bluuebunny/crossref_metadata_2025 huggingface dataset:
Growth of Epitaxial Cu/TiN/6H-SiC(0001) Heterostructures by Pulsed Laser Deposition
Authors: Kvit A. , Sharma A.K. , Narayan J.
Published: April 2011

Epitaxial Cu/TiN heterostructures were grown on hexagonal (6H)-SiC(0001) substrate by pulsed laser deposition using the domain epitaxy, where integral multiple of lattice constant or major planes match across the interface1. Such layers are needed for metallization of SiC bond integrated circuit devices. These Cu and TiN layers on SiC(0001) were grown at 600 degrees centigrade in a high vacuum (<10−6 Torr). This structure was characterized using X-ray diffraction technique and transmission electron microscopy. The X-ray diffraction recorded only (111) and (222) reflection of Cu and TiN. The full-width at half maximum of ω-rocking curve of (111) reflection of Cu (0.4 degree) and TEM results indicated a high epitaxial quality. The plan view transmission electron micrograph shows that Cu forms three-dimensional islands indicating that the Cu/TiN interface energy is very high. The island size varies from 0.2 to 2 μm. Analysis of selective aperture diffraction patterns and cross-sectional transmission electron microscopy, including high-resolution imaging, showed relationships Cu(111)//TiN(111)//6H-SiC(0001). The TiN/SiC an interface was locally atomically sharp and free from secondary phases or obvious interdiffusion. The typical defects in the TiN(111) layers consisted of threading domain boundaries. The mechanism of three-dimension growth of copper on TiN layers was discussed.
Role of a Free Energy Action Principle in Predicting Microstructure Formation
Authors: Kirkaldy J.S.
Published: April 2011

It is demonstrated that some twenty representative free boundary diffusion-reaction and hydrodynamic patterning systems fall within the compass of the isothermal variational principle where the Lagrangian density is the free energy density g, and η is an appropriate order parameter. To illustrate the universality of the formulation we survey in some detail its degree of equivalence to twenty-one currently adopted or promoted procedures for resolving pattern degeneracies, and critically reappraise theoretical descriptions of grain growth, ordinary diffusion, spinodal decomposition and Ostwald Ripening and their predictive success. The importance of a hierarchy of kinetic scaling laws is discussed. The physics of fluctuations is essential to understanding.
Growth Stress of Thin Ti-, Al- and TiAlx-Films Deposited Under UHV-conditions and its Dependence on Substrate Temperature
Authors: Lackner St. , Abermann R.
Published: April 2011

The growth stress of metal films was measured continuously both during as well as after their deposition under UHV-conditions with a cantilever beam technique. The metal films were deposited onto 10 rim thick alumina substrate films prepared by reactive evaporation of Al in an oxygen atmosphere. The substrate temperature for the metal deposition was varied from -20°C to 500°C.

The growth stress of both titanium and aluminum films deposited at room temperature and above is characteristic of island growth and the formation of a polycrystalline film. The film stress built up in these films decreases with increasing substrate temperature. Below RT the growth stress of titanium films indicates a transition from island growth to layer by layer growth due to a reduced adatom mobility. The temperature range in which this transition in the growth mode occurs is strongly affected by impurities in the Ti-evaporation source material and gas ambient.

In the last part of this paper we present results of experiments in which the above metals were evaporated simultaneously from separate sources to form alloy films with TiAl3-stoichiometry. Sudden changes in the incremental film stress are tentatively attributed to segregation and phase formation phenomena.
Modeling of Non-Random Nucleation Protocols
Authors: Pineda Eloi , Pradell Trinitat , Crespo Daniel
Published: April 2011

Non random nucleation processes are a subject of much interest in the study of first order phase transformations. However, the theory available to obtain the time evolution of the transformation for a nucleation and growth process, the well known Kolmogorov, Johnson-Mehl and Avrami kinetic equation (KJMA), is not accomplished if the nucleation process is nonrandom. Therefore, KJMA does not give an adequate description of the transformation kinetics.

In the present paper, a non-random nucleation protocol resulting from a reduced nucleation rate due to the nearby presence of other growing grains is considered. Monte-Carlo simulations of such processes are performed, and the deviations from the Avrami kinetics observed are analyzed in detail.
Phase Evolution and Transformations During Long-Term Creep of Two-Phase Titanium Aluminides
Authors: Appel F. , Oehring M. , Ennis P.J.
Published: April 2011

Titanium aluminide alloys based on the intermetallic γ (TiAl) and α2 (Ti3Al) phases are being considered as light-weight materials for high-temperature applications in advanced energy conversion systems. However, for such applications the material suffers from insufficient creep resistance at the intended service temperature of 700°C. The paper reports an electron microscope study of diffusion controlled mechanisms which apparently cause the degradation of the strength properties. The processes lead to significant structural changes involving the formation of extended ledges and recrystallization. The driving forces of these mechanisms probably arise from non-equilibrium phase compositions and significant coherency stresses occurring at the interfaces.
Evolution of Stress; Phase Formation and Microstructure in TiCux-Alloy Films
Authors: Bertel S. , Abermann R.
Published: April 2011

The internal stress of TiCux-alloy films on alumina substrates was measured in situ under UHV-conditions as a function of substrate temperature and stoichiometry using a cantilever beam technique.

The stress vs. thickness curves of alloy films with TiCu0.5, TiCu, TiCu2 and TiCu3 stoichiometry indicate that the film growth is amorphous at 130°C and polycrystalline at 350°C substrate temperature, which was confirmed by TEM-investigations. Furthermore TED-results of alloys deposited at 350°C imply that the TiCux-alloy-phases formed at that temperature are Ti2Cu, γ-TiCu, TiCu3 and TiCu4.

The influence of substrate temperature on the growth of TiCux-alloy films (x = 1) was investigated in more detail. At substrate temperatures below 300°C the stress vs. thickness curves indicate the formation of amorphous alloy films, again confirmed by TEM- and TED-analysis. At substrate temperatures around 300°C a strong tensile stress contribution above a mean thickness of about 20 nm indicates a change in the growth mode and thus microstructure of the alloy film. The corresponding TEM- and TED-micrographs show quasi single-crystalline films. Finally at 350°C substrate temperature the stress vs. thickness curves indicate once again a change in the film growth mode, the film structure is polycrystalline and the formation of γ-TiCu is deduced fore TED-results.
Stress Formation in Boron Nitride Films Prepared by Ion Beam Assisted Deposition
Authors: Rauschenbach B. , Sienz S.
Published: April 2011

The stress formation during N/Ar ion assisted deposition of boron nitride films on Si(001) substrates was measured in-situ by a very sensitive capacity technique in dependence on the ion energy, temperature during deposition and the ion to atom arrival rate.

The stress evolution in dependence on the layer thickness is characterized by a high tensile stress in the initial stage of the film growth, followed by a transition from the tensile to the compressive stress state, a strong increase of the compressive stress with the film thickness. A simultaneous UV-light irradiation during the deposition process leads to a reduction of the compressive stress.
An Electron Microscope Study of Diffusion Assisted Dislocation Processes in Intermetallic Gamma TiAl
Authors: Appel F. , Lorenz U. , Oehring M.
Published: April 2011

The paper reports an electron microscope study of diffusion controlled deformation mechanisms in two-phase titanium aluminides which apparently cause the degradation of the strength properties at elevated temperatures. Climb velocities were analyzed in terms the critical vacancy supersaturation necessary for the operation of diffusion assisted dislocation sources. Particular emphasis was paid on structural changes occurring during long-term creep, which are apparently associated with dislocation climb.
Site Occupancy Determination by ALCHEMI of Nb and Cr in γ-TiAl and Their Effects on the a to γ Massive Phase Transformation
Authors: Miller T.M. , Wang L. , Hofmeister W.H. , Wittig J.E. , Anderson I.M.
Published: April 2011

Atom location by channeling enhanced microanalysis (ALCHEMI) has been used to characterize the site distributions of Nb and Cr alloying additions in the L10-ordered γ phase of ternary titanium aluminides. Two alloys, Ti50Al48Cr2and Ti50A148Nb2, were processed by furnace cooling from 1300°C (within the α-γ two phase field) as well as by rapid solidification using twin-anvil splat quenching of electromagnetically levitated and undercooled samples. ALCHEMI studies of furnace cooled samples yield results generally consistent with those in the published literature. Nb alloying additions are found to partition exclusively to the ‘Ti’ sublattice, while Cr alloying additions exhibit an ‘Al‘ sublattice preference. However, a higher degree of disorder can be achieved with rapid solidification and high solid state cooling rates (105-106K/s). Significant distribution of the ternary elements between the ‘Ti’ and ‘Al‘ sublattices has been measured in the splat quenched samples, with up to 12% of the Nb atoms occupying the ‘Al‘ sublattice and the fraction of Cr atoms on the ‘Ti’ sublattice doubling to ∼30%. Rapid solidification of TiAl produces an equiaxed hexagonal α phase solidification structure that transforms in a massive fashion to the tetragonal γ phase. Although the amount of massively transformed γ is dependent upon the solid state cooling rate, ternary alloying additions can more strongly influence the transformation kinetics. The Nb-modified alloy exhibits significant amounts of the massively tranformed γ, similar to the Ti52Al48binary alloy, whereas little massively transformed γ is observed in the Cr-modified alloy. These results can be correlated with the relative atomic size, lattice distortion, and sublattice site occupancy of Nb and Cr in the L10unit cell.
Atomic-Scale Imaging of Dopant Atom Distributions Within Silicon δ-Doped Layers
Authors: Vanfleet R. , Muller D.A. , Gossmann H.J. , Citrin P.H. , Silcox J.
Published: April 2011

We report measurements of the distribution of Sb atoms in σ-doped Si, over a wide 2-D concentration range. Both annular dark-field imaging and electron energy loss spectroscopy proved sufficiently sensitive to locate Sb atoms at the atomic scale. Improvements in both detector sensitivities and specimen preparation were necessary to achieve these results, which offer a surprising explanation for the dramatic difference in electrical activity between 2-D and 3-D dopant distributions at the same effective volume concentrations. The prospects for the general identification of individual dopant atoms will be discussed.
Imaging Heterophase Molecular Materials in the Environmental SEM
Authors: Thiel B.L. , Donald A.M. , Stokes D.J. , Bache I.C. , Stelmashenko N.
Published: April 2011

The Environmental Scanning Electron Microscope allows imaging of hydrated specimens, as well as fluid-containing or even fully fluid microstructures. This is possible so long as all of the phases can be thermodynamically stabilized. Experimental operating parameters include specimen temperature and chamber gas chemistry and pressure. However, it is also possible to alter the thermodynamic properties of phases by various chemical and physical means. These approaches have been used in ESEM studies on soft condensed matter such as emulsions, complex fluids and gels. By deliberately moving away from stabilizing conditions, it is also possible to perform dynamic experiments. A number of applications are illustrated.
High Spatial Resolution X-ray Microanalysis of Radiation-Induced Segregation in Proton-Irradiated Stainless Steels
Authors: Kenik E.A. , Busby J.T. , Was G.S.
Published: April 2011

The spatial redistribution of alloying elements and impurities near grain boundaries in several stainless steel alloys arising from non-equilibrium processes have been measured by analytical electron microscopy (AEM) in a field emission scanning transmission electron microscope. Radiation-induced segregation (RIS) has been shown to result in significant compositional changes at point defects sinks, such as grain boundaries. The influence of irradiation dose and temperature, alloy composition, prior heat treatment, and post-irradiation annealing on the grain boundary composition profiles have been investigated. Understanding the importance of these microchemical changes relative to the radiation-induced microstructural change in irradiation-assisted stress corrosion cracking (IASCC) of the irradiated materials is the primary goal of this study.
Formation of AlN Films on Ti/TiN Arc-Layer Interface With AL-0.5%Cu Interconnects Evaluated by XPS and Energy-Filtered-TEM
Authors: Gazda J. , Zhao J. , Smith P. , White R. A.
Published: April 2011

Titanium/titanium nitride anti-reflective coatings (ARC) are widely used in the semiconductor industry during photolithography of aluminum metal interconnect lines. The quality and effectiveness of these coatings, however, depend strongly on the ability to control reaction products formed at film interfaces during processing. In the present study, formation of an Al-N compound at the interface between Ti/TiN ARC/BARC and Al-(0.5 wt. %)Cu interconnect was investigated. The effects of deposition temperatures for individual films and ensuing thermal cycling of the whole metal stack on formation of intermetallics were evaluated. The composition and chemical bonding state of an aluminum nitride interfacial layer was evaluated by x-ray photoelectron spectroscopy (XPS) of blanket wafers. These results were combined with measurements made by energy filtered transmission electron microscopy (EFTEM) of thickness and continuity of the film in specimens prepared by focused ion beam milling (FIB). Formation of AIN depends on the thermal cycling history of the metal stacks
Alkali-Metal Containing Amorphous Carbon: Reactivity and Electronic Structure
Authors: Töwe M. , Reinke P. , Oelhafen P.
Published: April 2011

Amorphous hydrogen-free carbon films (sp2-dominated a-C) were deposited under ultrahigh vacuum conditions between room temperature and 800°C. These films served as matrices for the in-situ incorporation of alkali-metal atoms (Li, Na). In-situ sample characterization was performed by photoelectron spectroscopy with both x-ray and ultraviolet excitation (XPS, UPS). While the clean metal-containing samples were prepared with metal contents of about 10 at%, a strong oxidation driven accumulation of metal atoms on the film surface exceeding 50 at% was observed upon exposure to molecular oxygen. Work-function measurements by UPS reflected the changes within the electronic structure of the material. Metal incorporation considerably decreased the work-function, but only after oxidation we observed work-functions below the values given for pure alkali metals.
Study of Carbon Nanotubes Under High Pressure
Authors: Tang J. , Qin L.C. , Matsushita A. , Kikegawa T. , Yudasaka M. , Bandow S. , Iijima S.
Published: April 2011

The elastic behavior and structural changes of single-walled carbon nanotubes under hydrostatic pressure produced by a gasketed diamond anvil cell has been studied using in situ synchrotron x-ray diffraction. The compaction of the raft-like bundles of single-walled carbon nanotube showed a linear behavior up to 1.5 GPa pressure and the volume compressibility deduced from the experimental data is 0.024 GPa−1. The elastic deformation is attributed to the combination of a reduction in the inter-tubular distance and the polygonization of the otherwise circular nanotube sections.
Study of Chromium-Doped Diamond-Like Carbon by Z-Contrast Imaging and Electron Energy Loss Spectroscopy
Authors: Fan X. , Dickey E. C. , Pennycook S. J.
Published: April 2011

Metal-doped diamond-like carbon films were produced for the purpose of an electrochemical nano-electrode. In this study we use Z-contrast scanning transmission electron microscopy to directly observe metal cluster formation and distributions within the chromium-doped carbon films. At low doping (∼6at%Cr), Cr is uniformly distributed; at high doping (∼12at%Cr), Cr-rich clusters are formed. Using electron energy loss spectroscopy, we find that the Cr clusters tend to be metallic-like at low doping levels and carbide-like at high doping levels according to the Cr L2.3 white line ratios. The carbon is more diamond-like at low doping and more graphite/carbide like at high doping according to the sp2/sp3 electron percentage measurements.
Electrical Behavior of Pure and Cu Doped Diamondlike Carbon Prepared by Pulsed Laser Deposition
Authors: Wei Q. , Sharma A. K. , Yamolenko S. , Sankar J. , Narayan J.
Published: April 2011

We have prepared pure diamondlike carbon films and Cu doped diamondlike carbon films through pulsed laser deposition. The Cu concentration does not exceed 3.0 atomic percent. Electrical conduction studies were carried out on the films to understand the electrical transport mechanism. It was found that both pure DLC and Cu doped DLC are of p-type conduction. Incorporation of Cu into the DLC films decreases the resistivity significantly. Transmission electron microscopy and radial distribution function analyses showed that the DLC films are typical tetrahedral amorphous carbon. The conductivity of Cu doped DLC films exhibited T1/2 temperature dependence, rather than the T1/4 dependence (Mott-Davis law). This dependence was observed within a wide temperature range (from below liquid nitrogen temperature to near room temperature). The T1/2 dependence was explained on the basis of the Efros-Shklovskii model which considers the long range Coulomb interaction between localized states
Diamond-Like Carbon Coatings for Rhenium Wire and Foils
Authors: Evans Edward A. , Hafeli U , Wusinka Ram , Morrison Philip W.
Published: April 2011

Diamond like carbon has been deposited as a protective layer for coronary stenting applications. Taking advantage of DLC's resistance to chemical attack, its flexibility, and other properties. our current technical objective is to develop DLC as a coating for radioactive rhenium stents. Radioactive rhenium stents are being investigated to limit smooth muscle cell growth following coronary surgery. The DLC coating is being investigated to reduce the release of radioactive rhenium (released activity) into the blood following the stenting procedure. An inductively coupled RF plasma system was used to deposit the DLC onto rhenium substrates. Foils, wires, and coils were coated and tested for adhesion, cytotoxicity, and release of radioactive rhenium. Our initial results indicate up to a three-fold decrease in released activity relative to uncoated rhenium
Altering Resistivity in Diamond Films Without Impurity Addition
Authors: Baker Colin C. , McNamara Karen M.
Published: April 2011

CVD Diamond films with resistivites comparable to that measured in natural type IIA diamond can be fabricated using a microwave-plasma assisted growth environment. Modification of the resistivity of these films is typically accomplished through the introduction of impurities, or dopants such as boron. Some applications, however, require that the purity of the carbon lattice be maintained, while still altering the resistivity of the film. This is the case for many applications of diamond in space. Here, varying the resistivity of CVD diamond is investigated by controlling the introduction of sp2coordinated bonds, yet maintaining the overall diamond structure and carbon purity. Experimental results will be presented, and the use of these materials in NASA's Genesis Discovery Mission will be discussed
Molecular Dynamics Simulation of Impurities in Nanocrystalline Diamond Grain Boundaries
Authors: Sternberg Michael , Zapoll Peter , Frauenheim Thomas , Gruen Dieter M. , Curtiss Larry A.
Published: April 2011

Nanocrystalline diamond films grown on Si substrates at 800°C from hydrogen-poorplasmas have a number of highly desirable mechanical and electronic properties. Impurities were found by SIMS measurements to be uniformly distributed throughout the thickness of the films at a level of 1017–1018 cm−3. It is likely that the impurities are located at the grain boundaries, which play a crucial role in controlling important characteristics of the films, such as electrical conductivity and electron emission. Density-functional based tight-binding (DFTB) molecular dynamics simulations were performed for diamond high-energy high-angle (100) twist grain boundaries with impurities such as N, Si and H
Nanocrystalline Silicon Carbide Film Growth Using Hot Filament CVD
Authors: Yu M.B. , S.F. Rusli , J. Yoon , Chew Cui K. , Ahn J. , Zhang Q.
Published: April 2011

Nanocrystalline cubic silicon carbide (nc-SiC) films embedded in an amorphous SiC matrix was fabricated by the hot filament chemical vapor deposition (HFCVD) technique using methane and silane as reactance gases. The presence of nanocrystalline grains was confirmed by the high resolution transmission electron microscope (HRTEM). x-ray photoelectron spectroscopy (XPS) measurements showed that the atomic percentages of Si and C are nearly 50%. X-ray diffraction spectrum of the sample revealed a diffraction peak of 3C-SiC (111) at 2ϕ=35.6°. Infrared absorption of the film had a strong peak at 800 cm−1 which is related to the transverse optical phonons of Si-C bonds in 3C-SiC. Raman spectrum of the sample showed that there are two peaks at 790 cm−l and 970 cm−1 which correspond to longitudinal and transverse optical phonons of SiC respectively. Room temperature photoluminescence (PL) study of these nc-SiC samples revealed a visible peak at 2.2 eV, which has not been observed so far for 3C-SiC.
Film Formation Behavior of the Endohedral Metallofullerene DY@C82
Authors: Huang Houjin , Yang Shihe
Published: April 2011

The Langmuir-Blodgett (LB) film formation behavior of the endohedral metallofullerene Dy@C82 was studied at the air/water and Ar/water interfaces. The LB film constructed at the Ar/water interface (2-4 layers) was found to be thinner and more uniform than at the air/water interface (4-6 layers). Particulate aggregates were observed in the LB films, which contrasts the extended wire networks formed by direct evaporation of the metallofullerene solution on a quartz plate. The UV-Vis absorption peaks are blue-shifted for the LB film deposited in air, which is attributed to the partial oxidation of the metallofullerene balls. They are red-shifted, however, for the LB film at the Ar/water interface presumably due to the interaction between the pristine metallofullerenes.
Synthesis and Characterization of Cluster-Assembled Carbon Films
Authors: Milani P. , Piseri P. , Barborini E. , Podestà A.
Published: April 2011

Nanostructured carbon films have been grown by deposition of supersonic cluster beams. A novel pulsed microplasma cluster source allows to obtain cluster beams of high intensity and stability. Cluster growth and beam formation have been charaterized. Separation effects typical of supersonic expansions cause inhomogeneities of cluster distribution in the beam, depending on their masses. This effect, observed for the first time, has been carefully characterized. The deposited films have a low density porous structure based on nanometer-size grains. The coordination is essentially three-fold with a large number of defects. Film density, morphology and surface roughness can be controlled by varying the precursor cluster mass distribution. Applications of cluster-assembled carbon films will be presented.
Creep Behavior of a Superplastic Y-TZP/Al2O3 Composite: An Examination of the Possibility for Diffusion Creep
Authors: Sosa Siari S. , Langdon Terence G.
Published: April 2011

The creep characteristics of a high purity superplastic Y-TZP/Al2O3 composite were studied. The test samples had a uniform initial grain size of essentially equiaxed grains and the phase distribution was also uniform. Creep tests were conducted at elevated temperatures in tension and measurements were taken after testing to determine the average size and shape of the grains. The creep curves showed the existence of a primary stage of creep and then a transition into a steady-state region where the strain rate remained reasonably constant. Observations by scanning electron microscopy revealed an elongation of the alumina grains with the grain strain essentially matching the overall strain within the sample. There was some grain growth after testing at the lower stresses. Preliminary observations using an atomic force microscope revealed direct evidence for the occurrence of some grain boundary sliding within the samples. The results are compared with earlier data reported for Y-TZP/Al2O3 composites and they are analyzed using the interface reaction-controlled diffusion creep model.
An Examination of the Deformation Process in Equal-Channel Angular Pressing
Authors: Berbon Patrick B. , Furukawa Minoru , Horita Zenji , Nemoto Minoru , Langdon Terence G.
Published: April 2011

In the past decade, there has been an important emphasis in materials science on the production and use of ultrafine-grained materials. These materials offer wide-ranging advantages such as an improvement in strength at low temperatures and enhanced superplastic behavior at high temperatures. New techniques to process these materials have been developed. Good properties have been achieved by powder metallurgy and by techniques of bulk processing. Equal-channel angular (ECA) pressing is a bulkprocessing technique which has led to some remarkable achievements in the production of sub-microcrystalline materials with excellent superplastic properties at low temperatures and high strain rates. When considering the currently available physical and mechanical properties of these materials, it appears that some aspects cannot be explained solely by the very small grain size. In fact, the specific mode of deformation occurring in ECA pressing appears to have an influence on the final properties. This paper reviews the details of this metal working technique and then provides an explanation for the observed microstructures, their thermal stability and their remarkable superplastic properties.
Superplastic Properties of an Aluminum-Based Alloy After Equal-Channel Angular Pressing
Authors: Wang Jingtao , Berbon Patrick B. , Xu Yuzhong , Wang Lizhong , Langdon Terence G.
Published: April 2011

It is now recognized that superplasticity requires a very small grain size, typically > 10 μm. A further reduction in grain size, to the submicrometer or nanometer level, offers the potential for attaining superplasticity at both faster strain rates and lower temperatures. This paper reports an investigation of the microstructure and tensile behavior of an Al-3% Mg-0.5% Zr alloy after processing by equal-channel angular pressing to an equivalent true strain of ∼8.
Comparative Study of Structural and Néel Transition Temperatures in FE-MN-SI Shape-Memory Alloys
Authors: da Silva M.I.N. , de Arruda G.J. , Côrtes P.E.F. , Andrade M.S. , Paniago R. , Speziali N.L.
Published: April 2011

Fe-Mn-Si based alloys exhibit the shape memory effect depending on their composition. Upon cooling, these alloys undergo a martensitic transformation γ (fcc) → ε (hcp), and a magnetic transition, at the Néel temperature, from paramagnetic to antiferromagnetic ordering in the γ-phase. In this work, the structural and magnetic phase transition temperatures were determined in an Fe-27Mn-2.5Si (in weight %) shape-memory alloy, using differential scanning calorimetry, dilatometry, electrical resistivity, Mossbauer spectroscopy, and X-ray diffraction. The transition temperatures measured by the different techniques were almost the same. It was observed, by calorimetry and electrical resistivity measurements, that the magnetic transition temperature upon cooling was very close and slightly higher than that of the start of the martensitic transformation, thus promoting the stabilization of the γ-phase. Consequently, the amount of thermally induced ε-martensite was very small. Mössbauer spectroscopy and X-ray diffraction measurements showed that only 10% of ε-martensite was formed upon cooling to quite low temperatures.
Molecular Recognition of Organic Compounds by Imprinted Silica
Authors: Gong Xiaoyi , Liu Jun , Samuels William D.
Published: April 2011

Specific interactions between silica and organic molecules play an important role in molecular imprinting, molecular recognition, and enzyme activity. To understand the specific interactions, six pairs of organic compounds were chosen and investigated for their molecular imprinting capabilities on silica. Silica adsorbents imprinted by methyl red or ρ-methyl red, methyl orange or ethyl orange, and histidine-alanine or histidine-leucine can recognize their imprinting molecules. Silica samples “imprinted” with methyl red or ethyl red, 4,9-diaminoflourenone or 3,3'-diaminodiphenylmethane, and l-histidine or d,l-histidine do not recognize their “imprinting” molecules. The molecular recognition is related to the structure of the imprinting molecules. The following lessons were learnt: 1) Three or more strong interaction sites on the imprinting molecules are necessary to endow silica with recognition capability; 2) Position of functional groups is more important than their size to achieve the molecular recognition; 3) Chiral recognition needs stronger interaction and/or more interaction sites
Control of Residual Stresses in As-Grown Polysilicon by Multi-Layer Deposition: The “Multipoly” Process
Authors: Yang Hie , Kahn H. , He A.Q. , Phillips S.M. , Heuer A.H.
Published: April 2011

LPCVD polysilicon thin films deposited between ∼550 and ∼600 °C have an equiaxed microstructure (resulting from crystallization of an initially amorphous deposit) and contain ∼200 MPa residual tensile stresses after deposition, whereas polysilicon films deposited above ∼600 °C have a columnar microstructure and contain ∼300 MPa residual compressive stresses after deposition. Both types of films also contain stress gradients.

We have grown films containing multiple layers of polysilicon ("MultiPoly") by cycling the growth temperature between 570 and 615 °C. The multilayer films thus formed are comprised of alternating tensile and compressive layers, and by control of the thickness of the individual layers, the overall stress of the polysilicon can display any value between that of the tensile layer and that of the compressive layer. We have focussed on producing films with zero overall residual stress, as measured by wafer curvature, and have characterized the microstructures by transmission electron microscopy (TEM) and X-ray diffraction (XRD).

Because of the stress gradients present in both layers, devices made from films with zero overall residual stress may show distortions after release. We have measured the stress gradients in each type of layer and can design films with zero overall stress and zero overall stress gradients. It is also possible to design films with any level of overall (tensile or compressive) stress but with controlled displacements upon release.
High-Resolution Measurement of Crack Growth in Micro-Machined Crystal Silicon
Authors: Fitzgerald A.M. , Dauskardt R.H. , Kenny T.W.
Published: April 2011

Time dependent sub-critical cracking associated with environmental species such as moisture may have significant implications for the reliability of MEMS devices made of silicon. However, the existence of such stress corrosion phenomena in silicon remains controversial. Sub-critical crack-growth behavior in brittle materials is commonly characterized using crack velocity versus applied stress intensity curves (v-K curves). Crack velocity is inferred by curve-fitting crack length versus time data taken at low sample rates (<100 Hz) under the assumption that crack growth is a continuous process. However, we have observed discrete crack growth behavior in a micro-machined compression-loaded double cantilever beam. The samples are fabricated from (100) single crystal silicon wafers. A thin film resistor sputtered onto the sample surface using a lithographic technique is used to directly measure crack extension. The crack growth in all samples is characterized by periods of rapid crack growth interspersed with long periods of arrest in which no evidence of sub-critical cracking was observed. High speed data acquisition (up to 100 MHz) was performed and crack velocities as high as 1.7 km/s were accurately measured during these rapid growth periods.
Group III Metal Sulfide Thin Films From Single-Source Precursors by Chemical Vapor Deposition (CVD) Techniques
Authors: Lazell Mike R. , O'brien Paul , Otway David J. , Park Jin-Ho
Published: April 2011

Several single-source precursors including In(SOCNiBu2)3, In(S2CNMeHex)3 and Ga(S2CNMeR)3, (R = Et, Bu, Hex) have been prepared and used for the deposition of Group 13 metal sulfide thin films. The α and β-In2S3thin films on borosilicate glass and oc-Ga 2S3thin films on GaAs(111) single crystal substrates were prepared from the precursors by various chemical vapour deposition (CVD) techniques. These semicondcuting materials have been characterized by XRD, SEM, XPS and EDAX.
Direct Fabrication of LiCoO2 Film Electrodes Using Soft Solution-Processing in LiOH Solution at 20 - 200°C
Authors: Song S.W. , Han K.S. , Yoshimura M. , Sato Y. , Tatsuhiro A.
Published: April 2011

Application of Soft Solution-Processing, which is defined by environmentally friendly processing using (aqueous) solution, to the field of rechargeable lithium microbattery has been demonstrated by fabricating LiCoO2 film on the cobalt metal substrate in LiOH solution under hydrothermal condition. The film formation mecahnism could be interpreted in terms of chemical dissolution of cobalt metal plate in LiOH solution at fixed temperature of 20 - 200°C, resulting in the formation of H1−nCoO2 where n value increases with fabrication temperature and precipitation as LiCoO2 by heterogeneous nucleation on the substrate followed by crystal growth. The crystal structure and film properties have been characterized by X-ray diffraction, X-ray photoelectron, micro-Raman spectroscopic and scanning electron microscopic analyses. The films exhibited a good crystallinity despite the low reaction temperature without any postsynthesis annealing. The films prepared under different conditions showed different phase selection such as spinel (Fd3m) or hexagonal (R3-m), surface morphology and film thickness. An electrochemical activity of the LiCoO2 films was evidenced by cyclic voltammogram revealing a good reversibility on Li-intercalation and -deintercalation.
Growth and Studies of Li (Mn, Co) Oxides for Battery Electrodes
Authors: Nieto-Ramos S. , Tomar M.S. , Katiyar R.S.
Published: April 2011

There is interest in lithium intercalation oxide materials for cathodes in rechargeable batteries. We have synthesized LiMOx, (where M = Mn, Co) by a less expensive solution route. Reagent grade acetates or hydroxides as precursors for lithium, manganese, and cobalt, respectively, with methoxy ethenol and acetic acid as solvents were used. Powders with different compositions were achieved at annealing temperature below 700 °C. Thin films were deposited by spin coating. X-ray diffraction, Raman spectroscopy, and impedance spectroscopic results are presented. These studies indicate that this synthetic route is suitable to produce good quality lithium-based oxides useful for cathode in lithium-ion rechargeable battery.
Crystallographic Orientation in Bulk Polycrystalline Silicon Carbide Produced by a Chemical Vapor Deposition (CVD) Process
Authors: Marzik James V. , Croft William J.
Published: April 2011

Polycrystalline, theoretically dense silicon carbide was deposited onto graphite substrates via the reductive pyrolysis of methyltrichlorosilane in a hot-walled chemical vapor deposition (CVD) chamber. The resulting product can be considered a bulk material with deposit thicknesses in the range of 4 to 8 millimeters. The material was characterized using powder x-ray diffraction and Laue back-reflection techniques. Under the deposition conditions investigated in this study, the crystallographic orientation varied as a function of distance from the substrate. The material exhibited a high degree of randomness in proximity to the substrate, and progressively showed a higher degree of preferred crystallographic orientation as the deposit progressed. This phenomenon is correlated with the microstructure of the material as well as such mechanical properties as hardness and fracture toughness.
The Control of Zn for ZST Microwave Ceramics With Low Sintering Temperature
Authors: Park Yong H. , Shin Moo Y. , Ryu Ji M. , Ko Kyung H.
Published: April 2011

ZnO addition for low-T sintering of ZST has serious side effects such as decrease of Q × f value. In this work, the curing of these side effects without any further chemical additivesand causing degradation of other dielectric properties have been presented. After sintered at 1350°C for 2h. samples were annealed in oxygen at 900 ∼ 1100°C for 5hr. It was observed that Q × f value of post-annealed sample at 900°C could recovered up to 46000 from the as-sintered value of 40000. Because there were no formations of second phases or significant changes inlattice constants, which could affect microwave properties of ZST. However, it was found that only for the specimens annealed at 900°C, Zn was almost depleted from grin inside and diffused toward grain boundary. So, it is suggested that the out-diffusion of Zn is responsible for the recovery of Q × f value. Moreover, when the amount of Zn incorporation increased via successive calcination and sintering of pre-mixed powder of ZST and ZnO, Q × f value of 33000 also could enhanced up to 39000 due to the redistribution of Zn near grain boundary by out-diffusion.
Application of Pulsed Injection MOCVD to the Deposition of Dielectric and Ferroelectric Oxide Layers and Superlattices
Authors: Senateur Jean-Pierre , Lindner Johannes , Weiss François , Dubourdieu Catherine , Jimenez Carmen , Abrutis Adolfas
Published: April 2011

The technique used for the control of the injection of fuel in thermal motors has been applied to the generation of active gases for MOCVD layers deposition. A wide variety of compounds and multilayers have already been grown using this new CVD source (from simple cxides, nitrides or metals to complex ternary oxides). Using two injection sources working sequentially, stackings like YBa2Cu307/CeO2 or SrTiO3/YBa2Cu3O7 double layers, Ta2O5/SiO2 amorphous or crystallized multilayers and SrTiO3/BaTiO3 or YBa2Cu3O7/PrBa2Cu3O7 epitaxial superlattices have been synthesized. The injection MOCVD seems to be a very promising technique for the stacking of multicomponents oxides having different electronic properties. This opens the way for the synthesis of a wide set of artificial materials, exhibiting completely new properties that cover a very large range of potential applications. After a description of the technique, we will demonstrate its performances on some results obtained on the synthesis of dielectric and ferroelectric layers and multilayers.
The Longest Wavelength OPO Pumped by a 1µm Laser
Authors: Vodopyanov K.L. , Maffetone J. , Zwieback I. , Ruderman W.
Published: April 2011

Singly resonant type-il AgGaS2OPO yielded continuously tunable 3.9–11.3 µm idler output with slope quantum efficiency up to 41 % (absolute photon efficiency 22%). The OPO has sub-100 µJ threshold pump energies for nanosecond 1.06µm Nd:YAG laser pulses.
Performance and Spectral Response of Far-Infrared Pb1−xSnxTe(In) Photodetectors
Authors: Ivanchik I. , Khokilov D. , Pipher J. , Raines N. , Watson D.
Published: April 2011

Direct comparison of performance has been done for a Pb1−xSnxTe(In) photodetector, a Si(Sb) BIB structure and a state of the art Ge(Ga) photoconductor in the integration cavity. The PblSnTe(In) photodetector shows several orders of magnitude higher responsivity S, then the Si(Sb) BIB at the wavelength λ ∼ 14 µm. Persistent photoresponse with SI ∼ 103 A/W at 40 mV bias and 1 s integration time at the wavelengths of, λ = 90 and 116 µm has been observed for the first time for the Pb1−xSnxTe(In) photodetector. This value is by a factor of ∼ 100 higher than the respective parameters of the Ge(Ga) photoconductor in the same conditions.
Mechanisms of Intersubband Transition in n-Type III-V Quantum Well Superlattice and Improvement on Absorption for TE Polarized Field
Authors: Cheah C. W. , Karunasiri G. , Tan L. S.
Published: April 2011

In this paper, the theoretical study of intersubband transitions in quantum well infrared photodetectors (QWIPs) applying the eight bands k.p model incorporated with envelope function approximation is described. The focus of the work is on the intersubband transition in n-type IIIV QWIP based on AIGaAs/GaAs and AlGaAs/InGaAs material system, with particular emphasis placed on the physics of TE excited transition and the improvement of resulted absorption. Various theoretical absorption spectra of the two material systems are compared, the distinct mechanisms of the intersubband transition for the two material systems are proposed. Possible ways of improving on the absorption for such excitation are also investigated and discussed.
High-Resolution X-ray Diffraction Analysis of p-Type Strained InGaAs/AlGaAs Multiple Quantum Well Structures
Authors: Shi W. , Zhang D. H. , Osotchan T. , Zhang P.H. , Yoon S. F. , Swaminathan S.
Published: April 2011

Be-doped InGaAs/AIGaAs multiple quantum well (MQW) structures, grown by solid-source molecular beam epitaxy with different doping concentration in the wells, were investigated by xray diffraction and transmission electron microscopy (TEM). Some features have been observed. (1) The MQW mean mismatch increases from 1.176 × 10−3 to 1.195 × 10−3 and 1.29 × 10−3 for the structures with doping concentration of 1 × 1017 cm−3, 1 × 1018cm−3and 2 × 1019 cm−3 in the wells, respectively. (2) The period of the MQW also increases with doping density. (3) The intensity of the first order satellite in the rocking curves decreases as the Be concentration is increased, indicating that indium diffusion in the heavily doped wells is likely more significant than that in the lightly doped ones. (4) The full width at half maximum of the zero-order satellite peak becomes widened as doping concentration increases, indicating that high Be-doping in the well likely deteriorates the interfaces of the multiple quantum well stacks. In addition, TEM measurement is conducted and clear pictures on well and barrier layers of the structures are observed. The information obtained is of great value for the design of p-doped quantum well infrared photodetectors.
The Development of Infrared Photosensitive Material Based on Polycrystalline PbS Films
Authors: Abarbanel C. , Shneck R. , Dashevsky Z. , Rotman S.
Published: April 2011

Polycrystalline thin films of lead sulphide were deposited on glass substrates by the hot wall technique. The grain size varied from 100 to 500 A by varying the growth rate and the substrate temperature. The grain boundaries are assumed to influence the optoelectronic properties of polycrystalline films by generating potential energy relieves, estimated to reach 0.1 eV. We investigated the influence of the barrier height by introducing impurity atmospheres into the grain boundaries. Oxygen and indium were introduced into the films by diffusion from a gas phase. Conductivity was measured in the 80-300 K range. It rises with increasing temperature in oxygen doped films, indicating that conductivity is a thermal activation process. In the same time the conductivity of In doped PbS films decreases with temperature like in PbS single crystals. Photoconductivity was observed in films annealed in oxygen, which was significant up to room temperature. Carrier lifetime was found to decrease with rising temperature and be larger in films annealed in oxygen.

A model is proposed to explain the optoelectronic behavior of the polycrystalline films. It is proposed that charge accumulation near grain boundaries set up potential barriers for free carriers. The barriers increase by oxygen and decreases by indium doping. The charge carriers generated by an illumination become spatially separated at grain boundaries. This separation retards their recombination and increases their lifetime, giving rise to persistent photoconductivity and potential high photosensitivity.
Evidence of High Electron Mobility in CdGeAs2 Single Crystals
Authors: Rud' V.Yu. , Rud' Yu.V. , Pandey R. , Ohmer M. C.
Published: April 2011

CdGeAs2 single crystals were prepared by low temperature crystallization from a nonstoichiometric melt. The results of the first study of the temperature dependencies of the electrical conductivity and the Hall coefficient of n-type CdGeAs2 single crystals prepared by this new technique are reported. All the as-grown crystals show n-type conductivity. These single crystals had free electron concentrations of (1 - 2) 1018 cm−3 and Hall mobilities of more than 10000 cm2/(Vs) at T=300 K. These room temperature electron mobility values are four times larger than previously reported. In the high temperature region (T> 150K), the temperature dependence of the Hall mobility exhibited a behavior characteristic of phonon scattering. Below 150 K, a deviation from this behavior indicated an increasing contribution of static lattice defects to scattering. The Hall mobility in these crystals was found to reach ∼ 36000 cm2/( V· s ) at 77 K. The first photosensitive n-type CdGeAs2/n-type InSe heterostructures were constructed by contact methods. Photosensitivities of 70-100 V/were observed. This is substantially better than for previous structures using conventionally grown CdGeAs2 and indicates the high quality of the crystals. It is concluded that the low temperature growth technique is promising for the preparation of more perfect CdGeAs2crystals.
Modeling of the Properties of Dopants in the NLO Semiconductor CdGeAs2
Authors: Pandey Ravindra , Ohmer Melvin C. , Costales A. , Recio J. M.
Published: April 2011

The results of a shell-model study on CdGeAs2 doped with Cu, Ag, B, Al, Ga, and In are presented here. The pairwise interatomic potential terms representing the interaction of dopants with the host lattice ions are derived using first principle methods while empirical fitting methods are used for the host-lattice potentials. Defect calculations based on Mott-Littleton methodology predict small binding energies for Cu and Ag substituting Cd in the lattice which are in agreement with the available experimental data. The group III dopants (i.e. B, Al, Ga and In) at the Ge site are predicted to have large binding energies for a hole placing acceptor levels in the middle of the band gap.
ITO/a-SiNx:H/a-Si:H Photodiode with Enhanced Photosensitivity and Reduced Leakage Current Using Polycrystalline ITO Deposited at Room Temperature
Authors: Tao S. , Ma Q. , Striakhilev D. , Nathan A.
Published: April 2011

We report an ITO/a-SiNx:H/a-Si:H MIS photodiode structure based on room temperature deposition of optically transparent polycrystalline ITO for applications in large area optical and x-ray imaging. The photodiode structure exhibits device characteristics with reduced leakage current and enhanced photosensitivity giving rise to a hundred-fold improvement in dynamic range. This notable improvement in performance is believed to be due to the reduced diffusion of oxygen from the ITO to the a-Si:H layer, and thus reducing the density of defect states inside the a-Si:H layer. The behavior of photo and dark current is consistent with an elaborate transport model for the Schottky barrier. The model agrees reasonably well with measurement data for the dark current and provides a consistent picture in terms of the photo current behavior in the MIS structure, where the insulating layer serves to reduce the oxygen diffusion.