Defect diffusion assisted formation of cesium metal clusters in cesium halide thin films

Abstract

This manuscript describes the evolution of grain structures in cesium halide films which leads to localized surface plasmon resonance (LSPR) peaks in UV–visible absorption spectra. Thin films of cesium halide age with time as grain boundaries recede making grains spherical in shape in order to minimize the free surface energy of the system. The process is also assisted by the presence of point defects/color centers in cesium halide films. The defects migrate outwards towards the grain surface, giving cesium metal clusters at the surface, resulting in core–shell structure. Along with volume diffusion, a surface diffusion of cesium takes place towards sites of facet grains boundaries resulting in a necking phenomenon, appearing like bridges between the daughter cesium halide grains (grains appearing due to the division of a single grain). Breaking away of the daughter cesium halide grains results in nano-rods that contribute to the SPR peak seen.