J.X. Liao

Structural and optical properties of BaxSr1−xTiO3 thin films on indium tin oxide/quartz substrates prepared by radio-frequency magnetron sputtering

BaxSr1−xTiO3 (x=0.6 and 0.8) thin films have been prepared on indium-doped tin oxide (ITO) coated quartz substrates using radio-frequency magnetron sputtering. Their structural properties and surface morphologies were examined by x-ray diffraction and atomic force microscopy, respectively. The BaxSr1−xTiO3 (BST) thin films with x=0.6 and 0.8 annealed at 650°C for 20min exhibit good surface morphology and well-crystallized perovskite structure. High quality BST ferroelectric thin films were further investigated by electrical measurements, showing the remnant polarization (Pr) of 6.75μC∕cm2 and the coercive field (Ec) of 43.2kV∕cm. Optical transmittance measurement indicated that the Ba concentration has an effect on the band gap energy (Eg) structure of the BaxSr1−xTiO3 thin films. The Eg decreases linearly with the increase of the Ba content. The refractive index (n) and extinction coefficient (k) of the BST films with x=0.6 and 0.8 were obtained by fitting the spectroscopic ellipsometric data using a par...

The influence of post-annealing on the chemical structures and dielectric properties of the surface layer of Ba0.6Sr0.4TiO3 films

Barium strontium titanate (Ba0.6Sr0.4TiO3, BST) films have been deposited on Pt/Ti/SiO2/Si substrates by radio frequency magnetron sputtering. The influences of conventional thermal annealing (CTA) and rapid thermal annealing (RTA) on the chemical structures of the surface layers of the BST films have been investigated. Grazing x-ray diffraction and atomic force microscopy show that the RTA-films exhibit more compact structure and more completed crystallization than the CTA-films. X-ray photoelectron spectroscopy (XPS) investigations show that the surface layer is composed of a non-perovskited BST phase and a perovskited BST phase. For the CTA-film, the surface contains about 70% non-perovskited BST phase, and the surface layer is approximately 3–5 nm thick, while for the RTA-film, the surface non-perovskited BST phase amounts to about 40%, and the surface layer is about 1nm. XPS also indicates that the CTA-film surface adsorbs a larger amount of carbon contaminations than the RTA-film. Fourier transform infrared reveals that the amount of the surface adsorbed water and/or OH groups may be ignored. The non-perovskited BST phase is mainly related to the surface structure and the adsorbed carbon contaminations. The effect of annealing temperature on the surface layer and the amount of non-perovskited BST phase has been discussed, and the dielectric properties have also been measured.

Tribological performance of ultrathin diamond-like carbon films prepared by plasma-based ion implantation

Ultrathin diamond-like carbon (DLC) films with thicknesses of 5–60 nm have been prepared on Si by plasma-based ion implantation. Raman spectrum and x-ray photoelectron spectroscopy (XPS) show that these DLC films present high sp3/sp2 ratios. XPS also displays that each DLC film firmly adheres to the Si substrate owing to a C–Si transition layer. Atomic force microscopy shows that the DLC films are smooth and compact with average roughness (Ra) of about 0.25 nm. Sliding friction experiments reveal that these DLC films show significantly improved tribological performance. With increase of DLC film thickness, the sp3/sp2 ratio increases, the roughness decreases, the hardness increases, the adhesive wear lightens and thereby the tribological performance becomes enhanced. Also, the effects of the applied load and the reciprocating frequency on the tribological performance are discussed.

The tribological properties of nanometre carbon films prepared by plasma-based ion implantation at various implanting voltages

About 30 nm thick nanometre carbon films have been prepared on Si wafers by plasma-based ion implantation at various implanting voltages. The ball-on-disc sliding friction experiments show that the tribological properties of these carbon films are in good agreement with the corresponding structure characteristics which strongly depend on the implanting voltage. These structure characteristics include the film roughness, the film thickness, the C–Si transition layer between the carbon film and the Si substrate and the sp3/sp2 ratio. As the implanting voltage increases, the roughness and the thickness decrease, the C–Si transition layer thickens and the sp3/sp2 ratio first increases to the maximum value at about 30 kV and then decreases. 3 kV and below correspond to bad tribological properties owing to polymer-like carbon (PLC) film and no C–Si transition layer with poor adhesion to the Si substrate. When the implanting voltage increases to over 3 kV, a C–Si transition layer is gradually formed and thickens with increasing adhesion, and the PLC film is gradually turned into a diamond-like carbon (DLC) film, and hence the tribological properties are gradually improved and reach the best values at 30 kV. 10–50 kV correspond to two orders of increase in wear life, close to zero volume wear rate, but about 0.3 friction coefficient at 0.1 N applied load. With the increase in the applied load, the wear life and the friction coefficient decrease and the wear rate increases. For Si wafers coated with the DLC films at 30 kV, in the range of 0.5–1 N, there is an appropriate value corresponding to the wear life of above 18 000 s, friction coefficient of about 0.1 and wear rate of 10−9 mm3 N−1 m−1 level. Additionally, the wear mechanism is discussed.

Effect of Annealing Temperature on the Microstructure of Barium Strontium Titanate Films

Barium strontium titanate (Ba1−xSrxTiO3, BST) films have been prepared on Pt/Ti/SiO2/Si by medium frequency (MF) magnetron sputtering, and subsequently in situ crystallized at 500-700°C. The microstructures of the MF-BST films are studied. BST films prepared by radio frequency (RF) magnetron sputtering and exhibited preferential (110) orientation, are compared. XRD shows that the MF-BST films exhibit preferential (111) orientation and better crystallization than the RF-BST films at the same annealing temperature. AFM displayed that the MF-BST films were smooth and compact. XPS analysis exhibited that the MF-BST films revealed better surface and interface structural characteristics. Their dielectric properties were also compared.

The Interfacial Characteristics of Ba0.6Sr0.4TiO3 Films Deposited by Radio Frequency Magnetron Sputtering

Ba0.6Sr0.4TiO3 (BST) thin films deposited on Pt/Ti/SiO2/Si substrates by radio frequency magnetron sputtering and crystallized by rapid thermal annealing (RTA) exhibit much thinner BST/Pt interfacial transition layer and higher dielectric properties than the films crystallized by conventional thermal annealing (CTA). HRTEM observations show that the transition layer is 2-3nm thick for RTA and 4-5nm thick for CTA. XPS investigations display that the transition layer is composed of perovskited BST phase and non-perovskited BST phase, and RTA corresponds to much less non-perovskited BST phase than CTA. The reason for non-perovskited BST phase and the dielectric properties of BST films are also presented.