Complete Report - University of New South Wales

Thus this represents a QD areal mapping technique. However, the voltage used at present is
high because the oxide layers are quite thick at 5nm. Hence the indicated tunnelling regions
may be either from very small QDs or from higher confi ned energy levels within QDs and only
indicate a lower limit on the QD density. Proof that these do indeed indicate QD locations was
obtained by a subsequent anneal of the sample in an ordinary ambient. A subsequent CAFM
scan showed no white regions, thus showing that the Si QDs had been oxidised in the anneal.
Further experiments will use thinner oxide layers and should give a more complete map of the
QD structure. Scans of such structures at various biases may give further information on
QD size and size distribution by effectively mapping the confi ned energy levels at a very high
areal resolution.
Figure 4.7.8: (a) Current image obtained at 10V applied voltage (probe tip grounded); the
white dots indicate areas of higher current conduction (up to 800 pA); (b) line scan of current
profi le in region shown by red arrow in (a).
125