bluuebunny/crossref_metadata_2025 huggingface dataset:
Nonlinear Optical Properties of PBT in Nematic Solutions
Authors: Mattoussi Hedi , Kaatz Philip G. , Patterson Gary D. , Berry Guy C.
Published: March 2011

Third-order nonlinear optical properties of lyotropic liquid crystal poly(1,4-phenylene-2,6-benzobisthiazole), PBT, solutions are studied by third harmonic generation measurements. Besides the enhancement observed for this coefficient with respect to the pure PBT, coupling is observed between the mean filed nematic director n and the incident fundamental polarization B0. Different geometries, with respect to the relative orientation of B0 and n, provided different harmonic Maker Fringe Patterns. These data are compared using refractive index measurements, independently achieved on these materials, and necessary for Maker Fringe analysis.
Dielectric Permittivity of Polymers Containing Conductive Inclusions
Authors: Kolesnicov A.N. , Lagar'kov A.N. , Matitsin S.M. , Novogrudskiy L.N. , Rozanov K.N. , Sarychev A.K.
Published: March 2011

Filled polymers containing conductive inclusions possess a number of unique microwave properties. The effective values of real ε1 and imaginary ε2 parts of complex dielectric permittivity ε=ε1 + εz of these materials may be easily changed by variation of their composition. The values of ε1 may have high (up to several hundreds) as well as negative meanings [1]. Besides, the filled polymers containing conductive inclusions may possess strong frequency dispersion of the effective dielectric permittivity at wavelengths λ∼1, where 1 is a size of inclusion. The investigation of dielectric properties of these materials at microwaves is of great interest as from the physical point of view as for technical applications.
Insoluble, Low Dielectric Polyimides
Authors: Stoakleya Diane M. , Clair Anne K. St.
Published: March 2011

Studies have been conducted at NASA Langley establishing structure-property relationships in polyimides that provide a means of lowering dielectric constants by reducing chain-chain electronic interactions and by incorporation of fluorine into the polymer molecular structure. The resulting polyimides exhibit excellent thermal stability and mechanical strength, improved resistance to moisture and enhanced solubility. Most polyimides containing fluorine in only one monomer are at least partially soluble in common organic solvents, and polyimides containing fluorine in both the dianhydride and the diamine are fully soluble. Although this enhanced solubility aides processability and is desirable for many applications, it is a severe disadvantage for aircraft applications where exposure to hydraulic fluids and other chemicals is likely to occur. This work involves the development of insoluble, low dielectric polymers prepared from 2, 2-bis[4-(3, 4-dicarboxyphenoxy)phenyl]hexafluoropropane dianhydride (BFDA) and selected fluorine-containing diamines.

BFDA-containing polyimide films had dielectric constants that ranged from 2.44 to 2.53 at 10 GHz and exhibited insolubility in solvents including N, N-dimethylacetamide, chloroform, diglyme and N-methylpyrrolidinone.
Polyanilines: In Situ Radiation and Thermal Induced Doping
Authors: Angelopoulos Marie , Shaw Jane M. , Lee Kam-Leung
Published: March 2011

Onium salts and amine triflate salts decompose upon exposure to radiation or thermal treatment respectively to generate protonic acids. These salts can be blended with polyaniline and upon decomposition the resulting acids act as insitu dopants for the polymer. These novel doping techniques eliminate the need for external dopant solutions and thereby simplify the processing of conducting polyaniline.
Rheo-Optical Properties of Ion Irradiated Polystyrene Films
Authors: Calcagno L. , Compagnini G. , Foti G. , Mezzasalma A. , Mondio G.
Published: March 2011

Rheological and optical properties of polystyrene are modified by 200 keV He irradiation because of new molecular bonds induced by ion energy deposition. Total amount of bonds, as calculated by optical measurements, increases linearly with ion fluence without any dependence on the initial molecular weight. Density of interchain bonds or crosslinks, as calculated by rheological measurements, increases linearly at low fluence (∼1013 ions/cm2), while for high values shows a saturation behaviour.

Correlation between optical and rheological measurements allows us to calculate the fractions of interchain and intrachain bonds of ion irradiated 9000, 35000 and 100000 initial molecular weight samples.
A Modified Extended Hückel Calculations For Q1D-Graphites
Authors: Raković D. , Kostić R. , Krstić S. , Davidova I. , Fayfel B. L. , Gribov L. A.
Published: March 2011

In this paper we have computed electronic density of states for several Q1D graphites: polyacene (PA), polyacenacene (PAA), polyphenanthrene (PP), polyphenanthrophenanthrene (PPhP), and polyperinaphthalene (PPN). The modified extended Hiickel method for finite Q1D chains has been adopted. The change of the electronic properties due to the growth of the Q1D-graphites toward the two-dimensional direction, starting from trans-polyacetylene, cis-polyacetylene or poly(p-phenylene), is discussed. Our calculations show that PA, PAA, and PPN are intrinsic conductors, while PP and PPh are semiconductors with energy gaps of 1,4 eV and 0,8 eV, respectively. The comparison with other computational results is presented.
Morphology and Conductivity of Polymer Blends Filled with Carbon Black
Authors: Geuskens G. , Kezel E. De , Blacher S. , Brouers F.
Published: March 2011

It has been shown that the electrical conductivity of polymer blends filled with carbon black (CB) can be much higher than that of each constituent for the same level of loading. It is very difficult to understand this phenomenon due to the complexity of the three phases system. In particular it has been argued that the results could not be explained if the morphology of the blend was independent of the amount of CB. Indeed, an image analysis of the TEM and SEM micrographs of polymer blends filled with Ketjenblack (KB), reveals that the size distribution of the polystyrene component of the blend changes with the concentration of KB. One observes that an increase of 5% in KB results in a reduction of the average size of the PS component by 50% Since the KB dispersion seems to be linked to the dispersion of the polystyrene component our findings could explain why the dispersion is improved in the blend and gives rise to a lower percolation threshold.
Free-Volume Properties of Amorphous Polymers Probed by Positron Annihilation Spectroscopy
Authors: Jean Y. C. , Zandiehnadem F. , Deng Q.
Published: March 2011

Positron annihilation spectroscopy (PAS) has been developed to characterize the free-volume properties of polymers. Positron annihilation lifetime measurements give direct information about the dimension, content, and hole-size distributions of free-volume in amorphous materials. The angular correlation of positron annihilation radiation measurements give additional information about the shape of the free-volume holes in oriented polymeric materials. The unique capability of PAS to probe free-volume properties is from the fact that positronium atom is preferentially trapped in the atomic-scale holes which have a size ranging from 1 to 10 Å.
Miscibility Enhancement of Polymer Blends by Specific Chemical Interactions
Authors: Lu X. , Weiss R. A.
Published: March 2011

Miscibility enhancement of polymer blends is a current topic of considerable activity. Many approaches have been suggested, though all involve the development of specific interactions between the two polymers. These interactions include hydrogen bonding, ion-dipole and ion-ion interactions, donor-acceptor interactions and transition metal complexation.
Dependence of Segmental Mobility in Polycarbonate on Time and Deformation
Authors: Smith Thor L. , Haidar Bassel
Published: March 2011

Studies are discussed which show that the segmental mobility In polycarbonate (Lexan from General Electric Co.) increases when a static deformation in either extension or simple compression (uniaxial stress) is applied to a specimen, but thereafter the mobility decreases progressively. These changes can be termed erasure (partial) of physical aging (strain softening) and physical aging (hardening), respectively. Because the volume of a specimen deformed in simple compression decreases, reversal of aging (de-aging) cannot be attributed to an increase in free volume, as usually defined. A proposed explanation will be mentioned. A study was also made of the yield stress modified by unconventional methods at several temperatures. The results can be explained In terms of the rate of physical aging and its temperature dependence determined on specimens at 2.6% extension over a broad range of temperatures. These results show that yielding results from progressive de-aging. The yield phenomena obtained by special methods results from both physical aging and de-aging.
OMVPE Growth of Epitaxial InSb Thin Films Using a Novel Group V Source Compound
Authors: Stauf Gregory T. , Gaskill D.K. , Bottka N. , Gedridge R.W.
Published: March 2011

To date, OMVPE has failed to grow epitaxial InSb at temperatures below about 400 °C. Therefore, we have studied InSb deposition using the novel group V source triisopropylantimony (TIPSb) with trimethylindium (TMIn), comparing this with results in the same reactor using trimethylantimony (TMSb). We have grown InSb on both GaAs and on high-resistivity p-type InSb substrates, exploring the effects of temperature, substrate, V/ill ratio, and thickness on film properties. Our best results with TMSb and TMIn were obtained using a V/ill ratio of 8 and growth temperature of 450 °C. The unintentionally doped films exhibited good crystallinity and were n-type about lx1015 cm-3 down to 5 K, with 77 K mobilities of 90,000 and 253,00°Cm2/V-sec for InSb on GaAs and on InSb, respectively. These results are comparable to the best published MBE data. While InSb films could not be grown well at temperatures below 425 °C using TMSb, specular epilayers were obtained with TIPSb at temperatures as low as 300 °C, though with a low deposition rate. Our best conditions with TIPSb were with a Vill ratio of about 12 and a substrate temperature of 350 °C. The results of variable temperature and variable magnetic field Hall, double crystal x-ray diffractometry, Nomarski microscopy, Auger electron spectroscopy and scanning electron microscopy will be presented.
Properties of Gainasp Alloys Investigated by Optically Detected Macnetic Resonance Techniques
Authors: Wetzel C. , Meyer B.K. , Grützmacher D. , Omling P.
Published: March 2011

The quaternary GaxIn1−xAsyP1−y semiconductor alloy system has considerable importance for present day optoelectronic and microwave device applications. For state of the art high mobility samples grown by metal organic chemical vapor deposition (MOVPE) there are few experimental techniques which both can asess band structure related properties (effective mass m*, g-values of free electrons) and impurity related properties (luminescence, mobility and lifetimes). In this paper we compare optical and transport properties of the quaternary compound GaxIn1−xAsyP1−y, (x=0.47,y-l; x=0.42,y=0.92; x=0.28,y=0.61; x=0.12,y=0.34) lattice matched to*{nP by optically detected magnetic resonance techniques.
Electron Mobility In N-Type Epitaxial ZnSe
Authors: Vaziri M. , Reifenberger R.
Published: March 2011

An analysis of the temperature dependent mobility in lightly doped ZnSe epitaxial layers grown on a semi-insulating GaAs substrate by Molecular Beam Epitaxy is reported. Our results indicate that the temperature dependence of the mobility is in poor agreement with calculated values based on typical phonon and ionized impurity scattering mechanisms. Good agreement between theory and experimental data call be obtained by including a scattering term associated with the space-charge region surrounding defects.
Orientation Dependence of the Stability of Strained Sn Eplayers Grown On Cd0.8Zn0.2Te Substrates
Authors: Niles David W. , HÖChst Hartmut
Published: March 2011

The strain energy density in epitaxial overlayers depends strongly on the substrate's surface orientation. The affect of a growth orientation dependent strain energy contribution to the phase stability was studied by growing overlayers of metastable, semiconducting a-Sn films on the (100) and (111) surfaces of Cd0.8Zn0.2Te substrates. On the (100) surface the α-phase of Sn remains stable for coverages up to and beyond 125 ML. On the (111) surface though, the Sn overlayer shows metallic behavior from a partial α→β phase separation for coverages lower than 100 ML. Static calculations using the stress-strain relationship bear out these experimental results by showing that the strain energy density for the (111) growth direction is 38% larger than for the (100) direction.
Implant Isolation of Device Structures Containing Buried, Highly-Doped Layers
Authors: Pearton S. J. , Ren F. , D'Asaro L. A. , Hobson W. S. , Fullowan T. R. , Lothian J. , Abernathy C. R. , Kopf R. F. , Kuo J.-M.
Published: March 2011

The formation of high resistivity (> 107 Ω□) regions in GaAs-AlGaAs HBT and SEED structures by oxygen and hydrogen ion implantation is described. Multiple energy implants in the dose range 1013 cm−3 (for O+) and 1015 cm−2 (for H+), followed by annealing around 500°C are necessary to isolate structures ∼2 μm thick. In each case, the evolution of the sheet resistance of the implanted material with annealing is consistent with a reduction in hopping probabilities of trapped carriers between deep level states for temperatures up to ∼600°C, followed by significant annealing of these deep levels. A comparison of the relative thermal stability of O+ or H+ ion implantisolated p+ material is given. Small geometry (2 × 9 μm2) HBTs exhibiting current gain of 44 and cut-off frequency fT as high as 45 GHz are demonstrated using implant isolation.
Phase Relations and Bulk Crystal Growth in the System CuInTe2-MnIn2Te4
Authors: Kelliher James T. , Bachmann Klaus J.
Published: March 2011

Recently manganese substituted I-III-VI2 compounds have been investigated. Their magnetic properties are similar to the paramagnetic transistion metal ion substituted II-VI materials, but their crystal structure is non-cubic resulting in anisotropies in their physico-chemical properties that do not exist in the zincblende structure diluted magnetic semiconductors (DMS) materials. In this paper, we report the phase relations on the pseudobinary cut CuInTe2-MnIn2Te4 based on x-ray diffraction and differential thermal analysis data. The range of chalcopyrite structure alloys of composition Cu1−xMnx□xIn2Te4 is limited to x<0.52 due to an eutectic at x=0.74, T= 734°C. A second eutectic exists at x = 0.97, T = 737.5°C. A heretofore unknown congruently melting compound exists in between the two eutectics at x= 0.85, Tm = 760°C. Also, the thus far unknown melting point of the compound MnIn2Te4 was determined (740°C ). Based on the analyses of the first to freeze parts of directionally solidified melts in this range of liquidus compositions by inductively coupled plasma emission spectroscopy the solidus is constructed.
Intrinsic Carrier Concentrations in Long Wavelength HgCdTe Based on the New, Nonlinear Temperature Dependence of Eg(x,T)
Authors: Seiler D. G. , Lowney J. R. , Littler C. L. , Yoon I. T.
Published: March 2011

Intrinsic carrier concentrations of narrow-gap Hg1-xCdxTe alloys (0.17≦ x ≦0.30) have been calculated as a function of temperature between 0 and 300 K by using the new nonlinear temperature dependence of the energy gap obtained previously by twophoton magneto-absorption measurements for samples with 0.24≦ x ≦0.26. We report here experimental values for Eg(x,T) for samples with x = 0.20 and 0.23 obtained by one-photon magneto-absorption measurements. These data confirm the validity of the new Eg(x,T) relationship for these : values. In this range of composition and temperature, the energy gap of mercury cadmium telluride is small, and very accurate values are needed for the gap to obtain reliable values for the intrinsic carrier density. Large percentage differences exist between our new calculations and previous values for ni at low temperatures. Even at 77 K, differences approaching 10 percent exist, confirming the importance of using the new ni results for materials and device characterization and a proper understanding of device operation in long-wavelength materials.
Process Control For Composites Using Computed Tomography
Authors: Engler Philip , Friedman William D. , Santana Mark W. , Chi Frank
Published: March 2011

Structural information provided by computed tomography (CT) can be used for quality control and optimization of processes for manufacturing better materials. The squeeze casting method for producing metal matrix composites involves infiltrating a preform of ceramic fibers with molten metal under high pressure. Part quality can be improved if CT is used before infiltration to determine if the preforms have the desired distribution of fibers and are free of defects. Measurements do not require uniform shapes, and CT systems can even be used to obtain accurate densities on complicated part shapes that are not amenable to bulk density measurements based on weight and size. With this quantitative distribution information as a guide, preform production can be modified to produce either a more uniform fiber distribution or to selectively increase the fiber concentration in critical areas. Problems occurring during later stages of processing can be detected in CT images of the completed part. For example. CT can be used to detect unreinforced regions in metal matrix composites caused by cracking of the preform during the squeeze casting process. CT scans of completed parts can also detect and distinguish variations in structure such as microporosity.
Impact of X-Ray Tomographic Microscopy on Deformation Studies of a SiC/Al MMC
Authors: Breunig T.M. , Stock S.R. , Kinney J.H. , Guvenilir A. , Nichols M.C.
Published: March 2011

Damage in a continuous, aligned-fiber SiC/Al metal matrix composite (MMC), e.g. fiber fracture, fiber-matrix interphase microcracking, intra-ply matrix voids and cracks, is examined with synchrotron x-ray tomographic microscopy (XTM). Quantitative three-dimensional measurements of damage are reported in as-fabricated and monotonically loaded SiC/Al. The XTM results indicate that increases in observed macroscopic structural stiffness during the first few fatigue cycles of an MMC coupon correspond to elimination of processing-related matrix porosity and to displacement of the fibers from a somewhat irregular arrangement into a more nearly hexagonal array. The XTM data also show that the carbon cores of the SiC fibers begin to fail at or below 828 MPa, that is, at loads far less than those for fracture of the entire fiber. The implications of these results and of the use of in situ loading for fatigue damage quantification are also discussed for mechanical/thermal modelling.
Response Time of a-Si:H Photosensors in Optically Addressed Spatial Light Modulators
Authors: Moddel Garret , Barbier Pierre R.
Published: March 2011

A successful application for a-Si:H is as the photosensor in a liquid crystal optically addressed spatial light modulator (OASLM). We analyze the response time of an a-Si:H p-i-n photodiode in a “pseudo-OALSM,” in which the liquid crystal is replaced by an equivalent capacitor, under both forward and reverse bias. Under reverse bias the two important effects are the photocurrent response time, and residual trapped charge. Under forward bias the mechanism shifts from double injection regimes to ohmic transport as a function of voltage. We relate these characteristics to the operation of an OASLM.
Comprehensive Kinetic of Defects in a-SI:H
Authors: Redfield David , Bube Richard H.
Published: March 2011

ABSTRACTL

The introduction of several new principles into the analysis of transition kinetics of metastable defects in a-Si:H has produced substantially improved rate equation for the density of defects as functions of time, light intensity, and temperature. The solution of this equation is stretched exponential (SE) having properties that explain in unifying way many observations of defect properties, including generation and anneal of the defect density in homogeneous films and degradation and anneal of solar cells. Major consequences are found for both the steady-state and transient properties of the defect density and for interpretations of microscopic models of the defects. These properties are also shown to be analogous to those of metastable centers in other materials, particularly the metastable DX center in AlGaAs which offers rare insight into the microscopic origins of stretched exponentials that can be applied to a-Si:H in ways that provide new perspectives on effects of alloying and hydrogen on stability.
Correlation Between Amorphous Silicon Solar Cell Parameters and Pbotoinduced Current Noise Power Spectrum
Authors: Demichelis F. , Rava P. , Tagliaferro A.
Published: March 2011

A new technique based on measurements of photoinduced current noise in amorphous silicon solar cells is reported. A 1/fn (n-1) component, superimposed to a frequency independent one due to simple shot noise, is attributed to the presence of defects limiting the conversion efficiency of the cell. In particular large defects can easily be detected since they are characterized by a very large increase of the l/fn component. In general a correlation is found between the intensity of the l/fn component and short circuit current density, fill factor and cell conversion efficiency.
The Structure of Hydrogenated Amorphous Silicon-Carbon Alloys as Investigated by Exafs
Authors: Pascarelli S. , Boscherini F. , Mobilio S. , Evangelisti F.
Published: March 2011

We have studied the local structure of hydrogenated amorphous silicon-carbon alloy films, a-Si1−xCx:H, by measuring the extended x-ray absorption fine-structure (EXAFS) at the Si K edge.

We find that first coordination shell average bond lengths are 2.35 Å for Si-Si and 1.86 Å for Si-C and are constant with concentration to within × 0.015 Å.

By comparing the composition of the first coordination shell around Si with the average concentration we show that the alloy tends to be chemically ordered, in that heteroatomic bonds are preferred.
Control of Photo-Induced Degradation in a-Si:H Prepared from Xe-Diluted Silane
Authors: Mashima Satoshi , Hasezaki Kazuhiro , Suzuki Atsushi , McElheny Peter J. , Matsuda Akihisa
Published: March 2011

Films were prepared by the Xe-dilution method in an attempt to mimic the microstructure found in low-photodegradation deuterated films which show a greater number of clustered deuterium and microvoids when compared to conventional hydrogenated films. Common features were found for the light soaking behaviors in the film properties characterized by the electron spin resonance, gas thermal evolution, Raman spectroscopy, and infrared spectroscopy among deuterated, conventional hydrogenated, and Xe-diluted films.
The Effect of Light Soaking on Electron Mobilities in Hydrogenated Amorphous Silicon
Authors: Antoniadis Homer , Wang Qi , Schiff E. A. , Guha S.
Published: March 2011

Electron drift mobilities μe were measured in undoped hydrogenated amorphous silicon specimens for different light soaking states. Standard transient photocurrent and time-of-flight techniques were employed; the light soaking state was monitored using the electron deep-trapping mobility-lifetime product μτe,t. Two different measurement series are reported. The first series measured a specimen from the reactor at Syracuse at room-temperature. No significant effects of light soaking on μe were found. The second series measured a solar-optimized specimen from Energy Conversion Devices, Inc. below 200°K. In these measurements we found a decrease in μe of about a factor 3.
Barrier Limited Transport Mechanisms in Doped μc-Si and μc-Si,C
Authors: Lucovsky G. , Wang C.
Published: March 2011

An analysis of the room-temperature dark conductivities and activation energies for doped μc-Si and μc-Si,C is used to develop a band alignment model which shows that the maximum attainable dark conductivities in these materials are determined by transport through, or over interfacial potential barriers between Si crystallites, c-Si, and the intervening amorphous regions: a-Si:H or a-Si,C:H, respectively. For all levels of doping in μc-Si,C, the transport is limited by thermionic emission over interfacial barriers at the c-Si/a-Si,C:H interface, placing a significant constraint on applications requiring both high optical transparency and high conductivity.
Influence of Doping on the Structural Properties of Micro-Crystalline Silicon Prepared with the VHF-GD Technique at Low Deposition Temperatures.
Authors: Fingera F. , Prasad K. , Dubail S. , Shah A. , Tang X.-M. , Weber J. , Beyer W.
Published: March 2011

In doped and undoped microcrystalline silicon prepared with Very High Frequency Glow Discharge, hydrogen is found to be mainly located at the grain boundaries from where it desorbs easily at low annealing temperatures. In undoped material hydrogen evolution peaks are between 400°C and 500°C. Upon doping, a new major peak appears at 300°C and a strong reduction of the typical Si-H infrared absorption bands are found for doped samples when annealed up to 300°C. This is accompanied by an increase of the conductivity due to either de-passivation of dopants in the crystallites or a favourable reconstruction at the grain boundaries. Hydrogen profiles show a hydrogen depletion at the film/air interface that is more profound in doped material, thus correlating with the appearance of the low temperature evolution peak. The high free carrier density in the crystallites of the doped material gives rise to strong optical absorption. Although correlating nicely with conductivity, the free carrier absorption cannot be evaluated simply in terms of die Drude theory. In view of the high conductivities and the dominance of Si-H surface bonds we argue that our material does not contain a large amount of amorphous tissue.
Device Application and Growth Mechanism for Hemispherical-Grained Si.
Authors: Watanabe Hirohito , Aoto Nahomi , Adachi Saburo , Kikkawa Takamaro
Published: March 2011

A polycrystalline-silicon surface with hemispherical-grain (HSG) is deposited by low-pressure chemical vapor deposition at the transition temperature of the film structure from amorphous to polycrystalline. The surface area of the HSG-Si film is about twice as large as Si films deposited at other temperatures. It is found that the HSG-Si is not formed during deposition, but formed during annealing of amorphous Si surface after deposition. At the annealing temperature which is maintained to be the transition temperature, HSG-Si is formed by the nuclei generation on the amorphous-Si surface and the outward crystalline growth of grains dixough migration of surface Si atoms. By applying the HSG-Si film as the storage electrode for a 64Mbit dynamic random access memory (DRAM) stacked-capacitor with a SiO2Si3N4 dielectric film, twice the capacitance is obtained. The increase in the capacitance makes it possible to reduce the DRAM cell area, even by using a relatively thick dielectric film for higher reliability. Consequently, the HSG-Si technique is applicable to the fabrication process for 64Mbit and larger DRAMs.
Physical Properties of Undoped and Doped Microcrystalline SiC:H Deposited by PECVD
Authors: Demichelis F. , Pirri C. F. , Tresso E. , Dellamea G. , Rigato V. , Rava P.
Published: March 2011

Experimental results on a systematic investigation on the elemental composition, structural, optical and electrical properties of undoped and doped microcrystalline silicon carbide films deposited by Plasma Enhanced Chemical Vapor Deposition.

The doped samples show high values of dark conductivity accompanied by good optical properties so to satisfy the requirements for heterojunction window material.
Dice (Dynamic Inner Collection Efficiency) Characterization of Photovoltaic Performance in A-Sl Solar Cells
Authors: Ohnishi M. , Takahama T. , Kuwano Y.
Published: March 2011

A new analytical method for amorphous silicon solar cells, called DICE (dynamic inner collection efficiency), has been developed. The depth profile of the photovoltaic characteristics of solar cells under any operating condition are obtained by this method in a non-destructive way for the first time. It was experimentally confirmed by the DICE characterization that 1ight-induced deterioration does not occur homogeneously in the thickness direction of the I-layer, and that the main deterioration region in the I-layer changes according to the duration and load condition of light exposure.

The DICE method also contributed to an improvement in the conversion efficiency of two kinds of a-Si solar cells, an integrated-type submodule and a new type of ultralight flexible module. A total area efficiency of 10.6% was obtained with a size of 10 cm × 10 cm integrated-type a-Si solar cell submodule on a glass substrate, and the world's highest powet—to-weight ratio of 275 mW/g was achieved in the flexible module on a plastic film.
Effect of Light Exposure Conditions on the Light-Induced Degradation in Amorphous Silicon Alloy Solar Cells
Authors: Nakata Y. , Yokota A. , Sannomiya H. , Moriuchi S. , Inoue Y. , Nomoto K. , Itoh M. , Tsuji T.
Published: March 2011

Light-induced changes in current-voltage characteristics of amorphous single-junction solar cells made of silicon alloys, a-SiC, a-Si, and a-SiGe have been studied systematically. The effect of the light intensity and the bias voltage on the light-induced degradation in the conversion efficiency and other photovoltaic parameters has been clarified quantitatively, and it has been shown that the light-induced degradation characteristics of the photovoltaic parameters can be described by a single function of some normalized parameters of exposure condition. Theoretical background for the experimental results is also examined and discussed by applying a defect creation model modified to an active layer of the a-Si alloy solar cells. Utilizing these analytical formula, we propose an accelerated test method by solar simulator indoor measurement instead of natural sunlight outdoor testing.
High Efficiency Stable a-Si Three Junction 12″ × 13″ Modules
Authors: Bennett Murray S. , Catalano A. , Newton J. , Poplawski C. , Arya R. , Rajan K. , Wood G. , Wiedeman S.
Published: March 2011

Three junction a-Si based photovoltaic modules have been made using a design which provides high initial efficiency and good resistance to photodegradation. The cells have a Si/Si/SiGe configuration in which the i-layer in the middle junction is 4000Å thick. The most efficient module measured to date has an aperture area efficiency of 9.82%. This design will limit light-induced efficiency losses to 15% or less, based on small area results, however defect related problems have increased this value to 17 – 23%. Preliminary data on the effect of shunts on stability is presented. We discuss various concerns related to large area deposition and scale-up.
Sub-Bandgap Optical Absorption in Amorphous Silicon using Photo-Pyroelectric Spectroscopy
Authors: Fan J. , Kakalios J.
Published: March 2011

Measurements of the optical absorption spectrum of doped and undoped hydrogenated amorphous silicon (a-Si:H) for photon energies ranging from 0.8 to 2.5 eV are obtained using photo-pyroelectric spectroscopy (PPES). This technique, based upon the pyroelectric effect, has a simpler experimental set-up than photo-thermal deflection spectroscopy, and presently has a sensitivity of ad > 10-3, where d is the sample thickness. In addition, using PPES we have measured the non-radiative quantum efficiency in a-Si:H, and find that it has a strong wavelength dependence for sub-bandgap illumination.
A Spatially Resolved Study of Chemical Vapor Deposition of a-Si:H with Pure Thermal Excitation of Disilane
Authors: Amato G. , Spagnolo R. , Fizzotti F. , Manfredotti C. , Menna P. , Nobile G.
Published: March 2011

Optical, electronic and structural properties of a-Si:H samples grown by Low Pressure Chemical Vapor Deposition have been investigated by means of IR spectroscopy, Raman scattering and Photothermal Deflection Spectros-copy.

Samples grown at different positions along the tube show very different properties that can be related to the amount of H and to the nature of the Si-H bonds.

The most important parameters governing the thermally excited growth of a-Si:H are presented and discussed.
Amorphous Hydrogenated Silicon Carbide Prepared from DC-Biased RF-Plasma-Enhanced Chemical Vapor Deposition
Authors: Lu Hsueh Yi , Petrich Mark A.
Published: March 2011

We present evidence that an independently applied dc bias voltage has a significant effect on the plasma deposition of amorphous hydrogenated silicon carbide. Deposition rates increase with either positive or negative dc voltages applied to the powered rf electrode. The microstructure of the films (as determined by infrared absorption) can be reduced by increasing the plasma potential (positive dc bias voltages). Negative dc biases, or excessively high positive biases, result in increased amounts of film microstructure. Film carbon content is increased when positive biases are applied, but the optical band gaps decrease suggesting increased amounts of graphitic bonding configurations. Negative biases do not change the carbon content of the films, but do increase both deposition rate and microstructure.
Hydrogen Dynamics and Tee Distribution of H Sites in Undoped a-Si:H and a-Ge:H
Authors: Shinar R. , Wu X.-L. , Mitra S. , Shinar J.
Published: March 2011

Secondary ion mass spectrometry and IR studies of long-range hydrogen motion in undoped a-Si:H and a-Ge:H of varying H content and microstructure are reviewed and discussed. In particular, their relation to the multiple trapping (MT) model, the role of microvoids, the significance of the Meyer-Neldel relation (MNR), and the nature of H sites is addressed. It is suggested that while the MT mechanism may be significant in a-Si:H of low H content Cfj, it is largely marginal in films where CH ≥ 10 at.% H and in a-Ge:H. Mono Si-H bonds on microvoid surfaces are apparently deep H trapping sites up to ∼ 400°C, but H is desorbed from such sites in a-Ge:H above 180°C. The MNR between the diffusional activation energy and prefactor is observed among the various a-Si:H and a-Ge:H, but its significance is questionable, and may be due to the MT mechanism only in low H content a-Si:H. The nature of the distribution of H sites is also discussed.
Deposition of Amorphous and Microcrystalline Si,C Alloy Thin Films by a Remote Plasma-Enhanced Chemical-Vapor Deposition Process
Authors: Wang C. , Lucovsky G. , Nemanich R. J.
Published: March 2011

We have extended the remote PECVD process to the deposition of intrinsic and doped, amorphous and microcrystalline silicon, carbon alloy films, a-Si,C:H and μc-Si,C, respectively. The electrical and optical properties of a-Si,C:H deposited by remote PECVD are comparable to those of films deposited by the glow discharge or GD process. The degree of crystallinity in the μc-Si,C alloys, as determined from the relative intensities of crystalline and amorphous features in the Raman spectra, is lower than that of μc-Si films deposited under comparable deposition conditions. The Raman spectra indicate that the crystallites in the μc-Si,C alloys are Si, while the infrared measurements establish that the intervening amorphous component is an a-Si,C:H alloy.
Composition and Properties of PECVD Silicon Nitride Films Deposited from SiH4, N2, He Gases
Authors: Souk J. H. , Parsons G. N. , Batey J.
Published: March 2011

Amorphous silicon nitride films deposited from a gas mixture of SiH4 and N2 with a large flow of He have shown many interesting characteristics. The films show a wide variety of electrical, optical, and mechanical properties with varying amounts of SiH4 and N2. The effect of N2 flow rate on film composition in N2-SiH4 processes is quite different from that of NH3 flow in NH3-SiH4 processes. The films were characterized by measurements of (1) Si-H and N-H bond density and bonded hydrogen content, both from infrared absorption, (2) Si/N ratio, (3) refractive index, (4) film stress, and (5) wet chemical etch rate and (6) electrical properties including current-voltage (I-V) and capacitance-voltage (C-V). We find that adding helium to the PECVD process enhances the incorporation of nitrogen in the film and an optimized flow of SiH4 improves the electrical properties. Films with optimum electrical properties with minimum charge trapping are obtained with N/Si ratio close to 1.33. These films have a small amount of Si-H and N-H bonds, and a low etch rate (> 100 A/min) in aqueous HF solution. The properties of these low temperature (250°C) PECVD nitrides have many similarities with LPCVD nitrides. Compared with films deposited from SiH4, NH3 mixture, these films exhibit very low wet etch rates and much lower H contents, but greater hysteresis in C-V characteristics.
Hopping Conduction in a-Si:H Studied by Transient Photoconductivity with Optical Bias Illumination
Authors: Chen Xing , Jayamaha Upali , Tai Chen-Yu
Published: March 2011

Charge transport in a-Si:H films is studied by measuring the intensity and the rate of decay of the transient photocurrent with optical bias illumination. The optical bias enhancement of the transient photocurrent due to the probe beam decreases at first as the temperature is decreased, reaches a minimum at about 21OK, and then increases as the temperature is further decreased. This observation, together with the decay time measurements, indicates a change in the mechanism of charge propagation from conduction band transport at high temperature to hopping conduction in the low temperature. A theory of hopping conduction in tail states is developed to explain the experimental results. A quantitative comparison of the theoretical and experimental results is made to determine the localization length of the tail states.
Phase Equilibria in Hydrogen Binary Mixtures From 63 to 280 K and Pressures to 6000 Bars
Authors: Streett William B. , Heintz Andreas , Clancy Paulette , Chokappa Dhanraj
Published: March 2011

Experimental measurements have been carried out to determine the compositions of coexisting gas and liquid phases for binary mixtures of hydrogen with the following substances as the second component: nitrogen, carbon monoxide, argon, methane, ethylene, ethane and carbon dioxide. For most of these mixtures the entire region of gas-liquid equilibrium has been explored for the first time. This region is bounded in pressure-temperature space by the vapor-pressure curve of the heavy component, the gas-liquid critical line (where gas and liquid phases become identical) and the 3-phase region solid-liquid-gas. In all of the systems described here the latter two lines intersect to form a critical end point. The general qualitative features of these phase diagrams are described, and compared to those of helium mixtures studied earlier.
Melting Processes and Crystal Structure of Solid 4He Al High Densities
Authors: Besson J.M. , Le Toullec R. , Loubeyre P. , Pinceaux J.P. , Hansen J.P.
Published: March 2011

Solid-fluid equilibrium has been measured in 4He between 7 and 18GPa (220 - 400K). The melting line is fitted up to 280K, for an f.c.c. solid, using an exponential pair potential. Experimental evidence for a b.c.c. phase at high temperature is discussed and compared with two calculations on the relative stability of the two structures.
Vibrational Dephasing and Collision Induced Scattering in Molecular Liquids
Authors: Jonas Jiri
Published: March 2011

The results of several Raman studies of vibrational dephasing in polyatomic molecular liquids at high pressure are reviewed. The density and temperature effects on vibrational dephasing of isotropic Raman bands for different vibrational models are reported for the following liquids: C(CH3)4; Si(CH3)4; Ge(CH3)4; ; Sn(CH3)4and isobutylene CH2; = C(CH3)2.The experimental data are used to test the current theoretical models of vibrational dephasing. Selected results of our high pressure experiments on collision induced scattering in polyatomic molecular liquids demonstrate well the essential role of high pressure in studying these phenomena.
Structure Transition of Metallic Glasses of Alloys Annealed at High Pressure for the Exploration of Superconducting Compounds
Authors: Shou-an HE , Wen-Kui Wang , Iwasaki Hiroshi , Syono Yasuhiko
Published: March 2011

In this article, the formation of superconducting compounds through structure transition of metallic glasses at high pressure high temperature are emphasized, and investigations on structure transition of metallic glasses made of niobiun alloys and lanthanun alloys are summarized.
Optimizing the Interface of Cylinders in Composite Design of Pressure Vessels
Authors: Newhall Donald H.
Published: March 2011

A method is presented of designing optimum proportions for cylinders in the composite design of a pressure vessel that limits catastrophic fatigue failure.
Monitoring the Progress of Partial Autofrettage
Authors: Newhall Donald H.
Published: March 2011

A method is shown to monitor the depth of plastic yielding, the permanent expansion of the cylinder and the amount of residual strain during hydraulic autofrettage. The significance of the residual stress is shown graphically.
The Nature of the Critical Point Phase Transition in Metals
Authors: Hensel F.
Published: March 2011

The paper presents recent experimental results of optical, electrical and thermophysical properties of fluid metals in the vicinity of the critical point. Special attention will be paid to the metal-nonmetal transition which occurs at reduced densities of a fluid metal and the plasma phase transitions which are connected with ionization phenomena and many particle interactions in the dense vapor. The interrelation between the gas-liquid critical point phase transition and these electronic transitions and their effect on the critical phenomena will be discussed.
Equation of State of Fluid NH3 from P-V-T and Ultrasound Measurements to 12 Kbar
Authors: Mills R. L. , Liebenberg D. H. , Le Sar R. , Pruzan PH.
Published: March 2011

A piston-cylinder apparatus was used to measure the pressure, volume, temperature, and ultrasonic velocity (P,V,T,u) of fluid NH3 from 195 to 320 K at pressures up to 12 kbar. Over 1200 sets of P-V-T-u and P-V-T data were fitted to a Tait-type equation of state (EOS) by non-linear least-squares minimization. With quadratic terms in T for the two fitted parameters, the rms deviation is ± 0.2% in V and ± 0.9% in u, which is comparable to the experimental error. The simple Tait EOS is useful over the entire fluid range between the vaporization and melting curves up to T exceeding room temperature. Measurements of u and calculations of the constant-pressure heat capacity Cp show regular behavior, differing noticeably from values given by a 44-parameter EOS recently published by NBS. It is concluded that incorporating u in the formulation of an EOS improves its self consistency markedly.
Direct Imaging of Ordering in Si-Ge Alloys, Ultrathin Superlattices, and Buried Ge Layers
Authors: Jesson D. E. , Pennycook S. J. , Baribeau J. -M.
Published: March 2011

We review recent Z-contrast imaging studies of Si-Ge ultrathin superlattices, alloys, and buried Ge layers. It is found that whenever Si is deposited onto a Ge (2 × 1) surface, Ge is pumped into the growing Si layer, and this is accompanied by interfacial ordering. This is explained by a novel Ge atom pump mechanism which occurs during MBE growth. Codeposition and alloy growth results in long range (111) ordering as a consequence of lateral segregation during nonequilibrium growth.
Electron Microdiffraction Investigation of a GexSi1−x Buffer for Strain-Symmetrised Superlattice Structures
Authors: Pike W. T. , Kubiak R. A. A. , Parker E. H. C. , Whall T. E.
Published: March 2011

A candidate GeSi buffer layer structure suitable for strain-symmetrised GeSi/Si superlattice overgrowth is grown by molecular-beam epitaxy and its strain state characterised using microdiffraction in a dedicated scanning transmission electron microscope. The structure consists of five alloy layers of increasing Ge concentration grown on a Si (100) substrate, with all but the last annealed at high temperature. Analysis of higher order Laue zone deficit lines in the microdiffraction patterns acquired from each layer indicate that relaxation is complete in all the layers. Images of the structure in the transmission electron microscope show good crystallinity of the final layer with low concentrations of threading dislocations.
The Selective Epitaxy of Silicon at Low Temperatures
Authors: Lou Jen-Chung , Oldham William G. , Kawayoshi Harry , Ling Peiching
Published: March 2011

Low-temperature selective epitaxial growth (SEG) of silicon using a dichlorosilane-hydrogen mixture in an LPCVD hot-wall reactor has been discussed with respect to the wafer preparation and the deposition cycle. The surface morphology and the quality of epilayers are strongly affected by residual oxide islands at interface. A reduction of local growth rate near interfacial oxides is attributed to the dissolution of oxide at interface, and this reduction can lead to pits and textured features on the Si epitaxial surface. An ex-situ HF vapor or an HF dip with an in-situ small DCS 900°C prebake step can completely remove surface oxide prior to the deposition and achieve defect-free Si epilayers at the deposition temperatures of 850°C and 800°C. It is also found that fluorine atoms can play a major role in the removal of surface oxide.
Electrical and Optical Properties of Erbium in MBE Silicon and Si/Ge Alloys
Authors: Efeoglu H. , Evans J. H. , Langer J. M. , Peaker A. R. , Rowell N. L. , Noel J-P , Perovic D. D. , Jackman T. E. , Houghton D. C.
Published: March 2011

This paper reports the incorporation of erbium into MBE Si and Si/Ge alloys with substrate temperatures of 500°C and 700°C. Using a solid source MBE system, concentrations of erbium between 1018 and 1022 cm−3 have been studied by photoluminescence, electrical measurements, SIMS and TEM. We find no shallow donors or acceptors attributable to erbium but we observe a high concentration of deep states with an activation energy of ∼360 meV. The photoluminescence output is of greatest magnitude when [Er] =2 × 1018 cm−3. Above this concentration the onset of erbium precipitates can just be observed using TEM and at even higher concentrations structured growths of erbium suicide are apparent. The effect on the optical activity of Si:Er that has subsequently been implanted with oxygen is also reported.
Wave Function Engineering of Linear and Non-Linear Optical Response in Si-Ge Quantum Well Structures and Superlattices
Authors: Jaros M. , Turton R. J. , Wong K. B.
Published: March 2011

We show that the infinite Si-Ge superlattices predicted to exhibit strong optical transitions across the fundamental gap and between conduction subbands also give rise to significant optical nonlinearities. Efficient optical transitions can also be achieved in finite-length structures grown on Si or Ge substrates. However, the zone folding argument does not apply and the electronic structure strongly reflects the finite length of such systems.