Detecting the direction of oxygen bonding in SrTiO3

Abstract

The near-edge fine structure of an ionization edge in electron energy-loss spectroscopy provides bonding and elemental information. We investigate the fine structure of the O K edge in SrTiO 3 , where the oxygen atoms have identical local bonding environments in three dimensions but differ in their two-dimensional projection. By removing the effects of elastic and thermal diffuse scattering in experimental data, we demonstrate a small difference between the O columns that are nonequivalent in projection, which was not evident before the removal of scattering of the probing electrons. We explore the robustness of this method to the uncertainty in various experimental parameters.

Probing core-electron orbitals by scanning transmission electron microscopy and measuring the delocalization of core-level excitations

“…Core-level orbitals can be determined by deconvolving channeled STEM probes from source-removed EDX maps, a notion that has also been discussed by others [16,18]. The EDX intensity for a given probe position can be evaluated as the convolution of depth-integrated channeling intensity for that probe position with the orbital excitation potential.…”

“…With the advent of aberration-correction [9,10], sub-angstrom STEM electron beams can be combined with EDX or electron energy-loss spectroscopy (EELS) to rapidly map solids with crisp atomic resolution [11][12][13][14]. Efforts to retrieve sub-atomic information from STEM-EELS spectrum images have been made [15,16], and the concept that core-level orbital information can be determined by deconvolving channeled STEM probes from spectrum images has also been discussed [16][17][18][19], both led by Allen and coworkers. However, acquiring experimental low-noise, atomic-resolution maps for such analyses has been challenging, and the outcomes have been suitable only for basic qualitative interpretation.…”

Atomically Resolved EELS Elemental and Fine Structure Mapping via Multi-Frame and Energy-Offset Correction Acquisition

“…We demonstrate that the energy-offset correction method reduces the correlated noise and helps resolve weak features of the near-edge fine structures. The final SI with improved SNR enables the extraction of individual component maps of the Ti-L 2,3 near-edge fine structure and of a Ti-O-Ti bonding direction map at atomic resolution in SrTiO 3 (Figure 2), which has been theoretically predicted but extremely difficult to detect experimentally due to the poor SNR of the spectrum [4]. Combining multi-frame SI and auto energy-offset-correction we demonstrate that these techniques will open new opportunities for atomically-resolved EELS fine structure mapping.…”

Real-space mapping of electronic orbitals

“…1c). Given the initial state, it is furthermore possible to obtain both the angular and the radial dependence of the final states [19,23,24] and, thus, bonding information on individual atomic columns [15,25]. To that end, specific transitions can be selected by using a sufficiently narrow energy range.…”

“…Owing to these two techniques, tremendous progress has been made over the last decade in mapping atom positions with ≈ 10 pm accuracy [2-4], determining charge densities [5][6][7], and performing atom-by-atom chemical mapping [8][9][10][11][12]. Furthermore, the fine-structures of the spectra allow the determination of the local chemical and structural environment as well as the hybridisation state of the scattering atoms [11][12][13][14][15][16][17][18] in the bulk, which can be substantially different from the surface states probed by STM. This suggests to use the EELS signal to probe the local environment in real-space and map, e.g., crystal fields, conduction states, bonds, and orbitals.…”