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Special Colloquium: Alan Drew, Oct 24, 2012.

Alan Drew
Queen Mary, University of London

Thursday, Oct. 24, 2012
102 JFB

Refreshments: 3:30 pm in 219 JFB
Lecture 4:15pm (102 JFB)

Title: Local Probe Investigation of Spin & Charge Dynamics in Organic Semiconductors


Organic semiconductors fall into a class of materials that shows significant potential for future applications and as a result, the field is becoming extremely topical. This is due to their ease of processing, low cost, highly tuneable electronic properties, favorable mechanical properties and long spin coherence times. The latter point makes them extremely promising for future spintronic applications. However, there is a lack of suitable techniques that can yield information on intrinsic spin and charge carrier dynamics in organic materials. For example, many of the experimental techniques available that probe the spin polarization of charge carriers in inorganic spintronic devices/materials are not always applicable to organic materials. Muon spectroscopy is a technique that has rarely been applied to study spintronic problems in inorganic systems, yet is ideally suited to studying them in organic semiconductors.

Low energy muon spin rotation can directly measure the depth resolved spin polarization of charge carriers in organic spin injection devices [1]. After giving a brief introduction to muon spin rotation in the context of these results, I will go on to demonstrate that it is possible to separate out the various contributions to spin decoherence in organic spin valves, differentiating between interface and bulk spacer layer effects [2].

A more exotic application of the muon technique, known as avoided level crossing (ALC) spectroscopy, can be used to probe the spin dynamics in organic semiconductors on a molecular lengthscale [3,4]. After briefly introducing this application of muons, I will go on to present measurements of temperature dependent electron spin relaxation rates, on a series of organic molecules of different morphology and molecular structure. These measurements, when combined with some of the latest results on the mass-dependence of electron spin relaxation rates, offer clues as to the underlying relaxation mechanism in organic semiconductors [4,5].

Finally, taking advantage of the intrinsic spatial sensitive of ALC spectroscopy, I will show how laser excited ALC spectroscopy (a technique I am currently developing) can offer unique insight into electron transfer in organic molecules. Not only is this an important process in organic electronics/spintronics, it also is fundamental to many biological processes, including photosynthesis, DNA repair and cell respiration.

[1] A. J. Drew et al., Nature Materials 8, 109 (2009)
[2] L. Schulz et al., Nature Materials 10, 39 (2011)
[3] A. J. Drew et al., Phys. Rev. Lett. 100, 116601 (2008)
[4] L. Schulz et al., Phys. Rev. B 84, 085209 (2011)
[5] L. Nuccio et al., submitted.


Astronomy Week

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Monday & Tuesday (Oct 15 & 16): Telescopes in the Park at Liberty Park, 11:00 am - 3:00 pm

Join the University of Utah Astronomy Outreach Group to view the Sun through specialized telescopes! Learn more...

Wednesday, October 17: Star Party, 8:30 pm - 11:30 pm

Let our observatory guides take you on a tour of the night sky! Learn more...

Thursday & Friday (Oct. 18-19) Astronomy Activities at the Natural History Museum of Utah, 12:00 pm - 4:00 pm

Come explore astronomy through hands-on activities and demonstrations! Look through telescopes and meet a "Dark Ranger" from Bryce Canyon National Park! Learn more...

Saturday October 20: Astrofest at Clark Planetarium 1:00 pm - 4:00 pm

Learn more about telescopes and how astronomers make discoveries with a variety of presentations and activities! Learn more...


Monica Allen Thesis Defense 10/15/12

Thesis Defense

Monica Allen

Monday, October 15, 2012
12:00pm (110 INSCC)

Title: Ultra High Energy Cosmic Ray Energy Spectrum and Composition using Hybrid Analysis with Telescope Array


Cosmic radiation was discovered in 1912. This year, the 100th anniversary of the discovery, marks not only the major progress that has been made in understanding these particles, but also the remaining questions about them. Questions about their sources, acceleration mechanisms, propagation and composition are still unanswered. There are only two experiments currently running which have the ability to study cosmic rays in the Ultra High Energy (E > 1018 eV) regime.

The Telescope Array studies Ultra High Energy Cosmic Rays (UHECRs) using a hybrid detector. Fluorescence telescopes measure the longitudinal development of the extensive air shower generated by a primary cosmic ray particle, while scintillator detectors measure the lateral distribution of secondary particles that hit the ground. The Middle Drum (MD) fluorescence telescope consists of 14 refurbished telescopes from the High Resolution Fly's Eye (HiRes) experiment, providing a direct link back to the HiRes experiment and data. The surface array is comprised of 507 Scintillator Detectors (SD) of a similar design as was used by the Akeno Giant Air Shower Array

(AGASA), providing a link to that experiment as well. Using events observed by both types of detectors improves the geometrical reconstruction of the showers significantly. This provides a more accurate reconstruction of the energy of the primary particle and makes it possible to make a measurement of the cosmic ray chemical composition. The spectral and composition measurements made by this hybrid detector will be presented.


This Week's Colloquium: John Krizmanic, Oct. 18, 2012

John Krizmanic

Thursday, Oct. 18, 2012
102 JFB

Refreshments: 3:30 pm in 219 JFB
Lecture 4:00pm (102 JFB)

Title: Phase Fresnel Lens Development for X-ray & Gamma-Ray Astronomy


Angular resolution and effective area are two key parameters that define the performance of a telescope. Historically, X-ray and gamma-ray telescopes have not achieved the angular resolution and flux sensitivity possible at longer wavelengths due to the difficulty in collecting and focusing high-energy photons. Currently, the best imaging ability in the X-ray band is given by the Chandra telescope, which has achieved sub-arcsecond imaging below 10 keV. The use of diffractive optics, especially Phase Fresnel Lenses (PFLs), offers a path to significantly improved high-energy performance. In principle, PFLs can achieve diffraction-limited angular resolution, which is orders of magnitude better than the current state-of-the-art, with high throughput at X-ray and gamma-ray energies, and the capability of scaling to meter-size dimensions. Micro-arcsecond angular resolution in the X-ray and gamma-ray band is achievable, which would allow for the direct imaging of the event horizon surrounding Black Holes. We have successfully fabricated PFLs in silicon using Micro-Electro-Mechanical-System (MEMS) fabrication techniques and measured near diffraction-limited performance at X-ray energies at the GSFC 600-meter Interferometry Testbed. The results demonstrate the superior imaging potential in the X-ray/gamma-ray energy band for PFL-based optics in a format that is scalable for astronomical applications.

In this talk I will discuss the astronomical motivation for improving in X-ray and gamma-ray imaging performance, the physics principles behind diffractive optics, our fabrication and characterization of PFLs, and describe potential space-based telescopes employing these optics.


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