Electronic Properties of Si Surfaces Modified by Aryl Diazonium Compounds

The specific functionalization of Si surfaces for manifold applications in optical and electronic devices is a great challenge in the engineering of semiconductor surfaces. Functionalization and the tailoring of the electronic properties of semiconductor surfaces can be performed by nanopatterning with self assembled monolayers [1, 2]. For example, the contact potential of TiO2 surfaces has been modified by organic molecules [3], the charge transfer rate across a Si 111 surface has been dramatically changed by n alkyl monolayers [4], and the electronic Si surface properties have been tuned over several hundreds of meV [5 7]. Furthermore, the functionalization of Si surfaces is of particular interest for biosensing due to the biocompatibility and the high technological relevance of Si [8 12]. In this context, the linkage possibility of covalent bonding of organic molecules to Si surfaces is important for directed surfaces engineering. Often, hydrogenated Si Si H surfaces are the starting point for the covalent bonding of organic molecules via radical reactions, as proposed by Linford and Chidsey [13, 14] for alkenes, or by Pinson and Allongue [15, 16] for the electrochemical radical reaction of diazonium compounds. The kinetics of radical formation and the surface reaction rate depend sensitively on the strength of the dipole moments of the aryl molecules radicals and their changes [6, 17]. However, the electronic properties of functionalized Si surfaces are important for electronic applications. As recently shown for the maleic anhydride Si 100 2 1 interface [18] or aryl compounds on Si 111 [6, 19, 20], the formation of Si C bonds does not lead to the generation of electronic states in the forbidden gap, as demonstrated by photoluminescence PL and photovoltage PV measurements. Moreover, in situ PL measurements allow tracking of the formation and passivation of dangling bond db complexes which act as recombination active defects and quench the band gap related PL. Therefore, PL measurements show in line the quality of the Si surface passivatio