Dynamic final-state nanoparticle-substrate interaction in the photoemission of dodecanethiolate-passivated Ag nanoparticles on graphite substrates

Abstract

We have carried out a photoemission study of dodecanethiolate-͑DT-͒ passivated Ag nanoparticles supported on the highly oriented pyrolytic graphite ͑HOPG͒ substrates. From detailed photoemission measurements, it is found that the Fermi-level onsets in the photoemission spectra of DT-passivated Ag nanoparticles on the HOPG substrates are not the metallic Fermi edge, with the steep slope being away from the Fermi level. We attribute the unusual spectral features in the vicinity of Fermi level to the dynamic final-state effect in photoemission, indicative of the interaction between the nanoparticle and substrate through the surface passivants on a femtosecond time scale.

Photoelectron spectroscopy on the charge reorganization energy and small polaron binding energy of molecular film

“…The lifetime broadening in photoemission appears differently from that in an electronic transition to a bound state. The lifetime broadening in photoemission from an ultrathin film of weakly interacting molecules may yield a skewed shape for the line while tailing to a higher kinetic energy, since the photoelectron kinetic energy increases by disappearance of the photo-generated hole potential during existing outside the film [47,48], which is resemble to phenomena due to the post collision interaction (PCI) in gas-phase inner-shell ionization [49,50]. The lifetime of the photogenerated-HOMO hole is dominated by the electronic interaction between ionized molecules and the substrate, also providing information, e.g., on the electron transfer rate from the substrate to the molecule.…”

“…When one considers the thermal energies of the samples in the measurements, the energy gain is expected to be negligibly small. It is thus considered that the important origin of the large low-energy tail at low temperature is the HOMO-hole lifetime [3,4,47,48].…”

Dependence of the final-state effect on the coupling between a CdSe nanoparticle and its neighbors studied with photoemission spectroscopy

“…[8][9][10] A simple dynamic model that takes into account the finite lifetime of the photohole provides a quantitative interpretation for the photoemission spectra of metallic clusters near the Fermi level; furthermore, the magnitude of the lifetime has been found to depend on the interaction between cluster and substrate. [11][12][13] In contrast, a detailed investigation of the energy shift, dependent on size, of core-level and valence-band photoemission spectra for semiconductor NPs is lacking. In their pioneer work Colvin et al discussed the relative shift in the valence band among NPs.…”

Surface-Passivant Dependence of Dynamic Charging Effect in Alkanethiolate-Passivated Au Nanoparticles on Graphite Substrates Studied by Photoelectron Spectroscopy

“…The samples were transferred into the photoelectron analysis chamber without exposure to air. Since the photoemission spectrum in the vicinity of Fermi level of HOPG substrate exhibits the featureless shape reflecting the vanishing semimetallic density of states toward the Fermi level [11], the observed spectral features of all the samples are not caused by the HOPG substrates, but are characteristic of Au nanoparticles. All measurements were performed at 40 K using a closed-cycle He refrigerator in order to minimize the thermal broadening effects.…”

“…The photoemission measurements were performed with the He I resonance line (hν=21.2 eV) as the excitation source. In general, the photoemission spectra reflect the change in the electronic structure of the sample (initial-state effect) and final-state effect originating from positively charged photohole created 0899-N07-07.2 by the photoionization [8][9][10][11]. The photoemission spectra showed no change in the course of the measurements.…”