High resolution SEM

The HRSEM is very often operated at low beam voltage, and the technique may be specifically referred to as high resolution low voltage SEM. As discussed in the previous section, the 

Theoretical prediction of the exact resolution achieved in the HRSEM is difficult. The thicker 

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Figure 2 Micrographs of the same region of a specimen in various imaging modes on a high-resolution SEM (a) and (b) SE micrographs taken at 25 and 5 keV, respectively (c) backscattered image taken at 25 keV (d) EDS spectrum taken from the Pb-rich phase of the Pb-Sn solder (e) and (f) elemental maps of the two elements taken by accepting only signals from the appropriate spectral energy regions.

Figure 5. High-resolution SEM images of the Si surface covalently linked to the nanoparticles stabilized by (A) C3, (B) C6, and (C) Cll. (Reprinted with permission from Ref [11a], 2004, American Chemical Society.)...

SEM Utilizes a focused electron beam that systematically scans across the surface of a sample. It can be used to characterize the surface topography of bulk powders or pellets. Early SEM developments have been described by Von Ardenne (1938) and by Smith et al (1977). The principal high-resolution SEM imaging method is surface sensitive with an escape depth lO nm and sensitive to or... 

High resolution SEM images of the freeze-fractured cross section of the RH-cycled samples were obtained. Many craze-like defects were observed on the cross section of samples that had been cycled from 80 to 120% RH, as shown in Fig. 16. In comparison,... 

Figure 12.10 shows a high resolution SEM micrograph of an about 5 pm thick layer of Al on gold substrate electrodeposited potentiostatically at 100 °C at —0.45 V (vs. Al) for 2 h in the upper phase ofthe mixture [Pyi JTFSA/l.O M AICI3. Generally, the electrodeposited layer contains very fine crystallites in the nanometer regime. 

The non-diamond carbon phase in polycrystalline diamond films (often referred to as graphite, although this conclusion is far from accurate [23]) is first and foremost the disordered carbon in the intercrystallite boundaries. Their exposure to the film surface can be visualized by using a high-resolution SEM techniques [24] the intercrystallite boundaries thickness comes to a few nanometers. In addition to the intercrystallite boundaries, various defects in the diamond crystal lattice contribute to the non-diamond carbon phase, not to mention a thin (a few nanometers in thickness) amorphous carbon layer on top of diamond. This layer would form during the latest, poorly controlled stage of the diamond deposition process, when the gas phase activation has ceased. The non-diamond layer affects the diamond surface conduc-... 

Figure 7. High-resolution SEM images of the activated fused iron catalyst for ammonia synthesis. The anisotropic meso-structure and the high internal surface area are visible. The small probe size of a 200keV electron beam in a JEOL CX 200 instrument was used for backscattering detection of the scanning image from very thin objects.

The resolution of SEMs is now suitable for nano-materials characterization. High resolution SEM is a powerful instrument for imaging fine structures of materials and nanoparticles fabricated by nanotechnology. In lens SE, BSE modes, and STEM mode are often performed to check the structure of CNT growths or CNT as delivered by commercial producers, and sometimes coupled with TEM. Even the single-walled carbon nanotubes can easily be observed by HR-SEM (see Figure 3.13). The STEM mode can also be used for free CNT observation (75). 

Some loss in resolution is apparent due largely to the conductive layer of gold used in the preparation of the cells for SEM. In conjunction with high resolution SEM, latex markers In this size range can be used to obtain information about the topographical distribution and mobility of specific cell surface components. 

FIGURE 17.33 Effect of electron beam exposition time on the low dielectric. The left picture is taken after 2 s of electron bombardment (minimum time to make acceptable focus). The right picture presents the same structure as on the left after 8 s of electron bombardment. The dielectric material has visibly shrunk. Note that these are low-resolution SEM images because the acquisition time of a high-resolution SEM image takes longer than 8 s. 

The high-resolution SEM image was reproduced with permission from Moon, J. -M. Wei, A. J. Phys. Chem. B 2005,109, 23336. Copyright 2005 American Chemical Society, http //w w w. microstartech.com/index/cryo.htm... 

It is therefore highly desirable to develop more quantitative methods for characterization of pore structures. The results of recent investigations, including ultrafiltration (water flux and rejection of a polydisperse solute), high-resolution SEM and nitrogen sorption/desorption analysis, are described below. 

Figures 7.6a and b show high resolution SEM images of the Co-Zr-Nb SUL surface without any treatment and that treated with PdCl solution, respectively. An island-like stmcture with the mean diameter of ca. 9 nm was formed on the SUL with a high density, where the mean distance between adjacent clusters was ca. 18 nm. From X-ray photospectroscopy and diffractometry, the island-like structure was identified as the Pd metal with fee stmcture [30], which is hereafter called Pd cluster seeds .

Fig. 60 High-resolution SEM top view image of a mesoporous Ti02 film following calcination at 400 °C. The pore diameter in the plane of the film is 10nm. (Reprinted with permission from [70], 2003, American Institute of Physics)...

Fig. 15 High resolution SEM image of the lamellar PS- -P2VP/CdSe nanoparticle composite thin film after annealing in CHCI3 for 1 day, without staining. The image is taken at 1 kV acceleration voltage. Reprinted with permission from Advanced Materials [86]. Copyright (2007) Wiley-VCH...

Figure 2. High resolution SEM images of the surface of as milled (top) and chemically etched (bottom) PdaGa (left) and PdGa (right).

Figure 6.2-22 shows a high-resolution SEM picture of an electrodeposited silicon layer on a gold substrate. As can be seen, the deposit contains small crystallites with sizes between 50 and 200 nm. The deposit can keep its dark appearance even under air. The EDX analysis showed only gold from the substrate and silicon, but no detectable chlorine. This proves that elemental silicon was electrodeposited. 

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