Simulated engineering of nanostructures

Results are reported from two molecular-dynamics simulations designed to yield insight into the engineering of nanometre-scale structures. The first is the initial stages of the indentation of a silicon substrate by an atomically-sharp diamond tip. Up to an indentation depth of approximately 0.6 nm the substrate responds elastically and the profile of the disturbed region of the substrate normal to the surface reflects the shape of the tip apex. The disturbed region in the plane of the surface, however, reflects the symmetry of the substrate rather than that of the tip. As indentation progresses the damage to the substrate becomes irreversible, and the profile of the damage normal to the substrate surface approximately matches that of the tip, while the in-plane profile appears roughly circular rather than displaying the symmetry of either the tip or substrate. The tip maintains its integrity throughout the simulation, which had a maximum indentation depth of 1.2 nm. The second study demonstrates patterning of a diamond substrate using a group of ethynyl radicals attached to a diamond tip. The tip is designed so that the terrace containing the radicals has an atomically-sharp protrusion that can protect the radicals during a tip crash. At contact between the tip and substrate the protrusion is elastically deformed, and five of six chemisorbed radicals abstract hydrogen atoms during the 1.25 ps the tip is in contact with the surface. Displacement of the tip an additional 2.5 Å, however, results in permanent damage to the protrusion with little deformation of the substrate.