BUSCADOR RECOLECTA

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. © 2022 by the authors. Licensee MDPI, Basel, Switzerland.

The critical current of a superconducting nanostructure can be suppressed by applying an electric field in its vicinity. This phenomenon is investigated throughout the fabrication and electrical characterization of superconducting tungsten-carbon (W-C) nanostructures grown by Ga+ focused ion beam induced deposition (FIBID). In a 45 nm-wide, 2.7 mu m-long W-C nanowire, an increasing side-gate voltage is found to progressively reduce the critical current of the device, down to a full suppression of the superconducting state below its critical temperature. This modulation is accounted for by the squeezing of the superconducting current by the electric field within a theoretical model based on the Ginzburg-Landau theory, in agreement with experimental data. Compared to electron beam lithography or sputtering, the single-step FIBID approach provides with enhanced patterning flexibility and yields nanodevices with figures of merit comparable to those retrieved in other superconducting materials, including Ti, Nb, and Al. Exhibiting a higher critical temperature than most of other superconductors, in which this phenomenon has been observed, as well as a reduced critical value of the gate voltage required to fully suppress superconductivity, W-C deposits are strong candidates for the fabrication of nanodevices based on the electric field-induced superconductivity modulation.

Ga+ Focused Ion Beam Induced Deposition (FIBID) is a highly flexible, single-step nanopatterning technique that makes use of a focused beam of Ga+ ions to locally induce the decomposition of a gaseous precursor material. In combination with the W(CO)6 precursor, Ga+ FIBID is known to yield a W–C compound that is superconducting below 4.7 ​K. While most reports on Ga+ FIBID-grown W–C focus on in-plane patterning, we demonstrate here that growth along the vertical direction may also be achieved by successively stacking a series of individual patterns that get deposited on top of each other. The nanopillars obtained following this procedure reach up to 10 ​μm in height, and have an aspect ratio of around 50. They exhibit a 68% of metallic W in terms of atomic content, higher than the 40% detected in their in-plane counterparts, while maintaining the superconducting properties. This approach also opens up the possibility of tuning their height and growth angle with respect to the substrate, exhibiting potential applicability in the design of 3D superconducting devices.

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 nanoSQUIDs based on narrow nanobridges (50 nm wide) that act as Josephson junctions. Albeit the SQUIDs exhibit a comparatively low modulation depth and obtain a high inductance, the observed transfer coefficient (output voltage to magnetic flux change) is comparable to other SQUIDs (up to 1300 μV/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.

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

In this Perspective article, we evaluate the current state of research on the use of focused electron and ion beams to directly fabricate nanoscale superconducting devices with application in quantum technologies. First, the article introduces the main superconducting devices and their fabrication by means of standard lithography techniques such as optical lithography and electron beam lithography. Then, focused ion beam patterning of superconductors through milling or irradiation is shown, as well as the growth of superconducting devices by means of focused electron and ion beam induced deposition. We suggest that the key benefits of these resist-free direct-growth techniques for quantum technologies include the ability to make electrical nanocontacts and circuit edit, fabrication of high-resolution superconducting resonators, creation of Josephson junctions and superconducting quantum interference device (SQUIDs) for on-tip sensors, patterning of high-Tc SQUIDs and other superconducting circuits, and the exploration of fluxtronics and topological superconductivity.

The critical current of a superconducting nanostructure can be suppressed by applying an electric field in its vicinity. This phenomenon is investigated throughout the fabrication and electrical characterization of superconducting tungsten-carbon (W-C) nanostructures grown by Ga+ focused ion beam induced deposition (FIBID). In a 45 nm-wide, 2.7 μm-long W-C nanowire, an increasing side-gate voltage is found to progressively reduce the critical current of the device, down to a full suppression of the superconducting state below its critical temperature. This modulation is accounted for by the squeezing of the superconducting current by the electric field within a theoretical model based on the Ginzburg–Landau theory, in agreement with experimental data. Compared to electron beam lithography or sputtering, the single-step FIBID approach provides with enhanced patterning flexibility and yields nanodevices with figures of merit comparable to those retrieved in other superconducting materials, including Ti, Nb, and Al. Exhibiting a higher critical temperature than most of other superconductors, in which this phenomenon has been observed, as well as a reduced critical value of the gate voltage required to fully suppress superconductivity, W-C deposits are strong candidates for the fabrication of nanodevices based on the electric field-induced superconductivity modulation., P.O. acknowledges Aragón Government for funding. The project that gave rise to these results received the support of a fellowship from “la Caixa” Foundation (ID 100010434). The fellowship code is LCF/BQ/PR19/11700008. Funding from the the European Union’s Horizon 2020 research and innovation programme under the grant agreement No 892427 has been received. Authors acknowledge financial support from the Spanish Ministry of Economy and Competitiveness through Projects MAT2018-102627-T and MAT2017-82970-C2-2-R, from CSIC through project PIE202060E187, and from the Aragón Regional Government (Construyendo Europa desde Aragón) through Project E13_20R, with European Social Fund funding. The microscopy works have been conducted in the Laboratory for Advanced Microscopies (LMA), at the Institute of Nanoscience and Materials of Aragón (INMA)—University of Zaragoza. Authors acknowledge the LMA for offering access to their instruments and expertise. Authors acknowledge the use of the Physical Measurements Service in Servicio General de Apoyo a la Investigación (SAI)—University of Zaragoza. This work has been supported by projects H2020 (FATMOLSproject) and Excellence Unit María de Maeztu (CEX2019-000919-M). This work has been supported by the German Research Foundation (DFG) project #FO 956/6-1 (Germany) and European Cooperation in Science and Technology—COST Action #CA16218 (NANOCOHYBRI). V.M.F. acknowledges partial support from the MEPhI (Russia)., Peer reviewed

This article belongs to the Special Issue Nanoscale Assembly and Integration for Applications., 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., This research was funded by European Union’s Horizon 2020 research and innovation program with grant number 892427. This project was supported by the Spanish Ministry of Science through grant numbers MAT2017-82970-C2-1-R, MAT2017-82970-C2-2-R and PID2020-112914RB-100, including FEDER funding, from CSIC through project PIE202060E187, and by Gobierno de Aragón through the grant number E13_20R with European Social Fund (Construyendo Europa desde Aragón). The following networking projects are acknowledged: Spanish Nanolito (MAT2018-102627-T) and COST-FIT4NANO (action CA19140)., Peer reviewed

This article belongs to the Special Issue Current Review in Synthesis, Interfaces, and Nanostructures., 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., This research was supported by the European Commission under H2020 FET Open grant ’FIBsuperProbes’ (number 892427), the grant PID2020-112914RB-I00 funded by MCIN/AEI/ 10.13039/501100011033, from CSIC through projects PIE202060E187 and Research Platform PTI-001, and by Gobierno de Aragón through the grant E13_20R with European Social Funds (Construyendo Europa desde Aragón). The following networking projects are acknowledged: Spanish Nanolito (RED2018-102627-T) and COST-FIT4NANO (action CA19140)., Peer reviewed

Ga+ Focused Ion Beam Induced Deposition (FIBID) is a highly flexible, single-step nanopatterning technique that makes use of a focused beam of Ga+ ions to locally induce the decomposition of a gaseous precursor material. In combination with the W(CO)6 precursor, Ga+ FIBID is known to yield a W–C compound that is superconducting below 4.7 ​K. While most reports on Ga+ FIBID-grown W–C focus on in-plane patterning, we demonstrate here that growth along the vertical direction may also be achieved by successively stacking a series of individual patterns that get deposited on top of each other. The nanopillars obtained following this procedure reach up to 10 ​μm in height, and have an aspect ratio of around 50. They exhibit a 68% of metallic W in terms of atomic content, higher than the 40% detected in their in-plane counterparts, while maintaining the superconducting properties. This approach also opens up the possibility of tuning their height and growth angle with respect to the substrate, exhibiting potential applicability in the design of 3D superconducting devices., This research was supported by the European Commission under H2020 FET Open grant ’FIBsuperProbes' (number 892427), the grant PID2020-112914RB-I00 funded by MCIN/AEI/10.13039/501100011033, from CSIC through projects PIE202060E187 and Research Platform PTI-001, and by Gobierno de Aragón through the grant E13_20R with European Social Funds (Construyendo Europa desde Aragón)., Peer reviewed

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 nanoSQUIDs based on narrow nanobridges (50 nm wide) that act as Josephson junctions. Albeit the SQUIDs exhibit a comparatively low modulation depth and obtain a high inductance, the observed transfer coefficient (output voltage to magnetic flux change) is comparable to other SQUIDs (up to 1300 μV/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., This research was supported by the European Commission under H2020 FET Open grant ‘FIBsuperProbes’ (number 892427), by the Spanish Ministry of Science through the grant PID2020-112914RB-I00, from CSIC through projects PIE202060E187 and Research Platform PTI-001, and by Gobierno de Aragón through the grant E13_20R with European Social Funds (Construyendo Europa desde Aragón). The following networking projects are acknowledged: Spanish Nanolito (RED2018-102627-T) and COST-FIT4NANO (action CA19140)., Peer reviewed

[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., This research was financially supported by the European Union’s Horizon 2020 research and innovation programme under the grant agreement No [892427](Focused Ion Beam fabrication of superconducting scanning Probes [FIBsuperProbes])., the grant PID2020-112914RB-I00 funded by MCIN/AEI/10.13039/501100011033 (recipient: J.M. De Teresa), from CSIC through projects PIE202060E187 (recipient: J.M. De Teresa) and Research Platform PTI-001 (recipient: J. García-Ripoll), and by Gobierno de Aragón through the grant E13\_20R (with European Social Funds (Construyendo Europa desde Aragón) (recipient: J.M. De Teresa)., Peer reviewed

Open data for the article "Low-resistivity, high-resolution W-C electrical contacts fabricated by direct-write focused electron beam induced deposition", which will be published in Open Research Europe., FIBsuperProbes - Focused Ion Beam fabrication of superconducting scanning Probes (892427), Peer reviewed

Resumen del trabajo presentado a la XXXVIII Reunión Bienal de la Real Sociedad Española de Física, celebrada en Murcia del 11 al 15 de julio de 2022., The FET-Open FIBSuperProbes project is funded by H2020 through the grant 892427., No

In this Perspective article, we evaluate the current state of research on the use of focused electron and ion beams to directly fabricate nanoscale superconducting devices with application in quantum technologies. First, the article introduces the main superconducting devices and their fabrication by means of standard lithography techniques such as optical lithography and electron beam lithography. Then, focused ion beam patterning of superconductors through milling or irradiation is shown, as well as the growth of superconducting devices by means of focused electron and ion beam induced deposition. We suggest that the key benefits of these resist-free direct-growth techniques for quantum technologies include the ability to make electrical nanocontacts and circuit edit, fabrication of high-resolution superconducting resonators, creation of Josephson junctions and superconducting quantum interference device (SQUIDs) for on-tip sensors, patterning of high-Tc SQUIDs and other superconducting circuits, and the exploration of fluxtronics and topological superconductivity., The research of our group on this topic has benefited from the following sponsors and grants: the European Commission under H2020 FET Open Grant 'FIBsuperProbes' (No. 892427), the Spanish Ministry of Science through the Grant PID2020-112914RB-I00, CSIC through Projects PIE202060E187 and Research Platform PTI-001, Gobierno de Aragón through the grant E13_20R with European Social Funds (Construyendo Europa desde Aragón). The following networking Projects are acknowledged: Spanish Nanolito (RED2018-102627-T) and COST-FIT4NANO (action CA19140)., Peer reviewed