Seminars Archive

Study of Self Assembly of Thiolated Organic Molecules on Metal Surfaces

Abstract
Self assembled monolayers (SAMs) of organic molecules is attracting extensive attention in recent years in relation to creation of cheaper, more versatile and large applications. The optical and electronic properties of SAMs are the key important issue to be investigated. Unfortunately, an understanding of the interaction between the molecular layer and metal substrate and the characteristics of adsorption, which we are interested in, are limited. In our work, the characteristics of SAMs of thiol and dithiol molecules on coinage metals and Pd were investigated. The transition from lying down phase to standing up phase in dithiol SAM is a controversial problem, although it is known that “standing up” dithiol SAMs can be formed. Indeed it is not obvious that an “end” of an e.g. alkanedithiol molecule, with both S ends attached to the substrate in an intermediate adsorption phase, could be removed from the substrate, leading to a standing phase. This aspect was investigated on the example of substitutional assembly of lying down phases of butanedithiol (C4DT) by octanethiols (C8T) in vapour phase. It was thus shown that substitutional assembly does occur. Also direct formation of C4DT standing up SAMs was investigated and this study extended to the case of formation of SAMs of 1,4-benzenedimethanethiol (BDMT) on Au(111), Ag(111) and Pd(111). Both on Au and a lesser extent on Ag there was clear evidence of molecular adsorption on "unusual" adsorption sites, characterized by different core level binding energies, which could be confused with atomic adsorption. Thus a potential problem in interpretating thiol SAM adsorption data and confusion with atomic S appearance were revealed. Additionally on Pd the formation of a PdS interface layer in thiol SAM formation was investigated. These studies were mainly performed by photoemission studies using synchrotron radiation and in some cases we performed time of flight scattering measurements and recoiling spectroscopy (TOF SARS) to ascertain that we were indeed forming a S or S terminated dithiol SAM. In this talk I will describe these studies and if time allows also touch upon some complementary studies of adsorption of S and Se atoms on Au(111), Ag(111), Cu(111) and Pd(111) performed to better understand the reaction of chalcogenide atoms as linkers of molecules with metal substrates.