Abstract
Multi-metallic alloy nanoparticles (NPs) can offer additional opportunities for modifying the electronic, optical and catalytic properties by the control of composition, configuration and size of individual nanostructures that are consisted of more than single element. In this paper, the fabrication of bimetallic Pd-Ag NPs is systematically demonstrated via the solid state dewetting of bilayer thin films on c-plane sapphire by governing the temperature, time as well as composition. The composition of Pd-Ag bilayer remarkably affects the morphology of alloy nanostructures, in which the higher Ag composition, i.e. Pd0.25Ag0.75, leads to the enhanced dewetting of bilayers whereas the higher Pd composition (Pd0.75Ag0.25) hinders the dewetting. Depending on the annealing temperature, Pd-Ag alloy nanostructures evolve with a series of configurations, i.e. nucleation of voids, porous network, elongated nanoclusters and round alloy NPs. In addition, with the annealing time set, the gradual configuration transformation from the elongated to round alloy NPs as well as size reduction is demonstrated due to the enhanced diffusion and sublimation of Ag atoms. The evolution of various morphology of Pd-Ag nanostructures is described based on the surface diffusion and inter-diffusion of Pd and Ag adatoms along with the Ag sublimation, Rayleigh instability and energy minimization mechanism. The reflectance spectra of bimetallic Pd-Ag nanostructures exhibit various quadrupolar and dipolar resonance peaks, peak shifts and absorption dips owing to the surface plasmon resonance of nanostructures depending on the surface morphology. The intensity of reflectance spectra is gradually decreased along with the surface coverage and NP size evolution. The absorption dips are red-shifted towards the longer wavelength for the larger alloy NPs and vice-versa.
Highlights
Metallic nanoparticles (NPs) play key roles in various applications such as solar cells, sensors and catalysis due to their plasmonic property, chemical stability, and larger surface to volume ratio. [1,2,3,4,5,6]
A broader light absorption of dye molecules was exhibited by the Au-Ag alloy NPs due to the localized surface plasmon resonance (LSPR) induced by both Au and Ag components, which resulted in the conversion efficiency improvement of dye-sensitized solar cells [13]
The investigation on evolution of various morphology of bimetallic Pd-Ag nanostructures was successfully demonstrated on sapphire (0001) via the solid state dewetting of Pd-Ag bilayers
Summary
Metallic nanoparticles (NPs) play key roles in various applications such as solar cells, sensors and catalysis due to their plasmonic property, chemical stability, and larger surface to volume ratio. [1,2,3,4,5,6]. Pd and Ag alloy can find the potentials to improve the performance of optical, sensing and catalysis applications owing to the strong catalytic activity of Pd and plasmonic resonance of Ag as well as electronic heterogeneity of alloy NPs [15,16,17,18]. Such bimetallic alloy NPs can be fabricated by various chemical and physical growth technique [19,20]. The variation in the intensity and shift of reflectance peaks and absorption dips are disused with the surface morphology
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