Symposium : C
|Nanopolycrystals : Marc Verdier|
|08:30||Local strains in polycrystalline thin films: investigation by coherent x-ray diffraction and microbeam x-ray scattering|
Authors : Olivier Thomas (a,b), Nicolas Vaxelaire (a,b), Stéphane Labat (a,b) (a) Aix-Marseille Université, IM2NP (b) CNRS, IM2NP (UMR 6242), Faculté des Sciences et Techniques, Campus de St Jérome, F-13397 Marseille Cedex, France
Resume : Very high stresses may arise in thin films and in nano-sized structures (lines, dots, etc) because of the constraint of the substrate to which they are attached. The origin and mag-nitude of these stresses are of great interest in technology as many fabrication and reliability problems are stress related. Robust methods (e.g. the sin2 method) exist for determining average strains in thin layers. In polycrystalline thin films very large strain variations may occur between grains and inside a single grain because of elastic and plastic anisotropy. High spatial resolution non-destructive mapping of these strains remains an important challenge in materials science. X-ray diffraction is an ideal tool to measure non-destructively displacement fields at very local scales. Thanks to third generation synchrotron radiation sources and the development of focusing x-ray optics it is possible to image strain fields with a spatial resolution as small as 10 nm. I will discuss two strategies that may be used for strain imaging: (i) sub-micrometer x-ray beams, which yield direct space resolution of the order of the beam size; (ii) coherent x-ray diffraction, where direct space resolution arises from high resolution in reciprocal space. These methods are fully compatible with in situ annealing and allow for thermo-mechanical evaluation of single grain behavior in polycrystalline films.
|09:00||Plastic deformation and mechanisms of fully dense nanocrystalline fcc noble metals|
Authors : Prof. Dr. Hans-Jörg Fecht University of Ulm, Institute of Micro and Nanomaterials Albert-Einstein-Allee 47, D-89081 Ulm, Germany Institute of Nanotechnology, Karlsruhe Institute of Technology KIT, D-76021 Karlsruhe, Germany
Resume : Recent results on the fundamentals of plastic deformation of fully dense nanocrystalline materials will be presented. The first model system investigated is Pd (fcc) and several single-phase Pd alloys while it is found that “pure” nanocrystalline Pd-samples are inherently unstable against grain growth. The experiments focus on mechanical tests using new testing equipment for miniaturized specimens with different stress state conditions. The aim is to obtain a significantly improved database of materials behaviour for these alloys at a grain size around 10 nm, since this has previously only been explored sporadically, and to elucidate and describe the microscopic mechanisms that mediate the deformation with maximum stress at fracture up to 1.8 GPa (comparable to Pd-based bulk metallic glass).These results are in compression whereas under tensile conditions all materials in the nanocrystalline state are inherently brittle.
|Thin films : Marc Verdier|
|09:30||Compressive stress and defect generation in sputtered thin films - influence of deposited energy and effect of grain size|
Authors : A. Fillon, A. Michel, G. Abadias, C. Jaouen Département Physique et Mécanique des Matériaux, Institut P', UPR 3346, CNRS-Université de Poitiers, SP2MI - Téléport 2, Bd Marie et Pierre Curie, BP 30179, 86962 Futuroscope-Chasseneuil, France
Resume : Nanoscale thin films may exhibit new physical properties with potential applications in novel electrical, optical or mechanical devices. To this end, a fine control of the film microstructure is essential, and the ability to tune the energy of the deposited species is a major advantage of magnetron sputtering. Here, the issue of energy transfer due to incoming particles during sputtering is addressed. In-situ substrate curvature measurements, using a multi-beam laser set-up provide real time determination of stress evolution during magnetron sputter deposition of Mo1-xSix thin films. The choice of this system was guided by the remarkable ability of modifying grain size, from ~10 nm up to ~1 µm by appropriate choice of seed layer and composition. Variables such as sputtering gas pressure, substrate biasing and crystalline grain size are shown to strongly affect the stress level measured during growth. To interpret the stress data, and elucidate processing-structure relationship, a detailed ex-situ microstructural and elastic strain characterization have been performed, using XRD, AFM and HRTEM. Compressive stress evolution due to atomic peening is observable only above a first critical energy threshold. Grain-size dependence of stress confirms that defect creation is confined to the grain boundaries. Further increase of the deposited energy results in a second threshold causing the creation of additional volume defects, i.e. expansion of the unit cell. Finally, a deposited energy - composition space diagram is proposed depicting the existence of biaxial or hydrostatic stress domains and evidencing the strong dependence of the critical energy thresholds with the material parameters.
|09:45||Electrical properties of composite films with columnar inclusions|
Authors : Martin Švec1, Stanislav Novák1, Rudolf Hrach1,2, Daniel Máslo1 1 Department of Physics, Faculty of Science, J. E. Purkinje University, České mládeže 8, 400 96 Ústí nad Labem, Czech Republic 2 Department of Surface and Plasma Science, Faculty of Mathematics and Physics, Charles University, V Holešovičkách 2, 180 00 Prague 8, Czech Republic
Resume : Composite films are very interesting materials for their extraordinary mechanical, electrical and optical properties. These properties can be strongly influenced by geometry of inclusions embedded into a matrix. We are dealing with particles of a columnar shape in our contribution. A correlation between a slant of inclusions and a resistivity of the structure was experimentally observed and measured. We study this phenomenon with a self-made computer experiment. The model consists of generation of the structures with columnar inclusions, their morphological and resistivity analysis. The generation of the structures is done with the Monte Carlo method, the morphological analysis uses the theory of percolation methods (the modified burning method) to determine an ohmic conductivity network, so-called infinite cluster, and electrical properties are studied with the network analysis methods. Our model corresponds with the experimental measurements and shows how the slant of inclusions influences the electrical resistivity. It is shown that the electrical resistivity increases with the angle of deposition, i.e. with the angle of inclusions slant. These observations are analysed and discussed.
|Miscellaneous : Yener Kuru|
|10:30||Trapping of molecular magnetic nanoparticles in a nanogap|
Authors : Y. Vaheb, L.E. Calvet, (Insitut d’Electonique Fondamentale, Unviersité Paris-Sud) N. Dia, T. Mallah, L. Catala (ICMMO, Université Paris-Sud)
Resume : Recently nanomagnets have attracted attention due to their potential applications in high density storage devices. Current transport has been investigated for Co nanoparticles and single molecules, however, molecular magnetic clusters have received much less attention. Such nanoparticles have spin intermediate between that of single molecules (S < 50) and metallic nanocrystals (S ~ 1000) and thus promise to also provide insights into fundamental physics. Molecular magnetism is typically explored using highly dilute powders; the properties of which can be attributed to the average response of a single nano-object. Here we consider positioning a few such molecular nanomagnets in a nm-size gap to probe electron transport. We report investigations of face-centered cubic nanoparticles of Prussian blue (Fe4III [FeII(CN)6]3.xH2O) and a Cs-Co-Cr analogue. Pd nanogaps from ~7-50 nm were fabricated on a Si02/Si substrate using standard electron beam lithography and lift-off. Nanomagnets were positioned via dielectrophoresis (DEP), in which an AC voltage applied between the electrodes results in a net polarization with the nanocrystals being directed towards the region of maximum electric field. Currents < 10 pA (V = 5 V) were observed at room temperature in arrays of CsCoCr. Prussian blue nanoparticles showed larger currents (I ~ 10 pA at V ~1 V) In addition, current in the latter could be increased (this much) by performing DEP post-assembly in de-ionized water.
|10:45||Tunable Optical Antennas Based on Metallic Nanoshells with Nanoknobs|
Authors : Andrey I. Denisyuk, Saint-Petersburg State University of Informational Technologies, Mechanics and Optics
Resume : Near-field optical probes for tip-enhanced spectroscopy can be based on metallic nanostructures due to their unique optical properties, which are underpinned by surface plasmon resonances. One of the possibilities to create such probes (known as optical antennas) is using spherical metallic nanoparticles. However the plasmon resonance frequency of metallic spheres has just faint dependence on particle diameter so it is hardly possible to tune the resonance to the desired part of the spectrum. In this paper optical properties of a complex metallic nanostructure are investigated. The structure consists of a spherical metallic nanoshell (dielectric sphere covered with a metallic layer) and a smaller metallic nanoparticle (“nanoknob”) on its surface. It was found that the plasmon resonant frequency of the entire structure illuminated with light is guided by the geometrical and material properties of the metallic nanoshell, while the local field enhancement is observed near the metallic “nanoknob”. The idea is supported with electromagnetic modeling: the resonant wavelength changes from 530 nm to 630 nm upon the decreasing of gold layer thickness of the nanoshell. The designed structures were created by means of a novel method based on precise manipulation under electron beam: a single 120 nm dielectric sphere was obtained at the tip of a tungsten needle. It was then covered with a 20 nm thick gold layer and a 40 nm platinum particle was formed on its surface afterwards.
|11:00||Understanding the antibacterial mechanism of ZnO and CuO nanoparticles|
Authors : G. Applerot‡1, A. Irzh‡, J. Lellouche‡§ and A. Gedanken‡ ‡Department of Chemistry, Kanbar Laboratory for Nanomaterials, Institute of Nanotechnology and Advanced Materials, Bar-Ilan University, Ramat-Gan 52900, Israel §The Mina and Everard Goodman Faculty of Life Sciences, Bar-Ilan University, Ramat-Gan 52900, Israel
Resume : An innovative study aimed at understanding the influence of the particle size of ZnO and CuO (from the microscale down to the nanoscale) on its antibacterial effect has been performed. The antibacterial activity of both ZnO and CuO has been found to be due to a reaction of the metal oxides surface with water. Electron-spin resonance measurements revealed that aqueous suspensions of small nanoparticles of the metal oxides produce increased levels of reactive oxygen species (ROS). Interestingly, a remarkable enhancement of the oxidative stress, beyond the level yielded by the metal oxides themselves, was detected following the antibacterial treatment. Likewise, an exposure of bacteria to the small metal oxides nanoparticles resulted in an increased cellular internalization of the nanoparticles and bacterial cell damage. The examination of the antibacterial effect was performed upon two bacterial species: Escherichia coli (Gram negative) and Staphylococcus aureus (Gram positive). The nanocrystalline particles of the metal oxides were synthesized using ultrasonic irradiation, and the particle sizes were controlled using different solvents during the sonication process. Collectively, it is apparent that the unique properties (i.e., small size and corresponding large surface area) of small nanometer-scale metal oxides particles impose several effects that govern its antibacterial action. These effects are size dependent and do not exist in the range of microscale particles.
|11:15||Photocatalytic activity of TiO2 thin films modified by Ag and Au nanoparticles|
Authors : T. Hrkac, B.Henkel, V. Zaporojtchenko, T. Strunskus, V.S.K. Chakravadhanula and F. Faupel Institute for Materials Science - Multicomponent Materials, Christian-Albrechts-University Kiel (CAU)
Resume : Photocatalytic activity of Ag/Au-TiO2 nanocomposite thin films with different filling factors and morphology were investigated. We developed a coating process based on a vapor phase co-sputtering of noble metals and ceramics which allows preparing not only nanocomposites with a defined nanoparticle size and concentration but also with different depth profiles and distribution of the nanoparticles . The optical and structural properties of the composite were characterized by UV-Vis, XRD, HRTEM and XPS. The photocatalytic activity was determined by organic dye photodegradation during UV illumination at wavelength ~ 365 nm. To optimize the preparation procedure, the influence of nanocomposite morphology, thickness as well as aging temperature on the photocatalytic activity was tested. Considering the different structures of nanocomposites the correlation of the photocatalytic activity with distribution of the Au and Ag nanoparticles will be discussed. Reference: V. S. K. Chakravadhanula, T. Hrkac, V. Zaporojtchenko et al., Journal of Nanoscience and Nanotechnology Vol. 11, 2011 in press.
|11:30||Thermal charging of colloidal quantum dots in apolar solvents, a current transient analysis |
Authors : Marco Cirillo†, Filip Strubbe‡, Kristiaan Neyts‡, Zeger Hens† † Physics and Chemistry of Nanostructures, Ghent University, Krijgslaan 281-S3, B-9000 Gent, Belgium ‡ Liquid crystals and photonics, Ghent University, Sint-Pieternieuwstraat 41, B-9000 Gent, Belgium
Resume : The synthesis and study of colloidal nanoparticles experienced a fast growth over the last two decades resulting in a wide tunability of the size, shape and optical properties of the nanoparticles. A recurring aspect in colloidal nanoparticle research is the presence of charges on the nanoparticles when dispersed in apolar solvents. This has been inferred from conductivity measurements, and a correlation between charges on nanoparticles and the formation of nanoparticle superlattices has been proposed. In this work, we investigated charges on CdSe quantum dots dispersed in dodecane and octylehter, using a current measurement method previously adopted in the study of charged micelles in apolar solvents. Using the transient current measured following a voltage step applied over the QD dispersion, we show that the dispersion should be seen as a 1:1 electrolyte with equally amount of positively and negatively charged QDs. Finally, we relate the fraction of charged QDs to the free energy needed to charge the QDs. The limited dependence of this charging energy on the dielectric constant of the solvent is interpreted by a model in which the charge on the QDs is screened by the solvent and the QD ligand shell. These results provide an overall framework to understand and control charges on colloidal QDs in apolar solvents, which is relevant for the manipulation of QDs with electric field and their self-assembly in nanoparticle superlattices.  Cirillo. M et al. DOI: 10.1021/nn103052r
|11:45||Magnetic-field-dependent optical transmission of SrFe12O19 plate-like particles colloidal dispersions|
Authors : Kushnir S.E.1, Gavrilov A.I.1, Grigorieva A.V.1, Trusov L.A.1, Kazin P.E.1,2, Tretiakov Yu.D.1,2 1. Moscow MV Lomonosov State University, Faculty of Materials Science, Moscow 119991, Russia 2. Moscow MV Lomonosov State University, Faculty of Chemistry, Moscow 119991, Russia
Resume : Effect of linear dichroism appears in magnetic fluids based on anisotropic particles under the influence of magnetic field. Thereby linearly polarized light transmission of such substances depends on the magnetic field and the mutual orientation of the polarization and magnetic field vectors . To improve this effect the shape anisotropy of particles should be increased. Thus, the most promising system manifesting linear dichroism in magnetic field is a colloidal solution of magnetic plate-like nanoparticles with the greatest aspect ratio, while the magnetic moment of particles should be oriented perpendicular to the basal plane to achieve the orientation under a magnetic field. In our work, we describe synthesis and optical properties of colloidal solutions of hard-magnetic plate-like strontium hexaferrite particles obtained via glass crystallization and hydrothermal processes. We have obtained hexaferrite particles with coercitive force more than 800 Oe, saturation magnetization >20 emu/g and aspect ratio 5-15. Colloidal solutions were characterized with optical spectroscopy. The difference in transmission is observed throughout the visible range, while degree of the effect increased crossing from red to purple. The ratio of optical densities of colloidal solution reached value of 3.8 (at the wavelength of 500 nm). Oscillations of the transmittance were observed in alternating magnetic field up to 2 KHz. 1. Llewellyn. J. Phys. D: Appl. Phys., 1983. 16(1): p. 95-104.
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