The effect of some instrument operating conditions on the x-ray microanalysis of particles in the environmental scanning electron microscope

The objective of this investigation was to evaluate the practical effects of electron beam broadening in the environmental scanning electron microscope (ESEM) on particle x-ray microanalysis and to determine some of the optimum operating conditions for this type of analysis. Four sets of experiments were conducted using a Faraday cage and particles of copper, glass, cassiterite, andrutile. The accelerating voltage and chamber pressure varied from 20 to 10 kV and from 665–66 Pa (5.0 to 0.5 torr), respectively. The standard gaseous secondary electron detectors (GSED) and the long environmental secondary dectectors (ESD) for the ESEM were evaluated at different working distances. The effect of these parameters on the presence of artifact peaks was evaluated. The particles were mounted on carbon tape on an aluminum specimen mount and were analyzed individually and as a mixture. Substrate peaks were present in almost all of the spectra. The presence of neighboring particle peaks and the number of counts in these depended upon the operating conditions. In general, few of these peaks were observed with the long ESD detector at 19 mm working distance and at low chamber pressures. More peaks and counts were observed with a deviation from these conditions. The most neighboring peaks and counts were obtained with the GSED detector at 21.5 mm working distance, 10 kV accelerating voltage, and 665 Pa (5.0 torr) chamber pressure. The results of these experiments support the idea that the optimum instrumental operating conditions for EDS analysis in the ESEM occur by minimizing the gas path length and the chamber water vapor pressure, and by maximizing the accelerating voltage. The results suggest that the analyst can expect x-ray counts from the mounting materials. These tests strongly support the recommendation of the manufacturer to use the long ESD detector and a 19 mm working distance for EDS analysis. The results of these experiments indicate that neighboring particles millimeters from the target may contribute x-ray counts to the spectrum.     

Mistakes encountered during automatic peak identification of minor and trace constituents in electron‐excited energy dispersive X‐ray microanalysis

Automated peak identification in electron beam‐excited X‐ray microanalysis with energy dispersive X‐ray spectrometry has been shown to be subject to occasional mistakes even on well‐separated, high‐intensity peaks arising from major constituents (arbitrarily defined as a concentration, C, which exceeds a mass fraction of 0.1). The peak identification problem becomes even more problematic for constituents present at minor (0.01≤C≤0.1) and trace (C<0.01) levels. “Problem elements” subject to misidentification as major constituents are even more vulnerable to misidentification when present at low concentrations in the minor and trace ranges. Additional misidentifications attributed to trace elements include minor X‐ray family members associated with major constituents but not assigned properly, escape and coincidence peaks associated with major constituents, and false peaks owing to chance groupings of counts in spectra with poor counting statistics. A strategy for robust identification of minor and trace elements can be based on application of automatic peak identification with careful inspection of the results followed by multiple linear least‐squares peak fitting with complete peak references to systematically remove each identified major element from the spectrum before attempting to assign remaining peaks to minor and trace constituents. SCANNING 31: 91–101, 2009. Published by Wiley Periodicals, Inc.     

The use of helium gas to reduce beam scattering in high vapour pressure scanning electron microscopy applications

Both image quality and the accuracy of x-ray analysis invariable pressure scanning electron microscopes (VPSEMs) are often limited by the spread of the primary electronbeam due to scattering by the introduced gas. The degree of electron scattering depends partly on the atomic number Z of the gas, and the use of a low Z gas such as helium should reduce beam scattering and enhance image quality. Using anuncoated test sample of copper iron sulphide inclusions in calcium fluorite, we show that the reduction in beam scatter produced by helium is more than sufficient to compensate for its reduced efficiency of charge neutralisation. The relative insensitivity to pressure of x-ray measurements in a helium atmosphere compared with air, and the consequent ability to work over a wider range of working distances, pressures, and voltages, make helium potentially the gas of choice for many routine VPSEM applications.     

Mistakes encountered during automatic peak identification in low beam energy X-ray microanalysis

Automated peak identification in electron beam excited X-ray microanalysis with energy dispersive X-ray spectrometry (EDS) is subject to occasional mistakes even on well-separated, high-intensity peaks arising from major constituents. The problem is exacerbated when analysis conditions are restricted to operation in the "low beam energy scanning electron microscopy" (i.e. "low voltage scanning electron microscopy" or LVSEM) regime where the incident beam energy is 5 keV or less. These low beam energy microanalysis conditions force the analyst to use low fluorescence yield L-shell and M-shell peaks rather than higher yield K-shell and L-shell peaks typically selected for elements of intermediate and high atomic number under conventional high beam energy (>10 keV) conditions. Misidentifications can arise in automated peak identification procedures when only a single energy channel is used to characterize an EDS peak. The effect of the EDS measurement process is to convolve the closely spaced Lalpha-Lbeta and Malpha-Mbeta peaks into a single peak with a peak channel shift of 20 eV or more from the Lalpha or Malpha value, which is typically sought in an X-ray database. An extensive list of problem situations encountered in low beam energy microanalysis is presented based upon observed peak identification mistakes as well as likely troublesome situations based upon proximity in peak energy. Robust automatic peak identification requires implementation of peak fitting that utilizes the full peak shape.     

A method of direct particle deposition on a carbon planchet to study mineral dust in human lung by scanning electron microscopy

Following Na-hypochlorite digestion of lung tissue, mineral particles extracted in the chloroform layer were deposited directly on a pre-smoothed carbon planchet for combined scanning electron microscopy and X-ray energy dispersive spectrometry (SEM and XEDS). Total mineral particle counts were obtained, and detailed physical characteristics of the fibrous particles were documented at 600, 1,500, 4,500 and 9,000 x in three lungs without, and one lung with, histories of occupational exposure. This preparation method was simple, collected more than 99% of identifiable mineral particles in the chloroform layer, gave excellent object to background contrast without heavy metal coatings, and was suitable for XEDS. Comparable fibrous particles from the chloroform layer could also be studied by selected-area electron diffraction to complement the results of XEDS. By this method, we found particles or fibers larger than 0.1 μm were readily counted and measured at 4,500 x. At 600 x, ferruginous bodies were found to be more than twice in number than when sought for by light microscopy. It was determined that 4,500 x is the most efficient magnification to examine and diagnose this type of specimen. The present study illustrates the importance of determining the most efficient magnification to be utilized in particle counts.     

能量色散X射线荧光光谱仪的现状

能量色散X射线荧光光谱分析以其快速、对试样无损、可以同时测定多种元素等优点,在许多领域中发挥巨大的作用。本文介绍能量色散X射线荧光光谱仪的原理和构造,并就目前仪器的研究现状和应用现状做介绍,指出X射线荧光分析技术的良好前景及进一步研究该仪器的必要性。     

Atomic force and scanning electron microscopy of atmospheric particles

Atomic force microscopy (AFM) and scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS) have been used for both morphological and elemental mass analysis study of atmospheric particles. As part of the geometrical particle analysis, and in addition to the traditional height profile measurement of individual particles, AFM was used to measure the volume relative to the projection area for each particle separately, providing a particle shape model. The element identification was done by the EDS analysis, and the element mass content was calculated based on laboratory calibration with particles of known composition. The SEM-EDS mass measurements from two samples collected at 150 and 500 m above the surface of the Mediterranean Sea were found to be similar to mass calculations derived from the AFM volume measurements. The AFM results show that the volume of most of the aerosols that were identified as soluble marine sulfate and nitrate aerosol particles can be better estimated using cylindrical shapes than spherical or conical geometry.     

Correlating auger electron spectroscopy with scanning electron microscopy-energy dispersive spectroscopy for the analysis of respirable particles

A method has been developed to characterize large populations of individual respirable particles. With the use of custom data collection and data correlation computer software, the same set of particles can be analyzed in multiple instruments. The method is demonstrated by the analysis of a sample of hard-metal particles. A series of particles are analyzed by Auger electron spectroscopy, and then the same particles are analyzed by scanning electron microscopy-energy dispersive spectroscopy.     

The use of scanning electron microscopy to quantify the burden of particles released from clean-room wiping materials

A procedure is described for the detection and direct enumeration of the number of particles that can potentially be released from wiping materials. The technique involves the use of a scanning electron microscope (SEM) to count the particles from a wiper, first by releasing them in deionized water and then filtering the entirety of the liquid through a submicron membrane filter. To obtain an accurate count, the filtration must produce a normal distribution of particles on the filter, and hence the details of the filtering technique must be performed in a very precise manner. The counting of the particles on the filter is accomplished by scanning a statistically representative number of fields and averaging the number of particles per field. The results can then be checked for statistical precision and accuracy. Our criterion for successful measurement was ± 10% accuracy at a 95% confidence level. We believe that the SEM method described in this article is sensitive enough to quantify very low levels of total particle burden without succumbing to the variability and limitations encountered with other enumeration techniques. Typically, this technique enables the accurate counting of particles of all shapes from below 0.1 μm to hundreds of micrometers. In addition, the SEM technique allows for morphologic identification of particles as well as chemical identification if an energy-dispersive x-ray system (EDS) is employed.     

Electron energy loss spectra and reflection images from surfaces

There is renewed interest in the interaction of high energy electron beams with surfaces at glancing angles of incidence, due partially to recent improvements in, and consequential resurgence of, reflection electron microscopy. In this paper electron energy loss of beams running parallel to a surface or at glancing incidence to it are studied and compared with predictions arising from the classical theory of dielectric excitation by a moving charge. There is good agreement for both the Cu and MgO surfaces studied here. It is pointed out that small angle energy loss from high energy electrons is insensitive to surface reconstructions or surface steps. Reflection energy filtered micrographs of the Cu surface are shown and the similarity between the zero and various energy loss images shows the preservation of contrast mechanisms for elastic and inelastic electrons.     

A new correction method for high-resolution energy-dispersive x-ray analyses in the environmental scanning electron microscope

Spurious x-ray signals, which previously prevented high-resolution energy-dispersive x-ray analysis (EDS) in the environmental scanning electron microscope (ESEM), can be corrected using a simple method presented here. As the primary electron beam travels through the gas in the ESEM chamber, a significant fraction of the primary electrons is scattered during collisions with gas molecules. These scattered electrons form a broad skirt that surrounds the primary electron beam as it impacts the sample. The correction method assumes that changes in the width of the electron skirt with pressure are less important than changes in the skirt intensity; this method works as follows: The influence of the gas on the overall x-ray data is determined by acquiring EDS spectra at two pressures. Subtracting the two spectra provides us with a difference spectrum which is then used to correct the original data, using extrapolation, back to the x-ray spectrum expected under high-vacuum conditions. Low-noise data are required to resolve small spectral peaks; however, the principle should apply equally to x-ray maps and even to low-magnification images.     

New pathways for improved quantification of energy‐dispersive X‐ray spectra of semiconductors with multiple X‐ray lines from thin foils investigated in transmission electron microscopy

Theoretical approaches to quantify the chemical composition of bulk and thin‐layer specimens using energy‐dispersive X‐ray spectroscopy in a transmission electron microscope are compared to experiments investigating (In)GaAs and Si(Ge) semiconductors. Absorption correctors can be improved by varying the take‐off angle to determine the depth of features within the foil or the samples thickness, or by definition of effective k‐factors that can be obtained from plots of k‐factors versus foil thickness or, preferably, versus the K/L intensity ratio for a suitable element. The latter procedure yields plots of self‐consistent absorption corrections that can be used to determine the chemical composition, iteratively for SiGe using a set of calibration curves or directly from a single calibration curve for InGaAs, for single X‐ray spectra without knowledge of sample thickness, density or mass absorption coefficients.     

Multiphase analysis of Bi-Sr-Ca-Cu-O high Tc superconductors with x-ray compositional mapping

Ba-Sr-Ca-Cu-O (BSCCO) high Tc superconductor specimens were prepared as part of a solid-solubility study in the region of the 2223 phase. The identification and determination of the amount of each phase in the final products were necessary. Quantitative digital x-ray compositional mapping with the electron microprobe was done with five wavelength spectrometers, one for each of the cations. To facilitate phase identification and quantification, image processing rules were developed for the nine possible phases, with each assigned a unique color. Using this procedure, at least six different phases were identified. Examples are cited in color.     

Accuracy and precision of quantitative energy-dispersive x-ray spectrometry in the environmental scanning electron microscope

The accuracy and precision of quantitative energy-dispersive x-ray spectrometry in the environmental scanning electron microscope have been estimated using a series of copper / gold alloys of known composition. The mean values (five to six replicate experiments) had relative errors within +/- 5%, and most were within +/- 3.5%. All relative standard deviations were < 5% and most were < 3%. Since the standard specimens were large (approximately 500 microm) in diameter, electron scattering in the 2 torr of water vapor above the specimen did not affect the results. This level of accuracy and precision was possible only by using a novel specimen surface charge neutralization scheme.     

Multielemental analysis of pharmaceuticals derived from plant seeds by energy dispersive X-ray fluorescence spectrometry

The concentrations of elements in pharmaceuticals derived from plant seeds were determined by energy dispersive X-ray fluorescence. The concentrations of Ca, Si, Cl, K, S, Ti, Cr, Mn, Fe, P, Cu, Zn, Br, Rb, Sr, Hg, and Zr were quantified; only Si (10 ± 1 to 70,000 ± 110 mg kg^?1), S (10 ± 2 to 12,4000 ± 243 mg kg^?1), K (4,000 ± 58 to 24,000 ± 70 mg kg^?1), Ca (2200 ± 35 to 87,000 ± 150 mg kg^?1), Mn (21 ± 4 to 1956 ± 17 mg kg^?1), and Fe (100 ± 7 to 5150 ± 70 mg kg^?1) were present in all samples. These results may validate the use of these pharmaceuticals for the treatment of disease due to high concentrations of essential elements Mn, Ca, Mn, K, Mg, Zn, Cl, Fe, and P. Mercury was present in some products below standard values. The results also have quality control applications because of the widespread use of these pharmaceuticals.     

Microscopic diagnosis of the leaf and stem of Piper solmsianum C.DC

Piper solmsianum C.DC., which is popularly known as pariparoba, is a shrub that measures 1–3 m in height and it inhabits areas with wet tropical soils. The objective of this study was to analyze the leaf and stem anatomy using light microscopy, scanning electron micrographs, and energy‐dispersive X‐ray spectroscopy in order to provide information for species identification. The anatomical profile showed the following main microscopic markers: hypostomatic leaf; hypodermis layer on both sides; pearl glands; biconvex midrib shape; five collateral vascular bundles in open arc with the central bundle larger than the others; circular stem shape; collateral vascular bundles arranged in two rings; sinuous sclerenchymatic sheath in the pith; secretory idioblasts; and starch grains in the mesophyll, in the ground parenchyma of the midrib, petiole, and in the stem; and six morphotypes of calcium oxalate crystals (styloids, cuneiform, tabular crystal rosettes, cuneiform crystal rosettes, elongated square dipyramids, as well as very elongated square dipyramids).     

Automated analysis of submicron particles by computer-controlled scanning electron microscopy

Automated analysis of submicron particles by computer-controlled scanning electron microscopy is generally possible. The minimum diameter of the detectable particles is dependent on the mean atomic number of the particles and the operating parameters of the scanning microscope. The main limitation with regard to particle size is set by the quality of the particle detection system, which generally is the backscatter electron detector. The accuracy of the results of the x-ray analyses is very often strongly affected by specimen damage, omnipresent especially for environmental particles even at low electron energies and probe currents. With the exception for light elements, the detection limit is approximately 1 wt%. Device-related limitations to automated analysis may be specimen drift and an unreliable autofocus function.     

Transformation reactions of partially gold-coated bioactive Ca-P glass granules investigated by analytical scanning electron microscopy

In the present work, we have clarified the detail of the surface transformation reactions of bioactive calcium-phosphate (Ca-P) glass granules induced by in vivo implantation in rabbit dorsal muscle sites. To this aim we have compared the behaviour, during the same implantation, between the as-prepared and gold-coated only-on-one-side glass granules. The deposited gold layer enabled us to determine very precisely the initial position of the surface of the glass before the transformation took place. In addition, since the gold layer acts as a diffusion barrier, it allowed the study of the direction and the mechanism of crystal growth which occurred at the glass surface. Lapped and polished cross-sections of the samples were examined by backscattered electron (BSE) imaging and quantitative (with standards) x-ray energy dispersive spectroscopy (EDS) in a scanning electron microscope (SEM). The observations showed the presence of an interlayered structure. Quantitative EDS microanalysis performed by profiling the electron beam across the samples indicated the presence of hydrated calcium phosphate in the external layer, an inhomogeneous silica-rich gel-type layer in the middle layer, and an unaffected original Ca-P glass in the centre. From the comparison with those granules gold-coated on one side, we deduced that the hydrated calcium phosphate layer grew towards the interior of the granules at the expense of the starting glass. A simple model, based on the balance of the concentrations of the elements which have diffused in the different layers, is proposed to explain the contribution of the elements constituting the original glass to the formation of the different layers. This result agrees with the experimental data obtained from image analysis and the microstructural behaviour of this type of glass is discussed.     

Scanning electron microscopy leads to identification of novel nonedible oil seeds as energy crops

Currently, exploration of alternative energy resources is hotly debated among the scientific community owing to rising energy crises and environmental issues. Biodiesel, as renewable energy source proves to be a better option and substitute to petro diesel. In this regard, nonedible seeds could be a better feedstock for synthesizing biodiesel due to their cost effectiveness and environmental friendly attributes. The present study, therefore, deals with the exploration and identification of micromorphologic features among eight novel nonedible oil yielding seeds via scanning electron microscopy (SEM) as potential feedstock for biodiesel industry. Light microscopic studies revealed that seeds size vary from 0.1–2.9 cm in length to 0.1–3 cm in width. Moreover, a great variation in seed color from black, green, and different shades of brown was also observed. Seeds ultra‐structure examination by SEM exhibit great variation in seed shape, size, color, sculpturing and periclinal wall shape and arrangement and so on. All the understudy seeds vary from rounded, irregular, subspherical, ellipsoidal, reniform, flattened, polygonal, ovate, pyriform, oblong, and globose shape. Seeds wall structure exhibits great variation from entire, angular, straight, irregular, polygonal, smooth, and elongated. The periclinal wall pattern exhibits variation from flat to slightly concave‐convex with straight, angular, undulate, or dentate seeds margin. Among the studied species only Argemone ochroleuca Linn. (Papaveraceae) possess micropylar peak, ridged raphe, and basal helium. The obtained results from the present study would therefore, suggest that SEM could be a useful tool in refreshing the veiled micromorphological features among different oil yielding seeds which in turn helps the researchers for their correct identification, exploration, authentication, and seeds classification in future.     

Elemental changes in the brain, muscle, and gut cells of the housefly, Musca domestica, exposed to heavy metals

The toxic effects of heavy metals on organisms are well established. However, their specific action at the cellular level in different tissues is mostly unknown. We have used the housefly, Musca domestica, as a model organism to study the toxicity of four heavy metals: copper (Cu), zinc (Zn), cadmium (Cd), and lead (Pb). These have been fed to larvae at low and high, semi-lethal concentrations, and their accumulation in the head, thorax, and abdomen was subsequently measured in adult flies. In addition, their impact on the cellular concentration of several elements important for cell metabolism-sodium (Na+), magnesium (Mg++), phosphorous (P), sulphur (S), chloride (Cl-) and potassium (K+)-were measured in neural cells, muscle fibers, and midgut epithelial cells. Our study showed that the heavy metals accumulate mainly in the abdomen, in which the concentrations of two of the xenobiotic metals, Cd and Pb, were 213 and 23 times more concentrated, respectively, than in controls. All the heavy metals affected the cellular concentration of light elements in all cell types, but the changes observed were dependent on tissue type and were specific for each heavy metal, and its concentration.