Enzyme-catalyzed polymerization of 8-hydroxyquinoline-5-sulfonate by in situ nuclear magnetic resonance spectroscopy

In this report, we describe the use of in situ NMR spectroscopy to elucidate the mechanism of horseradish peroxidase-catalyzed oxidative free-radical coupling of phenols. We demonstrate the potential of the technique for the polymerization of 8-hydroxyquinoline-5-sulfonate (HQS). Based on the structural changes, we establish the involvement of ortho- and para-position protons (to the hydroxyl group) in the oxidative free-radical coupling polymerization with their relative preferences. For example, in HQS, we establish that the positions 2, 4, and 7 are involved in the chemical bonding with the order of preference being 7 ≥ 2 > 4. Analyses of ¹³C-NMR data suggest the formation of C—C- and C—O—C-type coupling bonds during enzymatic polymerization. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 1257–1264, 1998     

Particle-assisted Ga(x)In(1-x)P nanowire growth for designed bandgap structures

Non-tapered vertically straight Ga(x)In(1-x)P nanowires were grown in a compositional range from Ga(0.2)In(0.8)P to pure GaP in particle-assisted mode by controlling the trimethylindium, trimethylgallium and hydrogen chloride flows in metal-organic vapor phase epitaxy. X-ray energy dispersive spectroscopy in transmission electron microscopy revealed homogeneous radial material composition in single nanowires, whereas variations in the material composition were found along the nanowires. High-resolution x-ray diffraction indicates a variation of the material composition on the order of about 19% measuring an entire sample area, i.e., including edge effects during growth. The non-capped nanowires emit room temperature photoluminescence strongly in the energy range of 1.43-2.16 eV, correlated with the bandgap expected from the material composition.     

Realizing lateral wrap-gated nanowire FETs: controlling gate length with chemistry rather than lithography

An important consideration in miniaturizing transistors is maximizing the coupling between the gate and the semiconductor channel. A nanowire with a coaxial metal gate provides optimal gate-channel coupling but has only been realized for vertically oriented nanowire transistors. We report a method for producing laterally oriented wrap-gated nanowire field-effect transistors that provides exquisite control over the gate length via a single wet etch step, eliminating the need for additional lithography beyond that required to define the source/drain contacts and gate lead. It allows the contacts and nanowire segments extending beyond the wrap-gate to be controlled independently by biasing the doped substrate, significantly improving the subthreshold electrical characteristics. Our devices provide stronger, more symmetric gating of the nanowire, operate at temperatures between 300 and 4 K, and offer new opportunities in applications ranging from studies of one-dimensional quantum transport through to chemical and biological sensing.     

Expression of basement membrane type IV collagen chains during postnatal development in the murine cochlea

An immunofluorescence study was performed to examine the temporal and spatial patterns of expression for the different type IV collagen chains during postnatal cochlear development. At birth, the classical chains (4A1 and 4A2) were widely expressed, while the novel chains (4A3, 4A4, and 4A5) were completely absent. Activation of the novel chains was observed at 4 days of age, with intense, widely distributed immunostaining suggesting that most of the cells in the cochlea express the novel chains at this developmental stage. From day 8 through day 14, developmental inactivation of the novel chains results in a reduction of generalized immunoreactivity with a concomitant elevation of specific staining in the membranous structures bounding the interdental cells of the spiral limbus, the inner sulcus, the basilar membrane, and in a fibrous bed of staining radiating from the spiral prominence into the region of the spiral ligament which corresponds to the location of the root cell processes. This pattern of intense immunostaining for the novel chains persists through adulthood. The classical chains are expressed in these same anatomical regions only transiently (from day 6 to day 10), after which a gradual developmental inactivation leads to the adult expression pattern where classical collagen chains are found primarily in the perineurium, in the membranes surrounding the spiral ganglion cell bodies, and in the vascular basement membranes of the spiral ligament and the stria vascularis. The complex developmental pattern of expression for the type IV collagen chains in the murine cochlea is similar to that observed in the murine kidney, which is the other major site for basement membrane pathology in Alport syndrome.     

Novel nanoelectronic triodes and logic devices with TBJs

In this letter, we demonstrate the realization of novel diodes, triodes, and logic gates with three-terminal ballistic junctions (TBJs) made from a semiconductor heterostructure. The approach exploits the ballistic nature of electron transport, which has emerged in the nanostructures. Importantly, we show that TBJs function as logic AND gates and can be used to construct other compound logic gates, such as NAND gates with voltage gain, when combined with a point contact (an inverter). The demonstrated devices show favorable characteristics such as low turn-on voltage in rectification and room-temperature operation.     

Vertical high-mobility wrap-gated InAs nanowire transistor

In this letter, the authors demonstrate a vertical wrap-gated field-effect transistor based on InAs nanowires [Proc. DRC, 2005, p. 157]. The nanowires have a diameter of 80 nm and are grown using selective epitaxy; a matrix of typically 10 /spl times/ 10 vertically standing wires is used as channel in the transistor. The authors measure current saturation at V/sub ds/=0.15 V (V/sub g/=0 V), and a high mobility, compared to the previous nanowire transistors, is deduced.