Effect of long duration UV irradiation on diamondlike carbon surfaces in the presence of a hydrocarbon gaseous atmosphere

Measurements of the effect of long duration UV irradiation (up to 2905 min) of flight quality diamondlike carbon charge state conversion surfaces for application in space research in the presence of a hydrocarbon atmosphere were done. An isopropanol atmosphere was used for simulating the hydrocarbon gaseous environment for an instrument on a satellite in space. Charge state conversion surfaces are used in neutral particle sensing instruments where neutral atoms have to be ionized prior to the analysis. A narrow-band ( 126 ± 5 nm ) discharge lamp and a broad-band deuterium lamp (112-370 nm) were used as sources of UV radiation. The UV irradiation of a surface results in the desorption of some volatiles present on the surface and the decomposition of others. Desorption of volatiles, mostly water, is observed for both UV sources. The decomposition of the hydrocarbons and the subsequent build-up of a hydrocarbonaceous layer is only observed for the broad-band UV lamp, which is more representative for the space environment. Unfortunately, the hydrocarbonaceous layer cannot be removed thermally, i.e., it is permanent, and causes a degradation of the performance of the charge state conversion surfaces. With the present measurements we can quantify the UV influence at which the degradation of the conversion surfaces becomes noticeable.