Few-cycle laser driven reaction nanoscopy on aerosolized silica nanoparticles

Nanoparticles offer unique properties as photocatalysts with large surface areas. Under irradiation with light, the associated near-fields can induce, enhance, and control molecular adsorbate reactions on the nanoscale. So far, however, there is no simple method available to spatially resolve the near-field induced reaction yield on the surface of nanoparticles. Here we close this gap by introducing reaction nanoscopy based on three-dimensional momentum-resolved photoionization. The technique is demonstrated for the spatially selective proton generation in few-cycle laser-induced dissociative ionization of ethanol and water on SiO2 nanoparticles, resolving a pronounced variation across the particle surface. The results are modeled and reproduced qualitatively by electrostatic and quasi-classical mean-field Mie Monte-Carlo (M3C) calculations. Reaction nanoscopy is suited for a wide range of isolated nanosystems and can provide spatially resolved ultrafast reaction dynamics on nanoparticles, clusters, and droplets

Photo-excitation band-structure engineering of 2H-NbSe2_2 probed by time- and angle-resolved photoemission spectroscopy

We investigated the nonequilibrium electronic structure of 2H-NbSe$_2$ by time- and angle-resolved photoemission spectroscopy. We find that the band structure is distinctively modulated by strong photo-excitation, as indicated by the unusual increase in the photoelectron intensities around E$_F$. In order to gain insight into the observed photo-induced electronic state, we performed DFT calculations with modulated lattice structures, and found that the variation of the Se height from the Nb layer results in a significant change in the effective mass and band gap energy. We further study the momentum-dependent carrier dynamics. The results suggest that the relaxation is faster at the K-centered Fermi surface than at the $\Gamma$-centered Fermi surface, which can be attributed to the stronger electron-lattice coupling at the K-centered Fermi surface. Our demonstration of band structure engineering suggests a new role for light as a tool for controlling the functionalities of solid-state materials.Comment: 7 pages, 5 figure

Insulator-to-metal transition induced by mid-IR vibrational excitation in a magnetoresistive manganite

Selective vibrational excitation of insulating Pr0.7Ca0.3MnO3 at 17 ?m triggers a transition to a metallic state. A four order of magnitude drop of the sample resistivity and ultrafast, nanosecond-lived reflectivity changes are observe

High-order harmonic generation from hybrid organic–inorganic perovskite thin films

The generation of high-order harmonics from hybrid organic–inorganic perovskites (HOIPs) is demonstrated by the excitation with a strong mid-infrared laser pulse. We prepare three types of HOIP polycrystalline thin film samples by solution processes (MAPbX3; MA = CH3NH3+;X = I, Br, Cl). The high-order harmonics from the sample (MAPbBr3) are more than tenfold stronger than those from the well-studied GaSe crystal despite their comparable bandgap energies, implying that the stronger band-to-band transition of the HOIPs causes the higher yields