Self-Assembled Monolayers

A Self-Assembled Monolayer (SAM) is a one molecule thick layer of material that bonds to a surface in an ordered way as a result of physical or chemical forces during a deposition process. Silanes can form SAMs by solution or vapor phase deposition processes. Most commonly, chlorosilanes or alkoxysilanes are used and once deposition occurs a chemical (oxane) bond forms with the surface rendering a permanent modification of the substrate. Applications for SAMs include micro-contact printing, soft lithography, dip-pen nanolithography, anti-stiction coatings and orientation layers involved in nanofabrication of MEMs, fluidic microassemblies, semiconductor sensors and memory devices.

Common long chain alkyl silanes used in the formation of SAMs are simple hydrocarbon, fluoroalkyl and end-group substituted silanes. Silanes with one hydrolysable group maintain interphase structure after deposition by forming a single oxane bond with the substrate. Silanes with three hydrolysable groups form siloxane (silsesquioxane) polymers after deposition, bonding both with each other as well as the substrate. The minimization of water condensation at the substrate can prevent the random aggregation and reaction among the silanes and increase attachment to the substrate. Formation of well ordered oxane bonds with surface hydroxyl groups does depend on the density (or frequency) of a materials surface hydroxyl groups, and this varies between different materials, so selecting a silane with the right number hydrolysable groups is important

The most widely used silanes for formation of SAMs are listed below:

Alkyl-Silanes

Fluoroalkyl-Silanes

End-Group Modified Long Chain Alkyl-Silanes