Case Western Reserve University Department of Physics
Research Experiences for Undergraduates
Summer 2009 Projects

Here is the list of projects available for the summer of 2009. The projects labeled E1 through E9 are primarily experimental in nature. The projects labeled T1 through T4 are theoretical or computational projects. Unless otherwise noted in the project description, no prior experience other than completion of first year college physics courses is required.

(E1) Liquid Crystals (project advisor Charles Rosenblatt):Liquid crystals are a branch of "soft condensed matter," a classification that includes colloids, polymers, and gels. Liquid crystals have large electric, magnetic, and mechanical responses, and have both practical applications (for instance, in liquid crystal displays) and are also of fundamental scientific importance in areas such as phase transitions, pattern formation and topology, and molecular interactions. In our laboratory we study electro- and magneto-optic properties of liquid crystals, their phases and phase transitions, interactions with surfaces, symmetry properties, and their use in device applications. In this REU project the student will use an atomic force microscope to write patterns on substrates that impose liquid crystal alignment on the nanometer length scale. The resulting behavior of the liquid crystal that resides on the substrate will be studied optically to determine the patterns' effects near one of several liquid crystal phase transitions. The student will have the opportunity to prepare his or her own samples and to use several scanning probe microscope techniques, including atomic force microscopy and near field scanning optical microscopy, as well as optical and electrical probes such as light scattering and possibly dielectric measurements.

(E2) Solar Energy (project advisor Kenneth Singer): Solar cells require the production and dissociation of bound electron-hole pairs (excitons) to occur at the interface between two semiconductors, one that transports holes (which can be viewed as the positively-charged absence of electrons in a partially filled energy band) and one that transports electrons. Organic solar cells are made from organic semiconductor materials rather than from the usual inorganic semiconductors, and hold promise for making solar cell technology cheaper, and therefore more widespread in use. In this project, the student will mix solutions of two different organic materials (some that are pure electron transporting materials, some that are pure hole transporting, and some mixtures of the two) that will self-organize on the nanometer scale, and then will measure their absorption spectra and luminescence spectra in order to gain information about how energy and charge are transferred in these systems. The results will help in the design of a new class of self-assembling photovoltaic cells.

(E3) Nanowire Spin-electronic Devices (project advisor Xuan Gao): The research field of spin-electronics (or spintronics) explores how one can take advantage of the spin degree of freedom of electrons in conventional electronic devices to achieve improved or new functionalities. We are interested in investigating if one can electrically create, detect and manipulate spin polarized electrical currents in semiconductor nanowire devices with ferromagnetic metal contacts. The student will use a chemical vapor deposition system in our lab to grow the nanowires (wires of the order of 10 nanometers in diameter) and then study the current-voltage characteristics of nanowire devices with various ferromagnetic metal contacts (e.g. Fe, Co). The magneto-resistance will then be measured to look for resistance switching (or spin-valve) effect when the magnetization of the two magnetic contacts changes direction. The student involved in this project will work with a graduate student and/or a postdoctoral researcher to learn how to grow nanowires and to fabricate the devices. Some knowledge of semiconductor physics and electronics would be helpful but is not required.

(E4) Synthesis and characterization of nitride semiconductors (project advisor Kathleen Kash): The family of semiconductors composed of gallium nitride, aluminum nitride, and indium nitride has become increasingly more important for the lighting industry. It provides, for instance, the bright blue light emitting diodes that are used, for example, in those large, bright, three-color highway billboard displays, and may even replace the incandescent light bulb, with tremendous energy savings. Zinc germanium nitride, zinc silicon nitride, and zinc tin nitride are members of a related family of semiconductors on which there has been very little research; in fact, no one has yet reported growing zinc tin nitride. Yet there is reason to expect that these materials may be superior to their better-understood counterparts for some important applications. The REU student will learn how to perform his or her own crystal growth of one or more of these new materials and will also learn how to use a scanning electron microscope to measure the elemental composition and observe the morphology of the material on the size scale of tens of nanometers, and how to do x ray diffraction to measure the crystal structure.

(E5) Magnetic Resonance Imaging in Medicine; MRI Electronics Design and Hands-On MRI Operations Experience (project advisor Robert Brown): We see much publicity around us highlighting the increasing importance of Magnetic Resonance Imaging. MRI is making remarkable headway in new studies of the brain, disease, and sports injuries. A robust, interdisciplinary research group involving the CWRU physics, radiology, and biomedical engineering departments and Cleveland MRI industry has an ongoing project for the design and construction of RadioFrequency coils to improve the MRI signal detection. The REU student would collaborate with members of this group to develop multiple arrays of small RF coils to speed up the scanning procedure and increase the sensitivity of brain imaging. The student would get an excellent grounding in the physics of MRI, electronics and circuit analysis, signal processing, coil tuning and impedance matching, the use of network analyzers, and the holy grail of optimizing the signal-to-noise ratio! And she or he will participate in the operation of state-of-the-art scanners. This is a great experience especially for students who are interested in biomedical MD/PhD career tracks.

(E6) Experimental astrophysics using Cherenkov light detectors (project advisor Corbin Covault): The High Energy Astrophysics group is developing a new optical detector system to measure the astrophysical properties of the highest energy cosmic rays. Our work is part of a larger effort to study the fundamental nature of cosmic rays: What are cosmic rays made of? Where in the Universe are cosmic rays coming from? Our group works with the Pierre Auger Cosmic Ray Observatory, a new experiment to measure the largest energy cosmic rays. For this summer project, the student will work to develop a prototype optical detector system that is being considered for future deployment as part of the Auger Observatory. The work requires fabrication, testing, calibration, astrophysical observations of cosmic rays using the new detector system, and data analysis. The work will be done collaboratively with other members of the HEA group.

(E7) Experimental Light Detectors and the Search for Extraterrestrial Intelligence (project advisor Corbin Covault): The High Energy Astrophysics group specializes in the detection of gamma-rays and cosmic rays from astrophysical sources. These same experimental techniques can be exploited for a new effort in the Search for Extraterrestrial Intelligence (SETI). In principle, an advanced civilization that wished to communicate across interstellar distances might find optical signaling processes using rapid-pulsed lasers quite attractive. If such light pulses are arriving at the Earth, we can detect them with a large-area light detector and fast coincidence electronics. For this summer project, the student will work to develop an new detector system that will serve as a prototype for a new kind of Optical SETI experiment. The work requires fabrication, testing, optical calibration, astrophysical observations using the new detector system, and data analysis. The work will be done collaboratively with other members of the HEA group.

(E8) The search for dark matter (project advisors Thomas Shutt and Daniel Akerib): The nature of dark matter is one of the primary problems in physics and cosmology, and the leading candidate for this matter is weakly interacting massive particles (WIMPs) that permeate our galaxy. Their rare interactions in a detector on Earth can be measured, provided that radioactive and cosmic ray backgrounds can be reduced by 8 or more orders of magnitude. Our group is playing a leading role in the newly-created LUX (Large Underground Xenon) experiment, which is carrying out a search for dark matter. LUX is building a detector with unprecedented WIMP sensitivity using liquified xenon as the target material. Ultimately, the detector will be housed in the newly created Sanford underground laboratory in the Homestake gold mine in South Dakota. At Case, the REU student will work with the research team to learn how to re-commission and use a chromatographic gas separator to purify xenon gas to remove low-level radioactive contamination (to below parts per trillion), to make it suitable for use in the LUX detector.

(T1) The search for dark matter; numerical simulations (project advisors Thomas Shutt and Daniel Akerib): (See project E8 for background). The prospect for detecting dark matter rests upon building detectors of sufficiently high sensitivity. The sensitivity of the experiment is affected by how well we can reject signals due to neutrons produced by radioactive decay and neutrons produced by cosmic rays interacting with the earth's crust. The REU student will learn how to use and modify Monte Carlo numerical simulation codes to simulate particle interactions with different shielding materials. The simulations will be of help in designing new shielding methods for the liquid xenon dark matter detector under development. Some experience with programming, for example with using Java, C++ or C, would be helpful, but is not required.

(T2) Effective masses in Zn-IV-N2 semiconductors (project advisor Walter Lambrecht): The charges in semiconductors involved in electrical conduction behave essentially as free electrons, but with either positive or negative charge, and masses that differ from the free electron mass as a result of their interaction with the periodic potential of the crystal. These effective masses are dependent on crystallographic directions. We have recently calculated the band structures of a family of semiconductors that include zinc germanium nitride, zinc silicon nitride, and zinc tin nitride. These materials are potentially useful for electro-optic applications such as light-emitting diodes, but not much is yet understood about their properties. The REU student involved in this project will work closely with a postdoctoral scholar to learn how to extract effective masses from the band structures, and to help develop and use software to display the details of the energy band surfaces. The project will give the student the opportunity to learn concepts of semiconductor physics as well as to become involved in numerical and computational work. This project is best suited to an upper level physics major who has taken a quantum mechanics course.

(T3) Computer Modeling of Proton-Conducting Membranes (project advisor Philip Taylor): This work is aimed at elucidating the nature of proton transport in ionomer membranes by means of a combination of analytical theory and molecular modeling. There are two broad thrusts. The first of these is directed towards understanding the equilibrium structure of Nafion, which is a typical membrane material used, for example, in fuel cells. The second thrust is concerned with the transport of protons through a membrane of this type. The research on structure will proceed by building on existing work, but with the introduction of some novel techniques, among which is a hybrid Molecular Dynamics--Monte Carlo approach. This method permits rapid computations by temporarily decoupling the motion of the hydrophilic polar side chains from that of the hydrophobic backbone. The work on transport of protons in Nafion-like membranes will also involve a combination of theory and simulation. Atomistic molecular-dynamics simulations will be employed to determine some of the characteristic parameters for the diffusion of protons in hydrated membranes. These results will be used in a theoretical model of nonlinear diffusion to predict transport coefficients. Undergraduates with some experience in computing have been very successful in this research program. The tools we use include various combinations of packaged programs like "Materials Studio", which are comparatively quick to learn, and programs that the students write themselves using Mathematica or one of the common programming languages.

(T4) Phase transitions in the early universe (project advisor Harsh Mathur): The focus of my work on cosmology is on the observable consequences of phase transitions in the early universe. Possible REU projects include numerical simulation of such a phase transition or analysis of the impact of such a phase transition on the cosmic microwave background. The minimum background needed is some familiarity with differential equations. Any prior experience with programming and courses in quantum mechanics, statistical mechanics and electromagnetism will be an asset but is not required. No background in cosmology or astrophysics is needed other than a general interest in the field. More information on our work in this area is available at http://www.sciencedaily.com/releases/2008/04/080415143816.htm