Etching with monolayer accuracy is a critical requirement for advancing nanoscience and nanotechnology. Current plasma etching techniques do not have the level of control or damage-free nature that is needed for patterning delicate sub-20 nm structures. In addition, ALET methods proposed thus far, based on pulsed gases with long reactant adsorption and purging steps, are very slow, even for etching extremely thin films. This project will develop the principles and techniques for a practical method of etching surfaces, one atomic layer at a time, using a combination of pulsed plasma and monoenergetic ion bombardment. With this novel methodology it should be possible to obtain ALET at a substantially higher rate (~30X), compared to other methods. Plasma experiments and simulations will be performed to understand the complex interaction between the pulsed plasma and the resulting ion energy distributions. Measurements of time-resolved ion bombardment energy and angular distributions will be coupled with etching experiments including the effect of noble gas ion mass, and reactant (Cl, Br, I) mass and electronegativity on sub-surface lattice damage and etching with monolayer accuracy. Plasma and surface diagnostics will be employed to measure product removal rate as a function of chemisorbed layer surface coverage and substrate damage. In-situ UHV-AFM/STM and XPS will provide valuable information on surface roughness and the spatial distribution of reactant in the modified surface layer.

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