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The structures and dynamic formation processes of adlayers of 5,10,15,20-tetrakis(N-methylpyridinium-4-yl)-21H,23H-porphine (TMPyP) on both bare Au(111) and iodine-modified Au(111) in perchloric acid have been investigated in detail by using in situ scanning tunneling microscopy (STM). Highly-ordered TMPyP arrays formed on iodine-modified Au(111), whereas disordered adlayers were consistently found on bare Au(111) surface. High-resolution STM images revealed the characteristic internal shape and orientation of each TMPyP molecule in ordered adlayers. Time-dependent in situ STM allowed direct observation of the dynamics of the self-ordering processes. Before the most stable adlayer was established in a relatively small domain, several structural changes were found to occur, including the formation of a one-dimensional ordered chain at an early stage and several phase transitions in the ordered adlayers. Once the most stable adlayer was formed as a nucleus in a domain, two-dimensional growth of the domain extended over the entire area of the terraces with the final packing arrangement.

The initial stages of copper deposition on gold single-crystal electrodes, comprising the formation of a Cu monolayer at underpotentials as well as nucleation and growth of small Cu clusters at overpotentials, has been studied in various electrolytes by in situ scanning tunnelling microscopy (STM). Individual atoms of the bare gold surface and of the Cu adlayer in the underpotential deposition (UPD) range could be clearly resolved. The nucleation-and-growth behaviour of Cu in the absence and presence of crystal violet has been investigated. In both cases nucleation starts preferentially at surface imperfections such as step edges with a high density of kinks, but the organic additive has a marked influence on the growth behaviour, favouring a quasi-two-dimensional spreading across the surface. The development of the shape of a Cu cluster with time during the deposition process has also been monitored. Finally, possible influences of the tip on the growth behaviour are discussed.

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The iodine-modified Ag(111) substrate was employed as an electrode to investigate the adsorption of 5,10,-15,20-tetrakis(N-methylpyridinium-4-yl)-21H,23H-porphine tetrakis(p-toluenesulfonate) (TMPyP) in an alkaline solution containing KI. It was found by using in situ scanning tunneling microscopy (STM) that water soluble TMPyP molecules were irreversibly adsorbed and formed highly ordered molecular adlayers on the surface of the iodine-modified Ag(111) electrode within the potential range of -0.35 to -0.10 V vs Ag/AgI. STM images revealed the characterstic shape, internal molecular structure, and molecular orientation of each TMPyP molecule in ordered adlayers. The ordered TMPyP adlayer usually consisted of stripes of several straight molecular rows with different orientations along the 3 direction of the underlying iodine adlayers. In each row, molecules were aligned with the same orientation. From the time-dependent imaging, the ordered molecular adlayer was found to grow in the specific 3 direction with an averaged growth rate of ca. 6 nm/s.

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