Ultracompact Electrical Double Layers at TiO(110) Electrified Interfaces.

Metal-oxide aqueous interfaces are important in areas as varied as photocatalysis and mineral reforming. Crucial to the chemistry at these interfaces is the structure of the electrical double layer formed when anions or cations compensate for the charge arising from adsorbed H or OH. This has proven extremely challenging to determine at the atomic level.

Extending the novel |ρ|-based phasing algorithm to the solution of anomalous scattering substructures from SAD data of protein crystals.

Owing to the importance of the single-wavelength anomalous diffraction (SAD) technique, the recently developed |ρ|-based phasing algorithm (S) incorporating the inner-pixel preservation (ipp) procedure [Rius & Torrelles (2021). Acta Cryst A77, 339-347] has been adapted to the determination of anomalous scattering substructures and its applicability tested on a series of 12 representative experimental data sets, mostly retrieved from the Protein Data Bank. To give an idea of the suitability of the data sets, the main indicators measuring their quality are also given.

A new density-modification procedure extending the application of the recent |ρ|-based phasing algorithm to larger crystal structures.

The incorporation of the new peakness-enhancing fast Fourier transform compatible ipp procedure (ipp = inner-pixel preservation) into the recently published S algorithm based on |ρ| [Rius (2020). Acta Cryst A76, 489-493] improves its phasing efficiency for larger crystal structures with atomic resolution data. Its effectiveness is clearly demonstrated via a collection of test crystal structures (taken from the Protein Data Bank) either starting from random phase values or by using the randomly shifted modulus function (a Patterson-type synthesis) as initial ρ estimate.

Growth-mode and interface structure of epitaxial ultrathin MgO/Ag(001) films.

MgO ultrathin films are of great technological importance as electron tunneling barrier in electronics and spintronics, and as template for metallic clusters in catalysis and for molecular networks for 2D electronics. The wide band-gap of MgO allows for a very effective decoupling from the substrate. The films morphology and the detailed structure of the interface are crucial for applications, controlling the electronic transfer.

Pristine and hydrated fluoroapatite (0001).

The surface structure of fluoroapatite (0001) (FAp) under quasi-dry and humid conditions has been probed with surface X-ray diffraction (SXRD). Lateral and perpendicular atomic relaxations corresponding to the FAp termination before and after HO exposure and the location of the adsorbed water molecules have been determined from experimental analysis of the crystal truncation rod (CTR) intensities. The surface under dry conditions exhibits a bulk termination with relaxations in the outermost atomic layers.

Water-Induced Reversal of the TiO(011)-(2 × 1) Surface Reconstruction: Observed with in Situ Surface X-ray Diffraction.

The (011) termination of rutile TiO is reported to be particularly effective for photocatalysis. Here, the structure of the interface formed between this substrate and water is revealed using surface X-ray diffraction. While the TiO(011) surface exhibits a (2 × 1) reconstruction in ultra-high vacuum (UHV), this is lifted in the presence of a multilayer of water at room temperature.

Structure of a Superhydrophilic Surface: Wet Chemically Prepared Rutile-TiO(110)(1 × 1).

Surface X-ray diffraction has been employed to quantitatively determine the geometric structure of an X-ray-induced superhydrophilic rutile-TiO(110)(1 × 1) surface. A scatterer, assumed to be oxygen, is found at a distance of 1.90 ± 0.

Epitaxial growth and structure of cobalt ferrite thin films with large inversion parameter on Ag(001).

Cobalt ferrite ultrathin films with the inverse spinel structure are among the best candidates for spin filtering at room temperature. High-quality epitaxial CoFeO films about 4 nm thick have been fabricated on Ag(001) following a three-step method: an ultrathin metallic CoFe alloy was first grown in coherent epitaxy on the substrate and then treated twice with O, first at room temperature and then during annealing. The epitaxial orientation and the surface, interface and film structure were resolved using a combination of low-energy electron diffraction, scanning tunnelling microscopy, Auger electron spectroscopy and in situ grazing-incidence X-ray diffraction.

Water Dissociates at the Aqueous Interface with Reduced Anatase TiO (101).

Elucidating the structure of the interface between natural (reduced) anatase TiO (101) and water is an essential step toward understanding the associated photoassisted water splitting mechanism. Here we present surface X-ray diffraction results for the room temperature interface with ultrathin and bulk water, which we explain by reference to density functional theory calculations. We find that both interfaces contain a 25:75 mixture of molecular HO and terminal OH bound to titanium atoms along with bridging OH species in the contact layer.

Structure of a model TiO photocatalytic interface.

The interaction of water with TiO is crucial to many of its practical applications, including photocatalytic water splitting. Following the first demonstration of this phenomenon 40 years ago there have been numerous studies of the rutile single-crystal TiO(110) interface with water. This has provided an atomic-level understanding of the water-TiO interaction.

Quantitative Structure of an Acetate Dye Molecule Analogue at the TiO-Acetic Acid Interface.

The positions of atoms in and around acetate molecules at the rutile TiO(110) interface with 0.1 M acetic acid have been determined with a precision of ±0.05 Å.

Geometry of α-CrO(0001) as a Function of HO Partial Pressure.

Surface X-ray diffraction has been employed to elucidate the surface structure of α-CrO(0001) as a function of water partial pressure at room temperature. In ultra high vacuum, following exposure to ∼2000 Langmuir of HO, the surface is found to be terminated by a partially occupied double layer of chromium atoms. No evidence of adsorbed OH/HO is found, which is likely due to either adsorption at minority sites, or X-ray induced desorption.

A novel model for the (√3 × √3)R30° alkanethiolate-Au(111) phase based on alkanethiolate-Au adatom complexes.

Self-assembled monolayers of thiols on Au(111) have attracted considerable interest from the theoretical and experimental points of view as model systems for understanding the organization of molecules on metallic surfaces, and also as key elements in nanoscience and nanotechnology. Today, there is strong theoretical and experimental evidence indicating that the surface chemistry of these monolayers at high coverage involves dithiolate-adatom (RS-Auad-SR) species, showing the existence of the (3 × 4) and c(4 × 2) lattices usually observed by scanning tunneling microscopy. However, concealing the existence of dithiolate-Au adatom species with the presence of the paradigmatic (√3 × √3)R30° lattice, which dominates the structure of long alkanethiols, still remains a challenge.

A Quantitative Structural Investigation of the 0.1 wt % Nb-SrTiO(001)/HO Interface.

Surface X-ray diffraction has been employed to elucidate the structure of the interface between a well-characterized (001) surface of 0.1 wt % Nb-SrTiO and liquid HO. Results are reported for the clean surface, the surface in contact with a drop of liquid water, and the surface after the water droplet has been removed with a flow of nitrogen.

Surface octahedral distortions and atomic design of perovskite interfaces.

Atomic engineering of perovskite films and interfaces is significantly improved by in situ optimization of reflection high-energy electron diffraction (RHEED) features resulting from surface BO₆ octahedral rotations seen during molecular-beam epitaxy growth. This approach yields Sr-doped manganite films across the phase diagram with magnetotransport properties that are, for the first time, identical to bulk single crystals. Careful structural analysis of manganite/titanate interfaces shows that cation intermixing and unit cell dilations are eliminated, while BO₆ rotations and Jahn-Teller-type elongations are nearly completely suppressed at the interface.

Structural phases of ordered FePc-nanochains self-assembled on Au(110).

Iron-phthalocyanine molecules deposited on the Au(110) reconstructed channels assemble into one-dimensional molecular chains, whose spatial distribution evolves into different structural phases at increasing molecular density. The plasticity of the Au channels first induces an ordered phase with a 5×5 symmetry, followed by a second long-range ordered structure composed by denser chains with a 5×7 periodicity with respect to the bare Au surface, as observed in the low-energy electron-diffraction (LEED) and grazing incidence X-ray diffraction (GIXRD) patterns. The geometry of the FePc molecular assemblies in the Au nanorails is determined by scanning tunneling microscopy (STM).

An EPR analysis of β-dimerization in α-blocked pyrroles in oxidant conditions.

Electron paramagnetic resonance (EPR) analysis of neutral and acidic solutions of 2,5-dimethyl-1-phenylpyrrol (1) and meta-, para-, and ortho-bis(2,5-dimethylpyrrol-1-yl)benzenes (4-6) in the presence of Tl(III) trifluoroacetate as oxidant reveals the poor stability of their generated monomeric radical cations which dimerize through C(β)-C(β) bond formation. EPR spectra of the monomeric radical cations 4(•+) , 5(•+) , and 6(•+) coincide with that of 1(•+) , suggesting that the unpaired electron in these charged species is confined in one of the pyrrolic rings. The very twisted angles between pyrrolic and phenyl planes due to steric hindrance in the X-ray analysis of the molecular structure of 4 confirm the absence of extended conjugation in the π-system.

Competitive adsorption of glycine and water on the fluorapatite (100) surface.

The atomic structure of the aqueous glycine-fluorapatite (100) interface was investigated using grazing incidence X-ray diffraction. Experimental data analysis of crystal truncation rod intensities revealed detailed information on lateral as well as perpendicular ordering of the adsorbate molecules and the nature of atomic relaxations in the fluorapatite (FAp) (100) surface. Glycine and water molecules are arranged in two periodically ordered layers at the aqueous glycine-mineral interface.

Geometric structure of TiO2(011)(2 x 1).

Surface x-ray diffraction has been employed to elucidate the surface structure of the (011)-(2 x 1) termination of rutile TiO2. The data are inconsistent with previously proposed structures. Instead, an entirely unanticipated geometry emerges from the structure determination, which is terminated by zigzag rows of twofold coordinated oxygen atoms asymmetrically bonded to fivefold titanium atoms.

Structure of interfacial water on fluorapatite (100) surface.

The structure relaxation mechanism of the fluorapatite (100) surface under completely hydrated ambient conditions has been investigated with the grazing incidence X-ray diffraction (GIXRD) technique. Detailed information on lateral as well as perpendicular ordering corresponding to the water molecules and atomic relaxations of the (100) surface of fluorapatite (FAp) crystal was obtained from the experimental analysis of the CTR intensities. Two laterally ordered water layers are present at the water/mineral interface.

Reducing power of simple polyphenols by electron-transfer reactions using a new stable radical of the PTM series, tris(2,3,5,6-tetrachloro-4-nitrophenyl)methyl radical.

The synthesis and characterization of a new radical and its use for testing the antioxidant activity of polyphenols by electron transfer are reported. This new and stable species of magnetic nature, tris(2,3,5,6-tetrachloro-4-nitrophenyl)methyl (TNPTM) radical, has been characterized by electron paramagnetic resonance and its molecular structure determined by X-ray analysis. This new radical of the PTM (perchlorotriphenylmethyl) series, unlike 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical, is stable in conditions of hydrogen abstraction reactions.

Crystalline order of a water/glycine film coadsorbed on the (104) calcite surface.

For biomineralization processes, the interaction of the surface of calcite crystals with organic molecules is of particular importance. Especially, biologically controlled biomineralization as in exoskeletons of mollusks and echinoderms, e.g.

A direct phasing method based on the origin-free modulus sum function and the FFT algorithm. XII.

An alternative way of refining phases with the origin-free modulus sum function S is shown that, instead of applying the tangent formula in sequential mode [Rius (1993). Acta Cryst. A49, 406-409], applies it in parallel mode with the help of the fast Fourier transform (FFT) algorithm.

Two-site adsorption model for the (square root 3 x square root 3)-R30 degrees dodecanethiolate lattice on Au(111) surfaces.

The surface structure of dodecanethiolate self-assembled monolayers (SAMs) on Au(111) surfaces, formed from the liquid phase, have been studied by grazing incidence X-ray diffraction (GIXRD), scanning tunneling microscopy (STM), and electrochemical techniques. STM images show that the surface structure consists of (square root 3 x square root 3)-R30 degrees domains with only a few domains of the c(4 x 2) lattice. The best fitting of GIXRD data for the (square root 3 x square root 3)-R30 degrees lattice is obtained with alkanethiolate adsorption at the top sites, although good fittings are also obtained for the fcc and hcp hollow sites.