Surface analysis electron probe microanalysis

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. 

Although conventional electron-probe microanalysis appears to be unsuitable for analysis of the exposed surface layer of atoms in an alloy catalyst, recent developments have shown that X-ray emission analysis can still be used for this purpose (89, 90). By bombarding the surface with high energy electrons at grazing incidence, characteristic Ka radiation from monolayer quantities of both carbon and oxygen on an iron surface was observed. Simultaneously, information about the structure of the surface layer was obtained from the electron diffraction pattern. 

Electron probe microanalysis functions by direct examination of the primary X-rays produced when the specimen is used as a target for an electron beam. Focused electron beams allow a spot analysis of a 1 pm3 section of the specimen. One current development employs the electron beam within a scanning electron microscope to provide both a visual picture of the surface of the sample and an elemental analysis of the section being viewed. Spectra obtained from primary X-rays always have the characteristic emission peaks superimposed on a continuum of background radiation (Figure 8.32). This feature limits the precision, sensitivity and resolution of electron probe microanalysis. 

To understand the wear mechanism in valve train wear tests, samples of the worn tappet surface were analyzed for surface elements by electron probe microanalysis (EPMA) and X-ray photo electron spectroscopy (XPS). Results of EPMA analysis of the worn surface in terms of concentration of phosphorus and sulfur atoms for oil with primary ZnDDP without MoDTC, showed an increase of zinc and sulfur intensity after 100 hrs of test time, in spite of decreasing phosphorus intensity. Examination of the worn surface by XPS with primary and secondary ZDDP with addition of MoDTC showed the presence of MoS2 in the tribofilm. Using mixtures of ZDDP and MoDTC, the friction coefficient is reduced, and wear is comparable to that of using ZDDP alone (Kasrai et ah, 1997). 

To find out the phase composition of the intermetallic compound layers formed, X-ray patterns were taken immediately from the polished surfaces of the Ni-Zn and Co-Zn cross-sections. Annealing and subsequent cooling the specimens of the type shown in Fig. 3.12b in most cases resulted in their rupture along the interface between the zinc phase and the intermetallic layers, with the latter remaining strongly adherent to nickel or cobalt plates. Therefore, preparation of the cross-sections for X-ray analysis presented no difficulties. These could readily made by successive grinding and polishing the plate surface until the Ni or Co phase was reached. In total, four layer sections parallel to the initial interface were analysed for each cross-section. Simultaneously, layer composition on each section of the interaction zone was determined by electron probe microanalysis. 

Electron microprobes permit chemical microanalysis as well as SEM and BSE detection, often referred to as analytical electron microscopy (AEM), or electron probe microanalysis (EPMA)56 57. This is because another product of the surface interaction with an incident electron beam is X-ray photons which have wavelengths and energies dependent on element identity and on the electron shell causing the emission. Analysis of these photons can give a local chemical analysis of the surface. Resolution of 1 pm is attainable. Two types of X-ray spectrometer can be employed ... 

Sample preparation for electron probe microanalysis (EPMA) requires sample chips or friable material to be impregnated in an epoxy resin. Sample surfaces are polished using progressively finer grades of diamond paste, with samples mounted onto aluminium stubs and coated with carbon prior to analysis. Samples should be clean, flat polished (2.5 cm diameter,... 

Electron probe microanalysis [18] is used for quantitative analysis of small volumes (pm ) of solid surfaces. The technique is most valuable for studying... 

During a considerable long period, the gaseous chemisorption method is the sole one to probe the surface species of solid catalysts. Some of the modern techniques for surface measuring are Measurements of effusion works, Auger electron spectroscopy (AES), Electron spectroscopy of chemical analysis (ESC A), X-ray photoelectron spectroscopy (XPS), Electron probe microanalysis (EPMA), Ion probe microanalysis (IPM), Ion scattering spectroscopy (ISS), Second ion mass spectroscopy (SIMS), Low energy electron diffraction (LEED), Vibration spectrum and Mossbauer spectroscopy etc. All these techniques provide favorable conditions for the surface research indepth. 

Electron probe microanalysis is used for characterising surface morphology and for microanalysis of inhomogeneous samples and small volumes. Bet-zold [136] has discussed the use of EPMA for the determination of plastics, fillers, reinforcing materials, pigments, stabilisers, etc. X-ray microanalysis (Br, Mo, Sb, Ti) has been used for determining flame retardant content in ABS granules before and after extraction [265]. Also EPMA analysis of automobile paint was described [158]. EPMA of a film surface of stored PE/4,4 -thiobis(3-methyl-6-r-butylphenol) has revealed that only material within exuded, crystalline platelets contained sulfur [266]. 

The localization of structural features in the electron probe is aided by scanning techniques " that produce electron microprobe images of small sectors of the sample surface. It is also possible to obtain scanning images of element distribution. The most attractive feature of electron probe microanalysis is the fact that a quantitative analysis is possible, with errors of less than 3 % relative in most cases. Data evaluation requires the use of a computer, but the... 

Due to their importance in commercial A1 alloys, there have been renewed interests on the phase equilibria of A1 comer. [1987Gril] and [1987Ste] studied the phase equilibria of A1 comer, using alloys up to 14 at.% Si and 35 at.% Fe, by means of thermal analysis, X-ray diffraction and electron probe microanalysis techniques. They reported a partial liquidus surface, and partial isothermal sections at 570 and 600°C. However,... 

The powders of zeolites of various trademarks are used to produce petroleum-refining catalysts. In this connection, it is very important to have complete information concerning not only chemical composition and distribution of impurity elements, but also shape, surface, stmcture and sizes of particles. It allows a more detailed analysis of the physical-chemical characteristics of catalysts, affecting their activity at different stages of technological process. One prospective for solving these tasks is X-ray microanalysis with an electron probe (EPMA). 

X-ray microanalysis techniques— in particular, electron probe x-ray microanalysis (EPXMA or EPMA) and SEM coupled with energy dispersive spectrometers (EDS, EDX) are, by far, one of the surface analysis techniques most extensively used in the field of art and art conservation, and they have actually become routine methods of analyzing art and archaeological objects and monitoring conservation treatments [34, 61, 63]. 

---