Novel Fabrication Methods

Some interesting new fabrication techniques have recently been developed. The impetus comes from the need to supplant existing technologies with methods that are less expensive, offer greater latitude for materials selection, and yield higher quality coatings. Further, recent restrictions on the emission of organic solvents, chlorinated hydrocarbons in particular, have emphasized the need to 

Pacansky et al. (1987) described the fabrication of dual-layer photoreceptors by radiation curing. The layers were coated with a polymerizable acrylate monomer or oligomer as the liquid component, then cured by a 175 kV electron beam or ultraviolet exposure. These methods were used for the preparation of generation layers containing bisazo and hydroxysquaraine pigments. 

Taylor et al. (1990) described the use of Langmuir-Blodgett techniques for the preparation of monolayers as blocking layers. Layers as thin as 0.002 (im were effective in suppressing the dark discharge and maximizing charge 

Generation layers have recently been prepared from aqueous dispersions. Hoshino et al. (1991) described the cathodic deposition of various phthalo-cyanines and perylenes from aqueous dispersions containing poly(oxyethylene dodecyl ether) and LiBr. The pigment-polymer aggregate was plated onto an Al cathode. The layer was then coated with a transport layer using conventional solvent coating techniques. Hiruta et al. (1991) described a related technique as thermoinduced deposition. Aqueous phthalocyanine dispersions, as described above, were found to adsorb on an Al substrate at 90 C. 

Hsieh and Melnyk (1996) report generation-layer fabrication by solvent coating of a pigment dissolved in a mixture of nitromethane and a Lewis acid. Subsequent water washing removes the Lewis acid to yield the pigment layer. 

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Nam YS, Yoon JJ, Park TG. A novel fabrication method of macroporous biodegradable polymer scaffolds using gas foaming salt as a porogen additive. J Biomed Mater Res 2000 53. 

Kondo et al. reported a novel fabrication method of polymer nanotubes by combination of an alternate layer-by-layer (LbL) assembly of PLLA and PDLA and the siliea template method. Silica nanoparticles with a diameter of 300 nm were alternately immersed in aeetonitrile solutions of PLLA and PDLA at 50 °C. The immersion process was performed for 10 cycles to deposit 10 double layers of PLLA and PDLA. The resulting partieles were then treated with 2.3% aqueous hydrofluoric acid to remove the siliea core. The hollow eapsules have a spherical shape with a diameter of 320 nm and a shell thiekness of approximately 60 nm. Tubular assemblies with an average diameter of 300 nm and lengths of 2-5 pm are obtained by evaporating water at ambient temperature from a water dispersion of the hollow eapsules on a polyethylene terephthalate (PET) substrate. 

On the basis of the dressed photon theory and the important role of electric dipole-forbidden molecular vibrational excitations, recent theoretical studies have proposed a simple model to describe atom or atom-cluster desorption due to the dressed photons from a nanometric particle deposited on a substrate [49]. Assuming an anharmonic potential for each atomic binding, an effective atom-nanodot potential was evaluated to determine the desorption energy and the stabilized dot size. The model shows that electric dipole-forbidden molecular vibrational excitations play an important role in the phonon-assisted process, which could potentially lead to a novel fabrication method, in addition to controlling the size and position of nanostructures [51]. 

Until now, the fabrication of defect-free high-quality graphene in large areas, which is critical for nanoelectronic devices, is still a big challenge. Surely, the establishment of controllable approaches for specific applications is the precondition toward real application. Various methods have been developed and more novel fabrication methods are still emerging. In this section, the most important preparation methods that have been used so far will be discussed in detail. 

To realize micro reactors with sensing and surface-control structures, the underlying fabrication methods have to go beyond MEMS and classical micro machining [75]. Plastic and glass manufacture and also novel innovative methods such as soft lithography have to be developed further and applied. 

In contrast to the molecular wire of molecular interface, electron mediators are covalently bound to a redox enzyme in such a manner as an electron tunneling pathway is formed within the enzyme molecule. Therefore, enzyme-bound mediators work as molecular interface between an enzyme and an electrode. Degani et al. proposed the intramolecular electron pathway of ferrocene molecules which were covalently bound to glucose oxidase [ 4 ]. However, few fabrication methods have been developed to form a monolayer of mediator-modified enzymes on the electrode surface. We have succeeded in development of a novel preparation of the electron transfer system of mediator-modified enzyme by self-assembly in a porous gold-black electrode as schematically shown in Fig.12 [14]. 

From the view point of nanoscience, many research efforts have been put forward to achieve simplicity in the steps leading from the material s synthesis to final applications of nanomaterials. Due to the small size inherent to nanomaterials, manipulation and assembly processes following their synthesis are much more complicated and time consuming than their bulk counterparts. Therefore, numerous studies focused on novel synthetic methods which allow spatial and orientational control of nanomaterials during their growth process. These efforts will be discussed more in Section 12.4. These approaches enable the use of nanomaterials directly upon their synthesis, without going through complex and costly fabrication steps to assemble nanomaterials into application-ready devices and platforms. 

In order to fully exploit the maximum product potential of polymers it may be necessary to sacrifice some of their useful melt processibility aspects. At present most polymers are manufactured as a compromise between processing and product qualities and this will continue. If however, maximum product performance is required novel processing methods that do not use melt processing will need to be found. Nature makes extensive use of polymers for a very wide range of functions, but does not appear to use melt processing as a route to fabrication. We still have a lot to learn. 

A development of novel fabrication approaches is another field of great interest in LED technologies. Assembly and self-assembly methods as bottom up approaches are assumed to be very attractive from the point of view of simplicity and fabrication costs. For these methods the functionality of the species (specific groups, surface charge, dipole moment, etc) to be assembled is of crucial... 

Layer-by-layer (LbL) assembly of proteins or enzymes with polyelectrolytes is a novel general method for protein film fabrication that emerged over the past decade... 

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