Abstract:Plasmonic nanostructures have been proposed as useful materials for photon harvesting applications. However, the mechanisms by which energy transfer occurs across interfaces formed between plasmonic materials and their environment are under debate. A commonly invoked mechanism is indirect hot charge carrier transfer, where hot carriers are generated in the plasmonic material by nonradiatve plasmon decay, followed by transfer of these carriers to interfacial species in a sequential process. Alternatively, chemi… Show more
“…4c, d ). Therefore, the near field driven direct energy transfer between molecules and metal 47 may not be the main mechanism for the reaction. Fig.…”
Surface plasmons (SPs) of metals enable the tight focusing and strong absorption of light to realize an efficient utilization of photons at nanoscale. In particular, the SP-generated hot carriers have emerged as a promising way to efficiently drive photochemical and photoelectric processes under moderate conditions. In situ measuring of the transport process and spatial distribution of hot carriers in real space is crucial to efficiently capture the hot carriers. Here, we use electrochemical tip-enhanced Raman spectroscopy (EC-TERS) to in situ monitor an SP-driven decarboxylation and resolve the spatial distribution of hot carriers with a nanometer spatial resolution. The transport distance of about 20 nm for the reactive hot carriers is obtained from the TERS imaging result. The hot carriers with a higher energy have a shorter transport distance. These conclusions can be guides for the design and arrangement of reactants and devices to efficiently make use of plasmonic hot carriers.
“…4c, d ). Therefore, the near field driven direct energy transfer between molecules and metal 47 may not be the main mechanism for the reaction. Fig.…”
Surface plasmons (SPs) of metals enable the tight focusing and strong absorption of light to realize an efficient utilization of photons at nanoscale. In particular, the SP-generated hot carriers have emerged as a promising way to efficiently drive photochemical and photoelectric processes under moderate conditions. In situ measuring of the transport process and spatial distribution of hot carriers in real space is crucial to efficiently capture the hot carriers. Here, we use electrochemical tip-enhanced Raman spectroscopy (EC-TERS) to in situ monitor an SP-driven decarboxylation and resolve the spatial distribution of hot carriers with a nanometer spatial resolution. The transport distance of about 20 nm for the reactive hot carriers is obtained from the TERS imaging result. The hot carriers with a higher energy have a shorter transport distance. These conclusions can be guides for the design and arrangement of reactants and devices to efficiently make use of plasmonic hot carriers.
“…The actual involvement of hot carriers in several chemistry experiments has been recently questioned, with the proposition of alternative mechanisms, such as direct photoexcitation of hybrid particle-adsorbate complexes [19][20][21] or simple heat generation [22][23][24] . Indeed, the further thermalization of these excited carriers via electron-phonon scattering leads to heating of the entire nanoparticle and further heat diffusion to the surrounding reaction medium, suggesting that photothermal effects may also contribute to the observed reactivity enhancement 25 .…”
Light absorption and scattering of plasmonic metal nanoparticles can lead to non-equilibrium charge carriers, intense electromagnetic near-fields, and heat generation, with promising applications in a vast range of fields, from chemical and physical sensing to nanomedicine and photocatalysis for the sustainable production of fuels and chemicals. Disentangling the relative contribution of thermal and non-thermal contributions in plasmon-driven processes is, however, difficult. Nanoscale temperature measurements are technically challenging, and macroscale experiments are often characterized by collective heating effects, which tend to make the actual temperature increase unpredictable. This work is intended to help the reader experimentally detect and quantify photothermal effects in plasmon-driven chemical reactions, to discriminate their contribution from that due to photochemical processes and to cast a critical eye on the current literature. To this aim, we review, and in some cases propose, seven simple experimental procedures that do not require the use of complex or expensive thermal microscopy techniques. These proposed procedures are adaptable to a wide range of experiments and fields of research where photothermal effects need to be assessed, such as plasmonic-assisted chemistry, heterogeneous catalysis, photovoltaics, biosensing, and enhanced molecular spectroscopy.
What is Plasmonic Catalysis? Plasmon-excitation-mediated chemistry, which is a rapidly growing field, is founded on a simple principle: the excitation of the localized surface plasmon resonance (LSPR) of metal nanoparticles triggers chemical reactions on the surfaces of the nanoparticles. [1][2][3][4] Early examples of plasmon-excitation-driven nanoparticle synthesis 5,6 and hotelectron-driven chemical reactions induced by ultrashort pulse excitation of metal nanoparticles 7 can be thought of as precursors to the findings of direct photocatalysis by plasmonic nanoparticles 3 , which is the focus of this Viewpoint. The field in its current state was, in large part, invigorated by a 2011 paper, 8 which showed that the excitation of the LSPR of Ag nanoparticles by continuouswave (CW), visible-frequency light triggered the dissociation of adsorbed O2. The O . atoms thus produced were utilized for industrially relevant oxidation reactions such as those of propylene and ethylene, which would have otherwise required high-temperature and -pressure conditions to proceed at appreciable rates. 8,9 In the absence of visible-light excitation, the bond dissociation and oxidation reactions proceeded at appreciably low rates, which indicated that plasmonic excitation enhanced the rates of these chemical reactions. The phenomenon is, therefore, termed as plasmonic catalysis or plasmonic photocatalysis. Another classic example of plasmonic catalysis involves the dissociation of H2 to H . on Au nanoparticles under visible-light excitation of the LSPR. 10,11 While a detailed electronic description of these phenomena is still being worked out, one proposed mechanistic picture is that the decay of the LSPR by Landau collisionless damping and electronelectron scattering in the metal results in the intraband (or interband) excitation of an sp-band (or d-band) electron 12 to a state above the equilibrium Fermi level of the metal. The kinetic energy of one or more such hot electrons is transferred to an adsorbate, such as O2, by electron-adsorbate scattering resulting in the nonthermal vibrational excitation of a bond in the adsorbate. 1,8 The excited adsorbate is then much more likely to undergo bond dissociation than one would expect from the equilibrium temperature. It must be noted that for adsorbates that form strong electronic admixtures with states of the metal, 13,14 such electron-adsorbate scattering can take place
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