Titanium dioxide dielectric layers made by anodization of titanium: the effect of dissolved nitrogen and oxygen

This work investigates improving the dielectric structure and properties of TiO2formed by anodization of nitrogen-and-oxygen-infused Ti substrates for electrolyticcapacitors. The controllable parameters of the diffusion process and the anodizationwere studied to evaluate the effect of nitrogen and oxygen dissolved in the Ti substrateon the formation of the anodic oxide and its properties, particularly the leakage currentdensity. The best diffusion treatment condition to decrease the leakage current densityfor Grade 1 Ti was found to be infusion at 1133 K (860 °C) for 22 ks. Under this condition, nitrogen and oxygen were managed to infuse into Ti as interstitial solutes without the formation of Ti oxides or nitrides. The increased solute concentration was measured by XRD. Moreover, concentration—depth profiles were recorded by XPS. SEM-XEDS and TEM-XEDS were used to characterize the structure and composition of TiO2. The presence of nitrogen could interfere with formation of crystalline oxide and contributes to an amorphous TiO2 layer. The formation of an amorphous oxide layer is beneficial for reducing the leakage current density. The results show that nitrogen and oxygen dissolved in Ti substrate can significantly lower the leakage current density of TiO2 formed by anodization. The microscopic mechanisms of oxide growth and leakage current are discussed, particularly with regard to the presence of nitrogen and oxygen, to explore the potential of solutes in the Ti substrate for improving the dielectric properties of the Ti oxide layer. It was found that the nitrogen atoms, as the main interstitial solute, interfere with the diffusion of oxygen through the TiO2 layer and therefore interfere with the growth of dielectric layer. As a result, the population of structural defects that enable leakage current is significantly reduced.

Name thesis:degree_name

Master of Sciences

Level thesis:degree_level

masters

Discipline thesis:degree_discipline

Materials Science and Engineering

Grantor dc:publisher

Case Western Reserve University School of Graduate Studies

Year dc:date

2013

Author dc:creator

• Li, Qiong

Contributors dc:contributor

• Ernst, Frank
• Welsch, Gerhard

• Engineering
• Materials Science
• Titanium Dioxide
• Anodization
• Dielectric Structure
• Nitrogen-and-oxygen Infusion

Statement dc:rights

• unrestricted
• This thesis or dissertation is protected by copyright: all rights reserved. It may not be copied or redistributed beyond the terms of applicable copyright laws.

Language dc:language

English

Repository record dc:identifier

http://rave.ohiolink.edu/etdc/view?acc_num=case1365198961

OAI identifier oai:identifier

oai:etd.ohiolink.edu:case1365198961