S. J. Stranick, P. S. Weiss,* A. N. Parikh, and D. L. Allara*
Journal of Vacuum Science and Technology A 11, 739 (1993).
We demonstrate the spectroscopic capabilities of an AC scanning tunneling microscope. This AC scanning tunneling microscope has a bias voltage modulation frequency tunable over the range DC-20 GHz and is thus capable of recording images and local spectra of insulating as well as conducting substrates. In this paper we detail the spectral sensitivity and the tip-sample separation dependence of the spectra recorded by simultaneously tuning the modulation and detection frequencies. Spectra of an evaporated gold film and of self-assembled monolayers of CH3(CH2)15SH and of CH3O2C(CH2)15SH on gold are presented.