We report on detailed and systematic investigations of the structural
properties of thin (t < 32 nm) granular PdxC1-x films with 0.1 < x < 0
.5, where x is the metal volume fraction. The films are prepared by co
evaporation of palladium (Pd) and carbon (C) onto quartz- and NaCl-cry
stal substrates at room temperature in an uhv system. Since carbon is
known to be insoluble in palladium within the whole composition region
, we obtain granular PdxC1-x films retaining their typical granular st
ructure upon large variations of the metal volume fraction x. As revea
led from transmission electron microscopic (TEM) investigations, granu
lar PdxC1-x films with x < 0.3 consist of mainly isolated small Pd clu
sters with mean diameters Phi of a few nanometers embedded in an amorp
hous carbon matrix. With increasing x clusters progressively coagulate
, until at a certain metal volume fraction x(p) = 0.3 -which is the so
-called percolation threshold-an infinite percolative network exists t
hroughout the entire sample. From the analysis of TEM micrographs, we
obtain size distributions for both cluster diameter Phi and cluster se
paration a for various films with different x, from which we obtain me
an values as well as typical values for Phi and s with respect to the
metal volume fraction x. This offers a quantitative comparison of the
structural properties of a real granular system with that of a simple
cubic model, often proposed being appropriate to describe the structur
al properties of granular systems.