Ion-beam-assisted deposition of textured NbN thin films

Abstract

Ion-beam-assisted deposition (IBAD) offers the opportunity to prepare thin textured films on non-textured substrates. The approach was used to study if superconducting NbN can be textured in this way. Therefore, a reactive process using pulsed laser deposition of pure Nb in combination with a nitrogen-containing ion beam was utilized for the preparation of textured NbN on amorphous seed layers. It is shown that NbN reveals a textured nucleation similar to IBAD-MgO or IBAD-TiN. The biaxial texture was stabilized in thicker layers using homoepitaxial growth leading to highly textured NbN layers with an in-plane alignment below 5 • . The dependence of the lattice parameter as well as of the superconducting transition temperature T c on the deposition conditions, such as, for example, the N 2 partial pressure during the homoepitaxial growth, was studied in detail. A clear correlation between structural and superconducting properties was found for the deposited NbN thin films. As a result, highly textured NbN layers were prepared showing a T c up to 14 K.

Long-term behaviour of Nb and Cr nitrides nanostructured coatings under steam at 650 °C. Mechanistic considerations

“…The oxide produced by this coating has higher volume than the corresponding nitride as it has reached 10 to 15 µm indicated by the Pilling-Bedworth ratio between the oxide and coating volume. This is not unexpected as according to Kidszum et al [22], the Pilling-Bedworth ratio for NbN was calculated to be 2.35 for Nb 2 O 5 as oxide. In the present case the oxide scale exhibits a complex morphology, likely indicating that it is rather a mixture of more than one oxide as shown in figure 13, and the presence of Cr, as well pores and inter-oxide detachment can cause an even higher apparent ratio.…”

“…These defects appear to be mostly caused by the substrate grinding marks However, thin voids or cracks can self-heal preventing steam to reach the substrate. Thin protective Cr and Nb rich oxides develop and grow progressively as a function of exposure time, and are certainly less stable than other Cr containing oxides such as Mn, Fe spinnels, which are known to be quite stable under the same conditions [22,23]. Nevertheless, the results of this study show that HIPIMS deposited CrN/NbN coatings improve the oxidation resistance of the bare P92 by factor of 10 after long 12,650 hours exposure to 650 o C.…”

Microstructure, mechanical properties and oxidation behaviors of magnetron sputtered NbNx coatings

“…One is the tensile stress while the compressive stress results in the peaks shifting to lower angles. The other is the Nb vacancies in overstoichiometric NbN x coatings (x > 1), since metal vacancies are found to commonly exist in the over-stoichiometric transition metal (group IVB, VB and VIB) nitride coatings (films), such as TiN x [21], ZrN x [22], NbN x [23,24], HfN x [25] and TaN x [26] (x > 1). In order to separate the respective influence of these two factors on XRD peak shifting, residual stress was determined by the sin 2 j method [27] and the (200) peaks of the d-NbN coatings with sufficient intensities were used.…”

Ultrathin NbN Films for Superconducting Single-Photon Detectors

“…However, for thicker NbN films (20 nm and above), the effect of RTP was opposite, as we observed rapid worsening of the layer's smoothness after annealing. The latter is due to the growth of columnar defects, which are typical for NbN, and nitrides in general [12].…”