Interfacial structure and bonding of nitrogen-containing organic molecules with silicon surfaces

The attachment of organic molecules to silicon surfaces has attracted substantial attention because of its potential applications in molecular electronics and chemical/biological sensors. Nitrogen-containing organic molecules are of particular interest due to their fundamental and technical importance in material science, organic chemistry and biology. In this dissertation, the interfacial structure and bonding of nitrogen-containing organic molecules with silicon surfaces have been systematically studied to address important issues such as reaction mechanism, reactivity and selectivity.; While studies of primary and secondary amines show dissociative adsorption via cleavage of the N–H bond on the Si(001) surface, tertiary amines can molecularly adsorb on the surface and form stable dative-bonded adducts through the nitrogen atom. Computational results show that the behaviors of amines on Si(001) can be explained by a nucleophilic reaction mechanism. Dative-bonding between tertiary amines and Si(001) is shown to significantly modify the reactivity of surface silicon atoms toward other molecules such as BF3. While BF3 dissociatively bonds to the clean Si(001) surface, adsorption onto a surface that has previously been exposed to trimethylamine (TMA) is shown to be molecular, forming a surface-mediated donor-acceptor complex, TMA-Si-Si-BF₃.; Studies of adsorption of various amines on the Si(111) surface show similar results to those observed on Si(001). Furthermore, the experimental data indicate that various silicon atoms within one unit cell on Si(111) present different reactivities to amines. A detailed mechanism is discussed.; The interactions of a series of N-containing cyclic molecules with the Si(001) surface was explored to address the question of the reaction selectivity. Studies of adsorption of aniline, pyrrole and 3-pyrroline on Si(001) indicate that while 3-pyrroline has multiple bonding configurations, both aniline and pyrrole primarily show one type of bonding configuration with retention of the aromatic character. Additionally, interfacial electronic properties of various substituted benzenes including styrene, aniline, phenol and benzenethiol tethering to the Si(001) surface was investigated. The experimental data indicate strong effects of the surface tether on conductivity of the single adsorbed molecules.