teaching

People

Graduate Students

Former

1. Santosh Kumar, M.S. Materials Science (July 2006)

    Santosh Kumar studied problems related to catalysis and electrochemistry using density-functional theory (DFT) methods. In particular, he was the first to show that gas-phase water adsorbed at ceria surfaces may actually increase the concentration of vacancies at the (111) surface. This is surprising because reduced ceria powders tend to be oxidized by water with the production of hdyrogen gas. He also showed the limited basis set LCAO models, in particular the SIESTA approach, can describe liquid water to a reasonable level of accuracy. This work provides a starting point for future water simulations using SIESTA.
    His work led to two journal articles. He recently became a Ph.D. student in the Materials Science Department at Purdue University.

2. Arun Bodapati, Ph.D. Materials Science, RPI (2006)

    Arun studied several systems to eluidate the role of atomic disorder on phonon transport, including in amorphous Si, nanocrystalline Si, and carbon nanotubes. Pawel Keblinski supported Arun and served as Chair on his Ph.D. examination committee. He is currently working in industry.

Current

1. Ashton Skye (Brian Becker) (Ph.D. physics)

    Ashton is studying intefacial phonon scattering at interfaces in nanowires and bulk crystals, in particular grain boundaries. He has developed phonon wave-packet methods to efficiently study fundamental scattering properties within a molecular-dynamics simulation. He has made a key contribution in showing how shape and symmetry can control transport properties. Also, for the first time he has show, in collaboration with Sylvie Aubry and Chris Kimmer at RPI, that grain-boundary phonon scattering mainly depends on the frequency of the incident wave.
     His work has led to two journal articles and one conference proceedings. He is expected to graduate with his Ph.D. in the summer of 2007.

2. Duc Nguyen

    Duc Nguyen is using electronic-structure methods, including VASP and more novel self-consistent tight-binding methods. Using self-consistent tight-binding methods, Duc has made a simple model to predict the concentration of vacancies at a (110) TiO₂surface. One key contribution was to show how the repulsive interaction of vacancies in bridging positions tends to limit the vacancy concentration at the surface. His current work involves studying the adsorption energetics of water on TiO₂and CeO₂surfaces. One important issue for ceria surfaces is the effect of using LDA+U methods on the adsorption.

3. Dat Nguyen (Ph.D. physics)

    Dat is developing a classical atomistic model for Nafion polymer. The principle appicatio of Nafion polymers is in proton exchange membrane (PEM) fuel cells. Dat has developed an extensive database using Hartree-Fock calculations. We have an atomistic model that seems to give reasonable vibrational properties, although we are working to improve agreement with first principles in the displacement eigenvectors as well as the frequencies. The basic approach we are using is to directly fit the Hessian, or force constant, matrix.
    The next step will be to study the diffusion of protons in water in the presence of the Nafion polymer using molecular dynamics. This will elucidate fundamental transport physics crucial for understanding and improving materials used in fuel cells.

4. Mark Nurge (Ph.D. physics)

    Mark is working at Kennedy Space Center on electrical capacitance tomography. The basic idea is to use an array of capacitors to image a dielectric material. The work involves experiment and algorithms to reconstruct the image of the dielectric material. His expected graduation date is May 2007. He is coadvised by Prof. Robert Peale.

Undergraduate Students

1. Tom Gordon

Tom used DFT methods to study silicon nanowires. Comparable to previous DFT calculations, Tom showed that silicon nanowires that are unpassivated become conductors due to undercoordinated surface atoms. Tom graduated with his B.S. degree in 2006.

2. Enrique Ortiz

    Enrique worked on electronic structure of oxygen adsorbed on small 6 atom gold clusters. He was supported by a UCF RAMP fellowship. Enrique presented his work at the UCF SURE forum, and also presented a posted at the Florida AVS meeting in 2006.

3. Nushien Shahnami

    Nushien is using wave packet studies to look at anharmonic effects at grain boundaries. We have developed a method to create highly non-equilibrium phonon populations that are showing that anharmonicity is extremely important. In particular, we find that when a heat current is comprised of waves in a narrow frequency range, that grain boundaries act strongly to scatter the incident waves into different frequencies. It appears that the dominant process may produce multiple low-frequency phonons from a single incident phonon at a higher frequency.

Collaborators

Simon Phillpot, U. Florida
Pawel Keblisnki, RPI
Sylvie Aubry, Sandia National Lab
Ed Webb, Sandia National Lab
Chris Kimmer, U. Louisville
J. Woods Halley, U. Minnesota
K. Coffey, UCF
Ken Goodson, Stanford
Li Shi, U. Texas-Austin