Nanostructured metal films of platinum, gold and silver up to 675 nm thick we prepared by electrochemical deposition through templates of 700 nm diameter polystyrene spheres assembled as hexagonal close packed monolayer on an evaporated gold surface followed by removal of the template by dissolution in tetrahydrofuran. The reflection spectra of the films at normal incidence were recorded as a function of film thickness and the spectra correlated with the local visual appearance of the film and the surface structure from SEM. For thin films, below one quarter sphere height, the spectra show a single reflectivity dip at a wavelength just below the sphere diameter consistent with surface-plasmon grating-like behaviour. For the thicker films several reflectivity dips are observed which move towards longer wavelength with increasing film thickness. This behaviour shown to be consistent with a model in which light reflected from the top of the structure interferes with light reflected from within the spherical segment cavities in the film.
We investigate the properties of gold surfaces patterned using a nanoscale "lost wax" technique by electrochemical deposition through a self-assembled latex template. Near-spherical gold nanocavities within the resulting porous films support localized surface plasmons which couple strongly to incident light, appearing as sharp spectral features in reflectivity measurements. The energy of the resonances is easily tunable from ultraviolet to near infrared by controlling the diameter and height of the nanocavities. The energies of these features agree well with the Mie resonances of a perfect spherical void.
ExperimentalFor the fabrication of n-ZnO/p-GaN heteroepitaxial nanorod EL devices, n-ZnO nanorods were vertically grown on 3 lm thick p-GaN layers coated on Al 2 O 3 (0001) using catalyst-free MOVPE. The pGaN layers exhibited a p-type carrier concentration of 2 10 17 cm ±3 and a mobility of 10 cm 2 V ±1 s ±1 . For ZnO nanorod MOVPE growth, diethyl-zinc (DEZn) and oxygen were employed as reactant sources, as previously reported [13]. Details in the growth parameters of ZnO nanorods on GaN substrates are the same as those on sapphire substrates except for the DEZn flow prior to ZnO growth. That is, in the initial ZnO growth stage, only DEZn with a carrier gas flowed for 30 s prior to ZnO nanorod growth in order to prevent GaN surface oxidation.The EL devices were fabricated by making good ohmic contacts on both p-GaN and n-ZnO. The ohmic contact on p-GaN was fabricated by evaporating Pt and Au bilayers. The typical Pt and Au layer thicknesses were 100 and 500 , respectively. After the metallization of p-GaN, the free space between the individual ZnO nanorods was filled with a thin photoresist by spin coating. This was followed by selective etching of the photoresist under an oxygen plasma in order to produce a nanorod array embedded in the photoresist with only the nanorod tips exposed (by 50±100 nm; Fig. 1c). For the metallization of the n-ZnO nanorods, 100 thick Ti and 500 thick Au layers were deposited on the nanorod tips through a shadow mask by electron-beam evaporation, resulting in a continuous contact layer on the ZnO nanorods (Fig. 1d). Good ohmic contacts on both n-ZnO and pGaN were made by rapid thermal annealing at 300 and 500 C for 1 min, respectively. The EL and I±V characteristics of the devices were measured by applying a DC voltage to the device using a source meter (Keithley 2400). The EL spectra were measured using a monochromator and a detection system equipped with a photomultiplier tube and a photon counter which had been used for photoluminescence spectroscopy [3]. All measurements were preformed at room temperature. Preparation of Arrays of Isolated Spherical Cavities by Self-Assembly of Polystyrene Spheres on Self-Assembled Pre-patterned Macroporous Films ReceivedBy Mamdouh E. Abdelsalam, Philip N. Bartlett,* Jeremy J. Baumberg, and Steve Coyle Self-assembly of colloidal spheres onto patterned (e.g., lithographically modified) [1] substrates is a promising approach to prepare complex three-dimensional (3D) geometries (e.g., assemble colloidal spheres into square pyramidal shapes) [2] that cannot be produced by self-assembly of colloidal spheres on flat substrates. Generally self-assembly alone is restricted to the formation of close-packed two-dimensional (2D) and 3D arrays of colloidal particles and does not lead to more complex lattice types and geometries. A certain degree of control over colloidal self-assembly has been achieved through external electric [3] or intense optical fields [4] and by manipulating the interaction potential.[5] Here, we demonstrate a simple scheme that com...
A simple scheme to produce large‐area colored metal surfaces by completely confining surface plasmons inside gold spherical nanocavities has been discovered. The negative nanocavity curvature localizes the electromagnetic fields into small volumes, which can be arranged non‐periodically. The Figure shows an image of a graded thickness sample composed of 700 nm diameter nanocavities.
We demonstrate a fabrication route to individual micron-scale metallic spherical mirrors. The mirrors are prepared by electrochemical growth through the interstitial voids of a self-assembled latex sphere template. Excellent spherical mirrors of Au and Pt are obtained with unusual polarization properties in which multiple reflections with distinct anisotropies are found due to geometric polarization rotation. Such micromirrors can form the basis of low-cost microcavity structures and microlasers.
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