Search results for "stacking"
showing 10 items of 215 documents
Reconstructed bcc Co films on the surface
2007
Abstract Ultrathin epitaxial Co films on Cr ( 1 1 0 ) are examined by scanning tunneling microscopy and spectroscopy (STM and STS). At room temperature Co grows as pseudomorphic bcc layers for the first two monolayers and forms close-packed Co layers with stacking faults for thicker coverages. A periodic lattice distortion appears in two equivalent (3 × 1) reconstruction domains in combination with a regular lattice of dislocation lines oriented along the in-plane close-packed row directions bcc [ 1 1 ¯ 1 ] and bcc [ 1 ¯ 1 1 ] . The reconstruction and the occurrence of dislocation lines are caused by the epitaxial strain. The local density-of-states function is mapped by scanning tunneling …
Unravelling the spin-state of solvated [Fe(bpp)2]2+ spin-crossover complexes: structure–function relationship
2018
This paper reports firstly the syntheses, crystal structures, and thermal and magnetic properties of spin crossover salts of formulae [Fe(bpp)2]3[Cr(CN)6]2·13H2O (1) and [Fe(bpp)2][N(CN)2]2·H2O (2) (bpp = 2,6-bis(pyrazol-3-yl)pyridine) exhibiting hydrogen-bonded networks of low-spin [Fe(bpp)2]2+ complexes and [Cr(CN)6]3− or [N(CN)2]− anions, with solvent molecules located in the voids. Desolvation of 1 is accompanied by a complete low-spin (LS) to a high-spin (HS) transformation that becomes reversible after rehydration by exposing the sample to the humidity of air. The influence of the lattice water on the magnetic properties of spin-crossover [Fe(bpp)2]X2 complex salts has been documented…
Study of inversion domain pyramids formed during the GaN:Mg growth
2003
AbstractThestudyofstructuraldefectsinducedbytheintroductionofMgduringthegrowthofMOCVDGaNispresented.Themagnesiumincorporationintothecrystalgrowthnotonlyinduceschangesinthestackingsequencefromhex-agonaltocubicstructures,butalsoinvertstheGaNpolarityfromGa-facetoN-face.Basedonthedifferentsurfacestructureandsurfacemigrationlengthofabsorbingprecursorsforeachpolaritytype(Ga-orN-face),the3DgrowthontopoftheN-facetriangulardefectisdescribed.TheN-facematerialischaracterizedbythreedanglingbondsofni-trogenthatpointuptowardthec-planesurface,enhancingthecrystalgrowthalongthec-axis. 2002ElsevierScienceLtd.Allrightsreserved. Keywords:Inversiondomain;Stackingfault;Polarity 1. IntroductionFurther progress tow…
Distorted f.c.c. arrangement of gold nanoclusters: a model of spherical particles with microstrains and stacking faults
2008
The structures of two samples of gold nanoclusters supported on silica were studied by X-ray powder diffraction (XRD) and X-ray absorption spectroscopy. The data relative to both techniques were analysed by an approach involving simulation based on structural models and fitting. The XRD model concerned a distorted f.c.c. (face-centred cubic) arrangement, with microstrains and parallel stacking faults in approximately spherical particles; as an alternative possibility, a linear combination of ordered f.c.c. and noncrystalline (decahedral and icosahedral) particles was also taken into account. Both approaches gave calculated patterns closely resembling the experimental data. X-ray absorption …
Electronic structure, lattice dynamics, and optical properties of a novel van der Waals semiconductor heterostructure: InGaSe2
2017
There is a growing interest in the property dependence of transition metal dichalcogenides as a function of the number of layers and formation of heterostructures. Depending on the stacking, doping, edge effects, and interlayer distance, the properties can be modified, which opens the door to novel applications that require a detailed understanding of the atomic mechanisms responsible for those changes. In this work, we analyze the electronic properties and lattice dynamics of a heterostructure constructed by simultaneously stacking InSe layers and GaSe layers bounded by van der Waals forces. We have assumed the same space group of GaSe, $P\overline{6}m2$ as it becomes the lower energy conf…
Ultra-thin film sensors based on porphyrin-5-ylphosphonate diesters for selective and sensitive dual-channel optical detection of mercury(II) ions
2020
International audience; Reusable dual-channel optical sensors for Hg2+ ions were prepared by Langmuir-Schaefer (LS) method from amphiphilic (trans-A2)BC-type porphyrins functionalized at meso-positions of the tetrapyrrolic macrocycle by sterically demanding diethoxyphosphoryl and mesityl groups as well as electron donating RO, RS or RNH substituents (R = n-C8H17). These three novel amphiphilic porphyrin derivatives were synthesized in good yields and their floating films at the air⎯water interface were investigated. In these monolayers, porphyrin molecules display a slipped stack-of-card orientation, but their strong π stacking is prohibited by bulky diethoxyphosphoryl and mesityl groups. T…
Dibenzoquinquethiophene- and Dibenzosexithiophene-Based Hole-Transporting Materials for Perovskite Solar Cells
2018
Fused oligothiophene-based π-conjugated organic derivatives have been widely used in electronic devices. In particular, two-dimensional (2D) heteroarenes offer the possibility of broadening the scope by extending the π-conjugated framework, which endows enhanced charge transport properties due to the potential intermolecular π–π stacking. Here, the synthesis and characterization of two new small-molecule hole-transporting materials (HTMs) for perovskite solar cells (PSCs) are reported. The newly custom-made compounds are based on dibenzoquinquethiophene (DBQT) and dibenzosexithiophene (DBST) cores, which are covalently linked to triphenylamine moieties to successfully afford the four-armed …
Molecular flattening effect to enhance the conductivity of fused porphyrin tape thin films.
2019
The straightforward synthesis of directly fused porphyrins (porphyrin tapes) from 5,15-diphenyl porphyrinato nickel(II) complexes with different substituents on the phenyl rings is achieved while processing from the gas phase. The porphyrin tapes, exhibiting NIR absorption, are readily obtained in thin film form. The gas phase approach cuts the need for solubilizing groups allowing for the first time the study of their conductivity according to the substituent. 2-Point probe and conductivity AFM measurements evidence that reducing the size of the meso substituents, phenyl < mesityl < di(3,5-tert-butyl)phenyl < di(2,6-dodecyloxy)phenyl, improves the thin film conductivity by several orders o…
Slow Magnetization Relaxation in a 1-D Double-Chain Coordination Polymer Composed of {Dy<sup>III</sup> <sub>4</sub>} Repeatin…
2013
The "unsuccessful" synthesis of the non-commercially available 'Dy(O2CPh)3' precursor from the stoichiomet- ric reaction of Dy(NO3)3·5H2O with 3 equivalents of NaO2CPh in MeCN/H2O has led instead to the "successful" isolation and structural characterization of the 1-D coordination polymer (Dy4(O2CPh)12(H2O)8)n·2n(PhCO2H)·n(MeCN) (1·2n(PhCO2H)·n(MeCN)) in excellent yields (~90%). The one-dimensional double-chain structure of 1 was resulted from the linkage of two parallel chains by syn,anti-� 1 :� 1 :μ PhCO2 - groups. The lattice structure of 1 is further extended to a 2-D network through hydrogen bonding and - stacking interactions. The observation of out-of-phase (� �� M) ac susceptibility…
Functionalized Calix[8]arenes, Synthesis and Self-assembly on Graphite
2005
With the intention of building hollow tubular structures by self-assembly, we have designed and successfully synthesized a series of calix[8]arene derivatives. Their phenolic units were functionalized in p-position by various groups which are able to interact via hydrogen bonding or π−π stacking. Ethynyl, amide, urea, or imide links were chosen for the covalent attachment of these functional groups, to ensure the adjustment of an optimal distance for their interaction. Two different kinds of nanostructures self-assembled on a highly oriented pyrolytic graphite (HOPG) surface were found by scanning force microscopy: parallel aligned nanorods in which the calixarene molecules are adsorbed ed…