Positron probing of quantum dots

CdSe quantum dots (QDs) of different sizes were deposited as thin layers on glass slides and examined by positrons with the two detector coincident Do ppler broadening technique (coPAS). Dots of 2.5 and 3.6 nm size were compar ed to the larger 4.4 nm size. It appears that the data on the smaller size (2.5 nm) display a shape consistent with positrons annihilating with electr ons confined in the quantum dots. The next larger size is on the limit of Q D behavior. The observed broadening in the annihilation line for the smalle st size sample is consistent with annihilation with quantum-dot confined el ectrons. (C) 1999 Elsevier Science B.V. All rights reserved.