Xia-Xing Xiong

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.

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.

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.

Studies of C60 Films Deposited Using Ionized Cluster Beam Deposition Technique

Films (with thicknesses about thousands A) of a new form of carbon allotrope, CIO also known as Fullerenes, are deposited on Si(111) substrates using ionized cluster beam deposition (ICBD) technique at low (65V) accelerating voltage V. X-ray &-20 diffraction (XRD) have been used to investigate the structural properties of C6Ofi lms, indicating hexagonal close-packed structure with strong (002) XRD assignment together with weak (100), (112) and(004) assignments. Raman spectra, X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) are carried out to make detailed studies of the electronic properties of the films and to illustrate differences between CO films and amorphous carbon films which are deposited by ICBD at high accelerating voltage V >400V. Cio soccer-balls are found to be broken into fragments as accelerating field overtakes about 400V, indicated by the results of XPS, Raman spectra, XRD, and UV/visible absorption spectra.

Doping of C60 Films Using High Energy Boron Ion Implantation

C 60 films, which are deposited by partially ionized beam deposition (PIBD), are doped by 100 keV boron ion implantation at dose ranging from 3*10 14 to 1*10 16 cm 2 The implantation process has been studied using Fourier transform infrared spectroscopy (FTIR), Raman spectra and X-ray diffraction (XRD) analyses. Almost all C 60 soccer-balls in the doped region in the films are found to be broken at dose of 1*10 16 cm 2 , while at dose less than 6*10 14 cm 2 a few C 60 molecules remain undestroyed and maintain the original structural properties.