Intrinsic molecular fluorescence from porphyrin molecules on Au(100) has been realized by using a nanoscale multimonolayer decoupling approach with nanoprobe excitation in the tunneling regime. The molecular origin of luminescence is established by the observed well-defined vibrationally resolved fluorescence spectra. The molecules fluoresce at low "turn-on" voltages for both bias polarities, suggesting an excitation mechanism via hot electron injection from either tip or substrate. The excited molecules decay radiatively through Franck-Condon pi(*)-pi transitions.

Epitaxial growth of topological insulator Bi 2 Se 3 thin films on nominally flat and vicinal Si(111) substrates is studied. In order to achieve planner growth front and better quality epifilms, a two-step growth method is adopted for the van der Waal epitaxy of Bi 2 Se 3 to proceed. By employing vicinal Si (111) substrate surfaces, the in-pane growth rate anisotropy of Bi 2 Se 3 is explored to achieve single crystalline Bi 2 Se 3 epifilms, in which threading defects and twins are effectively suppressed. Optimization of the growth parameters has resulted in vicinal Bi 2 Se 3 films showing a carrier mobility of ~ 2000 cm 2 V -1 s -1 and the background doping of ~ 3 × 10 18 cm -3 of the as-grown layers. Such samples not only show relatively high magnetoresistance but also a linear dependence on magnetic field.

A transparent ZnO homostructural light-emitting diode (LED) with a structure of Au electrode/p(i)-ZnO film/n-ZnO single crystal/In electrode was fabricated using the technique of N2O plasma-enhanced pulsed laser reactive deposition. The contact between the p(i)-ZnO layer and n-ZnO wafer was found to exhibit nonlinear and rectifying current–voltage (I–V) characteristics. A current injection emission with bluish-white light was clearly observed at room temperature, and its intensity increased with increases in the injected electric current.

P-type ZnO films with carrier density 3-6 Â 10 18 cm À3 , resistivity 2-5 O cm and Hall mobility=0.1-0.4 cm 2 V À1 s À1have been grown on fused silica and glass substrate by pulsed laser reactive deposition using a pure metal Zn target in N 2 O plasma. The N acceptor doping was effectively enhanced using the active N formed by N 2 O gas passing through an electron resonance source during the pulsed laser reactive deposition process. P-type conduction was achieved by optimizing the microwave-input power (E) and deposition pressure (P N2O ). These electrical properties are sufficient for some practical applications. We expect this result to facilitate the fabrication of transparent p-n homojunctions suitable for light-emitting diodes. #

The effect of Ca(2+) ions on the hydration shell of sodium dodecyl carboxylate (SDC) and sodium dodecyl sulfonate (SDSn) monolayer at vapor/liquid interfaces was studied using molecular dynamics simulations. For each surfactant, two different surface concentrations were used to perform the simulations, and the aggregation morphologies and structural details have been reported. The results showed that the aggregation structures relate to both the surface coverage and the calcium ions. The divalent ions can screen the interaction between the polar head and Na(+) ions. Thus, Ca(2+) ions locate near the vapor/liquid interface to bind to the headgroup, making the aggregations much more compact via the salt bridge. The potential of mean force (PMF) between Ca(2+) and the headgroups shows that the interaction is decided by a stabilizing solvent-separated minimum in the PMF. To bind to the headgroup, Ca(2+) should overcome the energy barrier. Among contributions to the PMF, the major repulsive interaction was due to the rearrangement of the hydration shell after the calcium ions entered into the hydration shell of the headgroup. The PMFs between the headgroup and Ca(2+) in the SDSn systems showed higher energy barriers than those in the SDC systems. This result indicated that SDSn binds the divalent ions with more difficulty compared with SDC, so the ions have a strong effect on the hydration shell of SDC. That is why sulfonate surfactants have better efficiency in salt solutions with Ca(2+) ions for enhanced oil recovery.