Fabrication of 3D photonic components on bulk crystalline silicon.

We have fabricated three dimensional photonic components such as waveguides and beam splitters from crystalline silicon using a process based on one or more ion irradiation steps with different energies and fluences, followed by electrochemical anodization and thermal annealing. We first demonstrate the fabrication of multilevel silicon waveguides and then extend this process to make multilevel beam splitters, in which three output waveguides are distributed over two depths. The dimensions of the waveguides can be defined within a range from 0.5 µm to several micrometers simply by varying the ion beam fluence.

Flow effects in the laser-induced thermal loading of optical traps and optofluidic devices.

Flow effects on the thermal loading in different optofluidic systems (optical trap and various microfluidic channels) have been systematically explored by using dye-based ratiometric luminescence thermometry. Thermal images obtained by fluorescence microscopy demonstrate that the flow rate plays a key role in determining both the magnitude of the laser-induced temperature increment and its spatial distribution. Numerical simulations were performed in the case of the optical trap. A good agreement between the experimental results and those predicted by mathematical modelling was observed. It has also been found that the dynamics of thermal loading is strongly influenced by the presence of fluid flow.

Single-cell electroporation using proton beam fabricated biochips.

We report the design and fabrication of a novel single cell electroporation biochip featuring high aspect ratio nickel micro-electrodes with smooth side walls between which individual cells are attached. The biochip is fabricated using Proton Beam Writing (PBW), a new direct write lithographic technique capable of fabricating high quality high-aspect-ratio nano and microstructures. By applying electrical impulses across the biochip electrodes, SYTOX® Green nucleic acid stain is incorporated into mouse neuroblastoma (N2a) cells and observed via green fluorescence when the stain binds with DNA inside the cell nucleus. Three parameters; electric field strength, pulse duration, and numbers of pulses have been investigated for the single cell electroporation process. The results indicate high transfection rates as well as cell viability of 82.1 and 86.7% respectively. This single cell electroporation system may represent a promising method for the introduction of a wide variety of fluorophores, nanoparticles, quantum dots, DNAs and proteins into cells.

Microstructuring of Nd:YAG crystals by proton-beam writing.

We report on the microstructuring of Nd:YAG crystals by direct proton-beam writing. Buried channel waveguides have been fabricated with full spatial control by the combined variation of crystal position and proton energy. The fluorescence images of the obtained structures have been used to evaluate the potential application of the fabricated structures for laser gain as well as to elucidate the mechanism at the basis of the refractive index increment induced at the end of the proton path. We have concluded that this increment is very likely a local enhancement in the electronic polarizability caused by nuclear collisions.

Imaging using pulses: a simple and fast (>100 kHz) solution.

Imaging is an important component of spectroscopy. A good imaging system is expected to work with a high-pixel resolution using signals of high count-rates with as little dead time as possible to deliver an image quickly and reliably. It is not uncommon for such a system to be highly specialized, expensive and to consist of many dedicated electronic components. In this work, we present a simple imaging algorithm that can be used with a pulse (TTL) data signal, such as that produced by some photomultipliers and electron detectors. This algorithm works with only a simple general purpose data acquisition computer card (NI PXI/PCI-6259) from National Instruments residing in a computer. The system has been tested with signal rates in excess of 100 kHz to produce images at a pixel resolution of 512 x 512. The system's ability to handle such high count-rates hinges on utilizing the buffered data collection feature on the said card, in a hitherto unreported configuration. This system now offers a simple and cost-effective manner of incorporating high count-rate imaging features, such as in a scanning electron microscope, into a purely spectroscopic system. Further, since the use of the NI DAQ cards are supported under other computer platforms, the current imaging formalism is readily transferrable to computer platforms such as Linux or Mac OS.

Effects of oxide formation around core circumference of silicon-on-oxidized-porous-silicon strip waveguides.

We have studied the effect of oxidation on the propagation loss and surface roughness of silicon-on-oxidized-porous-silicon strip waveguides fabricated using proton-beam irradiation and electrochemical etching. A thin thermal oxide is formed around the core of the waveguide, enabling the symmetric reduction of core size and roughness on all sides. Significant loss reduction from about 10 dB/cm to 1 dB/cm has been obtained in TE and TM polarizations after oxidation smoothening of both the bottom and the sidewalls by 20 nm. This corresponds well with simulations using the beam-propagation method that show significant contributions from both surfaces.

Fabrication of low-loss silicon-on-oxidized-porous-silicon strip waveguide using focused proton-beam irradiation.

We have successfully fabricated low-loss silicon-on-oxidized-porous-silicon (SOPS) strip waveguides with high-index contrast using focused proton-beam irradiation and electrochemical etching. Smooth surface quality with rms roughness of 3.1 nm is achieved for a fluence of 1x10(15)/cm(2) after postoxidation treatment. Optical characterization at a wavelength of 1550 nm shows a loss of 1.1+/-0.4 dB/cm and 1.2+/-0.4 dB/cm in TE and TM polarization respectively, which we believe is the lowest reported loss for SOPS waveguides. This opens up new opportunities for all-silicon-based optoelectronics applications.

Water-Bridge-Assisted Ionic Conduction in Probe-Induced Conical Polymer Pattern Formation.

Formation of conical polymer structures by atomic force microscopy (AFM) nanolithography and the electrical-conduction mechanism involved in the AFM- probe-induced patterning process are reported. The current is dominated by water-bridge-assisted ionic conduction. Polymer phase transition and mass redistribution occur without modification or degradation of the poly(methyl methacrylate) (PMMA) material.