Scanning tunneling microscopy of carbon nanotubes

This article reports on the application of scanning tunneling microscopy fo r the study of surface structures and electronic properties of carbon nanot ubes. Geometric effects resulting from the cylindrical shape of the tubes a s well as the particular band structure of the graphitic crystal lattice ca n lead to a variety of contrast patterns. On the atomic scale, it is someti mes possible to see the full honeycomb lattice structure but often differen t structures are observed. Besides distortions caused by tip-sample interac tions, we find that a complex superstructure superimposed on the simple ato mic contrast pattern arises from elastic scattering of the Fermi states at defects or impurities. From a careful analysis of high-resolution images it is possible to extract information about elastic strain of individual tube s. A new combination of scanning tunneling and scanning force microscopy en ables near-atomic point resolution of the force signal the tubes can be ide ntified without the need of a conducting substrate. This imaging mode is a crucial step for the characterization of electronic devices based on indivi dual single-wall tubes. This mode can be further enhanced by the use of sin gle-walled tubes as probe tips.