The studies of insulating specimen by using scanning electron microscopy (SEM) or associated microanalytical techniques such as electron probe microanalysis (EPMA), Auger electron spectroscopy (AES), etc., is limited by the charging phenomena. Different techniques have been found to minimize this problem: coating the specimen with a conductor, working at low energy [1], etc. But for a better knowledge of this effect, we have started a study of the mechanisms of charging as well as its effect on the electrons trajectories in the case of an insulating specimen. with the success, in past years, of Monte Carlo (MC) simulation of electron scattering in solid specimens [2], we have been developing a new Monte Carlo program for the simulation of the electron trajectory in insulators.

With this program, we want to understand the effect of the trapping charge on a insulating specimen. The new MC will be constructed by adding a succession of refined model. in each step, the model goes deeper in the mechanisms for the charging phenomena.

A common question, but one typically difficult to answer, is “How accurate is a microprobe or SEM analysis?” Commercial software for most EDS and WDS systems print out error limits that are typically calculated standard deviations using Gaussian counting statistics based on the accumulated peak and background counts. This is not a true measure of even the measurement precision, since random instrumental instabilities typically degrade “true” measurement precision (as determined by replicate measurements on standards) to 1.5 - 3+ times that predicted from Gaussian statistics. in addition to these random instrumental variations are a plethora of possible systematic and semirandom errors such as detector or faraday cup non-linearities, errors in estimation of background, EDS spectral deconvolution errors, WDS positional non-reproducibility, temperature and pressure variation effects on spectrometer efficiencies, high voltage drift or sample charging, surface contamination or oxidation, and sample roughness or tilt.

Quantitative procedures in electron probe microanalysis (EPMA) require the knowledge of various atomic parameters, the most fundamental of which is the ionization cross section. A number of semi-empirical, approximate analytical formulas have been proposed to calculate the ionization cross section. The simplicity of these formulas makes them suitable for quantitative EPMA procedures. However, it is difficult to assess their reliability because of the lack of accurate experimental data. Indeed, inspection of currently available data reveals that they are still scarce for many elements and, when they are available, one usually finds significant discrepancies between data from different authors. Fortunately, the inaccuracies in the semi-empirical cross section formulas used in EPMA have only a small effect on the analytical results when standards are used. Nonetheless, in quantitative EPMA studies at low overvoltages or using standardless methods, the evaluated compositions largely depend on the adopted ionization cross sections and, therefore, knowledge of accurate ionization cross sections is a requisite for the development of improved quantification methods.

Experimental conditions and setting up of an electron microprobe is directly linked to the assumption or the knowledge that can make the operator on the results of the measurements. Consequently, there is an increasing interest in modelling the X-ray spectrum in order to predict accurately and rapidly the response of the microprobe when a sample of approximately known composition is submitted to specific excitation conditions. Even if the spectra simulation is a current tool proposed in EDS, it always remains a challenge to create a complete absolute WDS spectrum. Indeed, the definition of the efficiency function was a limit to the calculation of absolute intensities.

In this work, we propose a new generation software for EPMA which uses the absolute simulation spectra to assist the operator in the choices of experimental conditions to achieve accurate measurements in a short time as well as to create new functionalities.

This paper presents the results of studies concerning the accuracy and precision of x-ray microanalysis (EDS) in the environmental scanning electron microscope (ESEM). The ESEM is distinguished by its use-of gas in the microscope specimen chamber for imaging and for charge neutralization. Previous work on EDS-ESEM has concentrated either on qualitative x-ray microanalysis or on correction methods to the enlarged x-ray spatial resolution due to the electron skirt. Recent work shows that quantitative analysis is possible once charge neutralization can be accomplished in practice.

Accuracy and precision were evaluated in the work presented here using NIST SRM 482 (goldcopper alloys) and NIST SRM K411 (glass beads). The gold-copper alloy wires were prepared by mounting them in epoxy mounts and polishing to a metallurgical finish. The glass spheres were prepared by sprinkling a small amount of the sample onto double-sided carbon tape mounted onto an aluminum SEM stub.

The National Institute of Standards and Technology’s (NIST) Standard Reference Material (SRM) 482 was issued by The National Bureau of Standards (NBS) in 1969 i has been continuously available to the public for over 30 years [1]. The standard cons of a set of 6 wires. Each wire is approximately 0.5 mm in diameter and 5 cm long. Tl wires represent different compositions within the binary copper-gold alloy system. Included in the set are the two end member compositions, pure copper and pure gold, along with 4 alloys of nominal composition: Au80-Cu20, Au60-Cu40, Au40-Cu60 an< Au20-Cu80. SRM 482 was produced specifically for the purpose of microanalysis usi the electron probe microanalyzer (EPMA).

Recent metallographic preparation of these wires revealed the presence of surface blemishes on some of the prepared wires (Figure la). Two of the authors from differei affiliations recently prepared cross-sections of SRM wires from separately purchased sets. Each was unaware of the procedures used by the other.

Lead lanthanum zirconium titanate (PLZT), or (Pb,La)(Zr,Ti)O3 solid solutions, ferroelectric ceramics are being studied for electro-optical applications, as well as for high-speed electrophoretic printing. Thin films of a related material, lead zirconium titanate, or Pb(Zr,Ti)O3 solid solutions (PZT), are used for non-volatile memories and actuators.1 Proper composition and compositional homogeneity of ferroelectric ceramics are essential for application, however the fabrication process may produce materials with element concentrations and thus physical characteristics that may differ from expectation. Therefore, a PLZT reference material for determining the composition of these ceramics would be useful. It will also be useful for quantitative microanalysis; it is stable under the point beam of the electron microprobe (EPMA) at excitation voltages up to 25 kV and probably higher at currents of more than 100 nA.

A specimen of PLZT prepared by the Ceramics Department of the Jozef Stefan Institute in Ljubljana, Slovenia was studied with the electron microprobe to determine the composition and the extent of heterogeneity.

Terrestrial experiments involving detached growth of GeSi crystals by the Bridgman technique have been performed in preparation for microgravity experiments to be conducted on the International Space Station. These experiments typically produce large GeSi crystals that are sectioned for microscopy, microprobe analysis, and electron-backscatter diffraction analysis. Accurate microanalysis of these crystals is essential for feedback to further growth experiments, but is problematic as the Ge-Si binary exhibits continuous solid solution and it is therefore difficult to prepare homogeneous intermediate standards. There are no experimental measurements on standards of known composition in the Ge-Si binary that could be used to evaluate analytical accuracy. The accuracy of analysis in mineral, oxide, and semiconductor systems has previously been studied using experimental x-ray intensity measurements, correction algorithms and their derived α-factors, and mass absorption coefficient data sets. This study continues that approach and includes results of Monte Carlo calculations in the Ge-Si binary.

The topic of this paper is to present a new Windows™ environment version of the CASINO Monte Carlo program. The goal of this program is to assist scanning electron microscope users in their routine analysis and also in more advanced topic such as electron beam lithography for example. Based on a single scattering algorithm, this software is specially designed for low beam interaction in a bulk and thin foil. This program uses tabulated Mott elastic cross-sections, which benefit of both fast calculation and accurate interaction at low beam energy. At the moment CASINO can either be used to generate X-rays or backscattered electron signals. The program used simple two-dimension geometry to represent real sample. in this version, vertical and horizontal planes can be generated to allow cross-section representation or multi-layers analysis. Then beam can be scanned across different regions to produce X-ray linescan or bascattered electron profiles.

Many new convenient features have been added to the version 2.0 of CASINO. The new interface lets the users to consult the results as the simulation is still in progress.

Usually, in electron probe microanalysis, the X-ray diffusion range is around lμm on the sample surface. For this reason, the maximum useful magnification of X-ray image seems to be limited to a few thousand times. The X-ray diffusion on the \im order takes place in the bulk sample. However, when a sample is cut to a thin film, it is likely that the X-ray diffusion range will be made smaller, and it is also possible to observe very a narrow area X-ray image at higher magnification. The thin film method is a sampling technique used often in transmission electron microscopy. The microtome method has been applied to organic materials, and the method using focus ion beam (FIB) has been applied to inorganic materials. Takahashi et al. have reported the effectiveness of the microtome application to EPMA of soft materials. in this report, the FIB method was applied to a sampling of inorganic materials in order to obtain high resolution X-ray images of real samples.

Monte Carlo simulation is a suitable tool for the numerical generation of x-ray spectra by electron beams and, more specifically, for the quantification in electron probe microanalysis (EPMA). in this communication we describe the application of the general-purpose code PENELOPE to EPMA. This code simulates electron-photon showers in complex material structures consisting of homogeneous regions of arbitrary composition limited by quadric surfaces. It is devised to cover a wide energy range (from ∼500 eV to about 1 GeV). The interaction models implemented in PENELOPE are based on the most reliable information available. They combine results from first principles calculations (this is the case, e.g., for electron elastic scattering, photon Compton scattering), semiempirical models (in electron inelastic scattering) and information from evaluated data bases. to facilitate the random sampling, the cross sections of various interaction mechanisms are described through analytical expressions, which are adjusted to yield accurate values of relevant transport properties (mass attenuation coefficients, transport mean free paths, stopping powers, . . . ).

Monte Carlo simulation of electron scattering has been widely used in various fields such as microanalysis, microscopy and microlithography. Various simulation models have been reported so far. in applications to quantitative x-ray microanalysis the accuracy of the model has been significantly improved by introducing the Mott cross section. However, in the analyses at low energies of an electron beam or at energies near the x-ray excitation energy, the simulation accuracy becomes worse. This is probably because the discrete energy loss process is not incorporated into the simulation model. to improve this default, we developed the model which includes the discrete energy loss process[l]. The outline of the model is described in the following.

1. 1) Elastic scattering

We used the Mott cross section. The Mott cross sections for Al, Cu, Ag and Au elements are calculated at various energies. From this data base we obtain the differential elastic scattering cross section and the total elastic cross section for arbitarary elements and energies by using the interporation or the extrapolation.

The classical schemes to convert the x-ray intensity into concentration, using the ZAF or the φ(ρ z ) methods, are valid for specimens having homogeneous composition and flat surfaces. Quantitative schemes have also been developed for x-ray microanalysis of multi-layered specimens. More recently, a quantitative method has been proposed for the microanalysis of spherical inclusions embedded in a matrix.

For the case of specimens having a non-planar surface, a quantitative method based on the peak to background ratio, using photons of the same energy, has been proposed. in order to test this correction method, a Monte Carlo program has been developed in order to compute the complete x-ray spectrum, characteristic lines plus bremstrallung, emitted from materials having rough surfaces. Figure [1] shows the geometry of the rough surfaces simulated. The parameters of these surfaces are the summit semi-angle, θ, and the height of the roughness, h.

In Castaing’s classic Ph.D. dissertation he described how the limiting value of x-ray spatial resolution for x-ray microanalysis, of about 1 μm, was not imposed by the diameter of the electron beam, but by the size of the region excited inside the specimen. Fifty years later this limit still applies to the majority of measurement made in EMAs and SEMs, even though there is often a need to analyze much finer structures. When high resolution chemical analysis is required, it is generally necessary to prepare thin sections and examine them in an analytical electron microscope where the maximum diameter of the excited volume may be as small as a few nanometers. Since it is not always possible or practical, it is important to determine just what is the best spatial resolution attainable for the examination of polished or “as received” samples with an EMA or SEM and how to achieve it experimentally.

In variable pressure (VPSEM) and environmental SEM (ESEM) caution is required in the intepretation of x-ray data from non-conductive and electrically isolated samples for unique reasons. This paper reviews the documented procedures and presents data on hither-to undefined aspects.

The most widely recognised artefacts are associated with the scatter of primary electrons from their convergent trajectory to the sample surface through interactions with the chamber gas. Beam ‘skirt’ measurements have been made by various researchers and this scatter is well characterised. “Point” analyses are corrupted by addition of components from the surrounding phases and x-ray maps are effectively ‘defocussed’ or ‘blurred’. The magnitude is a function of pressure, amongst many other variables, and it has been shown that these scatter effects can be reduced through extrapolation of data collected at differing chamber pressures2. Bremsstrahlung-based corrections for primary beam variations and drift have also been shown to be effective.

A number of methods have been proposed to correct for the electron beam scattering effects on xray microanalysis in the environmental scanning electron microscope (ESEM). This paper presents an evaluation of two of these methods. The Doehne method is based on the observation that x-ray counts due to the unscattered electron beam increase with decreasing chamber pressure whereas the inverse is true for x-ray counts due to scattered electrons. The x-ray count intercept, at zero pressure, of the regression lines relating x-ray counts to chamber vapor pressure is an estimate of the high-vacuum intensity. The Gauvin method is based on the relationship between x-ray counts and the fraction of the electron beam that is unscattered, fp.The fraction of the unscattered beam is calculated using an equation derived from scattering theory and uses the accelerating voltage, the gas path length, and the chamber vapor pressure.

An inevitable consequence of the presence of the gas in the sample chamber of a low-vacuum scanning electron microscope (LV-SEM) and environmental SEM (ESEM) is the electron beam broadening due to the scattering in the gas. The electron broadening has a large impact on x-ray analysis because the fluorescent characteristic x rays generated far from the center of the electron probe form a high background, which reduces the detection sensitivity of x-ray analysis and degrades the x-ray image contrast. We report in this paper of using a polycapillary focusing x-ray optic between the sample and the energy-dispersive spectrometer as a spatial filter to filter out unwanted x-rays generated far from the specimen. As a result, the x-ray image contrast and the detection sensitivity of the system were notably improved.

A polycapillary focusing optic collects a large solid angle of x rays from an x-ray source of small area at its input focus, guide them through the curved channels by multiple external total reflections, and focus them to the output focus.

There is increasing interest in performing x-ray microanalysis of uncoated insulators while operating in unconventional SEM operating modes such as “low voltage” scanning electron microscopy (LVSEM), where the accelerating voltage is ≤ 5 kV and the pressure is low (<10-4 Pa), or variable pressure environmental SEM (VP-ESEM), where a selected gas is maintained at pressures in the range of 1 Pa -1000 Pa. LVSEM and VP-ESEM as microscopy techniques have proven to be extremely successful for imaging uncoated insulators through various charge dissipation mechanisms that are not available under conventional SEM operating conditions (accelerating voltage ≥ 10 kV and pressure < 10-3 Pa). in LVSEM, surface charging of insulators can often be controlled by careful choice of the accelerating voltage, sample tilt, and scan rate, while in VP-ESEM the charged species in the relatively dense gas (ions, secondary electrons) form a self-neutralizing plasma to provide an additional route for discharging the specimen.

Energy-dispersive X-ray (EDX) spectrum imaging, where a full spectrum is acquired at each pixel in a rastered image, combines the advantages of imaging and analysis for quantitative compositional mapping. This method has great advantages for the analysis of compositional variations, because the contrast inherent in EDX spectrum images arises from the distinctiveness of the characteristic X-ray spectra in various regions of the surveyed microstructure. EDX spectrum imaging provides for simultaneous spatial, spectral and temporal resolution of the X-rays emitted from the specimen. Many EDX manufacturers have incorporated a spectrum imaging capability within their acquisition and analysis software, and ongoing improvements in computing power will enhance the practicality of spectrum imaging methods, in particular the acquisition, manipulation and analysis of the large raw data files that are generated with this method. This paper surveys the potential role of spectrum imaging in tasks that support true quantitative X-ray microanalysis of bulk specimens: robust qualitative analysis, the construction of representative spectra that describe the specimen, and the extraction of elemental concentrations from the representative spectra.

It is a conundrum that faces microanalysts every day: how do you comprehensively survey the chemistry of a microstructure in a reasonable time? Traditional solutions in the SEM would include taking an image and then collecting x-ray spectra from a series of points. This method relies heavily on the operator’s ability to identify chemically distinct regions. in addition, for a complex microstructure, this could take a considerable amount of time to do correctly. On the positive side, if care is taken, these ‘point spectra’ can be readily quantified. An alternative method that has been used widely is x-ray mapping, where a window of intensity in the spectra is integrated and displayed as an image. This has the advantage that qualitative elemental distributions from an area of a microstructure can be visualized. The disadvantages are that maps are generally not quantitative, can be susceptible to artifacts, and rely on fore knowledge of the elements to map.