We investigated the sensitivity of x-ray absorption near-edge structure (XANES) to the atomic structure of small (~ 4 nm) matrix-free Ge quantum dots. FDMNES package was used to calculate the theoretical XANES spectra that were compared to the experimental data of as-prepared and annealed nanoparticles. We found that XANES data for as-prepared sample can only be adequately described if the second coordination shell of the diamond-type structural model is included in FDMNES calculations. This is in contrast to the extended x-ray absorption fine structure data that show only the first shell signal. These results suggest that despite the high degree of disorder and a large surface-to-volume ratio, as-prepared small Ge quantum dots retain the diamond-type symmetry beyond the first shell. Furthermore, we utilised this sensitivity of XANES to the local symmetry to study annealed Ge quantum dots and found evidence of the signal we attribute to a metastable Ge phase.
Accepted by Journal of Synchrotron Radiation (AHEAD of PRINT)