Study of hydrogen release from carbon films by helium and deuterium glow discharges

Protium-rich carbon films were deposited by an RF-assisted DC glow- discharge in methane gas. The desorption characteristics of the trapped protium by ion bombardment in a subsequent glow-discharge were studied using partial pressure analysis of the desorbed species. Desorption by both helium and deuterium glow-discharges was investigated. In a helium glow, protium was released primarily as H2 and in a deuterium glow, as H2 and HD. The desorption rate over time cannot be described by a single e-folding rate. A desorption cross-section was estimated by fitting an exponential to the data measured near the beginning of the desorption run sequence. At a bias voltage of 350 V, both D and He ions show a near identical desorption cross-section of ∼7.5x10-17 cm2. Deuterium glows were found to desorb ∼4 times more protium than those from helium glows at comparable operating conditions