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The microstructure and energy-loss near-edge structure (ELNES) of pulsed cathodic arc and pulsed magnetron sputtered WO3 thin films were investigated. It was found that the cathodic arc deposited material consisted of the alpha-WO3 phase with a high degree of crystallinity. In contrast, the magnetron sputtered material was highly disordered making it difficult to determine its phase. A self-consistent real space multiple scattering approach was used to calculate the NES of the various phases of WO3. Each phase was found to exhibit a unique NES allowing different phases of WO3 to be identified. The real space approach also allowed the origin of the main features in the NES to be investigated as the cluster size increased. The calculated NES for the room temperature gamma-WO3 was found to compare well to previous X-ray absorption spectra and to NES obtained by full-potential band structure calculation.

Glassy carbon (GC) is usually considered the prototypical super-elastic material, which can almost fully recover its shape after compression of several gigapascals (GPa). In this work, nanoindentation is used to study the mechanical response of GC, which was subjected to a range of high pressures using a diamond anvil cell (DAC). We show that GC starts to lose its elasticity after compression to 6 GPa and becomes clearly mechanically anisotropic after being compressed beyond ∼30 GPa. Molecular dynamics (MD) simulations are used to calculate Young's modulus before and after compression. Through our experimental results and MD simulations, we show that the elasticity of GC is at a minimum around 30 GPa but recovers after compression to higher pressures along the DAC compression axis. [ABSTRACT FROM AUTHOR]

The phase behavior of carbon at high pressure and the search for carbon structures denser than diamond has been explored for decades showing large discrepancies, with many fundamental questions remaining unresolved. Here we show evidence of melting above the graphite-diamond-liquid (GDL) triple point (∼13 GPa, 4000 K) up to 50 GPa on samples recovered from single flash-heating events using spectroscopic and electron microscopic methods. The results show that for all pressures, diamond melts below the triple point temperature contradicting previous studies, most of which predict a positive slope of the melting curve. [ABSTRACT FROM AUTHOR]

We compare the use of externally applied pulsed and steady magnetic fields for the enhancement of deposition rate in reactive High Power Impulse Magnetron Sputtering (HiPIMS), using the deposition of amorphous hafnium oxide (a-HfO2) on Si as an example. The external magnetic fields were applied by a solenoidal coil, placed above the magnetron target. In the case of a steady magnetic field, a higher voltage was required to initiate the HiPIMS discharge, a longer delay time was observed for current onset, and the films became substoichiometric. For the pulsed magnetic field, film stoichiometry was maintained under all applied external magnetic field strengths. Varying the duration and delay times of the magnetic field after the application of HiPIMS voltage pulse revealed that the afterglow of the plasma between HiPIMS pulses was actively quenched by the presence of the magnetic field. Therefore, the optimum operation with the highest plasma density was obtained by applying the external magnetic field only when the plasma was established and removing it at the end of the HiPIMS pulse. A model to explain the findings is presented in which the target poisoning by oxide formation is determined by the conditions in the afterglow. We describe an approach to achieve maximum deposition rate while maintaining film stoichiometry and high film quality. Amorphous HfO2 films with leakage current through the film of less than 5 × 10-5 A/cm² at 0.1MV/cm were obtained at the maximum deposition rate. The refractive index, at a wavelength of 500nm, of the film prepared with pulsed magnetic field was 2.05 with a very low extinction coefficient of 8 × 10-5. [ABSTRACT FROM AUTHOR]

High-power impulse magnetron sputtering (HiPIMS) is used to deposit amorphous carbon thin films with sp3 fractions of 13% to 82%. Increasing the pulse length results in a transition from conventional HiPIMS deposition to a "mixed-mode" in which an arc triggers on the target surface, resulting in a large flux of carbon ions. The films are characterized using X-ray photoelectron spectroscopy, Raman spectroscopy, ellipsometry, nanoindentation, elastic recoil detection analysis, and measurements of stress and contact angle. All properties vary in a consistent manner, showing a high tetrahedral character only for long pulses, demonstrating that mixed-mode deposition is the source of the high carbon ion flux. Varying the substrate bias reveals an "nergy window" effect, where the sp3 fraction of the films is greatest for a substrate bias around -100V and decreases for higher or lower bias values. In the absence of bias, the films' properties show little dependence on the pulse length, showing that energetic ions are the origin of the highly tetrahedral character. [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]

Hafnium oxide films were deposited with a range of substrate temperatures using a filtered cathodic vacuum arc deposition system. The microstructure, electronic structure, and electrical breakdown of the films were characterized. In films deposited at temperatures above 200 °C, the microstructure became more ordered and x-ray diffraction indicated that the dominant phase was monoclinic hafnium oxide. Evidence for the presence of the tetragonal phase was also found in the films deposited at temperatures above 400 °C. The near edge structure of the oxygen K-edge measured using x-ray absorption spectroscopy, provided further evidence that films prepared at high temperatures contained a combination of the monoclinic and tetragonal phases. Films deposited at room temperature were disordered and exhibited the best electrical breakdown characteristics. The electrical breakdown of the films deteriorated as the crystallinity increased with increasing deposition temperature. These results support the proposition that electrical breakdown paths may occur along grain boundaries in polycrystalline hafnium oxide films and therefore a disordered microstructure is preferable. [ABSTRACT FROM AUTHOR]

The intrinsic stress of carbon thin films deposited by filtered cathodic arc was investigated as a function of ion energy and Ar background gas pressure. The microstructure of the films was analyzed using transmission electron microscopy, electron energy loss spectroscopy, and Raman spectroscopy. The stress at given substrate bias was reduced by the presence of an Ar background gas and by the presence of a Cu underlayer deposited onto the substrate prior to deposition. Auger electron spectroscopy depth profiles showed no evidence of Ar incorporation into the films. A sharp transition from a sp2 to sp3 rich phase was found to occur at a stress of 6.5±1.5 GPa, independent of the deposition conditions. The structural transition at this value of stress is consistent with available data taken from the literature and also with the expected value of biaxial stress at the phase boundary between graphite and diamond at room temperature. The microstructure of films with stress in the transition region near 6.5 GPa was consistent with a mixture of sp2 and sp3 rich structures. [ABSTRACT FROM AUTHOR]

Porous solids are very important from a scientific point of view as they provide a medium in which to study the behavior of confined fluids. Although some porous solids have a well defined pore geometry such as zeolites, many porous solids lack crystalline order and are usually described as amorphous. The description of the pore geometry in such structures is very difficult. The authors develop a modeling approach using a Monte Carlo algorithm to simulate porosity within amorphous systems based on constraints for the internal volume and surface area. To illustrate this approach, a model of microporous amorphous silicon is presented. Structural aspects of the porous model are then compared against hybrid reverse Monte Carlo simulations of nonporous amorphous silicon and published results from the literature. It is found that coordination defects are predominately located at the pore surface walls. [ABSTRACT FROM AUTHOR]

Al/AlN multilayers with bilayer thicknesses ranging from 10 to 50 nm were fabricated using a filtered cathodic arc deposition system. The effects on the microstructure of using two different deposition rates and applying an 8 kV pulsed voltage (plasma immersion ion implantation or PIII) to the substrate were explored. The microstructure was found to undergo a transition in which the Al transformed from layers to an aggregated phase under some conditions. This behavior is explained by a model in which the aggregation process is limited by diffusion. High deposition rates and the application of PIII were both found to encourage the transition by increasing diffusion. The model defines a phase diagram which predicts whether a multilayer or an aggregated structure will occur. A maximum in intrinsic stress was found to occur when the average feature size was 15 nm for both layers and aggregates. [ABSTRACT FROM AUTHOR]

We examine the effect of ion impact energy on the intrinsic stress and microstructure of aluminum nitride thin films deposited using a filtered cathodic arc. The dependence of intrinsic stress on ion impact energy is studied over the range from 0 to 350 V using dc bias and up to several kV for a fraction of the ions using pulse bias. For dc bias, the stress reaches a maximum at 200 V and decreases with further increase in ion bias. The preferred orientation of the crystallites was studied by cross-section transmission electron microscopy and diffraction. We found that there is a preference for the c crystallographic axis to lie in the plane of the film under high intrinsic stress conditions (4 GPa), whereas a c-axis orientation perpendicular to the plane of the film was observed for low intrinsic stress (0.25 GPa). We carried out calculations of the expected distribution of intensity in cross-sectional electron diffraction patterns to predict the effect of rotation freedom of crystallites with the c axis pinned. The calculated patterns agreed well with experiment. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Polycrystalline and microcrystalline materials grown as thin films often exhibit a preferred crystallographic orientation. The mechanism by which this preferred orientation develops has been the subject of some debate. In this article we present the results of electron microscopy and diffraction experiments examining preferred orientation in titanium-nitride (TiN) films deposited by physical vapor deposition with bombardment energies up to 18 keV using plasma immersion ion implantation. We show that as the bombardment energy increases the intrinsic stress is reduced. For example, at 3 kV more than a 50% reduction in stress is achieved. The results are consistent with a model in which the preferred orientation is the result of minimizing the energy, which includes both surface energy and bulk strain energy terms. [ABSTRACT FROM AUTHOR]

Theoretical studies [R. P. Fehlhaber and L. A. Bursill, Phys. Rev. B 60, 14147 (1999)] of small nanocrystalline diamond spheres, using the classical electrodynamic formalism with a well defined impact parameter and including all multipole modes, are used to analyze and discuss electron energy loss spectra recorded with a high resolution scanning transmission electron microscope. The theory is used to predict spectra for spheres of different radii with and without surface coatings. Due to the relatively large damping factor for diamond the surface, interface and bulk plasmon peaks overlap; but it is shown that the theory is nevertheless capable to allow particle diameter and coating thickness to be determined accurately. The theory is also applied to make some deductions concerning particle morphology by analysis of low-loss spectra from particles of different thickness and shape. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Discusses findings of an ab initio study of structure in boron nitride, aluminum nitride and mixed aluminum boron nitride amorphous alloys. Structural and elastic properties; Use of first principles quantum mechanical molecular dynamics; Use of density functional theory to calculate interatomic forces.

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 information on a study that found that the structures of the carbon nitride materials produced by cathodic arc deposition and nitrogen implantation of glassy carbon were similar. Experimental procedure; Results and discussion on the study; Conclusions.

Investigates the effects of dynamic and postimplantation annealing on glassy carbon using Raman spectroscopy. Activation energies for interstitial and vacancy mobilities; Effects of postimplantation annealing; Reason for the swelling of the implanted layer.