Optimization Of Alpha Tantalum Phase Formation In
Superconducting Tunnel Junction X-Ray Detectors

A thesis submitted to the faculty of
San Francisco State University
in partial fulfillment of
the Requirements for
the degree

Master of Science

Francisco Ponce
San Francisco, California
August 2012

This work examines the current fabrication techniques used to make superconducting 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 α-tantalum (Ta). Niobium (Nb) and aluminum (Al) underlayers are shown to comparably nucleate α-Ta making the use of an additional underlayer for the counter electrode unnecessary. Furthermore, an α-Ta counter electrode is shown to nucleate an α-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 Ar+

which is too low for implementing LEIB. However, LEIB is shown to influence the nucleation of α-Ta on an Al underlayer meaning that a joint LEIB-underlayer technique may produce higher quality α-Ta. Finally, changes in the substrate holder reveal that there is an unknown parameter assisting the nucleation of α-Ta in our system.

(* A copy of this thesis, in PDF format, is viewable by clicking on this link.)

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Updated 19 April 2013