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Sample records for ge intermediate layer

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

    NASA Astrophysics Data System (ADS)

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

    2012-10-01

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

  2. Single layer of Ge quantum dots in HfO2 for floating gate memory capacitors.

    PubMed

    Lepadatu, A M; Palade, C; Slav, A; Maraloiu, A V; Lazanu, S; Stoica, T; Logofatu, C; Teodorescu, V S; Ciurea, M L

    2017-04-28

    High performance trilayer memory capacitors with a floating gate of a single layer of Ge quantum dots (QDs) in HfO2 were fabricated using magnetron sputtering followed by rapid thermal annealing (RTA). The layer sequence of the capacitors is gate HfO 2/floating gate of single layer of Ge QDs in HfO 2/tunnel HfO 2/p-Si wafers. Both Ge and HfO2 are nanostructured by RTA at moderate temperatures of 600-700 °C. By nanostructuring at 600 °C, the formation of a single layer of well separated Ge QDs with diameters of 2-3 nm at a density of 4-5 × 10(15) m(-2) is achieved in the floating gate (intermediate layer). The Ge QDs inside the intermediate layer are arranged in a single layer and are separated from each other by HfO2 nanocrystals (NCs) about 8 nm in diameter with a tetragonal/orthorhombic structure. The Ge QDs in the single layer are located at the crossing of the HfO2 NCs boundaries. In the intermediate layer, besides Ge QDs, a part of the Ge atoms is segregated by RTA at the HfO2 NCs boundaries, while another part of the Ge atoms is present inside the HfO2 lattice stabilizing the tetragonal/orthorhombic structure. The fabricated capacitors show a memory window of 3.8 ± 0.5 V and a capacitance-time characteristic with 14% capacitance decay in the first 3000-4000 s followed by a very slow capacitance decrease extrapolated to 50% after 10 years. This high performance is mainly due to the floating gate of a single layer of well separated Ge QDs in HfO2, distanced from the Si substrate by the tunnel oxide layer with a precise thickness.

  3. Ge/graded-SiGe multiplication layers for low-voltage and low-noise Ge avalanche photodiodes on Si

    NASA Astrophysics Data System (ADS)

    Miyasaka, Yuji; Hiraki, Tatsurou; Okazaki, Kota; Takeda, Kotaro; Tsuchizawa, Tai; Yamada, Koji; Wada, Kazumi; Ishikawa, Yasuhiko

    2016-04-01

    A new structure is examined for low-voltage and low-noise Ge-based avalanche photodiodes (APDs) on Si, where a Ge/graded-SiGe heterostructure is used as the multiplication layer of a separate-absorption-carrier-multiplication structure. The Ge/SiGe heterojunction multiplication layer is theoretically shown to be useful for preferentially enhancing impact ionization for photogenerated holes injected from the Ge optical-absorption layer via the graded SiGe, reflecting the valence band discontinuity at the Ge/SiGe interface. This property is effective not only for the reduction of operation voltage/electric field strength in Ge-based APDs but also for the reduction of excess noise resulting from the ratio of the ionization coefficients between electrons and holes being far from unity. Such Ge/graded-SiGe heterostructures are successfully fabricated by ultrahigh-vacuum chemical vapor deposition. Preliminary pin diodes having a Ge/graded-SiGe multiplication layer act reasonably as photodetectors, showing a multiplication gain larger than those for diodes without the Ge/SiGe heterojunction.

  4. Interface properties of thin oxide layers grown on strained SiGe layers at low temperatures

    NASA Astrophysics Data System (ADS)

    Mukhopadhyay, M.; Ray, S. K.; Ghosh, T. B.; Sreemany, M.; Maiti, C. K.

    1996-03-01

    The chemical state and the electrical properties of the interfaces of thin oxide films grown on strained 0268-1242/11/3/014/img8 layers using plasma and thermal oxidation have been studied in detail. X-ray photoelectron spectroscopy studies show no Ge pile-up at the oxide/substrate interface. In the case of plasma oxidation, Ge at the oxide surface is found to be in a fully oxidized state, while the formation of an intermediate oxidized state is observed in the case of low-temperature thermal oxidation. High-frequency (1 MHz) capacitance - voltage (C - V) and conductance - voltage (G - V) measurements have indicated the growth of good quality gate oxides. The fixed oxide charge and interface state densities are comparable to those of low-temperature-grown metal - oxide - semiconductor capacitors on Si with aluminium gates.

  5. Energy band alignment of atomic layer deposited HfO{sub 2} oxide film on epitaxial (100)Ge, (110)Ge, and (111)Ge layers

    SciTech Connect

    Hudait, Mantu K.; Zhu Yan

    2013-03-21

    Crystallographically oriented epitaxial Ge layers were grown on (100), (110), and (111)A GaAs substrates by in situ growth process using two separate molecular beam epitaxy chambers. The band alignment properties of atomic layer hafnium oxide (HfO{sub 2}) film deposited on crystallographically oriented epitaxial Ge were investigated using x-ray photoelectron spectroscopy (XPS). Valence band offset, {Delta}E{sub v} values of HfO{sub 2} relative to (100)Ge, (110)Ge, and (111)Ge orientations were 2.8 eV, 2.28 eV, and 2.5 eV, respectively. Using XPS data, variation in valence band offset, {Delta}E{sub V}(100)Ge>{Delta}E{sub V}(111)Ge>{Delta}E{sub V}(110)Ge, was obtained related to Ge orientation. Also, the conduction band offset, {Delta}E{sub c} relation, {Delta}E{sub c}(110)Ge>{Delta}E{sub c}(111)Ge>{Delta}E{sub c}(100)Ge related to Ge orientations was obtained using the measured bandgap of HfO{sub 2} on each orientation and with the Ge bandgap of 0.67 eV. These band offset parameters for carrier confinement would offer an important guidance to design Ge-based p- and n-channel metal-oxide field-effect transistor for low-power application.

  6. Stacked Ge nanocrystals with ultrathin SiO₂ separation layers.

    PubMed

    Zschintzsch, Manuel; von Borany, Johannes; Jeutter, Nicole M; Mücklich, Arndt

    2011-11-18

    The aim of this work is the tailored growth of Ge nanocrystals (NCs) in (GeO(x)/SiO(2)) multilayers (ML) for photovoltaic applications. For this purpose the fabrication of regularly stacked Ge NCs separated by ultrathin SiO(2) layers is essential to enable charge carrier transport by direct tunnelling. In this paper we report on the fabrication of (GeO(x)/SiO(2))(50) multilayer stacks via reactive dc magnetron sputtering and Ge NCs formation after subsequent annealing. It is shown that magnetron sputtering allows us to deposit very regular ML stacks with a total thickness of about 300 nm, characterized by ultrathin (down to 1 nm) and very smooth (roughness ∼ 0.6 nm) SiO(2) separation layers. A main challenge is to keep these properties for a thermal budget necessary to form Ge NCs. For this reason, the temperature dependence of phase separation. Ge crystallization and ML morphology was investigated by Rutherford backscattering, x-ray scattering, Raman spectroscopy and electron microscopy. The formation of size confined Ge NCs of about 5 nm after annealing of only 550 °C is confirmed. This low thermal budget ensures the suppression of GeO emanation and multilayer stability. Spectroscopic ellipsometry was applied to determine the optical Ge NC bandgap to (1.65 ± 0.5) eV.

  7. Ion beam synthesis of SiGe alloy layers

    SciTech Connect

    Im, Seongil

    1994-05-01

    Procedures required for minimizing structural defects generated during ion beam synthesis of SiGe alloy layers were studied. Synthesis of 200 mm SiGe alloy layers by implantation of 120-keV Ge ions into <100> oriented Si wafers yielded various Ge peak concentrations after the following doses, 2 x 1016cm-2, 3 x 1016cm-2 (mid), and 5 x 1016cm-2 (high). Following implantation, solid phase epitaxial (SPE) annealing in ambient N2 at 800C for 1 hr. resulted in only slight redistribution of the Ge. Two kinds of extended defects were observed in alloy layers over 3 x l016cm-2cm dose at room temperature (RT): end-of-range (EOR) dislocation loops and strain-induced stacking faults. Density of EOR dislocation loops was much lower in alloys produced by 77K implantation than by RT implantation. Decreasing the dose to obtain 5 at% peak Ge concentration prevents strain relaxation, while those SPE layers with more than 7 at% Ge peak show high densities of misfit- induced stacking faults. Sequential implantation of C following high dose Ge implantation (12 at% Ge peak concentration in layer) brought about a remarkable decrease in density of misfit-induced stacking faults. For peak implanted C > 0.55 at%, stacking fault generation in the epitaxial layer was suppressed, owing to strain compensation by C atoms in the SiGe lattice. A SiGe alloy layer with 0.9 at% C peak concentration under a 12 at% Ge peak exhibited the best microstructure. Results indicate that optimum Ge/C ratio for strain compensation is between 11 and 22. The interface between amorphous and regrown phases (a/c interface) had a dramatic morphology change during its migration to the surface. Initial <100> planar interface decomposes into a <111> faceted interface, changing the growth kinetics; this is associated with strain relaxation by stacking fault formation on (111) planes in the a/c interface.

  8. Germanium segregation in CVD grown SiGe layers

    NASA Astrophysics Data System (ADS)

    Novikau, Andrei; Gaiduk, Peter

    2010-02-01

    A 2D layer of spherical, crystalline Ge nanodots embedded in a SiO2 layer was formed by low pressure chemical vapour deposition combined with furnace oxidation and rapid thermal annealing. The samples were characterized structurally by using transmission electron microscopy and Rutherford back scattering spectrometry, as well as electrically by measuring C-V and I-V characteristics. It was found that formation of a high density Ge dots took place due to oxidation induced Ge segregation. The dots were situated in the SiO2 at the average distance 5-6 nm from the substrate. Strong evidence of charge storage effect in the crystalline Ge-nanodot layer was demonstrated by the hysteresis behavior of the high-frequency C-V curves.

  9. Strain and stability of ultrathin Ge layers in Si/Ge/Si axial heterojunction nanowires

    SciTech Connect

    Ross, Frances M.; Stach, Eric A.; Wen, Cheng -Yen; Reuter, Mark C.; Su, Dong

    2015-02-05

    The abrupt heterointerfaces in the Si/Ge materials system presents useful possibilities for electronic device engineering because the band structure can be affected by strain induced by the lattice mismatch. In planar layers, heterointerfaces with abrupt composition changes are difficult to realize without introducing misfit dislocations. However, in catalytically grown nanowires, abrupt heterointerfaces can be fabricated by appropriate choice of the catalyst. Here we grow nanowires containing Si/Ge and Si/Ge/Si structures respectively with sub-1nm thick Ge "quantum wells" and we measure the interfacial strain fields using geometric phase analysis. Narrow Ge layers show radial strains of several percent, with a corresponding dilation in the axial direction. Si/Ge interfaces show lattice rotation and curvature of the lattice planes. We conclude that high strains can be achieved, compared to what is possible in planar layers. In addition, we study the stability of these heterostructures under heating and electron beam irradiation. The strain and composition gradients are supposed to the cause of the instability for interdiffusion.

  10. Strain and stability of ultrathin Ge layers in Si/Ge/Si axial heterojunction nanowires

    DOE PAGES

    Ross, Frances M.; Stach, Eric A.; Wen, Cheng -Yen; ...

    2015-02-05

    The abrupt heterointerfaces in the Si/Ge materials system presents useful possibilities for electronic device engineering because the band structure can be affected by strain induced by the lattice mismatch. In planar layers, heterointerfaces with abrupt composition changes are difficult to realize without introducing misfit dislocations. However, in catalytically grown nanowires, abrupt heterointerfaces can be fabricated by appropriate choice of the catalyst. Here we grow nanowires containing Si/Ge and Si/Ge/Si structures respectively with sub-1nm thick Ge "quantum wells" and we measure the interfacial strain fields using geometric phase analysis. Narrow Ge layers show radial strains of several percent, with a correspondingmore » dilation in the axial direction. Si/Ge interfaces show lattice rotation and curvature of the lattice planes. We conclude that high strains can be achieved, compared to what is possible in planar layers. In addition, we study the stability of these heterostructures under heating and electron beam irradiation. The strain and composition gradients are supposed to the cause of the instability for interdiffusion.« less

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

    NASA Astrophysics Data System (ADS)

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

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

  12. 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.

  13. Atomic layer-by-layer oxidation of Ge (100) and (111) surfaces by plasma post oxidation of Al{sub 2}O{sub 3}/Ge structures

    SciTech Connect

    Zhang, Rui; Huang, Po-Chin; Lin, Ju-Chin; Takenaka, Mitsuru; Takagi, Shinichi

    2013-02-25

    The ultrathin GeO{sub x}/Ge interfaces formed on Ge (100) and (111) surfaces by applying plasma post oxidation to thin Al{sub 2}O{sub 3}/Ge structures are characterized in detail using X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy. It is found that the XPS signals assigned to Ge 1+ and the 2+ states in the GeO{sub x} layers by post plasma oxidation have oscillating behaviors on Ge (100) surfaces in a period of {approx}0.3 nm with an increase in the GeO{sub x} thickness. Additionally, the oscillations of the signals assigned to Ge 1+ and 2+ states show opposite phase to each other. The similar oscillation behaviors are also confirmed on Ge (111) surfaces for Ge 1+ and 3+ states in a period of {approx}0.5 nm. These phenomena can be strongly regarded as an evidence of the atomic layer-by-layer oxidation of GeO{sub x}/Ge interfaces on Ge (100) and (111) surfaces.

  14. Silicon solar cell using optimized intermediate reflector layer

    NASA Astrophysics Data System (ADS)

    Khalifa, Ahmed E.; Swillam, Mohamed A.

    2016-03-01

    Thin film silicon based photovoltaic cells have the advantages of using low cost nontoxic abundant constituents and low thermal manufacturing budget. However, better long-term efficiencies need to be achieved overcoming its inherent bad electrical properties of amorphous and/or microcrystalline Silicon. For the goal of achieving best results, multijunction cells of amorphous and microcrystalline silicon thin layers are industrially and lab utilized in addition to using one or more light management techniques such as textured layers, periodic and plasmonic back reflectors, flattened reflective substrates and intermediate reflector layer (IRL) between multijunction cells. The latter, IRL, which is the focus of this paper, serves as spectrally selective layer between different cells of the multijunction silicon thin film solar cell. IRL, reflects to the top cell short wavelength while permitting and scattering longer ones to achieve the best possible short circuit current. In this study, a new optimized periodic design of Intermediate reflector layer in micromorph (two multijunction cells of Microcrystalline and Amorphous Silicon) thin film solar cells is proposed. The optically simulated short circuit current reaches record values for same thickness designs when using all-ZnO design and even better results is anticipated if Lacquer material is used in combination with ZnO. The design methodology used in the paper can be easily applied to different types of IRL materials and also extended to triple and the relatively newly proposed quadruple thin films solar cells.

  15. 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.

  16. Barrier enhancement of Ge MSM IR photodetector with Ge layer optimization

    NASA Astrophysics Data System (ADS)

    Asar, Tarık; Özçelik, Süleyman

    2015-12-01

    Germanium thin films were deposited on n-type Silicon substrates with three different sputter power by using DC magnetron sputtering system at room temperature. The structural and morphological properties of the samples have been obtained by means of X-ray diffraction and atomic force microscopy measurements. Then, Germanium metal-semiconductor-metal infrared photodetectors were fabricated on these structures. The carrier recombination lifetime and the diffusion length of the devices were also calculated by using the carrier density and mobility data was obtained from the room temperature Hall Effect measurements. The dark current-voltage measurements of devices were achieved at room temperature. The electrical parameters such as ideality factor, Schottky barrier height, saturation current and series resistance were extracted from dark current-voltage characteristics. Finally, it has been shown that the barrier enhancement of Ge MSM IR photodetector can be achieved by Ge layer optimization.

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

    PubMed

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

    2017-02-07

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

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

    NASA Astrophysics Data System (ADS)

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

    2017-02-01

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

  19. Investigations of segregation phenomena in highly strained Mn-doped Ge wetting layers and Ge quantum dots embedded in silicon

    SciTech Connect

    Prestat, E. Porret, C.; Favre-Nicolin, V.; Tainoff, D.; Boukhari, M.; Bayle-Guillemaud, P.; Jamet, M.; Barski, A.

    2014-03-10

    In this Letter, we investigate manganese diffusion and the formation of Mn precipitates in highly strained, few monolayer thick, Mn-doped Ge wetting layers and nanometric size Ge quantum dot heterostructures embedded in silicon. We show that in this Ge(Mn)/Si system manganese always precipitates and that the size and the position of Mn clusters (precipitates) depend on the growth temperature. At high growth temperature, manganese strongly diffuses from germanium to silicon, whereas decreasing the growth temperature reduces the manganese diffusion. In the germanium quantum dots layers, Mn precipitates are detected, not only in partially relaxed quantum dots but also in fully strained germanium wetting layers between the dots.

  20. Tandem photovoltaic cells with a composite intermediate layer

    SciTech Connect

    Travkin, V. V. Pakhomov, G. L.; Luk’anov, A. Yu.; Stuzhin, P. A.

    2015-11-15

    We have fabricated and tested tandem photovoltaic cells containing series-connected subcells of the “oxide–organic semiconductor–metal” type. The organic semiconductors were two phthalocyanine dyes (SubPc and PcVO); Al or Ag:Mg were used as capping metallic electrodes. A semitransparent composite metal–oxide layer formed by molybdenum oxide MoO{sub x} deposited over an ultrathin Al layer is used to join the subcells. Additionally, a MoO{sub x} layer deposited onto glass/ITO substrates serves as an anode buffer in the front subcell, and LiF deposited onto the dye layers serves as a cathode buffer in the front or rear subcells. Upon optimization of the thickness and composition of the intermediate layer, the open circuit voltage U{sub oc} amounts to 1.6 V reflecting total summation of the contributions from the each of the subcells at a wide spectral coating from 300–1000 nm. The fill factor in the tandem cell is not worse than in individually made single cells with the same scheme or in disconnected subcells.

  1. Intermediate coating layer for high temperature rubbing seals for rotary regenerators

    DOEpatents

    Schienle, James L.; Strangman, Thomas E.

    1995-01-01

    A metallic regenerator seal is provided having multi-layer coating comprising a NiCrAlY bond layer, a yttria stabilized zirconia (YSZ) intermediate layer, and a ceramic high temperature solid lubricant surface layer comprising zinc oxide, calcium fluoride, and tin oxide. Because of the YSZ intermediate layer, the coating is thermodynamically stable and resists swelling at high temperatures.

  2. Investigation of Diffusion Barrier Layers for Bi-Doped Mg2(Si,Ge) Thermoelectric Legs

    NASA Astrophysics Data System (ADS)

    Prahoveanu, Codrin; Laversenne, Laetitia; de Vaulx, Cédric; Bès, Alexandre; Azzouz, Kamel; Lacoste, Ana

    2016-11-01

    The performance of thermoelectric (TE) modules is governed not only by the thermoelectric materials whose properties are capitalized, but also on the quality of the electrical contacts which are ubiquitous in the design of the device. To ensure the necessary stability of the interfaces between the TE materials and the electrodes, diffusion barriers are generally used. In this study, attempts are presented in finding diffusion barriers that would be suitable for Mg2(Si,Ge) TE materials. These involved the deposition by microwave plasma-assisted co-sputtering of intermediate gradient layers starting from Mg and Si, ending up with a Ni layer, or the deposition of metallic layers (Ti, Cr, W and Ta). The effectiveness of the deposited layers as diffusion barriers is assessed after the legs were subjected to a brazing process, with the results favoring the use of gradient layers with a thick Ni layer and metallic layers based on Ta and Cr, despite some adherence issues for the latter.

  3. Characterization of Ultrathin Ta-oxide Films Formed on Ge(100) by ALD and Layer-by-Layer Methods

    NASA Astrophysics Data System (ADS)

    Mishima, K.; Murakami, H.; Ohta, A.; Sahari, S. K.; Fujioka, T.; Higashi, S.; Miyazaki, S.

    2013-03-01

    Atomic layer deposition (ALD) and Layer-by-Layer deposition of Ta-oxide films on Ge(100) with using tris (tert-butoxy) (tert-butylimido) tantalum have been studied systematically. From the analysis of the chemical bonding features of the interface between TaOx and Ge(100) using x-ray photoelectron spectroscopy (XPS), Ge atom diffusion into the Ta oxide layer and resultant TaGexOy formation during deposition at temperatures higher than 200°C were confirmed. Also, we have demonstrated that nanometer-thick deposition of Tantalum oxide as an interfacial layer effectively suppresses the formation of GeOx in the HfO2 ALD on Ge. By the combination of TaOx pre-deposition on Ge(100) and subsequent ALD of HfO2, a capacitance equivalent thickness (CET) of 1.35 nm and relative dielectric constant of 23 were achieved.

  4. Formation of alternating interfacial layers in Au-12Ge/Ni joints

    PubMed Central

    Lin, Shih-kang; Tsai, Ming-yueh; Tsai, Ping-chun; Hsu, Bo-hsun

    2014-01-01

    Au-Ge alloys are promising materials for high-power and high-frequency packaging, and Ni is frequently used as diffusion barriers. This study investigates interfacial reactions in Au-12Ge/Ni joints at 300°C and 400°C. For the reactions at 300°C, typical interfacial morphology was observed and the diffusion path was (Au) + (Ge)/NiGe/Ni5Ge3/Ni. However, an interesting phenomenon – the formation of (Au,Ni,Ge)/NiGe alternating layers – was observed for the reactions at 400°C. The diffusion path across the interface was liquid/(Au,Ni,Ge)/NiGe/···/(Au,Ni,Ge)/NiGe/Ni2Ge/Ni. The periodic thermodynamic instability at the NiGe/Ni2Ge interface caused the subsequent nucleation of new (Au,Ni,Ge)/NiGe pairs. The thermodynamic foundation and mechanism of formation of the alternating layers are elaborated in this paper. PMID:24690992

  5. Optimization of ISBD embedded SiGe layers to prevent delamination process for MOSFET applications

    NASA Astrophysics Data System (ADS)

    Wasyluk, Joanna; Ge, Yang; Wurster, Kai; Lenski, Markus; Reichel, Carsten

    2015-08-01

    An interaction between in situ boron doped SiGe layers deposited by low pressure chemical vapor deposition and NH3 plasma treatments was studied in this work. It is shown that NH3 plasma strips introduce H atoms into SiGe layer which further leads to unwanted blistering and exfoliation of the SiGe layer. The SiGe layers with varied boron profiles were examined in this work in order to understand influence of B doping on H accumulation. It is shown that B peak at SiGe/Si interface can be modulated by the temperature and pressure changes between the layers' deposition. It was found that less H atoms diffuse into ISBD SiGe layer with higher B peak at Si cap/main SiGe layer. The SiGe layer with removed B peak at buffer/main SiGe layer interface and increased B peak at Si cap was proven to be delamination free and robust for HN3 plasma strips.

  6. Long-Wavelength Stacked SiGe/Si Heterojunction Internal Photoemission Infrared Detectors Using Multiple SiGe/Si Layers

    NASA Technical Reports Server (NTRS)

    Park, J. S.; Lin, T. L.; Jones, E. W.; Castillo, H. M. Del; Gunapala, S. D.

    1994-01-01

    Utilizing low temperature silicon molecular beam epitaxy (MBE) growth, long-wavelength stacked SiGe/Si heterojunction internal photoemission (HIP) infrared detectors with multiple SiGe/Si layers have been fabricated and demonstrated. Using an elemental boron source, high doping concentrations (approximately equal to 4 x 10(sup 20) cm(sup -3)) has been achieved and high crystalline quality multiple Si(sub 0.7)Ge(sub 0.3)/Si layers have been obtained. The detector structure consists of several periods of degenerately boron doped (approximately equal to 4 x 10(sup 20) cm(sup -3)) thin (less than or equal to 50 u Si(sub 0.7)Ge(sub 0.3) layers and undoped thick (approximately equal to 300u Si layers. The multiple p(sup +) - Si(sub 0.7)Ge(sub 0.3)/undoped-Si layers show strong infrared absorption in the long-wavelength regime mainly through free carrier absorption. The stacked Si(sub 0.7)Ge(sub 0.3)/Si HIP detectors with p = 4 x 10(sup 20) cm(sup -3) exhibit strong photoresponse at wavelengths ranging from 2 to 20 (micro)m with quantum efficiencies of about 4% and 1.5% at 10 and 15 (micro)m wavelengths, respectively. The detectors show near ideal thermionic-emission limited dark current characteristics.

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

    SciTech Connect

    Antonov, A. V.; Drozdov, M. N.; Novikov, A. V. Yurasov, D. V.

    2015-11-15

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

  8. Modeled optical properties of SiGe and Si layers compared to spectroscopic ellipsometry measurements

    NASA Astrophysics Data System (ADS)

    Kriso, C.; Triozon, F.; Delerue, C.; Schneider, L.; Abbate, F.; Nolot, E.; Rideau, D.; Niquet, Y.-M.; Mugny, G.; Tavernier, C.

    2017-03-01

    The optical response of strained SiGe alloys, as well as thin Si layers, is analyzed using a sp3d5s∗ tight-binding model within the independent particle approximation. The theoretical results are compared to measurements obtained on samples with various Ge content and layer thicknesses. The dielectric function is extracted from spectroscopic ellipsometry allowing a separation of its real and imaginary parts. Theory and simulation show similar trends for the variation of the dielectric function of SiGe with varying Ge content. Variations are also well reproduced for thin Si layers with varying thickness and are attributed to quantum confinement.

  9. Improved interfacial and electrical properties of Ge MOS devices with ZrON/GeON dual passivation layer

    NASA Astrophysics Data System (ADS)

    Wenyu, Yuan; Jingping, Xu; Lu, Liu; Yong, Huang; Zhixiang, Cheng

    2016-05-01

    The interfacial and electrical characteristics of Ge metal-oxide-semiconductor (MOS) devices with a dual passivation layer of ZrON/GeON formed by NH3- or N2-plasma treatment are investigated. The experimental results show that the NH3-plasma treated sample exhibits significantly improved interfacial and electrical properties as compared to the samples with N2-plasma treatment and no treatment: a lower interface-state density at the midgap (1.64 × 1011 cm-2 · eV-1) and gate leakage current (9.32 × 10-5 A/cm2 at Vfb + 1 V), a small capacitance equivalent thickness (1.11 nm) and a high k value (32). X-ray photoelectron spectroscopy is used to analyze the involved mechanisms. It is indicated that more GeON and less GeOx (x < 2) are formed on the Ge surface during NH3-plasma treatment than the N2-plasma treatment, resulting in a high-quality high-k/Ge interface, because H atoms and NH radicals in NH3-plasma can enhance volatilization of the unstable low-k GeOx, creating high-quality GeON passivation layer. Moreover, more nitrogen incorporation in ZrON/GeON induced by NH3-plasma treatment can build a stronger N barrier and thus more effectively inhibit in-diffusion of O and Ti from high-k gate dielectric and out-diffusion of Ge. Project supported by the National Natural Science Foundation of China (Nos. 6127411261176100, 61404055).

  10. Infrared Detectors Containing Stacked Si(1-x)Ge(x)/Si Layers

    NASA Technical Reports Server (NTRS)

    Park, Jin S.; Lin, True-Lon; Jones, Eric; Del Castillo, Hector; Gunapala, Sarath

    1996-01-01

    Long-wavelength-infrared detectors containing multiple layers of high-quality crystalline p(+) Si(1-x)Ge(x) alternating with layers of Si undergoing development. Each detector comprises stack of Si(1-x)Ge(x)/Si heterojunction internal photoemission (HIP) photodetectors. In comparison with older HIP detectors containing single Si(1-x)Ge(x)/Si heterojunctions, developmental detectors feature greater quantum efficiencies and stronger photoresponses.

  11. Pourous Si(x)Ge(1-x) Layers Within Single Crystals Of Si

    NASA Technical Reports Server (NTRS)

    Fathauer, Robert W.; George, Thomas

    1994-01-01

    Layers of porous Si(x)Ge(1-x) buried within single crystals of Si formed by epitaxial growth of Si/Si(x)Ge(1-x)/Si structures followed by etching in solutions of HF:HNO3:H2O. Electroluminescence from these layers utilized in novel optoelectronic devices.

  12. Effect of GeO2 deposition temperature in atomic layer deposition on electrical properties of Ge gate stack

    NASA Astrophysics Data System (ADS)

    Kanematsu, Masayuki; Shibayama, Shigehisa; Sakashita, Mitsuo; Takeuchi, Wakana; Nakatsuka, Osamu; Zaima, Shigeaki

    2016-08-01

    We investigated the effect of GeO2 deposition temperature (T depo) on electronic properties of Al/Al2O3/GeO2/Ge MOS capacitors. Capacitance-voltage characteristics show frequency dispersions under depletion and strong inversion conditions, which can be attributed from the interface states at the atomic layer deposition (ALD)-GeO2/Ge interface and from the defect states in the quasi-neutral region in the Ge substrate, respectively. We found that the interface state density (D it) shows similar values and energy distributions as T depo decreases to 200 from 300 °C, while a higher D it is observed at a T depo of 150 °C. Also, from the temperature dependence of conductance, the frequency dispersion under the strong inversion condition can be related to the minority carrier diffusion to the quasi-neutral region of the Ge substrate. The frequency dependence of conductance reveals that the undesirable increment of the bulk defect density can be suppressed by decreasing T depo. In this study, the bulk defect density in a MOS capacitor prepared at a T depo of 200 °C decreases one tenth compared with that at a T depo of 300 °C. The ALD of GeO2 at a low temperature of around 200 °C is effective for both obtaining a low D it and preventing the undesirable introduction of bulk defect density.

  13. The nature of intermediate-range order in Ge-As-S glasses : results from reverse Monte Carlo modeling.

    SciTech Connect

    Soyer-Uzun, S.; Benmore, C. J.; Siewenie, J. E.; Sen, S.; X-Ray Science Division; Univ.of California at Davis; LANL

    2010-01-01

    The experimental neutron and x-ray diffraction data for stoichiometric and S-deficient Ge{sub x}As{sub x}S{sub 100-2x} glasses with x = 18.2, 25.0, and 33.3 at.% have been modeled simultaneously using the reverse Monte Carlo (RMC) technique. Nearest-neighbor coordination environments, as obtained in previous x-ray absorption spectroscopy and diffraction experiments, have been employed as short-range order constraints in these simulations. The large scale three-dimensional structural models thus obtained from RMC simulation are used to investigate the nature and compositional evolution of intermediate-range structural order in these ternary glasses. The intermediate-range structural order is controlled by (1) a corner-shared three-dimensional network of AsS{sub 3} pyramids and GeS{sub 4} tetrahedra in the stoichiometric Ge{sub 18.2}As{sub 18.2}S{sub 63.6} glass, (2) a heterogeneous structure that consists of homopolar bonded As-rich regions coexisting with a GeS{sub 2} network in the S-deficient Ge{sub 25}As{sub 25}S{sub 50} glass, and (3) a homogeneous structure resulting from the disruption of the topological continuity of the GeS{sub 2} network and As-rich clusters regions due to the formation of Ge-As bonds in the most S-deficient Ge{sub 33.3}As{sub 33.3}S{sub 33.3} glass. This scenario of the compositional evolution of intermediate-range structural order is consistent with and provides an atomistic explanation of the corresponding evolution in the position, width and intensity of the first sharp diffraction peak and the magnitude of small angle scattering in these glasses.

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

    NASA Astrophysics Data System (ADS)

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

    2017-02-01

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

  15. 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.

  16. Investigation of the phase relations in the U-Al-Ge ternary system: Influence of the Al/Ge substitution on the properties of the intermediate phases

    NASA Astrophysics Data System (ADS)

    Moussa, C.; El Sayah, Z.; Chajewski, G.; Berche, A.; Dorcet, V.; Pikul, A. P.; Pasturel, M.; Joanny, L.; Stepnik, B.; Tougait, O.

    2016-11-01

    The phase relations within the U-Al-Ge ternary system were studied for two isothermal sections, at 673 K for the whole Gibbs triangle and at 1173 K for the concentration range 25-100 at% U. The identification of the phases, their composition ranges and stability were determined by x-ray powder diffraction, scanning electron microscopy coupled to energy dispersive spectroscopy and differential thermal analysis. The tie-lines and the solubility domains were determined for the U-Ge and U-Al binaries, the UAl3-UGe3 solid-solution and for the unique ternary intermediate phase U3Al2-xGe3+x. The experimental isopleth section of the pseudo-binary UAl3-UGe3 reveals an isomorphous solid solution based on the Cu3Au-type below the solidus. The U3Al2-xGe3+x solid solution extends for -0.1≤x≤1.35 and -0.2≤x≤1.5 at 673 K and 1173 K respectively. It crystallizes in the I-centered tetragonal symmetry. The reciprocal lattice of several compositions of the U3Al2-xGe3+x solid solution was examined by electron diffraction at room temperature, revealing the presence of a c-glide plane. Their crystal structure was refined by single crystal x-ray diffraction suggesting an isomorphous solid solution best described with the non-centrosymmetric space group I4cm in the paramagnetic domain. The magnetic measurements confirm the ferromagnetic ordering of the solid solution U3Al2-xGe3+x with an increase of Tc with the Al content. The thermal variation of the specific heat bear out the magnetic transitions with some delocalized character of the uranium 5f electrons.

  17. Interfacial-layers-free Ga2O3(Gd2O3)/Ge MOS Diodes

    NASA Astrophysics Data System (ADS)

    Lee, C. H.; Lin, T. D.; Lee, K. Y.; Huang, M. L.; Tung, L. T.; Hong, M.; Kwo, J.

    2008-03-01

    High κ dielectric Ga2O3(Gd2O3) films were deposited directly on Ge by Molecular-Beam-Epitaxy without the employment of GeON interfacial layer. Excellent electrical properties, such as a high κ value of 14.5, a low leakage current density of only 3x10-9 A/cm^2 at Vfb+1V, and well-behaved CV characteristics, were demonstrated, even being subjected to a 500^oC annealing in N2 ambient for 5 min. An abrupt Ga2O3(Gd2O3)/Ge interface without any interfacial layer was revealed by high-resolution transmission electron microscopy as well as in-situ x-ray photoelectron spectroscopy (XPS). Detailed XPS studies indicate that the oxide/Ge interface consists of mainly Ge-O-Gd bonding, distinctly different from that of native oxide. Furthermore, the 500^oC annealing did not change the chemical bonding, implying a great thermodynamic stability of the hetero-structure. The outstanding electrical and thermodynamic properties qualified Ga2O3(Gd2O3) as a promising dielectric for Ge and proved the GeON interfacial layer to be unnecessary.

  18. The role of Ag buffer layer in Fe islands growth on Ge (111) surfaces

    SciTech Connect

    Fu, Tsu-Yi Wu, Jia-Yuan; Jhou, Ming-Kuan; Hsu, Hung-Chan

    2015-05-07

    Sub-monolayer iron atoms were deposited at room temperature on Ge (111)-c(2 × 8) substrates with and without Ag buffer layers. The behavior of Fe islands growth was investigated by using scanning tunneling microscope (STM) after different annealing temperatures. STM images show that iron atoms will cause defects and holes on substrates at room temperature. As the annealing temperature rises, iron atoms pull out germanium to form various kinds of alloyed islands. However, the silver layer can protect the Ag/Ge(111)-(√3×√3) reconstruction from forming defects. The phase diagram shows that ring, dot, and triangular defects were only found on Ge (111)-c(2 × 8) substrates. The kinds of islands found in Fe/Ge system are similar to Fe/Ag/Ge system. It indicates that Ge atoms were pulled out to form islands at high annealing temperatures whether there was a Ag layer or not. But a few differences in big pyramidal or strip islands show that the silver layer affects the development of islands by changing the surface symmetry and diffusion coefficient. The structure characters of various islands are also discussed.

  19. Effects of boron dopants of Si (001) substrates on formation of Ge layers by sputter epitaxy method

    SciTech Connect

    Tsukamoto, Takahiro; Suda, Yoshiyuki; Hirose, Nobumitsu; Kasamatsu, Akifumi; Mimura, Takashi; Matsui, Toshiaki

    2013-10-21

    The formation of Ge layers on boron-doped Si (001) substrates by our sputter epitaxy method has been investigated. The surface morphology of Ge layers grown on Si substrates depends on the substrate resistance, and flat Ge layers are obtained on Si substrates with 0.015 Ω cm resistivity. Highly boron-doped Si substrates cause a transition in the dislocation structure from complex dislocations with 60° dislocation glide planes to 90° pure-edge dislocations, resulting in the formation of flat Ge layers. Furthermore, we have found that the surface morphology of the Ge layers improves with increasing Ge layer thickness. Ge atoms migrating on the deposited Ge layers tend to position themselves at the reactive sites, where the reactivity is related to the number of bonding contacts between the Ge atom and the surface. This modifies the surface morphology, resulting in a flatter surface. Boron dopants together with the sputter epitaxy method effectively suppress the growth of Ge islands and result in the formation of flat Ge layers.

  20. Enhancement of carrier mobility in thin Ge layer by Sn co-doping

    NASA Astrophysics Data System (ADS)

    Prucnal, S.; Liu, F.; Berencén, Y.; Vines, L.; Bischoff, L.; Grenzer, J.; Andric, S.; Tiagulskyi, S.; Pyszniak, K.; Turek, M.; Drozdziel, A.; Helm, M.; Zhou, S.; Skorupa, W.

    2016-10-01

    We present the development, optimization and fabrication of high carrier mobility materials based on GeOI wafers co-doped with Sn and P. The Ge thin films were fabricated using plasma-enhanced chemical vapour deposition followed by ion implantation and explosive solid phase epitaxy, which is induced by millisecond flash lamp annealing. The influence of the recrystallization mechanism and co-doping of Sn on the carrier distribution and carrier mobility both in n-type and p-type GeOI wafers is discussed in detail. This finding significantly contributes to the state-of-the-art of high carrier mobility-GeOI wafers since the results are comparable with GeOI commercial wafers fabricated by epitaxial layer transfer or SmartCut technology.

  1. Bidimensional intercalation of Ge between SiC(0001) and a heteroepitaxial graphite top layer

    SciTech Connect

    Kubler, L.; Dentel, D.; Bischoff, J.-L.; Derivaz, M.; Aiet-Mansour, K.; Diani, M.

    2005-09-15

    High temperature annealing of 4H- or 6H-SiC(0001) crystals is well known to desorb Si from the surface and to generate a C-rich (6{radical}3x6{radical}3)R30 deg. (6{radical}3) reconstruction explained as a graphite monolayer in heteroepitaxial registry with the substrate. Ge deposition at room temperature and in the monolayer range on this graphitized reconstruction results in Ge islands. Using a number of surface techniques, we follow subsequent Ge morphology evolutions as a function of isochronal post-annealing treatments at increasing temperatures. In a particular temperature window Ge reacts with the substrate by diffusion under the graphite planes and wets the Si-terminated SiC surface. In spite of this bidimensional insertion of a Ge layer, the epitaxial relationship between the SiC substrate and the graphite is maintained as shown by very clear graphite-(1x1) LEED or RHEED patterns. They denote extended and well-ordered graphite planes at the surface of a graphite/Ge/SiC heterostructure. XPS analyses reveal a complete passivation of the intercalated Ge layer against oxidation by the overlying graphite sheets. Moreover, drastic spectroscopic changes on the bulk-SiC Si 2p and C 1s core levels are observed, depending on whether graphite(6{radical}3)/SiC or graphite(1x1)/Ge/SiC terminations are analyzed. In the latter case, the observed core level splitting of the bulk components is interpreted by a significant upward band bending ({approx}1.2 eV) of the n-doped SiC, making this second interface to act as a Schottky barrier. Above 1300 deg. C, a delayed Ge desorption takes place that allows the graphite sheets to re-form in their initial 6{radical}3 form, i.e., without Ge and with flatter bands.

  2. Electrochemistry of layered GaSe and GeS: applications to ORR, OER and HER.

    PubMed

    Tan, Shu Min; Chua, Chun Kiang; Sedmidubský, David; Sofer, Zdene Combining Breve K; Pumera, Martin

    2016-01-21

    Though many studies examined the properties of the class of IIIA-VIA and IVA-VIA layered materials, few have delved into the electrochemical aspect of such materials. In light of the burgeoning interest in layered structures towards various electrocatalytic applications, we endeavored to study the inherent electrochemical properties of representative layered materials of this class, GaSe and GeS, and their impact towards electrochemical sensing of redox probes as well as catalysis of oxygen reduction, oxygen evolution and hydrogen evolution reactions. In contrast to the typical sandwich structure of MoS2 layered materials, GeS is isoelectronic to black phosphorus with the same structure; GaSe is a layered material consisting of GaSe sheets bonded in the sequence Se-Ga-Ga-Se. We characterized GaSe and GeS by employing scanning electron microscopy, X-ray diffraction, Raman spectroscopy and X-ray photoelectron spectroscopy complemented by electronic structure calculations. It was found that the encompassing surface oxide layers on GaSe and GeS greatly influenced their electrochemical properties, especially their electrocatalytic capabilities towards hydrogen evolution reaction. These findings provide fresh insight into the electrochemical properties of these IIIA-VIA and IVA-VIA layered structures which enables development for future applications.

  3. Pulsed laser annealing of highly doped Ge:Sb layers deposited on different substrates

    NASA Astrophysics Data System (ADS)

    Batalov, R. I.; Bayazitov, R. M.; Faizrakhmanov, I. A.; Lyadov, N. M.; Shustov, V. A.; Ivlev, G. D.

    2016-10-01

    Germanium (Ge) is a promising material for micro- and optoelectronics to produce high speed field-effect transistors, photodetectors, light-emitting diodes and lasers. For such applications tensile-strained and/or highly n-doped Ge layers are needed. The authors have performed the formation of such layers by ion-beam sputtering of composite Sb/Ge target, deposition of thin amorphous Ge:Sb films (~200 nm thick) on different substrates (c-Si, c-Al2O3, α-SiO2) followed by pulsed laser annealing (PLA) for their crystallization and Sb dopant activation. Structural, electrical and optical characterization of Ge:Sb films was carried out using scanning electron microscopy, x-ray diffraction, micro-Raman spectroscopy, secondary ion mass spectrometry methods and by measuring sheet resistance, carrier concentration and photoluminescence. The obtained polycrystalline n-Ge:Sb layers (N Sb ~ 1 at.%) are characterized by increased values of tensile strain (up to 1%) and homogenious Sb dopant distribution within layer thickness. The electrical measurements at 300 K revealed the low sheet resistance (up to 40 Ω/□) and extremely high electron concentration (up to 5.5  ×  1020 cm-3) in Ge:Sb/SiO2 samples that indicated full electrical activation of Sb dopant on SiO2 substrate. The increased values of tensile strain and electron concentration of Ge:Sb films on α-SiO2 are explained by low values of thermal conductivity and thermal expansion coefficients of quartz substrate.

  4. Growth of homogeneous single-layer graphene on Ni-Ge binary substrate

    NASA Astrophysics Data System (ADS)

    Wang, Gang; Chen, Da; Lu, Zitong; Guo, Qinglei; Ye, Lin; Wei, Xing; Ding, Guqiao; Zhang, Miao; Di, Zengfeng; Liu, Su

    2014-02-01

    In contrast to the commonly used chemical vapor deposition growth that leads to multilayer graphene formation by carbon segregation from the Ni bulk, we designed a Ni-Ge binary system to directly grow graphene film on Ni-Ge binary substrate, via chemical vapor deposition with methane and hydrogen gas as precursors. Our system fully overcomes the fundamental limitations of Ni and yields homogenous single layer graphene over large areas. The chemical vapor deposition growth of graphene on Ni-Ge binary substrate shows that self limiting monolayer graphene growth can be obtained on these substrate.

  5. Dilute Group III-V nitride intermediate band solar cells with contact blocking layers

    DOEpatents

    Walukiewicz, Wladyslaw [Kensington, CA; Yu, Kin Man [Lafayette, CA

    2012-07-31

    An intermediate band solar cell (IBSC) is provided including a p-n junction based on dilute III-V nitride materials and a pair of contact blocking layers positioned on opposite surfaces of the p-n junction for electrically isolating the intermediate band of the p-n junction by blocking the charge transport in the intermediate band without affecting the electron and hole collection efficiency of the p-n junction, thereby increasing open circuit voltage (V.sub.OC) of the IBSC and increasing the photocurrent by utilizing the intermediate band to absorb photons with energy below the band gap of the absorber layers of the IBSC. Hence, the overall power conversion efficiency of a IBSC will be much higher than an conventional single junction solar cell. The p-n junction absorber layers of the IBSC may further have compositionally graded nitrogen concentrations to provide an electric field for more efficient charge collection.

  6. Dilute group III-V nitride intermediate band solar cells with contact blocking layers

    DOEpatents

    Walukiewicz, Wladyslaw; Yu, Kin Man

    2015-02-24

    An intermediate band solar cell (IBSC) is provided including a p-n junction based on dilute III-V nitride materials and a pair of contact blocking layers positioned on opposite surfaces of the p-n junction for electrically isolating the intermediate band of the p-n junction by blocking the charge transport in the intermediate band without affecting the electron and hole collection efficiency of the p-n junction, thereby increasing open circuit voltage (V.sub.OC) of the IBSC and increasing the photocurrent by utilizing the intermediate band to absorb photons with energy below the band gap of the absorber layers of the IBSC. Hence, the overall power conversion efficiency of a IBSC will be much higher than an conventional single junction solar cell. The p-n junction absorber layers of the IBSC may further have compositionally graded nitrogen concentrations to provide an electric field for more efficient charge collection.

  7. Interplay between relaxation and Sn segregation during thermal annealing of GeSn strained layers

    NASA Astrophysics Data System (ADS)

    Comrie, C. M.; Mtshali, C. B.; Sechogela, P. T.; Santos, N. M.; van Stiphout, K.; Loo, R.; Vandervorst, W.; Vantomme, A.

    2016-10-01

    The effect of thermal annealing on epitaxial GeSn (6.5% Sn) strained layers grown on Ge-buffered Si(100) wafers has been investigated using Rutherford backscattering spectrometry and X-ray diffraction to unambiguously determine the Sn substitutional content as well as the elastic strain in the layers. Vacuum annealing at temperatures below 400 °C for 20 min has no noticeable effect on the strain in the epitaxial layers. Once the temperature was raised above 400 °C, however, relaxation of the layer sets in and the GeSn layer has essentially completely relaxed following a 20 min anneal at 650 °C. Using Rutherford backscattering and channelling spectrometry to provide compositional information as a function of depth enables one to monitor the effect of the thermal anneal on the Sn distribution throughout the layer, and also to directly extract their substitutional fraction (i.e., their solubility in the lattice). The results obtained show that when the relaxation initially sets in both the Ge and the Sn remain firmly bound in substitutional lattice sites and it is only around 600 °C, and after substantial relaxation has taken place, that Sn is finally expelled from lattice sites and diffuses to the surface of the sample.

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

    PubMed

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

    2016-09-30

    The microstructure and magnetic properties of the FePt films grown on large mismatched ZrN (15.7%) intermediate layer were investigated. With using ZrN intermediate layer, FePt 10 nm films exhibited (001) texture except for some weaker FePt (110) texture. Good epitaxial relationships of FePt (001) <100>//ZrN (001) <100>//TiN (001) <100> among FePt and ZrN/TiN were revealed from the transmission electron microscopy (TEM) results. As compared with TiN intermediate layer, although FePt-SiO2-C films grown on ZrN/TiN intermediate layer showed isotropic magnetic properties, the large interfacial energy and lattice mismatch between FePt and ZrN would lead to form columnar structural FePt films with smaller grain size and improved isolation. By doping ZrN into the TiN layer, solid solution of ZrTiN was formed and the lattice constant is increased comparing with TiN and decreased comparing with ZrN. Moreover, FePt-SiO2-C films grown on TiN 2 nm-20 vol.% ZrN/TiN 3 nm intermediate layer showed an improved perpendicular magnetic anisotropy. Simultaneously, columnar structure with smaller grain size retained.

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

    PubMed Central

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

    2016-01-01

    The microstructure and magnetic properties of the FePt films grown on large mismatched ZrN (15.7%) intermediate layer were investigated. With using ZrN intermediate layer, FePt 10 nm films exhibited (001) texture except for some weaker FePt (110) texture. Good epitaxial relationships of FePt (001) <100>//ZrN (001) <100>//TiN (001) <100> among FePt and ZrN/TiN were revealed from the transmission electron microscopy (TEM) results. As compared with TiN intermediate layer, although FePt-SiO2-C films grown on ZrN/TiN intermediate layer showed isotropic magnetic properties, the large interfacial energy and lattice mismatch between FePt and ZrN would lead to form columnar structural FePt films with smaller grain size and improved isolation. By doping ZrN into the TiN layer, solid solution of ZrTiN was formed and the lattice constant is increased comparing with TiN and decreased comparing with ZrN. Moreover, FePt-SiO2-C films grown on TiN 2 nm-20 vol.% ZrN/TiN 3 nm intermediate layer showed an improved perpendicular magnetic anisotropy. Simultaneously, columnar structure with smaller grain size retained. PMID:27686046

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

    NASA Astrophysics Data System (ADS)

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

    2016-09-01

    The microstructure and magnetic properties of the FePt films grown on large mismatched ZrN (15.7%) intermediate layer were investigated. With using ZrN intermediate layer, FePt 10 nm films exhibited (001) texture except for some weaker FePt (110) texture. Good epitaxial relationships of FePt (001) <100>//ZrN (001) <100>//TiN (001) <100> among FePt and ZrN/TiN were revealed from the transmission electron microscopy (TEM) results. As compared with TiN intermediate layer, although FePt-SiO2-C films grown on ZrN/TiN intermediate layer showed isotropic magnetic properties, the large interfacial energy and lattice mismatch between FePt and ZrN would lead to form columnar structural FePt films with smaller grain size and improved isolation. By doping ZrN into the TiN layer, solid solution of ZrTiN was formed and the lattice constant is increased comparing with TiN and decreased comparing with ZrN. Moreover, FePt-SiO2-C films grown on TiN 2 nm-20 vol.% ZrN/TiN 3 nm intermediate layer showed an improved perpendicular magnetic anisotropy. Simultaneously, columnar structure with smaller grain size retained.

  11. Anomalously elastic intermediate phase in randomly layered superfluids, superconductors, and planar magnets.

    PubMed

    Mohan, Priyanka; Goldbart, Paul M; Narayanan, Rajesh; Toner, John; Vojta, Thomas

    2010-08-20

    We show that layered quenched randomness in planar magnets leads to an unusual intermediate phase between the conventional ferromagnetic low-temperature and paramagnetic high-temperature phases. In this intermediate phase, which is part of the Griffiths region, the spin-wave stiffness perpendicular to the random layers displays anomalous scaling behavior, with a continuously variable anomalous exponent, while the magnetization and the stiffness parallel to the layers both remain finite. Analogous results hold for superfluids and superconductors. We study the two phase transitions into the anomalous elastic phase, and we discuss the universality of these results, and implications of finite sample size as well as possible experiments.

  12. Enhancing crystalline silicon solar cell efficiency with SixGe1-x layers

    NASA Astrophysics Data System (ADS)

    Ali, Adnan; Cheow, S. L.; Azhari, A. W.; Sopian, K.; Zaidi, Saleem H.

    Crystalline silicon (c-Si) solar cell represents a cost effective, environment-friendly, and proven renewable energy resource. Industrially manufacturing of c-Si solar has now matured in terms of efficiency and cost. Continuing cost-effective efficiency enhancement requires transition towards thinner wafers in near term and thin-films in the long term. Successful implementation of either of these alternatives must address intrinsic optical absorption limitation of Si. Bandgap engineering through integration with SixGe1-x layers offers an attractive, inexpensive option. With the help of PC1D software, role of SixGe1-x layers in conventional c-Si solar cells has been intensively investigated in both wafer and thin film configurations by varying Ge concentration, thickness, and placement. In wafer configuration, increase in Ge concentration leads to enhanced absorption through bandgap broadening with an efficiency enhancement of 8% for Ge concentrations of less than 20%. At higher Ge concentrations, despite enhanced optical absorption, efficiency is reduced due to substantial lowering of open-circuit voltage. In 5-25-μm thickness, thin-film solar cell configurations, efficiency gain in excess of 30% is achievable. Therefore, SixGe1-x based thin-film solar cells with an order of magnitude reduction in costly Si material are ideally-suited both in terms of high efficiency and cost. Recent research has demonstrated significant improvement in epitaxially grown SixGe1-x layers on nanostructured Si substrates, thereby enhancing potential of this approach for next generation of c-Si based photovoltaics.

  13. Investigation of Interface between Ge Electrodes and Ionic Liquid Electrolytes for Electric Double Layer Capacitors

    NASA Astrophysics Data System (ADS)

    Abeysinghe, R. M.; Oguchi, H.; Kuwano, H.

    2016-11-01

    This study discusses novel way of use of ionic liquids to develop Ge-based electrodes for electric double layer capacitors (EDLC). We found that ionic liquids change their electrochemical properties depending on the amount of the absorbed water. Wet ionic liquids work as solvents to dissolve Ge and make porous structures, whereas dry ones work as electrolytes of the EDLCs. The former property was used to increase surface area of the electrodes which is desired to increase the capacity of EDLCs. This method showed another advantage in contrast to the dry ionic liquids; wet ones could fill the complex Ge pores in parallel to porous structure formation. Finally, after porous formation, we dried the ionic liquid at 100 °C and prepared the EDLCs composed of Ge porous electrodes. Cyclic voltammetry and impedance measurements indicated that the obtained devices can work as EDLCs.

  14. Relationship between structural changes, hydrogen content and annealing in stacks of ultrathin Si/Ge amorphous layers

    PubMed Central

    2011-01-01

    Hydrogenated multilayers (MLs) of a-Si/a-Ge have been analysed to establish the reasons of H release during annealing that has been seen to bring about structural modifications even up to well-detectable surface degradation. Analyses carried out on single layers of a-Si and a-Ge show that H is released from its bond to the host lattice atom and that it escapes from the layer much more efficiently in a-Ge than in a-Si because of the smaller binding energy of the H-Ge bond and probably of a greater weakness of the Ge lattice. This should support the previous hypothesis that the structural degradation of a-Si/a-Ge MLs primary starts with the formation of H bubbles in the Ge layers. PMID:21711697

  15. Relationship between structural changes, hydrogen content and annealing in stacks of ultrathin Si/Ge amorphous layers.

    PubMed

    Frigeri, Cesare; Serényi, Miklós; Khánh, Nguyen Quoc; Csik, Attila; Riesz, Ferenc; Erdélyi, Zoltán; Nasi, Lucia; Beke, Dezső László; Boyen, Hans-Gerd

    2011-03-01

    Hydrogenated multilayers (MLs) of a-Si/a-Ge have been analysed to establish the reasons of H release during annealing that has been seen to bring about structural modifications even up to well-detectable surface degradation. Analyses carried out on single layers of a-Si and a-Ge show that H is released from its bond to the host lattice atom and that it escapes from the layer much more efficiently in a-Ge than in a-Si because of the smaller binding energy of the H-Ge bond and probably of a greater weakness of the Ge lattice. This should support the previous hypothesis that the structural degradation of a-Si/a-Ge MLs primary starts with the formation of H bubbles in the Ge layers.

  16. Microstructure Effect of Intermediate Coat Layer on Corrosion Behavior of HVAF-Sprayed Bi-Layer Coatings

    NASA Astrophysics Data System (ADS)

    Sadeghimeresht, Esmaeil; Markocsan, Nicolaie; Nylén, Per

    2017-01-01

    The inherent pores and carbides of Cr3C2-NiCr coatings significantly reduce the corrosion resistance, the former by providing preferential paths for ion diffusion and the latter by forming cathodic sites in galvanic couples (between NiCr and Cr3C2). Adding a dense intermediate layer (intermediate coat layer) between the Cr3C2-NiCr coating (top coat) and substrate increases the corrosion protection of the coating if the layer acts as cathode in connection to the top coat. In the present work, NiCr, NiAl, and NiCoCrAlY layers were deposited by high-velocity air-fuel process as intermediate coat layers for the Cr3C2-NiCr top coat. Effects of coating microstructure on corrosion behavior of single- and bi-layer coatings were studied by open-circuit potential and polarization tests in 3.5 wt.% NaCl at room temperature. A zero resistance ammeter technique was used to study the galvanic corrosion of the coupled top and intermediate coat layers. Methods such as SEM and XRD were employed to characterize the as-sprayed and corroded coatings and to investigate the corrosion mechanisms. The results showed that the NiCoCrAlY coating not only presented a more positive corrosion potential ( Ecorr) than the Cr3C2-NiCr coating, but also provided a better passive layer than the single-phase NiCr and NiAl coatings.

  17. Ellipsometric study of Si(0.5)Ge(0.5)/Si strained-layer superlattices

    NASA Technical Reports Server (NTRS)

    Sieg, R. M.; Alterovitz, S. A.; Croke, E. T.; Harrell, M. J.

    1993-01-01

    An ellipsometric study of two Si(0.5)Ge(0.5)/Si strained-layer super lattices grown by MBE at low temperature (500 C) is presented, and results are compared with x ray diffraction (XRD) estimates. Excellent agreement is obtained between target values, XRD, and ellipsometry when one of two available Si(x)Ge(1-x) databases is used. It is shown that ellipsometry can be used to nondestructively determine the number of superlattice periods, layer thicknesses, Si(x)Ge(1-x) composition, and oxide thickness without resorting to additional sources of information. It was also noted that we do not observe any strain effect on the E(sub 1) critical point.

  18. Ellipsometric study of Si(0.5)Ge(0.5)/Si strained-layer superlattices

    NASA Technical Reports Server (NTRS)

    Sieg, R. M.; Alterovitz, S. A.; Croke, E. T.; Harrell, M. J.

    1993-01-01

    We present an ellipsometric study of two Si(0.5)Ge(0.5)/Si strained-layer superlattices grown by MBE at low temperature (500 C), and compare our results with X-ray diffraction (XRD) estimates. Excellent agreement is obtained between target values, XRD, and ellipsometry when one of two available Si(x)Ge(1-x) databases is used. We show that ellipsometry can be used to nondestructively determine the number of superlattice periods, layer thicknesses, Si(x)Ge(1-x) composition, and oxide thickness without resorting to additional sources of information. We also note that we do not observe any strain effect on the E1 critical point.

  19. GeSn-based p-i-n photodiodes with strained active layer on a Si wafer

    SciTech Connect

    Tseng, H. H.; Li, H.; Mashanov, V.; Yang, Y. J.; Cheng, H. H.; Chang, G. E.; Soref, R. A.; Sun, G.

    2013-12-02

    We report an investigation of GeSn-based p-i-n photodiodes with an active GeSn layer that is almost fully strained. The results show that (a) the response of the Ge/GeSn/Ge heterojunction photodiodes is stronger than that of the reference Ge-based photodiodes at photon energies above the 0.8 eV direct bandgap of bulk Ge (<1.55 μm), and (b) the optical response extends to lower energy regions (1.55–1.80 μm wavelengths) as characterized by the strained GeSn bandgap. A cusp-like spectral characteristic is observed for samples with high Sn contents, which is attributed to the significant strain-induced energy splitting of heavy and light hole bands. This work represents a step forward in developing GeSn-based infrared photodetectors.

  20. Intermediate range chemical ordering in amorphous and liquid water, Si, and Ge

    SciTech Connect

    Benmore, C.J.; Hart, R.T.; Mei, Q.; Price, D.L.; Yarger, J.; Tulk, C.A.; Klug, D.D.

    2005-10-01

    Neutron and x-ray diffraction data for low, high, and very high density amorphous ice and liquid water, silicon, and germanium have been compared in terms of the first sharp diffraction peak in the structure factor and at the radial distribution function level. The low and high density forms of H{sub 2}O, Si, and Ge are shown to have very similar structures if the contributions from the hydrogen correlations in water are neglected. The very high density amorphous ice form is shown to be structurally analogous to recently reported high pressure liquid forms of Si and Ge, although there are slight differences in the way interstitial atoms or molecules are pushed into the first coordination shell.

  1. Raman spectral shift versus strain and composition in GeSn layers with 6%-15% Sn content

    NASA Astrophysics Data System (ADS)

    Gassenq, A.; Milord, L.; Aubin, J.; Pauc, N.; Guilloy, K.; Rothman, J.; Rouchon, D.; Chelnokov, A.; Hartmann, J. M.; Reboud, V.; Calvo, V.

    2017-03-01

    GeSn alloys are the subject of intense research activities as these group IV semiconductors present direct bandgap behaviors for high Sn contents. Today, the control of strain becomes an important challenge to improve GeSn devices. Strain micro-measurements are usually performed by Raman spectroscopy. However, different relationships linking the Raman spectral shifts to the built-in strain can be found in the literature. They were deduced from studies on low Sn content GeSn layers (i.e., xSn < 8%) or on GeSiSn layers. In this work, we have calibrated the GeSn Raman relationship for really high Sn content GeSn binaries (6 < xSn < 15%). We have used fully strained GeSn layers and fully relaxed GeSn under-etched microstructures to clearly differentiate the contributions of strain and chemical composition on the Ge-Ge Raman spectral shift. We have shown that the GeSn Raman-strain coefficient for high Sn contents is higher compared with that for pure Ge.

  2. Waveguide-integrated vertical pin photodiodes of Ge fabricated on p+ and n+ Si-on-insulator layers

    NASA Astrophysics Data System (ADS)

    Ito, Kazuki; Hiraki, Tatsurou; Tsuchizawa, Tai; Ishikawa, Yasuhiko

    2017-04-01

    Vertical pin structures of Ge photodiodes (PDs) integrated with Si optical waveguides are fabricated by depositing Ge epitaxial layers on Si-on-insulator (SOI) layers, and the performances of n+-Ge/i-Ge/p+-SOI PDs are compared with those of p+-Ge/i-Ge/n+-SOI PDs. Both types of PDs show responsivities as high as 1.0 A/W at 1.55 µm, while the dark leakage current is different, which is consistent with previous reports on free-space PDs formed on bulk Si wafers. The dark current of the p+-Ge/i-Ge/n+-SOI PDs is higher by more than one order of magnitude. Taking into account the activation energies for dark current as well as the dependence on PD area, the dark current of the n+-Ge/i-Ge/p+-SOI PDs is dominated by the thermal generation of carriers via mid-gap defect levels in Ge, while for the p+-Ge/i-Ge/n+-SOI PDs, the dark current is ascribed to not only thermal generation but also other mechanisms such as locally formed conduction paths.

  3. Local atomic arrangements and lattice distortions in layered Ge-Sb-Te crystal structures

    PubMed Central

    Lotnyk, Andriy; Ross, Ulrich; Bernütz, Sabine; Thelander, Erik; Rauschenbach, Bernd

    2016-01-01

    Insights into the local atomic arrangements of layered Ge-Sb-Te compounds are of particular importance from a fundamental point of view and for data storage applications. In this view, a detailed knowledge of the atomic structure in such alloys is central to understanding the functional properties both in the more commonly utilized amorphous–crystalline transition and in recently proposed interfacial phase change memory based on the transition between two crystalline structures. Aberration-corrected scanning transmission electron microscopy allows direct imaging of local arrangement in the crystalline lattice with atomic resolution. However, due to the non-trivial influence of thermal diffuse scattering on the high-angle scattering signal, a detailed examination of the image contrast requires comparison with theoretical image simulations. This work reveals the local atomic structure of trigonal Ge-Sb-Te thin films by using a combination of direct imaging of the atomic columns and theoretical image simulation approaches. The results show that the thin films are prone to the formation of stacking disorder with individual building blocks of the Ge2Sb2Te5, Ge1Sb2Te4 and Ge3Sb2Te6 crystal structures intercalated within randomly oriented grains. The comparison with image simulations based on various theoretical models reveals intermixed cation layers with pronounced local lattice distortions, exceeding those reported in literature. PMID:27220411

  4. Local atomic arrangements and lattice distortions in layered Ge-Sb-Te crystal structures

    NASA Astrophysics Data System (ADS)

    Lotnyk, Andriy; Ross, Ulrich; Bernütz, Sabine; Thelander, Erik; Rauschenbach, Bernd

    2016-05-01

    Insights into the local atomic arrangements of layered Ge-Sb-Te compounds are of particular importance from a fundamental point of view and for data storage applications. In this view, a detailed knowledge of the atomic structure in such alloys is central to understanding the functional properties both in the more commonly utilized amorphous–crystalline transition and in recently proposed interfacial phase change memory based on the transition between two crystalline structures. Aberration-corrected scanning transmission electron microscopy allows direct imaging of local arrangement in the crystalline lattice with atomic resolution. However, due to the non-trivial influence of thermal diffuse scattering on the high-angle scattering signal, a detailed examination of the image contrast requires comparison with theoretical image simulations. This work reveals the local atomic structure of trigonal Ge-Sb-Te thin films by using a combination of direct imaging of the atomic columns and theoretical image simulation approaches. The results show that the thin films are prone to the formation of stacking disorder with individual building blocks of the Ge2Sb2Te5, Ge1Sb2Te4 and Ge3Sb2Te6 crystal structures intercalated within randomly oriented grains. The comparison with image simulations based on various theoretical models reveals intermixed cation layers with pronounced local lattice distortions, exceeding those reported in literature.

  5. Atomic Layering, Intermixing and Switching Mechanism in Ge-Sb-Te based Chalcogenide Superlattices

    PubMed Central

    Yu, Xiaoming; Robertson, John

    2016-01-01

    GeSbTe-based chalcogenide superlattice (CSLs) phase-change memories consist of GeSbTe layer blocks separated by van der Waals bonding gaps. Recent high resolution electron microscopy found two types of disorder in CSLs, a chemical disorder within individual layers, and SbTe bilayer stacking faults connecting one block to an adjacent block which allows individual block heights to vary. The disorder requires a generalization of the previous switching models developed for CSL systems. Density functional calculations are used to describe the stability of various types of intra-layer disorder, how the block heights can vary by means of SbTe-based stacking faults and using a vacancy-mediated kink motion, and also to understand the nature of the switching process in more chemically disordered CSLs. PMID:27853289

  6. 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.

  7. Growth of Ge nanofilms using electrochemical atomic layer deposition, with a "bait and switch" surface-limited reaction.

    PubMed

    Liang, Xuehai; Zhang, Qinghui; Lay, Marcus D; Stickney, John L

    2011-06-01

    Ge nanofilms were deposited from aqueous solutions using the electrochemical analog of atomic layer deposition (ALD). Direct electrodeposition of Ge from an aqueous solution is self-limited to a few monolayers, depending on the pH. This report describes an E-ALD process for the growth of Ge films from aqueous solutions. The E-ALD cycle involved inducing a Ge atomic layer to deposit on a Te atomic layer formed on Ge, via underpotential deposition (UPD). The Te atomic layer was then reductively stripped from the deposit, leaving the Ge and completing the cycle. The Te atomic layer was bait for Ge deposition, after which the Te was switched out, reduced to a soluble telluride, leaving the Ge (one "bait and switch" cycle). Deposit thickness was a linear function of the number of cycles. Raman spectra indicated formation of an amorphous Ge film, consistent with the absence of a XRD pattern. Films were more stable and homogeneous when formed on Cu substrates, than on Au, due to a larger hydrogen overpotential, and the corresponding lower tendency to form bubbles.

  8. Ge and GeOx films as sacrificial layer for MEMS technology based on piezoelectric AlN: etching and planarization processes (Invited Paper)

    NASA Astrophysics Data System (ADS)

    Sangrador, J.; Olivares, J.; Iborra, E.; Vergara, L.; Clement, M.; Sanz-Hervas, A.

    2005-07-01

    In this article we present a study of deposition and etching techniques of germanium (Ge) and amorphous oxygen germanium (GeOx) films, with the aim of using them as sacrificial layer in the fabrication of AlN-based MEMS by surface micromachining processes. The Ge and GeOx layers were deposited by RF magnetron sputtering in Ar and Ar/O2 atmospheres. By controlling the process parameters we were able to set the final composition of the GeOx films, which was assessed by FTIR measurements. We have studied the etch rates of GeOx films with x ranging from 0 to 1 in H2O2 and H2O2/acid solutions. Depending on the etching temperature and the oxygen content in the layers, etch rates ranging from 0.2 to 2 μm/min were obtained. Nearly stoichiometric germanium oxide (GeO2) was etched in pure H2O at very high rate (>1 μm/min at room temperature). We have also developed a chemomechanical polishing (CMP) process for the planarization of Ge and GeOx. The influence of the slurries containing diverse powders (CeO2, Al2O3) and chemical agents (NH4OH, HCl), the different pads, and the various process parameters on the removal rate and the final sample topography has been studied. Finally, we have analysed the compatibility of the materials involved in the process flow with the processes of planarization and removal of the sacrificial layers.

  9. Formation of an Intermediate Layer Between Grains in Nickel-Based Superalloy Turbine Blades

    NASA Astrophysics Data System (ADS)

    Kim, KeeHyun; Withey, Paul

    2017-03-01

    The boundary region formed on the surface of nickel-based single-crystal turbine blades was investigated by high-resolution microscopy observation. There was a distinguishable intermediate layer with the size of about 2 to 5 μm between the matrix and surface defect grains such as stray grains, multiple grains, freckle grains, and even low-angle grain boundaries which were formed during the solidification of turbine blades. The intermediate layer was composed of many elongated γ' as well as γ phases. In addition, only one side of the intermediate layer was coherent to the matrix grain or defect grain due to good orientation match. At the coherent interface, the γ' (as well as γ) phase started to extend from the parent grain and coincidently, rhenium-rich particles were detected. Furthermore, the particles existed within both elongated gamma prime and gamma phases, and even at their boundary. Based on experimental observations, the formation mechanism of this intermediate layer was discussed.

  10. Simulation of hole-mobility in doped relaxed and strained Ge layers

    NASA Astrophysics Data System (ADS)

    Watling, Jeremy R.; Riddet, Craig; Chan, Morgan Kah H.; Asenov, Asen

    2010-11-01

    As silicon based metal-oxide-semiconductor field-effect transistors (MOSFETs) are reaching the limits of their performance with scaling, alternative channel materials are being considered to maintain performance in future complementary metal-oxide semiconductor technology generations. Thus there is renewed interest in employing Ge as a channel material in p-MOSFETs, due to the significant improvement in hole mobility as compared to Si. Here we employ full-band Monte Carlo to study hole transport properties in Ge. We present mobility and velocity-field characteristics for different transport directions in p-doped relaxed and strained Ge layers. The simulations are based on a method for over-coming the potentially large dynamic range of scattering rates, which results from the long-range nature of the unscreened Coulombic interaction. Our model for ionized impurity scattering includes the affects of dynamic Lindhard screening, coupled with phase-shift, and multi-ion corrections along with plasmon scattering. We show that all these effects play a role in determining the hole carrier transport in doped Ge layers and cannot be neglected.

  11. Quantum size effects in the low temperature layer-by-layer growth of Pb on Ge(0 0 1)

    NASA Astrophysics Data System (ADS)

    Floreano, L.; Cvetko, D.; Bruno, F.; Bavdek, G.; Cossaro, A.; Gotter, R.; Verdini, A.; Morgante, A.

    2003-08-01

    The electronic properties of thin metallic films deviate from the corresponding bulk ones when the film thickness is comparable with the wavelength of the electrons at the Fermi level. This phenomenon, referred to as quantum size effect (QSE), is also expected to affect the film morphology and structure leading to the “electronic growth” of metals on semiconductors. Such effect may be observed when metals are grown on substrates held at low temperature and are manifested through the occurrence of “magical” thickness islands or critical thickness for layer-by-layer growth. In particular, layer-by-layer growth of Pb(1 1 1) films has been reported for deposition on Ge(0 0 1) below ∼130 K. An extremely flat morphology is preserved throughout deposition from four up to a dozen of monolayers. These flat films are shown to be metastable and to reorganize into large clusters uncovering the first Pb layer pseudomorphic to the underlying Ge(0 0 1) substrate already at room temperature. Indications of QSE induced structural variations of the growing films have been reported for Pb growth on both Si(1 1 1) and Ge(0 0 1). In the latter case, the apparent height of the Pb(1 1 1) monatomic step was shown to change in an oscillatory fashion by He atom scattering (HAS) during layer-by-layer growth at low temperature. The extent of the structural QSE has been obtained by a comparison of the HAS data with X-ray diffraction (XRD) and reflectivity experiments. Whereas step height variations as large as 20% have been measured by HAS reflectivity, the displacement of the atomic planes from their bulk position, as measured by XRD, has been found to mainly affect the topmost Pb layer, but with a lower extent, i.e. the QSE observed by HAS are mainly due to a perpendicular displacement of the topmost layer charge density. The effect of the variable surface relaxation on the surface vibration has been studied from the acoustic dispersion of the low energy phonons, as measured by

  12. ⁶⁸Ge content quality control of ⁶⁸Ge/⁶⁸Ga-generator eluates and ⁶⁸Ga radiopharmaceuticals--a protocol for determining the ⁶⁸Ge content using thin-layer chromatography.

    PubMed

    Eppard, Elisabeth; Loktionova, Natalia S; Rösch, Frank

    2014-09-01

    (68)Ge breakthrough from a (68)Ge/(68)Ga-generator appears to be one of the most critical parameters for the routine clinical application of this generator and (68)Ga-radiopharmaceuticals. We report a TLC-based (thin-layer chromatography) protocol which allows the (68)Ge breakthrough of a generator to be determined within 1 h post-initial elution. The protocol can also be adapted to allow the (68)Ge content of a (68)Ga-radiopharmaceutical preparation to be determined prior to in vivo application.

  13. High-pressure melt growth and transport properties of SiP, SiAs, GeP, and GeAs 2D layered semiconductors

    NASA Astrophysics Data System (ADS)

    Barreteau, C.; Michon, B.; Besnard, C.; Giannini, E.

    2016-06-01

    Silicon and Germanium monopnictides SiP, SiAs, GeP and GeAs form a family of 2D layered semiconductors. We have succeeded in growing bulk single crystals of these compounds by melt-growth under high pressure (0.5-1 GPa) in a cubic anvil hot press. Large (mm-size), shiny, micaceous crystals of GeP, GeAs and SiAs were obtained, and could be exfoliated into 2D flakes. Small and brittle crystals of SiP were yielded by this method. High-pressure sintered polycrystalline SiP and GeAs have also been successfully used as a precursor in the Chemical Vapor Transport growth of these crystals in the presence of I2 as a transport agent. All compounds are found to crystallize in the expected layered structure and do not undergo any structural transition at low temperature, as shown by Raman spectroscopy down to T=5 K. All materials exhibit a semiconducting behavior. The electrical resistivity of GeP, GeAs and SiAs is found to depend on temperature following a 2D-Variable Range Hopping conduction mechanism. The availability of bulk crystals of these compounds opens new perspectives in the field of 2D semiconducting materials for device applications.

  14. Intermediate high index layer for laser mode tuning in organic semiconductor lasers.

    PubMed

    Stroisch, M; Woggon, T; Teiwes-Morin, C; Klinkhammer, S; Forberich, K; Gombert, A; Gerken, M; Lemmer, U

    2010-03-15

    We modified the optical properties of organic semiconductor distributed feedback lasers by introducing a high refractive index layer consisting of tantalum pentoxide between the substrate and the active material layer. A thin film of tris-(8-hydroxyquinoline) aluminium doped with the laser dye 4-dicyanomethylene-2-methyl-6-(p-dimethylamino-styryl)-4H-pyran was used as the active layer. By varying the intermediate layer thickness we could change the effective refractive index of the guided laser mode and thus the laser wavelength. With this technique we were able to tune the laser emission range between 613 nm and 667 nm. For high index layer thicknesses higher than 40 nm the laser operated on the TE(1)-mode rather than the fundamental TE(0)-mode.

  15. Layered YSZ/SCSZ/YSZ Electrolytes for Intermediate Temperature SOFC Part I: Design and Manufacturing

    SciTech Connect

    Orlovskaya, Nina; Klimov, Mikhail; Huang, Xinyu; Cullen, David A; Graule, Thomas; Kuebler, Jakob

    2012-01-01

    (Sc2O3)0.1(CeO2)0.01(ZrO2)0.89 (SCSZ) ceramic electrolyte has superior ionic conductivity in the intermediate temperature range (700 800 C), but it does not exhibit good phase and chemical stability in comparison with 8 mol% Y2O3 ZrO2 (YSZ). To maintain high ionic conductivity and improve the stability in the whole electrolyte, layered structures with YSZ outer layers and SCSZ inner layers were designed. Because of a mismatch of coefficients of thermal expansion and Young's moduli of SCSZ and YSZ phases, upon cooling of the electrolytes after sintering, thermal residual stresses will arise, leading to a possible strengthening of the layered composite and, therefore, an increase in the reliability of the electrolyte. Laminated electrolytes with three, four, and six layers design were manufactured using tape-casting, lamination, and sintering techniques. After sintering, while the thickness of YSZ outer layers remained constant at 30 m, the thickness of the SCSZ inner layer varied from 30 m for a Y SC Y three-layered electrolyte, 60 m for a Y 2SC Y four-layered electrolyte, and 120 m for a Y 4SC Y six-layered electrolyte. The microstructure, crystal structure, impurities present, and the density of the sintered electrolytes were characterized by scanning and transmission electron microscopy, X-ray and neutron diffraction, secondary ion mass spectroscopy, and water immersion techniques.

  16. Spectroscopic ellipsometric characterization of Si/Si(1-x)Ge(x) strained-layer superlattices

    NASA Technical Reports Server (NTRS)

    Yao, H.; Woollam, J. A.; Wang, P. J.; Tejwani, M. J.; Alterovitz, S. A.

    1993-01-01

    Spectroscopic ellipsometry (SE) was employed to characterize Si/Si(1-x)Ge(x) strained-layer superlattices. An algorithm was developed, using the available optical constants measured at a number of fixed x values of Ge composition, to compute the dielectric function spectrum of Si(1-x)Ge(x) at an arbitrary x value in the spectral range 17 to 5.6 eV. The ellipsometrically determined superlattice thicknesses and alloy compositional fractions were in excellent agreement with results from high-resolution x ray diffraction studies. The silicon surfaces of the superlattices were subjected to a 9:1 HF cleaning prior to the SE measurements. The HF solution removed silicon oxides on the semiconductor surface, and terminated the Si surface with hydrogen-silicon bonds, which were monitored over a period of several weeks, after the HF cleaning, by SE measurements. An equivalent dielectric layer model was established to describe the hydrogen-terminated Si surface layer. The passivated Si surface remained unchanged for greater than 2 h, and very little surface oxidation took place even over 3 to 4 days.

  17. Electrical isolation of dislocations in Ge layers on Si(001) substrates through CMOS-compatible suspended structures.

    PubMed

    Shah, Vishal Ajit; Myronov, Maksym; Wongwanitwatana, Chalermwat; Bawden, Lewis; Prest, Martin J; Richardson-Bullock, James S; Rhead, Stephen; Parker, Evan H C; Whall, Terrance E; Leadley, David R

    2012-10-01

    Suspended crystalline Ge semiconductor structures are created on a Si(001) substrate by a combination of epitaxial growth and simple patterning from the front surface using anisotropic underetching. Geometric definition of the surface Ge layer gives access to a range of crystalline planes that have different etch resistance. The structures are aligned to avoid etch-resistive planes in making the suspended regions and to take advantage of these planes to retain the underlying Si to support the structures. The technique is demonstrated by forming suspended microwires, spiderwebs and van der Pauw cross structures. We finally report on the low-temperature electrical isolation of the undoped Ge layers. This novel isolation method increases the Ge resistivity to 280 Ω cm at 10 K, over two orders of magnitude above that of a bulk Ge on Si(001) layer, by removing material containing the underlying misfit dislocation network that otherwise provides the main source of electrical conduction.

  18. Electrical isolation of dislocations in Ge layers on Si(001) substrates through CMOS-compatible suspended structures

    NASA Astrophysics Data System (ADS)

    Ajit Shah, Vishal; Myronov, Maksym; Wongwanitwatana, Chalermwat; Bawden, Lewis; Prest, Martin J.; Richardson-Bullock, James S.; Rhead, Stephen; Parker, Evan H. C.; Whall, Terrance E.; Leadley, David R.

    2012-10-01

    Suspended crystalline Ge semiconductor structures are created on a Si(001) substrate by a combination of epitaxial growth and simple patterning from the front surface using anisotropic underetching. Geometric definition of the surface Ge layer gives access to a range of crystalline planes that have different etch resistance. The structures are aligned to avoid etch-resistive planes in making the suspended regions and to take advantage of these planes to retain the underlying Si to support the structures. The technique is demonstrated by forming suspended microwires, spiderwebs and van der Pauw cross structures. We finally report on the low-temperature electrical isolation of the undoped Ge layers. This novel isolation method increases the Ge resistivity to 280 Ω cm at 10 K, over two orders of magnitude above that of a bulk Ge on Si(001) layer, by removing material containing the underlying misfit dislocation network that otherwise provides the main source of electrical conduction.

  19. Formation, crystalline structure, and optical properties of Ge1-x-ySnxCy ternary alloy layers

    NASA Astrophysics Data System (ADS)

    Yamaha, Takashi; Terasawa, Kengo; Oda, Hiroki; Kurosawa, Masashi; Takeuchi, Wakana; Taoka, Noriyuki; Nakatsuka, Osamu; Zaima, Shigeaki

    2015-04-01

    We have investigated the crystalline and optical properties of epitaxial layers of the ternary alloy Ge1-x-ySnxCy grown on a Si substrate. We achieved the formation of epitaxial Ge1-x-ySnxCy layers with a C content as high as 2% even with a high C incorporation efficiency. X-ray photoemission spectra and Raman scattering spectroscopy measurements revealed that C atoms preferentially bond with Sn atoms in the Ge matrix, which is considered to enhance C introduction into substitutional sites in Ge with local strain compensation. We also demonstrated the control of the energy bandgaps of epitaxial Ge1-x-ySnxCy layers by controlling Sn and C contents.

  20. Electrical isolation of dislocations in Ge layers on Si(001) substrates through CMOS-compatible suspended structures

    PubMed Central

    Shah, Vishal Ajit; Myronov, Maksym; Wongwanitwatana, Chalermwat; Bawden, Lewis; Prest, Martin J; Richardson-Bullock, James S; Rhead, Stephen; Parker, Evan H C; Whall, Terrance E; Leadley, David R

    2012-01-01

    Suspended crystalline Ge semiconductor structures are created on a Si(001) substrate by a combination of epitaxial growth and simple patterning from the front surface using anisotropic underetching. Geometric definition of the surface Ge layer gives access to a range of crystalline planes that have different etch resistance. The structures are aligned to avoid etch-resistive planes in making the suspended regions and to take advantage of these planes to retain the underlying Si to support the structures. The technique is demonstrated by forming suspended microwires, spiderwebs and van der Pauw cross structures. We finally report on the low-temperature electrical isolation of the undoped Ge layers. This novel isolation method increases the Ge resistivity to 280 Ω cm at 10 K, over two orders of magnitude above that of a bulk Ge on Si(001) layer, by removing material containing the underlying misfit dislocation network that otherwise provides the main source of electrical conduction. PMID:27877523

  1. Modeling Metallic Ion Transport During the Lifetime of an Intermediate Layer

    NASA Astrophysics Data System (ADS)

    Bishop, R. L.; Earle, G. D.

    2001-05-01

    Intermediate layers are one of several phenomena that occur at midlatitudes in the nighttime E region. These ionization layers which typically form on the bottomside of the F region, are frequently observed by the Arecibo Incoherent Scatter Facility. Although their occurrence is relatively common, they exhibit diverse structure. Their altitude of formation, vertical thickness, and motion show significant nightly variations. Layer structure is influenced by a number of factors including composition, electric fields, and fluctuations in the neutral wind field. A numerical simulation has been employed to investigate the effects of composition on layer development. Specifically, the simulation, named LEAD (Layer Evolution And Dynamics), explores the transport of metallic ions during the formation and subsequent motion of a layer due to a time varying meridional wind field. We discuss the relative molecular/metallic ratio inside the layer during its evolution, the time scales for metallic ion dominance within the layer, and the motion of metallic ions in the adjacent altitude regions. We present animated results from LEAD which allow detailed inspection of ion composition variations throughout the process of layer evolution and descent.

  2. Acquiring Peak Samples from Phytoplankton Thin Layers and Intermediate Nepheloid Layers by an Autonomous Underwater Vehicle with Adaptive Triggering

    NASA Astrophysics Data System (ADS)

    Zhang, Y.; McEwen, R.; Ryan, J. P.; Bellingham, J. G.; Harvey, J.; Vrijenhoek, R.

    2010-12-01

    Phytoplankton thin layers (PTLs) affect many fundamental aspects of coastal ocean ecology including primary productivity, development of harmful algal blooms (HABs) and the survival and growth of zooplankton and fish larvae. Intermediate nepheloid layers (INLs) that contain suspended particulate matter transported from the bottom boundary layer of continental shelves and slopes also affect biogeochemistry and ecology of ocean margins. To better understand the impacts of these types of layers, we have developed an adaptive sampling method for an autonomous underwater vehicle (AUV) to detect a layer (adjusting detection parameters in situ), acquire water samples from peaks in the layer, and acquire control samples outside the layer. We have used the method in a number of field experiments with the AUV Dorado, which is equipped with ten water samplers (called "gulpers"). In real time, the algorithm tracks background levels of fluorescence and optical backscatter and the peaks' baseline to ensure that detection is tuned to the ambient conditions. The algorithm cross-checks fluorescence and backscatter signals to differentiate PTLs from INLs. To capture peak water samples with minimal delay, the algorithm exploits the AUV's sawtooth (i.e., yo-yo) trajectory: the vehicle crosses the detected layer twice in one yo-yo cycle. At the first crossing, it detects the layer's peak and saves its signal height. Sampling is triggered at the second crossing when the signal reaches the saved peak height plus meeting additional timing and depth conditions. The algorithm is also capable of triggering gulpers to acquire control samples outside the layer for comparison with ambient water. The sequence of peak and control samples can be set based on need. In recent AUV Dorado missions, the algorithm triggered the gulpers to acquire peak and control samples from INLs and PTLs in Monterey Bay. Zooplankton analysis of some peak samples showed very high concentrations of mussel and barnacle

  3. Low-frequency conductance fluctuations in Si:P and Ge:P δ-layers

    NASA Astrophysics Data System (ADS)

    Shamim, Saquib; Mahapatra, Suddhasatta; Scappucci, Giordano; Klesse, W. M.; Simmons, Michelle Y.; Ghosh, Arindam

    Delta doped Si:P and Ge:P devices offer a formidable platform for application towards quantum computation. The fabrication of single donor devices by STM-lithography takes us forward to address the solid state quantum bits. The atomic scale control however makes the devices extremely sensitive to fluctuations and disorder which affect their long term stability. Hence, a study of low frequency 1/f noise for these devices is desirable. We measure 1/f noise in Si:P and Ge:P δ-layers of varying doping density. Fluctuations in conductivity arise due to fluctuations in mobility and the Hooge parameter scales inversely with mobility as 1 /μ3 for all devices. For highly doped Ge:P δ-layer, the noise magnitude in a perpendicular magnetic field (B⊥) reduces by factors of two at the phase breaking breaking field and the Zeeman field indicating universal conductance fluctuations (UCF). The phase breaking length lϕUCF extracted by fitting the B⊥ dependence of noise to the crossover function matches well with lϕWL extracted from weak localization (WL) fits to magnetoconductivity indicating that both UCF and WL are governed by same scattering rates. Present Address: QuTech, Delft University of Technology, P.O. Box 5046, 2600 GA Delft, The Netherlands.

  4. Formation of Nanopits in Si Capping Layers on SiGe Quantum Dots

    PubMed Central

    2011-01-01

    In-situ annealing at a high temperature of 640°C was performed for a low temperature grown Si capping layer, which was grown at 300°C on SiGe self-assembled quantum dots with a thickness of 50 nm. Square nanopits, with a depth of about 8 nm and boundaries along 〈110〉, are formed in the Si capping layer after annealing. Cross-sectional transmission electron microscopy observation shows that each nanopit is located right over one dot with one to one correspondence. The detailed migration of Si atoms for the nanopit formation is revealed by in-situ annealing at a low temperature of 540°C. The final well-defined profiles of the nanopits indicate that both strain energy and surface energy play roles during the nanopit formation, and the nanopits are stable at 640°C. A subsequent growth of Ge on the nanopit-patterned surface results in the formation of SiGe quantum dot molecules around the nanopits. PMID:27502681

  5. Vertical thermo-haline structure of the Baltic Sea cold intermediate layer

    NASA Astrophysics Data System (ADS)

    Stepanova, Natalya

    2016-04-01

    Main characteristic features of vertical thermo-haline structure of the cold intermediate layer (CIL) of the Baltic Sea are identified on the base of data of vertical CTD soundings in the Baltic Proper in 2004-2013. Permanently existing components (i.e., the components which are observed during the entire period of the presence of the CIL in the vertical thermo-haline structure of the sea) are: (i) quasi-homosaline sublayer, with water salinity typical for that in the upper mixed layer in winter period, and water temperature irregularly changing with depth; (ii) the underlying sublayer with increasing salinity and low temperature (the gradient sublayer); and (iii) the core of CIL (the minimum temperature), which is located close to the interface between these sublayers. It is argued that the homosaline sublayer is formed by local mechanisms - vertical wind-wave and convective mixing and advection from nearby shelves and neighbouring regions. Advection is supported by (i) long-lasting winds and (ii) horizontal convection due to differential warming / cooling of shallower regions. The gradient sublayer is formed by waters with T,S - parameters typical for that of the upper mixed layer of south-western sea basins (Barnholm and Arcons basins) at the beginning of spring warming-up period (March). It is suggested that the up-estuary propagation of these waters (with salinity about 7.5-8.5 psu) above the pycnocline is driven by the estuarine salinity gradient. This branch of circulation of intermediate waters is overlooked in classical estuarine circulation model of the Baltic Sea, however it is important for sea-scale transport of upper-layer contaminants, microplastics, organic matter etc. towards intermediate and deep sea layers. The investigations are supported by Russian Science Foundation via grant number 15-17-10020.

  6. Influence of intermediate aminodextran layers on the signal response of surface acoustic wave biosensors.

    PubMed

    Länge, Kerstin; Rapp, Michael

    2008-06-15

    Surface acoustic wave (SAW) devices based on horizontally polarized surface shear waves enable direct and label-free detection of proteins in real time. Binding reactions on the sensor surface are detected by determining changes in surface wave velocity caused mainly by mass adsorption or change of viscoelasticity in the sensing layer. Intermediate hydrogel layers have been proven to be useful to immobilize capture molecules or ligands corresponding to the analyte. However, the SAW signal response strongly depends on the morphology of the hydrogel due to different relative changes of its acoustomechanical parameters such as viscoelasticity and density. In this work five aminodextrans (AMD) and one diamino polyethylene glycol (DA-PEG) were used as intermediate hydrogel layers. Sensors with immobilized streptavidin and samples containing biotinylated bovine serum albumin were used to exemplify affinity assays based on immobilized capture molecules for protein detection. The effects of the three-dimensional AMDs and the two-dimensional (2D) DA-PEG on the SAW signal response were investigated. The signal height decreased with increasing molar mass and increasing amount of immobilized AMD. Consequently, thin hydrogel layers are ideal to obtain optimum signal responses in this type of assay, whereas it is not necessarily a 2D hydrogel that gives the best results.

  7. A novel intermediate layer for Au/CdZnTe/FTO photoconductive structure

    NASA Astrophysics Data System (ADS)

    Zhang, Yuelu; Wang, Linjun; Xu, Run; Huang, Jian; Tao, Jun; Meng, Hua; Zhang, Jijun; Min, Jiahua

    2016-12-01

    In this work, graphene is tried to use to improve the performance of polycrystalline CdZnTe high-energy radiation and photon detectors. A graphene intermediate layer is prepared by spin-coating process on the surface of polycrystalline CdZnTe film, which forms a photoconductive Au/graphene/CdZnTe/FTO structure. XRD, Raman, photoelectric response and other characterisation methods are adopted to investigate the effect of graphene layer on the electrical characteristics and UV photo-response performance of CdZnTe photoconductive structure. It is demonstrated that graphene layer can significantly improve the contact property of Au/CdZnTe structure, and obviously enhance its UV photo-response and the UV sensitivity increased with one order of magnitude.

  8. Improved conductivity of indium-tin-oxide film through the introduction of intermediate layer

    NASA Astrophysics Data System (ADS)

    Ng, S. W.; Yam, F. K.; Beh, K. P.; Tneh, S. S.; Hassan, Z.

    2016-09-01

    A thin intermediate layer (Ag, AuSn, In, Ni, Sn, SiO2) was individually deposited on glass substrates prior to the deposition of indium-tin-oxide (ITO) thin film by radio-frequency (RF) magnetron sputtering employing ITO target (composition ratio of In2O3:SnO2 = 9:1). The structural, optical and electrical properties were investigated to compare the ITO thin film with and without an intermediate layer. The preferential orientation of all ITO films was along (222) plane. Although all thin films were polycrystalline, the presence of intermediate layer promoted the overall crystallinity. The sheet resistance and resistivity of the ITO film were reduced from ∼68 Ω/□ to ∼29-45 Ω/□, and 16.2 × 10-4 Ω cm up to 7.58 × 10-4 Ω cm, respectively, by inserting a thin metal layer underneath the ITO film, and it is dependent on the degree of crystallization. The optical transmittance in the visible region varies from 40 to 88% for different samples. Based on the evaluation from Tauc plot, the optical band gap falls in the range of 4.02-4.12 eV. Physical film thickness was compared with that evaluated by optical measurement in the visible range and the physical thickness was found to be smaller. Similarly, the carrier concentration/scattering time from Hall effect measurement were also compared with that from optical measurement in the infrared region. Haacke's figure of merit (FOM) was employed to assess the quality of the ITO films, and the highest FOM is credited to ITO/In up to ∼8 × 10-3 Ω-1 in the visible light region.

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

    NASA Technical Reports Server (NTRS)

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

    1992-01-01

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

  10. UV and visible Raman scattering of ultraheavily Ti implanted Si layers for intermediate band formation

    NASA Astrophysics Data System (ADS)

    Pastor, D.; Olea, J.; del Prado, A.; García-Hemme, E.; Mártil, I.; González-Díaz, G.; Ibáñez, J.; Cuscó, R.; Artús, L.

    2011-11-01

    We assess the degree of crystallinity by means of UV and visible Raman scattering measurements of Ti implanted Si layers with very high doses (1015-5 × 1016 cm-2) subsequently annealed by nanosecond pulsed laser melting (PLM). We obtain ultraheavily impurified Si layers with Ti concentrations six orders of magnitude above the solid solubility limit in a layer several tens of nanometers thick. The PLM annealing processes are needed to recover the crystal quality and to keep the high Ti concentration required to form an intermediate band (IB). The UV Raman analysis permits us to evaluate the lattice crystallinity of the different implanted doses probing only the implanted region and points out Ti interstitial location in the host lattice in agreement with theoretical predictions for IB formation. By contrast, visible Raman spectra are only sensitive to the presence of a fully amorphized implanted layer as in the rest of the crystalline layers the probing depth far exceeds the implanted layer thickness and the signal is dominated by the undamaged Si.

  11. Conformational change of the hexagonally packed intermediate layer of Deinococcus radiodurans monitored by atomic force microscopy.

    PubMed Central

    Müller, D J; Baumeister, W; Engel, A

    1996-01-01

    Both surfaces of the hexagonally packed intermediate (HPI) layer of Deinococcus radiodurans were imaged in buffer solution by atomic force microscopy. When adsorbed to freshly cleaved mica, the hydrophilic outer surface of the HPI layer was attached to the substrate and the hydrophobic inner surface was exposed to the stylus. The height of a single HPI layer was 7.0 nm, while overlapping edges of adjacent single layers adsorbed to mica had a height of 14.7 nm. However, double-layered stacks with inner surfaces facing each other exhibited a height of 17.4 nm. These stacks exposed the outer surface to the stylus. The different heights of overlapping layers and stacks are attributed to differences in the interaction between inner and outer surfaces. At high resolution, the inner surface revealed a protruding core with a central pore connected by six emanating arms. The pores exhibited two conformations, one with and the other without a central plug. Individual pores were observed to switch from one state to the other. PMID:8655475

  12. Surface ventilation of the Black Sea's cold intermediate layer in the middle of the western gyre

    NASA Astrophysics Data System (ADS)

    Gregg, M. C.; Yakushev, E.

    2005-02-01

    Understanding the origin of the shallow temperature minimum, known as the Cold Intermediate Layer (CIL), in the Black Sea has long been hampered by the scarcity of winter observations. During March 2003, we observed a cold-air outbreak over the center of the Black Sea's Western Gyre. Freezing winds drove convection that cooled the surface mixed layer to 6.1°C and deepened it to 40 m, directly ventilating the upper 80% of the CIL, whose lower boundary was at 49 m. Concentrations of dissolved oxygen were 350 μM in the mixed layer and decreased rapidly to 70 μM at the base of the CIL, 9 m below the mixed layer. A few meters deeper, at the top of the Sub-Oxic Layer (SOL), both oxygen and hydrogen sulfide became undetectable (<5 μM and <1 μM, respectively). Microstructure profiles revealed intermittent turbulence in the oxycline below the mixed layer. Average rates of turbulent dissipation were 10-9-10-8 W kg-1. The accompanying mixing produced diapycnal diffusivities, Kρ, that were only (1-4) × 10-6 m2 s-1. Consequently, turbulent fluxes were too weak to renew significantly either the lower 20% of the CIL or the SOL, whose top was 4 m below the bottom of the CIL and hence well-removed from direct surface replenishment.

  13. Inversion layer on the Ge(001) surface from the four-probe conductance measurements

    SciTech Connect

    Wojtaszek, Mateusz; Lis, Jakub Zuzak, Rafal; Such, Bartosz; Szymonski, Marek

    2014-07-28

    We report four-probe conductance measurements with sub-micron resolution on atomically clean Ge(001) surfaces. A qualitative difference between n-type and p-type crystals is observed. The scaling behavior of the resistance on n-type samples indicates two-dimensional current flow, while for the p-type crystal a three-dimensional description is appropriate. We interpret this in terms of the formation of an inversion layer at the surface. This result points to the surface states, i.e., dangling bonds, as the driving force behind band bending in germanium. It also explains the intrinsic character of band bending in germanium.

  14. Fast magnetization precession for perpendicularly magnetized MnAlGe epitaxial films with atomic layered structures

    NASA Astrophysics Data System (ADS)

    Mizukami, S.; Sakuma, A.; Kubota, T.; Kondo, Y.; Sugihara, A.; Miyazaki, T.

    2013-09-01

    Epitaxial growth and magnetization precessional dynamics for tetragonal MnAlGe films are investigated. The films are grown on MgO (100) with c axis parallel to the film normal and well-ordered layered structures. The film exhibits rectangular hysteresis loop with perpendicular magnetic anisotropy constant of 4.7 Merg/cm3 and saturation magnetization of 250 emu/cm3. Magnetization precession with precession frequency of ˜100 GHz is observed by time-resolved magneto-optical Kerr effect. Further, the Gilbert damping constant is found to be less than ˜0.05, which is much larger than that obtained using the first principles calculations.

  15. Highly Reversible and Superior Li-Storage Characteristics of Layered GeS2 and Its Amorphous Composites.

    PubMed

    Sung, Geon-Kyu; Jeon, Ki-Joon; Park, Cheol-Min

    2016-11-02

    A layered GeS2 material was assessed as an electrode material in the fabrication of superior rechargeable Li-ion batteries. The electrochemical Li insertion/extraction behavior of the GeS2 electrode was investigated from extended X-ray absorption measurements as well as by cyclic voltammetry and differential capacity plots to better understand its Li insertion/extraction behavior. Using the Li insertion/extraction reaction mechanism of the GeS2 electrode, an interesting amorphous GeS2-based composite was developed and tested for use as a high-performance electrode. Interestingly, the amorphous GeS2-based composite electrode exhibited highly reversible discharging and charging reactions, which were attributed to a conversion/recombination reaction. The amorphous GeS2-based composite electrode exhibited highly reversible and outstanding electrochemical performances, a highly reversible capacity (first charge capacity: 1298 mAh g(-1)) with a high first Coulombic efficiency (83.3%), rapid rate capability (ca. 800 mAh g(-1) at a high current rate of 700 mA g(-1)), and long capacity retention over 180 cycles with high capacity (1100 mAh g(-1)) thanks to its interesting electrochemical reaction mechanism. Overall, this layered GeS2 and its amorphous GeS2/C composite are novel alternative anode materials for the potential mass production of rechargeable Li-ion batteries with excellent performance.

  16. FePtC magnetic recording media with (200) textured MoC intermediate layer

    SciTech Connect

    Tsai, Jai-Lin Tseng, Yun-Ting; Li, Chia-Ru; Fu, Sheng-Chun

    2015-05-07

    The FePt films with thickness of 4–10 nm were deposited on MoC/CrRu/glass at 425 °C by using magnetron sputtering. The Mo{sub 40}C{sub 60} target was used to form the MoC and C two phases after deposition. The MoC intermediate layer was epitaxially grown on the (200) textured CrRu seed layer at 425 °C and the MoC (200) diffraction peak was not clearly indexed below 10 nm but observed at 25 nm. Finally, the FePt film was prepared on (200) textured MoC at 425 °C and shown the strong (001) texture. Perpendicular anisotropy of 1.7 × 10{sup 7} erg/cm{sup 3} and out-of-plane coercivity of 7.5 kOe has been demonstrated in 10 nm thick FePt film. From microstructure, the FePt grains were distributed in- or between-islands like structure and further separated by excess carbon from MoC intermediate layer. Thinner FePt film was more separated by excess carbon and shown higher coercivity.

  17. Electrical decoupling effect on intermediate band Ti-implanted silicon layers

    NASA Astrophysics Data System (ADS)

    Pastor, D.; Olea, J.; del Prado, A.; García-Hemme, E.; García-Hernansanz, R.; Mártil, I.; González-Díaz, G.

    2013-04-01

    We investigated the electrical transport properties of ultraheavily Ti-implanted silicon layers subsequently pulsed laser melted (PLM). After PLM, the samples exhibit anomalous electrical behaviour in sheet resistance and Hall mobility measurements, which is associated with the formation of an intermediate band (IB) in the implanted layer. An analytical model that assumes IB formation and a current limitation effect between the implanted layer and the substrate was developed to analyse this anomalous behaviour. This model also describes the behaviour of the function V/ΔV and the electrical function F that can be extracted from the electrical measurements in the bilayer. After chemical etching of the implanted layer, the anomalous electrical behaviour observed in sheet resistance and Hall mobility measurements vanishes, recovering the unimplanted Si behaviour, in agreement with the analytical model. The behaviour of V/ΔV and the electrical function F can also be successfully described in terms of the analytical model in the bilayer structure with the implanted layer entirely stripped.

  18. Endoneurial-CD34 positive cells define an intermediate layer in human digital Pacinian corpuscles.

    PubMed

    García-Piqueras, J; García-Suárez, O; Rodríguez-González, M C; Cobo, J L; Cabo, R; Vega, J A; Feito, J

    2017-02-02

    The endoneurial and/or perineurial origin of the outer core; i.e. the concentric and continuous lamellae located outside the complex formed by the axon and the Schwann-related cells, in human Pacinian corpuscles is still debated. Here we used immunohistochemistry coupled with a battery of antibodies to investigate the expression of perineurial (Glucose transporter 1 and epithelial membrane antigen) or endoneurial (CD34 antigen) markers in human digital Pacinian corpuscles. CD34 immunoreactivity was restricted to one layer immediately outside the inner core, whereas the proper outer core displayed antigens typical of the perineurial cells. These results demonstrate an intermediate endoneurial layer that divides the Pacinian corpuscles into two distinct compartments: the avascular inner neural compartment (formed by the axon and the Schwann-related cells that form the inner core), and the outer non-neural compartment (formed by the outer core). The functional relevance of these findings, if any, remains to be clarified.

  19. Investigation of the properties of BiFeO3/intermediate-layer structures fabricated by magnetron sputtering

    NASA Astrophysics Data System (ADS)

    Kamzin, A. S.; Kamzina, L. S.; Chang, H. W.; Yu, Y. C.; Tu, S. Y.

    2015-09-01

    The properties of BiFeO3/intermediate layer/substrate structures fabricated by radio-frequency magnetron sputtering at low temperatures (450°C) and by deposition on substrates and intermediate layers between the substrate and the BiFeO3 film have been investigated. In the structures, glass substrates or commercial Pt/Ti/SiO2/Si(001) substrates have been used, and intermediate layers have been prepared from L10 FePt or Pt films. Intermediate layers of Pt and L10 FePt have the (111) and (001) textures, respectively, induced by rapid thermal annealing. It has been revealed that the deposition on the commercial substrates leads to the formation of BiFeO3 isotropic films that have a large surface roughness and consist of grains ˜200 nm in size with the BiFeO3 perovskite structure. In the case of the deposition of a BiFeO3 film on a Pt(111) intermediate layer, the BiFeO3 phase is suppressed. The deposition on an intermediate layer of the L10 FePt film with the (001) texture results in the formation of a single-phase BiFeO3 film with the (001) texture and the perovskite structure, which (as compared to the BiFeO3 films grown on the commercial substrate) has a less pronounced roughness, smaller grain sizes, and significantly better ferroelectric properties.

  20. Evidence for Kinetic Limitations as a Controlling Factor of Ge Pyramid Formation: a Study of Structural Features of Ge/Si(001) Wetting Layer Formed by Ge Deposition at Room Temperature Followed by Annealing at 600 °C

    NASA Astrophysics Data System (ADS)

    Storozhevykh, Mikhail S.; Arapkina, Larisa V.; Yuryev, Vladimir A.

    2015-07-01

    The article presents an experimental study of an issue of whether the formation of arrays of Ge quantum dots on the Si(001) surface is an equilibrium process or it is kinetically controlled. We deposited Ge on Si(001) at the room temperature and explored crystallization of the disordered Ge film as a result of annealing at 600 °C. The experiment has demonstrated that the Ge/Si(001) film formed in the conditions of an isolated system consists of the standard patched wetting layer and large droplike clusters of Ge rather than of huts or domes which appear when a film is grown in a flux of Ge atoms arriving on its surface. We conclude that the growth of the pyramids appearing at temperatures greater than 600 °C is controlled by kinetics rather than thermodynamic equilibrium whereas the wetting layer is an equilibrium structure. PACS: Primary 68.37.Ef; 68.55.Ac; 68.65.Hb; 81.07.Ta; 81.16.Dn

  1. The convection of large and intermediate scale fluctuations in a turbulent mixing layer

    NASA Astrophysics Data System (ADS)

    Buxton, O. R. H.; de Kat, R.; Ganapathisubramani, B.

    2013-12-01

    The convection velocity of large and intermediate scale velocity fluctuations in a nominally two-dimensional planar mixing layer, and its dependence upon the length scale, is explored by carrying out particle image velocimetry (PIV) experiments. A "global" convection velocity, containing the convection of all the length scales present in the flow, is produced by examining the autocorrelation functions between velocity fluctuations in successive PIV records across the mixing layer. This "global" convection velocity is found to be similar to the mean flow, although fluctuations on the low speed side of the mixing layer on average convect at speeds greater than the mean and fluctuations on the high speed side of the mixing layer are observed to convect at speeds less than the mean. Scale specific convection velocity profiles are then produced by examining the phase difference between the spectral content specific to one wavenumber in streamwise velocity fluctuation traces in successive PIV records, offset by time τ. Probability density functions (pdfs) are produced of this phase difference, which is subsequently converted into a convection displacement, and these show that the convection of single length scale fluctuations exhibits a significant variance, particularly so for larger scale fluctuations and in the high speed side of the mixing layer. Convection velocity profiles are produced from these pdfs using both the mean convection distance and the modal convection distance. It is observed that the convection velocity is relatively insensitive to the length scale of the fluctuations considered, particularly when the mean convection distance is used. A slight sensitivity to length scale is, however, observed for convection velocities based on the modal convection distance. This dependence is primarily observed in the high speed side of the mixing layer, in which smaller length-scale fluctuations convect more quickly than larger length-scale fluctuations. It is also

  2. Choroid, Haller's, and Sattler's Layer Thickness in Intermediate Age-Related Macular Degeneration With and Without Fellow Neovascular Eyes

    PubMed Central

    Esmaeelpour, Marieh; Ansari-Shahrezaei, Siamak; Glittenberg, Carl; Nemetz, Susanne; Kraus, Martin F.; Hornegger, Joachim; Fujimoto, James G.; Drexler, Wolfgang; Binder, Susanne

    2014-01-01

    Purpose. To analyze choroidal, Sattler's, and Haller's layer thickness maps in age-related macular degeneration (AMD) patients having eyes with bilateral large drusen and pigment changes (intermediate AMD), in patients having intermediate AMD eyes with neovascular fellow eyes (nAMD), and in healthy subjects using three-dimensional (3D) 1060-nm optical coherence tomography (OCT). Methods. Automatically generated choroidal thickness (ChT), retinal thickness, and Sattler's and Haller's layer thickness maps were statistically analyzed in 67 subjects consisting of intermediate AMD (n = 21), intermediate AMD (n = 22) with fellow nAMD eyes (n = 22), and healthy eyes (n = 24) with no age and axial eye length difference between groups of eyes (P > 0.05, ANOVA). Eyes were imaged by a prototype high-speed (60,000 A-scans/s) spectral-domain 3D 1060-nm OCT over a 36° × 36° field of view. Results. The mean ± SD (μm) subfoveal ChT for healthy subjects and for bilateral intermediate AMD, unilateral intermediate AMD, and their nAMD fellow eyes was 259 ± 95 and 222 ± 98, 149 ± 60, and 171 ± 78, respectively. Choroidal thickness maps demonstrated significant submacular thinning in unilateral intermediate AMD in comparison to healthy and bilateral intermediate AMD eyes (P < 0.001, ANOVA, post hoc P < 0.001 and P < 0.05, respectively). Sattler's and Haller's layers were thinnest in intermediate AMDs that presented with nAMD fellow eyes (Kruskal-Wallis test P < 0.01). For the choroid and its sublayers, there was no difference between the intermediate AMD eyes and their fellow nAMD eyes (paired testing, P < 0.05). Conclusions. The 3D 1060-nm OCT choroidal imaging visualized significant changes in choroidal, Sattler's, and Haller's layer thickness in relation to the progression of AMD. This may be important for understanding the choroidopathy in the pathophysiology of AMD. PMID:25052997

  3. Formation and circulation of the cold intermediate layer in the Gulf of Saint Lawrence

    NASA Astrophysics Data System (ADS)

    Smith, G. C.; Saucier, F. J.; Straub, D.

    2006-06-01

    The local heat content and formation rate of the cold intermediate layer (CIL) in the Gulf of Saint Lawrence are examined using a combination of new in situ wintertime observations and a three-dimensional numerical model. The field observations consist of five moorings located throughout the gulf over the period of November 2002 to June 2003. The observations demonstrate a substantially deeper surface mixed layer in the central and northeast gulf than in regions downstream of the buoyant surface outflow from the Saint Lawrence Estuary. The mixed-layer depth in the estuary remains shallow (<60 m) throughout winter, with the arrival of a layer of near-freezing waters between 40 and 100 m depth in April. An eddy-permitting ice-ocean model with realistic forcing is used to hindcast the period of observation. The model simulates well the seasonal evolution of mixed-layer depth and CIL heat content. Although the greatest heat losses occur in the northeast, the most significant change in CIL heat content over winter occurs in the Anticosti Trough. The observed renewal of CIL in the estuary in spring is captured by the model. The simulation highlights the role of the northwest gulf, and in particular, the separation of the Gaspé Current, in controlling the exchange of CIL between the estuary and the gulf. In order to isolate the effects of inflow through the Strait of Belle Isle on the CIL heat content, we examine a sensitivity experiment in which the strait is closed. This simulation shows that the inflow has a less important effect on the CIL than was suggested by previous studies.

  4. Intermediate type excitons in Schottky barriers of A3B6 layer semiconductors and UV photodetectors

    NASA Astrophysics Data System (ADS)

    Alekperov, O. Z.; Guseinov, N. M.; Nadjafov, A. I.

    2006-09-01

    Photoelectric and photovoltaic spectra of Schottky barrier (SB) structures of InSe, GaSe and GaS layered semiconductors (LS) are investigated at quantum energies from the band edge excitons of corresponding materials up to 6.5eV. Spectral dependences of photoconductivity (PC) of photo resistors and barrier structures are strongly different at the quantum energies corresponding to the intermediate type excitons (ITE) observed in these semiconductors. It was suggested that high UV photoconductivity of A3B6 LS is due to existence of high mobility light carriers in the depth of the band structure. It is shown that SB of semitransparent Au-InSe is high sensitive photo detector in UV region of spectra.

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

    DTIC Science & Technology

    2011-04-07

    to protect the Si surface from cross-contamination. Growth of thin Ge on As-passivated (211)Si was carried out next at 525C for various times, and...RMS roughness values of the films were around 0.5 nm and 1 nm, respectively, for Ge grown on Si with and without As passivation, indicating a slight...time periods of (a) 5 min and (b) 10 min. It can be seen that Ge grows layer-by- layer, resulting in a very thin Ge film . Fig. 4. SEM image of Ge

  6. Ballistic-Electron-Emission-Microscopy of Strained Si(sub 1-x)Ge(sub x) Layers

    NASA Technical Reports Server (NTRS)

    Bell, L. D.; Milliken, A. M.; Manion, S. J.; Kaiser, W. J.; Fathauer, R. W.; Pike, W. T.

    1994-01-01

    Ballistic-electron-emission microscopy (BEEM) has been used to investigate the effects of strain on Si(sub 1-x)Ge(sub x) alloys. Lifting of the degeneracy of the conduction-band minimum of Si(sub 1-x)Ge(sub x), due to lattice deformation has been directly measured by application of BEEM spectroscopy to Ag/Si structures. Experimental values for this conduction-band splitting agree well with calculations. In addition, an unexpected heterogeneity in the strain of the Si(sub 1-x)Ge(sub x) layer is introduced by deposition of Au. This effect, not observed with Ag, is attributed to species interdiffusion and has important implications for metal-semiconductor devices based oil pseudomorphic Si(sub 1-x)Ge(sub x)/Si material systems.

  7. Fabrication of high quality, thin Ge-on-insulator layers by direct wafer-bonding for nanostructured thermoelectric devices

    NASA Astrophysics Data System (ADS)

    Veerappan, Manimuthu; Mukannan, Arivanandhan; Salleh, Faiz; Shimura, Yosuke; Hayakawa, Yasuhiro; Ikeda, Hiroya

    2017-03-01

    A simple means of fabricating thin Ge-on-insulator (GOI) layers with a strong bond at the Ge/SiO2 interface through direct wafer-bonding is described. In this work, high quality Ge/SiO2 bonding was achieved under ambient air and at room temperature as a result of the extremely hydrophilic bonding surfaces obtained by chemical treatment prior to direct bonding. Based on the results of this work, the first-ever bonding mechanism between ammonium hydroxide treated Ge and SiO2/Si wafer surfaces is proposed. In addition, strain generated during post-annealing as a consequence of the significant thermal-expansion mismatch between Ge and SiO2 was gradually relieved by applying a multistep-cooling process. Structural characteristics of the thin GOI layer were analyzed by cross-sectional scanning electron microscopy, Raman spectroscopy, x-ray diffraction and transmission electron microscopy. It was determined that direct wafer-bonding followed by polishing could produce a GOI layer as thin as 156 nm, with sub-nm surface roughness.

  8. Enhanced Sensitivity of Anti-Symmetrically Structured Surface Plasmon Resonance Sensors with Zinc Oxide Intermediate Layers

    PubMed Central

    Tu, Yi-Chen; Huang, Teng-Yi; Chiu, Nan-Fu

    2014-01-01

    We report a novel design wherein high-refractive-index zinc oxide (ZnO) intermediary layers are used in anti-symmetrically structured surface plasmon resonance (SPR) devices to enhance signal quality and improve the full width at half maximum (FWHM) of the SPR reflectivity curve. The surface plasmon (SP) modes of the ZnO intermediary layer were excited by irradiating both sides of the Au film, thus inducing a high electric field at the Au/ZnO interface. We demonstrated that an improvement in the ZnO (002) crystal orientation led to a decrease in the FWHM of the SPR reflectivity curves. We optimized the design of ZnO thin films using different parameters and performed analytical comparisons of the ZnO with conventional chromium (Cr) and indium tin oxide (ITO) intermediary layers. The present study is based on application of the Fresnel equation, which provides an explanation and verification for the observed narrow SPR reflectivity curve and optical transmittance spectra exhibited by (ZnO/Au), (Cr/Au), and (ITO/Au) devices. On exposure to ethanol, the anti-symmetrically structured showed a huge electric field at the Au/ZnO interface and a 2-fold decrease in the FWHM value and a 1.3-fold larger shift in angle interrogation and a 4.5-fold high-sensitivity shift in intensity interrogation. The anti-symmetrically structured of ZnO intermediate layers exhibited a wider linearity range and much higher sensitivity. It also exhibited a good linear relationship between the incident angle and ethanol concentration in the tested range. Thus, we demonstrated a novel and simple method for fabricating high-sensitivity, high-resolution SPR biosensors that provide high accuracy and precision over relevant ranges of analyte measurement. PMID:24361929

  9. Properties of PZT thick film made on LTCC substrates with dielectric intermediate layers

    NASA Astrophysics Data System (ADS)

    DÄ browski, Arkadiusz; Golonka, Leszek

    2016-11-01

    Results of experiments on application of various interlayers between LTCC (Low Temperature Cofired Ceramics) substrate and thick-film PZT (Lead Zirconate - Titanate) are described in this work. Thick-film intermediate layers were based on several dielectric materials: TiN, Al2O3, SiC, TiO2, SiC, YSZ, BN. Seven screen printable pastes were prepared on the base of powders of mentioned materials with addition of glass and organic vehicle. The substrates were made of 951 (DuPont), CeramTapeGC (CeramTec) and HL2000 (Heraeus) LTCC tapes. Sandwich type transducers, consisting of barrier layer, gold bottom electrode, PZT layer and silver top electrode were prepared and characterized. Basic piezoelectric parameters - permittivity, effective charge constant (d33(eff)) and remanent polarization were determined. The best properties were obtained for substrates made of 951. In general, interlayers based on TiO2, SiC and Al2O3 improved permittivity and charge constant comparing to bare substrates. For example, for 951 substrate the PZT layer exhibited d33(eff) equal to 160, 215, 250 and 230 pC/N for bare substrate, TiO2 interlayer, SiC interlayer and Al2O3 interlayer, respectively. In case of CeramTape GC substrates determined permittivity was equal to 215, 245, 235 and 275 for bare substrate, TiO2 interlayer, SiC interlayer and Al2O3 interlayer, respectively. In case of TiN and BN materials the parameters were considerably deteriorated.

  10. Intermediate valence to heavy fermion through a quantum phase transition in Yb3(Rh1-xTx)4Ge13 (T = Co, Ir) single crystals

    NASA Astrophysics Data System (ADS)

    Rai, Binod; Morosan, Emilia

    Single crystals of Yb3(Rh1-x Tx)4Ge13 (T = Co, Ir) have been grown using the self-flux method. Powder X-ray diffraction data on these compounds are consistent with the cubic structure with space group Pm 3 n . Intermediate valence behavior is observed in Yb3(Rh1-x Tx)4Ge13 upon T = Co doping, while T = Ir doping drives the system into a heavy fermion state. Antiferromagnetic order is observed in the Ir-doped samples Yb3(Rh1-x Tx)4Ge13 for 0.5 < x <= 1 with TN = 0.96 K for Yb3Ir4Ge13. With decreasing x, the magnetic order is suppressed towards a quantum critical point around xc = 0.5, accompanied by non-Fermi liquid behavior evidenced by logarithmic divergence of the specific heat and linear temperature dependence of the resistivity. The Fermi liquid behavior is recovered with the application of large magnetic fields. Gordon and Betty Moore Foundation EPiQS initiative through Grant GBMF4417 and Welch Foundation.

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

    NASA Astrophysics Data System (ADS)

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

    2016-11-01

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

  12. Growth and characterization of GaN thin films on Si(111) substrates using SiC intermediate layer

    SciTech Connect

    Lim, K.Y.; Lee, K.J.; Park, C.I.; Kim, K.C.; Choi, S.C.; Lee, W.H.; Suh, E.K.; Yang, G.M.; Nahm, K.S.

    2000-07-01

    GaN films have been grown atop Si-terminated 3C-SiC intermediate layer on Si(111) substrates using low pressure metalorganic chemical vapor deposition (LP-MOCVD). The SiC intermediate layer was grown by chemical vapor deposition (CVD) using tetramethylsilane (TMS) as the single source precursor. The Si terminated SiC surface was obtained by immediately flow of SiH{sub 4} gas after growth of SiC film. LP-MOCVD growth of GaN on 3C-SiC/Si(111) was carried out with trimethylgallium (TMG) and NH{sub 3}. Single crystalline hexagonal GaN layers can be grown on Si terminated SiC intermediate layer using an AlN or GaN buffer layer. Compared with GaN layers grown using a GaN buffer layer, the crystal qualities of GaN films with AlN buffer layers are extremely improved. The GaN films were characterized by x-ray diffraction (XRD), photoluminescence (PL) and scanning electron microscopy (SEM). Full width at half maximum (FWHM) of double crystal x-ray diffraction (DCXD) rocking curve for GaN (0002) on 3C-SiC/Si(111) was 890 arcsec. PL near band edge emission peak position and FWHM at room temperature are 3.38 eV and 79.35 meV, respectively.

  13. Polydopamine as an intermediate layer for silver and hydroxyapatite immobilisation on metallic biomaterials surface.

    PubMed

    Saidin, Syafiqah; Chevallier, Pascale; Abdul Kadir, Mohammed Rafiq; Hermawan, Hendra; Mantovani, Diego

    2013-12-01

    Hydroxyapatite (HA) coated implant is more susceptible to bacterial infection as the micro-structure surface which is beneficial for osseointegration, could also become a reservoir for bacterial colonisation. The aim of this study was to introduce the antibacterial effect of silver (Ag) to the biomineralised HA by utilising a polydopamine film as an intermediate layer for Ag and HA immobilisation. Sufficient catechol groups in polydopamine were required to bind chemically stainless steel 316 L, Ag and HA elements. Different amounts of Ag nanoparticles were metallised on the polydopamine grafted stainless steel by varying the immersion time in silver nitrate solution from 12 to 24 h. Another polydopamine layer was then formed on the metallised film, followed by surface biomineralisation in 1.5 Simulated Body Fluid (SBF) solution for 3 days. Several characterisation techniques including X-Ray Photoelectron Spectroscopy, Atomic Force Microscopy, Scanning Electron Microscopy and Contact Angle showed that Ag nanoparticles and HA agglomerations were successfully immobilised on the polydopamine film through an element reduction process. The Ag metallisation at 24 h has killed the viable bacteria with 97.88% of bactericidal ratio. The Ag was ionised up to 7 days which is crucial to prevent bacterial infection during the first stage of implant restoration. The aged functionalised films were considered stable due to less alteration of its chemical composition, surface roughness and wettability properties. The ability of the functionalised film to coat complex and micro scale metal make it suitable for dental and orthopaedic implants application.

  14. The structure and photoconductivity of SiGe/Si epitaxial layers modified by single-pulse laser radiation

    NASA Astrophysics Data System (ADS)

    Ivlev, G. D.; Kazuchits, N. M.; Prakopyeu, S. L.; Rusetsky, M. S.; Gaiduk, P. I.

    2014-12-01

    The effect of nanosecond pulses of ruby laser radiation on the structural state and morphology of the epitaxial layers of a SiO0.5Ge0.5 solid solution on silicon with the initiation of a crystal-melt phase transition has been studied by electron microscopy. Data on the photoelectric parameters of the laser-modified layers having a cellular structure owing to the segregation of germanium during the solidification of the binary melt have been derived.

  15. Strain distribution in Si capping layers on SiGe islands: influence of cap thickness and footprint in reciprocal space.

    PubMed

    Hrauda, N; Zhang, J J; Süess, M J; Wintersberger, E; Holý, V; Stangl, J; Deiter, C; Seeck, O H; Bauer, G

    2012-11-23

    We present investigations on the strain properties of silicon capping layers on top of regular SiGe island arrays, in dependence on the Si-layer thickness. Such island arrays are used as stressors for the active channel in field-effect transistors where the desired tensile strain in the Si channel is a crucial parameter for the performance of the device. The thickness of the Si cap was varied from 0 to 30 nm. The results of high resolution x-ray diffraction experiments served as input to perform detailed strain calculations via finite element method models. Thus, detailed information on the Ge distribution within the buried islands and the strain interaction between the SiGe island and Si cap was obtained. It was found that the tensile strain within the Si capping layer strongly depends on its thickness, even if the Ge concentration of the buried dot remains unchanged, with tensile strains degrading if thicker Si layers are used.

  16. Reduced-Pressure Chemical Vapor Deposition Growth of Isolated Ge Crystals and Suspended Layers on Micrometric Si Pillars.

    PubMed

    Skibitzki, Oliver; Capellini, Giovanni; Yamamoto, Yuji; Zaumseil, Peter; Schubert, Markus Andreas; Schroeder, Thomas; Ballabio, Andrea; Bergamaschini, Roberto; Salvalaglio, Marco; Miglio, Leo; Montalenti, Francesco

    2016-10-05

    In this work, we demonstrate the growth of Ge crystals and suspended continuous layers on Si(001) substrates deeply patterned in high aspect-ratio pillars. The material deposition was carried out in a commercial reduced-pressure chemical vapor deposition reactor, thus extending the "vertical-heteroepitaxy" technique developed by using the peculiar low-energy plasma-enhanced chemical vapor deposition reactor, to widely available epitaxial tools. The growth process was thoroughly analyzed, from the formation of small initial seeds to the final coalescence into a continuous suspended layer, by means of scanning and transmission electron microscopy, X-ray diffraction, and μ-Raman spectroscopy. The preoxidation of the Si pillar sidewalls and the addition of hydrochloric gas in the reactants proved to be key to achieve highly selective Ge growth on the pillars top only, which, in turn, is needed to promote the formation of a continuous Ge layer. Thanks to continuum growth models, we were able to single out the different roles played by thermodynamics and kinetics in the deposition dynamics. We believe that our findings will open the way to the low-cost realization of tens of micrometers thick heteroepitaxial layer (e.g., Ge, SiC, and GaAs) on Si having high crystal quality.

  17. Effect of high-pressure H{sub 2}O treatment on elimination of interfacial GeO{sub X} layer between ZrO{sub 2} and Ge stack

    SciTech Connect

    Huang, Chen-Shuo; Liu, Po-Tsun

    2011-08-22

    This investigation demonstrates the effect of high-pressure H{sub 2}O treatment on the elimination of the interfacial germanium suboxide (GeO{sub X}) layer between ZrO{sub 2} and Ge. The formation of GeO{sub X} interlayer increases the gate-leakage current and worsen the controllability of the gate during deposition or thermal cycles. X-ray photoelectron spectroscopy and high-resolution transmission electron microscopy reveal that high-pressure H{sub 2}O treatment eliminates the interfacial GeO{sub X} layer. The physical mechanism involves the oxidation of non-oxidized Zr with H{sub 2}O and the reduction of GeO{sub X} by H{sub 2}. Treatment with H{sub 2}O reduces the gate-leakage current of a ZrO{sub 2}/Ge capacitor by a factor of 1000.

  18. A study of the nonlinear refractive index in amorphous Ge-As-S layers and nanocomposites with gold nanoparticles

    NASA Astrophysics Data System (ADS)

    Khoroshikh, D. A.; Tsypkin, A. N.; Mel'nik, M. V.; Czingel, Kristian; Kokenyesi, Sandor

    2016-11-01

    Nonlinear refractive indices of simple and composite chalcogenide glasses with gold nanoparticles are measured by the Z-scan method using a femtosecond Ti:sapphire laser with a central wavelength of 800 nm and a pulse duration of 40 fs. It is shown that introduction of nanoparticles into thin layers of amorphous GeS2, As30Ge20S50, and As3Ge35S62 leads to a decrease in the total nonlinear refractive index due to additional absorption of femtosecond laser radiation without efficient excitation of localized plasmons outside the resonance region. For example, the nonlinear refractive index decreases with addition of gold nanoparticles from 16.1 × 10-12 to 13.0 × 10-12 cm2/W for GeS2, from 3.9 × 10-12 to 3.2 × 10-12 cm2/W for As30Ge20S50, and from 5.8 × 10-12 to 4.7 × 10-12 cm2/W for As3Ge35S62.

  19. Growth of Thin Epitaxial CaxSr1-xF2/SrF2 Layers with Low Leakage Current on Ge Substrates

    NASA Astrophysics Data System (ADS)

    Takahashi, Keita; Tsutsui, Kazuo

    2013-10-01

    Resonant tunneling structures composed of epitaxial fluoride layers with a large conduction band discontinuity grown on Si or Ge substrates are attractive for the monolithic integration of quantum devices with CMOS. We found that the leakage current of Ca0.42Sr0.58F2 (lattice-matched with Ge) layers on Ge substrates was unusually large, which has not been observed on Si substrates. From an investigation of the dependence of the alloy composition of the fluoride layers on the leakage, the introduction of a SrF2 buffer layer, i.e., a Ca0.42Sr0.58F2/SrF2/Ge structure, was proposed as a technique for the growth of an electron-tunneling barrier layer on Ge with low leakage current.

  20. Metal-HfO{sub 2}-Ge capacitor: Its enhanced charge trapping properties with S-treated substrate and atomic-layer-deposited HfO{sub 2} layer

    SciTech Connect

    Park, In-Sung; Jung, Yong Chan; Seong, Sejong; Ahn, Jinho; Lee, Sung Bo

    2015-01-15

    The charge trapping properties of metal-HfO{sub 2}-Ge capacitor as a nonvolatile memory have been investigated with (NH{sub 4}){sub 2}S-treated Ge substrate and atomic-layer-deposited HfO{sub 2} layer. The interfacial layer generated by (NH{sub 4}){sub 2}S-treated Ge substrate reveals a trace of -S- bonding, very sharp interface edges, and smooth surface morphology. The Ru-HfO{sub 2}-Ge capacitor with (NH{sub 4}){sub 2}S-treated Ge substrate shows an enhanced interface state with little frequency dispersion, a lower leakage current, and very reliable properties with the enhanced endurance and retention than Ru-HfO{sub 2}-Ge capacitor with cyclic-cleaned Ge substrate.

  1. Strain and Electrical Characterization of Boron-Doped SiGeC Layers Grown by Chemical Vapor Deposition

    NASA Astrophysics Data System (ADS)

    Hållstedt, J.; Parent, A.; Zhang, S.-L.; Östling, M.; Radamson, H. H.

    2004-01-01

    Incorporation, induced strain and electrical properties of boron and carbon in Si1 x yGexCy epitaxial layers (x = 0.23 and 0.28 with y = 0 and 0.005) grown by chemical vapour deposition (CVD) have been studied. The boron concentration in the epitaxial layers was in the range of 3 × 1018 1 × 1021cm 3. The growth rate enhanced weakly by increasing boron partial pressure up to 0.002 mtorr corresponding to 2 × 1019cm 3 where a significant increase in deposition rate was observed. In SiGeC layers, the active boron concentration was obtained from the strain compensation amount. It was also found that the boron atoms have a tendency to locate at substitutional sites more preferentially compared to carbon. The incorporation of boron in SiGeC layers was clearly improved in the range 2 × 1019 3 × 1020cm 3. These investigations also enabled an estimation of the Hall scattering factor of the SiGeC layers. A comparison between our results with the previous theoretical calculations showed a good agreement. This created the possibility to evaluate the drift mobility in our samples.

  2. Surface morphology of molecular-beam epitaxially grown Si(1-x)Ge(x) layers on (100) and (110) Si

    NASA Technical Reports Server (NTRS)

    Pike, W. T.; Fathauer, R. W.; Anderson, M. S.

    1992-01-01

    The surface morphology and dislocation structure of Si(1-x)Ge(x) layers grown on (100) and (110) Si substrates have been investigated using atomic force microscopy, and scanning and transmission electron microscopy. The layers, which have up to a 1.2 percent lattice mismatch with the substrates, were grown by molecular-beam epitaxy at 550 C at thicknesses above those required for the introduction of dislocations. Si(1-x)Ge(x) layers grown on (100) show a crosshatch morphology which is correlated to the underlying misfit dislocation network. Annealing greatly enhances the surface roughness producing a partial islanding growing on the preexisting crosshatch morphology. On the (110) substrates no annealing is necessary to produce a roughened surface. The roughened surface morphology is analyzed as a strain-reducing growth mode which enables partial relaxation of the near-surface atomic planes.

  3. Stability and electronic properties of SiGe-based 2D layered structures

    NASA Astrophysics Data System (ADS)

    Jamdagni, Pooja; Kumar, Ashok; Thakur, Anil; Pandey, Ravindra; Ahluwalia, P. K.

    2015-01-01

    The structural and electronic properties of the in-plane hybrids consisting of siligene (SiGe), and its derivatives in both mono and bilayer forms are investigated within density functional theory. Among several pristine and hydrogenated configurations, the so-called chair conformation is energetically favorable for monolayers. On the other hand, the bilayer siligane (HSiGeH) prefers AB-stacked chair conformation and bilayer siligone (HSiGe) prefers AA-stacked buckled conformation. In SiGe, the Dirac-cone character is predicted to be retained. HSiGe is a magnetic semiconductor with a band gap of ˜0.6 eV. The electronic properties show tunability under mechanical strain and transverse electric field; (i) the energy gap opens up in the SiGe bilayer, (ii) a direct-to-indirect gap transition is predicted by the applied strain in the HSiGeH bilayer, and (iii) a semiconductor-to-metal transition is predicted for HSiGe and HSiGeH bilayers under the application of strain and electric field, thus suggesting SiGe and its derivatives to be a potential candidate for electronic devices at nanoscale.

  4. Characteristics of the Baltic Sea Cold Intermediate Layer on the base of field data

    NASA Astrophysics Data System (ADS)

    Kozlova, Olga; Chubarenko, Natalia; Chubarenko, Irina

    2010-05-01

    Cold Intermediate Layer (CIL) is observed in the Baltic Sea deep areas (depth more than ~60 m) from March to September/October and is easily identifiable at depths 30-60 m by its low temperature (~2-4 C). The main objectives of the work were (i) to develop a criterion of allocation of the CIL in general thermo-haline structure, (ii) to define the CIL using this criterion on the basis of real field data for 2004-2006 years and (iii) to analyze a range of its characteristics (temperature, salinity, density, thickness, location, stability at interfaces, etc.) after those winters (of different severity). Even though cold intermediate layers are often found in inland seas with strong pycno/halocline (the Black Sea, the Marmara Sea, the Mediterranean), quite different criteria of their allocation are used. For the Baltic, there isn't commonly used criterion. It has been found most convenient to use the following one: the CIL in the Baltic Sea is to be defined as a layer between maximum negative and maximum positive temperature gradient within vertical water column. With this definition, allocation of the CIL on vertical temperature/salinity/density profiles was performed using field data obtained in 2005-2006 during cruises of r/v "Professor Stockman" (P.P.Shirshov Istitute of Oceanology RAS; data courtesy Dr.V.Paka, Dr.D.Dorohov) in the Baltic Sea coastal zone and of r/v "Gauss" (Baltic Sea Research Institute at Warnemuende; data courtesy Dr.R.Feistel) in the Baltic Proper. Analysis of mean annual data, published on CD with the book "State and Evolution of the Baltic Sea 1952-2005" (data of IOW), has demonstrated that from about 80 quadrates (1' x 1') of the Baltic Sea area, in 43 quadrates water temperature within the CIL is lower than the lowest water surface temperature. This shows that the CIL contains waters advected horizontally. In order to find spatial correlations, T-S analysis was applied, demonstrating that the CIL waters might drift from south-western rather

  5. As- or P-Doped Si Layers Grown by RPCVD for Emitter Application in SiGeC HBTs

    NASA Astrophysics Data System (ADS)

    Suvar, Erdal; Haralson, Erik; Hållstedt, Julius; Radamson, Henry H.; Östling, Mikael

    2004-01-01

    A new module for the emitter formation in a bipolar transistor is presented. Arsenic- or phosphorus-doped polycrystalline silicon layer for the emitter formation is deposited in a reduced pressure chemical vapor deposition reactor using silane as the silicon source gas. Characteristics such as the carrier concentration, conductivity, surface morphology, and thermal stability of the polycrystalline-silicon layer as well as the influence this layer has on a SiGeC transistor structure during the drive-in step area studied. The active carrier concentration of the as-grown sample is strongly dependent on the deposition temperature, especially arsenic doped layers which exhibit more than one order of magnitude difference. However, the carrier concentration for the As- or P-doped layer were comparable to that of a standard in-situ doped poly-crystalline layer after a dopant activation at 925°C for 10s.

  6. Interface induce growth of intermediate layer for bandgap engineering insights into photoelectrochemical water splitting

    PubMed Central

    Zhang, Jian; Zhang, Qiaoxia; Wang, Lianhui; Li, Xing’ao; Huang, Wei

    2016-01-01

    A model of interface induction for interlayer growing is proposed for bandgap engineering insights into photocatalysis. In the interface of CdS/ZnS core/shell nanorods, a lamellar solid solution intermediate with uniform thickness and high crystallinity was formed under interface induction process. Merged the novel charge carrier transfer layer, the photocurrent of the core/shell/shell nanorod (css-NR) array was significantly improved to 14.0 mA cm−2 at 0.0 V vs. SCE, nearly 8 times higher than that of the perfect CdS counterpart and incident photon to electron conversion efficiency (IPCE) values above 50% under AM 1.5G irradiation. In addition, this array photoelectrode showed excellent photocatalytic stability over 6000 s. These results suggest that the CdS/Zn1−xCdxS/ZnS css-NR array photoelectrode provides a scalable charge carrier transfer channel, as well as durability, and therefore is promising to be a large-area nanostructured CdS-based photoanodes in photoelectrochemical (PEC) water splitting system. PMID:27250648

  7. Growth of monolithic full-color GaN-based LED with intermediate carrier blocking layers

    NASA Astrophysics Data System (ADS)

    El-Ghoroury, Hussein S.; Yeh, Milton; Chen, J. C.; Li, X.; Chuang, Chih-Li

    2016-07-01

    Specially designed intermediate carrier blocking layers (ICBLs) in multi-active regions of III-nitride LEDs were shown to be effective in controlling the carrier injection distribution across the active regions. In principle, the majority of carriers, both holes and electrons, can be guided into targeted quantum wells and recombine to generate light of specific wavelengths at controlled current-densities. Accordingly we proposed and demonstrated a novel monolithic InGaN-based LED to achieve three primary colors of light from one device at selected current densities. This LED structure, which has three different sets of quantum wells separated with ICBLs for three primary red-green-blue (RGB) colors, was grown by metal-organic chemical vapor deposition (MOCVD). Results show that this LED can emit light ranging from 460 to 650 nm to cover the entire visible spectrum. The emission wavelength starts at 650 nm and then decreases to 460 nm or lower as the injection current increases. In addition to three primary colors, many other colors can be obtained by color mixing techniques. To the best of our knowledge, this is the first demonstration of monolithic full-color LED grown by a simple growth technique without using re-growth process.

  8. Interface induce growth of intermediate layer for bandgap engineering insights into photoelectrochemical water splitting

    NASA Astrophysics Data System (ADS)

    Zhang, Jian; Zhang, Qiaoxia; Wang, Lianhui; Li, Xing’Ao; Huang, Wei

    2016-06-01

    A model of interface induction for interlayer growing is proposed for bandgap engineering insights into photocatalysis. In the interface of CdS/ZnS core/shell nanorods, a lamellar solid solution intermediate with uniform thickness and high crystallinity was formed under interface induction process. Merged the novel charge carrier transfer layer, the photocurrent of the core/shell/shell nanorod (css-NR) array was significantly improved to 14.0 mA cm‑2 at 0.0 V vs. SCE, nearly 8 times higher than that of the perfect CdS counterpart and incident photon to electron conversion efficiency (IPCE) values above 50% under AM 1.5G irradiation. In addition, this array photoelectrode showed excellent photocatalytic stability over 6000 s. These results suggest that the CdS/Zn1‑xCdxS/ZnS css-NR array photoelectrode provides a scalable charge carrier transfer channel, as well as durability, and therefore is promising to be a large-area nanostructured CdS-based photoanodes in photoelectrochemical (PEC) water splitting system.

  9. Tuneable Magnetic Phase Transitions in Layered CeMn2Ge2-xSix Compounds

    PubMed Central

    Md Din, M. F.; Wang, J. L.; Cheng, Z. X.; Dou, S. X.; Kennedy, S. J.; Avdeev, M.; Campbell, S. J.

    2015-01-01

    The structural and magnetic properties of seven CeMn2Ge2-xSix compounds with x = 0.0–2.0 have been investigated in detail. Substitution of Ge with Si leads to a monotonic decrease of both a and c along with concomitant contraction of the unit cell volume and significant modifications of the magnetic states - a crossover from ferromagnetism at room temperature for Ge-rich compounds to antiferromagnetism for Si-rich compounds. The magnetic phase diagram has been constructed over the full range of CeMn2Ge2-xSix compositions and co-existence of ferromagnetism and antiferromagnetism has been observed in CeMn2Ge1.2Si0.8, CeMn2Ge1.0Si1.0 and CeMn2Ge0.8Si1.2 with novel insight provided by high resolution neutron and X-ray synchrotron radiation studies. CeMn2Ge2-xSix compounds (x = 0, 0.4 and 0.8) exhibit moderate isothermal magnetic entropy accompanied with a second-order phase transition around room temperature. Analysis of critical behaviour in the vicinity of TCinter for CeMn2Ge2 compound indicates behaviour consistent with three-dimensional Heisenberg model predictions. PMID:26090940

  10. Initial stage growth of GexSi1−x layers and Ge quantum dot formation on GexSi1−x surface by MBE

    PubMed Central

    2012-01-01

    Critical thicknesses of two-dimensional to three-dimensional growth in GexSi1−x layers were measured as a function of composition for different growth temperatures. In addition to the (2 × 1) superstructure for a Ge film grown on Si(100), the GexSi1−x layers are characterized by the formation of (2 × n) reconstruction. We measured n for all layers of Ge/GexSi1−x/Ge heterosystem using our software with respect to the video recording of reflection high-energy electron diffraction (RHEED) pattern during growth. The n reaches a minimum value of about 8 for clear Ge layer, whereas for GexSi1−x films, n is increased from 8 to 14. The presence of a thin strained film of the GexSi1−x caused not only the changes in critical thicknesses of the transitions, but also affected the properties of the germanium nanocluster array for the top Ge layer. Based on the RHEED data, the hut-like island form, which has not been previously observed by us between the hut and dome islands, has been detected. Data on the growth of Ge/GexSi1−x/Ge heterostructures with the uniform array of islands in the second layer of the Ge film have been received. PMID:23043796

  11. The influence of a Si cap on self-organized SiGe islands and the underlying wetting layer

    SciTech Connect

    Brehm, M.; Grydlik, M.; Groiss, H.; Hackl, F.; Schaeffler, F.; Fromherz, T.; Bauer, G.

    2011-06-15

    For the prototypical SiGe/Si(001) Stranski-Krastanow (SK) growth system, the influence of intermixing caused by the deposition of a Si cap layer at temperatures T{sub cap} between 300 deg. C and 700 deg. C is studied both for the SiGe wetting layer (WL) and the SiGe islands. Systematic growth experiments were carried out with an ultrahigh resolution of down to 0.005 monolayers (ML) of deposited Ge. The properties of the samples were investigated via photoluminescence (PL) spectroscopy, atomic force microscopy (AFM), and transmission electron microscopy. We studied in detail the influence of T{sub cap} in the three main coverage regions of SiGe SK growth, which are (i) the WL build-up regime, (ii) the island nucleation regime, where most of the Ge is supplied via material transfer from the WL, and (iii) the saturation regime, where the WL thickness remains initially stable. At T{sub cap} = 300 deg. C, we found that both the WL and the island are essentially preserved in composition and shape, whereas at 500 deg. C the WL becomes heavily alloyed during capping, and at 700 deg. C the islands also become alloyed. At T{sub cap} = 500 deg. C we found enhanced WL intermixing in the presence of dome-shaped islands, whereas at T{sub cap} 700 deg. C the WL properties become dominated by the dissolution of pyramid-shaped islands upon capping. At Ge coverages above {approx_equal}6 ML, we found an unexpected thickening of the WL, almost independently of T{sub cap}. This finding suggests that the density and the volume of the dome-shaped islands have an upper limit, beyond which excess Ge from the external source again becomes incorporated into the WL. Finally, we compared PL spectra with AFM-based evaluations of the integral island volumes in order to determine in a straightforward manner the average composition of the SiGe islands.

  12. Phase-change properties of GeSbTe thin films deposited by plasma-enchanced atomic layer depositon.

    PubMed

    Song, Sannian; Yao, Dongning; Song, Zhitang; Gao, Lina; Zhang, Zhonghua; Li, Le; Shen, Lanlan; Wu, Liangcai; Liu, Bo; Cheng, Yan; Feng, Songlin

    2015-01-01

    Phase-change access memory (PCM) appears to be the strongest candidate for next-generation high-density nonvolatile memory. The fabrication of ultrahigh-density PCM depends heavily on the thin-film growth technique for the phase-changing chalcogenide material. In this study, Ge2Sb2Te5 (GST) and GeSb8Te thin films were deposited by plasma-enhanced atomic layer deposition (ALD) method using Ge [(CH3)2 N]4, Sb [(CH3)2 N]3, Te(C4H9)2 as precursors and plasma-activated H2 gas as reducing agent of the metallorganic precursors. Compared with GST-based device, GeSb8Te-based device exhibits a faster switching speed and reduced reset voltage, which is attributed to the growth-dominated crystallization mechanism of the Sb-rich GeSb8Te films. These results show that ALD is an attractive method for preparation of phase-change materials.

  13. Differential Gene Expression of the Intermediate and Outer Interzone Layers of Developing Articular Cartilage in Murine Embryos

    PubMed Central

    IJpma, Arne; Cleary, Mairead; Heijsman, Daphne; Narcisi, Roberto; van der Spek, Peter J.; Kremer, Andreas; van Weeren, René; Brama, Pieter; van Osch, Gerjo J.V.M.

    2014-01-01

    Nascent embryonic joints, interzones, contain a distinct cohort of progenitor cells responsible for the formation of the majority of articular tissues. However, to date the interzone has largely been studied using in situ analysis for candidate genes in the context of the embryo rather than using an unbiased genome-wide expression analysis on isolated interzone cells, leaving significant controversy regarding the exact role of the intermediate and outer interzone layers in joint formation. Therefore, in this study, using laser capture microdissection (three biological replicates), we selectively harvested the intermediate and outer interzones of mouse embryos at gestational age 15.5 days, just prior to cavitation, when the differences between the layers should be most profound. Microarray analysis (Agilent Whole Mouse Genome Oligo Microarrays) was performed and the differential gene expression between the intermediate interzone cells and outer interzone cells was examined by performing a two-sided paired Student's t-test and pathway analysis. One hundred ninety-seven genes were differentially expressed (≥2-fold) between the intermediate interzone and the outer interzone with a P-value≤0.01. Of these, 91 genes showed higher expression levels in the intermediate interzone and 106 were expressed higher in the outer interzone. Pathway analysis of differentially expressed genes suggests an important role for inflammatory processes in the interzone layers, especially in the intermediate interzone, and hence in joint and articular cartilage development. The high representation of genes relevant to chondrocyte hypertrophy and endochondral ossification in the outer interzone suggests that it undergoes endochondral ossification. PMID:24738827

  14. Behavior and mixing of a cold intermediate layer near a sloping boundary

    NASA Astrophysics Data System (ADS)

    Cyr, Frédéric; Bourgault, Daniel; Galbraith, Peter S.

    2015-03-01

    As in many other subarctic basins, a cold intermediate layer (CIL) is found during ice-free months in the Lower St. Lawrence Estuary (LSLE), Canada. This study examines the behavior of the CIL above the sloping bottom using a high-resolution mooring deployed on the northern side of the estuary. Observations show successive swashes/backwashes of the CIL on the slope at a semi-diurnal frequency. It is shown that these upslope and downslope motions are likely caused by internal tides generated at the nearby channel head sill. Quantification of mixing from 322 turbulence casts reveals that in the bottom 10 m of the water column, the time-average dissipation rate of turbulent kinetic energy is 𝜖 10 m = 1.6×10-7Wkg-1, an order of magnitude greater than found in the interior of the basin, far from boundaries. Near-bottom dissipation during the flood phase of the M2 tide cycle (upslope flow) is about four times greater than during the ebb phase (downslope flow). Bottom shear stress, shear instabilities, and internal wave scattering are considered as potential boundary mixing mechanisms near the seabed. In the interior of the water column, far from the bottom, increasing dissipation rates are observed with both increasing stratification and shear, which suggests some control of the dissipation by the internal wave field. However, poor fits with a parametrization for large-scale wave-wave interactions suggests that the mixing is partly driven by more complex non-linear and/or smaller scale waves.

  15. Intermediate Progenitor Cohorts Differentially Generate Cortical Layers and Require Tbr2 for Timely Acquisition of Neuronal Subtype Identity.

    PubMed

    Mihalas, Anca B; Elsen, Gina E; Bedogni, Francesco; Daza, Ray A M; Ramos-Laguna, Kevyn A; Arnold, Sebastian J; Hevner, Robert F

    2016-06-28

    Intermediate progenitors (IPs) amplify the production of pyramidal neurons, but their role in selective genesis of cortical layers or neuronal subtypes remains unclear. Using genetic lineage tracing in mice, we find that IPs destined to produce upper cortical layers first appear early in corticogenesis, by embryonic day 11.5. During later corticogenesis, IP laminar fates are progressively limited to upper layers. We examined the role of Tbr2, an IP-specific transcription factor, in laminar fate regulation using Tbr2 conditional mutant mice. Upon Tbr2 inactivation, fewer neurons were produced by immediate differentiation and laminar fates were shifted upward. Genesis of subventricular mitoses was, however, not reduced in the context of a Tbr2-null cortex. Instead, neuronal and laminar differentiation were disrupted and delayed. Our findings indicate that upper-layer genesis depends on IPs from many stages of corticogenesis and that Tbr2 regulates the tempo of laminar fate implementation for all cortical layers.

  16. Low temperature formation of higher-k cubic phase HfO{sub 2} by atomic layer deposition on GeO{sub x}/Ge structures fabricated by in-situ thermal oxidation

    SciTech Connect

    Zhang, R.; Huang, P.-C.; Taoka, N.; Yokoyama, M.; Takenaka, M.; Takagi, S.

    2016-02-01

    We have demonstrated a low temperature formation (300 °C) of higher-k HfO{sub 2} using atomic layer deposition (ALD) on an in-situ thermal oxidation GeO{sub x} interfacial layer. It is found that the cubic phase is dominant in the HfO{sub 2} film with an epitaxial-like growth behavior. The maximum permittivity of 42 is obtained for an ALD HfO{sub 2} film on a 1-nm-thick GeO{sub x} form by the in-situ thermal oxidation. It is suggested from physical analyses that the crystallization of cubic phase HfO{sub 2} can be induced by the formation of six-fold crystalline GeO{sub x} structures in the underlying GeO{sub x} interfacial layer.

  17. Surface passivation of p-type Ge substrate with high-quality GeNx layer formed by electron-cyclotron-resonance plasma nitridation at low temperature

    NASA Astrophysics Data System (ADS)

    Fukuda, Yukio; Okamoto, Hiroshi; Iwasaki, Takuro; Otani, Yohei; Ono, Toshiro

    2011-09-01

    We have investigated the effects of the formation temperature and postmetallization annealing (PMA) on the interface properties of GeNx/p-Ge fabricated by the plasma nitridation of Ge substrates using an electron-cyclotron-resonance-generated nitrogen plasma. The nitridation temperature is found to be a critical parameter in improving the finally obtained GeNx/Ge interface properties. The GeNx/Ge formed at room temperature and treated by PMA at 400 °C exhibits the best interface properties with an interface trap density of 1 × 1011 cm-2 eV-1. The GeNx/Ge interface is unpinned and the Fermi level at the Ge surface can move from the valence band edge to the conduction band edge.

  18. GeP and (Ge{sub 1−x}Sn{sub x})(P{sub 1−y}Ge{sub y}) (x≈0.12, y≈0.05): Synthesis, structure, and properties of two-dimensional layered tetrel phosphides

    SciTech Connect

    Lee, Kathleen; Synnestvedt, Sarah; Bellard, Maverick; Kovnir, Kirill

    2015-04-15

    GeP and Sn-doped GeP were synthesized from elements in bismuth and tin flux, respectively. The layered crystal structures of these compounds were characterized by single crystal X-ray diffraction. Both phosphides crystallize in a GaTe structure type in the monoclinic space group C2/m (No. 12) with GeP: a=15.1948(7) Å, b=3.6337(2) Å, c=9.1941(4) Å, β=101.239(2)°; Ge{sub 0.93(3)}P{sub 0.95(1)}Sn{sub 0.12(3)}: a=15.284(9) Å, b=3.622(2) Å, c=9.207(5) Å, β=101.79(1)°. The crystal structure of GeP consists of 2-dimensional GeP layers held together by weak electron lone pair interactions between the phosphorus atoms that confine the layer. Each layer is built of Ge–Ge dumbbells surrounded by a distorted antiprism of phosphorus atoms. Sn-doped GeP has a similar structural motif, but with a significant degree of disorder emphasized by the splitting of all atomic positions. Resistivity measurements together with quantum-chemical calculations reveal semiconducting behavior for the investigated phosphides. - Graphical abstract: Layered phosphides GeP and Sn-doped GeP were synthesized from elements in bismuth and tin flux, respectively. The crystal structure of GeP consists of 2-dimensional GeP layers held together by weak electron lone pair interactions between the phosphorus atoms that confine the layer. Sn-doped GeP has a similar structural motif with a significant degree of disorder emphasized by the splitting of all atomic positions. Resistivity measurements together with quantum-chemical calculations reveal semiconducting behavior for the investigated phosphides. - Highlights: • GeP crystallizes in a layered crystal structure. • Doping of Sn into GeP causes large structural distortions. • GeP is narrow bandgap semiconductor. • Sn-doped GeP exhibits an order of magnitude higher resistivity due to disorder.

  19. Role of boundary layer diffusion in vapor deposition growth of chalcogenide nanosheets: the case of GeS.

    PubMed

    Li, Chun; Huang, Liang; Snigdha, Gayatri Pongur; Yu, Yifei; Cao, Linyou

    2012-10-23

    We report a synthesis of single-crystalline two-dimensional GeS nanosheets using vapor deposition processes and show that the growth behavior of the nanosheet is substantially different from those of other nanomaterials and thin films grown by vapor depositions. The nanosheet growth is subject to strong influences of the diffusion of source materials through the boundary layer of gas flows. This boundary layer diffusion is found to be the rate-determining step of the growth under typical experimental conditions, evidenced by a substantial dependence of the nanosheet's size on diffusion fluxes. We also find that high-quality GeS nanosheets can grow only in the diffusion-limited regime, as the crystalline quality substantially deteriorates when the rate-determining step is changed away from the boundary layer diffusion. We establish a simple model to analyze the diffusion dynamics in experiments. Our analysis uncovers an intuitive correlation of diffusion flux with the partial pressure of source materials, the flow rate of carrier gas, and the total pressure in the synthetic setup. The observed significant role of boundary layer diffusions in the growth is unique for nanosheets. It may be correlated with the high growth rate of GeS nanosheets, ~3-5 μm/min, which is 1 order of magnitude higher than other nanomaterials (such as nanowires) and thin films. This fundamental understanding of the effect of boundary layer diffusions may generally apply to other chalcogenide nanosheets that can grow rapidly. It can provide useful guidance for the development of general paradigms to control the synthesis of nanosheets.

  20. Facile Synthesis of Layer Structured GeP3/C with Stable Chemical Bonding for Enhanced Lithium-Ion Storage

    NASA Astrophysics Data System (ADS)

    Qi, Wen; Zhao, Haihua; Wu, Ying; Zeng, Hong; Tao, Tao; Chen, Chao; Kuang, Chunjiang; Zhou, Shaoxiong; Huang, Yunhui

    2017-02-01

    Recently, metal phosphides have been investigated as potential anode materials because of higher specific capacity compared with those of carbonaceous materials. However, the rapid capacity fade upon cycling leads to poor durability and short cycle life, which cannot meet the need of lithium-ion batteries with high energy density. Herein, we report a layer-structured GeP3/C nanocomposite anode material with high performance prepared by a facial and large-scale ball milling method via in-situ mechanical reaction. The P-O-C bonds are formed in the composite, leading to close contact between GeP3 and carbon. As a result, the GeP3/C anode displays excellent lithium storage performance with a high reversible capacity up to 1109 mA h g‑1 after 130 cycles at a current density of 0.1 A g‑1. Even at high current densities of 2 and 5 A g‑1, the reversible capacities are still as high as 590 and 425 mA h g‑1, respectively. This suggests that the GeP3/C composite is promising to achieve high-energy lithium-ion batteries and the mechanical milling is an efficient method to fabricate such composite electrode materials especially for large-scale application.

  1. Facile Synthesis of Layer Structured GeP3/C with Stable Chemical Bonding for Enhanced Lithium-Ion Storage

    PubMed Central

    Qi, Wen; Zhao, Haihua; Wu, Ying; Zeng, Hong; Tao, Tao; Chen, Chao; Kuang, Chunjiang; Zhou, Shaoxiong; Huang, Yunhui

    2017-01-01

    Recently, metal phosphides have been investigated as potential anode materials because of higher specific capacity compared with those of carbonaceous materials. However, the rapid capacity fade upon cycling leads to poor durability and short cycle life, which cannot meet the need of lithium-ion batteries with high energy density. Herein, we report a layer-structured GeP3/C nanocomposite anode material with high performance prepared by a facial and large-scale ball milling method via in-situ mechanical reaction. The P-O-C bonds are formed in the composite, leading to close contact between GeP3 and carbon. As a result, the GeP3/C anode displays excellent lithium storage performance with a high reversible capacity up to 1109 mA h g−1 after 130 cycles at a current density of 0.1 A g−1. Even at high current densities of 2 and 5 A g−1, the reversible capacities are still as high as 590 and 425 mA h g−1, respectively. This suggests that the GeP3/C composite is promising to achieve high-energy lithium-ion batteries and the mechanical milling is an efficient method to fabricate such composite electrode materials especially for large-scale application. PMID:28240247

  2. Impact of growth and annealing conditions on the parameters of Ge/Si(001) relaxed layers grown by molecular beam epitaxy

    SciTech Connect

    Yurasov, D. V.; Bobrov, A. I.; Daniltsev, V. M.; Novikov, A. V.; Pavlov, D. A.; Skorokhodov, E. V.; Shaleev, M. V.; Yunin, P. A.

    2015-11-15

    Influence of the Ge layer thickness and annealing conditions on the parameters of relaxed Ge/Si(001) layers grown by molecular beam epitaxy via two-stage growth is investigated. The dependences of the threading dislocation density and surface roughness on the Ge layer thickness, annealing temperature and time, and the presence of a hydrogen atmosphere are obtained. As a result of optimization of the growth and annealing conditions, relaxed Ge/Si(001) layers which are thinner than 1 μm with a low threading dislocation density on the order of 10{sup 7} cm{sup –2} and a root mean square roughness of less than 1 nm are obtained.

  3. Bonding mechanism of a yttrium iron garnet film on Si without the use of an intermediate layer

    SciTech Connect

    Pantzas, Konstantinos; Patriarche, Gilles; Talneau, Anne; Youssef, Jamal Ben

    2014-10-06

    Direct bonding of yttrium iron garnet (YIG) on silicon without the use of an intermediate bonding layer is demonstrated and characterized using scanning transmission electron microscopy and energy-dispersive x-ray spectroscopy. During the bonding experiment, the garnet is reduced in the presence of oxide-free silicon. As a result, a 5 nm thick SiO{sub 2}/amorphous-YIG bilayer is formed and welds the garnet to silicon.

  4. Low temperature thermal ALD of a SiNx interfacial diffusion barrier and interface passivation layer on SixGe1- x(001) and SixGe1- x(110).

    PubMed

    Edmonds, Mary; Sardashti, Kasra; Wolf, Steven; Chagarov, Evgueni; Clemons, Max; Kent, Tyler; Park, Jun Hong; Tang, Kechao; McIntyre, Paul C; Yoshida, Naomi; Dong, Lin; Holmes, Russell; Alvarez, Daniel; Kummel, Andrew C

    2017-02-07

    Atomic layer deposition of a silicon rich SiNx layer on Si0.7Ge0.3(001), Si0.5Ge0.5(001), and Si0.5Ge0.5(110) surfaces has been achieved by sequential pulsing of Si2Cl6 and N2H4 precursors at a substrate temperature of 285 °C. XPS spectra show a higher binding energy shoulder peak on Si 2p indicative of SiOxNyClz bonding while Ge 2p and Ge 3d peaks show only a small amount of higher binding energy components consistent with only interfacial bonds, indicating the growth of SiOxNy on the SiGe surface with negligible subsurface reactions. Scanning tunneling spectroscopy measurements confirm that the SiNx interfacial layer forms an electrically passive surface on p-type Si0.70Ge0.30(001), Si0.50Ge0.50(110), and Si0.50Ge0.50(001) substrates as the surface Fermi level is unpinned and the electronic structure is free of states in the band gap. DFT calculations show that a Si rich a-SiO0.4N0,4 interlayer can produce lower interfacial defect density than stoichiometric a-SiO0.8N0.8, substoichiometric a-Si3N2, or stoichiometric a-Si3N4 interlayers by minimizing strain and bond breaking in the SiGe by the interlayer. Metal-oxide-semiconductor capacitors devices were fabricated on p-type Si0.7Ge0.3(001) and Si0.5Ge0.5(001) substrates with and without the insertion of an ALD SiOxNy interfacial layer, and the SiOxNy layer resulted in a decrease in interface state density near midgap with a comparable Cmax value.

  5. Low temperature thermal ALD of a SiNx interfacial diffusion barrier and interface passivation layer on SixGe1- x(001) and SixGe1- x(110)

    NASA Astrophysics Data System (ADS)

    Edmonds, Mary; Sardashti, Kasra; Wolf, Steven; Chagarov, Evgueni; Clemons, Max; Kent, Tyler; Park, Jun Hong; Tang, Kechao; McIntyre, Paul C.; Yoshida, Naomi; Dong, Lin; Holmes, Russell; Alvarez, Daniel; Kummel, Andrew C.

    2017-02-01

    Atomic layer deposition of a silicon rich SiNx layer on Si0.7Ge0.3(001), Si0.5Ge0.5(001), and Si0.5Ge0.5(110) surfaces has been achieved by sequential pulsing of Si2Cl6 and N2H4 precursors at a substrate temperature of 285 °C. XPS spectra show a higher binding energy shoulder peak on Si 2p indicative of SiOxNyClz bonding while Ge 2p and Ge 3d peaks show only a small amount of higher binding energy components consistent with only interfacial bonds, indicating the growth of SiOxNy on the SiGe surface with negligible subsurface reactions. Scanning tunneling spectroscopy measurements confirm that the SiNx interfacial layer forms an electrically passive surface on p-type Si0.70Ge0.30(001), Si0.50Ge0.50(110), and Si0.50Ge0.50(001) substrates as the surface Fermi level is unpinned and the electronic structure is free of states in the band gap. DFT calculations show that a Si rich a-SiO0.4N0,4 interlayer can produce lower interfacial defect density than stoichiometric a-SiO0.8N0.8, substoichiometric a-Si3N2, or stoichiometric a-Si3N4 interlayers by minimizing strain and bond breaking in the SiGe by the interlayer. Metal-oxide-semiconductor capacitors devices were fabricated on p-type Si0.7Ge0.3(001) and Si0.5Ge0.5(001) substrates with and without the insertion of an ALD SiOxNy interfacial layer, and the SiOxNy layer resulted in a decrease in interface state density near midgap with a comparable Cmax value.

  6. Observations of low and intermediate-frequency-peaked BL Lacs above 100 GeV with VERITAS

    NASA Astrophysics Data System (ADS)

    Errando, M.

    2013-12-01

    Most of the ~ 50 blazars detected to date at TeV energies (E > 0.1 TeV) are high-frequency-peaked BL Lacs (HBLs). Only a handful episodic detections of low- and intermediate-frequency-peaked BL Lacs (LBL/IBLs, with synchrotron peak frequencies in the infrared and optical regime) have been reported by ground-based gamma-ray telescopes, typically during high-flux states. The VERITAS array located in southern Arizona has observed five known TeV LBL/IBLs since 2009: 3C 66A, WComae, PKS 1424+240, S5 0716+714 and BL Lacertae, with exposures of 5-10 hours/year, which so far resulted in the detection of a bright, sub-hour timescale gamma-ray flare of BL Lacertae in June 2011. We also report the detection and characterization of two new IBLs: VER J0521+211 and B2 1215+30.

  7. Interface magnetism of Co{sub 2}FeGe Heusler alloy layers and magnetoresistance of Co{sub 2}FeGe/MgO/Fe magnetic tunnel junctions

    SciTech Connect

    Tanaka, M. A. Maezaki, D.; Ishii, T.; Okubo, A.; Mibu, K.; Hiramatsu, R.; Ono, T.

    2014-10-28

    The interface magnetism between Co{sub 2}FeGe Heusler alloy layers and MgO layers was investigated using {sup 57}Fe Mössbauer spectroscopy. Interface-sensitive samples, where the {sup 57}Fe isotope was used only for the interfacial atomic layer of the Co{sub 2}FeGe layer on the MgO layer, were prepared using atomically controlled alternate deposition. The {sup 57}Fe Mössbauer spectra of the interface-sensitive samples at room temperature were found similar to those of the bulk-sensitive Co{sub 2}FeGe films in which the {sup 57}Fe isotope was distributed throughout the films. On the other hand, the tunnel magnetoresistance effect of magnetic tunnel junctions with Co{sub 2}FeGe layers as the ferromagnetic electrodes showed strong reduction at room temperature. These results indicate that the strong temperature dependence of the tunneling magnetoresistance of magnetic tunnel junctions using Heusler alloy electrodes cannot be attributed simply to the reduction of the magnetization at the interfaces between the Heusler alloy and insulator layers.

  8. Influence of intermediate layers on the surface condition of laser crystallized silicon thin films and solar cell performance

    SciTech Connect

    Höger, Ingmar Gawlik, Annett; Brückner, Uwe; Andrä, Gudrun; Himmerlich, Marcel; Krischok, Stefan

    2016-01-28

    The intermediate layer (IL) between glass substrate and silicon plays a significant role in the optimization of multicrystalline liquid phase crystallized silicon thin film solar cells on glass. This study deals with the influence of the IL on the surface condition and the required chemical surface treatment of the crystallized silicon (mc-Si), which is of particular interest for a-Si:H heterojunction thin film solar cells. Two types of IL were investigated: sputtered silicon nitride (SiN) and a layer stack consisting of silicon nitride and silicon oxide (SiN/SiO). X-ray photoelectron spectroscopy measurements revealed the formation of silicon oxynitride (SiO{sub x}N{sub y}) or silicon oxide (SiO{sub 2}) layers at the surface of the mc-Si after liquid phase crystallization on SiN or SiN/SiO, respectively. We propose that SiO{sub x}N{sub y} formation is governed by dissolving nitrogen from the SiN layer in the silicon melt, which segregates at the crystallization front during crystallization. This process is successfully hindered, when additional SiO layers are introduced into the IL. In order to achieve solar cell open circuit voltages above 500 mV, a removal of the formed SiO{sub x}N{sub y} top layer is required using sophisticated cleaning of the crystallized silicon prior to a-Si:H deposition. However, solar cells crystallized on SiN/SiO yield high open circuit voltage even when a simple wet chemical surface treatment is applied. The implementation of SiN/SiO intermediate layers facilitates the production of mesa type solar cells with open circuit voltages above 600 mV and a power conversion efficiency of 10%.

  9. Influence of intermediate layers on the surface condition of laser crystallized silicon thin films and solar cell performance

    NASA Astrophysics Data System (ADS)

    Höger, Ingmar; Himmerlich, Marcel; Gawlik, Annett; Brückner, Uwe; Krischok, Stefan; Andrä, Gudrun

    2016-01-01

    The intermediate layer (IL) between glass substrate and silicon plays a significant role in the optimization of multicrystalline liquid phase crystallized silicon thin film solar cells on glass. This study deals with the influence of the IL on the surface condition and the required chemical surface treatment of the crystallized silicon (mc-Si), which is of particular interest for a-Si:H heterojunction thin film solar cells. Two types of IL were investigated: sputtered silicon nitride (SiN) and a layer stack consisting of silicon nitride and silicon oxide (SiN/SiO). X-ray photoelectron spectroscopy measurements revealed the formation of silicon oxynitride (SiOxNy) or silicon oxide (SiO2) layers at the surface of the mc-Si after liquid phase crystallization on SiN or SiN/SiO, respectively. We propose that SiOxNy formation is governed by dissolving nitrogen from the SiN layer in the silicon melt, which segregates at the crystallization front during crystallization. This process is successfully hindered, when additional SiO layers are introduced into the IL. In order to achieve solar cell open circuit voltages above 500 mV, a removal of the formed SiOxNy top layer is required using sophisticated cleaning of the crystallized silicon prior to a-Si:H deposition. However, solar cells crystallized on SiN/SiO yield high open circuit voltage even when a simple wet chemical surface treatment is applied. The implementation of SiN/SiO intermediate layers facilitates the production of mesa type solar cells with open circuit voltages above 600 mV and a power conversion efficiency of 10%.

  10. New class of Si-based superlattices - Alternating layers of crystalline Si and porous amorphous Si(1-x)Ge(x) alloys

    NASA Technical Reports Server (NTRS)

    Fathauer, R. W.; George, T.; Jones, E. W.; Pike, W. T.; Ksendzov, A.; Vasquez, R. P.

    1992-01-01

    Superlattices consisting of alternating layers of crystalline Si and porous amorphous Si(1-x)Ge(x) have been fabricated. This is accomplished by first growing a Si/Si(0.7)Ge(0.3) superlattice by molecular beam epitaxy, followed by Ar-ion milling to form mesa structures, and finally by immersion in HF:HNO3:H2O. This solution creates a porous structure similar to that created by anodic etching, and a high selectivity is observed for the conversion of the alloy layers relative to the Si layers. The degree of selectivity is found to depend on alloy-layer thickness and strain. Superlattices have been fabricated from 1-micron wide mesas with Si(0.7)Ge(0.3) layers fully converted to 5-nm thick porous amorphous material.

  11. Identified Light and Strange Hadron Spectra at √{sNN} = 14.5 GeV and Systematic Study of Baryon/Meson Effect at Intermediate Transverse Momentum with STAR at RHIC BES I

    NASA Astrophysics Data System (ADS)

    Brandenburg, James D.

    2016-12-01

    With the recently measured Au+Au collisions at √{sNN} = 14.5 GeV, STAR completed its first phase of the Beam Energy Scan (BES) program at RHIC. The main motivation of the BES program is the study of the QCD phase diagram and the search for a conjectured critical point. Amongst the various collision energies of 7.7, 11.5, 19.6, 27, and 39 GeV, that have been previously presented by STAR, collisions at 14.5 GeV will provide data set in the relatively large chemical potential gap between the 11.5 and 19.6 GeV center-of-mass energies. In this contribution, we report new STAR measurements of Au+Au at √{sNN} = 14.5 GeV that include identified light particle RCP and spectra, as well as measurements of the strange hadrons (Ks0, Λ , Ξ , Ω, and ϕ). The spectra from both light and strange particles cover a significant range of the intermediate transverse momentum (2 GeV /c) in all beam energies. This provides a unique set of data for a systematic study of the baryon-to-meson ratio at intermediate pT from BES Phase I. We will discuss its physics implications and whether hadronic interactions at late stage dominate the collision dynamics.

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

    NASA Astrophysics Data System (ADS)

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

    2017-01-01

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

  13. High-Rate Charging Induced Intermediate Phases and Structural Changes of Layer-Structured Cathode for Lithium-Ion Batteries

    DOE PAGES

    Zhou, Yong-Ning; Yue, Ji-Li; Hu, Enyuan; ...

    2016-08-08

    Using fast time-resolved in situ X-ray diffraction, charge-rate dependent phase transition processes of layer structured cathode material LiNi1/3Mn1/3Co1/3O2 for lithium-ion batteries are studied. During first charge, intermediate phases emerge at high rates of 10C, 30C, and 60C, but not at low rates of 0.1C and 1C. These intermediate phases can be continuously observed during relaxation after the charging current is switched off. After half-way charging at high rate, sample studied by scanning transmission electron microscopy shows Li-rich and Li-poor phases' coexistence with tetrahedral occupation of Li in Li-poor phase. Also, the high rate induced overpotential is thought to be themore » driving force for the formation of this intermediate Li-poor phase. The in situ quick X-ray absorption results show that the oxidation of Ni accelerates with increasing charging rate and the Ni4+ state can be reached at the end of charge with 30C rate. Finally, these results give new insights in the understanding of the layered cathodes during high-rate charging.« less

  14. High-Rate Charging Induced Intermediate Phases and Structural Changes of Layer-Structured Cathode for Lithium-Ion Batteries

    SciTech Connect

    Zhou, Yong-Ning; Yue, Ji-Li; Hu, Enyuan; Li, Hong; Gu, Lin; Nam, Kyung-Wan; Bak, Seong-Min; Yu, Xiqian; Liu, Jue; Bai, Jianming; Dooryhee, Eric; Fu, Zheng-Wen; Yang, Xiao-Qing

    2016-08-08

    Using fast time-resolved in situ X-ray diffraction, charge-rate dependent phase transition processes of layer structured cathode material LiNi1/3Mn1/3Co1/3O2 for lithium-ion batteries are studied. During first charge, intermediate phases emerge at high rates of 10C, 30C, and 60C, but not at low rates of 0.1C and 1C. These intermediate phases can be continuously observed during relaxation after the charging current is switched off. After half-way charging at high rate, sample studied by scanning transmission electron microscopy shows Li-rich and Li-poor phases' coexistence with tetrahedral occupation of Li in Li-poor phase. Also, the high rate induced overpotential is thought to be the driving force for the formation of this intermediate Li-poor phase. The in situ quick X-ray absorption results show that the oxidation of Ni accelerates with increasing charging rate and the Ni4+ state can be reached at the end of charge with 30C rate. Finally, these results give new insights in the understanding of the layered cathodes during high-rate charging.

  15. Structural and electrical studies of ultrathin layers with Si{sub 0.7}Ge{sub 0.3} nanocrystals confined in a SiGe/SiO{sub 2} superlattice

    SciTech Connect

    Vieira, E. M. F.; Martin-Sanchez, J.; Rolo, A. G.; Levichev, S.; Gomes, M. J. M.; Parisini, A.; Buljan, M.; Capan, I.; Alves, E.; Barradas, N. P.; Conde, O.; Bernstorff, S.; Chahboun, A.

    2012-05-15

    In this work, SiGe/SiO{sub 2} multi-layer (ML) films with layer thickness in the range of a few nanometers were successfully fabricated by conventional RF-magnetron sputtering at 350 deg. C. The influence of the annealing treatment on SiGe nanocrystals (NCs) formation and crystalline properties were investigated by Raman spectroscopy and grazing incidence x-ray diffraction. At the annealing temperature of 800 deg. C, where well defined SiGe NCs were observed, a thorough structural investigation of the whole ML structure has been undertaken by Rutherford backscattering spectroscopy, grazing incidence small angle x-ray scattering, high resolution transmission electron microscopy, and annular dark field scanning transmission electron microscopy. Our results show that the onset of local modifications to the ML composition takes place at this temperature for annealing times of the order of a few tens of minutes with the formation of defective regions in the upper portion of the ML structure. Only the very first layers over the Si substrate appear immune to this problem. This finding has been exploited for the fabrication of a defect free metal-oxide-semiconductor structure with a well-defined single layer of SiGe NCs. A memory effect attributed to the presence of the SiGe NCs has been demonstrated by high frequency capacitance-voltage measurements.

  16. Electro-optical switching at 1550 nm using a two-state GeSe phase-change layer.

    PubMed

    Soref, Richard; Hendrickson, Joshua; Liang, Haibo; Majumdar, Arka; Mu, Jianwei; Li, Xun; Huang, Wei-Ping

    2015-01-26

    New designs for electro-optical free-space and waveguided 2 x 2 switches are presented and analyzed at the 1.55 μm telecoms wavelength. The proposed devices employ a ~10 nm film of GeSe that is electrically actuated to transition the layer forth-and-back from the amorphous to the crystal phase, yielding a switch with two self-sustaining states. This phase change material was selected for its very low absorption loss at the operation wavelength, along with its electro-refraction Δn ~0.6. All switches are cascadeable into N x M devices. The free-space prism-shaped structures use III-V prism material to match the GeSe crystal index. The Si/GeSe/Si "active waveguides" are quite suitable for directional-coupler switches as well as Mach-Zehnder devices-all of which have an active length 16x less than that in the free-carrier art.

  17. Intermediate valence in single crystals of (Lu{sub 1−x}Y b{sub x}){sub 3}Rh{sub 4}Ge{sub 13} (0 ≤ x ≤ 1)

    SciTech Connect

    Rai, Binod K.; Morosan, E.

    2015-04-01

    Single crystals of (Lu{sub 1−x}Y b{sub x}){sub 3}Rh{sub 4}Ge{sub 13} were characterized by magnetization, specific heat, and electrical resistivity measurements. Doping Yb into the non-magnetic Lu{sub 3}Rh{sub 4}Ge{sub 13} compound tunes this cubic system’s properties from a superconductor with disordered metal normal state (x < 0.05) to a Kondo for 0.05 ≤ x ≤0.2 and intermediate valence at the highest Yb concentrations. The evidence for intermediate Yb valence comes from a broad maximum in the magnetic susceptibility and X-ray photoelectron spectroscopy. Furthermore, the resistivity displays a local maximum at finite temperatures at intermediate compositions x, followed by apparent metallic behavior closest to the Yb end compound in the series.

  18. Hybrid ZnO/phthalocyanine photovoltaic device with highly resistive ZnO intermediate layer.

    PubMed

    Izaki, Masanobu; Chizaki, Ryo; Saito, Takamasa; Murata, Kazufumi; Sasano, Junji; Shinagawa, Tsutomu

    2013-10-09

    We report a hybrid photovoltaic device composed of a 3.3 eV bandgap zinc oxide (ZnO) semiconductor and metal-free phthalocyanine layers and the effects of the insertion of the highly resistive ZnO buffer layer on the electrical characteristics of the rectification feature and photovoltaic performance. The hybrid photovoltaic devices have been constructed by electrodeposition of the 300 nm thick ZnO layer in a simple zinc nitrate aqueous solution followed by vacuum evaporation of 50-400 nm thick-phthalocyanine layers. The ZnO layers with the resistivity of 1.8 × 10(3) and 1 × 10(8) Ω cm were prepared by adjusting the cathodic current density and were installed into the hybrid photovoltaic devices as the n-type and buffer layer, respectively. The phthalocyanine layers with the characteristic monoclinic lattice showed a characteristic optical absorption feature regardless of the thickness, but the preferred orientation changed depending on the thickness. The ZnO buffer-free hybrid 50 nm thick phthalocyanine/n-ZnO photovoltaic device showed a rectification feature but possessed a poor photovoltaic performance with a conversion efficiency of 7.5 × 10(-7) %, open circuit voltage of 0.041 V, and short circuit current density of 8.0 × 10(-5) mA cm(-2). The insertion of the ZnO buffer layer between the n-ZnO and phthalocyanine layers induced improvements in both the rectification feature and photovoltaic performance. The excellent rectification feature with a rectification ratio of 3188 and ideally factor of 1.29 was obtained for the hybrid 200 nm thick phthalocyanine/ZnO buffer/n-ZnO photovoltaic device, and the hybrid photovoltaic device possessed an improved photovoltaic performance with the conversion efficiency of 0.0016%, open circuit voltage of 0.31 V, and short circuit current density of 0.015 mA cm(-2).

  19. Untangling spatial and temporal trends in the variability of the Black Sea Cold Intermediate Layer and mixed Layer Depth using the DIVA detrending procedure

    NASA Astrophysics Data System (ADS)

    Capet, A.; Troupin, C.; Carstensen, J.; Grégoire, M.; Beckers, J.-M.

    2014-03-01

    Current spatial interpolation products may be biased by uneven distribution of measurements in time. This manuscript presents a detrending method that recognizes and eliminates this bias. The method estimates temporal trend components in addition to the spatial structure and has been implemented within the Data Interpolating Variational Analysis (DIVA) analysis tool. The assets of this new detrending method are illustrated by producing monthly and annual climatologies of two vertical properties of the Black Sea while recognizing their seasonal and interannual variabilities : the mixed layer depth and the cold content of its cold intermediate layer (CIL). The temporal trends, given as by-products of the method, are used to analyze the seasonal and interannual variability of these variables over the past decades (1955-2011). In particular, the CIL interannual variability is related to the cumulated winter air temperature anomalies, explaining 88 % of its variation.

  20. Effect of nonstoichiometry on the electrophysical properties of the layered compounds Ge{sub 3}Bi{sub 2}Te{sub 6} and GeBi{sub 2}Te{sub 4}

    SciTech Connect

    Shelimova, L.E.; Karpinskii, O.G.; Avilov, E.S.; Kretova, M.A.; Lubman, C.U.

    1994-12-01

    The objective of this work was to investigate the effect of deviation from stoichiometry on the electrophysical properties (electrical and thermal conductivity, thermoelectric power, and carrier concentration) of the ternary layered semiconducting compounds Ge{sub 3{plus_minus}{delta}1}Bi{sub 2+{delta}2}Te{sub 6+{delta}3} and Ge{sub 1{plus_minus}{delta}3}, which are promising for use in thermoelectric converters.The electrophysical properties were measured at 300 K. The Ge{sub 1-{delta}1}Bi{sub 2+{delta}3} alloys were studied by powder X-ray diffraction analysis on a DRON UM-1 diffractometer (CoK{sub {alpha}} radiation). It was found that Ge{sub 3{plus_minus}{delta}1} Bi{sub 2+{delta}2}Te{sub 6{plus_minus}{delta}3} is a nonstoichiometric phase with p-type conductivity throughout the {delta}{sub 1}, {delta}{sub 2}, and {delta}{sub 3} ranges examined. Our results suggest that cation vacancies are likely to be the dominant nonstoichiometric defects responsible for the high concentration of holes. The conductivity of Ge{sub 1{plus_minus}{delta}1}Bi{sub 2}Te{sub 4} changes from the p-type in the Ge-deficient alloys to the n-type in the Gerich alloys.

  1. Effects of patterning induced stress relaxation in strained SOI/SiGe layers and substrate

    NASA Astrophysics Data System (ADS)

    Hermann, P.; Hecker, M.; Renn, F.; Rölke, M.; Kolanek, K.; Rinderknecht, J.; Eng, L. M.

    2011-06-01

    Local stress fields in strained silicon structures important for CMOS technology are essentially related to size effects and properties of involved materials. In the present investigation, Raman spectroscopy was utilized to analyze the stress distribution within strained silicon (sSi) and silicon-germanium (SiGe) island structures. As a result of the structuring of initially unpatterned strained films, a size-dependent relaxation of the intrinsic film stresses was obtained in agreement with model calculations. This changed stress state in the features also results in the appearance of opposing stresses in the substrate underneath the islands. Even for strained island structures on top of silicon-on-insulator (SOI) wafers, corresponding stresses in the silicon substrate underneath the oxide were detected. Within structures, the stress relaxation is more pronounced for islands on SOI substrates as compared to those on bulk silicon substrates.

  2. Magnetic anisotropy of crystalline Fe films grown on (001) GaAs substrates using Ge buffer layers

    NASA Astrophysics Data System (ADS)

    Bac, Seul-Ki; Lee, Hakjoon; Lee, Sangyeop; Choi, Seonghoon; Yoo, Taehee; Lee, Sanghoon; Liu, X.; Furdyna, J. K.

    2016-05-01

    Magnetic anisotropy of Fe films grown on (001) GaAs substrates using Ge buffer layers were investigated by planar Hall effect measurements. In addition to phenomena arising from dominant cubic symmetry of the Fe specimen, the study of angular dependence of magnetization reversal revealed breaking of this symmetry in the form of systematic asymmetric shifts of magnetic hysteresis loops around the <110 > crystallographic directions. We ascribe such symmetry breaking to an admixture of uniaxial anisotropy associated with the [100] direction in the Fe film. To determine the parameters associated with this uniaxial anisotropy, we quantitatively analyze the asymmetric shifts of the hysteresis loop centers from the <110 > directions. Even though the value of these parameters turns out to be relatively small compared to that of the cubic anisotropy (by about two orders of magnitude), they survive up to room temperature.

  3. Electrical characterization of low temperature deposited TiO 2 films on strained-SiGe layers

    NASA Astrophysics Data System (ADS)

    Dalapati, G. K.; Chatterjee, S.; Samanta, S. K.; Maiti, C. K.

    2003-04-01

    Thin films of titanium dioxide have been deposited on strained Si 0.82Ge 0.18 epitaxial layers using titanium tetrakis-isopropoxide [TTIP, Ti(O-i-C 3H 7) 4] and oxygen by microwave plasma enhanced chemical vapor deposition (PECVD). The films have been characterized by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). Dielectric constant, equivalent oxide thickness (EOT), interface state density ( Dit), fixed oxide charge density ( Qf/ q) and flat-band voltage ( VFB) of as-deposited films were found to be 13.2, 40.6 Å, 6×10 11 eV -1 cm -2, 3.1×10 11 cm -2 and -1.4 V, respectively. The capacitance-voltage ( C- V), current-voltage ( I- V) characteristics and charge trapping behavior of the films under constant current stressing exhibit an excellent interface quality and high dielectric reliability making the films suitable for microelectronic applications.

  4. Intermediate honeycomb ordering to trigger oxygen redox chemistry in layered battery electrode

    PubMed Central

    Mortemard de Boisse, Benoit; Liu, Guandong; Ma, Jiangtao; Nishimura, Shin-ichi; Chung, Sai-Cheong; Kiuchi, Hisao; Harada, Yoshihisa; Kikkawa, Jun; Kobayashi, Yoshio; Okubo, Masashi; Yamada, Atsuo

    2016-01-01

    Sodium-ion batteries are attractive energy storage media owing to the abundance of sodium, but the low capacities of available cathode materials make them impractical. Sodium-excess metal oxides Na2MO3 (M: transition metal) are appealing cathode materials that may realize large capacities through additional oxygen redox reaction. However, the general strategies for enhancing the capacity of Na2MO3 are poorly established. Here using two polymorphs of Na2RuO3, we demonstrate the critical role of honeycomb-type cation ordering in Na2MO3. Ordered Na2RuO3 with honeycomb-ordered [Na1/3Ru2/3]O2 slabs delivers a capacity of 180 mAh g−1 (1.3-electron reaction), whereas disordered Na2RuO3 only delivers 135 mAh g−1 (1.0-electron reaction). We clarify that the large extra capacity of ordered Na2RuO3 is enabled by a spontaneously ordered intermediate Na1RuO3 phase with ilmenite O1 structure, which induces frontier orbital reorganization to trigger the oxygen redox reaction, unveiling a general requisite for the stable oxygen redox reaction in high-capacity Na2MO3 cathodes. PMID:27088834

  5. Intermediate honeycomb ordering to trigger oxygen redox chemistry in layered battery electrode

    NASA Astrophysics Data System (ADS)

    Mortemard de Boisse, Benoit; Liu, Guandong; Ma, Jiangtao; Nishimura, Shin-Ichi; Chung, Sai-Cheong; Kiuchi, Hisao; Harada, Yoshihisa; Kikkawa, Jun; Kobayashi, Yoshio; Okubo, Masashi; Yamada, Atsuo

    2016-04-01

    Sodium-ion batteries are attractive energy storage media owing to the abundance of sodium, but the low capacities of available cathode materials make them impractical. Sodium-excess metal oxides Na2MO3 (M: transition metal) are appealing cathode materials that may realize large capacities through additional oxygen redox reaction. However, the general strategies for enhancing the capacity of Na2MO3 are poorly established. Here using two polymorphs of Na2RuO3, we demonstrate the critical role of honeycomb-type cation ordering in Na2MO3. Ordered Na2RuO3 with honeycomb-ordered [Na1/3Ru2/3]O2 slabs delivers a capacity of 180 mAh g-1 (1.3-electron reaction), whereas disordered Na2RuO3 only delivers 135 mAh g-1 (1.0-electron reaction). We clarify that the large extra capacity of ordered Na2RuO3 is enabled by a spontaneously ordered intermediate Na1RuO3 phase with ilmenite O1 structure, which induces frontier orbital reorganization to trigger the oxygen redox reaction, unveiling a general requisite for the stable oxygen redox reaction in high-capacity Na2MO3 cathodes.

  6. Effect of SiO2 layer intermediation on direct carbothermal synthesis of SiC nanopowders.

    PubMed

    Hwang, Yeon; Riu, Doh-Hyung; An, Ju-Hyun; Chun, Dongil; Kim, Youngseok

    2013-09-01

    Beta-SiC was synthesized by direct carbothermal reaction using silicon and SiO2-layer-coated carbon powders. It is usually difficult to control the rate of the direct carbothermal reaction of silicon because the reaction rapidly progresses. Therefore coarse powders are obtained although it has the advantage of low synthesis temperature. To evade the above difficulty we tried to insert SiO2 layers between carbon and silicon powders, and the effect of SiO2 layer intermediation on the SiC synthesis was examined. SiO2 was coated on carbon black powders by using a 3-aminopropyltriethoxysilane (APTES) and tetraethoxysilane (TEOS) solution. The mixture of silicon and SiO2-coated carbon powders was reacted at 1200-1500 degrees C for 1 h in an Ar gas atmosphere. The morphologies of SiO2-coated carbon and synthesized SiC powders were observed. Thermal and phase evolution during the synthesis of SiC powders were analyzed. We obtained beta-SiC powders with a particle size of around 100 nm at the synthesis temperature of more than 1400 degrees C, which is a considerably lower reaction temperature than that of a usual carbothermal reaction.

  7. An intermediate nepheloid layer associated with high microbial metabolic rates and denitrification in the northwest Indian Ocean

    NASA Astrophysics Data System (ADS)

    Naqvi, S. W. A.; Kumar, M. D.; Narvekar, P. V.; de Sousa, S. N.; George, M. D.; D'Silva, C.

    1993-01-01

    Extensive optical, physical, chemical, and biochemical measurements made simultaneously in the northwest Indian Ocean reveal the occurrence of an intermediate nepheloid layer (INL) invariably associated with the secondary nitrite maximum. Maxima in particulate protein and the activity of the respiratory electron transport system (ETS) are also found within the INL. Since the INL persists long distances from the continental margin with an offshore intensification, it may not be related to the transport of material resuspended along the continental margin. An apparent correlation of the INL with the previously reported subsurface maximum in bacterial abundance suggests that a local increase in the abundance of bacteria may be responsible for the increased turbidity. Positive correlations of the beam attenuation anomaly with nitrite and nitrate deficit suggest that most of these bacteria may be denitrifiers. The organic carbon demand within the denitrifying layer, computed from the observed ETS activity, appears to be severalfold higher than the sinking carbon fluxes to the denitrifying layer, requiring additional modes of supply of the biodegradable organic matter. It is proposed that a bacterial maximum could be maintained with efficient utilization of the dissolved organic matter within the denitrifying waters.

  8. Boron diffusion layer formation using Ge cryogenic implantation with low-temperature microwave annealing

    NASA Astrophysics Data System (ADS)

    Murakoshi, Atsushi; Harada, Tsubasa; Miyano, Kiyotaka; Harakawa, Hideaki; Aoyama, Tomonori; Yamashita, Hirofumi; Kohyama, Yusuke

    2016-04-01

    It is shown that a low-sheet-resistance p-type diffusion layer with a small diffusion depth can be fabricated efficiently by cryogenic boron and germanium implantation combined with low-temperature (400 °C) microwave annealing. Compared with the conventional annealing at 1000 °C, a much smaller diffusion depth is obtained at the same sheet resistance. The low sheet resistance at 400 °C is due to microwave absorption in the surface amorphous layer, which is formed by cryogenic germanium implantation. However, the pn junction leakage was worse than that in conventional annealing, because crystal defects remain near the amorphous/crystal interface after microwave annealing. It is found that the pn junction leakage is improved greatly by cryogenic germanium implantation. These results show that a suitable combination of cryogenic implantation and microwave annealing is very promising for p-type diffusion layer technology.

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

    DOE PAGES

    Lu, T. M.; Gamble, J. K.; Muller, R. P.; ...

    2016-08-01

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

  10. Silica-decorated polypropylene microfiltration membranes with a mussel-inspired intermediate layer for oil-in-water emulsion separation.

    PubMed

    Yang, Hao-Cheng; Pi, Jun-Ke; Liao, Kun-Jian; Huang, He; Wu, Qing-Yun; Huang, Xiao-Jun; Xu, Zhi-Kang

    2014-08-13

    Silica-decorated polypropylene microfiltration membranes were fabricated via a facile biomimetic silicification process on the polydopamine/polyethylenimine-modified surfaces. The membranes exhibit superhydrophilicity and underwater superoleophobicity derived from the inherent hydrophilicity and the well-defined micronanocomposite structures of the silica-decorated surfaces. They can be applied in varieties of oil-in-water emulsions separation with high permeate flux (above 1200 L/m(2)h under 0.04 MPa) and oil rejection (above 99%). The membranes also have relatively high oil breakthrough pressure reaching 0.16 MPa due to the microporous structure, showing great potential for practical applications. Furthermore, such mussel-inspired intermediate layer provides us a convenient and powerful tool to fabricate organic-inorganic hybrid membranes for advanced applications.

  11. A high-sensitivity fiber-optic evanescent wave sensor with a three-layer structure composed of Canada balsam doped with GeO2.

    PubMed

    Zhong, Nianbing; Zhao, Mingfu; Zhong, Lianchao; Liao, Qiang; Zhu, Xun; Luo, Binbin; Li, Yishan

    2016-11-15

    In this paper, we present a high-sensitivity polymer fiber-optic evanescent wave (FOEW) sensor with a three-layer structure that includes bottom, inter-, and surface layers in the sensing region. The bottom layer and inter-layer are POFs composed of standard cladding and the core of the plastic optical fiber, and the surface layer is made of dilute Canada balsam in xylene doped with GeO2. We examine the morphology of the doped GeO2, the refractive index and composition of the surface layer and the surface luminous properties of the sensing region. We investigate the effects of the content and morphology of the GeO2 particles on the sensitivity of the FOEW sensors by using glucose solutions. In addition, we examine the response of sensors incubated with staphylococcal protein A plus mouse IgG isotype to goat anti-mouse IgG solutions. Results indicate very good sensitivity of the three-layer FOEW sensor, which showed a 3.91-fold improvement in the detection of the target antibody relative to a conventional sensor with a core-cladding structure, and the novel sensor showed a lower limit of detection of 0.2ng/l and a response time around 320s. The application of this high-sensitivity FOEW sensor can be extended to biodefense, disease diagnosis, biomedical and biochemical analysis.

  12. Growing 3C-SiC heteroepitaxial layers on α-SiC substrate by vapour-liquid-solid mechanism from the Al-Ge-Si ternary system

    NASA Astrophysics Data System (ADS)

    Lorenzzi, Jean; Ferro, Gabriel; Cauwet, François; Souliere, Véronique; Carole, Davy

    2011-03-01

    In this work, we present and compare the results obtained from different Si-based melts (Ge-Si, Al-Si and Al-Ge-Si) for growing SiC layers on α-SiC substrate by vapour-liquid-solid (VLS) mechanism. It was found that, depending on melt composition, the deposit could be either a complete 3C or α-SiC layer or even a mixture of these polytypes. The binary Al-Si melt leads systematically to a highly p-type homoepitaxial α-SiC deposit while Ge-Si melt gives a non-intentional n-type doped layers of either 3C or 6H polytypes depending on growth conditions. However, highly p-type doped 3C heteroepitaxial deposit can be obtained if a small amount of Al is added to the Ge-Si binary liquid phase. This means that the VLS mechanism is very flexible and allows growing either n- or p-type SiC layers of 3C or 6H polytypes.

  13. Enhancement of recombination process using silver and graphene quantum dot embedded intermediate layer for efficient organic tandem cells

    NASA Astrophysics Data System (ADS)

    Ho, Nhu Thuy; Tien, Huynh Ngoc; Jang, Se-Joeng; Senthilkumar, Velusamy; Park, Yun Chang; Cho, Shinuk; Kim, Yong Soo

    2016-07-01

    High performance of organic tandem solar cell is largely dependent on transparent and conductive intermediate layer (IML). The current work reports the design and fabrication of an IML using a simple solution process. The efficiency of a homo-tandem device with poly(3-hexylthiophene):phenyl-C61-butyric acid methyl ester as an active layer and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)/poly(ethylenimine) as an IML was initially found to be 3.40%. Further enhancement of the cell efficiency was achieved using silver nanoparticles (Ag-NPs) of different sizes and graphene quantum dot embedded IML. A maximum efficiency of 4.03% was achieved using 7 nm Ag-NPs that contribute to a better recombination process. Also, the performance of the tandem cell was solely based on the electrical improvements indicated by the current - voltage measurements, external quantum efficiency and impedance analysis. The use of Ag-NPs in the IML has been shown to lengthen the life time of electron-hole pairs in the device. This study thus paves way to develop such efficient IMLs for more efficient tandem solar cells.

  14. Enhancement of recombination process using silver and graphene quantum dot embedded intermediate layer for efficient organic tandem cells

    PubMed Central

    Ho, Nhu Thuy; Tien, Huynh Ngoc; Jang, Se-Joeng; Senthilkumar, Velusamy; Park, Yun Chang; Cho, Shinuk; Kim, Yong Soo

    2016-01-01

    High performance of organic tandem solar cell is largely dependent on transparent and conductive intermediate layer (IML). The current work reports the design and fabrication of an IML using a simple solution process. The efficiency of a homo-tandem device with poly(3-hexylthiophene):phenyl-C61-butyric acid methyl ester as an active layer and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)/poly(ethylenimine) as an IML was initially found to be 3.40%. Further enhancement of the cell efficiency was achieved using silver nanoparticles (Ag-NPs) of different sizes and graphene quantum dot embedded IML. A maximum efficiency of 4.03% was achieved using 7 nm Ag-NPs that contribute to a better recombination process. Also, the performance of the tandem cell was solely based on the electrical improvements indicated by the current - voltage measurements, external quantum efficiency and impedance analysis. The use of Ag-NPs in the IML has been shown to lengthen the life time of electron-hole pairs in the device. This study thus paves way to develop such efficient IMLs for more efficient tandem solar cells. PMID:27453530

  15. Microstructure and magnetic properties of FePt film with combined MoC/(Mg-X)O (X=Cu, Ni, Co) intermediate layers

    NASA Astrophysics Data System (ADS)

    Tsai, Jai-Lin; Tzeng, Jie-Lin; Hu, Keng-Chun; Li, Hsu-Kang; Pan, Zu-Yu; Chang, Yuan-Shuo; Liao, Chang-Chun

    2017-01-01

    The magnetic properties and microstructure of FePt films grown on MoC layer and MoC/(Mg-X)O (X=Cu, Ni, Co) combined intermediate layers were studied. The (Mg-X)O (X=Cu, Ni, Co) layer with thickness of 5 nm was deposited on CrRu seed layer at 395 °C. The CrRu (200) texture was enhanced which may due to well grains growth in specific orientation and small lattice mismatch with (Mg-X)O (X=Cu, Ni, Co). Finally, the FePt/MoC layers were deposited on (Mg-X)O layer at 425 °C. Using MoC/MgCuO combined intermediate layers, the rocking width of FePt (001) and CrRu (200) diffraction peak were changed from 7.1° to 6.1°, and 5.7° to 3.8°, respectively. For MoC/MgCoO dual intermediate layers, the rocking width of FePt (001) and CrRu (200) diffraction peak were 6.7° and 4.1°. The FePt/MoC/MgCoO film illustrates perpendicular magnetic anisotropy with out-of plane coercivity of 9.3 kOe which is higher than FePt film deposited on MoC layer (8.5 kOe) and the in-plane loops is linear. From microstructure, the FePt grains were more separated on MoC/(Mg-X)O (X=Cu, Ni, Co) combined intermediate layers.

  16. Coarse, Intermediate and High Resolution Numerical Simulations of the Transition of a Tropical Wave Critical Layer to a Tropical Storm

    NASA Technical Reports Server (NTRS)

    Montgomery, M. T.; Dunkerton, T. J.; Wang, Z.

    2010-01-01

    Recent work has hypothesized that tropical cyclones in the deep Atlantic and eastern Pacific basins develop from within the cyclonic Kelvin cat's eye of a tropical easterly wave critical layer located equatorward of the easterly jet axis. The cyclonic critical layer is thought to be important to tropical cyclogenesis because its cat's eye provides (i) a region of cyclonic vorticity and weak deformation by the resolved flow, (ii) containment of moisture entrained by the developing flow and/or lofted by deep convection therein, (iii) confinement of mesoscale vortex aggregation, (iv) a predominantly convective type of heating profile, and (v) maintenance or enhancement of the parent wave until the developing proto-vortex becomes a self-sustaining entity and emerges from the wave as a tropical depression. This genesis sequence and the overarching framework for describing how such hybrid wave-vortex structures become tropical depressions/storms is likened to the development of a marsupial infant in its mother's pouch, and for this reason has been dubbed the "marsupial paradigm". Here we conduct the first multi-scale test of the marsupial paradigm in an idealized setting by revisiting the Kurihara and Tuleya problem examining the transformation of an easterly wave-like disturbance into a tropical storm vortex using the WRF model. An analysis of the evolving winds, equivalent potential temperature, and relative vertical vorticity is presented from coarse (28 km), intermediate (9 km) and high resolution (3.1 km) simulations. The results are found to support key elements of the marsupial paradigm by demonstrating the existence of rotationally dominant region with minimal strain/shear deformation near the center of the critical layer pouch that contains strong cyclonic vorticity and high saturation fraction. This localized region within the pouch serves as the "attractor" for an upscale "bottom up" development process while the wave pouch and proto-vortex move together.

  17. Layered Seed-Growth of AgGe Football-like Microspheres via Precursor-Free Picosecond Laser Synthesis in Water

    PubMed Central

    Zhang, Dongshi; Gökce, Bilal; Notthoff, Christian; Barcikowski, Stephan

    2015-01-01

    Hybrid particles are of great significance in terms of their adjustable optical, electronic, magnetic, thermal and mechanical properties. As a novel technique, laser ablation in liquids (LAL) is famous for its precursor-free, “clean” synthesis of hybrid particles with various materials. Till now, almost all the LAL-generated particles originate from the nucleation-growth mechanism. Seed-growth of particles similar to chemical methods seems difficult to be achieved by LAL. Here, we not only present novel patch-joint football-like AgGe microspheres with a diameter in the range of 1 ~ 7 μm achievable by laser ablation in distilled water but also find direct evidences of their layered seed growth mechanism. Many critical factors contribute to the formation of AgGe microspheres: fast laser-generated plasma process provide an excellent condition for generating large amount of Ge and Ag ions/atoms, their initial nucleation and galvanic replacement reaction, while cavitation bubble confinement plays an important role for the increase of AgGe nuclei and subsequent layered growth in water after bubble collapse. Driven by work function difference, Ge acts as nucleation agent for silver during alloy formation. This new seed-growth mechanism for LAL technique opens new opportunities to develop a large variety of novel hybrid materials with controllable properties. PMID:26334136

  18. Layered Seed-Growth of AgGe Football-like Microspheres via Precursor-Free Picosecond Laser Synthesis in Water

    NASA Astrophysics Data System (ADS)

    Zhang, Dongshi; Gökce, Bilal; Notthoff, Christian; Barcikowski, Stephan

    2015-09-01

    Hybrid particles are of great significance in terms of their adjustable optical, electronic, magnetic, thermal and mechanical properties. As a novel technique, laser ablation in liquids (LAL) is famous for its precursor-free, “clean” synthesis of hybrid particles with various materials. Till now, almost all the LAL-generated particles originate from the nucleation-growth mechanism. Seed-growth of particles similar to chemical methods seems difficult to be achieved by LAL. Here, we not only present novel patch-joint football-like AgGe microspheres with a diameter in the range of 1 ~ 7 μm achievable by laser ablation in distilled water but also find direct evidences of their layered seed growth mechanism. Many critical factors contribute to the formation of AgGe microspheres: fast laser-generated plasma process provide an excellent condition for generating large amount of Ge and Ag ions/atoms, their initial nucleation and galvanic replacement reaction, while cavitation bubble confinement plays an important role for the increase of AgGe nuclei and subsequent layered growth in water after bubble collapse. Driven by work function difference, Ge acts as nucleation agent for silver during alloy formation. This new seed-growth mechanism for LAL technique opens new opportunities to develop a large variety of novel hybrid materials with controllable properties.

  19. Enhanced heteroepitaxial growth of CoCrPt-SiO{sub 2} perpendicular magnetic recording media on optimized Ru intermediate layers

    SciTech Connect

    Srinivasan, Kumar; Piramanayagam, S. N.

    2008-01-15

    The crystallographic growth, interfacial roughness, and magnetic properties of CoCrPt-SiO{sub 2} perpendicular magnetic recording media prepared on various types of Ru intermediate growth layers were systematically investigated based on high angle and omega offset x-ray diffraction scans, rocking curve scans, synchrotron radiation based grazing incidence reflectivity scans, and magneto-optical Kerr hysteresis loops. For samples that make use of one Ru growth layer, voltage bias applied on the Ru layer was seen to have two observable effects: (1) the dispersion in the Ru(00{center_dot}2) perpendicular texture increased, but that of the Co(00{center_dot}2) remained unchanged, leading to identical layered growth and (2) the in-plane a-lattice parameter of the Ru decreased leading to enhanced heteroepitaxy with the Co. There was no significant change in the Ru-Co interfacial roughness with changing the bias on the Ru layer. The bias effect can be used to optimize the design of the Ru intermediate layers. A scheme that makes use of two Ru growth layers consisting of a bottom Ru layer prepared under zero bias, which is inserted below a second Ru layer prepared under biased conditions, is shown to lead to significant benefits such as improved texture without affecting the magnetic properties. This is due to the different functional roles ascribed to each of the Ru growth layers.

  20. Magnetic anisotropy induced by crystal distortion in Ge{sub 1−x}Mn{sub x}Te/PbTe//KCl (001) ferromagnetic semiconductor layers

    SciTech Connect

    Knoff, W. Łusakowski, A.; Domagała, J. Z.; Minikayev, R.; Taliashvili, B.; Łusakowska, E.; Pieniążek, A.; Szczerbakow, A.; Story, T.

    2015-09-21

    Ferromagnetic resonance (FMR) study of magnetic anisotropy is presented for thin layers of IV-VI diluted magnetic semiconductor Ge{sub 1−x}Mn{sub x}Te with x = 0.14 grown by molecular beam epitaxy on KCl (001) substrate with a thin PbTe buffer. Analysis of the angular dependence of the FMR resonant field reveals that an easy magnetization axis is located near to the normal to the layer plane and is controlled by two crystal distortions present in these rhombohedral Ge{sub 1−x}Mn{sub x}Te layers: the ferroelectric distortion with the relative shift of cation and anion sub-lattices along the [111] crystal direction and the biaxial in-plane, compressive strain due to thermal mismatch.

  1. High-resolution x-ray diffraction investigation of relaxation and dislocations in SiGe layers grown on (001), (011), and (111) Si substrates

    SciTech Connect

    Zhylik, A.; Benediktovich, A.; Ulyanenkov, A.; Guerault, H.; Myronov, M.; Dobbie, A.; Leadley, D. R.; Ulyanenkova, T.

    2011-06-15

    This work presents a detailed characterization, using high-resolution x-ray diffraction, of multilayered Si{sub 1-x}Ge{sub x} heterostructures grown on (001), (011), and (111) Si substrates by reduced pressure chemical vapor deposition. Reciprocal space mapping has been used to determine both the strain and Ge concentration depth profiles within each layer of the heterostructures after initially determining the crystallographic tilt of all the layers. Both symmetric and asymmetric reciprocal space maps were measured on each sample, and the evaluation was performed simultaneously for the whole data set. The ratio of misfit to threading dislocation densities has been estimated for each individual layer based on an analysis of diffuse x-ray scattering from the defects.

  2. Growth of light-emitting SiGe heterostructures on strained silicon-on-insulator substrates with a thin oxide layer

    SciTech Connect

    Baidakova, N. A.; Bobrov, A. I.; Drozdov, M. N.; Novikov, A. V.; Pavlov, D. A.; Shaleev, M. V.; Yunin, P. A.; Yurasov, D. V.; Krasilnik, Z. F.

    2015-08-15

    The possibility of using substrates based on “strained silicon on insulator” structures with a thin (25 nm) buried oxide layer for the growth of light-emitting SiGe structures is studied. It is shown that, in contrast to “strained silicon on insulator” substrates with a thick (hundreds of nanometers) oxide layer, the temperature stability of substrates with a thin oxide is much lower. Methods for the chemical and thermal cleaning of the surface of such substrates, which make it possible to both retain the elastic stresses in the thin Si layer on the oxide and provide cleaning of the surface from contaminating impurities, are perfecte. It is demonstrated that it is possible to use the method of molecular-beam epitaxy to grow light-emitting SiGe structures of high crystalline quality on such substrates.

  3. 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.

  4. 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.

  5. Generation of conducting polymer-based heterojunctions, diodes, and capacitors using an intermediate-layer lithography method

    NASA Astrophysics Data System (ADS)

    Liu, Xinchuan; Chakraborty, Anirban; Parthasarathi, Ganga; Luo, Cheng

    2007-04-01

    In this work, conducting polymer-based heterojunctions, diodes and capacitors have been generated using an intermediate-layer lithography (ILL) approach which has been recently developed in our group. Polypyrrole (PPy) and poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS), Poly(methyl methacrylate) (PMMA) and aluminum were used as component materials in these devices. Compared with Si-based devices, conducting polymerbased devices have distinctive advantages of low weight and good flexibility, and may potentially replace the corresponding Si-based devices. A challenge is how to fabricate the conducting polymer-based microsystems. Most conducting polymers are sensitive to the environment, and their electrical properties tend to deteriorate over time due to overoxidation (air), moisture, high temperature and chemical alteration. The current fabrication techniques (e.g. lift-off, dry and wet etching processes) used in lithographic approaches involve ultra-violet, electron-beam, x-ray, gases (e.g., oxygen and nitrogen), DI water, and/or chemical solution (e.g. photoresist and acetone), making them improper to pattern conducting polymers. Since the ILL method does not involve aggressive chemistry in generation of patterns, it has been employed in this work to fabricate conducting polymer-based microdevices, particularly diodes and capacitors. In fabrication of the devices, multiple layers of polymers (e.g., PPy and PEDOT) and metals (e.g., Al) are coated on a PMMA sheet followed by the patterning with the insertion of Si molds. The detailed fabrication procedure and testing results are given in this paper.

  6. Development of CVD-W coatings on CuCrZr and graphite substrates with a PVD intermediate layer

    NASA Astrophysics Data System (ADS)

    Song, Jiupeng; Lian, Youyun; Lv, Yanwei; Liu, Junyong; Yu, Yang; Liu, Xiang; Yan, Binyou; Chen, Zhigang; Zhuang, Zhigang; Zhao, Ximeng; Qi, Yang

    2014-12-01

    In order to apply tungsten (W) coatings by chemical vapor deposition (CVD) for repairing or updating the plasma facing components (PFCs) of the first wall and divertor in existing or future tokomaks, where CuCrZr or graphite is the substrate material, an intermediate layer by physical vapor deposition (PVD) has been used to accommodate the interface stress due to the mismatch of thermal expansion or act as a diffusion barrier between the CVD-W coating and the substrate. The prepared CuCrZr/PVD-Cu/CVD-W sample with active cooling has passed thermal fatigue tests by electron beam with an absorbed power of 2.2 MW/m2, 50 s on/50 s off, for 100 cycles. Another graphite/PVD-Si/CVD-W sample without active cooling underwent thermal fatigue testing with an absorbed power density of 4.62 MW/m2, 5 s on/25 s off, for 200 cycles, and no catastrophic failure was found.

  7. High-Performanced Cathode with a Two-Layered R-P Structure for Intermediate Temperature Solid Oxide Fuel Cells.

    PubMed

    Huan, Daoming; Wang, Zhiquan; Wang, Zhenbin; Peng, Ranran; Xia, Changrong; Lu, Yalin

    2016-02-01

    Driven by the mounting concerns on global warming and energy crisis, intermediate temperature solid-oxide fuel cells (IT-SOFCs) have attracted special attention for their high fuel efficiency, low toxic gas emission, and great fuel flexibility. A key obstacle to the practical operation of IT-SOFCs is their sluggish oxygen reduction reaction (ORR) kinetics. In this work, we applied a new two-layered Ruddlesden-Popper (R-P) oxide, Sr3Fe2O7-δ (SFO), as the material for oxygen ion conducting IT-SOFCs. Density functional theory calculation suggested that SFO has extremely low oxygen ion formation energy and considerable energy barrier for O(2-) diffusion. Unfortunately, the stable SrO surface of SFO was demonstrated to be inert to O2 adsorption and dissociation reaction, and thus restricts its catalytic activity toward ORR. Based on this observation, Co partially substituted SFO (SFCO) was then synthesized and applied to improve its surface vacancy concentration to accelerate the oxygen adsorptive reduction reaction rate. Electrochemical performance results suggested that the cell using the SFCO single phase cathode has a peak power density of 685 mW cm(-2) at 650 °C, about 15% higher than those when using LSCF cathode. Operating at 200 mA cm(-2), the new cell using SFCO is quite stable within the 100-h' test.

  8. Questing and the application for silicon based ternary compound within ultra-thin layer of SIS intermediate region

    NASA Astrophysics Data System (ADS)

    Chen, Shumin; Gao, Ming; Wan, Yazhou; Du, Huiwei; Li, Yong; Ma, Zhongquan

    2016-12-01

    A silicon based ternary compound was supposed to be solid synthesized with In, Si and O elements by magnetron sputtering of indium tin oxide target (ITO) onto crystal silicon substrate at 250 °C. To make clear the configuration of the intermediate region, a potential method to obtain the chemical bonding of Si with other existing elements was exploited by X-ray photoelectron spectroscopy (XPS) instrument combined with other assisted techniques. The phase composition and solid structure of the interfacial region between ITO and Si substrate were investigated by X-ray diffraction (XRD) and high resolution cross sectional transmission electron microscope (HR-TEM). A photovoltaic device with structure of Al/Ag/ITO/SiOx/p-Si/Al was assembled by depositing ITO films onto the p-Si substrate by using magnetron sputtering. The new matter has been assumed to be a buffer layer for semiconductor-insulator-semiconductor (SIS) photovoltaic device and plays critical role for the promotion of optoelectronic conversion performance from the view point of device physics.

  9. Atomic layer deposition of crystalline SrHfO{sub 3} directly on Ge (001) for high-k dielectric applications

    SciTech Connect

    McDaniel, Martin D.; Ngo, Thong Q.; Ekerdt, John G.; Hu, Chengqing; Jiang, Aiting; Yu, Edward T.; Lu, Sirong; Smith, David J.; Posadas, Agham; Demkov, Alexander A.

    2015-02-07

    The current work explores the crystalline perovskite oxide, strontium hafnate, as a potential high-k gate dielectric for Ge-based transistors. SrHfO{sub 3} (SHO) is grown directly on Ge by atomic layer deposition and becomes crystalline with epitaxial registry after post-deposition vacuum annealing at ∼700 °C for 5 min. The 2 × 1 reconstructed, clean Ge (001) surface is a necessary template to achieve crystalline films upon annealing. The SHO films exhibit excellent crystallinity, as shown by x-ray diffraction and transmission electron microscopy. The SHO films have favorable electronic properties for consideration as a high-k gate dielectric on Ge, with satisfactory band offsets (>2 eV), low leakage current (<10{sup −5} A/cm{sup 2} at an applied field of 1 MV/cm) at an equivalent oxide thickness of 1 nm, and a reasonable dielectric constant (k ∼ 18). The interface trap density (D{sub it}) is estimated to be as low as ∼2 × 10{sup 12 }cm{sup −2 }eV{sup −1} under the current growth and anneal conditions. Some interfacial reaction is observed between SHO and Ge at temperatures above ∼650 °C, which may contribute to increased D{sub it} value. This study confirms the potential for crystalline oxides grown directly on Ge by atomic layer deposition for advanced electronic applications.

  10. Surface passivation and interface properties of bulk GaAs and epitaxial-GaAs/Ge using atomic layer deposited TiAlO alloy dielectric.

    PubMed

    Dalapati, G K; Chia, C K; Tan, C C; Tan, H R; Chiam, S Y; Dong, J R; Das, A; Chattopadhyay, S; Mahata, C; Maiti, C K; Chi, D Z

    2013-02-01

    High quality surface passivation on bulk-GaAs substrates and epitaxial-GaAs/Ge (epi-GaAs) layers were achieved by using atomic layer deposited (ALD) titanium aluminum oxide (TiAlO) alloy dielectric. The TiAlO alloy dielectric suppresses the formation of defective native oxide on GaAs layers. X-ray photoelectron spectroscopy (XPS) analysis shows interfacial arsenic oxide (As(x)O(y)) and elemental arsenic (As) were completely removed from the GaAs surface. Energy dispersive X-ray diffraction (EDX) analysis and secondary ion mass spectroscopy (SIMS) analysis showed that TiAlO dielectric is an effective barrier layer for reducing the out-diffusion of elemental atoms, enhancing the electrical properties of bulk-GaAs based metal-oxide-semiconductor (MOS) devices. Moreover, ALD TiAlO alloy dielectric on epi-GaAs with AlGaAs buffer layer realized smooth interface between epi-GaAs layers and TiAlO dielectric, yielding a high quality surface passivation on epi-GaAs layers, much sought-after for high-speed transistor applications on a silicon platform. Presence of a thin AlGaAs buffer layer between epi-GaAs and Ge substrates improved interface quality and gate dielectric quality through the reduction of interfacial layer formation (Ga(x)O(y)) and suppression of elemental out-diffusion (Ga and As). The AlGaAs buffer layer and TiAlO dielectric play a key role to suppress the roughening, interfacial layer formation, and impurity diffusion into the dielectric, which in turn largely enhances the electrical property of the epi-GaAs MOS devices.

  11. Coarse, intermediate and high resolution numerical simulations of the transition of a tropical wave critical layer to a tropical storm

    NASA Astrophysics Data System (ADS)

    Montgomery, M. T.; Wang, Z.; Dunkerton, T. J.

    2010-11-01

    Recent work has hypothesized that tropical cyclones in the deep Atlantic and eastern Pacific basins develop from within the cyclonic Kelvin cat's eye of a tropical easterly wave critical layer located equatorward of the easterly jet axis. The cyclonic critical layer is thought to be important to tropical cyclogenesis because its cat's eye provides (i) a region of cyclonic vorticity and weak deformation by the resolved flow, (ii) containment of moisture entrained by the developing flow and/or lofted by deep convection therein, (iii) confinement of mesoscale vortex aggregation, (iv) a predominantly convective type of heating profile, and (v) maintenance or enhancement of the parent wave until the developing proto-vortex becomes a self-sustaining entity and emerges from the wave as a tropical depression. This genesis sequence and the overarching framework for describing how such hybrid wave-vortex structures become tropical depressions/storms is likened to the development of a marsupial infant in its mother's pouch, and for this reason has been dubbed the "marsupial paradigm". Here we conduct the first multi-scale test of the marsupial paradigm in an idealized setting by revisiting the Kurihara and Tuleya problem examining the transformation of an easterly wave-like disturbance into a tropical storm vortex using the WRF model. An analysis of the evolving winds, equivalent potential temperature, and relative vertical vorticity is presented from coarse (28 km), intermediate (9 km) and high resolution (3.1 km) simulations. The results are found to support key elements of the marsupial paradigm by demonstrating the existence of a rotationally dominant region with minimal strain/shear deformation near the center of the critical layer pouch that contains strong cyclonic vorticity and high saturation fraction. This localized region within the pouch serves as the "attractor" for an upscale "bottom up" development process while the wave pouch and proto-vortex move together

  12. Efficiency enhancement using a Zn1- x Ge x -O thin film as an n-type window layer in Cu2O-based heterojunction solar cells

    NASA Astrophysics Data System (ADS)

    Minami, Tadatsugu; Nishi, Yuki; Miyata, Toshihiro

    2016-05-01

    Efficiency enhancement was achieved in Cu2O-based heterojunction solar cells fabricated with a zinc-germanium-oxide (Zn1- x Ge x -O) thin film as the n-type window layer and a p-type Na-doped Cu2O (Cu2O:Na) sheet prepared by thermally oxidizing Cu sheets. The Ge content (x) dependence of the obtained photovoltaic properties of the heterojunction solar cells is mainly explained by the conduction band discontinuity that results from the electron affinity difference between Zn1- x Ge x -O and Cu2O:Na. The optimal value of x in Zn1- x Ge x -O thin films prepared by pulsed laser deposition was observed to be 0.62. An efficiency of 8.1% was obtained in a MgF2/Al-doped ZnO/Zn0.38Ge0.62-O/Cu2O:Na heterojunction solar cell.

  13. Photoluminescence of dome and hut shaped Ge(Si) self-assembled islands embedded in a tensile-strained Si layer

    SciTech Connect

    Shaleev, M. V.; Novikov, A. V.; Yablonskiy, A. N.; Drozdov, Y. N.; Lobanov, D. N.; Krasilnik, Z. F.; Kuznetsov, O. A.

    2007-07-09

    The effect of the growth temperature (T{sub g}) on photoluminescence of Ge(Si) self-assembled islands embedded between tensile-strained Si layers was studied. The observed redshift of the photoluminescence peak of the dome islands with a decrease of T{sub g} from 700 to 630 deg. C is associated with an increase of Ge content in the islands and with the suppression of smearing of the strained Si layers. The blueshift of the photoluminescence peak with a decrease of T{sub g} from 630 to 600 deg. C is associated with a change of the type of islands on surface, which is accompanied by a decrease in islands' height.

  14. Two-temperature synthesis of non-linear optical compound CdGeAs2

    NASA Astrophysics Data System (ADS)

    Zhu, Chongqiang; Verozubova, G. A.; Mironov, Yuri P.; Lei, Zuotao; Song, Liangcheng; Ma, Tianhui; Okunev, A. O.; Yang, Chunhui

    2016-12-01

    In this work, we report on a new approach to synthesize large-scale nonlinear optical chalcopyrite compound CdGeAs2 (cadmium germanium arsenide), in which the arsenic (As) precursor and the mixture of the cadmium (Cd) and the germanium (Ge) were separated in two distinct temperature-defined zones of a furnace. Through probing the intermediate product prepared at pre-set temperature points of hot-zone area, it was revealed that the ternary compound CdGeAs2 was formed through chemical reactions among Cd3As2, CdAs2, GeAs, GeAs2 and Ge. A new intermediate crystalline compound, with determined crystal parameter c=0.9139 nm and unknown a parameter, was identified when the temperature of the mixture of Cd and Ge was set to 680 °C, which, however, disappeared when the temperature was set to 770 °C, yielding pure CdGeAs2 product. Most likely, the identified new intermediate compound has layered graphite-like structure. Moreover, we show that the described two-temperature synthesis method allows us to produce near 250 g CdGeAs2 product during one run in a horizontal furnace and 500 g in a tilted horizontal furnace with rotated reactor.

  15. Effective passivation and high-performance metal-oxide-semiconductor devices using ultra-high-vacuum deposited high- κ dielectrics on Ge without interfacial layers

    NASA Astrophysics Data System (ADS)

    Chu, L. K.; Chu, R. L.; Lin, T. D.; Lee, W. C.; Lin, C. A.; Huang, M. L.; Lee, Y. J.; Kwo, J.; Hong, M.

    2010-09-01

    Without using any interfacial passivation layers, high- κ dielectric Y 2O 3, HfO 2, and Ga 2O 3(Gd 2O 3) [GGO], by electron beam evaporation in ultra-high-vacuum (UHV), have been directly deposited on Ge substrate. Comprehensive investigations have been carried out to study the oxide/Ge interfaces chemically, structurally, and electronically: hetero-structures of all the studied oxides on Ge are highly thermally stable with annealing to 500 °C, and their interfaces remain atomically sharp. The electrical analyses have been conducted on metal-oxide-semiconductor (MOS) devices, i.e. MOS capacitors (MOSCAPs) and MOS field-effect-transistors (MOSFETs). Dielectrics constants of the Y 2O 3, HfO 2, and GGO have been extracted to be ˜17, 20, and 13-15, respectively, indicating no interfacial layer formation with 500 °C annealing. A low interfacial density of states ( Dits), as low as 3 × 10 11 cm -2 eV -1, has been achieved for GGO/Ge near mid-gap along with a high Fermi-level movement efficiency as high as 80%. The GGO/Ge pMOSFETs with TiN as the metal gate have yielded very high-performances, in terms of 496 μA/μm, 178 μS/μm, and 389 cm 2/V s in saturation drain current density, maximum transconductance, and effective hole mobility, respectively. The gate width and gate length of the MOSFET are 10 μm and 1 μm.

  16. Theory of hole mobility in strained Ge and III-V p-channel inversion layers with high-κ insulators

    NASA Astrophysics Data System (ADS)

    Zhang, Yan; Fischetti, M. V.; Sorée, B.; O'Regan, T.

    2010-12-01

    We present a comprehensive investigation of the low-field hole mobility in strained Ge and III-V (GaAs, GaSb, InSb, and In1-xGaxAs) p-channel inversion layers with both SiO2 and high-κ insulators. The valence (sub)band structure of Ge and III-V channels, relaxed and under biaxial strain (tensile and compressive) is calculated using an efficient self-consistent method based on the six-band k ṡp perturbation theory. The hole mobility is then computed using the Kubo-Greenwood formalism accounting for nonpolar hole-phonon scattering (acoustic and optical), surface roughness scattering, polar phonon scattering (III-Vs only), alloy scattering (alloys only) and remote phonon scattering, accounting for multisubband dielectric screening. As expected, we find that Ge and III-V semiconductors exhibit a mobility significantly larger than the "universal" Si mobility. This is true for MOS systems with either SiO2 or high-κ insulators, although the latter ones are found to degrade the hole mobility compared to SiO2 due to scattering with interfacial optical phonons. In addition, III-Vs are more sensitive to the interfacial optical phonons than Ge due to the existence of the substrate polar phonons. Strain—especially biaxial tensile stress for Ge and biaxial compressive stress for III-Vs (except for GaAs)—is found to have a significant beneficial effect with both SiO2 and HfO2. Among strained p-channels, InSb exhibits the largest mobility enhancement. In0.7Ga0.3As also exhibits an increased hole mobility compared to Si, although the enhancement is not as large. Finally, our theoretical results are favorably compared with available experimental data for a relaxed Ge p-channel with a HfO2 insulator.

  17. Overturning circulation that ventilates the intermediate layer of the Sea of Okhotsk and the North Pacific: The role of salinity advection

    NASA Astrophysics Data System (ADS)

    Matsuda, Junji; Mitsudera, Humio; Nakamura, Tomohiro; Sasajima, Yuichiro; Hasumi, Hiroyasu; Wakatsuchi, Masaaki

    2015-03-01

    Dense Shelf Water (DSW) formation in the northwestern continental shelf of the Sea of Okhotsk is the beginning of the lower limb of the overturning circulation that ventilates the intermediate layer of the North Pacific Ocean. The upper limb consisting of surface currents in the Okhotsk Sea and the subarctic gyre has not been clarified. Using a high-resolution North Pacific Ocean model with a curvilinear grid as fine as 3 km × 3 km in the Sea of Okhotsk, we succeeded in representing the three-dimensional structure of the overturning circulation including the narrow boundary currents and flows through straits that constitute the upper limb, as well as the lower limb consisting of DSW formation and ventilation. In particular, pathways and time scales from the Bering Sea to the intermediate layer via the ventilation in the Sea of Okhotsk were examined in detail using tracer experiments. Further, we found that the overturning circulation that connects the surface and intermediate layer is sensitive to wind stress. In the case of strong winds, the coastal current under polynyas where DSW forms is intensified, and consequently diapycnal transport from the surface layer to the intermediate layer increases. Strong winds also induce a positive sea surface salinity anomaly in the subarctic region, causing a significant decrease in the density stratification and increase in the DSW salinity (i.e., density). These processes act together to produce intense overturning circulation and deep ventilation, which may subduct even to the bottom of the Sea of Okhotsk if the wind is strong.

  18. Effect of process temperature on structure and magnetic properties of perpendicularly magnetized D022-Mn3Ge thin films on a Cr buffer layer

    NASA Astrophysics Data System (ADS)

    Sugihara, Atsushi; Suzuki, Kazuya; Miyazaki, Terunobu; Mizukami, Shigemi

    2015-08-01

    We investigated the effect of post-annealing on the perpendicular magnetic anisotropy constant (Ku) and surface roughness (Ra) of Mn3Ge thin films grown at comparatively low temperatures (room temperature, 150, 200, and 250 °C) on Cr buffer layers. The films grown at ≥200 °C exhibit a D022-ordered crystal structure in an as-deposited state. The post-annealing process demonstrates differences in trends between the 200-°C-grown film and the 250-°C-grown film. The 200-°C-grown film displays significant degradation of Ku and an increase in Ra upon annealing at >300 °C because of its poor thermal durability, while the 250-°C-grown film is still intact even at 500 °C. The 250-°C-grown film post-annealed at 300 °C displays relatively high Ku while Ra remains low. It may be possible to grow D022-Mn3Ge with higher Ku and low Ra using a buffer-layer material with a lattice-matched crystal structure with D022-Mn3Ge and higher thermal durability than Cr.

  19. Single Junction InGaP/GaAs Solar Cells Grown on Si Substrates using SiGe Buffer Layers

    NASA Technical Reports Server (NTRS)

    Ringel, S. A.; Carlin, J. A.; Andre, C. L.; Hudait, M. K.; Gonzalez, M.; Wilt, D. M.; Clark, E. B.; Jenkins, P.; Scheiman, D.; Allerman, A.

    2002-01-01

    Single junction InGaP/GaAs solar cells displaying high efficiency and record high open circuit voltage values have been grown by metalorganic chemical vapor deposition on Ge/graded SiGe/Si substrates. Open circuit voltages as high as 980 mV under AM0 conditions have been verified to result from a single GaAs junction, with no evidence of Ge-related sub-cell photoresponse. Current AM0 efficiencies of close to 16% have been measured for a large number of small area cells, whose performance is limited by non-fundamental current losses due to significant surface reflection resulting from greater than 10% front surface metal coverage and wafer handling during the growth sequence for these prototype cells. It is shown that at the material quality currently achieved for GaAs grown on Ge/SiGe/Si substrates, namely a 10 nanosecond minority carrier lifetime that results from complete elimination of anti-phase domains and maintaining a threading dislocation density of approximately 8 x 10(exp 5) per square centimeter, 19-20% AM0 single junction GaAs cells are imminent. Experiments show that the high performance is not degraded for larger area cells, with identical open circuit voltages and higher short circuit current (due to reduced front metal coverage) values being demonstrated, indicating that large area scaling is possible in the near term. Comparison to a simple model indicates that the voltage output of these GaAs on Si cells follows ideal behavior expected for lattice mismatched devices, demonstrating that unaccounted for defects and issues that have plagued other methods to epitaxially integrate III-V cells with Si are resolved using SiGe buffers and proper GaAs nucleation methods. These early results already show the enormous and realistic potential of the virtual SiGe substrate approach for generating high efficiency, lightweight and strong III-V solar cells.

  20. High-performance ultraviolet detection and visible-blind photodetector based on Cu{sub 2}O/ZnO nanorods with poly-(N-vinylcarbazole) intermediate layer

    SciTech Connect

    Perng, Dung-Ching

    2015-12-14

    This study reports a high-performance hybrid ultraviolet (UV) photodetector with visible-blind sensitivity fabricated by inserting a poly-(N-vinylcarbazole) (PVK) intermediate layer between low-cost processed Cu{sub 2}O film and ZnO nanorods (NRs). The PVK layer acts as an electron-blocking/hole-transporting layer between the n-ZnO and p-Cu{sub 2}O films. The Cu{sub 2}O/PVK/ZnO NR photodetector exhibited a responsivity of 13.28 A/W at 360 nm, a high detectivity of 1.03 × 10{sup 13} Jones at a low bias of −0.1 V under a low UV light intensity of 24.9 μW/cm{sup 2}. The photo-to-dark current ratios of the photodetector with and without the PVK intermediate layer at a bias of −0.5 V are 1.34 × 10{sup 2} and 3.99, respectively. The UV-to-visible rejection ratios (R{sub 360 nm}/R{sub 450 nm}) are 350 and 1.735, respectively. Several features are demonstrated: (a) UV photo-generated holes at the ZnO NRs can effectively be transported through the PVK layer to the p-Cu{sub 2}O layer; (b) the insertion of a PVK buffer layer significantly minimizes the reverse-bias leakage current, which leads to a larger amplification of the photocurrent; and (c) the PVK buffer layer greatly improves the UV-to-visible responsivity ratio, allowing the device to achieve high UV detection sensitivity at a low bias voltage using a very low light intensity.

  1. High-performance ultraviolet detection and visible-blind photodetector based on Cu2O/ZnO nanorods with poly-(N-vinylcarbazole) intermediate layer

    NASA Astrophysics Data System (ADS)

    Perng, Dung-Ching; Lin, Hsueh-Pin; Hong, Min-Hao

    2015-12-01

    This study reports a high-performance hybrid ultraviolet (UV) photodetector with visible-blind sensitivity fabricated by inserting a poly-(N-vinylcarbazole) (PVK) intermediate layer between low-cost processed Cu2O film and ZnO nanorods (NRs). The PVK layer acts as an electron-blocking/hole-transporting layer between the n-ZnO and p-Cu2O films. The Cu2O/PVK/ZnO NR photodetector exhibited a responsivity of 13.28 A/W at 360 nm, a high detectivity of 1.03 × 1013 Jones at a low bias of -0.1 V under a low UV light intensity of 24.9 μW/cm2. The photo-to-dark current ratios of the photodetector with and without the PVK intermediate layer at a bias of -0.5 V are 1.34 × 102 and 3.99, respectively. The UV-to-visible rejection ratios (R360 nm/R450 nm) are 350 and 1.735, respectively. Several features are demonstrated: (a) UV photo-generated holes at the ZnO NRs can effectively be transported through the PVK layer to the p-Cu2O layer; (b) the insertion of a PVK buffer layer significantly minimizes the reverse-bias leakage current, which leads to a larger amplification of the photocurrent; and (c) the PVK buffer layer greatly improves the UV-to-visible responsivity ratio, allowing the device to achieve high UV detection sensitivity at a low bias voltage using a very low light intensity.

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

    SciTech Connect

    Cariou, R.; Ruggeri, R.; Tan, X.; Nassar, J.; Roca i Cabarrocas, P.; Mannino, Giovanni

    2014-07-15

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

  3. Reduction and desorption of native oxides on GaAs and Ge during atomic layer deposition of Al2O3

    NASA Astrophysics Data System (ADS)

    Lee, Hang Dong; Feng, Tian; Yu, Lei; Mastrogiovanni, Daniel; Wan, Alan; Gustafsson, Torgny; Garfunkel, Eric

    2010-03-01

    The reduction of native oxides and control of interfacial defects is of central importance if materials such as GaAs and Ge are to be used for post-Si CMOS. We and others have earlier observed that under certain conditions such oxides are removed during atomic layer deposition (ALD) growth. We find, using medium energy ion scattering spectroscopy (MEIS) and XPS, that after just a single ALD half cycle (exposure to a trimethylaluminum (TMA) precursor) ˜65% of the native oxide is removed and a 5 å oxygen-rich aluminum oxide is formed. The source for the oxygen in the aluminum oxide is therefore the native oxide. For Ge substrates, one single TMA pulse removes a substantial amount of the native oxides and a 3å Al2O3 film is grown. The native oxides are also completely removed after > 450 C preheating of the substrate. The mechanisms for these processes will be discussed.

  4. Key role of the wetting layer in revealing the hidden path of Ge/Si(001) Stranski-Krastanow growth onset

    SciTech Connect

    Brehm, Moritz; Grydlik, Martyna; Lichtenberger, Herbert; Hrauda, Nina; Fromherz, Thomas; Schaeffler, Friedrich; Bauer, Guenther; Montalenti, Francesco; Vastola, Guglielmo; Miglio, Leo; Beck, Matthew J.

    2009-11-15

    The commonly accepted Stranski-Krastanow model, according to which island formation occurs on top of a wetting layer (WL) of a certain thickness, predicts for the morphological evolution an increasing island aspect ratio with volume. We report on an apparent violation of this thermodynamic understanding of island growth with deposition. In order to investigate the actual onset of three-dimensional islanding and the critical WL thickness in the Ge/Si(001) system, a key issue is controlling the Ge deposition with extremely high resolution [0.025 monolayer (ML)]. Atomic force microscopy and photoluminescence measurements on samples covering the deposition range 1.75-6.1 ML, taken along a Ge deposition gradient on 4 in. Si substrates and at different growth temperatures (T{sub g}), surprisingly reveal that for T{sub g}>675 deg. C steeper multifaceted domes apparently nucleate prior to shallow (105)-faceted pyramids, in a narrow commonly overlooked deposition range. The puzzling experimental findings are explained by a quantitative modeling of the total energy with deposition. We accurately matched ab initio calculations of layer and surface energies to finite-element method simulations of the elastic energy in islands, in order to compare the thermodynamic stability of different island shapes with respect to an increasing WL thickness. Close agreement between modeling and experiments is found, pointing out that the sizeable progressive lowering of the surface energy in the first few MLs of the WL reverts the common understanding of the SK growth onset. Strong similarities between islanding in SiGe and III/V systems are highlighted.

  5. Electronic properties of δ-doped Si:P and Ge:P layers in the high-density limit using a Thomas-Fermi method

    NASA Astrophysics Data System (ADS)

    Smith, J. S.; Cole, J. H.; Russo, S. P.

    2014-01-01

    We present a scalable method for calculating the electronic properties of a δ-doped phosphorus layer in silicon and germanium. Our calculations are based on an sp3d5s* tight-binding model and the Thomas-Fermi-Dirac approximation. The energy shift in the lowest conduction band states of the Ge band structure is characterized and a comparison is made to a δ-doped P layer in Si. The results for the δ-doped Si:P layer themselves compare well to the predictions of more "resource intensive" computational models. The Thomas-Fermi method presented herein scales easily to large system sizes. Efficient scaling is important for the calculation of quantum transport properties in δ-doped semiconductors that are currently of experimental interest.

  6. Low-temperature formation of the FePt phase in the presence of an intermediate Au layer in Pt /Au /Fe thin films

    NASA Astrophysics Data System (ADS)

    Vladymyrskyi, I. A.; Gafarov, A. E.; Burmak, A. P.; Sidorenko, S. I.; Katona, G. L.; Safanova, N. Y.; Ganss, F.; Beddies, G.; Albrecht, M.; Makogon, Yu N.; Beke, D. L.

    2016-01-01

    Pt /Fe and Pt /Au /Fe layered films were deposited at room temperature by dc magnetron sputtering on Al2O3(0 0 0 1) single crystalline substrates and heat treated in vacuum at 330 °C with different durations (up to 62 h). It is shown by secondary neutral mass spectrometry depth profiling and x-ray diffraction that the introduction of an additional Au layer between Pt /Fe layers leads to enhanced intermixing and formation of the partially chemically ordered L10 FePt phase. The underlying diffusion processes can be explained by the grain boundary diffusion induced reaction layer formation mechanism. During the solid state reaction between Pt and Fe, the Au layer moves towards the substrate interface replacing the Fe layer. This was explained by the much faster diffusion of Fe, as compared to Pt, along the grain boundaries in Au. Enhancement of the process and formation of the ordered FePt phase in the presence of the Au intermediate layer were interpreted by the effect of stress accumulation during the grain boundary reactions: the disordered FePt phase formed initially at different Au and Pt grain boundaries can experience appropriate compressive stress along the {1 0 0} directions, which can initiate the formation of the chemically ordered L10 FePt phase.

  7. Improving the electrical properties of lanthanum silicate films on ge metal oxide semiconductor capacitors by adopting interfacial barrier and capping layers.

    PubMed

    Choi, Yu Jin; Lim, Hajin; Lee, Suhyeong; Suh, Sungin; Kim, Joon Rae; Jung, Hyung-Suk; Park, Sanghyun; Lee, Jong Ho; Kim, Seong Gyeong; Hwang, Cheol Seong; Kim, HyeongJoon

    2014-05-28

    The electrical properties of La-silicate films grown by atomic layer deposition (ALD) on Ge substrates with different film configurations, such as various Si concentrations, Al2O3 interfacial passivation layers, and SiO2 capping layers, were examined. La-silicate thin films were deposited using alternating injections of the La[N{Si(CH3)3}2]3 precursor with O3 as the La and O precursors, respectively, at a substrate temperature of 310 °C. The Si concentration in the La-silicate films was further controlled by adding ALD cycles of SiO2. For comparison, La2O3 films were also grown using [La((i)PrCp)3] and O3 as the La precursor and oxygen source, respectively, at the identical substrate temperature. The capacitance-voltage (C-V) hysteresis decreased with an increasing Si concentration in the La-silicate films, although the films showed a slight increase in the capacitance equivalent oxide thickness. The adoption of Al2O3 at the interface as a passivation layer resulted in lower C-V hysteresis and a low leakage current density. The C-V hysteresis voltages of the La-silicate films with Al2O3 passivation and SiO2 capping layers was significantly decreased to ∼0.1 V, whereas the single layer La-silicate film showed a hysteresis voltage as large as ∼1.0 V.

  8. Elemental distribution and thermoelectric properties of layered tellurides 39R-M(0.067)Sb(0.667)Te(0.266) (M=Ge, Sn).

    PubMed

    Schneider, Matthias N; Fahrnbauer, Felix; Rosenthal, Tobias; Döblinger, Markus; Stiewe, Christian; Oeckler, Oliver

    2012-01-23

    The isostructural phases 39R-Ge(0.067)Sb(0.667)Te(0.266) (R3m, a=4.2649(1), c=75.061(2) Å) and 39R-Sn(0.067)Sb(0.667)Te(0.266) (R3m, a=4.2959(1), c=75.392(2) Å) were prepared by quenching stoichiometric melts of the pure elements and subsequent annealing at moderate temperatures. Their structures are comparable to "superlattices" synthesized by layer-by-layer deposition onto a substrate. These structures show no stacking disorder by electron microscopy. The structure of the metastable layered phases are similar to that of 39R-Sb(10)Te(3) (equivalent to Sb(0.769)Te(0.231)), which contains four A7 gray-arsenic-type layers of antimony alternating with Sb(2)Te(3) slabs. Joint refinements on single-crystal diffraction data using synchrotron radiation at several K edges were performed to enhance the scattering contrast. These refinements show that the elemental distributions at some atom positions are disordered whereas otherwise the structures are long-range ordered. The variation of the elemental concentration correlates with the variation in interatomic distance. Z-contrast scanning transmission electron microscopy (HAADF-STEM) on 39R-Ge(0.067)Sb(0.667)Te(0.266) confirms the presence of concentration gradients. The carrier-type of the isostructural metal (A7-type lamellae)-semiconductor heterostructures (Ge/Sn-doped Sb(2)Te(3) slabs) varies from n-type (Ge(0.067)Sb(0.667)Te(0.266)) to p-type (Sn(0.067)Sb(0.667)Te(0.266)). Although the absolute values of the Seebeck coefficient reached about 50-70 μV/K and the electrical conductivity is relatively high, the two isotypic phases exhibit a maximal thermoelectric figure of merit (ZT) of 0.06 at 400 °C as their thermal conductivity (κ≈8-9.5 W/mK at 400 °C) lies interestingly in between that of antimony and pure Sb(2)Te(3).

  9. Role of the superior colliculus in analyses of space: superficial and intermediate layer contributions to visual orienting, auditory orienting, and visuospatial discriminations during unilateral and bilateral deactivations.

    PubMed

    Lomber, S G; Payne, B R; Cornwell, P

    2001-12-03

    The superior colliculus (SC) has been implicated in spatial analyses of the environment, although few behavioral studies have explicitly tested this role. To test its imputed role in spatial analyses, we used a battery of four spatial tasks combined with unilateral and bilateral cooling deactivation of the upper and intermediate layers of the superior colliculus. We tested the abilities of cats to orient to three different stimuli: (1) moving visual, (2) stationary visual, (3) stationary white-noise aural. Furthermore, we tested the ability of the cats to discriminate the relative spatial position of a landmark. Unilateral cooling deactivation of the superficial layers of the SC induced a profound neglect of both moving and stationary visual stimuli presented in, and landmark objects located within, the contralateral hemifield. However, responses to auditory stimuli were unimpaired. Unilateral cooling deactivation of both the superficial and intermediate layers induced a profound contralateral neglect of the auditory stimulus. Additional and equivalent deactivation of the opposite SC largely restored orienting to either moving visual or auditory stimuli, and restored landmark position reporting to normal levels. However, during bilateral SC deactivation, orienting to the static visual stimulus was abolished throughout the entire visual field. Overall, unilateral SC deactivation results show that the upper and intermediate layers of the SC contribute in different ways to guiding behavioral responses to visual and auditory stimuli cues. Finally, bilateral superior colliculus deactivations reveal that other structures are sufficient to support spatial analyses and guide visual behaviors in the absence of neural operations in the superior colliculus, but only under certain circumstances.

  10. HfO2 gate dielectric on Ge (1 1 1) with ultrathin nitride interfacial layer formed by rapid thermal NH3 treatment

    NASA Astrophysics Data System (ADS)

    Agrawal, Khushabu S.; Patil, Vilas S.; Khairnar, Anil G.; Mahajan, Ashok M.

    2016-02-01

    Interfacial properties of the ALD deposited HfO2 over the surface nitrided germanium substrate have been studied. The formation of GeON (∼1.7 nm) was confirmed by X-ray photoelectron spectroscopy (XPS) and high resolution transmission electron spectroscopy (HRTEM) over the germanium surface. The effect of post deposition annealing temperature was investigated to study the interfacial and electrical properties of hafnium oxide/germanium oxynitride gate stacks. The high-k MOS devices with ultrathin GeON layer shows the good electrical characteristics including higher k value ∼18, smaller equivalent oxide thickness (EOT) around 1.5 nm and smaller hysteresis value less than 170 mV. The Qeff and Dit values are somewhat greater due to the (1 1 1) orientation of the germanium and may be due to the presence of nitrogen at the interface. The Fowler-Northeim (FN) tunneling of Ge MOS devices has been studied. The barrier height ΦB extracted from the plot is ∼1 eV.

  11. Influence of high-temperature AlN intermediate layer on the optical properties of MOCVD grown AlGaN films

    NASA Astrophysics Data System (ADS)

    Xie, Deng; Qiu, Zhi Ren; Liu, Yao; Talwar, Devki N.; Wan, Lingyu; Zhang, Xiong; Mei, Ting; Ferguson, Ian T.; Feng, Zhe Chuan

    2017-02-01

    By combining spectroscopic ellipsometry (SE) and optical transmission (OT) characterization methods we have systematically investigated the influence of AlN intermediate layer and AlN transition layer on the optical properties of AlGaN epilayers grown on sapphire by metalorganic chemical vapor deposition (MOCVD) method. Most dielectric functions of III-nitrides obtained by different research groups show significant band-tail absorption—which is not anticipated for such a direct band gap material. The dielectric functions are studied for a series of AlGaN/AlN/Al2O3 structures, with a four-layer model taking into account both high temperature grown AlN layer and low temperature grown AlN layer. The results obtained by fitting the optical parameters to experimental data show that the band-tail absorption should originate from the transition layer. AlGaN film without high temperature AlN epilayer exhibited a redshift of band gap around 0.24 eV.

  12. 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.

  13. Photoluminescence and electroluminescence from Ge/strained GeSn/Ge quantum wells

    NASA Astrophysics Data System (ADS)

    Lin, Chung-Yi; Huang, Chih-Hsiung; Huang, Shih-Hsien; Chang, Chih-Chiang; Liu, C. W.; Huang, Yi-Chiau; Chung, Hua; Chang, Chorng-Ping

    2016-08-01

    Ge/strained GeSn/Ge quantum wells are grown on a 300 mm Si substrate by chemical vapor deposition. The direct bandgap emission from strained GeSn is observed in the photoluminescence spectra and is enhanced by Al2O3/SiO2 passivation due to the field effect. The electroluminescence of the direct bandgap emission of strained GeSn is also observed from the Ni/Al2O3/GeSn metal-insulator-semiconductor tunneling diodes. Electroluminescence is a good indicator of GeSn material quality, since defects in GeSn layers degrade the electroluminescence intensity significantly. At the accumulation bias, the holes in the Ni gate electrode tunnel to the strained n-type GeSn layer through the ultrathin Al2O3 and recombine radiatively with electrons. The emission wavelength of photoluminescence and electroluminescence can be tuned by the Sn content.

  14. Pattern dependency in selective epitaxy of B-doped SiGe layers for advanced metal oxide semiconductor field effect transistors

    NASA Astrophysics Data System (ADS)

    Hâllstedt, J.; Kolahdouz, M.; Ghandi, R.; Radamson, H. H.; Wise, R.

    2008-03-01

    This study presents investigations about the physical mechanisms, origin, and methods to control the pattern dependency in selective epitaxial growth of Si1-xGex (x=0.14-0.32) layers. It is shown with a comprehensive experimental study that the local Si coverage of individual chips on patterned wafers is the main parameter for the layer profile in the epitaxial growth. This was explained by the gas depletion of the growth species in the low velocity boundary layer over the wafer. The gas depletion radius around each oxide opening was in the centimeter range which is related to the boundary layer thickness. The results from these experiments were applied to grow Si0.75Ge0.25 layers with B concentration of 4×1020cm-3 selectively for elevated source and drains in fully depleted ultrathin body silicon on insulator p metal oxide semiconductor field effect transistor (p-MOSFET) devices. The epitaxy control was maintained over a wide range of device sizes by optimized process parameters in combination with a wafer pattern design consisting of dummy features causing a uniform gas depletion over the chips on the wafer.

  15. Identification of the Chemical Bonding Prompting Adhesion of a-C:H Thin Films on Ferrous Alloy Intermediated by a SiCx:H Buffer Layer.

    PubMed

    Cemin, F; Bim, L T; Leidens, L M; Morales, M; Baumvol, I J R; Alvarez, F; Figueroa, C A

    2015-07-29

    Amorphous carbon (a-C) and several related materials (DLCs) may have ultralow friction coefficients that can be used for saving-energy applications. However, poor chemical bonding of a-C/DLC films on metallic alloys is expected, due to the stability of carbon-carbon bonds. Silicon-based intermediate layers are employed to enhance the adherence of a-C:H films on ferrous alloys, although the role of such buffer layers is not yet fully understood in chemical terms. The chemical bonding of a-C:H thin films on ferrous alloy intermediated by a nanometric SiCx:H buffer layer was analyzed by X-ray photoelectron spectroscopy (XPS). The chemical profile was inspected by glow discharge optical emission spectroscopy (GDOES), and the chemical structure was evaluated by Raman and Fourier transform infrared spectroscopy techniques. The nature of adhesion is discussed by analyzing the chemical bonding at the interfaces of the a-C:H/SiCx:H/ferrous alloy sandwich structure. The adhesion phenomenon is ascribed to specifically chemical bonding character at the buffer layer. Whereas carbon-carbon (C-C) and carbon-silicon (C-Si) bonds are formed at the outermost interface, the innermost interface is constituted mainly by silicon-iron (Si-Fe) bonds. The oxygen presence degrades the adhesion up to totally delaminate the a-C:H thin films. The SiCx:H deposition temperature determines the type of chemical bonding and the amount of oxygen contained in the buffer layer.

  16. Thickness dependent effects of an intermediate molecular blocking layer on the optoelectronic characteristics of organic bilayer photovoltaic cells

    NASA Astrophysics Data System (ADS)

    Steindamm, A.; Brendel, M.; Topczak, A. K.; Pflaum, J.

    2012-10-01

    In this work, we address the microscopic effects related to the implementation of a bathophenanthroline (BPhen) exciton blocking layer (EBL) sandwiched between Ag cathode and molecular diindenoperylene (DIP)/C60 bilayer of a photovoltaic cell. Complementary studies of current density, external quantum efficiency, and photoluminescence quenching for EBL thicknesses up to 50 nm indicate that Ag atoms are able to penetrate through the whole 35 nm thick C60 film into the polycrystalline DIP layer underneath, thereby enhancing exciton quenching if no blocking layer is applied. In contrast, an optimal trade-off between exciton blocking, suppression of metal penetration, and electron transport is achieved for a 5 nm thick BPhen layer yielding an improvement of power conversion efficiency by more than a factor of 2.

  17. Pseudo single crystal, direct-band-gap Ge{sub 0.89}Sn{sub 0.11} on amorphous dielectric layers towards monolithic 3D photonic integration

    SciTech Connect

    Li, Haofeng; Brouillet, Jeremy; Wang, Xiaoxin; Liu, Jifeng

    2014-11-17

    We demonstrate pseudo single crystal, direct-band-gap Ge{sub 0.89}Sn{sub 0.11} crystallized on amorphous layers at <450 °C towards 3D Si photonic integration. We developed two approaches to seed the lateral single crystal growth: (1) utilize the Gibbs-Thomson eutectic temperature depression at the tip of an amorphous GeSn nanotaper for selective nucleation; (2) laser-induced nucleation at one end of a GeSn strip. Either way, the crystallized Ge{sub 0.89}Sn{sub 0.11} is dominated by a single grain >18 μm long that forms optoelectronically benign twin boundaries with others grains. These pseudo single crystal, direct-band-gap Ge{sub 0.89}Sn{sub 0.11} patterns are suitable for monolithic 3D integration of active photonic devices on Si.

  18. Surface conductivity of Si(100) and Ge(100) surfaces determined from four-point transport measurements using an analytical N -layer conductance model

    NASA Astrophysics Data System (ADS)

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

    2017-02-01

    An analytical N -layer model for charge transport close to a surface is derived from the solution of Poisson's equation and used to describe distance-dependent electrical four-point measurements on the microscale. As the N -layer model comprises a surface channel, multiple intermediate layers, and a semi-infinite bulk, it can be applied to semiconductors in combination with a calculation of the near-surface band bending to model very precisely the measured four-point resistance on the surface of a specific sample and to extract a value for the surface conductivity. For describing four-point measurements on sample geometries with mixed 2D-3D conduction channels, often a very simple parallel-circuit model has so far been used in the literature, but the application of this model is limited, as there are already significant deviations, when it is compared to the lowest possible case of the N -layer model, i.e., the three-layer model. Furthermore, the N -layer model is applied to published distance-dependent four-point resistance measurements obtained with a multitip scanning tunneling microscope (STM) on germanium(100) and silicon(100) with different bulk doping concentrations resulting in the determination of values for the surface conductivities of these materials.

  19. Theoretical study of the effects of InAs/GaAs quantum dot layer's position in i-region on current-voltage characteristic in intermediate band solar cells

    NASA Astrophysics Data System (ADS)

    Gu, Yong-Xian; Yang, Xiao-Guang; Ji, Hai-Ming; Xu, Peng-Fei; Yang, Tao

    2012-08-01

    We theoretically investigated the current-voltage characteristic of InAs/GaAs quantum dot (QD) intermediate band solar cells by changing the QD layer's position in i-region. The open circuit voltage, short current density, fill factor, and conversion efficiency all vary with the position of QD layer. If the light generation coefficients through intermediate band (IB) are small, the IB mainly plays the role of a recombination energy level. If the light generation coefficients are improved, in order to ensure the highest QD layer performance, QD layer should be placed in an appropriate range.

  20. 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.

  1. High efficiency Cu(In,Ga)Se{sub 2} thin film solar cells without intermediate buffer layers

    SciTech Connect

    Ramanathan, K.; Wiesner, H.; Asher, S.; Niles, D.; Bhattacharya, R.N.; Keane, J.; Contreras, M.A.; Noufi, R.

    1998-09-01

    The nature of the interface between CuInGaSe{sub 2} (CIGS) and the chemical bath deposited CdS layer has been investigated. The authors show that heat-treating the absorbers in Cd- or Zn-containing solutions in the presence of ammonium hydroxide sets up an interfacial reaction with the possibility of an ion exchange occurring between Cd and Cu. The characteristics of devices made in this manner suggest that the reaction generates a thin, n-doped region in the absorber. The authors suggest that this aspect might be more important than the CdS layer in the formation of the junction. It is quite possible that the CdS/CuInSe{sub 2} device is a buried, shallow junction with a CdS window layer, rather than a heterojunction between CdS and CIGS. The authors use these ideas to develop methods for fabricating diodes without CdS or Cd.

  2. Variability of GeV gamma-ray emission in QSO B0218+357 due to microlensing on intermediate size structures

    NASA Astrophysics Data System (ADS)

    Sitarek, J.; Bednarek, W.

    2016-06-01

    Strong gravitational lensing leads to an occurrence of multiple images, with different magnifications, of a lensed source. Those magnifications can in turn be modified by microlensing on smaller mass scales within the lens. Recently, measurements of the changes in the magnification ratio of the individual images have been proposed as a powerful tool for estimation of the size and velocity of the emission region in the lensed source. The changes of the magnification ratios in blazars PKS1830-211 and QSO B0218+357, if interpreted as caused by a microlensing on individual stars, put strong constraints on those two variables. These constraints are difficult to accommodate with the current models of gamma-ray emission in blazars. In this paper we study if similar changes in the magnification ratio can be caused by microlensing on intermediate size structures in the lensing galaxy. We investigate in details three classes of possible lenses: globular clusters (GCs), open clusters (OCs) and giant molecular clouds (GMCs). We apply this scenario to the case of QSO B0218+357. Our numerical simulations show that changes in magnifications with similar time-scales can be obtained for relativistically moving emission regions with sizes up to 0.01 pc in the case of microlensing on the cores of GCs or clumps in GMCs. From the density of such structures in spiral galaxies we estimate however that lensing in GMCs would be more common.

  3. Yttrium passivation of defects in GeO2 and GeO2/Ge interfaces

    NASA Astrophysics Data System (ADS)

    Li, Hongfei; Robertson, John

    2017-01-01

    Alloying amorphous GeO2 with Y2O3 has been found experimentally to improve its chemical stability and electrical reliability as a gate dielectric in Ge-based field effect transistors. The mechanism is explained here based on density functional calculations. The GeO2 reliability problem is correlated with oxygen deficiency defects, which generate gap states near the band-edges of the underlying Ge. These can be passivated through Y doping. This shifts the defect gap state out of the gap up into the GeO2 conduction band, thus effectively passivating gap states in the GeO2 layer.

  4. Towards III-V solar cells on Si: Improvement in the crystalline quality of Ge-on-Si virtual substrates through low porosity porous silicon buffer layer and annealing

    SciTech Connect

    Calabrese, Gabriele; Baricordi, Stefano; Bernardoni, Paolo; Fin, Samuele; Guidi, Vincenzo; Vincenzi, Donato

    2014-09-26

    A comparison between the crystalline quality of Ge grown on bulk Si and on a low porosity porous Si (pSi) buffer layer using low energy plasma enhanced chemical vapor deposition is reported. Omega/2Theta coupled scans around the Ge and Si (004) diffraction peaks show a reduction of the Ge full-width at half maximum (FWHM) of 22.4% in presence of the pSi buffer layer, indicating it is effective in improving the epilayer crystalline quality. At the same time atomic force microscopy analysis shows an increase in root means square roughness for Ge grown on pSi from 38.5 nm to 48.0 nm, as a consequence of the larger surface roughness of pSi compared to bulk Si. The effect of 20 minutes vacuum annealing at 580°C is also investigated. The annealing leads to a FWHM reduction of 23% for Ge grown on Si and of 36.5% for Ge on pSi, resulting in a FWHM of 101 arcsec in the latter case. At the same time, the RMS roughness is reduced of 8.8% and of 46.5% for Ge grown on bulk Si and on pSi, respectively. The biggest improvement in the crystalline quality of Ge grown on pSi with respect to Ge grown on bulk Si observed after annealing is a consequence of the simultaneous reorganization of the Ge epilayer and the buffer layer driven by energy minimization. A low porosity buffer layer can thus be used for the growth of low defect density Ge on Si virtual substrates for the successive integration of III-V multijunction solar cells on Si. The suggested approach is simple and fast –thus allowing for high throughput-, moreover is cost effective and fully compatible with subsequent wafer processing. Finally it does not introduce new chemicals in the solar cell fabrication process and can be scaled to large area silicon wafers.

  5. Exchange of interlayer terephthalate anions from a Mg Al layered double hydroxide: formation of intermediate interstratified phases

    NASA Astrophysics Data System (ADS)

    Kaneyoshi, Masami; Jones, William

    1998-10-01

    The exchange of interlayer terephthalate (TA) anions from a Mg-Al layered double hydroxide (LDH) by carbonate, sulfate, chloride and nitrate anions is reported. It is shown that TA is readily exchanged by CO 32- and SO 42- but only partly by Cl - and NO 3-. We demonstrate that during the exchange process interstratified phases are observed. Such interstratification has previously been reported only for directly synthesised materials. The origin of the interstratification is believed to be associated with two preferred orientations of TA anions within the layers, i.e. vertical or horizontal to the clay sheets. Two models for the possible exchange mechanism which is operating in these systems are proposed.

  6. 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.

  7. Cobalt based layered perovskites as cathode material for intermediate temperature Solid Oxide Fuel Cells: A brief review

    NASA Astrophysics Data System (ADS)

    Pelosato, Renato; Cordaro, Giulio; Stucchi, Davide; Cristiani, Cinzia; Dotelli, Giovanni

    2015-12-01

    Nowadays, the cathode is the most studied component in Intermediate Temperature-Solid Oxide Fuel Cells (IT-SOFCs). Decreasing SOFCs operating temperature implies slow oxygen reduction kinetics and large polarization losses. Double perovskites with general formula REBaCo2O5+δ are promising mixed ionic-electronic conductors, offering a remarkable enhancement of the oxygen diffusivity and surface exchange respect to disordered perovskites. In this review, more than 250 compositions investigated in the literature were analyzed. The evaluation was performed in terms of electrical conductivity, Area Specific Resistance (ASR), chemical compatibility with electrolytes and Thermal Expansion Coefficient (TEC). The most promising materials have been identified as those bearing the mid-sized rare earths (Pr, Nd, Sm, Gd). Doping strategies have been analyzed: Sr doping on A site promotes higher electrical conductivity, but worsen ASR and TECs; B-site doping (Fe, Ni, Mn) helps lowering TECs, but is detrimental for the electrochemical properties. A promising boost of the electrochemical activity is obtained by simply introducing a slight Ba under-stoichiometry. Still, the high sensitivity of the electrochemical properties against slight changes in the stoichiometry hamper a conclusive comparison of all the investigated compounds. Opportunities for an improvement of double perovskite cathodes performance is tentatively foreseen in combining together the diverse effective doping strategies.

  8. Effect of 3C-SiC intermediate layer in GaN—based light emitting diodes grown on Si(111) substrate

    NASA Astrophysics Data System (ADS)

    Zhu, Youhua; Wang, Meiyu; Li, Yi; Tan, Shuxin; Deng, Honghai; Guo, Xinglong; Yin, Haihong; Egawa, Takashi

    2017-03-01

    GaN-based light emitting diodes (LEDs) have been grown by metalorganic chemical vapor deposition on Si(111) substrate with and without 3C-SiC intermediate layer (IL). Structural property has been characterized by means of atomic force microscope, X-ray diffraction, and transmission electron microscope measurements. It has been revealed that a significant improvement in crystalline quality of GaN and superlattice epitaxial layers can be achieved by using 3C-SiC as IL. Regarding of electrical and optical characteristics, it is clearly observed that the LEDs with its IL have a smaller leakage current and higher light output power comparing with the LEDs without IL. The better performance of LEDs using 3C-SiC IL can be contributed to both of the improvements in epitaxial layers quality and light extraction efficiency. As a consequence, in terms of optical property, a double enhancement of the light output power and external quantum efficiency has been realized.

  9. Performance enhancement of a plasmonic structure comprising of indium oxide-zirconium dioxide-silver-zinc oxide intermediate layers working in visible and infrared wavelength region

    NASA Astrophysics Data System (ADS)

    Brahmachari, Kaushik; Ray, Mina

    2016-07-01

    Modeling of a fused silica (SiO2) glass prism-based plasmonic structure comprising of indium oxide (In2O3)-zirconium dioxide (ZrO2)-silver (Ag)-zinc oxide (ZnO) intermediate layers showing enhancement in sensitivity and figure-of-merit (FOM) in visible and infrared regime has been reported in this paper. Performance of the proposed plasmonic structure has been demonstrated in terms of sensitivity, half width (HW), detection accuracy (DA), and FOM parameters in visible (632.8 nm) and infrared (1200 nm) wavelength of light. High sensitivity of fused silica glass material, In2O3, ZnO films along with high DA and high FOM of Ag and inclusion of ZrO2 as an oxidation protective layer in between In2O3 and Ag have been the most exciting and advantageous features of our proposed structure. Simulated sensitivity values of our proposed structure were found to be 73.8 deg/RIU at 632.8 nm wavelength and it was found enhanced to 109.6 deg/RIU at 1200 nm wavelength and simulated FOM values were also found enhanced from 23.3544 RIU-1 at 632.8 nm to 62.6285 RIU-1 at 1200 nm wavelength for change in sensing layer refractive indices from 1.30 RIU to 1.35 RIU.

  10. Vertical distribution and diel migration of macrozooplankton in the St. Lawrence marine system (Canada) in relation with the cold intermediate layer thermal properties

    NASA Astrophysics Data System (ADS)

    Harvey, Michel; Galbraith, Peter S.; Descroix, Aurélie

    2009-01-01

    Vertical distribution of various species and stages of macrozooplankton (euphausiacea, chaetognatha, cnidaria, mysidacea, amphipoda) were determined for different times of the day and related to the physical environment. Stratified sampling with the BIONESS was carried out during seven cruises in spring and fall 1998, 2000, and 2001, and fall 1999, in two different habitats in the St. Lawrence marine system: the lower St. Lawrence Estuary and the NW Gulf of St. Lawrence. Our results indicate that the various macrozooplankton species were distributed throughout the whole water column including the surface layer, the cold intermediate layer (CIL), and the deep layer at different times of day and night in both areas during all periods. Moreover, three types of migrational patterns were observed within this zooplanktonic community: (1) nocturnal ascent by the whole population, (2) segregation into two groups; one which performed nocturnal accent and another which remained in the deep, and (3) no detectable migration. We also observed that the diel vertical migration (DVM) amplitude in most of the macrozooplankton species varied as a function of physical factors, in particular the spatio-temporal variations of the CIL thermal properties, including the upper and the lower limits of the CIL and the depth of the CIL core temperature. Finally, the different DVM patterns coupled with estuarine circulation patterns and bottom topography could place animals in different flow regimes by night and by day and contribute to their retention (aggregation) and/or dispersion in different areas, time of the day, and seasons.

  11. Effect of 3C-SiC intermediate layer in GaN—based light emitting diodes grown on Si(111) substrate

    NASA Astrophysics Data System (ADS)

    Zhu, Youhua; Wang, Meiyu; Li, Yi; Tan, Shuxin; Deng, Honghai; Guo, Xinglong; Yin, Haihong; Egawa, Takashi

    2016-12-01

    GaN-based light emitting diodes (LEDs) have been grown by metalorganic chemical vapor deposition on Si(111) substrate with and without 3C-SiC intermediate layer (IL). Structural property has been characterized by means of atomic force microscope, X-ray diffraction, and transmission electron microscope measurements. It has been revealed that a significant improvement in crystalline quality of GaN and superlattice epitaxial layers can be achieved by using 3C-SiC as IL. Regarding of electrical and optical characteristics, it is clearly observed that the LEDs with its IL have a smaller leakage current and higher light output power comparing with the LEDs without IL. The better performance of LEDs using 3C-SiC IL can be contributed to both of the improvements in epitaxial layers quality and light extraction efficiency. As a consequence, in terms of optical property, a double enhancement of the light output power and external quantum efficiency has been realized.

  12. Pulse-height defect due to electron interaction in dead layers of Ge/Li/ gamma-ray detectors

    NASA Technical Reports Server (NTRS)

    Larsen, R. N.; Strauss, M. G.

    1969-01-01

    Study shows the pulse-height degradation of gamma ray spectra in germanium/lithium detectors to be due to electron interaction in the dead layers that exist in all semiconductor detectors. A pulse shape discrimination technique identifies and eliminates these defective pulses.

  13. Characterization of epitaxial GaAs MOS capacitors using atomic layer-deposited TiO2/Al2O3 gate stack: study of Ge auto-doping and p-type Zn doping

    PubMed Central

    2012-01-01

    Electrical and physical properties of a metal-oxide-semiconductor [MOS] structure using atomic layer-deposited high-k dielectrics (TiO2/Al2O3) and epitaxial GaAs [epi-GaAs] grown on Ge(100) substrates have been investigated. The epi-GaAs, either undoped or Zn-doped, was grown using metal-organic chemical vapor deposition method at 620°C to 650°C. The diffusion of Ge atoms into epi-GaAs resulted in auto-doping, and therefore, an n-MOS behavior was observed for undoped and Zn-doped epi-GaAs with the doping concentration up to approximately 1017 cm-3. This is attributed to the diffusion of a significant amount of Ge atoms from the Ge substrate as confirmed by the simulation using SILVACO software and also from the secondary ion mass spectrometry analyses. The Zn-doped epi-GaAs with a doping concentration of approximately 1018 cm-3 converts the epi-GaAs layer into p-type since the Zn doping is relatively higher than the out-diffused Ge concentration. The capacitance-voltage characteristics show similar frequency dispersion and leakage current for n-type and p-type epi-GaAs layers with very low hysteresis voltage (approximately 10 mV). PACS: 81.15.Gh. PMID:22297193

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

    SciTech Connect

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

    2016-08-01

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

  15. Intermediate and high resolution numerical simulations of the transition of a tropical wave critical layer to a tropical storm

    NASA Astrophysics Data System (ADS)

    Montgomery, M. T.; Wang, Z.; Dunkerton, T. J.

    2009-12-01

    Recent work has hypothesized that tropical cyclones in the deep Atlantic and eastern Pacific basins develop from the cyclonic Kelvin cat's eye of a tropical easterly wave critical layer located equatorward of the easterly jet axis that typifies the trade wind belt. The cyclonic critical layer is thought to be important to tropical cyclogenesis because its cat's eye provides (i) a region of cyclonic vorticity and weak deformation by the resolved flow, (ii) containment of moisture entrained by the developing flow and/or lofted by deep convection therein, (iii) confinement of mesoscale vortex aggregation, (iv) a predominantly convective type of heating profile, and (v) maintenance or enhancement of the parent wave until the developing proto-vortex becomes a self-sustaining entity and emerges from the wave as a tropical depression. This genesis sequence and the overarching framework for describing how such hybrid wave-vortex structures become tropical depressions/storms is likened to the development of a marsupial infant in its mother's pouch, and for this reason has been dubbed the "marsupial paradigm". Here we conduct the first multi-scale test of the marsupial paradigm in an idealized setting by revisiting the problem of the transformation of an easterly wave-like disturbance into a tropical storm vortex using the WRF model. An analysis of the evolving winds, equivalent potential temperature, and relative vertical vorticity is presented from coarse (28 km) and high resolution (3.1 km) simulations. The results are found to support key elements of the marsupial paradigm by demonstrating the existence of a vorticity dominant region with minimal strain/shear deformation within the critical layer pouch that contains strong cyclonic vorticity and high saturation fraction. This localized region within the pouch serves as the "attractor" for an upscale "bottom up" development process while the wave pouch and proto-vortex move together. Implications of these findings are

  16. A new family of two-dimensional zeolites prepared from the intermediate layered precursor IPC-3P obtained during the synthesis of TUN zeolite.

    PubMed

    Kubů, Martin; Roth, Wieslaw J; Greer, Heather F; Zhou, Wuzong; Morris, Russell E; Přech, Jan; Čejka, Jiří

    2013-10-04

    The crystallization of zeolite TUN with 1,4-bis(N-methylpyrrolidinium)butane as template proceeds through an intermediate, designated IPC-3P, following the Ostwald rule of successive transformations. This apparently layered transient product has been thoroughly investigated and found to consist of MWW monolayers stacked without alignment in register, that is, disordered compared with MCM-22P. The structure was confirmed based on X-ray diffraction and high-resolution (HR)TEM analysis. The layered zeolite precursor IPC-3P can be swollen and pillared affording a combined micro- and mesoporous material with enhanced Brunauer-Emmett-Teller (BET) surface area (685 m(2) g(-1) ) and greater accessibility of Brønsted acid sites for bulky molecules. This mesoporous material was probed with 2,6-di-tert-butylpyridine (DTBP). IPC-3P and its modification create a new layered zeolite sub-family belonging to the MWW family. FTIR data indicate that (Al)MWW materials MCM-22 and IPC-3 with Si/Al ratios greater than 20 exhibit a lower relative ratio of Brønsted to Lewis acid sites than MCM-22 (with Si/Al ratios of around 13), that is, less than 2 versus more than 3, respectively. This is maintained even upon pillaring and warrants further exploration of materials like IPC-3P with a higher Al content. The unique XRD features of IPC-3P indicating misaligned stacking of layers and distinct from MCM-22P, are also seen in other MWW materials such as EMM-10P, hexamethonium-templated (HM)-MCM-22, ITQ-30, and UZM-8 suggesting the need for more detailed study of their identity and properties.

  17. Reduced GeO2 Nanoparticles: Electronic Structure of a Nominal GeOx Complex and Its Stability under H2 Annealing

    PubMed Central

    Zhao, Jia; Yang, Linju; McLeod, John A.; Liu, Lijia

    2015-01-01

    A nominal GeOx (x ≤ 2) compound contains mixtures of Ge, Ge suboxides, and GeO2, but the detailed composition and crystallinity could vary from material to material. In this study, we synthesize GeOx nanoparticles by chemical reduction of GeO2, and comparatively investigate the freshly prepared sample and the sample exposed to ambient conditions. Although both compounds are nominally GeOx, they exhibit different X-ray diffraction patterns. X-ray absorption fine structure (XAFS) is utilized to analyse the detailed structure of GeOx. We find that the two initial GeOx compounds have entirely different compositions: the fresh GeOx contains large amorphous Ge clusters connected by GeOx, while after air exposure; the Ge clusters are replaced by a GeO2-GeOx composite. In addition, the two GeOx products undergo different structural rearrangement under H2 annealing, producing different intermediate phases before ultimately turning into metallic Ge. In the fresh GeOx, the amorphous Ge remains stable, with the GeOx being gradually reduced to Ge, leading to a final structure of crystalline Ge grains connected by GeOx. The air-exposed GeOx on the other hand, undergoes a GeO2→GeOx→Ge transition, in which H2 induces the creation of oxygen vacancies at intermediate stage. A complete removal of oxides occurs at high temperature. PMID:26634908

  18. Reduced GeO2 Nanoparticles: Electronic Structure of a Nominal GeOx Complex and Its Stability under H2 Annealing.

    PubMed

    Zhao, Jia; Yang, Linju; McLeod, John A; Liu, Lijia

    2015-12-04

    A nominal GeOx (x ≤ 2) compound contains mixtures of Ge, Ge suboxides, and GeO2, but the detailed composition and crystallinity could vary from material to material. In this study, we synthesize GeOx nanoparticles by chemical reduction of GeO2, and comparatively investigate the freshly prepared sample and the sample exposed to ambient conditions. Although both compounds are nominally GeOx, they exhibit different X-ray diffraction patterns. X-ray absorption fine structure (XAFS) is utilized to analyse the detailed structure of GeOx. We find that the two initial GeOx compounds have entirely different compositions: the fresh GeOx contains large amorphous Ge clusters connected by GeOx, while after air exposure; the Ge clusters are replaced by a GeO2-GeOx composite. In addition, the two GeOx products undergo different structural rearrangement under H2 annealing, producing different intermediate phases before ultimately turning into metallic Ge. In the fresh GeOx, the amorphous Ge remains stable, with the GeOx being gradually reduced to Ge, leading to a final structure of crystalline Ge grains connected by GeOx. The air-exposed GeOx on the other hand, undergoes a GeO2→GeOx→Ge transition, in which H2 induces the creation of oxygen vacancies at intermediate stage. A complete removal of oxides occurs at high temperature.

  19. New insight into magneto-structural phase transitions in layered TbMn2Ge2-based compounds

    PubMed Central

    Fang, Chunsheng; Li, Guoxing; Wang, Jianli; Hutchison, W. D.; Ren, Q. Y.; Deng, Zhenyan; Ma, Guohong; Dou, Shixue; Campbell, S. J.; Cheng, Zhenxiang

    2017-01-01

    The Tb1−xYxMn2Ge2 series (x = 0, 0.1, 0.2) compounds are found to exhibit two magnetic phase transitions with decreasing temperature: from the paramagnetic state to the antiferromagnetic interlayer state at TNinter and from an antiferromagnetic interlayer structure to a collinear ferrimagnetic interlayer structure at TCinter. Compared with the slight change of TNinter (409 K, 410 K and 417 K for x = 0, 0.1 and 0.2 respectively), the replacement of Y for Tb leads to a significant decrease in TCinter from 97.5 K for x = 0 to 74.6 K for x = 0.2. The variation in TCinter can be ascribed to the combination of two effects: (1) chemical pressure and (2) magnetic dilution effect by Y substitution for Tb. Besides, a strong anisotropic magnet-volume effect has been detected around TCinter in all compounds with Δa/a = 0.125%, 0.124% and 0.130% for x = 0, 0.1 and 0.2, respectively while no obvious effect is detected along the c-axis. The maximum magnetic entropy change were found to be −ΔSmax = 9.1 J kg−1 K−1, 11.9 J kg−1 K−1 and 6.3 J kg−1 K−1 with a field change from 0 T to 5 T for x = 0, 0.1, 0.2 respectively. PMID:28374763

  20. Morphological effects of single-layer graphene oxide in the formation of covalently bonded polypyrrole composites using intermediate diisocyanate chemistry

    NASA Astrophysics Data System (ADS)

    Whitby, Raymond L. D.; Korobeinyk, Alina; Mikhalovsky, Sergey V.; Fukuda, Takahiro; Maekawa, Toru

    2011-10-01

    Single-layer graphene oxide (SLGO) possesses carboxylic and hydroxyl groups suitable for reactions with aliphatic or aromatic diisocyanate molecules. TEM analysis reveals that aliphatic diisocyanate molecules caused SLGO to scroll into star-like formations, whereas aromatic diisocyanate molecules retained SGLO in a flat-sheet morphology. TGA confirms the stabilisation of the formed urea and urethane groups on SLGO, but the onset of sheet pyrolysis occurs at a lower temperature due to isocyanate reactions with anhydride and epoxide groups embedded in the sheet. Pendant isocyanate groups act as bridging units to facilitate the attachment of pyrrole molecules, which are then used as anchor sites for the covalent polymerisation of pyrrole to polypyrrole (PPy). The use of FeCl3 as the polymerisation catalyst generated both covalent and free PPy, but also iron hydroxide nanoparticles were observed decorating the SLGO surface. When using ammonium persulfate as a catalyst and dodecylbenzenesulfonate as a dopant, free PPy could be removed under treatment with solvents to leave a purely covalent system. Discrete regions of SLGO were observed decorated with nanoparticles of PPy along the edge or across the surface of individual sheets. It was found that the flexibility of the SLGO sheet and the type of diisocyanate used directly affected the electrical resistance of the final composite.

  1. P/N InP solar cells on Ge wafers

    NASA Technical Reports Server (NTRS)

    Wojtczuk, Steven; Vernon, Stanley; Burke, Edward A.

    1994-01-01

    Indium phosphide (InP) P-on-N one-sun solar cells were epitaxially grown using a metalorganic chemical vapor deposition process on germanium (Ge) wafers. The motivation for this work is to replace expensive InP wafers, which are fragile and must be thick and therefore heavy, with less expensive Ge wafers, which are stronger, allowing use of thinner, lighter weight wafers. An intermediate InxGs1-xP grading layer starting as In(0.49)Ga(0.51) at the GaAs-coated Ge wafer surface and ending as InP at the top of the grading layer (backside of the InP cell) was used to attempt to bend some of the threading dislocations generated by lattice-mismatch between the Ge wafer and InP cell so they would be harmlessly confined in this grading layer. The best InP/Ge cell was independently measured by NASA-Lewis with a one-sun 25 C AMO efficiently measured by NASA-Lewis with a one-circuit photocurrent 22.6 mA/sq cm. We believe this is the first published report of an InP cell grown on a Ge wafer. Why get excited over a 9 percent InP/Ge cell? If we look at the cell weight and efficiency, a 9 percent InP cell on an 8 mil Ge wafer has about the same cell power density, 118 W/kg (BOL), as the best InP cell ever made, a 19 percent InP cell on an 18 mil InP wafer, because of the lighter Ge wafer weight. As cell panel materials become lighter, the cell weight becomes more important, and the advantage of lightweight cells to the panel power density becomes more important. In addition, although InP/Ge cells have a low beginning-of-life (BOL) efficiency due to dislocation defects, the InP/Ge cells are very radiation hard (end-of-life power similar to beginning-of-life). We have irradiated an InP/Ge cell with alpha particles to an equivalent fluence of 1.6 x 10(exp 16) 1 MeV electrons/sq cm and the efficiency is still 83 percent of its BOL value. At this fluence level, the power output of these InP/Ge cells matches the GaAs/Ge cell data tabulated in the JPL handbook. Data are presented

  2. Bacterial processes in the intermediate and deep layers of the Ionian Sea in winter 1999: Vertical profiles and their relationship to the different water masses

    NASA Astrophysics Data System (ADS)

    Zaccone, R.; Monticelli, L. S.; Seritti, A.; Santinelli, C.; Azzaro, M.; Boldrin, A.; La Ferla, R.; Ribera D'Alcalã, M.

    2003-09-01

    Dissolved and particulate organic carbon, bacterial biomass, microbial enzymatic activities (EEA: leucine aminopeptidase, β-glucosidase, and alkaline phosphatase), bacterial production, respiration rates, and bacterial growth efficiency were determined in 10 stations of the Ionian Sea (winter 1998-1999) with the aim of characterizing the recycling of biogenic carbon and phosphorus in the different water masses, previously identified on the basis of their hydrographical properties. All microbial activities decreased markedly with depth, with a sharp increase in the benthic boundary layer, where potential remineralization rates of phosphorus up to 1.03 μg P·dm-3d-1 and bacterial carbon production of 0.078 μg C·dm-3 d-1 were recorded. Those rates were close to the surface ones; the bacterial growth efficiency was also around 20%, similar to the surface value, sustaining the microbial food chain at the bottom. The daily hydrolysis of the organic carbon pool estimated by EEA varied from 0.67% (Ionian Surface Water) to 0.02% (Deep Water). Alkaline phosphatase activity was generally low in the intermediate and deep layers, in relation to the higher inorganic P content. The last facts support the hypothesis that deep waters of Ionian Sea, and in general of the entire Mediterranean basin, because of their young age, carry a larger amount of labile dissolved organic carbon, which reduces the need for a high recycling activity by bacterial community. As a matter of fact, a relatively higher activity per cell in carbon production rates was found in the deep layer where a large volume of the very recently formed Cretan Sea Outflow Water was present.

  3. La{sub 4}(Si{sub 5.2}Ge{sub 2.8}O{sub 18})(TeO{sub 3}){sub 4} and La{sub 2}(Si{sub 6}O{sub 13})(TeO{sub 3}){sub 2}: Intergrowth of the lanthanum(III) tellurite layer with the XO{sub 4} (X=Si/Ge) tetrahedral layer

    SciTech Connect

    Kong Fang; Jiang Hailong; Mao Jianggao

    2008-02-15

    Two novel lanthanum(III) silicate tellurites, namely, La{sub 4}(Si{sub 5.2}Ge{sub 2.8}O{sub 18})(TeO{sub 3}){sub 4} and La{sub 2}(Si{sub 6}O{sub 13})(TeO{sub 3}){sub 2}, have been synthesized by the solid state reactions and their structures determined by single crystal X-ray diffraction. The structure of La{sub 4}(Si{sub 5.2}Ge{sub 2.8}O{sub 18})(TeO{sub 3}){sub 4} features a three-dimensional (3D) network composed of the [(Ge{sub 2.82}Si{sub 5.18})O{sub 18}]{sup 4-} tetrahedral layers and the [La{sub 4}(TeO{sub 3}){sub 4}]{sup 4+} layers that alternate along the b-axis. The germanate-silicate layer consists of corner-sharing XO{sub 4} (X=Si/Ge) tetrahedra, forming four- and six-member rings. The structure of La{sub 2}(Si{sub 6}O{sub 13})(TeO{sub 3}){sub 2} is a 3D network composed of the [Si{sub 6}O{sub 13}]{sup 2-} double layers and the [La{sub 2}(TeO{sub 3}){sub 2}]{sup 2+} layers that alternate along the a-axis. The [Si{sub 6}O{sub 13}]{sup 2-} double layer is built by corner-sharing silicate tetrahedra, forming four-, five- and eight-member rings. The TeO{sub 3}{sup 2-} anions in both compounds are only involved in the coordination with La{sup 3+} ions to form a lanthanum(III) tellurite layer. La{sub 4}(Si{sub 5.2}Ge{sub 2.8}O{sub 18})(TeO{sub 3}){sub 4} is a wide band-gap semiconductor. - Graphical abstract: The first lanthanum(III) silicate/germanate tellurites, namely, La{sub 4}[(Si{sub x}Ge{sub 8-x})O{sub 18}](TeO{sub 3}){sub 4} (x=5.18) and La{sub 2}(Si{sub 6}O{sub 13})(TeO{sub 3}){sub 2}, have been synthesized and structurally determined by single crystal X-ray diffraction. Both compounds feature complicated 3D network structures composed of the silicate/germanate tetrahedral layers alternating with the [LaTeO{sub 3}] layers.

  4. Evidence of the Ge nonreactivity during the initial stage of SiGe oxidation

    NASA Astrophysics Data System (ADS)

    Dkhissi, A.; Upadhyay, A. K.; Hemeryck, A.; Estève, A.; Landa, G.; Pochet, P.; Rouhani, M. Djafari

    2009-01-01

    Density functional theory calculations are used to identify preferential sites for oxygen adsorption on SiGe. It is shown that Ge atoms hinder O incorporation in their vicinity. Additionally, the silanone structure, known to be the key intermediate prior to silicon dioxide formation, is shown to be not favorable when close to a Ge site on the surface.

  5. Ion-Assisted Laser Deposition of Intermediate Layers for Yttrium BARIUM(2) COPPER(3) OXYGEN(7-DELTA) Thin Film Growth on Polycrystalline and Amorphous Substrates.

    NASA Astrophysics Data System (ADS)

    Reade, Ronald Paul

    The growth of YB_2Cu _3O_{7-delta} (YBCO) high-temperature superconductor thin films has largely been limited to deposition on single-crystal substrates to date. In order to expand the range of potential applications, growth on polycrystalline and amorphous substrates is desirable. In particular, the deposition of YBCO thin films with high critical current densities on polycrystalline metal alloys would allow the manufacture of superconducting tapes. However, it is shown that it is not possible to grow YBCO thin films directly on this type of substrate due to chemical and structural incompatibility. This work investigates the use of a yttria-stabilized zirconia (YSZ) intermediate layer to address this problem. An ion-assisted pulsed-laser deposition process is developed to provide control of orientation during the growth of the YSZ layers. The important properties of YBCO and YSZ are summarized and the status of research on thin film growth of these materials is reviewed. An overview of the pulsed-laser deposition (PLD) technique is presented. The use of ion -assisted deposition techniques to control thin film properties is discussed. Using an ion-assisted PLD process, the growth of (001) YSZ layers with controlled alignment of the in -plane crystal axes is achieved on polycrystalline metal and other polycrystalline and amorphous substrates. Studies of the important process parameters are presented. These layers are demonstrated to be appropriate for the subsequent deposition of c-axis YBCO thin films with alignment of the in-plane axes. A critical temperature of 92K and critical current densities (at 77K) of 6times 10^5 and 5times 10^4 A/cm ^2 without and with a 0.4T magnetic field, have been achieved. These critical current densities are higher than those demonstrated for competing technologies. The applicability of the developed technology is discussed. The control of film orientation using the ion-assisted PLD process is compared to the existing theory and

  6. Fabrication of multilayered Ge nanocrystals embedded in SiO xGeN y films

    NASA Astrophysics Data System (ADS)

    Gao, Fei; Green, Martin A.; Conibeer, Gavin; Cho, Eun-Chel; Huang, Yidan; Perez-Wurfl, Ivan; Flynn, Chris

    2008-09-01

    Multilayered Ge nanocrystals embedded in SiO xGeN y films have been fabricated on Si substrate by a (Ge + SiO 2)/SiO xGeN y superlattice approach, using a rf magnetron sputtering technique with a Ge + SiO 2 composite target and subsequent thermal annealing in N 2 ambient at 750 °C for 30 min. X-ray diffraction (XRD) measurement indicated the formation of Ge nanocrystals with an average size estimated to be 5.4 nm. Raman scattering spectra showed a peak of the Ge-Ge vibrational mode downward shifted to 299.4 cm -1, which was caused by quantum confinement of phonons in the Ge nanocrystals. Transmission electron microscopy (TEM) revealed that Ge nanocrystals were confined in (Ge + SiO 2) layers. This superlattice approach significantly improved both the size uniformity of Ge nanocrystals and their uniformity of spacing on the 'Z' growth direction.

  7. Si/Ge intermixing during Ge Stranski–Krastanov growth

    PubMed Central

    Hoummada, Khalid; Ronda, Antoine; Mangelinck, Dominique; Berbezier, Isabelle

    2014-01-01

    Summary The Stranski–Krastanov growth of Ge islands on Si(001) has been widely studied. The morphology changes of Ge islands during growth, from nucleation to hut/island formation and growth, followed by hut-to-dome island transformation and dislocation nucleation of domes, have been well described, even at the atomic scale, using techniques such as scanning tunneling microscopy and transmission electron microscopy. Although it is known that these islands do not consist of pure Ge (due to Si/Ge intermixing), the composition of the Ge islands is not precisely known. In the present work, atom probe tomography was used to study the composition of buried dome islands at the atomic scale, in the three-dimensional space. The core of the island was shown to contain about 55 atom % Ge, while the Ge composition surrounding this core decreases rapidly in all directions in the islands to reach a Ge concentration of about 15 atom %. The Ge distribution in the islands follows a cylindrical symmetry and Ge segregation is observed only in the {113} facets of the islands. The Ge composition of the wetting layer is not homogeneous, varying from 5 to 30 atom %. PMID:25551065

  8. Thermal Stability of Ge/GeSn Nanostructures Grown by MBE on (001) Si/Ge Virtual Wafers

    NASA Astrophysics Data System (ADS)

    Sadofyev, Yu. G.; Martovitsky, V. P.; Klekovkin, A. V.; Saraikin, V. V.; Vasil'evskii, I. S.

    A stack of five metastable 200-nm-thick elastically strained GeSn epitaxial layers separated by 20-nm-thick Ge spacers was grown on (001) Si/Ge virtual substrate by MBE. The molar fraction of Sn in different layers varied from 0.005 to 0.10, increasing with the layer distance from the Ge buffer. The phase separation of the GeSn alloy during postgrowth annealing takes place along with plastic relaxation. The phase separation begins well before the completion of the plastic relaxation process. The degree of phase separation at a given annealing temperature depends strongly on the Sn content in the GeSn alloy. The Sn released from the decomposed GeSn alloy predominantly accumulates as an amorphous layer on the surface of the sample.

  9. Application of x-ray nano-particulate markers for the visualization of intermediate layers and interfaces using scanning electron microscopy

    NASA Astrophysics Data System (ADS)

    Bessudnova, Nadezda O.; Bilenko, David I.; Zakharevich, Andrey M.

    2012-03-01

    In this study the methodology of biological sample preparation for dental research using SEM/EDX has been elaborated. (1)The original cutting equipment supplied with 3D user-controlled sample fixation and an adjustable cooling system has been designed and evaluated. (2) A new approach to the root dentine drying procedure has been developed to preserve structure peculiarities of root dentine. (3) A novel adhesive system with embedded X-Ray nanoparticulate markers has been designed. (4)The technique allowing for visualization of bonding resins, interfaces and intermediate layers between tooth hard tissues and restorative materials of endodontically treated teeth using the X-ray nano-particulate markers has been developed and approved. These methods and approaches were used to compare the objective depth of penetration of adhesive systems of different generations in root dentine. It has been shown that the depth of penetration in dentine is less for adhesive systems of generation VI in comparison with bonding resins of generation V, which is in agreement with theoretical evidence. The depth of penetration depends on the correlation between the direction of dentinal tubules, bonding resin delivery and gravity.

  10. Application of x-ray nano-particulate markers for the visualization of intermediate layers and interfaces using scanning electron microscopy

    NASA Astrophysics Data System (ADS)

    Bessudnova, Nadezda O.; Bilenko, David I.; Zakharevich, Andrey M.

    2011-10-01

    In this study the methodology of biological sample preparation for dental research using SEM/EDX has been elaborated. (1)The original cutting equipment supplied with 3D user-controlled sample fixation and an adjustable cooling system has been designed and evaluated. (2) A new approach to the root dentine drying procedure has been developed to preserve structure peculiarities of root dentine. (3) A novel adhesive system with embedded X-Ray nanoparticulate markers has been designed. (4)The technique allowing for visualization of bonding resins, interfaces and intermediate layers between tooth hard tissues and restorative materials of endodontically treated teeth using the X-ray nano-particulate markers has been developed and approved. These methods and approaches were used to compare the objective depth of penetration of adhesive systems of different generations in root dentine. It has been shown that the depth of penetration in dentine is less for adhesive systems of generation VI in comparison with bonding resins of generation V, which is in agreement with theoretical evidence. The depth of penetration depends on the correlation between the direction of dentinal tubules, bonding resin delivery and gravity.

  11. Understanding of interface structures and reaction mechanisms induced by Ge or GeO diffusion in Al{sub 2}O{sub 3}/Ge structure

    SciTech Connect

    Shibayama, Shigehisa; Kato, Kimihiko; Sakashita, Mitsuo; Takeuchi, Wakana; Taoka, Noriyuki; Nakatsuka, Osamu; Zaima, Shigeaki

    2013-08-19

    The reaction mechanisms at Al{sub 2}O{sub 3}/Ge interfaces with thermal oxidation through the Al{sub 2}O{sub 3} layer have been investigated. X-ray photoelectron spectroscopy reveals that an Al{sub 6}Ge{sub 2}O{sub 13} layer is formed near the interface, and a GeO{sub 2} layer is formed on the Al{sub 2}O{sub 3} surface, suggesting Ge or GeO diffusion from the Ge surface. It is also clarified that the Al{sub 6}Ge{sub 2}O{sub 13} layer is formed by the different mechanism with a small activation energy of 0.2 eV, compared with the GeO{sub 2} formation limited by oxygen diffusion. Formation of Al-O-Ge bonds due to the AlGeO formation could lead appropriate interface structures with high interface qualities.

  12. Novel Solution Process for Fabricating Ultra-Thin-Film Absorber Layers in Fe2SiS4 and Fe2GeS4 Photovoltaics

    SciTech Connect

    Orefuwa, Samuel A.; Lai, Cheng-Yu; Dobson, Kevin D.; Ni, Chaoying; Radu, Daniela R.

    2014-05-12

    Fe2SiS4 and Fe2GeS4 crystalline materials posses direct bandgaps of ~1.55 and ~1.4 eV respectively and an absorption coefficient larger than 10^5 cm–1; their theoretical potential as solar photovoltaic absorbers has been demonstrated. However, no solar devices that employ either Fe2SiS4 or Fe2GeS4 have been reported to date. In the presented work, nanoprecursors to Fe2SiS4 and Fe2GeS4 have been fabricated and employed to build ultra-thin-film layers via spray coating and rod coating methods. Temperature-dependent X-Ray diffraction analyses of nanoprecursors coatings show an unprecedented low temperature for forming crystalline Fe2SiS4 and Fe2GeS4. Fabricating of ultra-thin-film photovoltaic devices utilizing Fe2SiS4 and Fe2GeS4 as solar absorber material is presented.

  13. Ge/GeSn heterostructures grown on Si (100) by molecular-beam epitaxy

    SciTech Connect

    Sadofyev, Yu. G. Martovitsky, V. P.; Bazalevsky, M. A.; Klekovkin, A. V.; Averyanov, D. V.; Vasil’evskii, I. S.

    2015-01-15

    The growth of GeSn layers by molecular-beam epitaxy on Si (100) wafers coated with a germanium buffer layer is investigated. The properties of the fabricated structures are controlled by reflection high-energy electron diffraction, atomic-force microscopy, X-ray diffractometry, Rutherford backscattering, and Raman scattering. It is shown that GeSn layers with thicknesses up to 0.5 μm and Sn molar fractions up to 0.073 manifest no sign of plastic relaxation upon epitaxy. The lattice constant of the GeSn layers within the growth plane is precisely the same as that of Ge. The effect of rapid thermal annealing on the conversion of metastable elastically strained GeSn layers into a plastically relaxed state is examined. Ge/GeSn quantum wells with Sn molar fraction up to 0.11 are obtained.

  14. The performance of La0.6Sr1.4MnO4 layered perovskite electrode material for intermediate temperature symmetrical solid oxide fuel cells

    NASA Astrophysics Data System (ADS)

    Zhou, Jun; Chen, Gang; Wu, Kai; Cheng, Yonghong

    2014-12-01

    A layered perovskite electrode material, La0.6Sr1.4MnO4+δ (LSMO4), has been studied for intermediate temperature symmetrical solid oxide fuel cells (IT-SSOFCs) on La0.9Sr0.1Ga0.8Mg0.2O3-δ (LSGM) electrolyte. The chemical compatibility tests indicate that no reaction occurred between LSMO4 oxide and LSGM electrolyte at temperature up to 1000 °C both in air and 5% H2. The lower conductivity in 5% H2 and higher conduction activation energy than those in air would be caused by poorer overlap of both σ and π bonds. DFT + U calculations also show that oxygen vacancies which formed in reducing atmosphere may block the 3D hopping path for electrons or holes through Mn-O-Mn chains. For LSMO4 electrode, SEM results indicate that the electrode formed good contact with the electrolyte after being sintered at 900 °C for 2 h. At 800 °C, the polarization resistance of the LSMO4 cathode is about 0.87 Ω cm2 in air, while the polarization resistance of the LSMO4 anode is about 2.07 Ω cm2 in 5% H2. LSMO4 exhibits better electrochemical activity for oxygen reduction than that for hydrogen oxidation. A cell with LSGM electrolyte, LSMO4-LSGM mixture as anode and cathode simultaneously displays a maximum power density of 59 mW cm-2 at 800 °C.

  15. Direct gap Ge1-ySny alloys: Fabrication and design of mid-IR photodiodes

    NASA Astrophysics Data System (ADS)

    Senaratne, C. L.; Wallace, P. M.; Gallagher, J. D.; Sims, P. E.; Kouvetakis, J.; Menéndez, J.

    2016-07-01

    Chemical vapor deposition methods were developed, using stoichiometric reactions of specialty Ge3H8 and SnD4 hydrides, to fabricate Ge1-ySny photodiodes with very high Sn concentrations in the 12%-16% range. A unique aspect of this approach is the compatible reactivity of the compounds at ultra-low temperatures, allowing efficient control and systematic tuning of the alloy composition beyond the direct gap threshold. This crucial property allows the formation of thick supersaturated layers with device-quality material properties. Diodes with composition up to 14% Sn were initially produced on Ge-buffered Si(100) featuring previously optimized n-Ge/i-Ge1-ySny/p-Ge1-zSnz type structures with a single defected interface. The devices exhibited sizable electroluminescence and good rectifying behavior as evidenced by the low dark currents in the I-V measurements. The formation of working diodes with higher Sn content up to 16% Sn was implemented by using more advanced n-Ge1-xSnx/i-Ge1-ySny/p-Ge1-zSnz architectures incorporating Ge1-xSnx intermediate layers (x ˜ 12% Sn) that served to mitigate the lattice mismatch with the Ge platform. This yielded fully coherent diode interfaces devoid of strain relaxation defects. The electrical measurements in this case revealed a sharp increase in reverse-bias dark currents by almost two orders of magnitude, in spite of the comparable crystallinity of the active layers. This observation is attributed to the enhancement of band-to-band tunneling when all the diode layers consist of direct gap materials and thus has implications for the design of light emitting diodes and lasers operating at desirable mid-IR wavelengths. Possible ways to engineer these diode characteristics and improve carrier confinement involve the incorporation of new barrier materials, in particular, ternary Ge1-x-ySixSny alloys. The possibility of achieving type-I structures using binary and ternary alloy combinations is discussed in detail, taking into account

  16. Development of wider bandgap n-type a-SiOx:H and μc-SiOx:H as both doped and intermediate reflecting layer for a-Si:H/ a-Si1-xGex:H tandem solar cells

    NASA Astrophysics Data System (ADS)

    Chen, Po-Wei; Chen, Pei-Ling; Tsai, Chuang-Chuang

    2016-07-01

    In this work, we developed a-SiOx:H(n) and μc-SiOx:H(n) films as n-type layer, intermediate reflecting layer (IRL), and back-reflecting layer (BRL) to improve the light management in silicon thin-film solar cells. In the development of SiOx:H films, by properly adjusting the oxygen content of the films, the optical bandgap of μc-SiOx:H(n) can be increased while maintaining sufficient conductivity. Similar effect was found for a-SiOx:H(n). In a-Si:H single-junction cells, employing a-SiOx:H(n) as the replacement for a-Si:H(n) resulted in a relative efficiency enhancement of 11.4% due to the reduced parasitic absorption loss. We have also found that μc-SiOx:H(n) can replace back ITO layer as BRL, leading to a relative efficiency gain of 7.6%. For a-Si:H/ a-Si1- x Ge x:H tandem cell, employing μc-SiOx:H(n) as IRL increased the current density of top cell. In addition, employing a-SiOx:H(n) as a replacement of a-Si:H(n) in the top cell increased the current density of bottom cell due to the reduction of absorption loss. Combining all the improvements, the a-Si:H/ a-Si1-xGex:H tandem cell with efficiency of 9.2%, V OC = 1.58 V, J SC = 8.43 mA/cm2, and FF = 68.4% was obtained. [Figure not available: see fulltext.

  17. A numerical study of the relationship between atmospheric forcing, cold intermediate layer generation and primary production in the Black Sea over interannual time scales

    NASA Astrophysics Data System (ADS)

    Cannaby, Heather

    2015-04-01

    The Cold Intermediate Layer (CIL) is a characteristic feature of the Black Sea formed during winter when cool surface waters penetrate to the depth of the upper halocline. The CIL typically persists throughout the year and is defined at its upper and lower boundaries by the 8 °C isotherm. CIL formation is concentrated in the central regions of the Black Sea basin and on the NW shelf, although the relative contribution of these two sources is still debated. Previous studies have suggested that CIL formation on the NW shelf may play an important role in the subduction of nutrient rich shelf waters into the upper pycnocline, thus removing nutrients from the euphotic zone and impacting rates of primary production. A 20 year hydrodynamic model (Princeton Ocean Model) simulation extending from 1990-2009 and forced by the DMI atmospheric reanalysis is used to investigate (i) interactions between atmospheric forcing and regional CIL formation and (ii) rates of CIL formation and the subduction of NW shelf waters to depths below the euphotic zone. Model skill in simulating CIL characteristics is demonstrated. Results suggest that the ratio of CIL waters formed in the central regions of the Black Sea basin and on the NW shelf varies considerably from one year to another due to sub-domain scale atmospheric variability. Exceptionally warm years when CIL formation is considerably reduced are associated with anomalously high concentrations of fresh riverine water residing in the euphotic zone, and hence a higher percentage of riverine nutrients are available to fuel primary production. Years when anomalously large volumes of CIL water are formed on the NW shelf are not necessarily cold years when considering the domain as a whole. During these years an anomalously high volume of riverine water is subducted into the CIL where it remains trapped throughout the following spring and summer. This study provides a physics based explanation for the occurrence of higher phytoplankton

  18. Thermodynamic modeling of the Ge-La binary system

    NASA Astrophysics Data System (ADS)

    Liu, Miao; Li, Chang-rong; Du, Zhen-min; Guo, Cui-ping; Niu, Chun-ju

    2012-08-01

    The Ge-La binary system was critically assessed by means of the calculation of phase diagram (CALPHAD) technique. The associate model was used for the liquid phase containing the constituent species Ge, La, Ge3La5, and Ge1.7La. The terminal solid solution diamond-(Ge) with a small solubility of La was described using the substitutional model, in which the excess Gibbs energy was formulated with the Redlich-Kister equation. The compounds with homogeneity ranges, α(Ge1.7La), β(Ge1.7La), and (GeLa), were modeled using two sublattices as α(Ge,La)1.7La, β(Ge,La)1.7La, and (Ge,La)(Ge,La), respectively. The intermediate phases with no solubility ranges, Ge4La5, Ge3La4, Ge3La5, and GeLa3, were treated as stoichiometric compounds. The three allotropic modifications of La, dhcp-La, fcc-La, and bcc-La, were kept as pure element phases since no solubility of Ge in La was reported. A set of self-consistent thermodynamic parameters of the Ge-La binary system was obtained. The calculation results agree well with the available experimental data from literatures.

  19. Dopage p par BI3 de couches Ge/Ge ET Ge/GaAs; caractérisationélectrique

    NASA Astrophysics Data System (ADS)

    Étienne, D.; Achargui, N.; Bougnot, G.

    1986-01-01

    B doped Ge layers were obtained by chemical vapor transport using a disproportionation reaction 2GeI2=Ge+GeI4. They were p-type and their electric parameters: resistivity ϱ, Hall mobility μH and carrier concentration p were studied as a function of substrate temperature, partial pressure of BI3 and hydrogen flow rate on BI3 source. The incorporation of B into monocrystalline layers is studied thermodynamically.

  20. Enhancement of thermal stability and water resistance in yttrium-doped GeO{sub 2}/Ge gate stack

    SciTech Connect

    Lu, Cimang Hyun Lee, Choong; Zhang, Wenfeng; Nishimura, Tomonori; Nagashio, Kosuke; Toriumi, Akira

    2014-03-03

    We have systematically investigated the material and electrical properties of yttrium-doped GeO{sub 2} (Y-GeO{sub 2}) on Germanium (Ge). A significant improvement of both thermal stability and water resistance were demonstrated by Y-GeO{sub 2}/Ge stack, compared to that of pure GeO{sub 2}/Ge stack. The excellent electrical properties of Y-GeO{sub 2}/Ge stacks with low D{sub it} were presented as well as enhancement of dielectric constant in Y-GeO{sub 2} layer, which is beneficial for further equivalent oxide thickness scaling of Ge gate stack. The improvement of thermal stability and water resistance are discussed both in terms of the Gibbs free energy lowering and network modification of Y-GeO{sub 2}.

  1. PrBa0.5Sr0.5Co2O5+δ layered perovskite cathode for intermediate temperature solid oxide fuel cells

    SciTech Connect

    Ding, Hanping; Xue, Xingjian

    2010-02-06

    Layered perovskite oxides have ordered A-cations localizing oxygen vacancies, and may potentially improve oxygen ion diffusivity and surface exchange coefficient. The A-site-ordered layered perovskite PrBa0.5Sr0.5Co2O5+δ (PBSC) was evaluated as new cathode material for intermediate temperature solid oxide fuel cells (IT-SOFCs). The material was characterized using electrochemical impedance spectroscopy in a symmetrical cell system (PBSC/Ce0.9Sm0.1O1.9 (SDC)/PBSC), exhibiting excellent performance in the intermediate temperature range of 500–700 °C. An area-specific-resistance (ASR) of 0.23 Ω cm2 was achieved at 650 °C for cathode polarization. The low activation energy (Ea) 124 kJ mol-1 is comparable to that of La0.8Sr0.2CoO3-δ. A laboratory-scaled SDC-based tri-layer cell of Ni-SDC/SDC/PBSC was tested in intermediate temperature conditions of 550 to 700 °C. A maximum power density of 1045 mW cm-2 was achieved at 700 °C. The interfacial polarization resistance is as low as 0.285, 0.145, 0.09 and 0.05 Ω cm2 at 550, 600, 650 and 700 °C, respectively. Layered perovskite PBSC shows promising performance as cathode material for IT-SOFCs.

  2. Germanium-tin interdiffusion in strained Ge/GeSn multiple-quantum-well structure

    NASA Astrophysics Data System (ADS)

    Wang, Wei; Dong, Yuan; Zhou, Qian; Tok, Eng Soon; Yeo, Yee-Chia

    2016-06-01

    The thermal stability and germanium-tin (Ge-Sn) interdiffusion properties were studied in epitaxial Ge/GeSn multiple-quantum-well (MQW) structure. No obvious interdiffusion was observed for annealing temperatures of 300 °C or below, while observable interdiffusion occurred for annealing temperatures of 380 °C and above. High-resolution x-ray diffraction was used to obtain the interdiffusion coefficient by analyzing the decrease rate of Ge/GeSn periodic satellite peaks. The interdiffusion coefficient is much higher, and the activation enthalpy of 1.21 eV is substantially lower in Ge/GeSn MQW structure than that previously reported in silicon-germanium (Si-Ge) systems. When the annealing temperature is increased to above 500 °C, Ge-Sn interdiffusion becomes severe. Some small pits appear on the surface, which should be related to Sn out-diffusion to the Ge cap layer, followed by Sn desorption from the top surface. This work provides insights into the Ge-Sn interdiffusion and Sn segregation behaviors in Ge/GeSn MQW structure, and the thermal budget that may be used for fabrication of devices comprising Ge/GeSn heterostructures.

  3. Ohmic contact formation of metal/amorphous-Ge/n-Ge junctions with an anomalous modulation of Schottky barrier height

    SciTech Connect

    Liu, Hanhui; Wang, Peng; Qi, Dongfeng; Li, Xin; Han, Xiang; Wang, Chen; Chen, Songyan Li, Cheng; Huang, Wei

    2014-11-10

    The modulation of Schottky barrier height of metal/Ge inserting an amorphous Ge layer has been demonstrated. It is interested that the Schottky barrier height of Al/amorphous-Ge/n-Ge junctions is oscillated with increase of the a-Ge thickness from 0 to 10 nm, and when the thickness reaches above 10 nm, the Al/amorphous-Ge/n-Ge shows ohmic characteristics. Electron hopping through localized states of a-Ge layer, the alleviation of metal induced gap states, as well as the termination of dangling bonds at the amorphous-Ge/n-Ge interface are proposed to explain the anomalous modulation of Schottky barrier height.

  4. NiO gate GaN-based enhancement-mode hetrojunction field-effect transistor with extremely low on-resistance using metal organic chemical vapor deposition regrown Ge-doped layer

    NASA Astrophysics Data System (ADS)

    Suzuki, Asamira; Choe, Songbeak; Yamada, Yasuhiro; Otsuka, Nobuyuki; Ueda, Daisuke

    2016-12-01

    In this paper, we present a normally-off GaN-based transistor with an extremely low on-resistance (R on) fabricated by using a Ge-doped n++-GaN layer for ohmic contacts. We developed a novel GaN regrowth technique using Ge as a dopant, which achieved an extremely high doping concentration of 1 × 1020 cm-3, and thereby the lowest specific contact resistance of 1.5 × 10-6 Ω·cm2. The NiO gate fabricated using an atomic layer deposition technique reduced the spacing between the source and drain electrodes. The fabricated device showed the record-breaking R on of 0.95 Ω·mm with the maximum drain current and transconductance of 1.1 A/mm and 490 mS/mm, respectively. Note that the obtained threshold voltage was 0.55 V. This extremely low R on characteristic indicates the great potential of NiO-gate GaN-based heterojunction field-effect transistors.

  5. Indium gallium zinc oxide layer used to decrease optical reflection loss at intermediate adhesive region for fabricating mechanical stacked multijunction solar cells

    NASA Astrophysics Data System (ADS)

    Sameshima, Toshiyuki; Nimura, Takeshi; Sugawara, Takashi; Ogawa, Yoshihiro; Yoshidomi, Shinya; Kimura, Shunsuke; Hasumi, Masahiko

    2017-01-01

    Reduction of optical reflection loss is discussed in three mechanical stacked samples: top crystalline silicon and bottom crystalline germanium substrates, top crystalline GaAs and bottom crystalline silicon substrates, and top crystalline GaP and bottom crystalline silicon substrates using an epoxy-type adhesive with a reflective index of 1.47. Transparent conductive Indium gallium zinc oxide (IGZO) layers with a refractive index of 1.85 were used as antireflection layers. IGZO layers were formed on the bottom surface of the top substrate and the top surface of the bottom substrate of the three stacked samples with thicknesses of 188, 130, and 102 nm. The insertion of IGZO layers decreased the optical reflectivity of the stacked samples. The IGZO layers provided high effective optical absorbency of bottom substrates of 0.925, 0.943, and 0.931, respectively, for light wavelength regions for light in which the top substrates were transparent and the bottom substrates were opaque.

  6. Data requirements for intermediate energy nuclear applications

    SciTech Connect

    Pearlstein, S.

    1990-01-01

    Several applications that include spallation neutron sources, space radiation effects, biomedical isotope production, accelerator shielding and radiation therapy make use of intermediate energy nuclear data extending to several GeV. The overlapping data needs of these applications are discussed in terms of what projectiles, targets and reactions are of interest. Included is a discussion of what is generally known about these data and what is needed to facilitate their use in intermediate energy applications. 40 refs., 2 figs., 2 tabs.

  7. Investigation of GaInAs strain reducing layer combined with InAs quantum dots embedded in Ga(In)As subcell of triple junction GaInP/Ga(In)As/Ge solar cell.

    PubMed

    Li, Senlin; Bi, Jingfeng; Li, Mingyang; Yang, Meijia; Song, Minghui; Liu, Guanzhou; Xiong, Weiping; Li, Yang; Fang, Yanyan; Chen, Changqing; Lin, Guijiang; Chen, Wenjun; Wu, Chaoyu; Wang, Duxiang

    2015-01-01

    The InAs/GaAs quantum dots structure embedded in GaInP/Ga(In)As/Ge triple junction solar cell with and without Ga0.90In0.10As strain reducing layer was investigated. Conversion efficiency of 33.91% at 1,000 suns AM 1.5D with Ga0.90In0.10As strain reducing layer was demonstrated. A 1.19% improvement of the conversion efficiency was obtained via inserting the Ga0.90In0.10As strain reducing layer. The main contribution of this improvement was from the increase of the short-circuit current, which is caused by the reduction of the Shockley-Read-Hall recombination centers. Consequently, there was a decrease in open circuit voltage due to the lower thermal activation energy of confined carriers in Ga0.9In0.1As than GaAs and a reduction in the effective band gap of quantum dots.

  8. Heterogeneous integration of SiGe/Ge and III-V for Si photonics

    NASA Astrophysics Data System (ADS)

    Takenaka, Mitsuru; Kim, Younghyun; Han, Jaehoon; Kang, Jian; Ikku, Yuki; Cheng, Yongpeng; Park, Jinkwon; Takagi, Shinichi

    2016-05-01

    The heterogeneous integration of SiGe/Ge and III-V semiconductors gives us an opportunity to enhance functionalities of Si photonics platform through their superior material properties which lack in Si. In this paper we discuss what SiGe/Ge and III-V can bring to Si photonics. We have predicted that the light effective hole mass in strained SiGe results in the enhanced the free-carrier effects such as the plasma dispersion effect and free-carrier absorption. We observed significantly larger free-carrier absorption in the SiGe optical modulator than in the control Si device. By fabricating asymmetric Mach-Zehnder interferometer (MZI) SiGe optical modulators, the enhancement of the plasma dispersion effect in strained SiGe has been successfully demonstrated. Mid-infrared integrated photonics based on Ge waveguides on Si have also been investigated. Since Ge is transparent to the entire mid-infrared range, Ge photonic integrated circuits on the Ge-on-Insulator (GeOI) wafer are quite attractive. We have successfully fabricated the GeOI wafer with 2-μm-thick buried oxide (BOX) layer by wafer bonding. The passive waveguide components based on Ge strip waveguides have been demonstrated on the GeOI. We have also demonstrated carrier-injection Ge variable optical attenuators. We have proposed and investigate the III-V CMOS photonics platform by using the III-V on Insulator (IIIV- OI) on a Si wafer. The strong optical confinement in the III-V-OI enables us to achieve high-performance photonic devices. We have successfully demonstrated InGaAsP MZI optical switch with the low on-state crosstalk on the III-V-OI. Ultra-low dark current waveguide InGaAs PDs integrated with an InP grating coupler are also achieved.

  9. The effect of the interlayer element on the exfoliation of layered Mo2AC (A = Al, Si, P, Ga, Ge, As or In) MAX phases into two-dimensional Mo2C nanosheets

    NASA Astrophysics Data System (ADS)

    Khazaei, Mohammad; Arai, Masao; Sasaki, Taizo; Estili, Mehdi; Sakka, Yoshio

    2014-02-01

    The experimental exfoliation of layered, ternary transition-metal carbide and nitride compounds, known as MAX phases, into two-dimensional (2D) nanosheets, is a great development in the synthesis of novel low-dimensional inorganic systems. Among the MAX phases, Mo-containing ones might be considered as the source for obtaining Mo2C nanosheets with potentially unique properties, if they could be exfoliated. Here, by using a set of first-principles calculations, we discuss the effect of the interlayer ‘A’ element on the exfoliation of Mo2AC (A = Al, Si, P, Ga, Ge, As or In) MAX phases into the 2D Mo2C nanosheets. Based on the calculated exfoliation energies and the elastic constants, we propose that Mo2InC with the lowest exfoliation energy and the highest elastic constant anisotropy between C11 and C33 might be a suitable compound for exfoliation into 2D Mo2C nanosheets.

  10. GeSi photonics for telecommunication applications

    NASA Astrophysics Data System (ADS)

    Chaisakul, Papichaya; Vakarin, Vladyslav; Marris-Morini, Delphine; Frigerio, Jacopo; Wada, Kazumi; Isella, Giovanni; Vivien, Laurent

    2014-11-01

    We experimentally and theoretically investigate GeSi-based photonics for future on-chip optical interconnect on bulk Silicon substrates with dense wavelength division multiplexing (WDM) system. We experimentally show that Ge-rich Si1-xGex can be used as both a passive low loss waveguide and a substrate to facilitate low-temperature epitaxial growth of Ge-based active devices working at low optical loss wavelength of Ge-rich Si1-xGex waveguides. We also theoretically discussed the possibilities to realize a compact passive component based on Ge-rich Si1-xGex material system on bulk Si wafer. From simulation the system based on Ge-rich Si1-xGex waveguide and the Si1-yGey (y < x) lower cladding layer is good enough to ensure compactness of important on-chip photonic components including passive waveguide and GeSi-based array waveguide grating (AWG). The small refractive index contrast between Ge-rich Si1-xGex waveguide and the Si1-yGey lower cladding layer potentially avoid the polarization dependent loss and detrimental fabrication tolerance of WDM system. Our studies show that GeSi-based photonics could uniquely provide both passive and active functionalities for dense WDM system.

  11. High Quality GaAs Growth by MBE on Si Using GeSi Buffers and Prospects for Space Photovoltaics

    NASA Technical Reports Server (NTRS)

    Carlin, J. A.; Ringel, S. A.; Fitzgerald, E. A.; Bulsara, M.

    2005-01-01

    III-V solar cells on Si substrates are of interest for space photovoltaics since this would combine high performance space cells with a strong, lightweight and inexpensive substrate. However, the primary obstacles blocking III-V/Si cells from achieving high performance to date have been fundamental materials incompatabilities, namely the 4% lattice mismatch between GaAs and Si, and the large mismatch in thermal expansion coefficient. In this paper, we report on the molecular beam epitaxial (MBE) growth and properties of GaAs layers and single junction GaAs cells on Si wafers which utilize compositionally graded GeSi Intermediate buffers grown by ultra-high vacuum chemical vapor deposition (UHVCVD) to mitigate the large lattice mismatch between GaAs and Si. Ga As cell structures were found to incorporate a threading dislocation density of 0.9-1.5 x 10 (exp 6) per square centimeter, identical to the underlying relaxed Ge cap of the graded buffer, via a combination of transmission electron microscopy, electron beam induced current, and etch pit density measurements. AlGaAs/GaAs double heterostructures wre grown on the GeSi/Si substrates for time-resolved photoluminescence measurements, which revealed a bulk GaAs minority carrier lifetime in excess of 10 ns, the highest lifetime ever reported for GaAs on Si. A series of growth were performed to ass3ss the impact of a GaAs buffer to a thickness of only 0.1 micrometer. Secondary ion mass spectroscopy studies revealed that there is negligible cross diffusion of Ga, As and Ge at he III-V/Ge interface, identical to our earlier findings for GaAs grown on Ge wafers using MBE. This indicates that there is no need for a buffer to "bury" regions of high autodopjing,a nd that either pn or np configuration cells are easily accomodated by these substrates. Preliminary diodes and single junction Al Ga As heteroface cells were grown and fabricated on the Ge/GeSi/Si substrates for the first time. Diodes fabricated on GaAs, Ge and Ge/Ge

  12. GeSn/SiGeSn photonic devices for mid-infrared applications: experiments and calculations

    NASA Astrophysics Data System (ADS)

    Han, Genquan; Zhang, Qingfang; Liu, Yan; Zhang, Chunfu; Hao, Yue

    2016-11-01

    In this work, a fully strained GeSn photodetector with Sn atom percent of 8% is fabricated on Ge buffer on Si(001) substrate. The wavelength λ of light signals with obvious optical response for Ge0.92Sn0.08 photodetector is extended to 2 μm. The impacts of compressive strain introduced during the epitaxial growth of GeSn on Ge/Si are studied by simulation. Besides, the tensile strain engineering of GeSn photonic devices is also investigated. Lattice-matched GeSn/SiGeSn double heterostructure light emitting diodes (LEDs) with Si3N4 tensile liner stressor are designed to promote the further mid-infrared applications of GeSn photonic devices. With the releasing of the residual stress in Si3N4 liner, a large biaxial tensile strain is induced in GeSn active layer. Under biaxial tensile strain, the spontaneous emission rate rsp and internal quantum efficiency ηIQE for GeSn/SiGeSn LED are significantly improved.

  13. Intermediate-Scale Experimental and Numerical Study of Multiphase CO2 Attenuation in Layered Shallow Aquifers During Leakage from Geologic Sequestration Site

    NASA Astrophysics Data System (ADS)

    Plampin, M. R.; Pawar, R.; Porter, M. L.; Illangasekare, T. H.

    2015-12-01

    In order to effectively predict and mitigate the potential risks from leakage of stored CO2, we must first understand the physicochemical processes that CO2 undergoes during migration through shallow aquifers, including dissolved phase advection and dispersion as well as gas phase exsolution, multiphase flow, and dissolution. Since field sites are inherently large-scale, heterogeneous, 3-D systems, large-scale experimental data is important to validate numerical models and to make confident predictions regarding CO2 migration. A large, highly instrumented, two-dimensional tank was built and packed with porous media to represent a portion of a layered shallow aquifer. Flow of water across the tank was established by applying a small difference in head between the two ends. A separate stream of water was then saturated with dissolved CO2 and injected into the bottom of the tank near the upstream end. Various saturation sensors measured the spatiotemporal pattern of gas phase evolution in the tank, while an external sensor and an Ion Chromatograph were used to monitor the dissolved CO2 concentrations at various locations in the system. The top of the tank was baffled into four sealed compartments, each of which was connected to a gas flow meter to monitor the spatiotemporal pattern of gas phase CO2 release to the atmosphere. Numerical simulations were also performed to better understand the fundamental physics that drove the observed CO2 evolution processes, and to help validate a widely used code using the experimental data. The simulations were performed with the Finite Element Heat and Mass Transfer (FEHM) software that was developed at Los Alamos National Laboratory. The model domain, porous media properties, and initial conditions were set up to match those of the experiment, and the boundary conditions were adjusted to investigate the mass transfer between the dissolved and gaseous phases of CO2 that developed within the system. Results from both the experiments

  14. Status of GaAs/Ge solar cells

    NASA Technical Reports Server (NTRS)

    Iles, P. A.; Ho, F.; Yeh, Y. C. M.

    1991-01-01

    With experience at increasing production levels, GaAs/Ge cells are proving their effectiveness for some demanding missions. The experience in producing inactive-Ge structures should benefit parallel work on forming monolithic cascade cells using AlGaAs or GaAs top cell layers grown on Ge or other bottom cell materials. The adjustments needed to ensure that the GaAs/Ge interface is inactive are more likely to preserve the properties of a separately optimized bottom cell.

  15. Pulsed laser deposited GeTe-rich GeTe-Sb2Te3 thin films

    PubMed Central

    Bouška, M.; Pechev, S.; Simon, Q.; Boidin, R.; Nazabal, V.; Gutwirth, J.; Baudet, E.; Němec, P.

    2016-01-01

    Pulsed laser deposition technique was used for the fabrication of Ge-Te rich GeTe-Sb2Te3 (Ge6Sb2Te9, Ge8Sb2Te11, Ge10Sb2Te13, and Ge12Sb2Te15) amorphous thin films. To evaluate the influence of GeTe content in the deposited films on physico-chemical properties of the GST materials, scanning electron microscopy with energy-dispersive X-ray analysis, X-ray diffraction and reflectometry, atomic force microscopy, Raman scattering spectroscopy, optical reflectivity, and sheet resistance temperature dependences as well as variable angle spectroscopic ellipsometry measurements were used to characterize as-deposited (amorphous) and annealed (crystalline) layers. Upon crystallization, optical functions and electrical resistance of the films change drastically, leading to large optical and electrical contrast between amorphous and crystalline phases. Large changes of optical/electrical properties are accompanied by the variations of thickness, density, and roughness of the films due to crystallization. Reflectivity contrast as high as ~0.21 at 405 nm was calculated for Ge8Sb2Te11, Ge10Sb2Te13, and Ge12Sb2Te15 layers. PMID:27199107

  16. Comparative investigation of InGaP/InGaAs/Ge triple-junction solar cells using different Te-doped InGaP layers in tunnel junctions

    NASA Astrophysics Data System (ADS)

    Jung, Sang Hyun; Kim, Chang Zoo; Kim, Youngjo; Jun, Dong Hwan; Kang, Ho Kwan; Kim, Hogyoung

    2016-03-01

    Heavily tellurium (Te)-doped InGaP layers in tunnel junctions (TJs) grown by using metalorganic chemical vapor deposition (MOCVD) were investigated to improve the device performance of InGaP/InGaAs/Ge triple-junction solar cells. Three different doping techniques were employed to grow the Te-doped InGaP layers in the TJ; Te doping, Te and Si co-doping and Te pre-doping. Compared to other samples, the external quantum efficiency (EQE) profiles in the InGaP top cell were found to be higher for the sample with Te pre-doping. Under a concentrated light condition, higher fill factor (FF) and conversion efficiency were also observed for the sample with Te pre-doping. These indicate that the crystalline qualities of the upper TJ, composed of a p-GaAs/n-InGaP TJ, and the InGaP top cell were improved by using the Te pre-doping method.

  17. Reduction of critical current density for out-of-plane mode oscillation in a mag-flip spin torque oscillator using highly spin-polarized Co2Fe(Ga0.5Ge0.5) spin injection layer

    NASA Astrophysics Data System (ADS)

    Bosu, S.; Sepehri-Amin, H.; Sakuraba, Y.; Hayashi, M.; Abert, C.; Suess, D.; Schrefl, T.; Hono, K.

    2016-02-01

    We study spin torque oscillators comprised of a perpendicular spin injection layer (SIL) and a planar field generating layer to reveal the influence of the spin polarization of SIL material on the critical current density, JC, to induce microwave oscillation. Two systems with different SIL are compared: one with a highly spin-polarized Heusler alloy, Co2Fe(Ga0.5Ge0.5) (CFGG), and the other a prototypical Fe2Co alloy. Cross sectional scanning transmission electron microscopy observations show the B2-ordered structure in a 3-nm-thick CFGG SIL, a prerequisite for obtaining half-metallic transport properties. Current induced microwave oscillations are found at frequencies of ˜15 GHz for both systems. However, the current needed to cause the oscillations is ˜50% smaller for films with the CFGG SIL compared to those of the Fe2Co SIL. These results are in accordance with micromagnetic simulations that include spin accumulation at the SIL.

  18. Performance improvement for epitaxially grown SiGe on Si solar cell using a compositionally graded SiGe base

    NASA Astrophysics Data System (ADS)

    Li, Dun; Zhao, Xin; Wang, Li; Conrad, Brianna; Soeriyadi, Anastasia; Lochtefeld, Anthony; Gerger, Andrew; Perez-Wurfl, Ivan; Barnett, Allen

    2016-12-01

    Silicon germanium (SiGe) is a material with high mobility and relatively low bandgap making it an attractive candidate for the bottom subcell in a III-V tandem solar cell grown on silicon (Si) substrate. This paper reports on the performance improvement of an epitaxially grown SiGe on Si solar cell by growing a higher Ge composition SiGe layer in the base. The purpose of growing a higher Ge composition SiGe layer in the base is to improve the light absorption. The first iteration of this structure was an Si0.18Ge0.82 solar cell fabricated with a 1 μm thick Si0.12Ge0.88 layer in the base. This solar cell had a lower efficiency compared with the reference solar cell without the Si0.12Ge0.88 layer. One of the main reasons for the lower efficiency is believed to be the high threading dislocation density (TDD) caused by the abrupt change of lattice constant between Si0.18Ge0.82 and Si0.12Ge0.88 in the base. In order to reduce the TDD, the second iteration of the structure was fabricated with a compositionally graded SiGe base. With the new structure, an SiGe on Si solar cell with an efficiency of 3.1%, when filtered by a GaAs0.79P0.21 top cell, was fabricated. The Ge composition in the base of this solar cell gradually increased from 82% to 85% and then decreased again to 82%. The developed SiGe solar cell with graded base provides more flexibility for a highly efficient GaAsP/SiGe dual junction solar cell grown on an Si substrate.

  19. Ion-assisted laser deposition of intermediate layers for YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} thin film growth on polycrystalline and amorphous substrates

    SciTech Connect

    Reade, R.P.

    1993-11-01

    The growth of YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} (YBCO) high-temperature superconductor thin films has largely been limited to deposition on single-crystal substrates to date. In order to expand the range of potential applications, growth on polycrystalline and amorphous substrates is desirable. In particular, the deposition of YBCO thin films with high critical current densities on polycrystalline metal alloys would allow the manufacture of superconducting tapes. However, it is shown that it is not possible to grow YBCO thin films directly on this type of substrate due to chemical and structural incompatibility. This work investigates the use of a yttria-stabilized zirconia (YSZ) intermediate layer to address this problem. An ion-assisted pulsed-laser deposition process is developed to provide control of orientation during the growth of the YSZ layers. The important properties of YBCO and YSZ are summarized and the status of research on thin film growth of these materials is reviewed. An overview of the pulsed-laser deposition (PLD) technique is presented. The use of ion-assisted deposition techniques to control thin film properties is discussed.

  20. Study of low-defect and strain-relaxed GeSn growth via reduced pressure CVD in H2 and N2 carrier gas

    NASA Astrophysics Data System (ADS)

    Margetis, J.; Mosleh, A.; Al-Kabi, S.; Ghetmiri, S. A.; Du, W.; Dou, W.; Benamara, M.; Li, B.; Mortazavi, M.; Naseem, H. A.; Yu, S.-Q.; Tolle, J.

    2017-04-01

    High quality, thick (up to 1.1 μm), strain relaxed GeSn alloys were grown on Ge-buffered Si (1 0 0) in an ASM Epsilon® chemical vapor deposition system using SnCl4 and low-cost commercial GeH4 precursors. The significance of surface chemistry in regards to growth rate and Sn-incorporation is discussed by comparing growth kinetics data in H2 and N2 carrier gas. The role of carrier gas is also explored in the suppression of Sn surface segregation and evolution of layer composition and strain profiles via secondary ion mass spectrometry and X-ray diffraction. Transmission electron microscopy revealed the spontaneous compositional splitting and formation of a thin intermediate layer in which dislocations are pinned. This intermediate layer enables the growth of a thick, strain relaxed, and defect-free epitaxial layer on its top. Last, we present photoluminescence results which indicate that both N2 and H2 growth methods produce optoelectronic device quality material.

  1. New approach to the growth of low dislocation relaxed SiGe material

    NASA Astrophysics Data System (ADS)

    Powell, A. R.; Iyer, S. S.; LeGoues, F. K.

    1994-04-01

    In this growth process a new strain relief mechanism operates, whereby the SiGe epitaxial layer relaxes without the generation of threading dislocations within the SiGe layer. This is achieved by depositing SiGe on an ultrathin silicon on insulator (SOI) substrate with a superficial silicon thickness less than the SiGe layer thickness. Initially, the thin Si layer is put under tension due to an equalization of the strain between the Si and SiGe layers. Thereafter, the strain created in the thin Si layer relaxes by plastic deformation. Since the dislocations are formed and glide in the thin Si layer, no threading dislocation is ever introduced in to the upper SiGe material, which appeared dislocation free to the limit of the cross sectional transmission electron microscopy analysis. We thus have a method for producing very low dislocation, relaxes SiGe films with the additional benefit of an SOI substrate.

  2. Interfacial processes in the Pd/a-Ge:H system

    NASA Astrophysics Data System (ADS)

    Edelman, F.; Cytermann, C.; Brener, R.; Eizenberg, M.; Weil, R.; Beyer, W.

    1993-06-01

    The kinetics of phase transformation has been studied in a two-layer structure of Pd/a-Ge:H after vacuum annealing at temperatures from 180 to 500°C. The a-Ge:H was deposited at 250°C on both c-Si and cleaved NaCl substrates in an RF glow discharge from a GeH 4/H 2 mixture. It was found that, similarly to the Pd/c-Ge and the Pd/a-Ge (e-gun deposited) systems, in the case of 0.15-0.2 μm Pd/0.6-1.0 μm a-Ge:H interfacial germanides formed first through the production of Pd 2Ge (plus a small amount of PdGe), and then PdGe was produced. The growth of both compounds was found to be diffusion-controlled. The nonreacted a-Ge:H layer beneath the germanide overlayer crystallized at 400-500°C. A reverse sequence of germanides formation was revealed in the case of 50 nm Pd/30 nm a-Ge:H, studied by in situ heat treatment in the TEM utilizing non-supported samples. The first germanide detected was PdGe and then, as a result of PdGe and Ge reaction or the PdGe decomposition, Pd 2Ge formed. The temperature dependence of the incubation time before the first ˜ 10 nm PdGe grains formed, followed an Arrhenius curve with an activation energy of 1.45 eV.

  3. Solid state synthesis of Mn5Ge3 in Ge/Ag/Mn trilayers: Structural and magnetic studies

    NASA Astrophysics Data System (ADS)

    Myagkov, V. G.; Bykova, L. E.; Matsynin, A. A.; Volochaev, M. N.; Zhigalov, V. S.; Tambasov, I. A.; Mikhlin, Yu L.; Velikanov, D. A.; Bondarenko, G. N.

    2017-02-01

    The thin-film solid-state reaction between elemental Ge and Mn across chemically inert Ag layers with thicknesses of (0, 0.3, 1 and 2.2 μm) in Ge/Ag/Mn trilayers was studied for the first time. The initial samples were annealed at temperatures between 50 and 500 °C at 50 °C intervals for 1 h. The initiation temperature of the reaction for Ge/Mn (without a Ag barrier layer) was 120 °C and increased slightly up to 250 °C when the Ag barrier layer thickness increased up to 2.2 μm. In spite of the Ag layer, only the ferromagnetic Mn5Ge3 compound and the Nowotny phase were observed in the initial stage of the reaction after annealing at 500 °C. The cross-sectional studies show that during Mn5Ge3 formation the Ge is the sole diffusing species. The magnetic and cross-sectional transmission electron microscopy (TEM) studies show an almost complete transfer of Ge atoms from the Ge film, via a 2.2 μm Ag barrier layer, into the Mn layer. We attribute the driving force of the long-range transfer to the long-range chemical interactions between reacting Mn and Ge atoms.

  4. The effect of the interlayer element on the exfoliation of layered Mo2AC (A = Al, Si, P, Ga, Ge, As or In) MAX phases into two-dimensional Mo2C nanosheets

    PubMed Central

    Khazaei, Mohammad; Arai, Masao; Sasaki, Taizo; Estili, Mehdi; Sakka, Yoshio

    2014-01-01

    The experimental exfoliation of layered, ternary transition-metal carbide and nitride compounds, known as MAX phases, into two-dimensional (2D) nanosheets, is a great development in the synthesis of novel low-dimensional inorganic systems. Among the MAX phases, Mo-containing ones might be considered as the source for obtaining Mo2C nanosheets with potentially unique properties, if they could be exfoliated. Here, by using a set of first-principles calculations, we discuss the effect of the interlayer ‘A’ element on the exfoliation of Mo2AC (A = Al, Si, P, Ga, Ge, As or In) MAX phases into the 2D Mo2C nanosheets. Based on the calculated exfoliation energies and the elastic constants, we propose that Mo2InC with the lowest exfoliation energy and the highest elastic constant anisotropy between C11 and C33 might be a suitable compound for exfoliation into 2D Mo2C nanosheets. PMID:27877635

  5. RE2MAl6Si4 (RE = Gd, Tb, Dy; M = Au, Pt): layered quaternary intermetallics featuring CaAl2Si2-type and YNiAl4Ge2-type slabs grown from aluminum flux.

    PubMed

    Latturner, Susan E; Bilc, Daniel; Mahanti, S D; Kanatzidis, Mercouri G

    2003-12-01

    Six new intermetallic aluminum silicides--Gd(2)PtAl(6)Si(4), Gd(2)AuAl(6)Si(4), Tb(2)PtAl(6)Si(4), Tb(2)AuAl(6)Si(4), Dy(2)PtAl(6)Si(4), and Dy(2)AuAl(6)Si(4)--have been obtained from reactions carried out in aluminum flux. The structure of these compounds was determined by single-crystal X-ray diffraction. They form in space group Rthremacr;m with cell constants of a = 4.1623(3) A and c = 51.048(5) A for the Gd(2)PtAl(6)Si(4) compound. The crystal structure is comprised of hexagonal nets of rare earth atoms alternating with two kinds of layers that have been observed in other multinary aluminide intermetallic compounds (CaAl(2)Si(2) and YNiAl(4)Ge(2)). All six RE(2)MAl(6)Si(4) compounds show antiferromagnetic transitions at low temperatures (T(N) < 20 K); magnetization studies of the Dy compounds show metamagnetic behavior with reorientation of spins at 6000 G. Band structure calculations indicate that the AlSi puckered hexagonal sheets in this structure are electronically distinct from the other surrounding structural motifs.

  6. Crystal orientation dependence of current-perpendicular-to-plane giant magnetoresistance of pseudo spin-valves with epitaxial Co{sub 2}Fe(Ge{sub 0.5}Ga{sub 0.5}) Heusler alloy layers

    SciTech Connect

    Chen, Jiamin; Hono, K.; Li, Songtian; Furubayashi, T. Takahashi, Y. K.

    2014-06-21

    The magnetoresistive (MR) properties of Co{sub 2}Fe(Ge{sub 0.5}Ga{sub 0.5}) (CFGG) Heusler alloy-based current-perpendicular-to-plane giant magnetoresistance pseudo-spin-valves (PSVs) are investigated. The PSV films are epitaxially grown on a sapphire (112{sup ¯}0) substrate with an Ag or Cu spacer layer, and their magnetoresistive properties are compared with those of PSV grown on MgO(001) substrates. For substrates with an Ag spacer, the PSV with the (001)[110]{sub CFGG}//(001)[010]{sub Ag} interface grown on MgO(001) exhibits a higher MR output compared with the (110)[001]{sub CFGG}//(111)[11{sup ¯}0]{sub Ag} interface grown on sapphire (112{sup ¯}0). In contrast, a higher MR output is obtained using a Cu spacer with the (110)[001]{sub CFGG}//(111)[11{sup ¯}0]{sub Cu} interface. These results demonstrate that the MR outputs depend upon the crystal orientation at the interface, and that interfaces with a small misfit tend to exhibit a larger MR output. This indicates the influence of crystal orientation as well as lattice mismatch upon the interfacial spin scattering asymmetry.

  7. Similarity of Stranski-Krastanow growth of Ge/Si and SiGe/Si (001)

    SciTech Connect

    Norris, D. J.; Qiu, Y.; Walther, T.; Dobbie, A.; Myronov, M.

    2014-01-07

    This study investigates the onset of islanding (Stranski-Krastanow transition) in strained pure germanium (Ge) and dilute silicon-germanium (SiGe) alloy layers grown by chemical vapour deposition on Si(001) substrates. Integration of compositional profiles is compared to a novel method for quantification of X-ray maps acquired in cross-sectional scanning transmission electron microscopy, together with simulations of surface segregation of Ge. We show that Si{sub 1−x}Ge{sub x} alloys for germanium concentrations x ≤ 0.27 grow two-dimensionally and stay flat up to considerable layer thicknesses, while layers with concentrations in the range 0.28 < x ≤ 1 form islands after deposition of ∼3.0/x monolayers (=quarter unit cells in the diamond lattice, ML). The uncertainty in the amount of deposited material for pure Ge is ±(0.2–0.3) ML. Modelling shows that of the amount of germanium deposited, 0.7 ML segregate towards the free surface so that only ∼2.3/x ML are directly incorporated in the layer within a few nanometres, in good agreement with our measurements. For pure Ge (x = 1), this thickness is smaller than most values quoted in the literature, which we attribute to the high sensitivity of our method to fractional monolayer changes in the effective chemical width of such thin layers.

  8. Determination of Near-surface Ge and Si Site Occupation in Ge/Si(100)

    NASA Astrophysics Data System (ADS)

    Leskovar, M.; Meng, S.; Hessinger, Uwe; Olmstead, Marjorie A.

    1996-03-01

    When Ge is deposited on Si(001), the larger size and lower surface energy of the Ge should impede intermixing. However, the strain induced by the surface reconstruction has been predicted to result in a preference for Si in some near-surface sites. The specifics of the predicted site segregation depend on whether an empirical or ab-initio potential is used. We have investigated the near-surface site occupation of well-annealed <= 2 ML Ge films on single-domain Si(100)4 deg 2x1 surfaces using X-ray photoelectron diffraction (XPD) and low energy electron diffraction (LEED). Sub-monolayer Ge deposition at 500 degC results in the Ge residing in the top layer (no forward scattering in Ge XPD) while the LEED pattern remains mostly 2x1. This implies Ge exchange with the surface Si layer, followed by transport of the displaced Si to preserve the dimer row orientation relative to that of the steps. At higher temperatures and/or coverages some Si-Ge intermixing may be observed.

  9. Properties of slow traps of ALD Al2O3/GeOx/Ge nMOSFETs with plasma post oxidation

    NASA Astrophysics Data System (ADS)

    Ke, M.; Yu, X.; Chang, C.; Takenaka, M.; Takagi, S.

    2016-07-01

    The realization of Ge gate stacks with a small amount of slow trap density as well as thin equivalent oxide thickness and low interface state density (Dit) is a crucial issue for Ge CMOS. In this study, we examine the properties of slow traps, particularly the location of slow traps, of Al2O3/GeOx/n-Ge and HfO2/Al2O3/GeOx/n-Ge MOS interfaces with changing the process and structural parameters, formed by atomic layer deposition (ALD) of Al2O3 and HfO2/Al2O3 combined with plasma post oxidation. It is found that the slow traps can locate in the GeOx interfacial layer, not in the ALD Al2O3 layer. Furthermore, we study the time dependence of channel currents in the Ge n-MOSFETs with 5-nm-thick Al2O3/GeOx/Ge gate stacks, with changing the thickness of GeOx, in order to further clarify the position of slow traps. The time dependence of the current drift and the effective time constant of slow traps do not change among the MOSFETs with the different thickness GeOx, demonstrating that the slow traps mainly exist near the interfaces between Ge and GeOx.

  10. Tensile strain in Ge membranes induced by SiGe nanostressors

    NASA Astrophysics Data System (ADS)

    Barget, Michael R.; Lodari, Mario; Borriello, Mauro; Mondiali, Valeria; Chrastina, Daniel; Bollani, Monica; Bonera, Emiliano

    2016-09-01

    The monolithic integration of photonic functionality into silicon microtechnology is widely advanced. Yet, there is no final solution for the realization of a light source compatible with the prevailing complementary metal-oxide-semiconductor technology. A lot of research effort focuses on germanium (Ge) on silicon (Si) heterostructures and tensile strain application to Ge is accepted as one feasible route to make Ge an efficient light emitter. Prior work has documented the special suitability of Ge membranes to reach the high tensile strain. We present a top-down approach for the creation of SiGe stressors on Ge micro-bridges and compare the obtained strain to the case of an attached bulk-like Ge layer. We could show that the Ge influenced by a SiGe stressor is under tensile strain; absolute strain values are of the order of 0.7% for both micro-bridge and bulk. The relative strain induced by the nanostructures in the micro-bridge is 1.3% due to the high sharing of elastic energy between nanostructures and bridges.

  11. 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.

  12. Fabrication of GeSn-multiple quantum wells by overgrowth of Sn on Ge by using molecular beam epitaxy

    SciTech Connect

    Oliveira, F.; Fischer, I. A.; Schulze, J.; Benedetti, A.; Zaumseil, P.; Cerqueira, M. F.; Vasilevskiy, M. I.; Stefanov, S.; Chiussi, S.

    2015-12-28

    We report on the fabrication and structural characterization of epitaxially grown ultra-thin layers of Sn on Ge virtual substrates (Si buffer layer overgrown by a 50 nm thick Ge epilayer followed by an annealing step). Samples with 1 to 5 monolayers of Sn on Ge virtual substrates were grown using solid source molecular beam epitaxy and characterized by atomic force microscopy. We determined the critical thickness at which the transition from two-dimensional to three-dimensional growth occurs. This transition is due to the large lattice mismatch between Ge and Sn (≈14.7%). By depositing Ge on top of Sn layers, which have thicknesses at or just below the critical thickness, we were able to fabricate ultra-narrow GeSn multi-quantum-well structures that are fully embedded in Ge. We report results on samples with one and ten GeSn wells separated by 5 and 10 nm thick Ge spacer layers that were characterized by high resolution transmission electron microscopy and X-ray diffraction. We discuss the structure and material intermixing observed in the samples.

  13. Growth mechanism of Ge-doped CZTSSe thin film by sputtering method and solar cells.

    PubMed

    Li, Jinze; Shen, Honglie; Chen, Jieyi; Li, Yufang; Yang, Jiale

    2016-10-19

    Ge-doped CZTSSe thin films were obtained by covering a thin Ge layer on CZTS precursors, followed by a selenization process. The effect of the Ge layer thickness on the morphologies and structural properties of Ge-doped CZTSSe thin films were studied. It was found that Ge doping could promote grain growth to form a compact thin film. The lattice shrank in the top-half of the film due to the smaller atomic radius of Ge, leading to the formation of tensile stress. According to thermodynamic analysis, Sn was easier to be selenized than Ge. Thus, Ge preferred to remain on the surface and increased the surface roughness when the Ge layer was thin. CZTSe was easier to form than Ge-doped CZTSe, which caused difficulty in Ge doping. These results offered a theoretical and experimental guide for preparing Ge-doped CZTSSe thin films for the potential applications in low-cost solar cells. With a 10 nm Ge layer on the top of the precursor, the conversion efficiency of the solar cell improved to 5.38% with an open-circuit voltage of 403 mV, a short-circuit current density of 28.51 mA cm(-2) and a fill factor of 46.83% after Ge doping.

  14. Dysprosium-induced nanowires on Ge(001)

    NASA Astrophysics Data System (ADS)

    Lochner, M.; Bienert, R.; Kürpick, U.; Matzdorf, R.

    2015-07-01

    Dysprosium-induced, self-assembled nanowires on Ge(001) were studied by scanning tunneling microscopy (STM) and low energy electron diffraction (LEED). For this, submonolayers of dysprosium were deposited on Ge(001). After subsequent annealing, the surface shows a variety of structures as different kinds of wires with varying thickness, larger islands and surface defects like missing dimers and vacancy rows perpendicular to the Ge(001)-dimer rows. The structures are forming on all intact Ge(001)-terraces. In contrast to dysprosium on Si(001), on Ge(001) no wetting layer is found. In this work we focus on the thinnest nanowires, which have a width of four times the Ge(001)-lattice constant. STM topographies of the unoccupied states show a twofold superstructure on the wires. In contrast, topographies of the occupied states show that the structure of the wires is less regular. They exhibit elevations with distances, which are multiples higher than two of the Ge(001)-surface lattice constant. Density of states mapping reveals a cell structure of the nanowires. Possible explanations for this behaviour are discussed.

  15. Collectivity of light Ge and As isotopes

    NASA Astrophysics Data System (ADS)

    Corsi, A.; Delaroche, J.-P.; Obertelli, A.; Baugher, T.; Bazin, D.; Boissinot, S.; Flavigny, F.; Gade, A.; Girod, M.; Glasmacher, T.; Grinyer, G. F.; Korten, W.; Libert, J.; Ljungvall, J.; McDaniel, S.; Ratkiewicz, A.; Signoracci, A.; Stroberg, R.; Sulignano, B.; Weisshaar, D.

    2013-10-01

    Background: The self-conjugate nuclei of the A˜70 mass region display rapid shape evolution over isotopic or isotonic chains. Shape coexistence has been observed in Se and Kr isotopes reflecting the existence of deformed subshell gaps corresponding to different shell configurations. As and Ge isotopes are located halfway between such deformed nuclei and the Z=28 shell closure.Purpose: The present work aims at clarifying the low-lying spectroscopy of 66Ge and 67As, and providing a better insight into the evolution of collectivity in light even-even Ge and even-odd As isotopes.Methods: We investigate the low-lying levels and collectivity of the neutron deficient 67As and 66Ge through intermediate-energy Coulomb excitation, inelastic scattering, and proton knockout measurements. The experiment was performed using a cocktail beam of 68Se, 67As, and 66Ge nuclei at an energy of 70-80 MeV/nucleon. Spectroscopic properties of the low-lying states are compared to those calculated via shell model with the JUN45 interaction and beyond-mean-field calculations with the five-dimensional collective Hamiltonian method implemented using the Gogny D1S interaction. The structure evolution of the lower-mass Ge and As isotopes is discussed.Results: Reduced electric quadrupole transition probabilities B(E2) have been extracted from the Coulomb-excitation cross sections measured in 66Ge and 67As. The value obtained for the B(E2;01+→21+) in 66Ge is in agreement with a recent measurement, ruling out the existence of a minimum at N=34 in the B(E2) systematics as previously observed. New transitions have been found in 67As and were assigned to the decay of low-lying negative-parity states.

  16. Electrical characterization of SiGeSn grown on Ge substrate using ultra high vacuum chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Ahoujja, Mo; Kang, S.; Hamilton, M.; Yeo, Y. K.; Kouvetakis, J.; Menendez, J.

    2012-02-01

    There has been recently considerable interest in growing SiyGe1-x-ySnx alloys for the fabrication of photonic devices that could be integrated with Si technologies. We report temperature dependent Hall (TDH) measurements of the hole concentration and mobility from high quality p-type doped Si0.08Ge0.90Sn0.02 layers grown on p-type doped Ge substrates using ultra high vacuum chemical vapor deposition. The TDH measurements show the hole sheet density remains constant at low temperatures before slightly decreasing and dipping at ˜ 125 K. It then exponentially increases with temperature due to the activation of shallow acceptors. At temperatures above ˜ 450 K, the hole sheet density increases sharply indicating the onset of intrinsic conduction in the SiGeSn and/or Ge layers. To extract the electrical properties of the SiGeSn layer alone, a parametric fit using a multi layer conducting model is applied to the measured hole concentration and mobility data. The analysis yields boron and gallium doping concentrations of 3x10^17 cm-3 and 1x10^18 cm-3 with activation energies of 10 meV and 11 meV for the SiGeSn layer and Ge substrate, respectively. Furthermore, a temperature independent hole sheet concentration of ˜5x10^15 cm-2 with a mobility of ˜250 cm^2/Vs, which is believed to be due to an interfacial layer between the SiGeSn layer and the Ge substrate, is also determined.

  17. High frequency performance of Si(1-x)Ge(x)/Si(1-y)Ge(y)/Si(1-x)Ge(x) HBTs

    NASA Technical Reports Server (NTRS)

    Rosenfeld, D.; Alterovitz, S. A.

    1993-01-01

    The results of a theoretical study of the performance of high speed SiGe HBTs is presented. The study includes a group of SiGe HBTs in which the Ge concentration in the base is 20 percent higher than that in the emitter and collector (i.e., y = x + 0.2). It is shown that the composition dependences of f(T) and the f(max) are nonmonotonic. As the Ge composition in the emitter and collector layers is increased, f(T) and f(max) first decrease, then remain constant and finally increase to attain their highest values.

  18. Ge interactions on HfO{sub 2} surfaces and kinetically driven patterning of Ge nanocrystals on HfO{sub 2}

    SciTech Connect

    Stanley, Scott K.; Joshi, Sachin V.; Banerjee, Sanjay K.; Ekerdt, John G.

    2006-01-15

    Germanium interactions are studied on HfO{sub 2} surfaces, which are prepared through physical vapor deposition (PVD) and by atomic layer deposition. X-ray photoelectron spectroscopy and temperature-programed desorption are used to follow the reactions of germanium on HfO{sub 2}. Germanium chemical vapor deposition at 870 K on HfO{sub 2} produces a GeO{sub x} adhesion layer, followed by growth of semiconducting Ge{sup 0}. PVD of 0.7 ML Ge (accomplished by thermally cracking GeH{sub 4} over a hot filament) also produces an initial GeO{sub x} layer, which is stable up to 800 K. PVD above 2.0 ML deposits semiconducting Ge{sup 0}. Temperature programed desorption experiments of {approx}1.0 ML Ge from HfO{sub 2} at 400-1100 K show GeH{sub 4} desorption below 600 K and GeO desorption above 850 K. These results are compared to Ge on SiO{sub 2} where GeO desorption is seen at 550 K. Exploiting the different reactivity of Ge on HfO{sub 2} and SiO{sub 2} allows a kinetically driven patterning scheme for high-density Ge nanoparticle growth on HfO{sub 2} surfaces that is demonstrated.

  19. Unexpected Ge-Ge Contacts in the Two-Dimensional Ge4 Se3 Te Phase and Analysis of Their Chemical Cause with the Density of Energy (DOE) Function.

    PubMed

    Küpers, Michael; Konze, Philipp M; Maintz, Stefan; Steinberg, Simon; Mio, Antonio M; Cojocaru-Mirédin, Oana; Zhu, Min; Müller, Merlin; Luysberg, Martina; Mayer, Joachim; Wuttig, Matthias; Dronskowski, Richard

    2017-02-14

    A hexagonal phase in the ternary Ge-Se-Te system with an approximate composition of GeSe0.75 Te0.25 has been known since the 1960s but its structure has remained unknown. We have succeeded in growing single crystals by chemical transport as a prerequisite to solve and refine the Ge4 Se3 Te structure. It consists of layers that are held together by van der Waals type weak chalcogenide-chalcogenide interactions but also display unexpected Ge-Ge contacts, as confirmed by electron microscopy analysis. The nature of the electronic structure of Ge4 Se3 Te was characterized by chemical bonding analysis, in particular by the newly introduced density of energy (DOE) function. The Ge-Ge bonding interactions serve to hold electrons that would otherwise go into antibonding Ge-Te contacts.

  20. Material gain engineering in GeSn/Ge quantum wells integrated with an Si platform

    PubMed Central

    Mączko, H. S.; Kudrawiec, R.; Gladysiewicz, M.

    2016-01-01

    It is shown that compressively strained Ge1−xSnx/Ge quantum wells (QWs) grown on a Ge substrate with 0.1 ≤ x ≤ 0.2 and width of 8 nm ≤ d ≤ 14 nm are a very promising gain medium for lasers integrated with an Si platform. Such QWs are type-I QWs with a direct bandgap and positive transverse electric mode of material gain, i.e. the modal gain. The electronic band structure near the center of Brillouin zone has been calculated for various Ge1−xSnx/Ge QWs with use of the 8-band kp Hamiltonian. To calculate the material gain for these QWs, occupation of the L valley in Ge barriers has been taken into account. It is clearly shown that this occupation has a lot of influence on the material gain in the QWs with low Sn concentrations (Sn < 15%) and is less important for QWs with larger Sn concentration (Sn > 15%). However, for QWs with Sn > 20% the critical thickness of a GeSn layer deposited on a Ge substrate starts to play an important role. Reduction in the QW width shifts up the ground electron subband in the QW and increases occupation of the L valley in the barriers instead of the Γ valley in the QW region. PMID:27686056

  1. 70 °C synthesis of high-Sn content (25%) GeSn on insulator by Sn-induced crystallization of amorphous Ge

    SciTech Connect

    Toko, K. Oya, N.; Suemasu, T.; Saitoh, N.; Yoshizawa, N.

    2015-02-23

    Polycrystalline GeSn thin films are fabricated on insulating substrates at low temperatures by using Sn-induced crystallization of amorphous Ge (a-Ge). The Sn layer stacked on the a-Ge layer (100-nm thickness each) had two roles: lowering the crystallization temperature of a-Ge and composing GeSn. Slow annealing at an extremely low temperature of 70 °C allowed for a large-grained (350 nm) GeSn layer with a lattice constant of 0.590 nm, corresponding to a Sn composition exceeding 25%. The present investigation paves the way for advanced electronic optical devices integrated on a flexible plastic substrate as well as on a Si platform.

  2. TiO2/GeOxNy stacked gate dielectrics for Ge-MOSFETs

    NASA Astrophysics Data System (ADS)

    Bera, M. K.; Mahata, C.; Chakraborty, A. K.; Nandi, S. K.; Tiwari, Jitendra N.; Hung, Jui-Yi; Maiti, C. K.

    2007-12-01

    In this work, we present the results of physical and electrical characterization of Ti-based high-k gate dielectrics on Ge substrates. Titanium tetrakis iso- propoxide (TTIP) was used as the organometallic source for the deposition of ultra-thin TiO2 films on p-Ge (1 0 0) at low temperature (<200 °C) by plasma enhanced chemical vapor deposition (PECVD) technique in a microwave (700 W, 2.45 GHz) plasma cavity discharge system at a pressure of ~65 Pa. The presence of an ultra-thin lossy GeO2 interfacial layer between the deposited high-k film and the substrate, results in frequency-dependent capacitance-voltage (C-V) characteristics in strong accumulation and a high interface state density (~1013 cm-2 eV-1). To improve the electrical properties, nitrogen engineering has been employed to convert the lossy GeO2 interfacial layer to its oxynitride, thus forming TiO2/GeOxNy/Ge stacked-gate structure with improved interface/electrical properties. Different N sources, such as NO, NH3 and NO/NH3, have been used for nitrogen engineering. XPS and Raman spectroscopy analyses have been used for surface morphological study. Electrical properties, such as gate leakage current density, interface state density, charge trapping, flatband voltage shift, etc, have been studied in detail for TiO2/GeOxNy/Ge MIS capacitors using the current-voltage (I-V), capacitance-voltage (C-V), conductance-voltage (G-V) and stress (both constant voltage and current) measurements. Although a significant improvement in electrical characteristics has been observed after nitridation in general, the formation of the interfacial GeOxNy layer, obtained from NO-plasma nitridation, is found to provide the maximum improvement among all the nitridation techniques used in this study. It is shown that the insertion of an ultra-thin oxynitride (GeOxNy) interfacial layer is advantageous for producing gate-quality TiO2 high-k dielectric stacks on Ge substrates.

  3. Spontaneous Growth and Chemical Reduction Ability of Ge Nanoparticles

    PubMed Central

    Liu, Jun; Liang, Changhao; Tian, Zhenfei; Zhang, Shuyuan; Shao, Guosheng

    2013-01-01

    Forming colloidal solutions containing semiconductor quantum-sized nanoparticles (NPs) with clean surface has been a long-standing scientific challenge. In this contribution, we report a “top-down” method for the fabrication of Ge NPs by laser ablation of a Ge target in deionized water without adding any stabilizing reagents. The initial Ge NPs in amorphous structure showed spontaneous growth behavior by aging Ge colloids in deionized water under ambient temperature, which gradually evolved into a metastable tetragonal structure as an intermediate phase and then transformed into the stable cubic structure, being consistent with the Ostwald's rule of stages for the growth in a metastable system. The laser-induced initial Ge NPs demonstrate a unique and prominent size-dependent chemical reductive ability, which is evidenced by the rapid degradation of organic molecules such as chlorinated aromatic compounds, organic dyes, and reduction of heavy metal Cr(VI) ions.

  4. TEM studies of Ge nanocrystal formation in PECVD grown SiO2:Ge/SiO2 multilayers

    NASA Astrophysics Data System (ADS)

    Agan, S.; Dana, A.; Aydinli, A.

    2006-06-01

    We investigate the effect of annealing on the Ge nanocrystal formation in multilayered germanosilicate-oxide films grown on Si substrates by plasma enhanced chemical vapour deposition (PECVD). The multilayered samples were annealed at temperatures ranging from 750 to 900 °C for 5 min under nitrogen atmosphere. The onset of formation of Ge nanocrystals, at 750 °C, can be observed via high resolution TEM micrographs. The diameters of Ge nanocrystals were observed to be between 5 and 14 nm. As the annealing temperature is raised to 850 °C, a second layer of Ge nanocrystals forms next to the original precipitation band, positioning itself closer to the substrate SiO2 interface. High resolution cross section TEM images, electron diffraction and electron energy-loss spectroscopy as well as energy-dispersive x-ray analysis (EDAX) data all indicate that Ge nanocrystals are present in each layer.

  5. A GaAs metalorganic vapor phase epitaxy growth process to reduce Ge outdiffusion from the Ge substrate

    SciTech Connect

    Galiana, B.; Rey-Stolle, I.; Algora, C.

    2008-04-14

    A barrier based on GaAs for controlling the Ge out diffusion has been developed by metalorganic vapor phase epitaxy. It is based on a thin GaAs layer (50 nm) grown at a low temperature ({approx_equal}500 deg. C) on top of a predeposition layer, showing that GaAs prevents the Ge diffusing when it is grown at a low temperature. Additionally, two different predeposition monolayers have been compared, concluding that when the Ga is deposited first, the diffusions across the GaAs/Ge heterointerface decrease.

  6. Temperature spectra of conductance of Ge/Si p-i-n structures with Ge quantum dots

    NASA Astrophysics Data System (ADS)

    Izhnin, Ihor I.; Fitsych, Olena I.; Pishchagin, Anton A.; Kokhanenko, Andrei P.; Voitsekhovskii, Alexander V.; Dzyadukh, Stanislav M.; Nikiforov, Alexander I.

    2017-02-01

    This work presents results of investigation of Ge/Si p-i-n structures with Ge quantum dots in the i-region by the method of admittance spectroscopy. The structures contain multiple layers with Ge quantum dots separated by thin 5 nm layers of Si in the intrinsic region. Two peaks are observed on the temperature dependences of conductance of the investigated heterostructures. It is revealed that the second peak is broadened and corresponds to a system of closely lying energy levels.

  7. Metastability and relaxation in tensile SiGe on Ge(001) virtual substrates

    SciTech Connect

    Frigerio, Jacopo; Lodari, Mario; Chrastina, Daniel Mondiali, Valeria; Isella, Giovanni; Bollani, Monica

    2014-09-21

    We systematically study the heteroepitaxy of SiGe alloys on Ge virtual substrates in order to understand strain relaxation processes and maximize the tensile strain in the SiGe layer. The degree of relaxation is measured by high-resolution x-ray diffraction, and surface morphology is characterized by atomic force microscopy. The results are analyzed in terms of a numerical model, which considers dislocation nucleation, multiplication, thermally activated glide, and strain-dependent blocking. Relaxation is found to be sensitive to growth rate and substrate temperature as well as epilayer misfit and thickness, and growth parameters are found which allow a SiGe film with over 4 GPa of tensile stress to be obtained.

  8. Antimony segregation in Ge and formation of n-type selectively doped Ge films in molecular beam epitaxy

    SciTech Connect

    Yurasov, D. V. Antonov, A. V.; Drozdov, M. N.; Schmagin, V. B.; Novikov, A. V.; Spirin, K. E.

    2015-10-14

    Antimony segregation in Ge(001) films grown by molecular beam epitaxy was studied. A quantitative dependence of the Sb segregation ratio in Ge on growth temperature was revealed experimentally and modeled theoretically taking into account both the terrace-mediated and step-edge-mediated segregation mechanisms. A nearly 5-orders-of-magnitude increase in the Sb segregation ratio in a relatively small temperature range of 180–350 °C was obtained, which allowed to form Ge:Sb doped layers with abrupt boundaries and high crystalline quality using the temperature switching method that was proposed earlier for Si-based structures. This technique was employed for fabrication of different kinds of n-type Ge structures which can be useful for practical applications like heavily doped n{sup +}-Ge films or δ-doped layers. Estimation of the doping profiles sharpness yielded the values of 2–5 nm per decade for the concentration gradient at the leading edge and 2–3 nm for the full-width-half-maximum of the Ge:Sb δ-layers. Electrical characterization of grown Ge:Sb structures revealed nearly full electrical activation of Sb atoms and the two-dimensional nature of charge carrier transport in δ-layers.

  9. Structure of a passivated Ge surface prepared from aqueous solution.

    SciTech Connect

    Lyman, P. F.; Sakata, O.; Marasco, D, L.; Lee, T.-L.; Breneman, K. D.; Keane, D. T.; Bedzyk, M. J.; Materials Science Division; Northwestern Univ.; Univ. of Wisconsin at Milwaukee

    2000-08-10

    The structure of a passivating sulfide layer on Ge(001) was studied using X-ray standing waves and X-ray fluorescence. The sulfide layer was formed by reacting clean Ge substrates in (NH{sub 4}){sub 2}S solutions of various concentrations at 80{sup o}C. For each treatment, a sulfide layer containing approximately two to three monolayers (ML) of S was formed on the surface, and an ordered structure was found at the interface that contained approximately 0.4 ML of S. Our results suggest the rapid formation of a glassy GeS{sub x} layer containing 1.5-2.5 ML S residing atop a partially ordered interfacial layer of bridge-bonded S. The passivating reaction appears to be self-limited to 2-3 ML at this reaction temperature.

  10. Nonvolatile memories of Ge nanodots self-assembled by depositing ultrasmall amount Ge on SiO{sub 2} at room temperature

    SciTech Connect

    Hong, Seung Hui; Kim, Min Choul; Jeong, Pil Seong; Choi, Suk-Ho; Kim, Yong-Sung; Kim, Kyung Joong

    2008-03-03

    Ge nanodots (NDs) for nonvolatile memories (NVMs) have been self-assembled at room temperature (RT) by ion beam sputtering deposition of ultrasmall amount Ge (<72 ML) on SiO{sub 2} without postannealing. High-resolution transmission electron microscopy demonstrates the existence of well-defined Ge ND layers with respect to the SiO{sub 2}/Si interface. As Ge amount increases, the size of NDs increases, while their density decreases. A possible mechanism is proposed to explain the formation of Ge NDs at RT based on simple model calculations. The memory window that is estimated by capacitance-voltage hysteresis increases up to 18.7 V with increasing Ge amount up to 54 ML. The program speed is enhanced by increasing Ge amount and the charge-loss speed in the programed state is slower for larger Ge amount. These NVM properties are very promising in view of device application.

  11. Diffusion of Ge below the Si(100) Surface: Theory and Experiment

    NASA Astrophysics Data System (ADS)

    Uberuaga, Blas P.; Leskovar, Michael; Smith, Arthur P.; Jónsson, Hannes; Olmstead, Marjorie

    2000-03-01

    We have studied diffusion of Ge into subsurface layers of Si(100). Auger electron diffraction measurements show Ge in the fourth layer after submonolayer growth at temperatures as low as 500 °C. Density functional theory predictions of equilibrium Ge subsurface distributions are consistent with the measurements. We identify a surprisingly low energy pathway resulting from low interstitial formation energy in the third and fourth layers. Doping significantly affects the formation energy, suggesting that n-type doping may lead to sharper Si/Ge interfaces.

  12. Diffusion of Ge below the Si(100) surface: theory and experiment

    PubMed

    Uberuaga; Leskovar; Smith; Jonsson; Olmstead

    2000-03-13

    We have studied diffusion of Ge into subsurface layers of Si(100). Auger electron diffraction measurements show Ge in the fourth layer after submonolayer growth at temperatures as low as 500 degrees C. Density functional theory predictions of equilibrium Ge subsurface distributions are consistent with the measurements. We identify a surprisingly low energy pathway resulting from low interstitial formation energy in the third and fourth layers. Doping significantly affects the formation energy, suggesting that n-type doping may lead to sharper Si/Ge interfaces.

  13. Physico-chemical and electrical properties of rapid thermal oxides on Ge-rich SiGe heterolayers

    NASA Astrophysics Data System (ADS)

    Das, R.; Bera, M. K.; Chakraborty, S.; Saha, S.; Woitok, J. F.; Maiti, C. K.

    2006-11-01

    Rapid thermal oxidation of high-Ge content (Ge-rich) Si 1- xGe x ( x = 0.85) layers in dry O 2 ambient has been investigated. High-resolution X-ray diffraction (HRXRD) and strain-sensitive two-dimensional reciprocal space mapping X-ray diffractometry (2D-RSM) are employed to investigate strain relaxation and composition of as-grown SiGe alloy layers. Characterizations of ultra thin oxides (˜6-8 nm) have been performed using Fourier transform infrared spectroscopy (FTIR) and high-resolution X-ray photoelectron spectroscopy (HRXPS). Formation of mixed oxide i.e., (SiO 2 + GeO 2) and pile-up of Ge at the oxide/Si 1- xGe x interface have been observed. Enhancement in Ge segregation and reduction of oxide thickness with increasing oxidation temperature are reported. Interface properties and leakage current behavior of the rapid thermal oxides have been studied by capacitance-voltage (C-V) and current-voltage (J-V) techniques using metal-oxide-semiconductor capacitor (MOSCAP) structures and the results are reported.

  14. A Systematic Study of the Optical and Electrical Properties of Ge1-ySny and Ge1-x-ySixSny Semiconductor Alloys

    DTIC Science & Technology

    2014-03-27

    doped with Ga acceptor atoms (p = 6 × 1017 cm−3), which are typically used as platforms for multijunction solar cells . One of the Ge0.90Si0.08Sn0.02...Si can also be used as buffer layers for the subsequent growth of either tensile-strained Ge layers or III-V compound semiconductors such as GaAs and...examine the entire growth process for Ge1-x-ySixSny and hopes to produce high-quality films grown on either Si, Ge, or GaAs substrates. The ternary is of

  15. Impacts of excimer laser annealing on Ge epilayer on Si

    NASA Astrophysics Data System (ADS)

    Huang, Zhiwei; Mao, Yichen; Yi, Xiaohui; Lin, Guangyang; Li, Cheng; Chen, Songyan; Huang, Wei; Wang, Jianyuan

    2017-02-01

    The impacts of excimer laser annealing on the crystallinity of Ge epilayers on Si substrate grown by low- and high-temperature two-step approach in an ultra-high vacuum chemical vapor deposition system were investigated. The samples were treated by excimer laser annealing (ELA) at various laser power densities with the temperature above the melting point of Ge, while below that of Si, resulting in effective reduction of point defects and dislocations in the Ge layer with smooth surface. The full-width at half-maximum (FWHM) of X-ray diffraction patterns of the low-temperature Ge epilayer decreases with the increase in laser power density, indicating the crystalline improvement and negligible effect of Ge-Si intermixing during ELA processes. The short laser pulse time and large cooling rate cause quick melting and recrystallization of Ge epilayer on Si in the non-thermal equilibrium process, rendering tensile strain in Ge epilayer as calculated quantitatively with thermal mismatch between Si and Ge. The FWHM of X-ray diffraction patterns is significantly reduced for the two-step grown samples after treated by a combination of ELA and conventional furnace thermal annealing, indicating that the crystalline of Ge epilayer is improved more effectively with pre- annealing by excimer laser.

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

    NASA Astrophysics Data System (ADS)

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

    2016-10-01

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

  17. Evaluation of Transportation Options for Intermediate Non-destructive Examinations

    SciTech Connect

    Case, Susan; Hoggard, Gary

    2013-11-01

    Idaho National Laboratory (INL) shipments of irradiated experiments from the Advanced Test Reactor (ATR) to the Hot Fuels Examination Facility (HFEF) have historically been accomplished using the General Electric Model 2000 (GE 2000) Type B shipping container. Battelle Energy Alliance (BEA) concerns regarding the future availability and leasing and handling costs associated with the GE 2000 cask have warranted an evaluation of alternative shipping options. One or more of these shipping options may be utilized to perform non-destructive examinations (NDE) such as neutron radiography and precision gamma scans of irradiated experiments at HFEF and then return the experiments to ATR for further irradiation, hereafter referred to as “intermediate NDE.” This evaluation includes transportation options for intermediate NDE using the GE 2000 cask, BEA Research Reactor (BRR) package, Dry Transfer Cubicle (DTC) insert, and the General Electric Model 100 (GE 100) cask. The GE 2000 cask is the only Type B shipping container currently in use for shipments of irradiated material (exceeding Type A quantities) from ATR to HFEF; therefore it is included as one of the four shipping options in this evaluation. Cost and schedule estimates are provided for performing neutron radiography and precision gamma scans of a five-capsule drop-in-type ATR experiment for each transportation option. All costs provided in this evaluation are rough order-of-magnitude costs based on input from knowledgeable vendor employees and individuals at INL facilities.

  18. Ge doping of GaN beyond the Mott transition

    NASA Astrophysics Data System (ADS)

    Ajay, A.; Schörmann, J.; Jiménez-Rodriguez, M.; Lim, C. B.; Walther, F.; Rohnke, M.; Mouton, I.; Amichi, L.; Bougerol, C.; Den Hertog, M. I.; Eickhoff, M.; Monroy, E.

    2016-11-01

    We present a study of germanium as n-type dopant in wurtzite GaN films grown by plasma-assisted molecular-beam epitaxy, reaching carrier concentrations of up to 6.7  ×  1020 cm-3 at 300 K, well beyond the Mott density. The Ge concentration and free carrier density were found to scale linearly with the Ge flux in the studied range. All the GaN:Ge layers present smooth surface morphology with atomic terraces, without trace of pits or cracks, and the mosaicity of the samples has no noticeable dependence on the Ge concentration. The variation of the GaN:Ge band gap with the carrier concentration is consistent with theoretical calculations of the band gap renormalization due to electron-electron and electron-ion interaction, and Burstein-Moss effect.

  19. Pt- and Au-induced monodirectional nanowires on Ge(110)

    NASA Astrophysics Data System (ADS)

    Watanabe, T.; Yamada, Y.; Sasaki, M.; Sakai, S.; Yamauchi, Y.

    2016-11-01

    The adsorption of Pt or Au on Ge(110) and subsequent annealing resulted in formation of well-ordered monodirectional nanowires (NWs) throughout the surface over a cm-scale. The NWs were aligned along the [ 1 1 bar 0] direction, independent of the surface reconstruction of Ge(110). Metastable-atom deexcitation spectroscopy of Pt-NWs revealed that the topmost part of the NWs comprised Ge atoms, suggesting the exchange of the Ge and metal atoms, leaving an ultrathin Ge layer on top of the NWs. The increase in the electronic density of state near the Fermi energy was observed from both the MDS and UPS spectra of the Pt-NWs, suggesting a metallicity of the NWs.

  20. Auger electron diffraction study of the initial stage of Ge heteroepitaxy on Si(001)

    NASA Astrophysics Data System (ADS)

    Sasaki, M.; Abukawa, T.; Yeom, H. W.; Yamada, M.; Suzuki, S.; Sato, S.; Kono, S.

    1994-12-01

    The initial stage of pure and surfactant (Sb)-assisted Ge growth on a Si(001) surface has been studied by Auger electron diffraction (AED) and X-ray photoelectron diffraction (XPD). A single-domain Si(001)2 × 1 substrate was used to avoid the ambiguity arising from the usual double-domain substrate. For the pure Ge growth, 1 monolayer of Ge was deposited onto the room temperature substrate followed by annealing at 350°C-600°C, which appeared to have (1 × 2) periodicity by LEED. Ge LMM AED patterns were measured to find that a substantial amount of Ge atoms diffuse to the bulk Si positions up to the fourth layer at least. For the Sb-assisted Ge growth, a Sb(1 × 2)/Si(001) surface was first prepared and Sb 3d XPD patterns were measured to find that Sb forms dimers on the substrate. 1 ML of Ge was deposited onto the Sb(1 × 2)/Si(001) surface and then the surface was annealed at 600°C. Ge LMM AED and Sb 3d XPD patterns measured for this surface showed that surfactant Sb atoms are indeed present on the first layer forming dimers and that Ge atoms are present mainly on the second layer with a substantial amount of Ge diffused into the third and fourth layers.

  1. Atomistic simulation of damage accumulation and amorphization in Ge

    SciTech Connect

    Gomez-Selles, Jose L. Martin-Bragado, Ignacio; Claverie, Alain; Benistant, Francis

    2015-02-07

    Damage accumulation and amorphization mechanisms by means of ion implantation in Ge are studied using Kinetic Monte Carlo and Binary Collision Approximation techniques. Such mechanisms are investigated through different stages of damage accumulation taking place in the implantation process: from point defect generation and cluster formation up to full amorphization of Ge layers. We propose a damage concentration amorphization threshold for Ge of ∼1.3 × 10{sup 22} cm{sup −3} which is independent on the implantation conditions. Recombination energy barriers depending on amorphous pocket sizes are provided. This leads to an explanation of the reported distinct behavior of the damage generated by different ions. We have also observed that the dissolution of clusters plays an important role for relatively high temperatures and fluences. The model is able to explain and predict different damage generation regimes, amount of generated damage, and extension of amorphous layers in Ge for different ions and implantation conditions.

  2. Effect of spacer layer thickness on multi-stacked InGaAs quantum dots grown on GaAs (311)B substrate for application to intermediate band solar cells

    NASA Astrophysics Data System (ADS)

    Shoji, Yasushi; Narahara, Kohei; Tanaka, Hideharu; Kita, Takashi; Akimoto, Katsuhiro; Okada, Yoshitaka

    2012-04-01

    We have investigated the properties of multi-stacked layers of self-organized In0.4Ga0.6As quantum dots (QDs) on GaAs (311)B grown by molecular beam epitaxy. We found that a high degree of in-plane ordering of QDs structure with a six-fold symmetry was maintained though the growth has been performed at a higher growth rate than the conventional conditions. The dependence of photoluminescence characteristics on spacer layer thickness showed an increasing degree of electronic coupling between the stacked QDs for thinner spacer layers. The external quantum efficiency for an InGaAs/GaAs quantum dot solar cell (QDSC) with a thin spacer layer thickness increased in the longer wavelength range due to additive contribution from QD layers inserted in the intrinsic region. Furthermore, a photocurrent production by 2-step photon absorption has been observed at room temperature for the InGaAs/GaAs QDSC with a spacer layer thickness of 15 nm.

  3. Corrugated graphene layers for sea water desalination using capacitive deionization.

    PubMed

    Dahanayaka, Madhavi; Liu, Bo; Hu, Zhongqiao; Chen, Zhong; Law, Adrian Wing-Keung; Zhou, Kun

    2017-03-14

    The effect of the electric field and surface morphology of corrugated graphene (GE) layers on their capacitive deionization process is studied using molecular dynamics simulations. Deionization performances are evaluated in terms of water flow rate and ion adsorption and explained by analysing the water density distribution, radial distribution function and distribution of the ions inside the GE layers. The simulation results reveal that corrugation of GE layers reduces the water flow rate but largely enhances ion adsorption in comparison to the flat GE layers. Such enhancement is mainly due to the adsorption of ions on the GE layers due to the anchoring effect in the regions with wide interlayer distances. Moreover, it reveals that the entrance configuration of the GE layers also has a significant effect on the performance of deionization. Overall, the results from this study will be helpful in designing effective electrode configurations for capacitive deionization.

  4. Surfactant-mediated epitaxy of thin germanium films on SiGe(001) virtual substrates

    NASA Astrophysics Data System (ADS)

    Schmidt, J.; Tetzlaff, D.; Bugiel, E.; Wietler, T. F.

    2017-01-01

    We report on the impact of a surfactant on the growth mode and strain relaxation of thin Ge films on Si0.21Ge0.79 virtual substrates grown by surfactant mediated epitaxy on Si(001) wafers. Ge epitaxy without surfactant results in island formation after deposition of only 5 nm Ge. A certain part of the strain in the Ge islands is relaxed via interfacial misfit dislocations, which are located within the core part of the islands. We discuss the possibilities for the occurrence of three-dimensional growth at low Ge layer thickness. The use of Sb as a surfactant suppresses three-dimensional islanding and enables the growth of smooth pseudomorphically strained Ge films on Si0.21Ge0.79(001) virtual substrates up to a thickness of 10 nm. At thicknesses higher than 20 nm, the films relax via the formation of a misfit dislocation network at the Ge/ Si1-xGex interface. The surface roughness of up to 30 nm thick layers is below 1.6 nm. Our experimental results corroborate the calculated thickness for plastic relaxation of Ge on Si1-xGex. The effect of the surfactant on the growth of the virtual substrate and on the subsequent growth of Ge on Si0.21Ge0.79 is discussed.

  5. GeO{sub 2}/Ge structure submitted to annealing in deuterium: Incorporation pathways and associated oxide modifications

    SciTech Connect

    Bom, N. M.; Soares, G. V.; Hartmann, S.; Bordin, A.; Radtke, C.

    2014-10-06

    Deuterium (D) incorporation in GeO{sub 2}/Ge structures following D{sub 2} annealing was investigated. Higher D concentrations were obtained for GeO{sub 2}/Ge samples in comparison to their SiO{sub 2}/Si counterparts annealed in the same conditions. Oxygen vacancies produced during the annealing step in D{sub 2} constitute defect sites for D incorporation, analogous to defects at the SiO{sub 2}/Si interfacial region. Besides D incorporation, volatilization of the oxide layer is also observed as a consequence of D{sub 2} annealing, especially in the high temperature regime of the present study (>450 °C). In parallel to this volatilization, the stoichiometry and chemical structure of remnant oxide are modified as well. These results evidence the broader impact of forming gas annealing in dielectric/Ge structures with respect to SiO{sub 2}/Si counterparts.

  6. Interface traps and dangling-bond defects in (100)Ge/HfO2

    NASA Astrophysics Data System (ADS)

    Afanas'ev, V. V.; Fedorenko, Y. G.; Stesmans, A.

    2005-07-01

    Combined electrical and electron spin resonance analysis reveals dramatic differences in the interface defect properties of the (100)Ge/GeOxNy/HfO2 and (100)Ge/GeO2 interfaces from the seemingly similar interfaces of (100)Si with the HfO2 and SiO2. No dangling bond centers associated with Ge crystal surface atoms are detected. Only paramagnetic defects in the near-interfacial Ge oxide or Ge (oxy)nitride layers are observed. In contrast to the amphoteric traps related to the dangling bonds (Pb-type centers) commonly observed at the silicon/insulator interfaces, the major component of the Ge/insulator interface trap spectrum comes from slow acceptor states which show no correlation with paramagnetic centers and are resistant to passivation by hydrogen.

  7. Stark shift of the absorption spectra in Ge/Ge1-xSnx/Ge type-I single QW cell for mid-wavelength infra-red modulators

    NASA Astrophysics Data System (ADS)

    Yahyaoui, N.; Sfina, N.; Lazzari, J.-L.; Bournel, A.; Said, M.

    2015-09-01

    For mid-wavelength infra-red (MWIR) modulation or detection applications, we propose α-Sn rich Ge/Ge1-xSnx/Ge a type-I single quantum wells (SQW) partially strain compensated on Ge1-ySny relaxed layers grown onto (0 0 1)-oriented Ge substrate. Such elementary cells with W-like potential profiles of conduction and valence bands have been modeled by solving the one-dimensional Schrödinger equation under an applied external electrical field. First, strain effects on electrons, heavy holes (hh) and light holes (lh) energy bands for strained/relaxed Ge1-xSnx/Ge1-ySny heterointerfaces are investigated using the model-solid theory in the whole ranges (0 ⩽ x, y ⩽ 1) of Sn compositions. From the obtained band-discontinuities, band gaps and effective masses, Ge1-ySny/Ge/Ge0.80Sn0.20/Ge/Ge1-ySny cells are computed as a function of the Ge0.80Sn0.20 well width for three compositions of the Ge1-ySny buffer layer (y = 0.05, 0.07 and 0.09) in order to get the optimum quantum confinement of electrons and holes levels while keeping a reasonable amount of averaged strain in the cell. The electric field effect on the absorption spectra is given. An absorption coefficient in the 6× to 3 × 103 cm-1 range is reasonably obtained for a SQW at room temperature with a rather large Stark shift of the direct transition between 0.46 and 0.38 eV (i.e., λ = 3.26-2.70 μm) at large external fields (50 kV/cm). These characteristics are attractive for the design of MWIR optical modulators.

  8. Spin-polarized photoemission from SiGe heterostructures

    SciTech Connect

    Ferrari, A.; Bottegoni, F.; Isella, G.; Cecchi, S.; Chrastina, D.; Finazzi, M.; Ciccacci, F.

    2013-12-04

    We apply the principles of Optical Orientation to measure by Mott polarimetry the spin polarization of electrons photoemitted from different group-IV heterostructures. The maximum measured spin polarization, obtained from a Ge/Si{sub 0.31}Ge{sub 0.69} strained film, undoubtedly exceeds the maximum value of 50% attainable in bulk structures. The explanation we give for this result lies in the enhanced band orbital mixing between light hole and split-off valence bands as a consequence of the compressive strain experienced by the thin Ge layer.

  9. Direct synthesis of highly textured Ge on flexible polyimide films by metal-induced crystallization

    SciTech Connect

    Oya, N.; Toko, K. Suemasu, T.; Saitoh, N.; Yoshizawa, N.

    2014-06-30

    The highly (111)-textured Ge thin film (50-nm thickness) is demonstrated on a flexible polyimide film via the low-temperature crystallization (325 °C) of amorphous Ge using Al as a catalyst. Covering the polyimide with insulators significantly improved the crystal quality of the resulting Ge layer. In particular, SiN covering led to 97% (111)-oriented Ge with grains 200 μm in size, two orders larger than the grain size of polycrystalline Ge directly formed on the polyimide film. This achievement will give a way to realize advanced electronic and optical devices simultaneously allowing for high performance, inexpensiveness, and flexibility.

  10. MATERIALS FOR INTERMEDIATE TELUGU.

    ERIC Educational Resources Information Center

    KELLEY, GERALD B.

    ONE OF THE FOUR DRAVIDIAN LANGUAGES RECOGNIZED BY THE INDIAN CONSTITUTION OF 1950 AS OFFICIAL LANGUAGES OF THE COUNTRY, TELUGU IS SPOKEN BY 42 MILLION PEOPLE IN ANDHRA PRADESH. THESE INSTRUCTIONAL MATERIALS ARE DESIGNED FOR THE INTERMEDIATE STUDENT OF TELUGU AND ARE DIVIDED INTO NEWSPAPER READINGS AND DIALOGUES OF EVERYDAY CONVERSATION. SUBJECTS…

  11. Intermediate Pashto. Textbook.

    ERIC Educational Resources Information Center

    Tegey, Habibullah; Robson, Barbara

    The textbook for intermediate level Pashto instruction consists of 14 units (15-28) on a variety of cultural topics and linguistic structures. Cultural topics include engagement and marriage, children's education, agriculture and related subjects, the family, Pashtun history, genealogies of major Pashtun tribes, the Pashtun code of behavior,…

  12. Sara Intermediate Course.

    ERIC Educational Resources Information Center

    Thayer, James E.; Maraby, Julien

    This volume consists of an intermediate course in Sara, a language of the Chad Republic of Africa. It is designed for native speakers of English and includes forty reading selections in Sara and an English translation of each selection. The readings are followed by a corresponding set of dialogues in Sara, accompanied by an English translation.…

  13. SPACE: Intermediate Level Modules.

    ERIC Educational Resources Information Center

    Indiana State Dept. of Education, Indianapolis. Center for School Improvement and Performance.

    These modules were developed to assist teachers at the intermediate level to move away from extensive skill practice and toward more meaningful interdisciplinary learning. This packet, to be used by teachers in the summer Extended Learning Program, provides detailed thematic lesson plans matched to the Indiana Curriculum Proficiency Guide. The…

  14. Hispanic American Heritage, Intermediate.

    ERIC Educational Resources Information Center

    Shepherd, Mike

    This resource book features the cultural heritage of Hispanics living within the United States and includes ideas, materials, and activities to be used with students in the intermediate grades and middle school. This book explores the definition of the term "Hispanic Americans" and suggests a multilayered population with a variety of cultural…

  15. Synthesis and size differentiation of Ge nanocrystals in amorphous SiO2

    NASA Astrophysics Data System (ADS)

    Ağan, S.; Çelik-Aktaş, A.; Zuo, J. M.; Dana, A.; Aydınlı, A.

    2006-04-01

    Germanosilicate layers were grown on Si substrates by plasma enhanced chemical vapor deposition (PECVD) and annealed at different temperatures ranging from 700 1010 °C for durations of 5 to 60 min. Transmission electron microscopy (TEM) was used to investigate Ge nanocrystal formation in SiO2:Ge films. High-resolution cross section TEM images, electron energy-loss spectroscopy and energy dispersive X-ray analysis (EDX) data indicate that Ge nanocrystals are present in the amorphous silicon dioxide films. These nanocrystals are formed in two spatially separated layers with average sizes of 15 and 50 nm, respectively. EDX analysis indicates that Ge also diffuses into the Si substrate.

  16. Surfactant-Mediated Growth of Ge/Si(001) Interface Studied by XPD

    NASA Astrophysics Data System (ADS)

    Gunnella, R.; Castrucci, P.; Pinto, N.; Cucculelli, P.; Davoli, I.; Sébilleau, D.; de Crescenzi, M.

    The influence of Sb as a surfactant on the formation of Si/Ge interface is studied by means of XPD (X-ray photoelectron diffraction) and AED (Auger electron diffraction) from Ge and Si core levels. The technique employed is particularly suitable for checking the film tetragonal distortion, the growth morphology and the sharpness of the interface. We found a layer by layer growth mode for 3 ML of Ge on Si(001) and related values of strain of the film close to the value predicted by the elastic theory which enforces the use of such a surfactant to obtain high quality and sharp heterostructures. In addition, studying the influence of 3 ML of the Si cap layer on the 3 ML Ge, we obtain no indication of Ge segregation into the Si cap layer. Finally, evidences of quality degradation after high temperature (T > 600°C) annealing are shown.

  17. Ge auto-doping and out-diffusion in InGaP grown on Ge substrate and their effects on the ordering of InGaP

    NASA Astrophysics Data System (ADS)

    Wu, Hong-Ming; Tsai, Shi-Jane; Ho, Hao-I.; Lin, Hao-Hsiung

    2016-03-01

    We report on the Ge auto-doping and out-diffusion in InGaP epilayer with Cu-Pt ordering grown on 4-in. Ge substrate. Ge profiles determined from secondary ion mass spectrometry indicate that the Ge out-diffusion depth is within 100 nm. However, the edge of the wafer suffers from stronger Ge gas-phase auto-doping than the center, leading to ordering deterioration in the InGaP epilayer. In the edge, we observed a residual Cu-Pt ordering layer left beneath the surface, suggesting that the ordering deterioration takes place after the deposition rather than during the deposition and In/Ga inter-diffusion enhanced by Ge vapor-phase auto-doping is responsible for the deterioration. We thus propose a di-vacancy diffusion model, in which the amphoteric Ge increases the di-vacancy density, resulting in a Ge density dependent diffusion. In the model, the In/Ga inter-diffusion and Ge out-diffusion are realized by the random hopping of In/Ga host atoms and Ge atoms to di-vacancies, respectively. Simulation based on this model well fits the Ge out-diffusion profiles, suggesting its validity. By comparing the Ge diffusion coefficient obtained from the fitting and the characteristic time constant of ordering deterioration estimated from the residual ordering layer, we found that the hopping rates of Ge and the host atoms are in the same order of magnitude, indicating that di-vacancies are bound in the vicinity of Ge atoms.

  18. Effect of mixed Ge/Si cross-linking on the physical properties of amorphous Ge-Si-Te networks

    SciTech Connect

    Gunasekera, K.; Boolchand, P.; Micoulaut, M.

    2014-04-28

    Amorphous Ge{sub x}Si{sub x}Te{sub 1−2x} glasses are studied as a function of composition by a combination of experimental and theoretical methods, allowing for a full description of the network structure in relationship with physico-chemical properties. Calorimetric and thermal measurements reveal that such glasses display an anomalous behavior across a range of compositions x{sub c1}=7.5% and intermediate phase, where network rigidity onsets as the content x of Group IV atoms (Ge, Si) are increased. The structural manifestation of these anomalies is understood from  {sup 119}Sn Mössbauer spectroscopy and First Principles Molecular Dynamics at selected compositions (Ge{sub 20}Te{sub 80}, Si{sub 20}Te{sub 80}, and Ge{sub 10}Si{sub 10}Te{sub 80}). The numerical models reveal the quite different roles played by the modifier or network cross-linker Ge or Si atoms, Si being more tetrahedral in sp{sup 3} geometry, whereas Mössbauer spectroscopy shows that the nature of chemical bonding is dramatically changed around x≃ 8%. The precise evolution of the local structure and chemical bonding ultimately allows understanding the origin of the intermediate phase in these complex tellurides.

  19. Method of producing buried porous silicon-geramanium layers in monocrystalline silicon lattices

    NASA Technical Reports Server (NTRS)

    Fathauer, Robert W. (Inventor); George, Thomas (Inventor); Jones, Eric W. (Inventor)

    1997-01-01

    Lattices of alternating layers of monocrystalline silicon and porous silicon-germanium have been produced. These single crystal lattices have been fabricated by epitaxial growth of Si and Si--Ge layers followed by patterning into mesa structures. The mesa structures are stain etched resulting in porosification of the Si--Ge layers with a minor amount of porosification of the monocrystalline Si layers. Thicker Si--Ge layers produced in a similar manner emitted visible light at room temperature.

  20. GaAs/Ge/Si epitaxial substrates: Development and characteristics

    NASA Astrophysics Data System (ADS)

    Buzynin, Yury; Shengurov, Vladimir; Zvonkov, Boris; Buzynin, Alexander; Denisov, Sergey; Baidus, Nikolay; Drozdov, Michail; Pavlov, Dmitry; Yunin, Pavel

    2017-01-01

    We developed high quality 2-inch GaAs/Ge/Si (100) epitaxial substrates, which may be used instead of GaAs monolithic substrates for fabrication of solar cells, photodetectors, LEDs, lasers, etc. A 200-300 nm Ge buffer layer was grown on Si substrates using the HW-CVD technique at 300°C, a tantalum strip heated to 1400°C was used as the "hotwire". The MOCVD method was used to grow a 1 μ GaAs layer on a Ge buffer. The TDD in the GaAs layers did not exceed (1-2)•105 cm-2 and the surface RMS roughness value was under 1 nm.

  1. Stellar Laboratories: New GeV and Ge VI Oscillator Strengths and their Validation in the Hot White Dwarf RE0503-289

    NASA Technical Reports Server (NTRS)

    Rauch, T.; Werner, K.; Biemont, E.; Quinet, P.; Kruk, J. W.

    2013-01-01

    State-of-the-art spectral analysis of hot stars by means of non-LTE model-atmosphere techniques has arrived at a high level of sophistication. The analysis of high-resolution and high-S/N spectra, however, is strongly restricted by the lack of reliable atomic data for highly ionized species from intermediate-mass metals to trans-iron elements. Especially data for the latter has only been sparsely calculated. Many of their lines are identified in spectra of extremely hot, hydrogen-deficient post-AGB stars. A reliable determination of their abundances establishes crucial constraints for AGB nucleosynthesis simulations and, thus, for stellar evolutionary theory. Aims. In a previous analysis of the UV spectrum of RE 0503-289, spectral lines of highly ionized Ga, Ge, As, Se, Kr, Mo, Sn, Te, I, and Xe were identified. Individual abundance determinations are hampered by the lack of reliable oscillator strengths. Most of these identified lines stem from Ge V. In addition, we identified Ge VI lines for the first time. We calculated Ge V and Ge VI oscillator strengths in order to reproduce the observed spectrum. Methods. We newly calculated Ge V and Ge VI oscillator strengths to consider their radiative and collisional bound-bound transitions in detail in our non-LTE stellar-atmosphere models for the analysis of the Ge IV-VI spectrum exhibited in high-resolution and high-S/N FUV (FUSE) and UV (ORFEUS/BEFS, IUE) observations of RE 0503-289. Results. In the UV spectrum of RE 0503-289, we identify four Ge IV, 37 Ge V, and seven Ge VI lines. Most of these lines are identified for the first time in any star. We can reproduce almost all Ge IV, GeV, and Ge VI lines in the observed spectrum of RE 0503-289 (T(sub eff) = 70 kK, log g = 7.5) at log Ge = -3.8 +/- 0.3 (mass fraction, about 650 times solar). The Ge IV/V/VI ionization equilibrium, that is a very sensitive T(sub eff) indicator, is reproduced well. Conclusions. Reliable measurements and calculations of atomic data are a

  2. A new high-pressure strontium germanate, SrGe2O5.

    PubMed

    Nakatsuka, Akihiko; Sugiyama, Kazumasa; Ohkawa, Makio; Ohtaka, Osamu; Fujiwara, Keiko; Yoshiasa, Akira

    2016-10-01

    The Sr-Ge-O system has an earth-scientific importance as a potentially good low-pressure analog of the Ca-Si-O system, one of the major components in the constituent minerals of the Earth's crust and mantle. However, it is one of the germanate systems that has not yet been fully examined in the phase relations and structural properties. The recent findings that the SrGeO3 high-pressure perovskite phase is the first Ge-based transparent electronic conductor make the Sr-Ge-O system interesting in the field of materials science. In the present study, we have revealed the existence of a new high-pressure strontium germanate, SrGe2O5. Single crystals of this compound crystallized as a co-existent phase with SrGeO3 perovskite single crystals in the sample recovered in the compression experiment of SrGeO3 pseudowollastonite conducted at 6 GPa and 1223 K. The crystal structure consists of germanium-oxygen framework layers stacked along [001], with Sr atoms located at the 12-coordinated cuboctahedral site; the layers are formed by the corner linkages between GeO6 octahedra and between GeO6 octahedra and GeO4 tetrahedra. The present SrGe2O5 is thus isostructural with the high-pressure phases of SrSi2O5 and BaGe2O5. Comparison of these three compounds leads to the conclusion that the structural responses of the GeO6 and GeO4 polyhedra to cation substitution at the Sr site are much less than that of the SrO12 cuboctahedron to cation substitution at the Ge sites. Such a difference in the structural response is closely related to the bonding nature.

  3. The Intermediate Neutrino Program

    SciTech Connect

    Adams, C.; et al.

    2015-03-23

    The US neutrino community gathered at the Workshop on the Intermediate Neutrino Program (WINP) at Brookhaven National Laboratory February 4-6, 2015 to explore opportunities in neutrino physics over the next five to ten years. Scientists from particle, astroparticle and nuclear physics participated in the workshop. The workshop examined promising opportunities for neutrino physics in the intermediate term, including possible new small to mid-scale experiments, US contributions to large experiments, upgrades to existing experiments, R&D plans and theory. The workshop was organized into two sets of parallel working group sessions, divided by physics topics and technology. Physics working groups covered topics on Sterile Neutrinos, Neutrino Mixing, Neutrino Interactions, Neutrino Properties and Astrophysical Neutrinos. Technology sessions were organized into Theory, Short-Baseline Accelerator Neutrinos, Reactor Neutrinos, Detector R&D and Source, Cyclotron and Meson Decay at Rest sessions.This report summarizes discussion and conclusions from the workshop.

  4. Multi-Valence Magnetotransport in a Modulation-Doped p-TYPE Ge1-xSix/Ge/Ge1-xSix Quantum Well

    NASA Astrophysics Data System (ADS)

    Yakunin, M. V.; Alshanskii, G. A.; Neverov, V. N.; Arapov, Yu. G.; Harus, G. I.; Shelushinina, N. G.; Kuznetsov, O. A.; de Visser, A.; Ponomarenko, L.

    We show, from self-consistent calculations, that the effective mass for motion of holes along a two-dimensional (111) Ge layer is almost an order of magnitude smaller than the bulk heavy hole mass, which determines the intersubband distances. This creates a unique situation of multiple populated electric subbands at moderate hole densities ps and layer widths. Depopulation of two or more upper subbands in a 38 nm wide p-Ge layer with ps=5×1015m-2 has been revealed from the magnetoresistance in high parallel magnetic fields, while a collapse of the quantum Hall state for filling factor ν=1 indicates that two ground subbands merge in a self-formed double-quantum-well potential profile. The latter effect in the valence band is shown to be sensitive to the layer deformation.

  5. Improvement of J(sc) in a Cu2ZnSnS4 Solar Cell by Using a Thin Carbon Intermediate Layer at the Cu2ZnSnS4/Mo Interface.

    PubMed

    Zhou, Fangzhou; Zeng, Fangqin; Liu, Xu; Liu, Fangyang; Song, Ning; Yan, Chang; Pu, Aobo; Park, Jongsung; Sun, Kaiwen; Hao, Xiaojing

    2015-10-21

    Back contact modification plays an important role in improving energy conversion efficiency of Cu2ZnSnS4 (CZTS) thin film solar cells. In this paper, an ultrathin carbon layer is introduced on molybdenum (Mo)-coated soda lime glass (SLG) prior to the deposition of CZTS precursor to improve the back contact and therefore enhance CZTS solar cell efficiency. By introducing this layer, the short circuit current (Jsc) and device conversion efficiency increase for both nonvacuum (sol-gel) and vacuum (sputtering) methods. Specifically, for the sol-gel based process, Jsc increases from 13.60 to 16.96 mA/cm(2) and efficiency from 4.47% to 5.52%, while for the sputtering based process, Jsc increases from 17.50 to 20.50 mA/cm(2) and efficiency from 4.10% to 5.20%. Furthermore, introduction of this layer does not lead to any deterioration of either open circuit voltage (Voc) or fill factor (FF).

  6. Intermediate water recovery system

    NASA Technical Reports Server (NTRS)

    Deckman, G.; Anderson, A. R. (Editor)

    1973-01-01

    A water recovery system for collecting, storing, and processing urine, wash water, and humidity condensates from a crew of three aboard a spacecraft is described. The results of a 30-day test performed on a breadboard system are presented. The intermediate water recovery system produced clear, sterile, water with a 96.4 percent recovery rate from the processed urine. Recommendations for improving the system are included.

  7. Mechanism of the addition of nonenolizable aldehydes and ketones to (Di)metallenes (R(2)X=YR(2), X = Si, Ge Y = C, Si, Ge): a density functional and multiconfigurational perturbation theory study.

    PubMed

    Mosey, Nicholas J; Baines, Kim M; Woo, Tom K

    2002-11-06

    The mechanism of the addition of nonenolizable aldehydes and ketones to group 14 (di)metallenes has been examined through a theoretical study of the addition of formaldehyde to Si=C, Ge=C, Si=Si, Si=Ge, and Ge=Ge bonds at the B3LYP/6-311++G(d,p) and CAS-MCQDPT2/6-31++G(d,p) levels of theory. The reaction pathways located can be grouped as either involving the formation of singlet diradical or zwitterionic intermediates or as concerted processes. Within each group of reaction pathways, several different mechanisms have been located, with not all mechanisms being available to all of the (di)metallenes. It was found that for reactions in which a Si-O bond results (i.e., addition to Si=C, Si=Si, and Si=Ge) both diradical and zwitterionic intermediates are possible; however, the formation of diradical intermediates was not found for reactions that result in the formation of a Ge-O bond (addition to Ge=C and Ge=Ge). The underlying cause of this pathway selectivity is examined, as well as the effect of solvent on the relative energies of the pathways. The results of the study shed light on the cause of experimentally obtained results regarding the mechanism of the reaction of (di)metallenes with nonenolizable ketones and aldehydes.

  8. Modeling DNA Replication Intermediates

    SciTech Connect

    Broyde, S.; Roy, D.; Shapiro, R.

    1997-06-01

    While there is now available a great deal of information on double stranded DNA from X-ray crystallography, high resolution NMR and computer modeling, very little is known about structures that are representative of the DNA core of replication intermediates. DNA replication occurs at a single strand/double strand junction and bulged out intermediates near the junction can lead to frameshift mutations. The single stranded domains are particularly challenging. Our interest is focused on strategies for modeling the DNA of these types of replication intermediates. Modeling such structures presents special problems in addressing the multiple minimum problem and in treating the electrostatic component of the force field. We are testing a number of search strategies for locating low energy structures of these types and we are also investigating two different distance dependent dielectric functions in the coulombic term of the force field. We are studying both unmodified DNA and DNA damaged by aromatic amines, carcinogens present in the environment in tobacco smoke, barbecued meats and automobile exhaust. The nature of the structure adopted by the carcinogen modified DNA at the replication fork plays a key role in determining whether the carcinogen will cause a mutation during replication that can initiate the carcinogenic process. In the present work results are presented for unmodified DNA.

  9. Synthesis of Epitaxial Films Based on Ge-Si-Sn Materials with Ge/GeSn, Ge/GeSiSn, and GeSn/GeSiSn Heterojunctions

    NASA Astrophysics Data System (ADS)

    Timofeev, V. A.; Kokhanenko, A. P.; Nikiforov, A. I.; Mashanov, V. I.; Tuktamyshev, A. R.; Loshkarev, I. D.

    2015-11-01

    Results of investigations into the synthesis of heterostructures based on Ge-Si-Sn materials by the method of low-temperature molecular beam epitaxy are presented. The formation of epitaxial films during structure growth has been controlled by the reflection high-energy electron diffraction method. Films with Ge/GeSn, Ge/GeSiSn, and GeSn/GeSiSn heterojunctions are grown with Sn content changing from 2 to 10 % at temperatures in the interval 150-350°C. The stressed state, the composition, and the lattice parameter are studied by the x-ray diffraction method using Omega-scan curves and reciprocal space maps. A tensile strain in the Ge film during Ge/Ge0.9Sn0.1/Si structure growth has reached 0.86%.

  10. Low-temperature (180 °C) formation of large-grained Ge (111) thin film on insulator using accelerated metal-induced crystallization

    SciTech Connect

    Toko, K. Numata, R.; Oya, N.; Suemasu, T.; Fukata, N.; Usami, N.

    2014-01-13

    The Al-induced crystallization (AIC) yields a large-grained (111)-oriented Ge thin film on an insulator at temperatures as low as 180 °C. We accelerated the AIC of an amorphous Ge layer (50-nm thickness) by initially doping Ge in Al and by facilitating Ge diffusion into Al. The electron backscatter diffraction measurement demonstrated the simultaneous achievement of large grains over 10 μm and a high (111) orientation fraction of 90% in the polycrystalline Ge layer formed at 180 °C. This result opens up the possibility for developing Ge-based electronic and optical devices fabricated on inexpensive flexible substrates.

  11. Atomic-scale quantification of interdiffusion and dopant localization in GeSbTe-based memory devices

    NASA Astrophysics Data System (ADS)

    Chae, B.-G.; Seol, J.-B.; Song, J.-H.; Jung, W.-Y.; Hwang, H.; Park, C.-G.

    2016-09-01

    Fabrication of phase-change memory devices at modest or ambient temperatures leads to nanoscale compositional variations in phase-transition layers, where amorphous-polycrystalline phase change takes place via electrical switching, and can alter the device's performances. Here, by transmission electron microscopy and atom probe tomography, we address that thermal annealing at 400 °C for 20 min induces an elemental interdiffusion in the devices consisting of TiN (top electrode), carbon-doped GeSbTe (phase-transition layer), and TiSiN (bottom heater). With respect to the employed annealing process, the Ge atoms of GeSbTe layer have diffused into TiSiN layer at a given sample volume, while the Ti atoms of TiSiN layer into GeSbTe layer. Furthermore, non-random nature of dopant distribution in the GeSbTe materials leads to a Ti-localization including dopants at the GeSbTe/TiSiN interfaces. Our findings have two important implications: First, the annealing-driven interdiffusion of Ge and Ti is a predominant mechanism responsible for nanoscale compositional variations in GeSbTe layer; second, such an interdiffusion and the resultant dopant localization play a crucial role on the driving force for amorphous-polycrystalline transition of GeSbTe-based memory devices.

  12. Phonons in Ge nanowires

    NASA Astrophysics Data System (ADS)

    Peelaers, H.; Partoens, B.; Peeters, F. M.

    2009-09-01

    The phonon spectra of thin freestanding, hydrogen passivated, Ge nanowires are calculated by ab initio techniques. The effect of confinement on the phonon modes as caused by the small diameters of the wires is investigated. Confinement causes a hardening of the optical modes and a softening of the longitudinal acoustic modes. The stability of the nanowires, undoped or doped with B or P atoms, is investigated using the obtained phonon spectra. All considered wires were stable, except for highly doped, very thin nanowires.

  13. Different growth mechanisms of Ge by Stranski-Krastanow on Si (111) and (001) surfaces: An STM study

    NASA Astrophysics Data System (ADS)

    Teys, S. A.

    2017-01-01

    Structural and morphological features of the wetting layer formation and the transition to the three-dimensional Ge growth on (111) and (100) Si surfaces under quasi-equilibrium growth conditions were studied by means of scanning tunneling microscopy. The mechanism of the transition from the wetting layer to the three-dimensional Ge growth on Si was demonstrated. The principal differences and general trends of the atomic processes involved in the wetting layers formation on substrates with different orientations were demonstrated. The Ge growth is accompanied by the Ge atom redistribution and partial strain relaxation due to the formation of new surfaces, vacancies and surface structures of a decreased density. The analysis of three-dimensional Ge islands sites nucleation of after the wetting layer formation was carried out on the (111) surface. The transition to the three-dimensional growth at the Si(100) surface begins with single {105} facets nucleation on the rough Ge(100) surface.

  14. Strain and correlation of self-organized Ge1-xMnx nanocolumns embedded in Ge (001)

    NASA Astrophysics Data System (ADS)

    Tardif, S.; Favre-Nicolin, V.; Lançon, F.; Arras, E.; Jamet, M.; Barski, A.; Porret, C.; Bayle-Guillemaud, P.; Pochet, P.; Devillers, T.; Rovezzi, M.

    2010-09-01

    We report on the structural properties of Ge1-xMnx layers grown by molecular-beam epitaxy. In these layers, nanocolumns with a high Mn content are embedded in an almost-pure Ge matrix. We have used grazing-incidence x-ray scattering, atomic force and transmission electron microscopy to study the structural properties of the columns. We demonstrate how the elastic deformation of the matrix (as calculated using atomistic simulations) around the columns, as well as the average intercolumn distance can account for the shape of the diffusion around Bragg peaks.

  15. Formation of GeSn alloy on Si(100) by low-temperature molecular beam epitaxy

    SciTech Connect

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

    2014-12-29

    GeSn alloys grown on Si(100) by the low-temperature (100 °C) molecular beam epitaxy are studied using scanning tunneling microscopy and Raman spectroscopy. It is found that the effect of Sn as a surfactant modifies substantially the low-temperature growth mechanism of Ge on Si. Instead of the formation of small Ge islands surrounded by amorphous Ge, in the presence of Sn, the growth of pure Ge islands appears via the Stranski-Krastanov growth mode, and a partially relaxed Ge{sub 1−x}Sn{sub x} alloy layer with the high Sn-fraction up to 40 at. % is formed in the area between them. It is shown that the observed growth mode induced by high surface mobility of Sn and the large strain of the pseudomorphic state of Ge to Si ensures the minimum elastic-strain energy of the structure.

  16. Phonon transport control by nanoarchitecture including epitaxial Ge nanodots for Si-based thermoelectric materials

    PubMed Central

    Yamasaka, Shuto; Nakamura, Yoshiaki; Ueda, Tomohiro; Takeuchi, Shotaro; Sakai, Akira

    2015-01-01

    Phonon transport in Si films was controlled using epitaxially-grown ultrasmall Ge nanodots (NDs) with ultrahigh density for the purpose of developing Si-based thermoelectric materials. The Si/Ge ND stacked structures, which were formed by the ultrathin SiO2 film technique, exhibited lower thermal conductivities than those of the conventional nanostructured SiGe bulk alloys, despite the stacked structures having a smaller Ge fraction. This came from the large thermal resistance caused by phonon scattering at the Si/Ge ND interfaces. The phonon scattering can be controlled by the Ge ND structure, which was independent of Si layer structure for carrier transport. These results demonstrate the effectiveness of ultrasmall epitaxial Ge NDs as phonon scattering sources, opening up a route for the realisation of Si-based thermoelectric materials. PMID:26434678

  17. Phonon transport control by nanoarchitecture including epitaxial Ge nanodots for Si-based thermoelectric materials.

    PubMed

    Yamasaka, Shuto; Nakamura, Yoshiaki; Ueda, Tomohiro; Takeuchi, Shotaro; Sakai, Akira

    2015-10-05

    Phonon transport in Si films was controlled using epitaxially-grown ultrasmall Ge nanodots (NDs) with ultrahigh density for the purpose of developing Si-based thermoelectric materials. The Si/Ge ND stacked structures, which were formed by the ultrathin SiO2 film technique, exhibited lower thermal conductivities than those of the conventional nanostructured SiGe bulk alloys, despite the stacked structures having a smaller Ge fraction. This came from the large thermal resistance caused by phonon scattering at the Si/Ge ND interfaces. The phonon scattering can be controlled by the Ge ND structure, which was independent of Si layer structure for carrier transport. These results demonstrate the effectiveness of ultrasmall epitaxial Ge NDs as phonon scattering sources, opening up a route for the realisation of Si-based thermoelectric materials.

  18. Significantly Dense Two-Dimensional Hydrogen-Bond Network in a Layered Zirconium Phosphate Leading to High Proton Conductivities in Both Water-Assisted Low-Temperature and Anhydrous Intermediate-Temperature Regions.

    PubMed

    Gui, Daxiang; Zheng, Tao; Xie, Jian; Cai, Yawen; Wang, Yaxing; Chen, Lanhua; Diwu, Juan; Chai, Zhifang; Wang, Shuao

    2016-12-19

    A highly stable layered zirconium phosphate, (NH4)2[ZrF2(HPO4)2] (ZrP-1), was synthesized by an ionothermal method and contains an extremely dense two-dimensional hydrogen-bond network that is thermally stable up to 573 K, leading to combined ultrahigh water-assisted proton conductivities of 1.45 × 10(-2) S cm(-1) at 363 K/95% relative humidity and sustainable anhydrous proton conductivity of 1.1 × 10(-5) S cm(-1) at 503 K.

  19. High efficiency GaAs/Ge monolithic tandem solar cells

    NASA Technical Reports Server (NTRS)

    Tobin, S. P.; Vernon, S. M.; Bajgar, C.; Haven, V. E.; Geoffroy, L. M.; Sanfacon, M. M.; Lillington, D. R.; Hart, R. E., Jr.

    1988-01-01

    Two-terminal monolithic tandem cells consisting of a GaAs solar cell grown epitaxially on a Ge solar cell substrate are very attractive for space applications. Tandem cells of GaAs grown by metal-organic chemical vapor deposition on thin Ge were investigated to address both higher efficiency and reduced weight. Two materials growth issues associated with this heteroepitaxial system, autodoping of the GaAs layers by Ge and diffusion of Ga and As into the Ge substrate, were addressed. The latter appears to result in information of an unintentional p-n junction in the Ge. Early simulator measurements gave efficiencies as high as 21.7 percent for 4 cm2 GaAs/Ge cells, but recent high-altitude testing has given efficiencies of 18 percent. Sources of errors in simulator measurements of two-terminal tandem cells are discussed. A limiting efficiency of about 36 percent for the tandem cell at AMO was calculated. Ways to improve the performance of present cells, primarily by increasing the Isc and Voc of the Ge cell, are proposed.

  20. Atomic imaging of nucleation of trimethylaluminum on clean and H2O functionalized Ge(100) surfaces

    NASA Astrophysics Data System (ADS)

    Lee, Joon Sung; Kaufman-Osborn, Tobin; Melitz, Wilhelm; Lee, Sangyeob; Delabie, Annelies; Sioncke, Sonja; Caymax, Matty; Pourtois, Geoffrey; Kummel, Andrew C.

    2011-08-01

    The direct reaction of trimethylaluminum (TMA) on a Ge(100) surface and the effects of monolayer H2O pre-dosing were investigated using ultrahigh vacuum techniques, such as scanning tunneling microscopy (STM), scanning tunneling spectroscopy (STS), and x-ray photoelectron spectroscopy (XPS), and density functional theory (DFT). At room temperature (RT), a saturation TMA dose produced 0.8 monolayers (ML) of semi-ordered species on a Ge(100) surface due to the dissociative chemisorption of TMA. STS confirmed the chemisorption of TMA passivated the bandgap states due to dangling bonds. By annealing the TMA-dosed Ge surface, the STM observed coverage of TMA sites decreased to 0.4 ML at 250 °C, and to 0.15 ML at 450 °C. XPS analysis showed that only carbon content was reduced during annealing, while the Al coverage was maintained at 0.15 ML, consistent with the desorption of methyl (-CH3) groups from the TMA adsorbates. Conversely, saturation TMA dosing at RT on the monolayer H2O pre-dosed Ge(100) surface followed by annealing at 200 °C formed a layer of Ge-O-Al bonds with an Al coverage a factor of two greater than the TMA only dosed Ge(100), consistent with Ge-OH activation of TMA chemisorption and Ge-H blocking of CH3 chemisorption. The DFT shows that the reaction of TMA has lower activation energy and is more exothermic on Ge-OH than Ge-H sites. It is proposed that the H2O pre-dosing enhances the concentration of adsorbed Al and forms thermally stable Ge-O-Al bonds along the Ge dimer row which could serve as a nearly ideal atomic layer deposition nucleation layer on Ge(100) surface.

  1. SiGe/Si heterojunction internal photoemission long-wavelength infrared detectors fabricated by molecular beam epitaxy

    NASA Technical Reports Server (NTRS)

    Lin, True-Lon; Ksendzov, A.; Dejewski, Suzan M.; Jones, Eric W.; Fathauer, Robert W.; Krabach, Timothy N.; Maserjian, Joseph

    1991-01-01

    A new SiGe/Si heterojunction internal photoemission (HIP) long-wavelength infrared (LWIR) detector has been fabricated by molecular beam epitaxy (MBE). The detection mechanism of the SiGe/Si HIP detector is infrared absorption in the degenerately doped p+-SiGe layer followed by internal photoemission of photoexcited holes over a heterojunction barrier. By adjusting the Ge concentration in the SiGe layer, and, consequently, the valence band offset between SiGe and Si, the cutoff wavelength of SiGe HIP detectors can be extended into the LWIR (8-17-micron) regime. Detectors were fabricated by growing p+-SiGe layers using MBE on patterned p-type Si substrates. The SiGe layers were boron-doped, with concentrations ranging from 10 to the 19th/cu cm to 4 x 10 to the 20th/cu cm. Infrared absorption of 5-25 percent in a 30-nm-thick p+-SiGe layer was measured in the 3-20-micron range using a Fourier transform infrared spectrometer. Quantum efficiencies of 3-5 percent have been obtained from test devices in the 8-12-micron range.

  2. Structural investigations of the α12 Si–Ge superstructure

    PubMed Central

    Etzelstorfer, Tanja; Ahmadpor Monazam, Mohammad Reza; Cecchi, Stefano; Kriegner, Dominik; Chrastina, Daniel; Gatti, Eleonora; Grilli, Emanuele; Rosemann, Nils; Chatterjee, Sangam; Holý, Vaclav; Pezzoli, Fabio; Isella, Giovanni; Stangl, Julian

    2015-01-01

    This article1 reports the X-ray diffraction-based structural characterization of the α12 multilayer structure SiGe2Si2Ge2SiGe12 [d’Avezac, Luo, Chanier & Zunger (2012 ▶). Phys. Rev. Lett. 108, 027401], which is predicted to form a direct bandgap material. In particular, structural parameters of the superlattice such as thickness and composition as well as interface properties, are obtained. Moreover, it is found that Ge subsequently segregates into layers. These findings are used as input parameters for band structure calculations. It is shown that the direct bandgap properties depend very sensitively on deviations from the nominal structure, and only almost perfect structures can actually yield a direct bandgap. Photoluminescence emission possibly stemming from the superlattice structure is observed. PMID:26089750

  3. Novel Si(1-x)Ge(x)/Si heterojunction internal photoemission long-wavelength infrared detectors

    NASA Technical Reports Server (NTRS)

    Lin, T. L.; Maserjian, J.

    1990-01-01

    The feasibility of a novel p(+)-Si(1-x)Ge(x)-p-Si heterojunction internal photoemission (HIP) IR detector is demonstrated. A degenerately doped p(x)-Si(1-x)Ge(x) layer is required for strong IR absorption to generate photoexcited holes. The Si(1-x)Ge(x) layers are grown by molecular beam epitaxy, with boron concentrations up to 10 to the 20th/cu cm achieved by using an HBO2 source. Photoresponse at wavelengths ranging from 2 to 10 microns has been obtained with quantum efficiencies above 1 percent. The tailorable cutoff wavelength of the HIP detector has been demonstrated by varying the Ge composition ratio in the Si(1-x)Ge(x) layers.

  4. GeSi nanocrystals formed by high temperature annealing of GeO/SiO2 multilayers: structure and optical properties

    NASA Astrophysics Data System (ADS)

    Volodin, V. A.; Cherkov, A. G.; Vdovin, V. I.; Stoffel, M.; Rinnert, H.; Vergnat, M.

    2016-12-01

    The structural and optical properties of Ge and GeSi nanocrystals, formed by annealing of GeO/SiO2 multilayers have been investigated. According to Raman spectroscopy, the formation of pure Ge nanocrystals is observed after post growth annealing at 700 °C. Annealings at 800°C-900°C leads to the formation of intermixed GexSi1-x nanocrystals. High resolution transmission electron microscopy shows that the structure and the size of the nanocrystals strongly depend on annealing temperature. Spatial redistribution of Ge with the formation of large faceted clusters located near the Si substrate as well as GeSi intermixing at the substrate/film interface were observed. In the case of the sample containing 20 pairs of GeO/SiO2 layers annealed at 900 °C, some clusters exhibit a pyramid-like shape. FTIR absorption spectroscopy measurements demonstrate that intermixing between the GeO and SiO2 layers occurs leading to the formation of a SiGeO2 glass. Low temperature (10 K-100 K) photoluminescence was observed in the spectral range 1400-2000 nm for samples containing nanocrystals. The temperature dependence of the photoluminescence is studied.

  5. Intermediate inflation from a non-canonical scalar field

    SciTech Connect

    Rezazadeh, K.; Karami, K.; Karimi, P. E-mail: KKarami@uok.ac.ir

    2015-09-01

    We study the intermediate inflation in a non-canonical scalar field framework with a power-like Lagrangian. We show that in contrast with the standard canonical intermediate inflation, our non-canonical model is compatible with the observational results of Planck 2015. Also, we estimate the equilateral non-Gaussianity parameter which is in well agreement with the prediction of Planck 2015. Then, we obtain an approximation for the energy scale at the initial time of inflation and show that it can be of order of the Planck energy scale, i.e. M{sub P} ∼ 10{sup 18}GeV. We will see that after a short period of time, inflation enters in the slow-roll regime that its energy scale is of order M{sub P}/100 ∼ 10{sup 16}GeV and the horizon exit takes place in this energy scale. We also examine an idea in our non-canonical model to overcome the central drawback of intermediate inflation which is the fact that inflation never ends. We solve this problem without disturbing significantly the nature of the intermediate inflation until the time of horizon exit.

  6. Intermediate inflation from a non-canonical scalar field

    NASA Astrophysics Data System (ADS)

    Rezazadeh, K.; Karami, K.; Karimi, P.

    2015-09-01

    We study the intermediate inflation in a non-canonical scalar field framework with a power-like Lagrangian. We show that in contrast with the standard canonical intermediate inflation, our non-canonical model is compatible with the observational results of Planck 2015. Also, we estimate the equilateral non-Gaussianity parameter which is in well agreement with the prediction of Planck 2015. Then, we obtain an approximation for the energy scale at the initial time of inflation and show that it can be of order of the Planck energy scale, i.e. MP ~ 1018GeV. We will see that after a short period of time, inflation enters in the slow-roll regime that its energy scale is of order MP/100 ~ 1016GeV and the horizon exit takes place in this energy scale. We also examine an idea in our non-canonical model to overcome the central drawback of intermediate inflation which is the fact that inflation never ends. We solve this problem without disturbing significantly the nature of the intermediate inflation until the time of horizon exit.

  7. Large grain growth of Ge-rich Ge1-xSnx (x ≈ 0.02) on insulating surfaces using pulsed laser annealing in flowing water

    NASA Astrophysics Data System (ADS)

    Kurosawa, Masashi; Taoka, Noriyuki; Ikenoue, Hiroshi; Nakatsuka, Osamu; Zaima, Shigeaki

    2014-02-01

    We investigate Sn incorporation effects on the growth characteristics of Ge-rich Ge1-xSnx (x < 0.02) on SiO2 crystallized by pulsed laser annealing (PLA) in air and water. Despite the very low Sn content of 2%, Sn atoms within the GeSn layers play a role in preventing ablation and aggregation of the layers during these PLA. Raman and electron backscatter diffraction measurements demonstrate achievement of large-grain (˜800 nmϕ) growth of Ge0.98Sn0.02 polycrystals by using PLA in water. These polycrystals also show a tensile-strain of ˜0.68%. This result opens up the possibility for developing GeSn-based devices fabricated on flexible substrates as well as Si platforms.

  8. Lowering the effective work function via oxygen vacancy formation on the GeO2/Ge interface

    NASA Astrophysics Data System (ADS)

    Lee, Tae In; Seo, Yujin; Moon, Jungmin; Ahn, Hyun Jun; Yu, Hyun-Young; Hwang, Wan Sik; Cho, Byung Jin

    2017-04-01

    The use of a GeO2 interfacial layer (IL) between a high-k dielectric and a Ge substrate helps to reduce the interface state density in Ge MOS devices. We report that the presence of the GeO2 IL changes the effective work function (eWF) of the gate stack when annealed after high-k dielectric deposition. The eWF is reduced from 4.31 eV to 3.98 eV for TaN and from 5.00 eV to 4.44 eV for Ni. Consequently, the threshold voltage (Vth) decreases from 0.69 V to 0.21 V for Ni after post deposition annealing. Our investigation confirms that the generation of oxygen vacancies in the GeO2 IL near the Ge substrate is the main cause of the eWF modulation. In addition, the reliability of the GeO2 IL is investigated via the conductance method and a constant-current stress test.

  9. Charge trapping of Ge-nanocrystals embedded in TaZrO{sub x} dielectric films

    SciTech Connect

    Lehninger, D. Seidel, P.; Geyer, M.; Schneider, F.; Heitmann, J.; Klemm, V.; Rafaja, D.; Borany, J. von

    2015-01-12

    Ge-nanocrystals (NCs) were synthesized in amorphous TaZrO{sub x} by thermal annealing of co-sputtered Ge-TaZrO{sub x} layers. Formation of spherical shaped Ge-NCs with small variation of size, areal density, and depth distribution was confirmed by high-resolution transmission electron microscopy. The charge storage characteristics of the Ge-NCs were investigated by capacitance-voltage and constant-capacity measurements using metal-insulator-semiconductor structures. Samples with Ge-NCs exhibit a maximum memory window of 5 V by sweeping the bias voltage from −7 V to 7 V and back. Below this maximum, the width of the memory window can be controlled by the bias voltage. The fitted slope of the memory window versus bias voltage characteristics is very close to 1 for samples with one layer Ge-NCs. A second layer Ge-NCs does not result in a second flat stair in the memory window characteristics. Constant-capacity measurements indicate charge storage in trapping centers at the interfaces between the Ge-NCs and the surrounding materials (amorphous matrix/tunneling oxide). Charge loss occurs by thermal detrapping and subsequent band-to-band tunneling. Reference samples without Ge-NCs do not show any memory window.

  10. Chemical Bonding, Interfaces and Defects in Hafnium Oxide/Germanium Oxynitride Gate Stacks on Ge (100)

    SciTech Connect

    Oshima, Yasuhiro; Sun, Yun; Kuzum, Duygu; Sugawara, Takuya; Saraswat, Krishna C.; Pianetta, Piero; McIntyre, Paul C.; /Stanford U., Materials Sci. Dept.

    2008-10-31

    Correlations among interface properties and chemical bonding characteristics in HfO{sub 2}/GeO{sub x}N{sub y}/Ge MIS stacks were investigated using in-situ remote nitridation of the Ge (100) surface prior to HfO{sub 2} atomic layer deposition (ALD). Ultra thin ({approx}1.1 nm), thermally stable and aqueous etch-resistant GeO{sub x}N{sub y} interfaces layers that exhibited Ge core level photoelectron spectra (PES) similar to stoichiometric Ge{sub 3}N{sub 4} were synthesized. To evaluate GeO{sub x}N{sub y}/Ge interface defects, the density of interface states (D{sub it}) was extracted by the conductance method across the band gap. Forming gas annealed (FGA) samples exhibited substantially lower D{sub it} ({approx} 1 x 10{sup 12} cm{sup -2} eV{sup -1}) than did high vacuum annealed (HVA) and inert gas anneal (IGA) samples ({approx} 1x 10{sup 13} cm{sup -2} eV{sup -1}). Germanium core level photoelectron spectra from similar FGA-treated samples detected out-diffusion of germanium oxide to the HfO{sub 2} film surface and apparent modification of chemical bonding at the GeO{sub x}N{sub y}/Ge interface, which is related to the reduced D{sub it}.

  11. Dark current reduction of Ge photodetector by GeO₂ surface passivation and gas-phase doping.

    PubMed

    Takenaka, Mitsuru; Morii, Kiyohito; Sugiyama, Masakazu; Nakano, Yoshiaki; Takagi, Shinichi

    2012-04-09

    We have investigated the dark current of a germanium (Ge) photodetector (PD) with a GeO₂ surface passivation layer and a gas-phase-doped n+/p junction. The gas-phase-doped PN diodes exhibited a dark current of approximately two orders of magnitude lower than that of the diodes formed by a conventional ion implantation process, indicating that gas-phase doping is suitable for low-damage PN junction formation. The bulk leakage (Jbulk) and surface leakage (Jsurf) components of the dark current were also investigated. We have found that GeO₂ surface passivation can effectively suppress the dark current of a Ge PD in conjunction with gas-phase doping, and we have obtained extremely low values of Jbulk of 0.032 mA/cm² and Jsurf of 0.27 μA/cm.

  12. An observation of direct-gap electroluminescence in GaAs structures with Ge quantum wells

    SciTech Connect

    Aleshkin, V. Ya.; Dikareva, N. V.; Dubinov, A. A.; Zvonkov, B. N.; Kudryavtsev, K. E.; Nekorkin, S. M.

    2015-02-15

    A light-emitting diode structure based on GaAs with eight narrow Ge quantum wells is grown by laser sputtering. An electroluminescence line polarized predominately in the plane parallel to the constituent layers of the structure is revealed. The line corresponds to the direct optical transitions in momentum space in the Ge quantum wells.

  13. Effect of mixed Ge/Si cross-linking on the physical properties of amorphous Ge-Si-Te networks

    NASA Astrophysics Data System (ADS)

    Gunasekera, K.; Boolchand, P.; Micoulaut, M.

    2014-04-01

    Amorphous GexSixTe1-2x glasses are studied as a function of composition by a combination of experimental and theoretical methods, allowing for a full description of the network structure in relationship with physico-chemical properties. Calorimetric and thermal measurements reveal that such glasses display an anomalous behavior across a range of compositions xc1=7.5% and intermediate phase, where network rigidity onsets as the content x of Group IV atoms (Ge, Si) are increased. The structural manifestation of these anomalies is understood from 119Sn Mössbauer spectroscopy and First Principles Molecular Dynamics at selected compositions (Ge20Te80, Si20Te80, and Ge10Si10Te80). The numerical models reveal the quite different roles played by the modifier or network cross-linker Ge or Si atoms, Si being more tetrahedral in sp3 geometry, whereas Mössbauer spectroscopy shows that the nature of chemical bonding is dramatically changed around x ≃ 8%. The precise evolution of the local structure and chemical bonding ultimately allows understanding the origin of the intermediate phase in these complex tellurides.

  14. SiGe channel deposition by batch epitaxy

    NASA Astrophysics Data System (ADS)

    Reichel, Carsten; Schoenekess, Joerg; Dietel, Andreas; Wasyluk, Joanna; Chow, Yew Tuck; Kammler, Thorsten

    2015-08-01

    Batch epitaxy has been introduced for high volume manufacturing of SiGe channels in order to reduce the cost for this epitaxial process by a factor of 3. Beside cost, SiGe channel deposition by batch epitaxy offers many benefits for manufacturing. The stability of the process and the reduced variability of the SiGe thickness greatly improve the variation of VT. The batch epitaxy process does not show a pattern loading effect for SiGe thickness reducing the complexity for manufacturing significantly. However, since the tool concept is very different to that of the widely used single wafer tools, there are some tool specific issues that need to be managed. The wafer backside is critical for batch epitaxy. A nitride backside facing the front side of the wafer results in a clear degradation of the uniformity and a change of the morphology of the SiGe channel compared to that facing a Si backside. The thermal rounding is more pronounced for the channels deposited in a batch tool for both large and narrow width devices. The device parameters of the large width device are not affected by thermal rounding but the performance of the narrow width device is clearly degraded. The thin SiGe layer at the edge of the channel driven by thermal rounding affects the VT and thus the effective device width. An in-situ etching before SiGe deposition to avoid thermal rounding was not feasible due to defects issues which were induced by the wafer backside. Finally a thermal rounding of the Si by an aggressive H2 bake before SiGe deposition improves the SiGe channel uniformity and recovers the performance degradation of the narrow width device partly.

  15. A global Ge isotope budget

    NASA Astrophysics Data System (ADS)

    Baronas, J. Jotautas; Hammond, Douglas E.; McManus, James; Wheat, C. Geoffrey; Siebert, Christopher

    2017-04-01

    We present measurements of Ge isotope composition and ancillary data for samples of river water, low- and high-temperature hydrothermal fluids, and seawater. The dissolved δ74Ge composition of analyzed rivers ranges from 2.0 to 5.6‰, which is significantly heavier than previously determined values for silicate rocks (δ74Ge = 0.4-0.7‰, Escoube et al., Geostand. Geoanal. Res., 36(2), 2012) from which dissolved Ge is primarily derived. An observed negative correlation between riverine Ge/Si and δ74Ge signatures suggests that the primary δ74Ge fractionation mechanism during rock weathering is the preferential incorporation of light isotopes into secondary weathering products. High temperature (>150 °C) hydrothermal fluids analyzed in this study have δ74Ge of 0.7-1.6‰, most likely fractionated during fluid equilibration with quartz in the reaction zone. Low temperature (25-63 °C) hydrothermal fluids are heavier (δ74Ge between 2.9‰ and 4.1‰) and most likely fractionated during Ge precipitation with hydrothermal clays. Seawater from the open ocean has a δ74Gesw value of 3.2 ± 0.4‰, and is indistinguishable among the different ocean basins at the current level of precision. This value should be regulated over time by the isotopic balance of Ge sources and sinks, and a new compilation of these fluxes is presented, along with their estimated isotopic compositions. Assuming steady-state, non-opal Ge sequestration during sediment authigenesis likely involves isotopic fractionation Δ74Gesolid-solution that is -0.6 ± 1.8‰.

  16. Intermediate connector for stacked organic light emitting devices

    DOEpatents

    D& #x27; Andrade, Brian

    2013-02-12

    A device is provided, having an anode, a cathode, and an intermediate connector disposed between the anode and the cathode. A first organic layer including an emissive sublayer is disposed between the anode and the intermediate connector, and a second including an emissive sublayer is disposed between the intermediate connector and the cathode. The intermediate connector includes a first metal having a work function lower than 4.0 eV and a second metal having a work function lower than 5.0 eV. The work function of the first metal is at least 0.5 eV less than the work function of the second metal. The first metal is in contact with a sublayer of the second organic layer that includes a material well adapted to receive holes from a low work function metal.

  17. Intermediate filaments: a role in epithelial polarity

    PubMed Central

    Oriolo, Andrea S.; Wald, Flavia A.; Ramsauer, Victoria P.; Salas, Pedro J.I.

    2007-01-01

    Intermediate filaments have long been considered mechanical components of the cell that provide resistance to deformation stress. Practical experimental problems, including insolubility, lack of good pharmacological antagonists, and the paucity of powerful genetic models, have handicapped the research of other functions. In single-layered epithelial cells, keratin intermediate filaments are cortical, either apically polarized or apico-lateral. This review analyzes phenotypes of genetic manipulations of simple epithelial cell keratins in mice and C. elegans that strongly suggest a role of keratins in apico-basal polarization and membrane traffic. Published evidence that intermediate filaments can act as scaffolds for proteins involved in membrane traffic and signaling is also discussed. Such a scaffolding function would generate a highly polarized compartment within the cytoplasm of simple epithelial cells. While in most cases mechanistic explanations for the keratin-null or overexpression phenotypes are still missing, it is hoped investigators will be encouraged to study these as yet poorly understood functions of intermediate filaments. PMID:17425955

  18. Fabrication of composite based on GeSi with Ag nanoparticles using ion implantation

    NASA Astrophysics Data System (ADS)

    Batalov, R. I.; Vorobev, V. V.; Nuzhdin, V. I.; Valeev, V. F.; Bayazitov, R. M.; Lyadov, N. M.; Osin, Yu. N.; Stepanov, A. L.

    2016-12-01

    Comparative analysis of the structural and optical properties of composite layers fabricated with the aid of implantation of single-crystalline silicon ( c-Si) using Ge+ (40 keV/1 × 1017 ions/cm2) and Ag+ (30 keV/1.5 × 1017 ions/cm2) ions and sequential irradiation using Ge+ and Ag+ ions is presented. The implantation of the Ge+ ions leads to the formation of Ge: Si fine-grain amorphous surface layer with a thickness of 60 nm and a grain size of 20-40 nm. The implantation of c-Si using Ag+ ions results in the formation of submicron porous amorphous a-Si structure with a thickness of about 50 nm containing ion-synthesized Ag nanoparticles. The penetration of the Ag+ ions in the Ge: Si layer stimulates the formation of pores with Ag nanoparticles with more uniform size distribution. The reflection spectra of the implanted Ag: Si and Ag: GeSi layers exhibit a sharp decrease in the intensity in the UV (220-420 nm) spectral interval relative to the intensity of c-Si by more than 50% owing to the amorphization and structuring of surface. The formation of Ag nanoparticles in the implanted layers gives rise to a selective band of the plasmon resonance at a wavelength of about 820 nm in the optical spectra. Technological methods for fabrication of a composite based on GeSi with Ag nanoparticles are demonstrated in practice.

  19. Post-deposition growth kinetics of Ge on Ge(0 0 1)

    NASA Astrophysics Data System (ADS)

    Tinkham, B. P.; Jenichen, B.; Kaganer, V. M.; Shayduk, R.; Braun, W.; Ploog, K. H.

    2008-07-01

    We study the nucleation and growth kinetics on the Ge(0 0 1) surface at elevated temperatures using in situ surface X-ray diffraction. The time evolution of characteristic length scales on the surface is analyzed through the widths of the different components of the integer-order (morphology sensitive) and fractional-order (reconstruction sensitive) diffraction peaks. We find an activation energy of 0.58 eV for Ge island nucleation during homoepitaxy, which implies a diffusion activation energy higher than that obtained for both adatom and dimer diffusion on Ge(0 0 1) in previous studies. Sub-monolayer homoepitaxial Ge islands coarsen according to a power law, with a relatively low time exponent of n=0.2. The coarsening of small 2×1 reconstruction domains on a flat surface prepared by deposition of an integer number of layers shows a strong temperature dependence, whereby the coarsening exponent decreases from 0.41 to 0.2 as the temperature is increased.

  20. Ultra-low temperature (≤300 °C) growth of Ge-rich SiGe by solid-liquid-coexisting annealing of a-GeSn/c-Si structures

    SciTech Connect

    Sadoh, Taizoh Chikita, Hironori; Miyao, Masanobu; Matsumura, Ryo

    2015-09-07

    Ultra-low temperature (≤300 °C) growth of Ge-rich SiGe on Si substrates is strongly desired to realize advanced electronic and optical devices, which can be merged onto Si large-scale integrated circuits (LSI). To achieve this, annealing characteristics of a-GeSn/c-Si structures are investigated under wide ranges of the initial Sn concentrations (0%–26%) and annealing conditions (300–1000 °C, 1 s–48 h). Epitaxial growth triggered by SiGe mixing is observed after annealing, where the annealing temperatures necessary for epitaxial growth significantly decrease with increasing initial Sn concentration and/or annealing time. As a result, Ge-rich (∼80%) SiGe layers with Sn concentrations of ∼2% are realized by ultra-low temperature annealing (300 °C, 48 h) for a sample with the initial Sn concentration of 26%. The annealing temperature (300 °C) is in the solid-liquid coexisting temperature region of the phase diagram for Ge-Sn system. From detailed analysis of crystallization characteristics and composition profiles in grown layers, it is suggested that SiGe mixing is generated by a liquid-phase reaction even at ultra-low temperatures far below the melting temperature of a-GeSn. This ultra-low-temperature growth technique of Ge-rich SiGe on Si substrates is expected to be useful to realize next-generation LSI, where various multi-functional devices are integrated on Si substrates.

  1. Near-Infrared Photoluminescence Enhancement in Ge/CdS and Ge/ZnS Core/Shell Nanocrystals: Utilizing IV/II-VI Semiconductor Epitaxy

    SciTech Connect

    Guo, Yijun; Rowland, Clare E; Schaller, Richard D; Vela, Javier

    2014-08-26

    Ge nanocrystals have a large Bohr radius and a small, size-tunable band gap that may engender direct character via strain or doping. Colloidal Ge nanocrystals are particularly interesting in the development of near-infrared materials for applications in bioimaging, telecommunications and energy conversion. Epitaxial growth of a passivating shell is a common strategy employed in the synthesis of highly luminescent II–VI, III–V and IV–VI semiconductor quantum dots. Here, we use relatively unexplored IV/II–VI epitaxy as a way to enhance the photoluminescence and improve the optical stability of colloidal Ge nanocrystals. Selected on the basis of their relatively small lattice mismatch compared with crystalline Ge, we explore the growth of epitaxial CdS and ZnS shells using the successive ion layer adsorption and reaction method. Powder X-ray diffraction and electron microscopy techniques, including energy dispersive X-ray spectroscopy and selected area electron diffraction, clearly show the controllable growth of as many as 20 epitaxial monolayers of CdS atop Ge cores. In contrast, Ge etching and/or replacement by ZnS result in relatively small Ge/ZnS nanocrystals. The presence of an epitaxial II–VI shell greatly enhances the near-infrared photoluminescence and improves the photoluminescence stability of Ge. Ge/II–VI nanocrystals are reproducibly 1–3 orders of magnitude brighter than the brightest Ge cores. Ge/4.9CdS core/shells show the highest photoluminescence quantum yield and longest radiative recombination lifetime. Thiol ligand exchange easily results in near-infrared active, water-soluble Ge/II–VI nanocrystals. We expect this synthetic IV/II–VI epitaxial approach will lead to further studies into the optoelectronic behavior and practical applications of Si and Ge-based nanomaterials.

  2. Ultra-high frequency photoconductivity decay in GaAs/Ge/GaAs double heterostructure grown by molecular beam epitaxy

    SciTech Connect

    Hudait, M. K.; Zhu, Y.; Johnston, S. W.; Maurya, D.; Priya, S.; Umbel, R.

    2013-03-04

    GaAs/Ge/GaAs double heterostructures (DHs) were grown in-situ using two separate molecular beam epitaxy chambers. High-resolution x-ray rocking curve demonstrates a high-quality GaAs/Ge/GaAs heterostructure by observing Pendelloesung oscillations. The kinetics of the carrier recombination in Ge/GaAs DHs were investigated using photoconductivity decay measurements by the incidence excitation from the front and back side of 15 nm GaAs/100 nm Ge/0.5 {mu}m GaAs/(100)GaAs substrate structure. High-minority carrier lifetimes of 1.06-1.17 {mu}s were measured when excited from the front or from the back of the Ge epitaxial layer, suggests equivalent interface quality of GaAs/Ge and Ge/GaAs. Wavelength-dependent minority carrier recombination properties are explained by the wavelength-dependent absorption coefficient of Ge.

  3. Effects of rapid thermal annealing on the structural and local atomic properties of ZnO: Ge nanocomposite thin films

    SciTech Connect

    Ceylan, Abdullah Ozcan, Sadan; Rumaiz, Abdul K.; Caliskan, Deniz; Ozbay, Ekmel; Woicik, J. C.

    2015-03-14

    We have investigated the structural and local atomic properties of Ge nanocrystals (Ge-ncs) embedded ZnO (ZnO: Ge) thin films. The films were deposited by sequential sputtering of ZnO and Ge thin film layers on z-cut quartz substrates followed by an ex-situ rapid thermal annealing (RTA) at 600 °C for 30, 60, and 90 s under forming gas atmosphere. Effects of RTA time on the evolution of Ge-ncs were investigated by x-ray diffraction (XRD), scanning electron microscopy (SEM), hard x-ray photoelectron spectroscopy (HAXPES), and extended x-ray absorption fine structure (EXAFS). XRD patterns have clearly shown that fcc diamond phase Ge-ncs of sizes ranging between 18 and 27 nm are formed upon RTA and no Ge-oxide peak has been detected. However, cross-section SEM images have clearly revealed that after RTA process, Ge layers form varying size nanoclusters composed of Ge-ncs regions. EXAFS performed at the Ge K-edge to probe the local atomic structure of the Ge-ncs has revealed that as prepared ZnO:Ge possesses Ge-oxide but subsequent RTA leads to crystalline Ge structure without the oxide layer. In order to study the occupied electronic structure, HAXPES has been utilized. The peak separation between the Zn 2p and Ge 3d shows no significant change due to RTA. This implies little change in the valence band offset due to RTA.

  4. Structural properties of liquid Ge2Se3: A first-principles study

    NASA Astrophysics Data System (ADS)

    Le Roux, Sébastien; Zeidler, Anita; Salmon, Philip S.; Boero, Mauro; Micoulaut, Matthieu; Massobrio, Carlo

    2011-10-01

    The structural properties of liquid Ge2Se3were investigated by first-principles molecular dynamics using the Becke-Lee-Yang-Parr scheme for the treatment of the exchange-correlation functional in density functional theory. Our data for the total neutron structure factor and the total pair-distribution function are in excellent agreement with the experimental results. The structure is made predominantly (˜61%) from units comprising fourfold coordinated Ge atoms in the form of Ge-GeSe3 or Ge-Se4 motifs, but there is also a large variety of motifs in which Ge and Se are not fourfold and twofold coordinated, respectively. The miscoordinated atoms and homopolar bonds lead to a highly perturbed tetrahedral network, as reflected by diffusion coefficients that are larger than in the case of liquid GeSe2. The network does, nevertheless, exhibit intermediate range order which is associated with the Ge-Ge correlations and which manifests itself by a first sharp diffraction peak in the total neutron structure factor. The evolution of the properties of GexSe1-x liquids (0 ≤x≤ 1) with composition is discussed.

  5. Isotropic plasma etching of Ge Si and SiNx films

    SciTech Connect

    Henry, Michael David; Douglas, Erica Ann

    2016-08-31

    This study reports on selective isotropic dry etching of chemically vapor deposited (CVD) Ge thin film, release layers using a Shibaura chemical downstream etcher (CDE) with NF3 and Ar based plasma chemistry. Relative etch rates between Ge, Si and SiNx are described with etch rate reductions achieved by adjusting plasma chemistry with O2. Formation of oxides reducing etch rates were measured for both Ge and Si, but nitrides or oxy-nitrides created using direct injection of NO into the process chamber were measured to increase Si and SiNx etch rates while retarding Ge etching.

  6. Germanium oxide removal by citric acid and thiol passivation from citric acid-terminated Ge(100).

    PubMed

    Collins, Gillian; Aureau, Damien; Holmes, Justin D; Etcheberry, Arnaud; O'Dwyer, Colm

    2014-12-02

    Many applications of germanium (Ge) are underpinned by effective oxide removal and surface passivation. This important surface treatment step often requires H-X (X = Cl, Br, I) or HF etchants. Here, we show that aqueous citric acid solutions are effective in the removal of GeOx. The stability of citric acid-treated Ge(100) is compared to HF and HCl treated surfaces and analyzed by X-ray photoelectron spectroscopy. Further Ge surface passivation was investigated by thiolation using alkane monothiols and dithiols. The organic passivation layers show good stability with no oxide regrowth observed after 3 days of ambient exposure.

  7. Isotropic plasma etching of Ge Si and SiNx films

    DOE PAGES

    Henry, Michael David; Douglas, Erica Ann

    2016-08-31

    This study reports on selective isotropic dry etching of chemically vapor deposited (CVD) Ge thin film, release layers using a Shibaura chemical downstream etcher (CDE) with NF3 and Ar based plasma chemistry. Relative etch rates between Ge, Si and SiNx are described with etch rate reductions achieved by adjusting plasma chemistry with O2. Formation of oxides reducing etch rates were measured for both Ge and Si, but nitrides or oxy-nitrides created using direct injection of NO into the process chamber were measured to increase Si and SiNx etch rates while retarding Ge etching.

  8. Phenomenological Model of the Growth of Ultrasmooth Silver Thin Films Deposited with a Germanium Nucleation Layer.

    PubMed

    Zhang, Junce; Fryauf, David M; Garrett, Matthew; Logeeswaran, V J; Sawabe, Atsuhito; Islam, M Saif; Kobayashi, Nobuhiko P

    2015-07-21

    The structural properties of optically thin (15 nm) silver (Ag) films deposited on SiO2/Si(100) substrates with a germanium (Ge) nucleation layer were studied. The morphological and crystallographical characteristics of Ag thin films with different Ge nucleation layer thicknesses were assessed by cross-sectional transmission electron microscopy (XTEM), reflection high-energy electron diffraction (RHEED), X-ray diffractometry (XRD), grazing incidence X-ray diffractometry (GIXRD), X-ray reflection (XRR), and Fourier transform infrared spectroscopy (FTIR). The surface roughness of Ag thin films was found to decrease significantly by inserting a Ge nucleation layer with a thickness in the range of 1 to 2 nm (i.e., smoothing mode). However, as the Ge nucleation layer thickness increased beyond 2 nm, the surface roughness increased concomitantly (i.e., roughing mode). For the smoothing mode, the role of the Ge nucleation layer in the Ag film deposition is discussed by invoking the surface energy of Ge, the bond dissociation energy of Ag-Ge, and the deposition mechanisms of Ag thin films on a given characteristic Ge nucleation layer. Additionally, Ge island formation, the precipitation of Ge from Ag-Ge alloys, and the penetration of Ge into SiO2 are suggested for the roughing mode. This demonstration of ultrasmooth Ag thin films would offer an advantageous material platform with scalability for applications such as optics, plasmonics, and photonics.

  9. Growth and evolution of nickel germanide nanostructures on Ge(001).

    PubMed

    Grzela, T; Capellini, G; Koczorowski, W; Schubert, M A; Czajka, R; Curson, N J; Heidmann, I; Schmidt, Th; Falta, J; Schroeder, T

    2015-09-25

    Nickel germanide is deemed an excellent material system for low resistance contact formation for future Ge device modules integrated into mainstream, Si-based integrated circuit technologies. In this study, we present a multi-technique experimental study on the formation processes of nickel germanides on Ge(001). We demonstrate that room temperature deposition of ∼1 nm of Ni on Ge(001) is realized in the Volmer-Weber growth mode. Subsequent thermal annealing results first in the formation of a continuous NixGey wetting layer featuring well-defined terrace morphology. Upon increasing the annealing temperature to 300 °C, we observed the onset of a de-wetting process, characterized by the appearance of voids on the NixGey terraces. Annealing above 300 °C enhances this de-wetting process and the surface evolves gradually towards the formation of well-ordered, rectangular NixGey 3D nanostructures. Annealing up to 500 °C induces an Ostwald ripening phenomenon, with smaller nanoislands disappearing and larger ones increasing their size. Subsequent annealing to higher temperatures drives the Ni-germanide diffusion into the bulk and the consequent formation of highly ordered, {111} faceted Ni-Ge nanocrystals featuring an epitaxial relationship with the substrate Ni-Ge (101); (010) || Ge(001); (110).

  10. The role of SiGe buffer in growth and relaxation of Ge on free-standing Si(001) nano-pillars.

    PubMed

    Zaumseil, P; Kozlowski, G; Schubert, M A; Yamamoto, Y; Bauer, J; Schülli, T U; Tillack, B; Schroeder, T

    2012-09-07

    We study the growth and relaxation processes of Ge nano-clusters selectively grown by chemical vapor deposition on free-standing 90 nm wide Si(001) nano-pillars with a thin Si(0.23)Ge(0.77) buffer layer. We found that the dome-shaped SiGe layer with a height of about 28 nm as well as the Ge dot deposited on top of it partially relaxes, mainly by elastic lattice bending. The Si nano-pillar shows a clear compliance behavior-an elastic response of the substrate on the growing film-with the tensile strained top part of the pillar. Additional annealing at 800 °C leads to the generation of misfit dislocation and reduces the compliance effect significantly. This example demonstrates that despite the compressive strain generated due to the surrounding SiO(2) growth mask it is possible to realize an overall tensile strain in the Si nano-pillar and following a compliant substrate effect by using a SiGe buffer layer. We further show that the SiGe buffer is able to improve the structural quality of the Ge nano-dot.

  11. The role of SiGe buffer in growth and relaxation of Ge on free-standing Si(001) nano-pillars

    NASA Astrophysics Data System (ADS)

    Zaumseil, P.; Kozlowski, G.; Schubert, M. A.; Yamamoto, Y.; Bauer, J.; Schülli, T. U.; Tillack, B.; Schroeder, T.

    2012-09-01

    We study the growth and relaxation processes of Ge nano-clusters selectively grown by chemical vapor deposition on free-standing 90 nm wide Si(001) nano-pillars with a thin Si0.23Ge0.77 buffer layer. We found that the dome-shaped SiGe layer with a height of about 28 nm as well as the Ge dot deposited on top of it partially relaxes, mainly by elastic lattice bending. The Si nano-pillar shows a clear compliance behavior—an elastic response of the substrate on the growing film—with the tensile strained top part of the pillar. Additional annealing at 800 °C leads to the generation of misfit dislocation and reduces the compliance effect significantly. This example demonstrates that despite the compressive strain generated due to the surrounding SiO2 growth mask it is possible to realize an overall tensile strain in the Si nano-pillar and following a compliant substrate effect by using a SiGe buffer layer. We further show that the SiGe buffer is able to improve the structural quality of the Ge nano-dot.

  12. Synthesis of ZnO:Ge Thin Films via Plasma Gas Condensation

    NASA Astrophysics Data System (ADS)

    Ceylan, Abdullah; Ali, Janan; Ozcan, Sadan

    2013-03-01

    we introduce a new method for the synthesis of Ge nanoparticle embedded ZnO thin films that are considered to be a potential candidate for photovoltaic applications. As opposed to current techniques, for the independent preparation of Ge nanoparticles, Cluster Deposition Source (CDS) utilising gas condensation of sputtered Ge atoms is used. For the synthesis of ZnO thin film host material conventional sputtering is employed. In the proposed technique independently synthesized Ge nanoparticles and ZnO thin films are combined into a composite structure on Si. XRD patterns of the samples have revealed that Ge nanoparticles preferentially settle on (113) planes on top of the (002) oriented ZnO layer. It is realized that Ge nanoparticles with sizes ranging from 16 nm to 20 nm could be embedded into a well-defined ZnO matrix. In fact, TEM studies performed on Ge nanoparticles captured on a Cu grids have manifested that Ge reach to ZnO matrix as clusters composed of particles with sizes of about 7-8 nm and then eventually grow larger due to substrate heating implemented during capping layer deposition. Optical absorption measurements have revealed that Ge nanoparticle inclusion lead to an additional absorption edge at about 2.75 eV along with 3.17 eV edge resulting from ZnO host.

  13. Ge nanopillar solar cells epitaxially grown by metalorganic chemical vapor deposition

    PubMed Central

    Kim, Youngjo; Lam, Nguyen Dinh; Kim, Kangho; Park, Won-Kyu; Lee, Jaejin

    2017-01-01

    Radial junction solar cells with vertically aligned wire arrays have been widely studied to improve the power conversion efficiency. In this work, we report the first Ge nanopillar solar cell. Nanopillar arrays are selectively patterned on p-type Ge (100) substrates using nanosphere lithography and deep reactive ion etching processes. Nanoscale radial and planar junctions are realized by an n-type Ge emitter layer which is epitaxially grown by MOCVD using isobutylgermane. In situ epitaxial surface passivation is employed using an InGaP layer to avoid high surface recombination rates and Fermi level pinning. High quality n-ohmic contact is realized by protecting the top contact area during the nanopillar patterning. The short circuit current density and the power conversion efficiency of the Ge nanopillar solar cell are demonstrated to be improved up to 18 and 30%, respectively, compared to those of the Ge solar cell with a planar surface. PMID:28209964

  14. Ge nanopillar solar cells epitaxially grown by metalorganic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Kim, Youngjo; Lam, Nguyen Dinh; Kim, Kangho; Park, Won-Kyu; Lee, Jaejin

    2017-02-01

    Radial junction solar cells with vertically aligned wire arrays have been widely studied to improve the power conversion efficiency. In this work, we report the first Ge nanopillar solar cell. Nanopillar arrays are selectively patterned on p-type Ge (100) substrates using nanosphere lithography and deep reactive ion etching processes. Nanoscale radial and planar junctions are realized by an n-type Ge emitter layer which is epitaxially grown by MOCVD using isobutylgermane. In situ epitaxial surface passivation is employed using an InGaP layer to avoid high surface recombination rates and Fermi level pinning. High quality n-ohmic contact is realized by protecting the top contact area during the nanopillar patterning. The short circuit current density and the power conversion efficiency of the Ge nanopillar solar cell are demonstrated to be improved up to 18 and 30%, respectively, compared to those of the Ge solar cell with a planar surface.

  15. Interface bond relaxation on the thermal conductivity of Si/Ge core-shell nanowires

    SciTech Connect

    Chen, Weifeng; He, Yan; Ouyang, Gang; Sun, Changqing

    2016-01-15

    The thermal conductivity of Si/Ge core-shell nanowires (CSNWs) is investigated on the basis of atomic-bond-relaxation consideration and continuum mechanics. An analytical model is developed to clarify the interface bond relaxation of Si/Ge CSNWs. It is found that the thermal conductivity of Si core can be modulated through covering with Ge epitaxial layers. The change of thermal conductivity in Si/Ge CSNWs should be attributed to the surface relaxation and interface mismatch between inner Si nanowire and outer Ge epitaxial layer. Our results are in well agreement with the experimental measurements and simulations, suggesting that the presented method provides a fundamental insight of the thermal conductivity of CSNWs from the atomistic origin.

  16. Promising features of low-temperature grown Ge nanostructures on Si(001) substrates

    NASA Astrophysics Data System (ADS)

    Wang, Ze; Wang, Shuguang; Yin, Yefei; Liu, Tao; Lin, Dongdong; Li, De-hui; Yang, Xinju; Jiang, Zuimin; Zhong, Zhenyang

    2017-03-01

    High-quality Ge nanostructures are obtained by molecular beam epitaxy of Ge on Si(001) substrates at 200 °C and ex situ annealing at 400 °C. Their structural properties are comprehensively characterized by atomic force microscopy, transmission electron microscopy and Raman spectroscopy. It is disclosed that they are almost defect free except for some defects at the Ge/Si interface and in the subsequent Si capping layer. The misfit strain in the nanostructure is substantially relaxed. Dramatically strong photoluminescence (PL) from the Ge nanostructures is observed. Detailed analyses on the power- and temperature-dependent PL spectra, together with a self-consistent calculation, indicate the confinement and the high quantum efficiency of excitons within the Ge nanostructures. Our results demonstrate that the Ge nanostructures obtained via the present feasible route may have great potential in optoelectronic devices for monolithic optical–electronic integration circuits.

  17. Promising features of low-temperature grown Ge nanostructures on Si(001) substrates.

    PubMed

    Wang, Ze; Wang, Shuguang; Yin, Yefei; Liu, Tao; Lin, Dongdong; Li, De-Hui; Yang, Xinju; Jiang, Zuimin; Zhong, Zhenyang

    2017-03-17

    High-quality Ge nanostructures are obtained by molecular beam epitaxy of Ge on Si(001) substrates at 200 °C and ex situ annealing at 400 °C. Their structural properties are comprehensively characterized by atomic force microscopy, transmission electron microscopy and Raman spectroscopy. It is disclosed that they are almost defect free except for some defects at the Ge/Si interface and in the subsequent Si capping layer. The misfit strain in the nanostructure is substantially relaxed. Dramatically strong photoluminescence (PL) from the Ge nanostructures is observed. Detailed analyses on the power- and temperature-dependent PL spectra, together with a self-consistent calculation, indicate the confinement and the high quantum efficiency of excitons within the Ge nanostructures. Our results demonstrate that the Ge nanostructures obtained via the present feasible route may have great potential in optoelectronic devices for monolithic optical-electronic integration circuits.

  18. 193 nm Excimer laser processing of Si/Ge/Si(100) micropatterns

    NASA Astrophysics Data System (ADS)

    Gontad, F.; Conde, J. C.; Chiussi, S.; Serra, C.; González, P.

    2016-01-01

    193 nm Excimer laser assisted growth and crystallization of amorphous Si/Ge bilayer patterns with circular structures of 3 μm diameter and around 25 nm total thickness, is presented. Amorphous patterns were grown by Laser induced Chemical Vapor Deposition, using nanostencils as shadow masks and then irradiated with the same laser to induce structural and compositional modifications for producing crystalline SiGe alloys through fast melting/solidification cycles. Compositional and structural analyses demonstrated that pulses of 240 mJ/cm2 lead to graded SiGe alloys with Si rich discs of 2 μm diameter on top, a buried Ge layer, and Ge rich SiGe rings surrounding each feature, as predicted by previous numerical simulation.

  19. Effect of nanocavities on Ge nanoclustering and out-diffusion in SiO2

    NASA Astrophysics Data System (ADS)

    Li, Chen; Feng, Honglei; Liu, Bin; Liang, Wenshuang; Liu, Guiju; Ross, Guy G.; Wang, Yiqian; Barba, David

    2017-01-01

    Germanium nanocrystals (Ge-ncs) were synthesized by implantation of Ge+ ions into the fused silica, followed by a thermal annealing at 1000 °C. High-resolution transmission electron microscopy was employed to characterize both the morphology of the formed Ge-ncs and the evolution of their depth-distribution as a function of annealing durations. The formation of nanocavities in the vicinity of nanocrystal/SiO2 interface is evidenced, as well as their influence on the release of the compressive stress exerted on Ge-ncs by surrounding SiO2. Some Ge-ncs are found inside nanocavities, and can move into the implanted layer through a nanocavity-assisted diffusion mechanism. This finding sheds light on a new process that can explain the non-uniformity of the Ge-nanocrystal spatial distribution.

  20. Intermediate inputs and economic productivity.

    PubMed

    Baptist, Simon; Hepburn, Cameron

    2013-03-13

    Many models of economic growth exclude materials, energy and other intermediate inputs from the production function. Growing environmental pressures and resource prices suggest that this may be increasingly inappropriate. This paper explores the relationship between intermediate input intensity, productivity and national accounts using a panel dataset of manufacturing subsectors in the USA over 47 years. The first contribution is to identify sectoral production functions that incorporate intermediate inputs, while allowing for heterogeneity in both technology and productivity. The second contribution is that the paper finds a negative correlation between intermediate input intensity and total factor productivity (TFP)--sectors that are less intensive in their use of intermediate inputs have higher productivity. This finding is replicated at the firm level. We propose tentative hypotheses to explain this association, but testing and further disaggregation of intermediate inputs is left for further work. Further work could also explore more directly the relationship between material inputs and economic growth--given the high proportion of materials in intermediate inputs, the results in this paper are suggestive of further work on material efficiency. Depending upon the nature of the mechanism linking a reduction in intermediate input intensity to an increase in TFP, the implications could be significant. A third contribution is to suggest that an empirical bias in productivity, as measured in national accounts, may arise due to the exclusion of intermediate inputs. Current conventions of measuring productivity in national accounts may overstate the productivity of resource-intensive sectors relative to other sectors.

  1. [Intermediate endpoints in clinical research].

    PubMed

    Peters, Sanne A E; Groenwold, Rolf H H; Bots, Michiel L

    2013-01-01

    An intermediate variable such as blood pressure is part of the causal pathway of mechanisms to a clinical outcome, e.g. myocardial infarction. An intervention affects a clinical outcome through its effect on that intermediate variable. In studies designed to assess the effects of interventions an intermediate variable may be used as surrogate for clinical outcomes. Such an endpoint is also known as an intermediate endpoint. Intervention studies with intermediate endpoints are commonly performed in medical research to evaluate the effects of an intervention on clinical outcomes. Intervention studies with an intermediate endpoint are conducted in a smaller study population and with a shorter duration of follow-up than studies using clinical outcomes. An intermediate variable is not eligible as an intermediate endpoint when the intervention also affects other biological mechanisms that subsequently affect the clinical endpoint. Due to a smaller sample size and shorter study duration, side effects of intervention are more difficult to evaluate in studies with an intermediate endpoint than in studies with clinical endpoints.

  2. SrInGe and EuInGe: new Zintl phases with an unusual anionic network derived from the ThSi(2) structure.

    PubMed

    Mao, Jiang-Gao; Goodey, Joanna; Guloy, Arnold M

    2002-02-25

    Two new isostructural Zintl phases, EuInGe and SrInGe, are obtained from high-temperature reactions of the pure elements in welded Ta tubes. Both ternary phases crystallize in a new structure type in space group Pnma (No. 62), with a = 4.921(1) A, b = 3.9865(9) A, and c = 16.004(3) A for EuInGe; and a = 5.021(1) A, b = 4.0455(9) A, and c = 16.188(4) A for SrInGe. The crystal structures established by single-crystal X-ray diffraction feature zigzag chains of 3-bonded Ge atoms and puckered layers of 4-bonded In atoms. The two structural units are linked into an anionic network with channels composed of 5-membered and 7-membered rings. The channels are filled by the respective divalent cations. The chemical bonding of the anionic [InGe](2)(-) network, derived from a one-electron oxidative distortion of the alpha-ThSi(2) structure, is explained using extended-Hückel band structure calculations. Magnetic measurements indicate that EuInGe exhibits Curie-Weiss paramagnetic behavior above 35 K and antiferromagnetic behavior below 35 K. The calculated effective moment, mu(eff) = 8.11 mu(B), of EuInGe and the diamagnetic behavior of SrInGe are consistent with the oxidation states of Eu(II) and Sr(II), respectively.

  3. Structure and infrared photoluminescence of GeSi nanocrystals formed by high temperature annealing of GeOx/SiO2 multilayers

    NASA Astrophysics Data System (ADS)

    Volodin, V. A.; Gambaryan, M. P.; Cherkov, A. G.; Stoffel, M.; Rinnert, H.; Vergnat, M.

    2016-08-01

    Germanium and GeSi nanocrystals were synthesized in SiGeO2 glass by high temperature annealings of GeOx(5 nm)/SiO2(5 nm) multilayers. According to electron microscopy data, the size distribution and stoichiometry of the nanocrystals depend on the annealing temperature (700, 800, or 900 °C). Spatial redistribution of Ge with the formation of large faceted nanocrystals located near the Si substrate and GeSi intermixing at the substrate/film interface were observed. In the case of the 900 °C annealed sample, we note that some nanocrystals have a pyramid-like shape. Infrared absorption spectroscopy demonstrates that intermixing takes place between the GeOx and SiO2 layers leading to the formation of SiGeO2 glass. Raman spectroscopy confirms the formation of Ge nanocrystals after annealing at 700 °C and GeSi nanocrystals after annealing at 800 and 900 °C. For all annealed samples, we report the observation of infrared photoluminescence (PL) at low temperatures in the spectral range 1300-2100 nm. The observation of PL at wavelengths close to 2000 nm may be due to defect-induced radiative transitions in the nanocrystals.

  4. Structure and magnetism in strained Ge1-x-ySnxMny films grown on Ge(001) by low temperature molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Prestat, E.; Barski, A.; Bellet-Amalric, E.; Jacquot, J.-F.; Morel, R.; Tainoff, D.; Jain, A.; Porret, C.; Bayle-Guillemaud, P.; Jamet, M.

    2013-07-01

    In this letter, we study the structural and magnetic properties of Ge1-x-ySnxMny films grown on Ge(001) by low temperature molecular beam epitaxy using X-ray diffraction, high resolution transmission electron microscopy, and superconducting quantum interference device. Like in Mn doped Ge films, Mn atoms diffuse during the growth and aggregate into vertically aligned Mn-rich nanocolumns of a few nanometers in diameter. Transmission electron microscopy observations in plane view clearly indicate that the Sn incorporation is not uniform with concentration in Mn rich vertical nanocolumns lower than the detection limit of electron energy loss spectroscopy. The matrix exhibits a GeSn solid solution while there is a Sn-rich GeSn shell around GeMn nanocolumns. The magnetization in Ge1-x-ySnxMny layers is higher than in Ge1-xMnx films. This magnetic moment enhancement in Ge1-x-ySnxMny is probably related to the modification of the electronic structure of Mn atoms in the nanocolumns by the Sn-rich shell, which is formed around the nanocolumns.

  5. Tuning the properties of Ge-quantum dots superlattices in amorphous silica matrix through deposition conditions

    SciTech Connect

    Pinto, S.; Roldan Gutierrez, Manuel A; Ramos, M. M.D.; Gomes, M.J.M.; Molina, S. I.; Pennycook, Stephen J; Varela del Arco, Maria; Buljan, M.; Barradas, N.; Alves, E.; Chahboun, A.; Bernstorff, S.

    2012-01-01

    In this work, we investigate the structural properties of Ge quantum dot lattices in amorphous silica matrix, prepared by low-temperature magnetron sputtering deposition of (Ge+SiO{sub 2})/SiO{sub 2} multilayers. The dependence of quantum dot shape, size, separation, and arrangement type on the Ge-rich (Ge + SiO{sub 2}) layer thickness is studied. We show that the quantum dots are elongated along the growth direction, perpendicular to the multilayer surface. The size of the quantum dots and their separation along the growth direction can be tuned by changing the Ge-rich layer thickness. The average value of the quantum dots size along the lateral (in-plane) direction along with their lateral separation is not affected by the thickness of the Ge-rich layer. However, the thickness of the Ge-rich layer significantly affects the quantum dot ordering. In addition, we investigate the dependence of the multilayer average atomic composition and also the quantum dot crystalline quality on the deposition parameters.

  6. Tuning the properties of Ge-quantum dots superlattices in amorphous silica matrix through deposition conditions

    SciTech Connect

    Pinto, S. R. C.; Ramos, M. M. D.; Gomes, M. J. M.; Buljan, M.; Chahboun, A.; Roldan, M. A.; Molina, S. I.; Bernstorff, S.; Varela, M.; Pennycook, S. J.; Barradas, N. P.; Alves, E.

    2012-04-01

    In this work, we investigate the structural properties of Ge quantum dot lattices in amorphous silica matrix, prepared by low-temperature magnetron sputtering deposition of (Ge+SiO{sub 2})/SiO{sub 2} multilayers. The dependence of quantum dot shape, size, separation, and arrangement type on the Ge-rich (Ge + SiO{sub 2}) layer thickness is studied. We show that the quantum dots are elongated along the growth direction, perpendicular to the multilayer surface. The size of the quantum dots and their separation along the growth direction can be tuned by changing the Ge-rich layer thickness. The average value of the quantum dots size along the lateral (in-plane) direction along with their lateral separation is not affected by the thickness of the Ge-rich layer. However, the thickness of the Ge-rich layer significantly affects the quantum dot ordering. In addition, we investigate the dependence of the multilayer average atomic composition and also the quantum dot crystalline quality on the deposition parameters.

  7. Ba termination of Ge(001) studied with STM.

    PubMed

    Koczorowski, W; Grzela, T; Radny, M W; Schofield, S R; Capellini, G; Czajka, R; Schroeder, T; Curson, N J

    2015-04-17

    We use controlled annealing to tune the interfacial properties of a sub-monolayer and monolayer coverages of Ba atoms deposited on Ge(001), enabling the generation of either of two fundamentally distinct interfacial phases, as revealed by scanning tunneling microscopy. Firstly we identify the two key structural phases associated with this adsorption system, namely on-top adsorption and surface alloy formation, by performing a deposition and annealing experiment at a coverage low enough (∼0.15 ML) that isolated Ba-related features can be individually resolved. Subsequently we investigate the monolayer coverage case, of interest for passivation schemes of future Ge based devices, for which we find that the thermal evaporation of Ba onto a Ge(001) surface at room temperature results in on-top adsorption. This separation (lack of intermixing) between Ba and Ge layers is retained through successive annealing steps to temperatures of 470, 570, 670 and 770 K although a gradual ordering of the Ba layer is observed at 570 K and above, accompanied by a decrease in Ba layer density. Annealing above 770 K produces the 2D surface alloy phase accompanied by strain relief through monolayer height trench formation. An annealing temperature of 1070 K sees a further change in surface morphology but retention of the 2D surface alloy characteristic. These results are discussed in view of their possible implications for future semiconductor integrated circuit technology.

  8. Ba termination of Ge(001) studied with STM

    NASA Astrophysics Data System (ADS)

    Curson, Neil; Koczorowski, Wojciech; Grzela, Tomasz; Radny, Marian; Schofield, Steven; Capellini, Giovanni; Czajka, Ryszard; Schroeder, Thomas

    2015-03-01

    We use controlled annealing to tune the interfacial properties of a sub-monolayer and monolayer coverages of Ba atoms deposited on Ge(001), enabling the generation of either of two fundamentally distinct interfacial phases, as revealed by scanning tunneling microscopy (STM). Firstly we identify the two key structural phases associated with this adsorption system, namely on-top adsorption and surface alloy formation, by performing a deposition and annealing experiment at a coverage low enough (0.15 ML) such that isolated Ba-related features can be individually resolved. Subsequently we investigate the monolayer coverage case, of interest for passivation schemes of future Ge based devices, for which we find that thermal evaporation of Ba onto a Ge(001) surface at room temperature results in on-top adsorption. This separation (lack of intermixing) between Ba and Ge layers is retained through successive annealing steps up to 770 K with a gradual ordering of the Ba layer at 570 K and above and a decrease in Ba layer density. Annealing above 770 K produces the 2-D surface alloy phase accompanied by strain relief through monolayer height trench formation. At 1070 K the surface morphology changes again but remains a 2-D surface alloy. WK and NJC acknowledge EPSRC grant EP/I02865X/1. WK, MWR and R.C. acknowledge the Polish Ministry of Science and Higher Education for support (Project No. N-N202-195840).

  9. Comparative study of GeO2/Ge and SiO2/Si structures on anomalous charging of oxide films upon water adsorption revealed by ambient-pressure X-ray photoelectron spectroscopy

    NASA Astrophysics Data System (ADS)

    Mori, Daichi; Oka, Hiroshi; Hosoi, Takuji; Kawai, Kentaro; Morita, Mizuho; Crumlin, Ethan J.; Liu, Zhi; Watanabe, Heiji; Arima, Kenta

    2016-09-01

    The energy difference between the oxide and bulk peaks in X-ray photoelectron spectroscopy (XPS) spectra was investigated for both GeO2/Ge and SiO2/Si structures with thickness-controlled water films. This was achieved by obtaining XPS spectra at various values of relative humidity (RH) of up to ˜15%. The increase in the energy shift is more significant for thermal GeO2 on Ge than for thermal SiO2 on Si above ˜10-4% RH, which is due to the larger amount of water molecules that infiltrate into the GeO2 film to form hydroxyls. Analyzing the origins of this energy shift, we propose that the positive charging of a partially hydroxylated GeO2 film, which is unrelated to X-ray irradiation, causes the larger energy shift for GeO2/Ge than for SiO2/Si. A possible microscopic mechanism of this intrinsic positive charging is the emission of electrons from adsorbed water species in the suboxide layer of the GeO2 film to the Ge bulk, leaving immobile cations or positively charged states in the oxide. This may be related to the reported negative shift of flat band voltages in metal-oxide-semiconductor diodes with an air-exposed GeO2 layer.

  10. Strain distributions and electronic property modifications in Si/Ge axial nanowire heterostructures

    SciTech Connect

    Swadener, John Gregory; Picraux, Samuel T

    2008-01-01

    Molecular dynamics simulations were carried out for Si/Ge axial nanowire heterostructures using modified effective atom method (MEAM) potentials. A Si-Ge MEAM interatomic cross potential was developed based on available experimental data and used for these studies. The atomic distortions and strain distributions near the Si/Ge interfaces are predicted for nanowires with their axes oriented along the [111] direction. The cases of 10 and 25 nm diameter SilGe biwires and of 25 nm diameter Si/Ge/Si axial heterostructures with the Ge disc 1 nm thick were studied. Substantial distortions in the height of the atoms adjacent to the interface were found for the biwires, but not for the Ge discs. Strains as high as 3.5% were found for the Ge disc and values of 2 to 2.5% were found at the Si and Ge interfacial layers in the biwires. Deformation potential theory was used to estimate the influence of the strains on the band gap, and reductions in band gap to as small as 40% of bulk values are predicted for the Ge discs. Localized regions of increased strain and resulting energy minima were also found within the Si/Ge biwire interfaces with the larger effects on the Ge side of the interface. The regions of strain maxima near and within the interfaces are anticipated to be useful for tailoring band gaps and producing quantum confinement of carriers. These results suggest nanowire heterostructures provide greater design flexibility in band structure modification than is possible with planar layer growth.

  11. Interface-controlled layer exchange in metal-induced crystallization of germanium thin films

    NASA Astrophysics Data System (ADS)

    Hu, Shu; Marshall, Ann F.; McIntyre, Paul C.

    2010-08-01

    Low-temperature synthesis of polycrystalline germanium (poly-Ge) thin films is of great interest in thin-film photovoltaic and electronics applications. We demonstrate metal (Al)-induced crystallization to form poly-Ge thin films on both glass and polymer substrates at temperatures as low as 200 °C. An interfacial diffusion control layer, intentionally interposed between the Al and the underlying amorphous Ge (a-Ge) layer, is found to achieve layer exchange while suppressing uncontrolled Ge crystallization within the bilayer samples. Germanium thin films with micron-size grains and (111)-preferred orientation are prepared by controlled Ge nucleation and Ge lateral overgrowth of Al during a-Ge crystallization.

  12. Intermediate BL Lac objects

    NASA Astrophysics Data System (ADS)

    Bondi, M.; Marchã, M. J. M.; Dallacasa, D.; Stanghellini, C.

    2001-08-01

    The 200-mJy sample, defined by Marchã et al., contains about 60 nearby, northern, flat-spectrum radio sources. In particular, the sample has proved effective at finding nearby radio-selected BL Lac objects with radio luminosities comparable to those of X-ray-selected objects, and low-luminosity flat-spectrum weak emission-line radio galaxies (WLRGs). The 200-mJy sample contains 23 BL Lac objects (including 6 BL Lac candidates) and 19 WLRGs. We will refer to these subsamples as the 200-mJy BL Lac sample and the 200-mJy WLRG sample, respectively. We have started a systematic analysis of the morphological pc-scale properties of the 200-mJy radio sources using VLBI observations. This paper presents VLBI observations at 5 and 1.6GHz of 14 BL Lac objects and WLRGs selected from the 200-mJy sample. The pc-scale morphology of these objects is briefly discussed. We derive the radio beaming parameters of the 200-mJy BL Lac objects and WLRGs and compare them with those of other BL Lac samples and with a sample of FR I radio galaxies. The overall broad-band radio, optical and X-ray properties of the 200-mJy BL Lac sample are discussed and compared with those of other BL Lac samples, radio- and X-ray-selected. We find that the 200-mJy BL Lac objects fill the gap between HBL and LBL objects in the colour-colour plot, and have intermediate αXOX as expected in the spectral energy distribution unification scenario. Finally, we briefly discuss the role of the WLRGs.

  13. Monolithically integrated Ge CMOS laser

    NASA Astrophysics Data System (ADS)

    Camacho-Aguilera, Rodolfo

    2014-02-01

    Ge-on-Si devices are explored for photonic integration. Through the development of better growth techniques, monolithic integration, laser design and prototypes, it was possible to probe Ge light emitters with emphasis on lasers. Preliminary worked shows thermal photonic behavior capable of enhancing lamination at high temperatures. Increase luminescence is observed up to 120°C from L-band contribution. Higher temperatures show contribution from Δ -band. The increase carrier thermal contribution suggests high temperature applications for Ge light emitters. A Ge electrically pumped laser was probed under 0.2% biaxial strain and doping concentration ~4.5×1019cm-3 n-type. Ge pnn lasers exhibit a gain >1000cm-1 with 8mW power output, presenting a spectrum range of over 200nm, making Ge the ideal candidate for Si photonics. Large temperatures fluctuations and process limit the present device. Theoretically a gain of >4000cm- gain is possible with a threshold of as low as 1kA/cm2. Improvements in Ge work

  14. Observation of Ge bottom cells in InGaP/InGaAs/Ge triple-junction solar cells

    NASA Astrophysics Data System (ADS)

    Jung, Haeyong; Jung, Sang Hyun; Kim, Chang Zoo; Jun, Dong Hwan; Kang, Ho Kwan; Kim, Hogyoung

    2014-10-01

    After growing InGaP/InGaAs/Ge triple-junction solar cells, we prepared two different Ge cells by etching down to the GaAs buffer layer (sample A) and the AlGaAs layer (sample B). Then, the photovoltaic properties of these two Ge cells were investigated under various light concentrations in order to find the factors affecting the overall performance of the triple-junction solar cells. Under concentrated light, the open-circuit voltage ( V OC ), fill factor and conversion efficiency were higher for sample A than for sample B. The external quantum efficiency was shown to have a slightly higher value for sample A. Both the tunnel junction layer and the top contact resistance increased the series resistance, which also provided defects acting as leakage path. A comparison to previous works suggests that the conversion efficiency of Ge bottom, if present, is degraded marginally after the growth of the full structure of triple-junction solar cells.

  15. Sur le ternaire Tl sbnd Ge sbnd Te: Etude structurale de la phase Tl 2GeTe 5

    NASA Astrophysics Data System (ADS)

    Toure, Abdoulaye Abba; Kra, Gabrielle; Eholie, Rose; Olivier-Fourcade, Josette; Jumas, Jean-Claude; Maurin, Maurice

    1990-02-01

    Tl 2GeTe 5 is orthorhombic, space group Cmmm, with cell dimensions a = 11.657 (5), b = 11.657 (5), c = 14.917 (5), AandZ = 8. The crystal structure was determined by means of direct methods based on three-dimensional X-ray data. Atomic parameters were refined by a least-squares method to a final R value of 0.077 (507 observed reflexions). The structure can be described in terms of layers parallel to the [001] plane and characterized by (Ge 2Te 6) 4- anions and Te 4 clusters.

  16. Printing. Performance Objectives. Intermediate Course.

    ERIC Educational Resources Information Center

    Seivert, Chester

    Several intermediate performance objectives and corresponding criterion measures are listed for each of 13 terminal objectives for an intermediate printing course. The materials were developed for a two-semester (3 hours daily) course with specialized classroom, shop, and practical experiences designed to enable the student to develop proficiency…

  17. Masonry. Performance Objectives. Intermediate Course.

    ERIC Educational Resources Information Center

    Thompson, Moses

    Several intermediate performance objectives and corresponding criterion measures are listed for each of 13 terminal objectives for an intermediate masonry course. These materials, developed for a two-semester (3 hours daily) course, are designed to provide the student with the skills and knowledge necessary for entry level employment in the field…

  18. Welding. Performance Objectives. Intermediate Course.

    ERIC Educational Resources Information Center

    Vincent, Kenneth

    Several intermediate performance objectives and corresponding criterion measures are listed for each of nine terminal objectives for an intermediate welding course. The materials were developed for a 36-week (3 hours daily) course designed to prepare the student for employment in the field of welding. Electric welding and specialized (TIG & MIG)…

  19. Dee-Mack Intermediate School

    ERIC Educational Resources Information Center

    Northwest Evaluation Association, 2012

    2012-01-01

    Frank Reliford, the Principal at Dee-Mack Intermediate since 2005, is familiar to almost every child in the community. 260 Students attend Reliford's school, and their status is a point of pride: Dee-Mack Intermediate is consistently one of the highest performing schools in the state. The change in student performance correlates to the…

  20. Molten Au/Ge alloy migration in Ge nanowires.

    PubMed

    Liu, Qian; Zou, Rujia; Wu, Jianghong; Xu, Kaibing; Lu, Aijiang; Bando, Yoshio; Golberg, Dmitri; Hu, Junqing

    2015-05-13

    Herein, we report time-resolved in situ transmission electron microscopy observation of Au particle melting at a Ge nanowire tip, subsequent forming of Au/Ge alloy liquid, and its migrating within the Ge nanowire. The migration direction and position of the Au/Ge liquid can be controlled by the applied voltage and the migration speed shows a linear deceleration in the nanowire. In a migration model proposed, the relevant dynamic mechanisms (electromigration, thermodiffusion, and viscous force, etc.) are discussed in detail. This work associated with the liquid mass transport in the solid nanowires should provide new insights into the crystal growth, interface engineering, and fabrication of the heterogeneous nanostructure-based devices.

  1. Uniaxially stressed Ge:Ga and Ge:Be

    SciTech Connect

    Dubon, O.D. Jr.

    1992-12-01

    The application of a large uniaxial stress to p-type Ge single crystals changes the character of both the valence band and the energy levels associated with the acceptors. Changes include the splitting of the fourfold degeneracy of the valence band top and the reduction of the ionization energy of shallow acceptors. In order to study the effect of uniaxial stress on transport properties of photoexcited holes, a variable temperature photo-Hall effect system was built in which stressed Ge:Ga and Ge:Be could be characterized. Results indicate that stress increases the lifetime and Hall mobility of photoexcited holes. These observations may help further the understanding of fundamental physical processes that affect the performance of stressed Ge photoconductors including the capture of holes by shallow acceptors.

  2. Antimony segregation in stressed SiGe heterostructures grown by molecular beam epitaxy

    SciTech Connect

    Drozdov, M. N.; Novikov, A. V.; Yurasov, D. V.

    2013-11-15

    The effects of the growth temperature, composition, and elastic strains in separate layers on the segregation of antimony are studied experimentally for stressed SiGe structures grown by molecular beam epitaxy. It is established that the growth conditions and parameters of the structures exert an interrelated influence on the segregation of Sb: the degree of the influence of the composition and elastic stresses in the SiGe layers on Sb segregation depends on the growth temperature. It is shown that usage of a method previously proposed by us for the selective doping of silicon structures with consideration for the obtained dependences of Sb segregation on the growth conditions and parameters of the SiGe layers makes it possible to form SiGe structures selectively doped with antimony.

  3. High Curie temperature Mn5Ge3 thin films produced by non-diffusive reaction

    NASA Astrophysics Data System (ADS)

    Assaf, E.; Portavoce, A.; Hoummada, K.; Bertoglio, M.; Bertaina, S.

    2017-02-01

    Polycrystalline Mn5Ge3 thin films were produced on SiO2 using magnetron sputtering and reactive diffusion (RD) or non-diffusive reaction (NDR). In situ X-ray diffraction and atomic force microscopy were used to determine the layer structures, and magnetic force microscopy, superconducting quantum interference device, and ferromagnetic resonance were used to determine their magnetic properties. RD-mediated layers exhibit similar magnetic properties as molecular beam epitaxy-grown monocrystalline Mn5Ge3 thin films, while NDR-mediated layers show magnetic properties similar to monocrystalline C-doped Mn5Ge3Cx thin films with 0.1 ≤ x ≤ 0.2. NDR appears as a complementary metal oxide semi-conductor-compatible efficient method to produce good magnetic quality high-Curie temperature Mn5Ge3 thin films.

  4. Charge trapping properties and retention time in amorphous SiGe/SiO2 nanolayers

    NASA Astrophysics Data System (ADS)

    Vieira, E. M. F.; Diaz, R.; Grisolia, J.; Parisini, A.; Martín-Sánchez, J.; Levichev, S.; Rolo, A. G.; Chahboun, A.; Gomes, M. J. M.

    2013-03-01

    In this paper, we report on the electrical properties of metal-oxide-semiconductor (MOS) capacitors containing a well-confined 8 nm-thick SiGe amorphous layer (a-SiGe) embedded in a SiO2 matrix grown by RF magnetron sputtering at a low temperature (350 °C). Capacitance-voltage measurements show that the introduction of the SiGe layer leads to a significant enhancement of the charge trapping capabilities, with the memory effect and charge retention time larger for hole carriers. The presented results demonstrate that amorphous floating-gate SiGe layers embedded in SiO2 may constitute a suitable alternative for memory applications.

  5. Memory characteristics of metal-oxide-semiconductor structures based on Ge nanoclusters-embedded GeO(x) films grown at low temperature.

    PubMed

    Lin, Tzu-Shun; Lou, Li-Ren; Lee, Ching-Ting; Tsai, Tai-Cheng

    2012-03-01

    The memory devices constructed from the Ge-nanoclusters embedded GeO(x) layer deposited by the laser-assisted chemical vapor deposition (LACVD) system were fabricated. The Ge nanoclusters were observed by a high-resolution transmission electron microscopy. Using the capacitance versus voltage (C-V) and the conductance versus voltage (G-V) characteristics measured under various frequencies, the memory effect observed in the C-V curves was dominantly attributed to the charge storage in the Ge nanoclusters. Furthermore, the defects existed in the deposited film and the interface states were insignificant to the memory performances. Capacitance versus time (C-t) measurement was also executed to evaluate the charge retention characteristics. The charge storage and retention behaviors of the devices demonstrated that the Ge nanoclusters grown by the LACVD system at low temperature are promising for memory device applications.

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

    NASA Astrophysics Data System (ADS)

    Peterson, Jeffrey John

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

  7. Intermediate dosimetric quantities.

    PubMed

    Kellerer, A M; Hahn, K; Rossi, H H

    1992-04-01

    The transfer of energy from ionizing radiation to matter involves a series of steps. In wide ranges of their energy spectra photons and neutrons transfer energy to an irradiated medium almost exclusively by the production of charged particles which ionize and thereby produce electrons that can ionize in turn. The examination of these processes leads to a series of intermediate quantities. One of these is kerma, which has long been employed as a measure of the energy imparted in the first of the interactions. It depends only on the fluence of uncharged particles and is therefore--unlike absorbed dose and electron fluence--insensitive to local differences of receptor geometry and composition. An analogous quantity for charged-particle fields, cema (converted energy per unit mass), is defined, which quantifies the energy imparted in terms of the interactions of charged particles, disregarding energy dissipation by secondary electrons. Cema can be expressed as an integral over the fluence of ions times their stopping power. However, complications arise when the charged particles are electrons, and when their fluence cannot be separated from that of the secondaries. The resulting difficulty can be circumvented by the definition of reduced cema. This quantity corresponds largely to the concept employed in the cavity theory of Spencer and Attix. In reduced cema not all secondary electrons but all electrons below a chosen cutoff energy, delta, are considered to be absorbed locally. When the cutoff energy is reduced, cema approaches absorbed dose and thereby becomes sensitive to highly local differences in geometry or composition. With larger values of delta, reduced cema is a useful parameter to specify the dose-generating potential of a charged-particle field 'free in air' or in vacuo. It is nearly equal to the mean absorbed dose in a sphere with radius equal to the range of electrons of energy delta. Reduced cema is a function of the fluence at the specified location at

  8. Optical properties of individual site-controlled Ge quantum dots

    SciTech Connect

    Grydlik, Martyna E-mail: martyna.grydlik@jku.at; Brehm, Moritz E-mail: martyna.grydlik@jku.at; Tayagaki, Takeshi; Langer, Gregor; Schäffler, Friedrich; Schmidt, Oliver G.

    2015-06-22

    We report photoluminescence (PL) experiments on individual SiGe quantum dots (QDs) that were epitaxially grown in a site-controlled fashion on pre-patterned Si(001) substrates. We demonstrate that the PL line-widths of single QDs decrease with excitation power to about 16 meV, a value that is much narrower than any of the previously reported PL signals in the SiGe/Si heterosystem. At low temperatures, the PL-intensity becomes limited by a 25 meV high potential-barrier between the QDs and the surrounding Ge wetting layer (WL). This barrier impedes QD filling from the WL which collects and traps most of the optically excited holes in this type-II heterosystem.

  9. Study of High-Quality GeSn Alloys Grown by Chemical Vapor Deposition towards Mid-Infrared Applications

    NASA Astrophysics Data System (ADS)

    Al-Kabi, Sattar; Ghetmiri, Seyed Amir; Margetis, Joe; Du, Wei; Mosleh, Aboozar; Dou, Wei; Sun, Greg; Soref, Richard A.; Tolle, John; Li, Baohua; Mortazavi, Mansour; Naseem, Hameed A.; Yu, Shui-Qing

    2016-12-01

    Germanium-tin (GeSn) films with Sn compositions from 5% to 11% were grown on Ge-buffered Si using a reduced pressure chemical vapor deposition system with low-cost SnCl4 and GeH4 precursors. Material characterization showed that relaxed GeSn layers with thicknesses ranging from 400 nm to 1 μm were achieved. The strong photoluminescence (PL) intensity and the low defect density indicated very high material quality. In addition, temperature-dependent 10-300 K photoluminescence spectra showed that, due to strain relaxation of the material, the emission wavelength is longer than that of strained GeSn thin film samples ( t < 200 nm) having the same Sn composition. At 300 K, the PL peak at 2520 nm was observed from the sample with a 1- μm-thick GeSn layer and 11% Sn composition.

  10. On the doublet/triplet splitting and intermediate mass scales in locally supersymmetric SO(10)

    NASA Astrophysics Data System (ADS)

    Pulido, João

    1985-01-01

    In the light of the doublet/triplet splitting, the possibilities for an intermediate mass scale in locally supersymmetric SO(10) are analysed. It is found that the subgroup SU(4)c × SU(2)L × SU(2)R and more generally left-right symmetric models are unlikely to survive as intermediate symmetries since they imply too large values of the weak mixing angle. An alternative model using the subgroup SU(3)c × U(1)L × U(1)R is discussed. Requirements from global SUSY preservation impose an extra constraint and predictions for the grand unification and the intermediate masses are obtained at MX ~ 6 × 1015 GeV and MI ~ 1012 GeV. Address after March 1984: Centro de Fisica da Materia Condensada, Av. Prof. Gama Pinto, 2, 1699 Lisbon Codex, Portugal.

  11. Nanostructuring of GeTiO amorphous films by pulsed laser irradiation.

    PubMed

    Teodorescu, Valentin Serban; Ghica, Cornel; Maraloiu, Adrian Valentin; Vlaicu, Mihai; Kuncser, Andrei; Ciurea, Magdalena Lidia; Stavarache, Ionel; Lepadatu, Ana M; Scarisoreanu, Nicu Doinel; Andrei, Andreea; Ion, Valentin; Dinescu, Maria

    2015-01-01

    Laser pulse processing of surfaces and thin films is a useful tool for amorphous thin films crystallization, surface nanostructuring, phase transformation and modification of physical properties of thin films. Here we show the effects of nanostructuring produced at the surface and under the surface of amorphous GeTiO films through laser pulses using fluences of 10-30 mJ/cm(2). The GeTiO films were obtained by RF magnetron sputtering with 50:50 initial atomic ratio of Ge:TiO2. Laser irradiation was performed by using the fourth harmonic (266 nm) of a Nd:YAG laser. The laser-induced nanostructuring results in two effects, the first one is the appearance of a wave-like topography at the film surface, with a periodicity of 200 nm and the second one is the structure modification of a layer under the film surface, at a depth that is related to the absorption length of the laser radiation. The periodicity of the wave-like relief is smaller than the laser wavelength. In the modified layer, the Ge atoms are segregated in spherical amorphous nanoparticles as a result of the fast diffusion of Ge atoms in the amorphous GeTiO matrix. The temperature estimation of the film surface during the laser pulses shows a maximum of about 500 °C, which is much lower than the melting temperature of the GeTiO matrix. GeO gas is formed at laser fluences higher than 20 mJ/cm(2) and produces nanovoids in the laser-modified layer at the film surface. A glass transition at low temperatures could happen in the amorphous GeTiO film, which explains the formation of the wave-like topography. The very high Ge diffusivity during the laser pulse action, which is characteristic for liquids, cannot be reached in a viscous matrix. Our experiments show that the diffusivity of atomic and molecular species such as Ge and GeO is very much enhanced in the presence of the laser pulse field. Consequently, the fast diffusion drives the formation of amorphous Ge nanoparticles through the segregation of Ge atoms

  12. Heats of formation of GeH 4, GeF 4 and Ge(CH 3) 4

    NASA Astrophysics Data System (ADS)

    Koizumi, Hideya; Dávalos, Juan Z.; Baer, Tomas

    2006-05-01

    The heats of formation of GeH 4, GeF 4, and Ge(CH 3) 4 are computed at CCSD(T) level of theory at the complete basis set limit. Relativistic effects, core valence correlation, spin orbit effect, and zero point energy are explicitly calculated in this study. Relativistic recoveries for these molecules are investigated with different size of correlation space. An unusually large relativistic effect is observed in GeF 4. Our best calculated geometries for GeH 4 and GeF 4 are in excellent agreement with the high precision experiments. Anharmonic correction to the zero point energy is significant for Ge(CH 3) 4. Our best calculated values for the 298 K heats of formation of GeH 4, GeF 4, and Ge(CH 3) 4 are 82, -1194, and -123 kJ/mol, respectively.

  13. Collectivity at N=50: {sup 82}Ge and {sup 84}Se

    SciTech Connect

    Gade, A.; Baugher, T.; Brown, B. A.; Glasmacher, T.; McDaniel, S.; Meharchand, R.; Ratkiewicz, A.; Walsh, K. A.; Bazin, D.; Campbell, C. M.; Grinyer, G. F.; Weisshaar, D.; Honma, M.; Otsuka, T.; Tostevin, J. A.

    2010-06-15

    The neutron-rich N=50 isotones {sup 82}Ge and {sup 84}Se were investigated using intermediate-energy Coulomb excitation on a {sup 197}Au target and inelastic scattering on {sup 9}Be. As typical for intermediate-energy Coulomb excitation with projectile energies exceeding 70 MeV/nucleon, only the first 2{sup +} states were excited in {sup 82}Ge and {sup 84}Se. However, in the inelastic scattering on a {sup 9}Be target, a strong population of the first 4{sup +} state was observed for {sup 84}Se, while there is no indication of a similarly strong excitation of the corresponding state in the neighboring even-even isotone {sup 82}Ge. The results are discussed in the framework of systematics and shell-model calculations using three different effective interactions.

  14. Fission at intermediate nucleon energies

    NASA Astrophysics Data System (ADS)

    Lo Meo, S.; Mancusi, D.; Massimi, C.; Vannini, G.; Ventura, A.

    2014-07-01

    In the present work Monte Carlo calculations of fission of actinides and pre- actinides induced by protons and neutrons in the energy range from 100 MeV to 1 GeV are carried out by means of a recent version of the Liège Intranuclear Cascade Model, INCL++, coupled with different evaporation-fission codes, in particular GEMINI++ and ABLA07. Fission model parameters are adjusted on experimental (p, f) cross sections and used to predict (n, f) cross sections, in order to provide a theoretical support to the campaign of neutron cross section measurements at the n_TOF facility at CERN.

  15. Geiger mode theoretical study of a wafer-bonded Ge on Si single-photon avalanche photodiode

    NASA Astrophysics Data System (ADS)

    Ke, Shaoying; Lin, Shaoming; Wei, Huang; Wang, Jianyuan; cheng, Buwen; Liang, Kun; Li, Cheng; Chen, Songyan

    2017-02-01

    The investigation of the single-photon properties of a wafer-bonded Ge/Si single-photon avalanche photodiode (SPAD) is theoretically conducted. We focus on the effect of the natural GeO2 layer (hydrophilic reaction) at the Ge/Si wafer-bonded interface on dark count characteristics and single-photon response. It is found that the wafer-bonded Ge/Si SPAD exhibits very low dark current at 250 K due to the absence of threading dislocation (TD) in the Ge layer. Owing to the increase of the unit-gain bias applied on the SPAD, the primary dark current (I DM) increases with the increase in GeO2 thickness. Furthermore, the dependence of the linear-mode gain and 3 dB bandwidth (BW) for the dark count on GeO2 thickness is also presented. It is observed that the dark count probability of the Ge/Si SPAD significantly increases with the increase in GeO2 thickness due to the increase of the I DM and the reduction of the 3 dB BW. It is also found that with the increase in GeO2 thickness, the external quantum efficiency, which affects the single-photon detection efficiency (SPDE), drastically decreases because of the blocking effect of the GeO2 layer and the serious recombination at the wafer-bonded Ge/Si interface. The afterpulsing probability (AP) shows an abnormal behavior with GeO2 thickness. This results from the decrease in avalanche charge and increase in effective transit time.

  16. Sharp Fe/MgO/Ge(001) epitaxial heterostructures for tunneling junctions

    SciTech Connect

    Petti, D.; Cantoni, M.; Rinaldi, C.; Brivio, S.; Bertacco, R.; Gazquez Alabart, Jaume; Varela del Arco, Maria

    2011-01-01

    We report on the growth of epitaxial Fe/MgO/Ge(001) heterostructures by molecular beam epitaxy. The lowest oxidation and highest sharpness of the MgO/Ge interface, corresponding to a transition layer on the order of one Ge unit cell, is obtained for room temperature growth of the MgO layer followed by annealing in a vacuum at 500 C. In these conditions, the MgO layer grows epitaxially on Ge(001) with the [110] direction parallel to the [100] direction of Ge, at variance with the cube-on-cube growth on Si(001) and GaAs(001). However, in some cases, the cube-on-cube growth mode of MgO on Ge competes with the mode involving a 45{sup o} rotation, as revealed by transmission electron microscopy and photoelectron diffraction data on MgO films grown at 300 C without postannealing, and on p-doped Ge substrates. For the Fe overlayer, in all the cases reported, room temperature growth followed by annealing up to 200 C gives rise to a sharp interface and the well-known 45{sup o} rotation of the Fe lattice with respect to the MgO lattice.

  17. Effective Schottky Barrier Height Lowering of Metal/n-Ge with a TiO2/GeO2 Interlayer Stack.

    PubMed

    Kim, Gwang-Sik; Kim, Sun-Woo; Kim, Seung-Hwan; Park, June; Seo, Yujin; Cho, Byung Jin; Shin, Changhwan; Shim, Joon Hyung; Yu, Hyun-Yong

    2016-12-28

    A perfect ohmic contact formation technique for low-resistance source/drain (S/D) contact of germanium (Ge) n-channel metal-oxide-semiconductor field-effect transistors (MOSFETs) is developed. A metal-interlayer-semiconductor (M-I-S) structure with an ultrathin TiO2/GeO2 interlayer stack is introduced into the contact scheme to alleviate Fermi-level pinning (FLP), and reduce the electron Schottky barrier height (SBH). The TiO2 interlayer can alleviate FLP by preventing formation of metal-induced gap states (MIGS) with its very low tunneling resistance and series resistance and can provide very small electron energy barrier at the metal/TiO2 interface. The GeO2 layer can induce further alleviation of FLP by reducing interface state density (Dit) on Ge which is one of main causes of FLP. Moreover, the proposed TiO2/GeO2 stack can minimize interface dipole formation which induces the SBH increase. The M-I-S structure incorporating the TiO2/GeO2 interlayer stack achieves a perfect ohmic characteristic, which has proved unattainable with a single interlayer. FLP can be perfectly alleviated, and the SBH of the metal/n-Ge can be tremendously reduced. The proposed structure (Ti/TiO2/GeO2/n-Ge) exhibits 0.193 eV of effective electron SBH which achieves 0.36 eV of SBH reduction from that of the Ti/n-Ge structure. The proposed M-I-S structure can be suggested as a promising S/D contact technique for nanoscale Ge n-channel transistors to overcome the large electron SBH problem caused by severe FLP.

  18. Short, intermediate and mesoscopic range order in sulfur-rich binary glasses

    SciTech Connect

    Bychkov, E.; Miloshova, M.; Price, D.L.; Benmore, C.J.; Lorriaux, A.

    2008-09-29

    Pulsed neutron and high-energy X-ray diffraction, small-angle neutron scattering, Raman spectroscopy and DSC were used to study structural changes on the short, intermediate and mesoscopic range scale for sulfur-rich AsS{sub x} (x {ge} 1.5) and GeS{sub x} (x {ge} 2) glasses. Two structural regions were found in the both systems. (1) Between stoichiometric (As{sub 2}S{sub 3} and GeS{sub 2}) and 'saturated' (AsS{sub 2.2} and GeS{sub 2.7}) compositions, excessive sulfur atoms form sulfur dimers and/or short chains, replacing bridging sulfur in corner-sharing AsS{sub 3/2} and GeS{sub 4/2} units. (2) Above the 'saturated' compositions at [As] < 30.5 at.% and [Ge] < 27 at.%, sulfur rings and longer sulfur chains (especially in the AsS{sub x} system) appear in the glass network. The glasses become phase separated with the domains of 20-50 {angstrom}, presumably enriched with sulfur rings. The longer chains Sn are not stable and crystallize to c-S{sub 8} on ageing of a few days to several months, depending on composition.

  19. Chemical states and electronic structure of a HfO(-2) / Ge(001) interface

    SciTech Connect

    Seo, Kang-ill; McIntyre, Paul C.; Sun, Shiyu; Lee, Dong-Ick; Pianetta, Piero; Saraswat, Krishna C.; /Stanford U., Elect. Eng. Dept.

    2005-05-04

    We report the chemical bonding structure and valence band alignment at the HfO{sub 2}/Ge (001) interface by systematically probing various core level spectra as well as valence band spectra using soft x-rays at the Stanford Synchrotron Radiation Laboratory. We investigated the chemical bonding changes as a function of depth through the dielectric stack by taking a series of synchrotron photoemission spectra as we etched through the HfO{sub 2} film using a dilute HF-solution. We found that a very non-stoichiometric GeO{sub x} layer exists at the HfO{sub 2}/Ge interface. The valence band spectra near the Fermi level in each different film structure were carefully analyzed, and as a result, the valence band offset between Ge and GeO{sub x} was determined to be {Delta}E{sub v} (Ge-GeO{sub x}) = 2.2 {+-} 0.15 eV, and that between Ge and HfO{sub 2}, {Delta}E{sub v} (Ge-HfO{sub 2}) = 2.7 {+-} 0.15 eV.

  20. Tachyon field in intermediate inflation

    SciTech Connect

    Campo, Sergio del; Herrera, Ramon; Toloza, Adolfo

    2009-04-15

    The tachyonic inflationary universe model in the context of intermediate inflation is studied. General conditions for this model to be realizable are discussed. In the slow-roll approximation, we describe in great detail the characteristics of this model.

  1. Direct growth of Ge quantum dots on a graphene/SiO2/Si structure using ion beam sputtering deposition.

    PubMed

    Zhang, Z; Wang, R F; Zhang, J; Li, H S; Zhang, J; Qiu, F; Yang, J; Wang, C; Yang, Y

    2016-07-29

    The growth of Ge quantum dots (QDs) using the ion beam sputtering deposition technique has been successfully conducted directly on single-layer graphene supported by SiO2/Si substrate. The results show that the morphology and size of Ge QDs on graphene can be modulated by tuning the Ge coverage. Charge transfer behavior, i.e. doping effect in graphene has been demonstrated at the interface of Ge/graphene. Compared with that of traditional Ge dots grown on Si substrate, the positions of both corresponding photoluminescence (PL) peaks of Ge QDs/graphene hybrid structure undergo a large red-shift, which can probably be attributed to the lack of atomic intermixing and the existence of surface states in this hybrid material. According to first-principles calculations, the Ge growth on the graphene should follow the so-called Volmer-Weber mode instead of the Stranski-Krastanow one which is observed generally in the traditional Ge QDs/Si system. The calculations also suggest that the interaction between Ge and graphene layer can be enhanced with the decrease of the Ge coverage. Our results may supply a prototype for fabricating novel optoelectronic devices based on a QDs/graphene hybrid nanostructure.

  2. Direct growth of Ge quantum dots on a graphene/SiO2/Si structure using ion beam sputtering deposition

    NASA Astrophysics Data System (ADS)

    Zhang, Z.; Wang, R. F.; Zhang, J.; Li, H. S.; Zhang, J.; Qiu, F.; Yang, J.; Wang, C.; Yang, Y.

    2016-07-01

    The growth of Ge quantum dots (QDs) using the ion beam sputtering deposition technique has been successfully conducted directly on single-layer graphene supported by SiO2/Si substrate. The results show that the morphology and size of Ge QDs on graphene can be modulated by tuning the Ge coverage. Charge transfer behavior, i.e. doping effect in graphene has been demonstrated at the interface of Ge/graphene. Compared with that of traditional Ge dots grown on Si substrate, the positions of both corresponding photoluminescence (PL) peaks of Ge QDs/graphene hybrid structure undergo a large red-shift, which can probably be attributed to the lack of atomic intermixing and the existence of surface states in this hybrid material. According to first-principles calculations, the Ge growth on the graphene should follow the so-called Volmer-Weber mode instead of the Stranski-Krastanow one which is observed generally in the traditional Ge QDs/Si system. The calculations also suggest that the interaction between Ge and graphene layer can be enhanced with the decrease of the Ge coverage. Our results may supply a prototype for fabricating novel optoelectronic devices based on a QDs/graphene hybrid nanostructure.

  3. Kinetic study of GeO disproportionation into a GeO{sub 2}/Ge system using x-ray photoelectron spectroscopy

    SciTech Connect

    Wang Shengkai; Liu Honggang; Toriumi, Akira

    2012-08-06

    GeO disproportionation into GeO{sub 2} and Ge is studied through x-ray photoelectron spectroscopy. Direct evidence for the reaction 2GeO {yields} GeO{sub 2} + Ge after annealing in ultra-high vacuum is presented. Activation energy for GeO disproportionation is found to be about 0.7 {+-} 0.2 eV through kinetic and thermodynamic calculations. A kinetic model of GeO disproportionation is established by considering oxygen transfer in the GeO network. The relationship between GeO disproportionation and GeO desorption induced by GeO{sub 2}/Ge interfacial reaction is discussed, and the apparent contradiction between GeO desorption via interfacial redox reaction and GeO disproportionation into Ge and GeO{sub 2} is explained by considering the oxygen vacancy.

  4. GaAs/Ge crystals grown on Si substrates patterned down to the micron scale

    SciTech Connect

    Taboada, A. G. Kreiliger, T.; Falub, C. V.; Känel, H. von; Meduňa, M.; Salvalaglio, M.; Miglio, L.; Isa, F.; Barthazy Meier, E.; Müller, E.; Isella, G.

    2016-02-07

    Monolithic integration of III-V compounds into high density Si integrated circuits is a key technological challenge for the next generation of optoelectronic devices. In this work, we report on the metal organic vapor phase epitaxy growth of strain-free GaAs crystals on Si substrates patterned down to the micron scale. The differences in thermal expansion coefficient and lattice parameter are adapted by a 2-μm-thick intermediate Ge layer grown by low-energy plasma enhanced chemical vapor deposition. The GaAs crystals evolve during growth towards a pyramidal shape, with lateral facets composed of (111) planes and an apex formed by (137) and (001) surfaces. The influence of the anisotropic GaAs growth kinetics on the final morphology is highlighted by means of scanning and transmission electron microscopy measurements. The effect of the Si pattern geometry, substrate orientation, and crystal aspect ratio on the GaAs structural properties was investigated by means of high resolution X-ray diffraction. The thermal strain relaxation process of GaAs crystals with different aspect ratio is discussed within the framework of linear elasticity theory by Finite Element Method simulations based on realistic geometries extracted from cross-sectional scanning electron microscopy images.

  5. Sn-enriched Ge/GeSn nanostructures grown by MBE on (001) GaAs and Si wafers

    SciTech Connect

    Sadofyev, Yu. G. Martovitsky, V. P.; Klekovkin, A. V.; Saraykin, V. V.; Vasil’evskii, I. S.

    2015-12-15

    Elastically stressed metastable GeSn layers with a tin molar fraction as large as 0.185 are grown on (001) Si and GaAs wafers covered with a germanium buffer layer. A set of wafers with a deviation angle in the range 0°–10° is used. It is established that the GeSn crystal undergoes monoclinic deformation with the angle β to 88° in addition to tetragonal deformation. Misorientation of the wafers surface results in increasing efficiency of the incorporation of tin adatoms into the GeSn crystal lattice. Phase separation in the solid solution upon postgrowth annealing of the structures begins long before the termination of plastic relaxation of elastic heteroepitaxial stresses. Tin released as a result of GeSn decomposition predominantly tends to be found on the surface of the sample. Manifestations of the brittle–plastic mechanism of the relaxation of stresses resulting in the occurrence of microcracks in the subsurface region of the structures under investigation are found.

  6. Multi-stacks of epitaxial GeSn self-assembled dots in Si: Structural analysis

    SciTech Connect

    Oliveira, F.; Fischer, I. A.; Schulze, J.; Benedetti, A.; Cerqueira, M. F.; Vasilevskiy, M. I.; Stefanov, S.; Chiussi, S.

    2015-03-28

    We report on the growth and structural and morphologic characterization of stacked layers of self-assembled GeSn dots grown on Si (100) substrates by molecular beam epitaxy at low substrate temperature T = 350 °C. Samples consist of layers (from 1 up to 10) of Ge{sub 0.96}Sn{sub 0.04} self-assembled dots separated by Si spacer layers, 10 nm thick. Their structural analysis was performed based on transmission electron microscopy, atomic force microscopy, and Raman scattering. We found that up to 4 stacks of dots could be grown with good dot layer homogeneity, making the GeSn dots interesting candidates for optoelectronic device applications.

  7. Investigation of adatom adsorption on single layer buckled germanium selenide

    NASA Astrophysics Data System (ADS)

    Arkın, H.; Aktürk, E.

    2016-12-01

    A recent study of Hu et al. [1] predicted that 2D single layer of asymmetric washboard germanium selenide is found to be stable and display semiconducting properties. Motivating from this study, we have shown that another phase, which is 2D buckled honeycomb germanium selenide, is also stable. This phase exhibits semiconducting behavior with a band gap of 2.29 eV. Furthermore, on the basis of the first principles, spin-polarized density functional calculations, we investigate the effect of selected adatoms adsorption on the b-GeSe single layer. The adatoms Se, Ge, S, Si, C, Br and P are chemisorbed with significant binding energy where this effects modify the electronic structure of the single layer buckled GeSe locally by tuning the band gap. Net integer magnetic moment can be achieved and b-GeSe attains half metallicity through the adsorption of Si, Ge, P and Br.

  8. Nuclear Structure in 78Ge

    NASA Astrophysics Data System (ADS)

    Forney, Anne M.; Walters, W. B.; Sethi, J.; Chiara, C. J.; Harker, J.; Janssens, R. V. F.; Zhu, S.; Carpenter, M.; Alcorta, M.; Gürdal, G.; Hoffman, C. R.; Kay, B. P.; Kondev, F. G.; Lauristen, T.; Lister, C. J.; McCutchan, E. A.; Rogers, A. M.; Seweryniak, D.

    2017-01-01

    Owing to the importance of the structure of 76Ge in interpreting double β decay studies, the structures of adjacent nuclei have been of considerable interest. Recently reported features for the structures of 72,74,76Ge indicate both shape coexistence and triaxiality. New data for the excited states of 78Ge will be reported arising from Gammasphere studies of multinucleon transfer reactions between a 76Ge beam and thick heavy targets at the ATLAS facility at Argonne National Laboratory. The previously known yrast band is extended to higher spins, candidate levels for a triaxial sequence have been observed, and the associated staggering determined. The staggering in 78Ge found in this work is not in agreement with theoretical work. Candidates for negative-parity states and seniority-four states will be discussed. This material is based upon work supported by the U.S. DOE under DE-AC02-06CH11357 and DE-FG02-94ER40834. Resources of ANL's ATLAS setup, a DOE Office of Science user facility, were used.

  9. Strain relief during Ge hut cluster formation on Si(001) studied by high-resolution LEED and surface-stress-induced optical deflection

    SciTech Connect

    Horn-von Hoegen, M.; Mueller, B.H.; Grabosch, T.; Kury, P.

    2004-12-15

    The kinetics of Ge hut cluster formation and the evolution of film stress have been studied during Ge deposition at 400 and 500 deg. C by high-resolution low-energy electron diffraction and surface-stress-induced optical deflection. The hut clusters grow coherent to the Si substrate but show an increased layer distance of 4% due to strain-induced tetragonal distortion. The distortion of the Ge unit cell adds up to more than 8%. The sudden onset of hut formation is observed at 3.5 monolayers of Ge. Individual hut clusters instantly grow to a width of 20 nm. The strain relief of the order of 15%-20% is maximized by complete dissociation of the Ge wetting layer. Together with this Ge only two additional monolayers of Ge are necessary to cover the entire surface with fully evolved hut clusters.

  10. Observation of field emission from GeSn nanoparticles epitaxially grown on silicon nanopillar arrays

    NASA Astrophysics Data System (ADS)

    Di Bartolomeo, Antonio; Passacantando, Maurizio; Niu, Gang; Schlykow, Viktoria; Lupina, Grzegorz; Giubileo, Filippo; Schroeder, Thomas

    2016-12-01

    We apply molecular beam epitaxy to grow GeSn-nanoparticles on top of Si-nanopillars patterned onto p-type Si wafers. We use x-ray photoelectron spectroscopy to confirm a metallic behavior of the nanoparticle surface due to partial Sn segregation as well as the presence of a superficial Ge oxide. We report the observation of stable field emission (FE) current from the GeSn-nanoparticles, with turn on field of 65 {{V}} μ {{{m}}}-{{1}} and field enhancement factor β ˜ 100 at anode-cathode distance of ˜0.6 μm. We prove that FE can be enhanced by preventing GeSn nanoparticles oxidation or by breaking the oxide layer through electrical stress. Finally, we show that GeSn/p-Si junctions have a rectifying behavior.

  11. Transfer-free synthesis of highly ordered Ge nanowire arrays on glass substrates

    SciTech Connect

    Nakata, M.; Toko, K. Suemasu, T.; Jevasuwan, W.; Fukata, N.; Saitoh, N.; Yoshizawa, N.

    2015-09-28

    Vertically aligned Ge nanowires (NWs) are directly synthesized on glass via vapor-liquid-solid (VLS) growth using chemical-vapor deposition. The use of the (111)-oriented Ge seed layer, formed by metal-induced crystallization at 325 °C, dramatically improved the density, uniformity, and crystal quality of Ge NWs. In particular, the VLS growth at 400 °C allowed us to simultaneously achieve the ordered morphology and high crystal quality of the Ge NW array. Transmission electron microscopy demonstrated that the resulting Ge NWs had no dislocations or stacking faults. Production of high-quality NW arrays on amorphous insulators will promote the widespread application of nanoscale devices.

  12. Measurements of Local Strain Variation in Si(1-x)Ge(x)/Si Heterostructures

    NASA Technical Reports Server (NTRS)

    Bell, L. D.; Kaiser, W. J.; Manion, S. J.; Milliken, S. J.; Pike, W. T.; Fathauer, R. W.

    1995-01-01

    The energy splitting of the conduction-band minimum of Si(1-x), Ge(x), due to strain has been directly measured by the application of ballistic-electron-emission microscope (BEEM) spectroscopy to Ag/Si(1-x), Ge(x) structures. Experimental values for this conduction-band splitting agree well with calculations. For Au/Si(1-x), Ge(x), however, heterogeneity in the strain of the Si(1-x), Ge(x) layer is introduced by deposition of the Au. This variation is attributed to species interdiffusion, which produces a rough Si(1-x)Ge(x) surface. Preliminary modeling indicates that the observed roughness is consistent with the strain variation measured by BEEM.

  13. Nanoporosity induced by ion implantation in deposited amorphous Ge thin films

    SciTech Connect

    Romano, L.; Impellizzeri, G.; Ruffino, F.; Miritello, M.; Grimaldi, M. G.; Bosco, L.

    2012-06-01

    The formation of a nano-porous structure in amorphous Ge thin film (sputter-deposited on SiO{sub 2}) during ion irradiation at room temperature with 300 keV Ge{sup +} has been observed. The porous film showed a sponge-like structure substantially different from the columnar structure reported for ion implanted bulk Ge. The voids size and structure resulted to be strongly affected by the material preparation, while the volume expansion turned out to be determined only by the nuclear deposition energy. In SiGe alloys, the swelling occurs only if the Ge concentration is above 90%. These findings rely on peculiar characteristics related to the mechanism of voids nucleation and growth, but they are crucial for future applications of active nanostructured layers such as low cost chemical and biochemical sensing devices or electrodes in batteries.

  14. Ge/Si(001) heterostructures with dense arrays of Ge quantum dots: morphology, defects, photo-emf spectra and terahertz conductivity

    PubMed Central

    2012-01-01

    Issues of Ge hut cluster array formation and growth at low temperatures on the Ge/Si(001) wetting layer are discussed on the basis of explorations performed by high resolution STM and in-situ RHEED. Dynamics of the RHEED patterns in the process of Ge hut array formation is investigated at low and high temperatures of Ge deposition. Different dynamics of RHEED patterns during the deposition of Ge atoms in different growth modes is observed, which reflects the difference in adatom mobility and their ‘condensation’ fluxes from Ge 2D gas on the surface for different modes, which in turn control the nucleation rates and densities of Ge clusters. Data of HRTEM studies of multilayer Ge/Si heterostructures are presented with the focus on low-temperature formation of perfect films. Heteroepitaxial Si p–i–n-diodes with multilayer stacks of Ge/Si(001) quantum dot dense arrays built in intrinsic domains have been investigated and found to exhibit the photo-emf in a wide spectral range from 0.8 to 5 μm. An effect of wide-band irradiation by infrared light on the photo-emf spectra has been observed. Photo-emf in different spectral ranges has been found to be differently affected by the wide-band irradiation. A significant increase in photo-emf is observed in the fundamental absorption range under the wide-band irradiation. The observed phenomena are explained in terms of positive and neutral charge states of the quantum dot layers and the Coulomb potential of the quantum dot ensemble. A new design of quantum dot infrared photodetectors is proposed. By using a coherent source spectrometer, first measurements of terahertz dynamical conductivity (absorptivity) spectra of Ge/Si(001) heterostructures were performed at frequencies ranged from 0.3 to 1.2 THz in the temperature interval from 300 to 5 K. The effective dynamical conductivity of the heterostructures with Ge quantum dots has been discovered to be significantly higher than that of the structure with the same amount

  15. Buried Porous Silicon-Germanium Layers in Monocrystalline Silicon Lattices

    NASA Technical Reports Server (NTRS)

    Fathauer, Robert W. (Inventor); George, Thomas (Inventor); Jones, Eric W. (Inventor)

    1998-01-01

    Monocrystalline semiconductor lattices with a buried porous semiconductor layer having different chemical composition is discussed and monocrystalline semiconductor superlattices with a buried porous semiconductor layers having different chemical composition than that of its monocrystalline semiconductor superlattice are discussed. Lattices of alternating layers of monocrystalline silicon and porous silicon-germanium have been produced. These single crystal lattices have been fabricated by epitaxial growth of Si and Si-Ge layers followed by patterning into mesa structures. The mesa structures are strain etched resulting in porosification of the Si-Ge layers with a minor amount of porosification of the monocrystalline Si layers. Thicker Si-Ge layers produced in a similar manner emitted visible light at room temperature.

  16. Quaternary germanides RE4Mn2InGe4 (RE = La-Nd, Sm, Gd-Tm, Lu).

    PubMed

    Oliynyk, Anton O; Stoyko, Stanislav S; Mar, Arthur

    2013-07-15

    The quaternary germanides RE4Mn2InGe4 (RE = La-Nd, Sm, Gd-Tm, Lu) have been prepared by arc-melting reactions of the elements and annealing at 800 °C and represent the second example of the RE4M2InGe4 series previously known only for M = Ni. Single-crystal X-ray diffraction studies conducted on the earlier RE members of RE4Mn2InGe4 confirmed that they adopt the monoclinic Ho4Ni2InGe4-type structure [space group C2/m, a = 16.646(2)-15.9808(9) Å, b = 4.4190(6)-4.2363(2) Å, c = 7.4834(10)-7.1590(4) Å, β = 106.893(2)-106.304(1)° in the progression of RE from La to Gd]. The covalent framework contains Mn-centered tetrahedra and Ge2 dimers that build up [Mn2Ge4] layers, which are held weakly together by four-coordinate In atoms and outline tunnels filled by the RE atoms. This bonding picture is supported by band-structure calculations. An alternative description based on Ge-centered trigonal prisms reveals that RE4Mn2InGe4 is closely related to RE2InGe2. The electrical resistivity behavior of Pr4Mn2InGe4 is similar to that of Pr2InGe2.

  17. Positron annihilation studies of fluorine-vacancy complexes in Si and SiGe

    SciTech Connect

    Edwardson, C. J.; Coleman, P. G.; El Mubarek, H. A. W.; Gandy, A. S.

    2012-04-01

    The formation of fluorine-vacancy (FV) complexes in strained Si-SiGe-Si multilayer structures and relaxed SiGe layers of varying Ge content has been investigated using variable-energy positron annihilation spectroscopy, including Doppler-broadened spectra ratio curves. It has been found that in all sample types there are two distinct regions defined only by the damage created by the implanted F ions. The first, shallower region (from the surface to a depth of {approx}200 nm) was found to contain a mixture of undecorated vacancies and FV complexes; there is no correlation between the vacancy or F concentration in this region and the Ge content. The multi-layer samples may also have O contamination that is not present in the relaxed samples. The second region (at depths {approx}200-440 nm) contains primarily FV complexes in all samples. In the multi-layer samples secondary ion mass spectrometry (SIMS) results show peaks of F accumulating in, or at the interfaces of, each SiGe multi-layer; the FV complexes, however, are distributed over depths similar to those in the relaxed samples, with some localization at the SiGe layer located within the second region. The positron response is primarily to FV complexes formed by the F implant in all samples. The F: FV ratios are approximately 3-7: 1 in the relaxed samples. Positrons appear to be relatively insensitive to the largest of the F SIMS peaks which lies beyond the second region. This is probably because the F has filled all the open volume at the SiGe layer, leaving no positron trapping sites.

  18. Surface structure of thin pseudomorphous GeSi layers

    NASA Astrophysics Data System (ADS)

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

    2015-11-01

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

  19. Magneto-transport analysis of an ultra-low-density two-dimensional hole gas in an undoped strained Ge/SiGe heterostructure

    DOE PAGES

    Laroche, D.; Huang, S. -H.; Chuang, Y.; ...

    2016-06-06

    We report the magneto-transport, scattering mechanisms, and e ective mass analysis of an ultralow density two-dimensional hole gas capacitively induced in an undoped strained Ge/Si0:2Ge0:8 heterostructure. This fabrication technique allows hole densities as low as p 1:1 1010 cm² to be achieved, more than one order of magnitude lower than previously reported in doped Ge/SiGe heterostructures. The power-law exponent of the electron mobility versus density curve, / n , is found to be 0:29 over most of the density range, implying that background impurity scattering is the dominant scattering mechanism at intermediate densities in such devices. A charge migration modelmore » is used to explain the mobility decrease at the highest achievable densities. The hole e ective mass is deduced from the temperature dependence of Shubnikov-de Haas oscillations. At p 1:0 1011cm², the e ective mass m is 0:105 m0, which is signi cantly larger than masses obtained from modulation-doped Ge/SiGe two-dimensional hole gases.« less

  20. Magneto-transport analysis of an ultra-low-density two-dimensional hole gas in an undoped strained Ge/SiGe heterostructure

    SciTech Connect

    Laroche, D.; Huang, S. -H.; Chuang, Y.; Li, J. -Y.; Liu, C. W.; Lu, T. M.

    2016-06-06

    We report the magneto-transport, scattering mechanisms, and e ective mass analysis of an ultralow density two-dimensional hole gas capacitively induced in an undoped strained Ge/Si0:2Ge0:8 heterostructure. This fabrication technique allows hole densities as low as p 1:1 1010 cm² to be achieved, more than one order of magnitude lower than previously reported in doped Ge/SiGe heterostructures. The power-law exponent of the electron mobility versus density curve, / n , is found to be 0:29 over most of the density range, implying that background impurity scattering is the dominant scattering mechanism at intermediate densities in such devices. A charge migration model is used to explain the mobility decrease at the highest achievable densities. The hole e ective mass is deduced from the temperature dependence of Shubnikov-de Haas oscillations. At p 1:0 1011cm², the e ective mass m is 0:105 m0, which is signi cantly larger than masses obtained from modulation-doped Ge/SiGe two-dimensional hole gases.

  1. Diytterbium(II) lithium indium(III) digermanide, Yb2LiInGe2

    PubMed Central

    You, Tae-Soo; Bobev, Svilen

    2010-01-01

    The title compound, Yb2LiInGe2, a new ordered quaternary inter­metallic phase, crystallizes with the ortho­rhom­bic Ca2LiInGe2 type (Pearson code oP24). The crystal structure contains six crystallographically unique sites in the asymmetric unit, all in special positions with site symmetry .m.. The structure is complex and based on [InGe4] tetra­hedra, which share corners in two directions, forming layers parallel to (001). Yb atoms fill square-pyramidal (Yb1) and octa­hedral (Yb2) inter­stices between the [InGe4/2] layers, while the small Li+ atoms fill tetra­hedral sites. PMID:21578989

  2. Surface-induced charge at the Ge (001) surface and its interaction with self-interstitials

    SciTech Connect

    Kamiyama, Eiji; Sueoka, Koji; Vanhellemont, Jan

    2014-02-21

    The Ge (001) surface with dimer structure, is negatively charged while into the bulk, positive charges are observed even deeper than the fifteenth layer from the surface. This is different from the Si case. This charge distribution can lead to the repulsion of positively charged self-interstitials by the positively charged near surface layer in an implantation or irradiation process. Self-interstitial reflection by Ge surfaces had been proposed to explain the results of diffusion experiments during irradiation whereby positively charged self-interstitials are generated by collisions of highly energetic particles with Ge atoms. We investigated different Ge (001) surface comparing an as-cleaved surface with dangling bonds to a surface with dimer structure, and to a surface terminated by hydrogen atoms. The effect of these different surface terminations on the surface-induced charges in the near surface bulk were calculated by ab initio techniques.

  3. Theoretical modeling of epitaxial growth and properties of Mn/Ge (001) multilayers

    NASA Astrophysics Data System (ADS)

    Medvedeva, J. E.

    2005-03-01

    As part of the search for useful dilute magnetic semiconductors, structural, electronic and magnetic properties of Mn/Ge (001) digital alloys and multilayers are determined using our highly precise full-potential linearized augmented plane wave (FLAPW) methodootnotetextE.Wimmer, H.Krakauer, M.Weinert, A.J.Freeman, PRB 24, 864 (1981). First, the calculated formation energies of the fully relaxed structures with different Mn and Ge site locations (both substitutional and interstitial), predict the lowest-energy structure in an epitaxial growth process. We found that (i) substitutional positions are energetically more favorable for one (001) monolayer of Mn in the supercell and (ii) when the number of Mn layers increased, the magnetic atoms prefer a second-layer interstitial site and form a 45^o-rotated fcc structure on the Ge diamond structure. For the Mn/Ge (001) multilayers, which consist of 8 layers of Ge and 1 or 4 layers of fcc Mn, we found that the experimental ferromagnetic coupling between Mn atoms can be reproduced only when Coulomb interactions are taken into account; indeed, LDA+U estimates of Tc as a function of the Mn layer thickness are in good agreement with experimentootnotetextJ.J.Lee, J.E.Medvedeva, J.H.Song, Y.Cui, A.J.Freeman, J.B.Ketterson (to be published).

  4. Mushroom-free selective epitaxial growth of Si, SiGe and SiGe:B raised sources and drains

    NASA Astrophysics Data System (ADS)

    Hartmann, J. M.; Benevent, V.; Barnes, J. P.; Veillerot, M.; Lafond, D.; Damlencourt, J. F.; Morvan, S.; Prévitali, B.; Andrieu, F.; Loubet, N.; Dutartre, D.

    2013-05-01

    We have evaluated various Cyclic Selective Epitaxial Growth/Etch (CSEGE) processes in order to grow "mushroom-free" Si and SiGe:B Raised Sources and Drains (RSDs) on each side of ultra-short gate length Extra-Thin Silicon-On-Insulator (ET-SOI) transistors. The 750 °C, 20 Torr Si CSEGE process we have developed (5 chlorinated growth steps with four HCl etch steps in-between) yielded excellent crystalline quality, typically 18 nm thick Si RSDs. Growth was conformal along the Si3N4 sidewall spacers, without any poly-Si mushrooms on top of unprotected gates. We have then evaluated on blanket 300 mm Si(001) wafers the feasibility of a 650 °C, 20 Torr SiGe:B CSEGE process (5 chlorinated growth steps with four HCl etch steps in-between, as for Si). As expected, the deposited thickness decreased as the total HCl etch time increased. This came hands in hands with unforeseen (i) decrease of the mean Ge concentration (from 30% down to 26%) and (ii) increase of the substitutional B concentration (from 2 × 1020 cm-3 up to 3 × 1020 cm-3). They were due to fluctuations of the Ge concentration and of the atomic B concentration [B] in such layers (drop of the Ge% and increase of [B] at etch step locations). Such blanket layers were a bit rougher than layers grown using a single epitaxy step, but nevertheless of excellent crystalline quality. Transposition of our CSEGE process on patterned ET-SOI wafers did not yield the expected results. HCl etch steps indeed helped in partly or totally removing the poly-SiGe:B mushrooms on top of the gates. This was however at the expense of the crystalline quality and 2D nature of the ˜45 nm thick Si0.7Ge0.3:B recessed sources and drains selectively grown on each side of the imperfectly protected poly-Si gates. The only solution we have so far identified that yields a lesser amount of mushrooms while preserving the quality of the S/D is to increase the HCl flow during growth steps.

  5. Reactions of stabilized Criegee Intermediates

    NASA Astrophysics Data System (ADS)

    Vereecken, Luc; Harder, Hartwig; Novelli, Anna

    2014-05-01

    Carbonyl oxides (Criegee intermediates) were proposed as key intermediates in the gas phase ozonolysis of alkenes in 1975 by Rudolf Criegee. Despite the importance of ozonolysis in atmospheric chemistry, direct observation of these intermediates remained elusive, with only indirect experimental evidence for their role in the oxidation of hydrocarbons, e.g. through scavenging experiments. Direct experimental observation of stabilized CI has only been achieved since 2008. Since then, a concerted effort using experimental and theoretical means is in motion to characterize the chemistry and kinetics of these reactive intermediates. We present the results of theoretical investigations of the chemistry of Criegee intermediates with a series of coreactants which may be of importance in the atmosphere, in experimental setups, or both. This includes the CI+CI cross-reaction, which proceeds with a rate coefficient near the collision limit and can be important in experimental conditions. The CI + alkene reactions show strong dependence of the rate coefficient depending on the coreactants, but is generally found to be rather slow. The CI + ozone reaction is sufficiently fast to occur both in experiment and the free troposphere, and acts as a sink for CI. The reaction of CI with hydroperoxides, ROOH, is complex, and leads both to the formation of oligomers, as to the formation of reactive etheroxides, with a moderately fast rate coefficient. The importance of these reactions is placed in the context of the reaction conditions in different atmospheric environments ranging from unpolluted to highly polluted.

  6. Influence of layer charge and charge distribution of smectites on the flow behaviour and swelling of bentonites

    USGS Publications Warehouse

    Christidis, G.E.; Blum, A.E.; Eberl, D.D.

    2006-01-01

    The influence of layer charge and charge distribution of dioctahedral smectites on the rheological and swelling properties of bentonites is examined. Layer charge and charge distribution were determined by XRD using the LayerCharge program [Christidis, G.E., Eberl, D.D., 2003. Determination of layer charge characteristics of smectites. Clays Clay Miner. 51, 644-655.]. The rheological properties were determined, after sodium exchange using the optimum amount of Na2CO3, from free swelling tests. Rheological properties were determined using 6.42% suspensions according to industrial practice. In smectites with layer charges of - 0.425 to - 0.470 per half formula unit (phfu), layer charge is inversely correlated with free swelling, viscosity, gel strength, yield strength and thixotropic behaviour. In these smectites, the rheological properties are directly associated with the proportion of low charge layers. By contrast, in low charge and high charge smectites there is no systematic relation between layer charge or the proportion of low charge layers and rheological properties. However, low charge smectites yield more viscous suspensions and swell more than high charge smectites. The rheological properties of bentonites also are affected by the proportion of tetrahedral charge (i.e. beidellitic charge), by the existence of fine-grained minerals having clay size, such as opal-CT and to a lesser degree by the ionic strength and the pH of the suspension. A new method for classification of smectites according to the layer charge based on the XRD characteristics of smecites is proposed, that also is consistent with variations in rheological properties. In this classification scheme the term smectites with intermediate layer charge is proposed. ?? 2006 Elsevier B.V. All rights reserved.

  7. Band calculation of lonsdaleite Ge

    NASA Astrophysics Data System (ADS)

    Chen, Pin-Shiang; Fan, Sheng-Ting; Lan, Huang-Siang; Liu, Chee Wee

    2017-01-01

    The band structure of Ge in the lonsdaleite phase is calculated using first principles. Lonsdaleite Ge has a direct band gap at the Γ point. For the conduction band, the Γ valley is anisotropic with the low transverse effective mass on the hexagonal plane and the large longitudinal effective mass along the c axis. For the valence band, both heavy-hole and light-hole effective masses are anisotropic at the Γ point. The in-plane electron effective mass also becomes anisotropic under uniaxial tensile strain. The strain response of the heavy-hole mass is opposite to the light hole.

  8. Self-Organized Growth of Microsized Ge Wires on Si (111) Surfaces

    SciTech Connect

    Xu,Z.; Zhang, Y.; Headrick, R.; Zhou, H.; Zhou, L.; Fukamachi, T.

    2007-01-01

    Microsized Ge wires can appear spontaneously when grown on a vicinal Si (111) surface miscut by 4 along the [11-2] direction by using molecular-beam epitaxy. Time-resolved in situ grazing incidence small-angle scattering of x rays, atomic force microscopy, and micro-Raman scattering show that the formation of Ge microwires is due to coalescence of islands along the step edges and ripening of the structures accompanied by a partial consumption of the wetting layer.

  9. Au-induced deep groove nanowire structure on the Ge(001) surface: DFT calculations

    NASA Astrophysics Data System (ADS)

    Tsay, Shiow-Fon

    2016-09-01

    The atomic geometry, stability, and electronic properties of self-organized Au induced nanowires on the Ge(001) surface are investigated based on the density-functional theory in GGA and the stoichiometry of Au. A giant Ge zigzag chain structure is suggested for 0.75 ML Au coverage, which displays c(8 × 2) deep groove zigzag nanowire structure simulated STM images. The top layer Ge and Au atomic disorder introduces the chevron units into the zigzag nanowire structure STM image as per the experimental observations. The zigzag Ge nanowire exhibits a semi-metallic characteristic, and the electric transport occurs in between the Ge zigzag nanowire and the subsurface. The system exhibits obvious electronic correlations among the Ge nanowire, the nano-facet Au trimers and the deeper layer Ge atoms, that play an important role in the electronic structure. At surface Brillouin zone boundaries, an anisotropic two-dimensional upward parabolic surface-state band is consistent with the ARPES spectra reported by Nakatsuji et al. [Phys. Rev. B 80, 081406(R) (2009); Phys. Rev. B 84, 115411 (2011)]; this electronic structure is different from the quasi-one-dimensional energy trough reported by Schäfer et al. [Phys. Rev. Lett. 101, 236802 (2008); Phys. Rev. B 83, 121411(R) (2011)].

  10. Local charge trapping in Ge nanoclustersdetected by Kelvin probe force microscopy

    NASA Astrophysics Data System (ADS)

    Kondratenko, S. V.; Lysenko, V. S.; Kozyrev, Yu. N.; Kratzer, M.; Storozhuk, D. P.; Iliash, S. A.; Czibula, C.; Teichert, C.

    2016-12-01

    The understanding of local charge trapping on the nanoscale is crucial for the design of novel electronic devices and photodetectors based on SiGe nanoclusters (NCs). Here, the local spatial distribution of the surface potential of the Ge NCs was detected using Kelvin probe force microscopy (KPFM). Different surface potentials between Ge NCs and the wetting layer (WL) surface were detected at room temperature. Changes of the local contact potential differences (CPD) were studied after injection of electrons or holes into single Ge NCs on top of the Si layer using a conductive atomic force microscopy tip. The CPD image contrast was increased after electron injection by applying a forward bias to the n-tip/i-Ge NC/p-Si junction. Injecting holes into a single Ge NC was also accompanied by filling of two-dimensional states in the surrounding region, which is governed by leakage currents through WL or surface states and Coulomb charging effects. A long retention time of holes trapped by the Ge NC was found.

  11. Stranski-Krastanow growth of tensile strained Si islands on Ge (001)

    SciTech Connect

    Pachinger, D.; Groiss, H.; Lichtenberger, H.; Stangl, J.; Hesser, G.; Schaeffler, F.

    2007-12-03

    Stranski-Krastanow island growth is demonstrated for tensile strained silicon epilayers on Ge (001) substrates over a wide range of growth temperatures. Small, Si-rich islands show sidewall faces near {l_brace}1,1,10{r_brace}, whereas larger islands are {l_brace}113{r_brace}-terminated truncated pyramids with an aspect ratio near 0.1. In contrast to compressively strained Ge on Si, we find for Si on Ge a significantly thicker wetting layer of >8 ML and coexistence of islands and dislocations.

  12. Compact intermediates in RNA folding

    SciTech Connect

    Woodson, S.A.

    2011-12-14

    Large noncoding RNAs fold into their biologically functional structures via compact yet disordered intermediates, which couple the stable secondary structure of the RNA with the emerging tertiary fold. The specificity of the collapse transition, which coincides with the assembly of helical domains, depends on RNA sequence and counterions. It determines the specificity of the folding pathways and the magnitude of the free energy barriers to the ensuing search for the native conformation. By coupling helix assembly with nascent tertiary interactions, compact folding intermediates in RNA also play a crucial role in ligand binding and RNA-protein recognition.

  13. Intermediate and Definitive Cleft Rhinoplasty.

    PubMed

    Gary, Celeste; Sykes, Jonathan M

    2016-11-01

    Intermediate and definitive cleft rhinoplasties are a challenging part of definitive cleft care. The anatomy of the cleft nose is severely affected by the structural deficits associated with congenital orofacial clefting. A comprehensive understanding of the related anatomy is crucial for understanding how to improve the appearance and function in patients with secondary cleft nasal deformities. Timing of intermediate and definitive rhinoplasty should be carefully considered. A thorough understanding of advanced rhinoplasty techniques is an important part of providing adequate care for patients with these deformities.

  14. Intermediate tax sanctions: an overview.

    PubMed

    Peregrine, M W

    1997-07-01

    New federal tax law applies intermediate tax sanctions when tax-exempt organizations enter into so-called excess benefit transactions with corporate insiders. The sanctions take the form of a two-tiered penalty excise tax, which is assessed not on the tax-exempt organization itself but on the insider who receives the excess benefit and the organizational managers and board members who knowingly participate in an improper transaction. The intermediate tax sanctions, therefore, present tax-planning challenges for tax-exempt hospitals and integrated delivery systems as well as for 501(c)(4) HMOs. Forthcoming treasury regulations are expected to add clarity to the new law.

  15. Fabrication of Ta2O5/GeNx gate insulator stack for Ge metal-insulator-semiconductor structures by electron-cyclotron-resonance plasma nitridation and sputtering deposition techniques

    NASA Astrophysics Data System (ADS)

    Otani, Yohei; Itayama, Yasuhiro; Tanaka, Takuo; Fukuda, Yukio; Toyota, Hiroshi; Ono, Toshiro; Mitsui, Minoru; Nakagawa, Kiyokazu

    2007-04-01

    The authors have fabricated germanium (Ge) metal-insulator-semiconductor (MIS) structures with a 7-nm-thick tantalum pentaoxide (Ta2O5)/2-nm-thick germanium nitride (GeNx) gate insulator stack by electron-cyclotron-resonance plasma nitridation and sputtering deposition. They found that pure GeNx ultrathin layers can be formed by the direct plasma nitridation of the Ge surface without substrate heating. X-ray photoelectron spectroscopy revealed no oxidation of the GeNx layer after the Ta2O5 sputtering deposition. The fabricated MIS capacitor with a capacitance equivalent thickness of 4.3nm showed excellent leakage current characteristics. The interface trap density obtained by the modified conductance method was 4×1011cm-2eV-1 at the midgap.

  16. Large grain growth of Ge-rich Ge{sub 1−x}Sn{sub x} (x ≈ 0.02) on insulating surfaces using pulsed laser annealing in flowing water

    SciTech Connect

    Kurosawa, Masashi; Taoka, Noriyuki; Nakatsuka, Osamu; Zaima, Shigeaki; Ikenoue, Hiroshi

    2014-02-10

    We investigate Sn incorporation effects on the growth characteristics of Ge-rich Ge{sub 1−x}Sn{sub x} (x < 0.02) on SiO{sub 2} crystallized by pulsed laser annealing (PLA) in air and water. Despite the very low Sn content of 2%, Sn atoms within the GeSn layers play a role in preventing ablation and aggregation of the layers during these PLA. Raman and electron backscatter diffraction measurements demonstrate achievement of large-grain (∼800 nmϕ) growth of Ge{sub 0.98}Sn{sub 0.02} polycrystals by using PLA in water. These polycrystals also show a tensile-strain of ∼0.68%. This result opens up the possibility for developing GeSn-based devices fabricated on flexible substrates as well as Si platforms.

  17. In-situ crystallization of GeTe\\GaSb phase change memory stacked films

    SciTech Connect

    Velea, A.; Borca, C. N.; Grolimund, D.; Socol, G.; Galca, A. C.; Popescu, M.; Bokhoven, J. A. van

    2014-12-21

    Single and double layer phase change memory structures based on GeTe and GaSb thin films were deposited by pulsed laser deposition (PLD). Their crystallization behavior was studied using in-situ synchrotron techniques. Electrical resistance vs. temperature investigations, using the four points probe method, showed transition temperatures of 138 °C and 198 °C for GeTe and GaSb single films, respectively. It was found that after GeTe crystallization in the stacked films, Ga atoms from the GaSb layer diffused in the vacancies of the GeTe crystalline structure. Therefore, the crystallization temperature of the Sb-rich GaSb layer is decreased by more than 30 °C. Furthermore, at 210 °C, the antimony excess from GaSb films crystallizes as a secondary phase. At higher annealing temperatures, the crystalline Sb phase increased on the expense of GaSb crystalline phase which was reduced. Extended X-ray absorption fine structure (EXAFS) measurements at the Ga and Ge K-edges revealed changes in their local atomic environments as a function of the annealing temperature. Simulations unveil a tetrahedral configuration in the amorphous state and octahedral configuration in the crystalline state for Ge atoms, while Ga is four-fold coordinated in both as-deposited and annealed samples.

  18. Geometries and energies of GeHn and GeH + n (n=1-4)

    NASA Astrophysics Data System (ADS)

    Das, Kalyan K.; Balasubramanian, K.

    1990-10-01

    Complete active space MCSCF (multiconfiguration self-consistent field) (CASSCF) followed by second-order configuration interaction (SOCI) and multireference singles and doubles CI (MRSDCI) are carried out on the ground states of GeHn and GeH+n (n=1-4). The equilibrium geometries of these species, adiabatic ionization potentials, and stepwise bond energies [De(Hn-1Ge-H) and De(Hn-1Ge+-H)] are calculated. The ground sate of GeH+4 is a Jahn-Teller distorted 2A1(C2v) state with a GeH+2ṡH2 complex structure. The adiabatic ionization potentials (IPS) of GeHn exhibit even-odd alternation. GeH4 is the most stable among the neutral GeHn species while GeH+3 is the most stable of the GeH+n.

  19. Strong anisotropy and magnetostriction in the two-dimensional Stoner ferromagnet Fe3GeTe2

    DOE PAGES

    Zhuang, Houlong L.; Kent, P. R. C.; Hennig, Richard G.

    2016-04-06

    Comore » mputationally characterizing magnetic properies of novel two-dimensional (2D) materials serves as an important first step of exploring possible applications. Using density-functional theory, we show that single-layer Fe3GeTe2 is a potential 2D material with sufficiently low formation energy to be synthesized by mechanical exfoliation from the bulk phase with a van der Waals layered structure. In addition, we calculated the phonon dispersion demonstrating that single-layer Fe3GeTe2is dynamically stable. Furthermore, we find that similar to the bulk phase, 2D Fe3GeTe2 exhibits amagnetic moment that originates from a Stoner instability. In contrast to other 2D materials, we find that single-layer Fe3GeTe2 exhibits a significant uniaxial magnetocrystalline anisotropy energy of 920μ eV per Fe atom originating from spin-orbit coupling. In conclusion, we show that applying biaxial tensile strains enhances the anisotropy energy, which reveals strong magnetostriction in single-layer Fe3GeTe2 with a sizable magneostrictive coefficient. Our results indicate that single-layer Fe3GeTe2 is potentially useful for magnetic storage applications.« less

  20. High-pressure synthesis and superconductivity of a new binary barium germanide BaGe3.

    PubMed

    Fukuoka, Hiroshi; Tomomitsu, Yusuke; Inumaru, Kei

    2011-07-04

    A new binary barium germanide BaGe(3) was prepared by high-pressure and high-temperature reactions using a Kawai type multi-anvil press. It crystallizes in a hexagonal unit cell with a = 6.814(1) Å, c = 5.027(8) Å, and V = 202.2(5) Å(3) (the space group P6(3)/mmc, No. 194). The unit cell contains two layers along the c axis composed of Ba atoms and Ge(3) triangular units. The triangular units stack along the c axis to form 1D columns in which the adjacent Ge(3) units turn to opposite directions. The columns, therefore, can be described as the face-sharing stacking of elongated Ge(6) octahedra. Each Ba atom is surrounded by six columns. BaGe(3) is metallic and shows superconductivity at 4.0 K. The band structure calculations revealed that there are four conduction bands mainly composed of Ge 4p and Ba 5d orbitals. From Fermi surface analysis, we confirmed that three of them have a large contribution of Ge 4pz orbitals in the vicinity of the Fermi level and show a simple 1D appearance. The remaining one contains Ge 4px, 4py, and Ba 5d contributions and shows a 2D property.

  1. MULTI-VALENCE-SUBBAND MAGNETOTRANSPORT IN A MODULATION-DOPED p-TYPE Ge1-xSix/Ge/Ge1-xSix QUANTUM WELL

    NASA Astrophysics Data System (ADS)

    Yakunin, M. V.; Alshanskii, G. A.; Neverov, V. N.; Arapov, Yu. G.; Harus, G. I.; Shelushinina, N. G.; Kuznetsov, O. A.; de Visser, A.; Ponomarenko, L.

    2005-04-01

    We show, from self-consistent calculations, that the effective mass for motion of holes along a two-dimensional (111) Ge layer is almost an order of magnitude smaller than the bulk heavy hole mass, which determines the intersubband distances. This creates a unique situation of multiple populated electric subbands at moderate hole densities ps and layer widths. Depopulation of two or more upper subbands in a 38 nm wide p-Ge layer with ps = 5 × 1015 m-2 has been revealed from the magnetoresistance in high parallel magnetic fields, while a collapse of the quantum Hall state for filling factor ν = 1 indicates that two ground subbands merge in a self-formed double-quantum-well potential profile. The latter effect in the valence band is shown to be sensitive to the layer deformation.

  2. Conduction band offset at GeO{sub 2}/Ge interface determined by internal photoemission and charge-corrected x-ray photoelectron spectroscopies

    SciTech Connect

    Zhang, W. F.; Nishimula, T.; Nagashio, K.; Kita, K.; Toriumi, A.

    2013-03-11

    We report a consistent conduction band offset (CBO) at a GeO{sub 2}/Ge interface determined by internal photoemission spectroscopy (IPE) and charge-corrected X-ray photoelectron spectroscopy (XPS). IPE results showed that the CBO value was larger than 1.5 eV irrespective of metal electrode and substrate type variance, while an accurate determination of valence band offset (VBO) by XPS requires a careful correction of differential charging phenomena. The VBO value was determined to be 3.60 {+-} 0.2 eV by XPS after charge correction, thus yielding a CBO (1.60 {+-} 0.2 eV) in excellent agreement with the IPE results. Such a large CBO (>1.5 eV) confirmed here is promising in terms of using GeO{sub 2} as a potential passivation layer for future Ge-based scaled CMOS devices.

  3. Global transition path search for dislocation formation in Ge on Si(001)

    NASA Astrophysics Data System (ADS)

    Maras, E.; Trushin, O.; Stukowski, A.; Ala-Nissila, T.; Jónsson, H.

    2016-08-01

    Global optimization of transition paths in complex atomic scale systems is addressed in the context of misfit dislocation formation in a strained Ge film on Si(001). Such paths contain multiple intermediate minima connected by minimum energy paths on the energy surface emerging from the atomic interactions in the system. The challenge is to find which intermediate states to include and to construct a path going through these intermediates in such a way that the overall activation energy for the transition is minimal. In the numerical approach presented here, intermediate minima are constructed by heredity transformations of known minimum energy structures and by identifying local minima in minimum energy paths calculated using a modified version of the nudged elastic band method. Several mechanisms for the formation of a 90° misfit dislocation at the Ge-Si interface are identified when this method is used to construct transition paths connecting a homogeneously strained Ge film and a film containing a misfit dislocation. One of these mechanisms which has not been reported in the literature is detailed. The activation energy for this path is calculated to be 26% smaller than the activation energy for half loop formation of a full, isolated 60° dislocation. An extension of the common neighbor analysis method involving characterization of the geometrical arrangement of second nearest neighbors is used to identify and visualize the dislocations and stacking faults.

  4. Sub 10 ns fast switching and resistance control in lateral GeTe-based phase-change memory

    NASA Astrophysics Data System (ADS)

    Yin, You; Zhang, Yulong; Takehana, Yousuke; Kobayashi, Ryota; Zhang, Hui; Hosaka, Sumio

    2016-06-01

    In this study, we investigated the fast switching and resistance control in a lateral GeTe-based phase-change memory (PCM). The resistivity of GeTe as a function of annealing temperature showed that it changed by more than 6 orders of magnitude in a very narrow temperature range. X-ray diffraction patterns of GeTe films indicated that GeTe had only one crystal structure, that is, face-centered cubic. It was demonstrated that the lateral device with a top conducting layer had a good performance. The operation characteristics of the GeTe-based lateral PCM device showed that it could be operated even when sub-10-ns voltage pulses were applied, making it much faster than a Ge2Sb2Te5-based device. The device resistance was successfully controlled by applying a staircase-like pulse, which enables the device to be used for fast multilevel storage.

  5. Anomalous diffusion and non-monotonic relaxation processes in Ge-Se liquids

    NASA Astrophysics Data System (ADS)

    Yildirim, Can; Raty, Jean-Yves; Micoulaut, Matthieu

    2016-06-01

    We investigate the dynamical properties of liquid GexSe100-x as a function of Ge content by first-principles molecular dynamic simulations for a certain number of temperatures in the liquid state. The focus is set on ten compositions (where x ≤ 33%) encompassing the reported flexible to rigid and rigid to stressed-rigid transitions. We examine diffusion coefficients, diffusion activation energies, glassy relaxation behavior, and viscosity of these liquids from Van Hove correlation and intermediate scattering functions. At fixed temperature, all properties/functions exhibit an anomalous behavior with Ge content in the region 18%-22%, and provide a direct and quantitative link to the network rigidity.

  6. Material Voices: Intermediality and Autism

    ERIC Educational Resources Information Center

    Trimingham, Melissa; Shaughnessy, Nicola

    2016-01-01

    Autism continues to be regarded enigmatically; a community that is difficult to access due to perceived disruptions of interpersonal connectedness. Through detailed observations of two children participating in the Arts and Humanities Research Council funded project "Imagining Autism: Drama, Performance and Intermediality as Interventions for…

  7. Learning through Literature: Geography, Intermediate.

    ERIC Educational Resources Information Center

    Sterling, Mary Ellen

    This resource book provides specific strategies and activities for integrating the intermediate geography curriculum with related children's literature selections. The book includes the following sections: (1) "World Geography Overview"; (2) "Oceans"; (3) "Polar Regions"; (4) "Islands"; (5) "Rain Forests"; (6) "Mountains"; (7) "Forests"; (8)…

  8. Intermediality and the Child Performer

    ERIC Educational Resources Information Center

    Budd, Natasha

    2016-01-01

    This report details examples of praxis in the creation and presentation of "Joy Fear and Poetry": an intermedial theatre performance in which children aged 7-12 years generated aesthetic gestures using a range of new media forms. The impetus for the work's development was a desire to make an intervention into habituated patterns of…

  9. AIDS Elementary/Intermediate Curriculum.

    ERIC Educational Resources Information Center

    Kellogg, Nancy Rader

    This Acquired Immune Deficiency Syndrome (AIDS) Curriculum was developed for intermediate elementary (5th, 6th, and 7th grade) students. It is an integrated unit that encompasses health, science, social studies, math, and language arts. The curriculum is comprised of nine class activities designed to meet the following objectives: (1) to determine…

  10. Conversation at the Intermediate Level

    ERIC Educational Resources Information Center

    Dunlop, Ian

    1975-01-01

    Discusses the use of free conversation, especially with regard to vocabulary. Recommends group discussion in the FL, using, at the intermediate level, limited, familiar vocabulary. At a higher level, words from a special technical vocabulary may be introduced, aurally and visually. A teaching example ("Traffic") is given with thorough…

  11. Nondiffusive lattice thermal transport in Si-Ge alloy nanowires

    NASA Astrophysics Data System (ADS)

    Upadhyaya, M.; Aksamija, Z.

    2016-11-01

    We present a calculation of the lattice thermal conductivity of Si-Ge nanowires (NWs), based on solving the Boltzmann transport equation by the Monte Carlo method of sampling the phonon mean free paths. We augment the previous work with the full phonon dispersion and a partially diffuse momentum-dependent specularity model for boundary roughness scattering. We find that phonon flights are comprised of a mix of long free flights over several μ m interrupted by bursts of short flights, resulting in a heavy-tailed distribution of flight lengths, typically encountered in Lévy walk dynamics. Consequently, phonon transport in Si-Ge NWs is neither entirely ballistic nor diffusive; instead, it falls into an intermediate regime called superdiffusion where thermal conductivity scales with the length of the NW as κ ∝Lα with the exponent of length dependence α ≈0.33 over a broad range of wire lengths 10 nm Ge alloy NWs is length dependent up to 10 μ m and therefore can be tuned for thermoelectric applications.

  12. NpCoGe, near quantum criticality?

    NASA Astrophysics Data System (ADS)

    Colineau, E.; Eloirdi, R.; Griveau, J.-C.; Gaczynski, P.; Shick, A. B.

    2013-05-01

    The magnetic and electronic properties of NpCoGe are reported. NpCoGe orders antiferromagnetically at T N ≈ 13 K with an average ordered magnetic moment < µ N p > = 0.80 µ B . The comparison with NpRhGe and uranium analogues suggests the leading role of f-d hybridization, the rather delocalized character of 5f electrons in NpCoGe and its possible proximity to a magnetic quantum critical point.

  13. Intermediate plasmonic characteristics in a quasi-continuous metallic monolayer.

    PubMed

    Yun, Hansik; Lee, Il-Min; Lee, Seung-Yeol; Kim, Kyoung-Youm; Lee, Byoungho

    2014-01-15

    There has been a significant interest on plasmonics in a metallic structure with very narrow gaps for studies of nanophotonics. However, little attention has been paid to the behavior of surface plasmons (SPs) in quasi-continuous metallic structures. This study observes and analyzes intermediate characteristics between propagating SPs (PSPs) and localized SPs (LSPs) in a quasi-continuous metallic monolayer of core-shell nanocubes. We reveal that, in a very narrow region of few-nanometer gaps among the nanocubes, the intrinsic energy bands of PSPs and LSPs intersect each other to generate two hybrid bands and an anti-crossing. Using a self-assembly method instead of the lithographic techniques which have several limitations as of now, we materialize the quasi-continuous metallic layer with plenty of nano-gaps that exhibit intermediate plasmonic characteristics. The intermediate plasmonic characteristics observed in this study will lead to interesting subjects, such as band engineering and slow SPs, in nanophotonics.

  14. Thermal oxidation of Ge-implanted Si: Role of defects

    NASA Astrophysics Data System (ADS)

    Dedyulin, S. N.; Goncharova, L. V.

    2012-02-01

    kinetics at the SiGe/SiO interface [9,10,13]. The DG model for Si thermal oxidation [26] assumes that the oxidation occurs by diffusion of the oxidant to the SiO/Si interface where it reacts with Si. The oxidation rate is described by the parabolic equation: x02+Ax0=B(t+τ), where x0 is the oxide thickness, t is the oxidation time, A and B are constants for a given set of oxidation conditions, and τ={x}/{i2+AxiB} is the shift in the time coordinate due to the presence of the initial oxide layer, xi. Two different growth regimes are usually considered: a linear regime where t≪A2/4B that leads to the relation x0={B}/{A}(t+τ) and a parabolic regime where t≫A2/4B and x02=Bt for the oxide thickness. In the DG model the growth rates in the linear and parabolic regimes of growth are controlled by interface reaction and diffusion of the oxidant through the oxide layer, respectively. As proposed by Deal and Grove, the linear constant B/ A is relevant to the processes at the SiO/Si interface via the oxidation reaction rate at the interface. The parabolic constant B refers to the properties of the oxidant in the oxide layer via a dependence on the diffusion coefficient. A new model for Si oxidation has been recently suggested [27]. Despite using the same parabolic equation as in the DG model (Eq. (1)), Watanabe et al. arrive at this result from totally different assumptions. Namely, Watanabe et al. assume that diffusivity is suppressed in the strained oxide region (≈1 nm) near the SiO/Si interface. This assumption leaves Eq. (1) and the parabolic B constant unmodified and does not treat the interface reaction as a limiting stage.

  15. GE--Structured Analysis and Design Training.

    ERIC Educational Resources Information Center

    Towne, Violet A.

    At the request of General Electric-Utica (GE), the State University of New York Institute of Technology at Utica/Rome and the Mohawk Valley Regional Education Center for Economic Development have developed a program to train GE software development personnel. GE is involved in the development of aerospace electronic equipment and related software…

  16. Alleviation of fermi-level pinning effect at metal/germanium interface by the insertion of graphene layers

    SciTech Connect

    Baek, Seung-heon Chris; Seo, Yu-Jin; Oh, Joong Gun; Albert Park, Min Gyu; Bong, Jae Hoon; Yoon, Seong Jun; Lee, Seok-Hee; Seo, Minsu; Park, Seung-young; Park, Byong-Guk

    2014-08-18

    In this paper, we report the alleviation of the Fermi-level pinning on metal/n-germanium (Ge) contact by the insertion of multiple layers of single-layer graphene (SLG) at the metal/n-Ge interface. A decrease in the Schottky barrier height with an increase in the number of inserted SLG layers was observed, which supports the contention that Fermi-level pinning at metal/n-Ge contact originates from the metal-induced gap states at the metal/n-Ge interface. The modulation of Schottky barrier height by varying the number of inserted SLG layers (m) can bring about the use of Ge as the next-generation complementary metal-oxide-semiconductor material. Furthermore, the inserted SLG layers can be used as the tunnel barrier for spin injection into Ge substrate for spin-based transistors.

  17. Photo- and Thermo-Induced Changes in Optical Constants and Structure of Thin Films from GeSe2-GeTe-ZnTe System

    NASA Astrophysics Data System (ADS)

    Petkov, Kiril; Todorov, Rossen; Vassilev, Venceslav; Aljihmani, Lilia

    We examined the condition of preparation of thin films from GeSe2-GeTe-ZnTe system by thermal evaporation and changes in their optical properties after exposure to light and thermal annealing. The results for composition analysis of thin films showed absence of Zn independently of the composition of the bulk glass. By X-ray diffraction (XRD) analysis it was found that a reduction of ZnTe in ZnSe in bulk materials takes of place during the film deposition. A residual from ZnSe was observed in the boat after thin film deposition. Optical constants (refractive index, n and absorption coefficient, α) and thickness, d as well as the optical band gap, Eg, depending of the content of Te in ternary Ge-Se-Te system are determined from specrophotometric measurements in the spectral range 400-2500 nm applying the Swanepoel's envelope method and Tauc's procedure. With the increase of Te content in the layers the absorption edge is shifted to the longer wavelengths, refractive index increases while the optical band gap decreases from 2.02 eV for GeSe2 to 1.26 eV for Ge34Se42Te24. The values of the refractive index decrease after annealing of all composition and Eg increase, respectively. Thin films with composition of Ge27Se47Te9Zn17 and Ge28Se49Te10Zn13 were prepared by co-evaporation of (GeSe2)78(GeTe)22 and Zn from a boat and a crucible and their optical properties, surface morphology and structure were investigated. The existence of a correlation between the optical band gap and the copostion of thin films from the system studied was demonstrated.

  18. Passivation of multiple-quantum-well Ge0.97Sn0.03/Ge p-i-n photodetectors

    NASA Astrophysics Data System (ADS)

    Morea, Matthew; Brendel, Corinna E.; Zang, Kai; Suh, Junkyo; Fenrich, Colleen S.; Huang, Yi-Chiau; Chung, Hua; Huo, Yijie; Kamins, Theodore I.; Saraswat, Krishna C.; Harris, James S.

    2017-02-01

    We study the effect of surface passivation on pseudomorphic multiple-quantum-well Ge0.97Sn0.03/Ge p-i-n photodetectors. A combination of ozone oxidation to form GeOx and GeSnOx on the surface of the diodes followed by atomic layer deposition of Al2O3 for protection of these native oxides provides reduced dark current. With a temperature-dependent investigation of dark current, we calculate the activation energy to be 0.26 eV at a bias of -0.1 V and 0.05 eV at -1 V for the sample passivated by this ozone method. Based on these activation energy results, we find that the current is less dominated by bulk tunneling at lower reverse bias values; hence, the effect of surface passivation is more noticeable with nearly an order-of-magnitude improvement in dark current for the ozone-passivated sample compared to control devices without the ozone treatment at a voltage of -0.1 V. Passivation also results in a significant enhancement of the responsivity, particularly for shorter wavelengths, with 26% higher responsivity at 1100 nm and 16% higher performance at 1300 nm.

  19. Understanding and engineering of NiGe/Ge junction formed by phosphorus ion implantation after germanidation

    SciTech Connect

    Oka, Hiroshi Minoura, Yuya; Hosoi, Takuji; Shimura, Takayoshi; Watanabe, Heiji

    2014-08-11

    Modulation of the effective electron Schottky barrier height (eSBH) of NiGe/Ge contacts induced by phosphorus ion implantation after germanide formation was investigated by considering local inhomogeneity in the eSBH. Systematic studies of NiGe/Ge contact devices having various germanide thicknesses and ion implantation areas indicated the threshold dopant concentration at the NiGe/Ge interface required for eSBH modulation and negligible dopant diffusion even at NiGe/Ge interface during drive-in annealing, leading to variation in the eSBH between the bottom and sidewall portions of the NiGe regions. Consequently, this method makes it possible to design source/drain contacts with low-resistivity Ohmic and ideal rectifying characteristics for future Ge-based transistors.

  20. Fission at intermediate neutron energies

    NASA Astrophysics Data System (ADS)

    Lo Meo, S.; Mancusi, D.; Massimi, C.; Vannini, G.; Ventura, A.

    2014-09-01

    In the present work, as a theoretical support to the campaign of neutron cross section measurements at the n_TOF facility at CERN[1], Monte Carlo calculations of fission induced by neutrons in the energy range from 100 MeV to 1 GeV are carried out by means of a recent version of the Liege Intranuclear Cascade Model, INCL++[6], coupled with different evaporation-fission codes, such as Gemini++[7] and ABLA07[8]. Theoretical cross sections are compared with experimental data obtained by the n_TOF collaboration and perspectives for future theoretical work are outlined.