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Nonlinear optical organic molecules have advanced a wide range of fields spanning from integrated photonics to biological imaging. With advances in molecular design, an emerging application is multifunctional nonlinear organic...

Hot electron emission from waveguide integrated graphene has been recently shown to occur at optical power densities multiple orders of magnitude lower than metal tips excited by subworkfunction photons. However, the experimentally observed electron emission currents were small, limiting the practical uses of such a mechanism. Here, we explore the performance limits of hot electron emission in graphene through experimentally calibrated simulations. Two regimes of non-equilibrium emission in graphene are identified, (i) single particle hot electron emission, where an electron is excited by a photon, and is emitted before losing significant energy through scattering, and (ii) ensemble hot electron emission, where the photon source causes nonequilibrium heating of the electron population beyond the electron lattice temperature. It is shown that through appropriate selection of photon energy, optical power density, and applied electric field hot electron emission can be used to create ultra-high current electron emitters with ultra-fast temporal responses in both the single particle and ensemble heating regimes. These results suggest that through appropriate design, hot electron emitters may overcome the limitations of thermionic and field emitters.

Using hot electrons to drive electrochemical reactions has drawn considerable interest in driving high-barrier reactions and enabling efficient solar to fuel conversion. However, the conversion efficiency from hot electrons to electrochemical products is typically low due to high hot electron scattering rates. Here, it is shown that the hydrogen evolution reaction (HER) in an acidic solution can be efficiently modulated by hot electrons injected into a thin gold film by an Au–Al2O3–Si metal–insulator–semiconductor (MIS) junction. Despite the large scattering rates in gold, it is shown that the hot electron driven HER can reach quantum efficiencies as high as ∼85% with a shift in the onset of hydrogen evolution by ∼0.6 V. By simultaneously measuring the currents from the solution, gold, and silicon terminals during the experiments, we find that the HER rate can be decomposed into three components: (i) thermal electron, corresponding to the thermal electron distribution in gold; (ii) hot electron, corresponding to electrons injected from silicon into gold which drive the HER before fully thermalizing; and (iii) silicon direct injection, corresponding to electrons injected from Si into gold that drive the HER before electron–electron scattering occurs. Through a series of control experiments, we eliminate the possibility of the observed HER rate modulation coming from lateral resistivity of the thin gold film, pinholes in the gold, oxidation of the MIS device, and measurement circuit artifacts. Next, we theoretically evaluate the feasibility of hot electron injection modifying the available supply of electrons. Considering electron–electron and electron–phonon scattering, we track how hot electrons injected at different energies interact with the gold–solution interface as they scatter and thermalize. The simulator is first used to reproduce other published experimental pump–probe hot electron measurements, and then simulate the experimental conditions used here. These simulations predict that hot electron injection first increases the supply of electrons to the gold–solution interface at higher energies by several orders of magnitude and causes a peaked electron interaction with the gold–solution interface at the electron injection energy. The first prediction corresponds to the observed hot electron electrochemical current, while the second prediction corresponds to the observed silicon direct injection current. These results indicate that MIS devices offer a versatile platform for hot electron sources that can efficiently drive electrochemical reactions.

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