Molybdenum Trioxide on Anatase TiO2(101) - Formation of Monodispersed (MoO3)1 Monomers from Oligomeric (MoO3)n Clusters

<p>Complex oxide systems with hierarchical order are of critical importance in material science and catalysis. Despite their immense potential, their design and synthesis are rather difficult. In this study we demonstrate how the deposition of small oligomeric (MoO₃)_1-6 clusters, which can be formed by the sublimation of MoO₃ powders, leads to the formation of locally ordered layers of (MoO₃)₁ monomers on anatase TiO₂(101). Using both high-resolution imaging and theoretical calculations, we show that at room temperature, such oligomers undergo spontaneous dissociation to their monomeric units. In initial stages of the deposition, this is reflected by the observation of one to six neighboring (MoO₃)₁ monomers that parallel the size distribution of the oligomers. A transient mobility of such oligomers on both bare TiO₂(101) and (MoO₃)₁ covered areas is key to the formation of a complete layer with a saturation coverage of one (MoO₃)₁ per two undercoordinated surface Ti sites. We further show that such layers are stable to 500 K, making them highly suitable for a broad range of applications. </p>

Molybdenum Trioxide on Anatase TiO2(101) - Formation of Monodispersed (MoO3)1 Monomers from Oligomeric (MoO3)n Clusters

<p>Complex oxide systems with hierarchical order are of critical importance in material science and catalysis. Despite their immense potential, their design and synthesis are rather difficult. In this study we demonstrate how the deposition of small oligomeric (MoO₃)_1-6 clusters, which can be formed by the sublimation of MoO₃ powders, leads to the formation of locally ordered layers of (MoO₃)₁ monomers on anatase TiO₂(101). Using both high-resolution imaging and theoretical calculations, we show that at room temperature, such oligomers undergo spontaneous dissociation to their monomeric units. In initial stages of the deposition, this is reflected by the observation of one to six neighboring (MoO₃)₁ monomers that parallel the size distribution of the oligomers. A transient mobility of such oligomers on both bare TiO₂(101) and (MoO₃)₁ covered areas is key to the formation of a complete layer with a saturation coverage of one (MoO₃)₁ per two undercoordinated surface Ti sites. We further show that such layers are stable to 500 K, making them highly suitable for a broad range of applications. </p>

Molybdenum Trioxide on Anatase TiO2(101) - Formation of Monodispersed (MoO3)1 Monomers from Oligomeric (MoO3)n Clusters

<p>Complex oxide systems with hierarchical order are of critical importance in material science and catalysis. Despite their immense potential, their design and synthesis are rather difficult. In this study we demonstrate how the deposition of small oligomeric (MoO₃)_1-6 clusters, which can be formed by the sublimation of MoO₃ powders, leads to the formation of locally ordered layers of (MoO₃)₁ monomers on anatase TiO₂(101). Using both high-resolution imaging and theoretical calculations, we show that at room temperature, such oligomers undergo spontaneous dissociation to their monomeric units. In initial stages of the deposition, this is reflected by the observation of one to six neighboring (MoO₃)₁ monomers that parallel the size distribution of the oligomers. A transient mobility of such oligomers on both bare TiO₂(101) and (MoO₃)₁ covered areas is key to the formation of a complete layer with a saturation coverage of one (MoO₃)₁ per two undercoordinated surface Ti sites. We further show that such layers are stable to 500 K, making them highly suitable for a broad range of applications. </p>

Crystal Structure of the Compound Sc1.33Pd3Al8 with Layers of R Atoms and Al3 Triangles

The crystal structure of the new ternary aluminide Sc1.33Pd3Al8was refined by the Rietveld method from X-ray powder diffraction data. It crystallizes with a Gd1.33Pt3Al8-type structure:hR51-14.00,R-3m,a= 4.29142(4),c= 38.1638(4) Å,RB= 0.0344. The main feature of the structure is the statistical distribution of Sc atoms and Al3triangles within atomic layers of composition Sc2Al3(Sc0.67Al within the translation unit here), which is likely to correspond to stacking disorder of ordered layers. During the final cycles of the refinement, the occupancies of the corresponding sites were fixed at occ. = 2/3 for Sc in Wyckoff position 6cand occ. = 1/3 for Al in 18h. The unit cell of Sc1.33Pd3Al8contains six Sc0.67Al layers, nine Pd and eighteen Al atom layers along the crystallographic direction [001]. Together with the structure types Tb0.67PdAl3, Y2Co3Ga9, Sc0.67Fe2Si5, Er4Pt9Al24, Yb0.67Ni2Al6, and ErNi3Al9, the structure type Gd1.33Pt3Al8forms a family of intergrowth structures built up of three kinds of similar monoatomic layer.

Alkaline-earth tri-mercurides AIIHg3 (AII=Ca, Sr, Ba): binary intermetallic compounds with a common and a new structure type

The alkaline-earth tri-mercurides AHg3 (A=Ca, Sr, Ba) were yielded from stoichiometric melts of the elements in pure phase (in the case of Sr with Sr11Hg54 as a by-product) and their structures were determined by means of single crystal X-ray data. As reported long ago from powder data, CaHg3 and SrHg3 crystallize in the Ni3Sn-type (P63/mmc, a=662.26(2)/689.39(3), c=501.64(2)/510.38(3) pm, Z=2, R1=0.0233/0.0306 for A=Ca/Sr). The structure consists of a hexagonal close packing of ordered layers AHg3 or a dense packing of anti-cuboctahedra [AHg12] (as cation coordination polyhedra, CCP) and [Hg6] octahedra fused via opposite faces to form columns along c. BaHg3 crystallizes in a unique structure type (P4/ncc, a=1193.04(3), c=958.02(5) pm, Z=12, R1=0.0461). It contains three crystallographically different Hg atoms, which form layers of distorted flat square pyramids. In contrast to the layers of the BaAl4-type, ${1 \over 5}$ of the pyramids are missing. Due to the 45 degree rotation of adjacent layers, the connection between the layers is not a ‘apical-to-apical’ one like in BaAl4, but is established by ‘apical-to-basal’ bonds. Compared to the Ca and Sr compound, the CCPs of the two different Ba atoms, which are embedded between the pyramid layers, are increased to 12+4 and 14+2 (for Hg+Ba). For all title compounds and the Li phase LiHg3, which is isotypic to CaHg3, the electronic band structures were calculated within the framework of the FP-LAPW DFT method. Even though the compounds are metals and exhibit only very slight minima of the tDOS at the Fermi level, the electron transfer from the alkali/alkaline-earth element towards mercury is almost complete. Thus, Coulomb interactions and the optimized size and arrangement of the A CCPs, besides the flexible Hg–Hg bonding within the polyanion, determine the structure formation.

Recent advances in pericentriolar material organization: ordered layers and scaffolding gels

The centrosome is an unusual organelle that lacks a surrounding membrane, raising the question of what limits its size and shape. Moreover, while electron microscopy (EM) has provided a detailed view of centriole architecture, there has been limited understanding of how the second major component of centrosomes, the pericentriolar material (PCM), is organized. Here, we summarize exciting recent findings from super-resolution fluorescence imaging, structural biology, and biochemical reconstitution that together reveal the presence of ordered layers and complex gel-like scaffolds in the PCM. Moreover, we discuss how this is leading to a better understanding of the process of microtubule nucleation, how alterations in PCM size are regulated in cycling and differentiated cells, and why mutations in PCM components lead to specific human pathologies.

The fungal cerato-platanin protein EPL1 forms highly ordered layers at hydrophobic/hydrophilic interfaces

Cerato-platanin proteins (CPPs) and hydrophobins are two classes of small, secreted proteins that are exclusively found in fungi.