Self Assembly and Contact Printing Materials

Contact printing is a new technology that utilizes the principle of molecular self-assembly to transfer the micropattern on the elastomeric stamp to the substrate and reproduce the micropattern on the substrate. Contact printing can reproduce micropattern on a large area (≥50cm2). Furthermore, the self-assembly layer formed on the substrate can be used as a protective layer for some selective solutions, and complex structures can be obtained by further chemical etching. The key technologies of contact printing include: manufacturing elastomeric stamp, forming self-assembled monolayers(SAMs) and Microcontactprinting technology(μCP). Among them, the typical elastomeric stamp manufacture process is showed in figure1.

Figure 1. The typical manufacture process of elastomeric stamp.

Applications:

Compared with traditional technology, contact printing has the advantages of low cost, convenience, high efficiency, wide application range, and can be printed on the curved surface. Moreover, by introducing different end groups, the self-assembly layer of the stamp and ink molecules can modify the surface of the substrate, which can realize patterning the surface free energy on the substrate. This kind of patterned substrate has important research and practical significance in many fields.

• Microelectronic processing: Due to the advantages of convenience and high efficiency, contact printing is a promising technology applying in microelectronic processing. For example, Bell Labs used contact printing to make organic transistors, as shown in figure 2.

Figure 2. An example of using contact printing to make organic transistors.

• Analysis and test field: Using the high-resolution of contact printing, it can be coupled with some traditional analytical methods for more precise and convenient analysis. For example, contact printing technology combining with mass spectrum (MS) can realize single cell lipids analysis.

Classification:

Contact printing involves many steps and a lot of materials are needed to complete this process. According to the roles they play in this process, these materials can be classified into four classes.

• Substrate materials: The substrate material is usually gold membrane.
• Self-assembly materials: Self-assembly is a process that using non-covalent bonding force to assembly some certain patterns. In contact printing process self-assembly materials refer to the elastomeric stamp materials and ink materials. On the one hand, the materials that used to manufacture elastomeric stamp need to have elasticity. Many types of materials can be used, but the most widely used is polydimethylsiloxane (PDMS). On the other hand, after the ink is dipped or coated on the elastomeric stamp, the elastomeric stamp is stamped on the substrate and the pattern is transferred to the substrate. Moreover, the functional group in elastomeric stamp materials and ink materials can formed self-assembled monolayers by self- assembly.
• Etching agent: In the last step, the etching agent is used for chemical etching, and the fine pattern that is exactly the same as the original pattern can be obtained. Etching agent is usually a mixture of several chemicals. For example, a special gold etching agent is a mixture of K₂S₂O₃, KOH, K₃Fe and K₄Fe(CN)₆.
• Langmuir-Blodgett (LB) membrane forming reagent: When preparing the elastomeric stamp, the surface of the delicate pattern is often pitted, which will affect the quality of the final product and Langmuir-Blodgett (LB) membrane forming reagent can be applied to alleviate this problem.

Reference:

1. Rogers J A, Bao Z, Meier M, et al. Printing, molding, and near-field photolithographic methods for patterning organic lasers, smart pixels and simple circuits[J]. Synthetic Metals, 2000, 115(1-3):0-11.