Growth of in-plane textured LuNi₂B₂C thin films: correlation among structural, morphological and electrical properties

Abstract

Thin films of the intermetallic superconducting compound LuNi2B2C have been prepared by pulsed laser ablation, and different deposition parameters (substrate temperature, target-substrate distance, laser beam energy density and thickness) have been the subject of extensive studies to optimize growth. The best samples show electrical properties similar to those of single crystals (Tc = 16.4 K, ΔTc = 0.3 K, RRR = 13), are strongly c-axis-oriented, and present a high density of in-plane-oriented surface structures. This in-plane texturing is found only in films some thousands of ångström thick, while if the thickness is reduced below 1000-1500 Å the samples are very flat, but there is no evidence of in-plane texturing.

As-grown magnesium diboride superconducting thin films deposited by pulsed laser deposition

“…Furthermore, because a small amount of oxygen released by the substrate could hinder the formation of the correct phase, we used also MgO substrates which is very stable at high temperature. Moreover, due to its ionic character, MgO enables to obtain textured and epitaxial growth of other intermetallic superconductors like quaternary borocarbide compounds, even if the lattice mismatch is relevant [9]. Our first attempts to deposit MgB 2 films in high vacuum condition (10 -8 -10 -9 mbar) were carried out by scanning the different deposition parameters: mainly substrate temperature (ranging from room temperature up to 750°C) as well as the repetition rate (from 1 Hz to 30 Hz).…”

Biaxially textured LuNi2B2C thin films on MgO single crystals

“…(2) A strongly {1 1 0}-textured Lu 2 O 3 phase is observed as well. This oxide is most likely formed at the interface via a rare earth oxidation reaction with the substrate as described by other groups [21,28]. (3) For high temperatures, an increasing amount of secondary phases is formed at 880 • C. The most pronounced peak found at 2Â = 49.8 • can be addressed to a slightly off-stoichiometric Ni 2 B phase, which is likely formed as a consequence of the lutetium oxidation at the substrate interface.…”

“…Since that time, there was much interest to grow textured thin films of these materials using epitaxial growth. Different groups successfully prepared borocarbide thin films and studied their structural, intrinsic and extrinsic properties [18][19][20][21][22][23][24][25][26]. All those films were fabricated using physical vapor deposition techniques (PVD) on unbuffered or metal buffered oxidic single crystal substrates.…”

“…Secondly, oxygen interdiffusion into the film must be either hindered choosing suitable buffer materials or has to be at least controlled in a way that enables clean borocarbide phase growth on top. (3) High diffusion of metallic buffer materials: The use of refractory metal buffers such as tungsten can suppress the oxidation of the rare earth but at the same time, interface reactions resulting in compounds as for example tungsten carbide may lead to changes of the composition of the borocarbide phase [22,21]. To state the challenge more precisely, no stable buffer or substrate has been found that would allow direct growth of borocarbides without significant metallic or oxidic interdiffusion at all.…”

“…Various reports are present about the preparation of borocarbide thin films by sputtering or pulsed laser deposition (PLD), explicitly aiming for well-aligned textured RNi 2 B 2 C layers, high critical temperatures close to bulk values and high residual resistivity ratios, but achieving sufficient properties reproducibly at the same time has been reported only rarely. Mainly, two groups reported on significant progress in growing highly textured as well as in-plane ordered borocarbide thin films with good superconductive properties at the same time [21,23].…”