Kung-Jeng Ma

Fabrication of high-aspect-ratio microstructures using excimer laser

An excimer laser micromachining system is developed to study the ablation of high-aspect-ratio microstructures. The study examines the ablation efficiency, specifically, the impact of changing major laser operating parameters on the resulting microstructural shapes and morphology. The study focuses on glass, although results on silicon and aluminum are also included for comparison. In ablating grooved structures, the ablation depth has been observed to be linearly proportional to the operating parameters, such as the pulse number and fluence. The results specifically indicate that ablation at low fluence and high repetition rates tends to form a V-shaped cross-section or profile, while a U-shaped profile can be obtained at high fluence and low repetition rate. The ablation rate or ablated volume has then been quantified based on the ablation depth measured and the ablated profile observed. The threshold fluence has also been obtained by extrapolating experimental data of ablation rate. The extrapolation accuracy has been established by the good agreement between the extrapolated value and the one predicted by Beers law. Moreover, a one-dimensional analytical solution has been adopted to predict the ablated volume so as to compare with the experimental data. The reasonable agreement between the two indicates that a simple analytical solution can be used for guiding or controlling further laser operations in ablating glass structures. Finally, the experimental results have shown that increasing the repetition rate favors the morphology of ablated surfaces, though the effect of repetition rate on ablation depth is insignificant.

Excimer laser ablation of glass-based arrayed microstructures for biomedical, mechanical, and optical applications

An excimer laser has been used for ablation of glass-based substrates for making arrayed microstructures. The arrayed microstructures are fabricated by repetition of a simple-patterned mask associated with substrate movement controlled by an x-y stage synchronizing with laser pulses. The associated ablation efficiency, specifically the impact of changing major laser parameters on the resulting microstructural shapes and morphology, has been studied. Several microstructures have been machined by this repetition technique to demonstrate that the use of a single-slotted mask indeed can be cost effective in prototyping of various glass-based arrayed microstructures. The single and arrayed microstructures developed include microracks, waveguides, microprobes, and microstamps; the specific applications of these microstructures in mechanical, optical and biomedical areas are also discussed. The associated ablation techniques for different application are described and demonstrated. The defocusing effects on form...

Preparation of superhydrophobic surface for PTFE/ePTFE materials by oxygen plasma treatment

The PTFE and expanded PTFE (ePTFE) in sheets has been widely used in varied industrial environments based on its hydrophobic surface, elasticity and porous properties. To enhance their applications, sheet PTFE and ePTFE have been modified by various techniques. Most studies concentrated on the improvement of the hydrophilic properties. This study devoted to produce superhydrophobic surface on PTFE and ePTFE materials by RF plasma system using O2 as the reaction gas. The results showed that at a lower RF power (< 300W) can slightly improve the hydrophilic properties due to the occurrence of oxidation and cross-linking reaction. However, the wetting angle was significantly increased to over 160° when the surface modification operated under a higher RF power (> 400W). This can be attributed to the occurrence of the lotus effects, induced by the formation of porous and needle-like structure on PTFE or ePTFE surface after O2 plasma treatment.

Fabrication of high-aspect-ratio microstructures using excimer lasers

An excimer laser micromachining system is developed to study the process in fabricating high-aspect-ratio microstructures. Specifically, the study experimentally examines process efficiency and the impact of changing major laser operating parameters on the resulting microstructural shapes and morphology. The materials considered in the study include glass, silicon, and aluminum. The ablation or micromachining rate has been observed to be strongly dependent on the operating parameters, such as the pulse fluence, number, and repetition rate. The results specifically indicate that ablation at low fluence and high repetition rate tends to form a V-shaped cavity, while a U-shaped cavity can be obtained at high fluence and low repetition rate. Additionally, the present study also indicates that a three-dimensional V-shaped cavity with large vertex angle can be formed by varying the focus depth of excimer laser. Materials of low thermal conductivity and low melting temperature are indeed more applicable to laser ablation.An excimer laser micromachining system is developed to study the process in fabricating high-aspect-ratio microstructures. Specifically, the study experimentally examines process efficiency and the impact of changing major laser operating parameters on the resulting microstructural shapes and morphology. The materials considered in the study include glass, silicon, and aluminum. The ablation or micromachining rate has been observed to be strongly dependent on the operating parameters, such as the pulse fluence, number, and repetition rate. The results specifically indicate that ablation at low fluence and high repetition rate tends to form a V-shaped cavity, while a U-shaped cavity can be obtained at high fluence and low repetition rate. Additionally, the present study also indicates that a three-dimensional V-shaped cavity with large vertex angle can be formed by varying the focus depth of excimer laser. M...

Precision grinding of tungsten carbide mold insert for molding of sub-millimeter glass aspheric lenses

As the demand for precision optical components with sub-millimeter feature size steadily increasing, numerous efforts have been made in developing new techniques and in improving the existing approaches to efficiently and economically produce those components. Glass molding process (GMP) is one of these methods to enable mass production of precision glass optical components in recent years. One of the key issues in GMP is precision mold insert fabrication. Since the mould are normally made of hard and brittle materials such as tungsten carbide (WC) and silicon carbide (SiC), precision diamond grinding is by far the principal choice used to machine the GMP mould. As the feature size of optical component gets smaller, the size of mould and grinding wheel used to fabricate the mould gets smaller too. This makes the grinding process a very time consuming and expensive task. This research aimed to improve the small mold fabrication processes by developing an effective way of producing small diamond wheels and in-process monitoring wheel profile. Diamond wheels of around 0.2mm to 0.5mm in diameter after truing and WC aspheric mold insert of form accuracy around 0.47μm were successfully produced in this research.

Study on fabricating of micro-pyramid array by precision diamond turning

As the demand for micro-patterned parts getting bigger, the need for molds with micro/nano scaled patterns to duplicate these parts effectively and economically is increasing ever so rapidly. Over the years, numerous attempts have been made to fabricate these molds using various approaches such as lithography, FIB, laser ablation, and precision diamond turning. Amongst these approaches, diamond turning is by far the most commonly used method to generate the micropatterned rollers for roll-to-roll fabricating of precision optical parts such as BEF and 3D films. However, micro-burrs are frequently produced during the micro-cutting process which not only makes the mold un-usable but also increases the cost of machining. Efforts have been made to study the burr formation process during the micro-cutting by FEM simulation, micro-scratching and diamond turning. Influences of the machining parameters such as rake angle, cutting edge radius, included angle and cutting speed on the burr formation were systematically investigated. Array of micropyramids with 90° apex angle, 40*40μm2 basal area and minimised burr were successfully produced on a OFCu roller of 270mm in diameter. The results showed that (i) tool rake angle, included angle and cutting edge radius have profound effect on burr formation and achievable surface finish, (ii) simulation can supply very useful information for setting the machining parameters to suppress the burr formation during micro-cutting process.

Kinetic study of bacterial adhesion on biomaterials by using optical waveguide lightmode spectroscopy

The principles of bacterial identification are beginning to be understood at the kinetic level in the past few years, nevertheless, the crucial aspects to be taken into consideration are the spatial arrangements of molecules or atoms at the interacting surfaces and the profiles of the interfacial forces. In this study, the dynamics of attachment and detachment of E. coli K12 to ultra thin film biomaterials silica and zirconia surfaces with precisely coated by sol-gel method is measured by using optical waveguide lightmode spectroscopy (OWLS) are described.

Synthetic characterization and surface modification of FePt monodispersive nanoparticles

Monodispersive FePt magnetic nanoparticles with hydrophobic ligand were chemically synthesized and with controllable surface-functional properties. In order to compare and select the high saturation magnetization of FePt nanoparticles, the synthesized solvents were changed to effectively increase magnetization due to the increased particle size and isolated distance of each nanoparticles. The surface modification of FePt nanoparticles by using mercaptoacetic acid (thiol) and 11-mercaptoundecanoic acid (MUA) as a phase transfer reagent through ligand exchange turned the nanoparticles hydrophilic, and the nanoparticles were water-dispersible. Transmission electron microscopy images indicate the nanoparticles slightly agglomerate after ligand exchange. FTIR spectra suggest that thiol and MUA bind to the FePt atoms of the surface, respectively.