New approaches to quantitative x-ray microanalysis of thin films and surfaces

Quantitative analysis of thin films using an electron probe micro-analyser requires the accurate knowledge of the depth distributions of X-ray production (Ø(z) curves) and the influence of the thin film- substrate interface on that distribution. A Gaussian expression for Ø(z) curves has been used which is modified at the interface by the ratio of Ø(0) values. In this way, quantitative predictions of the dependence of X-ray intensity on depth and substrate have been made. Analysis requires the use of only pure element or compound standards. The sensitivity for detection of thin films is about one monolayer for most elements. By measuring X-ray intensity as a function of electron energy, concentration profiles up to a depth of approximately 1 um. can be measured with a depth resolution of the order of 1 nm. in favourable cases.     

Environmental scanning electron microscopy and microanalysis

It is shown that the environmental scanning electron microscope is the natural extension of the scanning electron microscope. The former incorporates all of the conventional functions of the latter and, in addition, it opens many new ways of looking at virtually any specimen, wet or dry, insulating or conducting. The environmental scanning electron microscope is characterised by the possibility of maintaining a gaseous pressure in the specimen chamber. All operational parameters can be varied within a range which is a function of pressure. It can be used with all types of gun and all basic modes of detection and, hence, it can be applied both to morphological and to microanalytical studies. It has opened many novel ways of looking at specimens and phenomena not previously accessible with scanning electron microscopy.     

Xylene-stream method for obtaining thin polyethylene specimens for electron microscopy

A new technique is described for obtaining thin specimens from melt-crystallized polyethylene surface for studying the lamellar structure with the electron microscope. The specimen was first backed with carbon–gelatin backing and then the polyethylene side was exposed to a temperature-controlled xylene stream. After dissolving most of the specimen, a very thin layer of polyethylene which shows certain aspects of the original lamellar structure was obtained. Stereoscopic micrographs revealed the structure of polyethylene consisting of curved layers, concave, convex and other forms. These curved layers were identified by analysis of the Bragg fringes to be the crystalline lamellae. A special pattern resembling a spider in shape caused by a spherical crystal was investigated.     

Identification of respirable asbestos fibres by quantitative x-ray microanalysis with a scanning transmission electron microscope (STEM)

Summary Quantitative X-ray microanalysis of respirable asbestos fibres, based on the ratio method, enables the identification of different asbestos varieties in the submicrometre diameter range. A new identification scheme is proposed and applied for samples from an asbestos-cement factory and from a mining site. STEM analysis is compared with other methods of single particle analysis.

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Identifizierung von lungengängigen Asbestfasern mittels quantitativer Röntgenmikroanalyse mit einem Rastertransmissionselektronenmikroskop

Zusammenfassung Die quantitative Röntgenmikroanalyse von lungengängigen Asbestfasern im Submikrometerbereich nach der Verhältnismethode ermöglicht die Identifizierung der verschiedenen Asbestarten. Ein Schema zur Identifizierung von Asbestfasern wird vorgeschlagen und zur Charakterisierung von zwei Asbestproben angewendet. Vorteile und Nachteile der Methode in Vergleich mit anderen Methoden werden diskutiert.

     

Determination of the depth profiles of ion-implanted impurities by electron probe x-ray microanalysis

The aim of this paper is to demonstrate the suitability of electron probe x-ray microanalysis (EPMA) for nondestructive determination of the depth profiles of ion-implanted impurities. The intensities of the characteristic x-ray emission of impurity atoms (P and As) were measured (on a WDX spectrometer) on the implanted specimens and references (GaP and GaAs) at three values of primary electron energy E_P. The range distribution of the implanted impurity as a first approximation is given by a Gaussian distribution. A two-parameter fitting has been developed for the determination of Gaussian parameters R_P and ΔR_P of the profiles, which give a minimal difference between the experimental and calculated x-ray intensities at different E_P. The dose of the implanted impurity is a third parameter that can be obtained here. The results were compared with those of depth profiles from AES (for P) and SIMS (for As) and good agreement is observed. A new method for the determination of the depth distribution of x-ray production for the characteristic x-rays of impurity atoms is also presented.     

X-ray microanalysis of thin film layered specimens containing light elements

Analysis of thin film layers on bulk substrates is carried out using a technique based on the (z) model of the depth distribution of X-ray emission. Both the composition and thickness of individual layers can be determined provided that the same element is not present in more than a single layer.The application of this method to the analysis of thin titanium-boron nitride bilayers on silicon or molybdenum substrates is discussed. X-ray intensities were measured by energy dispersive spectroscopy with a windowless or ultra thin window detector. The thickness of a 10 nm titanium layer could be estimated to within about ±1 nm, which is comparable with the depth resolution attainable by Auger sputter profiling.     

Software package for quantitative analysis of solid materials by energy-dispersive x-ray fluorescence spectrometry without absolute calibration

A software package for quantifying elements in solids from energy-dispersive x-ray fluorescence data is described. The algorithm is based on the fundamental parameter approach and facilitates the simultaneous determination of several elements at widely varying concentrations. The software comprises three programs. One program, for spectrometer control and data acquisition, resides in a dedicated microcomputer. The two other programs, for spectra deconvulution and data evaluation, reside in a larger central computer. On-line communication between the computers is feasible, and the system facilitates the implementation of new improved programs. The performance of the system was tested on standard reference materials, and satisfactory accuracy was obtained for up to 21 elements.     

Two calculation procedures for the determination of composition and mass thickness of thin samples by x-ray spectrometry

Two procedures are described for calculating the composition and mass thickness of thin samples from measured x-ray intensities. One procedure is suitable for use with a programmable hand calculator but gives correct results only for very thin samples. The other procedure utilizes the NRLXRF program and produces correct results for thin and thick films.     

Multi-element analysis of urine by energy-dispersive x-ray fluorescence spectrometry

For multi-element analysis of human urine, 25-ml samples doped with yttrium as internal standard are evaporated gently and then ashed up to 460°C overnight. The residue is pelletized and analysed by energy-dispersive x-ray fluorescence. Acid addition to facilitate the digestion is not mandatory. Recoveries are nearly quantitative for traces of Fe, Ni, Cu, Zn and Sr, to a lesser extent for lead, but not for arsenic or selenium. The standard deviation per measurement is typically around 6%. The detection limits are such that some 10 elements can be determined simultaneously in normal urine, and possibly more in cases of importance to toxicology or industrial hygiene.     

扫描电子显微镜-能谱分析仪(SEM-EDS)中面扫描法在高分子材料失效分析中的应用

用扫描电子显微镜搭载的有窗X射线能谱仪（EDS能谱）对荧光样品进行分析时,由于电子束的激发作用,样品受激自发产生的荧光将严重干扰EDS能谱探头对特征X射线的分析,最终导致定量困难甚至难以定性. 新型无窗EDS能谱由于其优异的低能量端信号采集与分析能力,结合单颗粒小区域采集的方法,可以成功实现荧光样品的正常EDS能谱分析. 由于无窗EDS能谱仪没有传统薄膜窗口的吸收作用,其最低可分析元素为锂. 通过优化加速电压,并借助样品表面钝化膜的保护作用,克服了背景噪音与样品污染的干扰,成功实现对单质锂的检测.     

Quantitative separation of traces of copper by electrodeposition and determination by electron probe microanalysis

Summary A combination of ion-exchange and micro-electrodeposition techniques permits the rapid separation of sub-microgram amounts of copper in a form suitable for determination with the electron probe microanalyser. Recoveries of 98% and standard deviations < 5% have been checked by other methods at the 10-g level.

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Zusammenfassung Eine Verbindung von Ionenaustausch und Elektrolyse ermöglicht die rasche Abscheidung von Submikrogrammengen Kupfer in einer für die Elektronenstrahlmikroanalyse geeigneten Form. Ausbeuten von 98% und Standardabweichungen von < 5% wurden mit anderen Verfahren im 10-g-Maßstab erwiesen.

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Presented at the VI. International Symposium on Microtechniques September 1970, Graz, Austria.     

Accuracy of film thickness determination in electron probe microanalysis

The thickness of copper films (100–450 nm) on silicon substrates was determined by electron probe microanalysis (EPMA) applying (z) procedures of Pouchou and Pichoir. Film thickness was calculated from experimental k-ratios analyzed with electron energies between 6 and 30 keV using commercial software (LAYERF distributed by CAMECA). The influence of the incident electron energy and X-ray line chosen for analysis on the results was investigated. Accuracy of film thickness determination was evaluated by comparison with Rutherford backscattering spectroscopy (RBS) and secondary ion mass spectrometry (SIMS). The difference between layer thicknesses determined with EPMA and RBS is in general less than 2%, if EPMA measurements are performed with various electron energies. Layer thicknesses determined with Cu-L are mostly closer to values obtained by RBS than those derived from Cu-K radiation. Preliminary SIMS measurements yielded inconsistent results and, thus, cannot be used in this case to determine the layer thickness of Cu films on Si accurately.     

A quantitative determination of the polymerization of benzoxazine thin coatings by time-of-flight secondary ion mass spectrometry

Phenol-paraphenylenediamine (P-pPDA) benzoxazines exhibit excellent barrier properties, adequate to protect aluminum alloys from corrosion, and constitute interesting candidates to replace chromate-containing coatings in the aeronautical industry. For the successful application of P-pPDA coatings, it is necessary to decrease the curing temperature to avoid the delamination of the coating while preserving the mechanical properties of the alloy, as well as the barrier properties of the coating. However, decreasing the curing temperature leads to less polymerized films, the extent of which requires a quantitative assessment. While the conversion rate of the polymerization reaction is commonly evaluated for bulk samples using differential scanning calorimetry (DSC), a tool for its evaluation in thin films is missing. Therefore, a new approach was developed for that matter using time-of-flight secondary ion mass spectrometry (ToF-SIMS). The relation between the SIMS data integrated from inside thin films and the DSC results obtained on bulk samples with the same curing cycle allowed to calibrate the SIMS data. With this preliminary calibration of the technique, the polymerization of P-pPDA coatings can be locally determined, at the surface and along the depth of the coating, using dual-beam depth profiling with large argon cluster beam sputtering.     

X-ray microanalysis and high-resolution transmission electron microscopy of the reduced titanium-niobium oxides

Phase relationships in TiNb₂O₇ and Ti₂Nb₁₀O₂₉ reductions at 1400°C were investigated by means of X-ray microanalytical electron microscopy and high-resolution transmission electron microscopy (TEM). Compositions of phases present in equilibrium were obtained by applying thin-crystal approximation by which $\text{Nb}\text{Ti}$ ratios in different phases were determined; their oxygen content was inferred from structural considerations. In this manner, phase relationships in that portion of the TiO₂NbO₂NbO_2.5 equilibrium diagram with 2.417 ≥ x (in MeO_x) ≥ 2 were defined. Data obtained, in combination with high-resolution electron microscopy observations, confirmed that the reduction reaction, in part, is a heterogeneous process controlled by outward diffusion of both metal and oxygen atoms. Recombination of the diffused particles leads to the formation of separate crystals. The original block structure phase undergoes transformation in a quasihomogeneous manner either to an isomorphous phase in the binary NbO system or to a structurally related lower composition oxide. A new superstructure Me₂₅O₆₀(Ti_7.16Nb_42.84O₁₂₀) has been detected as an intermediate metastable phase, generated in the reduction of TiNb₂O₇ to stable Me₁₂O₂₉(Ti_1.53Nb_10.47O₂₉) and MeO₂(Ti_0.52Nb_0.48O₂) phases. Consideration of phase relationships among Me₂₅O₆₀, Me₁₂O₂₉, and MeO₂ suggests a chemical mechanism for the reaction concerned. The Me₂₅O₆₀ superstructure has a monoclinic symmetry with cell parameters a = 19.0 Å, b = 3.8 Å, c = 26.6 Å, α = 90°, β = 90°, γ = 78.5°, as determined from the structure image calculations.     

Metrological characteristics of lead determination in rare earth phosphates by electron probe microanalysis

An equation for the calculation of the detection limit c _lim is presented. Relations for the limit of detection c _lim, limit of determination c _min, and relative error V of analyte determination are derived. The performance characteristics of lead determination in rare earth phosphates on a JXA-8100 microanalyzer are found. Under the typical conditions of the determination of monazite age (15 kV, probe current of 250 nA, count time in the positions of the line and background 400 s each) c _min using the 2σ-criterion is 0.006 wt % for an ordinary spectrometer and 0.004 wt % for a high-aperture one. In the simultaneous registration of lead by the scheme ”two ordinary plus one high-aperture channel,” c _min is reduced to 0.003%. For c _min = 0.006%, the acceptable error of age estimates V of 1–3 relative percent is attained at c _lim = 0.3-0.08%, respectively. As was found, the lowest capacity of microanalyzers for geochronology needs is 0.02–0.03% of PbO. Equations of constraints for the performance characteristics of methods ensure the revelation of the necessary conditions of analysis and compliance with them.     

Evaluation of multi-element analysis of blood serum by energy-dispersive x-ray spectrometry

Conventional energy-dispersive x-ray fluorescence is applied in the analysis of blood serum to give the concentrations of 7–10 elements simultaneously with minimal manipulation of the samples. Simple spotting onto a Mylar carrier of 250 μl of serum, doped with two internal standards, was chosen as the sample preparation step. Some 200 serum samples, analyzed in replicate (n = 2–6), were used to evaluate this procedure. The detection limits are 4 μg ml^-1 for K and Ca, 0.5–0.2 μg ml^-1 for Fe, Cu, Pb and Zn, and less than 0.1 μg ml^-1 for Se, Rb and Sr. Well above these limits, the standard deviation is around 10%. Comparison with the results of other measurements on the same samples indicates an accuracy of that order. The simplicity and high throughput, and the possibility of automating the x.r.f. measurements, make the proposed procedure suitable for screening large numbers of sera.     

Investigations on thin solid layers by analytical transmission electron microscopy

Summary Among the instruments for solid state characterization working with a free electron probe, the Transmission Electron Microscope (TEM) has the best lateral resolution. The application is restricted, however, by the demand that the samples need to be suitably thinned. TEMs operating in the scanning mode yield several advantages. Equipped additionally with spectrometers, the TEM becomes an Analytical TEM. Energy Dispersive X-ray Spectroscopy (EDXS) and Electron Energy Loss Spectroscopy (EELS) allow the chemical analysis of the observed details of structure; the EELS permits additionally investigations on the electron configuration and on binding relations. Technical developments have increased considerably the information possibilities, such as lateral resolution or detection sensitivity. Recently two new types of instruments are in development, the dedicated Scanning-TEM with a field emission gun, supplying scanning images and analyses up to the nanometer range, and the energy filtering (stationary beam-) microscope which yields images and diffraction diagrams with a sharpness in contrast not previously reached. In the future the construction of an aberration-free objective lens promises a further advance into the atomic dimension.     

Application of a fundamental parameter technique for solving peak-overlap problems in quantitative energy-dispersive x-ray fluorescence spectrometry

The procedure exploits the fundamental parameter technique for monoenergetic excitation. The algorithm describes each peak as a sum of line intensities, thus intensities from unresolved lines are included directly in the equations. The procedure includes the condition that the sum of all weight fractions equals unity, and so is valid only when all elements are measured by x-ray fluorescence spectrometry, e.g., in steel alloys. The procedure is tested with a set of theoretically calculated x-ray fluorescence intensities, and for two NBS standard steel alloys.