Incommensurability and atomic structure of c(2x2)N/Cu(100)

TL;DR

This study uses low-temperature STM to analyze the atomic structure of Cu2N on Cu(100), revealing incommensurate lattice mismatch and defect characteristics that influence surface chemistry and electronic properties.

Contribution

It provides detailed atomic-level characterization of Cu2N on Cu(100), including lattice mismatch, defect identification, and bias-dependent imaging, advancing understanding of surface self-assembly.

Findings

Cu2N lattice is 3% larger than Cu(100) surface.

Bias voltage affects STM image contrast.

Four types of defects identified and characterized.

Abstract

We use a scanning tunneling microscope operating in a low temperature, ultrahigh vacuum environment to study the atomic structure of single layer films of Cu2N grown on Cu(100). The c(2x2) lattice of Cu2N is incommensurate, with a lattice constant of 3.72 +/- 0.02 angstrom that is 3% larger than the bare Cu(100) surface. This finding suggests that strain due to lattice mismatch contributes to self assembly in this system. We find that the image contrast on Cu2N islands depends on bias voltage, which reconciles several interpretations in the literature. We assign features in these STM images to the Cu, N and hollow sites in the Cu2N lattice with the aid of co-adsorbed CO molecules. This atomic registry allows us to characterize four different defects on Cu2N, which influence the sticking coefficient and electronic coupling of adsorbates.