Strontium oxide segregation at SrLaAlO4 surfaces

We report observable segregation of strontium oxide at the surface of strontium lanthanum aluminate single-crystals annealed in oxidizing conditions. Electron microscopy imaging and energy-dispersive X-ray spectroscopy showed that Sr and O segregation occurs on strontium lanthanum aluminate surfaces in the form of polycrystalline islands. The appearance of islands on the (100) and other high-free energy surfaces is strongly suggestive of rocksalt SrO formation. The loss of strontium oxide from the bulk is not compensated solely by point defects, but rather by non-stoichiometric stacking faults which locally result in stable perovskite structures.     

Water adsorption on SrTiO3(001): I. Experimental and simulated STM

Density functional theory-based simulations of scanning tunneling micrographs were used for comparison to published experimental images of reconstructed SrTiO₃(001) surfaces. It was found that the addition of dissociatively adsorbed H₂O to the presently accepted structural solution of the 2 × 1 reconstruction is more consistent with the experimental data. A proposed model for the c(4 × 4) reconstruction, based on the hydrated 2 × 1 structure, agrees well with experiment and is consistent with a formation process consisting of the simple dehydration of a wet 2 × 1 structure.     

Water adsorption on SrTiO3(001): II. Water,water, everywhere

The role of water adsorption on Ti-rich SrTiO₃(001) surface reconstructions is studied. Density functional calculations with hybrid functionals of numerous adsorption configurations indicate that the relative stability of the different reconstructions is strongly altered by the addition of water, with all the reconstructions having comparable energy for half-monolayer coverage, most with a fair degree of hydrogen bonding. This strongly suggests that which reconstruction is observed depends upon a competition between the kinetics of ordering and dehydration. X-ray photoelectron spectra are consistent with the theoretical predictions for the dehydration of the 2 × 1 and c(4 × 2) reconstructions.     

Preparative isolation of (+)-beta-eudesmol fromAmyris balsamifera

Summary Optically pure (+)-beta-eudesmol is a possible starting material for the synthesis of several termite defense compounds. A two step procedure for the isolation of gram quantities of (+)-beta-eudesmol from commercially availableAmyris balsamifera oil (syn. West Indian sandalwood oil), containing 8% beta-eudesmol, was developed. Step one consisted of an efficient vacuum distillation of the total oil. Step two was a medium pressure LC separation with an AgNO₃ impregnated silica gel stationary phase. Several other separation procedures failed due to the presence of many closely related sesquiterpene alcohols (75% of the oil).     

HTMoL: full-stack solution for remote access,visualization, and analysis of molecular dynamics trajectory data

Research on biology has seen significant advances with the use of molecular dynamics (MD) simulations. The MD methodology enables explanation and discovery of molecular mechanisms in a wide range of natural processes and biological systems. The need to readily share the ever-increasing amount of MD data has been hindered by the lack of specialized bioinformatic tools. The difficulty lies in the efficient management of the data, i.e., in sending and processing 3D information for its visualization. In this work, we present HTMoL, a plug-in-free, secure GPU-accelerated web application specifically designed to stream and visualize MD trajectory data on a web browser. Now, individual research labs can publish MD data on the Internet, or use HTMoL to profoundly improve scientific reports by including supplemental MD data in a journal publication. HTMoL can also be used as a visualization interface to access MD trajectories generated on a high-performance computer center directly. Furthermore, the HTMoL architecture can be leveraged with educational efforts to improve learning in the fields of biology, chemistry, and physics.     

Vacant-site octahedral tilings on SrTiO(3) (001), the (sqrt[13]×sqrt[13])R33.7° surface, and related structures

The structure of the SrTiO(3) (001) (sqrt[13]×sqrt[13])R33.7° surface reconstruction has been determined using transmission electron diffraction combined with direct methods and density functional theory. It has a TiO(2)-rich surface with a 2D tiling of edge or corner-sharing TiO(5)□ octahedra. Additionally, different arrangements of these octahedral units at the surface, dictated by local bond-valence sums, form 2D networks that can account for many ordered surface reconstructions as well as disordered glasslike structures consistent with the multitude of structures observed experimentally, and potentially other materials and interfaces.     

c(4 × 2) and related structural units on the SrTiO3(001) surface: scanning tunneling microscopy, density functional theory, and atomic structure

Density functional theory is used to simulate high-bias, constant-current scanning tunneling micrographs for direct comparison with experimental images. Coupled to previous spectroscopic data, these simulations are used to determine the atomic structure of Ti-rich nanostructures on strontium titanate (001) surfaces. These nanostructures have three consecutive TiO(x) surface layers and exploit the distinctive structural motif of the c(4 × 2) reconstruction as their main building block. A structural model of a characteristic triline defect is also proposed.     

Surface and defect structure of oxide nanowires on SrTiO3

Processing the SrTiO(3)(001) surface results in the self-assembly of reduced titanate nanowires whose widths are approximately 1 nm. We have imaged these nanowires and their defects at elevated temperatures by atomic resolution scanning tunneling microscopy. The nanowire structure is modeled with density functional theory, and defects observed in the center of the nanowire are determined to be Ti(4)O(3) vacancy clusters. The activation energy for Ti(4)O(3) vacancy cluster diffusion is explicitly measured as 4.98±0.17 eV with an exponential prefactor of μ=6.57×10(29) (s(-1).