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.     

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.     

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.     

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.     

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.     

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.     

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.     

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.     

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.     

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.     

A scanning electron microscope based new method for determining degree of substitution of sodium carboxymethyl cellulose

Na-CMC or sodium carboxylmethyl cellulose is a water soluble anionic polymer obtained by introducing carboxymethyl groups along the cellulose chain. Na-CMC is usually synthesized by the alkali catalyzed reaction of cellulose with monochloroacetic acid. The functional properties of Na-CMC depend on the degree of substitution of the cellulose structure (i.e. how many of the hydroxyl groups are substituted per monomer unit), and also on the chain length of the cellulose backbone. The degree of substitution of Na-CMC is usually determined according to ASTM D1439 which evolves the conversion of the Na-CMC to free acid then again forming Na-CMC by adding excess alkali and finally titrating the excess alkali with standard hydrochloric acid (0.3 N). The used volume of the standard alkali determines the degree of substitution. These existing chemical methods for determining the degree of substitution are not very convenient and very time-consuming involving the use of hazardous chemicals. In this research, we have evaluated that the scanning electron microscope equipped with Energy Dispersive X-Ray Analysis can be used to directly determine the degree of substitution.     

Method for scuffing propagation assessment

This paper describes a method for the determination of scuffing propagation using a four‐ball extreme‐pressure tester. The method has been developed at the authors' laboratory and is a completely new approach to the investigation of scuffing phenomena. A series of lubricants was prepared by blending antiwear (AW) and extreme‐pressure (EP) additives with a mineral base oil. Tribological experiments were then performed using the new method. The aim was to investigate the influence of such additives on scuffing propagation. It is shown that there is a significant influence of AW and EP additives on scuffing. Surface analyses (SEM, EDS) show the decisive role of the chemical reactions of AW and EP additives with the steel surface and their creation of a surface layer whose good antiseizure properties mitigate scuffing propagation and reduce wear intensity. It must be emphasised that the authors consider scuffing to be a process leading to the cessation of the relative movement of a tribosystem, known as seizure.     

Application of scanning electron microscopy for pollution particle source determination in residential dust and soil

Many tons of electric furnace flue dust accumulated in an industrial area in Tifton, Georgia. Vehicles transporting the flue dust, classified as K061 hazardous waste because it contained lead and cadmium, initially dumped the material in a warehouse. Once the warehouse was full, the flue dust was dumped in uncovered piles. Run-off from the piles and wind-driven particles had the opportunity to contaminate nearby industries, residential buildings, and neighborhood soils over a period of many years. Scanning electron microscopy-energy dispersive x-ray spectrometry (SEM-EDS) was used to compare the morphology and chemical composition of fly ash dust from the suspect pile with samples collected from the surrounding buildings and soil. Adhesive samplers were used to collect dust that had accumulated in buildings surrounding the fly ash dump site. Suspect dust particles were analyzed by SEM-EDS and compared with known dust particles from the fly ash pile. Soil samples were dried, sieved, and the “fines” analyzed by SEM-EDS for comparison with samples from the fly ash pile. Fly ash particles similar in morphology and chemical composition to the fly ash in the suspect pile were identified in most of the buildings sampled surrounding the fly ash dump site and in all of the soil samples analyzed surrounding the dumpsite. This case study illustrates the usefulness of applying morphology and chemistry information acquired by SEM-EDS for pollution particle source determination.     

Investigation of foreign substances in food

Scanning electron microscopy (SEM) together with energy-dispersive spectroscopy (EDS) and Fourier transform infrared spectroscopy (FTIR) were used to investigate foreign substances from seven categories of foreign substances in food. (1) Naturally occurring foreign substances--Using FTIR, a foreign substance was identified as a natural resin probably from the product. (2) Foreign substances introduced during food processing. Scanning electron microscopy-EDS was used to identify a foreign material found on surf clams as calcium phosphate from a product/ingredient interaction. Using SEM-EDS, a crystalline material in a meat product was identified as calcium salts of chloride and phosphate. Fourier transform infrared spectroscopy was used to identify foreign material that clogged an aerosol valve as chipboard. Using SEM-EDS, the metal in the heel of a glass bottle was identified as copper sulfide-containing metal inclusion. (3) Insects, reptiles, and rodents--Scanning electron microscopy was used to determine that a mouse found in food was not processed with the food, but entered the container after it left the factory. (4) Glass fragments--Glass from various sources can be distinguished from one another using SEM-EDS either by the level of the major elements in glass or by the presence of elements in one glass, but not in another. (5) Glass-like particles--Using SEM-EDS, glass-like particles found on beets were determined to be a fatty acid. (6) Metal foreign objects--Using SEM-EDS, metals from a variety of sources can be easily distinguished. For example, a tin-soldered container can be distinguished from a lead-soldered can. Using SEM-EDS, the metal fiber found on the bottom of a two-piece can likely enter the can during the final stage of the manufacture of the drawn and ironed food can. (7) Drug capsule identification--Fourier transform infrared spectroscopy was used to determine that a pill found in food was ibuprofen.     

Electron energy loss spectroscopy for analysis of inhaled ultrafine particles in rat lungs

Epidemiologic studies have associated cardiovascular morbidity and mortality with ambient particulate air pollution. Particles smaller than 100 nm in diameter (ultrafine particles) are present in the urban atmosphere in very high numbers yet at very low mass concentration. Organs beyond the lungs are considered as targets for inhaled ultrafine particles, whereby the route of particle translocation deeper into the lungs is unclear. Five rats were exposed to aerosols of ultrafine titanium dioxide particles of a count median diameter of 22 nm (geometric standard deviation, GSD 1.7) for 1 hour. The lungs were fixed by intravascular perfusion of fixatives immediately thereafter. TiO(2) particles in probes of the aerosol as well as in systematic tissue samples were analyzed with a LEO 912 transmission electron microscope equipped with an energy filter for elemental microanalysis. The characteristic energy loss spectra were obtained by fast spectrum acquisition. Aerosol particles as well as those in the lung tissue were unambiguously identified by electron energy loss spectroscopy. Particles were mainly found as small clusters with a rounded shape. Seven percent of the particles in the lung tissue had a needle-like shape. The size distribution of the cluster profiles in the tissue had a count median diameter of 29 nm (GSD 1.7), which indicates no severe clustering or reshaping of the originally inhaled particles. Electron energy loss spectroscopy and related analytical methods were found to be suitable to identify and localize ultrafine titanium dioxide particles within chemically fixed and resin-embedded lung tissue.