Multiple scattering effects on the EXAFS of Ge nanocrystals

We present a detailed extended x-ray absorption fine structure (EXAFS) spectroscopy study on the influence of multiple scattering effects on the analysis of bulk polycrystalline Ge (c-Ge) and of four Ge nanocrystal (NC) distributions with mean sizes from 4 to 9 nm. A complete description of the EXAFS signal up to the third shell of nearest neighbours for both c-Ge and Ge NCs is only achieved by including at least two double scattering and one triple scattering path. Unlike reports for bulk semiconductors and Ge-Si quantum dots, our results show that including only the most prominent double scattering path is insufficient for accurately ascertaining the structural parameters of the second and third shells, leading to unphysically small coordination numbers for the NCs. The same is observed when no multiple scattering paths are taken into account. The size dependence of the interatomic distance distributions up to the third shell of nearest neighbours has been determined for the first time. A greater reduction in coordination numbers and higher structural disorder were observed for the outer shells, reflecting the increase of the surface-to-volume ratio and reinforcing the presence of an amorphous Ge layer between the SiO2 matrix and the NCs. © 2008, Institute of Physic