(a)Department of Materials Science and Engineering; North Carolina State University; Raleigh, NC 27695-7907.
(b)Department of Chemical and Materials Engineering; University of Kentucky; Lexington, KY 40506-0046.
(c)Chemistry Department; United States Naval Academy; Annapolis, MD 21402.
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Molecular-dynamics simulations can bridge the gap between theory and practice by providing extremely well-controlled `experimental' conditions under which many-body dynamics can be probed with atomic-scale resolution. In addition, atomically-resolved stresses and related mechanical properties can be determined exactly through the interatomic forces. Taking advantage of these features, we have been using atomistic simulations to model and predict routes to the engineering of novel structures and devices at the atomic and nanometer scales. This talk will cover two recent areas of our efforts. The first is the detailed simulation of tip-surface dynamics. In these calculations, stress distributions in hydrogen-terminated diamond and silicon tips have been estimated and related to their elastic-to-plastic behavior and failure. From the results of these simulations we are developing detailed models for the deliberate engineering of nanostructures using atomic-force microscopy, including the influence of the crystallographic orientation of the substrate, tip shape, composition, and applied normal and shear forces.
The second part of the talk will focus on a series of atomic trajectories of ethynyl radicals chemisorbed onto a scanning-probe microscope tip that are used to pattern a diamond substrate via hydrogen abstraction (an idea first suggested by Eric Drexler). Energy flow and reaction rates are characterized, and we conclude that they are sufficiently fast to make this approach feasible. We will also discuss the use of `load sensors', angstrom-scale asperities that surround a reactive site and provide protection from tip crashes as well as a signal via the load on the tip that abstraction has likely occurred.
*Supported in part by the Office of Naval Research and the National Science Foundation.