ELECTRON LOCALIZATION IN GRANULAR-MATERIALS

We have investigated the structural and electrical properties of granu lar Pd/C as well as granular Au/C thin films. As revealed by transmiss ion electron microscopy the films consist of small metallic clusters o f either Pd or Au embedded within amorphous carbon. Films with low met al volume fraction, x consist of structurally isolated clusters and sh ow exponential resistance behavior. Above the so-called percolation th reshold x(p), metallic clusters form a percolating network rendering m etallic conductivity. For metallic films with x much greater than x(p) we observe two dimensional (2d) electronic transport behavior at low temperatures via small additional contributions to the Boltzmann-resis tance as arising from weak electron localization (WEL) and enhanced el ectron-electron interaction (EEI). When approaching the percolation th reshold these additional resistance contributions grow in absolute mag nitude and the 2d transport behavior changes to 3d-behavior close to x (p). For both cases resistance as well as magnetoresistance data can b e well explained using theories for WEL and EEI in 2d and 3d respectiv ely.