Examination of even–odd distinction in magnetic susceptibility of silver nanoclusters on silver bromide in light of the Kubo effect

Abstract

Silver nanoclusters were formed on octahedral AgBr microcrystals by light and reduction, and characterized by examining their even–odd distinction in light of the Kubo effect. It was observed with an electron microscope that only one Ag cluster per microcrystal was formed by light, while many clusters per microcrystal were formed by reduction. It was found that the average magnetic susceptibility of Ag clusters formed by light was more than 3 orders of magnitude larger than that of Ag clusters formed by reduction when the average size and concentration were the same between them. According to the Kubo theory [R. Kubo, J. Phys. Soc. Jpn. 17, 740 (1962)], Ag nanoclusters should be electrically neutral, and the clusters composed of odd number of Ag atoms (i.e., odd clusters) should be paramagnetic, while even clusters should be diamagnetic. It is therefore considered that the clusters formed by reduction were even clusters, while the clusters formed by light contained many odd clusters. In accord with the Kubo theory that the electron-accepting level of an odd cluster should be lower than that of an even cluster with the same size, the activation energy of the rate of photographic development initiated by Ag clusters formed by light was smaller than that by Ag clusters formed by reduction. The above-stated results proved the hypothesis that the reduction of AgBr microcrystal directly formed Ag dimers, which were stabilized at surface kink sites to act as reduction sensitization centers and coagulated to form Ag nanoclusters when the sites were saturated with Ag dimers.