AVS 50th International Symposium
    Surface Science Wednesday Sessions
       Session SS+NS-WeA

Paper SS+NS-WeA10
Adsorption and Deprotonation of Dichlorothiophenol on Cu(111): STM-Based Hydrogen Abstraction and Thiolate Formation

Wednesday, November 5, 2003, 5:00 pm, Room 328

Session: Perspectives and New Opportunities
Presenter: L. Bartels, University of California at Riverside
Authors: B.V. Rao, University of California at Riverside
K.-Y. Kwon, University of California at Riverside
J. Zhang, University of California at Riverside
A. Liu, University of California at Riverside
L. Bartels, University of California at Riverside
Correspondent: Click to Email
We present low-temperature scanning tunneling microscope (STM) measurements of the initial steps of the adsorption of di-chloro-thio-phenol (DCTP), an aromatic thiol, on Cu(111). Upon adsorption of ultra-low coverages at 15 K individual molecules can be found on Cu(111) terraces which appear as large, flower-shaped protrusion in STM images. This is caused by the rotation of the molecule around the sulfur atom which rests at an on-top site of the substrate. Deprotonation to the thiolate may be caused by annealing to nitrogen temperatures or attachment/removal of electrons to/out of the molecule at a bias exceeding 300 mV. Following deprotonation, the sulfur atom shifts to a higher-coordinated substrate site and the molecules is fixed in place. STM-based vibrational spectroscopy reveals a pronounced S-H stretch mode at 320 meV before deprotonation, which is absent from spectra taken after deprotonation. The STM based hydrogen abstraction process can be accomplished reliably at -500mV with a first-order dependence on the current. Perfect selectivity for the sulfur bound hydrogen is achieved even if the excitation current targets the benzene ring. Adsorption of 1 L of DCTP at nitrogen followed by annealing to ambient temperatures leads to the formation of an ordered structure comprised of pairs of DCTPs of opposite chirality in the adsorbed state. Further increasing the adsorbate coverage, more and more of the molecules do not lie flat on the surface but have the benzene ring pointing up.