Quartz crystal microbalance study of the growth of indium(III) sulphide films from a chemical solution

The growth of indium(III) sulphide thin films from aqueous thioacetamide (TA)-In(III) solution has been studied with a quartz crystal microbalance (QCM). It is found that the growth of the film consists in the parallel deposition of In2S3 and In2O3. Both processes are induced by sulphide anions (S2-) produced after decomposition of thioacetamide. In2S3 is deposited by precipitation of crystallites formed in the bulk solution. On stirred solutions this reaction is hindered due to the disruption of the nucleation centres. On the other hand, In2O3 is deposited by electrochemical reduction of naturally dissolved oxygen (O-2) by the S2- anions, followed by chemical reaction with In3+. This process is of electroless-chemical nature and has important consequences on the properties of the films. Both reaction mechanisms, chemical and electroless-chemical, compete under different experimental conditions: temperature, solution composition, stirring. For instances, the deposit of In2O3 is favoured at low bath temperature, in aerated solution,,giving rise to films with higher oxide proportion. Additives like hydrochloric acid and acetic acid also favour In2O3 deposition. The system has easy possibility to tune chemical and physical properties of the films, like composition, transparency and absorption edge, of interest for photovoltaic applications. (C) 2003 Elsevier Ltd. All rights reserved.