Chemistry Reference
In-Depth Information
Fig. 11.1
Schematic representation of the step-bunching temperature ranges for different direc-
tions and types of the heating electrical current.
White areas
correspond to the regular steps and
dark areas
relate to the step bunches on the surface
⇔
bunches (SB) was observed on the silicon (111) surface. This RS
SB transition is
dependent on the direction of the heating direct current (DC) and the sample tem-
perature for the same direction of the heating current. This nontrivial dependence
is shown schematically in Fig.
11.1
. Dark areas correspond to the silicon surface
morphology with step bunches and white areas appropriate to the regular distributed
atomic steps on the surface. So DC heating of silicon crystal can drastically change
atomic steps spatial distribution on the surface at elevated temperatures.
The size (the number of steps in the bunch) of step bunch is increased with the
time of DC heating. For the sample heating by an alternative current with a fre-
quency higher than 1 Hz, an uniformly stepped Si(111) surface was stable at any
temperatures [
27
]. It should be pointed out that the origin of surface electromigra-
tion of silicon adatoms that seems to be responsible for step-bunching phenomena
on silicon surface is still under discussion in spite of mutual experimental verifica-
tions.
Thus, there are at least two markable instabilities of the Si(111) surface: step
bunching induced by electromigration at sublimation (at high temperature) and step
bunching induced by surface reconstruction initiated by metal adsorption (at low
temperature). While the importance of these instabilities is obvious and a lot of
papers deal with detailed studies of step bunch instabilities, there is restricted num-
ber of investigations on the influence of the adsorbed atoms on step bunching at
sublimation probably due to problems of carrying out in situ experiments at high
temperatures.
It was reported that submonolayer gold adsorption has strong influence on the
effect of step bunching during sublimation [
28
,
29
]. Gold deposition of 0.003ML
on Si(111) at 950
◦
C changed atomic step behavior. Step bunches, which usually
observed at this temperature on clean silicon surface when the direct current flows in
the step-down direction, dissolved in the system of regular steps after submonolayer
gold deposition. On the contrary, when the direct electrical current flowed in the
