SAMs formation

High quahty SAMs of alkyltrichlorosilane derivatives are not simple to produce, mainly because of the need to carefully control the amount of water in solution (126,143,144). Whereas incomplete monolayers are formed in the absence of water (127,128), excess water results in facile polymerization in solution and polysiloxane deposition of the surface (133). Extraction of surface moisture, followed by OTS hydrolysis and subsequent surface adsorption, may be the mechanism of SAM formation (145). A moisture quantity of 0.15 mg/100 mL solvent has been suggested as the optimum condition for the formation of closely packed monolayers. X-ray photoelectron spectroscopy (xps) studies confirm the complete surface reaction of the —SiCl groups, upon the formation of a complete SAM (146). Infrared spectroscopy has been used to provide direct evidence for the hiU hydrolysis of methylchlorosilanes to methylsdanoles at the soHd/gas interface, by surface water on a hydrated siUca (147). 

Wet preparation of metal nanoparticles and their covalent immobilization onto silicon surface has been surveyed in this manuscript. Thiol-metal interaction can be widely used in order to functionalize the surface of metal nanoparticles by SAM formation. Various thiol molecules have been used for this purpose. The obtained functionalized particles can be purified to avoid the effect of unbounded molecules. On the other hand, hydrogen-terminated silicon surface is a good substrate to be covered by Si-C covalently bonded monolayer and can be functionalized readily by this link formation. Nanomaterials, such as biomolecules or nanoparticles, can be immobilized onto silicon surface by applying this monolayer formation system. 

Many suitable molecules can be designed, with end-groups chosen for SAM formation with dissimilar metal electrodes. For instance, two Au and one A1 electrode could be used. The molecule 0 2A would have two -SH terminations to bond to Au, and one -COOH end group (on D2) to bond to Al. The electron path between the two Au electrodes would traverse a donor moiety Dj with low IPD and an acceptor moiety A, while the path from the Al electrode to the second Au electrode would traverse a weaker donor moiety D2 (with larger IPd) and the common acceptor moiety A. The larger electron current would flow between the two Au electrodes, because the intra-molecular electron mobility would be larger Dj —> A, while the smaller electron current would flow D2 —> A. The smaller... 

Fig. 9.13 a) Preparation of laterally structured SAMs by the microcontact printing (pCP) technique. A structured PDMS stamp is inked with self-assembling molecules (hexa-decanethiols HDT) and placed onto a planar substrate (gold). SAM formation occurs within seconds at the areas of contact (I). The structure can be further processed by etching (II) or deposition of a second SAM (III) onto... 

The most fascinating characteristic some amphiphile molecules exhibit is that, when mixed with water, they form self-assembly structures. This was already discussed in Chapter 2 on micelle formation. Since most of the biological lipids also exhibit self-assembly structure formation, this subject has been given much attention in the literature (Birdi, 1999). Lipid monolayer studies thus provide a very useful method to obtain information about SAM formation, both concerning technical systems and cell bilayer structures. 

Figure 6.12 Preparation of patterned LBL assemblies (a) by nanotransfer printing and (b) by sequentially using nanoimprinting lithography, CD SAM formation, and lift-off process. Reprinted with permission from Crespo-Biel et al. (2006).

Fig. 5 SAM formation of initiator is essential. Immobilization of DPE initiator followed by polymerization of styrene homopolymer to form PS brushes by SIP [72]...

Table 5.1 shows the results of the chemical assembly of compounds 2 and 3 using the two different deprotection techniques. As shown in the Table, under both basic and acid catalyzed conditions, mononitro compound 2 formed SAMs that are consistent with its theoretical calculated thickness. On the other hand, SAMs of compound 3 formed thinner layers under basis conditions and thicker layers under acid conditions when compared to the theoretical values. The thinner layer might be due to the formation of bond angles smaller than 180° or to incomplete SAM formation the thicker layer is likely a multi-layer. 

We fabricated the modified ITO electrodes4 by a combination of SAM formation with a terpyridine derivative and stepwise metal-terpyridine coordination reactions in a similar manner as that described in the previous section (Fig. II).11,13 A cleaned ITO was immersed in a 0.1 M solution of 4-[2,2 6, 2"-terpyridin]-4 -yl-benzoic acid (tpy-BzA) in chloroform for 12 h to anchor the carboxyl group to ITO. Subsequently, the modified ITO was immersed in an aqueous solution of 0.1 M CoCl2, Fe(BF4)2 or Zn(BF4)2 for 2—3 h to form metal-terpyridine coordination reactions. Finally, the metal-coordinated ITO was immersed in a 0.1 M acetonitrile solution of a terpyridine-functionalized porphyrin, tpy-ZnTPP, providing the target molecular wires, [M-ZnTPP], on electrodes (Fig. 11). In addition, a cleaned ITO was immersed in a 0.1 M ethanol solution of carboxylate-functionalized porphyrin, C10ZnTPP, to afford a modified ITO as a reference. 

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