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Danciu, A.-I..a b, Musat Busani Pinto Barros Maria Rego Maria Ferraria Carvalho Martins Fortunato V. a T. b. "Uniform arrays of ZnO 1D nanostructures grown on Al:ZnO seeds layers by hydrothermal method." Journal of Nanoscience and Nanotechnology. 13 (2013): 6701-6710. AbstractWebsite

In obtaining uniform array of ZnO 1D nanostructures, especially using solution based methods, the thickness and the morphology of the epitaxial seeds layer are very important. The paper presents the effect of the thickness and the morphology of the Al:ZnO seeds layer on the morphology and properties of ZnO nanowires array grown by hydrothermal method. Compact and vertically aligned ZnO 1D nanostructures were obtained. Concentration of 0.02 M of zinc nitrate was found to be optimal for growing nanowires with diameters up to 50 nm and lengths between 1.5 and 2.5 microns. Using 0.04 M solution, nanorods with diameter between 50 and 100 nm were obtained. The correlation between the crystal structure and optical properties of ZnO nanowires is discussed. From electrical measurements on single nanowire, resistivity value of 9×10?2 cm was obtained. The I-V curves of single ZnO NWs show quasi diode characteristic when an e-beam is irradiating the NWs, and a typical semiconductive behaviour when the e-beam is turned off. Copyright © 2013 American Scientific Publishers.

d Deuermeier, J.a b, Bayer Yanagi Kiazadeh Martins Klein Fortunato T. J. M. b. "Substrate reactivity as the origin of Fermi level pinning at the Cu2O/ALD-Al2O3 interface." Materials Research Express. 3 (2016). AbstractWebsite

The reduction of aCu2O layer on copper by exposure toTMAduring the atomic layer deposition of Al2O3 has recently been reported. (Gharachorlou et al 2015 ACS Appl. Mater. Interfaces 7 16428-16439). The study presented here analyzes a similar process, leading to the reduction of a homogeneous Cu2O thin film, which allows for additional observations. Angle-resolved in situ X-ray photoelectron spectroscopy confirms the localization of metallic copper at the interface. The evaluation of binding energy shifts reveals the formation of aCu2O/Cu Schottky barrier, which gives rise to Fermi level pinning in Cu2O. An initial enhancement of the ALD growth per cycle (GPC) is only observed for bulk Cu2O samples and is thus related to lattice oxygen, originating from regions lying deeper than just the first few layers of the surface. The oxygen out-take from the substrate is limited to the first few cycles, which is found to be due to a saturated copper reduction, rather than the oxygen diffusion barrier of Al2O3. © 2016 IOP Publishing Ltd.

c Deuermeier, J.a b, Wardenga Morasch Siol Nandy Calmeiro Martins Klein Fortunato H. F. b J. "Highly conductive grain boundaries in copper oxide thin films." Journal of Applied Physics. 119 (2016). AbstractWebsite

High conductivity in the off-state and low field-effect mobility compared to bulk properties is widely observed in the p-type thin-film transistors of Cu2O, especially when processed at moderate temperature. This work presents results from in situ conductance measurements at thicknesses from sub-nm to around 250 nm with parallel X-ray photoelectron spectroscopy. An enhanced conductivity at low thickness is explained by the occurrence of Cu(II), which is segregated in the grain boundary and locally causes a conductivity similar to CuO, although the surface of the thick film has Cu2O stoichiometry. Since grains grow with an increasing film thickness, the effect of an apparent oxygen excess is most pronounced in vicinity to the substrate interface. Electrical properties of Cu2O grains are at least partially short-circuited by this effect. The study focuses on properties inherent to copper oxide, although interface effects cannot be ruled out. This non-destructive, bottom-up analysis reveals phenomena which are commonly not observable after device fabrication, but clearly dominate electrical properties of polycrystalline thin films. © 2016 Author(s).

Dias, A.G., Guimarães Martins L. R. "The effect of static electric and magnetic fields on the optical properties of amorphous hydrogenated silicon films produced by r.f. glow discharge." Thin Solid Films. 89 (1982): 307-313. AbstractWebsite

The aim of the present work was to study the optical properties of amorphous hydrogenated silicon films produced by capacitive and inductive r.f. glow discharge in a 3%SiH4-Ar gas mixture. The effect of the application of static electric and magnetic fields during the film formation on the photoconductivity, photoactivation energy, recombination mechanisms and optical gap was thoroughly investigated. Films prepared in a capacitively or inductively coupled discharge show bias-dependent photoconductivities, which reach about 10-4 Ω-1 cm-1 for an inductive discharge with a negative bias and about 10-5 Ω-1 cm-1 for a capacitive discharge with a positive bias. The optical gap is of the order of 1.55 eV for capacitive films and is bias dependent for inductive films (1.45-1.85 eV). A superimposed magnetic field (of about 1 kG) increases the photoconductivity by one order of magnitude for both deposition methods. The optical gap is field dependent for inductive films (1.6-1.8 eV) and is about 1.6 eV for capacitive films. The main recombination mechanism at a moderate photon flux (less than 1014 cm-2 s-1) is monomolecular for all deposition conditions. The photoactivation energy lies between 0.1 and 0.2 eV for capacitive films and is about 0.1 eV for inductive films. It was also found that, by using suitable crossed electric and magnetic fields, it was possible to control the density and nature of the defect states in the films. These are correlated with the type of hydrogenated silicon species and with the amount of hydrogen incorporated into the films, which markedly influence the film properties. © 1982.

Dirani, E.A.T., Pereyra Andrade Soler Martins I. A. M. "Effect of the deposition parameters on the electro optical properties and morphology of microcrystalline hydrogenated silicon alloys." Conference Record of the IEEE Photovoltaic Specialists Conference. Vol. 2. 1990. 1588-1590. Abstract

Microcrystalline phosphorus-doped hydrogenated silicon alloy films were deposited in a remote plasma CVD (chemical vapor deposition) system. The film properties were studied as a function of RF power density and hydrogen concentration in the reaction gas mixture. The properties of the deposited films are extremely sensitive to the RF power density in the studied range of 250 mW/cm2 to 625 mW/cm2. Very low values of electrical resistivity were obtained. For an RF power density of 500 mW/cm2, ρ = 3 × 10-2 Ω-cm, while ρ = 1.9 × 103 Ω-cm for 625 mW/cm2, indicating the predominance of the amorphous tissue over the microcrystalline phase. High doping efficiencies which can be correlated to large grain size are indicated by the very low values of the activation energy as low as 30 meV for 500 mW/cm2, that were obtained.