Stabilization of the cubic phase of HfO2 by Y addition in films grown by metal organic chemical vapor deposition

Addition of yttrium in HfO2 thin films prepared on silicon by metal organic chemical vapor deposition is investigated in a wide compositional range (2.0-99.5 at. %). The cubic structure of HfO2 is stabilized for 6.5 at. %. The permittivity is maximum for yttrium content of 6.5-10 at. %; in this range, the effective permittivity, which results from the contribution of both the cubic phase and silicate phase, is of 22. These films exhibit low leakage current density (5x10(-7) A/cm(2) at -1 V for a 6.4 nm film). The cubic phase is stable upon postdeposition high temperature annealing at 900 degrees C under NH3. (c) 2006 American Institute of Physics

High magnetic field transport measurement of charge-ordered Pr0.5_{0.5}Ca0.5_{0.5}MnO3_3 strained thin films

We have investigated the magnetic-field-induced phase transition of charge-ordered (CO) Pr$_{0.5}$Ca$_{0.5}$MnO$_3$ thin films, deposited onto (100)-oriented LaAlO$_3$ and (100)-oriented SrTiO$_3$ substrates using the pulsed laser deposition technique, by measuring the transport properties with magnetic fields up to 22T. The transition to a metallic state is observed on both substrates by application of a critical magnetic field ($H_C>10T$ at 60K). The value of the field required to destroy the charge-ordered insulating state, lower than the bulk compound, depends on both the substrate and the thickness of the film. The difference of the critical magnetic field between the films and the bulk material is explained by the difference of in-plane parameters at low temperature (below the CO transition). Finally, these results confirm that the robustness of the CO state, depends mainly on the stress induced by the difference in the thermal dilatations between the film and the substrate.Comment: 10 pages, 6 figures. To be published in Phys. Rev.

Morphology and Photoluminescence of HfO2Obtained by Microwave-Hydrothermal

In this letter, we report on the obtention of hafnium oxide (HfO2) nanostructures by the microwave-hydrothermal method. These nanostructures were analyzed by X-ray diffraction (XRD), field-emission gum scanning electron microscopy (FEG-SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectrometry (EDXS), ultraviolet–visible (UV–vis) spectroscopy, and photoluminescence (PL) measurements. XRD patterns confirmed that this material crystallizes in a monoclinic structure. FEG-SEM and TEM micrographs indicated that the rice-like morphologies were formed due to an increase in the effective collisions between the nanoparticles during the MH processing. The EDXS spectrum was used to verify the chemical compositional of this oxide. UV–vis spectrum revealed that this material have an indirect optical band gap. When excited with 488 nm wavelength at room temperature, the HfO2nanostructures exhibited only one broad PL band with a maximum at around 548 nm (green emission)

Selective photocurrent generation in HfO2 and carbon nanotube hybrid nanocomposites under Ultra-Violet and visible photoexcitations

International audienceWe report on the photocurrent generation in HfO2-carbon nanotube (CNT) nanocomposites under Ultra-Violet (UV) and visible excitations at zero bias. Cubic phase HfO2 nanoparticles have been combined with multi-walled carbon nanotubes in this work. The cubic phase of HfO2 has been stabilized by oxygen vacancies which act as luminescent band gap states. In a broad UV-visible range of below band gap photoexcitation, a photocurrent is generated which was found to be most efficient under UV illumination. We discuss the possible mechanism in terms of a CNT assisted charge transfer involving optically active surface states of the HfO2 nanoparticles. The abrupt generation and relaxation responses of the photocurrent on/off cycles along with a constant steady state current as high as 200nA for 1mg of the nanocomposite, has potential in energy harvesting and other applications requiring stable charge retention

Metallic oxygen barrier diffusion applied to high-k deposition WODIM

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Investigations on new carbon-based nanohybrids combining carbon nanotubes, HfO2 and ZnO nanoparticles

International audienceIn this work, we present two types of hybrid materials. The first hybrid material is a combination of carbon nanotubes (CNT) with HfO2 nanoparticles. The latter constituent on its own exhibits unusual visible photoluminescence, which is in stark contrast to non-luminescent HfO2 in the bulk form. The small size of HfO2 nanoparticles, 2.6 nm in average, suggests surface-defect related origin of the observed photoluminescence. The other hybrid material is CNT-ZnO with the embedded ZnO nanoparticles ranging from 50nm to 100nm in size. ZnO represents a direct bandgap semiconductor renowned as highly-luminescent in a broad spectral range. The visible region is attributed to luminescence involving deep-level defects, and hence depends on the synthesis conditions. In this study we compare the morphology of the two hybrid materials with transmission electron microscopy. We further compare the photoluminescence properties and the influence of the CNT coupling on enhancing or suppressing defect related emissions. Finally, we present a novel hybrid material CNT-HfO2 capable of producing a photocurrent under zero bias

Non-aqueous Sol-Gel routes applied to atomic layer deposition

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Carboxylic Acids as Oxygen Supplying Agents for Atomic Layer Deposition of Oxide Thin Films

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