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

Abstract

The coverage of a self-assembled monolayer (SAM) of octadecyl silane on a silicon surface is analyzed by infrared external-reflection spectrometry via molecular orientation analysis. A commercially available octadecyl trimethoxy silane (ODS) solution is employed, which readily reacts with an oxidized surface of Si(100) prepared by a UV/ozone treatment in an ambient condition to yield a highly reproducible SAM. With the present technique, a very flat surface with no holes is obtained in the entire area of the SAM. IR external-reflection spectra of the SAM apparently indicate that the alkyl chains are highly ordered having the all-trans zigzag conformation, and the molecular orientation agrees with that of a Langmuir-Blodgett (LB) monolayer film of octadecanoic acid. Since the orientation analysis is based on an assumption that the surface is fully covered by the SAM as the LB film, the agreement of the orientation confirms that the surface coverage of the present SAM on Si(100) is on the same level as the LB film.

In Situ Observation of a Self-Assembled Monolayer Formation of Octadecyltrimethoxysilane on a Silicon Oxide Surface Using a High-Speed Atomic Force Microscope

“…21 In this manner, the band intensity is influenced by the molecular orientation as well as the molecular density. The spectrum at 0 t  sec of the present study quantitatively reproduces the spectra reported in a former study, 8 which confirms that the reproducibility of the SAM on silicon is very high. The band positions of the two modes (2917 and 2850 cm -1 ) tell us that the molecules have the all-trans zigzag conformation.…”

“…For the detail of the solvent, the reader is referred to the literature. 8 For the background measurements of the IR spectra, a hydrogen-terminated silicon wafer was prepared by using a standard technique described in the same literature. The domains marked by a~k are used to pursue the reaction with time (see Figure 6).…”

Optimal Experimental Condition of IR pMAIRS Calibrated by Using an Optically Isotropic Thin Film Exhibiting the Berreman Effect

“…To examine the analytical accuracy in the ordinate scale, the molecular orientation in a thin film of highly oriented molecules is checked. To do that, a self-assembled monolayer (SAM) 23,24 of octadecyl trimethoxy silane (ODS) 25 prepared on a Si substrate is employed. The IR pMAIRS spectra of the SAM measured by using the optimal angle set are presented in Figure 8.…”

Fluorous Property of a Short Perfluoroalkyl-Containing Compound Realized by Self-Assembled Monolayer Technique on a Silicon Substrate

“…Making a highly condensed and stable SAM on a Si surface is a little bit difficult task for normal hydrocarbons. [12][13][14][15][16][17] The SAM formation requires nucleation of molecules at the initial stage, and the nucleus is developed by connecting with each other two-dimensionally. 16 Very fortunately, Rf groups intrinsically have a nucleation property due to the SDA packing, which is quite suitable for the SAM formation.…”

“…3 In the present study, a silicon (Si) substrate is chosen as the substrate, and artificially arranged molecular aggregates are prepared by using the Langmuir-Blodgett (LB) 10 and selfassembled monolayer (SAM) techniques. [11][12][13][14][15][16][17][18] Since a SAM coverage is attained by controlling the surface reactivity with the substrate surface, SAM is an artificial molecular aggregate. As a result, very low surface energy is readily realized even for a short-Rf containing compound by the SAM technique; whereas the LB technique is inadequate for the stability of the hydrophobicity.…”