E. Hendry

Universiteit Twente, Enschede, Overijssel, Netherlands

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Publications (65)271.44 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: We study THz pulses generated from plasmonic metal nanostructures under femtosecond illumination of near-IR light. We find two regimes of excitation, according to the order of the dependence of the THz fluence on the incident near-IR intensity: less then second order at low intensities, changing to approximately fourth order for higher intensities. These regimes are most likely associated with two THz generation mechanisms: optical rectification, and the ponderomotive acceleration of ejected electrons. These data provide evidence that both mechanisms can be at work in the same experiment.
    02/2014; 89(12).
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    ABSTRACT: Films of colloidal TiO2 nanoparticles are widely used in photovoltaic and photocatalytic applications, and the nature of electrical conductivity in such materials is therefore of both fundamental and practical interest. The conductive properties of colloid TiO2 films depend strongly on their morphology and deviate greatly from the properties of the bulk material. We report ultrafast photoconductivity studies of films consisting of sintered TiO2 particles of very different sizes performed using time-resolved terahertz spectroscopy. Remarkably, identical photoconductivity spectra are observed for films of particles with diameters of tens and hundreds of nanometers, respectively. The independence of photoconductivity on particle size directly demonstrates that the terahertz photoconductive response of colloidal TiO2 films is not affected by carrier backscattering at particle boundaries as has previously been concluded, but rather by depolarization fields resulting from the spatial inhomogeneities in the dielectric function inherent to these types of films. Modeling of the influence of depolarization fields on the terahertz conductivity allows us to explain the measured data and gain insights into the morphology of the film. Specifically, we show that the observed photoconductivity spectra reflect percolated pathways in the colloidal TiO2 nanoparticles films, through which charge carrier diffusion can occur over macroscopic length scales.
    Journal of Physical Chemistry C. 01/2014; 118:1191-1197.
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    E. Alexeev, J. Moger, E. Hendry
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    ABSTRACT: The modification of single layer graphene due to intense, picoseconds near-infrared laser pulses is investigated. We monitor the stable changes introduced to graphene upon photoexcitation using Raman spectroscopy. We find that photoexcitation leads to both a local increase in hole doping and a reduction in compressive strain. Possible explanations for these effects, due to photo-induced oxygenation and photo-induced buckling of the graphene, are discussed.
    Applied Physics Letters 10/2013; 103(15). · 3.52 Impact Factor
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    ABSTRACT: The acoustic transmittance of two closely spaced solid plates, each perforated with a square array of cylindrical holes, exhibits a band of near-perfect acoustic attenuation originating from hybridization between a resonance in the gap separating the plates and pipe resonances in the holes. Displacement of one plate relative to the other, such that the holes are no longer aligned, or an increase in the plate separation leads to an increased center frequency of the stop band. This ability to easily tune the frequency of the stop band may prove advantageous.
    The Journal of the Acoustical Society of America 09/2013; 134(3):1754-9. · 1.65 Impact Factor
  • T. J. Davis, E. Hendry
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    ABSTRACT: We show theoretically that localized surface plasmons can generate optical fields with a chirality exceeding that of circularly polarized light by a factor of 50. This superchiral optical field can be formed from linearly polarized light incident on nonchiral metal structures. We identify three mechanisms that lead to large optical chirality involving the coupling between the incident light and the evanescent fields of the surface plasmons. Two of these mechanisms create superchiral regions with nonzero average chirality suitable for the excitation of chiral molecules in solution.
    Physical review. B, Condensed matter 02/2013; 87(8). · 3.77 Impact Factor
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    ABSTRACT: The “acoustic double fishnet” is a structure with holes running from its front to back faces, yet at a characteristic frequency it transmits very little sound. The transmittance of this structure, which is comprised of a pair of closely spaced, periodically perforated plates, is determined experimentally and analytically. The surprising acoustic properties are due to hybridization between a two-dimensional resonance within the gap between the plates, and pipe modes within the holes. At the center of the stop band the input impedance is imaginary, interpreted as a negative product of effective bulk modulus and density.
    Physical review. B, Condensed matter 06/2012; · 3.77 Impact Factor
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    ABSTRACT: Using a modal matching theory, we demonstrate the generation of short-range, chiral electromagnetic fields via the excitation of arrays of staggered nanoslits that are chiral in two dimensions. The electromagnetic near fields, which exhibit a chiral density greater than that of circularly polarized light, can enhance the chiroptical interactions in the vicinity of the nanoslits. We discuss the features of nanostructure symmetry required to obtain the chiral fields and explicitly show how these structures can give rise to detection and characterization of materials with chiral symmetry.
    Nano Letters 05/2012; 12(7):3640-4. · 13.03 Impact Factor
  • E. K. Stone, E. Hendry
    Physical review. B, Condensed matter 03/2012; 85(12). · 3.77 Impact Factor
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    ABSTRACT: We have experimentally studied the nonlinear nature of electrical conduction in monolayer graphene devices on silica substrates. This nonlinearity manifests itself as a nonmonotonic dependence of the differential resistance on applied DC voltage bias across the sample. At temperatures below ~70K, the differential resistance exhibits a peak near zero bias that can be attributed to self-heating of the charge carriers. We show that the shape of this peak arises from a combination of different energy dissipation mechanisms of the carriers. The energy dissipation at higher carrier temperatures depends critically on the length of the sample. For samples longer than 10um the heat loss is shown to be determined by optical phonons at the silica-graphene interface.
    Physical review. B, Condensed matter 02/2012; 85(16). · 3.77 Impact Factor
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    ABSTRACT: We report a new approach for creating chiral plasmonic nanomaterials. A previously unconsidered, far-field mechanism is utilized which enables chirality to be conveyed from a surrounding chiral molecular material to a plasmonic resonance of an achiral metallic nanostructure. Our observations break a currently held preconception that optical properties of plasmonic particles can most effectively be manipulated by molecular materials through near-field effects. We show that far-field electromagnetic coupling between a localized plasmon of a nonchiral nanostructure and a surrounding chiral molecular layer can induce plasmonic chirality much more effectively (by a factor of 10(3)) than previously reported near-field phenomena. We gain insight into the mechanism by comparing our experimental results to a simple electromagnetic model which incorporates a plasmonic object coupled with a chiral molecular medium. Our work offers a new direction for the creation of hybrid molecular plasmonic nanomaterials that display significant chiroptical properties in the visible spectral region.
    Nano Letters 02/2012; 12(2):977-83. · 13.03 Impact Factor
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    ABSTRACT: Graphene shows great potential for future electronic devices due to its high carrier mobility and thermal conductivity [1, 2]. An important consideration for such devices is thermal cooling of charge carriers. The use of large current densities results in over heating of charge carriers, and this power must be dissipated to avoid thermal breakdown of the graphene sheet [3]. The main cooling mechanisms are (1) direct transfer of heat to the metallic contacts forming the source and drain of the device via diffusion of electrons [4], (2) transfer of heat to the graphene lattice via scattering of electrons by acoustic phonons of the graphene sheet [5], and (3) transfer of heat directly to the underlying substrate via scattering of electrons by surface mode phonons of the substrate [6].
    Nanotechnology (IEEE-NANO), 2012 12th IEEE Conference on; 01/2012
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    ABSTRACT: The acoustic transmittance of two closely spaced rigid plates perforated with a square array of circular holes is studied both experimentally and numerically. The system exhibits a band of acoustic attenuation originating from hybridization between a two-dimensional resonance in the gap between the plates, and pipe modes in the holes. Misalignment of the holes in either one or both lateral dimensions shifts the centre frequency of the stop band to maintain the conditions required for zero transmission.
    Meta '12, Paris; 01/2012
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    ABSTRACT: We investigate the generation of THz pulses when arrays of silver nanoparticles are irradiated by femtosecond laser pulses, providing the first reproducible experimental evidence in support of recent theoretical predictions of such an effect. We assess our results in the context of a model where photoelectrons are produced by plasmon-mediated multiphoton excitation, and THz radiation is generated via the acceleration of the ejected electrons by ponderomotive forces arising from the inhomogeneous plasmon field. By exploring the dependence of the THz emission on the femtosecond pulse intensity and as a function of metal nanoparticle morphology, and by comparing measurements to numerical modeling, we are able to verify the role of the particle plasmon mode in this process.
    Nano Letters 11/2011; 11(11):4718-24. · 13.03 Impact Factor
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    ABSTRACT: Experimental verification of the “domino plasmon,” recently proposed by Cano &etal; [Opt. Express 18(2), 754, (2010)] is presented. Using microwaves, it is demonstrated that this mode propagates along a periodic chain of metallic cuboids (“dominos”) and the dispersion of the mode is determined with results being compared to the predictions of analytical and numerical models. This mode is found to be surprisingly insensitive to the lateral width of the chain, even on a subwavelength scale. Having such tight confinement, “domino plasmons” show considerable promise for one-dimensional subwavelength guiding and focusing of electromagnetic fields.
    Applied Physics Letters 08/2011; 99(5). · 3.52 Impact Factor
  • E. K. Stone, E. Hendry
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    ABSTRACT: Using phase sensitive microwave frequency measurements, we obtain the dispersion of spoof surface plasmon waves on a highly conducting sheet perforated with a two-dimensional array of subwavelength holes, and compare our results to an explicit analytical dispersion relation obtained by the modal matching method. We observe splitting into symmetric and antisymmetric surface modes, a behavior analogous to that of surface plasmons in thin metallic films at optical frequencies. We show that spoof surface modes play an important role in both near and far field transmissions. Specifically, we show that superfocussing effects which are present for surface plasmons in metallic films are absent for hole arrays (i.e., no amplification of near fields is possible for spoof surface plasmons). While many of the apparent properties of spoof surface plasmons resemble those of surface plasmons in thin metallic films, the analogy is therefore incomplete in the high frequency limit.
    Physical review. B, Condensed matter 07/2011; 84(3). · 3.77 Impact Factor
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    ABSTRACT: The microwave transmission through hole arrays in thick metal plates for both large holes (cut-off below onset of diffraction) and small holes (cut-off above onset of diffraction) have been compared through both experiment and modelling. Enhanced transmission is in part mediated by the excitation of diffractively coupled surface waves. Large holes, with cut-off below the onset of diffraction (due to the hole periodicity), are able to support multiple modes in transmission when the depth of the holes is sufficient to support quantisation in the propagation direction. Small holes, with cut-off above the onset of diffraction however only support two coupled surface modes (symmetric and anti-symmetric) below diffraction.
    Optics Express 07/2011; 19(15):13793-805. · 3.55 Impact Factor
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    ABSTRACT: We report the generation of THz pulses from arrays of silver nanoparticles when irradiated by femtosecond laser pulses. We suggest that this effect arises from the emission of photoelectrons by multi-photon excitation and subsequent acceleration of these emitted electrons by ponderomotive forces associated with the optical fields of the plasmons in the metallic nanostructures.
    Proc SPIE 05/2011;
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    ABSTRACT: In this contribution we concentrate on two aspects of THz science related to surface and particle plasmons. Firstly, we report on the generation of THz pulses via irradiation of arrays of silver nanoparticles by femtosecond laser pulses. We propose that this effect arises from the emission of photoelectrons by multi-photon excitation and subsequent acceleration of these emitted electrons by ponderomotive forces associated with the optical fields of the plasmons in the metallic nanostructures. Secondly, we demonstrate that semiconductors supports strongly confined surface plasmons in the THz frequency range. We show that these SPs can be utilized to enhance the light-matter interaction with dielectric layers above the semiconductor surface, thereby allowing us to detect the presence of layers around one thousand times thinner than the free space wavelength of the THz light. We discuss the viability of using semiconductor SPs for the purposes of THz sensing and spectroscopy.
    Proc SPIE 02/2011;
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    Review of Modern Physics 01/2011; 83:543. · 44.98 Impact Factor
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    ABSTRACT: Near infrared pump-probe spectroscopy has been used to measure the ultrafast dynamics of photoexcited charge carriers in monolayer and multilayer graphene. We observe two decay processes occurring on 100 fs and 2 ps timescales. The first is attributed to the rapid electron-phonon thermalisation in the system. The second timescale is found to be due to the slow decay of hot phonons. Using a simple theoretical model we calculate the hot phonon decay rate and show that it is significantly faster in monolayer flakes than in multilayer ones. In contrast to recent claims, we show that this enhanced decay rate is not due to the coupling to substrate phonons, since we have also seen the same effect in suspended flakes. Possible intrinsic decay mechanisms that could cause such an effect are discussed.
    Physical review. B, Condensed matter 12/2010; 83(12). · 3.77 Impact Factor

Publication Stats

1k Citations
271.44 Total Impact Points

Institutions

  • 2014
    • Universiteit Twente
      • Department of Complex Photonic Systems (COPS)
      Enschede, Overijssel, Netherlands
  • 2007–2012
    • University of Exeter
      • Department of Physics and Astronomy
      Exeter, England, United Kingdom
  • 2006
    • FOM Institute AMOLF
      Amsterdamo, North Holland, Netherlands
  • 2004–2005
    • Leiden University
      Leyden, South Holland, Netherlands