[en] The electron field emission characteristics of the nitrogenated tetrahedral amorphous carbon (ta-C:N) films deposited by a pulsed filtered vacuum arc deposition system at various conditions were investigated. The wider region of N content in the films (0-21 at.%) allow us to study systematically the effects of N content and the other related parameters on field emission characteristics of the films. It was found that the field emission for both batches of ta-C:N samples depended upon the N content and this effect dominated the effects of the other parameters, such as sp³ content, resistivity of the films, band gap of the films, and Fermi level position. The threshold field was found to first increase with increasing N content up to 5 at.%, then started to decrease up to a minimum of approximately 4 V/μm at 10 at.%. When the N content became higher than 10 at.%, the threshold field was found to increase again. Such complicated variation of the threshold field with the N content of the ta-C:N films was discussed in terms of a three-step field emission model

[en] A novel metal ion source, Electron Beam Evaporation Metal Ion Source, has been developed for material modifications. This ion source is based on the electron beam evaporation technology. It can provide gaseous, solid or gaseous and solid mixed intense ion beams for preparing a variety of thin films. In this ion source, a focusing electron beam is used to bombard and vaporize the metal or other solid element within same chamber where the metal or solid atoms are ionized and plasma medium from which ions are extracted is formed by arc discharge. A small aperture diameter extraction system is used for extracting the ion beam from this source. Ion beams of a series of elements, which include C, W, Ta, Mo, Cr, Ti, B, Cu, Ni, Al, Ar, N, C+N, Ti+N, Cr+N, etc., have been extracted. The source has a 3.6 cm extraction diameter. The beam energy ranges from 0.3 to 4 keV for single charge state ions, and the maximum beam current extractable is over 90 mA. The source has been used for preparing hard coatings. The films of carbon nitride and titanium nitride have been synthesized by direct deposition with C+N and Ti+N mixed ion beams. The results have shown to exhibit very high hardness value for carbon nitride films. The microhardness is up to HK 5800 kgf/mm². In comparison with other methods, it is also to exhibit higher hardness value for titanium nitride coating. The highest hardness value obtained for titanium nitride is about 3000 kgf/mm². The AES profile shows that there is a good intermixture between coating and substrate for both films. The principle, structure and performance of this ion source will be described. The preliminary results for forming hard coatings are also presented in this article

[en] High dose carbon implantation into silicon to form a β-SiC buried layer has been performed by using a metal vapor vacuum arc ion source. The implantation energy and dose are 65 keV and 1x10¹⁸ ions cm^-2, respectively. Post-implantation thermal annealing was carried out at 1250 deg. C for various time intervals in Ar ambient. The composition depth profile, chemical state of C and Si atoms, microstructure and optical properties of the samples have been studied using X-ray photoelectron spectroscopy, Fourier transform IR spectroscopy, cross-section transmission electron microscopy and spectroscopic ellipsometry. For the as-implanted sample, the carbon depth profile shows a Gaussian shape-like distribution with a maximum concentration exceeding the stoichiometric ratio. A clear redistribution of the implanted carbon from the Gaussian shape-like distribution to the two sides is observed during annealing. After annealing at 1250 deg. C for 10 h, a stoichiometric SiC buried layer of approximately 150 nm is formed. Results show the annealed sample is a multi-layered structure of SiO₂ surface layer/Si top layer/damaged Si layer/upper interface layer/β-SiC buried layer/lower interface layer on Si substrate. The optical constants of the β-SiC buried layer formed by ion beam synthesis are determined from simulation of the measured ellipsometric spectra (2.3-5.0 eV) using an appropriate multi-layered model and the Bruggeman effective medium approximation

[en] Amorphous Co_xC_1-x thin films, with x in the range of 60-75% in atomic percentage, have been prepared by pulsed filtered vacuum arc deposition. The structures of the films were characterized by transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The in-plane magnetic hysteresis loops were measured by a superconducting quantum interference device magnetometer at room temperature. The electrical transport properties were measured by the four-probe technique at various temperatures ranging from 20 to 300 K. The films were found to be magnetically soft with coercivities in the range of 2 to 12 Oe, resistivities in the range of 130 to 300 μΩ cm, and magnetic saturation flux densities in the range of 6 to 13 kG. The films also showed good thermal stability in their structural, electrical and magnetic properties upon annealing up to 200 deg. C in a vacuum furnace

[en] Nanocomposite Co-C thin films of about 15 nm thick were prepared by pulsed filtered vacuum arc deposition. The films were characterized by X-ray photoelectron spectroscopy, non-Rutherford backscattering spectrometry, X-ray diffraction, and magnetic force microscopy. The as-deposited films were amorphous. After annealing at 350 deg. C for 1 h in vacuum (<10^-3 Pa), the films were found to consist of nanocrystalline Co grains encapsulated in carbon. The superparamagnetism of the annealed Co₃₆C₆₄ film was demonstrated by the measurement of DC susceptibility and magnetic hysteresis using a SQUID magnetometer. The superparamagnetic relaxation blocking temperature was marked to be about 12 K by the peak of the zero-field-cooled magnetization under a field of 100 Oe. The magnetic properties of these annealed granular Co-C films transform from superparamagnetism to ferromagnetism when the Co concentration increases

[en] In this work, SiO₂ thin films containing Er and Si nanocrystals were prepared by implantation with a metal vapor vacuum arc (MEVVA) ion source. Photoluminescence (PL) properties of the films at 77 K and at room temperature (RT) were studied as functions of the Si ion dose. The PL intensities were strongly enhanced by the incorporation of nanocrystalline Si (nc-Si) in the SiO₂ films. The intensity of the 1.54 μm luminescence peak first increased with increasing Si dose, arriving at a maximum at a Si dose of 5x10¹⁷ cm^-2, then decreased with further increase in Si dose. These results are discussed and understood in terms of the role of nc-Si in Er luminescence mechanisms in silica containing nc-Si

[en] Nanocrystalline surface layers of WC and SiC are formed by a sequential high-dose metal vapour vacuum arc implantation of carbon and tungsten ions into Si(1 0 0) and subsequent rapid thermal annealing. These layer systems are shown to provide electron field emitter structures with turn-on-fields as low as 15-20 V/μm. The formation of carbide and silicide phases as well as that of cavities at the SiC/Si-substrate interface upon annealing are discussed on the basis of X-ray diffraction, X-ray photo electron spectroscopy, cross-section transmission electron microscopy and HREM measurements

[en] Buried SiC layers were formed by dual-energy implantation of carbon into silicon at 40 and 65 keV to doses of 6x10¹⁷ and 1.2x10¹⁸ cm^-2, respectively. Annealing was performed at temperatures from 600 deg. C to 1200 deg. C for various time intervals in nitrogen. The phase transformation characteristics in these SiC layers were studied using FTIR spectroscopy and a de-convolution scheme of the IR spectra into amorphous SiC and β-SiC components. The β-SiC fraction in the as-implanted samples was found to depend significantly on the order of the dual-energy implantation as a result of the IBIC effect. Further evolution of the relative amount of the various SiC phases upon annealing could well be described by the classical nucleation and growth theory using a two-dimensional growth model. The overall enthalpy of the transformation was determined to be 0.28 eV/atom

[en] The properties of diamond-like carbon (DLC) films can vary widely from graphite (sp² local bonding) to diamond (sp³ local bonding), strongly depending on the film preparation conditions. As the optical constants (n,k) of sp³ bonded carbon are quite different from those of sp² bonded carbon over the visible and near-infrared (VIS-NIR) spectral range, it is possible to provide precise quantitative information on sp³ C (sp² C) fractions using optical characterization methods. In the present work, spectroscopic ellipsometry (SE) using multiple sample analysis method has been applied to study a series of DLC films on silicon substrates prepared by filtered arc deposition (FAD) technique. In contrast to most reported SE studies, the DLC film was simulated by a mixture of sp³ C, sp² C and void constituents instead of treating it as a whole. From the interpretation of SE spectra, the film thickness and the volume fractions of sp³ C, sp² C and void have been derived, respectively. In addition, comparison between SE results and Rutherford backscattering spectroscopy (RBS) and electron energy loss spectroscopy (EELS) results will be given. This work shows that SE using multiple sample analysis method is a very useful optical method to determine sp³ C fractions in DLC films

[en] Purpose/Objective: A novel image-guided robotic radiosurgical system, capable of irradiating 102 non-coplanar nodes in 3 π geometry, produces complex dose distributions which are difficult or impractical to measure with conventional dosimetry instrumentation. The recently developed BANG polymer gel dosimetry system provides accurate, high resolution and three dimensional dose distributions data and is ideally suited for the task described above. In this study, the polymer gels were used for imaging the dose distributions produced by this extremely flexible radiosurgical system. Materials and Methods: The dosimeter materials consist of 2-liter BANG polymer gels in spherical, clear glass flasks, closed with ground glass stoppers, with glass rods extending to the center of the gel that serve as a target for the frameless robotic radiosurgery. A compact 6 MV x-band linac (285 lbs) is mounted and maneuvered by a 6 degree-of-freedom robotic arm. The gels were irradiated using a 25 mm circular insert. A total of 10 Gy was delivered at isocenter at a dose rate of 300 cGy/min using all of the available 102 nodes. The gels were then imaged by MRI(GE Signa) at 1.5 T, using a series of Hahn spin echoes of TR = 3s, TE = 20,100,200,400 ms. Transverse relaxation rate (R₂) maps were constructed from those multiple images, using the non-linear least-squares Lavenberg-Marquardt algorithm and a data analysis and display program 'DoseMap' which was written using the scientific computational program MATLAB. R₂ maps were converted to dose maps using an R₂-to-dose calibration curve. Dose maps and isodose curves were then compared with corresponding data from the treatment planning computer software. Results: The dose dependence of the NMR transverse relaxation rate, R₂, is reproducible (less than 2 % variation) and is linear up to about 10 Gy, with a slope of 0.25 s^-1Gy^-1 at 1.5 Tesla. Isodose curves in three orthogonal (axial, sagittal and coronal) planes show excellent agreement between the gel data with those calculated by the treatment planning system. Conclusion: The tissue-equivalent polymer-gel dosimeter provides a unique and reliable approach for visualization and validation of three dimensional dose distributions produced by the novel robotic radiosurgerical system. Furthermore, the polymer-gel dosimeter is stable and can be imaged with delays of several months if desired without a loss of the dose distribution data