Model for UV induced growth of semiconductor nanoparticles in polymer films

Abstract

A theoretical macrokinetic model for photoinduced growth of semiconductor nanoparticles was developed with allowance for specific features of their optical properties in the near ultraviolet region. In [A. A. Smirnov et al., Optical Materials Express, 8 (2018) 1603–1612] the Polymethylmethacrylate (PMMA) film containing good soluble CdS precursors [Cd(N(SCNEt2)2)2] (TEDBCd) was irradiated by an ultraviolet light emitting diode (UV LED) with a central wavelength of 365 nm at different fixed temperatures and at different fixed intensities. The authors in situ followed the evolution of absorbance at a wavelength of 405 nm where the film is initially transparent. The corresponding photon energy is larger than the bandgap of the bulk CdS crystals. The increase in absorbance of the irradiated film at this wavelength was associated with the CdS nanoparticle growth. The main result is that at a given temperature, the effect of UV radiation on the sample is determined by the exposure (dose) rather than the light intensity and the irradiation time separately. The presented paper aims at constructing a model of the semiconductor particle growth initiated by the light-induced destruction of good soluble precursor molecules and fitting this model to the experimental data, making it possible to estimate the most important parameters of the process. The photoinduced formation of CdS nanoparticles is a complicated process that includes photo-mediated destruction of the precursor molecules followed by diffusion-assisted growth of nanoclusters. The feature of the growing semiconductor nanoparticles is that rather small particles do not absorb radiation at a particular wavelength because of the quantum confinement. The theory also takes into account the finite thickness of the sample and the nonlinear effects of radiation shielding.