Replication techniques

Scanning electron microscopy and replication techniques provide information concerning the outer surfaces of the sample only. Accurate electron microprobe analyses require smooth surfaces. To use these techniques profitably, it is therefore necessary to incorporate these requirements into the experimental design, since the interfaces of interest are often below the external particle boundary. To investigate the zones of interest, two general approaches to sample preparation have been used. 

By means of the more advanced replication technique using tungsten as a pre-shadowing metal, the electron microscopic observation of both the pores and the morphological changes caused by annealing steps are reported in the present paper. 

These results were confirmed by an electron microscopy study using a freeze-etching replication technique (1 ). The aim of this technique was to conserve the real gel structure by blocking any diffusion processes in the gel sample by the freezing action of liquid nitrogen. The three-dimensional network is then recovered... 

Figure 3. Sclid-like gel network. Freeze-etching replication technique. (Reproduced with permission from Ref. 17. Copyright 1985 Academic Press.)...

The main advantage of using a ternary blend (as opposed to the direct replication of Fig. 1.6, where the width of the polymer structures was directly imposed by the substrate pattern), is the relative independence of the structure parameters (width, aspect ratio) with respect to the substrate pattern. The width (and thereby the aspect ratio) of the PMMA rings in Fig. 1.7 is controlled by the relative amount of PMMA in the PS/PMMA/PVP blend. While the lateral periodicity of the polymer structures is determined by the substrate, the structure size is controllable by the relative amount of PMMA in the blend. Similar to the replication technique using two polymers, pattern replication by demixing of ternary blends should be expandable to other polymer system, with the main requirement that one of the components wets the interface of the other two. 

FIGURE 1.17. Large area images of patterns replicated with the help of a temperature gradient. The four patterned areas are 200 x 200 pm2. The top-left and bottom right area he at a lateral distance of 2.7 mm on the sample, illustrating the reliability of this replication technique. From [39]. 

Ritzhaupt-Kleissl, H.-J., von Both, H., Dauscher, M. and Knitter, R. (2005) Further ceramic replication techniques, in Advanced Micro and Nanosystems Microengineering of Metals and Ceramics, vol. 4 (eds H. Baltes, O. Brand, G.K. Fedder, C. Hierold, J. Korvink and O. Tabata), Wiley-VCH Verlag GmbH, Weinheim, Germany, Chapter 15. 

Fig. 8 Freeze fracture replication technique for transmission electron microscopy (TEM). (From RefJ l)...

Clinical studies of tooth wear are complex long-term studies for reasons already described. Some researchers have attempted to make objective measures of tooth wear, often using replicate techniques, whilst others have employed tooth wear indices. 

Use of 3D foams is also a popular method for bone regeneration applications, although they are most often employed for trabecular bone regeneration [152,154]. There are a few methods utilized to create foams for this application, one of the most popular being a polymer foam replication technique, in which a polymer foam is either electrosprayed or immersed into a HAp/bioactive glass particle slurry in order to fully coat the foam and create a trabecular bone-like aichitecture. However, other methods are also utilized, including creating composite foam solutions that are injectable and form once inside the body [153]. Results of Fu et al. [152] have indicated mechanical properties similar to those of natural trabecular bone. 

Polymer materials find a wide application in replication technologies for producing structures with submicron elements of intricate shapes and for nano-scale surface replication [1-4]. They show considerable promise for smoothing out the surface roughness to obtain good-quality inexpensive substrates used in fabrication of X-ray optic components [5,6], In this work, the features of silicon wafer surface replication by polymers were studied by atomic-force microscopy (AFM) and X-ray reflectometry (XRR) with a view to applying this replication technique to produce smooth polymer-glass combination substrates to be used in multilayer X-ray mirrors. 

This paper describes a systematic study by electron microscopy of adsorbed monolayers of long-chain fatty acids ranging from C14 to C26 Improvements in replication techniques and the electron microscopes themselves since the time of Epstein s original work, as well as the successful applications of electron microscopy cited above, gave reason to believe that such an investigation would be a useful supplement to the previous experiments of Bigelow and Brockway in elucidating the structure of the adsorbed films. 

Image formation requires the electron beam to penetrate completely through the material being investigated and therefore imposes stringent requirements on the sample preparation methods. Micron has the facilities and expertise to meet these stringent requirements. Ultramicrotomy, Thin Foil and Replication techniques are routinely employed by Micron personnel. 

The joint use of a Whiter I concentrator based on multilayers to focus low energy (<40 keV) X-rays and a Bragg concentrator like HAXTEL to focus higher energy X-rays appears a possible telescope configuration that efficiently focuses X-rays in a broad energy band (from 1 keV to about 200 keV). A replication technique to fabricate multilayer mirrors is currently investigated, that would render feasible a Wolter I multilayer concentrator... 

The most widely applicable approach splits the fabrication of nanopatterned functional materials into two successive steps, namely the self-assembly driven formation of mesoporous templates and the replication of the templates with functional materials, as illustrated in Fig. 1.3. This strategy to nanostructured functional materials has the major advantage that it allows for the independent optimization of the template preparation. Since the same template can be used to structure various functional materials applying different replication techniques, such as sol-gel, atomic layer deposition (ALD), electrochemical deposition, and electroless plating, it is considered as an extremely versatile approach [14-17]. 

In FFTEM, the sample is a replica of the microstructure revealed by a fractured plane and possibly enhanced by shadowing. The contrast comes from mass-thickness variations almost exclusively, and interpretation is more straightforward. Also, there may be interfacial effects between the sample and the Pt/C coating material during sample preparation, thereby giving so-called phase detection effects [21] that permit identification of water and oil phases. However, in all replication techniques, the resolution is limited by the grain size of the replica as well as by inadvertent decoration effects that may result in loss of resolution. 

Figure 3.3. Electron micrograph (replica) of a graft-type high-impact polystyrene with polybutadiene as the rubbery component (Keskkula and Traylor, 1967). In the absence of agitation, phase inversion does not occur, and an interwoven cellular structure results, with polybutadiene remaining as the continuous phase. The specimen was prepared for electron microscopy by exposing a polished surface to isopropanol vapor, which preferentially swells the polystyrene phase a double replication technique was then used. The reader should compare the results obtained by this technique to results obtained using thin-section transmission techniques (see, for example. Figure 3.2).

Masuda et al. [109-113] developed a replication technique by which a nanohole array on alumina can be transferred on other metals. This way, it is possible to overcome some of the disadvantages presented by porous alumina (namely chemical... 

Fan et al. [114] used gold mask as achieved by replication technique from AAO template and used it to realize gold dots on GaN/Si substrate to obtain patterned ZnO nanowire array. The detailed scheme is shown in Figure 4.4. Figure 4.5 shows the obtained gold tubes and ZnO nanowires. 

Replication techniques are available for transforming complex silica shapes into the corresponding shapes of various polymers. Ihe process can also be extended in the opposite direction, by converting the silica into silicon. Specifically, a low-temperature reduction process has been developed to convert three-dimensional nanostructured silica micro-assemblies into microporous nanocrystalline silicon replicas. Such materials could be useful in a variety of applications, including sensors and biomedical devices. 

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