Large conductance modulation of gold thin films by huge charge injection via electrochemical gating

By using an electrochemical gating technique with a new combination of polymer and electrolyte, we were able to inject surface charge densities n(2D) as high as 3.5×10(15) e/cm(2) in gold films and to observe large relative variations in the film resistance, ΔR/R', up to 10% at low temperature. ΔR/R' is a linear function of n(2D)-as expected within a free-electron model-if the film is thick enough (≥25 nm); otherwise, a tendency to saturation due to size effects is observed. The application of this technique to 2D materials might allow extending the field-effect experiments to a range of charge doping where large conductance modulations and, in some cases, even the occurrence of superconductivity are expected.     

A new discrete particle swarm optimization approach for the single-machine total weighted tardiness scheduling problem with sequence-dependent setup times

In this paper we present a new Discrete Particle Swarm Optimization (DPSO) approach to face the NP-hard single machine total weighted tardiness scheduling problem in presence of sequence-dependent setup times. Differently from previous approaches the proposed DPSO uses a discrete model both for particle position and velocity and a coherent sequence metric. We tested the proposed DPSO mainly over a benchmark originally proposed by Cicirello in 2003 and available online. The results obtained show the competitiveness of our DPSO, which is able to outperform the best known results for the benchmark. In addition, we also tested the DPSO on a set of benchmark instances from ORLIB for the single machine total weighted tardiness problem, and we analysed the role of the DPSO swarm intelligence mechanisms as well as the local search intensification phase included in the algorithm.     

Iron sites in the FeCr ordered sigma phase

FeCr and Fe(CrNiMnMo) structurally ordered σ-phases have been studied. The Mössbauer parameters corresponding to the different crystallographic sites of iron atoms have been established. The spectral components have been attributed on the basis of both the order of symmetry around the sites and of an estimation of the isomer shift as a function of the number of Cr atoms n.n. of Fe atoms. Iron occupation of different sites obtained in this way are in good agreement with previous X-ray and synchrotron radiation diffraction results.     

Approach to a better understanding and modeling of (S)-dihydrofuran-2-yl, (S)-tetrahydrofuran-2-yl-, and furan-2-yl-β-dialkylaminoethanol ligands for enantioselective alkylation

This paper outlines our efforts to study the influence of an oxygen atom adjacent to the stereogenic center of β-aminoalcohol derivatives used as ligands for catalysts in the asymmetric alkylation of aldehydes. Thirty-four enantiomerically pure (S)-dihydrofuran-2-yl, (S)-tetrahydrofuran-2-yl-, and furan-2-yl-β-dialkylamino alcohols have been prepared from 1,4:3,6-dianhydromannitol, 1,4:3,6-dianhydrosorbitol, and aminoacids, and then have been evaluated as ligands for the enantioselective addition of diethylzinc to benzaldehyde. Attention has been focused on the structural features governing the extent of chiral induction, the reaction rate, and the chemical yield of 1-phenyl-1-propanol which has been promoted by this wide collection of β-dialkylamino alcohols.     

Synthesis and characterization of Zr(IV) and Y(III) complexes with monocyclopentadienyl ligands containing an additional site tethered by a coordinating 2,6-pyridine bridge. X-ray crystal structures of the zirconium complexes

A new monocyclopentadienyl ligand containing an additional site tethered by a coordinating 2,6-pyridine unit has been prepared, rac-2-(1′-hydroxy-2′,2′-dimethylpropyl)-6-(1″,1″-dimethyl-cyclopentadienylmethyl) pyridine dilithium salt, LLi₂ (rac-4) that is analogous to the ligands present in CGC. After reacting the dilithium salt of the ligand with ZrCl₄ in a molar ratio of 1:1 in THF the complex LZrCl₂·THF (rac-5) was obtained which forms an insoluble oligomeric species after the loss of THF upon purification. From the mater liquor two crystalline species of the formula LHZrCl₃ (rac-6) and LH₂ZrCl₄·THF (rac-7) were isolated, whose X-ray crystal structures are reported. The reaction of LLi₂ with Y(OTf)₃ afforded the probably dimeric species [LYOTf]₂ (rac-8) from which the complex [LY(CH₂Si(CH₃)₃)]₂ (rac-9) was obtained after reaction with LiCH₂Si(CH₃)₃.     

Photoemission band mapping via surface umklapp

We report the observation of a peak in the region of the sp band for 4 < hν < 10 eV in the normal emission UPS spectrum of the Cs-reconstructed Ag(110) surface. It disperses over ～ 2.5 eV and its therefore not due to the alkali itself, but rather to a bulk excitation which becomes visible because of surface umklapp. Using the appropriate reciprocal lattice vector, we have mapped the dispersion along the original direction in the three dimensional Brillouin zone and find good agreement with theory.     

Design and synthesis of multi-component 18 pi annulenic fluorofullerene ensembles suitable for donor-acceptor applications

A series of trannulene (all-trans annulene) derivatives of [60]fullerene have been prepared by reacting C(60)F(18) with methanetricarboxylate esters that incorporate a range of photoactive functions. All the compounds have the intense emerald-green colour of fullerene trannulenes, characterised by strong bands at ca. 612 and 667 nm. Single crystal X-ray studies show that the packing varies with the nature of the addend, attributable to differing steric effects. UV/vis absorption spectra display transitions of the respective fullerene and addend models, indicating absence of electronic interactions between them in the ground state. These now provide an extensive series for testing photoactive (light-harvesting) properties, with the exceptional properties of having strong visible light absorption. Their exceptional stability is attributed to the 18[small pi] aromatic circuit, inability to undergo nucleophilic substitution without disrupting this circuit, and a curved cage region that is shielded to reagents by the three bulky addends.     

Preparation of photoluminescent PMMA doped with tris(pyrazol-1-yl)borate lanthanide complexes

The neutral homoleptic Ln(III) complex Ln(Tp)₃ (Ln=Sm, Eu, Tb, Yb; Tp=hydrotris(pyrazol-1-yl)borate) were used as dopants for the preparation of novel photoluminescent poly(methyl methacrylate) glasses indicated as Ln(Tp)₃@PMMA. The doped polymers containing samarium, europium and terbium derivatives showed emission associated to f–f transitions in the visible range upon excitation with UV light, while a NIR emission was obtained from Yb(Tp)₃@PMMA. The maximum incident wavelength able to induce emissions from the Ln(Tp)₃-doped polymers depends upon the choice of the lanthanide ion. No meaningful antenna-effect was instead observed using dysprosium as metal centre.