A quantum chemical study of the self-directed growth mechanism of styrene and propylene molecular nanowires on the silicon (100) 2×1 surface

Abstract

We use density functional theory to investigate the self-directed growth mechanism of molecular nanowires on the Si (100)-2×1 monohydride surface from the molecular precursors styrene (H2C=CH–C6H5) and propylene (H2C=CH–CH3). The reaction is initiated using a scanning tunneling microscope tip to create a Si dangling bond on the surface. This dangling bond then attacks the C=C π bond to form a Si–C bond and a C radical. Next, the C radical abstracts a H atom from a neighboring surface site, which results in a new Si dangling bond to propagate the chain reaction. For the case of H2C=CH–C6H5 the predicted hydrogen abstraction barrier of 18.0 kcal/mol from a neighboring dimer along the dimer row for C–H bond formation is smaller than H2C=CH–C6H5 desorption energy of 22.6 kcal/mol. On the other hand, for the case of H2C=CH–CH3 the predicted hydrogen abstraction barrier of 10.8 kcal/mol for C–H bond formation from a neighboring dimer is significantly larger than H2C=CH–CH3 desorption barrier of 2.7 kcal/mol. Consequently, the predicted barriers indicate that the self-directed growth of nanowires on (100) silicon using styrene occurs while a self-directed chain reaction using propylene should not occur, in agreement with experimental observations.

Chemical manipulation of multifunctional hydrocarbons on silicon surfaces

“…Restricting these directions by using a Si (100) substrate ideally terminated with monohydride should result in a controllable growth of lines of molecules. It is indeed the case and a substantial amount of work on styrene has appeared recently in the literature [257,410,[413][414][415][416][417][418][419][420][421][422][423][424][425].…”

Intriguing properties of unusual silicon nanocrystals

“…The development of new silica-based and silicon-based technologies relies, however, on accurate and sound predictions for nanocrystals, where quantum mechanical studies represent an indispensable resource in the prediction of properties for molecular and electronic ensembles of crystals, lattices and atomistic units. 16,[19][20][21] With the use of quantum mechanics, electronic properties such as charge-transfer potentials, 22 electron delocalization, 21 bond metallicity, 23 electron localization, 24 aromaticity, 25 electronic gaps are generated, functioning directly as a basis for the structuring and synthesis of nanomaterials and nanocrystals.…”

How to Fabricate a Surface-Grafted Polythiophene on H-Si(100)2×1 Surface via Self-Assembling and in Situ Surface Polymerization: A Theoretical Guide

“…There have been several theoretical studies on the self-assembling mechanism of alkenes on silicon surfaces to form molecular arrays, where aligned molecules are absorbed on Si surfaces but they are not interlinked. ,, Only very recently, we proposed a surface in situ polymerization reaction for self-assembled 4-hydrazinyl-3-(pyridin-4-ylmethyl)-benzaldehyde (HPyMB) molecules to produce a conductive molecular wire based on pyridines alternating adsorption on a line of exposed surface Si atoms . In this work, we extended the study to thiophene-substituted alkanes self-assembling on H–Si/Ge surfaces, based on the experimental approved olefins surface self-assembling mechanism, to produce single molecular wires (surface-grafted polymers) via in situ polymerization reaction subsequently.…”