Xun Cai

The design of ZnS/Ag/ZnS transparent conductive multilayer films

Abstract In this paper, a ZnS/Ag/ZnS multilayer system for the transparent electrodes in flat panel displays was designed. The optical and electrical performance of an Ag and ZnS single layer films with nano-dimensions was investigated. The smallest thickness of the continuous single layer Ag film that could be deposited on SiO 2 surface by thermal evaporation is approximately 12 nm. The spectroscopic ellipsometry analysis indicated that the interlayer between the Ag and ZnS layer contains a physically mixed layer and a compound semiconductor layer. Based on these studies, according to the characteristic matrix theory, the design for the optimized system was carried out with complete searching strategy. A group of the optimized structures with good selective filtering performance were successfully prepared, including some new extremely asymmetric multilayer structures. These have low sheet resistance of 3 Ω/□ and a good spectral selectivity performance with luminous transmittance T lum approximately 90% and the reflectance near infrared region above 90%. The figure of merit F TC used for evaluating transparent electrodes reached 7.3×10 −2 at 550 nm wavelength.

Hardness measurements of thin films-determining the critical ratio of depth to thickness using FEM

Abstract The finite element method is used to simulate the indentation process of a wedge-shaped indenter (136 °) into Al Si , Si Sapphire and TiN HSS film substrate systems. The relationship between the mechanical properties of both film and substrate on the shape and size of the plastic deformed zone is studied in relation to the ratio of depth of penetration to film thickness. A key conclusion of this study is that the general rule not to exceed 10–20% of the film thickness in indentation experiments to obtain a true film hardness value is not a universal law. The critical ratio of depth of penetration to film thickness ( D t ) varies sensitively with the coated systems. Since the influence of the interlayer and the substrate on the hardness of composite systems grows just above the critical indentation depth and the permissible error of microhardness measurements is in general 5–10%, in the case of a very soft film on a hard substrate, because of the confinement of the plastic deformed volume by lateral spreading within the soft film, the critical ratio of D t is found to be greater than theoretically expected. For example, in the case of an aluminum film on silicon a relative indentation depth of more than 30% will still give negligible deviations from the true film hardness. On the contrary, in the case of a hard film it seems that one has to pay particular attention to the value of relative indentation depth, because the plastic deformation easily extends into the substrate.

Normal Hall–Petch behavior of mild steel with submicron grains

Abstract A mild steel with grains at submicron scale was investigated from the microstructure and mechanical behavior point of view. Engineering strain–stress curves of submicron grain steel in comparison with that of its conventional counterpart were performed. The results indicated that the grain size dependence of the microhardness and yield stress comply with the normal Hall–Petch relationship.

Finite-element analysis of the interface influence on hardness measurements of thin films

Abstract The finite-element method is used to simulate the indentation process of a wedge-shaped indenter (136°) into Al Si and TiN HSS film/substrate systems. To investigate the influence of the interface strength between coating and substrate on the indentation process of coated systems, the specimens are built up by a 3 μm thin coating, a semi-infinite substrate and a 0.1 μm interlayer. The interlayer is assumed with different yield strengths and strain-hardening moduli to simulate various kinds of situations. Based on calculation results from the indentation load vs. indentation displacement (depth) relationship and the distributions of stresses and strains near the indentation, the influence of the yield strength of the interlayer on the hardness of composite systems is calculated and is compared with results from non-interlayer film/substrate systems; in practice it may also be negligible.

The effect of rare earth CeO2 on microstructure and properties of in situ TiC/Al–Si composite

Abstract In this work, CeO 2 is investigated as an additive for in situ preparation of TiC/Al–Si composite using exothermal dispersion (XD)+casting technology. Experimental results show that CeO 2 at high temperature exhibits the same function as Ce, which is a kind of good modificator. When 0.5 wt.% CeO 2 additive is added, the microstructure of eutectic silicon is significantly changed (the size is greatly reduced). Meanwhile, the amount of TiC particles is increased and the size is reduced. Compared with the composite without added CeO 2 , the hardness value (HB) value, tensile strength and tensile elongation are greatly increased. However, under dry sliding friction test, weight loss of the composite is not significantly changed.

A submicron mild steel produced by simple warm deformation

One simple deformation process, through which a submicron ferrite grained mild steel was fabricated, was introduced. According to the transmission electron microscope images of the microstructures, most of the boundaries formed during the process might be low angle boundaries, which means that most of the ultrafine grains are subgrains. This deformation process is attractive because: (1) the necessary strain was only 1.5, (2) the deformation resistance decreased due to higher rolling temperature, and (3) the as warm-rolled mild steel had a microstructure with equiaxed grains of 0.7 μm in average diameter. The result of mechanical tests indicates that better properties, with comparison to its coarse-grained counterpart, were obtained, including doubled yield strength, high hardness, good work hardening and reliable elongation. Cross effect was observed during tensile process and interpreted from point view of conventional dislocation movement.

Mechanism of hydrogen desorption during palladium brush-plating

Abstract Continuous Pd deposits were fabricated by brush-plating. The morphologies of the Pd deposits were characterized by atom force microscopy (AFM). No micro-cracks were found in the deposits. The deposits were made up of spherical nano-clusters. Analyses of the morphology of Pd deposits brush-plated with different anode sliding speeds indicated that the H 2 bubbles desorbed from the deposits by two modes, passive and active, respectively. For the first mode, H 2 bubbles are removed by the anode movement. For the second mode, H 2 bubbles escape from the deposits actively. As a result, pores were avoided in the Pd deposit by brush-plating. A deposit self-repairing mechanism in Pd brush-plating is proposed.

Effects of Al and N plasma immersion ion implantation on surface microhardness, oxidation resistance and antibacterial characteristics of Cu

Al and N were introduced into copper substrate using plasma immersion ion implantation (PIII) in order to enhance its hardness and oxidation resistance. The dosage of N ion is 5×1016 cm−2, and range of dosage of Al ion is 5×1016–2×1017 cm−2. The oxidation tests indicate that the copper samples after undergoing PIII possess higher oxidation resistance. The degree of oxidation resistance is found to vary with implantation dosage of Al ion. The antibacterial tests also reveal that the plasma implanted copper specimens have excellent antibacterial resistance against Staphylococcus aureus, which are similar to pure copper.

Mechanism of enhanced adhesion between hydrogenated amorphous carbon films and tungsten preimplanted steel substrates

Hydrogenated amorphous carbon (a-C:H) films have good mechanical properties but poor adhesion on substrates such as tool steels thereby limiting their applications. Film adhesion can be improved by conducting tungsten preimplantation into the steel substrates before deposition of the carbon film. The enhancement mechanism is investigated in this study by depositing the films on W plasma-preimplanted (20kV, 5×1017ionscm−2) and untreated steel substrates using mixed acetylene and argon plasmas with different flow rate ratios by means of plasma immersion ion implantation and deposition. Preimplantation creates a graded WC interface that mitigates diffusion of the dissociated carbon atoms on the surface. Compared to the films deposited on untreated steel substrates, the ones deposited on the W-implanted steel substrates exhibit improved adhesion strength, especially for the lower acetylene to argon flow rate ratios. Tungsten preimplantation is critical to the successful fabrication of a-C:H films on steel sub...

Experimental and numerical evaluations of adhesion strength and stress in TiN films deposited on ti-implanted aluminum

Titanium ions were implanted into aluminum substrates at 40kV prior to magnetron sputtering deposition of the Ti interlayer and TiN film using our custom-designed multifunctional ion implanter without breaking vacuum. An 82-nm-thick modified layer was formed between the TiN film and the substrate. The characteristics of the implanted samples were compared to those of TiN∕Al and TiN∕Ti∕Al samples that were not preimplanted. Based on our scratch tests, the critical loading Lc of the TiN∕Ti∕Ti-implanted Al sample was significantly improved compared to the unimplanted TiN∕Al and TiN∕Ti∕Al samples. Finite element analysis was conducted to simulate the scratch process to help reveal the stress distributions in the vicinity of the interlayer. The results show that the stress around the interface is largely reduced in the TiN∕Ti∕Ti-implanted Al sample. Consequently, the mechanical properties such as resistance to loadings are enhanced.