Students and their Projects for the Summer of 2003


High Sensitivity Capacitance-Based Quartz Dilatometer for Measuring Thermal Expansion
at the National High Magnetic Field Laboratory
John Macaluso, Stockton State College, Advisor: John Neumeier

The construction and measurement of a high sensitivity capacitance-based quartz dilatometer cell will be presented.  Our dilatometer cell can currently detect changes in length of the order of 10-11m for a 1mm sample.  Analysis of the data collected for a sample La0.6Ca0.4MnO3 will be discussed.  The derivation of a, the coefficient of thermal expansion, from the capacitance (C) vs. temperature (T) data will be shown.  These data will reflect the sample’s behavior (specifically the change in the sample’s length deltaL) while being thermally cycled from 15K to 300K, including the observed ferromagnetic to paramagnetic transition at T~250K.  This dilatometer cell will ultimately be used at the National High Magnetic Field Laboratory for measurements of thermal expansion and magnetorestriction in fields of up to 30 tesla.

John presented this work at the 2004 American Physical Society's March Meeting held in Montreal, Canada.


AES Analysis of High Temperature CrN Oxidation for the Purpose of Developing a Metallic SOFC Interconnect Tristan Butterfield, Notre Dame, Advisor: Richard Smith

Although Solid Oxide Fuel Cells show much potential for becoming a feasible energy alternative, problems with interconnects in the fuel cell stack have begun to impede the deployment of SOFC units into consumer markets.  Because interconnects serve a wide variety of functions within the fuel cell stack and must operate under extremely corrosive conditions, it has been a challenge for the material science community to develop good interconnect candidates.  Currently, interconnects doped with lanthanum chromite (LaCrO3) are used, but this material is very expensive and thus impractical for widespread industrial and consumer use.  Due to the relatively low cost of metallic materials, an effort has been made to develop a metal-based interconnect.  Many iron-, chromium-, and nickel-based alloys are under consideration, but it is our objective to develop a coating to further the alloy’s resistance to oxidation and general corrosion.  In the past, CrN overlayers have been shown to impede oxidation, although for use as an interconnect coating we found it pertinent to examine its oxidation on a metallic substrate.  In this experiment we oxidized a sample of Stainless Steel (304) coated with CrN at 500˚C, 600˚C, 700oC, and 800˚C for varying lengths of time.  After each oxidation exposure an AES spectrum was taken and the resulting data was analyzed to show elemental surface concentration.  We found that during the exposures at 600˚C the chromium separated from the nitrogen and was oxidized.  Also, during the 700˚C exposures manganese appeared on the surface and during the 800˚C exposures the surface composition remained steady.  Chromium concentration remained relatively unchanged throughout the procedure and iron was only visible in small amounts (<5%).

AES Depth Profile Studies of CrN/AlN Superlattice Structure
River Hutchison, Harvey Mudd College, Advisor: Richard Smith

Results are discussed for Auger Electron Spectroscopy concentration-depth profiles of a superlattice composed of thin CrN and AlN layers for solid oxide fuel cell interconnects.  The experiment examined the differences in composition and in chemical shifts of the Auger peaks between oxidized and non-oxidized superlattice samples.  The first two or three layers of the superlattice were observed in all cases, and the chemical shifts of some peaks changed when the material was oxidized.



Investigations into Porphyrins using Fluorescence Spectroscopy
Jennifer Foster, SUNY Genesco, Advisor: Alex Rebane

The absorption, fluorescence, and excitation spectra were recorded for numerous porphyrins, a possible cancer drug.  A list of synthesized porphyrins must be narrowed down to the best candidate to continue cancer related studies on.  Due to its photodynamic qualities and the importance of two photon absorption, the wavelengths that each porphyrin absorbs and fluorescence at are important to the selection process.  Among the findings, are various peaks of porphyrins and the separate fluorescence of its synthesized legs.


EPR Analysis and comparison of manganese doped lithium niobate and lithium tantalate
Robert Petersen, Montana State University, Advisor: Galina Malovichko

Lithium niobate and tantalate are widely known isomorphic crystals used in a variety of physical applications, especially in optics due to their photorefractive and other significant optical properties.  Currently there is much emphasis on the characterization of these crystals with various dopants including Mn, Cr, and Fe due to their wide range of applications.  Because fo the paramagnetic nature of these dopants, EPR can be used to analyze their interactions with constituent atoms of the crystal to gain insight into the defect structure and the location of the defects.  With EPR I conducted an analysis of the two isomorphic crystals doped with Mn assuming they would be similar, but found something quite different.  Clearly LiNbO3:Mn and LiTaO3:Mn have two dissimilar defect structures and this will serve as a basis for further research.


Ferromagnetic manganese oxides for use in magnetic refrigeration
Joshua Garbe, University of Wisconsin, Stevens Point, Advisor: John Neumeier

In this research project some unusual ferromagnetic oxides are investigated for potential use in magnetic refrigeration. We have prepared samples of La1-xCaxMnO3 (0 ≤ x ≤ 0.54) using a solid state reaction at 1350ºC. The samples were characterized using a powder x-ray diffraction to ensure single phase structure. The samples were found to consist of one orthorhombic phase at room temperature.  We measured the magnetic properties using a vibrating sample magnetometer in temperature range 5 K < T < 350 K. The potential for use in magnetic refrigeration is evaluated using the thermodynamic Maxwell relation (∂S /∂H)T = (∂M/∂T)H, where S is the entropy, H is the magnetic field, M is the magnetization, T is the temperature. The heat Q extracted by changing the magnetic field is related to S through the relation ∂Q = T∂S.  The maximum ∂S was found to be 5 at the composition La0.76Ca0.24MnO3.

Josh presented this work at the 2004 American Physical Society's March Meeting held in Montreal, Canada.  It was also recently published in Physical Review B.  Click here to download the paper in pdf format.  Magnetocaloric Paper


GhettoMarsRover
Megan Miller, Stanford University, Advisor: Recep Avci

This summer I worked in the Imaging and Chemical Analysis Laboratory (ICAL) designing, building and testing an instrument that detects fluorescence. Ultimately, the instrument would be part of a larger device that would go on the next mars rover, with a goal to sift Martian soil for proteins, attach fluorescent dye to them, and image the fluorescence of that dye, thus identifying evidence of alien life. I worked with a graduate student named Patricia Jibben, and our advisor was Recep Avci. In my presentation I describe the process that went into the creation of the instrument and its testing.


Surface roughness and its influence on fuel cell operation
Mark Keremedjiev, Cornell University, Advisor: Yves Idzerda.

Different kinds of surface roughness on membrane material have varied effects on fuel cell operation.  Some types of roughness have a marginal effect on heat generation, while others tend to have a dramatic influence.  Using Femlab's finite element modeling, a general understanding of interface roughness can be achieved.


DC conductivity measurements of KTP crystals, Luke Galli
Colorado College, Advisor: Hugo Schmidt

KTP is a super ionic conductor and while previous studies have been conducted on measuring the DC conductivity, they all used silver electrodes, which may have interfered with their measurements. This study focused on the development of a liquid electrode apparatus to accurately and consistently measure the ionic current, and then applied the apparatus to characterize samples from different crystal growers. Crystals from different growers differed in resistivity and responded differently in time to applied voltages.


Dielectric Spectroscopy Classification of KTP Crystals for Optical Application
Marshall Swearingen, Colorado State, Advisor: Hugo Schmidt  

Potassium Titanyl Phosphate (KTP) crystals provide an excellent medium with which to make waveguides and other optical devices.  Variations that occur among different KTP producers, however, often result in inconsistent products.  These variations are thought to be linked to ionic conductivity, and in conjunction with local company AdvR, the use of dielectric spectroscopy is being developed as a method of classifying KTP crystals.  Through the use of impedance and permittivity characterization, it is hoped that the quality of individual KTP crystals may be determined prior to processing, allowing for increased quality of optical products.