bluuebunny/crossref_metadata_2025_split huggingface dataset:
A Model for Asymmetric Hysteresis in Piezoceramic Materials
Authors: Smith R.C. , Ounaies Z. 
Published: April 2011

AbstractThis paper focuses on the characterization of hysteresis exhibited by piezoelectric materials at moderate to high field levels. For soft materials in which dipoles are easily reconfigured, the hysteresis loop is observed to be rotationally symmetric about the zero field, zero polarization point and symmetric models can be employed. In harder materials, however, the loops are no longer rotationally symmetric which necessitates the development of commensurate characterization techniques. The model considered here is based upon the quantification of reversible and irreversible changes in polarization due to bending and translation of domain walls pinned at inclusions inherent to the materials. The performance of the model is illustrated through comparison with PZT4 data
Sr(Ti,Fe)O3: Materials for a Temperature Independent Resistive Oxygen Sensor
Authors: Menesklou W. , Schreiner H.-J. , Moos R. , Härdtl K.H. , Ivers-Tiffée E. 
Published: April 2011

AbstractThe metal oxide strontium titanate is a promising material for resistive high temperature oxygen sensors (T > 1000 K), that can be applied to control combustion engines. However, a disadvantage of this and of many other metal oxides is the strong temperature dependence of conductivity. In this work, we show that the temperature dependence of Sr(Ti1-x, Fex)O3-δ can be adjusted by the iron content. For x = 0.35 the thermal activation of the conductivity is near zero for a distinct temperature and oxygen partial pressure range (T = 1000 K - 1200 K, PO2 = 10 to 105 Pa). Short response times in the range of 10 ms can be realized by using sensors in thick film technology
Processing and Characterization of Cofired Capacitor and Varistor Ceramics
Authors: Malič B. , Kosec M. , Razinger J. , Živič Z. 
Published: April 2011

AbstractThe aim of the present work was to prepare a monolithic varistor-capacitor element from a commercial ZnO-based varistor and a relaxor based on lead-magnesium niobate. The materials were chosen on the basis of similar sintering temperatures, in the range from 900 to 1000°C. “Sandwich”-structured composite-pellets were uniaxially dry-pressed and sintered at the conditions that lead to shrinkages observed on the pellets of separately sintered materials. The microstructural analysis of the ‘sandwich’ interface revealed a good contact between the two parts without a noticeable interaction layer. Selected functional properties of both varistor and relaxor parts were adequate
Aluminum Nitride Thin Films for Microwave Filter and Microsystem Applications
Authors: Dubois M.-A. , Muralt P. , Sagalowicz L. 
Published: April 2011

AbstractResults on growth, characterization and resonator applications of AIN thin films grown by pulsed dc reactive magnetron sputtering are presented. In order to allow deposition on electrode films, moderate deposition temperatures of 300 to 400 °C were applied. On (001) sapphire, monocrystalline films were obtained. On (111)-textured platinum films, a columnar and (001) textured microstructure was established which exhibited quasi single-crystal properties in relevant materials constants, such as e33, e31, and c33. The films have been successfully applied in bulk wave resonators operating at GHz frequencies, allowing for the derivation of acoustic parameters. A zero thermal frequency drift was obtained with a membrane resonator due to a SiO2 layer as compensating element.
Wafer-Level Strength and Fracture Toughness Testing of Surface-Micromachined MEMS Devices
Authors: Kahn H. , Tayebi N. , Ballarini R. , Mullen R.L. , Heuer A.H. 
Published: April 2011

AbstractDetermination of the mechanical properties of MEMS (microelectromechanical systems) materials is necessary for accurate device design and reliability prediction. This is most unambiguously performed using MEMS-fabricated test specimens and MEMS loading devices. We describe here a wafer-level technique for measuring the bend strength, fracture toughness, and tensile strength of MEMS materials. The bend strengths of surface-micromachined polysilicon, amorphous silicon, and polycrystalline 3C SiC are 5.1±1.0, 10.1±2.0, and 9.0±1.0 GPa, respectively. The fracture toughness of undoped and P-doped polysilicon is 1.2±0.2 MPa√m, and the tensile strength of polycrystalline 3C SiC is 3.2±1.2 GPa. These results include the first report of the mechanical strength of micromachined polycrystalline 3C SiC.
Ferroelectric Composite of Ba1−xSrxTiO3 With Al2O3 and MgO Synthesized by Sol-Gel Method
Authors: Sharma Pramod K. , Jose K. A. , Varadan V. V. , Varadan V. K. 
Published: April 2011

AbstractBarium strontium titanate with low dielectric constant, low loss tangent and high tunability, has unique application as phase shifter in radar and antenna. This work presents an alternative fabrication of the composite of barium strontium titanate with metal oxides such as Al2O3 and MgO. Ba1−xSrxTiO3 (BST), xergels of various compositions (x = 0.2, 0.4, 0.5 and 0.6) were prepared by sol-gel method. Xerogels were calcined at 800 °C. The structure of the final powders was investigated by x-ray diffraction (XRD). The resultant BST was then mixed with metal oxides in the desired weight percentage and ball milled in an organic solvent (ethyl alcohol) with a binder (acrylic polymer). The final samples were sintered at 1250 °C in air. The dielectric properties of the composites were determined by using impedance analyzer at the frequency of 1MHz. This work has reported the effect of Al2O3 and MgO, on the electronic behavior of the final BST-metal oxide composites.
Deposition of Crack-Free BaTiO3 and Pb(Zr,Ti)O3 Films Over 1 μm Thick Via Single-Step Dip-Coating
Authors: Kozuka H. , Kajimura M. , Katayama K. , Isota Y. , Hirano T. 
Published: April 2011

AbstractBaTiO3 and PZT films were prepared by single-step dip-coating from alkoxide-acetate solutions containing polyvinylpyrrolidone (PVP). Crack-free BaTiO3 and PZT films over 1 μm in thickness were obtained via single-step deposition. Stepwise heating of the gel films was found to improve densification of BaTiO3 films, reducing the thickness and increasing the optical transmittance, which was not, however, the case with PZT films, where the stepwise heating rather induced crack formation, leading to degraded transmittance. Residual stress was evaluated on spin-coating BaTiO3 films by measuring the substrate curvature, where a significant reduction in tensile stress was found to be caused by PVP.
Tuned Infrared Emission From Lithographically-Defined Silicon Surface Structures
Authors: Daly James T. , Johnson Edward A. , Stevenson William A. , Greenwald Anton C. , A. Wollam John , George Thomas , Jones Eric W. 
Published: April 2011

AbstractPhotonic bandgap structures have received much attention as optical and infrared filters with controllable narrow-band absorbance. There is a need, however, for the same kind of control of the thermal emittance of surfaces for applications ranging from control of radiative heat transfer to gas absorption spectroscopy. We report on the fabrication of photonic bandgap structures on silicon surfaces using standard lithographic techniques. Substrate resistivity varied from n− to n+ and in some cases background surface emissivity was suppressed with a high reflectivity coating such as aluminum. We have measured the infrared reflectance and emittance of these patterned surfaces. Peak absorption wavelength and spectral purity (linewidth) correlate with photonic bandgap feature size and spacing as well as surface conductivity. We demonstrate band emission with a sharp short wavelength cut-off from these structures when heated.
Temperature Dependence of Photoresponse in p-Type GaAs/AlGaAs Multiple Quantum Wells: Theory and Experiment
Authors: Szmulowicz F. , Shen A. , Liu H. C. , Brown G. J. , Wasilewski Z. R. , Buchanan M. 
Published: April 2011

AbstractThis paper describes a study of the photoresponse of long-wavelength (LWIR) and mid-infrared (MWIR) p-type GaAs/AlGaAs quantum well infrared photodetectors (QWIPs) as a function of temperature and QWIP parameters. Using an 8x8 envelope-function model (EFA), we designed and calculated the optical absorption of several bound-to-continuum (BC) structures, with the optimum designs corresponding to the second light hole level (LH2) coincident with the top of the well. For the temperature-dependent study, one non-optimized LWIR and one optimized MWIR samples were grown by MBE and their photoresponse and absorption characteristics measured to test the theory. The theory shows that the placement of the LH2 resonance at the top of the well for the optimized sample and the presence of light-hole-like quasi-bound states within the heavy-hole continuum for the nonoptimized sample account for their markedly different thermal and polarization characteristics. In particular, the theory predicts that, for the LWIR sample, the LH-like quasi-bound states should lead to an increased Ppolarized photoresponse as a function of temperature. Our temperature dependent photoresponse measurements corroborate most of the theoretical findings with respect to the long-wavelength threshold, shape, and polarization and temperature dependence of the spectra.
Novel Diffraction Pattern for Optical Coupling in QWIP
Authors: Masalkar Prafulla , Nishino Hironori , Matsukura Yusuke , Tanaka Hitoshi , Yamamoto Kousaku , Miyamoto Yoshihiro , Fujii Toshio 
Published: April 2011

AbstractAn optical coupling diffraction pattern for quantum well infrared photodetectors is developed using simulation. It provides high coupling efficiency and fabrication ease. Improved performance has been experimentally verified.
Investigation of New Geometries for High Duty Cycle Far-Infrared p-Type Germanium Lasers
Authors: Chamberlin Danielle R. , Bruendermannw Erik , Haller Eugene E. 
Published: April 2011

AbstractWe report on increasing the pulse length and repetition rate of p-type germanium lasers through miniaturization, increased electric field uniformity, and improved cooling. We have recently demonstrated that it is possible to improve the electric field uniformity necessary for an efficient laser and at the same time decrease the electrical input power by using a geometry with d/L>>1, where d is the distance between electrical contacts and L is the length in the direction of the Hall field. In order to achieve good heat sinking along with a large d/L ratio, we have developed a new, planar contact geometry. Attaching an undoped, high-resistivity, single-crystal Si heat sink to the base of the Ge planar contact laser increases the duty cycle by a factor of 5.5. In order to further decrease the input power by decreasing the volume of laser crystals in the planar contact geometry, we show as a proof-of-concept the use of polished strontium titanate single crystals as electrically insulating far-infrared mirrors based on restrahl band reflection. The physical phenomena underlying these improvements in this novel geometry will be discussed.
Electronic Structure Engineering of the Linewidth Enhancement Factor in Mid-Infrared Semiconductor Laser Active Regions
Authors: Flatté Michael E. , Olesberg J.T. , Boggess T.F. 
Published: April 2011

AbstractThe linewidth enhancement factor is a fundamental parameter that characterizes the limit of spectral purity and the tendency for filamentation in a semiconductor laser. For either narrow-line or high-power operation, it is generally desirable that the linewidth enhancement factor be minimized. This parameter depends primarily on the shape of the differential gain spectrum of the active region material. In mid-infrared laser materials, band structure engineering has been used routinely to minimize the effects of nonradiative recombination. This same approach can be used to tailor the differential gain spectrum of these materials to minimize the linewidth enhancement factor.Favorable features of the electronic structure of the material include 1) band-edge dispersion in the conduction band which shifts the peak of the gain away from the band edgeCand 2) intersubband absorption resonances, which can be designed to lie above the peak gain in energy. Both of these strategies shift the peak of the differential gain closer to the peak gain, and thus reduce the linewidth enhancement factor. These electronic structure design strategies can be used to reduce the linewidth enhancement factor in type-II InAs/GaInSb systems to almost 1.0, which is significantly smaller than typical values of 2.5–5 in type-I strained quantum wells. We note that a linewidth enhancement factor close to 1 is much smaller even than a typical linewidth enhancement factor in visible or near-infrared semiconductor lasers. Furthermore in some materials the peak of the differential gain lies in a region of positive gain, indicating that a grating could be used to select a mode with negligible linewidth enhancement factor.
Positive and Negative Photoconductivity in Lead Telluride Doped With Gallium Epitaxial Films
Authors: Akimov B.A. , Bogoyavlenskiy V.A. , Ryabova L.I. , Vasil'kov V.N. 
Published: April 2011

AbstractWe report on the photoconductivity and transient in n-PbTe(Ga) epitaxial films prepared by the hot wall technique on the <11 I>-BaF2 substrates. Photoconductivity measurements performed under continuous and pulse illumination in the temperature range 4.2-300 K give the photoresponse to be composed from negative and positive parts. The experimental results are interpreted assuming the mixed valence of Ga in lead telluride.
Kinetics of Light Induced Changes in Protocrystalline Thin Film Materials and Solar Cells
Authors: Koval Randy , Niu Xinwei , Pearce Joshua , Jiao Lihong , Ganguly Gautam , Yang Jeffrey , Guha Subhendu , Collins Robert W. , Wronski Christopher R. 
Published: April 2011

ABSTRACTStudies have been carried out on the kinetics of light induced changes in thin films and solar cells fabricated in different laboratories. Unlike the many studies on undiluted a-Si:H films the kinetics reported here are for 1 sun illuminations carried out to the degraded steady state (DSS). The light induced changes at temperatures from 25 to 100°C were characterized with electron mobility lifetime products and subgap absorption in films and fill factors in solar cells. The significant changes in the degradation kinetics that occur in these materials in this t mperature range have further confirmed the importance of charged defects, not only in the annealed state, but also in the degraded steady states. Results are also presented on corresponding solar cell structures, which also indicate that defects other than neutral dangling bonds have to be taken into account if any meaningful evaluation is to be made of their solar cell properties.
Anisotropy In Hydrogenated Silicon Thin Films
Authors: Webb John D. , Nelson B. P. , Mahan A. H. , Theisen J. , Reedy R. , Perkins J. D. , Gedvilas L. M. 
Published: April 2011

ABSTRACTWe investigated spatial non-uniformity and optical anisotropy in hydrogenated silicon thin films using infrared spectroscopy and other techniques. The films ranged in morphology from amorphous to micro-crystalline, as determined by Raman spectroscopy and X-ray diffraction (XRD). Trace element analysis of the films was carried out using secondary ion mass spectrometry (SIMS). We used polarized attenuated total reflection (ATR) measurements together with Fourier transform infrared (FTIR) spectroscopy to investigate anisotropy in the Si-H covalent bonding structure of the films, and also to detect oxide impurity phases present at certain sites in some samples. The FTIR-ATR measurements were performed using a germanium (Ge) contact microprobe with a 100-micron sampling area, as well as on films deposited on standard crystalline Si and Ge ATR substrates. The Ge contact ATR microprobe enabled relatively interference-free measurements of the IR spectra of a-Si:H and µc-Si:H films deposited on conductive substrates such as stainless steel and transparent conductive oxides, and is also sensitive to the spatial distribution of oxide precipitates in the films. This measurement is difficult or impossible using transmission or reflection IR spectroscopy.
Manipulation and Control of Nucleation and Growth Kinetics with Hydrogen Dilution in Hot-Wire CVD Growth of Poly-Si
Authors: Swiatek Maribeth , Holt Jason K. , Goodwin David G. , Atwater Harry A. 
Published: April 2011

ABSTRACTWe systematically explore the relationship between gas-phase kinetics and film microstructure in the hot-wire CVD technique using diluted silane (1% in He) and additional hydrogen. Using a wire temperature of 2000°C, films were grown on Si (100) at 300°C using 1 mTorr SiH4 and 99 mTorr He at hydrogen pressures from 0-100 mTorr. Transmission electron microscopy and atomic force microscopy measurements indicated that continuous microcrystalline films had a columnar grain structure and that grain size increased from 40 nm using SiH4/He to 85 nm using SiH4/He/H2 with 20:1 H2:SiH4 ratio due to the etching of silicon by hydrogen. Etching rate measurements using a quartz deposition monitor show that, under the current deposition conditions, a transition from net film growth (0.17 nm/s using only SiH4) to net etching occurs at a H2:SiH4 ration of 80:1. The effect of atomic H on the nucleation density during the initial stages of growth has also been investigated, revealing a sublinear dependence of nucleation density with time and a decrease in nucleation density with increasing H2 dilution. High deposition rate growth with no H2 dilution has been achieved on a low-density array of seed nuclei produced using high H2 dilution.
A Case for Molecular Hydrogen Being the Mobile H Species in a-Si:H
Authors: Fedders P. A. 
Published: April 2011

ABSTRACTThe mechanism (or mechanisms) of hydrogen transport in a-Si:H is of great intrinsic interest but is also important for the understanding of a number of phenomena such as light induced defects. We find that the literature includes many calculations for the activation energy for hydrogen diffusion that are at best misleading and often interpreted incorrectly. In this paper we summarize a number of calculations that apply to particles hopping in complex media and apply the results to a-Si:H. These calculations, coupled with existing estimates of the energy of various H configurations in a-Si:H, show that the standard picture is likely to be incorrect. However, previous work on the mobility of molecular hydrogen in crystalline Si coupled with some molecular dynamics simulations presented in this paper show that the mobile species of hydrogen in a-Si:H may well be molecular.
Photodegradation in a-Si:H Prepared by Hot-Wire CVD as a Function of Substrate and Filament Temperatures
Authors: Han Daxing , Yue Guozhen , Lin Jing , Habuchi Hitoe , Iwaniczko Eugene , Wang Qi 
Published: April 2011

ABSTRACTWe have studied light-soaking effects, such as photoconductivity (PC) degradation kinetics, the changes of conductivity activation energy, Ea, and the defect density of states (DOS) in a-Si:H films deposited by hot-wire CVD. Films were deposited in a substrate temperature range from 280 to 440 °C for filament temperatures of 1900 and 2100 °C. We find that (a) the photodegradation kinetics does not follow the stretched exponential rule for all of the samples; (b) the Fermi level position moves up after light-soaking for most samples; and (c) the metastable defect DOS deduced from sub-band gap absorption is not consistent with that deduced from the electron mobility-lifetime product. The results are discussed according to the possible mechanism in which charged defects exist in hot-wire a-Si:H films.a
Device Quality Silicon Carbon Thin Films
Authors: Gemmer Christian , Schubert Markus B. 
Published: April 2011

ABSTRACTWe attain good quality hydrogenated silicon carbon films grown by plasma-enhanced chemical vapor deposition. Similar to hydrogenated silicon, we observe a characteristic edge of crystallinity at medium hydrogen dilution ratios of the feedstock gases. In the transition regime between amorphous and nanocrystalline phase, our thin films exhibit a remarkable ratio of photocarrier mobility-lifetime product to dark conductivity of 105... 106 cm3A-1 and minimum light-induced degradation. The static index of refraction increases and the resonance energy decreases for films below the onset of crystallinity which points towards a higher compactness of the protocrystalline material. Hence, alloying of hydrogenated silicon with small amounts of carbon leads to the formation of SiC:H layers that feature an optical bandgap of 2.0 eV and simultaneously maintain the superior optoelectronic properties of protocrystalline silicon.
TEM and HREM study of silicon and platinum nanoscale ensembles in 3D dielectric opal matrix
Authors: Feoktistov N. A. , Golubev V. G. , Hutchison J.L. , Kurdyukov D. A. , Pevtsov A. B. , Schwarz R. , Sloan J. , Sorokin L.M. 
Published: April 2011

ABSTRACTIn the present paper regular systems of silicon and platinum assemblies have been fabricated in a three-dimensional (3D) void sublattice of synthetic opal. The detailed TEM and HREM structure study of ‘opal-Si’ and ‘opal-Pt-Si’ composites was carried out. It was found that in regular composites ‘opal-Si’ the silica spheres were covered uniformly with a nanocrystalline silicon layer of up to 25-30 nm in thickness. To form the Pt-Si contact the silica spheres were coated with platinum layer before embedding silicon. The results obtained demonstrate a possibility of creating 3D multilayer semiconductor structure (p-n junctions, Schottky barriers etc.) on the inner surface of opal voids.
Poly-Si Thin Film Transistors Fabricated By Employing Selective Si Ion-Implantation And Excimer Laser Annealing
Authors: Lee Min-Cheol , Jeon Jae-Hong , Park Jin-Woo , Han Min-Koo 
Published: April 2011

ABSTRACTA new excimer laser annealing method is proposed in order to produce the poly-Si film with low defect density and large grain, by combining the selective Si ionimplantation and excimer laser annealing. Selective Si ion-implantation is employed to form artificial nucleation seeds in a-Si film prior to excimer laser annealing in order to increase the nucleation probability. The grain boundary location in poly-Si film has been controlled through implantation mask, and the grain size around micrometer order is obtained without any other process. TEM result shows that grain boundary is controlled according to mask pattern and the crystallinity of the poly-Si film is improved.
Light Intensity Exponents as Sensitive Tools for the Detection of Impurities in a-Si:H
Authors: Fonseca L. F. , Weisz S.Z. , Alpuim P. , Chu V. , Conde J.P. , Naides R. , Balberg I. 
Published: April 2011

ABSTRACTWe have shown recently that the temperature dependence of the phototransport properties can yield information regarding the state distribution in the forbidden gap of semiconductors. Of these properties the light intensity exponents of both, the majority carriers, γe, and the minority carriers, γh, were found to be very sensitive to the details of this distribution. In particular, noting that sub 1/2 values of the exponents are very unusual we have studied their origin in some a-Si:H materials. Finding experimentally such sub 1/2 values of γh and running computer simulations of the recombination processes in a-Si:H led us to the conclusion that these low values are due to acceptor-like centers which have a relatively high capture coefficient for the holes. We attribute these centers to the unintentional oxygen doping in a-Si:H. We will show that the oxygen presence, usually ignored in the discussions of the phototransport properties of a-Si:H, appears to be, in many cases, the dominant factor in the properties of “intrinsic” a-Si:H.