WFU Physics Colloquium

TITLE: “Computational Engineering of Thermoelectric Materials”
SPEAKER: Professor Kristian Berland
Centre for Materials Science and Nanotechnology,
University of Oslo
TIME:  Thursday, Feb. 8, 2018, at 4:00 PM
PLACE: George P. Williams, Jr. Lecture Hall, (Olin 101)

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

ABSTRACT

By converting heat to electricity and vice versa without the need for moving parts, thermoelectric modules have found many niche applications, such as in space exploration and mini-coolers. If even more progress is made on improving their conversion efficacy, they could also help recover some of the immense waste heat generated in power plants, transportation, and industrial processes. Based on examples from my own research, I will discuss how atomistic material modeling can aid the development of new and better thermoelectric materials. I will also illustrate how new methodologies can enhance the reliability of computational predictions on thermoelectric materials.

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WFU Physics Colloquium

TITLE: “Energy Policy and the EPA”
SPEAKER: Professor Stan Meiburg
Director, Graduate Studies in Sustainability
Wake Forest University

TIME: Wed. Jan. 31, 2018, at 4:00 PM
PLACE: George P. Williams, Jr. Lecture Hall, (Olin 101)

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

ABSTRACT

The mission of the U.S. Environmental Protection Agency has been inextricably bound up with the nation’s energy policy ever since the creation of the Agency in 1970. Controversies have flourished throughout this time, and while today’s debates have a different focus, EPA still finds itself in the middle of the action. Dr. Meiburg will review why this is so, give some examples of how past controversies resolved themselves, and suggest what to look for in the present debates.

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WFU Physics Colloquium

TITLE: “Effect of Crystal Packing on the Electronic Properties of Molecular Crystals”
SPEAKER: Professor Noa Marom
Department of Materials Science and Engineering,
Carnegie Mellon University,
Pittsburgh, PA

TIME: Wed. Dec. 6, 2017 at 4:00 PM
PLACE: George P. Williams, Jr. Lecture Hall, (Olin 101)

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

ABSTRACT

Molecular crystals have applications in nonlinear optics, organic electronics, and particularly in pharmaceuticals, as most drugs are marketed in the form of crystals of the pharmaceutically active ingredient. Molecular crystals are bound by dispersion (van der Waals) interactions, whose weak nature generates potential energy landscapes with many local minima that may be extremely close in energy. This often results in polymorphism, the crystallization of the same molecule in several different structures. Crystal structure may profoundly influence the physical and chemical properties, including the electronic and optical properties relevant for device applications.

We perform large scale quantum mechanical simulations to predict the structure of molecular crystals and investigate the effect of crystal packing on their electronic and optical properties. The massively parallel genetic algorithm (GA) package, GAtor, relies on the evolutionary principle of survival of the fittest to find low-energy crystal structures of a given molecule. Dispersion-inclusive density functional theory (DFT) is used for structural relaxation and accurate energy evaluations. Evolutionary niching is performed by using machine learning to perform clustering on the fly. The structure generation package, Genarris, performs fast screening of randomly generated structures with a Harris approximation, whereby the molecular crystal density is constructed by replicating the single molecule density, which is calculated only once. Many-body perturbation theory, within the GW approximation and the Bethe-Salpeter equation (BSE), is then employed to describe properties derived from charged and neutral excitations.

An emerging application of molecular crystals is singlet fission (SF), the down-conversion of one photogenerated singlet exciton into two triplet excitons. SF has the potential to significantly increase the efficiency of organic photovoltaics beyond the Shockley-Queisser limit by harvesting two charge carriers from one photon. However, the realization of SF-based solar cells is hindered by the dearth of suitable materials. We aim to discover new SF materials and optimize the crystal packing of known materials to enhance SF efficiency. We predict that crystalline quaterrylene and a lesser known monoclinic crystal structure of rubrene may exhibit high singlet fission efficiency, possibly rivaling that of the quintessential SF material, pentacene. Quaterrylene has the additional advantages of high stability, a narrow band gap, and a triplet energy in the optimal range to maximize photoconversion efficiency.

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WFU Physics Colloquium

TITLE: “Kinetic Luminosity of Quasar Outflows and its Implications to Galaxy Formation”

SPEAKER:Professor Nahum Arav
Department of Physics
Virginia Tech
Blacksburg, VA

TIME: Wed. Nov. 29, 2017 at 4:00 PM

PLACE: George P. Williams, Jr. Lecture Hall, (Olin 101)

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

ABSTRACT

Sub-relativistic mass-ejection outflows are seen as blue-shifted absorption troughs in the spectra of roughly one third of all quasars. I will describe recent results from observations with the Very Large
Telescope and the Hubble Space Telescope, that yield the mass flux and kinetic luminosity for the majority of these outflows. The derived values suggest that quasar absorption outflows have a profound effect on the formation of their host galaxy.

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WFU Physics Career Advising Event

SPEAKER: Jeremy W. Ward, Ph.D.

TIME: Tues. Nov. 28, 2017 at 12:00 – 1:00 PM

PLACE: Olin Lounge (Olin 106)

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

ABSTRACT

Dr. Jeremy W. Ward is currently a Research Scientist and Program Manager within the Materials and Manufacturing Directorate of the United States Air Force Research Laboratory (AFRL). He earned his B.A. in Physics and Mathematics from Simpson College in Indianola, IA, in 2010, and his Ph.D. in Physics from Wake Forest University in Winston-Salem, NC, in 2015. While earning both his B.A. and Ph.D., Jeremy also served as a crew chief for both F-16 and C-130 airframes in the United States Air National Guard. After completing his Ph.D., Jeremy then worked on staff within the United States Senate as a Science and Technology Policy Fellow, a position supported by the Materials Research Society (MRS) and the Minerals, Metals & Materials Society (TMS). In 2016, Jeremy accepted a position as a Research Scientist for UES, Inc. in Dayton, OH, where he performed research in the area of flexible and conformal electronics for the United States Air Force Research Laboratory (AFRL). In 2017, Jeremy accepted a position with AFRL, where he is leading both R&D of conformal sensing technologies as well as managing programs that address the materials and manufacturing challenges to meet the USAF needs in the area of Airmen Performance and Aeromedicine.

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WFU Physics Colloquium

TITLE: “What is fossilization? Casting new light (and electrons) on an old question”
SPEAKER: Professor Elizabeth Boatman
Department of Engineering,
Wake Forest University,
Winston-Salem, NC

TIME: Wed. Nov. 15, 2017 at 4:00 PM
PLACE: George P. Williams, Jr. Lecture Hall, (Olin 101)

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

ABSTRACT

Our accepted understanding of the structure-property relationships in bone tissue, and in particular, its intrinsic damage tolerance behavior and repair mechanisms, falls short. Yet, if our understanding as materials engineers could be improved, the result would be significant advances in structural materials engineered based on the mimicry of biological structural tissues (i.e., biomimicry). For many reasons, extinct species (especially dinosaurs) are an important source of data for such pursuits, despite the obvious problem: the bodies of extinct species typically persist only as fossilized skeletal elements. As it turns out, the process of validating the persistence of those specimens using advanced synchrotron light- and electron-based techniques is inherently rewriting our definition of “fossilization”, in addition to informing our understanding of the structure-property relationships in bone.

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WFU Physics Colloquium

TITLE: “Materials and Measurements for Printed and Flexible Electronics”
SPEAKER: Dean M. DeLongchamp
Leader, Polymers Processing Group
National Institute of Standards and Technology
Gaithersburg, MD 20899

TIME: Wed. Nov. 8, 2017 at 4:00 PM
PLACE: George P. Williams, Jr. Lecture Hall, (Olin 101)

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

ABSTRACT

Since the discovery of semiconducting organic molecules in the 70’s, they have enabled many new flexible electronics devices including transistors, solar cells, and displays. I will discuss the fundamentals of this technology and the important properties of materials that drive these exciting new applications. I will draw examples from the manufacturing of organic photovoltaics (OPV), a promising technology for low-cost solar cells. We have developed synchrotron-based X-ray scattering and a variety of benchtop spectroscopic methods to follow the structure evolution of these and other functional films as a printed ink dries. The measurements reveal the mechanisms by which the molecular design, formulation, and processing choices influence the nanoscale structure of the films.

The quest for structure-property relationships in OPV and other organic semiconductors has driven enormous advances in soft matter characterization over the past decade. Despite all the progress, surprisingly little consensus has been reached on what aspects of organic semiconductor film structure actually matter. Although order and orientation must matter, at what length scales are they relevant? I will discuss how a molecular-scale picture – the most difficult to obtain, particular in soft materials – may ultimately be required. We have recently made progress in developing new measurements that combine principles of spectroscopy, inelastic small-angle scattering, real-space imaging, and molecular simulation, which may at last provide a useful molecular scale structure measurement for soft materials and complex fluids.

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WFU Physics Meet the Speaker Event

SPEAKER: Dr. Yves Chabal
Department of Materials Science and Engineering,
University of Texas at Dallas,
Dallas, TX

TIME: Wed. Nov. 1, 2017, 12:00 – 1:00 PM

PLACE: Olin Lounge (Olin 106)

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

INFORMATION

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WFU Physics Colloquium

TITLE: “The fascinating world of Metal Organic Framework materials”
SPEAKER: Yves Chabal
Department of Materials Science and Engineering,
University of Texas at Dallas,
Dallas, TX

TIME: Wed. Nov. 1, 2017 at 4:00 PM
PLACE: George P. Williams, Jr. Lecture Hall, (Olin 101)

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

ABSTRACT

Metal Organic Frameworks (MOFs) are a new class of hybrid nanoporous materials that are attracting much interest due to their potential applications for gas storage and separation, pollutant sequestration including radioactive materials, sensing, biomedical devices, fuel production and more recently catalysis. They are crystalline, with metal centers at the corners of the unit cell connected by organic linkers, and are obtained by relatively straightforward synthesis methods (e.g. one-pot process). Consequently, a
large number of structures can be prepared, over 50,000 so far. With their well-defined crystalline structure (determined by X-ray diffraction), these materials are ideal to study fundamental processes, such as the interaction of small gases in nanopores, chemical functionalization of nanoporous networks
and potential catalytic activity. Recently, there has even been some effort to synthesize small metallic nanoparticles inside the pores of the network.

This talk will illustrate some of the fascinating behaviors and properties of MOFs by focusing on trapping small molecules into one of the best-characterized MOF structures (MOF-74), and on synthesizing directly 1nm-diameter Au nanoparticles inside the pores of a novel MOF structure (MOF-808). Along the way, it will also show how precise information can be derived from a host of spectroscopic (infrared, Raman, X-ray photoelectron spectroscopy, UV-vis, low-energy ion scattering) and imaging (TEM) measurements, in addition to the more conventional measurements (e.g. isotherms). The importance of
first-principles calculations will be highlighted as a means to extract quantitative information from IR spectroscopy and to gain fundamental understanding of important processes.

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WFU Physics Colloquium

TITLE: “Ions, Statistics, and simulations of macromolecules”
SPEAKER: Freddie Salsbury Jr.
Department of Physics,
Wake Forest University,
Winston-Salem, NC

TIME: Wed. Oct. 25, 2017 at 4:00 PM
PLACE: George P. Williams, Jr. Lecture Hall, (Olin 101)

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

ABSTRACT

Dr. Salsbury will present selected new strands of research in his group, which were enabled by his recent research sabbatical. These strands involve examining the effects of ion binding on the structure and dynamics of a therapeutic nucleic acid, and on the functions of different proteins such as thrombin and NEMO. These studies have also included applying and developing new clustering methods from statistics. If time permits, some simple applications of machine learning to these systems and more will be presented.

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