Spontaneous morphology and phase modification driven by sequence of deposition in superconducting Ni–Bi bilayers

Shape resonances and the T c dependence on film thickness of Ni/Bi systems

“…As reported by Liu et al [7] and discussed in section 3, the volume contraction favors the formation of NiBi 3 with its final morphology strongly affected by the sequence of deposition. To avoid this the NiyBi6y and Ni3Bix samples were prepared such that Bi is firstly deposited followed by Ni.…”

“…However part of the deposited Bi may not react and remain left until the very end of the reaction. The volume contraction caused by the conversion of Ni and Bi into NiBi 3 at the interface has been reported by Liu et al in [7]. It can be explained when considering the equations for the conservation of the number of atoms and the mass.…”

“…The densities are well known in the literature [7]: η n =8.91 g cm −3 , η b = 9.78 g cm −3 and η nb = 10.9 g cm −3 . The molar masses are M n = 58.69 g mol −1 and M b = 208.98 g mol −1 , thus the above equations turn into the following ones:…”

“…Recently we have shown that this process at the interface is thermodynamically favored by volume contraction. The morphology of the final layer strongly depends on the sequence of deposition [7].…”

“…Shape resonances were proposed long ago by Thompson and Blatt [20,21] and are manifest in thin superconducting films as oscillations of the critical temperature with respect to the film thickness. Shape resonances have been theoretically studied [22,23] and have been observed in epitaxially grown Pb films in the ultrathin regime [5][6][7][8][9][10][11][12][13][14][15][16][17][18]] [24,25] and also in distinct nanoparticles of Pb, Sn and V [26][27][28]. However, apart of the above cited publications, shape resonances have not been reported for other superconducting nanofilms, although they have been searched for in many others, such as in Nb films [29].…”