Berlin 2008 – scientific programme

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O: Fachverband Oberflächenphysik

O 34: Metal Substrates: Adsorption of Organic/Bio Molecules II

O 34.5: Talk

Tuesday, February 26, 2008, 14:45–15:00, MA 043

The Influence of Alkanespacers on the Structure of Biphenylalkanethiol SAMs on Au(111) Surfaces — •Michel Kazempoor and Gerhard Pirug — Institut für Bio- und Nanosysteme (IBN3) and Center of Nanoelectronic Systems; Forschungszentrum Jülich GmbH, D-52425 Jülich

We prepared self assembled monolayers of ω-(4’-methylbiphenyl-4-yl)-alkanethiols (BPn, n = number of CH₂ units) on Au(111) surfaces and analyzed the unit cell size by means of Low Energy Electron Diffraction (LEED). The structural dependency on the number of CH₂ units (n = 2 - 6) in the alkane chain has been studied systematically. The samples were prepared in a separate preparation chamber by gas phase deposition and subsequently transferred into the UHV analysis chamber. The formation of ordered phases after annealing for at least 12 h to temperatures between 298 K and 410 K was studied. All investigated molecules show commensurate structures on the Au(111) surface which are at variance to unit cells derived from repeating units seen by STM. The odd numbered molecules (BP3 and BP5) show the same ordered (2√3×√91) structure. In comparison the even numbered BPn molecules exhibit different phases clearly distinguished by their LEED patterns. While BP2 and BP6 show only one, but not the same dominant structure, BP4 forms three temperature dependent phases. Structure models will be presented based on the unit cells determined by LEED and the molecular packing seen by STM. Different unit cell sizes imply that the stress between the Au-S interface and the biphenyl overlayer is compensated within the alkane spacer.