Large scale inhomogeneities in granular metals

We present direct evidence for large-scale inhomogeneities in granular metal films. Using Rutherford backscattering data and measurements of the superconducting critical fields, we show that granular materials (Al:Al2Te3 and Al:Al2O3) are deposited in layers. Each film contains 3–5 layers approximately 400 A thick. The layer thicknesses are significantly less than the film thicknesses and are of the order of the coherence length. This layering has significant consequences when using such films to investigate dimensionally dependent theories.