Uniform MgB2 thin films grown on Si(111) and Al2O3(0001) substrates prepared by e-beam evaporation and in situ annealing methods

Abstract

Mg B 2 superconducting thin films on Si(111) and Al2O3(0001) substrates were prepared by high vacuum e-beam evaporation and two-step in situ annealing techniques. The precursor films [B(100Å)∕Mg(151Å)]6∕Al2O3 (or Si) were deposited at room temperature and 1×10−7mbar of background vacuum, then annealed in situ at 630°C for 30min in an argon atmosphere of 150Pa. The atomic force microscopy image showed that the films were uniform with grain sizes of about 100nm. An extremely sharp superconducting transition with a width of 0.1K and a zero-resistance temperature of 30.3K was obtained, indicating a film of high uniformity and purity in its phase with perfect connection between the MgB2 grains.

Superconductivity of MgB2in the BCS framework with emphasis on extrinsic effects on critical temperature

“…The reduction of T C of MgB 2 under external pressure, which is lattice compressive strain, is already discussed. Various strains exist in MgB 2 thin films grown on different substrates and thus the nature of the substrate material has a strong influence of the T C on MgB 2 films [31,147,152,153]. In MgB 2 theoretical calculations show that T C can be raised by increasing a/a and c/c, that is by applying suitable tensile stress [154].…”

Fabrication of superconducting magnesium diboride thin films by electron beam annealing

“…In the field of superconducting electronics, the key precondition for device applications is film quality. However, there are three main problems [3] blocking the path for obtaining good MgB 2 superconducting films. Firstly, magnesium (Mg) has a very high vapor pressure even below its melting point.…”

“…Third, there is thermal decomposition at high temperature in the synthesis of MgB 2 . To fabricate high quality superconducting MgB 2 thin films, several methods have been applied, including two-step in situ annealing techniques [3][4][5][6][7], two-step ex situ annealing techniques [7][8][9][10][11][12][13][14][15][16] and as-grown techniques [2,[17][18][19][20][21][22][23][24] such as hybrid physicalchemical vapor deposition (HPCVD) [2,[17][18][19][20][21][22][23]. In HPCVD B 2 H 6 is flammable, explosive, poisonous and expensive.…”

“…In HPCVD B 2 H 6 is flammable, explosive, poisonous and expensive. In two-step techniques, the precursor films are deposited in vacuum chambers with electron beam evaporation, pulsed laser deposition (PLD), chemical vapor deposition (CVD), thermal deposition, etc [3,7], and annealed in situ or ex situ by laser, conventional furnaces or a heater. The conventional annealing durations are usually more than several minutes or even 10 min, which may cause excessive volatilization of Mg, oxidation of Mg with O 2 and decomposition of MgB 2 in in situ annealing.…”

Growth of MgB2 thin films on alumina-buffered Si substrates by using hybrid physical–chemical vapor deposition method

“…The buffer-material should have the well-matched crystal structure to MgB 2 lattice parameters. The reasonable buffers [12,13] such as AlN, SiC, Al 2 O 3 , NbN, and TiB 2 materials on silicon substrates are used in various growth methods such as the in situ reactive evaporation [14,15], pulsed laser deposition [16][17][18] [19][20][21], and the sequential E-beam evaporation of Mg-B bilayer followed by an in situ annealing [22][23][24][25][26]. But the HPCVD growth of MgB 2 thin films using buffered silicon substrates has not yet been reported.…”