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122 results on '"Meldrum, Al"'

1. Momentum-resolved Electron Energy Loss Spectroscopy for Mapping the Photonic Density of States

Author

Shekhar, Prashant, Malac, Marek, Gaind, Vaibhav, Dalili, Neda, Meldrum, Al, and Jacob, Zubin

Subjects
Physics - Optics, Condensed Matter - Mesoscale and Nanoscale Physics
Abstract

Strong nanoscale light-matter interaction is often accompanied by ultra-confined photonic modes and large momentum polaritons existing far beyond the light cone. A direct probe of such phenomena is difficult due to the momentum mismatch of these modes with free space light however, fast electron probes can reveal the fundamental quantum and spatially dispersive behavior of these excitations. Here, we use momentum-resolved electron energy loss spectroscopy (q-EELS) in a transmission electron microscope to explore the optical response of plasmonic thin films including momentum transfer up to wavevectors (q) significantly exceeding the light line wave vector. We show close agreement between experimental q-EELS maps, theoretical simulations of fast electrons passing through thin films and the momentum-resolved photonic density of states (q-PDOS) dispersion. Although a direct link between q-EELS and the q-PDOS exists for an infinite medium, here we show fundamental differences between q-EELS measurements and the q-PDOS that must be taken into consideration for realistic finite structures with no translational invariance along the direction of electron motion. Our work paves the way for using q-EELS as the preeminent tool for mapping the q-PDOS of exotic phenomena with large momenta (high-q) such as hyperbolic polaritons and spatially-dispersive plasmons., Comment: 6 Pages, 4 Figures

Published
2017
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2. Conceptualization, Development and Validation of an Instrument for Investigating Elements of Undergraduate Physics Laboratory Learning Environments: The UPLLES (Undergraduate Physics Laboratory Learning Environment Survey)

Author

Thomas, Gregory P, Meldrum, Al, and Beamish, John

Abstract

First-year undergraduate physics laboratories are important physics learning environments. However, there is a lack of empirically informed literature regarding how students perceive their overall laboratory learning experiences. Recipe formats persist as the dominant form of instructional design in these sites, and these formats do not adequately support the development of students' inquiry processes. There may be valid reasons for the lack of research into students' views of their undergraduate physics laboratory learning environments, but work should be done to address these issues so that such research can occur. This paper describes the development and validation of a 23-item instrument, the UPLLES (Undergraduate Physics Laboratory Learning Environment Survey) that was undertaken as part of a multi-year project aimed to develop guided-inquiry oriented Physics laboratories for first-year students at the University of Alberta. The UPLLES was developed and validated through factor analysis using 476 student responses. The five sub-scales of the UPLLES are, Inquiry Orientation, Integration, Material Environment, Student Community, and Instructor Support. The value of the UPLLES within a battery of measures for evaluating reform efforts in undergraduate physics laboratories is discussed.

Published
2013

3. Students' Perceptions of Changes to the Learning Environments of Undergraduate Physics Laboratories

Author

Thomas, Gregory and Meldrum, Al

Abstract

Purpose: The purpose of this study was to explore students' perceptions to changes to the learning environment of their undergraduate physics laboratories, in which their scientific inquiry processes were stimulated. Design/methodology/approach: The activities students engaged in were redesigned to reflect a guided inquiry approach and to acknowledge modern-day advances in science and technology. Further, enhanced guidance was provided for laboratory instructors regarding the nature of scientific inquiry and how to structure students' inquiry experiences during laboratory sessions. Students' views were sought regarding their perceptions of the impact of the reforms on the laboratory learning environments, their thinking processes in those environments and their views regarding the reform's value and appropriateness. Findings: Analyses of quantitative and qualitative data suggested that students responded positively to the reforms implemented. Large effect sizes of between 0.70 and 1.20 suggested significant positive shifts in students' perceptions of dimensions of their laboratory learning environments. In interviews, students expressed that they had engaged in the cognitive processes of scientific inquiry and suggested that the reforms had stimulated such "inquiry" thinking. However, their perceptions of the value and appropriateness of such inquiry-oriented laboratory learning environments were mixed. Originality/value: Concerns persist in higher education in relation to the extent of students' inquiry processes in undergraduate physics laboratories. Reforms to both the activities that students engage in and to instructional strategies are necessary. Raising awareness of the views expressed by students might help inform future reforms that accommodate those views to further enhance similar reforms.

Published
2018
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8. Silicon-Based Light Sources

Author

Anopchenko, Aleksei, primary, Prokofiev, Alexei, additional, Yassievich, Irina, additional, Ossicini, Stefano, additional, Tsybeskov, Leonid, additional, Lockwood, David, additional, Saeed, Saba, additional, Gregorkiewicz, Tom, additional, Wojdak, Maciek, additional, Liu, Jifeng, additional, and Meldrum, Al, additional

Published
2013
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9. Effect of Ti on the optical properties of Ag nanocrystals in silica

Author

Magruder, R.H., III and Meldrum, Al

Subjects
Titanium compounds -- Optical properties, Silver compounds -- Optical properties, Silica -- Optical properties, Physics
Abstract

The effects of sequentially implanting Ti and Ag ions in silica are investigated. The results show that the incorporation of the Ti causes a shift in the wavelength of the surface-plasmon resonance of the Ag nanocrystals and a change in the magnitude of the surface-plasmon resonance absorption.

Published
2005

15. The influence of conjugated alkynyl(aryl) surface groups on the optical properties of silicon nanocrystals: photoluminescence through in-gap states

Author

Angı, Arzu, primary, Sinelnikov, Regina, additional, Heenen, Hendrik H, additional, Meldrum, Al, additional, Veinot, Jonathan G C, additional, Scheurer, Christoph, additional, Reuter, Karsten, additional, Ashkenazy, Or, additional, Azulay, Doron, additional, Balberg, Isaac, additional, Millo, Oded, additional, and Rieger, Bernhard, additional

Published
2018
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28. Silicon-Based Light Sources

Author

N Yassievich Irina, Anopchenko Aleksei, Wojdak Maciek, Liu Jifeng, Saeed Saba, J Lockwood David, Ossicini Stefano, Meldrum Al, Gregorkiewicz Tom, Prokofiev Alexei, and Tsybeskov Leonid

Subjects
Materials science, business.industry, Optoelectronics, business, Silicon nanostructures, silicon nanostructures, Silicon based
Published
2013

30. Ultrafast carrier dynamics in silicon nanocrystal films

Author

Titova, Lyubov V., Cocker, Tyler L., Wang, Xiongyao, Meldrum, Al, and Hegmann, Frank A.

Subjects
Filling fractions, Photoexcitation, Si nanocrystal, Silicon, Percolation (computer storage), Drude models, Thz spectroscopy, Percolation thresholds, Time-resolved, Ultrafast carrier dynamics, Percolation (fluids), Carrier localization, Photoexcited carriers, Nanocrystals, Time-scales, Optical waveguides, Interface defects, Silicon nanocrystals, Nanocrystal sizes, Interfaces (materials), Nanotechnology, Picosecond time scale, Time variations, Interface scattering, Optical emissions
Abstract

We have applied time-resolved THz spectroscopy to probe the transient photoexcited carrier dynamics and THz conductivity in Si nanocrystal films with varying silicon volume filling fractions and nanocrystal sizes on picosecond time scales. The THz conductivity reveals microscopic carrier motion with significant interface scattering within nanocrystals as well as percolative transport between nanocrystals. The time variation of the THz conductivity is analyzed within the framework of the Drude-Smith model, an extension of the Drude model that characterizes carrier localization in nanostructured materials. Below the percolation threshold, transport between nanocrystals is inhibited and photoexcited carriers are localized within individual nanocrystals. These films also exhibit efficient optical emission. In films with Si filling fractions above the percolation threshold, photoluminescence is suppressed and a transition from long-range inter-nanocrystal transport immediately after photoexcitation to increased carrier localization over a 50 ps time scale due to accumulation of charges at interface defect sites is observed., 2nd International Symposium on Nanoscale Luminescent Materials - 221st ECS Meeting, May 6-10, 2012, Seattle, WA, USA, Series: ECS Transactions

Published
2012

34. LASER-BASED SYNTHESIS, DIAGNOSTICS, AND CONTROL OF SINGLE-WALLED CARBON NANOTUBES AND NANOHORNS FOR COMPOSITES AND BIOLOGICAL NANOVECTORS

Author

GEOHEGAN, DAVID B., primary, PURETZKY, ALEX, additional, IVANOV, ILIA, additional, ERES, GYULA, additional, LIU, ZUQIN, additional, STYERS-BARNETT, DAVID, additional, HU, HUI, additional, ZHAO, BIN, additional, CUI, HONGTAO, additional, ROULEAU, CHRIS, additional, JESSE, STEPHEN, additional, BRITT, PHILLIP F., additional, CHRISTEN, HANS, additional, XIAO, KAI, additional, FLEMING, PAMELA, additional, and MELDRUM, AL, additional

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39. Ultrafast Terahertz Conductivity of Photoexcited Nanocrystalline Silicon

Author

Cooke, David, MacDonald, A. Nicole, Hryciw, Aaron, Meldrum, Al, Wang, Juan, Li, Q., Hegmann, Frank A., Cooke, David, MacDonald, A. Nicole, Hryciw, Aaron, Meldrum, Al, Wang, Juan, Li, Q., and Hegmann, Frank A.

Abstract

The ultrafast transient ac conductivity of nanocrystalline silicon films is investigated using time-resolved terahertz spectroscopy. While epitaxial silicon on sapphire exhibits a free carrier Drude response, silicon nanocrystals embedded in glass show a response that is best described by a classical Drude–Smith model, suitable for disorder-driven metal–insulator transitions. In this work, we explore the time evolution of the frequency dependent complex conductivity after optical injection of carriers on a picosecond time scale. Furthermore, we show the lifetime of photoconductivity in the silicon nanocrystal films is dominated by trapping at the Si/SiO2 interface states, occurring on a 1–100 ps time scale depending on particle size and hydrogen passivation

Published
2007

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