ICMCTF2011 Session G1: Innovations in Surface Coatings and Treatments

Hierarchical nanostructures that consist of various combinations of metal oxides semiconductors (TiO₂, ZnO, V₂O₅, etc.) were synthesized using the unbalanced magnetron sputtering processes on Si and glass substrates. These structures were created to be used primarily as photocatalysts to degrade pollutants in water and air but may be used for other applications that include solar energy harvesting. The crystal structure and the morphology of the nanostructures were evaluated using x-ray diffraction, scanning electron microscopy, and transmission electron microscopy. These properties were evaluated as a function of deposition conditions such as power to the targets, substrate temperature, oxygen partial pressure, and substrate bias. Finally, the performance of these materials was investigated by evaluating the photoluminescence spectra of these materials and the degradation characteristics of various dyes.

Cubic BN (cBN) has a set of extreme properties similar or even superior to diamond, which makes cBN a very promising material for fabrication of cutting tools, thermal, optical, and high-temperature and high-frequency electronic devices. Cubic BN is a synthetic material, and the study on the synthesis of cBN by high pressure high temperature (HPHT) method started in the early 1960s. Cubic BN films have also been prepared by a variety of ion-assisted physical vapor deposition (PVD) methods. The bombardment of deposited films by energetic species (tens to hundreds of eV) is, however, inevitably accompanied with a significant build-up of compressive stress (5-20 GPa) and leads to the nanocrystalline nature and delamination of the films with a thickness larger than 200 nm. Recent success in the growth of cBN films by chemical vapor deposition (CVD) methods based on fluorine chemistry results in considerable progresses in improving crystallinity, thickness, and adhesion of cBN films. This presentation aims to discuss the major issues hindering cBN films for practical applications, and review the recent progress in the nucleation, growth, and characterization techniques of cBN films. It describes various successful approaches in the interface engineering and growth techniques in increasing film thickness, improving crystallinity, and tuning the electrical properties of cBN films. New developments of cBN films in the applications of mechanical, electronic, and optoelectronic devices will also be addressed.

Southwest Research Institute has identified and demonstrated, at a proof of concept level, an innovative method of fabricating diamond-like carbon (DLC) coatings that involves chemical synthesis of hydrocarbon polymers possessing diamond-like structure at the atomic level and subsequent use of pyrolysis to convert the polymers to diamond-like carbon (s-DLC). The low-temperature, atmospheric, and solution-based processing allows for coating substrates previously considered impractical or impossible due to their size, geometry, or incompatibility with vacuum processes. Further, the properties of the films may be tuned by adjusting the precursor chemistry to control the sp², sp³ and H content. The chemical composition, microstructure, and properties of the s-DLC coatings were examined with and compared to those of traditional DLC using FTIR and Raman spectroscopy, electron energy loss spectroscopy (EELS), scanning electron microscopy (SEM), electrical impedance, and nanoindentation measurements. In this presentation, an overview of the synthesis, application, and performance of the s-DLC coatings will be given with a specific focus on areas for further development.

Improving the poor tribological properties of titanium alloys has been the subject of extensive research for many years. A number of oxidation processes have been developed for that purpose. In this study, surface hardening of Ti-6Al-4V is achieved by triode plasma oxidation (TPO) which differs from conventional diode plasma treatments through the use of a third electrode; a negatively biased tungsten filament to enhance the ionisation levels in the plasma. The resultant surface generally consists of a top oxide layer with an oxygen diffusion zone lying immediately underneath it. The effects of process parameters such as substrate temperature, current density and oxygen partial pressure are investigated. Surface hardness measurements at various indentation loads were carried out on all TPO-treated samples to assess the changes in hardness with depth across the diffusion layer. The hardness profiles obtained confirmed the gradual decrease in surface hardness with depth and provided a rough estimate of the thickness of the hardened layer produced. Ball-on-plate reciprocating sliding wear data and glancing angle XRD analysis of the oxidised samples are also presented. The results indicate that a harder and deeper case is achieved both at high substrate temperature and high oxygen partial pressure. Furthermore XRD data show that the substrate temperature significantly affects the structure of the oxide layer produced. All TPO-treated samples also exhibit better wear performance compared to the untreated material.

A novel method was used for antimony doped into tin oxide to form Sn,Sb-O_2-x. The Sb/ SnO₂ multilayer films were prepared by ion beam sputtering and RF magnetron sputtering deposition technology separately. The as deposited films were treated by UV 355 nm pulsed laser for the assistance of Sb-ion driven into SnO₂ to form antimony-doped structure.

Sn,Sb-O_2-x films have 45% resistivity decrease and over 90% transparent compared with non-doped SnO₂ thin films. The majority carrier concentration showed over 20% improvement at the laser power peak 50 mJ, 30 Hz condition. As the laser power increasing, the majority carrier amounts dropped gradually. The Sb content was decreased as laser power over 50 mJ because of Sb evaporation after high temperature laser ablation. The as deposited films surface morphology was observed by atomic focus microscope (AFM). The results showed roughness of laser treated films were worse than untreated films and some crystallization formed on the surface.

The effects of ultrasound and temperature on the nucleation mechanism, structure and properties of electrodeposited copper thin films on aluminum were studied using cyclic voltammetry (CV), X-ray diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM) techniques. It was found that deposition without ultrasound (silent) showed a mixed kinetics control while sonicated system was dominantly charge transfer control. Films were crystalline in structure. The deposits from the doubly activated bath have the distinct mushroom like morphologies, while in silent conditions there was a transition of morphology from dendritic structures to spherical grains with decrease in deposition temperature. Further, the addition of sonication environment has lead to substantial variations of thermal and mechanical properties of the copper thin films. There was a significant change in the variation of energy absorbed for films that deposited at different bath temperatures. The observed hardness values of the films were higher than the conventional polycrystalline copper. Further the soft films were found to have good wear properties. Thus, the beneficial sonication effect on deposits may be effortlessly and suitably tailored depending on the requirement, which holds a great promise for the future.