Ultrasound driven mound to self-affine surface structure transition in nanostructured films: one-pot route to cubic CuInS₂ quantum dots with controlled structure and tunable band gap energy

In the current study, the first method for synthesis of 3D assemblies composed by close-packed QDs of the cubic modification of CuInS₂ in thin film form is presented. The developed one-pot synthetic approach enables high tunability of materials’ properties by combining ultrasonic irradiation of the reactor with the one-step colloidal chemical approach or by controlled post-deposition annealing of the deposited samples. The average crystal size of the material can be tuned from ~ 1 up to ~ 36 nm. In-depth studies of the structure, surface morphology and optical properties were carried out. Manifestations of size-quantization effects in the optical properties were analyzed in details. Analysis of the second-order statistical properties of thin films’ surfaces has shown that ultrasonically-supported synthesis enables generation of self-affine surfaces, while the colloidal chemical one leads to mounded surfaces. Such change of the surfaces’ character was attributed to heterogeneous sonochemical effects, leading ultimately to more efficient transport of the clusters formed in the bulk liquid and their improved energizing, enabling them to overcome various diffusion barriers on the growing surface. Sonochemically deposited films are characterized by notably larger values of the Hurst exponent than the chemically deposited ones, and an order of magnitude smaller correlation length. Smaller fractal dimensions in sonochemical films are in line with the smoother surfaces generate by ultrasonically-assisted route.