Self-assembled monolayers solution-phase deposition

Another approach in generating molecular insulating layers without the need of chemical conversion after deposition is the use of preliminarily modified molecules which can form dense self-assembled monolayers. To create dense self-assembled monolayers with sufficient robustness and insulating properties, a modified alkyltrichlorosilane with an aromatic end-group (18-phenoxyoctadecyl)tri-chlorosilane (PhO-OTS chemical structure Fig. 6.15a) was synthesized and tested [50]. The SAMs were created in a one-step process from vapor phase or solution. On self-assembly on a natively oxidized silicon surface the n-n interaction between the phenoxy end-groups of adjacent molecules creates an intermolecular top-link, leading to a more closely packed surface compared to monolayer than when linear end groups are used. 

Two additional special cases that can be termed chemical vapor deposition are worthy of mention, since they are the vapor-phase analogues of solution techniques discussed above. These are self-assembling monolayer formation and vapor-phase surface chemical derivatization. In the former, it is necessary only to... 

Fig. 3 Schematic depiction of the Langmuir trough apparatus and the positioning of the electrodes used in the lateral monolayer flow experiments. The inset shows the Au-coated glass slide working electrode modified with a self-assembled monolayer (SAM) of dodecanethiol. The working electrode is touching the air/water interface. A compound that forms a Langmuir monolayer is deposited on the water surface. It immediately spreads to cover the entire interface. Subsequently, the Langmuir film flows across the triple phase boundary into the SAM/water interface forming a bilayer. The lateral flow is completed when the entire electrode/solution interface is coated with a bilayer (from Ref 37).

The first concept, the formation of a template layer, is suggested to enhance adsorption of the first monomer onto the surface as a single monolayer. A template layer is a self-assembled monolayer deposited fi om solution, which exposes a reactive functionality toward the first monomer, prior to introduction of the substrates to vapor phase assembly. This template layer dictate epitaxial growth and ensure the second concept of self-limiting growth of only one monolayer. Therefore, this layer bridges solution and vapor phase growth mechanisms in a unified concept... 

Besides the sol-gel processing, there are many aqueous routes to synthesize ceramic powders, fibers, films and bulks. Niesen and DeGuire reviewed these low temperature and non-electrochemical processes (Niesen and DeGuire, 2001). According to them, the processes include a chemical-bath deposition (CBD), successive ionic-layer adsorption and reaction (SILAR), liquid-phase deposition (LPD), electroless deposition (ED), and film deposition on organic self-assembled monolayers (SAMs). Of course, an electrochemical route is an important process. Another non-sol-gel route is a spray pyrolysis of solution or sol, and is applied to the direct preparation of oxide powders and films. Since these processes do not form the gel phase, they are not described here. 

These aqueous solutions can be applied to preparation oftitania films as well as nano-size anatase powder. The solution of ratio, Ti Lac NH4 = 1 2 2, was used for low temperature synthesis of a titania film on a self-assembled monolayer. The film was deposited by controlling the concentration, pH and temperature. The resultant film was anatase and Ti02(B) phase and up to -100 nm in thickness (Baskaran et al., 1998). Very fine anatase powders <20 nm were obtained by thermohydrolysis above 100°C (Mockel et al., 1999). 

Fluorinated self-assembled monolayers (F-SAM) can be deposited either in liquid phase, hy dipping the mold direcfly into a diluted solution of anti-sticking molecules [92], or in a vapor phase process. The latter can he done either by thermal evaporation of the liquid precursor at atmospheric pressure [93] or by vacuum evaporation at room temperature [94]. Chlorosilane molecules are very reactive and able to polymerize, producing particles that can precipitate onto the mold. This is why it is preferable to use the vapor phase process with this type of molecules, leading to smoother surfaces [95]. 

The semiconductor insulator interface is the primary factor that determines the field-effect mobility of charge carriers in an organic field effect transistor (OFET). Vapor phase or solution based treatments with an alkyl silane or silazine group forms a self-assembled monolayer on the surface of the insulator. Such treatments prior to the deposition of the semiconductor reduces the surface energy which improves the... 

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