Plasmon Spectroscopy and Chemical Structure of Small Bimetallic Cu_(1–x)Ag_x Clusters

Abstract

The optical properties of small Cu−Ag bimetallic clusters have been experimentally and theoretically investigated in relation to their chemical structure analyzed by high resolution transmission electron microscopy (HRTEM). Cu(1−x) Ag x clusters of about 5 nm in diameter are produced in a laser vaporization source with a well-defined stoichiometry (x = 0, 25, 50, 75, and 100%) and dispersed in an alumina matrix. Absorption spectra are dominated by a broad and strong surface plasmon resonance whose shape and location are dependent on both cluster composition and sample aging. Detailed modeling and systematic calculations of the optical response of pure and oxidized mixed clusters of various chemical structures have been carried out in the framework of classical and semiquantal formalisms. Optical and HRTEM measurements combined with theoretical predictions lead to the conclusion that these bimetallic clusters are not alloyed at the atomic scale but rather present a segregation of chemical phases. Most likely, they adopt a Cu@Ag core−shell configuration. Moreover, the nanoparticle oxidation process is consistent with the formation of a copper oxide layer by dragging out inner copper atoms to the cluster surface.

Tailoring Morphology of Cu–Ag Nanocrescents and Core–Shell Nanocrystals Guided by a Thermodynamic Model

“… While other spectra did not have the signal strength required to observe the loss features, all Ag 3p edges displayed the same asymmetric shape which again indicated the presence of Ag metal . The observed lack of Ag oxidation for Cu–Ag bimetallic particles may be caused by a large difference in the formation energies of Ag 2 O and Cu 2 O, which significantly favors the formation of the latter . Furthermore, any molecular oxygen coming in contact with Ag atoms is likely to move toward Cu domains, due to the binding energy differences …”

“…25 The observed lack of Ag oxidation for Cu-Ag bimetallic particles may be caused by a large difference in the formation energies of Ag 2 O and Cu 2 O, which significantly favors the formation of the latter. 17 Furthermore, any molecular oxygen coming in contact with Ag atoms is likely to move towards Cu domains, due to the binding energy differences. 36 Finally, it is worth mentioning that the transformation into Ag@Cu 2 O seems irreversible.…”

“…22,40 The optical extinction spectra obtained for our Cu-Ag bimetallic nanoparticles are in good agreement with previous reports. 17,22 As Ag is introduced into the particles, a strong resonance feature appears and redshifts towards the As metallic Cu turns into semiconducting Cu 2 O, the optical extinction undergoes significant changes (Figure 4b). These changes can only be observed for Cu/Ag crescents, where Cu is on the surface and prone to oxidation, as Cu@Ag does not oxidize.…”

CuAg and AuAg bimetallic nanoparticles for catalytic and heat transfer applications

“…1a. CuAg BNPs showed absorbance peak at 389 nm, while Cu and Ag NPs are exhibiting at 574 and 410 nm, respectively (Pellarin et al 2015;Cao et al 2019;Jolly et al 2021). The influence of pH on the optical properties of CuAg BNPs is depicted in Fig.…”

Nano-fried-eggs: Structural, optical, and magnetic characterization of physically prepared iron-silver nanoparticles

“…In pure FeAg particles we expect an iron core surrounded by a silver shell, given the difference in surface tension of the two metals [24]. In chemical synthesis typically segregated core-shell or dumbbellshaped structures are obtained [25,9,26]. In the few reported cases of chemically prepared Fe-Ag nanoparticles the core-shell structure prevails [13,27,28].…”