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  • 1.
    Aissaoui, Nesrine
    et al.
    Department of Chemistry and Chemical Engineering, Chalmers University of Technology, Gothenburg, Sweden.
    Moth-Poulsen, Kasper
    Department of Chemistry and Chemical Engineering, Chalmers University of Technology, Gothenburg, Sweden.
    Käll, Mikael
    Department of Applied Physics, Chalmers University of Technology, Gothenburg, Sweden.
    Johansson, Peter
    Örebro University, School of Science and Technology.
    Wilhelmsson, L. Marcus
    Department of Chemistry and Chemical Engineering, Chalmers University of Technology, Gothenburg, Sweden.
    Albinsson, Bo
    Department of Chemistry and Chemical Engineering, Chalmers University of Technology, Gothenburg, Sweden.
    FRET enhancement close to gold nanoparticles positioned in DNA origami constructs2017In: Nanoscale, ISSN 2040-3364, E-ISSN 2040-3372, Vol. 9, no 2, p. 673-683Article in journal (Refereed)
    Abstract [en]

    Here we investigate the energy transfer rates of a Förster resonance energy transfer (FRET) pair positioned in close proximity to a 5 nm gold nanoparticle (AuNP) on a DNA origami construct. We study the distance dependence of the FRET rate by varying the location of the donor molecule, D, relative to the AuNP while maintaining a fixed location of the acceptor molecule, A. The presence of the AuNP induces an alteration in the spontaneous emission of the donor (including radiative and non-radiative rates) which is strongly dependent on the distance between the donor and AuNP surface. Simultaneously, the energy transfer rates are enhanced at shorter D-A (and D-AuNP) distances. Overall, in addition to the direct influence of the acceptor and AuNP on the donor decay there is also a significant increase in decay rate not explained by the sum of the two interactions. This leads to enhanced energy transfer between donor and acceptor in the presence of a 5 nm AuNP. We also demonstrate that the transfer rate in the three "particle" geometry (D + A + AuNP) depends approximately linearly on the transfer rate in the donor-AuNP system, suggesting the possibility to control FRET process with electric field induced by 5 nm AuNPs close to the donor fluorophore. It is concluded that DNA origami is a very versatile platform for studying interactions between molecules and plasmonic nanoparticles in general and FRET enhancement in particular.

  • 2. Alegret, Joan
    et al.
    Johansson, Peter
    Örebro University, School of Science and Technology.
    Käll, Mikael
    Green’s tensor calculations of plasmon resonances of single holes and hole pairs in thin gold films2008In: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 10, no 105004Article in journal (Refereed)
    Abstract [en]

    We present numerical calculations of the plasmon properties of single-hole and hole-pair structures in optically thin gold films obtained with the Green’s tensor formalism for stratified media. The method can be used to obtain the optical properties of a given hole system, without problems associated with the truncation of the infinite metal film. The calculations are compared with previously published experimental data and an excellent agreement is found. In particular, the calculations are shown to reproduce the evolution of the hole plasmon resonance spectrum as a function of hole diameter, film thickness and hole separation.

  • 3. Alegret, Joan
    et al.
    Käll, Mikael
    Johansson, Peter
    Örebro University, Department of Natural Sciences.
    Top-down extended meshing algorithm and its applications to Green's tensor nano-optics calculations2007In: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics: Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics, ISSN 1063-651X, E-ISSN 1095-3787, Vol. 75, no 4Article in journal (Refereed)
    Abstract [en]

    We present a computational algorithm which speeds up Green's tensor nano-optics calculations by means of optimizing the mesh that represents the system we want to investigate. The algorithm automates the process of creating a variable-size mesh that describes an arbitrary nanostructure. The total number of elements of this mesh is smaller than that of a regular mesh representing the same structure, and thus the Green's tensor calculations can be performed faster. Precision, however, is kept at a similar level than for the regular mesh. Typically, the algorithm yields a mesh that speeds up Green's tensor calculations by a factor of 4, while giving a maximum error in the field magnitude of about 5%. The speed-up factor makes it very suitable for otherwise lengthy calculations, and the error should be acceptable for most applications.

  • 4.
    Andrén, Daniel
    et al.
    Department of Physics, Chalmers University of Technology, Göteborg, Sweden.
    Länk, Nils Odebo
    Department of Physics, Chalmers University of Technology, Göteborg, Sweden.
    Sípová-Jungová, Hana
    Department of Physics, Chalmers University of Technology, Göteborg, Sweden.
    Jones, Steven
    Department of Physics, Chalmers University of Technology, Göteborg, Sweden.
    Johansson, Peter
    Örebro University, School of Science and Technology. Department of Physics, Chalmers University of Technology, Göteborg, Sweden.
    Käll, Mikael
    Department of Physics, Chalmers University of Technology, Göteborg, Sweden.
    Surface Interactions of Gold Nanoparticles Optically Trapped against an Interface2019In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 123, no 26, p. 16406-16414Article in journal (Refereed)
    Abstract [en]

    Particles that diffuse in close proximity to a surface are expected to behave differently than in free solution because the surface interaction will influence a number of physical properties, including the hydrodynamic, optical, and thermal characteristics of the particle. Understanding the influence of such effects is particularly important in view of the increasing interest in laser tweezing of colloidal resonant nanoparticles for applications such as nanomotors and optical printing and for investigations of unconventional optical forces. Therefore, we used total internal reflection microscopy to probe the interaction between a glass surface and individual similar to 100 nm gold nanoparticles trapped by laser tweezers. The results show that particles can be optically confined at controllable distances ranging between similar to 30 and similar to 90 nm from the surface, depending on the radiation pressure of the trapping laser and the ionic screening of the surrounding liquid. Moreover, the full particle-surface distance probability distribution can be obtained for single nanoparticles by analyzing temporal signal fluctuations. The experimental results are in excellent agreement with Brownian dynamics simulations that take the full force field and photothermal heating into account. At the observed particle-surface distances, translational friction coefficients increase by up to 60% compared to freely diffusing particles, whereas the rotational friction and thermal dissipation are much less affected. The methodology used here is general and can be adapted to a range of single nanoparticle-surface interaction investigations.

  • 5.
    Andrén, Daniel
    et al.
    Department of Physics, Chalmers University of Technology, Göteborg, Sweden.
    Shao, Lei
    Department of Physics, Chalmers University of Technology, Göteborg, Sweden.
    Länk, Nils Odebo
    Department of Physics, Chalmers University of Technology, Göteborg, Sweden.
    Acimovic, Srdjan S.
    Department of Physics, Chalmers University of Technology, Göteborg, Sweden.
    Johansson, Peter
    Örebro University, School of Science and Technology. Department of Physics, Chalmers University of Technology, Göteborg, Sweden.
    Käll, Mikael
    Department of Physics, Chalmers University of Technology, Göteborg, Sweden.
    Probing Photothermal Effects on Optically Trapped Gold Nanorods by Simultaneous Plasmon Spectroscopy and Brownian Dynamics Analysis2017In: ACS Nano, ISSN 1936-0851, E-ISSN 1936-086X, Vol. 11, no 10, p. 10053-10061Article in journal (Refereed)
    Abstract [en]

    Plasmonic gold nanorods are prime candidates for a variety of biomedical, spectroscopy, data storage, and sensing applications. It was recently shown that gold nanorods optically trapped by a focused circularly polarized laser beam can function as extremely efficient nanoscopic rotary motors. The system holds promise for-applications ranging from nanofluidic flow control and nanorobotics to biomolecular actuation and analysis. However, to fully exploit this potential, one needs to be able to control and understand heating effects associated with laser trapping. We investigated photothermal heating of individual rotating gold nanorods by simultaneously probing their localized surface plasmon resonance spectrum and rotational Brownian dynamics over extended periods of time. The data reveal an extremely slow nanoparticle reshaping process, involving migration of the order of a few hundred atoms per minute, for moderate laser powers and a trapping wavelength close to plasmon resonance. The plasmon spectroscopy and Brownian analysis allows for separate temperature estimates based on the refractive index and the viscosity of the water surrounding a trapped nanorod. We show that both measurements yield similar effective temperatures, which correspond to the actual temperature at a distance of the order 10-15 nm from the particle surface. Our results shed light on photothermal processes on the nanoscale and will be useful in evaluating the applicability and performance of nanorod motors and optically heated nanoparticles for a variety of applications.

  • 6.
    Hajizadeh, Faegheh
    et al.
    Department of Physics, Chalmers University of Technology, Göteborg, Sweden; Department of Physics, Institute for Advanced Studies in Basic Sciences, Zanjan, Iran.
    Shao, Lei
    Department of Physics, Chalmers University of Technology, Göteborg, Sweden.
    Andrén, Daniel
    Department of Physics, Chalmers University of Technology, Göteborg, Sweden.
    Johansson, Peter
    Örebro University, School of Science and Technology. Department of Physics, Chalmers University of Technology, Göteborg, Sweden.
    Rubinsztein-Dunlop, Halina
    Department of Physics, Chalmers University of Technology, Göteborg, Sweden; Quantum Science Laboratory, School of Mathematics and Physics, The University of Queensland, Brisbane QLD, Australia.
    Käll, Mikael
    Department of Physics, Chalmers University of Technology, Göteborg, Sweden.
    Brownian fluctuations of an optically rotated nanorod2017In: Optica, ISSN 2334-2536, Vol. 4, no 7, p. 746-751Article in journal (Refereed)
    Abstract [en]

    Gold nanorods can be optically trapped in aqueous solution and forced to rotate at kilohertz rates by circularly polarized laser light. This enables detailed investigations of local environmental parameters and processes, such as medium viscosity and nanoparticle-molecule reactions. Future applications may include nanoactuation and single-cell analysis. However, the influence of photothermal heating on the nanoparticle dynamics needs to be better understood in order to realize widespread and quantitative use. Here we analyze the hot Brownian motion of a rotating gold nanorod trapped in two dimensions by an optical tweezers using experiments and stochastic simulations. We show that, for typical settings, the effective rotational and translational Brownian temperatures are drastically different, being closer to the nanorod surface temperature and ambient temperature, respectively. Further, we show that translational dynamics can have a non-negligible influence on the rotational fluctuations due to the small size of a nanorod in comparison to the focal spot. These results are crucial for the development of gold nanorods into generic and quantitative optomechanical sensor and actuator elements. (C) 2017 Optical Society of America

  • 7.
    Johansson, Peter
    Örebro University, School of Science and Technology.
    Electromagnetic Green's function for layered systems: applications to nanohole interactions in thin metal films2011In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 83, no 19, p. 195408-Article in journal (Refereed)
    Abstract [en]

    We derive expressions for the electromagnetic Green's function for a layered system using a transfer matrix technique. The expressions we arrive at make it possible to study symmetry properties of the Green's function, such as reciprocity symmetry, and the long-range properties of the Green's function which involves plasmon waves as well as boundary waves, also known as Norton waves. We apply the method by calculating the light-scattering cross section off a chain of nanoholes in a thin Au film. The results highlight the importance of nanohole interactions mediated by surface plasmon propagating along the chain of holes.

  • 8.
    Lehmuskero, Anni
    et al.
    Department of Applied Physics, Chalmers University of Technology, Göteborg, Sweden.
    Johansson, Peter
    Örebro University, School of Science and Technology.
    Rubinsztein-Dunlop, Halina
    Quantum Science Laboratory, School of Mathematics and Physics, University of Queensland, Brisbane Qld, Australia.
    Tong, Lianming
    Center for Nanochemistry, College of Chemistry and Molecular Engineering, Peking University, Beijing, China; Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing, China .
    Käll, Mikael
    Department of Applied Physics, Chalmers University of Technology, Göteborg, Sweden .
    Laser trapping of colloidal metal nanoparticles2015In: ACS Nano, ISSN 1936-0851, E-ISSN 1936-086X, Vol. 9, no 4, p. 3453-3469Article, review/survey (Refereed)
    Abstract [en]

    Optical trapping using focused laser beams (laser tweezers) has been proven to be extremely useful for contactless manipulation of a variety of small objects, including biological cells, organelles within cells, and a wide range of other dielectric micro- and nano-objects. Colloidal metal nanoparticles have drawn increasing attention in the field of optical trapping because of their unique interactions with electromagnetic radiation, caused by surface plasmon resonance effects, enabling a large number of nano-optical applications of high current interest. Here we try to give a comprehensive overview of the field of laser trapping and manipulation of metal nanoparticles based on results reported in the recent literature. We also discuss and describe the fundamentals of optical forces in the context of plasmonic nanoparticles, including effects of polarization, optical angular momentum, and laser heating effects, as well as the various techniques that have been used to trap and manipulate metal nanoparticles. We conclude by suggesting possible directions for future research.

  • 9.
    Lehmuskero, Anni
    et al.
    Department of Applied Physics, Chalmers University of Technology, Gothenburg, Sweden .
    Li, Yanming
    Electrical & Computer Engineering Department, NC State University, Raleigh, North Carolina, USA.
    Johansson, Peter
    Örebro University, School of Science and Technology. School of Science and Technology, Örebro University, Örebro, Sweden .
    Johansson, Mikael
    Plasmonic particles set into fast orbital motion by an optical vortex beam2014In: Optics express, ISSN 1094-4087, Vol. 22, no 4, p. 4349-4356Article in journal (Refereed)
    Abstract [en]

    We optically trap plasmonic gold particles in two dimensions and set them into circular motion around the optical axis using a helically phased vortex laser beam. The orbiting frequency of the particles reaches 86 Hz, which corresponds to a particle velocity of the order 1 mm per second, for an incident laser power of a few tens of milliwatts. The experimentally determined orbiting frequencies are found to be well in line with the notion that the beam carries an orbital angular momentum of ħl per photon.

  • 10. Lehmuskero, Anni
    et al.
    Ogier, Robin
    Gschneidtner, Tina
    Johansson, Peter
    Örebro University, School of Science and Technology.
    Kall, Mikael
    Ultrafast spinning of gold nanoparticles in water using circularly polarized light2013In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 13, no 7, p. 3129-3134Article in journal (Refereed)
    Abstract [en]

    Controlling the position and movement of small objects with light is an appealing way to manipulate delicate samples, such as living cells or nanoparticles. It is well-known that optical gradient and radiation pressure forces caused by a focused laser beam enables trapping and manipulation of objects with strength that is dependent on the particles optical properties. Furthermore, by utilizing transfer of photon spin angular momentum, it is also possible to set objects into rotational motion simply by targeting them with a beam of circularly polarized light. Here we show that this effect can set similar to 200 nm radii gold particles trapped in water in 2D by a laser tweezers into rotation at frequencies that reach several kilohertz, much higher than any previously reported light driven rotation of a microscopic object. We derive a theory for the fluctuations in light scattering from a rotating particle, and we argue that the high rotation frequencies observed experimentally is the combined result of favorable optical particle properties and a low local viscosity due to substantial heating of the particles surface layer. The high rotation speed suggests possible applications in nanofluidics, optical sensing, and microtooling of soft matter.

  • 11.
    Länk, Nils Odebo
    et al.
    Department of Physics, Chalmers University of Technology, Göteborg, Sweden.
    Johansson, Peter
    Örebro University, School of Science and Technology. Department of Physics, Chalmers University of Technology, Göteborg, Sweden.
    Käll, Mikael
    Department of Physics, Chalmers University of Technology, Göteborg, Sweden.
    Directional scattering and multipolar contributions to optical forces on silicon nanoparticles in focused laser beams2018In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 26, no 22, p. 29074-29085Article in journal (Refereed)
    Abstract [en]

    Nanoparticles made of high index dielectric materials have seen a surge of interest and have been proposed for various applications, such as metalenses, light harvesting and directional scattering. With the advent of fabrication techniques enabling colloidal suspensions, the prospects of optical manipulation of such nanoparticles becomes paramount. High index nanoparticles support electric and magnetic multipolar responses in the visible regime and interference between such modes can give rise to highly directional scattering, in particular a cancellation of back-scattered radiation at the first Kerker condition. Here we present a study of the optical forces on silicon nanoparticles in the visible and near infrared calculated using the transfer matrix method. The zero-backscattering Kerker condition is investigated as an avenue to reduce radiation pressure in an optical trap. We find that while asymmetric scattering does reduce the radiation pressure, the main determining factor of trap stability is the increased particle response near the geometric resonances. The trap stability for non-spherical silicon nanoparticles is also investigated and we find that ellipsoidal deformation of spheres enables trapping of slightly larger particles.

  • 12.
    Miljkovic, Vladimir D.
    et al.
    Dept Appl Phys, Chalmers, Gothenburg, Sweden.
    Pakizeh, Tavakol
    Dept Appl Phys, Chalmers, Gothenburg, Sweden; Dept Elect Engn, KN Toosi Univ Technol, Tehran, Iran.
    Sepulveda, Borja
    Res Ctr Nanosci & Nanotechnol CIN2, Nanobiosensors & Mol Nanobiophys Grp, CSIC ICN, Bellaterra, Spain.
    Johansson, Peter
    Örebro University, School of Science and Technology. Dept Appl Phys, Chalmers, Gothenburg, Sweden.
    Kall, Mikael
    Dept Appl Phys, Chalmers, Gothenburg, Sweden.
    Optical Forces in Plasmonic Nanoparticle Dimers2010In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 114, no 16, p. 7472-7479Article in journal (Refereed)
    Abstract [en]

    We present calculations of the optical forces between two metal nanospheres forming a hybridized plasmonic chiller. We consider homo- and heterodimers and investigate different plane wave illumination configurations. The forces between the particles are calculated using kill Mie theory combined with the Maxwell stress tensor (MST) formalism, as well as by approximate methods, such as the Lorentz force (LF) approach taken in the dipole limit and calculations based on an optical potential. We show that the simplified calculation schemes can lead to serious errors in the case of strongly interacting particles and low damping. In particular, we find that equilibrium configurations, corresponding to vanishing optical forces, only are possible for homodimers illuminated in the end-fire configuration and for heterodimers, although multipolar effects and clamping radically reduce the repulsive interactions in the latter case.

  • 13. Miljkovic, Vladimir D.
    et al.
    Shegai, Timur
    Johansson, Peter
    Örebro University, School of Science and Technology.
    Kall, Mikael
    Simulating light scattering from supported plasmonic nanowires2012In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 20, no 10, p. 10816-10826Article in journal (Refereed)
    Abstract [en]

    We present a method for calculating the differential scattering cross sections from nanostructures close to an interface separating two semi-infinitive dielectric media. The method combines a fast finite element software (Comsol multiphysics), used for calculations of the fields around and inside the structure, and the Green's functions method, which is used to find the far field distribution from the calculated total fields inside the nanostructure. We apply the method to calculations of scattering spectra from silver nanowires supported by an air-glass interface, a system that is of high current interest in relation to various nanophotonics applications. The results are analyzed in relation to analytical models and compared to experimentally measured spectra, to which we find a good agreement. 

  • 14. Miljkovic, Vladimir D.
    et al.
    Shegai, Timur
    Käll, Mikael
    Johansson, Peter
    Örebro University, School of Science and Technology.
    Mode-specific directional emission from hybridized particle-on-a-film plasmons2011In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 19, no 14, p. 12856-12864Article in journal (Refereed)
    Abstract [en]

    We investigate the electromagnetic interaction between a gold nanoparticle and a thin gold film on a glass substrate. The coupling between the particle plasmons and the surface plasmon polaritons of the film leads to the formation of two localized hybrid modes, one low-energy. film-like. plasmon and one high-energy plasmon dominated by the nanoparticle. We find that the two modes have completely different directional scattering patterns on the glass side of the film. The high-energy mode displays a characteristic dipole emission pattern while the low-energy mode sends out a substantial part of its radiation in directions parallel to the particle dipole moment. The relative strength of the two radiation patterns vary strongly with the distance between the particle and the film, as determined by the degree of particle-film hybridization. (C) 2011 Optical Society of America

  • 15.
    Odebo Länk, Nils
    et al.
    Department of Physics, Chalmers University of Technology, Göteborg, Sweden.
    Verre, Ruggero
    Department of Physics, Chalmers University of Technology, Göteborg, Sweden.
    Johansson, Peter
    Örebro University, School of Science and Technology. Department of Physics, Chalmers University of Technology, Göteborg, Sweden; School of Science and Technology, Örebro University, Örebro, Sweden .
    Käll, Mikael
    Department of Physics, Chalmers University of Technology, Göteborg, Sweden.
    Large-Scale Silicon Nanophotonic Metasurfaces with Polarization Independent Near-Perfect Absorption2017In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 17, no 5, p. 3054-3060Article in journal (Refereed)
    Abstract [en]

    Optically thin perfect light absorbers could find many uses in science and technology. However, most physical realizations of perfect absorption for the optical range rely on plasmonic excitations in nanostructured metallic metasurfaces, for which the absorbed light energy is quickly lost as heat due to rapid plasmon decay. Here we show that a silicon metasurface excited in a total internal reflection configuration can absorb at least 97% of incident near-infrared light due to interferences between coherent electric and magnetic dipole scattering from the silicon nanopillars that build up the metasurface and the reflected wave from the supporting glass substrate. This "near-perfect" absorption phenomenon loads more than 50 times more light energy into the semiconductor than what would be the case for a uniform silicon sheet of equal surface density, irrespective of incident polarization. We envisage that the concept could be used for the development of novel light harvesting and optical sensor devices.

  • 16.
    Ogier, Robin
    et al.
    Dept Appl Phys, Chalmers, Gothenburg, Sweden.
    Fang, Yurui
    Dept Appl Phys, Chalmers, Gothenburg, Sweden.
    Svedendahl, Mikael
    Dept Appl Phys, Chalmers, Gothenburg, Sweden.
    Johansson, Peter
    Örebro University, School of Science and Technology. Dept Appl Phys, Chalmers, Gothenburg, Sweden.
    Käll, Mikael
    Dept Appl Phys, Chalmers, Gothenburg, Sweden.
    Macroscopic Layers of Chiral Plasmonic Nanoparticle Oligomers from Colloidal Lithography2014In: ACS Photonics, E-ISSN 2330-4022, Vol. 1, no 10, p. 1074-1081Article in journal (Refereed)
    Abstract [en]

    Optical near-field coupling between closely spaced plasmonic metal nanoparticles is important to a range of nanophotonic applications of high contemporary interest, including surface-enhanced molecular spectroscopy, nanooptical sensing, and various novel light-harvesting concepts. Here we report on monolayers of chiral heterotrimers and heterotetramers composed of closely spaced silver and/or gold nanodisks of different heights fabricated through facile hole-mask colloidal lithography. These quasi-three-dimensional oligomers are interesting for applications because they exhibit "hot" gaps and crevices of nanometric dimensions, a pronounced circular dichroism, and optical chirality in the visible to near-infrared wavelength range, and they can be produced in large ensembles (>109) of identical orientation. We analyze the optical properties of the samples based on simulation results and find that the circular dichroism is due to strong near-field coupling and intricate phase retardation effects originating in the three-dimensional character of the individual oligomers.

  • 17.
    Schneider, Natalia L.
    et al.
    Institut für Experimentelle und Angewandte Physik, Christian-Albrechts-Universität zu Kiel, Kiel, Germany.
    Johansson, Peter
    Örebro University, School of Science and Technology.
    Berndt, Richard
    Institut für Experimentelle und Angewandte Physik, Christian-Albrechts-Universität zu Kiel, Kiel, Germany.
    Hot electron cascades in the scanning tunneling microscope2013In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 87, no 045409Article in journal (Refereed)
    Abstract [en]

    The nonequilibrium distribution of electrons at the junction of a scanning tunneling microscope is investigated by detecting photons with energies hv > eV, where V is the bias voltage. Electrons are found at energies exceeding the Fermi level by almost eV. While their distribution deviates from a Fermi-Dirac function it is consistent with a model of hot electrons and holes that diffuse in energy and real space. DOI: 10.1103/PhysRevB.87.045409

  • 18. Schull, Guillaume
    et al.
    Neel, Nicolas
    Johansson, Peter
    Örebro University, School of Science and Technology.
    Berndt, Richard
    Electron-Plasmon and Electron-Electron Interactions at a Single Atom Contact2009In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 102, no 5, p. 057401-Article in journal (Refereed)
    Abstract [en]

    The transition from tunneling to contact is investigated by detecting light emitted from Au(111) in a scanning tunneling microscope. Optical spectra reflect single and multielectron processes and their distinct evolutions as a single-atom contact is formed. The experimental data are analyzed in terms of plasmon excitation and hot-hole processes.

  • 19.
    Schwind, Markus
    et al.
    Department of Applied Physics, Chalmers University of Technology, Gothenburg, Sweden.
    Miljkovic, Vladimir D.
    Department of Applied Physics, Chalmers University of Technology, Gothenburg, Sweden.
    Zäch, Michael
    Department of Applied Physics, Chalmers University of Technology, Gothenburg, Sweden.
    Gusak, Viktoria
    Department of Applied Physics, Chalmers University of Technology, Gothenburg, Sweden.
    Käll, Mikael
    Department of Applied Physics, Chalmers University of Technology, Gothenburg, Sweden.
    Zoric, Igor
    Department of Applied Physics, Chalmers University of Technology, Gothenburg, Sweden.
    Johansson, Peter
    Örebro University, School of Science and Technology. Department of Applied Physics, Chalmers University of Technology, Gothenburg, Sweden.
    Diffraction from Arrays of Plasmonic Nanoparticles with Short-Range Lateral Order2012In: ACS Nano, ISSN 1936-0851, E-ISSN 1936-086X, Vol. 6, no 11, p. 9455-9465Article in journal (Refereed)
    Abstract [en]

    We have measured the angular distribution of light scattered off 2D plasmonic Al nanoparticle ensembles. We created.. these samples with disk-like nanoparticles, 175 and 500 nm in diameter, respectively, using hole-mask colloidal lithography and electron beam lithography. The nanoparticle arrangements In the samples display the Short-range order (but no long-range order) characteristic for an ensemble formed by random sequential adsorption. As a consequence of this, the ensemble scattering patterns can be quantitatively well described by combining the single-particle scattering pattern with a static structure factor that carries information about the diffraction effects caused by the short-range order of the ensemble. We also performed sensing experiments in which we monitored changes in the angle-resolved scattering intensity for a fixed wavelength as a function of the thickness of an ultrathin SiO2 coating covering the Al nanoparticles. The data show that the angle and strength of the main diffraction peak vary linearly, with SiO2 coating thickness In the range 1.5-4.5 nm and suggest that measurements of the scattering profile could be a competitive alternative to traditional transmission measurements in terms of sensitivity.

  • 20. Sepulveda, Borja
    et al.
    Alaverdyan, Yuri
    Alegret, Joan
    Käll, Mikael
    Johansson, Peter
    Örebro University, Department of Natural Sciences.
    Shape effects in the localized surface plasmon resonance of single nanoholes in thin metal films2008In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 16, no 8, p. 5609-5616Article in journal (Refereed)
    Abstract [en]

    We report on the polarization-dependent optical response of elongated nanoholes in optically thin gold films. We measured elastic scattering spectra of spatially isolated ellipsoidal nanoholes with varying aspect ratio and compared the results to electrodynamic simulations. Both experiments and theory show that the plasmon mode that is polarized parallel to the short axis of the ellipsoidal hole red-shifts with increasing aspect ratio. This behavior is completely opposite to the case of elongated metal particles. We present a simple analytical model that qualitatively explains the observations in terms of the different orientations of the induced dipole moments in holes and particles.

  • 21.
    Shao, Lei
    et al.
    Department of Physics, Chalmers University of Technology, Göteborg, Sweden.
    Andrén, Daniel
    Department of Physics, Chalmers University of Technology, Göteborg, Sweden.
    Jones, Steven
    Department of Physics, Chalmers University of Technology, Göteborg, Sweden.
    Johansson, Peter
    Örebro University, School of Science and Technology.
    Käll, Mikael
    Department of Physics, Chalmers University of Technology, Göteborg, Sweden.
    Optically controlled stochastic jumps of individual gold nanorod rotary motors2018In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 98, no 8, article id 085404Article in journal (Refereed)
    Abstract [en]

    Brownian microparticles diffusing in optical potential-energy landscapes constitute a generic test bed for nonequilibrium statistical thermodynamics and have been used to emulate a wide variety of physical systems, ranging from Josephson junctions to Carnot engines. Here we demonstrate that it is possible to scale down this approach to nanometric length scales by constructing a tilted washboard potential for the rotation of plasmonic gold nanorods. The potential depth and tilt can be precisely adjusted by modulating the light polarization. This allo`ws for a gradual transition from continuous rotation to discrete stochastic jumps, which are found to follow Kramers dynamics in excellent agreement with stochastic simulations. The results widen the possibilities for fundamental experiments in statistical physics and provide insights into how to construct light-driven nanomachines and multifunctional sensing elements.

  • 22.
    Shao, Lei
    et al.
    Department of Applied Physics, Chalmers University of Technology, Göteborg, Sweden.
    Yang, Zhong-Jian
    Department of Applied Physics, Chalmers University of Technology, Göteborg, Sweden.
    Andren, Daniel
    Department of Applied Physics, Chalmers University of Technology, Göteborg, Sweden.
    Johansson, Peter
    Örebro University, School of Science and Technology. Department of Applied Physics, Chalmers University of Technology, Göteborg, Sweden.
    Käll, Mikael
    Department of Applied Physics, Chalmers University of Technology, Göteborg, Sweden.
    Gold Nanorod Rotary Motors Driven by Resonant Light Scattering2015In: ACS Nano, ISSN 1936-0851, E-ISSN 1936-086X, Vol. 9, no 12, p. 12542-12551Article in journal (Refereed)
    Abstract [en]

    Efficient and robust artificial nanomotors could provide a variety of exciting possibilities for applications in physics, biology and chemistry, including nanoelectromechanical systems, biochemical sensing, and drug delivery. However, the application of current man-made nanomotors is limited by their sophisticated fabrication techniques, low mechanical output power and severe environmental requirements, making their performance far below that of natural biomotors. Here we show that single-crystal gold nanorods can be rotated extremely fast in aqueous solutions through optical torques dominated by plasmonic resonant scattering of circularly polarized laser light with power as low as a few mW. The nanorods are trapped in 2D against a glass surface, and their rotational dynamics is highly dependent on their surface plasmon resonance properties. They can be kept continuously rotating for hours with limited photothermal side effects and they can be applied for detection of molecular binding with high sensitivity. Because of their biocompatibility, mechanical and thermal stability, and record rotation speeds reaching up to 42 kHz (2.5 million revolutions per minute), these rotary nanomotors could advance technologies to meet a wide range of future nanomechanical and biomedical needs in fields such as nanorobotics, nanosurgery, DNA manipulation and nano/microfluidic flow control.

  • 23. Shegai, Timur
    et al.
    Chen, Si
    Miljkovic, Vladimir D.
    Zengin, Gulis
    Johansson, Peter
    Örebro University, School of Science and Technology.
    Kall, Mikael
    A bimetallic nanoantenna for directional colour routing2011In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 2, p. 481-Article in journal (Refereed)
    Abstract [en]

    Recent progress in nanophotonics includes demonstrations of meta-materials displaying negative refraction at optical frequencies, directional single photon sources, plasmonic analogies of electromagnetically induced transparency and spectacular Fano resonances. The physics behind these intriguing effects is to a large extent governed by the same single parameter-optical phase. Here we describe a nanophotonic structure built from pairs of closely spaced gold and silver disks that show phase accumulation through material-dependent plasmon resonances. The bimetallic dimers show exotic optical properties, in particular scattering of red and blue light in opposite directions, in spite of being as compact as similar to lambda(3)/100. These spectral and spatial photon-sorting nanodevices can be fabricated on a wafer scale and offer a versatile platform for manipulating optical response through polarization, choice of materials and geometrical parameters, thereby opening possibilities for a wide range of practical applications.

  • 24. Shegai, Timur
    et al.
    Johansson, Peter
    Örebro University, School of Science and Technology.
    Langhammer, Christoph
    Kall, Mikael
    Directional scattering and hydrogen sensing by bimetallic Pd-Au nanoantennas2012In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 12, no 5, p. 2464-2469Article in journal (Refereed)
    Abstract [en]

    Nanoplasmonic sensing is typically based on quantification of changes in optical extinction or scattering spectra. Here we explore the possibility of facile self-referenced hydrogen sensing based on angle-resolved spectroscopy. We found that heterodimers built from closely spaced gold and palladium nanodisks exhibit pronounced directional scattering, that is, for particular wavelengths, much more light is scattered toward the Au than toward the Pd particle in a dimer. The effect is due to optical phase shifts associated with the material asymmetry and therefore highly sensitive to changes in the permittivity of Pd induced by hydrogen loading. In a wider perspective, the results suggest that directional scattering from bimetallic antennas, and material asymmetry in general, may offer many new routes toward novel nanophotonic sensing schemes.

  • 25. Shegai, Timur
    et al.
    Miljkovic, Vladimir D.
    Bao, Kui
    Xu, Hongxing
    Nordlander, Peter
    Johansson, Peter
    Örebro University, School of Science and Technology.
    Kall, Mikael
    Unidirectional broadband light emission from supported plasmonic nanowires2011In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 11, no 2, p. 706-711Article in journal (Refereed)
    Abstract [en]

    Metal nanowires are thought to become key elements in future nanophotonics applications. Here we show that single crystal silver nanowires supported on a dielectric interface behave similar to broadband unidirectional antennas for visible, light. The degree of directionality can be controlled through the nanowire radius and its dielectric environment and the effect can be interpreted in terms of so-called leakage radiation from surface plasmons propagating in a single direction along a wire. We measure a forward-to-backward emission ratio exceeding 15 dB and an angular spread of 4 degrees for wires with radii of the order 150 nm on glass in air. These findings could pave the way for development of metal nanowires as subwavelength directors of light in solar, sensor, and spectroscopy applications.

  • 26. Svedendahl, Mikael
    et al.
    Johansson, Peter
    Örebro University, School of Science and Technology.
    Kall, Mikael
    Complete light annihilation in an ultrathin layer of gold nanoparticles2013In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 13, no 7, p. 3053-3058Article in journal (Refereed)
    Abstract [en]

    We experimentally demonstrate that an incident light beam can be completely annihilated in a single layer of randomly distributed, widely spaced gold nanoparticle antennas. Under certain conditions, each antenna dissipates more than 10 times the number of photons that enter its geometric cross-sectional area. The underlying physics can be understood in terms of a critical coupling to localized plasmons in the nanoparticles or, equivalently, in terms of destructive optical Fano interference and so-called coherent absorption.

  • 27. Tong, Lianming
    et al.
    Miljkovic, Vladimir D.
    Johansson, Peter
    Örebro University, School of Science and Technology.
    Kall, Mikael
    Plasmon hybridization reveals the interaction between individual colloidal gold nanoparticles confined in an optical potential well2011In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 11, no 11, p. 4505-4508Article in journal (Refereed)
    Abstract [en]

    The understanding of interaction forces between nanoparticles in colloidal suspension is central to a wide range of novel applications and processes in science and industry. However, few methods are available for actual characterization of such forces at the single particle level. Here we demonstrate the first measurements of colloidal interactions between two individual diffusing nanoparticles using a colorimetric assay based on plasmon hybridization, that is, strong near-field coupling between localized surface plasmon resonances. The measurements are possible because individual gold nanoparticle pairs can be loosely confined in an optical potential well created by a laser tweezers. We quantify the degree of plasmon hybridization for a large number of individual particle pairs as a function of increasing salt concentration. The data reveal a considerable heterogeneity at the single particle level but the estimated average surface separations are in excellent agreements with predictions based on the classical theory of Derjaguin, Landau, Verwey, and Overbeek.

  • 28.
    Wersäll, Martin
    et al.
    Department of Applied Physics, Chalmers University of Technology, Göteborg, Sweden.
    Verre, Ruggero
    Department of Applied Physics, Chalmers University of Technology, Göteborg, Sweden.
    Svedendahl, Mikael
    Department of Applied Physics, Chalmers University of Technology, Göteborg, Sweden.
    Johansson, Peter
    Örebro University, School of Science and Technology. Department of Applied Physics, Chalmers University of Technology, Göteborg, Sweden.
    Käll, Mikael
    Department of Applied Physics, Chalmers University of Technology, Göteborg, Sweden.
    Shegai, Timur
    Department of Applied Physics, Chalmers University of Technology, Göteborg, Sweden.
    Directional Nanoplasmonic Antennas for Self-Referenced Refractometric Molecular Analysis2014In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 118, no 36, p. 21075-21080Article in journal (Refereed)
    Abstract [en]

    Localized surface-plasmon resonance (LSPR) sensors are typically based on tracing resonance peak shifts that precisely follow changes in the local refractive index. Such measurements usually require a spectrometer, a stable light source, and an accurate LSPR position tracing technique. As a simple but efficient alternative, we investigated a self-referenced single-wavelength sensing scheme based on angle-dependent and highly directional radiation patterns originating from a monolayer of asymmetric gold nanodimers. We found that one could easily trace a model biotinneutravidin recognition reaction as well as minute bulk refractive index changes, by measuring the intensity ratio between the light scattered in two different directions with respect to the dimers. The refractometric resolution of the methodology was estimated to be on the order of Delta n approximate to 10(-5) RIU. These results may be particularly useful for label-free biosensing applications that require a combination of simple and cost-effective optical readout with a reasonable sensitivity.

  • 29.
    Zengin, Gulis
    et al.
    Chalmers University of Technology, Göteborg, Sweden.
    Johansson, Goran
    Chalmers University of Technology, Göteborg, Sweden.
    Johansson, Peter
    Örebro University, School of Science and Technology. Chalmers University of Technology, Göteborg, Sweden.
    Antosiewicz, Tomasz J.
    Chalmers University of Technology, Göteborg, Sweden; University of Warsaw, Warsaw, Poland.
    Käll, Mikael
    Chalmers University of Technology, Göteborg, Sweden.
    Shegai, Timur
    Chalmers University of Technology, Göteborg, Sweden.
    Approaching the strong coupling limit in single plasmonic nanorods interacting with J-aggregates2013In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 3, article id 3074Article in journal (Refereed)
    Abstract [en]

    We studied scattering and extinction of individual silver nanorods coupled to the J-aggregate form of the cyanine dye TDBC as a function of plasmon - exciton detuning. The measured single particle spectra exhibited a strongly suppressed scattering and extinction rate at wavelengths corresponding to the J-aggregate absorption band, signaling strong interaction between the localized surface plasmon of the metal core and the exciton of the surrounding molecular shell. In the context of strong coupling theory, the observed "transparency dips" correspond to an average vacuum Rabi splitting of the order of 100 meV, which approaches the plasmon dephasing rate and, thereby, the strong coupling limit for the smallest investigated particles. These findings could pave the way towards ultra-strong light-matter interaction on the nanoscale and active plasmonic devices operating at room temperature.

1 - 29 of 29
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