Ion beam assisted deposition of superconducting MgB2 thin films

Abstract We studied the structural and superconducting properties of MgB 2 thin films, deposited by co-evaporation of magnesium and boron in the presence and absence of an ion beam followed by ‘in-situ’ and ‘ex-situ’ annealing. The MgB 2 films were capped with a Mg and a B layer to provide an additional Mg source in the following annealing step and to prevent diffusion of Mg out of the films. Films deposited with an ion beam showed lower transition temperature ( T c 21 K), whereas MgB 2 films deposited without an ion beam showed a T c as high as 30.6 K. Third order susceptibility measurements demonstrated homogeneous MgB 2 films. Rutherford backscattering (RBS) measurements showed low oxygen concentration throughout the film. For ‘ex-situ’ annealed MgB 2 film transition temperatures up to 33.5 K are obtained. X-Ray diffraction suggests some degree of c -axis alignment, but omega scans showed random orientation. MgB 2 film on sapphire substrates always revealed a higher T c than the ones on silicon substrates. However, T c on silicon substrates was as high as 22.5 K.