Role of point and line defects on the electronic structure of LaAlO3/SrTiO3 interfaces

Abstract

Realization of heterostructures containing multiple two-dimensional electron liquids requires a fine control of the fabrication process. Here, we report a structural and spectroscopy study of LaAlO3/SrTiO3/LaAlO3 trilayers grown on the SrTiO3 substrate by pulsed-laser deposition. Scanning transmission electron microscopy with the help of ab initio calculations reveals that antisite defects associated with oxygen vacancies are primarily present in the SrTiO3 film (STO-f) close to the p-type interface (STO-f/LaAlO3), while oxygen vacancies prevail close to the top n-type interface (LaAlO3/STO-f). At the same interface, misfit dislocations relax the tensile strain of the top LaAlO3 layer. Combining x-ray absorption spectroscopy, x-ray linear dichroism, resonant photoemission spectroscopy, and electron energy loss spectroscopy, we observe that the 3d orbital reconstruction at the interface between LaAlO3 and the SrTiO3 substrate is confined over a few interfacial Ti planes while, at the top n-type interface (LaAlO3/STO-f), the absence of a dichroic signal can be related to the blurring of the interfacial orbital reconstruction due to the heterogeneity of defects.

Near-Atomic-Scale Mapping of Electronic Phases in Rare Earth Nickelate Superlattices

“…Compared to the aforementioned techniques, an atomic-resolution electron probe is used to scan the films under study and the transmitted electrons are collected by multiple detectors, each one providing complementary structural, chemical, and electronic information. STEM-EELS has already been demonstrated to be a powerful tool that can identify electronic state modulations occurring in specific lattice positions of transition metal oxide heterostructures. − For instance, this technique enabled the identification of local valence modulations occurring at the interfaces of LaNiO 3 -based heterostructures induced by charge transfer effects. ,, In our study, however, since the Ni valence changes neither across the MIT nor from one nickelate compound to another, we also do not expect it to vary across the different electronic domains. Our approach is instead based on locally assessing electronic properties by looking at specific fingerprints, buried in the O K and Ni L edge fine structures, which are characteristic of the distinct electronic phases, as previously observed in X-ray absorption spectroscopy (XAS) experiments. ,,− Here we demonstrate that this is possible, reaching around 3.5 Å spatial resolution.…”

Electrical characterization and extraction of activation energies of the defect states in the LaAlO3/SrTiO3 heterostructure

“…For example, A. Kalabukhov et al observed the impact of oxygen vacancies on the electrical properties using cathode and photoluminescence techniques. 52 N. Palina et al showed oxygen orbital states using X-ray spectroscopies, 44 A. Gloter et al observed the distribution of point defects at the interface using scanning transmission electron microscopy 53 and G. Yuan et al reported on the behavior of oxygen vacancies at the LaAlO3/SrTiO3 heterostrucutre using positron annihilation spectroscopy. 54 In our work we extracted defect properties that cannot be accessed using these methods, such as the activation energies and capture cross-sections of the defect states using Deep-Level Transient Fourier Spectroscopy (DLTFS).…”

Identifying Ionic and Electronic Charge Transfer at Oxide Heterointerfaces

“…The highly complex interplay of local defect structure and strongly confined electronic structure can induce multiple electronic and ionic phenomena at oxide interfaces. [1,2,[15][16][17][18][19][20] One prime example of such an interface is the LaAlO 3 /SrTiO 3 (LAO/STO) heterointerface where the polar nature of LAO induces charge transfer into the neighboring STO, generating a 2D-electron-gas (2DEG) at the interface of the two nominally insulating compounds. [15,[21][22][23] Free electrons are generated without local dopants.…”