Effects of Surface Treatments and Nanocrystal Proximity on Size Quantization in Chemical Bath Deposited Cdse Films and Precipitates
<-- Return to the list
Date: 08-08-2006
Start Time:
2:00pm
End Time: 3:00pm
Speaker: Gary Hodes
From:
Weizmann Institute of Science, Israel
Location: Interschool Lab, 7th floor, Schapiro/CEPSR
Hosted by:
Center for Integrated Science
Abstract:
Surface treatments of nanocrystal surfaces can strongly affect their light emission properties but normally have little effect on the optical absorption of the nanocrystals. Cyanide, which binds strongly to both Cd and S(e) in CdS(e) nanocrystals, is shown to increase the bandgap (blueshift the absorption spectrum) of aggregated nanocrystalline films by up to 0.3 eV, the shift being larger for small crystal size. This is explained by further localization of electrons in the nanocrystals by the negative cyanide. The effect is reversible: the original spectrum is recovered if the cyanide is rinsed off or oxidized. Freshly deposited films, of crystal size  4 nm, undergo a small red-shift (due to electron overlap between neighbouring crystals) upon drying due mainly to capillary forces compacting the films. Subsequent cyanide treatment electronically decouples neighbouring crystals.