Grazing-incidence small-angle X-ray scattering study on ultrananocrystalline diamond films

• First grazing-incidence small-angle X-ray scattering study of ultrananocrystalline diamond.
• Data analysed by modelling with monodispersed spherical diamond grains.
• Obtained grain size: 8.0-8.5 nm corresponds well to comparable TEM images.
• The crystallites do not touch each other with minimum distance of 2-4 nm.
• GISAXS is a non-destructive method providing averaged in-plane information in excellent sampling statistics without any sample preparation.

In this work, an ultrananocrystalline diamond film was studied with grazing-incidence small-angle X-ray scattering (GISAXS) to determine the diamond grain size and average distance of the grains with a non-destructive method and with excellent sampling statistics. The measured 2D GISAXS patterns were modelled with the assumption of monodisperse spheres. The best fits were obtained with the "buried layer" model where the spheres are correlated within the film plane. This correlation was approximated with a two-dimensional Percus–Yevick structure factor. The average diamond grain size of D = 8.0–8.5 nm and a centre-to-centre distance of the grains with 10.4–11.9 nm agrees well with transmission electron microscopy results of comparable samples.