COLL 197 |
| Jun Young Lee1, Soon Jung Jung1, Suklyun Hong2, and Sehun Kim1. (1) Department of Chemistry, KAIST, 373-1 Guseong-dong Yuseong-gu, Daejeon, 305-701, South Korea, (2) Department of Physics, Sejong, South Korea |
| The Ge(100)-2x1 surface was exposed to pyrimidine (C4H4N2) molecules at 300 K and the STM images of the pyrimidine adsorbed surfaces were recorded in real time. The oval shaped-bright spots are observed in the occupied-state STM image (Vs=-1.6 V) of Fig. 1(a) and contributed to adsorbed pyrimidine molecules. We noted that the pyrimidine molecules do not reside at the center of the Ge dimer and induced the buckling of neighboring bare Ge dimers. It suggests that pyrimidine adsorbed on Ge(100)-2x1 surface by Ge-N dative bonding on the down atoms of Ge dimers without loss of aromaticity as the nucleophilic reaction. In Fig. 1(b), theoretically calculated STM image shows that the lone-pair electrons of two N atoms in pyrimidine molecule make two Ge-N dative bonding to give the most stable configuration and the adsorbed pyrimidine molecule is tilted to the Ge surface. With the exposure of pyrimidine increased up to 0.25 ML, the well-ordered phase of c(4x2) is formed as shown in Fig. 2(a). The ordered c(4x2) structure indicates that pyrimidine molecules adsorbed on every other dimer due to steric hindrance. At 0.50 ML, bright but fuzzy zigzag lines are observed (Fig. 2(b)). It is suggested that incoming pyrimidine molecules adsorb on the unreacted down Ge atoms of every dimers with less steric hindrance. In this way, the p(2x2) structure is formed along the dimer row. However, the p(2x2) structure is likely to be unstable due to weak repulsive interaction between adjacent pyrimidine molecules. After time elapses, the unstable p(2x2) structure is transferred as c(4x2) structure. This observation is similar to our previous result of pyridine on the Ge(100)-2x1 surface. Thermal desorption spectra for pyrimidine adsorbed at 80 K reveals two desorption peaks at 330 K and 470 K as well as the physisorbed peak at 150 K. The two peaks are attributed to p(2x2) and c(4x2) site adsorption species, respectively. |
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Posters: Fundamental Research in Surface and Colloid Chemistry
6:00 PM-8:00 PM, Monday, March 29, 2004 Disneyland -- North Exhibit Hall, Poster
Division of Colloid and Surface Chemistry |
