Silane Self-Assembled Monolayers Jeffrey J. Weimer A 4 micron x 4 micron image taken with a scanning probe microscope from an assembled monolayer of silanes with two different chain lengths.

Silanes are useful compounds for anchoring an organic layer to an inorganic substrate. They contain Si-O bonds that react with surface hydroxides and pendant hydrocarbon chains to link with the organic overlayer, such as a polymer or protein molecules. The chemistry of the pendant group can be changed by selective chemical reactions. Silination therefore gives us a way to taylor the adhesion properties of a surface or to change its biocompatibility.

For applications where silanes are used to promote adhesion or alter biocompatibility, one goal is to form a uniform layer. In addition to this, one would like to use as little of the silane as needed.

One method of forming thin, uniform layers of silanes is to take advantage of a process called "self-assembly". This occurs primarily in long chain hydrocarbon molecules adsorbed on surfaces. The molecules associate into well-ordered domains after they adsorb. This association can lead to the formation of well organized, self-assembled monolayers, called SAMs, on surfaces.

We are investigating the process of self-assembly in silane monolayers. The investigations are being carried out using a scanning probe microscope (SPM). We are interested in studies using SAMs containing molecules of different chain lengths. The longer chain molecules will eventually carry functional groups that will act as chemical tethers for a polymer or protein overlayer. We want to have a uniform distribution of long chain molecules in the mixed layer to give the most uniform properties of the surface.

As seen in the figure above, longer chain molecules can form islands instead of a uniform layer in SAMs with silane molecules having different chain lengths. Studies are ongoing to determine the factors that lead to such island formation.