Date of Award
Doctor of Philosophy
Energy Science and Engineering
Jason D. Fowlkes
Philip D. Rack, Scott T. Retterer, Gerd Duscher
Focused electron beam induced deposition (FEBID) is a promising additive nanomanufacturing tool which has recently advanced from a trial-and-error experimental method to a controlled, predictable, and simulation-guided 3D nanoprinting technology. FEBID uses a finely focused electron probe to dissociate surface adsorbed precursor molecules resulting in a highly localized mesh style deposit. The mesh objects are constructed using interconnected nanowires, where the final shape of the 3D nanostructure is wholly dependent on the precision of the individual nanowires. However, these nanowires are prone to deflections and tapering effects, and thus 3D FEBID technology is precision limited. Here, the precision limiting effect has been quantified. Complementary experiments, models, and simulations identified that electron beam induced heating influenced the deposition rate during the direct-write process. The beam interaction driving deposition simultaneously triggers local heating. As the nanowire elongates, thermal resistance increases, and the temperature gradually rises at the beam impact region (BIR). The heat generated must flow through the 3D nanostructure to the heat sink, that is, the substate. This process mimics the classical heat transfer through fins. Simulations uncovered that the beam heating impacts the Arrhenius precursor surface residence time ((T)) such that, the rate of precursor desorption increases and consequently, the rate of deposition goes down. It was found that the vertical growth rate decreases and results in nanowire tapering and deflection with increasing length, even for temperature increments in the order of 10 K.
Mutunga, Eva Mumbua, "Electron Beam Heating Effects During 3D Nanoprinting Using Focused Electron Beam Induced Deposition. " PhD diss., University of Tennessee, 2020.