Chemisorption monomolecular film

Industrial Co., Ltd), Method for producing an alignment chemisorption monomolecular film, G02F 1/13 (427/510) (April 2000). 

The are two general mechanisms for the adsorption of a monomolecular film, as we have seen from earlier chapters physical adsorption and chemisorption. The simplest type of adsorption is the physical adsorption of materials such as hydrocarbons in which the only attractive factor is dispersion force interactions. If the solid surface is relatively hydrophobic and the hydrocarbon chain is relatively long, such adsorption can be quite strong. However, the adsorbed molecules will generally lie more or less horizontal along the surface (Fig. 18.13fl), which means that the thickness of the monolayer will be very small, about 0.25 nm. As a result, the effectiveness of such films will be limited and will decrease rapidly with repeated passing of the surfaces. 

Chemisorption requires direct contact between the chemisorbed molecule and the electrode surface as a result, the highest coverage achievable is usually a monomolecular layer. This may be contrasted with several of the methods to be discussed later that allow the electrode surface to be covered with thick films (i.e., multimolecular layers) of the desired molecule. In addition to this coverage limitation, chemisorption is rarely completely irreversible. In most cases, the chemisorbed molecules slowly leach into the contacting solution phase during electrochemical or other investigations of the chemisorbed layer. For these reasons, electrode modification via chemisorption was quickly supplanted by other methods, most notably polymer-coating methods. 

Film deposition refers to the preparation of polymer (organic, organometallic, and metal coordination) films which contain the equivalent of many monomolecular layers of electroactive sites. As many as 10 monolayer-equivalents may be present [9]. The polymer film is held on the electrode surface by a combination of chemisorptive and solubility effects. Since the polymer film bonding is rather nonspecific, this approach can be used to modify almost any type of... 

Modification of a snbstrate snrface by spontaneous adsorption (24), now more commonly referred to as self-assembly, is one of the most utilized modification pathways. These films are typically bound to the snbstrate by chanisorption however, intermolecular forces within the film are also important Chemisorption is the strong adsorption of a molecule onto a snrface throngh the spontaneous formation of a chemical bond (1). This chemical bond forms between a fnnctional group in the molecule and a site on the electtode. Monomolecular layers prepared by chemisorption are known as self-assembled monolayers (SAMs). These adlayers can be used to impart the desired function to the electrode directly, or can serve as a foundation for more complex electrode architectures. 

Simultaneously, a high spectral resolution is possible, which contrasts conventional infrared or electron energy loss spectroscopies. In this way, for example, different physisorption and chemisorption sites of ethylene on ZnO can be identified via their Raman resonances (Wijekoon et al. 1987). The structure and electronic properties of monomolecular organic films can also be in-vesfigafed sensitively using this technique. 

---