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Seminars

Spring 2017 Seminars

DateTitleAuthor
January 16, 2017<MLK day>
January 23, 2017

Exciton Dynamics and Optical Properties of Single Semiconductor Carbon Nanotubes and Nanotube Bundles

Andrei Piryatinski
January 30, 2017Diagnostic Imaging Physicists in the 21st Century: Ongoing Challenges and Future DevelopmentsRyan Bosca
February 3, 2017From Self-Assembly to Electrokinetics: Novel Predictive Capabilities for Dielectric EffectsErik Luijten
February 6, 2017TBA
Amit Sachan
February 13, 2017TBAEmmanuel Mbamala

February 20, 2017

<Presidents Day>
February 24, 2017<Special Day>TBAGerald Schneider
February 27, 2017
March 6, 2017
March 13, 2017<Spring Break, and APS March Meeting>
March 20, 2017Darrel Strobel
Harald Korb and Darrel Strobel
March 23, 2017Out-of-the-Box Solutions for Silicon Growth ProblemsHarald Korb
March 27, 2017

Electronic and optical properties of monolayer and few-layer black phosphorus: A DFT Perspective

Deniz Çakır

April 3, 2017
April 5, 2017TBAErik Mazur
April 10, 2017
April 17, 2017<Holiday>

April 24, 2017

May 1, 2017
May 8, 2017<Exam Week!>

 

 

The Atmosphere of Pluto: Results from the New Horizons Mission

Darrell F. Strobel

Johns Hopkins University
+ ALICE (Leslie Young, Josh Kammer, Andrew Steffl et al.)
&REX (Dave Hinson et al.)Teams
and Xun Zhu, Johns Hopkins Applied Physics Laboratory

 

Tuesday March 21, 3:3-4:30pm, Refreshments at 3:00.

227 South Engineering

 
Abstract:
On 14 July 2015, NASA’s New Horizons spacecraft observed an ultraviolet solar occultation of Pluto's atmosphere with its ALICE ultraviolet spectrograph and performed a radio occultation that sounded Pluto's atmosphere down to the surface with radio signals transmitted simultaneously by four antennas of the NASA Deep Space Network, each radiating 20 kW at a wavelength of 4.2 cm. From the solar occultation data we derive line-of-sight (los) optical depths that yield los column densities for 5 molecular species, and extinction coefficients for haze. The radio occultation data yield N2 number density, pressure, and temperature profiles from the surface to about 110 km of altitude at two diametric points on the planet. We find a very stable, spherically symmetry, lower atmosphere, with well-mixed portion restricted to a planetary boundary layer (surface to 5 km), peak temperature of ~ 106 K at ~ 25km, cold isothermal temperature ~ 68 K in Pluto’s upper atmosphere, and inferred CH4 surface mixing ratio ~ 0.3±0.02%. The inferred enhanced Jeans escape rates are 5±2 x 1022 N2 s-1 and 6.4±1.6 x 1025 CH4 s-1 at the exobase (r ~ 2900 km, where the Kn = 0.7). 

Semiconductor single-walled carbon nanotubes (CNTs) are near-perfect 1D materials with great potential for applications in opto-electronic and photonic devices. Their unique optical properties are determined by highly mobile interacting excitons. Motivated by experiment, we examine competition between exciton diffusion dynamics and their local interactions resulting in the exciton-exciton annihilation. [1] Our model explains experimentally observed dependence of the exciton emission profile on the intensity of the optical pump and further allows for the interpret of the photon counting statistics probed by measuring the 2 nd order photon number correlation function.

We also examine the effect of exciton states modulation by external periodic potential due to the acoustic wave propagating along CNT substrate, [2] and demonstrate that the potential induces Floquet sub-bands separated by dynamical gaps in the single particle spectrum. This leads to
redistribution of the exciton oscillator strength and subsequent fluorescence quenching. Finally, motivated by experimental studies, we examine spectral signatures of interacting intratube and intertube exciton states formed in bundles of CNTs. For this purpose, an exciton scattering model is developed. Considering optimized geometry hexagonal lattice CNT bundle, we identified the sites participating in the formation of the intertube excitons. These sites are treated as an interacting “impurity centers” giving rise to the delocalized intratube exciton scattering. Modeling of the Raman resonance excitation profiles in (6,5) CNTs demonstrates an appearance of a sharp feature at the red shoulder of the spectrum that has been observed experimentally. The model-based analysis confirms that the feature is due to the weakly coupled interband exciton states.

References:
[1] X. Ma, O.Roslyak, J. G. Duque, S. K. Doorn, A. Piryatinski, D. H. Dunlap, and H. Htoon. Influences of Exciton Diffusion and Exciton-Exciton Annihilation on Photon Emission Statistics of Carbon Nanotubes, Phys. Rev. Lett. 115 017401 (2015).
[2] O. Roslyak and A. Piryatinski. Effect of periodic potential on exciton states in semiconductor carbon nanotubes. Chem. Phys. 481 177 (2016).

This is a special award double seminar.

Presentation of Awards by Dean Wood, followed by

The New Horizons Mission to Pluto

Darrell F. Strobel

Johns Hopkins University

Abstract: On 19 January 2006, NASA launched its first mission to Pluto the ninth planet. Called New HorizonsMission, its spacecraft is only the size of a grand piano and operated on just 200 Watts of power. Atlaunch it was one of the fastest spacecraft to leave the Earth and made the trip to Pluto in a mere 9 ½years. In this talk I will discuss the early history of the mission, the launch, the planning of missionoperations and the remarkable scientific return from this largest known Kuiper-belt object during the 14July 2015 flyby. At the end of the talk I will be open to discuss: the ninth planet at launch and a dwarfplanet at arrival and more than a frozen water ice ball. New Horizons will study Kuiper Belt object2014 MU69 during a flyby on 1 January 2019.

Followed by the second talk:

From Wheat Fields to Watt FieldsLinks in the Silicon Food Chain

Harold Korb

Korb Consulting, LLC

Abstract: The phenomenal advances in electronics in the past 70 years since the invention of the transistor havebeen driven by the exquisite understanding of the basic physics of semiconductors and semiconductor devices and by the creativity and investment in new technology in the semiconductor device industry.Less publicized is the role played by the availability of silicon wafers engineered and optimized toenable the economical fabrication of all silicon-based devices. For the first 25 years of this era, theemphasis was on making defect-free silicon with electronic (chemical) properties tailored to eachapplication. Since then, it has become essential to create families of defects in the silicon and toengineer the defect properties for each application. I will describe the physics and engineeringinvolved in creating and controlling these families of defects.

Out-of-the-Box Solutions to Silicon Crystal Growth Problems

Harald Korb

Korb Consulting, LLC.

 

Thursday March 23, 3:30-4:30pm, Refreshments at 3:00.

271 Batcheller Technology Center

The Czochralski process for growing silicon crystals is capable of producing high quality crystals at high yield and reasonable cost. The expectation is that every wafer produced from those crystals will be free from measurable defects, and the manufacturing process will be error-free. If straightforward engineering changes can't provide solutions to quality problems, a more basic attack may help. I will describe three problems that benefitted from a different angle of attack: a) The creation of a method to pump liquid silicon using electromagnetic means; b) The identification of the mechanism by which small spherical bubbles can be grown into a silicon crystal, and c) (if time permits) The determination of the conditions under which electrical breakdown (arcing) in Ar should occur at high temperature and low pressure.

From Self-Assembly to Electrokinetics: Novel Predictive Capabilities for Dielectric Effects

Erik Luijten

Professor of Material Science and Engineering
Northwestern University

 

Friday February 3, 3:00-4:00pm, Refreshments at 2:30.

271 Batcheller Technology Center <NOTE THE DIFFERENT ROOM>

 

The ability of matter to self-organize in complex dynamic structures is increasingly used to generate new, active materials. Progress in this field critically depends on the predictive capabilities of reliable and efficient computer simulation strategies. Here, I will introduce new, computational methodologies for dielectric effects, and demonstrate that these methods make it possible to perform dynamic simulations that fully incorporate self-consistently calculated polarization charges. Notably, I will discuss how the impact of these developments ranges from the prediction and control of colloidal and nanoscale self-assembly and aggregation to the understanding of dynamical properties of self-propelled particles that form the basic building blocks of active matter. I will also show how these ideas have the potential to find application in the understanding of supercapacitors and other energy-related problems.

Diagnostic Imaging Physicists in the 21st Century: Ongoing Challenges and Future Developments

Dr. Ryan Bosca

Radiological Physicist
Sanford Health

 

Monday January 30, 3:00-4:00pm, Refreshments at 2:30.

221 South Engineering

Diagnostic imaging has a rich history rooted in Röntgen’s discovery of x-rays and the first radiographs taken over 120 years ago. Since that time, (medical) physicists have been heavily involved in the development of new imaging modalities and techniques, equipment performance evaluations, and operator education for the safe use of such equipment. Technological advancements, especially the development of computers, have resulted in the widespread use of imaging modalities such as computed tomography, positron emission tomography, digital radiography, and magnetic resonance imaging, to name a few. Continued developments from equipment manufacturers, professional organizations, and academic researchers require careful evaluation and implementation by clinical medical physicists. This presentation will briefly outline some of the physical principles used in safely acquiring medical images and summarize research opportunities in the Department of Imaging Physics at Sanford Health in Fargo.

 


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