Structural characterization of as-deposited cesium iodide films studied by X-ray diffraction and transmission electron microscopy techniques

TL;DR

This study investigates the structural properties of cesium iodide thin films of varying thickness using X-ray diffraction and transmission electron microscopy, revealing differences in crystallite and grain sizes and analyzing physical parameters like strain and stress.

Contribution

It provides a comparative analysis of crystallite and grain sizes in CsI films and applies modified Williamson-Hall methods to estimate physical parameters, highlighting differences based on film thickness.

Findings

Less deviation between crystallite and grain sizes in 4 nm films

Significant differences in larger films (20 nm, 100 nm, 500 nm)

Physical parameters like strain and stress are precisely estimated for thicker films

Abstract

In the present work, cesium iodide (CsI) thin films of different thickness have been prepared by thermal evaporation technique. The crystallite size and grain size of these films are compared by using X-ray diffraction (XRD) profile analysis as well as by transmission electron microscopy (TEM) counting, respectively. These two methods provide less deviation between crystallite size and grain size in the case of thin CsI films of 4 nm, but there is comparatively large difference in case of thicker CsI films (20 nm, 100 nm and 500 nm). It indicates that dislocations are arranged in a configuration which causes small orientational difference between two adjacent coherent regions. The size obtained from XRD corresponds to two separate regions, whereas in the TEM micrograph the two regions may seem to correspond one region particularly in case of thicker films. Other physical parameters such as strain, stress and deformation energy density are also estimated precisely for the prominent XRD peaks of thicker CsI films in the range $2\theta = 20^{0}-80^{0}$ by using a modified Williamson-Hall (W-H) analysis assuming uniform deformation model (UDM), uniform deformation stress model (UDSM) and uniform deformation energy density model (UDEDM).