Example Project: How impurity atoms dissolve in intermetallic compounds
If you dissolve an impurity atom in a solid, where does it go? This is an important question in the theory of solutions. Unlike in ionic compounds, preferred lattice sites in intermetallics are not obvious because the conduction electrons move to screen the coulomb interactions of ion charges. Our lab uses a spectroscopy from nuclear physics, perturbed angular correlations, or PAC, to detect lattice locations of radioactive “probe” atoms.
The locations are identified through hyperfine interactions of nuclear quadrupole moments of the probe atoms with local “fields” due to the neighboring atomic environments. The fields are electric-field gradients, primarily produced by atoms within the first neighbor shell of the probes. The various lattice locations occupied are labeled by characteristic spin-rotation frequencies of the nuclear spin, which are detected through time and angular correlations between emission of two gamma-rays in a cascade. The amplitudes of the signals equal the site-fractions of probes. In this way, PAC provides discrete, atom-scale resolution of the local environments occupied. The goal of current research is to arrive at a fundamental understanding of the partition, or division, of solute atoms between two sublattices of a binary compound in thermal equilibrium. Through measurements of changes in site-fractions, we seek a more fundamental understanding of how the partition is affected by the composition of the host compound, the mole-fraction of solute, and temperature.
REU project participation.
The REU scholar will work in a team with several graduate students and faculty mentor. She or he will be provided in-depth tutoring in solid-state physics and experimental methods necessary to participate effectively over the summer project.
Prof. Gary Collins’s research has been supported by the Metals Program of the National Science Foundation with nearly continuous funding over 38 years. His group is currently the only one in North America applying PAC to study the local structure of solids. He was honored with a faculty lifetime career achievement award by the College of Arts and Sciences in 2019. Collins has mentored 44 PhD and MS students, 27 undergraduates and 3 high-school students. Five undergraduates were REU students, of which four were women, one was Native American, and two have since earned PhD degrees in physics at Ohio State and Oregon State. Of the high-school students, one has an MBA degree from Northwestern, and the others PhD degrees from UNC and Stanford. The Stanford PhD student, Prastuti Singh, was semifinalist in the 2010 Intel Science Talent Search for a report based on her research in the group.
More information about Gary Collins and group
Academic profile
Archived group web site (current site is down)