Conductance peaks produced by kondo scattering from O2 in M-I-M tunnel junctions

Peaks centered about zero-bias in the dynamic conductance of Al-I-Au tunnel junctions condensed onto liquid-helium-cooled substrates are shown to be due to Kondo scattering from paramagnetic molecular oxygen trapped at the metal-insulator interface by studying the concentration dependence of the peaks in junctions intentionally doped with O₂.     

A New Route to Light Emitting Organic Materials Based on Triazine Derivatives

Novel light-emitting organic materials comprising conjugated oligomers chemically attached via a flexible spacer to an electron–or hole-conducting core were synthesized by Stille cross-coupling methodology and designed for tunable charge injection and optical properties. The hyperbranched structures have been characterized by ¹H NMR, ¹³C NMR, and UV-VIS spectroscopy. The obtained structures show good stability in common organic solvents such as CHCl₃, toluene, and CH₂Cl₂ and exhibit excellent thermal stability. A preliminary electroluminescence properties were also investigated. This class of materials will help to balance charge injection and transport and to spread out the charge recombination zone, thereby significantly improving the device efficiency and lifetime of unpolarized and polarized OLEDs.     

Nonequilibrium quantum criticality in open electronic systems

A theory is presented of quantum criticality in open (coupled to reservoirs) itinerant-electron magnets, with nonequilibrium drive provided by current flow across the system. Both departures from equilibrium at conventional (equilibrium) quantum critical points and the physics of phase transitions induced by the nonequilibrium drive are treated. Nonequilibrium-induced phase transitions are found to have the same leading critical behavior as conventional thermal phase transitions.     

Oxygen-related band gap state in single crystal rubrene

A molecular exciton signature is established and investigated under different ambient conditions in rubrene single crystals. An oxygen-related band gap state is found to form in the ambient atmosphere. This state acts as an acceptor center and assists in the fast dissociation of excitons, resulting in a higher dark and photoconductivity of oxidized rubrene. The band gap state produces a well-defined photoluminescence band at an energy 0.25 eV below the energy of the 0-0 molecular exciton transition. Two-photon excitation spectroscopy shows that the states are concentrated near the surface of naturally oxidized rubrene.     

Advances in methods and algorithms in a modern quantum chemistry program package

Advances in theory and algorithms for electronic structure calculations must be incorporated into program packages to enable them to become routinely used by the broader chemical community. This work reviews advances made over the past five years or so that constitute the major improvements contained in a new release of the Q-Chem quantum chemistry package, together with illustrative timings and applications. Specific developments discussed include fast methods for density functional theory calculations, linear scaling evaluation of energies, NMR chemical shifts and electric properties, fast auxiliary basis function methods for correlated energies and gradients, equation-of-motion coupled cluster methods for ground and excited states, geminal wavefunctions, embedding methods and techniques for exploring potential energy surfaces.     

Nanostructured electrochemical DNA biosensors for detection of the effect of berberine on DNA from cancer cells

Multi walled carbon nanotubes (MWNT) in dimethylformamide (DMF) or aqueous sodium dodecyl sulfate (SDS) solution, colloidal gold nanoparticles (GNP) in phosphate buffer solution (PBS), and a GNP–MWNT mixture in aqueous SDS solution have been investigated for chemical modification of a screen-printed carbon electrode used as the signal transducer of a dsDNA-based biosensor. Differential pulse voltammetry of the DNA redox marker and the guanine moiety anodic oxidation and cyclic voltammetry with K₃[Fe(CN)₆] as indicator revealed substantial enhancement of the response of the biosensor, particularly when MWNT in SDS solution was used. The biosensor was used in testing of berberine, an isoquinoline plant alkaloid with significant antimicrobial and anticancer activity. Berberine had a very strong, concentration-dependent, effect on the structural stability of DNA from the human cancer cells (U937 cells) whereas non-cancer cells were changed only when berberine concentrations were relatively high 75 and 50 μg mL⁻¹. Figure Schematic illustration of preparation of the nanostructured films: (a) layer-to-layer coverage (DNA/nanomaterial/SPE); (b) mixed coverage (DNA-nanomaterial/SPE)