Optimization of alpha tantalum phase formation in superconducting tunnel junction x-ray detectors

This work examines the current fabrication techniques used to make superconducting\ud tunnel junctions (STJs) at the Thin Film Laboratory located at San Francisco State University and investigates the implementation of low energy ion bombardment (LEIB) to nucleate a-tantalum (Ta). Niobium (Nb) and aluminum (Al) underlayers are shown to comparably nucleate a-Ta making the use of an additional underlayer for the counter electrode unnecessary. Furthermore, an a-Ta counter electrode is shown to nucleate an a-Ta wiring layer opening the way to thicker absorption layers. The deposition system, in its current form, is found to produce a maximum normalized ion flux of 1.5 4j w h i c h is too low for implementing LEIB. However, LEIB is shown to influence the nucleation of a-Ta on an Al underlayer meaning that that a joint LEIB-underlayer technique may produce higher quality a-Ta. Finally, changes in the substrate holder reveal that there is an unknown parameter assisting the nucleation of a-Ta in our system