Cross-Sectional Scanning Tunneling Microscopy for Complex Oxide Interfaces

Cross-sectional scanning tunneling microscopy (XSTM) is developed for studying the interfaces of the complex oxide heterostructures. Since most of the complex oxide materials have a perovskite structure, which does not have cleavage plane, it posed an experimental challenge for utilizing STM on the fractured surfaces. A well-controlled method for fracturing non-cleavable materials was developed by using the common subtrate: Nb-doped SrTiO3 (Nb:STO). Through systematically studies on the control of the fracturing conditions, on the tip-sample interactions and on the resulting fractured surfaces of Nb:STO, atomic flat terraces are routinely created and stable measurements are achieved. By harnessing the well-controlled fracturing method and the well-controlled tip conditions to a thin film system, La2/3Ca1/3MnO3/Nb:STO (LCMO/Nb:STO), XSTM as well as the ability of cross-sectional scanning tunneling spectroscopy (XSTS) directly revealed the band diagram mapping across the interface. The novel developed, well-controlled XSTM/S for the interfaces of complex oxide heterostructures opened a door for accurate determination of local electronic properties across and at the interface.