Self-assembled monolayers (SAMs) of thiols on gold have many potential applications, ranging from biology to electronics. To fully exploit the versatility of these thiols SAMs it is necessary to optimize their arquitecture to better establish their properties in relation with thiols molecular structure. This knowledge will help their design for specific applications, in particular for the fabrication of new molecular and unimolecular devices.
In this context, SAMs of aromatic and aliphatic thiols on gold were characterized by scanning tunneling microscopy (STM) and scanning tunneling spcectroscopy (STS). High-resolution STM images show that the molecular ordering and packing arrangement depend on the SAMs preparation conditions, namely, temperature, thiol concentration, and adsorption time and also on the thiol molecular structure.
Thiols SAMs are complex systems where the final structure is determined by a balance between all interations involved in the assembly process. It depends in particular on the thiol endgroup and the thiol chain length. The results obtained evidence significant differences between the adsorption kinetics of aromatic and alkane thiols, attributed to the stronger interaction between the aromatic thiol and gold compared with the alkane thiol. High-resolution structures and electronic properties of each thiol SAM were obtained by monitoring current-voltage characteristics. The combination of STM and STS measurements showed a strong correlation between the molecular organization and conductivity of the SAM.