Investigation of laser ablated ZnO thin films grown with Zn metal target: a structural study

High quality ZnO thin films were gown using the pulsed laser deposition technique on (0001) Al$_2$O$_3$ substrates in an oxidizing atmosphere, using a Zn metallic target. We varied the growth conditions such as the deposition temperature and the oxygen pressure. First, using a battery of techniques such as x-rays diffraction, Rutherford Backscattering spectroscopy and atomic force microscopy, we evaluated the structural quality, the stress and the degree of epitaxy of the films. Second, the relations between the deposition conditions and the structural properties, that are directly related to the nature of the thin films, are discussed qualitatively. Finally, a number of issues on how to get good-quality ZnO films are addressed.Comment: To be published in Jour. Appl. Phys. (15 August 2004

Tailoring magnetic anisotropy in epitaxial half metallic La0.7Sr0.3MnO3 thin films

We present a detailed study on the magnetic properties, including anisotropy, reversal fields, and magnetization reversal processes, of well characterized half-metallic epitaxial La0.7Sr0.3MnO3 (LSMO) thin films grown onto SrTiO3 (STO) substrates with three different surface orientations, i.e. (001), (110) and (1-18). The latter shows step edges oriented parallel to the [110] (in-plane) crystallographic direction. Room temperature high resolution vectorial Kerr magnetometry measurements have been performed at different applied magnetic field directions in the whole angular range. In general, the magnetic properties of the LSMO films can be interpreted with just the uniaxial term with the anisotropy axis given by the film morphology, whereas the strength of this anisotropy depends on both structure and film thickness. In particular, LSMO films grown on nominally flat (110)-oriented STO substrates presents a well defined uniaxial anisotropy originated from the existence of elongated in-plane [001]-oriented structures, whereas LSMO films grown on nominally flat (001)-oriented STO substrates show a weak uniaxial magnetic anisotropy with the easy axis direction aligned parallel to residual substrate step edges. Elongated structures are also found for LSMO films grown on vicinal STO(001) substrates. These films present a well-defined uniaxial magnetic anisotropy with the easy axis lying along the step edges and its strength increases with the LSMO thickness. It is remarkable that this step-induced uniaxial anisotropy has been found for LSMO films up to 120 nm thickness. Our results are promising for engineering novel half-metallic magnetic devices that exploit tailored magnetic anisotropy.Comment: 10 pages, 10 figures, 1 tabl

Isolation of structurally distinct lignin–carbohydrate fractions from maize stem by sequential alkaline extractions and endoglucanase treatment

Sequential fractionation of extractive-free maize stems was carried out using two mild alkaline extractions (0.5 and 2 M NaOH, 20 'C, 24 h) before and after endoglucanase treatment. This procedure provided two lignin–carbohydrate fractions (LC1 and LC2) recovered after each alkali treatment. LC1 and LC2 contained 39% and 8% of the total lignin amount, respectively. These two fractions contained structurally distinct lignin molecules. While the content of resistant interunit bonds in lignin was 77% in LC1, it was increased up to 98% in LC2. Not unexpectedly, both alkali-soluble fractions contained substantial amount of p-coumaric and ferulic acids ether-linked to lignins. These results outline heterogeneity of maize stem lignins related to fractionation of grass materials

Uncooled bolometer response of a low noise La2/3Sr1/3MnO3 thin film

We report measurements of the optical responses of a La2/3Sr1/3MnO3 (LSMO) sample at a wavelength of 533 nm in the 300-400 K range. The 200 nm thick film was grown by pulsed laser deposition on (100) SrTiO3 substrate and showed remarkably low noise. At 335 K the temperature coefficient of the resistance of a 100 micrometers wide 300 micrometers long LSMO line was 0.017 K-1 and the normalized Hooge parameter was 9 e-30 m3, which is among the lowest reported values. We then measured an optical sensitivity at I = 5 mA of 10.4 V.W-1 and corresponding noise equivalent power (NEP) values of 8.1 e-10 W.Hz-1/2 and 3.3 e-10 W. Hz-1/2 at 30 Hz and above 1kHz, respectively. Simple considerations on bias current conditions and thermal conductance G are finally given for further sensitivity improvements using LSMO films. The performances were indeed demonstrated on bulk substrates with G of 10-3 W.K-1. One could expect a NEP reduction by three orders of magnitude if a membrane-type geometry was used, which makes this LSMO device competitive against commercially available uncooled bolometers.Comment: 15 pages. Accepted for publication in Appl. Phys. Let

Etude de la variabilité de la production d’anticorps après immunisation en relation avec une sélection génétique sur la réponse inflammatoire mammaire chez la brebis

L’étude compare la production d’anticorps entre des lignées de brebis issues d’une sélection divergente sur la concentration de cellules somatiques dans le lait. Les brebis ont été immunisées par injection d’ovalbumine en adjuvant de Freund. Durant la phase mémoire, un rappel antigénique intra-mammaire a été réalisé. La quantité d’immunoglobulines G spécifiques a été mesurée par ELISA dans le sérum et le lactosérum. Il existe un effet significatif de la lignée CCS sur la production d’anticorps à la fois au cours de la réponse primaire et après stimulation intra-mammaire. Le stade de gestation module très significativement l’intensité de la réponse anticorps. La question de la relation entre réponse anticorps et résistance aux mammites est discutée. La différence de réponse humorale entre les brebis des deux lignées peut être due à un déterminisme génétique commun aux deux réponses. Elle peut aussi s’expliquer par la contribution des anticorps à la lutte contre les infections mammaires

Stokes-space formalism for Bragg scattering in a fiber

Optical frequency conversion by four-wave mixing (Bragg scattering) in a fiber is considered. The evolution of this process can be modeled using the signal and idler amplitudes, which are complex, or Stokes-like parameters, which are real. The Stokes-space formalism allows one to visualize power and phase information simultaneously, and produces a simple evolution equation for the Stokes parameters

Microbolomètres supraconducteurs YBCO suspendus<br />réalisés par micro-usinage du substrat de silicium

We demonstrated the feasibility of both sensitive and relatively fast YBaCuOsuspended bolometers by silicon micromachining. This work includes a technological partwhere three fabrication sequences are described and a characterisation part. The YBaCuOfilms on CeO2 / YSZ-buffered silicon are c axis textured and show only one epitaxial in-planeorientation. Their critical temperature Tc (zero resistance) is 88 K and their critical currentdensity is above 106 A / cm2 at 77 K. The reactive ionic etching (RIE) of silicon substratesenabled to fabricate a large number of samples and to confirm our calculations by comparisonwith the measurements. The technique of fabrication based on SIMOX substrates did notdegrade the YBaCuO superconducting properties and was found to be very promising fordetection. At last, we defined a meander line, constituted by seventeen 4 µm wide tracks andfabricated by RIE. The performances of this detector of 100 ´ 100 µm2 area, measured at 85 Kin the wavelength range 3-5 µm, are among the best reported results:Sensitivity (3-5 µm) = 11950 V / W.Thermal response time t = 564 µs.Optical NEP = 4,0 10-12 W Hz-1/2Detectivity D* = 2,5 109 cm Hz-1/2 / WNous avons démontré la faisabilité de bolomètres suspendus YBaCuO sensibles etrelativement rapides par micro-usinage du substrat de silicium. Ce travail comprend une partietechnologique décrivant trois techniques de fabrication de structures suspendues YBaCuO etune partie de caractérisation. Les films d'YBaCuO obtenus sur silicium avec une doublecouche tampon CeO2 / YSZ sont texturés dans la direction c et ne possèdent qu'une seuleorientation dans le plan. Leur température critique mesurée à résistance nulle vaut 88 K, etleur densité de courant critique dépasse 106 A / cm2 à 77 K. La gravure ionique réactive (GIR)du substrat de silicium nous a permis de réaliser un grand nombre d'échantillons et de validerainsi nos calculs par confrontation avec les mesures. La technique de fabrication utilisant unsubstrat SIMOX s'est révélée très peu dégradante pour l'YBaCuO et très prometteuse pour ladétection. Enfin, nous avons défini un méandre constitué de 17 brins de largeur de piste 4 µm,et fabriqué par GIR. Les performances de ce détecteur de surface 100 * 100 µm2, mesurées à85 K dans la gamme de longueur d'onde 3-5 µm, sont au niveau des meilleures publiées:Sensibilité (3-5 µm) = 11950 V / WTemps de réponse t = 564 µsNEP optique = 4,0 10-12 W Hz-1/2Détectivité D* = 2,5 109 cm Hz-1/2 /

Drug Use on Mont Blanc: A Study Using Automated Urine Collection

Mont Blanc, the summit of Western Europe, is a popular but demanding high-altitude ascent. Drug use is thought to be widespread among climbers attempting this summit, not only to prevent altitude illnesses, but also to boost physical and/or psychological capacities. This practice may be unsafe in this remote alpine environment. However, robust data on medication during the ascent of Mont Blanc are lacking. Individual urine samples from male climbers using urinals in mountain refuges on access routes to Mont Blanc (Goûter and Cosmiques mountain huts) were blindly and anonymously collected using a hidden automatic sampler. Urine samples were screened for a wide range of drugs, including diuretics, glucocorticoids, stimulants, hypnotics and phosphodiesterase 5 (PDE-5) inhibitors. Out of 430 samples analyzed from both huts, 35.8% contained at least one drug. Diuretics (22.7%) and hypnotics (12.9%) were the most frequently detected drugs, while glucocorticoids (3.5%) and stimulants (3.1%) were less commonly detected. None of the samples contained PDE-5 inhibitors. Two substances were predominant: the diuretic acetazolamide (20.6%) and the hypnotic zolpidem (8.4%). Thirty three samples were found positive for at least two substances, the most frequent combination being acetazolamide and a hypnotic (2.1%). Based on a novel sampling technique, we demonstrate that about one third of the urine samples collected from a random sample of male climbers contained one or several drugs, suggesting frequent drug use amongst climbers ascending Mont Blanc. Our data suggest that medication primarily aims at mitigating the symptoms of altitude illnesses, rather than enhancing performance. In this hazardous environment, the relatively high prevalence of hypnotics must be highlighted, since these molecules may alter vigilance