Sample preparation methods slurry technique

Abrasive particles are a key component in CMP slurry. The most commonly used abrasive particles include silica, alumina, ceria, zirconia, titania, and diamond. Table 21.1 listed a set of information on each type of abrasive particles such as density, microhardness, and isoelectric points (lEP). It is important to point out that the specific values for these properties depend highly on the preparation techniques and the specific states of the samples. The values listed in the table represent an average of the most commonly reported data. For example, the isoelectric point for silica is a function of the number of hydroxyl groups, type and level of adsorbed species, metal impurity in the solid matrix, and the treatment history of the materials [1]. There are three major types of silica according to their preparation methods fumed, colloidal, and precipitated. The common sources for obtaining these abrasive particles are listed in Table 21.2. As examples, some of the more specific information on... 

Overall methods using either different or no sample preparation procedures and various detection techniques have also been compared. Thus, fine ambient aerosol was analysed for 11 elements by using US-assisted slurry formation for 15 min prior to AAS, as well as by X-ray fluorescence spectroscopy and laser ablation ICP-MS. Sample treatments were found to provide similar results. However, the detection techniques compared the number of target analyte elements to be determined, detection limits and purchase costs [10],... 

Sample preparation may involve either a milling or a wet slurry technique. A recent study has evaluated these two processes using 10-kg samples of cocoa, green coffee, almonds and pistachios and has shown that the wet slurry process has a lower coefficient of variation than dry milling (Spanjer et al., 2006). The investigators concluded that this was due to the smaller particle size produced by the wet slurry process and that this method of sample preparation was to be preferred. 

Slurry nebulization has also proved very popular. In this technique, sample (typically 0.25 g) is placed in a 30 ml plastic bottle and 10 g of expanded zirconia beads are added. A dispersant is added and the bottle is sealed and then placed on a mechanical shaker for several hours. During the shaking, the zirconia beads grind the sample into very fine particles. After dilution to a known volume, the slurry may be aspirated directly into an atomic spectrometric instrument. Other methods of slurry preparation also exist, e.g. using a micronizer, but the bottle and bead method is the most common. 

A single multielement calibration standard is used to establish a relative sensitivity factor (R.) for each analyte (i) to be determined in the multielement analysis. For solution analysis, this multielement standard is usually prepared from high-purity metal salts dissolved in deionized water, with sufficient nitric acid added to stabilize their concentrations (pH 2 or less). Because this is only a semiquantitative analysis, matrix matching of the calibration standard to the matrix of the sample is not required. When using solid analysis techniques (i.e., slurry nebulization, laser ablation, etc.), an appropriate solid phase multielement calibration standard is most desirable however, novel approaches for the use of a solution standard have been used with some methods. 

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