Surface analysis of carbon on ozone treated metals

Abstract

To reduce gas desorption, especially dynamic gas desorption, of ultrahigh vacuum materials, it is necessary to reduce carbon on the surface and in the rear surface layer which deteriorates dynamic gas desorption coefficient. To eliminate carbon, an ozone treatment was applied to metal surfaces. The surfaces of aluminum, copper, and stainless steel without any treatment were exposed to 250 ppm ozone using air with flow rates of 1 ℓ/min for 24 or 48 hours. The samples were shown to decrease carbon levels, especially on Cu and Al surfaces, as detected by Auger electron spectroscopy (AES). In addition, no carbon was detected in the rear surface layers as detected by sputter profiling. The detectability of AES is on the order of 10−2 monolayers or approximately 3×1013 carbon atoms/cm2. The thickness of the oxidized layer was 6.3, 8.1, and 3.0 times the native oxide layer for Cu (120 Å), Al (170 Å), and stainless steel (60 Å), respectively. X-ray photoelectron spectroscopy shows (1) the ratio (O/Al) is 1.5 for the treated and 1.4 for the nontreated samples; (2) 24 at. % of Cu2+ is included in the treated but 78 at. % of Cu and Cu+ for the nontreated samples; (3) the oxide component excluding hydroxide is 29 at. % for the treated and 3 at. % for nontreated samples. The treated surfaces show low carbon adsorption characteristics: little carbon was detected by AES on copper and aluminum treated surfaces stored in a covered glass dish for more than four days and on an ozonized copper surface stored in aluminum foil for more than 100 days.