Professor Orr’s research centers on systems where the properties are
controlled by the characteristics of surfaces or interfaces. As
designed structures become ever smaller, their surface characteristics
begin to influence, or even control, their behavior. Often the research
involves scanning probe microscopies such as STM and AFM. Specific
examples of research interests include: studies of molecules adsorbed
on Si and Au surfaces; the molecular origin of negative differential
resistance in metal-insulator-metal devices; the mechanism for
composition modulation in compound semiconductors grown by
molecular-beam epitaxy; and the development of multifunctional
nanoparticles as therapeutics for cancer treatment.
The demand for smaller, faster silicon-based MOSFET’s necessitates
the creation of thinner, more stable insulating silicon oxide (SiO2)
layers. To achieve this a detailed understanding of the oxidation
process and the structure of the Si/SiO2 is key. His group’s research
involved examining a model of this interface and determining the
structure with atomic resolution. The theme of atomically resolved
surface structure continues in research on the MBE growth of compound
semiconductors and the spontaneous creation of compo-sitionally
modulated superlattices. His group is also examining novel molecules
that bind to gold and form self-assembled monolayers.
A second part of his research is the creation of targeted drugs for
chemotherapy. This work involves the study of functionalized
poly-(amidoamine)dendrimers as drug transport agents. We are studying
the interaction of these nanoparticles with lipid layers, cell
membranes and cells. In situ AFM has been used to examine cell
apoptosis (programmed cell death) that occurs as a result of
successfully killing the cancer cell.
Most of the research performed is interdisciplinary and falls in the
broad category of nanotechnology. He has active collaborations with
researchers in the Department of Chemistry and Materials Science as
well as the Medical School and the Center for Biologic Nanotechnology.
By combining our respective areas of expertise, we are able to address
problems from a number of angles. This has proven to be a very
successful and powerful style of research for his group.
Investigation of Hydridosilsequioxane-Based Silicon Oxide
Deposition on Si(111)-7x7, (Kevin S. Schneider, Thomas M. Owens,
Nicholson, Bonnie J. Laack, J. Neil Greeley, Bradford G. Orr, Mark M.
Banaszak Holl), Langmuir 18, 6233 (2002).
Near-Field Coherent Spectroscopy and Microscopy of a Nanoscopic
Quantum System, (J.R. Guest, T.H. Stievater, B.G. Orr, D.G. Steel,
D. Gammon, and D.S. Katzer), Science 293, 2224 (2001).
Lateral Composition Modulation in Short Period Superlattices: The
Role of Growth Mode, (C. Dorin and J. Mirecki Millunchick, Y. Chen,
B.G. Orr and C.A. Pearson), Applied Physics Letters 79, 4118 (2001).
Determination of Spherosiloxane Cluster Bonding to Si(100)-2x1 by Scanning Tunneling Microscopy, (K.S. Schneider, Z. Zhang, M.M.
Banaszak Holl, B.G. Orr, U.C. Pernisz), Phys. Review Lett. 85, 602 (2000).
Stable and Unstable Growth During Molecular Beam Epitaxy, (M.D.
Johnson, C. Orme, A. Hunt, J. Sudijono, D. Graff, L.M. Sander, and B.G.
Orr), Phys. Rev. Lett. 72, 116 (1994).