The growth of sodium rough ®lms on mica(0 0 0 1) as determined by helium atom scattering

Elastic helium atom scattering (HAS) and linear optical extinction measurements are used to investigate the growth of sodium (Na) ®lms on mica substrates in the surface temperature range between 90 and 300 K. At half a monolayer (ML) surface coverage we observe a maximum of scattered He intensity, which is addressed to Na atoms that ®ll cleavage-induced holes in the mica surface. It provides a convenient means of calibrating the coverage of the surface. With increasing surface coverage Na clusters are formed on the mica surface. A broad angular distribution of the scattered Helium intensity is observed with a coverage-independent angular width above eight monolayers coverage. From simultaneous optical extinction measurements we deduce that the clusters are oblate with a ratio of semiaxes perpendicular and parallel to the surface plane between 0.23 and 0.165. # 2001 Elsevier Science B.V. All rights reserved.