Characteristic X-ray Intensities Research Articles

Energy-Dispersive X-Ray Spectrum Simulation with NIST DTSA-II: Comparing Simulated and Measured Electron-Excited Spectra.

Electron-excited X-ray microanalysis with energy-dispersive spectrometry (EDS) proceeds through the application of the software that extracts characteristic X-ray intensities and performs corrections for the physics of electron and X-ray interactions with matter to achieve quantitative elemental analysis. NIST DTSA-II is an open-access, fully documented, and freely available comprehensive software platform for EDS quantification, measurement optimization, and spectrum simulation. Spectrum simulation with DTSA-II enables the prediction of the EDS spectrum from any target composition for a specified electron dose and for the solid angle and window parameters of the EDS spectrometer. Comparing the absolute intensities for measured and simulated spectra reveals correspondence within ±25% relative to K-shell and L-shell characteristic X-ray peaks in the range of 1–11 keV. The predicted M-shell intensity exceeds the measured value by a factor of 1.4–2.2 in the range 1–3 keV. The X-ray continuum (bremsstrahlung) generally agrees within ±10% over the range of 1–10 keV. Simulated EDS spectra are useful for developing an analytical strategy for challenging problems such as estimating trace detection levels.

Matrix effect correction method based on the main spectral parameters for rock samples in an in situ energy dispersive X-ray fluorescence analysis

Due to the differences in the matrix effects between different types of rocks, the target element contents in different rocks cannot be accurately determined by in situ X-ray fluorescence (XRF) analyses with the same parameters of the quantification procedure. We investigated the matrix effect correction methods of an in situ energy dispersive X-ray fluorescence (EDXRF) analysis for different matrix rock samples using Monte Carlo simulations (17 types of rock samples) and experimental verification (10 types of rock samples), in which both Cu and Zn were selected as target elements. The following conclusions were drawn. The matrix effect classification of the rock samples was not completely controlled by the detectable elemental composition or petrographic classification. According to the correlation between the spectral parameters and the characteristic X-ray intensity of the target elements, the matrix effect classification of rock samples could be more detailed. For rock samples in the same rock classification set and with the same target element content, the target element Kα X-ray intensity could be accurately described by the main spectral parameters, which include the scattering background at an energy interval of 4–19 keV, the Compton peak and the Rayleigh peak. Then, a matrix effect correction method was established, which allowed for the fast measurement of the target element contents of different rock samples by following the same parameters of the quantification procedure in the in situ EDXRF analysis. Simultaneously, six types of rock samples containing 3% Zn were selected as the validation set, and the relative errors of the target element content measurements in different rock samples were all less than 6% using the same parameters of the quantification procedure.

Relation Between the Characteristic X-Ray Intensity and Incident Electron Energy Using the Monte Carlo Method and Measurements

The characteristic X-ray of a target is of considerable significance in industrial applications and medical diagnosis and treatment, and its intensity is closely related to the incident electron energy. At a high energy, it is not easy to determine the relation between characteristic X-rays and the incident electron energy through measurements, but the Monte Carlo method has a wide energy calculation range. In this study, the X-ray energy spectra of six target materials (Cu, Mo, Rh, Ag, W, and Pt) were simulated at various incident electron energies (<3 MeV) using the Monte Carlo code MCNP5 and the relation curve between the characteristic X-ray intensity of each of the target materials, and the incident electron energy was obtained through a simulation. A Si-PIN detector was used to measure the low-energy output energy spectra of two X-ray tubes (Ag and W targets). The relation curve between the X-ray tube excitation voltage and the characteristic X-ray intensity was obtained by fitting the measured data to a linear function. The simulation fitting curve and measurement fitting curve agreed well in the low-energy range. Comparisons of the calculated and measured values revealed that most of the deviations for the Ag target were less than 5%, and those for the W target were less than 6%.

The f-ratio model for quantitative X-ray microanalysis

The f-ratio method is a new quantitative X-ray microanalysis method developed based on a cold field emission scanning electron microscope/energy dispersive spectroscopy system. The f-ratio is calculated with the characteristic X-ray intensities, and the Monte Carlo simulation is employed to build the theoretical relation between the system composition and the f-ratio. In this study, the f-ratio model is formulated with the elemental concentrations and the f-ratio coefficients. The f-ratio models in the binary S-Fe system and the ternary O-Al-Si system were studied, and the beam energy effects were investigated. The quantitative analyses were performed on the standard pyrite (FeS2) and kyanite (Al2SiO5) specimens, and the results show that the f-ratio model is able to achieve a satisfying accuracy.

Non-invasive XRF analysis of ancient Egyptian and near Eastern turquoise: A pilot study

More than 1400 turquoise stones associated with 98 archaeological artifacts from Egypt, the Near East, and Central Asia were analyzed using non-invasive point and scanning XRF. Geological specimens of turquoise from mines in the Sinai and Iran were also included in this study. The relative intensities of characteristic X-rays of Fe, Cu, Zn, and As were used to categorize the stones, which are discussed here in terms of their geographical contexts and assigned dates. The results indicate strong correlations between turquoise composition and archaeological attribution. Although these relationships likely reflect differences in turquoise sources that changed over the course of several millennia, it is not possible to associate the chemical signatures with specific mines solely using non-invasive XRF data.

Feasibility study of the high frequency X-ray communication using selective characteristic X-rays

It has been shown that X-ray communication is a significant way for the deep space communication, as well as can be applied when the spacecraft through the plasma sheath encountered during reentry into earth’s atmosphere period for the high frequency. The way of the X-ray frequency modulation is proposed to have a higher emission efficiency than the on–off​ control method. To develop this method for the further application, in this work, we set up an X-ray communication system consisting of a magnetic-modulated two-target X-ray tube and a silicon drift detector. Two kinds of selective characteristic X-rays, which are Cr-Kα of about 5.414 keV and Cu-Kα of about 8.047 keV, are employed as the carrier signals. The corrected results showed while the information was coded and modulated to emit X-rays, the characteristic X-ray intensities recorded by the detector changed a lot corresponding to the coded digital signals. Our method may provide a more selective way to optimize the X-ray communication system toward the practical application in space communication.

(Invited) Measurement of Salt Abundance on Weathering Steel Structures By Portable XRF

In suitable environments, weathering steels can be used for bridges without anticorrosion painting, because weathering steels have enough resistance to atmospheric corrosion by the protective rust generated on its surface. While, abundant supply of salt causes serious corrosion damage on weathering steels. Hence, deterioration due to corrosion is found in weathering steel bridges in conditions that salt abundantly supplied. When serious damages with corrosion are found in the components of weathering steel bridges, salt abundance on the components is measured to estimate reason of the corrosion and determine the repairing method. The salt abundance on the components is usually measured by surface salinity checker, which determines salt abundance by electrical conductivity of water that is in contact with an analyzed area. However, measurement of salt abundance by surface salinity checker is difficult for the component with serious corrosion damages, because porous rust or rough surface on the damaged component cause leakage of the contact water during the analysis. Therefore, measuring method for salt abundance without using water is needed to know salt abundance on corroded components for the maintenance of weathering steel bridges.In order to discuss the possibility of salt abundance measurement by portable XRF, characteristic X-ray intensity of Cl-and abundance of Cl- on five types of test pieces of weathering steels were analyzed by portable x-ray fluorescence analyzer (XRF) and gauze wipe method with ion chromatography respectively, in this study. The two types of test pieces are new weathering steels with coating of A-5 or C-5. Three types of test pieces were artificially corroded previously. For the two types of the corroded test pieces, coating with Ra-III or Rc-I were applied after removing rust. The other type of corroded test pieces was used without rust removing and coatings. The rust thickness on the test pieces was about a few 100 µm. To make air-born salt accumulation on each test pieces, sheltered exposure test was performed in the test site on the roof of the three-story building of the National institute of Technology, Matsue College, which is about 10 km far from sea. After that, characteristic X-ray intensity of Cl- on the test pieces was measured by portable XRF. Cl- on the test pieces was sampled by gauze wiping method, and the Cl- abundance was analyzed by ion chromatography. The characteristic X-ray intensity and abundance of Cl- on test pieces with coatings show good correlation (Fig. 1), suggesting that portable XRF is possible tool for measurement of Cl- abundance on the steels. While, the intensity of characteristic X-ray of Cl- on the corroded test pieces without removing rust shows poor correlation with the Cl- abundance. The intensity of characteristic X-ray of Cl- on the corroded test pieces without removing rust is extremely higher than that estimated from its Cl- abundance by gauze wiping method, considering the correlation among the test pieces with coatings. Since Cl- on weathering steels are known to be also in rust [3], completely sampling of Cl- by gauze wipe method is probably difficult for the corroded test pieces. Considering to the correlation line among the test pieces with coatings, the X-ray intensity of Cl- on corroded test pieces without removing rust potentially suggests that Cl- abundance on the test pieces are a few 100 mg/m2. For more accurate measurement of Cl- abundance on weathering steels with rust, the clear relation between characteristic X-ray intensity and Cl- abundance on weathering steels covered with rust should be revealed. To found the relation, method for complete sampling of Cl- on weathering steels with rust is required. In addition, it is needed to investigate detection range of Cl- in rust of weathering steels by portable XRF in terms of depth direction from surface.

Inverse modeling for quantitative X-ray microanalysis applied to 2D heterogeneous materials

Current quantitative X-ray microanalysis methods are only available for homogeneous materials. This paper presents a newly developed inverse modeling algorithm to determine both the structure and composition of two-dimensional (2D) heterogeneous materials from a series of X-ray intensity measurements under different beam energies and beam positions. It utilizes an iterative process of forward modeling to determine the optimal specimen to minimize the relative differences between the simulated and experimental characteristic X-ray intensities. The Monte Carlo method is used for the forward modeling to predict the X-ray radiation for a given specimen and experimental setup. Several examples of applications are presented for different types of samples with one-dimensional (1D) and 2D structures, in which the simulated X-ray intensities from phantom samples are used as input. Most of the results obtained from our algorithm agree well with the phantom samples. Some discrepancies are found for the voxels located at deeper depths of the 2D samples. And the discrepancies may be attributed to errors from the Monte Carlo simulations and from the variation of the X-ray range with beam energy. As a proof-of-concept work, this paper confirms the feasibility of our inverse modeling algorithm applied to 2D heterogeneous materials.

Angular distribution of characteristic X-ray emission from Fe and V following photoionization

&lt;sec&gt; The de-excitation process of vacancy in the inner shell of the target atom caused by collision ionization produces the characteristic X-ray or Auger electrons. The precise measurement of ionization cross sections plays an important role in many basic research fields, as well as in practical fields, such as chemical analysis of Particle Induced X-ray Emission (PIXE), atomic and nuclear processes, and X-ray fluorescence (XRF) spectroscopy. As we know, when ionization cross sections are measured precisely, whether the emission of X-ray is isotropic in collision process must be considered. However, there have been few experimental results for angular dependence of &lt;i&gt;K&lt;/i&gt;&lt;sub&gt;β&lt;/sub&gt;/&lt;i&gt;K&lt;/i&gt;&lt;sub&gt;α&lt;/sub&gt; intensity ratios in the literature until now. Therefore, this study aims to verify that the &lt;i&gt;K&lt;/i&gt;&lt;sub&gt;α&lt;/sub&gt; and &lt;i&gt;K&lt;/i&gt;&lt;sub&gt;β&lt;/sub&gt; X-rays originated from filling of the &lt;i&gt;K&lt;/i&gt; shell vacancies with total angular momentum quantum number 1/2 (&lt;i&gt;J&lt;/i&gt; = 1/2) are isotropic.&lt;/sec&gt;&lt;sec&gt; In this work, the typical &lt;i&gt;K&lt;/i&gt;-shell X-ray spectra for Fe and V, which induced by bremsstrahlung with central energy of 13.1 keV, have been measured at emission angles varied from 120° to 170° at intervals of 10°. The characteristic X-ray spectra obtained by the detector are fitted by Gauss function, where the absorption of incident X-rays by the detector, the absorption of emitted X-rays by the atmosphere and the self-absorption correction factor of incident and emitted X-rays by the target are all taken into account.&lt;/sec&gt;&lt;sec&gt; The experimental results of &lt;i&gt;K&lt;/i&gt;&lt;sub&gt;β&lt;/sub&gt;/&lt;i&gt;K&lt;/i&gt;&lt;sub&gt;α&lt;/sub&gt; intensity ratio in this experiment coincide with those of theoretical calculation, as well as the Ertuğral’s experimental result. The experimental results show that the intensity ratio of &lt;i&gt;K&lt;/i&gt;&lt;sub&gt;β&lt;/sub&gt;/&lt;i&gt;K&lt;/i&gt;&lt;sub&gt;α&lt;/sub&gt; is a constant at different detection angles. Therefore it can be concluded that the emission of &lt;i&gt;K&lt;/i&gt;&lt;sub&gt;α&lt;/sub&gt; and &lt;i&gt;K&lt;/i&gt;&lt;sub&gt;β&lt;/sub&gt; is isotropic in the detection range. Since the &lt;i&gt;K&lt;/i&gt; shell has no sub-shell, there is no Coster-Kronig transition in the collision ionization process. In the process of photoionization, the vacancies in the &lt;i&gt;K&lt;/i&gt; shell are produced by direct ionization. As a result, the cross section ratio of &lt;i&gt;K&lt;/i&gt; shell X-ray generation is independent of the &lt;i&gt;K&lt;/i&gt; shell photoionization cross section. In addition, the experimental results show that the &lt;i&gt;K&lt;/i&gt;&lt;sub&gt;β&lt;/sub&gt;/&lt;i&gt;K&lt;/i&gt;&lt;sub&gt;α&lt;/sub&gt; characteristic X-ray intensity ratio of target Fe is 8% higher than that of target V, which are consistent with the theoretical analysis results that the characteristic X-ray intensity ratio depends on the target atomic number &lt;i&gt;Z&lt;/i&gt;.&lt;/sec&gt;

Counterion Exchange in Peptide-Complexed Core-Shell Microgels.

The complexation of polyvalent macroions with oppositely charged polyelectrolyte microgels can lead to core-shell structures. The shell is believed to be highly deswollen with a high concentration of counter-macroions. The core is believed to be relatively free of macroions but under a uniform compressive stress due to the deswollen shell. We use cryo-scanning electron microscopy (SEM) with X-ray microanalysis to confirm this understanding. We study poly(acrylic acid) (PAA) microgels which form a core-shell structure when complexed with a small cationic antimicrobial peptide (L5). We follow the spatial distribution of polymer, water, Na counterions, and peptide based on the characteristic X-ray intensities of C, O, Na, and N, respectively. Frozen-hydrated microgel suspensions include buffers of known composition from which calibration curves can be generated and used to quantify both the microgel water and sodium concentrations, the latter with a minimum quantifiable concentration less than 0.048 M. We find that as-synthesized PAA microgels are enriched in Na relative to the surrounding buffer as anticipated from established ideas of counterion shielding of electrostatic charge. The shell in L5-complexed microgels is depleted in Na and enriched in peptide and contains relatively little water. Our measurements furthermore show that shell/core interface is diffuse over a length scale of a few micrometers. Within the limits of detection, the core Na concentration is the same as that in as-synthesized microgels, and the core is free of peptide. The core has a slightly lower water concentration than as-synthesized controls, consistent with the hypothesis that the core is under compression from the shell.

Effect of mechanical noise upon X-ray fluorescence analysis

The effect of the external mechanical noise on energy dispersive X-ray fluorescence (EDXRF) spectra has been investigated. A Nd2O3 sample was bombarded by the gamma-rays of 59.54 keV energy. The annular radioactive source (americium-241) with intensity equal to 1 Curie was used. The intensities of characteristic x-rays emitted from the Nd2O3 sample were measured using a high purity germanium detector. The mechanical noise applied to the experimental system had intensity values of 50 dB, 60 dB, 70 dB, 80 dB, 90 dB, and 100 dB. A sound level meter (Model 8928) was used to measure the external mechanical noise levels. The net area (P), background intensity (B), peak-to-background ratio (P/B), and full width at half-maximum (FWHM) of the characteristic peaks were determined in the energy dispersive X-ray fluorescence spectra obtained from Nd2O3 sample. It was observed that the background intensities of and peaks of the sample increased with the increasing mechanical noise level. The peak-to-background ratios (P/B) and the peak resolution decreased with increasing mechanical noise level.

Polarized XRF Spectrometer with a 40-mW X-Ray Tube

A three-dimensional polarized X-ray fluorescence (XRF) spectrometer was assembled with a low-power X-ray tube of 40 milliwatts, and a sample of stainless steel was measured with an acrylic polarizer. Based on the Schrodinger’s wave picture of Compton scattering, the dependence of the de Broglie wavelength and the scattering angle of a recoil electron on the incident X-ray energy were calculated. When the incident X-rays were scattered at an angle of 90°, the de Broglie of the recoil electron always went away at an angle of 45° with the incident X-rays and the de Broglie wavelength varied for any wavelength of the incident X-rays, i.e. we could select the scattering angle of the recoil electron to be 45°according to the incident X-ray energy and it could then be regarded as 45° Bragg diffraction that could produce highly polarized X-rays. The polarization measurement of scattered X-rays from an acrylic and lead plates substantiated that Compton scattered X-rays from the acrylic plate had higher degree of polarization than the elastically scattered X-rays from the lead plate. Highly polarized Compton scattered X-rays from the light-element polarizer led to the background reduction and the changes of the characteristic X-ray intensity in XRF spectra measured by our laboratory-made spectrometer. Key words: polarized X-ray fluorescence spectrometer, stainless steel, acrylic polarizer, Compton scattering, background. DOI: http://dx.doi.org/10.15826/analitika.2018.22.2.010

(Invited) Current Stage of the Investigation of the Composition of Oxygen Precipitates in Czochralski Silicon Wafers

The oxygen precipitates formed in Czochralski (CZ) silicon wafers in consequence of the thermal treatment were investigated since many decades. The main reason why so much effort was directed towards these defects was the impact which they have on integrated circuits and properties of silicon wafer itself. Oxygen precipitates can increase the resistivity of CZ silicon, change the wafer strength and cause warpage of the wafers. It was also demonstrated that metal impurities can be effectively trapped at oxygen precipitates in the process of gettering, what is a huge advantage. All these features of the oxygen precipitates require the control of precipitation in the production process of silicon devices. However, this cannot be optimally executed if the features of oxygen precipitates like their composition are not fully known. In spite of the wide knowledge of oxygen precipitation, the composition of oxygen precipitates SiO x still remains under ongoing discussion. This is due to the different x values varying from x=1 to x=2 which can be found in the literature. In this work, we look on the current stage of the investigation on the composition of oxygen precipitates obtained with the help of different techniques. Moreover, we present our recent investigation on the composition of oxygen precipitates carried out by means of energy dispersive X-ray spectroscopy (EDX), electron energy loss spectroscopy (EELS) and Fourier transform infrared spectroscopy (FTIR). The FTIR spectra measured at liquid helium temperature will be compared with the spectra simulated on the basis of experimental results obtained by scanning transmission electron microscopy (STEM). The EDX gives direct information about the composition of oxygen precipitates. However, the analysis of the EDX spectrum requires a special calibration. This is due to the limitation of EDX for light elements like oxygen. The intensity of characteristic X-rays of oxygen depends on the thickness of TEM lamellae. Therefore, in this work we measured a thermally grown SiO2 layer at different thickness of TEM lamellae in order to determine the influence of the lamellae thickness on the intensity of oxygen characteristic X-rays. After doing this, we measured the composition of oxygen precipitates located at very thin TEM lamellae. The results shown that x is in the range between 1.8 and 1.9 (1). To make sure that the EDX results are correct EELS measurements were carried out. EELS is a complementary method to EDX. It allows to avoid the limitation of EDX in the measurement of the composition of oxygen precipitate especially in the case if the precipitate does not go through the TEM lamellae. Deconvoluting the characteristic plasmons of Si, SiO2 and suboxides in the electron energy loss spectra we found that the oxygen precipitate consist of SiO2 and it is coated by thin 2-3nm SiO layer (2). Finally, we investigated the composition of oxygen precipitates by FTIR. The absorption band of oxygen precipitates were observed in FTIR spectra measured at liquid helium temperature. The position and the shape of the bands fit very well to the simulated spectra. The simulation of the spectra was conducted on the basis of the effective medium theory (EMT) where we considered SiO2 spheroids coated by SiO layers embedded in a Si matrix. In summary, the composition of oxygen precipitates was investigated by EDX, EELS and FTIR whereby the first two methods are direct methods and the latter one is an indirect method. All methods delivered similar results. Hence, we can conclude that the oxygen precipitates consist of a SiO2 core which is coated by an SiO layer. References 1D. Kot, G. Kissinger, M. A. Schubert, M. Klingsporn, A. Huber, and A. Sattler, Phys. Status Solidi RRL 9, 405 (2015). 2G. Kissinger, D. Kot, M. Klingsporn, M.A. Schubert, A. Sattler, T. Müller, ECS J. Solid State Sci. Technol. 4 (9), N124-N129 (2015).

Angular dependence of L X-rays emission for Ag by 10 keV electron-impact

Abstract The characteristic X-ray intensities of Ag-L α , L β1 , L β2 and L γ 1 are measured in electron-impact ionization at energy of 10 keV. The emission angle in this work ranges from 0° to 20° at interval of 5°. The angular dependence of L X-ray intensity ratios has been investigated for L α / L β1 , L β2 / L β1 and L γ1 / L β1 . It is found from the experimental results that the emissions of L β1 , L β2 and L γ 1 X-rays are spatially isotropic, while the L α X-rays exhibit anisotropic emission. Consequently, the alignment behavior of vacancy states is discussed with thorough analysis of vacancy transfer process.

Advanced β-ray-induced X-ray spectrometry for non-destructive measurement of tritium retained in fusion related materials

A new β-ray-induced X-ray measurement system equipped with a silicon drift detector, which was named “Advanced-BIXS”, was constructed to study in detail retention behavior of surface tritium by measurements of low energy X-rays below 1keV such as C(Kα) and O(Kα) as well as high energy X-rays induced by β-rays from tritium. In this study, basic performance of the present system has been examined using various tritium-containing samples. It was seen that energy linearity, energy resolution and sensitivity were quite enough for measurements of low energy X-rays induced by β-rays. Intensity of characteristic X-rays emitted from the surface and/or bulk of a tritium-containing sample was lowered by argon used as a working gas of the Advanced-BIXS. Pressure dependence of transmittance of C(Kα) and Fe(Kα) was examined as examples of low and high energy X-rays, and it was able to represent by using the mass absorption coefficient in argon. It was concluded, therefore, that the present system has high potentiality for nondestructive measurements of tritium retained in surface layers and/or bulk of fusion related materials.

Standardless Quantification Of Actinides By EPMA

Electron probe microanalysis (EPMA) is an analysis technique used to quantify with a high accuracy the amount of elements present on a sample of unknown composition. However, for some elements, such as the actinides, quantitative EPMA is not possible to achieve due to the lack of suitable reference standard samples. To overcome this difficulty, standardless methods can be employed with the use of virtual standards. Standardless method requires the accurate knowledge of absolute characteristic x-ray intensities. These x-ray intensities can be obtained by analytical calculations or by Monte Carlo (MC) simulations with mean of physical parameters. However, these parameters are not always well known and can lead to inaccurate results when used in standardless quantification methods. Validation by experimental measurements of the calculated x-ray intensities is needed.

X-ray spectrum emitted by the impact of 129Xe26+ of the different kinetic energies on Au surface

The characteristic X-ray spectra produced by the impact of 129Xe26+ with kinetic energies from 350 to 600 keV and from 1.8 to 3.9 MeV on Au surface are measured. It is found that 129Xe26+ with kinetic energies from 350 to 600 keV can excite only the characteristic X-ray spectra of Mα of Au, but 129Xe26+ with kinetic energies from 1.8 to 3.9 MeV can excite the characteristic X-ray spectra of Mζ, Mα, Mγ and Mδ. The relation between the characteristic X-ray intensity, the ratio of X-ray yield and the ion kinetic energy is analyzed. The kinetic energy threshold of L-X-ray of Xe emitted by Xe26+ is estimated.

Development of a low-energy PIXE analysis system based on an ion implanter

A low-energy particle-induced X-ray emission (LE-PIXE) analysis system with precise energy control was developed based on a 200kV ion implanter. The energy dependence of LE-PIXE was evaluated using a millimeter-sized low-energy proton beam by varying the incident energy with precision better than 5keV. LE-PIXE spectra were obtained for protons with an energy range of 40–120keV. The LE-PIXE sensitivity was approximately proportional to the sixth power of the incident proton energy. The characteristic X-ray intensity strongly depended on the depth distribution of elements in the target. Experimental evaluation with multilayered thin film samples demonstrated that LE-PIXE was effective for depth distribution analysis to 1000nm deep. Multilayered structures containing four different elements were characterized by LE-PIXE analysis using multiple probe energies.

Analysis of Biologically-Derived Small Particles—Searching for Geometry Correction Factors Using Monte Carlo Simulation

A Monte Carlo simulation was used to determine geometry correction factors that increase accuracy of quantitative X-ray microanalysis of laterally semithick biological materials. A model composed of cellulose with homogeneously distributed biological elements and lateral dimensions between 0.5-25 μm was chosen. The specimen was exposed to 5, 10, and 15 keV electrons, the net intensities of characteristic X-rays registered for the elements, and presented as a function of the lateral dimensions of the model. This showed the double decay exponential function fitted the distribution of X-ray intensities in relation to the model size. The applicability of the function as a correction method was successfully tested for 30 specimens with varying composition and dimensions. The value of relative error decreased from ±60% to ±5% when the correction was applied. Moreover, the minimal lateral size of the material was defined, below which the correction is not required. The simulation also revealed that the difference of the weighted sum of Z²/A between the unknown and the standard could reach 25% without significant influence on the quantitative results. The correction method could be helpful for accurate assessment of elemental composition in biological or organic matrices, when their lateral dimensions are smaller than the distribution range.

Void detection in copper interconnects using energy dispersive x-ray spectroscopy

The formation of small voids in narrow sub-50 nm Cu interconnect lines during their fabrication is a major challenge for the development of integrated circuits. Focused ion beam sectioning and scanning electron microscopy imaging are being used for void detection during process development, but as they are destructive, they are less suited for in-line metrology. Therefore, the authors developed a nondestructive method based on energy dispersive x-ray spectroscopy where voids can be detected as changes in x-ray intensity due to the direct proportionality of the generated characteristic x-ray intensity with the amount of copper atoms contained in the interaction volume. The procedure allows the detection of small voids down to 15 nm in a fast and nondestructive way. This is possible for thin and chemically mechanically polished Cu interconnects where intensity variations due to thickness variations can be ignored.