Instrumentation microscope

Isothermal examination can be more easily carried out at room temperature. However, special instruments (microscopes, diffractometers, etc.) and techniques can be used for high- (or low-) temperature work. 

Fig. 2.47 The scientific payioad of the Mars Expioration Rovers consists of the remote sensing Panoramic Camera (Pancam) and the Miniature Thermai Emission Spectrometer Mini-TES) the in situ or contact instruments Microscopic Imager (Ml), Alpha Particle X-ray Spectrometer (APXS), Mossbauer spectrometer (MB), and the Rock Abrasion Tool (RAT) the Magnetic Properties Experiment (NASA/JPL/Comeii) [77]...

Rank Brothers Mark II instrument was used fitted with a rectangular cell which was thermostatted at 27 0.5 C. The instruments microscope was used to determine the cell depth and its thickness. The stationary levels were determined (j.Chem.Tech. Biotechnol. 57(1993)97). See also J.Colloid Interface 5cf.65( 1978)548. Fig.A9.1 shows the results for some prepared titanias, the details of their preparation and their reflectance spectra are found in Solar 36(1986)168. 

This text covers quantitative analysis by electron energy-loss spectroscopy in the electron microscope along with instrumentation and applicable electron-scattering theory. 

The field of corrected microscopes has just begun with the instruments discussed above. The progress in this field is very rapid and proposals for a sub-Angstrom TEM (SATEM) or even the combination of this instrument with a corrected energy filter to fonn a sub-electronvolt/sub-Angstrom TEM (SESAM) are underway. 

Detection of cantilever displacement is another important issue in force microscope design. The first AFM instrument used an STM to monitor the movement of the cantilever—an extremely sensitive method. STM detection suffers from the disadvantage, however, that tip or cantilever contamination can affect the instrument s sensitivity, and that the topography of the cantilever may be incorporated into the data. The most coimnon methods in use today are optical, and are based either on the deflection of a laser beam [80], which has been bounced off the rear of the cantilever onto a position-sensitive detector (figme B 1.19.18), or on an interferometric principle [81]. 

Several devices are available commercially to measure mobihty. One of these (Zeta-Meter Inc., New York) allows direct microscopic measurement of individual particles. Another allows measurement in more concentrated suspensions (Numinco Instrument Corp., Monroeville, Pa.). The state of the charge can also be measured by a streaming-current detecdor (Waters Associates, Inc., Framingham, Mass.). For macromolecules, more elaborate devices such as the Tisehus moving-boundaiy apparatus are used. 

Austenitic steels have a number of advantages over their ferritic cousins. They are tougher and more ductile. They can be formed more easily by stretching or deep drawing. Because diffusion is slower in f.c.c. iron than in b.c.c. iron, they have better creep properties. And they are non-magnetic, which makes them ideal for instruments like electron microscopes and mass spectrometers. But one drawback is that austenitic steels work harden very rapidly, which makes them rather difficult to machine. 

Figure 1 illustrates a typical, good quality, analytical polarizing microscope. Polarizing microscopes are extraordinarily versatile instruments that enable the trained microscopist to characterize materials rapidly and accurately. 

The classical polarizing light microscope as developed 150 years ago is still the most versatile, least expensive analytical instrument in the hands of an experienced microscopist. Its limitations in terms of resolving power, depth of field, and contrast have been reduced in the last decade, in which we have witnessed a revolution in its evolution. Video microscopy has increased contrast electronically, and thereby revealed structures never before seen. With computer enhancement, unheard of resolutions are possible. There are daily developments in the X-ray, holographic, acoustic, confocal laser scanning, and scanning tunneling micro-... 

The general utility of the light microscope is also recognized by its incorporation into so many other kinds of analytical instrumentation. Continued development of new composites and materials, together with continued trends in microminiaturization make the simple, classical polarized-light microscope the instrument of choice for any initial analytical duty. 

Traditionally, the first instrument that would come to mind for small scale materials characterization would be the optical microscope. The optical microscope offered the scientist a first look at most samples and could be used to routinely document the progress of an investigation. As the sophistication of investigations increased, the optical microscope often has been replaced by instrumentation having superior spatial resolution or depth of focus. However, its use has continued because of the ubiquitous availability of the tool. 

For the purpose of a detailed materials characterization, the optical microscope has been supplanted by two more potent instruments the Transmission Electron Microscope (TEM) and the Scanning Electron Microscope (SEM). Because of its reasonable cost and the wide range of information that it provides in a timely manner, the SEM often replaces the optical microscope as the preferred starting tool for materials studies. 

Computers will be integrated more and more into commercial SEMs and there is an enormous potential for the growth of computer supported applications. At the same time, related instruments will be developed and extended, such as the scanning ion microscope, which uses liquid-metal ion sources to produce finely focused ion beams that can produce SEs and secondary ions for image generation. The contrast mechanisms that are exhibited in these instruments can provide new insights into materials analysis. 

STM and SFM belong to an expanding family of instruments commonly termed Scanning Probe Microscopes (SPMs). Other common members include the magnetic force microscope, the scanning capacitance microscope, and the scanning acoustic microscope. ... 

SPMs are simpler to operate than electron microscopes. Because the instruments can operate under ambient conditions, the set-up time can be a matter of minutes. Sample preparation is minimal. SFM does not require a conducting path, so samples can be mounted with double-stick tape. STM can use a sample holder with conducting clips, similar to that used for SEM. An image can be acquired in less than a minute in fact, movies of ten fiames per second have been demonstrated. ... 

The three-dimensional, digital nature of SFM and STM data makes the instruments excellent high-resolution profilometers. Like traditional stylus or optical profilometers, scanning probe microscopes provide reliable height information. However, traditional profilometers scan in one dimension only and cannot match SPM s height and lateral resolution. 

With modern detectors and electronics most Enei -Dispersive X-Ray Spectroscopy (EDS) systems can detect X rays from all the elements in the periodic table above beryllium, Z= 4, if present in sufficient quantity. The minimum detection limit (MDL) for elements with atomic numbers greater than Z = 11 is as low as 0.02% wt., if the peaks are isolated and the spectrum has a total of at least 2.5 X 10 counts. In practice, however, with EDS on an electron microscope, the MDL is about 0.1% wt. because of a high background count and broad peaks. Under conditions in which the peaks are severely overlapped, the MDL may be only 1—2% wt. For elements with Z < 10, the MDL is usually around 1—2% wt. under the best conditions, especially in electron-beam instruments. 

Historically, EELS is one of the oldest spectroscopic techniques based ancillary to the transmission electron microscope. In the early 1940s the principle of atomic level excitation for light element detection capability was demonstrated by using EELS to measure C, N, and O. Unfortunately, at that time the instruments were limited by detection capabilities (film) and extremely poor vacuum levels, which caused severe contamination of the specimens. Twenty-five years later the experimental technique was revived with the advent of modern instrumentation. The basis for quantification and its development as an analytical tool followed in the mid 1970s. Recent reviews can be found in the works by Joy, Maher and Silcox " Colliex and the excellent books by Raether and Egerton. ... 

R. F. Egerton. Electron Energy Loss Spectrometry in the Electron Microscope. Plenum Press, 1986. This is a comprehensive text on the use of EELS in the TEM. It covers instrumentation, theory and practical applications. 

Cathodoluminescence (CL), i.e., the emission of light as the result of electron-beam bombardment, was first reported in the middle of the nineteenth century in experiments in evacuated glass tubes. The tubes were found to emit light when an electron beam (cathode ray) struck the glass, and subsequendy this phenomenon led to the discovery of the electron. Currendy, cathodoluminescence is widely used in cathode-ray tube-based (CRT) instruments (e.g., oscilloscopes, television and computer terminals) and in electron microscope fluorescent screens. With the developments of electron microscopy techniques (see the articles on SEM, STEM and TEM) in the last several decades, CL microscopy and spectroscopy have emerged as powerfirl tools for the microcharacterization of the electronic propenies of luminescent materials, attaining spatial resolutions on the order of 1 pm and less. Major applications of CL analysis techniques include ... 

Optical CL microscopes are instruments that couple electron gun attachments to optical microscopes. Although such systems have a limited spatial resolution, they are used widely in the analysis of minerals. ... 

The development of the STEM is relatively recent compared to the TEM and the SEM. Attempts were made to build a STEM instrument within 15 years after the invention of the electron microscope in 1932. However the modern STEM, which had to await the development of modern electronics and vacuum techniques, was developed by Albert Crewe and his coworkers at the University of Chicago. ... 

The major STEM analysis modes are the imaging, diffraction, and microanalysis modes described above. Indeed, this instrument may be considered a miniature analytical chemistry laboratory inside an electron microscope. Specimens of unknown crystal structure and composition usually require a combination of two or more analysis modes for complete identification. 

In addition to cleanliness (contamination effects), surface morpholt and the alteration of composition during specimen preparation can cause serious artifacts in microanalysis. In some older instruments, the microscope itself produces undesirable high-energy X rays that excite the entire specimen, making difficult the accurate quantitation of locally changing composition. Artifacts also are observed in the EDS X-ray spectrum itself (see the article on EDS). 

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