Crystalline Niobium Carbide Superconducting Nanowires Prepared by Focused Ion Beam Direct Writing

Abstract

Superconducting planar nanostructures are widely used in applications, e.g., for highly sensitive magnetometers and in basic research, e.g., to study finite size effects or vortex dynamics. In contrast, 3D superconducting nanostructures, despite their potential in quantum information processing and nanoelectronics, have been addressed only in a few pioneering experiments. This is due to the complexity of fabricating 3D nanostructures by conventional techniques such as electron-beam lithography and to the scarce number of superconducting materials available for direct-writing techniques, which enable the growth of 3D free-standing nanostructures. Here, we present a comparative study of planar nanowires and free-standing 3D nanowires fabricated by focused electron-and ion (Ga+)-beam induced deposition (FEBID and FIBID) using the precursor Nb(NMe 2 ) 3 (N-t-Bu). FEBID nanowires contain about 67 atomic percent C, 22 atomic percent N, and 11 atomic percent Nb, while FIBID samples are composed of 43 atomic percent C, 13 atomic percent N, 15.5 atomic percent Ga, and 28.5 atomic percent Nb. Transmission electron microscopy shows that FEBID samples are amorphous, while FIBID samples exhibit a fcc NbC polycrystalline structure, with grains about 15−20 nm in diameter. Electrical transport measurements show that FEBID nanowires are highly resistive following a variable-range-hopping behavior. In contradistinction, FIBID planar nanowires become superconducting at T c ≈ 5 K. In addition, the critical temperature of free-standing 3D nanowires is as high as T c ≈ 11 K, which is close to the value of bulk NbC. In conclusion, FIBID-NbC is a promising material for the fabrication of superconducting nanowire single-photon detectors (SNSPD) and for the development of 3D superconductivity with applications in quantum information processing and nanoelectronics.

Temperature-Dependent Growth Characteristics of Nb- and CoFe-Based Nanostructures by Direct-Write Using Focused Electron Beam-Induced Deposition

“…No temperature dependence of the composition was detected within the experimental error of the EDX measurements, which we estimate to be about 2 at%. The composition of the samples written using Nb(NMe 2 ) 3 (N-t-Bu) was about Nb 11 at%, C 65 at%, and N 24 at%, very similar to the values reported by us recently [7]. Finally, for the samples fabricated using the Pt-precursor, we found the composition Pt 17 at% and C 83 at%, as known from several investigations; see, e.g., Reference [17].…”

“…The solid HCo 3 Fe(CO) 12 precursor was synthesized in a slightly modified procedure [16] to the originally described methodology by Chini et al [26] and finally recrystallized from toluene. The colorless Nb-precursor was prepared in a modified procedure [7] to the published salt elimination reaction described by Baunemann et al [27]. Purification can be carried out by sublimation at reduced pressure (∼ 10 −3 mbar) or by distillation (∼ 10 −1 mbar) and temperatures between 50 and 76 • C. The Pt-precursor was purchased from Sigma-Aldrich and used as supplied.…”

“…Direct-write nano-fabrication by focused electron and ion beam-induced deposition (FEBID/FIBID) has become one of the most promising approaches for the realization of two-and three-dimensional (3D) functional structures with particular relevance for the fields of nano-magnetism [1][2][3][4], nano-optics [5,6], and superconductivity of nanostructures [7,8]. This is due to essentially two important advantages that FEBID/FIBID have as compared to other technologies [9], which are their applicability on virtually any surface and the flexibility to fabricate wireframe- [3] as well as sheet-like [10] structures with sub-100 nm resolution.…”

“…Over the last few years, this has led to the evolution of a simulation-guided 3D computer aided design (CAD) approach which was pioneered by Fowlkes and collaborators [11] and has been further developed towards a reliable instrument for 3D nano-fabrication even of complex nano-architectures, as was recently reviewed by Winkler et al [12]. For the fields of 3D nano-magnetism and nano-superconductivity, the precursors Co 2 (CO) 8 [1], Fe 2 (CO) 9 [13], HCo 3 Fe(CO) 12 [3] (FEBID), W(CO) 6 [14], and Nb(NMe 3 ) 2 (N-t-Bu) [7] (FIBID) have been used and proven to be particularly suited. With a view to the simulation-guided 3D CAD approach to nano-fabrication which uses the continuum model of FEBID/FIBID growth, a set of simulation parameters is required; see Reference [15] for a recent review.…”

Spin-wave spectroscopy of individual ferromagnetic nanodisks

“…[1][2][3] This expansion is triggered by the development of advanced synthesis methods 4,5 and the discovery of novel geometry-and topologyinduced effects. 6 Among the various nanofabrication techniques, focused electron beam-induced deposition (FEBID) has unique advantages for 3D nanomagnetism, 2,3,7 magnonics 8,9 and superconducting electronics of the fluxonic type 10,11 as the magnetic properties of direct-write structures can be varied by selecting a writing strategy and beam parameters, 5 as well as via post-growth irradiation of structures with ions [12][13][14] and electrons. 15 In the context of superconductivity, hybrid ferromagnet/superconductor structures are used for the manipulation of magnetic flux quanta 16,17 and provide access to investigations of odd-frequency spin-triplet superconductivity.…”