223 research outputs found
Precipitation Behavior and Magnetic Properties of Cu-Fe-Co Alloys Containing Nanogranular Ferromagnetic-Element Particles
This work investigates the evolution of microstructures and magnetic properties during isothermal annealing of Cu-Fe-Co alloys, using electron microscopy and superconducting quantum interference device (SQUID) magnetometry. Small coherent granular precipitates composed of iron and cobalt formed in the copper matrix in the early stage of precipitation. As annealing proceeded, the precipitates lost coherency to the matrix after reaching a size of 15â20ânm and twin-like structures were consecutively introduced in the particles. The SQUID measurements revealed that the magnetic properties of the specimens correlated with the microstructural evolution. The coercive force initially increased with annealing time but decreased after reaching a peak. Lorentz Microscopy suggested that the initial large increase of magnetization was invoked by a structural transition from fcc to B2 in the precipitates
Atomic-scale perspective on the origin of attractive step interactions on Si(113)
Recent experiments have shown that steps on Si(113) surfaces self-organize
into bunches due to a competition between long-range repulsive and short-range
attractive interactions. Using empirical and tight-binding interatomic
potentials, we investigate the physical origin of the short-range attraction,
and report the formation and interaction energies of steps. We find that the
short-range attraction between steps is due to the annihilation of force
monopoles at their edges as they combine to form bunches. Our results for the
strengths of the attractive interactions are consistent with the values
determined from experimental studies on kinetics of faceting.Comment: 4 pages, 3 figures, to appear in Phys. Rev B, Rapid Communication
Magnetotransport properties of iron microwires fabricated by focused electron beam induced autocatalytic growth
We have prepared iron microwires in a combination of focused electron beam
induced deposition (FEBID) and autocatalytic growth from the iron
pentacarbonyl, Fe(CO)5, precursor gas under UHV conditions. The electrical
transport properties of the microwires were investigated and it was found that
the temperature dependence of the longitudinal resistivity (rhoxx) shows a
typical metallic behaviour with a room temperature value of about 88
micro{\Omega} cm. In order to investigate the magnetotransport properties we
have measured the isothermal Hall-resistivities in the range between 4.2 K and
260 K. From these measurements positive values for the ordinary and the
anomalous Hall coefficients were derived. The relation between anomalous Hall
resistivity (rhoAN) and longitudinal resistivity is quadratic, rhoAN rho^2 xx,
revealing an intrinsic origin of the anomalous Hall effect. Finally, at low
temperature in the transversal geometry a negative magnetoresistance of about
0.2 % was measured
Study of carbon dust formation and their structure using inductively coupled plasmas under high atomic hydrogen irradiation
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ć ±ćŠçł»Experiments on erosion and dust formation on graphite materials have been performed using high power induction plasmas containing high atomic hydrogen flux (âŒ1024 m-2 s-1). Chemical sputtering by atomic hydrogen irradiation with incident energy below 1 eV eroded the graphite targets significantly, and the sputtering yield was roughly estimated to be 0.002-0.005, which is as high as that obtained by ion beam and fusion plasma experiments. The transport of the released hydrocarbon along the gas flow, interacting with low temperature plasmas, results in carbon dust formation on the eroded graphite target and also on the silicon and graphite samples located at the remote position. The dust size and density observed on the samples decreases with distance from the graphite target. The dust shape strongly depends on the target surface temperature, and the graphite dust turns into polyhedral particle like diamond when the surface temperature rises to 1100 K. © 2009 Elsevier B.V. All rights reserved
Elucidating the Mechanism of IronâCatalyzed Graphitization:The First Observation of Homogeneous SolidâState Catalysis
Carbon is a critical material for existing and emerging energy applications and there is considerable global effort in generating sustainable carbons. A particularly promising area is ironâcatalyzed graphitization, which is the conversion of organic matter to graphitic carbon nanostructures by an iron catalyst. In this paper, it is reported that ironâcatalyzed graphitization occurs via a new type of mechanism that is called homogeneous solidâstate catalysis. Dark field in situ transmission electron microscopy is used to demonstrate that crystalline iron nanoparticles âburrowâ through amorphous carbon to generate multiwalled graphitic nanotubes. The process is remarkably fast, particularly given the solid phase of the catalyst, and in situ synchrotron Xâray diffraction is used to demonstrate that graphitization is complete within a few minutes
Optimizing both catalyst preparation and catalytic behaviour for the oxidative dehydrogenation of ethane of Ni-Sn-O catalysts
[EN] Bulk Ni-Sn-O catalysts have been synthesized, tested in the oxidative dehydrogenation of ethane and characterized by several physicochemical techniques. The catalysts have been prepared by evaporation of the corresponding salts using several additives in the synthesis gel, i.e. ammonium hydroxide, nitric acid, glyoxylic acid or oxalic acid, in the synthesis gel. The catalysts were finally calcined at 500 degrees C in air. Important changes in the catalytic behaviour have been observed depending on the additive. In fact, an important improvement in the catalytic performance is observed especially when some additives, such as glyoxylic or oxalic acid, are used. Thus the productivity to ethylene multiplies by 6 compared to the reference Ni-Sn-O catalyst if appropriate templates are used, and this is the result of an improvement in both the catalytic activity and the selectivity to ethylene. This improved performance has been explained in terms of the decrease of the crystallite size (and the increase in the surface area of catalyst) as well as the modification of the lattice parameter of nickel oxide.The authors would like to acknowledge the DGICYT in Spain (CTQ2015-68951-C3-1-R and CTQ2012-37925-C03-2) for financial support. We also thank the University of Valencia and SCSIE-UV for assistanceSolsona Espriu, BE.; LĂłpez Nieto, JM.; Agouram, S.; Soriano RodrĂguez, MD.; Dejoz, A.; VĂĄzquez, MI.; ConcepciĂłn Heydorn, P. (2016). Optimizing both catalyst preparation and catalytic behaviour for the oxidative dehydrogenation of ethane of Ni-Sn-O catalysts. Topics in Catalysis. 59(17-18):1564-1572. https://doi.org/10.1007/s11244-016-0674-zS156415725917-18Heracleous E, Lee AF, Wilson K, Lemonidou AA (2005) J Catal 231:159â171Heracleous E, Lemonidou AA (2006) J Catal 237:162â174Savova B, Loridant S, Filkova D, Millet JMM (2010) Appl Catal A 390:148â157Heracleous E, Lemonidou AA (2010) J Catal 270:67â75Solsona B, Nieto JML, Concepcion P, Dejoz A, Ivars F, Vazquez MI (2011) J Catal 280:28â39Skoufa Z, Heracleous E, Lemonidou AA (2012) Catal Today 192:169â176Zhu H, Ould-Chikh S, Anjum DH, Sun M, Biausque G, Basset JM, Caps V (2012) J Catal 285:292â303Skoufa Z, Heracleous E, Lemonidou AA (2012) Chem Eng Sci 84:48â56Zhu H, Rosenfeld DC, Anjum DH, Caps V, Basset JM (2015) ChemSusChem 8:1254â1263Heracleous E, Lemonidou AA (2015) J Catal 322:118â129Solsona B, Concepcion P, Demicol B, Hernandez S, Delgado JJ, Calvino JJ, Nieto JML (2012) J Catal 295:104â114Nieto JML, Solsona B, Grasselli RK, ConcepciĂłn P (2014) Top Catal 57:1248â1255Popescu I, Skoufa Z, Heracleous E, Lemonidou AA, Marcu IC (2015) PCCP 17:8138â8147Zhang X, Gong Y, Yu G, Xie Y (2002) J Mol Catal A 180:293â298Popescu I, Skoufa Z, Heracleous E, Lemonidou A, Marcu I-C (2015) Phys Chem Chem Phys 17:8138â8147Nakamura KI, Miyake T, Konishi T, Suzuki T (2006) J Mol Catal A 260:144â151Solsona B, Dejoz AM, Vazquez MI, Ivars F, Nieto JML (2009) Top Catal 52:751â757Bortolozzi JP, Gutierrez LB, Ulla MA (2013) Appl Catal A 452:179â188Takeguchi T, Furukawa S, Inoue M (2001) J Catal 202:14â24Richardson JT, Turk B, Twigg MV (1996) Appl Catal 148:97â112Biju V, Khadar MA (2002) J Nanopart Res 4:247â253Van Veenendaal MA, Sawatzky GA (1993) Phys Rev Lett 70:2459â2462Vedrine JC, Hollinger G, Duc TM (1978) J Phys Chem 82:1515â1520Salagre P, Fierro JLG, Medina F, Sueiras JE (1996) J Mol Catal A 106:125â13
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