Plasma induced dewetting of solid state metal films for nanostructure applications

Abstract

an optimum condition is suggested in order to maximize the power conversion efficiency via the near-field effect. The Au-nanoparticle array is also used to enhance the efficiency of the system, by means of the photocatalytic activity. The photocatalytic activity of Au nanoparticles(NPs)/TiO2 was evaluated by determining the photo-degradation of methylene blue (MB) under ultraviolet (UV) or visible-light irradiation. In addition to the nanoparticle array, a bi-continuous Au nano-film is used in transparent conductive electrodes (TCE) that are essential for providing electrical contact and transmittance for solar cells and display devices. The sheet resistance (Rs) and optical transmittance (T), which are key parameters of TCE, are determined by the thickness of the Au film and the plasma treatment time, respectively. The plasma-induced dewetting method constitutes a simple, fast, and efficient process for the fabrication of continuous metal nanostructures for use in TCE.

During solid-state dewetting, a physical phenomenon, thin films disintegrate into a set of droplets or particles at temperatures below the melting temperature. Plasma-induced dewetting, in contrast to thermal dewetting and pulsed-laser dewetting, is a rapid process that can be performed at low temperatures and over large-scaled areas. In addition, more uniform nanoparticle arrays can be fabricated (compared to those obtained via thermal dewetting) owing to the high density of holes nucleated during this process, which prevents the coarsening of nanoparticles. In this research, various metal nanoparticle arrays (Au, Ag, Cu) are fabricated using inductively coupled plasma and the mechanism of plasma-induced dewetting is discussed. The evolution of solid-state dewetting with plasma treatment time is examined. Furthermore, the open area of metallic films is calculated through image analysis of images obtained via field emission scanning electron microscopy (FE-SEM). The crystallographic evolution during dewetting is examined by using grazing-incidence small-angle X-ray scattering. Various parameters such as the film thickness, plasma treatment time, film density, and the interfacial energy between the film and the substrate are considered. The size, inter-particle spacing, and number of nanoparticles per unit-area are modified by varying these parameters. More importantly, a repeated dewetting process method that leads to significant changes in the nanoparticle array distribution is introduced. The nanoparticle array and bi-continuous nano-film fabricated by using the plasma-induced dewetting method are used for various applications such as organic solar cells, photocatalytic activity of TiO2, and transparent conductive electrodes materials. A Au-nanoparticle array on indium tin oxide (ITO) is used to improve the performance of organic solar cells via the plasmon-enhanced absorption effect. Moreover, the features of the array are varied in order to promote overlapping of the active layer absorption band and the Au nanoparticle plasmonic resonance frequency