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Register a new userQuasiparticle interference on cubic perovskite oxide surfaces
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We report the first observation of coherent surface states on cubic perovskite oxide SrVO3(001) thin films through spectroscopic imaging scanning tunneling microscopy. A direct link between the observed atomic-scale interference patterns and the formation of a dxy-derived surface state is supported by first-principles calculations. Furthermore, we show that the apical oxygens on the topmost VO2 plane play a critical role in controlling the spectral weight of the observed coherent surface state.
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Epitaxial strain is a proven route to enhancing the properties of complex oxides, however, the details of how the atomic structure accommodates strain are poorly understood due to the difficulty of measuring the oxygen positions in thin films. We present a general methodology for determining the atomic structure of strained oxide films via x-ray diffraction, which we demonstrate using LaNiO3 films. The oxygen octahedral rotations and distortions have been quantified by comparing the intensities of half-order Bragg peaks, arising from the two unit cell periodicity of the octahedral rotations, with the calculated structure factor. Combining ab initio density functional calculations with these experimental results, we determine systematically how strain modifies the atomic structure of this functional oxide.
The energetics of vicinal SrTiO$_3$(001) and DyScO$_3$(110), prototypical perovskite vicinal surfaces, has been studied using topographic atomic force microscopy imaging. The kink formation and strain relaxation energies are extracted from a statistical analysis of the step meandering. Both perovskite surfaces have very similar kink formation energies and exhibit a similar triangular step undulation. Our experiments suggest that the energetics of perovskite oxide surfaces is mainly governed by the local oxygen coordination.
In this paper, we report the electrical and structural properties of the oxide-based metal/ferroelectric/metal (MFM) junctions. The heterostructures are composed of ultrathin layers of La0.7Ca0.3MnO3 (LCMO) as a metallic layer and, BaTiO3 (BTO) as a ferroelectric layer. Junction based devices, having the dimensions of 400 x 200 micom2, have been fabricated upon LCMO/BTO/LCMO heterostructures by photolithography and Ar-ion milling technique. The DC current-voltage (I-V) characteristics of the MFM junctions were carried out. At 300 K, the devices showed the linear (I-V) characteristics, whereas at 77 K, (I-V) curves exhibited some reproducible switching behaviours with well-defined remnant currents. The resulting resistance modulation is very different from what was already reported in ultrathin ferroelectric layers displaying resistive switching. A model is presented to explain the datas
We report an experimental and theoretical analysis of the sqrt(3)x sqrt(3)-R30 and 2x2 reconstructions on the NiO (111) surface combining transmission electron microscopy, x-ray photoelectron spectroscopy, and reasonably accurate density functional calculations using the meta-GGA hybrid functional TPSSh. While the main focus here is on the surface structure, we also observe an unusual step morphology with terraces containing only even numbers of unit cells during annealing of the surfaces. The experimental data clearly shows that the surfaces contain significant coverage of hydroxyl terminations, and the surface structures are essentially the same as those reported on the MgO (111) surface implying an identical kinetically-limited water-driven structural transition pathway. The octapole structure can therefore be all but ruled out for single crystals of NiO annealed in or transported through humid air. . The theoretical analysis indicates, as expected, that simple density functional theory methods for such strongly-correlated oxide surfaces are marginal, while better consideration of the metal d-electrons has a large effect although, it is still not perfect.
Strain engineering with different substrate facets is promising for tuning functional properties of thin film perovskite oxides. By choice of facet, different surface symmetries and chemical bond directions for epitaxial interfaces can be tailored. Here, preparation of well-defined pseudo-cubic (111)-oriented orthorhombic substrates of DyScO3 , GdScO3 , and NdGaO3 is reported. The choice of orthorhombic facet, (011)o or (101)o , both corresponding to pseudo-cubic (111)pc , gives vicinal surfaces with single or double (111pc layer terrace step heights, respectively, impacting subsequent thin film growth. Orthorhombic LaFeO3 epitaxy on the (101)o facet reveals a distinction between alternating (111)pc layers, both during and after growth. The observed differences are explained based on the oxygen octahedral tilt pattern relative to the two orthorhombic (111)pc surfaces. This robust structural detail in the orthorhombic perovskite oxides enables utilisation of different (111)pc facets for property engineering, through polyhedral connectivity control and cation coordination at epitaxial interfaces.
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