title: Direct imaging of two-state dynamics on the amorphous silicon surface.
abstract: Amorphous silicon is an important material, amidst a debate whether or not it is a glass. We produce amorphous Si surfaces by ion bombardment and vapor growth, and image discrete Si clusters which hop by two-state dynamics at 295 K. Independent of surface preparation, these clusters have an average diameter of ∼5 atoms. Given prior results for metallic glasses, we suggest that this cluster size is a universal feature. The hopping activation free energy of 0.93±0.15  eV is rather small, in agreement with a previously untested surface glass model. Hydrogenation quenches the two-state dynamics, apparently by increasing surface crystallinity.
authors.affiliation: Beckman Institute for Advanced Science and Technology, University of Illinois, Urbana, Illinois 61801, USA.
authors.forename: S
authors.initials: S
authors.lastname: Ashtekar
authors.forename: G
authors.initials: G
authors.lastname: Scott
authors.forename: J
authors.initials: J
authors.lastname: Lyding
authors.forename: M
authors.initials: M
authors.lastname: Gruebele