| dc.description.abstract | This dissertation demonstrates the design, simulation, fabrication and characterization processes of a novel heated atomic force microscope cantilever for polymer based additive nanomanufacturing. Fabrication and integration of heterogeneous nanostructures is an essential task for manufacturing next generation organic electronic devices. Current state-of-the-art in heated tip additive manufacturing has a limited write time and cannot accurately control polymer deposition rate. The new design presented here includes two embedded joule heaters connected by a microchannel, where thermocapillary forces induced by the temperature gradient between heaters can deliver about 40 ng of polymer to the tip. The heated tip design presented here was informed by multiphysics finite element analysis to optimize the thermo-mechanical and thermo-fluidic performance of the device. Computational fluid dynamics simulations of molten polymer flowing in the microchannel shows the velocity of the leading edge depends significantly on the imposed temperature gradient. Thus, the cantilever tip can be inked, cleaned, and re-inked by controlling the temperature of the integrated heaters. Following design optimization, this work details the step-by-step microfabrication processes for manufacturing the heated cantilevers. Electrical and thermal characterizations are performed to evaluate the temperature response and electrical resistance of the fabricated cantilevers, and is compared to the developed models. Preliminary results show a maximum temperature of 500 °C before thermal runaway occurs in the fabricated cantilevers, with temperature gradients as large as 2.0E6 C/m.
Investigation of solid-liquid interactions at the nanoscale is crucially important to understand the mechanism of polymer spreading along the cantilever microchannel and tip. A new AFM-based measurement technique for dynamic measurement of polymer nanodroplet spreading at elevated temperatures is developed. The experimental setup is used to measure the spreading dynamics of polystyrene droplets with 2 µm diameters at 115-175 °C on flat surfaces. Custom image processing algorithms determine the droplet height, radius, volume, and contact angle of each AFM image over time to calculate the droplet spreading dynamics. The new cantilever design and the AFM-based spreading measurement technique presented here, provide a framework to make better tools for wafer scale heterogeneous polymer nanostructure fabrication with high throughput, multiple feature registration, and high spatial resolution. | en |
