Spectroscopic Characterization and Transport Properties of Aromatic Monolayers Covalently Attached to Si(111) Surfaces

Abstract

We fabricated self-assembled monolayers (SAMs) composed of aromatic molecules with different anchor groups on Si(111) surfaces by wet chemical reactions. We investigated the bonding structures and transport properties by spectroscopic and electrical measurements, respectively. By using simple aromatic molecules (phenol, styrene, and phenylacetylene) as initial precursors, we successfully fabricated aromatic SAMs covalently bonded to Si(111) surfaces through different anchor structures (Si–O–, Si–CH₂–CH₂–, and Si–CHCH−). Transmission infrared spectroscopy clarify that the phenyl rings in the SAMs are oriented almost perpendicular to the Si surfaces. High-resolution X-ray photoelectron spectroscopy reveals that the aromatic molecules attach to the Si surface with the surface coverage of ∼0.5. The experimental results of these spectroscopies lead to a conclusion that the aromatic SAMs form densely packed monolayers on Si(111). Current density–voltage measurements of Hg/aromatic SAM–Si(111) sandwiched structures revealed that the “Si­(111)–O–Ph” (SAM from phenol) show higher conductivity compared with the long-chain alkyl SAM on Si(111)