J.R. Shi

UV Raman characteristics of nanocrystalline diamond films with different grain size

Abstract Nanocrystalline diamond films with different size were characterized by ultraviolet (UV) (244 nm) Raman spectroscopy. It was found that a diamond peak at 1333 cm −1 was enhanced, while the D and G peak of graphite as well as photoluminescence was suppressed, compared with that measured by visible (514.5 nm) Raman. With decreasing the particle size from 120 to 28 nm, the diamond peak shifts from 1332.8 to 1329.6 cm −1 , the line width of the peak becomes broader, the intensity ratio of diamond and G peak decreases. The down shift and broadening of the diamond peak depending on the particle size by UV Raman measurements are consistent with the phonon confinement model.

Properties of nitrogen doped tetrahedral amorphous carbon films prepared by filtered cathodic vacuum arc technique

The properties of nitrogen doped tetrahedral amorphous carbon films prepared by the filtered cathodic vacuum arc technique have been studied. The doping species, nitrogen ions, were produced by an ion beam source. The nitrogen flow rate was varied from 0.5 to 10 sccm while keeping other deposition conditions constant. The nitrogen content in deposited films was determined by Rutherford backscattering technique and ranged from 5 to 34 at.% depending on the nitrogen flow rate. The surface morphology, mechanical, optical, and electronic properties of the films were measured. The compressive stress, the hardness and the optical band gap all increased at low nitrogen content to a maximum at 5 at.% nitrogen and then decreased with increasing nitrogen content. The activation energy first increased and then decreased with increasing nitrogen content. We attribute these changes to the Fermi level moving up in the band gap, from below the midgap to near conduction band. We achieved continuously adjustable band gap and complex refractive index with nitrogen incorporation. Possible mechanisms of N ion in the ta-C:N films are discussed.

Transport of vacuum arc plasma through an off-plane double bend filtering duct

A new magnetic macroparticle filter design consisting of an off-plane double-bend (OPDB) filter is described. The transport of the vacuum arc plasma through this OPDB filter is investigated using Langmuir and deposition probes. Films of amorphous hard carbon have been deposited using a 90° single bend and the OPDB filter and the macroparticle contents of the films are compared. The experimental results were found to be in good agreement with the simulations results based on an improved drift approximation model. The results demonstrate that OPDB filter has a relatively better transmission efficiency than the 90° single bend filter, lower macroparticle counts and is suitable for preparation of diamond-like carbon coatings with high quality.

Ultraviolet and visible Raman studies of nitrogenated tetrahedral amorphous carbon films

Nitrogenated, tetrahedral amorphous carbon (ta-C) films prepared by the filtered cathodic vacuum arc (FCVA) technique have been studied using ultraviolet (UV, 244 nm) and visible (514 nm) micro-Raman scattering. The nitrogen ions were produced by a RF ion-beam source with a nitrogen flow-rate varying from 0 to 10.0 sccm, which results in a nitrogen content from 0 to 10.8 at.% in the deposited films. In the visible Raman spectra, only vibrational modes of sp 2 -bonded carbon (G and D peaks) are observed, while a new wide peak, called the T peak, located at 1090‐1320 cm 21 , associated with the vibrational mode of sp 3 -bonded carbon, appears in the UV-Raman spectra. In the visible Raman spectra, the G-peak width (100‐113 cm 21 ) and the intensity ratio ID/IG (0.34‐0.94) are both sensitive to the structural changes induced by N incorporation. In the UV-Raman spectra, the G-peak position almost linearly decreases from 1665 to 1610 cm 21 , and the Tpeak position increases tremendously from 1095 to 1314 cm 21 with increasing N content. The G-peak position and width, and the T-peak position, are all sensitive to the bonding structure of the films. q 2000 Elsevier Science S.A. All rights reserved.

Resonant Raman studies of tetrahedral amorphous carbon films

Resonant Raman scattering has been used to study the tetrahedral amorphous carbon films deposited by the filtered cathodic vacuum arc technique. The excitation wavelengths were 244, 488, 514 and 633 nm, corresponding to photon energies of 5.08, 2.54, 2.41 and 1.96 eV, respectively. In the visible Raman spectra only vibrational modes of sp2-bonded carbon (G and D peaks) are observed, while a wide peak (called the T peak) can be observed at approximately 1100 cm−1 by UV-Raman spectra which is associated with the vibrational mode of sp3-bonded carbon. Both the position and the width of the G peak decrease almost linearly with increasing excitation wavelength, which is interpreted in terms of the selective ππ* resonant Raman scattering of sp2-bonded carbon clusters with various sizes. The G peak position in the UV-Raman spectra, the T peak position and the intensity ratios of ID/IG and IT/IG all exhibit maximum or minimum values at the carbon ion energy of 100 eV. The changes of these spectral parameters are discussed and correlated with the sp3 fraction of carbon atoms in the films.

Micro-Raman spectroscopic analysis of tetrahedral amorphous carbon films deposited under varying conditions

The structure of tetrahedral amorphous carbon (ta-C) films deposited by a filtered cathodic vacuum arc has been studied using micro-Raman spectroscopy in terms of substrate bias, nitrogen gas partial pressure (ta-C:N films) or aluminum content in a mixed aluminum/carbon target (ta-C:Al films) during deposition. The first-order Raman spectra generally show a broad feature overlaid by a disordered (D) peak and a graphitic (G) peak. The contribution of sp3 bonding to the Raman spectrum is not explicit, since the Raman phonon line is more sensitive to the sp2 carbon bonding due to its larger Raman scattering cross section. However by comparing the ratios of the intensities, the full widths at half maximum (FWHM), and the peak areas between the D and G peaks, the sp3 contribution may indirectly be reflected by the complex Raman features. The G peak position for the ta-C and ta-C:N films appears to not change significantly with the change of substrate bias voltage or N2 partial pressure, whereas the shift of th...

The effect of nitrogen on the mechanical properties of tetrahedral amorphous carbon films deposited with a filtered cathodic vacuum arc

The mechanical properties of both undoped and nitrogen containing tetrahedral amorphous carbon (ta-C and ta-C:N ) films, such as hardness and E-modulus, are investigated. The mechanical properties are related to the film structures. The ta-C and ta-C:N films are prepared in a filtered cathodic vacuum arc process. Nanoindentation testing is used to measure the mechanical properties of these films. Since the thickness of films prepared for this study is <100 nm, a continuous stiVness technique is therefore used to determine the mechanical properties of these films. For the lightly doped ta-C:N films, the mechanical properties are competitive with those of undoped ta-C. However, with a further increase in the nitrogen content in the films, the mechanical properties of the ta-C:N films drop. The extent of decrease of the mechanical properties of ta-C:N films shows the dependence on the N 2 partial pressure or N ion energy. The reason for this may be due to the nitrogen doping eYciency. The excess nitrogen atoms contained in the films may promote the transformation from the sp3 bonding structure to sp2 structure and further enlarge the size of sp2 clusters, which causes the evident reduction of mechanical properties of the films.

STRUCTURAL AND ELECTRICAL PROPERTIES OF COPPER THIN FILMS PREPARED BY FILTERED CATHODIC VACUUM ARC TECHNIQUE

Copper thin films with low electrical resistivity were successfully deposited by filtered cathodic vacuum arc technique at room temperature. The structure of the films was determined by X-ray diffraction, TEM and atomic force microscopy. All the copper films had a polycrystalline structure. The RMS roughness, the lateral size and the grain size all increased with increasing film thickness. There is a critical film thickness of approximately 135 nm. The electrical resistivity had an almost unchanged value of 1.8 μΩ cm above 135 nm and increased with decreasing thickness below 135 nm.

Properties and structures of diamond-like carbon film deposited using He, Ne, Ar/methane mixture by plasma enhanced chemical vapor deposition

Diamond-like carbon (DLC) films have been deposited by a magnetically enhanced plasma (MEP) chemical vapor deposition (CVD) system. The properties and structures of DLC films deposited by MEP-CVD using various gases (methane, He/methane, Ne/methane, and Ar/methane) were studied. The mechanical properties in terms of hardness, Young’s modulus and stress, and optical properties in terms of optical band gap and refractive index were enhanced by adding inert gas in methane plasma. The magnitude of the effects on the properties for various inert gases was found as Ne, Ar, and He, on the surface roughness was found as Ar, Ne, and He. The Raman characteristic shows a dependence of the bias voltage and inert-gas/methane ratio, as well as the inert gases dilution. The Raman spectroscopy analysis indicates that the changes of properties of the DLC films are due to the structural changes, such as sp2 and sp3 content in the films prepared under various deposition conditions. The films deposited in Ne/methane show the...

Nitrogenated tetrahedral amorphous carbon films prepared by ion-beam-assisted filtered cathodic vacuum arc technique for solar cells application

Fabrication and characterization of nitrogenated tetrahedral amorphous carbon (ta-C:N) semiconductor/crystalline p-type silicon (p-Si) heterojunction structures are reported. The electron-hole pairs generated from both ta-C:N and Si depletion regions were observed from photoresponse measurements. The peaks are centered at about 540 and 1020 nm, which correspond to the optical absorption edge of ta-C:N and p-Si, respectively. The reverse current increased by three orders of magnitude when the structures were exposed to AM1 light. A photovoltaic effect was observed from ta-C:N and the values of short circuit current, open circuit voltage, and field factor obtained are 5.05 mA cm−2, 270 mV, and 0.2631, respectively.