RESUMO
In this contribution, we present a study of the mechanical properties of porous nanoshells measured with a nanoindentation technique. Porous nanoshells with hollow designs can present attractive mechanical properties, as observed in hollow nanoshells, but coupled with the unique mechanical behavior of porous materials. Porous nanoshells display mechanical properties that are dependent on shell porosity. Our results show that, under smaller porosity values, deformation is closely related to the one observed for polycrystalline and single-crystalline nanoshells involving dislocation activity. When porosity in the nanoparticle is increased, plastic deformation was mediated by grain boundary sliding instead of dislocation activity. Additionally, porosity suppresses dislocation activity and decreases nanoparticle strength, but allows for significant strain hardening under strains as high as 0.4. On the other hand, Young's modulus decreases with the increase in nanoshell porosity, in agreement with the established theories of porous materials. However, we found no quantitative agreement between conventional models applied to obtain the Young's modulus of porous materials.
RESUMO
Eccentricity is a common feature consequence of several synthesis protocols of hollow nanoshells. Despite the crescent interest in these nanoparticles, it is still unclear how an irregular layer on the nanoparticle impacts the macroscopic properties. Here, we study the thermal stability of eccentric hollow nanoparticles (hNPs) for different sizes and eccentricity values by means of classical molecular dynamics simulations. Our results reveal that eccentricity displays a significant role in the thermal stability of hNPs. We attribute this behavior to the irregular shell contour, which collapses due to the thermal-activated diffusive process from the nanoparticle shell's most thin region. The mechanism is driven at low temperature by the nucleation of stacking faults until the amorphization for larger temperature values. Besides, for some particular eccentric hNPs, the shell suffers a surface reconstruction process, transforming the eccentric hNP into a concentric hNP. We believe that our study on thermal effects in eccentric hNPs has relevance because of their outstanding applications for plasmonic and sensing.
Assuntos
Ouro , Nanopartículas , TemperaturaRESUMO
Hollow nanoparticle structures play a major role in nanotechnology and nanoscience since their surface to volume ratio is significantly larger than that of filled ones. While porous hollow nanoparticles offer a significant improvement of the available surface area, there is a lack of theoretical understanding, and scarce experimental information, on how the porosity controls or dominates the stability. Here we use classical molecular dynamics simulations to shed light on the particular characteristics and properties of gold porous hollow nanoparticles and how they differ from the nonporous ones. Adopting gold as a prototype, we show how, as the temperature increases, the porosity introduces surface stress and minor transitions that lead to various scenarios, from partial shrinkage for small filling factors to abrupt compression and the loss of spherical shape for large filling. Our work provides new insights into the stability limits of porous hollow nanoparticles, with important implications for the design and practical use of these enhanced geometries.