Date of Award

Fall 1998

Document Type

Thesis

Degree Name

Master of Science in Materials Science and Engineering - (M.S.)

Department

Committee for the Interdisciplinary Program in Materials Science and Engineering

First Advisor

Trevor Tyson

Second Advisor

Roland A. Levy

Third Advisor

N. M. Ravindra

Fourth Advisor

Mark C. Croft

Abstract

Sputtered tantalum can be used as an effective corrosion resistant barrier if the coating is continuous, free from defects and is adherent to the substrate it is intended to protect. For corrosion-applications 100% bcc phase tantalum is preferred. X-ray diffraction results indicate that sputtered tantalum deposits typically contain a mixture of bcc and beta phases. Depending on the deposition conditions the morphology of tantalum coatings as studied using scanning electron microscopes can vary from irregular, dendritic structure to a defined step type structure. A "cauliflower type" structure has also been observed. Extended x-ray absorption fine structure measurement was used to investigate the local structure of tantalum coatings. The results show that tantalum coatings with 100% bcc phase possess a long-range crystalline order. For coatings with pure beta phase and a mixture of both phases XAFS measurements indicate that the near number coordinations around tantalum atom are not simply well ordered bcc or fcc and that the sample arehigly [sic] disordered on a local scale - a result not previously observed. The adhesion and delamination behaviour [sic] of tantlaum [sic] coatings indicated that coatings with pure bcc phase exhibited excellent adhesion characteristics while pure beta phase coatings and coatings with a mixture of both phases showed poor adhesion. The beta phase tantlaum coatings has [sic] an as deposited resistivity of 175 µΩ [mu-Omega] cm while for alpha phase the values are between 20-80 µΩ [mu-Omega] cm.

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