SURFACE CHARACTERIZATION OF TITANIUM AND TITANIUM DEUTERIDE GAS-PHASE AND SOLUTION-PHASE OXIDATION PROCESSES (SURFACE ANALYSIS, ANGER ELECTRON SPECTROSCOPY).

Abstract

The reactions of atomically clean, titanium film surfaces with oxygen, deuterium, and water have been investigated. Auger Electron Spectroscopy was utilized to monitor the formation 9f a surface oxide in the case of oxygen exposure, and to characterize the deuteride which formed upon deuterium absorption, and its subsequent oxidation. Quantification of surface oxide stoichiometries was facilitated by novel data acquisition and treatment schemes. The quartz crystal microbalance was used to measure the mass of adsorbed oxygen or deuterium with submonolayer sensitivity. Electron energy loss spectroscopy was sensitive to the presence of Ti⁺³ in the surface oxide. The initial oxidation of the titanium surface was characterized by the dissociative adsorption of three mono1ayers of oxygen atoms at a constant rate. The oxide formed during this reaction stage was a Ti₂0₃/Ti0₂ mixture with a total thickness of 13 A. The rate of oxygen adsorption then decreased such that oxide growth was logarithmic with time. When the oxide had attained a total thickness of 20 A, the initial suboxide was converted to Ti0₂, and subsequent oxide formed was purely Ti0₂. Oxide growth occurred by oxygen anion migration under the influence of an electrostatic field, set up across the oxide layer by electron transfer from the metal to adsorbed oxygen species. The pressure dependence of the oxide growth rate and terminal thickness suggested a constant field growth mechanism. Clean titanium films reacted with deuterium to form a bulk deuteride TiDₓ (x<2). The oxide layer which resulted from oxygen exposure was characterized by the above techniques. Oxide layers greater than 20 A completely inhibited deuterium absorption by prohibiting 02 dissociation, but did not act as a diffusional barrier when additional dissociation sites were provided. Iron adlayers were found to accelerate the D₂ absorption reaction. Removal of the titanium films from the vacuum chamber to an isolable electrochemical reaction chamber, without exposure to the atmosphere, allowed a determination of the effect of the various gas/solid reactions on the subsequent electrochemical oxidation processes.