bluuebunny/crossref_metadata_2025_split huggingface dataset:
Rheological Behaviour and Model of Metal - Polymer - Ceramic Composite
Authors: Kireitseu Maksim V. 
Published: April 2011

ABSTRACTIn the present paper rheological behaviour of composite coating consisting of Aluminum Oxide -Polymer – Chrome Carbide was examined by using rheological models for principal Hertzian contact of a sphere and a plate. The crystallography and morphologic texture was characterized and the fracture resistance was measured using fracture-mechanics. A rheological model of the composite coating has been proposed and confirmed by in situ experiments. Several requirements to rheological models were formulated regarding an adequate strain-deformation state of the composite coating. Load rating revealed ultimate strain-deformation rates. Analysis of the models and experimental results revealed better understanding of composite failure and degradation mechanics.
A Semiconductor Nano-Patterning Approach Using AFM-Scratching Through Oxide Thin Layers
Authors: Santinacci L. , Djenizian T. , Schmuki P. 
Published: April 2011

ABSTRACTAFM-scratching was performed through thin oxide layer which was either a native oxide layer (1.5 – 2 nm thick) or a thermal oxide layer (10 nm thick). Due to their insulating properties, the SiO2 films act as masks for the metal electrochemical deposition. In the scratched openings copper deposition can take place selectively and thus nano-scale metal lines could be successfully plated onto the p-type silicon substrates. Using particularly, if sufficiently thick thermal oxide has advantages over the native oxide, it allows a H-termination of the Si within the grooves (HF treatment) without eliminating the oxide layer on the rest of the surface.
Atomistically Informed Continuum Model of Polymer-Based Nanocomposites
Authors: Picu Catalin R. , Sarvestani Alireza , Ozmusul Murat S. 
Published: April 2011

ABSTRACTA model polymeric material filled with spherical nanoparticles is considered in this work. Monte Carlo simulations are performed to determine the polymer chain conformations in the vicinity of the curved interface with the filler. Several discrete models of increasing complexity are considered: the athermal system with excluded volume interactions only, the system in which entropic and energetic interactions take place while the filler is a purely repulsive sphere, and the system in which both filler-polymer and polymer-polymer energetic interactions are accounted for. The total density, chain end density, chain segment preferential orientation and chain size and shape variation with the distance from the filler wall are determined. The structure is graded, with the thickness of the transition region being dependent on the property and scale considered. Hence, the polymer in the vicinity of the filler is represented in the continuum sense by a material with graded properties whose elasticity is determined based on the local structure. Homogenization theory is the used to obtain the overall composite moduli. The filler size effect on the composite elasticity is evaluated.
Micromolding of Pb and Zn with Surface Engineered LiGA Mold Inserts
Authors: Cao D. M. , Guidry D. J. , Meng W. J. , Kelly K. W. 
Published: April 2011

ABSTRACTMolding of Pb and Zn metal plates with LiGA (Lithographie, Galvanoformung, Abformung) fabricated Ni micro-scale mold inserts was carried out with as fabricated Ni inserts and Ni inserts conformally coated with Ti-containing hydrocarbon (Ti-C:H) coatings. The molding performance was characterized using scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS), in terms of the generated features on the metal plates as well as the inserts condition after molding. The present results demonstrate that, in cases where significant metal/insert chemical interactions exist, surface modification of the mold insert is necessary to obtain satisfactory performance. Furthermore, conformal deposition of suitable engineered ceramic coatings onto Ni micro-scale mold inserts is effective for high temperature micromolding of reactive metals.
Planar Extrinsic Biasing Of Thin Film Shape-Memory MEMS Actuators.
Authors: Grummon D. S. , Gotthardt R. , LaGrange T. 
Published: April 2011

ABSTRACTAlthough slow and dissipative, sputtered thin-film shape-memory alloys like equiatomic titanium-nickel can exert a large ohmically-excited force·displacement product when deployed in photolithographically micromachined actuators. They give energy densities far exceeding those typically produced by competing microactuator materials [1], and their size can probably be scaled down to the nanometer range (where the benefits of high surface to volume ratio are best exploited for speed and efficiency). But a large, energetic, and resettable actuation stroke is possible only if some agency has imparted a non-trivial initial plastic strain, of between one and five percent, to the martensite phase. Is not always obvious how this strain is to be achieved when discrete mechanical manipulation of the active element is difficult. Furthermore, for cyclic actuation, a resetting-force that periodically re-deforms the martensite during the cooling interval must arise naturally from mechanical elements in the design. Here, several methods responding these requirements are discussed in relation to various kinematic themes.
Surface Oxide Effects on Static Fatigue of Polysilicon MEMS
Authors: Kahn H. , Ballarini R. , Heuer A.H. 
Published: April 2011

ABSTRACTStatic fatigue – crack growth causing delayed failure under constant stress and involving stress corrosion cracking – was investigated in polysilicon MEMS using two different surface-micromachined devices. One exploited residual tensile stresses to create stress concentrations at micromachined notches, and the other involved a single-edge notched beam specimen integrated with an electrostatic comb-drive microactuator. Tests with both devices revealed that polysilicon is not susceptible to static fatigue in humid environments. However, when a relatively thick (45 to 140 nm) surface oxide was thermally grown on the microactuator devices, the specimens demonstrated delayed fracture in a humid ambient, presumably due to static fatigue of the surface SiO2. The stress intensities at the resulting cracks in the SiO2were then sufficient to cause catastrophic crack propagation through the polysilicon specimens. The implications of our data on the issue of fatigue in polysilicon is discussed.
Pulsed Laser Annealing of Silicon-Germanium Films
Authors: Sedky Sherif , Schroeder Jeremy , Sands Timothy , Howe Roger , King Tsu-Jae 
Published: April 2011

ABSTRACTIn this work, we investigate the possibility of using pulsed laser annealing to locally tailor the physical properties of Si1-xGex (18% < × < 90%) prepared by low pressure chemical vapor deposition (LPCVD) at 400°C. Films which were amorphous as deposited showed, after laser annealing, strong {111} texture and a columnar grain microstructure and an average resistivity of 0.7 mΩ.cm. AFM showed that the first few laser pulses result in a noticeable reduction in surface roughness, which is proportional to the pulse energy. However, a large number of successive pulses dramatically increases the surface roughness.
Residual Stress Control to Optimize Pzt Mems Performance
Authors: Kennedy M.S. , Bahr D.F. , Richards C.D. , Richards R.F. 
Published: April 2011

ABSTRACTFlexing piezoelectric membranes can be used to convert mechanical energy to electrical energy. The overall deflection of individual membranes is impacted by the residual stress in the system. Membranes comprised of silicon dioxide, Ti/Pt, lead- zirconate- titanate (PZT), and TiW/Au layers deposited on a micromachined boron doped silicon wafer were examined for both morphology and residual stress. By characterizing the membrane residual stress induced during processing with x-ray diffraction, wafer curvature, and bulge testing and identifying methods to reduce stress, the membrane performance and reliability can be optimized. For Zr:Ti ratios of 52:48, the residual stress in the PZT was 350 MPa tensile, with an overall effective stress in the composite membrane of 150 MPa. A reduction of stress was accomplished by changing the PZT chemistry to 40:60 Zr:Ti in the PZT to obtain a stress in the PZT of 160 MPa tensile and an overall effective membrane stress of 100 MPa. The crystallization of the 52:48 PZT film at 700 °C causes a 28% reduction in the thickness of the film.
Investigation of Polymer Micro-Actuators Based on Electrostrictive Poly(vinylidene fluoride-trifluoroethylene) Copolymers
Authors: Xu Tian-bing , Xia Feng , Cheng Z.-Y. , Zhang Q. M. 
Published: April 2011

ABSTRACTMicromachined actuators based on the electrostrictive P(VDF-TrFE) copolymer, which possesses a high strain (∼5%) and high elastic energy density (∼ 1 J/cm3), have been designed and fabricated. The performance of the devices have been characterized and modeled in terms of the properties of the copolymer and dimensions of the devices. The experimental results on the device responses under high AC fields (electrostrictive mode), weak AC fields in DC field biased state, and frequency dependence, are very close to the modeling results. Due to the large field induced strain and high frequency capability of the electrostrictive P(VDF-TrFE), the device possesses the capability of operation at non-resonance mode with high displacement and force output, and hence, the device is capable to be used over a broad frequency range. For example, for a device of 1 mm lateral dimension, the displacement output can reach more than 50 μm and the ratio of the displacement/applied voltage is more than 20 nm/Vrms. Furthermore, over more than 3 frequency decades (up to 100 kHz), the dispersion of the displacement is less than 20%. The observed performance of the devices indicates that this class of the electrostrictive P(VDF-TrFE) based micro-actuators is attractive for micropumps and valves.
Microscale Measurement of Stresses in a Silicon Flexure Using Raman Spectroscopy
Authors: Srikar V. T. , Swan A. K. , Goldberg B.B. , Ünlü M. S. , Spearing S. M. 
Published: April 2011

ABSTRACTWe report the use of Raman spectroscopy to characterize the bending stresses in a deep reactive-ion etched, single-crystal, silicon flexure of length 2950 μm, width 480 μm, thickness 150 μm, and fillet radius 65 μm, subjected to a tip displacement of 69.5 μm. The spectral resolution of the measurement was 0.02 cm-1, which corresponds to a stress resolution of ∼10 MPa, and the spatial resolution was ∼1 μm. Line scans were performed across the thickness, at several locations along the length, of the flexure. The changes in the Raman shift were converted to stress values, assuming a uniaxial stress state, without the use of any fitting parameters. A comparison of the measured values with the predictions of analytical and numerical models indicates agreement to within 25–35 MPa (or ∼15%) at locations sufficiently distant from the root. At the root itself, the complex nature of the stress distribution precludes unambiguous stress determination using spectroscopic measurements.
Modeling Analysis of Free-Spreading Sublimation Growth of SiC Crystals
Authors: Bogdanov M. V. , Demina S. E. , Karpov S. Yu , Kulik A. V. , Ofengeim D. Kh , Ramm M. S. , Mokhov E. N. , Roenkov A. D. , Vodakov Yu. A. , Makarov Yu. A. , Helava H. 
Published: April 2011

ABSTRACTRecently, an advanced technique for growing free-spreading SiC bulk crystals by sublimation has been demonstrated. This method was used to grow 6H- and 4H-SiC boules free of polycrystalline deposits on the crystal periphery, up to 35 mm in diameter with the micropipe density less than 20 cm-2 and the dislocation density about 102-103 cm-2. In this paper, we report on the numerical modeling of free-spreading crystal growth. We consider the global heat transfer in an inductively heated growth system, species transport in the growth cell and in the powder charge, and thermoelastic stress, focusing on the crystallization front dynamics, poly-SiC deposition, and powder source evolution. Special attention was given to the validation of the simulations. The computed thermal field and evolution of the powder and crystal shape were found to agree qualitatively with observations.
Thermal Plasma Physical Vapor Deposition of Nanostructured SiC Coatings
Authors: Wang Xinhua , Eguchi Keisuke , Yamamoto Atsushi , Yoshida Toyonobu 
Published: April 2011

ABSTRACTNanostructured and thick SiC coatings have been successfully deposited on Si and graphite substrates by thermal plasma physical vapor deposition (TPPVD) using ultrafine SiC powder as a starting material. The control of processing parameters such as substrate temperature, composition of plasma gases, permits to the deposition of SiC coatings with a variety of microstructures and with various morphologies from dense to columnar. The maximum deposition rate reached 200 nm/s. Seebeck coefficient up to −480 μV/K was obtained for the non-doped coatings with stoichiometric composition. Nitrogen doping to the coatings made it possible to decrease the electrical resistivity from 10-2∼10-3 to 10-4∼10-5 Ωm and showing the maximum power factor of 1.0×10-3 Wm-1K-2 at 973 K.
Memory Switching in Ion Bombarded Amorphous Silicon Carbide Thin Film Devices
Authors: Gateru R. G. , Shannon J. M. , Silva S. R. P. 
Published: April 2011

ABSTRACTMetal-semiconductor-metal (MSM) memory devices have been made in hydrogenated amorphous silicon carbide (a-SiCx:H). Switching in silicon-rich amorphous silicon alloys is believed to be related to the concentration of defects in the semiconductor material. We have used ion bombardment to introduce a controlled number of damage centres into amorphous silicon carbide. Both analog and digital switching behaviours are reported.
Thermal Chemical Vapor Deposition of Silicon Carbide Films as Protective Coatings for Microfluidic Structures
Authors: Gallis Spyros , Futschik Ulrike , Castracane James , Kaloyeros Alain E. , Efstathiadis Harry , Sherwood Walter , Hayes Susan , Fountzoulas Costas G. 
Published: April 2011

ABSTRACTAmorphous silicon carbide (SiC) films were deposited on silicon substrates by thermal chemical vapor deposition (TCVD) technique, at substrate temperatures ranging from 620 °C - 850 °C. A novel, single-source halide free precursor, SP-4000, belonging to the family of polysilenemethylenes (PSM) (nominal structure [-SiH2-CH2-]n, n = 2–8 including branched and cyclic isomers) was used as source. Argon was used, as both the precursor carrier gas and the dilution gas. Other reactants, such as hydrogen or hydrocarbons, were not used. The deposition yielded films with Si/C ratio of 1±0.2. The highest achieved growth rate was 83 nm/min.The modulus of elasticity and the nanohardness of the SiC films were measured with the aid of a nanoindenter at various depths, which did not exceed 25% of the film thickness. The average nanohardness at indentation depths of approximately 10% of the film thickness was measured up to 13 ± 4 GPa. The results of the nanoindentation will be discussed in conjunction with the microstructural analysis of the films.In addition, the development of a viable TCVD SiC process presents significant opportunities in the nano/micro systems field. In particular, the ability to custom tailor the surfaces of microfluidic structures allows for the development of valves, pumps and channels for use in corrosive or high temperature environments. Initial results from the deposition of SiC films on prototype microfluidic components will be presented.
Spatially Resolved Photoluminescence and Thermally Stimulated Luminescence in Semi-Insulating SiC Wafers
Authors: Suleimanov Yu. M. , Lulu S. , Tarasov I. , Ostapenko S. , Saddow S. E. , Torchinska T. V. , Heydemann V. D. , Roth M. D. , Kordina O. , MacMillan M. F. 
Published: April 2011

ABSTRACTWe report on non-contact and non-destructive spatially resolved characterization of traps and luminescence centers in vanadium-free semi-insulating 6H-SiC. Two optical techniques were employed: photoluminescence (PL) mapping and thermally stimulated luminescence (TSL) imaging on SiC wafers. PL and TSL topography reveal inhomogeneity at the periphery regions of the wafers. Low-temperature PL spectra show broad bands with the maxima at 1.75eV and 1.2eV, including a sharp zero-phonon line at 1.344eV. The TSL glow curves at T>80K show different peaks in the visible and infrared bands. The luminescence spectrum of the 105K TSL peak replicates 1.75eV band, while the 120K peak corresponds to the 1.2eV band. Additionally, the high temperature TSL peak at 210K shows an excellent match with 1.344eV zero phonon line. The trap energies of different peaks are calculated. We discuss a model of complex defects composed of closely spaced electron (hole) trap and UD3 defect.
Accurate Lattice Constant and Mismatch Measurements of SiC Heterostructures by X-Ray Multiple-Order Reflections
Authors: Huang XianRong , Dudley Michael , Neudeck Philip G. , Anthony Powell J. 
Published: April 2011

ABSTRACTHigh-resolution X-ray diffraction (HRXRD) combined with other diffraction techniques is applied to characterize 3C SiC epilayers hoteroepitaxially grown on atomically flat mesas on 4H and 6H SiC substrates. Small-beam rocking curve scan and reciprocal mapping show extremely high crystalline perfection and homogeneity of the ideally grown 3C-SiC epilayers. Accurate lattice measurements based on X-ray multiple-order reflections reveal that: 1) no misorientation between the (0001) lattice planes across the 4H/3C or 6H/3C interface is detected, confirming the 2D nucleation mechanism of the 3C epilayer from a flat coherent interface; 2) in-plane substrate/epilayer lattice mismatch always exists, but the 3C epilayers do not correspond to a completely relaxed cubic structure, indicating that the epilayers are partially strained; 3) lattice mismatch varies for different regions, implying a complicated strain relaxation mechanism of 3C epilayers on various mesas.
Strained SiC: Ge Layers in 4H SiC formed by Ge Implantation
Authors: Dashiell M. W. , Xuan G. , Zhang Xin , Ansorge E. , Kolodzey J. 
Published: April 2011

ABSTRACTThe ion implantation of germanium into 4H-SiC at 1000 °C resulted in crystalline SiC:Ge layers that are coherently strained to the (0001) oriented 4H-SiC substrates. Germanium implantation energies of 140 keV and 50 keV were chosen to form approximately 100nm thick step-like SiC:Ge layers with Ge atomic fractions ranging from 0.0007 to 0.006. High-resolution x-ray diffraction (HRXRD) and reciprocal space mapping reveal a high-quality, compressively strained SiC:Ge layer. High-temperature annealing resulted in partial relaxation of the macroscopic layer strain, however the SiC:Ge layer remained strained with a coherent interface for annealing up to at least 1650°C. Because Ge is a group-IV atom like Si and C, its incorporation into the lattice is expected to act as an isoelectronic impurity, rather than a charged donor or acceptor. Thus, high-quality, SiC:Ge layers have the potential for bandgap and strain engineered electronics such as SiC-based high electron mobility transistors (HEMTs) for RF-power electronics. Currently there is no established heterojunction pair in SiC material technology for fabricating HEMTs and other heterojunction devices.
Towards Ferroelectric Field Effect Transistors in 4H-Silicon Carbide
Authors: Koo S.-M. , Khartsev S. I. , Zetterling C.-M. , Grishin A. M. , Östling M. 
Published: April 2011

ABSTRACTWe report on the integration of ferroelectric Pb(Zr,Ti)O3 (PZT) thin films on 4H-silicon carbide and their electrical properties. The structures of metal-ferroelectric-(insulator)-semiconductor MF(I)S and metal-ferroelectric-metal-insulator-semiconductor MFMIS have been fabricated and characterized. The MFMIS structures of Au/PZT/Pt/Ti/SiO2/SiC have shown fully saturated P-E hysteresis loops with remnant polarization Pr =14.2μC/cm2 and coercive field Ec = 58.9 kV/cm. The MFIS structures exhibited stable capacitance-voltage C-V loops with low conductance (<0.1 mS/cm2, tan d ∼ 0.0007 at 12 V, 400kHz) and memory window as wide as 10 V, when a 5 nm-thick Al2O3 was used as a high bandgap (Eg ∼ 9eV) barrier buffer layer between PZT (Eg ∼ 3.5eV) and SiC (Eg ∼ 3.2eV). Both structures on n- and p- SiC have shown electrical properties promising for the application to the gate stacks for the SiC field-effect transistors (FETs) and the design and process issues on different types of the metal-ferroelectric-silicon carbide field-effect transistors (FETs) have also been proposed.
Development of a High Lateral Resolution Electron Beam Induced Current Technique for Electrical Characterization of InGaN-Based Quantum Well Light Emitting Diodes
Authors: Bunker Kristin L. , Gonzalez Juan Carlos , Batchelor Dale , Stark Terrence J. , Russell Phillip E. 
Published: April 2011

ABSTRACTElectron Beam Induced Current (EBIC) is a Scanning Electron Microscope (SEM)-based technique that can provide information on the electrical properties of semiconductor materials and devices. This work focuses on the design and implemenation of an EBIC system in a dedicated Scanning Transmission Electron Microscope (STEM). The STEM-EBIC technique was used in the characterization of an Indium Gallium Nitride (InGaN) quantum well Light Emitting Diode (LED). The conventional “H-bar” Transmission Electron Microscopy (TEM) sample preparation method using Focused Ion Beam Micromachining (FIBM) was adapted to create an electron-transparent membrane approximately 300 nm thick on the sample while preserving the electrical activity of the device. A STEM-EBIC sample holder with two insulated electrical feedthroughs making contact to the thinned LED was designed and custom made for these experiments. The simultaneous collection of Z-contrast images, EBIC images, and In and Al elemental images allowed for the determination of the p-n junction location, AlGaN and GaN barrier layers, and the thin InGaN quantum well layer within the device. The relative position of the p-n junction with respect to the thin InGaN quantum well was found to be (19 ± 3) nm from the center of the InGaN quantum well.
Simultaneous TEM and Cathodoluminescence Imaging of Non Uniformity in In0.1Ga0.9N Quantum Wells
Authors: Boyall Nicholas M. , Durose Ken , Watson Ian M. 
Published: April 2011

ABSTRACTMonochromatic cathodoluminescence (CL) imaging of metal-organic vapour phase epitaxy (MOVPE) grown In0.1Ga0.9N single quantum wells (QW) has been performed in a scanning transmission electron microscope (STEM). Spatially resolved fluctuations in the CL emission wavelength and intensity of the QW luminescence were recorded. The presence of regions with luminescent features asymmetrically distributed either side of the QW peak emission was inferred. These fluctuations may be attributed to, by for example, variations of ±0.01 in the In fraction of the In0.1Ga0.9N alloy, to changes of up to 0.6nm in the QW thickness. However these factors do not explain the gross fluctuations in QW emission intensity observed in TEM-CL on the scale of ∼1μm.
Surface-Related Photoluminescence Effects in GaN
Authors: Reshchikov M. A. , Iqbal M. Zafar , Huang D. , He L. , Morkoç H. 
Published: April 2011

ABSTRACTPhotoluminescence (PL) from GaN epilayers is found to be sensitive to the ambient atmosphere and length of UV exposure. We studied the effect of UV illumination in different ambients including air, oxygen, nitrogen and hydrogen gases on room-temperature PL of GaN grown on sapphire by molecular beam epitaxy. In some samples the PL intensity increased markedly in vacuum as compared to excitation in air, whereas in others it decreased appreciably. While air and oxygen showed strong reversible variation of the PL intensity as compared to vacuum, nitrogen and hydrogen atmospheres led to a very small change. In some samples we observed a shift of the yellow luminescence band with change of ambient, in others no shift was detected. PL intensity also changed during UV irradiation when the sample was in air ambient. Possible reasons for our observations are discussed.