We present experimental and theoretical results of label-free molecular sensing using the transverse magnetic mode of a 0.22 µm thick silicon slab waveguide with a surface grating implemented in a guided mode resonance configuration. Due to the strong overlap of the evanescent field of the waveguide mode with a molecular layer attached to the surface, these sensors exhibit high sensitivity, while their fabrication and packaging requirements are modest. Experimentally, we demonstrate a resonance wavelength shift of ~1 nm when a monolayer of the protein streptavidin is attached to the surface, in good agreement with calculations based on rigorous coupled wave analysis. In our current optical setup this shift corresponds to an estimated limit of detection of 0.2% of a monolayer of streptavidin. Lamontagne, and J. H. Schmid, "Spiral-path high-sensitivity silicon photonic wire molecular sensor with temperature-independent response," Opt. Lett. 33 ©2009 Optical Society of America

The preparation of cubic NbN films by reactive dc magnetron sputtering is described. These superconductive films are deposited at a sufficiently low temperature (<90 °C) that photoresist liftoff techniques and can be used in fabricating Josephson junctions. The superconducting transition temperature has been measured as a function of gas composition and pressure. It reaches a maximum of 14.2 K at 15% N2–85% Ar and 1.06 Pa total pressure. The resistivity ratio of these films is close to unity. Structural studies by transmission electron microscopy and electron diffraction show that films 100-nm thick or less are randomly oriented, and noncolumnar with a crystallite diameter of 5 nm and a lattice parameter of 4.46 Å, which is significantly higher than the bulk value for cubic NbN. The films are dense with void diameters no larger than 0.7 nm. Films 300-400 nm thick show a small degree of texturing in x-ray studies with a Read camera. Auger analysis shows a monotonic increase in the N/Nb ratio with increase in the N2/Ar ratio in the sputtering ambient up to 30% N2. From 30% to 50% N2 in the sputtering mixture the N/Nb ratio is constant. Small amounts of carbon impurity are found in all films.

A complete photonic wire molecular biosensor microarray chip architecture and supporting instrumentation is described. Chip layouts with 16 and 128 independent sensors have been fabricated and tested, where each sensor can provide an independent molecular binding curve. Each sensor is 50 μm in diameter, and consists of a millimeter long silicon photonic wire waveguide folded into a spiral ring resonator. An array of 128 sensors occupies a 2 × 2 mm2 area on a 6 × 9 mm2 chip. Microfluidic sample delivery channels are fabricated monolithically on the chip. The size and layout of the sensor array is fully compatible with commercial spotting tools designed to independently functionalize fluorescence based biochips. The sensor chips are interrogated using an instrument that delivers sample fluid to the chip and is capable of acquiring up to 128 optical sensor outputs simultaneously and in real time. Coupling light from the sensor chip is accomplished through arrays of sub-wavelength surface grating couplers, and the signals are collected by a fixed two-dimensional detector array. The chip and instrument are designed so that connection of the fluid delivery system and optical alignment are automated, and can be completed in a few seconds with no active user input. This microarray system is used to demonstrate a multiplexed assay for serotyping E. coli bacteria using serospecific polyclonal antibody probe molecules.

Articles you may be interested inRoom temperature deposition of superconducting NbN for superconductor-insulator-superconductor junctions Summary Abstract: Low temperature deposition and properties of superconducting NbN by reactive dc magnetron sputtering

The object of this study was to screen a group of metal oxides as possible candidates for use as semitransparent mask materials. For this study, all masks were prepared by d‐c reactive sputtering onto glass. The uv‐visible spectra for the entire group of oxide films were recorded. The spectral characteristics desired for a photomask are (i) transmission of less than 1% in the region below 404 nm (for masking), and (ii) transmission of greater than 30% at 589 nm (for the see‐through characteristic). Because of inferior spectral absorption properties, the following systems were eliminated from further consideration: lead oxide‐silicon oxide, lead oxide‐germanium oxide, copper oxide, copper oxide‐vanadium oxide, molybdenum oxide, chromium oxide, uranium oxide, mercury oxide, and zinc oxide. Those systems which satisfied the spectral requirements were: iron oxide, vanadium oxide, nickel oxide, iron oxide‐nickel oxide, and iron oxide‐vanadium oxide. These materials were then further evaluated to assure etchability in solvents compatible with photoresist processsing and resistance to abrasion. These latter two properties will be discussed in greater detail in a forthcoming article. Considering only sputtered films, the 10 m/o (mole per cent) iron oxide‐90 m/o vanadium oxide is the most promising material based on these additional requirements.