Self-Assembled Electroactive Ultrathin Films

Abstract

Techniques used to deposit layers of materials generally depend on the size of the chemical entity used as a starting building block or precursor. For example, smaller entities (i.e., organometallic molecules) are preferably used under their gas form; larger ones (particles) require using other approaches, including Langmuir-Blodgett technique, layer-by- layer assembly or electrodeposition. When preformed nanosized objects are used to fabricate multilayer heterostructures soft-solution processing methods are preferred (electrochemical means will not be considered in that chapter). The choice of the method is dictated by the stability of the particles toward compression, oxidation, solubilization, chemicals, etc. At the nanometer scale, electrostatic, van der Waals, hydrophobic/hydrophilic, charge-transfer, π-π interactions, metal ligand coordination and hydrogen bonding become the predominant forces promoting an adsorption. The term “self” in self-assembly accounts for the fact that the building block units carry physical and chemical characteristics determining the “gluing” when interacting with an appropriate surface, It necessarily implies that the object is free of moving in a fluid (liquid) in order to reach the surface onto which it adsorbs. Such an object will be called a colloid, organic (polymers, surfactants) or inorganic (semiconducting or metallic nanoparticles, exfoliated sheets of a layered compound), with a size varying from few nanometers to a micrometer in one dimension at least.