Strukturelle und chemische Charakterisierung von selbst-assemblierten Monolagen organischer Moleküle auf Oberflächen

In this thesis self-assembled monolayers (SAM) of 4(4´methylbiphenyl4yl)butane 1thiol (BP4) on a gold(111) surface were fabricated. The deposited amount of molecules could be adjusted very precisely, using an upstream vessel. Two coverage depending phases could be observed: the alpha-Phase and the delta-phase. The letter has a lower areal density. BP4 adsorbs on a gold(111) surface in an Au-S-C-angle of 104° due to the sp3 hybridization of sulfur. Starting from a coverage of 0.07 island formation of the delta-phase occurs. The unit cell can be described with an unit cell. the film thickness is 6.4 Å. Two perpendicular glide planes parallel to the unit cell axes give rise to systematically vanishing LEED-Spots. At a coverage of 0.16 a homogenous film of the delta-phase exists. Adsorbing additional molecules leads to a disordered phase. At a coverage of 0.33 a chemisorbed monolayer is achieved. Only few weakly physisorbed molecules can be additionally deposited. Short time heating at 330 K leads to desorption of these molecules. The chemisorbed molecules desorb at temperatures between 340 and 380 K (DeltaH: AuS ~ 184 kJ/mol). Higher temperatures lead to dissociation of the BP4 molecules (DeltaH: CS = 289 kJ/mol). Heating between 340 and 380 K also leads to a deformation of the Au-S-C-angle from 104° to 144°. Therefore the molecules can arrange in the alpha-Phase. The more upright standing molecules give rise to a stronger intermolecular interaction. A homogenous chemisorbed monolayer of the alpha-phase exist at a coverage of 0.33. It can be described with an unit cell consisting of 16 molecules. The film thickness is 13.4 Å and thereby twice as much as in the delta-phase. At coverages between 0.19 and 0.22 both Phases can coexist. The transition from the alpha-Phase to the delta-Phase is thermic irreversible. Both phases can be distinct by their S2p binding energy. Due to the deformation of the Au-S-C-angle the electron density at the sulfur is higher in the alpha-phase. Therefore the S2p binding energy is higher in the alpha-phase. Further phases of BP4 on gold(111) could not be observed. Hence it is assumed that the previously observed beta- and gamma-phases are contaminated. The volume density of both observed phases is nearly the same: rho(alpha) = 1,46 g/cm3 vs. rho(delta) = 1,50 g/cm3. The molecules in the alpha-phase are standing more upright. Therefore it is assumed, that there is a better intermolecular interaction in the alpha-phase. For this reason it can be assumed, that the electronic properties are different in both phases