AVS 53rd International Symposium
    Surface Science Thursday Sessions
       Session SS2+EM-ThM

Paper SS2+EM-ThM5
The Electronic Structure and Polymerization of a Self-Assembled Monolayer

Thursday, November 16, 2006, 9:20 am, Room 2004

Session: Self-Assembled Monolayers
Presenter: D. Feng, University of Nebraska-Lincoln
Authors: D. Feng, University of Nebraska-Lincoln
D. Wisbey, University of Nebraska-Lincoln
Y. Tai, Universit@um a@t Heidelberg, Germany
Y. Losovyj, Louisiana State University
M. Zharnikov, Universit@um a@t Heidelberg, Germany
P. Dowben, University of Nebraska-Lincoln
Correspondent: Click to Email
Although organic adsorbates and thin films are generally regarded as "soft" materials, the effective Debye temperature, indicative of the dynamic motion of the lattice normal to the surface, can be very high, e.g., in the multilayer film formed from [1,1'-biphenyl]-4,4'-dimethanethiol (BPDMT).@footnote 1@ The effective Debye temperature, determined from core level photoemission from the all carbon arene rings, is comparable to that of graphite, and follows the expected Debye-Waller behavior for the core level photoemission intensities with temperature, but this is not always the case. (We associate this rigidity to the stiffness of the benzene rings, and the ordering in the ultrathin multilayer molecular thin film.) We find that a monomolecular film formed from [1,1â?T;4â?T,1'-terphenyl]-4,4'-dimethanethiol deviates from Debye-Waller temperature behavior and is likely caused by temperature dependent changes in molecular orientation.@footnote 2@ Intermolecular Ï?-Ï? lateral interactions for [1,1â?T;4â?T,1'-terphenyl]-4,4'-dimethanethiol (TPDMT), were evident from the considerable dispersion of the TPDMT molecular orbitals with changing the wave vector k. The highest occupied molecular orbitals hybridize to electronic bands, with a band dispersion of about 300 to 400 meV. The wave vector dependence is consistent with a lateral spacing of about 5.1 @Ao@, found in STM. We also find evidence for the increase in dielectric character with cross-linking in spite of the decrease in the HOMO-LUMO gap upon irradiation of TPDMT. The cross-linking processes are also accompanied by changes in molecular orientation. @FootnoteText@@footnote 1@D.Q. Feng, R. Rajesh, J. Redepenning and P.A. Dowben, Applied Physics Letters 87 (2005) 181918 @footnote 2@D.-Q. Feng, D. Wisbey, Y. Tai, Ya. B. Losovyj, M. Zharnikov and P.A. Dowben, J. Phys. Chem. B 110 (2006) 1095-1098.