Synchrotron X-ray diffraction in air and vacuum: Strain and structure at the nano-scale

The simultaneous use of symmetric and grazing incidence X-ray diffraction in the characterisation of a pnictide material is demonstrated using MnSb epi-layers grown on compound semiconductor substrates. This combination of diffraction geometries enables a comprehensive determination of the lattice parameters and complex structural behaviour of MnSb. For example, in the ultra-thin limit (<5 nm) of layers grown on GaAs an evolution from coherently strained to relaxed islands is observed with increasing thickness. However, a mixture of both strained and relaxed islands is seen beyond the calculated critical thickness. As film thickness increases, a cubic polymorph is observed and the relative content of this polymorph was probed using reciprocal space maps. Finally, recent surface X-ray diffraction work performed under ambient conditions is compared with similar data obtained at ultra-high vacuum conditions. The information found using these complementary diffraction geometries can readily be applied to a range of compound semiconductors.