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 has 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.