MICRO/NANOSTRUCTURED SURFACES THROUGH THIN FILM STENCIL LIFT-OFF: APPLICATIONS TO PATTERNING AND SENSING

Abstract

The rapid development of micro/nanofabrication techniques have enabled engineering of material interfacial properties. Micro/nanostructures with unique electrical, mechanical, thermal, magnetic, optical, and biological properties, have found applications in a wide range of fields such as electronics, photonics, biological/chemical sensing, tissue engineering, and diagnostics, etc. As such, numerous strategies have been developed for structuring materials into micro/nano- scale. However, the challenge still lies in the high cost, low throughput, complexity in fabrication, and difficulty in scaling up. This thesis aims to explore fabrication strategies for micro/nanostructured surfaces that are versatile, simple, and inexpensive. The thin film stencil lift-off technique with both Parylene and self-adhesive vinyl has been explored for this purpose. Further applications of the resulted micro/nanostructured surfaces are also presented in this thesis. Through improved Parylene stencil fabrication process, both spontaneously phase-segregated and arbitrary binary supported lipid bilayer patterns have been achieved. Also, the microstructured Parylene surfaces have been ddemonstrated for patterning stacked SLBs that are either homogeneous or phase-segregated. Without any lithography technique involved, vinyl stencil lift-off offers as a facile and inexpensive benchtop method for patterning thin films such as metal and glassy films. Combining the thermal shrinking of shape memory polymer, the patterned feature sizes are further decreased by 60% in both x and y dimensions, pushing the patterning resolution to down to sub-100 μm range. In addition, the shrinking process induces micro/nanostructures onto the deposited thin film, and the structure sizes are easily tunable with film thickness deposited. Further applications of such patterned micro/nanostructured surfaces has also been explored. The structured gold films have served as high-surface-area electrodes for electrochemical sensing. By introducing photoresist as a sacrificial layer, the structured gold thin films can be lifted off and transferred onto elastomeric substrate, and serve stretchable and flexible sensors. Such sensing devices exhibit great stability and reproducibility even when working under external strain. Finally, the micro/nanostructured glassy surfaces have been employed as substrate for cell growth to study topographical effect on cell morphology. It has been concluded that rougher surfaces lead to cell elongation, and finer structures promote filopodia generation. These results underscore the strength and suitability of thin film stencil lift-off as a powerful technique for creating micro- and nanostructured surfaces. These structured surfaces could find applications in many other areas, due to their great properties such as tunable structure size, high surface area, flexibility, and long-term stability.