PDMS stamp fabrication

The design for the photomask to be used for the PDMS stamp fabrication was designed using the Clewin software (PhoeniX Technologies, The Netherlands). Different patterns including squares, circles, lines and diamonds were designed... 

Patterning SAMs in the plane of the monolayer is useful in determining the two-dimensional distribution of chemical and physical properties on a surface. There are several methods available for generation of patterned SAMs. (jlCP is a convenient technique that stamps a pattern of SAM directly on a surface (Figure 8) [82,83]. In p,CP, an elastomeric poly(dimethylsiloxane) (PDMS) stamp — fabricated by casting and curing PDMS against masters that present patterned... 

Fig. 8 (a) Schematic representation of the fabrication process for MIP nanopatteming using a hydrophilic PDMS stamp, (b) Dark field microscopy image of an MIP nanopattemed by soft lithography. Inset AFM topography scan of the MIP nanopattem [85]... 

After the patterns on these polymer films are transferred into photoresist films coated on silicon substrates using photolithography, the developed photoresist patterns can serve as a master to make the required PDMS stamps. By combining this method of rapid prototyping with soft lithographic techniques, we can fabricate patterned microstructures of polymers and metals within 24 h of the time that the design is completed. Rapid prototyping makes it possible to produce substantial numbers of simple microstructures rapidly and inexpensively. 

Figure 14.8 Schematic representation of the fabrication of PDMS stamps and the process of microcontact printing.

Another way to overcome problems with wettability and compatibility with aqueous solutions of PDMS stamp is simply to use other materials for fabrication... 

The developed PR was then used as a master to fabricate the PDMS stamp... 

Fig. 10.27. Fabrication steps for a large area PDMS stamp.

Pre-polymer of PDMS was cured with holding down the edges of the slightly oversized Mylar backing film using vacuum plate at 67 °C on hotplate for 18 h. Thicker plates were fabricated as follows. To ensure the PDMS stamp were absolutely flat and uniform, two PDMS pre-polymer mixture (1 5) layers were coated and put in contact via lamination. Thus, a 25 pm thick layer of PDMS pre-polymer was directly coated on the PR master surface and another 25 pm thick layer was coated on to the stamp s Mylar backing (Fig. 10.27a, b). The two pre-polymer layers were then laminated before the curing step. 

Curing laminated PDMS stamp at room temperature for 48 h followed by delaminating from glass master completed the stamp fabrication. The thickness of cured PDMS layer obtained by following the later procedure is 50 pm (Fig. 10.27c, d). Atomic force microscopy (AFM) images of the developed PR are shown in Fig. 10.28a, b. 

Because PDMS stamps are soft, a mold was fabricated (with Norland optical adhesive (NOA 73)) and used for the AFM analysis (Fig. 10.28c). A 25 pm NOA 73 photopolymer film was first coated on to a 12-inch x 14-inch glass sheet and laminated on to a PDMS stamp. The replication was completed by crosslinking the NOA 73 by UV exposure and removing the PDMS stamp. AFM images of the Au lines on a Mylar substrate fabricated using pCP from the stamp is shown in Fig. 10.28d. 

Fig. 4.19 The fabrication of metal ion patterns on glass by pCP and DPN (i) Functionalisation of a glass slide with the amino-terminated TPEDA SAM (ii) functionalisation of the TPEDA SAM with a fluorophore (I ) and, (iii) with a ligand molecule (. y) in solution to produce a fully covered nonpatterned fluorescent SAM (F Lp. Subsequently, pCP or DPN are used to transfer metal ions (Mj from a PDMS stamp or an AFM tip onto the substrates thus creating metal ion patterns. Modulation of the fluorescence of the substrate is observed where the metal ions have been deposited.87 Copyright Wiley-VCH Verlag GmbH Co. KGaA. Reproduced with permission...

For the fabrication of metal ion patterns on glass by pCP, after the fabrication of the fluorescent monolayers, a PDMS stamp was used to deliver metal ions by aCP to the specific areas where the PDMS stamp was brought into contact with the functionalized substrate. Metal ions Cu2+, Co2+, Ca2+, and Pb2+ were transferred by aCP to a glass slide coated with the TM4 SAM (see Fig. 4.4 for SAM composition).87 After the pCP process, the layers were imaged with a fluorescence microscope. The images showed that the fluorescence emission intensity of the glass substrate in the areas where the metal ion was printed had changed (Fig. 4.20)... 

Microcontact printing ( J,CP) [17,29,30] is part of a set of nonphotolithographic fabrication techniques known as soft lithography. In iCP, features are patterned with inexpensive, elastomeric PDMS stamps (see Section 5.5.2 for details on stamp fabrication). Consequently, [iCP can be less expensive in terms of capital and operation costs compared to photolithography for patterning large-area micron- or submicron-sized, features [31,32]. 

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