S. Yoshida et al., Dynamic observation of reaction processes of Pd with Si on a Si(111)7x7 surface after thermal treatment using UHV-STM, LANGMUIR, 15(20), 1999, pp. 6813-6820
Dynamic transformation in the surface structure and the morphology of Pd-de
posited Si(lll) 7 x 7 surfaces with thermal treatment was observed using ul
trahigh vacuum scanning tunneling microscopy (UHV-STM). After Pd was deposi
ted on the surface at a coverage of <1 monolayer (ML) or >2 ML, the surface
reactions of Pd with Si on a Si(lll) 7 x 7 surface were studied in detail
depending on the annealing temperature by observing the real-space STM imag
es. At a low coverage of <1 hit, two-dimensional islands composed of Pd2Si
single crystals were clearly observed to be formed epitaxially after anneal
ing at 300 degrees C via the surface thermal reaction. The STM observation
permitted the identification of Pd2Si crystals from the six-fold symmetry l
attice of protrusions with root 3 x root 3R30 degrees structure on the Si(l
ll) surface. At a high coverage of >2 ML, Pd2Si crystals were observed to g
row epitaxially to form the films at 200 degrees C. In addition, after sequ
ential annealing, a specific superstructure, which has a 3 root 3 x 3 root
3B30 degrees structure on the Si(lll) surface, appeared over the Pd2Si surf
ace at 300 degrees C. This specific structure was demonstrated to be due to
Si segregation; that is, the inner Si diffused out from the silicide layer
as a result of the thermal treatment.