Hojin Jeong

Adsorption structures of benzene on a Si(5512)-2×1 surface: A combined scanning tunneling microscopy and theoretical study

In the first ever attempt to study the adsorption of organic molecules on high-index Si surfaces, we investigated the adsorption of benzene on Si(5 5 12)-(2x1) by using variable-low-temperature scanning tunneling microscopy and density-functional theory (DFT) calculations. Several distinct adsorption structures of the benzene molecule were found. In one structure, the benzene molecule binds to two adatoms between the dimers of D3 and D2 units in a tilted butterfly configuration. This structure is produced by the formation of di-sigma bonds with the substrate and of two C[Double Bond]C double bonds in the benzene molecule. In another structure, the molecule adsorbs on honeycomb chains with a low adsorption energy because of strain effects. Our DFT calculations predict that the adsorption energies of benzene are 1.03-1.20 eV on the adatoms and 0.22 eV on the honeycomb chains.

Di–σ and Dative Binding of Benzene and Pyridine on a Si(5,5,12)-2 ×1

We investigated the adsorption of benzene and pyridine on Si(5,5,12)-(2×1) at 80 K by using variable-low temperature scanning tunneling microscopy and density functional theory calculations. The benzene molecule most strongly binds to two adatoms on the D3 and D2 units in a tilted butterfly configuration, which consists of di–σ bonds between C atoms and Si adatoms and two C=C double bonds in the benzene molecule. Pyridine molecules interact with adatom(s) on the D2 and D3 units through both Si–N dative bonding and di–σ bonds. The dative bonding through the lone pair electrons of N atom produces a vertical configuration (pyridine-like), which is more stable than di–σ bonds. Di–σ bonds can be formed either through Si–N1 and Si–C4 or Si–C2 and Si–C5.

Structural Evolution on Ag/Si(111) Ag/Si(111)√3X√3 with Adatom Coverage

Using a first-principles total-energy method, we investigate structural and energy changes on Ag/Si(111)( hereafter) as the number of the additional Ag adatoms increases. The Ag coverage varies from 0.02 to 0.14 ML. Most Ag adatoms occupy the ST site, which is the center of small triangles of the substrate Ag layer that is composed of small and large triangles. One of the interesting adsorption features is that the adatoms immerse below the substrate layer. The total energy calculations show that the clusters become the most stable when the number of Ag atoms is three. This three-Ag cluster becomes the building block of the phase that shows a large surface conductivity. The simulated STM images show that the adatoms look dark in filled-state images while bright in empty-state images. This suggests that the adatoms donate their charge to the substrate. The simulated STM images agree well with the experimental images.