Spatial orientation of highly ordered self-assembled silane monolayers on glass surfaces

Abstract

The orientation behaviour of self-assembled silane monolayers deposited onto glass surfaces was investigated by conoscopic microscopy. Conoscopy is a suitable tool for characterizing the orientation behaviour of nanoscaled layers on such silane-modified glass surfaces. Compared with other methods, for instance X-ray reflection, infrared spectroscopy, X-ray photoelectron spectroscopy, and ellipsometry, it is possible to determine the tilt angle (φ) as well as the azimuthal direction (Φ) of the molecules in the chemisorbed silane layer. Even at low tilt angles different azimuthal angles were found. Reverse φ's were detectable for a close-packed octadecyltrichlorosilane (OTS) layer with a near-perpendicular chain orientation (φ 6° to 2°, Φ 0° and 180°). A random azimuthal distribution was found at tilt angles exceeding 10°. Examples are given for selected silane layers prepared from different solvents and solvent mixtures depending on the silane concentration and composition. The tilt angles of the liquid crystal molecules determined by conoscopy on glass were comparable to the tilt angles of the silane chains on silicon determined from ellipsometric measurements.

Keywords:

• Self-assembling
• silane monolayers
• orientation
• conoscopy
• glass surface