RBS characterization of MgB₂superconducting films annealedex situandin situ

Abstract

The elemental composition and depth profiles of MgB2 films prepared by successive e-beam evaporation as well as by thermal co-deposition of Mg and B components were investigated by Rutherford backscattering spectrometry (RBS). In the case of films deposited by e-beam evaporation we studied both Mg-B precursors and appropriate MgB2 films grown on glassy carbon, Si(100) and J-sapphire substrates annealed in situ. For the films co-deposited by thermal evaporation on R-sapphire substrates and annealed ex situ we investigated superconducting MgB2 films only. The Tco values of all MgB2 films ranged from 21 to 30 K. Because of a very fine granular structure of the annealed films, confirmed also by SEM observations, we could not identify any MgB2 phase from x-ray diffraction (XRD) patterns. On the other hand, Mg2Si phase has been detected by XRD on the film–substrate interface for the superconducting film deposited on Si(100) substrate. The RBS measurements were performed with a 3.1 MeV 4He+ beam. Under these conditions, the 16O(α,α)16 elastic resonance allowed us to detect oxygen in all studied samples especially in B layers. The depth profiles of precursors prepared by successive e-beam evaporation showed clearly the multilayer film structure consisting of B and Mg layers. A strong interdiffusion between B and Mg layers may be observed after an in situ annealing, but still some degree of non-homogeneous component distribution may be observed. On the other hand, the MgB2 films co-deposited by thermal evaporation and annealed ex situ are much more homogeneous, but a higher content of oxygen is present.

Vapor annealing synthesis of non-epitaxial MgB2films on glassy carbon

“…Molecular beam epitaxy [15,16], reactive evaporation [17], and hybrid physical-chemical vapor deposition (HPCVD) [6,7,14] have been particularly successful in making high-quality epitaxial films. In contrast, the growth of non-epitaxial MgB 2 films on amorphous or polycrystalline substrates has attracted relatively limited attention and yielded less promising results [9,[17][18][19][20][21][22]. Indeed, non-epitaxial films typically exhibit large surface roughness and reduced T c [9,[17][18][19][20][21][22].…”

“…In contrast, the growth of non-epitaxial MgB 2 films on amorphous or polycrystalline substrates has attracted relatively limited attention and yielded less promising results [9,[17][18][19][20][21][22]. Indeed, non-epitaxial films typically exhibit large surface roughness and reduced T c [9,[17][18][19][20][21][22]. For example, films prepared on glassy carbon substrates by co-deposition of Mg and B followed by annealing at 700 °C had large roughness, depressed T c values of 25-30 K, and compositional non-uniformity manifested as the Mg/B ratio varying as a function of depth [19,20].…”

“…Indeed, non-epitaxial films typically exhibit large surface roughness and reduced T c [9,[17][18][19][20][21][22]. For example, films prepared on glassy carbon substrates by co-deposition of Mg and B followed by annealing at 700 °C had large roughness, depressed T c values of 25-30 K, and compositional non-uniformity manifested as the Mg/B ratio varying as a function of depth [19,20].…”

Fabrication of superconducting magnesium diboride thin films by electron beam annealing

“…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.…”

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.…”