CCMR Sponsors 5 Hot Materials Talks throughout the summer. The talks are open to all REU students and take place on Thursdays at 12:00 pm.
Prof. Farhan Rana
School of Electrical and Computer Engineering, Cornell University, Ithaca, NY
Femtosecond pulses of light can be used to observe time-dependent dynamics of carriers, spins, and collective excitations in materials, nanostructures, and devices much like strobe light can be used to observe fast periodic oscillations of mechanical objects in slow motion. This talk will describe various forms of ultrafast spectroscopy techniques in the optical/IR/THz frequency ranges. Techniques will be demonstrated by our recent work on the ultrafast dynamics of electrons, holes, spins, and collective excitations, such as excitons, phonons, and plasmons, in different nanoscale materials and devices for electronic, optical, plasmonic, and MEMs device applications.
Prof. Gennady Shvets
Department of Applied and Engineering Physics, Cornell University, Ithaca, NY
Metamaterials are artificial electromagnetic materials exhibiting unusual optical responses that are difficult to elicit from naturally-occurring media. Those include negative refractive index, strong magneto-electric response, and strong concentration of optical energy. Metamaterials and their two-dimensional implementations (metasurfaces) represent a remarkably versatile platform for light manipulation, biological and chemical sensing, and nonlinear optics. Many of these applications rely on the resonant nature of metamaterials, which is the basis for extreme spectrally selective concentration of optical energy in the near field. In addition, metamaterial-based optical devices lend themselves to considerable miniaturization because of their sub-wavelength features. I will review the history of electromagnetic metamaterials, which is now fifteen years in the making, and review some of the more recent trends in metamaterials research and applications using the examples of my group’s work. Those include (i) the development of “active” (i.e. rapidly tunable and reconfigurable) metasurfaces functionalized with single-layer graphene, (ii) applications of metamaterials to chemical and biological sensing of proteins and cellular membranes, and (iii) the development of the so-called photonic topological insulators that emulate the eponymous electronic materials.
Prof. Itai Cohen
Department of Physics, Cornell University, Ithaca, NY
What would we be able to do if we could build machines on the scale of a micron that sense, interact, and control their local environment? Our collaboration has recently developed 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 technology behind our machines is the graphene-glass bimorph. We show that graphene sheets bound to nanometer thick layers of glass are ultrathin actuators that bend in response to small strain differentials. These bimorphs can bend to micron radii of curvature using strains that are two orders of magnitude lower than the fracture strain of graphene. 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 could 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.
Prof. Robert A. DiStasio Jr.
Department of Chemical and Chemical Biology, Cornell University, Ithaca, NY
In this work, I will present an accurate and efficient method for obtaining a first-principles based theoretical description of non-bonded van der Waals (vdW or dispersion) interactions that includes both long-range Coulomb electrodynamic response screening effects as well as treatment of the many-body vdW energy to infinite order. The resulting many-body dispersion (MBD) model goes well beyond the standard pairwise-additive approximation for treating vdW interactions and can easily be coupled to a wide array of theoretical methods, ranging from classical force fields to higher-level quantum chemical calculations. To demonstrate the increasingly important role played by many-body vdW interactions in large, structurally complex molecular systems, we use this method to investigate several pertinent molecular properties, such as binding energies/affinities in gas-phase molecular dimers and supramolecular complexes, relative conformational energetics in small polypeptides, the equilibrium structure and anomalous density properties of liquid water, and thermodynamic stabilities among competing molecular crystal polymorphs.
Prof. Nicole A. Benedek
Department of Materials Science and Engineering, Cornell University, Ithaca, NY
Most materials expand when heated, but others shrink – this phenomenon is known as negative thermal expansion. Although the laws that govern how heat flows at the macroscopic scale have been known for over a hundred years, we understand very little about how materials respond to temperature gradients at the atomic scale. In this talk, I will describe how we are using theory and simulation to elucidate the origins of negative thermal expansion in a family of ceramic oxides, and the ways in which we can use our knowledge to design materials with tailored thermal properties.