bluuebunny/crossref_metadata_2025 huggingface dataset:
Enzyme-Mediated Oscillatory Drug Release through Hydrogel Membranes
Authors: Baker John P. , Siegel Ronald S.
Published: April 2011

Implantable polymeric drug-delivery devices have been constructed to deliver drugs at welldefined rates. Typically, these devices have been designed to deliver drugs at a constant rate, or in response to the concentration of a certain body metabolite. For some drugs, pulsatile delivery is sought. For example, under normal conditions, human growth hormone is released in the body in periodic bursts. Current treatments for HGH deficiency often fail because HGH is not administered following the endogenous pattern. Thus, pulsatile hormone-replacement therapy should be considered. Also, it may be useful to deliver in a periodic, pulsatile manner drugs that exhibit significant acute tolerance.

Currently, an oscillator is under development that is fueled by endogenous compounds and contains a variable-permeability membrane. The membrane's permeability to the substrate of an enzymatic reaction is assumed to be dependent on the concentration of the product of the reaction in a manner that displays product inhibition. Under certain conditions, this negative-feedback control can lead to oscillations in the membrane's permeability to substrate. If the membrane's permeability to a drug is simultaneously affected, then this will lead to oscillatory drug release.

We report encouraging initial studies. A simple theoretical model has been developed for the membrane oscillator, and results of simulations based on the model are discussed.

Diffusion-cell studies have been performed with a variable-permeability poly(N-isopropylacrylamide- co-methacrylic acid) hydrogel membrane. Using glucose as a probe solute, the results show that lowering the pH induces hydrogel volume collapse and cessation of glucose permeation across the membrane.
Tailored Viscosity Reduction in Aqueous Hydroxypropylcellulose Solutions
Authors: Prevysh Victoria A. , Spontak Richard J. , Khan Saad A.
Published: April 2011

Polysaccharides, including cellulosic derivatives such as hydroxypropylcellulose (HPC), are used extensively in the pharmaceutical industry due to their biocompatibility and self-organization properties. While drug delivery vehicles employing, for instance, aqueous polysaccharide gels are desirable, production of such gels can be hindered by tremendously high solution viscosity. In this work, we describe a novel means by which to reduce the viscosity and enhance the solubility of aqueous HPC. Here, the efficacy of several additives which promote HPC viscosity reduction through molecular salting-in is examined by dynamic rheology and light/electron microscopy.
ECR-MBE and GSMBE of Gallium nitride on Si(111)
Authors: Rossner U. , Rouviere J.-L. , Bourret A. , Barski A.
Published: April 2011

Electron Cyclotron Resonance Plasma Assisted Molecular Beam Epitaxy (ECR-MBE) and Gas Source Molecular Beam Epitaxy (GSMBE) have been used to grow hexagonal GaN on Si (111). In the ECR-MBE configuration high purity nitrogen has been used as nitrogen source. In GSMBE ammonia was supplied directly to the substrate to be thermally cracked in the presence of gallium.

By a combined application of in-situ reflection high-energy electron-diffraction (RHEED) and cross-sectional transmission electron microscopy (TEM) the growth mode and structure of GaN were determined. The growth mode strongly depends on growth conditions. Quasi two dimensional growth was observed in ECR-MBE configuration for a substrate temperature of 640°C while three dimensional growth occured in GSMBE configuration in the temperature range from 640 to 800°C.

Low temperature (9 K) photoluminescence spectra show that for samples grown by ECR-MBE and GSMBE a strong near band gap emission peak dominates while transitions due to deep level states are hardly detectable. The best optical results (the highest near band gap emission peak intensity) have been observed for samples grown by GSMBE at high temperature (800°C). This could be explained by the increase of grain dimensions (up to 0,3 – 0,5 μm) observed in samples grown by GSMBE at 800°C.
Growth of High Quality InGaN Films by Metalorganic Chemical Vapor Deposition
Authors: Roberts J. C. , McIntosh F. G. , Boutros K. S. , Bedair S. M. , Moussa M. , Piner E. L. , He Y. , El-Masry N. A.
Published: April 2011

InGaN based optical devices can cover from the violet through orange regions of the visible spectrum. Difficulties in the growth of this alloy, which have impeded its applications, include problems such as the high vapor pressure of In, weak In-N bonds and lack of sufficient nitrogen during growth. We report on the MOCVD growth of InxGa1−xN (0 < x < 0.4) on sapphire substrates in the 750 - 800 °C temperature range. X-ray diffraction data show full width at half maximum line widths as narrow as 250 arcsec for low values of x, while films with higher lnN% exhibit broader line widths. Room temperature photoluminescence spectra exhibit band edge emission, with emission from deep levels increasing with x. Preliminary investigations of AlGaN/lnGaN/AlGaN double heterostructures have been conducted.
GaAsN Alloys and GaN/GaAs Double-Hetero Structures
Authors: Sato Michio
Published: April 2011

Ternary alloys; GaAsN (N<3%) were grown by plasma-assisted metalorganic chemical vapor deposition using triethylgallium, AsH3, and plasma-cracked NH3 or N2 as the precursors. More N atoms were incorporated into the alloys from N2 than NH3 at constant N/As ratios. Both photoluminescence peaks and optical absorption edges were redshifted from GaAs bandgap with increasing the N content, indicating the GaAsN alloys have narrower bandgaps than GaAs.

GaN/GaAs double-hetero structures were grown by exposing GaAs surfaces to N-radical flux to replace surface As atoms by N atoms, and by growing GaAs on the thin GaN layers. When the GaN thickness exceeded one-monolayer, the GaN/GaAs interfaces and the GaAs cap layers deteriorated drastically. The one-monolayer-thick GaN embedded in GaAs attracts electrons and shows intense photoluminescence, whereas the GaN cluster is non-radiative, probably because of the defects caused by the large lattice-mismatch between GaN and GaAs.
Single Crystal Wurtzitic Aluminum Nitride Growth on Silicon Using Supersonic Gas Jets
Authors: Ustin S. A. , Lauhon L. , Brown K. A. , Hu D. Q. , Ho W.
Published: April 2011

Highly oriented aluminum nitride (0001) films have been grown on Si(001) and Si (111) substrates at temperatures between 550° C and 775° C with dual supersonic molecular beam sources. Triethylaluminum (TEA;[(C2H5)3Al]) and ammonia (NH3) were used as precursors. Hydrogen, helium, and nitrogen were used as seeding gases for the precursors, providing a wide range of possible kinetic energies for the supersonic beams due to the disparate masses of the seed gases. Growth rates of AIN were found to depend strongly on the substrate orientation and the kinetic energy of the incident precursor; a significant increase in growth rate is seen when seeding in hydrogen or helium as opposed to nitrogen. Growth rates were 2–3 times greater on Si(001) than on Si(111). Structural characterization of the films was done by reflection high energy electron diffraction (RHEED) and x-ray diffraction (XRD). X-ray rocking curve (XRC) full-width half-maxima (FWHM) were seen as small as 2.5°. Rutherford back scattering (RBS) was used to determine the thickness of the films and their chemical composition. Films were shown to be nitrogen rich, deviating from perfect stoichiometry by 10%–20%. Surface analysis was performed by Auger electron spectroscopy (AES).
Analysis of Strain in GaN on Al2O3 and 6H-SiC: Near-Bandedge Phenomena
Authors: Edwards N. V. , Bremser M. D. , Weeks T. W. , Kern R. S. , Liu H. , Stall R. A. , Wickenden A. E. , Doverspike K. , Gaskill D. K. , Freitas J. A. , Rossow U. , Davis R. F. , Aspnes D. E.
Published: April 2011

We report the dielectric functions of various GaN samples as measured by spectroscopic ellipsometry. Structure related to the A and B excitons is resolved at room temperature, in principle allowing strain to be assessed. However, the data indicate that dead-layer and dispersion effects are present, preventing a simple interpretation. We discuss various complications including the Edn/dE contribution to dispersion, which is important for laser action. Our data appear to indicate that the spin-orbit splitting of GaN is about 15 meV, somewhat larger than the currently accepted value of about 11 meV.
Transition Metal Luminescence in AlN Crystals
Authors: Pressel K. , Heitz R. , Nilsson S. , Thurian P. , Hoffmann A. , Meyer B.K.
Published: April 2011

We study deep defects in AIN crystals in the near infrared by photoluminescence and compare the observed emissions with those in GaN. By below bandgap excitation with an Ar ion laser three no-phonon lines at 1.043 eV, 0.943 eV, and 0.797 eV were detected, which are caused by different residual transition metal contaminants. The weak emission at 1.043 eV and the intensive emission at 0.797 eV show A1N related phonon sidebands, whereas the emission at 0.943 eV has practically no phonon sideband. No hot lines could be detected for the emissions at 0.943 and 0.797 eV in temperature dependent measurements. We discuss possible identifications of the luminescence centers and the similarity between GaN and AIN in view of transition metals.
Dry Etching of III-V Nitrides
Authors: Pearton S. J. , Shul R. J. , McLane G. F. , Constantine C.
Published: April 2011

The chemical inertness and high bond strengths of the III-V nitrides lead to slower plasma etching rates than for more conventional III-V semiconductors under the same conditions. High ion density conditions (>3×1011cm−3) such as those obtained in ECR or magnetron reactors produce etch rates up to an order of magnitude higher than for RIE, where the ion densities are in the 109 cm−3 range. We have developed smooth anisotropic dry etches for GaN, InN, AlN and their alloys based on Cl2/CH4/H2/Ar, BCl3/Ar, Cl2/H2, C12/SF6, HBr/H2 and HI/H2 plasma chemistries achieving etch rates up to ∼4,000Å/min at moderate dc bias voltages (≤-150V). Ion-induced damage in the nitrides appears to be less apparent than in other III-V’s. One of the key remaining issues is the achievement of high selectivities for removal of one layer from another.
(Negative) Electron Affinity of AlN and AlGaN Alloys
Authors: Nemanich R.J. , Benjamin M.C. , Bozeman S.P. , Bremser M.D. , King S.W. , Ward B.L. , Davis R.F. , Chen B. , Zhang Z. , Bernholc J.
Published: April 2011

The electron affinity of a semiconductor defines the relationship of the vacuum level and the semiconductor band structure. It is dependent on the atomic orbitals of the material and the surface termination. We report experimental and theoretical results that support the presence of a negative electron affinity on AlN and the Al rich AlGaN alloys. The GaN surface is found to exhibit a (positive) electron affinity of 3.3eV. The experimental measurements employ UV-photoemission spectroscopy on in situ gas-source MBE samples and on CVD samples. Theoretical results indicate that the (negative) electron affinity of AlN depends sensitively on the surface reconstruction and adatom termination. The experimental dependence of the electron affinity on alloy concentration is presented. The results indicate that AlGaN alloys with band gap similar or greater than that of diamond will exhibit a negative electron affinity. Field emission results are reported, and the characteristics are similar to those obtained from a diamond film. Issues related to cold cathode electronic devices based on NEA surfaces are noted.
Negative Differential Resistivity in GaN Metal-Semiconductor-Metal Photoconductors
Authors: Huang Z.C. , Chen J.C. , Zheng Youdou , Mott D.B.
Published: April 2011

We have observed a negative differential resistivity (NDR) in metal-semiconductor-metal (M-S-M) photoconductor made from unintentionally doped GaN grown by metalorganic chemical vapor deposition. The threshold field for the onset of NDR was found to be independent of the spacing of M-S-M fingers, and was measured to be 1.91×105 V/cm for GaN with an n-type carrier concentration of 1014 cm−3. We believe that the observed NDR is due to transferred electron effect in GaN. The threshold field value is very close to the value obtained from the theoretical simulation. This observation, to the best of our knowledge, is the first experimental evidence of transferred-electron effects in GaN, which is important in understanding GaN energy band structure and in the application of Gunn-effect devices using GaN materials.
Ion Implantation Doping and High Temperature Annealing of GaN
Authors: Zolper J. C. , Hagerott crawford M. , Howard A. J. , Pearton S. J. , Abernathy C. R. , Vartuli C. B. , Yuan C. , Stalls R. A. , Ramer J. , Hersee S. D. , Wilson R. G.
Published: April 2011

The III-V nitride-containing semiconductors InN, GaN, and AIN and their ternary alloys are the focus of extensive research for application to visible light emitters and as the basis for high temperature electronics. Recent advances in ion implantation doping of GaN and studies of the effect of rapid thermal annealing up to 1100 °C are making new device structures possible. Both p- and n-type implantation doping of GaN has been achieved using Mg co-implanted with P for p-type and Si-implantation for n-type. Electrical activation was achieved by rapid thermal anneals in excess of 1000 °C. Atomic force microscopy studies of the surface of GaN after a series of anneals from 750 to 1100 °C shows that the surface morphology gets smoother following anneals in Ar or N2. The photoluminescence of the annealed samples also shows enhanced bandedge emission for both annealing ambients. For the deep level emission near 2.2 eV, the sample annealed in N2 shows slightly reduced emission while the sample annealed in Ar shows increased emission. These annealing results suggest a combination of defect interactions occur during the high temperature processing.
Ion Damage and Annealing of Epitaxial Gallium Nitride and Comparison With GaAs/AlGaAs Materials
Authors: Tan H.H. , Williams J.S. , Yuan C. , Pearton S.J.
Published: April 2011

Ion damage build up has been measured by ion channeling in good quality epitaxial GaN films on sapphire. GaN is found to be remarkably resistant to ion damage, with extremely efficient dynamic defect annihilation occurring at liquid nitrogen temperature during ion implantation. When disorder does accumulate at doses around 1016cm−2 of 90 keV Si ions, the surface appears to be a strong sink for damage build up and possibly the nucleation of amorphous layers. Once ion disorder has been produced in GaN, it is extremely difficult to remove by annealing. GaN exhibits disordering and annealing behaviour which is somewhat similar to that in high Al-content AlGaAs.
Growth of Silicon-Doped and High Quality, Highly Resistive GaN for FET Applications
Authors: Doverspike K. , Wickenden A.E. , Binari S.C. , Gaskill D.K. , Freitas J.A.
Published: April 2011

We have shown the ability to grow thin, high mobility, GaN channel layers on high quality, highly resistive GaN. The growth, characteristics, and device results of two types of MESFET structures were discussed. The first device structure consists of a 2000Ǻ, 2 × 1017cm−3 Si-doped channel layer, grown on 3µm of highly resistive GaN, while die second structure (recessed-gate MESFET) had a 1000Ǻ, 1 × 1018cm−3 Si-doped, n+ capping layer deposited on a 2000Ǻ, 2 × 1017cm−3 Si-doped channel layer. The first MESFET structure was operational at 500°C which is the highest reported operating temperature for a GaN device while the recessed-gate MESFET had a gmas high as 41mS/mm, which is the highest reported value for a GaN MESFET.
Pulsed Laser Ablation Growth and Doping of Epitaxial Compound Semiconductor Films
Authors: Lowndes Douglas H. , Rouleau Christopher M. , Geohegan D. B. , Puretzky A. A. , Strauss M. A. , Pedraza A. J. , Park J. W. , Budai J. D. , Poker D. B.
Published: April 2011

Pulsed laser ablation (PLA) has several characteristics that are potentially attractive for the growth and doping of chemically complex compound semiconductors including (1) stoichiometric (congruent) transfer of composition from target to film, (2) the use of reactive gases to control film composition and/or doping via energetic-beam-induced reactions, and (3) low-temperature nonequilibrium phase formation in the laser-generated plasma “plume.” However, the electrical properties of compound semiconductors are far more sensitive to low concentrations of defects than are the oxide metals/ceramics for which PLA has been so successful. Only recently have doped epitaxial compound semiconductor films been grown by PLA. Fundamental studies are being carried out to relate film electrical and microstructural properties to the energy distribution of ablated species, to the temporal evolution of the ablation pulse in ambient gases, and to beam-assisted surface and/or gas-phase reactions. In this paper we describe results of ex situ Hall effect, high-resolution x-ray diffraction, transmission electron microscopy, and Rutherford backscattering measurements that are being used in combination with in situ RHEED and time-resolved ion probe measurements to evaluate PLA for growth of doped epitaxial compound semiconductor films and heterostructures. Examples are presented and results analyzed for doped II–VI, I–III–VI, and column-Ill nitride materials grown recently in this and other laboratories.
Fabrication of CDS Thin Films Using Continuous Wave Laser Evaporation
Authors: Tenpas E.W. , Vuong K. D. , Orloff S. , Fagan J.G. , Wu V. , Wang X.W.
Published: April 2011

We report new results on continuous wave Nd: YAG laser deposition of Cadmium Sulfide (CdS) thin films. Substrates were soda-lime silicate (SLS) glass, silica glass, silicon, alumina, and copper coated formvar sheets. As-deposited films were characteristically mixtures of cubic and hexagonal phases. X-ray diffraction analysis reveals that two different grain size groups are present. As revealed by SEM micrographs, films had smooth surface morphology. Transmission electron microscopy analysis reveals that grain sizes were extremely small. Also, semiconductive behavior was noted.
Deposition of Diamond-Like Carbon Films by Excimer Lasers Using Frozen Source Gases
Authors: Hanabusa Mitsugu , Tsujihara Kiyohito , Zhengxin Liu , Ishihara Seiji , Uchida Hironaga
Published: April 2011

We deposited diamond-like carbon (DLC) films, using frozen acetylene and acetone as the target of laser ablation. The frozen gases were dissociated by an ArF laser and a KrF laser. The DLC films were deposited on quartz substrates below 300°C. We measured the Raman spectra to identify the deposited films as DLC. The films showed the broad Raman peak at 1540 cm-1. The number of particles mixed into the deposits was controlled by laser power densities. By using the ArF laser for frozen acetylene we could reduce the hydrogen concentration in the films, which showed a high degree of dissociation of the source gas. The oxygen content was kept at the same level in the films deposited from frozen acetone as from frozen acetylene. The present results suggested the importance of energetic and charged species ejected from the frozen gas target.
Applications of Laser Processing for Sensors and Actuators
Authors: Meunier M. , Izquierdo R. , Shen B. , Lecours A. , Allard M. , Bergeron A. , Hanus F. , Boughabah S. , Ivanov D. , Currie J.F. , Laude L. , Yelon A.
Published: April 2011

The fabrication of sensors and actuators requires new materials with multicomponent stoichiometry as well as new three-dimensional microstructures. We present several potential applications of laser processing for the fabrication of sensors and actuators. The first example concerns gas sensors which require ionic conductor multicomponent ceramics whose stoichiometry is not maintained by conventional sputtering methods. We have successfully employed pulsed laser deposition (PLD) for producing high quality NASICON (Na SuperIonic CONductor) thin films. XPS measurements show that all elements are transferred from a target of Na1+xZr2SixP3-xO12, (where 0 < x < 3 ) to the substrate, and that the composition of the thin film is very close to that of the target. Electrical measurements show good ionic conductivity. Thus, these films are suitable for the fabrication of electrochemical gas sensors. Since such ceramic thin films are very sensitive to liquids, wet etching is prohibited, and patterning is done using laser ablation. For other applications, a laser micromachining technique has been developed to make tunnels and cavities in Si under SiO2 films, based on the laser-induced CI2 etching of Si and high chlorine Si/SiO2 etch rate ratios. Tunnels with length of up to 3 mm and cavities of 100×100 cm2 were successfully fabricated in SiO2/Si bilayer samples. These are usable in microfluidic or gas pressure measurement systems.
Synthesis of Thin Films of Size Selected Silicon Nanocrystallites Using Pulsed Laser Ablation Supersonic
Authors: Werwa E. , Kolenbrander K.D.
Published: April 2011

Thin films composed of size selected silicon nanocrystallites have been fabricated and their photoluminescence behavior has been studied. The silicon nanocrystallites were produced using a pulsed laser ablation supersonic expansion source. This source typically generates silicon clusters of many different sizes, which leads to photoluminescence spectra with a large fiill width at half maximum. To best utilize our gas phase synthesis technique, we have performed size selection of the silicon clusters using a mechanical velocity selection apparatus. Films of these size selected nanocrystallites exhibited photoluminescence spectra which had a smaller full width at half maximum and which were peaked to the blue of the spectra of samples with a broader size distribution. These results suggest that the photoluminescence wavelength of these nanocrystallite thin films is determined by quantum confinement of the electrons and holes in the crystallites.
Raman Spectroscopy Study of Pulsed Laser Induced Structural Transformations in Amorphous Ge Films
Authors: García C. , Prieto A.C. , Jiménez J. , Siegel J. , Solís J. , Afonso C.N. , Chafai M.
Published: April 2011

Structural transformations induced in amorphous Ge films by picosecond laser pulses are studied by means of Raman spectroscopy and their dependence on parameters like the pulse fluence or the thermal conductivity of the substrate are analyzed. A correlation length model is used for studying the crystallization process, while the average bond angle distortion is used for determining the state of relaxation of the amorphous phase. Silicon and glass substrates are compared.
Real-Time Optical Monitoring of Tungsten Nucleation During Laser Induced Pyrolytic Cvd
Authors: Zhang Xiafang , Allen Susan D.
Published: April 2011

The nucleation of tungsten on bare Si and SiO2/Si surfaces by Ar ion laser induced CVD has been studied with high speed real-time specular reflection and scattering. Our experimental results show that the induction time of tungsten nucleation decreases with laser power and is longer on thicker SiO2 surfaces than on thin native SiO2 surfaces at the same laser power. The activation energy of tungsten nucleation on native SiO2/Si obtained from an Arrhenius plot of induction time is about 33 kJ/mol at temperatures less than 1000 K and 16 kJ/mol at temperatures higher than 1000 K. The results on bare Si with and without H2 reveal that the initial reaction mechanism appears to be the same in both cases. An Arrhenius plot of induction time shows two different apparent activation energies at different temperature ranges, which suggest that W nucleation is controlled by H atom desorption from the Si surface at temperatures less than 714 K and is dominated by Si atom reduction of WF6 molecules at surface temperatures greater than 800 K.
Laser Direct Writing of Aluminum Conductor Lines from a Liquid Phase Precursor
Authors: Chen Qijun , Allen Susan D.
Published: April 2011

Aluminum conductor lines were deposited on Si substrates from liquid phase triisobutylaluminum (TIBA) using a scanned argon ion laser. The vertical growth rate of Al lines initially increased, then decreased with increasing dwell time. The maximum vertical growth rate occurred at a particular dwell time depending upon the laser power. Lower vertical growth rates at longer dwell times are propably caused by the depletion of the reactant at the reaction site. A volcano deposit shape was observed, which became more pronounced as dwell time increased. The conductivity of the as-deposited Al lines decreased with increasing dwell time for our experimental conditions. To study the deposition kinetics and calculate the activation energy, the temperature rise on the Si surface was calculated by solving the nonlinear heat equation using finite difference method.
Epitaxial Silicon-Carbon Alloy Growth by Laser Induced Melting and Solidification
Authors: Kramer Kenneth M. , Thompson Michael O.
Published: April 2011

Ion implantation of carbon into single-crystal silicon followed by excimer laser irradiation was used to create supersaturated, epitaxial SixC1-x. films. Crystallization proceeded from the underlying single-crystal silicon through the carbon containing layers at velocities of approximately 5 m/s. Characterization by high-resolution x-ray diffraction and Fourier-transform infrared absorption indicate that the carbon is found predominantly on substi-tutional lattice sites for concentrations up to 1.4 at.% C. Secondary-ion mass spectrometry profiles and numerical mass transfer calculations were used to estimate the diffusion coefficient of carbon in the liquid as 2-3 × 10−4cm2/s with a segregation coefficient greater than 0.4. Unusual diffusion behavior was observed for the carbon at 1.4 at.% C. At higher concentrations, evidence of SiC precipitates was observed in transmission electron microscope images and FTIR absorption spectra.
Solid State Interfacial Reactions Between Tic Thin Films and Ti3AI Substrates
Authors: Si Weimin , Dudley Michael , Li Pengxing , Wu Renjie
Published: April 2011

The products and kinetics of solid state reactions between TiC and Ti3Al have been investigated using X-ray diffractometry (XRD) and Auger electron spectroscopy (AES) with Ar ion beam sputtering. Diffusion couples were prepared by sputtering TiC thin films onto polished Ti3AI substrates, and then isothermally annealed in vacuum in the temperature range of 800 to 1000°C for 0.25 to 2.25 hours. The thickness of the interfacial reaction layer was obtained from AES elemental concentration depth profiling, while the reaction products were identified from XRD spectra. In the TiC/Ti3Al system, the reaction product was primarily P(Ti3AlC) phase. The growth-rate of the reaction product was fitted to a parabolic growth law (dZ/dt = k1/Z) and the activation energy of the rate constant was about 36.16 kcal/mole. The reaction mechanism will be discussed on the basis of thermodynamical equilibrium in Ti-Al-C ternary system.
Nonisothermal Kinetics Study of Phase Evolution of Zn-Fe Intermetallics
Authors: Uwakweh O. N. C. , Liu Z. T. , Boisson M.
Published: April 2011

Through mechanical alloying of pure elemental powders of Fe and Zn, true homogeneous alloys of Γ (Fe3Zn10), Γ1(Fe5Zn21), δ (FeZn7) and ζ (FeZn13) intermetallic phases are formed. Based on nonisothermal kinetics analyses, the highest activation energies associated with the metastable to stable transformations of these phases are determined as follows: 170±1 kJ/mol, 2 51±2 kJ/mol, 176±1 kJ/mol and 73 7±4 kJ/mol for the Γ, Γ1, δ and ζ-phases, respectively. These values reflect different diffusion/thermally induced processes associated with the transition of each of these phases.
Phase Separation and Crystallization in the Bulk Amorphous Alloy Zr41Ti14Cu12.5Ni10Be22.5
Authors: Macht M.-P. , Wanderka N. , Wiedenmann A. , Wollenberger H. , Wei Q. , Klose S.G. , Sagel A. , Fecht H.J.
Published: April 2011

The decomposition and crystallization above the glass temperature of the bulk metallic glass Zr41Ti14Cu12.5Ni10Be22.5 and the crystallization during solidification of the melt were investigated by means of different analytical methods, including Transmission Electron Microscopy (TEM), Small Angle Neutron Scattering (SANS), Field Ion Microscopy with Atom Probe (FIM/AP).

Dependent on the thermal history these phase transitions lead to different phases and different microstructures of the alloy. During annealing above the glass tremperature the decomposition of the alloy into two supercooled liquid phases is observed by the formation of nanosized precipitates, which differ from the matrix by their Be and Ti contents. This decomposition retards significantly the subsequent crystallization, however it does not inhibit the formation of the phases which crystallize if the decomposition is bypassed by appropriate heat treatment. By stepwise crystallization a nanosized microstructure is formed consisting of three metastable phases and of stable Zr2Cu. This microstructure differ significantly from the crystalline equilibrium microstructure resulting from slow cooling of the melt. Crystallization of the amorphous alloy by very fast heating causes totally different microstructures.
Solid-Phase Epitaxial Growth of Amorphized GaAs: The Influence of Microscopic and Macroscopic Non-Stoichiometry
Authors: Belay K.B. , Llewellyn D.J. , Ridgway M.C.
Published: April 2011

The solid-phase epitaxial growth of amorphized GaAs has been characterized to investigate the influence of both microscopic and macroscopic non-stoichiometry on the onset of twinning and subsequent interfacial non-planarity. Microscopic non-stoichiometry or equivalently, chemical disorder on an atomic scale, was produced by implanting samples with equal doses of both Ga and As ions. In such samples, the onset of twinning and interfacial non-planarity where independent of the energy deposited in vacancy production, the latter considered a first estimate of relative differences in microscopic non-stoichiometry between samples. Twinning and interfacial non-planarity are thus independent of microscopic non-stoichiometry or alternatively, microscopic non-stoichiometry may approach saturation over the given dose range. In contrast, macroscopic non-stoichiometry produced by implanting samples with Ga or As ions influenced both the onset of twinning and interfacial non-planarity. Excess Ga was observed to have a greater effect than excess As. The influence of a macroscopic non-stoichiometry may be indicative that the availabiltiy of a lattice constitutent and/or defect is rate-limiting during solid-phase epitaxial growth. Macroscopic non-stoichiometry may also yield preferrential nuclueation sites for twinning and in the presence of excess Ga, molten precipitates could contribute to an observed rapid amorphous-to-crystalline transformation.
Kinetic Study on the Formation of the Aragonite-Like Phase Ba(CuOx)1-Y(CO3)y
Authors: Tomasi A. , Galvanetto E. , Matacotta F.C. , Nozar P. , Scardi P. , Migliori A.
Published: April 2011

A systematic study on phase formation and stabilisation in the Ba-Cu-C-O system in the temperature range 20-500°C, under various atmospheres, by traditional thermal analysis techniques, high temperature X-ray diffraction and high resolution electron microscopy, has permitted to identify and characterise the formation kinetics of a new copper containing phase isomorphic to γ-BaCO3.
Studies on Dynamics of Interfaces in Cu-Ai-Zn-Ni Alloy
Authors: Shen KM. , Huang Y.N. , Zhang Z.F. , Yang Z. , Wang X.M. , Wang Y.N. , Tan S.S.
Published: April 2011

An internal friction peak associated with the viscous motion of interfaces was measured in the 50–150kHz range for the Cu-Al-Zn-Ni sample. The internal friction formula based on the viscous motion of interfaces has been derived. Also, corresponding parameters, which play an important role in shape memory effect such as viscosity coefficient, pinned force constant etc., were obtained.
Effects of High Magnetic Field and Tensile Stress on Martensitic Transformation Behavior and Microstructure At 4 K in Fe-Ni-C Alloys
Authors: Ohtsuka H. , Nagai K. , Kajiwara S. , Kitaguchi H. , Uehara M.
Published: April 2011

Effects of high magnetic field and tensile stress on martensitic transformation behavior and microstructure at 4 K have been studied in Fe-31Ni-0.4C and Fe-27Ni-0.8C shape memory alloys. It was found that the critical magnetic field to induce martensitic transformation is between 7.5 T and 10 T. In the case of Fe-27Ni-0.8C, martensitic transformation is stress-induced at lower level of stress in magnetic field than in the case when no magnetic Field is applied. The amount of martensite formed by increasing the magnetic field under constant stress is larger than that formed by increasing the stress in the constant magnetic field.
Critical Behavior of Antiphase Boundaries in Fe-A127% Close to the D03→B2 Order Phase Transition
Authors: Floc'h D. Le , Loiseau A.
Published: April 2011

In this paper, we present the first quantitative determination of the divergence law of the correlation length ξ, when approaching the second order phase transition DO3→B2, by studying the behaviour of the APBs by transmission electron microscopy.
A Study of the Effect of Oxide Structure on the Synthesis of Nanocrystalline Ge from Si1-xGexO2
Authors: Blaser Juliana M. , Caragianis-Broadbridge Christine , Walden Barbara L. , Paine David C.
Published: April 2011

In this study, Si1-xGexO2 was produced by hydrothermal oxidation of Si1-xGex alloys at temperatures of 450–500°C and pressures of 30–40 MPa. The resulting Si1-xGexO2 samples were annealed in forming gas (85/15:N2/H2) and the precipitation and growth of Ge crystallites as a function of oxidation and annealing conditions were investigated using FTIR, Raman spectroscopy, XPS, AFM and high resolution SEM. The particle size distribution through the oxide thickness is accounted for by consideration of the incorporation of hydroxyl groups in the amorphous oxide network and their effect on the rate of diffusion of Ge in the amorphous structure during H2 annealing.
Reentrant Growth in Kinetic Thin-Film Deposition on Stepped Surfaces
Authors: Xiao Rong-Fu
Published: April 2011

We have studied the reentrant growth in kinetic thin-film deposition on stepped surfaces using a Monte Carlo simulation. The results show that the reentrant oscillation of two dimensional nucleation growth occurs as a result of the variation of surface diffusion length with deposition temperature, and that it is a natural phenomenon in kinetic thin-film epitaxy on a substrate with a permanent step source.
Strain Relaxation in Heteroepitaxial Si1-xGex Films via Surface Roughening Processes
Authors: Ozkan Cengiz S. , Nix William D. , Gao Huajian
Published: April 2011

Surface roughening associated with strain relaxation of Si1-xGex films grown epitaxially on (100) Si substrates has been investigated using transmission electron microscopy, atomic force microscopy and x-ray diffraction. Epitaxial films 100 Å in thickness and containing 18% Ge, which are subcritical with respect to the formation of misfit dislocations, show strain relaxation through surface roughening on annealing at 700 °C. Enhanced surface grooves aligned along <100> directions are observed in films annealed at 850 °C. Strain relaxation as measured by x-ray diffraction is significantly greater at the higher temperature. Prolonged anneals at 850 °C also result in islanding. The surface roughening processes have also been studied in subcritical films with 15% Ge at 900 °C. These films also show enhanced grooving aligned along <100> directions. These observations are consistent with an anisotropic elastic analysis which indicates that grooving should occur preferentially along <100> directions. Intermixing effects in these samples have also been investigated through depth profiling using Auger Electron Spectroscopy. In addition to the above subcritical films, other films with 18% and 22% Ge and supercritical thicknesses have also been studied. For these films, surface grooving is observed along <110> directions, which suggests that these grooves are related to the formation of misfit dislocation networks. The role of these surface roughening processes in the nucleation of dislocations has also been explored.
Characterization of Surface Morphology in Epitaxial Growth
Authors: Amar Jacques G. , Family Fereydoon
Published: April 2011

Simulated kinematic antiphase RHEED and HRLEED profiles are calculated for a model of Fe/Fe(100) deposition in order to clarify the interpretation of diffraction profiles in recent experiments on Fe/Fe(100) growth. Similar calculations are also presented for a self-affine surface. While self-affine surfaces do not exhibit a characteristic RHEED peak, in the case of surfaces with a typical length scale, the simulated RHEED profile exhibits a peak corresponding to the typical feature size, in agreement with recent experiments. The existence of this peak appears to be due to the large amount of shadowing present in low-angle RHEED which limits the amount of destructive interference between layers. In contrast, simulated HRLEED profiles exhibit an invariant profile for both self-affine and mound-like surface morphologies. The disappearance of the peak in HRLEED for surfaces which have large mound structures is explained in terms of the antiphase condition and the range of variation of terrace sizes and provides an alternative explanation for the HRLEED results observed in the experiment of Ref. 9.
Comparative Study of Thermodynamic Properties of Metallic and Semiconducting Nanoparticles in Dielectric Matrix
Authors: Stella A. , Cheyssac P. , Kofman R. , Merli P.G. , Migliori A.
Published: April 2011

The mechanism of growth as well as optical and microstructural data dealing with the process of melting of metallic (Pb, Sn) and semiconducting (Ge) particles in dielectric matrix are reported and discussed. Details are given on the growth of such systems based on a self organization method that allows a rather regular shape of the particles (truncated spheres) relative low size dispersion (≤ 20%), wide range of particle size variation and negligible effects due to stress or contamination. The features of these growth techniques allow a careful study of the melting behavior vs. size that has been investigated using optical reflectivity methods and transmission electron microscopy techniques. These experimental results have made possible a careful investigation on the thermodynamics of these systems and the deduction of interesting data concerning: a) conditions for the existence of surface melting and decrease of melting temperature; b) interfacial effects related to shape and curvature of the particles; c) onset of rotations and phase fluctuations in connection with surface melting.
Solidification of Intermetallic Compounds
Authors: Assadi H. , Greer A. L.
Published: April 2011

Kinetic modelling, incorporating variation in the degree of chemical order, is developed for the solidification of intermetallic compounds, and qualitative comparisons are made with experiment. It is found that a disordered phase can be obtained other than by the process of disorder trapping, and that partitioning can increase or invert with increasing solidification velocity. Solid-state ordering and its effects on final microstructure are also considered.
Electrical Properties of Pb5Ge3O11-Based Ferroelectric Glass-ceramics
Authors: Cornejo IvÁn A. , Haun Michael J.
Published: April 2011

Selected glass compositions in the Pb5Ge3O11-PbTiO3 (PG-PT) and Pb5Ge3O11-Pb(Zr1/2Ti1/2)O3(PG-PZT) systems were prepared by quenching from the molten state. After different heat treatments, a multiple ferroelectric composite crystallized at low temperatures, PG-PT or PG-PZT. In this paper the results obtained on the dielectric constant, dissipation factor, ferroelectric hysteresis loop, and pyroelectric coefficient of different bulk and thick-film samples of compositions in the PG-PT and PG-PZT ferroelectric glass-ceramic system are presented and discussed.
Synthesis of Nanocrystalline BaTiO3 by Electron Beam Evaporation
Authors: Li Shaoping , Eastman J. A. , Thompson L. J. , Baldo P.M.
Published: April 2011

Nanocrystalline BaTiO3 has been synthesized for the first time by a gas-condensation process using an electron beam evaporation system. BaTiO3 and Ti sources are vaporized simultaneously in either a mixed helium-oxygen or pure helium environment. Nano-BaTiO3 particles have an average particle size of approximately 18 nm. The processing parameters of the evaporation process are reported.
Selective TiSi2 Formation Using TiCl4(g), Si(s) and H2(g): A study of the Mask Loading Phenomena
Authors: Gladden D. B. , Weintraub C. E. , amp;O¨zttürk M. C.
Published: April 2011

In this paper, we explore the loading effect during reactions of TiC14(g) with Si(s) to form selective TiSi2 in a tungsten halogen lamp heated, cold wall rapid thermal chemical vapor deposition reactor. The process is intended as a replacement for the conventional sellaligned silicide process with the capability of reducing the process steps from four to one. In the absence of a Si source gas for this process, the Si is supplied from the substrate forming TiSi2 via consumption. The chemistry is highly selective to both Si02 and Si3N4. However, it has been previously shown by our group and others that TiSi2 formation can be accompanied by Si substrate etching which can be suppressed by adding H2 to the chemistry. In this study, we have considered cxposed Si area percentages ranging from 18% to 88% on 4” Si substrates. Two simplified gas systems are used to closely examine substrate etching and consumption: TiCI4 - Si(s) and TiCI4 - Si(s) - H2 The Si etch and consumption rates are evaluated for these varying exposure percentages. We have found that the substrate etch rate increases as the exposed area to be etched is decreased as does the substrate consumption rate.
Properties and Perspectives of Semiconducting Transition Metal silicides
Authors: Lange H.
Published: April 2011

The structural, electronic, optical, and electrical properties of semiconducting silicides with transition metals from the VIth to the Vlllth Group of the Periodic Table are reviewed. Main emphasis is put on ß-FeSi2. The review includes recent results on optical measurements from the infrared up to 24 eV. Typical similarities in the phonon and interband spectra are outlined. Gap energy determinations are critically discussed. Doping impurities are characterized by EPR. Electrical investigations revealed characteristic features of transport parameters depending on temperature and magnetic field. Possible fields of application are analyzed.
MBE Growth Considerations for the Fabrication of 640×480 IR Focal Plane Arrays of SiGe Hip Detectors
Authors: Hompson P. E. , Weeks M. , Tedrow P. , Hobart K.
Published: April 2011

Encouraging results have been reported for discrete heterojunction internal photoemission (HIP) infrared (IR) detectors composed of heavily boron doped Si1−3Gex layers on Si. We desired to build on those results and fabricate 640×480 IR focal plane arrays on 100 mm Si substrates, suitable for commercial microelectronic processing. In this paper we discuss the growth issues for growing these structures by molecular beam epitaxy. Since the wafers had already undergone processing and some had PtSi contacts, the growth temperature was constrained to be no greater than 600 °C. Precise temperature control was obtained by calibrating an optical pyrometer with a thermocouple embedded in the substrate heater assembly, which was calibrated using the eutectic emperatures of Au/Si and Al/Si. The final step of the cleaning process was a 1% HF dip/ spin dry, which resulted in a H-terminated surface. The H was removed at 550 °C in vacuum prior to rowth. The growth of the B-doped SiGe layer was done at 350 °C to minimize segregation and diffusion of the Ge and B. Doping levels of 2×1020/cm3 were obtained with near 100% activation. Using Si0.35, doped with 2×1020 B/cm3, a cut-off wavelength of 11.1 μm and an emission coefficient of 19.8 %/eV were obtained for discrete detectors. Preliminary results from the detector arrays show full functionality in the spectral range of 6.1 to 12.8 μm.
Electrical Resistivity of Three Polymorphs of Basi2 and P-T Phase Diagram
Authors: Imai M. , Hirano T.
Published: April 2011

This paper reports a pressure-temperature phase diagram for BaSi2 and evaluates the electrical resistivity of orthorhombic, cubic and trigonal BaSi2. In-situ X-ray diffraction measurements revealed the transition sequence of cubic and trigonal BaSi2 from orthorhombic BaSi2 at high pressures and high temperatures. The electrical resistivity measurements of three polymorphs show that the electrical properties depend on the crystal structure: orthorhombic BaSi2is an n-type semiconductor as previously reported; cubic BaSi2is an n-type semiconductor; trigonal BaSi2is a hole metal that shows superconductivity with an onset temperature of 6.8K.
Ti-Salicide Improvement by Preamorphization for ULSI Applications
Authors: Chenl Chun-Cho , Wang Q. F. , Jonckx Franky , Jenq Jyh-Shyang , Maex Karen
Published: April 2011

To improve Ti SALICIDE process, Si preamorphization by arsenic before Ti sputtering has been studied in two parts: process characterization and fundamental studies. Sheet resistance (Rs) reduction by the preamorphization is more pronounced on thinner and narrower-line silicide formation. At 60keV implantation energy, there is an optimum arsenic dose for the improvement. Through the treatment, more uniform silicide layer can be formed, indicated by the improved Rs uniformity. In the fundamental study, preamorphization appears to have little effect on promoting C49-to-C54 phase transformation. It is suggested that the treatment is able to enhance the reaction rate between Ti and amorphous Si, and results in C54-TiSi2 with larger grains and consequently slightly lower resistivity.
Reduction of the C54-TiSi2Phase Formation Temperature Using Metallic Impurities
Authors: Mann R. W. , Clevenger L. A. , Miles G. L. , Harper J. M. E. , Cabral C. , D'Heurle F. M. , Knotts T. A. , Rakowski D. W.
Published: April 2011

The effects of small concentrations of metallic impurities have been studied in conjunction with the formation of titanium disilicide. We report that, by introducing small quantities of a refractory metal such as molybdenum or tungsten at or near the titanium/silicon interface, the temperature required to form the C54 phase TiSi2can be reduced by as much as 100°C. Furthermore, the resulting C54-TiSi2film exhibits small (∼ 0.2μm) grain size and improved thermal stability. This discovery has the potential to reduce the complexity and cost associated with forming low resistivity TiSi2on submicron structures and to significantly improve the titanium silicide process window for future sub-half-micron VLSI applications.
Depth Dependence of Residual Strains in Textured Mo Thin Films Using High-Resolution X-Ray Diffraction
Authors: Malhotra S. G. , Rek Z. U. , Yalisove S. M. , Bilello J. C.
Published: April 2011

The magnitude of the average stress in a thin film can be obtained by measuring the curvature of the film-substrate couple. However, the details of the strain distribution, as a function of depth through the thickness of the film, can have important consequences in governing film quality and ultimate morphology. A high-resolution x-ray diffraction method was used to determine the depth dependence of strain in a textured Mo film, with a nominal thickness of 260 nm, which was deposited by planar magnetron sputtering onto Si (100) substrates. The principal strains, resolved onto a laboratory reference frame, displayed a negligible gradient in the azimuthal directions (x and y), but displayed a large gradient in the direction normal to the film (z). A similar trend was previously observed for a 100 nm polycrystalline film, but the magnitude of the normal strain very near the free surface was about a factor of 2 less. The increase in the normal strain may be due to the development of a preferred growth direction and grain facetting. A linear elastic model was also used to determine the strains in successive slabs of the film, where strain variations between slabs were indicated.