to be presented in American Vacuum Society, Seatle, USA, Oct. 1999.
Lateral compression of a Xe film physisorbed on the surface of a silver single crystal
S. Igarashi, A. Tosaka, T. Hirayama, and I. Arakawa
1Department of Physics, Gakushuin University, Toshima, Tokyo 171-8588,Japan
The layering transition of a physisorption system on a metal single crystal
has been investigated by means of an ellipsometry and an
eXtremely-low-current LEED (XLEED). Our XLEED system is operated at the
primary electron current of about 1 pA or less, which minimizes the effect
of desorption, defect formation, and charging.[1] We observed the surface
structure of Xe/Ag(111) by XLEED while monitoring the layer growth by the
ellipsometry from a submonolayer film to a thick one. An equilibrium
between the Xe film and coexisting three-dimensional Xe gas has been
maintained throughout the experiment. From a monolayer film to a
sufficiently thick film, the Xe overlayer has clear hexagonal structure
whose directions of the unit vectors are coincident with those of the
substrate. The Xe-Xe spacing in the monolayer film on Ag(111) is known to
be a few per cent larger than that of bulk. Our interest is how the Xe-Xe
spacing varies in the process of layer growth. We have made a systematic
observation of the change of the Xe-Xe spacing in one and two monolayer
films at pressures between 10-7 and 10-2 Pa and at temperatures between 50
and 100 K. In the case of isothermal growth at 78.4 K, for example, the
Xe-Xe spacing of the monolayer film is 4.53 A at immediately after the first
layer condensation at 1x10-5 Pa and decreases gradually to 4.5 A with increa
sing a surrounding pressure up to 1x10-3 Pa. Then the spacing decreases
rapidly and reaches almost that of bulk, 4.39 A just before the second layer condensation at the pressure of 4x10-2 Pa.
[1] S. Igarashi, Y. Abe, Y. Irie, T. Hirayama, and I. Arakawa, J. Vac. Sci. Technol. A16, 975 (1998).