Using LEED spot profile analysis (SPA-LEED) and thermal programmed desorpti
on spectroscopy (TDS), the pure Kr/NaCl(1 0 0) system and its mixture with
Xe has been studied. As substrate thin epitaxial NaCl films on a Ge(1 0 0)
substrate have been used. Kr in the monolayer (MC) regime forms a faint (2
x 1)pmg structure with glide plane symmetry, whereas the second layer forms
a quadratic lattice with a lattice constant close to the Kr bulk value. Fr
om the phase diagram for Kr condensation into the first and second monolaye
r heats of condensation of 9.5 +/- 2 and 9.0 +/- 2 kJ/mol have been derived
, respectively. These are significantly lower than those obtained from TDS.
Mixtures of Kr with preadsorbed Xe have been studied for preadsorbed Xe co
verages 0 less than or equal to Theta (Xe) less than or equal to 3 ML under
isobaric Kr pressures between 10(-7) less than or equal to p(Kr) less than
or equal to 10(-6) mbar and at surface temperatures between 35 less than o
r equal to T less than or equal to 60 K. Emphasis is put on investigations
of the first monolayer. The phase transition of Kr condensation into the fi
rst monolayer is shifted to higher transition temperature and broadens for
the mixtures. Whereas no new ordered structures have been observed compared
with the pure Xe and Kr systems, atomic mixture in the first layer is conf
irmed by the observation of a continuously varying average lattice constant
in one direction between the (2 x 1)pmg and the distorted hexagonal struct
ure of Xe. A miscibility gap depending on T, pK, and Ex, is found. At T, of
Kr condensation in the first layer, the solubilities are s(Kr) similar to
0.25 and s(Xe) similar to 0.3. For p(Kr) > 5 x 10(-7) mbar the miscibility
gap closes prior to the transition to a Kr three-dimensional layer. The mix
ture of Kr into the first layer of Xe is even observed for preadsorbed Xe c
overages above one monolayer. (C) 2001 Elsevier Science B.V. All rights res
erved.