| Several adsorption systems have been studied by atomic force microscopy (AFM) and scanning tunneling microscopy (STM) in this thesis.; The first system is Fe deposited on 3 x 3 -Al on Si(111). We found by STM that at a low coverage of less than 0.1ML and room temperature; most Fe atoms are incorporated to the 3 x 3 -Al adatom lattice. When the Fe coverage increases further, clustering of Fe atoms into three-dimensional islands occurs. These clusters draw neighboring silicon surface or sub-surface atoms and the formation of Fe-Si bonds is evident. Samples with Fe deposited at or above 400°C show Fe-Si with the CsCl crystalline structure and a top surface lattice of 2 x 2 Si (111) in nature. The crystalline island has a triangular shape and a preferred location along the step edges of the Si(111) surface.; Second, we have observed several dash-line structures on HOPG with STM. We suggest that the structures are formed by the gliding of some top surface layers of carbon atoms. The arrest of the gliding action causes the formation of a ridge of carbon atoms and the relaxation of the ridge at room temperature leads to the formation of amorphous carbon clusters queuing along the ridge. As such, the dash-line structures are formed. They are defect structures of HOPG.; Third, STM has been used successfully in determining the molecular morphology of some novel dendrimers. The morphology of dispersed individual molecule can be identified. In this study, we found that AFM is not applicable because of considerable tip-molecule interactions which distort the morphology of the probed molecule.; Fourth, we studied the growth of CF3 CH2SH on Au(111). We found that the adsorbed molecules mainly form low coverage phases even after a long time growth in solution. This is attributed to the strong dipole-dipole repulsion between the molecules. However, due to the special short molecular geometry, the molecules can pack with a denser packing arrangement in comparison to the long-chain fluorinated thiols. A "liquid phase" is present in all the samples studied, which solidifies quickly at elevated temperatures. Annealing causes both the growth of stable phases and desorption of weakly adsorbed molecules. Six different stripe phases with the configuration of p x 3 and p x 2a are observed on the surface. The inter-molecular interactions are either van der Waals in nature or the Columbic attraction between the slightly negatively charged F atoms and the slightly positively charged H atoms of the CH 2 group.; Finally, we have systematically investigated the SAMs of four specially designed anthracene-based thiols. These molecules include 9-mercaptoanthracene (MA), (4-mercaptophenyl) (9-anthryl) acetylene (MPAA), (4-mercaptophenyl) (10-nitro-9-anthryl) acetylene (MPNAA), and (4-mercaptophenyl) (10-carboxyl-9-anthryl) acetylene (MPCAA) adsorbed on Au(111). For all SAMs, the parallel-displaced pi-pi stacking interactions and adsorbate-substrate interactions are dominant, which leads to a common wave-like row structure along the pi-pi interaction direction. Compared to MA, the phenyl-acetylene group of MPAA acts as space, which enhances the molecular flexibility and improves the long-range ordering. The repulsive dipole-dipole interactions of MPCAA cause a slight enlargement of the unit cell. For MPCAA, a structure similar to that of MPNAA is formed first. Then with an extended growth time, hydrogen bonding drives the pairing of adjacent inter-row molecules in the expenses of compromising intea-row parallel-displaced pi-pi interaction. |
