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Oxide-based hetero-structures are promising candidates for building the next generation of functional devices. In order to achieve this goal, it is required to have solid and reliable sensors for monitoring the growth of thin films with single-atomic-layer sensitivity. So far, the most popular in-situ diagnostic tool is Reflection High Energy Electron Diffraction, which provides information on the structural properties of the growing films, and not a direct access to the desired interfacial physical properties of interest. Furthermore, it needs a strong human-machine interaction, preventing its use into industrial mass production. Standard optics applied on buried interfaces suffers the disadvantage to have a probing depth which is orders of magnitude larger than the interface layer. Here we propose to overcome this problem by resorting to optical Second Harmonic Generation and we present some example to show the potential of this technique as a real-time monitor system for thin-film crystal growth.

The polarization induced at the LaAlO3/SrTiO3 interface has been explored by optical second harmonic generation (SHG) spectroscopy. Our data reveal that an orbital reconstruction of the SrTiO3 surface occurs when three epitaxial monolayers of LaAlO3 are deposited on top of it. The reconstruction manifests as a spectral modification of a Ti4+(3d) state at the LaAlO3/SrTiO3 interface which is accompanied by a displacement of the Ti4+ ions in adjacent SrTiO3 monolayers in order to compensate for the polarization discontinuity induced at the interface. According to the SHG experiment, the carriers transferred to the interface are trapped because in spite of the orbital reconstruction, the interface remains insulating. The onset of conductivity with the formation of a two-dimensional electron liquid appears to be a subordinate effect related to a minority of carriers and occurs upon further increase of the LaAlO3 coverage.

The so-called "polar catastrophe", a sudden electronic reconstruction taking place to compensate for the interfacial ionic polar discontinuity, is currently considered as a likely factor to explain the surprising conductivity of the interface between the insulators LaAlO3 and SrTiO3. We applied optical second harmonic generation, a technique that a priori can detect both mobile and localized interfacial electrons, to investigating the electronic polar reconstructions taking place at the interface. As the LaAlO3 film thickness is increased, we identify two abrupt electronic rearrangements: the first takes place at a thickness of 3 unit cells, in the insulating state; the second occurs at a thickness of 4-6 unit cells, i.e., just above the threshold for which the samples become conducting. Two possible physical scenarios behind these observations are proposed. The first is based on an electronic transfer into localized electronic states at the interface that acts as a precursor of the conductivity onset. In the second scenario, the signal variations are attributed to the strong ionic relaxations taking place in the LaAlO3 layer.

We have studied the effect of thickness on the structure and superconductivity of Nd1.2Ba1.8Cu3Oz (NdBCO) epitaxial films deposited on SrTiO3 (100) substrates. High-quality NdBCO films were deposited by high oxygen pressure sputtering. The samples have been carefully characterized by transport measurements and x-ray diffraction using conventional and synchrotron radiation sources. Two structural transformations are observed. The first one is a crossover from the orthorhombic and twinned structure, typical of thick samples, to a pseudotetragonal phase at thickness lower than 60 unit cells. The pseudotetragonal phase exhibits peculiar x-ray diffuse scattering around the Bragg reflections, associated with nanostructured twinned domains. The second one appears at a thickness lower than 20 unit cells and is assigned to a pseudotetragonal-tetragonal transition. The transport properties are not modified at the first crossover, while a substantial decrease in Tc and in the number of holes is observed at the pseudotetragonal-tetragonal transformation. Our results suggest that the structural rearrangement and the transport properties are explained by the ordering of Cu(1)O chains. A simple model, able to explain the experimental results and capturing the essential features of the Cu(1)O chains nucleation process in the R1+xBa2-xCu3O7-d (R=Y and rare-earth elements) compounds, is presented.

The thermal stability of the superconducting phase of nominal composition YBa 2Cu 3O 7-x-sintered pellets has been studied with respect to different temperatures (ranging from 300 to 950° C), time (ranging from 1 to 72 h), oxygen partial pressure (from 4 Pa to 1 atm) and carbon dioxide partial pressure (from 10 -4 Pa to 1 atm). Annealed samples were characterized by X-ray diffraction analysis, optical microscopy, and resistive measurements of the superconductive transition temperature. A stability field of the orthorhombic and tetragonal phases was obtained, showing a region of coexistance. The decomposition of the 1 2 3 phase is found to be strongly influenced by the presence of a small amount of CO 2 (1 p.p.m.) in the sintering atmosphere. A sintering process is proposed to avoid the formation of by-products. © 1990 Chapman and Hall Ltd.

We present the development and validation of a construct map addressing introductory quantum mechanics topics at the high school level, as a subset of a larger learning progression on quantum mechanics. Topics include energy quantization, photon absorption and emission, the Heisenberg uncertainty principle, atom stability, orbitals, wave function, and electronic properties of materials. To validate the hypothesized construct map, we designed a multiple-choice questionnaire and a 14-h teaching-learning sequence (TLS) designed in strict relation with the levels of the construct map. Twenty-three classes of Italian students (ages 17–18, N=408) were involved in the study: about half (N=200) were exposed to the TLS, while N=208 students received a typical textbook instruction on the same topics targeted by the construct map. Data were analyzed using a 1D Rasch model. Results show that the proposed construct map consistently describes the increasing abilities of students when exposed to instruction. In particular, when exposed to the TLS activities, students more likely move towards the upper levels of the construct map. Findings have implications for instruction designed to support students’ learning in quantum mechanics at the high school level.

We report an empirical study on the development and validation of a learning progression (LP) in quantum mechanics (QM) at university level. Drawing on research results about students’ reasoning in QM, we designed a hypothetical LP (HLP) consisting of three Big Ideas: Measurement, A toms and Electrons, Wave function. We then developed ten Ordered-Multiple-Choice (OMC) items to assess the construct validity and hierarchy of HLP levels. We administered the questionnaire to 244 students attending the Bachelor in Physics, divided into three groups under different instruction conditions: no course, introductory course, introductory and upper-level course. An additional group of 43 non-physics students, who attended an introductory QM course, was also involved to inspect the role of physics background knowledge . We used exploratory factor analysis and Rasch analysis to analyse collected data. The results provided evidence for the revision of the HLP around only two Big Ideas – Atomic description and measurement; Wave function and its properties in the measurement process – which roughly match the topics covered in the introductory and upper-level courses, respectively. However, the hierarchy of hypothesised levels was substantially confirmed. Implications of our findings for the teaching of QM, and the improvement of the revised LP are also discussed.

The indirect effect of oxygen background gas on the La/Al ratio during the growth of LaAlO3 (LAO) films by pulsed laser deposition (PLD) is analyzed, in a pressure range between 10^-3 and 10^-1 mbar. We resort to two complementary investigation methods: Rutherford backscattering spectroscopy and spectrally resolved, time-gated imaging of the laser plume. The first technique allows us to analyze the stoichiometry of the deposited films, and the latter allows us to analyze the plume expansion phase of the PLD process by collecting chemically resolved two-dimensional images of the relevant atomic/molecular species. The comparison between the results obtained by the two techniques allows us to highlight the role of the plume-gas interaction in affecting cations stoichiometry. Our results indicate that, in the considered pressure range, the background oxygen pressure affects the cations stoichiometry of the LAO films, besides determining their oxygen content.

The time-resolved photoconductance of amorphous and crystalline LaAlO$_3$/SrTiO$_3$ interfaces, both hosting an interfacial 2-dimensional electron gas, is investigated under irradiation by variable-wavelengths, visible or ultraviolet photons. Unlike bare SrTiO$_3$ single crystals, showing relatively small photoconductance effects, both kinds of interfaces exhibit an intense and highly persistent photoconductance with extraordinarily long characteristic times. The temporal behaviour of the extra photoinduced conductance persisting after light irradiation shows a complex dependence on interface type (whether amorphous or crystalline), sample history and irradiation wavelength. \textcolor{black}{The experimental results indicate that different mechanisms of photoexcitation are responsible for the photoconductance of crystalline and amorphous LaAlO$_3$/SrTiO$_3$ interfaces under visible light. We propose that the response of crystalline samples is mainly due to the promotion of electrons from the valence bands of both SrTiO$_3$ and LaAlO$_3$. This second channel is less relevant in amorphous LaAlO$_3$/SrTiO$_3$, where the higher density of point defects plays instead a major role., 8 pages, 5 figures, 3 tables, accepted on Scientific Reports 2015

In this thesis valence changes at interfaces and surfaces of 3d and 4f systems are investigated by X-ray spectroscopy, in particular X-ray photoemission (XPS), X-ray absorption (XAS) and resonant photoemission spectroscopy (ResPES). The first part addresses the electronic properties of the oxides LaAlO3, LaGaO3 and NdGaO3 grown by pulsed laser deposition on TiO2-terminated SrTiO3 single crystals along (001)-direction. These polar/non-polar oxide interfaces share an insulator to metal phase transition as a function of overlayer thickness including the formation of an interfacial two dimensional electron gas. The nature of the charge carriers, their concentration and spatial distribution, and the band alignment near the interface are studied in a comparative manner and evaluated quantitatively. Irrespective of the different overlayer lattice constants and bandgaps, all the heterostructures behave similarly. Rising Ti3+ concentration is monitored by Ti 2p XPS, Ti L-edge XAS and by resonantly enhanced Ti 3d excitations in the vicinity of EF (ResPES) when the layer number n increases. This indicates that the active material is in all cases a near interface SrTiO3 layer of 4nm thickness. Band bending in SrTiO3 occurs but no electric field is detected inside the polar overlayers. Essential aspects of the findings are captured by scenarios where the polar forces are alleviated by surface defect creation or the separation of photon generated electron-hole pairs in addition to the electronic reconstruction at n = 4 unit cells layer thickness. Furthermore, deviations from an abrupt interface are found by soft X-ray photoemission spectroscopy which may affect the interface properties. The surface sensitivity of the measurements has been tuned by varying photon energy and emission angle. In contrast to the core levels of the other elements, the Sr 3d line shows an unexpected splitting for higher surface sensitivity, signaling the presence of a second strontium component. From a quantitative analysis it is concluded that during the growth process a small amount of Sr atoms diffuse away from the substrate and segregate at the surface of the heterostructure, possibly forming strontium oxide. In the second part of this thesis the heavy fermion superconductors CeMIn5 (M = Co, Rh, Ir) are investigated by temperature- and angle-dependent XPS. In this material class the subtle interplay between localized Ce 4f and itinerant valence electrons dominate the electronic properties. The Ce 3d core level has a very similar shape for all three materials and is indicative of weak f-hybridization. The spectra are analyzed using a simplified version of the Anderson impurity model, which yields a Ce 4f occupancy that is larger than 0.9. The temperature dependence shows a continuous, irreversible and exclusive broadening of the Ce 3d peaks, due to oxidation of Ce at the surface. In der vorliegenden Dissertation werden Valenzänderungen an Grenzflächen und Oberflächen mittels Verfahren der Röntgenspektroskopie untersucht, zu denen die Röntgenphotoelektronen- (XPS), die Röntgenabsorptions- (XAS) und die resonante Photoelektronenspektroskopie (ResPES) gehören. Kapitel 3 behandelt die elektronischen Eigenschaften der Oxide LaAlO3, LaGaO3 und NdGaO3, welche mittels Laserdeposition (PLD) auf TiO2-terminierte SrTiO3 Einkristalle entlang (001)-Richtung gewachsen wurden. Diese polaren/nicht-polaren Oxidgrenzflächen weisen einen Isolator-Metall Phasenübergang als Funktion der Schichtdicke auf, bei dem sich ein zwei dimensionales Elektronengas an der Grenzfläche bildet. Die Eigenschaften dieser Ladungsträger, deren Konzentration und räumliche Ausdehnung, sowie der Verlauf der Energiebänder an der Grenzfläche werden vergleichend untersucht und quantitativ bestimmt. Es wird gezeigt, dass sich die drei untersuchten Grenzflächen, trotz unterschiedlicher Gitterkonstanten und Energiebandlücken, ähnlich verhalten. Das mit der Schichtdicke ansteigende Ti3+ Signal wird im Ti 2p XPS, Ti L-Kante XAS und durch die resonant verstärkten Ti 3d Anregungen nahe EF (ResPES) nachgewiesen. Daraus lässt sich schlussfolgern, dass in allen Fällen eine SrTiO3 Schicht mit einer Dicke von 4nm der eigentlich aktive Bereich ist. Im SrTiO3 tritt eine Bandverbiegung auf, ein elektrisches Feld in der polaren Deckschicht kann jedoch nicht nachgewiesen werden. Grundlegende Aspekte dieser Ergebnisse sind in einem Szenario vereinbar, bei dem die polaren Kräfte durch die Entstehung von Oberflächendefekten, durch die Trennung von photoneninduzierten Elektronen-Lochpaaren und durch eine elektronische Umordnung bei 4 uc Schichtdicke eliminiert werden. Des Weiteren werden Abweichungen von einer abrupten Grenzfläche mittels weich-Röntgenphotoelektronenspektroskopie festgestellt, die die Grenzflächeneigenschaften beeinflussen können. Für oberflächenempfindlichere Messbedingungen zeigt die Sr 3d Anregung, im Gegensatz zu Rumpfniveaus anderer Elemente, eine unerwartete Aufspaltung, was nur durch das Vorhandensein einer zweiten chemischen Strontiumkomponente zu erklären ist. Aus quantitativen Betrachtungen lässt sich schließen, dass einige Strontiumatome während des Wachstums an die Oberfläche diffundieren und möglicherweise Strontiumoxid gebildet wird. Der zweite Schwerpunkt der vorliegenden Arbeit ist die Untersuchung von Schwer-Fermionen Supraleitern CeMIn5 (M = Co, Rh, Ir) mittels temperatur- und winkelabhängiger XPS. Bei dieser Materialklasse dominiert das feine Zusammenspiel zwischen lokalisierten Ce 4f und frei beweglichen Leitungselektronen die elektronischen Eigenschaften. Das Ce 3d Rumpfniveauspektrum besitzt für die drei Materialien eine sehr ähnliche Form, die auf eine schwache f-Hybridisierung schließen lässt. Die Spektren werden mittels einer vereinfachten Version des Anderson-Impurity Modells analysiert, wobei sich eine Ce 4f Besetzung von mehr als 0,9 ergibt. Die Temperaturabhängigkeit zeigt eine kontinuierliche und irreversible Verbreiterung ausschließlich für die Ce 3d Anregung, dieser Umstand kann einer Oxidation der reaktiven Ceratome an der Oberfläche zugeordnet werden.

By a combination of optical second harmonic generation and transport measurements, we have investigated interfaces formed by either crystalline or amorphous thin films of LaAlO3 grown on TiO2-terminated SrTiO3(001) substrates. Our approach aims at disentangling the relative role of intrinsic and extrinsic doping mechanisms in the formation of the two-dimensional electron gas. The different nature of the two mechanisms is revealed when comparing the sample response variation as a function of temperature during annealing in air. However, before the thermal treatment, the two types of interfaces show almost the same intensity of the second harmonic signal, provided the overlayer thickness is the same. As we will show, the second harmonic signal is proportional to the depth of the potential well confining the charges at the interface. Therefore, our result demonstrates that this depth is about the same for the two different material systems. This conclusion supports the idea that the electronic properties of the two-dimensional electron gas are almost independent of the doping mechanism of the quantum well.

The voltage-spectral density SV(f) of the 2-dimensional electron gas formed at the interface of LaAlO3 /SrTiO3 has been thoroughly investigated. The low-frequency component has a clear 1/f behavior with a quadratic bias current dependence, attributed to resistance fluctuations. However, its temperature dependence is inconsistent with the classical Hooge model, based on carrier-mobility fluctuations. The experimental results are, instead, explained in terms of carrier-number fluctuations, due to an excitation-trapping mechanism of the 2-dimensional electron gas., 4 pages, 4 figures

Optical second harmonic generation (SHG) spectra of LaAlO${}_{3}$/SrTiO${}_{3}$, LaGaO${}_{3}$/SrTiO${}_{3}$, and NdGaO${}_{3}$/SrTiO${}_{3}$ interfaces with SrTiO${}_{3}$ substrates have been measured up to 4.2 eV as a function of film thickness and temperature. This spectral range is characterized by two-photon transitions from the valence to conduction bands of SrTiO${}_{3}$ which are classified with a model based on symmetry, selection rules, and atomic orbital overlaps. This model is further confirmed in spectral measurements as a function of film thickness, material overlayer, and temperature. SHG enhancement at low temperature indicates an increase of the interfacial polarity with decreasing temperature. This confirms the relation between SHG and the spatial translation of Ti ions which are more prone to move at lower temperatures because of the quantum-paraelectric nature of SrTiO${}_{3}$. We finally show that SHG spectroscopy captures structural details of the interfaces. In particular, we find evidence for proximity effects such as LaAlO${}_{3}$-induced distortions of the TiO${}_{6}$ octahedra or bond buckling. We also observe a correlation between SHG and the in-plane lattice mismatch between the SrTiO${}_{3}$ substrate and the LaAlO${}_{3}$, LaGaO${}_{3}$, and NdGaO${}_{3}$ overlayers.

Phase-sensitive, spatially resolved optical second-harmonic-generation experiments were performed on LaAlO3/SrTiO3 heterostructures. Lateral inhomogeneities on a length scale of ≈ 30 μm are found when a one-unit-cell-thick epitaxial monolayer of LaAlO3 is grown on TiO2-terminated SrTiO3 single crystals. The inhomogeneity is absent in samples with LaAlO3 layers of more than one unit cell. The results are discussed in the framework of electronic, oxidic, and chemical inhomogeneities.

TiO(2) anatase thin films grown by pulsed laser deposition are investigated by high resolution transmission electron microscopy and high angle annular dark field scanning transmission electron microscopy. The analyses provide evidence of a peculiar growth mode of anatase on LaAlO(3) and SrTiO(3) characterized by the formation of an epitaxial layer at the film/substrate interface, due to cationic diffusion from the substrate into the film region. Pure TiO(2) anatase growth occurs in both specimens above a critical thickness of about 20 nm. The microstructural and chemical characterization of the samples is presented and discussed in the framework of oxide interface engineering.

We investigate pulsed laser ablation of LaAlO 3 and LaGaO 3 with a focus on the influence of oxygen background gas pressure on the plume expansion dynamics and deposition rate. The ablation plume is characterized by exploiting fast photography and time- and space-resolved optical emission spectroscopy. The variation of the deposition rate with the oxygen background pressure was obtained at 800 °C by reflection high-energy electron diffraction, and compared to that measured at room temperature by means of a quartz crystal microbalance. The experimental findings allow one to address the various stages of plume expansion as a function of the background oxygen pressure as well as the changes induced on the plume species kinetic energy and composition. On the base of our experimental results, the possible influence of various mechanisms, such as subplantation and oxygen vacancy formation, on the growth of oxides interfaces is addressed.

International audience; We describe some general features in the transient behaviour of strongly correlated transition metal oxides, following ultrafast excitation by a femtosecond laser pulse. Our analysis is based on time-resolved reflectivity measurements on (V1-xCrx)2O3, a prototype Mott-Hubbard material, and the manganite compound (La0.67Sr0.33)MnO3, performed over a time window of several tenths of ps. We point out the contribution of coherent lattice oscillations-both optical and acoustic-to the overall signal, and show how they can depend on the crystallographic orientation of the material with respect to the laser beam wavevector and polarisation. In particular, an acoustic wave is always found to be present in our measurements, and we show that its oscillating behaviour is superposed to the average time evolution of the material, which can be instead related in different ways to its electronic properties and thermodynamic phase. All these effects are to be taken into account in any further analysis leading to the estimation of relevant physical parameters for correlated materials, and they appear to play a significant role not only for reflectivity techniques, but also in other kinds of ultrafast pump-probe experiments.

In order to analyze the effect of strain on the magnetic properties of narrow-band manganites, temperature-and field-dependent susceptibilities of about 8.5-nm-thick epitaxial Pr(0.7)Ca(0.3)MnO(3) films, respectively, grown on (001) and (110) SrTiO(3) substrates, have been compared. For ultrathin samples grown on (001) SrTiO(3), a bulklike cluster-glass magnetic behavior is found, indicative of the possible coexistence of antiferromagnetic and ferromagnetic phases. On the contrary, ultrathin films grown on (110) substrates show a robust ferromagnetism with a strong spontaneous magnetization of about 3.4 mu(B)/Mn atom along the easy axis. On the base of high-resolution reciprocal space mapping analyses performed by x-ray diffraction, the different behaviors are discussed in terms of the crystallographic constraints imposed by the epitaxy of Pr(0.7)Ca(0.3)MnO(3) on SrTiO(3). We suggest that for growth on (110) SrTiO(3), the tensile strain on the film c axis, lying within the substrate plane, favors the ferromagnetic phase, possibly by allowing a mixed occupancy and hybridization of both in-plane and out-of-plane e(g) orbitals. Our data allow to shed some physics of inhomogeneous states in manganites and on the nature of their ferromagnetic insulating state.

The pulsed laser deposition of SrTiO(3)/LaGaO(3) and SrTiO(3)/LaAlO(3) interfaces is analyzed with a focus on the kinetic energy of the ablated species. LaGaO(3) and LaAlO(3) plasma plumes were studied by fast photography and space-resolved optical emission spectroscopy. Reflection high energy electron diffraction was performed proving a layer-by-layer growth up to 10(-1) mbar oxygen pressure. The role of the energetic plasma plume on the two-dimensional growth and on the presence of interfacial defects at different oxygen growth pressures is discussed in connection with the conducting properties of the polar/nonpolar interfaces. (C) 2010 American Institute of Physics. [doi:10.1063/1.3529487]

The properties of thin films of complex oxides, such as La1−xDxMnO3− D=Ba, Ca, Sr, etc., produced by pulsed laser deposition depend critically on the experimental parameters in which laser ablation is carried out. Here, we report a comparative analysis of the pulsed laser ablation process of La0.7Ba0.3MnO3−, in oxygen background, in the ambient pressure range from 10−2 to 1 mbar, typically employed in pulsed laser deposition of manganites. The laser ablation plume was studied by using time-gated imaging and optical emission spectroscopy techniques. It was found that at a pressure of 10−2 mbar, the plume species arriving at the substrate are characterized by hyperthermal kinetic energy 10 eV, and high degree of excitation. On the contrary, at larger oxygen pressure 0.1–1 mbar, the velocity of plume species reaching the substrate, and their degree of excitation are much reduced by the confining effects of the background gas. These features explain why an appropriate choice of the experimental conditions in which the deposition process is carried out leads to better quality films, providing helpful indications to improve control over the growth process of both La1−xDxMnO3− and other perovskitic oxides.

Weak ferromagnet/superconductor (F/S) proximity bilayers have been fabricated and characterized for basic physics studies concerning the ultrafast carrier dynamics in layered materials. The normalized reflectivity change (Δ R / R ) as a function of the time delay between the pump and the probe laser beams has been measured in F/S heterostructures formed by a low critical temperature superconductor (Nb) with a NiCu overlayer, and a high T c superconductor (YBCO) covered by Au/NiCu and manganite (LSMO) overlayers. The attention is mainly focused to the investigation of nonequilibrium excitation dynamics inside different bilayers in the low temperature region. The presence of the weak ferromagnetic overlayer produces faster optical relaxation times with respect to sole superconducting films. The results are promising in view of potential applications as ultrafast kinetic inductance superconducting photodetectors as confirmed by preliminary time-resolved photoimpedance experiments on both Nb and NiCu(21 nm)/Nb(70 nm) samples.

The blue-green photoluminescence emitted by pure and electron-doped strontium titanate under intense pulsed near-ultraviolet excitation is studied experimentally, as a function of excitation intensity and temperature. Both emission spectra and time-resolved decays of the emission are measured and analyzed in the framework of simple phenomenological models. We find an interesting blue-to-green transition occurring for increasing temperatures in pure samples, which is instead absent in doped materials. The luminescence yield and decay rate measured as a function of temperature can be modeled well as standard activated behaviors. The leading electron-hole recombination process taking place in the initial decay is established to be second-order, or bimolecular, in contrast to recent reports favoring a third-order interpretation as an Auger process. The temporal decay of the luminescence can be described well by a model based on two interacting populations of excitations, respectively identified with interacting defect-trapped (possibly forming excitons) and mobile charges. Finally, from the measured doping and sample dependence of the luminescence yield, we conclude that the radiative centers responsible for the luminescence are probably intrinsic structural defects other than bulk oxygen vacancies.

The growth of high quality epitaxial La0.7Sr0.3MnO3 thin films was controlled on various substrates, including SrTiO3 (001), (110), vicinal substrates and Si. The design and development of applications such as uncooled bolometers and spintronic devices could then be considered. In this work, different deposition techniques were used: sputtering, pulsed laser deposition, assisted or not by RHEED (Reflection High Energy Electron Diffraction). The samples were characterized by X-ray diffraction, particularly studying epitaxy and strain in the layers. Further analyzes using RHEED, LEED (Low Energy Electron Diffraction), and STM/AFM (Scanning Tunneling and Atomic Force Microscopies) were also conducted, as well as resistivity and magnetization measurements as a function of the temperature. The effect of the orientation of the SrTiO3 substrate has been demonstrated. Finally, three examples of spintronic devices based on dead layer, vicinal surfaces or spin injection are presented.; La croissance de couches minces épitaxiées de La0.7Sr0.3MnO3 a été réalisée sur différents substrats, dont SrTiO3 (001), (110), vicinal et Si. La conception de bolomètres et de dispositifs spintroniques est donc envisageable. Différentes techniques de dépôt ont été utilisées: la pulvérisation cathodique, l'ablation laser pulsée, assistée ou non par RHEED (Reflection High Energy Electron Diffraction). Les échantillons ont été caractérisés par diffraction de rayon X, en étudiant particulièrement l'épitaxie et la contrainte dans les couches. Des analyses complémentaires de RHEED, de LEED (Low Energy Electron Diffraction), et de STM/AFM (Scanning Tunneling/Atomic Force Microscopies) ont été également réalisées, ainsi que des mesures de résistivité et d'aimantation en fonction de la température. L'effet de l'orientation du substrat SrTiO3 a ainsi été montré. Trois dispositifs spintroniques utilisant une couche morte, des surfaces vicinales ou l'injection de spin sont finalement présentés.

Following the recent surge of interest in n-doped strontium titanate as a possible blue light emitter, a time-resolved photoluminescence analysis was performed on nominally pure, Nb-doped and oxygen-deficient single-crystal SrTiO3 samples. The doping effects on both the electronic states involved in the transition and the decay mechanism are respectively analyzed by comparing the spectral and dynamic features and the yields of the emission. Our time-resolved analysis, besides shedding some light on the basic recombination mechanisms acting in these materials, sets the intrinsic bandwidth limit of the proposed blue light emitting optoelectronic devices made of Ti-based perovskites heterostructures in the gigahertz range.

The authors have performed experiments on current-induced domain wall (DW) displacement in La0.7Sr0.3MnO3 nanostructures patterned by gallium (Ga) focused-ion-beam milling. A dc current is found to assist or hinder, according to polarity, an external magnetic field in the depinning of a DW trapped in a nanoconstriction. For large enough currents, the DW depinning occurs in the absence of external magnetic field. The depinning current depends on the transverse anisotropy constant of the region toward which the DW is displaced.

The structure of SrTiO3 (100) (STO) single crystal surfaces has been investigated by grazing incidence x-ray diffraction. The authors found that chemically etched STO is composed similar to 75% of an ideal TiO2 surface layer and similar to 25% of SrO and it is very stable when annealed in ultrahigh vacuum or in O-2 at high temperatures. A monolayer of SrO, epitaxially grown by pulsed laser deposition, is found to cover only a fraction of the TiO2 layers and exhibits a 2x2 reconstruction with strong structural changes after annealing in conditions typically used for the deposition of oxides. (c) 2007 American Institute of Physics.

The colossal magnetoresistance (CMR) manganese oxides, have been the subject of intense studies. To elucidate the mechanisms at work in the ferromagnetic metallic state is essential for the comprehension of the M–I transition and the associated CMR effect. We present here comparison among resistivities behavior in Ca and Sr-doped manganite films (x = 0.3) grown by different techniques and on several substrates allowing to analyze samples with different amounts of disorder. At low temperatures, a dominant T 2 term in the resistivity has generally been observed. Our analysis shows that for residual resistivity values larger than a critical one, there is a substantial deviation from the T 2-like behavior and that an unusual T 2.5 one is robust. This behavior supports the theoretical proposal of single magnon scattering in the presence of minority spin states localized by the disorder. In the high temperature insulating paramagnetic phase the resistivity shows the activated behavior characteristic of polaronic carriers. Finally in the whole range of temperatures the experimental data are found to be consistent with a phase separation scenario.

The quality of YBa2Cu3O7-delta blepitaxial grain boundary Josephson junctions has been improved and 'tunnel-like' characteristics are reproducibly obtained. The consequent low barrier transmission probabilities are apparently favourable to isolate intrinsic d-wave induced effects. Extrinsic and intrinsic d-wave effects are discussed within the framework of novel designs for pi-circultry and qubits.

Clear evidence about the influence of growth orientation on the stoichiometry of sputtered oxide thin films is reported and discussed. The growth of stoichiometric and of non-stoichiometric films is respectively obtained, from the same CaRuO3 target, on the surface of (110) and (100) perovskite substrates. Such phenomenon has been systematically investigated by deposition of pairs of samples in the same deposition run. Our data show that in samples deposited on (100) perovskites, Ca excess leads to the formation of a single Ca-rich phase with stoichiometry Ca1 + x Ru1-x O3, resulting in a dramatic effect on transport properties. Structural characterization based on X-ray diffraction proves that the orthorhombic structure is preserved in a wide stoichiometry range. The striking evidence that substrate orientation influences film stoichiometry is discussed in terms of growth kinetics and chemical properties of sputtered species.

We present various concepts and experimental procedures to fabricate biepitaxial YBa 2Cu 3O 7-x grain boundary Josephson junctions. Different types of structures can be realized including "π-loops" in which one of the junctions is intrinsically π-phase shifted. Due to its versatility the biepitaxial technique offers the possibility to investigate basic aspects of the physics of grain boundary Josephson junctions, and also the influence of intrinsic and extrinsic d-wave induced effects in transport properties. Further, we discuss the possibility to produce circuits in which "0-" and "π-loops" are controllably located on the same chip, and intrinsic d-wave effects can be exploited.