Environmental Engineering Reference
In-Depth Information
Fig. 3.1 Idealized view and structural model of SAM on metal substrate
chain organic molecules with various functionalities like -SH, -COOH, -NH
2
,
silanes, etc. These surfaces can be effectively used to build-up interesting nano
level architectures. Flexibility with respect to the terminal functionalities of the
organic molecules allows the control of the hydrophobicity or hydrophilicity of
the metal surface, while the selection of length scale can be used to tune the
distant-dependent electron transfer behavior. Organo-inorganic materials tai-
lored in this fashion are extremely important in nanotechnology to construct
nano electronic devices, sensor arrays, super capacitors, catalysts, rechargeable
power sources, etc. [11].
SAMs are perhaps the best model for studying these interfacial reactions.
Figure 3.1 shows an idealized view and structural model of a SAM on a metal
substrate. SAMs are defined as monomolecular films of a surfactant formed
spontaneously on a substrate upon exposure to a surfactant solution. Virtually
any functional group can be introduced in these monolayers as a tail group, and
this ability to precisely control surface composition makes them an invaluable
tool for studying interfacial reactions. Co-adsorption of two different types of
SAMs leads to formation of a mixed monolayer, thus enhancing control over
surface composition. SAMs can also be prepared on highly curved surfaces,
such as colloids, which makes it possible to use conventional analytical techni-
ques for characterization [12].
Because of the wide use of SAMs in surface science and technologies, this
review focuses predominately on interfacial reactions based on SAMs.
3.2.2 Self-Assembled Monolayers
SAMs have aroused wide spread interest as they provide an opportunity to
define the chemical functionality of surfaces with molecular precision. SAM
modified surfaces are highly useful for investigating several fundamental phe-
nomena such as distance-dependent electron transfer [13], mechanism of single
electron transfer, observation of molecular event such as coulomb staircase [14],
etc., on artificially designed nanostructures. Due to the highly ordered nature
and tight packing, these monolayers on metallic surfaces are also important for
several practical applications such as chemical sensing [15], control of surface
properties like wettability and friction [16], corrosion protection, patterning,
semiconductor passivation, and optical second harmonic generation [17]. For-
mation of SAM also provides unique applications such as stabilization of nano
