Ultra-high vacuum investigation of the surface chemistry of zirconium

A description of a new ultra-high vacuum chamber for studying zirconium sur face chemistry is presented. The design includes low-energy electron diffra ction (LEED) and scanning tunneling microscopy, a gas-handling system for c ontrolled gas exposure, a mass spectrometer for temperature programmed deso rption (TPD), an electron gun for electronically inducing surface chemistry , and Auger electron spectroscopy (AES). Schematic representations of the a pparatus are described, followed by the first application of TPD and LEED i n 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 feat ure near 550 K. Data from LEED indicate that this adsorption does not resul t in ordered layers until 700 K annealing, and that formation of ordered st ructures depends on exposure and annealing conditions. These TPD and LEED d ata indicate a competition between the kinetics of recombination and desorp tion with those of diffusion involving the subsurface regions. (C) 2000 Els evier Science B.V. All rights reserved.