Surface modification/patterning

Besides the spatial control of surface modification (patterning), control over surface coverage (functional group densities) is a centrally important point. As in any organic chemical reaction, the functional groups involved, the medium and the reaction conditions (such as temperatme) influence the reactivity. However, for surface-based reactions, additional factors must be taken into accoimt [36,37]. These include, among others, steric and an-chimeric effects of the reactants, prevented or hindered access of the reactive species from the solution to the reaction centers, or interactions of neighbor-... 

Patterns of ordered molecular islands surrounded by disordered molecules are common in Langmuir layers, where even in zero surface pressure molecules self-organize at the air—water interface. The difference between the two systems is that in SAMs of trichlorosilanes the island is comprised of polymerized surfactants, and therefore the mobihty of individual molecules is restricted. This lack of mobihty is probably the principal reason why SAMs of alkyltrichlorosilanes are less ordered than, for example, fatty acids on AgO, or thiols on gold. The coupling of polymerization and surface anchoring is a primary source of the reproducibihty problems. Small differences in water content and in surface Si—OH group concentration may result in a significant difference in monolayer quahty. Alkyl silanes remain, however, ideal materials for surface modification and functionalization apphcations, eg, as adhesion promoters (166—168) and boundary lubricants (169—171). 

The bonding of phosphonic acids to Si02 surfaces has also been reported in an organic solvent, Si-O-P bonds are formed by Si-OH/P-OH condensation [159] however, in an aqueous medium, no bonding was observed [127]. This behavior, which may be ascribed to the sensitivity of Si-O-P bonds to hydrolysis, has been utihzed for the micro- and nanopatterning of surfaces by selective surface modification of Ti02 patterns within a matrix ofSiOz [128]. 

One strategy is to fabricate a template structure using polymeric material (thus, using the same chemistry as described in Sects. 5.2 and 5.3) and back-fill or coat this structure with inorganic materials. For example, surface modification, followed by electroless deposition of Ag [217-219] or Cu [220], or by chemical reduction of Au solutions by surface functionalities [220], has been used to obtain metallized structures, while infiltration of polymeric photonic bandgap-type structures with Ti(0 Pr)4 solution, followed by hydrolysis and calcination, has been used to obtain highly refractive inverted Xi02 structures [221]. Au has also been deposited onto multiphoton-patterned matrices of biomaterials [194]. 

The pattern of the isotherms thus confirms the preservation of the mesoporous system during the surface modification. 

Various experimental routes towards surface modification have been utilized in order to control the microphase separation in thin films, as well as to achieve large-area patterns with desirable orientation relative to the film plane [2, 19, 21, 51]. 

Figure 9.6 (A) Sensor tip and dimensions prior to modification with enzyme and xerogel pattern (B) sensor after surface modification. Reprinted with permission from Ref. 44. Copyright 2005 Elsevier.

J. Zhu, M. Yudasaka, M. F. Zhang, D. Kasuya, and S. Iijima, Surface modification approach to the patterned assembly of single-walled carbon nanomaterials, Nano Lett. 3(9), 1239-1243 (2003). 

Keywords Core-shell particles Modification Patterned surfaces Roughness Wettability... 

Ellipsometry is probably the only easy-to-use surface analysis method which can be operated in situ and in real time. On the contrary, multiple internal reflection Fourier transform infrared spectroscopy is a very powerful technique [38] but it is rather tricky to implement. Ellipsometry allows real time studies of the surface modification during exposure to the plasma, and after the treatment. Figure 10 shows for example the variation of and A ellipsometry angles upon fluorination of Si in fluorine-based plasmas as a function of pressure and gas mixture [39], thus demonstrating the sensitivity of the technique. Infrared ellipsometry has also been used with success to investigate reaction layer composition and formation on Si in CF4-based plasmas [40,41], or to monitor patterning [42]. 

Surface-relief grating (SRG, regular topological surface modification) formed via irradiation with an interference pattern of coherent light has been demonstrated only recently/ " and is perhaps the most attractive target in the current research of azo polymers (Chapters 13 and 14 of this book focus on this subject). It is still unclear whether there are any common mechanisms involved between SRG formation and the photomechanical response observed in monolayers described in Section 15.4.1. Nevertheless, with regard to photoinduced motions in Az polymers, it is quite important to proceed with SRG experiments. 

The problem of lateral modification of HTSC surface layers, and the local electrosynthesis of HTSCs on the surface of patterned substrates including the precursors is very interesting. Such processes can occur, for example, during electrooxidation of metals when the process in its initial stages takes place only on isolated microscopic regions. Thus, Josephon junctions on the surface of Bi-Sn alloys [222] and on ceramic YBCO samples [295,444] were obtained by using electrochemical oxidation without any special local techniques. But it is hard to control such oxidation processes, and sufficient reproducibility cannot be ensured for most systems. Josephson tunnel junctions based on electrochemically synthesized BKBO crystals have been described [445]. 

PDMS), to replicate patterns from a master by molding. PD MS is inexpensive, biocompatible, gas permeable, amenable to surface modification, and optically transparent [15]. Soft lithography enables high-volume production of disposable devices and lowers the cost for frequent design changes common in biological research. 

On the other hand, there are many cases where the chemical or electrochemical reactions taking place on the surface are the rate-limiting steps in the patterning process. This will limit the patterning rate or will require development of other approaches whereby the whole pattern is made at the same time. At present, the common approaches used in SECM, i.e., the direct and feedback modes, cannot compete with the conventional photolithography methods. Nonetheless, future approaches such as multitip configuration may dramatically enhance the SECM capabilities in terms of speed of surface modification. 

If speed is an obstacle to the wide application of scanning probe techniques as surface modification tools, their resolution keeps them in the running. The resolution of the patterns formed by the SECM depends on the size and geometry of the UME, as well as the distance it is held above the surface. At the same time, the resolution of the patterns can easily be controlled (as compared to other SPM techniques) by approaches such as the chemical lens. Pattern width can be controlled merely by varying the electrolyte and the surface-UME distance. The UME need not be altered. 

A conceptually simple example of surface modification for lithographic imaging was based on the use of focused ion beam to write a pattern onto the sub-... 

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