Fig. 1: Schematic of the band structure and estimation of La/Al ratio using XPS.
From: Stoichiometric control of electron mobility and 2D superconductivity at LaAlO3-SrTiO3 interfaces
a Schematic illustration of LaAlO3/SrTiO3 (LAO/STO) heterostructure with two-dimensional electron gas (2DEG) at the interface. The zoomed-in view highlights the interfacial region of the crystal structure where the 2DEG exists. b, c Sketch of the quantum well in real and momentum space, respectively. Three non-degenerate t2g orbitals split due to the confinement potential: the dxz/yz orbitals (blue) are shifted higher in energy compared to the dxy orbitals (red). The conduction electrons, corresponding to dxy orbitals, are closer to the interface, exhibiting lower electron mobility compared to the mobility for dxz/yz orbitals, which extend deeper into the STO. d The reflection high-energy electron diffraction (RHEED) intensity as a function of time, depicting a layer-by-layer growth, from which thickness can be inferred for the LaAlO3 layer. e RHEED patterns obtained during the pulsed laser deposition (PLD) growth show a smooth film deposition. f Atomic force microscopy (AFM) topography images of a film. The well-aligned terraces indicate the surface smoothness. Scale bar: 500 nm. g The XPS spectra for all films. h The modulation of sheet resistance at room temperature as a function of the ratio of La/Al extracted from XPS spectra. i La/Al ratio in different samples extracted from scanning transmission electron microscopy coupled with electron energy-loss spectroscopy (STEM-EELS) and X-ray photoelectron spectroscopy (XPS) analysis.
