Showing papers by "John B Ketterson published in 2011"

Infrared Plasmonics with Indium–Tin-Oxide Nanorod Arrays

Abstract: This article reports the study of infrared plasmonics with both random and periodic arrays of indium–tin-oxide (ITO) nanorods (NR). A description is given on the synthesis, patterning, and characterization of physical properties of the ITO NR arrays. A classical scattering model, along with a 3-D finite-element-method and a 3-D finite-difference-time-domain numerical simulation method has been used to interpret the unique light scattering phenomena. It is also shown that the intrinsic plasma frequency can be varied through careful postsynthesis processing of the ITO NRs. Examples are given on how coupled plasmon resonances can be tuned through patterning of the ITO NR arrays. In addition, environment dielectric sensing has been demonstrated through the shift of the resonances as a result of index change surrounding the NRs. These initial results suggest potential for further improvement and opportunities to develop a good understanding of infrared plasmonics using ITO and other transparent conducting oxid...

Surface-enhanced Raman scattering from silver-coated opals

Abstract: We describe surface-enhanced Raman scattering measurements from a benzenethiol monolayer adsorbed on a silver-coated film that is, in turn, deposited on an artificial opal, where the latter is a close-packed three-dimensional dielectric lattice formed from polystyrene spheres. Data for a range of sphere sizes, silver film thicknesses, and laser excitation wavelengths are obtained. Enhancement factors can be in the range of 107. To partially explain these large enhancements, we have performed model finite-difference time domain simulations of the position-dependent electric fields generated at the opal surfaces for several experimentally studied laser wavelengths and sphere diameters.

Long-range surface plasmon polaritons propagating on a dielectric waveguide support

Abstract: In the traditional long-range surface plasmon geometry, an ultrathin metal film is sandwiched between two layers having identical dielectric constants. Here we demonstrate the long-range surface plasmon polariton (LRSPP) properties for a new structure where a thin layer with a dielectric constant exceeding that of the surroundings is inserted within the sandwich, provided the layer thickness d satisfies the condition k(⊥)d=mπ where k(⊥) is the component of the guide wavevector perpendicular to the layer and m is an integer. The resulting plasmon modes have smaller losses and nearly the same phase velocity as the original LRSPP. This provides a strategy to support silver films having thicknesses of 10's of nanometers to create plasmonic devices for sensor applications.

Silver-coated inverse opals formed from polystyrene spheres for surface-enhanced Raman scattering

Abstract: We have developed a new substrate for surface-enhanced Raman scattering (SERS) measurements involving a thin silver layer deposited over an ion-etched TiO2 inverse opal. The latter is formed by chemically infiltrating a polystyrene opal array with TiO2 followed by a thermal decomposition of the spheres. The SERS response of the these substrates is examined for several sphere sizes and lasers wavelengths; the results show that such substrates yield high enhance factors, comparable to substrates involving a silver layer deposited directly on a polystyrene opal array. Copyright © 2010 John Wiley & Sons, Ltd.

Multi-Terminal Superconducting Nonequilibrium Device With a Ferromagnetic Screen

Abstract: We have fabricated and characterized double-barrier multi-terminal superconducting transistor-like devices with the Nb/Al/AlOx/Al/Nb/Ni/Al/AlOx/Al/Nb (S1IS2FIS3) structure, where S, I, and F refer to superconducting, insulating, and ferromagnetic layers, respectively. A thin ferromagnetic Ni layer screens the superconductivity of the middle Nb layer on the injector-barrier side, so that the Nb/Ni bilayer manifests itself as a superconductor in the current-voltage characteristic (I-V curve) of the acceptor S1IS2 junction, but as a normal metal in the I-V curve of the injector S2FIS3 junction. It is shown that this property allows for considerable improvement of the input-output isolation of the quasiparticle-injection devices as compared with that for the formerly reported quiteron.

Low-field FMR studies of magnetic confinement effects in patterned ferromagnetic thin films

Abstract: We have performed broad-band (10 MHz–20 GHz) and tuned cavity (9.7 GHz) ferromagnetic resonance measurements on permalloy thin films patterned with square lattices of circular, square and diamond-shaped antidots of various sizes and separations. We observe remarkably reproducible mode structures in the low-frequency, hysteretic regime in which various domain wall patterns and unsaturated magnetization textures exist and are strongly affected by the geometry of the antidot lattice. The field, frequency and angular dependences of the observed modes (some of which have not been previously observed) are generally in good agreement with our micromagnetic simulations.