Correlating structural dynamics and catalytic activity of AgAu nanoparticles with ultrafast spectroscopy and all-atom molecular dynamics simulations

In this study, we investigated hollow AgAu nanoparticles with the goal of improving our understanding of the compositiondependent catalytic activity of theses nanoparticles. AgAu nanoparticles were synthesized via the galvanic replacement method with controlled size and nanoparticle compositions. We studied extinction spectra with UV-Vis spectroscopy and simulations based on Mie theory and the boundary element method, and ultrafast spectroscopy measurements to characterize decay constants and the overall energy transfer dynamics as a function of AgAu composition. Electronphonon coupling times for each composition were obtained from pump-power dependent pump-probe transients. These spectroscopic studies showed how nanoscale surface segregation, hollow interiors and porosity affect the surface plasmon resonance wavelength and fundamental electron-phonon coupling times. Analysis of the spectroscopic data was used to correlate electron-phonon coupling times to AgAu composition, and thus to surface segregation and catalytic activity. We have performed all-atom molecular dynamics simulations of model hollow AgAu core-shell nanoparticles to characterize nanoparticle stability and equilibrium structures, besides providing atomic level views of nanoparticle surface segregation. Overall, the basic atomistic and electron-lattice dynamics of core-shell AgAu nanoparticles characterized here thus aid the mechanistic understanding and performance optimization of AgAu nanoparticle catalysts

Mixed Media. Maine Public Radio (MPR) is about to make its first substantial

Mixed Media. Maine Public Radio (MPR) is about to make its first substantial programming changes in five years. Comments of MPR vice president Charles Beck

Size dependence of ultrafast charge dynamics in monodisperse Au nanoparticles supported on TiO2 colloidal spheres

Sub-nanosecond charge dynamics in monodisperse Au nanoparticles (NPs) supported on TiO2 colloidal spheres are studied as a function of NP diameter using ultrafast transient absorption spectroscopy. The decay of the transmittance changes observed in the region of the plasmon resonance of the Au NPs following photoexcitation of the TiO2 spheres are well-described by a bi-exponential function consisting of a fast component of 2 ps duration associated with electron–phonon scattering, followed by a slow and relatively weak component associated with phonon–phonon scattering. The decay constant characterising the latter component was found to be dependent on the size of the Au NPs, rising from 49 ± 3 to 128 ± 6 ps as the diameter of the Au NPs increased from 12.2 ± 2.2 nm to 24.5 ± 2.8 nm, respectively

Automated single-particle reconstruction of heterogeneous inorganic nanoparticles

Single-particle reconstruction can be used to perform three-dimensional (3D) imaging of homogeneous populations of nano-sized objects, in particular viruses and proteins. Here, it is demonstrated that it can also be used to obtain 3D reconstructions of heterogeneous populations of inorganic nanoparticles. An automated acquisition scheme in a scanning transmission electron microscope is used to collect images of thousands of nanoparticles. Particle images are subsequently semi-automatically clustered in terms of their properties and separate 3D reconstructions are performed from selected particle image clusters. The result is a 3D dataset that is representative of the full population. The study demonstrates a methodology that allows 3D imaging and analysis of inorganic nanoparticles in a fully automated manner that is truly representative of large particle populations