We show that correlation currents arising from the superposition of pairs of states on distinct sides of a potential barrier in metal-barrier-metal structures can result in inelastic tunneling through the emission of surface plasmons. Net gain of an externally excited plasmon field is possible.

The theoretical predictions of the relative excitation probabilities of surface plasmons, using the coherent-state theory, are in good agreement with the experimentally observed relative heights of the surface plasmon peaks, This is partially because the field created by the induced charges on the support surface is not properly taken into account in the quantum theory.The Classical energy loss theory is based on Ritchie's work. Consider the total potential distribution in the space created by an incident electron under the non-retardation approximation (as shown in fig. 1), is the field created by the induced charges. Matching the solution of ψ on the boundaries, as a function of the incident electron position rt, the excitation probability of the surface plasmon as a function of ω is:

Anisotropic excitation of surface plasmon polaritons on a metal film by a scattering-type scanning near-field microscope with a non-rotationally-symmetric probe tip We investigated the excitation of surface plasmon polaritons on gold films with the metallized probe tip of a scattering-type scanning near-field optical microscope (s-SNOM). The emission of the polaritons from the tip, illuminated by near-infrared laser radiation, was found to be anisotropic and not circularly symmetric as expected on the basis of literature data. We furthermore identified an additional excitation channel via light that was reflected off the tip and excited the plasmon polaritons at the edge of the metal film. Our results, while obtained for a non-rotationally-symmetric type of probe tip and thus specific for this situation, indicate that when an s-SNOM is employed for the investigation of plasmonic structures, the unintentional excitation of surface waves and anisotropic surface wave propagation must be considered in order to correctly interpret the signatures of plasmon polariton generation and propagation. Published in Nanophotonics

Electronic excitations in condensed biological matter. In living matter, electronic excitations may have a collective character which is reviewed here in simple physical terms. In liquids and ordered solids the collective excitations appear as plasmons or excitons. Plasmons are delocalized electronic perturbations of a huge number of oscillating electrons decaying very quickly into localized electronic perturbations, mainly low-energy ionizations. Excitons are very light, moving quantum quasi-particles carrying energy, charge and information in structured biological systems. In deformable soft structures collective excitations appear as solitons behaving as rather massive quasi-particles of combined quantum and classical character. Solitons are relatively stable micro-objects able to transfer energy, charge, mass, and biological information along such biological structures as (chains of) macromolecules, fibres, membranes and surfaces. Some photobiological and radiation biological consequences of collective electronic excitations are suggested. Published in International journal of radiation biology and related studies in physics, chemistry, and medicine (1985)

Per- and poly-fluoroalkyl substances (PFAS) are a group of forever synthetic chemicals. They are widely utilized in industries and household appliances because of their remarkable stability and distinctive oil- and water-repellent properties. Despite their broad applications, unfortunately, PFAS are hazardous to all forms of life, including humans. In recent years, the environmental persistence of PFAS has raised significant interest in degrading these substances. However, the strong C−F bonds in these chemicals pose several challenges to their degrada- tion. Plasmons of noble metal nanoparticles (NPs) offer many exciting applications, including photocatalytic reactions. However, an atomistic understanding of plasmon-driven processes remains elusive. In this work, using the real-time time-dependent density functional theory, we have studied the real-time formation of plasmons, hot-carrier generation, and subsequent direct hot-carrier transfer from metal NP to the PFAS. Our simulations show that there is an apparent direct hot-electron transfer from NP to PFAS. Moreover, using Ehrenfest dynamics simulations, we demonstrated that the transferred hot-electrons can efficiently degrade PFAS without requiring any external thermal bath. Thus, our work provides an atomistic picture of plasmon-induced direct hot-carrier transfer from NP to PFAS and the efficient degradation of PFAS. We strongly believe that this work generates the impetus to utilize plasmonic NPs to mitigate PFAS.

Ultrafast light emission from plasmonic nanostructures provides a sensitive probe of the energetic electrons generated by intense optical excitation. The way this emission scales with excitation intensity has long been read through the lens of heated electron populations at an elevated temperature, yet this picture cannot reconcile the variety of behaviors seen across different materials and experiments. We argue that transient nonthermal electrons play a far larger role than has been appreciated. We present a unified description that reproduces emission behavior across diverse systems and outline experiments needed to resolve their signatures.

cy (single-particle excitations). There is no change in S C ( ω , t ) from 17 to 39 fs because there are no laser nor electron–electron interactions. We have also calculated Δ O j ( t ) defined by equation (8) in Methods section, which is the occupation change on the j th eigen state. The numbers of excited electrons (positive Δ O j ( t )) on all eigen states are shown in Fig. 4a . Because the occupation change on an eigen state j can have both resonant and off-resonant transitions from different states i , Δ O j ( t ) is a combination of both slowly varying and rapidly oscillating components as shown in Fig. 4a , different from C j , i ( t ) in Fig. 3 . We find the major excited electrons are on the eigen states around the Fermi energy (for example, the 302nd and 303rd eigen states) after 20 fs. Thus, the single-particle excitations (resonant to the plasmon frequency) from low-energy d -states to the eigen states around the Fermi energy are the major plasmon decay (hot-carrier generation) channels. Figure 4. The time-dependent excitations in Ag 55 . Open in a new tab ( a ) The number of excited electrons on every eigen state as a function of time. Several important eigen states are labelled. The major excitations are onto the 302nd and 303rd eigen states. ( b ) The energies stored in the plasmon and single-particle excitations. The blue line is the single-particle energy generated by the plasmon, which is defined as the energy difference in the single-particle mode between the real system (rt-TDDFT simulation) and the non-interacting system (in which plasmons cannot exist) under the same laser illumination. The pink-dashed line is an exponential decay of exp(− ω p t / Q ) with Q =13.3. ( c , d ) The number of excited electrons (positive) and holes (negative) as a function of the corresponding eigen energy with respect to the Fermi energy at t =8 and 30 fs. At 8 fs, most excitations are around the Fermi energy and at 30 fs the excitations are concentrated in a few s

Au and n‐type TiO 2 is again used as an example. In the case of direct electron transfer, the noble metal (Au) and semiconductor (TiO 2 ) are in intimate contact. As shown in Figure 3 b, when Au comes into contact with TiO 2 , the equilibration of Fermi levels causes the bending of the conduction band of TiO 2 at the interface and a Schottky barrier is thus formed. Usually, if the metal nanoparticle is sufficiently large (i.e., above quantum confinement) and cannot induce size‐dependent bandgaps, the electron states of the metal are continuous and follow the Fermi–Dirac distribution.[[qv: 7a]] Upon illumination, if the plasmon band overlaps the interband transition of Au, electrons oscillating collectively may create a uniform probability for electrons to transfer to the energy level between E f (Fermi level energy of Au) and E f + hν . 25 Due to electron‐electron scattering, electron energy is redistributed and creates a non‐equilibrium Fermi–Dirac distribution within 10 femtoseconds. 18 , 25 Meanwhile, electrons transfer from the noble metal (i.e., Au) to the semiconductor (i.e., TiO 2 ) through two different ways. The first one is a coherent process. After excitation, the generated electrons directly inject into the conduction band of TiO 2 without interacting with other electrons ( Figure 4 a). The second process is incoherent. The energy states of electrons revert back to the Fermi–Dirac distribution via electron‐electron relaxation but with a higher Fermi level (Figure 4 b).[[qv: 7a]] The hot electrons continuously transfer to the conduction band of the semiconductor from the tail portion of the electron distribution of noble metal until the electron states return to the standard Fermi–Dirac distribution and associated dissipation of the surface energy (Figure 4 c).[[qv: 7a]] Figure 4. Open in a new tab Direct electron transfer mechanism. a) Electrons are excited to higher energy states under illumination and are fed to the conduction band of the n‐type semic