Abstract text (incl. figure legends and references)

<Introduction and objectives>

Recently, we reported on the anisotropic electron orbital mapping of oxygen 2p-state in SrTiO₃ using STEM-ELNES mapping [1]. It is important to understand the origin of shape in ELNES mapping for further development of this field because even conventional elemental maps with the intensity of a wide energy region of ELNES, can generate artifacts, for instance due to volcano effect [2], delocalization of inelastic scattering [3] and so on. Here, we report different image contrasts between atomic resolution HAADF and EELS mapping in rutile TiO₂ due to the unique electron channeling and the difference of scattering potentials.

<Materials and method>

HAADF images and EELS spectra (Ti L_2,3- and O K-ELNES) were simultaneously obtained along [001] axis of rutile TiO₂ by spectrum imaging (SI) mode using a JEOL ARM200F operated at 60 kV. The well averaged dark reference was subtracted from the SI data to randomize the dark noise [4]. Next, the distorted SI data were corrected using a non-rigid registration technique [5]. Finally, more than six thousand templates of SI data were accumulated to improve S/N ratio. μSTEM software was used to calculate HAADF image, elemental maps (Ti L_2,3- and O K-edges) and probe propagation in the TiO₂ crystal [6].

<Results>

The elemental maps of Ti and O visualize each elemental site with atomic resolution and the O map exhibits projected octahedral structures rotating 90 degrees for their neighbors (Fig. 1 (e, f)). The Ti L_2,3 map shows an anisotropic ellipsoidal distribution extending along the axial bonds of the projected octahedral structure, while Ti atomic columns in the HAADF image do not show such anisotropy (Fig. 1 (d)). The simulated images agree well with the experimental images (Fig. 1 (g-i)). Probe propagation inside of the TiO₂ crystal was also simulated and revealed that the causes of the anisotropic intensity distribution of Ti L_2,3-signal are the unique channeling effects of the rutile structure and the differences of scattering potential between HAADF and EELS.

<Conclusion>

It has elucidated that the channeling effects could influence on the shape of atomic contrast in elemental mapping by STEM-EELS. Therefore, it is important to well understand the origin of the shape of image contrasts in elemental and orbital mapping for correct interpretation.

<Reference>

[1] C. Iwashimizu, M. Haruta and H. Kurata, Appl. Phys. Lett. 119, (2021) 232902

[2] A. J. D"Alfonso, S. D. Findlay, M. P. Oxley and L. J. Allen, Ultramicroscopy, 108 (2008) 677

[3] P. Wang, A. J. D"Alfonso, S. D. Findlay, L. J. Allen and A. L. Bleloch, Phys. Rev. Lett. 101 (2008) 236102

[4] M. Haruta, Y. Fujiyoshi, T. Nemoto, A. Ishizuka, K. Ishizuka and H. Kurata, Ultramicroscopy, 207 (2019) 112827

[5] L. Jones, H. Yang, T.J. Pennycook, M.S.J. Marshall, S. Van Aert, N.D. Browning, M. R. Castell and P. D. Nellist, Advanced Structural and Chemical Imaging, 1 (2015) 8

[6] L.J.Allen, A.J.D׳Alfonso and S.D.Findlay, Ultramicroscopy, 151 (2015) 11

<Acknowledge>

This work was supported by Kakenhi Grants-in-Aid No. 22H01956 from the Japan Society for the Promotion of Science (JSPS)

<Figure legend>

Figure 1 (a) Crystal structure of rutile TiO₂. (b) Crystal structure projected along [001] axis. (c) EELS spectrum. (d) Experimental HAADF image, (e) Ti-L_2,3 map and (f) O-K map, respectively. (g-j) Simulated images corresponding to (d-f).