Toward the nanoscopic "electronic nose": hydrogen vs carbon monoxide discrimination with an array of individual metal oxide nano- and mesowire sensors

The array of chemiresistors made of individual pristine SnO2, surface doped (Ni)-SnO2 nanowires, and TiO2 and In2O3 mesoscopic whiskers was fabricated on a Si/SiO2 wafer. Their conductance was measured under pulses of H2 and CO reducing gases in oxygen as background gas. The nanostructures were shown to be n-type semiconductors possessing high sensitivity to the target gases. Following the "electronic nose" concept, correlation analysis of response of three-chemiresistor array is shown to be sufficient to discriminate between H2 and CO signals.     

Circular arrays of magnetic sensors for current measurement

A single solid-state magnetic sensor can measure a current flowing in a conductor in a noncontact way. In order to improve the accuracy of the measuring system and to reduce the crosstalk effects of other magnetic fields, circular arrays of magnetic sensors can be fabricated, still preserving low costs. In those kind of arrays, the sensing elements are assembled on a circle around the conductor. The sum of the sensor output signals is an approximation of Ampere's circulation. A quite satisfactory crosstalk effects reduction can be thus achieved. More sophisticated algorithms that combine sensor output signals are necessary in order to further reduce crosstalk effects. This paper presents an algorithm that is able to calculate the intensity of a dc current flowing in a rectangular bus-bar, in the presence of crosstalk fields     

Integrated semiconductor hydrogen sensors

The results are presented of an experimental investigation of the temporal drift and the hydrogen response of five types of integrated semiconductor sensors with palladium films, and a refined model is proposed for the hydrogen sensitivity of sensors with a palladium-insulator-semiconductor structure.Translated from Izmeritel'naya Tekhnika, No. 1, pp. 22–25, January, 1995.     

Amperometric sensors for simultaneous superoxide and hydrogen peroxide detection

A two-channel sensor capable of almost instantaneous simultaneous detection of superoxide radical and hydrogen peroxide in the concentration range 10(-)(7)-10(-)(4) M is very important for understanding of a number of rapid kinetics processes. A glassy carbon working microelectrode covered by an electrodeposited polypyrrole/horseradish peroxidase (PPy/HRP) membrane was employed as a H(2)O(2) sensor. Another glassy carbon microelectrode covered by a composite membrane of an inside layer of PPy/HRP and an outside layer of superoxide dismutase was employed as a working electrode for superoxide detection. These two working electrodes with Pt counter and tungsten oxide (WO(3)) reference electrodes were contained in one 6 mm diameter Teflon cylinder. Simultaneous measurements were performed at a potential of -60 mV (vs WO(3) reference, pH 5.1). Additional sensor characterization was performed for pH 5.1-9.0. Superoxide sensor behavior as a function of membrane deposition conditions and coating time is reported. Sensors' mutual influence, selectivity, response times, linearity, stability, and sensitivity for hydrogen peroxide and superoxide are presented and discussed. A mathematical model of sensors' responses is proposed, with model calculation corresponding to experiment within 10%.     

Hydrogen bond acidic polymers for surface acoustic wave vapor sensors and arrays

Four hydrogen bond acidic polymers are examined as sorbent layers on acoustic wave devices for the detection of basic vapors. A polysiloxane polymer with pendant hexafluoro-2-propanol groups and polymers with hexafluorobisphenol groups linked by oligosiloxane spacers yield sensors that respond more rapidly and with greater sensitivity than fluoropolyol, a material used in previous SAW sensor studies. Sensors coated with the new materials all reach 90% of full response within 6 s of the first indication of a response. Unsupervised learning techniques applied to pattern-normalized sensor array data were used to examine the spread of vapor data in feature space when the array does or does not contain hydrogen bond acidic polymers. The radial distance in degrees between pattern-normalized data points was utilized to obtain quantifiable distances that could be compared as the number and chemical diversity of the polymers in the array were varied. The hydrogen bond acidic polymers significantly increase the distances between basic vapors and nonpolar vapors when included in the array.     

Molecular sensors and sensor arrays based on polyaniline microtubules

This paper describes the fabrication of microtubular biosensors and sensor arrays based on polyaniline with superior transducing ability. These sensors have been tested for the estimation of glucose, urea, and triglycerides. As compared to that of a macro sensor, the response of the microtubular sensor for glucose is higher by a factor of more than 10(3). Isoporous polycarbonate membranes have been used to fabricate inexpensive devices by simple thermal evaporation of gold using appropriate machined masks. Polyaniline deposition and enzyme immobilization have been done electrochemically. Electrochemical potential control has been used to direct enzyme immobilization to the chosen membrane device and avoid cross talk with adjacent devices. This has enabled the immobilization of a set of three different enzymes on three closely spaced devices, resulting in a microtubule array that can analyze a sample containing a mixture of glucose, urea, and triglycerides in a single measurement. This, in essence, is an "electronic tongue".     

Amorphous TiO(2) nanotube arrays for low-temperature oxygen sensors

Titania nanotube arrays (TNTA) were synthesized on a titanium substrate using anodic oxidation in an electrolyte containing ammonium fluoride and evaluated for low-temperature oxygen sensing. Their sensing properties were tested at different temperatures (50, 100, 150, 200, 250 and 300?°C) when exposed to various oxygen concentrations. The as-prepared TNTA are amorphous and exhibit much higher carrier concentration than that of annealed TNTA. Such amorphous TNTA show much higher sensitivity than that of annealed TNTA, SrTiO(3) and Ga(2)O(3) sensors. This sample demonstrates the lowest detectable oxygen concentration of 200 ppm, excellent recovery and good linear correlation at 100?°C. These results indicate that TNTA are indeed very attractive oxygen-sensing materials.     

Tin oxide nanocluster hydrogen and ammonia sensors

We have prepared sensitive hydrogen and ammonia sensors from thin films of tin nanoclusters with diameters between 3 and 10?nm. By baking the samples at 200?°C in ambient air the clusters were oxidized, resulting in very stable films of tin oxide clusters with similar diameters to the original Sn clusters. By monitoring the electrical resistance, it is shown that the cluster films are highly responsive to hydrogen and ammonia at relatively low temperatures, thereby making them attractive for commercial applications in which low power consumption is required. Doping of the films by depositing Pd on top of the clusters resulted in much improved sensor response and response times. It is shown that optimal sensor properties are achieved for very thin cluster films (a few monolayers of clusters).     

Characterization and modeling of transition edge sensors for high resolution X-ray calorimeter arrays

Characterizing and understanding, in detail, the behavior of a Transition Edge Sensor (TES) is required for achieving an energy resolution of 2 eV at 6 keV desired for future X-ray observatory missions. This paper will report on a suite of measurements (e.g. impedance and I–V among others) and simulations that were developed to extract a comprehensive set of TES parameters such as heat capacity, thermal conductivity, and R(T,I), (T,I), and β_i(T,I) surfaces. These parameters allow for the study of the TES calorimeter behavior at and beyond the small signal regime.     

A self-reconfigurable hardware architecture for mesh arrays using single/double vertical track switches

This paper deals with the issue of reconfiguring mesh-connected processor arrays (mesh arrays) in the presence of faulty processors. For massively parallel systems, it has become necessary to develop built-in self-reconfigurable systems that can automatically reconfigure partially faulty systems. Many reconfiguration methods have been proposed to date; however, most of them are not suitable for self-reconfiguration. In this paper, we propose a self-reconfiguration method based on simple column bypass and south directional rerouting schemes. This proposal offers the combined advantages of high probability of successful reconfiguration, low hardware overhead, and simplicity of implementation. A switching mechanism, which can determine the desired switch functions automatically using the states of neighboring processors, makes the implementation of our method easier. Simulated results show that the proposed method achieves a higher system yield than that of previous methods with half the number of redundant switches and interconnections. The prototype system of self-reconfigurable mesh arrays is implemented using a field-programmable gate array (FPGA) and the hardware overhead is discussed.     

Large-scale remotely interrogated arrays of fiber-optic interferometric sensors for underwater acoustic applications

The fiber-optic interferometric acoustic sensor array has established itself as a potential alternative to the conventional sonar array based on electroceramic transducers. In this paper, we discuss all the aspects of a large-scale fiber-optic interferometric sensor array. We review the basic operating principles of the fiber-optic interferometric sensor, signal processing, and multiplexing techniques, we present results from a noise model for a full size system, and we determine the benefit of incorporating a remotely-pumped optical amplifier in the array. As a practical example we describe the design and construction of a prototype array with 96 hydrophones incorporating a remotely pumped erbium-doped fiber amplifier, called the fiber-optic bottom mounted array, which is based on a dense wavelength division and time division multiplexed architecture. These arrays have applications in military sonar and seismic surveying.     

Highly ordered nanowire arrays on plastic substrates for ultrasensitive flexible chemical sensors

The development of a robust method for integrating high-performance semiconductors on flexible plastics could enable exciting avenues in fundamental research and novel applications. One area of vital relevance is chemical and biological sensing, which if implemented on biocompatible substrates, could yield breakthroughs in implantable or wearable monitoring systems. Semiconducting nanowires (and nanotubes) are particularly sensitive chemical sensors because of their high surface-to-volume ratios. Here, we present a scalable and parallel process for transferring hundreds of pre-aligned silicon nanowires onto plastic to yield highly ordered films for low-power sensor chips. The nanowires are excellent field-effect transistors, and, as sensors, exhibit parts-per-billion sensitivity to NO2, a hazardous pollutant. We also use SiO2 surface chemistries to construct a 'nano-electronic nose' library, which can distinguish acetone and hexane vapours via distributed responses. The excellent sensing performance coupled with bendable plastic could open up opportunities in portable, wearable or even implantable sensors.     

Oxide nanoparticle arrays for sensors of CO and NO2 gases

Metal oxide sensors with active films from Fe₂O₃ and CoFe₂O₄ hexagonally assembled nanoparticle (NP) arrays were studied. NPs were synthesized by high-temperature solution phase reaction. Sensing NP layers were deposited by Langmuir-Blodgett (LB) technique. LB layers were characterized by XRD, SEM and magnetic measurements. NPs are monodomain and superparamagnetic at RT. Sensor active films are formed from 1 or 7 LB monolayers deposited on the alumina substrates equipped with heating meander and interdigitated contacts. LB layers were heat-treated or UV irradiated to remove the insulating surfactant. Sensing properties were studied in a test chamber containing reducing (CO) or oxidizing (NO₂) gas in concentrations between 5 and 100 ppm in the mixture with dry air. Response current signal (I_gas/I_air) vs. temperature and response vs. gas concentration calibration curves were measured. Best response values were obtained with CoFe₂O₄ devices between 300 and 400 °C, being 3 and 10 for 100 ppm of CO and 5 ppm of NO₂, respectively. The response and recovery times of sensors are between 3 and 30 min. The Fe₂O₃ and CoFe₂O₄ sensors with response of 8 or 10 to 5 ppm of NO₂ might be of practical applications in the detection of explosives.     

Read/write schemes analysis for novel complementary resistive switches in passive crossbar memory arrays

Recently a prototype of complementary resistive switches has been proposed to solve the sneak-path problem in passive crossbar memory arrays. To further evaluate the potential of this novel cell structure for practical applications, we present a modeling analysis to capture its switching dynamics and analyze its unique read/write schemes. The model is corroborated by experimental data. We found a trade-off between the read voltage window and write voltage window. The constraint from avoiding disturbance on unselected cells is critical for proper functionality, which in turn limits the writing speed.     

Gas gap thermal switches using neon or hydrogen and sorption pump

The very low pressure obtained thanks to adsorption phenomenon at low temperature can be used to build cryogenic heat switches, which offer the possibility to make or break thermal contact between two parts of a cryogenic system. The ON (conducting) and OFF (insulating) states of the switch are obtained by varying the gas pressure between two copper blocks separated by a gap of 100 μm. This pressure is controlled by acting upon the temperature of a small sorption pump (activated charcoal) connected to the gap space. For a “high” sorption pump temperature, the gas previously adsorbed in the sorption pump is released to the gap between the two blocks, allowing a good thermal conduction through the gas (ON state). On the opposite, cooling the sorption pump allows a very good vacuum between the copper blocks, which efficiently break the thermal contact (OFF state). Experimental thermal characteristics (Conductance in the ON and OFF state, ON-OFF switching temperature) of such a “Gas Gap Heat Switch” are described using hydrogen or neon as exchange gas and are compared with theoretical calculations.     

Platinum nanoparticle decorated silicon nanowire arrays for photoelectrochemical hydrogen production

Wafer-scale high density aligned p-type silicon nanowire (SiNW) arrays decorated with discrete platinum nanoparticles (PtNPs) have been fabricated by metal assisted electroless etching followed by an electroless platinum deposition process, and systematic investigations of photoelectrochemical behavior of Pt/SiNW were also reported in this study. Coating of PtNPs on SiNW sidewalls yielded a more positive onset potential (Vos), which enhances the photoelectrochemical hydrogen generation performance of the photoelectrodes, though excessive PtNPs deposition leads to a decreased photocurrent. Additionally, we have demonstrated that the photoelectrode consisting of longer SiNWs yielded a higher limiting current. However, when the length of SiNWs was increased further to >4 μm, the limiting current dramatically reduced, which is presumably because an increased interface recombination and scattering resulting from the increased surface area of SiNWs begin to play a dominant role. The results demonstrate Pt/SiNW to be a promising hybrid system for photoelectrochemical water splitting, and device performance may be further improved via optimal conditions of PtNPs deposition time and SiNWs length.     

Stretchable,self-healable and anti-freezing conductive hydrogel based on double network for strain sensors and arrays

Journal of Materials Science - The application of hydrogels for flexible sensor is gravely hampered due to their poor freezing resistance and fatigue fracture associated with durable deformation,...     

Low-cost satellite attitude control sensors based on integratedinfrared detector arrays

This paper describes attitude control systems (ACS) for satellites and a new, static system based on an integrated infrared (IR) detector array. After a short introduction on the use and control of satellites in general, we explain the advantage of static systems, made possible by the use of integrated IR detector arrays. In particular, the static system is lighter and smaller than the previous systems, and requires less power. The electronics is updated to state-of-the art, increasing the autonomy of the system and thereby reducing its dependence upon the satellite microcontroller. The detectors are based on a bipolar silicon process for the mechanical structure (using electrochemically controlled etching-KOH etching), with an SiN membrane for thermal isolation of the pixels, which have a polymer black coating for transduction of radiation to heat and n-type versus p-type polysilicon thermopiles for heat detection. The pixel pitch is 600 μm, the black area is approximately 495 × 440 μm², and the pixel sensitivity is approximately 55 V/W, at a thermopile resistance of 23 kΩ. Two types of detectors have been designed: a single-array type with 32 pixels in two staggered arrays, and a chip with four 32-pixel arrays integrated in a cross. This has made it possible to make a family of earth sensors for the different missions in space     

Scalable arrays of chemical vapor sensors based on DNA-decorated graphene

Arrays of chemical vapor sensors based on graphene field effect transistors functionalized with single-stranded DNA have been demonstrated. Standard photolithographic processing was adapted for use on large-area graphene by including a metal protection layer, which protected the graphene from contamination and enabled fabrication of high quality field-effect transistors （GFETs）. Processed graphene devices had hole mobilities of 1,640 ± 250 cm2.V-1.s-1 and Dirac voltages of 15 ± 10 V under ambient conditions. Atomic force microscopy was used to verify that the graphene surface remained uncontaminated and therefore suitable for controlled chemical functionalization. Single-stranded DNA was chosen as the functionalization layer due to its affinity to a wide range of target molecules and π-π stacking interaction with graphene, which led to minimal degradation of device characteristics. The resulting sensor arrays showed analyte- and DNA sequence-dependent responses down to parts-per-billion concentrations. DNA/GFET sensors were able to differentiate among chemically similar analytes, including a series of carboxylic acids, and structural isomers of carboxylic acids and pinene. Evidence for the important role of electrostatic chemical gating was provided by the observation of understandable differences in the sensor response to two compounds that differed only by the replacement of a （deprotonating） hydroxyl group by a neutral methyl group. Finally, target analytes were detected without loss of sensitivity in a large background of a chemically similar, volatile compound. These results motivate further development of the DNA/graphene sensor family for use in an electronic olfaction system.     

Tin dioxide-based gas sensors for detection of hydrogen fluoride in air

This research concentrates on the sensitivity of semiconductor tin dioxide-based gas sensors to hydrogen fluoride in air. After evaluating the characteristic detection temperature, the sensor's signals were studied for different HF concentrations. Despite the corrosive effects of hydrogen fluoride, a reproducibility of the signal was found. Likewise, we did not observe any long-term degradation to the sensor. For the experiment, the sensor was exposed to a gas mixture formed by HF, O₂, N₂ with a constant flow rate of 150 ml min⁻¹. The semiconductor gas sensor reached maximum sensitivity near 380 °C, and a minimum concentration was detected approximately 50 ppb. Moreover, the detection phenomenon appears to be reversible when considering the electrical response under a constant air flow.