1,720,992 research outputs found
Early stage in low-energy ion-induced damage on InP(110) surface
No full textThe change in the short-range order created by ion milling in the near surface region of InP single crystals wasinvestigated by primary beam diffraction modulated electron emission (PDMEE). The very early stage of the damagecreation by low energy (0.6-1 keV) Ar ions in normal and oblique incidence was studied. A simple model based on theweighted combination of perfectly crystalline and completely amorphous regions was used to model the experimental results.Evidence of a subsurface nucleation of the amorphization process was found. We also found that the total sputtering yield ismarkedly dependent on the ion dose, being on the undamaged surface much larger than its steady state value. Low energyelectron diffraction (LEED) measurements were also performed to correlate long-range and short-range order removal by ionbombardment. Finally, the ion damage on the GaAs and InP surfaces was comparatively discussed
Laterally confined magnetic nanometric structures
No full textBasic and applied aspects of magnetic nanostructures are presented and discussed, with emphasis on the state of the art fabrication methods and modeling
ZnO nanostructure formation on the Mo(001) surface
No full textIn this paper we have determined the role of oxidizing pressure and annealing temperature in the formation of ZnO nanostructures on the Mo surface. ZnO has been grown on Mo(001) by means of physical vapor deposition of Zn in molecular oxygen pressure. Combining STM, XPS, and XRD we have studied the relation between morphology, composition, and structure. ZnO grows as a film with (101Â ̄1) preferential orientation up to a thickness of 10 Ã, catalyzed by the Mo surface that provides oxygen available for oxide formation and limited by the residual polarity of the surface. Increasing the deposited amount, the role of the Mo interface becomes less effective, and part of the Zn remains metallic, forming clusters on the surface that catalyze the further growth of ZnO in the form of polycrystalline nanostructures. Surfactant Zn is removed by annealing, and peculiar oxide nanostructures are left on the surface. Increasing O pressure or reducing Zn flux allows control of nanostructure density and shape, while the continuous film underneath does not modify
In-Operando Optical Spectroscopy of Field-Effect-Gated Al-Doped ZnO
No full textTransparent conductive oxides (TCO) have the unique characteristics of combining optical transparency with high electrical conductivity; such a property makes them uniquely alluring for applications in visible and infrared photonics. One of their most interesting features is the large sensitivity of their optical response to the doping level. We performed the active electrical manipulation of the dielectric properties of aluminum-doped ZnO (AZO), a TCO-based on Earth-abundant elements. We actively tuned the optical and electric performances of AZO films by means of an applied voltage in a parallel-plate capacitor configuration, with SrTiO3 as the dielectric, and monitored the effect of charge injection/depletion by means of in-operando spectroscopic ellipsometry. Calculations of the optical response of the gated system allowed us to extract the spatially resolved variations in the dielectric function of the TCO and infer the injected/depleted charge profile at the interface
Growth and study of 3d Ni nanoparticles films deposited on inert substrates
No full textThe interest in metal nanostructured films has grown in the last years because of their fascinating physical properties and their potentiality in various applications, like magnetic recording industry and tribology. As an example, smaller particles are required in order to realize advanced magnetic memory units. This request constitutes an important challenge, because of the super-paramagnetic limit for the density of recorded bits, which makes conventional recording media with three-dimensional particles unstable [1].
We performed a study of 3d (Cu, Ni and Fe) metal nanoparticles films grown on oxidized Si and MgO inert substrates. The deposition has been obtained by making use of a recently developed experimental system, with a gas aggregation cluster source, a quadrupole mass filter and a deposition chamber [2,3]. The source can produce high flux of particles with variable size distribution in a range from 1 to 10 nm. We produced films of Cu, Ni and Fe particles of different size (from 3 to 5 nm average diameter) and thickness values, from 1 to 10 nm corresponding to regimes where the nanoparticles are sparse or they constitute a nanostructured film. The samples have been characterized ex-situ with scanning electron microscopy, atom force microscopy, scanning tunneling microscopy and electron spectroscopy techniques to check morphology and composition.
Magneto Optical Kerr Effect (MOKE) experiments have been performed on Ni grown on MgO(100) to investigate the role played by the magnetic dipole interaction between the particles. Results have shown that samples are paramagnetic at Room Temperature. We also performed a low temperature MOKE experiment on a 7 nm thick film of Ni nanoparticles with 5 nm average diameter grown on MgO(100), and we obtained a ferromagnetic hysteresis at T=100 K, revealing magnetic blocking at this temperature.
[1] see, for instance S. D. Bader, Rev. of Mod. Phys. 78 (2006) 1 and ref.s therein.
[2] C. Binns, SUrf. Sci. Rep. 44 (2001) 1.
[3] C. Binns et al., J. Phys. D: Appl Phys. 38 (2005) R357
Scanning tunnelling microscopy of MgO ultrathin films on Ag(001)
No full textThe morphology of ultrathin epitaxial MgO layers reactively grown on Ag~001! was investigated by usingscanning tunnelling microscopy. In the initial deposition stage Ag atoms are partially removed from thesubstrate and form extended monoatomic islands leaving vacancy islands in the substrate itself. On individualsubstrate terraces Ag is thereafter found at three atomic levels. For submonolayer deposition MgO condensatesin form of small islands of monoatomic height, located on the original substrate, on the protruding Ag islandsand on the vacancy islands as well. The largest Ag~001! fractional coverage by monoatomic MgO islands is70%. A limited amount of MgO bilayers or trilayers has also been detected ~about 1% fractional coverage!. Atthe nominal deposition of 1 ML flat, squared and connected MgO domains of about 10 nm in width form, withedges along the @110# directions. The actual substrate fractional coverage is about 85% and the occurrence ofbilayers and multilayers becomes significant ~about 30 and 5% fractional coverage, respectively!, resulting inthe formation of three-dimensional pyramidal MgO islands
Morphology and Magnetic Properties of size-selected Ni nanoparticle films
No full textWe present the results of a study on the morphology and magnetic properties of size-selected Ni nanoparticles films grown on Si/SiOx substrates. The films were produced by deposition of preformed Ni nanoparticles, using a gas aggregation nanocluster source and an electric quadrupole mass filter. The diameter d of the produced particles ranged between 3 and 10 nm. The morphology of the films, with average thickness t varying from t = 0.5 up to t = 7nm, was studied with Atomic Force Microscopy and Scanning Electron Microscopy, combining in this way information about height and lateral topography. We observed the presence of some small aggregates made of 2 o 3 particles at the early stage of film formation, probably due to some degree of cluster diffusion on the substrate, and particle average flattening. For increasing values of t, large agglomerates are formed in the films, resulting in a porous structure. Information about the magnetic properties was obtained with Field Cooled-Zero Field Cooled (FC/ZFC) magnetization curves. We observed a reversibility-irreversibility transition at temperatures 70 K TI, even for the lowest coverage studied (t = 2 nm for ZFC/FC measurements, = 5.5 nm). A comparison with Montecarlo simulations of the FC/ZFC curves reveals the concurrence between inter-particle exchange interaction and single particle random anisotropy
Graphite/epoxy composite for building Bipolar Plates
Full text linkBipolar plates (BPs) are important components of Proton Exchange Membrane Fuel Cells (PEMFC). Graphite-epoxy composites, having a better corrosion resistance than metal-based BPs and better mechanical properties than graphite BPs, are a promising alternative. In this study, we tried to develop graphite-epoxy composites meeting the technical US DOE targets for 2020, with a proper choice of manufacturing conditions that ensure a good compromise between conductivity, flexural strength, and gas permeability. In particular, we studied the influence of the filler to binder ratio, changed the molding temperature and time, and investigated the effects of increasing pressure both on in-plane conductivity and on helium permeability. We found that both formulation and molding pressure are crucial in determining the permeability of the graphite-epoxy composites, whereas molding temperature and time seem to play a minor role
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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