Formation and Removal of Alloyed Bimetallic Au–Ag Nanoparticles from Silicon Substrates for Tunable Surface Plasmon Resonance

Abstract

The formation of alloyed Au–Ag bimetallic nanoparticles (NPs) by the solid-state thermal dewetting of Au–Ag bilayer thin films on Si substrates was reported in this work. Complete dewetting of the bilayer thin films to form alloyed Au–Ag bimetallic NPs can be achieved at temperatures above the Tammann temperature of at least one of the metal components. The NP size depends heavily on the total thickness of the bilayer thin films, whereas the atomic ratio of Au/Ag and the sputtering order in the bilayer films do not affect the NP size significantly. It has been demonstrated by X-ray photoelectron spectroscopy (XPS) analysis that the produced Au–Ag bimetallic NPs are alloyed and the sputtering order of Au and Ag in the initial bilayer films has no impact on the final configuration of the produced NPs. To further characterize the surface plasmon resonance (SPR) of Au–Ag NPs, a procedure involving the use of poly­(vinyl alcohol) (PVA) and poly­(methyl methacrylate) (PMMA) was developed to remove the bimetallic NPs from the optically opaque Si substrates. The SPR peak wavelength of the bimetallic Au–Ag alloy NPs has been shown to vary linearly with the atomic percentage of Au in the NPs, allowing for the tuning of the resonance wavelength by changing the alloy composition. The ability to produce uniform Au–Ag alloy NPs by thermal dewetting, the successful removal of the Au–Ag NPs from the Si substrates into the colloidal solution, the tunable SPR, and the excellent long-term stability of the alloy NPs in solution open up many opportunities for the potential applications of these Au–Ag alloy NPs, for example, for surface functionalization, sensing, and catalysis.

Pt-Rich Core/Au-Rich Shell Nanoparticle Formation Using Pulsed Laser-Induced Dewetting and Their Electrochemical Characteristics

“…From the plots of NP diameter as a function of laser fluence in the range of 250 to 500 mJ cm –2 for all samples shown in Figure , it is clear that the total bilayer thickness plays a determining role in the size of the NPs, whereas the NP size does not change much with the different sputtering order and laser fluence for the same thickness. The same dependence of NP size on the bilayer thickness was found for the Au-Ag NPs produced on Si substrates using the method of thermal dewetting …”

“…The same dependence of NP size on the bilayer thickness was found for the Au-Ag NPs produced on Si substrates using the method of thermal dewetting. 21 From Figure 1, it can be seen that the Au-Pt NPs by PLiD of the two thinner bilayer films have better dimple coverage. Here, we define the dimple coverage as the percentage of dimples that are occupied by a single NP.…”

“…Morphology evolution during the dewetting of bilayer Au-Pt thin films by thermal heating, where metals remain in their solid phase, has been studied by Müller et al Recent work on thermal dewetting to prepare Au-Pt nanostructures has shown that it produces phase-segregated structures, consisting of an Au-rich phase and a Pt-rich phase . Although thermal dewetting has been successfully used for the fabrication of Au-Ag NPs, , the high melting point of Pt limited the complete dewetting of the Au-Pt bilayer films to form Au-Pt NPs at temperatures not causing substrate deformation. Pulsed-laser-induced dewetting (PLiD), a liquid-state dewetting technique where the incident laser irradiation causes the melting of metals, can be used to address the challenge.…”

Formation of Agshell/Aucore Bimetallic Nanoparticles by Pulsed Laser Ablation and Chemical Reduction Methods: The Effect Green Laser Wavelength and Colloidal/Solution Concentration

“…The only peak is occurs at 390 nm due to the LSPR absorption of each silver NPs. An extra intense peak has occurred for BNPs (s3-s6), indicating the excitation of longitudinal plasmon vibrations of the AgNPs [37,66]. Examination of peak locations associated with samples, may provide valuable information on the size, morphology and composition of NPs.…”

“…Photochemical method [21], plane wave pseudopotential method [22], replacement reaction method [23], catalytic reduction [24], spray pyrolysis [25], wet-chemical method [7], chemical reduction [26,27], green synthesize [28][29][30], post-modi cation [31], electron beam deposition [32], ion implantation [33,34], electrochemical reduction [35], solid state dewetting (SSD) [36,37], pulse laser deposition (PLD) [38] and PLAL [39][40][41][42].…”