Advantages of a Programmed Surface Designed by Organic Monolayers [chapter]

Naoto Shirahata
2011 Nanofabrication  
Introduction Increasing attention has been paid to the control over surface chemical property of bare metals, semiconductors, ceramics, and polymers in the development of nanoscience and nanotechnology. The appropriate functionalization has a potential to lead to the appearance of new function. Organic monolayers, i.e., self-assembled monolayers (SAMs), are simple monomolecular system, convenient, and flexible to tailor the substrate's surface chemical and physical properties including wetting
more » ... including wetting property, conductivity, and thermal, chemical, photochemical stabilities, etc. In the following molecular diagram of organic monolayers, its molecular anatomy and characteristics are highlighted as shown in Figure 1 . Such monolayer structures are formed by chemisorption of organic constituents onto the specific solid substrate through liquid or gas phase. A headgroup of the organic constituent reacts to the outermost atoms on the substrate to give a chemical linkage. The chemisorbates organize epitaxially to form crystalline monomolecular film structures. As shown in the molecular Fig. 1. Schematic diagram of organic monolayers formed on solid substrates Chemical modification of a polymer surface 2.1 Motivation Recently, the deposition of inorganic materials, e.g., ceramics, metals, and semiconductors, has interestingly attracted attention in the development of mechanically-flexible device applications including OLED, flexible flat panel and wearable displays, electronic papers, biomedical tools. These technological developments take advantage of polymer's excellent properties including mechanical flexibility, lightweight, ease-of-design and coloring, lowcost and good impact resistance. In order to fabricate such flexible device applications, it is a key to control chemical properties of polymer's surface that induce the nucleus formation of inorganic crystals, and accelerates subsequent crystalline growth or film growth. Organosilane SAMs have been frequently employed to modify surface chemically properties of inorganic substrates [1] [2] [3] [4] [5] . The resultant surfaces play important roles in molecular recognition events. For example, some of functional groups induce the nucleus formation of inorganic crystals, and accelerates subsequent crystalline growth or film growth. This section describes the preparation of well-ordered SAM structures on polymer sheet, and then the deposition of metal and ceramics films on the SAM-covered polymer sheets through solution processes. SAM formation When silane molecules are treated directly on as-received polymer sheet, they cannot form a monomolecular structure. Similar can be seen even on photochemically treated polymer sheet. In other words, when silane precursors are directly treated on surface-activated polymer substrates, well-ordered SAM formation cannot effectively proceed, since the polar-functional groups formed on a polymer surface through surface modification methods using plasma or UV light are generally inhomogeneous and randomly distributed [5] . Such a heterogeneous surface cannot provide adequate support for the preparation of a wellordered SAM. As an example, Table 1 summarizes the contact angles and surface free energies of polyimide surfaces covered with NH2-and CF 3 -terminated SAMs, and their values are compared with those of SAM-covered silicon substrates used as standards. The formation of the SAMs is performed on photooxidized polyimide and silica-covered silicon substrates, respectively. The details of the SAM preparation method are described in elsewhere [5] , but the surface energies of each sample are calculated using the following equation:
doi:10.5772/39030 fatcat:gumcajxy6jad3oxtv5mi3mhvna