Probing electron charging in nanocrystalline Si dots using Kelvin probe force microscopy

By using Kelvin probe force microscopy, we investigate the contact potential difference (CPD) of nanocrystalline silicon (nc-Si) dots with various sizes before and after the dots charging. Few electrons are injected into the nc-Si dots using the atomic force microscope tip. A remarkable change in the dot potential is observed under the normal ambient conditions. Since the change in the dot potential represents the charging energy of the nc-Si dots, the number of electrons stored in the individual dots can be estimated by comparing the calculated charging energy and the measured CPD change caused by charging. We demonstrate that charge quanta are indeed injected and directly detected by this method by analyzing the dot diameter dependence of the CPD change for each dot.