The real background and peak asymmetry in diffraction on nanocrystalline metals

A method to analytically calculate the column length distribution (CLD) from a single reflection of a strain-free nanocrystalline metal is proposed. It involves precise estimation of the peak background level using a physical criterion – the positivity of the CLD. The method can be applied to materials showing a dependence of the lattice constant on the crystal size, because of which the diffraction peaks display asymmetry. The analysis can provide an estimation of this dependence. Results for platinum and gold nanocrystals are presented, showing and explaining the different asymmetry of their peaks. By applying the proposed method to diffraction patterns of in situ treated gold nanocrystals, it is shown that the nanocrystal shape changes in response to changing environment.