Oscillator-Based Volatile Detection System Using Doubly- Clamped Micromechanical Resonators

AbstractIn this paper, we demonstrate a functionalized and resonant piezo-actuated volatile sensor which is interfaced by electronics for frequency shift detection. Enhanced signal sensing is achieved via the effective feed-through capacitance cancellation scheme. The closed-loop oscillator, realized with off-the-shelf components, attains a frequency stability of 2.7Hz for the 1.8MHz resonant mode of the gas sensor. The sensor was exposed to pulses of water and ethanol vapor mixtures, yielding a temporary dip in resonance frequency as well as volatile-specific recovery times

Matching and surface barrier effects of the flux-line lattice in superconducting films and multilayers.

The flux-line lattice dissipation and the pinning force of Bi2Sr2CaCu2O8 and YBa2Cu3O7 films and a Nb/Cu multilayer are investigated with the vibrating reed technique. In magnetic fields oriented under a small angle with respect to the film surfaces the Bi-2:2:1:2 film shows a series of pronounced dissipation maxima at matching fields BN in the irreversible region of the magnetic phase diagram. The Y-1:2:3 film shows tiny damping maxima, whereas no structure in the dissipation of the Nb/Cu multilayer is detected below the upper critical field. The comparison of the matching fields to an anisotropic London model shows that the dissipation maxima are caused by rearrangements of the flux-line lattice configuration due to interactions with the sample surface. The different behavior of the high-temperature superconductors and the Nb/Cu multilayer is understood by explicitly taking the surface barrier into account. Deviations from the surface induced commensurability of the flux-line lattice due to the intrinsic pinning are discussed. Our results indicate that pancake vortices in the Bi-2:2:1:2 film should be coupled below the irreversibility line and below magnetic fields B??0.5 T perpendicular to the film surface

Quantum Interference in Superconducting Wire Networks and Josephson Junction Arrays: Analytical Approach based on Multiple-Loop Aharonov-Bohm Feynman Path-Integrals

We investigate analytically and numerically the mean-field superconducting-normal phase boundaries of two-dimensional superconducting wire networks and Josephson junction arrays immersed in a transverse magnetic field. The geometries we consider include square, honeycomb, triangular, and kagome' lattices. Our approach is based on an analytical study of multiple-loop Aharonov-Bohm effects: the quantum interference between different electron closed paths where each one of them encloses a net magnetic flux. Specifically, we compute exactly the sums of magnetic phase factors, i.e., the lattice path integrals, on all closed lattice paths of different lengths. A very large number, e.g., up to $10^{81}$ for the square lattice, exact lattice path integrals are obtained. Analytic results of these lattice path integrals then enable us to obtain the resistive transition temperature as a continuous function of the field. In particular, we can analyze measurable effects on the superconducting transition temperature, $T_c(B)$, as a function of the magnetic filed $B$, originating from electron trajectories over loops of various lengths. In addition to systematically deriving previously observed features, and understanding the physical origin of the dips in $T_c(B)$ as a result of multiple-loop quantum interference effects, we also find novel results. In particular, we explicitly derive the self-similarity in the phase diagram of square networks. Our approach allows us to analyze the complex structure present in the phase boundaries from the viewpoint of quantum interference effects due to the electron motion on the underlying lattices.Comment: 18 PRB-type pages, plus 8 large figure

Gas sensing with vertical functionalized InAs nanowire arrays

Nanowires show great promise for use in next generation (bio-)chemical sensing devices because of their high surface to volume ratio enabling efficient modulation of their current by charges or dipoles present at the surface. Here, we present a gas sensing device based on vertical InAs nanowire arrays grown without metal catalyst particles. The nanowires are contacted ohmically in their as-grown locations using an air bridge construction, leaving the nanowire surface free for gas adsorption. Noise measurements were performed to determine the measurement resolution for gas detection. The bare devices show sensitivity to NO\2 concentrations well below 75 ppb at room temperature. We furthermore find that these nanowires can be functionalized with metalloporphyrins resulting in sensitivity to both NO\2 and NO concentrations below 75 ppb

Sensitivity Enhancement of Metal Oxide Thin Film Transistor with Back Gate Biasing

AbstractIn this work, a room-temperature sensing device for detecting carbon monoxide using a ZnO thin film is presented. The ZnO layer (thickness close to the Debye length), which has a polycrystalline structure, is deposited with atomic- layer deposition (ALD) on an Al2O3/Si substrate. The operating principle of the sensor is based on measuring resistance change of the ZnO thin film upon exposure to CO in ambient environment. The ZnO-based sensor shows a large response to low CO concentrations ranging from 5 to 25ppm in air with 40% relative humidity at room temperature. Results show that the sensitivity of the sensor to CO at room temperature can be modulated with a back gate voltage

Leis study of ald WNXCy growth on dielectric layers

The required thickness for closure of WNxCy layers deposited with the Atomic Layer Deposition (ALD) technique on Plasma Enhanced CVD SiOx and. Aurora® low-k dielectric was investigated using Low Energy Ion Scattering Spectroscopy (LEIS). This analysis technique has proven to be very surface sensitive and uniquely suited to determine closure of deposited layers with atomic precision. It was shown that the WN xCy layer closes around 40 ALD deposition cycles, setting the upper thickness limit for closure at 3.2 nm. This thickness is in line with the requirements for copper diffusion barriers for the metallization of Si-devices for 45 nm node and beyond. copyright The Electrochemical Society