Ding-Fwu Lii

The effects of r.f. power and substrate temperature on the properties of ZnO films

ZnO thin films were prepared by r.f. magnetron sputtering from a zinc oxide target. The effects of r.f. power and substrate temperature on the properties of ZnO films were studied. The composition of ZnO films was analyzed by X-ray photoemission spectroscopy. The Zn atomic composition in the films was higher than the O atomic composition at any r.f. power and growth temperature conditions. This behavior might be explained by the preferential sputtering of zinc atoms rather than oxygen atoms in the ceramic target. In this study, ZnO films with epitaxial grain growth had a preferred (0 0 2) orientation. The crystallographic orientation and the piezoelectric properties of ZnO films were influenced by the sputtering parameters. A good condition exists for making the c-axis oriented films in the range of deposition rate and substrate temperature under the experimental conditions in this study. ZnO films showed different surface morphologies and surface roughness under different deposition conditions. ZnO films were transparent in the visible region, but had obvious absorption in the UV region. There were no obvious changes in the optical properties of ZnO films by varying the r.f. power and substrate temperature in this study. The phase velocity in this study was relatively higher at the optimal r.f. power and substrate temperature.

Effects of r.f. bias and nitrogen flow rates on the reactive sputtering of TiA1N films

Abstract The effects of r.f. bias and nitrogen flow on the microstructurc and mechanical properties of TiA1N films were investigated. The preferred orientations, grain size, density, adhesive strength and hardness were substantially affected by substrate bias and nitrogen flow rate. The optimized wear resistance occurred 6 ml min −1 higher than the critical N 2 flow rate at which a stoichiometric composition could be obtained. This could be related to different kinetics of nitridation of Ti and A1.

Formation of BN films on carbon fibers by dip-coating

Turbostratic boron nitride (BN) films (amorphous with some microcrystallinity) were successfully deposited onto carbon fibers and graphite substrates by dip-coating in methanolic boric acid and urea solutions, followed by nitriding in an ammonia flow at 1000 °C. BN coatings exhibited an orange-peel or pebble-like structure. Surface morphology results indicated that the sizes of the grain-like particles increased with the concentration of the dipping solution. The thickness of the BN film exhibited parabolic relationships with the viscosity of the dipping solution and the withdrawal speed. With the homogeneous surface, the thickness of the BN film increased with the concentration of the reactant in the solution. However, stripping and cracking at the surface have been observed while the reactant concentration was higher than 0.9 M. The yield of BN increased with the nitriding temperature. The increasing trend was slowed down at 800 °C and attained a maximum at 1000 °C.

Effects of oxygen contents on the electrical and optical properties of indium molybdenum oxide films fabricated by high density plasma evaporation

Indium molybdenum oxide (IMO) films were made from an oxidized target with In2O3 and MoO3 in a weight proportion of 99:1 by using a high density plasma evaporation with the substrate maintained at room temperature. Effects of the oxygen contents of 1%–28.6% on the structural and optoelectronic properties of the IMO films have been investigated. Results revealed that the addition of oxygen showed an increase in the mobility of the IMO films. Optimized oxygen vacancies and high mobility could dominant the conducting mechanism. X-ray photoelectron spectroscopy and x-ray diffraction analyses indicated that enhanced crystalline structure improved the mobility and transmittance of the film. Uniform IMO films with resistivity of 3.56×10−4 Ω cm and average transmittance of 85.06% over the wavelength of 450–800 nm were obtained.

The mechanical properties of AlN/Al composites manufactured by squeeze casting

Abstract Porous aluminum nitride (AlN) preform was formed by sintering in N 2 at 1600°C for 1 h. The molten pure Al was infiltrated into the preform to make AlN/Al composite with different compositions by squeeze casting. The AlN composition in AlN/Al composite increased from 51.2 to 70.0% when the pressing pressures of AlN preforms increased from 10 to 60 MPa, respectively. The hardness of the composite increased from 93 to 145 H v , the fracture strength increased from 328 to 490 MPa, and the compressive strength increased from 210 to 340 MPa for the corresponding composites. The fracture modes in AlN/Al composites included (1) ductile neck fracture in Al, (2) brittle intergranular fracture between smaller AlN grains, (3) brittle transgranular fracture within larger AlN grains. Three crack growth paths along (1) Al/Al interface, (2) AlN/AlN interface, and (3) AlN/Al interface were observed in the AlN/Al composites. The fracture toughness of the squeeze casting AlN/Al composites was between 14.5 and 15.7 MPa m 1/2 . No obvious trend between the fracture toughness and the composition of the composite has been observed. However, the ductility of the composite decreased with the increase of AlN content.

Microstructure, fracture behavior and mechanical properties of TiN/Si3N4 composites

The grain morphology, microstructure, mechanical properties and fracture behavior of hot-pressed silicon nitride containing two different sizes of TiN particles were investigated in this study. No interfacial interactions were noticeable between TiN and Si3N4 up to a temperature of 1850 °C. The average aspect ratio and grain thickness of β-Si3N4 grains decreased slightly with the addition of TiN particles. The amplitude and frequency of the propagating path, and the crack deflection angles, increased with the content of large TiN particles. The toughening mechanisms in TiN/Si3N4 were attributed to the crack deflection, microcrack toughening, and crack impedance by the periodic compressive stress in the β-Si3N4 matrix. The fracture toughness of Si3N4 was enhanced by 35% with the addition of 20% large TiN particles, hot-pressed at 1850 °C.

The effects of aluminium composition on the mechanical properties of reactivity sputtered TiAlN films

TiAlN films were deposited on tool materials through an r.f. bias reactive sputtering process. The effects of the aluminium composition in the films on the hardness, oxidation resistance and wear properties were studied. The results indicated that both the aluminium composition and cutting speed had substantial effects on wear resistance. The oxide phases formed at elevated cutting temperatures, especially alumina, had important effects on the cutting performance. An optimum improvement of nine times in wear resistance compared to uncoated tools, was observed.

The effects of TiAl interlayer on PVD TiA1N films

Abstract TiAlN films with a TiAl interlayer were deposited on high-speed steel through a reactive sputtering process. A semi-coherent interface was observed between TiAl and TiAlN. Owing to the diffusion of nitrogen, a good bonding had formed between these layers. The TiAl interlayer substantially increased the adhesive strength of TiAlN films and, therefore, significantly affected the wear behavior. In addition, TiAlN films with a 1 μm TiAl interlayer exhibited the highest wear resistance.

The electromagnetic shielding effectiveness of indium tin oxide films

Indium tin oxide (ITO) films were deposited on acrylics by low temperature reactive magnetron sputtering. The influence of film thickness on the shielding effectiveness of the films was investigated. The electric conductivity increased with ITO film thickness. This is probably due to the scattering of charge carriers by the external surfaces of thin films which is higher for films with smaller thickness. Results of magnetic moment versus magnetic field suggested that ITO film is basically a non-magnetic material. An increase in reflection loss with film thickness was observed, which was very similar to that observed for the electrical conductivity. The absorption loss was extremely small when compared with the reflection loss and therefore could be neglected when considering the total shielding effectiveness.

Investigation of Al2O3/Cr3C2 composites prepared by pressureless sintering (Part 2)

Abstract Alumina containing Cr3C2 of different sizes and compositions of was pressurelessly sintered at 1550°C for 2 h in 1 atm Ar atmosphere. The fracture toughness values of Al2O3/Cr3C2 composites were consistently observed to be higher than that of monolithic alumina. An optimum toughness of 5.9 MPa m1/2 was obtained for the 30 vol.% Cr3C2(2 μm)/Al2O3 composite. Small Cr3C2 (2 μm) particles had a more positive toughening effect than did large Cr3C2 (7 μm) particles. Cracks were observed to radiate from the Cr3C2 particles. Coalescence and necking of Cr3C2 were observed in composites with high Cr3C2 contents. Pores due to the pull out of Cr3C2 particles were also observed. The observed toughening effects were attributed to the mechanisms of crack deflection and microcracking. Theoretical toughness was calculated and compared with the experimental results.