Fabrication of nanodiamond loaded photoresist microstructures using two-photon polymerization

Abstract

Diamond is known for its outstanding material properties, including highest hardness, excellent chem­ ical resistance and high thermal conductivity. Diamond, which is normally formed in high pressure and temperature environments, can also be produced as polycrystalline thin films in reduced pressure environments through chemical vapor deposition (CVD). Microfabricated diamond microstructures find their applications in a variety of micro­devices and sensors exploiting diamond’s physical and chemical properties. Current diamond microfabrication methods are limited to simple 2D and 2.5D structures, and rely on costly processes to pattern the diamond films after their growth. At present, a method to produce ar­ bitrary 3D diamond microstructures is not available, thereby limiting the exploitation of microstructured diamond . Therefore, a novel bottom­up approach to produce diamond loaded microstructures using the principle of two­photon polymerization (2PP) was explored in this MSc thesis project. The diamond loaded microstructures were developed through a monodispersed nanodiamond loaded photoresist (1 weight percentage), produced by mixing photoresist SU­8 2075 with an acetone based nanofluid containing diamond nanoparticles ranging from 3.5 to 6.0 nm in size. Using the loaded resin, the 2PP process was optimized for micropillar arrays of 20 microns in diameter and height. As a result, by utilizing the optimized parameters, microstructures with features of 2 microns and aspect ratios of 1:5 were obtained. Furthermore, the loaded microstructures showed to have a Young’s modulus of 3.2 ± 0.22 GPa compared to 2.4 ± 0.10 GPa for the base resin, thus exhibiting an increase of 33%. The obtained diamond loaded microstructures are expected to form a base for future pyrolysis and CVD processes, thereby enabling the fabrication of complex 3D diamond coated glassy carbon core­ shell microstructures. These microstructures with high surface­to­volume ratios might solve the largest bottleneck in the advance of hierarchical boron­doped diamond microelectrodes for various electro­ chemical applications.