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2006 SPS Outstanding Student Awards for Undergraduate Research
Recipients: 2013 | 2012 | 2011 | 2010 | 2009 | 2008 | 2007 | 2006 | 2005 | 2004 | 2003 | About the Award

Note: The awardees represented SPS and presented their research at the 2006 International Conference of Physics Students (ICPS) in Bucharest, Romania, August 14-21, 2006.

Anthony Davidson, Towson University

Anthony Davidson"Effects of Visible Light, Electric Field and Magnetic field on the Electrical Resistance in 'CMR Manganite' Thin Films"
Meeting Report | Towson University Press Release

Faculty Mentor: Dr. Rajeswari Kolagani

Research Abstract
The ‘CMR manganite’ family of materials has been a recent focus of materials research, due to their very large magnetoresistance (termed “colossal magnetoresistance”) with potential for magnetic information storage applications. In addition, the resistance of these materials is also sensitive to changes in temperature thus offering the potential for bolometric infrared detector applications. We have studied the effect of incident visible light (photoresponse), electric field and magnetic field on the electrical resistance of thin films of the CMR manganite material (La,Pr)0.67Ca0.33MnO3 (LPCMO). We fabricate thin films of this material using a technique known as the “Pulsed Laser Deposition”. To study the light-induced resistance changes, we measure the electrical resistance of the thin films as a function of temperature in a continuous flow cryostat while the films are illuminated by modulated visible radiation from a Laser Diode. Current-voltage characteristics and magnetoresistance are measured in a 4-probe configuration. We will present our studies the photoresponse and the correlation of the observed non-thermal photoresponse with magnetoresistance as well as current-voltage (I-V) characteristics. We find that in addition to the expected resistance change due to the heating effect of the radiation, there is a non-thermal component of the light-induced resistance change in the vicinity of the insulator-metal transition. LPCMO is known to have the co-existence of insulating and metallic regions. On cooling the metallic regions grow at the expense of the insulating regions, giving rise to a percolative insulator-metal transition. Our studies indicate that light may cause electronic changes in the insulating regions thus decreasing the electrical resistance. The initial results of the I-V measurements show that there is a current induced change in resistance which not due to the joule heating effects. This may be due the effect of the high electric fields in the sample causing an electronic change leading to a large decrease in sample resistance. This effect is only seen in the metal-insulator transition range of the samples, similar to the nonthermal photoresponse. This suggests a common origin for these two phenomena. The effects of magnetic field however are seen to be distinct from these two. A large magnetoresistance is seen at lower temperatures where the light and current induced effects are absent, thus suggesting a very different physical origin for the magnetic field effects.

This work was supported by undergraduate research awards from FCSM and by a Towson University undergraduate research award.

1. R.M. Kolagani, M. Overby, V. Smolyaninova, D.E. Cox and A. Davidson, Appl. Phys. Lett. 88, 052504 (2006)
2. M. Uehara, S. Mori, C. H. Chen, and S. W. Cheong, Nature London 399, 560 (1999)

Kasandra Jorgensen, Lewis & Clark College

Kasandra Jorgensen"The Evolution of the 44i Bootes Eclipsing Binary System over 90 Years"
Meeting Report

Faculty Mentor: Dr. Thomas Olsen

Research Abstract
  University of Central Florida
I present calculations related to the incorporation of the presence of a third star companion of the eclipsing binary star 44i Bootes into the analysis of the period variations of the eclipsing pair. I have used Mathematica™ to calculate the effect of the third star according to five different sets of orbital parameters and I have found a best fit to the data. I give a new ephemeris to predict future eclipse times that incorporates a steady period increase of 8.53 µs/Epoch , the so called Light-Time effect that takes the third star into consideration, and also a sinusoidal term with a period of 61.5 years. I found that adding the Light-Time effect decreases the already known rate of increase of period of the eclipsing system. This consideration of the third star also leaves intact sinusoidal residuals, implying that these are in fact a true phenomena of the system.

Cary Pint, University of Northern Iowa (UNI)

Cary Pint "Understanding Aspects of the Melting Transition in Thin Films of Rod-Like Chain Molecules Physisorbed onto a Graphite Substrate"
Meeting Report | UNI Physics Department Profile

Faculty Mentor: Dr. Michael W. Roth

Research Abstract
A temperature-induced phase transition is one of the most fundamental thermodynamic processes that occur in nature. In the past, such phase transitions occurring in the bulk have been well-characterized and understood. However, with the current progress in micro- and nanotechnology, it is often the case that the desired system involves one or two atomic/molecular layers forming a thin film on a solid substrate. In such a case, the phase transitions in these films become more complex as the dimensionality of the system decreases.

My work has been focused on studying how the solid-liquid phase transition in such adsorbed molecular films (composed of molecules with a rod-like geometry) at an interface depends upon both the aspects of the film and the architecture of the molecules adsorbed into the film. In particular, this work gives evidence that many features, including those such as: the adsorbed solid phase of the film, film coverage, and chain length and rigidity of the molecules in the film (among other features), play a significant role in the melting transition. It is well known that thermal fluctuations perpetuate a temperature-induced solid-liquid phase transition, but this work suggests that different adsorbed films have different "allowed" fluctuations which are uniquely defined by these characteristics. Through use of extensive molecular dynamics simulations, complimenting available experimental results, this study emphasizes the role that these features play in the melting transition in a variety of thin adsorbed films, and suggests the novel idea that there exists a relationship between these features and the "allowed" fluctuations that fully predicts the nature and properties of the phase transition. Understanding this relationship would allow a framework for design of thin films in a thermal environment by only knowing a few parameters describing known features of the system.

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