Untersuchungen zur Adsorptionsdynamik von Tetrahydrofuran, Trimethylamin und Cyclooctin auf Silizium-(001)

The adsorption dynamics of tetrahydrofuran, trimethylamine and cyclooctyne on the Si(001)-surface was studied by means of molecular beam techniques. It was shown that all three molecules follow a fundamentally different adsorption pathway and therefore feature a different potential energy surface. To characterize the adsorption dynamics, sticking coeffcients where measured using the King-and-Wells method, optical second harmonic generation (SHG) and Auger electron spectroscopy (AES). By using a molecular beam, adsorption experiments where performed at a well defined kinetic beam energy Ekin of the impinging molecules. The King-and-Wells-method as well as the measurement of the SHG-Signal during molecular beam exposure allowed the in-situ evaluation of the sticking coefficient s or the reactivity of adsorbates on the sample surface. By combining the measurements of the initial sticking coefficient s0 at different kinetic beam energies Ekin and at different sample temperatures Ts a clear picture of the potential energy surfaces, the corresponding adsorption dynamics, and the energy dissipation of the systems could be drawn. Tetrahydrofuran is a cyclic ether, which is often used as a solvent because of its inert behavior towards other organic molecules. In contrast, the molecular beam experiments performed in this work show that tetrahydrofuran reacts with a high initial sticking propability of s0 ' 0:9 on the Si(001)-surface when adsorbed at low kinetic beam energies Ekin and surface temperatures Ts. The initial sticking coefficient remains at this level up to surface temperatures of Ts 350 K, at higher surface temperatures, the initial sticking coefficient drops and reaches s0 = 0:2 at Ts 700 K. This temperature dependence was qualitatively and quantitatively described by taking into account an intermediate state in the adsorption pathway. The difference of the energy barriers for conversion from the intermediate state into the final state and desorption back into the gas phase where determined to be "d