Electronically Driven Fragmentation of Silver Nanocrystals Revealed by Ultrafast Electron Crystallography

Abstract

We report an ultrafast electron diffraction study of silver nanocrystals under surface plasmon resonance excitation, leading to a concerted fragmentation. By examining simultaneously transient structural, thermal, and Coulombic signatures of the prefragmented state, an electronically driven nonthermal fragmentation scenario is proposed.

Structural dynamics of two-dimensional charge-density waves in CeTe3investigated by ultrafast electron crystallography

“…The origin of the ultrafast phase fluctuation might be attributed to the reduction of the long-range coherence of the CDW collective state. Electronically induced fragmentation has been seen previously in nanoparticles under surface plasmon resonance excitation [35] without significantly transferring energy into the lattice sub-system, as evidenced by a rapid nonthermal recovery in the structure factor following the electronic recovery. The presence of this electronically induced fragmentation of CDW is further supported by the observation of topological defects in the optical reflectivity signals as a first step for the recovery of CDW in the electronic subsystem [12].…”

Ultrafast Electron Diffractive Voltammetry: General Formalism and Applications

“…Since neither the carrier concentration nor the carrier temperature can be increased significantly for metallic nanoparticles by photoexcitation, as compared to Si substrate, the early electron migration to Si surface might suggest a laserinduced surface plasmon effect being present, excited in the gold nanoparticles that promotes a surface-field assisted or multi-photon internal ionization for nanoparticle charging. [50] (2) A 'reverse' charging process occurs as the fluence is increased beyond 11 mJ/cm 2 , as evidenced in the surging of V s after 10 ps at F=15 mJ/cm 2 , which reaches a positive value at ∼ 22 ps. The reversal of nanoparticle charging is driven by the overcharging of Si surface.…”

“…With UEC operated in such circumstances, the intensity of transmitted Bragg peaks have been used to monitor the integrity of the lattice structure, including laser-induced thermal fluctuations and phase transition, [33] and have been exploited to investigate the surface-supported nanoparticles. [49,50] What's essential here for formulating the surface diffractive voltammetry is that the diffraction condition under a = 0 has: θ i + θ o = θ tot = nλ/c, where λ is the electron wavelength, n is the diffraction order, and c is the lattice constant, can be used to formulate the diffracted beam trajectory under the presence of transient surface field, as described in Fig. 3.…”

Single-electron pulses for ultrafast diffraction

“…These resolutions are provided by ultrafast electron diffraction and microscopy techniques, which are based on pump-probe arrangements with a femtosecond laser for excitation and with ultrashort electron packets for measuring sequences of atomic-scale structures during changes (1). Recently reported studies include such of reaction pathways during phase transformations (2), chemical reactions (3), laser ablation (4), molecular alignment (5), changes at interfaces (6), heating and melting processes (7)(8)(9), cantilever motion (10), or evanescent fields around nanostructures (11), among many others (12). Possibilities to access the attosecond regime of charge density motion are also discussed (13), taking into account the generation of pulses (14)(15)(16) and the quantum dynamics of the scattering process (17).…”