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

Abstract

Superconducting thin films of MgB 2 were deposited by Pulsed Laser Deposition on magnesium oxide and sapphire substrates. Samples grown at 450ºC in an argon buffer pressure of about 10 -2 mbar by using a magnesium enriched target resulted to be superconducting with a transition temperature of about 25 K. Film deposited from a MgB 2 sintered pellet target in ultra high vacuum conditions showed poor metallic or weak semiconducting behavior and they became superconducting only after an ex-situ annealing in Mg vapor atmosphere. Up to now, no difference in the superconducting properties of the films obtained by these two procedures has been evidenced.The recent outstanding discovery of 40K superconductivity in MgB 2 [1, 2] is a breakthrough that stimulated a worldwide excitement in the scientific community renewing the interest on superconductivity. This material exhibits a lot of intriguing properties: it is the compound with the highest T c among non-oxides materials and first reports indicate a phonon mediated mechanism for the superconductivity making MgB 2 also the BCS materials with the highest T C [3]. Furthermore, the grains boundaries have not dramatic effects on the critical current densities, being of its coherence length longer than those of HTSC. The reported properties, the very simple structure and the commercial availability of this material make MgB 2 a favorite candidate for large scale and electronic applications and suggest the possibility of further progress in technology based on superconducting materials. The main limitation for the application seems to be related to the considerable small value of the irreversibility field (about 7 Tesla at liquid helium temperature) [4]. High quality epitaxial thin film are needed to implement a new class of electronic devices. Actually, thin film deposition of this material is a quite difficult task due to the high volatility of Mg, so that MgB 2 growth seems impossible in vacuum conditions. This necessity imposes severe restrictions on deposition systems and, up to now, superconducting thin films have been produced only via ex-situ annealing in magnesium atmosphere [5,6]. Very recently, an in situ annealing has been proposed [7] to react, after the deposition, stoichiometric or Mg rich mixture of magnesium and

As-grown superconducting MgB2 thin films prepared by molecular beam epitaxy

“…There have already been several reports on MgB 2 thin film preparation techniques. [2][3][4][5][6][7][8][9] Most of them, however, require a postdeposition annealing process to produce superconducting MgB 2 thin films. Although these methods provide fair quality MgB 2 thin films, as-grown thin films are preferable for fabricating junctions and multilayers.…”

Energetics of Mg and B adsorption on polar zinc oxide surfaces from first principles

“…An asgrown process without postannealing is desirable for developing devices such as tunneling junctions and multilayer structure of MgB 2 . Several groups have reported lowtemperature growth of MgB 2 films on the Al 2 O 3 ͑0001͒ or Si ͑111͒ substrates using molecular beam epitaxy ͑MBE͒, [2][3][4] electron-beam evaporation, 5 pulsed laser deposition, 6 and sputtering. 7 However, these substrates have rather large lattice mismatch with MgB 2 ͑␦ Ӎ 20% ͒, which is unfavorable for the epitaxial growth.…”

In situ epitaxial MgB2 thin films for superconducting electronics

“…The main difficulty in depositing MgB 2 thin films is that a very high Mg vapor pressure is necessary for the thermodynamic stability of the MgB 2 phase at elevated temperatures [3]. The films deposited by the current technologies either have reduced T c and poor crystallinity [4,5,6,7,8,9,10], or require ex situ annealing in Mg vapor [11,12,13].…”