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1
Inkoom, Godfred. "Ferromagnetic Resonance of LSMO Thin Film." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for fysikk, 2011. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-12933.
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The magnetic properties of a 15uc thick LSMO thin film on SrTiO3 (STO) substrate atT=150K was investigated using the technique of ferromagnetic resonance (FMR). The FMRmeasurement of the 15uc thick LSMO thin film at a frequency f = 9.75GHz and powerP = 0.6325mW as a function of the angle between the static magnetic field H, and theeasy direction of magnetization within the sample plane in the "in-plane" (IP) configuration displayed an FMR spectrum. This resonance spectrum shows unequal resonance field peaks. The unequal peaks in the resonance field may be attributed to the uniaxial anisotropy field which satisfies the conditions for ferromagnetic resonance. The unequal peaks in the resonance field shows a maximum and minimum with negative and positive curvature which either increases or decreases with respect to the resonance field respectively. This increase or decrease in the resonance field depends on the magnetization direction. It has been shown that for a thick 15uc LSMO thin film at T = 150K the center position and the full width half maximum (FWHM) of the resonance field were 1070.1875 Oe and 159.3125 Oe respectively.
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Kim, Joo-Hyung. "Micromachined epitaxial colossal mognetoresistors for uncooled infrared bolometer." Doctoral thesis, KTH, Microelectronics and Information Technology, IMIT, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-535.
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High quality perovskite manganites, La1-xAxMnO3 (A = Ca, Sr, Ba) are very attractive materials due to their great application potential for magnetic memory, uncooled infrared (IR) microbolometer and spintronics devices. This thesis presents studies of the growth and material characterization (including structural, electrical, magnetic and noise) of epitaxial manganite films on Si and GaAs. Furthermore, investigations about strain effect on structural and electrical properties of manganites, and finally fabrication of self-supported free standing microstructures for uncooled IR bolometer are also demonstrated.
To obtain high quality epitaxial manganite films on semiconductor substrates at room temperature, using a combination of La0.67Sr0.33MnO3 (LSMO) and La0.67Ca0.33MnO3 (LCMO) compounds, La0.67(Sr,Ca)0.33MnO3 (LSCMO) films were successfully grown on Si substrates with Bi4Ti3O12(BTO)/CeO2/YSZ buffers by pulsed laser deposition (PLD) technique. Crystallographic relations between layers shows cube-on-cube for BTO/CeO2/YSZ/Si and diagonal-on-side for LSCMO films on BTO layer. 4.4 %K-1 maximum temperature coefficient of resistivity (TCR = 1/ρ·dρ/dT) and 2.9 %kOe-1 colossal magnetoresistance (CMR) were obtained at room temperature. Assuming of a prototype of temperature sensor, 1.2 μK/√Hz of noise equivalent temperature difference (NETD) and 2.9×108 cm√Hz/W of detectivity are expected to achieve at 294 K, 30 Hz. For GaAs substrates, using MgO buffer layer, LCMO films shows 9.0 %K-1 of TCR at 223 K while LSMO exhibits 2 %K-1 at 327 K.
Systematic strain effects on structural and electrical properties of La0.75Sr0.25MnO3 LSMO) films on BTO/CeO2/YSZ-buffered Si, Si1-xGex/Si (compressive strain, x = 0.05-0.20) and Si1-yCy/Si (tensile, y = 0.01) were investigated. The strain induced from Si1-xGex/Si and Si0.99C0.01/Si has a tendency to decrease the roughness of CMR films compared to Si sample. High resistivity and low TCR values are observed for Si0.8Ge0.2/Si and Si0.99C0.01/Si samples due to excessive strains whereas Si0.9Ge0.1/Si and Si0.95Ge0.05/Si show slight improvements of films quality and TCR value.
To fabricate LSCMO manganite bolometer on Si, wet etching with KOH and BHF and dry etching methods with Ar ion beam etching (IBE) were studied. For KOH wet etching, LSCMO films show high chemical resistance with lower than 0.2 nm/min of etch rate. BHF wet etching shows high etching selectivity over photoresist mask and silicon substrates. The etch rates for LSCMO and BTO layers are 22 and 17 nm/min. For Ar IBE, LSCMO films and oxide buffer layers show similar etch rates, 16-17 nm/min that are lower compared to 24 nm/min for Si.
Free standing, self-supported heteroepitaxial LSCMO/BTO/CeO2/YSZ membranes for bolometer pixels on Si was successfully fabricated by Ar IBE and ICP etching techniques using a preannealed photoresist. The structural investigation by TEM revealed the sharp interfaces between layers. The electrical property of the free standing membrane was slightly degraded due to strain release and multi-step etching effect. These results demonstrate feasibility to use heteroepitaxial oxide structures as a thermally isolated membrane with conventional photoresist patterning.
3
Calbucci, Marco <1987>. "Charge and spin transport in memristive organic LSMO/Alq3/AlOx/Co spin valves." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2016. http://amsdottorato.unibo.it/7244/1/Tesi_Calbucci.pdf.
Full textAbstract:
In this thesis I studied La0.7Sr0.3MnO3/Alq3/AlOx/Co organic spin valves, which are multifunctional devices showing an interesting interplay between magnetoresistive effects and memristive switching.
In particular this work aims at elucidating the elusive mechanisms for spin injection and transport in this archetypal structure.
While spin injection in organic materials was demonstrated by different spectroscopic techniques, the origin of magnetoresistive effect in organic spin valves is still debated. In fact, the Hanle effect, considered to be the only reliable proof for spin transport across the organic spacer layer, has not been observed in such a device, yet.
I investigated the thickness and temperature dependence of charge transport and magnetoresistive properties, and demonstrated the absence of the Hanle effect. Moreover I studied how the resistance and magnetoresistance of our devices were affected by memristive switching, which turned out to be a fundamental tool to enlighten the comprehensive picture.
Two clearly distinguishable conduction regimes have been found for non magnetoresistive and magnetoresistive devices.
The former is compatible with models for charge transport in organic materials, the latter can be described by an equivalent circuit where metallic paths and hopping channels act in parallel. In the framework of this model, a coherent description for the interplay between MR and memristive switching can be given. SV signals can be explained as tunnel magnetoresistance (TMR) or ballistic magnetoresistance (BMR) occurring across shortened regions of the organic bulk, which is an explanation compatible with the absence of Hanle effect.
This work demonstrates that SV signals can be explained without resorting to spin injection and transport into the organic layer.
4
Calbucci, Marco <1987>. "Charge and spin transport in memristive organic LSMO/Alq3/AlOx/Co spin valves." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2016. http://amsdottorato.unibo.it/7244/.
Full textAbstract:
In this thesis I studied La0.7Sr0.3MnO3/Alq3/AlOx/Co organic spin valves, which are multifunctional devices showing an interesting interplay between magnetoresistive effects and memristive switching.
In particular this work aims at elucidating the elusive mechanisms for spin injection and transport in this archetypal structure.
While spin injection in organic materials was demonstrated by different spectroscopic techniques, the origin of magnetoresistive effect in organic spin valves is still debated. In fact, the Hanle effect, considered to be the only reliable proof for spin transport across the organic spacer layer, has not been observed in such a device, yet.
I investigated the thickness and temperature dependence of charge transport and magnetoresistive properties, and demonstrated the absence of the Hanle effect. Moreover I studied how the resistance and magnetoresistance of our devices were affected by memristive switching, which turned out to be a fundamental tool to enlighten the comprehensive picture.
Two clearly distinguishable conduction regimes have been found for non magnetoresistive and magnetoresistive devices.
The former is compatible with models for charge transport in organic materials, the latter can be described by an equivalent circuit where metallic paths and hopping channels act in parallel. In the framework of this model, a coherent description for the interplay between MR and memristive switching can be given. SV signals can be explained as tunnel magnetoresistance (TMR) or ballistic magnetoresistance (BMR) occurring across shortened regions of the organic bulk, which is an explanation compatible with the absence of Hanle effect.
This work demonstrates that SV signals can be explained without resorting to spin injection and transport into the organic layer.
5
Leufke, Philipp Moritz [Verfasser], Horst [Akademischer Betreuer] Hahn, and Andreas [Akademischer Betreuer] Klein. "Magnetoelectric coupling in layered LSMO/PZT nanostructures / Philipp Moritz Leufke. Betreuer: Horst Hahn ; Andreas Klein." Darmstadt : Universitäts- und Landesbibliothek Darmstadt, 2014. http://d-nb.info/1108094775/34.
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Leufke, Philipp M. [Verfasser], Horst [Akademischer Betreuer] Hahn, and Andreas [Akademischer Betreuer] Klein. "Magnetoelectric coupling in layered LSMO/PZT nanostructures / Philipp Moritz Leufke. Betreuer: Horst Hahn ; Andreas Klein." Darmstadt : Universitäts- und Landesbibliothek Darmstadt, 2014. http://nbn-resolving.de/urn:nbn:de:tuda-tuprints-37843.
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7
Chaluvadi, Sandeep kumar. "Influence of the epitaxial strain on magnetic anisotropy in LSMO thin films for spintronics applications." Thesis, Normandie, 2017. http://www.theses.fr/2017NORMC248/document.
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Nous présentons une étude des effets de contrainte induits par l’épitaxie dans des couches minces La1-xSrxMnO3 (LSMO) (001) (x = 0.33) pour 3 épaisseurs de films (50, 25 et 12 nm) déposés par Ablation Laser Pulsée (PLD) sur différents substrats tels que SrTiO3 (STO) (001), STO buffered MgO (001), NdGaO3 (NGO) (110) et (LaAlO3)0.3(Sr2AlTaO6)0.7 (LSAT) (001). L’étude est complétée par l’effet de la composition sur les propriétés magnétiques de couches minces de La1-xSrxMnO3 avec x=0,33 et 0,38 déposées par Epitaxie à Jets Moléculaires (MBE). Des caractérisations par diffraction de rayons X (XRD), et microscopie à force atomique (AFM), des mesures de résistivité électrique en quatre points en fonction de la température, d’aimantation par magnetometrie à SQUID (Superconducting Quantum Interference Device) et d’anisotropie magnétique par magnétométrie magnéto-optique Kerr vectorielle (MOKE) sont présentées. Les évolutions angulaires de l’anisotropie magnétique, de l’aimantation à rémanence, du champ coercitif et du champ de renversement d’aimantation ont ainsi pu être analysées pour des films épitaxiés LSMO de différentes épaisseurs. Des études en fonction de la température complètent les données. L’origine de l’anisotropie (magnétique, magnétocristalline, magnétostrictive ou liée aux effets de marches et d’angle de désorientation du substrat) est finalement discutéeWe report a quantitative analysis of thickness dependent epitaxial strain-induced effects in La1-xSrxMnO3 (LSMO) (001) (x = 0.33) thin films of thicknesses (50, 25 and 12 nm) grown on various single crystal substrates such as SrTiO3 (STO) (001), STO buffered MgO (001), NdGaO3 (NGO) (110) and (LaAlO3)0.3(Sr2AlTaO6)0.7 (LSAT) (001) by Pulsed Laser Deposition (PLD) technique. We also report the composition dependent magnetic properties of LSMO thin films with x = 0.33 and 0.38 in particular grown onto LSAT (001) substrate by Molecular Beam Epitaxy (MBE). The study mainly includes measurements such as X-ray Diffraction (XRD), Atomic Force Microscopy (AFM), temperature dependent four-probe resistivity, magnetization properties by Superconducting Quantum Interference Device (SQUID), magnetic anisotropy by Magneto-Optical Kerr Magnetometry (MOKE). Our results highlight the detailed study of angular evolution and thickness dependent magnetic anisotropy, remanence, coercivity and switching field in epitaxial LSMO thin films. Temperature-dependent studies are also performed on few selected films. We will also discuss the cause of magnetic anisotropy in LSMO films i.e., magneto-crystalline and magnetostriction anisotropy and the effects of steps or substrate mis-cut induced anisotropy
8
Zuccatti, Elisabetta. "Fabrication of a New Multifunctional Interface Between La,Sr manganite and C60." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2016.
Find full textAbstract:
In questo lavoro abbiamo sperimentato due modi diversi per ottenere un monolayer di C60 su La,Sr manganite (LSMO): desorbendo C60 da un campione di 5nm cresciuto su un substrato di LSMO e crescendo, sempre su LSMO, sei campioni di C60 a diversi spessori nominali. Il campione desorbito è stato analizzato mediante misure STS ed STM, mentre i campione cresciuti a diversi spessori sono stati misurati mediante non-cntact AFM. Ciò che è emerso in entrambi i casi è che le molecole di C60 non interagiscono con il substrato di LSMO.
Nel primo caso infatti si è visto che è stato desorbito quasi tutto il C60 presente sul campione; la superficie della manganite risulta solo parzialmente ricoperta da molecole di C60. Nel secondo caso invece si nota che il C60 cresce formando isole che arrivano a ricoprire la superficie di LSMO solo per film dallo spessore nominale superiore a 30nm.
9
Gellé, Florian. "Hétérostructures épitaxiées avec des propriétés dépendantes de spin et de charges pour des applications en spintronique." Thesis, Strasbourg, 2019. http://www.theses.fr/2019STRAE032/document.
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L’objectif de la thèse est de développer un système de type jonction tunnel tout oxyde à base de La2/3Sr1/3MnO3 (LSMO) où il serait possible de contrôler l’aimantation des électrodes magnétiques par des processus à faible consommation d’énergie. Des jonctions tunnel épitaxiées de LSMO/SrTiO3/LSMO ont été obtenues montrant un double renversement de l’aimantation à température ambiante et un taux de magnétorésistance de 71 % à 10 K. En exerçant une contrainte sur le LSMO par le substrat il a été possible de moduler l’anisotropie des couches magnétiques. Des anisotropies perpendiculaire ou dans le plan ont pu être obtenues. Afin de contrôler le renversement des moments magnétiques dans une des électrodes ferromagnétiques trois options ont été envisagées : l’utilisation de l’injection de spin à partir d’un métal à fort couplage spin-orbite (Pt, Ir) ou d’un oxyde contenant de tels ions (ici Ru dans SrRuO3), et l’utilisation du Bi2FeCrO6, un oxyde multiféroïque pouvant présenter un couplage magnétoélectrique. Malgré des résultats prometteurs, aucune solution n’a permis des tests sur des jonctions afin d’estimer leur efficacité. L’objectif final n’est pas encore atteint mais des avancées intéressantes ont été faites afin d’envisager des dispositifs permettant le stockage et la manipulation de l’informationThe objective of this work is to develop La2/3Sr1/3MnO3 (LSMO) based all-oxide magnetic tunnel junction systems where it would be possible to control the magnetization of magnetic electrodes by low energy consumption processes. Epitaxial tunnel junctions of LSMO/SrTiO3/LSMO were obtained showing a double magnetization switching at room temperature and a magnetoresistance ratio of 71 % at 10 K. Using strain engineering, it was possible to modulate the anisotropy of the LSMO magnetic layers. Perpendicular or in plane anisotropies could be thus obtained. In order to control the reversal of the magnetic moments in one of the ferromagnetic electrodes three options were considered : the use of spin injection from a metal with a strong spin-orbit coupling (Pt, Ir) or an oxide containing this type of ions (here Ru in SrRuO3), and the use of Bi2FeCrO6 multiferroic oxide that may exhibit a magnetoelectric coupling. Despite promising results, no solution has allowed tests on junctions to be carried out to estimate their effectiveness. Although the final objective is not yet achieved, interesting progress has been made on the way to information storage and manipulation devices
10
Thiele, Christian. "Multiferroische Schichtsysteme: Piezoelektrisch steuerbare Gitterverzerrungen in Lanthanmanganat-Dünnschichten." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2006. http://nbn-resolving.de/urn:nbn:de:swb:14-1164036126087-50324.
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In der vorliegenden Arbeit werden durch den inversen piezoelektrischen Effekt kontrolliert Dehnungen in Lanthanmanganatschichten eingebracht und ihr Einfluss auf die Eigenschaften der Schichten untersucht. Dazu wird im ersten Teil der Arbeit ein Zweischichtsystem bestehend aus einer Manganatschicht aus La0,7Sr0,3MnO3, La0,8Ca0,2MnO3 oder La0,7Ce0,3MnO3 und einer piezoelektrischen Schicht aus PbZr0,52Ti0,48O3 untersucht. Der epitaktisch auf Einkristallsubstraten abgeschiedene Aufbau entspricht einer Feldeffekt-Transistor-Struktur. Neben den Effekten der Dehnung auf den elektrischen Widerstand der Manganatschicht wird auch der elektrische Feldeffekt untersucht. Durch mechanische Klemmung des Substrats können nur kleine Dehnungen in die Manganatschichten eingebracht werden. Um größere und homogene Dehnungen steuerbar in Manganatschichten einzubringen, werden im zweiten Teil der Arbeit La0,7Sr0,3MnO3 - Schichten auf piezoelektrischen Einkristallsubstraten der Verbindung (1-x)Pb(Mg1/3Nb2/3)O3 - xPbTiO3 mit x = 0,28 epitaktisch abgeschieden. Der Einfluss von mechanischen Dehnungen von bis zu 0,1% auf den elektrischen Transport, die ferromagnetische Übergangstemperatur und die Magnetisierung kann so eingehend untersucht werden. Es wird ein außergewöhnlich großer Einfluss von Dehnungen auf die Eigenschaften von La0,7Sr0,3MnO3 gefundenIn this work, strain arising from the inverse piezoelectric effect is induced into lanthanum manganite thin films in order to change and control their properties. In the first part of this work, manganite films of the compositions La0.7Sr0.3MnO3, La0.8Ca0.2MnO3 or La0.7Ce0.3MnO3 are combined with a piezoelectric layer of the composition PbZr0.52Ti0.48O3 in a bilayer system. This structure is grown epitaxially on single crystal substrates and corresponds to a field-effect transistor setup. Besides effects of strain on the electrical resistance of the manganite layers, field effects are observed. Due to clamping of the substrate, only small strains can be induced to the manganite films. In order to apply larger and homogeneous controllable strain to the manganite layers, thin films of La0.7Sr0.3MnO3 are grown epitaxially on piezoelectric single crystal substrates of the composition (1-x)Pb(Mg1/3Nb2/3)O3 - xPbTiO3, x = 0.28. Strain levels up to 0.1% are reached. The influence of the strain on electrical transport, ferromagnetic transition temperature and magnetization is analyzed. A remarkably large influence of the strain on the properties of La0.7Sr0.3MnO3 is found
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Fugattini, Silvio. "Studio mediante magnetometro moke di film sottili di manganite per applicazioni in spintronica." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2015. http://amslaurea.unibo.it/8334/.
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In questo lavoro di tesi è stata studiata l'anisotropia magnetica di film sottili epitassiali di La0.7Sr0.3MnO3 (LSMO), cresciuti con la tecnica Channel Spark Ablation su substrati monocristallini di SrTiO3 (001).
L'interesse nei confronti di questi materiali nasce dal fatto che, grazie alla loro proprietà di half-metallicity, sono usati come iniettori di spin in dispositivi per applicazioni in spintronica, l'elettronica che considera elemento attivo per l'informazione non solo la carica elettrica ma anche lo spin dei portatori. Un tipico esempio di dispositivo spintronico è la valvola di spin (un dispositivo costituito da due film ferromagnetici metallici separati da uno strato conduttore o isolante) il cui stato resistivo dipende dall'orientazione relativa dei vettori magnetizzazione (parallela o antiparallela) degli strati ferromagnetici. E’ quindi di fondamentale importanza conoscere i meccanismi di magnetizzazione dei film che fungono da iniettori di spin.
Questa indagine è stata effettuata misurando cicli di isteresi magnetica grazie ad un magnetometro MOKE (magneto-optical Kerr effect). Le misure di campo coercitivo e della magnetizzazione di rimanenza al variare dell'orientazione del campo rispetto al campione, permettono di identificare l'anisotropia, cioè gli assi di facile e difficile magnetizzazione.
I risultati delle misure indicano una diversa anisotropia in funzione dello spessore del film: anisotropia biassiale (cioè con due assi facili di magnetizzazione) per film spessi 40 nm e uniassiale (un asse facile) per film spessi 20 nm. L'anisotropia biassiale viene associata allo strain che il substrato cristallino induce nel piano del film, mentre l'origine dell'uniassialità trova la giustificazione più probabile nella morfologia del substrato, in particolare nella presenza di terrazzamenti che potrebbero indurre una step-induced anisotropy. Il contributo di questi fattori di anisotropia alla magnetizzazione è stato studiato anche in temperatura.
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Malowney, Josh. "Ordered Patterns of Functional Oxide Nanostructures Grown from Chemical Solutions." Doctoral thesis, Universitat Autònoma de Barcelona, 2012. http://hdl.handle.net/10803/108098.
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La generación de nanoestructuras de oxido por medio de impresión litográfica (NIL) y litografía por haz de electrones (EBL) se ha convertido en una estrategia más refinada durante los últimos años. Por medio de NIL hemos fabricado matrices de nanoagujeros y nanopuntos de La0.7Sr0.3MnO3 (LSMO), así como nanopuntos y nanohilos de LaxSr1-xOy por medio de EBL.
Las nanoestructuras echas por NIL se han fabricado después de espinar una capa de precursor de oxido de metal encima de un substrato de cristal solo aislante. Después se ha hecho un estampado con un molde duro de silicona masculino, un etching con plasma anisótropo y al final un recocido en atmosfera de oxigeno. El precursor está formado por el 15% en peso de polyvinyl alcohol (PVOH) y una proporción estequiométrica de sales de nitrato o acetato de La, Sr, Mn para poder formar LSMO epitaxiál después del recocido de la capa encima de los substratos de zirconio estabilizado con yttrium (YSZ), titanato de strontium (STO) y aluminato de lanthanum (LAO). El procedimiento de nanoimpresión se ha hecho presionando un molde con patrones altos 120nm encima de una capa precursora con un grosor de 250nm a una temperatura de 160º C durante cinco minutos y a una presión de 40 bars. Despues se ha hecho un etching de la capa con oxigen o argón para generar patrones positivos o negativos respectivamente. Finalmente la capa ha sido cocida a 900 ºC durante cuatro horas para remover los residuos orgánicos y para formar nanoagujeros y nanopuntos cristalinos de LSMO.
El etching de oxigeno de plasma anisótropo se ha hecho a 1200 W durante 120 segundos con un flujo de gas de 200 sccm. Con estos valores se ha podido remover la mayoría de los precursores impresos exponiendo la base de los nanoagujeros al substrato de cristal solo. Durante el plasma los atomos de oxigenos han reaccionado químicamente con los precursores removiendo los componentes orgánicos. Cuando el argón ha sido utilizado como gas de plasma en el etcher de iones reactivos (RIE) los valores han sido 150 W durante 15 minutos a 200 sccm. El plasma de argón no ha reaccionado químicamente con los precursores, así que ha removido mecánicamente la capa impresa. El resultado ha sido una serie de nanopuntos por debajo de los nanoagujeros. Este fenómeno podría haber pasado por una variación de densidad local en la capa impresa donde la parte por debajo del agujero ha sido comprimido y entonces ha resistido al bombardeo de los iones de argón más que la capas da circundante.
Por medio de EBL fueron fabricadas también matrices de nanoestructuras de oxido encima de substratos de cristal solo. Nanopuntos y nanohilos de LaxSr1-xOy han sido fabricados despues de espinar una capa de precursor de oxido de metal, exponiéndola a los electrones, desarrollándola en agua y recociéndolo en atmosfera de oxigeno. El precursor está formado por el 2% en peso de PVOH y una proporción estoquiometrica de sales de nitrato y acetato de La, Sr, Mn de tal manera para formar LSMO epitaxial después de la cocción de la capa fina encima de los substrtaos YSZ, STO y LAO así como en las estructuras hechas por NIL. Por medio de EBL la capa precursora de 200nm gruesa ha sido expuesta a una dosis de electrones de 0.1 pC para formar nanopuntos y a una dosis de 1500 pC para formar nanohilos. La propiedad aislante de los substratos ha prevenido el uso de una dosis alta de voltaje de haz de electrones. Una dosis de 5kV con una media de 150pA de corriente en alto vacio ha sido utilizada.
El mecanismo detrás la formación de los nanopuntos es la reticulación local del polímero por medio de los electrones. La capa restante soluble en agua ha sido quitada dejando nada más los puntos que habían estado expuestos a los electrones. El substrato ha sido cocido a 900ºC durante cuatro horas para quitar los componentes orgánicos restantes de las nanoestructuras y de los cristales. Los nanopuntos resultantes fueron analizados por TEM y EELS para demonstrar la presencia de nanoestructuras de cristales epitaxiales de oxido de anthanum. Estos nonopuntos han crecido con una morfología triangular con una altura que va de 15nm a 45nm utilizando dosis que van de 0.05 pC a 0.15 pC respectivamente. Dosis menores de estos valores no logran reticular una cantidad de PVOH suficiente y dosis mayores no producen estructuras solas. Un substrato de 9mm2 fue recubierto de nanopuntos con una distancia entre picos de 750nm en doce horas.
Para fabricar nanohilos, la dosis ha sido aumentada con el límite inferior de 150pC. Cuando la dosis era menos del límite, no se ha observado ningún hilo. El procedimiento para la fabricación de nanohillos ha sido la misma que él para fabricar los nanopuntos, la única diferencia ha sido en los parámetros del haz de electrones. Los nanohilos han crecido lejos de la región que ha sido irradiada. Por TEM se ha visto que son nanohilos de oxido de lanthanum epitaxial. El mecanismo propuesto que explica la formación de los nanohilos es que la región central irradiada ha cristalizado de los electrones primarios. El altura de los nanohilos era de 30nm en promedio y largos de no mas de 15um.The generation of oxide nanostructures by imprint lithography (NIL) and electron beam lithography (EBL) has become a more refined technique in the last few years. Through the use of NIL, arrays of La0.7Sr0.3MnO3 (LSMO) nanoholes and nanodots were fabricated here as well as estampado con plasma nanodots and nanowires by EBL were made. Nanoimprint lithography induced nanostructures were written by spin coating a metal oxide precursor onto an insulating single crystal substrate, then stamping with a hard silicon male mold, etching with anisotropic plasma, and finally annealing in an oxygen atmosphere. The precursor had 15 wt% polyvinyl alcohol (PVOH) and a stoichiometric ratio of La, Sr, Mn nitrate or acetate salts so as to form epitaxial despues) when annealed as a thin film on the substrates yttrium stabilized zirconium (YSZ), strontium titanate (STO), and lanthanum aluminate (LAO). The nanoimprinting procedure was to press a mold with 120 nm high features into a 250 nm thick precursor film at a temperature of 160 C for five minutes at 40 bars before demolding at 80 C. This insured that the precursor film was nanoperforated uniformly. The film was then etched with either oxygen or argon to generate negative or positive features respectively. Finally, the film was annealed at 900 °C for four hours to remove any organic components and form crystalline LSMO nanoholes or nanodots. The oxygen plasma anisotropic etching was set at 1200 W for 120 seconds with a gas flow of 200 sccm. This removed the majority of the imprinted precursor and in doing so exposed the floor of the nanoholes to the single crystal substrate. The reason for this was the oxygen atoms chemically reacting with the precursor and thereby removing organic components. This contrasted sharply to when argon was used as the plasma gas in the etcher. The settings used with the argon reactive ion etcher (RIE) were 150 W for 15 minutes at 200 sccm. The argon plasma did not chemically react with the precursor and thus removed the imprinted film mechanically. This revealed a series of nanodot features underneath where the nanohole had been prior to etching. This phenomenon is thought to have sprung from a local density variation in the imprinted film where the part directly underneath the nanohole was compressed and thus able to withstand the bombardment of argon ions more easily than the surrounding film. Through the use of electron beam lithography, arrays of oxide nanostructures were also generated here on insulating single crystal substrates. Specificallydesarrolandola nanodots and nanowires were written by spin coating a metal oxide precursor, then exposing with electrons, developing in water, and finally annealing in an oxygen atmosphere. The precursor had 2 wt% polyvinyl alcohol (PVOH) and a stoichiometric ratio of La, Sr, Mn nitrate or acetate salts so as to form epitaxial La0.7Sr0.3MnO3 (LSMO) when annealed as a thin film on the substrates yttrium stabilized zirconium (YSZ), strontium titanate (STO), and lanthanum aluminate (LAO), similar to the NIL structures. For electron beam lithography, the 200 nm thick precursor film was exposed to electrons at dosages as low 0.1 pC to form nanodots and as high as 1500 pC to form nanowires. The inslating nature of the substrates prevented the use of a high voltage beam thus a 5 kV beam with an average 150 pA current in high vacuum was used. The mechanism behind the formation of nanodots was cross-linking the polymer locally with focused electrons which topically ablated the film. The remaining water soluble film was removed, leaving only the locations which were exposed with electrons. The substrate was then annealed for four hours at 900 C so as to remove any remaining organic components from the nanostructures and form crystals. The resulting nanodots were inspected with transmission electron microscope (TEM) and electron energy loss spectroscopy (EELS) to reveal a single crystal epitaxial lanthanum oxide nanostructures. These nanodots grew with a triangular morphology for dosages ranging from 0.05 pC to 0.15 pC giving and 15 nm to 45 nm heights respectively. Dosages lower than this will not cross-link a sufficient amount of PVOH to be developed and dosages higher than this will not produce single structures. The nanodots may be written with a peak-to-peak distance (pitch) as low as 750 nm and were written to cover 9 mm2 of a substrate with nanodots in twelve hours. To create nanowires, the dosage was increased significantly with a lower limit of 150 pC while the pitch varied between 1000 nm and 250 nm. When the dosage was below the limit, no nanowires were observed to have grown, as well when the pitch was too little or too much. The procedure to grow the nanowires was the same as for the nanodot case, only differing in electron beam parameters. The nanowires were seen to grow away from the region which was irradiated. They were observed with TEM to be epitaxial lanthanum oxide nanowires. The mechanism proposed to explain the growth of nanowires is that the central square irradiated region crystallized from the initial primary electrons and that the feed material was that of adjacent cross-linked precursor from secondary electrons. The height of the nanowires averaged 30 nm and had lengths never in excess of 15 µm.
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Yang, Weibing. "Probing electronic, magnetic and structural heterogeneity in advanced materials and Nanostructures with x-ray imaging, scattering and spectroscopic techniques." Diss., Temple University Libraries, 2018. http://cdm16002.contentdm.oclc.org/cdm/ref/collection/p245801coll10/id/588064.
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PhysicsPh.D.
In this dissertation, we have used a combination of synchrotron-based x-ray spectroscopic, scattering and imaging techniques to investigate the electronic, magnetic and structural properties of materials and material systems which exhibit natural as well as engineered nanoscale structural distortions. In order to investigate the interplay between the above-mentioned degrees of freedom with spatial and depth resolution, we have utilized non-destructive techniques, such as x-ray absorption spectroscopy (XAS), polarization-dependent photoemission electron microscopy (PEEM), nanoscale scanning x-ray diffraction microscopy (nano-SXDM) and standing-wave x-ray photoemission spectroscopy (SW-XPS). The results were compared to several types of state-of-the-art first-principles theoretical calculations. In the first part of the dissertation, we have investigated the nanoscale magneto-elastic structure of the Fe3Ga magnetic alloy, which was recently reported to exhibit non-volume conserving magnetostriction. As the result of our combined PEEM and nano-SXDM study, we have discovered the structural basis for this phenomenon – periodic long-wavelength (~269 nm) elastic domain walls, with domains (regions of zero-strain) existing as narrow transition regions. Atto-scale elastic gradients and self-strain across the elastic domain walls were quantitatively measured and imaged by nano-SXDM. Our measurements revealed that the gradients inside the elastic walls are accommodated by gradually increasing/decreasing inter-planar spacing resembling a longitudinal wave. Our element-specific polarization-dependent PEEM measurements revealed that the magnetic structure of the crystal modulates with similar periodicity (~255 nm), and the resulting magneto-elastic coupling produces a ‘giant’ field-induced bulk deformation, which is equal to the measured self-strain of the elastic domain wall. In the second part of this dissertation, we utilized a combination of soft x-ray standing-wave photoemission spectroscopy (SW-XPS), hard x-ray photoemission spectroscopy (HAXPES) and scanning transmission electron microscopy (STEM) to probe the depth-dependent and single-unit-cell resolved electronic structure of isovalent manganite superlattices (Eu0.7Sr0.3MnO3/La0.7Sr0.3MnO3)15 wherein the electronic and magnetic properties are intentionally modulated with depth via engineered O octahedral rotations and A-site displacements. Standing-wave-excited spectroscopy of the Mn 2p and O 1s core-levels confirmed the isovalent nature of the Mn ions in the superlattice and revealed significant depth-dependent variations in the local chemical and electronic environment around the O atoms, consistent with the state-of-the-art theoretical calculations. Furthermore, it was shown that a surface relaxation and orbital reconstruction in the several top Eu0.7Sr0.3MnO3 atomic layers produces substantial changes in the observed electronic structure, which, according to the first-principles theoretical calculations, occur due to the establishment of orbital stripe order in the top unit cell. In summary, we have used synchrotron-based x-ray spectroscopic and microscopic techniques, in conjunction with high-resolution electron microscopy, to study the electronic, magnetic and structural properties of advanced functional materials exhibiting strong nanoscale heterogeneity. We discovered a strong coupling between the nanoscale structural and magnetic properties in the non-conventional magnetostrictive Fe3Ga single crystal. Our results suggest that this coupling provides the fundamental basis for the non-conventional magnetostriction phenomenon in this material. We have also discovered that the electronic properties of the Eu0.7Sr0.3MnO3/La0.7Sr0.3MnO3 superlattices can be epitaxially tuned via engineered A-site cation displacement, which is a result of the strong interfacial coupling between the Eu0.7Sr0.3MnO3 and La0.7Sr0.3MnO3 layers. This suggests a new way of tailoring and spatially-confining electronic and ferroic behavior in complex oxide heterostructures and creating novel ordered surface-reconstruction effects.
Temple University--Theses
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Hordagoda, Mahesh. "Growth, characterization, and function of ferroelectric, ferromagnetic thin films and their heterostructures." Scholar Commons, 2017. http://scholarcommons.usf.edu/etd/7037.
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With recent trends in miniaturization in the electronics sector, ferroelectrics have gained popularity due to their applications in non-volatile RAM. Taking one step further researchers are now exploring multiferroic devices that overcome the drawbacks of ferroelectric (FE) and ferromagnetic (FM) RAM’s while retaining the advantages of both. The work presented in this dissertation focuses on the growth of FE and FM thin film structures. The primary goals of this work include, (1) optimization of the parameters in the pulsed laser deposition (PLD) of FE and FM films and their heterostructures, (2) development of a structure-property relation that leads to enhancements in electric and magnetic polarizations of these structures, (3) investigation of doping on further enhancement of polarizations and coupling between the FE and FM layers. The materials of choice are La0.7Sr0.3MnO3 (LSMO) as the ferromagnetic and PbZr0.52Ti0.48O3 (PZT) as the ferroelectric component. Epitaxial thin film capacitors were grown using PLD. The work starts with the establishment of the optimum deposition conditions for PZT and goes on to describe results of attempts at performance enhancement and tuning using two methods. It is demonstrated that ferroelectric and ferromagnetic properties can be tuned by inserting a ferromagnetic buffer layer of CoFe2O4 (CFO) between PZT and LSMO. One of the key findings of this work was the anomalously high ferroelectric polarizations produced by lanthanum (La) doped PZT films. This work attempts to shine light on a possible mechanism that leads to such high enhancements in polarization.
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Grobosch, Mandy. "Experimentelle Bestimmung der elektronischen Eigenschaften anwendungsrelevanter Grenzflächen organischer Halbleiter mittels Photoelektronenspektroskopie." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2009. http://nbn-resolving.de/urn:nbn:de:bsz:14-ds-1245078865618-45903.
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Diese Dissertation unter dem Titel Experimentelle Bestimmung der elektronischen Eigenschaften anwendungsrelevanter Grenzflächen organischer Halbleiter mittels Photoelektronenspektroskopie wurde am Leibniz Institut für Festkürper- und Werkstoffforschung (IFW) Dresden am Institut für Festkörperforschung (IFF) unter der Betreuung von Prof. Dr. B. Büchner angefertigt. Zur wissenschaftlichen Untersuchung kamen hierbei zwei Typen anwendungsrelevanter Grenzflächen. Zum einem wurde der Einfluss einer Elektrodenpräparation unter Normalbedingungen mittels ex-situ Reinigungsverfahren im Vergleich zu insitu präparierten Kontakten auf das elektronische Verhalten des organischen Halbleiters Sexithiophen an Grenzflächen zu metallischen Substraten studiert. Als Substratmaterialien kamen hierbei die Metalle Silber, Palladium, Gold und Platin zum Einsatz. In einer zweiten Studie wurden die Grenzflächen der organischen Halbleiter Sexithiophen und Kupfer(II)- Phthalocyanin in Kontakt zu dünnen Filmen des Übergangsmetalloxides La0.7Sr0.3MnO3 untersucht. Auch hier wurde eine vergleichende Untersuchung für ex-situ und in-situ gereinigte La0.7Sr0.3MnO3-Kontakte durchgeführt. Die hierzu verwendeten Filme wurden im IFW Dresden am Institut für Metallische Werkstoffe (IMW) hergestellt. Auch im Rahmen dieser Untersuchungen stand der Einfluss von Sauerstoff auf das elektronische und chemische Verhalten an den Grenzflächen im Vordergrund.
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Esteve, David. "Développement d'une technique de caractérisation optique appliquée au suivi in situ de la croissance d'oxydes fonctionnels par ablation laser pulsé." Paris 11, 2010. http://www.theses.fr/2010PA112385.
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Une instrumentation optique entièrement statique permettant le suivi in situ de la croissance d'oxydes fonctionnels par ablation laser pulsé, est présenté. Au travers de l'étude de deux système modèles, que sont la croissance de films minces de La₀. ₆₇Sr₀. ₃₃LMnO₃ sur des pseudo-substrats de SrTiO₃/Si et de couches minces de SrRuO₃ déposées sur des substrats de SrTiO₃ vicinaux, le dispositif proposé permet d'obtenir une précision de mesure sur les épaisseurs de l'ordre de la maille atomique (4Å), d'extraire les paramètres physiques de diffusion des espèces en surface (énergie d'activation de diffusion), mais aussi d'observer et d'identifier les modes de croissance. Ces résultats sont en parfait accord avec la simulation numérique développée, reposant sur des modèles de traitement de réflectivité de systèmes multi couches combiné avec la théorie des milieux effectifsA fully static set up allowing in situ observation of the growth of functionnal oxides grown by pulsed laser deposition, is presented. Through the study of two model systems, those are the growth of thin films of La₀. ₆₇Sr₀. ₃₃LMnO₃ on pseudo-substrate of SrTiO₃/Si and thin layers of SrRuO₃ grown on vicinal substrate of SrTiO₃, the proposed instrumentation permit to achieve a precision about one unit cell (4Å) on thickness measurments, to extract physical parameters of the diffusion of species on the surface (activation energy of diffusion), but also observing and identifying growth modes. These results are in good agreement with the numerical simulation developped, based on the treatment of the reflectivity of multi-layers systems combined with effective medium theory
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Sheffield, Matthew E. "Developing New Techniques for Investigating Static and Dynamic Magnetic Degrees of Freedom." The Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu153304892098996.
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Ortega, Hernández Rafael. "Resistive memory devices based on complex oxides." Doctoral thesis, Universitat Autònoma de Barcelona, 2015. http://hdl.handle.net/10803/377759.
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Los dispositivos de Memoria Resistiva de Acceso Aleatorio (RRAM) han sido propuestos como posibles candidatos para substituir a las tecnologías actualmente empleadas como dispositivos de memoria no volátil. El origen de esta propuesta se basa en la observación de las extraordinarias propiedades requeridas para el escalamiento de este tipo de dispositivos. En este sentido, una gran variedad de óxidos que exhiben fenómenos de conmutación resistiva se han estudiado últimamente. Sin embargo, la falta de comprensión del mecanismo físico que produce la conmutación resistiva ha limitado principalmente su comercialización. En esta tesis, se exploran las propiedades de conmutación resistiva del óxido complejo La1-xSrxMnO3 y bicapa CeO2-x/La1-x SrxMnO3 para aplicaciones de dispositivos de memoria no volátil. En primer lugar se estudia la técnica de depósito de capas delgadas de La1-xSrxMnO3 y se realizan medidas de caracterización de las propiedades físicas y estructurales con el fin de optimizar al máximo este proceso. Además, se emplean técnicas de microfabricación para obtener dispositivos laterales tipo memristor metal/La1-xSrxMnO3/metal y metal/CeO2-x/La1-x SrxMnO3/CeO2-x/metal en los cuales se evalúa la conmutación resistiva a través de medidas I-V. De acuerdo con los resultados, se propone un mecanismo basado en el intercambio de iones de oxígeno como responsable de la conmutación resistiva de tipo bipolar y complementario inducida en este tipo de dispositivos laterales. Asimismo, basándonos en la conmutación de volumen inducida en dispositivos bicapa metal/CeO2-x/La1-x SrxMnO3/CeO2-x/metal se presenta un dispositivo de tres terminales como parte innovadora de este trabajo. La conducción de corriente a lo largo de la capa de La1-x SrxMnO3 se modula mediante el uso de un electrodo metálico que actúa como terminal de puerta. Como consecuencia de la observación de la conmutación de volumen, se confirma que la capa de CeO2-x actúa como reservorio de oxígeno la cual favorece el intercambio de iones de oxígeno con la capa de La1-xSrxMnO3 y que además modifica las propiedades de conmutación resistiva. También, se demuestra que la conmutación resistiva se produce homogéneamente en el interior de la capa de La1-xSrxMnO3 y que el proceso de electroformado para inducir el cambio de resistencia en los dispositivos bicapa no produce ruptura alguna ni en la capa de CeO2-x ni en la capa de La1-xSrxMnO3. Finalmente, las conclusiones obtenidas de los resultados de este trabajo pueden ser de relevancia para la comprensión de los fenómenos de conmutación resistiva en óxidos complejos.Resistive Random Access Memory (RRAM) devices have been proposed as candidates to replace the actual technologies employed as non-volatile memory devices. The origin of this proposal relies on the observation of the extraordinary properties required for the scaling down of this kind of devices. In this regard, a great variety of oxide materials displaying resistive switching phenomena have been studied lately. However, the lack of understanding of the physical mechanism producing the resistive switching has limited mainly their commercialization. In this thesis, we explore the resistive switching properties of the complex oxide La1-xSrxMnO3 and bilayer CeO2-x/La1-x SrxMnO3 for non-volatile memory applications. First, we study the La1-xSrxMnO3 thin layer deposition technique and perform physical and structural characterization measurements in order to fully optimize this process. In addition, microfabrication techniques are used to obtain the memristor-like metal/La1-xSrxMnO3/metal and metal/CeO2-x/La1-x SrxMnO3/CeO2-x/metal lateral micro-devices where the resistive switching is evaluated through I-V measurements. In line with the results, a mechanism based on the oxygen ion exchange is proposed as responsible of the bipolar and complementary resistive switching induced in this kind of lateral devices. Furthermore, based on volume switching induced in metal/CeO2-x/La1-xSrxMnO3/CeO2-x/metal bilayers, a three-terminal device is presented as innovative part of this work. The current conduction along the La1-xSrxMnO3 layer is modulated by using a metal electrode which acts as a gate terminal. As a consequence of the evaluation of the volume switching, we confirm that the CeO2-x layer acts as an oxygen reservoir favouring the oxygen ion exchange with the La1-xSrxMnO3 layer and modify its resistive switching properties. In addition, we demonstrate that the resistive switching is homogenously produced inside of the La1-xSrxMnO3 layer and that the electroforming process to induce the resistive switching in bilayer devices does not produce any breakdown neither in the CeO2-x nor in the La1-x SrxMnO3 layer. Finally, the conclusions derived from our results can be of relevance for the understanding of the resistive switching phenomena in complex oxides.
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Muppavarapu, Mridula. "mRNA degradation factors as regulators of the gene expression in Saccharomyces cerevisiae." Doctoral thesis, Umeå universitet, Institutionen för molekylärbiologi (Medicinska fakulteten), 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-127358.
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Messenger RNA degradation is crucial for the regulation of eukaryotic gene expression. It not only modulates the basal mRNA levels but also functions as a quality control system, thereby controlling the availability of mRNA for protein synthesis. In Saccharomyces cerevisiae, the first and the rate-limiting step in the process of mRNA degradation is the shortening of the poly(A) tail by deadenylation complex. After the poly(A) tail shortens, mRNA can be degraded either through the major 5' to 3' decapping dependent or the 3' to 5' exosome-mediated degradation pathway. In this thesis, we show some of the means by which mRNA decay factors can modulate gene expression. First, Pat1 is a major cytoplasmic mRNA decay factor that can enter the nucleus and nucleo-cytoplasmically shuttle. Recent evidence suggested several possible nuclear roles for Pat1. We analyzed them and showed that Pat1 might not function in pre-mRNA decay or pre-mRNA splicing, but it is required for normal rRNA processing and transcriptional elongation. We show that the mRNA levels of the genes related to ribosome biogenesis are dysregulated in the strain lacking Pat1, a possible cause of the defective pre-rRNA processing. In conclusion, we theorize that Pat1 might regulate gene expression both at the level of transcription and mRNA decay. Second, Edc3 and Lsm4 are mRNA decapping activators and mRNA decay factors that function in the assembly of RNA granules termed P bodies. Mutations in mRNA degradation factors stabilize mRNA genome-wide or stabilize individual mRNAs. We demonstrated that paradoxically, deletion of Edc3 together with the glutamine/asparagine-rich domain of Lsm4 led to a decrease in mRNA stability. We believe that the decapping activator Edc3 and the glutamine/asparagine-rich domain of Lsm4 functions together, to modify mRNA decay pathway by altering cellular mRNA decay protein abundance or changing the mRNP composition or by regulating P bodies, to enhance mRNA stability. Finally, mRNA decay was recently suggested to occur on translating ribosomes or within P bodies. We showed that mRNA degradation factors associate with large structures in sucrose density gradients and this association is resistant to salt and sensitive to detergent. In flotation assay, mRNA decay factors had buoyancy consistent with membrane association, and this association is independent of stress, translation, P body formation or RNA. We believe that such localization of mRNA degradation to membranes may have important implications in gene expression. In conclusion, this thesis adds to the increasing evidence of the importance of the mRNA degradation factors in the gene expression.
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Bui, Meura Kim Anh. "Réalisation des couches minces PMN-PT dans la technologie MEMS pour les applications hyperfréquences." Phd thesis, Université Paris Sud - Paris XI, 2012. http://tel.archives-ouvertes.fr/tel-00755519.
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Les systèmes d'information actuels reposent fortement sur les technologies micro-ondes utilisées pour les communications hertziennes. L'amélioration des performances des MEMS radio fréquence aptes à fonctionner dans la bande X (8 GHz et 12 GHz) est un enjeu important pour des applications de télécommunications mais aussi pour les applications radar. Pour y parvenir l'intégration de matériaux ferroélectriques à haute constante diélectrique est requise. Les matériaux qui possèdent de telles propriétés et qui sont les plus adaptés, sont les composés qui dérivent de la structure pérovskite. Intégrer ce type de matériaux dans des commutateurs radio-fréquence (MEMS-RF) pose de nouveaux chalenges en termes de maîtrise du matériau et de compatibilité avec les technologies MEMS existantes. Cette thèse s'est portée sur le composé PMN-PT avec la composition 65/35 qui possède une permittivité relative supérieure à 10000 sous forme de matériau massif.Ce travail de thèse a été consacré à l'étude de l'intégration du composé PMN-PT dans des composants passifs que sont les commutateurs MEMS. Dans la gamme de fréquence d'intérêt, de 500 MHz jusqu'à 20 GHz, les propriétés de ces matériaux ont été peu étudiées sur les matériaux massifs et encore moins sous forme de films minces. L'objectif de cette thèse était de réaliser les couches minces ferroélectriques et de tester leur compatibilité dans l'ensemble du fonctionnement d'un composant MEMS mais aussi de mener une étude réciproque : l'analyse des FeMEMS (MEMS basé sur les ferroélectriques) permettant de compléter les connaissances de ces matériaux dans cette gamme de fréquence. Ce travail est d'intérêt pour l'industrie de la technologie MEMS mais aussi pour la science des matériaux ferroélectriques mais aussi par la compréhension des mécanismes physiques gouvernant aux propriétés diélectriques en termes de pertes notamment dans ce domaine de fréquences.Les caractérisations des MEMS-RF présentées dans cette thèse ont démontré la compatibilité du MEMS PMN-PT dans la gamme de fréquence entre 500MHz et 10 GHz avec de très bonnes performances. En utilisant cette adaptation, la technologie actuelle est ainsi capable de couvrir tous les bandes de fréquence les plus importantes : la bande de télécommunication civile de 1 GHz à 5 GHz en utilisant le PMN-PT, la bande X pour les satellites entre 5 GHz et 15 GHz avec PZT et la bande de haute fréquence de 15 GHz à 40 GHz pour la défense avec les diélectriques traditionnels (Si3N4).
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Mukherjee, Devajyoti. "Growth and Characterization of Epitaxial Thin Films and Multiferroic Heterostructures of Ferromagnetic and Ferroelectric Materials." Scholar Commons, 2010. http://scholarcommons.usf.edu/etd/3622.
Full textAbstract:
Multiferroic materials exhibit unique properties such as simultaneous existence of
two or more of coupled ferroic order parameters (ferromagnetism, ferroelectricity,
ferroelasticity or their anti-ferroic counterparts) in a single material. Recent years have
seen a huge research interest in multiferroic materials for their potential application as
high density non-volatile memory devices. However, the scarcity of these materials in
single phase and the weak coupling of their ferroic components have directed the
research towards multiferroic heterostructures. These systems operate by coupling the
magnetic and electric properties of two materials, generally a ferromagnetic material and
a ferroelectric material via strain. In this work, horizontal heterostructures of composite
multiferroic materials were grown and characterized using pulsed laser ablation technique.
Alternate magnetic and ferroelectric layers of cobalt ferrite and lead zirconium titanate,
respectively, were fabricated and the coupling effect was studied by X-ray stress analysis.
It was observed that the interfacial stress played an important role in the coupling effect
between the phases. Doped zinc oxide (ZnO) heterostructures were also studied where
the ferromagnetic phase was a layer of manganese doped ZnO and the ferroelectric phase
was a layer of vanadium doped ZnO. For the first time, a clear evidence of possible room
temperature magneto-elastic coupling was observed in these heterostructures. This work
provides new insight into the stress mediated coupling mechanisms in composite
multiferroics.
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Reijns, Martin. "An analysis of Lsm protein complexes." Thesis, University of Edinburgh, 2006. http://hdl.handle.net/1842/12856.
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Recombinant yeast Lsm proteins were purified from Escherichia coli and tested for their ability to promote annealing of the U4 and U6 snRNAs and to unwind a DNA/RNA duplex resembling the 3’ stem-loop of U6 snRNA. For comparison, Hfq, the Sm-like protein from E. coli, and recombinant human Lsm complexes were used in the same in vitro assays. The results are consistent with their ability to promote RNA/RNA annealing and to modulate RNA secondary structure, which, in vivo, may also allow them to affect RNA/protein interactions. The function of LSM4 was studied by overexpression and depletion of wild-type Lsm4p, and by expression of an Lsm4p C-terminal deletion mutant. Results suggest that Lsm4p affects cell morphology and that its C-terminus promotes efficient recruitment of Lsm1-7p to P-bodies and may promote P-body formation. LSM5 was shown to be dispensable for cell visibility, and its depletion was shown to affect levels of U4, U6 and U4/U6 RNAs similar to effects in Ism6Δ and Ism7Δ strains. The involvement of the different domains of Lsm1p and Lsm8p in localisation of these proteins to the cytoplasm (to P-bodies under stress conditions) and nucleus respectively was investigated by creating (deletion) mutants and hybrids of various domains of these proteins. Results suggest that the N-termini of both proteins play a central role in targeting them to their respective cellular locations. The in vitro studies reveal that the RNA chaperone function of Sm-like proteins appears to have been conserved from bacteria to eukaryotes. Presumably, gene duplication and formation of hetereo-multimeric complexes in higher organisms has allowed functional diversification.
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Bataitis, ANDRIUS. "LSMU MA studentų darbo su kompiuteriu ergonomika ir nusiskundimai sveikata." Master's thesis, Lithuanian Academic Libraries Network (LABT), 2011. http://vddb.laba.lt/obj/LT-eLABa-0001:E.02~2011~D_20110628_155550-82243.
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Darbo tikslas: įvertinti studentų darbo su kompiuteriu ergonomines sąlygas bei nusiskundimus sveikata.
Darbo uždaviniai: nustatyti studentų naudojimosi kompiuteriu stažą, vidutinę darbo su kompiuteriu trukmę ir įvertinti kompiuterinę įrangą; nustatyti, kaip studentai vertina savo darbo su kompiuteriu vietą, išsiaiškinti dažniausias darbo vietos ergonomines problemas; įvertinti studentų sveikatos nusiskundimus dirbant kompiuteriu ir nustatyti ryšį tarp darbo vietos bei laiko praleisto prie kompiuterio ir juntamų sveikatos nusiskundimų; įvertinti studentų subjektyvią sveikatą.
Tyrimo medžiaga ir metodai. Tyrimas buvo atliktas 2011 metais Kauno mieste. Tiriamųjų grupę sudarė Lietuvos sveikatos mokslų universiteto, medicinos, odontologijos bei visuomenės sveikatos fakultetų studentai. Buvo išdalinta 300 anketų, o grąžinta 258 anketos. Tyrimo atsako dažnumas buvo 86 proc. Duomenys buvo kaupiami programoje Excel. Matematinė statistinė analizė atlikta naudojant programą SPSS 18.0, rezultatai laikyti statistiškai reikšmingais kai p<0,05.
Tyrimo Rezultatai: Studentai vidutiniškai naudojasi kompiuteriu 10 metų: apie 11 metų vyrai ir apie 9 metus moterys. Per dieną tiek vyrai, tiek moterys vidutiniškai praleidžia po 3,32 valandas. Apie 82 proc. studentų dirbdami kompiuteriu daro pertraukas, tačiau dirbantys ne ilgiau nei 1 valandą per dieną, pertraukas daro retai. Studentai dažniausiai naudojasi ne senesniais nei 8 metai, 15 colių įstrižainės nešiojamaisiais kompiuteriais. Dažniausios... [toliau žr. visą tekstą]Aim of the study: to evaluate student‘s work with computer ergonomic conditions and health issues. Objectives of the research: to rate student’s computer experience, the average duration of working with the computers and evaluate computer software, determine how students assess their computer work place, to identify the most common workplace ergonomic issues and assess the health problems of students working with the computers and to establish a ratio between the workplace and time spent working with the computer and perceived health complaints. Material and methods. The study was performed in 2011 in Kaunas. The group consisted of the students of Lithuanian University of Health Sciences. 300 questionnaires were distributed and 258 returned. The study response rate was 86 %. Data were collected in Microsoft Excel. Mathematical analysis was performed using the statistical program SPSS 18.0 for windows, the results were statistically significant at p <0.05. Results of the study. Average experience of computer use among students was 10 years: 11 years among men and 9 years among women. Both genders approximately work with computer 3.32 hours per day. About 82 % of the students make intervals during work with computer. Most students use not older than 8 years, 15 inch laptops. The most common computer work station ergonomic problems related with the work chair, reflections on the screen and desktop space and height. 91 % of the students thought that work with computer effects... [to full text]
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Wason, Akshita. "Investigation of lsm proteins as scaffolds in bionanotechnology." Thesis, University of Canterbury. School of Biological Sciences, 2014. http://hdl.handle.net/10092/10065.
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Self-assembling materials have gained attention in the field of nanotechnology due to their potential to be used as building blocks for fabricating complex nanoscale devices. The biological world is abundant with examples of functional self-assembling biomolecules. Proteins are one such example, found in a variety of geometries and shapes. This research is focussed on the use of ring-shaped self-assembling proteins, called Lsm proteins, as componentary for applications in bionanotechnology. Lsm proteins were used because of their spontaneous association into stable rings, tolerance to mutations, and affinity to RNA. This thesis primarily focussed on the thermophilic Lsmα (from Methanobacterium. thermoautotrophicum) that assembles as heptameric rings.
The oligomeric state of the heptameric protein, and hence the diameter of its central cavity, was manipulated by judiciously altering appropriate residues at the subunit interface. Lsmα presented a complex set of interactions at the interface. Out of the mutations introduced, R65P yielded a protein for which SEC and SAXS data were consistent with a hexameric state. Moreover, key residues, L70 and I71, were identified that contribute to the stability of the toroid structure.
Covalent linking of rings provided nanotubular structures. To achieve this, the surface of the Lsmα ring scaffold was modified with Cys residues. This approach led to the formation of novel Lsmα nanotubes approximately 20 nm in length. Importantly, the assembly could be controlled by changing the redox conditions. As an alternative method to manipulate the supramolecular assembly, His6-tags were attached at the termini of the Lsmα sequence. The higher-order organisation of the constructs was influenced by the position of the His6-tag. The N-terminally attached His6-tag version of Lsmα showed a metal-dependent assembly into cage-like structures, approximately 9 nm across. This organisation was highly stable, reproducible, and reversible in nature.
The results presented in this thesis aid the understanding of generating complex nanostructures via in vitro self-assembly. The Lsmα rings were assembled into higher-order architectures at the quaternary level by employing protein engineering strategies. Future work is necessary to functionalise these supramolecular structures; however, this study confirms the potential role of Lsmα proteins as a molecular building block in bionanotechnology.
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Pincelli, T. "PROBING ELECTRON CORRELATION DYNAMICS: A MULTI-TECHNIQUE STUDY APPLIED TO THE HALF-METALLIC OXIDE LA1-XSRXMNO3." Doctoral thesis, Università degli Studi di Milano, 2017. http://hdl.handle.net/2434/543731.
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This thesis completes my work as doctoral student of the Scuola di Dottorato in Fisica, Astrofisica e Fisica Applicata at the Università degli Studi di Milano that has been carried out, starting in November 2014, mostly at the Laboratorio TASC of IOM-CNR in the premises of the Elettra - Sincrotrone Trieste and FERMI@Elettra infrastructures, in the framework of the NFFA and APE-beamline facilites, as well as by accessing international large scale infrastructures and laboratories.
The activity has addressed the development of experimental methodologies and novel instrumentation oriented to the study of the dynamical properties of highly correlated materials after high energy excitation. The science programme has been carried out by exploiting ultrafast femtosecond probes from the optical regime (Ti-Sa lasers, fibre laser oscillators) to the extreme UV-soft X rays at FERMI, to the picosecond hard X-rays from the SPring-8 and Diamond synchrotron radiation source. The sample synthesis of correlated oxides and its characterization has been performed within the NFFA facility and APE-group collaboration in Trieste as well as the design and construction of the all new laser High Harmonic Generation beam line NFFA-SPRINT and its end station for time resolved vectorial electron spin polarimetry.
This report concentrates on the main scientific concern of my work that has been the relaxation of external perturbations in a correlated electron material both in the time and space domain.
I have employed Photoelectron Spectroscopy (PES) mostly in the Hard X-ray regime (HAXPES), pushing the boundaries of its application to achieve a coherent perspective. The material I have mainly focused on is La0.67Sr0.33MnO3 (LSMO), of high interest for spintronics. This system is prototypical, yielding the highest simplicity in the class of transition metal oxides.
In the spatial investigation, I have controlled with high precision the PES probing depth and I have observed the evolution of one spectral feature. I have identified it as probe of electronic hybridization and long-range ordering. I have studied LSMO films of 40 nm in three substrate-induced strain states (1% tensile in-plane, relaxed, 1% compressive in-plane) and a 18 nm film of (Ga,Mn)As (GMA), a well-studied diluted magnetic semiconductor. I have found that the electronic properties to be modified at significant distances from the surface, 4 nm for LSMO and 1.2 nm for GMA, while strain had no detectable effects.
In the temporal study, I have employed HAXPES in pump-probe mode (TR-HAXPES) to observe the evolution of the electronic structure after intense optical excitation. A detailed dynamical characterization with optical techniques has allowed me to identify the characteristic time of the collapse of long-range magnetic order to be significantly longer than the one of elemental transition metals. I have ascribed this effect to the half-metallic character of LSMO. With TR-HAXPES I have observed that the whole electronic band-structure evolution is bottlenecked by the slow response of the magnetization, proceeding on hundreds of picoseconds timescales.
Finally, I have described the techniques and the instrumentation that can be used to push these investigations to shorter spatial and temporal scales. This has been realized in the form of the NFFA-SPRINT laboratory, a facility open to users, which I participated in designing and developing.
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Page, David. "Analysis of the function of the Lsm8 protein complex in Saccharomyces cerevisiae." Thesis, University of Edinburgh, 2002. http://hdl.handle.net/1842/15572.
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To enter the spliceosome, U6 snRNP must associate with the U4 snRNP to form a U4/U6 di-snRNP. This involves RNA-RNA interactions between U4 and U6 RNAs, as the two have extensive sequence complementary and form Watson-Crick base-pair interactions over their length. During splicing, the U4 snRNP dissociates from the U6 snRNP and U6 snRNA undergoes several structural rearrangements. Therefore, U4 and U6 snRNA must be reannealed following spliceosome disassembly in order to recycle the factors back into the splicing pathway. A group of seven proteins, Lsm2-Lsm8p, has previously been identified that interact with U6 snRNA and are essential for U6 snRNA stability and pre-mRNA splicing in the yeast Saccharomyces cerevisiae. In this thesis the Lsm (like-Sm) proteins have been produced either as recombinant protein in E. coli or as the product of a coupled in vitro transcription/translation reaction. Using these proteins it has been demonstrated that the Lsm proteins can facilitate U4/U6 RNA duplex formation. Another U6-ascoiated protein, Prp24p, did not facilitate U4/U6 duplex formation in the absence of the Lsm proteins. This was in contrast to previous reports suggesting a role for Prp24p in U4/U6 annealing. Prp24p is, however, required when the 3’ terminal Lsm binding site is deleted from U6 snRNA. Evidence is presented suggesting that the Lsm8 complex can facilitate U4/U6 duplex formation in vivo as well as in vitro. In particular, Lsm6p appears to be essential for stable U4/U6 duplex formation, whereas Lsm7p does not. The data presented, therefore, suggest a model where the Lsm8 complex, in particular Lsm6p, is sufficient and necessary for U4/U6 duplex formation. Other factors such as Prp24p may facilitate this process, but are not essential for it to occur.
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Dhallu, Manjit. "Oxygen transport in mixed conducting LSM-YSZ composite materials." Thesis, Imperial College London, 2006. http://hdl.handle.net/10044/1/11340.
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Milius, Justinas. "Pašarų bazės ir karvių produktyvumo analizė LSMU VA Praktinio mokymo ir bandymų centre." Master's thesis, Lithuanian Academic Libraries Network (LABT), 2013. http://vddb.laba.lt/obj/LT-eLABa-0001:E.02~2013~D_20130618_095629-21676.
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Darbo tikslas: išanalizuoti LSMU VA Praktinio mokymo ir bandymų centro pašarų, naudojamų melžiamų karvių šėrime, kiekybinius ir kokybinius rodiklius bei racionus ir karvių produktyvumą.
Darbo uždaviniai: 1. Nustatyti kiek ir kokių pašarų sukaupta ūkyje melžiamų karvių šėrimui per pastaruosius 2 metus. 2. Išanalizuoti ūkio melžiamų karvių šėrimą ganykliniu ir tvartiniu laikotarpiais. 3. Išanalizuoti karvių produktyvumo ir pieno kokybinius rodiklius.
Atlikus analizę buvo nustatyta, kad tirtame ūkyje daugiausiai laikoma Vokietijos juodmargių veislės (~50 proc.) ir Lietuvos juodmargių (~30 proc.) karvių. Daugiausiai bandoje buvo 1 – 3 laktacijų karvių (78,6 - 83,5 proc. visos bandos karvių). Vidutinis karvių produktyvumas 6835 kg pieno 4,23 proc. riebumo, 3,3 proc. baltymingumo; vidutinis somatinių ląstelių skaičius - 287 tūkst./ml. Atlikus melžiamų karvių šėrimui pašarų bazės analizę nustatėme, kad ūkis daugiausiai sukaupė vienmečių žolių siloso (873,9 t). Pašarų kokybės parametrų analizė parodė, kad siloso kokybės parametrų fermentacijos rodiklis kokybė ir stabilumas yra geri. Tyrimų metu išanalizuoti karvių racionai pagal mitybinius rodiklius tiek tvartiniu, tiek ganykliniu laikotarpiu buvo praktiškai panašūs ir orientuoti į 21 l pieno primilžį.
Išvados: 1. Tirtame ūkyje melžiamų karvių skaičius padidėjo nuo 145 vnt. 2011m. iki 199 vnt. 2012 m. Bandos analizė pagal karvių veisles parodė, kad daugiausiai laikomų karvių yra Vokietijos juodmargių veislės (apie puse bandos... [toliau žr. visą tekstą]Aim of paperwork: To analize the feed, used for feeding dairy cows at the LUHS VA Practical training and testing centre and to analyze their quantative and qualitative indicators, rations and productivity of cows. The goals: 1. Determine the amount and type of feed accumulated in the farm for dairy cows feeding in the last 2 years. 2. To analyze the feeding of dairy cows on pasture and indoor feeding periods. 3. To analyze the productivity of cows and milk quality indicators. The analysis showed that the studied farm mainly considered German Black & White (~50 per cent.), and the Lithuanian Black and White (~ 30 percent) cows. Most herds were 1 -3 lactation cows (78.6 to 83.5 percent. entire herd of cows). Average productivity of 6835 kg of cow, milk fat - 4.23 percent., mikk protein - 3.3 per cent. The average somatic cell count - 287 thous./ml. Dairy cows feed database analysis found that the farm mainly accumulated perennial grass silage (873.9 t). Feed quality parameters showed that quality parameters of silage fermentation rate quality and stability is good. Studies to analyze the rations by nutritional indicators both indoor and outdoor period was practically similar and focus on the 21 l milk yield.
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Salgado, Ananay Aguilar. "Recording classical music : LSO live and the transforming record industry." Thesis, Royal Holloway, University of London, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.586610.
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My doctoral research explores the values of classical music through its recording practices. I define recording practices broadly, including-but not limiting them to- engineers' recording techniques, current marketing strategies and the management of rights. The recent transformations of the record industry, with the shift from physical discs to digital downloads, the reduction in production and distribution costs, and the subsequent change in consumption patterns and accompanying legislation, provide an exceptionally rich arena for this discussion. The ongoing success of the London Symphony Orchestra's young label, LSO Live, is a case in point as it highlights the many features that intervene in music-making and reception, shaping the practices and perception of music in unpredictable ways. Based on fieldwork with the LSO, I trace the spaces where the values of classical music are negotiated on a daily basis. The time is the 2007/2008 season, when the orchestra, conducted by Valery Gergiev, performed and recorded all Mahler symphonies. The creation of LSO Live is explored through observation of and interviews with members of staff, musicians and recordists, who explained their experiences of setting up the label and its impact on their respective professional practices. The accounts bring into the picture their idea of classical music with considerations ranging from performance and listening practices, recording technologies, marketing strategies and current developments in copyright law. Further, I join debates on the artwork concept reflecting upon its role in mediating, sanctioning and perpetuating the values of classical music in its recorded form. Finally, I address musicology's traditional conceptualisation of music and, in particular, its slow engagement with the record industry's developments affecting the production of classical music. In so doing, I discuss the potential of this type of trans-disciplinary study to impact on the reconfiguration of the broader field of music studies and the record industry more widely.
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Rodrigues, Ranieri Andrade. "Estudo da formação de fases secundárias no compósito LSM/YSZ." Universidade de São Paulo, 2007. http://www.teses.usp.br/teses/disponiveis/85/85134/tde-19062008-110417/.
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O compósito de manganito de lantânio dopado com estrôncio (La1-xSrxMnO3 - LSM) e zircônia estabilizada com ítria (ZrO2/Y2O3 - YSZ), tem sido indicado como catodo das células a combustível de óxido sólido, por apresentar melhor desempenho como eletrodo catódico na região da tripla fase reacional (TRIPLE PHASE BOUNDARY - TPB), formada na interface entre eletrólito e eletrodo. Para as temperaturas superiores a 1100 °C, o LSM e o YSZ podem-se reagir formando-se zirconatos de lantânio (La2Zr2O7 - LZO) e zirconatos de estrôncio (SrZrO3 - SZO). Neste sentido, o presente trabalho pretende contribuir no estudo da formação das fases LZO e SZO, estudando diferentes proporções mássicas entre LSM e YSZ e temperaturas de sinterização variando-se entre 1000 °C e 1400 °C. Para obtenção dos pós precursores foram adotadas as rotas de co-precitação para a obtenção do YSZ e mistura convencional de pós para preparação de LSM. Para a preparação do compósito LSM/YSZ, as composições químicas do LSM sintetizado neste trabalho foram para as duas concentrações 30 e 40 % mol de Sr (LSM7 e LSM6) e para YSZ 10 % mol de ítria. Os resultados obtidos por fluorescência de raios X mostraram que as rotas adotadas para síntese de pós foram eficazes na obtenção das composições LSM6, LSM7 e YSZ, com valores próximos aos estequiométricos. As proporções mássicas estudadas foram: 50 % de LSM e 50 % de YSZ (1:1), 25 % de LSM e 75 % de YSZ (1:3) e 75 % de LSM e 25 % de YSZ (3:1). Tais proporções de misturas foram conformadas e submetidas a diferentes condições de temperaturas e tempos de sinterização: 1000 °C, 1200 °C, 1300 °C, 1350 °C e 1400 °C, por 4 e 8 horas. Tanto os valores de tamanho médio das partículas como os valores da área de superfície específica para a mistura de LSM6/YSZ e LSM7/YSZ, após a mistura em um moinho atritor e em diferentes proporções mássicas, são da mesma ordem de grandeza. Na análise por difração de raios X dos compósitos LSM6/YSZ e LSM7/YSZ preparados na proporção 1:1 submetidos às temperaturas a 1200 ºC e a 1400 ºC por 4 horas, verificou-se que não há formação de fases secundárias tais como LZO e SZO. Para estas amostras sinterizadas nestas duas temperaturas, o valor da porosidade obtida é maior para a amostra sinterizada a 1200 ºC. Para as amostras LSM6/YSZ e LSM7/YSZ, com proporções mássicas de 1:3, 1:1 e 3:1, sinterizadas a 1300 °C e 1350 °C, por 8 horas, observou-se o aparecimento de fases de LZO e SZO. Verificou-se também que as intensidades destas fases são maiores para proporção mássica de 3:1, ou seja, para amostras contendo 75 % em massa de LSM no compósito. Para preparação de filmes finos do compósito LSM/YSZ para células a combustível do tipo SOFC, de acordo com as condições adotadas neste trabalho, a temperatura de sinterização adequada é de 1200 °C por tempo abaixo ou igual a 8 horas, sendo que, em tais condições não há formação de fases secundárias como LZO e SZO.The composite of strontium-doped lanthanum manganite (La1-xSrxMnO3 - LSM) and yttria-stabilized zirconia (ZrO2/Y2O3 - YSZ), is indicated as cathode of the Solid Oxide Fuel Cells (SOFC). It presents better acting as cathode due to the Triple Phase Boundary (TPB) formed in the interface area between the cathode and the electrolyte. For the temperatures up to 1100 °C, LSM and YSZ can react producing lanthanum zirconate (La2Zr2O7 - LZO) and strontium zirconate (SrZrO3 - SZO). In this sense, the present work intends to contribute in the study of the formation of phases LZO and SZO, studying different massic proportions between LSM and YSZ with sintering temperatures varying between 1000 °C and 1400 °C. For the obtention of the precursory powders the co-precipitation routes were adopted to obtain YSZ and conventional powder mixture for the preparation of LSM. The composite LSM/YSZ, studied in this work, is prepared with two concentrations of Sr for LSM (30 mol % - LSM7 and 40 mol % - LSM6) and one concentration of yttria for YSZ (10 mol %). The results obtained by X-ray fluorescence showed that the routes adopted for synthesis of powders were effective in the obtention of the compositions LSM6, LSM7 and YSZ, with close values to the stoichiometrics. The studied massic proportions were: 50 % of LSM and 50 % of YSZ (1:1), 25 % of LSM and 75 % of YSZ (1:3), and 75 % of LSM and 25 % of YSZ (3:1). Such proportions of mixtures were conformed and submitted at different conditions of temperatures and times of sintering: 1000 °C, 1200 °C, 1300 °C, 1350 °C and 1400 °C for 4 and 8 hours. The values of medium size of the particles and the specific surface area values for the mixture of LSM6/YSZ and LSM7/YSZ, are of the same order of largeness after the mixture in a attritor mill and in different massic proportions. Secondary phases like LZO and SZO weren\'t found in the analysis for X-ray diffraction of the composites LSM6/YSZ and LSM7/YSZ prepared in the proportion 1:1 submitted to the temperatures to 1200 ºC and 1400 ºC for 4 hours. For these sintered samples in these two temperatures, the value of the obtained porosity is larger for the sintered sample at 1200 ºC. For the samples LSM6/YSZ and LSM7/YSZ, with massic proportions of 1:3, 1:1 and 3:1, sintered to 1300 °C and 1350 °C for 8 hours, it was observed the emergence of phases of LZO and SZO. It was also verified that the intensities of these phases are larger for the massic proportion of 3:1, in other words, for samples containing 75 % in mass of LSM in the composite. For the preparation of thin films of the composite LSM/YSZ for SOFC, in agreement with the conditions adopted in this work, the appropriate sintering temperature is 1200 °C for 8 hours or less, conditions where there isn\'t the formation of secondary phases like LZO and SZO.
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RODRIGUES, RANIERI A. "Estudo da formação de fases secundárias no compósito LSM/YSZ." reponame:Repositório Institucional do IPEN, 2007. http://repositorio.ipen.br:8080/xmlui/handle/123456789/11563.
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Dissertação (Mestrado)
IPEN/D
Instituto de Pesquisas Energéticas e Nucleares - IPEN-CNEN/SP
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Luhtala, Natalie. "LSM1 AND RNY1: CLUES IN THE SEARCH FOR HOW RNA METABOLIC PATHWAYS CONTROL CANCER." Diss., The University of Arizona, 2011. http://hdl.handle.net/10150/204114.
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Carcinogenesis requires numerous alterations to gene expression to evade normal controls on cellular growth, invasion, and immortality. Traditionally, these changes have been examined in the context of deregulated transcriptional control of oncogenes and tumor suppressors. However, in recent years, research has revealed that processes outside of transcription such as RNA splicing, translation, and decay are also deregulated in cancers, sustaining tumorigenic potential. This dissertation details our investigation into the cellular functions of two RNA metabolic proteins whose human orthologs are deregulated in tumors: a putative oncogene, Lsm1, and a putative tumor suppressor, Rny1. Herein, we reveal interesting functions for these proteins that might provide insight into their roles in carcinogenesis. First, we demonstrate a role for Lsm1 over-expression in altered splicing through depletion of U6 snRNA levels. Second, we clarify the mechanism for Rny1's activity against RNA substrates and identify cis regions required for its non-catalytic role in growth inhibition. Overall, this knowledge expands our understanding of how RNA metabolism might be deregulated in cancer and could provide novel pathways to target for synthetic lethal responses in cancers with altered expression of these proteins.
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Hänni, Sandra Silvia. "Generation and characterization of monospecific antibodies against Sm- and LSm-Proteins." Zürich : ETH, Eidgenössische Technische Hochschule Zürich, Departement Angewandte Biowissenschaften, Institut für Pharmazeutische Wissenschaften, 2002. http://e-collection.ethbib.ethz.ch/show?type=dipl&nr=75.
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Anstensrud, Ole-Petter Bård. "Pricing a Bermudan Swaption using the LIBOR Market Model : A LSM approach." Thesis, Norwegian University of Science and Technology, Department of Mathematical Sciences, 2008. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-9787.
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This study will focus on the pricing of interest rate derivatives within the framework of the LIBOR Market Model. First we introduce the mathematical and financial foundations behind the basic theory. Then we give a rather rigouros introduction to the LIBOR Market Model and show how to calibrate the model to a real data set. We use the model to price a basic swaption contract before we choose to concentrate on a more exotic Bermudan swaption. We use the Least Squares Monte Carlo (LSM) algorithm to handle the early exercise features of the Bermuda swaption. All major results are vizualised and the C++ implementation code is enclosed in appendix B.
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Kumar, Sanjay M. "Tenure in transition : case of the LSM Cooperative Housing Estate, Lublin, Poland." Thesis, Massachusetts Institute of Technology, 1992. http://hdl.handle.net/1721.1/68263.
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Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Architecture, 1992.Includes bibliographical references (p. 98-101).
This thesis explores various tenure models as a means to understand development in transition. The emergence of new markets, aspirations, needs and varied agendas of the actors in the LSM Cooperative Housing Estate in Lublin, Poland, has resulted in conflicts in tenure claims to land and building. The tenure options that evolve from these conflicts are in effect choices that open up for the community. This thesis recognizes the fact that there are other development models apart from the Western free market model that have their advantages and disadvantages in given situations. Development models that have been used in other countries are considered end-state scenarios, which become a means to explore tenure options. The end-state scenarios could range from individual rights (private freehold) to communal tenure holding. Here the argument is that, in-between these end-state scenarios exists a range of development options that can be used in the transition stage. The end-state scenarios discussed are: the Western market model, Cooperative land banks, Sweden's leasehold of land and rental housing system, Britain's council housing, US housing cooperatives, and Hong Kong's land management system. Tradeoffs between scenarios are evaluated by fIltering each scenario through six criteria: efficiency, equity, subsidy, management and community participation, mobility, and difficulty in transition. The implications of each scenario on the LSM Housing Cooperative are studied under three site specific issues: development of neighborhoods, development of the Zana street commercial area and development of vacant land in the estate. An evaluation of end-state scenarios against the various criteria, indicates that given the transition process, there is no single model that can be applied uniformly. The housing neighborhoods, Zana street and vacant land would benefit most if developed with different models. Scenarios that appear more workable than the others are: the Western market model, Cooperative land bank, Hong Kong's land management system and the US housing cooperative. Transference of models does not ensure their success in LSM. Simplicity and clarity of the models is critical to the transition period and the identified models need to be modified to adapt to local conditions. The LSM case study exemplifies housing estates in Poland and other countries undergoing transition in Eastern Europe. This thesis does not attempt to recommend a conclusive tenure system, but gives a methodology that would help identify a tenure system.
by Sanjay M. Kumar.
M.S.
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Espejel, Cabrera Josué. "Desarrollo de algoritmos para traductor automático de lenguaje de señas mexicanas (LSM)." Tesis de doctorado, Universidad Autónoma del Estado de México, 2021. http://hdl.handle.net/20.500.11799/111836.
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En años recientes, el desarrollo de algoritmos que asistan en la comunicación con gente sorda es un reto importante. El desarrollo de sistemas automatizados para traducir el lenguaje de señas es un tema de investigación vigente. Sin embargo, esto involucra varios procesos que van desde la captura del video, pre-procesamiento hasta la identificación y clasificación de las señas. El desarrollo de sistemas capaces de extraer características discriminativas para acentuar la capacidad de generalización de un clasificador es aun un problema muy complejo. El significado de una seña es a combinación del movimiento de la mano, forma de la mano y el punto de contacto de la mano con el cuerpo. Este trabajo presenta un método para detectar y traducir señas de las manos. Primero, se obtienen 15 cuadros por palabra, obteniendo 3 regiones de interés (manos y cara) de las cuales se obtienen características geométricas. Finalmente, se emplean diferentes clasificadores y se muestran los resultados experimentales.
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Deng, Chenxin. "Operating Stresses and their Effects on Degradation of LSM-Based SOFC Cathodes." Case Western Reserve University School of Graduate Studies / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=case1625694112996196.
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Galão, Rui Pedro Ribeiro. "Role of the cellular decapping activator LSM1-7 complex in the replication of positive-strand RNA viruses." Doctoral thesis, Universitat Pompeu Fabra, 2010. http://hdl.handle.net/10803/7222.
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By using the ability of the positive-strand RNA ((+)RNA) virus BMV to replicate in yeast it was previously shown that subunits of the LSm1-7 ring, as well as Pat1 and Dhh1 play an essential role in the transit of the BMV genome from translation to replication. In non-infected cells, these proteins mediate the transition of cellular mRNAs from a translational to a non-translational state by activating decapping in the 5'-3' - deadenylation-dependent mRNA decay pathway. Given the conservation of this pathway from yeast to humans and the common need of all (+)RNA viruses to regulate the transition of their genomes from active translation to a translationally inactive state to allow replication, an exciting possibility, and our working hypothesis, was that LSm1-7, Dhh1 and Pat1 are used not only by BMV to replicate in yeast but also by human (+) RNA viruses, such as HCV, to replicate in mammalian cells. Furthermore, given the key role of these proteins in a common step to all (+)RNA viruses, it is essential to characterize the not yet defined molecular mechanisms associated with such function. In this regard, we also hypothesized that the LSm1-7 complex, as member of the Sm family of proteins, would directly interact with viral genomes of (+)RNA viruses in order to play their role in the virus life cycle in a similar way that other family counterparts directly interact with their RNA targets in order to achieve their different cellular functions. In this work we were able to confirm both hypothesis showing that human homologues of the upper mentioned proteins LSm1-7, Rck/p54 and PatL1, are required for HCV RNA translation and replication. Additionally, we also showed that reconstituted LSm1-7 complexes specifically recognize important signals, either in BMV or HCV genomes, that regulate their translation and/or replication. These observations constitute the first evidence that the LSm1-7 complex is able to directly interact with viral genomes representing also novel LSm1-7 interaction sites. Given the common replication strategies of (+)RNA viruses and the conserved cellular functions of LSm1-7, Pat1 and Dhh1 from yeast to humans, our findings pinpoint a weak spot that may be exploited to generate broad-spectrum antiviral drugs.Utilizando la capacidad del BMV, un virus de ARN de cadena positiva (ARN(+)), para replicar en levaduras se ha demostrado previamente que las subunidades del anillo LSm1-7, así como Pat1 y Dhh1, desempeñan un papel esencial en la transición del genoma del virus de BMV desde traducción a replicación. En células no infectadas, estas proteínas median la transición de ARNm celulares de la traducción a un estado de no-traducción mediante la activación del proceso de decapping en la via 5'-3' de degradación de los ARNs celulares dependiente de deadenilación. Teniendo en cuenta la conservación de esta vía desde levaduras a humanos y la necesidad común de todos los virus ARN(+) para regular la transición de sus genomas desde un estado activo de traducción a otro no activo para permitir la replicación, una posibilidad interesante, y nuestra hipótesis de trabajo, es que LSm1-7, Dhh1 y Pat1 son utilizadas no solo por BMV para replicar en levaduras, sino también por otros virus ARN(+) que infectan a humanos, como el virus de la hepatitis C, para replicar en células de mamíferos. Por otra parte, dado el papel clave de estas proteínas en un paso común en todos los virus de ARN(+), es esencial caracterizar los mecanismos moleculares aun no conocidos y asociados a dicha función. En este sentido, también estudiamos la hipótesis de que el complejo LSm1-7, como miembro de la familia de proteínas Sm, pueda interactuar directamente con los genomas virales de virus de ARN(+) con el fin de desempeñar su papel en el ciclo de vida del virus de una manera similar a la que otros miembros de su familia interactúan con sus ARN con el fin de lograr sus diferentes funciones celulares. En este trabajo hemos podido confirmar ambas hipótesis demostrando que los homólogos humanos de las proteínas anteriormente mencionadas, LSm1-7, Rck/p54 y PatL1, son necesarios para la traducción y replicación del ARN del virus de la Hepatitis C. Por otra parte, los anillos reconstituidos de LSm1-7 reconocen específicamente señales importantes, tanto en el genoma de BMV como en el de la Hepatitis C que regulan su traducción y/o replicación. Estas observaciones constituyen la primera evidencia de que el complejo LSm1-7 es capaz de interactuar directamente con genomas virales y representan también novedosos patrones de interacción de este complejo con ARN. Teniendo en cuenta las estrategias de replicación en común de los virus de ARN de cadena positiva y las funciones celulares conservadas de LSm1-7, Pat1 y Dhh1 de levaduras a humanos, nuestros resultados señalan la posibilidad de explotar estas proteínas para la generación de medicamentos antivirales de amplio espectro.
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Jeridi, Aicha [Verfasser], and Vigo [Akademischer Betreuer] Heissmeyer. "Functional analysis of the mRNA decay factor Lsm1 in the immune system / Aicha Jeridi ; Betreuer: Vigo Heissmeyer." München : Universitätsbibliothek der Ludwig-Maximilians-Universität, 2018. http://d-nb.info/1202011322/34.
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Daume, Michael [Verfasser], and Lennart [Akademischer Betreuer] Randau. "L7Ae- and LSm-RNA interactomes of Sulfolobus acidocaldarius / Michael Daume ; Betreuer: Lennart Randau." Marburg : Philipps-Universität Marburg, 2018. http://d-nb.info/1173322450/34.
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Walker, Matthew David. "Quantitative dynamic 3D PET scanning of the body and brain using LSO tomographs." Thesis, University of Manchester, 2009. http://www.manchester.ac.uk/escholar/uk-ac-man-scw:78135.
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Danielsson, Johan, and Gustav Gistvik. "Estimation, model selection and evaluation of regression functions in a Least-squares Monte-Carlo framework." Thesis, Linköpings universitet, Produktionsekonomi, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-110927.
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This master thesis will investigate one solution to the problem issues with nested stochastic simulation arising when the future value of a portfolio need to be calculated. The solution investigated is the Least-squares Monte-Carlo method, where regression is used to obtain a proxy function for the given portfolio value. We will further investigate how to generate an optimal regression function that minimizes the number of terms in the regression function and reduces the risk of overtting the regression.
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Jungfleisch, Jennifer 1986. "Unraveling novel roles of the cellular decapping activators Lsm1-7 and Dhh1 in translation control through viral studies." Doctoral thesis, Universitat Pompeu Fabra, 2015. http://hdl.handle.net/10803/288313.
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Translation control is a vital aspect of gene expression for both viruses and their cellular hosts. We have previously shown that the cellular mRNA decay activators Dhh1 and Lsm1-7 promote translation of positive-strand RNA [(+)RNA] viral genomes and their subsequent transport from the cellular translation machinery to replication complexes, a process that requires translation repression. These key steps in the replication of all (+)RNA viruses require profound rearrangements of the viral ribonucleoprotein (RNP) composition. How cellular decapping activators promote translation and replication of viral genomes remains unknown. Using the replication of the Brome mosaic virus in yeast, a fruitful model system for (+)RNA viral replication, we show that Dhh1 and Lsm1-7 function differentially in viral RNA translation and replication by assembling alternative mRNP complexes. The dependence on Dhh1 for viral RNA translation initiation is mediated by specific cis-acting sequences in the viral UTRs and a stem-loop in the ORF. Excitingly, by ribosome profiling analyses we identify a specific subset of cellular mRNAs that also depends on Dhh1 for translation. These mRNAs have as (+)RNA genomes long 5´UTR and highly structured 5´UTRs and ORFs. Moreover, they are enriched in mRNAs related to ribosome biogenesis. Interestingly, ribosome biogenesis is often altered in cancer cells and we and others determine that DDX6, the human ortholog of Dhh1, is indeed overexpressed in pancreatic and colon cancer.
In conclusion, our results demonstrate that components of the cellular decapping machinery have a broad function in translational regulation. This enables fast fine-tuning of gene expression in response to perturbations.El control de la traducción es un aspecto vital de la expresión génica tanto para los virus como para sus huéspedes celulares. Nuestro laboratorio ha demostrado que los activadores de la degradación del ARN mensajero celular, Dhh1 y Lsm1-7, promueven la traducción de los genomas de virus de ARN de cadena sencilla y polaridad positiva [(+)ARN] así como su transporte desde la maquinaria de traducción celular a los complejos de replicación, un proceso que necesita represión de la traducción. Estos pasos clave en la replicación de todos los virus (+)ARN requieren de una profunda reorganización en la composición de la ribonucleoproteina (RNP) viral. Cómo los activadores del decapping celular promueven la traducción y replicación de los genomas virales aún es desconocido. Utilizando la replicación del virus del mosaico del Bromus en levadura, un modelo muy usado para el estudio de la replicación de virus (+)ARN, hemos demostrado que Dhh1 y Lsm1-7 funcionan de manera distinta en la traducción y replicación del ARN viral mediante el ensamblaje de complejos alternativos de RNP. La dependencia de Dhh1 para la iniciación de la traducción del ARN viral está mediada por secuencias específicas cis-acting localizadas en las regiones no traducidas (RNTs) del virus y un stem-loop en el marco de lectura. Sorprendentemente, mediante el uso del ribosome profiling hemos identificado un grupo específico de ARN mensajeros celulares que también dependen de Dhh1 para su traducción. Estos ARN mensajeros tienen, como los genomas de los virus (+)ARN, 5’RNT largos y altamente estructurados, así como marcos de lectura altamente estructurados. Además, entre ellos abundan los ARN mensajeros relacionados con biogénesis ribosomal. Es interesante mencionar que la biogénesis ribosomal está normalmente alterada en células cancerosas y nosotros, y otros grupos, hemos determinado que DDX6, el ortólogo en humanos de Dhh1, está sobreexpresado en cáncer pancreático y de colon. En conclusión, nuestros resultados demuestran que componentes de la maquinaria de decapping celular tienen una amplia función en la regulación de la traducción. Este hecho permite un rápido y preciso ajuste de la expresión génica en respuesta a perturbaciones.
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Mosset, Jean-Baptiste. "Développement d'un module de détection phoswich LSO/LuYAP pour le prototype de caméra à positrons ClearPET /." [S.l.] : [s.n.], 2006. http://library.epfl.ch/theses/?nr=3596.
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Goncalves, Juliana Bittencourt. "Calibração do modelo de superfície noah lsm: aplicação em uma região agrícola no sul do Brasil." Universidade Federal de Santa Maria, 2016. http://repositorio.ufsm.br/handle/1/3934.
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Conselho Nacional de Desenvolvimento Científico e TecnológicoIn this study, simulated to net radiation and energy flux in a region with rotation of crops, for two distinct periods: Period 1 (01 / Feb / 2009 to 31 / Jan / 2010) and period 2 (14 / Dec / 2009 to 28 / Apr / 2010). In these simulations we used the NOAH LSM surface model. For the period 1 initially, without any calibration simulations were performed only with the input of the local weather conditions, an adjustment of an experiment controlfile file and spin up for the stabilization of the initial conditions. In these simulations, the results were very poor, indicating a need to test the sensitivity of the model especially because of the launch conditions of temperature and soil moisture. After these tests it was found that the initial predictions of impact can be considerable conditions for the two cases. It is noticed that the soil moisture changes generate greater impact in the model that temperature variations boot. As a result, proposed a calibration for the model. The calibration method was to make some simulations manually varying the parameters of soil and vegetation, or both, according to the deficiencies of the NOAH LSM. The tests were carried out until they could get a more optimized forecast for the period studied. The initial analysis of the local conditions of the experimental site was very important for calibration, as it allowed establishing previous parameters corresponding to values close to those parameters when calibrated. Simulation results after calibration applied satisfactorily exhibited liquid radiation and heat flows. So it can be said that the calibration is proposed representing characteristics of vegetation and soil correctly. Nevertheless, the corrections that the model still needs, especially in sensible and latent heat fluxes, may be associated with representation in heat distribution processes and water, or by the fact that the colder months had considerable regime rains. So when there is cloud cover, the model still has problems in representation. Results for long periods of data, as in this work, may lose some of representativeness due to the seasonality of the vegetation parameters, for which varied the parameters for periods culture and fallow. The most important contribution made in this work was a model fit for an agricultural ecosystem area and validate it for the future, it may be used as an initial boundary condition in numerical weather prediction models. The implementation variations in LAI and albedo parameter applied in the simulations of period 2 (soybean) improved the description of the heat flux and net radiation.
Neste estudo simulou-se a radiação líquida e os fluxos de energia para uma região com rotações de cultivos agrícolas, para dois períodos distintos: Período 1 (01/Fev/2009 até 31/Jan/2010) e período 2 (14/Dez/2009 até 28/Abr/2010). Nestas simulações utilizou-se o modelo de superfície NOAH LSM. Inicialmente, para o período 1, foram feitas simulações sem nenhuma calibração, apenas com a entrada das condições meteorológicas locais, um ajuste do arquivo controlfile e um experimento spin up para a estabilização das condições iniciais. Nestas simulações, os resultados foram muito insatisfatórios, indicando uma necessidade de testar a sensibilidade do modelo principalmente frente às condições de inicialização da temperatura e da umidade do solo. Após estes testes verificou-se que impactos das previsões às condições iniciais podem ser consideráveis para os dois casos. Percebe-se que as variações de umidade do solo geram maior impacto no modelo devido à temperatura do solo que é simulada. Na sequência, propôs-se uma calibração para o modelo. O método de calibração consistiu em fazer algumas simulações variando-se manualmente os parâmetros de solo e vegetação, ou ambos, de acordo com as deficiências do NOAH LSM. Assim, os testes foram realizados até que se conseguisse uma previsão mais otimizada para o período estudado. A análise inicial das condições locais do sítio experimental foi de suma importância para a calibração, pois ela possibilitou estabelecer parâmetros prévios que correspondem a valores próximos dos parâmetros quando calibrados. Os resultados das simulações, após a calibração aplicada, representaram satisfatoriamente a radiação líquida e os fluxos de calor. Portanto, pode-se dizer que a calibração proposta está representando as características de vegetação e de solo de forma correta. Apesar disso, as correções que o modelo ainda necessita, principalmente nos fluxos de calor sensível e latente, podem estar associadas a representação nos processos de distribuição do calor e da água, ou ainda pelo fato de que os meses mais frios tiveram um considerável regime de chuvas. Assim, quando há nebulosidade, o modelo ainda apresenta problemas na representação. Os resultados para períodos longos de dados, os quais foram considerados neste trabalho podem perder um pouco da representatividade em função da sazonalidade dos parâmetros de vegetação, motivo pelo qual variou-se os parâmetros para períodos com cultura e com pousios. A contribuição mais importante realizada neste trabalho foi um ajuste do modelo para uma região de ecossistema agrícola e a sua validação para que futuramente, possa ser utilizado como condição de contorno inicial em modelos de previsão numérica do Tempo. A implementação das variações diárias no parâmetro IAF e no albedo, aplicada nas simulações do período 2 na cultura de soja, melhorou a descrição dos fluxos de calor e da radiação líquida.
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Yan, Miaolei. "Defect Analysis and Microstructural Effects on the Surface Exchange Properties of La0.7Sr0.3MnO3(LSM) Epitaxial Thin Films." Research Showcase @ CMU, 2015. http://repository.cmu.edu/dissertations/650.
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La0.7Sr0.3MnO3 (LSM) is a perovskite oxide material that possesses many interesting electromagnetic and electrochemical properties, making it desirable as magnetic tunnel junction (MTJ) and solid oxide fuel cell (SOFC) electrodes.
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Uher, Martin. "Oceňování swing opcí na trzích elektrické energie." Master's thesis, Vysoká škola ekonomická v Praze, 2013. http://www.nusl.cz/ntk/nusl-199521.
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Swing options had been part of natural gas market before its embedded option feature was appreciated. The flexibility of delivery is valuable because of characteristic features of energy commodities as non-storability, high frequency of events and seasonality. Swing options enable this flexibility. Holder of the option is allowed to react to market situation in flexible way and change the amount of delivery up or down in some known intervals. Total deviation from negotiated amount can't exceed some boundaries in case of "take-or-pay" condition. It is not unique general valuation form of such flexible contracts as swing options. General definition of Longstaff Schwartz Least Square approximation method (LSM) is provided at first. Then it is shown other standard valuation concept as finite difference method. It is also mentioned tree method and more complex dynamic stochastic programming method. Analysis of energy commodities time series of central Europe is done and it is shown example of LSM approach use in valuing swing option with underlying asset of base load electricity in Czech Republic.
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Shieh, Chun-Pei, and 謝君珮. "The surface magnetic domain pattern study of LSMO/LAO thin-film and (LSMO/STO)6/LAO." Thesis, 2003. http://ndltd.ncl.edu.tw/handle/30021393609936702903.
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碩士國立東華大學
應用物理研究所
91
In the work, we study surface magnetic domain pattern properties of a 300-nm-thick thin-film of La0.67Sr0.3MnO3 (LSMO) and a 135-nm-thick La0.67Sr0.3MnO3/SrTiO3 superlattice of 6 double-layers (LSMO/STO)6. The LSMO thin-film is a perovskite structure of the type R1-xAxMnO3 (R is a trivalent rare-earth ion and A is a divalent dopant) and exhibits the colossal magnetoresistance (CMR) effect. According to magnetic measurements of a superconducting quantum interference device (SQUID), the Curie temperature (Tc) and room-temperature coercive field (Hc) of the thin-film LSMO are about 356.5 K and 32 Oe, respectively. In addition, those of the (LSMO/STO)6 superlattice are about 348 K and 6.5 Oe, respectively. X-ray adsorption edge structure (XAES) spectra of photoemission electron microscopy □PEEM□ show that the LSMO thin-film has a mixed Mn3+/Mn4+ valence band. Mapping of intensities of the XAES spectra gives a surface image and shows surface chemical-composition distribution. X-ray diffraction □XRD□ spectra show crystalline phases of the LSMO thin film and the (LSMO/STO)6 superlattic and each thickness of the superlattice. The period of superlattice is about 1.16 nm obtained from calculating positions of main and satellite peaks in the specta. In addition, using a magnetic force microscope (MFM), series of MFM images of surface magnetic domain patterns observed under Tc at various applied magnetic fields show a magnetic hysteresis phenomenon on transformation of surface magnetic domain patterns.
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Leufke, Philipp Moritz. "Magnetoelectric coupling in layered LSMO/PZT nanostructures." Phd thesis, 2014. https://tuprints.ulb.tu-darmstadt.de/3784/1/thesis_12pt_a5_final.pdf.
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Multiferroic thin film composites with electric field-effect driven magnetoelectric (ME) coupling offer the possibility to reversibly tune magnetic properties in materials intended for device applications. The structural and functional versatility of such artificial heterostructures makes them attractive not only for various data processing, storage and sensor applications but also for studying the fundamental ME coupling mechanisms.
La_(1−x)Sr_(x)MnO_(3) (LSMO)/PbZr_(y)Ti_(1−y)O_(3) (PZT) is an ideal choice for such a composite, combining the unrivaled ferroelectric (FE) properties of PZT with the multiple electronic and magnetic phenomena exhibited by the mixed valency manganite LSMO. The main physical feature used in realization of the LSMO/PZT ME composites is a striking sensitivity of LSMO magnetism to the charge carrier density. Here, the low-doping region is of particular interest, where the competition between the fundamental magnetic coupling mechanisms, Double-Exchange (DE) versus Superexchange (SE), is most distinctive.
In the present work an unconventional sputtering technique – the Large-Distance Magnetron Sputtering (LDMS) method – has been established, which allowed for epitaxial deposition of these heterostructures with highest crystallinity and markedly smooth interfaces, necessary for effective field-effect control of magnetism. The large target-substrate distance effectively suppressed the destructive oxygen ion bombardment, inherently connected with oxide sputtering, and yielded an outstanding lateral uniformity of the film stack. The latter was vital for the fabrication of large capacitor structures of several square millimeter area that were required for detecting the ME coupling in a Superconductive Quantum Interference Device (SQUID) magnetometer.
The growth of LSMO on various single crystalline substrates was mastered by exploring a vast deposition parameter space, encompassing Radio Frequency (RF) and Direct Current (DC) sputtering. Commensurately grown on SrTiO_(3) (STO) substrates, the x = 13 %-doped LSMO thin films were found to be stabilized in a metallic low-temperature phase, exhibiting an elevated Curie temperature (T_(C)), as compared to their bulk counterparts.
Regarding the PZT deposition, the LDMS technique naturally compensated for high volatility of the PbO vapor yielding a stoichiometric and phase pure film. Thus, with an optimal choice of deposition conditions, LSMO/PZT/Au thin film capacitors with excellent FE properties, i.e., high polarizability and long retention time, were obtained.
The high yield of 75 % of 1 mm² large capacitor structures was an excellent starting point for the ME tuning studies which were then carried out in a SQUID magnetometer in order to enable a quantitative analysis of the ME coupling. For this purpose, the measurement device needed to be modified, to allow for in situ application of electric fields. Furthermore, a SQUID measurement cell was designed to be used at low-temperatures and to keep the spurious magnetic signals as low as possible. All key in situ measurements were performed in FE remanence mode in order to avoid artifacts of leakage current and to protect the samples from Time-Dependent Dielectric Breakdown (TDDB).
The ME tuning measurements revealed a direct correlation of the FE remanent hysteresis and the magnetic response of the LSMO layer, evidencing a purely field-effect driven coupling and a virtual absence of any magnetostrictive coupling to possible piezo-strain of the PZT layer.
In temperature-dependent measurements, a reversal of the sign of the ME effect was observed, with a positive extremum for the electron hole (h^(+)) accumulation mode around the Curie temperature of the magnetic transition. The effect gradually decreased with the lowered temperature to become negative eventually. On the basis of the phase diagram and the dependence of the Mn magnetic moment on the Sr doping level, the shape of the curve was phenomenologically modeled by a transformation of the original Field Cooling (FC) curve. The resultant transformation was a superposition of a FC curve shift along the temperature axis and a rescaling of the magnetic moment.
The dependence of the magnetic response to the modulation of the surface charge showed a mostly linear behavior with a coupling coefficient of α_(MQ) ≈ −3.6 μ_(B)/h^(+) for low charge concentration. As this value stunningly matches the magnetic moment of a Mn atom per one formula unit, this result suggests an appearance of antiferromagnetic (AF) coupling upon surface charging. At higher charge modulation, the absolute value of the tuning coefficient decreased, indicating the onset of another magnetic exchange mechanism.
Eventually, the quantitative analysis of the ME coupling at the LSMO/PZT interface has allowed for developing a physical picture based on the electronic phase separation of competing AF and ferromagnetic (FM) phases immanent to LSMO.
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Huang, Yao-hui, and 黃耀輝. "Preparation of LSMO composite materials and it’s microwave properties characteristics." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/84217989026431801955.
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碩士逢甲大學
材料與製造工程所
97
In this study, microwave absorption composites filler with perovskite type oxide powders (La1-xSrx MnO3 , LSMO)、Carbon Black (CB), Carbon Nanotubes (CNTs), LSMO-CB and LSMO-CNTs were prepared, individually. The effects of filled content on complex permittivity, complex permeability and reflection loss for microwave absorption composites were investigated. According to the results of electromagnetic properties, we found a relationship between complex permittivity and complex permeability for LSMO composites. LSMO possess extra oxygen vacancies would cause to decrease the permittivity、exhibit anti-ferromagnetism behavior (real part of permeability below 1) and increase image part of permeability. To increase the filler content of microwave absorption would enhance the anti-ferromagnetism behavior. The permittivity of CNTs composites not only increase with filled ratio increasing but the real part of permeability also present the anti-ferromagnetic behavior. LSMO composites added within CB or CNTs would cause the center frequency of reflection loss shift to lower frequency. In the present study, a composite sample filled with 80 wt% La0.7Sr0.3MnO3-δ and 2 wt% CNTs exhibit the optimum performance which microwave absorbing peak is -22.85 dB at 9.5 GHz and the effective absorbing bandwidth above 10 dB reaches 3.3 GHz for the sample with the thickness of 3 mm. Moreover, a composite sample filled with 60 wt% La0.7Sr0.3MnO3-δ and 2 wt%CNTs which maxima reflection loss approach -43dB at 7 GHz with the thickness of 4 mm.