Octadecyltrichlorosilane Film Research Articles

Structure and Stability of Patterned Self-Assembled Films of Octadecyltrichlorosilane Formed by Contact Printing

The structures of thin films of octadecyltrichlorosilane (OTS) formed by contact printing and adsorption from solution on Al and SiO2/Si surfaces have been investigated by X-ray photoelectron spectroscopy (XPS), ellipsometry, reflection−absorption infrared spectroscopy (RAIRS), scanning electron microscopy (SEM), and atomic force microscopy (AFM). The structures of the OTS films were found to be strongly influenced by the method of preparation used. The films formed by contact printing for 30 s with an OTS “ink” are composed of close-packed, predominantly all-trans alkyl chains aligned nearly perpendicular to the surface, while films formed by adsorption of OTS for 30 s from a solution of comparable concentration are made up of sparsely adsorbed and more randomly oriented chains. Large changes in the film structure (from conformationally disordered, poorly oriented to well-packed, highly oriented hydrocarbon chains) were observed as the reaction time was increased for samples prepared by immersion in an OTS-containing solution (e.g. 15−30 min in a 1 mM solution). On the other hand, films prepared by contact printing reached or exceeded full monolayer mass coverages after only 30 s of substrate contact with an elastomeric stamp inked with a 10 mM solution of OTS in hexane. The OTS films formed by contact printing are stable at the high temperatures and aggressive reaction conditions necessary for their use as molecular resists in directing the selective deposition of metal and ceramic thin films by MOCVD and sol-gel methods, respectively. In this paper we show how such factors as the OTS ink concentration and stamp contact time influence the patterning of OTS thin films by microcontact printing. We find that reactive spreading and island formation of OTS domains in regions of the pattern not in contact with the stamp limit the fidelity of the patterning carried out at dimensions less than a few microns. We discuss several aspects of the physical processing which mediate these effects and propose possible methods for eliminating or greatly reducing them.

Adsorption of alkyl-trichlorosilanes on glass and silicon: a comparative study using sum-frequency spectroscopy and XPS

Chemisorbed films of octadecyltrichlorosilane and propyltrichlorosilane on glass have been studied in a natural laboratory environment. Information on the molecular conformation and orientation is obtained from sum-frequency spectroscopy (SFS). The cleaning procedure preceding the coating process was monitored by SFS and X-ray photoelectron spectroscopy. In-situ monitoring of surface contaminations under normal atmospheric conditions by SFS provides valuable information on the effectiveness of cleaning and activation procedures.

Self‐assembly of octadecyltrichlorosilane films on mica

AbstractSelf‐assembled films of Octadecyltrichlorosilane (OTS) have been deposited on freshly cleaved mica. A combination of argon plasma pretreatment, long adsorption times in solution, and a posttreatment at a moderate temperature (60°C) were required to form homogeneous OTS layers exhibiting good adherence to the mica. This process is more complex than the procedure required to form similar layers on glass. Advancing contact angles of water droplets ranged from 113 to 116°, with receding angles of 107 to 110°.

Structure and topography of molecular assemblies on solid substrates by infrared spectroscopy and scanning tunneling microscopy

Recently we have combined infrared spectroscopy and atomic resolution scanning tunneling microscopy (STM) to probe the local structure and intermolecular arrangement of molecules within thin films. IR spectroscopy provides spatially averaged information about orientation of the molecules with respect to the surface and about intermolecular arrangement within the crystallographic unit cell. STM data yields a local picture of molecular packing within the film. The requirements of an atomically flat (over distances of hundreds of angstroms) conducting substrate for the STM are fulfilled by an epitaxially grown film of gold on a cleaved mica substrate which also provides a good infrared reflective surface, enabling IR and STM measurements on identical samples. Systems investigated include Langmuir-Blodgett films of cadmium arachidate and self-assembled films of octadecyltrichlorosilane.