Microscope/microprobe

Figure 12 Schematic of (A) compound optical and (B) combined scanning electron microscope-microprobe analyzer. (From Ref. 82, with permission of VCH Publishers, Inc.)...

In the hamster, multiple short-term intratracheal instillations of zirconium lactate produced lesions beginning with exudative pneumonia followed by pneumonitis (interstitial pneumonia) and foreign body granulomas. Electron microscope microprobe analysis demonstrated the metallic component of the instilled compound in membrane-bound cytoplasmic inclusions of macrophages (Leininger et al. 1977). 

A principal advantage of the Raman microprobe is that the optics are those of a conventional light microscope a wide variety of special-purpose objectives developed for materials and biological microscopy are available. The Raman microprobe also offers the advantage of fluorescence reduction owing to the high spatial resolution of the microscope if a region of low fluorescence can be chosen for observation. 

The spatial resolution of the Raman microprobe is about an order of magnitude better than that obtainable using an infrared microscope. Measurement times, typically of a few seconds, are the same as for other Raman spectrographs. To avoid burning samples, low (5—50-mW) power lasers are employed. 

Laser Raman Microprobe. A more sophisticated microscope is the Laser Raman Microprobe, sometimes referred to as MOLE (the molecular orbital laser examiner). This instmment is designed around a light microscope to yield a Raman spectmm (45) on selected areas or particles, often <1 ia volume. The data are related, at least distantly, to iafrared absorption, siace the difference between the frequency of the exciting laser and the observed Raman frequency is the frequency of one of the IR absorption peaks. Both, however, result from rotational and vibrational states. Unfortunately, strong IR absorption bands are weak Raman scatterers and vice versa hence there is no exact correspondence between the two. 

Sample preparation is straightforward for a scattering process such as Raman spectroscopy. Sample containers can be of glass or quartz, which are weak Raman scatterers, and aqueous solutions pose no problems. Raman microprobes have a spatial resolution of - 1 //m, much better than the diffraction limit imposed on ir microscopes (213). Eiber-optic probes can be used in process monitoring (214). 

Infrared microscopes can focus the beam down to a 20-pm spot size for microprobing in either the transmission or reflection mode. Trace analysis, microparticle analysis, and spatial profiling can be performed routinely. 

Scanning Auger Electron Spectroscopy (SAM) and SIMS (in microprobe or microscope modes). SAM is the most widespread technique, but generally is considered to be of lesser sensitivity than SIMS, at least for spatial resolutions (defined by primary beam diameter d) of approximately 0.1 im. However, with a field emission electron source, SAM can achieve sensitivities tanging from 0.3% at. to 3% at. for Pranging from 1000 A to 300 A, respectively, which is competitive with the best ion microprobes. Even with competitive sensitivity, though, SAM can be very problematic for insulators and electron-sensitive materials. 

Gray, H. R., Ion and Laser Microprobes Applied to the Measurement of Corrosion-Produced Hydrogen on a Microscopic Scale , Corrosion, 28, 47 (1972)... 

The apparatus has also been made into an x-ray emission electron-microprobe (9.9) by replacing the target with a transparent section of a rock or mineral sample. The spot being excited could be located easily by viewing it through the sample with an optical microscope. 

The fine-focus electron optical system of the General Electric X-ray Microscope has been used as the basis for an x-ray emission electron-microprobe.9 10... 

Microprobe, electron-, x-ray emission, 261-265, 292, 294, 295 Microscope, X-ray, General Electric, 294-296... 

Other instruments which have been devised for microstructure examination include the X-ray microscope, with greater resolving power than the EM (Ref 41), and the electron microprobe, capable of indicating subtle changes in composition over small specimen areas (Refs 57 62)... 

The characteristic feature of solid—solid reactions which controls, to some extent, the methods which can be applied to the investigation of their kinetics, is that the continuation of product formation requires the transportation of one or both reactants to a zone of interaction, perhaps through a coherent barrier layer of the product phase or as a monomolec-ular layer across surfaces. Since diffusion at phase boundaries may occur at temperatures appreciably below those required for bulk diffusion, the initial step in product formation may be rapidly completed on the attainment of reaction temperature. In such systems, there is no initial delay during nucleation and the initial processes, perhaps involving monomolec-ular films, are not readily identified. The subsequent growth of the product phase, the main reaction, is thereafter controlled by the diffusion of one or more species through the barrier layer. Microscopic observation is of little value where the phases present cannot be unambiguously identified and X-ray diffraction techniques are more fruitful. More recently, the considerable potential of electron microprobe analyses has been developed and exploited. 

An accurate determination of critical load Wcr is sometimes difficult. Several techniques, such as (1) microscopic observation (optical or SEM) during the test, (2) chemical analysis of the bottom of the scratch channel (with electron microprobes), and (3) acoustic emission, have been used to obtain the critical load. 

Microprobe analysis was initially developed at the University of Paris by R. Castaing, who fitted an X-ray spectrometer to a converted electron microscope in the early 1950s, and the first commercial instrument, developed in France by the Cameca company, appeared in 1958. The following years saw commercial instruments produced in the UK, USA and Japan. 

Figure 3. Starting with the binocular microscope, discriminatory power increases in a counterclockwise direction, as indicated by the circular background. Variations in flowline width reflect the differential sampling capabilities of the techniques. Special petrological techniques include X-ray diffraction, electron and proton microprobe, staining, and heavy mineral separation.

Aircraft turbines in jet engines are usually fabricated from nickel-based alloys, and these are subject to combustion products containing compounds of sulphur, such as S02, and oxides of vanadium. Early studies of the corrosion of pure nickel by a 1 1 mixture of S02 and 02 showed that the rate of attack increased substantially between 922 K and 961 K. The nickel-sulphur phase diagram shows that a eutectic is formed at 910 K, and hence a liquid phase could play a significant role in the process. Microscopic observation of corroded samples showed islands of a separate phase in the nickel oxide formed by oxidation, which were concentrated near the nickel/oxide interface. The islands were shown by electron microprobe analysis to contain between 30 and 40 atom per cent of sulphur, hence suggesting the composition Ni3S2 when the composition of the corroding gas was varied between S02 02 equal to 12 1 to 1 9. The rate of corrosion decreased at temperatures above 922 K. 

As indicated in Fig. 7.2, X-rays are among the by-products in an electron microscope. Already at the beginning of this century, people knew that matter emits X-rays when it is bombarded with electrons. The explanation of the phenomenon came with the development of quantum mechanics. Nowadays, it is the basis for determining composition on the submicron scale and, with still increasing spatial resolution, is used in the technique referred to as Electron Microprobe Analysis (EMA), Electron Probe Microanalysis (EPMA) or Energy Dispersive Analysis of X-rays (EDAX, EDX) [21]. 

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