Tevian Dray, PhD
Department of Mathematics
Oregon State University
George P. Williams, Jr. Lecture Hall, (Olin 101)
Wednesday, March 20, 2019, at 4:00 PM


There will be a reception with refreshments at 3:30 PM in the lounge. All interested persons are cordially invited to attend.


ABSTRACT

Calculus as taught by mathematicians typically involves a large toolbox of algebraic manipulations. Almost all computations are done using rectangular coordinates and, later, the associated standard basis of unit vectors. Vector calculus as used by physicists, on the other hand, typically involves geometric reasoning, and the frequent use of coordinates and basis vectors adapted to the symmetries that are present. Thermodynamics goes even further, fundamentally altering the notion of “standard coordinates.” These treatments are sufficiently different from each other that they constitute different languages; students are often unable to translate.

Our research group at Oregon State University has been working to bridge this gap between mathematics and physics for more than two decades, primarily by restructuring upper-division physics courses, but also by developing materials for second-year calculus that emphasize geometric reasoning. The Paradigms in Physics project, continuously supported since 1997 by the NSF, has evolved from “merely” designing novel curricula to studying student learning of mathematical concepts such as partial derivatives.

This talk describes several examples of these language differences, the curricular materials we have developed to help students bridge this gap (including an online textbook and a website featuring more than 300 classroom activities), and some of the education research in which our materials are grounded.

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Steven Erwin, PhD,
Head of the Center for Materials Physics and Technology at The Naval Research Laboratory
George P. Williams, Jr. Lecture Hall, (Olin 101)
Wednesday, February 27, 2019, at 4:00 PM


There will be a reception with refreshments at 3:30 PM in the lounge. All interested persons are cordially invited to attend.


ABSTRACT

The mechanisms which control the growth of nanocrystals are difficult to investigate because nanocrystals occupy a position awkwardly intermediate between molecules and solids. Two case studies highlight these difficulties and their solution.

(1) Cation exchange is a chemical reaction in which all the cations of a material are replaced by different cations, thus creating a new material. In semiconductor nanocrystals, cation exchange happens extremely fast – many orders of magnitude faster than for macroscopic crystals and far faster than simple size-scaling would suggest. I propose a theoretical mechanism for cation exchange in nanocrystals that reveals a surprising consequence of Coulomb interactions acting at nanometer length scales.

(2) Semiconductor nanostructures take a wide variety of physical forms. One of the most active areas of this research focuses on semiconductor “nanoplatelets,” the name given to nanostructures that are very thin and very wide. An early question asked by researchers was, what causes materials to form these very thin shapes in the first place? The question is even more puzzling when you learn that even materials with an underlying isotropic crystal structure form these extremely asymmetrical shapes. I will propose an explanation of this “kinetic instability” in the growth and show how this theory can be be used by researchers to create new families of nanoplatelet materials.

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Thomas Anthopoulos, PhD,
Professor of Material Science and Engineering at King Abdullah University of Science and Technology
George P. Williams, Jr. Lecture Hall, (Olin 101)
Wednesday, February 20, 2019, at 4:00 PM


There will be a reception with refreshments at 3:30 PM in the lounge. All interested persons are cordially invited to attend.


ABSTRACT

In traditional optoelectronics the ability to downscale critical device dimensions has proven extremely successful over the past sixty years in increasing their functionality and performance. These extraordinary developments have been achieved through a virtuous circle of scientific and engineering breakthroughs which have led to the proliferation of information & communication technologies with an extraordinary impact on our daily life and society. However, adopting established manufacturing methods to emerging technologies such as printed optoelectronics, has proven challenging both in terms of technology and economics. This talk will focus on progress being made downscaling emerging forms of large-area optoelectronics through a new fabrication paradigm and their application in a variety of functional devices including, light-emitting nanogap diodes, photo-detectors and rectifying diodes.

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Peijun Guo, PhD,
Named Fellowship-Enrico Fermi, Argonne National Laboratory
George P. Williams, Jr. Lecture Hall, (Olin 101)
Wednesday, February 13, 2019, at 4:00 PM


There will be a reception with refreshments at 3:30 PM in the lounge. All interested persons are cordially invited to attend.


ABSTRACT

The need for exquisite control of light is ubiquitous in energy-relevant applications, optoelectronics, and information science. In this talk, I will discuss how hybrid materials consisting of distinct sub-lattices and periodically nanostructured materials allow for dramatically enhanced light absorption, emission, and charge carrier generation at various time- and length-scales. I will first focus on hybrid organic-inorganic perovskites. These solution-processed, scalable materials exhibit remarkable optoelectronic properties such as strong light absorption, defect tolerance, and long carrier lifetimes. I will describe how electronic excitations in these materials are coupled to and influenced by the vibrational degrees of freedom of the organic and inorganic sublattices, investigated using an array of optical spectroscopic techniques. The unique soft nature of the lead-halide octahedral framework gives rise to dynamic fluctuations in the electronic bandgap, which distinguishes hybrid perovskites from traditional inorganic semiconductors. Furthermore, strong quantum confinement can be easily imparted to hybrid perovskites with the use of organic spacer-cations, leading to hyperbolic dispersion relation and enhanced light-emitting properties. Beyond solution-processed semiconductors, I will demonstrate how widely-used materials, such as indium-tin-oxide (ITO), can be grown in ordered, nanoscale array form by chemical vapor phase epitaxy to exhibit well-defined localized surface plasmon resonances in the infrared spectral range. The unique band structure and carrier concentration of ITO result in an unusual type of optical nonlinearity that is significantly larger and faster than the noble metal counterparts. I will conclude by discussing how such material platforms open new avenues for infrared molecular sensing, ultrafast optical switching and active photonic devices.

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WFU Physics Career Advising Event

SPEAKER:  Dr. Charles W. Miller, Consultant in Nuclear and Radiological Environmental Health

TIME: Wednesday, March 6, 2019, from 12:00 – 1:00 PM

PLACE: Olin Physical Laboratory, Lounge


Lunch will be provided. All interested persons are cordially invited to attend.


Dr. Miller is retired from the Centers for Disease Control (CDC) where he was the Chief of the Radiation Studies Branch, Division of Environmental Hazards and Health Effects, National Center for Environmental Health.  He also worked for the Office of Environmental Safety, Illinois Department of Nuclear Safety and the Health and Safety Research Division, Oak Ridge National Laboratory (ORNL), to name a few.

Dr. Miller’s primary area of expertise is centered on the transport and dose assessment of radionuclides released to the atmosphere, as well as other facets of environmental radiological dose assessment.

Dr. Miller will be happy to answer questions regarding his career path, and what let him to it.

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Charles W. Miller, PhD,
Consultant in Nuclear and Radiological Environmental Health
George P. Williams, Jr. Lecture Hall, (Olin 101)
Wednesday, March 6, 2019, at 4:00 PM


There will be a reception with refreshments at 3:30 PM in the lounge. All interested persons are cordially invited to attend.


ABSTRACT

Many people believe that the detonation of an Improvised Nuclear Device (IND) will automatically result in massive death and destruction.  Such an event will almost certainly result in many deaths, but many other people will survive IF they know what to do to protect themselves.  The key message is to “Go in, stay in, and tune in” (see https://emergency.cdc.gov/radiation/). The purpose of this presentation is to explain what an IND is, how it works, what its impact will be, and how, because some of the effects of an IND decreases with time, people can survive the initial impact if they act quickly and appropriately.  This presentation will also discuss the role that scientifically literate citizens can have in helping to educate their family members, friends, and neighbors on these important concepts.

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Zijie Yan, PhD,
Chemical & Biomolecular Engineering, Clarkson University
George P. Williams, Jr. Lecture Hall, (Olin 101)
Wednesday, February 6, 2019, at 4:00 PM


There will be a reception with refreshments at 3:30 PM in the lounge. All interested persons are cordially invited to attend.


ABSTRACT

The ability to reconfigure nanoscale building blocks into different architectures, as if they were Lego pieces, has enormous potential for nanoscience. The development of colloidal synthesis has largely increased the availability of nanocrystals with well-controlled sizes and shapes. Bottom-up assembly of these nanoscale building blocks opens the prospect of creating novel artificial materials and systems with unusual properties and functionalities. However, it is still a great challenge to achieve precise, controlled, and reconfigurable assembly of nanomaterials. This seminar will introduce an optical approach to address this fundamental challenge in nanoscience. My research group exploits light-driven self-organization to create artificial nanomaterials. Shaped optical fields are created by modulating the intensity, phase, and polarization of laser beams in space and time. Self-organization arises from electrodynamic interactions among strongly scattering plasmonic nanoparticles, leading to a new type of material: reconfigurable optical matter with nanoparticle superlattices. New science has emerged in these artificial materials, for example, negative optical torque in optical matter arrays, and the developed optical methods will lead to more research opportunities and applications in microfluidics, microrheology, optical physics, and cell biology.

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Dr. Ajay Ram Srimath Kandada,
Marie Sklodowska Curie Fellow (Global)
Georgia Institute of Technology,
George P. Williams, Jr. Lecture Hall, (Olin 101)
Wednesday, January 16, 2019, at 4:00 PM


There will be a reception with refreshments at 3:30 PM in the lounge. All interested persons are cordially invited to attend.


ABSTRACT

Excitonic interactions in 2D semiconductors garner considerable attention, both due to their relevance in quantum opto-electronics and to the richness of their physics. Quantum-well like derivatives of organic-inorganic perovskites are emerging material systems where strongly bound two-dimensional excitons have been observed even at room temperature.1 These hybrid semiconductors feature complex lattice dynamics due to the ‘softness’ arising from non-covalent bonds between molecular moieties and the inorganic network and due to the ionic character of the crystal.2 I will discuss the profound and unique consequences of such dynamic structural complexity on the fundamental character of primary photo-excitations. I will present evidences of polaronic effects3 and multi-body correlations,2 both of which are strongly affected by the lattice dynamics, based on various ultrafast optical spectroscopies. Going beyond the conventional ultrafast optical tools, I will also discuss a new proposal to use entangled photon-pairs as probe of correlations in matter.

 

(1)       Neutzner, S.; Thouin, F.; Cortecchia, D.; Petrozza, A.; Silva, C.; Kandada, A. R. S. Exciton-Polaron Spectral Structures in Two Dimensional Hybrid Lead-Halide Perovskites. Phys. Rev. Mater. 2018, 2, 064605.

(2)       Thouin, F.; Neutzner, S.; Cortecchia, D.; Dragomir, V. A.; Soci, C.; Salim, T.; Lam, Y. M.; Leonelli, R.; Petrozza, A.; Kandada, A. R. S.; et al. Stable Biexcitons in Two-Dimensional Metal-Halide Perovskites with Strong Dynamic Lattice Disorder. Phys. Rev. Mater. 2018, 2, 034001.

(3)       Thouin, F.; Chávez, D. A. V.; Quarti, C.; Cortecchia, D.; Bargigia, I.; Beljonne, D.; Petrozza, A.; Silva, C.; Kandada, A. R. S. Phonon Coherences Reveal the Polaronic Character of Excitons in Two-Dimensional Lead-Halide Perovskites. Nat. Mater. 2018, in press.

 

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Dr. Ilaria Bargigia,
Georgia Institute of Technology
George P. Williams, Jr. Lecture Hall, (Olin 101)
Thursday, January 17, 2019, at 2:00 PM


There will be a reception with refreshments at 1:30 PM in the lounge. All interested persons are cordially invited to attend.


ABSTRACT

Conjugated polymers are widely used as bio-electronic interfaces thanks to their inherent softness, biocompatibility, electronic properties, and unparalleled versatility. In particular, thin films of poly(3-exylthiophene) have demonstrated the capability to restore light sensitivity in animal models and are now being proposed as artificial retinal implants. However, there is no clear understanding of the mechanism behind light-induced activation of cellular activity mediated by the photophysical characteristics of the conjugated polymers. In particular, there is a need to address how structural properties control the various functionalities and the role played by the interface between the polymer and biological media. In this talk, I will present our recent efforts made towards the understanding of how photo-physical properties transform in the presence of relevant biological media and what these transformations entail in the context of in-vivo biological applications.

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