Shear-strain-induced Spatially Varying Super-lattice Structures on Graphite studied by STM

TL;DR

This study uses STM to observe shear-strain-induced, spatially varying super-lattice structures on graphite, revealing how strain causes complex moire patterns and lattice transformations.

Contribution

It introduces a simple Fourier-based method to understand and simulate shear-strain-induced moire patterns and lattice variations on graphite surfaces.

Findings

Observation of linear fringes and super-lattice structures on graphite surface.

Identification of shear strain as the cause of spatially varying lattice patterns.

Successful simulation of observed patterns using Fourier transform approach.

Abstract

We report on the Scanning Tunneling Microscope (STM) observation of linear fringes together with spatially varying super-lattice structures on (0001) graphite (HOPG) surface. The structure, present in a region of a layer bounded by two straight carbon fibers, varies from a hexagonal lattice of 6nm periodicity to nearly a square lattice of 13nm periodicity. It then changes into a one-dimensional (1-D) fringe-like pattern before relaxing into a pattern-free region. We attribute this surface structure to a shear strain giving rise to a spatially varying rotation of the affected graphite layer relative to the bulk substrate. We propose a simple method to understand these moire patterns by looking at the fixed and rotated lattices in the Fourier transformed k-space. Using this approach we can reproduce the spatially varying 2-D lattice as well as the 1-D fringes by simulation. The 1-D fringes are found to result from a particular spatial dependence of the rotation angle.