Superconducting properties of Nb thin films deposited on porous silicon templates

Abstract

Porous silicon, obtained by electrochemical etching, has been used as a substrate for the growth of nanoperforated Nb thin films. The films, deposited by UHV magnetron sputtering on the porous Si substrates, inherited their structure made of holes of 5 or 10 nm diameter and of 10 to 40 nm spacing, which provide an artificial pinning structure. The superconducting properties were investigated by transport measurements performed in the presence of magnetic field for different film thickness and substrates with different interpore spacing. Perpendicular upper critical fields measurements present peculiar features such as a change in the H c2⊥ (T ) curvature and oscillations in the field dependence of the superconducting resistive transition width at H ≈ 1 Tesla. This field value is much higher than typical matching fields in perforated superconductors, as a consequence of the small interpore distance.

Evidence of fractional matching states in nanoperforated Nb thin film grown on porous silicon

“…The resulting samples then consist of porous Nb thin films with in plane geometrical dimensions, a 0 and Ø, comparable with the superconducting coherence length, ξ(T ). In these samples, matching fields of the order of 1 Tesla were experimentally observed [18]. Aim of this work is to deepen the study of the matching effect in superconducting Nb thin films deposited on PS.…”

“…To prepare Al 2 O 3 substrates bulk Al [16], Al foils [17], and deposited thick Al films were used [15]. Very recently, another very promising material for selfassembled substrates and an optimum candidate for the Nb growth was proposed, namely, porous silicon (PS) [18]. PS is constituted by a network of pores immersed in a nanocrystalline matrix [19] and it is a material which offers a considerable technological interest in different fields, as for instance micro and optoelectronics [20] and gas sensing [21,22].…”

Nonlinear current-voltage characteristics due to quantum tunneling of phase slips in superconducting Nb nanowire networks

“…On this mask Nb ultrathin films were deposited by UHV dc diode magnetron sputtering system with a base pressure in the low 10 −8 mbar regime following the same fabrication procedure described elsewhere. [20,21] Since the effect of the periodicity of the template tends to disappear when d Nb > ∼ Ø, [20] films thicker than 12 nm can hardly be used to obtain a Nb nanowire network. The value d Nb ∼ 12 nm also assures that individual nanowires are continuous and that the presence of a well defined network is still preserved.…”

“…[1,9] Porous templates were fabricated by electrochemical anodic etching of n-type, 0.01 Ω cm, monocrystalline Silicon wafers. [20,21] The resulting robust porous substrates, about 2 cm 2 large, have average pore diameter Ø = 15 nm and average interpore distance a = 50 nm.…”

Superconducting properties in tantalum decorated three-dimensional graphene and carbon structures

“…In Figure 2(b), we plotted the B c as a function of temperature. In general, B c follows a linear dependence on T. We fit this linear temperature dependence using the standard Ginzburg-Landau theory for an isotropic superconductor, H c2 =  0 /20) 2  (1-T/T c ) [16,17]. Here  0 = h/2e is the flux quantum, 0) is the superconducting coherence length at T = 0.…”