New phase of superconducting NbN stabilized by heteroepitaxial film growth

Abstract

Thin films of a new, metastable phase of superconducting niobium nitride have been grown using pulsed laser deposition (PLD). This new NbN phase is stabilized by heteroepitaxial growth on (100) Mgo and is shown to be a primitive cubic (Pm3m) distortion from the typical B1, or rocksalt structure. Structural and electrical characterization reveals that this NbN phase has a highersuperconducting critical temperature and a larger lattice parameter when compared with films of B1-NbN. Growth of this new phase demonstrates that PLD can be used as a synthesis tool to deposit new, metastable materials.The next generation of microelectronic devices will be based on the discovery of new materials and the development of related processing technology. The traditional methods of synthesis and preparation, typically involving high temperatures and long reaction times, have been used to investigate a large number of combination of elements. These reactions usually occur near chemical equilibrium, producing the thermodynamically stable products. The materials of the future will require the production of metastable compounds, synthesized far from chemical equilibrium by new reaction methods. Currently, high-powered lasers are being incorporated in a new physical vapor deposition technique called pulsed laser deposition (PLD). ' PLD is being used in the development of new synthesis routes to the formation of metastable compounds so that their intrinsic properties can be accurately measured and evaluated for use in future applications. The deposition of thin films of metastable compounds, such as the infinite layer oxides Ca, "Sr"CuOz,cubic boron nitride (c-BN), carbon nitride (CN"), and amorphous Ge, C",using PLD has been reported.In this paper, we report on the synthesis of a new phase of superconducting NbN by PLD and the structural and electrical characterization of this material. Niobium nitride is a refractory material with a bulk superconducting transition temperature (T, ) of -16 K.Thin films of NbN, typically deposited by sputtering methods, ' also are being studied for applications in electronics. The low chemical reactivity, mechanical durability, high T, ( T, ))4.2 K), and ease with which Josephson junctions can be reproducibly manufactured make NbN a good candidate for use in low-temperature digital electronics. We have demonstrated that, depending on the pressure of the reactive gas atmosphere [Nz/H2 (10%)], any one of several different NbN"(0(x (1.4) phases could be grown on 600'C (100) MgO substrates by ablating niobium targets. ' '" At deposition pressures between 1 and 20 mTorr, metallic Nb2N was deposited, and at pressures greater than 100 mTorr, insulating Nb3N~was grown. Superconducting NbN films were deposited at 60 mTorr. The NbN films grew in one of two different structures. One of these structures has never been reported. In this paper, we describe this new phase of NbN and compare it to the well-known NbN phase with the B1 structure.The films were grown on heated (100) MgO by ablating Nb foil with a pulsed ...

Characterization of NbC and (Nb,Ti)N nanoprecipitates in TRIP assisted multiphase steels

“…In comparison, pure TiN and pure NbN are rocksalt phases (space group m Fm3 ) with lattice parameters a TiN =4.27 Å [32] and a NbN =4.44 Å [33]. Therefore, the experimentally found lattice parameter of 8.09 Å of the composite (Nb,Ti)N phase suggests a doubling of the rocksalt unit cell (i.e.…”

Impact of Gd Doping on Morphology and Superconductivity of NbN Sputtered Thin Films

“…Particularly for superconducting devices (tunnel junctions etc. ), one needs to employ thin films [4][5][6][7]. Niobium Nitride (NbN) thin films have been intensively investigated in the past because of their interesting physical properties and technological applications (superconducting micro-devices, microelectronic catalytic probes and coating) [8].…”

XAFS investigations of nitrided NbN–SiO2 sol–gel derived films

“…For NbN thin films, the following phases are reported in the literature: cubic fcc δ-NbN, hexagonal δ'-NbN, hexagonal β-NbN (e.g. [14,15]) and primitive cubic (metastable superconducting phase [16]). In the case of the thin films obtained by the nitridation of Nb 2 O 5 -SiO 2 coatings with ammonia, the local structure exhibits cubic fcc δ-NbN symmetry, and the mean length of the Nb-N bond is only slightly shorter (by about 1%) than the values found in the literature for films obtained by other techniques, such as magnetron sputtering [15], pulsed laser deposition [17], or temperature programmed reaction (TPR) carried out under N 2 -H 2 gas stream [13].…”