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Abstract: Scanning tunneling microscopy (STM) is used to investigate surface structures of barium and barium oxide grown on (22× )-reconstructed Au(111) surfaces. Evaporated Ba attaches to the Au herringbones after ultrahigh vacuum (UHV) annealing, forming a stripe pattern. Oxidation of the Ba stripes gives rise to a BaO x structure pinned to the Au herringbones. Conversely, well-ordered epitaxial BaO x structures can be obtained with oxidation of the deposited Ba by residual oxygen and subsequent UHV annealing. The two ordered BaO x phases, a (6×6) and a (2 ×2)-R30° structure, coexist on the surface and lift the Au reconstruction. [Copyright &y& Elsevier]

Strontium titanate is seeing increasing interest in fields ranging from thin-film growth to water-splitting catalysis and electronic devices. Although the surface structure and chemistry are of vital importance to many of these applications, theories about the driving forces vary widely. We report here a solution to the 3×1 SrTiO3(110) surface structure obtained through transmission electron diffraction and direct methods, and confirmed through density functional theory calculations and scanning tunnelling microscopy images and simulations, consisting of rings of six or eight corner-sharing TiO4 tetrahedra. Further, by changing the number of tetrahedra per ring, a homologous series of n×1 (n≥2) surface reconstructions is formed. Calculations show that the lower members of the series (n≤6) are thermodynamically stable and the structures agree with scanning tunnelling microscopy images. Although the surface energy of a crystal is usually thought to determine the structure and stoichiometry, we demonstrate that the opposite can occur. The n×1 reconstructions are sufficiently close in energy for the stoichiometry in the near-surface region to determine which reconstruction is formed. Our results indicate that the rules of inorganic coordination chemistry apply to oxide surfaces, with concepts such as homologous series and intergrowths as valid at the surface as they are in the bulk. [ABSTRACT FROM AUTHOR]

Palladium nanocrystals were grown on a nanostructured SrTiO3(001) surface and annealed in ultrahigh vacuum at 620 °C. This leads to the so-called strong metal−support interaction (SMSI) state, characterized by encapsulation of the metal clusters with an oxide layer. Scanning tunneling microscopy (STM) of the oxide adlayer on the Pd(111) cluster surface reveals two superstructures with different lattice parameters and crystallographic rotations. Interpretation of the STM images is most readily achieved via noncommensurate TiOx surface layers which result in two distinct Moiré patterns. [ABSTRACT FROM AUTHOR]

Atomic resolution scanning tunnelling microscopy of the SrTiO3(0 0 1) surface reveals that certain treatments give rise to two types of self-assembled nanostructures. Surfaces prepared through Ar ion sputtering and ultrahigh vacuum (UHV) annealing up to 900 °C form terraces with straight step edges that have a c(4×2) reconstruction. Following further UHV annealing above 900 °C nanolines of 1 nm width, 0.2 nm height, and variable length are created that run in 〈1 0 0〉 directions. On closest packing the nanolines are 2.4 nm apart and form a (6×2) overlayer. On further annealing the nanolines break up into nanodots of 0.2 nm height that form regular arrays. It is proposed that both structure types are created through non-stoichiometry of the surface region that results in nanocrystalline growth of either SrO or TiOx. SrTiO3 surfaces patterned in this way have the potential to serve as a template for the growth of metallic or semiconducting quantum structures. [Copyright &y& Elsevier]

The growing use of secondary electron imaging in the scanning electron microscope (SEM) to map dopant distributions has stimulated an increasing interest in the mechanism that gives rise to so-called dopant contrast. In this paper a range of experimental results are used to demonstrate the wide applicability of the technique. These results are then incorporated into a model where, in particular, the effect of the surface barrier and the vacuum level are considered. It is found that the dominant contribution to the contrast mechanism is due to the three-dimensional variation of the vacuum level outside the semiconductor. [ABSTRACT FROM PUBLISHER]

Truncated pyramid-shaped Ni nanocrystals were epitaxially grown on SrTiO3(001) surfaces and characterised by scanning tunneling microscopy (STM). These nanocrystals were shown to be catalytically active for the synthesis of carbon nanotubes (CNTs). The narrow size distribution of the Ni nanocrystals results in a similar narrow distribution of CNT diameters. [ABSTRACT FROM AUTHOR]

Substrate mediated ordering and intermolecular interactions are used to create a long-range supramolecular network of perylenetetracarboxylic diimide and melamine on a reconstructed [formula] surface. Scanning tunneling microscopy reveals that the network is composed of a succession of double width honeycomb cell rows separated by a more closely packed row of parallelograms. This periodicity of the supramolecular configuration matches that of the reconstructed gold substrate allowing an epitaxial relationship between network and substrate reconstruction. [ABSTRACT FROM AUTHOR]

In this paper, we report on the use of two PTCDI-melamine supramolecular networks on Au(111) to trap C70 molecules. The different supramolecular networks were formed by changing the postannealing temperature after molecular deposition. We observed, using scanning tunneling microscopy, that the deposition of C70 onto a PTCDI melamine network with parallelogram cavities results in the long-range ordering of paired C70, whereas the deposition of C70 molecules onto a PTCDI-melamine honeycomb network results in the trapping of C70 heptamers. [ABSTRACT FROM AUTHOR]

We have investigated the structure and morphology of self-assembled silver nanocrystals supported on a SrTiO3(001)-(2×1) substrate using scanning tunneling microscopy. Ag forms nanocrystals with five-fold symmetry which have an icosahedral shape. Nanocrystals with point, edge, and face orientation (five-fold, two-fold, and three-fold symmetry, respectively) have been studied. The images of these nanocrystals allow a crystallographic identification of the supported shape of the icosahedral form. [ABSTRACT FROM AUTHOR]

We have investigated the structure and morphology of self-assembled cobalt nanocrystals supported on a SrTiO3(001)-(2×2) substrate using scanning tunneling microscopy. Nanocrystals with a truncated pyramid shape were imaged, allowing crystallographic identification of the cluster facets. These nanocrystals result from the epitaxial growth of fcc Co on SrTiO3(001). The dimension of the nanocrystal facets at equilibrium and an energy minimization calculation result in γadh=(3.96±0.37)J/m2 for the adhesion energy of face-centered-cubic Co/SrTiO3(001)-(2×2). [ABSTRACT FROM AUTHOR]

Scanning tunneling microscopy is used to investigate the appearance of nanoscale islands on the SrTiO3(001) surface following cycles of repetitive annealing. Atomic-resolution images reveal that the surface of the islands is covered by features typical of the anatase TiO2(001) surface reconstruction. Small islands display a mixed (1×4) and (1×5) reconstruction, whereas only the single-domain (1×4) reconstruction is observed on large islands. These results reveal a simple process for the creation of single-domain anatase nanoislands. [ABSTRACT FROM AUTHOR]

We report tight-binding and density functional theory calculations of magnetocrystalline anisotropy energy (MAE) of free Fe (body-centered-cubic) and Co (face-centered-cubic) slabs and nanocrystals. The nanocrystals are truncated square pyramids which can be grown experimentally by deposition of metal on a SrTiO3(001) substrate. For both elements our local analysis shows that the total MAE of the nanocrystals is largely dominated by the contribution of (001) facets. However, while the easy axis of Fe(001) is out-of-plane, it is in-plane for Co(001). This has direct consequences on the magnetic reversal mechanism of the nanocrystals. Indeed, the very high uniaxial anisotropy of Fe nanocrystals makes them a much better potential candidate for magnetic storage devices. [ABSTRACT FROM AUTHOR]

Ultrathin titanium and barium oxide films were grown on SrTiO3(001) substrate surfaces via Ti/Ba deposition and oxidation. When Ti is deposited onto the SrTiO3(001) surface, it forms a series of SrTiO3 surface reconstructions such as c(4×2), , (6×2) and (9×2), which can be controlled by varying the Ti concentration. Epitaxial anatase TiO2(001) islands with (1×3) and (1×5) reconstructions are formed by further increasing the Ti deposition amount and post-annealing. The initial growth of BaO thin films depends on the surface condition of the substrate. BaO nanoparticles form on reconstructed SrTiO3(001), while a locally ordered c(4×4) BaO structure is observed on the disordered sample surface. Co-deposition of Ba and Ti on SrTiO3(001) results in phase separation with the deposited Ba forming BaO nanoparticles and the Ti contributing to Ti-rich SrTiO3 surface reconstructions. No formation of BaTiO3 is observed at the initial growth stages between 0.3 monolayer (ML) and 1.8MLs. [ABSTRACT FROM AUTHOR]

Abstract: Scanning tunneling microscopy (STM) is used to investigate the (001) surface structure of Nb doped SrTiO3 single crystals annealed in ultra high vacuum (UHV). Atomically resolved images of the (2×2) reconstructed surface are obtained after annealing a chemically etched sample. With further annealing dotted row domains appear, which coexist with the (2×2) reconstruction. The expansion of these domains with further annealing gives rise to the formation of a TiO2 enriched c(4×4) reconstruction. [Copyright &y& Elsevier]

High-resolution x-ray photoelectron spectroscopy (XPS) was performed on the surface of 0.7 at.% Nb-doped SrTiO3(00l) decorated with self-assembled linear nanostructures termed dilines, trilines, and tetralines. All three nanoline types share a common side-row feature, while the triline is shown to contain Ti in the 2 + oxidation state as a structural component of the linear backbone. Atomic-resolution scanning tunneling microscopy images and models developed using density functional theory are used to relate the structures to the spectroscopic data, showing that the nanolines consist of a three-layer hill and valley-type structure. Valence band XPS reveals the presence of a well-defined mid-band-gap state at approximately 1 eV, which emerges as a result of nanoline formation. [ABSTRACT FROM AUTHOR]

High resolution X-ray photoelectron spectroscopy (XPS) was performed on the (001) surfaces of Nb-doped and La-doped single crystals of SrTiO3. For the Nb-doped samples the XPS results demonstrate that the fraction of Ti3+ ions increases with increasing Nb dopant concentration. The Nb dopants are shown to be in a 5+ ionization state. Atomic resolution scanning tunneling microscopy (STM) images of the 0.7 at.% Nb-doped SrTiO3(001) surface show that Nb-dopant atoms can be imaged on the surface as bright four-point square clusters. No evidence of Nb segregation to the (001) surface was found under ultrahigh vacuum (UHV) annealing. However, UHV annealing of the 0.7 at.% La-doped SrTiO3(001) samples at 1400 °C for 1 h resulted in La surface segregation as determined by Auger electron spectroscopy. STM on these samples shows that the segregated La results in La-rich linear surface structures. [ABSTRACT FROM AUTHOR]

Abstract: Scanning tunneling microscopy study showed that the (2×2) reconstruction on the (001) surface of SrTiO3 should have a surface structure with a 4-fold symmetry. The previously proposed solution for the (2×2) reconstruction with the p2gm symmetry only has a 2-fold symmetry. In this study density functional theory study was carried out to propose a possible surface structure with the p4mm surface symmetry which matches the scanning tunneling microscopy images and suggests that two different (2×2) surface structures exist. The formation of the (2×2) reconstruction with the p4mm symmetry may be due to the kinetics as it has slightly higher surface energy than the one with the p2gm symmetry. [Copyright &y& Elsevier]

Morphological control of gold nanocrystals is important as their catalytic and optical properties are highly shape dependent. In this paper we report the shapes of gold nanocrystals which deviate from the equilibrium Wulff shape due to the influence of the SrTiO3 single crystal substrates. The gold crystals are characterized by scanning tunneling microscopy (STM) and scanning electron microscopy (SEM). The nanocrystals have an equilibrium shape of a truncated octahedron with {111} and {001} facets. On all three substrate surfaces, i.e., SrTiO3(001)-(2 × 1), SrTiO3(001)-c(4 × 2), and SrTiO3(111)-(4 × 4) + (6 × 6), the height-to-width ratio of the gold crystals is not a constant as would be expected for equilibrium crystals, but instead it increases with crystal height. We propose that as the crystals increase in size, their aspect ratio heightens to relax the interfacial strain. The ratio between the {111} and {001} surface areas of our gold crystals is found to differ on the three substrates, which we speculate is due to the selective adsorption of surfactants on the {111} and {001} gold facets resulting from the different substrate surfaces. Reentrant facets of gold crystals that should be present according to their Wulff shape are not observed because these concave sites typically grow out due to kinetic considerations. This study demonstrates the significant effect of the crystal facet termination and surface reconstruction of an oxide substrate on the shape of supported gold nanocrystals.