Improving the hydrogen gas sensing performance of Pt/MoO3 nanoplatelets using a nano thick layer of La2O3

In this paper, we present how a thin RF sputtered layer of lanthanum oxide (La2O3) can alter electrical and improve hydrogen gas sensing characteristics of Pt/molybdenum oxide (MoO3) nanostructures Schottky diodes. We derived the barrier height, ideality factor and dielectric constant from the measured I–V characteristics at operating temperatures in the range of 25–300 ◦C. The dynamic response, response and recovery times were obtained upon exposure to hydrogen gas at different concentrations. Analysis of the results indicated a substantial improvement to the voltage shift sensitivity of the sensors incorporating the La2O3 layer. We associate this enhancement to the formation of numerous trap states due to the presence of the La2O3 thin film on the MoO3 nanoplatelets. These trap states increase the intensity of the dipolar charges at the metal–semiconductor interface, which induce greater bending of the energy bands. However, results also indicate that the presence of La2O3 trap states also increases response and recover times as electrons trapping and de-trapping processes occur before they can pass through this thin dielectric layer.

Characterization of tight gas reservoir pore structure using USANS/SANS and gas adsorption analysis

Small-angle and ultra-small-angle neutron scattering (SANS and USANS) measurements were performed on samples from the Triassic Montney tight gas reservoir in Western Canada in order to determine the applicability of these techniques for characterizing the full pore size spectrum and to gain insight into the nature of the pore structure and its control on permeability. The subject tight gas reservoir consists of a finely laminated siltstone sequence; extensive cementation and moderate clay content are the primary causes of low permeability. SANS/USANS experiments run at ambient pressure and temperature conditions on lithologically-diverse sub-samples of three core plugs demonstrated that a broad pore size distribution could be interpreted from the data. Two interpretation methods were used to evaluate total porosity, pore size distribution and surface area and the results were compared to independent estimates derived from helium porosimetry (connected porosity) and low-pressure N2 and CO2 adsorption (accessible surface area and pore size distribution). The pore structure of the three samples as interpreted from SANS/USANS is fairly uniform, with small differences in the small-pore range (<2000 Å), possibly related to differences in degree of cementation, and mineralogy, in particular clay content. Total porosity interpreted from USANS/SANS is similar to (but systematically higher than) helium porosities measured on the whole core plug. Both methods were used to estimate the percentage of open porosity expressed here as a ratio of connected porosity, as established from helium adsorption, to the total porosity, as estimated from SANS/USANS techniques. Open porosity appears to control permeability (determined using pressure and pulse-decay techniques), with the highest permeability sample also having the highest percentage of open porosity. Surface area, as calculated from low-pressure N2 and CO2 adsorption, is significantly less than surface area estimates from SANS/USANS, which is due in part to limited accessibility of the gases to all pores. The similarity between N2 and CO2-accessible surface area suggests an absence of microporosity in these samples, which is in agreement with SANS analysis. A core gamma ray profile run on the same core from which the core plug samples were taken correlates to profile permeability measurements run on the slabbed core. This correlation is related to clay content, which possibly controls the percentage of open porosity. Continued study of these effects will prove useful in log-core calibration efforts for tight gas.

Multidisciplinary design and flight testing of a remote gas/particle airborne sensor system

The main objective of this paper is to describe the development of a remote sensing airborne air sampling system for Unmanned Aerial Systems (UAS) and provide the capability for the detection of particle and gas concentrations in real time over remote locations. The design of the air sampling methodology started by defining system architecture, and then by selecting and integrating each subsystem. A multifunctional air sampling instrument, with capability for simultaneous measurement of particle and gas concentrations was modified and integrated with ARCAA’s Flamingo UAS platform and communications protocols. As result of the integration process, a system capable of both real time geo-location monitoring and indexed-link sampling was obtained. Wind tunnel tests were conducted in order to evaluate the performance of the air sampling instrument in controlled nonstationary conditions at the typical operational velocities of the UAS platform. Once the remote fully operative air sampling system was obtained, the problem of mission design was analyzed through the simulation of different scenarios. Furthermore, flight tests of the complete air sampling system were then conducted to check the dynamic characteristics of the UAS with the air sampling system and to prove its capability to perform an air sampling mission following a specific flight path.

Pt/Nanostructured RuO2/SiC Schottky Diode based hydrogen gas sensors

In this paper, we report the development of novel Pt/nanostructured RuO2/SiC Schottky diode based sensors for hydrogen gas applications. The nanostructured ruthenium oxide thin films were deposited on SiC substrates using radio frequency sputtering technique. Scanning electron microscopy revealed the sputtered RuO2 layer consists of nano-cubular structures with dimensions ranging between 10 and 50 nm. X-ray diffraction confirmed the presence of tetragonal ruthenium (IV) oxide, with preferred orientation along the (101) lattice plane. The current-voltage characteristics of the sensors were investigated towards hydrogen gas in synthetic air at different temperatures from 25 °C to 240 °C. The dynamic responses of the sensors were studied at an optimum temperature of 240 °C and a voltage shift of 304 mV was recorded toward 1% hydrogen gas.

Hydrogen Gas Sensor Based on Highly Ordered Polyaniline/Multiwall Carbon Nanotubes Composite

In this work, the structural and gas sensing properties of an electropolymerized, polyaniline (PANI)/multiwall carbon nanotube (MWNT) composite based surface acoustic wave (SAW) sensor are reported. Thin films made of PANI nanofibers were deposited onto 36 lithium tantalate (LiTaO3) SAW transducers using electropolymerization and were subsequently dedoped. Scanning electron microscopy (SEM) revealed the compact growth of the composites which is much denser than that of PANI nanofibers. The PANI/MWNT composite based SAW sensor was then exposed to different concentrations of hydrogen (H2) gas at room temperature with a demonstrated electrical response.

Hydrogen gas sensing performance of Pt/SnO2 nanowires/SiC MOS devices

This paper presents material and gas sensing properties of Pt/SnO2 nanowires/SiC metal oxide semiconductor devices towards hydrogen. The SnO2 nanowires were deposited onto the SiC substrates by vapour-liquid-solid growth mechanism. The material properties of the sensors were investigated using scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectroscopy. The current-voltage characteristics have been analysed. The effective change in the barrier height for 1% hydrogen was found to be 142.91 meV. The dynamic response of the sensors towards hydrogen at different temperatures has also been studied. At 530°C, voltage shift of 310 mV for 1% hydrogen was observed.

Hydrogen gas sensors based on thermally evaporated nanostructured MoO3 Schottky diode : a comparative study

In this paper, a comparative study of Pt/nanostructured MoO3/SiC Schottky diode based hydrogen gas sensors is presented. MoO3 nanostructured films with three different morphologies (nanoplatelets, nanoplateletsnanowires and nano-flowers) were deposited on SiC by thermal evaporation. We compare the current-voltage characteristics and the dynamic response of these sensors as they are exposed to hydrogen gas at temperatures up to 250°C. Results indicate that the sensor based on MoO3 nanoflowers exhibited the highest sensitivity (in terms of a 5.79V voltage shift) towards 1% hydrogen; while the sensor based on MoO3 nanoplatelets showed the quickest response (t90%- 40s).

A study of hydrogen gas sensing performance of Pt/Graphene/GaN devices

In this work, we present an investigation on Pt/graphene/GaN devices for hydrogen gas sensing applications. The graphene layer was deposited on GaN substrate using a chemical vapour deposition (CVD) technique and was characterised via Raman and X-ray photoelectron spectroscopy. The current-voltage (I-V) and dynamic response of the developed devices were investigated in forward and reverse bias operation at an optimum temperature of 160°C. Voltage shifts of 661.1 and 484.9 mV were recorded towards 1% hydrogen at forward and reverse constant bias current of 1 mA, respectively.

Pt/TiO2 nanotubes/SiC schottky diodes for hydrogen gas sensing applications

Titanium oxide nanotubes Schottky diodes were fabricated for hydrogen gas sensing applications. The TiO2 nanotubes were synthesized via anodization of RF sputtered titanium films on SiC substrates. Two anodization potentials of 5 V and 20 V were used. Scanning electron microscopy of the synthesized films revealed nanotubes with avarage diameters of 20 nm and 75 nm. X-ray diffraction analysis revealed that the composition of the oxide varied with the anodization potential. TiO2 (anatase) being formed preferentially at 5 V and TiO (no anatase) at 20 V. Current-voltage characteristics of the diodes were studied towards hydrogen at temperatures from 25°C to 250°C. At constant current bias of −500 μA and 250°C, the lateral voltage shifts of 800 mV and 520 mV were recorded towards 1% hydrogen for the 5 V and 20 V anodized nanotubes, respectively.

Pt/MoO3 nano-flower/SiC Schottky diode based hydrogen gas sensor

In this paper, we report the development of a novel Pt/MoO3 nano-flower/SiC Schottky diode based device for hydrogen gas sensing applications. The MoO3 nanostructured thin films were deposited on SiC substrates via thermal evaporation. Morphological characterization of the nanostructured MoO3 by scanning electron microscopy revealed randomly orientated thin nanoplatelets in a densely packed formation of nano-flowers with dimensions ranging from 250 nm to 1 μm. Current-voltage characteristics of the sensor were measured at temperatures from 25°C to 250°C. The sensor showed greater sensitivity in a reverse bias condition than in forward bias. Dynamic response of the sensor was investigated towards different concentrations of hydrogen gas in a synthetic air mixture at 250°C and a large voltage shift of 5.7 V was recorded upon exposure to 1% hydrogen.

Oriented graphitic carbon films for hydrogen gas sensors

An oriented graphitic nanostructured carbon film has been employed as a conductometric hydrogen gas sensor. The carbon film was energetically deposited using a filtered cathodic vacuum arc with a -75 V bias applied to a stainless steel grid placed 1cm from the surface of the Si substrate. The substrate was heated to 400°C prior to deposition. Electron microscopy showed evidence that the film consisted largely of vertically oriented graphitic sheets and had a density of 2.06 g/cm3. 76% of the atoms were bonded in sp2 or graphitic configurations. A change in the device resistance of >; 1.5% was exhibited upon exposure to 1 % hydrogen gas (in synthetic, zero humidity air) at 100°C. The time for the sensor resistance to increase by 1.5 % under these conditions was approximately 60 s and the baseline (zero hydrogen exposure) resistance remained constant to within 0.01% during and after the hydrogen exposures.

Pt/Graphene Nano-sheet Based Hydrogen Gas Sensor

In this paper, we present gas sensing properties of Pt/graphene-like nano-sheets towards hydrogen gas. The graphene-like nano-sheets were produced via the reduction of spray-coated graphite oxide deposited on SiC substrates by hydrazine vapor. Structural and morphological characterizations of the graphene sheets were analyzed by scanning electron and atomic force microscopy. Current-voltage and dynamic responses of the sensors were investigated towards different concentrations of hydrogen gas in a synthetic air mixture at 100°C. A voltage shift of 100 mV was recorded at 1 mA reverse bias current.

Pt/ZnO/SiC thin film for hydrogen gas sensing

Zinc oxide (ZnO) is one of the most promising electronic and photonic materials to date. In this work, we present an enhanced ZnO Schottky gas sensor deposited on SiC substrates in comparison to those reported previously in literature. The performance of ZnO/SiC based Schottky thin film gas sensors produced a forward lateral voltage shift of 12.99mV and 111.87mV in response to concentrations of hydrogen gas at 0.06% and 1% in air at optimum temperature of 330 ºC. The maximum change in barrier height was calculated as 37.9 meV for 1% H2 sensing operation at the optimum temperature.

Graphene-like nano-sheets/36° LiTaO3 surface acoustic wave hydrogen gas sensor

Presented is the material and gas sensing properties of graphene-like nano-sheets deposited on 36° YX lithium tantalate (LiTaO3) surface acoustic wave (SAW) transducers. The graphene-like nano-sheets were characterized via scanning electron microscopy (SEM), atomic force microscopy(AFM)and X-ray photoelectron spectroscopy (XPS). The graphenelike nano-sheet/SAW sensors were exposed to different concentrations of hydrogen (H2) gas in a synthetic air at room temperature. The developed sensors exhibit good sensitivity towards low concentrations of H2 in ambient conditions, as well as excellent dynamic performance towards H2 at room temperature.