Carbonaceous deposits produced on Ru-capped multilayer mirrors under extreme ultraviolet (EUV) irradiation in the presence of adventitious gaseous hydrocarbons are a major obstacle to process implementation of EUV lithography, the key to fabrication of next generation semiconductor chips. The technical problem has been simulated by examining graphitic film growth on Ru(0001) under low-energy electron irradiation in the presence of 1-butene, C5-C8 linear alkanes, and toluene. We show that this provides a practical and reliable means of simulating the photon-induced chemistry and of distinguishing between benign and harmful species. Linear alkanes up to n-heptane are relatively benign, whereas n-octane and toluene are much more harmful, giving rise to rapid growth of graphitic films of a thickness sufficient to seriously impair mirror reflectivity. 1-Butene exhibits behavior in between these extremes. These properties may be understood in terms of the surface residence lifetimes of the various adsorbates on graphitic surfaces.

The dissociative adsorption and decomposition on a range of metal surfaces of an alkane, an alkene, and an aromatic, all representative of species present in an important technological application, has been studied under conditions relevant to selective gas sensing based on solid electrolyte potentiometry. At 870 K, pure polycrystalline Pt surfaces do not discriminate between n-hexane, toluene, and 1-butene: graphitic carbon accumulation occurs at almost the same rate. However, by varying the composition of polycrystalline bimetallic Pt/Au surfaces, good discrimination between these species can be achieved. Thus at a nominal surface composition of approximately 75% Au (XPS), good selectivity toward 1-butene and toluene uptake is achieved, with essentially no response to n-hexane. At approximately 80% Au the system is selective to 1-butene alone. Particular merits of these systems include good high-temperature stability and good tunability of their chemical selectivity. This makes possible the development of array devices in which the elements have overlapping but different selectivity profiles.

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A potentiometric device based on interfacing a solid electrolyte oxygen ion conductor with a thin platinum film acts as a robust, reproducible sensor for the detection of hydrocarbons in high- or ultrahigh-vacuum environments. Sensitivities in the order of approximately 5 x 10(-10) mbar are achievable under open circuit conditions, with good selectivity for discrimination between n-butane on one hand and toluene, n-octane, n-hexane, and 1-butene on the other hand. The sensor's sensitivity may be tuned by operating under constant current (closed circuit) conditions; injection of anodic current is also a very effective means of restoring a clean sensing surface at any desired point. XPS data and potentiometric measurements confirm the proposed mode of sensing action: the steady-state coverage of Oa, which sets the potential of the Pt sensing electrode, is determined by the partial pressure and dissociative sticking probability of the impinging hydrocarbon. The principles established here provide the basis for a viable, inherently flexible, and promising means for the sensitive and selective detection of hydrocarbons under demanding conditions.