Zhong-Min Ren

Electronic and mechanical properties of carbon nitride films prepared by laser ablation graphite under nitrogen ion beam bombardment

Carbon nitride films have been formed on Si(100) substrates by laser ablation of graphite under a low energy nitrogen ion beam bombardment. Data of Raman shift and x‐ray photoelectron spectroscopy indicate the existence of carbon‐nitrogen bonds in the films. Time‐of‐flight measurements suggest the existence of paracyanogen‐like materials, such as C4N4, in the films. High energy backscattering spectrometry has shown that the percentage of N content in the film is 41% or so. The x‐ray diffraction and transmission electron micrograph measurements have also been taken to characterize the crystal properties of the obtained films. Qualitative tests indicate the films of high Vickers hardness Hv, and of good adhesion to the silicon substrates.

Optical emission spectroscopy of the nitrogen arc in an arc-heated beam source used for synthesis of carbon nitride films

An exhaustive study of optical emission from a nitrogen arc produced by an arc-heated beam source is reported. Atomic nitrogen emission lines in the spectral region provide unequivocal evidence that the arc-heated beam source generates an appreciable flux of nitrogen atoms. Experimental results show that the ratio of [N] to increased as the arc pressure decreased. It is believed that this is because of the reduced probability of recombination of [N] atoms. Using this arc-heated beam source for pulsed laser deposition (PLD) film growth, we have synthesized carbon nitride and other nitride films with a high nitrogen content. AES and XPS results indicate that composition ratios ([N]/[C]) in the deposited films were between 0.2 and 0.6. It has been considered that [N] atoms, rather than molecules in the arc, are the most likely species responsible for the synthesis of nitride films.

An arc discharge nitrogen atom source

An intense nitrogen atom beam source of simple construction, with easy handling and maintenance was built and tested. Nitrogen atom beams with an intensity estimated to be 1019 atom/sr s and with an average kinetic energy of 0.8–2 eV in the forward direction were obtained. This novel atom source can be successfully ignited using pure nitrogen gas and operated stably during several hours of continuous performance. The temperature-rise effect of calorimetric sensors due to the bombardment of the N atom beam was used to analyze the intensities and kinetic energies of nitrogen atom beams. The emission spectra from the arc also show that a high concentration of atomic nitrogen was produced using this source. Experiments such as the nitrogen atom beams interacting with substrates to form a TiON film and a carbon nitride film indicate the high concentration of atomic nitrogen in the beam.

Destruction of C60 films by boron ion bombardment

Abstract C 60 films are bombarded by 100 keV boron ion beams at doses ranging from 3 × 10 14 to 1 × 10 16 /cm 2 . The bombarded films are analyzed using Fourier transform infrared spectroscopy (FTIR), Raman spectra and X-ray diffraction (XRD) measurements. Most C 60 soccer-balls in the implanted region in the films are found to be broken at a dose over 1 × 10 15 /cm 2 , while at a dose less than 6 × 10 14 /cm 2 a few C 60 molecules remain undestroyed and maintain some crystal structure. The results of the analyses suggest a complete disintegration of a C 60 molecule under B + bombardment.

Study of the growth of thin nitride films under low-energy nitrogen-ion bombardment

Bombardment of silicon surfaces by low-energy (300–1000 eV) nitrogen ions has been investigated as a potential process for growing ultrathin films at relatively low temperatures (<500°C). The thicknesses and chemical states of the obtained films are analysed using ellipsometry, X-ray Photoelectron Spectroscopy (XPS), and Auger Electron Spectroscopy (AES). All the analyses show that ultrathin (∽ 60 Å) silicon nitride films have been directly grown on silicon substrates. Detailed studies of the influence of different process parameters on the obtained films have been carried out. The thicknesses of the obtained films appear to increase with ion energy. The nitridation is found to be a rapid process which can be divided into two steps. The thicknesses are also observed to vary slightly with substrate temperature. The average active energy of nitridation rates is about 3.5 meV which indicates nonthermal process kinetics. For AES analysis, the films are found to be nitrogen-rich ones with the stoichiometric factor x≈1.7 larger than that of pure silicon nitride (x=1.33). In both AES and XPS studies, the chemical state of the silicon atoms resembles the existence of silicon oxynitride films of low oxygen concentration. The growth mechanism is also discussed briefly.

Light emission of C60 embedded in porous silicon

We have fabricated samples with C60 implanted into porous silicon with the ionized cluster beam deposition approach for improving the light emission of C60. We have obtained intense and well‐resolved photoluminescence spectra under excitation of Ar+ laser (514.5 nm) at room temperature. The depth analysis of secondary ion mass spectroscopy showed that C60 had been incorporated into porous silicon. A large number of fine‐structure peaks in the photoluminescence spectrum indicated the strong coupling of vibrational progressions with electronic states of C60 induced by the interaction between C60 molecule and nanometer‐sized silicon particles.

Boron-carbon-nitrogen films synthesized by laser ablation under ion beam bombardment

Abstract Boron-carbon-nitrogen thin films were deposited by laser ablation of boron carbide (B 4 C) under nitrogen ion beam bombardment. The as-deposited films were analyzed by X-ray photoelectron spectroscopy and Raman measurements. The results showed that carbon, nitrogen and boron species were chemically bonded to each other instead of simple mixtures. Detailed analyses showed that the ion beam bombardment had led to breaking of B-C bonds and formation of C-N and B-N bonds. An appropriate ion beam energy (probably less than 1 keV) was proposed for the purpose of the synthesis of high quality boron-carbon-nitrogen films.

Structural and electronic studies of C60 films deposited using ionized cluster beam deposition

Films of a new form of carbon allotrope, C60, also known as fullerenes are deposited on Si(111) substrates by the ionized cluster beam deposition technique under an accelerating field less than 100 V. Raman spectra and X-ray photoelectron spectroscopy measurements are carried out to analyse the electronic properties of the films, to indicate the existence of C60 soccer-balls in the films. The resistance of this C60 film deposited here to oxygen contamination is better than that deposited by molecular beam epitaxy. Binding energies of C 1s peaks for C60 and highly oriented pyrolytic graphite are 284.7 and 284.3 eV, respectively. X-ray theta -2 theta diffraction investigations show that C60 films deposited under Va=0 V have highly textured close-packed structure with X-ray diffraction assignment (110), while those deposited under Va=65 V turn out to be more polycrystalline. C60 soccer-balls are found to be broken into fragments as accelerating field exceeds about 400 V, indicated by the results of X-ray photoelectron spectroscopy, Raman spectra, X-ray diffraction, and ultraviolet visible absorption spectra.

DEPOSITION OF C60 FILMS BY PARTIALLY IONIZED FULLERENE BEAMS

C60 films have been deposited by partially ionized cluster beam deposition in which a C60 beam is partially ionized by electron impact and then accelerated by an acceleration field Va towards the substrate where the films are deposited. The experimental results show that the ionized C60 molecules in the evaporated beam are fragmented upon collision with the substrate under the elevated accelerating fields Va. Particularly, as Va exceeds about 400 V, almost all the C60 molecules including ionized and unionized ones are broken into fragments in the deposition films and the resulting films turn out to be amorphous carbon layers, as indicated by the measurements of Raman spectra, x‐ray diffraction, and ellipsometry.

Studies of Ag films deposited using partially ionized beam deposition

Partially ionized beam deposition, in which the starting material Ag is evaporated form a crucible with a restricted nozzle, partially ionized by electron bombardment, and the ions accelerated to the deposition substrate, has been used to deposit Ag films on both Si(111) and Si(100) substrates. Characterization of the deposited films has been carried out by x‐ray diffraction, scanning electron microscopy, α‐step roughness, Auger electron spectroscopy, and ellipsometry. As a comparison, Ag films deposited without ion acceleration and by evaporated conventionally from an open crucible were also investigated. Highly textured Ag films with strong (111) orientation on Si(111) have been obtained at high accelerating voltage Va=4 kV. The surface flatness improves and the resistance of the films to impurity diffusion from the surface increases as the accelerating voltage increases.