Self-assembly of hexane- and nonane-dithiols from solutions

H. HAMOUDI, C. DABLEMONT, V. A. ESAULOV, M. A. DAZA MILLONE, M. E. VELA, R.C. SALVAREZZA, L.M. RODRÍGUEZ, J. E. GAYONE, E. A. SÁNCHEZ, O. GRIZZI3

Parma

Conferencia; 26th European Conference o Surface Science; 2009

Dithiols present an interesting case of molecules in that Self-Assembled Monolayers (SAMs) with free mercapto groups, allowing attachment of eg metal aggregates, could be formed. However many reports point to the fact that these SAMs are not well organised as opposed to alkanethiol SAMs and there is the possibility of both thiol endgroups binding to the substrate (“lying down” configuration) and also disulfide bridges could form. In this work, we performed a study of the self-assembly of hexane (HDT) and nonane-alkanedithiol (NDT) monolayers on gold from solutions of n-hexane and ethanol. It extends an earlier work1 done on NDT using reflection-absorption infrared spectroscopy (RAIRS), spectroscopic ellipsometry and sum frequency generation (SFG). In this work SAMs are characterised by RAIRS, electrochemistry, XPS and time of flight direct recoil spectroscopy. For NDT, TOF-DRS, XPS and electrochemical measurements are consistent with the presence of a nearly complete monolayer of thiolate species in a “standing-up” arrangement. The measurements and RAIRS show that nicely organized NDT SAMs can be obtained in n-hexane provided that N2-degassed solutions are used and all preparation steps are performed in the absence of ambient light. In the case of HDT some samples exhibit mixed domains of lying-down and standing-up molecules while the degree of order decreases, showing the  effect of chain length in SAM dithiol organization. In case of the ethanolic solution HDT samples prepared in the dark and with  N2 bubbling  did not exhibit ordering. Also in electrochemistry, the time dependent behaviour was consistent with a chemical transformation of the SH end group into other chemical species: dithiol bridges between the SAM molecules and  additional dithiol molecules linked to the SAM.   1. Hicham Hamoudi, Zhiang Guo, Mirko Prato, Céline Dablemont, Wan Quan Zheng, Bernard Bourguignon, Maurizio Canepa, Vladimir A. Esaulov, Phys. Chem. Chem. Phys., 2008, (45),6836-6841 begin_of_the_skype_highlighting            6836-6841      end_of_the_skype_highlighting
DOI: 10.1039/b809760g