Colloquium Fall 2001

All Department Seminars and Colloquium

 

August 27

Yet Another Solar Neutrino Talk
Werner Däppen
Dept. of Physics, University of Southern California

September 3

No Colloquium: Labor Day, University Holiday

September 10

No Colloquium

September 17

Periodic Analysis of the Labeled Release Experiments from the Viking Landers
Joe Miller
Dept. of Cell and Neurobiology, USC School of Medicine

September 24

Wetting, Prewetting, and Sticky Superfluids
Peter Taborek
Department of Physics & Astronomy, University of California, Irvine

October 1

High Performance Computing and Visualization: Opportunities and Challenges at the Information-Bio-Nano Interface
Priya Vashishta
Concurrent Computing Laboratory for Materials Simulations, Louisiana State University

October 8

Scaling Behavior of Cracks in Dynamic Fracture: Multiscale Simulations from Atoms to Continuum
Rajiv K. Kalia
Concurrent Computing Laboratory for Materials Simulations, Louisiana State University

October 15

Trillions of Quantum Dots, Fingerprints, Nanolithography with Diblock Copolymers, and the Formation of Striped Patterns
Paul Chaikin
Dept. of Physics, Princeton University

Abstract

In order to develop new technologies for lithography on the nanometer scale we have been investigating the use of diblock copolymers, systems which form periodic structures on the 5-50 nm scale. Diblock copolymers consist of A and B monomers which are immiscible and would normally phase separate like oil and water. When they are covalently bound as A-A .-A-A-B-B-. B-B-B-B the best they can do to avoid each other is to put all the A ends together in spheres or cylinders surrounded by the B's. We have used a monolayer mask of the diblock to transfer the periodic patterns to a number of different substrates as holes, posts, and semiconductor and metal quantum dots producing ultradense arrays, e.g. 3 trillion dots on a 3 inch wafer. Along the way we have developed novel methods for three dimensional imaging on the nanometer scale and for tracking the annealing of the two dimensional monolayer patterns. Time lapse atomic force microscopy of the cylindrical phase (which forms fingerprint like patterns in the monolayer) reveals the solution to a common problem in many fields of science, how striped patterns order. Instead of two defects (disclinations) annihilating our movies show quadra-defect annihilation explaining the much slower (fourth root time) behavior seen in many striped system.

October 22

Nonlinear and Quantum Atom Optics
Michael G. Moore
Institute for Theoretical Atomic and Molecular Physics, Harvard-Smithsonian Center for Astrophysics

October 29

Nanomechanics
Kamil L. Ekinci
Condensed Matter Physics, California Institute of Technology

Abstract

Electromechanical systems are being miniaturized, following the trend in commercial transistor electronics. First generation miniature electromechanical systems, Microelectromechanical Systems (MEMS), have been successfully integrated as low frequency sensors and actuators. With the advances in surface nanomachining processes, their submicron counterparts Nanoelectromechanical Systems (NEMS) are emerging as strong candidates for a host of technological applications. Their high operation frequencies, low power requirements, compactness and full integrability with modern semiconductor electronics offer exciting device prospects such as ultrafast sensors and actuators and mechanical signal processing components. There are, however, a number of technological and fundamental challenges to NEMS optimization, the most important being the unprecedented energy losses and resonance instabilities due to their extreme surface to volume ratios and small sizes.

In this talk, I will introduce nanomechanics with emphasis on device fabrication and RF measurement techniques. I will focus on our recent results on effects due to surfaces and surface related phenomena in NEMS. In particular, I will discuss prospects for NEMS based mass spectrometry in the light of our recent mass sensitivity measurements in the attogram (10-18 g) range. I will also propose NEMS based energy dissipation measurements in surface adsorbates.

[Work done in collaboration with Y.T. Yang, X.M.H. Huang and M.L. Roukes.]

November 5

Experiments with Laser-Cooled Ion Crystals
Jason Kriesel
Ion Storage Group, Time & Frequency Division, NIST, Boulder

Abstract

At NIST-Boulder, we laser-cool clouds of Be+ ions to temperatures T < 10mK. At these extremely low temperatures an ion experiences a Coulomb potential that is larger than its thermal energy, and the ions form so-called "Coulomb Liquids" or "Coulomb Crystals." These novel states of matter provide an excellent laboratory system for basic studies of strongly-coupled plasmas, soft condensed matter, and atomic physics, with applications to such topics as precision spectroscopy, quantum information, and anti-matter trapping. In this talk I will give an overview of recent experiments with these ion crystals. In particular, I will show results on studies for which we used a laser "push" beam to generate wakes in the crystal, analogous to wakes behind a ship.

November 12

Manipulation of Magnetic Flux Quantum to Realize 100 GHz+ Digital Logic
Nate Newman
Dept. of Chemical and Materials Engineering, Arizona State University

Abstract

Circuits that can process digital information at over 100+ Gigabits per second are desired for a number of communication applications. The realization of such a system would, for example, facilitate a 16 fold increase in existing fiber network's transmission speed. A new circuit family that can operate at these ultra-fast speeds has been proposed by Likharev. In contrast to using electrons as in conventional electronics, it works by manipulating single quanta of magnetic flux. My group at ASU and our collaborators have developed the first material and device technology that can achieve the desired speeds. It is based on superconductor Josephson technology containing normal metal barriers tuned near the Metal-Insulator barrier. These devices are fabricated on Si wafers and are a "drop-in" replacement in structures currently fabricated by low-Tc superconductor device foundries. In the talk, I will describe the materials, physics and engineering of this exciting new technology.

November 19

Physics with Rare Isotopes
Thomas Glasmacher
Department of Physics and Astronomy and National Superconducting Cyclotron Laboratory (NSCL),
Michigan State University, East Lansing, MI

November 26

Charge Transport in Nanoscale Devices
Jia G. Lu
Electrical Engineering, Washington University, St. Louis

December 3

Surface Melting of Ice
Yuen-Ron Shen
Department of Physics, Univ. of California, Berkeley

December 10

Fun with Dirac-like Quasiparticles in a d-wave Superconductor
Phuan Ong
Dept. of Physics, Princeton University

Abstract

In a superconductor, a fraction of the Cooper pairs exist as `broken pairs', or quasiparticles. In the cuprates, the quasiparticle (qp) population remains large even at low temperatures because of the existence of nodes in the d-wave gap. Near the nodes, the qp dispersion is Dirac-like. I will provide a pedagogical discussion of what is currently known about the d-wave qps and describe a few experiments that probe their transport properties.

  • Department of Physics and Astronomy
  • University of Southern California
  • 825 Bloom Walk
  • ACB 439
  • Los Angeles, CA 90089-0484