AVS 50th International Symposium
    Surface Science Thursday Sessions
       Session SS+OM-ThA

Paper SS+OM-ThA4
Short Aromatic Thiols on Cu(111): Initial Adsorption Configuration and the Formation of an Ordered Monolayer

Thursday, November 6, 2003, 3:00 pm, Room 327

Session: Self-Assembled Monolayers
Presenter: B.V. Rao, 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 orientation of di-chloro-thio-phenol (DCTP) and S-phenyl-thio-acetate (SPTA), a thio-phenol whose sulfur-bound hydrogen is replaced by an acetyl group. The latter is a common practice in order to protect the thiol group during the synthesis of poly-functional organic molecules. This poster compares the impact of the acetyl substitution on the initial steps of the molecules interaction with a Cu(111) surface. DCTP adsorbs at low temperatures (15K) with the sulfur atom at an on-top site and is able to rotate around it. This results in the observation of a flower shaped species on STM images. There are two chiral adsorption configurations which can be distinguished by STM. In contrast, SPTA adsorbs in a position in which both the phenyl and the second carbon of the acetyl group point upward resulting in a double protrusion in STM images. While tunneling electrons of less than 500meV of either bias can cause the abstraction of hydrogen from the thiol group of DCTP, SPTA is stable beyond 1V in tunneling bias. Increasing the coverage by adsorption at nitrogen temperatures, DCTP forms an ordered monolayer consisting of dimers, both of which have the phenyl group lying flat on the surface. The formation of extended islands of the ordered monolayer requires annealing of the sample beyond liquid nitrogen temepratures. Further increase of the coverage results in pronounced protrusion at defect sites of the ordered monolayer, which we interpret as molecules that point the phenyl ring away from the surface. STM resolution on a film consisting entirely of such species is poor; however, it can confirm that an ordered film is formed.