35 research outputs found
High Resolution Pdf Measurements On Ag Nanoparticles
No full textThe quantitative analysis of structural defects in Ag nanoparticles was addressed in this work. We performed atomic scale structural characterization by a combination of x-ray diffraction (XRD) using the Pair Distribution Function analysis (PDF) and High Resolution Transmission Electron Microscopy (HRTEM). The XRD measurements were performed using an innovative instrumentation setup to provide high resolution PDF patterns. © 2009 American Institute of Physics.1092102106Rocha, T.C.R., Winnischofer, H., Westphal, E., Zanchet, D., Formation Kinetics of Silver Triangular Nanoplates (2007) J. Phys. Chem. C, 111, p. 2885Petkov, V., Jeong, I.-K., Chung, J.S., Thorpe, M.F., Kycia, S., Billinge, S.J.L., High Real-Space Resolution Measurement of the Local Structure of Ga 1-xIn xAs Using X-Ray Diffraction (1997) Phys. Rev. Lett, 83, pp. 4089-409
Magnetic Behavior Of Ni Nanoparticles With High Disordered Atomic Structure
No full textThis report concerns the magnetic properties of colloidal Ni nanoparticles (NPs) obtained by chemical reduction of Ni(II) salt in an organic solvent. The NPs present a complex and disordered atomic structure, where small clusters of a few Ni atoms appear to coexist within each NP. These NPs exhibit interesting magnetic properties, with a low temperature ferromagnetic order followed by a transition from ferromagnetic to a "spin-glass-like" state as the temperature decreases. The results are discussed considering the role of the atomic ordering of the NPs on the corresponding magnetic behavior. © 2008 American Institute of Physics.9218Nunes, W.C., Socolovsky, L.M., Denardin, J.C., Cebollada, F., Brandl, A.L., Knobel, M., (2005) Phys. Rev. B, 72, p. 212413Bonetti, E., Del Bianco, L., Fiorani, D., Rinaldi, D., Caciuffo, R., Hernando, A., (1999) Phys. Rev. Lett., 83, p. 2829Childress, J.R., Chien, C.L., (1991) Phys. Rev. B, 43, p. 8089Martinez, B., Obradors, X., Balcells, L., Rouanet, A., Monty, C., (1998) Phys. Rev. Lett., 80, p. 181Hadjipanayis, G.C., Prinz, G.A., (1991), 259. , Science and Technology of Nanostructured Magnetic Materials, NATO Advanced Study Institute, Series B: Physics (Plenum, New York), Vol.Dormann, J.L., Fiorani, D., (1992), Magnetic Properties of Fine Particles (North-Holland, Amsterdam)Diehl, M.R., Yu, J.Y., Heath, J.R., Held, G.A., Doyle, H., Sun, S.H., Murray, C.B., (2001) J. Phys. Chem. B, 105, p. 7913Nogues, J., Skumryev, V., Sort, J., Stoyanov, S., Givord, D., (2006) Phys. Rev. Lett., 97, p. 157203Murray, C.B., Kagan, C.R., Bawendi, M.G., (2000) Annu. Rev. Mater. Sci., 30, p. 546Winnischofer, H., Rocha, T.C.R., Nunes, W.C., Socolovsky, L.M., Knobel, M., Zanchet, D., ACS Nano (to be published)Denardin, J.C., Brandl, A.L., Knobel, M., Panissod, P., Pakhomov, A.B., Liu, H., Zhang, X.X., (2002) Phys. Rev. B, 65, p. 064422González, E.M., Montero, M.I., Cebollada, F., De Julián, C., Vicent, J.L., González, J.M., (1998) Europhys. Lett., 42, p. 91Mydosh, J.A., (1993), Spin Glass (Taylor and Francis, New York)Thomassen, J., May, F., Feldmann, B., Wuttig, M., Ibach, H., (1992) Phys. Rev. Lett., 69, p. 3831Johanson, G.J., McGirr, M.B., Wheeler, D.A., (1970) Phys. Rev. B, 1, p. 3208Marcus, P.M., Qiu, S.L., Moruzzi, V.L., (1999) J. Phys.: Condens. Matter, 11, p. 5709Krüger, P., (2001) Phys. Rev. B, 64, p. 094404Jeon, Y.T., Moon, J.Y., Lee, G.H., Park, J., Chang, Y., (2005) J. Phys. Chem. B, 110, p. 1187Hernando, A., Marín, P., Vázquez, M., Barandiarán, J.M., Herzer, G., (1998) Phys. Rev. B, 58, p. 366De Biasi, E., Ramos, C.A., Zysler, R.D., Romero, H., (2002) Phys. Rev. B, 65, p. 144416Winkler, E., Zysler, R.D., Vasquez Mansilla, M., Fiorani, D., (2005) Phys. Rev. B, 72, p. 132409Abiko, S., Niidera, S., Matsubara, F., (2005) Phys. Rev. Lett., 94, p. 22720
Evolución cambiaria y tipo de cambio real en Colombia en el período 1990-1994
No full textRESUMEN: En el presente trabajo se analizan las principales medidas cambiarias, implementadas en el país entre 1990 y 1994 como también su relación con la evolución de la Tasa de Cambio Real. Se utiliza un modelo del tipo IS-LM para la determinación de la T.C.R., que muestra las acciones del gobierno como factores que afectan la tasa de interés doméstica, provocando flujos internacionales de capitales, modificadores del nivel de la T.C.R.ABSTRACT: In the present work the author analyses the main exchange rate measures implemented in the country between 1990 and 1994 as well as their relation with the evolution of the Real Exchange Rate (RER). To determine the RER an IS-LM model is used which shows the government actions as factors affecting domestic interest rate, leading to international capital flows, which affect the level of RER
Improvement On A New Concept Of Beamline Delivering High Purity Vuv Photons Starting At 7.3 Ev
No full textWe report recent improvements and performance on the Toroidal Grating Monochromator (TGM) beamline at the Laboratório Nacional de Luz Síncrotron-LNLS. Compared to normal incidence monochromators, (NIMs), TGMs provide substantially wider energy range, less resolving power and very poor higher harmonic rejection (HHR). A new concept, MIRHACLLE [1], developed at LNLS, allows reaching more than five orders of harmonic rejection (NIM gives 10%). Previously, we were not able to reach below 12 eV using MIRHACLLE. Here we report improvements extending the lower limit to 7.3 eV. Furthermore, HHR is maintained down to the lower limit using a special gas mixture, the upper limit given by 330 eV is kept.425PART 12Cavasso Filho, R.L., Homen, M.G.P., Fonseca, P.T., Naves De Brito, A., A synchrotron beamline for delivering high purity vacuum ultraviolet photons (2007) Rev. Sci. Instrum., 78 (11), p. 115104. , 10.1063/1.2813341 0034-6748Craievich, A.F., Rodrigues, A.R., (1998) Hyperfine Interactions, 113 (1-4), p. 465. , 10.1023/A:1012689530867 0304-3834Fonseca, P.T., Pacheco, J.G., Samogin, E.D.A., Castro, A.R.B., (1992) Rev. Sci. Instrum., 63 (1), p. 1256. , 10.1063/1.1143094 0034-6748Fonseca, P.T., (1993), Master ThesisCoutinho, L.H., Cavasso, R.L., Rocha, T.C.R., Homem, M.G.P., Figueira, D.S.L., Fonseca, P.T., Cruz, F.C., Naves De Brito, A., (2004) Phys. Rev. Lett., 93 (18), p. 183001. , 10.1103/PhysRevLett.93.183001 0031-9007Gaie-Levre, F., Garcia, G.A., Schwel, M., Nahon, L., (2011) Phys. Chem. Chem. Phys., 13 (15), pp. 7024-7036. , 10.1039/c0cp02798g 1463-9076Reininger, R., Kriesel, K., Hulbert, S.L., Sánchez-Hanke, C., Arena, D.A., (2008) Rev. Sci. Instrum., 79 (3), p. 033108. , 10.1063/1.2897587 0034-6748http://www.zeiss.com/C1256F2B00321E60/EmbedTdfitelIntern/ MirrorsforSynchrotronRadiation/$File/ Brochure_Synchrotron_mit_References_FINAL.pd
The Oxidation of Rhenium and Identification of Rhenium Oxides During Catalytic Partial Oxidation of Ethylene An In Situ XPS Study
No full textRhenium is catalytically active for many valuable chemical reactions, and consequently has been the subject of scientific investigation for several decades. However, little is known about the chemical identity of the species present on rhenium surfaces during catalytic reactions because techniques for investigating catalyst surfaces in-situ – such as near-ambient-pressure X-ray photoemission spectroscopy (NAP-XPS) – have only recently become available. In the current work, we present an in-situ XPS study of rhenium catalysts. We examine the oxidized rhenium species that form on a metallic rhenium foil in an oxidizing atmosphere, a reducing atmosphere, and during a model catalytic reaction (i.e. the partial-oxidation of ethylene). We find that, in an oxidizing environment, a Re2O7 film forms on the metal surface, with buried layers of sub-oxides that contain Re4+, Re2+ and Reδ+ (δ ∼ 1) species at the Re2O7/Re interface. The Re2+ containing sub-oxide is not a known bulk oxide, and is only known to exist on rhenium-metal surfaces. The Re2O7 film sublimes at a very low temperature (ca. 150 ℃), while the Re4+, Re2+ and Reδ+ species remain stable in oxidizing conditions up to at least 450 ℃. In a reducing atmosphere of H2, the Re2+ species remain on the surface up to a temperature of 330 ℃, while Reδ+ species can be detected even at 550 ℃. Under conditions for partial-oxidation of ethylene, we find that the active rhenium catalyst surface contains no bulk-stable oxides, but consists of mainly Re2+ species and small amounts of Re4+ species. When the catalyst is cooled and inactive, Re2O7 is found to form on the surface. These results suggest that Re2+ and Re4+ species may be active species in heterogeneous rhenium catalysts
Interplay Between Crystallization And Particle Growth During The Isothermal Annealing Of Colloidal Iron Oxide Nanoparticles
No full textThe relationship between crystallization and growth of colloidal iron oxide nanoparticles during isothermal annealing was addressed in this work. The structural, morphological and chemical modifications of the nanoparticles during thermal treatments were followed by combination of electron microscopy, X-ray diffraction and spectroscopic methods. The initially monodisperse spherical nanoparticles with amorphous and partially oxidized structure evolved during the treatments, depending on the temperature and treatment time. Core-void-shell nanoparticles or single crystal nanoparticles and hollow polycrystalline nanoparticles, both with well defined Fe3O4 oxide phase, are formed depending on the conditions. This evolution was interpreted as a result of the Kirkendall effect associated to mass redistribution and fragmentation of the nanoparticles, bringing new information about the effect of post-synthesis treatments on the crystallinity and morphology of colloidal nanoparticles. © 2009 Elsevier Inc. All rights reserved.3392344350Murray, C.B., Kagan, C.R., Bawendi, M.G., (2000) Annu. Rev. Mater. Sci., 30, p. 545Morales, M.P., Veintemillas-Verdaguer, S., Montero, M.I., Serna, C.J., Roig, A., Casas, L., Martinez, B., Sandiumenge, F., (1999) Chem. Mater., 11, p. 3058Newnham, R.E.M., Ikawa, H., (1990) Mater. Res. Soc. Symp. Proc., 175, p. 161Vollath, D., Szabo, D.V., Taylor, R.D., Willis, J.O., Sickafus, K.E., (1995) Nanostruct. Mater., 6, p. 941Morales, M.P., Pecharroman, C., Carreno, T.G., Serna, C.J., (1994) J. Solid State Chem., 108, p. 158Kroll, E., Winnik, F.M., Ziolo, R.F., (1996) Chem. Mater., 8, p. 1594Pileni, M.P., (2001) Adv. Funct. Mater., 11, p. 323Sun, S.H., Murray, C.B., Weller, D., Folks, L., Moser, A., (2000) Science, 287, p. 1989Lee, K.B., Park, S., Mirkin, C.A., (2004) Angew. Chem. - Int. Ed., 43, p. 3048Pankhurst, Q.A., Connolly, J., Jones, S.K., Dobson, J., (2003) J. Phys. D - Appl. Phys., 36, pp. R167Zhu, G.X., Wei, X.W., Jiang, S., (2007) J. Mater. Chem., 17, p. 2301Hogemann, D., Josephson, L., Weissleder, R., Basilion, J.P., (2000) Bioconjugate Chem., 11, p. 941Josephson, L., Perez, J.M., Weissleder, R., (2001) Angew. Chem. - Int. Ed., 40, p. 3204Tang, J., Fabbri, J., Robinson, R.D., Zhu, Y.M., Herman, I.P., Steigerwald, M.L., Brus, L.E., (2004) Chem. Mater., 16, p. 1336Yin, M., O'Brien, S., (2003) J. Am. Chem. Soc., 125, p. 10180Borchert, H., Shevehenko, E.V., Robert, A., Mekis, I., Kornowski, A., Grubel, G., Weller, H., (2005) Langmuir, 21, p. 1931Yu, W.W., Falkner, J.C., Shih, B.S., Colvin, V.L., (2004) Chem. Mater., 16, p. 3318Pastoriza-Santos, I., Liz-Marzan, L.M., (2008) J. Mater. Chem., 18, p. 1724Manna, L., Milliron, D.J., Meisel, A., Scher, E.C., Alivisatos, A.P., (2003) Nat. Mater., 2, p. 382Winnischofer, H., Rocha, T.C.R., Nunes, W.C., Socolovsky, L.M., Knobel, M., Zanchet, D., (2008) ACS Nano, 2, p. 1313Park, J., Kang, E., Son, S.U., Park, H.M., Lee, M.K., Kim, J., Kim, K.W., Hyeon, T., (2005) Adv. Mater., 17, p. 429Wang, Z.K., Kuok, M.H., Ng, S.C., Lockwood, D.J., Cottam, M.G., Nielsch, K., Wehrspohn, R.B., Gosele, U., (2002) Phys. Rev. Lett., 89, p. 27201Zhang, W.Q., Tang, K.B., Liu, Y.K., Zhu, Y.C., Yu, W.C., Qian, Y.T., (2007) Carbon, 45, p. 1571Rocha, T.C.R., Zanchet, D., (2007) J. Phys. Chem. C, 111, p. 6989Vargas, J.M., Socolovsky, L.M., Goya, G.F., Knobel, M., Zanchet, D., (2003) IEEE Trans. Magn., 39, p. 2681Rosado, M.T., Duarte, M., Fausto, R., (1998) Vib. Spectrosc., 16, p. 35Monte, F.D., Morales, M.P., Levy, D., Fernandez, A., Ocana, M., Roig, A., Molins, E., Serna, C.J., (1997) Langmuir, 13, p. 3627Cannas, C., Casula, M.F., Concas, G., Corrias, A., Gatteschi, D., Falqui, A., Musinu, A., Spano, G., (2001) J. Mater. Chem., 11, p. 3180Roberts-Austen, W.C., (1896) Phil. Trans. Roy. Soc. A, 187, p. 383Yin, Y.D., Rioux, R.M., Erdonmez, C.K., Hughes, S., Somorjai, G.A., Alivisatos, A.P., (2004) Science, 304, p. 711Casula, M.F., Jun, Y.W., Zaziski, D.J., Chan, E.M., Corrias, A., Alivisatos, A.P., (2006) J. Am. Chem. Soc., 128, p. 1675Peng, S., Sun, S.H., (2007) Angew. Chem. - Int. Ed., 46, p. 4155Peng, S., Wang, C., Xie, J., Sun, S.H., (2006) J. Am. Chem. Soc., 128, p. 10676Greenwood, G.W., (1956) Acta Metall, 4, p. 243Biasi, E.D., Ramos, C.A., Zysler, R.D., Romero, H., (2002) Phys. Rev. B, 65, p. 144416Gangopadhyay, S., Hadjipanayis, G.C., Dale, B., Sorensen, C.M., Klabunde, K.J., Papaefthymiou, V., Kostikas, A., (1992) Phys. Rev. B, p. 9778Goya, G.F., Berquó, T.S., Fonseca, F.C., Morales, M.P., (2003) J. Appl. Phys., 94, p. 352
Effects Of Magnetic Interparticle Coupling On The Blocking Temperature Of Ferromagnetic Nanoparticle Arrays
No full textIn this work we report on the study of the magnetic properties of 2D arrays and 3D dispersions of colloidal iron oxide nanoparticles prepared by Langmuir-Blodgett technique and by dilution in paraffin wax solid solution, respectively. The influence of magnetic interparticle coupling on the superparamagnetic relaxation behavior was investigated by means of DC magnetization measurements. A quantitative analysis of the field dependence of the blocking temperature and the role of the interparticle coupling is presented. We explain our results using a phenomenological model based on the random anisotropy and micromagnetic theories that account for particle coupling effects in the superparamagnetic properties. © 2007 Elsevier B.V. All rights reserved.35308/10/15743747Néel, L., (1949) Ann. Geophysique, 5, p. 99Binns, C., Maher, M.J., (2002) New J. Phys., 4, p. 85Nunes, W.C., Cebollada, F., Knobel, M., Zanchet, D., (2006) J. Appl. Phys., 99, pp. 08N705Vargas, J.M., Nunes, W.C., Socolovsky, L.M., Knobel, M., Zanchet, D., (2005) Phys. Rev. B, 72, p. 184428Dormann, J.L., Fiorani, D., Tronc, E., (1999) J. Magn. Magn. Mat., 202, p. 251Dormann, J.L., Fiorani, D., Tronc, E., (1997) Adv. Chem. Phys., XCVIII, p. 283Hansen, M.F., Mørup, S., (1998) J. Magn. Magn. Mat., 184, p. 2015Allia, P., Coisson, M., Tiberto, P., Vinai, F., Knobel, M., Novak, M.A., Nunes, W.C., (2001) Phys. Rev. B, 64, p. 144420Nunes, W.C., Socolovsky, L.M., Denardin, J.C., Cebollada, F., Brandl, A.L., Knobel, M., (2005) Phys. Rev. B, 72, p. 212413Puntes, V.F., Gorostiza, P., Maruguete, D., Bastus, N.G., Alivisatos, A.P., (2004) Nat. Mater., 3, p. 263Denardin, J.C., Brandl, A.L., Knobel, M., Panissod, P., Pakhomov, A.B., Liu, H., Zhang, X.X., (2002) Phys. Rev. B, 65, p. 64422Wernsdorfer, W., Bonet Orozco, E., Hasselbach, K., Benoit, A., Barbara, B., Demoncy, N., Loiseau, A., Mailly, D., (1997) Phys. Rev. Lett., 78, p. 1791Zhang, Y.D., Budnick, J.I., Hines, W.A., Chien, C.L., Xiao, J.Q., (1998) Appl. Phys. Lett., 72 (16), p. 2053Victora, R.H., (1989) Phys. Rev. Lett., 63, p. 457Kechrakos, D., Trohidou, K.N., (2005) Phys. Rev. B, 71, p. 054416Allia, P., Coisson, M., Knobel, M., Tiberto, P., Vinai, F., (1999) Phys. Rev. B, 60 (12), p. 207Hansen, M.F., Koch, C.B., Morup, S., (2000) Phys. Rev. B, 62, p. 1124Hauschild, J., Elmers, H.J., Gradmann, U., (1998) Phys. Rev. B, 57, pp. R677Alben, R., Becker, J.J., Chi, M.C., (1978) J. Appl. Phys., 49, p. 1653Herzer, G., (2005) J. Magn. Magn. Mat., 294, p. 99Michels, A., Viswanath, R.N., Barker, J.G., Birringer, R., Weissmüller, J., (2003) Phys. Rev. Lett., 91, p. 267204Löffler, J.F., Braun, H.B., Wagner, W., (2000) Phys. Rev. Lett., 85, p. 1990Binns, C., Maher, M.J., Pankhurst, Q.A., Kechrakos, D., Trohidou, K.N., (2002) Phys. Rev. B, 66, p. 184413Chudnovsky, E.M., (1988) J. Appl. Phys., 64, p. 577
Magnetic And Structural Properties Of Fcc/hcp Bi-crystalline Multilayer Co Nanowire Arrays Prepared By Controlled Electroplating
No full textWe report on the structural and magnetic properties of crystalline bi-phase Co nanowires, electrodeposited into the pores of anodized alumina membranes, as a function of their length. Co nanowires present two different coexistent crystalline structures (fcc and hcp) that can be controlled by the time of pulsed electrodeposition. The fcc crystalline phase grows at the early stage and is present at the bottom of all the nanowires, strongly influencing their magnetic behavior. Both structural and magnetic characterizations indicate that the length of the fcc phase is constant at around 260-270 nm. X-ray diffraction measurements revealed a strong preferential orientation (texture) in the (1 0-1 0) direction for the hcp phase, which increases the nanowire length as well as crystalline grain size, degree of orientation, and volume fraction of oriented material. The first-order reversal curve (FORC) method was used to infer both qualitatively and quantitatively the complex magnetization reversal of the nanowires. Under the application of a magnetic field parallel to the wires, the magnetization reversal of each region is clearly distinguishable; the fcc phase creates a high coercive contribution without an interaction field, while the hcp phase presents a smaller coercivity and undergoes a strong antiparallel interaction field from neighboring wires. © 2011 American Institute of Physics.1098Routkevitch, D., Tager, A.A., Haruyama, J., Almawlawi, D., Moskovits, M., Xu, J.M., (1996) IEEE Trans. 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A near ambient pressure XPS study of Au oxidation
No full textThe surface of a gold foil under ozone oxidation was examined by near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) and scanning electron microscopy (SEM). Our in-situ observations show that a surface oxide phase is formed during the exposure to ozone; however this phase decomposes in vacuum and even in the presence of ozone at temperatures higher than 300°C. Assuming an oxide overlayer completely covering the Au surface, the thickness of the oxide phase was estimated to be between 2.9 and 5.8 Å by energy-dependent XPS depth profiling. The surface oxidation led to structural modifications of the gold surface. These morphological changes do not disappear even under vacuum. In the Au 4f spectra, an additional component at low binding energy (83.3 eV), which appears during/after O3 treatment, is assigned to the presence of low-coordinated atoms which appear on the Au surface as a result of surface restructuring under oxidation. Ex-situ SEM images demonstrate that only the region of the sample that was exposed to O3 shows the presence of ridges on the Au surfac
