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We compare in a systematic way spectrometric, photometric and mid-infrared (VLTI/MIDI) interferometric measurements with different types of model atmospheres. Self-consistent dynamic model atmospheres in particular were used to interpret in a consistent way the dynamic behavior of gas and dust. The results underline how the joint use of different kind of observations, as photometry, spectroscopy and interferometry, is essential to understand the atmospheres of pulsating C-rich AGB stars. The sample of C-rich stars discussed in this work provides crucial constraints for the atmospheric structure.
Fundamental aspects of (electro-)luminescence of Cu(In,Ga)Se2 solar cells and modules are investigated by means of spectrally and spatially resolved measurements. The validity of the reciprocity relation between spectrally resolved electroluminescence emission and photovoltaic quantum efficiency is verified for the case of industrially produced ZnO/CdS/Cu(In,Ga)Se2 heterojunction solar cells. Further we find that photo- and electroluminescent emission in these devices obey a superposition principle only in a limited range of the applied electrical or illumination bias. This range depends on the light soaking history of the sample and extends up to an injected current density of approximately 15 mAcm-2 after 3 h of light soaking at a temperature of 400 K. In the state prior to light soaking this range is limited to 4 mAcm-2. At higher bias, a characteristic discrepancy between electroluminescence and electro-modulated photoluminescence appears. We attribute this anomaly to a potential barrier behavior close to the CdS/ Cu(In,Ga)Se2 interface. Metastable defect reactions induced by holes injected into the space charge region partly reduce this barrier. We further find that the luminescence efficiency is enhanced by a factor of 3 by light soaking at 400 K. Spatially resolved electroluminescence measurements conducted during application of voltage or current bias at ambient temperature in the dark are qualitatively compatible with the conclusions drawn from the spectrally resolved measurements.
In this contribution, we show that the dominant electroluminescent emission of hydrogenated amorphous silicon (a-Si:H) thin-film solar cells follows a diode law, whose radiative ideality factor nr is larger than one. This is in contrast to crystalline silicon and Cu(In, Ga)Se2 solar cells for which nr equals one. As a consequence, the existing quantitative analysis for the extraction of the local junction voltage Vj(r) from luminescence images fails for a-Si:H solar cells. We expand the existing analysis method, and include the radiative ideality factor nr into the model. With this modification, we are able to determine the local junction voltage Vj(r) for a-Si:H solar cells and modules. We investigated the local junction voltage Vj(r) and the radiative ideality factor nr for both initial and stabilized a-Si:H solar modules. Furthermore, we show that the apparent radiative ideality factor is affected by the spectral sensitivity of the used camera system.
The lattice reconstructed bec Ni (001) in Fe/Ni (001) ultrathin layers allows one to engineer films in which the in-plane 4-fold anisotropies and coercive fields can be varied and adjusted according to specific requirements. Magnetization reversals have been studied in layered structures of Fe/Ag/Fe/Ni (001). For Ag (001) interlayers thicker than 13 ML Magnetization reversal can proceed in two steps. In these samples the minor loops switch the magnetization of the Fe (001) layer from the parallel to the antiparallel configurations with respect to the magnetic moment of the Fe/Ni film. Such Minor loops exhibit a rectangular behavior with switching fields of 15–25 Oe. The lattice transformed Fe/Ni layers could be useful in spin-valve structures.
Single layers of Co82?l8 with thickness in me ranee of 100–1500Å and multilayers of Co-Cr/Al with Co-Cr thickness in the range of 100–200A and Al at 7Å were prepared by dc magnetron sputtering. The films were deposited on to Si (111) and glass substrates at room temperature. A 100Å thick Al buffer layer was deposited to improve the c-axis orientation. X-ray diffraction (XRD) Measurements on the multilayers show a predominant Co-Cr (00.2) peak. Polar Magneto-optic measurements were performed to determine the Kerr rotation (θK) and figure of Merit. The results indicated an enhancement in the figure of merit at λ = 632.8 nm for the multilayered structures compared to single layer samples. All of the films show a 4πMs value around 6 kG and ferromagnetic resonance measurements indicate an enhancement in the perpendicular anisotropy field for the 150Å multilayered sample.
Cobalt-platinum alloys and multilayers are now well known for their potentialities in Magneto-optical recording Media. The growth of ultrathin layers and sandwiches is thought to be useful to find the relationship between the structural and magnetic properties at an atomic level. Low Energy Electron Diffraction (LEED) and Auger spectroscopy (AES) are used here to study the crystallography and the growth modes of Pt on Co (0001) surfaces. Co/Pt/Co sandwiches are also built and investigated by the same Methods. At room temperature we show the evidence of a good epitaxy of platinum on the Co (0001) surface leading to the possibility of obtaining ordered Co/Pt/Co sandwiches. Annealings at moderate temperatures lead to an epitaxial alloy formation. Auger results show that alloying indeed induces a magnetic moment on platinum atoms. This could explain the magnetic properties already observed in CO/Pt (111) Multilayers.
To establish the structural origins of the perpendicular magnetic anisotropy in Co-Pt alloys, a variety of magnetic and structural characterization techniques have been utilized. We have determined that the development of out-of-plane magnetization in these alloys, strongly depends on growth temperature and in contrast to CO/Pt Multilayers, the highest anisotropics and coercivities are observed in polycrystalline alloys with negligible preferred crystallographic orientation. Lattice strain Measurements, surface roughness determination and crystal growth studies indicate that contributions from magnetostrictive and magnetostatic contributions to the perpendicular anisotropy in these alloys are not significant. H RTEM and synchrotron-based x-ray diffraction experiments, on the other hand, confirm the existence of ordered CoPt3 at elevated temperatures. We suggest that the strong temperature dependence of the perpendicular anisotropy is correlated to the onset of spontaneous chemical ordering during the growth which results in anisotropie pair ordering. A tentative model explaining this strong temperature dependence is described.
The resistance and magnetoresistance of Gd/W Multilayers have been measured at temperatures between 300K and 4K and in fields of up to 7 Tesla. The temperature coefficent of resistance is strongly influenced by the thickness of the Gd layers, becoming negative at a Gd layer thickness of 0.8nm. The Magnetoresistance is dominated by the Gd below about 100K. Multilayers which show reduced saturation magnetisation at 4K also have an unusual form of magnetoresistance around 100K. We suggest that this may be due to antiferromagnetic alignment of the Gd and W Moments at low applied fields.
Circular Dichroic X-ray Photoemission Spectroscopy (CDXPS) experiments have been performed on the 2p core level spectra of polycrystalline Fe film which was magnetized by a low excitation field. The ability to perform the CDXPS experiments in a non remanent mode at a photon energy of 2100 eV opens new and interesting possibilities for the MCD technique in the study of surface and interface Magnetism. Our work on this polycrystalline iron gives some new insights into the understanding of the MCD Mechanism. First results show a similar angular variation for the measured asymmetry, as those observed on a Fe bcc (100) single crystal remanently magnetized in the  direction. Our results make clear that the parameters governing the behaviour of the asymmetry factor (A) are not completely described by the relative direction of the Magnetization (M) with the polarization vector of the incident beam (q) and the direction of detection of the photoelectrons (z). The specific outcoming of this work is to clearly show that this behaviour of A is not connected to the crystalline structure of the film for our geometries.
We study the effects of quantum-well states on the calculated RKKY coupling. We find that the bound states of a finite-size potential well of depth V give an added oscillation period of size For the simplest case of a spherical free-electron Fermi surface, thus two periods appear: the original, “fast,” π/kf oscillation, and the quantum-well one The quantum-well contributions have larger amplitude, and are in fact the predominant oscillation. For physically reasonable V (tenths of an eV) this period is around 8–10Å. We discuss evidence for these effects in experimental systems.
Wc report the observation of giant magnctorcsistance in granular systems prepared by either Melt-spinning or sputtering. For Melt-spun CoxCu1-x alloys, with x varying between 5 and 30%, Magnctoresitancc amplitudes of 20% in 50 kOc at 5 K were obtained, similar to those reported for the same alloys prepared by sputtering. For sputtered (Ni80Fe20)xAg1-x alloys, three different contributions to the magnetorcsisiancc have been clearly identified: The spin-valve (or giant) Magnctorcsistance, scattering on magnetic fluctuations, and anisotropie Magnetorcsistancc. These three contributions have their own dependences on the size of the magnetic particles, on the degree of intermixing between NiFe and Ag, and on the temperature. In the third scries of samples, sputtered (Co70Fe30)xAg1-x, very large magnctorcsistance amplitude has been observed (AR/R as high as 20% at room temperature in 10 kOc and 60% at 10 K).
We present a comparative in situ RHEED and Polar Magneto-optic Kerr Effect study of the first stages of the growth of a Au overlayer on top of a (111) Co ultrathin film. Drastic behaviours are evidenced on the RHEED diagram, Magnetic anisotropy and coercive force, around 1,5 ML of Au coverage.
Indirect Magnetic coupling in sputtered Ni/Ag Multilayers has been recently studied by magnetization and magnetoresistance techniques. These experiments indicate that coupling is anti ferromagnetic through 11 and 30 A of silver, and probably ferromagnetic through 20 Å. We present here direct evidence for such a magnetic coupling for all three thicknesses, as obtained from low angle neutron scattering experiments. Multilayers in which the Ag layer thickness is either 11 or 30 Å both exhibit a supplementary diffraction peak at a q value corresponding to twice the chemical period. Its evolution with both temperature and applied field confirms its purely magnetic origin. In order to study the coupling through 20 Å of silver, we prepared a multilayer in which the Ag layers are alternately 11 and 20 Å thick. In this case, we also observe a doubling of the chemical period. The coupling through 11 Å being anti ferromagnetic, this unambiguously shows that the coupling through 20 Å is ferromagnetic.
The Magnetoresistive properties of sputtered Ni8.1Fe1.9/Ag Multilayers have been investigated as a function of both Ag and NiFe layer thicknesses and thermal treatments. For the virgin sample, the Magnetoresistance (MR) ratio at room temperature goes through a maximum of 17% for a Ag thickness of about 11 A. In addition, the R (H) curve is found to be perfectly linear and reversible. Contrary to the MR ratio, the saturation field is observed to decrease continuously as the Ag thickness increases, leading to an increasing slope of the R (H) curves. Upon annealing, we observe both an increase of the MR ratio and a decrease of the saturation field, leading to a three fold increase of the MR slope for annealing temperatures of 280°C. Such a behavior appears to be highly dependent on the layer thicknesses.
The conditions for an almost perfect growth of smooth Cr (001) films on an iron whisker substrate have been investigated by means of reflection high energy electron diffraction (RHEED). The exchange interaction between 20 Monolayer thick Fe (001) films separated from a bulk whisker Fe (001) substrate by a variable number of Cr (001) Monolayers (ML) has been investigated by means of Brillouin light scattering experiments (BLS). These experiments show unambiguously that the exchange coupling strength between the iron film and the iron whisker can be described by a short wavelength oscillatory term superposed on a slowly varying antiferromagnetic background. The BLS data enabled one to separate the bilinear and the biquadratic contributions to the antiferromagnetic exchange coupling terms. Both the bilinear and the biquadratic coupling strengths exhibited a short period oscillatory dependence on the Cr interlayer thickness (∼2 Monolayers). Maxima in the bilinear antiferromagnetic coupling strength occur for an odd number of Cr Monolayers. This observation is not in agreement with first principles calculations. The first phase inversion has been found to occur between 4 and 5 ML of Cr.
We have investigated structural and magnetic properties of CoPt alloy films with strong perpendicular magnetic anisotropy in the thickness range between 100Å and 400A. From a detailed x-ray analysis we find highly (111) -textured CoPt Microcrystal-lites in all samples. STM studies reveal a granular topography with grain diameters of up to 250Å. Measurements of hysteresis loops yield a saturation field which increases with thickness, and which is consistent with a freely mobile domain Model. Brillouin light scattering measurements of the frequencies of the surface and standing spin wave modes yield a bulk exchange constant, which is strongly dependent on the Pt content.
Livestock-associated methicillin-resistant Staphylococcus aureus (LA-MRSA) have been isolated from a number of livestock species and persons involved in animal production. We investigated the prevalence of LA-MRSA in fattening turkeys and people living on farms that house fattening turkeys. Eighteen (90%) of 20 investigated flocks were positive for MRSA, and on 12 of the farms 22 (37·3%) of 59 persons sampled were positive for MRSA. People with frequent access to the stables were more likely to be positive for MRSA. In most flocks MRSA that could be assigned to clonal complex (CC) 398 were detected. In five flocks MRSA of spa-type t002 that is not related to CC398 were identified. Moreover, other methicillin-resistant Staphylococcus spp. were detected on 11 farms and in eight people working on the farms.
The phase stability of C-22 alloy (UNS #N06022) was studied by aging samples at 593, 649, 704 and 760°C for 2000 h (2.7 mo) and 16,000 h (1.8 yr). The tensile properties and the Charpy impact toughness of these samples were measured in the mill annealed condition as well as after aging. The microstructures of samples aged 16,000 hours were examined using scanning and transmission electron microscopy (SEM and TEM). Preliminary TEM results suggest that μse forms at all temperatures investigated. Discrete carbide particles in addition to a film with very uniform thickness which appears to be μ phase formed on grain boundaries in the sample aged at 593°C. The ordered Ni2(Cr, Mo) phase was also seen in this sample. At the higher aging temperatures, mainly μ phase forms covering all the grain boundaries and also distributed throughout the bulk. Although strength increased somewhat with aging. the ductility decreased due to the formation of these grain boundary precipitates and brittle intermetallics.
The CRESST-II direct Dark Matter search is located in the Gran Sasso underground laboratories, Italy. CaWO4 crystals are used as scintillating targets for WIMP (weakly interacting massive particle) interactions. They are operated as cryogenic calorimeters in combination with a second cryogenic detector used to measure the scintillation light produced in the target crystal. For each particle interaction, the combination of phonon and light signals provides an event by event discrimination which allows to distinguish known particles (alphas, betas, gammas, neutrons) from the expected signal of WIMPs. A major upgrade of the setup comprises modifications of the shielding, installation of a muon-veto, and new read out electronics, as well as a new detector-support structure to accommodate up to 33 detector modules, i.e. 10 kg of target mass. The experiment was thereafter successfully commissioned in 2007. Data obtained during this commissioning phase from 2 detector modules are presented here. Combining the data collected with these two detector modules with data from one single module obtained during the CRESST-I phase, the experiment could already place a limit of ~6 × 10-7 pb for the spin independent WIMP-nucleon scattering cross section at a WIMP mass of ~60 GeV/c2.