Münster 1999 – wissenschaftliches Programm

Bereiche | Tage | Auswahl | Suche | Downloads | Hilfe

O: Oberflächenphysik

O 44: Fachsitzung

O 44.1: Vortrag

Dienstag, 23. März 1999, 12:45–13:00, PC4

Surface X-Ray Diffraction on Monolayers of Large Organic Molecules — •H.L. Meyerheim and Th. Gloege — Inst. f. Kristallographie u. Angew. Mineralogie der LMU München Theresienstr. 41, 80333 München

We present the first surface x-ray diffraction experiments of the structure analysis of the adsorption geometry of large organic monolayers. As model systems we have used different uracile derivates, namely 5-I-uracile (IU) and 2-S-uracile (SU) which on Ag(111) form an uniaxially incommensurate and a commensurate superstructure, respectively. Due to the large two-dimensional unit cells (typically 20 times the size of the Ag(1x1) surface unit cell, the low symmetry and the weak scatterers the measured reflection intensities are extremely low (about 2-4 orders of magnitude weaker than those of a Ag-monolayer). For both systems about 40 independent inplane reflections (hk0) could be measured allowing the development of structure models. In the case of IU we interpret the data that a surface chemical reaction takes place where a di-uracile molecule is formed after separation of the I-atom from the pyrimidine ring. Two diuracile molecules are connected via hydrogen bonds within one unit cell. For SU no dimerization is observed and four molecules are arranged within the unit cell.