A thin Ag film was formed on an Si(1 0 0) substrate at 200 degreesC in UHV, and the Ag film resistance was measured up to a 15-nm thickness by the four-terminal method. The same measurement was performed using an H terminated Si(I 0 0) substrate, where measurements were carried out at 200 degreesC. In the case of the Si/Ag system, the resistance change showed a regular oscillation period for every 0.56 nm of Ag film thickness up to 2 nm. This oscillation period corresponds to that of an Ag dimer's length, and the same oscillation period was obtained for different substrates. This phenomenon suggests that electron. conduction is mainly limited to Very thin surfaces with an Si/Ag interface and to each Ag island. An Ag island works as a quantum dot (QD) whose conduction electron density changes periodically depending on the island's dimensions. In the case of the Si/H/Ag system, H appears to block the electron coupling between Ag and Si. Here, oscillation in resistance change also occurs, but for every 0.25 nm of Ag film thickness up to 1 nm. (C) 2002 Elsevier Science B.V. All rights reserved.