  This manuscript describes the evolution of grain structures in Cesium Halide
films which results in appearance of Surface Plasmon Resonance (SPR) peaks in
UV-visible absorption spectra. Thin films of Cesium Halide grown by thermal
evaporation are polycrystalline in nature with large irregular tightly packed
grains with sharp grain boundaries. With time these grain boundaries recede to
become smaller and 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. These defects which appear due to
the absence of massive halide atoms from the lattice results in residual
tensile stress within the lattice which results in defect diffusion. The
defects migrate outwards towards the grain surface giving rise to Cesium metal
clusters. The lattice mismatch appearing between the lattices at the grain
boundary and the bulk giving rise to Core-shell structure further contributes
to grain division. Along with this volume diffusion, a surface diffusion of
Cesium takes place towards sites of faceted grain boundaries resulting in a
necking phenomenon, appearing like bridges between the daughter Cesium Halide
grains (grains appearing due to division of a single grain). Breaking away of
the daughter Cesium Halide grains results in nano-rods that contribute to the
SPR peak seen.
