AVS 46th International Symposium
    Electronic Materials and Processing Division Wednesday Sessions
       Session EM+NS-WeM

Invited Paper EM+NS-WeM3
Single Molecule Vibrational Spectroscopy with a Variable Temperature STM

Wednesday, October 27, 1999, 9:00 am, Room 6C

Session: Nano-characterization of Molecules, Materials, and Devices
Presenter: L.J. Lauhon, Cornell University
Authors: L.J. Lauhon, Cornell University
W. Ho, Cornell University
Correspondent: Click to Email
The ultimate sensitivity for vibrational spectroscopy is the detection of a single bond. The vibrational spectrum of a single molecular adsorbate carries information about the effects of the local environment on chemical bonding. Such effects are the basis of important processes such as catalysis. Single bond sensitivity was recently demonstrated by using a scanning tunneling microscope to perform inelastic electron tunneling spectroscopy (STM-IETS) on a single acetylene molecule.@footnote 1@ We have extended this technique to other molecules at temperatures from 8 K to 60 K in an effort to both better understand and widen the applicability of STM-IETS. Two 'tunneling-active' vibrational modes have been identified for CO adsorbed on Cu(001) and Cu(110). The effects of monatomic steps and coadsorbed potassium on the vibrational spectra, including peak shifting and quenching, were found to be local in nature. The increase in the vibrational peak width with temperature was measured up to 40 K, beyond which thermal diffusion prevented STM-IETS spectra from being recorded. STM-IETS was also performed on pyridine and benzene adsorbed on Cu(001). Though these molecules differ only in the substitution of a nitrogen atom for one C-H group, their bonding geometries and vibrational spectra are very different. Achieving the spatial limit of nanotechnology depends on the ability to perform chemistry on the atomic scale. To this end, tunneling electrons were used to dissociate individual pyridine and benzene molecules. The adsorbtion geometries of the reaction products differ from the parent molecules and lead to changes in the vibrational spectra which provide insights into the identities of the reaction products and the tunneling mechanism. The extension of STM-IETS to new functional groups, including larger molecules, will also be discussed. @FootnoteText@ @footnote 1@ B. S. Stipe, M. A. Rezaei, and W. Ho, Science Vol. 280, p. 1732 (1998).