Coating methods sublimation

C. Alternative matrix application Solvent-free and matrix-free methods. Sublimation of matrix was successfully developed for matrix application [23, 61, 62], This approach provided a homogeneous coating of matrix for high-resolution IMS of GPL species from tissue sections. The apparatus used for the method is relatively simple and commercially available. The advantages of sublimation include the elimination of diffusion of the lipid molecules because no solvent is used during the matrix application, the increased purity of the matrix, and the reduction of the crystal size. 

Fig. I. Methods for forming metal vapors, (a) Evaporation from a resistance-heated, alumina-coated Mo or W spiral. This is a method suitable for Cr, Mn, Fe, Co, Ni, Cu, Pd, Ag, Au and other metals that do not attack alumina, (b) Evaporation from a resistance-heated Ta or W boat. This method is useful for V, Cr, and some lanthanides, (c) Sublimation from a resistance-heated free-hanging loop of wire, e.g., Ti, Mo, or W. (d) Evaporation from a cooled hearth using laser or electron bombardment heating. This method may be used with all metals.

The process for the thennal sensor network is as follows. Organic diodes, to be used as sheet-type thermal sensors, are manufactured on an ITO-coated PEN film. A 30-mn thick p-type semiconductor of copper phthalocyanine (CuPc) and a 50-nm thick n-type semiconductor of 3,4,9,10-perylene-tetracarboxylic-diimide (PTCDI) are deposited by vacuum sublimation. A 150-mn thick gold film is then deposited to form cathode electrodes having an area of 0.19 mm. The film with the organic diodes is coated with a 2-pm thick parylene layer and the electronic interconnections are made by the method similar to that mentioned before. The diode film is also mechanically processed to form net-shaped structures. Finally, to complete the thermal sensor network, we laminated the transistor and diode net films together with silver paste patterned by a microdispenser. This is shown in Figure 6.3.11. 

Some complex compact heat exchanger surfaces have been studied using mass transfer methods, for example, naphthalene sublimation [109] and chemical reaction between a surface coating and ammonia added to the air stream [110]. These elegant but tedious methods yield local mass transfer coefficients that can be used to infer heat transfer coefficients by the usual analogy. This detailed information, in turn, should aid in the development of more efficient surfaces. Numerical studies have also yielded useful predictions for laminar flows [111, 112]. 

Sections, 10-12 p thick, were cut from flash-frozen tissue, thaw-mounted on MALDI plates, and dried in a desiccator prior to deposition of the matrix. Sublimation of 2,5-dihydroxy-benzoic acid over -4 min resulted in a homogenous 5-10 p coating. Alternatively, the tissue was dry-coated with matrix that was passed through a 20 p sieve for 20 min. Both methods were stable in the vacuum for 24 h, although back-sublimation is a risk that can create artificial analyte concentration gradients. 

Besides the electrochemical method, other methods such as the chemically initiated polymerization method, the vapor-phase methods, and the Langmuir-Blodgett method have been devised for the preparation of conducting polymers. In the chemical method, a chemical oxidant such as ferric chloride initiates the polymerization. Polymerization usually results in a powdery product and the resultant powder is then compressed into a pellet or dissolved in a suitable solvent such as methylene chloride or chloroform and spin coated on a substrate. In the vapor-phase technique, which is a variation of the chemical method, a monomer film is vacuum sublimed onto a glass substrate and then exposed to a solution or vapor of ferric chloride for oxidative polymerization. Films thus prepared are usually thick, of the order of micrometers. For some applications in which ultrathin and very uniform films are required, the Langmuir-Blodgelt technique for depositing monolayers has also been tried successfully [5]. 

The dipping operation is repeated to build up multilayer films. The moving barrier maintains constant pressure and the dipping operation is automated with pressure measurement through microprocessor controls. By this process layered films are formed by alternate molecular orientations. This technique offers better control over order, film thickness and reproducibility of the response behaviour of the layers formed than traditional methods such as vacuum sublimation, spin coating, etc. Each layer consists of domains which provide a uniaxial texture of the films [185]. In order to make use of these layers as components in optical and electrooptic devices the size and orientation of the individual molecules or crystal axis of the domains of the individual layer should be adjusted with reference to the external reference system. 

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