Transparent conducting oxides for active hybrid metamaterial devices

We present here a study of the combined nonlinear response of plasmonic antenna—transparent conducting oxide hybrids for activation of metamaterial devices. Nanoantenna layers consisting of randomly positioned gold nanodisk dimers are fabricated using hole-mask lithography. The nanoantenna layers are covered with a 20 nm thin layer of transparent conducting oxide (TCO). We investigate the response of atomic layer deposited aluminum-doped zinc oxide (AZO) next to indium–tin oxide (ITO) produced using sputter coating. We show that our results are in agreement with the hypothesis of fast electron-mediated cooling, facilitated by the Ohmic interface between the gold nanodisks and the TCO substrate, which appears a universal mechanism for providing a new hybrid functionality to active metamaterial device

Ultrafast Plasmonic Nanoantenna-ITO Hybrid Switches

We present here a new type of device using nonlinear hybrid antenna-semiconductor (ITO) interaction. We observe a picosecond transient response from the antenna that cannot be explained by either pure ITO or antenna nonlinearities independently. We study the dependence of the hybrid interaction on several experimental parameters, including the polarization of excitation and detection

Pseudo-classical theory for fidelity of nearly resonant quantum rotors

Using a semiclassical ansatz we analytically predict for the fidelity of delta-kicked rotors the occurrence of revivals and the disappearance of intermediate revival peaks arising from the breaking of a symmetry in the initial conditions. A numerical verification of the predicted effects is given and experimental ramifications are discussed.Comment: Shortened and improved versio

Surface-enhanced infrared spectroscopy using ultra-compact indium tin oxide (ITO) sensor arrays

Reduced cross section and strong plasmon confinement allows ITO antennas to be integrated at extremely high densities with no loss in performance due to long-range transverse interactions and to hold promise for extremely sub-wavelength SEIRS

Exploring the Molecular Conformation Space by Soft Molecule–Surface Collision

Biomolecules function by adopting multiple conformations. Such dynamics are governed by the conformation landscape whose study requires characterization of the ground and excited conformation states. Here, the conformational landscape of a molecule is sampled by exciting an initial gas-phase molecular conformer into diverse conformation states, using soft molecule-surface collision (0.5-5.0 eV). The resulting ground and excited molecular conformations, adsorbed on the surface, are imaged at the single-molecule level. This technique permits the exploration of oligosaccharide conformations, until now, limited by the high flexibility of oligosaccharides and ensemble-averaged analytical methods. As a model for cellulose, cellohexaose chains are observed in two conformational extremes, the typical "extended" chain and the atypical "coiled" chain-the latter identified as the gas-phase conformer preserved on the surface. Observing conformations between these two extremes reveals the physical properties of cellohexaose, behaving as a rigid ribbon that becomes flexible when twisted. The conformation space of any molecule that can be electrosprayed can now be explored

Fast Molecular Compression by a Hyperthermal Collision Gives Bond-Selective Mechanochemistry

Using electrospray ion beam deposition, we collide the complex molecule Reichardt’s Dye (C41H30NO+) at low, hyperthermal translational energy (2 - 50 eV) with a Cu(100) surface and image the outcome at single-molecule level by scanning tunneling microscopy. We observe bond-selective reaction induced by the translational kinetic energy. The collision impulse compresses the molecule and bends specific bonds, prompting them to react selectively. This dynamics drives the system to seek thermally inaccessible reactive pathways, since the compression timescale (sub-ps) is much shorter than the thermalization timescale (ns), thereby yielding reaction products that are unobtainable thermally

All-optical control of a single plasmonic nanoantenna–ITO hybrid

We demonstrate experimentally picosecond all-optical control of a single plasmonic nanoantenna embedded in indium tin oxide (ITO). We identify a picosecond response of the antenna–ITO hybrid system, which is distinctly different from transient bleaching observed for gold antennas on a nonconducting SiO2 substrate. Our experimental results can be explained by the large free-carrier nonlinearity of ITO, which is enhanced by plasmon-induced hot-electron injection from the gold nanoantenna into the conductive oxide. The combination of tunable antenna–ITO hybrids with nanoscale plasmonic energy transfer mechanisms, as demonstrated here, opens a path for new ultrafast devices to produce nanoplasmonic switching and control.<br/

Hotspot-mediated ultrafast nonlinear control of multifrequency plasmonic nanoantennas

Plasmonic devices have a unique ability to concentrate and convert optical energy into a small volume. There is a tremendous interest in achieving active control of plasmon resonances, which would enable switchable hotspots for applications such as surface-enhanced spectroscopy and single molecule emission. The small footprint and strong-field confinement of plasmonic nanoantennas also holds great potential for achieving transistor-type devices for nanoscale-integrated circuits. To achieve such a functionality, new methods for nonlinear modulation are required, which are able to precisely tune the nonlinear interactions between resonant antenna elements. Here we demonstrate that resonant pumping of a nonlinear medium in a plasmonic hotspot produces an efficient transfer of optical Kerr nonlinearity between different elements of a multifrequency antenna. By spatially and spectrally separating excitation and readout, isolation of the hotspot-mediated ultrafast Kerr nonlinearity from slower, thermal effects is achieved

All-optical control of hybrid plasmonic semiconductor-metal nanostructures

This thesis is dedicated to the study of linear and nonlinear properties of closely spaced gold nanoparticle dimers, so-called nanoantennas, and hybrid nanoantenna devices consisting of metals and semiconductors. Coupled nanoparticles are of particular interest for nanophotonics because of their ability to focus light into subwavelength volumes and the associated large field enhancement in the gap.The samples used in this thesis are gold rectangles designed by electron-beam lithography, with both symmetric and asymmetric arms, as well as symmetric closely spaced 100 nm disk dimers which were fabricated by colloidal lithography in combination with angle-dependent evaporation. We investigate the linear interplay of modes in the two arms with Spatial Modulation Microscopy, an experimental technique which results in a measure directly proportional to the extinction cross-section. We find a variety of constructive and destructive interference between different order modes, which we can better understand by comprehensive simulations of antennas, varying the parameter space of gap size (coupling strength) and length-length ratio using advanced numerical methods such as the Fourier Domain Time Difference and the Boundary Element Method. We find that the presence of nonradiative modes is made visible by Electromagnetically Induced Transparency.In order to probe the nonlinear properties of the antennas and their interaction with Indium Tin Oxide substrates, a pump-probe setup is used to get an insight into ultrafast nonlinear response with picosecond resolution. These measurements (and corresponding fits using numerical simulations) lead us to identify a new energy transfer mechanism where fast electrons are injected from the nanoparticles into the semiconductor, resulting in a refractive index change due to heating of the surroundings. In follow-up experiments, we find this mechanism to be universal (and versatile) for other types of transparent conductive oxides. These results open new avenues towards application of nanoantennas for ultrafast switching