Semiconducting In₂S₃ quantum dots in thin film form: sonochemical versus conventional chemical synthesis and investigation of their structural and optical properties

Abstract

Indium(III) sulfide quantum dots were deposited in thin film form using both a conventional chemical bath deposition method and a sonochemical route. The developed routes allow deposition of cubic α-In₂S₃ nanocrystals in thin film form. The as-deposited films produced by the conventional and sonochemical approaches are highly nanocrystalline, with average crystal sizes of 2.5 and 2.0 nm correspondingly (as determined from the Scherrer formula), which increase to 4.1 nm upon annealing treatment, due to coalescence and crystal-growth processes. Refinement of the lattice-constant value in the case of as-deposited and annealed films was performed using linear regression analysis. Blue-shifted band-gap energy values of as-deposited films with respect to those corresponding to bulk specimen, accompanied with the red shift of absorption onset upon annealing, strongly indicate the quantum-dot behavior of the synthesized nanocrystals. The detected three-dimensional quantum-confinement effects in the synthesized nanocrystals were discussed in terms of the Brus model. On the basis of optical spectroscopic data, we estimated the Bohr's excitonic radius value in this semiconductor.