NIU Logo Northern Illinois University
Department of Physics
College of Liberal Arts and Sciences

Research

Current research themes

  • Studies of structure, chemistry and morphology during vapor phase materials processing (OMVPE, MOCVD) using x-ray scattering as real-time probes of growth and processing. 
  • Limits of ferroelectricity in ultra-thin (nanoscale) films
  • Relaxation mechanisms and defect incorporation in epitaxial films
  • Time-resolved studies in structural and lattice response in ferroelectric thin films: polarization reversal and piezoresponse studied via x-ray scattering.
  • X-ray studies of relaxation processes and incorporation of In during growth of InGaN by MOCVD
  • Oscillatory reactions during MOCVD growth of InGaN and InN

Why do different materials behave the way they do? What are the physical principles that allow us to predict and control their physical properties? Can we understand the interplay between structure and properties even at the nanoscale? Why do so many physical properties, such as, magnetism, conductivity, color, transparency, superconductivity, strength, toughness, viscosity, or chemical reactions change with changes in structure? Will these properties change as the size changes? Does a thin layer that is only 10 atoms thick behave like a bulk crystal that is 1023 (a lot!) of atoms thick? How does the presence of an interface between two different materials change the position of atoms nearby? Are properties at a surface different than within the bulk? How far inside do the changes extend? Thompson's group studies surface, interface and bulk structures to understand the correlation between structure to physical properties such as those listed above.

Current aspects of her research emphasize studies during processing and under in situ conditions. In situ is the term used for classes of experiments designed to study what happens while it is happening. That is, studying systems when the structure is changing with time due to the environment; and measuring the evolution of these changes as they are occurring.

Thompson’s experimental programs have been based at the Advanced Photon Source at Argonne National Laboratory and at the Center for Nanoscale Materials at Argonne. The high brilliance of the x-rays at synchrotrons provides unique access to techniques that study fundamental structure-property questions in materials physics. Her access to this facilities is as a general user through their peer reviewed proposal process.

Unique to her current programs is the access to a specially constructed chamber for materials synthesis at the Advanced Photon Source designed and operated by her collaborators and her group. It allows in situ x-ray characterization techniques to be performed simultaneously during the growth of layers of atoms onto a substrate, and the ability to study structure at the nanoscale. This particular chamber is capable of organo-metallic vapor phase epitaxy (OMVPE) in oxide and nitride systems.

Research has concentrated on the ferroelectric oxide perovskite system that have properties interesting for integration as non-volatile high-speed memories as well as having many other physical properties useful for sensors and actuators. Some of these properties are fundamentally altered by the size of the system. We have studied interesting questions of the organic metal vapor phase epitaxial (OMVPE) growth mechanisms in these systems and for the effect of thickness, strain, and chemical stoichiometry on the ferroelectric phase transition in the epitaxial films.

Thompson and collaborators also study the growth of indium gallium nitride, (InGaN), the material used in light emitting diodes for solid state lighting applications in consumer and business markets. In our work, we explore during OMVPE growth how the indium incorporates as an oversaturated impurity in gallium nitride. Can we understand the complex interplay between the surface and bulk thermodynamics, and the non-equilibrium kinetics of the growth process? A systematic study of potential mechanisms would be fascinating for its fundamental scientific interest and its broader impact.

Former members of Thompson's research group

Highlights of the NIU/Argonne collaborative research program

Contact Info

LaTourette Hall 207
Department of Physics
Northern Illinois University
DeKalb, IL 60115 USA

Phone: 815-753-1772
Fax: 815-753-8565
cthompson@niu.edu

Argonne Phone:
630-252-7378