Physics Research Group Openings for Fall 2009

Daniel Dougherty, Experimental Surface Science
Current Undergraduate Research Students: Andy Hewitt
Potential Projects:

• Electron Tunneling Spectroscopy of Organic Paramagnets In the quest for new materials for applications in spin-based electronics("spintronics") organic paramagnets offer the chance to create designer spins associated with unpaired electrons by synthetic chemistry. However, the physical properties of organic paramagnets incorporated into solid state device environments has not been extensively explored. Undergraduate researchers in our group will work to characterize ultrathin films of unique organic paramagnets using a technique called electron tunneling spectroscopy. This employs the quantum tunneling of electrons between metal electrodes to probe electronic and vibrational excitations of molecules sandwiched between the electrodes. Students will learn to grow thin films in high vacuum and make very low noise electrical measurements at cryogenic temperatures.
• Numerical Modeling of Image Potential States An electron just outside of a surface can be transiently bound by the electrical polarization it induces near the surface. The interaction between the electron and the solid is analgous to a 1-D hydrogen atom: the bound states the electron can occupy form a nearly hydrogenic series converging on the vacuum level. The details of the energetics of these states are a sensitive probe of the electrostatic potential near the surface. This is particularly important for understanding the assembly and physical properties of surface nanostructures. Undergraduate students will explore the energetics of image potential states by numerically integrating the 1D time independent Schrodinger equation for experimentally-parametrized model potentials. Of particular interest will be incorporating the influence of STM tips into the model potential calculations.

Russell Philbrick
Potential Projects:

• Lidar Applications in Remote Sensing Lidar techniques using differential absorption (DIAL) and scattering (Raman scatter) provide very useful ways to measure the profiles of chemical species (H₂O, O₃, CO₂... ) and physical properties (temperature, dynamical processes, turbulence... ). Research is undertaken to improve capabilities to measure smaller concentrations of molecules for investigations of air pollution chemicals and aerosols with added capability at infrared and ultraviolet wavelengths.
• Optical Scattering Characterizations of Aerosols Measurements of scattering intensity of polarization components from a laser beam as a function of angle provides data that can be used to determine properties of the aerosols (number density, size, size distribution, and type based upon refractive index). The technique is being extended to measure and characterize aerosols over a larger range of aerosol sizes by adding capabilities to measure in the infrared region.
• Raman Lidar Experiments(In collaboration with Hans Hallen) Raman lidar gives the opportunity to investigate water vapor, ozone, and particulate matter from near ground to several kilometers up, in real time, for environmental studies. The data can also be viewed to provide graphical illustrations of many atmospheric properties and processes. Lidar units have been recently moved from Penn State University where they are being assembled and will soon be operated in the new NCSU Lidar Laboratory.

Hans Hallen, Optics
Current Undergraduate Research Students: Evan Adamek, Brandon Long
Potential Projects:

• Multiple media ellipsometry. Ellipsometry is well known and developed as a technique to measure the thickness and index of refraction of overlayers on samples. It fails to be able to extract both quantities when the layer becomes very thin, such as for a self-assembled monolayer. This is unfortunate, since both (index => layer density and thickness => really one layer?) are required. We have developed (mostly) analysis methods for multiple media ellipsometry that enables both to be measured for very thin samples, even for 'complex' substrates.
• Near-field photoemission. Photoemission is a powerful tool for characterization. This project attempts to bring it into the nanoscale. A near-field microscope tip provides localized light, and the metal aperture collects the electrons. The proximity of the collector permits ambient operation, but precludes electron energy analysis. This can be overcome by excitation tuning or voltage assisted photoemission, the latter is a largely uninvestigated field that will be dominant in near-field photoemission.
• Raman lidar experiments, in collaboration with Russell Philbrick. Raman lidar gives the oportunity to investigate water vapor, ozone, and particulate matter from near ground to several kilometers up, in real time, for environmental studies. The data can also be viewed to provide graphical illustrations of many atmospheric events. The lidar units need to be re-assembled after their move from Penn. State, and measurements taken, either in Raleigh or at a site in the Pisgah national forest.

Keith Weninger, Biophysics
Potential Projects:

• Measureing Protein Dynamics. We have an undergraduate project to participate in development of a new optical instrument for high time resolution measurements of protein dynamics. Opportunities for studying biological functions of proteins using this instrument will follow its development.

Chueng Ji, Theoretical Nuclear Physics
Current Undergraduate Research Students: Patrick Bowen
Potential Projects:

• Lepton and Quark Flavor Mixing in Quantum Field Theory. Although the flavor mixing problem has been thoroughly explored with quantum mechanics, advances have been made in our understanding of elementary particles through the quantum field theory. By taking the effects of the vacuum on a particle into account, the quantum field theory offers more accuracy than quantum mechanics. These advances may shed more light and offer far more precision to our understanding of flavor mixing, and as of yet have not been applied to the flavor mixing problem.

John Blondin, Computational Astrophysics
Current Undergraduate Research Students: Tony Allen, Chris Pope, Joseph Barton, Patrick Keene
Potential Projects:

• Ablation of Giant Molecular Clouds in NGC 1068. Design and run 2D (and later 3D) simulations to study the ablation of giant molecular clouds by an intense wind from the AGN in the core of the galaxy. Simulations will be used to interprest spectroscopic data obtained by Gerald Cecil (UNC-CH) showing the gradual acceleration of molecular material away from the AGN.
• Spherical Accretion Shock Instability. Using 2D time-dependent hydrodynamic simulations as a laboratory, the student will design experiments to investigate the nature of this instability of a supernova shockwave in its first few hundred milliseconds of existance. The goal is to develop an experiment that can discriminate between the two competing theories proposed for the SASI.