Zhifeng Ying

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.

Preparation of thin films of carbon-based compounds

Abstract We present the preparation and characterization of thin films of several carbon-based compounds. Boron carbide films were prepared by pulsed laser deposition (PLD) in vacuum using sintered B4C as raw material. In the environment of an ECR nitrogen plasma and with bombardment by the low-energy plasma stream, carbon nitride films were prepared by ablating a graphite target, while a sintered B4C target was used to prepare thin films of boron carbon nitride (BCN). The prepared films with smooth surface were found to be adhesive to the substrates and contain several chemical bonds with atomic hybridization rather than a simple mixture of BN, BC and CN phases. Pulsed laser ablation of the target is efficient for the target material to be transferred to a nearby substrate. For nitride film preparation, the assistance of the reactive ECR nitrogen plasma is responsible for nitrogen incorporation and favorable for nitride formation.

Chemical structure and micro-mechanical properties of ultra-thin films of boron carbide prepared by pulsed-laser deposition

Ultra-thin boron carbide films with a thickness of about 40 nm were deposited on silicon substrates by means of pulsed-laser ablation of a sintered B4C target in vacuum. Together with the determination of the film composition by X-ray photoelectron spectroscopy (XPS) and the observation of the surface topography by atomic force microscopy (AFM), the chemical structure of the films was studied by Fourier transform infrared (FTIR) spectroscopy. Mechanical characterization of the films was performed on the micron and sub-micron scales by means of nano-indentation and micro-scratch tests, from which the hardness, Youngs modulus and micro mar resistance of the films were determined. The optimal values were obtained for the films prepared at elevated temperature of 600 °C, with hardness of 39 GPa, Youngs modulus of 348 GPa and micro mar resistance (MMR) of 5.0 × 103 GPa, in comparison with those of 23, 252, and 7.1 × 102 GPa, respectively, for the films prepared at room temperature.

Arsenic doping for synthesis of nanocrystalline p-type ZnO thin films

Nanocrystalline p-type arsenic-doped ZnO (ZnO:As) films have been synthesized on (0001) sapphire substrates by pulsed laser deposition using a ZnO target mixed with 6.6wt% As2O3. The process of synthesizing p-type ZnO:As films was performed in an ambient gas of ultrapure (<99.99%) oxygen. The ambient gas pressure was 5Pa with the substrate temperature in the range of 350–500°C. The ZnO:As films grown at 500°C are p type, and the acceptor concentration in ZnO:As films is about 1.9×1018at.∕cm3 as determined by Hall effect measurements. The concentration of As in ZnO:As films is estimated to be about 1.7% from the x-ray photoemission spectroscopy (XPS) spectrum. Guided by the XPS analysis and a model for large-sized-mismatched group-V dopant in ZnO, an AsZn–2VZn complex was thought to be the most possible acceptor.Nanocrystalline p-type arsenic-doped ZnO (ZnO:As) films have been synthesized on (0001) sapphire substrates by pulsed laser deposition using a ZnO target mixed with 6.6wt% As2O3. The process of synthesizing p-type ZnO:As films was performed in an ambient gas of ultrapure (<99.99%) oxygen. The ambient gas pressure was 5Pa with the substrate temperature in the range of 350–500°C. The ZnO:As films grown at 500°C are p type, and the acceptor concentration in ZnO:As films is about 1.9×1018at.∕cm3 as determined by Hall effect measurements. The concentration of As in ZnO:As films is estimated to be about 1.7% from the x-ray photoemission spectroscopy (XPS) spectrum. Guided by the XPS analysis and a model for large-sized-mismatched group-V dopant in ZnO, an AsZn–2VZn complex was thought to be the most possible acceptor.

Electron cyclotron resonance plasma-assisted pulsed laser deposition of boron carbon nitride films

Abstract Boron carbon nitride thin films have been prepared on Si (100) substrates by means of plasma-assisted pulsed laser deposition at low temperatures ( 4 C) target was ablated by laser pulses in the environment of a nitrogen plasma, generated from electron cyclotron resonance (ECR) microwave discharge in pure nitrogen gas, while the growing film was simultaneously being bombarded by the plasma stream. The prepared films are composed of boron, carbon and nitrogen with an average atomic B/C/N ratio of 3:1:3.8 as revealed by X-ray photoelectron spectroscopy (XPS) analysis. XPS, Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy were used for structural characterization. The results suggested that the prepared BCN films contain several chemical bonds with BCN atomic hybridization rather than a simple mixture of BN, BC and CN phases. The BCN films were also found to show good adhesion to the substrates and have a high transparency in the near-infrared region. For comparison, we have also grown BC films in vacuum without plasma assistance. We have found that the assistance of the ECR nitrogen plasma facilitated nitrogen incorporation and film formation.

Growth of ZnSe nanowires by pulsed-laser deposition

Stoichiometric ZnSe nanowires have been grown by pulsed-laser deposition on GaAs (100) substrates coated with gold layers. The gold layer plays a key role as catalyst in the deposition of ZnSe nanowires. The thickness of the gold film greatly affected the density of the ZnSe nanowires synthesized on the substrate. No ZnSe nanowires were synthesized on the bare GaAs (100) substrate. The microstructures and the chemical compositions of the as-synthesized nanowires were investigated by scanning electron microscopy, x-ray diffraction, and Raman spectroscopy. The results reveal that the as-grown thin films consist of ZnSe nanowires with diameters ranging from 20to40nm, and the nanowires appear to be randomly oriented on the Au-coated substrate. The as-grown nanowires were also observed to be elongated along different crystallographic directions.

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.

Production of intense atomic nitrogen beam used for doping and synthesis of nitride film

An arc‐heated source for producing an intense nitrogen atom beam with intensity of 1019 atoms/sr s and kinetic energies of 0.5–4 eV is presented. The arc discharge has been carried out in pure nitrogen gas and maintained stable in an arc operating pressure of 30–300 Torr. The beam kinetic energy changes with the arc pressure, and is insensitive to the arc current. Auger electron spectroscopy analysis showed that a TiNO layer with a thickness of about 100 A was formed on the smooth Ti wafer at room temperature with interaction of the atomic nitrogen beam.An arc‐heated source for producing an intense nitrogen atom beam with intensity of 1019 atoms/sr s and kinetic energies of 0.5–4 eV is presented. The arc discharge has been carried out in pure nitrogen gas and maintained stable in an arc operating pressure of 30–300 Torr. The beam kinetic energy changes with the arc pressure, and is insensitive to the arc current. Auger electron spectroscopy analysis showed that a TiNO layer with a thickness of about 100 A was formed on the smooth Ti wafer at room temperature with interaction of the atomic nitrogen beam.