Of the different aspects of electron probe microanalysis(EPMA)which were studied by Castaing during his doctorate the work on characteristic x-ray fluorescence was the most definitive. In his thesis, which was completed in 1951, Castaing established the physical and mathematical framework for a correction procedure for fluorescence which is essentially still used in EPMA today. Much of the effort since then has been in refining and improving the accuracy of the correction and extending the scope of the correction to a wider range of specimen types. The Castaing formula was developed for the case of a K x-ray from element A being excited by a K xray from element B (K-K fluorescence) and in 1965 Reed extended the range of the correction by including the K-L, L-L and L-K interactions. In the same paper Reed also introduced the expression from Green and Cosslett for the calculation of K intensities, which was believed to be more accurate than the expression used by Castaing. The original formula included a somewhat unrealistic exponential term to allow for the depth of the production of the primary x-rays and a number of workers have tried replacing this term with a more accurate expression, however, in general this has led to only small changes in the final correction. Reed also simplified the formula in order to make the calculation easier in the days before fast computers; in particular he replaced the jump ratio variable by two constants, one for the K-shell and one for the L-shell. Much later Heinrich showed that this simplification was no longer necessary and that the jump ratio could in fact be calculated directly.

The development of quantitative X-ray microanalysis in the 1950s spurred the need for knowledge of the many parameters which describe the electron interaction, such as the ionization cross-sections, fluorescent yields, the electron stopping power, mass absorption coefficients, and others. Although classical microanalysis, which proceeds by measurements of the unknown specimen against a standard, can eliminate the need to know many of these parameters accurately, much current microanalysis is done on highly inhomogeneous samples for which comparison with a standard is much less useful procedure. The increased use of low beam energies also means that data is now required for L-, and M-lines which previously have been little used. Consequently there is an enhanced need for a reliable and agreed set of data on which to base calculations.

A common misconception is the belief that all of the quantities that are needed must already have been measured by somebody and so it is simply a matter of accessing this data.

Quantitative analysis with the electron microprobe analyzer (EMPA) has yielded more accurate results over time as a result of improvements in ZAF and other correction routines, mass absorption coefficients, synthetic pseudocrystals for ultralight elements, computers, software programs, backscattered electron (BSE) and energy dispersive (EDS) X-ray detectors. Consequently, many geoscientists view EMPA as routine, and details of procedures, standards, and operating conditions are seldom provided in current publications. However, in overseeing a facility with many users, we have learned that acceptable analytical data are sometimes difficult to obtain even with established analytical procedures and a choice of several hundred standards. After novice users have mastered the routines of sample polishing, cleaning, coating, handling and machine focus, their choice of nonoptimal standards often prevents them from obtaining the most accurate results possible. Optimal analysis for geological problems requires choosing appropriate standards, selection of optimal operating conditions, as well as consideration of the possibility of omitted elements, peak and background overlaps, matrix absorption effects, beam damage and elemental migration, reintegration of heterogeneous materials, fluorescence effects, and variations in the oxidation state of iron.

The purpose of this paper is to present a few examples of art objects that have been analyzed with the electron microprobe over the past 40 years at the Boston Museum of Fine Arts. The results of many examinations have led to the fact that the object was a forgery. However, the results of most examinations have proved that the object has the necessary structure and chemistry to be authentic. It should be pointed out, that an object can be proved to be a forgery. But you cannot prove authenticity. The materials used for the object may not fit the time frame for the period, therefore a forgery, or the materials may fit the time period, the structure and style may fit the work of a particular artist or craftsman and still be a copy.

In the early 1960’s a 15th century painting, a Portrait of a Lady, see FIG. 1, was brought to the laboratory at the Boston Museum of Fine Arts for examination.

Castaing first presented his idea to use secondary X-rays excited by a focused electron beam from a polished solid sample for microanalysis in 1949 at the First European Regional Conference on Electron Microscopy in Delft, Netherlands. As part of his dissertation, he then not only built the first electron probe microanalyzer (EPM), but also established many of the theoretical and analytical principles of the technique. This technique offered enormous analytical advantages to earth scientists over other analytical methods available at the time. For example, it allows qualitative and quantitative analysis of individual mineral grains a few microns in diameter; mineral grains can be viewed during analysis, thus ensuring accurate correlation between composition and grain morphology; for most purposes, the method is non-destructive; in situ analysis of minerals in polished thin sections results in retention of textural relationships among coexisting minerals; because of the small excitation volume, the technique is ideally suited for the study of zoned minerals, minute inclusions, exsolution lamellae, etc.; and once suitable standards are prepared and correction procedures are established, a large number of quantitative analyses can be obtained in a comparatively short time.

The matrix of bio-organic samples is composed primarily of carbon, hydrogen, oxygen and nitrogen. Dispersed within this matrix there is a wide spectrum of other elements whose local concentration can be measured in situ by x-ray spectroscopy. The analysis continues to present a challenge because most samples are highly hydrated, beam sensitive and of low density. In light of these restrictions there is only one sensible approach to the use of an analytical procedure which depends on the intereaction of high energy beam electrons with a labile specimen. Samples must be prepared by the least invasive preparative procedure and irradiated with the minimum amount of energy in order to obtain the maximun amount of chemical information. Low temperature sample preparation and low voltage electron beam instruments are central to these processes. By way of example, a brief description will be given of an on-going biological investigation which makes full use of these processes.

Electron probe microanalysis (EPMA) is being utilized to characterize the composition of superconductors in the Bi-Sr-Ca-Cu-O system (BSCCO) that are doped with minor amounts of transition metal s. Specifically, the Fe Group (Fe, Ru, Os), the Co Group (Co, Rh, Ir), the Ni Group (Ni, Pd, Pt), the Zn Group (Zn, Cd, Hg), and the other elements in the Cu Group (Ag, Au) can be used as dopants. These first long period ions in their common valence states have similar ionic radii, so only small lattice distortions are expected when other first period ions are substituted for Cu. Our research involves the systematic study of the effect of transition metal substitutions (for Cu) on the properties of the two high temperature superconductors, Bi2Sr2CaCu2O8+δ (2212) and Bi2Sr2Ca2Cu3O10+δ (2223).

Substitution for Cu with transition metal ions enables one to see what effect the changing d and s character of the ions have on the superconducting properties of these compounds.

Quantitative X-Ray microanalysis is a well established technique for the chemical analysis of homogeneous materials having a flat surface. Precision better than 2% can be routinely obtained if the analysis is performed used the so called ZAF where standards of known composition must be used for all the elements presents in the system under analysis. However, real materials have generally different phases and their composition in a specific phase is not necessary homogeneous. Also, real materials may have surfaces that are not flat and where it is inappropriate to polish them, like a fractured or a corroded surface. It is therefore of paramount importance to develop quantitative schemes for such materials. The first step is to understand the shape of the φ(ρz) curves of heterogeneous materials. This paper present some of these curves that have been obtained with the Monte Carlo program CASINO available for free at www.gme.usherb.ca/casino.

In 1971, Art Chodos and Arden Albee of Caltech contracted Corning Glass Works to produce synthetic glasses containing a number of elements at about 1 weight percent, to be used as electron microprobe trace element standards. Three glasses were produced, 95IRV, 95IRW, and 95IRX (informally known as Corning/Caltech glasses GLV, GLW, and GLX, respectively, in the microanalysis community), which contain the following elements in a Ca-Mg-Al borosilicate glass matrix:

95IRV K Ti Cr Fe Ce Hf

95IRW V Mn Co Cu Cs Ba La Th

95IRX Ni Zn Rb Sr Y Zr Pb U

The source materials for each oxide were weighed-in at 0.80 percent, and each glass was batched in 2 pound lots and drawn into a 0.25 inch cane that was cut into 9 rods of approximately 5 inch length. Initial distribution to end-users was of 1/8 inch slices from the beginning of each cane, as well as sufficient material for chemical analysis to be performed by volunteers. The glass standards were formed in much the same way as the NBS 612, 614, and 616-series trace element glasses, but used a different matrix composition to avoid problems with alkali migration under the electron beam.

A technique has been developed for the interpretation of composition depth profiles from angleresolved x-ray data using a Monte Carlo electron scattering simulation. Conventional methods for the interpretation of angle-resolved depth profiles used in the fields of x-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) assume that the outgoing signal is exponentially attenuated along its path. This assumption if not valid for angle-resolved x-ray techniques, as the x-ray signal is dependent on both the paths of the incident electrons and the path of the emitted x-rays. In this case, while the latter can be treated using an exponential attenuation, the path of the incident beam is more complex and corresponds to the well known “pear-shaped” interaction volume. In order to reliably interpret angle-resolved depth profiles in which the angle of the incident beam is varied, it is necessary to be able to obtain the distribution of x-ray emission within the sample for any angle of incidence.

Knowledge of inner-shell ionization cross sections by electron impact is needed for quantitative procedures in electron probe microanalysis (EPMA) and Auger electron spectroscopy (AES) The common practice is to use semi-empirical formulas, based on the asymptotic limit of the Bethe theory, which sometimes are used beyond their domain of validity. Experimental measurements of ionization cross sections are scarce and affected by considerable uncertainties, thus a mere comparison with experimental data does not permit to draw a definite conclusion abou the accuracy of the various formulas. In this communication, we present new measurements o the relative variation of K- and L-shell ionization cross sections deduced from the counting rate of characteristic x-rays emitted by extremely thin films of Cr, Ni, Cu, Te, Au and Bi bombardec by keV electrons.

The studied films were produced by thermal evaporation on backing self-supported 30 nm carbon films.

It has previously been shown that microbial polyphosphate bodies are the main sites of metal sequestration. In our present study, we have exposed Synechococcus leopoliensis, grown to log phase and to overplus phase, to five different heavy metals, Al, Cu, Cd, Pb, and Zn, independently. The cells were analyzed using the STEM mode of a transmission electron microscope in conjunction with a PGT IMIX energy dispersive x-ray spectrometer.

Cells of Synechococcus leopoliensis were grown for two weeks at 21°C on a 12-hour light/dark cycle in modified Fizgerald’s medium The second cell type were the overplus cells, which were grown as previously described. The cells were exposed to 100PPM of each metal for two hours, then were fixed and embedded in EPON according to Luff’s procedure.

For x-ray analysis, cells of interest were first located using the TEM mode. The microscope was then switched to the STEM mode.

Ultra-thin polymer x-ray windows have been developed for energy dispersive spectroscopy (EDS) that enable analysis of the elements lighter in mass than sodium while protecting the detector from light and gases. Windowless detectors produce the ultimate in detector sensitivity, however that sensitivity is lost when ice and other contaminants form on the detector. Polymer windows have had a problem with icing in the past, however modern ultra-thin polymer windows contain metalized layers to prevent the diffusion of water. Nevertheless, over the course of time it has been observed that some detectors with polymer windows that are kept continually cool with liquid nitrogen form a thin layer of ice that attenuates light element sensitivity. The source of this water has been hypothesized to be a gradual leak of water vapor through the polymer x-ray window. This hypothesis has been questioned on the basis that the windows were helium leak tight to 1 x 10−9 mbar L/sec and helium is a smaller molecule than water.

It is well known that chemical bonding affects elemental x-ray emission spectra. The spectra of low atomic number elements show energy shifts which depend on the bonding of the element. To observe these shifts, a high resolution wavelength dispersive (WDS) x-ray spectrometer is required. Intensity variations of the L series can be observed with an EDS system which also show chemical effects.

The L Alphal and the L L radiations are produced from a vacancy in the L III shell. Normally the L L line is about 5 to 6% of the intensity of the L Alphal line. However, in the atomic number range of Z=21 to 28, it is easily observed that the L L line becomes more intense. The L Alphal is no longer present at Z=20. These intensity changes are due to the outer electron shells of these atoms being unfilled. The L Alphal comes from the L3-M5 transition, while the L L comes from L3-M1 transition. The M5 (3d level) of the M shell is partially filled for Z=21 to 28; empty for Z<21and full for Z> 28. Holliday observed a Ti LL which was 17% greater than the Ti L Alphal.

Analysis parameters for an electron microprobe are numerous, and the accuracy of the quantitative analysis is very sensitive to the selection of these experimental conditions. The expert system intends to optimize the choice of each analysis parameter as well as to automate the phases of a quantitative analysis on all kinds of materials. To summarise, the aim of the expert system is to simplify the procedures, improve the accuracy of results and control the analysis time. The figure 1 illustrates the various stages of the expert system.

The starting point of the expert system is an interactive questionnaire concerning the sample,( ie, what is already known), and about the expectations on the analysis,( ie, the accuracy of the results and/or the duration of the analysis required by the operator). Then, the expert system performs a semi-quantitative analysis on the sample. Based on the acquisition of a wavelength qualitative spectrum, this method is a way to obtain the sample composition in a short time with the advantages of the WDS system, and with a reasonable accuracy.

Japanese color woodblock prints ("ukiyo-e") from the Edo (1615-1868) and Meiji periods (1868- 1912) are among the most celebrated examples of color printmaking in the world. Full-color prints became technically and commercially viable around 1765. Traditional ukiyo-e colorants were watersoluble, uniform, translucent, organic (vegetal) and inorganic pigments of very small particle size. (Synthetic colorants were also introduced from the West in the 19th C, probably beginning with "Prussian blue" in the 1820s.) A pigment was applied with a brush to a color block, and then rice flour paste was mixed with the pigment to thicken it, facilitate control and rubbing into the paper, improve the uniformity of the colorant, and avoid a dry or granular texture. The dampened paper, sized with cooked bovine skins and alum, was then placed on the block (aligning with registration marks cut into the blocks). The colorants were then pressed into the paper by rubbing a bamboo pad against the back of the paper so that the colors were absorbed on the front surface.

Studies of Pd foil cathodes have indicated that when electrolyzed for long times in electrolytes containing both deuterium and hydrogen ions along with sulfuric acid, the cathodes undergo compositional, topographical, evolutionary, and isotopic changes. The results reported here describe the changes which are produced in Pd cathodes after only a few minutes of electrolysis.

In June 1993 a cold-rolled, Pd (AESAR lot #12E06) cathode of 40μm thickness was submerged at one end into an electrolyte containing 20 ml D2O and 3.5 ml H2SO4 and electrolyzed for six minutes at about 0.6 A/cm2 and 3.65 V. An identical Pd cathode (cut from the same strip) was submerged at one end into an electrolyte containing 20 ml H2O and 3.5 H2SO4 and electrolyzed for six minutes using 0.6 A/cm2 and 4.11 V. A Pt foil acted as the anode in each case. The two cells were connected in series. An ionic current flowed between the electrodes for each system as the voltages were applied.

A series of experiments were conducted with titanium cathodes and platinum anodes electrolyzed in heavy water-sulfuric acid electrolyte in closed cells. Each of the cathodes in these experiments was cut from the same titanium foil (99.99% Ti). Each cathode underwent a pre-experiment and a post-experiment SEM (ISI-SS40) and EDS (LINK AN10000) analysis. Of the eight experimental cathodes, three showed post-experimental evidence of localized chemical changes. This is consistent with other findings from this lab. Results obtained on one of these cathodes are presented here.

This cathode was electrolyzed for 115 hours at 0.40A (current density about 2A/cm2). The cathode was ultrasonically cleaned in deionized water for five minutes prior to the pre experiment analysis. Fig. 1 shows the smooth surface of the cathode before electrolysis. No other elements besides titanium were found. After electrolysis in 19.4g D2O +l.0g H2SO4 the cathode was removed from the cell and rinsed by gentle agitation in deionized water for several minutes.

Conventional water treatment plants that use alum (aluminum sulfate) as a coagulant have been dealing with the issue of residual alum carry over from the treatment plant into the distribution system. The basic product formed whe alum is added to water is aluminum hydroxide floc. This floc grows in size and density as it captures suspended particulates and then is settled out. Smaller floc aggregates that pass through the settling process are in the most part removed by sand filtration. However due to the amphoteric characteristics and solubility properties of aluminum alon with it’s many different compounds, carry over of aluminum compounds through the filter is a phenomena that is a great concern to the water industry. These residual aluminum compounds produce small hydroxide floes that coat the inner surfaces of distribution pipes causing head loss or increased energy requirements for water pumping.In addition phosphate compounds (poly and ortho blends) have recently been added to the distribution system to reduce the leaching and corrosion of lead and copper from pipes.

Solder joints provide mechanical and electronic connections between solders and components for various levels in microelectronic package. However, due to different thermal expansion coefficients and elastic modulus of the associated materials, solder joints are susceptible to fatigue degration, microcracks and fracture. The solder joint reliability is, therefore, critical in the evalution of the joint quality. Recently, the employment of lead-free solder is attractive due to the environmental concern of the Pb-containing solder. Hence, the investigation on the unleaded solder joint is of practical importance in the field of microelectronic package.

Intermetallic compounds (IMC), which form and grow between solders and metallizations, are considered to be a source of mechanical weakness for its brittleness and different coefficient of thermal expansion from the metallization or the solder.