bluuebunny/crossref_metadata_2025_split huggingface dataset:
Study of Glass Transition of a Poly(Imide Siloxane) Copolymer Using Thermal Analysis
Authors: Shi L. T. 
Published: March 2011

AbstractFilms of a poly(imidc siloxane) thermoplastic copolymer with a thickness of 0.5 mm have been characterized using thermal analytic techniques including DSC, TMA, and DMA. It was found that the glass transition temperature depends not only on heating rates but also on loading conditions. The mechanism of the glass transition in this copolymer is shown to involve two interconnected steps, namely volume change and phase ordering.
Structure and Dynamics of Syndiotactic Poly(n-Butyl Methacrylate) Near the Glass Transition
Authors: Paiterson G. D. , Jue P. K. , Stevens J. R. 
Published: March 2011

AbstractAn optically homogeneous sample of highly syndiotactic poly(n-butyl methacrylate) (PBMA) has been prepared. The glass transition temperature was observed to be Tg=55C. Measurements of the scattered intensity of the sample followed the expected behavior for a pure liquid above Tg. The intensity rose as the sample was cooled further towards the glass transition temperature for atactic PBMA. These results illuminate the importance of regions of different stereoisomers in methacrylate polymers. Measurements of the Rayleigh- Brillouin spectrum were carried out from -15 to 130 C. The ratio of the the central peak intensity to the Brillouin intensities at temperatures above Tg was consistent with a viscoelastic liquid and had a magnitude near 3. The Brillouin linewidth remained large near Tg. and decreased continuosly with no apparent change in slope in the glass transition region. The presence and importance of rapid motions in polymers near the glass transistion is demonstrated by these results. Slowly relaxing density fluctuations near Tg. were measured by photon correlation spectroscopy. Relaxation functions were obtained from 10−6 to 10 s. Average relaxation times <τ> were obtained from the integral of the relaxation function and were found to follow the relation <τ>=Aexp(B/(T−T0)), where for our sample B=2940K and T0=273K. The observed relaxation function decayed over a wider time range as the sample was cooled. Quantitative analysis of this effect using the Williams-Watts empirical function yielded a decrease in β from 0.35 at 90 C to 0.18 at 65 C. The relaxation functions were also analyzed to give a distribution of relaxation rates. The observed distributions were bimodal at 70 and 80 C. The two features behaved in a manner consistent with the primary and secondary relaxations observed for methacrylate polymers by other techniques.
Theory of Spinodal Decomposition in Very Viscous Binary Liquid Mixtures
Authors: Jäckle Josef , Pieroth M. 
Published: March 2011

AbstractWe have developed a theory for the evolution of concentration fluctuations after a temperature quench which takes the effect of slow structural relaxation into account. In its linear and non-linear forms, it generalizes the theories of Cahn, Hilliard and Cook, and of Langer, Bar-on and Miller.
Bending and Torsional Fatigue of Nylon 66 Monofilaments
Authors: Toney Mary M. , Schwartz Peter 
Published: March 2011

AbstractUsing newly developed test equipment, the fatigue behavior of nylon 66 monofilaments was studied under two loading conditions, pure bending or simple torsion. In each case, the deformation was applied in balanced cycles of positive and negative strains. For each mode, results are expressed in terms of the measured decay in stiffness with numbers of cycles over a range of maximum applied strain levels. Fatigue lifetimes are presented in S-N format where the log number of cycles of fatigue for a 40% decay in stiffness (N) is plotted as a function of applied strain (S). The failure mechanism for these fibers in each fatigue mode reflects the morphology of semicrystalline oriented synthetic fibers. In torsion, many longitudinal cracks formed around the perimeter of the fiber as the result of cleavage of the relatively weak interfibrillar bonds in the nylon 66 fibers. In bending, cracks grew across the fiber at an oblique angle to the fiber axis along kink band boundaries.
Cooperative Domain Model for Yield Phenomenon
Authors: Matsuoka S. 
Published: March 2011

AbstractA molecular model for cooperative segmental relaxation has been proposed, which leads to the Adam-Gibbs type dependence of the characteristic relaxation time on temperature and the configurational entropy. When the size distribution for the cooperative domains is introduced, the resulting relaxation spectrum is similar to the Kohlrausch-Williams-Watts (KWW) equation in the frequency range near the loss maximum, but the fit is actually better in the high frequency extremes where the KWW equation always underpredicts the intensity. The model also predicts the broad spread of the spectrum in the non-equilibrium state from the distribution of the apparent activation energy arising from the different sizes of domains.We now extend this model to the yield phenomenon in glassy polymers. Under the stress, a domain has two alternatives to dissipate the strain energy. One way is to relieve the stress at the rate dictated by the linear viscoelastic relaxation time. This process is possible only when the strain rate is low. At above a certain strain rate, the stress reaches the strength of the domain, forcing to irreversibly break up the domain structure in the manner that can be described by the classical plasticity. It can be shown that the yield stress of a real polymer is a combination of the above two types of stresses. Namely, at a given strain rate, the small domains with short relaxation time will attain the linear viscoelastic steady stress while the larger domains reach the (limiting) plastic yield stress. Thus, the strain rate dependence of yield stress can be predicted from the linear viscoelastic relaxation spectra, even though the yield phenomenon is clearly in the realm of nonlinear viscoelasticity.
Torsional Relaxation and Volume Response During Physical Aging in Epoxy Glasses Subjected to Large Torsional Deformations
Authors: Santore Maria M. , McKenna Gregory B. 
Published: March 2011

AbstractWe present torsional dilatometry experiments to simultaneously measure torque relaxation and volume recovery in an epoxy glass quenched from above its glass transition temperature to below it. Two strain histories are employed: one with strains of equal sizes and a second where small strains follow a large one. The baseline for the thermally induced volume recovery is insensitive to intermittent torsional strains whose magnitude can be well into the non-linear regime. The torque relaxations from equal intermittent mechanical stimuli can be superposed by a time-aging time shift in a way that indicates fast changes cease to occur at ∼104 seconds after the quench, a “mechanical equilibration” time. Stimuli of different sizes can confound superposition via nonlinear effects, but do not affect the ultimate volume recovery of the glass or its mechanical equilibration time. Our results show the signature of rejuvenation; however, this may result from the nonlinear response of the material in a nonisochoric strain history. Our data firmly show that mechanical stimuli do not erase aging or rejuvenate this epoxy.
Binary Optics Microlens Arrays in CdTe.
Authors: Stem M.B. , Delaney W.F. , Holz M. , Kunz K.P. , Maschhoff K.R. , Welsch J. 
Published: March 2011

ABSTRACTArrays of miniature focusing optics located at the focal plane can improve the performance of focal plane systems. By more completely collecting the light at the focal plane and concentrating it into a smaller spot size on the detector plane, the photodetector area can be substantially reduced. Increased gamma radiation hardening and noise reduction result from the decrease in photodetector surface area. Binary optics technology, a process for fabricating large arrays of diffractive optical elements, is especially attractive for infrared materials. In this paper, diffractive Fresnel microlens arrays containing over six thousand F/0.9 lenslets are patterned in the surface of CdTe substrates by successive photolithographic and Ar+ ion-beam-etching steps. Results on smaller arrays of monolithically integrated binary-optics lenslets with II-VI detectors, demonstrating enhanced photodetector responsivities, are presented for the first time.
Stabilisation of Hg1-xCdxTe:Hg1-yCdyTex ≠ y) Heterointerfaces and Applications in Infra Red Devices
Authors: Clifton Paul A. , Brown Paul D. 
Published: March 2011

ABSTRACTThe interface between Hg1-xCdxTe(0 ≦ x ≦ 1) and Hg1-yCdyTe(0 ≦ y ≦ 1) epitaxial layers of different composition (x ≠ y) is unstable with regard to the intermixing of the Hg and Cd cations within the Group II sublattice. This phenomenon may give rise to long-term stability problems in HgTe-(Hg,Cd)Te superlattices and composition grading between (Hg,Cd)Te absorber layers and CdTe buffer or passivation layers in epitaxial infra red detectors. In this paper, a novel approach to the inhibition of interdiffusion in these systems is discussed. This involves the growth of an intervening ZnTe barrier layer at the heterointerface between two (Hg,Cd)Te layers. Initial results are presented which indicate the effectiveness of this technique in reducing interdiffusion in an experimental heterostructure grown by MOVPE. Some possible applications in a variety of HgTe-based long wavelength devices are discussed.
Development of Infrared Detectors Based on Type II, InAsSb Strained-Layer Superlattices
Authors: Kurtz Steven R. 
Published: March 2011

ABSTRACTAn overview is provided of long wavelength, photovoltaic detectors constructed with type II (also known as “staggered”), III-V superlattices. Specifically, the electronic properties of InAsSb strained-layer superlattices and prototype detectors utilizing these structures are described.
Characterization of Gasb-Based Alloy Semiconductors
Authors: Uekita H. , Kitamura N. , Ichimura M. , Usami A. , Wada T. 
Published: March 2011

ABSTRACTGaSb, AlxGa1-xSb, and AlxGa1-xSb epitaxial layers were grown by the liquid-phase epitaxy and characterized by photoluminescence, Raman spectroscopy, and double-crystal X-ray diffraction. The concentration of residual acceptors which are related to structural defects decreased with lowering growth temperature, but the GaSb epitaxial layer grown at an extremely low temperature of 270°C had poor crystalline quality. The AlxGa1-xSb (x≥0.15) and AlxGa1-xSb (x=0.02) epitaxial layers grown at 270 °C, however, had much better quality than the GaSb epitaxial layer grown at the same temperature.
Optical Properties of MBE-Grown Gainassb
Authors: Bi Wengang , Li Aizhen , Tan Songsheng 
Published: March 2011

ABSTRACTThe infrared optical absorption properties near and above the fundamental absorption edge of MBE grown undoped GaInAsSb quaternary semiconductor alloy deposited on GaSb and GaAs substrates have been measured and analyzed at room temperature by means of a Fourier Transform Infrared Spectrometer, and were found to be fully characterized by the interband transition theory and Urbach's rule. The optical band gap of MBE-GaInAsSb has been determined using a linear extrapolation of (ɑhv )2 as a function of the photon energy hv, and the refractive index n deduced from the interference pattern, which shows good agreement with the theory of Sadao Adachi's.
Interface Properties of Heterovalent InSb Multilayer Structures
Authors: Kobayashi M. , Gunshor R. L. , Glenn J. L. , O Sungki , Han J. , Menke D.R. , Kolodziejski L. A. 
Published: March 2011

ABSTRACTMultilayer InSb/CdTe and InSb/MnTe heterostructures are grown by molecular beam epitaxy. The analysis of multilayer structures by transmission electron microscopy (TEM) and x-ray rocking curves confirms the presence of periodic heterointerfaces. TEM, x-ray, and x-ray photoelectron spectroscopy (XPS) measurements are found to provide a sensitive indicator for the presence of ultra-thin interfacial layers. Double barrier structures in the MnTe/InSb/MnTe configuration exhibit the negative differential resistance which is characteristic of resonant tunneling diodes.
Rbs and Pixe Analysis Of Hg1-xCdxTe grown by MOCVD.
Authors: Russo S.P. , Elliman R.G. , Johnston P.N. , Pain G.N. 
Published: March 2011

ABSTRACTThe techniques, Particle Induced X-ray Emission (PIXE) and Rutherford Backscattering Spectrometry (RBS) have been used to investigate compositional and thickness uniformity of Hg1-xCdxTe (MCT) grown on GaAs substrates by Metal Organic Chemical Vapour Deposition (MOCVD). Composition and thickness variations are reported for orientations perpendicular and parallel to gas flow in the MOCVD reactor. Crystalline quality of the MCT layer was also determined by RBS channelling analysis.
Raman and Secondary Ion Mass Spectroscopy of Epitaxial CdTe/InSb Interfaces Grown by Low-Energy Bias Sputtering
Authors: Das Suhit R. , Lockwood David J. , Rolfe Stephen J. , McCaffrey John P. , Cook John G. 
Published: March 2011

ABSTRACTHeteroepitaxial (100)CdTe || (100)InSb structures have been fabricated by growing CdTe epilayers, at growth temperatures below 200°C, on single crystal InSb substrates by low-energy bias sputtering. Controlled low-energy ion bombardment at the substrate was employed to clean the growth surface in-situ just prior to film deposition and to modify the growth kinetics and enhance adatom mobility during deposition. Raman spectroscopy of the interface revealed no evidence of In2Te3 and secondary ion mass spectroscopy showed the interface to be chemically abrupt.
Reactive Ion Etching of GaSb, (Ai,Ga)Sb, and InAs for Novel Device Applications.
Authors: La Tulipe D.C. , Frank D.J. , Munekata H. 
Published: March 2011

ABSTRACT-Although a variety of novel device proposals for GaSb/(Al,Ga)Sb/InAs heterostructures have been made, relatively little is known about processing these materials. We have studied the reactive ion etching characteristics of GaSb, (AI,Ga)Sb, and InAs in both methane/ hydrogen and chlorine gas chemistries. At conditions similar to those reported elsewhere for RIE of InP and GaAs in CH4/H2, the etch rate of (AI,Ga)Sb was found to be near zero, while GaSb and InAs etched at 200Å/minute. Under conditions where the etch mechanism is primarily physical sputtering, the three compounds etch at similar rates. Etching in Cl2 was found to yield anisotropic profiles, with the etch rate of (AI,Ga)Sb increasing with Al mole fraction, while InAs remains unetched. Damage to an InAs “stop layer” was investigated by sheet resistance and mobility measurements. These etching techniques were used to fabricate a novel InAs-channel FET composed of these materials. Several scanning electron micrographs of etching results are shown along with preliminary electrical characteristics.
Ion Implantation in InSb Grown on GaAs
Authors: Rao M. V. , Echard R. , Thompson P. E. , Berry A. K. , Mulpuri S. , Moore F. G. 
Published: March 2011

ABSTRACTBe, S, Si, and Ne implantations were performed at room temperature into InSb layers grown on undoped semi-insulating GaAs substrates. The implant damage in InSb is of ntype behavior. The implanted material was subjected to both isochronal and isothermal annealing schemes using a molybdenum strip heater. A maximum p-type activation of 90 % and si-type activation of 16 % was achieved for Be and S implants, respectively. Si implant has an amphoteric doping behavior.
The Epitaxial Growth by Movpe of (Hg,Mn)Te On (001) Gaas Substrates
Authors: Al-Allak H. M. , Brinkman A. W. , Clifton P. A. , Brown P. D. 
Published: March 2011

ABSTRACTEpitaxial thin films of the dilute magnetic semiconductor Hg1-xMnxTe have been grown by MOVPE on (100) GaAs substrate with or without buffer layers. Deposition took place in a horizontal, atmospheric pressure reactor at temperatures in the range 350–400° C, using tricarbonyl (methyl cyclopentadienyl) manganese, di-isopropyl tellurium and elemental mercury. Buffer layers consisted of thin layers of ZnTe and an upper thick layer (∼1μm) of CdTe. The good crystallinity was confirmed by RHEED and double crystal x-ray diffraction with rocking curve widths of 500–600 arc. sec. for non-buffered layers, and 315 arc. sec. for buffered layers. TEM investigations show that layers grown on buffered substrates had improved microstructure defect content. Electrical transport measurements revealed that as-grown layers were ptype with Hall mobilities in excess of 0.1 m2V−1s−1.
A Systematic TEM and Rheed Investigation of the MBE Growth of InxGa1−xAs a Function of Composition
Authors: Edirisinghe S.P. , Staton-Bevan A.E. , Pashley D.W. , Fawcett P. , Joyce B.A. 
Published: March 2011

ABSTRACT0.15µm epilayers of InxGa1−xAs grown on GaAs (001) by MBE, having In concentrations in the range x = 0.05 - 0.30, have been investigated using RHEED and TEM. RHEED patterns indicate a 2-D growth mode for low In concentrations changing to Stranski-Krastanov growth for x > 0.30. TEM showed misfit dislocations for x > 0.05 only, which were found to relieve only a small part of the misfit strain. Although threading dislocations were rarely found in the epilayers, dislocations originating at the interface and penetrating the buffer layer were observed for 0.1 < x < 0.25.
Photovoltaic Infrared Devices in Epitaxial Narrow Gap Lead Chalcogenides on Silicon Substrates
Authors: Zogg H. , Maissen C. , Masek J. , Hoshino T. , Blunier S. 
Published: March 2011

ABSTRACTWe review MBE growth of epitaxial IV-VI layers on Si(111) substrates and fabrication of photovoltaic infrared devices in the layers. Cut-off wavelengths are chemically tailored from 3 µm up to above 12 µm by using PbS, PbTe, Pb1−xEuxSe and Pb1−xSnxSe. An intermediate epitaxial stacked CaF2-BaF2 bilayer of 200 nm thickness serves to overcome the large lattice- and thermal expansion mismatch, and device quality IV-VI layers are obtained with layer thicknesses of only 2–4 µm. The layers are untwinned single crystal, exhibit perfectly smooth surfaces with surface defect concentrations down to 103 cm−2, and x-ray rocking curve line-width of ≈150 arcsec. Despite the large thermal expansion mismatch, the (111)-oriented layers withstand multiple cooling cycles down to 15K without problems.Although our IR-device fabrication technique is far from optimized, the sensitivities of our best photovoltaic sensors are comparable to MCT. IV-VI on Si IR sensors have the potential for a low cost technique of large IR focal plane arrays both for the 3–5 µm and 8–12 µm range because of the easy fabrication procedure and because uniformity problems are much less severe in IV-Vls due to the weaker dependence of the band-gap of Pb1−xSnxSe on composition x compared to MCT.
Experimental Method of Determination of Structural Correlations in Surface Layers of Oxide Glass
Authors: BochyŃski Zenon 
Published: March 2011

ABSTRACTA new method of X-ray diffraction analysis of structural inhomogeneities in the quartz/Si02/n based inorganic glasses is presented. The method enables the determination of structural changes occuring in the real nodal lattice in the regions of 10…20 Å or more as well as substructural changes in the regions 5…15 Å comparable to the molecular size of SiO2…SiO4. In consequence these changes can be correlated with approximate nodal lattice models of different degree of ordering. The applied method provided the possibility of constructing structural models of nodal lattices describing the surface and inner layers of the real glasses, changes in the local inhomogeneities as well as boundaries in water-gel associates.
Chemical Design and Structural Chemistry of Lwir Optical Materials
Authors: Lowe-Ma C.K. , Kipp D.O. , Vanderah T.A. 
Published: March 2011

ABSTRACTSome applications for long-wavelength infrared (LWIR) windows require environmental durability and mechanical strength in addition to infrared optical transparency; i.e., the windows must simultaneously serve as optical and as structural ceramics. The requirement of optical transparency at long IR wavelengths eliminates from consideration all ceramics based on oxides and other light-anion compounds, making this a particularly difficult materials problem. The structure-property relationships and chemical rationale used to guide both the screening of known compounds and the synthesis of new compounds likely to possess the desired properties rely on factors such as atomic mass, electronic configuration, coordination number, and crystal structure type.Our research has included the directed synthesis and characterization of a number of ternary indium sulfides as well as ternary calcium yttrium sulfides. Ternary indium sulfides feature both tetrahedral and octahedral coordination of indium. The crystal structure of KInS2 and its relationship to structures observed in other systems such as AIn2S4, A = Ca,Sr,Ba, is described. The crystal structure of CaY2S4 along with studies of yttrium-doped CaS are also described. The AIn2S4 compounds are more fully described in references [1] and [2].
Tem Studies of CD:ZN:TE-Based II-VI Superlattices and Epitaxial Layers
Authors: Brown P.D. , Kelly H. , Clifton P.A. , Mullins J.T. , Simmons M.Y. , Durose K. , Brinkman A.W. , Golding T.D. , Dinan J. 
Published: March 2011

ABSTRACTA TEM study is presented charting the development of a MOVPE growth process for the deposition of CdTe//ZnTe superlattices. In addition, MBE grown (Cd,Zn)Te//CdTe superlattices deposited onto GaAs and InSb substrates are compared.
A Study of the Interface Between THM Grown MCT Crystals and Cdte Seeds.
Authors: Shilo I. , Kedar E. , Szafranek D. 
Published: March 2011

ABSTRACTHgCdTe crystals have been grown from CdTe seeds by the travelling heater method (THM). Three different kinds of interfaces between the growing crystal and the seed were found: a sharp planar interface; a non-planar interface which is caused by meltback near the ampoule walls; a diffuse zone, where an interface cannot be discerned. A correlation was found between the initial growth parameters and the interface structure. Microprobe analysis revealed a boundary layer which, in the case of the planar interface, had an unusual shape. This layer had a thickness varying from 400 to 800 microns. It consisted mostly of HgTe, and contained holes as defects.
GaAs Quantum Well Infrared Photodetectors Grown by OMVPE
Authors: Hobson W. S. , Zussman A. , Levine B. F. , Pearton S. J. , Swaminathan V. , Luther L. C. 
Published: March 2011

ABSTRACTWe have grown, fabricated, and measured GaAs quantum well infrared photodetectors (QWIPs) using organometallic vapor phase epitaxy (OMVPE). The epitaxial layers were characterized by electrochemical capacitance-voltage profiling, double-crystal X-ray diffraction, cathodoluminescence, and infrared absorption. Dark current, responsivity spectra, and detectivity were measured for the QWIP devices. The performance of these QWIPs was comparable to detectors grown using MBE. This is of importance since OMVPE has advantages for wafer throughout and cost.
The Role of Rare Earths in Narrow Energy Gap Semiconductors
Authors: Partin D.L. , Heremans J. , Morelli D.T. , Thrush C.M. 
Published: March 2011

ABSTRACTNarrow energy band gap semiconductors are potentially useful for various devices, including infrared detectors and diode lasers. Rare earth elements have been introduced into lead chalcogenide semiconductors using the molecular beam epitaxy growth process. Europium and ytterbium increase the energy band gap, and nearly lattice-matched heterojunctions have been grown. In some cases, valence changes in the rare earth element cause doping of the alloy. Some initial investigations of the addition of europium to indium antimonide will also be reported, including the variation of lattice parameter and optical transmission with composition and a negative magnetoresistance effect.