bluuebunny/crossref_metadata_2025 huggingface dataset:
Failure of micron scale Single Crystal Silicon bars due to torsion developed by MEMS micro instruments
Authors: Saif Taher , MacDonald N. C.
Published: April 2011

We present an experimental study on a single crystal silicon (SCS) bar subjected to pure torsion using MEMS micro instruments. The bar is in the form of a pillar, anchored at one end to the silicon substrate. It is attached to a lever arm at the other end. The pillar has a minimum cross sectional area at its mid height. The cross section coincides with the (100) plane of SCS. Torsion is generated by applying two equal forces on the lever arm on either side of the pillar. Two micro instruments apply the forces. Each consists of an electrostatic actuator and a component that calibrates it. The actuator generates high force (≈ 200 µN at 50 V) and is capable of developing large displacements (≈ 10 μm). Calibration involves determination of the force generated by the actuator at an applied voltage, as well as the linear and higher order spring constants of its springs. Each microinstrument is thus calibrated independently.

With the application of forces by the two micro instruments, a torque is generated which twists the pillar. The angle of twist at different applied voltages are recorded using an angular scale. The corresponding torques are determined from the calibration parameters of the actuators. Torque is applied until the pillar fractures. Two such sample pillars, samples 1 and 2, are tested. There cross sectional areas are 1 and 2.25 µm2. We find that both the pillars behave linearly until failure. The stresses prior to fracture are evaluated based on anisotropic theory of elasticity. Samples 1 and 2 fail at shear stresses of 5.6 and 2.6 GPa respectively. The fracture surfaces seem to coincide with the (111) plane of SCS.
Investigation of The Mechanical Properties and Adhesion of P.V.D. Tungsten Films on Si and Silicon Compounds by Bulge and Blister Tests
Authors: Dupeux Michel , Bosseboeuf Alain , Buttard Denis
Published: April 2011

P.V.D. tungsten films deposited on silicon wafers (covered or not with a P.E.C.V.D. silicon oxide, nitride or oxynitride sublayer) were submitted to bulge and blister tests. The mechanical equilibrium and geometry of the bulged tungsten membranes is compared to various models. From this analysis, values of the residual stresses and the Young's moduli in the films are derived, and found to be consistent with previous values deduced from curvature radius measurements or other mechanical test methods, as functions of the deposition conditions. Decohesion of the films from their substrates is easily observed on the W / SiO2 / Si membranes, and the film / sublayer interfacial fracture energy is estimated about 1 J/m2. This energy increases when the sublayer is changed from SiO2 to silicon oxi-nitride and to nitride. The W / Si membranes show a much stronger adhesion than the abovementioned ones and could not be debonded before bursting.
Transversal Type Piezoelectric Resonator Using ZnO Thin Film on Micro-Fabricated Elinver (Fe-Ni-Cr-Ti) Alloy
Authors: Yoshino Y.
Published: April 2011

A transversal type 3.58MHz piezoelectric resonator has been fabricated using piezoelectric ZnO thin film on ELINVER (Fe-Ni-Cr-Ti ) alloy. The ZnO/ELINVER structure piezoelectric resonator has been designed to have 2 ppm temperature coefficient of frequency (TCF) per degree from -20 degrees to 80 degrees centigrade. The temperature coefficient of ELINVER alloy can be controlled to cancel the TCF of ZnO thin film by heat annealing. The ZnO thin film on ELINVER alloy shows c-axis orientation. The c-axis orientation of the ZnO thin film is strongly influenced by the surface roughness of the ELINVER alloy. The wet etching process has been adopted to shape the resonator made from ELINVER alloy substrate. The cross section of the resonator is a structure tapered about 10 degrees, created using different sized photo masks on each side of the ELINVER surface. The tapered cross section of the transversal type resonator greatly improves the frequency characteristics of the resonator. The electrical characteristics of the resonator after the improvement include a resonance frequency of 3.58MHz trimmed by a YAG laser, and resonance resistance of about 200 Ω. The temperature coefficient of frequency is about 1.5 ppm per degree at a temperature range of-20 degrees to 80 degrees centigrade.
Application of Energy-Filtering Transmission Electron Microscopy on Advanced IC Device Processing
Authors: Yin K. M. , Chang L. , Chen F. R. , Kai J. J. , Chang H. L.
Published: April 2011

Energy-filtering TEM is applied to characterize the microstructures in ULSI devices. Three cases are shown for EFTEM applications: interfacial reactions in Al metallization, phase identification after arcing in Al metallization, and ONO structure.
A Study of Substrate Orientation Dependence of the Solid-Phase Epitaxial Growth of Amorphised GaAs
Authors: Belay K. B. , Llewellyn D. J. , Ridgway M. C.
Published: April 2011

In-situ transmission electron microscopy (TEM) has been utilized in conjunction with conventional ex-situ Rutherford backscattering spectrometry and channeling (RBS/C), in-situ time resolved reflectivity (TRR) and ex-situ TEM to study the influence of substrate orientation on the solid-phase epitaxial growth (SPEG) of amorphised GaAs. A thin amorphous layer was produced on semi-insulating (100), (110) and (111) GaAs substrates by ion implantation of 190 and 200 keV Ga and As ions, respectively, to a total dose of 1e14/cm2. During implantation, substrates were maintained at liquid nitrogen temperature. In-situ annealing at ∼260°C was performed in the electron microscope and the data obtained was quantitatively analysed. It has been demonstrated that the non-planarity of the crystalline-amorphous (c/a)-interface was greatest for the (111) substrate orientation and least for the (110) substrate orientation. The roughness was measured in terms of the length of the a/c-interface in given window as a function of depth on a frame captured from the recorded video of the in-situ TEM experiments. The roughness of the c/a-interface was determined by the size of the angle subtended by the microtwins with respect to the interface on ex-situ TEM cross-sectional micrographs. The angle was both calculated and measured and was the largest in the case of (111) plane. The twinned fraction as a function of orientation, was calculated in terms of the disorder measured from the RBS/C and it was greatest for the (111) orientation.
Anisotropy of NH4Ap Crystal X-Ray Susceptibility for Bragg Reflection Near Ck Absorption Edge
Authors: Okotrub A. V. , Belikova G. S. , Turskaya T. N. , Mazalov L. N.
Published: April 2011

Bragg reflection (001) of high-quality crystal of ammonium acid phthalate (2d = 52.28 A˚) is investigated in the region of CK absorption edge. First order reflection for this crystal is forbidden. Due to anisotropic additions, it appears only near CK edge. Two-crystal optical scheme was used for the measurement of the crystal reflectivity. As shown, the change of crystal azimuth in X-ray spectrometer leads to ability to control the resolution. Rotation effects of X-ray beam polarization on 90° angle is considered for the forbidden reflection.
Maximum at ALS: A Powerful Tool to Investigate Open Problems in Micro and Optoelectronics
Authors: Lorusso G. F. , Solak H. , Singh S. , Batson P. J. , Underwood J. H. , Cerrina F.
Published: April 2011

We present recent results obtained by MAXIMUM at the Advanced Light Source (ALS), at the Lawrence Berkeley National Laboratory. MAXIMUM is a scanning photoemission microscope, based on a multilayer coated Schwarzschild objective. An electron energy analyzer collects the emitted photoelectrons to form an image as the sample itself is scanned. The microscope has been purposely designed to take advantage of the high brightness of the third generation synchrotron radiation sources, and it installation at ALS has been recently completed. The spatial resolution of 100 nm and the spectral resolution of 200 meV make our instrument an extremely interesting tool to investigate current problems in opto- and microelectronics. In order to illustrate the potential of MAXIMUM in these fields, we report new results obtained by studying the electromigration in Al-Cu lines and the Al segregation in AIGaN thin films.
Synchrotron Radiation Diffraction Imaging Study of the Magnetoacoustically Induced X-Ray Focusing Effect in FeBO3
Authors: Matsouli I. , Kvardakov V. V. , Espeso J. I. , Chabert L. , Baruchel J.
Published: April 2011

Synchrotron radiation diffraction imaging (‘topography’) was used at the ESRF to visualize ultrasonic standing waves in a magnetoacoustically excited FeBO3 crystal. Images were recorded at long sample-to-film distances (up to 1.5 m) without substantial loss of resolution. The resonant patterns reveal that the crystal acts as a pulsed X-ray focusing lens and strongly depend on both the amplitude of the magnetic field and the sample-to-detector distance. Different resonant frequencies can also lead to more complicated images due to interference effects of several vibrating modes present in the crystal. A model is proposed followed by a numerical integration which predicts the focusing of the X-ray beam and demonstrates the agreement between theory and experiment. This effect could be used to simultaneously monochromatize and focus the X-ray beam.
X-Ray Diffuse Scattering Investigation of Defects in Ion Implanted and Annealed Silicon
Authors: Chang C. H. , Beck U. , Metzger T. H. , Patel J. R.
Published: April 2011

To characterize the point defects and point defect clusters introduced by ion implantation and annealing, we have used grazing incidence x-rays to measure the diffuse scattering in the tails of Bragg peaks (Huang Scattering). An analysis of the diffuse scattered intensity will allow us to characterize the nature of point defects or defect clusters introduced by ion implantation. We have also observed unexpected satellite peaks in the diffuse scattered tails. Possible causes for the occurrence of the peaks will be discussed.
Pulsed Laser Deposition of (Ba,Sr)TiO3 Ferroelectric thin Films
Authors: Horwitz J.S. , Chang W. , Carter A.C. , Pond J.M. , Kirchoefer S.W. , Chrisey D.B. , Stroud R.M. , Levy J. , Hubert C.
Published: April 2011

Single phase, (100) oriented Ba0.5Sr0.5TiO3 (BST) thin films have been deposited onto (100) LaAlO3, SrTiO3, and MgO substrates using pulsed laser deposition (PLD). Interdigitated capacitors patterned on top of the ferroelectric film have been used to measure the dielectric constant and dissipation factor of these films as a function of DC bias and temperature at 1 MHz and as a function of DC bias and frequency (1 to 20 GHz) at room temperature. At room temperature, the capacitance can be reduced by as much as a factor of 4 using an electric field of ≤ 80 kV/cm. The dielectric properties (% tuning and dielectric loss) of the ferroelectric film is sensitive to both the deposition and post processing conditions. Optical imaging of the ferroelectric films using confocal scanning optical microscopy (CSOM) shows reproducible polarization fluctuations over sub-micrometer length scales. Dielectric loss in the ferroelectric film is reduced through a combination of post deposition processing and donor/acceptor doping of the films. A zero field tan5 = 0.01 - 0.005 has been measured for BST films which show significant tuning at microwave frequencies.
Removal of Plasma-Etch-Induced Polymers from Submicron Via Holes by Excimer Laser Ablation
Authors: Lu Y. F. , Lee Y. P. , Zhou M. S.
Published: April 2011

A relatively new approach in removing the sidewall and bottom polymers resulting from reactive ion etching of via holes, using a non-contact dry excimer laser cleaning technique has been investigated. Pulsed excimer laser ablation at 248 nm has been found to be capable of removing the via-etch-induced polymers at fluences limited by the damage threshold of the underlying Al-Cu metal film with TiN anti-reflective coating of 250-280 mJ cm-2. A fluence window of 150-200 mJ cm-2 for efficient laser cleaning is also determined from the ablation rate data using the relation in the limit of Beer's law absorption. Experimental results have also shown that the ablation rate when irradiating at an angle is not only comparable to that at vertical incidence, but even register higher values for most of the ablation rate data obtained. An optimum incident angle for laser cleaning of 45° can be determined from the results.
New Ceramic Cluster Materials by Laser Ablation and Reaction
Authors: Froben Friedrich W. , Lu Yimin
Published: April 2011

Laser ablation of metals and reaction with hydrocarbon produces clusters of metal carbides. Metal precursors are from group IVb to VIb of the periodic system. The mass distribution is analysed by TOF in the gas phase. The clusters are deposited on carbon and investigated by TEM and STM. The materials are very hard and very flat and include Ti-C, Zr-C, V-C, Nb-C, and TaC.
Spectroscopic Study of Pulsed Laser Induced Plasma from Aluminum Surface
Authors: Lu Y. F. , Tao Z. B. , Hong M. H. , Chan D.S.H. , Low T.S.
Published: April 2011

Optical emission spectrum of aluminum plasma induced by a 1064 nm Nd:YAG laser is investigated by an Optical Multichannel Analyzer (OMA). Spectroscopic study shows that more number of Al, Al+, and Al++ spectral lines can be observed with increasing the incident laser fluence. Al, Al+, Al++ spectral lines are also observed successively with high fluence. The atomic spontaneous radiation is analyzed to interpret the calibrated plasma spectrum. The laser energy threshold for the appearance of excited Al, Al+, and Al++ spectral lines are about 0.8, 1.0 and 1.5 J/cm2 respectively. Assuming LTE (Local Thermodynamic Equilibrium) conditions, the plasma density is derived to be in the range of 0.7×1017 to 2×1017 cm-3 from the profiles of Al+ (358.7 and 286.1 nm) spectral lines with different gated times and incident laser fluences. The plasma temperature is also estimated to be 4000 ~ 8000 K, from relative intensities of two different Al I spectral lines (309.2 and 396.2 nm) with different fluence.
From Solid State Diffusion to Configurational Kinetics
Authors: Martin G. , Athènes M. , Desgranges C. , Nastar M. , Soisson F.
Published: April 2011

A single model is proposed to describe the cohesive energy and the vacancy jump frequencies as a function of the alloy configuration at the atomic level. The very same model therefore yields both equilibrium and kinetic properties, close and far away from equilibrium. The model is handled at two levels of approximation: Monte Carlo techniques and mean-field type approximations. The model yields equilibrium properties (including the transport coefficients and complex diffusion mechanisms in ordered compounds close to equilibrium) as well as the kinetic path for phase separation, with or without ordering. This allows to identify specific effects of the vacancy diffusion mechanism on the kinetic path for alloy decomposition. Here, we summarise the main results of the above approach.
Crystalline Structure Around the Single Vacancy in Silicon: Formation Volume and Stress Effects
Authors: Antonelli A. , Kaxiras Efthimios , Chadi D. J.
Published: April 2011

The crystalline structure surrounding a single neutral vacancy in silicon is investigated through extensive first-principles total-energy calculations. The results indicate the existence of two distinct distortions of the lattice around the vacancy with essentially the same formation energies at zero pressure, but, however, with different formation volumes. The effect of hydrostatic and biaxial stresses on the relative concentration of each distortion is discussed, suggesting experimental ways to investigate the crystalline structure around the single vacancy and its role as a mediator of atomic diffusion in silicon.
Interdiffusion Behavior of Si/Si1−x Gex. Layers in Inert and Oxidizing Ambients
Authors: Griglione Michelle , Anderson Tim , Haddara Yaser , Law Mark , Jones Kevin
Published: April 2011

Interdiffusion of Si/Si0.85Ge0.15 heterojunctions subjected to annealing in inert and oxidizing ambients was investigated as a function of temperature (900 to 1200 °C) and time, allowing comparison between intrinsic diffusion and diffusion under interstitial injection. The Ge diffusivity was extracted using the process simulation program FLOOPS. A time-independent diffusivity was observed for all temperatures. The calculated Ge diffusivity in oxidizing ambient was comparable to that in inert ambient indicating that the interstitial concentration plays a minimal role in interdiffusion. A fractional interstitial component, f1, equal to 0.10 is estimated for annealing temperatures in the range 900 to 1100 °C, while f1 increases to approximately 0.17 at 1200 °C. This may indicate a change in diffusion mechanism at a temperature greater than 1100 °C
Ultra Shallow Junction Formation by B+/BF2+ Implantation at Energy of 0.5 KEV
Authors: Kase M. , Kikuchi Y , Niwa H. , Kimura T.
Published: April 2011

This paper describes ultra shallow junction formation using 0.5 keV B+/BF2+ implantation, which has the advantage of a reduced channeling tail and no transient enhanced diffusion. In the case of l × 1014 cm−2, 0.5 keV BF2 implantation a junction depth of 19 nm is achieved after RTA at 950°C.
A Quasi-2d Model for Reverse Short Channel Effect
Authors: Zhu Huilong
Published: April 2011

A new physically-based model for reverse short channel effects has been developed. This kinetic model considers three species: neutral interstitial, immobile dopant and mobile interstitial-dopant pairs. To consider ion-implantation damage and stress effects on the Si/SiO2 interface, a non-uniform sink strength at the Si/SiO2 interface for interstitials has been assumed. ALAMODE, a PDE solver, was used to solve the model. Lateral boron distributions of NMOS devices in the channel near the Si/SiO2 interface have been simulated. Significant boron pile-up was found at the gate edges which is in quantitative agreement with the doping profiles extracted from experimental C-V data. The mechanism of the B diffusion in the channel region is discussed.
Activation Enthalpy of Sb Diffusion in Biaxially Compressed SiGe Layers
Authors: Kuznetsovt A. Yu. , Cardenast J. , Svenssont B. G. , Larsen A. Nylandsted , Hansen J. Lundsgaard
Published: April 2011

Enhanced Sb diffusion in biaxially compressed Si1-x-Gex layers is observed. Assuming the prefactors to be stress independent the Sb diffusion coefficients in biaxially compressed Si0.9Ge0.2 and Si0 8 Ge0.2 were extracted as 0.4 × 102 exp[− (3.98(eV) ± 0.12)/kT] and 1.3x 102 exp[− (3.85(eV) ±0.12)/kT] cm2 /s, respectively. The activation volume of Sb diffusion in Si1-xGex (x ≤ 0.2) is estimated to be close to ω, where ω is the volume corresponding to a silicon lattice site.
Lateral Ordering of Self-Assembled Ge Islands
Authors: Zhu Jian-Hong , Brunner K. , Abstreiter G.
Published: April 2011

Two-dimensionally ordered arrays of Ge islands are realized by molecular beam epitaxy on vicinal Si(001) surfaces with regular ripples. Deposition of a 2.5 nm Si0.55Ge0.45/10 nm Si multilayer on vicinal Si(001) surfaces gives rise to the formation of regular ripples with a typical period of 100 nm, due to step-bunching. The ripples lead to the long-range line-up of the Ge islands along their direction, while the strong repulsive interaction between the dense Ge islands determines their relative arrangement on different step bunches of a ripple. The ordering pattern can be controlled by the Ge coverage as well as the direction of the ripples. The Ge islands show a narrow size distribution with the lateral size limited by the ripple period

In contrast, when deposited directly on well-prepared biatomic-stepped vicinal Si(001) surfaces under the same growth conditions, only weak ordering of Ge islands along the step direction is achieved. No ordering of Ge islands has been observed, when a flat Si(001) surface is employed, where no obvious step-bunching occurs.

The results promise efficient control on the position and size of self-assembled and selfordered Ge islands by the steps prepared on vicinal surfaces.
Photoluminescence In Strain Compensated Siisigec Multiple Quantum Wells
Authors: Hartmann R. , Gennser U. , Grützmacher D. , Sigg H. , Müller E. , Ensslin K.
Published: April 2011

The effect of strain compensation on the band gap and band alignment of Si/SiGeC MQWs is studied by photoluminescence (PL) spectroscopy. Evidence for type-I band alignment of strain reduced SiGeC MQWs is found. Values for the conduction and valence band offsets are given. A band gap reduction for exactly strain compensated SiGeC compared to compressive SiGeC is observed. This behavior is interpreted in terms of strain induced splitting and confinement shifts of the quantum well states. A good agreement between the model and the PL data is obtained.
Influence Of Growth Conditions On The Thermal Quenching Of Photoluminescence From Sige/Si Quantum Structures
Authors: Buyanova I. A. , Chen W. M. , Ni W.-X. , Hansson G. V. , Monemar B.
Published: April 2011

In this work we study effects of growth temperature and use of surfactant during growth on thermal quenching of photoluminescence (PL) from SiGe/Si quantum wells (QWs) grown by molecular beam epitaxy (MBE). We show that although all investigated structures demonstrate intense and sharp excitonic emissions from the SiGe QWs at liquid helium temperature, thermal quenching of this PL critically depends on the growth conditions. In particular, the use of low (⁤ 550°C) growth temperatures or employing Sb as a surfactant during high temperature (620°C) growth considerably degrades the PL thermal quenching behaviour by introducing some competing quenching processes with low activation energies of about 5 meV. The optimum growth conditions judging from the PL thermal behaviour are realised during high temperature growth without surfactant (620°C). Even higher growth temperature is shown to be required during surfactant mediated growth to improve the thermal quenching behaviour. From optically detected magnetic resonance (ODMR) studies, the competing quenching processes are attributed to a thermal activation of non-radiative defects introduced during either low-temperature MBE growth or during surfactant-mediated growth.
A Novel Layer-By-Layer Hetero-Epitaxy Of Germanium On Silicon (100) Surface
Authors: Sugahara S. , Matsuyama M. , Hosaka K. , Ikeda K. , Uchida Y. , Matsumura M.
Published: April 2011

Layer-by-layer hetero-epitaxy of Ge has been successfully demonstrated on the Si(100) surface by combining the initial IML-Ge film growth on the Si surface and the successive Ge atomic-layer-epitxy (ALE), for the first time. The former was achieved using the substrate temperature modulation with alternate exposures of GeCL4 and atomic H, and the later was established by cyclic exposures of (CH 3)2GeH2 and atomic H under isothermal conditions. XPS measurements confirmed a discrete and uniform increase in the grown Ge film thickness with one monolayer/cycle step up to the critical Ge thickness, and no C contamination at the Ge/Si interface. Critical exposure for the saturated Ge adsorption was different from that for the homo-ALE on the bulk Ge surface.
Metalorganic Molecular Beam Epitaxy of GaAsP for Visible Light-Emitting Devices on Si
Authors: Yoshimoto M. , Saraie J. , Yasui T. , HA S. , Matsunami H.
Published: April 2011

GaAs1–xPx (0.2 <; x < 0.7) was grown by metalorganic molecular beam epitaxy with a GaP buffer layer on Si for visible light-emitting devices. Insertion of the GaP buffer layer resulted in bright photoluminescence of the GaAsP epilayer. Pre-treatment of the Si substrate to avoid SiC formation was also critical to obtain good crystallinity of GaAsP. Dislocation formation, microstructure and photoluminescence in GaAsP grown layer are described. A GaAsP pn junction fabricated on GaP emitted visible light (˜1.86 eV). An initial GaAsP pn diode fabricated on Si emitted infrared light.
Fabrication of Integrated Ferrite/Semiconductor Circulators
Authors: Oliver S. A. , How H. , Shi P. , Hu W. , Kozulin I. , McGruer N. E. , Zavracky P. M. , Vittoria C.
Published: April 2011

Integrated planar circulator circuits operating at frequencies near 10 GHz have been fabricated using transferred film techniques. A 100 micrometer thick film of single-crystal yttrium iron garnet was transferred onto a metallized silicon die using a bond and lap-back process. The alloy bond layer was formed through a low-temperature solid-liquid interdiffusion process using films of indium and gold. This bond layer proved of sufficient strength to permit removal of the gadolinium gallium garnet substrate through grinding, but chemical analysis of the bond shows that interdiffusion occurs between the bond and metallization layers. These integrated gamet/silicon circulator circuits show good device performance.
In Situ Monitoring of III-V Processing
Authors: Terry F. L.
Published: April 2011

Fabrication of high performance III-V devices and integrated circuits depends on careful control of layer thicknesses and compositions in the as-grown epitaxial layers and in the etching of these layers. The relatively high value of compound semiconductor devices (compared with high-volume Si devices) makes the use of advanced process control (with expensive in situ sensors) potentially advantageous. Considerable attention has been given to the problems of realtime feedback control of MBE growth systems. In this paper, I will discuss experiences with use of both in situ and ex situ monitors for controlling reactive ion etching (RIE) of III-V materials. Specific examples from an electron cyclotron resonance (ECR) RIE base contact etch from an AlInAs/GalnAs HBT process will be given. The relative merits of reflection-based wafer sensors vs. process state sensors (optical emission spectroscopy and mass spectroscopy) will be discussed. The unique opportunities and problems associated with the III-V materials and required etch processes will be contrasted to implementation of advanced wafer state endpoint detection schemes in Si and flat panel display processes. Specific problems and solutions from our research which I will discuss include chamber seasoning effects on the drift of optical emission based endpoint detection schemes and signal processing techniques for accounting for this drift, modeling of the optical dielectric function of the compounds of interest vs. composition, and the effects of surface roughness on optical thickness measurements.
In Situ Control of Wet Etching Using Spectroscopic Ellipsometry
Authors: Cho Sang-Jun , Snyder P. G.
Published: April 2011

Etching of a GaAs/Al0.3Ga0.7As/GaAs heterostructure in a nonselective etch solution of 25:1:75 (citric acid: H2O2:H2O) was studied in-situ using real time spectroscopic ellipsometry (RTSE). Etch rates for GaAs and AIGaAs of 15.3 nm/min and 17.6 nm/min, respectively, were determined by numerically fitting RTSE data. RTSE was successfully used to stop the etch after removal of the thin GaAs cap, while removing very little of the underlying AlGaAs layer. In addition, etch depth into the AIGaAs layer was accurately controlled, using RTSE to stop the etch with 100 nm remaining. Finally, RTSE data for wet etching of a patterned sample (75% coverage with photoresist) showed similar behavior to that for the unpattemed sample.
Mobility characterization of p-type and n-type strained sil-x-yGexcy/Si Epilayer hall devices
Authors: Petersoa Jeff J. , Hunt Charles E. , Zappe Stefan F. , Obeneier Ernst , Westhoff Richard , Robinson McDonald
Published: April 2011

Mobilities in Si1-x-yGex Cy layers were measured using mesa etched Van der Pauw structures for alloy layers with 0 < x < 0.30 and 0 < y < 0.02 and doping levels of 1015 < N < 1018 cm-3. Mobilities in Si1-x-yGex Cy layers with x = 0.27 were found to approach Si mobilities for both μn and μp.While electron mobilities in phosphorous-doped SiGeC decrease with doping concentration, hole mobilities in boron-doped SiGeC increase with doping level, indicating ionized impurity scattering is not dominant for μp over the temperature range studied.
Kinetic Monte Carlo Simulation of Dislocation Dynamics
Authors: Lin Karin , Chrzan D. C.
Published: April 2011

A kinetic Monte Carlo simulation of dislocation motion is introduced. The dislocations are assumed to be composed of pure edge and screw segments only, and are assumed to be confined to a fixed lattice. The stress and temperature dependence of the dislocation velocity is studied. It is also noted that the simulated dislocations display kinetic roughening.
Shock Wave Response of Materials at Different Length Scales
Authors: Gupta Y.M.
Published: April 2011

After a brief introduction to shock wave propagation in solids, recent experimental developments to understand the real time response of shocked materials at various length scales are outlined. Results from two representative studies are summarized: xray diffraction to examine elastic-plastic deformation in shocked LiF crystals; and picosecond optical absorption to examine structural transformation in shocked CdS crystals. Issues related to examining material processes at different length scales in shock wave experiments are discussed briefly.
Modeling of Segregation and Microstructural Evolution near Grain Boundary in FE-CR-NI Alloy Under Irradiation
Authors: Sakaguchi N. , Watanabe S. , Takahashi H.
Published: April 2011

We have investigated the solute segregation and simultaneous evolution of extended defects in an Fe-Cr-Ni alloy during irradiation by computer simulation. It sheds a light on the accomplishment of performing “the combined total calculation” or “the muliscale modeling” which deals with both radiation-induced segregation and various kinds of internal sink evolution. The formation of dislocation-free zone (DLFZ) was predicted in the vicinity of a grain boundary. It indicated that DLFZ formation is controlled by solute diffusional process via point defects diffusion near the grain boundary and the activation energy obtained by the width of DLFZ corresponds to the half of the value of the radiation-enhanced solute diffusivity.
Kinetic Lattice Monte Carlo Simulations of Cascade Aging in Iron and Dilute Iron-Copper Alloys
Authors: Wirth B. D. , Odette G. R.
Published: April 2011

Neutron hardening and embrittlement of pressure vessel steels is due to a high density of nm scale features, including copper-manganese-nickel rich precipitates and what are generally believed to be defect cluster-solute complexes. It has been postulated that the sub nanometer defect cluster-solute complexes form directly in displacement cascades. Cluster-complexes that are thermally unstable mediate the effect of flux on embrittlement kinetics. Larger cluster-complexes, that are relatively thermally stable for irradiation times up to 1 Gs, cause embrittlement in low copper steels. Robust characterization of these two types of so-called matrix defects has been an elusive goal. In this work, Kinetic Lattice Monte Carlo (KLMC) simulations of the long term evolution of the vacancy-rich cascade core regions were carried out for both pure iron and dilute iron-copper alloys at the nominal irradiation temperature of 563°K up to times when the vacancy clusters completely dissolve. Energetics were based on lattice embedded atom method potentials. Special time scaling and pulse annealing techniques were used to deal with the enormous range of inherent time scales involved, viz., rapid free vacancy jumps to slow emission from large complexes. Three-dimensional clusters rapidly form, containing a wide range of vacancies, as well as copper atoms in alloys. Small complexes are very mobile and growth takes place primarily by coalescence. The vacancy clusters ultimately dissolve at times from less than 0.1 to more than 100 MS. These simulations support the hypotheses that cascade cluster-complexes constitute both thermally stable and unstable matrix defect features.
Irradiation-Enhanced Diffusion in Metallic Glasses
Authors: Schuler T. , Scharwaechter P. , Frank W.F.J.
Published: April 2011

The influence of irradiation with particles (H+, He+, 15N+) on the self-diffusion in relaxed metallic glasses (59Fe in Fe91Zr9, 59Fe in Co58Fe5Ni10Si11B16, 95Zr in Fe24Zr76) has been investigated by means of the radiotracer technique using ion-beam sputtering for serial sectioning of the specimens. Combination of the results of these experiments with accompanying molecular-dynamics simulations not only leads to an understanding of a novel phenomenon of irradiation-enhanced diffusion observed on these materials, but also confirms and refines our previous view that, in the absence of irradiation, diffusion in relaxed metallic glasses occurs by collective diffusion mechanisms not involving intrinsic point defects as diffusion vehicles.
Structural Analysis of a Completely Amorphous 238Pu-Doped Zircon by Neutron Diffraction
Authors: Fortner Jeffrey A. , Badyal Yaspal , Price David C. L. , Hanchar John M. , Weber William J.
Published: April 2011

The structure of a completely amorphous zircon was determined by time-of-flight neutron diffraction at Argonne's Intense Pulsed Neutron Source (IPNS). The sample of metamict zircon (ZrSiO4), initially doped to 8.85 weight percent 238pu, had been completely amorphized by alpha-recoil damage since its synthesis in 1981 at the Pacific Northwest National Laboratory (PNNL). The measured diffraction structure factor, S(Q), indicated a completely amorphous sample, with no signs of residual zircon microcrystallinity. The pair distribution function obtained indicated that the structure was that of an oxide glass, retaining the Si–O, Zr–O, and O–O bond lengths of crystalline zircon.
Cathodoluminescence Microanalysis of Electron Irradiation Damage in Wide Band Gap Materials
Authors: Kalceff M.A. stevens , Phillips M.R. , Toth M. , Moon A.R. , Jamieson D.N. , Orwa J.O. , Prawer S.
Published: April 2011

Cathodoluminescence (CL) microanalysis (spectroscopy and microscopy) in an electron microscope enables both pre-existing and irradiation induced local variations in the bulk and surface defect structure of wide band gap materials to be characterized with high spatial (lateral and depth) resolution and sensitivity. CL microanalytical techniques allow the in situ monitoring of electron irradiation induced damage, the post irradiation assessment of damage induced by other energetic radiation, and the investigation of irradiation induced electromigration of mobile charged defect species. Electron irradiated silicon dioxide polymorphs and MeV H+ ion implanted Type Ila diamond have been investigated using CL microanalytical techniques.
Structure and Thermoelectric Properties of SrBiTe3; 12-Fold Superstructure Caused by Distortion of the Two-Dimensional Te-Nets
Authors: Choi Kyoung-Shin , Chung Duck-Young , Heising Joy , Brazis Paul W. , Kannewurf Carl R. , Kanatzidis Mercouri G.
Published: April 2011

The ternary compound, SrBiTe3, was prepared by the molten flux method. It crystallizes in the orthorhombic space group Pmmn with a=4.665(2)Å, b=4.517(2)Å, c=16.129Å, and Z=2. The compound is composed of a NaCl-type [Bi2Te4]2- layer and a flat square (Te2)2- net with equal Te-Te distances of 3.24Å. The Sr2+ ions are stabilized between the layers in monocapped square antiprismatic sites. X-ray and electron diffraction studies reveal a 12-fold superstructure due to subtle distortions within the Te net of the compound. The superstructure was refined in the monoclinic space group C2 with a=27.923(5)Å, b=32.228(6)Å, c=4.5069(9)Å, β=90.000(3)°. The compound is a semiconductor with a band gap value of 0.14 eV. It melts incongruently at 613 °C.
Laser Machining with Ultrashort Pulses: Effects of Pulse-Width, Frequency and Energy
Authors: Bliss D. E. , Adams D. P. , Cameron S. M. , Luk T.S.
Published: April 2011

The benefits of short pulse (femtosecond) laser machining over conventional nanosecond lasers have been well demonstrated: higher aspect ratio features with smaller remelt zones and less recast material. However, shock induced defects can degrade the mechanical, electrical and optical properties of the remaining material, especially in brittle materials. Our focus is to reduce the amount of defects created while maintaining the machining advantages of using ultra-short pulses. Utilizing a chirped pulse amplified Ti:Sapphire laser with a pulse energy of 1 mJ and a pulsewidth of 120 fs we investigated the effects of pulsewidth, laser frequency and pulse energy on the controlled micro-ablation of Kovar and silicon films. Hole morphology and diameter were characterized by SEM. Hole depth was measured by laser profilometry. Hole volumes were determined by a combination of profilometry and SEM to determine the rate of material removal. The ablation thresholds for both Kovar and Si are between 200–300 mJcm−2.
Sequential N-Fold (N<4) Electrodeposition of YBa2Cu3O7-δ HTSC Films on Silver Substrates
Authors: Martín-Gonzilez M. S. , Morán E. , Sáez-Puche R. , Alario-Franco M. Á.
Published: April 2011

Electrodeposition of multimetallic films at room temperature on metallic substrates followed by oxidation at high temperature (~ 900°C) has often been employed to prepare high temperature superconducting (HTSC) films. A difficulty with this otherwise cheap and simple process is that the degree of surface covering is usually not very high. We have attempted to remediate this problem by sequentially repeating the deposition process on the same film. In this way, we have improved quite markedly critical current density (Jc) of films obtained on Silver substrates.

To quote some figures, Jc at 1 T is ~ 400 A/cm2 after the first deposition/oxidation process and it increases to ~ 2 000 A/cm2 after the fourth one. The evolution of the morphology of the films has been followed by means of scanning electron microscopy (SEM). It shows that, although the degree of surface coverage never attains 100 %, a substantial proportion of the substrate is well coated.

We have also studied the influence of mechanical pressure on the metallic film before the thermal treatment; after the fourth deposition, a pressure of ~15 KBar was applied. In this case a ~ 7% increase in Jc was observed and the density after compression (6.98 g/cm3) attains almost 100 % of the theoretical value for YBa2Cu3O7-δ (Ybacuo).
Hydrothermal Synthesis and Electrochemical Properties of Layered Vanadates
Authors: Livage J. , Boujhedja L. , Castro-Garcia S. , Julien C.
Published: April 2011

The synthesis of vanadates from aqueous solutions leads to a large variety of crystalline materials. The nature of molecular precursors mainly depends on pH and three different pH ranges can be distinguished. Cationic precursors are formed at low pH. Precipitation is obtained via the addition of anions leading to materials in which [VO6] octahedra are linked through anions. V2O5,nH2O gels are formed around the Point of Zero Charge (pH=2). They are made of ribbon-like particles and exhibit interesting properties as cathodic materials. Electrochemical properties depend on the drying procedure. Moreover, intercalation reactions lead to a whole range of new inorganic and organic bronzes. Chain metavanadates are precipitated from anionic precursors in basic aqueous solutions. Vanadium coordination decreases and they are made of corner sharing [VO4] tetrahedra. Layered structures are formed in the pH range where negatively charged species such as [VO(OH)4(OH2)]− should behave as precursors. Condensation occurs via V-OH groups in the equatorial plane leading to layered structures in which cations are inserted between the vanadate planes. Some reduction occurs when organic cations such as tetramethyl ammonium [N(CH3)4]+ are used leading to mixed valence vanadates. Electron delocalization is observed in these compounds but Li insertion is hindered by large organic cations. Better electrochemical properties are observed with smaller inorganic cations. Fibrous crystals of NaV3O8,H2O are formed in the presence of NaOH whereas the mixed valence bronze α'-NaxV2O5 is obtained when both NaOH and TMAOH react with V2O5. This fibrous morphology appears to improve diffusion processes at the electrode-electrolyte interface.
Investigations of The Local Structure in Lithium Nickel Cobalt Oxide Cathode Materials
Authors: Castro-Garcia S. , Massot M. , Julien C.
Published: April 2011

We have studied the modifications of structural and physical properties which occur during delithiation of lithium-nickel-cobalt oxide cathode materials. Long-range and short-range orders have been investigated using XRD, Raman and FTIR spectroscopies. Different samples LixNi0.7Co0.3O2 (0.5≤x_≤1) were prepared by electrochemical lithium deintercalation from LixNi0.7Co0.3O2. Electrochemical extraction of lithium was carried out using Li/LiCIO4 in PC/LixNi0.7Co0.3O2 cells in the potentiometric method with potential step of 10 mV. During the first charge of the Li//LixNi0.7Co0.3O2 cell, the change in the cathode structure was followed by x-ray powder diffraction and vibrational spectroscopies at room temperature. A good correlation is found between XRD data and the local environment of the host lattice. Detailled analysis of vibrational spectra shows that the octahedral oxygen environment of Li+ ions remains stable in the investigated domain of concentration.
High Surface Reticulated Ceramics for Catalytic Applications
Authors: Sweeting T. B. , Karst D. L. , Norris D. A.
Published: April 2011

The physical surface characteristics of three reticulated ceramic materials with and without wash coating are presented. The effect of an addition of 30 volume percent, 15-micron fugitive material on these characteristics is also reported. The fugitive increased pore volume but had little impact on surface area and strength.
Production, Consolidation, Sintering, and Stability of Novel Nano-Crystalline Zirconia Catalyst Support Powders
Authors: Darab John G. , Neuenschwander Gary G. , Elliott Douglas C. , Frye John G. , Strauss Joseph T.
Published: April 2011

Nano-crystalline, zirconium oxide/oxyhydroxide particulates were produced using a novel, continuous, flow-through hydrothermal technology developed at the Pacific Northwest National Laboratory. Homogeneous aqueous solutions containing ZrO(NO 3)2 and urea were pumped at pressures of 6000-8000 psi through a heated stainless steel reaction tube at 340-350°C. Flow at pressure was maintained using a nozzle at the down-stream end of the reaction tube. In this process, termed Rapid Thermal Decomposition of precursors in Solution (RTDS), the formation of zirconium oxide/oxyhydroxide nano-crystals (diameters of generally less than 15-nm) occurred during the solution's brief residence time (<15 seconds) in the reaction tube, yielding aqueous slurries of agglomerated particulates. Powders were separated from these slurries, washed, then dried. RTDS powder prepared from 0.3M ZrO(NO3)2 and 0.6M urea were mixed with binder and formed into pellets using a commercial screw extruder. These extrudates were subsequently sintered at 500°C, yielding zirconia catalyst support pellets with a measured surface area of 113 m2/g. After application of 3% ruthenium metal to the sintered RTDS zirconia extrudates, the resulting catalyst was evaluated for catalytic activity using the hydrothermal hydrogenation of the sugar xylose to xylitol as a model reaction. After 3 hours at 140°C, the RTDS catalyst exhibited useful activity with 92% conversion and 66% selectivity to xylitol formation.
Pillaring of a Layered Titanate With Alumina: Effect of Hydrolysis Solution
Authors: Kooli F. , Sasaki T. , Rives V. , Watanabe M.
Published: April 2011

A layered titanate with a lepidocrocite-type structure has been pillared with Al13 Keggin ions to prepare a porous and high-surface-area material. Pillaring was achieved by ion exchange of hexylammonium (HA-Ti) or tetrabuthylammonium (TBA-Ti) intercalated titanates with Keggin Al13 complex. The thermal stability of the Al13 intercalates depended on the amount of aluminum incorporated. The surface area and porosity can be tailored by controlling the amount of aluminum uptake and by the nature of base used to prepare the aluminium pillaring solution. In addition, the material derived from HA-Ti exhibited a sharp pore size distribution with an average diameter of 2 nm, while the pillared product obtained from TBA-Ti showed mostly a broad mesoporous distribution with an average pore diameter of 4 nm.
Synthesis of Hydrotalcite-Like Precursor Compounds MgCo(11) Co(111).-HTlcs
Authors: Zeng H.C. , Xu Z.P. , Qian M.
Published: April 2011

Precursor compounds of MgCo(11)Co(111)-HTlcs for Mg-Co oxide catalysts have been synthesized by coprecipitation in an ammoniacal solution and hydrothermal treatments under various O2/N2 atmospheres. Using elemental analysis (EA) and redox titration, it is found that about 23% of original Co2+ are oxidized to Co+3, resulting in formation of hydrotalcite-like (HTI) structure. The anion (NO3) intercalation increases with the rise in O2 partial pressure. X-ray diffraction pattern shows a conversion from brucite-like to HTl structures with increase of O2 partial pressure. It is found that thermal stability of the HTl-compounds is proportional to the Mg content. Higher specific surface areas are observed for decomposed products with low Co/Mg ratio. A trace amount of CO3O4 is also detected by FTIR for samples synthesized under high O2 partial pressures, which can be attributed to a deeper oxidation of Co2+.
Resorbable Structures for Schwann Cell Enhanced Peripheral Nerve Regeneration
Authors: Silva A.E. , Summerhayes LC. , Trantolo D.J. , Wise D.L. , Catftaneo M.V. , Gresser J.D. , Holway A. , Wang K-K , Bryan D.J.
Published: April 2011

Schwann cells play a dual role serving as a physical framework for regenerating nerves, providing extracellular matrix proteins and specific adhesion molecules facilitating attachment and cell movement, and as a source of stimulatory factors mediated by the release or reception of different ligands important in growth and cell signaling events. To investigate the role of one such ligand, glial growth factor (GGF), in peripheral nerve regeneration, a bioabsorbable nerve guide, prepared from a poly(lactic-co-glycolic) acid (PLGA) foam was seeded with autogenous Schwann cells in the presence and absence of growth factor and evaluated in vivo using a rat sciatic nerve regeneration model. Four weeks post-operatively peripheral nerve regeneration was evident. The resorbable foam implant demonstrated extensive neo-vascularization in and around the guide with no evidence of an inflammatory response or encapsulation. The study showed a statistically significant increase in all measured parameters of nerve regeneration in the presence of GGF. Increased numbers of blood vessels in the regenerated tissue accompanied increased total axon counts after twelve weeks. The addition of exogenous Schwann cells resulted in reduced total axon counts perhaps due to the competition for limited growth factors released by the regenerating tissues. The Schwann cell groups, however, displayed the highest myelination indices recorded likely reflecting the role of Schwann cells in the myelination process. Measurements of conduction velocities (EMGs) revealed the highest conductance velocities recorded in nerves regenerated in the presence of both GGF and Schwann cells. Clearly, the inclusion of GGF in the nerve regenerative process is beneficial with respect to both the generation of new axons and the establishment of a functional endpoint.