A detailed understanding of the nitride refractive indices is essential for the modeling and design of III–N laser structures. In this article, we report on the assessment of the refractive index data available for the nitride alloys and present formulas for evaluating the refractive indices for variations in both composition and photon energy. For AlxGa1−xN, an expression is given which fits well to experimental data below x<0.38, sufficient for the molefractions found in the cladding layers of III–N lasers. Due to the almost complete lack of experimental refractive index data for InyGa1−yN, we propose an expression to give a first-order approximation for the refractive index.

A close-packed monolayer of zinc 5,10,15,20-tetrakis(3-carboxyphenyl)porphyrin has been prepared and deposited on the thin native oxide covering the surface of an SOI-MOSFET (silicon-on-insulator metal-oxide-semiconductor field effect transistor) using Langmuir-Blodgett techniques. When the device is exposed to amine vapors in a nitrogen atmosphere, the amine coordinates to the zinc atom. The resulting change in electron distribution within the porphyrin leads to a large change in the drain current of the transistor, biased via a back gate. This change is sensitive to both the amount of amine present and the base strength of the amine. Only very small changes in drain current were observed with a monolayer of free base porphyrin or palmitic acid. After exposure to high pyridine concentrations, the device response saturates, but partially recovers after overnight exposure to flowing nitrogen gas. Interestingly, the device response is instantaneously reset by exposure to visible light, suggesting that photode-ligation occurs. An electrical model for the hybrid device that describes its response to ligand binding in terms of a change in the work function of the porphyrin monolayer has been developed. A transistor response to a few hundred attomoles of bound pyridine can be readily detected. This extreme sensitivity, coupled with the ability to reset the device using light, suggests that such systems might be useful as sensors.

We present a method for microfabricating apertures in a silicon substrate using well-known cleanroom technologies resulting in highly reproducible giga-seal resistance bilayer formations. Using a plasma etcher, 150μm apertures have been etched through a silicon wafer. Teflon™ has been chemically vapor deposited so that the surface resembles bulk Teflon and is hydrophobic. After fabrication, reproducible high resistance bilayers were formed and characteristic measurements of a self-inserted single OmpF porin ion channel protein were made.

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We report on the use of Kelvin probe force microscopy in measuring the shift of the contact potential difference of micron-scale areas. The experimental results provide important information required for understanding and modeling the electrical characteristics of chemically sensitive field-effect transistors (ChemFETs). The temporal evolution in the shift of the contact potential difference of chemically sensitive monolayers of free-base porphyrin and zinc-porphyrin on exposure to pyridine gas was studied and their different behavior observed. The Kelvin probe force microscopy data on nanometer-scale areas were in agreement with those obtained with a conventional Kelvin probe on centimeter-scale areas. The accuracy of the measured shift in contact potential difference upon exposure to trace amounts of gas indicates the utility of Kelvin probe force microscopy as a means to characterize the operation of exposed-gate ChemFETs.