Long range orientation of meta-stable atomic hydrogen adsorbate clusters on the graphite(0001) surface

We present scanning tunneling microscopy (STM) images of meta-stable hydrogen adsorbate structures on the highly oriented pyrolytic graphite (HOPG) (0 0 0 1) surface and identify two unique and stable hydrogen structures. One of these is observed after thermal anneals to 525 K at both high and low hydrogen coverage and is identified as a hydrogen dimer structure. The other, a novel, more complex structure not previously observed, appears only after thermal anneals at high hydrogen coverage and is observed to exhibit long range orientation within each micro-crystallite region on the HOPG surface. (C) 2007 Elsevier B.V. All rights reserved.