choice of metal gate structure and its post-metal deposition annealing are important parameters to optimize the process and possibly address the energy efficiency of CMOS electronics at nano scales. Atomic layer deposition technique is used throughout this work because of its known deposition kinetics resulting in excellent electrical properties and conformal structure of the device. The dynamics of annealing greatly influence the electrical properties of the gate stack and consequently the reliability of the process as well as manufacturable device. Again, the choice of the annealing technique (migration of thermal flux into the layer), time-temperature cycle and sequence are key parameters influencing the device's output characteristics. This work presents a careful selection of annealing process parameters to provide sufficient thermal budget to Si MOSCAP with atomic layer deposited HfSiO high-k gate dielectric and TiN gate metal. The post-process annealing temperatures in the range of 600°C -1000°C with rapid dwell time provide a better trade-off between the desirable performance of Capacitance-Voltage hysteresis and the leakage current. The defect dynamics is thought to be responsible for the evolution of electrical characteristics in this Si MOSCAP structure specifically designed to tune the trade-off at low frequency for device application.

  11. Effect of Thermal Budget on the Electrical Characterization of Atomic Layer Deposited HfSiO/TiN Gate Stack MOSCAP Structure

    PubMed Central

    Khan, Z. N.; Ahmed, S.; Ali, M.

    2016-01-01

    Metal Oxide Semiconductor (MOS) capacitors (MOSCAP) have been instrumental in making CMOS nano-electronics realized for back-to-back technology nodes. High-k gate stacks including the desirable metal gate processing and its integration into CMOS technology remain an active research area projecting the solution to address the requirements of technology roadmaps. Screening, selection and deposition of high-k gate dielectrics, post-deposition thermal processing, choice of metal gate structure and its post-metal deposition annealing are important parameters to optimize the process and possibly address the energy efficiency of CMOS electronics at nano scales. Atomic layer deposition technique is used throughout this work because of its known deposition kinetics resulting in excellent electrical properties and conformal structure of the device. The dynamics of annealing greatly influence the electrical properties of the gate stack and consequently the reliability of the process as well as manufacturable device. Again, the choice of the annealing technique (migration of thermal flux into the layer), time-temperature cycle and sequence are key parameters influencing the device’s output characteristics. This work presents a careful selection of annealing process parameters to provide sufficient thermal budget to Si MOSCAP with atomic layer deposited HfSiO high-k gate dielectric and TiN gate metal. The post-process annealing temperatures in the range of 600°C -1000°C with rapid dwell time provide a better trade-off between the desirable performance of Capacitance-Voltage hysteresis and the leakage current. The defect dynamics is thought to be responsible for the evolution of electrical characteristics in this Si MOSCAP structure specifically designed to tune the trade-off at low frequency for device application. PMID:27571412

  12. Role of atomic terraces and steps in the electron transport properties of epitaxial graphene grown on SiC

    NASA Astrophysics Data System (ADS)

    Kuramochi, H.; Odaka, S.; Morita, K.; Tanaka, S.; Miyazaki, H.; Lee, M. V.; Li, S.-L.; Hiura, H.; Tsukagoshi, K.

    2012-03-01

    Thermal decomposition of vicinal SiC substrates with self-organized periodic nanofacets is a promising method to produce large graphene sheets toward the commercial exploitation of graphene's superior electronic properties. The epitaxial graphene films grown on vicinal SiC comprise two distinct regions of terrace and step; and typically exhibit anisotropic electron transport behavior, although limited areas in the graphene film showed ballistic transport. To evaluate the role of terraces and steps in electron transport properties, we compared graphene samples with terrace and step regions grown on 4H-SiC(0001). Arrays of field effect transistors were fabricated on comparable graphene samples with their channels parallel or perpendicular to the nanofacets to identify the source of measured reduced mobility. Minimum conductivity and electron mobility increased with the larger proportional terrace region area; therefore, the terrace region has superior transport properties to step regions. The measured electron mobility in the terrace region, ˜1000 cm2/Vs, is 10 times larger than that in the step region, ˜100 cm2/Vs. We conclusively determine that parasitic effects originate in regions of graphene that grow over step edges in 4H-SiC(0001).

  13. Following electron impact excitation of single (N, O, F, Ne, Na, Mg, Al, Si) atom L subshells ionization cross section calculations by using Lotz's equation

    NASA Astrophysics Data System (ADS)

    Aydinol, Mahmut

    2017-02-01

    L shell and L subshells ionization cross sections σL and σLi (i = 1, 2, 3) following electron impact on (N,O, F, Ne, Na, Mg, Al, Si) atoms calculated. By using Lotz' equation for nonrelativistic cases in Matlab σL and σLi cross section values obtained for ten electron impact(Eo) values in the range of ELiatom. Starting from Eo=ELi(each subshell ionization threshold energy), σL and σLi are increasing rapidly with Eo. For a fixed Eo value(≈3.ELi), while Z value increases from 7≤Z≤14 σL and σLi decrease. Results show that for smaller values of Eo(close to ELi), x-ray yields formation of Li(i=1,2,3) subshells decreases while competing other yields are increase. Results may help to understand similar findings which obtained from other electron impact excitation of L shell σL and subshells σLi studies for single atoms.

  14. Growth of InN Nanowires with Uniform Diameter on Si(111) Substrates: Competition Between Migration and Desorption of In Atoms.

    PubMed

    Gao, Fangliang; Wen, Lei; Xu, Zhenzhu; Han, Jinglei; Yu, Yuefeng; Zhang, Shuguang; Li, Guoqiang

    2017-04-06

    The effects of the growth parameters on the uniformity and the aspect ratio of InN nanowires grown on Si(111) substrates have been studied systematically, and a modified quasi-equilibrium model is proposed. The growth temperature is of great importance for both the nucleation of the nanowires and the migration of In and N atoms, thus affecting the uniformity of the InN nanowires. In order to improve the uniformity of the InN nanowires, both traditional substrate nitridation and pre-In-droplet deposition have been implemented. It is found that the substrate nitridation is favorable for the nucleation of InN nanowires. However, the initial In atoms adhered to the substrate are insufficient to sustain the uniform growth of the InN nanowires. We have found that the initial In droplet on the substrate is not only advantageous for the nucleation of the InN nanowire, but also favorable for the In atom equilibrium between the initial In droplets and the direct In flux. Therefore, InN nanowires with a uniform aspect ratio and optimal diameter can be achieved. The results reported herein provide meaningful insights to understanding the growth kinetics during the InN nanowires growth, and open up great possibilities of developing high-performance group III-nitride-based devices.

  15. O atoms loss coefficient on porous SiO2 and TiO2 measured by plasma induced fluorescence

    NASA Astrophysics Data System (ADS)

    Allegraud, Katia; Gatilova, Lina; Guaitella, Olivier; Guillon, Jean; Rousseau, Antoine

    2006-10-01

    The time evolution of O atoms density in the gas phase during the post-discharge of a pulsed plasma is studied using a plasma induced fluorescence technique (PIF): a main long pulse creates the plasma and a shorter one re-excites atoms in the time post-discharge was used. The gas pressure is 133 Pa in N2/O2 mixture and the plasma is a pulsed DC discharge. The surface loss coefficient of O atoms on pyrex, porous silica, porous TiO2 is measured, this latter being a photocatalytic material. It is shown that the presence of porous silica or TiO2 leads to a stong increase of the O atom surface loss coefficient. When nano cluster of TiO2 are deposited on porous silica, the loss coefficient is first high and comparable to the case of the porous silica, but decreases after few milliseconds. Such a decrease of the surface loss coefficient has recently been reported in a pulsed microwave discharge [1]. The effect of the pre-irradiation of the porous materials by external ultraviolet is also studied. [1] G. Cartry, X. Duten and A. Rousseau Plasma Sources Sci. Technol. 15 (2006) 479--488

  16. Low-temperature in situ large strain plasticity of ceramic SiC nanowires and its atomic-scale mechanism.

    PubMed

    Han, X D; Zhang, Y F; Zheng, K; Zhang, X N; Zhang, Z; Hao, Y J; Guo, X Y; Yuan, J; Wang, Z L

    2007-02-01

    Large strain plasticity is phenomenologically defined as the ability of a material to exhibit an exceptionally large deformation rate during mechanical deformation. It is a property that is well established for metals and alloys but is rarely observed for ceramic materials especially at low temperature ( approximately 300 K). With the reduction in dimensionality, however, unusual mechanical properties are shown by ceramic nanomaterials. In this Letter, we demonstrated unusually large strain plasticity of ceramic SiC nanowires (NWs) at temperatures close to room temperature that was directly observed in situ by a novel high-resolution transmission electron microscopy technique. The continuous plasticity of the SiC NWs is accompanied by a process of increased dislocation density at an early stage, followed by an obvious lattice distortion, and finally reaches an entire structure amorphization at the most strained region of the NW. These unusual phenomena for the SiC NWs are fundamentally important for understanding the nanoscale fracture and strain-induced band structure variation for high-temperature semiconductors. Our result may also provide useful information for further studying of nanoscale elastic-plastic and brittle-ductile transitions of ceramic materials with superplasticity.

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

    DTIC Science & Technology

    2009-06-15

    the grafted TiO2 were in a highly dispersed amorphous form.19 Atomic layer deposition (ALD) is a thin film growth technique, which relies on self... Thin Films . U.S. Patent 4058430, 1977. (21) Ritala, M. Appl. Surf. Sci. 1997, 112, 223. TiO2 /SiO2 Catalysts Prepared by ALD J. Phys. Chem. C, Vol. 113...Surface Acidity and Properties of TiO2 /SiO2 Catalysts Prepared by Atomic Layer Deposition: UV-visible Diffuse Reflectance, DRIFTS, and Visible Raman

  18. Band alignment study on Al/SiO2and Cu/SiO2 metal-oxide interface with the presence of H atom impurity and external electric field

    NASA Astrophysics Data System (ADS)

    Huang, Jianqiu; Tea, Eric; Hin, Celine

    Metal-Oxide interface has a wide use in electronic devices. Currently, technological development is aiming on the shrinkage of electronic devices' size. Based on the knowledge of electron tunneling effect, the reduction of dielectric thickness would cause an exponential increase on electron tunneling probability, which contributes to current leakage. It might cause dielectric breakdown, which could make a severe and irreversible damage to the devices. Therefore, the main purpose of this study is to explore the possible factors that could lead to dielectric breakdown at metal-oxide interface. Density functional theory ab initio calculation has been applied to study the Al/SiO2and Cu/SiO2 metal-oxide interface. Previous study revealed the facts that oxygen (di)vacancies at interface might trap electron and vary potential barrier height. In this study, we introduced the H atom impurity at interface, and applied external electric field to the system. Charge density differences have been calculated to observe the charge alternation at the interface when impurity and external electric field existed. Band alignment revealed the potential barrier height variation due to the impurity and external electric field, which provided us how barrier height would respond to these two types of defects. Supported by Air Force.

  19. In situ synchrotron based x-ray fluorescence and scattering measurements during atomic layer deposition: Initial growth of HfO2 on Si and Ge substrates

    NASA Astrophysics Data System (ADS)

    Devloo-Casier, K.; Dendooven, J.; Ludwig, K. F.; Lekens, G.; D'Haen, J.; Detavernier, C.

    2011-06-01

    The initial growth of HfO2 was studied by means of synchrotron based in situ x-ray fluorescence (XRF) and grazing incidence small angle x-ray scattering (GISAXS). HfO2 was deposited by atomic layer deposition (ALD) using tetrakis(ethylmethylamino)hafnium and H2O on both oxidized and H-terminated Si and Ge surfaces. XRF quantifies the amount of deposited material during each ALD cycle and shows an inhibition period on H-terminated substrates. No inhibition period is observed on oxidized substrates. The evolution of film roughness was monitored using GISAXS. A correlation is found between the inhibition period and the onset of surface roughness.

  20. Fluorocarbon assisted atomic layer etching of SiO2 and Si using cyclic Ar/C4F8 and Ar/CHF3 plasma

    SciTech Connect

    Metzler, Dominik; Li, Chen; Engelmann, Sebastian; Bruce, Robert L.; Joseph, Eric A.; Oehrlein, Gottlieb S.

    2015-11-11

    The need for atomic layer etching (ALE) is steadily increasing as smaller critical dimensions and pitches are required in device patterning. A flux-control based cyclic Ar/C4F8 ALE based on steady-state Ar plasma in conjunction with periodic, precise C4F8 injection and synchronized plasma-based low energy Ar+ ion bombardment has been established for SiO2.1 In this work, the cyclic process is further characterized and extended to ALE of silicon under similar process conditions. The use of CHF3 as a precursor is examined and compared to C4F8. CHF3 is shown to enable selective SiO2/Si etching using a fluorocarbon (FC) film build up. Other critical process parameters investigated are the FC film thickness deposited per cycle, the ion energy, and the etch step length. Etching behavior and mechanisms are studied using in situ real time ellipsometry and X-ray photoelectron spectroscopy. Silicon ALE shows less self-limitation than silicon oxide due to higher physical sputtering rates for the maximum ion energies used in this work, ranged from 20 to 30 eV. The surface chemistry is found to contain fluorinated silicon oxide during the etching of silicon. As a result, plasma parameters during ALE are studied using a Langmuir probe and establish the impact of precursor addition on plasma properties.

  1. Fluorocarbon assisted atomic layer etching of SiO{sub 2} and Si using cyclic Ar/C{sub 4}F{sub 8} and Ar/CHF{sub 3} plasma

    SciTech Connect

    Metzler, Dominik; Oehrlein, Gottlieb S.; Li, Chen; Engelmann, Sebastian; Bruce, Robert L.; Joseph, Eric A.

    2016-01-15

    The need for atomic layer etching (ALE) is steadily increasing as smaller critical dimensions and pitches are required in device patterning. A flux-control based cyclic Ar/C{sub 4}F{sub 8} ALE based on steady-state Ar plasma in conjunction with periodic, precise C{sub 4}F{sub 8} injection and synchronized plasma-based low energy Ar{sup +} ion bombardment has been established for SiO{sub 2} [Metzler et al., J. Vac. Sci. Technol. A 32, 020603 (2014)]. In this work, the cyclic process is further characterized and extended to ALE of silicon under similar process conditions. The use of CHF{sub 3} as a precursor is examined and compared to C{sub 4}F{sub 8}. CHF{sub 3} is shown to enable selective SiO{sub 2}/Si etching using a fluorocarbon (FC) film build up. Other critical process parameters investigated are the FC film thickness deposited per cycle, the ion energy, and the etch step length. Etching behavior and mechanisms are studied using in situ real time ellipsometry and x-ray photoelectron spectroscopy. Silicon ALE shows less self-limitation than silicon oxide due to higher physical sputtering rates for the maximum ion energies used in this work, ranged from 20 to 30 eV. The surface chemistry is found to contain fluorinated silicon oxide during the etching of silicon. Plasma parameters during ALE are studied using a Langmuir probe and establish the impact of precursor addition on plasma properties.

  2. Atomic-Level Simulations of Epitaxial Recrystallization and Amorphous-to-Crystalline Transition in 4H-SiC

    SciTech Connect

    Gao, Fei; Zhang, Yanwen; Posselt, Matthias; Weber, William J.

    2006-09-01

    The amorphous-to-crystalline (a-c) transition in 4H-SiC has been studied using molecular dynamics (MD) methods, with simulation times of up to a few hundred ns and at temperatures ranging from 1000 to 2000 K. Two nano-sized amorphous layers, one with the normal of a-c interfaces along the [ -12-10] direction and the other along the [ -1010] direction, were created within a crystalline cell to study expitaxial recrystallization and the formation of secondary phases. The recovery of bond defects at the interfaces is an important process driving the epitaxial recrystallization of the amorphous layers. The amorphous layer with the a-c interface normal along the [-12-10] direction can be completely recrystallized at the temperatures of 1500 and 2000 K, but the recrystallized region is defected with dislocations and stacking faults. On the other hand, the recrystallization process for the a-c interface normal along [-1010] direction is hindered by the nucleation of polycrystalline phases, and these secondary ordered phases are stable for longer simulation times. A general method to calculate activation energy spectra is employed to analyze the MD annealing simulations, and the recrystallization mechanism in SiC consists of multiple stages with activation energies ranging from 0.8 to 1.7 eV.

  3. Atomic scale study of corrugating and anticorrugating states on the bare Si(1 0 0) surface

    NASA Astrophysics Data System (ADS)

    Yengui, Mayssa; Pinto, Henry P.; Leszczynski, Jerzy; Riedel, Damien

    2015-02-01

    In this article, we study the origin of the corrugating and anticorrugating states through the electronic properties of the Si(1 0 0) surface via a low-temperature (9 K) scanning tunneling microscope (STM). Our study is based on the analysis of the STM topographies corrugation variations when related to the shift of the local density of states (LDOS) maximum in the [1 \\bar{{1}} 0] direction. Our experimental results are correlated with numerical simulations using the density-functional theory with hybrid Heyd-Scuseria-Ernzerhof (HSE06) functional to simulate the STM topographies, the projected density of states variations at different depths in the silicon surface as well as the three dimensional partial charge density distributions in real-space. This work reveals that the Si(1 0 0) surface exhibits two anticorrugating states at +0.8 and +2.8 V that are associated with a phase shift of the LDOS maximum in the unoccupied states STM topographies. By comparing the calculated data with our experimental results, we have been able to identify the link between the variations of the STM topographies corrugation and the shift of the LDOS maximum observed experimentally. Each surface voltage at which the STM topographies corrugation drops is defined as anticorrugating states. In addition, we have evidenced a sharp jump in the tunnel current when the second LDOS maximum shift is probed, whose origin is discussed and associated with the presence of Van Hove singularities.

  4. Cyclic surface morphology change related to Li ion movement in Li secondary microbattery embedded in Si substrate: Atomic force microscopy studies

    NASA Astrophysics Data System (ADS)

    Kushida, K.; Kuriyama, K.

    2004-05-01

    Surface morphology and charge/discharge characteristic in a 5×5 μm2 area of an all-solid-state Li secondary battery (Al/Li/SiO2-15 at. %P2O5/LiMn2O4/polycrystalline silicon) embedded in a Si substrate are simultaneously observed by atomic force microscopy with a conductive probe. The battery area of 5×5 μm2 shows charge/discharge behavior corresponding to the movement of ˜2.9×1010 Li+ ions/μm2, reflecting the cyclic movement of Li+ ions. The Al electrode consisting of scale-shaped grains of 0.1-1.5 μm in size rises by ˜30 nm during the first charge operation. The surface of the Al electrode shows a cyclic change from scaly to wrinkled structures with the charge/discharge operations, indicating the drawing of the excess Li in the anode into the glassy electrolyte. These results are promising for the realization of a micrometer-sized battery.

  5. Surface passivation of a photonic crystal band-edge laser by atomic layer deposition of SiO2 and its application for biosensing

    NASA Astrophysics Data System (ADS)

    Cha, Hyungrae; Lee, Jeongkug; Jordan, Luke R.; Lee, Si Hoon; Oh, Sang-Hyun; Kim, Hyo Jin; Park, Juhun; Hong, Seunghun; Jeon, Heonsu

    2015-02-01

    We report on the conformal surface passivation of photonic crystal (PC) laser devices with an ultrathin dielectric layer. Air-bridge-type Γ-point band-edge lasers (BELs) are fabricated by forming a honeycomb lattice two-dimensional PC structure into an InGaAsP multiple-quantum-well epilayer. Atomic layer deposition (ALD) is employed for conformal deposition of a few-nanometer-thick SiO2 layer over the entire device surface, not only on the top and bottom surfaces of the air-bridge membrane but also on the air-hole sidewalls. Despite its extreme thinness, the ALD passivation layer is found to protect the InGaAsP BEL devices from harsh chemicals. In addition, the ALD-SiO2 is compatible with the silane-based surface chemistry, which allows us to use ALD-passivated BEL devices as label-free biosensors. The standard streptavidin-biotin interaction shifts the BEL lasing wavelength by ~1 nm for the dipole-like Γ-point band-edge mode. A sharp lasing line (<0.2 nm, full width at half-maximum) and a large refractive index sensitivity (~163 nm per RIU) produce a figure of merit as high as ~800 for our BEL biosensor, which is at least an order of magnitude higher than those of more common biosensors that rely on a broad resonance peak, showing that our nanolaser structures are suitable for highly sensitive biosensor applications.

  6. The atomic-scale unit, entity: key to a direct and easily understood definition of the SI base unit for amount of substance

    NASA Astrophysics Data System (ADS)

    Leonard, B. P.

    2007-10-01

    The atomic-scale unit, entity (ent), is defined as the number-specific amount of substance, n/N, the amount of substance of a single entity. This unit is an invariant physical quantity (the reciprocal of the Avogadro constant) that serves as the basis for redefining the SI base unit for amount of substance in a direct and easily understood manner. It is argued here that the kilomole should be the base unit in order to avoid factors of 10-3 or 103 appearing in relationships involving both mass and amount of substance expressed in base units. Since, in a compatible formulation, the amount-specific number of entities, N/n (= NA), is equal to Mu/Da, exactly, where Mu = kg kmol-1 = g mol-1 = Da ent-1, exactly, then NA = (kg/Da) kmol-1 = (g/Da) mol-1 = 1 ent-1, exactly. The kilomole can thus be defined very simply as: kmol = \\cal N^{\\ast}\\,ent , exactly, where \\cal N^{\\ast} , the exact kilomole-to-entity amount ratio, is identical to the kilogram-to-dalton mass ratio: \\cal N^{\\ast} \\equiv kmol/ent\\equiv kg/Da . The Avogadro constant, N_A = \\cal N^{\\ast}\\,kmol^{-1} , does not appear explicitly in the defining equation, its reciprocal having been replaced by one entity. Like the dalton, the entity would be categorized as a unit in use with SI.

  7. On the reliability of nanoindentation hardness of Al{sub 2}O{sub 3} films grown on Si-wafer by atomic layer deposition

    SciTech Connect

    Liu, Xuwen Haimi, Eero; Hannula, Simo-Pekka; Ylivaara, Oili M. E.; Puurunen, Riikka L.

    2014-01-15

    The interest in applying thin films on Si-wafer substrate for microelectromechanical systems devices by using atomic layer deposition (ALD) has raised the demand on reliable mechanical property data of the films. This study aims to find a quick method for obtaining nanoindentation hardness of thin films on silicon with improved reliability. This is achieved by ensuring that the film hardness is determined under the condition that no plastic deformation occurs in the substrate. In the study, ALD Al{sub 2}O{sub 3} films having thickness varying from 10 to 600 nm were deposited on a single-side polished silicon wafer at 300 °C. A sharp cube-corner indenter was used for the nanoindentation measurements. A thorough study on the Si-wafer reference revealed that at a specific contact depth of about 8 nm the wafer deformation in loading transferred from elastic to elastic–plastic state. Furthermore, the occurrence of this transition was associated with a sharp increase of the power-law exponent, m, when the unloading data were fitted to a power-law relation. Since m is only slightly material dependent and should fall between 1.2 and 1.6 for different indenter geometry having elastic contact to common materials, it is proposed that the high m values are the results from the inelastic events during unloading. This inelasticity is linked to phase transformations during pressure releasing, a unique phenomenon widely observed in single crystal silicon. Therefore, it is concluded that m could be used to monitor the mechanical state of the Si substrate when the whole coating system is loaded. A suggested indentation depth range can then be assigned to each film thickness to provide guidelines for obtaining reliable property data. The results show good consistence for films thicker than 20 nm and the nanoindentation hardness is about 11 GPa independent of film thickness.

  8. Processing of n+/p-/p+ strip detectors with atomic layer deposition (ALD) grown Al2O3 field insulator on magnetic Czochralski silicon (MCz-si) substrates

    NASA Astrophysics Data System (ADS)

    Härkönen, J.; Tuovinen, E.; Luukka, P.; Gädda, A.; Mäenpää, T.; Tuominen, E.; Arsenovich, T.; Junkes, A.; Wu, X.; Li, Z.

    2016-08-01

    Detectors manufactured on p-type silicon material are known to have significant advantages in very harsh radiation environment over n-type detectors, traditionally used in High Energy Physics experiments for particle tracking. In p-type (n+ segmentation on p substrate) position-sensitive strip detectors, however, the fixed oxide charge in the silicon dioxide is positive and, thus, causes electron accumulation at the Si/SiO2 interface. As a result, unless appropriate interstrip isolation is applied, the n-type strips are short-circuited. Widely adopted methods to terminate surface electron accumulation are segmented p-stop or p-spray field implantations. A different approach to overcome the near-surface electron accumulation at the interface of silicon dioxide and p-type silicon is to deposit a thin film field insulator with negative oxide charge. We have processed silicon strip detectors on p-type Magnetic Czochralski silicon (MCz-Si) substrates with aluminum oxide (Al2O3) thin film insulator, grown with Atomic Layer Deposition (ALD) method. The electrical characterization by current-voltage and capacitance-voltage measurement shows reliable performance of the aluminum oxide. The final proof of concept was obtained at the test beam with 200 GeV/c muons. For the non-irradiated detector the charge collection efficiency (CCE) was nearly 100% with a signal-to-noise ratio (S/N) of about 40, whereas for the 2×1015 neq/cm2 proton irradiated detector the CCE was 35%, when the sensor was biased at 500 V. These results are comparable with the results from p-type detectors with the p-spray and p-stop interstrip isolation techniques. In addition, interestingly, when the aluminum oxide was irradiated with Co-60 gamma-rays, an accumulation of negative fixed oxide charge in the oxide was observed.

  9. Covalent immobilization of glucose oxidase on well-defined poly(glycidyl methacrylate)-Si(111) hybrids from surface-initiated atom-transfer radical polymerization.

    PubMed

    Xu, F J; Cai, Q J; Li, Y L; Kang, E T; Neoh, K G

    2005-01-01

    A simple one-step procedure was employed for the covalent immobilization of an atom-transfer radical polymerization (ATRP) initiator, via the robust Si-C bond, on the hydrogen-terminated Si(111) surface (Si-H surface). Well-defined poly(glycidyl methacrylate) [P(GMA)] brushes, tethered directly on the (111)-oriented single-crystal silicon surface, were prepared via surface-initiated ATRP. Kinetics study on the surface-initiated ATRP of glycidyl methacrylate revealed that the chain growth from the silicon surface was consistent with a "controlled" process. A relatively high concentration of glucose oxidase (GOD; above 0.2 mg/cm2) could be coupled directly to the well-defined P(GMA) brushes via the ring-opening reaction of the epoxide groups with the amine moieties of the enzyme. The resultant GOD-functionalized P(GMA) brushes, with the accompanying hydroxyl groups from the ring-opening reaction of the epoxide groups, serves as an effective spacer to provide the GOD with a higher degree of conformational freedom and a more hydrophilic environment. An equivalent enzyme activity above 1.6 units/cm2 [micromoles of beta-D-(+)-glucose oxidized to d-gluconolactone per minute per square centimeter] and a corresponding relative activity of about 60% could be readily achieved. The immobilized GOD also exhibited an improved stability during storage over that of the free enzyme. The GOD-functionalized silicon substrates are potentially useful to the development of silicon-based glucose biosensors.

  10. Spectroscopic and electrical calculation of band alignment between atomic layer deposited SiO{sub 2} and β-Ga{sub 2}O{sub 3} (2{sup ¯}01)

    SciTech Connect

    Jia, Ye; Zeng, Ke; Singisetti, Uttam; Wallace, Joshua S.; Gardella, Joseph A

    2015-03-09

    The energy band alignment between atomic layer deposited (ALD) SiO{sub 2} and β-Ga{sub 2}O{sub 3} (2{sup ¯}01) is calculated using x-ray photoelectron spectroscopy and electrical measurement of metal-oxide semiconductor capacitor structures. The valence band offset between SiO{sub 2} and Ga{sub 2}O{sub 3} is found to be 0.43 eV. The bandgap of ALD SiO{sub 2} was determined to be 8.6 eV, which gives a large conduction band offset of 3.63 eV between SiO{sub 2} and Ga{sub 2}O{sub 3}. The large conduction band offset makes SiO{sub 2} an attractive gate dielectric for power devices.

  11. Characterization of electrical properties in axial Si-Ge nanowire heterojunctions using off-axis electron holography and atom-probe tomography

    NASA Astrophysics Data System (ADS)

    Gan, Zhaofeng; Perea, Daniel E.; Yoo, Jinkyoung; He, Yang; Colby, Robert J.; Barker, Josh E.; Gu, Meng; Mao, Scott X.; Wang, Chongmin; Picraux, S. T.; Smith, David J.; McCartney, Martha R.

    2016-09-01

    Nanowires (NWs) consisting of P-doped Si/B-doped Ge axial heterojunctions were grown via vapor-liquid-solid synthesis using a combination of Au and AuGa catalyst particles. Off-axis electron holography (EH) was used to measure the electrostatic potential profile across the junction resulting from electrically active dopants, and atom-probe tomography (APT) was used to map total dopant concentration profiles. A comparison of the electrostatic potential profile measured from EH with simulations that were based on the APT results indicates that Ga atoms unintentionally introduced during AuGa catalyst growth were mostly electronically inactive. This finding was also corroborated by in situ electron-holography biasing experiments. Electronic band structure simulations guided by the experimental results helped to provide a much better explanation of the NW electrical behavior. Overall, this work demonstrates that the combination of EH, APT, in situ biasing, and simulations allows a more complete understanding of NW electrical properties to be developed.

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

    PubMed Central

    2011-01-01

    We report a direct observation of Ge hut nucleation on Si(001) during UHV molecular beam epitaxy at 360°C. Nuclei of pyramids and wedges were observed on the wetting layer (WL) (M × N) patches starting from the coverage of 5.1 Å and found to have different structures. Atomic models of nuclei of both hut species have been built as well as models of the growing clusters. The growth of huts of each species has been demonstrated to follow generic scenarios. The formation of the second atomic layer of a wedge results in rearrangement of its first layer. Its ridge structure does not repeat the nucleus. A pyramid grows without phase transitions. A structure of its vertex copies the nucleus. Transitions between hut species turned out to be impossible. The wedges contain point defects in the upper corners of the triangular faces and have preferential growth directions along the ridges. The derived structure of the {105} facet follows the paired dimer model. Further growth of hut arrays results in domination of wedges, and the density of pyramids exponentially drops. The second generation of huts arises at coverages >10 Å; new huts occupy the whole WL at coverages ~14 Å. Nanocrystalline Ge 2D layer begins forming at coverages >14 Å. PMID:21711886

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

    PubMed

    Arapkina, Larisa V; Yuryev, Vladimir A

    2011-04-15

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

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

    PubMed

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

    2017-03-28

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

  15. Imaging of oxide charges and contact potential difference fluctuations in atomic layer deposited Al2O3 on Si

    NASA Astrophysics Data System (ADS)

    Sturm, J. M.; Zinine, A. I.; Wormeester, H.; Poelsema, Bene; Bankras, R. G.; Holleman, J.; Schmitz, J.

    2005-03-01

    Ultrathin 2.5nm high-k aluminum oxide (Al2O3) films on p-type silicon (001) deposited by atomic layer deposition (ALD) were investigated with noncontact atomic force microscopy (NC-AFM) in ultrahigh vacuum, using a conductive tip. Constant force gradient images revealed the presence of oxide charges and experimental observations at different tip-sample potentials were compared with calculations of the electric force gradient based on a spherical tip model. This model could be substantially improved by the incorporation of the image of the tip in the semiconductor substrate. Based on the signals of different oxide charges observed, a homogenous depth distribution of those charges was derived. Application of a potential difference between sample and tip was found to result in a net electric force depending on the contact potential difference (CPD) and effective tip-sample capacitance, which depends on the depletion or accumulation layer that is induced by the bias voltage. CPD images could be constructed from height-voltage spectra with active feedback. Apart from oxide charges large-scale (150-300nm lateral size) and small-scale (50-100nm) CPD fluctuations were observed, the latter showing a high degree of correlation with topography features. This correlation might be a result from the surface-inhibited growth mode of the investigated layers.

  16. Observation of Atomic Steps on Vicinal Si(111) Annealed in Hydrogen Gas Flow by Scanning Tunneling Microscopy

    NASA Astrophysics Data System (ADS)

    Kitahara, Kuninori; Ueda, Osamu

    1993-12-01

    The surface of vicinal Si(111) annealed in H2 flow was observed by equipping the chemical vapor deposition chamber with the scanning tunneling microscope. Samples were annealed at 1000°C for 10 min by passing an electric current under the H2 pressure of 7 Torr. Their surface morphology was compared with those annealed in ultrahigh vacuum (UHV) and in N2 flow at the same temperature. We found that the step motion during annealing in H2 was obviously smaller than that for annealing in UHV and N2. The multisteps formed during the annealing in UHV and N2 were not observed for H2 annealing except in the case of heating by direct current in the direction of lower to higher terraces. The mechanism of the interruption of the step motion is discussed from the viewpoint of the interaction between the surface and hydrogen.

  17. Step-structure dependent step-flow: models for the homoepitaxial growth at the atomic steps on Si(111)7 × 7

    NASA Astrophysics Data System (ADS)

    Shimada, Wataru; Tochihara, Hiroshi

    1994-05-01

    Step-flow models of homoepitaxial growth at atomic steps on Si(111)7 × 7 are considered within the framework of the dimer-adatom-stacking-fault (DAS) model with the aid of a scanning tunneling microscopy (STM) image published by Köhler, Demuth and Hamers [J. Vac. Sci. Technol. A 7 (1989) 2860]. The image was taken at room temperature for a surface epitaxially grown at 330°C. From the image around the growing step, we find that the step flow is separated into two processes; the initial growth on the end zone of the lower terrace where the (7 × 7) DAS reconstruction is not formed due to its insufficient space, and the subsequent growth where the (7 × 7) DAS reconstruction at the lower step-edge has to be canceled to grow epitaxially. For the initial growth we propose step-structure dependent step-flow models, according to our classification of the atomic steps. For the subsequent growth, in addition to our previously proposed model for the cancelation of the (7 × 7) DAS structure during homoepitaxial growth on terraces (termed as the coalescent destruction model), we postulate the following four guidelines to construct models. (i) The destruction of the faulted halves and dimers at lower step-edge is the rate-determining step for step-flow, (ii) The epitaxial growth on the unfaulted halves at the lower step-edge is rapid, (iii) The faulted half at the "macrokink" is much easier to be broken than that at the straight step. (iv) The advanced step grows faster than the receded step does. By using the guidelines and the coalescent destruction model, we propose models for the subsequent growth at the U and F steps whose outward normal of the risers are the [1¯1¯2] and [112¯] directions, respectively. As the step-flows proceed with increasing Si deposition, the proposed model naturally leads to the following change of macroscopic shapes of the atomic steps: The straight F step converts to a zigzag step consisting of the U steps, while the straight U step maintains

  18. Predation of stink bugs (Hemiptera: Pentatomidae) by a complex of predators and adjoining soybean habitats in Georgia, USA

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Molecular gut-content analysis was used to examine predation on stink bugs (Hemiptera: Pentatomidae) by arthropod predators in habitats of soybean with and without buckwheat and adjoining cotton. Nezara viridula (L.), Euschistus servus (Say), Chinavia hilaris (Say), and Euschistus quadrator Rolston,...

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

    SciTech Connect

    Mohammadi, V. Nihtianov, S.

    2016-02-15

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

  20. Atomic and electronic structures of Si(1 1 1)-\\left(\\sqrt{\\mathbf{3}}\\times\\sqrt{\\mathbf{3}}\\right)\\text{R}\\mathbf{3}{{\\mathbf{0}}^{\\circ}} -Au and (6 × 6)-Au surfaces

    NASA Astrophysics Data System (ADS)

    Patterson, C. H.

    2015-12-01

    Si(1 1 1)-Au surfaces with around one monolayer of Au exhibit many ordered structures and structures containing disordered domain walls. Hybrid density functional theory (DFT) calculations presented here reveal the origin of these complex structures and tendency to form domain walls. The conjugate honeycomb chain trimer (CHCT) structure of the \\sqrt{3} -Au phase contains Si atoms with non-bonding surface states which can bind Au atoms in pairs in interstices of the CHCT structure and make this surface metallic. Si adatoms adsorbed on the \\sqrt{3} -Au surface induce a gapped surface through interaction with the non-bonding states. Adsorption of extra Au atoms in interstitial sites of the \\sqrt{3} -Au surface is stabilized by interaction with the non-bonding orbitals and leads to higher coverage ordered structures including the ≤ft(6× 6\\right) -Au phase. Extra Au atoms bound in interstitial sites of the \\sqrt{3} -Au surface result in top layer Si atoms with an SiAu4 butterfly wing configuration. The structure of a ≤ft(6× 6\\right) -Au phase, whose in-plane top atomic layer positions were previously determined by an electron holography technique (Grozea et al 1998 Surf. Sci. 418 32), is calculated using total energy minimization. The Patterson function for this structure is calculated and is in good agreement with data from an in-plane x-ray diffraction study (Dornisch et al 1991 Phys. Rev. B 44 11221). Filled and empty state scanning tunneling microscopy (STM) images are calculated for domain walls and the ≤ft(6× 6\\right) -Au structure. The ≤ft(6× 6\\right) -Au phase is 2D chiral and this is evident in computed and actual STM images. ≤ft(6× 6\\right) -Au and domain wall structures contain the SiAu4 motif with a butterfly wing shape. Chemical bonding within the Si-Au top layers of the \\sqrt{3} -Au and ≤ft(6× 6\\right) -Au surfaces is analyzed and an explanation for the SiAu4 motif structure is given.

  1. Atomic packing and diffusion in Fe{sub 85}Si{sub 2}B{sub 9}P{sub 4} amorphous alloy analyzed by ab initio molecular dynamics simulation

    SciTech Connect

    Wang, Yaocen; Takeuchi, Akira; Makino, Akihiro; Liang, Yunye; Kawazoe, Yoshiyuki

    2015-05-07

    In the work reported in this paper, ab initio molecular dynamics simulation was performed on Fe{sub 85}Si{sub 2}B{sub 9}P{sub 4} amorphous alloy. Preferred atomic environment of the elements was analyzed with Voronoi polyhedrons. It showed that B and P atoms prefer less neighbors compared with Fe and Si, making them structurally incompatible with Fe rich structure and repulsive to the formation of α-Fe. However, due to the low bonding energy of B and P caused by low coordination number, the diffusion rates of them were considerably large, resulting in the requirement of fast annealing for achieving optimum nano-crystallization for its soft magnetic property. The simulation work also indicates that diffusion rate in amorphous alloy is largely determined by bonding energy rather than atomic size.

  2. Ph(i-PrO)SiH2: An Exceptional Reductant for Metal-Catalyzed Hydrogen Atom Transfers.

    PubMed

    Obradors, Carla; Martinez, Ruben M; Shenvi, Ryan A

    2016-04-13

    We report the discovery of an outstanding reductant for metal-catalyzed radical hydrofunctionalization reactions. Observations of unexpected silane solvolysis distributions in the HAT-initiated hydrogenation of alkenes reveal that phenylsilane is not the kinetically preferred reductant in many of these transformations. Instead, isopropoxy(phenyl)silane forms under the reaction conditions, suggesting that alcohols function as important silane ligands to promote the formation of metal hydrides. Study of its reactivity showed that isopropoxy(phenyl)silane is an exceptionally efficient stoichiometric reductant, and it is now possible to significantly decrease catalyst loadings, lower reaction temperatures, broaden functional group tolerance, and use diverse, aprotic solvents in iron- and manganese-catalyzed hydrofunctionalizations. As representative examples, we have improved the yields and rates of alkene reduction, hydration, hydroamination, and conjugate addition. Discovery of this broadly applicable, chemoselective, and solvent-versatile reagent should allow an easier interface with existing radical reactions. Finally, isotope-labeling experiments rule out the alternative hypothesis of hydrogen atom transfer from a redox-active β-diketonate ligand in the HAT step. Instead, initial HAT from a metal hydride to directly generate a carbon-centered radical appears to be the most reasonable hypothesis.

  3. Examination of the Atomic Pair Distribution Function (PDF) of SiC Nanocrystals by In-situ High Pressure Diffraction

    NASA Technical Reports Server (NTRS)

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

    2003-01-01

    Key properties of nanocrystals are determined by their real atomic structure, therefore a reasonable understanding and meaningful interpretation of their properties requires a realistic model of the structure. In this paper we present an evidence of a complex response of the lattice distances to external pressure indicating a presence of a complex structure of Sic nanopowders. The experiments were performed on nanocrystalline Sic subjected to hydrostatic or isostatic pressure using synchrotron and neutron powder diffraction. Elastic properties of the samples were examined based on X-ray diffraction data using a Diamond Anvil Cell (DAC) in HASYLAB at DESY. The dependence'of the lattice parameters and of the Bragg reflections width with pressure exhibits a ha1 nature of the properties (compressibilities) of the powders and indicates a complex structure of the grains. We interpreted tws behaviour as originating from different elastic properties of the grain interior and surface. Analysis of the dependence of individual interatomic distances on pressure was based on in-situ neutron diffraction measurements done with HbD diffractometer at LANSCE in Los Alamos National Laboratory with the Paris-Edinburgh cell under pressures up to 8 GPa (Qmax = 26/A). Interatomic distances were obtained by PDF analysis using the PDFgetN program. We have found that the interatomic distances undergo a complex, non-monotonic changes. Even under substantial pressures a considerable relaxation of the lattice may take place: some interatomic distances increase with an increase in pressure. We relate this phenomenon to: (1), changes of the microstructure of the densified material, in particular breaking of its fractal chain structure and, (2), its complex structure resembling that of a material composed of two phases, each with its distinct elastic properties.

  4. Tectonic and depositional model of the Arabian and adjoining plates during the Silurian-Devonian

    SciTech Connect

    Husseini, M.I. )

    1991-01-01

    During the Late Ordovician and Early Silurian, the western part of the Arabian Peninsula was covered by polar glaciers that advanced from the south pole in African Gondwana. During this period, nondeposition, erosion, or marginal marine conditions prevailed in eastern and northern Arabia. When the glaciers melted in the Early Silurian, sea level rose sharply and the paleo-Tethys Ocean transgressed the Arabian and adjoining plates depositing a thick, organic-rich shale directly over the glaciogenic and periglacial rocks and related unconformities. The post-glacial sequence coarsens upward reflecting the passage of a coastline prograding northward from African and Arabian Gondwana to northern Arabia. A sea level drop in the Late Silurian placed the study area in a terrestrial environment; however, as sea level recovered in the Early Devonian, a carbonate sequence blanketed most of the area. The transgression, however, was interrupted by regional uplift and local orogenic movements in the Middle and Late Devonian. These movements constitute the onset of Hercynian tectonism, which resulted in erosion of the older sequences, depositional hiatuses, and regional facies changes.

  5. Ground water contamination in the area adjoining zinc smelter effluent stream.

    PubMed

    Garg, V K; Totawat, K L

    2004-01-01

    A preliminary survey of the area adjoining to zinc smelter effluent stream was undertaken to assess ground water contamination. Twenty-five ground water samples from the wells located in the study area were collected and grouped into nine groups based on their lateral and longitudinal position from the stream carrying the effluent discharged from zinc smelter, Debari- Udaipur. The study indicate that waters of wells situated in the vicinity of effluent stream (255m radius) were of medium salinity having higher levels of Ca and Mg and lower values of pH as compared to the waters of the reference wells situated far away from the effluent stream. The Fe, Zn, Cd, Cl, F and SO4 contents ofthe water from the wells located within 80m vicinity of the effluent stream were above the permissible limits for drinking purposes. Furthermore the Zn, Cl and SO4 levels in these waters were so high that they were even not suitable for irrigation, indicating a gradual encroachment of effluent into the native ground water.

  6. Tectonic and deposition model of late Precambrian-Cambrian Arabian and adjoining plates

    SciTech Connect

    Husseini, M.I. )

    1989-09-01

    During the late Precambrian, the terranes of the Arabian and adjoining plates were fused along the northeastern flank of the African plate in Gondwanaland. This phase, which ended approximately 640 to 620 Ma, was followed by continental failure (620 to 580 Ma) and intracontinental extension (600 to approximately 550 Ma). During the Infracambrian extensional phase, a triple junction may have evolved near the Sinai Peninsula and may have consisted of the (1) Jordan Valley and Dead Sea rift branch, (2) Sinai and North Egypt rift branch, and (3) the Najd wrench-rift branch. The Najd, Hawasina, and Zagros fault systems may have been transverse faults that accompanied rifting in the Arabian Gulf and Zagros Mountains, southern Oman, Pakistan, and Kerman in central Iran. While the area was extending and subsiding, the Tethys Ocean flooded the eastern side of the Arabian plate and Iran and deposited calcareous clastics, carbonates, and evaporites (including the Hormuz and Ara halites). This transgression extended into the western part of the Arabian plate via the Najd rift system. The termination of the extensional phase during the late Early Cambrian was accompanied by a major regression and terrestrial conditions on the Arabian Peninsula. However, by the Early Ordovician, as sea level peaked to a highstand, the Arabian plate was blanketed with marginal marine sediments. 11 figs., 2 tabs.

  7. Hydrochemical profile for assessing the groundwater quality of Sambhar lake city and its adjoining area.

    PubMed

    Joshi, Anita; Seth, Gita

    2011-03-01

    Quality assessment of water is essential to ensure sustainable safe use of it for drinking, agricultural, and industrial purposes. For the same purpose the study was conducted for the samples of water of Sambhar lake city and its adjoining areas. The standard methods of APHA were used to analysis 15 samples collected from hand pumps and tube wells of the specified area. The analytical results show higher concentration of total dissolved solids, electrical conductivity sodium, nitrate, sulfate, and fluoride, which indicate signs of deterioration but values of pH, calcium, magnesium, total hardness, and carbonate are within permissible limits as per WHO standards. From the Hill-piper trilinear diagram, it is observed that the majority of groundwater from sampling stations are sodium-potassium-chloride-sulfate type water. The values of sodium absorption ratio and electrical conductivity of the groundwater were plotted in the US salinity laboratory diagram for irrigation water. Only the one sample fall in C(3)S(1) quality with high salinity hazard and low sodium hazard. Other samples fall in high salinity hazard and high sodium hazard. Chemical analysis of groundwater shows that mean concentration of cation is in order sodium > magnesium > calcium > potassium while for the anion it is chloride > bicarbonate > nitrate > sulfate.

  8. Low-temperature self-limiting atomic layer deposition of wurtzite InN on Si(100)

    NASA Astrophysics Data System (ADS)

    Haider, Ali; Kizir, Seda; Biyikli, Necmi

    2016-04-01

    In this work, we report on self-limiting growth of InN thin films at substrate temperatures as low as 200 °C by hollow-cathode plasma-assisted atomic layer deposition (HCPA-ALD). The precursors used in growth experiments were trimethylindium (TMI) and N2 plasma. Process parameters including TMI pulse time, N2 plasma exposure time, purge time, and deposition temperature have been optimized for self-limiting growth of InN with in ALD window. With the increase in exposure time of N2 plasma from 40 s to 100 s at 200 °C, growth rate showed a significant decrease from 1.60 to 0.64 Å/cycle. At 200 °C, growth rate saturated as 0.64 Å/cycle for TMI dose starting from 0.07 s. Structural, optical, and morphological characterization of InN were carried out in detail. X-ray diffraction measurements revealed the hexagonal wurtzite crystalline structure of the grown InN films. Refractive index of the InN film deposited at 200 °C was found to be 2.66 at 650 nm. 48 nm-thick InN films exhibited relatively smooth surfaces with Rms surface roughness values of 0.98 nm, while the film density was extracted as 6.30 g/cm3. X-ray photoelectron spectroscopy (XPS) measurements depicted the peaks of indium, nitrogen, carbon, and oxygen on the film surface and quantitative information revealed that films are nearly stoichiometric with rather low impurity content. In3d and N1s high-resolution scans confirmed the presence of InN with peaks located at 443.5 and 396.8 eV, respectively. Transmission electron microscopy (TEM) and selected area electron diffraction (SAED) further confirmed the polycrystalline structure of InN thin films and elemental mapping revealed uniform distribution of indium and nitrogen along the scanned area of the InN film. Spectral absorption measurements exhibited an optical band edge around 1.9 eV. Our findings demonstrate that HCPA-ALD might be a promising technique to grow crystalline wurtzite InN thin films at low substrate temperatures.

  9. Structural and electronic properties of AB- and AA-stacking bilayer-graphene intercalated by Li, Na, Ca, B, Al, Si, Ge, Ag, and Au atoms

    NASA Astrophysics Data System (ADS)

    Tayran, Ceren; Aydin, Sezgin; Çakmak, Mehmet; Ellialtıoğlu, Şinasi

    2016-04-01

    The structural and electronic properties of X (=Li, Na, Ca, B, Al, Si, Ge, Ag, and Au)-intercalated AB- and AA-stacking bilayer-graphene have been investigated by using ab initio density functional theory. It is shown that Boron (Lithium)-intercalated system is energetically more stable than the others for the AB (AA) stacking bilayer-graphene systems. The structural parameters, electronic band structures, and orbital nature of actual interactions are studied for the relaxed stable geometries. It is seen that the higher the binding energy, the smaller is the distance between the layers, in these systems. The electronic band structures for these systems show that different intercalated atoms can change the properties of bilayer-graphene differently. For qualitative description of the electronic properties, the metallicities of the systems are also calculated and compared with each other. The Mulliken analysis and electron density maps clearly indicate that the interactions inside a single layer (intralayer interactions) are strong and highly covalent, while the interactions between the two layers (interlayer interactions) are much weaker.

  10. Influences of annealing on structural and compositional properties of Al2O3 thin films grown on 4H-SiC by atomic layer deposition

    NASA Astrophysics Data System (ADS)

    Tian, Li-Xin; Zhang, Feng; Shen, Zhan-Wei; Yan, Guo-Guo; Liu, Xing-Fang; Zhao, Wan-Shun; Wang, Lei; Sun, Guo-Sheng; Zeng, Yi-Ping

    2016-12-01

    Annealing effects on structural and compositional performances of Al2O3 thin films on 4H-SiC substrates are studied comprehensively. The Al2O3 films are grown by atomic layer deposition through using trimethylaluminum and H2O as precursors at 300 °C, and annealed at various temperatures in ambient N2 for 1 min. The Al2O3 film transits from amorphous phase to crystalline phase as annealing temperature increases from 750 °C to 768 °C. The refractive index increases with annealing temperature rising, which indicates that densification occurs during annealing. The densification and grain formation of the film upon annealing are due to crystallization which is relative with second-nearest-neighbor coordination variation according to the x-ray photoelectron spectroscopy (XPS). Although the binding energies of Al 2p and O 1s increase together during crystallization, separations between Al 2p and O 1s are identical between as-deposited and annealed sample, which suggests that the nearest-neighbour coordination is similar. Project supported by the National Basic Research Program of China (Grant No. 2015CB759600), the National Natural Science Foundation of China (Grant Nos. 61474113, 61574140, and 61274007), and the Beijing Nova Program, China (Grant No. xx2016071), and the CAEP Microsystem and THz Science and Technology Foundation (Grant No. CAEPMT201502).

  11. Three-Dimensional Assignment of the Structures of Atomic Clusters: an Example of Au8M (M=Si, Ge, Sn) Anion Clusters

    PubMed Central

    Liu, Yi-Rong; Huang, Teng; Gai, Yan-Bo; Zhang, Yang; Feng, Ya-Juan; Huang, Wei

    2015-01-01

    Identification of different isomer structures of atomic and molecular clusters has long been a challenging task in the field of cluster science. Here we present a three-dimensional (3D) assignment method, combining the energy (1D) and simulated (2D) spectra to assure the assignment of the global minimum structure. This method is more accurate and convenient than traditional methods, which only consider the total energy and first vertical detachment energies (VDEs) of anion clusters. There are two prerequisites when the 3D assignment method is ultilized. First, a reliable global minimum search algorithm is necessary to explore enough valleys on the potential energy surface. Second, trustworthy simulated spectra are necessary, that is to say, spectra that are in quantitative agreement. In this paper, we demonstrate the validity of the 3D assignment method using Au8M− (M = Si, Ge, Sn) systems. Results from this study indicate that the global minimum structures of Au8Ge− and Au8Sn− clusters are different from those described in previous studies. PMID:26631620

  12. Effects of Al concentration on microstructural characteristics and electrical properties of Al-doped ZnO thin films on Si substrates by atomic layer deposition.

    PubMed

    Lee, Ju Ho; Lee, Jae-Won; Hwang, Sooyeon; Kim, Sang Yun; Cho, Hyung Koun; Lee, Jeong Yong; Park, Jin-Seong

    2012-07-01

    Al-doped ZnO (AZO) thin films with various Al concentrations were synthesized on Si(001) substrates with native oxide layers by atomic layer deposition process. The effects of the Al concentration on the microstructural characteristics of the AZO thin films grown at 250 degrees C and the correlation between their microstructural characteristics and electrical properties of the AZO thin films were investigated by AFM, XRD, HRTEM and Hall measurements. The XRD and HRTEM results revealed that the crystallinity and electrical properties of the undoped ZnO thin films were enhanced by 2.48 at% Al doping. However, 12.62 at% Al doping induced the deterioration of their crystallinity and electrical properties due to the formation of nano-sized metallic Al clusters and randomly oriented ZnO-based nano-crystals. To enhance the electrical properties of the AZO thin films while maintaining their crystallinity and electrical properties, a moderate Al concentration has to be chosen under the solubility limit of Al in ZnO.

  13. Band structure of silicene on zirconium diboride (0001) thin-film surface: Convergence of experiment and calculations in the one-Si-atom Brillouin zone

    NASA Astrophysics Data System (ADS)

    Lee, Chi-Cheng; Fleurence, Antoine; Yamada-Takamura, Yukiko; Ozaki, Taisuke; Friedlein, Rainer

    2014-08-01

    So far, it represents a challenging task to reproduce angle-resolved photoelectron (ARPES) spectra of epitaxial silicene by first-principles calculations. Here, we report on the resolution of the previously controversial issue related to the structural configuration of silicene on the ZrB2(0001) surface and its band structure. In particular, by representing the band structure in a large Brillouin zone associated with a single Si atom, it is found that the imaginary part of the one-particle Green's function follows the spectral weight observed in ARPES spectra. By additionally varying the in-plane lattice constant, the results of density functional theory calculations and ARPES data obtained in a wide energy range converge into the "planarlike" phase and provide the orbital character of electronic states in the vicinity of the Fermi level. It is anticipated that the choice of a smaller commensurate unit cell for the representation of the electronic structure will be useful for the study of epitaxial two-dimensional materials on various substrates in general.

  14. Tsunami Simulations for Regional Sources in the South China and Adjoining Seas

    NASA Astrophysics Data System (ADS)

    Okal, Emile A.; Synolakis, Costas E.; Kalligeris, Nikos

    2011-06-01

    We present 14 scenarios of potential tsunamis in the South China Sea and its adjoining basins, the Sulu and Sulawezi Seas. The sources consist of earthquake dislocations inspired by the the study of historical events, either recorded (since 1900) or described in historical documents going back to 1604. We consider worst-case scenarios, where the size of the earthquake is not limited by the largest known event, but merely by the dimension of the basin over which a coherent fault may propagate. While such scenarios are arguably improbable, they may not be impossible, and as such must be examined. For each scenario, we present a simulation of the tsunami's propagation in the marine basin, exclusive of its interaction with the coastline. Our results show that the South China, Sulu and Sulawezi Seas make up three largely independent basins where tsunamis generated in one basin do not leak into another. Similarly, the Sunda arc provides an efficient barrier to tsunamis originating in the Indian Ocean. Furthermore, the shallow continental shelves in the Java Sea, the Gulf of Thailand and the western part of the South China Sea significantly dampen the amplitude of the waves. The eastern shores of the Malay Peninsula are threatened only by the greatest—and most improbable—of our sources, a mega-earthquake rupturing all of the Luzon Trench. We also consider two models of underwater landslides (which can be triggered by smaller events, even in an intraplate setting). These sources, for which there is both historical and geological evidence, could pose a significant threat to all shorelines in the region, including the Malay Peninsula.

  15. Application of Powder Diffraction Methods to the Analysis of Short- and Long-Range Atomic Order in Nanocrystalline Diamond and SiC: The Concept of the Apparent Lattice Parameter (alp)

    NASA Technical Reports Server (NTRS)

    Palosz, B.; Grzanka, E.; Gierlotka, S.; Stelmakh, S.; Pielaszek, R.; Bismayer, U.; Weber, H.-P.; Palosz, W.

    2003-01-01

    Two methods of the analysis of powder diffraction patterns of diamond and SiC nanocrystals are presented: (a) examination of changes of the lattice parameters with diffraction vector Q ('apparent lattice parameter', alp) which refers to Bragg scattering, and (b), examination of changes of inter-atomic distances based on the analysis of the atomic Pair Distribution Function, PDF. Application of these methods was studied based on the theoretical diffraction patterns computed for models of nanocrystals having (i) a perfect crystal lattice, and (ii), a core-shell structure, i.e. constituting a two-phase system. The models are defined by the lattice parameter of the grain core, thickness of the surface shell, and the magnitude and distribution of the strain field in the shell. X-ray and neutron experimental diffraction data of nanocrystalline SiC and diamond powders of the grain diameter from 4 nm up to micrometers were used. The effects of the internal pressure and strain at the grain surface on the structure are discussed based on the experimentally determined dependence of the alp values on the Q-vector, and changes of the interatomic distances with the grain size determined experimentally by the atomic Pair Distribution Function (PDF) analysis. The experimental results lend a strong support to the concept of a two-phase, core and the surface shell structure of nanocrystalline diamond and SiC.

  16. Characterizing Fluorocarbon Assisted Atomic Layer Etching of Si Using Cyclic Ar/C4F8 and Ar/CHF3 Plasma

    SciTech Connect

    Metzler, Dominik; Li, Chen; Engelmann, Sebastian; Bruce, Robert L; Joseph, Eric A; Oehrlein, Gottlieb S

    2016-09-08

    With the increasing interest in establishing directional etching methods capable of atomic scale resolution for fabricating highly scaled electronic devices, the need for development and characterization of atomic layer etching (ALE) processes, or generally etch processes with atomic layer precision, is growing. In this work, a flux-controlled cyclic plasma process is used for etching of SiO2 and Si at the Angstrom-level. This is based on steady-state Ar plasma, with periodic, precise injection of a fluorocarbon (FC) precursor (C4F8 and CHF3), and synchronized, plasma-based Ar+ ion bombardment [D. Metzler et al., J Vac Sci Technol A 32, 020603 (2014), and D. Metzler et al., J Vac Sci Technol A 34, 01B101 (2016)]. For low energy Ar+ ion bombardment conditions, physical sputter rates are minimized, whereas material can be etched when FC reactants are present at the surface. This cyclic approach offers a large parameter space for process optimization. Etch depth per cycle, removal rates, and self-limitation of removal, along with material dependence of these aspects, were examined as a function of FC surface coverage, ion energy, and etch step length using in situ real time ellipsometry. The deposited FC thickness per cycle is found to have a strong impact on etch depth per cycle of SiO2 and Si, but is limited with regard to control over material etching selectivity. Ion energy over the 20 to 30 eV range strongly impacts material selectivity. The choice of precursor can have a significant impact on the surface chemistry and chemically enhanced etching. CHF3 has a lower FC deposition yield for both SiO2 and Si, and also exhibits a strong substrate dependence of FC deposition yield, in contrast to C4F8. The thickness of deposited FC layers using CHF3 is found to be greater for Si than for SiO2. X-ray photoelectron spectroscopy was used to study surface chemistry

  17. Atomic arrangement and electron band structure of Si(1 1 1)-ß-\\sqrt{3}\\times \\sqrt{3} -Bi reconstruction modified by alkali-metal adsorption: ab initio study

    NASA Astrophysics Data System (ADS)

    Eremeev, S. V.; Chukurov, E. N.; Gruznev, D. V.; Zotov, A. V.; Saranin, A. A.

    2015-08-01

    Using ab initio calculations, atomic structure and electronic properties of Si(1 1 1)\\sqrt{3}× \\sqrt{3} -Bi surface modified by adsorption of 1/3 monolayer of alkali metals, Li, Na, K, Rb and Cs, have been explored. Upon adsorption of all metals, a similar atomic structure develops at the surface where twisted chained Bi trimers are arranged into a honeycomb network and alkali metal atoms occupy the {{T}4} sites in the center of each honeycomb unit. Among other structural characteristics, the greatest variation concerns the relative heights at which alkali metals reside with respect to Bi-trimer layer. Except for Li, the other metals reside higher than Bi layer and their heights increase with atomic number. All adsorbed surface structures display similar electron band structures of which the most essential feature is metallic surface-state band with a giant spin splitting. This electronic property allows one to consider the Si(1 1 1)\\sqrt{3}× \\sqrt{3} -Bi surfaces modified by alkali metal adsorption as a set of material systems showing promise for spintronic applications.

  18. Atomic arrangement and electron band structure of Si(1 1 1)-ß-√3 x √3-Bi reconstruction modified by alkali-metal adsorption: ab initio study.

    PubMed

    Eremeev, S V; Chukurov, E N; Gruznev, D V; Zotov, A V; Saranin, A A

    2015-08-05

    Using ab initio calculations, atomic structure and electronic properties of Si(1 1 1)[Formula: see text]-Bi surface modified by adsorption of 1/3 monolayer of alkali metals, Li, Na, K, Rb and Cs, have been explored. Upon adsorption of all metals, a similar atomic structure develops at the surface where twisted chained Bi trimers are arranged into a honeycomb network and alkali metal atoms occupy the [Formula: see text] sites in the center of each honeycomb unit. Among other structural characteristics, the greatest variation concerns the relative heights at which alkali metals reside with respect to Bi-trimer layer. Except for Li, the other metals reside higher than Bi layer and their heights increase with atomic number. All adsorbed surface structures display similar electron band structures of which the most essential feature is metallic surface-state band with a giant spin splitting. This electronic property allows one to consider the Si(1 1 1)[Formula: see text]-Bi surfaces modified by alkali metal adsorption as a set of material systems showing promise for spintronic applications.

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

    NASA Astrophysics Data System (ADS)

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

    2013-08-01

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

  20. Growth and structure of GaN layers on silicon carbide synthesized on a Si substrate by the substitution of atoms: A model of the formation of V-defects during the growth of GaN

    NASA Astrophysics Data System (ADS)

    Kukushkin, S. A.; Osipov, A. V.; Rozhavskaya, M. M.; Myasoedov, A. V.; Troshkov, S. I.; Lundin, V. V.; Sorokin, L. M.; Tsatsul'nikov, A. F.

    2015-09-01

    This paper presents the results of the electron microscopic study of GaN/AlGaN/AlN/SiC/Si(111) structures grown by the metal-organic vapor phase epitaxy. A SiC epitaxial buffer nanolayer has been grown by a new method of substitution of atoms on the Si(111) substrate. It has been found that there is a strong dependence of the density of dislocations and V-defects on the synthesis conditions of SiC and the thickness of the AlN layer. It has been proved experimentally that the creation of a low-temperature AlN insert with a simultaneous decrease in the thickness of the AlN layer to values of no more than 50 nm makes it possible to almost completely prevent the formation of V-defects in the GaN layer. The density of screw and mixed dislocations in the GaN layer of the studied samples lies in the range from 5 × 109 to 1 × 1010 cm-2. A theoretical model of the formation of V-defects during the growth of GaN has been developed.

  1. Spectrometric analysis of process etching solutions of the photovoltaic industry--determination of HNO3, HF, and H2SiF6 using high-resolution continuum source absorption spectrometry of diatomic molecules and atoms.

    PubMed

    Bücker, Stefan; Acker, Jörg

    2012-05-30

    The surface of raw multicrystalline silicon wafers is treated with HF-HNO(3) mixtures in order to remove the saw damage and to obtain a well-like structured surface of low reflectivity, the so-called texture. The industrial production of solar cells requires a consistent level of texturization for tens of thousands of wafers. Therefore, knowing the actual composition of the etch bath is a key element in process control in order to maintain a certain etch rate through replenishment of the consumed acids. The present paper describes a novel approach to quantify nitric acid (HNO(3)), hydrofluoric acid (HF), and hexafluosilicic acid (H(2)SiF(6)) using a high-resolution continuum source graphite furnace absorption spectrometer. The concentrations of Si (via Si atom absorption at the wavelength 251.611 nm, m(0),(Si)=130 pg), of nitrate (via molecular absorption of NO at the wavelength 214.803 nm, [Formula: see text] ), and of total fluoride (via molecular absorption of AlF at the wavelength 227.46 nm, m(0,F)=13 pg) were measured against aqueous standard solutions. The concentrations of H(2)SiF(6) and HNO(3) are directly obtained from the measurements. The HF concentration is calculated from the difference between the total fluoride content, and the amount of fluoride bound as H(2)SiF(6). H(2)SiF(6) and HNO(3) can be determined with a relative uncertainty of less than 5% and recoveries of 97-103% and 96-105%, respectively. With regards to HF, acceptable results in terms of recovery and uncertainty are obtained for HF concentrations that are typical for the photovoltaic industry. The presented procedure has the unique advantage that the concentration of both, acids and metal impurities in etch solutions, can be routinely determined by a single analytical instrument.

  2. Interfacial reactions of ultrahigh-vacuum-deposited Cu thin films on atomically cleaned (111)Si. II. Oxidation of silicon catalyzed by eta script-Cu3Si at room temperature

    NASA Astrophysics Data System (ADS)

    Liu, C. S.; Chen, L. J.

    1993-11-01

    Room-temperature oxidation of (111)Si catalyzed by η`-Cu3Si has been studied by transmission electron microscopy, x-ray diffractometry (XRD), and Auger electron spectroscopy. XRD analysis showed that volume fractions of η`-Cu3Si and Cu decrease and increase with exposure time in air ambient, respectively. From TEM diffraction analysis, Cu precipitates were found to be epitaxially related to Si. After prolonged exposure in air, the Cu precipitates were found to form an irregular network structure in the SiO2 layer. Examination of the same area of annealed samples with intermittent exposure in air indicated that the oxidation was mainly initiated at the grain boundaries. Significant differences in room-temperature oxidation behavior between (111) and (001) samples were found.

  3. Formation of atomically ordered and chemically selective Si—O—Ti monolayer on Si0.5Ge0.5(110) for a MIS structure via H2O2(g) functionalization

    NASA Astrophysics Data System (ADS)

    Park, Sang Wook; Choi, Jong Youn; Siddiqui, Shariq; Sahu, Bhagawan; Galatage, Rohit; Yoshida, Naomi; Kachian, Jessica; Kummel, Andrew C.

    2017-02-01

    Si0.5Ge0.5(110) surfaces were passivated and functionalized using atomic H, hydrogen peroxide (H2O2), and either tetrakis(dimethylamino)titanium (TDMAT) or titanium tetrachloride (TiCl4) and studied in situ with multiple spectroscopic techniques. To passivate the dangling bonds, atomic H and H2O2(g) were utilized and scanning tunneling spectroscopy (STS) demonstrated unpinning of the surface Fermi level. The H2O2(g) could also be used to functionalize the surface for metal atomic layer deposition. After subsequent TDMAT or TiCl4 dosing followed by a post-deposition annealing, scanning tunneling microscopy demonstrated that a thermally stable and well-ordered monolayer of TiOx was deposited on Si0.5Ge0.5(110), and X-ray photoelectron spectroscopy verified that the interfaces only contained Si—O—Ti bonds and a complete absence of GeOx. STS measurements confirmed a TiOx monolayer without mid-gap and conduction band edge states, which should be an ideal ultrathin insulating layer in a metal-insulator-semiconductor structure. Regardless of the Ti precursors, the final Ti density and electronic structure were identical since the Ti bonding is limited by the high coordination of Ti to O.

  4. Distribution of the Hoskinnini tongue of the Cutler formation in southwestern Utah and adjoining parts of Arizona and Colorado

    USGS Publications Warehouse

    Stewart, John H.; Mullens, T.E.; Williams, G.A.

    1954-01-01

    Recent field work indicates the Hoskinnini tongue of the Cutler formation is present in much of southeastern Utah and adjoining parts of Colorado. Previously the Hoskinnini had been recognized only in the Monument Valley region of southeastern Utah and northeastern Arizona. The Hoskinnini tongue is pale reddish brown and is composed mainly of silt and very fine-grained sand and minor quantities of fine, medium, and coarse sand grains. The Hoskinnini is indistinctly bedded in horizontal beds generally ranging from 1 to 2 feet thick, and individual beds are composed of indistinct discontinuous wavy laminae bounded by grayish-red clay or silt films. The Hoskinnini is generally 50 to 120 feet thick but ranges up to 126 feet thick' Pinchouts of the Hoskinnini on the west are abrupt, and the Hoskinnini near some of these pinchouts contains unusual features such as intraformational and chert pebble conglomerates, contorted stratification, and petroliferous material. The combination of coarse grains in the finer-grained matrix and discontinuous wavy laminae serve to differentiate the Hoskinnini tongue from the underlying and overlying formations' The distinctive combination of grain size and wavy laminae also assures correlation of the Hoskinnini with rocks not previously correlated with the Hoskinnini in southeastern Utah and adjoining parts of Colorado. Although the Hoskinnini tongue is cUJITently classified as a part of the Permian Cutler formation, stratigraphic relations show the Hoskinnini to be conttasted with typical Cutler rocks and to be closely related to the Lower and Middle (?) Triassic Moenkopi formation.

  5. Si(hhm) surfaces: Templates for developing nanostructures

    SciTech Connect

    Bozhko, S. I. Ionov, A. M.; Chaika, A. N.

    2015-06-15

    The fabrication of ordered low-dimensional structures on clean and metal-atom-decorated stepped Si(557) and Si(556) surfaces is discussed. The formation conditions and atomic structure of regular step systems on clean Si(557) 7 × 7 and Si(556) 7 × 7 surfaces are studied. The atomic structure of stepped Si(hhm), Ag/Si(557), and Gd/Si(557) surfaces is studied using high-resolution scanning tunneling microscopy and low-energy electron diffraction. The possibility of fabricating 1D and 2D structures of gadolinium and silver atoms on the Si(557) surface is demonstrated.

  6. Influence of the energy parameters of the deposited laser-induced flow of platinum atoms on characteristics of a Pt/n-6H-SiC thin-film structure

    SciTech Connect

    Fominskii, V. Yu. Romanov, R. I.; Gnedovets, A. G.; Zuev, V. V.; Demin, M. V.

    2010-04-15

    The features of platinum film formation on n-6H-SiC substrates were experimentally studied for different methods of pulsed laser deposition, i.e., by both the conventional method in vacuum and in an inert gas atmosphere. In the latter case, a disk screen was placed on the plume expansion axis between the laser target and substrate to protect the latter from micrometer and submicrometer particles. A numerical model of such a process was developed, which makes it possible to predict the deposited film distribution over the substrate surface, energy and angular parameters of the atomic flow as laser plume properties, inert gas pressure, and screen position are varied. Simulation results were used to explain electrical properties of Pt/n-6H-SiC thin-film structures fabricated by different methods.

  7. Annealing study of H2O and O3 grown Al2O3 deposited by atomic layer chemical vapour deposition on n-type 4H-SiC

    NASA Astrophysics Data System (ADS)

    Avice, Marc; Grossner, Ulrike; Nilsen, Ola; Christensen, Jens S.; Fjellvåg, Helmer; Svensson, Bengt G.

    2006-09-01

    Al2O3 has been grown by atomic layer chemical vapour deposition on HF cleaned n-type 4H-SiC using either H2O or O3 as an oxidant. After post-deposition annealing at high temperature (1000°C) in argon atmosphere for different durations (1, 2 and 3 h), bulk and interface properties of the films were studied by capacitance-voltage (CV), current-voltage (IV) and secondary ion mass spectrometry (SIMS) measurements. Electrical measurements show a decreasing shift of the flatband voltage indicating a diminution of the negative oxide charges with increasing annealing time. The SIMS measurements reveal accumulation of boron, sodium and potassium at the Al2O3/SiC interface but the accumulation decreases with annealing at 1000°C where also out diffusion of silicon into the Al2O3 film takes place.

  8. Electronic Origins of the Variable Efficiency of Room-Temperature Methane Activation by Homo- and Heteronuclear Cluster Oxide Cations [XYO2](+) (X, Y = Al, Si, Mg): Competition between Proton-Coupled Electron Transfer and Hydrogen-Atom Transfer.

    PubMed

    Li, Jilai; Zhou, Shaodong; Zhang, Jun; Schlangen, Maria; Weiske, Thomas; Usharani, Dandamudi; Shaik, Sason; Schwarz, Helmut

    2016-06-29

    The reactivity of the homo- and heteronuclear oxide clusters [XYO2](+) (X, Y = Al, Si, Mg) toward methane was studied using Fourier transform ion cyclotron resonance mass spectrometry, in conjunction with high-level quantum mechanical calculations. The most reactive cluster by both experiment and theory is [Al2O2](•+). In its favorable pathway, this cluster abstracts a hydrogen atom by means of proton-coupled electron transfer (PCET) instead of following the conventional hydrogen-atom transfer (HAT) route. This mechanistic choice originates in the strong Lewis acidity of the aluminum site of [Al2O2](•+), which cleaves the C-H bond heterolytically to form an Al-CH3 entity, while the proton is transferred to the bridging oxygen atom of the cluster ion. In addition, a comparison of the reactivity of heteronuclear and homonuclear oxide clusters [XYO2](+) (X, Y = Al, Si, Mg) reveals a striking doping effect by aluminum. Thus, the vacant s-p hybrid orbital on Al acts as an acceptor of the electron pair from methyl anion (CH3(-)) and is therefore eminently important for bringing about thermal methane activation by PCET. For the Al-doped cluster ions, the spin density at an oxygen atom, which is crucial for the HAT mechanism, acts here as a spectator during the course of the PCET mediated C-H bond cleavage. A diagnostic plot of the deformation energy vis-à-vis the barrier shows the different HAT/PCET reactivity map for the entire series. This is a strong connection to the recently discussed mechanism of oxidative coupling of methane on magnesium oxide surfaces proceeding through Grignard-type intermediates.

  9. Observing the semiconducting band-gap alignment of MoS{sub 2} layers of different atomic thicknesses using a MoS{sub 2}/SiO{sub 2}/Si heterojunction tunnel diode

    SciTech Connect

    Nishiguchi, Katsuhiko Yamaguchi, Hiroshi; Fujiwara, Akira; Castellanos-Gomez, Andres; Zant, Herre S. J. van der; Steele, Gary A.

    2015-08-03

    We demonstrate a tunnel diode composed of a vertical MoS{sub 2}/SiO{sub 2}/Si heterostructure. A MoS{sub 2} flake consisting four areas of different thicknesses functions as a gate terminal of a silicon field-effect transistor. A thin gate oxide allows tunneling current to flow between the n-type MoS{sub 2} layers and p-type Si channel. The tunneling-current characteristics show multiple negative differential resistance features, which we interpret as an indication of different conduction-band alignments of the MoS{sub 2} layers of different thicknesses. The presented tunnel device can be also used as a hybrid-heterostructure device combining the advantages of two-dimensional materials with those of silicon transistors.

  10. Voltage linearity modulation and polarity dependent conduction in metal-insulator-metal capacitors with atomic-layer-deposited Al{sub 2}O{sub 3}/ZrO{sub 2}/SiO{sub 2} nano-stacks

    SciTech Connect

    Zhu, Bao; Liu, Wen-Jun; Wei, Lei; Zhang, David Wei; Jiang, Anquan; Ding, Shi-Jin

    2015-07-07

    Excellent voltage linearity of metal-insulator-metal (MIM) capacitors is highly required for next generation radio frequency integration circuits. In this work, employing atomic layer deposition technique, we demonstrated how the voltage linearity of MIM capacitors was modulated by adding different thickness of SiO{sub 2} layer to the nano-stack of Al{sub 2}O{sub 3}/ZrO{sub 2}. It was found that the quadratic voltage coefficient of capacitance (α) can be effectively reduced from 1279 to −75 ppm/V{sup 2} with increasing the thickness of SiO{sub 2} from zero to 4 nm, which is more powerful than increasing the thickness of ZrO{sub 2} in the Al{sub 2}O{sub 3}/ZrO{sub 2} stack. This is attributed to counteraction between the positive α for Al{sub 2}O{sub 3}/ZrO{sub 2} and the negative one for SiO{sub 2} in the MIM capacitors with Al{sub 2}O{sub 3}/ZrO{sub 2}/SiO{sub 2} stacks. Interestingly, voltage-polarity dependent conduction behaviors in the MIM capacitors were observed. For electron bottom-injection, the addition of SiO{sub 2} obviously suppressed the leakage current; however, it abnormally increased the leakage current for electron top-injection. These are ascribed to the co-existence of shallow and deep traps in ZrO{sub 2}, and the former is in favor of the field-assisted tunnelling conduction and the latter contributes to the trap-assisted tunnelling process. The above findings will be beneficial to device design and process optimization for high performance MIM capacitors.

  11. Atomic oxygen interactions with FEP Teflon and silicones on LDEF

    NASA Technical Reports Server (NTRS)

    Banks, Bruce A.; Gebauer, Linda

    1991-01-01

    The Long Duration Exposure Facility (LDEF) spacecraft represents the first controlled unidirectional exposure of high-fluence atomic oxygen on fluorinated ethylene propylene (FEP Teflon) and silicones. The atomic oxygen erosion yield for FEP Teflon was found to be significantly in excess of previous low fluence orbital data and is an order of magnitude below that of polyimide Kapton. LDEF FEP Teflon erosion yield data as a function of angle of attack is presented. Atomic oxygen interaction with silicon polymers results in crazing of the silicones as well as deposition of dark contaminant oxidation products on adjoining surfaces. Documentation of results and possible mechanistic explanations are presented.

  12. Regional disconformities in Turonian and Coniacian (Upper Cretaceous) strata in Colorado, Wyoming, and adjoining states - Biochronological evidence

    USGS Publications Warehouse

    Merewether, E.A.; Cobban, W.A.; Obradovich, J.D.

    2007-01-01

    Siliciclastic and calcareous sedimentary rocks of early Late Cretaceous age in the Western Interior of the United States have been assigned to, in ascending order, the Graneros Shale, Greenhorn Formation, Carlile Shale, Niobrara Formation, and their lateral equivalents (including members of the Frontier Formation and overlying formations). This sequence of formations was deposited intermittently within and near an epicontinental seaway during the Cenomanian, Turonian, and Coniacian stages of the Cretaceous. It encloses three conspicuous and widespread disconformities that reflect regional marine regressions and transgressions as well as moderate tectonism. The disconformities and associated lacunae occupy three large areas within Wyoming, Colorado, and adjoining states. In parts of that region, as in northwestern Wyoming, a lacuna can represent more than one period of erosion and more than a single disconformity. Evidence for these disconformities was obtained from about 175 collections of molluscan fossils and from sedimentological studies of outcrops and borehole logs, supplemented by previously published data.

  13. Effect of Chemistry and Particle Size on the Performance of Calcium Disilicide Primers. Part 1 - Synthesis of Calcium Silicide (CaSi2) by Rotary Atomization

    DTIC Science & Technology

    2010-02-01

    refs. 8 and 9); electrolysis (refs. 10 and 11); calcium hydride (CaH2) and Si (ref. 12); SiC and CaO (ref. 13); and combustion synthesis (ref. 14...obtained using a goiniometer (Phillips Model PW 3040, Phillips, Eindhoven, the Netherlands) using copper (Cu) K„ radiation (X - 1.54183 A) with a graphite...34 Electrolysis of Molten Alkali and Alkaline Earth Silicates." Bull. Soc. Chim., 6,206, 1939. 12. Louis, V. and Franck, H. H., "Silicide of Calcium," Z. Anorq

  14. Low-energy operation of the Livermore electron beam ion traps: Atomic spectroscopy of Si V, S VII, and Ar IX

    SciTech Connect

    Lepson, J K; Beiersdorfer, P

    2004-01-02

    As part of a project to compile a comprehensive catalog of astrophysically relevant emission lines, we used the low-energy capability of the Lawrence Livermore electron beam ion traps to extend the spectroscopy of neon-like ions and the neighboring charge states to silicon, sulfur, and argon. They present wavelength data of Si V and demonstrate the effect of collisional deexcitation of electric dipole forbidden lines on the 2-3 L-shell spectra of Si V, S VII, and Ar IX.

  15. High-energy X-ray powder diffraction and atomic-pair distribution-function studies of charged/discharged structures in carbon-hybridized Li2MnSiO4 nanoparticles as a cathode material for lithiumion batteries

    SciTech Connect

    Moriya, Maki; Miyahara, Masahiko; Hokazono, Mana; Sasaki, Hirokazu; Nemoto, Atsushi; Katayama, Shingo; Akimoto, Yuji; Hirano, Shin-ichi; Ren, Yang

    2014-10-01

    The stable cycling performance with a high discharge capacity of similar to 190 mAh g(-1) in a carbon-hybridized Li2MnSiO4 nanostructured powder has prompted an experimental investigation of the charged/discharged structures using synchrotron-based and laboratory-based X-rays and atomic-pair distributionfunction (PDF) analyses. A novel method of in-situ spray pyrolysis of a precursor solution with glucose as a carbon source enabled the successful synthesis of the carbon-hybridized Li2(M)nSiO(4) nanoparticles. The XRD patters of the discharged (lithiated) samples exhibit a long-range ordered structure characteristic of the (beta) Li2MnSiO4 crystalline phase (space group Pmn2(1)) which dissipates in the charged (delithiated) samples. However, upon discharging the long-range ordered structure recovers in each cycle. The disordered structure, according to the PDF analysis, is mainly due to local distortions of the MnO4 tetrahedra which show a mean Mn-O nearest neighbor distance shorter than that of the long-range ordered phase. These results corroborate the notion of the smaller Mn3+/Mn4+ ionic radii in the Li extracted phase versus the larger Mn2+ ionic radius in Li inserted phase. Thus Li extraction/insertion drives the fluctuation between the disordered and the long-range ordered structures. (C) 2014 Elsevier B.V. All rights reserved.

  16. Structural Investigation of Au Catalysts on TiO2-SiO2 Supports: Nature of the Local Structure of Ti and Au Atoms by EXAFS and XANES

    SciTech Connect

    Schwartz,V.; Mullins, D.; Yan, W.; Zhu, H.; Dai, S.; Overbury, S.

    2007-01-01

    X-ray absorption spectroscopy (XAS) was utilized to investigate both the Au particle size on several supports composed by silica and titanium oxide, and the coordination of TiO2 in the support phase. Particularly, we wanted to utilize the technique to probe mixing in the support phase, by using different synthetic methods such as by functionalizing silica or by ALD (atomic layer deposition) techniques as prepared in our laboratories, and the growth and stability of Au nanoparticles deposited on these supports. The study using cosynthesis techniques to dope bulk mesoporous SiO2 with TiO2 resulted in TiO2 being dispersed in the SiO2 matrix; however, a second phase starts forming as the TiO2 content increases as indicated by the EXAFS Ti-O shell shift in position and increase of coordination number. On the supports prepared by cosynthesis, Au particles were smaller and more stable. The study using the surface sol-gel technique for deposition of single monolayers of an oxide such as TiO2 produced Ti environments in which the Ti-O shell and the next two Ti-Ti shells lie on the same position as expected for an anatase structure. Although undercoordinated, the presence of the Ti-Ti shells indicate that the titania species are not molecularly dispersed on the SiO2 surface as hypothesized, but there is indeed a cross-linking of the titania moieties.

  17. Structural investigation of Au catalysts on TiO2-SiO2 supports - on the nature of the local structure of Ti and Au atoms by EXAFS and XANES

    SciTech Connect

    Schwartz, Viviane; Mullins, David R; Yan, Wenfu; Zhu, Haoguo; Dai, Sheng

    2007-01-01

    X-ray absorption spectroscopy (XAS) was utilized to investigate both the Au particle size on several supports composed by silica and titanium oxide, and the coordination of TiO2 in the support phase. Particularly, we wanted to utilize the technique to probe mixing in the support phase, by using different synthetic methods such as by functionalizing silica or by ALD (atomic layer deposition) techniques as prepared in our laboratories, and the growth and stability of Au nanoparticles deposited on these supports. The study using cosynthesis techniques to dope bulk mesoporous SiO2 with TiO2 resulted in TiO2 being dispersed in the SiO2 matrix; however, a second phase starts forming as the TiO2 content increases as indicated by the EXAFS Ti-O shell shift in position and increase of coordination number. On the supports prepared by cosynthesis, Au particles were smaller and more stable. The study using the surface sol-gel technique for deposition of single monolayers of an oxide such as TiO2 produced Ti environments in which the Ti-O shell and the next two Ti-Ti shells lie on the same position as expected for an anatase structure. Although undercoordinated, the presence of the Ti-Ti shells indicate that the titania species are not molecularly dispersed on the SiO2 surface as hypothesized, but there is indeed a cross-linking of the titania moieties.

  18. Strong electroluminescence from SiO{sub 2}-Tb{sub 2}O{sub 3}-Al{sub 2}O{sub 3} mixed layers fabricated by atomic layer deposition

    SciTech Connect

    Rebohle, L. Braun, M.; Wutzler, R.; Helm, M.; Skorupa, W.; Liu, B.; Sun, J. M.

    2014-06-23

    We report on the bright green electroluminescence (EL) with power efficiencies up to 0.15% of SiO{sub 2}-Tb{sub 2}O{sub 3}-mixed layers fabricated by atomic layer deposition and partly co-doped with Al{sub 2}O{sub 3}. The electrical, EL, and breakdown behavior is investigated as a function of the Tb and the Al concentration. Special attention has been paid to the beneficial role of Al{sub 2}O{sub 3} co-doping which improves important device parameters. In detail, it increases the maximum EL power efficiency and EL decay time, it nearly doubles the fraction of excitable Tb{sup 3+} ions, it shifts the region of high EL power efficiencies to higher injection currents, and it reduces the EL quenching over the device lifetime by an approximate factor of two. It is assumed that the presence of Al{sub 2}O{sub 3} interferes the formation of Tb clusters and related defects. Therefore, the system SiO{sub 2}-Tb{sub 2}O{sub 3}-Al{sub 2}O{sub 3} represents a promising alternative for integrated, Si-based light emitters.

  19. Revision of the Li13Si4 structure

    PubMed Central

    Zeilinger, Michael; Fässler, Thomas F.

    2013-01-01

    Besides Li17Si4, Li16.42Si4, and Li15Si4, another lithium-rich representative in the Li–Si system is the phase Li13Si4 (trideca­lithium tetra­silicide), the structure of which has been determined previously [Frank et al. (1975 ▶). Z. Naturforsch. Teil B, 30, 10–13]. A careful analysis of X-ray diffraction patterns of Li13Si4 revealed discrepancies between experimentally observed and calculated Bragg positions. Therefore, we redetermined the structure of Li13Si4 on the basis of single-crystal X-ray diffraction data. Compared to the previous structure report, decisive differences are (i) the introduction of a split position for one Li site [occupancy ratio 0.838 (7):0.162 (7)], (ii) the anisotropic refinement of atomic displacement parameters for all atoms, and (iii) a high accuracy of atom positions and unit-cell parameters. The asymmetric unit of Li13Si4 contains two Si and seven Li atoms. Except for one Li atom situated on a site with symmetry 2/m, all other atoms are on mirror planes. The structure consists of isolated Si atoms as well as Si–Si dumbbells surrounded by Li atoms. Each Si atom is either 12- or 13-coordinated. The isolated Si atoms are situated in the ab plane at z = 0 and are strictly separated from the Si–Si dumbbells at z = 0.5. PMID:24454148

  20. Surface chemistry of a Cu(I) beta-diketonate precursor and the atomic layer deposition of Cu{sub 2}O on SiO{sub 2} studied by x-ray photoelectron spectroscopy

    SciTech Connect

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

    2014-07-01

    The surface chemistry of the bis(tri-n-butylphosphane) copper(I) acetylacetonate, [({sup n}Bu{sub 3}P){sub 2}Cu(acac)] and the thermal atomic layer deposition (ALD) of Cu{sub 2}O using this Cu precursor as reactant and wet oxygen as coreactant on SiO{sub 2} substrates are studied by in-situ x-ray photoelectron spectroscopy (XPS). The Cu precursor was evaporated and exposed to the substrates kept at temperatures between 22 °C and 300 °C. The measured phosphorus and carbon concentration on the substrates indicated that most of the [{sup n}Bu{sub 3}P] ligands were released either in the gas phase or during adsorption. No disproportionation was observed for the Cu precursor in the temperature range between 22 °C and 145 °C. However, disproportionation of the Cu precursor was observed at 200 °C, since C/Cu concentration ratio decreased and substantial amounts of metallic Cu were present on the substrate. The amount of metallic Cu increased, when the substrate was kept at 300 °C, indicating stronger disproportionation of the Cu precursor. Hence, the upper limit for the ALD of Cu{sub 2}O from this precursor lies in the temperature range between 145 °C and 200 °C, as the precursor must not alter its chemical and physical state after chemisorption on the substrate. Five hundred ALD cycles with the probed Cu precursor and wet O{sub 2} as coreactant were carried out on SiO{sub 2} at 145 °C. After ALD, in-situ XPS analysis confirmed the presence of Cu{sub 2}O on the substrate. Ex-situ spectroscopic ellipsometry indicated an average film thickness of 2.5 nm of Cu{sub 2}O deposited with a growth per cycle of 0.05 Å/cycle. Scanning electron microscopy and atomic force microscopy (AFM) investigations depicted a homogeneous, fine, and granular morphology of the Cu{sub 2}O ALD film on SiO{sub 2}. AFM investigations suggest that the deposited Cu{sub 2}O film is continuous on the SiO{sub 2} substrate.

  1. Visualization of thermally fluctuating surface structure in noncontact atomic-force microscopy and tip effects on fluctuation: theoretical study of Si(111)-(square root[3] x square root[3])-Ag surface.

    PubMed

    Sasaki, Naruo; Watanabe, Satoshi; Tsukada, Masaru

    2002-01-28

    We investigated noncontact atomic-force microscopy (NC-AFM) images of a thermally fluctuating surface structure together with tip effects based on the first-principles electronic state calculation. As an example the Si(111)-(square root[3] x square root[3])-Ag (square root[3]-Ag) surface is studied. We have succeeded in theoretically visualizing the thermal fluctuation of the square root[3]-Ag surface at room temperature, and in reproducing the observed NC-AFM image for the first time. Further, the pinning effect of the thermal fluctuation of the square root[3]-Ag surface by the tip is clarified, which shows a novel ability of NC-AFM to modify the surface structure.

  2. AI-Li/SiCp composites and Ti-AI alloy powders and coatings prepared by a plasma spray atomization (PSA) technique

    NASA Astrophysics Data System (ADS)

    Khor, K. A.; Boey, F. Y. C.; Murakoshi, Y.; Sano, T.

    1994-06-01

    There has been increasing use of Al-Li alloys in the aerospace industry, due mainly to the low density and high elastic modulus of this material. However, the problem of low ductility and fracture toughness of this material has limited its present application to only weight- and stiffness-critical components. Development of Al-Li/ceramic composites is currently being investigated to enhance the service capabilities of this material. The Ti-Al alloy is also of interest to aerospace-type applications, engine components in particular, due to its attractive high-temperature properties. Preparation of fine powders by plasma melting of composite feedstock and coatings formed by plasma spraying was carried out to examine the effect of spray parameters on the microstructure and properties of these materials. Characterization of the powders and coatings was performed using the scanning electron microscope and image analyzer. Examination of the plasma-sprayed powders and coatings has shown that in the Al-Li/SiC composite there is melting of both materials to form a single composite particle. The SiC reinforcement was in the submicron range and contributed to additional strengthening of the composite body, which was formed by a cold isostatic press and consolidated by hot extrusion or hot forging processes. The plasma-sprayed Ti-Al powder showed four categories of microstructures: featureless, dendritic, cellular, and martensite-like.

  3. Atomic and electronic structure of trilayer graphene/SiC(0001): Evidence of Strong Dependence on Stacking Sequence and charge transfer

    NASA Astrophysics Data System (ADS)

    Pierucci, Debora; Brumme, Thomas; Girard, Jean-Christophe; Calandra, Matteo; Silly, Mathieu G.; Sirotti, Fausto; Barbier, Antoine; Mauri, Francesco; Ouerghi, Abdelkarim

    2016-09-01

    The transport properties of few-layer graphene are the directly result of a peculiar band structure near the Dirac point. Here, for epitaxial graphene grown on SiC, we determine the effect of charge transfer from the SiC substrate on the local density of states (LDOS) of trilayer graphene using scaning tunneling microscopy/spectroscopy and angle resolved photoemission spectroscopy (ARPES). Different spectra are observed and are attributed to the existence of two stable polytypes of trilayer: Bernal (ABA) and rhomboedreal (ABC) staking. Their electronic properties strongly depend on the charge transfer from the substrate. We show that the LDOS of ABC stacking shows an additional peak located above the Dirac point in comparison with the LDOS of ABA stacking. The observed LDOS features, reflecting the underlying symmetry of the two polytypes, were reproduced by explicit calculations within density functional theory (DFT) including the charge transfer from the substrate. These findings demonstrate the pronounced effect of stacking order and charge transfer on the electronic structure of trilayer or few layer graphene. Our approach represents a significant step toward understand the electronic properties of graphene layer under electrical field.

  4. Atomic and electronic structure of trilayer graphene/SiC(0001): Evidence of Strong Dependence on Stacking Sequence and charge transfer

    PubMed Central

    Pierucci, Debora; Brumme, Thomas; Girard, Jean-Christophe; Calandra, Matteo; Silly, Mathieu G.; Sirotti, Fausto; Barbier, Antoine; Mauri, Francesco; Ouerghi, Abdelkarim

    2016-01-01

    The transport properties of few-layer graphene are the directly result of a peculiar band structure near the Dirac point. Here, for epitaxial graphene grown on SiC, we determine the effect of charge transfer from the SiC substrate on the local density of states (LDOS) of trilayer graphene using scaning tunneling microscopy/spectroscopy and angle resolved photoemission spectroscopy (ARPES). Different spectra are observed and are attributed to the existence of two stable polytypes of trilayer: Bernal (ABA) and rhomboedreal (ABC) staking. Their electronic properties strongly depend on the charge transfer from the substrate. We show that the LDOS of ABC stacking shows an additional peak located above the Dirac point in comparison with the LDOS of ABA stacking. The observed LDOS features, reflecting the underlying symmetry of the two polytypes, were reproduced by explicit calculations within density functional theory (DFT) including the charge transfer from the substrate. These findings demonstrate the pronounced effect of stacking order and charge transfer on the electronic structure of trilayer or few layer graphene. Our approach represents a significant step toward understand the electronic properties of graphene layer under electrical field. PMID:27629702

  5. Do not judge a cell by its cover--diversity of CNS resident, adjoining and infiltrating myeloid cells in inflammation.

    PubMed

    Brendecke, Stefanie M; Prinz, Marco

    2015-11-01

    Specialized populations of tissue-resident myeloid cells inhabit every organ of the body. While many of these populations appear similar morphologically and phenotypically, they exhibit great functional diversity. The central nervous system (CNS), as an immune privileged organ, possesses a unique tissue-resident macrophage population, the microglia, as well as numerous myeloid cell subsets at its boarders and barriers in CNS-adjoining tissues, namely the meninges, the perivascular space, and the choroid plexus. Recent research has added much to our knowledge about microglia, whereas the populations of CNS-surrounding phagocytes are just starting to be appreciated. As guardians of CNS homeostasis, these myeloid cells perform immune surveillance and immune modulatory tasks in health and disease. As such, microglia and CNS-surrounding antigen-presenting cells have been shown to be crucially involved not only in the initiation and progression but also resolution of multiple sclerosis (MS). MS and its rodent model, experimental autoimmune encephalomyelitis, are autoimmune inflammatory demyelinating CNS pathologies. While some crucial aspects of the disease pathogenesis have been solved, much of the complex involvement and interplay of the innate immune compartment remains yet to be clarified. Here, we will discuss the current understanding of the scope of phenotypes and functions of myeloid cells involved in CNS neuroinflammation.

  6. Role of Ge and Si substrates in higher-k tetragonal phase formation and interfacial properties in cyclical atomic layer deposition-anneal Hf1-xZrxO2/Al2O3 thin film stacks

    NASA Astrophysics Data System (ADS)

    Dey, Sonal; Tapily, Kandabara; Consiglio, Steven; Clark, Robert D.; Wajda, Cory S.; Leusink, Gert J.; Woll, Arthur R.; Diebold, Alain C.

    2016-09-01

    Using a five-step atomic layer deposition (ALD)-anneal (DADA) process, with 20 ALD cycles of metalorganic precursors followed by 40 s of rapid thermal annealing at 1073 K, we have developed highly crystalline Hf1-xZrxO2 (0 ≤ x ≤ 1) thin films (<7 nm) on ˜1 nm ALD Al2O3 passivated Ge and Si substrates for applications in higher-k dielectric metal oxide semiconductor field effect transistors below 10 nm technology node. By applying synchrotron grazing incidence x-ray d-spacing maps, x-ray photoelectron spectroscopy (XPS), and angle-resolved XPS, we have identified a monoclinic to tetragonal phase transition with increasing ZrO2 content, elucidated the role of the Ge vs Si substrates in complete tetragonal phase formation (CTPF), and determined the interfacial characteristics of these technologically relevant films. The ZrO2 concentration required for CTPF is lower on Ge than on Si substrates (x ˜ 0.5 vs. x ˜ 0.86), which we attribute as arising from the growth of an ultra-thin layer of metal germanates between the Hf1-xZrxO2 and Al2O3/Ge, possibly during the first deposition and annealing cycle. Due to Ge-induced tetragonal phase stabilization, the interfacial metal germanates could act as a template for the subsequent preferential growth of the tetragonal Hf1-xZrxO2 phase following bottom-up crystallization during the DADA ALD process. We surmise that the interfacial metal germanate layer also function as a diffusion barrier limiting excessive Ge uptake into the dielectric film. An ALD Al2O3 passivation layer of thickness ≥1.5 nm is required to minimize Ge diffusion for developing highly conformal and textured HfO2 based higher-k dielectrics on Ge substrates using the DADA ALD process.

  7. Mössbauer study of the proximity gettering of cobalt atoms to He-induced nanosized voids in c-Si

    NASA Astrophysics Data System (ADS)

    Deweerd, W.; Barancira, T.; Bukshpan, S.; Demuynck, S.; Langouche, G.; Milants, K.; Moons, R.; Verheyden, J.; Pattyn, H.

    1996-06-01

    We observe a strong gettering of ion implanted 57Co to the internal surface of empty nanosized voids in c-Si, hampering normal silicide formation. The cavities are introduced by implanting He far above the solubility limits and subsequent desorption at 700 °C during 30 min. After 57Co implantation and thermal treatment, a previously unobserved Mössbauer spectrum was recorded that could be fitted consistently with two quadrupole doublets. They differ largely in binding strength and electric-field gradient Vzz and we preliminarily interpret them as an edge site (strong binding, smaller Vzz) and a surface site (loose binding, larger Vzz) at the internal surface of the faceted voids. The spectra are stable upon high-temperature annealing.

  8. The effect of atomic ions on model σ-hole bonded complexes of AH3Y (A = C, Si, Ge; Y = F, Cl, Br).

    PubMed

    McDowell, Sean A C; Joseph, Jerelle A

    2014-06-14

    A computational study of ionic X···AH3-Y complexes (X = F(-), Cl(-), Br(-), Li(+), Be(2+); A = C, Si, Ge; Y = F, Cl, Br) predicted optimized structures which are held together by a combination of attractive forces, including ion-dipole and ion-σ-hole electrostatic interactions, and polarization forces. The trends (with variation in the halogen Y) for selected properties were rationalized by considering the electron density shifts due to the ion's electric field. Although it has been found previously that the trends for binding energies in neutral complexes follow the sigma-hole strength, the present study found that the dependence on the dipole polarizability of the A-Y bond can explain the trends for binding energies in these more strongly bound ionic complexes.

  9. Near interface oxide degradation in high temperature annealed Si/SiO{sub 2}/Si structures

    SciTech Connect

    Devine, R.A.B.; Mathiot, D.; Warren, W.L.; Fleetwood, D.M.

    1993-12-31

    Degradation of 430 nm thick SiO{sub 2} layers in Si/SiO{sub 2}/Si structures which results from high temperature annealing (1320 C) has been studied using electron spin resonance, infra-red and refractive index measurements. Large numbers of oxygen vacancies are found in a region {le}100 nm from each Si/SiO{sub 2} interface. Two types of paramagnetic defects are observed following {gamma} or x-irradiation or hole injection. The 1106 cm{sup {minus}1} infra-red absorption associated with O interstitials in the Si substrate is found to increase with annealing time. The infra-red and spin resonance observations can be explained qualitatively and quantitatively in terms of a model in which oxygen atoms are gettered from the oxide into the under or overlying Si, the driving force being the increased O solubility limit associated with the anneal temperature.

  10. Interface-structure of the Si/SiC heterojunction grown on 6H-SiC

    SciTech Connect

    Li, L. B.; Chen, Z. M.; Zang, Y.

    2015-01-07

    The Si/SiC heterojunctions were prepared on 6H-SiC (0001) C-face by low-pressure chemical vapour deposition at 850 ∼ 1050 °C. Transmission electron microscopy and selected area electron diffraction were employed to investigate the interface-structure of Si/SiC heterojunctions. The Si/6H-SiC heterostructure of large lattice-mismatch follows domain matching epitaxy mode, which releases most of the lattice-mismatch strain, and the coherent Si epilayers can be grown on 6H-SiC. Si(1-11)/6H-SiC(0001) heterostructure is obtained at 900 °C, and the in-plane orientation relationship of Si/6H-SiC heterostructure is (1–11)[1-1-2]{sub Si}//(0001)[-2110]{sub 6H-SiC}. The Si(1-11)/6H-SiC(0001) interface has the same 4:5 Si-to-SiC matching mode with a residual lattice-mismatch of 0.26% along both the Si[1-1-2] and Si[110] orientations. When the growth temperature increases up to 1000 °C, the 〈220〉 preferential orientation of the Si film appears. SAED patterns at the Si/6H-SiC interface show that the in-plane orientation relationship is (-220)[001]{sub Si}//(0001)[2-1-10]{sub 6H-SiC}. Along Si[110] orientation, the Si-to-SiC matching mode is still 4:5; along the vertical orientation Si[001], the Si-to-SiC mode change to approximate 1:2 and the residual mismatch is 1.84% correspondingly. The number of the atoms in one matching-period decreases with increasing residual lattice-mismatch in domain matching epitaxy and vice versa. The Si film grows epitaxially but with misfit dislocations at the interface between the Si film and the 6H-SiC substrate. And the misfit dislocation density of the Si(1-11)/6H-SiC(0001) and Si(-220)/6H-SiC(0001) obtained by experimental observations is as low as 0.487 × 10{sup 14 }cm{sup −2} and 1.217 × 10{sup 14 }cm{sup −2}, respectively, which is much smaller than the theoretical calculation results.

  11. Endotaxial Si nanolines in Si(001):H

    NASA Astrophysics Data System (ADS)

    Owen, James; Bianco, François; Köster, Sigrun A.; Mazur, Daniel; Renner, Christoph; Bowler, David

    2011-03-01

    The study of one dimensional wires is of great interest in the area of low-dimensional physics, and these structures also have potential applications in future nanodevices. A perfectly straight nanoline embedded in a H-terminated silicon surface has been fabricated by a process of hydrogenation of a Bi nanoline surface using an atomic H beam source, and comprises a triangular core of Si embedded in the top five layers of the Si substrate. The defect density of this nanoline is extremely low, and being H- terminated, it is stable in air for limited periods of time. Scanning Tunnelling Microscopy experimental data and Density Functional Theory calculations have been used to determine the atomic structure of this nanoline, so-called the Haiku Stripe, and have revealed that there exists a 1D state localised to the nanoline core, lying just above the conduction band minimum. This work is supported by the Swiss National Science Fundation.

  12. Effect of the energy of recoil atoms on conductivity compensation in moderately doped n-Si and n-SiC under irradiation with MeV electrons and protons

    NASA Astrophysics Data System (ADS)

    Kozlovski, V. V.; Lebedev, A. A.; Emtsev, V. V.; Oganesyan, G. A.

    2016-10-01

    Processes of radiation defect formation and conductivity compensation in silicon and silicon carbide irradiated with 0.9 MeV electrons are considered in comparison with the electron irradiation at higher energies. The experimental values of the carrier removal rate at the electron energy of 0.9 MeV are nearly an order of magnitude smaller than the similar values of the parameter for higher energy electrons (6-9 MeV). At the same time, the formation cross-section of primary radiation defects (Frenkel pairs, FPs) is nearly energy-independent in this range. It is assumed that these differences are due to the influence exerted by the energy of primary knocked-on atoms (PKAs). As the PKA energy increases, the average distance between the genetically related FPs grows and, as a consequence, the fraction of FPs unrecombined under irradiation becomes larger. The FP recombination radius is estimated (∼1.1 nm), which makes it possible to ascertain the charge state of the recombining components. Second, the increase in the PKA energy enables formation of new, more complex secondary radiation defects. At electron energies exceeding 15 MeV, the average PKA energies are closer to the values obtained under irradiation with 1 MeV protons, compared with an electron irradiation at the same energy. As for the radiation-induced defect formation, the irradiation of silicon with MeV protons can be, in principle, regarded as a superposition of the irradiation with 1 MeV electrons and that with silicon ions having energy of ∼1 keV, with the ;source; of silicon ions generating these ions uniformly across the sample thickness.

  13. The localization and crystallographic dependence of Si suboxide species at the SiO2/Si interface

    NASA Technical Reports Server (NTRS)

    Grunthaner, P. J.; Hecht, M. H.; Grunthaner, F. J.; Johnson, N. M.

    1987-01-01

    X-ray photoemission spectroscopy has been used to examine the localization and crystallographic dependence of Si(+), Si(2+), and Si(3+) suboxide states at the SiO2/Si interface for (100)and (111)-oriented substrates with gate oxide quality thermal oxides. The Si(+) and Si(2+) states are localized within 6-10 A of the interface while the Si(3+) state extends about 30 A into the bulk SiO2. The distribution of Si(+) and Si(2+) states shows a strong crystallographic dependence with Si(2+) dominating on (100) substrates and Si(+) dominating on (111) substrates. This crystallographic dependence is anticipated from consideration of ideal unreconstructed (100) and (111) Si surfaces, suggesting that (1) the Si(+) and Si(2+) states are localized immediately within the first monolayer at the interface and (2) the first few monolayers of substrate Si atoms are not significantly displaced from the bulk. The total number of suboxide states observed at the SiO2/Si interface corresponds to 94 and 83 percent of a monolayer for these (100) and (111) substrates, respectively.

  14. High-performance solid-state on-chip supercapacitors based on Si nanowires coated with ruthenium oxide via atomic layer deposition

    NASA Astrophysics Data System (ADS)

    Zheng, Wen; Cheng, Qingmei; Wang, Dunwei; Thompson, Carl V.

    2017-02-01

    Solid-state on-chip supercapacitors based on ruthenium oxide coated silicon nanowires were fabricated using a process that is compatible with silicon integrated circuit processing. Ordered arrays of silicon nanowires were fabricated using metal-assisted anodic etching (MAAE). Atomic layer deposition (ALD) was used to form a uniform coating of ruthenium oxide on high-aspect-ratio silicon nanowires at a moderate temperature of 290 °C. Coated nanowire electrodes were studied using cyclic voltammetry and charge-discharge tests in a neutral Na2SO4 electrolyte, and a specific capacitance of 19 mFcm-2 was achieved at 5 mVs-1. Solid state nanowire capacitors were then fabricated with symmetric face to face nanowire arrays separated by a polymer-based electrolyte. This device exhibited a specific capacitance as high as 6.5 mFcm-2 at 2 mVs-1. The full device was tested over 10000 cycles under galvanostatic charge-discharge at 0.4 mAcm-2, and showed a retention of 92% of the specific capacitance. The specific capacitance was found to scale with the total nanowire surface area, as controlled by controlling the aspect ratios of the wires. The solid state nanowire-based device also achieved high specific energies without sacrificing power performance.

  15. An electrostatic ion pump with nanostructured Si field emission electron source and Ti particle collectors for supporting an ultra-high vacuum in miniaturized atom interferometry systems

    NASA Astrophysics Data System (ADS)

    Basu, Anirban; Velásquez-García, Luis F.

    2016-12-01

    We report a field emission-based, magnetic-less ion pump architecture for helping maintain a high vacuum within a small chamber that is compatible with miniaturized cold-atom interferometry systems. A nanostructured silicon field emitter array, with each nano-sharp tip surrounded by a self-aligned proximal gate electrode, is used to generate a surplus of electrons that cause impact ionization of gas molecules. A two-stage cylindrical electron collector, made of titanium, is used to increase the travel distance of the electrons, augmenting the ionization probability; gas ionization is subsequently followed by gettering of the ions by a negatively charged, annular-shaped titanium electrode. A proof-of-concept pump prototype was characterized using a 25 cm3 stainless steel vacuum chamber backed up by an external turbomolecular pump, a diaphragm pump, and a standard ion pump. Pumping action was observed with the electrostatic pump operating alone after an initial rapid rise of the chamber pressure due to electron/ion scrubbing. In addition, running the electrostatic pump in combination with the standard ion pump results in a lower vacuum level compared to the vacuum level produced by the standard ion pump acting alone. A proposed reduced-order model accurately predicts the functional dependence of the pressure versus time data and provides a good estimate of the characteristic pumping time constant inferred from the experiments.

  16. PtSi/Si LWIR Detectors Made With p+ Doping Spikes

    NASA Technical Reports Server (NTRS)

    Lin, True-Lon; Park, Jin S.; George, Thomas; Fathauer, Robert W.; Jones, Eric W.; Maserjian, Joseph

    1996-01-01

    PtSi/Si Schottky-barrier devices detecting long-wavelength infrared (LWIR) photons demonstrated. Essential feature of one of these devices is p+ "doping spike"; layer of Si about 10 Angstrom thick, located at PtSi/Si interface, and doped with electron acceptors (boron atoms) at concentration between 5 x 10(19) and 2 x 10(20) cm(-3). Doping spikes extend cutoff wavelengths of devices to greater values than otherwise possible.

  17. Direct observation of a long-lived single-atom catalyst chiseling atomic structures in graphene.

    PubMed

    Wang, Wei Li; Santos, Elton J G; Jiang, Bin; Cubuk, Ekin Dogus; Ophus, Colin; Centeno, Alba; Pesquera, Amaia; Zurutuza, Amaia; Ciston, Jim; Westervelt, Robert; Kaxiras, Efthimios

    2014-02-12

    Fabricating stable functional devices at the atomic scale is an ultimate goal of nanotechnology. In biological processes, such high-precision operations are accomplished by enzymes. A counterpart molecular catalyst that binds to a solid-state substrate would be highly desirable. Here, we report the direct observation of single Si adatoms catalyzing the dissociation of carbon atoms from graphene in an aberration-corrected high-resolution transmission electron microscope (HRTEM). The single Si atom provides a catalytic wedge for energetic electrons to chisel off the graphene lattice, atom by atom, while the Si atom itself is not consumed. The products of the chiseling process are atomic-scale features including graphene pores and clean edges. Our experimental observations and first-principles calculations demonstrated the dynamics, stability, and selectivity of such a single-atom chisel, which opens up the possibility of fabricating certain stable molecular devices by precise modification of materials at the atomic scale.

  18. Revealing heterogeneous nucleation of primary Si and eutectic Si by AlP in hypereutectic Al-Si alloys

    PubMed Central

    Li, Jiehua; Hage, Fredrik S.; Liu, Xiangfa; Ramasse, Quentin; Schumacher, Peter

    2016-01-01

    The heterogeneous nucleation of primary Si and eutectic Si can be attributed to the presence of AlP. Although P, in the form of AlP particles, is usually observed in the centre of primary Si, there is still a lack of detailed investigations on the distribution of P within primary Si and eutectic Si in hypereutectic Al-Si alloys at the atomic scale. Here, we report an atomic-scale experimental investigation on the distribution of P in hypereutectic Al-Si alloys. P, in the form of AlP particles, was observed in the centre of primary Si. However, no significant amount of P was detected within primary Si, eutectic Si and the Al matrix. Instead, P was observed at the interface between the Al matrix and eutectic Si, strongly indicating that P, in the form of AlP particles (or AlP ‘patch’ dependent on the P concentration), may have nucleated on the surface of the Al matrix and thereby enhanced the heterogeneous nucleation of eutectic Si. The present investigation reveals some novel insights into heterogeneous nucleation of primary Si and eutectic Si by AlP in hypereutectic Al-Si alloys and can be used to further develop heterogeneous nucleation mechanisms based on adsorption. PMID:27120994

  19. Revealing heterogeneous nucleation of primary Si and eutectic Si by AlP in hypereutectic Al-Si alloys

    NASA Astrophysics Data System (ADS)

    Li, Jiehua; Hage, Fredrik S.; Liu, Xiangfa; Ramasse, Quentin; Schumacher, Peter

    2016-04-01

    The heterogeneous nucleation of primary Si and eutectic Si can be attributed to the presence of AlP. Although P, in the form of AlP particles, is usually observed in the centre of primary Si, there is still a lack of detailed investigations on the distribution of P within primary Si and eutectic Si in hypereutectic Al-Si alloys at the atomic scale. Here, we report an atomic-scale experimental investigation on the distribution of P in hypereutectic Al-Si alloys. P, in the form of AlP particles, was observed in the centre of primary Si. However, no significant amount of P was detected within primary Si, eutectic Si and the Al matrix. Instead, P was observed at the interface between the Al matrix and eutectic Si, strongly indicating that P, in the form of AlP particles (or AlP ‘patch’ dependent on the P concentration), may have nucleated on the surface of the Al matrix and thereby enhanced the heterogeneous nucleation of eutectic Si. The present investigation reveals some novel insights into heterogeneous nucleation of primary Si and eutectic Si by AlP in hypereutectic Al-Si alloys and can be used to further develop heterogeneous nucleation mechanisms based on adsorption.

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

    SciTech Connect

    Bordihn, Stefan; Mertens, Verena; Müller, Jörg W.; Kessels, W. M. M.

    2014-01-15

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

  1. FeSi diffusion barriers in Fe/FeSi/Si/FeSi/Fe multilayers and oscillatory antiferromagnetic exchange coupling

    NASA Astrophysics Data System (ADS)

    Stromberg, F.; Bedanta, S.; Antoniak, C.; Keune, W.; Wende, H.

    2008-10-01

    We study the diffusion of 57Fe probe atoms in Fe/FeSi/Si/FeSi/Fe multilayers on Si(111) prepared by molecular beam epitaxy by means of 57Fe conversion electron Mössbauer spectroscopy (CEMS). We demonstrate that the application of FeSi boundary layers successfully inhibits the diffusion of 57Fe into the Si layer. The critical thickness for the complete prevention of Fe diffusion takes place at a nominal FeSi thickness of tFeSi = 10-12 Å, which was confirmed by the evolution of the isomer shift δ of the crucial CEM subspectrum. The formation of the slightly defective c-FeSi phase for thicker FeSi boundary layers (~20 Å) was confirmed by CEMS and reflection high-energy electron diffraction (RHEED). Ferromagnetic resonance (FMR) shows that, for tFeSi = 0-14 Å, the Fe layers in all samples are antiferromagnetically coupled and we observe an oscillatory antiferromagnetic coupling strength with FMR and superconducting quantum interference device (SQUID) magnetometry for varying FeSi thickness with a period of ~6 Å.

  2. Physico-chemical characterization of total suspended particulate matter over two coastal stations of Antarctica and adjoining ocean

    NASA Astrophysics Data System (ADS)

    Ali, Kaushar; Trivedi, D. K.; Sahu, Saroj

    2015-12-01

    Physical and chemical characteristics of the total suspended particulate matter (TSPM) measured during 11 January-21 March, 2009 and 09 December 2009-09 January, 2010 over two stations of Antarctica (Larsemann Hills and Maitri) and adjoining ocean are investigated. It is found that the concentration of TSPM is low over all the observational locations. Day-to-day variation in the concentration of TSPM is mainly controlled by variation in the weather systems and associated meteorological parameters. Average concentration of TSPM over Larsemann Hills is 7.6 μg/m3 during Jan-Mar 2009 and 2.4 μg/m3 during Dec. 2009-Jan 2010. It is 9.0 μg/m3 over Maitri during Jan-Mar 2009. On excluding the TSPM data of the disturbed weather days during Jan-Mar 2009, the concentration of TSPM is found to be 4.2 μg/m3 over Larsemann Hills and 4.3 μg/m3 over Maitri. The TSPM at all the observational locations is acidic in nature with a maximum pH value of 5.56 at Larsemann Hills. The pH value of TSPM over Maitri is found to be 5.28. The acidic nature of TSPM indicates the absence of sufficient neutralizing alkaline minerals. Among the measured chemical anions Cl- dominates at all the locations except at Maitri where SO42- ion shows maximum concentration. The dominant cation is Na+ at all the observational stations. Sizeable fraction of SO42- is found at all the observational locations. Abundance of SO42- in the atmosphere of Antarctica and its surrounding region is mainly due to emission of dimethylsulfide (DMS) phytoplankton and its oxidation finally to SO42- particles by gas-to-particle conversion. The highest concentration of SO42- over Maitri is attributed to the contribution from anthropogenic activity at Maitri, in addition to the biogenic SO42- . NH4+ plays dominant role in neutralizing the acidic components of the aerosols.

  3. Helimagnetic order in bulk MnSi and CoSi/MnSi superlattices

    NASA Astrophysics Data System (ADS)

    Loh, G. C.; Khoo, K. H.; Gan, C. K.

    2017-01-01

    Skyrmions are nanoscopic whirls of spins that reside in chiral magnets. It is only fairly recent that a plethora of applications for these quasiparticles emerges, especially in data storage. On the other hand, spin spirals are the periodic analogs of skyrmions, and are equally imperative in the course of exploration to enhance our understanding of helimagnetism. In this study, a new infrastructure based on the B20 compound, MnSi is propounded as a hosting material for spin spirals; alternating thin layers of CoSi and MnSi in the superlattice form provides a facile way of varying the properties of the spin spirals across a continuum. Using first-principles calculations based on full-potential linearized augmented plane-wave (FLAPW)-based density functional theory (DFT), the spin order of bulk MnSi, MnSi film, and the CoSi/MnSi superlattice is investigated. Spin dispersion plots as a function of propagation vectors show that the spiral size changes in the presence of CoSi - we find that the size of the spiral is reduced in the superlattice with thin CoSi layers (CoSi:MnSi=1:1 thickness ratio), whilst at a larger CoSi:MnSi=2:1 thickness ratio, the material behaves as a ferromagnet. In a similar fashion, the spin moment and orbital occupancy depend significantly on the thickness of the CoSi layers. However, the exchange interaction between Mn atoms appears to be generally impervious to the presence of CoSi. Succinctly, the CoSi/MnSi superlattice could be an excellent functional material in data storage applications.

  4. Photo-electron emission and atomic force microscopies of the hydrogen etched 6H-SiC(0 0 0 1) surface and the initial growth of GaN and AlN

    NASA Astrophysics Data System (ADS)

    Hartman, J. D.; Naniwae, K.; Petrich, C.; Nemanich, R. J.; Davis, R. F.

    2005-04-01

    Photo-emission electron microscopy (PEEM) and atomic force microscopy (AFM) have been used to characterize the surfaces of hydrogen etched 6H-SiC(0 0 0 1) wafers and the microstructure of the initial stages of growth of GaN and AlN on these surfaces via molecular beam epitaxy. The PEEM images were obtained using a free electron laser as the photon source. A stepped structure was evident in these images of the surfaces etched at 1600-1700 °C for 15 min. Comparison with the AFM images revealed that emission was occurring from the intersection of the steps and the terraces. Images of the initial stages of deposition of the GaN thin films at 700 and 800 °C revealed three-dimensional island growth. The degree of coalescence of these films was dependent upon the step structure: regions containing steps having unit cell height exhibited complete or nearly complete coalescence; regions containing steps with half unit cell height showed voids in the films parallel to the steps. PEEM of the initial stages of growth of AlN revealed immediate nucleation and rapid coalescence during deposition at 900 °C, except in areas on the substrate surface containing steps having half unit cell height. Incomplete coalescence and pits were also observed in the latter areas.

  5. Atomic Chain Electronics

    NASA Technical Reports Server (NTRS)

    Yamada, Toshishige; Saini, Subhash (Technical Monitor)

    1998-01-01

    Adatom chains, precise structures artificially created on an atomically regulated surface, are the smallest possible candidates for future nanoelectronics. Since all the devices are created by combining adatom chains precisely prepared with atomic precision, device characteristics are predictable, and free from deviations due to accidental structural defects. In this atomic dimension, however, an analogy to the current semiconductor devices may not work. For example, Si structures are not always semiconducting. Adatom states do not always localize at the substrate surface when adatoms form chemical bonds to the substrate atoms. Transport properties are often determined for the entire system of the chain and electrodes, and not for chains only. These fundamental issues are discussed, which will be useful for future device considerations.

  6. Electronic structure and charge transfer in α- and β-Si3N4 and at the Si(111)/Si3N4(001) interface

    NASA Astrophysics Data System (ADS)

    Zhao, G. L.; Bachlechner, M. E.

    1998-07-01

    Using a self-consistent linear combination of atomic orbitals method based on density-functional theory in a local-density approximation, the electronic structure in the high-temperature ceramics α-Si3N4 and β-Si3N4 and at the Si(111)/Si3N4(001) interface have been calculated. The resulting charge transfer suggests that the ionic formula can be written as Si+1.243N-0.934. For the Si(111)/Si3N4(001) interface, the silicon atoms from the silicon side lose some electrons to the nitrogen atoms of the silicon nitride side forming Si-N bonds at the interface. The calculated electronic density of states spectrum of Si 2p core levels for this interface is in good agreement with x-ray photoemission spectroscopy experiments.

  7. Location and Electronic Nature of Phosphorus in the Si Nanocrystal − SiO2 System

    PubMed Central

    König, Dirk; Gutsch, Sebastian; Gnaser, Hubert; Wahl, Michael; Kopnarski, Michael; Göttlicher, Jörg; Steininger, Ralph; Zacharias, Margit; Hiller, Daniel

    2015-01-01

    Up to now, no consensus exists about the electronic nature of phosphorus (P) as donor for SiO2-embedded silicon nanocrystals (SiNCs). Here, we report on hybrid density functional theory (h-DFT) calculations of P in the SiNC/SiO2 system matching our experimental findings. Relevant P configurations within SiNCs, at SiNC surfaces, within the sub-oxide interface shell and in the SiO2 matrix were evaluated. Atom probe tomography (APT) and its statistical evaluation provide detailed spatial P distributions. For the first time, we obtain ionisation states of P atoms in the SiNC/SiO2 system at room temperature using X-ray absorption near edge structure (XANES) spectroscopy, eliminating structural artefacts due to sputtering as occurring in XPS. K energies of P in SiO2 and SiNC/SiO2 superlattices (SLs) were calibrated with non-degenerate P-doped Si wafers. results confirm measured core level energies, connecting and explaining XANES spectra with h-DFT electronic structures. While P can diffuse into SiNCs and predominantly resides on interstitial sites, its ionization probability is extremely low, rendering P unsuitable for introducing electrons into SiNCs embedded in SiO2. Increased sample conductivity and photoluminescence (PL) quenching previously assigned to ionized P donors originate from deep defect levels due to P. PMID:25997696

  8. Location and Electronic Nature of Phosphorus in the Si Nanocrystal--SiO2 System.

    PubMed

    König, Dirk; Gutsch, Sebastian; Gnaser, Hubert; Wahl, Michael; Kopnarski, Michael; Göttlicher, Jörg; Steininger, Ralph; Zacharias, Margit; Hiller, Daniel

    2015-05-22

    Up to now, no consensus exists about the electronic nature of phosphorus (P) as donor for SiO2-embedded silicon nanocrystals (SiNCs). Here, we report on hybrid density functional theory (h-DFT) calculations of P in the SiNC/SiO2 system matching our experimental findings. Relevant P configurations within SiNCs, at SiNC surfaces, within the sub-oxide interface shell and in the SiO2 matrix were evaluated. Atom probe tomography (APT) and its statistical evaluation provide detailed spatial P distributions. For the first time, we obtain ionisation states of P atoms in the SiNC/SiO2 system at room temperature using X-ray absorption near edge structure (XANES) spectroscopy, eliminating structural artefacts due to sputtering as occurring in XPS. K energies of P in SiO2 and SiNC/SiO2 superlattices (SLs) were calibrated with non-degenerate P-doped Si wafers. results confirm measured core level energies, connecting and explaining XANES spectra with h-DFT electronic structures. While P can diffuse into SiNCs and predominantly resides on interstitial sites, its ionization probability is extremely low, rendering P unsuitable for introducing electrons into SiNCs embedded in SiO2. Increased sample conductivity and photoluminescence (PL) quenching previously assigned to ionized P donors originate from deep defect levels due to P.

  9. Effect of postdeposition annealing on the electrical properties of β-Ga{sub 2}O{sub 3} thin films grown on p-Si by plasma-enhanced atomic layer deposition

    SciTech Connect

    Altuntas, Halit; Donmez, Inci; Ozgit-Akgun, Cagla; Biyikli, Necmi

    2014-07-01

    Ga{sub 2}O{sub 3} dielectric thin films were deposited on (111)-oriented p-type silicon wafers by plasma-enhanced atomic layer deposition using trimethylgallium and oxygen plasma. Structural analysis of the Ga{sub 2}O{sub 3} thin films was carried out using grazing-incidence x-ray diffraction. As-deposited films were amorphous. Upon postdeposition annealing at 700, 800, and 900 °C for 30 min under N{sub 2} ambient, films crystallized into β-form monoclinic structure. Electrical properties of the β-Ga{sub 2}O{sub 3} thin films were then investigated by fabricating and characterizing Al/β-Ga{sub 2}O{sub 3}/p-Si metal–oxide-semiconductor capacitors. The effect of postdeposition annealing on the leakage current densities, leakage current conduction mechanisms, dielectric constants, flat-band voltages, reverse breakdown voltages, threshold voltages, and effective oxide charges of the capacitors were presented. The effective oxide charges (Q{sub eff}) were calculated from the capacitance–voltage (C-V) curves using the flat-band voltage shift and were found as 2.6 × 10{sup 12}, 1.9 × 10{sup 12}, and 2.5 × 10{sup 12} cm{sup −2} for samples annealed at 700, 800, and 900 °C, respectively. Effective dielectric constants of the films decreased with increasing annealing temperature. This situation was attributed to the formation of an interfacial SiO{sub 2} layer during annealing process. Leakage mechanisms in the regions where current increases gradually with voltage were well fitted by the Schottky emission model for films annealed at 700 and 900 °C, and by the Frenkel–Poole emission model for film annealed at 800 °C. Leakage current density was found to improve with annealing temperature. β-Ga{sub 2}O{sub 3} thin film annealed at 800 °C exhibited the highest reverse breakdown field value.

  10. Electronic structure, charge distribution, and charge transfer in α- and β-Si3N4 and at the Si(111)/Si3N4(001) interface

    NASA Astrophysics Data System (ADS)

    Zhao, G. L.; Bachlechner, M. E.

    1997-02-01

    The electronic structure, charge distribution, and charge transfer in α- and β- Si3N4 and at the Si(111)/Si3N4(001) interface have been studied using a self-consistent first-principles LCAO method. The calculated charge transfer suggests that both in α- and β-phases, the ionic formula may be written as Si3+1.24N4-0.93. For the Si(111)/Si3N4(001) interface, the silicon atoms from the Si(111) side give some electrons to the N atoms of Si3N4 forming the Si-N bonds at the interface. One Si-N bond is associated with a charge transfer of about 0.31 electrons.

  11. Atomic emission spectroscopy

    NASA Technical Reports Server (NTRS)

    Andrew, K. H.

    1975-01-01

    The relationship between the Slater-Condon theory and the conditions within the atom as revealed by experimental data was investigated. The first spectrum of Si, Rb, Cl, Br, I, Ne, Ar, and Xe-136 and the second spectrum of As, Cu, and P were determined. Methods for assessing the phase stability of fringe counting interferometers and the design of an autoranging scanning system for digitizing the output of an infrared spectrometer and recording it on magnetic tape are described.

  12. Atomistic study of the structural and electronic properties of a-Si:H/c-Si interfaces.

    PubMed

    Santos, Iván; Cazzaniga, Marco; Onida, Giovanni; Colombo, Luciano

    2014-03-05

    We investigate the structural and electronic properties of the interface between hydrogenated amorphous silicon (a-Si:H) and crystalline silicon (c-Si) by combining tight-binding molecular dynamics and DFT ab initio electronic structure calculations. We focus on the c-Si(100)(1×1)/a-Si:H, c-Si(100)(2×1)/a-Si:H and c-Si(111)/a-Si:H interfaces, due to their technological relevance. The analysis of atomic rearrangements induced at the interface by the interaction between H and Si allowed us to identify the relevant steps that lead to the transformation from c-Si(100)(1×1)/a-Si:H to c-Si(100)(2×1)/a-Si:H. The interface electronic structure is found to be characterized by spatially localized mid-gap states. Through them we have identified the relevant atomic structures responsible for the interface defect states, namely: dangling-bonds, H bridges, and strained bonds. Our analysis contributes to a better understanding of the role of such defects in c-Si/a-Si:H interfaces.

  13. Analysis of the dynamics of reactions of SiCl2 at Si(100) surfaces

    NASA Astrophysics Data System (ADS)

    Anzai, Keisuke; Kunioshi, Nílson; Fuwa, Akio

    2017-01-01

    The dynamics of reactions of SiCl2 at Si(100) surfaces was investigated through the molecular orbital method at the B3LYP/6-31G(d,p) level of theory, with the surface being modeled using clusters of silicon atoms. The intradimer adsorption of a SiCl2 molecule proceeded with no energy barrier, and in the structure of the product of the adsorption reaction the Si atom of the SiCl2 adsorbate formed a triangular structure with the two Si atoms of the surface dimer, in agreement with theoretical predictions published recently in the literature for a small cluster. However, the dynamics reported in this work indicates that SiCl2 undergoes molecular adsorption at the silicon surface, in contrast with the dissociative adsorption suggested by some available kinetic models. Intradimer adsorption of a second SiCl2 molecule, and interdimer adsorptions of a first, a second, and a third SiCl2 molecule were also seen to proceed without significant energy barriers, suggesting that the formation of the first additional layer of silicon atoms on the surface would be fast if the adsorption of SiCl2 were the only type of reaction proceeding in the system. The diffusion of the SiCl2 adsorbate over the surface and its desorption from the surface were found to have comparable activation energies, so that these reactions are expected to compete at high temperatures.

  14. Si clusters are more metallic than bulk Si

    NASA Astrophysics Data System (ADS)

    Jackson, Koblar; Jellinek, Julius

    2016-12-01

    Dipole polarizabilities were computed using density functional theory for silicon clusters over a broad range of sizes up to N = 147 atoms. The calculated total effective polarizabilities, which include contributions from permanent dipole moments of the clusters, are in very good agreement with recently measured values. We show that the permanent dipole contributions are most important for clusters in the intermediate size range and that the measured polarizabilities can be used to distinguish between energetically nearly degenerate cluster isomers at these sizes. We decompose the computed total polarizabilities α into the so-called dipole and charge transfer contributions, αp and αq, using a site-specific analysis. When the per-atom values of these quantities are plotted against N-1 /3, clear linear trends emerge that can be extrapolated to the large size limit (N-1 /3→0 ), resulting in a value for α/N of 30.5 bohrs3/atom that is significantly larger than the per-atom polarizability of semiconducting bulk Si, 25.04 bohrs3/atom. This indicates that Si clusters possess a higher degree of metallicity than bulk Si, a conclusion that is consistent with the strong electrostatic screening of the cluster interiors made evident by the analysis of the calculated atomic polarizabilities.

  15. Doping of Semiconducting Atomic Chains

    NASA Technical Reports Server (NTRS)

    Toshishige, Yamada; Kutler, Paul (Technical Monitor)

    1997-01-01

    Due to the rapid progress in atom manipulation technology, atomic chain electronics would not be a dream, where foreign atoms are placed on a substrate to form a chain, and its electronic properties are designed by controlling the lattice constant d. It has been shown theoretically that a Si atomic chain is metallic regardless of d and that a Mg atomic chain is semiconducting or insulating with a band gap modified with d. For electronic applications, it is essential to establish a method to dope a semiconducting chain, which is to control the Fermi energy position without altering the original band structure. If we replace some of the chain atoms with dopant atoms randomly, the electrons will see random potential along the chain and will be localized strongly in space (Anderson localization). However, if we replace periodically, although the electrons can spread over the chain, there will generally appear new bands and band gaps reflecting the new periodicity of dopant atoms. This will change the original band structure significantly. In order to overcome this dilemma, we may place a dopant atom beside the chain at every N lattice periods (N > 1). Because of the periodic arrangement of dopant atoms, we can avoid the unwanted Anderson localization. Moreover, since the dopant atoms do not constitute the chain, the overlap interaction between them is minimized, and the band structure modification can be made smallest. Some tight-binding results will be discussed to demonstrate the present idea.

  16. Dual-Beam Atom Laser Driven by Spinor Dynamics

    NASA Technical Reports Server (NTRS)

    Thompson, Robert; Lundblad, Nathan; Maleki, Lute; Aveline, David

    2007-01-01

    An atom laser now undergoing development simultaneously generates two pulsed beams of correlated Rb-87 atoms. (An atom laser is a source of atoms in beams characterized by coherent matter waves, analogous to a conventional laser, which is a source of coherent light waves.) The pumping mechanism of this atom laser is based on spinor dynamics in a Bose-Einstein condensate. By virtue of the angular-momentum conserving collisions that generate the two beams, the number of atoms in one beam is correlated with the number of atoms in the other beam. Such correlations are intimately linked to entanglement and squeezing in atomic ensembles, and atom lasers like this one could be used in exploring related aspects of Bose-Einstein condensates, and as components of future sensors relying on atom interferometry. In this atom-laser apparatus, a Bose-Einstein condensate of about 2 x 10(exp 6) Rb-87 atoms at a temperature of about 120 micro-K is first formed through all-optical means in a relatively weak singlebeam running-wave dipole trap that has been formed by focusing of a CO2-laser beam. By a technique that is established in the art, the trap is loaded from an ultrahigh-vacuum magnetooptical trap that is, itself, loaded via a cold atomic beam from an upstream two-dimensional magneto-optical trap that resides in a rubidium-vapor cell that is differentially pumped from an adjoining vacuum chamber, wherein are performed scientific observations of the beams ultimately generated by the atom laser.

  17. Atomic polarizabilities

    SciTech Connect

    Safronova, M. S.; Mitroy, J.; Clark, Charles W.; Kozlov, M. G.

    2015-01-22

    The atomic dipole polarizability governs the first-order response of an atom to an applied electric field. Atomic polarization phenomena impinge upon a number of areas and processes in physics and have been the subject of considerable interest and heightened importance in recent years. In this paper, we will summarize some of the recent applications of atomic polarizability studies. A summary of results for polarizabilities of noble gases, monovalent, and divalent atoms is given. The development of the CI+all-order method that combines configuration interaction and linearized coupled-cluster approaches is discussed.

  18. Synthesis of micro-sized interconnected Si-C composites

    DOEpatents

    Wang, Donghai; Yi, Ran; Dai, Fang

    2016-02-23

    Embodiments provide a method of producing micro-sized Si--C composites or doped Si--C and Si alloy-C with interconnected nanoscle Si and C building blocks through converting commercially available SiO.sub.x (0atoms.

  19. Survey and census of hoolock gibbon (Hoolock hoolock) in the Inner-Line Reserve Forest and the adjoining areas of Cachar district, Assam, India.

    PubMed

    Islam, Mofidul; Choudhury, Parthankar; Bhattacharjee, P C

    2013-01-01

    A detailed survey of Hoolock hoolock was carried out in the Inner-Line Reserve Forest and the adjoining areas of Cachar district of southern Assam, India, from July 2010 to December 2011. About 150 km2 of the area was covered. In direct sighting, groups and individuals were counted in 7 localities (39.7 km2). Only 3.96 km2 of the actual forest area were occupied by these gibbons. Nine family groups and a solitary subadult, 33 individuals in all, made up the total count. Of these, adult males and females comprised 54.5% of the population while the subadults, juveniles and infants comprised 27.3, 12.1 and 6.1%, respectively. Each family group's home range was 0.31-0.51 km2. Of the 7 localities, only 1 had more than 1 family group. Habitat destruction and diverse threats to the hoolock gibbon in this area are examined in this paper.

  20. Fundamental Properties and Devices Applications of Ge(x)Si(1-x)/Si Superlattices.

    DTIC Science & Technology

    1987-01-01

    atomic fractions of the reaction species, Si, Si oxide, 0, have been plotted as a function of the silicon flux and are shown in Fig. 9. With this study...v.c 0 0 8 I0 12 Ai’ SILICON FLUX (;irmn) Fig. 9 Evolution of the Si, Si oxide and 0 atomic fractions in function of the silicon flux (O<Jsi᝾.5 A/min...G. Karunasiri, J. S. Park, C. H. Chern, and K. L. Wang, "Reflection High-Energy Electron Diffraction Observation of Substrate Cleaning During Silicon

  1. Possible magmatic underplating beneath the west coast of India and adjoining Dharwar craton: Imprint from Archean crustal evolution to breakup of India and Madagascar

    NASA Astrophysics Data System (ADS)

    Saikia, Utpal; Das, Ritima; Rai, S. S.

    2017-03-01

    The shear wave velocity of the crust along a ∼660 km profile from the west to the east coast of South India is mapped through the joint inversion of receiver functions and Rayleigh wave group velocity. The profile, consisting of 38 broadband seismic stations, covers the Archean Dharwar craton, Proterozoic Cuddapah basin, and rifted margin and escarpment. The Moho is mapped at a depth of ∼40 km beneath the mid-Archean Western Dharwar Craton (WDC), Cuddapah Basin (CB), and the west and east coasts formed through the rifting process. This is in contrast with a thin (∼35 km) crust beneath the late-Archean Eastern Dharwar Craton (EDC). Along the profile, the average thickness of the upper, middle and lower crust is ∼4 km, 12 ± 4 km and 24 ± 4 km respectively. Above the Moho, we observe a high-velocity layer (HVL, Vs > 4 km/s) of variable thickness increasing from 3 ± 1 km beneath the EDC to 11 ± 3 km beneath the WDC and the CB, and 18 ± 2 km beneath the west coast of India. The seismic wave velocity in this layer is greater than typical oceanic lower crust. We interpret the high-velocity layer as a signature of magmatic underplating due to past tectonic processes. Its significant thinning beneath the EDC may be attributed to crustal delamination or relamination at 2.5 Ga. These results demonstrate the dual signature of the Archean Dharwar crust. The change in the geochemical character of the crust possibly occurred at the end of Archean when Komatiite volcanism ceased. The unusually thick HVL beneath the west coast of India and the adjoining region may represent underplated material formed due to India-Madagascar rifting, which is supported by the presence of seaward dipping reflectors and a 85-90 Ma mafic dyke in the adjoining island.

  2. Phase transformation in SiOx/SiO₂ multilayers for optoelectronics and microelectronics applications.

    PubMed

    Roussel, M; Talbot, E; Pratibha Nalini, R; Gourbilleau, F; Pareige, P

    2013-09-01

    Due to the quantum confinement, silicon nanoclusters (Si-ncs) embedded in a dielectric matrix are of prime interest for new optoelectronics and microelectronics applications. In this context, SiO(x)/SiO₂ multilayers have been prepared by magnetron sputtering and subsequently annealed to induce phase separation and Si clusters growth. The aim of this paper is to study phase separation processes and formation of nanoclusters in SiO(x)/SiO₂ multilayers by atom probe tomography. Influences of the silicon supersaturation, annealing temperature and SiO(x) and SiO₂ layer thicknesses on the final microstructure have been investigated. It is shown that supersaturation directly determines phase separation regime between nucleation/classical growth and spinodal decomposition. Annealing temperature controls size of the particles and interface with the surrounding matrix. Layer thicknesses directly control Si-nc shapes from spherical to spinodal-like structures.

  3. Covalent bonds in AlMnSi icosahedral quasicrystalline approximant

    PubMed

    Kirihara; Nakata; Takata; Kubota; Nishibori; Kimura; Sakata

    2000-10-16

    Electron density distributions were obtained using the maximum entropy method with synchrotron radiation powder data. In the metallic Al12Re, metallic bonding was observed for the icosahedral Al12 cluster with central Re atom. In the nonmetallic alpha-AlMnSi 1/1 approximant, covalent bonds were found in the electron density distribution of the Mackay icosahedral cluster without central atom. Rather than the Hume-Rothery mechanism, the covalency of Al (Si) icosahedron and that between Al (Si) and Mn atoms is considered to be the origin of the pseudogap and nonmetallic behavior of alpha-AlMnSi.

  4. Using Hydrogen and Chlorine on Si(111) to Store Data

    NASA Technical Reports Server (NTRS)

    Bauschlicher, Charles W., Jr.; Arnold, James O. (Technical Monitor)

    2000-01-01

    The interaction of a pyridine molecule with H and Cl atoms on a Si(111) surface is studied using a cluster model in conjunction with the B3LYP/6-3 1G level of theory. Regardless of the type of the neighboring atoms, the interaction of the pyridine with a hydrogen atom is very different from its interaction a chlorine atom. This system is discussed in terms of our atomic data storage proposal.

  5. Molecular dynamics simulation of C/Si ratio effect on the irradiation swelling of β-SiC

    NASA Astrophysics Data System (ADS)

    Li, Yingying; Xiao, Wei; Li, Huailin

    2016-11-01

    The C/Si atom ratio effect on the irradiation swelling of β-SiC is studied using molecular dynamics (MD) simulations. The irradiation swelling decreases with the increase of C/Si ratio under the same irradiation conditions. The carbon cluster is the key issue for the irradiation swelling of non-stoichiometric SiC. The carbon cluster size increases with the increase of C/Si ratio and the number of cluster decreases with the increase of C/Si ratio after irradiation process. An analytical model is established to describe the C/Si ratio effect on irradiation swelling and it fits the MD data well.

  6. Au20Si12: A hollow Catalan pentakis dodecahedron.

    PubMed

    Guo, J J; Zhao, H Y; Wang, J; Ai, L Y; Liu, Y

    2017-02-14

    A stable hollow Au20Si12 cage with Ih symmetry has been predicted using first-principles density functional theory. The stability of the cage-like Au20Si12 structure is verified by vibrational frequency analysis and molecular dynamics simulations. A relatively large highest occupied molecular orbital-lowest unoccupied molecular orbital gap of 1.057 eV is found. Electronic structure analysis shows that clearly p-d hybridizations between Si atoms and Au atoms are of great importance for the stability of Au20Si12 cage. The cage-like Au20Si12 structure may have potential applications in semiconductor industry and microelectronics.

  7. Au20Si12: A hollow Catalan pentakis dodecahedron

    NASA Astrophysics Data System (ADS)

    Guo, J. J.; Zhao, H. Y.; Wang, J.; Ai, L. Y.; Liu, Y.

    2017-02-01

    A stable hollow Au20Si12 cage with Ih symmetry has been predicted using first-principles density functional theory. The stability of the cage-like Au20Si12 structure is verified by vibrational frequency analysis and molecular dynamics simulations. A relatively large highest occupied molecular orbital-lowest unoccupied molecular orbital gap of 1.057 eV is found. Electronic structure analysis shows that clearly p-d hybridizations between Si atoms and Au atoms are of great importance for the stability of Au20Si12 cage. The cage-like Au20Si12 structure may have potential applications in semiconductor industry and microelectronics.

  8. Atomic supersymmetry

    NASA Technical Reports Server (NTRS)

    Kostelecky, V. Alan

    1993-01-01

    Atomic supersymmetry is a quantum-mechanical supersymmetry connecting the properties of different atoms and ions. A short description of some established results in the subject are provided and a few recent developments are discussed including the extension to parabolic coordinates and the calculation of Stark maps using supersymmetry-based models.

  9. High Mobility SiGe/Si n-MODFET Structures and Devices on Sapphire Substrates

    NASA Technical Reports Server (NTRS)

    Mueller, Carl; Alterovitz, Samuel; Croke, Edward; Ponchak, George

    2004-01-01

    Si/Ge/Si n-type modulation doped field effect structures and transistors (n-MODFET's) have been fabricated on r-plane sapphire substrates. Mobilities as high as 1380 cm(exp 2)/Vs were measured at room temperature. Excellent carrier confinement was shown by Shubnikov-de Haas measurements. Atomic force microscopy indicated smooth surfaces, with rm's roughness less than 4 nm, similar to the quality of SiGe/Si n-MODFET structures made on Si substrates. Transistors with 2 micron gate lengths and 200 micron gate widths were fabricated and tested.

  10. Carbon Diffusion through SiO2 from a Hydrogenated Amorphous Carbon Layer and Accumulation at the SiO2/Si Interface

    NASA Astrophysics Data System (ADS)

    Krafcsik, Olga H.; Vida, György; Pócsik, István; Josepovits, Katalin V.; Deák, Péter

    2001-04-01

    Carbon diffusion in a SiO2/Si system was investigated. The source was provided by chemical vapor deposition of a hydrogenated amorphous carbon layer onto the oxide at low temperature. From layers with low oxygen content, no carbon outdiffusion was detected up to 1190°C@. If the O content was high, the diffusion would start suddenly at 1140°C, and carbon accumulation would be found on the Si side of the SiO2/Si interface in the form of SiC precipitates. These results are interpreted by assuming oxygen-assisted dissociation of carbon atoms from the carbon layer in form of CO molecules, fast CO diffusion through SiO2 and an exothermic reaction of CO with Si. No carbon segregation was found in SiO2. Consequences of carbon island formation during SiC oxidation are pointed out.

  11. Crystallization mechanisms and recording characteristics of Si/CuSi bilayer for write-once blu-ray disc

    NASA Astrophysics Data System (ADS)

    Ou, Sin-Liang; Kuo, Po-Cheng; Chen, Sheng-Chi; Tsai, Tsung-Lin; Yeh, Chin-Yen; Chang, Han-Feng; Lee, Chao-Te; Chiang, Donyau

    2011-09-01

    The crystallization mechanisms of Si/CuSi bilayer and its recording characteristics for write-once blu-ray disc (BD-R) were investigated. It was found that Cu3Si phase appeared during the room temperature sputtered deposition. Then, the Si atoms in CuSi layer segregated and crystallized to cubic Si in Cu3Si nucleation sites as the film was annealed at 270 °C. After heating to 500 °C, the grains size of cubic Si phase grew and the hexagonal Si phase was observed. The dynamic tests show that the Si/CuSi bilayer has great feasibility for 1-4× BD-R with the bottom jitter values below 6.5%.

  12. Optical atomic clocks

    NASA Astrophysics Data System (ADS)

    Poli, N.; Oates, C. W.; Gill, P.; Tino, G. M.

    2013-12-01

    In the last ten years extraordinary results in time and frequency metrology have been demonstrated. Frequency-stabilization techniques for continuous-wave lasers and femtosecond optical frequency combs have enabled a rapid development of frequency standards based on optical transitions in ultra-cold neutral atoms and trapped ions. As a result, today's best performing atomic clocks tick at an optical rate and allow scientists to perform high-resolution measurements with a precision approaching a few parts in 1018. This paper reviews the history and the state of the art in optical-clock research and addresses the implementation of optical clocks in a possible future redefinition of the SI second as well as in tests of fundamental physics.

  13. Crystallization of amorphous Si nanoclusters in SiO(x) films using femtosecond laser pulse annealings.

    PubMed

    Korchagina, T T; Gutakovsky, A K; Fedina, L I; Neklyudova, M A; Volodin, V A

    2012-11-01

    The SiO(x) films of various stoichiometries deposited on Si substrates with the use of the co-sputtering from two separate Si and SiO2 targets were annealed by femtosecond laser pulses. Femtosecond laser treatments were applied for crystallization of amorphous silicon nanoclusters in the silicon-rich oxide films. The treatments were carried out with the use of Ti-Sapphire laser with wavelength 800 nm and pulse duration about 30 fs. Regimes of crystallization of amorphous Si nanoclusters in the initial films were found. Ablation thresholds for SiO(x) films of various stoichiometries were discovered. The effect of laser assisted formation of a-Si nanoclusters in the non-stoichiometric dielectric films with relatively low concentration of additional Si atoms was also observed. This approach is applicable for the creation of dielectric films with semiconductor nanoclusters on non-refractory substrates.

  14. Lateral Ge Diffusion During Oxidation of Si/SiGe Fins.

    PubMed

    Brewer, William M; Xin, Yan; Hatem, C; Diercks, D; Truong, V Q; Jones, K S

    2017-04-12

    This Letter reports on the unusual diffusion behavior of Ge during oxidation of a multilayer Si/SiGe fin. It is observed that oxidation surprisingly results in the formation of vertically stacked Si nanowires encapsulated in defect free epitaxial strained SixGe1-x. High angle annular dark field scanning transmission electron microscopy (HAADF-STEM) shows that extremely enhanced diffusion of Ge occurs along the vertical Si/SiO2 oxidizing interface and is responsible for the encapsulation process. Further oxidation fully encapsulates the Si layers in defect free single crystal SixGe1-x (x up to 0.53), which results in Si nanowires with up to -2% strain. Atom probe tomography reconstructions demonstrate that the resultant nanowires run the length of the fin. We found that the oxidation temperature plays a significant role in the formation of the Si nanowires. In the process range of 800-900 °C, pure strained and rounded Si nanowires down to 2 nm in diameter can be fabricated. At lower temperatures, the Ge diffusion along the oxidizing Si/SiO2 interface is slow, and rounding of the nanowire does not occur, while at higher temperatures, the diffusivity of Ge into Si is sufficient to result in dilution of the pure Si nanowire with Ge. The use of highly selective etchants to remove the SiGe could provide a new pathway for the creation of highly controlled vertically stacked nanowires for gate all around transistors.

  15. Atomically Traceable Nanostructure Fabrication.

    PubMed

    Ballard, Josh B; Dick, Don D; McDonnell, Stephen J; Bischof, Maia; Fu, Joseph; Owen, James H G; Owen, William R; Alexander, Justin D; Jaeger, David L; Namboodiri, Pradeep; Fuchs, Ehud; Chabal, Yves J; Wallace, Robert M; Reidy, Richard; Silver, Richard M; Randall, John N; Von Ehr, James

    2015-07-17

    Reducing the scale of etched nanostructures below the 10 nm range eventually will require an atomic scale understanding of the entire fabrication process being used in order to maintain exquisite control over both feature size and feature density. Here, we demonstrate a method for tracking atomically resolved and controlled structures from initial template definition through final nanostructure metrology, opening up a pathway for top-down atomic control over nanofabrication. Hydrogen depassivation lithography is the first step of the nanoscale fabrication process followed by selective atomic layer deposition of up to 2.8 nm of titania to make a nanoscale etch mask. Contrast with the background is shown, indicating different mechanisms for growth on the desired patterns and on the H passivated background. The patterns are then transferred into the bulk using reactive ion etching to form 20 nm tall nanostructures with linewidths down to ~6 nm. To illustrate the limitations of this process, arrays of holes and lines are fabricated. The various nanofabrication process steps are performed at disparate locations, so process integration is discussed. Related issues are discussed including using fiducial marks for finding nanostructures on a macroscopic sample and protecting the chemically reactive patterned Si(100)-H surface against degradation due to atmospheric exposure.

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

    PubMed

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

    2014-05-27

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

  17. Metal-semiconductor interfacial reactions - Ni/Si system

    NASA Technical Reports Server (NTRS)

    Cheung, N. W.; Grunthaner, P. J.; Grunthaner, F. J.; Mayer, J. W.; Ullrich, B. M.

    1981-01-01

    X-ray photoelectron spectroscopy and channeling measurements with MeV He-4(+) ions have been used to probe the structure of the interface in the Ni/Si system. It is found that reactions occur where Ni is deposited on Si at 10 to the -10th torr: Si atoms are displaced from lattice sites, the Ni atoms are in an Si-rich environment, and the Ni/Si interface is graded in composition. Composition gradients are present at both interfaces in the Si/Ni2/Si/Ni system. For the Ni-Si system, cooling the substrate to 100 K slows down the reaction rate. The temperature dependence of the interfacial reactivity indicates the kinetic nature of metal-semiconductor interfaces.

  18. Acting Atoms.

    ERIC Educational Resources Information Center

    Farin, Susan Archie

    1997-01-01

    Describes a fun game in which students act as electrons, protons, and neutrons. This activity is designed to help students develop a concrete understanding of the abstract concept of atomic structure. (DKM)

  19. Kinetic Atom.

    ERIC Educational Resources Information Center

    Wilson, David B.

    1981-01-01

    Surveys the research of scientists like Joule, Kelvin, Maxwell, Clausius, and Boltzmann as it comments on the basic conceptual issues involved in the development of a more precise kinetic theory and the idea of a kinetic atom. (Author/SK)

  20. Dynamics of SiO2 Buried Layer Removal from Si-SiO2-Si and Si-SiO2-SiC Bonded Substrates by Annealing in Ar

    NASA Astrophysics Data System (ADS)

    Li, L.-G.; Rubino, S.; Vallin, Ö.; Olsson, J.

    2014-02-01

    Silicon-on-silicon-carbide substrates could be ideal for high-power and radiofrequency silicon devices. Such hybrid wafers, when made by wafer bonding, contain an intermediate silicon dioxide layer with poor thermal characteristics, which can be removed by high-temperature annealing in an inert atmosphere. To understand the dynamics of this process, removal of 2.4-nm-thick SiO2 layers from Si-SiO2-Si and Si-SiO2-SiC substrates has been studied at temperatures ranging from 1100°C to 1200°C. The substrates were analyzed by transmission electron microscopy, electron energy-loss spectroscopy, secondary-ion mass spectroscopy, and ellipsometry, before and after annealing. For oxide thickness less than 2.4 nm, the activation energy for oxide removal was estimated to be 6.4 eV, being larger than the activation energy reported for removal of thicker oxides (4.1 eV). Under the same conditions, the SiO2 layer became discontinuous. In the time domain, three steps could be distinguished: bulk diffusion, bulk diffusion with void formation, and bulk diffusion with disintegration. The void formation, predominant here, has an energetic cost that could explain the larger activation energy. The oxide remaining after prolonged annealing corresponds to one layer of oxygen atoms.

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

    NASA Astrophysics Data System (ADS)

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

    2017-01-01

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

  2. Evolution of secondary defects in arsenic implanted Si

    NASA Astrophysics Data System (ADS)

    Zhu, He; Wang, Miao; Zhang, Bingpo; Wu, Huizhen; Sun, Yan; Hu, Gujin; Dai, Ning

    2016-04-01

    Behavior of defects in ion-implanted semiconductors is an everlasting topic and becomes even more critical as semiconductor devices continuously shrink and ion implantation technique has been increasingly employed. High resolution transmission electron microscope (HRTEM) and energy dispersive X-ray (EDX) were employed to investigate the structural evolution of arsenic (As) implanted silicon (Si). Project range (PR) defects and end of range (EOR) dislocations are observed via HRTEM. EDX characterization proves the two types of defects are related to dopant atoms precipitations. The sizes of both PR defects and EOR dislocations enlarge at the expense of small ones with the elevation of annealing temperature. The characterizations of electrochemical capacitance-voltage and EDX conclude that the SiO2/Si interface is playing an indispensable role in the deactivation of dopant atoms during the annealing process. As atoms are detected in the As-implanted Si region near the SiO2/Si interface but not in the silica layer. Nanoparticles composed of Si atoms in the silica layer are observed in the 1150 °C-annealed samples, which proves the migration of oxygen atoms at the SiO2/Si interface.

  3. Comparison of trimethylgallium and triethylgallium as “Ga” source materials for the growth of ultrathin GaN films on Si (100) substrates via hollow-cathode plasma-assisted atomic layer deposition

    SciTech Connect

    Alevli, Mustafa; Haider, Ali; Kizir, Seda; Leghari, Shahid A.; Biyikli, Necmi

    2016-01-15

    GaN films grown by hollow cathode plasma-assisted atomic layer deposition using trimethylgallium (TMG) and triethylgallium (TEG) as gallium precursors are compared. Optimized and saturated TMG/TEG pulse widths were used in order to study the effect of group-III precursors. The films were characterized by grazing incidence x-ray diffraction, atomic force microscopy, x-ray photoelectron spectroscopy, and spectroscopic ellipsometry. Refractive index follows the same trend of crystalline quality, mean grain, and crystallite sizes. GaN layers grown using TMG precursor exhibited improved structural and optical properties when compared to GaN films grown with TEG precursor.

  4. Atomic research

    NASA Technical Reports Server (NTRS)

    Hadaway, James B.; Connatser, Robert; Cothren, Bobby; Johnson, R. B.

    1993-01-01

    Work performed by the University of Alabama in Huntsville's (UAH) Center for Applied Optics (CAO) entitled Atomic Research is documented. Atomic oxygen (AO) effects on materials have long been a critical concern in designing spacecraft to withstand exposure to the Low Earth Orbit (LEO) environment. The objective of this research effort was to provide technical expertise in the design of instrumentation and experimental techniques for analyzing materials exposed to atomic oxygen in accelerated testing at NASA/MSFC. Such testing was required to answer fundamental questions concerning Space Station Freedom (SSF) candidate materials and materials exposed to atomic oxygen aboard the Long-Duration Exposure Facility (LDEF). The primary UAH task was to provide technical design, review, and analysis to MSFC in the development of a state-of-the-art 5eV atomic oxygen beam facility required to simulate the RAM-induced low earth orbit (LEO) AO environment. This development was to be accomplished primarily at NASA/MSFC. In support of this task, contamination effects and ultraviolet (UV) simulation testing was also to be carried out using NASA/MSFC facilities. Any materials analysis of LDEF samples was to be accomplished at UAH.

  5. Atom probe tomography in nanoelectronics

    NASA Astrophysics Data System (ADS)

    Blavette, Didier; Duguay, Sébastien

    2014-10-01

    The role of laser assisted atom probe tomography (APT) in microelectronics is discussed on the basis of various illustrations related to SiGe epitaxial layers, bipolar transistors or MOS nano-devices including gate all around (GAA) devices that were carried out at the Groupe de Physique des Matériaux of Rouen (France). 3D maps as provided by APT reveal the atomic-scale distribution of dopants and nanostructural features that are vital for nanoelectronics. Because of trajectory aberrations, APT images are subjected to distortions and local composition at the nm scale may either be biased. Procedures accounting for these effects were applied so that to correct images.

  6. Spatial confinement of muonium atoms

    NASA Astrophysics Data System (ADS)

    Khaw, K. S.; Antognini, A.; Prokscha, T.; Kirch, K.; Liszkay, L.; Salman, Z.; Crivelli, P.

    2016-08-01

    We report the achievement of spatial confinement of muonium atoms (the bound state of a positive muon and an electron). Muonium emitted into a vacuum from mesoporous silica reflects between two SiO2 confining surfaces separated by 1 mm. From the data, one can extract that the reflection probability on the confining surfaces kept at 100 K is about 90% and the reflection process is well described by a cosine law. This technique enables new experiments with this exotic atomic system and is a very important step towards a measurement of the 1 S -2 S transition frequency using continuous-wave laser spectroscopy.

  7. Structure, composition, and strain profiling of Si/SiO{sub 2} interfaces

    SciTech Connect

    Duscher, G. |; Pennycook, S.J.; Gao, H.J. |; Browning, N.D.; Singh, R.

    1998-03-01

    Recently, the scanning transmission electron microscope has become capable of forming electron probes of atomic dimensions. This makes possible the technique of Z-contrast imaging, a method of forming incoherent images at atomic resolution having high compositional sensitivity. An incoherent image of this nature also allows the positions of atomic columns in a crystal to be directly determined, without the need for model structures and image simulations. Furthermore, atomic resolution chemical analysis can be performed by locating the probe over particular columns or planes seen in the image while electron energy loss spectra are collected. The authors present images of the Si/SiO{sub 2} interface showing no crystalline oxide, compositional profiles across a nitrided sample at 2.5 {angstrom} resolution showing an extended sub-stoichiometric zone, and strain profiles at a rough interface showing static rms displacements {approximately}0.1 {angstrom} extending 10 {angstrom} into the crystalline Si.

  8. Abiologic silicon isotope fractionation between aqueous Si and Fe(III)-Si gel in simulated Archean seawater: Implications for Si isotope records in Precambrian sedimentary rocks

    NASA Astrophysics Data System (ADS)

    Zheng, Xin-Yuan; Beard, Brian L.; Reddy, Thiruchelvi R.; Roden, Eric E.; Johnson, Clark M.

    2016-08-01

    Precambrian Si-rich sedimentary rocks, including cherts and banded iron formations (BIFs), record a >7‰ spread in 30Si/28Si ratios (δ30Si values), yet interpretation of this large variability has been hindered by the paucity of data on Si isotope exchange kinetics and equilibrium fractionation factors in systems that are pertinent to Precambrian marine conditions. Using the three-isotope method and an enriched 29Si tracer, a series of experiments were conducted to constrain Si isotope exchange kinetics and fractionation factors between amorphous Fe(III)-Si gel, a likely precursor to Precambrian jaspers and BIFs, and aqueous Si in artificial Archean seawater under anoxic conditions. Experiments were conducted at room temperature, and in the presence and absence of aqueous Fe(II) (Fe(II)aq). Results of this study demonstrate that Si solubility is significantly lower for Fe-Si gel than that of amorphous Si, indicating that seawater Si concentrations in the Precambrian may have been lower than previous estimates. The experiments reached ˜70-90% Si isotope exchange after a period of 53-126 days, and the highest extents of exchange were obtained where Fe(II)aq was present, suggesting that Fe(II)-Fe(III) electron-transfer and atom-exchange reactions catalyze Si isotope exchange through breakage of Fe-Si bonds. All experiments except one showed little change in the instantaneous solid-aqueous Si isotope fractionation factor with time, allowing extraction of equilibrium Si isotope fractionation factors through extrapolation to 100% isotope exchange. The equilibrium 30Si/28Si fractionation between Fe(III)-Si gel and aqueous Si (Δ30Sigel-aqueous) is -2.30 ± 0.25‰ (2σ) in the absence of Fe(II)aq. In the case where Fe(II)aq was present, which resulted in addition of ˜10% Fe(II) in the final solid, creating a mixed Fe(II)-Fe(III) Si gel, the equilibrium fractionation between Fe(II)-Fe(III)-Si gel and aqueous Si (Δ30Sigel-aqueous) is -3.23 ± 0.37‰ (2σ). Equilibrium

  9. Atom Interferometry

    ScienceCinema

    Mark Kasevich

    2016-07-12

    Atom de Broglie wave interferometry has emerged as a tool capable of addressing a diverse set of questions in gravitational and condensed matter physics, and as an enabling technology for advanced sensors in geodesy and navigation. This talk will review basic principles, then discuss recent applications and future directions. Scientific applications to be discussed include measurement of G (Newton’s constant), tests of the Equivalence Principle and post-Newtonian gravity, and study of the Kosterlitz-Thouless phase transition in layered superfluids. Technology applications include development of precision gryoscopes and gravity gradiometers. The talk will conclude with speculative remarks looking to the future: Can atom interference methods be sued to detect gravity waves? Can non-classical (entangled/squeezed state) atom sources lead to meaningful sensor performance improvements?

  10. Atom Interferometry

    SciTech Connect

    Kasevich, Mark

    2008-05-08

    Atom de Broglie wave interferometry has emerged as a tool capable of addressing a diverse set of questions in gravitational and condensed matter physics, and as an enabling technology for advanced sensors in geodesy and navigation. This talk will review basic principles, then discuss recent applications and future directions. Scientific applications to be discussed include measurement of G (Newton's constant), tests of the Equivalence Principle and post-Newtonian gravity, and study of the Kosterlitz-Thouless phase transition in layered superfluids. Technology applications include development of precision gyroscopes and gravity gradiometers. The talk will conclude with speculative remarks looking to the future: Can atom interference methods be used to detect gravity waves? Can non-classical (entangled/squeezed state) atom sources lead to meaningful sensor performance improvements?

  11. Atom Interferometry

    SciTech Connect

    Mark Kasevich

    2008-05-07

    Atom de Broglie wave interferometry has emerged as a tool capable of addressing a diverse set of questions in gravitational and condensed matter physics, and as an enabling technology for advanced sensors in geodesy and navigation. This talk will review basic principles, then discuss recent applications and future directions. Scientific applications to be discussed include measurement of G (Newton’s constant), tests of the Equivalence Principle and post-Newtonian gravity, and study of the Kosterlitz-Thouless phase transition in layered superfluids. Technology applications include development of precision gryoscopes and gravity gradiometers. The talk will conclude with speculative remarks looking to the future: Can atom interference methods be sued to detect gravity waves? Can non-classical (entangled/squeezed state) atom sources lead to meaningful sensor performance improvements?

  12. Growth and reactions of SiOx/Si nanostructures on surface-templated molecule corrals.

    PubMed

    Liu, Yi; Zhang, Zhanping; Wells, Matthew C; Beebe, Thomas P

    2005-09-13

    Surface-templated nanostructures on the highly oriented pyrolytic graphite (HOPG) basal plane were created by controlled Cs+- or Ga+)ion bombardment, followed by subsequent oxidation at high temperature, forming molecule corrals. The corrals were then used for template growth of SiOx/Si nanostructures. We demonstrate here that, for SiOx/Si nanostructures formed in controlled molecule corrals, the amount of silicon deposited on the surface is directly correlated with the corral density, making it possible to generate patterned SiOx/Si nanostructures on HOPG. Since the size, depth, position, and surface density of the nanostructures can be controlled on the HOPG, it is possible to produce surfaces with patterned or gradient functionalities for applications in fields such as biosensors, microelectronics, and biomaterials (e.g., neuron pathfinding). If desired, the SiOx structures can be reduced in size by etching in dilute HF, and further oxidation of the nanostructures is slow enough to provide plenty of time to functionalize them using ambient and solution reactions and to perform surface analysis. Organosilane monolayers on surface-templated SiOx/Si nanostructures were examined by X-ray photoelectron spectroscopy, time-of-flight secondary ion mas spectrometry, and atomic force microscopy. Silanes with long alkyl chains such as n-octadecyltrichlorosilane (C18) were found to both react on SiOx/Si nanostructures and to condense on the HOPG basal plane. Shorter-chain silanes, such as 11-bromoundicyltrimethoxysilane (C11) and 3-mercaptopropyltrimethoxysilane (C3) were found to react preferentially with SiOx/Si nanostructures, not HOPG. The SiOx/Si nanostructures were also found to be stable toward multiple chemical reactions. Selective modification of SiOx/Si nanostructures on the HOPG basal plane is thus achievable.

  13. Small Si clusters on surfaces of carbon nanotubes

    SciTech Connect

    Meng, Lijun; Zhang, Kaiwang; Stocks, George Malcolm; Zhong, Jianxin

    2006-01-01

    Structures of small Si clusters, Sin, on surfaces of carbon nanotubes have been studied by molecular dynamics simulation. We show that the lowest-energy structures of Sin are three-dimensional clusters rather than thin Si sheets covering the surface of a nanotube. As n increases from 10 to 30, Sin undergoes structural transitions from a tent-like structure (with nanotube surface as its base) to a cage-like structure (without interior atoms) and further to a spherical compact structure (with interior atoms). Our results are different from the structures of small Si clusters found in a free space without Si-nanotube interaction.

  14. Silicon interstitial injection during dry oxidation of SiGe /Si layers

    NASA Astrophysics Data System (ADS)

    Napolitani, E.; Di Marino, M.; De Salvador, D.; Carnera, A.; Spadafora, M.; Mirabella, S.; Terrasi, A.; Scalese, S.

    2005-02-01

    The injection of Si self-interstitial atoms during dry oxidation at 815°C of very shallow SiGe layers grown on Si (001) by molecular-beam epitaxy (MBE) has been investigated. We first quantified the oxidation enhanced diffusion (OED) of two boron deltas buried into the Si underlying the oxidized SiGe layers. Then, by simulating the interstitial diffusion in the MBE material with a code developed on purpose, we estimated the interstitial supersaturation (S) at the SiGe /Si interface. We found that S (a) is lower than that observed in pure Si, (b) is Ge-concentration dependent, and (c) has a very fast transient behavior. After such a short transient, the OED is completely suppressed, and the suppression lasts for long annealing times even after the complete oxidation of the SiGe layer. The above results have been related to the mechanism of oxidation of SiGe in which the Ge piles up at the SiO2/SiGe interface by producing a thin and defect-free layer with a very high concentration of Ge.

  15. Source apportionment and spatial-temporal variations in the metal content of surface dust collected from an industrial area adjoining Delhi, India.

    PubMed

    Pathak, Aditya Kumar; Yadav, Sudesh; Kumar, Pawan; Kumar, Rakesh

    2013-01-15

    Surface dust collected during three different seasons from Faridabad industrial area adjoining Delhi is studied for different metals, their spatial and temporal variations, and sources. Al, Fe, Mn, Ti, Ca and Mg show limited variations and lower abundances compared to Upper Continental Crust (UCC); Fe shows enrichment and seasonal changes. Cd, V, Co, Ba, Ti, Ni, Cu, Cr and Zn show significant spatial and temporal variations, and enrichments compared to UCC indicate their anthropogenic sources. Seasonal variability could be due to: 1) different types of industries, 2) variations in the emissions, 3) very frequent shifting of small scale industry within the region, and 4) changes in the land use pattern. The sampling sites, according to the geo-accumulation index, are: 1) least polluted for Ca, Mg, Al and Ti except for Ti in winter, 2) least to moderately polluted for Ba, Co and V but season specific, and 3) moderately to extremely polluted for other metals. Average pollution load index of 2.67-2.87 indicates consistently high level of pollution at all sites in all sampling seasons. The sites located in the residential areas near small to medium scale unorganized industry are more polluted compared to sites near large industries suggesting that the small scale unorganized industries causes more pollution. Three dominant sources of metals were identified: 1) mixed industrial, 2) crustal, and 3) vehicular, oil and battery related burnings. The third component related to Ba, Pb, Cd, Zn and Cr, further splits into two components in the pre-monsoon and winter samples. Surface dust, enriched in metals, is likely to cause serious danger to public health. There is an urgent need to make a shift from unorganized to formally organized industry to reduce the metal pollution and protect human health and environment as a whole.

  16. The Dependency of Probabilistic Tsunami Hazard Assessment on Magnitude Limits of Seismic Sources in the South China Sea and Adjoining Basins

    NASA Astrophysics Data System (ADS)

    Li, Hongwei; Yuan, Ye; Xu, Zhiguo; Wang, Zongchen; Wang, Juncheng; Wang, Peitao; Gao, Yi; Hou, Jingming; Shan, Di

    2016-08-01

    The South China Sea (SCS) and its adjacent small basins including Sulu Sea and Celebes Sea are commonly identified as tsunami-prone region by its historical records on seismicity and tsunamis. However, quantification of tsunami hazard in the SCS region remained an intractable issue due to highly complex tectonic setting and multiple seismic sources within and surrounding this area. Probabilistic Tsunami Hazard Assessment (PTHA) is performed in the present study to evaluate tsunami hazard in the SCS region based on a brief review on seismological and tsunami records. 5 regional and local potential tsunami sources are tentatively identified, and earthquake catalogs are generated using Monte Carlo simulation following the Tapered Gutenberg-Richter relationship for each zone. Considering a lack of consensus on magnitude upper bound on each seismic source, as well as its critical role in PTHA, the major concern of the present study is to define the upper and lower limits of tsunami hazard in the SCS region comprehensively by adopting different corner magnitudes that could be derived by multiple principles and approaches, including TGR regression of historical catalog, fault-length scaling, tectonic and seismic moment balance, and repetition of historical largest event. The results show that tsunami hazard in the SCS and adjoining basins is subject to large variations when adopting different corner magnitudes, with the upper bounds 2-6 times of the lower. The probabilistic tsunami hazard maps for specified return periods reveal much higher threat from Cotabato Trench and Sulawesi Trench in the Celebes Sea, whereas tsunami hazard received by the coasts of the SCS and Sulu Sea is relatively moderate, yet non-negligible. By combining empirical method with numerical study of historical tsunami events, the present PTHA results are tentatively validated. The correspondence lends confidence to our study. Considering the proximity of major sources to population-laden cities

  17. Comparison of 19th century ship log wind data and adjoining land-based Royal Observatory data (1843 to 1855): Spot the difference?

    NASA Astrophysics Data System (ADS)

    Brown, Alexa; Lennard, Chris; Grab, Stefan

    2016-04-01

    Historical weather and climate data are essential for the establishment of long-term climate patterns and future projections. For South Africa, where there is a paucity of such long-term climate data, it undermines the ability to establish climate changes and variability over longer periods of the past few centuries. Consequently, analyses of climate change in the region have relied on relatively poor resolution proxy records. Yet, the recently discovered instrumental meteorological records of the Royal Astronomical Observatory in Cape Town provides South Africa's (and possibly the southern hemisphere's) longest continuous time series of daily recorded weather measurements, including temperature, rainfall, barometric pressure and wind (1835 to present). Wind specifically is a reliable indicator of dynamic atmospheric circulation and lends supporting data for understanding the Mediterranean climate of the region. This project has manually digitized, pre-processed and validated wind data from the earliest records by comparing these data with the only other known wind data for that time in the region - namely ship log data. Ship log data, recovered and digitized by the CLIWOC project, are used for statistical correlation (using wavelet query analysis) and trend analysis for the period 1843 to 1855. Both data sources indicate the same general wind climatological trends. The similarly decreasing trend in average wind velocity over the time period investigated, suggests that the data have been adequately captured and that ship log data are representative of adjoining land-based synoptic conditions. It is hoped that short term cyclic/extreme events can be extracted using a wavelet query analysis by correlating the data at various time steps. Differences in the timing of recordings and spatial scales between data sets present challenges for such a comparison. This work is part of a larger digitization project which is analysing Cape instrumental and documentary weather

  18. ZnO/porous-Si and TiO{sub 2}/porous-Si nanocomposite nanopillars

    SciTech Connect

    Wang, Dong Yan, Yong; Schaaf, Peter; Sharp, Thomas; Schönherr, Sven; Ronning, Carsten; Ji, Ran

    2015-01-01

    Porous Si nanopillar arrays are used as templates for atomic layer deposition of ZnO and TiO{sub 2}, and thus, ZnO/porous-Si and TiO{sub 2}/porous-Si nanocomposite nanopillars are fabricated. The diffusion of the precursor molecules into the inside of the porous structure occurs via Knudsen diffusion and is strongly limited by the small pore size. The luminescence of the ZnO/porous-Si nanocomposite nanopillars is also investigated, and the optical emission can be changed and even quenched after a strong plasma treatment. Such nanocomposite nanopillars are interesting for photocatalysis and sensors.

  19. Dislocation engineering in SiGe heteroepitaxial films on patterned Si (001) substrates

    NASA Astrophysics Data System (ADS)

    Gatti, R.; Boioli, F.; Grydlik, M.; Brehm, M.; Groiss, H.; Glaser, M.; Montalenti, F.; Fromherz, T.; Schäffler, F.; Miglio, Leo

    2011-03-01

    We demonstrate dislocation engineering without oxide masks. By using finite element simulations we show how nanopatterning of Si substrates with {111} trenches provides anisotropic elastic relaxation in a SiGe film, generates preferential nucleation sites for dislocation loops, and allows for dislocation trapping, leaving wide areas free of threading dislocations. These predictions are confirmed by atomic force and transmission electron microscopy performed on overcritical Si0.7Ge0.3 films. These were grown by molecular beam epitaxy on a Si(001) substrate patterned with periodic arrays of selectively etched {111}-terminated trenches.

  20. Dislocation engineering in SiGe heteroepitaxial films on patterned Si (001) substrates

    SciTech Connect

    Gatti, R.; Boioli, F.; Montalenti, F.; Miglio, Leo; Grydlik, M.; Brehm, M.; Groiss, H.; Glaser, M.; Fromherz, T.; Schaeffler, F.

    2011-03-21

    We demonstrate dislocation engineering without oxide masks. By using finite element simulations we show how nanopatterning of Si substrates with (111) trenches provides anisotropic elastic relaxation in a SiGe film, generates preferential nucleation sites for dislocation loops, and allows for dislocation trapping, leaving wide areas free of threading dislocations. These predictions are confirmed by atomic force and transmission electron microscopy performed on overcritical Si{sub 0.7}Ge{sub 0.3} films. These were grown by molecular beam epitaxy on a Si(001) substrate patterned with periodic arrays of selectively etched (111)-terminated trenches.

  1. Optical anisotropies of Si grown on step-graded SiGe(110) layers

    NASA Astrophysics Data System (ADS)

    Balderas-Navarro, R. E.; Lastras-Martínez, L. F.; Arimoto, K.; Castro-García, R.; Villalobos-Aguilar, O.; Lastras-Martínez, A.; Nakagawa, K.; Sawano, K.; Shiraki, Y.; Usami, N.; Nakajima, K.

    2010-03-01

    Macroreflectance and microreflectance difference spectroscopies have been used to measure the strain induced optical anisotropies of semiconductor structures comprised of strained Si(110) thin films deposited on top of step-graded SiGe virtual substrates. The stress relaxation mechanism mainly occurs by the introduction of microtwin formation, whose fluctuation depends strongly on growth conditions. Correlations of such optical diagnostics with x-ray diffraction measurements and atomic force microscopy images, allow for the in situ study of the strain within both the top Si layer and the SiGe underneath with an spatial resolution of at least 5 μm.

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

    NASA Astrophysics Data System (ADS)

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

    2016-05-01

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

  3. Ion Beam Synthesis Of Metal - Silicon Carbide - Si Multilayer Structures

    NASA Astrophysics Data System (ADS)

    Lindner, J. K. N.; Tsang, W. M.; Stritzker, B.; Wong, S. P.

    2003-08-01

    High doses of Ti, Ni, Mo, or W ions were implanted at elevated temperatures either conventionally or using a MEVVA ion source into ion beam synthesized Si/SiC/Si or SiC/Si layer structures in order to create metallic layers contacting the SiC. The depth distribution of metal atoms and the formation of silicide and carbide phases as well as the formation of cavities at the lower SiC/Si interface are studied by Rutherford backscattering spectroscopy (RBS) and cross-sectional transmission electron microscopy (XTEM). A brief survey of the effects ocurring in the ion beam metallization of SiC films is given and the benefit of using ion beams for metallization of thin films is elucidated.

  4. Formation of nanocrystalline silicon in SiO x by soft X-ray irradiation at low temperature

    NASA Astrophysics Data System (ADS)

    Heya, Akira; Kusakabe, Fumito; Matsuo, Naoto; Kanda, Kazuhiro; Kohama, Kazuyuki; Ito, Kazuhiro

    2017-03-01

    The low-temperature formation of nanocrystalline Si (nc-Si) in SiO x film is one of the key technologies in the realization of Si-based photonics and memories. We proposed a low-temperature nc-Si formation method with soft X-ray irradiation. The nc-Si formation depended on the Si/O atomic ratio in the pristine SiO x film. The Si-rich regions in SiO x films with Si/O ratios higher than 0.67 were crystallized by atomic migration via electron excitation with soft X-ray irradiation at a photon energy near the core level of Si 2p. nc-Si with a mean size of 20 nm was formed by soft X-ray irradiation at a low temperature of 660 °C.

  5. Status of the atomized uranium silicide fuel development at KAERI

    SciTech Connect

    Kim, C.K.; Kim, K.H.; Park, H.D.; Kuk, I.H.

    1997-08-01

    While developing KMRR fuel fabrication technology an atomizing technique has been applied in order to eliminate the difficulties relating to the tough property of U{sub 3}Si and to take advantage of the rapid solidification effect of atomization. The comparison between the conventionally comminuted powder dispersion fuel and the atomized powder dispersion fuel has been made. As the result, the processes, uranium silicide powdering and heat treatment for U{sub 3}Si transformation, become simplified. The workability, the thermal conductivity and the thermal compatibility of fuel meat have been investigated and found to be improved due to the spherical shape of atomized powder. In this presentation the overall developments of atomized U{sub 3}Si dispersion fuel and the planned activities for applying the atomizing technique to the real fuel fabrication are described.

  6. Direct growth of graphene on Si(111)

    SciTech Connect

    Thanh Trung, Pham Joucken, Frédéric; Colomer, Jean-François; Robert, Sporken; Campos-Delgado, Jessica; Raskin, Jean-Pierre; Hackens, Benoît; Santos, Cristiane N.

    2014-06-14

    Due to the need of integrated circuit in the current silicon technology, the formation of graphene on Si wafer is highly desirable, but is still a challenge for the scientific community. In this context, we report the direct growth of graphene on Si(111) wafer under appropriate conditions using an electron beam evaporator. The structural quality of the material is investigated in detail by reflection high energy electron diffraction, Auger electron spectroscopy, X-ray photoemission spectroscopy, Raman spectroscopy, high resolution scanning electron microscopy, atomic force microscopy, and scanning tunneling microscopy. Our experimental results confirm that the quality of graphene is strongly dependent on the growth time during carbon atoms deposition.

  7. Atomic scale investigation of silicon nanowires and nanoclusters

    PubMed Central

    2011-01-01

    In this study, we have performed nanoscale characterization of Si-clusters and Si-nanowires with a laser-assisted tomographic atom probe. Intrinsic and p-type silicon nanowires (SiNWs) are elaborated by chemical vapor deposition method using gold as catalyst, silane as silicon precursor, and diborane as dopant reactant. The concentration and distribution of impurity (gold) and dopant (boron) in SiNW are investigated and discussed. Silicon nanoclusters are produced by thermal annealing of silicon-rich silicon oxide and silica multilayers. In this process, atom probe tomography (APT) provides accurate information on the silicon nanoparticles and the chemistry of the nanolayers. PMID:21711788

  8. Microstructural Properties of NC-Si/SiO2 Films IN SITU Grown by Reactive Magnetron Co-Sputtering

    NASA Astrophysics Data System (ADS)

    Lu, Wanbing; Guo, Shaogang; Wang, Jiantao; Li, Yun; Wang, Xinzhan; Yu, Gengxi; Fan, Shanshan; Fu, Guangsheng

    2012-01-01

    Nanocrystalline silicon embedded in silicon oxide (nc-Si/SiO2) films have been in situ grown at a low substrate temperature of 300°C by reactive magnetron co-sputtering of Si and SiO2 targets in a mixed Ar/H2 discharge. The influences of H2 flow rate (FH) on the microstructural properties of the deposited nc-Si/SiO2 films were investigated. The results of XRD and the deposition rate of nc-Si/SiO2 films show that the introduction of H2 contributes to the growth of nc-Si grains in silicon oxide matrix. With further increasing FH, the average size of nc-Si grains increases and the deposition rate of nc-Si/SiO2 films decreases gradually. Fourier transform infrared spectra analyses reveal that introduction of hydrogen contributes to the phase separation of nc-Si and SiOx in the deposited films. Moreover, the Si-O4-nSin(n = 0, 1) concentration of the deposited nc-Si/SiO2 films reduces with the increase of FH, while that of Si-O4-nSin(n = 2, 3) concentration increases. These results can be explained by that active hydrogen atoms increase the probability of reducing oxygen from precursor in the plasma and prompting oxygen desorption from the growing surface. This low-temperature procedure for preparing nc-Si/SiO2 films opens up the possibility of fabricating the silicon-based thin-film solar cells onto low-cost glass substrates using nc-Si/SiO2 films.

  9. Phase separation in SiGe nanocrystals embedded in SiO{sub 2} matrix during high temperature annealing

    SciTech Connect

    Mogaddam, N. A. P.; Turan, R.; Alagoz, A. S.; Yerci, S.; Foss, S.; Finstad, T. G.

    2008-12-15

    SiGe nanocrystals have been formed in SiO{sub 2} matrix by cosputtering Si, Ge, and SiO{sub 2} independently on Si substrate. Effects of the annealing time and temperature on structural and compositional properties are studied by transmission electron microscopy, x-ray diffraction (XRD), and Raman spectroscopy measurements. It is observed that Ge-rich Si{sub (1-x)}Ge{sub x} nanocrystals do not hold their compositional uniformity when annealed at high temperatures for enough long time. A segregation process leading to separation of Ge and Si atoms from each other takes place. This process has been evidenced by a double peak formation in the XRD and Raman spectra. We attributed this phase separation to the differences in atomic size, surface energy, and surface diffusion disparity between Si and Ge atoms leading to the formation of nonhomogenous structure consist of a Si-rich SiGe core covered by a Ge-rich SiGe shell. This experimental observation is consistent with the result of reported theoretical and simulation methods.

  10. Controlling the half-metallicity of Heusler/Si(1 1 1) interfaces by a monolayer of Si-Co-Si.

    PubMed

    Nedelkoski, Zlatko; Kepaptsoglou, Demie; Ghasemi, Arsham; Kuerbanjiang, Balati; Hasnip, Philip J; Yamada, Shinya; Hamaya, Kohei; Ramasse, Quentin M; Hirohata, Atsufumi; Lazarov, Vlado K

    2016-10-05

    By using first-principles calculations we show that the spin-polarization reverses its sign at atomically abrupt interfaces between the half-metallic Co2(Fe,Mn)(Al,Si) and Si(1 1 1). This unfavourable spin-electronic configuration at the Fermi-level can be completely removed by introducing a Si-Co-Si monolayer at the interface. In addition, this interfacial monolayer shifts the Fermi-level from the valence band edge close to the conduction band edge of Si. We show that such a layer is energetically favourable to exist at the interface. This was further confirmed by direct observations of CoSi2 nano-islands at the interface, by employing atomic resolution scanning transmission electron microscopy.

  11. Controlling the half-metallicity of Heusler/Si(1 1 1) interfaces by a monolayer of Si-Co-Si

    NASA Astrophysics Data System (ADS)

    Nedelkoski, Zlatko; Kepaptsoglou, Demie; Ghasemi, Arsham; Kuerbanjiang, Balati; Hasnip, Philip J.; Yamada, Shinya; Hamaya, Kohei; Ramasse, Quentin M.; Hirohata, Atsufumi; Lazarov, Vlado K.

    2016-10-01

    By using first-principles calculations we show that the spin-polarization reverses its sign at atomically abrupt interfaces between the half-metallic Co2(Fe,Mn)(Al,Si) and Si(1 1 1). This unfavourable spin-electronic configuration at the Fermi-level can be completely removed by introducing a Si-Co-Si monolayer at the interface. In addition, this interfacial monolayer shifts the Fermi-level from the valence band edge close to the conduction band edge of Si. We show that such a layer is energetically favourable to exist at the interface. This was further confirmed by direct observations of CoSi2 nano-islands at the interface, by employing atomic resolution scanning transmission electron microscopy.

  12. First-principles study of twin grain boundaries in epitaxial BaSi2 on Si(111)

    NASA Astrophysics Data System (ADS)

    Baba, Masakazu; Kohyama, Masanori; Suemasu, Takashi

    2016-08-01

    Epitaxial films of BaSi2 on Si(111) for solar cell applications possess three epitaxial variants and exhibit a minority carrier diffusion length (ca. 9.4 μm) much larger than the domain size (ca. 0.2 μm); thus, the domain boundaries (DBs) between the variants do not act as carrier recombination centers. In this work, transmission electron microscopy (TEM) was used to observe the atomic arrangements around the DBs in BaSi2 epitaxial films on Si(111), and the most stable atomic configuration was determined by first-principles calculations based on density functional theory to provide possible interface models. Bright-field TEM along the a-axis of BaSi2 revealed that each DB was a twin boundary between two different epitaxial variants, and that Ba(II) atoms form hexagons containing central Ba(I) atoms in both the bulk and DB regions. Four possible interface models containing Ba(I)-atom interface layers were constructed, each consistent with TEM observations and distinguished by the relationship between the Si tetrahedron arrays in the two domains adjacent across the interface. This study assessed the structural relaxation of initial interface models constructed from surface slabs terminated by Ba(I) atoms or from zigzag surface slabs terminated by Si tetrahedra and Ba(II) atoms. In these models, the interactions or relative positions between Si tetrahedra appear to dominate the relaxation behavior and DB energies. One of the four interface models whose relationship between first-neighboring Si tetrahedra across the interface was the same as that in the bulk was particularly stable, with a DB energy of 95 mJ/m2. There were no significant differences in the partial densities of states and band gaps between the bulk and DB regions, and it was therefore concluded that such DBs do not affect the minority carrier properties of BaSi2.

  13. Method for the hydrogenation of poly-si

    SciTech Connect

    Wang, Qi

    2013-11-12

    A method for hydrogenating poly-si. Poly-si is placed into the interior of a chamber. A filament is placed into the interior of a chamber. The base pressure of the interior of the chamber is evacuated, preferably to 10.sup.-6 Torr or less. The poly-si is heated for a predetermined poly-si heating time. The filament is heated by providing an electrical power to the filament. Hydrogen is supplied into the pressurized interior of the chamber comprising the heated poly-si and the heated filament. Atomic hydrogen is produced by the filament at a rate whereby the atomic hydrogen surface density at the poly-si is less than the poly-si surface density. Preferably, the poly-si is covered from the atomic hydrogen produced by the heated filament for a first predetermined covering time. Preferably, the poly-si is then uncovered from the atomic hydrogen produced by the heated filament for a first hydrogenation time.

  14. Density relative change and interface zone mutual diffusion of BiFeO3 films prepared on Si (1 0 0), SiO2 and SiO2/Si (1 0 0)

    NASA Astrophysics Data System (ADS)

    Xiao, RenZheng; Wang, ZeSong; Yuan, XianBao; Zhou, JianJun; Mao, ZhangLiang; Su, HuaShan; Li, Bo; Fu, DeJun

    2016-10-01

    The mutual diffusion taken place in the interface zone between BiFeO3 (BFO) films and substrates (Si (1 0 0), SiO2 and SiO2/Si (1 0 0)) has been revealed by energy dispersive X-ray spectroscopy (EDS) and Rutherford Backscattering Spectrometry (RBS). RBS spectra provide the relative atomic concentrations of Bi, Fe, Si, and O elements changed with the samples' depth as analyzed by RBS spectra fitting SIMNRA software. A certain width of the intermixing layer is probably formed between BFO films and individual substrate which is attributed to mutual diffusion in the interface zone during annealing process. The mechanism of concerted exchange component can explain the interface zone mutual diffusion phenomenon between BFO films and substrates. The width of the interface zone between BFO film and Si (1 0 0), SiO2, and SiO2/Si (1 0 0) substrate is about 1.94 × 1017, 2.01 × 1017 and 3.05 × 1017 atoms/cm2, respectively, which are equivalent to 30.9, 36.7, and 52.9 nm, respectively. It has been declared that the effect on density relative to BFO film is loosen or attenuation is presented in the interface zone, which can be interpreted as a migration or diffusion of various atoms during the annealing. This can also provide an evidence of atomic dynamics and defect engineering on interface diffusion.

  15. Stable silaimines with three- and four-coordinate silicon atoms.

    PubMed

    Samuel, Prinson P; Azhakar, Ramachandran; Ghadwal, Rajendra S; Sen, Sakya S; Roesky, Herbert W; Granitzka, Markus; Matussek, Julia; Herbst-Irmer, Regine; Stalke, Dietmar

    2012-10-15

    The reactions of silylenes with organic azides are quite diverse, depending on the substituents of the silylene center and on the nature of the azide employed. Elusive silaimine with three-coordinate silicon atom L(1)SiN(2,6-Triip(2)-C(6)H(3)) (5) {L(1) = CH[(C═CH(2))(CMe)(2,6-iPr(2)C(6)H(3)N)(2)] and Triip = 2,4,6-triisopropylphenyl} was synthesized by treatment of the silylene L(1)Si (1) with a sterically demanding 2,6-bis(2,4,6-triisopropylphenyl)phenyl azide (2,6-Triip(2)C(6)H(3)N(3)). The reaction of Lewis base-stabilized dichlorosilylene L(2)SiCl(2) (2) {L(2) = 1,3-bis(2,6-iPr(2)C(6)H(3))imidazol-2-ylidene} with Ph(3)SiN(3) afforded four-coordinate silaimine L(2)(Cl(2))SiNSiPh(3) (6). Treatment of 2,6-Triip(2)C(6)H(3)N(3) with L(3)SiCl (3) (L(3) = PhC(NtBu)(2)) yielded silaimine L(3)(Cl)SiN(2,6-Triip(2)-C(6)H(3)) (7) possessing a four-coordinate silicon atom. The reactions of L(3)SiN(SiMe(3))(2) (4) with adamantyl and trimethylsilyl azide furnished silaimine compounds with a four-coordinate silicon atom L(3)(N(Ad)SiMe(3))SiN(SiMe(3)) (8) (Ad = adamantyl) and L(3)(N(SiMe(3))(2))SiN(SiMe(3)) (9). Compound 8 was formed by migration of one of the SiMe(3) groups. Compounds 5-9 are stable under inert atmosphere and were characterized by elemental analysis, NMR spectroscopy, and single-crystal X-ray studies.

  16. Energy-band alignment of atomic layer deposited (HfO2)x(Al2O3)1 - x gate dielectrics on 4H-SiC

    NASA Astrophysics Data System (ADS)

    Jia, Ren-Xu; Dong, Lin-Peng; Niu, Ying-Xi; Li, Cheng-Zhan; Song, Qing-Wen; Tang, Xiao-Yan; Yang, Fei; Zhang, Yu-Ming

    2015-03-01

    We study a series of (HfO2)x(Al2O3)1 - x /4H-SiC MOS capacitors. It is shown that the conduction band offset of HfO2 is 0.5 eV and the conduction band offset of HfAlO is 1.11-1.72 eV. The conduction band offsets of (HfO2)x(Al2O3)1 - x are increased with the increase of the Al composition, and the (HfO2)x(Al2O3)1 - x offer acceptable barrier heights (> 1 eV) for both electrons and holes. With a higher conduction band offset, (HfO2)x(Al2O3)1 - x/4H-SiC MOS capacitors result in a ˜ 3 orders of magnitude lower gate leakage current at an effective electric field of 15 MV/cm and roughly the same effective breakdown field of ˜ 25 MV/cm compared to HfO2. Considering the tradeoff among the band gap, the band offset, and the dielectric constant, we conclude that the optimum Al2O3 concentration is about 30% for an alternative gate dielectric in 4H-SiC power MOS-based transistors. Project supported by the National Natural Science Foundation of China (Grant Nos. 51272202 and 61234006) and the Science Project of State Grid, China (Grant No. SGRI-WD-71-14-004).

  17. Domain formation and polarization reversal under atomic force microscopy-tip voltages in ion-sliced LiNbO{sub 3} films on SiO{sub 2}/LiNbO{sub 3} substrates

    SciTech Connect

    Gainutdinov, R. V.; Volk, T. R.; Zhang, H. H.

    2015-10-19

    We report on studies on writing of micro- and nanodomains and specified domain patterns by AFM-tip voltages U{sub DC} in thin (0.5 μm thick) ion-sliced LiNbO{sub 3} films embedded to SiO{sub 2}/LiNbO{sub 3} substrates. A peculiar feature is an overlapping of domains as the distance between them decreases. Piezoelectric hysteresis loops were measured in a wide range of U{sub DC} pulse durations. Domain dynamics and characteristics of hysteresis loops reveal marked distinctions from those observed so far in LiNbO{sub 3} films and bulk crystals.

  18. Atomic arias

    NASA Astrophysics Data System (ADS)

    Crease, Robert P.

    2009-01-01

    The American composer John Adams uses opera to dramatize controversial current events. His 1987 work Nixon in China was about the landmark meeting in 1972 between US President Richard Nixon and Chairman Mao Zedong of China; The Death of Klinghoffer (1991) was a musical re-enactment of an incident in 1985 when Palestinian terrorists kidnapped and murdered a wheelchair-bound Jewish tourist on a cruise ship. Adams's latest opera, Doctor Atomic, is also tied to a controversial event: the first atomic-bomb test in Alamogordo, New Mexico, on 16 June 1945. The opera premièred in San Francisco in 2005, had a highly publicized debut at the Metropolitan Opera in New York in 2008, and will have another debut on 25 February - with essentially the same cast - at the English National Opera in London.

  19. Atomic rivals

    SciTech Connect

    Goldschmidt, B.

    1990-01-01

    This book is a memoir of rivalries among the Allies over the bomb, by a participant and observer. Nuclear proliferation began in the uneasy wartime collaboration of the United States, England, Canada, and Free France to produce the atom bomb. Through the changes of history, a young French chemist had a role in almost every act of this international drama. This memoir is based on Goldschmidt's own recollections, interviews with other leading figures, and 3,000 pages of newly declassified documents in Allied archives. From his own start as Marie Curie's lab assistant, Goldschmidt's career was closely intertwined with Frances complicated rise to membership in the nuclear club. As a refugee from the Nazis, he became part of the wartime nuclear energy project in Canada and found himself the only French scientist to work (although briefly) on the American atom bomb project.

  20. Imaging of trapped charge in SiO{sub 2} and at the SiO{sub 2}{endash}Si interface

    SciTech Connect

    Ludeke, R.; Cartier, E.

    2001-06-18

    Charged defects in SiO{sub 2} and at the SiO{sub 2}{endash}Si(111) interface were imaged with a noncontact atomic force microscope. Electrons and holes trapped at interfacial P{sub b} centers in n- and p-type samples were identified from simultaneously recorded Kelvin images. Limited trap occupancy, determined by the local, bias controlled Fermi level, and strong band bending lead to unusually sharp images of trapped charge. {copyright} 2001 American Institute of Physics.

  1. Atomic physics

    SciTech Connect

    Livingston, A.E.; Kukla, K.; Cheng, S.

    1995-08-01

    In a collaboration with the Atomic Physics group at Argonne and the University of Toledo, the Atomic Physics group at the University of Notre Dame is measuring the fine structure transition energies in highly-charged lithium-like and helium-like ions using beam-foil spectroscopy. Precise measurements of 2s-2p transition energies in simple (few-electron) atomic systems provide stringent tests of several classes of current atomic- structure calculations. Analyses of measurements in helium-like Ar{sup 16+} have been completed, and the results submitted for publication. A current goal is to measure the 1s2s{sup 3}S{sub 1} - 1s2p{sup 3}P{sub 0} transition wavelength in helium-like Ni{sup 26+}. Measurements of the 1s2s{sup 2}S{sub 1/2} - 1s2p{sup 2}P{sub 1/2,3/2} transition wavelengths in lithium-like Kr{sup 33+} is planned. Wavelength and lifetime measurements in copper-like U{sup 63+} are also expected to be initiated. The group is also participating in measurements of forbidden transitions in helium-like ions. A measurement of the lifetime of the 1s2s{sup 3}S{sub 1} state in Kr{sup 34+} was published recently. In a collaboration including P. Mokler of GSI, Darmstadt, measurements have been made of the spectral distribution of the 2E1 decay continuum in helium-like Kr{sup 34+}. Initial results have been reported and further measurements are planned.

  2. Preparation and characterization of pulsed laser deposition (PLD) SiC films

    NASA Astrophysics Data System (ADS)

    Tang, Y. H.; Sham, T.-K.; Yang, D.; Xue, L.

    2006-03-01

    Si K-edge XAFS was used to characterize a stoichiometric SiC film prepared by pulsed KrF laser deposition. The film was deposited on a p-type Si(1 0 0) wafer at a substrate temperature of 250 °C in high vacuum with a laser fluence of ˜5 J/cm 2. The results reveal that the film contains mainly a SiC phase with an amorphous structure in which the Si atoms are bonded to C atoms in its first shell similar to that of crystalline SiC powder but with significant disorder.

  3. Atomic Databases

    NASA Astrophysics Data System (ADS)

    Mendoza, Claudio

    2000-10-01

    Atomic and molecular data are required in a variety of fields ranging from the traditional astronomy, atmospherics and fusion research to fast growing technologies such as lasers, lighting, low-temperature plasmas, plasma assisted etching and radiotherapy. In this context, there are some research groups, both theoretical and experimental, scattered round the world that attend to most of this data demand, but the implementation of atomic databases has grown independently out of sheer necessity. In some cases the latter has been associated with the data production process or with data centers involved in data collection and evaluation; but sometimes it has been the result of individual initiatives that have been quite successful. In any case, the development and maintenance of atomic databases call for a number of skills and an entrepreneurial spirit that are not usually associated with most physics researchers. In the present report we present some of the highlights in this area in the past five years and discuss what we think are some of the main issues that have to be addressed.

  4. Luminescence of Nanoporous Si and ALD-Deposited ZnO on Nanoporous Si Substrate

    NASA Astrophysics Data System (ADS)

    Pham, Vuong-Hung; Tam, Phuong Dinh; Dung, Nguyen Huu; Nguyen, Duy-Hung; Huy, Pham Thanh

    2017-03-01

    This paper reports the attempt at synthesizing nanoporous silicon (Si) with a dendritic-like structure and atomic layer deposition (ALD) of ZnO on nanoporous Si to control light emission intensity and emission center by applying an optimum voltage, etching time and thickness of ZnO layer. The dendritic-like structure of nanoporous Si was formed with low etching voltages of 5-10 V. Fourier transform infrared absorption spectra of the nanoporous Si reveals that the intensities of hydride stretching, SiH2 scissor mode and Si-O-Si vibration peak increase with the increasing of etching time. The formation of a thick dendritic-like structure with an increasing SiH2 bond resulted in significant enhancement of luminescence. In addition, the ALD-deposited ZnO layer on nanoporous Si resulted in light emission from both ZnO and nanoporous Si under a single excitation source. These results suggest the potential application of an ALD-deposited ZnO layer on nanoporous Si in designing materials for advanced optoelectronics.

  5. Geminal (2)J((29)Si-O-(29)Si) couplings in oligosiloxanes and their relation to direct (1)J((29) Si-(13)C) couplings.

    PubMed

    Kurfürst, Milan; Blechta, Vratislav; Schraml, Jan

    2011-08-01

    Absolute values of (79) geminal (2)J((29) Si-O-(29)Si) couplings were measured in an extensive series of (55) unstrained siloxanes dissolved in chloroform-d. Signs of (2)J((29)Si-O-(29)Si) in some (9) silicon hydrides were determined relative to (1)J((29)Si-(1)H) which are known to be negative. It is supposed that positive sign of the (2)J((29)Si-O-(29)Si) coupling found in all studied hydrides is common to all siloxanes. Theoretical calculations for simple model compounds failed to reproduce this sign and so their predictions of bond length and angle dependences cannot be taken as reliable. Useful empirical correlations were found between the (2)J((29)Si-O-(29)Si) couplings on one side and the total number m of oxygen atoms bonded to the silicon atoms, sum of (29)Si chemical shifts or product of (1)J((29)Si-(13)C) couplings on the other side. The significance of these correlations is briefly discussed.

  6. Tight-binding quantum chemical molecular dynamics simulations for the elucidation of chemical reaction dynamics in SiC etching with SF6/O2 plasma.

    PubMed

    Ito, Hiroshi; Kuwahara, Takuya; Kawaguchi, Kentaro; Higuchi, Yuji; Ozawa, Nobuki; Kubo, Momoji

    2016-03-21

    We used our etching simulator [H. Ito et al., J. Phys. Chem. C, 2014, 118, 21580-21588] based on tight-binding quantum chemical molecular dynamics (TB-QCMD) to elucidate SiC etching mechanisms. First, the SiC surface is irradiated with SF5 radicals, which are the dominant etchant species in experiments, with the irradiation energy of 300 eV. After SF5 radicals bombard the SiC surface, Si-C bonds dissociate, generating Si-F, C-F, Si-S, and C-S bonds. Then, etching products, such as SiS, CS, SiFx, and CFx (x = 1-4) molecules, are generated and evaporated. In particular, SiFx is the main generated species, and Si atoms are more likely to vaporize than C atoms. The remaining C atoms on SiC generate C-C bonds that may decrease the etching rate. Interestingly, far fewer Si-Si bonds than C-C bonds are generated. We also simulated SiC etching with SF3 radicals. Although the chemical reaction dynamics are similar to etching with SF5 radicals, the etching rate is lower. Next, to clarify the effect of O atom addition on the etching mechanism, we also simulated SiC etching with SF5 and O radicals/atoms. After bombardment with SF5 radicals, Si-C bonds dissociate in a similar way to the etching without O atoms. In addition, O atoms generate many C-O bonds and COy (y = 1-2) molecules, inhibiting the generation of C-C bonds. This indicates that O atom addition improves the removal of C atoms from SiC. However, for a high O concentration, many C-C and Si-Si bonds are generated. When the O atoms dissociate the Si-C bonds and generate dangling bonds, the O atoms terminate only one or two dangling bonds. Moreover, at high O concentrations there are fewer S and F atoms to terminate the dangling bonds than at low O concentration. Therefore, few dangling bonds of dissociated Si and C atoms are terminated, and they form many Si-Si and C-C bonds. Furthermore, we propose that the optimal O concentration is 50-60% because both Si and C atoms generate many etching products producing fewer C

  7. Optical properties of passivated Si nanocrystals and SiOx nanostructures

    NASA Astrophysics Data System (ADS)

    Dinh, L. N.; Chase, L. L.; Balooch, M.; Siekhaus, W. J.; Wooten, F.

    1996-08-01

    Thin films of Si nanoclusters passivated with oxygen or hydrogen, with an average size of a few nanometers, have been synthesized by thermal vaporization of Si in an Ar buffer gas, followed by subsequent exposure to oxygen or atomic hydrogen. High-resolution transmission electron microscopy and x-ray diffraction revealed that these nanoclusters were crystalline. However, during synthesis, if oxygen was the buffer gas, a network of amorphous Si oxide nanostructures (an-SiOx) with occasional embedded Si dots was formed. All samples showed strong infrared and/or visible photoluminescence (PL) with varying decay times from nanoseconds to microseconds depending on synthesis conditions. Absorption in the Si cores for surface passivated Si nano- crystals (nc-Si), but mainly in oxygen related defect centers for an-SiOx, was observed by photoluminescence excitation spectroscopy. The visible components of PL spectra were noted to blueshift and broaden as the size of the nc-Si was reduced. There were differences in PL spectra for hydrogen and oxygen passivated nc-Si. Many common PL properties between oxygen passivated nc-Si and an-SiOx were observed. Our data can be explained by a model involving absorption between quantum confined states in the Si cores and emission for which the decay times are very sensitive to surface and/or interface states. The emission could involve a simple band-to-band recombination mechanism within the Si cores. The combined evidence of all of our experimental results suggests, however, that emission between surface or interface states is a more likely mechanism.

  8. Thermal decomposition of silane to form hydrogenated amorphous Si film

    DOEpatents

    Strongin, Myron; Ghosh, Arup K.; Wiesmann, Harold J.; Rock, Edward B.; Lutz, III, Harry A.

    1980-01-01

    This invention relates to hydrogenated amorphous silicon produced by thermally decomposing silano (SiH.sub.4) or other gases comprising H and Si, at elevated temperatures of about 1700.degree.-2300.degree. C., and preferably in a vacuum of about 10.sup.-8 to 10.sup.-4 torr, to form a gaseous mixture of atomic hydrogen and atomic silicon, and depositing said gaseous mixture onto a substrate outside said source of thermal decomposition to form hydrogenated amorphous silicon.

  9. Thermal decomposition of silane to form hydrogenated amorphous Si

    DOEpatents

    Strongin, M.; Ghosh, A.K.; Wiesmann, H.J.; Rock, E.B.; Lutz, H.A. III

    Hydrogenated amorphous silicon is produced by thermally decomposing silane (SiH/sub 4/) or other gases comprising H and Si, at elevated temperatures of about 1700 to 2300/sup 0/C, in a vacuum of about 10/sup -8/ to 10/sup -4/ torr. A gaseous mixture is formed of atomic hydrogen and atomic silicon. The gaseous mixture is deposited onto a substrate to form hydrogenated amorphous silicon.

  10. Optically active zwitterionic lambda(5)Si,lambda(5)Si'-disilicates: syntheses, crystal structures, and behavior in aqueous solution.

    PubMed

    Theis, Bastian; Burschka, Christian; Tacke, Reinhold

    2008-01-01

    The zwitterionic lambda(5)Si,lambda(5)Si'-disilicates 1-8 were synthesized and characterized by solid-state and solution NMR spectroscopy. In addition, compounds 26 H(2)O, 32 CH(3)CN, 45/2 CH(3)CN, 6CH(3)OH, 7, and 8CH(3)OHCH(3)CN were studied by single-crystal X-ray diffraction. The optically active (Delta,Delta,R,R,R,R)-configured compounds 1-8 contain two pentacoordinate (formally negatively charged) silicon atoms and two tetracoordinate (formally positively charged) nitrogen atoms. One (ammonio)alkyl group is bound to each of the two silicon centers, and two tetradentate (R,R)-tartrato(4-) ligands bridge the silicon atoms. Although these lambda(5)Si,lambda(5)Si'-disilicates contain SiO(4)C skeletons, some of them display a remarkable stability in aqueous solution as shown by NMR spectroscopy and ESI mass spectrometry.

  11. Thermodynamic and kinetic control of the lateral Si wire growth

    SciTech Connect

    Dedyulin, Sergey N. Goncharova, Lyudmila V.

    2014-03-24

    Reproducible lateral Si wire growth has been realized on the Si (100) surface. In this paper, we present experimental evidence showing the unique role that carbon plays in initiating lateral growth of Si wires on a Si (100) substrate. Once initiated in the presence of ≈5 ML of C, lateral growth can be achieved in the range of temperatures, T = 450–650 °C, and further controlled by the interplay of the flux of incoming Si atoms with the size and areal density of Au droplets. Critical thermodynamic and kinetic aspects of the growth are discussed in detail.

  12. Microstructural investigations of light-emitting porous Si layers

    NASA Technical Reports Server (NTRS)

    George, T.; Anderson, M. S.; Pike, W. T.; Lin, T. L.; Fathauer, R. W.; Jung, K. H.; Kwong, D. L.

    1992-01-01

    The structural and morphological characteristics of visible-light-emitting porous Si layers produced by anodic and stain etching of single-crystal Si substrates are compared using transmission electron microscopy and atomic force microscopy (AFM). AFM of conventionally anodized, laterally anodized and stain-etched Si layers show that the layers have a fractal-type surface morphology. The anodized layers are rougher than the stain-etched films. At higher magnification 10 nm sized hillocks are visible on the surface. Transmission electron diffraction patterns indicate an amorphous structure with no evidence for the presence of crystalline Si in the near-surface regions of the porous Si layers.

  13. Enhanced and Retarded SiO2 Growth on Thermally Oxidized Fe-Contaminated n-Type Si(001) Surfaces

    NASA Astrophysics Data System (ADS)

    Shimizu, Hirofumi; Hagiwara, Hiroyuki

    2013-04-01

    At the beginning of the oxidation of Fe-contaminated n-type Si(001) surfaces, Fe reacted with oxygen (O2) on the silicon (Si) substrate to form Fe2O3 and oxygen-induced point defects (emitted Si + vacancies). SiO2 growth was mainly enhanced by catalytic action of Fe. At 650 °C, SiO2 growth of the contaminated samples was faster than in reference samples rinsed in RCA solution during the first 60 min. However, it substantially slowed and became less than that of the reference samples. As the oxidation advanced, approximately half of the contaminated Fe atoms became concentrated close to the surface area of the SiO2 film layer. This Fe2O3-rich SiO2 layer acted as a diffusion barrier against oxygen species. The diffusion of oxygen atoms toward the SiO2/Si interface may have been reduced, and in turn, the emission of Si self-interstitials owing to oxidation-induced strain may have been decreased at the SiO2/Si interface, resulting in the retarded oxide growth. These results are evidence that emitted Si self-interstitials are oxidized not in the Fe2O3-rich SiO2 layer, but at the SiO2/Si interface in accordance with a previously proposed model. A possible mechanism based on the interfacial Si emission model is discussed. The activation energies for the oxide growth are found to be in accord with the enhanced and reduced growths of the Fe-contaminated samples.

  14. Collisional atomic mixing

    NASA Astrophysics Data System (ADS)

    Biersack, Jochen P.

    The collisional mixing of thin metal markers in silicon is investigated with the computer program TRIM-DYNAMIC (T-DYN). This code assumes that at high dose irradiation, the substrate Si or Ge, will get fully amorphized, and the recoil atom can stop in any position after slowing down below a certain final energy Ef (taken here as 3 eV). In order to avoid chemical effects, the system Au marker in a silicon matrix was chosen for the TRIM simulation. The results are in good agreement with the experimental findings, as compiled in the review article by Paine and Averback. Similar collisional mixing effects occur in the process of SIMS or Auger electron depth profiling, and cannot be avoided. An example is given here for a thin layer of arsenic vapor deposited on Si and covered by amorphous silicon. The analysing ion beam in this case was 14.5 keV Cs+ incident at 37° towards the surface normal. In comparison with the SIMS measurements by modern depth profiling equipment, again good agreement was found between the T-DYN results and the experiment.

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

    NASA Astrophysics Data System (ADS)

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

    2010-12-01

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

  16. Si/SiGe MMIC's

    NASA Astrophysics Data System (ADS)

    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.

  17. Graphene growth at the interface between Ni catalyst layer and SiO2/Si substrate.

    PubMed

    Lee, Jeong-Hoon; Song, Kwan-Woo; Park, Min-Ho; Kim, Hyung-Kyu; Yang, Cheol-Woong

    2011-07-01

    Graphene was synthesized deliberately at the interface between Ni film and SiO2/Si substrate as well as on top surface of Ni film using chemical vapor deposition (CVD) which is suitable for large-scale and low-cost synthesis of graphene. The carbon atom injected at the top surface of Ni film can penetrate and reach to the Ni/SiO2 interface for the formation of graphene. Once we have the graphene in between Ni film and SiO2/Si substrate, the substrate spontaneously provides insulating SiO2 layer and we may easily get graphene/SiO2/Si structure simply by discarding Ni film. This growth of graphene at the interface can exclude graphene transfer step for electronic application. Raman spectroscopy and optical microscopy show that graphene was successfully synthesized at the back of Ni film and the coverage of graphene varies with temperature and time of synthesis. The coverage of graphene at the interface depends on the amount of carbon atoms diffused into the back of Ni film.

  18. Probing the valence orbitals of transition metal-silicon diatomic anions: ZrSi, NbSi, MoSi, PdSi and WSi.

    PubMed

    Gunaratne, K Don Dasitha; Berkdemir, Cuneyt; Harmon, C L; Castleman, A W

    2013-04-28

    Evolution of electronic properties and the nature of bonding of the 4d-transition metal silicides (ZrSi, NbSi, MoSi and PdSi) are discussed, revealing interesting trends in the transition metal-silicon interactions across the period. The electronic properties of select transition metal silicide diatomics have been determined by anion photoelectron imaging spectroscopy and theoretical methods. The electron binding energy spectra and photoelectron angular distributions obtained by 2.33 eV (532 nm) photons have revealed the distinct features of these diatomics. The theoretical calculations were performed at the density functional theory (DFT) level using the unrestricted B3LYP hybrid functional and at the ab initio unrestricted coupled cluster singles and doubles (triplets) (UCCSD(T)) methods to assign the ground electronic states of the neutral and anionic diatomics. The excited electronic states were calculated by the DFT (TD-DFT)/UB3LYP method. We have observed that the valence molecular orbital configuration of the ZrSi and NbSi anions are significantly different from that of the MoSi and PdSi anions. By combining our experimental and theoretical results, we report that the composition of the highest occupied molecular orbitals shift from a majority of transition metal s- and d-orbital contribution in ZrSi and NbSi, to mainly silicon p-orbital contribution for MoSi and PdSi. We expect these observed atomic scale transition metal-silicon interactions to be of increasing importance with the miniaturization of devices approaching the sub-nanometer size regime.

  19. Si Tight-Binding Parameters from Genetic Algorithm Fitting

    NASA Technical Reports Server (NTRS)

    Klimeck, G.; Bowen, R.; Boykin, T.; Salazar-Lazaro, C.; Cwik, T.; Stoica, A.

    1999-01-01

    Quantum mechanical simulations of carrier transport in Si require an accurate model of the complicated Si bandstructure. Tight-binding models are an attractive method of choice since they bear the full electronic structure symmetry in them and they can discretize a realistic device on an atomic scale.

  20. Atom-by-Atom Construction of a Quantum Device.

    PubMed

    Petta, Jason R

    2017-03-28

    Scanning tunneling microscopes (STMs) are conventionally used to probe surfaces with atomic resolution. Recent advances in STM include tunneling from spin-polarized and superconducting tips, time-domain spectroscopy, and the fabrication of atomically precise Si nanoelectronics. In this issue of ACS Nano, Tettamanzi et al. probe a single-atom transistor in silicon, fabricated using the precision of a STM, at microwave frequencies. While previous studies have probed such devices in the MHz regime, Tettamanzi et al. probe a STM-fabricated device at GHz frequencies, which enables excited-state spectroscopy and measurements of the excited-state lifetime. The success of this experiment will enable future work on quantum control, where the wave function must be controlled on a time scale that is much shorter than the decoherence time. We review two major approaches that are being pursued to develop spin-based quantum computers and highlight some recent progress in the atom-by-atom fabrication of donor-based devices in silicon. Recent advances in STM lithography may enable practical bottom-up construction of large-scale quantum devices.

  1. Si/Cu Interface Structure and Adhesion

    NASA Astrophysics Data System (ADS)

    Wang, Xiao-Gang; Smith, John

    2006-03-01

    An ab initio investigation of the Si(111)/Cu(111) interfacial atomic structure and adhesion is reported [1]. Misfit dislocations appear naturally, as do hcp interfacial silicide phases that vary with temperature. The silicides form in the interface even at relatively low temperatures. These results are consistent with available experimental data. [1] Xiao-Gang Wang, John Smith, Physical Review Letters 95, 156102 (2005).

  2. Unipolar resistive switching and tunneling oscillations in isolated Si-SiO x core-shell nanostructure

    NASA Astrophysics Data System (ADS)

    Ghanta, Ujjwal; Ray, Mallar; Ratan Bandyopadhyay, Nil; Minhaz Hossain, Syed

    2016-11-01

    Unipolar resistive switching (URS) is observed in isolated Si-SiO x core-shell nanostructures. I-V characteristics recorded by a conductive atomic force microscope tip show SET and RESET processes with self compliance behavior. Hopping of carriers through defect states in the high resistance state (HRS) and space charge limited conduction in the low resistance state (LRS) are found to be the dominant carrier transport mechanisms in Si-SiO x core-shell nanostructures. URS between LRS and HRS may be attributed to the transition between hydrogen bridge (Si-H-Si) and hydrogen doublet (Si-HH-Si) defects. During RESET process, charge carriers tunnel through the nanostructure giving rise to oscillatory conduction.

  3. Atom Skimmers and Atom Lasers Utilizing Them

    NASA Technical Reports Server (NTRS)

    Hulet, Randall; Tollett, Jeff; Franke, Kurt; Moss, Steve; Sackett, Charles; Gerton, Jordan; Ghaffari, Bita; McAlexander, W.; Strecker, K.; Homan, D.

    2005-01-01

    Atom skimmers are devices that act as low-pass velocity filters for atoms in thermal atomic beams. An atom skimmer operating in conjunction with a suitable thermal atomic-beam source (e.g., an oven in which cesium is heated) can serve as a source of slow atoms for a magneto-optical trap or other apparatus in an atomic-physics experiment. Phenomena that are studied in such apparatuses include Bose-Einstein condensation of atomic gases, spectra of trapped atoms, and collisions of slowly moving atoms. An atom skimmer includes a curved, low-thermal-conduction tube that leads from the outlet of a thermal atomic-beam source to the inlet of a magneto-optical trap or other device in which the selected low-velocity atoms are to be used. Permanent rare-earth magnets are placed around the tube in a yoke of high-magnetic-permeability material to establish a quadrupole or octupole magnetic field leading from the source to the trap. The atoms are attracted to the locus of minimum magnetic-field intensity in the middle of the tube, and the gradient of the magnetic field provides centripetal force that guides the atoms around the curve along the axis of the tube. The threshold velocity for guiding is dictated by the gradient of the magnetic field and the radius of curvature of the tube. Atoms moving at lesser velocities are successfully guided; faster atoms strike the tube wall and are lost from the beam.

  4. Analysis and recommendations for DPA calculations in SiC

    SciTech Connect

    Heinisch, H.L.

    1998-09-01

    Recent modeling results, coupled with the implications of available experimental results, provide sufficient information to achieve consensus on the values of threshold displacement energies to use in displacements per atom (DPA) calculations. The values recommended here, 20 eV for C and 35 eV for Si, will be presented for adoption by the international fusion materials community at the next IEA SiC/SiC workshop.

  5. Removal of B from Si by Hf addition during Al–Si solvent refining process

    PubMed Central

    Lei, Yun; Ma, Wenhui; Sun, Luen; Wu, Jijun; Dai, Yongnian; Morita, Kazuki

    2016-01-01

    Abstract A small amount of Hf was employed as a new additive to improve B removal in the electromagnetic solidification refinement of Si with an Al–Si melt, because Hf has a very strong affinity for B. The segregation ratio of Hf between the solid Si and Al–Si melt was estimated to range from 4.9 × 10−6 to 8.8 × 10−7 for Al concentrations of 0 to 64 at.%, respectively. The activity coefficient of Hf in solid Si at its infinite dilution was also estimated. A small addition of Hf (<1025 parts per million atoms, ppma) significantly improved the B removal. It was confirmed that the use of an increased Hf addition, slower cooling rate, and Al-rich Al–Si melt as the refining solvent removed B more efficiently. B in Si could be removed as much as 98.2% with 410 ppma Hf addition when the liquidus temperature of the Al–Si melt was 1173 K and the cooling rate was 4.5–7.6 K min–1. The B content in Si could be controlled from 153 ppma to 2.7 ppma, which meets the acceptable level for solar-grade Si. PMID:27877853

  6. Morphology Analysis of Si Island Arrays on Si(001)

    PubMed Central

    2010-01-01

    The formation of nanometer-scale islands is an important issue for bottom-up-based schemes in novel electronic, optoelectronic and magnetoelectronic devices technology. In this work, we present a detailed atomic force microscopy analysis of Si island arrays grown by molecular beam epitaxy. Recent reports have shown that self-assembled distributions of fourfold pyramid-like islands develop in 5-nm thick Si layers grown at substrate temperatures of 650 and 750°C on HF-prepared Si(001) substrates. Looking for wielding control and understanding the phenomena involved in this surface nanostructuring, we develop and apply a formalism that allows for processing large area AFM topographic images in a shot, obtaining surface orientation maps with specific information on facets population. The procedure reveals some noticeable features of these Si island arrays, e.g. a clear anisotropy of the in-plane local slope distributions. Total island volume analysis also indicates mass transport from the substrate surface to the 3D islands, a process presumably related to the presence of trenches around some of the pyramids. Results are discussed within the framework of similar island arrays in homoepitaxial and heteroepitaxial semiconductor systems. PMID:21170139

  7. New Insights into Understanding Irreversible and Reversible Lithium Storage within SiOC and SiCN Ceramics

    PubMed Central

    Graczyk-Zajac, Magdalena; Reinold, Lukas Mirko; Kaspar, Jan; Sasikumar, Pradeep Vallachira Warriam; Soraru, Gian-Domenico; Riedel, Ralf

    2015-01-01

    Within this work we define structural properties of the silicon carbonitride (SiCN) and silicon oxycarbide (SiOC) ceramics which determine the reversible and irreversible lithium storage capacities, long cycling stability and define the major differences in the lithium storage in SiCN and SiOC. For both ceramics, we correlate the first cycle lithiation or delithiation capacity and cycling stability with the amount of SiCN/SiOC matrix or free carbon phase, respectively. The first cycle lithiation and delithiation capacities of SiOC materials do not depend on the amount of free carbon, while for SiCN the capacity increases with the amount of carbon to reach a threshold value at ~50% of carbon phase. Replacing oxygen with nitrogen renders the mixed bond Si-tetrahedra unable to sequester lithium. Lithium is more attracted by oxygen in the SiOC network due to the more ionic character of Si-O bonds. This brings about very high initial lithiation capacities, even at low carbon content. If oxygen is replaced by nitrogen, the ceramic network becomes less attractive for lithium ions due to the more covalent character of Si-N bonds and lower electron density on the nitrogen atom. This explains the significant difference in electrochemical behavior which is observed for carbon-poor SiCN and SiOC materials.

  8. On the local electronic and atomic structure of Ce1-xPrxO2-δ epitaxial films on Si

    SciTech Connect

    Niu, Gang Schubert, Markus Andreas; Zoellner, Marvin Hartwig; D'Acapito, Francesco; Boscherini, Federico

    2014-09-28

    The local electronic and atomic structure of (111)-oriented, single crystalline mixed Ce1-xPrxO2-δ (x = 0, 0.1 and 0.6) epitaxial thin films on silicon substrates have been investigated in view of engineering redox properties of complex oxide films. Non-destructive X-ray absorption near edge structure reveals that Pr shows only +3 valence and Ce shows only nominal +4 valence in mixed oxides. Extended x-ray absorption fine structure (EXAFS) studies were performed at K edges of Ce and Pr using a specially designed monochromator system for high energy measurements. They demonstrate that the fluorite lattice of ceria (CeO₂) is almost not perturbed for x = 0.1 sample, while higher Pr concentration (x = 0.6) not only generates a higher disorder level (thus more disordered oxygen) but also causes a significant reduction of Ce–O interatomic distances. The valence states of the cations were also examined by techniques operating in highly reducing environments: scanning transmission electron microscopy-electron energy loss spectroscopy and X-ray photoemission spectroscopy; in these reducing environments, evidence for the presence of Ce³⁺ was clearly found for the higher Pr concentration. Thus, the introduction of Pr³⁺ into CeO₂ strongly enhances the oxygen exchange properties of CeO₂. This improved oxygen mobility properties of CeO₂ are attributed to the lattice disorder induced by Pr mixing in the CeO₂ fluorite lattice, as demonstrated by EXAFS measurements. Thus, a comprehensive picture of the modifications of the atomic and electronic structure of Ce1-xPrxO2-δ epitaxial films and their relation is obtained.

  9. Growth kinetics of SiO2 on (001) Si catalyzed by Cu3Si at elevated temperatures

    NASA Astrophysics Data System (ADS)

    Huang, H. Y.; Chen, L. J.

    2000-08-01

    The oxidation of Si catalyzed by 170-nm-thick Cu3Si at elevated temperatures has been investigated by transmission electron microscopy, glancing angle x-ray diffraction, and Auger electron spectroscopy. For wet oxidation at 140-180 °C, the thickness of the oxide was found to increase parabolically with time with an activation energy of 0.4±0.2 eV. The activation energy is close to that of diffusivity of Cu in Si. At 180-200 °C, the growth rate became slower with increasing temperature. The growth of oxide tended to be discontinuous at the surface as the oxidation temperature was increased to a temperature at or higher than 300 °C. The anomalously fast growth of oxide at low temperatures is attributed to the presence of filamentary structures of Cu clusters in the oxide to expedite the diffusion of the oxidants through oxide. At 200-250 °C, more Cu atoms diffuse to the Cu3Si/Si interface and less Cu atoms stay in the oxide, which slows down the oxide growth. The lack of filamentary structures of Cu as diffusion paths retards the growth of SiO2. At 300 °C or higher temperatures, the lack of filamentary structures of Cu clusters stopped the growth of continuous oxide layer altogether.

  10. Mechanical and dynamical behaviors of ZrSi and ZrSi{sub 2} bulk metallic glasses: A molecular dynamics study

    SciTech Connect

    Ju, Shin-Pon; Wu, Tsang-Yu; Liu, Shih-Hao

    2015-03-14

    The mechanical and dynamical properties of ZrSi and ZrSi{sub 2} bulk metallic glasses (BMGs) have been investigated by molecular dynamics simulation. The Honeycutt-Anderson (HA) index analysis indicates that the major indexes in ZrSi and ZrSi{sub 2} bulk metallic glasses are 1551, 1541, and 1431, which refers to the liquid structure. For uniaxial tension, the results show that the ZrSi and ZrSi{sub 2} BMGs are more ductile than their crystal counterparts. The evolution of the distribution of atomic local shear strain clearly shows the initialization of shear transformation zones (STZs), the extension of STZs, and the formation of shear bands along a direction 45° from the tensile direction when the tensile strain gradually increases. The self-diffusion coefficients of ZrSi and ZrSi{sub 2} BMGs at temperatures near their melting points were calculated by the Einstein equation according to the slopes of the MSD profiles at the long-time limit. Because the HA fraction summation of icosahedral-like structures of ZrSi BMG is higher than that of ZrSi{sub 2} BMG, and these local structures are more dense, the self-diffusion coefficients of the total, Zr, and Si atoms of ZrSi{sub 2} BMG are larger than those of ZrSi BMG. This can be attributed to the cage effect, where a denser local structure has a higher possibility of atoms jumping back to form a backflow and then suppress atomic diffusivity. For ZrSi{sub 2} BMG, the self-diffusion coefficient of Si increases with temperature more significantly than does that of Zr, because more open packing rhombohedra structures are formed by the Si-Si pair.

  11. High Atom Number in Microsized Atom Traps

    DTIC Science & Technology

    2015-12-14

    cooling of some atoms in atomic beam. We have reconfigured the apparatus for applying bichromatic forces transverse to the atomic beam, as it will be...apparatus for applying bichromatic forces transverse to the atomic beam, as it will be easier to extend this to two dimensions. Research to develop

  12. First principles study of the C/Si ratio effect on the ideal shear strength of β-SiC

    NASA Astrophysics Data System (ADS)

    Su, Wen; Li, Yingying; Nie, Chu; Xiao, Wei; Yan, Liqin

    2016-07-01

    The effect of the C/Si atomic ratio on the ideal shear strength of β-SiC is investigated with first principles calculations. β -SiC samples with different C/Si ratios are generated by Monte Carlo (MC) simulations with empirical inter-atomic SiC potential. Each SiC sample is sheared along the < 100> direction and the stress-strain curve is calculated from first principles. The results show that the ideal shear strength of SiC decreases with the increase of C/Si ratio. For a non-stoichiometric SiC sample, a C-C bond inside a large carbon cluster breaks first under shear strain condition due to the internal strain around the carbon clusters. Because the band gap is narrowed under shear strain conditions, a local maximum stress appears in the elastic region of the stress-strain curve for each SiC sample at certain strain condition. The yield strength may increase with the increase of C/Si ratio.

  13. Buckling reversal of the Si(111) bilayer termination of 2-dimensional ErSi2 upon H dosing

    NASA Astrophysics Data System (ADS)

    Wetzel, P.; Pirri, C.; Gewinner, G.

    1997-05-01

    Hydrogen-induced reconstruction of 2-dimensional (2D) ErSi2 epitaxially grown on Si(111) is studied by Auger-electron diffraction (AED) and low-energy electron diffraction (LEED). The intensity of the Er MNN Auger line is measured vs. polar angle along the [1 - 2 1] and [- 1 2 - 1] azimuths for clean and H-saturated (1 × 1) ErSi2 silicides. The atomic structure of clean 2D silicide, previously established by AED as well as other techniques, consists of a hexagonal monolayer of Er located underneath a buckled Si layer comparable to the Si(111) substrate double layers. Moreover, for clean 2D ErSi2 only the B-type orientation is observed, i.e. the buckled Si top layer is always rotated by 180° around the surface normal relative to the relevant double layers of the substrate. After atomic H saturation, AED reveals drastic changes in the silicide structure involving a major most remarkable reconstruction of the Si bilayer termination. The latter is found to switch from B-type to A-type orientation upon H dosing, i.e. H-saturated 2D ErSi2 exhibits a buckled Si top layer oriented in the same way as the substrate double layers. A comparison with single scattering cluster simulations demonstrates that the latter phenomenon is accompanied by a large expansion of the Er-Si interlayer spacing close to 0.3 Å.

  14. Atomic magnetometer

    DOEpatents

    Schwindt, Peter [Albuquerque, NM; Johnson, Cort N [Albuquerque, NM

    2012-07-03

    An atomic magnetometer is disclosed which uses a pump light beam at a D1 or D2 transition of an alkali metal vapor to magnetically polarize the vapor in a heated cell, and a probe light beam at a different D2 or D1 transition to sense the magnetic field via a polarization rotation of the probe light beam. The pump and probe light beams are both directed along substantially the same optical path through an optical waveplate and through the heated cell to an optical filter which blocks the pump light beam while transmitting the probe light beam to one or more photodetectors which generate electrical signals to sense the magnetic field. The optical waveplate functions as a quarter waveplate to circularly polarize the pump light beam, and as a half waveplate to maintain the probe light beam linearly polarized.

  15. Atomic-scale measurement of ultraslow Li motions in glassy LiAlSi2O6 by two-time L6i spin-alignment echo NMR correlation spectroscopy

    NASA Astrophysics Data System (ADS)

    Wilkening, M.; Kuhn, A.; Heitjans, P.

    2008-08-01

    L6i spin-alignment echo (SAE) nuclear-magnetic-resonance (NMR) spectroscopy is used to monitor single-particle two-time correlation functions in LiAlSi2O6 glass. The method, here applied in the temperature range from 300 to 400 K, is sensitive to ultraslow Li hopping processes with rates (1/τSAE) down to 10 jumps/s. The use of a sample with natural L6i abundance allowed the measurement of pure NMR spin-alignment echoes which are damped with increasing mixing time exclusively by slow Li jumps, i.e., free of influences arising from, e.g., interfering spin-diffusion effects. The considerably stretched correlation functions reveal the presence of a broad distribution of jump rates. The results are comprehensively compared with those recently obtained from both L7i SAE and L7i spin-lattice relaxation NMR as well as from dc conductivity measurements. Interestingly, the activation energy of the latter, which are sensitive to long-range Li transport parameters, is in good agreement with that microscopically probed by L6i SAE NMR, here.

  16. DFT Optimization of Symmetric Be2Si Cage Clusters

    NASA Astrophysics Data System (ADS)

    Binning, Robert; Bacelo, Daniel

    2009-05-01

    Density functional theory calculations have been performed on several beryllium silicide cage clusters in which the atoms occupy the vertices of classic Archimedean solids. The BPW91 functionals with numerical basis sets were employed in the optimizations. The calculations were carried out to confirm the hypothesis that stable Be2Si clusters may be obtained by substituting Si for Be atoms in stable pure beryllium clusters. Stable beryllium clusters are obtained from symmetrical Ben polyhedra in which sides are triangular or capped pentagonal, and the Archimedean clusters composed of these elements with Si substitutions are indeed found to produce stable beryllium silicides.

  17. Misfit dislocation gettering by substrate pit-patterning in SiGe films on Si(001)

    SciTech Connect

    Grydlik, Martyna; Groiss, Heiko; Brehm, Moritz; Schaeffler, Friedrich; Boioli, Francesca; Montalenti, Francesco; Miglio, Leo; Gatti, Riccardo; Devincre, Benoit

    2012-07-02

    We show that suitable pit-patterning of a Si(001) substrate can strongly influence the nucleation and the propagation of dislocations during epitaxial deposition of Si-rich Si{sub 1-x}Ge{sub x} alloys, preferentially gettering misfit segments along pit rows. In particular, for a 250 nm layer deposited by molecular beam epitaxy at x{sub Ge} = 15%, extended film regions appear free of dislocations, by atomic force microscopy, as confirmed by transmission electron microscopy sampling. This result is quite general, as explained by dislocation dynamics simulations, which reveal the key role of the inhomogeneous distribution in stress produced by the pit-patterning.

  18. Atomic data from the iron project. 3: Rate coefficients for electron impact excitation of boron-like ions: Ne VI, Mg VIII, Al IX, Si X, S XII, Ar XIV, Ca XVI and Fe XXII

    NASA Technical Reports Server (NTRS)

    Zhang, Hong Lin; Graziani, Mark; Pradhan, Anil K.

    1994-01-01

    Collison strengths and maxwellian averaged rate coefficients have been calculated for the 105 transitions among all 15 fine structure levels of the 8 LS terms 2s(sup 2) 2 P(P-2(sup 0 sub 1/, 3/2)), 2s2p(sup 2)(P-4(sub 1/2,3/2,5/2), D-2(sub 3/2, 5/2), S-2(sub 1/2), P-2(sub 1/2, 3/2)), 2p(sup 3)(S-4(sup 0)(sub 3/2), D-2(sup 0 sub 3/2, 5/2), P-2(sup 0 sub 1/2, 3/2)) in highly- charged B-like Ne, Mg, Al, Si, S, Ar, Ca and Fe. Rate coefficients have been tabulated at a wide range of temperatures, depending on the ion charge and abundance in plasma sources. Earlier work for O IV has also been extended to include the high temperature range. A brief discussion of the calculations, sample results, and comparison with earlier works is also given. While much of the new data should be applicable to UV spectral diagnostics, the new rates for the important ground state fine structure transition P-2(sup 0 sub 1/2)-P-2(sup 0 sub 3/2) should result in significant revision of the IR cooling rates in plasmas where B-like ions are prominent constituents, since the new rate coefficients are generally higher by several factors compared with the older data.

  19. Effects of interface bonding and defects on boron diffusion at Si/SiO{sub 2} interface

    SciTech Connect

    Kim, Geun-Myeong; Oh, Young Jun; Chang, K. J.

    2013-12-14

    We perform first-principles density functional calculations to find the migration pathway and barrier for B diffusion at the Si/SiO{sub 2} interface. For various interface models, in which crystalline α-quartz or amorphous silica (a-SiO{sub 2}) is placed on Si, we examine stable and metastable configurations of B-related defects which play a role in B diffusion. While a substitutional B alone is immobile in Si, it tends to diffuse to the interface via an interstitialcy mechanism in the presence of a self-interstitial and then changes into an interstitial B in oxide via a kick-out mechanism, leaving the self-interstitial at the interface. At the defect-free interface, where bridging O atoms are inserted to remove interface dangling bonds, an interstitial B prefers to intervene between the interface Si and bridging O atoms and subsequently diffuses through the hollow space or along the network of the Si-O-Si bonds in oxide. The overall migration barriers are calculated to be 2.02–2.12 eV at the Si/α-quartz interface, while they lie in the range of 2.04 ± 0.44 eV at the Si/a-SiO{sub 2} interface, similar to that in α-quartz. The migration pathway and barrier are not significantly affected by interface defects such as suboxide bond and O protrusion, while dangling bonds in the suboxide region can increase the migration barrier by about 1.5 eV. The result that the interface generally does not hinder the B diffusion from Si to SiO{sub 2} assists in understanding the underlying mechanism for B segregation which commonly occurs at the Si/SiO{sub 2} interface.

  20. EDITORIAL: Atomic layer deposition Atomic layer deposition

    NASA Astrophysics Data System (ADS)

    Godlewski, Marek

    2012-07-01

    The growth method of atomic layer deposition (ALD) was introduced in Finland by Suntola under the name of atomic layer epitaxy (ALE). The method was originally used for deposition of thin films of sulphides (ZnS, CaS, SrS) activated with manganese or rare-earth ions. Such films were grown for applications in thin-film electroluminescence (TFEL) displays. The ALE mode of growth was also tested in the case of molecular beam epitaxy. Films grown by ALD are commonly polycrystalline or even amorphous. Thus, the name ALE has been replaced by ALD. In the 80s ALD was developed mostly in Finland and neighboring Baltic countries. Deposition of a range of different materials was demonstrated at that time, including II-VI semiconductors (e.g. CdTe, CdS) and III-V (e.g. GaAs, GaN), with possible applications in e.g. photovoltaics. The number of publications on ALD was slowly increasing, approaching about 100 each year. A real boom in interest came with the development of deposition methods of thin films of high-k dielectrics. This research was motivated by a high leakage current in field-effect transistors with SiO2-based gate dielectrics. In 2007 Intel introduced a new generation of integrated circuits (ICs) with thin films of HfO2 used as gate isolating layers. In these and subsequent ICs, films of HfO2 are deposited by the ALD method. This is due to their unique properties. The introduction of ALD to the electronics industry led to a booming interest in the ALD growth method, with the number of publications increasing rapidly to well above 1000 each year. A number of new applications were proposed, as reflected in this special issue of Semiconductor Science and Technology. The included articles cover a wide range of possible applications—in microelectronics, transparent electronics, optoelectronics, photovoltaics and spintronics. Research papers and reviews on the basics of ALD growth are also included, reflecting a growing interest in precursor chemistry and growth