The search for ferromagnetism above room temperature in dilute magnetic semiconductors has been intense in recent years. We report the first observations of ferromagnetism above room temperature for dilute (<4 at.%) Mn-doped ZnO. The Mn is found to carry an average magnetic moment of 0.16 mu(B) per ion. Our ab initio calculations find a valance state of Mn(2+) and that the magnetic moments are ordered ferromagnetically, consistent with the experimental findings. We have obtained room-temperature ferromagnetic ordering in bulk pellets, in transparent films 2-3 microm thick, and in the powder form of the same material. The unique feature of our sample preparation was the low-temperature processing. When standard high-temperature (T > 700 degrees C) methods were used, samples were found to exhibit clustering and were not ferromagnetic at room temperature. This capability to fabricate ferromagnetic Mn-doped ZnO semiconductors promises new spintronic devices as well as magneto-optic components.

The ultrafast timescale of electron transfer processes is crucial to their role in many biological systems and technological devices. In dye-sensitized solar cells, the electron transfer from photo-excited dye molecules to nanostructured semiconductor substrates needs to be sufficiently fast to compete effectively against loss processes and thus achieve high solar energy conversion efficiencies. Time-resolved laser techniques indicate an upper limit of 20 to 100 femtoseconds for the time needed to inject an electron from a dye into a semiconductor, which corresponds to the timescale on which competing processes such as charge redistribution and intramolecular thermalization of excited states occur. Here we use resonant photoemission spectroscopy, which has previously been used to monitor electron transfer in simple systems with an order-of-magnitude improvement in time resolution, to show that electron transfer from an aromatic adsorbate to a TiO(2) semiconductor surface can occur in less than 3 fs. These results directly confirm that electronic coupling of the aromatic molecule to its substrate is sufficiently strong to suppress competing processes.

Phosphorene has been attracted intense interest due to its unexpected high carrier mobility and distinguished anisotropic optoelectronic and electronic properties. In this work, we unraveled strain engineered phosphorene as a photocatalyst in the application of water splitting hydrogen production based on density functional theory calculations. Lattice dynamic calculations demonstrated the stability for such kind of artificial materials under different strains. The phosphorene lattice is unstable under compression strains and could be crashed. Whereas, phosphorene lattice shows very good stability under tensile strains. Further guarantee of the stability of phosphorene in liquid water is studied by ab initio molecular dynamics simulations. Tunable band gap from 1.54 eV at ambient condition to 1.82 eV under tensile strains for phosphorene is evaluated using parameter-free hybrid functional calculations.Appropriate band gaps and band edge alignments at certain pH demonstrate the potential application of phosphorene as a sufficiently efficient photocatalyst for visible light water splitting. We found that the strained phosphorene exhibits significantly improved photocatalytic properties under visible-light irradiation by 2 calculating optical absorption spectra. Negative splitting energy of absorbed H 2 O indicates the water splitting on phosphorene is energy favorable both without and with strains.

We report the results of our first-principles investigation on the interaction of the nucleobases adenine (A), cytosine (C), guanine (G), thymine (T), and uracil (U) with graphene, carried out within the density functional theory framework, with additional calculations utilizing Hartree-Fock plus second-order Møller-Plesset perturbation theory. The calculated binding energy of the nucleobases shows the following hierarchy: G > T ≈ C ≈ A > U, with the equilibrium configuration being very similar for all five of them. Our results clearly demonstrate that the nucleobases exhibit significantly different interaction strengths when physisorbed on graphene. The stabilizing factor in the interaction between the base molecule and graphene sheet is dominated by the molecular polarizability that allows a weakly attractive dispersion force to be induced between them. The present study represents a significant step towards a first-principles understanding of how the base sequence of DNA can affect its interaction with carbon nanotubes, as observed experimentally. PACS numbers: 68.43.-h, 81.07.De, 82.37.RsDNA-coated carbon nanotubes represent a hybrid system which unites the biological regime and the nanomaterials world. They possess features which make them attractive for a broad range of applications, e.g., as an efficient method to separate carbon nanotubes (CNTs) according to their electronic properties [1, 2, 3], as highly specific nanosensors, or as an in vivo optical detector for ions. Potential applications of single-stranded DNA (ss-DNA) covered CNTs range from electron sensing of various odors [4], to probing conformational changes in DNA triggered by shifts in the surrounding ionic concentration [5], and detection of hybridization between complementary strands of DNA [6,7]. The interaction of DNA with CNT is not limited to the outer surface of the tube; it has also been experimentally demonstrated that ssDNA can be inserted into a CNT [8], further enhancing the potential applications of this nano-bio system.The details of the interaction of DNA with CNTs have not yet been fully understood, though it is generally assumed to be mediated by the π-electron networks of the base parts of DNA and the graphene-like surface of CNTs. One would like to obtain a better understanding of the binding mechanism, and the relative strength of base-CNT binding as it is indicated experimentally from sequence-dependent interactions of DNA with CNTs [3,4]. In this Letter, we present the results of our first-principles study of the interaction of nucleobases with a graphene sheet as a significant step towards a deeper understanding of the interaction of ssDNA with * Corresponding authors. CNTs.Previous theoretical studies focused on the adsorption of the nucleobase adenine on graphite [9]. In the present study, we have considered all five nucleobases of DNA and RNA, namely the two purine bases adenine (A) and guanine (G), and the three pyrimidine bases cytosine (C), thymine (T), and uracil (U). Our specific interest is to assess the subtl...