Metal nanostructures, such as nanoparticles and nanowires, have been proposed as building blocks for several applications in nanofabrication and nanoelectronics. However, even when atmospheric corrosion is common in metals, there is a lack of information about the stability of those nanostructures against such phenomenon. Therefore, we decided to study the atmospheric corrosion of silver nanowires and nanoparticles synthesized by the polyol method using poly(vinylpyrrolidone) (PVP) as the capping agent by different techniques, including transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). After synthesis and purification, the silver nanostructures were deposited on different substrates and exposed to laboratory air at ambient conditions. The structural changes in the samples were monitored by TEM as a function of time for a period of time of 24 weeks. Our results demonstrated that these silver nanostructures are susceptible to atmospheric corrosion and that, in most cases, a thin layer of silver sulfide nanocrystals is formed on their surfaces. The enhanced reactivity of regions with defects and dislocations could explain the observation that the corrosion rate of the nanowires is higher than the corrosion rate of the nanoparticles, since it is well-known that the structure of the nanowires synthesized by the polyol method is multitwinned, while most of the nanoparticles that remained after synthesis are single crystals. Additionally, part of the original sample of silver nanostructures was sulfidized using hydrogen sulfide (H 2 S) as corrodent gas. After performing XPS studies of this sample, we confirmed the presence of PVP on the surface of the sulfidized silver nanostructures. This result agrees with the observation that in the atmospherically corroded samples, even when in some cases the original silver nanostructure was completely corroded, the silver sulfide nanocrystals remained together adopting the shape of silver nanostructure. Finally, our results indicate that the corrosion at the nanoscale seems to be similar to that of the bulk silver.

Pt-Au bimetallic nanoparticles have been synthesized by the polyol method and stabilized with poly(vinylpyrrolidone) (PVP), modifying the temperature of synthesis. Interesting structure changes were observed in the nanoparticles as the temperature was varied. At lower temperatures no bimetallic nanoparticles were detected, but as the temperature increased bimetallic nanoparticles started to appear, commonly obtaining core-shell nanoparticles, always covered by the polymer. This originates the modification of the optical response of the system in the UV-visible region. An absorption peak centered at 520 nm at low temperatures was observed (100-110 degrees C); at higher temperatures (130-170 degrees C) there were non detectable absorption peaks, and finally at the two highest temperatures (180-190 degrees C) the reappearance of an absorption feature centered at 510 nm was noticed. These UV-visible results indirectly imply the composition of the surface of the particle. The structure of the particles has been determined using transmission electron microscopy and high-angle annular dark field (HAADF), the latter being a powerful technique to determine the structural composition of the particles and allowing a direct correlation of the optical response with their structural composition. X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) studies were also performed on the samples and their results support the idea of a Pt(core)-Au(shell) structure with the elements segregated from each other. The combination of these experimental techniques with calculated UV-vis absorption spectra allowed, in a reliable way, the elucidation of the nanoparticles structure and elemental distribution.

No abstract

No abstract