Thickness Dependence of Ti Buffer Layers for Fabricating As-Grown MgB2 Films

In this study, we have investigated the effects of Ti buffer layer for the fabrication of MgB₂ crystalline film on ZnO (0001) substrate. The Ti buffer layers (thickness of 5-50 nm) and MgB₂ films were deposited by molecular beam epitaxy apparatus. The MgB₂/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 MgB₂ 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.