Temperature Dependence of Oxide Decomposition on Titanium Surfaces in UHV

It is well known that the titanium surface forms stable oxides of Ti{sub 2}O, TiO, Ti{sub 2}O{sub 3}, Ti{sub 3}O{sub 5}, Ti{sub n}O{sub 2n-1} (4 < n < 38) and TiO{sub 2} and, as a result, exhibits a high degree of immunity against attack by acids and chlorides. However, titanium is also a very active getter. In the gettering characterizing the process, we have investigated the temperature dependence of stable titanium oxides on titanium in ultra-high vacuum (UHV) using Auger electron spectroscopy (AES), quadrupole mass spectrometry (QMS) and x-ray photoelectron spectroscopy (XPS) in the temperature range RT- 600 C. Surfaces of titanium specimens were prepared by electropolishing (EP) and a thin titanium oxide layer was formed on the surface, principally TiO{sub 2}. On increasing the temperature to above 300 C, the O{sub KLL} Auger intensity began to decrease in a drastic way while, in contrast, the Ti{sub LMM} Auger intensity was increased. Above 450 C, no oxygen was detected on the titanium surface in UHV. However, the outgassing rates of H{sub 2}O, O{sub 2}, CO, and CO{sub 2} from the surface did not show any changes in QMS measurements below 450 C. This behavior is explained as gettering, which ismore » an enhancement of diffusion of oxygen from the surface into the bulk. To investigate the temperature dependence of the chemical states of titanium oxides on an EP surface, XPS analysis was also performed in the range 200-450 C in the same way. The results showed drastic changes of the titanium oxide core levels such that the TiO{sub 2} decomposed to suboxides at 180 C, and even the remaining TiO{sub 2} was still decreasing on heating up to 420 C. The titanium surface has a very sensitive oxide composition, depending on temperature.« less