Site-specific angular dependent determination of inelastic mean free path of 300 keV electrons in GaN nanorods

Inelastic mean free path (IMFP) of the electron is a very important parameter for quantitative analysis of several electron spectroscopies and transport properties. In spite of being a fundamental material property, its experimental determination is not trivial due to complexity of the various electron scattering processes in matter. In this report, we demonstrate a procedure to determine the IMFP of 300 keV electrons in GaN, using the log-ratio technique where the local specimen thickness needs to be accurately known. The GaN nanorod morphology of the sample used here allows the accurate measurement of thickness by 'thickness map' under EFTEM measurements which enable the site specific determination of IMFP. IMFP for different collection semi angles have also been measured to validate the angular dependence. Our experimental results estimates the IMFP of GaN for 300 keV electrons to be 143 ± 11 nm at no-aperture condition and exhibit a strong inverse angular dependence at smaller collection semi angles (β < 20 mrad) and a near angular independence at larger collection semi angles (β > 30 mrad). We discuss these results in the light of three different theoretical models prevalent in the literature.