Optical Energy Conversion Research Articles

МАТЕМАТИЧЕСКОЕ МОДЕЛИРОВАНИЕ РАСПРОСТРАНЕНИЯ ПУЧКОВ ЛАЗЕРНОГО ИЗЛУЧЕНИЯ В НЕРАВНОВЕСНОЙ ДВИЖУЩЕЙСЯ ОБЛУЧАЕМОЙ НЕЙТРОНАМИ ПЫЛЕВОЙ ПЛАЗМЕ, СОДЕРЖАЩЕЙ НАНОЧАСТИЦЫ УРАНА

The use of uranium nanoparticles dispersed in a laser-active medium instead of traditionally used methods of heterogeneous nuclear pumping of active gas medium can increase the fraction of energy carried by fission fragments from the condensed phase into the gas medium by more than an order of magnitude. This creates the conditions for increasing the efficiency of nuclear into optical radiation energy conversion. However, the scattering and absorption of laser radiation by an active medium containing uranium nanoparticles are important factors preventing the laser radiation generation in such a medium. Mathematical modeling of the generation and amplification of laser radiation in a moving spatially inhomogeneous nuclear-excited neutron-irradiated argon-xenon medium containing uranium nanoparticles injected into a cylindrical laser-active dusty element, taking into account optical inhomogeneities caused by the dust component. The process of amplification and intensity distribution of a master oscillator laser beam in a moving spatially inhomogeneous nuclear-excited argon-xenon neutron-irradiated medium containing uranium nanoparticles has been studied for the first time. Data were also obtained on the propagation of a light beam near a relatively sharp dust component concentration decrease in moving gas medium. As a brief result: moving spatially inhomogeneous nuclear-excited neutron-irradiated argon-xenon medium containing uranium nanoparticles does not have a pronounced destructive effect on the propagation of laser radiation in it, on condition that the light flux is not wider than the dust component.

Mechanism of Extreme Optical Nonlinearities in Spiral WS2 above the Bandgap.

Layered two-dimensional transition-metal dichalcogenides (2D-TMDs) are promising building blocks for ultracompact optoelectronic applications. Recently, a strong second harmonic generation (SHG) was observed in spiral stacked TMD nanostructures which was explained by its low crystal symmetry. However, the relationship between the efficiency of SHG signals and the electronic band structure remains unclear. Here, we show that the SHG signal in spiral WS2 nanostructures is strongly enhanced (∼100 fold increase) not only when the second harmonic signal is in resonance with the exciton states but also when the excitation energy is slightly above the electronic band gap, which we attribute to a large interband Berry connection associated with certain optical transitions in spiral WS2. The giant SHG enhancement observed and explained in this study could promote the understanding and utility of TMDs as highly efficient nonlinear optical materials and potentially lead to a new pathway to fabricate more efficient optical energy conversion devices.

Improvement of photo-thermal energy conversion performance of MWCNT/Fe3O4 hybrid nanofluid compared to Fe3O4 nanofluid

The thermal, optical, and photo-thermal energy conversion characteristics of Fe3O4 and multi-walled carbon nanotube (MWCNT)/Fe3O4 hybrid nanofluids, which was suspended in the mixture of water and ethylene glycol (weight ratio = 8:2) base fluid, were experimentally investigated under various conditions. The highest light transmittances of the Fe3O4 and MWCNT/Fe3O4 hybrid nanofluids were 89% and 29%, respectively. Besides, the maximum thermal conductivities of the Fe3O4 and MWCNT/Fe3O4 hybrid nanofluids were 0.541 and 0.562 W/m∙oC, respectively, at a concentration of 0.01 wt%. The MWCNT/Fe3O4 hybrid nanofluid containing the high amount of MWCNT nanoparticles had almost two times higher photo-thermal energy conversion efficiency than that of the Fe3O4 nanofluid at the same weight concentration, thus it had a high potential to improve the heat transfer efficiency in the thermal system.

<p style="text-align: left;">History, current developments, and future directions of near-field optical science

This paper reviews the science of the optical near-field (ONF), which is created and localized in a nanometer-sized material (NM) or on its surface. It is pointed out that work on near-field optics was started in order to break through the diffraction limit in optical microscopy and had already come to an end without giving answers to the essential questions on the origin of the near-field optical interaction. However, recent studies have reincarnated these studies and identified the ONF as an off-shell quantum field. Based on this identification, a novel science called off-shell science has started on the basis that the dispersion relation between energy and momentum is invalid for the ONF. This quantum field is called the dressed photon because it is created as a result of the interaction between photons and electrons (or excitons) in a NM and, thus, it accompanies the energies of electrons or excitons. In reviewing current developments, this paper presents fifteen novel phenomena that are contrary to the common views in conventional optical science. Novel technologies developed by applying these phenomena are also reviewed. These include: nanometer-sized optical devices, nano-fabrication technology, and energy conversion technology. High-power Si light emitting diodes, Si lasers, and SiC polarization rotators are reviewed as examples of electrical to optical energy conversion. For future directions, this paper also reviews novel theoretical studies that have commenced recently by relying on physical and mathematical bases.

Azo Initiator Loaded Black Mesoporous Titania with Multiple Optical Energy Conversion for Synergetic Photo-Thermal-Dynamic Therapy.

To date, the limited light conversion ability and the oxygen-dependent therapeutic process of most photosensitizers make it difficult to achieve satisfactory therapeutic effects in the complex tumor microenvironment, especially the anoxic environment. Herein, the black mesoporous titania (BMT) with large pore size (∼8 nm) is synthesized as a new-style carrier for radical generator drug (AIBI) loading. The BMT as a light transducer can convert near-infrared (NIR) light energy into thermal energy and chemical energy (•OH), contributing to photothermal therapy (PTT) and photodynamic therapy (PDT), respectively. More importantly, AIBI would be thermally decomposed into alkyl radicals (•R) for thermodynamic therapy (TDT). The high concentration of free radicals produced by BMT@AIBI NCs resulted in double-strand breaks (DSBs) of DNA and finally induced cancer cell apoptosis. Since the generation of radicals is unrelated to oxygen, the BMT@AIBI NCs with NIR irradiation presented excellent in vitro and in vivo anticancer results under hypoxic conditions. The reported NIR-induced platform based on BMT@AIBI NCs, which could perform triple energy-conversion processes including light energy to thermal energy, to chemical energy, and to thermal energy then to chemical energy, realizes synergetic photo-thermal-dynamic therapy (PTT, PDT, and TDT) to overcome the problem of tumor hypoxia for enhanced anticancer effects.

Large area and low-cost nanoholes-based plasmonic back reflector fabricated by a simple nanofabrication technique for photovoltaics applications

Plasmonic back reflectors (PBRs) are employed in thin film and ultra-thin film solar cells to increase their optical thickness and energy conversion efficiency. Here, we report a wet-chemical etching based nanofabrication technique to prepare large area and low-cost nanoholes-based plasmonic back reflectors (n-PBRs). The n-PBR is a 150 nm thick Ag thin film embedded with random nanoholes with varying structure and morphology. We successfully incorporated the n-PBR into a standard a-Si:H thin film solar cell built on a randomly textured FTO substrate; the textured FTO serves as both the front contact and light-entry side light trapping medium. Three n-PBRs each with different density of random nanoholes were studied. All the plasmonic a-Si:H solar cells with n-PBRs exhibited an optical absorption enhancement in the spectrally intense 550–800 nm wavelength range with an overall enhancement factor of 1.1 and a maximum enhancement factor of 1.3 in the 720–780 nm wavelength range. The n-PBRs produced a haze of 65% in the 700–800 wavelength range. The hazy back contact effectively scatters the unabsorbed light back into the active medium of the solar cell with increased path length and hence, contributes to the enhanced absorption in the solar cell. The method of nanofabrication reported here to produce plasmonic back reflectors can be easily adopted into commercial fabrication of various types of solar cells including ultrathin inorganic and organic, polymer, perovskite and dye-sensitized solar cells to enhance their energy conversion efficiency without adding any cost/watt to the solar cells.

A novel polythioether-based rhodamine B fluorescent probe via successive click reaction and its application in iron ion detection and cell imaging.

Polythioether has good chemical stability and biocompatibility and is a kind of promising polymers for the application of optical materials, medical materials and energy conversion materials. However, the fluorescent probe based on polythioether is still rare. Herein, a series of polythioether based polymer fluorescent probes were synthesized by successive thiol click reaction under ultraviolet light at room temperature. The poly(thioether)s have good selectivity and responsiveness to iron ions and can be applied in cell imaging, which indicate that the broad application prospects of polythioether-based fluorescent probes in ion detection and bioimaging.

(Invited) Ultrafast Optical Spectroscopy of Plasmonic and Energy Conversion Materials

Ultrafast photoprocesses can play a leading role in determining the efficiency of optically induced catalysis and energy conversion. As a result, a rigorous understanding of the ultrafast radiative and nonradiative processes in relevant materials, such as plasmonic and semiconductor materials, and learning how to amplify the magnitude of the favorable photoprocesses, is important for ultimately improving their performance. For example, in nanostructured plasmonic materials the creation of energetic electrons before thermalization has been proposed for a wide number of applications in optical energy conversion and ultrafast nanophotonics. However, the use of "nonthermal" electrons is primarily limited by both a low generation efficiency and their ultrafast decay. We report experimental and theoretical results on the use of broadband plasmonic nanopatch metasurfaces comprising a gold substrate coupled to silver nanocubes that produce large concentrations of hot electrons, which we measure using transient absorption spectroscopy. The metasurfaces bear resemblance to perfect absorber type structures. We further find evidence for three subpopulations of nonthermal carriers, which we propose are due to localization of energetic carriers near the three band crossings of the Fermi surface. The bimetallic character of the metasurface strongly impacts the physics, with dissipation occurring primarily in the gold whereas the quantum process of hot electron generation takes place in both components. Our calculations show that the choice of geometry and materials is crucial for producing strong ultrafast nonthermal electron components and may help to guide future efforts in this area. Additional ultrafast studies of light harvesting and energy conversion materials are described, particularly in using assemblies of chromophore-functionalized biomolecules and also in perovskite materials. This work was performed, in part, at the Center for Nanoscale Materials, a U.S. Department of Energy Office of Science User Facility, and supported by the U.S. Department of Energy, Office of Science, under Contract No. DE-AC02-06CH11357.

Single compound in-situ synthesis of core-shell CaF2 nanoparticles based broad band antireflective coatings for solar energy conversion

A unique in-situ synthesis approach of formation-deformation-reformation routes lead to high crystalline core-shell Calcium Fluoride (CaF2) nanoparticles. They were tuned by the solvothermal process to achieve superior antireflection property (>95%) in the broadband region (400–1500 nm) after fabricating films by a dip coating method. These nanoparticles capped by cetyltrimethylammonium bromide (CTAB), to increase the porosity in single layer antireflective (AR) film to reduce the refractive index. This efficient antireflection layer with glass implemented on the c-Si solar cell to measure the efficiency and found out to be an improved performance (>5.7% net enhancement) compared to uncoated glass. In addition, the AR coatings exhibited a good mechanical strength which gives us the direction of future development for practical applications like highly transparent window coatings, optical and solar energy conversion applications.

Nanoscale nonreciprocity via photon-spin-polarized stimulated Raman scattering

Time reversal symmetry stands as a fundamental restriction on the vast majority of optical systems and devices. The reciprocal nature of Maxwell’s equations in linear, time-invariant media adds complexity and scale to photonic diodes, isolators, circulators and also sets fundamental efficiency limits on optical energy conversion. Though many theoretical proposals and low frequency demonstrations of nonreciprocity exist, Faraday rotation remains the only known nonreciprocal mechanism that persists down to the atomic scale. Here, we present photon-spin-polarized stimulated Raman scattering as a new nonreciprocal optical phenomenon which has, in principle, no lower size limit. Exploiting this process, we numerically demonstrate nanoscale nonreciprocal transmission of free-space beams at near-infrared frequencies with a 250 nm thick silicon metasurface as well as a fully-subwavelength plasmonic gap nanoantenna. In revealing all-optical spin-splitting, our results provide a foundation for compact nonreciprocal communication and computing technologies, from nanoscale optical isolators and full-duplex nanoantennas to topologically-protected networks.

Coexistence of doping and strain to tune electronic and optical properties of GaN monolayer

Abstract GaN monolayer is a prospective two-dimensional (2D) graphene-like material due to its excellent physical and chemical properties. Band gap engineering plays a crucial role for extending potential applications of GaN-based optoelectronic devices. We performed first-principles calculations to study the structural, electronic and optical properties of GaN monolayers by Al and In atoms doping with different concentrations. We found that Al atom doping can increase the band gap and result in the blue-shift with the increase of doping concentration, while In atom doping presents the opposite results. However, the band gap characteristics remains indirect which is unfavourable for the optical transition and solar energy conversion. Next, biaxial strains within magnitude range of −10% to 13% are applied in Al and In-doped GaN monolayers. Coexistence of doping and strain to tune electronic and optical properties of GaN monolayer are systematically studied for the first time. The results show the band gap increases at first then decreases under compressive strain and decreases monotonically under tensile strain. Moreover, the band gap characteristics changes from indirect to direct in the certain compressive strain. For the optical property modification, compressive strain can cause blue-shift in the whole energy range, while tensile strain can result in red-shift in the visible energy range and blue-shift at first then red-shift in the ultraviolet energy range. Our results confirm coexistence of doping and strain induced in GaN monolayer is an effective method in band gap engineering for the applications in tunable nano-optoelectronic devices.

Investigation on Optical Properties and Solar Energy Conversion Efficiency of Spectral Splitting PV/T system

Abstract This paper taken SiO2 nanofluid spectral splitting PV/T system on as the object of the research, considering the effects of scattering, the Mie scattering theory combined with Monte Carlo Ray Tracing (Tracepro software) method was developed to study optical properties and solar energy conversion efficiency with SiO2 nanofluid volume fraction and particle diameter. It is found that with the diameter of the nanoparticle is 5 nm, the spectral transmittance does not change with the increasing volume fraction, and the scattering effect of the nanofluid can be neglected, while the diameter of the nanoparticle is larger than 15 nm, the spectral transmittance change greatly, and the scattering needs to be considered; with the volume fraction and the diameter of SiO2 nanofluids becoming larger, the total energy absorbed by the photothermal conversion of nanofluid increase slightly, so the scattering of SiO2 nanofluid have minor effect on photothermal conversion of PV/T system, while the photoelectric conversion efficiency reduce because of the increasing scattering coefficient, which made total solar energy conversion efficiency reduced.

Enhanced Wide‐Angle Energy Conversion Using Structure‐Tunable Waveguide Arrays as Encapsulation Materials for Silicon Solar Cells

The authors report on the enhancement in optical energy conversion in silicon solar cells encapsulated with a polymer film comprising of waveguide array structures. The structures are fabricated through light‐induced self‐writing with periodic arrangements of optical beams transmitted through a binary component photopolymer, wherein a periodic core‐cladding architecture is produced. The size, spacing, and arrangement of the cores are varied through the size and arrangement of the optical beams via photomask design. A range of waveguide array structures are produced using different masks and component weight fractions. External quantum efficiency (EQE) measurements reveal structures that provide the greatest enhancement for normal and non‐normal incidence irradiation, the latter for which reveals wide‐angle light capture and conversion. Encapsulated solar cells yield an approximate 10% enhancement in EQE and a 20% increase in the short circuit current, up to an incident angle of 40°, as compared to uniform encapsulants. The experimental results are corroborated by beam propagation simulations that show the spatial confinement of transmitted optical energy is the main effect that increases conversion efficiency. Principles that establish a structure‐property‐performance relationship are discussed, toward rational materials processing to increase energy conversion.

Correlation between composition, microstructure, and emission properties in Nd-doped Si-rich Si oxynitride films: investigation into the nature of the sensitizer

Rare earth (RE) ions doped in Si-based materials, compatible with Si technology, are promising compounds with regards to optical communication and energy conversion. In this article, we show the emission properties of Nd-doped Si-rich Si oxynitride (Nd-SRSON) films, and their dependence on the dangling bond density and the nature of the sensitizer. These films were prepared by reactive magnetron sputtering and post-annealing. The film composition, microstructure, and emission properties were investigated as a function of deposition parameters and annealing temperatures. Both Fourier transform infrared (FTIR) and ellipsometry spectroscopy measurements have confirmed that the sample composition (Si/N ratio) can be carefully tuned by varying the ratio of reactive nitrogen to argon in the sputtering plasma. Moreover, FTIR and x-ray photoelectron spectroscopy measurements demonstrate the existence of both nitrogen and oxygen dangling bonds (N· and O·) in as-deposited samples. These dangling bonds were passivated during annealing. Under non-resonant excitation at 488 nm, the films exhibit a significant photoluminescence (PL) signal from Nd3+ ions demonstrating the occurrence of an effective sensitization of Nd3+ ions in the host matrix. Both PL excitation and ellipsometry results (the energy band gap from new amorphous model) exclude the sensitization by an exciton with energy over the band gap, whereas the presence of Si agglomerates, at the atomic scale, have been identified as effective sensitizers towards Nd3+ ions. This work not only provides knowledge to optimize Si-based materials for favorable emission properties, but also, presents a universal methodology to investigate the nature of sensitizers for RE emitters. This allows one to find correlations between composition, microstructure, and emission properties.

(Invited) Ultrafast Generation and Characterization of Hot Carriers in Plasmonic Nanostructures for Solar Light Harvesting

Photoexcitation of plasmonic materials can create energetic electrons and holes that are of strong interest for solar energy conversion, photocatalysis, and light harvesting applications. Since intraband photoexcitation can create energetic (other terminology includes “hot” or “nonthermal”) carriers that are up to the photon excitation energy above the Fermi energy, their potential for increasing the efficiency of optical energy conversion is clear. However, in practice there are several challenges to realizing the potential of hot carriers. First, the efficiency of hot carrier generation is low in many plasmonic materials. Second, the energetic carriers generally thermalize very quickly, on the order of 10-100 femtoseconds, thereby making their extraction before energy loss difficult. Third, the energetic carriers tend to produce small changes in the permittivity of the metal that require advanced spectroscopic experimentation or devices in order to characterize them. In this talk I begin with describing the principles of hot carrier generation and the large advantages of using nanostructured metals to improve their generation efficiency. This is followed by our efforts to spectroscopically characterize hot electrons on an ultrafast timescale, as well as to design new nanostructures for creating hot electrons in greater numbers. Physical insights into how to extract the hot carriers before loss of energy to thermalization is given, and our efforts to understand the anisotropic decay of hot carriers is described. Recent efforts to directly extract the energetic distribution of hot carriers as a function of time are also discussed. I further describe recent experiments on specific photocatalytic processes and new biomimetic nanostructures for light harvesting. These biomimetic structures enable unique opportunities for tuning structure and energy transport properties. This work focuses on the use of chromophore-doped peptide amphiphiles to create varied and potentially self-healing structures for transporting energy. A closing description of the research opportunities and capabilities at the Center for Nanoscale Materials user facility is also given. This work was performed, in part, at the Center for Nanoscale Materials, a U.S. Department of Energy Office of Science User Facility, and supported by the U.S. Department of Energy, Office of Science, under Contract No. DE-AC02-06CH11357.

Sensitive singular-phase optical detection without phase measurements with Tamm plasmons

Spectrally-tailored interactions of light with material interfaces offer many exciting applications in sensing, photo-detection, and optical energy conversion. In particular, complete suppression of light reflectance at select frequencies accompanied by sharp phase variations in the reflected signal forms the basis for the development of ultra-sensitive singular-phase optical detection schemes such as Brewster and surface plasmon interferometry. However, both the Brewster effect and surface-plasmon-mediated absorption on planar interfaces are limited to one polarization of the incident light and oblique excitation angles, and may have limited bandwidth dictated by the material dielectric index and plasma frequency. To alleviate these limitations, we design narrow-band super-absorbers composed of plasmonic materials embedded into dielectric photonic nanostructures with topologically-protected interfacial Tamm plasmon states. These structures have planar geometry and do not require nanopatterning to achieve perfect absorption of both polarizations of the incident light in a wide range of incident angles, including the normal incidence. Their absorption lines are tunable across a very broad spectral range via engineering of the photon bandstructure of the dielectric photonic nanostructures to achieve reversal of the geometrical phase across the interface with the plasmonic absorber. We outline the design strategy to achieve perfect absorptance in Tamm structures with dissipative losses via conjugate impedance matching. We further demonstrate via modeling how these structures can be engineered to support sharp asymmetric amplitude resonances, which can be used to improve the sensitivity of optical sensors in the amplitude-only detection scheme that does not require use of bulky and expensive ellipsometry equipment.

Thermal to optical energy conversion: A multi megawatt carbon dioxide laser driven by an extremely high temperature gas cooled reactor

In the conversion of ionizing radiation into energy, the production of heat is the most common first step in energy conversion systems, but it is also possible to use ions and excited states as the first step. The difference being that nearly all of the energy content of ionizing radiation is converted to heat but only 40–50% of the energy content of ionizing radiation is converted into ions and excited states. Conversion of the energy contained in ionizing radiation into ions and excited states starts out at a considerable disadvantage. Nuclear-pumped lasers have typically depended on the conversion of ionizing radiation into ions and excited states as a first step. Among the reasons that nuclear-pumped lasers have had low system efficiencies (1–2.5%) is the considerable inefficiencies in producing ions and excited states from ionizing radiation. A nuclear-pumped laser system which uses heat produced from the energy content of ionizing radiation as the driver for the laser system is described in this paper. The conversion of heat into vibrational states in molecular nitrogen allows energy to be stored in a long lived molecular state which can then be transported spatially where its energy is collisionally conveyed to carbon dioxide molecules in a resonance transfer process to produce the carbon dioxide upper laser level. The carbon dioxide laser emits a laser beam with a wavelength centered at 10.4 μm. The nitrogen vibrational state and its resonance conversion into the carbon dioxide upper laser level is one of nature's most efficient processes in laser physics (with laser efficiencies approaching ∼20% primarily being driven by the resonance process-extremely high for a laser). The laser system described here takes advantage of this highly efficient mechanism for conversion of thermal energy to optical energy. The feasibility of using nuclear rocket core technology for the generation of high temperature gas flows to power this thermal to optical conversion process is described. This study indicates that the thermal to optical conversion process can lead to a carbon dioxide laser with efficiencies on the order of 7% or perhaps better. Such a system would have potential applications in power beaming, space propulsion, asteroid mining, asteroid deflection and potential military applications.

Terahertz Wave Generation From Noble Gas Plasmas Induced by a Wavelength-Tunable Femtosecond Laser

We investigated the effects of pump wavelength on terahertz wave generation via two-color laser-induced plasma in various gas targets including nitrogen and noble gases. The terahertz energy was measured as functions of pump wavelength, input pulse energy, gas species, and pressure. The results suggest that the plasmas in the heavier gases induced by relatively longer wavelength lasers are more likely to generate higher energy terahertz waves. However, the existence of phase slippage in the neutral gases causes distinct fluctuations in the terahertz energy as the gas pressure increases. Meanwhile, the terahertz waves produced in the heavier gas are more likely to saturate at relatively higher pressures or incident optical powers. We propose an ionization rate formula associated with the gas species and pump wavelength to theoretically explain the validity of the experimental results. As a result, the terahertz pulse energy approaches a maximum value of 0.099 μJ per pulse in xenon with a 1500-nm excitation laser, and the terahertz wave to optical pulse energy conversion efficiency reaches 5.6 × 10–3, which is an order of magnitude higher than that of a conventional 800-nm pump laser.

Resonantly enhanced multiple exciton generation through below-band-gap multi-photon absorption in perovskite nanocrystals

Multi-photon absorption and multiple exciton generation represent two separate strategies for enhancing the conversion efficiency of light into usable electric power. Targeting below-band-gap and above-band-gap energies, respectively, to date these processes have only been demonstrated independently. Here we report the combined interaction of both nonlinear processes in CsPbBr3 perovskite nanocrystals. We demonstrate nonlinear absorption over a wide range of below-band-gap excitation energies (0.5–0.8 Eg). Interestingly, we discover high-order absorption processes, deviating from the typical two-photon absorption, at specific energetic positions. These energies are associated with a strong enhancement of the photoluminescence intensity by up to 105. The analysis of the corresponding energy levels reveals that the observed phenomena can be ascribed to the resonant creation of multiple excitons via the absorption of multiple below-band-gap photons. This effect may open new pathways for the efficient conversion of optical energy, potentially also in other semiconducting materials.

Enhanced generation and anisotropic Coulomb scattering of hot electrons in an ultra-broadband plasmonic nanopatch metasurface

The creation of energetic electrons through plasmon excitation of nanostructures before thermalization has been proposed for a wide number of applications in optical energy conversion and ultrafast nanophotonics. However, the use of “nonthermal” electrons is primarily limited by both a low generation efficiency and their ultrafast decay. We report experimental and theoretical results on the use of broadband plasmonic nanopatch metasurfaces comprising a gold substrate coupled to silver nanocubes that produce large concentrations of hot electrons, which we measure using transient absorption spectroscopy. We find evidence for three subpopulations of nonthermal carriers, which we propose arise from anisotropic electron–electron scattering within sp-bands near the Fermi surface. The bimetallic character of the metasurface strongly impacts the physics, with dissipation occurring primarily in the gold, whereas the quantum process of hot electron generation takes place in both components. Our calculations show that the choice of geometry and materials is crucial for producing strong ultrafast nonthermal electron components.