Hydrogen sensitivity

Fogelberg, J. and Petersson, L.-G., Kinetic modeling of the H sub 2-0 sub 2 reaction on palladium and of its influence on the hydrogen response of a hydrogen sensitive palladium metal-oxide-semiconductor device, Surface Science, 350(1-3), 91,1996. 

The hydrogen sensitivity of palladinm-oxide-semiconductor (Pd-MOS) strnctnres was first reported hy Lnndstrom et al. in 1975 [61]. A variety of devices can he nsed as field-effect chemical sensor devices (Fignre 2.6) and these are introdnced in this section. The simplest electronic devices are capacitors and Schottky diodes. SiC chemical gas sensors based on these devices have been under development for several years. Capacitor devices with a platinum catalytic layer were presented in 1992 [62], and Schottky diodes with palladium gates the same year [63]. In 1999 gas sensors based on FET devices were presented [64, 65]. There are also a few publications where p-n junctions have been tested as gas sensor devices [66, 67]. 

Weidemann et al. found that wet etching of a GaN surface before Pd deposition also produced an interfacial oxide, which increased the hydrogen sensitivity by approximately a factor of 50 [14], They concluded that comparing device parameters between different GaN Schottky diode gas sensors requires a defined standard treatment of the GaN surface to introduce a controlled interfacial oxide. 

Recently, Yamazoe et al. observed an extremely high hydrogen sensitivity for Ag-Sn02 sensors ([16). They attributed this to the Fermi level of SnOx being pinned at the redox potential of Ag+/Ag° when the sensor was in air, and at the work function of Ag°... 

Table II. Interference to the Device Hydrogen Sensitivity at RT Due to Water Vapor ( 0) and O2... 

Figure 14. Effect of CO on the hydrogen sensitivity and response time of a Pd/Si02 ( vlOOO X)/n-Si capacitor. Device kinetic response to 2% H2/96% N2 at RT. Curve 1, the device is not exposed to 4% CO/96% N2 and initial ambient is 100% O2 curve 2, the device is exposed to 4% CO/96% N2 prior to the initial ambient 100% O2 and curve 3) the initial ambient is 4% CO/96% l. ...

In general, for T > 100°C, water vapor gives little interference to hydrogen sensitivity due to its volatilizing from the device surface. We also note that CO is found to provide little interference to device H2 sensitivity at room temperatures (15). 

The effect of water vapor on the device hydrogen sensitivity however, is the same for both C-I-S diode and C-I-S capacitor structures that is, high concentrations of water vapor speed up the response but significantly reduce the sensitivities. 

CO has no effect on sensitivity. On the other hand, high concentrations of oxygen in the ambient decrease hydrogen sensitivity. Water vapor has the same effect but only for T < 100°C. 

Detection via mass spectrometry can be used to analyse all the elements in the periodic table, including hydrogen. Sensitivity to light elements is one of the advantages of SIMS in relation to microanatysis techniques based on induced X-rays, The limited mass resolution of the quadrupole leads, in certain cases, to interference (for example. - Si = Fe ). 

Monetti M. A. and Scranton M. 1. (1992) Fatty acid oxidation in anoxic marine sediments the importance of hydrogen sensitive reactions. Biogeochemistry 17, 23-47. 

Up until now, there has been little interest in electrolytic deposition of iron metals and chromium from nonaqueous solutions, because such deposits are easily obtained from aqueous electrolytes. On the other hand, adhesive layers can be applied to reactive metals like titanium, beryllium, and magnesium, for example through nickel deposition from nonaqueous solutions. By depositing such metals out of nonaqueous solutions, hydrogen sensitive materials, such as low-alloy high-strength steel, can be coated without danger of embrittlement. Materials coated in this way with a compact poreless metal layer can be further coated in an aqueous electrolyte. 

A.S. Tomlin, M.J. Pilling, T. Turanyi, J.H. Merkin and J. Brindley, Mechanism Reduction for the Oscillatory Oxidation of Hydrogen Sensitivity and Quasi-Steady-State Analyses, Comb, and Flame 91 (1992) 107-130. 

Liindstrom, I. Shivaramn, S. Svenson, C. Lundkvist, L., A hydrogen-sensitive MOS field-effect transistor, Appl. Phys. Lett. 1975, 26, 55-57... 

LundstrOm I 1981 Hydrogen sensitive MOS-structures. Part 1. Principles and... 

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