STM contrast of a CO dimer on a Cu(1 1 1) surface: a wave-function analysis

TL;DR

This paper introduces a wave-function analysis method to interpret STM contrast by examining substrate and tip wave functions, applied to a CO dimer on Cu(111) surface, enhancing understanding of STM imaging.

Contribution

The paper presents a novel wave-function based approach for intuitive STM contrast interpretation, including wave function optimization and symmetry analysis.

Findings

Effective reduction of wave function combinations in transmission calculations

Enhanced understanding of STM contrast mechanisms for CO on Cu(111)

Method applicable to other surface-adsorbate systems

Abstract

We present a method used to intuitively interpret the STM contrast by investigating individual wave functions originating from the substrate and tip side. We use localized basis orbital density functional theory, and propagate the wave functions into the vacuum region at a real-space grid, including averaging over the lateral reciprocal space. Optimization by means of the method of Lagrange multipliers is implemented to perform a unitary transformation of the wave functions in the middle of the vacuum region. The method enables (i) reduction of the number of contributing tip-substrate wave function combinations used in the corresponding transmission matrix, and (ii) to bundle up wave functions with similar symmetry in the lateral plane, so that (iii) an intuitive understanding of the STM contrast can be achieved. The theory is applied to a CO dimer adsorbed on a Cu(1 1 1) surface scanned by a single-atom Cu tip, whose STM image is discussed in detail by the outlined method.