Master of Philosophy
Institute for Superconducting and Electronic Materials
George, Jonathan, A study of vortex dynamics in patterned superconducting thin films, Master of Philosophy thesis, Institute for Superconducting and Electronic Materials, University of Wollongong, 2016. http://ro.uow.edu.au/theses/4914
This thesis can be divided into two primary works, examining the effects of uniform and non-uniform pinning arrays of antidots in YBCO thin films, and optimising the deposition of Nb thin films. The ultimate goal was compare the poorly investigated effect of pinning arrays of large antidots in Nb and YBCO thin films, which have different intrinsic pinning properties and different vortex sizes.
The non-uniform graded pinning arrays etched into YBCO thin films such as graded, inverted and evenly spaced rings of triangular antidots indicated the success of novel artificial pinning arrays of large antidots could come from the suppression of interstitial flux channels between the edge of the film and the centre, and from some suppression of flux hopping. However, the success of these non-uniform arrays may also be attributed to the formation of a 'vortex vacuum' if vortices penetrate the thin film in a non-Bean like flux distribution because of the antidot array. This work is now published in Annalen der Physik in 2017 (J. George, et al., Ann. Phys. (Berlin), 1600283 (2017) / DOI 10.1002/andp.201600283).
To begin investigations into Nb, the first step was optimise the process of deposition to reliably produce consistent thin films, and then start investigating pinning arrays. Despite the obstructions in this stage it was determined that in order to deposit films via DC Magnetron Sputtering, the sputtering chamber needs to be exceedingly clean, and free from contaminants, and a deposition temperature of 350C strikes an ideal balance between vortex pinning and current transparency. Unfortunately the system from Mantis Deposition Systems continues to remain excessively fragile and prone to