Single layers of isolated, size-controlled silicon nanocrystals were prepared by thermal crystallization of a thin amorphous silicon layer sandwiched between silicon dioxide layers. A subsequent oxidation treatment ensured controlled increase in their lateral separation. The size of the nanocrystals, separation of the nanocrystals (from < 1 nm to ∼ 4 nm), stoichiometry of the resulting oxide and surface morphology were monitored with transmission electron microscopy, scanning transmission electron microscopy, atomic force microscopy, and x-ray photoelectron spectroscopy. Mesoscopic charge transport studies performed with an electrostatic force microscope (EFM) revealed rapid lateral transport of charges when the nanocrystals were tightly packed (< 1 nm average separation) and interconnected. As the inter-nanocrystal separation was increased, lateral charge transport was rapidly suppressed. Nanocrystals separated by up to 3.6 nm retained the injected charges in a well-defined localized region (∼ 62 nm diameter region) for a time of the order of several days. The ability to switch from a very short to a very long retention time using the same structure by simply changing the post-growth processing conditions is attractive for various applications involving charge transport and localization.