THE REACTION OF H2O, O-2 AND ENERGETIC O2+ ON BORON-CARBIDE

Reaction of polycrystalline B4C with energetic O-2(+) was investigated mainly using Rutherford backscattering spectroscopy (RBS). For 5 keV O-2(+) irradiation, all of the irradiated oxygen was retained up to the fluence of 2 x 10(17) O/cm(2) in a temperature range from RT to 600 degrees C. The areal density of saturated retention was similar to 3 x 10(17) O/cm(2). The release of the implanted oxygen begins above 600 degrees C and almost all the oxygen desorbs at similar to 1000 degrees C. The depth profile of oxygen retained at RT had a big maximum around 8 nm, while the depth profile at 600 degrees C had a broad peak near 8 nm. In contrast to the above results by RBS, retained oxygen was hardly measured by Auger electron spectroscopy and X-ray photoelectron spectroscopy with Ar+ sputtering. This implies that there are at least two types of trapped states: one is the physically trapped state of a gaseous form (CO or O-2) and the other is a chemically bound state (B-O bond). It was also found that boron oxide is formed even at RT using simultaneous electron/He+ irradiation during H2O exposure, while the oxygen molecule scarcely reacts with the B4C surface under the simultaneous irradiation of electron/He+.