Refreshments at 3:30, Talk 4:00 - 5:00 p.m., in CII 3051, unless otherwise noted.
Refreshments at 3:30, Talk 4:00 - 5:00 p.m., in CII 3051, unless otherwise noted.
We are developing origami into a tool for fabricating autonomous, cell-sized machines. These devices can interact with their environment, be manufactured en masse, and carry the full power of modern information technology. Our approach starts with origami in the extreme limit of atomic thickness: we make actuators from 2D membranes, like graphene, that can bend to micron radii of curvature. By patterning rigid panels on top of these actuators, we can localize bending to produce folds, and scale down existing origami patterns to produce a wide range of machines. These machines change shape in fractions of a second in response to environmental changes, and perform useful functions on time and length scales comparable to microscale biological organisms. Beyond simple stimuli, we demonstrate how to fabricate voltage responsive actuators that can be powered by on-board photovoltaics. Finally, we demonstrate that these actuation technologies can be combined with silicon-based electronics to create a powerful platform for robotics at the cellular scale.
Symmetry, interaction and topological effects, as well as environmental screening, dominate many of the quantum properties of reduced-dimensional systems and nanostructures. These effects often lead to manifestation of counter-intuitive concepts and phenomena that may not be so prominent or have not been seen in bulk materials. In this talk, I present some fascinating physical phenomena discovered in recent studies of atomically thin two-dimensional (2D) materials. A number of highly interesting and unexpected behaviors have been found – e.g., strongly bound excitons (electron-hole pairs) with unusual energy level structures and new topology-dictated optical selection rules, massless excitons, tunable magnetism and plasmonic properties, electron supercollimation, novel topological phases, etc. – adding to the promise of these 2D materials for exploration of new science and valuable applications.
I will discuss how topological phases arise in quantum matter through spin-orbit coupling effects in the presence of protections provided by time-reversal, crystalline and particle-hole symmetries, and highlight our recent work aimed at predicting new classes of topological insulators (TIs), topological crystalline insulators, Weyl semi-metals, and quantum spin Hall insulators. [1-7] Surfaces of three-dimensional (3D) topological materials and edges of two-dimensional (2D) topological materials support novel electronic states. For example, the surface of a 3D TI supports gapless or metallic states, which are robust against disorder and non-magnetic impurities, and in which the directions of momentum and spin are locked with each other. Similarly, in 2D TIs, also called quantum spin Hall insulators, the 1D topological edge states are not allowed to scatter since the only available backscattering channel is forbidden by constraints of time-reversal symmetry. The special symmetry protected electronic states in topological materials hold the exciting promise of providing revolutionary new platforms for exploring fundamental science questions, including novel spin textures and exotic superconductors, and for the realization of multifunctional topological devices for thermoelectric, spintronics, information processing and other applications. Work supported by the U. S. Department of Energy.
 Bansil, Lin and Das, Reviews of Modern Physics 88, 021004 (2016).
 Xu et al., Science Advances 3, e1603266 (2017).
 Vargas et al., Science Advances 3, e1601741 (2017).
 Hafiz et al., Science Advances 3, e1700971 (2017).
 Chang et al., Physical Review Letters 119,156401 (2017).
 Okada et al., Physical Review Letters 119, 086801 (2017).
 Chang et al., Physical Review Letters (2017).
Short bio: Bansil is a University Distinguished Professor in physics at Northeastern University (NU). He served at the US Department of Energy managing the flagship Theoretical Condensed Matter Physics program (2008-10). He is an academic editor of the international Journal of Physics and Chemistry of Solids (1994-), the founding director of NU’s Advanced Scientific Computation Center (1999-), and serves on various international editorial boards and commissions. He has authored/co-authored over 370 technical articles and 18 volumes of conference proceedings covering a wide range of topics in theoretical condensed matter and materials physics, and a major book on X-Ray Compton Scattering (Oxford University Press, Oxford, 2004). Bansil is a 2017 Highly Cited Researcher (Web of Science/Clarivate Analytics).
This talk reviews some of the applications of topology and topological defects in phase transitions in two-dimensional systems for which Kosterlitz and Thouless split half the 2016 Physics Nobel Prize. The theoretical predictions and experimental verification in two dimensional superfluids, superconductors and crystals will be reviewed because they provide very convincing quantitative agreement with topological defect theories.
Quantum Chromodynamics (QCD) is no doubt the correct theory of strong interactions within the Standard Model of Physics. However, despite decades of significant theoretical progress made based on a broad range of experimental observations, some of the most intellectually compelling questions remain unanswered. For example, how do quark, gluons and their interactions, collectively result in the observed fundamental properties of hadrons such as the spin and mass? What is the QCD/partonic origin of the nucleon-nucleon forces in nuclei? How does nuclear environment impact the parton’s momentum distribution in confined nucleons? Does the gluon density in nucleons and nuclei saturate at extremely high energy, and form a universal form of gluonic matter? Such questions can now be addressed quantitatively through a polarized high-energy high-luminsity Electron Ion Collider (EIC), now possible with the advances in accelerator technology. Theoretical frame work is now mature enough to put the resulting measurements in to a comprehensive picture within QCD that could directly address the compelling questions in QCD. The EIC was recommended in the 2015 US Longe Range Plan prepared by the US Nuclear Science Advisory Committee (NSAC) as the highest priority facility for new construction in the US. I will summarize its science case, and present the status
and plans for its realization.
The recent Dawn mission was sent to asteroid 4 Vesta to inspect, close up, an intact protoplanet from the origin of the solar system. Except... Vesta's overall density is too low, and its core and crust too big, to fit anything like what we expect an intact protoplanet to look like. Was it ripped apart and re-assembled? It looks like Vesta is giving us new clues to planet formation and evolution in a violent early solar system.
In a periodic solid, electrons can only occupy certain bands of allowed energies. This fact, together with the Fermi-Dirac statistics of electrons, explains the sharp difference between metals and insulators and seems to leave no room for any kind of ``in-between” material. However, we know now that not all band structures are born equal: There are subtle but robust differences captured by topological invariants, integer numbers computed from the Berry curvature of Bloch functions. Topologically non-trivial insulators are precisely ``in-between” materials, because they display both a metallic surface and an insulating bulk. The idea that a topologically non-trivial bulk dictates a metallic surface is dubbed the bulk-boundary correspondence, and there are myriads of heuristic arguments and numerical experiments for open boundary conditions that support it. Nonetheless, our understanding of this conjecture is arguably shallow: What exactly is the mechanism by which a purely bulk property, completely reliant on translation symmetry for its existence, forces robust edge states? In this talk I will introduce a new tool of band structure theory, a generalization of Bloch’s theorem for arbitrary boundary conditions,* and an associated algorithm for solving exactly tight binding models subjected to arbitrary boundary conditions on two parallel hyperplanes. The generalized Bloch theorem yields a sharp description of the possible wave functions of tight-binding models, showing that power-law modes and perfectly localized modes can coexist with the usual oscillating or exponentially decaying modes. One finds by simple trial and error that boundary conditions can break the classifying symmetries of the topological system badly without affecting the edge modes: it is apparent that from the point of view of the metallic surface there are relevant and irrelevant directions in boundary space and these directions are not simply determined by bulk symmetries.
*Abhijeet Alase, Emilio Cobanera, Gerardo Ortiz, and Lorenza Viola, Generalization of Bloch's theorem for arbitrary boundary conditions: Theory, Phys. Rev. B 96, 195133.
Since the isolation of graphene in 2004, a monolayer of covalently-bonded carbon atoms, the field of two-dimensional (2D) materials has been rapidly expanding to other atomic layers, presenting a plethora of fascinating new discoveries. In particular, 2D hexagonal transition metal dichalcogenides (TMDCs), a class of direct gap semiconductors, have been attracting much recent attention due to their unique optoelectronic properties. In this talk, I will discuss our recent studies on high-quality monolayer tungsten diselenide (1L-WSe2), a 2D TMDC, whose excitonic excitations exhibit intriguing valleytronic properties. We found that with efficient removal of disorder and phonon, the exciton, composed of an electron and a hole in 1L-WSe2, can radiate not only as the 1s ground state, but also as the excited 2s Rydberg state. Interestingly, the 2s exciton shows superior valleytronic properties compared to 1s, providing key information on the fundamental valley scattering processes in TMDCs.1 In a strong magnetic field up to 31 Tesla, we further observe excitonic emissions due to the 3s and 4s states; at lower energies, complexes due to bound states of more than three particles emerge. These interesting optical features provide a rich variety of quasi-particle states for manipulating the valley degree of freedom in monolayer TMDCs.
1. Chen, S.-Y. et al. Superior Valley Polarization and Coherence of 2s Excitons in Monolayer WSe2. Phys. Rev. Lett. 120, 46402 (2018).
Over the past two decades, researches on low-dimensional carbon and silicon based nanostructured materials designed for a variety of applications have made remarkable progress. However scalable fabrication and engineering of tightly controlled extreme nanostructures and building multifunctional systems that harness 2-3 dimensional architectures of these nanostructured materials have remained largely elusive. Such methodologies will allow unprecedented nanostructures and superior physical and chemical properties for multifunctional applications. Here we present some of our progresses in synthesis and engineering of carbon and silicon based extreme nanostructures and building their 2-3D architectures for broad ranges of applications such as chemical, optical and ion sensors, multifunctional fibers and various energy storage devices etc. by combining state-of-the-art synthesis, assembly and transfer based nanomanufacturing strategies developed in our laboratory.
Risks that threaten modern societies form an intricately interconnected network, so it is important to understand how risk activations in distinct domains influence each other. We study the global risks network defined by World Economic Forum experts. Risks are modeled as Cascading Alternating Renewal Processes (CARP) with variable intensities driven by hidden values of exogenous and endogenous failure probabilities. We use maximum likelihood evaluation to find the optimal model parameters based on the expert assessments and historical status of each risk. This approach enables us to analyze risks that are particularly difficult to quantify, such as geo-political or social risks in addition to more quantitative risks such as economic, technological and natural.
In the talk, we describe model dynamics and discuss how to use the model to provide quantitative means for measuring interdependence and materialization of risks in the network. We also talk about limits of the predictability of the system parameters from historical data and model ability to recover hidden variable. We also describe how the network evolved recently by comparing steady state which would be reached if the risks were left unabated at different time points. We also analyze the model resilience and optimal control. Our findings elucidate the identity of risks most detrimental to system stability at various points in time. The model provides quantitative means for measuring the adverse effects of risk interdependence and the materialization of risks in the global risk network.
BIO OF THE PRESENTER: Dr. Boleslaw K. Szymanski is the Claire and Roland Schmitt Distinguished Professor and the Director of the ARL Social and Cognitive Networks Academic Research Center at the Rensselaer Polytechnic Institute and the Rensselaer Network Science and Technology (NeST) Center. He received his Ph.D. in Computer Science from Institute of Informatics of National Academy of Science in Warsaw, Poland, in 1976. He published over 300 scientific articles, is a foreign member of the National Academy of Science in Poland and an IEEE Fellow and was a National Lecturer for the ACM. In 2009, he received the Wilkes Medal of British Computer Society and in 2003, William H. Wiley 1866 Distinguished Faculty Award from RPI. His current research interests focus on computer networks and technology-based social networks.
Terahertz time domain spectroscopy (THz-TDS) is a relatively new analytical method for characterizing samples in a nondestructive manner. Absorption features over THz frequencies correspond to rotational transitions in gases and low energy intra- and inter-molecular vibronic and torsional transitions in crystalline solids. Much attention has been given to the use of THz-TDS to distinguish polymorphs within crystalline formulations and to establish thicknesses of layers within product preparations.
My presentation will focus on studies in our research group to establish the power of THz-TDS for quantification and characterization of different types of materials. Our work focuses on measurements over the 0.5-100 cm-1 spectral range. Results indicate that analytical measurements over these THz frequencies offer superior selectivity compared to conventional infrared measurements, thereby establishing a practical basis for exploring THz-TDS as an analytical tool. In addition, our work probes the utility of THz-TDS for characterizing cocrystals as a means to guide crystal engineering with the objective of optimizing material properties based on structure-function relationships. An example is the measurement of dielectric and polarizability properties of cocrystals and the relationship between these properties and crystal hardness.
Modern scientific computing has certain limitations when it comes to calculations with many-body quantum systems. A possible solution to this problem is the idea of quantum computing, or quantum simulation, suggested by Richard Feynman. Here, the actual computer used to calculate is itself a quantum system, overcoming the limitations from regular computers. In this talk I will discuss mathematical methods, specifically the tensor renormalization group, which allow one to understand and possibly create a particular kind of quantum simulator using very cold atoms trapped in a lattice made of laser light. I will discuss this for two physically relevant models and mention possible future directions the research could take.
Nonlinear optical processes, such as second harmonic generation (SHG) are an important component of modern technology such as imaging and high speed data communication. However, traditional materials have a small response which limits the efficiency of devices. The inherently small size of two dimensional (2D) materials makes them attractive options to seamlessly interface with existing technology. In addition, 2D materials have been shown to exhibit extraordinary SHG response. In this talk we will characterize the SHG response of 2D materials using first principles density functional theory plus Bethe-Salpeter equation (BSE) calculations. We examine how strain, alloying, and excitons affect the response. In addition, theoretical structures are studied to gain insight into ways to enhance the SHG response.
The question of the identity of dark matter remains one of the most important outstanding puzzles in modern physics. Weakly Interacting Massive Particles (WIMPs) have long been the frontrunner dark matter candidate, with the supersymmetric neutralino serving as the canonical WIMP. In this talk, I’ll discuss recent results relevant to the search for dark matter, supersymmetric and otherwise, and highlight the spectrum of theoretical and phenomenological approaches to its study. As I’ll demonstrate, even canonical WIMPs may reveal themselves in surprising ways!
Abstract: Increasingly powerful computers and better theoretical insights continue to improve the predictive power of numerical simulations, from atmospheric dynamics to jet engines to lattice quantum chromodynamics. As our resolution power advances, we can study ever larger systems at fine grained detail, exposing multiple scales of physics. However, this comes at a superlinear cost, as with extra detail comes the phenomena of critical slowing down. One class of algorithms tackles critical slowing down, literally at all scales: multigrid algorithms. In this talk I will discuss the anatomy of multigrid from the scale-invariant Laplace equation to the multiscale dynamics in lattice QCD.
Thermoelectrics are semiconductor materials that have a strong interaction between the flows of heat and electricity. They are used in solid state refrigerators, or in converting heat flow to electrical power. We review their history and device applications. We define their “figure of merit” which determines which materials are the best thermoelectrics. Then we discuss the electrical properties that make the figure of merit large. We prove the Mahan-Sofo theorem which defines the best material. This theorem is used to guide the quest for new or revised materials. We also discuss their properties at low temperatures.
"In past several years, materials called halide perovskites have been reshaping researchers’ understanding on designing and developing high-performance optoelectronic/electro-optical semiconductors. In this talk, I will present our recent observations and understanding in the field of halide perovskite materials. Several topics will be covered: epitaxy of the thin film crystals, dimensionality and strain engineering, and hidden carrier dynamics."
Andrew Cupo: “Nanostructures and Phonon Anharmonicity in Atomically-Thin Black Phosphorus.”
Abstract: Atomically-thin black phosphorus has been of interest recently  due to its high carrier mobility  and band gap which remains direct independent of the number of layers . Using first-principles density functional theory (DFT) calculations we have investigated nanoribbons , nanopores , antidot lattices , and phonon anharmonicity in black phosphorus. We showed that the few-nm wide armchair and zigzag nanoribbons fabricated by collaborators have similar electronic properties as their single-layer counterparts. Furthermore, we rationalized the asymmetric opening of nanopores in black phosphorus under uniform irradiation by showing that the energy barrier for removing atoms from the edge is anisotropic in phosphorene. In addition, we explored the electronic properties of phosphorene antidot lattices. We demonstrated a tunable band gap due to quantum confinement with deviations from the general trend attributed to self-passivating edge morphologies. The spatial distribution of the band gap is bimodal with higher band gap atoms emanating from the zigzag nanoconstrictions, which reflects the material anisotropy. Lastly, we carried out ab initio molecular dynamics simulations in combination with the power spectrum method to show that phosphorene’s phonon frequencies decrease with increasing temperature. This accounts for the observed temperature dependence of the phonon frequencies from Raman spectroscopy .
 Quantum Confinement in Black Phosphorus-Based Nanostructures, A. Cupo and V. Meunier, Journal of Physics: Condensed Matter, 29 (28), 2017
 Achieving Ultrahigh Carrier Mobility in Two-Dimensional Hole Gas of Black Phosphorus, G. Long et al., Nano Letters, 16 (12), pp 7768-7773, 2016
 Direct Observation of the Layer-Dependent Electronic Structure in Phosphorene, L. Li et al., Nature Nanotechnology, 12, pp 21-25, 2017
 Controlled Sculpture of Black Phosphorus Nanoribbons, P. M. Das*, G. Danda*, A. Cupo* et al., ACS Nano, 10 (6), pp 5687-5695, 2016
 Periodic Arrays of Phosphorene Nanopores as Antidot Lattices with Tunable Properties, A. Cupo*, P. M. Das* et al., ACS Nano, 11 (7), pp 7494-7507, 2017
 Temperature Evolution of Phonon Properties in Few-Layer Black Phosphorus, A. Łapińska et al., The Journal of Physical Chemistry C, 120 (9), pp 5265-5270, 2016
Alaa Moussawi: “Cascading Overload Failures in Power Grids: Analysis and Mitigation”
Abstract: Cascading overload failures (blackouts) are a common and catastrophic vulnerability of spatially-embedded distributed flow networks that are poorly understood. The efficiencies that locally connected networks afford us come at an also high cost. With increasing energy demands taxing old infrastructures, power grids are currently operating at a critical phase where the capacity of these systems is approaching load demands. This highlights the importance of understanding the dynamics of power systems so that they can most effectively be utilized at this critical phase without major failure. Mitigation techniques will be presented, and their effectiveness under varying constraints will be investigated. A simple strategy for approximating the severity of multi-node failures will be presented. Finally, it will be shown that such networks exhibit a phase transition at a given capacity threshold. Moreover, we show that cascade size distributions measured in this region exhibit a power-law decay.
Via nanophotonics, one can tailor the laws of physics (as far as light is concerned) almost at will. This way, a variety of novel physical phenomena can be enabled and observed. Some examples in topology and light-matter interaction will be presented. Nanophotonics can also enable many new potential applications; examples in energy conversion and lighting will be presented.
“The primary goal of a dividing cell is to accurately and equally segregate its genome into two new daughter cells. In eukaryotes, this process is carried out by a self-organized structure called the mitotic spindle. It has long been appreciated that mechanical forces must be applied to chromosomes. At the same time, the network of microtubules that do not directly interact with kinetochores must be able to sustain large forces to maintain spindle integrity and allow for efficient remodeling and repair of the spindle. The goal of the Forth lab at RPI is to directly measure the forces generated within microtubule networks by ensembles of key mitotic proteins, including motor proteins that push microtubules apart and non-motor proteins that act as sources of viscous drag. New paradigms of mechanical regulation, such as length-dependent force generation and protein clustering by asymmetric friction, will help advance models of force generation across the spindle.”
The path integral formulation of time-dependent quantum mechanics provides the ideal framework for rigorous quantum-classical or quantum-semiclassical treatments, as the spatially localized, trajectory-like nature of the quantum paths circumvents the need for mean-field-type assumptions. However, the number of system paths grows exponentially with the number of propagation steps. In addition, each path of the quantum system generally gives rise to a distinct classical solvent trajectory. This exponential proliferation of trajectories with propagation time is the quantum-classical manifestation of time nonlocality, familiar from influence functional approaches. A real-time quantum-classical path integral (QCPI) methodology has been developed. The starting point is the identification of two components in the effects induced on a quantum system by a polyatomic environment. The first, “classical decoherence mechanism” dominates completely at high temperature/low-frequency solvents and/or when the system-environment interaction is weak. Within the QCPI framework, the memory associated with classical decoherence is removable. A second, nonlocal in time, “quantum decoherence process” is also operative at low temperatures, although the contribution of the classical decoherence mechanism continues to play the most prominent role. The classical decoherence is analogous to the treatment of light absorption via an oscillating dipole, while quantum decoherence is primarily associated with spontaneous emission, whose description requires quantization of the radiation field. The QCPI methodology takes advantage of the memory-free nature of system-independent solvent trajectories to account for all classical decoherence effects on the dynamics of the quantum system in an inexpensive fashion. Inclusion of the residual quantum decoherence is accomplished via phase factors in the path integral expression, which is amenable to large time steps and iterative decompositions. The methodology can be used to perform an all-atom simulation of nonadiabatic processes in condensed phase environments with unprecedented accuracy. Applications to charge transfer reactions in solution will be discussed.
We exploit strong light matter interaction in graphene for graphene based optoelectronic devices. We use both scanning photocurrent microscopy and optical pump terahertz (THz) probe spectroscopy to reveal hot carrier behavior in graphene. This hot carrier behavior is crucial to understand the effect of optical excitation on graphene and can potentially lead to efficient solar energy conversion and ultrafast optoelectronic devices. We also exploit the strong light matter interaction in THz regime to make graphene based THz modulator.
Transitional metal dichalcogenide (TMD) is a new class of 2D semiconductors which become direct bandgap semiconductor at a single layer limit. MX2 exhibits intriguing excitonic physics as well as strong absorption. We combine optical spectroscopy and scanning tunneling microscopy to determine the extraordinarily large exciton binding energy of MoSe2. This giant exciton binding energy presents a challenge for efficient carrier separation in solar cell applications. We demonstrate that, by using MoS2/WS2 heterostructure, we can achieve a type-II band alignment and realize extremely fast carrier separation.
Advances in Power, Performance and Area scaling of semiconductor devices have been mostly driven by aggressive scaling of device dimensions. This approach has allowed a dramatic increase in integration density, power efficiency, and performance. However, atomic limits have been reached on some of the key device elements, giving rise to the need to look for new optimization pathways. The exploration of novel materials as well as emerging architectures becomes paramount for continuing performance and power advances. In this talk, I will discuss the use of atomistic simulations to optimize materials and devices for future semiconductor technologies.
The group 14 graphane analogues represent a unique class of covalently modifiable 2D materials, as there have been many recent exciting predictions of the existence of 2D quantum spin Hall behavior at room temperature in these materials. Here, we will describe our recent efforts in the creation and properties of hydrogen and organic-terminated group IV graphane analogues, from the topochemical deintercalation of precursor Zintl phases in order to create these topological phases. First, through the synthesis and characterization of a wide array of ligand terminated germanane analogues we have established experimental limits to which the electronic structure can be manipulated via surface chemistry. Second, we will discuss our recent efforts on the synthesis and properties of ligand-terminated Sn-contain graphane analogues to create systems that span from trivial insulators to 2D topological phases depending on the surface functionalization group. Finally, we will describe our emerging discoveries on the existence of topological insulating and magnetic phenomena in Sn-containing layered Zintl phase materials.
In the past decade, there has been enormous progress in materials science and engineering at the very limits of quantum confinement. Ground-breaking discoveries and innovations have resulted from a range of atomically-thin systems such as carbon nanotubes, graphene, 2D transition metal dichalcogenides and other layered materials. These developments in ultrathin matter at the very quantum limit of stability have spearheaded an explosive growth in new science and technology. This talk will attempt to outline the contributions of our research group in this exciting new field, including our attempts to develop and manipulate new types of atomically-thin materials, exploring the behaviour of charge, photons and phonons in them, and utilizing their unique properties to develop applications in the nanoelectronics, optoelectronics, sensing, detection, actuation, energy, and other areas. Through these discussions, I will try to motivate how quantum matter can potentially transform several important applications and enable them to operate at ultra-high and unprecedented performances.
Bio: Prof. Kar received his BSc degree in Physics (Honours) from Presidency College, Kolkata, in 1995, and obtained his MS (1998) and PhD (2004) degrees in Physics from the Indian Institute of Science, India. He worked as a postdoc at the Universitaet Karlsruhe, Germany, and Rensselaer Polytechnic Institute, USA (with Prof. PM Ajayan). He also held a research assistant professor position at RPI with Prof. Saroj Nayak, before joining Northeastern University, USA, as an assistant professor of physics, in 2010. Prof. Kar has published about 65 papers in peer-reviewed journals, including in Nature Nanotechnology, Nature Materials, Nature Photonics, Nature Communications, and Science Advances. Prof. Kar has presented over 45 invited talks worldwide, and has 6 patent applications. He currently serves as an Editorial Board member of Scientific Reports, and has served on several US and international grant application review panels. Prof. Kar enthusiastically promotes the science and technology of 2D materials and systems by regularly organizing conferences and symposia at top international physics and materials science congresses venues.
"The reduction in price of solar modules coupled with policies geared towards the use of renewable sources for electricity generation has resulted in a dramatic increase in the deployment of photovoltaic panels, at residential, commercial and utility levels. Crystalline and multi-crystalline silicon panels are still the option of lowest cost. However, where thin-film modules were only considered for “niche” applications that required low weight and flexibility, the increase in efficiency achieved in the past few years are turning them a more mainstream alternative. A general discussion of the metrology needs, and the tools available for the production of thin-film photovoltaic materials and characterization of the modules, before and after deployment, will be presented."
Metal nanoparticles sustain a collective oscillation of their free electrons, called a localized surface plasmon resonance (LSPR), when excited by an electromagnetic wave. When this incident wave is resonant with the LSPR frequency, the field intensity is strongly increased in the near field of the nanoantenna. Plasmonics thus provides a unique setting for the manipulation of light via the confinement of the electromagnetic field to regions well below the diffraction limit. This has opened up a wide range of applications based on extreme light concentration, including nanophotonic lasers and amplifiers optical metamaterials, biochemical sensing and antennas transmitting and receiving light signals at the nanoscale. However, many difficulties remain in experimentally measuring the shape, size, and enhanced field properties of the localized electromagnetic modes in the vicinity of the nano-particles due to the limitations of optical microscopy. In this seminar, I will discuss how we can unravel the coupling of light to a nano-antenna through single-molecule fluorescence imaging. This technique is a powerful tool to optically study structures beyond the diffraction limit by localizing isolated fluorophores and fitting the emission profile to the microscope point-spread function. By using the random motion of single dye molecules in solution to stochastically scan the surface, and by assessing emission intensity, wavelength, and density of emitters as a function of position, we gain new insight into the properties of these systems and pave the way for the development of better plasmonic devices.
The three pillars in semiconductor device technologies are (1) the p-n diode, (2) the MOSFET and (3) the Bipolar Junction Transistor (BJT). They have enabled the unprecedented growth in the information technology that we see today. Here, we will describe our efforts to fabricate and characterize these three benchmark devices in two-dimensional (2D) materials, including graphene and transition metal dichalcogenide semiconductors (TMDs).
Although graphene is gapless, we will describe device concepts based on graphene p-n junctions that can lead to steep subthreshold slope devices. Critical to realizing such devices is the demonstration of relativistic Klein tunneling, a property of chiral carriers in graphene that arises from the Dirac equation. We will describe the fabrication and characterization of graphene p-n junctions and discuss the unique tunneling properties of these junctions.
Using TMD materials, we have fabricated a single device that can reconfigure into p-n, MOSFET, and BJT devices. These devices allow us to provide fundamental linkages between material properties and device performance not possible by fabricating these devices individually. We will describe our method of fabrication and discuss both the electrical and optical properties of these devices. Finally, we will describe compact logic circuits that can be realized from the single reconfigurable device.
The LUX collaboration has recently released its 1-year WIMP search result. LUX remains at the forefront of the search for this dark matter candidate particle in the 10 GeV and higher range, the Weakly Interacting Massive Particle, a potential explanation for a "missing" 25% of the mass-energy of the Universe. Plans for LUX’s 10-ton-scale, Generation-2 successor LZ, plus the NEST quantum chemistry simulation model of WIMP-Xe interactions, will be discussed. Lastly, progress on Generation-3 R&D in collaboration with RPI with superheated Xe will be highlighted from a 100-g-scale prototype at UAlbany (BubXe) focused on also informing existing G-2 experiments like LZ and XENON.