Wafer-based preparation

The idea to prepare solid catalysts as thin-film spots on the surface of wafer substrates had been inspired by technologies that were developed for high-throughput discovery of materials by Hanak [39], by Symyx [40-44] and others [45, 46], Hundreds to thousands of small spots of differently composed 

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Similar setups with shorter optical path lengths based on common 100-mm Si wafers with 100 or 111 orientation with sizes of approximately 37.5 mm x 15 mm x 0.5 mm are described (Chabal et al., 1989 Pietsch et al., 1994 Weldon et al., 1996). In order to avoid confusion, these sometimes-called MIR elements should be named wafer-based multi-reflection elements (wMREs). The use of standard Si wafers allows processing in conventional semiconductor equipment, for example in order to deposit a specific material. With the geometry specified above, up to 75 reflections (Chabal et al., 1989 Pietsch et al., 1995) occur giving a higher signal fraction of the total reflection. The optical path in the wMRE is still relatively long, and so they are subjected to similar restrictions as standard MREs in case of applications with wavenumbers >1000 cm (Weldon et al., 1996). Additionally, the preparation of the 45° bevel has to be done individually/separately for each wMRE and accessories are needed to focus/collect the IR radiation onto/from the small bevelled faces. 

Fabrication of Planar Ion-selective Electrodes on Kapton Wafers (Site Preparations and Wire Connections The fabrication sequence is based on integrated circuit technology and is described in detail in (2,5). 

The encapsulation and release of l,3-bis(2-chloroethyl)nitrosourea (BCNU) in P(CPP-SA) 20 80 wafers was the first implantable controlled release device based on polyanhydrides that was FDA-approved and marketed (Gliadel ) (Chasin et al., 1988). BCNU was encapsulated by two techniques, trituration and co-dissolution, resulting in different release profiles (Chasin et al., 1990, 1991). The triturated samples released faster than those prepared by co-dissolution, presumably due to more homogeneous loading in the samples prepared by co-dissolution. 

Based on this approach Schouten et al. [254] attached a silane-functionalized styrene derivative (4-trichlorosilylstyrene) on colloidal silica as well as on flat glass substrates and silicon wafers and added a five-fold excess BuLi to create the active surface sites for LASIP in toluene as the solvent. With THF as the reaction medium, the BuLi was found to react not only with the vinyl groups of the styrene derivative but also with the siloxane groups of the substrate. It was found that even under optimized reaction conditions, LASIP from silica and especially from flat surfaces could not be performed in a reproducible manner. Free silanol groups at the surface as well as the ever-present impurities adsorbed on silica, impaired the anionic polymerization. However, living anionic polymerization behavior was found and the polymer load increased linearly with the polymerization time. Polystyrene homopolymer brushes as well as block copolymers of poly(styrene-f)lock-MMA) and poly(styrene-block-isoprene) could be prepared. 

Orbital motion offers the capability of achieving high relative velocities without sacrificing tool footprint. This point is especially important as the semiconductor industry prepares to make the transition to 300-mm wafers. Several CMP tool concepts have been developed based on orbital motion. Some orbit the carrier while rotating the platen [13]. Others orbit the polishing pad while rotating the carrier [14]. Another design involves orbital (as well as arbitrary nonrotational) motion on a fixed polish pad [15]. 

Apart from ybco, thin films with reasonable microwave properties have been prepared from the thallium-based compounds Tl2Ba2CaCu208 (Tc 105 K) and Tl2Ba2Ca2Cu30io (Tc 115 K) [10], hts films with reasonable and qualified microwave properties nowadays can be grown on wafers up to more than 4 in diameter, the most common size are 2 and 3 for microwave applications. A very important step was the preparation of double-sided coating, which have turned out to be essential for planar microwave devices, where the metal ground plane needs to be superconducting in order to achieve high quality factors. 

Consider the polymer-on-metal interface, which might be prepared by coating a thin metal film with polymer in a polymer-based LED. The case of the counter electrode, formed by vapor-deposition, is discussed subsequently. First, assume that the substrates have clean surfaces hydrocarbon and oxide free, or naturally oxidized but still hydrocarbon free (pointed out as necessary). Typically, in connection with polymer-based LEDs, the metallic substrate could be gold, ITO (indium tin oxide) coated glass, the clean natural oxide of aluminum ( 20 A in thickness), the natural oxide which forms upon freshly etched Si( 110) wafers ( 10 A), or possibly even a polyaniline film. Dirt , which may be either a problem or an advantage, will not be taken up here. Discussions will alternate between coated polymer films and condensed model molecular solid films, as necessary to illustrate points. 

In order to maintain the advantage of the microfabrication approach which is intended for a reproducible production of multiple devices, parallel development of membrane deposition technology is of importance. Using modified on-wafer membrane deposition techniques and commercially available compounds an improvement of the membrane thickness control as well as the membrane adhesion can be achieved. This has been presented here for three electrochemical sensors - an enzymatic glucose electrode, an amperometric free chlorine sensor and a potentiometric Ca + sensitive device based on a membrane modified ISFET. Unfortunately, the on-wafer membrane deposition technique could not yet be applied in the preparation of the glucose sensors for in vivo applications, since this particular application requires relatively thick enzymatic membranes, whilst the lift-off technique is usable only for the patterning of relatively thin membranes. 

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