FAR-INFRARED ABSORPTION BY FRACTAL METAL-CLUSTERS

We show numerically that fractal clusters of metal particles embedded in a dielectric host have a much larger specific absorption in the far infrared than do randomly distributed metal particles. We model the composites as two-dimensional (2D) impedance networks with fractal clusters of Drude-like metal bonds in a background of insulating bonds. The conductivities of the networks are computed exactly using the Y-DELTA-algorithm of Frank and Lobb. The conductivity in the far infrared is found to vary as Re-sigma-e almost-equal-to B(e)p-omega-2 where omega is the frequency and p is the fraction of metallic bonds. The enhancement coefficient B(e) is found to depend primarily on the fractal dimension d(f) and cluster radius R. Reasonable agreement is found with the differential effective-medium prediction B(e) almost-equal-to (R/a) 3(2-df), where a is the length of a single bond.