2009 Condensed Matter and LASER Physics REU Participants and Projects

David Daumiller, Texas A&M University--Kingsville, Kingsville, TX (Advisor: Dr. Randall Babbitt)

Raman Conversion of Laser Light

Raman scattering is a well-known optical process, which changes the color of laser light passing through a gas by taking energy from the incident photons (and sometimes giving energy back). This process is an appealing way to turn common laser types into unusual colors with high efficiency and convenient equipment, but details about the best ways to do this efficiently at high powers are still lacking. In this project, a pulsed 1064 nm Nd:YAG laser was put through a hollow-core photonic crystal fiber. The experimental effects of pressure, photon polarization, and laser power were analyzed for their relevance in the production of a controlled range of laser wavelengths.

Michael Todt, Augustana College, Siouz Falls, SD (Advisor: Hugo Schmidt)

Development of Anode Supported Solid Oxide Fuel Cells:

The performance of Solid Oxide Fuel Cells (SOFCs) is dependent on a number of factors including, but not limited to, porosity, electrolyte material, cathode and anode composition, interlayer use and composition, and fuel concentration. The purpose of this project was to improve the performance of the SOFCs made in this lab through the use of various anode interlayers (which increases the Triple Phase Boundary), different cathodes, and the preparation process of the anodes, specifically the component concerned with porosity. Tests carried out have shown a thin interlayer made with nano-size NiO powder works best. Porosity dependence results may be skewed due to improvement of the cell fabrication over the summer, but tentatively shows 15 wt% cornstarch added to the anodes is more effective than only 10 wt%. Tests on the cathode materials were not carried out to completion. Based on the results achieved, LSM ((La_0.8Sr_0.2)MnO_3-δ) was the best cathode material.   It is believed that LSCF ((La_0.6Sr_0.4)(Fe_0.8Co_0.2)O_3-δ) would be better, but the LSCF cell test showed extremely low open circuit voltage, due probably to a “pinhole” in the electrolyte.

Chaz Goodwine, Rensselaer Polytechnic Institute, Troy, NY (Advisor: Recep Avci)

Mechanical Properties of Bacterial Surface Layers

The presence of a paracrystalline protein lattice on the surface of the gram-negative Caulobacter crescentus is expected to contribute to the mechanical strength of the bacteria. This was investigated by means of puncturing the cell wall of live bacteria, immobilized on a flat surface, by using a sharp Atomic Force Microscopy (AFM) tip. Data was taken by measuring the pressure necessary to puncture the cell wall and determining the modulus of elasticity of the cell wall subjected to indentation before it was punctured by the sharp AFM tip. The results were compared with those of the gram-negative Salmonella enterica Typhimurium and gram-positive Staphylococcus aureus, both of which lack a protein surface layer. Here we report our current finding which might change as we improve the bacterial immobilization techniques. Our results show that Caulobacter can withstand twenty five percent more pressure for cell wall puncture than the surface layer lacking Salmonella. Gram positive Staphylococcus can support a hundred and nineteen percent more pressure than the gram negative Samonella. Further method development is being done to achieve better surface attachment of bacterial cells by manipulating surface topography by means of electron nanolithography where it is expected that the cells would be better immobilized so that the quality of the puncturing data can be improved. Furthermore, a mutant variety of Caulobacter that sheds its S-layer will also be studied to give a better comparison for the specific strength of the S-layer.

James Shin, Carnegie Mellon, Pittsburgh, PA (Advisor: Yves Idzerda)

Effects of Heat Treatment and Temperature on the Magnetic Properties of Fe-Ga alloys

Fe-Ga alloys were deposited on (001) GaAs and (001) MgO substrates via molecular beam epitaxy (MBE). Magnetization curves were measured as a function of temperature, orientation, and heat treatment with the use of a vibrating sample magnetometer (VSM). Temperatures at which the samples lose their magnetization or undergo phase changes were determined and interesting anomalies in the hysteresis loops of high Ga content samples were observed.

Amy Su, Texas A&M, College Station, TX (Advisor: Galina Malovicho)

EPR Study of Two Variously Doped Lithium Niobate Samples at Room Temperature

Materials that have a permanent magnetic moment due to electron spin from unpaired electrons can be analyzed using electron paramagnetic resonance (EPR). Extensive EPR studies have been done on lithium niobate, an important crystal for optical applications, to characterize its atomic structure after the addition of various dopants. Study of the EPR spectra can yield not only the identity of the dopant but also its location in the crystal lattice and charge compensations around it. The spectra from two samples of lithium niobate undergo a rudimentary analysis, pending further research.

Ryan Hanna, Pacific Lutheran University, Tacoma, WA (Advisor: Stephen Sofie)

Fabrication of Graded Porous Ceramics for Aerospace Life Support Systems

Any closed system that includes human life will naturally accumulate water vapor due to respiration. In space, resulting condensation from water vapor poses certain risks to electrical equipment and other vital, life-sustaining systems. It is thus of great importance to capture this vapor and maintain safe humidity levels in spacesuits, crew exploration vehicles, and Mars/Lunar habitats. We have undertaken the construction of a prototype solid-state, modular dehumidifier that aims to draw moisture from the local atmosphere through use of a thermoelectric cooler, where captured condensation then passes through a porous ceramic and comes into contact with two electrodes. The heart of this device is a porous ceramic substrate with an engineered porosity gradient fabricated by a novel processing technique developed at MSU. Through a solidification-based ceramic process, functionally graded pores are created to serve as a directional water transport medium. Water is driven thermodynamically by surface area as opposed to classic pumping techniques that are prone to vapor lock in a zero G environment. Capillary pressure gradients across the 4mm thick porous alumina membrane of 0.2883MPa have been achieved. The water undergoes electrolysis through the addition of an electric current, and its constituent elements are subsequently stored for further use as breathable oxygen and hydrogen fuel achieving the means of in-situ resource utilization (ISRU). The development and characterization of aluminum oxide porous ceramics is reported. Preliminary tests of fully functional prototypes are also discussed.

Cale Gentry, The University of Oklahoma, Norman, OK (Advisor: Kevin Repasky)

Construction and Characterization of an External Cavity Diode Laser for Injection Seeding an Optical Parametric Oscillator for Down-Looking LIDAR

Down-looking LIDAR systems capable of penetrating into water at optimal depths require a pulsed laser source that can be tuned from 450 nm – 490 nm to account for variations in the physical properties of the water. Constructing a tunable optical parametric oscillator (OPO) in the 900 nm – 980 nm range and subsequently frequency doubling the output is one method of achieving a tunable laser source for this application. For narrow line width operation this OPO requires a tunable continuous-wave injection-seeding source. To create such a source, a continuous wave tunable external cavity diode laser (ECDL) was constructed in the Littman-Metcalf configuration and tested. A tunable operating wavelength range was measured to be between 963 nm and 978 nm with an output power greater than 5 mW.

Michael Olson, University of Wisconsin-La Crosse (Advisor: Alan Craig)

Characterization of Silicon Nanospheres using an STM

Colloidal silicon nanoparticles can be created through the electrochemical etching of porous silicon wafers. In order to analyze the created nanoparticles they were viewed using a scanning tunneling microscope. It was found that the silicon nanoparticles lined up along atomic ridges in the carbon substrate and were from 1 to 3 nm in diameter.

D. James Regar, Duquesne University, Pittsburgh, PA (Advisor: Richard Smith)

Silicon Volatility and Thin Film Growth Studies with SOFC Applications

The volatilization rates of silicon compounds were studied to provide a better understanding of the factors contributing to degradation of gas-feed tubes and insulations used in Solid Oxide Fuel Cell (SOFC) systems. Silicon dioxide vapor was condensed on carbon substrates by flowing humid air through a Si source under a temperature-controlled environment over various time intervals. Rutherford Backscattering Spectroscopy (RBS) and X-Ray Photoelectron Spectroscopy (XPS) were used to determine the accumulation rate and composition of the resultant thin films. Silicon was found to continually collect over time with no indication of reaching a maximum film thickness. Higher H₂0 partial pressures were found to increase the volatility of Si. Future research will include further examination of the effects temperature and air environments have on various aluminosilicates and SOFC materials.

Jennifer Black, Southern Polytechnic State University, Marietta, GA (Advisor: John Neumeier)

Capacitive-based dilatometer cell constructed of Sapphire

A capacitive-based dilatometer cell of unique design has been constructed in order to measure the thermal expansion of solids. The dilatometer (or thermal expansion cell) has been constructed of Sapphire because of its superb thermal conductivity and well-behaved thermal expansion. Ideally this will improve the thermal response and low-temperature (below 20 K) measurement capabilities that currently exist. Also the cell’s small design will allow it to be used in a Physical Properties Measurement System (PPMS) for future measurements to temperatures as low as 0.3 K.