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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 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. [ABSTRACT FROM AUTHOR]

Describes the proportional regime of a double superconducting tunnel junction detector in terms of the diffusion equation of the nonequilibrium quasiparticles excited in the absorber by the impinging radiation. Information on the double-probe particle detector; Data on the mapping of the images of the absorber films; Equations describing the diffusion of the quasiparticles.

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. [ABSTRACT FROM AUTHOR]

We have designed an experiment that could allow to investigate, on the same sample, the interplay between the morphological anisotropy of high critical temperature superconductors and the effects related to the order parameter symmetry. To this aim we have employed c-axis tilt biepitaxial grain boundary YBa2Cu3O 7 - δ Josephson junctions and measured the junction properties for different junction interface orientations. The results give evidence of the possibility to tune normal state resistance and critical current density of a Josephson junction almost independently of each other. We interpret the results of this experiment as an indication that Cooper pairs and quasi-particles transport properties may be ruled by different mechanisms. Measurements apparently give evidence of the possibility to determine to some extent the presence of “ π-loops” and “0” loops along the same grain boundary line. [ABSTRACT FROM AUTHOR]

(110) and (103) YBa[sub 2]Cu[sub 3]O[sub 7] films have been grown onto exact and vicinal (110) SrTiO[sub 3] substrates, and on vicinal (110) MgO substrates with a SrTiO[sub 3] buffer layer. The samples are carefully characterised by reciprocal space mapping with x-ray diffraction, in order to investigate the features of the typical double domain of (110) and (103) YBa[sub 2]Cu[sub 3]O[sub 7] structure. It is demonstrated that vicinal cut substrates allow to select one film/substrate epitaxial relation. The growth properties of these thin films deposited on vicinal surfaces are discussed. [ABSTRACT FROM AUTHOR]

We present the results of collaboration between the groups of Naples and Genoa Universities/INFM, focused on thin films superconducting borocarbides. In particular a careful study of the deposition of non-magnetic LuNi[sub 2]B[sub 2]C thin films by Pulsed Laser Deposition (PLD) on MgO and other substrates will be presented. While samples with good c-orientation and superconducting properties are obtained in a wide range of deposition parameters, in-plane micrometric oriented structures are obtained only in a narrow range of conditions, as evidenced by X-rays measurements and AFM (atomic force microscopy) analyses. A special set-up for the in situ interchanging of shadow masks has been developed in order to deposit the different patterned layers and different buffer and/or barrier layers. New results on the temperature dependence of the LuNi[sub 2]B[sub 2]C gap using S/N contact junctions are presented and discussed. The obtained value of the superconducting gap and its temperature dependence agrees very well with the BCS prediction. We present also microwave measurements of the surface impedance performed on large area films obtained by sputtering technique on low loss sapphire substrates. The data confirm the overall BCS-like behavior of these compounds. [ABSTRACT FROM AUTHOR]

Concepts and experimental procedures to obtain different types of YBa[sub 2]Cu[sub 3]O[sub 7] grain boundaries Josephson junctions through the biepitaxial technique have been developed. Various seed layers (MgO, CeO[sub 2] and SrTiO[sub 3]) and substrates (MgO, SrTiO[sub 3]) have been used providing, for the biepitaxial technique, additional flexibility in circuit design. A detailed investigation on transport properties evidenced good performances for both junctions and superconducting quantum interference devices. Experimental evidence is given of a conventional magnetic field behavior in 45° tilt Artificial Grain Boundary (AGB) for which no π-loops are predicted along the interface. [ABSTRACT FROM AUTHOR]

Some of the main anomalies in conductance characteristics of high- T tunnel junctions are considered. Mainly, the extreme, depression of gap structures, the presence of conductance peaks in corrispondence to the counterelectrode gap, and «zero-bias anomalies» will be examined. The possibility of application of the proximity McMillan model to describe the behaviour in conductance of high- T junctions is considered. Discussion and preliminary comparison with experimental data on YBCO junctions are also reported. [ABSTRACT FROM AUTHOR]

Preparation procedure and sample characterization of 112 BiSCCO pellets exhibiting high- T superconductivity are discussed. Typical I-V and d V/d I curves of Nb/BiSCCO point conctact junctions at various temperatures are presented. [ABSTRACT FROM AUTHOR]

We investigate the effects of ambient pressure and substrate temperature on the deposition rate of oxides grown by pulsed laser deposition in oxygen atmosphere. The deposition rate of LaGaO3 (LGO) and LaAlO3 (LAO) is studied at room temperature by means of a quartz crystal microbalance and at 800 °C by exploiting reflection high energy electron diffraction. We observe a clear dependence of the deposition rate on temperature for an oxygen pressure between 10-2 and 1 mbar. A simple model based on multiple-elastic-scattering processes thoroughly describes the observed dependence of the deposition rate on the pressure/density of the background gas. [ABSTRACT FROM AUTHOR]

The pulsed laser deposition of SrTiO3/LaGaO3 and SrTiO3/LaAlO3 interfaces is analyzed with a focus on the kinetic energy of the ablated species. LaGaO3 and LaAlO3 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. [ABSTRACT FROM AUTHOR]

We show that the growth of the heterostructure LaGaO3/SrTiO3 yields the formation of a highly conductive interface. Our samples were carefully analyzed by high resolution electron microscopy, in order to assess their crystal perfection and to evaluate the abruptness of the interface. Their carrier density and sheet resistance are compared to the case of LaAlO3/SrTiO3 and a superconducting transition is found. The results open the route to widening the field of polar-nonpolar interfaces, pose some phenomenological constrains to their underlying physics and highlight the chance of tailoring their properties for future applications by adopting suitable polar materials. [ABSTRACT FROM AUTHOR]

A simple technique for the growth of SrO-terminated SrTiO3 surfaces is reported. High quality SrTiO3 epitaxial films were grown by reflection high energy electron diffraction assisted pulsed laser deposition on suitably prepared NdGaO3 (110) substrates. The surface properties, analyzed within a growth/characterization multichamber ultrahigh vacuum system by photoemission spectroscopy performed on the core-level spectra of Sr and Ti, low energy electron diffraction-, scanning tunneling-, and atomic force microscopy, are fully consistent with a single Sr oxide termination. The availability of such high quality SrO-terminated SrTiO3 surfaces is of major importance for the controlled growth of oxide epilayers and interfaces. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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 ∼75% of an ideal TiO2 surface layer and ∼25% of SrO and it is very stable when annealed in ultrahigh vacuum or in O2 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 2×2 reconstruction with strong structural changes after annealing in conditions typically used for the deposition of oxides. [ABSTRACT FROM AUTHOR]

The magnetic and magnetotransport properties of La0.7Sr0.3MnO3/Permalloy heterostructures are investigated. La0.7Sr0.3MnO3 films were grown on (110) SrTiO3 in order to induce an in-plane anisotropy with the easy axis along the [001] direction. An easy axis of magnetization was induced in the Permalloy in the same direction through the application of a magnetic field during the growth. The magnetic characterization of the bilayer is presented and discussed. The transport properties of devices operated in the current perpendicular to plane mode are shown. The possibility of fabricating magnetoresistive devices by simply depositing a ferromagnetic counterelectrode on a manganite film is demonstrated. [ABSTRACT FROM AUTHOR]

In this study, we investigate student performance using grades and "grade anomalies" across periods before, during, and after COVID-19 remote instruction in courses for bioscience and health-related majors. Additionally, we explore gender equity in these courses using these measures. We define grade anomaly as the difference between a student's grade in a course of interest and their overall grade point average (GPA) across all other courses taken up to that point. If a student's grade in a course is lower than their GPA in all other courses, we refer to this as a "grade penalty". Students received grade penalties in all courses studied, consisting of twelve courses taken by the majority of bioscience and health-related majors. Overall, we found that both grades and grade penalties improved during remote instruction but deteriorated after remote instruction. Additionally, we find more pronounced gender differences in grade anomalies than in grades. We hypothesize that women's decisions to pursue STEM careers may be more influenced by the grade penalties they receive in required science courses than men's, as women tend to experience larger penalties across all periods studied. Furthermore, institutions concerned with equity should consider grade penalties as a straightforward measure and make a conscious effort to consider their implications. [ABSTRACT FROM AUTHOR]

Astronomy is seen as a "gateway" science, inspiring students to pursue Science-Technology-Engineering-Mathematics (STEM) related careers. However, there is little evidence that students' attitudes towards astronomy remain stable over time. By integrating Self-Determination Theory (SDT) and Theory of Planned Behaviour (TPB), we identified three dimensions of students' attitudes towards astronomy - intrinsic, which refers to the enjoyment of studying astronomy, extrinsic, which refers to the will to pursue a career in astronomy, and utilitarian, which refers to the relevance of astronomy to society. We used these dimensions as indicators for a Latent Profile Analysis (LPA) to identify attitudinal profiles of 2650 Italian students in grades 9-13. We identified seven profiles, ranging from completely negative to completely positive attitudes. In particular, students enter secondary school mostly interested in astronomy and with a positive view of astronomy. By the end of secondary school, students have significantly lower attitudes towards astronomy in all three dimensions identified. From a theoretical perspective, our study shows that the SDT/TPB framework can be used to develop future instruments aimed at measuring students' attitudes towards science. From a practical point of view, our results call for better support for teachers to maintain students' attitudes towards astronomy throughout secondary school. [ABSTRACT FROM AUTHOR]

A valid, reliable, and practical instrument is needed to evaluate ESL textbooks in Malaysian community colleges. Thus, a questionnaire guided by the Litz Theory (2005) was designed to evaluate ESL textbooks in Malaysian community colleges. This paper assessed the validation of the questionnaire using the Rasch Model analysis of construct validity and reliability. The questionnaire investigates community college students' perceptions of the ESL textbooks they use in their classrooms. The sample of this study comprised 123 community college students in Malaysia. The Rasch Model produced construct validity and reliability measurements using the dimensionality, item fit, and item polarity parameters and the person and item separation analysis. The results of the Rasch Model Analysis reveal that the construct validity in the study shows the uniformity of the instruments in the good category. This indicates that the items used in this study are related to the material's content. Hence, this questionnaire is valid and reliable to evaluate ESL textbooks in Malaysian community colleges. [ABSTRACT FROM AUTHOR]

Copyright of Pedagogy Studies / Pedagogika is the property of Vytautas Magnus University and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Administração: Ensino e Pesquisa is the property of Administracao: Ensino e Pesquisa and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Extended abstract of a paper presented at Microscopy and Microanalysis 2011 in Nashville, Tennessee, USA, August 7–August 11, 2011. [ABSTRACT FROM PUBLISHER]

Students ability to build correct knowledge relies on their understanding of concepts. Students must understand the concept well before applying it in real-life situations. With the advent of technology, teaching and learning quantum physics has been made easier and more effective in enhancing students' critical thinking and conceptual understanding. A multimedia-based learning approach is one way to enhance conceptual understanding. With the help of the multimedia application, this study aims to assess its impact on students' conceptual understanding of quantum physics at the University of Rwanda College of Education (UR-CE). The study adopted a quasi-experimental pre-test–post-test design with control and treatment group. Three hundred eighty-five undergraduate students in the UR-CE were purposively selected and allocated into the treatment group (193 students) and the control group (192 students). Control group students were taught eight quantum physics topics for six weeks using the traditional teaching approach, while treatment group students were taught the same topics using animations, PhET simulations, and YouTube videos. The study resulted in a very high statistically significant difference (p <.001) between teaching interventions provided after post-testing in favor of students who learned with multimedia (with a large effect size of 0.694). The use of multimedia resulted in a statistically significant increase in the student's conceptual understanding of quantum physics. The study's findings suggest that multimedia tools are effective for learning because they can enhance students' conceptual understanding of quantum physics. However, interactions between teachers and students or student-to-student are essential to facilitate conceptual learning and help the students gain a valuable understanding of their learning. [ABSTRACT FROM AUTHOR]

YBa2Cu3Ox (YBCO) thin films were deposited on 14°–22° tilted-axes NdGaO3 (NGO) substrates with pulsed laser deposition. Two orientations of the film are possible due to the presence of symmetrically equivalent (110) and (1 − 1 0) facets on the substrate surface. At high deposition rates, the pseudo-a grains, (100)YBCO||(110)NGO, gradually overgrow the pseudo-c grains, (001)YBCO||(110)NGO, forming high-tilted (tilt angle of the c axis 69°–74°) YBCO films. The substrate tilt angles in the vicinity of 18.43° promote formation of high-tilted films as a result of graphoepitaxial seeding of the pseudo-a grains on the (110) facets on the substrate surface due to the matching of the c lattice constant of the film with the length of the (110) terraces on the substrate surface. The effect of graphoepitaxial seeding was observed for the substrate tilt angles in the range 16°–21°, probably due to undulating edges of steps on the substrate surface. An increase of the deposition rate above a threshold level of ~ 3 nm/s results in a change of the growth mode with the formation of films with smooth surface morphology. The probable reason is a transition from vapor phase epitaxy to vapor–liquid–solid crystallization mechanism. The tilted-axes YBCO films demonstrate superconducting transition temperature superior to standard samples fabricated on (110) NGO substrates. The width of the superconducting transition for tilted-axes films increases due to the suppression of the critical current in the direction normal to the tilt axis. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

We investigate pulsed laser deposition of LaGaO3/SrTiO3 at 10-1 mbar oxygen background pressure, demonstrating the critical effect of the target-to-substrate distance, dTS, on the interface sheet resistance, Rs. The interface turns from insulating to metallic by progressively decreasing dTS. The analysis of the LaGaO3 plume evidences the important role of the plume propagation dynamics on the interface properties. These results demonstrate the growth of conducting interfaces at an oxygen pressure of 10-1 mbar, an experimental condition where a well-oxygenated heterostructures with a reduced content of oxygen defects is expected. [ABSTRACT FROM AUTHOR]