H2 Gas Sensor Research Articles

Carrier generation and carrier determination in dipyridyldiketopyrrolopyrrole-based H2 gas sensors

Operation mechanism of dipyridyldiketopyrrolopyrrole (DPPP)-based H2 sensor has been investigated with special attention to the electric-field-assisted dissociation of H2 in the presence of Pd or Pt, as well as the carrier generation and carrier determination. H2 is found to dissociate exponentially with an increase of the electric field above 102–3V∕cm as monitored by an electric current. The dissociation is greatly enhanced by the presence of DPPP which serves as a proton acceptor due to its pyridyl-N atom. The detection of H2 starts with dissociation of H2, followed by protonation of atomic hydrogen (H) at the N atom of the pyridyl ring of DPPP, ending up with a release of an electron which contributes to the electrical conduction: H+pyridyl ring→protonated pyridyl ring (N+–H)+e′. The electron conduction is confirmed by the Seebeck effect. Judging from the above process, the atomic hydrogen is pictured as an electron donor. However, the present doping is rather characterized by an instantaneous one, since the extent of doping depends on the ambient H2 concentration.

Sensitivity of Pyrrolopyrrole H2 Gas Sensors as Viewed from Crystal Structures

not Available.

Effect of co-sputtering with Pd and glass on sensing characteristics of optical H2 gas sensor

Effect of co-sputtering with Pd and glass on sensing characteristics of optical H2 gas sensor

N,N′-Bis(4-pyridyl)naphthalene-3,4:7,8-dicarboximide dimethylformamide disolvate

In the title compound, C24H12N4O4·2C3H7NO, the naphthalene imide, which is an organic pigment utilized for H2 gas sensors, has inversion symmetry. The pyridyl rings are twisted, in the same direction, out of the plane of the naphthalene imide skeleton by 69.5 (2)°.

3,6-Di-2-pyridylpyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione

The title compound, C16H10N4O2, is an organic red pigment utilized for H2 gas sensors. The asymmetric unit contains two half-molecules, each molecule being centrosymmetric. The two independent centrosymmetric diketopyrrolo­pyrrole moieties are connected by N—H⋯N hydrogen bonds to form a ribbon structure along [100]. The mol­ecules are stacked in a `hunter's fence' fashion (viz. when viewed from the side, molecles, slipped by about 70° within moleclar stacks, cross each other in a fence-like structure) along the b axis.

N,N′-Di-4-pyridylperylene-3,4:9,10-bis(dicarboximide)

The title compound, C34H16N4O4, is a peryl­ene–imide pigment utilized for H2 gas sensors. The mol­ecule has Ci symmetry. The angle between each of the pyridyl rings and the perylene-imide skeleton is 74.5 (2)°. The mol­ecules are stacked along the c axis with a tilt angle of about 31.5° between adjacent molecules.

N,N′-Di-3-pyridylperylene-3,4:9,10-bis(dicarboximide)

The title compound, C34H16N4O4, is a peryl­ene–imide pigment utilized for H2 gas sensors. The mol­ecule has Ci symmetry with one half-molecule in the asymmetric unit. The angle between each of the pyridyl rings and the perylene-imide skeleton is 54.88 (10)°. The mol­ecules are stacked in a `hunter's fence' fashion (viz. when viewed from the side, molecules, slipped by 45° within molecular stacks, cross each other in a fence-like structure) along the b axis.

3,6-Di-4-pyridylpyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione

The centrosymmetric title compound, C16H10N4O2, is an organic red pigment utilized for H2 gas sensors. The centrosymmetric diketo­pyrrolo­pyrrole moieties are connected by bifurcated N⋯H⋯O hydrogen bonds to form a ribbon structure along [110] and [1\overline 10] alternately. The mol­ecules are stacked in a `hunter's fence' (viz. when viewed from the side, molecules, slipped by 45° within molecular stacks, cross each other in a fence-like structure) fashion along the a axis.

N,N′-Di-2-pyridylperylene-3,4:9,10-bis(dicarboximide)

The title compound, C34H16N4O4, is a peryl­ene–imide pigment utilized for H2 gas sensors. There are two independent half- mol­ecules in the asymmetric unit. The symmetry of both mol­ecules is Ci. The angles between the each of the pyridyl rings and the perylene-imide skeleton are 77.7 (1) and 72.8 (1) in the two mol­ecules. The independent mol­ecules are stacked alternately along the b axis.

Hydrogen Response of Pd Schottky Diodes Formed on AlGaN/GaN Heterostructure

Basic H2 gas-sensing characteristics of Pd Schottky diodes formed on the AlGaN/GaN heterostructure were investigated in vacuum. By introducing a novel surface control process to reduce reverse leakage currents, an unprecedented high H2 sensitivity was achieved where 1 Torr hydrogen caused five orders of magnitude change of current. Surprisingly, the surface control process did not change the C-V characteristics which showed an unexpectedly large shift 1000 mV on H2 exposure. Transient waveforms were almost exponential for the logarithm of current, and response speed increased with increase of H2 pressure and temperature. These results were explained in terms of Schottky barrier height due to adsorption of atomic hydrogen generated by Pd together with a due consideration of the current transport mechanism under reverse bias. [DOI: 10.1380/ejssnt.2005.314]

The influence of grinding conditions on the mechanochemical synthesis of zinc stannate

The aim of this work is the investigation of experimental conditions for mechanochemical synthesis of spinel zinc stannate (Zn2SnO4). Application of this material include manufacturing of CO, H2, NO, NO2, i-C4H10 and C2H5OH gas sensors, production of transparent conducting electrodes, window coatings and anode for use in photoelectrochemistry. Starting powder mixtures of zinc oxide and tin oxide in the molar ratio, in accordance with the stoichiometrics of spinel zinc stannate, were mechanically activated by grinding in a planetary mill for various periods of time in the interval of 0 to 160 min. Changes of physico-chemical characteristics and microstructural parameters in the ZnO-SnO2 system after grinding were followed using surface area analysis and X-ray powder diffraction, while thermal behavior was examined by differential thermal analysis and sensitive dilatometer. The beginning of zinc stannate phase formation was noticed after 40 min of grinding, and prolonged grinding leads to the formation of spinel zinc stannate as the major phase with insignificant amount of unreacted zinc oxide and tin oxide. The formation of spinel was accelerated with the increase of sintering temperature, and monophased zinc stannate was obtained when powder mixture was grinded for 160 min followed by sintering at 1200°C.

Sensitivity of optically readable H2 gas sensor using a masked Pd thin film

Sensitivity of optically readable H2 gas sensor using a masked Pd thin film

H2 selective gas sensor based on SnO2

A highly selective H2 gas sensor was developed based on a ‘hot wire type’ gas sensor commercially available. Tin oxide semiconductor was sintered in a bead (0.5 mm in diameter) covering over a platinum wire (0.02 mm in diameter) coil. The gas sensor was operated by a bridge electric circuit. A dense layer of ≈0.1 mm in depth near the surface of the porous bead, was formed by chemical vapor deposition of hexamethyldisiloxane (HMDS). The dense layer functioned as a ‘molecular sieve’, thereby the diffusion of gases with large molecular diameters, except for H2, was effectively controlled, resulting in a prominent selectivity for H2. On the other hand, diffusion control of O2 caused a strong H2 reduction of the tin oxide in the inner layer covered with the dense layer, resulting in decay in sensor output and irreversible reduction of the hydrogen sensitivity (deactivation of tin oxide). As a countermeasure against the damage, addition effect of cerium oxide from 0.5 to 5.0 at% was investigated. The H2 selective gas sensor thus obtained, had a significantly minor humidity dependence and a prominent long term stability.

Characterization of SnO2-based H2 gas sensors fabricated by different deposition techniques

Thick and thin films of SnO2 are extensively used for resistive gas sensors. Characteristics are compared for films produced by four different techniques – chemical vapour deposition (CVD), spray pyrolysis, vacuum evaporation and screen printing. The films are characterized for H2 sensing only, using a static measurement system to investigate their temperature selectivity. The samples are tested at a concentration of 300 p.p.m. H2 gas, a typical value for comparison. No selective peak is observed for CVD and spray deposited samples, and the selective peak for vacuum evaporated samples has a low sensitivity. But the selective peak for screen printed samples has a sensitivity of 55% (δR/Rair). And what is more, the screen printed samples have a repeatable response.

Interface studies on magnetron-sputtered SnO2-films

Thin SnO2 films have been prepared for H2-gas sensor application by RF magnetron sputtering onto different SiO2 based glasses. ARXPS and sputter-AES measurements have been performed to evaluate the compounds at SnO2-TiN-Au contacts as well as the depth-dependent composition at SnO2-substrate-interfaces. A Tioxynitride compound has been identified as a boundary layer between SnO2 and TiN. Enrichments of the substrate components Ba, B or Na have been percepted at the interface of SnO2 and glass. These observations explain the activated interface conduction path by a strongly doped interdiffusion layer.

Carbon Monoxide and Hydrogen Detection by Anatase Modification of Titanium Dioxide

From the viewpoint of industrial and automobile exhaust pollution control, a sensor capable of detecting and measuring the concentration of harmful gases such as carbon monoxide and hydrogen in the ambient is desired. This paper describes the development and use of a titania (TiO2)‐based semiconducting oxide material as a reliable and rugged CO and H2 gas sensor in the temperature range of 773 to 1073 K. Significant change in the sensing characteristic of the anatase modification of TiO2 was observed when admixed with an insulating second phase, such as alumina or yttria. In the case of TiO2–10 wt% Al2O3, the sensor response was found to be exclusively dependent on the hydrogen concentration alone; the presence of CO or CO2 did not affect the sensitivity. On the other hand, the sensor based on TiO2–10 wt% Y2O3 showed increased sensitivity to CO and decreased sensitivity to H2, compared to that of the undoped TiO2. Addition of elemental iron, in small concentration, to the two‐phase mixture of titania and yttria seemed to further improve the sensitivity and selectivity of the latter to CO.

Influence of thickness on H2 gas sensor properties in polycrystalline SnO x films prepared by ion-beam sputtering

Amorphous SnO x films were deposited on sintered alumina substrates by ion-beam sputtering. They were annealed at 500° C for 2 h in air and polycrystalline films with thickness varying from about 1 to 700 nm were prepared. Film-sensor properties against 0.47% H2 gas were measured as a function of thickness and the operating temperature for 150 to 350° C. The film thickness exhibiting a sensitivity maximum increased gradually with temperature. The optimum thickness shifted from 7 nm at 150° C to 175 nm at 350° C. Highly sensitive films lay in a narrow thickness range of 60 to 180 nm and films thinner or thicker than this were relatively insensitive at 300 and 350°C. A model was proposed to interpret the sensitivity behaviour in terms of thickness and grain-boundary effect.

Study of sputtered ZnOPd thin films as solid state H2 and NH3 gas sensors

Abstract ZnO thin films have been prepared by an r.f. sputtering technique. After coating the ZnO surface with a thin discontinuous Pd film, the structure has been used as a gas sensor element for H2 and NH3 gases. The electrical resistance of the sensor changes under H2 or NH3 ambient gas and, before a saturation value is reached, the resistance vs. time curve shows peculiar features with a particular negative characteristic. Gas-sensing properties of the sensor show that the sensor is highly sensitive to H2 and selective between H2 and NH3 and that its response time is in the range of a few seconds. When the H2 or NH3 ambient gas is restored to its initial composition, the change in electrical resistance of the sensor is reversible at elevated temperatures under N2 ambient and the presence of O2 is not needed to obtain reversibility.

Thickness dependence of H2 gas sensor in amorphous SnQx films prepared by ion-beam sputtering

Amorphous SnOx films were deposited by ion-beam sputtering on sintered alumina substrates. Amorphous film sensors were prepared by annealing the films at 300° C for 2 h in air. The thickness dependence of resistivity and hydrogen gas sensitivity were measured at 150° C over the thickness range ∼ 1 to 700 nm. A resistivity maximum was observed in ultrathin films. Resistivity increased by three orders of magnitude with increasing film thickness from 0.9 to 7.4 nm and then decreased by five orders of magnitude from 7.4 to 35 nm. Ultrathin film sensors showed sensitivity maxima around a thickness of 10 nm. Sensitivity and resistivity of ultrathin films were significantly influenced by the thermal expansion coefficient and the surface state of the substrate.

β-alumina-like thin films

Sodium β alumina-like thin films on α-Al2OF3 substrates are prepared by R.F. sputtering, Mg2+ implantation and subsequent solid state reaction at 1270°C. Structural characterization are performed by Raman scattering and X Ray techniques. The thin films exhibit a fast ionic conduction as high as 10−3Ω−1 cm−1 at room temperature with an activation energy of 0.26 eV; that is almost similar to that of single crystals. The ionic transport number estimated by the E.M.F. method is close to unity. A prototype of H2 gas sensor has been realized.