Linear and Nonlinear Spectroscopy with the Tunable AC Scanning Tunneling Microscope

S. J. Stranick, L. A. Bumm, M. M. Kamna, and P. S. Weiss*

Photons and Local Probes, O. Marti and R. Müller, eds., NATO ASI Series E: Applied Sciences 300, 221 (Kluwer Academic, 1995).

The tunable microwave frequency AC scanning tunneling microscope (ACSTM) has opened the possibility of recording local spectra and local chemical information on insulator surfaces much as the conventional STM has done for metals and semiconductors. We describe the various types of spectroscopies that can be performed with the ACSTM. These include linear spectroscopies where the amplitude at the modulation frequency is measured as well as nonlinear spectroscopies utilizing the amplitudes of the harmonics of the modulation frequency generated in the tunneling junction. Spectroscopy in the microwave frequency range also enables heretofore unrealizable measurements on conducting substrates such as the rotational spectroscopy of a single adsorbed molecule.