Evolution of morphological and optical properties of various AuxPd1−x bimetallic nanostructures by the systematic control of composition

Abstract

Bimetallic nanostructures (BMNSs) have gained significant attention because of their multi-functionality, site-specific response and electronic heterogeneity along with the additional opportunities to tune physical and optical properties. In this paper, the systematic evolution of AuxPd1−x BMNS is thoroughly investigated in terms of morphological and optical properties through the solid state dewetting on c-plane sapphire. The bilayer composition and deposition order change are coherently tested along with the conventional growth parameter control. By the systematic control of annealing temperature, annealing duration and deposition thickness, the formation of various BMNSs demonstrate sharp distinctions at different AuxPd1−x compositions (x = 0.25, 0.50 and 0.75). In specific, the high Au percentage in the AuxPd1−x bilayers shows an enhanced dewetting due to the higher diffusivity and lower surface energy of Au atoms as compared to the Pd. Furthermore, the deposition order also induces a significant alteration on the dewetting process. Upon annealing, the evolution of BMNSs relies on the combination of atomic diffusion, inter-diffusion, alloying, surface and interface energy minimization and Rayleigh-like instability. Furthermore, the analysis of reflectance spectra demonstrates the development of the quadrupolar and dipolar resonance peaks, absorption band and their shift, induced by the localized surface plasmon resonance (LSPR) of various AuxPd1−x BMNSs. Specifically, the quadrupolar resonance peak is consistent ∼380 nm whereas the dipolar resonance peak and absorption dip are readily blue-shifted and narrowed along with the evolution of isolated and uniform BMNSs.