Different Concentrations Of Hydrogen Gas Research Articles

Silver Nanoparticle-Decorated Tin Oxide Thin Films: Synthesis, Characterization, and Hydrogen Gas Sensing

In this work, sputtered tin oxide films, decorated with silver nanoparticles were fabricated as hydrogen sensors. The fabricated thin films were characterized for their structural, compositional, morphological properties using various characterization techniques including X-ray photoelectron spectroscopy, UV-Vis absorption, X-Ray diffraction, field emission scanning electron microscope, and atomic force microscopy. The morphological characterization confirmed the formation of nanoparticles decorated SnO2 thin films. X-ray photoelectron spectroscopy spectroscopic analysis established the presence of silver/silver oxide on SnO2 thin films. The gas sensing properties of the fabricated sensors were investigated at different concentrations of hydrogen gas, over an operating temperature range of room temperature to 500 °C. It was found that the prepared sensor can detect a low hydrogen concentration (50 ppm) at high operation temperature, while the higher concentration (starting from 600 ppm) can be detected even at room temperature. Furthermore, on the basis of the electronic interaction between the SnO2 and the Ag nanoparticles, we propose a reaction model to explain the qualitative findings of the study.

Gas Sensing and Structural Properties of a Nano-structure MoO3-based Hydrogen Sensor

In this research, thin films of molybdenum trioxide were deposited on a glass substrate using Doctor Blade method. Ammonium Heptamolbudate tetrahydrate (NH4)6Mo7O24 powder is considered as a precursor to this study. Growth of the samples in three main directions of (020), (040) and (060) showed the formation of a layered structure and also the formation of α-phase of molybdenum oxide. In addition, scanning electron microscope imaging of the samples showed flat micro-capsule like structure. Furthermore, gas sensing properties of the fabricated structure were studied in expose to different concentrations of hydrogen gas. The highest and lowest sensitivities were reported about 16 and 91%, for 100 and 1000 ppm of hydrogen gas, respectively, which shows more sensitivity compare to previous studies. Moreover, the fabricated sensor exhibits good stability as well as repeatability for H2 gas detection.

Room temperature hydrogen gas sensor based on palladium decorated tin oxide/molybdenum disulfide ternary hybrid via hydrothermal route

This paper demonstrates a hydrogen gas sensor based on palladium-tin oxide- molybdenum disulfide (Pd-SnO2/MoS2) ternary hybrid via hydrothermal route. The morphologies, microstructures and compositional characteristics of the Pd-SnO2/MoS2 nanocomposite were sufficiently examined by X-ray diffraction (XRD), Raman spectroscopy (RS), nitrogen sorption analysis, energy dispersive spectrometer (EDS), scanning electron microscopy (SEM), transmission electron microscope (TEM) and X-ray photoelectron spectroscopy (XPS). The gas-sensing performances of the Pd-SnO2/MoS2 sensor were investigated by exposed to different concentrations of hydrogen gas from 30ppm to 5000ppm at room temperature. The experimental results showed that the hydrogen gas sensor has a quite sensitive response, swift response-recovery time, good repeatability and selectivity toward hydrogen gas. Furthermore, the effect of Pd loading in the hybrid on the hydrogen gas sensing was investigated. The sensing mechanism of the Pd-SnO2/MoS2 sensor was attributed to the synergistic effect of the ternary nanostructures and the modulation of potential barrier with electron transfer. This work indicates that the as-prepared Pd-SnO2/MoS2 composite is a candidate for detecting hydrogen gas in various applications at room temperature.

Changes in Work Function and Electrical Resistance of Pt Thin Films in the Presence of Hydrogen Gas

The changes in the electrical properties, such as work function and resistance, of Pt thin films in the presence of hydrogen gas were studied. They were simultaneously measured with a flow-through cell at different concentrations of hydrogen gas in atmosphere containing gaseous nitrogen and that containing air. The resistance was measured by a four-terminal sensing method and the relative work function changes were measured using a field effect transistor. In both atmospheres, the resistance decreased as the concentration of hydrogen gas increased. This result was repeatable only in air because of the differences in the dynamic mechanism of increased density of electrical carriers inside the Pt film as a result of diffused H atoms. In the nitrogen atmosphere, the diffused H atoms were not easily released because of the surface barrier. On the other hand, oxygen gas reacted with H atoms at the surface and this reaction accelerated atom release into air. The work function showed repeatable responses in both atmospheres, but the response characteristics were different. The equilibrium reaction between the adsorption and desorption of hydrogen occurred at the surface in the nitrogen atmosphere, whereas the equilibrium reaction of hydrogen and oxygen to form water molecules occurred in air. The changes in work function and resistance in the presence of hydrogen were due to changes in dissociated hydrogen intensity in the bulk, as well as to the surface reactions.

Polyaniline/MWCNT Nanocomposite Based Hydrogen Sensor Operating at Room Temperature

A nanocornposite of polyaniline (PANI) and multiwall carbon nanotubes (MWCNT) has been synthesized and investigated as a sensing material for hydrogen gas at room temperature. The PANI/MWCNT nanocomposite was prepared by in situ chemical polymerization. The nanomaterial characterization was conducted through Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). From these data it was concluded that the PANI formed conformal layer with thickness of approximately 7 nm aligned to the outer layer of the MWCNT. A hydrogen sensor was developed by airbrushing the solution over the surface of heated conductometric transducer. The sensor was tested towards different concentrations of hydrogen gas at room temperature. At 1% of H(2) an increase in the sensing film resistance of 112 Omega was observed. The sensor maintained its stable baseline and repeatability during the testing period which makes it useful for commercialization purposes.

A Room Temperature Conductometric Hydrogen Sensor with Polyaniline/WO3 Nanocomposite

Polyaniline/W03 nanocomposite with high volume of W03 compared to polyaniline has been synthesized through a template-free synthetic route. Characterization of the developed nanomaterial was conducted through Scanning Electron Microscopy (SEM), X-Ray Diffraction (XRD), and Fourier Transform Infrared Spectroscopy (FT-IR). A conductometric transducer was fabricated and used to measure the resistance of polyaniline/W03 nanofiber films during interaction with different concentrations of hydrogen gas at room temperature. The concentration of aniline monomer to W03 was 1 to 8 on the solution. It was observed that the sensor has a stable baseline of 33.2 KO under synthetic air. A decrease in the sensitive film resistance of i .4 K!l was noticed during the Interaction with 1% H2 with 90% response time of 60 seconds. Due to the high operating temperature of ali metal oxides based gas sensors, this sensor offers low power consumption because of its room temperature operation.

Investigations of hydrogen sensors made of porous silicon

Porous silicon layer was formed by electrochemical anodization on n- and p-type silicon surface. Thereafter n-type TiO 1.98 and ZnO〈Al〉 thin films were deposited onto porous silicon surface by electron-beam evaporation and magnetron sputtering, respectively. A Pt catalytic layer and Au electrical contacts for further electrical measurements were deposited by ion-beam sputtering. Changes in sensitivity versus time of obtained structures were examined for different concentrations of hydrogen gas and propane–butane mixture. High sensitivity and selectivity to hydrogen gas was detected. All measurements were carried out at 40 °C.

Conductometric Hydrogen Gas Sensor Based on Polypyrrole Nanofibers

Polypyrrole nanofibers are synthesized through a template-free chemical route and used as the active component for hydrogen gas sensing at room temperature. The synthesis of polypyrrole nanofibers was achieved by using bipyrrole as an initiator to speed up the polymerization of pyrrole with FeCl as the oxidizing agent. Scanning and transmission electron microscopy studies indicate that the resulting polypyrrole forms a nanofibrous mat with average nanofiber diameter of 18 nm. Fourier transform infrared spectroscopy and elemental analysis confirms that the structure of the nanofibers is comparable to bulk polypyrrole. Gas sensing properties of polypyrrole nanofibers were investigated by depositing nanofiber dispersions on an interdigited conductometric transducer. The sensor performance was tested through programmable exposure towards different concentrations of hydrogen gas diluted in synthetic air in an environmental cell at different temperatures. A short response time of 43 s was observed upon exposure to a concentration of 1% hydrogen with a decrease in film resistance of 312 at room temperature. The sensor sensitivity was analyzed with gradual elevation of the operating temperature.

Cone Kinetics Model: Insights into the Morphologies of Mixed-phase Silicon Film Growth

ABSTRACTThe ‘cone kinetics’ model, which explains development of cone-shaped inclusions during nanocrystalline silicon film growth and during low-temperature silicon epitaxy breakdown, is extended to protocrystalline (‘edge’) amorphous silicon, Si heterojunctions and other Si film morpholologies. We generalize the physics underlying cone formation and present diagrams that delineate the deposition regimes giving rise to the different film morphologies; these regimes are determined by the nucleation rate of the second phase and the relative growth rate of the phases present. The model predicts cone growth during thin-film deposition by plasma-enhanced and other chemical vapor deposition techniques when isotropic growth is coupled with the isolated nucleation of a second phase with a higher growth rate. Protocrystalline amorphous silicon and other embedded crystallite phases are formed when a second phase successfully nucleates but has a smaller growth rate than the surrounding amorphous film. The cone kinetics phase diagram provides a simple explanation of the various nanocrystalline film morphologies observed when silane precursors are diluted with different concentrations of hydrogen gas.

Hydrogen sensitive GA 2O 3 Schottky diode sensor based on SiC

Pt/Ga 2O 3/SiC metal-reactive insulator-silicon carbide (MRISiC) devices operated as Schottky diodes were characterized for their hydrogen gas sensitivity. The sensors have been tested towards different concentrations of hydrogen gas as a function of operating temperature. This study shows advantages of this structure compared to the pure thin film (90 nm) Ga 2O 3 conductometric sensor. The Ga 2O 3 thin films were prepared by the sol–gel process and deposited onto the transducers by spin-coating. For both types of sensors, the operating temperature was controlled by a micro heater located beneath the structure. It was found that cycling the ambient from synthetic air (SA) to 1% H 2 in SA air produces repeatable changes of the forward voltage at fixed forward bias. At high temperature (above 500 °C), the response time of the sensors decreases. Furthermore, the sensor shows remarkable stability and the decrease in bias voltage subject to 1% H 2 was 210 mV.

Characterization of reflectivity inversion, α- and β-phase transitions and nanostructure formation in hydrogen activated thin Pd films on silicon based substrates

Optically thin palladium metal films evaporated on different silicon based substrates are investigated following exposure to different concentrations of hydrogen gas in air. Laser modulated reflectance off the palladium surface of silicon oxide and silicon nitride substrates is used to recover information regarding the reflectivity inversion and α/β-phases of the palladium complex after both first and multiple gas cycling. Atomic force microscopy confirms the formation of metal nanostructures following exposure to hydrogen of the optically thin palladium films.

Optically thin palladium films on silicon-based substrates and nanostructure formation: effects of hydrogen

Optically thin palladium films evaporated on different silicon-based substrates are investigated following exposure to different concentrations of hydrogen gas in air. Laser modulated reflectance off the palladium surface of silicon oxide, silicon nitrite and polycrystalline silicon substrates is used to recover information regarding changes in optical properties of the samples due to the absorption of hydrogen. Simple index of refraction arguments are sufficient to explain the results. Structural changes of the palladium films have been investigated using atomic force microscopy before and after hydrogen exposure. An interesting nanostructure formation is evident in some of the samples, leading to a possible means of fabricating nanodevices.