Solution-based techniques

Particularly desirable among film deposition processes are solution-based techniques, because of the relative simplicity and potential economy of these approaches. However, the covalent character of the metal chalcogenides, which provides the benefit of the desired electronic properties (e.g., high electrical mobility), represents an important barrier for solution processing. Several methods have been developed to overcome the solubility problem, including spray deposition, bath-based techniques, and electrochemical routes, each of which will be discussed in later chapters. In this chapter, a very simple dimensional reduction approach will be considered as a means of achieving a convenient solution-based route to film deposition. 

Atomic absorption completely replaced OES in archaeological chemistry during the 1980s, and differs from it in a number of ways. Firstly, it is primarily a solution-based technique, therefore requiring solid samples to be dissolved prior to analysis. Secondly, it is based on the absorption of light by atomized samples in a flame, in contrast to OES which is based on emission. Because of this, AAS requires a source of light that has a wavelength... 

During a single run, which may take all day if a large number of samples are to be analyzed, the instrument may drift from its optimum settings. To detect this drift in solution-based techniques, and also to compensate for some matrix effects, a known amount of an element may be added to each sample before analysis. This internal standard (also called a spike) is added to all the samples and blanks, with the exception of the instrument blank (which is defined as zero concentration for all elements see below). It is important that the element (or isotope) chosen as the spike is not an element which is to be determined in the samples, and preferably which does not occur naturally in the samples. It must not be an element which will cause, or suffer from, interference with the other elements to be determined. In solution ICP-MS,... 

The chapter by Coe and Storer reviews the current state of library generation using solution-based techniques. Examples are given where these techniques are being used to prepare both mixtures and single compounds for use in both lead discovery and optimization. Possibly the most valuable use of these solution techniques is for the rapid optimization of existing leads. 

One of the primary differences between CVD (or in the case of polymers, commonly referred to, as chemical vapor polymerization or CVP) and other conventional deposition techniques, particularly for polymer thin films, is that CVD is a dry process. There is no liquid intermediate between the gas phase reactants and the resultant solid thin film and thus, problems due to surface tension such as pulling away from the corners, sharp edges etc, are not present. Additionally, CVD enables deposition of uniform thin films in recesses, holes and other difficult three dimensional configurations unlike solution based techniques which are limited to planar substrates. In the terminology of thin film device fabrication, CVD films have excellent gap-filling and step coverage characteristics. 

To fabricate different polymer layers in a device using solution based techniques, mutually exclusive solvents have to be identified, which is often very difficult. CVD eliminates these difficulties and excellent heterojunctions and multilayered films can be fabricated relatively easily. Also, the capability to co-deposit compounds can be achieved. This ease of co-depositing compounds has enabled the synthesis of several inorganic-organic hybrids, which can also be tailored as nanocomposites at the molecular level. 

The dry nature of CVD process enables copolymerization more easily than solution based techniques. This approach has been utilized to tailor the thermal and electrical properties of parylene thin films for ULSI applications. One of the first reports of vacuum copolymerization of xylylene was done with maleic anhydride as the comonomer. Subsequently, 9-vinylanthracene, 4-vinylbiphenyl and perfluoro-octyl methacrylate were successfully copolymerized with parylenes, and reported in... 

Affinity Capillary Electrophoresis-Mass Spectrometry. Affinity capillary electrophoresis was originally used for the determination of the binding constants of small molecules to proteins (47-49). This solution-based technique is rapid and requires only small amounts of ligands. Affinity constants are measured based on the mobility change of the ligand on interaction with the receptor present in the electrophoretic buffer (50). By combining affinity capillary electrophoresis with on-line mass spectrometric detection and... 

Conventional (spectroscopic) analysis techniques are also readily applied to determine structural details (e.g., the epoxy ring and the repeat unit) and can also be applied to determine the degree of polymerization, particularly where the poor solubility of the oligomer may hamper solution-based techniques. Mertzel and Koenig presented a thorough spectral characterization of EPON 828 (a commercial grade of DGEBA). 

In solution-based techniques (wet techniques), such as dip coating... 

Today most catalysts are prepared using solution-based techniques. Therefore it could be exported, that adapting these techniques to HTE demands will lead in all likelihood to catalysts with more comparable qualities. 

A drawback of all these solution-based techniques are the different excitation processes between wet and dry plasma conditions occurring in the ICP, resulting in different signal responses... 

A powder with good characteristics (high purity, good homogeneity, fine particle size, narrow particle size distribution, absence of hard agglomerates) is a must to get the desired properties and microstructure in the final component and thus synthesis of high quality powder is extremely important. Powders of ZrB and HfB are synthesized by (a) reaction between elements (Brochu et al., 2008 Tamburini et al., 2008) (b) borothermic reduction of metal oxide (Peshev et al., 1968), (c) boron carbide reduction of metal oxide in presence of carbon (Sonber et al, 2010 2011) (d) carbothermic reduction of metal oxide and B Oj (Fahrenholtz et al., 2007) (e) Metallothermic reduction of metal oxide and B Oj (Setoudeh et al., 2006 Kobayashi et al., 1993),(f) molten salt electrolysis (Frazer et al.,1975) (g) solution based techniques (Yan et al., 2006) and (h) s3mthesis from polymer precursors (Suetal., 1991). 

Solution based techniques Low temperature proeess Ultrafine powder Technique is not mature Suitable for Laboratory only... 

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