Abstract
Multi-metallic alloy nanoparticles (NPs) can offer tunable or modifiable localized surface plasmon resonance (LSPR) properties depending upon their configurational and elemental alterations, which can be utilized in various applications, that is, in photon energy harvesting, optical sensing, biomedical imaging, photocatalysis, and spectroscopy. In this work, a systematic investigation on the morphological and LSPR properties of multi-metallic alloy NPs incorporating Ag, Au, Pd, and Pt is presented on c-plane sapphire (0001). The resulting NPs exhibit much enhanced and tunable LSPR bands in the UV–VIS wavelength as compared to the previously reported mono-metallic NPs based on the considerable improvement in size and shape of nanostructures along with the electronic heterogeneity. Solid-state dewetting of sputtered bilayers (Ag/Pt), tri-layers (Ag/Au/Pt), and quad-layers (Ag/Au/Pd/Pt) is employed to demonstrate a wide variety of configurations, sizes, densities, and elemental compositions of Pt, AgPt, AuPt, AgAuPt, AgAuPt, and AgAuPdPt NPs by the systematic control of annealing temperature and deposition schemes. The distinct morphology and elemental composition of surface nanostructures are obtained by means of surface diffusion, intermixing, and surface/interface energy minimization along with the applied thermal energy. In addition, the sublimation of Ag atoms from the alloy nanostructure matrix significantly influences the structural, elemental, and thus optical properties of NPs by reducing the average size and Ag percentage in the alloy NPs. Based on the specific size, shape, and elemental composition of NPs, the excitation of LSPR is correlated to the dipolar, quadrupolar, multi-polar, and higher order (HO) modes along with the finite difference time domain simulation of local electric-field. The LSPR intensity is generally stronger with a higher percentage of Ag atoms in the alloy NPs and gradually diminished by the sublimation loss. However, even the mono-metallic and alloy NPs without Ag exhibited significantly improved and dynamic nature of plasmonic bands in the UV and VIS wavelength.
Highlights
Metallic nanostructures can exhibit the localized surface plasmon resonance (LSPR) through the coherent electron oscillations induced by the photon incidence, which can lead to the strong light absorption, scattering, hot carrier generation, and so forth, at the surface of NPs.[1−4] In recent years, the localized surface plasmon resonance (LSPR) of metallic nanoparticles (NPs) have been extensively exploited for the development of advanced device applications in various fields such as energy conversion,[5] electronics,[6] photonics,[7] sensors,[8] biomedical,[9] and optical spectroscopy.[10]
Ag atom sublimation significantly affects the surface morphology evolution as well as the LSPR properties of alloy nanostructures at above 650 °C, and the dynamic behaviors of LSPR bands such as intensity, position, and bandwidth are exploited based on the structure and elemental compositions of the alloy NPs
Pt, AgPt, AgAuPt, and AgAuPdPt alloy NPs of various sizes, shapes, and densities were fabricated based on the self-assembly of sputtered metallic Ag/Pt bilayers, Ag/Au/Pt tri-layers, and Ag/Au/Pd/Pt quad-layers
Summary
Metallic nanostructures can exhibit the localized surface plasmon resonance (LSPR) through the coherent electron oscillations induced by the photon incidence, which can lead to the strong light absorption, scattering, hot carrier generation, and so forth, at the surface of NPs.[1−4] In recent years, the localized surface plasmon resonance (LSPR) of metallic nanoparticles (NPs) have been extensively exploited for the development of advanced device applications in various fields such as energy conversion,[5] electronics,[6] photonics,[7] sensors,[8] biomedical,[9] and optical spectroscopy.[10]. Ag atom sublimation significantly affects the surface morphology evolution as well as the LSPR properties of alloy nanostructures at above 650 °C, and the dynamic behaviors of LSPR bands such as intensity, position, and bandwidth are exploited based on the structure and elemental compositions of the alloy NPs
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