Chemical synthesis, structural and optical properties of quantum sized semiconducting tin(II) selenide in thin film form

A chemical route to nanocrystalline photoconducting tin(ll) selenide quantum dots in thin film form was developed and the structural and optical properties of the synthesized materials were studied. The synthesized SnSe nanocrystals deposited as thin films belong to the orthorhombic crystalline system. Unit cell parameters of the as-deposited and thermally treated semiconducting quantum dots in thin film form were determined from experimental X-ray diffraction data employing multiple regression analysis technique. An average crystal size of 14.8 nm was estimated for as-deposited SnSe quantum dots using the Debye-Scherrer approach which increases to 23.3 nm upon annealing. Average crystal size increase upon thermal treatment is accompanied by slight enlargement of the unit cell parameters. On the basis of optical absorption studies of the SnSe films, conclusions regarding the band structure of this material in reciprocal space were derived. The as-deposited films are characterized by indirect band gap energy of 1.20 eV which exhibits a slight red shift to 1.10 eV upon annealing. Additional electronic transition of a direct type was found to occur at 1.74 eV in the case of as-deposited films, shifting to 1.65 eV in the course of annealing. All these values are blue-shifted with respect to the macrocrystalline material ones, which along with the red shift detected upon annealing, is a strong indication of the three-dimensional confinement effects in the studied nanocrystals. (c) 2006 Elsevier B.V. All rights reserved.