The displacement damage cross section of the neutron–GaN interaction is calculated in the energy range from millielectronvolts to gigaelectronvolts. Different calculation methods are used and discussed to estimate the modeling uncertainty. The nonionizing energy loss (NIEL) and the relative damage factors are also deduced. Differences with the neutron–silicon interactions are presented, and the impacts on the estimation of total nonionizing dose (TNID) levels are evaluated as a function of neutron energy.

We use cathodoluminescence (CL) spectroscopy in a transmission electron microscope to probe the radial breathing mode of plasmonic silver nanodisks. A two-mirror detection system sandwiching the sample collects the CL emission in both directions, that is, backward and forward with respect to the electron beam trajectory. We unambiguously identify a spectral shift of about 8 nm in the CL spectra acquired from both sides and show that this asymmetry is induced by the electron beam itself. By numerical simulations, we confirm the observations and identify the underlying physical effect due to the interference of the CL emission patterns of an electron-beam-induced dipole and the breathing mode. This effect can ultimately limit the achievable fidelity in CL measurements on any system involving multiple excitations and should therefore be considered with care in high-precision experiments.

La microscopie de photoémission d’électrons constitue une technique non intrusive d’investigation du champ proche optique. Son domaine d’application actuel autorise une approche physique multidimensionnelle des phénomènes d’optique de champ proche aux échelles spatiale (nm), temporelle (fs) et spectrale (meV).

We report on a novel way of performing stimulated electron energy-loss and energy-gain spectroscopy (sEELS/sEEGS) experiments that does not require a pulsed gun. In this scheme, a regular scanning transmission electron microscope (STEM) equipped with a conventional continuous electron gun is fitted with a modified EELS detector and a light injector in the object chamber. The modification of the EELS detector allows one to expose the EELS camera during tunable time intervals that can be synchronized with nanosecond laser pulses hitting the sample, therefore allowing us to collect only those electrons that have interacted with the sample under light irradiation. Using similar to 5 ns laser pulses of similar to 2 eV photon energy on various plasmonic silver samples, we obtain evidence of sEELS/sEEGS through the emergence of up to two loss and gain peaks in the spectra at +/- 2 and +/- 4 eV. Because this approach does not involve any modification of the gun, our method retains the original performances of the microscope in terms of energy resolution and spectral imaging with and without light injection. Compared to pulsed-gun techniques, our method is mainly limited to a perturbative regime (typically no more that one gain event per incident electron), which allows us to observe resonant effects, in particular when the plasmon energy of a silver nanostructure matches the laser photon energy. In this situation, EELS and EEGS signals are enhanced in proportion to n + 1 and n, respectively, where n is the average plasmon population due to the external illumination. The n term is associated with stimulated loss and gain processes, and the term of 1 corresponds to conventional (spontaneous) loss. The EELS part of the spectrum is therefore an incoherent superposition of spontaneous and stimulated EEL events. This is confirmed by a proper quantum-mechanical description of the electron/light/plasmon system incorporating light-plasmon and plasmon-electron interactions, as well as inelastic plasmon decay.

We present measurements on a few cycle OPCPA laser chain where due to careful characterization and compensation of the spectral phase and spatio-temporal couplings, we are able achieve efficient HHG with very low pulse energy.

We demonstrate the control of multiphoton electron excitations in InAs nanowires (NWs) by altering the crystal structure and the light polarization. Using few-cycle, near-infrared laser pulses from an optical parametric chirped-pulse amplification system, we induce multiphoton electron excitations in InAs nanowires with controlled wurtzite (WZ) and zincblende (ZB) segments. With a photoemission electron microscope, we show that we can selectively induce multiphoton electron emission from WZ or ZB segments of the same wire by varying the light polarization. Developing ab initio GW calculations of first to third order multiphoton excitations and using finite-difference time-domain simulations, we explain the experimental findings: While the electric-field enhancement due to the semiconductor/vacuum interface has a similar effect for all NW segments, the second and third order multiphoton transitions in the band structure of WZ InAs are highly anisotropic in contrast to ZB InAs. As the crystal phase of NWs can be precisely and reliably tailored, our findings open up for new semiconductor optoelectronics with controllable nanoscale emission of electrons through vacuum or dielectric barriers.

We study the evolution of the surface-plasmon resonances of individual ion-beam-shaped prolate gold nanoparticles embedded in a dielectric SiO 2 environment by electron-energy-loss spectroscopy mapping in a scanning transmission electron microscope. The controlled symmetric dielectric environment obtained through the ion-beam-shaping method allows a direct quantitative comparison with numerical results obtained through simulations (auxiliary differential-equation finite-difference time-domain and boundary-element method) and with theoretical results obtained through analytical models (quasistatic model for prolate nanoellipsoids and waveguide model for infinite one-dimensional plasmonic waveguides), with which our experimental results are in very good agreement. We confirm the accuracy of state-of-the-art numerical tools and analytical theories that establish ion-beam shaping as a very promising method to design metal-dielectric nanocomposites with well-predicted optical properties, and with many possible applications in surface-enhanced Raman spectroscopy and second-harmonic generation, as well as in conventional applications of metamaterials like negative refraction, superimaging, and invisibility cloaking.

We present efficient high-order harmonic generation (HHG) based on a high-repetition rate, few-cycle, near infrared (NIR), carrier-envelope phase stable, optical parametric chirped pulse amplifier (OPCPA), emitting 6 fs pulses with 9 μJ pulse energy. In krypton, we reach conversion efficiencies from the NIR to the extreme ultraviolet (XUV) radiation pulse energy on the order of ∼10−6 with less than 3 μJ driving pulse energy. This is achieved by optimizing the OPCPA for a spatially and temporally clean pulse and by a specially designed high-pressure gas target. In the future, the high efficiency of the HHG source will be beneficial for high-repetition rate two-colour (NIR-XUV) pump-probe experiments, where the available pulse energy from the laser has to be distributed economically between pump and probe pulses.

Due to a vanishing dipole moment, radial breathing modes in small flat plasmonic nanoparticles do not couple to light and have to be probed with a near-field source, as in electron energy loss spectroscopy (EELS). With increasing particle size, retardation gives rise to light coupling, enabling probing breathing modes optically or by cathodoluminescence (CL). Here, we investigate single silver nanodisks with diameters of 150-500 nm by EELS and CL in an electron microscope and quantify the EELS/CL ratio, which corresponds to the ratio of full to radiative damping of the breathing mode. For the investigated diameter range, we find the CL signal to increase by about 1 order of magnitude, in agreement with numerical simulations. Due to reciprocity, our findings corroborate former optical experiments and enable a quantitative understanding of the light coupling of dark plasmonic modes.

Nanoscale plasmonic systems combine the advantages of optical frequencies with those of small spatial scales, circumventing the limitations of conventional photonic systems by exploiting the strong field confinement of surface plasmons. As a result of this miniaturization to the nanoscale, electron microscopy techniques are the natural investigative methods of choice. Recent years have seen the development of a number of electron microscopy techniques that combine the use of electrons and photons to enable unprecedented views of surface plasmons in terms of combined spatial, energy, and time resolution. This review aims to provide a comparative survey of these different approaches from an experimental viewpoint by outlining their respective experimental domains of suitability and highlighting their complementary strengths and limitations as applied to plasmonics in particular.

We propose a semianalytical formalism based on a time-domain resonant-mode-expansion theory to analyze the ultrafast temporal dynamics of optical nanoresonators. We compare the theoretical predictions with numerical data obtained with the FDTD method, which is commonly used to analyze experiments in the field. The comparison reveals that the present formalism (i) provides deeper physical insight onto the temporal response and (ii) is much more computationally efficient. Since its numerical implementation is easy, the formalism, albeit approximate, can be advantageously used to both analyze and design ultrafast nano-optics experiments.

Journal Article Unveiling Nanometric Plasmons Optical Properties With Advanced Electron Spectroscopy in the Scanning Transmission Electron Microscope Get access M Kociak, M Kociak Laboratoire de Physique des Solides, CNRS UMR8502, Université Paris-Sud XI, Orsay, France Search for other works by this author on: Oxford Academic Google Scholar A Losquin, A Losquin Laboratoire de Physique des Solides, CNRS UMR8502, Université Paris-Sud XI, Orsay, France Search for other works by this author on: Oxford Academic Google Scholar N Kawasaki, N Kawasaki Morphological Research Laboratory, Toray Research Center Inc., Otsu, Shiga Japan Search for other works by this author on: Oxford Academic Google Scholar H Lourenço-Martins, H Lourenço-Martins Laboratoire de Physique des Solides, CNRS UMR8502, Université Paris-Sud XI, Orsay, France Search for other works by this author on: Oxford Academic Google Scholar A Campos, A Campos Laboratoire de Physique des Solides, CNRS UMR8502, Université Paris-Sud XI, Orsay, France Search for other works by this author on: Oxford Academic Google Scholar P Das, P Das Laboratoire de Physique des Solides, CNRS UMR8502, Université Paris-Sud XI, Orsay, France Search for other works by this author on: Oxford Academic Google Scholar S Meuret, S Meuret Laboratoire de Physique des Solides, CNRS UMR8502, Université Paris-Sud XI, Orsay, France Search for other works by this author on: Oxford Academic Google Scholar M Tencé, M Tencé Laboratoire de Physique des Solides, CNRS UMR8502, Université Paris-Sud XI, Orsay, France Search for other works by this author on: Oxford Academic Google Scholar L F Zagonel, L F Zagonel Gleb Wataghin” Institute of Physics-University of Campinas-UNICAMP-13083-970, Campinas, São Paulo, Brazil Search for other works by this author on: Oxford Academic Google Scholar K March, K March Laboratoire de Physique des Solides, CNRS UMR8502, Université Paris-Sud XI, Orsay, France Search for other works by this author on: Oxford Academic Google Scholar ... Show more F J Javier Garcia de Abajo, F J Javier Garcia de Abajo ICFO-Institut de Ciencies Fotoniques, Mediterranean Technology Park, Castelldefels (Barcelona), Spain Search for other works by this author on: Oxford Academic Google Scholar O Stéphan O Stéphan Laboratoire de Physique des Solides, CNRS UMR8502, Université Paris-Sud XI, Orsay, France Search for other works by this author on: Oxford Academic Google Scholar Microscopy and Microanalysis, Volume 22, Issue S3, 1 July 2016, Pages 300–301, https://doi.org/10.1017/S143192761600235X Published: 25 July 2016

Surface plasmons are capable of concentrating light on both a nanometre spatial and femtosecond temporal scale, thus serving as a basis for nanotechnology at optical frequencies. However, the simultaneously small and fast nature of surface plasmons leads to new challenges for spatiotemporal characterization of the electric fields. An especially successful method for this purpose is photoemission electron microscopy (PEEM) in combination with ultrashort laser pulses. This method uses the high spatial resolution offered by electron microscopy together with the temporal resolution offered by femtosecond laser technology. By combining PEEM with state‐of‐the‐art sources of ultrashort bursts of light, we have contributed to two pathways towards the ultimate goal: the full spatiotemporal reconstruction of the surface electric field at arbitrary nanostructures. The first approach is based on extending interferometric time‐resolved PEEM (ITR‐PEEM) [1] to the few light cycle regime by using two synchronized pulses from an ultra‐broadband oscillator. Because the photon energy (1.2‐2.0 eV) is well below the material work function, photoemission occurs through a multiphoton process. The measurement is performed by scanning the delay between two identical, sub‐6 fs pulses and measuring the local photoemission intensity (Fig. 1a). We have applied this method to a variety of nanostructures, including rice‐shaped silver particles, nanocubes, and gold bow‐tie nanoantennas. As an example, results from the rice‐shaped silver nanoparticles are shown in Fig. 1. We excited multipolar surface plasmons at grazing incidence, and imaged the photoelectrons emitted from the two ends of the nanoparticle (Fig. 1b). Upon scanning the delay between the two pulses, the interference fringes measured from the two ends of the nanoparticle are shifted with respect to each other (Fig. 1c). We show that these shifts correspond to locally different instantaneous frequencies of the near‐field within the same nanoparticle, and that these differences occur due to a combination of retardation effects and the excitation of multiple surface plasmon modes [2]. The second approach is based on using high‐order harmonic generation (HHG) to produce attosecond pulses in the extreme ultraviolet (XUV) region. Attosecond XUV pulses have been proposed to enable a direct spatiotemporal measurement of nanoplasmonic fields with a temporal resolution down to 100 as [3]. However, PEEM imaging using HHG light sources has turned out to be a major challenge due to numerous issues such as space charge effects, chromatic aberration, and poor image contrast [4‐6]. To address these issues, we perform HHG using a new optical parametric chirped pulse amplification system delivering 7 fs pulses at 200 kHz repetition rate. We show how the XUV pulses generated by this system allow for PEEM imaging with both higher resolution and shorter acquisition times. For comparison, Fig. 2 shows PEEM images of silver nanowires on a gold substrate, imaged using high‐order harmonics at 1 kHz repetition rate (Fig. 2a, acquisition time is 400 s) and at 200 kHz repetition rate (Fig. 2b, acquisition time is 30 s). The image quality is clearly improved (Fig. 2c). We also show how the higher repetition rate allows for PEEM imaging using only primary (“true”) photoelectrons, whereas previous studies have acquired images using secondary electrons [4‐6].

We present a few-cycle high-repetition rate optical parametric amplifier for multiphoton PEEM experiments on semiconductor nanowires. This parametric amplifier is also used for the generation of high-order harmonics at 200kHz for future atto-PEEM experiments.

The local enhancement of few-cycle laser pulses by plasmonic nanostructures opens up for spatiotemporal control of optical interactions on a nanometer and few-femtosecond scale. However, spatially resolved characterization of few-cycle plasmon dynamics poses a major challenge due to the extreme length and time scales involved. In this Letter, we experimentally demonstrate local variations in the dynamics during the few strongest cycles of plasmon-enhanced fields within individual rice-shaped silver nanoparticles. This was done using 5.5 fs laser pulses in an interferometric time-resolved photoemission electron microscopy setup. The experiments are supported by finite-difference time-domain simulations of similar silver structures. The observed differences in the field dynamics across a single particle do not reflect differences in plasmon resonance frequency or dephasing time. They instead arise from a combination of retardation effects and the coherent superposition between multiple plasmon modes of the particle, inherent to a few-cycle pulse excitation. The ability to detect and predict local variations in the few-femtosecond time evolution of multimode coherent plasmon excitations in rationally synthesized nanoparticles can be used in the tailoring of nanostructures for ultrafast and nonlinear plasmonics.

A combination of coarse-grained molecular dynamics and kinetic Monte-Carlo modeling shows that electron transport in fullerene multi-adducts is limited by energetic disorder due to different isomers rather than by structural disorder.

Electron energy loss spectroscopy (EELS) and cathodoluminescence (CL) have proved during the past few years to be tremendous tools to study surface plasmons in metallic nanoparticles, thanks to an extremely high spatial resolution combined with a broad spectral range. Despite their apparent close resemblance, qualitative differences between EELS and CL have been theoretically as well as experimentally pinpointed. We demonstrate that these differences are recovered when comparing the full electromagnetic local density of states (EMLDOS) and the radiative EMLDOS. Following the known relation established between EELS and the projection along the electron trajectory of the full EMLDOS, we introduce a formalism based on the Maxwell electric Green tensor to draw a link between CL and the projection along the electron trajectory of the radiative EMLDOS. We discuss in simple terms the differences between EELS (projected full EMLDOS) and CL (projected radiative EMLDOS) through modal decompositions obtained in the quasistatic approximation. Contrary to EELS, CL probes only the radiative modes. Furthermore, CL resonant line shapes may be shifted and asymmetric compared to EELS. The CL asymmetry is due to interferences in the far-field radiation from spectrally and spatially overlapping modes. Our analytical expressions are illustrated through boundary element method numerical simulations.

Plasmon modes of the exact same individual gold nanoprisms are investigated through combined nanometer-resolved electron energy-loss spectroscopy (EELS) and cathodoluminescence (CL) measurements. We show that CL only probes the radiative modes, in contrast to EELS, which additionally reveals dark modes. The combination of both techniques on the same particles thus provides complementary information and also demonstrates that although the radiative modes give rise to very similar spatial distributions when probed by EELS or CL, their resonant energies appear to be different. We trace this phenomenon back to plasmon dissipation, which affects in different ways the plasmon signatures probed by these techniques. Our experiments are in agreement with electromagnetic numerical simulations and can be further interpreted within the framework of a quasistatic analytical model. We therefore demonstrate that CL and EELS are closely related to optical scattering and extinction, respectively, with the addition of nanometer spatial resolution.

We demonstrate the control of near-field localization within individual silver nanocubes through photoemission electron microscopy combined with broadband, few-cycle laser pulses. We find that the near-field is concentrated at the corners of the cubes, and that it can be efficiently localized to different individual corners depending on the polarization of the incoming light. The experimental results are confirmed by finite-difference time-domain simulations, which also provide an intuitive picture of polarization dependent near-field localization in nanocubes.