Infrared Characterization of Interfacial Si−O Bond Formation on Silanized Flat SiO₂/Si Surfaces

Abstract

Chemical functionalization of silicon oxide (SiO(2)) surfaces with silane molecules is an important technique for a variety of device and sensor applications. Quality control of self-assembled monolayers (SAMs) is difficult to achieve because of the lack of a direct measure for newly formed interfacial Si-O bonds. Herein we report a sensitive measure of the bonding interface between the SAM and SiO(2), whereby the longitudinal optical (LO) phonon mode of SiO(2) provides a high level of selectivity for the characterization of newly formed interfacial bonds. The intensity and spectral position of the LO peak, observed upon silanization of a variety of silane molecules, are shown to be reliable fingerprints of formation of interfacial bonds that effectively extend the Si-O network after SAM formation. While the IR absorption intensities of functional groups (e.g., >C=O, CH(2)/CH(3)) depend on the nature of the films, the blue-shift and intensity increase of the LO phonon mode are common to all silane molecules investigated and their magnitude is associated with the creation of interfacial bonds only. Moreover, results from this study demonstrate the ability of the LO phonon mode to analyze the silanization kinetics of SiO(2) surfaces, which provides mechanistic insights on the self-assembly process to help achieve a stable and high quality SAM.

Analysis of the Surface Coverage of a Self-Assembled Monolayer of Octadecyl Silane on a Si(100) Surface by Infrared External-Reflection Spectroscopy

“…The lattice vibration of the silicon oxide (Si-O-Si) is known to be split into the TO and LO phonon modes, 17,18 which are aligned parallel and perpendicular to the surface, respectively. In fact, the TO and LO peaks appear at 1047 and 1228 cm -1 as negative and positive peaks, respectively, which perfectly matches the surface selection rule.…”

Structural and chemical analysis of annealed plasma-enhanced atomic layer deposition aluminum nitride films

“…40 Second, the relatively strong valleys around 1110 cm À1 can be credited to Si-O stretching vibrations likely arising from the native oxides of the substrates. 18,41 Also, other interpretations have been given to this band such as the (C-N), 22 and the (Al-OH), 42 and it is possible that the effect of all three molecules are superimposed to this valley. However, especially the Al-OH is not very likely since O-H group associated absorption is not visible in the higher wavenumbers of 3200 cm…”

The molecular level modification of surfaces: from self-assembled monolayers to complex molecular assemblies

“…chemical composition, thickness, orientation and lateral order of the alkyl chains have been investigated in detail. [28][29][30][31] As shown by various studies, a precise depiction of the interface between the SAM and the silica is not trivial. A range of factors, including surface hydration and/or water traces in the deposition solution, dictate the precise chemical nature of the interface.…”

“…3 has been greatly simplified for clarity purposes. 31 There has been considerable debate on the mechanism of chemisorption. 32 The deposition process is especially complicated; it proceeds through a number of stages, and strongly depends on various parameters, including the solvent and adsorber concentrations, 33 aging of solutions, water content, 34 deposition time and temperature.…”