Studies Of The Self-assembled Monolayer Of Organic Molecules On The Semimetal Film By STM

In this thesis,utilizing UHV-STM and organic molecular beam deposition (OMBD), we have studied the preparation methods of high quality of semi-metallic Ga film as well as the growth modes of perfluoropentacene. By depositing 1/3 monolayer(ML) of Ga atoms onto the Si(111)-7x7 surface at room temperature with subsequent annealing at-770 K, a highly ordered Si(111)-(?)3×(?)3-Ga surface has been obtained. On Si(111)-(?)3×(?)3-Ga, we grew the Ga bilayer at RT. At the Ga coverage of 5 ML, the growth of second Ga layer is complete. The second Ga layer has large, atomically smooth terraces, which is very important to the organic films. Therefore we chose this Ga bilayer as a weakly reactive substrate to grow the perfluoropentacene (PFP) films. Secondly we have studied the adsorption and two-dimensional self-assembly of PFP on the semimetal Ga film. At low coeverage single PFP molecule exhibits very high mobility. When the coverage increased to 1 ML, PFP dimerizaton takes place with disordered arrangement. Delicate annealing leads to the formation of two dimensional self-assembled monolayer: PFP dimers are organized into one-dimensional molecular ribbons arrays, in which PFP dimers have the brick-wall packing. In the high-resolution STM images, each PFP molecule exhibits two round protrusions with one brighter than the other,and the neighboring two PFP molecules have the opposite brightness polarization, indicating each PFP molecule has the net dipole moment, and each PFP dimer has the net quadrople moment. Therefore the formation mechanism of PFP dimers can be attributed phenomenally to the electrostatic attraction between the opposite dipole, and the brick-wall packing of PFP dimers can be attributed to the electrostatic repulsive force between the same quadrople moments.