Applications of tunnel junctions in low-dimensional nanostructures
This thesis concentrates on studies of AlOx based tunnel junctions and their feasibility for cooling, thermometry and strain sensing in suspended nanostructures. The main result of the thesis is cooling of one dimensional phonon modes of a suspended nanowire with normal metal insulator superconductor (NIS) tunnel junctions. Simultaneous cooling of both electrons and phonons was achieved, and the lowest phonon temperature reached in the system was 42 mK with an initial temperature of 100 mK. In addition, suspended devices show cooling still at a bath temperature of 600 mK. The observed thermal transport characteristics show, that the heat flow is limited by the scattering of phonons at the bulk nanowire interface. The properties of Al AlOx Al tunnel junctions can be improved by thermal annealing in vacuum at 350 450 C. Annealing treatment will lead to complete stabilization of the junctions, and on increase in both tunneling resistance and charging energy. In addition, the annealing process shows a marked improvement in the tunneling conductance spectrum, indicated by a disappearance of several resonances, which are a fingerprint of either resonant or inelastic tunneling processes caused typically by impurities located in the tunneling barrier. The superconducting gap of Al is not affected, but the supercurrent is reduced, consistent with the increase of tunneling resistance. Feasiblity of conventional, sub micron sized Al AlOx Al tunnel junctions in sensing strain, and therefore displacement, is demonstrated in the final chapter of this thesis. Tunnel junctions show a good response to applied strain (gauge factor), which is competitive with existing strain and displacement detectors. ...
PublisherUniversity of Jyväskylä
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Julin, Juhani (2009)
Superconducting tunnel junction fabrication on three-dimensional topography based on direct laser writing Heiskanen, Samuli; Maasilta, Ilari J. (American Institute of Physics, 2020)Superconducting junctions are widely used in a multitude of applications ranging from quantum information science and sensing to solidstate cooling. Traditionally, such devices must be fabricated on flat substrates using ...
Chaudhuri, Saumyadip; Maasilta, Ilari (American Institute of Physics, 2014)We report the development of superconducting tantalum nitride (TaN x ) normal metal-insulator-superconductor (NIS) tunnel junctions. For the insulating barrier, we used both AlO x and TaO x (Cu-AlO x -Al-TaN x and ...
Stability, sub-gap current, 1/f-noise, and elemental depth profiling of annealed Al:Mn-AlOX-Al normal metal-insulator-superconducting tunnel junctions Julin, Juhani; Chaudhuri, Saumyadip; Laitinen, Mikko; Sajavaara, Timo; Maasilta, Ilari (American Institute of Physics, 2016)In this paper we report a study of the effect of vacuum annealing at 400◦C on the properties of normal metal-insulator-superconductor (NIS) tunnel junctions, with manganese doped aluminium (Al:Mn) as the normal metal, ...
Torgovkin, Andrii (2012)Filtering of external unwanted RF-noise and thermal noise generated at the high-temperature parts of the measuring circuit is essential for successful measurements of thermal transport of nanostructures at low temperatures. ...