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We report on the low-temperature electrical transport properties of large area boron and nitrogen codoped graphene layers (BNC). The temperature dependence of resistivity (5 K < T < 400 K) of BNC layers show semiconducting nature and display a band gap which increases with B and N content, in sharp contrast to large area graphene layers, which shows metallic behavior. Our investigations show that the amount of B dominates the semiconducting nature of the BNC layers. This experimental observations agree with the density functional theory (DFT) calculations performed on BNC structures similar in composition to the experimentally measured samples. In addition, the temperature dependence of the electrical conductivity of these samples displays two regimes: at higher temperatures, the doped samples display an Arrhenius-like temperature dependence thus indicating a well-defined band gap. At the lowest temperatures, the temperature dependence of the conductivity deviates from activated behavior and displays a conduction mechanism consistent with Mott's two-dimensional (2D) variable range hopping (2D-VRH). The ability to tune the electronic properties of thin layers of BNC by simply varying the concentration of B and N will provide a tremendous boost for obtaining materials with tunable electronic properties relevant to applications in solid state electronics.

Undoped and iron doped ZnO nanocrystals are observed to be ferromagnetic at room temperature. The role of short-range disorder in stabilizing ferromagnetism is evident from structural, optical, and electron paramagnetic resonance (EPR) measurements. The substitutional incorporation of Fe3+ at Zn sites is reflected in optical and EPR studies. Isolated as well as interacting Fe3+ ions are observed in EPR. An increase in saturation magnetization is associated with broadening of a ferromagnetic resonance feature with an increase in doping level. Co-, Mn-, and Fe-doped ZnO nanocrystals prepared by the same synthesis protocol confirm anticorrelation between photoluminescence efficiency and ferromagnetic ordering. M(T) curves indicate that the ferromagnetic nanocrystals are formed by the short-range exchange forces associated with the bound magnetic polaron at defect sites.

Room temperature ferromagnetic ordering is observed in chemically grown ZnO nanocrystals. Nanocrystals are simultaneously capped by two different organic molecules inducing p-type and n-type defects. A saturation magnetization of 0.008 emu/g is achieved at 300 K. Incorporation of Mn2+ ions at substitutional sites in nanocrystals gives rise higher saturation magnetic moment at lower doping level. ZnO nanocrystals codoped with Mn2+ and Co2+ and prepared under identical conditions revealed an increase in saturation magnetization. However, the saturation magnetic moment remains lower than that obtained for Co2+-doped ZnO nanocrystals prepared by the same method. An increase in saturation magnetization was invariably associated with quenching of photoluminescence emission. These findings reaffirm that magnetism in nanocrystals is a defect induced phenomenon that can be controlled by choice of capping agent as well as incorporation of the transition metal impurity. Magnetization as a function of temperature [M(...