Intense intrashell luminescence of Eu-doped single ZnO nanowires at room temperature by implantation created Eu-Oi complexes.

Successful doping and excellent optical activation of Eu(3+) ions in ZnO nanowires were achieved by ion implantation. We identified and assigned the origin of the intra-4f luminescence of Eu(3+) ions in ZnO by first-principles calculations to Eu-Oi complexes, which are formed during the nonequilibrium ion implantation process and subsequent annealing at 700 °C in air. Our targeted defect engineering resulted in intense intrashell luminescence of single ZnO:Eu nanowires dominating the photoluminescence spectrum even at room temperature. The high intensity enabled us to study the luminescence of single ZnO nanowires in detail, their behavior as a function of excitation power, waveguiding properties, and the decay time of the transition.

Stability of Subnanometer MoS Wires under a Realistic Environment.

The interaction of small molecules with low-dimensional structures plays a major role in many important practical processes such as metal hydride formation, energy storage systems, and catalysis. In this work, we carried out first-principles density functional theory calculations of hydrogen and oxygen adsorption as well as their diffusion on subnanometer MoS nanowires. The nanowires are robust against adsorption of hydrogen. On the other hand, interaction with oxygen shows that the nanowires can oxidize with a small barrier (0.20 eV). In addition, our findings indicate that the interaction with hydrogen or oxygen does not modify the metallic character of the nanowire. The calculations also show that the singlet state is the most stable for 2O adsorbed on the MoS nanowire. Such results open the path for understanding the behavior of MoS nanowires under a realistic environment.

Electronic structure of molecular hydrogen in MoS2nanopores.

Atom controlled sub-nanometer MoS2pores have been recently fabricated with promising applications, such gas sensing, hydrogen storage and DNA translocation. In this work we carried out first-principles calculations of hydrogen adsorption in tiny MoS2nanopores. Some of the pores show metallic behaviour whereas others have a sizeable band gap. Whereas adsorption of molecular hydrogen on bare pores are dominated by physisorption, adsorption in the nanopores show chemisorption behaviour with high selectivity depending on the pore inner termination. Finally, we show that functionalization with copper atoms leads to does not improve dignificantly the adsorption energies of selected pores.

Toward an Accurate Density-Functional Tight-Binding Description of Zinc-Containing Compounds.

An extended self-consistent charge density-functional tight-binding (SCC-DFTB) parametrization for Zn-X (X = H, C, N, O, S, and Zn) interactions has been derived. The performance of this new parametrization has been validated by calculating the structural and energetic properties of zinc solid phases such as bulk Zn, ZnO, and ZnS; ZnO surfaces and nanostructures; adsorption of small species (H, CO2, and NH3) on ZnO surfaces; and zinc-containing complexes mimicking the biological environment. Our results show that the derived parameters are universal and fully transferable, describing all the above-mentioned systems with accuracies comparable to those of first-principles DFT results.