The growth of sodium rough films on mica(0001) as determined by helium atom scattering

Elastic helium atom scattering (HAS) and linear optical extinction measurem ents are used to investigate the growth of sodium (Na) films on mica substr ates in the surface temperature range between 90 and 300 K. At half a monol ayer (ML) surface coverage we observe a maximum of scattered He intensity, which is addressed to Na atoms that fill 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 mi ca surface. A broad angular distribution of the scattered Helium intensity is observed with a coverage-independent angular width above eight monolayer s coverage. From simultaneous optical extinction measurements we deduce tha t the clusters are oblate with a ratio of semiaxes perpendicular and parall el to the surface plane between 0.23 and 0.165. (C) 2001 Elsevier Science B .V. All rights reserved.