Structure of Very Thin Tantalum and Molybdenum Films

Observations of thin-film growth in a continuously recording electron diffraction instrument show fcc phases in very thin films of tantalum and molybdenum. These films transform slowly to the expected bcc structures as the thickness is increased. The bcc phase is first detected in films 40 and 80 Å thick for molybdenum and tantalum, respectively; no fcc tantalum has been detected in films thicker than 250 Å. fcc tantalum films have been prepared in another high-vacuum station on different substrates at various temperatures. Epitaxial fcc tantalum has been grown on MgO.