Microprobe mapping

Figure 6. Grayscale wavelength-dispersive electron microprobe map of arsenic distribution in a segment of a pyritized fossil fragment, LP-l core, 81.2 meters. Arsenic-rich pyrite occurs as overgrowths (bright bands) onframboids (darker spheres). Arsenic contents of the points shown are as follows I 6.6 wt. % 2 7.2 wt. % 3 6.9 wt.% 4 6.7 wt. % 5 6.8 wt. % 6 8.5 wt. % 7 2.0 wt. % 8 1.0 wt. %. Area shown is approximately 400 x 450 0.50 pm pixels.

Figure 7. Grayscale wavelength-dispersive electron microprobe map of oxygen distribution showing iron oxyhydroxide rim (bright band) on quartz, in till sample LHP 8 from oxidized zone, Huron County, MI. Arsenic contents of points shown are as follows I 1,200 ppm 2 1,300 ppm 3 3,300 ppm 4 1,400 ppm 5 2,800 ppm 6 1,000 ppm. The maximum As concentration determined for this sample is 7,300ppm. Map area is 500 x 500 0.5 pm pixels.

Sadekov, a. Y., Eggins, S. M. De Deckker, P. 2005. Characterization of Mg/Ca distributions in planktonic foraminifera species by electron microprobe mapping. Geochemistry Geophysics Geosystems, 6, Q12P06, http //dx.doi.Org/10.1029/2005 GC000973. 

Microprobe mappings and measurements of minor element concentrations were obtained at the Analytical Centre of the Mineralogical Laboratory of the Natural History Museum (London) using a CAMECA SX 50 instrument equipped with four wave-length dispersive detectors. Atomic force observations were carried out with a Dimension 3000 microscope (Digital Instrument) using the... 

Figure 6.13 Synchrotron radiation microprobe mapping of potassium and chromium oxidation states in a single human epithelial cell exposed to particulate chromate, and corresponding optical microscopy view. Beam spatial resolution (VxH) 0.5x1 pm, color scale in counts per pixel. Cr(VI) distribution shows a perinuclear localization. 2005 American Chemical Society.

Electron Probe Microanalysis, EPMA, as performed in an electron microprobe combines EDS and WDX to give quantitative compositional analysis in the reflection mode from solid surfaces together with the morphological imaging of SEM. The spatial resolution is restricted by the interaction volume below the surface, varying from about 0.2 pm to 5 pm. Flat samples are needed for the best quantitative accuracy. Compositional mapping over a 100 x 100 micron area can be done in 15 minutes for major components Z> 11), several hours for minor components, and about 10 hours for trace elements. 

With a special optical system at the sample chamber, combined with an imagir system at the detector end, it is possible to construct two-dimensional images of the sample displayed in the emission of a selected Raman line. By imaging from their characteristic Raman lines, it is possible to map individual phases in the multiphase sample however, Raman images, unlike SEM and electron microprobe images, have not proved sufficiently useful to justify the substantial cost of imaging optical systems. 

In the scanning (or microprobe) mode the image is measured sequentially point-bypoint. Because the lateral resolution of the element mapping in scanning SIMS is dependent solely on the primary beam diameter, LMISs are usually used. Beam diameters down to 50 nm with high currents of 1 nA can be reached. 

Recently, scanning Kelvin probes and microprobes, as high-resolution surface analysis devices, have been developed. They allow one to investigate the lateral distribution of the work functions of the surfaces of various phases, including the determination of the potential profiles of metals and semiconductors under very thin films of electrolytic solution, and also of the surface potential map of various polymer- and biomembranes [50-56], The lateral resolution and the sensitivity are in the 100 nm and ImV ranges, respectively [54],... 

Inorganic Compounds. The Raman microprobe has been used by Berg and Kerridge (2000) to obtain computer mappings of the structures of salt eutectics solidified from their melts. In contrast to metallic eutectics, which commonly occur... 

Modern spectrometers only require electron beam currents in the range 0.1 lOnA and hence probe sizes of 20-200 nm may be readily achieved with thermionic sources and 5-15 nm with a FEG. Spatially resolved compositional information on heterogeneous samples may be obtained by means of the Scanning Auger Microprobe (SAM), which provides compositional maps of a surface by forming an image from the Auger electrons emitted by a particular element. 

It is possible to measure nearly any type of sample for almost any element with little or no preparation. Only a few mg of sample is required, and the measurements are non-destructive in that the sample is generally undamaged. Measurements take only 1-20 min of beam time. Elemental mapping showing the variations in elemental concentrations can be measured over the surface of a sample using the ion microprobe for an area as large as 5 x 5 mm. 

Four samples were similarly selected for the EPMA experiments. The samples were dried and embedded in polished epoxy cylindrical plugs. Backscattered electron (BSE) images as well as elemental maps of As, Fe and Ni (EDS/WDS) were collected using a JEOL 8600 Superprobe electron microprobe analyzer (Dept, of Geological Sciences, University of Saskatchewan). 

Elemental maps obtained using an ion microprobe will be highly surface specific as in SAM. However, since ion sputtering is destructive, repeated scans over the field of particles will penetrate deeper and deeper into the particle interiors. McHugh and Stevens have demonstrated the utility of IMP elemental maps in the identification and chemical characterization of oil soot particles in the atmosphere (38). 

Electron microprobes can be used in spot mode to measure the chemical compositions of individual minerals. Mineral grains with diameters down to a few microns are routinely measured. The chemical composition of the sample is determined by comparing the measured X-ray intensities with those from standards of known composition. Sample counts must be corrected for matrix effects (absorption and fluorescence). The spatial resolution of the electron microprobe is governed by the interaction volume between the electron beam and the sample (Fig. A.l). An electron probe can also be operated in scanning mode to make X-ray maps of a sample. You will often see false-color images of a sample where three elements are plotted in different colors. Such maps allow rapid identification of specific minerals. EMP analysis has become the standard tool for characterizing the minerals in meteorites and lunar samples. 

Raman Spectroscopy Detecting forged medieval manuscripts (Anal. Chem. 2002, 74, 3658-3661. "Analysis of Pigmentary Materials on the Vinland Map and Tartar Relation by Raman Microprobe Spectroscopy")... 

The utility of ANNs as a pattern recognition technique in the field of microbeam analysis was demonstrated by Ro and Linton [99]. Back-propagation neural networks were applied to laser microprobe mass spectra (LAMMS) to determine interparticle variations in molecular components. Selforganizing feature maps (Kohonen neural networks) were employed to extract information on molecular distributions within environmental microparticles imaged in cross-section using SIMS. 

An advantage of the scanning Auger microprobe (SAM) is that it can scan a surface and provide a map of each element in question. As such, these results are similar to an electron microprobe except the SAM is much more surface sensitive. 

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