O. V. Kononenko

Luminescence of bound excitons in epitaxial ZnO thin films grown by plasma-assisted molecular beam epitaxy

Luminescence properties of ZnO films, which have been epitaxially grown on c-sapphire (0001) substrates by plasma-assisted molecular beam epitaxy, are investigated by means of different excitation sources and their measurement conditions. With the increase of measurement temperature, photoluminescence spectra clearly present, the appearance of different bound-exciton peaks (I10 line) with an abrupt increase of emission intensity at the measurement temperature of 30-50K. Hypothetical explanations on the basis of thermalization effects, vibronic/rotational resonance states, and the involvement of the B-valence level in emission are given. In cathodoluminescence (CL), the deep level emission intensity was enlarged with the electron beam penetration depth due to the higher defect density near the interface between ZnO and the sapphire. From the CL image of the ZnO film, the dislocation density was estimated as 6×108-3×109∕cm2. The lasing phenomenon was observed at the threshold power density of 1.3MW∕cm2 at 300K.

Elemental vapor-phase synthesis of nanostructured zinc oxide

We systematize experimental data on the elemental vapor-phase synthesis of zinc oxide nanocrystal arrays on substrates. This process may yield nanostructures differing in shape and dimensions, in particular, well-aligned ZnO nanorod arrays. A model is proposed in which aligned zinc oxide nanorod arrays may grow by the vapor-liquid-solid (VLS) mechanism, and liquid zinc nanodroplets forming on the substrate surface at the beginning of the process catalyze one-dimensional growth. The VLS process is accompanied by zinc oxide deposition onto the lateral surface of the nanorods from the vapor phase. The relative rates of these processes influence the shape of the nanorods and the thickness of the polycrystalline underlayer. Optimizing the deposition conditions, one can grow uniform arrays of aligned high-quality ZnO nanorods with no catalysts and with no special substrate preparation steps.

Surface acoustic wave propagation in graphene film

Surface acoustic wave (SAW) propagation in a graphene film on the surface of piezoelectric crystals was studied at the BESSY II synchrotron radiation source. Talbot effect enabled the visualization of the SAW propagation on the crystal surface with the graphene film in a real time mode, and high-resolution x-ray diffraction permitted the determination of the SAW amplitude in the graphene/piezoelectric crystal system. The influence of the SAW on the electrical properties of the graphene film was examined. It was shown that the changing of the SAW amplitude enables controlling the magnitude and direction of current in graphene film on the surface of piezoelectric crystals.

SYNTHESIS OF ZNO NANOTETRAPODS

ZnO tetrapods have been grown on silicon substrates by chemical vapor deposition, and the effect of synthesis conditions on their morphology and size has been studied. The cathodoluminescence spectra of the tetrapods show two emissions characteristic of ZnO, in the UV and green spectral regions. Their relative intensities depend on the vapor composition during synthesis and annealing conditions. A mechanism of tetrapod growth at significant supersaturations is discussed.

Size effect relating to the extraordinary and the ordinary Hall effect in ultrathin Fe-Pt films

An experimental study is presented on the extraordinary and the ordinary Hall effect in ultrathin Fe-Pt films down to 1.5 nm thick deposited by laser ablation in a high vacuum. The variation of the Hall coefficients with film thickness is investigated. It is shown that the extraordinary Hall coefficient varies as film resistivity and grows with decreasing film thickness. The extraordinary and the ordinary Hall coefficient are found to depend on the substrate material.

ZnO Nanorods: Synthesis by Catalyst-Free CVD and Thermal Growth from Salt Composites and Application to Nanodevices

Oleg V. Kononenko1, Arkady N. Redkin1, Andrey N. Baranov3, Gennady N. Panin1,2, Artem A. Kovalenko4 and Anatoly A. Firsov1 1Institute of Microelectronics Technology and High Purity Materials, RAS Chernogolovka, Moscow region, 2Quantum-Functional Semiconductor Research Center, Department of Physics, Dongguk University, Seoul, 3Chemistry Department, Moscow State University Moscow, 4Department of Materials Science, Moscow State University, Moscow, 1,3,4Russia 2South Korea

Electrical and Magnetic Properties of Doped ZnO Nanowires

ZnO nanowires doped with Mn, Fe, Sn, and Li during the thermal growth following direct chemical synthesis were investigated using electric and magnetic measurements. Currentvoltage characteristics of individual nanowires configured as a two-terminal device with Al electrodes show apparent rectify behavior indicating the Schottky-like barrier formation and resistivity being less 3 Ω·cm. Reproducible resistance modulation by a dc voltage at room temperature is observed. Magnetic susceptibility of the doped nanowires as a function of temperature demonstrates Curie–Weiss behavior. Magnetization versus field curves show hysteresis with the coercive field of about 200 Oe. The spatially-resolved magnetic force measurements of individual nanowires revealed the magnetic domain structure. The domains align perpendicular to c-axis and can be polarized in the external magnetic field.

Resistance Switching Induced by an Electric Field in ZnO:Li, Fe Nanowires

We report on a stable hysteresis in the current‐voltage curve of an individual ZnO nanowire doped by Li and Fe impurities and a persisting reproducible resistance modulation by a dc voltage at room temperature. I‐V curves corresponding to resistive switching are explained by a nonuniform distribution of trapped charges and their electric polarization when the voltage is varied.

Relationship Between Structure and Electromigration Characteristics of Pure Aluminum Films

Aluminum films were deposited from a high purity aluminum source by the self-ion assisted technique onto oxidized silicon wafers with TiN sub-layers. The ions were accelerated toward the substrate by potentials of 0, 3 and 6 kV. The films were patterned into strips 670 μm long and 8 μm wide using photo-lithographic procedures and wet etching. Average drift velocities were measured in the films tested under electromigration conditions. Electromigration activation energy was obtained for the films. It was found that electromigration activation energy increased with the acceleration potential. The strength of the (111) fiber texture, however, decreased with the acceleration potential. Therefore, the weaker textures resulted in higher electromigration activation energies. These results can be explained in terms of grain boundary structure, which controls electromigration behavior. By using orientation imaging microscopy to characterize the structures, it was shown that the weaker textured specimens contained a high fraction of low angle and low diffusivity grain boundaries.

Structure of graphene nanotube hybrid materials produced via single-stage CVD

The structures of graphene layer-carbon nanotube hybrid films produced via CVD with a single-stage flow of acetylene into a chamber containing a prepared substrate are studied. It is shown that such films have a hybrid double-layer structure consisting of a graphene layer and a dense continuous network of nanotubes. The graphene layer contains continuous extended areas 10–50 μm in size and island areas ∼0.1 μm in size. TEM images lead to the conclusion that the graphene layer and carbon nanotubes are bound by covalent bonds.