Abstract
Self-assembly of ultrathin Au, W, and Au-W bilayer thin films is investigated using a rapid thermal annealing technique in an inert ambient. The solid-state dewetting of Au films is briefly revisited in order to emphasize the role of initial film thickness. W films deposited onto SiO2 evolve into needle-like nanocrystals rather than forming particle-like agglomerates upon annealing at elevated temperatures. Transmission electron microscopy reveals that such nanocrystals actually consist of tungsten (VI) oxide (WO3) which is related to an anisotropic oxide crystal growth out of the thin film. The evolution of W films is highly sensitive to the presence of any residual oxygen. Combination of both the dewetting of Au and the oxide crystal growth of WO3 is realized by using various bilayer film configurations of the immiscible Au and W. At low temperature, Au dewetting is initiated while oxide crystal growth is still suppressed. Depending on the stacking sequence of the Au-W bilayer thin film, W acts either as a substrate or as a passivation layer for the dewetting of Au. Being the ground layer, W changes the wettability of Au which clearly modifies its initial state for the dewetting. Being the top layer, W prevents Au from dewetting regardless of Au film thickness. Moreover, regular pattern formation of Au-WO3 nanoparticles is observed at high temperature demonstrating how bilayer thin film dewetting can create unique nanostructure arrangements.
Highlights
IntroductionSolid-state dewetting (SSD) of Au thin films has been investigated in a number of studies.[6,7,8,9,10] A comprehensive view on the microstructural evolution of continuous films is provided by Müller and Spolenak.[11] Upon annealing, it is found that void as well as grain growth in the film correlate with (111) intensities of X-ray diffraction
Solid-state dewetting (SSD) of metallic thin films is well known as a simple and effective way to obtain tailored micro- and nanostructures for potential applications in catalysis, ecology, information technology, or plasmonics.[1,2,3,4,5]SSD of Au thin films has been investigated in a number of studies.[6,7,8,9,10] A comprehensive view on the microstructural evolution of continuous films is provided by Müller and Spolenak.[11]
Depending on Au film thickness, morphology evolution and final particle size distribution will be different:[12] An increasing layer thickness gives rise to continuous films after deposition and, upon annealing, bigger particles are formed which are less dense-packed on the substrate.[13]
Summary
SSD of Au thin films has been investigated in a number of studies.[6,7,8,9,10] A comprehensive view on the microstructural evolution of continuous films is provided by Müller and Spolenak.[11] Upon annealing, it is found that void as well as grain growth in the film correlate with (111) intensities of X-ray diffraction. This change in intensity can be used to trace the dewetting. A brief review on the influence of Au film thickness on morphology evolution will be given
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