A hydrogen sensor based on graphitic carbon

A Pt/oriented graphitic carbon heterojunction has been fabricated and tested as a conductometric hydrogen gas sensor. The carbon layer, deposited between planar Au substrate contacts using a filtered cathodic vacuum arc (with an applied substrate bias of - 500 V), has a low density of 1.7 g/cm(3) and with 67% of the atoms bonded in sp(2) or graphitic configurations. Electron diffraction analysis showed evidence that the film has a microstructure consisting largely of vertically oriented graphitic sheets. These sheets have good through-film electrical conductivity and contributed to a low device resistance of similar to 60 Omega. A 3-nm Pt layer was deposited subsequently on the carbon layer. A change in the device resistance of > 2% was exhibited upon exposure to 1% hydrogen gas (in synthetic, zero humidity air) at room temperature. The time for the sensor resistance to decrease by 2% under these conditions was 60 s and the baseline (zero hydrogen exposure) resistance remained constant to within 0.03% during and after the exposure tests.