On the Rectification of Anodic Oxide Films of Titanium

Abstract

The phenomenon of electrolytic rectification in anodic oxide films has been studied extensively for the valve metal-valve metal oxide-electrolyte system for many years. This paper describes experimental results on the rectification of the electric current in anodic oxide films, especially TiO2 enclosed between two metallic electrodes. The rectification of the electric current is interpreted on the basis of a p-n junction within these oxide films. In addition, these junctions can exhibit photovoltaic effects and can be used for the fabrication of field effect devices. In these field effect transistors the electrical current flowing between two narrowly spaced electrodes deposited on the oxide surface can be modulated by the application of voltage to the titanium boatom electrode. This experiment shows that a conductive surface layer is adjacent to an insulating layer underneath.

Growth Characteristics of Rutile Film by Chemical Vapor Deposition

“…The excellent agreement of the calculated activation energy of saturation nucleation density (Eq. [6]) with the experimental data (Fig. 2) also seems to validate earlier conclusions on the mechanism of the surface nucleation.…”

“…14 eV/kT [6] where C,, C2, and C are constants, and Eo A ~ 0.45 eV and • ----2.58 eV (14). The excellent agreement of the calculated activation energy of saturation nucleation density (Eq.…”

“…Thus, above 1125~ the nucleation density (Ns) can be described by Eq. [6] modified by an additional factor for the amount of unreacted TIC14 present. A similar adjustment can be made to describe the deposition rate above 1125~ Orientation behavior.--Some variations were observed in the crystallographic orientations adopted by TiO2 films, on the several types of substrates used.…”

“…The former include the evaporation of titanium followed by oxidation, reactive sputtering of titanium in oxygen, and rf sputtering of titanium dioxide (3). The pyrolysis of titanium alcoholates (e.g., tetraisopropyl titanate) (4), hydrolysis of titanium tetrachloride (5), and anodization of titanium films (6) are examples of chemical deposition of titanium dioxide. In this study, a new chemical vapor deposition process to form TiO2 has been explored on a variety of substrates.…”

Rectification by Anodic Oxide Films on Zirconium

“…The presence of a p-n or p-i-n junction, resulting from nonstoichiometry induced by the oxide growth process, is often proposed in explaining mechanisms of thermal oxidation and rectification. The decrease in capacitance to be expected with applied d-c bias in the anodic (reverse) direction is a means of checking for the existence of such junctions in the oxide or at the oxide-counterelectrode boundary (8,9). It is also believed that transition from homogeneous conduction by bulk oxide to the heterogeneous or local response at flaws occurs with increase in oxide thickness (10).…”