2003 REU Presentations

Thursday, 31 July 2003
147 PS

2:30 pm

Adam Wood

TEMPERATURE DEPENDENCE OF PHOTOREFRACTION IN BGO:Mo

Adam W. Wood (NSF-REU), Dr. Joel J. Martin, Department of Physics, Oklahoma State University, Stillwater, OK.

The photoinduced optical absorption of molybdenum doped bismuth germanium oxide was investigated at a number of illumination wavelengths within the visible spectrum. The absorption spectrum of as-grown Mo-doped BGO is relatively unaltered from that of the undoped material. However, exposing the BGO:Mo sample to blue light at low temperatures induces a new absorption band at 980 nm that must be related to the presence of the dopant. The power dependence of photorefractive gratings was studied in both undoped BGO and BGO:Mo. BGO shows only a change in the write speed with power fluctuations while BGO:Mo shows a change in write speed and grating strength. The photorefractive response of BGO:Mo over the temperature range of 296 K to 76 K was tested and compared to the response of undoped BGO over the same temperature range. Undoped BGO shows a grating write speed that is proportional to temperature, as does BGO:Mo. Undoped BGO has a consistent grating strength while the grating in BGO:Mo fluctuates as a function of temperature.

2:50 pm

Daniel Bergman

OCCURRENCE AND GROWTH RATES OF BAND PATTERN FORMATION IN A ROTATING SUSPENSION OF SETTLING PARTICLES WITHIN A CYLINDER

Daniel Bergman, Robert Matson, Dr. Penger Tong, Dr. Bruce Ackerson, Department of Physics, Oklahoma State University, Stillwater, OK.

We report an experimental study of band formation in a settling suspension of non-Brownian glass spheres of 200 micrometers in diameter. These particles are uniform in size and density and are suspended in an aqueous solution of glycerin with viscosity ranged between 10-55 centipoise. The suspension is filled completely in a horizontal rotating cylinder. For a certain range of rotation rates the suspension forms periodic density variations along the rotating axis of the cylinder. Using a standard video imaging technique, we measure the concentration profile of the particles and obtain the growth rate of the band formation as a function of the solution viscosity and the rotation rate of the cylinder. The measured growth rate is found to depend strongly on the solution viscosity but is less dependent on the rotation rate within the band phase. In addition, new methods of analyzing the wavelength of the perturbations reveal important characteristics of the actual occurrence of the band phase. These results will aid us in understanding the dynamics of the band pattern formation.

3:10 pm

Carolyn Horton

ELECTROLUMINESCENCE IN LEAD/MERCURY CHALCOGENIDE-PVK NANOCOMPOSITES AND APPLICATIONS TO MICRORESONATORS**

Carolyn V. Horton*, Albert T. Rosenberger, Department of Physics, Oklahoma State University, Stillwater, Oklahoma 74078.

Nanocomposites comprised of semiconductor quantum-dot crystals, including PbS and HgTe, dispersed in a poly(N-vinylcarbazole) (PVK) matrix were synthesized and coated onto an indium-tin-oxide (ITO) coated glass substrate. The electroluminescence and conductivity of these samples were studied, but further experimentation is necessary for more conclusive results. The electroluminescence of the samples can be determined using spectroscopic techniques. The significance of electroluminescence in these samples is being studied in possible applications to microresonators, fabricated from fused silica optical fibers, and to microlasers. Similar experimentations have been conducted finding an infrared electroluminescence by using PbS in a conducting polymer matrices of poly(2-methoxy-5-(ethyl-hexyloxy)-1,4-phenylene vinylene) (MEH-PPV) and poly(2-(6-cyano-6´-methylheptyloxy)-1,4-phenylene) (CN-PPP).

3:30 pm

Andrew Thornberg

Effects of Heating Rate on Thermoluminescence Efficiencies

Andrew Thornburg, R. Gaza, S.W.S. McKeever, Department of Physics, Oklahoma State University, Stillwater, Ok.

The radiation in space consists of a variety of charged particles such as protons, He, Fe, and many others. These particles can threaten people and equipment sent into space. As mankind expands its reach, it is important that radiation in space can be measured. One method for measuring radiation is Thermoluminescence (TL). The efficiency of an irradiated crystal to emit light depends on the type of particle used for irradiation, and also on the technique of measuring luminescence. For example, heating rate changes efficiency when TL is the chosen technique. LiF:Mg,Ti is one of the more common materials used in dosimetry today. A TL method was used to investigate the dose response of LiF irradiated with beta and alpha radiation. Different heating rates of 1, 0.5, 1, and 5 oC/s were used. Some LiF crystals irradiated with 12C, 28Si, and 20Ne at the NIRS facilities in Chiba, Japan, were also investigated. The efficiencies of these LiF crystals were calculated for heating rates of 0.1,1, and 10oC/s.

3:50 pm

Lesley Hess

FRACTURE DETECTION OF CERAMIC MATERIAL USING TERAHERTZ IMPULSE RANGING

Lesley A. Hess, Matthew T. Reiten, R. Alan Cheville , Department of Electrical and Computer Engineering, Oklahoma State University, OK.

Ceramic materials find widespread use in precision applications because of their high temperature tolerance, wear resistance, and surface toughness. Failure modes of ceramic parts tend to be catastrophic resulting in a need to detect surface and subsurface fractures in a non-destructive manner. Here we use a Terahertz (THz) impulse ranging system to compare undamaged spheres of Aluminum Oxide with spheres damaged by thermal stress. Using two different time domain techniques, late time target response and quasi time domain target modulation, the samples were compared to determine the presence of discontinuities. The results show a definite distinction between the pre-thermal stress sample scans and the post-thermal stress sample scans. These distinctions occurred in each of the different time domain techniques, therefore indicating discontinuities in the post-thermal stress samples. THz impulse ranging is non-contact, requires no liquid medium and is insensitive to ambient temperatures making it an ideal candidate for industrial and research applications.

Friday, 1 August 2003
147 PS

2:00 pm

Ryan Scott

ELECTRONIC PROPERTIES OF THE LOWEST EXCITED TRIPLET STATE OF PORPHYRIN

Ryan Scott, Tim Wilson, Department of Physics, Oklahoma State University, Stillwater, OK.

Ab initio calculations were made using GAUSSIAN 98W to geometry optimize the first triplet state of porphyrin using density functional method B3LYP and a 6-31G(d,p) basis set. The energy of the unrelaxed singlet ground state was then calculated using the same geometry, theory, and basis set. A CIS calculation was also done on the triplet state of the porphyrin at optimized geometry. The first excited states transitional energies up to 5 eV, wavelengths, and oscillator strengths are tabulated. Results are compared to experimental values.

2:20 pm

L. Suzanne Leslie

LASER COOLING AND BOSE-EINSTEIN CONDENSATION

L. Suzanne Leslie*, Gil Summy, Department of Physics, Oklahoma State University, Stillwater, OK.

Rubidium atoms can be cooled to approximately 70µK with frequency-stabilized diode lasers. A magneto-optical trap (MOT) can be created by using anti-helmholtz coils and six circularly-polarized counter-propagating laser beams. A Bose-Einstein Condensate (BEC) can be achieved by continuing to cool the trapped Rb atoms to approximately 180nK. Analogous to a pendulum kicked at regular intervals by a rotor, the BEC can be "kicked" by pulsing a standing wave of light from two diode lasers located on opposite sides of the BEC.

*Department of Physics, Truman State University, Kirksville, MO.

2:40 pm

Jerrod Stutzman

VIBRATIONAL SPECTROSCOPY OF BUTYRAMIDE AND ITS APPLICATION TO STRUCTURE-FUNCTION STUDIES OF PHOTOACTIVE YELLOW PROTEIN

Jerrod J. Stutzman, Aihua Xie, Oklahoma State University, Stillwater, OK.

The amino acid asparagine (asn) is structurally and functionally important in proteins. Its effect on a protein chain can vary with chain position, pH value, or solvent. Therefore, to fully understand the importance of asn, measurements must be made in several conditions. Fourier Transform Infrared (FTIR) spectroscopy is used to study asn in these different conditions. Gaussian03 PC software is employed to predict theoretically the C=O vibrational frequencies for the asn monomer in different pH levels as well as for butyramide in different solvents. The effect of asn in a protein chain is observed by measuring the site-specific mutants N43! A and N43S in Photoactive Yellow Protein (PYP). Comparing the mutant data to that of wild type PYP, a shift can be seen in the 1685-1690cm-1 range. This shift is therefore directly related to the replacement of asn with a different amino acid.

3:10 pm

Eric Tong

TEMPERATURE EFFECTS ON THE SURFACE PRESSURE-AREA ISOTHERMS OF TRI-OCTYL PHOSPHINE OXIDE MONOLAYERS

Eric A. Tong*, Bret N. Flanders, Department of Physics, Oklahoma State University, Stillwater, OK.

The surface pressure-area isotherms of tri-octyl phosphine oxide (TOPO) monolayers on the air-water interface were collected across the 2oC to 35oC temperature range. All isotherms exhibited a plateau in its surface pressure at lower molecular areas. This region roughly began at a molecular area of 90 Å2 and persisted to the minimum attainable molecular area of 15 Å2. As the temperature increased, the surface pressure of the plateau region decreased. A linear dependence on temperature was observed in the data. In the compression and expansion cycling of the tri-octyl phosphine oxide monolayer, little hysteresis was observed. These behaviors suggest that tri-octyl phosphine oxide monolayers undergo a reversible, thermally activated process such as the 2D-to-3D buckling transition.

*Department of Physics, Duke University, Durham, North Carolina

3:30 pm

Trenton McKinney

CHARACTERIZATION OF PRISTINE AND HNO3 FUNCTIONALIZED SINGLE WALL CARBON NANOTUBES USING RAMAN SPECTROSCOPY

Trenton J. McKinney*, James P. Wicksted, Muhammed Gheith, (National Science Foundation), Department of Physics, Oklahoma State University, Stillwater, OK.

Changes between pristine and HNO3 functionalized HiPCO SWCNT (single wall carbon nanotubes) were characterized utilizing Raman spectroscopy. In particular, comparisons of the characteristic Raman peaks in SWCNTs, e.g. the radial breathing mode (RBM), the tangential C-C stretching mode (G mode) and the disordered mode (D-mode), were made. Specifically, the ratio of the D-mode to G-mode of pristine SWCNT was compared to the same ratio for the functionalized SWCNT. Results indicate the ratio for the functionalized SWCNT should be greater than that of the pristine SWCNT. Additionally, the frequency at which the maximum intensity for the RBM occurs indicates a similar diameter for both pristine and functionalized SWCNT.

* Portland State University, Portland, OR