Heteroepitaxial growth of In{sub 0.30}Ga{sub 0.70}As high-electron mobility transistor on 200 mm silicon substrate using metamorphic graded buffer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kohen, David, E-mail: david.kohen@asm.com; Nguyen, Xuan Sang; Made, Riko I

We report on the growth of an In{sub 0.30}Ga{sub 0.70}As channel high-electron mobility transistor (HEMT) on a 200 mm silicon wafer by metal organic vapor phase epitaxy. By using a 3 μm thick buffer comprising a Ge layer, a GaAs layer and an InAlAs compositionally graded strain relaxing buffer, we achieve threading dislocation density of (1.0 ± 0.3) × 10{sup 7} cm{sup −2} with a surface roughness of 10 nm RMS. No phase separation was observed during the InAlAs compositionally graded buffer layer growth. 1.4 μm long channel length transistors are fabricated from the wafer with I{sub DS} of 70more » μA/μm and g{sub m} of above 60 μS/μm, demonstrating the high quality of the grown materials.« less

Study of the influence of strained superlattices introduced into a metamorphic buffer on the electrophysical properties and the atomic structure of InAlAs/InGaAs MHEMT heterostructures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Galiev, G. B.; Pushkarev, S. S., E-mail: s_s_e_r_p@mail.ru; Vasil'evskii, I. S.

The results of studying the influence of strained superlattices introduced into a metamorphic buffer on the electrophysical properties and atomic crystal structure of In{sub 0.70}Al{sub 0.30}As/In{sub 0.76}Ga{sub 0.24}As/In{sub 0.70}Al{sub 0.30}As metamorphic high-electron-mobility transistor (MHEMT) nanoheterostructures on GaAs substrates are presented. Two types of MHEMT structures are grown by molecular beam epitaxy, namely, one with a linear increase in x in the In{sub x}Al{sub 1-x}As metamorphic buffer, and the second with two mismatched superlattices introduced inside the metamorphic buffer. The electrophysical and structural parameters of the grown samples are studied by the van der Pauw method, transmission electron microscopy (including scanningmore » and high-resolution microscopy), atomic-force microscopy, and energy dispersive X-ray analysis. It is revealed that the introduction of superlattices into a metamorphic buffer substantially improves the electrophysical and structural characteristics of MHEMT structures.« less

Design considerations for λ ˜ 3.0- to 3.5-μm-emitting quantum cascade lasers on metamorphic buffer layers

NASA Astrophysics Data System (ADS)

Rajeev, Ayushi; Sigler, Chris; Earles, Tom; Flores, Yuri V.; Mawst, Luke J.; Botez, Dan

2018-01-01

Quantum cascade lasers (QCLs) that employ metamorphic buffer layers as substrates of variable lattice constant have been designed for emission in the 3.0- to 3.5-μm wavelength range. Theoretical analysis of the active-region (AR) energy band structure, while using an 8-band k•p model, reveals that one can achieve both effective carrier-leakage suppression as well as fast carrier extraction in QCL structures of relatively low strain. Significantly lower indium-content quantum wells (QWs) can be employed for the AR compared to QWs employed for conventional short-wavelength QCL structures grown on InP, which, in turn, is expected to eliminate carrier leakage to indirect-gap valleys (X, L). An analysis of thermo-optical characteristics for the complete device design indicates that high-Al-content AlInAs cladding layers are more effective for both optical confinement and thermal dissipation than InGaP cladding layers. An electroluminescence-spectrum full-width half-maximum linewidth of 54.6 meV is estimated from interface roughness scattering and, by considering both inelastic and elastic scattering, the threshold-current density for 3.39-μm-emitting, 3-mm-long back-facet-coated QCLs is projected to be 1.40 kA/cm2.

Investigation of InP/In0.65Ga0.35As metamorphic p-channel doped-channel field-effect transistor

NASA Astrophysics Data System (ADS)

Tsai, Jung-Hui

2016-07-01

In this article, the device mechanism and characteristics of InP/InGaAs metamorphic p-channel field-effect transistor (FET), which has a high indium mole fraction of InGaAs channel, grown on the GaAs substrate is demonstrated. The device was fabricated on the top of the InxGa1-xP graded metamorphic buffer layer, and the In0.65Ga0.35As pseudomorphic channel was employed to elevate the transistor performance. For the p-type FET, due to the considerably large valence band discontinuity at InP/In0.65Ga0.35As heterojunction and a relatively thin as well as heavily doped pseudomorphic In0.65Ga0.35As channel between two undoped InP layers, a maximum extrinsic transconductance of 27.3 mS/mm and a maximum saturation current density of -54.3 mA/mm are obtained. Consequently, the studied metamorphic FET is suitable for the development in signal amplification, integrated circuits, and low supply-voltage complementary logic inverters.

2.8 {mu}m emission from type-I quantum wells grown on InAs{sub x}P{sub 1-x}/InP metamorphic graded buffers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jung, Daehwan; Song, Yuncheng; Larry Lee, Minjoo

We report 2.8 {mu}m emission from compressively strained type-I quantum wells (QWs) grown on InP-based metamorphic InAs{sub x}P{sub 1-x} step-graded buffers. High quality metamorphic graded buffers showed smooth surface morphology and low threading dislocation densities of approximately 2.5 Multiplication-Sign 10{sup 6} cm{sup -2}. High-resolution x-ray diffraction scans showed strong satellites from multiple quantum wells grown on metamorphic buffers, and cross-sectional transmission electron microscopy revealed smooth and coherent quantum well interfaces. Room-temperature photoluminescence emission at 2.8 {mu}m with a narrow linewidth ({approx}50 meV) shows the promise of metamorphic growth for mid-infrared laser diodes on InP.

Growth temperature optimization of GaAs-based In0.83Ga0.17As on InxAl1-xAs buffers

NASA Astrophysics Data System (ADS)

Chen, X. Y.; Gu, Y.; Zhang, Y. G.; Ma, Y. J.; Du, B.; Zhang, J.; Ji, W. Y.; Shi, Y. H.; Zhu, Y.

2018-04-01

Improved quality of gas source molecular beam epitaxy grown In0.83Ga0.17As layer on GaAs substrate was achieved by adopting a two-step InxAl1-xAs metamorphic buffer at different temperatures. With a high-temperature In0.83Al0.17As template following a low-temperature composition continuously graded InxAl1-xAs (x = 0.05-0.86) buffer, better structural, optical and electrical properties of succeeding In0.83Ga0.17As were confirmed by atomic force microscopy, photoluminescence and Hall-effect measurements. Cross-sectional transmission electron microscopy revealed significant effect of the two-step temperature grown InAlAs buffer layers on the inhibition of threading dislocations due to the deposition of high density nuclei on GaAs substrate at the low growth temperature. The limited reduction for the dark current of GaAs-based In0.83Ga0.17As photodetectors on the two-step temperature grown InxAl1-xAs buffer layers was ascribed to the contribution of impurities caused by the low growth temperature of InAlAs buffers.

Electrical and structural characteristics of metamorphic In{sub 0.38}Al{sub 0.62}As/In{sub 0.37}Ga{sub 0.63}As/In{sub 0.38}Al{sub 0.62}As HEMT nanoheterostructures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Galiev, G. B., E-mail: s_s_e_r_p@mail.ru; Klimov, E. A.; Klochkov, A. N.

The influence of the metamorphic buffer design and epitaxial growth conditions on the electrical and structural characteristics of metamorphic In{sub 0.38}Al{sub 0.62}As/In{sub 0.37}Ga{sub 0.63}As/In{sub 0.38}Al{sub 0.62}As high electron mobility transistor (MHEMT) nanoheterostructures has been investigated. The samples were grown on GaAs(100) substrates by molecular beam epitaxy. The active regions of the nanoheterostructures are identical, while the metamorphic buffer In{sub x}Al{sub 1-x}As is formed with a linear or stepwise (by {Delta}{sub x} = 0.05) increase in the indium content over depth. It is found that MHEMT nanoheterostructures with a step metamorphic buffer have fewer defects and possess higher values of two-dimensionalmore » electron gas mobility at T = 77 K. The structures of the active region and metamorphic buffer have been thoroughly studied by transmission electron microscopy. It is shown that the relaxation of metamorphic buffer in the heterostructures under consideration is accompanied by the formation of structural defects of the following types: dislocations, microtwins, stacking faults, and wurtzite phase inclusions several nanometers in size.« less

Extended wavelength mid-infrared photoluminescence from type-I InAsN and InGaAsN dilute nitride quantum wells grown on InP

NASA Astrophysics Data System (ADS)

Wheatley, R.; Kesaria, M.; Mawst, L. J.; Kirch, J. D.; Kuech, T. F.; Marshall, A.; Zhuang, Q. D.; Krier, A.

2015-06-01

Extended wavelength photoluminescence emission within the technologically important 2-5 μm spectral range has been demonstrated from InAs1-xNx and In1-yGayAs1-xNx type I quantum wells grown onto InP. Samples containing N ˜ 1% and 2% exhibited 4 K photoluminescence emission at 2.0 and 2.7 μm, respectively. The emission wavelength was extended out to 2.9 μm (3.3 μm at 300 K) using a metamorphic buffer layer to accommodate the lattice mismatch. The quantum wells were grown by molecular beam epitaxy and found to be of a high structural perfection as evidenced in the high resolution x-ray diffraction measurements. The photoluminescence was more intense from the quantum wells grown on the metamorphic buffer layer and persisted up to room temperature. The mid-infrared emission spectra were analysed, and the observed transitions were found to be in good agreement with the calculated emission energies.

Quality-enhanced In{sub 0.3}Ga{sub 0.7}As film grown on GaAs substrate with an ultrathin amorphous In{sub 0.6}Ga{sub 0.4}As buffer layer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gao, Fangliang; Li, Guoqiang, E-mail: msgli@scut.edu.cn

2014-01-27

Using low-temperature molecular beam epitaxy, amorphous In{sub 0.6}Ga{sub 0.4}As layers have been grown on GaAs substrates to act as buffer layers for the subsequent epitaxial growth of In{sub 0.3}Ga{sub 0.7}As films. It is revealed that the crystallinity of as-grown In{sub 0.3}Ga{sub 0.7}As films is strongly affected by the thickness of the large-mismatched amorphous In{sub 0.6}Ga{sub 0.4}As buffer layer. Given an optimized thickness of 2 nm, this amorphous In{sub 0.6}Ga{sub 0.4}As buffer layer can efficiently release the misfit strain between the In{sub 0.3}Ga{sub 0.7}As epi-layer and the GaAs substrate, trap the threading and misfit dislocations from propagating to the following In{sub 0.3}Ga{submore » 0.7}As epi-layer, and reduce the surface fluctuation of the as-grown In{sub 0.3}Ga{sub 0.7}As, leading to a high-quality In{sub 0.3}Ga{sub 0.7}As film with competitive crystallinity to that grown on GaAs substrate using compositionally graded In{sub x}Ga{sub 1-x}As metamorphic buffer layers. Considering the complexity of the application of the conventional In{sub x}Ga{sub 1-x}As graded buffer layers, this work demonstrates a much simpler approach to achieve high-quality In{sub 0.3}Ga{sub 0.7}As film on GaAs substrate and, therefore, is of huge potential for the InGaAs-based high-efficiency photovoltaic industry.« less

Tunable High Brightness Semiconductor Sources

DTIC Science & Technology

2015-05-01

possible to accomplish this through use of metamorphic buffer layers, which allow for nearly full relaxation of a ternary crystal on a binary substrate...45433-7320 AIR FORCE MATERIEL COMMAND UNITED STATES AIR FORCE NOTICE AND SIGNATURE PAGE Using Government drawings, specifications, or other data...any rights or permission to manufacture, use , or sell any patented invention that may relate to them. This report was cleared for public release by

Broadband light sources based on InAs/InGaAs metamorphic quantum dots

DOE Office of Scientific and Technical Information (OSTI.GOV)

Seravalli, L.; Trevisi, G.; Frigeri, P.

We propose a design for a semiconductor structure emitting broadband light in the infrared, based on InAs quantum dots (QDs) embedded into a metamorphic step-graded In{sub x}Ga{sub 1−x}As buffer. We developed a model to calculate the metamorphic QD energy levels based on the realistic QD parameters and on the strain-dependent material properties; we validated the results of simulations by comparison with the experimental values. On this basis, we designed a p-i-n heterostructure with a graded index profile toward the realization of an electrically pumped guided wave device. This has been done by adding layers where QDs are embedded in In{submore » x}Al{sub y}Ga{sub 1−x−y}As layers, to obtain a symmetric structure from a band profile point of view. To assess the room temperature electro-luminescence emission spectrum under realistic electrical injection conditions, we performed device-level simulations based on a coupled drift-diffusion and QD rate equation model. On the basis of the device simulation results, we conclude that the present proposal is a viable option to realize broadband light-emitting devices.« less

Control of metamorphic buffer structure and device performance of In(x)Ga(1-x)As epitaxial layers fabricated by metal organic chemical vapor deposition.

PubMed

Nguyen, H Q; Yu, H W; Luc, Q H; Tang, Y Z; Phan, V T H; Hsu, C H; Chang, E Y; Tseng, Y C

2014-12-05

Using a step-graded (SG) buffer structure via metal-organic chemical vapor deposition, we demonstrate a high suitability of In0.5Ga0.5As epitaxial layers on a GaAs substrate for electronic device application. Taking advantage of the technique's precise control, we were able to increase the number of SG layers to achieve a fairly low dislocation density (∼10(6) cm(-2)), while keeping each individual SG layer slightly exceeding the critical thickness (∼80 nm) for strain relaxation. This met the demanded but contradictory requirements, and even offered excellent scalability by lowering the whole buffer structure down to 2.3 μm. This scalability overwhelmingly excels the forefront studies. The effects of the SG misfit strain on the crystal quality and surface morphology of In0.5Ga0.5As epitaxial layers were carefully investigated, and were correlated to threading dislocation (TD) blocking mechanisms. From microstructural analyses, TDs can be blocked effectively through self-annihilation reactions, or hindered randomly by misfit dislocation mechanisms. Growth conditions for avoiding phase separation were also explored and identified. The buffer-improved, high-quality In0.5Ga0.5As epitaxial layers enabled a high-performance, metal-oxide-semiconductor capacitor on a GaAs substrate. The devices displayed remarkable capacitance-voltage responses with small frequency dispersion. A promising interface trap density of 3 × 10(12) eV(-1) cm(-2) in a conductance test was also obtained. These electrical performances are competitive to those using lattice-coherent but pricey InGaAs/InP systems.

Photoconductive antennas based on epitaxial films In0.5Ga0.5As on GaAs (1 1 1)A and (1 0 0)A substrates with a metamorphic buffer

NASA Astrophysics Data System (ADS)

Kuznetsov, K. A.; Galiev, G. B.; Kitaeva, G. Kh; Kornienko, V. V.; Klimov, E. A.; Klochkov, A. N.; Leontyev, A. A.; Pushkarev, S. S.; Maltsev, P. P.

2018-07-01

The terahertz (THz) wave generation by the spiral photoconductive antennas fabricated on the low-temperature and high-temperature grown undoped and Si-doped In0.5Ga0.5As films is studied by the terahertz time-domain spectroscopy method. The In0.5Ga0.5As layers were grown by molecular beam epitaxy on GaAs substrates with (1 0 0) and (1 1 1)A crystallographic orientations utilizing step-graded In x Ga1‑x As metamorphic buffer. The antennas are excited by radiation of Er3+-fiber laser at 1.56 μm wavelength in two regimes: with pulse durations of 2.5 ps or 100 fs. It is found that the THz wave generation is 3–4 times more effective in the case of InGaAs-based antennas on (1 1 1)A GaAs substrates as compared to the (1 0 0) substrates. Power-voltage characteristic of the LT-InGaAs antenna up to and beyond threshold breakdown voltage are reported.

Design and characterization of thick InxGa1-xAs metamorphic buffer layers grown by hydride vapor phase epitaxy

NASA Astrophysics Data System (ADS)

Schulte, K. L.; Zutter, B. T.; Wood, A. W.; Babcock, S. E.; Kuech, T. F.

2014-03-01

Thick InxGa1-xAs metamorphic buffer layers (MBLs) grown by hydride vapor phase epitaxy (HVPE) were studied. Relationships between MBL properties and growth parameters such as grading rate, cap layer thickness, final xInAs, and deposition temperature (TD) were explored. The MBLs were characterized by measurement of in-plane residual strain (ɛ¦¦), surface etch pit density (EPD), and surface roughness. Capping layer thickness had a strong effect on strain relaxation, with thickly capped samples exhibiting the lowest ɛ¦¦. EPD was higher in samples with thicker caps, reflecting their increased relaxation through dislocation generation. ɛ¦¦ and EPD were weakly affected by the grading rate, making capping layer thickness the primary structural parameter which controls these properties. MBLs graded in discrete steps had similar properties to MBLs with continuous grading. In samples with identical thickness and 10-step grading style, ɛ¦¦ increased almost linearly with final xInAs, while total relaxation stayed relatively constant. Relaxation as a function of xInAs could be described by an equilibrium model in which dislocation nucleation is impeded by the energy of the existing dislocation array. EPD was constant from xInAs = 0 to 0.24 then increased exponentially, which is related to the increased dislocation interaction and blocking seen at higher dislocation densities. RMS roughness increased with xInAs above a certain strain rate (0.15%/µm) samples grown below this level possessed large surface hillocks and high roughness values. The elimination of hillocks at higher values of xInAs is attributed to increased density of surface steps and is related to the out-of-plane component of the burgers vector of the dominant type of 60° dislocation. TD did not affect ɛ¦¦ for samples with a given xInAs. EPD tended to increase with TD, indicating dislocation glide likely is impeded at higher temperatures.

Investigation of InP/InGaAs metamorphic co-integrated complementary doping-channel field-effect transistors for logic application

NASA Astrophysics Data System (ADS)

Tsai, Jung-Hui

2014-01-01

DC performance of InP/InGaAs metamorphic co-integrated complementary doping-channel field-effect transistors (DCFETs) grown on a low-cost GaAs substrate is first demonstrated. In the complementary DCFETs, the n-channel device was fabricated on the InxGa1-xP metamorphic linearly graded buffer layer and the p-channel field-effect transistor was stacked on the top of the n-channel device. Particularly, the saturation voltage of the n-channel device is substantially reduced to decrease the VOL and VIH values attributed that two-dimensional electron gas is formed and could be modulated in the n-InGaAs channel. Experimentally, a maximum extrinsic transconductance of 215 (17) mS/mm and a maximum saturation current density of 43 (-27) mA/mm are obtained in the n-channel (p-channel) device. Furthermore, the noise margins NMH and NML are up to 0.842 and 0.330 V at a supply voltage of 1.5 V in the complementary logic inverter application.

Conduction- and Valence-Band Energies in Bulk InAs(1-x)Sb(x) and Type II InAs(1-x) Sb(x)/InAs Strained-Layer Superlattices

DTIC Science & Technology

2013-03-08

tions in the studied SLS structures . The fit of the dependence of the valence- band energy of unstrained InAs1!xSbx on the composition x with a... band . STRUCTURES Bulk InAsSb epilayers on metamorphic buffers and InAsSb/InAs strained-layer superlattices (SLS) were grown on GaSb substrates by solid...meV in InAs and Ev = 0 meV in InSb. For InAsSb with 22.5% Sb grown on GaSb , an unstrained valence- band energy of Ev = !457 meV was obtained. For the

InP-based type-I quantum well lasers up to 2.9 μm at 230 K in pulsed mode on a metamorphic buffer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gu, Y.; Zhang, Y. G., E-mail: ygzhang@mail.sim.ac.cn; Ma, Y. J.

This work reports on up to 2.9 μm lasing at 230 K of InP-based type-I quantum well lasers. This record long wavelength lasing is achieved by applying InP-based Sb-free structures with eight periods of strain-compensated InAs quantum wells grown on metamorphic In{sub 0.8}Al{sub 0.2}As template layers. The continuous-wave threshold current density is 797 A/cm{sup 2} and the idealized extrapolated threshold current density for infinite cavity length is as low as 58 A/cm{sup 2} per quantum well at 120 K. This scheme is a promising pathway for extending the wavelength range of type-I quantum well lasers on InP substrates.

Metamorphic InAs quantum well lasers on InP substrates with different well shapes and waveguides

NASA Astrophysics Data System (ADS)

Gu, Y.; Zhang, Y. G.; Chen, X. Y.; Ma, Y. J.; Ji, W. Y.; Xi, S. P.; Du, B.; Shi, Y. H.; Li, A. Z.

2017-11-01

The effects of well shapes and waveguide materials on InP-based InAs quantum well lasers have been investigated. The laser structures were grown on metamorphic In0.65Al0.35As buffers. A novel trapezoidal quantum well composed of InyGa1-yAs grading and InAs layer was used to improve the quality of quantum well. Quaternary In0.65Al0.2Ga0.15As waveguide was applied instead of ternary In0.65Ga0.35As to enhance the carrier injection. The material qualities have been characterized by X-ray diffraction, transmission electron microscopy and photoluminescence measurements, while the device properties of the lasers with various structures were investigated at different temperatures. Results show that the laser performances have been improved by the use of trapezoidal quantum wells and InAlGaAs waveguides.

Anisotropic strain relaxation of Si-doped metamorphic InAlAs graded buffers on InP

NASA Astrophysics Data System (ADS)

Gu, Yi; Zhang, Yonggang; Chen, Xingyou; Ma, Yingjie; Zheng, Yuanliao; Du, Ben; Zhang, Jian

2017-09-01

The effects of Si doping on the strain relaxation of InP-based metamorphic In x Al1-x As graded buffers have been investigated. The highly Si-doped sample shows an increased ridge period along the [1 1 0] direction in the cross-hatch morphology measured by atomic force microscope. X-ray diffraction reciprocal space mapping measurements reveal that the high Si-doping induced incomplete relaxation as well as inhomogeneous residual strain along the [1 -1 0] direction, which was also observed in micro-Raman measurements. The anisotropic strain relaxation is attributed to the Si-doping enhanced anisotropy of misfit dislocations along the orthogonal directions. The α-misfit dislocations along the [1 -1 0] direction are further delayed to generate in highly Si-doped InAlAs buffer, while the β-misfit dislocations along the [1 1 0] direction are not. These results supply useful suggestions on the design and demonstration of semiconductor metamorphic devices.

Growth and characterization of metamorphic InAs/GaSb tunnel heterojunction on GaAs by molecular beam epitaxy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Jheng-Sin; Clavel, Michael B.; Hudait, Mantu K., E-mail: mantu.hudait@vt.edu

The structural, morphological, optical, and electrical transport characteristics of a metamorphic, broken-gap InAs/GaSb p-i-n tunnel diode structure, grown by molecular beam epitaxy on GaAs, were demonstrated. Precise shutter sequences were implemented for the strain-balanced InAs/GaSb active layer growth on GaAs, as corroborated by high-resolution X-ray analysis. Cross-sectional transmission electron microscopy and detailed micrograph analysis demonstrated strain relaxation primarily via the formation of 90° Lomer misfit dislocations (MDs) exhibiting a 5.6 nm spacing and intermittent 60° MDs at the GaSb/GaAs heterointerface, which was further supported by a minimal lattice tilt of 180 arc sec observed during X-ray analysis. Selective area diffraction and Fastmore » Fourier Transform patterns confirmed the full relaxation of the GaSb buffer layer and quasi-ideal, strain-balanced InAs/GaSb heteroepitaxy. Temperature-dependent photoluminescence measurements demonstrated the optical band gap of the GaSb layer. Strong optical signal at room temperature from this structure supports a high-quality material synthesis. Current–voltage characteristics of fabricated InAs/GaSb p-i-n tunnel diodes measured at 77 K and 290 K demonstrated two bias-dependent transport mechanisms. The Shockley–Read–Hall generation–recombination mechanism at low bias and band-to-band tunneling transport at high bias confirmed the p-i-n tunnel diode operation. This elucidated the importance of defect control in metamorphic InAs/GaSb tunnel diodes for the implementation of low-voltage and high-performance tunnel field effect transistor applications.« less

Optimization of structural and growth parameters of metamorphic InGaAs photovoltaic converters grown by MOCVD

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rybalchenko, D. V.; Mintairov, S. A.; Salii, R. A.

Metamorphic Ga{sub 0.76}In{sub 0.24}As heterostructures for photovoltaic converters are grown by the MOCVD (metal–organic chemical vapor deposition) technique. It is found that, due to the valence-band offset at the p-In{sub 0.24}Al{sub 0.76}As/p-In{sub 0.24}Ga{sub 0.76}As (wide-gap window/emitter) heterointerface, a potential barrier for holes arises as a result of a low carrier concentration in the wide-gap material. The use of an InAlGaAs solid solution with an Al content lower than 40% makes it possible to raise the hole concentration in the widegap window up ~9 × 10{sup 18} cm{sup –3} and completely remove the potential barrier, thereby reducing the series resistance ofmore » the device. The parameters of an GaInAs metamorphic buffer layer with a stepwise In content profile are calculated and its epitaxial growth conditions are optimized, which improves carrier collection from the n-GaInAs base region and provides a quantum efficiency of 83% at a wavelength of 1064 nm. Optimization of the metamorphic heterostructure of the photovoltaic converter results in that its conversion efficiency for laser light with a wavelength of 1064 nm is 38.5%.« less

Metamorphic Epitaxy for Multijunction Solar Cells

DOE Office of Scientific and Technical Information (OSTI.GOV)

France, Ryan M.; Dimroth, Frank; Grassman, Tyler J.

Multijunction solar cells have proven to be capable of extremely high efficiencies by combining multiple semiconductor materials with bandgaps tuned to the solar spectrum. Reaching the optimum set of semiconductors often requires combining high-quality materials with different lattice constants into a single device, a challenge particularly suited for metamorphic epitaxy. In this article, we describe different approaches to metamorphic multijunction solar cells, including traditional upright metamorphic, state-of-the-art inverted metamorphic, and forward-looking multijunction designs on silicon. We also describe the underlying materials science of graded buffers that enables metamorphic subcells with low dislocation densities. Following nearly two decades of research, recentmore » efforts have demonstrated high-quality lattice-mismatched multijunction solar cells with very little performance loss related to the mismatch, enabling solar-to-electric conversion efficiencies over 45%.« less

Highly Transparent Compositionally Graded Buffers for New Metamorphic Multijunction Solar Cell Designs

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schulte, Kevin L.; France, Ryan M.; Geisz, John F.

The development of compositionally graded buffer layers (CGBs) with enhanced transparency would enable novel five and six junction solar cells, with efficiencies approaching 50% under high concentration. Here, we demonstrate highly transparent grades between the GaAs and InP lattice constants on both A- and B-miscut GaAs substrates, employing Al xGayIn 1-x-yAs and highly Se-doped Burstein-Moss (BM) shifted Ga xIn 1-xP. Transparency to >810 and >890 nm wavelengths is demonstrated with BM-shifted Ga xIn 1-xP on B-miscut substrates and Al xGayIn 1-x-yAs/Ga xIn 1-xP(Se) combined grades on A-miscut substrates, respectively. 0.74 eV GaInAs solar cells grown on these transparent CGBs exhibitmore » Woc = 0.41 V at mA/ cm 2, performance comparable with the state-of-the-art Ga xIn 1-xP grade employed in the four-junction-inverted metamorphic multijunction (IMM) cell. A GaAs/0.74cV GaInAs tandem cell was grown with a transparent BM-shifted Ga xIn 1-xP CGB to verify the CGB performance in a multijunction device structure. Quantum efficiency measurements indicate that the CGB is completely transparent to photons below the GaAs bandedge, validating its use in 4-6 junction IMM devices with a single-graded buffer. Furthermore, this tandem represents a highly efficient two-junction band gap combination, achieving 29.6% ± 1.2% efficiency under the AM1.5 global spectrum, demonstrating how the additional transparency enables new device structures.« less

Highly Transparent Compositionally Graded Buffers for New Metamorphic Multijunction Solar Cell Designs

DOE PAGES

Schulte, Kevin L.; France, Ryan M.; Geisz, John F.

2016-11-11

The development of compositionally graded buffer layers (CGBs) with enhanced transparency would enable novel five and six junction solar cells, with efficiencies approaching 50% under high concentration. Here, we demonstrate highly transparent grades between the GaAs and InP lattice constants on both A- and B-miscut GaAs substrates, employing Al xGayIn 1-x-yAs and highly Se-doped Burstein-Moss (BM) shifted Ga xIn 1-xP. Transparency to >810 and >890 nm wavelengths is demonstrated with BM-shifted Ga xIn 1-xP on B-miscut substrates and Al xGayIn 1-x-yAs/Ga xIn 1-xP(Se) combined grades on A-miscut substrates, respectively. 0.74 eV GaInAs solar cells grown on these transparent CGBs exhibitmore » Woc = 0.41 V at mA/ cm 2, performance comparable with the state-of-the-art Ga xIn 1-xP grade employed in the four-junction-inverted metamorphic multijunction (IMM) cell. A GaAs/0.74cV GaInAs tandem cell was grown with a transparent BM-shifted Ga xIn 1-xP CGB to verify the CGB performance in a multijunction device structure. Quantum efficiency measurements indicate that the CGB is completely transparent to photons below the GaAs bandedge, validating its use in 4-6 junction IMM devices with a single-graded buffer. Furthermore, this tandem represents a highly efficient two-junction band gap combination, achieving 29.6% ± 1.2% efficiency under the AM1.5 global spectrum, demonstrating how the additional transparency enables new device structures.« less

Modeling of defect tolerance of IMM multijunction photovoltaics for space application

NASA Astrophysics Data System (ADS)

Mehrotra, Akhil; Freundlich, Alex

2013-03-01

Reduction of defects by use of thick sophisticated graded metamorphic buffers in inverted metamorphic solar cells has been a requirement to obtain high efficiency devices. With increase in number of metamorphic junctions to obtain higher efficiencies, these graded buffers constitute a significant part of growth time and cost for manufacturer of the solar cells. It's been shown that ultrathin 3 and 4 junction IMM devices perform better in presence of dislocations or/and radiation harsh environment compared to conventional thick IMM devices. Thickness optimization of the device would result in better defect and radiation tolerant behavior of 0.7ev and 1.0ev InGaAs sub-cells which would in turn require thinner buffers with higher efficiencies, hence reducing the total device thickness. It is also shown that for 3 and 4 junc. IMM, with an equivalent 1015 cm-2 1 MeV electron fluence radiation, very high EOL efficiencies can be afforded with substantially higher dislocation densities (<2×107 cm-2) than those commonly perceived as acceptable for IMM devices with remaining power factor as high as 0.85. The irregular radiation degradation behavior in 4-junc IMM is also explained by back photon reflection from gold contacts and reduced by using thickness optimization of 0.7ev and 1.0ev InGaAs sub-cells.

Optimization of metamorphic buffers for MBE growth of high quality AlInSb/InSb quantum structures: Suppression of hillock formation

NASA Astrophysics Data System (ADS)

Shi, Y.; Gosselink, D.; Gharavi, K.; Baugh, J.; Wasilewski, Z. R.

2017-11-01

The optimization of metamorphic buffers for InSb/AlInSb QWs grown on GaAs (0 0 1) substrates is presented. With increasing surface offcut angle towards [ 1 1 bar 0 ] direction, the interaction of spiral growth around threading dislocations (TDs) with the offcut-induced atomic steps leads to a gradual change in the morphology of the AlSb buffer from one dominated by hillocks to that exhibiting near-parallel steps, and finally to a surface with increasing number of localized depressions. With the growth conditions used, the smoothest AlSb surface morphology was obtained for the offcut angles range of 0.8-1.3°. On substrates with 0° offcut, subsequent 3 repeats of Al0.24In0.76 Sb/Al0.12In0.88 Sb interlayers reduces the TD density of AlSb buffer by a factor of 10, while 70 times reduction in the surface density of TD-related hillocks is observed. The remaining hillocks have rectangular footprint and small facet angles with respect to GaAs (0 0 1) surface: 0.4° towards [ 1 1 bar 0 ] direction and 0.7° towards [1 1 0] direction. Their triangular-shaped sidewalls with regularly spaced atomic steps show occasional extra step insertion sites, characteristic of TD outcrops. Many of the observed sidewalls are dislocation free and offer atomically smooth areas of up to 1 μm2, already suitable for high-quality InSb growth and subsequent top-down fabrication of InSb nanowires. It is proposed that the sidewalls of the remaining hillocks offer local vicinal surfaces with atomic step density optimal for suppression of TD-induced spiral growth, thus providing the important information on the exact substrate offcut needed to achieve large hillock-free and atomically smooth areas on AlInSb metamorphic buffers.

Fluid-absent metamorphism in the Adirondacks

NASA Technical Reports Server (NTRS)

Valley, J. W.

1986-01-01

Results on late Proterozoic metamorphism of granulite in the Adirondacks are presented. There more than 20,000 sq km of rock are at granulite facies. Low water fugacites are implied by orthopyroxene bearing assemblages and by stability of k'spar-plag-quartz assemblages. After mentioning the popular concept of infiltration of carbon dioxide into Precambrian rocks and attendent generation of granulite facies assemblages, several features of Adirondack rocks pertinent to carbon dioxide and water during their metamorphism are summarized: wollastonite occurs in the western lowlands; contact metamorphism by anorthosite preceeding granulite metamorphism is indicated by oxygen isotopes. Oxygen fugacity lies below that of the QFM buffer; total P sub water + P sub carbon dioxide determined from monticellite bearing assemblages are much less than P sub total (7 to 7.6 kb). These and other features indicate close spatial association of high- and low-P sub carbon dioxide assemblages and that a vapor phase was not present during metamorphism. Thus Adirondack rocks were not infiltrated by carbon dioxide vapor. Their metamorphism, at 625 to 775 C, occurred either when the protoliths were relatively dry or after dessication occurred by removal of a partial melt phase.

Metamorphic and geochronogical study of the Triassic El Oro metamorphic complex, Ecuador: Implications for high-temperature metamorphism in a forearc zone

NASA Astrophysics Data System (ADS)

Riel, N.; Guillot, S.; Jaillard, E.; Martelat, J.-E.; Paquette, J.-L.; Schwartz, S.; Goncalves, P.; Duclaux, G.; Thebaud, N.; Lanari, P.; Janots, E.; Yuquilema, J.

2013-01-01

In the forearc of the Andean active margin in southwest Ecuador, the El Oro metamorphic complex exhibits a well exposed tilted forearc section partially migmatized. We used Raman spectroscopy on carbonaceous matter (RSCM) thermometry and pseudosections coupled with mineralogical and textural studies to constrain the pressure-temperature (P-T) evolution of the El Oro metamorphic complex during Triassic times. Our results show that anatexis of the continental crust occurred by white-mica and biotite dehydration melting along a 10 km thick crustal domain (from 4.5 to 8 kbar) with increasing temperature from 650 to 700 °C. In the biotite dehydration melting zone, temperature was buffered at 750-820 °C in a 5 km thick layer. The estimated average thermal gradient during peak metamorphism is of 30 °C/km within the migmatitic domain can be partitioned into two apparent gradients parts. The upper part from surface to 7 km depth records a 40-45 °C/km gradient. The lower part records a quasi-adiabatic geotherm with a 10 °C/km gradient consistent with an isothermal melting zone. Migmatites U-Th-Pb geochronology yielded zircon and monazite ages of 229.3 ± 2.1 Ma and 224.5 ± 2.3 Ma, respectively. This thermal event generated S-type magmatism (the Marcabeli granitoid) and was immediately followed by underplating of the high-pressure low-temperature (HP-LT) Arenillas-Panupalí unit at 225.8 ± 1.8 Ma. The association of high-temperature low-pressure (HT-LP) migmatites with HP-LT unit constitutes a new example of a paired metamorphic belt along the South American margin. We propose that in addition to crustal thinning, underplating of the Piedras gabbroic unit before 230 Ma provided the heat source necessary to foster crustal anatexis. Furthermore, its MORB signature shows that the asthenosphere was involved as the source of the heat anomaly. S-type felsic magmatism is widespread during this time and suggests that a large-scale thermal anomaly affected a large part of the South American margin during the late Triassic. We propose that crustal anatexis is related to an anomaly that arose during subduction of the Panthalassa ocean under the South American margin. Slab verticalization or slab break-off can be invoked as the origin of the upwelling of the asthenosphere.

Progress in the Development of Metamorphic Multi-Junction III-V Space-Solar Cells at Essential Research Incorporated

NASA Technical Reports Server (NTRS)

Sinharoy, Samar; Patton, Martin O.; Valko, Thomas M., Sr.; Weizer, Victor G.

2002-01-01

Theoretical calculations have shown that highest efficiency III-V multi-junction solar cells require alloy structures that cannot be grown on a lattice-matched substrate. Ever since the first demonstration of high efficiency metamorphic single junction 1.1 eV and 1.2 eV InGaAs solar cells by Essential Research Incorporated (ERI), interest has grown in the development of multi-junction cells of this type using graded buffer layer technology. ERI is currently developing a dual-junction 1.6 eV InGaP/1.1 eV InGaAs tandem cell (projected practical air-mass zero (AM0), one-sun efficiency of 28%, and 100-sun efficiency of 37.5%) under a Ballistic Missile Defense Command (BMDO) SBIR Phase II program. A second ongoing research effort at ERI involves the development of a 2.1 eV AlGaInP/1.6 eV InGaAsP/1.2 eV InGaAs triple-junction concentrator tandem cell (projected practical AM0 efficiency of 36.5% under 100 suns) under a SBIR Phase II program funded by the Air Force. We are in the process of optimizing the dual-junction cell performance. In case of the triple-junction cell, we have developed the bottom and the middle cell, and are in the process of developing the layer structures needed for the top cell. A progress report is presented in this paper.

Reduction of Crosshatch Roughness and Threading Dislocation Density in Metamorphic GaInP Buffers and GaInAs Solar Cells

DOE Office of Scientific and Technical Information (OSTI.GOV)

France, R. M.; Geisz, J. F.; Steiner, M. A.

Surface crosshatch roughness typically develops during the growth of lattice-mismatched compositionally graded buffers and can limit misfit dislocation glide. In this study, the crosshatch roughness during growth of a compressive GaInP/GaAs graded buffer is reduced by increasing the phosphine partial pressure throughout the metamorphic growth. Changes in the average misfit dislocation length are qualitatively determined by characterizing the threading defect density and residual strain. The decrease of crosshatch roughness leads to an increase in the average misfit dislocation glide length, indicating that the surface roughness is limiting dislocation glide. Growth rate is also analyzed as a method to reduce surfacemore » crosshatch roughness and increase glide length, but has a more complicated relationship with glide kinetics. Using knowledge gained from these experiments, high quality inverted GaInAs 1 eV solar cells are grown on a GaInP compositionally graded buffer with reduced roughness and threading dislocation density. The open circuit voltage is only 0.38 V lower than the bandgap potential at a short circuit current density of 15 mA/cm{sup 2}, suggesting that there is very little loss due to the lattice mismatch.« less

FinalTechRep_DE_EE0007363_15

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ahrenkiel, Phil

The primary objective of the project was to develop Ga0.82In0.18As (GaInAs) solar cells grown on epilayers of elemental Al. At this composition, GaInAs has a nearly optimal bandgap (1.16 eV) for a single-junction photovoltaic device. However, GaInAs lacks a convenient, lattice-matched substrate, restricting most investigations to metamorphic structures. The metal Al is, in fact, precisely lattice-matched to GaInAs in the orientation GaInAs (001)[100]||Al(001)[110]. At present, however, epi-ready Al substrates are not readily available commercially and are subject to oxidation. However, epitaxial Al buffer layers could enable control of defect generation, thermal and light management, and rapid epitaxial lift-off for ultrathinmore » devices.« less

High-efficiency inverted metamorphic 1.7/1.1 eV GaInAsP/GaInAs dual-junction solar cells

NASA Astrophysics Data System (ADS)

Jain, Nikhil; Schulte, Kevin L.; Geisz, John F.; Friedman, Daniel J.; France, Ryan M.; Perl, Emmett E.; Norman, Andrew G.; Guthrey, Harvey L.; Steiner, Myles A.

2018-01-01

Photovoltaic conversion efficiencies of 32.6 ± 1.4% under the AM1.5 G173 global spectrum, and 35.5% ± 1.2% at 38-suns concentration under the direct spectrum, are demonstrated for a monolithic, dual-junction 1.7/1.1 eV solar cell. The tandem cell consists of a 1.7 eV GaInAsP top-junction grown lattice-matched to a GaAs substrate, followed by a metamorphic 1.1 eV GaInAs junction grown on a transparent, compositionally graded metamorphic AlGaInAs buffer. This bandgap combination is much closer to the dual-junction optimum and offers headroom for absolute 3% improvement in efficiency, in comparison to the incumbent lattice-matched GaInP/GaAs (˜1.86/1.41 eV) solar cells. The challenge of growing a high-quality 1.7 eV GaInAsP solar cell is the propensity for phase separation in the GaInAsP alloy. The challenge of lattice-mismatched GaInAs solar cell growth is that it requires minimizing the residual dislocation density during the growth of a transparent compositionally graded buffer to enable efficient metamorphic tandem cell integration. Transmission electron microscopy reveals relatively weak composition fluctuation present in the 1.7 eV GaInAsP alloy, attained through growth control. The threading dislocation density of the GaInAs junction is ˜1 × 106 cm-2, as determined from cathodoluminescence measurements, highlighting the quality of the graded buffer. These material advances have enabled the performance of both junctions to reach over 80% of their Shockley-Queisser limiting efficiencies, with both the subcells demonstrating a bandgap-voltage offset, WOC (=Eg/q-VOC), of ˜0.39 V.

High-efficiency inverted metamorphic 1.7/1.1 eV GaInAsP/GaInAs dual-junction solar cells

DOE PAGES

Jain, Nikhil; Schulte, Kevin L.; Geisz, John F.; ...

2018-01-29

Photovoltaic conversion efficiencies of 32.6 +/- 1.4% under the AM1.5 G173 global spectrum, and 35.5 +/- 1.2% at 38-suns concentration under the direct spectrum, are demonstrated for a monolithic, dual-junction 1.7/1.1 eV solar cell. The tandem cell consists of a 1.7 eV GaInAsP top-junction grown lattice-matched to a GaAs substrate, followed by a metamorphic 1.1 eV GaInAs junction grown on a transparent, compositionally graded metamorphic AlGaInAs buffer. This bandgap combination is much closer to the dual-junction optimum and offers headroom for absolute 3% improvement in efficiency, in comparison to the incumbent lattice-matched GaInP/GaAs (~1.86/1.41 eV) solar cells. The challenge ofmore » growing a high-quality 1.7 eV GaInAsP solar cell is the propensity for phase separation in the GaInAsP alloy. The challenge of lattice-mismatched GaInAs solar cell growth is that it requires minimizing the residual dislocation density during the growth of a transparent compositionally graded buffer to enable efficient metamorphic tandem cell integration. Transmission electron microscopy reveals relatively weak composition fluctuation present in the 1.7 eV GaInAsP alloy, attained through growth control. The threading dislocation density of the GaInAs junction is ~1 x 10^6 cm-2, as determined from cathodoluminescence measurements, highlighting the quality of the graded buffer. These material advances have enabled the performance of both junctions to reach over 80% of their Shockley-Queisser limiting efficiencies, with both the subcells demonstrating a bandgap-voltage offset, WOC (=Eg/q-VOC), of ~0.39 V.« less

High-efficiency inverted metamorphic 1.7/1.1 eV GaInAsP/GaInAs dual-junction solar cells

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jain, Nikhil; Schulte, Kevin L.; Geisz, John F.

Photovoltaic conversion efficiencies of 32.6 +/- 1.4% under the AM1.5 G173 global spectrum, and 35.5 +/- 1.2% at 38-suns concentration under the direct spectrum, are demonstrated for a monolithic, dual-junction 1.7/1.1 eV solar cell. The tandem cell consists of a 1.7 eV GaInAsP top-junction grown lattice-matched to a GaAs substrate, followed by a metamorphic 1.1 eV GaInAs junction grown on a transparent, compositionally graded metamorphic AlGaInAs buffer. This bandgap combination is much closer to the dual-junction optimum and offers headroom for absolute 3% improvement in efficiency, in comparison to the incumbent lattice-matched GaInP/GaAs (~1.86/1.41 eV) solar cells. The challenge ofmore » growing a high-quality 1.7 eV GaInAsP solar cell is the propensity for phase separation in the GaInAsP alloy. The challenge of lattice-mismatched GaInAs solar cell growth is that it requires minimizing the residual dislocation density during the growth of a transparent compositionally graded buffer to enable efficient metamorphic tandem cell integration. Transmission electron microscopy reveals relatively weak composition fluctuation present in the 1.7 eV GaInAsP alloy, attained through growth control. The threading dislocation density of the GaInAs junction is ~1 x 10^6 cm-2, as determined from cathodoluminescence measurements, highlighting the quality of the graded buffer. These material advances have enabled the performance of both junctions to reach over 80% of their Shockley-Queisser limiting efficiencies, with both the subcells demonstrating a bandgap-voltage offset, WOC (=Eg/q-VOC), of ~0.39 V.« less

Method of depositing an electrically conductive oxide buffer layer on a textured substrate and articles formed therefrom

DOEpatents

Paranthaman, M. Parans; Aytug, Tolga; Christen, David K.

2005-10-18

An article with an improved buffer layer architecture includes a substrate having a textured metal surface, and an electrically conductive lanthanum metal oxide epitaxial buffer layer on the surface of the substrate. The article can also include an epitaxial superconducting layer deposited on the epitaxial buffer layer. An epitaxial capping layer can be placed between the epitaxial buffer layer and the superconducting layer. A method for preparing an epitaxial article includes providing a substrate with a metal surface and depositing on the metal surface a lanthanum metal oxide epitaxial buffer layer. The method can further include depositing a superconducting layer on the epitaxial buffer layer, and depositing an epitaxial capping layer between the epitaxial buffer layer and the superconducting layer.

Method of depositing an electrically conductive oxide buffer layer on a textured substrate and articles formed therefrom

DOEpatents

Paranthaman, M. Parans; Aytug, Tolga; Christen, David K.

2003-09-09

An article with an improved buffer layer architecture includes a substrate having a textured metal surface, and an electrically conductive lanthanum metal oxide epitaxial buffer layer on the surface of the substrate. The article can also include an epitaxial superconducting layer deposited on the epitaxial buffer layer. An epitaxial capping layer can be placed between the epitaxial buffer layer and the superconducting layer. A method for preparing an epitaxial article includes providing a substrate with a metal surface and depositing on the metal surface a lanthanum metal oxide epitaxial buffer layer. The method can further include depositing a superconducting layer on the epitaxial buffer layer, and depositing an epitaxial capping layer between the epitaxial buffer layer and the superconducting layer.

Mid-infrared electroluminescence from InAs type-I quantum wells grown on InAsP/InP metamorphic buffers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jung, Daehwan, E-mail: daehwan.jung@yale.edu; Larry Lee, Minjoo; Yu, Lan

We report room-temperature (RT) electroluminescence (EL) from InAs/InAs{sub x}P{sub 1−x} quantum well (QW) light-emitting diodes (LEDs) over a wide wavelength range of 2.50–2.94 μm. We demonstrate the ability to accurately design strained InAs QW emission wavelengths while maintaining low threading dislocation density, coherent QW interfaces, and high EL intensity. Investigation of the optical properties of the LEDs grown on different InAs{sub x}P{sub 1−x} metamorphic buffers showed higher EL intensity and lower thermal quenching for QWs with higher barriers and stronger carrier confinement. Strong RT EL intensity from LEDs with narrow full-width at half-maximum shows future potential for InAs QW mid-infrared lasermore » diodes on InAsP/InP.« less

Metamorphic III–V Solar Cells: Recent Progress and Potential

DOE Office of Scientific and Technical Information (OSTI.GOV)

Garcia, Ivan; France, Ryan M.; Geisz, John F.

Inverted metamorphic multijunction solar cells have been demonstrated to be a pathway to achieve the highest photovoltaic (PV) conversion efficiencies. Attaining high-quality lattice-mismatched (metamorphic) semiconductor devices is challenging. However, recent improvements to compositionally graded buffer epitaxy and junction structures have led to the achievement of high-quality metamorphic solar cells exhibiting internal luminescence efficiencies over 90%. For this high material quality, photon recycling is significant, and therefore, the optical environment of the solar cell becomes important. In this paper, we first present recent progress and performance results for 1- and 0.7-eV GaInAs solar cells grown on GaAs substrates. Then, an electroopticalmore » model is used to assess the potential performance improvements in current metamorphic solar cells under different realizable design scenarios. The results show that the quality of 1-eV subcells is such that further improving its electronic quality does not produce significant Voc increases in the four-junction inverted metamorphic subcells, unless a back reflector is used to enhance photon recycling, which would significantly complicate the structure. Conversely, improving the electronic quality of the 0.7-eV subcell would lead to significant Voc boosts, driving the progress of four-junction inverted metamorphic solar cells.« less

High Performance 50 nm InAlAs/In0.75GaAs Metamorphic High Electron Mobility Transistors with Si3N4 Passivation on Thin InGaAs Layer

NASA Astrophysics Data System (ADS)

Yeon, Seongjin; Seo, Kwangseok

2008-04-01

We fabricated 50 nm InAlAs/InGaAs metamorphic high electron mobility transistors (HEMTs) with a very thin barrier. Through the reduction of the gate-channel distance (dGC) in the epitaxial structure, a channel aspect ratio (ARC) of over three was achieved when Lg was 50 nm. We inserted a thin InGaAs layer as a protective layer, and tested various gate structures to reduce surface problems induced by barrier shrinkage and to optimize the device characteristics. Through the optimization of the gate structure with the thin InGaAs layer, the fabricated 50 nm metamorphic HEMT exhibited high DC and RF characteristics, Gm of 1.5 S/mm, and fT of 490 GHz.

Reducing interface recombination for Cu(In,Ga)Se{sub 2} by atomic layer deposited buffer layers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hultqvist, Adam; Bent, Stacey F.; Li, Jian V.

2015-07-20

Partial CuInGaSe{sub 2} (CIGS) solar cell stacks with different atomic layer deposited buffer layers and pretreatments were analyzed by photoluminescence (PL) and capacitance voltage (CV) measurements to investigate the buffer layer/CIGS interface. Atomic layer deposited ZnS, ZnO, and SnO{sub x} buffer layers were compared with chemical bath deposited CdS buffer layers. Band bending, charge density, and interface state density were extracted from the CV measurement using an analysis technique new to CIGS. The surface recombination velocity calculated from the density of interface traps for a ZnS/CIGS stack shows a remarkably low value of 810 cm/s, approaching the range of single crystallinemore » II–VI systems. Both the PL spectra and its lifetime depend on the buffer layer; thus, these measurements are not only sensitive to the absorber but also to the absorber/buffer layer system. Pretreatment of the CIGS prior to the buffer layer deposition plays a significant role on the electrical properties for the same buffer layer/CIGS stack, further illuminating the importance of good interface formation. Finally, ZnS is found to be the best performing buffer layer in this study, especially if the CIGS surface is pretreated with potassium cyanide.« less

Reducing interface recombination for Cu(In,Ga)Se 2 by atomic layer deposited buffer layers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hultqvist, Adam; Li, Jian V.; Kuciauskas, Darius

2015-07-20

Partial CuInGaSe2 (CIGS) solar cell stacks with different atomic layer deposited buffer layers and pretreatments were analyzed by photoluminescence (PL) and capacitance voltage (CV) measurements to investigate the buffer layer/CIGS interface. Atomic layer deposited ZnS, ZnO, and SnOx buffer layers were compared with chemical bath deposited CdS buffer layers. Band bending, charge density, and interface state density were extracted from the CV measurement using an analysis technique new to CIGS. The surface recombination velocity calculated from the density of interface traps for a ZnS/CIGS stack shows a remarkably low value of 810 cm/s, approaching the range of single crystalline II-VImore » systems. Both the PL spectra and its lifetime depend on the buffer layer; thus, these measurements are not only sensitive to the absorber but also to the absorber/buffer layer system. Pretreatment of the CIGS prior to the buffer layer deposition plays a significant role on the electrical properties for the same buffer layer/CIGS stack, further illuminating the importance of good interface formation. Finally, ZnS is found to be the best performing buffer layer in this study, especially if the CIGS surface is pretreated with potassium cyanide.« less

Reducing interface recombination for Cu(In,Ga)Se 2 by atomic layer deposited buffer layers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hultqvist, Adam; Li, Jian V.; Kuciauskas, Darius

2015-07-20

Partial CuInGaSe2 (CIGS) solar cell stacks with different atomic layer deposited buffer layers and pretreatments were analyzed by photoluminescence (PL) and capacitance voltage (CV) measurements to investigate the buffer layer/CIGS interface. Atomic layer deposited ZnS, ZnO, and SnOx buffer layers were compared with chemical bath deposited CdS buffer layers. Band bending, charge density, and interface state density were extracted from the CV measurement using an analysis technique new to CIGS. The surface recombination velocity calculated from the density of interface traps for a ZnS/CIGS stack shows a remarkably low value of 810 cm/s, approaching the range of single crystalline II–VImore » systems. Both the PL spectra and its lifetime depend on the buffer layer; thus, these measurements are not only sensitive to the absorber but also to the absorber/buffer layer system. Pretreatment of the CIGS prior to the buffer layer deposition plays a significant role on the electrical properties for the same buffer layer/CIGS stack, further illuminating the importance of good interface formation. Finally, ZnS is found to be the best performing buffer layer in this study, especially if the CIGS surface is pretreated with potassium cyanide.« less

Leakage effects in n-GaAs MESFET with n-GaAs buffer layer

NASA Technical Reports Server (NTRS)

Wang, Y. C.; Bahrami, M.

1983-01-01

Whereas improvement of the interface between the active layer and the buffer layer has been demonstrated, the leakage effects can be important if the buffer layer resistivity is not sufficiently high and/or the buffer layer thickness is not sufficiently small. It was found that two buffer leakage currents exist from the channel under the gate to the source and from drain to the channel in addition to the buffer leakage resistance between drain and source. It is shown that for a 1 micron gate-length n-GaAs MESFET, if the buffer layer resistivity is 12 OHM-CM and the buffer layer thickness h is 2 microns, the performance of the device degrades drastically. It is suggested that h should be below 2 microns.

Effect of ZnO seed layer on the morphology and optical properties of ZnO nanorods grown on GaN buffer layers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nandi, R., E-mail: rajunandi@iitb.ac.in; Mohan, S., E-mail: rajunandi@iitb.ac.in; Major, S. S.

2014-04-24

ZnO nanorods were grown by chemical bath deposition on sputtered, polycrystalline GaN buffer layers with and without ZnO seed layer. Scanning electron microscopy and X-ray diffraction show that the ZnO nanorods on GaN buffer layers are not vertically well aligned. Photoluminescence spectrum of ZnO nanorods grown on GaN buffer layer, however exhibits a much stronger near-band-edge emission and negligible defect emission, compared to the nanorods grown on ZnO buffer layer. These features are attributed to gallium incorporation at the ZnO-GaN interface. The introduction of a thin (25 nm) ZnO seed layer on GaN buffer layer significantly improves the morphology andmore » vertical alignment of ZnO-NRs without sacrificing the high optical quality of ZnO nanorods on GaN buffer layer. The presence of a thick (200 nm) ZnO seed layer completely masks the effect of the underlying GaN buffer layer on the morphology and optical properties of nanorods.« less

Back contact buffer layer for thin-film solar cells

DOEpatents

Compaan, Alvin D.; Plotnikov, Victor V.

2014-09-09

A photovoltaic cell structure is disclosed that includes a buffer/passivation layer at a CdTe/Back contact interface. The buffer/passivation layer is formed from the same material that forms the n-type semiconductor active layer. In one embodiment, the buffer layer and the n-type semiconductor active layer are formed from cadmium sulfide (CdS). A method of forming a photovoltaic cell includes the step of forming the semiconductor active layers and the buffer/passivation layer within the same deposition chamber and using the same material source.

Methods for improved growth of group III nitride buffer layers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Melnik, Yurity; Chen, Lu; Kojiri, Hidehiro

Methods are disclosed for growing high crystal quality group III-nitride epitaxial layers with advanced multiple buffer layer techniques. In an embodiment, a method includes forming group III-nitride buffer layers that contain aluminum on suitable substrate in a processing chamber of a hydride vapor phase epitaxy processing system. A hydrogen halide or halogen gas is flowing into the growth zone during deposition of buffer layers to suppress homogeneous particle formation. Some combinations of low temperature buffers that contain aluminum (e.g., AlN, AlGaN) and high temperature buffers that contain aluminum (e.g., AlN, AlGaN) may be used to improve crystal quality and morphologymore » of subsequently grown group III-nitride epitaxial layers. The buffer may be deposited on the substrate, or on the surface of another buffer. The additional buffer layers may be added as interlayers in group III-nitride layers (e.g., GaN, AlGaN, AlN).« less

Doped LZO buffer layers for laminated conductors

DOEpatents

Paranthaman, Mariappan Parans [Knoxville, TN; Schoop, Urs [Westborough, MA; Goyal, Amit [Knoxville, TN; Thieme, Cornelis Leo Hans [Westborough, MA; Verebelyi, Darren T [Oxford, MA; Rupich, Martin W [Framingham, MA

2010-03-23

A laminated conductor includes a metallic substrate having a surface, a biaxially textured buffer layer supported by the surface of the substrate, the biaxially textured buffer layer comprising LZO and a dopant for mitigating metal diffusion through the LZO, and a biaxially textured conductor layer supported by the biaxially textured buffer layer.

Simulation study on single event burnout in linear doping buffer layer engineered power VDMOSFET

NASA Astrophysics Data System (ADS)

Yunpeng, Jia; Hongyuan, Su; Rui, Jin; Dongqing, Hu; Yu, Wu

2016-02-01

The addition of a buffer layer can improve the device's secondary breakdown voltage, thus, improving the single event burnout (SEB) threshold voltage. In this paper, an N type linear doping buffer layer is proposed. According to quasi-stationary avalanche simulation and heavy ion beam simulation, the results show that an optimized linear doping buffer layer is critical. As SEB is induced by heavy ions impacting, the electric field of an optimized linear doping buffer device is much lower than that with an optimized constant doping buffer layer at a given buffer layer thickness and the same biasing voltages. Secondary breakdown voltage and the parasitic bipolar turn-on current are much higher than those with the optimized constant doping buffer layer. So the linear buffer layer is more advantageous to improving the device's SEB performance. Project supported by the National Natural Science Foundation of China (No. 61176071), the Doctoral Fund of Ministry of Education of China (No. 20111103120016), and the Science and Technology Program of State Grid Corporation of China (No. SGRI-WD-71-13-006).

Photo-induced wettability of TiO{sub 2} film with Au buffer layer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Purkayastha, Debarun Dhar; Sangani, L. D. Varma; Krishna, M. Ghanashyam

2014-04-24

The effect of thickness of Au buffer layer (15-25 nm) between TiO{sub 2} film and substrate on the wettability of TiO{sub 2} films is reported. TiO{sub 2} films grown on Au buffer layer have a higher contact angle of 96-;100° as compared to 47.6o for the film grown without buffer layer. The transition from hydrophobicity to hydrophilicity under UV irradiation occurs within 10 min. for the buffer layered films whereas it is almost 30 min. for the film grown without buffer layer. The enhanced photo induced hydrophilicity is shown to be surface energy driven.

Enhanced electrical stability of flexible indium tin oxide films prepared on stripe SiO 2 buffer layer-coated polymer substrates by magnetron sputtering

NASA Astrophysics Data System (ADS)

Yu, Zhi-nong; Zhao, Jian-jian; Xia, Fan; Lin, Ze-jiang; Zhang, Dong-pu; Leng, Jian; Xue, Wei

2011-03-01

The electrical stability of flexible indium tin oxide (ITO) films fabricated on stripe SiO 2 buffer layer-coated polyethylene terephthalate (PET) substrates by magnetron sputtering was investigated by the bending test. The ITO thin films with stripe SiO 2 buffer layer under bending have better electrical stability than those with flat SiO 2 buffer layer and without buffer layer. Especially in inward bending text, the ITO thin films with stripe SiO 2 buffer layer only have a slight resistance change when the bending radius r is not less than 8 mm, while the resistances of the films with flat SiO 2 buffer layer and without buffer layer increase significantly at r = 16 mm with decreasing bending radius. This improvement of electrical stability in bending test is due to the small mismatch factor α in ITO-SiO 2, the enhanced interface adhesion and the balance of residual stress. These results indicate that the stripe SiO 2 buffer layer is suited to enhance the electrical stability of flexible ITO film under bending.

Buffer architecture for biaxially textured structures and method of fabricating same

DOEpatents

Norton, David P.; Park, Chan; Goyal, Amit

2004-04-06

The invention relates to an article with an improved buffer layer architecture comprising a substrate having a metal surface, and an epitaxial buffer layer on the surface of the substrate. The epitaxial buffer layer comprises at least one of the group consisting of ZrO.sub.2, HfO.sub.2, and compounds having at least one of Ca and a rare earth element stabilizing cubic phases of ZrO.sub.2 and/or HfO.sub.2. The article can also include a superconducting layer deposited on the epitaxial buffer layer. The article can also include an epitaxial capping layer between the epitaxial buffer layer and the superconducting layer. A method for preparing an epitaxial article comprises providing a substrate with a metal surface, depositing on the metal surface an epitaxial buffer layer comprising at least one material selected from the group consisting of ZrO.sub.2, HfO.sub.2, and compounds having at least one of Ca and a rare earth element stabilizing cubic phases of at least one of ZrO.sub.2 and HfO.sub.2. The epitaxial layer depositing step occurs in a vacuum with a background pressure of no more than 1.times.10.sup.-5 Torr. The method can further comprise depositing a superconducting layer on the epitaxial layer, and depositing an epitaxial capping layer between the epitaxial buffer layer and the superconducting layer.

Thin film photovoltaic devices with a minimally conductive buffer layer

DOEpatents

Barnes, Teresa M.; Burst, James

2016-11-15

A thin film photovoltaic device (100) with a tunable, minimally conductive buffer (128) layer is provided. The photovoltaic device (100) may include a back contact (150), a transparent front contact stack (120), and an absorber (140) positioned between the front contact stack (120) and the back contact (150). The front contact stack (120) may include a low resistivity transparent conductive oxide (TCO) layer (124) and a buffer layer (128) that is proximate to the absorber layer (140). The photovoltaic device (100) may also include a window layer (130) between the buffer layer (128) and the absorber (140). In some cases, the buffer layer (128) is minimally conductive, with its resistivity being tunable, and the buffer layer (128) may be formed as an alloy from a host oxide and a high-permittivity oxide. The high-permittivity oxide may further be chosen to have a bandgap greater than the host oxide.

Structural evaluation of InAsP/InGaAsP strained-layer superlattices with dislocations as grown by metal-organic molecular beam epitaxy

NASA Astrophysics Data System (ADS)

Nakashima, Kiichi; Sugiura, Hideo

1997-08-01

The relaxation process in InAsP/InGaAsP strained-layer superlattices (SLSs) with interfacial misfit dislocations has been investigated systematically by transmission electron microscopy (TEM) and x-ray analyses. The TEM analysis reveals that dislocations locate a little inside the buffer layer near the interface between the buffer and first well layer in the SLS. The x-ray analysis of (400) azimuthal angle dependence indicates the buffer layer has a large macroscopic tilt. Using a curve fitting analysis of various (hkl) x-ray profiles and reciprocal lattice mapping measurements, residual strain was determined quantitatively, i.e., Δa∥ and Δa⊥, in the SLS and buffer layer. These results reveal that the dislocations mainly cause lattice distortion of the buffer layer rather than relaxation of the SLS layer. The most remarkable result is that the change of a∥ is not equal to that of a⊥ in the buffer layer. This phenomenon strongly suggests that microplastic domains are generated in the buffer layer.

Doped Y.sub.2O.sub.3 buffer layers for laminated conductors

DOEpatents

Paranthaman, Mariappan Parans [Knoxville, TN; Schoop, Urs [Westborough, MA; Goyal, Amit [Knoxville, TN; Thieme, Cornelis Leo Hans [Westborough, MA; Verebelyi, Darren T [Oxford, MA; Rupich, Martin W [Framingham, MA

2007-08-21

A laminated conductor includes a metallic substrate having a surface, a biaxially textured buffer layer supported by the surface of the metallic substrate, the biaxially textured buffer layer comprising Y.sub.2O.sub.3 and a dopant for blocking cation diffusion through the Y.sub.2O.sub.3, and a biaxially textured conductor layer supported by the biaxially textured buffer layer.

Near-isothermal conditions in the middle and lower crust induced by melt migration.

PubMed

Depine, Gabriela V; Andronicos, Christopher L; Phipps-Morgan, Jason

2008-03-06

The thermal structure of the crust strongly influences deformation, metamorphism and plutonism. Models for the geothermal gradient in stable crust predict a steady increase of temperature with depth. This thermal structure, however, is incompatible with observations from high-temperature metamorphic terranes exhumed in orogens. Global compilations of peak conditions in high-temperature metamorphic terranes define relatively narrow ranges of peak temperatures over a wide range in pressure, for both isothermal decompression and isobaric cooling paths. Here we develop simple one-dimensional thermal models that include the effects of melt migration. These models show that long-lived plutonism results in a quasi-steady-state geotherm with a rapid temperature increase in the upper crust and nearly isothermal conditions in the middle and lower crust. The models also predict that the upward advection of heat by melt generates granulite facies metamorphism, and widespread andalusite-sillimanite metamorphism in the upper crust. Once the quasi-steady-state thermal profile is reached, the middle and lower crust are greatly weakened due to high temperatures and anatectic conditions, thus setting the stage for gravitational collapse, exhumation and isothermal decompression after the onset of plutonism. Near-isothermal conditions in the middle and lower crust result from the thermal buffering effect of dehydration melting reactions that, in part, control the shape of the geotherm.

Metamorphic sole formation and early plate interface rheology: Insights from Griggs apparatus experiments

NASA Astrophysics Data System (ADS)

Soret, Mathieu; Agard, Philippe; Dubacq, Benoît; Hirth, Greg; Yamato, Philippe; Ildefonse, Benoît; Prigent, Cécile

2016-04-01

Metamorphic soles correspond to m to ~500 m thick highly strained metamorphic rock units found beneath mylonitic banded peridotites at the base of large-scale ophiolites, as exemplified in Oman. Metamorphic soles are mainly composed of metabasalts deriving from the downgoing oceanic lithosphere and metamorphosed up to granulite-facies conditions by heat transfer from the mantle wedge. Pressure-temperature peak conditions are usually estimated at 1.0±0.2 GPa and 800±100°C. The absence of HP-LT metamorphism overprint implies that metamorphic soles have been formed and exhumed during subduction infancy. In this view, metamorphic soles were strongly deformed during their accretion to the mantle wedge (corresponding, now, to the base of the ophiolite). Therefore, metamorphic soles and banded peridotites are direct witnesses of the dynamics of early subduction zones, in terms of thermal structure, fluid migration and rheology evolution across the nascent slab interface. Based on fieldwork and EBSD analyses, we present a detailed (micro-) structural study performed on samples coming from the Sumeini window, the better-preserved cross-section of the metamorphic sole of Oman. Large differences are found in the deformation (CPO, grain size, aspect ratio) of clinopyroxene, amphibole and plagioclase, related to mineralogical changes linked with the distance to the peridotite contact (e.g., hardening due to the appearance of garnet and clinopyroxene). To model the incipient slab interface in laboratory, we carried out 5 hydrostatic annealing and simple-shear experiments on Griggs solid-medium apparatus. Deformation experiments were conducted at axial strain rates of 10-6 s-1. Fine-grained amphibolite was synthetized by adding 1 wt.% water to a (Mid-Ocean Ridge) basalt powder as a proxy for the metamorphic sole (amphibole + plagioclase + clinopyroxene ± garnet assemblage). To synthetize garnet, 2 experiments were carried out in hydrostatic conditions and with deformation at 800°C with confining pressure of 2 GPa. Another simple-shear experiment has been carried out at 800°C and 1 GPa with fined-grained natural garnet. With the aim of mimicking the early slab interface (between the metamorphic sole and banded peridotites at the base of the ophiolite), 2 simple-shear deformation experiments with 2 layers have been carried out at 800°C and confining pressure of 1 GPa. The bottom layer was made of hydrated basalt powder and the top layer was made of olivine. Fined-grained garnet-free amphibolite is significantly weaker than dunite but the appearance of harder minerals in the amphibolite (garnet and clinopyroxene) has major implications on its rheological evolution. These results allow liking field observations of strain localization at the interface to the metamorphic sole formation.

Characterization of Cu buffer layers for growth of L10-FeNi thin films

NASA Astrophysics Data System (ADS)

Mizuguchi, M.; Sekiya, S.; Takanashi, K.

2010-05-01

A Cu(001) layer was fabricated on a Au(001) layer to investigate the use of Cu as a buffer layer for growing L10-FeNi thin films. The epitaxial growth of a Cu buffer layer was observed using reflection high-energy electron diffraction. The flatness of the layer improved drastically with an increase in the substrate temperature although the layer was an alloy (AuCu3). An FeNi thin film was epitaxially grown on the AuCu3 buffer layer by alternate monatomic layer deposition and the formation of an L10-FeNi ordered alloy was expected. The AuCu3 buffer layer is thus a promising candidate material for the growth of L10-FeNi thin films.

Method of deforming a biaxially textured buffer layer on a textured metallic substrate and articles therefrom

DOEpatents

Lee, Dominic F.; Kroeger, Donald M.; Goyal, Amit

2000-01-01

The present invention provides methods and biaxially textured articles having a deformed epitaxial layer formed therefrom for use with high temperature superconductors, photovoltaic, ferroelectric, or optical devices. A buffer layer is epitaxially deposited onto biaxially-textured substrates and then mechanically deformed. The deformation process minimizes or eliminates grooves, or other irregularities, formed on the buffer layer while maintaining the biaxial texture of the buffer layer. Advantageously, the biaxial texture of the buffer layer is not altered during subsequent heat treatments of the deformed buffer. The present invention provides mechanical densification procedures which can be incorporated into the processing of superconducting films through the powder deposit or precursor approaches without incurring unfavorable high-angle grain boundaries.

John Simon | NREL

Science.gov Websites

novel crystalline substrates for growth of III-V Nitride semiconductors for solid-state lighting applications. Since then he has been involved in various projects involving the growth of III-V semiconductor .; Romero, M.; and Lee, M.J. "Metamorphic GaAsP buffers for growth of wide-bandgap InGaP solar cells

Selectively Enhanced UV-A Photoresponsivity of a GaN MSM UV Photodetector with a Step-Graded AlxGa1-xN Buffer Layer.

PubMed

Lee, Chang-Ju; Won, Chul-Ho; Lee, Jung-Hee; Hahm, Sung-Ho; Park, Hongsik

2017-07-21

The UV-to-visible rejection ratio is one of the important figure of merits of GaN-based UV photodetectors. For cost-effectiveness and large-scale fabrication of GaN devices, we tried to grow a GaN epitaxial layer on silicon substrate with complicated buffer layers for a stress-release. It is known that the structure of the buffer layers affects the performance of devices fabricated on the GaN epitaxial layers. In this study, we show that the design of a buffer layer structure can make effect on the UV-to-visible rejection ratio of GaN UV photodetectors. The GaN photodetector fabricated on GaN-on-silicon substrate with a step-graded Al x Ga -x N buffer layer has a highly-selective photoresponse at 365-nm wavelength. The UV-to-visible rejection ratio of the GaN UV photodetector with the step-graded Al x Ga 1-x N buffer layer was an order-of-magnitude higher than that of a photodetector with a conventional GaN/AlN multi buffer layer. The maximum photoresponsivity was as high as 5 × 10 - ² A/W. This result implies that the design of buffer layer is important for photoresponse characteristics of GaN UV photodetectors as well as the crystal quality of the GaN epitaxial layers.

Mitigation of substrate defects in reticles using multilayer buffer layers

DOEpatents

Mirkarimi, Paul B.; Bajt, Sasa; Stearns, Daniel G.

2001-01-01

A multilayer film is used as a buffer layer to minimize the size of defects on a reticle substrate prior to deposition of a reflective coating on the substrate. The multilayer buffer layer deposited intermediate the reticle substrate and the reflective coating produces a smoothing of small particles and other defects on the reticle substrate. The reduction in defect size is controlled by surface relaxation during the buffer layer growth process and by the degree of intermixing and volume contraction of the materials at the multilayer interfaces. The buffer layers are deposited at near-normal incidence via a low particulate ion beam sputtering process. The growth surface of the buffer layer may also be heated by a secondary ion source to increase the degree of intermixing and improve the mitigation of defects.

Buffer layer dependence of magnetoresistance effects in Co2Fe0.4Mn0.6Si/MgO/Co50Fe50 tunnel junctions

NASA Astrophysics Data System (ADS)

Sun, Mingling; Kubota, Takahide; Takahashi, Shigeki; Kawato, Yoshiaki; Sonobe, Yoshiaki; Takanashi, Koki

2018-05-01

Buffer layer dependence of tunnel magnetoresistance (TMR) effects was investigated in Co2Fe0.4Mn0.6Si (CFMS)/MgO/Co50Fe50 magnetic tunnel junctions (MTJs). Pd, Ru and Cr were selected for the buffer layer materials, and MTJs with three different CFMS thicknesses (30, 5, and 0.8 nm) were fabricated. A maximum TMR ratio of 136% was observed in the Ru buffer layer sample with a 30-nm-thick CFMS layer. TMR ratios drastically degraded for the CFMS thickness of 0.8 nm, and the values were 26% for Cr buffer layer and less than 1% for Pd and Ru buffer layers. From the annealing temperature dependence of the TMR ratios, amounts of interdiffusion and effects from the lattice mismatch were discussed.

Buffer layers for REBCO films for use in superconducting devices

DOEpatents

Goyal, Amit; Wee, Sung-Hun

2014-06-10

A superconducting article includes a substrate having a biaxially textured surface. A biaxially textured buffer layer, which can be a cap layer, is supported by the substrate. The buffer layer includes a double perovskite of the formula A.sub.2B'B''O.sub.6, where A is rare earth or alkaline earth metal and B' and B'' are different transition metal cations. A biaxially textured superconductor layer is deposited so as to be supported by the buffer layer. A method of making a superconducting article is also disclosed.

AlGaSb Buffer Layers for Sb-Based Transistors

DTIC Science & Technology

2010-01-01

transistor ( HEMT ), molecular beam epitaxy (MBE), field-effect transistor (FET), buffer layer INTRODUCTION High-electron-mobility transistors ( HEMTs ) with InAs...monolayers/s. The use of thinner buffer layers reduces molecular beam epitaxial growth time and source consumption. The buffer layers also exhibit...source. In addition, some of the flux from an Sb cell in a molecular beam epitaxy (MBE) system will deposit near the mouth of the cell, eventually

Textural and isotopic development of marble assemblages during the Barrovian-style M2 metamorphic event, Naxos, Greece

NASA Astrophysics Data System (ADS)

Baker, Judy; Matthews, Alan

1994-03-01

A detailed petrological analysis of the marble assemblages observed within the M2 metamorphic complex on Naxos is presented. Two distinct periods of mineral growth are documented; the first is associated with prograde M2 metamorphism and the second with retrograde M2 metamorphism occurring during ductile extensional thinning of the complex. The textural and miner-alogical characteristics and the carbon and oxygen isotope compositions of each generation are described, and the P-T-X CO 2 conditions at which these two mineral generations were stable, and the compositions of the fluids present during metamorphism are characterised. Whereas the low variance and stable isotope compositions of prograde siliceous dolomite assemblages are consistent with internally buffered fluid evolution, the retrograde mineral generation is shown to have grown as a result of the infiltration of a water-rich fluid phase that transported silica, Al2O3, Na2O and FeO into the host rocks. This observation, together with the stable isotope compositions of the retrograde calcite, and the fact that occurrences of veins of this type are limited to marbles in the highest grade areas ( T>600° C) of the metamorphic complex, suggests that the fluids responsible for vein formation were generated during the crystallisation of melts as the metamorphic complex cooled from peak temperatures. The existence of this second generation of minerals has significant implications for previous studies of heat transport by fluid flow on Naxos, because many of the unusually low δ18O compositions of pelites at high grades may be ascribable to the effects of interaction with retrograde M2 fluids, rather than with prograde fluids.

Selective excitation of window and buffer layers in chalcopyrite devices and modules

DOE PAGES

Glynn, Stephen; Repins, Ingrid L.; Burst, James M.; ...

2018-02-02

Window and buffer layers in chalcopyrite devices are well known to affect junctions, conduction, and photo-absorption properties of the device. Some of these layers, particularly 'buffers,' which are deposited directly on top of the absorber, exhibit metastable effects upon exposure to light. Thus, to understand device performance and/or metastability, it is sometimes desirable to selectively excite different layers in the device stack. Absorption characteristics of various window and buffer layers used in chalcopyrite devices are measured. These characteristics are compared with emission spectra of common and available light sources that might be used to optically excite such layers. Effects ofmore » the window and buffer absorption on device quantum efficiency and metastability are discussed. For the case of bath-deposited Zn(O,S) buffers, we conclude that this layer is not optically excited in research devices or modules. Furthermore, this provides a complimentary mechanism to the chemical differences that may cause long time constants (compared to devices with CdS buffers) associated with reaching a stable 'light-soaked' state.« less

Selective excitation of window and buffer layers in chalcopyrite devices and modules

DOE Office of Scientific and Technical Information (OSTI.GOV)

Glynn, Stephen; Repins, Ingrid L.; Burst, James M.

Window and buffer layers in chalcopyrite devices are well known to affect junctions, conduction, and photo-absorption properties of the device. Some of these layers, particularly 'buffers,' which are deposited directly on top of the absorber, exhibit metastable effects upon exposure to light. Thus, to understand device performance and/or metastability, it is sometimes desirable to selectively excite different layers in the device stack. Absorption characteristics of various window and buffer layers used in chalcopyrite devices are measured. These characteristics are compared with emission spectra of common and available light sources that might be used to optically excite such layers. Effects ofmore » the window and buffer absorption on device quantum efficiency and metastability are discussed. For the case of bath-deposited Zn(O,S) buffers, we conclude that this layer is not optically excited in research devices or modules. Furthermore, this provides a complimentary mechanism to the chemical differences that may cause long time constants (compared to devices with CdS buffers) associated with reaching a stable 'light-soaked' state.« less

Buffer layer for thin film structures

DOEpatents

Foltyn, Stephen R.; Jia, Quanxi; Arendt, Paul N.; Wang, Haiyan

2006-10-31

A composite structure including a base substrate and a layer of a mixture of strontium titanate and strontium ruthenate is provided. A superconducting article can include a composite structure including an outermost layer of magnesium oxide, a buffer layer of strontium titanate or a mixture of strontium titanate and strontium ruthenate and a top-layer of a superconducting material such as YBCO upon the buffer layer.

Buffer layer for thin film structures

DOEpatents

Foltyn, Stephen R.; Jia, Quanxi; Arendt, Paul N.; Wang, Haiyan

2010-06-15

A composite structure including a base substrate and a layer of a mixture of strontium titanate and strontium ruthenate is provided. A superconducting article can include a composite structure including an outermost layer of magnesium oxide, a buffer layer of strontium titanate or a mixture of strontium titanate and strontium ruthenate and a top-layer of a superconducting material such as YBCO upon the buffer layer.

On buffer layers as non-reflecting computational boundaries

NASA Technical Reports Server (NTRS)

Hayder, M. Ehtesham; Turkel, Eli L.

1996-01-01

We examine an absorbing buffer layer technique for use as a non-reflecting boundary condition in the numerical simulation of flows. One such formulation was by Ta'asan and Nark for the linearized Euler equations. They modified the flow inside the buffer zone to artificially make it supersonic in the layer. We examine how this approach can be extended to the nonlinear Euler equations. We consider both a conservative and a non-conservative form modifying the governing equations in the buffer layer. We compare this with the case that the governing equations in the layer are the same as in the interior domain. We test the effectiveness of these buffer layers by a simulation of an excited axisymmetric jet based on a nonlinear compressible Navier-Stokes equations.

The Effect of Buffer Types on the In0.82Ga0.18As Epitaxial Layer Grown on an InP (100) Substrate.

PubMed

Zhang, Min; Guo, Zuoxing; Zhao, Liang; Yang, Shen; Zhao, Lei

2018-06-08

In 0.82 Ga 0.18 As epitaxial layers were grown on InP (100) substrates at 530 °C by a low-pressure metalorganic chemical vapor deposition (LP-MOCVD) technique. The effects of different buffer structures, such as a single buffer layer, compositionally graded buffer layers, and superlattice buffer layers, on the crystalline quality and property were investigated. Double-crystal X-ray diffraction (DC-XRD) measurement, Raman scattering spectrum, and Hall measurements were used to evaluate the crystalline quality and electrical property. Scanning electron microscope (SEM), atomic force microscope (AFM), and transmission electron microscope (TEM) were used to characterize the surface morphology and microstructure, respectively. Compared with the In 0.82 Ga 0.18 As epitaxial layer directly grown on an InP substrate, the quality of the sample is not obviously improved by using a single In 0.82 Ga 0.18 As buffer layer. By introducing the graded In x Ga 1−x As buffer layers, it was found that the dislocation density in the epitaxial layer significantly decreased and the surface quality improved remarkably. In addition, the number of dislocations in the epitaxial layer greatly decreased under the combined action of multi-potential wells and potential barriers by the introduction of a In 0.82 Ga 0.18 As/In 0.82 Al 0.18 As superlattice buffer. However, the surface subsequently roughened, which may be explained by surface undulation.

New MBE buffer for micron- and quarter-micron-gateGaAs MESFETs

NASA Technical Reports Server (NTRS)

1988-01-01

A new buffer layer has been developed that eliminates backgating in GaAs MESFETs and substantially reduces short-channel effects in GaAs MESFETs with 0.27-micron-long gates. The new buffer is grown by molecular beam epitaxy (MBE) at a substrate temperature of 200 C using Ga and As sub 4 beam fluxes. The buffer is crystalline, highly resistive, optically inactive, and can be overgrown with high quality GaAs. GaAs MESFETs with a gate length of 0.27 microns that incorporate the new buffer show improved dc and RF properties in comparison with a similar MESFET with a thin undoped GaAs buffer. To demonstrate the backgating performance improvement afforded by the new buffer, MESFETs were fabricated using a number of different buffer layers and structures. A schematic cross section of the MESFET structure used in this study is shown. The measured gate length, gate width, and source-drain spacing of this device are 2,98, and 5.5 microns, respectively. An ohmic contact, isolated from the MESFET by mesa etching, served as the sidegate. The MESFETs were fabricated in MBE n-GaAs layers grown on the new buffer and also in MBE n-GaAs layers grown on buffer layers of undoped GaAs, AlGaAs, and GaAs/AlGaAs superlattices. All the buffer layers were grown by MBE and are 2 microns thick. The active layer is doped to approximately 2 x 10 to the 17th/cu cm with silicon and is 0.3 microns thick.

Mitigation of substrate defects in reflective reticles using sequential coating and annealing

DOEpatents

Mirkanimi, Paul B.

2002-01-01

A buffer-layer to minimize the size of defects on a reticle substrate prior to deposition of a reflective coating on the substrate. The buffer-layer is formed by either a multilayer deposited on the substrate or by a plurality of sequentially deposited and annealed coatings deposited on the substrate. The plurality of sequentially deposited and annealed coating may comprise multilayer and single layer coatings. The multilayer deposited and annealed buffer layer coatings may be of the same or different material than the reflecting coating thereafter deposited on the buffer-layer.

Group-III nitride based high electron mobility transistor (HEMT) with barrier/spacer layer

DOEpatents

Chavarkar, Prashant; Smorchkova, Ioulia P.; Keller, Stacia; Mishra, Umesh; Walukiewicz, Wladyslaw; Wu, Yifeng

2005-02-01

A Group III nitride based high electron mobility transistors (HEMT) is disclosed that provides improved high frequency performance. One embodiment of the HEMT comprises a GaN buffer layer, with an Al.sub.y Ga.sub.1-y N (y=1 or y 1) layer on the GaN buffer layer. An Al.sub.x Ga.sub.1-x N (0.ltoreq.x.ltoreq.0.5) barrier layer on to the Al.sub.y Ga.sub.1-y N layer, opposite the GaN buffer layer, Al.sub.y Ga.sub.1-y N layer having a higher Al concentration than that of the Al.sub.x Ga.sub.1-x N barrier layer. A preferred Al.sub.y Ga.sub.1-y N layer has y=1 or y.about.1 and a preferred Al.sub.x Ga.sub.1-x N barrier layer has 0.ltoreq.x.ltoreq.0.5. A 2DEG forms at the interface between the GaN buffer layer and the Al.sub.y Ga.sub.1-y N layer. Respective source, drain and gate contacts are formed on the Al.sub.x Ga.sub.1-x N barrier layer. The HEMT can also comprising a substrate adjacent to the buffer layer, opposite the Al.sub.y Ga.sub.1-y N layer and a nucleation layer between the Al.sub.x Ga.sub.1-x N buffer layer and the substrate.

Inverted bulk-heterojunction organic solar cells with the transfer-printed anodes and low-temperature-processed ultrathin buffer layers

NASA Astrophysics Data System (ADS)

Itoh, Eiji; Sakai, Shota; Fukuda, Katsutoshi

2018-03-01

We studied the effects of a hole buffer layer [molybdenum oxide (MoO3) and natural copper oxide layer] and a low-temperature-processed electron buffer layer on the performance of inverted bulk-heterojunction organic solar cells in a device consisting of indium-tin oxide (ITO)/poly(ethylene imine) (PEI)/titanium oxide nanosheet (TiO-NS)/poly(3-hexylthiopnehe) (P3HT):phenyl-C61-butyric acid methylester (PCBM)/oxide/anode (Ag or Cu). The insertion of ultrathin TiO-NS (˜1 nm) and oxide hole buffer layers improved the open circuit voltage V OC, fill factor, and rectification properties owing to the effective hole blocking and electron transport properties of ultrathin TiO-NS, and to the enhanced work function difference between TiO-NS and the oxide hole buffer layer. The insertion of the TiO-NS contributed to the reduction in the potential barrier at the ITO/PEI/TiO-NS/active layer interface for electrons, and the insertion of the oxide hole buffer layer contributed to the reduction in the potential barrier for holes. The marked increase in the capacitance under positive biasing in the capacitance-voltage characteristics revealed that the combination of TiO-NS and MoO3 buffer layers contributes to the selective transport of electrons and holes, and blocks counter carriers at the active layer/oxide interface. The natural oxide layer of the copper electrode also acts as a hole buffer layer owing to the increase in the work function of the Cu surface in the inverted cells. The performance of the cell with evaporated MoO3 and Cu layers that were transfer-printed to the active layer was almost comparable to that of the cell with MoO3 and Ag layers directly evaporated onto the active layer. We also demonstrated comparable device performance in the cell with all-printed MoO3 and low-temperature-processed silver nanoparticles as an anode.

Buffer layers on metal alloy substrates for superconducting tapes

DOEpatents

Jia, Quanxi; Foltyn, Stephen R.; Arendt, Paul N.; Groves, James R.

2004-06-29

An article including a substrate, a layer of an inert oxide material upon the surface of the substrate, a layer of an amorphous oxide or oxynitride material upon the inert oxide material layer, a layer of an oriented cubic oxide material having a rock-salt-like structure upon the amorphous oxide material layer, and a layer of a SrRuO.sub.3 buffer material upon the oriented cubic oxide material layer is provided together with additional layers such as a HTS top-layer of YBCO directly upon the layer of a SrRuO.sub.3 buffer material layer. With a HTS top-layer of YBCO upon at least one layer of the SrRuO.sub.3 buffer material in such an article, J.sub.c 's of up to 1.3.times.10.sup.6 A/cm.sup.2 have been demonstrated with projected IC's of over 200 Amperes across a sample 1 cm wide.

Chemical solution deposition method of fabricating highly aligned MgO templates

DOEpatents

Paranthaman, Mariappan Parans [Knoxville, TN; Sathyamurthy, Srivatsan [Knoxville, TN; Aytug, Tolga [Knoxville, TN; Arendt, Paul N [Los Alamos, NM; Stan, Liliana [Los Alamos, NM; Foltyn, Stephen R [Los Alamos, NM

2012-01-03

A superconducting article includes a substrate having an untextured metal surface; an untextured barrier layer of La.sub.2Zr.sub.2O.sub.7 or Gd.sub.2Zr.sub.2O.sub.7 supported by and in contact with the surface of the substrate; a biaxially textured buffer layer supported by the untextured barrier layer; and a biaxially textured superconducting layer supported by the biaxially textured buffer layer. Moreover, a method of forming a buffer layer on a metal substrate includes the steps of: providing a substrate having an untextured metal surface; coating the surface of the substrate with a barrier layer precursor; converting the precursor to an untextured barrier layer; and depositing a biaxially textured buffer layer above and supported by the untextured barrier layer.

Effect of hydrogen on the device performance and stability characteristics of amorphous InGaZnO thin-film transistors with a SiO2/SiNx/SiO2 buffer

NASA Astrophysics Data System (ADS)

Han, Ki-Lim; Ok, Kyung-Chul; Cho, Hyeon-Su; Oh, Saeroonter; Park, Jin-Seong

2017-08-01

We investigate the influence of the multi-layered buffer consisting of SiO2/SiNx/SiO2 on amorphous InGaZnO (a-IGZO) thin-film transistors (TFTs). The multi-layered buffer inhibits permeation of water from flexible plastic substrates and prevents degradation of overlying organic layers. The a-IGZO TFTs with a multi-layered buffer suffer less positive bias temperature stress instability compared to the device with a single SiO2 buffer layer after annealing at 250 °C. Hydrogen from the SiNx layer diffuses into the active layer and reduces electron trapping at loosely bound oxygen defects near the SiO2/a-IGZO interface. Quantitative analysis shows that a hydrogen density of 1.85 × 1021 cm-3 is beneficial to reliability. However, the multi-layered buffer device annealed at 350 °C resulted in conductive characteristics due to the excess carrier concentration from the higher hydrogen density of 2.12 × 1021 cm-3.

Final Report: Rational Design of Wide Band Gap Buffer Layers for High-Efficiency Thin-Film Photovoltaics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lordi, Vincenzo

The main objective of this project is to enable rational design of wide band gap buffer layer materials for CIGS thin-film PV by building understanding of the correlation of atomic-scale defects in the buffer layer and at the buffer/absorber interface with device electrical properties. Optimized wide band gap buffers are needed to reduce efficiency loss from parasitic absorption in the buffer. The approach uses first-principles materials simulations coupled with nanoscale analytical electron microscopy as well as device electrical characterization. Materials and devices are produced by an industrial partner in a manufacturing line to maximize relevance, with the goal of enablingmore » R&D of new buffer layer compositions or deposition processes to push device efficiencies above 21%. Cadmium sulfide (CdS) is the reference material for analysis, as the prototypical high-performing buffer material.« less

Buffer layers for high-Tc thin films on sapphire

NASA Technical Reports Server (NTRS)

Wu, X. D.; Foltyn, S. R.; Muenchausen, R. E.; Cooke, D. W.; Pique, A.; Kalokitis, D.; Pendrick, V.; Belohoubek, E.

1992-01-01

Buffer layers of various oxides including CeO2 and yttrium-stabilized zirconia (YSZ) have been deposited on R-plane sapphire. The orientation and crystallinity of the layers were optimized to promote epitaxial growth of YBa2Cu3O(7-delta) (YBCO) thin films. An ion beam channeling minimum yield of about 3 percent was obtained in the CeO2 layer on sapphire, indicating excellent crystallinity of the buffer layer. Among the buffer materials used, CeO2 was found to be the best one for YBCO thin films on R-plane sapphire. High Tc and Jc were obtained in YBCO thin films on sapphire with buffer layers. Surface resistances of the YBCO films were about 4 mOmega at 77 K and 25 GHz.

Non-polar a-plane ZnO films grown on r-Al2O3 substrates using GaN buffer layers

NASA Astrophysics Data System (ADS)

Xu, C. X.; Chen, W.; Pan, X. H.; Chen, S. S.; Ye, Z. Z.; Huang, J. Y.

2016-09-01

In this work, GaN buffer layer has been used to grow non-polar a-plane ZnO films by laser-assisted and plasma-assisted molecular beam epitaxy. The thickness of GaN buffer layer ranges from ∼3 to 12 nm. The GaN buffer thickness effect on the properties of a-plane ZnO thin films is carefully investigated. The results show that the surface morphology, crystal quality and optical properties of a-plane ZnO films are strongly correlated with the thickness of GaN buffer layer. It was found that with 6 nm GaN buffer layer, a-plane ZnO films display the best crystal quality with X-ray diffraction rocking curve full-width at half-maximum of only 161 arcsec for the (101) reflection.

Improving fatigue resistance of Pb(Zr,Ti)O3 thin films by using PbZrO3 buffer layers

NASA Astrophysics Data System (ADS)

Mensur Alkoy, Ebru; Uchiyama, Kiyoshi; Shiosaki, Tadashi; Alkoy, Sedat

2006-05-01

Ferroelectric Pb(Zr0.52Ti0.48)O3 (PZT) thin films with PbZrO3 (PZ) buffer layers were prepared on Pt(111)/Ti/SiO2/Si(100) substrates using a hybrid rf magnetron sputtering and sol-gel process. Texture of PZT films was found to depend on Pb content of PZ buffer layers. Buffered PZT films displayed comparable ferroelectric properties (2Pr=38-53 μC/cm2,2Ec=136-170 kV/cm) with unbuffered PZT. Asymmetric leakage current and fatigue behavior with superior fatigue resistance was observed in PZ buffered PZT compared to unbuffered films. PZ buffer layers were found to affect crystallization and texture of PZT, and act as a capacitive interface layer possibly blocking charge injection from electrodes.

Rare earth zirconium oxide buffer layers on metal substrates

DOEpatents

Williams, Robert K.; Paranthaman, Mariappan; Chirayil, Thomas G.; Lee, Dominic F.; Goyal, Amit; Feenstra, Roeland

2001-01-01

A laminate article comprises a substrate and a biaxially textured (RE.sub.x A.sub.(1-x)).sub.2 O.sub.2-(x/2) buffer layer over the substrate, wherein 0

Improvement in temperature dependence and dielectric tunability properties of PbZr0.52Ti0.48O3 thin films using Ba(Mg1/3Ta2/3)O3 buffer layer

NASA Astrophysics Data System (ADS)

Wu, Zhi; Zhou, Jing; Chen, Wen; Shen, Jie; Yang, Huimin; Zhang, Shisai; Liu, Yueli

2016-12-01

In this paper, Pb(Zr0.52Ti0.48)O3 (PZT) thin films were prepared via sol-gel method. The effects of Ba(Mg1/3Ta2/3)O3 (BMT) buffer layer on the temperature dependence and dielectric tunability properties of PZT thin films were studied. As the thickness of BMT buffer layer increases, the tan δ and tunability of PZT thin films decrease while tunability still maintains above 10%. This result shows that BMT buffer layer can improve the dielectric tunability properties of PZT thin films. Furthermore, the temperature coefficient of the dielectric constant decreases from 2333.4 to 906.9 ppm/°C with the thickness of BMT buffer layer increasing in the range from 25 to 205 °C, indicating that BMT buffer layer can improve the temperature stability of PZT thin films. Therefore, BMT buffer layer plays a critical role in improving temperature dependence and dielectric tunability properties of PbZr0.52Ti0.48O3 thin films.

Study of the effects of GaN buffer layer quality on the dc characteristics of AlGaN/GaN high electron mobility transistors

DOE PAGES

Ahn, Shihyun; Zhu, Weidi; Dong, Chen; ...

2015-04-21

Here we studied the effect of buffer layer quality on dc characteristics of AlGaN/GaN high electron mobility (HEMTs). AlGaN/GaN HEMT structures with 2 and 5 μm GaN buffer layers on sapphire substrates from two different vendors with the same Al concentration of AlGaN were used. The defect densities of HEMT structures with 2 and 5 μm GaN buffer layer were 7 × 10 9 and 5 × 10 8 cm ₋2, respectively, as measured by transmission electron microscopy. There was little difference in drain saturation current or in transfer characteristics in HEMTs on these two types of buffer. However, theremore » was no dispersion observed on the nonpassivated HEMTs with 5 μm GaN buffer layer for gate-lag pulsed measurement at 100 kHz, which was in sharp contrast to the 71% drain current reduction for the HEMT with 2 μm GaN buffer layer.« less

Reduced dislocation density in Ga xIn 1–xP compositionally graded buffer layers through engineered glide plane switch

DOE PAGES

Schulte, Kevin L.; France, Ryan M.; McMahon, William E.; ...

2016-11-17

In this work we develop control over dislocation glide dynamics in Ga xIn 1-xP compositionally graded buffer layers (CGBs) through control of CuPt ordering on the group-III sublattice. The ordered structure is metastable in the bulk, so any glissile dislocation that disrupts the ordered pattern will release stored energy, and experience an increased glide force. Here we show how this connection between atomic ordering and dislocation glide force can be exploited to control the threading dislocation density (TDD) in Ga xIn 1-xP CGBs. When ordered Ga xIn 1-xP is graded from the GaAs lattice constant to InP, the order parametermore » ..eta.. decreases as x decreases, and dislocation glide switches from one set of glide planes to the other. This glide plane switch (GPS) is accompanied by the nucleation of dislocations on the new glide plane, which typically leads to increased TDD. We develop control of the GPS position within a Ga xIn 1-xP CGB through manipulation of deposition temperature, surfactant concentration, and strain-grading rate. We demonstrate a two-stage Ga xIn 1-xP CGB from GaAs to InP with sufficiently low TDD for high performance devices, such as the 4-junction inverted metamorphic multi-junction solar cell, achieved through careful control the GPS position. Here, experimental results are analyzed within the context of a model that considers the force balance on dislocations on the two competing glide planes as a function of the degree of ordering.« less

Carboniferous high-pressure metamorphism of Ordovician protoliths in the Argentera Massif (Italy), Southern European Variscan belt

NASA Astrophysics Data System (ADS)

Rubatto, Daniela; Ferrando, Simona; Compagnoni, Roberto; Lombardo, Bruno

2010-04-01

The age of high-pressure metamorphism is crucial to identify a suitable tectonic model for the vast Variscan orogeny. Banded H P granulites from the Gesso-Stura Terrain in the Argentera Massif, Italy, have been recently described (Ferrando et al., 2008) relicts of high-pressure metamorphism in the western part of the Variscan orogen. Bulk rock chemistry of representative lithologies reveals intermediate silica contents and calc-alkaline affinity of the various cumulate layers. Enrichment in incompatible elements denotes a significant crustal component in line with intrusion during Ordovician rifting. Magmatic zircon cores from a Pl-rich layer yield scattered ages indicating a minimum protolith age of 486 ± 7 Ma. Carboniferous zircons (340.7 ± 4.2 and 336.3 ± 4.1 Ma) are found in a Pl-rich and a Pl-poor layer, respectively. Their zoning, chemical composition (low Th/U, flat HREE pattern and Ti-in-zircon temperature) and deformation indicate that they formed during the high-pressure event before decompression and mylonitisation. The proposed age for high-pressure metamorphism in the Argentera Massif proves that subduction preceded anatexis by less than 20 Ma. The new data allow a first-order comparison with the Bohemian Massif, which is located at the eastern termination of the Variscan orogen. Similarities in evolution at either end of the orogen support a Himalayan-type tectonic model for the entire European Variscides.

Buffer layers on metal alloy substrates for superconducting tapes

DOEpatents

Jia, Quanxi; Foltyn, Stephen R.; Arendt, Paul N.; Groves, James R.

2004-10-05

An article including a substrate, at least one intermediate layer upon the surface of the substrate, a layer of an oriented cubic oxide material having a rock-salt-like structure upon the at least one intermediate layer, and a layer of a SrRuO.sub.3 buffer material upon the oriented cubic oxide material layer is provided together with additional layers such as a HTS top-layer of YBCO directly upon the layer of a SrRuO.sub.3 buffer material layer. With a HTS top-layer of YBCO upon at least one layer of the SrRuO.sub.3 buffer material in such an article, J.sub.c 's of up to 1.3.times.10.sup.6 A/cm.sup.2 have been demonstrated with projected I.sub.c 's of over 200 Amperes across a sample 1 cm wide.

Lightweight, durable lead-acid batteries

DOEpatents

Lara-Curzio, Edgar [Lenoir City, TN; An, Ke [Knoxville, TX; Kiggans, Jr., James O.; Dudney, Nancy J [Knoxville, TN; Contescu, Cristian I [Knoxville, TN; Baker, Frederick S [Oak Ridge, TN; Armstrong, Beth L [Clinton, TN

2011-09-13

A lightweight, durable lead-acid battery is disclosed. Alternative electrode materials and configurations are used to reduce weight, to increase material utilization and to extend service life. The electrode can include a current collector having a buffer layer in contact with the current collector and an electrochemically active material in contact with the buffer layer. In one form, the buffer layer includes a carbide, and the current collector includes carbon fibers having the buffer layer. The buffer layer can include a carbide and/or a noble metal selected from of gold, silver, tantalum, platinum, palladium and rhodium. When the electrode is to be used in a lead-acid battery, the electrochemically active material is selected from metallic lead (for a negative electrode) or lead peroxide (for a positive electrode).

Lightweight, durable lead-acid batteries

DOEpatents

Lara-Curzio, Edgar; An, Ke; Kiggans, Jr., James O; Dudney, Nancy J; Contescu, Cristian I; Baker, Frederick S; Armstrong, Beth L

2013-05-21

A lightweight, durable lead-acid battery is disclosed. Alternative electrode materials and configurations are used to reduce weight, to increase material utilization and to extend service life. The electrode can include a current collector having a buffer layer in contact with the current collector and an electrochemically active material in contact with the buffer layer. In one form, the buffer layer includes a carbide, and the current collector includes carbon fibers having the buffer layer. The buffer layer can include a carbide and/or a noble metal selected from of gold, silver, tantalum, platinum, palladium and rhodium. When the electrode is to be used in a lead-acid battery, the electrochemically active material is selected from metallic lead (for a negative electrode) or lead peroxide (for a positive electrode).

Petrology, geochemistry and isotope data on a ultrahigh-pressure jadeite quartzite from Shuanghe, Dabie Mountains, East-central China

NASA Astrophysics Data System (ADS)

Liou, J. G.; Zhang, R. Y.; Jahn, Bor-ming

1997-08-01

In the Dabie ultrahigh-pressure terrane of east-central China, coesite-bearing jadeite quartzites occur locally as intercalated layers with marble and mafic eclogite. This rock assemblage is, in turn, enclosed within quartzofeldspathic gneisses. Metamorphic parageneses and kelyphitic textures reveal a multistage metamorphic evolution and complex exhumation history. The primary peak metamorphic assemblage consists of jadeite + garnet + coesite + rutile ± apatite. Minor coesite and coesite pseudomorphs occur as inclusions in jadeite and garnet. Three stages of retrograde assemblages are observed in the jadeite quartzites. Stage A is represented by the polymorphic transformation of coesite to quartz aggregates. Stage B is characterized by formation of coronas around jadeite porphyroblasts consisting of an inner layer of oligoclase + amphibole and an outer layer of albite ± aegirine—augite. The last stage (stage C) involved total replacement of jadeite and most garnets by taramitic amphibole + albite + aegirine-augite. Peak metamorphic P-T conditions were > 26 kbar at 660°C and are consistent with the estimates from the adjacent coesite-bearing eclogites. The jadeite quartzites display clockwise P-T path that matches those of the adjacent eclogites. Major and trace element data suggest that the protolith of the jadeite quartzite could have been an albitized siltstone enriched in Na and depleted in K and Ca. The highly negative present-day ɛNd value (-24.7) indicates a very old age for the protolith. Its late Archean model age (TDM) of 2.58 Ga is among the oldest so far identified for rocks from the Dabie UHPM terrane. Concordant field relations and petrogenetic considerations suggest that all mafic, politic, carbonate and gneissic rocks have experienced in-situ UHP metamorphism during Triassic continental collision between the Sino-Korean and Yangtze cratons.

Method of depositing buffer layers on biaxially textured metal substrates

DOEpatents

Beach, David B.; Morrell, Jonathan S.; Paranthaman, Mariappan; Chirayil, Thomas; Specht, Eliot D.; Goyal, Amit

2002-08-27

A laminate article comprises a substrate and a biaxially textured (RE.sup.1.sub.x RE.sup.2.sub.(1-x)).sub.2 O.sub.3 buffer layer over the substrate, wherein 0

Tunneling Injection and Exciton Diffusion of White Organic Light-Emitting Diodes with Composed Buffer Layers

NASA Astrophysics Data System (ADS)

Yang, Su-Hua; Wu, Jian-Ping; Huang, Tao-Liang; Chung, Bin-Fong

2018-02-01

Four configurations of buffer layers were inserted into the structure of a white organic light emitting diode, and their impacts on the hole tunneling-injection and exciton diffusion processes were investigated. The insertion of a single buffer layer of 4,4'-bis(carbazol-9-yl)biphenyl (CBP) resulted in a balanced carrier concentration and excellent color stability with insignificant chromaticity coordinate variations of Δ x < 0.023 and Δ y < 0.023. A device with a 2,9-Dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) buffer layer was beneficial for hole tunneling to the emission layer, resulting in a 1.45-fold increase in current density. The tunneling of holes and the diffusion of excitons were confirmed by the preparation of a dual buffer layer of CBP:tris-(phenylpyridine)-iridine (Ir(ppy)3)/BCP. A maximum current efficiency of 12.61 cd/A with a luminance of 13,850 cd/m2 was obtained at 8 V when a device with a dual-buffer layer of CBP:6 wt.% Ir(ppy)3/BCP was prepared.

Zircon geochronology of the Webb Canyon Gneiss and the Mount Owen Quartz Monzonite, Teton Range, Wyoming: Significance to dating late Archean metamorphism in the Wyoming craton

USGS Publications Warehouse

Zartman, R.E.; Reed, J.C.

1998-01-01

The Webb Canyon Gneiss is a strongly foliated and lineated orthogneiss intercalated with layered Archean gneisses in the northern part of the Teton Range in northwestern Wyoming. The Mount Owen Quartz Monzonite is a non-foliated or weakly flow foliated rock which forms a discordant pluton exposed in the central part of the range and that cuts the Webb Canyon Gneiss and the associated layered gneisses. U-Pb zircon geochronology reported here indicates that euhedral pink zircon grew in the Webb Canyon Gneiss at about 2680 Ma, probably during the peak of regional metamorphism and that the Mount Owen was emplaced at 2547??3 Ma. These dates provide the best constraints so far reported on the age of Late Archean regional metamorphism in the western part of the Wyoming craton.

Matching characteristics of different buffer layers with VO2 thin films

NASA Astrophysics Data System (ADS)

Yang, Kai; Zhang, Dongping; Liu, Yi; Guan, Tianrui; Qin, Xiaonan; Zhong, Aihua; Cai, Xingmin; Fan, Ping; Lv, Weizhong

2016-10-01

VO2 thin films were fabricated by reactive DC magnetron sputtering on different buffer layers of MgF2, Al2O3 and TiO2, respectively. The crystallinity and orientation relationship, thickness of VO2 thin films, atoms vibrational modes, optical and electrical property, surface morphology of films were characterized by X-ray diffraction, Raman scattering microscopy, step profiler, spectrophotometer, four-probe technique, and scanning electron microscopy, respectively. XRD results investigated that the films have preferential crystalline planes VO2 (011). The crystallinity of VO2 films grown on TiO2 buffer layers are superior to VO2 directly deposited on soda-lime glass. The Raman bands of the VO2 films correspond to an Ag symmetry mode of VO2 (M). The sample prepared on 100nm TiO2 buffer layer appears nanorods structure, and exhibits remarkable solar energy modulation ability as high as 5.82% in full spectrum and 23% in near infrared spectrum. Cross-sectional SEM image of the thin films samples indicate that MgF2 buffer layer has clear interface with VO2 layer. But there are serious interdiffusion phenomenons between Al2O3, TiO2 buffer layer with VO2 layer.

CHEMICAL SOLUTION DEPOSITION BASED OXIDE BUFFERS AND YBCO COATED CONDUCTORS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Paranthaman, Mariappan Parans

We have reviewed briefly the growth of buffer and high temperature superconducting oxide thin films using a chemical solution deposition (CSD) method. In the Rolling-Assisted Biaxially Textured Substrates (RABiTS) process, developed at Oak Ridge National Laboratory, utilizes the thermo mechanical processing to obtain the flexible, biaxially oriented copper, nickel or nickel-alloy substrates. Buffers and Rare Earth Barium Copper Oxide (REBCO) superconductors have been deposited epitaxially on the textured nickel alloy substrates. The starting substrate serves as a template for the REBCO layer, which has substantially fewer weak links. Buffer layers play a major role in fabricating the second generation REBCOmore » wire technology. The main purpose of the buffer layers is to provide a smooth, continuous and chemically inert surface for the growth of the REBCO film, while transferring the texture from the substrate to the superconductor layer. To achieve this, the buffer layers need to be epitaxial to the substrate, i.e. they have to nucleate and grow in the same bi-axial texture provided by the textured metal foil. The most commonly used RABiTS multi-layer architectures consist of a starting template of biaxially textured Ni-5 at.% W (Ni-W) substrate with a seed (first) layer of Yttrium Oxide (Y2O3), a barrier (second) layer of Yttria Stabilized Zirconia (YSZ), and a Cerium Oxide (CeO2) cap (third) layer. These three buffer layers are generally deposited using physical vapor deposition (PVD) techniques such as reactive sputtering. On top of the PVD template, REBCO film is then grown by a chemical solution deposition. This article reviews in detail about the list of oxide buffers and superconductor REBCO films grown epitaxially on single crystal and/or biaxially textured Ni-W substrates using a CSD method.« less

GaAs buffer layer technique for vertical nanowire growth on Si substrate

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xu, Xiaoqing, E-mail: steelxu@stanford.edu; Parizi, Kokab B.; Huo, Yijie

2014-02-24

Gold catalyzed vapor-liquid-solid method is widely applied to III–V nanowire (NW) growth on Si substrate. However, the easy oxidation of Si, possible Si contamination in the NWs, high defect density in the NWs, and high sensitivity of the NW morphology to growth conditions largely limit its controllability. In this work, we developed a buffer layer technique by introducing a GaAs thin film with predefined polarity as a template. It is found that samples grown on these buffer layers all have high vertical NW yields in general, due to the single-orientation of the buffer layers. Low temperature buffer with smoother surfacemore » leads to highest yield of vertical NWs, while high temperature (HT) buffer with better crystallinity results in perfect NW quality. The defect-free property we observed here is very promising for optoelectronic device applications based on GaAs NW. Moreover, the buffer layers can eliminate Si contamination by preventing Si-Au alloy formation and by increasing the thickness of the Si diffusion barrier, thus providing more flexibility to vertical NW growth. The buffer layer technique we demonstrated here could be easily extended to other III-V on Si system for electronic and photonic applications.« less

Nitrogen-Polar (000 1 ¯ ) GaN Grown on c-Plane Sapphire with a High-Temperature AlN Buffer.

PubMed

Song, Jie; Han, Jung

2017-03-02

We demonstrate growing nitrogen-polar (N-polar) GaN epilayer on c-plane sapphire using a thin AlN buffer layer by metalorganic chemical vapor deposition. We have studied the influence of the AlN buffer layer on the polarity, crystalline quality, and surface morphology of the GaN epilayer and found that the growth temperature of the AlN buffer layer played a critical role in the growth of the GaN epilayer. The low growth temperature of the AlN buffer results in gallium-polar GaN. Even a nitridation process has been conducted. High growth temperature for an AlN buffer layer is required to achieve pure N-polarity, high crystalline quality, and smooth surface morphology for a GaN epilayer.

MgO buffer layers on rolled nickel or copper as superconductor substrates

DOEpatents

Paranthaman, Mariappan; Goyal, Amit; Kroeger, Donald M.; List, III, Frederic A.

2001-01-01

Buffer layer architectures are epitaxially deposited on biaxially-textured rolled-Ni and/or Cu substrates for high current conductors, and more particularly buffer layer architectures such as MgO/Ag/Pt/Ni, MgO/Ag/Pd/Ni, MgO/Ag/Ni, MgO/Ag/Pd/Cu, MgO/Ag/Pt/Cu, and MgO/Ag/Cu. Techniques used to deposit these buffer layers include electron beam evaporation, thermal evaporation, rf magnetron sputtering, pulsed laser deposition, metal-organic chemical vapor deposition (MOCVD), combustion CVD, and spray pyrolysis.

Method for making MgO buffer layers on rolled nickel or copper as superconductor substrates

DOEpatents

Paranthaman, Mariappan; Goyal, Amit; Kroeger, Donald M.; List, III, Frederic A.

2002-01-01

Buffer layer architectures are epitaxially deposited on biaxially-textured rolled-Ni and/or Cu substrates for high current conductors, and more particularly buffer layer architectures such as MgO/Ag/Pt/Ni, MgO/Ag/Pd/Ni, MgO/Ag/Ni, MgO/Ag/Pd/Cu, MgO/Ag/Pt/Cu, and MgO/Ag/Cu. Techniques used to deposit these buffer layers include electron beam evaporation, thermal evaporation, rf magnetron sputtering, pulsed laser deposition, metal-organic chemical vapor deposition (MOCVD), combustion CVD, and spray pyrolysis.

Critical CuI buffer layer surface density for organic molecular crystal orientation change

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ahn, Kwangseok; Kim, Jong Beom; Lee, Dong Ryeol, E-mail: drlee@ssu.ac.kr

We have determined the critical surface density of the CuI buffer layer inserted to change the preferred orientation of copper phthalocyanine (CuPc) crystals grown on the buffer layer. X-ray reflectivity measurements were performed to obtain the density profiles of the buffer layers and out-of-plane and 2D grazing-incidence X-ray diffraction measurements were performed to determine the preferred orientations of the molecular crystals. Remarkably, it was found that the preferred orientation of the CuPc film is completely changed from edge-on (1 0 0) to face-on (1 1 −2) by a CuI buffer layer with a very low surface density, so low thatmore » a large proportion of the substrate surface is bare.« less

Contribution of ion beam analysis methods to the development of second generation high temperature superconducting wires

NASA Astrophysics Data System (ADS)

Usov, I. O.; Arendt, P. N.; Foltyn, S. R.; Stan, L.; DePaula, R. F.; Holesinger, T. G.

2010-06-01

One of the crucial steps in the second generation high temperature superconducting wire program was development of the buffer-layer architecture. The architecture designed at the Superconductivity Technology Center at Los Alamos National Laboratory consists of several oxide layers wherein each layer plays a specific role, namely: nucleation layer, diffusion barrier, biaxially textured template, and intermediate layer providing a suitable lattice match to the superconducting Y 1Ba 2Cu 3O 7 (YBCO) compound. This report demonstrates how a wide range of ion beam analysis techniques (SIMS, RBS, channeling, PIXE, PIGE, NRA and ERD) was employed for analysis of each buffer layer and the YBCO film. These results assisted in understanding of a variety of physical processes occurring during the buffer layer fabrication and helped to optimize the buffer-layer architecture as a whole.

Modified band alignment effect in ZnO/Cu2O heterojunction solar cells via Cs2O buffer insertion

NASA Astrophysics Data System (ADS)

Eom, Kiryung; Lee, Dongyoon; Kim, Seunghwan; Seo, Hyungtak

2018-02-01

The effects of a complex buffer layer of cesium oxide (Cs2O) on the photocurrent response in oxide heterojunction solar cells (HSCs) were investigated. A p-n junction oxide HSC was fabricated using p-type copper (I) oxide (Cu2O) and n-type zinc oxide (ZnO); the buffer layer was inserted between the Cu2O and fluorine-doped tin oxide (FTO). Ultraviolet-visible (UV-vis) and x-ray and ultraviolet photoelectron spectroscopy analyses were performed to characterize the electronic band structures of cells, both with and without this buffer layer. In conjunction with the measured band electronic structures, the significantly improved visible-range photocurrent spectra of the buffer-inserted HSC were analyzed in-depth. As a result, the 1 sun power conversion efficiency was increased by about three times by the insertion of buffer layer. The physicochemical origin of the photocurrent enhancement was mainly ascribed to the increased photocarrier density in the buffer layer and modified valence band offset to promote the effective hole transfer at the interface to FTO on the band-alignment model.

Intrinsic oxygen fugacity measurements on seven chondrites, a pallasite, and a tektite and the redox state of meteorite parent bodies

USGS Publications Warehouse

Brett, R.; Sato, M.

1984-01-01

Intrinsic oxygen-fugacity (fO2) measurements were made on five ordinary chondrites, a carbonaceous chondrite, an enstatite chondrite, a pallasite, and a tektite. Results are of the form of linear log fO2 - 1 T plots. Except for the enstatite chondrite, measured results agree well with calculated estimates by others. The tektite produced fO2 values well below the range measured for terrestrial and lunar rocks. The lowpressure atmospheric regime that is reported to follow large terrestrial explosions, coupled with a very high temperature, could produce glass with fO2 in the range measured. The meteorite Salta (pallasite) has low fO2 and lies close to Hvittis (E6). Unlike the other samples, results for Salta do not parallel the iron-wu??stite buffer, but are close to the fayalite-quartz-iron buffer in slope. Minor reduction by graphite appears to have taken place during metamorphism of ordinary chondrites. fO2 values of unequilibrated chondrites show large scatter during early heating suggesting that the constituent phases were exposed to a range of fO2 conditions. The samples equilibrated with respect to fO2 in relatively short time on heating. Equilibration with respect to fO2 in ordinary chondrites takes place between grades 3 and 4 of metamorphism. Application of P - T - fO2 relations in the system C-CO-CO2 indicates that the ordinary chondrites were metamorphosed at pressures of 3-20 bars, as it appears that they lay on the graphite surface. A steep positive thermal gradient in a meteorite parent body lying at the graphite surface will produce thin reduced exterior, an oxidized near-surface layer, and an interior that is increasingly reduced with depth; a shallow thermal gradient will produce the reverse. A body heated by accretion on the outside will have a reduced exterior and oxidized interior. Meteorites from the same parent body clearly are not required to have similar redox states. ?? 1984.

Current isolating epitaxial buffer layers for high voltage photodiode array

DOEpatents

Morse, Jeffrey D.; Cooper, Gregory A.

2002-01-01

An array of photodiodes in series on a common semi-insulating substrate has a non-conductive buffer layer between the photodiodes and the semi-insulating substrate. The buffer layer reduces current injection leakage between the photodiodes of the array and allows optical energy to be converted to high voltage electrical energy.

Semiconductor films on flexible iridium substrates

DOEpatents

Goyal, Amit

2005-03-29

A laminate semiconductor article includes a flexible substrate, an optional biaxially textured oxide buffer system on the flexible substrate, a biaxially textured Ir-based buffer layer on the substrate or the buffer system, and an epitaxial layer of a semiconductor. Ir can serve as a substrate with an epitaxial layer of a semiconductor thereon.

AlGaN/GaN High Electron Mobility Transistor Grown and Fabricated on ZrTi Metallic Alloy Buffer Layers

DOE PAGES

Ren, Fan; Pearton, Stephen J.; Ahn, Shihyun; ...

2017-09-26

AlGaN/GaN high electron mobility transistors (HEMTs) were demonstrated for structures grown on ZrTi metallic alloy buffer layers, which provided lattice matching of the in-plane lattice parameter (“a-parameter”) to hexagonal GaN. The quality of the GaN buffer layer and HEMT structure were confirmed with X-ray 2θ and rocking scans as well as cross-section transmission electron microscopy (TEM) images. The X-ray 2θ scans showed full widths at half maximum (FWHM) of 0.06°, 0.05° and 0.08° for ZrTi alloy, GaN buffer layer, and the entire HEMT structure, respectively. TEM of the lower section of the HEMT structure containing the GaN buffer layer andmore » the AlN/ZrTi/AlN stack on the Si substrate showed that it was important to grow AlN on the top of ZrTi prior to growing the GaN buffer layer. Finally, the estimated threading dislocation (TD) density in the GaN channel layer of the HEMT structure was in the 10 8 cm -2 range.« less

Long life hydrocarbon conversion catalyst and method of making

DOEpatents

Tonkovich, Anna Lee Y [Pasco, WA; Wang, Yong [Richland, WA; Gao, Yufei [Kennewick, WA

2002-11-12

The present invention includes a catalyst that has at least four layers, (1) porous support, (2) buffer layer, (3) interfacial layer, and optionally (4) catalyst layer. The buffer layer provides a transition of thermal expansion coefficient from the porous support to the interfacial layer thereby reducing thermal expansion stress as the catalyst is heated to high operating temperatures. The method of the present invention for making the at least three layer catalyst has the steps of (1) selecting a porous support, (2) solution depositing an interfacial layer thereon, and optionally (3) depositing a catalyst material onto the interfacial layer; wherein the improvement comprises (4) depositing a buffer layer between the porous support and the interfacial layer.

Enhanced adhesion for LIGA microfabrication by using a buffer layer

DOEpatents

Bajikar, Sateesh S.; De Carlo, Francesco; Song, Joshua J.

2004-01-27

The present invention is an improvement on the LIGA microfabrication process wherein a buffer layer is applied to the upper or working surface of a substrate prior to the placement of a resist onto the surface of the substrate. The buffer layer is made from an inert low-Z material (low atomic weight), a material that absorbs secondary X-rays emissions from the substrate that are generated from the substrate upon exposure to a primary X-rays source. Suitable materials for the buffer layer include polyamides and polyimide. The preferred polyimide is synthesized form pyromellitic anhydride and oxydianiline (PMDA-ODA).

Enhanced adhesion for LIGA microfabrication by using a buffer layer

DOEpatents

Bajikar, Sateesh S.; De Carlo, Francesco; Song, Joshua J.

2001-01-01

The present invention is an improvement on the LIGA microfabrication process wherein a buffer layer is applied to the upper or working surface of a substrate prior to the placement of a resist onto the surface of the substrate. The buffer layer is made from an inert low-Z material (low atomic weight), a material that absorbs secondary X-rays emissions from the substrate that are generated from the substrate upon exposure to a primary X-rays source. Suitable materials for the buffer layer include polyamides and polyimide. The preferred polyimide is synthesized form pyromellitic anhydride and oxydianiline (PMDA-ODA).

Structural and Optical Studies of ZnCdSe/ZnSe/ZnMgSSe Separate Confinement Heterostructures with Different Buffer Layers

NASA Astrophysics Data System (ADS)

Tu, Ru-Chin; Su, Yan-Kuin; Huang, Ying-Sheng; Chen, Giin-Sang; Chou, Shu-Tsun

1998-09-01

Detailed structural and optical studies of ZnCdSe/ZnSe/ZnMgSSe separate confinementheterostructures (SCH) grown on ZnSe, ZnSe/ZnSSe strained-layer superlattices (SLS),and GaAs buffer layers at the II VI/GaAs interface have been carried out by employingtransmission electron microscopy, variable temperature photoluminescence (PL), andcontactless electroreflectance (CER) measurements. A significant improvement onthe defect reduction and the optical quality has been observed by using either theZnSe/ZnSSe SLS or GaAs as the buffer layers when compared to that of the sample usingonly ZnSe as the buffer layer. However, the sample grown with the SLS buffer layersreveals a room temperature PL intensity higher than that of the sample grown witha GaAs buffer layer, which may still suffer from the great ionic differences betweenthe II V and III V atoms. Using 15 K CER spectra, we have also studied variousexcitonic transitions originating from strained Zn0.80Cd0.20Se/ZnSe single quantumwell in SCH with different buffer layers. An analysis of the CER spectra has ledto the identification of various excitonic transitions, mnH (L), between the mthconduction band state and the nth heavy (light)-hole band state. An excellentagreement between experiments and theoretical calculations based on the envelopefunction approximation model has been achieved.

Improved properties of barium strontium titanate thin films grown on copper foils by pulsed laser deposition using a self-buffered layer.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, S.; Ma, B.; Narayanan, M.

2012-01-01

Ba{sub 0.6}Sr{sub 0.4}TiO{sub 3} (BST) films were deposited by pulsed laser deposition on copper foils with low-temperature self-buffered layers. The deposition conditions included a low oxygen partial pressure and a temperature of 700 C to crystallize the films without the formation of secondary phases and substrate oxidation. The results from x-ray diffraction and scanning electron microscopy indicated that the microstructure of the BST films strongly depended on the growth temperature. The use of the self-buffered layer improved the dielectric properties of the deposited BST films. The leakage current density of the BST films on the copper foil was 4.4 xmore » 10{sup -9} A cm{sup -2} and 3.3 x 10{sup -6} A cm{sup -2} with and without the self-buffered layer, respectively. The ferroelectric hysteresis loop for the BST thin film with buffer layer was slim, in contrast to the distorted loop observed for the film without the buffer layer. The permittivity (7 0 0) and dielectric loss tangent (0.013) of the BST film on the copper foil with self-buffered layer at room temperature were comparable to those of the film on metal and single-crystal substrates.« less

Silicate-Oxide Equilibria in the Wilson Lake Terrane, Labrador - Evidence for a Pre- Metamorphic Oxidizing Event

NASA Astrophysics Data System (ADS)

Korhonen, F. J.; Stout, J. H.

2006-05-01

The presence of Fe3+ and Ti in silicates and their presumed equilibration with Fe2+-Fe3+-Ti oxide minerals has long been recognized as an important factor in metamorphic phase equilibria. The Red Wine Mountains massif is a granulite facies unit in the Wilson Lake terrane of central Labrador, where this equilibration is especially important for estimating both temperature and fO2 during peak metamorphism. Peak assemblages are sapphirine + quartz, and orthopyroxene + sillimanite + quartz. The coexisting oxides, which are largely responsible for the pronounced aeromagnetic high of the massif, consist of nearly pure magnetite and an exsolved titanohematite. Estimates of fO2 based on magnetite + integrated titanohematite compositions are slightly below that defined by the pure magnetite-hematite buffer. This assemblage is also responsible for the magnetic signature of metagabbro and metanorite dikes, a fact which challenges the conventional wisdom that the high Fe3+ content of the host paragneisses was inherited from a highly oxidized ferruginous shale. We suggest here that prior to granulite facies metamorphism, an oxidizing hydrothermal event either coeval or following the emplacement of mafic dikes into the paragneiss host was responsible for the highly oxidized nature of the massif as a whole. Subsequent metamorphism then produced the observed assemblages. This scenario is supported by recent U-Pb zircon and monazite ages of ca. 1626 ± 10 Ma, which indicate that both metagabbro dikes and host paragneiss were metamorphosed at the same time. Dike emplacement and the oxidizing event must have preceded 1626 Ma. The implications of this pre-metamorphic oxidizing event is that Fe3+ becomes an inherent and fixed component in the chemical system during metamorphism. Phase relationships, preliminary thermodynamic modeling, and geothermobarometric constraints indicate that peak temperatures are lower than those previously determined for Fe3+-absent systems. More appropriate modeling of these rocks would benefit from a sapphirine mixing model involving Fe3+.

Single quantum dot emission at telecom wavelengths from metamorphic InAs/InGaAs nanostructures grown on GaAs substrates

DOE Office of Scientific and Technical Information (OSTI.GOV)

Seravalli, L.; Trevisi, G.; Frigeri, P.

We report on the growth by molecular beam epitaxy and the study by atomic force microscopy and photoluminescence of low density metamorphic InAs/InGaAs quantum dots. subcritical InAs coverages allow to obtain 10{sup 8} cm{sup -2} dot density and metamorphic In{sub x}Ga{sub 1-x}As (x=0.15,0.30) confining layers result in emission wavelengths at 1.3 {mu}m. We discuss optimal growth parameters and demonstrate single quantum dot emission up to 1350 nm at low temperatures, by distinguishing the main exciton complexes in these nanostructures. Reported results indicate that metamorphic quantum dots could be valuable candidates as single photon sources for long wavelength telecom windows.

Infiltration-driven metamorphism, New England, USA: Regional CO2 fluxes and implications for Devonian climate and extinctions

NASA Astrophysics Data System (ADS)

Stewart, E. M.; Ague, Jay J.

2018-05-01

We undertake thermodynamic pseudosection modeling of metacarbonate rocks in the Wepawaug Schist, Connecticut, USA, and examine the implications for CO2 outgassing from collisional orogenic belts. Two broad types of pseudosections are calculated: (1) a fully closed-system model with no fluid infiltration and (2) a fluid-buffered model including an H2O-CO2 fluid of a fixed composition. This fluid-buffered model is used to approximate a system open to infiltration by a water-bearing fluid. In all cases the fully closed-system model fails to reproduce the observed major mineral zones, mineral compositions, reaction temperatures, and fluid compositions. The fluid-infiltrated models, on the other hand, successfully reproduce these observations when the XCO2 of the fluid is in the range ∼0.05 to ∼0.15. Fluid-infiltrated models predict significant progressive CO2 loss, peaking at ∼50% decarbonation at amphibolite facies. The closed-system models dramatically underestimate the degree of decarbonation, predicting only ∼15% CO2 loss at peak conditions, and, remarkably, <1% CO2 loss below ∼600 °C. We propagate the results of fluid-infiltrated pseudosections to determine an areal CO2 flux for the Wepawaug Schist. This yields ∼1012 mol CO2 km-2 Myr-1, consistent with multiple independent estimates of the metamorphic CO2 flux, and comparable in magnitude to fluxes from mid-ocean ridges and volcanic arcs. Extrapolating to the area of the Acadian orogenic belt, we suggest that metamorphic CO2 degassing is a plausible driver of global warming, sea level rise, and, perhaps, extinction in the mid- to late-Devonian.

The role of hydrogenated amorphous silicon oxide buffer layer on improving the performance of hydrogenated amorphous silicon germanium single-junction solar cells

NASA Astrophysics Data System (ADS)

Sritharathikhun, Jaran; Inthisang, Sorapong; Krajangsang, Taweewat; Krudtad, Patipan; Jaroensathainchok, Suttinan; Hongsingtong, Aswin; Limmanee, Amornrat; Sriprapha, Kobsak

2016-12-01

Hydrogenated amorphous silicon oxide (a-Si1-xOx:H) film was used as a buffer layer at the p-layer (μc-Si1-xOx:H)/i-layer (a-Si1-xGex:H) interface for a narrow band gap hydrogenated amorphous silicon germanium (a-Si1-xGex:H) single-junction solar cell. The a-Si1-xOx:H film was deposited by plasma enhanced chemical vapor deposition (PECVD) at 40 MHz in a same processing chamber as depositing the p-type layer. An optimization of the thickness of the a-Si1-xOx:H buffer layer and the CO2/SiH4 ratio was performed in the fabrication of the a-Si1-xGex:H single junction solar cells. By using the wide band gap a-Si1-xOx:H buffer layer with optimum thickness and CO2/SiH4 ratio, the solar cells showed an improvement in the open-circuit voltage (Voc), fill factor (FF), and short circuit current density (Jsc), compared with the solar cells fabricated using the conventional a-Si:H buffer layer. The experimental results indicated the excellent potential of the wide-gap a-Si1-xOx:H buffer layers for narrow band gap a-Si1-xGex:H single junction solar cells.

Early Cretaceous Ductile Deformation of Marbles from the Western Hills of Beijing, North China Craton

NASA Astrophysics Data System (ADS)

Feng, H.; Liu, J.

2017-12-01

During the Early Cretaceous tectonic lithosphere extension, the pre-mesozoic rocks from the Western Hills in the central part of the North China Craton suffered from weak metamorphism but intense shear deformation. The prominent features of the deformation structures are the coexisting layer-parallel shear zones and intrafolia folds, and the along-strike thickness variations of the marble layers from the highly sheared Mesoproterozoic Jing'eryu Formation. Platy marbles are well-developed in the thinner layers, while intrafolia folds are often observed in the thicker layers. Most folds are tight recumbent folds and their axial planes are parallel to the foliations and layerings of the marbles. The folds are A-type folds with hinges being always paralleling to the stretching lineations consistently oriented at 130°-310° directions throughout the entire area. SPO and microstructural analyses of the sheared marbles suggest that the thicker layers suffered from deformations homogeneously, while strain localization can be distinguished in the thinner layers. Calcite twin morphology and CPO analysis indicate that the deformation of marbles from both thinner and thicker layers happened at temperatures of 300 to 500°C. The above analysis suggests that marbles in the thicker layers experienced a progressive sequence of thermodynamic events: 1) regional metamorphism, 2) early ductile deformation dominated by relatively higher temperature conditions, during which all the mineral particles elongated and oriented limitedly and the calcite grains are deformed mainly by mechanical twinning, and 3) late superimposition of relatively lower temperature deformation and recrystallization, which superposed the early deformation, and made the calcites finely granulated, elongated and oriented by dynamical recrystallization along with other grains. Marbles from the thinner layers, however, experienced a similar, but different sequence of thermo-dynamic events, i.e. regional metamorphism, early ductile deformation and weak superimposition by subsequent deformation, which caused the development of the strain localization. It is also shown that the intensity of progressive superimposition deformation contributed to the thinning and thickening of the marble layers.

Low-Cd CIGS solar cells made with a hybrid CdS/Zn(O,S) buffer layer

DOE PAGES

Garris, Rebekah L.; Mansfield, Lorelle M.; Egaas, Brian; ...

2016-10-27

In Cu(In,Ga)Se2 (CIGS) solar cells, CdS and Zn(O,S) buffer layers were compared with a hybrid buffer layer consisting of thin CdS followed Zn(O,S). We explore the physics of this hybrid layer that combines the standard (Cd) approach with the alternative (Zn) approach in the pursuit to unlock further potential for CIGS technology. CdS buffer development has shown optimal interface properties, whereas Zn(O,S) buffer development has shown increased photocurrent. Although a totally Cd-free solar module is more marketable, the retention of a small amount of Cd can be beneficial to achieve optimum junction properties. As long as the amount of Cdmore » is reduced to less than 0.01% by weight, the presence of Cd does not violate the hazardous substance restrictions of the European Union (EU). We estimate the amount of Cd allowed in the EU for CIGS on both glass and stainless steel substrates, and we show that reducing Cd becomes increasingly important as substrate weights decrease. As a result, this hybrid buffer layer had reduced Cd content and a wider space charge region, while achieving equal or better solar cell performance than buffer layers of either CdS or Zn(O,S) alone.« less

The effect of the carbon nanotube buffer layer on the performance of a Li metal battery

NASA Astrophysics Data System (ADS)

Zhang, Ding; Zhou, Yi; Liu, Changhong; Fan, Shoushan

2016-05-01

Lithium (Li) metal is one of the most promising candidates as an anode for the next-generation energy storage systems because of its high specific capacity and lowest negative electrochemical potential. But the growth of Li dendrites limits the application of the Li metal battery. In this work, a type of modified Li metal battery with a carbon nanotube (CNT) buffer layer inserted between the separator and the Li metal electrode was reported. The electrochemical results show that the modified batteries have a much better rate capability and cycling performance than the conventional Li metal batteries. The mechanism study by electrochemical impedance spectroscopy reveals that the modified battery has a smaller charge transfer resistance and larger Li ion diffusion coefficient during the deposition process on the Li electrode than the conventional Li metal batteries. Symmetric battery tests show that the interfacial behavior of the Li metal electrode with the buffer layer is more stable than the naked Li metal electrode. The morphological characterization of the CNT buffer layer and Li metal lamina reveals that the CNT buffer layer has restrained the growth of Li dendrites. The CNT buffer layer has great potential to solve the safety problem of the Li metal battery.Lithium (Li) metal is one of the most promising candidates as an anode for the next-generation energy storage systems because of its high specific capacity and lowest negative electrochemical potential. But the growth of Li dendrites limits the application of the Li metal battery. In this work, a type of modified Li metal battery with a carbon nanotube (CNT) buffer layer inserted between the separator and the Li metal electrode was reported. The electrochemical results show that the modified batteries have a much better rate capability and cycling performance than the conventional Li metal batteries. The mechanism study by electrochemical impedance spectroscopy reveals that the modified battery has a smaller charge transfer resistance and larger Li ion diffusion coefficient during the deposition process on the Li electrode than the conventional Li metal batteries. Symmetric battery tests show that the interfacial behavior of the Li metal electrode with the buffer layer is more stable than the naked Li metal electrode. The morphological characterization of the CNT buffer layer and Li metal lamina reveals that the CNT buffer layer has restrained the growth of Li dendrites. The CNT buffer layer has great potential to solve the safety problem of the Li metal battery. Electronic supplementary information (ESI) available. See DOI: 10.1039/c6nr00465b

High dielectric constant and energy density induced by the tunable TiO2 interfacial buffer layer in PVDF nanocomposite contained with core-shell structured TiO2@BaTiO3 nanoparticles

NASA Astrophysics Data System (ADS)

Hu, Penghao; Jia, Zhuye; Shen, Zhonghui; Wang, Peng; Liu, Xiaoru

2018-05-01

To realize application in high-capacity capacitors and portable electric devices, large energy density is eagerly desired for polymer-based nanocomposite. The core-shell structured nanofillers with inorganic buffer layer are recently supposed to be promising in improving the dielectric property of polymer nanocomposite. In this work, core-shell structured TO@BT nanoparticles with crystalline TiO2 buffer layer coated on BaTiO3 nanoparticle were fabricated via solution method and heat treatment. The thickness of the TO buffer layer can be tailored by modulating the additive amount of the titanate coupling agent in preparation process, and the apparent dielectric properties of nanocomposite are much related to the thickness of the TO layer. The relatively thin TO layer prefer to generate high polarization to increase dielectric constant while the relatively thick TO layer would rather to homogenize field to maintain breakdown strength. Simulation of electric field distribution in the interfacial region reveals the improving effect of the TO buffer layer on the dielectric properties of nanocomposite which accords with the experimental results well. The optimized nanoparticle TO@BT-2 with a mean thickness of 3-5 nm buffer layer of TO is effective in increasing both the ε and Eb in the PVDF composite film. The maximal discharged energy density of 8.78 J/cm3 with high energy efficiency above 0.6 is obtained in TO@BT-2/PVDF nanocomposite with 2.5 vol% loading close to the breakdown strength of 380 kV/mm. The present study demonstrates the approach to optimize the structure of core-shell nanoparticles by modulating buffer layer and provides a new way to further enlarge energy density in polymer nanocomposite.

Cooptimization of Adhesion and Power Conversion Efficiency of Organic Solar Cells by Controlling Surface Energy of Buffer Layers.

PubMed

Lee, Inhwa; Noh, Jonghyeon; Lee, Jung-Yong; Kim, Taek-Soo

2017-10-25

Here, we demonstrate the cooptimization of the interfacial fracture energy and power conversion efficiency (PCE) of poly[N-9'-heptadecanyl-2,7-carbazole-alt-5,5-(4',7'-di-2-thienyl-2',1',3'-benzothiadiazole)] (PCDTBT)-based organic solar cells (OSCs) by surface treatments of the buffer layer. The investigated surface treatments of the buffer layer simultaneously changed the crack path and interfacial fracture energy of OSCs under mechanical stress and the work function of the buffer layer. To investigate the effects of surface treatments, the work of adhesion values were calculated and matched with the experimental results based on the Owens-Wendt model. Subsequently, we fabricated OSCs on surface-treated buffer layers. In particular, ZnO layers treated with poly[(9,9-bis(3'-(N,N-dimethylamino)propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)] (PFN) simultaneously satisfied the high mechanical reliability and PCE of OSCs by achieving high work of adhesion and optimized work function.

Laminate article

DOEpatents

Williams, Robert K.; Paranthaman, Mariappan; Chirayil, Thomas G.; Lee, Dominic F.; Goyal, Amit; Feenstra, Roeland

2002-01-01

A laminate article comprises a substrate and a biaxially textured (RE.sub.x A.sub.(1-x)).sub.2 O.sub.2-(x/2) buffer layer over the substrate, wherein 0

The effects of GaN nanocolumn arrays and thin SixNy buffer layers on the morphology of GaN layers grown by plasma-assisted molecular beam epitaxy on Si(111) substrates

NASA Astrophysics Data System (ADS)

Shubina, K. Yu; Pirogov, E. V.; Mizerov, A. M.; Nikitina, E. V.; Bouravleuv, A. D.

2018-03-01

The effects of GaN nanocolumn arrays and a thin SixNy layer, used as buffer layers, on the morphology of GaN epitaxial layers are investigated. Two types of samples with different buffer layers were synthesized by PA-MBE. The morphology of the samples was characterized by SEM. The crystalline quality of the samples was assessed by XRD. The possibility of synthesis of continuous crystalline GaN layers on Si(111) substrates without the addition of other materials such as aluminum nitride was demonstrated.

Redox buffered hydrofluoric acid etchant for the reduction of galvanic attack during release etching of MEMS devices having noble material films

DOEpatents

Hankins, Matthew G [Albuquerque, NM

2009-10-06

Etchant solutions comprising a redox buffer can be used during the release etch step to reduce damage to the structural layers of a MEMS device that has noble material films. A preferred redox buffer comprises a soluble thiophosphoric acid, ester, or salt that maintains the electrochemical potential of the etchant solution at a level that prevents oxidation of the structural material. Therefore, the redox buffer preferentially oxidizes in place of the structural material. The sacrificial redox buffer thereby protects the exposed structural layers while permitting the dissolution of sacrificial oxide layers during the release etch.

Method for producing chemical energy

DOEpatents

Jorgensen, Betty S.; Danen, Wayne C.

2004-09-21

Fluoroalkylsilane-coated metal particles having a central metal core, a buffer layer surrounding the core, and a fluoroalkylsilane layer attached to the buffer layer are prepared by combining a chemically reactive fluoroalkylsilane compound with an oxide coated metal particle having a hydroxylated surface. The resulting fluoroalkylsilane layer that coats the particles provides them with excellent resistance to aging. The particles can be blended with oxidant particles to form energetic powder that releases chemical energy when the buffer layer is physically disrupted so that the reductant metal core can react with the oxidant.

Energetic powder

DOEpatents

Jorgensen, Betty S.; Danen, Wayne C.

2003-12-23

Fluoroalkylsilane-coated metal particles. The particles have a central metal core, a buffer layer surrounding the core, and a fluoroalkylsilane layer attached to the buffer layer. The particles may be prepared by combining a chemically reactive fluoroalkylsilane compound with an oxide coated metal particle having a hydroxylated surface. The resulting fluoroalkylsilane layer that coats the particles provides them with excellent resistance to aging. The particles can be blended with oxidant particles to form energetic powder that releases chemical energy when the buffer layer is physically disrupted so that the reductant metal core can react with the oxidant.

The effect of the MgO buffer layer thickness on magnetic anisotropy in MgO/Fe/Cr/MgO buffer/MgO(001)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kozioł-Rachwał, Anna, E-mail: a.koziolrachwal@aist.go.jp; AGH University of Science and Technology, Faculty of Physics and Applied Computer Science, al. Mickiewicza 30, 30-059 Kraków; Nozaki, Takayuki

2016-08-28

The relationship between the magnetic properties and MgO buffer layer thickness d was studied in epitaxial MgO/Fe(t)/Cr/MgO(d) layers grown on MgO(001) substrate in which the Fe thickness t ranged from 0.4 nm to 1.1 nm. For 0.4 nm ≤ t ≤ 0.7 nm, a non-monotonic coercivity dependence on the MgO buffer thickness was shown by perpendicular magneto-optic Kerr effect magnetometry. For thicker Fe films, an increase in the buffer layer thickness resulted in a spin reorientation transition from perpendicular to the in-plane magnetization direction. Possible origins of these unusual behaviors were discussed in terms of the suppression of carbon contamination at the Fe surface and changes inmore » the magnetoelastic anisotropy in the system. These results illustrate a method to control magnetic anisotropy in MgO/Fe/Cr/MgO(d) via an appropriate choice of MgO buffer layer thickness d.« less

Effects of Terrestrial Buffer Zones on Amphibians on Golf Courses

PubMed Central

Puglis, Holly J.; Boone, Michelle D.

2012-01-01

A major cause of amphibian declines worldwide is habitat destruction or alteration. Public green spaces, such as golf courses and parks, could serve as safe havens to curb the effects of habitat loss if managed in ways to bolster local amphibian communities. We reared larval Blanchard's cricket frogs (Acris blanchardi) and green frogs (Rana clamitans) in golf course ponds with and without 1 m terrestrial buffer zones, and released marked cricket frog metamorphs at the golf course ponds they were reared in. Larval survival of both species was affected by the presence of a buffer zone, with increased survival for cricket frogs and decreased survival for green frogs when reared in ponds with buffer zones. No marked cricket frog juveniles were recovered at any golf course pond in the following year, suggesting that most animals died or migrated. In a separate study, we released cricket frogs in a terrestrial pen and allowed them to choose between mown and unmown grass. Cricket frogs had a greater probability of using unmown versus mown grass. Our results suggest that incorporating buffer zones around ponds can offer suitable habitat for some amphibian species and can improve the quality of the aquatic environment for some sensitive local amphibians. PMID:22761833

Laminate articles on biaxially textured metal substrates

DOEpatents

Beach, David B.; Morrell, Jonathan S.; Paranthaman, Mariappan; Chirayil, Thomas; Specht, Eliot D.; Goyal, Amit

2003-12-16

A laminate article comprises a substrate and a biaxially textured (RE.sup.1.sub.x RE.sup.2.sub.(1-x)).sub.2 O.sub.3 buffer layer over the substrate, wherein 0

Improved high temperature integration of Al{sub 2}O{sub 3} on MoS{sub 2} by using a metal oxide buffer layer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Son, Seokki; Choi, Moonseok; Kim, Dohyung

2015-01-12

We deposited a metal oxide buffer layer before atomic layer deposition (ALD) of Al{sub 2}O{sub 3} onto exfoliated molybdenum disulfide (MoS{sub 2}) in order to accomplish enhanced integration. We demonstrate that even at a high temperature, functionalization of MoS{sub 2} by means of a metal oxide buffer layer can effectively provide nucleation sites for ALD precursors, enabling much better surface coverage of Al{sub 2}O{sub 3}. It is shown that using a metal oxide buffer layer not only allows high temperature ALD process, resulting in highly improved quality of Al{sub 2}O{sub 3}/MoS{sub 2} interface, but also leaves MoS{sub 2} intact.

Method of depositing epitaxial layers on a substrate

DOEpatents

Goyal, Amit

2003-12-30

An epitaxial article and method for forming the same includes a substrate having a textured surface, and an electrochemically deposited substantially single orientation epitaxial layer disposed on and in contact with the textured surface. The epitaxial article can include an electromagnetically active layer and an epitaxial buffer layer. The electromagnetically active layer and epitaxial buffer layer can also be deposited electrochemically.

High quality Ge epilayer on Si (1 0 0) with an ultrathin Si1-x Ge x /Si buffer layer by RPCVD

NASA Astrophysics Data System (ADS)

Chen, Da; Guo, Qinglei; Zhang, Nan; Xu, Anli; Wang, Bei; Li, Ya; Wang, Gang

2017-07-01

The authors report a method to grow high quality strain-relaxed Ge epilayer on a combination of low temperature Ge seed layer and Si1-x Ge x /Si superlattice buffer layer by reduced pressure chemical vapor deposition system without any subsequent annealing treatment. Prior to the growth of high quality Ge epilayer, an ultrathin Si1-x Ge x /Si superlattice buffer layer with the thickness of 50 nm and a 460 nm Ge seed layer were deposited successively at low temperature. Then an 840 nm Ge epilayer was grown at high deposition rate with the surface root-mean-square roughness of 0.707 nm and threading dislocation density of 2.5  ×  106 cm-2, respectively. Detailed investigations of the influence of ultrathin low-temperature Si1-x Ge x /Si superlattice buffer layer on the quality of Ge epilayer were performed, which indicates that the crystalline quality of Ge epilayer can be significantly improved by enhancing the Ge concentration of Si1-x Ge x /Si superlattice buffer layer.

Conductive layer for biaxially oriented semiconductor film growth

DOEpatents

Findikoglu, Alp T.; Matias, Vladimir

2007-10-30

A conductive layer for biaxially oriented semiconductor film growth and a thin film semiconductor structure such as, for example, a photodetector, a photovoltaic cell, or a light emitting diode (LED) that includes a crystallographically oriented semiconducting film disposed on the conductive layer. The thin film semiconductor structure includes: a substrate; a first electrode deposited on the substrate; and a semiconducting layer epitaxially deposited on the first electrode. The first electrode includes a template layer deposited on the substrate and a buffer layer epitaxially deposited on the template layer. The template layer includes a first metal nitride that is electrically conductive and has a rock salt crystal structure, and the buffer layer includes a second metal nitride that is electrically conductive. The semiconducting layer is epitaxially deposited on the buffer layer. A method of making such a thin film semiconductor structure is also described.

The effect of the carbon nanotube buffer layer on the performance of a Li metal battery.

PubMed

Zhang, Ding; Zhou, Yi; Liu, Changhong; Fan, Shoushan

2016-06-07

Lithium (Li) metal is one of the most promising candidates as an anode for the next-generation energy storage systems because of its high specific capacity and lowest negative electrochemical potential. But the growth of Li dendrites limits the application of the Li metal battery. In this work, a type of modified Li metal battery with a carbon nanotube (CNT) buffer layer inserted between the separator and the Li metal electrode was reported. The electrochemical results show that the modified batteries have a much better rate capability and cycling performance than the conventional Li metal batteries. The mechanism study by electrochemical impedance spectroscopy reveals that the modified battery has a smaller charge transfer resistance and larger Li ion diffusion coefficient during the deposition process on the Li electrode than the conventional Li metal batteries. Symmetric battery tests show that the interfacial behavior of the Li metal electrode with the buffer layer is more stable than the naked Li metal electrode. The morphological characterization of the CNT buffer layer and Li metal lamina reveals that the CNT buffer layer has restrained the growth of Li dendrites. The CNT buffer layer has great potential to solve the safety problem of the Li metal battery.

Metamorphic P-T evolution of the Gotsu blueschists from the Suo metamorphic belt in SW Japan: Implications for tectonic correlation with the Heilongjiang Complex, NE China

NASA Astrophysics Data System (ADS)

Kabir, Md. Fazle; Takasu, Akira; Li, Weimin

2018-05-01

In the Gotsu area of the c. 200 Ma high-P/T Suo metamorphic belt in the Inner Zone of southwest Japan, blueschists occur as lenses or layers within pelitic schists. Prograde, peak, and retrograde stages are distinguished in the blueschists, and the prograde and the peak metamorphic conditions are determined using pseudosection modelling in the NCKFMASHO system. The prograde metamorphic stage is defined by inclusions in porphyroblastic epidote and glaucophane, such as phengite, chlorite, albite, epidote and glaucophane/winchite, and the estimated metamorphic conditions are <325 °C and < 4-5 kbar at the boundary between the glaucophane schist facies and the greenschist facies. The peak metamorphic stage is well-defined by the schistosity-forming minerals, i.e. epidote, glaucophanic amphibole, phengite, and chlorite, suggesting the glaucophane schist facies conditions of 475-500 °C and 14-16 kbar. Actinolite/magnesiohornblende, chlorite, and albite replacing the peak stage minerals suggest the retrograde metamorphism into the greenschist facies. The metamorphic facies series of the Suo belt is defined by pumpellyite-actinolite facies to epidote-blueschist facies, and it has a relatively lower-P/T compared with the c. 300 Ma Renge belt in the Inner Zone of southwest Japan, which is defined by a sequence of lawsonite-blueschist facies to glaucophane-eclogite facies. The P- {M}_{{H}_2O} pseudosection and water isopleth show that the rocks were dehydrated during the initial stage of the exhumation and remained in water-saturated conditions. Similarities of the detrital zircon and peak metamorphic ages of the blueschists from the Suo metamorphic belt in southwest Japan and the Heilongjiang Complex in northeast China suggest that both metamorphic belts were probably formed in the same Paleo-Pacific subduction system in the Late Triassic to Jurassic period.

Near single-crystalline, high-carrier-mobility silicon thin film on a polycrystalline/amorphous substrate

DOEpatents

Findikoglu, Alp T [Los Alamos, NM; Jia, Quanxi [Los Alamos, NM; Arendt, Paul N [Los Alamos, NM; Matias, Vladimir [Santa Fe, NM; Choi, Woong [Los Alamos, NM

2009-10-27

A template article including a base substrate including: (i) a base material selected from the group consisting of polycrystalline substrates and amorphous substrates, and (ii) at least one layer of a differing material upon the surface of the base material; and, a buffer material layer upon the base substrate, the buffer material layer characterized by: (a) low chemical reactivity with the base substrate, (b) stability at temperatures up to at least about 800.degree. C. under low vacuum conditions, and (c) a lattice crystal structure adapted for subsequent deposition of a semiconductor material; is provided, together with a semiconductor article including a base substrate including: (i) a base material selected from the group consisting of polycrystalline substrates and amorphous substrates, and (ii) at least one layer of a differing material upon the surface of the base material; and, a buffer material layer upon the base substrate, the buffer material layer characterized by: (a) low chemical reactivity with the base substrate, (b) stability at temperatures up to at least about 800.degree. C. under low vacuum conditions, and (c) a lattice crystal structure adapted for subsequent deposition of a semiconductor material, and, a top-layer of semiconductor material upon the buffer material layer.

Effect of organic buffer layer in the electrical properties of amorphous-indium gallium zinc oxide thin film transistor.

PubMed

Wang, Jian-Xun; Hyung, Gun Woo; Li, Zhao-Hui; Son, Sung-Yong; Kwon, Sang Jik; Kim, Young Kwan; Cho, Eou Sik

2012-07-01

In this research, we reported on the fabrication of top-contact amorphous-indium gallium zinc oxide (a-IGZO) thin-film transistors (TFTs) with an organic buffer layer between inorganic gate dielectric and active layer in order to improve the electrical properties of devices. By inserting an organic buffer layer, it was possible to make an affirmation of the improvements in the electrical characteristics of a-IGZO TFTs such as subthreshold slope (SS), on/off current ratio (I(ON/OFF)), off-state current, and saturation field-effect mobility (muFE). The a-IGZO TFTs with the cross-linked polyvinyl alcohol (c-PVA) buffer layer exhibited the pronounced improvements of the muFE (17.4 cm2/Vs), SS (0.9 V/decade), and I(ON/OFF) (8.9 x 10(6)).

Dependence of magnetic properties on different buffer layers of Mn3.5Ga thin films

NASA Astrophysics Data System (ADS)

Takahashi, Y.; Sato, K.; Shima, T.; Doi, M.

2018-05-01

D022-Mn3.5Ga thin films were prepared on MgO (100) single crystalline substrates with different buffer layer (Cr, Fe, Cr/Pt and Cr/Au) using an ultra-high-vacuum electron beam vapor deposition system. From XRD patterns, a fundamental (004) peak has clearly observed for all samples. The relatively low saturation magnetization (Ms) of 178 emu/cm3, high magnetic anisotropy (Ku) of 9.1 Merg/cm3 and low surface roughness (Ra) of 0.30 nm were obtained by D022-Mn3.5Ga film (20 nm) on Cr/Pt buffer layer at Ts = 300 °C, Ta = 400 °C (3h). These findings suggest that MnGa film on Cr/Pt buffer layer is a promising PMA layer for future spin electronics devices.

Y1Ba2Cu3O(6+delta) growth on thin Y-enhanced SiO2 buffer layers on silicon

NASA Technical Reports Server (NTRS)

Robin, T.; Mesarwi, A.; Wu, N. J.; Fan, W. C.; Espoir, L.; Ignatiev, A.; Sega, R.

1991-01-01

SiO2 buffer layers as thin as 2 nm have been developed for use in the growth of Y1Ba2Cu3O(6+delta) thin films on silicon substrates. The SiO2 layers are formed through Y enhancement of silicon oxidation, and are highly stoichiometric. Y1Ba2Cu3O(6+delta) film growth on silicon with thin buffer layers has shown c orientation and Tc0 = 78 K.

The effects of the porous buffer layer and doping with dysprosium on internal stresses in the GaInP:Dy/por-GaAs/GaAs(100) heterostructures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Seredin, P. V.; Gordienko, N. N.; Glotov, A. V.

2009-08-15

In structures with a porous buffer layer, residual internal stresses caused by a mismatch between the crystal-lattice parameters of the epitaxial GaInP alloy and the GaAs substrate are redistributed to the porous layer that acts as a buffer and is conducive to disappearance of internal stresses. Doping of the epitaxial layer with dysprosium exerts a similar effect on the internal stresses in the film-substrate structure.

Tetradymite layer assisted heteroepitaxial growth and applications

DOEpatents

Stoica, Vladimir A.; Endicott, Lynn; Clarke, Roy; Uher, Ctirad

2017-08-01

A multilayer stack including a substrate, an active layer, and a tetradymite buffer layer positioned between the substrate and the active layer is disclosed. A method for fabricating a multilayer stack including a substrate, a tetradymite buffer layer and an active layer is also disclosed. Use of such stacks may be in photovoltaics, solar cells, light emitting diodes, and night vision arrays, among other applications.

Chemical zoning and homogenization of Pasamonte-type pyroxene and their bearing on thermal metamorphism of a howardite parent body

NASA Technical Reports Server (NTRS)

Miyamoto, M.; Duke, M. B.; Mckay, D. S.

1985-01-01

The Mg-Fe zoning of pyroxenes in Pasamonte and Juvinas eucrites is examined in order to gain a better understanding of the metamorphism in the surface layer of a eucrite/howardite parent body. Three distinct types of Ca-Mg-Fe zoning of Pasamonte pyroxenes are identified. The wide compositional range of the zoned pyroxenes suggests that Pasamonte is less metamorphosed than previously believed. It is also found that a Pasamonte-type pyroxene may yield a Juvinas-type pyroxene by thermal metamorphism. Calculations imply that the homogenization of Juvinas pyroxenes may have occurred during later reheating events rather than during initial cooling.

Effect of ZnO buffer layer on phase transition properties of vanadium dioxide thin films

NASA Astrophysics Data System (ADS)

Zhu, Huiqun; Li, Lekang; Li, Chunbo

2016-03-01

VO2 thin films were prepared on ZnO buffer layers by DC magnetron sputtering at room temperature using vanadium target and post annealing at 400 °C. The ZnO buffer layers with different thickness deposited on glass substrates by magnetron sputtering have a high visible and near infrared optical transmittance. The electrical resistivity and the phase transition properties of the VO2/ZnO composite thin films in terms of temperature were investigated. The results showed that the resistivity variation of VO2 thin film with ZnO buffer layer deposited for 35 min was 16 KΩ-cm. The VO2/ZnO composite thin films exhibit a reversible semiconductor-metal phase transition at 48 °C.

Efficiency enhancement of polymer solar cells by applying poly(vinylpyrrolidone) as a cathode buffer layer via spin coating or self-assembly.

PubMed

Wang, Haitao; Zhang, Wenfeng; Xu, Chenhui; Bi, Xianghong; Chen, Boxue; Yang, Shangfeng

2013-01-01

A non-conjugated polymer poly(vinylpyrrolidone) (PVP) was applied as a new cathode buffer layer in P3HT:PCBM bulk heterojunction polymer solar cells (BHJ-PSCs), by means of either spin coating or self-assembly, resulting in significant efficiency enhancement. For the case of incorporation of PVP by spin coating, power conversion efficiency (PCE) of the ITO/PEDOT:PSS/P3HT:PCBM/PVP/Al BHJ-PSC device (3.90%) is enhanced by 29% under the optimum PVP spin-coating speed of 3000 rpm, which leads to the optimum thickness of PVP layer of ~3 nm. Such an efficiency enhancement is found to be primarily due to the increase of the short-circuit current (J(sc)) (31% enhancement), suggesting that the charge collection increases upon the incorporation of a PVP cathode buffer layer, which originates from the conjunct effects of the formation of a dipole layer between P3HT:PCBM active layer and Al electrodes, the chemical reactions of PVP molecules with Al atoms, and the increase of the roughness of the top Al film. Incorporation of PVP layer by doping PVP directly into the P3HT:PCBM active layer leads to an enhancement of PCE by 13% under the optimum PVP doping ratio of 3%, and this is interpreted by the migration of PVP molecules to the surface of the active layer via self-assembly, resulting in the formation of the PVP cathode buffer layer. While the formation of the PVP cathode buffer layer is fulfilled by both fabrication methods (spin coating and self-assembly), the dependence of the enhancement of the device performance on the thickness of the PVP cathode buffer layer formed by self-assembly or spin coating is different, because of the different aggregation microstructures of the PVP interlayer.

Integration of (208) oriented epitaxial Hf-doped Bi4Ti3O12 with (0002) GaN using SrTiO3/TiO2 buffer layer

NASA Astrophysics Data System (ADS)

Luo, W. B.; Zhu, J.; Li, Y. R.; Wang, X. P.; Zhang, Y.

2009-05-01

Hf-doped Bi4Ti3O12 (BTH) ferroelectric films with excellent electrical properties were epitaxially integrated with GaN semiconductor using (111) SrTiO3 (STO)/rutile (200) TiO2 as buffer layer. The STO/TiO2 buffer layer was deposited by laser molecular beam epitaxy. The structural characteristics of the buffer layer were in situ and ex situ characterized by reflective high energy electron diffraction, x-ray diffraction (XRD), and high resolution transmission microscopy. The overlaying SrRuO3 (SRO) and BTH films were then deposited by pulsed laser deposition. XRD spectra, including θ-2θ and Φ scans, show that the (208) BTH films were epitaxially grown on GaN, and the BTH films inherit the in-plane twin-domain of STO buffer layer. Electrical measurements demonstrate that the non-c axis BTH films possess a large remnant polarization (2Pr=45 μC/cm2), excellent fatigue endurance (10.2% degradation after 1.1×1010 switching cycles), and a low leakage current density (1.94×10-7 A/cm2 at an electric field of 200 kV/cm). These results reveal that the (208) BTH films with favorable electrical performance could be epitaxially grown on GaN template using STO/TiO2 buffer layer.

Electrical properties of n-type GaSb substrates and p-type GaSb buffer layers for InAs/InGaSb superlattice infrared detectors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mitchel, W. C., E-mail: William.Mitchel.1@us.af.mil; Haugan, H. J.; Mou, Shin

2015-09-15

Lightly doped n-type GaSb substrates with p-type GaSb buffer layers are the preferred templates for growth of InAs/InGaSb superlattices used in infrared detector applications because of relatively high infrared transmission and a close lattice match to the superlattices. We report here temperature dependent resistivity and Hall effect measurements of bare substrates and substrate-p-type buffer layer structures grown by molecular beam epitaxy. Multicarrier analysis of the resistivity and Hall coefficient data demonstrate that high temperature transport in the substrates is due to conduction in both the high mobility zone center Γ band and the low mobility off-center L band. High overallmore » mobility values indicate the absence of close compensation and that improved infrared and transport properties were achieved by a reduction in intrinsic acceptor concentration. Standard transport measurements of the undoped buffer layers show p-type conduction up to 300 K indicating electrical isolation of the buffer layer from the lightly n-type GaSb substrate. However, the highest temperature data indicate the early stages of the expected p to n type conversion which leads to apparent anomalously high carrier concentrations and lower than expected mobilities. Data at 77 K indicate very high quality buffer layers.« less

Improvement of transmission properties of visible pilot beam for polymer-coated silver hollow fibers with acrylic silicone resin as buffer layer for sturdy structure

NASA Astrophysics Data System (ADS)

Iwai, Katsumasa; Takaku, Hiroyuki; Miyagi, Mitsunobu; Shi, Yi-Wei; Zhu, Xiao-Song; Matsuura, Yuji

2017-02-01

Flexible hollow fibers with 530-μm-bore size were developed for infrared laser delivery. Sturdy hollow fibers were fabricated by liquid-phase coating techniques. A silica glass capillary is used as the substrate. Acrylic silicone resin is used as a buffer layer and the buffer layer is firstly coated on the inner surface of the capillary to protect the glass tube from chemical damages due to the following silver plating process. A silver layer was inner-plated by using the conventional silver mirror-plating technique. To improve adhesion of catalyst to the buffer layer, a surface conditioner has been introduced in the method of silver mirror-plating technique. We discuss improvement of transmission properties of sturdy polymer-coated silver hollow fibers for the Er:YAG laser and red pilot beam delivery.

Finding the lost open-circuit voltage in polymer solar cells by UV-ozone treatment of the nickel acetate anode buffer layer.

PubMed

Wang, Fuzhi; Sun, Gang; Li, Cong; Liu, Jiyan; Hu, Siqian; Zheng, Hua; Tan, Zhan'ao; Li, Yongfang

2014-06-25

Efficient polymer solar cells (PSCs) with enhanced open-circuit voltage (Voc) are fabricated by introducing solution-processed and UV-ozone (UVO)-treated nickel acetate (O-NiAc) as an anode buffer layer. According to X-ray photoelectron spectroscopy data, NiAc partially decomposed to NiOOH during the UVO treatment. NiOOH is a dipole species, which leads to an increase in the work function (as confirmed by ultraviolet photoemission spectroscopy), thus benefitting the formation of ohmic contact between the anode and photoactive layer and leading to increased Voc. In addition, the UVO treatment improves the wettability between the substrate and solvent of the active layer, which facilitates the formation of an upper photoactive layer with better morphology. Further, the O-NiAc layer can decrease the series resistance (Rs) and increase the parallel resistance (Rp) of the devices, inducing enhanced Voc in comparison with the as-prepared NiAc-buffered control devices without UVO treatment. For PSCs based on the P3HT:PCBM system, Voc increases from 0.50 to 0.60 V after the NiAc buffer layer undergoes UVO treatment. Similarly, in the P3HT:ICBA system, the Voc value of the device with a UVO-treated NiAc buffer layer increases from 0.78 to 0.88 V, showing an enhanced power conversion efficiency of 6.64%.

Evaluation of AlGaN/GaN high electron mobility transistors grown on ZrTi buffer layers with sapphire substrates

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ren, Fan; Pearton, Stephen J.; Ahn, Shihyun

Here, AlGaN/GaN high electron mobility transistors (HEMTs) have been grown on sapphire substrates, using ZrTi buffer layers to provide in-plane lattice-matching to hexagonal GaN. X-ray diffraction (XRD) as well as cross-section transmission electron microscopy (TEM) were used to assess the quality of the HEMT structure. The XRD 2θ scans showed full-width-at-half-maximum values of 0.16°, 0.07°, and 0.08° for ZrTi alloy, GaN buffer layer, and the entire HEMT structure, respectively. TEM studies of the GaN buffer layer and the AlN/ZrTi/AlN stack showed the importance of growing thin AlN buffer layers on the ZrTi layer prior to growth of the GaN buffermore » layer. The density of threading dislocations in the GaN channel layer of the HEMT structure was estimated to be in the 10 8 cm –2 range. The HEMT device exhibited a saturation drain current density of 820 mA/mm, and the channel of the fabricated HEMTs could be well modulated. A cutoff frequency (f T) of 8.9 GHz and a maximum frequency of oscillation (f max) of 17.3 GHz were achieved for HEMTs with gate dimensions of 1 × 200 μm.« less

Evaluation of AlGaN/GaN high electron mobility transistors grown on ZrTi buffer layers with sapphire substrates

DOE PAGES

Ren, Fan; Pearton, Stephen J.; Ahn, Shihyun; ...

2016-09-21

Here, AlGaN/GaN high electron mobility transistors (HEMTs) have been grown on sapphire substrates, using ZrTi buffer layers to provide in-plane lattice-matching to hexagonal GaN. X-ray diffraction (XRD) as well as cross-section transmission electron microscopy (TEM) were used to assess the quality of the HEMT structure. The XRD 2θ scans showed full-width-at-half-maximum values of 0.16°, 0.07°, and 0.08° for ZrTi alloy, GaN buffer layer, and the entire HEMT structure, respectively. TEM studies of the GaN buffer layer and the AlN/ZrTi/AlN stack showed the importance of growing thin AlN buffer layers on the ZrTi layer prior to growth of the GaN buffermore » layer. The density of threading dislocations in the GaN channel layer of the HEMT structure was estimated to be in the 10 8 cm –2 range. The HEMT device exhibited a saturation drain current density of 820 mA/mm, and the channel of the fabricated HEMTs could be well modulated. A cutoff frequency (f T) of 8.9 GHz and a maximum frequency of oscillation (f max) of 17.3 GHz were achieved for HEMTs with gate dimensions of 1 × 200 μm.« less

Effect of Homo-buffer Layers on the Properties of Sputtering Deposited Ga2O3 Films

NASA Astrophysics Data System (ADS)

Huang, Jian; Li, Bing; Ma, Yuncheng; Tang, Ke; Huang, Haofei; Hu, Yan; Zou, Tianyu; Wang, Linjun

2018-05-01

β- Ga2O3 films were grown by radio-frequency magnetron sputtering method. The influence of Ga2O3 buffer layers and annealing treatment on the structural, optical, morphological and electrical properties of Ga2O3 films was studied. The results revealed an improvement of crystalline quality and transmittance of annealed β- Ga2O3 films prepared with homo-buffer layers. Ga2O3 film UV photodetectors were fabricated with a new B and Ga co-doped ZnO films (BGZO)/Au interdigitated electrode. A good ohmic contact was formed between the film and the electrode. For the detector based on Ga2O3 films with buffer layers, a higher value of photo response and faster response times was obtained.

Optimization of the Energy Level Alignment between the Photoactive Layer and the Cathode Contact Utilizing Solution-Processed Hafnium Acetylacetonate as Buffer Layer for Efficient Polymer Solar Cells.

PubMed

Yu, Lu; Li, Qiuxiang; Shi, Zhenzhen; Liu, Hao; Wang, Yaping; Wang, Fuzhi; Zhang, Bing; Dai, Songyuan; Lin, Jun; Tan, Zhan'ao

2016-01-13

The insertion of an appropriate interfacial buffer layer between the photoactive layer and the contact electrodes makes a great impact on the performance of polymer solar cells (PSCs). Ideal interfacial buffer layers could minimize the interfacial traps and the interfacial barriers caused by the incompatibility between the photoactive layer and the electrodes. In this work, we utilized solution-processed hafnium(IV) acetylacetonate (Hf(acac)4) as an effective cathode buffer layer (CBL) in PSCs to optimize the energy level alignment between the photoactive layer and the cathode contact, with the short-circuit current density (Jsc), open-circuit voltage (Voc), and fill factor (FF) all simultaneously improved with Hf(acac)4 CBL, leading to enhanced power conversion efficiencies (PCEs). Ultraviolet photoemission spectroscopy (UPS) and scanning Kelvin probe microscopy (SKPM) were performed to confirm that the interfacial dipoles were formed with the same orientation direction as the built-in potential between the photoactive layer and Hf(acac)4 CBL, benefiting the exciton separation and electron transport/extraction. In addition, the optical characteristics and surface morphology of the Hf(acac)4 CBL were also investigated.

Photovoltaic devices comprising zinc stannate buffer layer and method for making

DOEpatents

Wu, Xuanzhi; Sheldon, Peter; Coutts, Timothy J.

2001-01-01

A photovoltaic device has a buffer layer zinc stannate Zn.sub.2 SnO.sub.4 disposed between the semiconductor junction structure and the transparent conducting oxide (TCO) layer to prevent formation of localized junctions with the TCO through a thin window semiconductor layer, to prevent shunting through etched grain boundaries of semiconductors, and to relieve stresses and improve adhesion between these layers.

Metamorphic InAsSb/AlInAsSb Heterostructures for Optoelectronic Applications

DTIC Science & Technology

2013-03-20

respectively. VC 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4796181] The development of highly efficient light emitting devi...C12 elastic constants 14 and the standard relationship between strains in perpendicular directions (e ¼ 2 c12c11 ejj) 15 we deter- mined the residual...line as the cloud of reflexes from the pseudomorphic part of the compositionally graded buffers. To obtain information about electroluminescence char

19.5%-Efficient CuIn1-xGaxSe2 Photovoltaic Cells Using A Cd-Zn-S Buffer Layer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bhattacharya. R. N.

2008-01-01

CuIn1-xGaxSe2 (CIGS) solar cell junctions prepared by chemical-bath-deposited (CBD) Zn1-xCdxS (CdZnS), ZnS, and CdS buffer layers are discussed. A 19.52%-efficient, CIGS-based, thin-film photovoltaic device has been fabricated using a single-layer CBD CdZnS buffer layer. The mechanism that creates extensive hydroxide and oxide impurities in CBD-ZnS and CBD-CdZnS thin films (compared to CBD-CdS thin film) is presented.

Electron-Selective TiO 2 Contact for Cu(In,Ga)Se 2 Solar Cells

DOE PAGES

Hsu, Weitse; Sutter-Fella, Carolin M.; Hettick, Mark; ...

2015-11-03

The non-toxic and wide bandgap material TiO 2 is explored as an n-type buffer layer on p-type Cu(In,Ga)Se 2 (CIGS) absorber layer for thin film solar cells. The amorphous TiO 2 thin film deposited by atomic layer deposition process at low temperatures shows conformal coverage on the CIGS absorber layer. Solar cells from non-vacuum deposited CIGS absorbers with TiO 2 buffer layer result in a high short-circuit current density of 38.9 mA/cm 2 as compared to 36.9 mA/cm 2 measured in the reference cell with CdS buffer layer, without compromising open-circuit voltage. The significant photocurrent gain, mainly in the UVmore » part of the spectrum, can be attributed to the low parasitic absorption loss in the ultrathin TiO 2 layer (~10 nm) with a larger bandgap of 3.4 eV compared to 2.4 eV of the traditionally used CdS. Overall the solar cell conversion efficiency was improved from 9.5% to 9.9% by substituting the CdS by TiO 2 on an active cell area of 10.5 mm2. In conclusion, optimized TiO 2/CIGS solar cells show excellent long-term stability. The results imply that TiO 2 is a promising buffer layer material for CIGS solar cells, avoiding the toxic CdS buffer layer with added performance advantage.« less

Effect of annealing on magnetoresistance and microstructure of multilayered CoFe/Cu systems with different buffer layer

NASA Astrophysics Data System (ADS)

Bannikova, N. S.; Milyaev, M. A.; Naumova, L. I.; Proglyado, V. V.; Krinitsina, T. P.; Chernyshova, T. A.; Ustinov, V. V.

2015-02-01

The effects of annealing on the structure, magnetic hysteresis, and magnetoresistance of [Co90Fe10(15 Å)/Cu(23 Å)] n superlattices with Cr and Co90Fe10 buffer layers of different thicknesses have been studied. The optimum temperature and time of annealing that increase the magnetoresistance were shown to depend on the buffer layer thickness. The coefficients of effective interlayer diffusion due to the annealing have been determined.

The roles of buffer layer thickness on the properties of the ZnO epitaxial films

NASA Astrophysics Data System (ADS)

Tang, Kun; Huang, Shimin; Gu, Shulin; Zhu, Shunming; Ye, Jiandong; Xu, Zhonghua; Zheng, Youdou

2016-12-01

In this article, the authors have investigated the optimization of the buffer thickness for obtaining high-quality ZnO epi-films on sapphire substrates. The growth mechanism of the buffers with different thickness has been clearly revealed, including the initial nucleation and vertical growth, the subsequent lateral growth with small grain coalescence, and the final vertical growth along the existing larger grains. Overall, the quality of the buffer improves with increasing thickness except the deformed surface morphology. However, by a full-scale evaluation of the properties for the epi-layers, the quality of the epi-film is briefly determined by the surface morphology of the buffer, rather than the structural, optical, or electrical properties of it. The best quality epi-layer has been grown on the buffer with a smooth surface and well-coalescent grains. Meanwhile, due to the huge lattice mismatch between sapphire and ZnO, dislocations are inevitably formed during the growth of buffers. More importantly, as the film grows thicker, the dislocations may attracting other smaller dislocations and defects to reduce the total line energy and thus result in the formation of V-shape defects, which are connected with the bottom of the threading dislocations in the buffers. The V-defects appear as deep and large hexagonal pits from top view and they may act as electron traps which would affect the free carrier concentration of the epi-layers.

Chemically Deposited CdS Buffer/Kesterite Cu2ZnSnS4 Solar Cells: Relationship between CdS Thickness and Device Performance.

PubMed

Hong, Chang Woo; Shin, Seung Wook; Suryawanshi, Mahesh P; Gang, Myeng Gil; Heo, Jaeyeong; Kim, Jin Hyeok

2017-10-25

Earth-abundant, copper-zinc-tin-sulfide (CZTS), kesterite, is an attractive absorber material for thin-film solar cells (TFSCs). However, the open-circuit voltage deficit (V oc -deficit) resulting from a high recombination rate at the buffer/absorber interface is one of the major challenges that must be overcome to improve the performance of kesterite-based TFSCs. In this paper, we demonstrate the relationship between device parameters and performances for chemically deposited CdS buffer/CZTS-based heterojunction TFSCs as a function of buffer layer thickness, which could change the CdS/CZTS interface conditions such as conduction band or valence band offsets, to gain deeper insight and understanding about the V oc -deficit behavior from a high recombination rate at the CdS buffer/kesterite interface. Experimental results show that device parameters and performances are strongly dependent on the CdS buffer thickness. We postulate two meaningful consequences: (i) Device parameters were improved up to a CdS buffer thickness of 70 nm, whereas they deteriorated at a thicker CdS buffer layer. The V oc -deficit in the solar cells improved up to a CdS buffer thickness of 92 nm and then deteriorated at a thicker CdS buffer layer. (ii) The minimum values of the device parameters were obtained at 70 nm CdS thickness in the CZTS TFSCs. Finally, the highest conversion efficiency of 8.77% (V oc : 494 mV, J sc : 34.54 mA/cm 2 , and FF: 51%) is obtained by applying a 70 nm thick CdS buffer to the Cu 2 ZnSn(S,Se) 4 absorber layer.

Pressure-temperature evolution of Neoproterozoic metamorphism in the Welayati Formation (Kabul Block), Afghanistan

NASA Astrophysics Data System (ADS)

Collett, Stephen; Faryad, Shah Wali

2015-11-01

The Welayati Formation, consisting of alternating layers of mica-schist and quartzite with lenses of amphibolite, unconformably overlies the Neoarchean Sherdarwaza Formation of the Kabul Block that underwent Paleoproterozoic granulite-facies and Neoproterozoic amphibolite-facies metamorphic events. To analyze metamorphic history of the Welayati Formation and its relations to the underlying Sherdarwaza Formation, petrographic study and pressure-temperature (P-T) pseudosection modeling were applied to staurolite- and kyanite-bearing mica-schists, which crop out to the south of Kabul City. Prograde metamorphism, identified by inclusion trails and chemical zonation in garnet from the micaschists indicates that the rocks underwent burial from around 6.2 kbar at 525 °C to maximum pressure conditions of around 9.5 kbar at temperatures of around 650 °C. Decompression from peak pressures under isothermal or moderate heating conditions are indicated by formation of biotite and plagioclase porphyroblasts which cross-cut and overgrow the dominant foliation. The lack of sillimanite and/or andalusite suggests that cooling and further decompression occurred in the kyanite stability field. The results of this study indicate a single amphibolite-facies metamorphism that based on P-T conditions and age dating correlates well with the Neoproterozoic metamorphism in the underlying Sherdarwaza Formation. The rocks lack any paragenetic evidence for a preceding granulite-facies overprint or subsequent Paleozoic metamorphism. Owing to the position of the Kabul Block, within the India-Eurasia collision zone, partial replacement of the amphibolite-facies minerals in the micaschist could, in addition to retrogression of the Neoproterozoic metamorphism, relate to deformation associated with the Alpine orogeny.

Benzocyclobutene (BCB) Polymer as Amphibious Buffer Layer for Graphene Field-Effect Transistor.

PubMed

Wu, Yun; Zou, Jianjun; Huo, Shuai; Lu, Haiyan; Kong, Yuecan; Chen, Tangshen; Wu, Wei; Xu, Jingxia

2015-08-01

Owing to the scattering and trapping effects, the interfaces of dielectric/graphene or substrate/graphene can tailor the performance of field-effect transistor (FET). In this letter, the polymer of benzocyclobutene (BCB) was used as an amphibious buffer layer and located at between the layers of substrate and graphene and between the layers of dielectric and graphene. Interestingly, with the help of nonpolar and hydrophobic BCB buffer layer, the large-scale top-gated, chemical vapor deposited (CVD) graphene transistors was prepared on Si/SiO2 substrate, its cutoff frequency (fT) and the maximum cutoff frequency (fmax) of the graphene field-effect transistor (GFET) can be reached at 12 GHz and 11 GHz, respectively.

An over 18%-efficiency completely buffer-free Cu(In,Ga)Se2 solar cell

NASA Astrophysics Data System (ADS)

Ishizuka, Shogo; Nishinaga, Jiro; Koida, Takashi; Shibata, Hajime

2018-07-01

In this letter, an independently certified photovoltaic efficiency of 18.4% demonstrated from a completely buffer-layer-free Cu(In,Ga)Se2 (CIGS) solar cell is reported. A Si-doped CIGS thin film was used as the photoabsorber layer and a conductive B-doped ZnO (BZO) front electrode layer was directly deposited on the CIGS layer. Metastable acceptor activation by heat-light soaking treatment was performed to maximize the efficiency. The results presented here are expected to serve as a benchmark for simplified-structure CIGS devices as well as a reference for discussions on the role of buffer layers used in conventional CIGS solar cells.

Domain matched epitaxial growth of (111) Ba{sub 0.5}Sr{sub 0.5}TiO{sub 3} thin films on (0001) Al{sub 2}O{sub 3} with ZnO buffer layer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Krishnaprasad, P. S., E-mail: pskrishnaprasu@gmail.com, E-mail: mkj@cusat.ac.in; Jayaraj, M. K., E-mail: pskrishnaprasu@gmail.com, E-mail: mkj@cusat.ac.in; Antony, Aldrin

2015-03-28

Epitaxial (111) Ba{sub 0.5}Sr{sub 0.5}TiO{sub 3} (BST) thin films have been grown by pulsed laser deposition on (0001) Al{sub 2}O{sub 3} substrate with ZnO as buffer layer. The x-ray ω-2θ, Φ-scan and reciprocal space mapping indicate epitaxial nature of BST thin films. The domain matched epitaxial growth of BST thin films over ZnO buffer layer was confirmed using Fourier filtered high resolution transmission electron microscope images of the film-buffer interface. The incorporation of ZnO buffer layer effectively suppressed the lattice mismatch and promoted domain matched epitaxial growth of BST thin films. Coplanar inter digital capacitors fabricated on epitaxial (111) BSTmore » thin films show significantly improved tunable performance over polycrystalline thin films.« less

Cu(In,Ga)Se2 solar cells with In2S3 buffer layer deposited by thermal evaporation

NASA Astrophysics Data System (ADS)

Kim, SeongYeon; Rana, Tanka R.; Kim, JunHo; Yun, JaeHo

2017-12-01

We report on physical vapor deposition of indium sulfide (In2S3) buffer layers and its application to Cu(In,Ga)Se2 (CIGSe) thin film solar cell. The Indium sulfide buffer layers were evaporated onto CIGSe at various substrate temperatures from room temperature (RT) to 350 °C. The effect of deposition temperature of buffer layers on the solar cell device performance were investigated by analyzing temperature dependent current-voltage ( J- V- T), external quantum efficiency (EQE) and Raman spectroscopy. The fabricated device showed the highest power conversion efficiency of 6.56% at substrate temperature of 250 °C, which is due to the decreased interface recombination. However, the roll-over in J- V curves was observed for solar cell device having buffer deposited at substrate temperature larger than 250 °C. From the measurement results, the interface defect and roll-over related degradation were found to have limitation on the performance of solar cell device.

Sulfide and Oxide Heterostructures For the SrTiO3 Thin Film Growth on Si and Their Structural and Interfacial Stabilities

NASA Astrophysics Data System (ADS)

Yoo, Young‑Zo; Song, Jeong‑Hwan; Konishi, Yoshinori; Kawasaki, Masashi; Koinuma, Hideomi; Chikyow, Toyohiro

2006-03-01

Epitaxial SrTiO3 (STO) thin films with high electrical properties were grown on Si using ZnS single- and SrS/MnS hetero-buffer layers. STO films on both ZnS-buffered and SrS/MnS-buffered Si showed two growth orientations, (100) and (110). The temperature dependence of the growth orientation for STO films was different for the ZnS single-buffer layer in comparison with the SrS/MnS heterobuffer layers. (100) growth of STO films on SrS/MnS-buffered Si became dominant at high temperatures about 700 °C, while (100) growth of STO films on ZnS-buffered Si became dominant at a relatively low growth temperature of 550 °C. STO(100) films on ZnS-buffered and SrS/MnS-buffered Si showed lattice and domain matches for epitaxial relationships with [001]ZnS\\parallel[011]STO and SrS[001]\\parallel[011]STO, respectively via 45° in-plane rotation of STO films relative to both ZnS and SrS layers. The ZnS buffer layer contained many stacking faults because of the mismatch between ZnS and Si, however, those defects were terminated at the ZnS/STO interface. In contrast, the MnS buffer was very stable against stacking defect formation. Transmission electron microscopy measurements revealed the presence of a disordered region at the ZnS/Si and MnS/Si interfaces. Auger electron spectroscopy and transmission electron microscopy results showed that a good MnS/Si interface at the initial growth stage degraded to a SiS2-x-rich phase during MnS deposition and again into a SiO2-x-rich phase during STO deposition at the high growth temperature of 700 °C. It was also observed that STO on SrS/MnS-buffered Si showed a markedly high dielectric constant compared with that of STO on ZnS-buffered Si.

Carbon doped GaN buffer layer using propane for high electron mobility transistor applications: Growth and device results

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, X.; Nilsson, D.; Danielsson, Ö.

2015-12-28

The creation of a semi insulating (SI) buffer layer in AlGaN/GaN High Electron Mobility Transistor (HEMT) devices is crucial for preventing a current path beneath the two-dimensional electron gas (2DEG). In this investigation, we evaluate the use of a gaseous carbon gas precursor, propane, for creating a SI GaN buffer layer in a HEMT structure. The carbon doped profile, using propane gas, is a two stepped profile with a high carbon doping (1.5 × 10{sup 18 }cm{sup −3}) epitaxial layer closest to the substrate and a lower doped layer (3 × 10{sup 16 }cm{sup −3}) closest to the 2DEG channel. Secondary Ion Mass Spectrometry measurement showsmore » a uniform incorporation versus depth, and no memory effect from carbon doping can be seen. The high carbon doping (1.5 × 10{sup 18 }cm{sup −3}) does not influence the surface morphology, and a roughness root-mean-square value of 0.43 nm is obtained from Atomic Force Microscopy. High resolution X-ray diffraction measurements show very sharp peaks and no structural degradation can be seen related to the heavy carbon doped layer. HEMTs are fabricated and show an extremely low drain induced barrier lowering value of 0.1 mV/V, demonstrating an excellent buffer isolation. The carbon doped GaN buffer layer using propane gas is compared to samples using carbon from the trimethylgallium molecule, showing equally low leakage currents, demonstrating the capability of growing highly resistive buffer layers using a gaseous carbon source.« less

Polyethylenimine Interfacial Layers in Inverted Organic Photovoltaic Devices: Effects of Ethoxylation and Molecular Weight on Efficiency and Temporal Stability.

PubMed

Courtright, Brett A E; Jenekhe, Samson A

2015-12-02

We report a comparative study of polyethylenimine (PEI) and ethoxylated-polyethylenimine (PEIE) cathode buffer layers in high performance inverted organic photovoltaic devices. The work function of the indium-tin oxide (ITO)/zinc oxide (ZnO) cathode was reduced substantially (Δφ = 0.73-1.09 eV) as the molecular weight of PEI was varied from 800 g mol(-1) to 750 000 g mol(-1) compared with the observed much smaller reduction when using a PEIE thin film (Δφ = 0.56 eV). The reference inverted polymer solar cells based on the small band gap polymer PBDTT-FTTE (ITO/ZnO/PBDTT-FTTE:PC70BM/MoO3/Ag), without a cathode buffer layer, had an average power conversion efficiency (PCE) of 6.06 ± 0.22%. Incorporation of a PEIE cathode buffer layer in the same PBDTT-FTTE:PC70BM blend devices gave an enhanced performance with a PCE of 7.37 ± 0.53%. In contrast, an even greater photovoltaic efficiency with a PCE of 8.22 ± 0.10% was obtained in similar PBDTT-FTTE:PC70BM blend solar cells containing a PEI cathode buffer layer. The temporal stability of the inverted polymer solar cells was found to increase with increasing molecular weight of the cathode buffer layer. The results show that PEI is superior to PEIE as a cathode buffer layer in high performance organic photovoltaic devices and that the highest molecular weight PEI interlayer provides the highest temporal stability.

Ultra-high current density thin-film Si diode

DOEpatents

Wang; Qi

2008-04-22

A combination of a thin-film .mu.c-Si and a-Si:H containing diode structure characterized by an ultra-high current density that exceeds 1000 A/cm.sup.2, comprising: a substrate; a bottom metal layer disposed on the substrate; an n-layer of .mu.c-Si deposited the bottom metal layer; an i-layer of .mu.c-Si deposited on the n-layer; a buffer layer of a-Si:H deposited on the i-layer, a p-layer of .mu.c-Si deposited on the buffer layer; and a top metal layer deposited on the p-layer.

Structural characteristics of a non-polar ZnS layer on a ZnO buffer layer formed on a sapphire substrate by mist chemical vapor deposition

NASA Astrophysics Data System (ADS)

Okita, Koshi; Inaba, Katsuhiko; Yatabe, Zenji; Nakamura, Yusui

2018-06-01

ZnS is attractive as a material for low-cost light-emitting diodes. In this study, a non-polar ZnS layer was epitaxially grown on a sapphire substrate by inserting a ZnO buffer layer between ZnS and sapphire. The ZnS and ZnO layers were grown by a mist chemical vapor deposition system with a simple setup operated under atmospheric pressure. The sample was characterized by high-resolution X-ray diffraction measurements including 2θ/ω scans, rocking curves, and reciprocal space mapping. The results showed that an m-plane wurtzite ZnS layer grew epitaxially on an m-plane wurtzite ZnO buffer layer formed on the m-plane sapphire substrate to provide a ZnS/ZnO/sapphire structure.

Properties of unrelaxed InAs{sub 1-X}Sb{sub X} alloys grown on compositionally graded buffers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Belenky, G.; Donetsky, D.; Kipshidze, G.

Unrelaxed InAs{sub 1-x}Sb{sub x} layers with lattice constants up to 2.1% larger than that of GaSb substrates were grown by molecular beam epitaxy on GaInSb and AlGaInSb compositionally graded buffer layers. The topmost section of the buffers was unrelaxed but strained. The in-plane lattice constant of the top buffer layer was grown to be equal to the lattice constant of unrelaxed and unstrained InAs{sub 1-x}Sb{sub x} with given X. The InAs{sub 0.56}Sb{sub 0.44} layers demonstrate photoluminescence peak at 9.4 {mu}m at 150 K. The minority carrier lifetime measured at 77 K for InAs{sub 0.8}Sb{sub 0.2} was {tau} = 250 ns.

Neoarchean high-pressure metamorphism from the northern margin of the Palghat-Cauvery Suture Zone, southern India: Petrology and zircon SHRIMP geochronology

NASA Astrophysics Data System (ADS)

Saitoh, Yohsuke; Tsunogae, Toshiaki; Santosh, M.; Chetty, T. R. K.; Horie, Kenji

2011-08-01

We report the metamorphic pressure-temperature ( P- T) history of mafic granulites from two localities in southern India, one from Kanja Malai in the northern margin and the other from Perundurai in the central domain of the Palghat-Cauvery Suture Zone (PCSZ). The PCSZ is described in recent models as the trace of the suture along which crustal blocks were amalgamated within the Gondwana supercontinent during Late Neoproterozoic-Cambrian. The mafic granulite from Kanja Malai yields P- T conditions of 750-800 °C and 8-12 kbar reflecting the partially retrograded conditions following a peak high-pressure (HP) metamorphic event. The common Grt + Cpx + Qtz assemblage in these rocks and lack of decompression texture suggest that peak metamorphism was probably buffered by Grt + Cpx + Opx + Pl + Qtz assemblage, following which the rocks were exhumed through a gradual P- T decrease. The mafic granulite from Perundurai (Grt + Cpx + Pl) contains Opx + Pl symplectite commonly occurring between garnet and clinopyroxene, suggesting the progress of reaction: Grt + Cpx + Qtz → Opx + Pl, with the Grt + Cpx + Qtz representing the peak metamorphic assemblage. The reaction microstructures and calculated P- T conditions suggest that the mafic granulites from Perundurai underwent peak HP metamorphism at P > 12 kbar and T = 800-900 °C and subsequent isothermal decompression along a clockwise P- T path, in contrast to the P- T path inferred for Kanja Malai. The contrasting P- T paths obtained from the two localities suggest that whereas Perundurai is a part of the metamorphic orogen developed within the PCSZ during Gondwana assembly, the high-pressure granulites of Kanja Malai belong to a different orogenic regime. In order to evaluate this aspect further, we analyzed zircons in a charnockite and garnet-bearing quartzo-feldspathic gneiss associated with the HP granulites from Kanja Malai which yielded mean 207Pb/ 206Pb magmatic protolith emplacement ages of 2536.1 ± 1.4 Ma and 2532.4 ± 3.7 Ma, and peak metamorphic ages of 2477.6 ± 1.8 Ma and 2483.9 ± 2.5 Ma, respectively. These results closely compare with the available magmatic (2530-2540 Ma) and metamorphic (2470-2480 Ma) ages reported from charnockites in the Salem Block at the southern fringe of the Archean Dharwar craton, immediately north of the PCSZ. The Neoarchean/Paleoproterozoic ages obtained from Kanja Malai correlate with the tectonic history at the margin of the Archean craton. Although no age data are available for the Perundurai mafic granulite, the close correspondence of their P- T data and exhumation path with those reported for Late Neoproterozoic-Cambrian HP-UHT metamorphism within the PCSZ suggest that these rocks form part of the Gondwana-forming orogen.

Dependence of Magnetic Properties of Co/Pt Multilayers on Deposition Temperature of Pt Buffer Layers

NASA Astrophysics Data System (ADS)

Shiomi, Shigeru; Nishimura, Tomotaka; Kobayashi, Tadashi; Masuda, Morio

1993-04-01

A 15-nm-thick Pt buffer layer was deposited on a glass slide at temperature Ts(Ptbuf) ranging from 30 to 300°C by e-gun evaporation. Following the cooling in vacuum to ambient temperature, Co and Pt layers have been alternately deposited on it. Very large perpendicular anisotropy and coercivity have been obtained at Ts(Ptbuf) higher than 200°C. The (111) preferred orientation of the Co/Pt multilayer as well as the Pt buffer layer became more pronounced with elevating Ts(Ptbuf), to which the enhancement of perpendicular anisotropy with elevating Ts(Ptbuf) might be ascribable.

Cathode buffer composed of fullerene-ethylenediamine adduct for an organic solar cell

NASA Astrophysics Data System (ADS)

Kimoto, Yoshinori; Akiyama, Tsuyoshi; Fujita, Katsuhiko

2017-02-01

We developed a fullerene-ethylenediamine adduct (C60P-DC) for a cathode buffer material in organic bulk heterojunction solar cells, which enhance the open-circuit voltage (V oc). The evaporative spray deposition using ultra dilute solution (ESDUS) technique was employed to deposit the buffer layer onto the organic active layer to avoid damage during the deposition. By the insertion of a C60P-DC buffer layer, V oc and power conversion efficiency (PCE) were increased from 0.41 to 0.57 V and from 1.65 to 2.10%, respectively. The electron-only device with the C60P-DC buffer showed a much lower current level than that without the buffer, indicating that the V oc increase is caused not by vacuum level shift but by hole blocking. The curve fitting of current density-voltage (J-V) characteristics to the equivalent circuit with a single diode indicated that the decrease in reversed saturation current by hole blocking increased caused the V oc.

Enhancing Hole Mobility in III-V Semiconductors

DTIC Science & Technology

2012-05-21

acteristics of the digital superlattice (n¼1,0, andþ 1) that was used in the metamorphic buffer. The GaSb channel peak gets buried in the n¼ 0...materials have been used for a variety of analog and high frequency applications driven by the high electron mobilities in III-V materials. On the other...hand, the hole mobility in III-V materials has always lagged compared to group-IV semiconductors such as germanium. In this paper, we explore the use

ALD Al2O3 passivation of Lg = 100 nm metamorphic InAlAs/InGaAs HEMTs with Si-doped Schottky layers on GaAs substrates

NASA Astrophysics Data System (ADS)

Sun, Bing; Chang, Hudong; Wang, Shengkai; Niu, Jiebin; Liu, Honggang

2017-12-01

In0.52Al0.48As/In0.7Ga0.3As metamorphic high-electron-mobility transistors (mHEMTs) on GaAs substrates have been demonstrated. The devices feature an epitaxial structure with Si-doped InP/In0.52Al0.48As Schottky layers, together with an atomic layer deposition (ALD) Al2O3 passivation process. In comparison to the GaAs mHEMTs with plasma enhanced chemical vapor deposition (PECVD) SiN passivation, the devices with ALD Al2O3 passivation exhibit more than one order of magnitude lower gate leakage current (Jg) and much lower contact resistance (RC) and specific contact resistivity (ρC). 100-nm gate length (Lg) In0.52Al0.48As/In0.7Ga0.3As mHEMTs with Si-doped InP/In0.52Al0.48As Schottky layers and ALD Al2O3 passivation exhibit excellent DC and RF characteristics, such as a maximum oscillation frequency (fmax) of 388.2 GHz.

Simultaneous enhancement of photovoltage and charge transfer in Cu{sub 2}O-based photocathode using buffer and protective layers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Changli; Delaunay, Jean-Jacques, E-mail: jean@mech.t.u-tokyo.ac.jp; Hisatomi, Takashi

2016-07-18

Coating n-type buffer and protective layers on Cu{sub 2}O may be an effective means to improve the photoelectrochemical (PEC) water-splitting performance of Cu{sub 2}O-based photocathodes. In this letter, the functions of the buffer layer and protective layer on Cu{sub 2}O are examined. It is found that a Ga{sub 2}O{sub 3} buffer layer can form a buried junction with Cu{sub 2}O, which inhibits Cu{sub 2}O self-reduction as well as increases the photovoltage through a small conduction band offset between the two semiconductors. The introduction of a TiO{sub 2} thin protective layer not only improves the stability of the photocathode but alsomore » enhances the electron transfer from the photocathode surface into the electrolyte, thus resulting in an increase in photocurrent at positive potentials. These results show that the selection of overlayers with appropriate conduction band positions provides an effective strategy for obtaining a high photovoltage and high photocurrent in PEC systems.« less

Simple O2 plasma-processed V2O5 as an anode buffer layer for high-performance polymer solar cells.

PubMed

Bao, Xichang; Zhu, Qianqian; Wang, Ting; Guo, Jing; Yang, Chunpeng; Yu, Donghong; Wang, Ning; Chen, Weichao; Yang, Renqiang

2015-04-15

A simple O2 plasma processing method for preparation of a vanadium oxide (V2O5) anode buffer layer on indium tin oxide (ITO)-coated glass for polymer solar cells (PSCs) is reported. The V2O5 layer with high transmittance and good electrical and interfacial properties was prepared by spin coating a vanadium(V) triisopropoxide oxide alcohol solution on ITO and then O2 plasma treatment for 10 min [V2O5 (O2 plasma)]. PSCs based on P3HT:PC61BM and PBDTTT-C:PC71BM using V2O5 (O2 plasma) as an anode buffer layer show high power conversion efficiencies (PCEs) of 4.47 and 7.54%, respectively, under the illumination of AM 1.5G (100 mW/cm(2)). Compared to that of the control device with PBDTTT-C:PC71BM as the active layer and PSS (PCE of 6.52%) and thermally annealed V2O5 (PCE of 6.27%) as the anode buffer layer, the PCE was improved by 15.6 and 20.2%, respectively, after the introduction of a V2O5 (O2 plasma) anode buffer layer. The improved PCE is ascribed to the greatly improved fill factor and enhanced short-circuit current density of the devices, which benefited from the change in the work function of V2O5, a surface with many dangling bonds for better interfacial contact, and the excellent charge transport property of the V2O5 (O2 plasma) layer. The results indicate that an O2 plasma-processed V2O5 film is an efficient and economical anode buffer layer for high-performance PSCs. It also provides an attractive choice for low-cost fabrication of organic electronics.

Effect of Alloy 625 Buffer Layer on Hardfacing of Modified 9Cr-1Mo Steel Using Nickel Base Hardfacing Alloy

NASA Astrophysics Data System (ADS)

Chakraborty, Gopa; Das, C. R.; Albert, S. K.; Bhaduri, A. K.; Murugesan, S.; Dasgupta, Arup

2016-04-01

Dashpot piston, made up of modified 9Cr-1Mo steel, is a part of diverse safety rod used for safe shutdown of a nuclear reactor. This component was hardfaced using nickel base AWS ER NiCr-B alloy and extensive cracking was experienced during direct deposition of this alloy on dashpot piston. Cracking reduced considerably and the component was successfully hardfaced by application of Inconel 625 as buffer layer prior to hardface deposition. Hence, a separate study was undertaken to investigate the role of buffer layer in reducing the cracking and on the microstructure of the hardfaced deposit. Results indicate that in the direct deposition of hardfacing alloy on modified 9Cr-1Mo steel, both heat-affected zone (HAZ) formed and the deposit layer are hard making the thickness of the hard layer formed equal to combined thickness of both HAZ and deposit. This hard layer is unable to absorb thermal stresses resulting in the cracking of the deposit. By providing a buffer layer of Alloy 625 followed by a post-weld heat treatment, HAZ formed in the modified 9Cr-1Mo steel is effectively tempered, and HAZ formed during the subsequent deposition of the hardfacing alloy over the Alloy 625 buffer layer is almost completely confined to Alloy 625, which does not harden. This reduces the cracking susceptibility of the deposit. Further, unlike in the case of direct deposition on modified 9Cr-1Mo steel, dilution of the deposit by Ni-base buffer layer does not alter the hardness of the deposit and desired hardness on the deposit surface could be achieved even with lower thickness of the deposit. This gives an option for reducing the recommended thickness of the deposit, which can also reduce the risk of cracking.

Interplay between strain, quantum confinement, and ferromagnetism in strained ferromagnetic semiconductor (In,Fe)As thin films

NASA Astrophysics Data System (ADS)

Sasaki, Daisuke; Anh, Le Duc; Nam Hai, Pham; Tanaka, Masaaki

2014-04-01

We systematically investigated the influence of strain on the electronic structure and ferromagnetism of (In,Fe)As thin films. It is found that while the shift of the critical point energies of compressive-strained (In,Fe)As layers grown on (In1-y,Gay)As (y = 0.05, 0.1) buffer layers can be explained by the hydrostatic deformation effect (HDE) alone, those of tensile-strained (In,Fe)As layers grown on (Ga1-z,Alz)Sb (z = 0, 0.5, 1) buffer layers can be explained by the combination of HDE and the quantum confinement effect (QCE). The Curie temperature TC of the (In,Fe)As layers strongly depends on the strain, and shows a maximum for the (In,Fe)As layer grown on a GaSb buffer layer. The strain dependence of TC can be explained by the s-d exchange mechanism taking into account HDE and QCE.

Fluorinated tin oxide back contact for AZTSSe photovoltaic devices

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gershon, Talia S.; Gunawan, Oki; Haight, Richard A.

A photovoltaic device includes a substrate, a back contact comprising a stable low-work function material, a photovoltaic absorber material layer comprising Ag.sub.2ZnSn(S,Se).sub.4 (AZTSSe) on a side of the back contact opposite the substrate, wherein the back contact forms an Ohmic contact with the photovoltaic absorber material layer, a buffer layer or Schottky contact layer on a side of the absorber layer opposite the back contact, and a top electrode on a side of the buffer layer opposite the absorber layer.

Effect of dopent on the structural and optical properties of ZnS thin film as a buffer layer in solar cell application

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vashistha, Indu B., E-mail: indu-139@yahoo.com; Sharma, S. K.; Sharma, Mahesh C.

2015-08-28

In order to find the suitable alternative of toxic CdS buffer layer, deposition of pure ZnS and doped with Al by chemical bath deposition method have been reported. Further as grown pure and doped thin films have been annealed at 150°C. The structural and surface morphological properties have been characterized by X-Ray diffraction (XRD) and Atomic Force Microscope (AFM).The XRD analysis shows that annealed thin film has been polycrystalline in nature with sphalerite cubic crystal structure and AFM images indicate increment in grain size as well as growth of crystals after annealing. Optical measurement data give band gap of 3.5more » eV which is ideal band gap for buffer layer for solar cell suggesting that the obtained ZnS buffer layer is suitable in a low-cost solar cell.« less

Growth and micro structural studies on Yittria Stabilized Zirconia (YSZ) and Strontium Titanate (STO) buffer layers

NASA Technical Reports Server (NTRS)

Srinivas, S.; Pinto, R.; Pai, S. P.; Dsousa, D. P.; Apte, P. R.; Kumar, D.; Purandare, S. C.; Bhatnagar, A. K.

1995-01-01

Microstructure of Yittria Stabilized Zirconia (YSZ) and Strontium Titanate (STO) of radio frequency magnetron sputtered buffer layers was studied at various sputtering conditions on Si (100), Sapphire and LaAlO3 (100) substrates. The effect of substrate temperatures up to 800 C and sputtering gas pressures in the range of 50 mTorr. of growth conditions was studied. The buffer layers of YSZ and STO showed a strong tendency for columnar growth was observed above 15 mTorr sputtering gas pressure and at high substrate temperatures. Post annealing of these films in oxygen atmosphere reduced the oxygen deficiency and strain generated during growth of the films. Strong c-axis oriented superconducting YBa2Cu3O7-x (YBCO) thin films were obtained on these buffer layers using pulsed laser ablation technique. YBCO films deposited on multilayers of YSZ and STO were shown to have better superconducting properties.

Buffer layer between a planar optical concentrator and a solar cell

DOE Office of Scientific and Technical Information (OSTI.GOV)

Solano, Manuel E.; Barber, Greg D.; Department of Chemistry, Pennsylvania State University, University Park, PA 16802

2015-09-15

The effect of inserting a buffer layer between a periodically multilayered isotropic dielectric (PMLID) material acting as a planar optical concentrator and a photovoltaic solar cell was theoretically investigated. The substitution of the photovoltaic material by a cheaper dielectric material in a large area of the structure could reduce the fabrication costs without significantly reducing the efficiency of the solar cell. Both crystalline silicon (c-Si) and gallium arsenide (GaAs) were considered as the photovoltaic material. We found that the buffer layer can act as an antireflection coating at the interface of the PMLID and the photovoltaic materials, and the structuremore » increases the spectrally averaged electron-hole pair density by 36% for c-Si and 38% for GaAs compared to the structure without buffer layer. Numerical evidence indicates that the optimal structure is robust with respect to small changes in the grating profile.« less

Tuning the Two-Dimensional Electron Liquid at Oxide Interfaces by Buffer-Layer-Engineered Redox Reactions.

PubMed

Chen, Yunzhong; Green, Robert J; Sutarto, Ronny; He, Feizhou; Linderoth, Søren; Sawatzky, George A; Pryds, Nini

2017-11-08

Polar discontinuities and redox reactions provide alternative paths to create two-dimensional electron liquids (2DELs) at oxide interfaces. Herein, we report high mobility 2DELs at interfaces involving SrTiO 3 (STO) achieved using polar La 7/8 Sr 1/8 MnO 3 (LSMO) buffer layers to manipulate both polarities and redox reactions from disordered overlayers grown at room temperature. Using resonant X-ray reflectometry experiments, we quantify redox reactions from oxide overlayers on STO as well as polarity induced electronic reconstruction at epitaxial LSMO/STO interfaces. The analysis reveals how these effects can be combined in a STO/LSMO/disordered film trilayer system to yield high mobility modulation doped 2DELs, where the buffer layer undergoes a partial transformation from perovskite to brownmillerite structure. This uncovered interplay between polar discontinuities and redox reactions via buffer layers provides a new approach for the design of functional oxide interfaces.

La0.7Sr0.3MnO3: A single, conductive-oxide buffer layer for the development of YBa2Cu3O7-δ coated conductors

NASA Astrophysics Data System (ADS)

Aytug, T.; Paranthaman, M.; Kang, B. W.; Sathyamurthy, S.; Goyal, A.; Christen, D. K.

2001-10-01

Coated conductor applications in power technologies require stabilization of the high-temperature superconducting (HTS) layers against thermal runaway. Conductive La0.7Sr0.3MnO3 (LSMO) has been epitaxially grown on biaxially textured Ni substrates as a single buffer layer. The subsequent epitaxial growth of YBa2Cu3O7-δ (YBCO) coatings by pulsed laser deposition yielded self-field critical current densities (Jc) of 0.5×106A/cm2 at 77 K, and provided good electrical connectivity over the entire structure (HTS+conductive-buffer+metal substrate). Property characterizations of YBCO/LSMO/Ni architecture revealed excellent crystallographic and morphological properties. These results have demonstrated that LSMO, used as a single, conductive buffer layer, may offer potential for use in fully stabilized YBCO coated conductors.

Implementation of a physically based water percolation routine in the Crocus/SURFEX (V7.3) snowpack model

NASA Astrophysics Data System (ADS)

D'Amboise, Christopher J. L.; Müller, Karsten; Oxarango, Laurent; Morin, Samuel; Schuler, Thomas V.

2017-09-01

We present a new water percolation routine added to the one-dimensional snowpack model Crocus as an alternative to the empirical bucket routine. This routine solves the Richards equation, which describes flow of water through unsaturated porous snow governed by capillary suction, gravity and hydraulic conductivity of the snow layers. We tested the Richards routine on two data sets, one recorded from an automatic weather station over the winter of 2013-2014 at Filefjell, Norway, and the other an idealized synthetic data set. Model results using the Richards routine generally lead to higher water contents in the snow layers. Snow layers often reached a point at which the ice crystals' surface area is completely covered by a thin film of water (the transition between pendular and funicular regimes), at which feedback from the snow metamorphism and compaction routines are expected to be nonlinear. With the synthetic simulation 18 % of snow layers obtained a saturation of > 10 % and 0.57 % of layers reached saturation of > 15 %. The Richards routine had a maximum liquid water content of 173.6 kg m-3 whereas the bucket routine had a maximum of 42.1 kg m-3. We found that wet-snow processes, such as wet-snow metamorphism and wet-snow compaction rates, are not accurately represented at higher water contents. These routines feed back on the Richards routines, which rely heavily on grain size and snow density. The parameter sets for the water retention curve and hydraulic conductivity of snow layers, which are used in the Richards routine, do not represent all the snow types that can be found in a natural snowpack. We show that the new routine has been implemented in the Crocus model, but due to feedback amplification and parameter uncertainties, meaningful applicability is limited. Updating or adapting other routines in Crocus, specifically the snow compaction routine and the grain metamorphism routine, is needed before Crocus can accurately simulate the snowpack using the Richards routine.

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

DOEpatents

Mandal, Krishna C.; Terry, J. Russell

2016-12-06

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

Magnetic properties of Pr-Fe-B thick-film magnets deposited on Si substrates with glass buffer layer

NASA Astrophysics Data System (ADS)

Nakano, M.; Kurosaki, A.; Kondo, H.; Shimizu, D.; Yamaguchi, Y.; Yamashita, A.; Yanai, T.; Fukunaga, H.

2018-05-01

In order to improve the magnetic properties of PLD-made Pr-Fe-B thick-film magnets deposited on Si substrates, an adoption of a glass buffer layer was carried out. The glass layer could be fabricated under the deposition rate of approximately 70 μm/h on a Si substrate using a Nd-YAG pulse laser in the vacuum atmosphere. The use of the layer enabled us to reduce the Pr content without a mechanical destruction and enhance (BH)max value by approximately 20 kJ/m3 compared with the average value of non-buffer layered Pr-Fe-B films with almost the same thickness. It is also considered that the layer is also effective to apply a micro magnetization to the films deposited on Si ones.

Improved fill factor in inverted planar perovskite solar cells with zirconium acetate as the hole-and-ion-blocking layer.

PubMed

Zhang, Xuewen; Liang, Chunjun; Sun, Mengjie; Zhang, Huimin; Ji, Chao; Guo, Zebang; Xu, Yajun; Sun, Fulin; Song, Qi; He, Zhiqun

2018-03-14

Planar perovskite solar cells (PSCs) have gained great interest due to their low-temperature solution preparation and simple process. In inverted planar PSCs, an additional buffer layer is usually needed on the top of the PCBM electron-transport layer (ETL) to enhance the device performance. In this work, we used a new buffer layer, zirconium acetate (Zr(Ac) 4 ). The inclusion of the Zr(Ac) 4 buffer layer leads to the increase of FF from ∼68% to ∼79% and PCE from ∼14% to ∼17% in the planar PSCs. The UPS measurement indicates that the Zr(Ac) 4 layer has a low HOMO level of -8.2 eV, indicating that the buffer layer can act as a hole-blocking layer. Surface morphology and surface chemistry investigations reveal that the elements I, MA and Pb can diffuse across the PCBM ETL, damaging the device performance. The covering Zr(Ac) 4 molecules fill in the pinholes of the PCBM layer and effectively block the ions/molecules of the perovskite from diffusion across the ETL. The resulting more robust PCBM/Zr(Ac) 4 ETL leads to weaker ionic charge accumulation and lower diode leakage current. The double role of hole-and-ion blocking of the Zr(Ac) 4 layer explains the improved FF and PCE in the PSCs.

Substrate Structures For Growth Of Highly Oriented And/Or Epitaxial Layers Thereon

DOEpatents

Arendt, Paul N.; Foltyn, Stephen R.; Groves, James R.; Jia, Quanxi

2005-07-26

A composite substrate structure including a substrate, a layer of a crystalline metal oxide or crystalline metal oxynitride material upon the substrate, a layer of an oriented cubic oxide material having a rock-salt-like structure upon the crystalline metal oxide or crystalline metal oxynitride material layer is provided together with additional layers such as one or more layers of a buffer material upon the oriented cubic oxide material layer. Jc's of 2.3×106 A/cm2 have been demonstrated with projected Ic's of 320 Amperes across a sample 1 cm wide for a superconducting article including a flexible polycrystalline metallic substrate, an inert oxide material layer upon the surface of the flexible polycrystalline metallic substrate, a layer of a crystalline metal oxide or crystalline metal oxynitride material upon the layer of the inert oxide material, a layer of an oriented cubic oxide material having a rock-salt-like structure upon the crystalline metal oxide or crystalline metal oxynitride material layer, a layer of a buffer material upon the oriented cubic oxide material layer, and, a top-layer of a high temperature superconducting material upon the layer of a buffer material.

Impact of the deposition conditions of buffer and windows layers on lowering the metastability effects in Cu(In,Ga)Se2/Zn(S,O)-based solar cell

NASA Astrophysics Data System (ADS)

Naghavi, Negar; Hildebrandt, Thibaud; Bouttemy, Muriel; Etcheberry, Arnaud; Lincot, Daniel

2016-02-01

The highest and most reproducible (Cu(In,Ga)Se2 (CIGSe) based solar-cell efficiencies are obtained by use of a very thin n-type CdS layer deposited by chemical bath deposition (CBD). However because of both Cadmium's adverse environmental impact and the narrow bandgap of CdS (2.4-2.5 eV) one of the major objectives in the field of CIGSe technology remains the development and implementation in the production line of Cd-free buffer layers. The CBDZn( S,O) remains one the most studied buffer layer for replacing the CdS in Cu(In,Ga)Se2-based solar cells and has already demonstrated its potential to lead to high-efficiency solar cells up to 22.3%. However one of the key issue to implement a CBD-Zn(S,O) process in a CIGSe production line is the cells stability, which depends both on the deposition conditions of CBD-Zn(S,O) and on a good band alignment between CIGSe/Zn(S,O)/windows layers. The most common window layers applied in CIGSe solar cells consist of two layers : a thin (50-100 nm) and highly resistive i-ZnO layer deposited by magnetron sputtering and a transparent conducting 300-500 nm ZnO:Al layer. In the case of CBD-Zn(S,O) buffer layer, the nature and deposition conditions of both Zn(S,O) and the undoped window layer can strongly influence the performance and stability of cells. The present contribution will be specially focused on the effect of condition growth of CBD-Zn(S,O) buffer layers and the impact of the composition and deposition conditions of the undoped window layers such as ZnxMgyO or ZnxSnyO on the stability and performance of these solar cells.

FIBER AND INTEGRATED OPTICS: Investigation of a fiber-optic polarizer with a metal film and a dielectric buffer layer

NASA Astrophysics Data System (ADS)

Gelikonov, V. M.; Gusovskiĭ, D. D.; Konoplev, Yu N.; Leonov, V. I.; Mamaev, Yu A.; Turkin, A. A.

1990-01-01

A model of a plane-layer waveguide is used in a theoretical analysis of the attenuation coefficients of the TM0 and TE0 waves in a fiber-optic polarizer with a metal film and two dielectric buffer layers, one of which is the residual part of the fiber cladding. A report is given of the construction and experimental investigation of polarizers with a buffer layer of magnesium fluoride and an aluminum film operating at wavelengths of 0.63 and 0.81 μm and characterized by extinction coefficients of at least 53 and 46 dB, respectively, and by losses not exceeding 0.5 dB.

Liftoff process for exfoliation of thin film photovoltaic devices and back contact formation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Haight, Richard A.; Hannon, James B.; Oida, Satoshi

A method for forming a back contact on an absorber layer in a photovoltaic device includes forming a two dimensional material on a first substrate. An absorber layer including Cu--Zn--Sn--S(Se) (CZTSSe) is grown over the first substrate on the two dimensional material. A buffer layer is grown on the absorber layer on a side opposite the two dimensional material. The absorber layer is exfoliated from the two dimensional material to remove the first substrate from a backside of the absorber layer opposite the buffer layer. A back contact is deposited on the absorber layer.

Junction formation of Cu3BiS3 investigated by Kelvin probe force microscopy and surface photovoltage measurements

PubMed Central

Mesa, Fredy; Chamorro, William; Vallejo, William; Baier, Robert; Dittrich, Thomas; Grimm, Alexander; Lux-Steiner, Martha C

2012-01-01

Summary Recently, the compound semiconductor Cu3BiS3 has been demonstrated to have a band gap of ~1.4 eV, well suited for photovoltaic energy harvesting. The preparation of polycrystalline thin films was successfully realized and now the junction formation to the n-type window needs to be developed. We present an investigation of the Cu3BiS3 absorber layer and the junction formation with CdS, ZnS and In2S3 buffer layers. Kelvin probe force microscopy shows the granular structure of the buffer layers with small grains of 20–100 nm, and a considerably smaller work-function distribution for In2S3 compared to that of CdS and ZnS. For In2S3 and CdS buffer layers the KPFM experiments indicate negatively charged Cu3BiS3 grain boundaries resulting from the deposition of the buffer layer. Macroscopic measurements of the surface photovoltage at variable excitation wavelength indicate the influence of defect states below the band gap on charge separation and a surface-defect passivation by the In2S3 buffer layer. Our findings indicate that Cu3BiS3 may become an interesting absorber material for thin-film solar cells; however, for photovoltaic application the band bending at the charge-selective contact has to be increased. PMID:22497001

Junction formation of Cu(3)BiS(3) investigated by Kelvin probe force microscopy and surface photovoltage measurements.

PubMed

Mesa, Fredy; Chamorro, William; Vallejo, William; Baier, Robert; Dittrich, Thomas; Grimm, Alexander; Lux-Steiner, Martha C; Sadewasser, Sascha

2012-01-01

Recently, the compound semiconductor Cu(3)BiS(3) has been demonstrated to have a band gap of ~1.4 eV, well suited for photovoltaic energy harvesting. The preparation of polycrystalline thin films was successfully realized and now the junction formation to the n-type window needs to be developed. We present an investigation of the Cu(3)BiS(3) absorber layer and the junction formation with CdS, ZnS and In(2)S(3) buffer layers. Kelvin probe force microscopy shows the granular structure of the buffer layers with small grains of 20-100 nm, and a considerably smaller work-function distribution for In(2)S(3) compared to that of CdS and ZnS. For In(2)S(3) and CdS buffer layers the KPFM experiments indicate negatively charged Cu(3)BiS(3) grain boundaries resulting from the deposition of the buffer layer. Macroscopic measurements of the surface photovoltage at variable excitation wavelength indicate the influence of defect states below the band gap on charge separation and a surface-defect passivation by the In(2)S(3) buffer layer. Our findings indicate that Cu(3)BiS(3) may become an interesting absorber material for thin-film solar cells; however, for photovoltaic application the band bending at the charge-selective contact has to be increased.

Direct charge carrier injection into Ga2O3 thin films using an In2O3 cathode buffer layer: their optical, electrical and surface state properties

NASA Astrophysics Data System (ADS)

Cui, W.; Zhao, X. L.; An, Y. H.; Guo, D. Y.; Qing, X. Y.; Wu, Z. P.; Li, P. G.; Li, L. H.; Cui, C.; Tang, W. H.

2017-04-01

Conductive Ga2O3 thin films with an In2O3 buffer layer have been prepared on c-plane sapphire substrates using a laser molecular beam epitaxy technique. The effects of the In2O3 buffer layer on the structure and optical, electrical and surface state properties of the Ga2O3 films have been studied. The change in conductivity of the thin films is attributed to different thicknesses of the In2O3 buffer layer, which determine the concentration of charge carriers injected into the upper Ga2O3 layer from the interface of the bilayer thin films. In addition, the increase in flat band voltage shift and capacitance values as the In2O3 buffer layer thickens are attributed to the increase in surface state density, which also contributes to the rapid shrinkage of the optical band gap of the Ga2O3. With transparency to visible light, high n-type conduction and the ability to tune the optical band gap and surface state density, we propose that Ga2O3/In2O3 bilayer thin film is an ideal n-type semiconductor for fabrication of transparent power devices, solar cell electrodes and gas sensors.

Example of trondhjemite genesis by means of alkali metasomatism: Rockford Granite, Alabama Appalachians

DOE Office of Scientific and Technical Information (OSTI.GOV)

Drummond, M.S.; Wesolowski, D.; Ragland, P.C.

1985-01-01

An alternative model for trondhjemite genesis is proposed where granite is transformed to trondhjemite via infiltration by a Na-rich metamorphic fluid. The Rockford Granite serves as the case example for this process and is characterized as a synmetamorphic, peraluminous trondhjemite-granite suite. The major process operative in the conversion of granite to trondhjemite involves cation exchange of Na for K in the feldspar and mica phases through a volatile fluid medium. Whole-rock delta/sup 18/O values for the trondhjemites are negatively correlated with the atomic prop. K/Na ratio indicating a partial reequilibration of the altered granitoids with a Na- and /sup 18/O-richmore » metamorphically derived fluid. Biotite decomposition to an Al-epidote-paragonitic muscovite-quartz assemblage is also associated with the Na-metasomatism, as are apatite replacement by Al-epidote and secondary zircon crystallization. The replacement of magmatic phases by metasomatic phases exemplifies the chemical changes produced during infiltration metasomatism where the trondhjemites are depleted in all REE's. The timing of the infiltration metasomatism is thought to have occurred during regional metamorphism, producing a discrete fluid phase in the surrounding amphibolite-grade metasediments. Foliation planes in the granitoid apparently served as conduts for fluid flow with reaction enhanced permeability accompanying the 8% molar volume reduction during Na for K exchange in the feldspars. A model is proposed where metamorphic fluids migrated updip and along strike from their source and were buffered by the presence or absence of two feldspars in the metasediments.« less

Conductive and robust nitride buffer layers on biaxially textured substrates

DOEpatents

Sankar, Sambasivan [Chicago, IL; Goyal, Amit [Knoxville, TN; Barnett, Scott A [Evanston, IL; Kim, Ilwon [Skokie, IL; Kroeger, Donald M [Knoxville, TN

2009-03-31

The present invention relates to epitaxial, electrically conducting and mechanically robust, cubic nitride buffer layers deposited epitaxially on biaxially textured substrates such as metals and alloys. The invention comprises of a biaxially textured substrate with epitaxial layers of nitrides. The invention also discloses a method to form such epitaxial layers using a high rate deposition method as well as without the use of forming gases. The invention further comprises epitaxial layers of oxides on the biaxially textured nitride layer. In some embodiments the article further comprises electromagnetic devices which may have superconducting properties.

Noble Metal Arsenides and Gold Inclusions in Northwest Africa 8186

NASA Technical Reports Server (NTRS)

Srinivasan, P.; McCubbin, F. M.; Rahman, Z.; Keller, L. P.; Agee, C. B.

2016-01-01

CK carbonaceous chondrites are a highly thermally altered group of carbonaceous chondrites, experiencing temperatures ranging between approximately 576-867 degrees Centigrade. Additionally, the mineralogy of the CK chondrites record the highest overall oxygen fugacity of all chondrites, above the fayalite-magnetite-quartz (FMQ) buffer. Me-tallic Fe-Ni is extremely rare in CK chondrites, but magnetite and Fe,Ni sulfides are commonly observed. Noble metal-rich inclusions have previously been found in some magnetite and sulfide grains. These arsenides, tellurides, and sulfides, which contain varying amounts of Pt, Ru, Os, Te, As, Ir, and S, are thought to form either by condensation from a solar gas, or by exsolution during metamorphism on the chondritic parent body. Northwest Africa (NWA) 8186 is a highly metamorphosed CK chondrite. This meteorite is predominately composed of NiO-rich forsteritic olivine (Fo65), with lesser amounts of plagioclase (An52), augite (Fs11Wo49), magnetite (with exsolved titanomagnetite, hercynite, and titanohematite), monosulfide solid solution (with exsolved pentlandite), and the phosphate minerals Cl-apatite and merrillite. This meteorite contains coarse-grained, homogeneous silicates, and has 120-degree triple junctions between mineral phases, which indicates a high degree of thermal metamorphism. The presence of NiO-rich olivine, oxides phases all bearing Fe3 plus, and the absence of metal, are consistent with an oxygen fugacity above the FMQ buffer. We also observed noble metal-rich phases within sulfide grains in NWA 8186, which are the primary focus of the present study.

Noble Metal Arsenides and Gold Inclusions in Northwest Africa 8186

NASA Technical Reports Server (NTRS)

Srinivasan, P.; McCubbin, F. M.; Rahman, Z.; Keller, L. P.; Agee, C. B.

2016-01-01

CK carbonaceous chondrites are a highly thermally altered group of carbonaceous chondrites, experiencing temperatures ranging between approx.576-867 C. Additionally, the mineralogy of the CK chondrites record the highest overall oxygen fugacity of all chondrites, above the fayalite-magnetite-quartz (FMQ) buffer. Metallic Fe-Ni is extremely rare in CK chondrites, but magnetite and Fe,Ni sulfides are commonly observed. Noble metal-rich inclusions have previously been found in some magnetite and sulfide grains. These arsenides, tellurides, and sulfides, which contain varying amounts of Pt, Ru, Os, Te, As, Ir, and S, are thought to form either by condensation from a solar gas, or by exsolution during metamorphism on the chondritic parent body. Northwest Africa (NWA) 8186 is a highly metamorphosed CK chondrite. This meteorite is predominately composed of NiO-rich forsteritic olivine (Fo65), with lesser amounts of plagioclase (An52), augite (Fs11Wo49), magnetite (with exsolved titanomagnetite, hercynite, and titanohematite), monosulfide solid solution (with exsolved pentlandite), and the phosphate minerals Cl-apatite and merrillite. This meteorite contains coarse-grained, homogeneous silicates, and has 120deg triple junctions between mineral phases, which indicates a high degree of thermal metamorphism. The presence of NiO-rich olivine, oxides phases all bearing Fe3+, and the absence of metal, are consistent with an oxygen fugacity above the FMQ buffer. We also observed noble metal-rich phases within sulfide grains in NWA 8186, which are the primary focus of the present study.

The Functions of Metamorphic Metallothioneins in Zinc and Copper Metabolism.

PubMed

Krężel, Artur; Maret, Wolfgang

2017-06-09

Recent discoveries in zinc biology provide a new platform for discussing the primary physiological functions of mammalian metallothioneins (MTs) and their exquisite zinc-dependent regulation. It is now understood that the control of cellular zinc homeostasis includes buffering of Zn 2+ ions at picomolar concentrations, extensive subcellular re-distribution of Zn 2+ , the loading of exocytotic vesicles with zinc species, and the control of Zn 2+ ion signalling. In parallel, characteristic features of human MTs became known: their graded affinities for Zn 2+ and the redox activity of their thiolate coordination environments. Unlike the single species that structural models of mammalian MTs describe with a set of seven divalent or eight to twelve monovalent metal ions, MTs are metamorphic. In vivo, they exist as many species differing in redox state and load with different metal ions. The functions of mammalian MTs should no longer be considered elusive or enigmatic because it is now evident that the reactivity and coordination dynamics of MTs with Zn 2+ and Cu⁺ match the biological requirements for controlling-binding and delivering-these cellular metal ions, thus completing a 60-year search for their functions. MT represents a unique biological principle for buffering the most competitive essential metal ions Zn 2+ and Cu⁺. How this knowledge translates to the function of other families of MTs awaits further insights into the specifics of how their properties relate to zinc and copper metabolism in other organisms.

NiFeCo/Cu superlattices with high magnetoresistive sensitivity and weak hysteresis

NASA Astrophysics Data System (ADS)

Bannikova, N. S.; Milyaev, M. A.; Naumova, L. I.; Krinitsina, T. P.; Patrakov, E. I.; Proglyado, V. V.; Chernyshova, T. A.; Ustinov, V. V.

2016-10-01

The microstructure and the magetoresistive characteristics of [NiFeCo/Cu]8 superlattices prepared by magnetron sputtering with various thickness of the buffer NiFeCr layer and exhibiting a giant magnetoresistive effect have been studied. It has been found that these nanostructures are formed with a strong or weak hysteresis depending on the structure (bcc or fcc) formed in the NiFeCr buffer layer. The method of the substantial decrease in the hysteresis loop width of the magnetoresistance by using the composite Ta/NiFeCr buffer layer has been suggested.

Effect of InSb/In0.9Al0.1Sb superlattice buffer layer on the structural and electronic properties of InSb films

NASA Astrophysics Data System (ADS)

Zhao, Xiaomeng; Zhang, Yang; Guan, Min; Cui, Lijie; Wang, Baoqiang; Zhu, Zhanping; Zeng, Yiping

2017-07-01

The effect of InSb/In0.9Al0.1Sb buffer layers on InSb thin films grown on GaAs (0 0 1) substrate by molecular beam epitaxy (MBE) is investigated. The crystal quality and the surface morphology of InSb are characterized by XRD and AFM. The carrier transport property is researched through variable temperature hall test. The sharp interface between InSb/In0.9Al0.1Sb is demonstrated important for the high quality InSb thin film. We try different superlattice buffer layers by changing ratios, 2-0.5, thickness, 300-450 nm, and periods, 20-50. According to the function of the dislocation density to the absolute temperature below 150 K with different periods of SL buffers, we can find that the number of periods of superlattice is a major factor to decrease the density of threading dislocations. With the 50 periods SL buffer layer, the electron mobility of InSb at the room temperature and liquid nitrogen cooling temperature is ∼63,000 and ∼4600 cm2/V s, respectively. We deduce that the interface in the SL structure works as a filter layer to prevent the dislocation propagating to the upper InSb thin films.

Effect of CoSi2 buffer layer on structure and magnetic properties of Co films grown on Si (001) substrate

NASA Astrophysics Data System (ADS)

Hu, Bo; He, Wei; Ye, Jun; Tang, Jin; Syed Sheraz, Ahmad; Zhang, Xiang-Qun; Cheng, Zhao-Hua

2015-01-01

Buffer layer provides an opportunity to enhance the quality of ultrathin magnetic films. In this paper, Co films with different thickness of CoSi2 buffer layers were grown on Si (001) substrates. In order to investigate morphology, structure, and magnetic properties of films, scanning tunneling microscope (STM), low energy electron diffraction (LEED), high resolution transmission electron microscopy (HRTEM), and surface magneto-optical Kerr effect (SMOKE) were used. The results show that the crystal quality and magnetic anisotropies of the Co films are strongly affected by the thickness of CoSi2 buffer layers. Few CoSi2 monolayers can prevent the interdiffusion of Si substrate and Co film and enhance the Co film quality. Furthermore, the in-plane magnetic anisotropy of Co film with optimal buffer layer shows four-fold symmetry and exhibits the two-jumps of magnetization reversal process, which is the typical phenomenon in cubic (001) films. Project supported by the National Basic Research Program of China (Grant Nos. 2011CB921801 and 2012CB933102), the National Natural Science Foundation of China (Grant Nos. 11374350, 11034004, 11274361, and 11274033), and the Research Fund for the Doctoral Program of Higher Education of China (Grant No. 20131102130005).

Influence of C or In buffer layer on photoluminescence behaviour of ultrathin ZnO film

DOE Office of Scientific and Technical Information (OSTI.GOV)

Saravanan, K., E-mail: saravanan@igcar.gov.in; Jayalakshmi, G.; Krishnan, R.

We study the effect of the indium or carbon buffer layer on the photoluminescence (PL) property of ZnO ultrathin films deposited on a Si(100) substrate. The surface morphology of the films obtained using scanning tunnelling microscopy shows spherical shaped ZnO nanoparticles of size ∼8 nm in ZnO/C/Si and ∼22 nm in ZnO/Si samples, while the ZnO/In/Si sample shows elliptical shaped ZnO particles. Further, the ZnO/C/Si sample shows densely packed ZnO nanoparticles in comparison with other samples. Strong band edge emission has been observed in the presence of In or C buffer layer, whereas the ZnO/Si sample exhibits poor PL emission. The influencemore » of C and In buffer layers on the PL behaviour of ZnO films is studied in detail using temperature dependent PL measurements in the range of 4 K–300 K. The ZnO/C/Si sample exhibits a multi-fold enhancement in the PL emission intensity with well-resolved free and bound exciton emission lines. Our experimental results imply that the ZnO films deposited on the C buffer layer showed higher particle density and better exciton emission desired for optoelectronic applications.« less

Design of optimal buffer layers for CuInGaSe2 thin-film solar cells(Conference Presentation)

NASA Astrophysics Data System (ADS)

Lordi, Vincenzo; Varley, Joel B.; He, Xiaoqing; Rockett, Angus A.; Bailey, Jeff; Zapalac, Geordie H.; Mackie, Neil; Poplavskyy, Dmitry; Bayman, Atiye

2016-09-01

Optimizing the buffer layer in manufactured thin-film PV is essential to maximize device efficiency. Here, we describe a combined synthesis, characterization, and theory effort to design optimal buffers based on the (Cd,Zn)(O,S) alloy system for CIGS devices. Optimization of buffer composition and absorber/buffer interface properties in light of several competing requirements for maximum device efficiency were performed, along with process variations to control the film and interface quality. The most relevant buffer properties controlling performance include band gap, conduction band offset with absorber, dopability, interface quality, and film crystallinity. Control of an all-PVD deposition process enabled variation of buffer composition, crystallinity, doping, and quality of the absorber/buffer interface. Analytical electron microscopy was used to characterize the film composition and morphology, while hybrid density functional theory was used to predict optimal compositions and growth parameters based on computed material properties. Process variations were developed to produce layers with controlled crystallinity, varying from amorphous to fully epitaxial, depending primarily on oxygen content. Elemental intermixing between buffer and absorber, particularly involving Cd and Cu, also is controlled and significantly affects device performance. Secondary phase formation at the interface is observed for some conditions and may be detrimental depending on the morphology. Theoretical calculations suggest optimal composition ranges for the buffer based on a suite of computed properties and drive process optimizations connected with observed film properties. Prepared by LLNL under Contract DE-AC52-07NA27344.

Mineralogy and geochemistry of two metamorphosed sedimentary manganese deposits, Sierra Nevada, California, USA

USGS Publications Warehouse

Flohr, M.J.K.; Huebner, J.S.

1992-01-01

Laminated to massive rhodochrosite, hausmannite, and Mn-silicates from the Smith prospect and Manga-Chrome mine, Sierra Nevada, California were deposited as ocean floor sediments associated with chert and shale. The principal lithologies at Smith are chert, argillite, rhodochrosite-, hausmannite- and chlorite-rich layers, and relatively uncommon layers of jacobsite. The Manga-Chrome mine also contains layers rich in manganoan calcite and caryopilite. Tephroite, rhodonite, spessartine, and accessory alleghanyite and sonolite formed during metamorphism. Volcaniclastic components are present at Manga-Chrome as metavolcanic clasts and as Mn-poor, red, garnet- and hematite-rich layers. There is no evidence, such as relict lithologies, that Mn was introduced into Mn-poor lithologies such as chert, limestone or mudstone. Replacement of Mn-poor phases by Mn-rich phases is observed only in the groundmass of volcanic clasts that appear to have fallen into soft Mn-rich mud. Manganiferous samples from the Smith prospect and Manga-Chrome mine have high Mn Fe and low concentrations of Ni, Cu, Zn, Co, U, Th and the rare-earth elements that are similar to concentrations reported from other ancient Mn deposits found in chert-greenstone complexes and from manganiferous sediments and crusts that are forming near modern sea floor vents. The Sierra Nevada deposits formed as precipitates of Mn-rich sediments on the sea floor, probably from mixtures of circulating hydrothermal fluids and seawater. The composition of a metabasalt from the Smith prospect is consistent with those of island-arc tholeiites. Metavolcanic clasts from the Manga-Chrome mine are compositionally distinct from the Smith metabasalt and have alkaline to calc-alkaline affinities. A back-arc basin is considered to be the most likely paleoenvironment for the formation of the Mn-rich lenses at the Manga-Chrome mine and, by association, the Smith prospect. Layers of rhodochrosite, hausmannite and chert preserve the composition and some textures of the sedimentary protoliths at both Sierra Nevada deposits. Jacobsite-rich layers probably represent a Fe-rich protolith. Caryopilite and manganoan calcite represent additional protoliths at the Manga-Chrome mine. The metamorphic assemblage prehnite-chlorite-epidote-calcite in a metabasalt from the Smith prospect constrains regional metamorphic conditions to a maximum temperature of 325??C and a pressure of 2 kbar. Slightly higher temperatures are indicated by the presence of actinolite in another metabasalt. Compositions of Mn-rich minerals in Smith samples are consistent with these metamorphic conditions. ?? 1992.

Hafnium nitride buffer layers for growth of GaN on silicon

DOEpatents

Armitage, Robert D.; Weber, Eicke R.

2005-08-16

Gallium nitride is grown by plasma-assisted molecular-beam epitaxy on (111) and (001) silicon substrates using hafnium nitride buffer layers. Wurtzite GaN epitaxial layers are obtained on both the (111) and (001) HfN/Si surfaces, with crack-free thickness up to 1.2 {character pullout}m. However, growth on the (001) surface results in nearly stress-free films, suggesting that much thicker crack-free layers could be obtained.

Aligned crystalline semiconducting film on a glass substrate and method of making

DOEpatents

Findikoglu, Alp T.

2010-08-24

A semiconducting structure having a glass substrate. In one embodiment, the glass substrate has a softening temperature of at least about 750.degree. C. The structure includes a nucleation layer formed on a surface of the substrate, a template layer deposited on the nucleation layer by one of ion assisted beam deposition and reactive ion beam deposition, at least on biaxially oriented buffer layer epitaxially deposited on the template layer, and a biaxially oriented semiconducting layer epitaxially deposited on the buffer layer. A method of making the semiconducting structure is also described.

Polycrystalline ferroelectric or multiferroic oxide articles on biaxially textured substrates and methods for making same

DOE Office of Scientific and Technical Information (OSTI.GOV)

Goyal, Amit; Shin, Junsoo

A polycrystalline ferroelectric and/or multiferroic oxide article includes a substrate having a biaxially textured surface; at least one biaxially textured buffer layer supported by the substrate; and a biaxially textured ferroelectric or multiferroic oxide layer supported by the buffer layer. Methods for making polycrystalline ferroelectric and/or multiferroic oxide articles are also disclosed.

Ultralow threading dislocation density in GaN epilayer on near-strain-free GaN compliant buffer layer and its applications in hetero-epitaxial LEDs.

PubMed

Shih, Huan-Yu; Shiojiri, Makoto; Chen, Ching-Hsiang; Yu, Sheng-Fu; Ko, Chung-Ting; Yang, Jer-Ren; Lin, Ray-Ming; Chen, Miin-Jang

2015-09-02

High threading dislocation (TD) density in GaN-based devices is a long unresolved problem because of the large lattice mismatch between GaN and the substrate, which causes a major obstacle for the further improvement of next-generation high-efficiency solid-state lighting and high-power electronics. Here, we report InGaN/GaN LEDs with ultralow TD density and improved efficiency on a sapphire substrate, on which a near strain-free GaN compliant buffer layer was grown by remote plasma atomic layer deposition. This "compliant" buffer layer is capable of relaxing strain due to the absorption of misfit dislocations in a region within ~10 nm from the interface, leading to a high-quality overlying GaN epilayer with an unusual TD density as low as 2.2 × 10(5) cm(-2). In addition, this GaN compliant buffer layer exhibits excellent uniformity up to a 6" wafer, revealing a promising means to realize large-area GaN hetero-epitaxy for efficient LEDs and high-power transistors.

Alternative buffer layer development in Cu(In,Ga)Se2 thin film solar cells

NASA Astrophysics Data System (ADS)

Xin, Peipei

Cu(In,Ga)Se2-based thin film solar cells are considered to be one of the most promising photovoltaic technologies. Cu(In,Ga)Se2 (CIGS) solar devices have the potential advantage of low-cost, fast fabrication by using semiconductor layers of only a few micrometers thick and high efficiency photovoltaics have been reported at both the cell and the module levels. CdS via chemical bath deposition (CBD) has been the most widely used buffer option to form the critical junction in CIGS-based thin film photovoltaic devices. However, the disadvantages of CdS can’t be ignored - regulations on cadmium usage are getting stricter primarily due to its toxicity and environmental impacts, and the proper handling of the large amount of toxic chemical bath waste is a massive and expensive task. This dissertation is devoted to the development of Cd-free alternative buffer layers in CIGS-based thin film solar cells. Based on the considerations of buffer layer selection criteria and extensive literature review, Zn-compound buffer materials are chosen as the primary investigation candidates. Radio frequency magnetron sputtering is the preferred buffer deposition approach since it’s a clean and more controllable technique compared to CBD, and is readily scaled to large area manufacturing. First, a comprehensive study of the ZnSe1-xOx compound prepared by reactive sputtering was completed. As the oxygen content in the reactive sputtering gas increased, ZnSe1-xOx crystallinity and bandgap decreased. It’s observed that oxygen miscibility in ZnSe was low and a secondary phase formed when the O2 / (O2 + Ar) ratio in the sputtering gas exceeded 2%. Two approaches were proposed to optimize the band alignment between the CIGS and buffer layer. One method focused on the bandgap engineering of the absorber, the other focused on the band structure modification of the buffer. As a result, improved current of the solar cell was achieved although a carrier transport barrier at the junction interface still limited the device performance. Second, an investigation of Zn(S,O) buffer layers was completed. Zn(S,O) films were sputtered in Ar using a ZnO0.7S0.3 compound target. Zn(S,O) films had the composition close to the target with S / (S+O) ratio around 0.3. Zn(S,O) films showed the wurtzite structure with the bandgap about 3.2eV. The champion Cu(In,Ga)Se2 / Zn(S,O) cell had 12.5% efficiency and an (Ag,Cu)(In,Ga)Se2 / Zn(S,O) cell achieved 13.2% efficiency. Detailed device analysis was used to study the Cu(In,Ga)Se2 and (Ag,Cu)(In,Ga)Se2 absorbers, the influence of absorber surface treatments, the effects of device treatments, the sputtering damage and the Na concentration in the absorber. Finally alternative buffer layer development was applied to an innovative superstrate CIGS configuration. The superstrate structure has potential benefits of improved window layer properties, cost reduction, and the possibility to implement back reflector engineering techniques. The application of three buffer layer options - CdS, ZnO and ZnSe was studied and limitations of each were characterized. The best device achieved 8.6% efficiency with a ZnO buffer. GaxOy formation at the junction interface was the main limiting factor of this device performance. For CdS / CIGS and ZnSe / CIGS superstrate devices extensive inter-diffusion between the absorber and buffer layer under CIGS growth conditions was the critical problem. Inter-diffusion severely deteriorated the junction quality and led to poorly behaved devices, despite different efforts to optimize the fabrication process.

Anisotropic structural and optical properties of semi-polar (11-22) GaN grown on m-plane sapphire using double AlN buffer layers.

PubMed

Zhao, Guijuan; Wang, Lianshan; Yang, Shaoyan; Li, Huijie; Wei, Hongyuan; Han, Dongyue; Wang, Zhanguo

2016-02-10

We report the anisotropic structural and optical properties of semi-polar (11-22) GaN grown on m-plane sapphire using a three-step growth method which consisted of a low temperature AlN buffer layer, followed by a high temperature AlN buffer layer and GaN growth. By introducing double AlN buffer layers, we substantially improve the crystal and optical qualities of semi-polar (11-22) GaN, and significantly reduce the density of stacking faults and dislocations. The high resolution x-ray diffraction measurement revealed that the in-plane anisotropic structural characteristics of GaN layer are azimuthal dependent. Transmission electron microscopy analysis showed that the majority of dislocations in the GaN epitaxial layer grown on m-sapphire are the mixed-type and the orientation of GaN layer was rotated 58.4° against the substrate. The room temperature photoluminescence (PL) spectra showed the PL intensity and wavelength have polarization dependence along parallel and perpendicular to the [1-100] axis (polarization degrees ~ 0.63). The realization of a high polarization semi-polar GaN would be useful to achieve III-nitride based lighting emission device for displays and backlighting.

Effect of Mg doping in ZnO buffer layer on ZnO thin film devices for electronic applications

NASA Astrophysics Data System (ADS)

Giri, Pushpa; Chakrabarti, P.

2016-05-01

Zinc Oxide (ZnO) thin films have been grown on p-silicon (Si) substrate using magnesium doped ZnO (Mg: ZnO) buffer layer by radio-frequency (RF) sputtering method. In this paper, we have optimized the concentration of Mg (0-5 atomic percent (at. %)) ZnO buffer layer to examine its effect on ZnO thin film based devices for electronic and optoelectronic applications. The crystalline nature, morphology and topography of the surface of the thin film have been characterized. The optical as well as electrical properties of the active ZnO film can be tailored by varying the concentration of Mg in the buffer layer. The crystallite size in the active ZnO thin film was found to increase with the Mg concentration in the buffer layer in the range of 0-3 at. % and subsequently decrease with increasing Mg atom concentration in the ZnO. The same was verified by the surface morphology and topography studies carried out with scanning electron microscope (SEM) and atomic electron microscopy (AFM) respectively. The reflectance in the visible region was measured to be less than 80% and found to decrease with increase in Mg concentration from 0 to 3 at. % in the buffer region. The optical bandgap was initially found to increase from 3.02 eV to 3.74 eV by increasing the Mg content from 0 to 3 at. % but subsequently decreases and drops down to 3.43 eV for a concentration of 5 at. %. The study of an Au:Pd/ZnO Schottky diode reveals that for optimum doping of the buffer layer the device exhibits superior rectifying behavior. The barrier height, ideality factor, rectification ratio, reverse saturation current and series resistance of the Schottky diode were extracted from the measured current voltage (I-V) characteristics.

Effect of different thickness crystalline SiC buffer layers on the ordering of MgB{sub 2} films probed by extended x-ray absorption fine structure

DOE Office of Scientific and Technical Information (OSTI.GOV)

Putri, W. B. K.; Tran, D. H.; Kang, B., E-mail: bwkang@chungbuk.ac.kr

2014-03-07

Extended X-ray absorption fine structure (EXAFS) spectroscopy is a powerful method to investigate the local structure of thin films. Here, we have studied EXAFS of MgB{sub 2} films grown on SiC buffer layers. Crystalline SiC buffer layers with different thickness of 70, 100, and 130 nm were deposited on the Al{sub 2}O{sub 3} (0001) substrates by using a pulsed laser deposition method, and then MgB{sub 2} films were grown on the SiC buffer layer by using a hybrid physical-chemical vapor deposition technique. Transition temperature of MgB{sub 2} film decreased with increasing thickness of SiC buffer layer. However, the T{sub c} droppingmore » went no farther than 100 nm-thick-SiC. This uncommon behavior of transition temperature is likely to be created from electron-phonon interaction in MgB{sub 2} films, which is believed to be related to the ordering of MgB{sub 2} atomic bonds, especially in the ordering of Mg–Mg bonds. Analysis from Mg K-edge EXAFS measurements showed interesting ordering behavior of MgB{sub 2} films. It is noticeable that the ordering of Mg–B bonds is found to decrease monotonically with the increase in SiC thickness of the MgB{sub 2} films, while the opposite happens with the ordering in Mg–Mg bonds. Based on these results, crystalline SiC buffer layers in MgB{sub 2} films seemingly have evident effects on the alteration of the local structure of the MgB{sub 2} film.« less

Direct solar-to-hydrogen conversion via inverted metamorphic multi-junction semiconductor architectures

DOE PAGES

Young, James L.; Steiner, Myles A.; Döscher, Henning; ...

2017-03-13

Solar water splitting via multi-junction semiconductor photoelectrochemical cells provides direct conversion of solar energy to stored chemical energy as hydrogen bonds. Economical hydrogen production demands high conversion efficiency to reduce balance-of-systems costs. For sufficient photovoltage, water-splitting efficiency is proportional to the device photocurrent, which can be tuned by judicious selection and integration of optimal semiconductor bandgaps. Here, we demonstrate highly efficient, immersed water-splitting electrodes enabled by inverted metamorphic epitaxy and a transparent graded buffer that allows the bandgap of each junction to be independently varied. Voltage losses at the electrolyte interface are reduced by 0.55 V over traditional, uniformly p-dopedmore » photocathodes by using a buried p-n junction. Lastly, advanced on-sun benchmarking, spectrally corrected and validated with incident photon-to-current efficiency, yields over 16% solar-to-hydrogen efficiency with GaInP/GaInAs tandem absorbers, representing a 60% improvement over the classical, high-efficiency tandem III-V device.« less

Direct solar-to-hydrogen conversion via inverted metamorphic multi-junction semiconductor architectures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Young, James L.; Steiner, Myles A.; Döscher, Henning

Solar water splitting via multi-junction semiconductor photoelectrochemical cells provides direct conversion of solar energy to stored chemical energy as hydrogen bonds. Economical hydrogen production demands high conversion efficiency to reduce balance-of-systems costs. For sufficient photovoltage, water-splitting efficiency is proportional to the device photocurrent, which can be tuned by judicious selection and integration of optimal semiconductor bandgaps. Here, we demonstrate highly efficient, immersed water-splitting electrodes enabled by inverted metamorphic epitaxy and a transparent graded buffer that allows the bandgap of each junction to be independently varied. Voltage losses at the electrolyte interface are reduced by 0.55 V over traditional, uniformly p-dopedmore » photocathodes by using a buried p-n junction. Lastly, advanced on-sun benchmarking, spectrally corrected and validated with incident photon-to-current efficiency, yields over 16% solar-to-hydrogen efficiency with GaInP/GaInAs tandem absorbers, representing a 60% improvement over the classical, high-efficiency tandem III-V device.« less

Characterization of ZrO2 buffer layers for sequentially evaporated Y-Ba-CuO on Si and Al2O3 substrates

NASA Technical Reports Server (NTRS)

Valco, George J.; Rohrer, Norman J.; Pouch, John J.; Warner, Joseph D.; Bhasin, Kul B.

1988-01-01

Thin film high temperature superconductors have the potential to change the microwave technology for space communications systems. For such applications it is desirable that the films be formed on substrates such as Al2O3 which have good microwave properties. The use of ZrO2 buffer layers between Y-Ba-Cu-O and the substrate has been investigated. These superconducting films have been formed by multilayer sequential electron beam evaporation of Cu, BaF2 and Y with subsequent annealing. The three layer sequence of Y/BaF2/Cu is repeated four times for a total of twelve layers. Such a multilayer film, approximately 1 micron thick, deposited directly on SrTiO3 and annealed at 900 C for 45 min produces a film with a superconducting onset of 93 K and critical temperature of 85 K. Auger electron spectroscopy in conjunction with argon ion sputtering was used to obtain the distribution of each element as a function of depth for an unannealed film, the annealed film on SrTiO3 and annealed films on ZrO2 buffer layers. The individual layers were apparent. After annealing, the bulk of the film on SrTiO3 is observed to be fairly uniform while films on the substrates with buffer layers are less uniform. The Y-Ba-Cu-O/ZrO2 interface is broad with a long Ba tail into the ZrO2, suggesting interaction between the film and the buffer layer. The underlying ZrO2/Si interface is sharper. The detailed Auger results are presented and compared with samples annealed at different temperatures and durations.

Strained layer Fabry-Perot device

DOEpatents

Brennan, Thomas M.; Fritz, Ian J.; Hammons, Burrell E.

1994-01-01

An asymmetric Fabry-Perot reflectance modulator (AFPM) consists of an active region between top and bottom mirrors, the bottom mirror being affixed to a substrate by a buffer layer. The active region comprises a strained-layer region having a bandgap and thickness chosen for resonance at the Fabry-Perot frequency. The mirrors are lattice matched to the active region, and the buffer layer is lattice matched to the mirror at the interface. The device operates at wavelengths of commercially available semiconductor lasers.

Polarization characteristics of semipolar (112̄2) InGaN/GaN quantum well structures grown on relaxed InGaN buffer layers and comparison with experiment.

PubMed

Park, Seoung-Hwan; Mishra, Dhaneshwar; Eugene Pak, Y; Kang, K; Park, Chang Yong; Yoo, Seung-Hyun; Cho, Yong-Hee; Shim, Mun-Bo; Kim, Sungjin

2014-06-16

Partial strain relaxation effects on polarization ratio of semipolar (112̄2) InxGa1−xN/GaN quantum well (QW) structures grown on relaxed InGaN buffers were investigated using the multiband effective-mass theory. The absolute value of the polarization ratio gradually decreases with increasing In composition in InGaN buffer layer when the strain relaxation ratio (ε0y′y′−εy′y′)/ε0y′y′ along y′-axis is assumed to be linearly proportional to the difference of lattice constants between the well and the buffer layer. Also, it changes its sign for the QW structure grown on InGaN buffer layer with a relatively larger In composition (x > 0.07). These results are in good agreement with the experiment. This can be explained by the fact that, with increasing In composition in the InGaN subsrate, the spontaneous emission rate for the y′-polarization gradually increases while that for x′-polarization decreases due to the decrease in a matrix element at the band-edge (k‖ = 0).

Buffer layers on biaxially textured metal substrates

DOEpatents

Shoup, Shara S.; Paranthamam, Mariappan; Beach, David B.; Kroeger, Donald M.; Goyal, Amit

2001-01-01

A method is disclosed for forming a biaxially textured buffer layer on a biaxially oriented metal substrate by using a sol-gel coating technique followed by pyrolyzing/annealing in a reducing atmosphere. This method is advantageous for providing substrates for depositing electronically active materials thereon.

Method to adjust multilayer film stress induced deformation of optics

DOEpatents

Mirkarimi, Paul B.; Montcalm, Claude

2000-01-01

A buffer-layer located between a substrate and a multilayer for counteracting stress in the multilayer. Depositing a buffer-layer having a stress of sufficient magnitude and opposite in sign reduces or cancels out deformation in the substrate due to the stress in the multilayer. By providing a buffer-layer between the substrate and the multilayer, a tunable, near-zero net stress results, and hence results in little or no deformation of the substrate, such as an optic for an extreme ultraviolet (EUV) lithography tool. Buffer-layers have been deposited, for example, between Mo/Si and Mo/Be multilayer films and their associated substrate reducing significantly the stress, wherein the magnitude of the stress is less than 100 MPa and respectively near-normal incidence (5.degree.) reflectance of over 60% is obtained at 13.4 nm and 11.4 nm. The present invention is applicable to crystalline and non-crystalline materials, and can be used at ambient temperatures.

Structural development of the Red Hill portion of the Feather River ultramafic complex, Pulmas County, California

DOE Office of Scientific and Technical Information (OSTI.GOV)

Weisenberg, C.W.

1979-01-01

The Feather River Ultramafic Complex is a partially serpentinized body of metamorphosed alpine peridotite and gabbro that lies along the northern part of the Melones fault zone, a NNW trending belt in the Northern Sierra Nevada. The complex was studied in the area of Red Hill, near the canyon of the North Fork, Feather River. The complex is separated from the Calaveras Terrain and Arlington Formation country rocks by steep faults; the Melones Fault on the east and the Rich Bar Fault on the west. Units recognized within the complex include Rich Bar metamorphic rocks, peridotite, metaperidotite, tremolite-olivine schist, hornblendemore » schist, and layered metagabbro. The Rich Bar metamorphic rocks are tectonic slices of amphibolite grade hornblende schist, mica schist, and quartzite found along the Rich Bar Fault. The complex shows evidence of 4 major events. E-1 (Pennsylvania-Permian) was formation of the peridotite-gabbro complex. E-2 (Permo-Triassic) consisted of pervasive shearing parallel to the Rich Bar Fault associated with initial emplacement within the Sierra Nevada. E-3 is believed to be compression and metamorphism (serpentinization) associated with the Nevadan orogeny. E-4 was associated with intrusion of nearby plutons. The regional association of the complex with late paleozoic arc volcanics of the Taylorsville area suggest formation near or under an island arc. Metamorphism during emplacement indicates association with the arc at that time. Left-lateral shear during emplacement along the Rich Bar Fault indicates NW directed thrusting when the layering in metagabbro is rotated to horizontal.« less

Metamorphism and plutonism around the middle and south forks of the Feather River, California

USGS Publications Warehouse

Hietanen, Anna Martta

1976-01-01

The area around the Middle and South Forks of the Feather River provides information on metamorphic and igneous processes that bear on the origin of andesitic and granitic magmas in general and on the variation of their potassium content in particular. In the north, the area joins the Pulga and Bucks Lake quadrangles studied previously. Tectonically, this area is situated in the southern part of an arcuate segment of the Nevadan orogenic belt in the northwestern Sierra Nevada. The oldest rocks are metamorphosed calcalkaline island-arc-type andesite, dacite, and sodarhyolite with interbedded tuff layers (the Franklin Canyon Formation), all probably correlative with Devonian rocks in the Klamath Mountains. Younger rocks form a sequence of volcanic, volcaniclastic, and sedimentary rocks including some limestone (The Horseshoe Bend Formation), probably Permian in age. All the volcanic and sedimentary rocks were folded and recrystallized to the greenschist facies during the Nevadan (Jurassic) orogeny and were invaded by monzotonalitic magmas shortly thereafter. A second lineation and metamorphism to the epidote-amphibolite facies developed in a narrow zone around the plutons. In light of the concept of plate tectonics, it is suggested that the early (Devonian?) island-arc-type andesite, dacite, and sodarhyolite (the Franklin Canyon Formation) were derived from the mantle above a Benioff zone by partial melting of peridotite in hydrous conditions. The water was probably derived from an oceanic plate descending to the mantle. Later (Permian?) magmas were mainly basaltic; some discontinuous layers of potassium-rich rhyolite indicate a change into anhydrous conditions and a deeper level of magma generation. The plutonic magmas that invaded the metamorphic rocks at the end of the Jurassic may contain material from the mantle, the subducted oceanic lithosphere, and the downfolded metamorphic rocks. The ratio of partial melts from these three sources may have changed with time, giving rise to the diversity in composition of magmas.

Polarization induced doped transistor

DOEpatents

Xing, Huili; Jena, Debdeep; Nomoto, Kazuki; Song, Bo; Zhu, Mingda; Hu, Zongyang

2016-06-07

A nitride-based field effect transistor (FET) comprises a compositionally graded and polarization induced doped p-layer underlying at least one gate contact and a compositionally graded and doped n-channel underlying a source contact. The n-channel is converted from the p-layer to the n-channel by ion implantation, a buffer underlies the doped p-layer and the n-channel, and a drain underlies the buffer.

Layer-based buffer aware rate adaptation design for SHVC video streaming

NASA Astrophysics Data System (ADS)

Gudumasu, Srinivas; Hamza, Ahmed; Asbun, Eduardo; He, Yong; Ye, Yan

2016-09-01

This paper proposes a layer based buffer aware rate adaptation design which is able to avoid abrupt video quality fluctuation, reduce re-buffering latency and improve bandwidth utilization when compared to a conventional simulcast based adaptive streaming system. The proposed adaptation design schedules DASH segment requests based on the estimated bandwidth, dependencies among video layers and layer buffer fullness. Scalable HEVC video coding is the latest state-of-art video coding technique that can alleviate various issues caused by simulcast based adaptive video streaming. With scalable coded video streams, the video is encoded once into a number of layers representing different qualities and/or resolutions: a base layer (BL) and one or more enhancement layers (EL), each incrementally enhancing the quality of the lower layers. Such layer based coding structure allows fine granularity rate adaptation for the video streaming applications. Two video streaming use cases are presented in this paper. The first use case is to stream HD SHVC video over a wireless network where available bandwidth varies, and the performance comparison between proposed layer-based streaming approach and conventional simulcast streaming approach is provided. The second use case is to stream 4K/UHD SHVC video over a hybrid access network that consists of a 5G millimeter wave high-speed wireless link and a conventional wired or WiFi network. The simulation results verify that the proposed layer based rate adaptation approach is able to utilize the bandwidth more efficiently. As a result, a more consistent viewing experience with higher quality video content and minimal video quality fluctuations can be presented to the user.

Conductive and robust nitride buffer layers on biaxially textured substrates

DOEpatents

Sankar, Sambasivan; Goyal, Amit; Barnett, Scott A.; Kim, Ilwon; Kroeger, Donald M.

2004-08-31

The present invention relates to epitaxial, electrically conducting and mechanically robust, cubic nitride buffer layers deposited epitaxially on biaxially textured substrates such as metal and alloys. The invention comprises of a biaxially textured substrate with epitaxial layers of nitrides. The invention also discloses a method to form such epitaxial layers using a high rate deposition method as well as without the use of forming gases. The invention further comprises epitaxial layers of oxides on the biaxially textured nitride layers. In some embodiments the article further comprises electromagnetic devices which may be super conducting properties.

Solution-processed MoS(x) as an efficient anode buffer layer in organic solar cells.

PubMed

Li, Xiaodong; Zhang, Wenjun; Wu, Yulei; Min, Chao; Fang, Junfeng

2013-09-25

We reported a facile solution-processed method to fabricate a MoSx anode buffer layer through thermal decomposition of (NH4)2MoS4. Organic solar cells (OSCs) based on in situ growth MoSx as the anode buffer layer showed impressive improvements, and the power conversion efficiency was higher than that of conventional PEDOT:PSS-based device. The MoSx films obtained at different temperatures and the corresponding device performance were systematically studied. The results indicated that both MoS3 and MoS2 were beneficial to the device performance. MoS3 could result in higher Voc, while MoS2 could lead to higher Jsc. Our results proved that, apart from MoO3, molybdenum sulfides and Mo(4+) were also promising candidates for the anode buffer materials in OSCs.

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).

Growth of ZnO(0001) on GaN(0001)/4H-SiC buffer layers by plasma-assisted hybrid molecular beam epitaxy

NASA Astrophysics Data System (ADS)

Adolph, David; Tingberg, Tobias; Ive, Tommy

2015-09-01

Plasma-assisted molecular beam epitaxy was used to grow ZnO(0001) layers on GaN(0001)/4H-SiC buffer layers deposited in the same growth chamber equipped with both N- and O-plasma sources. The GaN buffer layers were grown immediately before initiating the growth of ZnO. Using a substrate temperature of 445 °C and an O2 flow rate of 2.5 standard cubic centimeters per minute, we obtained ZnO layers with statistically smooth surfaces having a root-mean-square roughness of 0.3 nm and a peak-to-valley distance of 3 nm as revealed by atomic force microscopy. The full-width-at-half-maximum for x-ray rocking curves obtained across the ZnO(0002) and ZnO(10 1 bar 5) reflections was 198 and 948 arcsec, respectively. These values indicated that the mosaicity of the ZnO layer was comparable to the corresponding values of the underlying GaN buffer layer. Reciprocal space maps showed that the in-plane relaxation of the GaN and ZnO layers was 82% and 73%, respectively, and that the relaxation occurred abruptly during the growth. Room-temperature Hall-effect measurements revealed that the layers were inherently n-type and had an electron concentration of 1×1019 cm-3 and a Hall mobility of 51 cm2/V s.

High-Efficiency Polycrystalline CdS/CdTe Solar Cells on Buffered Commercial TCO-Coated Glass

NASA Astrophysics Data System (ADS)

Colegrove, E.; Banai, R.; Blissett, C.; Buurma, C.; Ellsworth, J.; Morley, M.; Barnes, S.; Gilmore, C.; Bergeson, J. D.; Dhere, R.; Scott, M.; Gessert, T.; Sivananthan, Siva

2012-10-01

Multiple polycrystalline CdS/CdTe solar cells with efficiencies greater than 15% were produced on buffered, commercially available Pilkington TEC Glass at EPIR Technologies, Inc. (EPIR, Bolingbrook, IL) and verified by the National Renewable Energy Laboratory (NREL). n-CdS and p-CdTe were grown by chemical bath deposition (CBD) and close space sublimation, respectively. Samples with sputter-deposited CdS were also investigated. Initial results indicate that this is a viable dry-process alternative to CBD for production-scale processing. Published results for polycrystalline CdS/CdTe solar cells with high efficiencies are typically based on cells using research-grade transparent conducting oxides (TCOs) requiring high-temperature processing inconducive to low-cost manufacturing. EPIR's results for cells on commercial glass were obtained by implementing a high-resistivity SnO2 buffer layer and by optimizing the CdS window layer thickness. The high-resistivity buffer layer prevents the formation of CdTe-TCO junctions, thereby maintaining a high open-circuit voltage and fill factor, whereas using a thin CdS layer reduces absorption losses and improves the short-circuit current density. EPIR's best device demonstrated an NREL-verified efficiency of 15.3%. The mean efficiency of hundreds of cells produced with a buffer layer between December 2010 and June 2011 is 14.4%. Quantum efficiency results are presented to demonstrate EPIR's progress toward NREL's best-published results.

A new approach to epitaxially grow high-quality GaN films on Si substrates: the combination of MBE and PLD.

PubMed

Wang, Wenliang; Wang, Haiyan; Yang, Weijia; Zhu, Yunnong; Li, Guoqiang

2016-04-22

High-quality GaN epitaxial films have been grown on Si substrates with Al buffer layer by the combination of molecular beam epitaxy (MBE) and pulsed laser deposition (PLD) technologies. MBE is used to grow Al buffer layer at first, and then PLD is deployed to grow GaN epitaxial films on the Al buffer layer. The surface morphology, crystalline quality, and interfacial property of as-grown GaN epitaxial films on Si substrates are studied systematically. The as-grown ~300 nm-thick GaN epitaxial films grown at 850 °C with ~30 nm-thick Al buffer layer on Si substrates show high crystalline quality with the full-width at half-maximum (FWHM) for GaN(0002) and GaN(102) X-ray rocking curves of 0.45° and 0.61°, respectively; very flat GaN surface with the root-mean-square surface roughness of 2.5 nm; as well as the sharp and abrupt GaN/AlGaN/Al/Si hetero-interfaces. Furthermore, the corresponding growth mechanism of GaN epitaxial films grown on Si substrates with Al buffer layer by the combination of MBE and PLD is hence studied in depth. This work provides a novel and simple approach for the epitaxial growth of high-quality GaN epitaxial films on Si substrates.

Experimental observation of motion of edge dislocations in Ge/Ge{sub x}Si{sub 1–x}/Si(001) (x = 0.2–0.6) heterostructures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bolkhovityanov, Yu. B., E-mail: bolkhov@isp.nsc.ru; Gutakovskii, A. K.; Deryabin, A. S.

2016-11-15

The Ge/Ge{sub x}Si{sub 1–x}/Si(001) (x = 0.2–0.6) heterostructures grown by the molecular epitaxy method are analyzed using high-resolution electron microscopy with atomic resolution. The thickness of the Ge{sub x}Si{sub 1–x} buffer layer is 7–35 nm. It is shown that such heterostructures relax in two stages: an ordered network of edge dislocations is formed during their growth (500°C) at the Ge/GeSi interface and then, contrary to the generally accepted opinion concerning their immobility, some of the edge dislocations move through the buffer GeSi layer to the GeSi/Si(001) interface during annealing at higher temperatures and x > 0.3. It is found thatmore » plastic relaxation of the GeSi buffer layer occurs due to motion of dislocation complexes of the edge type, consisting of a pair of complementary 60° dislocations with the ends of (111) extra planes located approximately at a distance from 2 to 12 interplanar spacings. It is shown that the penetration of dislocation complexes into the GeSi buffer layer and further to the GeSi/Si interface is intensified with increasing annealing temperature (600–800°C) and the fraction of Ge in the buffer layer.« less

Studies of molecular-beam epitaxy growth of GaAs on porous Si substrates

NASA Technical Reports Server (NTRS)

Mii, Y. J.; Kao, Y. C.; Wu, B. J.; Wang, K. L.; Lin, T. L.; Liu, J. K.

1988-01-01

GaAs has been grown on porous Si directly and on Si buffer layer-porous Si substrates by molecular-beam epitaxy. In the case of GaAs growth on porous Si, transmission electron microscopy (TEM) reveals that the dominant defects in GaAs layers grown on porous Si are microtwins and stacking faults, which originate from the GaAs/porous Si interface. GaAs is found to penetrate into the porous Si layers. By using a thin Si buffer layer (50 nm), GaAs penetration diminishes and the density of microtwins and stacking faults is largely reduced and localized at the GaAs/Si buffer interface. However, there is a high density of threading dislocations remaining. Both Si (100) aligned and four degree tilted substrates have been examined in this study. TEM results show no observable effect of the tilted substrates on the quality of the GaAs epitaxial layer.

Sol-gel deposition of buffer layers on biaxially textured metal substances

DOEpatents

Shoup, Shara S.; Paranthamam, Mariappan; Beach, David B.; Kroeger, Donald M.; Goyal, Amit

2000-01-01

A method is disclosed for forming a biaxially textured buffer layer on a biaxially oriented metal substrate by using a sol-gel coating technique followed by pyrolyzing/annealing in a reducing atmosphere. This method is advantageous for providing substrates for depositing electronically active materials thereon.

Structural and Optical Characteristics of Metamorphic Bulk InAsSb

DTIC Science & Technology

2014-01-01

0.815 0.820 0.825 InAsSb 5 /a ⊥ ( Å ) 3√2/a|| (Å) 0.25 0.40 0.75 1.3 1.5 1.8 2.2 hkl = 335 GaSb Structural and Optical Characteristics of Metamorphic...Conduction- and Valence- Band Energies in Bulk InAs1−xSbx and Type II InAs1−xSbx/InAs Strained-Layer Superlattices”, J. of Electron. Mater., 42, 918...0188 3. DATES COVERED (From - To) - UU UU UU UU Approved for public release; distribution is unlimited. Structural and Optical Characteristics of

Improvement of the interfacial Dzyaloshinskii-Moriya interaction by introducing a Ta buffer layer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kim, Nam-Hui; Jung, Jinyong; Cho, Jaehun

2015-10-05

We report systematic measurements of the interfacial Dzyaloshinskii-Moriya interaction (iDMI) by employing Brillouin light scattering in Pt/Co/AlO{sub x} and Ta/Pt/Co/AlO{sub x} structures. By introducing a tantalum buffer layer, the saturation magnetization and the interfacial perpendicular magnetic anisotropy are significantly improved due to the better interface between heavy metal and ferromagnetic layer. From the frequency shift between Stokes- and anti-Stokes spin-waves, we successively obtain considerably larger iDM energy densities (D{sub max} = 1.65 ± 0.13 mJ/m{sup 2} at t{sub Co} = 1.35 nm) upon adding the Ta buffer layer, despite the nominally identical interface materials. Moreover, the energy density shows an inverse proportionality with the Co layer thickness,more » which is the critical clue that the observed iDMI is indeed originating from the interface between the Pt and Co layers.« less

Epitaxial growth of YBa2Cu3O7 - delta films on oxidized silicon with yttria- and zirconia-based buffer layers

NASA Astrophysics Data System (ADS)

Pechen, E. V.; Schoenberger, R.; Brunner, B.; Ritzinger, S.; Renk, K. F.; Sidorov, M. V.; Oktyabrsky, S. R.

1993-09-01

A study of epitaxial growth of YBa2Cu3O7-δ films on oxidized Si with yttria- and zirconia-based buffer layers is reported. Using substrates with either SiO2 free or naturally oxidized (100) surfaces of Si it was found that a thin SiO2 layer on top of the Si favors high-quality superconducting film formation. Compared to yttria-stabilized ZrO2 (YSZ) single layers, YSZY2O3 double and YSZ/Y2O3YSZ triple layers allows the deposition of thin YBa2Cu3O7-δ films with improved properties including reduced aging effects. In epitaxial YBa2Cu3O7-δ films grown on the double buffer layers a critical temperature Tc(R=0)=89.5 K and critical current densities of 3.5×106 A/cm2 at 77 K and 1×107 A/cm2 at 66 K were reached.

Ultralow threading dislocation density in GaN epilayer on near-strain-free GaN compliant buffer layer and its applications in hetero-epitaxial LEDs

PubMed Central

Shih, Huan-Yu; Shiojiri, Makoto; Chen, Ching-Hsiang; Yu, Sheng-Fu; Ko, Chung-Ting; Yang, Jer-Ren; Lin, Ray-Ming; Chen, Miin-Jang

2015-01-01

High threading dislocation (TD) density in GaN-based devices is a long unresolved problem because of the large lattice mismatch between GaN and the substrate, which causes a major obstacle for the further improvement of next-generation high-efficiency solid-state lighting and high-power electronics. Here, we report InGaN/GaN LEDs with ultralow TD density and improved efficiency on a sapphire substrate, on which a near strain-free GaN compliant buffer layer was grown by remote plasma atomic layer deposition. This “compliant” buffer layer is capable of relaxing strain due to the absorption of misfit dislocations in a region within ~10 nm from the interface, leading to a high-quality overlying GaN epilayer with an unusual TD density as low as 2.2 × 105 cm−2. In addition, this GaN compliant buffer layer exhibits excellent uniformity up to a 6” wafer, revealing a promising means to realize large-area GaN hetero-epitaxy for efficient LEDs and high-power transistors. PMID:26329829

High-pressure crystallization vs. recrystallization origin of garnet pyroxenite-eclogite within subduction related lithologies

NASA Astrophysics Data System (ADS)

Faryad, S. W.; Jedlicka, R.; Hauzenberger, C.; Racek, M.

2018-03-01

Mafic layers displaying transition between clinopyroxenite and eclogite within peridotite from felsic granulite in the Bohemian Massif (Lower Austria) have been investigated. The mafic-ultramafic bodies shared a common granulite facies metamorphism with its hosting felsic rocks, but they still preserve evidence of eclogite facies metamorphism. The selected mafic layer for this study is represented by garnet with omphacite in the core of coarse-grained clinopyroxene, while fine-grained clinopyroxene in the matrix is diopside. In addition, garnet contains inclusions of omphacite, alkali feldspars, hydrous and other phases with halogens and/or CO2. Textural relations along with compositional zoning in garnet from the clinopyroxenite-eclogite layers favour solid-state recrystallization of the precursor minerals in the inclusions and formation of garnet and omphacite during subduction. Textures and major and trace element distribution in garnet indicate two stages of garnet growth that record eclogite facies and subsequent granulite facies overprint. The possible model explaining the textural and compositional changes of minerals is that the granulite facies overprint occurred after formation and exhumation of the eclogite facies rocks.

Propagation of misfit dislocations from buffer/Si interface into Si

DOEpatents

Liliental-Weber, Zuzanna [El Sobrante, CA; Maltez, Rogerio Luis [Porto Alegre, BR; Morkoc, Hadis [Richmond, VA; Xie, Jinqiao [Raleigh, VA

2011-08-30

Misfit dislocations are redirected from the buffer/Si interface and propagated to the Si substrate due to the formation of bubbles in the substrate. The buffer layer growth process is generally a thermal process that also accomplishes annealing of the Si substrate so that bubbles of the implanted ion species are formed in the Si at an appropriate distance from the buffer/Si interface so that the bubbles will not migrate to the Si surface during annealing, but are close enough to the interface so that a strain field around the bubbles will be sensed by dislocations at the buffer/Si interface and dislocations are attracted by the strain field caused by the bubbles and move into the Si substrate instead of into the buffer epi-layer. Fabrication of improved integrated devices based on GaN and Si, such as continuous wave (CW) lasers and light emitting diodes, at reduced cost is thereby enabled.

Fluid evolution during burial and Variscan deformation in the Lower Devonian rocks of the High-Ardenne slate belt (Belgium): sources and causes of high-salinity and C-O-H-N fluids

NASA Astrophysics Data System (ADS)

Kenis, I.; Muchez, Ph.; Verhaert, G.; Boyce, A.; Sintubin, M.

2005-08-01

Fluid inclusions in quartz veins of the High-Ardenne slate belt have preserved remnants of prograde and retrograde metamorphic fluids. These fluids were examined by petrography, microthermometry and Raman analysis to define the chemical and spatial evolution of the fluids that circulated through the metamorphic area of the High-Ardenne slate belt. The earliest fluid type was a mixed aqueous/gaseous fluid (H2O-NaCl-CO2-(CH4-N2)) occurring in growth zones and as isolated fluid inclusions in both the epizonal and anchizonal part of the metamorphic area. In the central part of the metamorphic area (epizone), in addition to this mixed aqueous/gaseous fluid, primary and isolated fluid inclusions are also filled with a purely gaseous fluid (CO2-N2-CH4). During the Variscan orogeny, the chemical composition of gaseous fluids circulating through the Lower Devonian rocks in the epizonal part of the slate belt, evolved from an earlier CO2-CH4-N2 composition to a later composition enriched in N2. Finally, a late, Variscan aqueous fluid system with a H2O-NaCl composition migrated through the Lower Devonian rocks. This latest type of fluid can be observed in and outside the epizonal metamorphic part of the High-Ardenne slate belt. The chemical composition of the fluids throughout the metamorphic area, shows a direct correlation with the metamorphic grade of the host rock. In general, the proportion of non-polar species (i.e. CO2, CH4, N2) with respect to water and the proportion of non-polar species other than CO2 increase with increasing metamorphic grade within the slate belt. In addition to this spatial evolution of the fluids, the temporal evolution of the gaseous fluids is indicative for a gradual maturation due to metamorphism in the central part of the basin. In addition to the maturity of the metamorphic fluids, the salinity of the aqueous fluids also shows a link with the metamorphic grade of the host-rock. For the earliest and latest fluid inclusions in the anchizonal part of the High-Ardenne slate belt the salinity varies respectively between 0 and 3.5 eq.wt% NaCl and between 0 and 2.7 eq.wt% NaCl, while in the epizonal part the salinity varies between 0.6 and 17 eq.wt% NaCl and between 3 and 10.6 eq.wt% for the earliest and latest aqueous fluid inclusions, respectively. Although high salinity fluids are often attributed to the original sedimentary setting, the increasing salinity of the fluids that circulated through the Lower Devonian rocks in the High-Ardenne slate belt can be directly attributed to regional metamorphism. More specifically the salinity of the primary fluid inclusions is related to hydrolysis reactions of Cl-bearing minerals during prograde metamorphism, while the salinity of the secondary fluid inclusions is rather related to hydration reactions during retrograde metamorphism. The temporal and spatial distribution of the fluids in the High-Ardenne slate belt are indicative for a closed fluid flow system present in the Lower Devonian rocks during burial and Variscan deformation, where fluids were in thermal and chemical equilibrium with the host rock. Such a closed fluid flow system is confirmed by stable isotope study of the veins and their adjacent host rock for which uniform δ180 values of both the veins and their host rock demonstrate a rock-buffered fluid flow system.

Growth and characterization of an InSb infrared photoconductor on Si via an AlSb/GaSb buffer

NASA Astrophysics Data System (ADS)

Jia, Bo Wen; Tan, Kian Hua; Loke, Wan Khai; Wicaksono, Satrio; Yoon, Soon Fatt

2018-05-01

A 99.6% relaxed InSb layer is grown on a 6° offcut (1 0 0) Si substrate via an AlSb/GaSb buffer using molecular beam epitaxy (MBE). A 200 nm GaSb buffer is first grown on Si and the lattice mismatch between them is accommodated by an interfacial misfit (IMF) array consisting of uniformly distributed 90° misfit dislocations. Si delta doping is introduced during the growth of GaSb to reduce the density of threading dislocation. Subsequently, a 50 nm AlSb buffer is grown followed by a 0.8 μm InSb layer. The InSb layer exhibits a 300 K electron mobility of 22,300 cm2/Vs. An InSb photoconductor on Si is demonstrated with a photoconductive gain from 77 K to 200 K under a 700 °C maintained blackbody.

Kulkeite, a new metamorphic phyllosilicate mineral: Ordered 1∶1 chlorite/talc mixed-layer

NASA Astrophysics Data System (ADS)

Schreyer, W.; Medenbach, O.; Abraham, K.; Gebert, W.; Müller, W. F.

1982-09-01

Kulkeite occurs as platy, colorless, porphyroblastic, single crystals up to 2 mm in size in a low-grade dolomite rock associated with a Triassic meta-evaporite series at Derrag, Tell Atlas, Algeria, It is associated with sodian aluminian talc, unusual chlorite polytypes, and both K and Na phlogopite. Kulkeite is optically biaxial, negative, n x=1.552, n y=1.5605, n z=1.5610, 2Vz=24° (obs.). Based on microprobe analysis the empirical formula is (Na0.38K0.01Ca0.01)(Mg8.02Al0.99)[Al1.43Si6.57O20](OH)10 with some variation in Na, Si, and tetrahedral Al. The crystals are monoclinic with a=5.319(1), b=9.195(2), c=23.897(10) Å, β=97° 1(3)'; Z=2; the calculated density is 2.70 g cm-3. The four strongest lines in the X-ray powder pattern are (d, I, hkl): 7.90, 100, 003; 1.533, 100, 060; 7.42, 80, 002; 3.38, 80, 007; the 001 reflection with 23.7 Å has intensity 10. Transmission electron microscopy confirms the nature of a regular 1∶1 mixed-layer, which consists of 14 Å chlorite (clinochlore) sheets alternating with sheets of one-layer (9.5 Å) talc characterized by the lattice substitution NaAl→Si just as in the talc occurring as a discrete mineral co-existing with kulkeite. Kulkeite is intergrown with lamellae of clinochlore that represent two-layer and five-layer (70 Å) polytypes with optical birefringence exceeding the normal value for clinochlore by a factor of 3. The origin of kulkeite is due to low-grade metamorphism with temperatures probably not exceeding 400° C. As the clinochlore lamellae and sodian aluminian talc are found in mutual contact, kulkeite seems to represent a metastable mineral at least during the latest phase of metamorphism. However, at an earlier stage, prior to clinochlore formation, kulkeite might have been stable, and the incorporation of Na and Al into its talc component could indeed be the decisive factor for the formation of the mixed-layer.

SnS2 films deposited from molecular ink as Cd-free alternative buffer layer for solar cells

NASA Astrophysics Data System (ADS)

Jariwala, Akshay; Chaudhuri, Tapas K.; Toshniwal, Aditi; Patel, Sanjay; Kheraj, Vipul; Ray, Abhijit

2018-05-01

This work investigates the potential of SnS2 as a Cd-free alternative buffer layer for CIGS solar cells. The suitability of SnS2 film as a buffer layer has been evaluated by numerical analysis using SCAPS software. A new simple method for preparation of SnS2 films by dip-coating from molecular ink is reported. The formation of SnS2 is confirmed by Raman spectroscopy. The films are smooth and shiny with roughness of 2-3 nm. The films are n-type with band gap of 2.6 eV and electrical conductivity of 10-3 S/cm.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ok, Kyung-Chul; Park, Jin-Seong, E-mail: hkim-2@naver.com, E-mail: jsparklime@hanyang.ac.kr; Ko Park, Sang-Hee

We demonstrated the fabrication of flexible amorphous indium gallium zinc oxide thin-film transistors (TFTs) on high-temperature polyimide (PI) substrates, which were debonded from the carrier glass after TFT fabrication. The application of appropriate buffer layers on the PI substrates affected the TFT performance and stability. The adoption of the SiN{sub x}/AlO{sub x} buffer layers as water and hydrogen diffusion barriers significantly improved the device performance and stability against the thermal annealing and negative bias stress, compared to single SiN{sub x} or SiO{sub x} buffer layers. The substrates could be bent down to a radius of curvature of 15 mm and themore » devices remained normally functional.« less

Effect of buffer layer on photoresponse of MoS2 phototransistor

NASA Astrophysics Data System (ADS)

Miyamoto, Yuga; Yoshikawa, Daiki; Takei, Kuniharu; Arie, Takayuki; Akita, Seiji

2018-06-01

An atomically thin MoS2 field-effect transistor (FET) is expected as an ultrathin photosensor with high sensitivity. However, a persistent photoconductivity phenomenon prevents high-speed photoresponse. Here, we investigate the photoresponse of a MoS2 FET with a thin Al2O3 buffer layer on a SiO2 gate insulator. The application of a 2-nm-thick Al2O3 buffer layer greatly improves not only the steady state properties but also the response speed from 1700 to 0.2 s. These experimental results are well explained by the random localized potential fluctuation model combined with the model based on the recombination of the bounded electrons around the trapped hole.

Buffer-regulated biocorrosion of pure magnesium.

PubMed

Kirkland, Nicholas T; Waterman, Jay; Birbilis, Nick; Dias, George; Woodfield, Tim B F; Hartshorn, Richard M; Staiger, Mark P

2012-02-01

Magnesium (Mg) alloys are being actively investigated as potential load-bearing orthopaedic implant materials due to their biodegradability in vivo. With Mg biomaterials at an early stage in their development, the screening of alloy compositions for their biodegradation rate, and hence biocompatibility, is reliant on cost-effective in vitro methods. The use of a buffer to control pH during in vitro biodegradation is recognised as critically important as this seeks to mimic pH control as it occurs naturally in vivo. The two different types of in vitro buffer system available are based on either (i) zwitterionic organic compounds or (ii) carbonate buffers within a partial-CO(2) atmosphere. This study investigated the influence of the buffering system itself on the in vitro corrosion of Mg. It was found that the less realistic zwitterion-based buffer did not form the same corrosion layers as the carbonate buffer, and was potentially affecting the behaviour of the hydrated oxide layer that forms on Mg in all aqueous environments. Consequently it was recommended that Mg in vitro experiments use the more biorealistic carbonate buffering system when possible.

Method for improving performance of high temperature superconductors within a magnetic field

DOEpatents

Wang, Haiyan; Foltyn, Stephen R.; Maiorov, Boris A.; Civale, Leonardo

2010-01-05

The present invention provides articles including a base substrate including a layer of an oriented cubic oxide material having a rock-salt-like structure layer thereon; and, a buffer layer upon the oriented cubic oxide material having a rock-salt-like structure layer, the buffer layer having an outwardly facing surface with a surface morphology including particulate outgrowths of from 10 nm to 500 run in size at the surface, such particulate outgrowths serving as flux pinning centers whereby the article maintains higher performance within magnetic fields than similar articles without the necessary density of such outgrowths.

Portable heatable container

NASA Technical Reports Server (NTRS)

Yang, L. C. (Inventor)

1980-01-01

A container is provided which can be designed to heat its outer surface to sterilize it, or to heat its inner surface and any contents therewithin. In a container that self sterilizes its outer surface, the container includes a combustible layer of thermite-type pyrotechnic material which can be ignited to generate considerable heat, and a thin casing around the combustible layer which is of highly thermally conductive materials such as aluminum which can be heated to a high temperature by the ignited combustible layer. A buffer layer which may be of metal, lies within the combustible layer, and a layer of insulation such as Teflon lies within the buffer layer to insulate the contents of the container from the heat.

Portable heatable container

NASA Astrophysics Data System (ADS)

Yang, L. C.

1980-03-01

A container is provided which can be designed to heat its outer surface to sterilize it, or to heat its inner surface and any contents therewithin. In a container that self sterilizes its outer surface, the container includes a combustible layer of thermite-type pyrotechnic material which can be ignited to generate considerable heat, and a thin casing around the combustible layer which is of highly thermally conductive materials such as aluminum which can be heated to a high temperature by the ignited combustible layer. A buffer layer which may be of metal, lies within the combustible layer, and a layer of insulation such as Teflon lies within the buffer layer to insulate the contents of the container from the heat.

Effects of V2O3 buffer layers on sputtered VO2 smart windows: Improved thermochromic properties, tunable width of hysteresis loops and enhanced durability

NASA Astrophysics Data System (ADS)

Long, Shiwei; Cao, Xun; Sun, Guangyao; Li, Ning; Chang, Tianci; Shao, Zewei; Jin, Ping

2018-05-01

Vanadium dioxide (VO2) is one of the most well-known thermochromic materials, which exhibits a notable optical change from transparent to reflecting in the infrared region upon a metal-insulator phase transition. For practical applications, VO2 thin films should be in high crystalline quality to obtain a strong solar modulation ability (ΔTsol). Meanwhile, narrow hysteresis loops and robust ambient durability are also indispensable for sensitivity and long-lived utilization, respectively. In this work, a series of high-quality V2O3/VO2 bilayer structures were grown on quartz glass substrates by reactive magnetron sputtering. Basically, the bottom V2O3 acts as the buffer layer to improve the crystallinity of the top VO2, while the VO2 serves as the thermochromic layer to guarantee the solar modulation ability for energy-saving. We observed an obvious increase in ΔTsol of 76% (from 7.5% to 13.2%) for VO2 films after introducing V2O3 buffer layers. Simultaneously, a remarkable reduction by 79% (from 21.9 °C to 4.7 °C) in width of hysteresis loop was obtained when embedding 60 nm V2O3 buffer for 60 nm VO2. In addition, VO2 with non-stoichiometry of V2O3±x buffer demonstrates a broadening hysteresis loops width, which is derived from the lattice distortion caused by lattice imperfection. Finally, durability of VO2 has been significantly improved due to positive effects of V2O3 buffer layer. Our results lead to a comprehensive enhancement in crystallinity of VO2 and shed new light on the promotion of thermochromic property by homologous oxides for VO2.

MBE grown III-V strain relaxed buffer layers and superlattices characterized by atomic force microscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Howard, A.J.; Fritz, I.J.; Drummond, T.J.

1993-11-01

Using atomic force microscopy (AFM), the authors have investigated the effects of growth temperature and dopant incorporation on the surface morphology of MBE grown graded buffer layers and strained layer superlattices (SLSs) in the InGaAlAs/GaAs and InAsSb/InSb material systems. The AFM results show quantitatively that over the temperature range from 380 to 545 C, graded in{sub x}Al{sub 1{minus}x}As(x = 0.05 {minus} 0.32) buffer layers grown at high temperatures ({approximately}520 C), and graded In{sub x}Ga{sub 1{minus}x}As (x = 0.05 {minus} 0.33) buffer layers and In{sub 0.4}Ga{sub 0.6}As/In{sub 0.26}Al{sub 0.35}Ga{sub 0.39}As SLSs grown at low temperatures ({approximately}400 C) have the lowest RMSmore » roughness. Also, for SLSs InAs{sub 0.21}Sb{sub 0.79}/InSb, undoped layers grown at 470 C were smoother than undoped layers grown at 420 C and Be-doped layers grown at 470 C. These results illustrate the role of surface tension in the growth of strained layer materials near the melting temperature of the InAs{sub x}Sb{sub {minus}x}/InSb superlattice. Nomarski interference and transmission electron microscopies, IR photoluminescence, x-ray diffraction, and photocurrent spectroscopy were also used to evaluate the relative quality of the material but usually, the results were not conclusive.« less

Demonstrating antiphase domain boundary-free GaAs buffer layer on zero off-cut Si (0 0 1) substrate for interfacial misfit dislocation GaSb film by metalorganic chemical vapor deposition

NASA Astrophysics Data System (ADS)

Ha, Minh Thien Huu; Hoang Huynh, Sa; Binh Do, Huy; Nguyen, Tuan Anh; Luc, Quang Ho; Chang, Edward Yi

2017-08-01

High quality 40 nm GaSb thin film was grown on the zero off-cut Si (0 0 1)-oriented substrate using metalorganic chemical vapor deposition with the temperature-graded GaAs buffer layer. The growth time of the GaAs nucleation layer, which was deposited at a low temperature of 490 °C, is systematically investigated in this paper. Cross-sections of the high resolution transmission electron microscopy images indicate that the GaAs compound formed 3D-islands first before to quasi-2D islands, and finally formed uniform GaAs layer. The optimum thickness of the 490 °C-GaAs layer was found to be 10 nm to suppress the formation of antiphase domain boundaries (APDs). The thin GaAs nucleation layer had a root-mean-square surface roughness of 0.483 nm. This allows the continued high temperature GaAs buffer layer to be achieved with low threading dislocation density of around 7.1  ×  106 cm-2 and almost invisible APDs. Finally, a fully relaxed GaSb film was grown on the top of the GaAs/Si heterostructure using interfacial misfit dislocation growth mode. These results indicate that the GaSb epitaxial layer can be grown on Si substrate with GaAs buffer layer for future p-channel metal-oxide-semiconductor field effect transistors (MOSFETs) applications.

Investigations of YBa2Cu3O y films sputtered onto a substrate of amorphous quartz with a platinum buffer layer

NASA Astrophysics Data System (ADS)

Blinova, Yu. V.; Snigirev, O. V.; Porokhov, N. V.; Evlashin, S. A.

2017-10-01

Results of investigations using X-ray diffraction and scanning electron microscopy of composite materials made from YBa2Cu3O y films sputtered (using various regimes) onto a substrate of amorphous quartz with a platinum buffer layer, have been given.

Fabrication and properties of ZnO/GaN heterostructure nanocolumnar thin film on Si (111) substrate

PubMed Central

2013-01-01

Zinc oxide thin films have been obtained on bare and GaN buffer layer decorated Si (111) substrates by pulsed laser deposition (PLD), respectively. GaN buffer layer was achieved by a two-step method. The structure, surface morphology, composition, and optical properties of these thin films were investigated by X-ray diffraction, field emission scanning electron microscopy, infrared absorption spectra, and photoluminiscence (PL) spectra, respectively. Scanning electron microscopy images indicate that the flower-like grains were presented on the surface of ZnO thin films grown on GaN/Si (111) substrate, while the ZnO thin films grown on Si (111) substrate show the morphology of inclination column. PL spectrum reveals that the ultraviolet emission efficiency of ZnO thin film on GaN buffer layer is high, and the defect emission of ZnO thin film derived from Zni and Vo is low. The results demonstrate that the existence of GaN buffer layer can greatly improve the ZnO thin film on the Si (111) substrate by PLD techniques. PMID:23448090

Fabrication and properties of ZnO/GaN heterostructure nanocolumnar thin film on Si (111) substrate.

PubMed

Wei, Xianqi; Zhao, Ranran; Shao, Minghui; Xu, Xijin; Huang, Jinzhao

2013-02-28

Zinc oxide thin films have been obtained on bare and GaN buffer layer decorated Si (111) substrates by pulsed laser deposition (PLD), respectively. GaN buffer layer was achieved by a two-step method. The structure, surface morphology, composition, and optical properties of these thin films were investigated by X-ray diffraction, field emission scanning electron microscopy, infrared absorption spectra, and photoluminiscence (PL) spectra, respectively. Scanning electron microscopy images indicate that the flower-like grains were presented on the surface of ZnO thin films grown on GaN/Si (111) substrate, while the ZnO thin films grown on Si (111) substrate show the morphology of inclination column. PL spectrum reveals that the ultraviolet emission efficiency of ZnO thin film on GaN buffer layer is high, and the defect emission of ZnO thin film derived from Zni and Vo is low. The results demonstrate that the existence of GaN buffer layer can greatly improve the ZnO thin film on the Si (111) substrate by PLD techniques.

Great enhancement of pyroelectric properties for Ba{sub 0.65}Sr{sub 0.35}TiO{sub 3} films on Pt-Si substrates by inserting a self-buffered layer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu, C. G.; Li, Y. R.; Zhu, J.

2009-02-15

(100)-Ba{sub 0.65}Sr{sub 0.35}TiO{sub 3} (BST) films were deposited on Pt/Ti/SiO{sub 2}/Si substrates using a low-temperature self-buffered layer. X-ray diffraction and atomic force microscope investigations show that the microstructure of BST films strongly depends on surface morphology of annealed self-buffered layer. The mechanism of nucleus formation and the growth initiation of BST films on self-buffered layers were proposed. It was found that the pyroelectric properties of BST films can be greatly enhanced. The pyroelectric coefficient and material merit figure of (100)-BST films are 1.16x10{sup 4} {mu}C m{sup -2} K{sup -1} and 2.18x10{sup -4} Pa{sup -1/2}, respectively. The detectivity of 9.4x10{sup 7}more » cm Hz{sup 1/2} W{sup -1} was obtained in the (100)-BST film capacitors thermally isolated by 500 nm SiO{sub 2} films.« less

Improvement in performance and reliability with CF4 plasma pretreatment on the buffer oxide layer for low-temperature polysilicon thin-film transistor

NASA Astrophysics Data System (ADS)

Fan, Ching-Lin; Lin, Yi-Yan; Yang, Chun-Chieh

2012-03-01

This study applies CF4 plasma pretreatment to a buffer oxide layer to improve the performance of low-temperature polysilicon thin-film transistors (LTPS TFTs). Results show that the fluorine atoms piled up at the interface between the bulk channel and buffer oxide layer and accumulated in the bulk channel. The reduction of the trap states density by fluorine passivation can improve the electrical characteristics of the LTPS TFTs. It is found that the threshold voltage reduced from 4.32 to 3.03 V and the field-effect mobility increased from 29.71 to 45.65 cm2 V-1 S-1. In addition, the on current degradation and threshold voltage shift after stressing were significantly improved about 31% and 70%, respectively. We believe that the proposed CF4 plasma pretreatment on the buffer oxide layer can passivate the trap states and avoid the plasma induced damage on the polysilicon channel surface, resulting in the improvement in performance and reliability for LTPS-TFT mass production application on AMOLED displays with critical reliability requirement.

High performance polymer solar cells with as-prepared zirconium acetylacetonate film as cathode buffer layer

PubMed Central

Tan, Zhan'ao; Li, Shusheng; Wang, Fuzhi; Qian, Deping; Lin, Jun; Hou, Jianhui; Li, Yongfang

2014-01-01

Low-work-function active metals are commonly used as cathode in polymer solar cells (PSCs), but sensitivity of the active metals towards moisture and oxygen results in poor stability of the devices. Therefore, solution-proceessable and stable cathode buffer layer is of great importance for the application of PSCs. Here we demonstrate high performance PSCs by employing as-prepared zirconium acetylacetonate (a-ZrAcac) film spin-cast from its ethanol solution as cathode buffer layer. The PSCs based on a low bandgap polymer PBDTBDD as donor and PC60BM as acceptor with a-ZrAcac/Al cathode demonstrated an average power conversion efficiency (PCE) of 8.75% which is significantly improved than that of the devices with traditional Ca/Al cathode. The improved photovoltaic performance is benefitted from the decreased series resistance and enhanced light harvest of the PSCs with the a-ZrAcac/Al cathode. The results indicate that a-ZrAcac is a promising high performance cathode buffer layer for fabricating large area flexible PSCs. PMID:24732976

Annealing induced structural changes in amorphous Co{sub 23}Fe{sub 60}B{sub 17} film on Mo buffer layer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dwivedi, Jagrati, E-mail: jdwivedi.phy@gmail.com; Mishra, Ashutosh; Gupta, Ranjeeta

2016-05-23

Structural changes occurring in a thin amorphous Co{sub 23}Fe{sub 60}B{sub 17} film sandwiched between two Mo layers, as a function of thermal annealing has been studied. Thermal stability of the Co{sub 23}Fe{sub 60}B{sub 17} film is found to be significantly lower than the bulk ribbons. SIMS measurements show that during crystallization, boron which is expelled out of the crystallites, has a tendency to move towards the surface. No significant diffusion of boron in Mo buffer layer is observed. This result is in contrast with some earlier studies where it was proposed that the role of buffer layer of refractory metalmore » is to absorb boron which is expelled out of the bcc FeCo phase during crystallization.« less

High bandgap III-V alloys for high efficiency optoelectronics

DOEpatents

Alberi, Kirstin; Mascarenhas, Angelo; Wanlass, Mark

2017-01-10

High bandgap alloys for high efficiency optoelectronics are disclosed. An exemplary optoelectronic device may include a substrate, at least one Al.sub.1-xIn.sub.xP layer, and a step-grade buffer between the substrate and at least one Al.sub.1-xIn.sub.xP layer. The buffer may begin with a layer that is substantially lattice matched to GaAs, and may then incrementally increase the lattice constant in each sequential layer until a predetermined lattice constant of Al.sub.1-xIn.sub.xP is reached.

Optimization by simulation of the nature of the buffer, the gap profile of the absorber and the thickness of the various layers in CZTSSe solar cells

NASA Astrophysics Data System (ADS)

Chadel, Meriem; Chadel, Asma; Moustafa Bouzaki, Mohammed; Aillerie, Michel; Benyoucef, Boumediene; Charles, Jean-Pierre

2017-11-01

Performances of ZnO/ZnS/CZTSSe polycrystalline thin film solar cells (Copper Zinc Tin Sulphur Selenium-solar cell) were simulated for different thicknesses of the absorber and ZnS buffer layers. Simulations were performed with SCAPS (Solar Cell Capacitance Simulator) software, starting with actual parameters available from industrial data for commercial cells processing. The influences of the thickness of the various layers in the structure of the solar cell and the gap profile of the CZTSSe absorber layer on the performance of the solar cell were studied in detail. Through considerations of recent works, we discuss possible routes to enhance the performance of CZTSSe solar cells towards a higher efficiency level. Thus, we found that for one specific thickness of the absorber layer, the efficiency of the CZTSSe solar cell can be increased when a ZnS layer replaces the usual CdS buffer layer. On the other hand, the efficiency of the solar cell can be also improved when the absorber layer presents a grad-gap. In this case, the maximum efficiency for the CZTSSe cell was found equal to 13.73%.

Series interconnected photovoltaic cells and method for making same

DOEpatents

Albright, S.P.; Chamberlin, R.R.; Thompson, R.A.

1995-01-31

A novel photovoltaic module and method for constructing the same are disclosed. The module includes a plurality of photovoltaic cells formed on a substrate and laterally separated by interconnection regions. Each cell includes a bottom electrode, a photoactive layer and a top electrode layer. Adjacent cells are connected in electrical series by way of a conductive-buffer line. The buffer line is also useful in protecting the bottom electrode against severing during downstream layer cutting processes. 11 figs.

Strain relaxation of thin Si{sub 0.6}Ge{sub 0.4} grown with low-temperature buffers by molecular beam epitaxy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhao, M.; Hansson, G. V.; Ni, W.-X.

A double-low-temperature-buffer variable-temperature growth scheme was studied for fabrication of strain-relaxed thin Si{sub 0.6}Ge{sub 0.4} layer on Si(001) by using molecular beam epitaxy (MBE), with particular focuses on the influence of growth temperature of individual low-temperature-buffer layers on the relaxation process and final structural qualities. The low-temperature buffers consisted of a 40 nm Si layer grown at an optimized temperature of {approx}400 deg. C, followed by a 20 nm Si{sub 0.6}Ge{sub 0.4} layer grown at temperatures ranging from 50 to 550 deg. C. A significant relaxation increase together with a surface roughness decrease both by a factor of {approx}2, accompaniedmore » with the cross-hatch/cross-hatch-free surface morphology transition, took place for the sample containing a low-temperature Si{sub 0.6}Ge{sub 0.4} layer that was grown at {approx}200 deg. C. This dramatic change was explained by the association with a certain onset stage of the ordered/disordered growth transition during the low-temperature MBE, where the high density of misfit dislocation segments generated near surface cusps largely facilitated the strain relaxation of the top Si{sub 0.6}Ge{sub 0.4} layer.« less

Power Conversion Efficiency and Device Stability Improvement of Inverted Perovskite Solar Cells by Using a ZnO:PFN Composite Cathode Buffer Layer.

PubMed

Jia, Xiaorui; Zhang, Lianping; Luo, Qun; Lu, Hui; Li, Xueyuan; Xie, Zhongzhi; Yang, Yongzhen; Li, Yan-Qing; Liu, Xuguang; Ma, Chang-Qi

2016-07-20

We have demonstrated in this article that both power conversion efficiency (PCE) and performance stability of inverted planar heterojunction perovskite solar cells can be improved by using a ZnO:PFN nanocomposite (PFN: poly[(9,9-bis(3'-(N,N-dimethylamion)propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctyl)-fluorene]) as the cathode buffer layer (CBL). This nanocomposite could form a compact and defect-less CBL film on the perovskite/PC61BM surface (PC61BM: phenyl-C61-butyric acid methyl ester). In addition, the high conductivity of the nanocomposite layer makes it works well at a layer thickness of 150 nm. Both advantages of the composite layer are helpful in reducing interface charge recombination and improving device performance. The power conversion efficiency (PCE) of the best ZnO:PFN CBL based device was measured to be 12.76%, which is higher than that of device without CBL (9.00%), or device with ZnO (7.93%) or PFN (11.30%) as the cathode buffer layer. In addition, the long-term stability is improved by using ZnO:PFN composite cathode buffer layer when compare to that of the reference cells. Almost no degradation of open circuit voltage (VOC) and fill factor (FF) was found for the device having ZnO:PFN, suggesting that ZnO:PFN is able to stabilize the interface property and consequently improve the solar cell performance stability.

High Temperature Superconducting Thick Films

DOEpatents

Arendt, Paul N.; Foltyn, Stephen R.; Groves, James R.; Holesinger, Terry G.; Jia, Quanxi

2005-08-23

An article including a substrate, a layer of an inert oxide material upon the surface of the substrate, (generally the inert oxide material layer has a smooth surface, i.e., a RMS roughness of less than about 2 nm), a layer of an amorphous oxide or oxynitride material upon the inert oxide material layer, a layer of an oriented cubic oxide material having a rock-salt-like structure upon the amorphous oxide material layer is provided together with additional layers such as at least one layer of a buffer material upon the oriented cubic oxide material layer or a HTS top-layer of YBCO directly upon the oriented cubic oxide material layer. With a HTS top-layer of YBCO upon at least one layer of a buffer material in such an article, Jc's of 1.4×106 A/cm2 have been demonstrated with projected Ic's of 210 Amperes across a sample 1 cm wide.

Metamorphic reactions in ruby corundum amphibolite from the Chunky Gal Mountain mafic-ultramafic complex, Clay County, North Carolina

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ranson, W.A.; Garihan, J.M.; Ulmer, K.E.

1992-01-01

Amphibolite outcrops of unusual mineralogy within the Chunky Gal Mountain mafic-ultramafic complex display cm-scale rhythmic layers with moderate-steep dips. Layers are troctolitic, gabbroic, and anorthositic in composition, locally in contact with dunite of the Buck Creek ultramafic body. Meta-gabbroic layers contain striking bladed, emerald green amphibole as the chief mafic phase and relict bronzite with reacted margins. An additional major phase is plagioclase, [approximately]An 95 based on microprobe analysis. Ruby corundum is a minor (> 5%) constituent, which in some of the gabbroic rocks is mantled by a reaction rim of fibrolite. The clinoamphibole has optical properties resembling magnesio-cummingtonite: colorlessmore » to pale green in plane light with (+) sign and 2V = 60--70[degree]. However, microprobe analysis of the clinoamphibole indicates alumino-magnesio-hornblende. Although the texture of the bronzite shows that it is breaking down, it is clear that the clinoamphibole and corundum could not be the reaction products without the addition of Al, Ca, and Si in an aqueous fluid. Associated meta-troctolitic layers contain plagioclase and coarse, anhedral olivines displaying an inner corona of bladed orthopyroxene, rimmed by symplectite. The granulite facies reactions is: plagioclase + olivine = clinopyroxene + garnet. The mesoscopic-scale proximity of troctolitic and gabbroic rhythmic layers indicates both underwent granulite facies metamorphism. Retrogression to amphibolite grade is apparent only in the gabbroic layers, resulting in assemblages distinguished locally by abundant emerald green clinoamphibole and corundum porphyroblasts rimmed by fibrolite.« less

Development of Manufacturable Process to Deposit Metal Matrix Composites on Inverted Metamorphic Multijunction Solar Cells

DTIC Science & Technology

2015-01-14

substrates using a titanium adhesion layer, and (3) characterized hardness and electrical conductivity of plated silver before and after rapid thermal...layer composite films. We observed that the silver erosion during carboxylated carbon nanotube deposition leads to significant porosity within the...composite films. We plan to explore amine-terminated carbon nanotubes in the near future to eliminate the porosity and study how different

Modified secondary lithium metal batteries with the polyaniline-carbon nanotube composite buffer layer.

PubMed

Zhang, Ding; Yin, Yanli; Liu, Changhong; Fan, Shoushan

2015-01-07

A modified secondary lithium metal battery inserted with a polyaniline-carbon nanotube nanoporous composite buffer layer was fabricated. This unique and simple design of battery has the great potential to decrease the safety risk of the secondary Li metal battery in cycles of recharging processes and improve its cycle life in the future.

FIBER AND INTEGRATED OPTICS: Emission properties of graded-index corrugated waveguides with a metal or semiconductor coating

NASA Astrophysics Data System (ADS)

Ataya, B. A.; Osovitskiĭ, A. N.

1992-02-01

A numerical method was used to investigate the emission of TE-polarized light from a graded-index corrugated waveguide coated with a metal or semiconductor and either with or without a buffer layer. The main emission characteristics of these systems were analyzed. In the case of metallized dielectric structures an optimal corrugation depth was established for which the emitted power is a maximum. It was found that when the parameters of a structure with a buffer layer were correctly chosen and a highly reflective metal coating was used, practically all the power in the waveguide wave could be emitted along a specified direction. A structure with a buffer layer and an aluminum coating was investigated experimentally.

Investigation of AlGaN/GaN high electron mobility transistor structures on 200-mm silicon (111) substrates employing different buffer layer configurations.

PubMed

Lee, H-P; Perozek, J; Rosario, L D; Bayram, C

2016-11-21

AlGaN/GaN high electron mobility transistor (HEMT) structures are grown on 200-mm diameter Si(111) substrates by using three different buffer layer configurations: (a) Thick-GaN/3 × {Al x Ga 1-x N}/AlN, (b) Thin-GaN/3 × {Al x Ga 1-x N}/AlN, and (c) Thin-GaN/AlN, so as to have crack-free and low-bow (<50 μm) wafer. Scanning electron microscopy, energy-dispersive X-ray spectroscopy, high resolution-cross section transmission electron microscopy, optical microscopy, atomic-force microscopy, cathodoluminescence, Raman spectroscopy, X-ray diffraction (ω/2θ scan and symmetric/asymmetric ω scan (rocking curve scan), reciprocal space mapping) and Hall effect measurements are employed to study the structural, optical, and electrical properties of these AlGaN/GaN HEMT structures. The effects of buffer layer stacks (i.e. thickness and content) on defectivity, stress, and two-dimensional electron gas (2DEG) mobility and 2DEG concentration are reported. It is shown that 2DEG characteristics are heavily affected by the employed buffer layers between AlGaN/GaN HEMT structures and Si(111) substrates. Particularly, we report that in-plane stress in the GaN layer affects the 2DEG mobility and 2DEG carrier concentration significantly. Buffer layer engineering is shown to be essential for achieving high 2DEG mobility (>1800 cm 2 /V∙s) and 2DEG carrier concentration (>1.0 × 10 13  cm -2 ) on Si(111) substrates.

Investigation of AlGaN/GaN high electron mobility transistor structures on 200-mm silicon (111) substrates employing different buffer layer configurations

PubMed Central

Lee, H.-P.; Perozek, J.; Rosario, L. D.; Bayram, C.

2016-01-01

AlGaN/GaN high electron mobility transistor (HEMT) structures are grown on 200-mm diameter Si(111) substrates by using three different buffer layer configurations: (a) Thick-GaN/3 × {AlxGa1−xN}/AlN, (b) Thin-GaN/3 × {AlxGa1−xN}/AlN, and (c) Thin-GaN/AlN, so as to have crack-free and low-bow (<50 μm) wafer. Scanning electron microscopy, energy-dispersive X-ray spectroscopy, high resolution-cross section transmission electron microscopy, optical microscopy, atomic-force microscopy, cathodoluminescence, Raman spectroscopy, X-ray diffraction (ω/2θ scan and symmetric/asymmetric ω scan (rocking curve scan), reciprocal space mapping) and Hall effect measurements are employed to study the structural, optical, and electrical properties of these AlGaN/GaN HEMT structures. The effects of buffer layer stacks (i.e. thickness and content) on defectivity, stress, and two-dimensional electron gas (2DEG) mobility and 2DEG concentration are reported. It is shown that 2DEG characteristics are heavily affected by the employed buffer layers between AlGaN/GaN HEMT structures and Si(111) substrates. Particularly, we report that in-plane stress in the GaN layer affects the 2DEG mobility and 2DEG carrier concentration significantly. Buffer layer engineering is shown to be essential for achieving high 2DEG mobility (>1800 cm2/V∙s) and 2DEG carrier concentration (>1.0 × 1013 cm−2) on Si(111) substrates. PMID:27869222

Back contact to film silicon on metal for photovoltaic cells

DOEpatents

Branz, Howard M.; Teplin, Charles; Stradins, Pauls

2013-06-18

A crystal oriented metal back contact for solar cells is disclosed herein. In one embodiment, a photovoltaic device and methods for making the photovoltaic device are disclosed. The photovoltaic device includes a metal substrate with a crystalline orientation and a heteroepitaxial crystal silicon layer having the same crystal orientation of the metal substrate. A heteroepitaxial buffer layer having the crystal orientation of the metal substrate is positioned between the substrate and the crystal silicon layer to reduce diffusion of metal from the metal foil into the crystal silicon layer and provide chemical compatibility with the heteroepitaxial crystal silicon layer. Additionally, the buffer layer includes one or more electrically conductive pathways to electrically couple the crystal silicon layer and the metal substrate.

Simulation of Seasonal Snow Microwave TB Using Coupled Multi-Layered Snow Evolution and Microwave Emission Models

NASA Technical Reports Server (NTRS)

Brucker, Ludovic; Royer, Alain; Picard, Ghislain; Langlois, Alex; Fily, Michel

2014-01-01

The accurate quantification of SWE has important societal benefits, including improving domestic and agricultural water planning, flood forecasting and electric power generation. However, passive-microwave SWE algorithms suffer from variations in TB due to snow metamorphism, difficult to distinguish from those due to SWE variations. Coupled snow evolution-emission models are able to predict snow metamorphism, allowing us to account for emissivity changes. They can also be used to identify weaknesses in the snow evolution model. Moreover, thoroughly evaluating coupled models is a contribution toward the assimilation of TB, which leads to a significant increase in the accuracy of SWE estimates.

Reduction of shunt current in buffer-free IrMn based spin-valve structures

NASA Astrophysics Data System (ADS)

Kocaman, B.; Akdoğan, N.

2018-06-01

The presence of thick buffer layers in magnetic sensor devices decreases sensor sensitivity due to shunt currents. With this motivation, we produced IrMn-based spin-valve multilayers without using buffer layer. We also studied the effects of post-annealing and IrMn thickness on exchange bias field (HEB) and blocking temperature (TB) of the system. Magnetization measurements indicate that both HEB and TB values are significantly enhanced with post-annealing of IrMn layer. In addition, we report that IrMn thickness of the system strongly influences the magnetization and transport characteristics of the spin-valve structures. We found that the minimum thickness of IrMn layer is 6 nm in order to achieve the lowest shunt current and high blocking temperature (>300 K). We also investigated the training of exchange bias to check the long-term durability of IrMn-based spin-valve structures for device applications.

The early growth and interface of YBa 2Cu 3O y thin films deposited on YSZ substrates

NASA Astrophysics Data System (ADS)

Gao, J.; Tang, W. H.; Yau, C. Y.

2001-11-01

Epitaxial thin films of YBa 2Cu 3O y (YBCO) have been prepared on yttrium-stabilized zirconia substrates with and without a buffer layer. The early growth, crystallinity and surface morphology of these thin films have been characterized by X-ray diffraction, rocking curves, scanning electron microscope, in situ conductance measurements, and surface step profiler. The full width at half maximum of the ( 0 0 5 ) peak of rocking curve was found to be less than 0.1°. Over a wide scanning range of 2000 μm the average surface roughness is just 5 nm, indicating very smooth films. Grazing incident X-ray reflection and positron annihilation spectroscopy shows well-defined interfaces between layers and substrate. By applying a new Eu 2CuO 4 (ECO) buffer layer the initial formation of YBCO appears to grow layer-by-layer rather than the typical island growth mode. The obtained results reveal significant improvements at the early formation and crystallinity of YBCO by using the 214-T ‧ ECO as a buffer layer.

Ruthenium (Ru) peeling and predicting robustness of the capping layer using finite element method (FEM) modeling

NASA Astrophysics Data System (ADS)

Jang, Il-Yong; John, Arun; Goodwin, Frank; Lee, Su-Young; Kim, Byung-Gook; Kim, Seong-Sue; Jeon, Chan-Uk; Kim, Jae Hyung; Jang, Yong Hoon

2014-07-01

Ruthenium (Ru) film used as capping layer in extreme ultraviolet (EUV) mask peeled off after annealing and in-situ UV (IUV) cleaning. We investigated Ru peeling and found out that the mechanical stress caused by the formation of Si oxide due to the penetration of oxygen atoms from ambient or cleaning media to top-Si of ML is the root cause for the problem. To support our experimental results, we developed a numerical model of finite element method (FEM) using commercial software (ABAQUS™) to calculate the stress and displacement forced on the capping layer. By using this model, we could observe that the displacement agrees well with the actual results measured from the transmission electron microscopy (TEM) image. Using the ion beam deposition (IBD) tool at SEMATECH, we developed four new types of alternative capping materials (RuA, RuB, B4C, B4C-buffered Ru). The durability of each new alternative capping layer observed by experiment was better than that of conventional Ru. The stress and displacement calculated from each new alternative capping layer, using modeling, also agreed well with the experimental results. A new EUV mask structure is proposed, inserting a layer of B4C (B4C-buffered Ru) at the interface between the capping layer (Ru) and the top-Si layer. The modeling results showed that the maximum displacement and bending stress observed from the B4C-buffered Ru are significantly lower than that of single capping layer cases. The durability investigated from the experiment also showed that the B4C-buffered structure is at least 3X stronger than that of conventional Ru.

Effects of a GaSb buffer layer on an InGaAs overlayer grown on Ge(111) substrates: Strain, twin generation, and surface roughness

NASA Astrophysics Data System (ADS)

Kajikawa, Y.; Nishigaichi, M.; Tenma, S.; Kato, K.; Katsube, S.

2018-04-01

InGaAs layers were grown by molecular-beam epitaxy on nominal and vicinal Ge(111) substrates with inserting GaSb buffer layers. High-resolution X-ray diffraction using symmetric 333 and asymmetric 224 reflections was employed to analyze the crystallographic properties of the grown layers. By using the two reflections, we determined the lattice constants (the unit cell length a and the angle α between axes) of the grown layers with taking into account the rhombohedral distortion of the lattices of the grown layers. This allowed us the independent determination of the strain components (perpendicular and parallel components to the substrate surface, ε⊥ and ε//) and the composition x of the InxGa1-xAs layers by assuming the distortion coefficient D, which is defined as the ratio of ε⊥ against ε//. Furthermore, the twin ratios were determined for the GaSb and the InGaAs layers by comparing asymmetric 224 reflections from the twin domain with that from the normal domain of the layers. As a result, it has been shown that the twin ratio in the InGaAs layer can be decreased to be less than 0.1% by the use of the vicinal substrate together with annealing the GaSb buffer layer during the growth interruption before the InGaAs overgrowth.

Growth and characterization of PbSe and Pb{sub 1{minus}x}Sn{sub x}Se layers on Si (100)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sachar, H.K.; Chao, I.; Fang, X.M.

1998-12-31

Crack-free layers of PbSe were grown on Si (100) by a combination of liquid phase epitaxy (LPE) and molecular beam epitaxy (MBE) techniques. The PbSe layer was grown by LPE on Si(100) using a MBE-grown PbSe/BaF{sub 2}/CaF{sub 2} buffer layer structure. Pb{sub 1{minus}x}Sn{sub x}Se layers with tin contents in the liquid growth solution equal to 3%, 5%, 6%, 7%, and 10%, respectively, were also grown by LPE on Si(100) substrates using similar buffer layer structures. The LPE-grown PbSe and Pb{sub 1{minus}x}Sn{sub x}Se layers were characterized by optical Nomarski microscopy, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electronmore » microscopy (SEM). Optical Nomarski characterization of the layers revealed their excellent surface morphologies and good growth solution wipe-offs. FTIR transmission experiments showed that the absorption edge of the Pb{sub 1{minus}x}Sn{sub x}Se layers shifted to lower energies with increasing tin contents. The PbSe epilayers were also lifted-off from the Si substrate by dissolving the MBE-grown BaF{sub 2} buffer layer. SEM micrographs of the cleaved edges revealed that the lifted-off layers formed structures suitable for laser fabrication.« less

H2-rich fluids from serpentinization: Geochemical and biotic implications

PubMed Central

Sleep, N. H.; Meibom, A.; Fridriksson, Th.; Coleman, R. G.; Bird, D. K.

2004-01-01

Metamorphic hydration and oxidation of ultramafic rocks produces serpentinites, composed of serpentine group minerals and varying amounts of brucite, magnetite, and/or FeNi alloys. These minerals buffer metamorphic fluids to extremely reducing conditions that are capable of producing hydrogen gas. Awaruite, FeNi3, forms early in this process when the serpentinite minerals are Fe-rich. Olivine with the current mantle Fe/Mg ratio was oxidized during serpentinization after the Moon-forming impact. This process formed some of the ferric iron in the Earth's mantle. For the rest of Earth's history, serpentinites covered only a small fraction of the Earth's surface but were an important prebiotic and biotic environment. Extant methanogens react H2 with CO2 to form methane. This is a likely habitable environment on large silicate planets. The catalytic properties of FeNi3 allow complex organic compounds to form within serpentinite and, when mixed with atmospherically produced complex organic matter and waters that circulated through basalts, constitutes an attractive prebiotic substrate. Conversely, inorganic catalysis of methane by FeNi3 competes with nascent and extant life. PMID:15326313

Method to prevent/mitigate steam explosions in casting pits

DOEpatents

Taleyarkhan, Rusi P.

1996-01-01

Steam explosions can be prevented or mitigated during a metal casting process by the placement of a perforated flooring system in the casting pit. An upward flow of compressed gas through this perforated flooring system is introduced during the casting process to produce a buffer layer between any spilled molten metal and the cooling water in the reservoir. This buffer layer provides a hydrodynamic layer which acts to prevent or mitigate steam explosions resulting from hot, molten metal being spilled into or onto the cooling water.

Methods of producing free-standing semiconductors using sacrificial buffer layers and recyclable substrates

DOEpatents

Ptak, Aaron Joseph; Lin, Yong; Norman, Andrew; Alberi, Kirstin

2015-05-26

A method of producing semiconductor materials and devices that incorporate the semiconductor materials are provided. In particular, a method is provided of producing a semiconductor material, such as a III-V semiconductor, on a spinel substrate using a sacrificial buffer layer, and devices such as photovoltaic cells that incorporate the semiconductor materials. The sacrificial buffer material and semiconductor materials may be deposited using lattice-matching epitaxy or coincident site lattice-matching epitaxy, resulting in a close degree of lattice matching between the substrate material and deposited material for a wide variety of material compositions. The sacrificial buffer layer may be dissolved using an epitaxial liftoff technique in order to separate the semiconductor device from the spinel substrate, and the spinel substrate may be reused in the subsequent fabrication of other semiconductor devices. The low-defect density semiconductor materials produced using this method result in the enhanced performance of the semiconductor devices that incorporate the semiconductor materials.

Strain effect in epitaxial VO2 thin films grown on sapphire substrates using SnO2 buffer layers

NASA Astrophysics Data System (ADS)

Kim, Heungsoo; Bingham, Nicholas S.; Charipar, Nicholas A.; Piqué, Alberto

2017-10-01

Epitaxial VO2/SnO2 thin film heterostructures were deposited on m-cut sapphire substrates via pulsed laser deposition. By adjusting SnO2 (150 nm) growth conditions, we are able to control the interfacial strain between the VO2 film and SnO2 buffer layer such that the semiconductor-to-metal transition temperature (TC) of VO2 films can be tuned without diminishing the magnitude of the transition. It is shown that in-plane tensile strain and out-of-plane compressive strain of the VO2 film leads to a decrease of Tc. Interestingly, VO2 films on SnO2 buffer layers exhibit a structural phase transition from tetragonal-like VO2 to tetragonal-VO2 during the semiconductor-to-metal transition. These results suggest that the strain generated by SnO2 buffer provides an effective way for tuning the TC of VO2 films.

Molecular beam epitaxy growth of high electron mobility InAs/AlSb deep quantum well structure

NASA Astrophysics Data System (ADS)

Wang, Juan; Wang, Guo-Wei; Xu, Ying-Qiang; Xing, Jun-Liang; Xiang, Wei; Tang, Bao; Zhu, Yan; Ren, Zheng-Wei; He, Zhen-Hong; Niu, Zhi-Chuan

2013-07-01

InAs/AlSb deep quantum well (QW) structures with high electron mobility were grown by molecular beam epitaxy (MBE) on semi-insulating GaAs substrates. AlSb and Al0.75Ga0.25Sb buffer layers were grown to accommodate the lattice mismatch (7%) between the InAs/AlSb QW active region and GaAs substrate. Transmission electron microscopy shows abrupt interface and atomic force microscopy measurements display smooth surface morphology. Growth conditions of AlSb and Al0.75Ga0.25Sb buffer were optimized. Al0.75Ga0.25Sb is better than AlSb as a buffer layer as indicated. The sample with optimal Al0.75Ga0.25Sb buffer layer shows a smooth surface morphology with root-mean-square roughness of 6.67 Å. The electron mobility has reached as high as 27 000 cm2/Vs with a sheet density of 4.54 × 1011/cm2 at room temperature.

Preparation and Optoelectronic Characteristics of ZnO/CuO-Cu2O Complex Inverse Heterostructure with GaP Buffer for Solar Cell Applications

PubMed Central

Hsu, Chih-Hung; Chen, Lung-Chien; Lin, Yi-Feng

2013-01-01

This study reports the optoelectronic characteristics of ZnO/GaP buffer/CuO-Cu2O complex (COC) inverse heterostructure for solar cell applications. The GaP and COC layers were used as buffer and absorber in the cell structure, respectively. An energy gap widening effect and CuO whiskers were observed as the copper (Cu) layer was exerted under heat treatment for oxidation at 500 °C for 10 min, and arose from the center of the Cu2O rods. For preparation of the 30 nm-thick GaP buffer by sputtering from GaP target, as the nitrogen gas flow rate increased from 0 to 2 sccm, the transmittance edge of the spectra demonstrated a blueshift form 2.24 to 3.25 eV. Therefore, the layer can be either GaP, GaNP, or GaN by changing the flow rate of nitrogen gas. PMID:28788341

Geology of Precambrian rocks and isotope geochemistry of shear zones in the Big Narrows area, northern Front Range, Colorado

USGS Publications Warehouse

Abbott, Jeffrey T.

1970-01-01

Rocks within the Big Narrows and Poudre Park quadrangles located in the northern Front Range of Colorado are Precambrian metasedimentary and metaigneous schists and gneisses and plutonic igneous rocks. These are locally mantled by extensive late Tertiary and Quaternary fluvial gravels. The southern boundary of the Log Cabin batholith lies within the area studied. A detailed chronology of polyphase deformation, metamorphism and plutonism has been established. Early isoclinal folding (F1) was followed by a major period of plastic deformation (F2), sillimanite-microcline grade regional metamorphism, migmatization and synkinematic Boulder Creek granodiorite plutonism (1.7 b.y.). Macroscopic doubly plunging antiformal and synformal structures were developed. P-T conditions at the peak of metamorphism were probably about 670?C and 4.5 Kb. Water pressures may locally have differed from load pressures. The 1.4 b.y. Silver Plume granite plutonism was post kinematic and on the basis of petrographic and field criteria can be divided into three facies. Emplacement was by forcible injection and assimilation. Microscopic and mesoscopic folds which postdate the formation of the characteristic mineral phases during the 1.7 b.y. metamorphism are correlated with the emplacement of the Silver Plume Log Cabin batholith. Extensive retrograde metamorphism was associated with this event. A major period of mylonitization postdates Silver Plume plutonism and produced large E-W and NE trending shear zones. A detailed study of the Rb/Sr isotope geochemistry of the layered mylonites demonstrated that the mylonitization and associated re- crystallization homogenized the Rb87/Sr 86 ratios. Whole-rock dating techniques applied to the layered mylonites indicate a probable age of 1.2 b.y. Petrographic studies suggest that the mylonitization-recrystallization process produced hornfels facies assemblages in the adjacent metasediments. Minor Laramide faulting, mineralization and igneous activity occurred within this area. A sinuous band of gravel deposits trending into the Livermore embayment and lying well above the present drainage is believed to represent a late Tertiary course of the Cache La Poudre river.

Electrocatalytic cermet sensor

DOEpatents

Shoemaker, E.L.; Vogt, M.C.

1998-06-30

A sensor is described for O{sub 2} and CO{sub 2} gases. The gas sensor includes a plurality of layers driven by a cyclic voltage to generate a unique plot characteristic of the gas in contact with the sensor. The plurality of layers includes an alumina substrate, a reference electrode source of anions, a lower electrical reference electrode of Pt coupled to the reference source of anions, a solid electrolyte containing tungsten and coupled to the lower reference electrode, a buffer layer for preventing flow of Pt ions into the solid electrolyte and an upper catalytically active Pt electrode coupled to the buffer layer. 16 figs.

Electrocatalytic cermet sensor

DOEpatents

Shoemaker, Erika L.; Vogt, Michael C.

1998-01-01

A sensor for O.sub.2 and CO.sub.2 gases. The gas sensor includes a plurality of layers driven by a cyclic voltage to generate a unique plot characteristic of the gas in contact with the sensor. The plurality of layers includes an alumina substrate, a reference electrode source of anions, a lower electrical reference electrode of Pt coupled to the reference source of anions, a solid electrolyte containing tungsten and coupled to the lower reference electrode, a buffer layer for preventing flow of Pt ions into the solid electrolyte and an upper catalytically active Pt electrode coupled to the buffer layer.

Characterization of SiGe/Ge heterostructures and graded layers using variable angle spectroscopic ellipsometry

NASA Technical Reports Server (NTRS)

Croke, E. T.; Wang, K. L.; Heyd, A. R.; Alterovitz, S. A.; Lee, C. H.

1996-01-01

Variable angle spectroscopic ellipsometry (VASE) has been used to characterize Si(x)Ge(1-x)/Ge superlattices (SLs) grown on Ge substrates and thick Si(x)Ge(1-x)/Ge heterostructures grown on Si substrates. Our VASE analysis yielded the thicknesses and alloy compositions of all layers within the optical penetration depth of the surface. In addition, strain effects were observed in the VASE results for layers under both compressive and tensile strain. Results for the SL structures were found to be in close agreement with high resolution x-ray diffraction measurements made on the same samples. The VASE analysis has been upgraded to characterize linearly graded Si(x)Ge(1-x) buffer layers. The algorithm has been used to determine the total thickness of the buffer layer along with the start and end alloy composition by breaking the total thickness into many (typically more than 20) equal layers. Our ellipsometric results for 1 (mu)m buffer layers graded in the ranges 0.7 less than or = x less than or = 1.0, and 0.5 less than or = x less than or = 1.0 are presented, and compare favorably with the nominal values.

Spray-Pyrolyzed Three-Dimensional CuInS2 Solar Cells on Nanocrystalline-Titania Electrodes with Chemical-Bath-Deposited Inx(OH)ySz Buffer Layers

NASA Astrophysics Data System (ADS)

Nguyen, Duy-Cuong; Mikami, Yuki; Tsujimoto, Kazuki; Ryo, Toshihiro; Ito, Seigo

2012-10-01

Three-dimensional (3D) compound solar cells with the structure of have been fabricated by spray pyrolysis deposition of CuInS2 and chemical-bath deposition of Inx(OH)ySz for the light absorber and buffer layer, respectively. The effect of deposition and annealing conditions of Inx(OH)ySz on the photovoltaic properties of 3D CuInS2 solar cells was investigated. Inx(OH)ySz annealed in air ambient showed a better cell performance than those annealed in nitrogen ambient and without annealing. The improvement of the performance of cells with Inx(OH)ySz buffer layers annealed in air ambient is due to the increase in oxide concentration in the buffer layers [confirmed by X-ray photoelectron spectroscopy (XPS) measurement]. Among cells with Inx(OH)ySz buffer layers deposited for 1, 1.5, 1.75, and 2 h, that with Inx(OH)ySz deposited for 1.75 h showed the best cell performance. The best cell performance was observed for Inx(OH)ySz deposited for 1.75 h with annealing at 300 °C for 30 min in air ambient, and cell parameters were 22 mA cm-2 short-circuit photocurrent density, 0.41 V open-circuit voltage, 0.35 fill factor, and 3.2% conversion efficiency.

Conditions for the formation and atmospheric dispersion of a toxic, heavy gas layer during thermal metamorphism of coal and evaporite deposits by sill intrusion

NASA Astrophysics Data System (ADS)

Storey, Michael; Hankin, Robin K. S.

2010-05-01

There is compelling evidence for massive discharge of volatiles, including toxic species, into the atmosphere at the end of the Permian. It has been argued that most of the gases were produced during thermal metamorphism of coal and evaporite deposits in the East Siberia Tunguska basin following sill intrusion (Retallack and Jahren, 2008; Svensen et al., 2009). The release of the volatiles has been proposed as a major cause of environmental and extinction events at the end of the Permian, with venting of carbon gases and halocarbons to the atmosphere leading to global warming and atmospheric ozone depletion (Svensen et al., 2009) Here we consider the conditions required for the formation and dispersion of toxic, heavier than air, gas plumes, made up of a mixture of CO2, CH4, H2S and SO2 and formed during the thermal metamorphism of C- and S- rich sediments. Dispersion models and density considerations within a range of CO2/CH4 ratios and volatile fluxes and temperatures, for gas discharge by both seepage and from vents, allow the possibility that following sill emplacement much of the vast East Siberia Tunguska basin was - at least intermittently - covered by a heavy, toxic gas layer that was unfavorable for life. Dispersion scenarios for a heavy gas layer beyond the Siberian region during end-Permian times will be presented. REFERENCES G. J. Retallack and A. H. Jahren, Methane release from igneous intrusion of coal during Late Permian extinction events, Journal of Geology, volume 116, 1-20, 2008 H. Svensen et al., Siberian gas venting and the end-Permian environmental crisis, Earth and Planetary Science Letters, volume 277, 490-500, 2009

Buffer transport mechanisms in intentionally carbon doped GaN heterojunction field effect transistors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Uren, Michael J.; Cäsar, Markus; Kuball, Martin

2014-06-30

Temperature dependent pulsed and ramped substrate bias measurements are used to develop a detailed understanding of the vertical carrier transport in the buffer layers in a carbon doped GaN power heterojunction field effect transistor. Carbon doped GaN and multiple layers of AlGaN alloy are used in these devices to deliver an insulating and strain relieved buffer with high breakdown voltage capability. However, understanding of the detailed physical mechanism for its operation is still lacking. At the lowest electric fields (<10 MV/m), charge redistribution within the C doped layer is shown to occur by hole conduction in the valence band withmore » activation energy 0.86 eV. At higher fields, leakage between the two-dimensional electron gas and the buffer dominates occurring by a Poole-Frenkel mechanism with activation energy ∼0.65 eV, presumably along threading dislocations. At higher fields still, the strain relief buffer starts to conduct by a field dependent process. Balancing the onset of these leakage mechanisms is essential to allow the build-up of positive rather than negative space charge, and thus minimize bulk-related current-collapse in these devices.« less

Transition from subduction- to exhumation-related fabrics in glaucophane-bearing eclogites, Oman: evidence from relative fabric chronology and 40Ar/ 39Ar ages

NASA Astrophysics Data System (ADS)

Gray, David R.; Miller, John McL.; Foster, David A.; Gregory, Robert T.

2004-09-01

Controversy over the age of peak metamorphism and therefore the tectonic evolution of the Arabian margin relates to the polydeformed and polymetamorphosed nature of glaucophane-bearing eclogites from the Saih Hatat window beneath the allochthonous Samail ophiolite in NE Oman. These eclogites contain relicts of earlier fabrics, structures and metamorphic assemblages and provide a record of change from subduction to exhumation. The eclogites are part of a mafic layer that was disrupted into boudins up to 0.5 km in length within a lower plate shear zone (As Sifah shear zone). The megaboudins not only preserve the relicts of the highest grade of metamorphism but also an early ENE-trending lineation and sheathlike isoclines enveloped by the flat-lying schistosity. The boudin-bearing layer is isoclinally folded with calc-schist, mafic schist and quartz-mica schist, where the regional folds have axes parallel to the NE-trending stretching lineation (a-type folds). Textural evidence suggests multiple growth events for garnet and clinopyroxene, requiring polymetamorphism of the mafic layers that formed the eclogite megaboudins. The surrounding calc-schist and quartz-mica schist are both intensely deformed with transposition foliation containing an NE-trending lineation in phengite and asymmetric shear indicators such as C'-type shear bands and asymmetric pressure shadows around garnets, that give top-to-the-NE sense of shear. Although consistent ENE-trending lineations in all the boudins suggest that they have largely acted as passive, nonrotating rigid bodies, the presence of NE-vergent asymmetric mesofolds, extensive dynamic recrystallisation, multiple generations of phengites and a range of 40Ar- 39Ar apparent ages within the megaboudins suggest, however, that they have not acted entirely passively during the later deformation. Phengites isolated from the high- P/low- T fabrics show groupings in 40Ar- 39Ar apparent ages interpreted as distinct metamorphic/cooling intervals at ˜140-135, ˜120-98 and ˜ 92-80 Ma. Microstructural relations suggest that age groupings younger than 100 Ma reflect phengite growth during exhumation with the top-to-the-NE shearing. The older ages (˜120-110 Ma) from fabrics that give top-to-the-S shear sense may reflect growth during the subduction phase. The combination of groupings of apparent argon ages older than the crystallisation age of the Samail Ophiolite, the suggestion of different geothermal gradients, and superposed metamorphism suggest that the eclogites and garnet blueschists formed as a result of underthrusting along a break that was not directly related to the metamorphic sole of the ophiolite. The glaucophane-eclogites are interpreted as having formed at different times under varying pressure-temperature conditions during underthrusting with variations in the rate of underthrusting, allowing thermal equilibration and/or rapid cooling at different crustal levels.

Growth mechanisms of GaSb heteroepitaxial films on Si with an AlSb buffer layer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vajargah, S. Hosseini; Botton, G. A.; Brockhouse Institute for Materials Research, McMaster University, Hamilton, Ontario L8S 4M1

2013-09-21

The initial growth stages of GaSb epilayers on Si substrates and the role of the AlSb buffer layer were studied by high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). Heteroepitaxy of GaSb and AlSb on Si both occur by Volmer-Weber (i.e., island mode) growth. However, the AlSb and GaSb islands have distinctly different characteristics as revealed through an atomic-resolution structural study using Z-contrast of HAADF-STEM imaging. While GaSb islands are sparse and three dimensional, AlSb islands are numerous and flattened. The introduction of 3D island-forming AlSb buffer layer facilitates the nucleation of GaSb islands. The AlSb islands-assisted nucleation of GaSbmore » islands results in the formation of drastically higher quality planar film at a significantly smaller thickness of films. The interface of the AlSb and GaSb epilayers with the Si substrate was further investigated with energy dispersive X-ray spectrometry to elucidate the key role of the AlSb buffer layer in the growth of GaSb epilayers on Si substrates.« less

Very low-grade metamorphic rocks in some representative districts in Tibet

NASA Astrophysics Data System (ADS)

Bi, X.; Mo, X.

2011-12-01

*Response author: Bi,Xianmei,bixm10@sina.com Very low grade metamorphic rocks are widely distributed in Tibet, providing an insight into deformation and metamorphism during the evolution of the Tibetan Plateau. Eighty five Samples of clay mineral-bearing rocks has been collected from various strata including D, P1, T1, T2, T3, J1, J3, K1, K2 and N strata in the Qiangtang terrane, the Gangdese, the Yarlung Zangbo suture and the Tethyan Himalaya. Analyses and refining of clay minerals in samples have been conducted in the Laboratory of X-ray Diffraction, Institute of Petroleum Exploration. Index of illite crystallinity (Ic) along with average thickness of crystal layers of illite, reflectivity of vitrinite and of clay mineral association have been employed as indicators of degree of very low-grade metamorphism. The scheme of classification[1,2] of very-low grade metamorphism based on clay mineral indexes ( mainly index of illite crystallinity) has been used in the present work, that is, low metamorphism (Ic<0.25), higher very-low grade metamorphism (Ic = 0.25-0.30), lower very-low grade metamorphism (Ic = 0.30-0.42) and diagenesis (Ic>0.42). The analytical results show interesting information. In the Qiangtang terrane, clay minerals in the Jurassic strata have indexes of illite crystalinity (Ic) 0.47-0.70, indicating higher diagenesis and in favor of petroleum-generation. However, index of illite crystalinity (Ic) for the Devonian is 0.23, indicating low metamorphism. Indexes of illite crystalinity (Ic) for the J-K strata in middle Gangdese are mostly 0.37-0.25 (very-low grade metamorphism) and a few 0.78-0.48 (diagenesis). Indexes of illite crystalinity (Ic) for the C-P strata in eastern Gangdese are mostly 0.25-0.42 (very-low grade metamorphism) and a few 0.20-0.25 (low metamorphism). The Mesozoic and Cenozoic magmatism and related mineralization are very strong in the Gangdese, which may affect in some extent on indexes of illite crystalinity. In Tethyan Himalaya, clay mineral-bearing rocks from P1, T1, T2, T3, J1 and J3 strata underwent low-very low grade metamorphism, having indexes of illite crystalinity (Ic) 0.12 for P1 stratum, 0.21 for T1 stratum and 0.22-0.33 for the strata from T2 to J3, whereas K1 and N strata underwent diagenesis, having Ic = 0.52 and 1.61, respectively. Metamorphic degree generally reduced from older strata to younger strata according to clay mineral indexes. The rocks affected by magmatism or by major faulting, however, were out of the general trend and increased their metamorphic degree by 0.1-0.3 units reduction of index of illite crystallinity. Rocks within Yarlung Zangbo suture show higher metamorphic degree than those in Tethyan Himalaya. For instance, while the late Triassic has 0.19 of index of illite crystallinity in the former (the Yarlung Zangbo suture), 0.27-0.33 of indexes of illite crystallinity in the latter. The early Cretaceous has 0.28 of index of illite crystallinity in the former, whereas 0.52 in the latter. However, the late Cretaceous Xigaze Group formed in a fore-arc environment was weakly metamorphosed, having Ic 0.7-1.6 and all falling into diagenesis field.

Modeling of defect-tolerant thin multi-junction solar cells for space application

NASA Astrophysics Data System (ADS)

Mehrotra, A.; Alemu, A.; Freundlich, A.

2012-02-01

Using drift-diffusion model and considering experimental III-V material parameters, AM0 efficiencies of lattice-matched multijunction solar cells have been calculated and the effects of dislocations and radiation damage have been analyzed. Ultrathin multi-junction devices perform better in presence of dislocations or/and radiation harsh environment compared to conventional thick multijunction devices. Our results show that device design optimization of Ga0.51In0.49P/GaAs multijunction devices leads to an improvement in EOL efficiency from 4.8%, for the conventional thick device design, to 12.7%, for the EOL optimized thin devices. In addition, an optimized defect free lattice matched Ga0.51In0.49P/GaAs solar cell under 1016cm-2 1Mev equivalent electron fluence is shown to give an EOL efficiency of 12.7%; while a Ga0.51In0.49P/GaAs solar cell with 108 cm-2 dislocation density under 1016cm-2 electron fluence gives an EOL efficiency of 12.3%. The results suggest that by optimizing the device design, we can obtain nearly the same EOL efficiencies for high dislocation metamorphic solar cells and defect filtered metamorphic multijunction solar cells. The findings relax the need for thick or graded buffer used for defect filtering in metamorphic devices. It is found that device design optimization allows highly dislocated devices to be nearly as efficient as defect free devices for space applications.

Modeling and optimal designs for dislocation and radiation tolerant single and multijunction solar cells

NASA Astrophysics Data System (ADS)

Mehrotra, A.; Alemu, A.; Freundlich, A.

2011-02-01

Crystalline defects (e.g. dislocations or grain boundaries) as well as electron and proton induced defects cause reduction of minority carrier diffusion length which in turn results in degradation of efficiency of solar cells. Hetro-epitaxial or metamorphic III-V devices with low dislocation density have high BOL efficiencies but electron-proton radiation causes degradation in EOL efficiencies. By optimizing the device design (emitter-base thickness, doping) we can obtain highly dislocated metamorphic devices that are radiation resistant. Here we have modeled III-V single and multi junction solar cells using drift and diffusion equations considering experimental III-V material parameters, dislocation density, 1 Mev equivalent electron radiation doses, thicknesses and doping concentration. Thinner device thickness leads to increment in EOL efficiency of high dislocation density solar cells. By optimizing device design we can obtain nearly same EOL efficiencies from high dislocation solar cells than from defect free III-V multijunction solar cells. As example defect free GaAs solar cell after optimization gives 11.2% EOL efficiency (under typical 5x1015cm-2 1 MeV electron fluence) while a GaAs solar cell with high dislocation density (108 cm-2) after optimization gives 10.6% EOL efficiency. The approach provides an additional degree of freedom in the design of high efficiency space cells and could in turn be used to relax the need for thick defect filtering buffer in metamorphic devices.

Buffer Layer Effects on Tandem InGaAs TPV Devices

NASA Technical Reports Server (NTRS)

Wilt, David M.; Wehrer, Rebecca J.; Maurer, William F.

2004-01-01

Single junction indium gallium arsenide (InGaAs) based TPV devices have demonstrated efficiencies in excess of 20% at radiator temperatures of 1058 C. Modeling suggests that efficiency improvements in single bandgap devices should continue although they will eventually plateau. One approach for extending efficiencies beyond the single bandgap limit is to follow the technique taken in the solar cell field, namely tandem TPV cells. Tandem photovoltaic devices are traditionally composed of cells of decreasing bandgap, connected electrically and optically in series. The incident light impinges upon the highest bandgap first. This device acts as a sieve, absorbing the high-energy photons, while allowing the remainder to pass through to the underlying cell(s), and so on. Tandem devices reduce the energy lost to overexcitation as well as reducing the current density (Jsc). Reduced Jsc results in lower resistive losses and enables the use of thinner and lower doped lateral current conducting layers as well as a higher pitch grid design. Fabricating TPV tandem devices utilizing InGaAs for all of the component cells in a two cell tandem necessitates the inclusion of a buffer layer in-between the high bandgap device (In0.53 Ga0.47As - 0.74eV) and the low bandgap device (In0.66Ga0.34As - 0.63eV) to accommodate the approximately 1% lattice strain generated due to the change in InGaAs composition. To incorporate only a single buffer layer structure, we have investigated the use of the indium phosphide (InP) substrate as a superstrate. Thus the high-bandgap, lattice- matched device is deposited first, followed by the buffer structure and the low-bandgap cell. The near perfect transparency of the high bandgap (1.35eV) iron-doped InP permits the device to be oriented such that the light enters through the substrate. In this paper we examine the impact of the buffer layer on the underlying lattice-matched InGaAs device. 0.74eV InGaAs devices were produced in a variety of configurations both with and without buffer layers. All structures were characterized by reciprocal space x-ray diffraction to determine epilayer composition and residual strain. Electrical characterization of the devices was performed to examine the effect of the buffer on the device performance. The effect of the buffer structure depends upon where it is positioned. When near the emitter region, a 2.6x increase in dark current was measured, whereas no change in dark current was observed when it was near the base region.

Fabrication of a Tantalum-Based Josephson Junction for an X-Ray Detector

NASA Astrophysics Data System (ADS)

Morohashi, Shin'ichi; Gotoh, Kohtaroh; Yokoyama, Naoki

2000-06-01

We have fabricated a tantalum-based Josephson junction for an X-ray detector. The tantalum layer was selected for the junction electrode because of its long quasiparticle lifetime, large X-ray absorption efficiency and stability against thermal cycling. We have developed a buffer layer to fabricate the tantalum layer with a body-centered cubic structure. Based on careful consideration of their superconductivity, we have selected a niobium thin layer as the buffer layer for fabricating the tantalum base electrode, and a tungsten thin layer for the tantalum counter electrode. Fabricated Nb/AlOx-Al/Ta/Nb and Nb/Ta/W/AlOx-Al/Ta/Nb Josephson junctions exhibited current-voltage characteristics with a low subgap leakage current.

Selective growth of Pb islands on graphene/SiC buffer layers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, X. T.; Miao, Y. P.; Ma, D. Y.

2015-02-14

Graphene is fabricated by thermal decomposition of silicon carbide (SiC) and Pb islands are deposited by Pb flux in molecular beam epitaxy chamber. It is found that graphene domains and SiC buffer layer coexist. Selective growth of Pb islands on SiC buffer layer rather than on graphene domains is observed. It can be ascribed to the higher adsorption energy of Pb atoms on the 6√(3) reconstruction of SiC. However, once Pb islands nucleate on graphene domains, they will grow very large owing to the lower diffusion barrier of Pb atoms on graphene. The results are consistent with first-principle calculations. Sincemore » Pb atoms on graphene are nearly free-standing, Pb islands grow in even-number mode.« less

Ultrathin Polyaniline-based Buffer Layer for Highly Efficient Polymer Solar Cells with Wide Applicability

PubMed Central

Zhao, Wenchao; Ye, Long; Zhang, Shaoqing; Fan, Bin; Sun, Mingliang; Hou, Jianhui

2014-01-01

Interfacial buffer layers often attribute the improved device performance in organic optoelectronic device. Herein, a water-soluble hydrochloric acid doped polyanilines (HAPAN) were utilized as p-type electrode buffer layer in highly efficient polymer solar cells (PSC) based on PBDTTT-EFT and several representative polymers. The PBDTTT-EFT-based conventional PSC featuring ultrathin HAPAN (1.3 nm) delivered high PCE approximately 9%, which is one of the highest values among conventional PSC devices. Moreover, ultrathin HAPAN also exhibited wide applicability in a variety of efficient photovoltaic polymers including PBDTTT-C-T, PTB7, PBDTBDD, PBTTDPP-T, PDPP3T and P3HT. The excellent performances were originated from the high transparency, small film roughness and suitable work function. PMID:25300365

Photovoltaic Properties in Interpenetrating Heterojunction Organic Solar Cells Utilizing MoO3 and ZnO Charge Transport Buffer Layers

PubMed Central

Hori, Tetsuro; Moritou, Hiroki; Fukuoka, Naoki; Sakamoto, Junki; Fujii, Akihiko; Ozaki, Masanori

2010-01-01

Organic thin-film solar cells with a conducting polymer (CP)/fullerene (C60) interpenetrating heterojunction structure, fabricated by spin-coating a CP onto a C60 deposit thin film, have been investigated and demonstrated to have high efficiency. The photovoltaic properties of solar cells with a structure of indium-tin-oxide/C60/poly(3-hexylthiophene) (PAT6)/Au have been improved by the insertion of molybdenum trioxide (VI) (MoO3) and zinc oxide charge transport buffer layers. The enhanced photovoltaic properties have been discussed, taking into consideration the ground-state charge transfer between PAT6 and MoO3 by measurement of the differential absorption spectra and the suppressed contact resistance at the interface between the organic and buffer layers. PMID:28883360

Chemical Bath Deposited Zinc Sulfide Buffer Layers for Copper Indium Gallium Sulfur-selenide Solar Cells and Device Analysis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kundu, Sambhu N.; Olsen, Larry C.

2005-01-03

Cd free CIGSS thin film solar cell structures with a MgF2/TCO/CGD-ZnS/CIGSS/Mo/SLG structure have been fabricated using chemical bath deposited (CBD)-ZnS buffer layers and high quality CIGSS absorber layers supplied from Shell Solar Industries. The use of CBD-ZnS, which is a higher band gap materials than CdS, improved the quantum efficiency of fabricated cells at lower wavelengths, leading to an increase in short circuit current. The best cell to date yielded an active area (0.43 cm2) efficiency of 13.3%. This paper also presents a discussion of the issues relating to the use of the CBD-ZnS buffer materials for improving device performance.

Carbonate-orthopyroxenite lenses from the Neoproterozoic Gerf ophiolite, South Eastern Desert, Egypt: The first record in the Arabian Nubian Shield ophiolites

NASA Astrophysics Data System (ADS)

Gahlan, Hisham A.; Arai, Shoji

2009-01-01

Carbonate-orthopyroxenites (classic sagvandites) are reported in the Gerf ophiolite, South Eastern Desert, Egypt: the first finding from the Arabian Nubian Shield (ANS) ophiolites. They form massive lenses at the southern tip of the Gerf ophiolite, along the contact between the Shinai granite and Gerf serpentinized peridotites. The lenses show structural concordance with the neighboring country rocks and the granite contact. They consist mainly of metamorphic orthopyroxene + magnesite, among other metamorphic, relict primary and retrograde secondary minerals. Based only on chemistry, two types of carbonate-orthopyroxenites can be recognized, Types I (higher-Mg) and II (lower-Mg and higher-Fe). Field constraints, petrography and mineral chemistry indicate a metamorphic origin for the Gerf carbonate-orthopyroxenites. The euhedral form of relict primary chromian spinels combined with their high Cr#/low-TiO 2 character, and absence of clinopyroxene suggest that the protolith for the Gerf carbonate-orthopyroxenites is a highly depleted mantle peridotite derived from a sub-arc setting. Contact metamorphism accompanied by CO 2-metasomatism resulted in formation of the Gerf carbonate-orthopyroxenites during intrusion of the Shinai granite. The source of CO 2-rich fluids is most likely the neighboring impure carbonate layers. Correlation of the carbonate-orthopyroxenite mineral assemblages with experimental data for the system MgO-SiO 2-H 2O-CO 2 suggests metamorphic/metasomatic conditions of 520-560 °C, Pfluid = 2 kbar and extremely high X values (0.87-1).

Plasma-assisted molecular beam epitaxy of ZnO on in-situ grown GaN/4H-SiC buffer layers

NASA Astrophysics Data System (ADS)

Adolph, David; Tingberg, Tobias; Andersson, Thorvald; Ive, Tommy

2015-04-01

Plasma-assisted molecular beam epitaxy (MBE) was used to grow ZnO (0001) layers on GaN(0001)/4H-SiC buffer layers deposited in the same growth chamber equipped with both N- and O-plasma sources. The GaN buffer layers were grown immediately before initiating the growth of ZnO. Using a substrate temperature of 440°C-445°C and an O2 flow rate of 2.0-2.5 sccm, we obtained ZnO layers with smooth surfaces having a root-mean-square roughness of 0.3 nm and a peak-to-valley distance of 3 nm shown by AFM. The FWHM for X-ray rocking curves recorded across the ZnO(0002) and ZnO(10bar 15) reflections were 200 and 950 arcsec, respectively. These values showed that the mosaicity (tilt and twist) of the ZnO film was comparable to corresponding values of the underlying GaN buffer. It was found that a substrate temperature > 450°C and a high Zn-flux always resulted in a rough ZnO surface morphology. Reciprocal space maps showed that the in-plane relaxation of the GaN and ZnO layers was 82.3% and 73.0%, respectively and the relaxation occurred abruptly during the growth. Room-temperature Hall-effect measurements showed that the layers were intrinsically n-type with an electron concentration of 1019 cm-3 and a Hall mobility of 50 cm2·V-1·s-1.

Comparison of different photoresist buffer layers in SPR sensors based on D-shaped POF and gold film

NASA Astrophysics Data System (ADS)

Cennamo, Nunzio; Pesavento, Maria; De Maria, Letizia; Galatus, Ramona; Mattiello, Francesco; Zeni, Luigi

2017-04-01

A comparative analysis of two optical fiber sensing platforms is presented. The sensors are based on surface plasmon resonance (SPR) in a D-shaped plastic optical fiber (POF) with a photoresist buffer layer between the exposed POF core and the thin gold film. We show how the sensor's performances change when the photoresist layer changes. The photoresist layers proposed in this analysis are SU-8 3005 and S1813. The experimental results are congruent with the numerical studies and it is instrumental for chemical and bio-chemical applications. Usually, the photoresist layer is required in order to increase the performance of the SPR-POF sensor.

A comparative study of the annealing behavior of Cu(In,Ga)(S,Se){sub 2} based solar cells with an indium sulfide buffer layer, partly submitted to wet chemical treatments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hönes, C., E-mail: christian.hoenes@de.bosch.com; Laboratory for Photovoltaics, University of Luxembourg, 41 rue du Brill, L-4422 Belvaux; Hackenberg, J.

2015-03-07

Indium sulfide thin films deposited via thermal evaporation from compound source material have been successfully utilized as a cadmium free buffer layer for Cu(In,Ga)Se{sub 2} based solar cells. However, high efficiencies are only reached after an additional annealing step. In this work, the annealing behavior of Cu(In,Ga)(S,Se){sub 2} based indium sulfide buffered solar cells is compared to the annealing behavior of similar cells, which were submitted to wet chemical treatments partly containing cadmium ions. Upon annealing a significant improvement of the initial solar cell characteristics is observed for the untreated cell and is related to the increase of activation energymore » for the carrier recombination process and a decrease of the ideality factor within the one diode model. It is shown here that this improvement can also be achieved by wet treatments of the absorber prior to buffer layer deposition. Upon annealing these treated cells still gain in collection length but lose open circuit voltage, which is explained here within a model including a highly p-doped absorber surface layer and supported by simulations showing that a decrease in doping density of such a surface layer would lead to the observed effects.« less

Modelling and simulation of high-frequency (100 MHz) ultrasonic linear arrays based on single crystal LiNbO3.

PubMed

Zhang, J Y; Xu, W J; Carlier, J; Ji, X M; Nongaillard, B; Queste, S; Huang, Y P

2012-01-01

High-frequency ultrasonic transducer arrays are essential for high resolution imaging in clinical analysis and Non-Destructive Evaluation (NDE). However, the fabrication of conventional backing-layer structure, which requires a pitch (distance between the centers of two adjacent elements) of half wavelength in medium, is really a great challenge. Here we present an alternative buffer-layer structure with a silicon lens for volumetric imaging. The requirement for the size of the pitch is less critical for this structure, making it possible to fabricate high-frequency (100MHz) ultrasonic linear array transducers. Using silicon substrate also makes it possible to integrate the arrays with IC (Integrated Circuit). To compare with the conventional backing-layer structure, a finite element tool, COMSOL, is employed to investigate the performances of acoustic beam focusing, the influence of pitch size for the buffer-layer configuration, and to calculate the electrical properties of the arrays, including crosstalk effect and electrical impedance. For a 100MHz 10-element array of buffer-layer structure, the ultrasound beam in azimuth plane in water could be electronically focused to obtain a spatial resolution (a half-amplitude width) of 86μm at the focal depth. When decreasing from half wavelength in silicon (42μm) to half wavelength in water (7.5μm), the pitch sizes weakly affect the focal resolution. The lateral spatial resolution is increased by 4.65% when the pitch size decreases from 42μm to 7.5μm. The crosstalk between adjacent elements at the central frequency is, respectively, -95dB, -39.4dB, and -60.5dB for the 10-element buffer, 49-element buffer and 49-element backing arrays. Additionally, the electrical impedance magnitudes for each structure are, respectively, 4kΩ, 26.4kΩ, and 24.2kΩ, which is consistent with calculation results using Krimholtz, Leedom, and Matthaei (KLM) model. These results show that the buffer-layer configuration is a promising alternative for the fabrication of high-frequency ultrasonic linear arrays dedicated to volumetric imaging. Copyright © 2011 Elsevier B.V. All rights reserved.

Economic potential of the Rooiberg Group: volcanic rocks in the floor and roof of the Bushveld Complex

NASA Astrophysics Data System (ADS)

Schweitzer, J. K.; Hatton, C. J.; de Waal, S. A.

1995-04-01

Volcanic rocks of the Rooiberg Group are preserved in the floor and roof of the mafic Rustenburg Layered Suite of the Bushveld Complex. Field and geochemical characteristics of these volcanic rocks imply that they are genetically related to the Rustenburg Layered Suite. Four major ore-forming events are identified in the Rooiberg Group. The first phase was accompanied by volcanic hosted, fault controlled, hydrothermal copper mineralisation, which is found in the lowermost portion of the Rooiberg Group, underlying the Rustenburg Layered Suite. This type of mineralisation is tentatively linked to initial Rustenburg Layered Suite intrusions. Stratabound arsenic mineralisation that possibly formed in response to contact metamorphism, characterises the second phase, and occurred after extrusion of the Damwal Formation, possibly due to shallow granophyric intrusion. The third mineralising event occurred in response to contact metamorphism during the final stages of the Rustenburg Layered Suite, where especially Pb and Zn were introduced into the felsite roof rocks. This type of mineralisation affected the majority of the Rooiberg Group, but is most pronounced towards the contact with the Rustenburg Layered Suite. The fourth phase is restricted to the Rooiberg Group in the Nylstroom area and is linked to the granite intrusions of the Lebowa Granite Suite, from which Sn and F were introduced into the uppermost felsite succession. Mineralisation in the Rooiberg Group appears to be controlled by the character and intrusion level of the associated Bushveld magmas. Different styles of mineralisation in Rooiberg Group volcanic rocks are encountered at various stratigraphic levels. Major primary volcanogenic ore deposits appear to be absent.

Development of buffer layer structure for epitaxial growth of (100)/(001)Pb(Zr,Ti)O3-based thin film on (111)Si wafer

NASA Astrophysics Data System (ADS)

Hayasaka, Takeshi; Yoshida, Shinya; Tanaka, Shuji

2017-07-01

This paper reports on the development of a novel buffer layer structure, (100)SrRuO3/(100)LaNiO3/(111)Pt/(111)CeO2, for the epitaxial growth of a (100)/(001)-oriented Pb(Zr,Ti)O3 (PZT)-based thin film on a (111)Si wafer. (111)Pt and (111)CeO2 were epitaxially grown on (111)Si straightforwardly. Then, the crystal orientation was forcibly changed from (111) to (100) at the LaNiO3 layer owing to its strong (100)-self-orientation property, which enabled the cube-on-cube epitaxial growth of the subsequent (100)SrRuO3 layer and preferentially (100)/(001)-oriented PZT-based thin film. The PZT-based epitaxial thin films were comprehensively characterized in terms of the crystallinity, in-plane epitaxial relationships, piezoelectricity, and so forth. This buffer layer structure for the epitaxial growth of PZT can be applied to piezoelectric micro-electro-mechanical systems (MEMS) vibrating ring gyroscopes.

Superconducting structure

DOEpatents

Kwon, Chuhee; Jia, Quanxi; Foltyn, Stephen R.

2003-04-01

A superconductive structure including a dielectric oxide substrate, a thin buffer layer of a superconducting material thereon; and, a layer of a rare earth-barium-copper oxide superconducting film thereon the thin layer of yttrium-barium-copper oxide, the rare earth selected from the group consisting of samarium, gadolinium, ytterbium, erbium, neodymium, dysprosium, holmium, lutetium, a combination of more than one element from the rare earth group and a combination of one or more elements from the rare earth group with yttrium, the buffer layer of superconducting material characterized as having chemical and structural compatibility with the dielectric oxide substrate and the rare earth-barium-copper oxide superconducting film is provided.

Superconducting Structure

DOEpatents

Kwon, Chuhee; Jia, Quanxi; Foltyn, Stephen R.

2005-09-13

A superconductive structure including a dielectric oxide substrate, a thin buffer layer of a superconducting material thereon; and, a layer of a rare earth-barium-copper oxide superconducting film thereon the thin layer of yttrium-barium-copper oxide, the rare earth selected from the group consisting of samarium, gadolinium, ytterbium, erbium, neodymium, dysprosium, holmium, lutetium, a combination of more than one element from the rare earth group and a combination of one or more elements from the rare earth group with yttrium, the buffer layer of superconducting material characterized as having chemical and structural compatibility with the dielectric oxide substrate and the rare earth-barium-copper oxide superconducting film is provided.

Self-Functionalization Behind a Solution-Processed NiOx Film Used As Hole Transporting Layer for Efficient Perovskite Solar Cells.

PubMed

Ciro, John; Ramírez, Daniel; Mejía Escobar, Mario Alejandro; Montoya, Juan Felipe; Mesa, Santiago; Betancur, Rafael; Jaramillo, Franklin

2017-04-12

Fabrication of solution-processed perovskite solar cells (PSCs) requires the deposition of high quality films from precursor inks. Frequently, buffer layers of PSCs are formed from dispersions of metal oxide nanoparticles (NPs). Therefore, the development of trustable methods for the preparation of stable colloidal NPs dispersions is crucial. In this work, a novel approach to form very compact semiconducting buffer layers with suitable optoelectronic properties is presented through a self-functionalization process of the nanocrystalline particles by their own amorphous phase and without adding any other inorganic or organic functionalization component or surfactant. Such interconnecting amorphous phase composed by residual nitrate, hydroxide, and sodium ions, proved to be fundamental to reach stable colloidal dispersions and contribute to assemble the separate crystalline nickel oxide NPs in the final film, resulting in a very homogeneous and compact layer. A proposed mechanism behind the great stabilization of the nanoparticles is exposed. At the end, the self-functionalized nickel oxide layer exhibited high optoelectronic properties enabling perovskite p-i-n solar cells as efficient as 16.6% demonstrating the pertinence of the presented strategy to obtain high quality buffer layers processed in solution at room temperature.

Buffer Layer Doping Concentration Measurement Using VT-VSUB Characteristics of GaN HEMT with p-GaN Substrate Layer

NASA Astrophysics Data System (ADS)

Hu, Cheng-Yu; Nakatani, Katsutoshi; Kawai, Hiroji; Ao, Jin-Ping; Ohno, Yasuo

To improve the high voltage performance of AlGaN/GaN heterojunction field effect transistors (HFETs), we have fabricated AlGaN/GaN HFETs with p-GaN epi-layer on sapphire substrate with an ohmic contact to the p-GaN (p-sub HFET). Substrate bias dependent threshold voltage variation (VT-VSUB) was used to directly determine the doping concentration profile in the buffer layer. This VT-VSUB method was developed from Si MOSFET. For HFETs, the insulator is formed by epitaxially grown and heterogeneous semiconductor layer while for Si MOSFETs the insulator is amorphous SiO2. Except that HFETs have higher channel mobility due to the epitaxial insulator/semiconductor interface, HFETs and Si MOSFETs are basically the same in the respect of device physics. Based on these considerations, the feasibility of this VT-VSUB method for AlGaN/GaN HFETs was discussed. In the end, the buffer layer doping concentration was measured to be 2 × 1017cm-3, p-type, which is well consistent with the Mg concentration obtained from secondary ion mass spectroscopy (SIMS) measurement.

Transparent TiO 2 nanotube array photoelectrodes prepared via two-step anodization

DOE PAGES

Kim, Jin Young; Zhu, Kai; Neale, Nathan R.; ...

2014-04-04

Two-step anodization of transparent TiO 2 nanotube arrays has been demonstrated with aid of a Nb-doped TiO 2 buffer layer deposited between the Ti layer and TCO substrate. Enhanced physical adhesion and electrochemical stability provided by the buffer layer has been found to be important for successful implementation of the two-step anodization process. As a result, with the proposed approach, the morphology and thickness of NT arrays could be controlled very precisely, which in turn, influenced their optical and photoelectrochemical properties.

Series interconnected photovoltaic cells and method for making same

DOEpatents

Albright, Scot P.; Chamberlin, Rhodes R.; Thompson, Roger A.

1995-01-01

A novel photovoltaic module (10) and method for constructing the same are disclosed. The module (10) includes a plurality of photovoltaic cells (12) formed on a substrate (14) and laterally separated by interconnection regions (15). Each cell (12) includes a bottom electrode (16), a photoactive layer (18) and a top electrode layer (20). Adjacent cells (12) are connected in electrical series by way of a conductive-buffer line (22). The buffer line (22) is also useful in protecting the bottom electrode (16) against severing during downstream layer cutting processes.

Method to prevent/mitigate steam explosions in casting pits

DOEpatents

Taleyarkhan, R.P.

1996-12-24

Steam explosions can be prevented or mitigated during a metal casting process by the placement of a perforated flooring system in the casting pit. An upward flow of compressed gas through this perforated flooring system is introduced during the casting process to produce a buffer layer between any spilled molten metal and the cooling water in the reservoir. This buffer layer provides a hydrodynamic layer which acts to prevent or mitigate steam explosions resulting from hot, molten metal being spilled into or onto the cooling water. 3 figs.

Single orthorhombic b axis orientation and antiferromagnetic ordering type in multiferroic CaMnO3 thin film with La0.67Ca0.33MnO3 buffer layer

NASA Astrophysics Data System (ADS)

Wang, F.; Dong, B. J.; Zhang, Y. Q.; Liu, W.; Zhang, H. R.; Bai, Y.; Li, S. K.; Yang, T.; Sun, J. R.; Wang, Z. J.; Zhang, Z. D.

2017-09-01

The detailed crystal structure and antiferromagnetic properties of a 42 nm thick CaMnO3 film grown on a LaAlO3 substrate with a 9 nm La0.67Ca0.33MnO3 buffer layer have been investigated. Compared with a CaMnO3 film directly grown on a LaAlO3 substrate, only one kind of orthorhombic b axis orientation along the [100] axis of the substrate is observed in the CaMnO3 film with a La0.67Ca0.33MnO3 buffer layer. To determine the antiferromagnetic ordering type of our CaMnO3 film with a buffer layer, the first-principles calculations were carried out with the results, indicating that the CaMnO3 film, even under a tensile strain of 1.9%, is still a compensated G-type antiferromagnetic order, the same as the bulk. Moreover, the exchange bias effect is observed at the interface of the CaMnO3/La0.67Ca0.33MnO3 film, further confirming the antiferromagnetic ordering of the CaMnO3 film with a buffer layer. In addition, it is concluded that the exchange bias effect originates from the spin glass state at the La0.67Ca0.33MnO3/CaMnO3 interface, which arises from a competition between the double-exchange ferromagnetic La0.67Ca0.33MnO3 and super-exchange antiferromagnetic CaMnO3 below the spin glass freezing temperature.

Data Elevator

DOE Office of Scientific and Technical Information (OSTI.GOV)

BYNA, SUNRENDRA; DONG, BIN; WU, KESHENG

Data Elevator: Efficient Asynchronous Data Movement in Hierarchical Storage Systems Multi-layer storage subsystems, including SSD-based burst buffers and disk-based parallel file systems (PFS), are becoming part of HPC systems. However, software for this storage hierarchy is still in its infancy. Applications may have to explicitly move data among the storage layers. We propose Data Elevator for transparently and efficiently moving data between a burst buffer and a PFS. Users specify the final destination for their data, typically on PFS, Data Elevator intercepts the I/O calls, stages data on burst buffer, and then asynchronously transfers the data to their final destinationmore » in the background. This system allows extensive optimizations, such as overlapping read and write operations, choosing I/O modes, and aligning buffer boundaries. In tests with large-scale scientific applications, Data Elevator is as much as 4.2X faster than Cray DataWarp, the start-of-art software for burst buffer, and 4X faster than directly writing to PFS. The Data Elevator library uses HDF5's Virtual Object Layer (VOL) for intercepting parallel I/O calls that write data to PFS. The intercepted calls are redirected to the Data Elevator, which provides a handle to write the file in a faster and intermediate burst buffer system. Once the application finishes writing the data to the burst buffer, the Data Elevator job uses HDF5 to move the data to final destination in an asynchronous manner. Hence, using the Data Elevator library is currently useful for applications that call HDF5 for writing data files. Also, the Data Elevator depends on the HDF5 VOL functionality.« less

Emission wavelength red-shift by using ;semi-bulk; InGaN buffer layer in InGaN/InGaN multiple-quantum-well

NASA Astrophysics Data System (ADS)

Alam, Saiful; Sundaram, Suresh; Li, Xin; El Gmili, Youssef; Elouneg-Jamroz, Miryam; Robin, Ivan Christophe; Patriarche, Gilles; Salvestrini, Jean-Paul; Voss, Paul L.; Ougazzaden, Abdallah

2017-12-01

We report an elongation of emission wavelength by inserting a ∼70 nm thick high quality semi-bulk (SB) InyGa1-yN buffer layer underneath the InxGa1-xN/InyGa1-yN (x > y) multi-quantum-well (MQW).While the MQW structure without the InGaN SB buffer is fully strained on the n-GaN template, the MQW structure with the buffer has ∼15% relaxation. This small relaxation along with slight compositional pulling induced well thickness increase of MQW is believed to be the reason for the red-shift of emission wavelength. In addition, the SB InGaN buffer acts as an electron reservoir and also helps to reduce the Quantum Confined Stark Effect (QCSE) and thus increase the emission intensity. In this way, by avoiding fully relaxed buffer induced material degradation, a longer emission wavelength can be achieved by just using InGaN SB buffer while keeping all other growth conditions the same as the reference structure. Thus, a reasonably thick fully strained or very little relaxed InGaN buffer, which is realized by ;semi-bulk; approach to maintain good InGaN material quality, can be beneficial for realizing LEDs, grown on top of this buffer, emitting in the blue to cyan to green regime without using excess indium (In).

LPE growth of crack-free PbSe layers on Si(100) using MBE-Grown PbSe/BaF2CaF2 buffer layers

NASA Astrophysics Data System (ADS)

Strecker, B. N.; McCann, P. J.; Fang, X. M.; Hauenstein, R. J.; O'Steen, M.; Johnson, M. B.

1997-05-01

Crack-free PbSe on (100)-oriented Si has been obtained by a combination of liquid phase epitaxy (LPE) and molecular beam epitaxy (MBE) techniques. MBE is employed first to grow a PbSe/BaF2/CaF2 buffer structure on the (100)-oriented Si. A 2.5 μm thick PbSe layer is then grown by LPE. The LPE-grown PbSe displays excellent surface morphology and is continuous over the entire 8×8 mm2 area of growth. This result is surprising because of the large mismatch in thermal expansion coefficients between PbSe and Si. Previous attempts to grow crack-free PbSe by MBE alone using similar buffer structures on (100)-oriented Si have been unsuccessful. It is speculated that the large concentration of Se vacancies in the LPE-grown PbSe layer may allow dislocation climb along higher order slip planes, providing strain relaxation.

Bimetallic nanocomposite as hole transport co-buffer layer in organic solar cell

NASA Astrophysics Data System (ADS)

Mola, Genene Tessema; Arbab, Elhadi A. A.

2017-12-01

Silver-zinc bimetallic nanocomposite (Ag:Zn BiM-NPs) was used as an inter-facial buffer layer in the preparation of thin film organic solar cell (TFOSC). The current investigation focuses on the effect of bimetallic nanoparticles on the performance of TFOSC. A number experiments were conducted by employing Ag:Zn nanocomposite buffer layer of thickness 1 nm at various positions of the device structure. In all cases, we found significant improvement on the power conversion efficiency of the solar cells. It is also noted that the open circuit voltage of the devices are decreasing when Ag:Zn form direct contact with the ITO electrode and without the inclusion of PEDOT:PSS. However, all results show that the introduction of Ag:Zn nanocomposite layer close to PEDOT:PSS could be beneficial to improve the charge transport processes in the preparation of thin film organic solar cell. The Ag:Zn BiM-NPs and the device properties were presented and discussed in terms of optical, electrical and film morphologies of the devices.

V2O5 thin film deposition for application in organic solar cells

NASA Astrophysics Data System (ADS)

Arbab, Elhadi A. A.; Mola, Genene Tessema

2016-04-01

Vanadium pentoxide V2O5 films were fabricated by way of electrochemical deposition technique for application as hole transport buffer layer in organic solar cell. A thin and uniform V2O5 films were successfully deposited on indium tin oxide-coated glass substrate. The characterization of surface morphology and optical properties of the deposition suggest that the films are suitable for photovoltaic application. Organic solar cell fabricated using V2O5 as hole transport buffer layer showed better devices performance and environmental stability than those devices fabricated with PEDOT:PSS. In an ambient device preparation condition, the power conversion efficiency increases by nearly 80 % compared with PEDOT:PSS-based devices. The devices lifetime using V2O5 buffer layer has improved by a factor of 10 over those devices with PEDOT:PSS.

Methods for improved growth of group III nitride semiconductor compounds

DOEpatents

Melnik, Yuriy; Chen, Lu; Kojiri, Hidehiro

2015-03-17

Methods are disclosed for growing group III-nitride semiconductor compounds with advanced buffer layer technique. In an embodiment, a method includes providing a suitable substrate in a processing chamber of a hydride vapor phase epitaxy processing system. The method includes forming an AlN buffer layer by flowing an ammonia gas into a growth zone of the processing chamber, flowing an aluminum halide containing precursor to the growth zone and at the same time flowing additional hydrogen halide or halogen gas into the growth zone of the processing chamber. The additional hydrogen halide or halogen gas that is flowed into the growth zone during buffer layer deposition suppresses homogeneous AlN particle formation. The hydrogen halide or halogen gas may continue flowing for a time period while the flow of the aluminum halide containing precursor is turned off.

Inclined dislocation arrays in AlGaN/AlGaN quantum well structures emitting at 290 nm

NASA Astrophysics Data System (ADS)

Chang, T. Y.; Moram, M. A.; McAleese, C.; Kappers, M. J.; Humphreys, C. J.

2010-12-01

We report on the structural and optical properties of deep ultraviolet emitting AlGaN/AlGaN multiple quantum wells (MQWs) grown on (0001) sapphire by metal-organic vapor phase epitaxy using two different buffer layer structures, one containing a thin (1 μm) AlN layer combined with a GaN interlayer and the other a thick (4 μm) AlN layer. Transmission electron microscopy analysis of both structures showed inclined arrays of dislocations running through the AlGaN layers at an angle of ˜30°, originating at bunched steps at the AlN surface and terminating at bunched steps at the surface of the MQW structure. In all layers, these inclined dislocation arrays are surrounded by AlGaN with a relatively higher Ga content, consistent with plan-view cathodoluminescence maps in which the bunched surface steps are associated with longer emission wavelengths. The structure with the 4 μm-thick AlN buffer layer had a dislocation density lower by a factor of 2 (at (1.7±0.1)×109 cm-2) compared to the structure with the 1 μm thick AlN buffer layer, despite the presence of the inclined dislocation arrays.

Inorganic Substrates and Encapsulation Layers for Transient Electronics

DTIC Science & Technology

2014-07-01

surface oxidation of the nitrides, the measurements were conducted shortly after oxide removal in buffered oxide etchant (BOE) 6:1 (Transene Company Inc...values for the time-dependent dissolution of thermally grown SiO2 (dry oxidation) in buffer solutions (black, pH 7.4; red, pH 8; blue, pH 10...22 5.1.3 Contractor will Identify and Measure Key Performance Characteristics of Candidate Metal Conductive Layers for

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sun, Rui; University of Chinese Academy of Sciences, Beijing 100049; Makise, Kazumasa

We have developed epitaxial NbN/AlN/NbN tunnel junctions on Si (100) substrates with a TiN buffer layer. A 50-nm-thick (200)-oriented TiN thin film was introduced as the buffer layer for epitaxial growth of NbN/AlN/NbN trilayers on Si substrates. The fabricated NbN/AlN/NbN junctions demonstrated excellent tunneling properties with a high gap voltage of 5.5 mV, a large I{sub c}R{sub N} product of 3.8 mV, a sharp quasiparticle current rise with a ΔV{sub g} of 0.4 mV, and a small subgap leakage current. The junction quality factor R{sub sg}/R{sub N} was about 23 for the junction with a J{sub c} of 47 A/cm{supmore » 2} and was about 6 for the junction with a J{sub c} of 3.0 kA/cm{sup 2}. X-ray diffraction and transmission electron microscopy observations showed that the NbN/AlN/NbN trilayers were grown epitaxially on the (200)-orientated TiN buffer layer and had a highly crystalline structure with the (200) orientation.« less

Stress in (Al, Ga)N heterostructures grown on 6H-SiC and Si substrates byplasma-assisted molecular beam epitaxy

NASA Astrophysics Data System (ADS)

Koshelev, O. A.; Nechaev, D. V.; Sitnikova, A. A.; Ratnikov, V. V.; Ivanov, S. V.; Jmerik, V. N.

2017-11-01

The paper describes experimental results on low temperature plasma-assisted molecular beam epitaxy of GaN/AlN heterostructures on both 6H-SiC and Si(111) substrates. We demonstrate that application of migration enhanced epitaxy and metal-modulated epitaxy for growth of AlN nucleation and buffer layers lowers the screw and edge(total)threading dislocation (TD) densities down to 1.7·108 and 2·109 cm-2, respectively, in a 2.8-μm-thick GaN buffer layer grown atop of AlN/6H-SiC. The screw and total TD densities of 1.2·109 and 7.4·109 cm-2, respectively, were achieved in a 1-μm-thickGaN/AlNheterostructure on Si(111). Stress generation and relaxation in GaN/AlN heterostructures were investigated by using multi-beam optical stress sensor (MOSS) to achieve zero substrate curvature at room temperature. It is demonstrated that a 1-μm-thick GaN/AlN buffer layer grown by PA MBE provides planar substrate morphology in the case of growth on Si substrates whereas 5-μm-thick GaN buffer layers have to be used to achieve the same when growing on 6H-SiC substrates.

Defect prevention in silica thin films synthesized using AP-PECVD for flexible electronic encapsulation

NASA Astrophysics Data System (ADS)

Elam, Fiona M.; Starostin, Sergey A.; Meshkova, Anna S.; van der Velden-Schuermans, Bernadette C. A. M.; van de Sanden, Mauritius C. M.; de Vries, Hindrik W.

2017-06-01

Industrially and commercially relevant roll-to-roll atmospheric pressure-plasma enhanced chemical vapour deposition was used to synthesize smooth, 80 nm silica-like bilayer thin films comprising a dense ‘barrier layer’ and comparatively porous ‘buffer layer’ onto a flexible polyethylene 2,6 naphthalate substrate. For both layers, tetraethyl orthosilicate was used as the precursor gas, together with a mixture of nitrogen, oxygen and argon. The bilayer films demonstrated exceptionally low effective water vapour transmission rates in the region of 6.1  ×  10-4 g m-2 d-1 (at 40 °C, 90% relative humidity), thus capable of protecting flexible photovoltaics and thin film transistors from degradation caused by oxygen and water. The presence of the buffer layer within the bilayer architecture was mandatory in order to achieve the excellent encapsulation performance. Atomic force microscopy in addition to solvent permeation measurements, confirmed that the buffer layer prevented the formation of performance-limiting defects in the bilayer thin films, which likely occur as a result of excessive plasma-surface interactions during the deposition process. It emerged that the primary function of the buffer layer was therefore to act as a protective coating for the flexible polymer substrate material.

On the influence of recrystallization on snow fabric and microstructure: study of a snow profile in Central East Antarctica

NASA Astrophysics Data System (ADS)

Calonne, Neige; Schneebeli, Martin; Montagnat, Maurine; Matzl, Margret

2016-04-01

Temperature gradient metamorphism affects the Antarctic snowpack up to 5 meters depth, which lead to a recrystallization of the ice grains by sublimation of ice and deposition of water vapor. By this way, it is well known that the snow microstructure evolves (geometrical changes). Also, a recent study shows an evolution of the snow fabric, based on a cold laboratory experiment. Both fabric and microstructure are required to better understand mechanical behavior and densification of snow, firn and ice, given polar climatology. The fabric of firn and ice has been extensively investigated, but the publications by Stephenson (1967, 1968) are to our knowledge the only ones describing the snow fabric in Antarctica. In this context, our work focuses on snow microstructure and fabric in the first meters depth of the Antarctic ice sheet, where temperature gradients driven recrystallization occurs. Accurate details of the snow microstructure are observed using micro-computed tomography. Snow fabrics were measured at various depths from thin sections of impregnated snow with an Automatic Ice Texture Analyzer (AITA). A definite relationship between microstructure and fabric is found and highlights the influence of metamorphism on both properties. Our results also show that the metamorphism enhances the differences between the snow layers properties. Our work stresses the significant and complex evolution of snow properties in the upper meters of the ice sheet and opens the question of how these layer properties will evolve at depth and may influence the densification.

Dynamics and mitigation of six pesticides in a "Wet" forest buffer zone.

PubMed

Passeport, Elodie; Richard, Benjamin; Chaumont, Cédric; Margoum, Christelle; Liger, Lucie; Gril, Jean-Joël; Tournebize, Julien

2014-04-01

Pesticide pollution is one of the main current threats on water quality. This paper presents the potential and functioning principles of a "Wet" forest buffer zone for reducing concentrations and loads of glyphosate, isoproturon, metazachlor, azoxystrobin, epoxiconazole, and cyproconazole. A tracer injection experiment was conducted in the field in a forest buffer zone at Bray (France). A fine time-scale sampling enabled to illustrate that interactions between pesticides and forest buffer substrates (soil and organic-rich litter layer), had a retarding effect on molecule transfer. Low concentrations were observed for all pesticides at the forest buffer outlet thus demonstrating the efficiency of "Wet" forest buffer zone for pesticide dissipation. Pesticide masses injected in the forest buffer inlet directly determined concentration peaks observed at the outlet. Rapid and partially reversible adsorption was likely the major process affecting pesticide transfer for short retention times (a few hours to a few days). Remobilization of metazachlor, isoproturon, desmethylisoproturon, and AMPA was observed when non-contaminated water flows passed through the forest buffer. Our data suggest that pesticide sorption properties alone could not explain the complex reaction mechanisms that affected pesticide transfer in the forest buffer. Nevertheless, the thick layer of organic matter litter on the top of the forest soil was a key parameter, which enhanced partially reversible sorption of pesticide, thus retarded their transfer, decreased concentration peaks, and likely increased degradation of the pesticides. Consequently, to limit pesticide pollution transported by surface water, the use of already existing forest areas as buffer zones should be equally considered as the most commonly implemented grass buffer strips.

Deformation behavior of coherently strained InAs/GaAs(111)A heteroepitaxial systems: Theoretical calculations and experimental measurements

NASA Astrophysics Data System (ADS)

Zepeda-Ruiz, Luis A.; Pelzel, Rodney I.; Nosho, Brett Z.; Weinberg, W. Henry; Maroudas, Dimitrios

2001-09-01

A comprehensive, quantitative analysis is presented of the deformation behavior of coherently strained InAs/GaAs(111)A heteroepitaxial systems. The analysis combines a hierarchical theoretical approach with experimental measurements. Continuum linear elasticity theory is linked with atomic-scale calculations of structural relaxation for detailed theoretical studies of deformation in systems consisting of InAs thin films on thin GaAs(111)A substrates that are mechanically unconstrained at their bases. Molecular-beam epitaxy is used to grow very thin InAs films on both thick and thin GaAs buffer layers on epi-ready GaAs(111)A substrates. The deformation state of these samples is characterized by x-ray diffraction (XRD). The interplanar distances of thin GaAs buffer layers along the [220] and [111] crystallographic directions obtained from the corresponding XRD spectra indicate clearly that thin buffer layers deform parallel to the InAs/GaAs(111)A interfacial plane, thus aiding in the accommodation of the strain induced by lattice mismatch. The experimental measurements are in excellent agreement with the calculated lattice interplanar distances and the corresponding strain fields in the thin mechanically unconstrained substrates considered in the theoretical analysis. Therefore, this work contributes direct evidence in support of our earlier proposal that thin buffer layers in layer-by-layer semiconductor heteroepitaxy exhibit mechanical behavior similar to that of compliant substrates [see, e.g., B. Z. Nosho, L. A. Zepeda-Ruiz, R. I. Pelzel, W. H. Weinberg, and D. Maroudas, Appl. Phys. Lett. 75, 829 (1999)].

Growth and characterization of low composition Ge, x in epi-Si1‑x Gex (x  ⩽  10%) active layer for fabrication of hydrogenated bottom solar cell

NASA Astrophysics Data System (ADS)

Ajmal Khan, M.; Sato, R.; Sawano, K.; Sichanugrist, P.; Lukianov, A.; Ishikawa, Y.

2018-05-01

Semiconducting epi-Si1‑x Ge x alloys have promising features as solar cell materials and may be equally important for some other semiconductor device applications. Variation of the germanium compositional, x in epi-Si1‑x Ge x , makes it possible to control the bandgap between 1.12 eV and 0.68 eV for application in bottom solar cells. A low proportion of Ge in SiGe alloy can be used for photovoltaic application in a bottom cell to complete the four-terminal tandem structure with wide bandgap materials. In this research, we aimed to use a low proportion of Ge—about 10%—in strained or relaxed c-Si1‑x Ge x /c-Si heterojunctions (HETs), with or without insertion of a Si buffer layer grown by molecular beam epitaxy, to investigate the influence of the relaxed or strained SiGe active layer on the performance of HET solar cells grown using the plasma enhanced chemical vapor deposition system. Thanks to the c-Si buffer layer at the hetero-interface, the efficiency of these SiGe based HET solar cells was improved from 2.3% to 3.5% (fully strained and with buffer layer). The Jsc was improved, from 8 mA cm‑2 to 15.46 mA cm‑2, which might be supported by strained c-Si buffer layer at the hetero-interface, by improving the crystalline quality.

A Chlorine-Centric Perspective on Fluid-Mediated Processes at Convergent Plate Boundaries

NASA Astrophysics Data System (ADS)

Selverstone, J.

2014-12-01

The release and migration of metamorphic fluids from subducting slabs into overlying mantle is widely recognized as a major mechanism in producing arc geochemical signatures and returning fluid-mobile elements to earth's crust and surface environments. Although the magnitudes of many geochemical fluxes are well constrained, the processes whereby mass transfer occurs in different portions of the subduction system are less well known. Chlorine stable isotopes provide a new perspective on some of these processes: Cl is hydrophilic, but decarbonation reactions favor Cl retention in minerals. Cl also shows less isotopic fractionation than other fluid-sensitive systems and may thus preserve evidence of specific fluid sources and/or fluid mixing events. Detailed studies of sedimentary sequences show that individual beds are isotopically homogeneous but large heterogeneities in δ37Cl exist across beds on a cm to m scale and vary as a function of depositional environment. Compositionally correlative medium-, high-, and ultrahigh-pressure metamorphic sequences in the Alps record decreases of 30-50% in Cl contents in the earliest stages of metamorphism, but little change thereafter. No statistically significant change in isotopic composition occurs during prograde metamorphism of individual horizons, and the same large degree of isotopic heterogeneity (up to 6‰) persists throughout the prograde devolatilization history of the rocks. Likewise, analysis of HP/UHP serpentinites and altered oceanic crust show that heterogeneous protolith compositions are preserved during transport to sub-arc depths, despite large-scale devolatilization. However, upward transport of rocks within the subduction channel results in highly localized interaction with isotopically distinct, Cl-bearing fluid packets. Overlying forearc wedge rocks also record heterogeneous and channelized interaction with distinct fluid components with different δ37Cl. Within-layer fluid compartmentalization during continuous devolatilization reactions must thus be reconciled with discontinuous, cross-layer fluid percolation out of the slab and into the wedge. The resulting implications of the chlorine data for recent mechanical models of slab-to-wedge fluid transport will be discussed.

Petrologic Constraints on the Exhumation of the Sierra Blanca Metamorphic Core Complex (AZ)

NASA Astrophysics Data System (ADS)

Koppens, K. M.; Gottardi, R.

2017-12-01

The Sierra Blanca metamorphic core complex (SBMCC), located 90 miles west of Tucson, is part of the southern belt of metamorphic core complexes that stretches across southern Arizona. The SBMCC exposes Jurassic age sedimentary rocks that have been metamorphosed by intruding Late Cretaceous peraluminous granites and pegmatites. Evidence of this magmatic episode includes polysythetic twinning in plagioclase, albite exsolution of potassium feldspar resulting in myrmekitic texture, and garnet, mica and feldspar assemblages. The magmatic fabric is overprinted by a Tertiary (Miocene?) tectonic fabric, associated with the exhumation of the Sierra Blanca metamorphic core along a low-angle detachment fault, forming the SBMCC. The NW-SE elongated dome of metamorphic rocks forms the footwall of the detachment shear zone, and is separated from the hanging wall, composed of Paleozoic and Mesozoic metasedimentary rocks, by a low-angle detachment shear zone. Foliation is defined by gneissic layering and aligned muscovite, and is generally sub-horizontal, defining the dome. The NNW-SSE mineral stretching lineation is expressed by plagioclase and K-feldspar porphyroclasts, and various shear sense indicators are all consistent with a top-to the-NNW shear sense. Lineation trends in a NNW-SSE orientation; however, plunge changes across the domiform shape of the MCC. Much of the deformation is preserved in the blastomylonitic gneiss derived from the peraluminous granite, including epidote porphyroclasts, grain boundary migration in quartz, lozenged amphiboles, mica fish, and retrograde mineral alterations. Detailed petrologic observation and microstructural analysis presented here provide thermomechanical constraints on the evolution of the SBMCC.

Buffers more than buffering agent: introducing a new class of stabilizers for the protein BSA.

PubMed

Gupta, Bhupender S; Taha, Mohamed; Lee, Ming-Jer

2015-01-14

In this study, we have analyzed the influence of four biological buffers on the thermal stability of bovine serum albumin (BSA) using dynamic light scattering (DLS). The investigated buffers include 4-(2-hydroxyethyl)piperazine-1-ethanesulfonic acid (HEPES), 4-(2-hydroxyethyl)-1-piperazine-propanesulfonic acid (EPPS), 4-(2-hydroxyethyl)piperazine-1-ethanesulfonic acid sodium salt (HEPES-Na), and 4-morpholinepropanesulfonic acid sodium salt (MOPS-Na). These buffers behave as a potential stabilizer for the native structure of BSA against thermal denaturation. The stabilization tendency follows the order of MOPS-Na > HEPES-Na > HEPES ≫ EPPS. To obtain an insight into the role of hydration layers and peptide backbone in the stabilization of BSA by these buffers, we have also explored the phase transition of a thermoresponsive polymer, poly(N-isopropylacrylamide (PNIPAM)), a model compound for protein, in aqueous solutions of HEPES, EPPS, HEPES-Na, and MOPS-Na buffers at different concentrations. It was found that the lower critical solution temperatures (LCST) of PNIPAM in the aqueous buffer solutions substantially decrease with increase in buffer concentration. The mechanism of interactions between these buffers and protein BSA was probed by various techniques, including UV-visible, fluorescence, and FTIR. The results of this series of studies reveal that the interactions are mainly governed by the influence of the buffers on the hydration layers surrounding the protein. We have also explored the possible binding sites of BSA with these buffers using a molecular docking technique. Moreover, the activities of an industrially important enzyme α-chymotrypsin (α-CT) in 0.05 M, 0.5 M, and 1.0 M of HEPES, EPPS, HEPES-Na, and MOPS-Na buffer solutions were analyzed at pH = 8.0 and T = 25 °C. Interestingly, the activities of α-CT were found to be enhanced in the aqueous solutions of these investigated buffers. Based upon the Jones-Dole viscosity parameters, the kosmotropic or chaotropic behaviors of the investigated buffers at 25 °C have been examined.

Bendability optimization of flexible optical nanoelectronics via neutral axis engineering

PubMed Central

2012-01-01

The enhancement of bendability of flexible nanoelectronics is critically important to realize future portable and wearable nanoelectronics for personal and military purposes. Because there is an enormous variety of materials and structures that are used for flexible nanoelectronic devices, a governing design rule for optimizing the bendability of these nanodevices is required. In this article, we suggest a design rule to optimize the bendability of flexible nanoelectronics through neutral axis (NA) engineering. In flexible optical nanoelectronics, transparent electrodes such as indium tin oxide (ITO) are usually the most fragile under an external load because of their brittleness. Therefore, we representatively focus on the bendability of ITO which has been widely used as transparent electrodes, and the NA is controlled by employing a buffer layer on the ITO layer. First, we independently investigate the effect of the thickness and elastic modulus of a buffer layer on the bendability of an ITO film. Then, we develop a design rule for the bendability optimization of flexible optical nanoelectronics. Because NA is determined by considering both the thickness and elastic modulus of a buffer layer, the design rule is conceived to be applicable regardless of the material and thickness that are used for the buffer layer. Finally, our design rule is applied to optimize the bendability of an organic solar cell, which allows the bending radius to reach about 1 mm. Our design rule is thus expected to provide a great strategy to enhance the bending performance of a variety of flexible nanoelectronics. PMID:22587757

Bendability optimization of flexible optical nanoelectronics via neutral axis engineering.

PubMed

Lee, Sangmin; Kwon, Jang-Yeon; Yoon, Daesung; Cho, Handong; You, Jinho; Kang, Yong Tae; Choi, Dukhyun; Hwang, Woonbong

2012-05-15

The enhancement of bendability of flexible nanoelectronics is critically important to realize future portable and wearable nanoelectronics for personal and military purposes. Because there is an enormous variety of materials and structures that are used for flexible nanoelectronic devices, a governing design rule for optimizing the bendability of these nanodevices is required. In this article, we suggest a design rule to optimize the bendability of flexible nanoelectronics through neutral axis (NA) engineering. In flexible optical nanoelectronics, transparent electrodes such as indium tin oxide (ITO) are usually the most fragile under an external load because of their brittleness. Therefore, we representatively focus on the bendability of ITO which has been widely used as transparent electrodes, and the NA is controlled by employing a buffer layer on the ITO layer. First, we independently investigate the effect of the thickness and elastic modulus of a buffer layer on the bendability of an ITO film. Then, we develop a design rule for the bendability optimization of flexible optical nanoelectronics. Because NA is determined by considering both the thickness and elastic modulus of a buffer layer, the design rule is conceived to be applicable regardless of the material and thickness that are used for the buffer layer. Finally, our design rule is applied to optimize the bendability of an organic solar cell, which allows the bending radius to reach about 1 mm. Our design rule is thus expected to provide a great strategy to enhance the bending performance of a variety of flexible nanoelectronics.

Method for making high-critical-current-density YBa.sub.2 Cu.sub.3 O.sub.7 superconducting layers on metallic substrates

DOEpatents

Feenstra, Roeland; Christen, David; Paranthaman, Mariappan

1999-01-01

A method is disclosed for fabricating YBa.sub.2 Cu.sub.3 O.sub.7 superconductor layers with the capability of carrying large superconducting currents on a metallic tape (substrate) supplied with a biaxially textured oxide buffer layer. The method represents a simplification of previously established techniques and provides processing requirements compatible with scale-up to long wire (tape) lengths and high processing speeds. This simplification has been realized by employing the BaF.sub.2 method to grow a YBa.sub.2 Cu.sub.3 O.sub.7 film on a metallic substrate having a biaxially textured oxide buffer layer.

ZnO buffer layer for metal films on silicon substrates

DOEpatents

Ihlefeld, Jon

2014-09-16

Dramatic improvements in metallization integrity and electroceramic thin film performance can be achieved by the use of the ZnO buffer layer to minimize interfacial energy between metallization and adhesion layers. In particular, the invention provides a substrate metallization method utilizing a ZnO adhesion layer that has a high work of adhesion, which in turn enables processing under thermal budgets typically reserved for more exotic ceramic, single-crystal, or metal foil substrates. Embodiments of the present invention can be used in a broad range of applications beyond ferroelectric capacitors, including microelectromechanical systems, micro-printed heaters and sensors, and electrochemical energy storage, where integrity of metallized silicon to high temperatures is necessary.

Growth And Characterization Of LPE CdHgTe/CdZnTe/CdZnTe Structure

NASA Astrophysics Data System (ADS)

Pelliciari, B.; Chamonal, J. P.; Destefanis, G. L.; Dicioccio, L.

1988-05-01

The liquid phase epitaxial technique is used to grow Hgl_x Cdx Te (x = .23) from a Te - rich solution onto a Cdl_y ZnyTe (y = .04) buffer layer grown from a Te-rich solution onto a Cdi_yZnyTe bulk substrate in an open tube multibin horizontal slider apparatus.Growth conditions and physical characterizations of both the buffer layer and the CdHgTe layer are given ; electrical properties of the CdHgTe layer are also presen-ted. PV detectors were successfully obtained on such a structure using an ion-implanted technology and their characteristics at 77 K for a 10.1 ,um cut-off wavelength are given.

Particle-based Nano-Antennas at the Vis-NIR regime

DTIC Science & Technology

2013-11-01

PSS (poly(3,4-ethylenedioxythiophene) :poly(styrene sulfonate) is then spin coated and dried at 110oC to form a 50nm buffer layer partially covering...dominant effect is that during the spin coating of the 50nm PEDOT buffer a residual very thin layer coated also the top 50nm part of the Au disks...antennas, capacitive versus conductive coupling, on-demand design (termed ‘popcorn’ antennas), broadband plasmonic metamaterials, and light

Investigation of noble metal substrates and buffer layers for BiSrCaCuO thin films

NASA Astrophysics Data System (ADS)

Matthiesen, M. M.; Rubin, L. M.; Williams, K. E.; Rudman, D. A.

Noble metal buffer layers and substrates for Bi2Sr2CaCu2O8 (BSCCO) films were investigated using bulk ceramic processing and thin-film techniques. Highly oriented, superconducting BSCCO films were fabricated on polycrystalline Ag substrates and on Ag/MgO and Ag/YSZ structures. Such films could not be produced on Au or Pt substrates under any annealing conditions. In addition, superconducting BSCCO films could not be produced on Ag/Al2O3, Ag/SiO2/Si, or Ag/(Haynes 230 alloy) structures using high annealing temperatures (870 C). However, oriented although poorly connected, superconducting BSCCO films were fabricated on Ag/Al2O3 structures by using lower annealing temperatures (820 C). Once lower processing temperatures are optimized, Ag may be usable as a buffer layer for BSCCO films.

GaSb solar cells grown on GaAs via interfacial misfit arrays for use in the III-Sb multi-junction cell

NASA Astrophysics Data System (ADS)

Nelson, George T.; Juang, Bor-Chau; Slocum, Michael A.; Bittner, Zachary S.; Laghumavarapu, Ramesh B.; Huffaker, Diana L.; Hubbard, Seth M.

2017-12-01

Growth of GaSb with low threading dislocation density directly on GaAs may be possible with the strategic strain relaxation of interfacial misfit arrays. This creates an opportunity for a multi-junction solar cell with access to a wide range of well-developed direct bandgap materials. Multi-junction cells with a single layer of GaSb/GaAs interfacial misfit arrays could achieve higher efficiency than state-of-the-art inverted metamorphic multi-junction cells while forgoing the need for costly compositionally graded buffer layers. To develop this technology, GaSb single junction cells were grown via molecular beam epitaxy on both GaSb and GaAs substrates to compare homoepitaxial and heteroepitaxial GaSb device results. The GaSb-on-GaSb cell had an AM1.5g efficiency of 5.5% and a 44-sun AM1.5d efficiency of 8.9%. The GaSb-on-GaAs cell was 1.0% efficient under AM1.5g and 4.5% at 44 suns. The lower performance of the heteroepitaxial cell was due to low minority carrier Shockley-Read-Hall lifetimes and bulk shunting caused by defects related to the mismatched growth. A physics-based device simulator was used to create an inverted triple-junction GaInP/GaAs/GaSb model. The model predicted that, with current GaSb-on-GaAs material quality, the not-current-matched, proof-of-concept cell would provide 0.5% absolute efficiency gain over a tandem GaInP/GaAs cell at 1 sun and 2.5% gain at 44 suns, indicating that the effectiveness of the GaSb junction was a function of concentration.

Effect of fluid flux on the width of contact metamorphic aureoles: evidence from Silver Star, Montana

DOE Office of Scientific and Technical Information (OSTI.GOV)

Foote, M.V.; Frost, B.R.; Angevine, C.L.

1985-01-01

Contact metamorphism of Paleozoic carbonate-rich sediments by the Boulder Batholith near Silver Star, Montana has resulted in the formation of the following six metamorphic zones: (1) calcite (cc) - dolomite (dol) - quartz (q) - phlogopite (phl) +/- kspar (ksp); (b) cc - dol - tremolite (tr) - q - ksp; (c) cc - dol - tr - diopside (di) - phl; (d) cc - dol - di - forsterite (fo) - phl; (e) cc - dol - fo, and cc - di - fo; and (f) cc - fo - periclase +/- dol. The presence of periclase in themore » highest zone indicates that these rocks crystallized in the presence of a water-rich fluid. Calculations of reaction progress indicate that between zone e and zone f, 4.5 rock-volumes of water had to be introduced. Comparison of the aureole at Silver Star with other contact aureoles studied around the Boulder Batholith shows a distinct correlation between the width of the aureole and the inferred fluid flux. The Boulder and Marysville aureoles are internally buffered throughout and have a width (measured to the tremolite-in isograd) of up to 1.5 km, while the Black Butte aureole, which has largely external control of the fluid, has a width of approximately 80 meters. Silver Star, which is intermediate in behavior, has an aureole width of approximately 250 meters. The indicates that in environments of low fluid flux heat is transported largely by conduction, while in environments of low fluid flux most of the heat is transported upward by convective flow, resulting in correspondingly narrower aureoles.« less

Exploring Cd-Zn-O-S alloys for improved buffer layers in thin-film photovoltaics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Varley, J. B.; Lordi, V.; He, X.

Here, to compete with existing and more mature solar cell technologies such as crystalline Si, thin-film photovoltaics require optimization of every aspect in the device heterostructure to reach maximum efficiencies and cost effectiveness. For absorbers like CdTe, Cu(In,Ga)Se 2 (CIGSe), and Cu 2ZnSn(S,Se) 4 (CZTSSe), improving the n-type buffer layer partner beyond conventional CdS is one avenue that can reduce photocurrent losses and improve overall performance. Here, we use first-principles calculations based on hybrid functionals to explore alloys spanning the Cd-, Zn-, O-, and S-containing phase space to identify compositions that may be superior to common buffers like pure CdSmore » or Zn(O,S). We address issues highly correlated with device performance such as lattice-matching for improved buffer-absorber epitaxy and interface quality, dopability, the band gap for reduced absorption losses in the buffer, and the conduction-band offsets shown to facilitate improved charge separation from photoexcited carriers. We supplement our analysis with device-level simulations as parameterized from our calculations and real devices to assess our conclusions of low-Zn and O content buffers showing improved performance with respect to CdS buffers.« less

Exploring Cd-Zn-O-S alloys for improved buffer layers in thin-film photovoltaics

DOE PAGES

Varley, J. B.; Lordi, V.; He, X.; ...

2017-07-17

Here, to compete with existing and more mature solar cell technologies such as crystalline Si, thin-film photovoltaics require optimization of every aspect in the device heterostructure to reach maximum efficiencies and cost effectiveness. For absorbers like CdTe, Cu(In,Ga)Se 2 (CIGSe), and Cu 2ZnSn(S,Se) 4 (CZTSSe), improving the n-type buffer layer partner beyond conventional CdS is one avenue that can reduce photocurrent losses and improve overall performance. Here, we use first-principles calculations based on hybrid functionals to explore alloys spanning the Cd-, Zn-, O-, and S-containing phase space to identify compositions that may be superior to common buffers like pure CdSmore » or Zn(O,S). We address issues highly correlated with device performance such as lattice-matching for improved buffer-absorber epitaxy and interface quality, dopability, the band gap for reduced absorption losses in the buffer, and the conduction-band offsets shown to facilitate improved charge separation from photoexcited carriers. We supplement our analysis with device-level simulations as parameterized from our calculations and real devices to assess our conclusions of low-Zn and O content buffers showing improved performance with respect to CdS buffers.« less

Fluid heterogeneity during granulite facies metamorphism in the Adirondacks: stable isotope evidence

USGS Publications Warehouse

Valley, J.W.; O'Neil, J.R.

1984-01-01

The preservation of premetamorphic, whole-rock oxygen isotope ratios in Adirondack metasediments shows that neither these rocks nor adjacent anorthosites and gneisses have been penetrated by large amounts of externally derived, hot CO2-H2O fluids during granulite facies metamorphism. This conclusion is supported by calculations of the effect of fluid volatilization and exchange and is also independently supported by petrologic and phase equilibria considerations. The data suggest that these rocks were not an open system during metamorphism; that fluid/rock ratios were in many instances between 0.0 and 0.1; that externally derived fluids, as well as fluids derived by metamorphic volatilization, rose along localized channels and were not pervasive; and thus that no single generalization can be applied to metamorphic fluid conditions in the Adirondacks. Analyses of 3 to 4 coexisting minerals from Adirondack marbles show that isotopic equilibrium was attained at the peak of granulite and upper amphibolite facies metamorphism. Thus the isotopic compositions of metamorphic fluids can be inferred from analyses of carbonates and fluid budgets can be constructed. Carbonates from the granulite facies are on average, isotopically similar to those from lower grade or unmetamorphosed limestones of the same age showing that no large isotopic shifts accompanied high grade metamorphism. Equilibrium calculations indicate that small decreases in ??18O, averaging 1 permil, result from volatilization reactions for Adirondack rock compositions. Additional small differences between amphibolite and granulite facies marbles are due to systematic lithologie differences. The range of Adirondack carbonate ??18O values (12.3 to 27.2) can be explained by the highly variable isotopic compositions of unmetamorphosed limestones in conjunction with minor 18O and 13C depletions caused by metamorphic volatilization suggesting that many (and possibly most) marbles have closely preserved their premetamorphic isotopic compositions. Such preservation is particularly evident in instances of high ??18O calcites (25.0 to 27.2), low ??18O wollastonites (-1.3 to 3.5), and sharp gradients in ??18O (18 permil/15m between marble and anorthosite, 8 permil/25 m in metasediments, and 6 permil/1 m in skarn). Isotopic exchange is seen across marble-anorthosite and marble-granite contacts only at the scale of a few meters. Small (<5 m) marble xenoliths are in approximate exchange equilibrium with their hosts, but for larger xenoliths and layers of marble there is no evidence of exchange at distances greater than 10 m from meta-igneous contacts. ?? 1984 Springer-Verlag.

Origins of interlayer formation and misfit dislocation displacement in the vicinity of InAs/GaAs quantum dots

DOE Office of Scientific and Technical Information (OSTI.GOV)

Huang, S.; Kim, S. J.; Pan, X. Q.

We have examined the origins of interlayer formation and misfit dislocation (MD) displacement in the vicinity of InAs/GaAs quantum dots (QDs). For QDs formed by the Stranski-Krastanov mode, regularly spaced MDs nucleate at the interface between the QD and the GaAs buffer layer. In the droplet epitaxy case, both In island formation and In-induced “nano-drilling” of the GaAs buffer layer are observed during In deposition. Upon annealing under As flux, the In islands are converted to InAs QDs, with an InGaAs interlayer at the QD/buffer interface. Meanwhile, MDs nucleate at the QD/interlayer interface.

H2-rich fluids from serpentinization: geochemical and biotic implications.

PubMed

Sleep, N H; Meibom, A; Fridriksson, Th; Coleman, R G; Bird, D K

2004-08-31

Metamorphic hydration and oxidation of ultramafic rocks produces serpentinites, composed of serpentine group minerals and varying amounts of brucite, magnetite, and/or FeNi alloys. These minerals buffer metamorphic fluids to extremely reducing conditions that are capable of producing hydrogen gas. Awaruite, FeNi3, forms early in this process when the serpentinite minerals are Fe-rich. Olivine with the current mantle Fe/Mg ratio was oxidized during serpentinization after the Moon-forming impact. This process formed some of the ferric iron in the Earth's mantle. For the rest of Earth's history, serpentinites covered only a small fraction of the Earth's surface but were an important prebiotic and biotic environment. Extant methanogens react H2 with CO2 to form methane. This is a likely habitable environment on large silicate planets. The catalytic properties of FeNi3 allow complex organic compounds to form within serpentinite and, when mixed with atmospherically produced complex organic matter and waters that circulated through basalts, constitutes an attractive prebiotic substrate. Conversely, inorganic catalysis of methane by FeNi3 competes with nascent and extant life. Copyright 2004 The National Academy of Sciencs of the USA

Stratigraphy, structure and regional correlation of eastern Blue Ridge sequences in southern Virginia and northwestern North Carolina: an interim report from new USGS mapping

USGS Publications Warehouse

Carter, Mark W.; Merschat, Arthur J.

2014-01-01

The contact between eastern Blue Ridge stratified rocks above Mesoproterozoic basement rocks is mostly faulted (Gossan Lead and Red Valley). The Callaway fault juxtaposes Ashe and Lynchburg rocks above Wills Ridge Formation. Alligator Back Formation rocks overlie Ashe and Lynchburg rocks along the Rock Castle Creek fault, which juxtaposes rocks of different metamorphism. The fault separates major structural domains: rocks with one penetrative foliation in the footwall, and pin-striped recrystallized compositional layering, superposed penetrative foliations, and cleavage characterize the hanging wall. These relationships are ambiguous along strike to the southwest, where the Ashe and Alligator Back formations are recrystallized at higher metamorphic grades.

Cd-free buffer layer materials on Cu2ZnSn(SxSe1-x)4: Band alignments with ZnO, ZnS, and In2S3

NASA Astrophysics Data System (ADS)

Barkhouse, D. Aaron R.; Haight, Richard; Sakai, Noriyuki; Hiroi, Homare; Sugimoto, Hiroki; Mitzi, David B.

2012-05-01

The heterojunctions formed between Cu2ZnSn(SxSe1-x)4 (CZTSSe) and three Cd-free n-type buffers, ZnS, ZnO, and In2S3, were studied using femtosecond ultraviolet photoemission and photovoltage spectroscopy. The electronic properties including the Fermi level location at the interface, band bending in the CZTSSe substrate, and valence and conduction band offsets were determined and correlated with device properties. We also describe a method for determining the band bending in the buffer layer and demonstrate this for the In2S3/CZTSSe system. The chemical bath deposited In2S3 buffer is found to have near optimal conduction band offset (0.15 eV), enabling the demonstration of Cd-free In2S3/CZTSSe solar cells with 7.6% power conversion efficiency.

Coincident site lattice-matched growth of semiconductors on substrates using compliant buffer layers

DOEpatents

Norman, Andrew

2016-08-23

A method of producing semiconductor materials and devices that incorporate the semiconductor materials are provided. In particular, a method is provided of producing a semiconductor material, such as a III-V semiconductor, on a silicon substrate using a compliant buffer layer, and devices such as photovoltaic cells that incorporate the semiconductor materials. The compliant buffer material and semiconductor materials may be deposited using coincident site lattice-matching epitaxy, resulting in a close degree of lattice matching between the substrate material and deposited material for a wide variety of material compositions. The coincident site lattice matching epitaxial process, as well as the use of a ductile buffer material, reduce the internal stresses and associated crystal defects within the deposited semiconductor materials fabricated using the disclosed method. As a result, the semiconductor devices provided herein possess enhanced performance characteristics due to a relatively low density of crystal defects.

Tandem organic light-emitting diodes with buffer-modified C60/pentacene as charge generation layer

NASA Astrophysics Data System (ADS)

Wang, Zhen; Zheng, Xin; Liu, Fei; Wang, Pei; Gan, Lin; Wang, Jing-jing

2017-09-01

Buffer-modified C60/pentacene as charge generation layer (CGL) is investigated to achieve effective performance of charge generation. Undoped green electroluminescent tandem organic light-emitting diodes (OLEDs) with multiple identical emissive units and using buffer-modified C60/pentacene organic semiconductor heterojunction (OHJ) as CGL are demonstrated to exhibit better current density and brightness, compared with conventional single-unit devices. The current density and brightness both can be significantly improved with increasing the thickness of Al. However, excessive thickness of Al seriously decreases the transmittance of films and damages the interface. As a result, the maximum current efficiency of 1.43 cd·A-1 at 30 mA·cm-2 can be achieved for tandem OLEDs with optimal thickness of Al. These results clearly demonstrate that Cs2CO3/Al is an effective buffer for C60/pentacene-based tandem OLEDs.

Substrate nitridation induced modulations in transport properties of wurtzite GaN/p-Si (100) heterojunctions grown by molecular beam epitaxy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bhat, Thirumaleshwara N.; Rajpalke, Mohana K.; Krupanidhi, S. B.

Phase pure wurtzite GaN films were grown on Si (100) substrates by introducing a silicon nitride layer followed by low temperature GaN growth as buffer layers. GaN films grown directly on Si (100) were found to be phase mixtured, containing both cubic ({beta}) and hexagonal ({alpha}) modifications. The x-ray diffraction (XRD), scanning electron microscopy (SEM), photoluminescence (PL) spectroscopy studies reveal that the significant enhancement in the structural as well as in the optical properties of GaN films grown with silicon nitride buffer layer grown at 800 deg. C when compared to the samples grown in the absence of silicon nitridemore » buffer layer and with silicon nitride buffer layer grown at 600 deg. C. Core-level photoelectron spectroscopy of Si{sub x}N{sub y} layers reveals the sources for superior qualities of GaN epilayers grown with the high temperature substrate nitridation process. The discussion has been carried out on the typical inverted rectification behavior exhibited by n-GaN/p-Si heterojunctions. Considerable modulation in the transport mechanism was observed with the nitridation conditions. The heterojunction fabricated with the sample of substrate nitridation at high temperature exhibited superior rectifying nature with reduced trap concentrations. Lowest ideality factors ({approx}1.5) were observed in the heterojunctions grown with high temperature substrate nitridation which is attributed to the recombination tunneling at the space charge region transport mechanism at lower voltages and at higher voltages space charge limited current conduction is the dominating transport mechanism. Whereas, thermally generated carrier tunneling and recombination tunneling are the dominating transport mechanisms in the heterojunctions grown without substrate nitridation and low temperature substrate nitridation, respectively.« less

ZnS/Zn(O,OH)S-based buffer layer deposition for solar cells

DOEpatents

Bhattacharya, Raghu N [Littleton, CO

2009-11-03

The invention provides CBD ZnS/Zn(O,OH)S and spray deposited ZnS/Zn(O,OH)S buffer layers prepared from a solution of zinc salt, thiourea and ammonium hydroxide dissolved in a non-aqueous/aqueous solvent mixture or in 100% non-aqueous solvent. Non-aqueous solvents useful in the invention include methanol, isopropanol and triethyl-amine. One-step deposition procedures are described for CIS, CIGS and other solar cell devices.

Multicolor Nanostructured High Efficiency Photovoltaic Devices

DTIC Science & Technology

2007-06-30

the surface of strained buffer layer starts to form some nanoholes and nanogrooves. The depth of these nanoholes and nanogrooves is more than 3 nm...This indicates that the nanoholes and nanogrooves are formed not only just in the top GaAs (5 ML) layer, but also deep in the strained GaAsSb buffer...temperature during the InAs growth. As the InAs growth temperature decreases, the density of the nanoholes and nanogrooves is significantly reduced

Specific Heat and Thermal Diffusivity of YBCO Coated Conductors

NASA Astrophysics Data System (ADS)

Naito, Tomoyuki; Fujishiro, Hiroyuki; YasuhisaYamamura; Saito, Kazuya; Okamoto, Hiroshi; Hayashi, Hidemi; Gosho, Yoshihiro; Ohkuma, Takeshi; Shiohara, Yuh

We have measured the temperature dependence of specific heat,C(T), for Ag deposited YBCO coated conductor (YCC),YCC reinforced by a thin Cutape (YCC-Cu), andthe Hastelloy substrate with buffer layer. C(T) of HastelloyC-276 with buffer layer agrees well with the reported oneof HastelloyC-276, indicating that the contribution of the buffer layer to the measured C(T) is negligibly small. C(T)of both YCC and YCC-Cu tapes was successfully reproduced by the simple sum rule using the C(T) values reported for Hastelloy, Ag and Cu. The results demonstrate that C(T) of various YCC tapes can be estimated using the reported C(T)of constitutional materials. The estimated thermal diffusivity, a = K/C, at 300K of YCC, which was estimated using the thermal conductivity, K, did not agree with the reported a of Ag. This resultwas in consistent with the fact that the applied heat flew through the Aglayer, suggesting that a relation of a = K/Cfor homogeneous material cannot be applicable for the layered material such as YCC.

Perpendicularly magnetized (001)-textured D0{sub 22} MnGa films grown on an (Mg{sub 0.2}Ti{sub 0.8})O buffer with thermally oxidized Si substrates

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, Hwachol; Sukegawa, Hiroaki, E-mail: sukegawa.hiroaki@nims.go.jp; Liu, Jun

2015-10-28

We report the growth of (001)-textured polycrystalline D0{sub 22} MnGa films with perpendicular magnetic anisotropy (PMA) on thermally oxidized Si substrates using an (Mg{sub 0.2}Ti{sub 0.8})O (MTO) buffer layer. The ordered D0{sub 22} MnGa film grown at the optimum substrate temperature of 530 °C on the MTO buffer layer shows PMA with magnetization of 80 kA/m, PMA energy density of 0.28 MJ/m{sup 3}, and coercivity of 2.3 T. The scanning transmission electron microscope analysis confirms the formation of a highly (001)-textured structure and the elementally sharp interfaces between the MTO layer and the MnGa layer. The achieved D0{sub 22} MnGa PMA films on anmore » amorphous substrate will provide the possible pathway of integration of a Mn-based PMA film into Si-based substrates.« less

Magneto-optical properties of CoFeB ultrathin films: Effect of Ta buffer and capping layer

NASA Astrophysics Data System (ADS)

Husain, Sajid; Gupta, Nanhe Kumar; Barwal, Vineet; Chaudhary, Sujeet

2018-05-01

The effect of adding Ta as a capping and buffer layer on ultrathin CFB(Co60Fe20B20) thin films has been investigated by magneto-optical Kerr effect. A large difference in the coercivity and saturation field is observed between the single layer CFB(2nm) and Ta(5nm)/CFB(2nm)/Ta(2nm) trilayer structure. In particular, the in-plane anisotropy energy is found to be 90kJ/m3 on CFB(2nm) and 2.22kJ/m3 for Ta(5nm)/CFB(2nm)/Ta(2nm) thin films. Anisotropy energy further reduced to 0.93kJ/m3 on increasing the CFB thinness in trilayer structure i.e., Ta(5nm)/CFB(4nm)/Ta(2nm). Using VSM measurement, the saturation magnetization is found to be 1230±50 kA/m. Low coercivity and anisotropy energy in capped and buffer layer thin films envisage the potential of employing CFB for low field switching applications of the spintronic devices.

Fabrication and characterization of {110}-oriented Pb(Zr,Ti)O3 thin films on Pt/SiO2/Si substrates using PdO//Pd buffer layer

NASA Astrophysics Data System (ADS)

Oshima, Naoya; Uchiyama, Kiyoshi; Ehara, Yoshitaka; Oikawa, Takahiro; Ichinose, Daichi; Tanaka, Hiroki; Sato, Tomoya; Uchida, Hiroshi; Funakubo, Hiroshi

2017-10-01

A strongly {110}-oriented perovskite-type thin film of tetragonal Pb(Zr0.4Ti0.6)O3 (PZT) was successfully obtained on a (100)Si substrate using a {101}PdO//{111}Pd thin film as a buffer layer. The {101}PdO//{111}Pd thin film buffer layer was obtained by oxidizing {111}Pd after depositing {111}Pd on a {111}Pt/TiO x /SiO2/{100}Si substrate. Using this buffer layer, a {110} c -oriented SrRuO3 (SRO) thin film was deposited by sputtering as a bottom electrode of PZT thin films. Subsequently, the {110}-oriented PZT thin film can be deposited on a (110) c SRO thin film by metal-organic chemical deposition (MOCVD) and its properties can be compared with those of PZT thin films with other orientations of {100} and {111}. Among the {100}, {110}, {111}-oriented PZT films, the {100}-oriented one showed the largest remnant polarization, which is in good agreement with those of the PZTs epitaxially grown in the 〈100〉, 〈110〉, and 〈111〉 directions. The other properties, i.e., piezoelectricity and dielectric constants, also showed similar anisotropic tendencies, which is in good agreement with the data reported in the epitaxially grown PZTs.

Accessing the band alignment in high efficiency Cu(In,Ga)(Se,S)2 (CIGSSe) solar cells with an InxSy:Na buffer based on temperature dependent measurements and simulations

NASA Astrophysics Data System (ADS)

Schoneberg, Johannes; Ohland, Jörg; Eraerds, Patrick; Dalibor, Thomas; Parisi, Jürgen; Richter, Michael

2018-04-01

We present a one-dimensional simulation model for high efficiency Cu(In,Ga)(Se,S)2 solar cells with a novel band alignment at the hetero-junction. The simulation study is based on new findings about the doping concentration of the InxSy:Na buffer and i-ZnO layers as well as comprehensive solar cell characterization by means of capacitance, current voltage, and external quantum efficiency measurements. The simulation results show good agreement with the experimental data over a broad temperature range, suggesting the simulation model with an interface-near region (INR) of approximately 100 nm around the buffer/absorber interface that is of great importance for the solar cell performance. The INR exhibits an inhomogeneous doping and defect density profile as well as interface traps at the i-layer/buffer and buffer/absorber interfaces. These crucial parameters could be accessed via their opposing behavior on the simulative reconstruction of different measurement characteristics. In this work, we emphasize the necessity to reconstruct the results of a set of experimental methods by means of simulation to find the most appropriate model for the solar cell. Lowly doped buffer and intrinsic window layers in combination with a high space charge at the front of the absorber lead to a novel band alignment in the simulated band structure of the solar cell. The presented insights may guide the strategy of further solar cell optimization including (alkali-) post deposition treatments.

Preliminary geologic map of the Winchester 7.5' quadrangle, Riverside County, California

USGS Publications Warehouse

Morton, Douglas M.

2003-01-01

The Winchester quadrangle is located in the northern part of the Peninsular Ranges Province within the central part of the Perris block, a relatively stable, rectangular in plan view, area located between the Elsinore and San Jacinto fault zones (see location map). The quadrangle is underlain by Cretaceous and older basement rocks. Cretaceous plutonic rocks are part of the composite Peninsular Ranges batholith, which indicates wide variety of granitic rocks, ranging from granite to gabbro. Parts of three major plutonic complexes are within the quadrangle, the Lakeview Mountains pluton, the Domenigoni Valley pluton and the Paloma Valley ring complex. In the northern part of the quadrangle is the southern part of the Lakeview Mountains pluton, a large composite body, most of which lies in the quadrangle to the north. In the center part of the quadrangle is the eastern part of the Domenigoni Valley pluton, which consists of massive biotite-hornblende granodiorite and tonalite; some tonalite in the southern part of the pluton has a relatively pronounced foliation produced by oriented biotite and hornblende. Common to abundant equant-shaped, mafic inclusions occur through out the pluton except in the outermost part where inclusions are absent. The pluton was passively emplaced by piecemeal stoping of a variety of older rocks and the eastern contact is well exposed in the quadrangle. Associated with the Domenigoni Valley pluton is a swarm of latite dikes; the majority of these dikes occur in the Winchester quadrangle, but they extend into the Romoland quadrangle to the west. The latite dikes intrude both the pluton and adjacent metamorphic rocks, most are foliated, and most have a well developed lineation defined by oriented biotite and/or hornblende crystals. Dikes intruding the pluton were emplaced in northwest striking joints; and dikes intruding the metamorphic rocks were emplaced along foliation planes. In the eastern part of the quadrangle a Cretaceous age suture juxtaposes low-metamorphic grade Mesozoic rocks against high-metamorphic grade gneissic-textured Mesozoic rocks. Juxtaposition occurred when the high-metamorphic grade rocks were at upper amphibolite grade temperatures, and produced a steep thermal gradient in the low-metamorphic grade Mesozoic rocks. Age of suturing and attendant metamorphism, based on metamorphic mineral ages, is about 100 Ma (L. Snee, personal communication, 2002). The suture zone appears to vary in thickness, and includes within it a number of metadunite bodies and related rocks. Prebatholithic rocks of Mesozoic age include a wide variety of sedimentary rocks of greenschist or lower metamorphic grade, in the western and central part of the quadrangle, and upper amphibolite grade near the eastern edge of the quadrangle. The metamorphic grade increases from greenschist to upper amphibolite grade over a distance of less than two miles; andalusite and sillimanite isograds are closely spaced near the suture. Metamorphism was Buchan type of relatively high temperature and relatively low pressure (Schwarcz, 1969). Common lithologies of the low metamorphic grade suite include phyllite, lithic greywacke, impure quartzite, meta-arkose, and interlayered quartzite and phyllite. Most of the layering and foliation in the metamorphic rocks is the result of intense structural transposition. Relic bedding appears to be restricted to very local occurrences in hinges of slip folds. The upper amphibolite grade, gneissic-textured Mesozoic rocks consist of sillimanite-biotite gneiss, black amphibolite, and impure quartzite. Anatectic gneiss containing igneous textured segregations of quartz and feldspar is commonly inter leaved with biotite gneiss.

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.

First principles calculations of point defect diffusion in CdS buffer layers: Implications for Cu(In,Ga)(Se,S){sub 2} and Cu{sub 2}ZnSn(Se,S){sub 4}-based thin-film photovoltaics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Varley, J. B.; Lordi, V.; He, X.

2016-01-14

We investigate point defects in CdS buffer layers that may arise from intermixing with Cu(In,Ga)Se{sub 2} (CIGSe) or Cu{sub 2}ZnSn(S,Se){sub 4} (CZTSSe) absorber layers in thin-film photovoltaics (PV). Using hybrid functional calculations, we characterize the migration barriers of Cu, In, Ga, Se, Sn, Zn, Na, and K impurities and assess the activation energies necessary for their diffusion into the bulk of the buffer. We find that Cu, In, and Ga are the most mobile defects in CIGS-derived impurities, with diffusion expected to proceed into the buffer via interstitial-hopping and cadmium vacancy-assisted mechanisms at temperatures ∼400 °C. Cu is predicted to stronglymore » favor migration paths within the basal plane of the wurtzite CdS lattice, which may facilitate defect clustering and ultimately the formation of Cu-rich interfacial phases as observed by energy dispersive x-ray spectroscopic elemental maps in real PV devices. Se, Zn, and Sn defects are found to exhibit much larger activation energies and are not expected to diffuse within the CdS bulk at temperatures compatible with typical PV processing temperatures. Lastly, we find that Na interstitials are expected to exhibit slightly lower activation energies than K interstitials despite having a larger migration barrier. Still, we find both alkali species are expected to diffuse via an interstitially mediated mechanism at slightly higher temperatures than enable In, Ga, and Cu diffusion in the bulk. Our results indicate that processing temperatures in excess of ∼400 °C will lead to more interfacial intermixing with CdS buffer layers in CIGSe devices, and less so for CZTSSe absorbers where only Cu is expected to significantly diffuse into the buffer.« less

Magnetotelluric Imaging of the Lithosphere Across the Variscan Orogen (Iberian Autochthonous Domain, NW Iberia)

NASA Astrophysics Data System (ADS)

Alves Ribeiro, J.; Monteiro-Santos, F. A.; Pereira, M. F.; Díez Fernández, R.; Dias da Silva, Í.; Nascimento, C.; Silva, J. B.

2017-12-01

A new magnetotelluric (MT) survey comprising 17 MT soundings throughout a 30 km long N30°W transect in the Iberian autochthons domain of NW Iberia (Central Iberian Zone) is presented. The 2-D inversion model shows the resistivity structure of the continental crust up to 10 km depth, heretofore unavailable for this region of the Variscan Orogen. The MT model reveals a wavy structure separating a conductive upper layer underlain by a resistive layer, thus picturing the two main tectonic blocks of a large-scale D2 extensional shear zone (i.e., Pinhel shear zone). The upper layer represents a lower grade metamorphic domain that includes graphite-rich rocks. The lower layer consists of high-grade metamorphic rocks that experienced partial melting and are associated with granites (more resistive) emplaced during crustal thinning. The wavy structure is the result of superimposed crustal shortening responsible for the development of large-scale D3 folds (e.g., Marofa synform), later deflected and refolded by a D4 strike-slip shear zone (i.e., Juzbado-Penalva do Castelo shear zone). The later contribution to the final structure of the crust is marked by the intrusion of postkinematic granitic rocks and the propagation of steeply dipping brittle fault zones. Our study demonstrates that MT imaging is a powerful tool to understand complex crustal structures of ancient orogens in order to design future prospecting surveys for mineral deposits of economic interest.

Isotopic and trace element characteristics of an unusual refractory inclusion from Essebi

NASA Technical Reports Server (NTRS)

Deloule, E.; Kennedy, A. K.; Hutcheon, I. D.; Elgoresy, A.

1993-01-01

The isotopic and chemical properties of Ca-Al-rich inclusions (CAI) provide important clues to the early solar nebula environment. While the abundances of refractory major and trace elements are similar to those expected for high temperature condensates, the variety of textural, chemical, and isotopic signatures indicate most CAI experienced complex, multi-stage histories involving repeated episodes of condensation, evaporation, and metamorphism. Evidence of multiple processes is especially apparent in an unusual refractory inclusion from Essebi (URIE) described by El Goresy et al. The melilite (mel)-rich core of URIE contains polygonal framboids of spinel (sp) and hibonite (hb) or sp and fassaite (fas) and is surrounded by a rim sequence consisting of five layers. In contrast to rims on Allende, the mineralogy of the URIE rim layers becomes increasingly refractory from the core outwards, ending in a layer of spinel-Al2O3 solid solution + Sc-rich fassaite. The chemical and mineralogical features of URIE are inconsistent with crystallization from a homogeneous melt, and El Goresy et al. proposed a multi-step history involving condensation of sp + hb and aggregation into framboids, capture of framboids by a refractory silicate melt droplet, condensation of rim layers, and alteration of mel to calcite and feldspathoid. The PANURGE ion probe was used to investigate the isotopic and trace element characteristics of URIE to develop a more complete picture of the multiple processes leading to formation and metamorphism.

Versatile buffer layer architectures based on Ge1-xSnx alloys

NASA Astrophysics Data System (ADS)

Roucka, R.; Tolle, J.; Cook, C.; Chizmeshya, A. V. G.; Kouvetakis, J.; D'Costa, V.; Menendez, J.; Chen, Zhihao D.; Zollner, S.

2005-05-01

We describe methodologies for integration of compound semiconductors with Si via buffer layers and templates based on the GeSn system. These layers exhibit atomically flat surface morphologies, low defect densities, tunable thermal expansion coefficients, and unique ductile properties, which enable them to readily absorb differential stresses produced by mismatched overlayers. They also provide a continuous selection of lattice parameters higher than that of Ge, which allows lattice matching with technologically useful III-V compounds. Using this approach we have demonstrated growth of GaAs, GeSiSn, and pure Ge layers at low temperatures on Si(100). These materials display extremely high-quality structural, morphological, and optical properties opening the possibility of versatile integration schemes directly on silicon.

Molecular beam epitaxy growth of SrO buffer layers on graphite and graphene for the integration of complex oxides

DOE PAGES

Ahmed, Adam S.; Wen, Hua; Ohta, Taisuke; ...

2016-04-27

Here, we report the successful growth of high-quality SrO films on highly-ordered pyrolytic graphite (HOPG) and single-layer graphene by molecular beam epitaxy. The SrO layers have (001) orientation as confirmed by X-ray diffraction (XRD) while atomic force microscopy measurements show continuous pinhole-free films having rms surface roughness of <1.5 Å. Moreover, transport measurements of exfoliated graphene, after SrO deposition, show a strong dependence between the Dirac point and Sr oxidation. As a result, the SrO is leveraged as a buffer layer for more complex oxide integration via the demonstration of (001) oriented SrTiO3 grown atop a SrO/HOPG stack.

Molecular beam epitaxy growth of SrO buffer layers on graphite and graphene for the integration of complex oxides

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ahmed, Adam S.; Wen, Hua; Ohta, Taisuke

Here, we report the successful growth of high-quality SrO films on highly-ordered pyrolytic graphite (HOPG) and single-layer graphene by molecular beam epitaxy. The SrO layers have (001) orientation as confirmed by X-ray diffraction (XRD) while atomic force microscopy measurements show continuous pinhole-free films having rms surface roughness of <1.5 Å. Moreover, transport measurements of exfoliated graphene, after SrO deposition, show a strong dependence between the Dirac point and Sr oxidation. As a result, the SrO is leveraged as a buffer layer for more complex oxide integration via the demonstration of (001) oriented SrTiO3 grown atop a SrO/HOPG stack.

Electron density and currents of AlN/GaN high electron mobility transistors with thin GaN/AlN buffer layer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bairamis, A.; Zervos, Ch.; Georgakilas, A., E-mail: alexandr@physics.uoc.gr

2014-09-15

AlN/GaN high electron mobility transistor (HEMT) structures with thin GaN/AlN buffer layer have been analyzed theoretically and experimentally, and the effects of the AlN barrier and GaN buffer layer thicknesses on two-dimensional electron gas (2DEG) density and transport properties have been evaluated. HEMT structures consisting of [300 nm GaN/ 200 nm AlN] buffer layer on sapphire were grown by plasma-assisted molecular beam epitaxy and exhibited a remarkable agreement with the theoretical calculations, suggesting a negligible influence of the crystalline defects that increase near the heteroepitaxial interface. The 2DEG density varied from 6.8 × 10{sup 12} to 2.1 × 10{sup 13} cm{sup −2} as themore » AlN barrier thickness increased from 2.2 to 4.5 nm, while a 4.5 nm AlN barrier would result to 3.1 × 10{sup 13} cm{sup −2} on a GaN buffer layer. The 3.0 nm AlN barrier structure exhibited the highest 2DEG mobility of 900 cm{sup 2}/Vs for a density of 1.3 × 10{sup 13} cm{sup −2}. The results were also confirmed by the performance of 1 μm gate-length transistors. The scaling of AlN barrier thickness from 1.5 nm to 4.5 nm could modify the drain-source saturation current, for zero gate-source voltage, from zero (normally off condition) to 0.63 A/mm. The maximum drain-source current was 1.1 A/mm for AlN barrier thickness of 3.0 nm and 3.7 nm, and the maximum extrinsic transconductance was 320 mS/mm for 3.0 nm AlN barrier.« less

Enhanced Efficiency of Polymer Light-Emitting Diodes by Dispersing Dehydrated Nanotube Titanic Acid in the Hole-buffer Layer

NASA Astrophysics Data System (ADS)

Qian, L.; Xu, Z.; Teng, F.; Duan, X.-X.; Jin, Z.-S.; Du, Z.-L.; Li, F.-S.; Zheng, M.-J.; Wang, Y.-S.

2007-06-01

Efficiency of polymer light-emitting diodes (PLEDs) with poly(2-methoxy-5-(2-ethyl hexyloxy)- p-phenylene vinylene) (MEH-PPV) as an emitting layer was improved if a dehydrated nanotubed titanic acid (DNTA) doped hole-buffer layer polyethylene dioxythiophene (PEDOT) was used. Photoluminescence (PL) and Raman spectra indicated a stronger interaction between DNTA and sulfur atom in thiophene of PEDOT, which suppresses the chemical interaction between vinylene of MEH-PPV and thiophene of PEDOT. The interaction decreases the defect states in an interface region to result in enhancement in device efficiency, even though the hole transporting ability of PEDOT was decreased.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Adhikari, R., E-mail: rajdeep.adhikari@jku.at; Capuzzo, G.; Bonanni, A., E-mail: alberta.bonanni@jku.at

Polarization induced degenerate n-type doping with electron concentrations up to ∼10{sup 20 }cm{sup −3} is achieved in graded Al{sub x}Ga{sub 1−x}N layers (x: 0% → 37%) grown on unintentionally doped and on n-doped GaN:Si buffer/reservoir layers by metal organic vapor phase epitaxy. High resolution x-ray diffraction, transmission electron microscopy, and electron dispersive x-ray spectroscopy confirm the gradient in the composition of the Al{sub x}Ga{sub 1−x}N layers, while Hall effect studies reveal the formation of a three dimensional electron slab, whose conductivity can be adjusted through the GaN(:Si) buffer/reservoir.

Experimental and Numerical Investigation of Internal Gravity Waves Excited by Turbulent Penetrative Convection in Water Around Its Density Maximum

NASA Astrophysics Data System (ADS)

Perrard, Stéphane; Le Bars, Michaël; Le Gal, Patrice

This study is devoted to the experimental and numerical analysis of the excitation of gravity waves by turbulent convection. This situation is representative of many geophysical or astrophysical systems such as the convective bottom layer of the atmosphere that radiates internal waves in the stratosphere, or the interaction between the convective and the radiative zones in stars. In our experiments, we use water as a working fluid as it possesses the remarkable property of having a maximum density at 4 °C. Therefore, when establishing on a water layer a temperature gradient between 0 °C at the bottom and room temperature at the top, a turbulent convective region appears spontaneously under a stably stratified zone. In these conditions, gravity waves are excited by the convective fluid motions penetrating the stratified layer. Although this type of flow, called penetrative convection, has already been described, we present here the first velocity field measurement of wave emission and propagation. We show in particular that an intermediate layer that we call the buffer layer emerges between the convective and the stratified zones. In this buffer layer, the angle of propagation of the waves varies with the altitude since it is slaved to the Brunt-Väisälä frequency which evolves rapidly between the convective and the stratified layer. A minimum angle is reached at the end of the buffer layer. Then we observe that an angle of propagation is selected when the waves travel through the stratified layer. We expect this process of wave selection to take place in natural situations.

Compatibility of buffered uranium carbides with tungsten.

NASA Technical Reports Server (NTRS)

Phillips, W. M.

1971-01-01

Results of compatibility tests between tungsten and hyperstoichiometric uranium carbide alloys run at 1800 C for 1000 and 2500 hours. These tests compared tungsten-buffered uranium carbide with tungsten-buffered uranium-zirconium carbide. The zirconium carbide addition appeared to widen the homogeneity range of the uranium carbide, making additional carbon available for reaction. Reaction layers could be formed by either of two diffusion paths, one producing UWC2, while the second resulted in the formation of W2C. UWC2 acts as a diffusion barrier for carbon and slows the growth of the reaction layer with time, while carbon diffusion is relatively rapid in W2C, allowing equilibrium to be reached in less than 2500 hours at a temperature of 1800 C.

Tunneling-Magnetoresistance Ratio Comparison of MgO-Based Perpendicular-Magnetic-Tunneling-Junction Spin Valve Between Top and Bottom Co2Fe6B2 Free Layer Structure.

PubMed

Lee, Du-Yeong; Lee, Seung-Eun; Shim, Tae-Hun; Park, Jea-Gun

2016-12-01

For the perpendicular-magnetic-tunneling-junction (p-MTJ) spin valve with a nanoscale-thick bottom Co2Fe6B2 free layer ex situ annealed at 400 °C, which has been used as a common p-MTJ structure, the Pt atoms of the Pt buffer layer diffused into the MgO tunneling barrier. This transformed the MgO tunneling barrier from a body-centered cubic (b.c.c) crystallized layer into a mixture of b.c.c, face-centered cubic, and amorphous layers and rapidly decreased the tunneling-magnetoresistance (TMR) ratio. The p-MTJ spin valve with a nanoscale-thick top Co2Fe6B2 free layer could prevent the Pt atoms diffusing into the MgO tunneling barrier during ex situ annealing at 400 °C because of non-necessity of a Pt buffer layer, demonstrating the TMR ratio of ~143 %.

Zircon (Hf, O isotopes) as melt indicator: Melt infiltration and abundant new zircon growth within melt rich layers of granulite-facies lenses versus solid-state recrystallization in hosting amphibolite-facies gneisses (central Erzgebirge, Bohemian Massif)

NASA Astrophysics Data System (ADS)

Tichomirowa, Marion; Whitehouse, Martin; Gerdes, Axel; Schulz, Bernhard

2018-03-01

In the central Erzgebirge within the Bohemian Massif, lenses of high pressure and ultrahigh pressure felsic granulites occur within meta-sedimentary and meta-igneous amphibolite-facies felsic rocks. In the felsic granulite, melt rich parts and restite form alternating layers, and were identified by petrology and bulk rock geochemistry. Mineral assemblages representing the peak P-T conditions were best preserved in melanocratic restite layers. In contrast, in the melt rich leucocratic layers, garnet and related HP minerals as kyanite are almost completely resorbed. Both layers display differences in accessory minerals: melanosomes have frequent and large monazite and Fe-Ti-minerals but lack xenotime and apatite; leucosomes have abundant apatite and xenotime while monazite is rare. Here we present a detailed petrographic study of zircon grains (abundance, size, morphology, inclusions) in granulite-facies and amphibolite-facies felsic gneisses, along with their oxygen and hafnium isotope compositions. Our data complement earlier Usbnd Pb ages and trace element data (REE, Y, Hf, U) on zircons from the same rocks (Tichomirowa et al., 2005). Our results show that the degree of melting determines the behaviour of zircon in different layers of the granulites and associated amphibolite-facies rocks. In restite layers of the granulite lenses, small, inherited, and resorbed zircon grains are preserved and new zircon formation is very limited. In contrast, new zircons abundantly grew in the melt rich leucocratic layers. In these layers, the new zircons (Usbnd Pb age, trace elements, Hf, O isotopes) best preserve the information on peak metamorphic conditions due to intense corrosion of other metamorphic minerals. The new zircons often contain inherited cores. Compared to cores, the new zircons and rims show similar or slightly lower Hf isotope values, slightly higher Hf model ages, and decreased oxygen isotope ratios. The isotope compositions (Hf, O) of new zircons indicate partial Hf isotope homogenization in the melt, and melt infiltration from an external source. New zircon was most likely formed by a peritectic reaction with melt above the wet solidus (peritectic zircon). Conversely, the amphibolite-facies host gneisses lack indications of significant melt production. Pre-metamorphic zircons experienced mainly solid-state recrystallization and variable Pb loss with only minor new zircon formation. However, subtle changes in cathodoluminescence pattern, in the Hf and O isotopes, and in the Lu/Hf, Yb/Hf ratios of zircons suggest that small volumes of melt were locally present. In difference to granulites, melt was internally produced. The detection of low degree melts (inferred from zircon geochemistry) is extremely important for the rheology because these amphibolite-facies rocks could act as large scale ductile shear zones. The new zircon data support a different P-T path for closely spaced amphibolite- and granulite-facies rocks.

Tailoring Curie temperature and magnetic anisotropy in ultrathin Pt/Co/Pt films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Parakkat, Vineeth Mohanan; Ganesh, K. R.; Anil Kumar, P. S., E-mail: anil@physics.iisc.ernet.in

The dependence of perpendicular magnetization and Curie temperature (T{sub c}) of Pt/Co/Pt thin films on the thicknesses of Pt seed (Pt{sub s}) and presence of Ta buffer layer has been investigated in this work. Pt and Co thicknesses were varied between 2 to 8 nm and 0.35 to 1.31 nm (across the spin reorientation transition thickness) respectively and the T{sub c} was measured using SQUID magnetometer. We have observed a systematic dependence of T{sub c} on the thickness of Pt{sub s}. For 8 nm thickness of Pt{sub s} the Co layer of 0.35 nm showed ferromagnetism with perpendicular anisotropy atmore » room temperature. As the thickness of the Pt{sub s} was decreased to 2 nm, the T{sub c} went down below 250 K. XRD data indicated polycrystalline growth of Pt{sub s} on SiO{sub 2}. On the contrary Ta buffer layer promoted the growth of Pt(111). As a consequence Ta(5 nm)/Pt(3 nm)/Co(0.35 nm)/Pt(2 nm) had much higher T{sub c} (above 300 K) with perpendicular anisotropy when compared to the same stack without the Ta layer. Thus we could tune the ferromagnetic T{sub c} and anisotropy by varying the Pt{sub s} thickness and also by introducing Ta buffer layer. We attribute these observations to the micro-structural evolution of Pt{sub s} layer which hosts the Co layer.« less

The fabrication of white light-emitting diodes using the n-ZnO/NiO/p-GaN heterojunction with enhanced luminescence.

PubMed

Abbasi, Mazhar Ali; Ibupoto, Zafar Hussain; Hussain, Mushtaque; Nur, Omer; Willander, Magnus

2013-07-13

Cheap and efficient white light-emitting diodes (LEDs) are of great interest due to the energy crisis all over the world. Herein, we have developed heterojunction LEDs based on the well-aligned ZnO nanorods and nanotubes on the p-type GaN with the insertion of the NiO buffer layer that showed enhancement in the light emission. Scanning electron microscopy have well demonstrated the arrays of the ZnO nanorods and the proper etching into the nanotubes. X-ray diffraction study describes the wurtzite crystal structure array of ZnO nanorods with the involvement of GaN at the (002) peak. The cathodoluminescence spectra represent strong and broad visible emission peaks compared to the UV emission and a weak peak at 425 nm which is originated from GaN. Electroluminescence study has shown highly improved luminescence response for the LEDs fabricated with NiO buffer layer compared to that without NiO layer. Introducing a sandwich-thin layer of NiO between the n-type ZnO and the p-type GaN will possibly block the injection of electrons from the ZnO to the GaN. Moreover, the presence of NiO buffer layer might create the confinement effect.

Dual role of TiO2 buffer layer in Pt catalyzed BiFeO3 photocathodes: Efficiency enhancement and surface protection

NASA Astrophysics Data System (ADS)

Shen, Huanyu; Zhou, Xiaoxue; Dong, Wen; Su, Xiaodong; Fang, Liang; Wu, Xi; Shen, Mingrong

2017-09-01

Polycrystalline ferroelectric BiFeO3 (BFO) films deposited on transparent indium tin oxide (ITO) electrodes have shown to be an interesting photocathode for photoelectrochemical (PEC) water splitting; however, its PEC performance and stability are far from perfection. Herein, we reported an amorphous TiO2 buffer layer, inserted between BFO and Pt catalyst, improves significantly both its PEC activity and stability. A photocathodic current density of -460 μA/cm2 at 0 V vs. reversible hydrogen electrode (RHE) and an onset potential of 1.25 V vs. RHE were obtained in ITO/BFO/TiO2/Pt photocathode under 100 mW/cm2 Xe-lamp illumination. TiO2 functions as a buffer layer to remove the upward barrier between BFO and Pt, and makes the photogenerated carriers separate efficiently. The photocathode also shows high stability in acid solution after a 10-h PEC continuous testing.

Automotive assessment of carbon-silicon composite anodes and methods of fabrication

NASA Astrophysics Data System (ADS)

Karulkar, Mohan; Blaser, Rachel; Kudla, Bob

2015-01-01

To assess the potential of carbon silicon composite anodes for automotive applications, C-Si anodes were fabricated and certain improvements employed. The use of a PVDF buffer layer is demonstrated for the first time with a C-Si composite material. The buffer layer increases adhesion by 89%, and increases capacity by 50-80%. Also, a limited capacity range is employed to improve cycle life by up to 200%, and enable currents as high as 2 mA cm-1. The combined use of a buffer layer and limited capacity range has not been reported before. A model is also presented for comparing C-Si performance with real-world automotive targets from USABC, including energy density, power density, specific energy, and specific power. The analysis reveals a capacity penalty that arises from pairing C-Si with a traditional cathode (NCA), and which prevents the cell from meeting all targets. Scenarios are presented in which a higher-capacity cathode (250 mAh g-1) allows all targets to be hypothetically met.

Stress-induced magnetization for epitaxial spinel ferrite films through interface engineering

NASA Astrophysics Data System (ADS)

Wakiya, Naoki; Shinozaki, Kazuo; Mizutani, Nobuyasu

2004-08-01

This study found "stress-induced magnetization" for epitaxial ferrite films with spinel structure. We grew (111)- and (001)-epitaxial Ni0.17Zn0.23Fe2.60O4(NZF) films on CeO2/Y0.15Zr0.85O1.93(YSZ )/Si(001) and oxide single-crystal substrates, respectively. There is a window of lattice mismatch (between 0 and 6.5%) to achieve bulk saturation magnetization (Ms). An NZF film grown on CeO2/YSZ //Si(001) showed tensile stress, but that stress was relaxed by introducing a ZnCo2O4(ZC ) buffer layer. NZF films grown on SrTiO3(ST )(001) and (La,Sr)(Al,Ta)O3(LSAT)(001) had compressive stress, which was enhanced by introducing a ZC buffer layer. In both cases, bulk Ms was achieved by introducing the ZC buffer layer. This similarity suggests that magnetization can be controlled by the stress.

Assessment of polyelectrolyte coating stability under dynamic buffer conditions in CE.

PubMed

Swords, Kyleen E; Bartline, Peter B; Roguski, Katherine M; Bashaw, Sarah A; Frederick, Kimberley A

2011-09-01

Dynamic buffer conditions are present in many electrophoretically driven separations. Polyelectrolyte multilayer coatings have been employed in CE because of their chemical and physical stability as well as their ease of application. The goal of this study is to measure the effect of dynamic changes in buffer pH on flow using a real-time method for measuring EOF. Polyelectrolyte multilayers (PEMs) were composed of pairs of strong or completely ionized polyelectrolytes including poly(diallyldimethylammonium) chloride and poly(styrene sulfonate) and weak or ionizable polyelectrolytes including poly(allylamine) and poly(methacrylic acid). Polyelectrolyte multilayers of varying thicknesses (3, 4, 7, 8, 15, or 16 layers) were also studied. While the magnitude of the EOF was monitored every 2 s, the buffer pH was exchanged from a relatively basic pH (7.1) to increasingly acidic pHs (6.6, 6.1, 5.5, and 5.1). Strong polyelectrolytes responded minimally to changes in buffer pH (<1%), whereas substantial (>10%) and sometimes irreversible changes were measured with weak polyelectrolytes. Thicker coatings resulted in a similar magnitude of response but were more likely to degrade in response to buffer pH changes. The most stable coatings were formed from thinner layers of strong polyelectrolytes. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Ultrathin epitaxial barrier layer to avoid thermally induced phase transformation in oxide heterostructures

DOE PAGES

Baek, David J.; Lu, Di; Hikita, Yasuyuki; ...

2016-12-22

Incorporating oxides with radically different physical and chemical properties into heterostructures offers tantalizing possibilities to derive new functions and structures. Recently, we have fabricated freestanding 2D oxide membranes using the water-soluble perovskite Sr 3Al 2O 6 as a sacrificial buffer layer. Here, with atomic-resolution spectroscopic imaging, we observe that direct growth of oxide thin films on Sr 3Al 2O 6 can cause complete phase transformation of the buffer layer, rendering it water-insoluble. More importantly, we demonstrate that an ultrathin SrTiO 3 layer can be employed as an effective barrier to preserve Sr 3Al 2O 6 during subsequent growth, thus allowingmore » its integration in a wider range of oxide heterostructures.« less

Research into the use of pyrolytic oxides and polymers for the fabrication of thin film high energy capacitors

NASA Technical Reports Server (NTRS)

Nevin, J. H.

1983-01-01

Construction, capacitance and dissipation factor, and electrode materials for single layer capacitors are discussed. Basic construction, phosphosilicate glass, ten layer capacitors, twenty layer capacitors, stress measurements, buffered oxide layers, and 30 layer capacitors are also discussed. Spin-on phosphosilicate glass is addressed. Polymers as dielectric materials are also considered.

Organic Solar Cells Based on WO2.72 Nanowire Anode Buffer Layer with Enhanced Power Conversion Efficiency and Ambient Stability.

PubMed

You, Longzhen; Liu, Bin; Liu, Tao; Fan, Bingbing; Cai, Yunhao; Guo, Lin; Sun, Yanming

2017-04-12

Tungsten oxide as an alternative to conventional acidic PEDOT:PSS has attracted much attention in organic solar cells (OSCs). However, the vacuum-processed WO 3 layer and high-temperature sol-gel hydrolyzed WO X are incompatible with large-scale manufacturing of OSCs. Here, we report for the first time that a specific tungsten oxide WO 2.72 (W 18 O 49 ) nanowire can function well as the anode buffer layer. The nw-WO 2.72 film exhibits a high optical transparency. The power conversion efficiency (PCE) of OSCs based on three typical polymer active layers PTB7:PC 71 BM, PTB7-Th:PC 71 BM, and PDBT-T1:PC 71 BM with nw-WO 2.72 layer were improved significantly from 7.27 to 8.23%, from 8.44 to 9.30%, and from 8.45 to 9.09%, respectively compared to devices with PEDOT:PSS. Moreover, the photovoltaic performance of OSCs based on small molecule p-DTS(FBTTh 2 ) 2 :PC 71 BM active layer was also enhanced with the incorporation of nw-WO 2.72 . The enhanced performance is mainly attributed to the improved short-circuit current density (J sc ), which benefits from the oxygen vacancies and the surface apophyses for better charge extraction. Furthermore, OSCs based on nw-WO 2.72 show obviously improved ambient stability compared to devices with PEDOT:PSS layer. The results suggest that nw-WO 2.72 is a promising candidate for the anode buffer layer materials in organic solar cells.

Growth and characterization of CdS buffer layers by CBD and MOCVD

DOE Office of Scientific and Technical Information (OSTI.GOV)

Morrone, A.A.; Huang, C.; Li, S.S.

1999-03-01

Thin film CdS has been widely used in thin-film photovoltaic devices. The most efficient Cu(In,&hthinsp;Ga)Se{sub 2} (CIGS) solar cells reported to date utilized a thin CdS buffer layer prepared by a reactive solution growth technique known as chemical bath deposition (CBD). Considerable effort has been directed to better understand the role and find a replacement for the CBD CdS process in CIGS-based solar cells. We reported a low temperature ({approximately}150&hthinsp;{degree}C) Metalorganic Chemical Vapor Deposition (MOCVD) CdS thin film buffer layer process for CIGS absorbers. Many prior studies have reported that CBD CdS contains a mixture of crystal structures. Recent investigationsmore » of CBD CdS thin films by ellipsometry suggested a multilayer structure. In this study we compare CdS thin films prepared by CBD and MOCVD and the effects of annealing. TED and XRD are used to characterize the crystal structure, the film microstructure is studied by HRTEM, and the optical properties are studied by Raman and spectrophotometry. All of these characterization techniques reveal superior crystalline film quality for CdS films grown by MOCVD compared to those grown by CBD. Dual Beam Optical Modulation (DBOM) studies showed that the MOCVD and CBD CdS buffer layer processes have nearly the same effect on CIGS absorbers when combined with a cadmium partial electrolyte aqueous dip. {copyright} {ital 1999 American Institute of Physics.}« less

Stress generation and evolution in oxide heteroepitaxy

NASA Astrophysics Data System (ADS)

Fluri, Aline; Pergolesi, Daniele; Wokaun, Alexander; Lippert, Thomas

2018-03-01

Many physical properties of oxides can be changed by inducing lattice distortions in the crystal through heteroepitaxial growth of thin films. The average lattice strain can often be tuned by changing the film thickness or using suitable buffer layers between film and substrate. The exploitation of the full potential of strain engineering for sample or device fabrication rests on the understanding of the fundamental mechanisms of stress generation and evolution. For this study an optical measurement of the substrate curvature is used to monitor in situ how the stress builds up and relaxes during the growth of oxide thin films by pulsed laser deposition. The relaxation behavior is correlated with the growth mode, which is monitored simultaneously with reflection high-energy electron diffraction. The stress relaxation data is fitted and compared with theoretical models for stress evolution which were established for semiconductor epitaxy. The initial stage of the growth appears to be governed by surface stress and surface energy effects, while the subsequent stress relaxation is found to be fundamentally different between films grown on single-crystal substrates and on buffer layers. The first case can be rationalized with established theoretical models, but these models fail in the attempt to describe the growth on buffer layers. This is most probably due to the larger average density of crystalline defects in the buffer layers, which leads to a two-step stress relaxation mechanism, driven first by the nucleation and later by the migration of dislocation lines.

Health status of tadpoles and metamorphs of Rhinella arenarum (Anura, Bufonidae) that inhabit agroecosystems and its implications for land use.

PubMed

Babini, María Selene; Bionda, Clarisa de Lourdes; Salas, Nancy Edith; Martino, Adolfo Ludovico

2015-08-01

Perturbations of water bodies near agricultural and livestock systems can affect embryonic and larval stages of anurans and negatively impact adult populations and structure of amphibian communities. This study is focused on early development of Rhinella arenarum, for which body growth, abnormalities in the oral disc and genetic damage on erythrocytes were analyzed to establish the impact of agroecosystems on local populations of amphibians. Tadpoles and metamorphs of R. arenarum were collected in three agroecosystems (namely, C1, C2, and C3) and in a site without agricultural and livestock activities (SM) from central Argentina. Egg masses of C1 were extracted for breeding tadpoles under laboratory conditions (Lab). Tadpoles were in small size and lighter in weight in C1 and C2. Metamorphs were shorter and lighter in weight in C1 and C3. In SM and Lab samples, no tadpoles with abnormal LTRF (labial tooth row formula) or without labial teeth were observed. In C1, the highest frequency of abnormal LTRF was recorded and was the only site in which tadpoles without labial teeth were found. In C1 and C2 the tadpoles had highest micronucleus frequencies and nuclear abnormalities. C1 can be considered as the site with the highest anthropogenic perturbation and with less healthy tadpoles. Livestock practices such as alternating cattle between parcel and keeping a buffer between crops and water bodies, would allow a better development of the first aquatic stages that are essential for the conservation of the anuran populations. Copyright © 2015 Elsevier Inc. All rights reserved.

Formation of ore minerals in metamorphic rocks of the German continental deep drilling site (KTB)

NASA Astrophysics Data System (ADS)

Kontny, A.; Friedrich, G.; Behr, H. J.; de Wall, H.; Horn, E. E.; Möller, P.; Zulauf, G.

1997-08-01

The German Continental Deep Drilling Program (KTB) drilled a 9.1 km deep profile through amphibolite facies metamorphic rocks and reached in situ temperatures of 265°C. Each lithologic unit is characterized by typical ore mineral assemblages related to the regional metamorphic conditions. Paragneisses contain pyrrhotite + rutile + ilmenite ± graphite, metabasic units bear ilmenite + rutile + pyrrhotite ± pyrite, and additionally, the so-called variegated units yield pyrrhotite + titanite assemblages. In the latter unit, magnetite + ilmenite + rutile + titanite assemblages related to the lower amphibolite facies breakdown of ilmenite-hematite solid solution also occur locally. Retrograde hydrothermal mineralization which commenced during Upper Carboniferous times is characterized by the following geochemical conditions: (1) low saline Na-K-Mg-Cl fluids with sulfur and oxygen fugacities at the pyrite-pyrrhotite buffer and temperatures of 400-500°C, (2) fluids with CO2, CH4±N2, andpH, Eh, sulfur, and oxygen fugacity in the stability field of graphite + pyrite at temperatures of 280-350° and (3) moderate to high saline Ca-Na-Cl fluids with CH4+ N2; sulfur and oxygen fugacity are in the stability field of pyrrhotite at temperatures <300°C. The latter environment is confirmed by in situ conditions found at the bottom of the deep drilling. Monoclinic, ferrimagnetic pyrrhotite is the main carrier of magnetization which disappears below about 8.6 km, corresponding to in situ temperatures of about 250°C. Below this depth, hexagonal antiferromagnetic pyrrhotite with a Curie temperature of 260°C is the stable phase. Temperature-dependent transformation of pyrrhotite and the reaching of its Curie isotherm within the Earth crust are one of the striking results of the KTB deep drilling project.

Characterization of Mason Gully (H5): The second recovered fall from the Desert Fireball Network

NASA Astrophysics Data System (ADS)

Dyl, Kathryn A.; Benedix, Gretchen K.; Bland, Phil A.; Friedrich, Jon M.; Spurný, Pavel; Towner, Martin C.; O'Keefe, Mary Claire; Howard, Kieren; Greenwood, Richard; Macke, Robert J.; Britt, Daniel T.; Halfpenny, Angela; Thostenson, James O.; Rudolph, Rebecca A.; Rivers, Mark L.; Bevan, Alex W. R.

2016-03-01

Mason Gully, the second meteorite recovered using the Desert Fireball Network (DFN), is characterized using petrography, mineralogy, oxygen isotopes, bulk chemistry, and physical properties. Geochemical data are consistent with its classification as an H5 ordinary chondrite. Several properties distinguish it from most other H chondrites. Its 10.7% porosity is predominantly macroscopic, present as intergranular void spaces rather than microscopic cracks. Modal mineralogy (determined via PS-XRD, element mapping via energy dispersive spectroscopy [EDS], and X-ray tomography [for sulfide, metal, and porosity volume fractions]) consistently gives an unusually low olivine/orthopyroxene ratio (0.67-0.76 for Mason Gully versus ~1.3 for typical H5 ordinary chondrites). Widespread "silicate darkening" is observed. In addition, it contains a bright green crystalline object at the surface of the recovered stone (diameter ≈ 1.5 mm), which has a tridymite core with minor α-quartz and a rim of both low- and high-Ca pyroxene. The mineralogy allows the calculation of the temperatures and ƒ(O2) characterizing thermal metamorphism on the parent body using both the two-pyroxene and the olivine-chromite geo-oxybarometers. These indicate that MG experienced a peak metamorphic temperature of ~900 °C and had a similar ƒ(O2) to Kernouvé (H6) that was buffered by the reaction between olivine, metal, and pyroxene. There is no evidence for shock, consistent with the observed porosity structure. Thus, while Mason Gully has some unique properties, its geochemistry indicates a similar thermal evolution to other H chondrites. The presence of tridymite, while rare, is seen in other OCs and likely exogenous; however, the green object itself may result from metamorphism.

Intermixing at the absorber-buffer layer interface in thin-film solar cells: The electronic effects of point defects in Cu(In,Ga)(Se,S) 2 and Cu 2ZnSn(Se,S) 4 devices

DOE Office of Scientific and Technical Information (OSTI.GOV)

Varley, J. B.; Lordi, V.

We investigate point defects in the buffer layers CdS and ZnS that may arise from intermixing with Cu(In,Ga)(S,Se) 2 (CIGS) or Cu 2ZnSn(S,Se) 4 (CZTS) absorber layers in thin-film photovoltaics. Using hybrid functional calculations, we characterize the electrical and optical behavior of Cu, In, Ga, Se, Sn, Zn, Na, and K impurities in the buffer. We find that In and Ga substituted on the cation site act as shallow donors in CdS and tend to enhance the prevailing n-type conductivity at the interface facilitated by Cd incorporation in CIGS, whereas they are deep donors in ZnS and will be lessmore » effective dopants. Substitutional In and Ga can favorably form complexes with cation vacancies (A-centers) which may contribute to the “red kink” effect observed in some CIGS-based devices. For CZTS absorbers, we find that Zn and Sn defects substituting on the buffer cation site are electrically inactive in n-type buffers and will not supplement the donor doping at the interface as in CIGS/CdS or ZnS devices. Sn may also preferentially incorporate on the S site as a deep acceptor in n-type ZnS, which suggests possible concerns with absorber-related interfacial compensation in CZTS devices with ZnS-derived buffers. Cu, Na, and K impurities are found to all have the same qualitative behavior, most favorably acting as compensating acceptors when substituting on the cation site. Lastly, our results suggest one beneficial role of K and Na incorporation in CIGS or CZTS devices is the partial passivation of vacancy-related centers in CdS and ZnS buffers, rendering them less effective interfacial hole traps and recombination centers.« less

Intermixing at the absorber-buffer layer interface in thin-film solar cells: The electronic effects of point defects in Cu(In,Ga)(Se,S){sub 2} and Cu{sub 2}ZnSn(Se,S){sub 4} devices

DOE Office of Scientific and Technical Information (OSTI.GOV)

Varley, J. B.; Lordi, V.

We investigate point defects in the buffer layers CdS and ZnS that may arise from intermixing with Cu(In,Ga)(S,Se){sub 2} (CIGS) or Cu{sub 2}ZnSn(S,Se){sub 4} (CZTS) absorber layers in thin-film photovoltaics. Using hybrid functional calculations, we characterize the electrical and optical behavior of Cu, In, Ga, Se, Sn, Zn, Na, and K impurities in the buffer. We find that In and Ga substituted on the cation site act as shallow donors in CdS and tend to enhance the prevailing n-type conductivity at the interface facilitated by Cd incorporation in CIGS, whereas they are deep donors in ZnS and will be lessmore » effective dopants. Substitutional In and Ga can favorably form complexes with cation vacancies (A-centers) which may contribute to the “red kink” effect observed in some CIGS-based devices. For CZTS absorbers, we find that Zn and Sn defects substituting on the buffer cation site are electrically inactive in n-type buffers and will not supplement the donor doping at the interface as in CIGS/CdS or ZnS devices. Sn may also preferentially incorporate on the S site as a deep acceptor in n-type ZnS, which suggests possible concerns with absorber-related interfacial compensation in CZTS devices with ZnS-derived buffers. Cu, Na, and K impurities are found to all have the same qualitative behavior, most favorably acting as compensating acceptors when substituting on the cation site. Our results suggest one beneficial role of K and Na incorporation in CIGS or CZTS devices is the partial passivation of vacancy-related centers in CdS and ZnS buffers, rendering them less effective interfacial hole traps and recombination centers.« less

Intermixing at the absorber-buffer layer interface in thin-film solar cells: The electronic effects of point defects in Cu(In,Ga)(Se,S) 2 and Cu 2ZnSn(Se,S) 4 devices

DOE PAGES

Varley, J. B.; Lordi, V.

2014-08-08

We investigate point defects in the buffer layers CdS and ZnS that may arise from intermixing with Cu(In,Ga)(S,Se) 2 (CIGS) or Cu 2ZnSn(S,Se) 4 (CZTS) absorber layers in thin-film photovoltaics. Using hybrid functional calculations, we characterize the electrical and optical behavior of Cu, In, Ga, Se, Sn, Zn, Na, and K impurities in the buffer. We find that In and Ga substituted on the cation site act as shallow donors in CdS and tend to enhance the prevailing n-type conductivity at the interface facilitated by Cd incorporation in CIGS, whereas they are deep donors in ZnS and will be lessmore » effective dopants. Substitutional In and Ga can favorably form complexes with cation vacancies (A-centers) which may contribute to the “red kink” effect observed in some CIGS-based devices. For CZTS absorbers, we find that Zn and Sn defects substituting on the buffer cation site are electrically inactive in n-type buffers and will not supplement the donor doping at the interface as in CIGS/CdS or ZnS devices. Sn may also preferentially incorporate on the S site as a deep acceptor in n-type ZnS, which suggests possible concerns with absorber-related interfacial compensation in CZTS devices with ZnS-derived buffers. Cu, Na, and K impurities are found to all have the same qualitative behavior, most favorably acting as compensating acceptors when substituting on the cation site. Lastly, our results suggest one beneficial role of K and Na incorporation in CIGS or CZTS devices is the partial passivation of vacancy-related centers in CdS and ZnS buffers, rendering them less effective interfacial hole traps and recombination centers.« less

Evidence for Chemical and Electronic Nonuniformities in the Formation of the Interface of RbF-Treated Cu(In,Ga)Se2 with CdS.

PubMed

Nicoara, Nicoleta; Kunze, Thomas; Jackson, Philip; Hariskos, Dimitrios; Duarte, Roberto Félix; Wilks, Regan G; Witte, Wolfram; Bär, Marcus; Sadewasser, Sascha

2017-12-20

We report on the initial stages of CdS buffer layer formation on Cu(In,Ga)Se 2 (CIGSe) thin-film solar cell absorbers subjected to rubidium fluoride (RbF) postdeposition treatment (PDT). A detailed characterization of the CIGSe/CdS interface for different chemical bath deposition (CBD) times of the CdS layer is obtained from spatially resolved atomic and Kelvin probe force microscopy and laterally integrating X-ray spectroscopies. The observed spatial inhomogeneity in the interface's structural, chemical, and electronic properties of samples undergoing up to 3 min of CBD treatments is indicative of a complex interface formation including an incomplete coverage and/or nonuniform composition of the buffer layer. It is expected that this result impacts solar cell performance, in particular when reducing the CdS layer thickness (e.g., in an attempt to increase the collection in the ultraviolet wavelength region). Our work provides important findings on the absorber/buffer interface formation and reveals the underlying mechanism for limitations in the reduction of the CdS thickness, even when an alkali PDT is applied to the CIGSe absorber.

Buffer layer enhanced stability of sodium-ion storage

NASA Astrophysics Data System (ADS)

Wang, Xusheng; Yang, Zhanhai; Wang, Chao; Chen, Dong; Li, Rui; Zhang, Xinxiang; Chen, Jitao; Xue, Mianqi

2017-11-01

Se-Se buffer layers are introduced into tin sequences as SnSe2 single crystal to enhance the cycling stability for long-term sodium-ion storage by blazing a trail of self-defence strategy to structural pulverization especially at high current density. Specifically, under half-cell test, the SnSe2 electrodes could yield a high discharge capacity of 345 mAh g-1 after 300 cycles at 1 A g-1 and a high discharge capacity of 300 mAh g-1 after 2100 cycles at 5 A g-1 with stable coulombic efficiency and no capacity fading. Even with the ultrafast sodium-ion storage at 10 A g-1, the cycling stability still makes a positive response and a high discharge capacity of 221 mAh g-1 is demonstrated after 2700 cycles without capacity fading. The full-cell test for the SnSe2 electrodes also demonstrates the superior cycling stability. The flexible and tough Se-Se buffer layers are favourable to accommodate the sodium-ion intercalation process, and the autogenous Na2Se layers could confine the structural pulverization of further sodiated tin sequences by the slip along the Na2Se-NaxSn interfaces.

Mean-velocity profile of smooth channel flow explained by a cospectral budget model with wall-blockage

DOE PAGES

McColl, Kaighin A.; Katul, Gabriel G.; Gentine, Pierre; ...

2016-03-16

A series of recent studies has shown that a model of the turbulent vertical velocity variance spectrum (F vv) combined with a simplified cospectral budget can reproduce many macroscopic flow properties of turbulent wall-bounded flows, including various features of the mean-velocity profile (MVP), i.e., the "law of the wall". While the approach reasonably models the MVP's logarithmic layer, the buffer layer displays insufficient curvature compared to measurements. The assumptions are re-examined here using a direct numerical simulation (DNS) dataset at moderate Reynolds number that includes all the requisite spectral and co-spectral information. Starting with several hypotheses for the cause ofmore » the "missing" curvature in the buffer layer, it is shown that the curvature deficit is mainly due to mismatches between (i) the modelled and DNS-observed pressure-strain terms in the cospectral budget and (ii) the DNS-observed F vv and the idealized form used in previous models. By replacing the current parameterization for the pressure-strain term with an expansive version that directly accounts for wall-blocking effects, the modelled and DNS reported pressure-strain profiles match each other in the buffer and logarithmic layers. Forcing the new model with DNS-reported F vv rather than the idealized form previously used reproduces the missing buffer layer curvature to high fidelity thereby confirming the "spectral link" between F vv and the MVP across the full profile. A broad implication of this work is that much of the macroscopic properties of the flow (such as the MVP) may be derived from the energy distribution in turbulent eddies (i.e., F vv) representing the microstate of the flow, provided the link between them accounts for wall-blocking.« less

Magnetic Anisotropy and Chemical Order of Artificially Synthesized L10-Ordered FeNi Films on Au-Cu-Ni Buffer Layers

NASA Astrophysics Data System (ADS)

Kojima, Takayuki; Mizuguchi, Masaki; Koganezawa, Tomoyuki; Osaka, Keiichi; Kotsugi, Masato; Takanashi, Koki

2012-01-01

L10-FeNi films were grown by alternate monatomic layer deposition on Au-Cu-Ni buffer layers at several substrate temperatures (Ts), and the relation between the uniaxial magnetic anisotropy energy (Ku) and the long-range chemical order parameter (S) was investigated. A large Ku of (7.0 ±0.2) ×106 erg/cm3 and S of 0.48 ±0.05 were obtained. The value of Ku was larger than those reported previously for artificially synthesized FeNi films. It was first found that both Ku and S increased with Ts, and Ku was roughly proportional to S.

Fabrication and electrochemical properties of insoluble fullerene-diamine adduct thin-films as buffer layer by alternate immersion process

NASA Astrophysics Data System (ADS)

Saito, Jo; Akiyama, Tsuyoshi; Suzuki, Atsushi; Oku, Takeo

2017-01-01

Insoluble fullerene-diamine adduct thin-films consisting of C60 and 1,2-diaminoethane were easily fabricated on an electrode by an alternate immersion process. Formation of the C60-diamine adduct films were confirmed using transmission absorption spectroscopy and atomic force microscopy. An inverted-type organic solar cells were fabricated by using the C60-diamine adduct film as the electron transport layer. The resultant photoelectric conversation performance of the solar cells suggested that photocurrent is generated via the photoexcitation of polythiophene. The result suggests that the present insoluble fullerene-diamine adduct films worked as buffer layer for organic thin-film solar cells.

First description of a metamorphic sole related to ophiolite obduction in the northern Caribbean: Geochemistry and petrology of the Güira de Jauco Amphibolite complex (eastern Cuba) and tectonic implications

NASA Astrophysics Data System (ADS)

Lázaro, C.; Blanco-Quintero, I. F.; Rojas-Agramonte, Y.; Proenza, J. A.; Núñez-Cambra, K.; García-Casco, A.

2013-10-01

The Güira de Jauco Amphibolite Complex underlies the Mayarí-Baracoa Ophiolitic Belt (eastern Cuba) and is composed of highly foliated amphibolite, locally with blocks of sheared serpentinitie that enclose concordant layers of amphibolite. These amphibolites are interpreted as remnants of a sub-ophiolitic metamorphic sole likely formed during late Cretaceous times before the initiation of the collision between the Caribbean and the North American plates. The complex includes common amphibolites (Hbl + Pl ± Ep ± Ttn ± Rt ± Qtz ± Ap), garnet amphibolites (Hbl + Grt + Pl + Ep ± Ttn ± Qtz ± Ap) and clinopyroxene amphibolites (Hbl + Pl + Cpx ± Ep ± Ttn ± Qtz ± Ap). Geochemical data indicates that the protoliths are igneous mafic rocks of basaltic composition that likely formed part of the upper and lower(?)crust of an oceanic lithosphere. Rare Earth element contents suggest a Mid-Ocean Ridge Basalt (MORB) origin. However, the enrichment in Large-Ion Lithophile elements and the depletion in NbTaTi as compared to Normal-MORB, suggests a suprasubduction scenario, either a back-arc or a fore-arc setting. The pressure-temperature estimates of metamorphism indicate that the entire amphibolite body underwent similar peak metamorphic conditions at 650-665 °C and 8.5-8.7 kbar (ca. 30 km depth), corresponding to a relatively high apparent geothermal gradient of 23 °C/km.

MBE growth and optical properties of GaN layers on SiC/Si(111) hybrid substrate

NASA Astrophysics Data System (ADS)

Reznik, R. R.; Kotlyar, K. P.; Soshnikov, I. P.; Kukushkin, S. A.; Osipov, A. V.; Nikitina, E. V.; Cirlin, G. E.

2017-11-01

The fundamental possibility of the growth of GaN layers by molecular-beam epitaxy on a silicon substrate with nanoscale buffer layer of silicon carbide without any AlN layers has been demonstrated for the first time. Morphological properties of the resulting system have been studied.

Catalyst, method of making, and reactions using the catalyst

DOEpatents

Tonkovich, Anna Lee Y [Pasco, WA; Wang, Yong [Richland, WA; Gao, Yufei [Kennewick, WA

2009-03-03

The present invention includes a catalyst having a layered structure with, (1) a porous support, (2) a buffer layer, (3) an interfacial layer, and optionally (4) a catalyst layer. The invention also provides a process in which a reactant is converted to a product by passing through a reaction chamber containing the catalyst.

Catalyst, method of making, and reactions using the catalyst

DOEpatents

Tonkovich, Anna Lee Y [Pasco, WA; Wang, Yong [Richland, WA; Gao, Yufei [Kennewick, WA

2002-08-27

The present invention includes a catalyst having a layered structure with, (1) a porous support, (2) a buffer layer, (3) an interfacial layer, and optionally (4) a catalyst layer. The invention also provides a process in which a reactant is converted to a product by passing through a reaction chamber containing the catalyst.

Catalyst, Method Of Making, And Reactions Using The Catalyst

DOEpatents

Tonkovich, Anna Lee Y.; Wang, Yong; Gao, Yufei

2004-07-13

The present invention includes a catalyst having a layered structure with, (1) a porous support, (2) a buffer layer, (3) an interfacial layer, and optionally (4) a catalyst layer. The invention also provides a process in which a reactant is converted to a product by passing through a reaction chamber containing the catalyst.

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yun, Yu; Meng, Dechao; Wang, Jianlin

2015-07-06

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

Structure and thermochronology of the metamorphic core of the Brooks Range, Alaska

NASA Astrophysics Data System (ADS)

Toro, Jaime

1999-11-01

Detailed field studies were undertaken in two key areas of the Central Belt of the Brooks Range: (1) the north flank of Mt. Igikpak in the Survey Pass Quadrangle and (2) in the Shishakshinovik Pass area in the eastern Ambler River Quadrangle. In both areas structural, stratigraphic, petrologic, 40Ar/39Ar, apatite fission-track and U-Pb data were used to constrain the kinematic and thermal history of metamorphic rocks of those areas. North of the Mt. Igikpak massif a crustal section ˜15 km thick is exposed. There are upper greenschist facies rocks in the deeper portions, and very low grade metamorphic rocks at higher structural levels. Two foliations are found: a higher grade relict S1 fabric and a lower grade S 2 fabric that controls the metamorphic layering. 40Ar/ 39Ar analyses from S1 white mica in the low-grade rocks at the northern end of the transect indicate that peak M1 metamorphism occurred before ˜112 Ma. We ascribe M1 to shortening that occurred during collision of an island arc against the Arctic Alaska margin. S 2 involved the retrogression of earlier assemblages. Kinematic indicators on S2 are top-to-the-north. A rapid cooling event from 500 +/- 50°C to 300 +/- 50°C took place between ˜98 and ˜90 Ma. The driving mechanism for ductile deformation during S2, and for rapid cooling documented by our thermochronologic data, was probably the gravitational collapse of the core of the orogen, over-thickened during the preceding collision. At Shishakshinovik Pass there are Mississippian Lisburne Group strata surrounded by metamorphic rocks typical of the Central Belt of the Brooks Range. All the rocks at Shishakshinovik Pass are intensely deformed, so that one cannot distinguish between an autochthonous and an allochthonous sequence. Furthermore the Mississippian rocks, instead of being attached to the underlying basement, are in the hanging wall of a northwest dipping shear zone. Based on the variations in metamorphic grade and the 40Ar/ 39Ar thermochronology, we argue that this shear zone was an extensional structure active during the mid-Cretaceous orogenic collapse of the Brooks Range. A consequence of this structural interpretation is that the Endicott Mountains allochthon need not be restored south of the Shishakshinovik orthogneiss.

Resetting of Mg isotopes between calcite and dolomite during burial metamorphism: Outlook of Mg isotopes as geothermometer and seawater proxy

NASA Astrophysics Data System (ADS)

Hu, Zhongya; Hu, Wenxuan; Wang, Xiaomin; Lu, Yizhou; Wang, Lichao; Liao, Zhiwei; Li, Weiqiang

2017-07-01

Magnesium isotopes are an emerging tool to study the geological processes recorded in carbonates. Calcite, due to its ubiquitous occurrence and the large Mg isotope fractionation associated with the mineral, has attracted great interests in applications of Mg isotope geochemistry. However, the fidelity of Mg isotopes in geological records of carbonate minerals (e.g., calcite and dolomite) against burial metamorphism remains poorly constrained. Here we report our investigation on the Mg isotope systematics of a dolomitized Middle Triassic Geshan carbonate section in eastern China. Magnesium isotope analysis was complemented by analyses of Sr-C-O isotopic compositions, major and trace element concentrations, and petrographic and mineralogical features. Multiple lines of evidence consistently indicated that post-depositional diagenesis of carbonate minerals occurred to the carbonate rocks. Magnesium isotope compositions of the carbonate rocks closely follow a mixing trend between a high δ26Mg dolomite end member and a low δ26Mg calcite end member, irrespective of sample positions in the section and calcite/dolomite ratio in the samples. By fitting the measured Mg isotope data using a two-end member mixing model, an inter-mineral Δ26Mgdolomite-calcite fractionation of 0.72‰ was obtained. Based on the experimentally derived Mg isotope fractionation factors for dolomite and calcite, a temperature of 150-190 °C was calculated to correspond to the 0.72‰ Δ26Mgdolomite-calcite fractionation. Such temperature range matches with the burial-thermal history of the local strata, making a successful case of Mg isotope geothermometry. Our results indicate that both calcite and dolomite had been re-equilibrated during burial metamorphism, and based on isotope mass balance of Mg, the system was buffered by dolomite in the section. Therefore, burial metamorphism may reset Mg isotope signature of calcite, and Mg isotope compositions in calcite should be dealt with caution in studies of carbonate rocks with thermal history. By contrast, Mg isotopes of dolomite are less prone to post-depositional resetting due to a number of properties including high Mg abundance and high thermodynamic stability, and Mg isotopes in dolomite may be a more robust recorder for original carbonate precipitates.

Optimization of the buffer surface of CoFeB/MgO/CoFeB-based magnetic tunnel junctions by ion beam milling

NASA Astrophysics Data System (ADS)

Martins, L.; Ventura, J.; Ferreira, R.; Freitas, P. P.

2017-12-01

Due to their high tunnel magnetoresistance (TMR) ratios at room temperature, magnetic tunnel junctions (MTJs) with a crystalline MgO insulating barrier and CoFeB ferromagnetic (FM) layers are the best candidates for novel magnetic memory applications. To overcome impedance matching problems in electronic circuits, the MgO barrier must have an ultra-low thickness (∼1 nm). Therefore, it is mandatory to optimize the MTJ fabrication process, in order to prevent relevant defects in the MgO barrier that could affect the magnetic and electrical MTJ properties. Here, a smoothing process aiming to decrease the roughness of the buffer surface before the deposition of the full MTJ stack is proposed. An ion beam milling process was used to etch the surface of an MTJ buffer structure with a Ru top layer. The morphologic results prove an effective decrease of the Ru surface roughness with the etching time. The electrical and magnetic results obtained for MTJs with smoothed buffer structures show a direct influence of the buffer roughness and coupling field on the improvement of the TMR ratio.

Lithogeochemical character of near-surface bedrock in the New England coastal basins

USGS Publications Warehouse

Robinson, Gilpin R.; Ayotte, Joseph D.; Montgomery, Denise L.; DeSimone, Leslie A.

2002-01-01

This geographic information system (GIS) data layer shows the generalized lithologic and geochemical, termed lithogeochemical, character of near-surface bedrock in the New England Coastal Basin (NECB) study area of the U.S. Geological Survey's National Water Quality Assessment (NAWQA) Program. The area encompasses 23,000 square miles in western and central Maine, eastern Massachusetts, most of Rhode Island, eastern New Hampshire and a small part of eastern Connecticut. The NECB study area includes the Kennebec, Androscoggin, Saco, Merrimack, Charles, and Blackstone River Basins, as well as all of Cape Cod. Bedrock units in the NECB study area are classified into lithogeochemical units based on the relative reactivity of their constituent minerals to dissolution and the presence of carbonate or sulfide minerals. The 38 lithogeochemical units are generalized into 7 major groups: (1) carbonate-bearing metasedimentary rocks; (2) primarily noncalcareous, clastic sedimentary rocks with restricted deposition in discrete fault-bounded sedimentary basins of Mississipian or younger age; (3) primarily noncalcareous, clastic sedimentary rocks at or above biotite-grade of regional metamorphism; (4) mafic igneous rocks and their metamorphic equivalents; (5) ultramafic rocks; (6) felsic igneous rocks and their metamorphic equivalents; and (7) unconsolidated and poorly consolidated sediments.

Planar regions of GaAs (001) prepared by Ga droplet motion

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zheng, Changxi, E-mail: changxi.zheng@monash.edu; Tang, Wen-Xin; Jesson, David E., E-mail: jessonDE@cardiff.ac.uk

2016-07-15

The authors describe a simple method for obtaining planar regions of GaAs (001) suitable for surface science studies. The technique, which requires no buffer layer growth, atomic hydrogen source, or the introduction of As flux, employs controllable Ga droplet motion to create planar trail regions during Langmuir evaporation. Low-energy electron microscopy/diffraction techniques are applied to monitor the droplet motion and characterize the morphology and the surface reconstruction. It is found that the planar regions exhibit atomic flatness at the level of a high-quality buffer layer.

Buffer layers and articles for electronic devices

DOEpatents

Paranthaman, Mariappan P.; Aytug, Tolga; Christen, David K.; Feenstra, Roeland; Goyal, Amit

2004-07-20

Materials for depositing buffer layers on biaxially textured and untextured metallic and metal oxide substrates for use in the manufacture of superconducting and other electronic articles comprise RMnO.sub.3, R.sub.1-x A.sub.x MnO.sub.3, and combinations thereof; wherein R includes an element selected from the group consisting of La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Y, and A includes an element selected from the group consisting of Be, Mg, Ca, Sr, Ba, and Ra.

Toward a structural understanding of turbulent drag reduction: nonlinear coherent states in viscoelastic shear flows.

PubMed

Stone, Philip A; Waleffe, Fabian; Graham, Michael D

2002-11-11

Nontrivial steady flows have recently been found that capture the main structures of the turbulent buffer layer. We study the effects of polymer addition on these "exact coherent states" (ECS) in plane Couette flow. Despite the simplicity of the ECS flows, these effects closely mirror those observed experimentally: Structures shift to larger length scales, wall-normal fluctuations are suppressed while streamwise ones are enhanced, and drag is reduced. The mechanism underlying these effects is elucidated. These results suggest that the ECS are closely related to buffer layer turbulence.

Advanced Technologies for Heterodyne Radio Astronomy Instrumentation - Part1 By A. Pavolotsky, and Advanced Technologies for Heterodyne Radio Astronomy Instrumentation - Part2 By V. Desmaris

NASA Astrophysics Data System (ADS)

Desmaris, Vincent

2018-01-01

We present the advanced micro/nano technological engineering at the atomic level producing state-of-the-art epitaxial NbN thin-films on GaN buffer layers. Furthermore, we report the outstanding performance of the hot electron bolometers fabricated on epitaxial NbN thin films on GaN buffer layers. Finally we present advanced passive devices such as waveguide hybrids, IF hybrids and combiners for the realization of heterodyne THz receivers.

Epitaxial ferromagnetic oxide thin films on silicon with atomically sharp interfaces

DOE Office of Scientific and Technical Information (OSTI.GOV)

Coux, P. de; CEMES-CNRS, 29 rue Jeanne Marvig, BP 94347, Toulouse Cedex 4; Bachelet, R.

A bottleneck in the integration of functional oxides with silicon, either directly grown or using a buffer, is the usual formation of an amorphous interfacial layer. Here, we demonstrate that ferromagnetic CoFe{sub 2}O{sub 4} films can be grown epitaxially on Si(111) using a Y{sub 2}O{sub 3} buffer layer, and remarkably the Y{sub 2}O{sub 3}/Si(111) interface is stable and remains atomically sharp. CoFe{sub 2}O{sub 4} films present high crystal quality and high saturation magnetization.

BaFe2As2/Fe Bilayers with [001]-tilt Grain Boundary on MgO and SrTiO3 Bicrystal Substrates

NASA Astrophysics Data System (ADS)

Iida, K.; Haindl, S.; Kurth, F.; Hänisch, J.; Schulz, L.; Holzapfel, B.

Co-doped BaFe2As2 (Ba-122) can be realized on both MgO and SrTiO3 bicrystal substrates with [001]-tilt grain boundary by employing Fe buffer layers. However, an additional spinel (i.e. MgAl2O4) buffer between Fe and SrTiO3 is necessary since an epitaxial, smooth surface of Fe layer can not be grown on bare SrTiO3. Both types of bicrystal films show good crystalline quality.

Exciton confinement in strain-engineered metamorphic InAs/I nxG a1 -xAs quantum dots

NASA Astrophysics Data System (ADS)

Khattak, S. A.; Hayne, M.; Huang, J.; Vanacken, J.; Moshchalkov, V. V.; Seravalli, L.; Trevisi, G.; Frigeri, P.

2017-11-01

We report a comprehensive study of exciton confinement in self-assembled InAs quantum dots (QDs) in strain-engineered metamorphic I nxG a1 -xAs confining layers on GaAs using low-temperature magnetophotoluminescence. As the lattice mismatch (strain) between QDs and confining layers (CLs) increases from 4.8% to 5.7% the reduced mass of the exciton increases, but saturates at higher mismatches. At low QD-CL mismatch there is clear evidence of spillover of the exciton wave function due to small localization energies. This is suppressed as the In content x in the CLs decreases (mismatch and localization energy increasing). The combined effects of low effective mass and wave-function spillover at high x result in a diamagnetic shift coefficient that is an order of magnitude larger than for samples where In content in the barrier is low (mismatch is high and localization energy is large). Finally, an anomalously small measured Bohr radius in samples with the highest x is attributed to a combination of thermalization due to low localization energy, and its enhancement with magnetic field, a mechanism which results in small dots in the ensemble dominating the measured Bohr radius.

Effect of annealing time on optical and electrical properties of CdS thin films

NASA Astrophysics Data System (ADS)

Soliya, Vanshika; Tandel, Digisha; Patel, Chandani; Patel, Kinjal

2018-05-01

Cadmium sulphide (CdS) is semiconductor compound of II-VI group. Thin film of CdS widely used in the applications such as, a buffer layer in copper indium diselenide (CIS) hetrojunction based solar cells, transistors, photo detectors and light emitting diodes. Because of the ease of making like chemical bath deposition (CBD), screen printing and thermal evaporation. It is extensively used in the CIS based solar cells as a buffer layers. The buffer layers usually used for reducing the interface recombination of the photo generated carriers by means of improving the lattice mismatch between the layers. The optimum thickness and the optoelectronics properties of CdS thin films like, optical band gap, electrical resistivity, structure, and composition etc., are to be considering for its use as a buffer layer. In the present study the CdS thin film were grown by simple dip coating method. In this method we had prepared 0.1M Cadmium-thiourea precursor solution. Before the deposition process of CdS, glass substrate has been cleaned using Methanol, Acetone, Trichloroethylene and De-ionized (DI) water. After coating of precursor layer, it was heated at 200 °C for themolysis. Then after CdS films were annealed at 200 °C for different time and studied its influence on the optical transmission, band gap, XRD, raman and the electrical resistivity. As increasing the annealing time we had observed the average transmission of the films was reduce after the absorption edge. In addition to the blue shift of absorption edge was observed. The observed optimum band gap was around 2.50 eV. XRD and raman analysis confirms the cubuc phase of CdS. Hot probe method confirms the n-type conductivity of the CdS film. Hall probe data shows the resistivity of the films was in the order of 103 Ωcm. Observed data signifies its future use in the many optoelectronics devices.

Fabrication of nanocrystal ink based superstrate-type CuInS₂ thin film solar cells.

PubMed

Cho, Jin Woo; Park, Se Jin; Kim, Woong; Min, Byoung Koun

2012-07-05

A CuInS₂ (CIS) nanocrystal ink was applied to thin film solar cell devices with superstrate-type configuration. Monodispersed CIS nanocrystals were synthesized by a colloidal synthetic route and re-dispersed in toluene to form an ink. A spray method was used to coat CIS films onto conducting glass substrates. Prior to CIS film deposition, TiO₂ and CdS thin films were also prepared as a blocking layer and a buffer layer, respectively. We found that both a TiO₂ blocking layer and a CdS buffer layer are necessary to generate photoresponses in superstrate-type devices. The best power conversion efficiency (∼1.45%) was achieved by the CIS superstrate-type thin film solar cell device with 200 and 100 nm thick TiO₂ and CdS films, respectively.

Transparent-conductive-oxide (TCO) buffer layer effect on the resistive switching process in metal/TiO2/TCO/metal assemblies

NASA Astrophysics Data System (ADS)

Filatova, E. O.; Baraban, A. P.; Konashuk, A. S.; Konyushenko, M. A.; Selivanov, A. A.; Sokolov, A. A.; Schaefers, F.; Drozd, V. E.

2014-11-01

The effect of a transparent conductive oxide (TCO) buffer layer on the insulator matrix and on the resistive switching process in the metal/TiO2/TCO/metal assembly was studied depending on the material of the TCO (ITO-(In2O3)0.9(SnO2)0.1 or SnO2 or ZnO). For the first time electro-physical studies and near edge x-ray absorption fine structure (NEXAFS) studies were carried out jointly and at the same point of the sample, providing direct experimental evidence that the switching process strongly influences the lowest unoccupied bands and the local atomic structure of the TiO2 layers. It was established that a TCO layer in a metal/TiO2/TCO/metal assembly is an additional source of oxygen vacancies for the TiO2 film. The RL (RH) states are achieved presumably with the formation (rupture) of the electrically conductive path of oxygen vacancies. Inserting an Al2O3 thin layer between the TiO2 and TCO layers to some extent restricts the processes of migration of the oxygen ions and vacancies, and does not allow the anti-clockwise bipolar resistive switching in a Au/TiO2/Al2O3/ITO/Au assembly. The greatest value of the ratio RH/RL is observed for the assembly with a SnO2 buffer layer that will provide the maximum set of intermediate states (recording analog data) and increase the density of information recording in this case.

Seismic imaging of slab metamorphism and genesis of intermediate-depth intraslab earthquakes

NASA Astrophysics Data System (ADS)

Hasegawa, Akira; Nakajima, Junichi

2017-12-01

We review studies of intermediate-depth seismicity and seismic imaging of the interior of subducting slabs in relation to slab metamorphism and their implications for the genesis of intermediate-depth earthquakes. Intermediate-depth events form a double seismic zone in the depth range of c. 40-180 km, which occur only at locations where hydrous minerals are present, and are particularly concentrated along dehydration reaction boundaries. Recent studies have revealed detailed spatial distributions of these events and a close relationship with slab metamorphism. Pressure-temperature paths of the crust for cold slabs encounter facies boundaries with large H2O production rates and positive total volume change, which are expected to cause highly active seismicity near the facies boundaries. A belt of upper-plane seismicity in the crust nearly parallel to 80-90 km depth contours of the slab surface has been detected in the cold Pacific slab beneath eastern Japan, and is probably caused by slab crust dehydration with a large H2O production rate. A seismic low-velocity layer in the slab crust persists down to the depth of this upper-plane seismic belt, which provides evidence for phase transformation of dehydration at this depth. Similar low-velocity subducting crust closely related with intraslab seismicity has been detected in several other subduction zones. Seismic tomography studies in NE Japan and northern Chile also revealed the presence of a P-wave low-velocity layer along the lower plane of a double seismic zone. However, in contrast to predictions based on the serpentinized mantle, S-wave velocity along this layer is not low. Seismic anisotropy and pore aspect ratio may play a role in generating this unique structure. Although further validation is required, observations of these distinct low P-wave velocities along the lower seismic plane suggest the presence of hydrated rocks or fluids within that layer. These observations support the hypothesis that dehydration-derived H2O causes intermediate-depth intraslab earthquakes. However, it is possible that dual mechanisms generate these earthquakes; the initiation of earthquake rupture may be caused by local excess pore pressure from H2O, and subsequent ruptures may propagate through thermal shear instability. In either case, slab-derived H2O plays an important role in generating intermediate-depth events.

Behavior of Photocarriers in the Light-Induced Metastable State in the p-n Heterojunction of a Cu(In,Ga)Se2 Solar Cell with CBD-ZnS Buffer Layer.

PubMed

Lee, Woo-Jung; Yu, Hye-Jung; Wi, Jae-Hyung; Cho, Dae-Hyung; Han, Won Seok; Yoo, Jisu; Yi, Yeonjin; Song, Jung-Hoon; Chung, Yong-Duck

2016-08-31

We fabricated Cu(In,Ga)Se2 (CIGS) solar cells with a chemical bath deposition (CBD)-ZnS buffer layer grown with varying ammonia concentrations in aqueous solution. The solar cell performance was degraded with increasing ammonia concentration, due to actively dissolved Zn atoms during CBD-ZnS precipitation. These formed interfacial defect states, such as hydroxide species in the CBD-ZnS film, and interstitial and antisite Zn defects at the p-n heterojunction. After light/UV soaking, the CIGS solar cell performance drastically improved, with a rise in fill factor. With the Zn-based buffer layer, the light soaking treatment containing blue photons induced a metastable state and enhanced the CIGS solar cell performance. To interpret this effect, we suggest a band structure model of the p-n heterojunction to explain the flow of photocarriers under white light at the initial state, and then after light/UV soaking. The determining factor is a p+ defect layer, containing an amount of deep acceptor traps, located near the CIGS surface. The p+ defect layer easily captures photoexcited electrons, and then when it becomes quasi-neutral, attracts photoexcited holes. This alters the barrier height and controls the photocurrent at the p-n junction, and fill factor values, determining the solar cell performance.

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Calabrese, Gabriele; Baricordi, Stefano; Bernardoni, Paolo

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,more » 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.« less

Test evaluation of shock buffering concept for hydrodynamic ram induced by yawing projectile impacting a simulated integral fuel tank

NASA Technical Reports Server (NTRS)

Zabel, P. H.

1979-01-01

A concept for containing the shock inputs due to hydrodynamic ram caused by an impacting projectile within a fuel cell is discussed. This is to provide a buffering layer of foam, flexible, rigid or a combination thereof, which is sealed from the liquid. A program is described in which this buffering concept was tested. The effectiveness of a novel muzzle-mounted, 'tumble', test device is shown.

GaN Micromechanical Resonators with Meshed Metal Bottom Electrode.

PubMed

Ansari, Azadeh; Liu, Che-Yu; Lin, Chien-Chung; Kuo, Hao-Chung; Ku, Pei-Cheng; Rais-Zadeh, Mina

2015-03-17

This work describes a novel architecture to realize high-performance gallium nitride (GaN) bulk acoustic wave (BAW) resonators. The method is based on the growth of a thick GaN layer on a metal electrode grid. The fabrication process starts with the growth of a thin GaN buffer layer on a Si (111) substrate. The GaN buffer layer is patterned and trenches are made and refilled with sputtered tungsten (W)/silicon dioxide (SiO₂) forming passivated metal electrode grids. GaN is then regrown, nucleating from the exposed GaN seed layer and coalescing to form a thick GaN device layer. A metal electrode can be deposited and patterned on top of the GaN layer. This method enables vertical piezoelectric actuation of the GaN layer using its largest piezoelectric coefficient ( d 33 ) for thickness-mode resonance. Having a bottom electrode also results in a higher coupling coefficient, useful for the implementation of acoustic filters. Growth of GaN on Si enables releasing the device from the frontside using isotropic xenon difluoride (XeF₂) etch and therefore eliminating the need for backside lithography and etching.

High-quality III-nitride films on conductive, transparent (2̅01)-oriented β-Ga2O3 using a GaN buffer layer

PubMed Central

Muhammed, M. M.; Roldan, M. A.; Yamashita, Y.; Sahonta, S.-L.; Ajia, I. A.; Iizuka, K.; Kuramata, A.; Humphreys, C. J.; Roqan, I. S.

2016-01-01

We demonstrate the high structural and optical properties of InxGa1−xN epilayers (0 ≤ x ≤ 23) grown on conductive and transparent (01)-oriented β-Ga2O3 substrates using a low-temperature GaN buffer layer rather than AlN buffer layer, which enhances the quality and stability of the crystals compared to those grown on (100)-oriented β-Ga2O3. Raman maps show that the 2″ wafer is relaxed and uniform. Transmission electron microscopy (TEM) reveals that the dislocation density reduces considerably (~4.8 × 107 cm−2) at the grain centers. High-resolution TEM analysis demonstrates that most dislocations emerge at an angle with respect to the c-axis, whereas dislocations of the opposite phase form a loop and annihilate each other. The dislocation behavior is due to irregular (01) β-Ga2O3 surface at the interface and distorted buffer layer, followed by relaxed GaN epilayer. Photoluminescence results confirm high optical quality and time-resolved spectroscopy shows that the recombination is governed by bound excitons. We find that a low root-mean-square average (≤1.5 nm) of InxGa1−xN epilayers can be achieved with high optical quality of InxGa1−xN epilayers. We reveal that (01)-oriented β-Ga2O3 substrate has a strong potential for use in large-scale high-quality vertical light emitting device design. PMID:27412372

High-quality III-nitride films on conductive, transparent (2̅01)-oriented β-Ga2O3 using a GaN buffer layer.

PubMed

Muhammed, M M; Roldan, M A; Yamashita, Y; Sahonta, S-L; Ajia, I A; Iizuka, K; Kuramata, A; Humphreys, C J; Roqan, I S

2016-07-14

We demonstrate the high structural and optical properties of InxGa1-xN epilayers (0 ≤ x ≤ 23) grown on conductive and transparent (01)-oriented β-Ga2O3 substrates using a low-temperature GaN buffer layer rather than AlN buffer layer, which enhances the quality and stability of the crystals compared to those grown on (100)-oriented β-Ga2O3. Raman maps show that the 2″ wafer is relaxed and uniform. Transmission electron microscopy (TEM) reveals that the dislocation density reduces considerably (~4.8 × 10(7) cm(-2)) at the grain centers. High-resolution TEM analysis demonstrates that most dislocations emerge at an angle with respect to the c-axis, whereas dislocations of the opposite phase form a loop and annihilate each other. The dislocation behavior is due to irregular (01) β-Ga2O3 surface at the interface and distorted buffer layer, followed by relaxed GaN epilayer. Photoluminescence results confirm high optical quality and time-resolved spectroscopy shows that the recombination is governed by bound excitons. We find that a low root-mean-square average (≤1.5 nm) of InxGa1-xN epilayers can be achieved with high optical quality of InxGa1-xN epilayers. We reveal that (01)-oriented β-Ga2O3 substrate has a strong potential for use in large-scale high-quality vertical light emitting device design.

Delayed release film coating applications on oral solid dosage forms of proton pump inhibitors: case studies.

PubMed

Missaghi, Shahrzad; Young, Cara; Fegely, Kurt; Rajabi-Siahboomi, Ali R

2010-02-01

Formulation of proton pump inhibitors (PPIs) into oral solid dosage forms is challenging because the drug molecules are acid-labile. The aim of this study is to evaluate different formulation strategies (monolithic and multiparticulates) for three PPI drugs, that is, rabeprazole sodium, lansoprazole, and esomeprazole magnesium, using delayed release film coating applications. The core tablets of rabeprazole sodium were prepared using organic wet granulation method. Multiparticulates of lansoprazole and esomeprazole magnesium were prepared through drug layering of sugar spheres, using powder layering and suspension layering methods, respectively. Tablets and drug-layered multiparticulates were seal-coated, followed by delayed release film coating application, using Acryl-EZE(R), aqueous acrylic enteric system. Multiparticulates were then filled into capsules. The final dosage forms were evaluated for physical properties, as well as in vitro dissolution testing in both compendial acid phase, 0.1N HCl (pH 1.2), and intermediate pH, acetate buffer (pH 4.5), followed by phosphate buffer, pH 6.8. The stability of the delayed release dosage forms was evaluated upon storage in accelerated conditions [40 degrees C/75% relative humidity] for 3 months. All dosage forms demonstrated excellent enteric protection in the acid phase, followed by rapid release in their respective buffer media. Moreover, the delayed release dosage forms remained stable under accelerated stability conditions for 3 months. Results showed that Acryl-EZE enteric coating systems provide excellent performance in both media (0.1N HCl and acetate buffer pH 4.5) for monolithic and multiparticulate dosage forms.

Revealing the Bonding Environment of Zn in ALD Zn(O,S) Buffer Layers through X-ray Absorption Spectroscopy

PubMed Central

2017-01-01

Zn(O,S) buffer layer electronic configuration is determined by its composition and thickness, tunable through atomic layer deposition. The Zn K and L-edges in the X-ray absorption near edge structure verify ionicity and covalency changes with S content. A high intensity shoulder in the Zn K-edge indicates strong Zn 4s hybridized states and a preferred c-axis orientation. 2–3 nm thick films with low S content show a subdued shoulder showing less contribution from Zn 4s hybridization. A lower energy shift with film thickness suggests a decreasing bandgap. Further, ZnSO4 forms at substrate interfaces, which may be detrimental for device performance. PMID:29083141

III-V/Active-Silicon Integration for Low-Cost High-Performance Concentrator Photovoltaics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ringel, Steven

This FPACE project was motivated by the need to establish the foundational pathway to achieve concentrator solar cell efficiencies greater than 50%. At such an efficiency, DOE modeling projected that a III-V CPV module cost of $0.50/W or better could be achieved. Therefore, the goal of this project was to investigate, develop and advance a III-V/Si mulitjunction (MJ) CPV technology that can simultaneously address the primary cost barrier for III-V MJ solar cells while enabling nearly ideal MJ bandgap profiles that can yield efficiencies in excess of 50% under concentrated sunlight. The proposed methodology was based on use of ourmore » recently developed GaAsP metamorphic graded buffer as a pathway to integrate unique GaAsP and Ga-rich GaInP middle and top junctions having bandgaps that are adjustable between 1.45 – 1.65 eV and 1.9 – 2.1 eV, respectively, with an underlying, 1.1 eV active Si subcell/substrate. With this design, the Si can be an active component sub-cell due to the semi-transparent nature of the GaAsP buffer with respect to Si as well as a low-cost alternative substrate that is amenable to scaling with existing Si foundry infrastructure, providing a reduction in materials cost and a low cost path to manufacturing at scale. By backside bonding of a SiGe, a path to exceed 50% efficiency is possible. Throughout the course of this effort, an expansive range of new understanding was achieved that has stimulated worldwide efforts in III-V/Si PV R&D that spanned materials development, metamorphic device optimization, and complete III-V/Si monolithic integration. Highlights include the demonstration of the first ideal GaP/Si interfaces grown by industry-standard MOCVD processes, the first high performance metamorphic tunnel junctions designed for III-V/Si integration, record performance of specific metamorphic sub-cell designs, the first fully integrated GaInP/GaAsP/Si double (1.7 eV/1.1 eV) and triple (1.95 eV/1.5 eV/1.1 eV) junction solar cells, the first high performance GaAsP/Si double junction cell, the demonstration of a new method that allow for rapid, quantitative and non-destructive characterization of dislocations (ECCI-electron channeling contrast imaging), the first observation, explanation and solution of the now commonly reported lifetime degradation and recovery phenomena in III-V/Si MOCVD growth, the first demonstration of a high performance SiGe cell with a bandgap of 0.9 eV, amongst other highlights. The impact of the program on the international community has been significant. At the start of our FPACE1 project and for the immediate prior years, 1-2 conference papers/annually were presented at IEEE PVSC. Once FPACE1 commenced in 2011, related efforts sprouted across the US, Europe and Asia and by 2015 there were 26 papers presented on III-V/Si multijunctions in the 2015 PVSC, demonstrating the excitement that was stimulated by the results of this FPACE1 effort.« less

Use of bicarbonate buffer systems for dissolution characterization of enteric-coated proton pump inhibitor tablets.

PubMed

Shibata, Hiroko; Yoshida, Hiroyuki; Izutsu, Ken-Ichi; Goda, Yukihiro

2016-04-01

The aim of this study was to assess the effects of buffer systems (bicarbonate or phosphate at different concentrations) on the in vitro dissolution profiles of commercially available enteric-coated tablets. In vitro dissolution tests were conducted using an USP apparatus II on 12 enteric-coated omeprazole and rabeprazole tablets, including innovator and generic formulations in phosphate buffers, bicarbonate buffers and a media modified Hanks (mHanks) buffer. Both omeprazole and rabeprazole tablets showed similar dissolution profiles among products in the compendial phosphate buffer system. However, there were large differences between products in dissolution lag time in mHanks buffer and bicarbonate buffers. All formulations showed longer dissolution lag times at lower concentrations of bicarbonate or phosphate buffers. The dissolution rank order of each formulation differed between mHanks buffer and bicarbonate buffers. A rabeprazole formulation coated with a methacrylic acid copolymer showed the shortest lag time in the high concentration bicarbonate buffer, suggesting varied responses depending on the coating layer and buffer components. Use of multiple dissolution media during in vitro testing, including high concentration bicarbonate buffer, would contribute to the efficient design of enteric-coated drug formulations. © 2016 Royal Pharmaceutical Society, Journal of Pharmacy and Pharmacology.

Study on high breakdown voltage GaN-based vertical field effect transistor with interfacial charge engineering for power applications

NASA Astrophysics Data System (ADS)

Du, Jiangfeng; Liu, Dong; Liu, Yong; Bai, Zhiyuan; Jiang, Zhiguang; Liu, Yang; Yu, Qi

2017-11-01

A high voltage GaN-based vertical field effect transistor with interfacial charge engineering (GaN ICE-VFET) is proposed and its breakdown mechanism is presented. This vertical FET features oxide trenches which show a fixed negative charge at the oxide/GaN interface. In the off-state, firstly, the trench oxide layer acts as a field plate; secondly, the n-GaN buffer layer is inverted along the oxide/GaN interface and thus a vertical hole layer is formed, which acts as a virtual p-pillar and laterally depletes the n-buffer pillar. Both of them modulate electric field distribution in the device and significantly increase the breakdown voltage (BV). Compared with a conventional GaN vertical FET, the BV of GaN ICE-VFET is increased from 1148 V to 4153 V with the same buffer thickness of 20 μm. Furthermore, the proposed device achieves a great improvement in the tradeoff between BV and on-resistance; and its figure of merit even exceeds the GaN one-dimensional limit.

Epitaxial integration of CoFe2O4 thin films on Si (001) surfaces using TiN buffer layers

NASA Astrophysics Data System (ADS)

Prieto, Pilar; Marco, José F.; Prieto, José E.; Ruiz-Gomez, Sandra; Perez, Lucas; del Real, Rafael P.; Vázquez, Manuel; de la Figuera, Juan

2018-04-01

Epitaxial cobalt ferrite thin films with strong in-plane magnetic anisotropy have been grown on Si (001) substrates using a TiN buffer layer. The epitaxial films have been grown by ion beam sputtering using either metallic, CoFe2, or ceramic, CoFe2O4, targets. X-ray diffraction (XRD) and Rutherford spectrometry (RBS) in random and channeling configuration have been used to determine the epitaxial relationship CoFe2O4 [100]/TiN [100]/Si [100]. Mössbauer spectroscopy, in combination with XRD and RBS, has been used to determine the composition and structure of the cobalt ferrite thin films. The TiN buffer layer induces a compressive strain in the cobalt ferrite thin films giving rise to an in-plane magnetic anisotropy. The degree of in-plane anisotropy depends on the lattice mismatch between CoFe2O4 and TiN, which is larger for CoFe2O4 thin films grown on the reactive sputtering process with ceramic targets.

Growth of High-Quality GaAs on Ge by Controlling the Thickness and Growth Temperature of Buffer Layer

NASA Astrophysics Data System (ADS)

Zhou, Xu-Liang; Pan, Jiao-Qing; Yu, Hong-Yan; Li, Shi-Yan; Wang, Bao-Jun; Bian, Jing; Wang, Wei

2014-12-01

High-quality GaAs thin films grown on miscut Ge substrates are crucial for GaAs-based devices on silicon. We investigate the effect of different thicknesses and temperatures of GaAs buffer layers on the crystal quality and surface morphology of GaAs on Ge by metal-organic chemical vapor deposition. Through high resolution x-ray diffraction measurements, it is demonstrated that the full width at half maximum for the GaAs epilayer (Ge substrate) peak could achieve 19.3 (11.0) arcsec. The value of etch pit density could be 4×104 cm-2. At the same time, GaAs surfaces with no pyramid-shaped pits are obtained when the buffer layer growth temperature is lower than 360°C, due to effective inhibition of initial nucleation at terraces of the Ge surface. In addition, it is shown that large island formation at the initial stage of epitaxial growth is a significant factor for the final rough surface and that this initial stage should be carefully controlled when a device quality GaAs surface is desired.

Epitaxial growth and dielectric properties of Pb0.4Sr0.6TiO3 thin films on (00l)-oriented metallic Li0.3Ni0.7O2 coated MgO substrates

NASA Astrophysics Data System (ADS)

Li, X. T.; Du, P. Y.; Mak, C. L.; Wong, K. H.

2007-06-01

Highly (00l)-oriented Li0.3Ni0.7O2 thin films have been fabricated on (001) MgO substrates by pulsed laser deposition. The Pb0.4Sr0.6TiO3 (PST40) thin film deposited subsequently also shows a significant (00l)-oriented texture. Both the PST40 and Li0.3Ni0.7O2 have good epitaxial behavior. The epitaxial growth of the PST40 thin film is more perfect with the Li0.3Ni0.7O2 buffer layer due to the less distortion in the film. The dielectric tunability of the PST40 thin film with Li0.3Ni0.7O2 buffer layer therefore reaches 70%, which is 75% higher than that without Li0.3Ni0.7O2 buffer layer, and the dielectric loss of the PST40 thin film is 0.06.

PZT Films Fabricated by Metal Organic Decomposition Method

NASA Astrophysics Data System (ADS)

Sobolev, Vladimir; Ishchuk, Valeriy

2014-03-01

High quality lead zirconate titanate films have been fabricated on different substrates by metal organic decomposition method and their ferroelectric properties have been investigated. Main attention was paid to studies of the influence of the buffer layer with conditional composition Pb1.3(Zr0.5Ti0.5) O3 on the properties of Pb(Zr0.5Ti0.5) O3 films fabricated on the polycrystalline titanium and platinum substrates. It is found that in the films on the Pt substrate (with or without the buffer layer) the dependencies of the remanent polarization and the coercivity field on the number of switching cycles do not manifest fatigue up to 109 cycles. The remanent polarization dependencies for films on the Ti substrate with the buffer layer containing an excess of PbO demonstrate an fundamentally new feature that consists of a remanent polarization increase after 108 switching cycles. The increase of remanent polarization is about 50% when the number of cycles approaches 1010, while the increase of the coercivity field is small. A monotonic increase of dielectric losses has been observed in all cases.

Quantitative theory of electroosmotic flow in fused-silica capillaries using an extended site-dissociation--site-binding model.

PubMed

Zhou, Marilyn X; Foley, Joe P

2006-03-15

To optimize separations in capillary electrophoresis, it is important to control the electroosmotic mobility of the running buffer and the factors that affect it. Through the application of a site-dissociation-site-binding model, we demonstrated that the electroosmotic mobility could be controlled qualitatively and quantitatively by the parameters related to the physical and chemical properties of the running buffer: pH, cation valence, ionic strength, viscosity, activity, and dissociation constant. Our study illustrated that the logarithm of the number of apparent silanol sites on a fused-silica surface has a linear relationship with the pH of a buffer solution. The extension of the chemical kinetics approach allowed us to obtain the thickness of the electrical double layer when multivalent inorganic cations are present with monovalent cations in a buffer solution, and we found that the thickness of the electrical double layer does not depend on the charge of anions. The general equation to predict the electroosmotic mobility suggested here also indicates the increase of electroosmotic mobility with temperature. The general equation was experimentally verified by three buffer scenarios: (i) buffers containing only monovalent cations; (ii) buffers containing multivalent inorganic cations; and (iii) buffers containing cations and neutral additives. The general equation can explain the experimental observations of (i) a maximum electroosmotic mobility for the first scenario as the pH was varied at constant ionic strength and (ii) the inversion and maximum value of the electroosmotic mobility for the second scenario when the concentration of divalent cations was varied at constant pH. A good agreement between theory and experiment was obtained for each scenario.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schulte, Kevin L.; France, Ryan M.; McMahon, William E.

In this work we develop control over dislocation glide dynamics in Ga xIn 1-xP compositionally graded buffer layers (CGBs) through control of CuPt ordering on the group-III sublattice. The ordered structure is metastable in the bulk, so any glissile dislocation that disrupts the ordered pattern will release stored energy, and experience an increased glide force. Here we show how this connection between atomic ordering and dislocation glide force can be exploited to control the threading dislocation density (TDD) in Ga xIn 1-xP CGBs. When ordered Ga xIn 1-xP is graded from the GaAs lattice constant to InP, the order parametermore » ..eta.. decreases as x decreases, and dislocation glide switches from one set of glide planes to the other. This glide plane switch (GPS) is accompanied by the nucleation of dislocations on the new glide plane, which typically leads to increased TDD. We develop control of the GPS position within a Ga xIn 1-xP CGB through manipulation of deposition temperature, surfactant concentration, and strain-grading rate. We demonstrate a two-stage Ga xIn 1-xP CGB from GaAs to InP with sufficiently low TDD for high performance devices, such as the 4-junction inverted metamorphic multi-junction solar cell, achieved through careful control the GPS position. Here, experimental results are analyzed within the context of a model that considers the force balance on dislocations on the two competing glide planes as a function of the degree of ordering.« less

An AlGaN/GaN high-electron-mobility transistor with an AlN sub-buffer layer

NASA Astrophysics Data System (ADS)

Shealy, J. R.; Kaper, V.; Tilak, V.; Prunty, T.; Smart, J. A.; Green, B.; Eastman, L. F.

2002-04-01

The AlGaN/GaN high-electron-mobility transistor requires a thermally conducting, semi-insulating substrate to achieve the best possible microwave performance. The semi-insulating SiC substrate is currently the best choice for this device technology; however, fringing fields which penetrate the GaN buffer layer at pinch-off introduce significant substrate conduction at modest drain bias if channel electrons are not well confined to the nitride structure. The addition of an insulating AlN sub-buffer on the semi-insulating SiC substrate suppresses this parasitic conduction, which results in dramatic improvements in the AlGaN/GaN transistor performance. A pronounced reduction in both the gate-lag and the gate-leakage current are observed for structures with the AlN sub-buffer layer. These structures operate up to 50 V drain bias under drive, corresponding to a peak voltage of 80 V, for a 0.30 µm gate length device. The devices have achieved high-efficiency operation at 10 GHz (>70% power-added efficiency in class AB mode at 15 V drain bias) and the highest output power density observed thus far (11.2 W mm-1). Large-periphery devices (1.5 mm gate width) deliver 10 W (continuous wave) of maximum saturated output power at 10 GHz. The growth, processing, and performance of these devices are briefly reviewed.

Growth of crack-free GaN films on Si(111) substrate by using Al-rich AlN buffer layer

NASA Astrophysics Data System (ADS)

Lu, Yuan; Cong, Guangwei; Liu, Xianglin; Lu, Da-Cheng; Zhu, Qinsheng; Wang, Xiaohui; Wu, Jiejun; Wang, Zhanguo

2004-11-01

GaN epilayers were grown on Si(111) substrate by metalorganic chemical vapor deposition. By using the Al-rich AlN buffer which contains Al beyond stoichiometry, crack-free GaN epilayers with 1 μm thickness were obtained. Through x-ray diffraction (XRD) and secondary ion mass spectroscopy analyses, it was found that a lot of Al atoms have diffused into the under part of the GaN epilayer from the Al-rich AlN buffer, which results in the formation of an AlxGa1-xN layer at least with 300 nm thickness in the 1 μm thick GaN epilayer. The Al fraction x was estimated by XRD to be about 2.5%. X-ray photoelectron spectroscopy depth analysis was also applied to investigate the stoichiometry in the Al-rich buffer before GaN growth. It is suggested that the underlayer AlxGa1-xN originated from Al diffusion probably provides a compressive stress to the upper part of the GaN epilayer, which counterbalances a part of tensile stress in the GaN epilayer during cooling down and consequently reduces the cracks of the film effectively. The method using the Al diffusion effect to form a thick AlGaN layer is really feasible to achieve the crack-free GaN films and obtain a high crystal quality simultaneously.

Architecture for coated conductors

DOEpatents

Foltyn, Stephen R.; Arendt, Paul N.; Wang, Haiyan; Stan, Liliana

2010-06-01

Articles are provided including a base substrate having a layer of an oriented cubic oxide material with a rock-salt-like structure layer thereon, and, a layer of epitaxial titanium nitride upon the layer of an oriented cubic oxide material having a rock-salt-like structure. Such articles can further include thin films of high temperature superconductive oxides such as YBCO upon the layer of epitaxial titanium nitride or upon a intermediate buffer layer upon the layer of epitaxial titanium nitride.

Biaxially textured composite substrates

DOEpatents

Groves, James R.; Foltyn, Stephen R.; Arendt, Paul N.

2005-04-26

An article including a substrate, a layer of a metal phosphate material such as an aluminum phosphate material upon the surface of the substrate, and a layer of an oriented cubic oxide material having a rock-salt-like structure upon the metal phosphate material layer is provided together with additional layers such as a HTS top-layer of YBCO directly upon a layer of a buffer material such as a SrTi.sub.x Ru.sub.1-x O.sub.3 layer.

Co-solvent enhanced zinc oxysulfide buffer layers in Kesterite copper zinc tin selenide solar cells.

PubMed

Steirer, K Xerxes; Garris, Rebekah L; Li, Jian V; Dzara, Michael J; Ndione, Paul F; Ramanathan, Kannan; Repins, Ingrid; Teeter, Glenn; Perkins, Craig L

2015-06-21

A co-solvent, dimethylsulfoxide (DMSO), is added to the aqueous chemical "bath" deposition (CBD) process used to grow ZnOS buffer layers for thin film Cu2ZnSnSe4 (CZTSe) solar cells. Device performance improves markedly as fill factors increase from 0.17 to 0.51 upon the co-solvent addition. X-ray photoelectron spectroscopy (XPS) analyses are presented for quasi-in situ CZTSe/CBD-ZnOS interfaces prepared under an inert atmosphere and yield valence band offsets equal to -1.0 eV for both ZnOS preparations. When combined with optical band gap data, conduction band offsets exceed 1 eV for the water and the water/DMSO solutions. XPS measurements show increased downward band bending in the CZTSe absorber layer when the ZnOS buffer layer is deposited from water only. Admittance spectroscopy data shows that the ZnOS deposited from water increases the built-in potential (Vbi) yet these solar cells perform poorly compared to those made with DMSO added. The band energy offsets imply an alternate form of transport through this junction. Possible mechanisms are discussed, which circumvent the otherwise large conduction band spike between CZTSe and ZnOS, and improve functionality with the low-band gap absorber, CZTSe (Eg = 0.96 eV).

Growth and characterization of InSb on (1 0 0) Si for mid-infrared application

NASA Astrophysics Data System (ADS)

Jia, Bo Wen; Tan, Kian Hua; Loke, Wan Khai; Wicaksono, Satrio; Yoon, Soon Fatt

2018-05-01

Monolithic integration of InSb on (1 0 0) Si is a practical approach to realizing on-chip mid-infrared photonic devices. An InSb layer was grown on a (1 0 0) Si substrate using an AlSb/GaSb buffer containing InSb quantum dots (QDs). The growth process for the buffer involved the growth of GaSb on Si using an interfacial misfit array, followed by InSb QDs on AlSb to decrease the density of microtwins. InSb layers were separately grown on AlSb and GaSb surfaces to compare the effect of different interfacial misfit arrays. The samples were characterized using transmission electron microscopy and X-ray diffraction to determine the structural properties of the buffer and InSb layers. The InSb on the AlSb sample exhibited higher crystal quality than the InSb on GaSb sample due to a more favorable arrangement of interfacial misfit dislocations. Hall measurements of unintentionally doped InSb layers demonstrated a higher carrier mobility in the InSb on the AlSb sample than in InSb on GaSb. Growing InSb on AlSb also improved the photoresponsivity of InSb as a photoconductor on Si.

Improved Epitaxy and Surface Morphology in YBa2Cu3Oy Thin Films Grown on Double Buffered Si Wafers

NASA Astrophysics Data System (ADS)

Gao, J.; Kang, L.; Wong, H. Y.; Cheung, Y. L.; Yang, J.

Highly epitaxial thin films of YBCO have been obtained on silicon wafers using a Eu2CuO4/YSZ (yttrium-stabilized ZrO2) double buffer. Our results showed that application of such a double buffer can significantly enhance the epitaxy of grown YBCO. It also leads to an excellent surface morphology. The average surface roughness was found less than 5 nm in a large range. The results of X-ray small angle reflection and positron spectroscpy demonstrate a very clear and flat interface between YBCO and buffer layers. The Eu2CuO4/YSZ double buffer could be promising for coating high-TC superconducting films on various reactive substrates.

Preliminary report on the geology and deposits of monazite, thorite and niobium-bearing rutile of the Mineral Hill district, Lemhi County, Idaho

USGS Publications Warehouse

Kaiser, Edward Peck

1956-01-01

Deposits of minerals containing niobium (columbium), thorium, and rare earths occur in the Mineral Hill district, 30 miles northwest of Salmon, Lemhi County, Idaho. Monazite, thorite, allanite, and niobium-bearing rutile form deposits in metamorphic limestone layers less than 8 feet thick. The known deposits are small, irregular, and typically located in or near small folds. Minor faults are common. Monazite generally is coarsely crystalline and contains less than one percent thorium. Rutile forms massive lumps up to 3 inches across; it contains between 5 and 10 percent niobium. Rutile occurs in the northwestern half of the district, thorite in the central and southeastern parts. Monazite occurs in all deposits. Allanite is locally abundant and contains several percent thorium. Magnetite and ilmenite are also locally abundant. A major thrust fault trending northwest across the map-area separates moderately folded quartzite and phyllitic rocks of Belt age, on the northeast, from more intensely metamorphosed and folded rocks on the southwest. The more metamorphosed rocks include amphibolite, porphyroblastic feldspar gneiss, quartzite, and limestone, all probably of sedimentary origin, and probably also of Belt (late Precambrian) age. The only rocks of definite igneous origin are rhyolite dikes of probable Tertiary age. The more metamorphosed rocks were formed by metasomatic metamorphism acting on clastic sediments, probably of Belt age, although they may be older than Belt. Metamorphism doubtless was part of the episode of emplacement of the Idaho batholith, but the history of that episode is not well understood. The rare-element deposits show no evidence of fracture-controlled hydrothermal introduction, such as special fracture systems, veining, and gangue material. They may, however, be of hydrothermal type. More likely they are metamorphic segregations or secretions, deposited in favorable stratigraphic and structural positions during regional metamorphism.

Effect of oxide insertion layer on resistance switching properties of copper phthalocyanine

NASA Astrophysics Data System (ADS)

Joshi, Nikhil G.; Pandya, Nirav C.; Joshi, U. S.

2013-02-01

Organic memory device showing resistance switching properties is a next-generation of the electrical memory unit. We have investigated the bistable resistance switching in current-voltage (I-V) characteristics of organic diode based on copper phthalocyanine (CuPc) film sandwiched between aluminum (Al) electrodes. Pronounced hysteresis in the I-V curves revealed a resistance switching with on-off ratio of the order of 85%. In order to control the charge injection in the CuPc, nanoscale indium oxide buffer layer was inserted to form Al/CuPc/In2O3/Al device. Analysis of I-V measurements revealed space charge limited switching conduction at the Al/CuPc interface. The traps in the organic layer and charge blocking by oxide insertion layer have been used to explain the absence of resistance switching in the oxide buffer layered memory device cell. Present study offer potential applications for CuPc organic semiconductor in low power non volatile resistive switching memory and logic circuits.

Effects of coating layer and release medium on release profile from coated capsules with Eudragit FS 30D: an in vitro and in vivo study.

PubMed

Moghimipour, Eskandar; Rezaei, Mohsen; Kouchak, Maryam; Fatahiasl, Jafar; Angali, Kambiz Ahmadi; Ramezani, Zahra; Amini, Mohsen; Dorkoosh, Farid Abedin; Handali, Somayeh

2018-05-01

The aim of the present research was to evaluate the impact of coating layers on release profile from enteric coated dosage forms. Capsules were coated with Eudragit FS 30D using dipping method. The drug profile was evaluated in both phosphate buffer and Hank's solutions. Utilization X-ray imaging, gastrointestinal transmission of enteric coated capsules was traced in rats. According to the results, no release of the drug was found at pH 1.2, and the extent of release drug in pH 6.8 medium was decreased by adding the coating layers. The results indicated single-layer coated capsules in phosphate buffer were significantly higher than that in Hank's solution. However, no significant difference was observed from capsules with three coating layers in two different dissolution media. X-ray imaging showed that enteric coated capsules were intact in the stomach and in the small intestine, while disintegrated in the colon.

Self-Aligned ALD AlOx T-gate Insulator for Gate Leakage Current Suppression in SiNx-Passivated AlGaN/GaN HEMTs

DTIC Science & Technology

2010-01-01

Heterostructure epitaxial material growth was performed by RF plasma-assisted molecular - beam epitaxy (MBE) on a 2-in. semi- insulating 4H SiC wafer. From... beam epitaxy of beryllium-doped GaN buffer layers for AlGaN/GaN HEMTs . J Cryst Growth 2003;251:481–6. [25] Storm DF, Katzer DS, Binari SC, Glaser ER...Shanabrook BV, Roussos JA. Reduction of buffer layer conduction near plasma-assisted molecular - beam epitaxy grown GaN/AlN interfaces by beryllium

Mantle Lithosphere Rheology, Vertical Tectonics, and the Exhumation of (U)HP Rocks

NASA Astrophysics Data System (ADS)

Bodur, Ömer F.; Göǧüş, Oǧuz H.; Pysklywec, Russell N.; Okay, Aral I.

2018-02-01

Numerical modeling results indicate that mantle lithosphere rheology can influence the pressure-temperature-time (P-T-t) trajectories of continental crust subducted and exhumed during the onset of continental collision. Exhumation of ultrahigh-pressure ( 35 kbar)/high-temperature ( 750°C) metamorphic rocks is more prevalent in models with stronger continental mantle lithosphere (e.g., dry), whereas high-pressure ( 9-22 kbar)/low-temperature (350°C-630°C) metamorphic rocks occur in models with weaker rheology (e.g., hydrated) for the same layer. In the latter case, the buried crustal rocks can remain encased in ablatively subducting mantle lithosphere, reach only moderate temperatures, and exhume by dripping/detachment of the lithospheric root. In this transition from subduction to a dripping style of "vertical tectonics," burial and exhumation of crustal rocks are driven without imposed far-field plate convergence. The model results are compared against thermobarometric P-T estimates from major (ultra)high-pressure metamorphic terranes. We propose that the exhumation of high-pressure/low-temperature metamorphic rocks in Tavşanlı and Afyon zones in western Anatolia may be caused by viscous dripping of mantle lithosphere suggesting a weaker continental mantle lithosphere, whereas (ultra)high-pressure exhumation (e.g., Dabie Shan-eastern China and Dora Maira-western Alps) may be associated with plate-like subduction. In the latter case, the slab is much stronger and deformation is localized to the subduction interface along which rocks are buried to >100 km depth before they are exhumed to the near surface.

Biaxially textured articles formed by plastic deformation

DOEpatents

Goyal, Amit

2001-01-01

A method of preparing a biaxially textured article comprises the steps of providing a metal preform, coating or laminating the preform with a metal layer, deforming the layer to a sufficient degree, and rapidly recrystallizing the layer to produce a biaxial texture. A superconducting epitaxial layer may then be deposited on the biaxial texture. In some embodiments the article further comprises buffer layers, electromagnetic devices or electro-optical devices.

Method for making biaxially textured articles by plastic deformation

DOEpatents

Goyal, Amit

2002-01-01

A method of preparing a biaxially textured article comprises the steps of providing a metal preform, coating or laminating the preform with a metal layer, deforming the layer to a sufficient degree, and rapidly recrystallizing the layer to produce a biaxial texture. A superconducting epitaxial layer may then be deposited on the biaxial texture. In some embodiments the article further comprises buffer layers, electromagnetic devices or electro-optical devices.

Accelerating the dissolution of enteric coatings in the upper small intestine: evolution of a novel pH 5.6 bicarbonate buffer system to assess drug release.

PubMed

Varum, Felipe J O; Merchant, Hamid A; Goyanes, Alvaro; Assi, Pardis; Zboranová, Veronika; Basit, Abdul W

2014-07-01

Despite rapid dissolution in compendial phosphate buffers, gastro resistant (enteric coated) products can take up to 2 h to disintegrate in the human small intestine, which clearly highlights the inadequacy of the in vitro test method to predict in vivo behaviour of these formulations. The aim of this study was to establish the utility of a novel pH 5.6 bicarbonate buffer, stabilized by an Auto pH™ System, as a better surrogate of the conditions of the proximal small intestine to investigate the dissolution behaviour of standard and accelerated release enteric double coating formulations. Prednisolone tablets were coated with 3 or 5 mg/cm(2) of partially neutralized EUDRAGIT(®) L 30 D-55, HP-55 or HPMC adjusted to pH 6 or 8. An outer layer of EUDRAGIT(®) L 30 D-55 was applied at 5mg/cm(2). For comparison purposes, a standard single layer of EUDRAGIT(®) L 30 D-55 was applied to the tablets. Dissolution was carried out using USP II apparatus in 0.1 M HCl for 2 h, followed by pH 5.6 bicarbonate buffer. EUDRAGIT(®) L 30 D-55 single-coated tablets showed a slow drug release with a lag time of 75 min in buffer, whereas release from the EUDRAGIT(®) L 30 D-55 double-coated tablets was accelerated. These in vitro lag times closely match the in vivo disintegration times for these coated tablets reported previously. Drug release was further accelerated from modified double coatings, particularly in the case of coatings with a thinner inner layer of HP-55 or HPMC (pH 8 and KH2PO4). This study confirms that the pH 5.6 bicarbonate buffer system offers significant advantages during the development of dosage forms designed to release the drug in the upper small intestine. Copyright © 2014. Published by Elsevier B.V.

Carbon Dioxide Cycling And The Climate of Ancient Earth

NASA Technical Reports Server (NTRS)

Zahnle, Kevin; Sleep, Norman H.; DeVincenzi, Donald (Technical Monitor)

2001-01-01

The continental cycle of silicate weathering and metamorphism dynamically buffers atmospheric CO2 and climate. Feedback is provided by the strong temperature dependence of silicate weathering. Here we argue that hydrothermal alteration of oceanic basalts also dynamically buffers CO2. The oceanic cycle links with the mantle via subduction and the midocean ridges. Feedback is provided by the dependence of carbonatization on dissolved carbonates in seawater. Unlike the continental cycle, the oceanic cycle has no thermostat. Currently the continental cycle is more important, but earlier in Earth's history, especially if heat flow were higher than it is now, more vigorous plate tectonics would have made the oceanic cycle dominant. We find that CO2 greenhouses thick enough to defeat the faint early sun are implausible and that, if no other greenhouse gases are invoked, very cold climates are expected for much of the Proterozoic and the Archean. We echo current fashion and favor biogenic methane as the chief supplement to CO2. Fast weathering and probable subduction of abundant impact ejecta would have reduced CO2 levels still further in the Hadean. Despite its name, the Hadean would have been the coldest era in the history of the Earth.

Carbon Dioxide Cycling and the Climate of Ancient Earth

NASA Technical Reports Server (NTRS)

Zahnle, Kevin; Sleep, Norman H.

2001-01-01

The continental cycle of silicate weathering and metamorphism dynamically buffers atmospheric CO2 and climate. Feedback is provided by the strong temperature dependence of silicate weathering. Here we argue that hydrothermal alteration of oceanic basalts also dynamically buffers CO2. The oceanic cycle links with the mantle via subduction and the midocean ridges. Feedback is provided by the dependence of carbonatization on dissolved carbonates in seawater. Unlike the continental cycle, the oceanic cycle has no thermostat. Currently the continental cycle is more important, but earlier in Earth's history, especially if heat flow were higher than it is now, more vigorous plate tectonics would have made the oceanic cycle dominant. We find that CO2 greenhouses thick enough to defeat the faint early Sun are implausible and that, if no other greenhouse gases are invoked, very cold climates are expected for much of the Proterozoic and the Archean. We echo current fashion and favor biogenic methane as the chief supplement to CO2. Fast weathering and probable subduction of abundant impact ejecta would have reduced CO2 levels still further in the Hadean. Despite its name, the Hadean would have been the coldest era in the history of the Earth.

An experimental study of the wall-pressure fluctuations beneath low Reynolds number turbulent boundary layers.

PubMed

Van Blitterswyk, Jared; Rocha, Joana

2017-02-01

A more complete understanding of the physical relationships, between wall-pressure and turbulence, is required for modeling flow-induced noise and developing noise reduction strategies. In this study, the wall-pressure fluctuations, induced by low Reynolds number turbulent boundary layers, are experimentally studied using a high-resolution microphone array. Statistical characteristics obtained using traditional cross-correlation and cross-spectra analyses are complimented with wall-pressure-velocity cross-spectra and wavelet cross-correlations. Wall-pressure-velocity correlations revealed that turbulent activity in the buffer layer contributes at least 40% of the energy to the wall-pressure spectrum at all measured frequencies. As Reynolds number increases, the low-frequency energy shifts from the buffer layer to the logarithmic layer, as expected for regions of uniform streamwise momentum formed by hairpin packets. Conditional cross-spectra suggests that the majority of broadband wall-pressure energy is concentrated within the packets, with the pressure signatures of individual hairpin vortices estimated to decay on average within traveling ten displacement thicknesses, and the packet signature is retained for up to seven boundary layer thicknesses on average.

Possibility of material cost reduction toward development of low-cost second-generation superconducting wires

NASA Astrophysics Data System (ADS)

Ichinose, Ataru; Horii, Shigeru; Doi, Toshiya

2017-10-01

Two approaches to reducing the material cost of second-generation superconducting wires are proposed in this paper: (1) instead of the electrical stabilizing layers of silver and copper presently used on the superconducting layer, a Nb-doped SrTiO3 conductive buffer layer and cube-textured Cu are proposed as an advanced architecture, and (2) the use of an electromagnetic (EM) steel tape as a metal substrate of coated conductors in a conventional architecture. In structures fabricated without using electrical stabilizing layers on the superconducting layer, the critical current density achieved at 77 K in a self-field was approximately 2.6 MA/cm2. On the other hand, in the case of using EM steel tapes, although the critical current density was far from practical at the current stage, the biaxial alignment of YBa2Cu3O y (YBCO) and buffer layers was realized without oxidation on the metal surface. In this study, the possibility of material cost reduction has been strongly indicated toward the development of low-cost second-generation superconducting wires in the near future.

EUVL mask patterning with blanks from commercial suppliers

NASA Astrophysics Data System (ADS)

Yan, Pei-Yang; Zhang, Guojing; Nagpal, Rajesh; Shu, Emily Y.; Li, Chaoyang; Qu, Ping; Chen, Frederick T.

2004-12-01

Extreme Ultraviolet Lithography (EUVL) reflective mask blank development includes low thermal expansion material fabrication, mask substrate finishing, reflective multi-layer (ML) and capping layer deposition, buffer (optional)/absorber stack deposition, EUV specific metrology, and ML defect inspection. In the past, we have obtained blanks deposited with various layer stacks from several vendors. Some of them are not commercial suppliers. As a result, the blank and patterned mask qualities are difficult to maintain and improve. In this paper we will present the evaluation results of the EUVL mask pattering processes with the complete EUVL mask blanks supplied by the commercial blank supplier. The EUVL mask blanks used in this study consist of either quartz or ULE substrates which is a type of low thermal expansion material (LTEM), 40 pairs of molybdenum/silicon (Mo/Si) ML layer, thin ruthenium (Ru) capping layer, tantalum boron nitride (TaBN) absorber, and chrome (Cr) backside coating. No buffer layer is used. Our study includes the EUVL mask blank characterization, patterned EUVL mask characterization, and the final patterned EUVL mask flatness evaluation.

Improved Optical Transmittance and Crystal Characteristics of ZnS:TbOF Thin Film on Bi4Ti3O12/Indium Tin Oxide/Glass Substrate by Using a SiO2 Buffer Layer

NASA Astrophysics Data System (ADS)

Chia, Wei‑Kuo; Yokoyama, Meiso; Yang, Cheng‑Fu; Chiang, Wang‑Ta; Chen, Ying‑Chung

2006-07-01

Bi4Ti3O12 thin films are deposited on indium tin oxide (ITO)/glass substrates using RF magnetron sputtering technology and are annealed at 675 °C in a rapid thermal annealing furnace in an oxygen atmosphere. The resulting films have high optical transmittances and good crystalline characteristics. ZnS:TbOF films are then deposited on the Bi4Ti3O12 films, causing the originally highly transparent specimens to blacken and to resemble a glass surface coated with carbon powder. The optical transmittance of the specimen is less than 15% under the visible wavelength range, and neither a crystalline phase nor a distinct ZnS grain structure is evident in X-ray diffractometer (XRD) and scanning electronic microscope (SEM). Secondary ion mass spectrometer (SIMS) analysis reveals the occurrence of interdiffusion between the ZnS and Bi4Ti3O12 layers. This suggests that one or more unknown chemical reactions take place among the elements Bi, S, and O at the interface during the deposition of ZnS:TbOF film on a Bi4Ti3O12/ITO/glass substrate. These reactions cause the visible transmittance of the specimens to deteriorate dramatically. To prevent interdiffusion, a silicon dioxide (SiO2) buffer layer 100 nm thick was grown on the Bi4Ti3O12/ITO/glass substrate using plasma-enhanced chemical vapor deposition (PECVD), then the ZnS:TbOF film was grown on the SiO2 buffer layer. The transmittance of the resulting specimen is enhanced approximately 8-fold in the visible region. XRD patterns reveal the ZnS(111)-oriented phase is dominant. Furthermore, dense, crack-free ZnS:TbOF grains are observed by SEM. The results imply that the SiO2 buffer layer sandwiched between the ZnS:TbOF and Bi4Ti3O2 layers effectively separates the two layers. Therefore, interdiffusion and chemical reactions are prevented at the interface of the two layers, and the crystalline characteristics of the ZnS:TbOF layer and the optical transmittance of the specimen are improved as a result. Finally, the dielectric constant of the stacked structure is lower than that of the single layer structure without SiO2, but the dielectric breakdown strength is enhanced.

High rate buffer layer for IBAD MgO coated conductors

DOEpatents

Foltyn, Stephen R [Los Alamos, NM; Jia, Quanxi [Los Alamos, NM; Arendt, Paul N [Los Alamos, NM

2007-08-21

Articles are provided including a base substrate having a layer of an oriented material thereon, and, a layer of hafnium oxide upon the layer of an oriented material. The layer of hafnium oxide can further include a secondary oxide such as cerium oxide, yttrium oxide, lanthanum oxide, scandium oxide, calcium oxide and magnesium oxide. Such articles can further include thin films of high temperature superconductive oxides such as YBCO upon the layer of hafnium oxide or layer of hafnium oxide and secondary oxide.

Solid-solution Zn(O,S) thin films: Potential alternative buffer layer for Cu2ZnSnS4 solar cells

NASA Astrophysics Data System (ADS)

Jani, Margi; Raval, Dhyey; Chavda, Arvind; Mukhopadhyay, Indrajit; Ray, Abhijit

2018-05-01

This report investigates the alternative buffer material as Zn(O,S) for chalcogenide Cu2ZnSnS4 (CZTS) solar cell application. Using the band gap tailoring (band bowing) properties of Zn(O,S) system, performance of CZTS solar cell is explore in the present study. Reducing the band offsets with the hetero-junction partners plays a deterministic role in the performance of the device using Zn(O,S) as buffer layer. The experimental performance of the device with the CZTS/Zn(O,S) film developed by Spray pyrolysis method and analyze using J-V characterization in dark and illuminated configuration. Device with the best achievable performance shows Voc of 150 mV and Jsc of 0.47 mA/cm2 has been presented with the possibility of application in the energy harvesting.

Growth of magnesium diboride thin films on boron buffered Si and silicon-on-insulator substrates by hybrid physical chemical vapor deposition

NASA Astrophysics Data System (ADS)

Withanage, Wenura K.; Penmatsa, Sashank V.; Acharya, Narendra; Melbourne, Thomas; Cunnane, D.; Karasik, B. S.; Xi, X. X.

2018-07-01

We report on the growth of high quality MgB2 thin films on silicon and silicon-on-insulator substrates by hybrid physical chemical vapor deposition. A boron buffer layer was deposited on all sides of the Si substrate to prevent the reaction of Mg vapor and Si. Ar ion milling at a low angle of 1° was used to reduce the roughness of the boron buffer layer before the MgB2 growth. An Ar ion milling at low angle of 1° was also applied to the MgB2 surface to reduce its roughness. The resultant MgB2 films showed excellent superconducting properties and a smooth surface. The process produces thin MgB2 films suitable for waveguide-based superconducting hot electron bolometers and other MgB2-based electronic devices.

Microscopic analysis of irradiated AGR-1 coated particle fuel compacts

DOE Office of Scientific and Technical Information (OSTI.GOV)

Scott A. Ploger; Paul A. Demkowicz; John D. Hunn

The AGR-1 experiment involved irradiation of 72 TRISO-coated particle fuel compacts to a peak compact-average burnup of 19.5% FIMA with no in-pile failures observed out of 3 x 105 total particles. Irradiated AGR-1 fuel compacts have been cross-sectioned and analyzed with optical microscopy to characterize kernel, buffer, and coating behavior. Six compacts have been examined, spanning a range of irradiation conditions (burnup, fast fluence, and irradiation temperature) and including all four TRISO coating variations irradiated in the AGR-1 experiment. The cylindrical specimens were sectioned both transversely and longitudinally, then polished to expose from 36 to 79 individual particles near midplanemore » on each mount. The analysis focused primarily on kernel swelling and porosity, buffer densification and fracturing, buffer–IPyC debonding, and fractures in the IPyC and SiC layers. Characteristic morphologies have been identified, 981 particles have been classified, and spatial distributions of particle types have been mapped. No significant spatial patterns were discovered in these cross sections. However, some trends were found between morphological types and certain behavioral aspects. Buffer fractures were found in 23% of the particles, and these fractures often resulted in unconstrained kernel protrusion into the open cavities. Fractured buffers and buffers that stayed bonded to IPyC layers appear related to larger pore size in kernels. Buffer–IPyC interface integrity evidently factored into initiation of rare IPyC fractures. Fractures through part of the SiC layer were found in only four classified particles, all in conjunction with IPyC–SiC debonding. Compiled results suggest that the deliberate coating fabrication variations influenced the frequencies of IPyC fractures and IPyC–SiC debonds.« less

The influence of buffer system and biological fluids on the degradation of magnesium.

PubMed

Törne, Karin; Örnberg, Andreas; Weissenrieder, Jonas

2017-08-01

The influence of frequently used buffer system 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES) compared to CO 2 /HCO3- on the corrosion of magnesium is investigated. Samples were immersed in simulated body fluid (m-SBF) while monitored by electrochemical impedance spectroscopy (EIS) for up to 30 days. In CO 2 /HCO3- the initial corrosion rate was 0.11 mm yr -1 . An inner protective layer of magnesium oxide was formed within the first 30 min exposure and subsequently covered by an outer layer of apatite within 24 h . The corrosion mechanism thereafter is best described as passive pitting with a porosity of ∼10%. Using HEPES as buffer agent increased the corrosion rate to 3.37 mm yr -1 . Cross sectional microscopy show a porous outer corrosion layer allowing rapid diffusion of aggressive ions through the film. Here the EIS results are best described by an active pitting model with an inner layer 5 to 10 times less protective compared to the inner layer formed without HEPES. Further the suitability of human whole blood and plasma as in vitro models for Mg degradation was evaluated. Mg corrosion caused coagulation after 24 h in both biological fluids. The corrosion during the first 24 h is similar to the corrosion in m-SBF with HEPES. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 1490-1502, 2017. © 2016 Wiley Periodicals, Inc.

Electrodeposition of ZnO-doped films as window layer for Cd-free CIGS-based solar cells

NASA Astrophysics Data System (ADS)

Tsin, Fabien; Vénérosy, Amélie; Hildebrandt, Thibaud; Hariskos, Dimitrios; Naghavi, Negar; Lincot, Daniel; Rousset, Jean

2016-02-01

The Cu(In,Ga)Se2 (CIGS) thin film solar cell technology has made a steady progress within the last decade reaching efficiency up to 22.3% on laboratory scale, thus overpassing the highest efficiency for polycrystalline silicon solar cells. High efficiency CIGS modules employ a so-called buffer layer of cadmium sulfide CdS deposited by Chemical Bath Deposition (CBD), which presence and Cd-containing waste present some environmental concerns. A second potential bottleneck for CIGS technology is its window layer made of i-ZnO/ZnO:Al, which is deposited by sputtering requiring expensive vacuum equipment. A non-vacuum deposition of transparent conductive oxide (TCO) relying on simpler equipment with lower investment costs will be more economically attractive, and could increase competitiveness of CIGS-based modules with the mainstream silicon-based technologies. In the frame of Novazolar project, we have developed a low-cost aqueous solution photo assisted electrodeposition process of the ZnO-based window layer for high efficiency CIGS-based solar cells. The window layer deposition have been first optimized on classical CdS buffer layer leading to cells with efficiencies similar to those measured with the sputtered references on the same absorber (15%). The the optimized ZnO doped layer has been adapted to cadmium free devices where the CdS is replaced by chemical bath deposited zinc oxysulfide Zn(S,O) buffer layer. The effect of different growth parameters has been studied on CBD-Zn(S,O)-plated co-evaporated Cu(In,Ga)Se2 substrates provided by the Zentrum für Sonnenenergie-und Wasserstoff-Forschung (ZSW). This optimization of the electrodeposition of ZnO:Cl on CIGS/Zn(S,O) stacks led to record efficiency of 14%, while the reference cell with a sputtered (Zn,Mg)O/ZnO:Al window layer has an efficiency of 15.2%.

High-Quality GaN Epilayers Achieved by Facet-Controlled Epitaxial Lateral Overgrowth on Sputtered AlN/PSS Templates.

PubMed

He, Chenguang; Zhao, Wei; Zhang, Kang; He, Longfei; Wu, Hualong; Liu, Ningyang; Zhang, Shan; Liu, Xiaoyan; Chen, Zhitao

2017-12-13

It is widely believed that the lack of high-quality GaN wafers severely hinders the progress in GaN-based devices, especially for defect-sensitive devices. Here, low-cost AlN buffer layers were sputtered on cone-shaped patterned sapphire substrates (PSSs) to obtain high-quality GaN epilayers. Without any mask or regrowth, facet-controlled epitaxial lateral overgrowth was realized by metal-organic chemical vapor deposition. The uniform coating of the sputtered AlN buffer layer and the optimized multiple modulation guaranteed high growth selectivity and uniformity of the GaN epilayer. As a result, an extremely smooth surface was achieved with an average roughness of 0.17 nm over 3 × 3 μm 2 . It was found that the sputtered AlN buffer layer could significantly suppress dislocations on the cones. Moreover, the optimized three-dimensional growth process could effectively promote dislocation bending. Therefore, the threading dislocation density (TDD) of the GaN epilayer was reduced to 4.6 × 10 7 cm -2 , which is about an order of magnitude lower than the case of two-step GaN on the PSS. In addition, contamination and crack in the light-emitting diode fabricated on the obtained GaN were also effectively suppressed by using the sputtered AlN buffer layer. All of these advantages led to a high output power of 116 mW at 500 mA with an emission wavelength of 375 nm. This simple, yet effective growth technique is believed to have great application prospects in high-performance TDD-sensitive optoelectronic and electronic devices.

Electrochemical Behavior Assessment of As-Cast Mg-Y-RE-Zr Alloy in Phosphate Buffer Solutions (X Na3PO4 + Y Na2HPO4) Using Electrochemical Impedance Spectroscopy and Mott-Schottky Techniques

NASA Astrophysics Data System (ADS)

Fattah-alhosseini, Arash; Asgari, Hamed

2018-05-01

In the present study, electrochemical behavior of as-cast Mg-Y-RE-Zr alloy (RE: rare-earth alloying elements) was investigated using electrochemical tests in phosphate buffer solutions (X Na3PO4 + Y Na2HPO4). X-ray diffraction techniques and Scanning electron microscopy equipped with energy dispersive x-ray spectroscopy were used to investigate the microstructure and phases of the experimental alloy. Different electrochemical tests such as potentiodynamic polarization (PDP), electrochemical impedance spectroscopy (EIS) and Mott-Schottky (M-S) analysis were carried out in order to study the electrochemical behavior of the experimental alloy in phosphate buffer solutions. The PDP curves and EIS measurements indicated that the passive behavior of the as-cast Mg-Y-RE-Zr alloy in phosphate buffer solutions was weakened by an increase in the pH, which is related to formation of an imperfect and less protective passive layer on the alloy surface. The presence of the insoluble zirconium particles along with high number of intermetallic phases of RE elements mainly Mg24Y5 in the magnesium matrix can deteriorate the corrosion performance of the alloy by disrupting the protective passive layer that is formed at pH values over 11. These insoluble zirconium particles embedded in the matrix can detrimentally influence the passivation. The M-S analysis revealed that the formed passive layers on Mg-Y-RE-Zr alloy behaved as an n-type semiconductor. An increase in donor concentration accompanying solutions of higher alkalinity is thought to result in the formation of a less resistive passive layer.

Petrology and physical conditions of metamorphism of calcsilicate rocks from low- to high-grade transition area, Dharmapuri District, Tamil Nadu

NASA Technical Reports Server (NTRS)

Narayana, B. L.; Natarajan, R.; Govil, P. K.

1988-01-01

Calc-silicate rocks comprising quartz, plagioclase, diopside, sphene, scapolite, grossularite-andradite and wollastonite occur as lensoid enclaves within the greasy migmatitic and charnockitic gneisses of the Archaean amphibolite- to granulite-facies transition zone in Dharmapuri district, Tamil Nadu. The calc-silicate rocks are characterized by the absence of K-feldspar and primary calcite, presence of large modal quartz and plagioclase and formation of secondary garnet and zoisite rims around scapolite and wollastonite. The mineral distributions suggest compositional layering. The chemical composition and mineralogy of the calc-silicate rocks indicate that they were derived from impure silica-rich calcareous sediments whose composition is similar to that of pelite-limestone mixtures. From the mineral assemblages the temperature, pressure and fluid composition during metamorphism were estimated. The observed mineral reaction sequences require a range of X sub CO2 values demonstrating that an initially CO2-rich metamorphic fluid evolved with time towards considerably more H2O-rich compositions. These variations in fluid composition suggest that there were sources of water-rich fluids external to the calc-silicate rocks and that mixing of these fluids with those of calc-silicate rocks was important in controlling fluid composition in calc-silicate rocks and some adjacent rock types as well.

Bulk-heterojunction organic solar cells sandwiched by solution processed molybdenum oxide and titania nanosheet layers

NASA Astrophysics Data System (ADS)

Itoh, Eiji; Goto, Yoshinori; Fukuda, Katsutoshi

2014-02-01

The contributions of ultrathin titania nanosheet (TN) crystallites were studied in both an inverted bulk-heterojunction (BHJ) cell in an indium-tin oxide (ITO)/titania nanosheet (TN)/poly(3-hexylthiophene) (P3HT):phenyl-C61-butyric acid methylester (PCBM) active layer/MoOx/Ag multilayered photovoltaic device and a conventional BHJ cell in ITO/MoOx/P3HT:PCBM active layer/TN/Al multilayered photovoltaic device. The insertion of only one or two layers of poly(diallyldimethylammonium chloride) (PDDA) and TN multilayered film prepared by the layer-by-layer deposition technique effectively decreased the leakage current and increased the open circuit voltage (VOC), fill factor (FF), and power conversion efficiency (η). The conventional cell sandwiched between a solution-processed, partially crystallized molybdenum oxide hole-extracting buffer layer and a TN electron extracting buffer layer showed comparable cell performance to a device sandwiched between vacuum-deposited molybdenum oxide and TN layers, whereas the inverted cell with solution-processed molybdenum oxide showed a poorer performance probably owing to the increment in the leakage current across the film. The abnormal S-shaped curves observed in the inverted BHJ cell above VOC disappeared with the use of a polyfluorene-based cationic semiconducting polymer as a substitute for an insulating PDDA film, resulting in the improved cell performance.

Fission product release and survivability of UN-kernel LWR TRISO fuel

DOE Office of Scientific and Technical Information (OSTI.GOV)

T. M. Besmann; M. K. Ferber; H.-T. Lin

2014-05-01

A thermomechanical assessment of the LWR application of TRISO fuel with UN kernels was performed. Fission product release under operational and transient temperature conditions was determined by extrapolation from fission product recoil calculations and limited data from irradiated UN pellets. Both fission recoil and diffusive release were considered and internal particle pressures computed for both 650 and 800 um diameter kernels as a function of buffer layer thickness. These pressures were used in conjunction with a finite element program to compute the radial and tangential stresses generated within a TRISO particle undergoing burnup. Creep and swelling of the inner andmore » outer pyrolytic carbon layers were included in the analyses. A measure of reliability of the TRISO particle was obtained by computing the probability of survival of the SiC barrier layer and the maximum tensile stress generated in the pyrolytic carbon layers from internal pressure and thermomechanics of the layers. These reliability estimates were obtained as functions of the kernel diameter, buffer layer thickness, and pyrolytic carbon layer thickness. The value of the probability of survival at the end of irradiation was inversely proportional to the maximum pressure.« less

Photoluminescence of phosphorus atomic layer doped Ge grown on Si

NASA Astrophysics Data System (ADS)

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

2017-10-01

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

Sustained ophthalmic delivery of highly soluble drug using pH-triggered inner layer-embedded contact lens.

PubMed

Zhu, Qiang; Cheng, Hongbo; Huo, Yingnan; Mao, Shirui

2018-06-10

In the present work the feasibility of using inner layer-embedded contact lenses (CLs) to achieve sustained release of highly water soluble drug, betaxolol hydrochloride (BH) on the ocular surface was investigated. Blend film of cellulose acetate and Eudragit S100 was selected as the inner layer, while silicone hydrogel was used as outer layer to construct inner layer-embedded contact lenses. Influence of polymer ratio in the blend film on in vitro drug release behavior in phosphate buffered solution or simulated tear fluid was studied and drug-polymer interaction, erosion and swelling of the blend film were characterized to better understand drug-release mechanism. Storage stability of the inner layer-embedded contact lenses in phosphate buffer solution was also conducted, with ignorable drug loss and negligible change in drug release pattern within 30 days. In vivo pharmacokinetic study in rabbits showed sustained drug release for over 240 h in tear fluid, indicating prolonged drug precorneal residence time. In conclusion, cellulose acetate/Eudragit S100 inner layer-embedded contact lenses are quite promising as controlled-release carrier of highly water soluble drug for ophthalmic delivery. Copyright © 2018 Elsevier B.V. All rights reserved.

Iron silicide formation at different layers of (Fe/Si)3 multilayered structures determined by conversion electron Mössbauer spectroscopy

NASA Astrophysics Data System (ADS)

Badía-Romano, L.; Rubín, J.; Magén, C.; Bürgler, D. E.; Bartolomé, J.

2014-07-01

The morphology and the quantitative composition of the Fe-Si interface layer forming at each Fe layer of a (Fe/Si)3 multilayer have been determined by means of conversion electron Mössbauer spectroscopy (CEMS) and high-resolution transmission electron microscopy (HRTEM). For the CEMS measurements, each layer was selected by depositing the Mössbauer active 57Fe isotope with 95% enrichment. Samples with Fe layers of nominal thickness dFe = 2.6 nm and Si spacers of dSi = 1.5 nm were prepared by thermal evaporation onto a GaAs(001) substrate with an intermediate Ag(001) buffer layer. HRTEM images showed that Si layers grow amorphous and the epitaxial growth of the Fe is good only for the first deposited layer. The CEMS spectra show that at all Fe/Si and Si/Fe interfaces a paramagnetic c-Fe1-xSi phase is formed, which contains 16% of the nominal Fe deposited in the Fe layer. The bottom Fe layer, which is in contact with the Ag buffer, also contains α-Fe and an Fe1-xSix alloy that cannot be attributed to a single phase. In contrast, the other two layers only comprise an Fe1-xSix alloy with a Si concentration of ≃0.15, but no α-Fe.

Fabrication of 80-nm T-gate high indium In0.7Ga0.3As/In0.6Ga0.4As composite channels mHEMT on GaAs substrate with simple technological process

NASA Astrophysics Data System (ADS)

Xian, Ji; Xiaodong, Zhang; Weihua, Kang; Zhili, Zhang; Jiahui, Zhou; Wenjun, Xu; Qi, Li; Gongli, Xiao; Zhijun, Yin; Yong, Cai; Baoshun, Zhang; Haiou, Li

2016-02-01

An 80-nm gate length metamorphic high electron mobility transistor (mHEMT) on a GaAs substrate with high indium composite compound-channels In0.7Ga0.3 As/In0.6Ga0.4 As and an optimized grade buffer scheme is presented. High 2-DEG Hall mobility values of 10200 cm2/(V·s) and a sheet density of 3.5 × 1012 cm-2 at 300 K have been achieved. The device's T-shaped gate was made by utilizing a simple three layers electron beam resist, instead of employing a passivation layer for the T-share gate, which is beneficial to decreasing parasitic capacitance and parasitic resistance of the gate and simplifying the device manufacturing process. The ohmic contact resistance Rc is 0.2 ω·mm when using the same metal system with the gate (Pt/Ti/Pt/Au), which reduces the manufacturing cycle of the device. The mHEMT device demonstrates excellent DC and RF characteristics. The peak extrinsic transconductance of 1.1 S/mm and the maximum drain current density of 0.86 A/mm are obtained. The unity current gain cut-off frequency (fT) and the maximum oscillation frequency (fmax) are 246 and 301 GHz, respectively. Project supported by the Key Laboratory of Nano-Devices and Applications, Nano-Fabrication Facility of SINANO, Chinese Academy of Sciences, the National Natural Science Foundation of China (Nos. 61274077, 61474031, 61464003), the Guangxi Natural Science Foundation (Nos. 2013GXNSFGA019003, 2013GXNSFAA019335), the National Basic Research Program of China (Nos. 2011CBA00605, 2010CB327501), the Project (No. 9140C140101140C14069), and the Innovation Project of GUET Graduate Education (Nos. GDYCSZ201448, GDYCSZ201449, YJCXS201529).

Twenty-Fourth Lunar and Planetary Science Conference. Part 3: N-Z

NASA Technical Reports Server (NTRS)

1993-01-01

Papers from the conference are presented, and the topics covered include the following: planetary geology, meteorites, planetary composition, meteoritic composition, planetary craters, lunar craters, meteorite craters, petrology, petrography, volcanology, planetary crusts, geochronology, geomorphism, mineralogy, lithology, planetary atmospheres, impact melts, K-T Boundary Layer, volcanoes, planetary evolution, tectonics, planetary mapping, asteroids, comets, lunar soil, lunar rocks, lunar geology, metamorphism, chemical composition, meteorite craters, planetary mantles, and space exploration.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Huntsman, J.R.

Eastern slate belt lithologies in the central Flowers quadrangle consist of metavolcanic and metasedimentary rocks. Very fine-grained quartz-white mica phyllite containing narrow, discontinuous layers of thinly laminated chlorite-rich rock and fine-grained, thinly layered, feldspar crystal felsic metatuff comprise the dominant, mappable units consistent across the quadrangle. An increase in grain size accompanied by a replacement of chlorite-rich lithologies with biotite [+-] garnet assemblages suggest metamorphic grade increases towards the western half of the quadrangle (quartz-muscovite schist and biotite-quartz-muscovite-feldspar gneiss). An early, northeast-trending foliation (050[degree] to 060[degree]) dipping moderately to steeply southeast persists across the quadrangle and is axial planar tomore » tight to isoclinal, recumbent to moderately inclined folds. Later non-coaxial folding produced steeply plunging, northerly trending (000[degree] to 020[degree]), open, asymmetric structures verging towards the east/southeast. Shear zones formed locally along the axial trend of these later folds and produced protomylonitic to mylonitic ( ) fabrics. Map patterns and cross-sectional interpretations are best explained by modification of zig-zag fold interference patterns. Thin section examination reveals garnets growing across the early axial planar foliation. The observed increase in metamorphic grade across the quadrangle matches the regional Alleghanian prograde event and constrains relative timing of observed deformational fabrics. Noticeably absent are regional, late-stage upright folds.« less

Multi-stage barites in partially melted UHP eclogite: implications for fluid/melt activities during deep continental subduction in the Sulu orogenic belt

NASA Astrophysics Data System (ADS)

Wang, Songjie; Wang, Lu

2015-04-01

Barite (BaSO4) is well-known from deep-sea sedimentary environments but has received less attention to its presence in high-grade metamorphic rocks. Recently, barite in ultrahigh pressure (UHP) eclogite has drawn increasing attention from geologists, especially in the Dabie-Sulu orogen, since it is an important indicator for high-salinity fluid events, thus aiding in further understanding HP-UHP fluid / melt evolution. However, its formation time and mechanism in UHP eclogite are still controversial, with three representative viewpoints: (1) Liu et al. (2000) found barite-anhydrite-coesite inclusions in zircon and interpreted them to have formed by UHP metamorphic fluids; (2) Zeng et al. (2007) recognized isolated barite within K-feldspar (Kfs) and Quartz (Qz) surrounded by radial cracks in omphacite, and interpreted Kfs+Qz to be reaction products of potassium-rich fluid/melt and coesite, with the barite formed by prograde metamorphic fluids; (3) Gao et al. (2012) and Chen et al. (2014) found barite-bearing Multiphase Solid (MS) inclusions within garnet and omphacite and assumed that the barite formed by phengite breakdown possibly caused by eclogite partial melting during exhumation, though no direct evidence were proposed. The controversy above is mainly due to the lack of direct formation evidence and absence of a clear link with the metamorphic evolution of UHP eclogite along the subduction-exhumation path. We report detailed petrological and micro-structural analyses revealing four types of barites clearly linked with (1) the prograde, (2) earlier stage of partial melting and (3) later stage of crystallization differentiation, as well as (4) high-grade amphibolite-facies retrogression of a deeply subducted and partially melted intergranular coesite-bearing eclogite from Yangkou Bay, Sulu Orogen. Round barite inclusions (type-I) within UHP-stage garnet and omphacite are formed by internally buffered fluids from mineral dehydration during prograde metamorphism. Zr-in-rutile thermometry shows their formation temperature to be 586-664 oC at 1.5-2.5 GPa. Barite-bearing MS inclusions with Ba-bearing K-feldspar (type-II) connected by Kfs+Pl+Bt veinlets of in-situ phengite breakdown and thin barite veinlets along grain boundaries (type-III) are products of phengite breakdown and induced fluid flow during exhumation. These barites have witnessed the gradational separation process of melt/ fluid from miscibility on/above the second critical endpoint during UHP metamorphism, to immiscibility along the exhumation path of the subducted slab. Associated reactions from pyrite to hematite and goethite with the type-III barite ring surrounding the pyrite provide evidence for a local high oxygen fugacity environment during eclogite partial melting and subsequent melt/fluid crystallization processes. Moreover, large grain barite aggregations (type-IV) modified by amphibole+albite symplectite are most likely formed by release of molecular and hydroxyl water from anhydrous minerals of eclogite during high-grade amphibolite-facies retrogression. The growth of multi-stage barites in UHP eclogite further advances our understanding of fluid/melt transfer, crystallization processes along the subduction-exhumation path of the partially melted eclogite, broadening our knowledge of melt/fluid evolution within subduction-collision zones worldwide. REFERENCES Chen Y.X., et al., 2014, Lithos, 200, 1-21. Liu J.B., et al., 2000, Acta Petrologica Sinica 16(4), 482-484. Zeng L.S., et al., 2007, Chinese Science Bulletin, 52(21), 2995-3001. Gao X.Y., et al., 2012, Journal of Metamorphic Geology, 30(2), 193-212.

The occurrence of extreme events a tsunami and storm deposit in Chilcatay formation, Ica, Peru.

NASA Astrophysics Data System (ADS)

Poma Porras, O. A.; Cayo, R., Jr.; Casas, N.; Figueroa, F.

2016-12-01

The Chilcatay Formation (Oligocene to middle Miocene) south of Peru is in the Pisco Basin contains a thick sequence of Cenozoic sediments that record at least three marine transgressions characterized by successions of fine sandstones, siltstones, and diatomaceous mudstones. The sequence records certain facies that are typical of high-energy events, including extreme storms, tsunamis and earthquakes. The studied deposit is characterized by the presence of two layers of varying thickness. The lower layer, which is in markedly erosive contact with the underlying layer, is a very coarse-grained sandstone, highly sorted and with subrounded to subangular grains. The thickness varies laterally from one to 50 cm. The top layer, which is 40-60 cm thick and exposed for approximately 200 m, consists of a dense matrix of coarse-grained size fragments of molluscs (oysters), barnacles, and lithoclasts. The biogenic matrix contains many igneous (gabbro, granite) and metamorphic cobbles and boulders, and lithic tuffs, clusters of barnacles, and fragments consisting of vermetid gastropods reefs. The abundant igneous and metamorphic cobbles and boulders are rounded and subrounded, with a larger diameter between 3 and 140 cm, and occurring at a density of 3-8 clasts by square meter. The lithic tuffs are subrounded, have an ovoid morphology and a greater diameter between 1 and 44 cm. All these clasts occur scattered and 'floating' in the bioclastic matrix. The characteristics of the studied layer suggest that it was deposited by an extreme event that eroded the area between shoreface and backshore redepositing the materials and leaving a chaotic facies distribution with cobbles and boulders of different lithology. The large waves caused heavy erosion of the sediments in the shallow seafloor and the basement, mixing the biogenic and lithogenic clasts. The large size of these clasts suggests that such an event may have been a tsunami.

Microhabitats in the tropics buffer temperature in a globally coherent manner

PubMed Central

Scheffers, Brett R.; Evans, Theodore A.; Williams, Stephen E.; Edwards, David P.

2014-01-01

Vegetated habitats contain a variety of fine-scale features that can ameliorate temperate extremes. These buffered microhabitats may be used by species to evade extreme weather and novel climates in the future. Yet, the magnitude and extent of this buffering on a global scale remains unknown. Across all tropical continents and using 36 published studies, we assessed temperature buffering from within microhabitats across various habitat strata and structures (e.g. soil, logs, epiphytes and tree holes) and compared them to non-buffered macro-scale ambient temperatures (the thermal control). Microhabitats buffered temperature by 3.9°C and reduced maximum temperatures by 3.5°C. Buffering was most pronounced in tropical lowlands where temperatures were most variable. With the expected increase in extreme weather events, microhabitats should provide species with a local layer of protection that is not captured by traditional climate assessments, which are typically derived from macro-scale temperatures (e.g. satellites). Our data illustrate the need for a next generation of predictive models that account for species' ability to move within microhabitats to exploit favourable buffered microclimates. PMID:25540160

Structural characterization and magnetic properties of L10-MnAl films grown on different underlayers by molecular beam epitaxy

NASA Astrophysics Data System (ADS)

Takata, Fumiya; Gushi, Toshiki; Anzai, Akihito; Toko, Kaoru; Suemasu, Takashi

2018-03-01

We grow MnAl films on different underlayers by molecular beam epitaxy (MBE), and investigate their structural and magnetic properties. L10-ordered MnAl films were successfully grown both on an MgO(0 0 1) single-crystalline substrate and on an Mn4N(0 0 1) buffer layer formed on MgO(0 0 1) and SrTiO3(0 0 1) substrates. For the MgO substrate, post rapid thermal annealing (RTA) drastically improved the crystalline quality and the degree of L10-ordering, whereas no improvement in the crystallinity was achieved by altering the substrate temperature (TS) during MBE growth. However, high-quality L10-MnAl films were formed on the Mn4N buffer layer by simply varying TS. Structural analysis using X-ray diffraction showed MnAl on an MgO substrate had a cubic structure whereas MnAl on the Mn4N buffer had a tetragonal structure. This difference in crystal structure affected the magnetic properties of the MnAl films. The uniaxial magnetic anisotropy constant (Ku) was drastically improved by inserting an Mn4N buffer layer. We achieved a perpendicular magnetic anisotropy of Ku = 5.0 ± 0.7 Merg/cm3 for MnAl/Mn4N film on MgO and 6.0 ± 0.2 Merg/cm3 on STO. These results suggest that Mn4N has potential as an underlayer for L10-MnAl.