Microwire formation based on dielectrophoresis of electroless gold plated polystyrene microspheres

Microspheres coated with a perfectly conductive surface have many advantages in the applications of biosensors and micro-electromechanical systems. Polystyrene microspheres with the diameter of 10 μm were coated with a 50 nmthick gold layer using an electroless gold plating approach. Dielectrophoresis （DEP） for bare microspheres and shelled microspheres was theoretically analysed and the real part of the Clausius Mossotti factor was calculated for the two kinds of microspheres. The experiments on the dielectrophoretic characterisation of the uncoated polystyrene microspheres and gold coated polystyrene microspheres （GCPMs） were carried out. Experimental results showed that the gold coated polystyrene microspheres were only acted by a positive dielectrophoretic force when the frequency was below 40M Hz, while the uncoated polystyrene microspheres were governed by a negative dielectrophoretic force in this frequency range. The gold coated polystyrene microspheres were exploited to form the rnicrowire automatically according to their stable dielectrophoretic and electric characterisations.

Near-field holography enhanced with antireflection coatings--an improved method for fabricating diffraction gratings

Near-field holography（NFH）, with its virtues of precise critical dimensions and high throughput, has a great potential for the realization of soft x-ray diffraction gratings. We show that NFH with reflections reduced by the integration of antireflective coatings（ARCs） simplifies the NFH process relative to that of setups using refractive index liquids. Based on the proposed NFH with ARCs, gold-coated laminar gratings were fabricated using NFH and subsequent ion beam etching. The efficiency angular spectrum shows that the stray light of the gratings is reduced one level of magnitude by the suppression of interface reflections during NFH.

Manipulation of gold coated microspheres using electrorotation

The electrorotation of microspheres coated with conductive surface is a novel and important technology for label-free biosensors. Using the electroless plating approach, the polystyrene microspheres with 15 μm and 25 μm in diameters were coated with 50 nm gold layer in thickness. The electrorotation experiments on those gold coated polystyrene microspheres (GCPMs) were carried out. The results showed that they rotated in the opposite direction of the electric field in a low frequency range (100-100 kHz), and the maximum rotation speed was higher than that of uncoated microspheres. Based on the theory of traveling wave electroosmosis(TWEO) and induced charge electroosmosis (ICEO), the electrorotation of GCPMs was quantitively analyzed and confirmed by observing the fluid flow around GCPM. The equations describing the electroration speed of GCPMs were proposed, which are consistent with the experiment results.

Fabrication and measurement of optical characterization of one dimensional photonic crystal with defect

Numerical calculations based on the transfer matrix method are carried out, and the results of band gap with resonance peaks are obtained. The electron beam lithography technology （EBL） and induction coupling plasma （ICP） etching are used to make the photonic crystal （PC） structures, and from several scanning electron microscope images, the PC structures are observed with features closing to the design. In order to create the tiny PC structures in the right places of the waveguide by the EBL technology at different time, some alignment markers are deposited on the chip, which are made of gold that deposited on titanium for its good adhesion to the underlying Si. An optical testing bed is designed for measurement of the optical characterization of PC structures. Through the analysis of the measured data, a △λ value of 0.8 nm is obtained and for the centre frequency of 1547 nm, a very high quality factor value of 1933 can be obtained. The 3-rim difference represents only a 0.2% error from the theoretical centre.

Stacking-faults-free zinc blende GaAs/AlGaAs axial heterostructure nanowires during vapor-liquid-solid growth

Pure zinc blende structure GaAs/AlGaAs axial heterostructure nanowires （NWs） are grown by metal organic chemical vapor deposition on GaAs（111） B substrates using Au-catalyzed vapor-liquid-solid mechanism. Al adatom enhances the influence of diameters on NWs growth rate. NWs are grown mainly through the contributions from the direct impingement of the precursors onto the alloy droplets and not so much from adatom diffusion. The results indicate that the droplet acts as a catalyst rather than an adatom collector.