Visualization of atomic structure using AFM: theoretical description

TL;DR

This paper presents a theoretical model explaining how AFM can visualize atomic structures, including contrast inversion and false atom artifacts, especially in cases with large contact areas during scanning.

Contribution

It introduces a simple model of AFM image formation considering contact deformations, explaining visualization of atomic structures under specific conditions.

Findings

AFM can visualize atomic structures when contact area exceeds atomic surface area.

Contrast inversion in AFM images can occur due to contact deformation effects.

False atoms may appear in AFM images at atomic vacancies.

Abstract

We suggest simple model of image formation in atomic force microscope (AFM) taking into account contact deformations of probe and sample during scanning. The model explains the possibility of AFM visualization of regular atomic or molecular structure when probe-sample contact area is greater than an area per atom or molecule in surface lattice. (This is usually the case when lattice to be studied has subnanometer unit cell parameters and AFM investigations are carried out in air in contact mode). Two special peculiarities of AFM visualization of two-dimensional lattice could be observed under such conditions: 1) the inversion of contrast of AFM images, and 2) visualization of "false atom" under single atomic vacancy of surface studied.