FRACTAL INTERNAL INTERFACES IN NANOSTRUCTURED AMORPHOUS SI-AU-ALLOYS

Small Angle Neutron Scattering (SANS) was employed to characterize the microstructure of nanostructured amorphous Si1-xAux alloys (0.1<x<0.3 5). Contrast variation of SANS by immersion in liquids has been shown to be a powerful tool to identify the scattering contributions in thes e nanostructured samples. At small values of the momentum transfer Q t he SANS intensity decreases according so a power law d sigma(Q)/Omega similar to Q(-3.37), due to the scattering of a surface fractal struct ure of dimension D-S=2.63. This fractal structure is the internal surf ace between regions of highly densified amorphous material and agglome rates of free volumes, forming a system of interconnected channels acr oss the whole sample. Filling the pore system with a contrast liquid l eads to a strong change of the scattering intensity, while the exponen t alpha=3.37 of the low Q power law remained unchanged. The results ve rify the fractal nature of the internal surface, as well as the micros tructural concept of dense nanometer-sized amorphous grains embedded i n a less dense ''matrix'' formed by grain boundaries and free volumes. Using C6D12, CS2 and D2O, a molecule-size effect of different access to smaller pores was observed.