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.