Hydrogen outgasing from titanium-modified layers with various surface treatments

In an extremely high-vacuum (XHV) system, hydrogen outgassing is the most i mportant factor to obtain vacuum pressure below LOX 10(-10) Pa. Titanium is an interesting material for applications in XHV construction. This work wi ll demonstrate a clear correlation between hydrogen outgassing and surface structures of pure titanium in vacuum technology. The titanium surfaces wer e prepared following treatments such as chemical, electrical, buffing, and mechanochemical polishing. Characterization of oxide layers has been carrie d out using Auger electron spectroscopy and angle-resolved x-ray photoelect ron spectroscopy, and a cross section of the modified layer has been observ ed by using an optical microscope. The hydrogen distribution in a surface r egion was measured by elastic recoil detection analysis. The oxide thicknes ses were from 20 to 50 nm, although the finished titanium surfaces were cov ered with TiO2 for chemical polish, electrical polish, buffing polish (BP), and mechanochemical polish (MCP); also, TiO was formed under the top layer for MCP. The thick modified layers (about 1 um) on the surfaces were made in BP and MCP processing, and the modified layers had extremely high-densit y distributions of hydrogen (H/Ti of about 1 to 2). Thermal desorption spec troscopy measurements indicated that the desorption behavior of hydrogen wa s not strongly dependent on the thickness of the oxide layer, and the hydro gen outgassing rates from the surfaces of samples were less than 4.0X 10(-7 ) Pa m s(-1) at room temperature. We report the results of the relation bet ween the quantities of desorbed hydrogen gas and the structure of modified layers on titanium polished surfaces. (C) 2001 American Vacuum Society.