The emission of CdSe quantum dots linked to the 5'-end of a DNA sequence is efficiently quenched by hybridisation with a complementary DNA strand with a gold nanoparticle attached at the 3'-end; contact of the quantum dot and gold nanoparticle occurs.

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A solid-state picosecond laser is used to ablate semiconductor thin films in spatially localized areas, providing an alternative to device isolation strategies based on chemical or ion etching techniques. Field-effect transistors (FET) of emerging organic and inorganic materials often utilize continuous semiconductor film and an array of top-contact electrodes. Electrically isolating individual FET components from other circuit elements is essential in order to reduce parasitic capacitances and unwanted current pathways, in order both to improve device performance and to enable the observation of new or enhanced physical phenomena. We pattern FET arrays with ultrafast pulse duration (1.5 ps) and low fluence (0.09 J cm-2) optical pulses using the fundamental wavelength (1030 nm) of an Yb-YAG laser. We investigate two representative semiconductor materials. First, zinc oxide (ZnO) is deposited onto Si/SiO 2 substrates by sol-gel methods and used to create n-channel FETs with aluminum top electrodes. Isolation of individual FETs enables the clear observation of photomodulation of the FET device parameters via photoinduced electron donation from an adsorbed chromophore. The second system comprises thin-film bilayers of tellurium and organic semiconductor molecules sequentially vapor-deposited onto Si/SiO 2 substrates, with gold electrodes deposited last. Charge carrier mobility is maintained for devices isolated by picosecond lasers, but leakage currents through the FET dielectric are drastically reduced.

Optical couplings in large core optical waveguides have many similarities with those in conventional optical fibers but pose some unconventional challenges as well. The larger geometry, looser manufacturing tolerances and reduced dimensional stability compound the problems associated with making low-loss couplings in large core waveguides. The individual factors contributing to coupling losses are discussed to develop an understanding of the extant loss mechanisms. Individual methods and materials employed to mitigate the impact of each of the dominant loss mechanisms are discussed in detail. A combination of endface geometry control, axial alignment constraint and refractive index matching are employed to produce highly efficient optical couplings in large core waveguides. The combination of these elements has significantly reduced the insertion losses due to connector couplings. Prior to implementing the current methods losses of 15% and greater were common but these have been reduced to 2%–5% with the current methods.

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Planar photonic crystals comprised of metals and dielectrics show huge enhancements in the surface-enhanced Raman scattering of attached molecules. Plasmon engineering is key to these properties including reproducibility (std.dev.<9%), beamed output, resonances and orientation. Surface Enhanced Raman Scattering (SERS) is a widely utilised technique to enhance the weak Raman spectrum of molecules, enabling detection and identification of ultralow concentrations of particular species. Discovered exactly 30 years ago,[1] it employs a roughened metal surface in the vicinity of a molecule to act as an antenna that couples laser light in and SERS photons out. However the major block to its application has been the extreme variability of the SERS signals from the substrates used to elicit this effect. Despite many experiments, there is still considerable debate over how the SERS enhancement arises on a metal, and no first-principle calculations can model the observed effect. We show both experimentally and theoretically how localised surface plasmons engineered on 2D photonic crystals (PCs) fabricated from metals and dielectrics can produce SERS enhancements >10 4 . Our PC SERS substrates [2] exhibit extremely good reproducibility and will enable a new generation of applications based on quantification of the adsorbed molecular concentration, and low-cost widely-applicable SERS devices.Our samples are based on 2D photonic crystal waveguide technologies, in which we have previously demonstrated photonic bandgaps [3], slow light [4], superprism operation [5], and tri-refringence [6]. High refractive index dielectric waveguides are sandwiched between silica buffer and cladding (all grown on silicon wafers), and e-beam lithography is used to pattern a variety of photonic crystal designs. Data is presented here on structures with square lattices of holes, of pitch varying from 500nm-6000nm, and hole diameters from 300-4000nm. The aspect ratio of the holes is varied from depth:width of 1:1 to >10:1. The dielectric samples are then gold-or silver-coated by rfsputtering in an optimised process to produce the SERS substrates (Fig.1).

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