Abstract
Noble metallic nanoparticles (NPs) can exhibit valuable properties such as localized surface plasmon resonance (LSPR) and large surface to volume ratio, which can find various optoelectronic and catalytic applications. In this work, the improved configuration and uniformity of platinum (Pt) NPs are demonstrated by using a sacrificial indium (In) layer via the enhanced solid state dewetting of In-Pt bilayers on sapphire (0001). In a sharp contrast to the conventional dewetting of intrinsic Pt film, the introduction of In component can significantly enhance the global dewetting process and thus can result in the fabrication of well-defined Pt NPs with the improved uniformity. This can be due to the fact that In possess high diffusivity, low surface energy and low sublimation temperature. Upon annealing, the intermixing of In and Pt atoms can occur at the interface due to the inter-diffusion, which forms In-Pt alloy system. As a result, the overall diffusivity and dewetting degree of system can be significantly improved and this can produce more isolated, uniform and semispherical Pt NPs at much lower temperatures as compared to the pure Pt film dewetting. Conveniently, the In atoms preferentially can be removed from the NP matrix by the sublimation even at relatively low temperatures. These Pt NPs exhibit dynamic LSPR band in the UV-visible wavelength based on the excitation of dipolar, quadrupolar and higher order resonance modes. Specifically, the LSPR wavelength can be tuned between ~480 and 580 nm by the fabrication of small to large size Pt NPs with the distinct configuration and interparticle spacing. Furthermore, at a constant Pt thickness, the size, spacing and density of Pt NPs can be readily tuned by the control of In layer thickness. The introduction of sacrificial In component can enable an additional flexibility for the control of surface morphologies of metallic NPs with the low diffusivity materials.
Highlights
For the low annealing temperature samples, the visible region shoulder was much wider, which became narrower with the increased temperature likely due to the improved uniformity of Pt NPs. From the transmittance spectra in Figure 8 shows the evolution of wiggly Pt nanoclusters on sapphire with the increased Pt layer thickness to 15 nm, 3 times higher, while keeping the same In layer thickness (5 nm) as in the first set
Semi-spherical Pt NPs with the variety of size and spacing were demonstrated via the enhanced dewetting of Pt thin films using a sacrificial In layer
Along with the increased temperature, the In atoms were completely desorbed by the sublimation, which resulted in the formation of more isolated and well-developed Pt NPs
Summary
For the low annealing temperature samples, the visible region shoulder was much wider, which became narrower with the increased temperature likely due to the improved uniformity of Pt NPs. From the transmittance spectra in Figure 8 shows the evolution of wiggly Pt nanoclusters on sapphire with the increased Pt layer thickness to 15 nm, 3 times higher, while keeping the same In layer thickness (5 nm) as in the first set.
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