Proton beam writing applications in microfluidics and nanoimprint lithography

Abstract

This thesis describes the development of proton beam writing for microfluidic applications.In first part of the thesis we used a focused beam of protons to fabricate throughdirect writing microfluidic structures in solid sheets of poly(methylmethacrylate)PMMA resist. The microchannels have been sealed and used for fluidic characterization.Electrokinetic force has been used to flow a fluid inside the channels. Aseries of experimental and theoretical fluid dynamic studies have been carried outto characterize the fluid flow inside the channels by measuring the flow rate, theflow velocity profile and the electric potential at the surface of the channels (zetapotential). The characterization methods are developed in house and involve particleimage velocimetry (PIV) and current monitoring. Using these methods, quantitiessuch as electrophoresis mobility of sub-micron plastic microspheres and electroosmosismobility and zeta potential of the direct written microchannels have been measuredwhich are comparable to the values reported in the literature. These characteristicstogether with lithographic parameters such as side wall smoothness, and verticalityof the side walls indicate that proton beam has high potential for fabrication of threedimensional high aspect ratio fluidic structures.The second part of the thesis is focused on developing a low-cost and highthroughputimprinting method to fabricate microfluidic structures into different polymers.Using a combination of proton beam writing and nickel electroplating, metallicstamps with micron size and nano size features on its surface have been fabricated.This approach produces a simple fabrication process with material flexibility and precisedepth control. High quality Ni stamps with smooth and vertical three dimensional micon size and nano size surface features have been fabricated. The stamps have beenused for imprint lithography with successful replication into PMMA polymers.