Au−Cu Alloy Nanoparticles with Tunable Compositions and Plasmonic Properties: Experimental Determination of Composition and Correlation with Theory

Abstract

For plasmonic alloy nanoparticles, theoretical modeling and experimental characterization are both central to our capabilities involving predictable synthesis and targeted applications. This article uses composition-tunable colloidal Au−Cu nanoparticles as a model system for exploring the issue of reliable experimental determination of composition in plasmonic alloy nanoparticles and correlation of this experimental data with theoretical predictions. Highly uniform spherical Au1-x Cu x alloy nanoparticles were synthesized with compositions ranging from x = 0 to 0.5. The particle compositions were analyzed independently using both powder X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDS), which represent two of the most common nanoparticle composition analysis techniques. The plasmon resonance frequencies, determined experimentally for each sample using UV−vis spectroscopy, red shift with increasing copper content as expected. These experimentally determined plasmon resonance frequencies were then compared to the values predicted theoretically based upon the XRD and EDS composition measurements. Although EDS and XRD are both found to be acceptable methods for experimentally determining the composition, careful data analysis suggests that XRD composition measurements are more accurate for smaller values of x, whereas EDS measurements are more accurate for larger values of x. In addition, some discrepancies between the experimentally determined plasmon resonance frequencies and those predicted by theory suggest inaccuracies in using a simple linear mixing rule to determine the dielectric constant of the Au−Cu alloys.

Synergistic geometric and electronic effects for electrochemical reduction of carbon dioxide using gold–copper bimetallic nanoparticles

“…Au and Cu nanoparticles in their pure phase exhibit characteristic surface plasmon resonance (SPR) peaks at B523 and B570 nm (refs 26,30,31). As the content of Cu increases in a pure Au nanoparticle by forming an alloy, the SPR peak of Au red-shifts towards the SPR peak of Cu with some broadening 26,30 (Fig. 1c).…”

Understanding the synergistic effects of gold bimetallic catalysts

“…Thus, Au-Ag and Au-Cu bimetallic NPs with homogeneous composition can be expected. The synthesis of Au-Ag and Au-Cu bimetallic NPs has led to great progress in the optical applications [55,56], while it has been less reported for the purpose of catalysis. Mou and Zhang's groups are among the first that reported synergistic effects of Au-Ag [27] and Au-Cu [21] in catalytic reactions.…”

Simulated study of plasmonic coupling in noble bimetallic alloy nanosphere arrays

“…The experimentally obtained complex dielectric functions for Ag, Au and Cu are given by Palik 35 and for alloys it is calculated by using average weighted method. 14,15 The real and imaginary parts of the metal dielectric functions and their alloys of selected compositions are shown in Figure 1.…”

“…[5][6][7] With this flexibility in tunability of their optical properties, noble metal nanoparticles can be used in variety of emerging applications such as thin-film solar cells, 2, 4 plasmon sensors, 8 surface enhanced Raman spectroscopy (SERS) 9 and biomedical applications 10 etc. The optical properties of individual noble metal nanoparticles (Ag, Au and Cu) have been studied by many researchers [11][12][13] but their bimetallic nanoparticles such as alloys 14,15 and core-shell nanostructures 16 have attracted much attention, because of their large tunability in LSPR as compared to the individual noble metals. The optical properties of alloy nanoparticles can be tuned by varying the metal and their composition in the alloy nanoparticles.…”

“…The formation of alloys results in the broadening of resonance peak with an LSPR that lies in between the LSPRs of the individual metals. Moreover, the advancement in the bimetallic nanostructures synthesis of Au-Cu, 14 Ag-Au 17 and AgCu 18 with controlled optical properties makes them suitable for practical applications. In our recent study, 19 the LSPR based scattering efficiency for noble metals Au, Ag and Cu with all their possible BANSs such as Au-Cu, Ag-Au and Ag-Cu have been studied by using Mie theory and it was found that Ag 0.50 -Cu 0.50 BANSs are the best material of choice in comparison to the other two alloys, to enhance the efficiency of plasmonic thin-film solar cells.…”