In situ observation of morphological change of Pd-based bimetallic nanoparticles synthesized by co-sputtering

Abstract

The formation process of Pd-based bimetallic nanoparticles synthesized by co-sputtering is investigated by performing in situ morphological observation using resistive spectroscopy. The segregation of the metal with lower surface energy on the nanoparticle surface is observed, and it is found that the formation process of the alloy nanoparticles tends to be similar to that of the nanoparticles composed of the core metal even when the atomic fraction of the shell metal is higher than that of the core metal. The co-sputtering process is simulated by the molecular dynamics analysis, and the observed formation process is theoretically confirmed.

Ab initio morphology prediction of Pd, Ag, Au, and Pt nanoparticles on (0001) sapphire substrates

“…This interpretation could successfully explain the formation dynamics of core-shell nanoparticles synthesized by sputtering different metals onto nanoparticles. 10,11 Applying this interpretation to the present results for single-element nanoparticles, Fig. 4 indicates that Pd and Pt nanoparticles may be flatter than Ag and Au nanoparticles, with Ag and Au having higher contact angles.…”

“…This phenomenon is attributable to the lower surface energy of Ag and Au, resulting in the nanoparticles being flattened on the substrate. Thus, although we discussed the morphology of nanoparticles on the substrate only using the surface energy of nanoparticle in our previous study, 11 not only the surface energy, but the interfacial effect between the nanoparticle and substrate is also important; the competition between adhesion energy W X-Al2O3 and surface energy γ X is crucial for understanding the morphology of nanoparticles on the substrate, with these values being highly species-dependent.…”

“…In our previous studies, we introduced a novel real-time method based on acoustic techniques for evaluating the morphology 9 and growth of nanoparticles on sapphire substrates. 10,11 We analyzed the morphology of Pd-based core-shell nanoparticles by examining the time-dependent variations in the full width at half maximum (FWHM) of the resonant peak in relation with the surface energy of each species. The shape and internal structure of the core-shell nanoparticles were clarified considering the surface energy of each metal.…”

“…To validate our ab initio morphology prediction, we compared our results with our previous experimental data, specifically, the FWHM timings for Pd, Ag, Au, and Pt. The film thickness vs FWHM curves for pure Pd, Ag, Au, and Pt atoms, obtained during sputtering onto the sapphire substrate in our previous work, 10,11 were re-plotted in Fig. 4.…”

“…However, the suggestion for Ag nanoparticles contradicts our predictions. To find the reason of the above contradictions between the calculation and experimental observation, considering that the diffusivity of sputtered atoms onto the substrate also affects the nanoparticle morphology and thus the timing of FWHM peaks, 10,11 we investigated the activation energy of the diffusion of single X atoms on a sapphire (0001) surface using the drag method, while detecting the minimum energy path (MEP). 33 One X atom was placed at the FCC A stacking position on the surface of the Model (b) unit cell shown in Fig.…”