Date of Award
Doctor of Philosophy in Applied Physics - (Ph.D.)
Federated Physics Department
Kenneth Rudolph Farmer
Michael Chien-Yueh Huang
Tantalum (Ta) is a metal that is highly prized for its applications in a variety of industries, including the microelectronics industry, where it is largely used in thin film modifications in order to achieve various electronic, magnetic and structural capabilities in solid-state devices. Ta frequently forms metastable phases, including the well-known ß-phase, during the preparation of thin Ta films by standard film deposition methods such as sputtering and electro-deposition. In order to gain insight into Ta metastable phase formation, the Bain transformation mechanism is studied for Ta and the neighboring body centered cubic (bcc) transition metals in Groups 5 and 6 of the Periodic Table, resulting in the prediction of hypothetical body centered tetragonal (bct) and face centered cubic (fcc) phases for all the studied metals at c/a ratios greater than 1.6 and equal to /2 respectively.
Density Functional Theory (DFT) in the Linearized Augmented Plane Wave (LAPW) formalism and the Lowest Order Variational Approximation (LOVA) for the solution of the Boltzmann transport equation have been used to calculate the temperature dependent resistivity for the studied metals and reveal that substrate-induced film strain is not by itself sufficient to cause the formation of ß-Ta. Fermi surface calculations of the mean electron velocity in the proposed P42/mnm structure of ß-Ta suggest that the high values of resistivity frequently measured for ß-Ta are not an intrinsic property.
Nnolim, Neme Okechukwu, "Understanding the origins of metastability in thin film growth; tantalum and the early group VB-VIB metals" (2003). Dissertations. 594.