Thermal substrate deposition

This device comprises a hydrophobic surface using the wettability pattern of hydrophilic stripes for a surface-guided flow, micro channels [102], As substrates, hydrophobic materials were employed. The hydrophilic stripes were generated by mask-through thermal vapor deposition of MgF2 on a silicone mbber or thiolated gold substrate. 

The substrate holders are machined from nickel and bolted directly onto their mountings. Two types of substrates were used namely 0.010 Inch gold foil, bolted directly to the holder, or 0,020 Inch x 0.5 Inch diameter sapphire discs, mounted by means of gallltim solder to ensure good thermal contact. Deposition rates were determined by the weight gain of the sapphire substrates. The substrates could be covered by a removable Inverted pan maintained at ground potential such that In the covered condition no reaction occured at the anode. This facility allowed the plasma to be established and stabilized before exposure of the substrates. 

Figure 5.14 Microstructure of calcium phosphate coatings deposited from a solution containing 0.7 mmol CaCI2 and 0.3 mmol Ca(H2P04)2 by the thermal substrate technique. (a) Monetite (DCPA, pH 4, 150°C,...

Kuroda, K., Ichino, R., Okido, M., and Tokai, O. (2002a) Effect of ion concentration and pH on hydroxyapatite deposition from aqueous solution onto titanium by the thermal substrate method. Biomed. Mater. Res., 61, 354-359. 

For some applications, the high temperature required for rigorous mass transport limited control, or, occasionally, to a greatly reduced extent, even the lower temperature required for kinetic limited control, can induce thermal substrate damage. One potential solution to these problems is to employ alternate forms of energy input, permitting deposition at lower substrate temperatures (see Sect. 1.3.1.3). 

Chemical vapor deposition (CVD) is a method of forming dense and stable structural parts or coatings using the decomposition of relatively high vapor pressure gases. Gaseous compounds of the materials to be deposited are transported to a substrate surface where a thermal reaction/ deposition occurs. Reaction by-products are then exhausted out of the system. 

A trend in electrode preparation is to reduce the catalyst layer thickness to improve the mass transfer efficiency at the interface, such as the efficient movement of protons, electrons, and dissolved reactants in the reaction zone. In addition, a thinner electrode will be beneficial to reduce catalyst loading and increase mass power density. The deposition technique is an effective way to achieve a thinner electrode through depositing a nano-scale catalyst film on the substrate. Deposition methods include chemical vapor deposition, physical or thermal vapor deposition, sputtering deposition, electrochemical deposition, chemical deposition, as well as ion beam deposition. The following sections will focus on electrodes fabricated with these various deposition methods. 

The vacuum deposition methods include chemical vapor deposition (CVD), physical (PVD) or thermal vapor deposition, and sputtering. PVD coatings involve atom-by-atom, molecule-by-molecule, or ion deposition of various materials on solid substrates in vacuum systems. 

Fig. 8.4 (a) SEM image of indium-coated quartz substrate prepared by vacuum thermal vapor deposition with mass thickness of 25 nm. The scale bar is 200 nm. (b) Raman spectra of 1-nm-thick adenine films deposited on the indium-coated substrate and on a bare fused silica substrate... 

Germane is used primarily to produce high purity germanium metal or epitaxial deposits of germanium on substrates for electronics by thermal decomposition at about 350°C (see Germaniumand germanium compounds). 

Membranes. Membranes comprised of activated alumina films less than 20 )J.m thick have been reported (46). These films are initially deposited via sol—gel technology (qv) from pseudoboehmite sols and are subsequently calcined to produce controlled pore sizes in the 2 to 10-nm range. Inorganic membrane systems based on this type of film and supported on soHd porous substrates have been introduced commercially. They are said to have better mechanical and thermal stabiUty than organic membranes (47). The activated alumina film comprises only a miniscule part of the total system (see Mel rane technology). 

In most cases, CVD reactions are activated thermally, but in some cases, notably in exothermic chemical transport reactions, the substrate temperature is held below that of the feed material to obtain deposition. Other means of activation are available (7), eg, deposition at lower substrate temperatures is obtained by electric-discharge plasma activation. In some cases, unique materials are produced by plasma-assisted CVD (PACVD), such as amorphous siHcon from silane where 10—35 mol % hydrogen remains bonded in the soHd deposit. Except for the problem of large amounts of energy consumption in its formation, this material is of interest for thin-film solar cells. Passivating films of Si02 or Si02 Si N deposited by PACVD are of interest in the semiconductor industry (see Semiconductors). 

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