Adsorption induced gas transport phenomena in narrow air channels recorded with work function detectors

Abstract

Gas transport in narrow air channels (length-to-height ratio 1 mm/1 μm) is characterized by work function detectors like hybrid suspended gate field effect transistors (HSGFETs) with sensitive areas located in the middle of the channel. A thin platinum layer covered one side of the channel. In order to separate the influence of the size of the channel structure on the gas exchange Kelvin probe measurements with platinum coated reference electrodes were carried out simultaneously. For the HSGFET we have observed time lags and suppressions of reactions, which indicate a strong adsorption dependence of gas exchange for the investigated testing gas mixture of hydrogen in nitrogen or synthetic air, respectively. The results are discussed in relation to common models for the flow in thin capillaries. We also point out the special features of narrow air channels for investigating adsorption related phenomena and for improving chemical sensor characteristics by incorporating them into small air gaps.

Hydrogen Detection by Polyaniline Nanofibers on Gold and Platinum Electrodes

“…38-40 A recent value using the Kelvin probe method gave ∆Φ ) -0.75 eV leading to a value of 4.89 eV for the work function of platinum hydride in nitrogen. 40 Gold does not form a hydride upon exposure to hydrogen, and therefore the work function does not change. This is consistent with the I-V curves presented in Figure 5 which confirms that the work function of gold does not change in the presence of hydrogen.…”

“…There is a significant range in the literature for the work function (Φ) of platinum hydride. The measurements are often obtained relative to bare platinum showing changes in work function ranging from ΔΦ = −1.16 eV to −0.55 eV giving work functions for platinum hydride ranging from 4.48 to 5.09 eV. − A recent value using the Kelvin probe method gave ΔΦ = −0.75 eV leading to a value of 4.89 eV for the work function of platinum hydride in nitrogen . Gold does not form a hydride upon exposure to hydrogen, and therefore the work function does not change.…”

<title>Gas detection with work function sensors</title>

“…The calculation of the transconductance from these measurement data lead to an airgap height of 2 jim for a given WIL ratio of 20. The crosscuts of the complete sensor in figure 3 (right: sensing region) prove this airgap distance.…”