A comprehensive development of the charge-transfer theory of surface enhanced Raman scattering (SERS) is presented. We incorporate the Herzberg–Teller mixing of zero-order Born–Oppenheimer electronic states by means of vibronic interaction terms in the Hamiltonian. This is similar to the theory of Tang and Albrecht12 except that we include metal states as part of a molecule–metal system. When this is done we may no longer discard a term involving mixing of ground-state vibrations. The theory is comprehensive in that both molecule-to-metal and metal-to-molecule transfer is considered. Furthermore, both Franck–Condon and Herzberg–Teller contributions to the intensity are obtained. The former, however, contribute only to the intensity of totally symmetric vibrations, while the latter contribute to nontotally symmetric vibrations as well. Since overtones are observed in SERS only weakly if at all, the Herzberg–Teller terms are most consistent with experimental findings. The resulting formulas may be interpreted as a type of resonance Raman effect in which intensity for the charge transfer transitions is borrowed from an allowed molecular transition. We may also carry out the sum over metal states. This procedure predicts a logarithmic resonance at the Fermi level of the metal. We thus predict intensity vs voltage profiles such as I ∝ ‖ln(ωFI−ω+iΓ)‖2 which fits the experimental curves quite well.

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Ten years ago, three teams experimentally demonstrated the first spasers, or plasmonic nanolasers, after the spaser concept was first proposed theoretically in 2003. An overview of the significant progress achieved over the last 10 years is presented here, together with the original context of and motivations for this research. After a general introduction, we first summarize the fundamental properties of spasers and discuss the major motivations that led to the first demonstrations of spasers and nanolasers. This is followed by an overview of crucial technological progress, including lasing threshold reduction, dynamic modulation, room-temperature operation, electrical injection, the control and improvement of spasers, the array operation of spasers, and selected applications of single-particle spasers. Research prospects are presented in relation to several directions of development, including further miniaturization, the relationship with Bose-Einstein condensation, novel spaser-based interconnects, and other features of spasers and plasmonic lasers that have yet to be realized or challenges that are still to be overcome.

Selective hydrogenation of unsaturated aldehydes to unsaturated alcohols is a valuable but challenging task for synthesizing fine chemicals. We report that single Rh atoms anchored to the edges of 2D MoS2 sheets can efficiently convert crotonaldehyde to crotyl alcohol with 100% selectivity via a steric confinement effect of pocketlike active sites. Characterization results suggest that the synthesized Rh1/MoS2 single-atom catalysts (SACs) possess a unique geometric and electronic configuration, which confines the adsorption mode of the reactant molecule by a steric effect. The DFT calculations suggest that the MoS2 sheets terminate with oxidized Mo edges and the Rh1 stably anchors at the Mo cation vacancy site, which can facilely dissociate H2 to H atoms. The dissociated H atoms spill over to react with the edge O atoms to form OH species and create an HO–Mo–Rh1–Mo–OH configuration, resembling a pocketlike active site, which confines the adsorption mode of the crotonaldehyde due to steric effects. Such specific adsorption configuration yields 100% selectivity. The strategy of constructing pocketlike active centers with single metal atoms and 2D nanosheets opens new approaches to designing highly selective SACs for specific classes of catalytic transformations.

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Single-atom catalysts (SACs) exhibit unique catalytic property and maximum atom e ciency of rare, expensive metals. A critical barrier to applications of SACs is sintering of active metal atoms under operating conditions. Anchoring metal atoms onto oxide supports via strong metal-support bonds may alleviate sintering. Such an approach, however, usually comes at a cost: stabilization results from passivation of metal sites by excessive oxygen ligation-too many open coordination sites taken up by the support, too few left for catalytic action. Furthermore, when such stabilized metal atoms are activated by reduction at elevated temperatures they become unlinked and so move and sinter, leading to loss of catalytic function. We report a new strategy, con ning atomically dispersed metal atoms onto functional oxide nanoclusters (denoted as nanoglues) that are isolated and immobilized on a robust, high-surfacearea support-so that metal atoms do not sinter under conditions of catalyst activation and/or operation.High-number-density, ultra-small and defective CeOx nanoclusters were grafted onto high-surface-area SiO2 as nanoglues to host atomically dispersed Pt. The Pt atoms remained on the CeOx nanoglue islands under both O2 and H2 environment at high temperatures. Activation of CeOx supported Pt atoms increased the turnover frequency for CO oxidation by 150 times. The exceptional stability under reductive conditions is attributed to the much stronger a nity of Pt atoms for CeOx than for SiO2-the Pt atoms can move but they are con ned to their respective nanoglue islands, preventing formation of larger Pt particles. The strategy of using functional nanoglues to con ne atomically dispersed metal atoms and simultaneously enhance catalytic performance of localized metal atoms is general and takes SACs one major step closer to practical applications as robust catalysts for a wide range of catalytic transformations Main TextThe design strategy integrates three components into the nal catalyst: 1) a robust, high-surface-area support (e.g., SiO 2 , Al 2 O 3 , etc.), 2) nanoscale functional metal oxides (e.g., CeO x , TiO x , FeO x , etc.) anchored stably onto the robust support as isolated nanoglue islands, and 3) single metal atoms (M 1 ) selectively localized to only the nanoglue islands. The nanoglue selection criteria include a) its stability in dispersed form on the support surface due to strong bonding, b) a much stronger a nity for the active metal atoms than the support, and c) interactions with the active metal that enhance activity and/or selectivity for the desired catalytic reactions. The selected nanoglue not only behaves as a "double-sided tape" but also contributes to the desired functions for the targeted catalytic reaction.We selected SiO 2 , an irreducible, inexpensive support widely used in processing industries, to demonstrate our strategy because of its high-surface-area, structural stability, and availability in various forms 14 . Because metal atoms anchor onto reducible metal oxides (e.g., CeO 2 , TiO 2 ,...

A new self-powered broadband photodetector was fabricated by coating an n-silicon nanowire (n-Si NW) array with a layer of p-cupric oxide (CuO) nanoflakes through a new simple solution synthesis method. The p-n heterojunction shows excellent rectification characteristics in the dark and distinctive photovoltaic behavior under broadband light illumination. The photoresponse of the detector at zero bias voltage shows that this self-powered photodetector is highly sensitive to visible and near-infrared light illuminations, with excellent stability and reproducibility. Ultrafast response rise and recovery times of 60 and 80 μs, respectively, are shown by the CuO based nanophotodetector. In addition, the broadband photodetector can also provide a rapid binary response, with current changing from positive to negative upon illumination under a small bias. The binary response arises from the photovoltaic behavior and the low turn-on voltage of the CuO/Si NW device. These properties make the CuO/Si NW broadband photodetector suitable for applications that require high response speeds and self-sufficient functionality.

High-performance broadband photodetectors have recently attracted signifi cant interest [1][2][3][4][5] because of their importance to a variety of applications, including imaging, remote sensing, environmental monitoring, astronomical detection, photometers and analytical applications. Graphene is a promising material for broadband photodetection applications because of its ability to absorb incident light over a wide wavelength range, from at least the visible (VIS) spectrum to the infrared. [ 6 ] Recent works have demonstrated that zerobandgap single-or few-layer graphene-based photodetectors based on a fi eld-effect transistor (FET) structure could operate in the near-infrared (NIR) and VIS parts of the electromagnetic spectrum. [ 7,8 ] However, no working spectra have been demonstrated for these zero-bandgap graphene photodetectors in longer wavelength ranges. Theoretical calculations indicated that opening and varying the bandgap of