Dec. 12, 2018

11:00 a.m.

Bldg. 402 GALLERY

Atomic Origami:  A Technology Platform for Nanoscale Machines, Sensors, and Robots,  Itai Cohens, Cornell University, Host: Xiao-Min Lin

What would we be able to do if we could build cell-scale machines that sense, interact, and control their micro environment? Can we develop a Moore’s law for machines and robots? In Richard Feynman’s classic talk ​“There’s Plenty of Room at the Bottom” he foretold of the coming revolution in the miniaturization of electronics components. This vision is largely being achieved and pushed to its ultimate limit as Moore’s Law comes to an end. In this same lecture, Feynman also points to the possibilities that would be opened by the miniaturization of machines. This vision, while far from being realized, is equally as tantalizing. For example, even achieving miniaturization to micron length scales would open the door to machines that can interface with biological organisms through biochemical interactions, as well as machines that self-organize into superstructures with mechanical, optical, and wetting properties that can be altered in real time. If these machines can be interfaced with electronics, then at the 10’s of micron scale alone, semiconductor devices are small enough that we could put the computational power of the spaceship Voyager onto a machine that could be injected into the body. Such robots could have on board detectors, power sources, and processors that enable them to make decisions based on their local environment allowing them to be completely untethered from the outside world​.In this talk I will describe the work our collaboration is doing to develop a new platform for the construction of micron sized origami machines that change shape in fractions of a second in response to environmental stimuli. The enabling technologies behind our machines are graphene-glass and graphene-platinum bimorphs. These ultra-thin bimorphs bend to micron radii of curvature in response to small strain differentials. By patterning thick rigid panels on top of bimorphs, we localize bending to the unpatterned regions to produce folds. Using panels and bimorphs, we can scale down existing origami patterns to produce a wide range of machines. These machines can sense their environments, respond, and perform useful functions on time and length scales comparable to microscale biological organisms. With the incorporation of electronic, photonic, and chemical payloads, these basic elements will become a powerful platform for robotics at the micron scale.  As such, I will close by offering a few forward looking proposals to use these machines as basic programmable elements for the assembly of multifunctional materials and surfaces with tunable mechanical, optical, hydrophilic properties. 

Epitaxial Nanocomposite:  A Pathway for Tunable Functionalities, Quanxi Jia, State University of New York (SUNY), Host:  Liliana Stan

Epitaxial nanocomposites provide a pathway to produce tunable and improved properties that are often not accessible from the individual constituents. Over the years, new discoveries and major advances have been made to synthesize epitaxial nanocomposite films and to gain fundamental understanding of their physical properties such as ferromagnetism ferroelectricity, and multiferroicity. In this talk, I will overview our effort to understand, exploit, and control competing interactions of a range of epitaxial nanocomposite metal oxide films. Using both ferroelectric and ferromagnetic oxides as model systems, we have illustrated that certain physical properties of the materials could be systematically tuned by controlling the strain state of the epitaxial nanocomposite films. Our phase field simulations have suggested that the ultimate strain in the interested phase is related to the vertical interfacial area and interfacial dislocation density of the epitaxial nanocomposite films.

“Multimodal Microscopy Applied to Emerging Energy materials: Perovskite Solar Cells”, David S. Ginger, University of Washington, Host: Pierre Darancet

From halide perovskite solar cells, to new polymer electrolytes for batteries, many emerging materials being explored for solar energy harvesting and storage show performance that depends sensitively on nanoscale structure. Rapid advances in the capability and accessibility of scanning probe microscopy methods have made it possible to study processing/structure/function relationships ranging from photocurrent collection, to ion uptake, to photocarrier lifetimes with resolutions on the scale of tens of nanometers or better in these materials. Importantly, such scanning probe methods offer the potential to combine measurements of local structure with local function, and they can be implemented to study materials in situ or devices in operando to better understand how materials evolve in time in response to an external stimulus or environmental perturbation. This talk highlights recent advances in the development and application of both scanning probe and optical microscopy methods to help address such questions while filling key gaps between the capabilities of conventional electron microscopy and newer super-resolution optical methods, with a specific focus on perovskite semiconductors. This talk will emphasize the application of multimodal microscopy to characterize perovskite solar cells, and discuss how these insights led us to surface passivation schemes that can achieve 96% of the Shockley-Queisser quasi-Fermi level splitting in these materials.

Apr. 18, 2018

Theory and Practice of Nanoparticle Self Assembly, Nicholas A. Kotov, University of Michigan.  Host:  Gleiciani de Queiros Silveira
 
Inorganic nanoparticles (NPs) have the ability to self-organize into variety of structures with sophisticated and dynamic geometries. Analysis of experimental data for different types of NPs indicates a general trend of self-assembly under a wider range of conditions and having broader structural variability than self-assembling units from organic matter. Remarkably, the internal organization of self-assembled NP systems rival in complexity to those found in biology which reflects the biomimetic behavior of nanoscale inorganic matter. In this talk, the following questions will be addressed:
 
(a) What are the differences and similarities of NP self-organization compared with similar phenomena involving organic and biological building blocks?
(b) What are the forces and related theoretical assumptions essential for NP interactions?
© What is the significance of NP self-assembly for understanding emergence of life?
(d) What are the technological opportunities of NP self-organization?
Self-organization of chiral nanostructures will illustrate the importance of subtle anisotropic effects stemming from collective behavior of NPs and non-additivity of their interactions. The fundamental significance of studies in this area from this and other groups will be discussed in relation to the origin of homochirality on Earth and spontaneous compartmentalization (protocells). The practicality of self-organization of nanoparticles will be discussed in relation to charge storage technologies, DNA/protein biosensing, chiral catalysis, and combating antibiotic resistant bacteria and other infections including rapidly mutating viruses.
 
References:
1. Tang, Z.; Kotov, N. A.; Giersig, M. Spontaneous organization of single CdTe nanoparticles into luminescent nanowires, Science, 2002, 297, 237.
2. Kotov, N. A. Inorganic Nanoparticles as Protein Mimics, Science, 2010, 330(6001), 188–189.
3. Srivastava S.; et al., Light-Controlled Self-Assembly of Semiconductor Nanoparticles into Twisted Ribbons, Science, 2010, 327, 1355.
4. Yeom, J.; et al., Chiral Templating of Self-Assembling Nanostructures by Circularly Polarized Light, Nature Mater. 2015, 14, 66.
5. Batista-Silvera, C.; Larson, R.; Kotov, N. A. Non-Additivity of Nanoparticle Interactions, Science, 2015, DOI: 10.1126/science.1242477.
6. L.Liu, et al. Low-Current Field-Assisted Assembly of Copper Nanoparticles for Current Collectors, Faraday Disc. 2015, 181, 383-401.
7. M. Yang, H. Chan, G. Zhao, J.H. Bahng, P. Zhang, P. Král, N.A. Kotov, Self-Assembly of Nanoparticles into Biomimetic Capsid-Like Nanoshells, Nature Chemistry, 2016, 9, 287–294.
8. J. H. Bahng, B. Yeom, Y. Wang, S. O. Tung, N.A. Kotov, Anomalous Dispersions of Hedgehog Particles, Nature, 2015, 517, 596–599.
9. W. Feng, J.-Y. Kim, et al. Assembly of Mesoscale Helices with Near Unity Enantiomeric Excess and Light-Matter Interactions for Chiral Semiconductors, Science Advances, 2017, 3(3), e1601159.
10. S. Jiang, et al. Chiral Ceramic Nanoparticles of Tungsten Oxide and Peptide Catalysis, Journal of the American Chemical Society, 2017, 139 (39), 13701–13712

“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.

“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.

“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. 

“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.