Determining the structure of Ru(0001) from low-energy electron diffraction of a single terrace

TL;DR

This study uses low-energy electron diffraction to analyze a single Ru(0001) terrace, revealing its true three-fold symmetry and surface contraction at high temperature through detailed experimental and computational methods.

Contribution

First direct measurement of a single terrace diffraction pattern on Ru(0001) revealing its true symmetry and precise surface contraction.

Findings

Surface contracted by 3.5% at 456 K

Confirmed three-fold symmetry of a single terrace

Achieved high-quality fit with low Pendry R-factor

Abstract

While a perfect hcp (0001) surface has three-fold symmetry, the diffraction patterns commonly obtained are six-fold symmetric. This apparent change in symmetry occurs because on a stepped surface, the atomic layers on adjacent terraces are rotated by 180 degrees. Here we use a Low-Energy Electron Microscope to acquire the three-fold diffraction pattern from a single hcp Ru terrace and measure the intensity-vs-energy curves for several diffracted beams. By means of multiple scattering calculations fitted to the experimental data with a Pendry R-factor of 0.077, we find that the surface is contracted by 3.5(+-0.9) at 456 K.