Main Content

2016

• Inhalt ausklappen Inhalt einklappen M. Reutzel, N. Münster, M. A. Lipponer, C. Länger, U. Höfer, U. Koert, M. Dürr, Chemoselective reactivity of bifunctional cyclooctynes on Si(001), The Journal Physical Chemistry C 120, 26284-26289 (2016).

  Controlled organic functionalization of silicon surfaces as an integral part of semiconductor technology offers new perspectives for a wide range of applications. The high reactivity of the silicon dangling bonds, however, presents a major hindrance for the first basic reaction step of such a functionalization, that is, the chemoselective attachment of bifunctional organic molecules on the pristine silicon surface. We overcome this problem by employing cyclooctyne as the major building block of our strategy. Functionalized cyclooctynes are shown to react on Si(001) selectively via the strained cyclooctyne triple bond while leaving the side groups intact. The achieved selectivity originates from the distinctly different adsorption dynamics of the separate functionalities: A direct adsorption pathway is demonstrated for cyclooctyne as opposed to the vast majority of other organic functional groups. The latter ones react on Si(001) via a metastable intermediate, which makes them effectively unreactive in competition with the direct pathway of cyclooctyne’s strained triple bond.

  DOI: 10.1021/acs.jpcc.6b07501

• Inhalt ausklappen Inhalt einklappen M. A. Lipponer, M. Reutzel, M. Dürr, and U. Höfer, Energy dependent sticking coefficients of trimethylamine on Si(001) – influence of the datively bonded intermediate state on the adsorption dynamics, Surface Science 653, 118-122 (2016).

  The adsorption dynamics of the datively bonded trimethylamine (TMA) on Si(001) was investigated by means of molecular beam techniques. The initial sticking probability s0 of TMA on Si(001) was measured as a function of kinetic energy at two different surface temperatures (230 and 550 K). At given surface temperature, s0 was found to decrease with increasing kinetic energy (0.1 to 0.6 eV) indicating a non-activated reaction channel. At increased surface temperature, s0 is reduced due to the onset of desorption into the gas phase. The energy dependence of s0 is compared to the results for the adsorption of tetrahydrofuran (THF) on Si(001), which reacts via a datively bonded intermediate into a covalently bound final state. As s0 follows the same energy dependence both for TMA and THF, the datively bonded intermediate state is concluded to dominate the reaction dynamics in the latter case as well.

  DOI: 10.1016/j.susc.2016.04.005

• Inhalt ausklappen Inhalt einklappen A. Stegmüller, K. Werner, M. Reutzel, A. Beyer, P. Rosenow, U. Höfer, W. Stolz, K. Volz, M. Dürr, and R. Tonner, Surface Chemistry of tert-Butylphoshine (TBP) on Si(001) in the nucleation phase of thin-film growth, Chemistry – A European Journal 22, 14920-14928 (2016).

  We combine density functional theory calculations and scanning tunneling microscopy investigations to identify the relevant chemical species and reactions in the nucleation phase of chemical vapor deposition. tert-Butylphosphine (TBP) was deposited on a silicon substrate under conditions typical for surface functionalization and growth of semiconductor materials. On the activated hydrogen-covered surface H/Si(001) it forms a strong covalent P−Si bond without loss of the tert-butyl group. Calculations show that site preference for multiple adsorption of TBP is influenced by steric repulsion of the adsorbate's bulky substituent. STM imaging furthermore revealed an anisotropic distribution of TBP with a preference for adsorption perpendicular to the surface dimer rows. The adsorption patterns found can be understood by a mechanism invoking stabilization of surface hydrogen vacancies through electron donation by an adsorbate. The now improved understanding of nucleation in thin-film growth may help to optimize molecular precursors and experimental conditions and will ultimately lead to higher quality materials.

  DOI: 10.1002/chem.201602418