Local structure of amorphous and nanoscale systems by numerical XANES calculations

We examined sensitivity of the x-ray absorption near edge structure (XANES) to the local atomic arrangements in amorphous GaSb and nanoscale Ge. We demonstrate that XANES can be reliably used to obtain information about the local symmetry in these systems where lack of periodicity precludes the use of powerful diffraction methods. We used well-studied bulk amorphous GaSb as a reference to verify our approach and then extended it to matrix-free Ge nanoparticles. We show that in small (~ 4 nm) Ge nanoparticles prepared by colloidal synthesis where there is evidence for structural disorder, the local tetrahedral (diamond-type) symmetry is still preserved out to the second coordination shell on average. We find the XANES data collected in transmission and optical detection modes for Ge nanoparticles show distinctive differences with the bulk samples and attribute this to particles size and surface effects. This approach is thus capable of delivering structural information on local symmetry, structure and morphology in nanoscale systems.