Scanning in transmission

1988 Lin et al. 1985 Wade and Meyyappan 1987 Wey and Kessler 1989) the insonification is broadcast throughout the specimen, and the detection is by a focused optical probe that measures local surface tilt on the surface of the specimen. But in the scanning acoustic microscope both the illumination and the detection are performed by focusing elements and, since these are focused at the same point, the configuration may be described as confocal. The first con-focal acoustic microscopes worked in transmission and, although this is now of mainly historical interest, the transmission arrangement will be described first because in some respects it is simpler and will serve to introduce some principles. 

An early high-resolution transmission scanning acoustic microscope is illustrated in Fig. 2.3. Two acoustic lenses are mounted facing each other on a common axis, and with a common focal plane. A continuous radio-frequency (r.f.) signal is fed to the transducer on one of the lenses, which converts this to 

In a conventional optical microscope, provided the lenses have been ground with spherical symmetry, the magnification is inevitably the same in both horizontal and vertical directions of the image. In a scanning microscope this 

The operation of a transmission scanning acoustic microscope requires the lenses to be set up so that they are accurately confocal. This requires holders that can be moved relative to each other along three axes, with rather fine adjustment, and that are rigid to better than a wavelength even when a specimen is vibrating between them. The separation must first be set. If ro is the radius of curvature of each lens, ciq the aperture radius, and n the refractive index, then the focal planes of the two lenses will coincide when the separation between their front surfaces is 

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Figure 16-28. Oocl-OPV5 111 its nenialic phase ai I 8) C. Left polari/ed-light optical micrograph (scale ban SO pm Zeiss pliolomieroscopc). Right X-ray dillraclioii scan (0-20 scanning in transmission mode. CuKu radiation. /.= 1.5418 A).

If, as usual, the spectra are not scanned in % transmission but in absorption, it is easy to quantitatively analyze the compound in question (absorbance concentration). If the resolution of the instrument is higher than the half-width of a recorded band, then the height of the band is proportional to the concentration of the species. 

Figure 16-28. Ooct-OPV5 in its nematic phase at 190°C. Left polarized-light optical micrograph (scale bar 50 pm Zeiss photomicroscope). Right X-ray diffraction scan (d-2d scanning in transmission mode, CuKa radiation, 2=1.5418 A).

The powder X ray diffraction patterns were scanned in transmission technique with a GO-2000 diffractometer (Ital Structures, Riva del Garda, Italy) operating in the Seemann-Bohlin geometry and equipped with a quartz-curved crystal monochromator of the Johansson type aligned on the primary beam. The Cu-K i radiation (X 1.5406 A) was employed, and an instrumental 26 step of 0.1° every 10 s was selected. 

Electron micrographs (scanning and transmission) showed that tungsten carbide is well dispersed on the surface of each support as nanosized particles (20 - 50 nm) as typified by the images in Figs. 3 (a b). However, BET surface area decreased in the order alumina > silica > titania > zirconia. With highest surface area obtained for each support being 240,133,18 and 9 m g respectively. 

Scanning and transmission electron microscopies show that CNTs were coated with a homogeneous layer of ECPs (up to 50 nm). In the case of the composites based on TEG, ECP fibers with diameters up to 1 pm are observed on the TEG particles. 

One problem with methods that produce polycrystalline or nanocrystalline material is that it is not feasible to characterize electrically dopants in such materials by the traditional four-point-probe contacts needed for Hall measurements. Other characterization methods such as optical absorption, photoluminescence (PL), Raman, X-ray and electron diffraction, X-ray rocking-curve widths to assess crystalline quality, secondary ion mass spectrometry (SIMS), scanning or transmission electron microscopy (SEM and TEM), cathodolumi-nescence (CL), and wet-chemical etching provide valuable information, but do not directly yield carrier concentrations. 

These structures were recorded by a vectorial focal spot scanning in a spiral-by-spiral method rather in a raster layer-by-layer mode using a PZT stage. Such spiral structures fabricated in SU-8 have optical spot bands in near-lR [24], telecommunication [25], and 2-5 pm-IR region [26] or can be used as templates for Si infiltration [11]. It is obvious, that direct laser scanning is well suited for defect introduction into 3D PhC, as demonstrated in resin where a missing rod of a logpUe structure resulted in the appearance of a cavity mode in an optical transmission spectriun [27]. 

The ultrasonic C-scan technique is the most widely used nondestructive method of locating defects in the composite microstructure. The through transmission C-scan is easy to implement and a large composite panel can be scanned in a matter of minutes. The problem with this technique is that a C-scan cannot reveal the type of defect present. Hence, there is no way to determine if a flaw detected by the C-scan is due to incomplete contact of an interply interface or some other type of defect in the composite microstructure. 

Fig. 2.3. One of the original scanning acoustic microscopes. It worked in transmission, so that it was not necessary to use pulsed waves, and the detected transmitted signal could be used directly to modulate the beam in a cathode ray tube. The slow scan was provided by a small motor driving a lead screw, and the fast scan by a modified loudspeaker coil (Lemons and Quate 1974,1979).

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