Copyright 2004 by Marcel Dekker, Inc. All Rights Reserved.

Figure 14 (a) Tunneling spectra measured on InAs QDs f2 nm in radius. Thesolid curve was measured in the QD/HOPG geometry, and the dashed curve wasmeasured in the QD/linker molecule/Au geometry. (b) Calculated spectra showingthe effect of tunneling-rate ratio. The dashed and solid curves were calculated withG 2 /G 1f1 and 10, respectively.geometry, possibly due to small degeneracy lifting within the s and p states.We note that the charging multiplets were absent even when the peaks didnot exhibit significant broadening (e.g., the s peak in the upper curve of Fig.16). A similar behavior is seen also for the more complex VB. We attributethe difference between the two spectra to the different tunneling-rate ratiosG 2 /G 1 achieved in either of the DBTJs. A significantly lower tunnel barrier ofthe QD–substrate junction is expected in the QD/HOPG configuration.To confirm this interpretation, we performed theoretical simulationsusing the method described in Section II. The solid and dashed theoreticalcurves presented in Fig. 14b were calculated assuming twofold and sixfolddegenerate (s and p) CB levels and two fourfold degenerate VB states. TheCopyright 2004 by Marcel Dekker, Inc. All Rights Reserved.