ABSTRACT
We present the results of a systematic study of photoelectron emission from isolated dielectric nanoparticles (SiO2) irradiated by intense 25 fs, 780â nm linearly polarized laser pulses as a function of particle size (20â nm to 750â nm in diameter) and laser intensity. We also introduce an experimental technique to reduce the effects of focal volume averaging. The highest photoelectron energies show a strong size dependence, increasing by a factor of six over the range of particles sizes studied at a fixed intensity. For smaller particle sizes (up to 200â nm), our findings agree well with earlier results obtained with few-cycle, â¼4 fs pulses. For large nanoparticles, which exhibit stronger near-field localization due to field-propagation effects, we observe the emission of much more energetic electrons, reaching energies up to â¼200 times the ponderomotive energy. This strong deviation in maximum photoelectron energy is attributed to the increase in ionization and charge interaction for many-cycle pulses at similar intensities.
ABSTRACT
The solubility of ca. 5.0 nm gold nanoparticles was studied systematically as a function of ligand shell and solvent. The ligands were octane-, decane-, dodecane- and hexadecanethiols; the solvents were the n-alkanes from hexane to hexadecane and toluene. Supernatant concentrations in equilibrium with precipitated superclusters of nanoparticles were measured at room temperature (23 °C) with UV-Vis spectrophotometry. The solubility of nanoparticles ligated with decane- and dodecanethiol was greatest in n-decane and n-dodecane, respectively. In contrast, the solubility of nanoparticles ligated with octane- and hexadecanethiol showed decreasing solubility with increasing solvent chain length. In addition the solubility of the octanethiol ligated system showed a nonmonotonic solvent carbon number functionality with even numbered solvents being better solvents than neighboring odd numbered solvents.
