Direct Visualization of Photomorphic Reaction Dynamics of Plasmonic Nanoparticles in Liquid by Four-Dimensional Electron Microscopy

Abstract

Liquid-cell electron microscopy (LC-EM) provides a unique approach for in-situ imaging morphology change of nanocrystals in liquids under electron beam irradiation. However, nanoscale real-time imaging of chemical/physical reaction processes in liquids under optical stimulus is still challenging. Here, we report direct observation of photomorphic reaction dynamics of gold nanoparticles (AuNPs) in water by liquid-cell four-dimensional electron microscopy (4D-EM) with high spatiotemporal resolution. The photoinduced agglomeration, coalescence, and fusion dynamics of AuNPs at different temperatures are studied. At low laser fluences, the AuNPs show a continuous aggregation in several seconds, and the aggregate size decreases with increasing fluence. At higher fluences close to melting threshold of AuNP, the aggregates further coalesced into nanoplates. While at fluences far above the melting threshold, the aggregates fully fuse into bigger NPs, which completes within tens of nanoseconds. This liquid-cell 4D-EM would also permit study of other numerical physical/chemical reaction processes in their native environments. TOC GraphicPage 2 of 28 ACS Paragon Plus EnvironmentThe Journal of Physical Chemistry Letters 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 3 Main TextOwing to the unique optical and electronic properties that are not available in either molecules or bulk counterparts, noble metallic nanoparticles (NPs), for example gold NPs (AuNPs), have attracted great interests and found vast applications in a wide range of fields such as solar cells, [1][2] photocatalysis, 3-4 biosensors [5][6] and drug delivery. [7][8] In general, metallic NPs exhibit a surface-enhanced plasmon band as a result of intraband transitions through the photoexcitation of free conduction electrons on their surface. The surface plasmonic properties (e.g., peak position, width and intensity) of the NPs are determined by their size and shape. 9 It has been widely demonstrated that the morphology and size of the metal colloidal NPs can be significantly modified by light or laser irradiation. Because of subsequent aggregation, coalescence and fusion of NPs, other nanostructures including nanorods, nanobipyramids, nanoprisms and nanodisks can form, where the structures of the products strongly depend on the light wavelength, light intensity and capping ligands. [10][11][12][13][14][15] The control of the morphology and size of the metallic NPs by light not only provides a unique avenue of synthesis but also allows one to modulate their surface plasmon properties in a highly dynamic fashion. 15 In previous studies, however, the prevailing methods for detecting the morphological change of NPs under light irradiation, e.g., time-resolved or static optical scattering and absorption spectroscopies only provided indirect information of the NPs morphology ...

Observation and Control of Unidirectional Ballistic Dynamics of Nanoparticles at a Liquid–Gas Interface by 4D Electron Microscopy

“…It has been demonstrated that, because of the resonant surface plasmon excitation enhanced optical absorption and thus the strong photothermal effect, , repetitive femtosecond laser pulse excitation on gold NPs in water results in randomly rapid nucleation, expansion, and collapse/detachment of plasmonic NBs around the NP surface, which could generate random driving forces and propel the NP diffusion. , This mechanism is further verified by transient creation of a plasmonic bubble around a gold NP cluster and subsequent ejected motion of the cluster captured by our single-pulse imaging experiment, which will be discussed later. In our experiment, because of the capillary flow drag due to the different vapor rate at the curved surface or the meniscus effect , arising from the liquid surface tension, the gold NP is strongly constrained at the liquid–gas interface (see Figure S1a and b) and thus can only move along the interface under the plasmonic NB propulsion.…”

“…e ., single-pulse imaging mode, where the time delay between the nanosecond electron pulse and the femtosecond laser pulse was precisely controlled by a digital delay generator and the temporal resolution was not affected by the response time of the charge-coupled device (CCD). Details of the imaging procedures have been also reported in our previous studies. ,,, …”

Reverse Monte Carlo modeling for local structures of noble metal nanoparticles using high-energy XRD and EXAFS

“…In some cases, if metallic nanoparticles are crystallized, single crystal X-ray methods can be used to determine their structures, or atomic resolution tomographic images of individual nanoparticles can be obtained. However, in general, additional methods for quantitative and rapid 3D atomic structural characterization of disordered nanomaterials are needed because traditional techniques such as powder X-ray diffraction (XRD), highresolution transmission electron microscopy (HRTEM), 7,8 Xray absorption ne structure (XAFS), 9,10 small-angle X-ray scattering (SAXS), 11,12 grazing incident small-angle X-ray scattering (GISAXS), 13,14 differential scanning calorimetry (DSC), 15,16 and others, are well suited to bulk-like crystalline materials for the determination of phase behavior, particle size, and so on. XAFS techniques such as XANES and EXAFS have widely been used to probe the valence state and nearest-atomic neighbor arrangement, but they are not sensitive to the longer range atomic structure in nanomaterials.…”

Ultrafast rotational motions of supported nanoclusters probed by electron diffraction

“…2 The dynamics of nanoparticles in liquids have been examined experimentally by four-dimensional electron microscopy. [9][10][11] In a recent article, 12 some of the authors have used femtosecond electron diffraction (FED) 13 to investigate ultrafast atomic motions of Au NCs on thin-films under nonequilibrium conditions. The observed dynamics of diffraction peaks could be explained in terms of energy flow between the electrons and the atomic vibrations of the NCs and the substrate.…”