Y. P. Guo

Photoluminescence studies of SiC nanocrystals embedded in a SiO2 matrix

Abstract The dependence of the photoluminescence (PL) from SiC nanocrystals embedded in a SiO 2 matrix on annealing is presented. Blue-green PL has been observed at room temperature from annealed SiC–SiO 2 composite films. The intensity of the single emission band at 460 nm (2.7 eV) shows a strong dependence on the annealing temperature. The combination of high-resolution transmission electron microscopy (HRTEM), Fourier transform infrared (FTIR) transmission spectra and PL results suggest that SiC nanocrystals have been incorporated into the SiO 2 matrix and O-deficient defects were formed. The origin of luminescence is attributed to the creation of defects in silicon oxide.

The effect of thermal annealing on reactive radio-frequency magnetron-sputtered carbon nitride films

Carbon nitride (CN) thin films were deposited on Si(111) substrates by reactive radio-frequency magnetron sputtering. The effect of thermal annealing on the structural properties of the films has been studied by Fourier-transform infrared spectroscopy (FTIR) and x-ray photoelectron spectroscopy (XPS). Both FTIR and XPS results show that the amount of the CN phase decreases upon annealing and that it is eliminated by annealing at C. Increasing the annealing temperature leads to the formation of a more prominent peak corresponding to the tetrahedral CN bonds in the FTIR absorption spectra. XPS N 1s peaks indicate that the third component due to the CN bonding state is significantly weaker than the others, relatively speaking. These results reveal that annealing causes a substantial decrease in the number of weakly bound nitrogen and carbon dangling bonds. The C-N phase is stable with respect to thermal treatment at C.

The effects of nitrogen flow on the Raman spectra of polycrystalline diamond films

Abstract The effects of nitrogen on the formation and structure of polycrystalline diamond films prepared using a microwave plasma chemical vapour deposition system have been studied using Raman scattering, X-ray diffraction and X-ray photoelectron spectroscopy. It is found that the Raman spectra are significantly affected by nitrogen flow ratio, while the X-ray diffraction spectra only show certain changes in their peak intensity. Five Raman scattering peaks at 1140, 1190, 1350, 1480 and 1550 cm −1 , respectively, are clearly observed. With increasing nitrogen flow ratio, the 1480 cm −1 peak decreases significnatly and the 1140 and 1190 cm −1 peaks remain almost unchanged in comparison with the 1350 and 1550 cm −1 peaks. These results indicate that nitrogen plays an important role in modifying the structure of polycrystalline diamond films.

Investigation of tungsten incorporated amorphous carbon film

Metal incorporated carbon films (Me-C:H) were deposited using a new technique with two W screen grids incorporated inside an electron cyclotron resonance chemical vapour deposition (ECR-CVD) chamber. This technique is versatile when applied to the deposition of Me-C:H films as the degree of plasma ionisation, the sputtering rate of the metal grids and the energy of the impinging ions can be independently controlled. In this work, the proposed technique is demonstrated through W-C:H deposition at different flow ratios of CH4 to Ar. A DC bias of 2 330V was applied to the upper and lower grids with either the substrate floating or under direct DC bias. The films were characterised in terms of their conductivity, atomic concentration (RBS), atomic configuration(XPS and XRD), hardness and optical absorption. The resistivities and the optical gaps of the films were noted to decrease drastically upon incorporation of several atomic percentage of W. WC formation is only observed for films deposited with the substrate under direct DC bias. q 1999 Elsevier Science S.A. All rights reserved.

Post-annealing effect in reactive r.f.-magnetron-sputtered carbon nitride thin films

Thin films of CN x were deposited by reactive r.f.-magnetron sputtering on Si(100) substrates. The effect of annealing temperatures on the structural properties of the films has been studied by Fourier transform infrared (FTIR) spectroscopy, x-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). Both FTIR and XPS results show that the population of the C≡N phase decreases upon annealing in a vacuum. The XPS N Is peaks indicate the component due to the C≡N bond to be significantly weaker than the others. An increase of the annealing temperature leads to a more prominent peak corresponding to the C-N phase in the FTIR absorption spectra. These results suggest a substantial decrease of the weakly bound nitrogen and carbon dangling bonds. Electron diffraction measurements reveal the existence of polycrystalline C 3 N 4 structures in films annealed at 700°C in a vacuum. The XPS studies confirmed that these crystalline phases are composed exclusively of carbon and nitrogen.

DETERMINATION OF MULTILAYER RELAXATIONS OF THE Cu(210) STEPPED SURFACE BY CALCULATION OF LEED INTENSITIES

In this report, we investigate the surface multilayer relaxation of clean Cu(210) by the Barbieri/Van Hove symmetrized automated tensor LEED calculation, based upon the multiple scattering theory. We have examined the change of Pendry R factor as a function of the structural and nonstructural variables in the calculation. The results show that a Rp factor of 0.20 can be achieved when the top 10 interlayer spacings of clean Cu(210) were optimized to experimental data using a muffin-tin radius of 1.217 A and a muffin-tin zero of 8 eV. The first three interlayer spacings are d12=0.761± 0.04 A, d23=0.759± 0.04 A and d34=0.862± 0.03 A, respectively (versus the bulk value of 0.807 A). It therefore appears that the Cu(210) surface contracts to some extent, decreasing the surface roughness. The strain-induced multilayer relaxation of Cu(210) surface is discussed.

(2×1) OXYGEN SUPERSTRUCTURE ON Cu(210) SURFACE STUDIED BY QUANTITATIVE LEED ANALYSIS AND STM

Adsorption of oxygen at elevated temperatures on Cu(210) surface leads to the formation of a (2×1) superstructure similar to that found on Cu(110). Previous STM work done on this system showed diperiodic Cu–O rows running along the [001] direction. In this work, low energy electron diffraction (LEED) experiments were done on the Cu(210)-(2×1)O surface structure. Ten diffracted beams at normal incidence were used for multiple scattering calculations using the Barberi/Van Hove symmetrized tensor LEED code. Four models were optimized for the calculations and the best fit to experiment is found to be the model with alternate missing –Cu–0– rows and oxygen atom occupying the long bridge site. Oxygen to first and second Cu nearest neighbors are optimized to 1.81 and 1.92 A respectively and the position of the oxygen atom above the (110) plane have been optimized to about 0.12 A.

Tungsten-carbon thin films deposited using screen grid technique in an electron cyclotron resonance chemical vapour deposition system

A new technique for depositing metal‐carbon(Me‐C:H ) thin films is proposed based on two metal screen grids embedded within an electron cyclotron resonance chemical vapour deposition(ECR‐CVD) system. The grids are negatively biased and supported at adjustable distances above the substrate holder in the deposition chamber. With source gases of methane and argon, sputtering of the metal grids by Ar+ results in the incorporation of metal in the growing carbon films. The amount of metal in the films can be very well controlled over a wide range by varying the bias voltage of the grids, the separation of the grids from the substrate holder and the ratio of CH 4 /Ar. Furthermore, by separately biasing the substrate holder, the properties of the films can be varied resulting in the formation of a great variety of Me‐C:H films with very diVerent mechanical and structural properties. Tungsten incorporated carbon films( W‐C:H ) were deposited using this technique with two tungsten ( W ) grids biased at ’330 V. The fraction of W in the films was controlled by varying the flow ratio of CH 4 /Ar. The films were characterized using Rutherford backscattering and X-ray photoelectron spectroscopy measurements, and also in terms of their conductivity, optical absorption and hardness. The conductivity was found to increase by six orders of magnitude whereas the optical gap decreased by 1.5 eV with an increasing atomic fraction of W in the films from 2% to 8%. WC bonds were not detected, and the W detected was mainly in the form of WO 2 and WO 3 .

Synthesis and characterization of Ge nanocrystals immersed in amorphous SiOx matrix

Germanium nanocrystals immersed in amorphous SiO x matrix have been synthesized by r.f. co-sputter deposition of Ge and quartz with post-growth annealing at 600-900 °C. The structures of the Ge nanocrystals and SiO x matrix have been studied with x-ray diffraction, high-resolution transmission electron microscopy and XPS depth profiling. Broad-band photoluminescence spectra have been observed from samples annealed at temperatures higher than 600°C. Possible photoluminescence mechanisms have also been discussed.