Date of Award

Summer 2001

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

Marek Sosnowski

Third Advisor

Lisa Axe

Abstract

Sputtered tantalum forms two phases - α and β. The α and β phases have distinctly different crystalline structures and properties. The structure and the causes of formation of the β phase are still being studied by researchers. This is a study to distinguish and characterize these two phases. Samples from Bennet Labs and NJIT were characterized using techniques such as SEM, EDX, XRF, XRD, TEM and XAFS. Samples deposited at NJIT were used for an experimental study on the conditions favoring the formation of the phases, by depositing tantalum on heated steel and silicon substrates, additionally TEM analysis was carried out for a sample having a mixture of α and β phases to study its differences. The XRD results shows one of the sample to be highly textured β Tantalum. The XAFS results also show the α. phase to have a bcc structure with the characterstic coordination of bulk tantalurn.The local structure of β tantalum is compared to a theoretical model of P41mnm space group. The study confirm that the structure of tantalum belongs to this space group and has a 30-atom unit cell isomorphous with Uranium. The coordination of Ta atoms in the β phase is seen to be non isotropic. The results of the heating experiments suggest that coatings deposited on substrates without heating favored the formation of the β phase. The TEM analysis shows the β phase to be made up of larger grains of size 100-120 nm, which are about 4 times the size of the (αphase grains.

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