Carrie Heyman -- Tests of CPT in Hydrogen/Antihydrogen Systems

Advisor: Professor Bluhm

The CPT theorem states that particle interactions are invariant under the combined operations of charge conjugation C, parity reversal P, and time reversal T. One prediction of the CPT theorem is that hydrogen and antihydrogen should have equal energies and transition rates. Experiments at CERN will test the CPT theorem by comparing the 1s -> 2s transitions in hydrogen and antihydrogen. Carrie is doing theoretical calculations for trapped hydrogen and antihydrogen that are relevant for testing CPT. In particular, she is examining the ways in which the trapping potentials affect the energy levels of hydrogen and antihydrogen and whether these effects are important in tests of CPT.

 Emily Reith -- Designing Organic Molecules to Make Fantastic Transistors!

Advisor: Professor Nelson

Emily's work explores the electronic properties of pentacene at the molecular level. Transistors made from thin films of pentacene have shown promise for large area electronic applications, such as liquid crystal displays. The mechanism for charge transport in pentacene, which is a p-type semiconductor, is not yet fully understood. Investigation into this question is being done using AM1 semi-empirical calculations and studies of electron density distributions of molecules and their radical cations. In these calculations, the geometry on one molecule of pentacene was first optimized. Next, a molecule of the radical cation of pentacene was placed at varying distances from the neutral molecule, and the dependence of the electronic delocalization on the intermolecular distance was calculated. In addition, charge transfer mechanisms are being investigated between other molecules having different substituents at various positions on the pentacene rings. These systems may also exhibit favorable conductive properties.

 Alex Sobel -- Electrical Measurements and Atomic Force Microscopy of Pentacene Thin-Film Transistors

Advisor: Professor Nelson

Alex is investigating the effect of various annealing procedures on the electrical properties of pentacene thin-film transistors. It is believed that in supplying thermal energy to a crystal structure trapped in a local energy minimum, the structure may adjust to a conformation of lower, if not absolute minimal, energy. Thus, the crystal structure will present fewer conduction barriers. Alex placed pentacene samples in a quartz tube and annealed them while flowing N2(g) and varying both temperature and duration. This procedure yielded no reproducible improvement in the electrical properties of the crystal. He is currently investigating a variant of this procedure where the pentacene crystal is annealed in an inert N2(g) environment using a thin-rod heat source that is passed over the crystal. A copper block, cooled by liquid nitrogen, will serve as a heat sink from below. Hopefully, this thermal gradient will encourage the formation of low energy crystal structure. Atomic force microscopy is being used to investigate the relationship between the topography of the pentacene crystal and its transistor properties. Reproducible improvements in these properties of pentacene thin-film transistors may suggest a general scheme for enhancing the electrical properties of organic thin-film transistors such that they become viable and cost-effective in transistor applications.

 Darren Perry -- Microwave Multiphoton Transitions in Potassium Rydberg Atoms

Advisor: Professor Conover

Darren is studying multiphoton transitions in Potassium which are driven by frequency swept pulses. Darren began last summer by writing computer programs to conduct a numerical study of the experiments to be performed. Since then, he has been working on constructing and machining the appropriate devices that are needed in the experiment, such as new field plates. Once these are in place, Darren will perform measurements on Rydberg atoms subjected to strong, frequency swept, microwave electric field pulses.

 Myles Merrel -- Numerical Studies of Classical Chaos

Advisor: Professor Bluhm

Myles is writing computer programs to perform numerical studies of nonlinear dynamics in a variety of physical systems. His programs will analyze systems governed by difference equations as well as other systems that obey differential equations. He will examine the transition from regular to chaotic behavior in these systems and effects such as period doubling, bifurcations, and strange attractors. Myles will write graphics routines to illustrate the divergence of nearby trajectories in phase space and to display Poincare sections and bifurcation diagrams.

 Josh Walton -- High Resolution Doppler-Free Spectroscopy of Atomic Rubidium and Chlorine

Advisor: Professor Tate

Josh is working on the construction of two external cavity diode lasers. Once constructed, these lasers will be used to perform high resolution Doppler-free spectroscopy of atomic rubidium and chlorine. The measured spectra will then be fitted to obtain the hyperfine structure coupling constants of certain states in Rb and Cl. We will also use the diode lasers to trap rubidium atoms in a magneto-optical trap (MOT).