Fangqing Zhang

Deposition of high quality cubic boron nitride films on nickel substrates

The well‐crystallized cubic boron nitride (c‐BN) films have been prepared on polycrystalline Ni substrates using a hot filament assisted rf plasma chemical vapor deposition method. X‐ray diffraction showed that high quality c‐BN films had been deposited without hexagonal BN (h‐BN) or amorphous BN codeposition. Both (111) and (100) faces were observed in scanning electron microscopy images. These results suggested that Ni had catalyst effects on the nucleation and the growth of c‐BN phase and inhibited the formation of h‐BN.

TEXTURED GROWTH OF CUBIC BORON NITRIDE FILM ON NICKEL SUBSTRATES

Textured cubic boron nitride (c‐BN) films have been deposited on (220) oriented crystallized polycrystalline nickel substrate by a hot filament assisted rf plasma chemical vapor deposition method. X‐ray diffraction shows that the films are (220) preferentially grown, the peak ratio of (220) to the main peak [i.e., the (111) peak] is about 5.2. The scanning electron microscopy images exhibit regular grain shapes. Most of the grains are rectangular, also indicating the (220) growth. The grain size is about 5 μm. The well‐matched Ni lattice with c‐BN, the catalytic effect of Ni, and the appropriate rf bias are considered to be the key factors in the textured growth.

In situ observations of optical emission spectra in the diamond deposition environment of arc discharge plasma chemical vapor deposition

In order to investigate the growth mechanism of diamond thin films, the in situ optical emission spectra of direct current (dc) arc discharge plasma, including the spatial distributions and different CH4/H2 ratios, have been measured during the growth processes of diamond thin films prepared by the dc arc discharge plasma chemical vapor deposition method. The results show that there are a great number of atomic hydrogens in the arc discharge plasma. This is the key factor for the growth of diamond films with a high rate and high quality. In addition, the effects of the CH4/H2 ratio on the quality of diamond films are discussed in detail in this letter.

Structure studies of synthetic diamond thin films by x-ray diffraction

The depth profile of the structure of synthetic diamond thin films prepared by the d.c. arc discharge plasma chemical vapour deposition (CVD) method has been investigated by sample-tilting X-ray diffraction. The results show that, at first, a layer of carbide is deposited which saturates the substrate surface. For a single-crystal silicon (c-Si) substrate, the compound is silicon carbide (SiC); for a molybdenum wafer substrate, the compound is molybdenum carbide (Mo2C). A diamond film grows on the carbide layer. The orientation of the crystal grains with depth in the polycrystalline diamond thin films is irregular. The main contaminant in diamond thin films prepared by the d.c. arc discharge plasma CVD method is tungsten carbide (WC).

X-ray phase analysis with depth profiling for thin films☆

Abstract A conventional X-ray diffractometer with a sample tilting X-ray diffraction (STD) mode is a useful tool which can better characterize the phase composition of films from 100 A to a few micrometers thick with random or preferred orientations. In this paper equations of an asymmetrical Bragg reflection intensity and the observed crystal plane azimuthal angle are given, and it is shown through a few examples that this STD technique can be used to solve some problems related to phase analysis with depth profiling for thin films.

A study of electroluminescence in hydrogenated amorphous carbon films

Abstract Blue white electroluminescence (EL) in glass/SnO2/a-C:H/Al structure has been observed directly by naked eyes at room temperature. It is found that the EL spectra depend strongly on the deposition conditions of a-C:H layer and can cover almost the whole visible region by optimizing the deposition conditions. Typical EL spectrum exhibits two peaks: one is at 2.34 eV and another at 2.12 eV. The photoluminescence spectra of a-C:H films have also been investigated for comparison.

Effects of annealing on the electrical conductivity of C60 films

Abstract We report the annealing effects on the electrical conductivity of C60 films. Films sublimed using C60 powder from the same batch were used. The studies show that the C60 films have clear semiconducting behavior in the temperature range extending from room temperature to 473 K. The room-temperature conductivity is in the range of 10−5 to 10−7(Ωcm)−1. From the measurements of conductivity versus time when the film is maintained at 473 K, we explained that the increase of conductivity before 2.5 h of annealing is the result of a decrease of the unstable hcp phase and an increase of the number of connected crystallites, the decrease of conductivity after 2.5 h of annealing is due to the decrease of the number of connected crystallites. The decrease in the number of connected crystallites makes the intercrystalline potential barrier higher, and thus decreases the conductivity. The reason for the increase of the activation energy is the decrease of defects between connected crystallites. These defects may introduce states in the energy gap of C60 films. The deviation of the conductivity from straight lines in the high-temperature region in the σ versus 1 T plots are due to unstable structural phases which transform toward a stable fcc phase in the annealing process.

Surface energies and morphologies of chemical‐vapor‐deposited diamond films

Using a model where a fraction of carbon dangling bonds on the growth surface are saturated by hydrogen, the surface energies of chemical‐vapor‐deposited diamond crystals during the preparation process have been calculated. The results show that the surface energies increase with the increasing substrate temperature, and the surface energy‐temperature curves of the three most energetically favored crystal planes, (100), (110), and (111), intersect at a critical substrate temperature. Then, the changes of predominant facets in the surface morphology from {100} to {111} with the increasing substrate temperature can be interpreted. Furthermore, it is found that the surface energies of diamond are lower than that of graphite in the chemical‐vapor‐deposition process of diamond.

A study of the pressure-temperature conditions for diamond growth

An attempt to unify the growth mechanisms and conditions for diamond formation is developed via the growth probability calculated by a barrier model between the two phases. From the distribution law of the equal growth probability lines plotted in a pressure-temperature ( P-T ) diagram, five regions of different growth methods and mechanisms were reasonably delineated. Many experimental results can be generalized and explained by our theory, and the unity of diamond growth mechanism was discussed over the wide region of the P-T condition.

High-photosensitivity a-SiGe: H films prepared by RF glow discharge plasma CVD method

Abstract Highly photosensitive and narrow band gap a-SiGe: H films have been prepared by the RF glow discharge plasma CVD method. The photosensitivity was 2.01 × 10 5 for the film with an optical band gap of E g = 1.47 eV. H 2 dilution and a relatively high RF power are attributed to the improving of the optoelectrical properties. Thermally induced changes of the a-SiGe:H films have been also investigated.