Fabrication of thick metallic microstructures using microfluidic technique and Tollens’ reaction for microfluidic components

• Main Authors: Tzu-Heng Wu, 吳咨亨
• Other Authors: Horn-Jiunn Sheen
• Format: Others
• Language: en_US
• Published: 2012
• Online Access: http://ndltd.ncl.edu.tw/handle/58251137220782068480

博士 === 國立臺灣大學 === 應用力學研究所 === 100 === A simple micromachined process based on one photomask is developed for a novel micropreconcentrator (μPCT) used in a micro gas chromatograph (μGC). Unique thick silver heating microstructures with a high surface area for microheaters of μPCT are fabricated by combining the microfluidic technique and the Tollens’ reaction within a microchannel. In this study, two types of micropreconcentrator were developed and tested. Silver deposition using this laminar flow patterning technique provides a higher deposition rate and easier microfabrication compared to conventional micromachined technologies for thick metal microstructures (> 200 μm). An amorphous and porous carbon film that functions as an adsorbent is grown conformally on microheaters inside the microchannel. The μPCT can be heated to >300℃ rapidly by applying a constant electrical power of ~5 W with a heating rate of 23℃/s. Four volatile organic compounds (VOCs), acetone, benzene, toluene, and xylene, are collected through the proposed novel μPCTs and separated successfully using a 17-m-long gas chromatography (GC) column. The peak widths at half height (PWHH) of the four compounds are relatively narrow (<6 s), and the minimum PWHH of 3.75 s is obtained for acetone. The preconcentration factors are >38 000 for benzene and toluene. The second type of μPCT with high-aspect-ratio pillar array at the adsorption region was designed and fabricated. The silver thin film heater was formed by injecting Tollens’ solutions alternately. Numerous micropreconcentrators were arranged in series to complete the silver deposition for mass production. A heating rate of 60 ℃/s could be obtained with an applied power of 5W. The peak widths at half height (PWHH) of 2.76 s, 3.24 s, 2.88 s, and 3.48 s were examined for acetone, benzene, toluene, and xylene, respectively. A high-throughput micro/nanoparticle separation device with 3D electrodes was manufactured using laminar flow patterning. The 3D electrodes were manufactured to provide dielectrophoresis (DEP) force. Only one photomask was required during the fabrication process without additional vacuum-based metal deposition processes. The optimal deposition condition was tested and two parallel 3D electrodes were successfully formed at the liquid–liquid interfaces. Multi-walled carbon nanotubes (MWCNTs) were purified using DEP force according to the electrical characteristics. Raman spectroscopy, ID/IG ratio, and current-voltage measurements were employed to compare the purification performance between 3D electrodes and planar electrodes. The ID/IG ratio of conducting MWCNTs could be reduced to 0.71. This indicates that 3D electrodes can provide greater purification.