First Stages of Metal Junction Formation on Grafted Si(111) Surface

M. F. JUAREZ; E. M. PATRITO; P. PAREDES OLIVERA

Niza

Congreso; 61st annual meeting of the international society of electrochemistry: electrochemistry form biology to physics; 2010

International Society of Electrochemistry

Understanding the interaction of metal atoms with organic surfaces at a molecular level is becoming increasingly important as the number of applications involving metal−organic interfaces grows. Of particular interest recently has been the emergence of polymer and molecular electronic devices in which the issue of optimizing top metal contacts is of critical importance [1] The formation of metallic islands on well-defined periodic arrays of organic molecules on semiconductor surfaces is of fundamental importance in the development of various technologies ranging from optical applications to magnetic devices. Metal deposition on silicon has been investigated in various conditions and with different surface functionalization. Recent studies have found that the presence of alkyl monolayers on the surface of Si (111) alters the mechanism by which metal atoms are deposited [2]. The factors that cause the desorption of the monolayer on the semiconductor surface after the formation of metal deposits have not yet been established. The aim of this paper is to study from a theoretical point of view the interaction of coinage metals with different funtionalized Si(111) surfaces. We consider Au, Ag and Cu and silicon surfaces functionalized with -H, -CH3, -CH2CH2CH3 and -CH2CH2SH. In the last two cases, we investigated the influence of the terminal group on the penetration of metal atoms through the monolayer. To understand the reactivity of grafted Si(111) surfaces toward metal atoms, we found that the reaction path involves three different steps. First, the metal atom is adsorbed on the grafted surface. In the second step the metal atom approaches to a surface Si atom, breaking the Si-H or S-R bond to form a Si-Me-H or Si-Me-R structure. The last step consists in breaking the Me-R or Me-H bond and the release of the adsorbate attached to the metal. On the Si(111)-H surface, activation energy barriers for the second step are 6.4, 15.2 and 9.2 kcal/mol for Au, Ag and Cu, respectively. When we replace 25% of the -H atoms by –CH3, the activation energies increase to 18.7, 27.0 and 14.1 kcal/mol, respectively. The increase of more than 10 kcal/mol in the activation energy for the detachment of a surface methyl group by the Ag atom is in agreement with previous experimental studies showing that on functionalized Si(111) surfaces, the deposition of Ag atoms does not cause the breakage of the Si-C bond [2].