jablonkagroup/rise_ai_scientists huggingface dataset:
Authors: Serhii Krykun | Igor V. Levkov | Tetyana Yegorova | Zoia Voïtenko
Source: Bulletin of Taras Shevchenko National University of Kyiv Chemistry (article, 2018-01-01)
Field: Materials Science — Electronic, Optical and Magnetic Materials

SYNTHESIS OF THE OXIDIZED FORM OF DITHIENO-TTF BY ELECTROCRYSTALLIZATION General principles of the electrocrystallization technique in application to organic molecules are shown, as some historical background. Based on this, we were able to rationalize main variables in the experiment which are needed in order to get crystals of the oxidized form, that are suitable for further applications such as for example single crystal x-ray diffraction analysis or conductivity measurements. The biggest impact comes from such factors as choice of solvent and supporting electrolyte, which influence directly the solubility of both the starting compound and its oxidized form. Purity of all components is also paramount. In order to avoid formation of by-products, experiment is usually performed in a sealed U-shaped electrochemical cell with a glass filter between the anodic and cathodic compartments and under inert atmosphere such as argon or nitrogen. Other parameters considered here, such as temperature of the solution and intensity of the current, help to fine-tune the result, but have less impact on whether the crystallization will occur at all. It is also critical to maintain both parameters at constant values in order to obtain high quality single crystals. Galvanostatic oxidation mode is more favourable comparing to the potentiostatic as it allows steady rate of oxidation by providing fixed intensity of the electrical current and subsequently more stable rate of crystal grows, although potentiostatic mode or alternating current can be used to grow bigger amounts when quality of the single crystal is less important. Further we used this approach to electrocrystalize previously obtained by our group dithieno-TTF, based on the exTTF scaffold. According to the literature cyclic voltammetry data, dithieno-TTF undergoes reversible single-wave two electron oxidation to form bis-cation similar to classic exTTF, but in our case only radical-cation salt was obtained in a form of shiny, dark-red, needle-like single crystals. This could be attributed to its extremely low solubility and corresponding formation of the kinetic product, which correlate well with relatively fast crystallization just within 3 days. Another possibility is a comproportionation reaction involving the starting neutral molecule and oxidized dication. Crystallization ; Crystal (programming language) ; Electrochemistry ; Electrolyte ; Single crystal ; Materials science ; Inert gas ; Anode ; Diffraction ; Solvent ; Molecule ; Intensity (physics) ; Electrical resistivity and conductivity ; Analytical Chemistry (journal) ; Chemistry ; Electrode ; Crystallography ; Physical chemistry ; Organic chemistry ; Optics Organic and Molecular Conductors Research ; Electrochemical Analysis and Applications ; Crystallography and molecular interactions
Authors: Roger D. Johnson | D. D. Khalyavin | Pascal Manuel | L. Zhang | Kazunari Yamaura | Alexei А. Belik
Source: arXiv (Cornell University) (preprint, 2018-08-28)
Field: Materials Science — Electronic, Optical and Magnetic Materials

The magnetic structures of rare-earth quadruple perovskite manganites $R$Mn$_7$O$_{12}$ We report a neutron powder diffraction study of $R$Mn$_7$O$_{12}$ quadruple perovskite manganites with $R$ = La, Ce, Nd, Sm, and Eu. We show that in all measured compounds concomitant magnetic ordering of the $A$ and $B$ manganese sublattices occurs on cooling below the N$\mathrm{\acute{e}}$el temperature. The respective magnetic structures are collinear, with one uncompensated Mn$^{3+}$ moment per formula unit as observed in bulk magnetisation measurements. We show that both LaMn$_7$O$_{12}$ and NdMn$_7$O$_{12}$ undergo a second magnetic phase transition at low temperature, which introduces a canting of the $B$ site sublattice moments that is commensurate in LaMn$_7$O$_{12}$ and incommensurate in NdMn$_7$O$_{12}$. This spin canting is consistent with a magnetic instability originating in the $B$ site orbital order. Furthermore, NdMn$_7$O$_{12}$ displays a third magnetic phase transition at which long range ordering of the Nd sublattice modifies the periodicity of the incommensurate spin canting. Our results demonstrate a rich interplay between transition metal magnetism, orbital order, and the crystal lattice, which may be fine tuned by cation substitution and rare earth magnetism. Spin canting ; Condensed matter physics ; Magnetism ; Neutron diffraction ; Perovskite (structure) ; Magnetic moment ; Magnetization ; Magnetic structure ; Manganite ; Manganese ; Crystal structure ; Materials science ; Formula unit ; Crystallography ; Chemistry ; Ferromagnetism ; Physics ; Magnetic field Magnetic and transport properties of perovskites and related materials ; Thermal Expansion and Ionic Conductivity ; Multiferroics and related materials
Authors: Jose Ali Espitia
Source: scholarworks - UTEP (The University of Texas at El Paso) (article, 2018-01-01)
Field: Materials Science — Materials Chemistry

The Hierarchical Structure of Nanoporous Carbon Electrode Materials Elucidated by Water Sorption: A Comparison of Multiple Structural Models The total amount of energy that an electrical double layer capacitor (EDLC) can store depends on the voltage and the accessible surface area for ion electrosorption. Nanoporous carbon materials with a high specific surface area, such as carbide derived carbon (CDC), make ideal electrodes for EDLC devices. CDC materials have fine-tuned pore sizes in the subnanometer range which are controlled by the initial carbide (TiC) and annealing conditions. Water can enter TiC-CDC pores and give filling fractions in excess of 0.6 g/g (H2O/C). Recent reports of water's diffusional dynamics dependence on CDC pore size indicate confinement effects similar to that observed in pores of 16 Å. Though other studies have gleaned insights into the porous structure of CDC, there is currently no direct structural information on the sorption of water at intermediate stages between completely empty and full. Small-angle neutron scattering (SANS) was used to find to what degree pores are filled with water (D2O) at intermediate stages of loading for four TiC-CDC powders, each with different pore size distributions. We present models to reproduce the SANS data and extract information on the structure of CDC, consisting of subnanometer pores as well as mesopores. The subnanometer pores exhibit a narrow size distribution whereas the mesopores are polydisperse. In addition, the structure of the room temperature ionic liquid (RTIL) [C4mim]+[Tf2N]- and water confined inside the micropores (&lt; 2 nm) of carbide derived carbon (CDC) were investigated using small angle x-ray scattering (SAXS). RTILs, composed entirely of ions, have high thermal and electrochemical stability which make them interesting candidates as electrolytes in EDLCs. Water is usually removed from working devices due to the breakdown of H2O at low voltages, but the interaction between the two fluids in confinement is still not fully understood. SAXS/WAXS measurements were carried out on dry CDC, samples which were partially (50%), completely (100%), and over-filled with RTIL (150%), as well as RTIL-filled samples exposed to100% water-saturated air. This study provides information on the length scales of the CDC porosity, the extent to which RTIL enters micropores, and how confinement affects the charge-ordered structure of the RTIL. Sorption ; Nanoporous ; Materials science ; Electrode ; Carbon fibers ; Chemical engineering ; Nanotechnology ; Composite material ; Chemistry ; Physical chemistry ; Adsorption ; Engineering Mesoporous Materials and Catalysis ; Nanoporous metals and alloys ; Electrocatalysts for Energy Conversion
Authors: Richard Betz
Source: Open Chemistry (article, 2018-01-01)
Field: Chemistry — Physical and Theoretical Chemistry

The structure of<i>ortho</i>-(trifluoromethyl)phenol in comparison to its homologues – A combined experimental and theoretical study Abstract The molecular and crystal structure of commercially-available ortho -(trifluoromethyl)phenol were determined by means of single-crystal X-ray diffractometry (XRD) and represent the first structural characterization of an ortho -substituted (trihalomethyl) phenol. The unexpected presence of a defined hydrate in the solid state was observed.Intermolecular contacts and hydrogen bonding were analyzed. The compound was further characterized by means of multi-nuclear nuclear magnetic resonance (NMR) spectroscopy ( 1 H, 13 C{ 1 H}, 19 F) and Fourier-Transform infrared (FT-IR) vibrational spectroscopy. To assess the bonding situation as well as potential reaction sites for reactions with nucleophiles and electrophiles in the compound by means of natural bonding orbital (NBO) analyses, and density functional theory (DFT) calculations were performed for the title compound as well as its homologous chlorine, bromine and iodine compounds. As far as possible, experimental data were correlated to DFT data. Natural bond orbital ; Chemistry ; Density functional theory ; Trifluoromethyl ; Electrophile ; Intermolecular force ; Nuclear magnetic resonance crystallography ; Phenol ; Crystallography ; Hydrogen bond ; Crystal structure ; Nuclear magnetic resonance spectroscopy ; Single crystal ; Bromine ; Hydrate ; Computational chemistry ; Physical chemistry ; Fluorine-19 NMR ; Molecule ; Organic chemistry ; Catalysis Crystallography and molecular interactions ; Fluorine in Organic Chemistry ; Crystal structures of chemical compounds
Authors: Dong Yang | Won Il Park
Source: Journal of the Korean Ceramic Society (article, 2018-03-26)
Field: Materials Science — Materials Chemistry

Epitaxial Growth of Three-Dimensional ZnO and GaN Light Emitting Crystals The increasing demands for three-dimensional (3D) electronic and optoelectronic devices have triggered interest in epitaxial growth of 3D semiconductor materials. However, most of the epitaxially-grown nano-and micro-structures available so far are limited to certain forms of crystal arrays, and the level of control is still very low. In this review, we describe our latest progress in 3D epitaxy of oxide and nitride semiconductor crystals. This paper covers issues ranging from (i) low-temperature solutionphase synthesis of a well-regulated array of ZnO single crystals to (ii) systematic control of the axial and lateral growth rate correlated to the diameter and interspacing of nanocrystals, as well as the concentration of additional ion additives. In addition, the critical aspects in the heteroepitaxial growth of GaN and InGaN multilayers on these ZnO nanocrystal templates are discussed to address its application to a 3D light emitting diode array. Materials science ; Epitaxy ; Optoelectronics ; Semiconductor ; Light-emitting diode ; Nanocrystal ; Diode ; Nitride ; Nanotechnology ; Template ; Layer (electronics) ZnO doping and properties ; GaN-based semiconductor devices and materials ; Ga2O3 and related materials
Authors: Frady Gouany | Hannah E. Bollard | Michael G. Gardiner | Ashraf Ghanem
Source: Preprints.org (preprint, 2018-05-07)
Field: Chemistry — Inorganic Chemistry

Chiral Dirhodium(II) Carboxylates: New Insights into the Effect of Ligand Stereo-Purity on Catalyst Structure and Enantioselectivity The current report contributes to the understanding of the stereoselectivity of the chiral dirhodium(II) carboxylate catalysts derived from N-protected amino acid ligands. Investigating the possible effect of ligand stereo-purity on catalyst structure and enantioselectivity was carried out. This was justified through a new X-ray crystal structure for Rh2(S,S,S,R-PTTL)4 diastereomer. Diastereomer ; Stereoselectivity ; Ligand (biochemistry) ; Catalysis ; Chemistry ; Carboxylate ; Stereochemistry ; Crystal structure ; Combinatorial chemistry ; Crystallography ; Organic chemistry ; Receptor ; Biochemistry Asymmetric Hydrogenation and Catalysis ; Cyclopropane Reaction Mechanisms ; Asymmetric Synthesis and Catalysis
Authors: George Farid
Source: CUNY Academic Works (City University of New York) (article, 2018-01-01)
Field: Materials Science — Materials Chemistry

Flexible and Versatile Soft Templates for Mesoporous Silicas and Organosilicas Based on Pluronic Block Copolymer Surfactants and their Mixtures In this dissertation, the work will be discussed that was focused on the synthesis of consolidated periodic mesoporous materials such as 2-D hexgonal ordered mesoporous silicas (SBA-15) as well as single-micelle-templated silica and organosilica nanotubes and nanospheres using triblock copolymer surfactants and their mixtures in the presence of a swelling agent. The introductory section, Chapter 1, will address the current state of the tunability of single-micelle-templated silica and organosilica nanotubes and will compare it with the work presented in this dissertation on the use of a dual-surfactant templating systems. Chapter 2 of the dissertation discusses transmission electron microscopy characterization of Pluronic surfactant templated nanotubes and 2-D hexagonal ordered mesoporous silicas based on tilt-series imaging at different angles. Chapter 3 shows the effects of stirring rate on fragmentation in silica nanotubes and the resulting nanosphere contamination in the synthesis that utilizes a single Pluronic surfactant. In Chapter 4, the synthesis of ultra-large-pore SBA-15 silica, nanotubes with adjustable pore diameter with the use of a dual-surfactant system will be discussed. Chapter 5 utilizes similar system as discussed in Chapter 4 to synthesize a variety of organosilica nanotubes with different organosilane precursors. Chapter 6 discusses the synthesis of microemulstion v droplet-templated silica and organosilica nanospheres of large size. The dissertation end with same conclusions. Copolymer ; Poloxamer ; Mesoporous organosilica ; Materials science ; Template ; Block (permutation group theory) ; Mesoporous material ; Chemical engineering ; Polymer chemistry ; Polymer science ; Polymer ; Organic chemistry ; Chemistry ; Mesoporous silica ; Nanotechnology ; Catalysis ; Composite material ; Engineering Mesoporous Materials and Catalysis ; Polyoxometalates: Synthesis and Applications ; Chemical Synthesis and Reactions
Authors: Pillar-Little
Source: UKnowledge (University of Kentucky) (article, 2018-01-01)
Field: Materials Science — Materials Chemistry

Carbon Quantum Dots Carbon quantum dots (CQDs) are the latest generation of carbon nanomaterials in applications where fullerenes, carbon nanotubes, and graphene are abundantly used. With several attractive properties such as tunable optical property, edge-functionalization, and defect-rich chemical structure, CQDs have the potential to revolutionize optoelectronics, electro- and photocatalysis, and biomedical applications. Chemical modifications through the addition of heteroatoms, chemical reduction, and surface passivation are found to alter the band gap, spectral position, and emission pathways of CQDs. Despite extensive studies, fundamental understanding of structure-property relationship remains unclear due to the inhomogeneity in chemical structure and a complex emission mechanism for CQDs. This dissertation outlines a series of works that investigate the structure-property relationship of CQDs and its impact in a variety of applications. First, this relationship was explored by modifying specific chemical functionalities of CQDs and relating them to differences observed in optical, catalytic, and pharmacological performance. While a number of scientific articles reported that top-down or bottom-up synthesized CQDs yielded similar properties, the results herein present dissimilar chemical structures as well as photoluminescent and metal sensing properties. Second, the role of nitrogen heteroatoms in top-down synthesized CQD was studied. The effect of nitrogen atoms on spectral position and fluorescence quantum yield was considerably studied in past reports; however, thorough investigation to differentiate various nitrogen related chemical states was rarely reported. By finely tuning both the quantity of nitrogen doping and the distribution of nitrogen-related chemical states, we found that primary amine and pyridine induce a red-shift in emission while pyrrolic and graphitic nitrogen produced a blue-shift in emission. The investigation of nitrogen chemical states was extended to bottom-up synthesized CQDs with similar results. Finally, top-down, bottom-up, nitrogen-doped and chemically reduced CQDs were separately tested for their ability to act as photodynamic anti-cancer agents. This series of experiments uncovered the distribution of reactive oxygen species produced during light exposure which elucidated the photodynamic mechanisms of cancer cytotoxicity. The results presented in this dissertation provide key insight into engineering finely-tailored CQDs as the ideal nanomaterial for a broad range of applications. Bridging (networking) ; Quantum dot ; Band gap ; Carbon fibers ; Nanotechnology ; Materials science ; Carbon quantum dots ; Engineering physics ; Physics ; Computer science ; Optoelectronics ; Composite material Carbon and Quantum Dots Applications ; Graphene research and applications ; TiO2 Photocatalysis and Solar Cells
Authors: Linfeng Chen
Source: eScholarship (California Digital Library) (article, 2018-01-01)
Field: Materials Science — Materials Chemistry

Tunable transition-metal-linked Preyssler type polyoxometalate frameworks: Synthesis, structural characterization and optical proprieties Polyoxometalates (POMs), a class of molecularly defined transition metal-oxide clusters (TM= Cr, V, Mo, W, Nb), have been developed due to their properties in the field of catalysis, magnetism, electronics, gas sensor, supramolecular chemistry and drug deliver. Among all POMs, tungsten oxide (WOx), as a nontoxic and photostable semiconductor with a narrow bandgap about 2.6 eV, is the most attractive cluster for the researchers. Due to the narrow bandgap of WOx, only the blue and near ultraviolet regions of the solar spectrum can be excited. The photocatalytic performance of WOx can be increased by doping numerous elements to reduce bandgap effectively. POMs offer the advantage of precisely placed atoms and well-defined W:O ratios. Besides, POMs can be used as building blocks for frameworks in which the POMs are linked with all-inorganic linkers. All-inorganic frameworks have high stability, high catalytic activity, photochemical and electrochemical activity. Here, we develop a strategy to synthesize six frameworks based on the Preyssler cluster [P5W30O110]15- linked with various transition metals such as Mn, Fe, Co, Ni, Cu and Zn. Besides, bimetallic POM frameworks have been prepared where the transition metals are distributed homogeneously within all crystals of the sample. In addition, the transition metal ratio was varied from 0 to 1, affording materials with absorption that varies as a function of metal identity and content. The diffuse reflectance from single metallic POM frameworks to bimetallic POM frameworks were shown to illustrate the tunable optical properties of these POM frameworks. Polyoxometalate ; Bimetallic strip ; Transition metal ; Materials science ; Photocatalysis ; Band gap ; Catalysis ; Cluster (spacecraft) ; Nanotechnology ; Oxide ; Metal ; Chemistry ; Optoelectronics ; Organic chemistry ; Metallurgy Polyoxometalates: Synthesis and Applications ; Metal-Organic Frameworks: Synthesis and Applications ; Advanced Nanomaterials in Catalysis
Authors: Chiara Busà
Source: ORCA Online Research @Cardiff (Cardiff University) (article, 2018-07-01)
Field: Materials Science — Surfaces, Coatings and Films

Novel bottom-up sub-micron architectures for advanced functional devices This thesis illustrates two novel routes for fabricating hierarchical micro-to-nano structures with interesting optical and wetting properties. The co-presence of asperities spanning the two length scales enables the fabrication of miniaturised, tuneable surfaces exhibiting a high potential for applications in for instance, waterproof coatings and nanophotonic devices, while exploiting the intrinsic properties of the structuring materials.&#13;\n&#13;\nFirstly, scalable, superhydrophobic surfaces were produced via carbon nanotubes (CNT)-based electrohydrodynamic lithography, fabricating multiscale polymeric cones and nanohair-like architectures with various periodicities. CNT forests were used for manufacturing essential components for the electrohydrodynamic setup and producing controlled micro-to-nano features on a millimetre scale. The achieved high contact angles introduced switchable Rose-to-Lotus wetting regimes. &#13;\n&#13;\nSecondly, a cost-effective method was introduced as a route towards plasmonic bandgap metamaterials via electrochemical replication of three-dimensional (3D) DNA nanostructures as sacrificial templates. A range of sub-30nm 3D DNA polyhedrons, immobilised onto conductive and insulating surfaces, were replicated with gold via electrochemical deposition and sputtering. Microscopic characterisation revealed detailed gold replicas preserving both edges and cavities of the DNA nanostructures. Accurate tuning of both polyhedrons’ dimensions and gold plating conditions finally enabled sub-100nm structures which show promising optical properties such as, birefringence for potential applications in photonics, metamaterials and sensing.&#13;\n Materials science ; Nanotechnology ; Electrohydrodynamics ; Fabrication ; Photonics ; Metamaterial ; Carbon nanotube ; Nanostructure ; Lithography ; Nanophotonics ; Nanoscopic scale ; Template ; Plasmon ; Wetting ; Optoelectronics ; Electric field ; Composite material Surface Modification and Superhydrophobicity ; Nanofabrication and Lithography Techniques ; Optical Coatings and Gratings