Controlled growth of silver nanoparticles on indium tin oxide substrates by plasma-assisted hot-filament evaporation: Physical properties, composition, and electronic structure

Abstract

High-density silver (Ag) nanoparticles of controllable size and uniformity were used to enhance conductivity and luminance efficiency in an organic light emitting diode device. As part of this experiment, Ag nanoparticles were deposited on indium tin oxide (ITO) substrates by using plasma-assisted hot-filament evaporation. These nanoparticles mainly exhibited spherical grain morphology, with average diameters ranging between 7.5 and 45.7 nm depending on substrate temperature; the size of Ag nanoparticles are known to increase with rises in substrate temperatures up to 250 °C, a phenomenon attributable to thermally induced surface diffusion. With regards to the optical spectra, the characteristics of the localised surface plasmon resonance were directly affected by changes in the physical properties of the Ag nanoparticles, such as diameter and interparticle distance. The X-ray photoemission spectroscopy results revealed the formation of a shell layer of silver oxide on the Ag nanoparticles. This resulted in a significant effect on the optical and electrical properties of the Ag nanoparticles/ITO. The highest density of Ag nanoparticles deposited at 80 °C were associated with the lowest sheet resistance and work function at 7.45 Ohm/square and 3.97 eV, respectively, while increases in the oxide formation significantly increased the sheet resistance and work function up to 200 °C. The effects of substrate temperature on the morphology, structure, as well as optical and electrical properties of the deposited Ag nanoparticles on ITO are discussed in further detail in this report.