David W. McComb

Electron energy-loss spectroscopy (EELS) of surface plasmons in single silver nanoparticles and dimers: influence of beam damage and mapping of dark modes

We demonstrate the use of a scanning transmission electron microscope (STEM) equipped with a monochromator and an electron energy loss (EEL) spectrometer as a powerful tool to study localized surface plasmons in metallic nanoparticles. We find that plasmon modes can be influenced by changes in nanostructure geometry and electron beam damage and show that it is possible to delineate the two effects through optimization of specimen preparation techniques and acquisition parameters. The results from the experimental mapping of bright and dark plasmon energies are in excellent agreement with the results from theoretical modeling.

High-resolution mapping of electron-beam-excited plasmon modes in lithographically defined gold nanostructures.

We demonstrate the use of high-resolution electron beam lithography to fabricate complex nanocavities with nanometric spatial and positional control. The plasmon modes of these nanostructures are then mapped using electron energy-loss spectroscopy in a scanning transmission electron microsope. This powerful combination of patterning and plasmon mapping provides direct experimental verification to theoretical predictions of plasmon hybridization theory in complex metal nanostructures and allows the determination of the full mode spectrum of such cavities.

DNA tunneling detector embedded in a nanopore.

We report on the fabrication and characterization of a DNA nanopore detector with integrated tunneling electrodes. Functional tunneling devices were identified by tunneling spectroscopy in different solvents and then used in proof-of-principle experiments demonstrating, for the first time, concurrent tunneling detection and ionic current detection of DNA molecules in a nanopore platform. This is an important step toward ultrafast DNA sequencing by tunneling.

Observation of Bragg reflection in photonic crystals synthesized from air spheres in a titania matrix

Three-dimensional photonic crystals made of close-packed air spheres in an interconnected titania matrix have been fabricated using a self-organized template of polystyrene microspheres of 400 nm diameter. The matrix was obtained by vacuum-assisted infiltration of a precursor, with subsequent removal of the microspheres by calcination. Electron microscopy has confirmed the ordering of the structure and the presence of features likely to enlarge the photonic band gap. The reflection spectra of the crystal measured at different angles of incidence are consistent with Bragg’s law and with theoretical calculations, confirming the photonic nature of the material.

Fluorescent or not? Size-dependent fluorescence switching for polymer-stabilized gold clusters in the 1.1-1.7 nm size range

The synthesis of fluorescent water-soluble gold nanoparticles by the reduction of a gold salt in the presence of a designed polymer ligand is described, the size and fluorescence of the particles being controlled by the polymer to gold ratio; the most fluorescent nanomaterial has a 3% quantum yield, a 1.1 nm gold core and a 6.9 nm hydrodynamic radius.

Inverted organic photovoltaic devices with high efficiency and stability based on metal oxide charge extraction layers

A substantial increase in device performance and operational stability in solution processed inverted bulk heterojunction (BHJ) organic photovoltaic devices (OPV) is demonstrated by introducing a zinc oxide (ZnO) interlayer between the electron collecting bottom electrode and the photoactive blend of poly(3-hexylthiophene) (P3HT) and phenyl-C61-butyric acid methyl ester (PCBM). The structure and morphology of the dense, planar ZnO layers were controlled either by electro-deposition or spray pyrolysis techniques. Metal oxide sandwich OPV devices based on the photoactive blend on an electro-deposited ZnO interlayer with a (100) preferential crystal orientation, and using a tungsten oxide (WOx) interlayer on the opposite electrode, resulted in a remarkable increase in power conversion efficiency with a value of 4.91% under AM1.5 illumination and an external quantum efficiency of 74%. Electro-deposition of the ZnO at low temperature proved to be the most promising method for forming the ZnO interlayers, allowing the highest control of film structure and morphology, as well as leading to significantly improved device efficiency and stability.

Thin film photonic crystals: synthesis and characterisation

The results of an investigation of the major factors that influence colloidal self-assembly of thin film photonic crystals are reported. The effect of temperature, relative humidity, sphere diameter, colloidal concentration and substrate angle were investigated: the results establish clearly that temperature is the most critical factor. Quantitative analysis of the results using Design of Experiments methodology has identified the optimum conditions for the growth of large area, low defect density thin film photonic crystals.

Synthesis and optical properties of opal and inverse opal photonic crystals

We describe the synthesis of two complementary photonic crystals: opal and an inverted opal structure consisting of air spheres in a titania matrix. From optical measurements and comparison with the literature, the mechanical strength and effective refractive index are increased by sintering for opal and because of compression for the inverse opal. However, this is at the expense of reducing the PBG in the [1 1 1] direction.

Growth of strained InGaAs layers on InP substrates

A series of InGaAs films, compressively or tensilely strained, were grown on (001)InP substrates at 490 °C by gas source molecular beam epitaxy. Compressively strained (−0.5%) (and lattice matched) layers were morphologically stable, but layers grown under tension (+0.5 to +0.6% strain) developed facets on (113)A or (114)A planes. In the first stages of growth of films under tension, and throughout all stages of growth for the compressively strained films, a fine scale (10 nm wavelength) composition modulation was found in the [110] direction. In the later stages of growth of films under tension, the regions of composition segregation were confined to the peaks and valleys of the faceted surface. Regions of high and low stress concentration (the valleys and the peaks) exhibit In/Ga ratios higher or lower, respectively, than the flat faceted surfaces. The elastic strain energy built into the film, associated with the [110] composition modulation, depends on the ratio of the modulation wavelength to film th...

The role of trace additions of alumina to yttria–tetragonal zirconia polycrystals (Y–TZP)

Abstract We demonstrate, using high spatial resolution electron microscopy and surface science techniques, the segregation of Al 3+ and relative increase in the Y 3+ concentration at grain boundaries in a 5.2 wt.% yttria stabilised TZP doped with 0.15 wt.% Al 2 O 3 ; free of any intergranular glassy film.