Strong electron correlations in the normal state of FeSe0.42Te0.58

We investigate the normal state of the '11' iron-based superconductor FeSe0.42Te0.58 by angle resolved photoemission. Our data reveal a highly renormalized quasiparticle dispersion characteristic of a strongly correlated metal. We find sheet dependent effective carrier masses between ~ 3 - 16 m_e corresponding to a mass enhancement over band structure values of m*/m_band ~ 6 - 20. This is nearly an order of magnitude higher than the renormalization reported previously for iron-arsenide superconductors of the '1111' and '122' families but fully consistent with the bulk specific heat.Comment: 5 pages, 4 figures, to appear in Phys. Rev. Let

L'archivio Laterza: lettere di economisti all'editore (1901 - 1959)

In un recente lavoro sugli Archivi nella Puglia ci si è chiesti se sia vera l’opinione comune secondo cui nel Sud si nasce e poi ci si allontana, portandosi via le proprie carte. Se questa è la regola, la storia che si racconta in questo lavoro è quella di un’eccezione: l’editore Laterza ha infatti richiamato nel Sud, controcorrente, cultura e carte. Questa storia è possibile raccontarla grazie all’Archivio Laterza, un fondo documentario che testimonia gli eventi storici del «secolo breve» e che delinea, sullo sfondo dei grandi avvenimenti, la vita di un gruppo di grandi intellettuali. Questo saggio si occupa degli economisti che hanno avuto contatti più intensi con l’editore, vale a dire Giustino Fortunato, Francesco Saverio Nitti, Maffeo Pantaleoni, Luigi Einaudi e Umberto Ricci

STM study of the nanostructures prepared bydeposition of NiO on Ag(001)

Submonolayers of nickel oxide were grown on the Ag(001) surface by evaporation of Ni in the presence of O2 at a pressure of 1 × 10−6 mbar. In the early stages of deposition, two-dimensional oxide islands with a (2 × 1) periodicity grow on Ag(001). After annealing at about 500 K, the (2 × 1) single atomic layer transforms into NiO(001) double layer islands. The 1:1 stoichiometry of the film is not influenced by whether the annealing is carried out in vacuum or in the presence of oxygen. However, the oxide islands exhibit different morphologies depending on the O2 pressure during the annealing process

Mechanism of growth and structure of titanium oxide ultrathin films deposited on Cu(001) Surface Science 602 (2008) 1101-1113.

The growth mechanism, composition and structure of ultrathin films of titanium oxide deposited on the Cu(001) surface were investigated by means of XPS, LEIS, LEED and STM. Titanium oxide films were deposited on the Cu(001) surface previously saturated witha (p2 2p2)R45 structure of chemisorbed oxygen. The oxide films were prepared by evaporation of titanium in O2 atmosphere (pO2 in the 106 mbar range) while the substrate temperature was kept at 573 K. The Cu LEIS signal versus the amount of deposited titanium (as determined by means of XPS) indicates the growth of 2D islands in the early stages of deposition. Upon increasing the amount of deposited titanium multilayer islands begin to grow. The XPS results indicate that the oxide phases formed for Ti coverages above 1ML have a TiO2 stoichiometry. At very low coverages, a LEED pattern with a centred rectangular unit cell is observed. STM measurements show that at this stage of the growth the oxide islands are incorporated in the outermost layer of the substrate and the removed copper atoms form islands around the oxide regions. The very early stages of titanium oxide growth corresponding to the formation of this rectangular phase were also investigated by Ti deposition on the oxygen chemisorbed phase under UHV conditions at 573 K. In this way it is possible to study the reaction of Ti with chemisorbed oxygen. Upon increasing the Ti coverage above 0.5 ML, an oxide film with a slightly distorted hexagonal unit cell begins to grow. The quasi-hexagonal phase of titanium oxide can also be formed by annealing at 773 K the rectangular phase. At higher coverages, when the substrate surface is completely covered by the oxide, the film exhibits a LEED pattern with a regular hexagonal unit cell

Electrodeposition of manganese dioxide coatings onto graphene foam substrates for electrochemical capacitors

Optimisation of electrodeposition routes of birnessite manganese dioxide (MnO2) coatings onto 3D graphene foam substrates enabled greater attainable capacitances. Current pulse deposition method resulted in highest achievable areal capacitance of 530 mF/cm2 under a 10 mA/cm2 current rate, cycling performance with 91% retention after 9000 cycles, as well as improved rate capability when compared to the cyclic voltammetry or galvanostatic deposition. Introduction of oxygen functional groups to the graphene foam added initial pseudocapacitance and accelerated the rate for nucleation and growth of the MnO2 crystal grains, resulting in an areal capacitance of 410 mF/cm2 under a 10 mA/cm2 current rate. However, in this case the increase in specific capacitance was accompanied by sluggish kinetics for charge storage seen via impedance spectroscopy. The charge storage mechanism of the deposited MnO2 films was investigated using in situ Raman microscopy and analysis of peak shifts revealed expansion and contraction of birnessite MnO2, relating to exchange of Na+ and H2O at the MnO2 interface

A LEED I-V structural determination of the c(4x2) Ni3O4/Pd(100) monolayer phase: an ordered array of Ni vacancies

The structure of the interface-stabilized c(4x 2) Ni3O4/Pd(100) monolayer has been determined by using Low EnergyElectron Diffraction (LEED) I\u2013V experiments. Tensor LEED simulations converged to a Rp factor of 0.22 with a structural model based on the NiO(100) surface, where all the atoms of the oxide phase are coplanar. In order to obtain the correct c(4 x 2) periodicityof the phase, a Ni vacancy array has been introduced into the model. In details, oxygen atoms sit on top of palladium atoms, while nickel atoms occupy the fourfold hollow sites. The lattice constant of NiO was contracted in order to match the substrate periodicity, and only a very small buckling of the Ni atoms (0.04 A ) was introduced. The most relevant change with respect to a rigid NiO(100) structure is the in-plane displacement of oxygen atoms by about 0.2 A \ub0 along directions almost coinciding with the (010) substrate azimuths, awayfrom the vacant Ni site. The proposed structure is perfectlycompatible with the STM images preliminarly reported in the literature