Determining molecule diffusion coefficients on surfaces from a locally fixed probe: On the analysis of signal fluctuations

TL;DR

This paper refines methods for determining surface molecule diffusion coefficients from signal fluctuations, emphasizing the molecule's size and introducing a new interval distribution method, validated on STM measurements of CuPc molecules.

Contribution

It develops a new method based on interval distributions and compares it with existing autocorrelation and residence time methods for surface diffusion analysis.

Findings

The new interval distribution method provides accurate diffusion coefficients.

Combining multiple methods improves reliability of results.

Application to STM data demonstrates practical effectiveness.

Abstract

Methods of determining surface diffusion coefficients of molecules from signal fluctuations of a locally fixed probe are revisited and refined. Particular emphasis is put on the influence of the molecule's extent. In addition to the formerly introduced autocorrelation method and residence time method, we develop a further method based on the distribution of intervals between successive peaks in the signal. The theoretical findings are applied to STM measurements of copper phthalocyanine (CuPc) molecules on the Ag(100) surface. We discuss advantages and disadvantages of each method and suggest a combination to obtain accurate results for diffusion coefficients.