A rapid sonochemical approach to semiconductor thin films: The case of metal iodides

Thin films of metal iodides (e.g., CuI, AgI and PbI2) were rapidly synthesized by a sonochemical method. For example, perfect CuI crystals with uniform polyhedral structures could be formed directly on copper foils with the irradiation time as short as 10 s via interfacial reaction between copper foils and elemental iodine in ethanol at ambient temperature. The products were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and photoluminescence spectra (PL). A probable mechanism was proposed to explain the rapid growth of CuI crystals. This facile approach could also be used to grow other metal iodides such as AgI and PbI2 nanocrystals. It was found experimentally that the resultant metal iodide films could better resist spinning under the drastic ultrasound irradiations in a liquid media. Particularly, the resulting CuI films showed strong, room temperature PL emissions at the energy around their band gaps. This method is believed to be the fastest way for in-situ fabrication of semiconductor films on various metal substrates for subsequent applications related to the metal iodide semiconductor films.