A VARIABLE PRESSURE TEMPERATURE SCANNING TUNNELING MICROSCOPE FOR SURFACE SCIENCE AND CATALYSIS STUDIES

We describe the design and construction of a scanning tunneling microscope (STM), which is contained in a reactor cell and allows in situ operation throughout a wide range of pressures and temperatures. This STM is capable of imaging in pressures ranging from ultrahigh vacuum up to several atmospheres. Samples can also be easily moved in and out of the STM cell in a small separate vacuum transfer chamber for external characterization and treatment. The equilibration time and stability of the microscope after temperature changes was determined at atmospheric pressures, by monitoring the evolution of atomically resolved images of highly oriented pyrolytic graphite at temperatures ranging from 300 to 425 K. We have also examined the stability when flowing gases are used instead of stationary pressures. In preliminary experiments using Pt (111) and (110) crystals, we have observed the effect of atmospheres of H-2 and O2 on the structure of these surfaces.