Aligned Organic Molecular Wires in Methionine Nanofilm Growth on Si(111)-√3×√3-Ag

Abstract

Interfacial interactions of biomolecular materials with semiconductor surfaces have been of immense interest because of their technological applications in biosensors and biomolecular nanoelectronics. The fabrication of highly ordered, extended low-dimensional molecular patterns on Si surfaces promises to be an important breakthrough in the field of Si-based biomolecular nanodevices. Even though these remarkable biomolecular self-assemblies have been more often observed on metal surfaces, there are fewer relevant studies on Si surfaces because of the high reactivity of their dangling bonds. On the other hand, the presence and indeed the saturation of these dangling bonds provide a unique approach to engineer robust supramolecular architectures on these surfaces. In the present work, methionine nanofilm growth on a benchmark metal silicide surface, Si(111)-√3×√3-Ag, at room and lower temperature has been investigated by X-ray photoelectron spectroscopy and scanning tunneling microscopy. Our results show the formation of extended one-dimensional molecular wires consisting of methionine dimer rows with zwitterionic intermolecular interactions similar to those observed on single-crystal metal surfaces. Notable surface defects such as step edges and antiphase boundaries are found to play a crucial role in the initiation and directed growth of the adsorption structures, while terrace sites appear to be more conducive to the development of aligned one-dimensional (nanowires, nanoboomerangs) and two-dimensional (nanogratings, and concentric nanotriangles) self-organized nanostructures. Our complementary density functional theory calculations further provide plausible adsorption configurations of individual molecular adspecies and self-organized oriented molecular wires on the terraces of the surface. We further illustrate the importance of molecule–molecule and molecule–substrate interactions that give rise to key differences between methionine adsorption arrangements on bare Si and the silver silicide surfaces.

Covalent and Hydrogen Bonding in Adsorption of Alanine Molecules on Si(111)7×7

“…Although the methyl group is not chemically reactive, it increases the size and complexity of the molecular structure of the amino acid, potentially introducing steric constraint, all of which could affect how alanine bonds to the surface and how it interacts with one another during film growth. Adsorption of alanine, cysteine, aspartic acid, proline, glutamic acid and methionine on single crystalline metal surfaces [Cu(110), Au(111), Ag(100), Ni(100)] and on nonreactive Si(111)- √3×√3-Ag surface, have been extensively studied by using XPS, reflection–absorption infrared spectroscopy, temperature-programmed desorption, low-energy electron diffraction, and STM. − In particular, a comprehensive adsorption phase diagram of alanine on Cu(110) has been reported to include four alaninate (NH 2 C α H­(CH 3 )­COO – ) phases depending on the coverage and substrate temperature . At room temperature, individual alanine molecules were found to bond tridentately to Cu(110) at low coverage through both carboxylate O atoms and the amino N atom, following deprotonation of the carboxylic acid group.…”