Na Adsorption on the Si(111)-(7 × 7) Surface: From Two-Dimensional Gas to Nanocluster Array - Kehui Wu; Y. Fujikawa; T. Nagao; Y. Hasegawa; K.S. Nakayama; Q.K. Xue; E.G. Wang; T. Briere; V. Kumar; Y. Kawazoe; S.B. Zhang; T. Sakurai (Physical Review Letters, 2003)