Wenxiong Li

Carbon nitride films synthesized by NH3-ion-beam-assisted deposition

Carbon nitride thin films have been prepared by NH3-ion-beam-assisted deposition with bombardment energies of 200-800 eV at room temperature. These films have been characterized by transmission electron microscopy, Auger electron spectroscopy and x-ray photoelectron spectroscopy for chemical analysis. It was found that the structure of the films varied with the bombardment energy. In the case of 400 eV bombardment, the tiny crystallites immersed on an amorphous matrix were identified to be beta -C3N4. X-ray photoelectron spectroscopy indicated that some carbon atoms and nitrogen atoms form unpolarized covalent bonds in these films.

Deposition of PTFE thin films by ion beam sputtering and a study of the ion bombardment effect

Abstract Ion beam sputtering technique was employed to prepare thin films of Polytetrafluroethylene (PTFE). Simultaneous ion beam bombardment during film growth was also conducted in order to study the bombardment effects. Infrared absorption (IR), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) analysis was used to evaluate the materials integrity. It was found that PTFE thin films could be grown at room temperature by direct sputtering of a PTFE target. The films composition and structure were shown to be dependent on the sputtering energy. Films deposited by single sputtering at higher energy (∼1500 eV) were structurally quite similar to the original PTFE material. Simultaneous ion beam bombarding during film growth caused defluorination and structural changes. Mechanism for sputtering deposition of such a polymeric material is also discussed.

Formation of β-C3N4 grains by nitrogen-ion-beam-assisted deposition

Abstract Carbon nitride thin films were prepared by nitrogen-ion-beam-assisted deposition. Auger electron spectroscopy shows that the N/C atomic composition ratio increases with increasing current density and decreasing bombarding energy of the nitrogen ion beam. At a bombarding energy of 200 eV and a current density of 0.2 mA cm −2 , a maximum N/C ratio of 0.54 is obtained and crystalline β -C 3 N 4 grains with dimensions of about 0.1 μm are observed by transmission electron microscopy. This film displays a high Knoop hardness of 4450 kgf mm −2 and a resistivity of 10 9 Ω cm.

Plastic properties of nano-scale ceramic–metal multilayers

Abstract Nanoscale TiC–metal (Al, Cu, Fe, W) multilayers were prepared by ion beam sputtering deposition with an intent to study the plastic properties of the ceramic–metal combinations. The multilayers were designed to have different layer thickness arrangements, including component fraction, modulation wavelength, etc. Their toughness and hardness were systematically investigated as well as the laminated structures. It was found that for most TiC–metal multilayers the toughness was significantly improved in comparison with monolithic TiC, but the hardness showed great dependence on the material system. In TiC–Fe and TiC–W systems, the multilayer hardness exhibited a peak value which was even higher than the hardness of TiC. In TiC–Al and TiC–Cu systems, no superhardness effect was detected.

Observations of Laue pattern and stability of beta -C3N4 grains

Carbon nitride films have been prepared by ion beam assisted deposition with high N-ion fluxes up to the order of 1 mA cm-2. Both Auger electron spectroscopy and Rutherford backscattering spectroscopy measurements show that an average nitrogen concentration of up to 45 at.% has been incorporated into the films. The nitrogen concentration in some local areas reaches as high as 59 at.% examined by energy-dispersive X-ray analysis. In such a high nitrogen content area, Laue spots of the predicted beta -C3N4 structure have been observed for the first time by transmission electron microscopy. Under continuous electron irradiation, beta -C3N4 grains refine to dimensions of <0.1-0.4 mu m in diameter.

Simulation of nacre with TiN/Pt multilayers and a study of their hardness

TiN/Pt multilayers with individual thicknesses between 1 and 8 nm were prepared by ion beam sputtering deposition to simulate the micro-laminated architecture of nacre. Multilayer hardness and the laminated structure were investigated. It was found that sharp but incoherent interfaces were formed between individual layers. The multilayer hardness had strong dependence on layer arrangement. The range of layer thickness appropriate for high hardness was experimentally determined. Hardness enhancement of 30–70% was generally observed. With the layer thickness properly adjusted, the multilayer can even be harder than the hard component (TiN). Annealing experiments indicated that the hardness enhancement was an intrinsic property of the TiN/Pt multilayers.

Simulation of nacre with TiN/Pt multilayers and a study of their mechanical properties

Abstract TiN/Pt multilayers with individual layer thickness between 1 and 8 nm have been prepared by ion beam sputtering deposition to simulate the nacreous structure in natural nacre. Both the hardness and toughness were systematically investigated together with a study of structures of the multilayer. It was found that [111] texture developed during the alternative deposition of TiN and Pt. The multilayer toughness was higher than that of pure TiN. The hardness was greater than the volume weighted mean of the hardness of two components (i.e. TiN and Pt). Both the multilayer hardness and toughness showed a strong dependence on the individual layer thickness arrangement. When the individual thickness was properly adjusted, the multilayer can even be harder than its hard component (TiN) while the toughness was also greatly improved. Annealing experiment indicated that such an enhancement was an intrinsic property of the multilayers. Some suggestions for microdesigning of materials are thus proposed.

Optical Observations of the Type Ia Supernova SN 2011fe in M101 for Nearly 500 Days

We present well-sampled optical observations of the bright Type Ia supernova (SN~Ia) SN 2011fe in M101. Our data, starting from

IBAD processing of surface coatings and nanocrystalline multi-layers

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Simulation of nacre with TiC/Teflon multilayers and a study of their properties

days before maximum light and extending to