Surface patterning by atomically-controller chemical forces: molecular dynamics simulations

The use of atomi~ly-controlled reactive chemical forces via modified sca~~g-probe microscope tips provides a potentially powerful way of building nanodevices. In this work, we use atomistic simulations to explore the feasibility of one such system, namely the selective abs~action of hydrogen from a diamond surface using a tip with a chemisorbed ethynyl radical. We characterize reaction rates and energy flow at the tip, and conclude that they are sufficiently fast to make this approach feasible. We propose a novel tip design to perform the abstraction without inadvertently damaging the surface or probe tip. Sc~~g-~nneling microscopy (STM) and atomicforce microscopy ( AFM) are powerful techniques not just for imaging, but also for the engineering of matter at the atomic scale. To date, the manipulation of atomic structures with these techniques has included the controlled movement of atoms on surfaces by “sliding’” the tip across the sample [ 11, the pick-up and movement of chemisorbed species by careful control of both the position and the potential difference between the tip and the surface [ 2 3, and the transfer of species from the tip to the surface by field emission [ 31. Some of these atomic-scale manipulations are a result of the application of chemical forces in combination with field-induced forces. One approach that has yet to be realized, however, is the exploitation of specific chemical reactions with the atomic-scale precision offered by the AFM. If mastered, this approach would provide another importaut method for engineering new materials and devices at the atomic scale. An ingenious use of reactive chemical forces has recently been proposed by Drexler [4], where he sug* ~~es~nding author. E-mail: si~ot~alchemy.~~.navy.~l. gested an ethynyl radical attached to the end of an STM or AFM tip could abstract hydrogen from a diamond surface with atomic-scale precision through the reaction: tip-C=C + H~iamond + tipC=CH + di~ond,