Multi-step atomic reaction enhanced by an atomic force microscope probe on Si(111) and Ge(111) surfaces

TL;DR

This study uses first-principles calculations to understand how atomic force microscope tips influence adatom exchange reactions on Ge(111) and Si(111) surfaces, revealing mechanisms and energy barrier reductions.

Contribution

It demonstrates that AFM tips can facilitate adatom interchange by altering reaction pathways and lowering energy barriers, providing microscopic insights into atomic manipulation.

Findings

AFM tips reduce energy barriers for adatom migration and exchange.

Dimer structures are spontaneously formed on Ge surfaces but not on Si at room temperature.

Bond formation with the AFM tip is crucial for atom manipulation.

Abstract

We present first-principles total-energy electronic-structure calculations that provide the microscopic mechanism of the adatom interchange reaction on the Sn- and Pb-covered Ge(111)-(2x8) and the Sb-covered Si(111)-(7x7) surfaces with and without the tip of the atomic force microscope (AFM). We find that, without the presence of the AFM tip on the Ge surface, the adatom interchange occurs through the migration of the adatom, the spontaneous formation of the dimer structures of the two adatoms, the dimer-dimer structural transitions that induce the exchange of the positions of the two adatoms, and then the backward migration of the adatom. We also find that the dimer structure is unfeasible at room temperature on the Si surface and the adatom interchange are hereby unlikely. With the presence of the tip, we find that the reaction pathways are essentially the same for the Ge surface but that the energy barriers of the migration and the exchange processes are substantially reduced by the AFM tip. We further find that the AFM tip induces the spontaneous formation of the dimer structure even on the Si surface, hereby opening a channel of the interchange of the adatoms. Our calculations show that the bond formation between the AFM tip atom and the surface adatom is essential for the atom manipulation using the AFM tip.