He+ focused ion beam for fabricating vertical superconducting crystalline hollow nanowires

Superconducting materials are widely used in applications for energy generators and storage due to their capability of transporting electricity without energy losses. However, their required performance for those applications is normally achieved by using nanostructuring. When the sizes of the superconductors are scaled down to the nanoscale in the range of their superconducting coherence length the novel physical properties emerge. To the end, the use of nano superconductivity is extended to quantum computing and nanoelectronics. The available nanoscale approaches are capable of fabricating quasi-1-dimensional superconducting nanowires that preserve a dissipation-free energy state.

However, the difficulty of fabricating 3D superconducting nano-objects still represents a challenge and only a few examples of 3D nanosuperconductors have been reported in literature.

A group of researchers at the Material Science Institute of Aragon (ICMA), from the Council of Research of Spain (CSIC) and the University of de Zaragoza, Dr. Rosa Córdoba, Dr. Alfonso Ibarra and Professor José Mª De Teresa, in collaboration with Dr. Dominique Mailly from CNRS developed a novel methodology for fabricating 3D superconducting crystalline WC hollow nanowires with diameters down to 32 nm and aspect ratio above 200. The methodology was based on using highly- focused He⁺ ion-beam in spot mode to decompose a W(CO)₆ precursor. The growth of the WC pillar occurs around the ion beam spot, mainly due to the interaction of secondary electrons with the adsorbed precursor molecules, while it forms a cavity at the center of the pillar due to the simultaneous He⁺ beam milling.

The high resolution achieved for the growth of the nanowires was attributed to the use of a small 0.3 nm He⁺ beam spot. The large grains sizes and structure displayed also conformed well with the WC_1-x face-centered cubic (FCC) phase.

Such nanowires become superconductors at 6.4 K and also exhibit large critical magnetic fields and current densities. Consequently, their superconducting properties were improved compared to those obtained in the nanowires grown by the Ga⁺ FIB method, as done so far.

The study by Professor José M De Teresa and his research team is the first to successfully develop a novel methodology for fabricating 3D superconducting crystalline WC hollow nanowires and will, therefore, pave the way for the development of 3D nano superconductors. Furthermore, the robust superconducting properties shown by these nanowires are excellent for broad applications in various fields such as quantum computing and nanoelectronics.