College of Arts and Sciences

Lecture 1: SPONTANEOUSLY-SYMMETRY-BROKEN ARCHIMEDES SCREWS: In the first technical lecture, I will use the tool box developed in treating time-dependent magnetoelectronic problems to consider a more general class of nonequilibrium phenomena in heterostructures with arbitrary spontaneous symmetry breaking. Motivated by the richness of physics in magnetic nanostructures, we are led to explore analogous phenomena in other symmetry-broken systems. As a first step in this direction, I will discuss a systematic way to construct “Archimedes screws” that are operated by semiclassical control of local orders. The “pumping” is achieved by means of a time-dependent order parameter which characterizes a broken symmetry and is controlled by external fields.

Continue reading… Michelson Postdoctoral Prize Lecture – Yaroslav Tserkovnyak

We will present the results of Monte Carlo simulations of nematic liquid crystals described by Lebwohl-Lasher-Rapini model. Detailed information on local order makes possible a calculation of diffractive index in case of inhomogeneous NLC order due to inhomogeneous electric field on the surface, resulting from laser illumination. The chess-box type of order will be discussed. A new phase diagram in variables external field-anchoring force will be discussed. The method for calculation of diffraction efficiency in an external modulated electric field will be discussed. Some applications to twisted NLC cell will be presented. Further possibilities of the approach will be discussed.

Continue reading… Monte Carlo simulations of inhomogeneous order in nematic liquid crystal cells: optical applications – Antoni C. Mitus

Atomic Force Microscopy (AFM) has become an indispensable tool in nanoscience and nanotechnology. In this talk, I will not only show routine application of topographical imaging with nanometer resolution, but also demonstrate further studies that benefit from quantitative measurements of small forces. Examples include complete force profiles between SAMs, interfacial electric dipole, and energy level alignment in organic thin-film-transistors.

Continue reading… Forces on Small Scales – Liwei Chen

Continue reading… Scanned Probe Magnetic Resonance: The Magnetic Resonance Force Microscope – Chris Hammel

Orientational order is a universal feature of numerous soft-matter systems, most notably liquid crystals. These systems are extremely flexible, producing a rich variety of complex 3D patterns of order parameter. Non-destructive techniques to study and control these patterns are in a great demand. This talk discusses how a tightly focused laser beam can serve as a tool to image complex patterns of the director and to manipulate them. (1) In the fluorescence confocal polarizing microscopy (FCPM), the focused laser beam allows one to image 3D patterns of orientational order. We employ the property of anisotropic media to align fluorescent dye molecules.

Continue reading… Focused laser beams and liquid crystals: Three-dimensional imaging and control of topological defects and measurements of colloidal interactions – Oleg Lavrentovich

The ability to manipulate spin of charge carries in a controllable fashion is central to the rapidly developing field of spintronics, as well as for the development of spin-based devices for quantum information processing. Electrical injection of spin-polarized currents is proven to be a formidable challenge. We realized a solid-state analog of the famous Stern-Gerlach experiment in atomic physics, with spin-orbit interactions playing the role of the gradient of magnetic field. We achieved spatial separation of spins and bipolar spin filtering using cyclotron motion in a weak magnetic field.

Continue reading… Spin separation in cyclotron motion – Leonid Rokhinson

Organic conjugated macromolecules have received great attention due to their use in optical and electronic applications. Certain molecular aggregate systems have shown enhanced nonlinear optical properties by virtue of excitonic coupling in the multi-chromophore system. Organic dendrimers and other branched multi-chromophore systems (where the chromophores are covalently attached) have also shown characteristic properties of strong intramolecular interactions which have been utilized in light harvesting processes, light emitting diodes, as well as for enhanced nonlinear optical effects. The mechanism of the strong intramolecular interactions in branched chromophores depends on the nature of the branching center, the geometrical orientation of covalently attached chromophores,

Continue reading… Investigations of Light Harvesting and Enhanced Nonlinear Optical Properties in Organic Dendrimers and Branched Macromolecules – Theodore Goodson III

Continue reading… Correlations Stablize Blue Phases – Lech Longa

In addition to its large scale in-plane properties, transport in (quasi) two-dimensional electron systems is sensitive to microscopic details in the transverse direction. An efficient tool to study the interplay between both is a parallel magnetic field, which probes the structure of wave functions perpendicular to the plane. Due to the Berry-Robnik symmetry effect, one finds that the magnetoresistance contains information on the geometry of the confining potential as well as characteristics of the disorder.

Continue reading… Magnetoresistance in Parallel Fields – Julia Meyer

Radiation trapping in an illuminated gas of atoms refers to the reabsorption of spontaneously emitted photons. This reabsorption prevents the formation of colder denser atomic samples for quantum degenerate studies in ultracold trapped gases. Furthermore, the decoherence induced by this reabsorption significantly affects a vast variety of important experiments that rely on the preparation of macroscopic coherent atomic samples, for example, experiments that propose a practical implementation of a quantum computer. Clearly, it is of interest to devise experimental techniques that detect extremely small amounts of radiation trapping in dilute gases. We will show that the photon statistics of the light scattered from a trapped sample of cold dilute gas is a highly sensitive non-invasive probe of radiation trapping in the sample.

Continue reading… Sensitive Detection of Radiation Trapping in a Cold Dilute Gas – Samir Bali

Dave will discuss nanotechnology education as a challenge in both the areas of public education in science (for the K-99 audience ) and as another battle of hype against reality; science fiction against science. How he currently teaches freshman-level nanotechnology will be discussed as will the experimental platform he uses, called the Nanopedia, the Web Encyclopedia of Nanotechnology, for which he has a modest NSF grant, shared with Alexis Abramson of the engineering school. He will particularly discuss some of the science fiction aspects of Michael Chrichton’s novel “Prey,” about nanotechnology gone awry, asking for audience comments on whats right and what’s not.

Continue reading… Challenge of Public and Workforce Education in Nanotechnology: Science vs Science Fiction – David Smith

ZnO is one of the top candidates for blue light optoelectronics because of its wide bandgap properties. However, fabricating high quality p-type ZnO has proven to be difficult. While none of the group-I doping yields p-type behavior and Nitrogen doping shows only limited success, doping with larger group-V elements, which should cause high strain and has low solubility on the oxygen site, show some preliminary surprising success. Based on first principles calculations, we have developed a model involving complex doping that could explain the observed p-type behavior in P-, As-, and Sb-doped ZnO and fits well with experimental growth/annealing conditions.

Continue reading… First-principles investigations of p-type doping in ZnO – Sukit Limpijumnong

Semiconductor quantum dots have optical properties similar to simple atomic systems, unlike higher dimensional semiconductor structures that are dominated by manybody physics associated with the continuum states. They also provide a potentially ideal electronic structure appropriate for quantum computing. The data shows that these structures can be coherently controlled on a time scale short compared to the quantum decoherence time and that entangled states of qubits (represented by exciton optical Bloch vectors) can be created. The system is remarkably robust against pure dephasing and we have been able to demonstrate a simple conditional quantum logic device involving multiple Rabi flops of the exciton and biexciton.

Continue reading… Optical control in semiconductor dots for quantum operations – Duncan Steel

I will describe two applications of entropy. The first one is relevant to mixing in polymer processing. The other one is relevant to developing a diagnostic tool for low back pain. I analyze the advection of light particles carried by a high viscosity fluid set in motion in a long channel of rectangular cross section and covered by an infinite plate moving at constant velocity. This is a model of a screw extruder, a basic tool for polymer processing. I present an analytic solution of the creeping flow (zero Reynolds number). I analyze the quality and rate of mixing of the particles by calculating Renyi entropies.

Continue reading… Entropy Applications to Engineering and Health Science – Miron Kaufman

Electronic transport and charge carrier trapping in the nanocrystalline Si/amorphous SiO2 superlattices were investigated by impedance spectroscopy, dc photoconductivity, and transient photocurrent measurements. The method for evaluation of the density of interface traps from the impedance spectroscopy measurements was developed to controll the quality of the superlattices. Transport of charge carrier in the superlattices at low temperatures was found to be the resonant tunneling of holes between quantum confined states of the valence band of Si nanocrystals. The measured electronic structure of the valence band of Si nanocrystal is in good agreement with the TB calculations. Application of the nanocryslalline Si/amorphous SiO2 superlattices to non-volatile memory cells will be discussed.

Continue reading… Resonant charge carrier tunneling in nanocrystalline Si/amorphous SiO2 superlattices – Volodimyr Duzhko

The generation of widely tunable coherent terahertz (THz) frequencies is of great interest for a variety of applications in basic and applied sciences. Broadband THz sources, particularly those based on femtosecond lasers, have already shown much promise in addressing these applications. In this seminar, I will present a narrow bandwidth approach to THz generation by means of difference frequency generation (DFG) between two lasers. Provided that one or both of the laser sources are tunable, the DFG technique offers a pathway to tunable narrowband THz frequencies. Our results based on mixing the output of two seeded optical parametric generators will show narrow-bandwidth and tunable operation from 1.6 to 4.5 THz.

Continue reading… Exploring the terahertz region with a narrowband tunable source – Peter Powers

Devices based on organic semiconductors are a new, growing sector of the electronics market. For use as, e.g., field-effect transistors, a primary determinant of the utility of a material is the mobility, the proportionality coefficient between charge velocity and electric field. We report detailed pulsed-laser time-of-flight measurements on a simple crystalline system, 1,4-diiodobenzene, with a room temperature mobility at least an order of magnitude larger than competing inorganic materials (e.g., amorphous silicon). I will discuss purification, crystal growth, and a detailed analysis we have developed to extract other properties besides mobilities from the time-of-flight data. Finally, I will mention ab-initio calculations of electronic structure that indicate that the iodine constituents possibly play a major role in transport.

Continue reading… Old Method, New Results: Ultra-High Mobility in a Simple Organic Crystalline Semiconductor – Brett Ellman

Time- and frequency-domain 3-wave mixing spectroscopies (infrared + visible Sum Frequency Generation, SFG) are presented as the lowest-order nonlinear techniques that are both surface-selective and capable of measuring vibrational coherences. Application to ordered Langmuir-Blodgett monolayers shows vibrational quantum beats in time domain, which are connected to the frequency-domain spectrum by a simple Bloch-type model. The beat pattern is shown to be sensitive to the molecular order in the film. A mixed time-frequency domain version of this technique is applied to study ultrafast dynamics of the hydrogen bond network of interfacial water. Along with the vibrational dephasing, we observe ultrafast spectral diffusion of the OD stretch of D2O at the CaF2 surface,

Continue reading… Coherent time-resolved vibrational spectroscopy of surfaces and interfaces – Alex V. Benderskii

The biaxial nematic phase was predicted more than three decades ago and discovered in lyotropic liquid crystalline systems by Yu and Saupe in 1980. However, several attempts to invent and synthesize new thermotropic materials likely to form this phase did not succeed. Several reports of its discovery in the thermotropic materials have proven to be without merit. While investigating the structure of smectic phases in bent-core (or, banana) mesogens, we came across unusual diffraction pattern in their nematic phase. The experimental investigations that followed and modeling, have established their biaxial nature. Recently synthesized materials exhibit the existence of, both, the uniaxial and the biaxial nematic phase.

Continue reading… The mystery of the thermotropic biaxial nematic phase – Satyen Kumar

An exciton is bound state of a free, negatively charged electron and a postively charged hole in a semiconductor. Excitons act in many ways like hydrogen atoms which can move through a semiconductor and interact with each other much like a gas of atoms. While often excitons have very short lifetime (a few picoseconds), we have developed methods to extend their lifetime by several orders of magnitude, up to 10 microseconds, so that they can travel hundreds of microns across a semiconductor structure. We can also apply a force to the excitons to cause them to move in the direction we want,

Continue reading… A Gas of Excitons: Moving and Trapping Electronic Quasi-Atoms – David Snoke

Electron spin injection efficiencies up to 40% have been obtained in Fe/AlGaAs(n) Schottky barriers. The spin polarized electrons are collected by a GaAs well and recombine with unpolarized holes. The optical polarization of the emitted excitonic electroluminescence yields a direct measurement of the electron spin polarization in the well. We will concentrate on the following aspects of the spin injection process in this system: a. Phonon assisted recombination b. The effect of confined electrons in the GaAs quantum well c. The transition from a bulk-like three-dimensional to a two-dimensional regime in wide well spin LEDs

Continue reading… Spin injection from ferromagnetic Fe contacts into GaAs/AlGaAs spin LEDs – Athos Petrou

Continue reading… Defect dynamics in nematic liquid crystals – Maurizio Nobili

Langmuir Blodget (LB) monolayer films of the lithium salt of 10,12-nonacosadiynoic acid monomer and polymer LB monolayers were studied by AFM and electron diffraction. The fast Fourier transform of the AFM image was compared to electron diffraction results. The comparison gave insights into both sets of results. The analysis and conclusions will be discussed.

Continue reading… Surface Structure Determination of a Diacetylene of Monomer and Polymer LB Monolayers by AFM as Compared to Electron Diffraction – J. B. Lando

The search for technological solutions for ultra high density magnetic storage devices requires to achieve thermal stability and higher signal to noise ratio for dramatically decreasing media grain size and geometrical dimensions of the field sensing elements. In this work we consider a few specific examples where it is necessary to consider atomic scale effects and correspondingly to achieve a quantitative level of understanding magnetic interactions as possible future design factors for ultra-high density magnetic storage devices. One of the possible and most researched options to advance in the magnetic recording media is to use large magneto-crystalline anisotropy (MCA) materials,

Continue reading… Magnetic interactions and properties of 3d-5d/4d nano-particles: exchange interactions mediated by non-magnetic metallic atoms – Oleg N. Mryasov