ZnO is a promising material for the fabrication of light emitting devices. One approach to achieve this goal is to use ZnO nanorods because of their expected high crystalline and optical quality. Catalyst free growth of nanorods by metalorganic chemical vapour deposition (MOCVD) was carried out on (0001) sapphire substrates. Arrays of well-aligned, vertical nanorods were obtained with uniform lengths and diameters. A thin wetting layer in epitaxy with the sapphire substrate is formed first, followed by pyramids and nanorods. The nucleation of nanorods occurs either directly at the interface, or later on top of some of the pyramids, suggesting various nucleation mechanisms. It is shown that crystal polarity plays a critical role in the growth mechanism with nanorods of Zn polarity and their surrounding pyramids with O polarity. A growth mechanism is proposed to explain that most threading dislocations lie in the wetting layer, with only a few in the pyramids and none in the nanorods.

We report room-temperature Raman scattering results on perovskite-type [(La0.7Sr0.3MnO3)m/(SrTiO3)n]15 multilayers, m and n being the thicknesses of layers alternated 15 times. Distinct changes in the Raman spectra for different n and m have been analysed in the light of structural modifications and point to a tensile-strain-induced rhombohedral-to-orthorhombic phase transition in the La0.7Sr0.3MnO3 (LSMO) layers. As a matter of fact, the presented results provide a new structural basis for the earlier proposed magnetic phase separation model. The present work validates tensile strain as an important variable in thin films, which not only allows us to distort the perovskite structure within a crystallographic space group but can readily induce a transition towards another space group and its related physical properties. As shown in this study, the fabrication of superlattice materials then constitutes a powerful method to stabilize such artificial crystal structures (here artificial orthorhombic LSMO at 300 K) over a greater overall thickness than would be possible in single films.

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( La 0.7 Sr 0.3 MnO 3 / SrTiO 3 ) 15 superlattices have been grown by pulsed liquid-injection metalorganic chemical vapor deposition on monocrystalline substrates such as LaAlO3, SrTiO3, and MgO. The pulsed-injection technique allows one to control precisely the amount of precursors delivered to the deposition chamber and thus the thickness of each individual layer. The period of the superlattices depends indeed linearly on the number of injected droplets. In our deposition conditions, the average growth rates are ∼0.130 nm/injection for La0.7Sr0.3MnO3 and 0.042 nm/injection for SrTiO3, with no significant difference as regard to the substrate used. The strain’s state of the superlattices depends on the relative thicknesses of the La0.7Sr0.3MnO3 and SrTiO3 layers and also on the substrate used. Finally, the deposition of superlattices with ultrathin interlayers of few unit cells has been demonstrated.

We report on the collective integration technology of vertically aligned nanowires (NWs). Si and ZnO NWs have been used in order to develop a generic technological process. Both mineral and organic planarizations of the as-grown nanowires have been achieved. Chemical vapour deposition (CVD) oxides, spin on glass (SOG), and polymer have been investigated as filling materials. Polishing and/or etching of the composite structures have been set up so as to obtain a suitable morphology for the top and bottom electrical contacts. Electrical and optical characterizations of the integrated NWs have been performed. Contacts ohmicity has been demonstrated and specific contact resistances have been reported. The photoconducting properties of polymer-integrated ZnO NWs have also been investigated in the UV-visible range through collective electrical contacts. A small increase of the resistivity in the ZnO NWs under sub-bandgap illumination has been observed and discussed. A comparison of the photoluminescence (PL) spectra at 300 K of the as-grown and SOG-integrated ZnO nanowires has shown no significant impact of the integration process on the crystal quality of the NWs.

We investigate the behavior of silicon and ZnO nanowires in the evanescent field on the surface of a silicon nitride waveguide. The nanowires in aqueous solution are attracted to the waveguide by the gradient force and then propelled along the waveguide by the radiation pressure. Observed experimental velocities are higher for silicon nanowires than for ZnO nanowires, with relatively large variations for both kinds of nanowires. Simulations with the finite element method show that the forces on the nanowires are very dependent on their geometrical parameters and refractive index, which explains the observed variations.

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