Physics Seminars

Follow

• 

  Controlling Surface Chemistry of Liquid Metals to Enhance their Fluidic Properties

  Nahid Ilyas

  Gallium liquid metal alloys (GaLMA) are one of the key components of emerging technologies in reconfigurable, flexible, and printable electronics. Surface properties of GaLMA play important roles in its application in reconfigurable devices, such as tunable radio frequency antennas and electronic swilches. Reversible flow of GaLMA in microchannels of these types of devices is hindered by the presence of an oxide skin that forms spontaneously in ambient environment. The oxide film sticks to most surfaces leaving unwanted residues behind that can cause undesired electronic properties. This presentation describes a novel method that enables the movement of gallium liquid metal alloys through microfluidic channels without leaving any metallic residues on the channel walls. An interface modification layer (alkyl phosphonic acids) was introduced into the microfluidic system and the modified surface chemistry of the liquid metal was characterized by surface spectroscopy and microscopy methods.

• 

  Si/SiGe BiCMOS Microsystems for Microwave and Millimeter-Wave Sensing and Communications

  Hermann Schumacher

  Since the early 1990’s, Silicon-Germanium heterojunction bipolar transistors revolutionized the way we build microwave and millimeter wave systems. Rivaling the once-dominant group III-V semiconductor devices in terms of speed, SiGe technologies also harness the maturity, yield and resulting complexity of Silicon based technology. The presentation will discuss this trend using examples from the author’s research in recent years.

  The first example will show how a very inexpensive and „old“ SiGe HBT technology (0.8 μm feature size) was used to implement efficient impulse radio ultra-wideband (IUWB) sensors for vital sign detection and object tracking.

  The second example, taken from a recently concluded major European research project, discusses how RFMEMS components were included in a state-of-the-art Si/SiGe BiCMOS process to realize band-switchable millimeter-wave ICs, and finally a complex integrated circuit which introduces active phase and amplitude control to a reflect array antenna. The IC contains four reversible T/R modules, digital to analog converters offering eight bit control, and a joint I2C control interface.

  The final example is taken from an on-going large European research project and shows how advanced Si/SiGe BiCMOS processes (130 nm feature size) can be used to establish a front-end for a 140 GHz MIMO radar system intended for security scanning of baggage. The presentation will include proof-of-concept sensing experiments, while the full MIMO radar system is the object of on-going research work.

• 

  Laser Induced Ignition with Resonant Multiphoton Absorption in Oxygen

  Steven F. Adams

  A novel resonant laser-induced breakdown scheme has been demonstrated to provide precision spatial guidance of spark formation within an air flow and has been further demonstrated successfully in resonant laser-induced ignition of a moderate-speed flow of an air-propane mixture. This scheme could potentially provide ignition within a combustion system with a laser trigger leading to breakdown of an air-fuel flow within a high-voltage gap using a compact low power laser source. The laser scheme involves resonant enhanced multiphoton ionization (REMPI) in molecular oxygen and subsequent laser field-enhanced electron avalanche to generate a pre-ionized micro-plasma path between high voltage electrodes and thus guide the ignition spark through fuel-rich areas of the air-fuel flow. With this resonant method, sufficient photo-ionization and laser field-enhanced electron avalanche ionization have been generated for inducing air breakdown at a relatively low laser power compared to most laser breakdown concepts. This low power requirement may allow for a laser source to be transmitted to an ignition chamber via fiber optic coupling. Results of this study include high speed photographic analyses of flame ignition in an air-propane flow, showing the spatial and temporal evolution of the laser-induced spark and flame kernel leading to combustion.

• 

  Plastic Low-Cost Circuits Enabled Through Nanotechnology

  Paul R. Berger

  The dawn of tunnel diodes, commonly attributed to Leo Esaki in the late 1950’s, predates much of the innovation and infrastructure investment into CMOS technology. But, the lack of a mass production process and inability to monolithically integrate these devices into complex circuits paved the way for the CMOS juggernaut seen today.

  However, the unique negative differential resistance (NDR) systemic to all tunnel diodes provides a pathway to exploit new hybrid-CMOS circuit topologies with compact latches and reduced power consumption that could mitigate some of the bottlenecks perceived for scaled CMOS. A new paradigm of computing is possible, capitalizing upon transistor/tunnel diode integration if a viable Si-based tunnel diode could be developed. This talk will explore these opportunities.

  This talk will provide a background on Si-based tunnel diode devices and circuits and summarize the results of Si-based RITD device optimization, their monolithic integration with Si-based transistors and present a range of circuit prototyping. The extension of NDR to ultra-low voltage memory will also be discussed.

  Quantum functional circuitry exploiting negative differential resistance (NDR) devices offers a paradigm shift in computational architectures for a multitude of circuitries (low-power embedded memory, mixed-signal and logic), that enables continued Si/SiGe scaling according to Moore’s Law. The advantage of quantum functional circuits is illustrated by the N-shaped electrical characteristics of two serially connected NDR devices which can be exploited to easily fashion two stable latching points. NDR-based circuitry facilitates simple circuit topologies to fashion latches etc., permitting tunnel diode/transistor circuits that require fewer devices, less chip area and reduced power consumption

  We will present results on room temperature NDR devices and circuits using a Si-based resonant interband tunnel diode (RITD) developed by this team that is a hybrid NDR device that uses quantum wells formed by delta-doping and appropriate band offsets to facilitate robust tunneling across a p-n junction. This talk will illustrate this pathway for silicon, and then this will be extended to conjugated polymer based devices that are in their initial investigations.

  The polymer device to be presented leverages the unique flexible and solution-processable properties of conjugated polymer semiconductors. We will demonstrate robust room temperature negative differential resistance and logic circuit operations using polymer tunnel diodes (ITO/TiO2/MEH-PPV/Al), suitable for SmartCard topologies.

• 

  Growth of Low-Dimensional Carbon Nanomaterials

  John J. Boeckl, Weijie Lu, William Mitchel, Howard Smith, Larry Grazulis, Gerry Landis, Said Elhamri, and Kurt G. Eyink

  Low dimensional carbon nanostructures, carbon nanotubes (CNTs) and graphene, have attracted significant interest due to promising applications ranging from high-speed electronics to sensing. However, insight into growth mechanisms of low-dimensional carbon nanomaterials remains a challenge. Metal-free nanocarbon/SiC structures offer an excellent platform to gain a fundamental understanding of carbon nano-materials. In this talk, metal-free nanocarbon/SiC structures are used as a platform to gain a fundamental understanding of the growth mechanisms of CNTs and graphene. Specifically, an understanding and control of the SiC surface graphitization process and interface structure needs to be established. In this review, we focus on graphene growth on SiC (0 0 0 1) (Si-face) as a model system in comparison with aligned CNT growth on SiC. The experimental aspects for graphene growth, including vacuum and ambient growth environments, and growth temperature will be presented, then, proposed decomposition and growth mechanisms are discussed. Both thermal and chemical decomposition processes are presented and special emphasis is given to the role of oxygen. The chemical reactions driving the graphitization process and ultimately the carbon nanostructure growth on SiC are discussed. The composition of the residual gases in the growth environment is a critical parameter as well as gas composition at the growth temperature.

• 

  Applied Human Factors Research in Minimally Invasive Surgery

  Caroline G. L. Cao

  Health care is probably the last remaining unsafe critical system. A large proportion of reported medical errors occur in the hospital operating room (OR), a highly complex sociotechnical environment. From the technological point of view, there is a natural progression from traditional open surgery to minimally invasive surgery to robotic surgery. However, technology is being introduced into the OR faster than surgeons can learn to use them. Surgical errors have been attributed to the unfamiliar instrumentation, increased motoric, perceptual and cognitive demands on the surgeons, as well as the lack of adequate training. Effective technology design requires an understanding of the system constraints of minimally invasive surgery, and the complex interaction between humans and technology in the OR. This talk will describe research activities in the Ergonomics in Remote Environments Laboratory, which address some of these human factors issues, such as communication barriers, lack of 3D visual feedback, and reduced tactile and force feedback to the surgeon.

• 

  Enhancing IR Sensor Coupling Using Surface Plasmon Resonances

  John S. Cetnar

  The mid-infrared (mid-IR) region of the electromagnetic spectrum is defined from λ ~ 8 – 14 μm. There are many important applications for mid-IR sensing including military, scientific, medical, and commercial. Unfortunately, the performance of current mid-IR detectors is limited by low optical absorption. Surface plasmons (SPs) can be used to enhance the coupling between mid-IR radiation and mid-IR detectors. There are many structures that can generate SPs in the mid-IR region. Two particular structures, the grating coupler and the Sierpinski carpet, seem particularly interesting. The grating coupler is of interest because of its good performance and simplicity of fabrication. The Sierpinski carpet is of interest because of its wide-band nature. The transmissivity of these two structures was investigated by numerical simulation using a full wave Finite Element Method software package called High Frequency Structure Simulator (HFSS). Preliminary results of the transmissivity calculations will be presented and discussed. In addition, the performance of HFSS for this application will be discussed.

• 

  Understanding the Magnetic Ground States for Improper Multiferroic Materials

  Jason T. Haraldsen

  Multiferroic materials have the unique multi-functionality of controlling magnetism through electric field and/or electric polarization through magnetic field, which presents possibilities for new technological advances and applications. To fully understand the connection between magnetism and electric polarization, one must have a full understanding of the underlying magnetic ground states within these materials. Through an investigation of the multiferroic material CuFeO2, I examine the effects of anisotropy and magnetic field on the frustrated triangular lattice and determine the magnetic ground states. Through a rotational algorithm of the Holstein-Primakoff expansion for the spin Hamiltonian, the spin-wave dynamics for the multiferroic and high-magnetic-field phases are determined. With the dynamics of the multiferroic phase, I modeled the experimental data of doped CuFeO2. From this detail analysis, it was concluded that the multiferroic ground state is that of a distorted incommensurate spiral, which provides insight into the effects of magnetic frustration within these materials. In closing, I will briefly discuss further research developments on the understanding of interfacial phenomena through magneto-electric coupling, and I will conclude with some future research directions in the pursuit of a full understanding multifunctional materials.

  This work was performed, in part, at the Center for Integrated Nanotechnologies, an Office of Science User Facility operated for the U.S. Department of Energy (DOE) Office of Science by Los Alamos National Laboratory (Contract DE-AC52-06NA25396).

• 

  A Bioinformatics Method for Identifying RNA Structures within Human Cells

  Stephen Donald Huff

  Single-stranded, negative-sense RNA (ssRNA-) serves many varied roles within the eukaryotic cell. Currently known examples include snRNA (short nuclear), snoRNA (short nucleolar), tRNA (transfer), siRNA (silencing), miRNA (micro), and others [1,2]. Unknown examples are currently being studied, also, including the long, non-coding ssRNA- found in the nuclear paraspeckle, a component of unknown function located within the eukaryotic nucleus and comprised of ssRNA- sequences transcribed from so-called ‘junk’ DNA [3,4]. While a growing list of confirmed physiological functions have been attributed to ssRNA-, additional roles likely exist and have yet to be discovered. Further, since ssRNA- is known to bind to proteins, nucleic polymers (DNA and RNA), small molecules and metallic ions, unknown roles attributable to such sequences are likely to be surprisingly diverse and of potential benefit to the modern warfighter. Unfortunately, contemporary biological assays for identifying functional ssRNA- sequences within eukaryotic cells are cumbersome, time-consuming and costly. Further, despite recent advances in software for folding ssRNA-, the computational process of folding the entire human genome remains an intractable problem.

  To resolve the traditional problems associated with this process, the proposed method leverages the long-term evolution of obligate intracellular parasites with small ssRNA- genomes to reduce the size and scope of the problem domain. These species have been evolving, adapting and attenuating cellular behavior to affect human physiology over the course of eons. Recent evidence suggests inter-genomic host-parasite interactions are vital to their continuing exploitation of eukaryotic physiology and successful evasion of host immunities [5, and unpublished dissertation results]. As a result of natural, long-term experimentation, these organisms have hypothetically derived many secondary and tertiary ssRNA- structures exhibiting vital influence within human physiology. Therefore, the proposed method will use inexpensive and open source software (Rosetta or ViennaRNA) to fold various pathogenic ssRNA- genomes, isolate functional single-stranded ‘loop’ sequences among the resultant structures, and then compare these short sequences to the human transcriptome using a novel computational protocol to identify structures related to human genes of interest (e.g., genes related to physiology, toxicity or to mitigation of toxicity). The resultant RNA sequence library should provide a rich source of multi-functional molecules with diverse applications to eukaryotic cellular control and potential association with high level physiological behaviors and dynamics.

• 

  From Solute Transport to Chemical Weathering

  Allen Hunt and Thomas E. Skinner

  A theory for conservative solute transport, based on concepts from percolation theory, is applied directly to reactive solute transport. Chemical reactions are assumed to have reached equilibrium at the scale of an individual pore, but at larger length scales, equilibration is limited by solute transport velocities, which are not the same as fluid velocities! The results of this theory already predicted observed dispersivity values for conservative solute transport over ten orders of magnitude of length scale as well as the variation of solute arrival time distributions with medium saturation. We now show that the solute velocity predicts the time-dependence of the weathering of silicate minerals over twelve orders of magnitude of time scale, an unprecedented result. Silicate weathering is a major input in the global carbon cycle.

• 

  Nanocomposite Alloy Design for Power Electronic Applications

  Michael McHenry

  Recent USDOE workshops highlight the need for advanced soft magnetic materials leveraged in novel designs of power electronic components and systems for power conditioning and grid integration. Similarly soft magnetic materials figure prominently in applications in electric vehicles and high torque motors. Dramatic weight and size reductions are possible in such applications by hold potential for applications in active magnetocaloric cooling of such devices. Bulk and thin film soft magnet sensors can contribute to the search for oil and critical materials. Opportunities for state of the art soft magnetic to impact such applications have been furthered by investment by USDOD Programs and other world wide efforts to advance these materials for applications in military electric vehicle technologies. This talk will focus on the framework for developing high frequency (f) magnetic materials for grid integration of renewable energy sources bridging the gap between materials development, component design, and system analysis. Examples from recent efforts to develop magnetic technology for lightweight, solid-state, medium voltage (>13 kV) energy conversion for MW-scale power applications will be illustrated. The potential for materials in other energy applications (motors, cooling, sensors, RF metal joining, etc.) will also be discussed. The scientific framework for nanocomposite magnetic materials that make high frequency components possible will be presented in terms of the materials paradigm of synthesis à structure à properties à performance. In particular, novel processing and the control of phase transformations and ultimately nanostructures has relied on the ability to probe structures on a nanoscale. Examples of nanostructural control of soft magnetic properties will be illustrated.

• 

  Sapling Learning's Online Homework System for Science Courses

  Jon Monahan

  Created and supported by educators, Sapling Learning’s online homework drives student success and saves educators time.

  Passionately Crafted Content: Sapling Learning authors are experienced educators. They are passionate about creating problem sets, targeted instructional feedback, and solutions which both challenge and guide students. Student errors are met with more than just hints. Authors write the same quality, detailed feedback that they would deliver to students in person. Multi-step tutorials and engaging, intuitive question types lead students through a dynamic study process with variation that strengthens comprehensive understanding.

  Targeted Instructional Feedback: Every question and tutorial from Sapling Learning is embedded with targeted instructional feedback to elicit common misconceptions and guide students down the right path. The experienced educators who craft each problem set express their passion in developing rich, quality feedback that mimics the instruction you provide your students. This just-in-time feedback leads students into a rewarding study process. The presentation within real student workflow means that the instant feedback is applied more effectively.

  Homework Management & Analytics: Sapling Learning helps you easily manage your course--from auto-graded assignments that feed into your gradebook to easy to use analytics that allow you to improve retention. Student results can be analyzed quickly to diagnose topics of weakness in your course and new assignments and quizzes can be assembled from a large library of relevant and customizable questions. Our authoring tool allows you to create new questions with your own specific feedback.

• 

  Quantum Tricks in the Shadows of Relativity and the Coulomb Force: Teaching Devices and Students How to Think Ultra-Fast

  Ilias Perakis

  The technological demand to bump the Gigahertz switching speed limit of today's magnetic memory and logic devices into the Terahertz regime underlies the entire field of spin-electronics and integrated multi-functional nano-devices. In this talk, I use theory and experiment to show how all-optical switching based on the quantum-mechanical manipulation of spins with a train of laser pulses could meet this challenge. The creation of magnetic correlations within femtoseconds, i.e. faster than one period of lattice oscillations, reveals a new temporal regime of magnetism. This field opened new directions for manipulating materials out-of-equilibrium using Terahertz, Mid-infrared, and X-ray pulses.

• 

  Slip Flow Regimes and Induced Fluid Structure in Nanoscale Polymer Films: Recent Results from Molecular Dynamics Simulations

  Nikolai V. Priezjev

  Over the last decade, there has been enormous interest in understanding transport phenomena in micro and nanofluidic systems and, in particular, in accurate prediction of fluid flows with slip boundary conditions at liquid-solid interfaces. In this presentation we will discuss recent results obtained from molecular dynamics simulations of fluids that consist of monomers or linear polymer chains confined by crystalline surfaces. The effects of shear rate and wall lattice orientation on the slip behavior are studied for a number of material parameters of the interface, such as fluid and wall densities, wall-fluid interaction energy, polymer chain length, and wall lattice type. A detailed analysis of the substrate-induced fluid structure and interfacial diffusion of fluid molecules is performed to identify slip flow regimes at low and high shear rates. It was found that at sufficiently high shear rates, the slip flow over flat crystalline surfaces is anisotropic, i.e., the slippage is enhanced when the flow direction is parallel to the crystallographic axis of the substrate. Furthermore, it is demonstrated numerically that the friction coefficient (the ratio of shear viscosity and slip length) undergoes a transition from a constant value to the power-law decay as a function of the slip velocity. The characteristic velocity of the transition correlates well with the diffusion velocity of monomers in the first fluid layer. We also show that in the linear regime, the friction coefficient is well described by a function of a single variable, which is a product of the magnitude of surface-induced peak in the structure factor and the contact density of the adjacent fluid layer.

• 

  Exploiting Quantum Phenomena Toward Technological Advancement

  Deborah Santamore

  Technological advancement is often associated with scaling down electronic devices. As the size decreases, quantum phenomena start to govern the device performance. Electron transport through real, and artificial, suspended molecular systems have revealed a rich tapestry of physical effects. Single-molecule electronics offer the promise of observing and controlling quantum effects in massive objects. In addition, the molecules provide the benefit of stronger coupling of vibrational and oscillatory modes to the transport process and a large range of practical applications than traditional nanoelectromechanical systems (NEMS). In this talk, I will discuss the steady-state electronic transport through a suspended dimer molecule transistor. When strongly coupled to a vibrational mode, the electron transport is enhanced at the phonon resonant frequency and higher-order resonances. Our results indicate the possibility of compensating the current decrease due to the thermal environment. Finally, I will describe my future research plans.

• 

  Dynamics and Kinetics of Radicals: Combustion to Multiscale Materials Modeling

  Amit R. Sharma

  Current combustion models have been developed and validated with low-pressure experimental data, and they fail at the high pressures of real devices. The goal of my research is to explore the fundamental effects of high pressure on the chemical kinetics of combustion relevant reactions. This knowledge will be used in the development of accurate models for combustion at the high pressures of current and future engines and novel alternate fuels. Some recent experimental studies of the recombination reactions have demonstrated a second-rise in the rate constant for loss of reactants at very high pressures. It has been speculated that this second-rise is due to the effect of the formation of complexes between the radical and the bath gas, however, no theoretical rate calculations have every been made. I will present a two transition state model; one at long-range, correlated with centrifugal barriers, and one at short range, correlated with the loss of entropy as a chemical bond is formed. The pressure-induced stabilization of an intermediate metastable complex (between the two transition states) could explain this increase. The onset of the radical-complex mechanism is governed by the equilibrium constant of the radical-complex species and the recombination rate coefficient is expected to rise above the traditional high-pressure limit, thus explaining the ``second-rise". An outlook to new class of reactions will be presented.

  Beyond the gas phase, radical chemistry is very important in the atomic/molecular scale dynamics of materials. Plasma-wall interaction in the fusion reactor results in the formation of codeposits and hydrocarbon flakes. Adsorption isotherms and transmission electron microscopy measurements reveal a multiscale structure made of meso- and macro-pores separated by semi-crystalline graphite and amorphous hydrocarbons. I will present a dynamical atomistic model of hydrocarbon radical interaction with amorphous hydrocarbon flake. A multiscale model for hydrogen isotope diffusion in codeposits will be presented. Similarities in the structural properties between energy storage materials, elementary transport processes in electrolyte membrane and the reactive-diffusion process of H atom in codeposits is seen. An outlook to develop multiscale modeling capabilities for materials modeling in energy storage devices will be presented.

• 

  High-Performance Thermal Management

  Kirk Yerkes

  Traditionally thermal management systems are designed for steady-state behavior. Air Force systems tend to be highly complex, coupled, and highly-dynamic. The concept of high-performance thermal management offers a paradigm shift in the technical approach to thermal management to one that addresses the inherent need to develop thermal management systems. This seminar will address the conceptual and philosophical approach to addressing the science and engineering needed to evolve thermal management technologies for high-performance and rapidly responding thermal management systems.