Thiocyanate and thiol self-assembling process on platinum investigated by means of sum-frequency generation

In the field of self-assembled monolayers (SAMs), recent works have shown that thiocyanate functions seem to be a good alternative to the use of thiols groups for adsorption on gold surfaces. In order to check if this is also valid for platinum substrates, we use Sum-Frequency Generation spectroscopy (SFG) to study two similar SAMs: decanethiol (DT) and decyl thiocyanate (DTCN) adsorbed on platinum surfaces. By comparing the intensities of the methyl/methylene vibration modes, we can conclude that the DTCN SAMs are less ordered than the DT ones. These effects are related to the SAMs quality which depends on the molecular packing. In order to confirm these assumptions, we use other techniques of surface characterisation like Scanning Tunneling Microscopy (STM) and X-Ray Photoelectron Spectroscopy (XPS). This last one shows that DTCN SAMs are partially composed of cyanide free groups lying on the surface. Finally, we propose an adsorption mechanism for thiocyanate-based monolayers.