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Register a new userEvolution of the Surface Structures on SrTiO$_3$(110) Tuned by Ti or Sr Concentration
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The surface structure of the SrTiO$_3$(110) polar surface is studied by scanning tunneling microscopy and X-ray photoelectron spectroscopy. Monophased reconstructions in (5$times$1), (4$times$1), (2$times$8), and (6$times$8) are obtained, respectively, and the evolution between these phases can be tuned reversibly by adjusting the Ar$^{+}$ sputtering dose or the amount of Sr/Ti evaporation. Upon annealing, the surface reaches the thermodynamic equilibrium that is determined by the surface metal concentration. The different electronic structures and absorption behaviors of the surface with different reconstructions are investigated.
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The interaction of water with oxide surfaces is of great interest for both fundamental science and applications. We present a combined theoretical [density functional theory (DFT)] and experimental [Scanning Tunneling Microscopy (STM), photoemission spectroscopy (PES)] study of water interaction with the two-dimensional titania overlayer that terminates the SrTiO$_3$(110)-(4$times$1) surface and consists of TiO$_4$ tetrahedra. STM, core-level and valence band PES show that H$_2$O neither adsorbs nor dissociates on the stoichiometric surface at room temperature, while it dissociates at oxygen vacancies. This is in agreement with DFT calculations, which show that the energy barriers for water dissociation on the stoichiometric and reduced surfaces are 1.7 and 0.9 eV, respectively. We propose that water weakly adsorbs on two-dimensional, tetrahedrally coordinated overlayers.
The many surface reconstructions of (110)-oriented lanthanum--strontium manganite (La$_{0.8}$Sr$_{0.2}$MnO$_3$, LSMO) were followed as a function of the oxygen chemical potential ($mu_text{O}$) and the surface cation composition. Decreasing $mu_text{O}$ causes Mn to migrate across the surface, enforcing phase separation into A-site-rich areas and a variety of composition-related, structurally diverse B-site-rich reconstructions. The composition of these phase-separated structures was quantified with scanning tunneling microscopy (STM), and these results were used to build a 2D phase diagram of the LSMO(110) equilibrium surface structures.
The authors report on the crystallographic orientation dependence of the Schottky properties for heterojunctions between a half-metallic ferromagnet La$_0.6$Sr$_0.4$MnO$_3$ (LSMO) and Nb-doped SrTiO3 semiconductor. The Schottky barrier height determined by in situ photoemission measurements is independent for the substrate orientations (001) and (110), while the magnetic properties of LSMO (110) films are more enhanced than for (001) films. These results suggest that the performance of magnetic devices based on ferromagnetic manganite is improved by using (110)-oriented substrates.
We have performed angle resolved photoemission spectroscopy (ARPES) experiments on the surface states of SrTiO$_3$(001) using linearly and circularly polarized light to investigate the subband structures of out-of-plane $d_{xz/yz}$ orbitals and chiral orbital angular momentum (OAM). The data taken in the first Brillouin zone reveal new subbands for $d_{xz/yz}$ orbitals with Fermi wave vectors of 0.25 and 0.45 $mathrm{AA}^{-1}$ in addition to the previously reported ones. As a result, there are at least two subbands for all the Ti 3d t$_{2g}$ orbitals. Our circular dichroism ARPES data is suggestive of a chiral OAM structure in the surface states and may provide clues to the origin of the linear Rashba-like surface band splitting.
The surfaces of perovskite oxides affect their functional properties, and while a bulk-truncated (1$times$1) termination is generally assumed, its existence and stability is controversial. Here, such a surface is created by cleaving the prototypical SrTiO$_3$(001) in ultra-high vacuum, and its response to thermal annealing is observed. Atomically resolved nc-AFM shows that intrinsic point defects on the as-cleaved surface migrate at temperatures above 200,$^circ$C. At 400--500,$^circ$C, a disordered surface layer forms, albeit still with a (1$times$1) pattern in LEED. Purely TiO$_2$-terminated surfaces, prepared by wet-chemical treatment, are also disordered despite their (1$times$1) periodicity in LEED.
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