Final Thinning

Three methods of final thinning are described here electrolytic thinning for metal specimens that are good electric conductors, ion milling for metal and ceramic specimens, and ultramicrotome cutting for polymeric and biological specimens. 

Ion milling uses a beam of energetic ions to bombard specimen surfaces in order to reduce the thickness by knocking atoms out of a specimen. The specimen does not need to be electrically conductive for ion milling. Thus, the technique is suitable for metal, ceramics and 

Ultramicrotomy is basically the same type of method as microtomy for preparing soft specimens for light microscopy. However, ultramicrotomy can be used to section a specimen to the 100 nm scale. It is commonly used to prepare polymeric or biological TEM specimens. 

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On heating to 1500 °C/6 h/Ar, the Zr material crystallizes to a mixture of monoclinic and tetragonal zirconia and crystobalite with loss of considerable original surface area (36 m2 g 1). The Hf material behaves similarly, although it partially crystallizes at 1000 °C to produce cubic or tetragonal hafnia. Cristobalite is only observed in materials heated to 1400 °C. Finally, thin films of the Zr and Hf derivatives could be cast from hydrocarbon solutions on quartz and then converted to thin films of the corresponding amorphous or ceramic materials. 

Figure 9.5. Specimen geometries prior to the final thinning step (a) dimpled specimen (b) wedge sample (c) lacquered window for chemical or electropolishing.

Table 9.4. Summary of Some Final Thinning Techniques for TEM ...

Finally, thin-walled tubing is wound on. Rather more care will be required and the flame must not be too hot. Winding will proceed somewhat faster and there must be no interruption of the work until only about 15 cm of mbe remain in the right hand. 

NaOH dropwise until the pH was at about 6 as determined by the use of external dampened universal pH paper. The solution was vigorously stirred and 2.8 g sodium cyanoborohydride was added. Concentrated HCI was added as needed, to keep the pH constant at about 6. The addition required about two days, during which time the reaction mixture first became quite cottage-cheese like, and then finally thinned out again. 

For the first group the following types of dryers are generally used convective (tray, band, fluid bed, flash dryers, and their modifications) or contact (vacuum dryers such as double-cone dryer-blender, conical dryer with rotating helical mixer, paddle dryer). Pastelike materials are dried in tray dryers, band dryers equipped with extruding devices, and spin-flash dryers. Finally, thin pastes can be dried in spray dryers or on fluid beds or spouted beds of inert particles. Small amounts of solutions and suspensions are generally freeze-dried, especially if the product is thermolabile. 

The cupels are removed upon completion of the reaction, which can be monitored visually, the bead brightening when the final thin layer of oxide has been absorbed. 

Before a description of the final thinning stage it is necessary to outline initial preparation. (1) Cut a slice as thin as possible, realistically 200-500 pm. (2) This is mechanically polished to 50-100 pm. (3) Punch/drill out a 3 mm disk. (4) Preferentially polish the center of the disk by dimpling the sample (optional). 

A) Specimen is cut into thin slabs B) Slabs ate glued on a glass slide C) Composite specimen is thinned mechanically D) Thin specimen is dimpled E) Final thinning is done by ion bombardment from one side while the specimen is rotated a) Integrated circuit b) Glue line c) and d) Glass slide (Courtesy of IMEC)... 

Petermann and Gohil [94] produced isotactic PP melts from o-xylene solutions at 130°C. Schultz et al. [97] and Schultz and Petermann [98] also used this method to study the oriented fibrous microstructure of annealed PP films crystallized from a highly extended melt. TEM was applied to the observation of the fibrillar to lamellar transformations. Finally, thin spherulitic films were formed [99] from a drop of a dilute PE solution in xylene placed on the surface of glycerol at 140°C. Following solvent evaporation. 

Figure 6-17. Coaxial electrical cable s PS insulation buttons are here being injection molded, using a cold runner system, but it could also use a hot runner one. In this continuous production process, the injection-molding machine (IMM) is on a platform that moves in a rectangular pattern to permit the platens to open and move away from the buttons, as well as to move at the speed of the six-cable copper wire line when the mold is closed and the IMM is injecting the PS. Copper wires are started out with large diameters and are pulled through reduction squeeze rolls to their final thin diameter prior to entering the IMM. The wire-reduction line is to the left of the IMM, with the wire pullers to its left. Automatic devices remove the runners on-line just after they leave the IMM and the additional cooling station fiiat is shown in this view.

Glass is a transparent, sometimes colored, inorganic material, which is fragile and predominantly noncrystalline. It has no well-defined melting point, but with continuous heating it changes from being viscous to a soft and finally thin fluid state (i.e., an imdercooled melt without cyrstallization). 

Table 8.4 Summary of inferences from the final thinned posterior sample.

Sample preparation is often the most time-consuming aspect of transmission electron microscopy. It is relatively straightforward if the sample is a homogeneous metal or alloy and if a thin foil can be produced from any part of it. Problems arise if areas near to the surface or to a boundary between two dissimilar materials are required to be analyzed. Normally a thin section of material 1 mm in diameter is produced mechanically, which is then polished to the minimum practical thickness before being finally thinned to electron transparency. The final stage is carried out using either electrolytic or ion-thinning methods. When... 

Adaptation of the fractal dimension of titania oligomeric primary particles allows engineering of the optical properties of Ti02 [87]. A smaller Df of these structures leads to a higher refractive index in the final thin film. The... 

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