Lateral manipulation of single iron adatoms by means of combined atomic force and scanning tunneling microscopy using CO-terminated tips

Abstract

CO-terminated tips currently provide the best spatial resolution obtainable in atomic force microscopy. Due to their chemical inertness, they allow to probe interactions dominated by Pauli repulsion. The small size and inertness of the oxygen front atom yields unprecedented resolution of organic molecules, metal clusters and surfaces. We study the capability of CO-terminated tips to laterally manipulate single iron adatoms on the Cu(111) surface with combined atomic force and scanning tunneling microscopy at 7 K. Furthermore, we find that even a slight asymmetry of the tip results in a distortion of the lateral force field. In addition, the influence of the tilt of the CO tip on the lateral force field is inverted compared to the use of a monoatomic metal tip which we can attribute to the inverted dipole moment of a CO tip with respect to a metal tip. Moreover, we demonstrate atom-by-atom assembly of iron clusters with CO tips while using the high-resolution capability of the CO tips in between to determine the arrangement of the individual iron atoms within the cluster. Additionally, we were able to laterally manipulate single copper and silicon adatoms without changing or losing the CO from the tip's apex. arXiv:1804.04382v3 [cond-mat.mes-hall]

Atomically Resolved Chemical Reactivity of Small Fe Clusters

“…In this Letter, we are combining the ability of NCAFM with CO tips to assemble small Fe clusters atom by atom in a controlled fashion [26] with its unprecedented atomic resolution capability to measure the vertical short-range force [F z;SR ðz; c à Þ] on manually created Fe clusters of different sizes (3-15 atoms). F z;SR ðz; c Ã Þ is a function of distance z and c à , the reduced coordination number that refers to the neighboring cluster atoms which can be expressed by using the atom's coordination number c via c à ¼ c − 3 (see Sec.…”

“…Next, Fe clusters containing 3-15 atoms are created via lateral manipulation using CO tips, which allows us to position each atom with atomic precision [26]. The inset of Fig.…”

Quantifying the evolution of atomic interaction of a complex surface with a functionalized atomic force microscopy tip

“…A major breakthrough in nc-AFM was the ability to resolve the internal structure of simple organic molecules in real space 2 , which was enabled by functionalizing a metallic AFM tip apex with a carbon-monoxide (CO) molecule. Since then, CO-terminated tips (CO tips) have been widely applied in AFM experiments to study molecular adsorbates [3][4][5][6][7][8][9] and various types of surfaces and adsorbates with atomic resolution [10][11][12][13][14][15] . The interaction of a CO tip with a sample surface is composed of different physical mechanisms, including van der Waals attraction and Pauli repulsion, which can be described by a Lennard-Jones potential 12,16,17 , and electrostatic interaction between the complex electric field of the CO tip and the sample electron density 12,13,18 .…”

Probing the Nature of Chemical Bonds by Atomic Force Microscopy

“…CO terminated tips also enable atomic resolution of metal clusters [ 61 ]. In spite of their lateral flexibility [ 59 ], these tips have the capability to atomically manipulate metal atoms on surfaces [ 62 ] and to study the chemical reactivity of small metal clusters as a function of the atomic site [ 63 ]. Surprisingly, the reactivity of CO terminated tips scatters somewhat even if the CO tip termination sits at the foremost single front atom of the tip, apparently depending on the tip cluster behind the metal front atom that holds the CO tip molecule (see Figure 1 in [ 63 ]).…”