Patterned SAMs

Fig. 18—Patterned SAMs composed of OTS (light) and APTES (dark) arranged in striped (a) and dotted patterns (b).

SAMs controlling electrochemistry, whereas the reverse holds for the other one, both topics are inseparably intertwined as exemplified by the underpotential deposition of metal on SAM-modified electrodes where patterned SAMs allow localization of metal UPD, which in turn affects the monolayer. 

The possibilities afforded by SAM-controlled electrochemical metal deposition were already demonstrated some time ago by Sondag-Huethorst et al. [36] who used patterned SAMs as templates to deposit metal structures with line widths below 100 nm. While this initial work illustrated the potential of SAM-controlled deposition on the nanometer scale further activities towards technological exploitation have been surprisingly moderate and mostly concerned with basic studies on metal deposition on uniform, alkane thiol-based SAMs [37-40] that have been extended in more recent years to aromatic thiols [41-43]. A major reason for the slow development of this area is that electrochemical metal deposition with, in principle, the advantage of better control via the electrochemical potential compared to none-lectrochemical methods such as electroless metal deposition or evaporation, is quite critical in conjunction with SAMs. Relying on their ability to act as barriers for charge transfer and particle diffusion, the minimization of defects in and control of the structural quality of SAMs are key to their performance and set the limits for their nanotechnological applications. 

Metal UPD at the SAM/substrate interface is of interest for several reasons. Firstly, from an application point of view as the intercalation of another metal alters the thiol-substrate bond and, thus, the stability of a SAM that can be exploited to generate heterogeneous and patterned SAMs, a point we will return to later. Secondly, the intercalation and alteration of the thiol-substrate bond changes the morphology of a... 

ChiUcoti et al. took advantage of the pCP method to prepare patterned SAM of mercaptoundecanoic acid (MUA) for the binding of 2,2 -azobisisobutyramidine. Thermal SIP resulted in the topographical enhancement of the originally printed SAM structure with feature size of about 40 pm [219]. Also, the selective binding of thiols onto gold can be used for spatio-selective SIP. Dryer et al. [215] used gold... 

Microcontact printing (pCP) is a technique that uses an elastomeric stamp with relief on its surface to generate patterned SAMs on the surface of both planar and curved substrates [87,88]. SAMs are highly ordered molecular assemblies that form spontaneously by chemisorption of functionalized long-chain molecules on the surfaces of appropriate substrates [79,89]. Well-established systems of SAMs include alkanethiolates on coinage metals (Au, Ag, Cu) [90] alkyl-siloxanes on hydroxyl-terminated surfaces (Si/Si02, glass) [91] carboxylic and... 

SAMs function as ultrathin resists against certain types of etches, and patterned SAMs can also be used as templates to control the nucleation and deposition of other materials (e.g. polymers [96],copper [97] and mammalian cells [98]). 

Figure 13.12 The preparation of spherically shaped nanoparticle crystals. A chemically patterned SAM with attached droplets of a SiC>2 nanoparticle solution was immersed in decalin. The interfacing between two solutions and shrinkage of the particle droplets resulted in rearrangement of the nanopaiticles to form close-packed spherical particle assemblies.

Huskens et al. utilized NIL as a tool to pattern SAMs on silicon substrates.94 As shown in Figure 13.17, a prefabricated silicon wafer with a pattern was pressed against... 

Figure 13.17 Schematic description of the NIL process to form chemical or topographically patterned SAMs. The nanoparticles were subsequently attached specifically onto the SAM by electrostatic...

Carboxylic groups positioned at the open ends of SWCNTs were coupled to amines to form AFM probes with basic or hydrophobic functionalities by Wong et al. [117] (Scheme 1.8). Force titrations recorded between the ends of the SWCNT-AFM tips and hydroxy-terminated SAMs confirmed the chemical sensitivity and robustness of the AFM tips. Images recorded on patterned SAM allowed real molecular-resolution imaging [117]. 

Fine metal wiring can be fabricated by the selective deposition of gold, copper, nickel, etc. onto patterned SAMs on substrates of silicon or plastics like polyimide. The nickel and copper patterns on silicon substrates are shown in... 

In addition, the patterning method presented here is not restricted only to glass substrates unlike the use of patterned SAMs (self-assembled monolayers), where the choice of substrates is limited. In general this method would allow for the photogeneration of patterns of CaCOj on a variety of substrates, including e.g. conducting polymers, which would be beneficial for electrical stimulation of cells to enhance their proliferation and differentiation. 

Table 3 Methods that have been used for patterning SAMs of thiolates...

The ability to form patterned SAMs allows us to engineer the interfacial properties of a surface with one more degree of freedom, in addition to the flexibility offered by SAMs themselves. It provides immediate opportunities to prepare systems in which structures can be controlled in the plane of the interface. SAMs can be used to control the nucleation, adsorption, and wetting of other materials, and thus patterned SAMs can be used as templates to direct and control the assemblies of other materials to form useful structures they ean also be used as patterned resists in directing the dissolution of the substrate to form patterns and structures in the underlying substrates (Au, Si02 and Si) [95]. 

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