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| Home > Publications database > NanoSQUIDs with proximity effect nanobridge Josephson junctions and Py nanostructures |
| Conference Presentation (After Call) | FZJ-2024-05859 |
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2024
Abstract: Nanoscale superconducting quantum interference devices (nanoSQUIDs) with nanobridge Josephson junctions (nJJs) were prepared on SiN and SiC membranes for experiments in a transmission electron microscope (TEM) at temperatures below 10 K. As thin-film materials for the nanobridges, metals Ti and Nb or nitrides TiN and NbN were combined into 3-layer heterostructures for adjusting superconducting parameters through the proximity effect. This allowed to reduce spread of parameters in ultrathin superconducting films and to fit operation temperature to the most stable temperature of the commercial TEM sample holder that was cooled using flow of liquid helium. The sample holder thermometer was also used as a heater, allowing the sample temperature to be brought from 600 K to 5 K and back in a few seconds. The nanoSQUIDs had a sub-micrometer loop size, which limited the dimensions of the nJJs to below ~100 nm. Electron beam lithography and high selectivity reactive ion etching with pure SF6 gas were used to pattern nJJs with down to 10 nm width that is comparable to coherence length in thin films of Nb and NbN and provide a better reproducibility in the case of Nb functional layer but a better long term stability due to an enhanced corrosion resistance in the case of NbN layer. Nanoscale superconducting quantum interference devices (nanoSQUIDs) with nanobridge Josephson junctions (nJJs) were prepared at a distance of below 200 nm from the tip of a cantilever by using a focused ion beam to achieve bulk nanosculpturing of the substrate. High-resolution TEM revealed that NbN films on SiN have a columnar structure while they observe cube-on-cube epitaxial growth on SiC membranes. Measurements revealed non-hysteretic I(V) characteristics of the nJJs and nanoSQUIDs, peak-to-peak quantum oscillations in the V(B)-characteristics of the nanoSQUIDs with an amplitude of >20 µV and a white noise spin resolution of approximately 400 μB/√Hz that was obtained without use of SQUID array preamplifier. Towards future realization of hybrid superconductor-ferromagnetic nanostructures for spintronics experiments in TEM, Permalloy (Py) nanodots and triangles with dimensions down to ~100 nm were prepared on SiN membranes and studied by Lorentz microscopy and electron holography TEM methods. These technologies are promising for the fabrication of superconducting electronics based on nJJs for operation inside a TEM.
Keyword(s): Information and Communication (1st)
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