英語翻譯
The DIP molecules adsorbed at the step edges align their long molecular axis parallel to the step direction and consequently form rows in a head-to-tail configuration.In contrast,the adsorption at the reconstruction elbows does not give clear evidence of any preferred molecular orientation.Upon further growth of the nuclei,no order is developed among the molecules.This is a signature of the low intermolecular interactions,as expected from the absence of functional groups with the potential to form H-bonds or give rise to any other interactions stronger than the van der Waals contribution.Only in large DIP assemblies extending over more than 100 nm2 do
we find a long range ordered structure.A discrete number of rotational domains is observed,evidencing the role of the substrate as template directing the molecular ordering.Interestingly,the different domains are not separated by abrupt boundaries but often follow a gradual transition among the different orientations.This can be observed in Figure 1a (which shows three different domains) between the domains numbered #2 and #3.This is the product of weak and smooth interaction potentials (both molecule-substrate and molecule-molecule) in these organic systems,which allow a much higher accommodation of strain than is generally known from inorganic materials.The reconstruction of the underlying Au(111) surface remains visible below the DIP layer,which is a consequence of the weak molecule-substrate interaction.In other words,the moleculesubstrate interactions (van der Waals) are on the one hand too weak to affect the Au(111) surface reconstruction but,on the other hand,strong enough to dictate the epitaxial growth of the organic overlayer.Nevertheless,the observation that many of the borders of these DIP assemblies follow the corrugation lines of the herringbone reconstruction (as shown for example by two dashed lines in Figure 1a) reveals a non-negligible energetic barrier for the growth processes (i.e.,diffusion or incorporation onto the 2D molecular crystal sites) across these lines.