SciCombinator

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Concept: Valence electron

165

Resistive random access memory based on the resistive switching phenomenon is emerging as a strong candidate for next generation non-volatile memory. So far, the resistive switching effect has been observed in many transition metal oxides, including strongly correlated ones, such as, cuprate superconductors, colossal magnetoresistant manganites and Mott insulators. However, up to now, no clear evidence of the possible relevance of strong correlation effects in the mechanism of resistive switching has been reported. Here, we study Pr0.7Ca0.3MnO3, which shows bipolar resistive switching. Performing micro-spectroscopic studies on its bare surface we are able to track the systematic electronic structure changes in both, the low and high resistance state. We find that a large change in the electronic conductance is due to field-induced oxygen vacancies, which drives a Mott metal-insulator transition at the surface. Our study demonstrates that strong correlation effects may be incorporated to the realm of the emerging oxide electronics.

Concepts: Oxygen, Oxide, Valence electron, Correlation and dependence, Superconductivity, Electrical resistance, Computer data storage, High-temperature superconductivity

30

The remarkable properties of graphene have renewed interest in inorganic, two-dimensional materials with unique electronic and optical attributes. Transition metal dichalcogenides (TMDCs) are layered materials with strong in-plane bonding and weak out-of-plane interactions enabling exfoliation into two-dimensional layers of single unit cell thickness. Although TMDCs have been studied for decades, recent advances in nanoscale materials characterization and device fabrication have opened up new opportunities for two-dimensional layers of thin TMDCs in nanoelectronics and optoelectronics. TMDCs such as MoS(2), MoSe(2), WS(2) and WSe(2) have sizable bandgaps that change from indirect to direct in single layers, allowing applications such as transistors, photodetectors and electroluminescent devices. We review the historical development of TMDCs, methods for preparing atomically thin layers, their electronic and optical properties, and prospects for future advances in electronics and optoelectronics.

Concepts: Optics, Molecule, Carbon, Zinc, Valence electron, Transistor, Materials science, Electronics

28

Single crystal EPR studies of Ni(II) in hexaimidazolecobalt(II) dichloride tetrahydrate have been carried out at ambient temperature to obtain g and zero-field tensors, making it one of the very few systems having room temperature EPR data. The results show rhombic distortion around the Ni(II) ion, with the ion being entered the lattice substitutionally in place of Co(II). The optical data suggest trigonally distorted electronic structure around Ni(II) and collaboration with EPR data provided a few bonding parameters.

Concepts: Fundamental physics concepts, Atom, Valence electron, Algebraic structure, Solid, Crystal system, Distortion

28

Widespread adoption of superconducting technologies awaits the discovery of new materials with enhanced properties, especially higher superconducting transition temperatures T©. The unexpected discovery of high T© superconductivity in cuprates suggests that the highest T©s occur when pressure or doping transform the localized and moment-bearing electrons in antiferromagnetic insulators into itinerant carriers in a metal, where magnetism is preserved in the form of strong correlations. The absence of this transition in Fe-based superconductors may limit their T©s, but even larger T©s may be possible in their isostructural Mn analogs, which are antiferromagnetic insulators like the cuprates. It is generally believed that prohibitively large pressures would be required to suppress the effects of the strong Hund’s rule coupling in these Mn-based compounds, collapsing the insulating gap and enabling superconductivity. Indeed, no Mn-based compounds are known to be superconductors. The electronic structure calculations and X-ray diffraction measurements presented here challenge these long held beliefs, finding that only modest pressures are required to transform LaMnPO, isostructural to superconducting host LaFeAsO, from an antiferromagnetic insulator to a metallic antiferromagnet, where the Mn moment vanishes in a second pressure-driven transition. Proximity to these charge and moment delocalization transitions in LaMnPO results in a highly correlated metallic state, the familiar breeding ground of superconductivity.

Concepts: Electron, Fundamental physics concepts, Condensed matter physics, Valence electron, Pressure, Superconductivity, Transformer, Niobium

27

The syntheses of the transition metal complexes cis-[(4-tBu-2,6-{P(O)(OiPr)2 }2 C6 H2 SnCl)2 MX2 ] (1, M=Pd, X=Cl; 2, M=Pd, X=Br; 3, M=Pd, X=I; 4, M=Pt, X=Cl), cis-[{2,6-(Me2 NCH2 )2 C6 H3 SnCl}2 MX2 ] (5, M=Pd, X=I; 6, M=Pt, X=Cl), trans-[{2,6-(Me2 NCH2 )2 C6 H3 SnI}2 PtI2 ] (7) and trans-[(4-tBu-2,6-{P(O)(OiPr)2 }2 C6 H2 SnCl)PdI2 ]2 (8) are reported. Also reported is the serendipitous formation of the unprecedented complexes trans-[(4-tBu-2,6-{P(O)(OiPr)2 }2 C6 H2 SnCl)2 Pt(SnCl3 )2 ] (10) and [(4-tBu-2,6-{P(O) (OiPr)2 }2 C6 H2 SnCl)3 Pt(SnCl3 )2 ] (11). The compounds were characterised by elemental analyses, (1) H, (13) C, (31) P, (119) Sn and (195) Pt NMR spectroscopy, single-crystal X-ray diffraction analysis, UV/Vis spectroscopy and, in the cases of compounds 1, 3 and 4, also by Mössbauer spectroscopy. All the compounds show the tin atoms in a distorted trigonal-bipyramidal environment. The Mössbauer spectra suggest the tin atoms to be present in the oxidation state III. The kinetic lability of the complexes was studied by redistribution reactions between compounds 1 and 3 as well as between 1 and cis-[{2,6-(Me2 NCH2 )2 C6 H3 SnCl}2 PdCl2 ]. DFT calculations provided insights into both the bonding situation of the compounds and the energy difference between the cis and trans isomers. The latter is influenced by the donor strength of the pincer-type ligands.

Concepts: Spectroscopy, Diffraction, X-ray, Valence electron, X-ray crystallography, Absorption spectroscopy, Ultraviolet-visible spectroscopy, Protein nuclear magnetic resonance spectroscopy

26

Through first-principles computations, we investigated Li4NiTeO6, which is a new layered Ni-based cathode material for Li ion batteries, by focusing on the sequence of Li removal when it is charged. According to our computations, Li4NiTeO6 exhibits satisfactory structural stability with a volume change of 7.2% and electrical conductivity similar to Li2MnO3. We also examined the electronic configuration of this cathode material during its electrochemical progress and found a weak hybridization of Ni3d and O2p. Moreover, by analyzing the Bader charges of different elements, we confirmed that O and Ni are exclusively responsible for electron loss and gain. In addition, O evolution reactions occur when half of Li(+) ions are extracted. Finally, we investigated Li(+) migration paths and concluded that migration barriers depend on the charge distribution around migration paths.

Concepts: Electron, Cathode, Electric charge, Chemistry, Atom, Ion, Valence electron, Atomic orbital

26

A series of luminescent ion exchanged zeolite are synthesized by introducing various ions into NaY zeolite. Monometal ion (Eu(3+) , Tb(3+) , Ce(3+) , Y(3+) , Zn(2+) , Cd(2+) , Cu(2+) ) exchanged zeolite, rare earth ion (Eu(3+) , Tb(3+) , Ce(3+) ) exchanged zeolite modified with Y(3+) and rare earth ion (Eu(3+) , Tb(3+) , Ce(3+) ) exchanged zeolite modified with Zn(2+) are discussed here. The resulting materials are characterized by FTIR, XRD, SEM, PLE, PL and luminescence lifetime measurements. The photoluminescence spectrum of NaY indicates that emission band of host matrix exhibits a blue shift of about 70 nm after monometal ion exchange process. The results show that transition metal ion exchanged zeolites possess a similar emission band due to dominant host luminescence. A variety of luminescence phenomenon of rare earth ion broadens the application of zeolite as a luminescent host. The Eu(3+) ion exchanged zeolite shows white light luminescence with a great application value and Ce(3+) exchanged zeolite steadily exhibits it characteristic luminescence in ultraviolet region no matter in monometal ion exchanged zeolite or bimetal ions exchanged zeolite. This article is protected by copyright. All rights reserved.

Concepts: Hydrogen, Valence electron, Silver, Transition metal, Copyright, Lutetium, Ytterbium, Neodymium

26

Band-bending in organic semiconductors, occurring at metal/alkali-halide cathodes in organic-electronic devices, is experimentally revealed and electrostatically modeled. Metal-to-organic charge transfer through the insulator, rather than doping of the organic by alkali-metal ions, is identified as the origin of the observed band-bending, which is in contrast to the localized interface dipole occurring without the insulating buffer layer.

Concepts: Electron, Cathode, Hydrogen, Chemistry, Valence electron, Organic semiconductor

25

The synthesis of a molecule containing four adjacent different pnictogens was attempted by conversion of a group 15 allyl analogue anion [Mes*NAsPMes*]- (Mes* = 2,4,6-tri-tertbutylphenyl) with antimony(III) chloride. A suitable precursor is Mes*N(H)AsPMes* (1) for which several syntheses were investigated. The anions afforded by deprotonation of Mes*N(H)AsPMes* were found to be labile and therefore, salts could not be isolated. However, the in situ generated anions could be quenched with SbCl3, yielding Mes*N(SbCl2)AsPMes* (4).

Concepts: Electron, Molecule, Chemistry, Atom, Sodium chloride, Ion, Valence electron, Polyatomic ion

25

Single- or few-layer phosphorene is a novel two-dimensional direct-bandgap nanomaterial. Based on first-principles calculations, we present a systematic study on the binding energy, geometry, magnetic moment and electronic structure of 20 different adatoms adsorbed on phosphorene. The adatoms cover a wide range of valences, including s and p valence metals, 3d transition metals, noble metals, semiconductors, hydrogen and oxygen. We find that adsorbed adatoms produce a rich diversity of structural, electronic and magnetic properties. Our work demonstrates that phosphorene forms strong bonds with all studied adatoms while still preserving its structural integrity. The adsorption energies of adatoms on phosphorene are more than twice higher than on graphene, while the largest distortions of phosphorene are only ∼0.1-0.2 Å. The charge carrier type in phosphorene can be widely tuned by adatom adsorption. The unique combination of high reactivity with good structural stability is very promising for potential applications of phosphorene.

Concepts: Electron, Atom, Nuclear fusion, Uranium, Valence electron, Periodic table, Silver, Iridium