Few-cycle laser driven reaction nanoscopy on aerosolized silica nanoparticles

Abstract

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.

Three-dimensional Imaging of Nanoplasma by Ion Nanoscopy

“…Their nal energy mainly arises from long-range electrostatic repulsion 22,34 , which occurs over the time scale of picoseconds. It is also worth mentioning that the Coulomb attraction between the fast escaping electrons and the slow ions created on the nanosphere is negligible and has no signi cant effect on the nal ion momenta 22 .…”

“…Their nal energy mainly arises from long-range electrostatic repulsion 22,34 , which occurs over the time scale of picoseconds. It is also worth mentioning that the Coulomb attraction between the fast escaping electrons and the slow ions created on the nanosphere is negligible and has no signi cant effect on the nal ion momenta 22 . Since the trajectories of the ions are also hardly affected by the laser electric eld, a relatively simple and straightforward static electrostatic model 34 is then applicable to correlate the ion momentum distribution with the charge distribution on the surface of the nanosphere.…”

“…At very low radiation intensities, much progress has been made experimentally in understanding how the nanostructure affects localized plasmons [15][16][17] , owing to the development of detection solutions for the plasmonic spatial distribution from two-dimensional (2D) planar (such as photoemission electron microscopy and near-eld scanning optical microscopy) to three-dimensional (3D) planes [18][19][20][21][22][23] . However, we cannot apply these technologies to image nanoplasmas generated at high radiation intensities because the underlying physics for plasmons is different from that for plasma generated at high radiation intensities as discussed here.…”

Strong-field physics with nanospheres

“…These effects can be accounted for in higher level descriptions such as the semi-classical Mie Mean-field Monte-Carlo (M 3 C) model [22,41,47] or via microscopic particle-in-cell (MicPic) models [62,63]. In the following, the details of M 3 C are discussed, as this method has been utilized in most of the scenarios presented in this review [41,43,44,[46][47][48]54,55,64] and was recently also extended for the description of strong-field ionization from metal nanotips [65].…”

“…We will start the discussion in Section 4 by reviewing early surprises where rescattering from small dielectric nanospheres was first observed [36] and continue with inspecting the decisive impacts of charge interaction on the electron emission [43,44]. Section 5 focuses on the effects induced by field propagation within larger dielectric nanospheres and resulting implications and applications [41,[45][46][47][48]. In Section 6 we will review the ultrafast laser-induced metallization of initially dielectric spheres.…”