Radiation damage assessment of atomically thin membranes

Abstract

This thesis investigates the methodologies and results of gas transport across atomically thin membranes, which are relevant to reducing Tritium inventory in fusion reactors by separating Helium from the plasma exhaust stream. A novel experimental apparatus and set-up is devised to measure the gas transport rate across a membrane by containing a pool of liquid water that evaporates over time and passes through the membrane interface to the environment. This device minimizes flow resistance on both sides, allowing for membrane resistance changes to be appropriately assessed. This apparatus also measures less than 5 % error between trials on the same membrane, which can be improved with more data collection for each transport measurement. Graphene is transferred onto high pore density polyimide (-50 nm pore diameter, 6E9 pores cm⁻²) and is imaged with a scanning electron microscope (SEM) to assess graphene transfer fidelity. It is found that graphene coverage (defined as the fraction of the polyimide covered by visibly intact graphene) for samples can be as high as 98% using the transfer method explained in this work. The resulting membranes are irradiated with varying levels of Gallium ion radiation in a focused ion beam machine. It is found that irradiating the sample with ion beam settings of 8 keV acceleration voltage and a dosage of 2.53E+13 Gallium ions cm 2 causes no noticeable change in membrane performance of water vapor transport. Future work will include irradiating the sample at higher dosages and assessing membrane performance while correlating these dosages to what is expected in a fusion reactor setting.