PNNL

Abstract

Ba deposition on a ?-Al2O3/NiAl(100) substrate and its oxidation with gas phase O2 at various surface temperatures are investigated using X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES) and temperature programmed desorption (TPD) techniques. Oxidation of metallic Ba in gas phase O2 at 800 K results in the growth of 2D and 3D BaO surface domains. Saturation of a metallic Ba layer deposited on ?-Al2O3/NiAl(100) with O2(g) at 300 K reveals the formation of BaO2-like surface states. These metastable peroxide (O22-) states are converted to regular oxide (O2-) states at higher temperatures (800 K). In terms of thermal stability, BaO surface layers that are formed by O2(g) assisted oxidation on the ?-Al2O3/NiAl(100) substrate are significantly more stable (with a desorption/decomposition temperature of c.a. 1050 K) than the metallic/partially oxidized Ba layers prepared in the absence of gas phase O2, which desorb at temperatures as low as 700 K.