In this articlle we describe an x-ray pbotoelectron spectrometer that can either be used as an ultra-high vacuum instrument ( , P < lo-'' mhar) or, after insertion of a movable aperture, to analyse materials at ambient pressures up to 1 mbar. We will describe the basic design of the instrument, and the methods used to determine the pressure at the location of photoelectron ejection. One way to estimate the pressure is by attenuation of the substrate signal by the gas phase and comparing experimental with published ionization cross-se~tioas; tbe second method l~ses condensatiooi isobars. Examples are given for gas-phase spectra. Application of the instrument in surface science studies is demonstrated by two examples where surfaces were analysed under high-pressure coditions as a function of temperature, showing that tbe instrument allows steady-state equilibrium measurements of surface composition.

Chemical surface cleaning procedures for metals using oxidation/reduction cycles by exposure to oxidizing (O2, NO) and reducing (H2, NH3 ) gases are summarized and an update of the original compilation for chemical cleaning procedures published by Musket et al. [Appl. Surf. Sci. 10, 143 (1982)] is given. Examples discussed in this paper are cleaning procedures for iron, nickel, palladium, copper, and silver surfaces. We also present data on the reduction of gaseous contaminants in a stainless-steel UHV system by flowing nitric oxide through the system during bakeout.

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