An x-ray photoemission spectroscopy investigation of thermal activation induced changes in surface composition and chemical bonds of two gettering alloys: Zr2Fe versus Zr57V36Fe7

Abstract

We report comparative XPS (hν=1253.6 eV) core level (Zr 3d; C 1s; O 1s; Fe 2p; V 2p) results from two relevant gettering alloys: Zr2Fe and Zr57V36Fe7. The samples were studied as-received (after in-air fracturing of bulk ingots) and after different annealing treatments (up to 700 °C) performed in ultrahigh vacuum. With increasing temperature both alloys show a progressive dissolution of Zr oxides, an increase in the metallic character of the surface, the gradual loss of C based adsorbates, and a progressive increase in the surface Zr content and at the expense of the C concentration. At temperatures in the range 300–550 °C a fraction of the C atoms form metallic carbides. OH-based groups are depleted from the surface at low temperatures (200 °C), resulting in a sizable decrease of the near surface O content, while a nearly constant O concentration is found at intermediate and high temperatures. Only minor changes are observed for the near surface concentrations of Fe in Zr2Fe and Fe and V in Zr57V36Fe7 as a function of temperature. The two alloys show strong differences in the activation kinetics of these changes, with surface metallization being initiated at lower temperatures and proceeding faster in Zr57V36Fe7. Metallic carbides are found to almost completely dissolve in Zr57V36Fe7 at 600–700 °C, while they are retained even at high temperatures in Zr2Fe. The kinetic differences determined via XPS are consistent with the differences in gettering behavior of Zr2Fe and Zr57V36Fe7.