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

Paper SS+OM-ThA3
Photoemission Study of Dodecanethiol on Ag(111) and Au(111)

Thursday, November 6, 2003, 2:40 pm, Room 327

Session: Self-Assembled Monolayers
Presenter: H. Geisler, Xavier University
Authors: H. Geisler, Xavier University
J.M. Burst, University of New Orleans
S.N. Thornburg, University of New Orleans
C.A. Ventrice, University of New Orleans
Y. Losovyj, Louisiana State University
P.T. Sprunger, Louisiana State University
Correspondent: Click to Email
Self-assembled monolayers show great promise for use in many technological applications such as in chemical and biological sensing, chemical resists in lithography, corrosion protection, and molecular electronics. However, there are several fundamental properties of these systems that are not well understood. For instance, the adsorption of alkanethiols on Au(111) results in a (@sr@3 x @sr@3)R30° overlayer; whereas, adsorption on Ag(111) results in an incommensurate overlayer even though Au and Ag are isoelectronic and are lattice matched to 0.3%. Although there have been several studies of the geometric structure of thiols on Au(111) and to a lesser extent on Ag(111), there have been very few studies of the electronic structure of these films. Angle-resolved ultra-violet photoelectron spectroscopy studies of the growth of dodecanethiol on Au(111) and Ag(111) have been performed in UHV by vapor deposition. By using vapor deposition, the submonolayer striped phase, full monolayer upright phase, and the multilayer phase can be studied. The monolayer coverage of thiol results in peaks at binding energies of 20 eV, 14 eV, 10 eV, and 7 eV. By comparing the dispersion of the Ag(111) d-band emission for the clean surface to the surface after deposition of a monolayer of thiol, it was determined that there is a loss of order of the Ag surface atoms. Similar measurements for Au(111) reveal that the Au(111) surface remains in an ordered state. This result provides a mechanism for the different adsorption geo metries of alkanethiols on Au(111) and Ag(111). Since there is no ordered template of Ag atoms after thiol adsorption, the van der Waals interaction between the CH@sub 2@ chains dominates, resulting in an ordered, incommensurate overlayer. Measurements of the thiols in the multilayer regime reveal a uniform shift of the thiol peaks to higher binding energy, presumably due to sample charging effects from the insulating nature of these films at 150 K.