Chemistry Reference
In-Depth Information
10.3 Formation and Properties of Nanostructures
10.3.1 Formation of Ge Nanodots
Figure
10.1
shows STM images of Ge nanodots on an ultrathin SiO
2
-covered
Si(001) surface with linear clean Si windows having about 20 nm width after 8ML
thick Ge was deposited on the surface at 400
◦
C. This experiment was performed
using a different apparatus where an ultrahigh vacuum scanning reflection electron
microscope and STM were combined [
10
]. Linear clean Si windows were produced
by irradiating a focused electron beam on ultrathin Si oxide-covered Si(001) at room
temperature and by subsequently annealing the sample at 750
◦
C for 30 s. Selective
thermal decomposition of the Si oxide from the focused electron beam-irradiated
areas produced clean Si windows on the surface [
11
].
Ge nanoislands with
20 nm size were grown on the linear Si windows due to
the SK growth mode. Ge nanodots with less than 10 nm size and the density of
∼
∼
10
12
cm
−
2
were grown on ultrathin Si oxides. The growth mode on the SiO
2
areas
was caused by the chemical reactions of Ge atoms with ultrathin SiO
2
films such
as Ge
SiO(gas) [
5
]. This chemical reaction formed hetero-
geneous nucleation sites for Ge nanodots on the SiO
2
surface region resulting in
ultrahigh density. The Ge nanodot size could be controlled by the total Ge deposition
amount.
Figure
10.2
shows reflection high-energy electron diffraction (RHEED) pat-
terns ((b) and (d)) from the Ge nanodots and their STM images ((a) and (c)). In
+
SiO
2
→
GeO(gas)
+
Fig. 10.1
Three-dimensional and conventional STM images of Ge nanodots grown on ultrathin Si
oxides with linear Si(001) windows. Nanoislands indicated by
arrow
are the same ones
