Ppm H2 Gas Research Articles

Direct Fabrication of ZnO Whiskers Bridging Between Micron-gap Electrodes in Aqueous Solution for Highly Gas Sensing

AbstractA simple but convenient method for fabricating ZnO micro-sized structure selectively and artificially between two micron-gap electrodes was proposed and investigated. The technique is based on electrolytic deposition in aqueous solution of zinc nitrate or zinc acetate, which selectively occurs between the electrodes being enhanced by electric field. The deposition characteristics were investigated in terms of the deposition conditions, and under the optimized condition ZnO micro-sized structure was obtained with bridging between the electrodes. The gas sensing characteristics of the structure was investigated by exposing to a 500 ppm H2 gas, resulting in 23% variation of the resistance at room temperature. The device dimensions can be downsized to nanometer scale by applying nano-gap electrodes, and therefore this technique is promising for fabrication of highly functional nano-sized sensors at low cost, contributing to mass applications.

Selective CO gas detection of Zn2SnO4 gas sensor

The ability of semiconductor gas sensors to differentiate between gases is essential but difficult to obtain. In this study, Zn2SnO4 was made to be CO selective and the possible mechanism for the selectivity was studied. The electrical and the gas-sensing properties of uncoated and CuO-coated Zn2SnO4 were investigated. In order to obtain an ohmic contact to Zn2SnO4, a ZnO layer was stacked on top of Zn2SnO4 and co-fired. CuO was coated by immersing the sintered sample in Cu-containing solution. Both uncoated and CuO-coated samples showed the higher sensitivity to 200 ppm CO gas than to 200 ppm H2 gas. However, the CuO-coated Zn2SnO4 showed much enhanced sensitivity and thus good selectivity for CO gas (S CO/S H 2 ∼ 6) compared to the uncoated sample. The excellent selectivity of Zn2SnO4-based materials for CO gas was explained by the difference in the mechanisms of CO and H2 oxidation.

(Ba,Sr)TiO3 thin films by RF multitarget co-sputtering and hydrogen gas sensing properties

Ferroelectric (Ba,Sr)TiO3 thin films have been prepared by RF co-sputtering process, and characterized using dielectric characterizations and gas sensing measurements for the H2 detection. Experimental results show that the leakage current of these co-sputtered BST thin films is closely related to the deposition parameters and electronic defects in the films. The I-V performances of our Pd/BST/Pt capacitive devices exhibit the typical Schottky behavior, both in air and in hydrogen gas. The turn-on voltage shift at 1024 ppm H2 gas diluted in air has been observed due to the H2 blocking effect by BST films at the interface with the catalytic Pd metal layer. It is believed that the electronic defects cause the degradation of the RF co-sputtered films to H2 gas detection, and weaken the induced H2 potential build-up across the space charge layer at the interface.

Study of hydrogen polarization potential in MFM device using amorphous (Ba, Sr)TiO3 type thin films and hydrogen gas sensing preporties

Ferroelectric (Ba,Sr)TiO3 type thin films, with and without Ti and La doping, have been prepared by the sol-gel technology and characterized using TGA, DTA, X-ray diffraction, dielectric characterizations, and gas sensing measurements for H2 detection. The BST thin film capacitive devices are made on Si substrate to detect H2 gas and to study the hydrogen induced interfacial polarization potential. Experimental results show that the Schottky I-V behavior exhibits in these Pd/amorphous (Ba,Sr)TiO3 type thin film/metal capacitive devices, and that the enhanced interfacial polarization potential as large as 4.5 V at 1042 ppm H2 gas diluted in air has been observed, which is about 7 times larger than the best value reported in the literature. It has been clearly shown that the hydrogen induced interfacial polarization potential is closely correlated with the microstructure in ferroelectric thin films and the enhancement of this polarization potential is mainly attributed to the high dielectric constant of amorphous ferroelectric thin films. A hydrogen-blocking model is proposed to explain this interesting phenomenon. Other factors such as compositions, stoichiometry, processing conditions, are also discussed.

Ferroelectric (Ba, Sr)TiO3 thin films for H2 gas detection by sol-gel and RF sputtering

Ferroelectric (Ba, Sr)Ti03 thin films for hydrogen gas detection have been prepared by sol-gel and RF sputtering methods, and characterized using X-ray diffraction, dielectric characterization, and gas sensing measurements. The sol gel approach can easily produce BST amorphous films for H2 gas detection, however, no amorphous films, but partially crystallized ones, have been obtained using our RF sputtering coating system. Experimental results show that the Schottky I-V behavior appears in these Pd/amorphous BST thin fildmetal capacitor devices, both in air and in diluted hydrogen gas. The sol-gel prepared films display an excellent gas sensitivity and the turn-on voltage shift as large as 4.5V at 1024 ppm H2 gas in air has been observed due to the H2 blocking effect by amorphous BST films. The relatively poorer performance of the RF sputtered films to H2 gas detection may originate from the trapped charges in these partially crystallized films, and therefore, weaken the induced H2 potential build-up across the space charge layer at the interface.