Since its discovery in 1911, superconductivity has represented an equally inciting and fascinating field of study in several areas of physics and materials science, ranging from its most fundamental theoretical understanding, to its practical application in different areas of engineering. The fabrication of superconducting materials can be downsized to the nanoscale by means of Focused Ion/Electron Beam Induced Deposition: nanopatterning techniques that make use of a focused beam of ions or electrons to decompose a gaseous precursor in a single step. Overcoming the need to use a resist, these approaches allow for targeted, highly-flexible nanopatterning of nanostructures with lateral resolution in the range of 10 nm to 30 nm. In this review, the fundamentals of these nanofabrication techniques are presented, followed by a literature revision on the published work that makes use of them to grow superconducting materials, the most remarkable of which are based on tungsten, niobium, molybdenum, carbon, and lead. Several examples of the application of these materials to functional devices are presented, related to the superconducting proximity effect, vortex dynamics, electric-field effect, and to the nanofabrication of Josephson junctions and nanoSQUIDs. Owing to the patterning flexibility they offer, both of these techniques represent a powerful and convenient approach towards both fundamental and applied research in superconductivity.

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Focused Ion Beam-Induced Deposition (FIBID) is a single-step nanopatterning technique that applies a focused beam of ions to induce the decomposition of a gaseous precursor. The processing rate of FIBID increases by two orders of magnitude when the process is performed at cryogenic temperatures (Cryo-FIBID): the precursor forms a condensed layer on the surface of the cooled substrate, greatly enhancing the amount of material available for decomposition. Cryo-FIBID has been achieved so far by making use of liquid nitrogen-based cooling circuits, which require the passage of a flowing gas as a cooling agent. Here, the Cryo-FIBID of the W(CO)6 precursor is performed using a coolant-free thermoelectric plate utilizing the Peltier effect. Performed at −60 ∘C, the procedure yields a W–C-based material with structural and electrical properties comparable to those of its counterpart grown in coolant-based Cryo-FIBID. The use of the thermoelectric plate significantly reduces the vibrations and sample drift induced by the flow of passing coolant gas and allows for the fabrication of similar nanostructures. In summary, the reported process represents a further step towards the practical implementation of the Cryo-FIBID technique, and it will facilitate its use by a broader research community.

NanoSQUIDs are quantum sensors that excel in detecting a small change in magnetic flux with high sensitivity and high spatial resolution. Here, we employ resist-free direct-write Ga+ Focused Ion Beam...

The cubic phase mixed ionic-electronic conductor (Ba 0.5 Sr 0.5 )(Co 0.8 Fe 0.2 )O 3−δ (BSCF) is well-known for its excellent oxygen ion conductivity and high catalytic activity. However, formation of secondary phases impedes oxygen ion transport and consequentially a widespread application of BSCF as oxygen transport membrane. B-cation substitution by 1, 3 and 10 at.% Y was employed in this work for stabilization of the cubic BSCF phase. Secondary phase formation was quantified on bulk and powder samples exposed to temperatures between 640 and 1100°C with annealing time up to 44 days. The phase composition, cation valence states, and chemical composition of all samples were analyzed by high-resolution analytical electron microscopic techniques. Y doping effectively suppresses the formation of Ba n+1 Co n O 3n+3 (Co 8 O 8 ) (n ≥ 2) and Co x O y phases which would otherwise act as nucleation centers for the highly undesirable hexagonal BSCF phase. This work validates for 10 at.% Y cation substitution perfect stabilization of the cubic BSCF phase at temperatures ≥800°C, while a negligible small volume fraction of the hexagonal BSCF phase was found at lower temperatures. A newly developed model describes the effect of Y doping on the formation of secondary phases and their effective suppression with increasing Y concentration. K E Y W O R D SBSCF, energy dispersive X-ray spectroscopy, oxygen transport membrane, transmission electron microscopy, Y-doping

Background: The use of a focused ion beam to decompose a precursor gas and produce a metallic deposit is a widespread nanolithographic technique named focused ion beam induced deposition (FIBID). However, such an approach is unsuitable if the sample under study is sensitive to the somewhat aggressive exposure to the ion beam, which induces the effects of surface amorphization, local milling, and ion implantation, among others. An alternative strategy is that of focused electron beam induced deposition (FEBID), which makes use of a focused electron beam instead, and in general yields deposits with much lower metallic content than their FIBID counterparts. Methods: In this work, we optimize the deposition of tungsten-carbon (W-C) nanowires by FEBID to be used as electrical contacts by assessing the impact of the deposition parameters during growth, evaluating their chemical composition, and investigating their electrical response. Results: Under the optimized irradiation conditions, the samples exhibit a metallic content high enough for them to be utilized for this purpose, showing a room-temperature resistivity of 550 μΩ cm and maintaining their conducting properties down to 2 K. The lateral resolution of such FEBID W-C metallic nanowires is 45 nm. Conclusions: The presented optimized procedure may prove a valuable tool for the fabrication of contacts on samples where the FIBID approach is not advised

The effect of Y-, Nb-and Ti-doping on the stability of the cubic (Ba 0.5 Sr 0.5 )(Co 0.8 Fe 0.2 )O 3-δ (c-BSCF) phase in O 2 -and CO 2 -containing atmospheres was studied in a temperature range between 640 and 880 °C. Electron microscopy investigations demonstrate that secondary phase formation in 10 at% Y-doped BSCF (BSCF10Y) is almost completely suppressed and XRD analyses on powders also show improved stability for 10 at% Nb-and Tidoped BSCF. Furthermore, electrochemical impedance spectroscopy measurements of symmetrical cells in CO 2containing atmospheres show significantly less poisoning effect on oxygen reduction reaction for BSCF10Y compared to undoped BSCF cathodes, while the latter developed a high density of small precipitates on the surface after exposure to CO 2 .

NanoSQUIDs are quantum sensors that excel in detecting a small change in magnetic flux with high sensitivity and high spatial resolution. Here, we employ resist-free direct-write Ga + Focused Ion Beam Induced Deposition (FIBID) techniques to grow W-C nanoSQUIDs, and we investigate their electrical response to changes in the magnetic flux. Remarkably, FIBID allows the fast (3 min) growth of 700 nm×300 nm Dayem-bridge nanoSQUIDs based on narrow nanowires (50 nm wide) that act as Josephson junctions. The observed transfer coefficient (output voltage to magnetic flux change) is very high (up to 1301 µ V/Φ0), which correlates with the high resistivity of W-C in the normal state. We discuss here the potential of this approach to reduce the active area of the nanoSQUIDs to gain spatial resolution as well as their integration on cantilevers for scanning-SQUID applications.