Kinetics of silver photo-diffusion in Ag/GeS2 films: observation of the layer structure in the depth direction and the large-scale in-plane structure by specular neutron reflection and off-specular neutron scattering

This study delves into the kinetics of silver photo-diffusion in Ag/GeS2 films, focusing on the layer structure in both depth and lateral directions. Through specular neutron reflection and off-specular neutron scattering, the research reveals the formation of an Ag-rich reaction layer and the subsequent diffusion of Ag ions into the GeS2 host layer. The findings highlight the two-step diffusion process, where Ag ions first form a metastable reaction layer and then diffuse into the host layer, leading to a uniform reaction layer. Additionally, the study observes the formation of a GeO2 oxide layer on the surface due to photo-oxidation, which significantly roughens the surface. The research also compares the diffusion kinetics between Ag/GeS2/SiO2 and Ag/GeS2/Si substrates, noting differences in the persistence of the dip in the scattering length density profile and the extent of surface roughening. The implications of these findings are crucial for the development of optical devices and memory applications, where understanding the diffusion kinetics is essential for optimizing device performance.