46 research outputs found

    Electrochemically assembled quasi-periodic quantum dot arrays

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    doi: 10.1088/0957-4484/7/4/010We describe two electrochemical self- assembly processes for producing highly ordered quasi-periodic arrays of quantum dots on a surface. The advantages of these techniques are: (i) they are `gentle' and do not cause radiation damage to nanostructures unlike beam lithography, (ii) they have high throughput and are amenable to mass production unlike direct-write lithography, (iii) structures can be delineated on non- planar substrates, and (iv) the techniques are potentially orders of magnitude cheaper to implement than conventional nanosynthesis. Samples produced by these techniques have been characterized by microscopy, optical and transport measurements, Auger and x-ray. These measurements reveal intriguing properties of the nanostructures. In this paper, we describe our initial results and show the promise of such techniques for low-cost and high-yield nanosynthesis.This work was supported by the Department of Energy grant DE-FG02-90ER45427 administered by the Midwest Superconductivity Consortium (Nebraska, Notre Dame and Missouri), and by the US Army Research Office under grants DAAH04-95-1-0586 (Nebraska and Notre Dame) and DAAL03-92-G0381 and EPSCoR DAAL03-92- G0367 (Missouri). The work at Argonne was supported by the US Department of Energy under grant BESDMS-W-31-109-ENG-38

    High-pressure study of the Raman modes in YBa2(Cu0.96Ni0.04)4O8

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    URL:http://link.aps.org/doi/10.1103/PhysRevB.60.4363 DOI:10.1103/PhysRevB.60.4363We present a study of the Raman phonons in YBa2(Cu0.96Ni0.04)4O8 under hydrostatic pressure in the superconducting phase. A comparison with our earlier work on the undoped YBa2Cu4O8 shows that the pressure coefficients of two vibrational modes involving oxygen atoms differ significantly from those of the corresponding modes in the undoped material. These are the O(1) chain mode which shifts 33% faster and the O(2)-O(3) in-phase mode which shifts 23% slower than the undoped counterparts. The other Raman modes in the Ni-doped sample shift in a manner similar to the undoped material. The observed behavior of the O(1) chain and O(2)-O(3) in-phase modes in YBa2(Cu0.96Ni0.04)4O8 under pressure and the softening of the Cu(1) Ag mode frequency with increasing Ni doping suggest that the Ni atoms substitute for the Cu atoms in the chain, which in turn decreases the compressibility in the vicinity of the Cu(Ni) chain atom.This work was supported by U.S. Department of Energy Grant No. DE-FG02-90ER45427 through the Midwest Superconductivity Consortium. D.J.P. thanks the U.S. Department of Education for support through Grant No.P200A50259

    Examining Preservice Elementary Teachers’ Technology Self-Efficacy: Impact of Mobile Technology-Based Physics Curriculum

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    While iPads and other mobile devices are gaining popularity in educational settings, challenges associated with teachers’ use of technology continue to hold true. Preparing preservice teachers within teacher preparation programs to gain experience learning and teaching science using mobile technologies is critical for them to develop positive beliefs and self-efficacy for future technology integration. The purpose of this study was to investigate changes in preservice elementary teachers’ technology self-efficacy during their participation in a specialized science content course that utilized a mobile technology-based physics curriculum, Exploring Physics. The Exploring Physics curriculum is available as a hybrid online-offline application running on multiple platforms (iOS, Android, PC/Mac). Participants included 34 preservice elementary teachers who participated in preand post-implementation of a technology self-efficacy survey. Data sources also included two focus-group and individual interviews with six participants, weekly classroom observations, and artifacts. Results showed significant positive changes in participants’ technology self-efficacy regarding the use of mobile technologies in science teaching. Factors that supported participants’ technology self-efficacy included: (a) firsthand experiences with iPads, (b) enhanced science content understandings, (c) high interactivity and engagement, and (c) instructor modeling the use of technology. Findings have implications for preservice teacher preparation for technology integration in science teaching

    Towards a High Diffraction Efficiency of Photorefractive Multiple Quantum Wells

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    doi:10.1063/1.1994721 http://link.aip.org/link/?APCPCS/772/1579/1We propose a method to improve the diffraction efficiency of photorefractive multiple quantum well devices in the transverse-field geometry. Higher efficiencies have been achieved through systematic electrical modulation studies

    Impact of mobile technology‐based physics curriculum on preservice elementary teachers’ technology self‐efficacy

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    The growing popularity of mobile technologies in educational settings, from grade schools through college, has prompted science educators to prepare preservice teachers to successfully integrate technology into science teaching. This mixed‐methods study explores the effectiveness of a mobile technology‐based physics curriculum, Exploring Physics, on preservice elementary teachers’ technology self‐efficacy. Participants included 67 preservice elementary teachers enrolled in a specialized physics content course at a large public university in the United States. The experimental group (N = 34) used the Exploring Physics curriculum on iPads, and the comparison group (N = 33) used a hardcopy version of a similar curriculum. Data sources included a technology self‐efficacy survey administered as pre‐ and posttests, focus group and individual interviews with 24 participants at two time points, weekly classroom observations, and artifacts. Data analyses included repeated measures analysis of variance and posthoc t tests with Bonferroni adjustments and grounded theory techniques. The results showed significant positive changes in the experimental group participants’ technology self‐efficacy. In contrast, there was a significant decrease in the comparison group participants’ technology self‐efficacy. Several affordances of the curriculum assisted the experimental group participants in developing an appreciation for using mobile technologies in science teaching. Implications for preservice teacher preparation for technology integration in science teaching are discussed

    Pressure studies of impurity levels in AlxGa1-xAs

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    doi: 10.1088/0268-1242/4/4/033The authors present a study of the deep and shallow donor levels under hydrostatic pressure. The shallow levels follow the conduction bands, while the deep levels are strongly sublinear with pressure. The temperature dependence of the intensities and energies is used to obtain an energy level diagram of the deep levels at high pressures.This work was supported by theU S Army under grant number DAAL03-86K-0083, the US Department of Energy under grant number DE-AC02 84ER45048, and Amoco Corporation. M Chandrasekhar is a n A P Sloan Foundation Fellow

    Functional Imaging Using InGaAs/GaAs Photorefractive Multiple Quantum Wells

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    doi:10.1063/1.1994722 http://link.aip.org/link/?APCPCS/772/1581/1We propose the use of an InGaAs/GaAs photorefractive quantum well (PRQW) as an adaptive beam combiner for holographic optical coherence imaging applications. Holograms have been observed by using a diode laser and an interferometer. A weaker quantum confined exciton leads to the saturation of electroabsorption and hence diffraction, under a high external electric field, in the InGaAs PRQW. A careful choice of external electric field modulation seems to reduce this effect. We examine several characteristics that govern the use of an InGaAs PRQW in a functional imaging system

    Planarity of para Hexaphenyl

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    URL:http://link.aps.org/doi/10.1103/PhysRevLett.82.3625 DOI:10.1103/PhysRevLett.82.3625We present experimental and theoretical findings on the geometry of polycrystalline para hexaphenyl via Raman scattering. The planarity of the molecule is affected by hydrostatic pressure and temperature. Our studies indicate that the potential energy curve which governs the torsional motion between neighboring phenyl rings is “W” shaped. We determine the activation energy to promote the molecule from a nonplanar to a planar state to be 0.04 eV, in good agreement with our quantum chemical calculations. From the relative intensities of the 1280cm-1 to the 1220cm-1 Raman modes we show that high pressure planarizes the molecules, modifying the “W”-shaped potential energy curve to a “U”-shaped one.We acknowledge the financial support from U.S. Army Grant No. DAAL03-92-0381, University of Missouri Research Board and Österreichische Nationalbank (Project No. 6608)

    Learning Science With Mobile Technologies: Opportunities for Enhancing Preservice Elementary Teachers’ Science Conceptual Understanding

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    The use of technology is increasing rapidly in our society, and classroom teachers must recognize the impact and importance of technology in the lives of their students. It is crucial that college faculty involved in teacher training design courses that integrate mobile technologies to prepare the next generation of teachers. In this study, we investigate the effectiveness of an iPadbased curriculum app, Exploring Physics, to enhance preservice elementary teachers’ physics conceptual understanding in a physical science content course. Data were collected using a pre-and postPhysics Conceptual Understanding (PCU) survey and open-ended questionnaires. We found significant statistical gains in participants’ (N = 73) physics conceptual understanding at the end of the course. Qualitative findings suggest that the learning experience allowed participants to experience the pedagogical affordances of mobile technologies as learners and future teachers and found themselves to be more comfortable with the idea of integrating technology into their future classrooms. The results of this study provide insights into the importance of providing preservice teachers with opportunities to experience the use of mobile technologies in their teacher preparation programs

    Hydrostatic pressure dependence of the luminescence and Raman frequencies in polyfluorene

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    DOI: 10.1103/PhysRevB.68.115203 http://link.aps.org/doi/10.1103/PhysRevB.68.115203We present studies of the photoluminescence (PL), absorption, and Raman scattering spectra from poly[2,7-(9,9â€Č-bis(2-ethylhexyl))fluorene] under hydrostatic pressures of 0-100 kbar at room temperature. The well-defined PL and associated vibronics that are observed at atmospheric pressure change dramatically around 20 kbar in the bulk sample and at around 35 kbar for the thin-film sample. Beyond these pressures the PL emission from the backbone is swamped by strong peaks due to aggregates and keto defects in the 2.1-2.6 eV region. The Raman peaks shift to higher energies and exhibit unexpected antiresonance line shapes at higher pressures, indicating a strong electron-phonon interaction.S.G. acknowledges the donors of the American Chemical Society Petroleum Research Fund No. 38193-B7! for partial support of this research. U.S. thanks SONY International Europe, Stuttgart, and the Deutsche Forschungsgemeinschaft (DFG) for financial support
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