Building with ions: towards direct write of platinum nanostructures using in situ liquid cell helium ion microscopy.

Direct write with a liquid precursor using an ion beam in situ, allows fabrication of nanostructures with higher purity than using gas phase deposition. Specifically, positively charged helium ions, when compared to electrons, localize the reaction zone to a single-digit nanometer scale. However, to control the interaction of the ion beam with the liquid precursor, as well as enable single digit fabrication, a comprehensive understanding of the radiolytic process, and the role of secondary electrons has to be developed. Here, we demonstrate an approach for directly writing platinum nanostructures from aqueous solution using a helium ion microscope, and discuss possible mechanisms for the beam-induced particle growth in the framework of Born-Oppenheimer and real-time electron dynamics models. We illustrate the nanoparticle nucleation and growth parameters through data analysis of in situ acquired movie data, and correlate these results to a fully encompassing, time-dependent, quantum dynamical simulation that takes into account both quantum and classical interactions. Finally, sub-15 nm resolution platinum structures generated in liquid are demonstrated.