Atomically resolved STM imaging with a diamond tip: simulation and experiment

Abstract

The spatial resolution of a scanning tunneling microscope (STM) can be enhanced using light element-terminated probes with spatially localized electron orbitals at the apex atom. Conductive diamond probes can provide carbon atomic orbitals suitable for STM imaging with sub-Ångström lateral resolution and high apex stability crucial for the small tunneling gaps necessary for high-resolution experiments. Here we demonstrate that high spatial resolution can be achieved in STM experiments with single-crystal diamond tips, which are generally only considered for use as probes for atomic force microscopy. The results of STM experiments with a heavily boron-doped, diamond probe on a graphite surface; density functional theory calculations of the tip and surface electronic structure; and first-principles tunneling current calculations demonstrate that the highest spatial resolution can be achieved with diamond tips at tip–sample distances of 3–5 Å when frontier p-orbitals of the tip provide their maximum contribution to the tunneling current. At the same time, atomic resolution is feasible even at extremely small gaps with very high noise in the tunneling current.

High Resolution STM Imaging

“…Both images show nonequivalence of the a and b atoms in accordance with the DOS shown in panels (e) and (f) (Panels (a-f) are reprinted with permission from Ref. [57]. Copyright 2014 by IOP Publishing) the W[001] tip (Fig.…”

“…15.33e, f) and the charge density map (Fig. 15.33g) were calculated at a tip-sample distance of 4.5 Å where the orbital structure of the tip and surface atoms is not substantially modified by the interaction and relaxations of the tip and surface atoms are minimal [57]. The excellent agreement between experimental and theoretical images (Fig.…”

“…High spatial resolution has been achieved using the f-orbitals of an Sm atom at the apex of a Co 6 Fe 3 Sm tip [25] and p-orbitals of the light-element atoms at the apexes of Be [52] and conductive diamond tips [53][54][55][56][57].…”

“…15.32) and high apex stability at small tunneling gaps necessary for high-resolution experiments. It has been demonstrated recently that high spatial resolution can be achieved in STM experiments with single crystal diamond tips [57], which are generally considered for use as probes for atomic force microscopy. (Fig.…”

“…In particular, carbon atomic orbitals are further protruded in the z-direction and more localized in the x-y plane than tungsten d-orbitals. DFT calculations [57] reveal a minor difference in the DOS corresponding to the a and b atoms of the graphite surface (Fig. 15.33e, f).…”