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

While a perfect hcp (0 0 0 1) surface has threefold symmetry, the diffraction patterns commonly obtained are sixfold symmetric. This apparent change in symmetry occurs because on a stepped surface, the atomic layers on adjacent terraces are rotated by 180'. Here we use a low-eneray electron microscope to acquire the threefold 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. (c) 2006 Elsevier B.V. All rights reserved.