Fall 2008

September 5, 2008
"Sherlock Holmes's Watchdog and the Classical Limit of Quantum Mechanics" by Professor Dan Styer, Department of Physics, Oberlin College
3:10 pm
Franklin Miller, Jr. Lecture Hall (RBH 109)
Abstract: A paradox concerning quantal time development in the infinite square well opens the door to a variety of rich, yet expected insights into quantum mechanics.

September 12, 2008
"The Private Lives of Quantum Particles" by Dr. Benjamin Schumacher, Department of Physics, Kenyon College
3:10 pm
Franklin Miller, Jr. Lecture Hall (RBH 109)
Abstract: Quantum entanglement is a weird sort of connection between quantum particles. Einstein called it "spooky action at a distance" and thought it proved that quantum theory was incomplete. Later, John Bell used its peculiarities to overturn our "common-sense" understanding of the world. In this talk we will learn that quantum entanglement must also be "monogamous" -- a relationship between particles that is so intimate, so profoundly private, that it can never be shared with the outside world.

September 19, 2008
"The LHC Era: What Will We Find? (And How Will We Know?)" by Dr. Matthew Buckley, Department of Physics, California Institute of Technology
3:10 pm
Franklin Miller, Jr. Lecture Hall (RBH 109)
Abstract: The Large Hadron Collider (LHC) in CERN will soon access energies never before available in the lab. It is widely expected that this will allow the origin of particle mass, the Higgs mechanism, to be probed. However, the LHC will put many other more arcane theories to the test. This talk will cover the basics of the experiment and what we hope to learn, as well as the difficulties we face in unraveling the results. Original work in spin measurements at colliders will be presented as an example of the latter. Reception to follow.

September 26, 2008
"A Physicist on Mars" by Dr. Geoffrey A. Landis, NASA John Glenn Research Center
3:10 pm
Franklin Miller, Jr. Lecture Hall (RBH 109)
Abstract: The Mars Exploration Rovers have now been exploring the surface of Mars for over four year. This talk will discuss the Pathfinder and MER missions to Mars, where we are and what we are doing, and what we are doing next in Mars exploration.

October 3, 2008
Organic Photovoltaics: Not Just for Hippies -- Senior Exercise Talk by Michael Machala, Kenyon College, '09
3:10 pm
Franklin Miller, Jr. Lecture Hall (RBH 109)
Michael Machala is a synoptic major in chemical physics. Abstract: As global concern over fossil fuel availability and environmental impact intensifies, researchers are increasingly looking toward the sun -- a virtually inexhaustible source of energy -- for solutions. The traditional solar cell industry has focused on crystalline silicon photovoltaics for which the fabrication process is energy-intensive and specialized, leading to high prices for consumers. Among alternatives to silicon are organic photovoltaics (OPV), which offer potentially low cost production methods and the ability to be manufactured on flexible substrates. Currently, organic solar cells have relatively lower efficiencies and shorter lifetimes than traditional cells due to fundamental material and mechanical property differences. Summer research conducted at the National Renewable Energy Laboratory involved fabricating cells based on donor/acceptor polymeric chromophores. It focused on a specific layer of the cell called the transparent conducting oxide (TCO) which transmits over 80% of visible light while maintaining conductivity. This work involved: studying novel TCO materials, developing a novel surface treatment for improved charge transfer between cell layers, and developing a patterning technique for TCOs to speed up prototyping and to increase productivity. The versatility in OPV design makes this technology rich with opportunity and the potential to become a future light-harvesting device that most everyone can afford.

October 7, 2008
"Theoretical Neuroscience: If I Only Had A Brain" by Gilad Barlev, '09 - Senior Honors Talk
11:10 am
Franklin Miller, Jr. Lecture Hall (RBH 109)
Abstract: The 1963 Nobel Prize in Physiology went to English biophysicists Alan Lloyd Hodgkin and Andrew Huxley for their investigations into the workings of neurons. Nearly fifty years later, their so-called Hodgkin-Huxley model, which provides a mathematical description of ionic channels in the cell membrane, is still our most accurate and physically rich model for the behavior of physical neurons. As such, investigations into the global properties of networks of such neurons (i.e. tendency towards synchronization) may yield physical insights into the chemical mechanisms involved in certain neuropathologies such as epilepsy. In this talk, we will build a Hodgkin-Huxley neuron out of analogous electrical circuit components, give an overview of the global behaviors we expect to observe in our neural networks, and propose an investigation into the influence of astrocytes-brain cells once thought to be mere "silent partners" to the neurons-on perturbing the behavior of our system. In doing so, we hope to add theoretical support to recent findings that suggest such cells may be responsible for the propagation of epileptiform behavior in the brain.

October 17, 2008
"Inhibiting the Spread of Nuclear Weapons - How We Try to Do This" by Dr. Stephen J. Tobin, Los Alamos National Laboratory
3:10 pm
Franklin Miller, Jr. Lecture Hall (RBH 109)
Abstract: Given the extreme destructive power of nuclear weapons, great care must be taken to reduce the likelihood that they will be used. In the 1960s the countries of the world largely agreed on the response to this threat; it took the form of the Treaty on the Non-proliferation of Nuclear Weapons (NPT). This presentation/discussion will start with the "Grand Bargain" struck among the nations of the world and drill down to what scientist and engineers are doing today to maintain/strengthen the goals of the NPT. This drilling down path leads to the present focus of Dr. Tobin's work which is quantifying plutonium in used (spent) fuel assemblies. In addition to the stated purpose of the talk, an additional goal is to provide insight into career options at U.S. national laboratories, Los Alamos in particular.

October 24, 2008
"Writing on a Superhydrophobic Surface - A Bottom-up Method for Nanoscale Materials Deposition" by Dr. Benjamin Hatton, School of Engineering and Applied Science, Harvard University
3:10 pm
Franklin Miller, Jr. Lecture Hall (RBH 109)
Abstract: Superhydrophobicity is a property of hydrophobic, rough materials such that water droplets remain in a non-wetting state. As a result, an aqueous droplet on a superhydrophobic nanowire array is only exposed to the very tops of the nanowire posts. Therefore sites for the heterogeneous nucleation of precipitates, colloidal deposition, or polymeric adsorption from solution can be limited to only those areas of the surface. Herein we demonstrate conditions for the localized deposition of various different materials from aqueous droplets on the posts of a superhydrophobic array of Si posts (300 nm diameter, 6-8 mm tall, pitch spacing 1-4 mm), etched by deep reactive ion etching (DRIE). Examples include the precipitation of CaCO3 and Fe3O4 onto the tips of the posts. It has also been extended to the deposition of colloidal particles, and polymeric fibers. As a result, highly uniform arrays of precipitate deposits can be grown locally onto nanoscale posts, in a rapid, room temperature process, which could be applied quite generally to a wide range of deposition reactions from solution. This method could be applied to the bottom-up synthesis of novel functionalized nanowire arrays and 3D nanostructures.

October 31, 2008
"Semiconducting Nanowires: Growth, Structure, Electronic and Optical Properties" by Prof. Fengyuan Yang, Department of Physics, The Ohio State University
3:10 pm
Franklin Miller, Jr. Lecture Hall (RBH 109)
Abstract: Single-crystal semiconductor nanowires made by "bottom-up" synthesis represent one of the most exciting developments in nanoscience and nanotechnology in the past decade. A large variety of prototype semiconductor nanowire electronic and optoelectronic devices have been demonstrated with exceptional performance. I will first review the fascinating science and prospects for future technological applications offered by semiconductor nanowires. Using pulsed laser ablation with control of partial pressure and ultrahigh vacuum sputtering, we have grown InP, GaAs, GaP, and Si nanowires catalyzed by gold nanoparticles. The single-crystal structure and geometry of the nanowires have been characterized for various growth conditions using scanning and transmission electron microscopy, energy dispersion spectroscopy, and x-ray diffraction. Electrical contacts on single nanowires have been fabricated by electron-beam lithography and metal deposition. Ohmic contacts with linear I-V curves as well as Schottky contacts with rectifying behavior were observed for nanowires made from different fabrication procedures. Nanowire field-effect transistors have also been fabricated and the conductivity of individual nanowire can be tuning by a gate voltage. In addition, semiconductor nanowires exhibit strong optical polarization effect due to their large aspect ratio. We use dielectric coating on the nanowires to control the optical polarization of semiconductor nanowires.

November 7, 2008
Barbie Bungee Jumping Competition
3:10 pm
Franklin Miller, Jr. Lecture Hall (RBH 109)
Mini Colloquium - "Gravity, Energy and Bungee Jumping" by Ben Schumacher In preparation for Friday's Bungee Barbie competition, we will take a quick look at the basic physics of bungee jumping. Bungee jumping is not simply falling (the initial acceleration of the jumper is actually faster than free-fall), and careful calculation is required to prevent unfortunate results. We will discuss an idealized "extreme sports" version -- and also why Barbie's rubber-band plunge might be very different. Competition: Come test your engineering skills at the "Barbie Bungee Jumping Competition"! Competitors will construct rubber band bungees attached to a Barbie doll to be dropped down the Tomsich stairwell. Whoever's Barbie comes closest to the basement floor without hitting it is the winner!

November 14, 2008
"Neutrinos, Nuclei, and Neutrons" by Tova Yoast-Hull, '09
3:10 pm
Franklin Miller, Jr. Lecture Hall (RBH 109)
Senior Exercise Talk Abstract: Over the past decade, research in elementary particle physics has reemerged into the public spotlight; a current example is the search for the Higgs-Boson with the Large Hadron Collider. The neutrino, an elementary particle, is one of the more difficult particles to study because its nearly negligible mass and neutral charge makes detecting it rather difficult. Although neutrinos have been studied for over thirty years, their interactions with nuclei have yet to be observed. The behavior of neutrinos and nuclei is important in the field of astrophysics because neutrinos are produced in massive quantities during star-collapse processes in the formation of supernovae. Summer research conducted at Duke University focused on simulating the cosmic ray background for the proposed CLEAR detector, a liquid scintillator designed to observe neutrinos.

December 12, 2008
Talk by Kathy Aidala, Assistant Professor of Physics, Mount Holyoke College
3:10 pm
Franklin Miller, Jr. Lecture Hall (RBH 109)
Abstract: To follow

December 12, 2008
"Scanning Probe Microscopy in Nanoscience" by Kathy Aidala, Assistant Professor of Physics, Mount Holyoke College
3:10 pm
Franklin Miller, Jr. Lecture Hall (RBH 109)
Abstract: Scanning probe microscopy encompasses a class of techniques that are related by the common method of bringing a sharp (~10 nm) probe close to or in contact with the surface of a sample. I will discuss measurements that can be implemented with an atomic force microscope (AFM), and draw on examples from my research. While many are familiar with AFM as a tool for topographic imaging, fewer realize the full versatility of the system. I will focus on two rather different projects: bacterial biofilms in their native state, and ferromagnetic nanostructures. We have generated the first images of bacteria without any artificial means of fixation and measured their physical properties, demonstrating that some fixation methods alter the results. Magnetic nanorings show unique closed-flux states, and the AFM offers a promising way of controlling and measuring the evolution of magnetic states.