Color Atomic Force Microscopy with on-the-fly Morse parameters mapping

TL;DR

This paper presents a novel AFM control scheme and data analysis method that enable rapid chemical contrast imaging by mapping Morse potential parameters at the pixel level.

Contribution

It introduces a new control and mathematical approach for fast potential field mapping in AFM, specifically using Morse parameters for chemical contrast.

Findings

Robust control in UHV at low frequencies

Successful identification of Morse parameters per pixel

Resolution of decay length parameter at 10 pm

Abstract

Atomic Force Microscopy has enabled 2D imaging at the sub-molecular level, and 3D mapping of the potential field. However, fast identification of the surface still remains a challenging topic. In this paper, as a step towards implementation of such function, we introduce a control scheme and mathematical treatment of the acquired data that enable retrieval of essential information characterizing the potential field, leading to fast acquisition of images with chemical contrast. The control scheme is based on tip sample distance modulation at an angular frequency of ${\omega}$, and null control of the ${1\omega}$ component of the self excitation frequency of the oscillator. It is demonstrated that the control is robust in UHV for a frequency well as small as a few Hz/MHz, and that the mathematical treatment results in satisfactory identification of the potential field. Morse potential is chosen as a case study for identifying the Morse parameters per pixel. Atomic features with similar topography were distinguished by differences in the parameters. The decay length parameter was resolved with a resolution of 10 pm. The method was demonstrated on quenched Silicon at a scan rate comparable to normal imaging.