The Center for Nanoscale Materials holds a regular biweekly colloquium on alternate Wednesdays at 11:00 a.m. in Bldg. 440, Room A105/106. The goal of the series is to provide a forum for topical multidisciplinary talks in areas of interest to the CNM and also to offer a mechanism for fostering interactions with potential facility users.
- Xiao-Min Lin (Chair)
- Pierre Darancet
- Ralu Divan
- Xuedan Ma
- Elena Rozhkova
- Jianguo Wen
|Jan. 10, 2018||
"Electronic Excitations in the Condensed Phase", Tim Berkelbach, University of Chicago. Host: Pierre Darancet
I will present recent work developing predictive theories and ab initio computational techniques for the description of excited states in nanoscale and condensed-phase materials. First, I will describe a low-energy theory of band gaps and excitons in atomically-thin semiconductors, focusing on the transition-metal dichalcogenides. In particular, the theory is naturally adapted to include environmental effects, which are critically important for such atomically-thin materials. The presented approach can be viewed as a poor-man's GW+BSE, which is a successful suite of techniques for excitations in solids, but one which breaks down for more strongly correlated materials. To address this, I will describe the software development and applications of wavefunction-based quantum chemistry techniques for solid-state problems. In particularly the use of coupled-cluster theory for solids is demonstrated to provide an accurate description of satellite structure in the photoemission of metals, correlation-driven bandwidth narrowing, and high-accuracy band gaps in semiconductors. The formal relation to the GW approximation will be briefly discussed.
|Jan. 24, 2018||
"AWE-somes: All Water-Emulsion Bodies formed by Polelectrolytes at Interfaces", Kathleen J. Stebe, University of Pennsylvania, Host: Xiao-Min Lin
Interfaces between fluids are rich environments to trap materials and build films. Particles and molecules adsorb at interfaces to lower the interfacial energy, and so can be collected from bulk fluid phases to form interfaces covered with monolayer or multilayer structures. This system is an excellent platform for capsule formation. By placing droplets in an external phase, materials from either the dispersed or continuous phases can be incorporated into films. Judicious selection of these components can lead to highly versatile, tailored structures. We are developing encapsulation methods via interfacial complexation of polyelectrolytes and other charged species in all aqueous two phase systems to make multi-functional all water emulsion bodiesAWE-somes. Such capsules might be particularly interesting for sequestration of delicate components, including proteins and microbes, which should not be placed in contact with oils or hydrophobic media. Here we discuss the example of the PEG-Dextran-water system, which separates into PEG-rich and dextran-rich phases. The interfacial tension between the phases is quite low. Furthermore, many molecules, including polyelectrolytes, partition freely between the two phases. These factors make interfacial structure formation especially challenging. We develop strategies to build membranes from complementary polyelectrolytes in each phase by balancing their rates of transport to the interface. To impart additional functionality, we develop methods to include charged nanoparticles (NPs) in such membranes. Here, nanoparticles can be selected that preferentially partition into one of the phases, facilitating interfacial transport, and creating an osmotic imbalance that leads to spontaneous formation of encapsulated multiple emulsions. These AWE-somes, with internal structures reminiscent of membraneless organelles in cells, provide a rich platform for separation, partitioning, reaction, and transport, suggesting AWE-somes might be developed into capsules that mimic biological-cell functions, or protocell systems.
|Feb. 7, 2018||
"Quantum Dynamics of Confined Molecules", Pierre-Nicholas Roy, University of Waterloo, Host: Stephen Gray
Molecular assemblies are often described using classical concepts and simulated using Newtonian dynamics or Classical Monte Carlo methods. At low temperatures, this classical description fails to capture the nature of the dynamics of molecules, and a quantum description is required in order to explain and predict the outcome of experiments. In this context, the Feynman path integral formulation of quantum mechanics is a very powerful tool that is amenable to large-scale simulations. We will show how path integral simulations can be used to predict the properties of molecular rotors trapped in superfluid helium and hydrogen clusters. We will show that microscopic Andronikashvili experiments can be viewed as a measurement of superfluidity in a quantum mechanical frame of reference. We will also show that path integral ground state simulations can be used to predict the Raman spectra of parahydrogen clusters and solids. We will present ongoing work on the simulation of molecular rotors confined in endohedral fullerene materials such as H2O@C60. The questions we will address include symmetry breaking, spin conversion, the nature of dipole correlations and dielectric response, and entanglement measures.
|Feb. 21, 2018||
"Emerging Materials for Nanophotonics and Plasmonics", Alexandra Boltasseva, Purdue University, Host: Gary Wiederrecht
The fields of nanophotonics and plasmonics have taught us unprecedented ways to control the flow light at the nanometer scale, unfolding new optical phenomena and redefining centuries-old optical elements. As we continue to transfer the recent advances into applications, the development of new material platforms has become one of the centerpieces in the field of nanophotonics. In this presentation, I will discuss emerging material platforms including transparent conducting oxides, transition metal nitrides, oxides and carbides as well as two- and quasi-two-dimensional materials for future practical optical components across the fields of on-chip optics and optoelectronics, sensing, spectroscopy and energy conversion.
|Apr. 18, 2018||Nicholas A. Kotov, University of Michigan. Host: Gleiciani de Queiros Silveira|
|May 2, 2018||David S. Ginger, University of Washington, Host: Pierre Darancet|
|May 16, 2018||Gong Gu, University of Tennessee, Host: Lifen Wang|
|May 30, 2018||Yugang Sun, Temple University. Host: Gary Wiederrecht|
|Jun. 13, 2018||Mike Arnold, University of Wisconsin, Host: Nathan Guisinger|
|Jun. 27, 2018||James Alexander Liddle, National Institute of Standards and Technology (NIST), Host: Ralu Divan|
|Jul. 11, 2018|
|Jul. 25, 2018||Quanxi Jia, State University of New York (SUNY), Host: Liliana Stan|
|Aug. 8, 2018||Itai Cohens, Cornell University, Host: Xiao-Min Lin|
|Sep. 5, 2018||Dongling Ma, Institut National de la Recherche Scientifiue (INRS), Host: Gary Wiederrecht|
|Sep. 19, 2018|
|Oct. 3, 2018|
|Oct. 17, 2018||Stephan Lany, National Renewable Energy Laboratory (NREL), Host: Maria Chan|
|Oct. 31, 2018|
|Nov. 14, 2018||
Stephen G. Sligar, University of Illinois, Host: Elena Rozhkova
|Dec. 12, 2018||P. James Schuck, Columbia University, Host: Pierre Darancet|
|Jan. 16, 2019||Juejun Hu, Massachusetts Institute of Technology (MIT), Host: Peijun Guo|