Corrosion at the Nanoscale:  The Case of Silver Nanowires and Nanoparticles

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 (H2S) 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.