Growth, thermal desorption and low dose ion bombardment damage of C60 films deposited on Cu(111)

Auger Electron Spectroscopy (AES), Low Energy Electron Diffraction (LEED) and Reflection Electron Energy Loss Spectrometry (REELS) were used to characterize the growth and thermal stability of C60 films deposited on Cu(111). By means of LEED we found that while C60 grows in an ordered fashion up to the first monolayer (ML) at room temperature (RT), it turns amorphous beyond that point. On the other hand, when the substrate temperature is kept at 450K films up to two ML with crystalline structure are obtained. For substrate temperatures beyond 570K thick films (more than 1 ML) do not grow at all. By using AES, we found that a thick C60 film starts to desorb at a temperature around 470K but the first monolayer remains stable up to temperatures as high as 900K. A monolayer with a better crystalline order is obtained after desorption than that growth with the substrate at RT or higher temperatures. When the substrate is heated at 970K, the first monolayer is not fully removed but the C60 molecular structure is altered or molecules break up into smaller pieces. The ion induced damage on C60 on Cu(111) films was studied for typical ions, incoming energies and irradiation doses used in Low Energy Ion Scattering (LEIS) experiments. The D-value of C(KLL) Auger spectra and the -plasmon of REELS, were monitored to characterize the damage caused to the film. We found that, at low doses ( 1014 ions/cm2), damage is only detectable for massive ions like Ar, but not for H and He in the 2-8 keV range.Fil: Bonetto, Fernando Jose. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Física del Litoral. Universidad Nacional del Litoral. Instituto de Física del Litoral; Argentina. Universidad Nacional del Litoral. Facultad de Ingeniería Química. Departamento de Materiales; ArgentinaFil: Vidal, Ricardo Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Física del Litoral. Universidad Nacional del Litoral. Instituto de Física del Litoral; Argentina. Universidad Nacional del Litoral. Facultad de Ingeniería Química. Departamento de Física; ArgentinaFil: Quintero Riascos, Vanessa Alexandra. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Física del Litoral. Universidad Nacional del Litoral. Instituto de Física del Litoral; ArgentinaFil: Bonin, Claudio Julio. Universidad Nacional del Litoral. Facultad de Ingeniería Química. Departamento de Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Física del Litoral. Universidad Nacional del Litoral. Instituto de Física del Litoral; ArgentinaFil: Ferron, Julio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Física del Litoral. Universidad Nacional del Litoral. Instituto de Física del Litoral; Argentina. Universidad Nacional del Litoral. Facultad de Ingeniería Química. Departamento de Materiales; Argentin

Experimental artifact in MOKE measurements when using paramagnetic sample holders

We describe here an artifact that may affect to magneto-optical Kerr measurements. When paramagnetic sample holders (SH) with non-negligible susceptibilities are used, the inhomogeneity of the applied magnetic field can induce forces and torques on it, shifting the reflected beam, and altering its intensity at the photodetector. The effect is even and can be avoided using low susceptibility paramagnetic or diamagnetic SH We also present a detailed analytical description of the magnetic forces involved and provide some estimated values of the SH shifting, showing that they might distort the magneto-optical Kerr effect signal. Moreover, in this paper we show how the artifact can be removed from the experimental curves with an appropriated data analysis.Fil: Munoz-Noval, Alvaro. Comunidad de Madrid; EspañaFil: Bonin, Claudio Julio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Física del Litoral. Universidad Nacional del Litoral. Instituto de Física del Litoral; ArgentinaFil: Bonetto, Fernando Jose. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Física del Litoral. Universidad Nacional del Litoral. Instituto de Física del Litoral; ArgentinaFil: Garcia, Miguel Angel. Institute For Ceramic And Glass; Españ

v-MOKE magnetometry: a solution for devices with fixed electromagnet

We introduce a novel method aimed to obtain the scale factor between in-plane magnetization components, indispensable for vectorial-magneto-optic Kerr effect (v-MOKE) experiments, convenient for experimental setups where it is difficult or unfeasible to rotate the electromagnet. Unlike the original method, in our proposal the electromagnet (and all other optical components) are fixed, extending in this way the possibility to implement v-MOKE magnetometry. Two films, FePt 9 and 100 nm thickness, were used as sample probes, presenting in-plane magnetic uniaxial anisotropy and in-plane magnetic isotropy, respectively. All experiments were carried out at room temperature and employing an home-made MOKE system. We also introduce a closed mathematical expression for the scale factor linking both magnetization components in terms of experimental and sample dependent parameters.Fil: Bonetto, Fernando Jose. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Física del Litoral. Universidad Nacional del Litoral. Instituto de Física del Litoral; ArgentinaFil: Tacca, Marcos Sebastian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Física del Litoral. Universidad Nacional del Litoral. Instituto de Física del Litoral; ArgentinaFil: Aguzin, Ana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; ArgentinaFil: Butera, Alejandro Ricardo. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro. Archivo Histórico del Centro Atómico Bariloche e Instituto Balseiro | Universidad Nacional de Cuyo. Instituto Balseiro. Archivo Histórico del Centro Atómico Bariloche e Instituto Balseiro.; ArgentinaFil: Ferron, Julio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Física del Litoral. Universidad Nacional del Litoral. Instituto de Física del Litoral; ArgentinaFil: Bonin, Claudio Julio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Física del Litoral. Universidad Nacional del Litoral. Instituto de Física del Litoral; Argentin

Quasi-equilibrium states in thermotropic liquid crystals studied by multiple quantum NMR

Previous work showed that by means of the Jeener-Broekaert JB experiment, two quasiequilibrium states can be selectively prepared in the proton spin system of thermotropic nematic liquid crystals LCs in a strong magnetic field. The similarity of the experimental results obtained in a variety of LC in a broad Larmor frequency range, with crystal hydrates, supports the assumption that also in LC the two spin reservoirs, into which the Zeeman order is transferred, originate in the dipolar energy and that they are associated with a separation in energy scales: A constant of motion related to the stronger dipolar interactions S, and a second one W corresponding to the secular part of the weaker dipolar interactions with regard to the Zeeman and the strong dipolar part. We study the nature of these quasi-invariants in nematic 5CB 4-pentyl-4-biphenyl-carbonitrile and measure their relaxation times by encoding the multiple-quantum coherences of the states following the JB pulse pair on two orthogonal bases, Z and X. The experiments were also performed in powder adamantane at 301 K which is used as a reference compound having only one dipolar quasi-invariant. We show that the evolution of the quantum states during the buildup of the quasiequilibrium state in 5CB prepared under the S condition is similar to the case of powder adamantane and that their quasiequilibrium density operators have the same tensor structure. In contrast, the second constant of motion, whose explicit operator form is not known, involves a richer composition of multiple-quantum coherences of even order on the X basis, in consistency with the truncation inherent in its definition. We exploited the exclusive presence of coherences of 4,6,8, besides 0 and 2 under the W condition to measure the spin-lattice relaxation time TW accurately, so avoiding experimental difficulties that usually impair dipolar order relaxation measurement such as Zeeman contamination at high fields and also superposition of the different quasi-invariants. This procedure opens the possibility of measuring the spin-lattice relaxation of a quasi-invariant independent of the Zeeman and S reservoirs, so incorporating a new relaxation parameter useful for studying the complex molecular dynamics in mesophases. In fact, we report the first measurement of TW in a LC at high magnetic fields. Comparison of the obtained value with the one corresponding to a lower field 16 MHz points out that the relaxation of the W-order strongly depends on the intensity of the external magnetic field, similarly to the case of the S reservoir, indicating that the relaxation of the W-quasi-invariant is also governed by the cooperative molecular motions.Fil: Buljubasich Gentiletti, Lisandro. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomia y Física. Sección Física. Grupo de Resonancia Magnética Nuclear; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Monti, Gustavo Alberto. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomia y Física. Sección Física. Grupo de Resonancia Magnética Nuclear; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Acosta, Rodolfo Héctor. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomia y Física. Sección Física. Grupo de Resonancia Magnética Nuclear; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Bonin, Claudio Julio. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: González, Cecilia Élida. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Zamar, Ricardo César. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomia y Física. Sección Física. Grupo de Resonancia Magnética Nuclear; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

MAGNETOMETRÍA V-MOKE: ESCALEO ENTRE COMPONENTES DE LAMAGNETIZACIÓN EN EL PLANO DE LA MUESTRA

Se presenta un procedimiento alternativo al descripto en la bibliografía para determinar el factor de escala, necesario para comparar cuantitativamente dos de las componentes coplanares de la magnetización (componentes en el plano de la superficie de la muestra) de una película magnética mediante v-MOKE (vectorial-MOKE). El procedimientopropuesto posee la ventaja de no necesitar la reorientación del electroimán generador del campo magnetizante, ya que, dependiendo de las dimensiones y peso del mismo, esta acción puede resultar dificultosa o directamente impracticable.De esta manera, el experimento que permite adquirir las dos componentes en el plano de la magnetización de manera simultánea, se ejecuta sin necesidad de modificar la disposición experimental inicial (montaje fijo). Como muestras de prueba usamos dos películas de FePt de 9 nm y 100 nm de espesor, presentando la primera anisotropía uniaxial.Todos los experimentos se realizaron a temperatura ambiente y usando un sistema MOKE construido en el Grupo de Física de Superficies del IFIS-Litoral, el cual permite detectar dos componentes de la magnetización simultáneamente (v-MOKE).Fil: Aguzin, Ana. Universidad Nacional del Litoral; ArgentinaFil: Bonetto, Fernando Jose. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Física del Litoral. Universidad Nacional del Litoral. Instituto de Física del Litoral; ArgentinaFil: Tacca, Marcos Sebastian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Física del Litoral. Universidad Nacional del Litoral. Instituto de Física del Litoral; ArgentinaFil: Butera, Alejandro Ricardo. Comision Nacional de Energia Atomica. Unidad Ejecutora Instituto de Nanociencia y Nanotecnologia. - Consejo Nacional de Investigaciones Cientificas y Tecnicas. Oficina de Coordinacion Administrativa Ciudad Universitaria. Unidad Ejecutora Instituto de Nanociencia y Nanotecnologia.; ArgentinaFil: Bonin, Claudio Julio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Física del Litoral. Universidad Nacional del Litoral. Instituto de Física del Litoral; Argentin

A Low-Cost and Accurate Method for Measuring Weak Magnetic Susceptibilities

The magnetic properties of any substance in nature can be condensed into a unique parameter: the volume magnetic susceptibility χ . Its value and sign indicate if a given material is diamagnetic, paramagnetic, or ferromagnetic. Accurate measurements of χ for paramagnetic or diamagnetic substances are generally performed with high-tech devices with relatively complex methods. Simple methods proposed to determine χ for everyday materials result in inaccurate measurements ( ≥50 %). Here, we propose a simple, practical, and low-cost method to accurately obtain χ , via measurements performed with an ordinary balance and a set of neodymium magnets. The force exerted by the magnets on a given sample is sensed by the balance and, via comparison with exact numerical calculations of the magnetic force on the whole sample, the magnetic susceptibility can be determined. The shape, size, and position of the sample relative to the magnets as well as the number of neodymium magnets are optimized to maximize the magnetic force on the sample and, therefore, minimize the experimental uncertainties in the determination of χ .Fil: Bonin, Claudio Julio. Universidad Nacional del Litoral. Facultad de Ingeniería Química. Departamento de Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Física del Litoral. Universidad Nacional del Litoral. Instituto de Física del Litoral; ArgentinaFil: Bonetto, Fernando Jose. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Física del Litoral. Universidad Nacional del Litoral. Instituto de Física del Litoral; Argentina. Universidad Nacional del Litoral. Facultad de Ingeniería Química. Departamento de Física; Argentin

Growth, thermal desorption and ion bombardment damage inC60films deposited on Cu(111)

En el presente trabajo caracterizamos el crecimiento y desorción térmica de C60 sobre Cu(111) por medio de espectroscopia de electrones Auger (AES) y difracción de electrones de baja energía (LEED). Las películas de C60 fueron crecidas sobre el sustrato por sublimación de C60 desde una celda de Knudsen a 350°C, dentro de una cámara de ultra alto vacío (~10-9Torr). También,determinamos las condiciones de medición de espectros de dispersión de iones lentos (LEIS), estimando el daño por irradiación producido por las dosis típicas utilizadas en estos experimentos (~1014 iones/cm2). Para analizar el daño por bombardeo iónico (H+, He+ y Ar+, con energías de incidencia de 2, 4 y 8 keV) de las películas de C60 se siguió la evolución temporal del plasmón característico de los enlaces p de los átomos de Carbono que conforman la molécula de C60, mediante espectroscopia de pérdidade energía de electrones (EELS). Además, se tomaron espectros Auger antes y después del bombardeo para caracterizar y cuantificar el daño producido.El presente estudio muestra que: el crecimiento de C60 sobre Cu(111) es capa tras capa; la desorción de la primera monocapa es diferente a las demás, quedando solo una monocapa cuando es calentado a 500°C; y solo se detectódaño por irradiación, para las dosis relevantes, cuando la muestra fue bombardeada con Ar+Auger Electron Spectroscopy (AES) and Low Energy Electron Diffraction (LEED) were used to characterize the growth and thermal desorption of C60 on Cu(111). C60 films were grown by sublimation from a Knudsen cell at 350°C, placed in an ultra-high vacuum chamber (UHV) (~10-9Torr). We estimated the best conditions to obtain low energy ion scattered spectra (LEIS) by measuring the irradiation damage produced by typical doses used in theseexperiments (~1014iones/cm2 ). In order to analyze the potential damage of the sample by ion bombardment (2 , 4 and 8 keV H+ , He+ and Ar+ ), we monitored the evolution of the characteristicplasmon due to π-bonds of the C60 molecule C atoms by Electron Energy Loss Spectroscopy (EELS). In addition, Auger spectra (AES) were taken before and after irradiation to characterize and quantify the damage. Our study shows that: C60 growths on Cu(111) layer by layer; the desorption of the first monolayer is different to the desorption of the other layers, remaining the first monolayer even when the substrate is heated up to 500°C and; damage by ion bombardment, at the used dose, was only detected when the sample was under Ar+ irradiationFil: Vidal, Ricardo Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Física del Litoral. Universidad Nacional del Litoral. Instituto de Física del Litoral; ArgentinaFil: Bonetto, Fernando Jose. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Física del Litoral. Universidad Nacional del Litoral. Instituto de Física del Litoral; ArgentinaFil: Quintero Riascos, Vanessa Alexandra. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Física del Litoral. Universidad Nacional del Litoral. Instituto de Física del Litoral; ArgentinaFil: Bonin, Claudio Julio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Física del Litoral. Universidad Nacional del Litoral. Instituto de Física del Litoral; ArgentinaFil: Ferron, Julio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Física del Litoral. Universidad Nacional del Litoral. Instituto de Física del Litoral; Argentin

NMR dipolar constants of motion in liquid crystals: Jeener-Broekaert, double quantum coherence experiments and numerical calculation on a 10-spin cluster

Two proton quasi-equilibrium states were previously observed in nematic liquid crystals, namely the S and W quasi-invariants. Even though the experimental evidence suggested that they originate in a partition of the spin dipolar energy into a strong and a weak part, respectively, from a theoretical viewpoint, the existence of an appropriate energy scale which allows such energy separation remains to be confirmed and a representation of the quasi-invariants is still to be given. We compare the dipolar NMR signals yielded both by the Jeener?Broekaert (JB) experiment as a function of the preparation time and the free evolution of the double quantum coherence (DQC) spectra excited from the S state, with numerical calculations carried out from first principles under different models for the dipolar quasiinvariants, in a 10-spin cluster which represents the 5CB (40-pentyl-4-biphenyl-carbonitrile) molecule. The calculated signals qualitatively agree with the experiments and the DQC spectra as a function of the single-quantum detection time are sensible enough to the different models to allow both to probe the physical nature of the initial dipolar-ordered state and to assign a subset of dipolar interactions to each constant of motion, which are compatible with the experiments. As a criterion for selecting a suitable quasi-equilibrium model of the 5CB molecule, we impose on the time evolution operator consistency with the occurrence of two dipolar quasi-invariants, that is, the calculated spectra must be unaffected by truncation of non-secular terms of the weaker dipolar energy. We find that defining the S quasiinvariant as the subset of the dipolar interactions of each proton with its two nearest neighbours yields a realistic characterization of the dipolar constants of motion in 5CB. We conclude that the proton-spin system of the 5CB molecule admits a partition of the dipolar energy into a bilinear strong and a multiple-spin weak contributions therefore providing two orthogonal constants of motion, which can be prepared and observed by means of the JB experiment. This feature, which implies the existence of two timescales of very different nature in the proton-spin dynamics, is ultimately dictated by the topology of the spin distribution in the dipole network and can be expected in other liquid crystals. Knowledge of the nature of the dipolar quasi-invariants will be useful in studies of dipolar-order relaxation, decoherence and multiple quantum NMR experiments where the initial state is a dipolar ordered one.Fil: Segnorile, Hector Hugo. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; ArgentinaFil: Bonin, Claudio Julio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentina. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; ArgentinaFil: González, Cecilia Élida. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; ArgentinaFil: Acosta, Rodolfo Héctor. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; ArgentinaFil: Zamar, Ricardo César. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentin

Health-status outcomes with invasive or conservative care in coronary disease

BACKGROUND In the ISCHEMIA trial, an invasive strategy with angiographic assessment and revascularization did not reduce clinical events among patients with stable ischemic heart disease and moderate or severe ischemia. A secondary objective of the trial was to assess angina-related health status among these patients. METHODS We assessed angina-related symptoms, function, and quality of life with the Seattle Angina Questionnaire (SAQ) at randomization, at months 1.5, 3, and 6, and every 6 months thereafter in participants who had been randomly assigned to an invasive treatment strategy (2295 participants) or a conservative strategy (2322). Mixed-effects cumulative probability models within a Bayesian framework were used to estimate differences between the treatment groups. The primary outcome of this health-status analysis was the SAQ summary score (scores range from 0 to 100, with higher scores indicating better health status). All analyses were performed in the overall population and according to baseline angina frequency. RESULTS At baseline, 35% of patients reported having no angina in the previous month. SAQ summary scores increased in both treatment groups, with increases at 3, 12, and 36 months that were 4.1 points (95% credible interval, 3.2 to 5.0), 4.2 points (95% credible interval, 3.3 to 5.1), and 2.9 points (95% credible interval, 2.2 to 3.7) higher with the invasive strategy than with the conservative strategy. Differences were larger among participants who had more frequent angina at baseline (8.5 vs. 0.1 points at 3 months and 5.3 vs. 1.2 points at 36 months among participants with daily or weekly angina as compared with no angina). CONCLUSIONS In the overall trial population with moderate or severe ischemia, which included 35% of participants without angina at baseline, patients randomly assigned to the invasive strategy had greater improvement in angina-related health status than those assigned to the conservative strategy. The modest mean differences favoring the invasive strategy in the overall group reflected minimal differences among asymptomatic patients and larger differences among patients who had had angina at baseline