AVS 50th International Symposium
    Surface Science Tuesday Sessions
       Session SS2-TuM

Invited Paper SS2-TuM1
The Dynamics of Crystallite Shape Transformations

Tuesday, November 4, 2003, 8:20 am, Room 328

Session: Nucleation and Growth
Presenter: J.E. Reutt-Robey, University of Maryland
Authors: J.E. Reutt-Robey, University of Maryland
D.B. Dougherty, University of Maryland
Correspondent: Click to Email
At the nanoscale, the shape of a crystallite is remarkably sensitive to the local chemical potential. While much is known about equilibrium crystal shapes (ECS), the mechanism and rate by which a crystallite morphology evolves in response to abrupt changes in temperature and gaseous environments are largely unknown. Using variable temperature STM as our experimental probe, we have investigated the reshaping dynamics of submicron lead crystallites prepared in their near-ECS on Ru(OOO1). In the case of chemical (oxygen) adsorption, we observe a dramatic particle reshaping into a heavily faceted structure.@footnote 1@ We show that this reshaping is triggered by surface impurities, which are needed to nucleate lead oxide grains. Once nucleated, an oxide grain grows laterally on the crystallite surface in an apparent autocatalytic process. Although nucleation is temperature insensitive, subsequent oxide grain growth rates depend on temperature, presumably due to limiting lead mobility at our temperature of investigation. These results are consistent with independent measurements of step fluctuation kinetics. We show how temperature reduction leads to a "flattening" of supported neat crystallites through a monolayer-by-monolayer peeling mechanism.@footnote 2@ From the step peeling kinetics, and simulations with continuum models, we find that the kinetics of monolayer peeling is limited by multi-layer relaxations. Atomistically, these relaxations represent limited mass transfer across the curved facet boundary. Within the thermal window of our measurements, we show that particle reshaping is not reversible and discuss the limiting nucleation barriers.@footnote 3@ @FootnoteText@ @footnote 1@K. Thurmer, E. Williams, and J.E. Reutt-Robey, Science 297, 33-35 (2002). @footnote 2@K. Thurmer, J.E. Reutt-Robey, E.D. Williams, M. Uwaha, A. Edmundts, H.P. Bonzel, Phys. Rev. Lett. 87 (2001) 186102. @footnote 3@K. Thurmer, J.E. Reutt-Robey, E.D. Williams, Surf. Sci., in press.