Thickness Dependence of Ti Buffer Layers for Fabricating As-Grown ${\rm MgB}_{2}$ Films

In this study, we have investigated the effects of Ti buffer layer for the fabrication of MgB
₂
crystalline film on ZnO (0001) substrate. The Ti buffer layers (thickness of 5-50 nm) and MgB
₂
films were deposited by molecular beam epitaxy apparatus. The MgB
₂
/Ti bilayers were characterized by in-situ RHEED and ex-situ XRD measurements, and the superconducting properties were studied by magnetic measurements using SQUID magnetometer. It is found that Ti layers were grown epitaxially on the substrates and the MgB
₂
films were c-axis oriented with two types of in-plane rotational domains. The crystallinity reflected on the rocking curve width and the superconducting transition temperature T
_c
were enhanced with increasing the thickness of Ti buffer layer. The highest T
_c
in this study was obtained to be 37 K when the Ti buffer layer thickness is 50 nm.