Papers by Author: Wei Haw Fan

Abstract: Ultrasonic machining (USM) technique has long been used for fabricating various patterns and drilling holes on brittle materials. However, the surfaces generated by USM are normally rather rough and covered by deep penetrated cracks. This has greatly limited USM being used in micro-machining and fine machining. This research aimed to study the surface integrity of the USMed surface and develop a feasible way to minimize the scattered cracks so that good surface finish could be achieved. Machining parameters such as type and concentration of abrasive particles, grit size, and feed rate were systematically investigated to check their influences on the surface obtained. A ‘multi-stage’ micro-USM process was developed in this study and surface with Ra value better than 0.2m was achieved using the proposed process.

Abstract: Diamond is one of the most important engineering materials for its extreme hardness, high thermal conductivity value and chemical inertness. Due to its high hardness and strength, it can be ideal candidates for AFM probe or micro-needle. In this research, micro cone-like shaped diamond tips with high aspect ratio formed using reactive ion etching (RIE) method. The scanning electron microscope (SEM), transmission electron microscope (TEM) and micro-Raman spectroscopy were used to study the surface morphology and sub-surface micro-structure before and after RIE process. The results showed that gold could be adopted as mask material during the RIE process. Different microstructures could be obtained using different RIE parameters such as etch duration and reactant gas. After RIE (O2 50sccm, 200W) for 5min the micro cone-like structures (aspect ratio~8) could be observed on the surface if a thin layer of gold was applied as mask. However, under the same RIE conditions, the irregular pillar-like microstructures started to emerge if the etching time was stretched longer.

Abstract: Polycrystalline CVD diamond film possesses many advanced physical and mechanical properties which makes it a very important engineering material. However, high hardness value and extreme brittleness have made CVD diamond film a very difficult material to be machined by conventional grinding and polishing processes. In the present research, diamond wafers were pretreated with RIE in an attempt to weaken the top layer and pave the way for subsequent thermochemically polishing. It was found that the diamond grains were anisotropically etched and some high aspect ratio pillar-like micro-structures were formed during the RIE process. These micropillars are relatively easy to be ruptured and removed by the subsequent polishing process. The results showed that this method could effectively speed up the polishing of CVD diamond films.