Atom-By-Atom Extraction Using the Scanning Tunneling Microscope Tip-Cluster Interaction

We investigate the atomistic details of a single atom-extraction process realized by using the scanning tunneling microscope tip-cluster interaction on a Ag(111) surface at 6 K. Single atoms are extracted from a silver cluster one atom at a time using small tunneling biases less than 35 mV. Combined total energy calculations and molecular dynamics simulations show a lowering of the atom-extraction barrier upon approaching the tip to the cluster. Thus, a mere tuning of the proximity between the tip and the cluster governs the extraction process. The atomic precision and reproducibility of this procedure are demonstrated by repeatedly extracting single atoms from a silver cluster on an atom-by-atom basis.

Figure 1

Atom extraction. (a) A 3D STM image of a silver nanocluster deposited by tip-surface contact. The tip is brought close to the protruded part of the cluster and then moved laterally towards a destination on the surface. (b) The STM image acquired after this shows a height reduction of the cluster protrusion and the extracted atom on the surface destination. (c) The manipulation signal of this event reveals the atomistic details of the atom extraction. (d) The drawings demonstrating the two types of tip-height peaks.

Figure 2

Atom-by-atom extraction sequence. A sequence of STM images from an STM movie [21] shows atom-by-atom extraction from a silver cluster. This series proves the reliability of our atom-extraction process.

Figure 3

Threshold resistance and tip height. (a) ${\mathit{L}}_{\mathrm{atom}}/{\mathit{L}}_{\mathrm{tip}}$ versus tunneling current at a fixed bias of 18 mV shows a characteristic step function at 400 nA. (b) The threshold tunneling current versus bias plot shows a linear relationship. ${\mathit{R}}_{\mathrm{th}}$ is determined from the slope of this curve. (c) The tip-cluster distance of 0.6 Å corresponding to ${\mathit{R}}_{\mathrm{th}}=47\pm 2\mathrm{k}\Omega$ is obtained (shown with a dashed line) from the tunneling resistance versus tip-height plot. (d) A model demonstrates the tip-cluster distance of 0.6 Å to extract the topmost cluster atom.

Figure 4

Theoretical modeling. (a) The geometry of the tip, adatom, cluster, and silver substrate used for the calculation. (b) The minimum energy diffusion path of the atom after extraction. (c) Transfer of the atom from $A$ to $B$ and from $B$ to $A$ will cost the same energy. (d) The energy barrier for atom extraction vs the tip-cluster distance plot.