Excited carrier dynamics in plasmonic nanostructures determines many important optical properties such as nonlinear optical response and photocatalytic activity. Here it is shown that mesoscopic plasmonic covellite nanocrystals with low free‐carrier concentration exhibit a much faster carrier relaxation than in traditional plasmonic materials. A nonequilibrium hot‐carrier population thermalizes within first 20 fs after photoexcitation. A decreased thermalization time in nanocrystals compared to a bulk covellite is consistent with the reduced Coulomb screening in ultrathin films. The subsequent relaxation of thermalized, equilibrium electron gas is faster than in traditional plasmonic metals due to the lower carrier concentration and agrees well with that in a bulk covellite showing no evidence of quantum confinement or hot‐hole trapping at the surface states. The excitation of coherent optical phonon modes in a covellite is also demonstrated, revealing coherent lattice dynamics in plasmonic materials, which until now was mainly limited to dielectrics, semiconductors, and semimetals. These findings show advantages of this new mesoscopic plasmonic material for active control of optical processes.
Sylwester Gawinkowski opened a general discussion of the paper by Jorge Salmon-Gamboa: Why you are using SiO 2 nanoparticles? Do they have any function or are they only the substrate to attach other active nanoparticles to? You have shown that only gold nanoparticles attached to silica nanoparticles do not inuence the rate of reaction signicantly. You have also demonstrated that adding platinum decorations on the gold nanoparticles causes a strong increase in the reaction rate. The signicance of the gold nanoparticles would be more clearly shown with a simple experiment in which you have no gold nanoparticles but still have platinum decorations. Jorge Salmon-Gamboa replied: Silica nanoparticles were chosen as a nanosized inert substrate for Au nanoparticles. This choice of substrate provides a larger surface area covered with the active Au-Pt nanoparticles, in contrast to the situation when the active particles are placed directly onto a at substrate. Aiming for applications, the SiO 2-Au-Pt nanoparticles can then in turn be attached onto a at surface, forming a solid device that can be submerged into water, avoiding the problem of water contamination by nanoparticles. The role of the Au nanoparticles was investigated. Under illumination in the LSP spectral band (556-566 nm), SiO 2-Pt did not enhance the reaction rate. In contrast, under the same conditions, SiO 2-Au-Pt showed a considerably enhanced rate, proving that hot carriers were generated in Au (see Fig. 1 below). (601:[601]601) Yuri Diaz Fernandez continued the discussion: I have two questions: (1) Can you comment on the dispersity of the size distribution of metal and SiO 2 particles and how well controlled are these in your system? (2) In the DIS C9FD90014D
Copper sulphide (covellite) nanoplatelets have recently emerged as a plasmonic platform in the near- infrared with ultrafast nonlinear optical properties. Here we demonstrate that the free-carrier density in CuS, which...
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