Synthesis of pans and mesas using a beam of self-ions

We report the synthesis of pans and mesas ∼10 νm in diameter on Pt(111), in ultra-high vacuum, using a beam of Pt^- ions as the processing tool, and a low energy electron microscope to observe the surface microtopography. Mesas are perfect terraces surrounded by a bunch of outward pointing steps; an ion beam of low energy was used to create excess adatoms that accrete to expand that terrace and increase the height of the step bunch. Pans are similar, but with reversed steps, and a beam of high energy ions was used to sputter the surface, creating advacancies that expand the pan terrace. The critical constraint that leads to successful synthesis is preventing new steps from nucleating on the terrace, by gradually reducing the driving force of the ion beam as time progresses. A model of this process is presented on the basis of a recent theoretical description that models the flow as a quasistatic process with negligible Gibbs-Thompson forces, so that the evolution is reversible, as observed. The model successfully reproduces the main features of the observations.