Item

Abstract

Growth, thermal reaction, and crystalline structure of
ultrathin iron silicide films on Si(111) are studied by low-
energy electron diffraction (LEED) and Auger electron
spectroscopy (AES). The structural development of silicide
layers is monitored in dependence on iron coverage and
annealing temperature. Below approximately 10 monolayers (ML)
of iron, two film structures appear, that are not stable in
bulk material, while above that limit a switch to the bulk
structures is observed. The morphology of the films is strongly
dependent on the growth conditions. Their homogeneity can be
considerably improved by simultaneous deposition
(coevaporation) of Fe and Si in the desired stoichiometry
compared to annealing predeposited Fe films. This improvement
is accompanied by the suppression of pinholes in the film. The
Fe:Si stoichiometry of the (1x1) and (2x2) phase can be
assigned 1:1 and 1:2, respectively. The crystal structure of
the former was previously determined to be CsCl, so called c-
FeSi. For codeposition in 1:2 stoichiometry an initially
disordered (1x1) phase transforms to a well ordered (2x2) phase
after annealing. For these phases, gamma-FeSi2 in CaF2
structure, the tetragonal alpha-FeSi2 or an iron depleted
variant of the CsCl structure are compatible with LEED and
angle resolved AES results. In case of 1:2 stoichiometric
films, the stability range of the (2x2) periodic phase can be
extended to more than 60 Angstrom (equivalent to more than 20
ML Fe) by coevaporation. (C) 2002 American Institute of
Physics.