Ultra-high vacuum investigation of the surface chemistry of zirconium

A description of a new ultra-high vacuum chamber for studying zirconium surface chemistry is presented. The design includes low-energy electron diffraction (LEED) and scanning tunneling microscopy, a gas-handling system for controlled gas exposure, a mass spectrometer for temperature programmed desorption (TPD), an electron gun for electronically inducing surface chemistry, and Auger electron spectroscopy (AES). Schematic representations of the apparatus are described, followed by the first application of TPD and LEED in this system to water adsorption on Zr(0 0 0 1). Water adsorption at 180 K followed by linear heating results in water desorption in a broad TPD feature near 550 K. Data from LEED indicate that this adsorption does not result in ordered layers until 700 K annealing, and that formation of ordered structures depends on exposure and annealing conditions. These TPD and LEED data indicate a competition between the kinetics of recombination and desorption with those of diffusion involving the subsurface regions.