Sulphurization of In thin films using Bi2S3 and Sb2S3 and self-organized fabrication of In2S3 nanodots by electrochemical etching

Thin In films are exposed to the vapor of Sb₂S₃ and Bi₂S₃ at high temperatures for sulphurization. The release of Sb and Bi in the reaction alters the properties of the synthesized $\beta$-In₂S₃ films by introducing surfactant effects. For using Sb₂S₃, the texture of the films is not sensitive to the sulphurization temperature. A morphological change takes place at a critical thickness of the In films of about 50 nm. Below the critical thickness, the constitution of the synthesized films is grain-like with a uniform grain size of about 100 nm. Above the critical thickness, the granularity looses the characteristic size as if the films consist of fine particles. Bumps emerge in the latter situation due to the surface instability of the In melt against the volume expansion in the solidification. The grains in the films prepared using Bi₂S₃ are submicron-sized and loosely connected to each other regardless of the thickness. The films are hence homogeneous with exhibiting no surface bulging. More importantly, hexagon-shaped disks are interwoven in the In₂S₃ films for a range of the synthesis temperature. The two-dimensional material is suggested to be an unknown compound having an approximate composition of Bi₉In₁₃S₁₈, where Bi is incorporated in the alloy when the Bi production is significantly faster than its loss by the evaporation. The formation of the ternary alloy in the present case evidences that the elastic energy associated with the lattice coincidence to the substrate influences the inclusion of Bi in the sulfide. Furthermore, nanodots are observed to be produced in a self-organized fashion in the electrochemical etching of the In₂S₃ films.