Hexin Li

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.

In vitro and in vivo evaluation of degradability of hydroxyapatite coatings synthesized by ion beam-assisted deposition

Abstract Degradability is among the most important properties in the biomedical field, which is crucial to bone apposition on implants, bone-implant bonding and implantation longevity. The present paper evaluated the degradability of ion beam-assisted deposition (IBAD) hydroxyapatite (HA) coatings in vitro and in vivo. In vitro testing showed that IBAD HA coatings degraded little in 37°C sterile Hank’s physiologic (pH 5.2) balanced salt solution throughout the testing time, while the plasma-sprayed HA coating tested in comparison underwent an increasing degradation: the concentration of Ca increased from the initial 1 ml to 2.75 ml at 3 days post-incubation. In vivo testing revealed that no significant degradation occurred throughout the whole implant period (12 weeks). All the results consistently suggest that the IBAD HA coating is slightly degradable. High magnification SEM observation and HRTEM investigations of the coating further pointed out that the low degradability of the IBAD HA coating derives from its dense microstructure and unique properties such as no sharp grain boundaries. The present study demonstrates that IBAD HA coatings are much more chemically stable than plasma-sprayed HA coatings. The IBAD HA coating possesses more superior adhesive properties, as would be of clinical importance in that it may favor a longer longevity of orthopedic implants.

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.

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.

Hardness study of nanoscale TiNPt multilayers

Abstract Nanometer scale TiN Pt multilayers have been prepared by ion beam sputtering deposition to mimic the structure of natural nacre. The hardness of these multilayers was studied. It was found that the multilayer hardness was greater than the volume weighted mean of the component hardness. It also showed a dependence on the individual layer thickness arrangement. With the individual thickness property adjusted, the multilayer was even harder than its hard component (TiN). Annealing experiments indicated that such a hardness enhancement was an intrinsic property of multilayers.

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

Abstract Ion beam sputter deposition was employed to prepare nanoscale multilayers of TiC and a polymeric material, Teflon. The multilayers were synthesized to simulate nacre not only on laminated structures but also on individual layer thicknesses. The laminated architecture was studied as well as the structures of individual layers. Multilayer toughness and hardness were systematically investigated. It was found that the toughness of TiC/Teflon multilayers was significantly improved in comparison with monolithic TiC. But the multilayer hardness experienced a serious decrease. The individual layer thickness arrangement had an influence on both the multilayer hardness and the toughness.

Experimental observations on the mechanical properties of nanoscale ceramic/Teflon multilayers

Abstract Inspired by the ingenious architecture of nacre and its outstanding mechanical properties, we prepared nanoscale ceramic (TiC, Si3N4, B4C) /Teflon multilayers by ion beam sputtering deposition at room temperature. The toughness, hardness and tribological properties were systematically investigated as well as the multilayer structures. It was found that the toughness of ceramic/Teflon multilayers were all significantly improved in comparison with the corresponding monolithic ceramic material, but the hardness was decreased. However, there were optimized layer thickness arrangements with which the multilayer toughness and hardness can be favorably combined to obtain better comprehensive properties. It was found by this study that ceramic/polymer multilayers with the optimized layer thickness arrangement had good performance in wear resistance.

Pore structure control of Si3N4 ceramics based on particle-stabilized foams

Porous Si3N4 ceramics with open, closed pores and nest-like structures were prepared by direct foaming method, and the stability of bubbles and the microstructures of sintered Si3N4 foam ceramics were investigated. The bubbles produced by short-chain amphiphiles have higher stability as compared with that produced by long-chain surfactants. Si3N4 ceramic foams using short-chain amphiphiles are particle-stabilized one, porous Si3N4 ceramics with open and closed pores can be easily prepared with this method, and the nest-like microstructure in Si3N4 foam ceramics is achieved at high gas-pressure sintering conditions. The decrease of flexural strength due to the increase of porosity can be weakened by decreasing pore size.

Electrochemical synthesis and characterization of mesoporous Cu/Cu2O films

In summary, a new method for the electrochemical preparation of mesoporous alloy of Cu/Cu2O film was introduced. In terms of hierarchical order structure, the best results were achieved using low concentration of the anionic surfactant SDS (<10 wt.%). Through XRD, TEM, SEM and energy spectrum analysis, the film has been characterized as a mesoporous Cu/Cu2O film with hexagonal mesophase and high-quality atom-scale cubic crystalline framework. In combination with the results, this suggests that the growth of the film is accomplished through a deposition process of copper ions-coated rod-like micelles.