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The crystallization of amorphous solids impacts fields ranging from inorganic crystal growth to biophysics. Promoting or inhibiting nanoscale epitaxial crystallization and selecting its final products underpin applications in cryopreservation, semiconductor devices, oxide electronics, quantum electronics, structural and functional ceramics, and advanced glasses. As precursors for crystallization, amorphous solids are distinguished from liquids and gases by the comparatively long relaxation times for perturbations of the mechanical stress and for variations in composition or bonding. These factors allow experimentally controllable parameters to influence crystallization processes and to drive materials toward specific outcomes. For example, amorphous precursors can be employed to form crystalline phases, such as polymorphs of Al2O3, VO2, and other complex oxides, that are not readily accessible via crystallization from a liquid or through vapor-phase epitaxy. Crystallization of amorphous solids can further be guided to produce a desired polymorph, nanoscale shape, microstructure, or orientation of the resulting crystals. These effects enable advances in applications in electronics, magnetic devices, optics, and catalysis. Directions for the future development of the chemical physics of crystallization from amorphous solids can be drawn from the structurally complex and nonequilibrium atomic arrangements in liquids and the atomic-scale structure of liquid–solid interfaces. [ABSTRACT FROM AUTHOR]

The highly coherent and tightly focused x-ray beams produced by hard x-ray light sources enable the nanoscale characterization of the structure of electronic materials but are accompanied by significant challenges in the interpretation of diffraction and scattering patterns. X-ray nanobeams exhibit optical coherence combined with a large angular divergence introduced by the x-ray focusing optics. The scattering of nanofocused x-ray beams from intricate semiconductor heterostructures produces a complex distribution of scattered intensity. We report here an extension of coherent x-ray optical simulations of convergent x-ray beam diffraction patterns to arbitrary x-ray incident angles to allow the nanobeam diffraction patterns of complex heterostructures to be simulated faithfully. These methods are used to extract the misorientation of lattice planes and the strain of individual layers from synchrotron x-ray nanobeam diffraction patterns of Si/SiGe heterostructures relevant to applications in quantum electronic devices. The systematic interpretation of nanobeam diffraction patterns from semiconductor heterostructures presents a new opportunity in characterizing and ultimately designing electronic materials. [ABSTRACT FROM AUTHOR]

Experimental and theoretical investigations into the electronic properties and structure of cubic yttria-stabilized zirconia are presented. Medium-energy x-ray photoemission spectroscopy measurements have been carried out for material with a concentration of 8-9mol.% yttria. Resonant photoemission spectra are obtained for a range of photon energies that traverse the L2 absorption edge for both zirconium and yttrium. Through correlation with results from density-functional theory (DFT) calculations, based on structural models proposed in the literature, we assign photoemission peaks appearing in the spectra to core lines and Auger transitions. An analysis of the core level features enables the identification of shifts in the core level energies due to different local chemical environments of the constituent atoms. In general, each core line feature can be decomposed into three contributions, with associated energy shifts. Their identification with results of DFT calculations carried out for proposed atomic structures, lends support to these structural models. The experimental results indicate a multi-atom resonant photoemission effect between nearest-neighbour oxygen and yttrium atoms. Near-edge x-ray absorption fine structure spectra for zirconium and yttrium are also presented, which correlate well with calculated Zr- and Y-4d electron partial density-of-states and with Auger electron peak area versus photon energy curve. [ABSTRACT FROM AUTHOR]

The formation of Al nanocrystals from an amorphous Al92Sm8 alloy involves kinetic phenomena with very different characteristic length and timescales, including initial nucleation and later growth and coarsening. Insight into these processes can be derived from the evolution of the sizes of nanocrystals as a function of time. Synchrotron small angle x-ray scattering (SAXS) experiments provide information about the evolution of the nanocrystal size distribution, particularly at times after nucleation has reached saturation. Accurately interpreting the distribution of intensity measured using SAXS requires a nanoparticle model consisting of nanocrystalline core of pure Al surrounded by a shell enriched in Sm. With this approach, statistical parameters derived from SAXS are independent of detailed assumptions regarding the distribution of Sm around the nanocrystals and allow the maximum radius of nanocrystals within the distribution to be determined unambiguously. Sizes determined independently using transmission electron microcopy are in excellent agreement with the SAXS results. The maximum radius obtained from SAXS is proportional to the cube root of time at large sizes and long times, consistent with a coarsening model. The diffusivity of Al within the Al-Sm alloy is obtained from a quantitative analysis of the coarsening process. Further analysis with this diffusivity and a particle growth model provides a satisfactory account for the particle size evolution at early times before the kinetic transition to coarsening. [ABSTRACT FROM AUTHOR]

Mixed metal oxides provide a convenient means to produce coatings with tailored physical properties. We investigate the possibility of synthesizing novel coatings of mixed titanium and aluminum oxide using atomic layer deposition (ALD). Results show that ALD films were prepared with compositions ranging between Al2O3 and TiO2 having refractive indices between 1.6 and 2.4 (at λ = 550 nm) at low temperature. The microstructure and bonding environment within the films was investigated using electron microscopy and x-ray absorption spectroscopy. The films were amorphous, and the Ti and Al atoms were mixed at the atomic scale. The electrical breakdown characteristics of the films were measured and showed that films with intermediate compositions had poor leakage current properties, believed to be caused by the presence of distorted bonding configurations. This study shows that ALD can be used to deposit high quality thin films with tailored optical properties, particularly suitable for applications in which complex topographies are required. [ABSTRACT FROM AUTHOR]

A sensing principle, operating regime, and composition range are identified for force sensing with Galfenol alloys. Magnetization measurements of Fe79.1Ga20.9 and Fe81.6Ga18.4 are performed under applied magnetic field at constant stress. Stress-dependent, linear regions with negligible hysteresis are observed in the Fe79.1Ga20.9 sample over a large range of fields and stresses, for which an analytic model for unbiased loops is formulated. Similar regions are observed in the Fe81.6Ga18.4 sample, with a more limited stress and field range. The small signal operating regime (small in field, not in stress) centered about zero magnetic field is particularly advantageous because in this regime there is no observable hysteresis, since the magnetization process occurs by domain rotation only. The measurements and model show that in this region the susceptibility of Fe79.1Ga20.9 is more sensitive to stress (owing to a significantly lower fourth-order anisotropy constant) with only a small reduction in the saturation magnetization and magnetostriction as compared to Fe81.6Ga18.4. For force sensing, these results suggest the use of Galfenol with an ideal Ga content in the range of 19-22 at. % in which a small, positive fourth-order anisotropy constant is obtained, though in this composition range the magnetostriction is sacrificed. [ABSTRACT FROM AUTHOR]

We present a discrete energy-averaged model for the nonlinear and hysteretic relation of magnetization and strain to magnetic field and stress. Analytic expressions from energy minimization describe three-dimensional rotations of domains about easy crystal directions in regions where domain rotation is the dominant process and provide a means for direct calculation of magnetic anisotropy constants. The anhysteretic material behavior due to the combined effect of domain rotation and domain wall motion is described with an energy weighted average while the hysteretic material behavior is described with an evolution equation for the domain volume fractions. As a result of using a finite set of locally defined energy expressions rather than a single globally defined expression, the model is 100 times faster than previous energy weighting models and is accurate for materials with any magnetocrystalline anisotropy. The model is used to interpret magnetization and strain measurements of <100> oriented Fe79.1Ga20.9 and Fe81.5Ga18.5 as well as <110> oriented Fe81.6Ga18.4. [ABSTRACT FROM AUTHOR]

The growth of pentacene thin films for applications in thin-film transistors and other organic electronic devices results in a variety of extended structural defects including dislocations, grain boundaries, and stacking faults. We have used scanning tunneling microscopy (STM) to probe the molecular-scale structure of grain boundaries and stacking faults in a pentacene thin film on a Si (001) surface modified with styrene. Styrene/Si (001) substrates produce pentacene films that are structurally similar to those grown on insulating substrates, but which are sufficiently smooth and conductive for STM studies. STM images show two types of grain boundaries: in-plane high-angle tilt grain boundaries at the junctions between pentacene islands, and twist boundaries between molecular layers. Segments of the tilt grain boundaries are faceted along low-energy crystallographic directions. Stacking faults are found in the plane of individual pentacene grains. Two rows of molecules near the stacking fault are shifted along the surface normal by 60 pm. Electronically relevant trap states may thus be associated with stacking faults in pentacene thin films. [ABSTRACT FROM AUTHOR]

Interfaces between wide-bandgap semiconductors and polymeric electronic materials are model systems for geometrically more complicated interfaces formed in nanostructured composite electronic, photonic, and photovoltaic devices. The wide-bandgap semiconductor GaN is readily available with well-defined electronic and structural properties, including reproducible control of doping and conductivity type, and can ideally serve as the inorganic side of the model system. Electron transport through a GaN/poly(3-hexylthiophene) (P3HT) semiconductor heterojunction depends on the conductivity type of the GaN and on the doping level in the polymer. The total contact resistance of a planar P3HT film with GaN contacts in a symmetric p-GaN/P3HT/p-GaN structure is consistent with the contribution of reversed-biased junction at one of the GaN/P3HT interfaces. An n-GaN/P3HT/n-GaN structure has a lower total resistance than the p-GaN structure, possibly arising from band-to-band tunneling at the interface. Doping the P3HT layer with iodine greatly reduced the contact resistance for interfaces with both conductivity types of GaN. [ABSTRACT FROM AUTHOR]

A fully coupled, nonlinear model is presented that characterizes the three-dimensional (3D) strain and magnetization response to magnetic field at constant stress in cubic magnetostrictive materials. A multiscale thermodynamic approach is taken which accounts for nonlinear anisotropy, material texture, and hysteresis effects. The model is validated with measurements of textured polycrystalline Galfenol. The model provides an efficient framework for characterization, design, and control of Galfenol (Fe–Ga) devices with 3D functionality subjected to combined magnetic field and stress loading. [ABSTRACT FROM AUTHOR]

Optical properties of metal (Al, Ag, Sb, and Sn)-ion-implanted ZnO films have been studied by ultraviolet-visible spectroscopy and spectroscopic ellipsometric techniques. The effects of metal-ion doping on the optical band gap (Eg), refractive index (n), and extinction coefficient (k) of nanocrystalline ZnO films have been studied for the similar implantation dose of all the metal ions. The ellipsometric spectra of the ion-implanted samples could be well described by considering an air/roughness/ZnO–M (layer 1)/ZnO (layer 2)/glass model. The band gap of ZnO films increases with Al ion doping and decreases with doping of Ag, Sb, and Sn ions. The refractive index of ZnO films in the visible spectral region increases substantially on Sb and Sn ion doping, while it decreases to some extent with Al ion doping. [ABSTRACT FROM AUTHOR]

The manipulation of strain in micromachined silicon structures presents an opportunity in the control of surface processes in epitaxial growth. With appropriate fabrication techniques, the magnitude, crystallographic direction, and symmetry of the strain at a Si surface can be precisely controlled with this strategy. Synchrotron x-ray microdiffraction techniques allow simultaneous independent measurements of the strain and bending in these structures and serve to calibrate the fabrication process. Bending is the dominant source of strain in a microfabricated Si bridge loaded at its ends by silicon nitride thin films that we have used as a strained substrate in studies of Ge epitaxial growth. The total strain difference between the top and bottom of the bent bridge exceeds 10-3 in present structures and can potentially be increased in optimized devices. These micromachined substrates complement other methods for producing strained silicon and silicon- germanium structures for improved electrical device performance and for fundamental studies of epitaxial growth. [ABSTRACT FROM AUTHOR]

Donor-acceptor-pair (DAP) luminescence is a direct probe of the acceptors in ZnO. We report the near-surface doping of a ZnO single crystal by ion implantation with nitrogen and titanium. Secondary-ion-mass spectroscopy shows that the doping depth is approximately 80 nm (N) and 50 nm (Ti). The DAP photoluminescence centered at 3.232 eV is observed from both the undoped and doped ZnO single-crystal samples. The luminescence spectrum of the nitrogen-doped sample shows enhancement of the DAP transition compared to the “pure” ZnO sample. The acceptor energy is calculated to be 177 meV, consistent with nitrogen as the acceptor in DAP luminescence. The DAP recombination lifetime is found to be ∼5.5 ns. The temperature evolution of spectra shows the gradual transition from DAP luminescence to electron+acceptor recombination luminescence at temperatures above 37 K. Our experimental results suggest that ion implantation is an effective way of doping nitrogen into ZnO. [ABSTRACT FROM AUTHOR]

When plasma immersion ion implantation is performed in the condensable plasma stream produced by a cathodic vacuum arc, deposition as well as implantation usually occurs. In this article we describe a method of achieving pure implantation by orienting the substrate so that it is shadowed from the plasma beam. Implantation depth profiles measured in glassy carbon and CR39 polymer using Rutherford backscattering are compared to illustrate the effectiveness of the technique for conducting and insulating substrates. Charging of the insulating substrate was found to cause a reduction in implantation depth compared to a conducting substrate. The depth profiles in glassy carbon were comparable to those achieved by conventional extracted ion beam implantation. Implantation of magnesium into hydroxyapatite and alumina was carried out to improve the bone cell adhesion onto these materials for prosthetic applications. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Presents a study that examined the effects of hydrogen plasma erosion of glassy carbon implanted with tungsten. Use of Raman measurements; Background on glassy carbon; Role of tungsten in the inhibition of hydrogen plasma erosion.

Examines the compaction, distribution and chemical bonding of tungsten-implanted glassy carbon. Microstructure of glassy carbon; Effect of ion implantation on the resistance of glassy carbon; Rutherford backscattering spectrometry for various tungsten doses.

Focuses on a study which examined the transport of majority carriers across the potential barriers found at grain boundaries in semiconductors. Transport processes that were considered; Observation about boundary transport; Details of a numerical calculations for a given barrier height with a range of bulk doping levels; Evaluation of a deconvolution scheme to determine defect-state densities.

Describes a vacuum arc centrifuge (VAC) which produces a rapidly rotating metal plasma column by means of the Lorentz force between the arc current and an applied axial magnetic field. Types of sample analysis employed in the studies of mass separation in VAC; Components of VAC; Techniques employed to analyze the samples which were deposited on strips of aluminum foil in the plasma stream; Similarities of the copper/zinc system to that of aluminum/titanium.

Presents a study which described measurements of porous silicon using a monoenergetic positron beam in conjunction with the Doppler broadening technique. Appropriateness of the technique to thin porous silicon layers; Effects of etching porous silicon using hydrofluoric acid; Information on the photoluminescence spectra measured from the samples.

We demonstrate how epitaxial FM (Ni) films can be grown by ECD directly onto GaAs(001) without outdiffusion or surface segregation of As or Ga. The thickness dependence of electrical and magnetic properties (saturation magnetic moment) verify the good quality of the layers and indicate that electrochemical deposition is a suitable candidate for the growth of epitaxial Ni films with sharp interfaces on GaAs(001). X-ray photoelectron spectroscopy (XPS) analysis on electroplated (epitaxial) Ni films showed no interdiffusion for annealing up to 250 °C. Annealing at higher temperatures, up to 350 °C, significantly increases both the As outdiffusion and the Schottky barrier heights, which indicates the correlation between intermixing and the diode quality. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Ni, Co, and iron-rich FeNi films were grown onto n-GaAs (011) substrates using electrodeposition from metal sulfate solutions, at room temperature, with a current density of 3.5 mA/cm[SUP2]at a pH of 2.5. The structure of Ni film is found to be fcc with a (111) preferred orientation, whereas Co films show a mixed fcc and hcp structure that is confirmed by x-ray diffraction and transmission electron microscopy data. The structure of iron-rich (>90%) FeNi films remains unclear at the moment. The films show a well-defined, in-plane, uniaxial anisotropy with the easy axis along the [011] GaAs direction for Ni, and [01&sline;1] GaAs direction for Co and FeNi films (i.e., anisotropy rotated by 90° compared to Ni). Co films maintain their anisotropy even for large thicknesses (>250 nm) and so does Ni (up to 90 nm). Surprisingly, thin Ni films exhibit a larger H[SUBK] value(950 Oe) than what would be expected from a purely crystalline anisotropy. This effect is ascribed to internal stresses in the as-deposited films. [ABSTRACT FROM AUTHOR]

Using x-ray submicrobeam, we spatially mapped the strain in epitaxial La[sub l-χ]Sr[sub χ]MnO[sub 3] films grown on SrTiO[sub 3](001) bicrystal substrates. Our results show that there is an elastic strain gradient at the artificial grain boundary, which decays over a length scale of ∼1 µm. The tensile strain at the interior of the grain—due to the lattice mismatch between La[sub l-χ]Sr[sub χ]MnO[sub 3] and SrTiO[sub 3]—relaxes as the film nears the grain boundary, yielding a grain boundary lattice constant which approaches the value of that in bulk La[sub l-χ]Sr[sub χ]MnO[sub 3]. [ABSTRACT FROM AUTHOR]

The creation of thin SrTiO3 crystals from (001)-oriented SrTiO3 bulk single crystals using focused ion beam milling techniques yields sheets with submicron thickness and arbitrary orientation within the (001) plane. Synchrotron x-ray nanodiffraction rocking curve widths of these SrTiO3 sheets are less than 0.02°, less than a factor of two larger than bulk SrTiO3, making these crystals suitable substrates for epitaxial thin film growth. The change in the rocking curve width is sufficiently small that we deduce that dislocations are not introduced into the SrTiO3 sheets. Observed lattice distortions are consistent with a low concentration of point defects. [ABSTRACT FROM AUTHOR]

Provides information on a study that presented data demonstrating the effect that cavity length, and thus Q loss, has upon quantum well heterostructure edge-emitting laser diodes that are reduced to microcavity thickness. Details on the fabrication of the edge-emitting lasers; Results and discussion on the study.

Disorder in the potential-energy landscape presents a major obstacle to the more rapid development of semiconductor quantum device technologies. We report a large-magnitude source of disorder, beyond commonly considered unintentional background doping or fixed charge in oxide layers: nanoscale strain fields induced by residual stresses in nanopatterned metal gates. Quantitative analysis of synchrotron coherent hard x-ray nanobeam diffraction patterns reveals gate-induced curvature and strains up to 0.03% in a buried Si quantum well within a Si/SiGe heterostructure. Electrode stress presents both challenges to the design of devices and opportunities associated with the lateral manipulation of electronic energy levels. [ABSTRACT FROM AUTHOR]

Thin films of the lead-free ferroelectric Na0.5Bi0.5TiO3 grown on thin-film Pt electrodes supported by SrTiO3 substrates have a complex microstructure consisting of crystalline grains with three distinct major crystallographic orientations. The piezoelectric response measured in spatially separated sub-micron grains using time-resolved synchrotron x-ray microdiffraction is highly inhomogeneous even among grains sharing the same major orientation. The piezoelectric coefficient d33 varies by nearly a factor of two in a series of areas sharing the (001) orientation. The piezoelectric inhomogeneity is linked to the peculiar microstructure of the film, arising from local variations in the stress imposed by surrounding grains with different crystallographic orientations and differing directions of the ferroelectric remnant polarization. A systematic nonlinearity of the piezoelectric strain is observed in applied electric fields with small magnitudes in all regions, consistent with the coexistence of domains of differing polarization direction at zero applied electric field. [ABSTRACT FROM AUTHOR]

The short pulse x-ray imaging and microscopy beamline is one of the two x-ray beamlines that will take full advantage of the short pulse x-ray source in the Advanced Photon Source (APS) upgrade. A horizontally diffracting double crystal monochromator which includes a sagittally focusing second crystal will collect most of the photons generated when the chirped electron beam traverses the undulator. A Kirkpatrick-Baez mirror system after the monochromator will deliver to the sample a beam which has an approximately linear correlation between time and vertical beam angle. The correlation at the sample position has a slope of 0.052 ps/μrad extending over an angular range of 800 μrad for a cavity deflection voltage of 2 MV. The expected time resolution of the whole system is 2.6 ps. The total flux expected at the sample position at 10 keV with a 0.9 eV energy resolution is 5.7 × 1012 photons/s at a spot having horizontal and vertical full width at half maximum of 33 μm horizontal by 14 μm vertical. This new beamline will enable novel time-dispersed diffraction experiments on small samples using the full repetition rate of the APS. [ABSTRACT FROM AUTHOR]

In recent years, attention has focused on the use of alternative metal nitride coatings as replacements for TiN for not only improved wear resistance and surface hardness but also for increased corrosion resistance in selected environments. While these coatings display excellent wear resistance and surface hardness, like many nitride coatings, their corrosion behavior is determined to a large extent by the presence of defects such as pinholes within the coating. Improved corrosion resistance is expected through minimizing the porosity/number of pinholes within the coating, through postdeposition surface modification. The aim of this study was to modify the surface of CrN coatings using metal vapor vacuum arc ion implantation. CrN coatings were deposited on AISI 316 stainless steel and AISI 1020 mild steel substrates using physical vapor deposition technology, followed by implantation of Zr ions into the coating at doses varying from 6×1016 to 2×1017 ions/cm2. The corrosion behavior was assessed in saline environments using linear polarization techniques and the corroded surface of the coatings was characterized using x-ray photoelectron spectroscopy and scanning electron microscopy. The results of the study showed that implantation of Zr ions into CrN resulted in a lowering of the corrosion current density, suggesting improved corrosion resistance. This was though to be associated with two factors. Firstly, partial closure of the pinholes as a result of the implantation process and secondly, the formation of ZrN, CrZrN, and various oxynitrides/oxides at the surface. [ABSTRACT FROM AUTHOR]

We present three-dimensional numerical simulations of the flow of a thin liquid coating on a rotating horizontal right circular cylinder. The liquid motion is described using a lubrication model. The model evolution equation is discretized and solved numerically using an alternating-direction implicit algorithm. The cylinder rotates about its axis, carrying liquid around its circumference, resulting in the formation of a relatively thick coating where the cylinder surface moves upward. For coatings which are initially nearly uniform along the cylinder axis, this results in a ridge of liquid aligned with the cylinder axis. Over time, this ridge may break up into one of several possible configurations, including drops near the underside, and rings enveloping the cylinder. Simulations show that on larger cylinders, under certain circumstances this ridge may develop undulations which grow to form long fingers. These fingers drain down the cylinder. The simulation results are compared with a simple laboratory experiment, which exhibits similar fingering. [ABSTRACT FROM AUTHOR]

A model for the evolution of a thin liquid coating on a horizontal cylinder is presented. The cylinder rotates about its axis, carrying liquid around its circumference. For a viscous coating, this leads to formation of a relatively thick coating where the cylinder surface moves upward. The model is based on lubrication theory, as the coating is thin compared to the cylinder radius, and includes the effects of cylinder rotation, gravity, surface tension, and flow along the cylinder axis. A two-dimensional numerical scheme based on finite differences is produced, for investigation of the case when axial flow is neglected. This numerical scheme is validated in appropriate limiting cases. Coating cross sections are obtained over a range of cylinder rotation rates, for realistic parameter values. These show a transition from pendant drops hanging beneath the cylinder to a nearly uniform coating wrapped around it as rotation rate is increased. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A simple and cost-effective method for detecting propagation of acoustic waves based on the harmonic oscillations of a piezoresistive microcantilever is presented. Monitoring the Fourier amplitude of the microcantilever's fundamental frequency, the dependence of the detected amplitude upon the acoustic source location, is measured. At a fixed probe-source distance, the solid angular dependence of the cantilever plane relative to the source is studied. The potential use of a microelectromechanical cantilever as an acoustic leak sensor for pressurized gas reservoirs is addressed. [ABSTRACT FROM AUTHOR]

Following the pioneering work on metal vapor vacuum arc (MEVVA) ion sources at Lawrence Berkeley Laboratory by Brown and co-workers, the Australian Nuclear Science and Technology Organization (Ansto) commenced a program of research aimed at constructing a MEVVA based ion implanter. This phase of the program has been completed and the system is now in routine use for surface modification studies. The purpose of the present article is to give an overview of the Ansto implanter with particular reference to those features, such as triggering reliability, which entailed some developmental work. Finally, current ion implantation research activities on this system are briefly described. [ABSTRACT FROM AUTHOR]