Visualizing nanoscale electronic band alignment at the ${\text{La}}_{2/3}{\text{Ca}}_{1/3}{\text{MnO}}_3/\text{Nb}:{\text{SrTiO}}_3$ interface

Cross-sectional scanning tunneling microscopy and spectroscopy (XSTM/S) were used to map out the band alignment across the complex oxide interface of ${\text{La}}_{2/3}{\text{Ca}}_{1/3}{\text{MnO}}_3/\text{Nb}$-doped ${\text{SrTiO}}_3$. By a controlled cross-sectional fracturing procedure, unit-cell high steps persist near the interface between the thin film and the substrate in the noncleavable perovskite materials. The abrupt changes in the mechanical and electronic properties were visualized directly by XSTM/S. Using changes in the density of states as probe by STM, the electronic band alignment across the heterointerface was mapped out providing an approach to directly measure the electronic properties at complex oxide interfaces.

Figure 1

(Color online) (a) The schematic atomic arrangement near the heterointerface of LCMO and STO. (b) Optical microscopy image of fractured LCMO/Nb:STO surface. (c) SEM image with same scale as in (b). (d) A magnified SEM image, which reveals contrast between thin film (LCMO) and substrate (Nb:STO).

Figure 2

(Color online) (a) Topography measured by STM at sample edge. (b) $dI/dV$ recorded simultaneously with the topography with set point as 3.0 V; 20 pA. (c) SEM image with the same scale at sample edge. (d) $dI/dV$ curves measured at points A, B, and C, indicated in (b), on LCMO, ${\text{TiO}}_2$- and SrO-terminated Nb:STO, respectively.

Figure 3

(Color online) LDOS mapping at $-2.5\text{V}$ distinguishes LCMO and Nb:STO electronically.

Figure 4

(Color online) (a) Averaged $dI/dV$ curves measured along from LCMO crossing the interface into Nb:STO, as indicated with an arrow in Fig. 3 and (b) experimental band diagram across LCMO/Nb:STO interface. The Fermi energy is indicated as the dashed line at zero bias. The CBM and VBM were obtained from each individual $dI/dV$ curve. The average values and errors are marked as open red circles and error bars, respectively, connected with lines, which shows the band mapping across the LCMO/Nb:STO interface.