Electronic properties of single semiconductor nanocrystals: optical and electrostatic force microscopy measurements

We review the room temperature optical and electronic properties of single semiconductor nanocrystals, which are made by chemical synthesis. Confocal luminescence spectroscopy of single nanocrystals reveals a blinking behavio r apparently due to an intermittent photoionization. To investigate this fu rther, the dielectric constant and electrostatic charge of single CdSe nano crystals was measured. The static dielectric constant among single CdSe nan ocrystals is uniform, and its value is consistent with the value of the die lectric constant of the bulk material. However, the electrostatic polarizat ion among individual nanocrystals is non-uniform, with a significant fracti on of the nanocrystals possessing a partial positive charge (Q similar to 0 .5 e), and/or a permanent dipole (P similar to 35 D). A small fraction of t he nanocrystals has a positive polarization, which blinks 'on' and 'off' ov er time. In addition, photoexcitation with frequencies greater than the ban d gap of the nanocrystal results in photoionization. (C) 2000 Elsevier Scie nce S.A. All rights reserved.