L. Wang, X. Xu
University of Science and Technology Beijing,
Keywords: nanoparticle, In2O3, thin film, device
Summary:Oil soluble In2O3 nanoparticles and In2O3−SnO2 nanocomposites were prepared in oleylamine via decomposition of precursors of indium acetylacetonate, indium and tin acetylacetonate, respectively. Transmission electron microscopy (TEM), scanning electron microscopy (SEM), atomic force electron microscopy (AFM), X-ray diffraction (XRD), ultraviolet-visible (UV−vis) and photoluminescence (PL) spectroscopy were used to investigate the properties of the nanoparticles and thin films. The In2O3 nanoparticles are of cubic-phased spheres with a diameter of ~8 nm, having a broad emission peak centered at 348 nm. The In2O3−SnO2 nanocomposites are composed of smaller sized In2O3 and larger sized In2O3−SnO2 co-particles, having a broad emission peak located at 355 nm. Furthermore, the oil soluble characteristic of the nanoparticles and nanocomposites brings advantages for processing and makes them readily form thin films using spin-coating technique. Thin films of In2O3 and In2O3−SnO2 were obtained by spin-coating the oil soluble In2O3 nanoparticles and In2O3−SnO2 nanocomposites on substrates followed by calcination. The films are highly transparent and conductive with smooth surfaces, which may find applications in many fields such as sensors and optical devices. The In2O3−SnO2 nanocomposite thin film calcined at 400 °C is highly transparent and conductive with a thickness of 30−40 nm, the surface of which is quite smooth and crack-free. In addition, In2O3 nanoparticle thin films were prepared by spin-coating the dichloromethane solution of the In2O3 nanoparticles on Si/SiO2 substrates and annealing at various temperatures. XRD and SEM measurements show that the In2O3 nanoparticles are spherical and the quality of thin film surface varies with annealing temperature and time. The thin film with good surface quality, annealed at 400 °C for 10 min, has been used to fabricate a device. Field−effect transistor devices of In2O3 nanoparticles were fabricated and tested. I−V curves indicate that the devices exhibit as conductor in N2 and as semiconductor in air. The semiconductor property can be tuned by exposing time in air. The changes of electron mobility and on−off current ratio exposed in air for a certain time ranging from 1 min to 5 days were studied. The electron mobility and on−off current ratio have a dramatic change in the starting stage exposed in air, suggesting the device is sensitive to oxygen due to the presence of In2O3 nanostructures. This oxygen sensing property suggests that the In2O3 thin film device may find applications in gas sensors.