seminar abstracts
.................................................................................................................................................................................

ISIS DISTINGUISHED LECTURE Dr. Roberto Car Ralph W. Dornte *31 Professor in Chemistry Princeton University Monday, May 5, 2008 4:00 pm 104 Rowland Hall Title: Quantum Water Abstract: Water, the most important liquid on earth, owes its unusual properties to a fluctuating network of hydrogen bonds. This causes adjacent molecules to become strongly correlated and makes this liquid quite different from a simple fluid. Quantum mechanics profoundly affects the behavior of water at the molecular scale. On the one hand it defines the adiabatic dynamics of the electrons which is at the origin of intermolecular correlations. On the other hand also the nuclei, and particularly the protons, need a quantum mechanical treatment as indicated by the large isotope effects that are observed experimentally. In this talk I will review some of the challenges faced by first-principles simulations in this field and will discuss future perspectives. Host:  Reg Penner PHYSICS COLLOQUIUM Dr. Roberto Car Ralph W. Dornte *31 Professor in Chemistry Princeton University Thursday, May 8, 2008 3:30 pm 101 Rowland Hall Title: Band Alignment and Tunneling Conductance through Long Molecular Wires Abstract: Experiments indicate that the linear, low bias, conductance of devices made by long insulating molecular chains connected to metallic electrodes decays exponentially with the number n of monomers in the molecular chain, according to a simple tunneling law which depends on two parameters, the decay constant and the pre-exponential factor . Understanding how , the contact conductance, and depend on the properties of the molecule, of the electrodes, and of the contacts is an issue of relevant current interest. In this talk I will show that the above tunneling law can be derived under general assumptions from linear response theory within the Kohn Sham density functional formalism. This approach shows that depends on the alignment of the molecular band edges with respect to the Fermi energy of the electrodes, while is directly related to the chemistry of the contacts. Calculations based on this approach will be presented, emphasizing open problems and future perspectives. Host:  Kieron Burke THEORETICAL CHEMISTRY SEMINAR Professor Annabella Selloni Princeton University Friday, May 9, 2008 2:00 pm 2201 Natural Sciences II Title: Structure and sensitization of titanium dioxide surfaces Abstract: This talk will give an overview of recent theoretical work meant at obtaining insights into issues relevant to TiO2-based photocatalysis. Topics to be discussed include the influence of surface structure on the adsorption of different species, and surface sensitization via adsorbed chromophores  as used in dye sensitized solar cells. Host:  Kieron Burke The Institute for Surface and Interface Science (ISIS) and The Department of Physics and Astronomy present: Dr. Matthias Bode Center for Nanoscale Materials, Argonne National Laboratory Wednesday, march 5, 2008 4:00 pm 1201 Natural Sciences II Title:  The many faces of magnetism in Fe nanostructures imaged by spin-polarized STM Abstract:  Continuum micromagnetic theory has successfully been used in the past to model spin structures of surfaces and films.  Since this theoretical approach disregards the atomic structure of matter it is expected to breakdown as the spin orientation changes on length scales comparable with the lattice constant.  Only recently, the high lateral resolution of spin-polarized scanning tunneling microscopy (SP-STM) allows to scrutinize continuum micromagnetic theory.  In my talk I will present results which reveal a variety of magnetic domain and spin structures, all obtained on Fe epitaxially grown on single-crystalline tungsten substrates, ranging from magnetic vortices, over stripe domain phases and single domain islands, down to superparamagnetic islands and antiferromagnetic Fe.    The data show that micromagnetic theory is capable of describing the spin structure of domain walls as narrow as a few nanometer. Host: Doug Mills

The Institute for Surface and Interface Science (ISIS) presents: Jim De Yoreo Lawrence Livermore National Laboratory Title: “Physical controls on assembly of biomolecular materials”   Abstract: Systematic organization of protein complexes as well as protein-directed formation of inorganic solids enables living organisms to achieve a high density of functionality and create hierarchical materials with unique properties.  Conversely, when these processes proceed without the proper level of control, they often result in disease.   Consequently, developing a fundamental understanding of the thermodynamic and kinetic controls on protein and protein-directed assembly can define new strategies towards both materials synthesis and the treatment of disease.  To develop that understanding, we have used in situ force microscopy, molecular modeling, and X-ray absorption spectroscopy to investigate macromolecular assembly and protein-directed crystallization.       In the first part of the talk, I will present the results of investigations into biomineralization that argue for a change in the paradigm commonly used to explain controls on mineral shape and kinetics.  The results show that small molecules, organic modifiers, and proteins exhibit a wide range of control mechanisms, but in all cases crystal shape is driven kinetically by recognition of the modifiers for the atomic structure at step edges.  While the effects of proteins and peptides on step kinetics are inhibitory at high concentrations, at low levels they act to accelerate the kinetics to a degree that scales with their hydrophobicity.  These results demonstrate the importance of solution structure on mediating protein-surface interactions and reveal the physical mechanisms by which control is established.       In the second portion of this talk, I will show how protein engineering combined with chemical synthesis and scanned probe nanolithography can be used to template deposition and assembly of macromolecules.  In particular, using engineered viruses as adsorbates and a set of alkyl thiol "inks" that act as either protein resists, covalent binders, or reversible linkers, one can direct the adsorption of these viruses into nanoscale arrays that subsequently act as nucleation sources for virus assembly.  By varying surface chemistry, virus concentration, and  solution composition, one can tune the mobility, flux, and interaction potentials that drive assembly.  In situ measurements reveal characteristic growth laws and lead to the hypothesis that templated assembly of macromolecules can be described as the one-dimensional equivalent of colloidal crystallization with tuneable interactions. Monday, January 14, 2008 4:00 pm 2201 Natural Sciences II Host: Greg Weiss

The Institute for Surface and Interface Science (ISIS) presents: Dr. Ofir Alon University of Heidelberg Friday, January 11, 2008 2:00 pm 1201 Natural Sciences II Title: “Statics and dynamics of interacting Bose gases: Multi-orbital mean-field and beyond”   Abstract: The necessity to go beyond the popular Gross-Pitaevskii theory to properly describe strongly-interacting cold bosonic atoms, and even weakly-interacting atoms in double- and multi-well traps has by now become well-accepted by the community. We present new theoretical and computational approaches going beyond standard mean-field. These have enabled us to predict new physical phenomena. I discuss fragmentation of repulsive and attractive condensates; a zoo of Mott-insulator phases in optical lattices [thereby going beyond the popular Bose-Hubbard model]; demixing scenarios of bosonic mixtures in optical lattices on various length scales; the pathway to fermionization of trapped cold bosonic systems; interferences in the density of two condensates consisting of identical or different atoms; and how to split a Bose-Einstein condensate. Host: Vladimir Mandelshtam

The Institute for Surface and Interface Science (ISIS) presents: Dr. Andreas Heinrich IBM Almaden Research Center December 10, 2007 11:00 am 2111 FRH Title: Magnetism on the Atomic Scale Abstract: Understanding and controlling the magnetic properties of nanoscale systems is crucial for the implementation of future data storage and computation paradigms. Here we show how the magnetic properties of individual atoms can be probed with a low-temperature, high-field scanning tunneling microscope when the atom is placed on a thin insulator. We find clear evidence of magnetic anisotropy in the spin excitation spectra of individual magnetic atoms embedded in a non-magnetic surface. In extended one-dimensional spin chains, which we build one atom at a time, we find strong spin-coupling into collective quantum-spins, even for the longest chains of length 3.5nm. The spectroscopic results can be understood with the model of spin-excitations in a system with antiferromagnetic coupling, controlled on the atomic scale. High-spin atoms can show an interesting form of the Kondo effect when the magnetic anisotropy places a degenerate, low-spin Kramers-doublet in the ground-state. Host: Ruqian Wu The Institute for Surface and Interface Science (ISIS) presents: Professor Joanna Aizenberg Gordon McKay Professor of Materials Science Professor of Chemistry and Chemical Biology Harvard University Monday, November 5, 2007 3:00 pm 1201 NSII Title: Designing organic-inorganic interfaces for controlled crystallization: A bio-inspired approach Abstract: Nature produces a wide variety of exquisite mineralized tissues fulfilling diverse functions, and often from simple inorganic salts.  Organisms exercise a level of molecular control over the physico-chemical properties of inorganic crystals that is unparalleled in today's technology.  This reflects directly or indirectly the controlling activity of biological organic surfaces that are involved in the formation of these materials.  Biomineralization occurs within specific microenvironments, which implies stimulation of crystal formation at certain interfacial sites and relative inhibition of the process at all other sites.  Our approach to artificial crystallization is based on the combination of the two latter concepts: that is, the use of organized organic surfaces patterned with specific initiation domains on a sub-micron scale to study and orchestrate the crystallization process.  This bio-inspired engineering effort made it possible to achieve a remarkable level of control over various aspects of the crystal nucleation and growth, including the precise localization of particles, nucleation density, crystal sizes, morphology, crystallographic orientation, arbitrary  shapes, microstructure, stability and architecture.  The ability to construct large, defect-free, micropatterned single crystals with controlled microporosity; periodic arrays of uniform, oriented crystals or films presenting patterns of crystals offers a new synthetic methodology to materials engineering. Host: Zhibin Guan

Chemical Bonding Center (CBC) and ISIS present: Dr. Erik Muller Center for Functional Nanomaterials Brookhaven National Laboratory Thursday, October 25, 2007 12:00 pm - 1:00 pm 2201 Natural Sciences II Title: Electric force microscopy of pentacene transistors and scanning tunneling microscopy of hydrogen dissociation in sodium alanate Abstract: I will discuss results of scanning probe techniques applied to organic semi-conducting devices and model systems for hydrogen storage. First, electric force microscopy is applied to investigate charge traps in pentacene devices. Correlating topography with charge trap distributions and surface potential shows that the trap spatial distribution is not related to topography. Measurements of the trap dynamics support the assertion that the origin of trapping in these devices is chemical in nature. Second, scanning tunneling microscopy is used to investigate hydrogen dissociation catalysis in a promising hydrogen storage material, sodium alanate. Titanium doped aluminum surfaces are used as a model surface for studying the interaction with atomic and molecular hydrogen. The presence of a large population of predicted catalytically active sites are determined. Host: Wilson Ho

The Institute for Surface and Interface Science & the Chemical Bonding Center (ISIS & CBC) present: Kristin L. Wustholz University of Washington October 1, 2007 12:00 pm 2201 Natl Sci II Title: Dispersive Kinetics from Single Molecules Oriented in Single Crystals of Potassium Acid Phthalate Abstract:  The intermittent emission or "blinking" of single violamine R (VR) and 2',7'- dichlorofluorescein (DCF) molecules incorporated into single crystals of potassium acid phthalate (KAP) is studied using confocal fluorescence microscopy. Blinking dynamics are quantified in terms of switching rates and on- and off-time probability distributions. Mixed crystals of KAP/VR and KAP/DCF consist of photophysical sub-populations with ~40% and ~20% exhibiting persistent emission, respectively, and the remainder demonstrating a broad range of blinking behavior that is well described by a power-law distribution. The blinking dynamics are modeled using Monte Carlo simulations based on a three-level electronic system with the rate constants for population and depopulation of the "dark" state being distributed. No correlation between molecular orientation and blinking dynamics is observed, suggesting that intermolecular electron-transfer is not the origin of the power-law behavior. Alternative origins for this behavior (e.g., conformational flexibility and spectral diffusion) are explored using a combination of experimental and computational techniques HOST:  Rob Corn

Kohei Uosaki Professor of Physical Chemistry Division of Chemistry Graduate School of Science Hokkaido University Sapporo 060-0810, Japan September 4, 2007 3 pm NS II 2201 Title: Molecular Structures at Solid/Liquid Interfaces by Sum Frequency Generation Spectroscopy To understand the properties and chemical reaction mechanisms at solid/liquid interfaces, it is essential to determine the structure of molecules at the interfaces including water and short-lived reaction intermediates. One needs to use surface specific techniques for this purpose because there is much larger number of molecules in solution. Sum frequency generation (SFG) spectroscopy is an interface-selective probe and has been applied to determine the interfacial molecular structure in many systems, including solid/liquid interfaces. Furthermore, time-resolved surface vibrational spectroscopy to investigate the mechanism of chemical reactions at solid/liquid interfaces based on SFG is possible because short pulse laser is used. We used two SFG systems, one based on a ps Nd:YAG laser and the other based on a Ti:sapphire regenerative amplifier system. We have carried out SFG investigations at a wide variety of interfaces including: 1. SFG intensity of OH stretching vibration at the interfaces between an aqueous electrolyte solution and a quartz surface modified by a self-assembled monolayer (SAM) was found to be very strongly dependent on the terminal group of the SAM and pH and ionic strength of the solution. 2. Interfacial structures of alkylated polyvinylpyridine (Cn-PVP) brushes with various side chain lengths (n = 0, 2, 6, 12) in dry nitrogen, water vapor, liquid water, and aqueous electrolyte solution were investigated by SFG. The conformational order of the side chain depended on the chain length with the highest at hexyl side chain. Molecular conformations of all the brushes became less ordered upon contact with water and were almost completely disordered in liquid water. 3. SFG intensity of the hydrogen-bonded OH bands on TiO2 surface increased after UV illumination, reflecting the increase of orientational order of water as a result of UV induced increase of hydrophilicity of the TiO2 surface. 4. Potential dependent water structures at metal electrodes such as Pt and Au were also studied. References: (1) S. Ye, S. Nihonyanagi and K. Uosaki, PCCP, 3, 3463 (2001). (2) S. Nihonyanagi, D. Miyamoto, S. Idojiri, and K. Uosaki, J. Am. Chem. Soc., 126, 7034 (2004). (3) K. Uosaki, T. Yano, and S. Nihonyanagi, J. Phys. Chem. B, 108, 19086 (2004). (4) S. Nihonyanagi, S. Ye, K. Uosaki, L. Dreesen, C. Humbert, P. Thiry and A. Paremans, Surf. Sci., 573, 11 (2004). (5) H. Noguchi, T. Okada, and K, Uosaki, J. Phys. Chem. B, 110, 15055 (2006). HOST:  Rob Corn

The Institute for Surface and Interface Science & the Chemical Bonding Center (ISIS & CBC) present: Mats Persson Surface Science Research Centre/Department of Chemistry The University of Liverpool, UK August 27, 2007 3 pm 1201 Nat  Sci II Title: Electronic Friction and Excitations in Molecule-Surface Interactions Abstract: A long-standing issue in surface science has been the role of electronic non-adiabaticity in the interactions of atoms and molecules with metal surfaces. The absence of any energy gap for electron-hole pair excitations of a metal substrate results in general of a breakdown of the adiabatic (Born-Oppenheimer) approximation for the electronic motion in response to ionic motion. A key question is whether this electronic non-adiabaticity is sufficiently strong to be important in dynamical processes at surfaces or not. The progress in the theoretical description of the electronic structure of adsorbates using density functional theory has made it possible to calculate the electronic non-adiabatic coupling for more or less realistic systems and we can now address this question in a more quantitative manner. A most elementary case is provided by electron-hole pair damping of adsorbate vibrations, whose theoretical treatment will be the starting point for this talk that will cover theory of electronic adiabaticity in transition state dynamics, hot-electron induced surface chemistry, chemically-induced electronic excitations upon adsorption of atoms and molecules, and exo-electron emission in vibrational de-excitation in scattering from surfaces.

Professor H.-J Freund Director of the Fritz-Haber-Institute of the Max Planck Society, Berlin August 9, 2007 3:00 p.m. NS2 1201 Title: Photochemistry and Metal nanoparticles Abstract:  We are interested in the influence of the finite size of metal particles onto the photochemistry at their surfaces. To this end we prepare Ag nano particles by nucleation and growth on thin oxide (alumina) film surfaces and apply scanning tunneling microscopy not only to unravel their morphology but also to investigate their excited states, i.e. their surface plasmons. Using a photon-STM we are able to do this on individual particles.The goal of our studies is to learn more about the influence of the plasmonic excited states on the photodesorption from the nano particles. We study photodesorption using time of flight mass spectrometry and also quantum state resolved techniques and apply it to NO and Xe.

Wolfgang Knoll Max-Planck-Institute for Polymer Research Mainz, Germany Email: knoll@mpip-mainz.mpg.de Wednesday, June 20, 2007 1:00 p.m. 1201 Nat. Sci. II Title: Tethered Bimolecular Lipid Membranes-a Novel Model Membrane Platform Abstract:  This contribution summarizes some of our efforts in designing, synthesizing, assembling, and characterizing functional tethered lipid bilayer membranes (tBLMs) as a novel platform for biophysical studies of and with artificial membranes or for sensor development employing, e.g., membrane integral receptor proteins. Chemical coupling schemes based on thiol groups for Au substrates or silanes used in the case of oxide surfaces allow for the covalent and, hence, chemically and mechanically robust attachment of anchor lipids to the solid support, stabilizing the proximal layer of a tethered membrane on the transducer surface. Surface plasmon optics, the quartz crystal microbalance, fluorescence- and IR spectroscopies, and electrochemical techniques are used to characterize the build-up of these complex supramolecular interfacial architectures. We demonstrate, in particular, that bilayers with a specific electrical resistance of better than 10 M_cm2 can be achieved routinely with this approach. The functionalization of the lipid membranes by the incorporation of peptides is demonstrated for the carrier valinomycin which shows in our tBLMs the expected discrimination by four orders of magnitude between the translocation of K+ and Na+ -ions across the hydrophobic barrier. For the synthetic channel-forming peptide M2 the high electrical resistance of the bilayer with the correspondingly low background current allows for the recording of even single channel current fluctuations. >From the many membrane proteins that we reconstituted so far we describe results obtained with the redox-protein Cytochrome c Oxidase. Here, we also use a genetically modified mutant with a his-tag at either the C- or the N-terminus for the oriented attachment of the protein via the NTA/Ni2+ approach. With this strategy, we not only can control the density of the immobilized functional units, we introduce a completely new and alternative concept for the stabilization of lipid bilayers, i.e., the protein-tethered membrane. Our efforts in experimentally characterizing the resulting membrane functions and correlating the data with the structural details of the bilayer architectures are complemented by theoretical studies modeling the electrical and electrochemical response of functional tethered lipid bilayer membranes by extended SPICE simulations.

ISIS Distinguished Lecture: Wolfgang Knoll Max-Planck-Institute for Polymer Research Mainz, Germany Email: knoll@mpip-mainz.mpg.de Thursday, June 21, 2007 4 p.m 1201 NSII  Title: Nanoscopic Building Blocks from Polymers, Metals, and Semiconductors for Hybrid Assemblies and Nanostructured Materials Abstract:  This contribution summarizes some of our efforts in designing, synthesizing, and characterizing – both structurally and functionally – hybrid aggregates and materials assembled from nanoscopic building blocks of polymers, (noble) metals, and semiconductors (cf. Figure 1) for future applications, e.g., in opto-electronics and for biosensing. Dendrimers are introduced as a novel class of polymers that are strictly monodisperse, hence have all the same molecular mass. In the case of paraphenylene dendrimers that are in addition to their excellent chemical stability also shape-persistent it is thus justified to speak of polymeric objects that can be regarded as building blocks for complex architectures. Noble metals play a particularly exciting role for the fabrication of nanoscopic structures due to their localized plasmonic resonances that can be observed, e.g., in Au particles of different sizes and shapes. Optical field enhancements of up to a factor of 106 have been reported experimentally and predicted theoretically. We will present the fabrication and optical characterization of non-trivial Au colloids prepared in the shape of nano-crescents that exhibit interesting optical properties that might result in novel bio-sensor designs based on single resonant objects. And finally, nanoparticles from semiconducting materials, the quantum dots, will be discussed. The possibility of engineering their bandgap, thus tuning their optical emission properties make them most interesting candidates for various device concepts in opto-electronics and as labels for bio-affinity studies.

The Institute for Surface and Interface Science (ISIS) and CBC present: Professor H. Kumar Wickramasinghe IBM Fellow Professor of Electrical Engineering and Computer Science and The Henry Samueli Endowed Chair University of California, Irvine May 25, 2007 2:00 pm 1114 Nat Sci I Title: Scanning Probe Microscopy and their Applications to Technology Abstract:  Scanning Probe Microscopes have become essential tools for nanotechnology. We will discuss the development of this field from its very early days. The first part of the talk will focus on the speaker's experiences driving the AFM technology from its infancy into fully hardened instruments for use both within and outside IBM. The second part will describe some recent projects the speaker has initiated and driven. They range from apertureless near-field optics for thermally assisted magnetic recording aimed at extending the super paramagnetic limit in magnetic recording to nanoscale strain measurement to work on a novel x-ray nano-scope, and the  development of an ultra high speed DNA separation technology which can separate DNA strands at speeds that are 10,000 times faster than current micro fluidic separation technologies. Implications for some these technologies will be discussed. Host: Wilson Ho

The Institute for Surface and Interface Science (ISIS) and CBC present: Sergei Smirnov Department of Chemistry and Biochemistry New Mexico State University, Las Cruces, NM May 4, 2007 4135 FRH 2 p.m. Title: PHOTOINDUCED CHARGE TRANSFER IN ORGANIC MONOLAYERS Abstract:  Charge transfer and photoinduced charge transfer in particular are in the heart of various applications as well as of many natural phenomena. Studying such phenomena on molecular systems using electrical measurements is often hindered and controlled by poor quality of electrical contacts to molecules. Can electrical properties of molecules be studied without making Ohmic contacts? The bulk of this presentation is dedicated to demonstration of the capacitive coupling approach for investigating intramolecular photoinduced charge transfer.1-6 Molecules in solution and on solid surfaces can be studied and each method offers unique advantages and disadvantages, which will be demonstrated. The latter method is realized with molecules covalently linked to metal oxides.5-8 For small molecules the signal has unexpendingly strong dependence on solvent polarity and even is opposite in sign in the gas phase. The amplitude is maximal in vacuum and declines in accordance with increasing collision frequency dependent on the gas pressure and its mass. Collisions with paramagnetic oxygen induce intersystem crossing to long-lived triplet charge transfer states with the rate close to the half of that for the collision. Other applications originated from exploring chemistry of molecules linked to solid surfaces will be briefly described as well. They are based on using modified nanoporous membranes for biochemical sensinng.9-14 References 1. S. Smirnov, P.A. Liddell, I. Vlassiouk, A.Teslja, D. Kuciauskas, C.L.Braun, A.L. Moore, T. A. Moore, and D. Gust,, J. Phys. Chem. A, 2003, 107, 7567 2. F.-P. Montforts, I. Vlassiouk, S. Smirnov; M. Wedel, J. Porph. Phthal., 2003, 7, 651 3. S. Smirnov, I. Vlassiouk, O.Kutzki, M.Wedel, F.Montforts,  JACS, 2002, 124, 4212 4. I.Vlassiouk, S.Smirnov, O.Kutzki, M.Wedel, F.-P.Montforts, J. Phys. Chem., 2002, 106, 8657 5. Krasnoslobodtsev A., Smirnov S.,  J. Phys. Chem., 2006, 110, 17931 6. Krasnoslobodtsev A., Smirnov S., J. Phys. Chem., 2006, 110, 17941 7. Krasnoslobodtsev A., Smirnov S., Langmuir, 2001, 17, 7539 8. Krasnoslobodtsev A., Smirnov S., Langmuir, 2002, 18, 3181 9. I. Vlassiouk, A.Krasnoslobodtsev, S.Smirnov,M.Germann, Langmuir, 2004, 20 9913 10. I. Vlassiouk, P.Takmakov, S.Smirnov, Langmuir, 2005, 21, 4776 11. I. Vlassiouk, C.-D.Park, S.A.Vail, D. Gust, S. Smirnov, Nano Letters, 2006, 6, 1013 12. V. Szczepanski, I. Vlassiouk, S. Smirnov, J. Membr. Sci., 2006, 281, 587 13. P. Takmakov, I. Vlassiouk, S. Smirnov, Anal. Bioanal. Chem., 2006, 385, 954 14. P. Takmakov, I. Vlassiouk, S. Smirnov, Analyst, 2006, 131, 1248 Host:  Zuzanna Siwy

The Institute for Surface and Interface Science (ISIS) and CBC present: Marat Khafizov Department of Physics and Astronomy and Laboratory for Laser Energetics University of Rochester April 25, 2007 2201 Natural Sciences II 1 p.m. Title: Photoresponse Mechanism in Superconducting Magnesium Diboride Abstract:  Understanding the photoresponse mechanism of materials subject to short optical pulses is important for optimal design of optical detectors. Superconducting detectors offer broadband detection capability from deep infrared to X-rays. Until recently due to low-temperature operations they were developed for astronomical applications only. Recent demonstration of single photon detection in niobium nitride made them attractive for quantum key distribution and some biological applications. Superconductivity in MgB2 is one of the recent discoveries. In this work we study the photoresponse mechanism of this material excited by train of 100-fs wide, 800-nm wavelength optical pulses. First set of experiments employs all-optical time resolved pump probe spectroscopy of thin films. Second set of measurements studies the transient photoimpedance of current-biased microbridge structures. Both experiments allow us to observe the superconducting recovery dynamics in MgB2. Transient photoimpedance measurements demonstrate hot electron resistive and kinetic inductive responses which represent two detection mechanisms. Kinetic inductive responses observed under low optical excitation powers are as fast as 100-ps. Resistive responses observed at high excitation powers in general are longer than 500-ps wide and depend on biasing conditions.   Observed voltage responses make MgB2 as an attractive material for fast superconducting hot electron detectors and mixers. Host: Eric Potma

The Institute for Surface and Interface Science (ISIS) Presents: Sergei Smirnov Department of Chemistry and Biochemistry New Mexico State University, Las Cruces,