Scanning probe microscopy of oxide surfaces: atomic structure and properties

Abstract

The intersection of two fields, oxide surface science and scanning probe microscopy (SPM), has yielded considerable insight on atomic processes at surfaces. Oxide surfaces, especially those containing transition metals, offer a rich variety of structures and localized physical phenomena that are exploited in a wide range of applications. Nonlinear optics, superconductivity, ferroelectricity and chemical catalytic activity are but a few. Furthermore, the challenges and solutions associated with the chemistry of these surfaces and particularly the solutions to these problems have led to important understanding of tip-surface interactions that can inform SPM studies of all materials. Here, the development of understanding of the model systems TiO 2 and SrTiO 3 are considered in detail, to demonstrate the role of nonstoichiometry in surface structure evolution and the approach to interpreting structure at the atomic level. Then a combination of scanning tunneling microscopy, noncontact atomic force microscopy and theory are applied to a variety of oxide systems including Al 2 O 3 , NiO, ferroelectric BaTiO 3 , tungstates and molybdates. Recently developed sophisticated probes of local properties include spin-polarized tunneling, Fourier mapping of charge density waves, band gap mapping of superconductors and ultra fast imaging of atomic diffusion. The impact of these studies on our understanding of the behavior of oxides and of tip-surface interactions is summarized.

Charge stripe order near the surface of 12-percent doped La2−xSrxCuO4

“…Our finding may, for example, help to relate the apparent similarities in the Fermi-surfaces of LNSCO 34 and LSCO 35 to the different superconducting properties of these compounds. In scanning tunnelling spectroscopy experiments, spatial modulations of the local density of states have been observed for different cuprate systems 37,38 . For 12-per cent doped LSCO spatial modulations on different length scales have been observed 39 ; for the interpretation of these, the existence of charge stripes may matter 40 .…”

Atomically Precise Lateral Modulation of a Two-Dimensional Electron Liquid in Anatase TiO2 Thin Films

“…Lateral confinement was achieved in a top-down approach and exploited in nano-electronic devices 10,11 . On the other hand, bottom-up microscopic electronic structure engineering based on intrinsic atomic scale lateral reconstructions, which are ubiquitous 18,19 in oxides, has received little attention.…”

Atomic and electronic structures of single-layer FeSe on SrTiO3(001): The role of oxygen deficiency

“…Even though a number of reconstructions have been observed on the SrTiO 3 (001) surface [24][25][26], we focused on the so-called double-layer-TiO 2 (2×1) surfaces [27,28] because other more complex surfaces are not compatible with the (2×1) reconstruction under study here. It has been found that, on the double-layer-TiO 2 (2×1) surface, the role of O vacancy is the same as that in the missingrow structure described above.…”