Strong interactions of electromagnetic fields with plasmonic nanomaterials have been exploited in various applications. These applications have centred on plasmon-enhanced scattering rates in nearby ...molecules or plasmon-induced heating. A question that has emerged recently is whether it is possible to use plasmonic nanostructures in a range of hot electron (hole) applications, including photocatalysis, photovoltaics and photodetection. These applications require coupling of a plasmonic component, which amplifies the interaction of light with the material, to an attached non-plasmonic component that extracts this energy in the form of electronic excitations to perform a function. In this Perspective, we discuss recent work in the emerging field of hybrid plasmonics. We focus on fundamental questions related to the nanoscopic flow of energy and excited charge carriers in these multicomponent materials. We also address critical misconceptions, challenges and opportunities that require more attention.
It has been shown that photoexcitation of plasmonic metal nanoparticles (Ag, Au and Cu) can induce direct photochemical reactions. However, the widespread application of this technology in catalysis ...has been limited by the relatively poor chemical reactivity of noble metal surfaces. Despite efforts to combine plasmonic and catalytic metals, the physical mechanisms that govern energy transfer from plasmonic metals to catalytic metals remain unclear. Here we show that hybrid core-shell nanostructures in which a core plasmonic metal harvests visible-light photons can selectively channel that energy into catalytically active centres on the nanostructure shell. To accomplish this, we developed a synthetic protocol to deposit a few monolayers of Pt onto Ag nanocubes. This model system allows us to conclusively separate the optical and catalytic functions of the hybrid nanomaterial and determine that the flow of energy is strongly biased towards the excitation of energetic charge carriers in the Pt shell. We demonstrate the utility of these nanostructures for photocatalytic chemical reactions in the preferential oxidation of CO in excess H
. Our data demonstrate that the reaction occurs exclusively on the Pt surface.
The Andes‐Amazon transition, along the eastern Peruvian Andes, features “hot spots” with strong precipitation. Using 15 years of Tropical Rainfall Measuring Mission PR data we established a robust ...relation between terrain elevation and mean surface precipitation, with the latter peaking around 1000 m above sea level (asl), coinciding with the moisture flux peak of the South American Low Level Jet (SALLJ). There is strong diurnal variability, with afternoon (13–18 LT) convection in the Amazon plains, while on the eastern slopes (1000–2000 m asl), after the forcing associated with the thermal heating of the Andes subsides, convection grows during the night and surface precipitation peaks around 01–06 LT and organizes into mesoscale convective systems (MCSs). These then displace downslope to an terrain elevation of 700 m asl with stratiform regions spreading upslope and downslope and then decay during the remainder of the morning. The large MCSs contribute with at least 50% of daily rainfall (60% of the 01–06 LT rainfall). On synoptic scales, the large MCSs are more common in stronger SALLJ conditions, although subtropical cold surges are responsible for 16% of the cases.
Key Points
Robust relation found between precipitation and terrain elevation with a peak at ~1000 m asl coincident with the SALLJ moisture flux profile
Mean precipitation depends strongly on the diurnal cycle and indicates nocturnal organization of storms into mesoscale convective systems
Large precipitation features (MCS) are relatively rare but contribute at least 50% of the total precipitation on the eastern Andes
The inclusion of metal nanoparticle electrocatalysts on semiconductor photoelectrodes is often used to increase the efficiency of photocatalytic reactions on semiconductors. It is well established ...that metal electrocatalysts can limit overpotential losses associated with many important photocatalytic reactions, significantly increasing the efficiency of the conversion of solar into chemical energy. On the other hand, the introduction of metal nanoparticles can also impact the light-absorbing properties of semiconductors. We have studied the impact of the introduction of Pt nanoparticles on the optical and catalytic properties of flat Si photoelectrodes for the photoelectrocatalytic evolution of hydrogen. We demonstrate that the deposition of platinum nanoparticles onto planar Si photocathodes results in improved catalytic rates for the hydrogen evolution reaction, but also a diminished light-limited rate of photon to hydrogen conversion. We also show that by embedding Pt nanoparticles into Si, the light-limited rates are significantly improved while preserving the improved catalytic rates. We provide mechanistic insights that allow us to shed light on these experimental findings and discuss design principles to simultaneously improve the kinetic and optical properties of a planar Si photocathode through the judicious introduction of metal nanoparticles.
The strong coupling of optical absorbers (e.g., molecules or semiconductors) to confined photonic modes fundamentally alters the physical properties of the coupled system via the formation of hybrid ...light-matter states. One potential application of strong light-matter coupling relies on exploiting it to localize light-induced charge excitation processes to small volumes of material. Applications that would benefit from this localization include thin-film photovoltaics, photodetection, photocatalysis, and others, where the overall performance depends on the ability of a material to amplify light absorption (i.e., the formation of electron-hole pairs) within specific locations in space. This contribution investigates how strong light-matter coupling affects light absorption rates in molecular absorbers coupled to photonic nanostructures. Our results show that the molecular light absorption efficiencies are highest in configurations where the strongly coupled molecules interact directly with the incoming photon flux. We also identify a nonlinear dependence in the molecular absorption as a function of concentration, unique to the strongly coupled systems. Based on these results, we propose design principles for engineering nanostructured systems that allow for high efficiencies of charge carrier localization into strongly coupled absorbers.
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•Strong coupling increases charge carrier generation rates in coupled molecular absorbers.•Efficiencies are highest when the coupled molecules interact directly with incoming photons.•Light absorption is nonlinear as a function of concentration in strongly coupled molecules.
The sensitivity of warm orographic cloud development to aerosol indirect effects was investigated through aerosol-aware Weather Research and Forecast model simulations contrasting ...aerosol-cloud-precipitation interactions using the default (generic) aerosol and regional aerosol measurements from the Integrated Precipitation and Hydrology Experiment in the Southern Appalachian Mountains for three rainfall events: 1) enhanced local convection; 2) a frontal system, and 3) a tropical system. Using the regional aerosol activation spectrum yields higher number of drops than using the default, smaller cloud droplets and delayed rainfall onset under weak synoptic forcing conditions. Evaluation against aircraft measurements in isolated convective clouds reveals that while the model microphysics falls short of reproducing the vertical structure of nonprecipitating clouds, the liquid water content, and the concentration of cloud droplets near cloud base are in keeping with observations. The simulated cloud vertical structure shows the regional signature of orographic enhancement over the mountains vis-a-vis the adjacent plains. In the inner region, valley-ridge circulations organize the spatial patterns of cloudiness under weak synoptic forcing. The formation of early afternoon low-level clouds over the ridges in the summertime reflects the aerosol indirect effect. By contrast, for large-scale systems with strong and sustained moisture convergence at low levels (frontal and tropical systems), mechanically forced rainfall efficiency is enhanced, there is no delay in the onset of precipitation, and the aerosol indirect effect is negligible. This study shows that the impact of aerosol-cloud-precipitation interactions on the spatial variability of orographic rainfall is conditional on weather regime.
The decay of localized surface plasmons supported by plasmonic metal nanoparticles results in the formation of energetic charge carriers within the nanoparticles. Once formed, these charge carriers ...can transfer to chemically attached materials where they can perform a function. The efficient extraction and utilization of these charge carriers in various applications hinges on the ability to design plasmonic nanostructures with highly localized charge carrier generation at specific locations in the nanostructure. Herein, we shed light on the physical mechanisms governing the flow of energy in resonantly excited multimetallic plasmonic nanoparticles. We demonstrate that coating plasmonic nanostructures with nonplasmonic metals can result in the preferential dissipation of energy (i.e., formation of charge carriers) in the nonplasmonic metal and that the extent of this dissipation depends heavily on the electronic structure of the constituent metals. We use experimental and modeling studies of various core–shell nanostructures to develop a transparent physical framework of energy transfer in these systems and discuss how this framework can be used to engineer nanostructures that allow for high efficiencies of charge carrier extraction.
We use experimental and computational studies of core-shell metal-semiconductor and metal-molecule systems to investigate the mechanism of energy flow and energetic charge carrier generation in ...multicomponent plasmonic systems. We demonstrate that the rates of plasmon decay through the formation of energetic charge carriers are governed by two factors: (1) the intensity of the local plasmon induced electric fields at a specific location in the multicomponent nanostructure, and (2) the availability of direct, momentum conserved electronic excitations in the material located in that specific location. We propose a unifying physical framework that describes the flow of energy in all multicomponent plasmonic systems and leads us towards molecular control of the energy flow and excited charge carrier generation in these systems.
Direct electronic transitions act as a preferential dissipation pathway for plasmon energy in multicomponent plasmonic systems.
Strong interactions of electromagnetic fields with plasmonic nanomaterials have been exploited in various applications. These applications have centred on plasmon-enhanced scattering rates in nearby ...molecules or plasmon-induced heating. A question that has emerged recently is whether it is possible to use plasmonic nanostructures in a range of hot electron (hole) applications, including photocatalysis, photovoltaics and photodetection. These applications require coupling of a plasmonic component, which amplifies the interaction of light with the material, to an attached non-plasmonic component that extracts this energy in the form of electronic excitations to perform a function. Here, in this Perspective, we discuss recent work in the emerging field of hybrid plasmonics. We focus on fundamental questions related to the nanoscopic flow of energy and excited charge carriers in these multicomponent materials. We also address critical misconceptions, challenges and opportunities that require more attention.
The Andes/Amazon transition is among the rainiest regions of the world and the interactions between large‐scale circulation and the topography that determine its complex rainfall distribution remain ...poorly known. This work provides an in‐depth analysis of the spatial distribution, variability, and intensity of rainfall in the southern Andes/Amazon transition, at seasonal and intraseasonal time scales. The analysis is based on comprehensive daily rainfall data sets from meteorological stations in Peru and Bolivia. We compare our results with high‐resolution rainfall TRMM‐PR 2A25 estimations. Hotspot regions are identified at low elevations in the Andean foothills (400–700 masl) and in windward conditions at Quincemil and Chipiriri, where more than 4000 mm rainfall per year are recorded. Orographic effects and exposure to easterly winds produce a strong annual rainfall gradient between the lowlands and the Andes that can reach 190 mm/km. Although TRMM‐PR reproduces the spatial distribution satisfactorily, it underestimates rainfall by 35% in the hotspot regions. In the Peruvian hotspot, exceptional rainfall occurs during the austral dry season (around 1000 mm in June–July–August; JJA), but not in the Bolivian hotspot. The direction of the low‐level winds over the Andean foothills partly explains this difference in the seasonal rainfall cycle. At intraseasonal scales in JJA, we found that, during northerly wind regimes, positive rainfall anomalies predominate over the lowland and the eastern flank of the Andes, whereas less rain falls at higher altitudes. On the other hand, during southerly regimes, rainfall anomalies are negative in the hotspot regions. The influence of cross‐equatorial winds is particularly clear below 2000 masl.
Key Points:
TRMM‐PR and 95 stations describe rainfall contrasts in Amazon‐Andes transition
Rainfall hotspots extreme events are related to synoptic atmospheric circulation
Rainfall day‐to‐day variability is associated with cross‐equatorial winds
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