bluuebunny/crossref_metadata_2025_split huggingface dataset:
In-Situ Ellipsometry Study of Amorphous Silicon Interfaces
Authors: Antoine A. M. , Drevillon B. , Godet C. 
Published: March 2011

ABSTRACTA systematic comparison of the growth of plasma deposited amorphous silicon a-Si:H on chromium and glass substrates using real-time ellipsometry is presented. In order to compare the optical properties of the substrates before and after a-Si:H deposition, the amorphous films are removed by H-etching. Although the early stage of the growth of a-Si:H on chromium substrates is compatible with a nucleation mechanism, chromium suicides are probably produced at the film substrate interface. A faster chemical reaction between a-Si:H and the glass substrate is observed.
Ge and Gesl Heteroepitaxy on Si(100) by MBE
Authors: Houghton D. C. , Baribeau J.-M. , Maigne P. , Jackman T. E. , Bassignana I. C. , Tan C. C. , Holt R. 
Published: March 2011

ABSTRACTWe have grown a series of Ge and graded Si1-xGex epilayers on (100)Si substrates by MBE under different conditions. The quality of the layers has been characterized by cross-sectional TEM, Rutherford backscattering/ channeling and x-ray diffraction. This work addresses the optimization of growth temperature, (300–700°C) an evaluation of compositional grading, the effect of the incorporation of strained layer superlattice dislocation filters and post growth anneal cycles. Particular attention has been paid to grading GexSi1-x, x = 0 to 1 and the growth morphology of intermediate alloy epilayers.
Temperature Dependent and Time Resolved Optical Studies of Single Quantum Wells Produced by Interrupted Growth MBE
Authors: Elman B. S. , Koteles Emil S. , Jagannath C. , Chen Y. J. , Charbonneau S. , Thewalt M. L. W. 
Published: March 2011

ABSTRACTMultiple peaks, recently observed in the low temperature photoluminescence (PL) spectra of GaAs/AlGaAs single quantum wells fabricated by momentarily interrupting the molecular beam epitaxial growth between adjacent but different semiconductor layers, have been interpreted as originating within smooth regions in the quantum well layer differing in width by exactly one monolayer. We have observed similar structure in similarly grown samples but find that low temperature PL can be misleading. However, higher temperature PL or PL excitation spectroscopy do provide unambiguous evidence for the model of interface smoothing due to growth interruption. Further, time-resolved spectra yield decay times of the individual peaks which are consistent with this idea.
Direct Observation of Valence-Band Mixing in GaAs/GaPAs Strained-Layer Superlattices
Authors: Jones E. D. , Biefeld R. M. , Fritz I. J. , Gourley P. L. , Osbourn G. C. , Schirber J. E. , Heiman D. , Foner S. 
Published: March 2011

ABSTRACTLow-temperature magneto-luminescence studies are used to examine the in-plane valence-band dispersion in GaAs/GaPAs strained-layer-superlattice structures. The results provide a direct observation of valence-band mixing effects in strained-layer systems.Theoretical and experimental studies of the effect of valence-band mixing upon the magneto-transport properties and magneto-luminescence data for GaAs/AlGaAs latticed-matched superlattices have been recently reported.[1–] Due to the presence of the 2D-quantum well, the valence-band degeneracy between the light-hole and heavy-hole bands at is removed. These studies show, however, that the lowest energy valence-band mass is still strongly dependent upon due to valence-band mixing. On the other hand, because of the large biaxial compression in strained-layer-super lattices (SLS), valence-band mixing effects should be minimal.[8–9] Recent magneto-transport measurements[10] on p-type InGaAs/GaAs SLS structures have provided information regarding nonparabolic valence-bands in these structures.
Evaluation of AlGaAs/GaAs Heterointerface by Shubnikov-de Haas Oscillation Measurements
Authors: Kasai Kazumi , Tanaka H. , Itoh H. , Oh-Hori T. , Takikawa M. , Komeno J. 
Published: March 2011

ABSTRACTThe measurement of Shubnikov-de Haas(SdH) oscillation is proposed as a new technique for evaluating the quality of a heterointerface. The first excited state of 2-dimensional electron energy levels is determined for several samples using the measurements of SdH oscillation. Lower values of the first excited state energy are found for the samples with a low mobility. The low value can be approximately explained in terms of graded interface model.
Magnetic Transitions in Fe/Cr Superlattices
Authors: Sellers Charles H. , Shiroishi Yoshihiro , Hilliard John E. , Ketterson John B. 
Published: March 2011

ABSTRACTSeveral series of multilayered Fe/Cr films have been studied, each with a fixed thickness of Fe and several thicknesses of Cr. The coer-civity and in plane anisotropy field were found to increase abruptly for larger Cr thicknesses. The origin of this change in behavior may involve a paramagnetic/antiferromagnetic transition in the Cr.
Characterization of Al and Al-Cr-Al Thin Films
Authors: De Lima O. F. , Lepetre Y. , Brodsky M. B. 
Published: March 2011

ABSTRACTTEM, X-ray diffraction, and electrical resistivity measurements were used to study the microstructure and the growth of AI-Cr-AI film sandwiches, where the individual Al layers were 300 Å thick and the Cr thickness was varied between 0–10 atomic layers. The base vacuum was around 1.0 × 10−10 torr, substrate temperatures varied between 100–350 °C, and evaporation rates were 3Å/s for Al and ∼0.1 – 0.2 Å/s for Cr. All Al films had a strong (111) texture and showed a non-percolative island structure at 350 °C. The films became connected at lower substrate temperatures, reaching perfect continuity at 100°C. However, electrical conductivity is achieved also for the films deposited at 350 °C when one or more atomic layers of Cr are sandwiched between the Al layers. Results for the superconducting critical temperature and resistivity are discussed in terms of Cr diffusion into Al and the film size effect.
Optical Properties of RF-Sputtered a-SiGe:H:O Alloys
Authors: Pereira J. M. T. , Banerjee P. K. , Mitra S. S. 
Published: March 2011

ABSTRACTAmorphous thin films of SixGe1-x:O (x = 0.70) were prepared by RF-sputtering at several substrate temperatures. The structural properties of these films were studied by IR spectroscopy and revealed features characteristic of hydrogen and/or oxygen bonded to silicon. The optical constants (n,k) were determined from reflection and transmission measurements at near-normal incidence for photon energies in the range of 1 eV and 2.6 eV. The optical gap was derived from the Taue plot and correlated with the composition of the samples. The increase of hydrogen and/or oxygen decreases the value of the refractive index and increases the optical gap.
Electrical and Optical Properties of Amorphous Si1-xSnx: H Structures
Authors: Girginoudi D. , Thanailakis A. , Christou A. 
Published: March 2011

ABSTRACTAmorphous hydrogenated silicon-tin films (α — Six Snx:H) have been prepared by co-electron beam and Knudsen cell deposition. It is shown that the dependence of Eg on x, over the entire range of 0 < x < 0.51 studied, cannot be described by a single linear relationship. The d.c. conductivity measurements indicate two distinct conduction regions as a function of x. The addition of Sn up to x = 0.10 creates a high density of dangling bonds and moves the band edges so a significant conductivity increase is observed. The bonding between Si and H is preferred to Sn and H. Sn-H bonds were observed only for x > 0.40. Photoluminescence measurements show that band edge luminescence dominates at 1.3–1.4 eV.
Structural Characterization of MBE Grown (001) CdTe Films by Means of Transmission Electron Microscopy, Low Temperature Photoluminescence and Double Crystal Rocking Curves.
Authors: Burke M. G. , Choyke W. J. , Doyle N. J. , Feng Z. C. , Hanes M. H. , Mascarenhas A. 
Published: March 2011

ABSTRACTThe effects of chemical etching, mechanical thinning, and ion milling on the low temperature photoluminescence spectra of MBE grown (001) CdTe films are reported. Line defects observed by TEM are correlated with photoluminescence. It is shown that X-ray D.C.R.C, measurements in these films are weighted averages over the whole thickness of the films and therefore weakly reflect the structural perfection of the samples near the surface as deduced by photoluminescence.
Exchange of Bonded Hydrogen in Amorphous Silicon by Deuterium
Authors: Abeles B. , Yang L. , Leta D. P. , Majkrzak C. 
Published: March 2011

ABSTRACTWe show that bonded hydrogen in a-Si:H is readily exchanged by atomic deuterium when exposed to a deuterium plasma discharge. The effective diffusion coefficient for the D.H exchange, 10∼14 cnr/sec at 160°C, is comparable to that of interstitial hydrogen in c-Si.
Structure and Magnetic Properties of Fe/Cu Multilayered Thin Film
Authors: Fukizawa A. , Naoe M. 
Published: March 2011

ABSTRACTFe/Cu multilayered films prepared by means of Facing Targets Sputtering have distinct multilayered structure at layer thicknesses above 7Å. The saturation magnetization of Fe in the multilayered film takes almost the bulk thicknesses Fe value above this thickness. However, multilayerd structures did not clearly form at layer thicknesses below 7Å and the saturation magnetization decreased to about half of the bulk value. Considerable variation of confirmed layer thickness, saturation magnetization and coercivity in the multilayerd films were obtained when the total thickness was below 1000Å.
Core and Valence Levels in Hydrogemated Amorphous Silicon
Authors: Burnhara N. A. , Fisher R. F. , Asher S. E. , Kazmerski L. L. , Lucovsky G. , Parsons G. N. 
Published: March 2011

ABSTRACTSilicon core and valence levels were studied in hydrogenated amorphous silicon (a-Si:H) as a function of hydrogen concentration. The techniques used to establish the core levels were X-ray Photoelectron Spectroscopy and core-level Electron Energy Loss Spectroscopy. Changes in the local densities of states of the silicon 3s and 3p levels were examined with Auger Electron Spectroscopy. The a-Si:H samples were grown by RF sputtering. Their hydrogen concentrations varied from zero to nearly fifteen percent.
Multilayer Fe/Cu Films
Authors: Liou S. H. , Xiao Gang , Chien C. L. , Unruh K. M. 
Published: March 2011

ABSTRACTMultilayer films consisting of alternating Fe and Cu thin films have been made by a twin-gun sputtering device with a rotating substrate platform. Both proportional modulated films and films with a fixed Cu layer have been fabricated, where the Fe layer has been varied between 10 and 150 Å. These films have been studied by x-ray diffraction, Mö;ssbauer spectroscopy and SQUID magnetometry. Thin Fe layers with thicknesses less than 25 Å, exist only as fee α-Fe. Thicker Fe layers contain both bec and fee Fe. The interface between Fe and Cu appears very sharp with no evidence of Fe-Cu alloys. The α-Fe state orders magnetically below 100 K with a small magnetic moment.
Electron Localization and the Aharonov-Bohm Effect in Two-Dimensional Metal Systems
Authors: Van Haesendonck C. , Bruynseraede Y. 
Published: March 2011

ABSTRACTDuring the last few years, it became clear that electron interference phenomena strongly modify the conductance of disordered systems. In thin metal films, this interference produces an anomalous low temperature magneto-resistance which enables to obtain detailed information about the inelastic, spin-orbit and magnetic scattering mechanisms. In a multiply-connected geometry, the interference leads to magnetoresistance oscillations. In long metal cylinders, only the oscillations which are not destroyed by impurity averaging, can be observed (flux period h/2e). In single loops, the original Aharonov-Bohm oscillations with flux period h/e are also present. A review will be presented of recent experimental results obtained for quasi two-dimensional plane films, cylinders, rings and arrays.
Infrared Ellipsometry Study of Oriented Langmuir-Blodgett Monolayers
Authors: Benferhat R. , Drevillon B. , Robin P. 
Published: March 2011

ABSTRACTThe first experimental investigation of the vibrational properties of 1–19 raonolayers of behenic acid deposited on various substrates using a new IR technique : Spectroscopie Phase Modulated Ellipsometry (SPME) is presented. The influence of the cleaning procedure of the substrate is discussed. The preferential tilting direction of the aliphatic chain along the withdrawal direction is confirmed. High sensitivity makes SPME a useful tool to study the structure of more complex organic molecules.
Electrical Transport and In-Situ X-Ray Studies of the Formation of TiSi2 Thin Films on Si
Authors: Hensel J. C. , Vandenberg J. M. , Mattheiss L. F. , Unterwald F. C. , Maury A. 
Published: March 2011

ABSTRACTThe formation of TiSi2 thin films on Si has been investigated by in situ x-ray diffraction and by electrical transport. The x-ray results show unequivocally that the staging proceeds through two orthorhombic polytypes of TiSi2 according to the sequence: sputter-deposited metallic Ti films on Si (001) → TiSi2 (C49 structure) → TiSi2 (C54 structure), with no evidence of lower suicides. Electrical transport shows metallic behavior for all phases and distinctive features in the annealing curves which correlate with the structural transformations. Most importantly, the resistivity, characteristically very high for the C49 phase, undergoes a precipitous drop at the C49 → C54 transition. Total energies for both phases are calculated and, consistent with the occurrence of a structural phase transformation, are found not to differ appreciably.
The Effect of Temperature and Si Concentration on the Mixing of AlAs/GaAs Superlattices
Authors: Mei Ping , Yoon H. W. , Venkatesan T. , Schwarz S. A. , Harbison J. P. 
Published: March 2011

ABSTRACTThe intermixing of AlAs/GaAs superlattices has been investigated as a function of Si concentration following anneals in the range of 500 to 900 C. The superlattice samples were grown by molecular beam epitaxy(MBE) and the near surface layers were doped with silicon at concentrations of 2×10 to 5×1018 cm-3. Si and Al depth profiles were measured with secondary ion mass spectrometry (SIMS).The diffusion length and activation energy of Al as a function of silicon dopant concentration are derived from the SIMS data. In the temperature range studied an activation energy for the Al interdiffusion of -4eV is observed with the diffusion coefficients increasing rapidly with Si concentration.
Comparative Thickness Measurements of Heterojunction Layers by Ellipsometric, RBS, and XTEM Analysis
Authors: Woollam J. A. , Snyder P. G. , McCOrmick A. W. , Rai A. K. , Ingram D. C. , Pronko P. P. , Geddes J. J. 
Published: March 2011

ABSTRACTVariable Angle of incidence Spectroscopie Ellipsometry (VASE), Rutherford Backscattering (RBS) and Cross-sectional Transmission Electron Microscopy (XTEM), are used to measure heterojunction layer thicknesses in an AlGaAs/GaAs sample. All three techniques yield the same thickness values within error limits.
Variable Angle of Incidence Spectroscopic Ellipsometric Measurement of the Franz-Keloysh Effect in Modfet Structures
Authors: Snyder P. G. , Oh J. E. , Woollam J. A. 
Published: March 2011

ABSTRACTIt has been shown recently that variable angle of incidence spectroscopie ellipsometry (VASE) is a sensitive technique for determining semiconductor multilayer model parameters, e.g. layer thicknesses and ternary compositions. In this paper we show that VASE is, in addition, sensitive to the Franz-Keldysh effect induced by band bending in the barrier layer of a GaAs-AlGaAs-GaAs (MODFET) structure. VASE measurements differ from electro-reflectance and photoreflectance, in that the internal heterojunction region electric field is directly probed, without the application of a modulating field. The Franz-Keldysh effect appears in the VASE spectra near the AlGaAs bandgap energy. Data for two samples, with different doping profiles, are quantitatively modeled to determine the internal electric field amplitudes.
Surface Structure Investigation of Epitaxial Nickel Silicides on Si(001)
Authors: Huang Judy H. , Stanley Williams R. 
Published: March 2011

ABSTRACTLow Energy Ion Scattering (LEIS) techniques have been used to examine epitaxial NiS2 films grown on the (001) surface of Si. The experimental results support a model of a NiSi2(001) surface that is a bulk-like but relaxed (001) Si plane with a 25%-30% concentration of vacancies. The 1/3-, 1/4-, and 1/5-order LEED spots observed for these surfaces may be the result of ordering of the vacancies, such that there are domains in which every 3rd, 4th, or 5th [110]-type atomic rows are missing in the Si terminated (001) plane.
TEM Investigation of Epitaxial Growth of Semiconductor Superlattices on Structured Substrates
Authors: Hwang D. M. , Kapon E. , Tamargo M. C. , Bhat R. 
Published: March 2011

ABSTRACTIn exploring new techniques to produce controllable lateral variations in the physical properties of semiconductor superiattices, substrates containing etched patterns were used for epitaxial crystal growth. High resolution TEM was used for the first time to study this kind of structures. It was found that the resultant superlattices exhibit wavy or zigzag layers which register the history of the topographic evolution of the crystal surfaces during growth and reveal useful information on the fundamental mechanism of the epitaxial process.Alternate layers of Al0.3Ga0.7As and GaAs were grown by MBE and OMCVD on (100) GaAs substrates patterned with grooves and mesas along the [011] and [011] directions. The morphology of the superlattices grown on the grooves and mesas was analyzed with TEM cross-sectional imaging. It was found that the evolution of non-planar crystal surfaces depends not only on the source flux and surface affinity, but also on the lateral diffusion of the adsorbed atoms or molecules on the crystal surfaces. Several growth features at the intersections of adjacent facets are illustrated in this work. Implications on the epitaxial process are discussed.
Electrical and Optical Properties of GaAs Heteroepitaxial Films on Si Substrates
Authors: Nishioka Takashi , Itoh Yoshio , Yamaguchi Masafumi 
Published: March 2011

ABSTRACTElectrical and optical properties of single-domain GaAs heteroepitaxial films grown on Si(100) by using metalorganic chemical vapor deposition have been investigated. Cathodolumi-nescence and electron-beam induced current experiments have revealed that signal nonuniformities on the film surface agree in number with GaAs microdefect densities observed through chemical etching, rather than conventional aligned etch-pit densities. The cathodoluminescence experiments also indicate that GaAs properties are improved with increases in film thickness. This nonuniformity and the film-thickness dependence are related to GaAs solar cell characteristics fabricated on the Si substrate. A GaAs/Si interface study proves that p-type Si substrates cause type conversions near the interface due to GaAs growth. Evidence of positive interface charges in the GaAs/Si system is determined by using Hall effect measurements, secondary-ion mass spectroscopy and electron-beam induced current experiments.
Crack Propagation in MG-PSZ
Authors: Readey M. J. , Heuer A. H. , Steinbrech R. W. 
Published: March 2011

ABSTRACTCertain coarse-grained Mg-PSZ's exhibit marked R-curve behavior, e.g., the crack resistance increases from ∼5 to ∼15 MPam1/2 with the first 500 microns of crack extension. These high toughness materials also show unusually-good flaw tolerance.Crack propagation and crack path development in Mg-PSZ were investigated during stable crack growth using a modified DCB specimen geometry. Crack extension was monitored with a traveling microscope equipped with a video recording system. PSZ's with various heat-treatments were tested to determine the effect of microstructure on R-curve behavior.Cracks were found to propagate discontinuously and to arrest. Smaller microcracks would develop around the arrested crack, and link together to form the macrocrack which led to eventual failure.
Mechanical Properties and Thermal Stability of Yttria-Doped Tetragonal Zirconia Polycrystals with Diffused Ceria in the Surface
Authors: Sato T. , Ohtaki S. , Fukushima T. , Endo T. , Shimada M. 
Published: March 2011

ABSTRACTYttria-doped tetragonal zirconia polycrystals (Y-TZP) containing 2 and 3 mol% of Y2O3 uniformly alloyed by 0-15 mol% of CeO2 or diffusing CeO2 on the surface were fabricated, and the mechanical properties and thermal stability of the sintered bodies were evaluated by annealing in humidity conditions at 50–600° C. The tetragonal-to-monoclinic phase transformation proceeded at 100–500°C in air, and accompanied microcracks. The phase transformation proceeded rapidly on the surface, but slowly inside the body. The bending strength of the annealed specimens depended on the depth of the transformation layer thickness, but not on the degree of the phase transformation on the surface. Alloying CeO2 was useful to improve the thermal stability of Y-TZP, but noticeably decreased the fracture strength. Diffusing CeO2 on the suface of Y-TZP seemed to be useful to improve the thermal stability without loss of the fracture strength.
Zirconia Dispersed Mullite Ceramics Through Hot-Pressing Of Amorphous ZrO 2 -SiO 2 -Al 2 O 3 Obtained by Rapid Quenching
Authors: Yoshimura Masahiro , Noma Tatsuo , Hanaue Yasuhiro , Sōmiva Shigeyuki 
Published: March 2011

ABSTRACTZirconia dispersed mullite ceramics were fabricated through hot-pressinq at a pressure of 25 MPa from the amorphous material of 2Owt%ZrO2-8Owt%(3Al2O3 2SiO2) obtained by rapid quenching of the melts. The densification was initiated at ∼950°C and accelerated by crystallization of mullite and t-ZrO2 to yield almost pore free samples about 1050°C. This sample seemed to contain Si02-rich glassy phase in addition to A12O3-rich mullite and t-ZrO2 The further heat-treatments with/without pressing brought about the reaction between the Si02-rich glassy phase and the A1203-rich mullite phase to yield nearly stoichiometric mullite. and growth of the mullite grains and the t-ZrO2 particles up to 1 u m in size at 1600°C. The TEM observation revealed a duplex microstructure of twinned m-ZrO2 at the triple points and fine t-ZrO2 in the center of the mullite grains. The fracture toughness of the specimen increased with hot-pressing temperatures up to 2.2 MPam1/2 in the samples at 1600°C.
A Study of Rhombohedral Phase in Y2 O3 -Partially Stabilized Zirconia
Authors: Kitano Jukishige , Mori Y. , Ishitani A. , Masaki T. 
Published: March 2011

ABSTRACTTetragonal to rhombohedral phase transformation was studied by X-ray diffraction technique on the ground surfaces of tetragonal zirconia polycrystals (Y-TZP) and partially stabilized zirconia (Y-PSZ) with 2.0 to 5.0 mol% Y2 O3 contents prepared by hot isostatic pressing. The rhombohedral phase increased with increase of Y2 O3 content from 2.0 to 5.0 mol%, and also with the increase of HIPing temperature from 1400 to 1600°C. The stability of the phase was also studied with regard to the surface finish and annealing. The subsequent heat treatment of the samples was found to promote the reverse rhombohedral to tetragonal transformation.