We present the design and performance of a high-pressure scanning tunneling microscope (HP–STM), which allows atom-resolved imaging of metal surfaces at pressures ranging from ultrahigh vacuum (UHV) to atmospheric pressures (1×10−10–1000 mbar) on a routine basis. The HP–STM is integrated in a gold-plated high-pressure cell with a volume of only ∼0.5 l, which is attached directly to an UHV preparation/analysis chamber. The latter facilitates quick sample transfer between the UHV chamber and the high-pressure cell, and allows for in situ chemical and structural analysis by a number of analytical UHV techniques incorporated in the UHV chamber. Reactant gases are admitted to the high-pressure cell via a dedicated gas handling system, which includes several stages of gas purification. The use of ultrapure gasses is essential when working at high pressures in order to achieve well-defined experimental conditions. The latter is demonstrated in the case of H/Cu(110) at atmospheric H2 pressures where impurity-related structures were observed.

The dissociative sticking probability, ${\mathrm{S}}_0$, of ${\mathrm{O}}_2$ on Al(111) has been measured as a function of incident translational and vibrational energy. ${\mathrm{S}}_0$ rises from ≈${10}^{\mathrm{-}2}$ for energies ≈30 meV to near unity in the range 0.6–2.0 eV, demonstrating an activated dissociation event. Vibrational excitation enhances the sticking. Surface temperature has no effect on ${\mathrm{S}}_0$. A peculiar dependence on polar angle is observed. The results are used to discuss possible mechanisms for the recent observation [H. Brune et al. Phys. Rev. Lett. 68, 624 (1992)] of widely separated O atoms after ${\mathrm{O}}_2$ dissociation on Al(111).