Ron Atkinson

Growth and properties of gold and nickel nanorods in thin film alumina

Arrays of nickel and gold nanorods have been grown on glass and silicon substrates using porous alumina templates of less than 500 nm thickness. A method is demonstrated for varying the diameter of the nanorods whilst keeping the spacing constant. Optical extinction spectra for the gold nanorods show two distinct maxima associated with the transverse and longitudinal axes of the rods. Adding small quantities of oxygen to the aluminium before anodization is found to improve the sharpness of the extinction peaks. The spectral position of the longitudinal peak is shown to be sensitive to the nanorod diameter for constant length and spacing. For the nickel nanorods it is shown that the magnetic properties are governed by both interactions between the wires and shape anisotropy.

Thin films of barium ferrite with perpendicular magnetic anisotropy produced by laser ablation deposition

Barium ferrite thin films with perpendicular magnetic anisotropy have been prepared on heated (001) sapphire substrates by laser ablation deposition in an oxygen atmosphere using a KrF excimer laser. X-ray diffraction patterns reveal highly oriented films of the magnetoplumbite phase with a c-axis angular spread of 1.8” . Scanning electron micrographs reveal that these films are polycrystalline with a crystallite size of 0.4 ,um. There is no surface particulate contamination. The saturation magnetization was similar to bulk barium ferrite, and the coercivity was 145 mT. The magneto-optical properties of the films are compared with those derived from the optical and magneto-optical constants of the bulk material.

Fabrication and optical properties of gold nanotube arrays

Arrays of gold nanotubes with polypyrrole cores were grown on glass substrates by electrodeposition into thin film porous alumina templates. Measurements of optical transmission revealed strong extinction peaks related to plasmonic resonances, which were sensitive to the polarization state and angle of incidence. On prolonging the electrodeposition of gold, the polypyrrole core became fully encapsulated and this had a dramatic effect on the optical properties of the arrays, which was rationalized by finite element simulation of the local field intensities resulting from plasmon excitation.

Polarization conversion through collective surface plasmons in metallic nanorod arrays

For two-dimensional (2D) arrays of metallic nanorods arranged perpendicular to a substrate several methods have been proposed to determine the electromagnetic near-field distribution and the surface plasmon resonances, but an analytical approach to explain all optical features on the nanometer length scale has been missing to date. To fill this gap, we demonstrate here that the field distribution in such arrays can be understood on the basis of surface plasmon polaritons (SPPs) that propagate along the nanorods and form standing waves. Notably, SPPs couple laterally through their optical near fields, giving rise to collective surface plasmon (CSP) effects. Using the dispersion relation of such CSPs, we deduce the condition of standing-wave formation, which enables us to successfully predict several features, such as eigenmodes and resonances. As one such property and potential application, we show both theoretically and in an experiment that CSP propagation allows for polarization conversion and optical filtering in 2D nanorod arrays. Hence, these arrays are promising candidates for manipulating the light polarization on the nanometer length scale.

The controlled fabrication and geometry tunable optics of gold nanotube arrays

Arrays of vertically aligned gold nanotubes are fabricated over several square centimetres which display a geometry tunable plasmonic extinction peak at visible wavelengths and at normal incidence. The fabrication method gives control over nanotube dimensions with inner core diameters of 15-30 nm, wall thicknesses of 5-15 nm and nanotube lengths of up to 300 nm. It is possible to tune the position of the extinction peak through the wavelength range 600-900 nm by varying the inner core diameter and wall thickness. The experimental data are in agreement with numerical modelling of the optical properties which further reveal highly localized and enhanced electric fields around the nanotubes. The tunable nature of the optical response exhibited by such structures could be important for various label-free sensing applications based on both refractive index sensing and surface-enhanced Raman scattering.

Optical and magneto-optical characterization of TbFeCo and GdFeCo thin films for high-density recording

Thin, optically semi-infinite films of amorphous TbFeCo and GdFeCo, suitable for magneto-optical recording, have been deposited by DC magnetron sputtering onto glass. Ellipsometric techniques have been used to determine the complex refractive index and complex magneto-optical parameter of the films in the wavelength range 400–900 nm, thus characterizing the materials. A review of the literature is presented and shows that the results for the TbFeCo films compare favourably with published results obtained from measurements conducted in situ, with the films protected with ZnS barrier layers. It is found that GdFeCo and TbFeCo are optically very similar, but magneto-optically the materials are quite different.

Domain observation in MnBi films with the scanning electron microscope

The scanning electron microscope (SEM) has been successfully used to detect (type I) magnetic contrast in thin films of MnBi. The domain structures observed consisted of an irregular patchwork, typical of these films in the as-deposited condition, with a domain width in the region of 3 mu m. Efforts to resolve the maze domain configuration (spacing approximately 0.3 mu m) with the SEM were however not successful.

Fundamental advantages of metal/dielectric superlattices for magneto-optic recording media

Abstract By treating magnetic superlattices in terms of their single equivalent layer analogue, and by considering the most meaningful figure-of-merit indicating a materials potential for readout in magneto-optic recording, it has been possible to show that metal/dielectric systems have distinct advantages over metal/metal systems. Specifically, it has been proved theoritically that the magneto-optic potential of a metal/dielectric superlattice, where the metal is the only magnetic component, is independent of the material of the dielectric and the thickness of the sublayers; providing these are much smaller than the wavelength of the radiation used in the readout process. Hence, the ultimate magneto-optic performance is determined by and more importantly is equal to that of the pure metallic component. The significance of this conclusion is that the dielectric medium and the sublayer thickness can be regarded as independent variables which can be adjusted to obtain desirable magnetic and structural properties without affecting magneto-optic performance.

The design and optimization of disk structures for MAMMOS/MSR magneto-optic recording

Existing quadrilayer and trilayer techniques for optimizing the magneto-optical effects from magnetic materials have been applied to new generation recording media to investigate the possibility of maximizing the signal-to-noise readout performance. Various methods are reviewed and the designs they produce are compared with each other and with the working media found in the literature. In order to address a number of inadequacies, a new numerical approach to the optimization of a quadrilayer structure is used to find further solutions that are considered more suitable for the practical recording media. The effects on design and performance of medium of incidence, type of storage layer and wavelength are all considered.

MAGNETO-OPTICAL NORMAL INCIDENCE POLAR KERR EFFECT OF INHOMOGENEOUS MULTILAYERS

The normal incidence magneto-optical (MO) polar Kerr effect is considered on the basis of an idealized phenomenological model of plane wave reflection from inhomogeneous multilayers. They may be periodic or non-periodic, and each layer may have any thickness and constant refractive index, with the small MO Q-parameter being an arbitrary function of the coordinate along the direction of wave propagation. A new algorithm, involving a regular perturbation method for solving the wave equation, to find the state of polarization (Kerr angle and ellipticity) and amplitude reflectance is comprehensively outlined and shown to be conveniently used in terms of the characteristic matrix technique as well as being free from any numerical disadvantages. A few model distributions of the inhomogeneity are used to illustrate its influence on the Kerr effect. An exact analytical solution, found for a semi-infinite MO medium with Q-parameter (not necessarily small) as an exponential function, is given to confirm the validity and good accuracy of the results produced by means of the general approach.