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

Figure 17 Absorption (solid lines) and emission spectra (dash-dotted lines) for twotypes of core–shell for different shell thickness. Left frame: InAs/CdSe core–shells;the nominal shell thickness and QY from bottom to top are core = 0.9%, 0.7 ML =11%, 1.2 ML = 17%, and 1.6 ML = 14%. Right frame: InAs/ZnSe core–shells; thenominal shell thickness and QY from bottom to top are core = 0.9%, 0.7 ML =13%, 1.3 ML = 20%, and 2.2 ML = 15%.difference with respect to the bandgap shift can be attributed to the differentband offsets of the two shell materials compared with InAs. For ZnSe, largeband offsets lead to confinement of the CB and VB ground states to the coreregion and the bandgap therefore remains intact upon shell growth. ForCdSe, due to the significantly smaller CB offset and the light electron effectivemass in InAs, the 1S e state is delocalized from the core into the shell regionand is therefore red-shifted upon shell growth.B. Tunneling and Optical Spectroscopy Of InAs/ZnSeCore–ShellThe combined tunneling and optical spectroscopy approach has been appliedto further investigate the effect of shell growth on the electronic structure [72].Figure 18 shows tunneling–conductance spectra measured on two InAs/ZnSecore–shell nanocrystals with 2 and 6 ML shells, along with a typical curve forCopyright 2004 by Marcel Dekker, Inc. All Rights Reserved.