Reference-free X-ray Fluorescence Analysis Research Articles

Reference-free x-ray fluorescence analysis with a micrometer-sized incident beam

Spatially resolved x-ray fluorescence (XRF) based analysis employing incident beam sizes in the low micrometer range (μXRF) is widely used to study lateral composition changes of various types of microstructured samples. However, up to now the quantitative analysis of such experimental datasets could only be realized employing adequate calibration or reference specimen. In this work, we extent the applicability of the so-called reference-free XRF approach to enable reference-free μXRF analysis. Here, no calibration specimen are needed in order to derive a quantitative and position sensitive composition of the sample of interest. The necessary instrumental steps to realize reference-free μXRF are explained and a validation of ref.-free μXRF against ref.-free standard XRF is performed employing laterally homogeneous samples. Finally, an application example from semiconductor research is shown, where the lateral sample features require the usage of ref.-free μXRF for quantitative analysis.

Quantitative manganese dissolution investigation in lithium-ion batteries by means of X-ray spectrometry techniques

The manganese deposition of an aged anode has been investigated with K-edge and L-edge NEXAFS to determine the manganese species. In addition, the absolute amount of manganese could be revealed with reference-free X-ray fluorescence analysis.

Interaction of nanoparticle properties and X-ray analytical techniques

In this work, Pt–Ti core–shell nanoparticles were characterized using reference-free X-ray fluorescence analysis and used for the investigation of the modification of the X-Ray Standing Wave (XSW) field intensity with increasing NP surface coverage.

Validation of secondary fluorescence excitation in quantitative X-ray fluorescence analysis of thin alloy films

Reference-free X-ray fluorescence analysis of multilayered, alloyed thin films in the μm regime with significant secondary fluorescence contributions.

Determination of SiO2 and C layers on a monocrystalline silicon sphere by reference-free x-ray fluorescence analysis

The redefinition of the kilogram will be based on Planck’s constant, which can be calculated from Avogadro’s constant, and hence by ‘counting’ the silicon atoms in a monocrystalline 28Si sphere weighing one kilogram. To reduce the influence of the surface layers on the determined value requires, amongst other issues, an accurate quantification of these layers on the 28Si spheres. Apart from the native SiO2 layer, carbonaceous contamination layers and adsorbed water molecules are expected to be crucial in determining the surface composition. The overall mass contribution of these surface layers must be determined with an accuracy below 10% in order to be able to meet the targeted uncertainty budget for the redefinition. In this work, we performed a quantification of these surface layers, applying reference-free x-ray fluorescence spectrometry using a modified manipulator within an ultra-high vacuum chamber. Using this setup, we are able to quantitatively assess the surface of the spheres on a large area (about 20%) with quantification uncertainties below the required target of 10% for oxygen and carbon in order to meet an absolute uncertainty value of the mass below 10 µg.

Traceable Quantitative Raman Microscopy and X-ray Fluorescence Analysis as Nondestructive Methods for the Characterization of Cu(In,Ga)Se2 Absorber Films.

The traceability of measured quantities is an essential condition when linking process control parameters to guaranteed physical properties of a product. Using Raman spectroscopy as an analytical tool for monitoring the production of Cu(In1-xGax)Se2 thin-film solar cells, proper calibration with regard to chemical composition and lateral dimensions is a key prerequisite. This study shows how the multiple requirements of calibration in Raman microscopy might be addressed. The surface elemental composition as well as the integral elemental composition of the samples is traced back by reference-free X-ray fluorescence analysis. Reference Raman spectra are then generated for the relevant Cu(In1-xGax)Se2 related compounds. The lateral dimensions are calibrated with the help of a novel dimensional standard whose regular structures have been traced back to the International System of Units by metrological scanning force microscopy. On this basis, an approach for the quantitative determination of surface coverage values from lateral Raman mappings is developed together with a complete uncertainty budget. Raman and X-ray spectrometry have here been proven as complementary nondestructive methods combining surface sensitivity and in-depth information on elemental and species distribution for the reliable quality control of Cu(In1-xGax)Se2 absorbers and Cu(In1-xGax)3Se5 surface layer formation.

Gaining improved chemical composition by exploitation of Compton-to-Rayleigh intensity ratio in XRF analysis.

The high specificity of the coherent (Rayleigh), as well as incoherent (Compton) X-ray scattering to the mean atomic number of a specimen to be analyzed by X-ray fluorescence (XRF), is exploited to gain more information on the chemical composition. Concretely, the evaluation of the Compton-to-Rayleigh intensity ratio from XRF spectra and its relation to the average atomic number of reference materials via a calibration curve can reveal valuable information on the elemental composition complementary to that obtained from the reference-free XRF analysis. Particularly for matrices of lower mean atomic numbers, the sensitivity of the approach is so high that it can be easily distinguished between specimens of mean atomic numbers differing from each other by 0.1. Hence, the content of light elements which are "invisible" for XRF, particularly hydrogen, or of heavier impurities/additives in light materials can be calculated "by difference" from the scattering calibration curve. The excellent agreement between such an experimental, empirical calibration curve and a synthetically generated one, on the basis of a reliable physical model for the X-ray scattering, is also demonstrated. Thus, the feasibility of the approach for given experimental conditions and particular analytical questions can be tested prior to experiments with reference materials. For the present work a microfocus X-ray source attached on an SEM/EDX (scanning electron microscopy/energy dispersive X-ray spectroscopy) system was used so that the Compton-to-Rayleigh intensity ratio could be acquired with EDX spectral data for improved analysis of the elemental composition.

A novel instrument for quantitative nanoanalytics involving complementary X-ray methodologies

A novel ultra-high vacuum instrument for X-ray reflectometry and spectrometry-related techniques for nanoanalytics by means of synchrotron radiation has been constructed and commissioned. This versatile instrument was developed by the Physikalisch-Technische Bundesanstalt, Germany's national metrology institute, and includes a 9-axis manipulator that allows for an independent alignment of the samples with respect to all degrees of freedom. In addition, a rotational and translational movement of several photodiodes as well as a translational movement of an aperture system in and out of the beam is provided. Thus, the new instrument enables various analytical techniques based on energy dispersive X-ray detectors such as reference-free X-ray fluorescence analysis (XRF), total-reflection XRF, grazing-incidence XRF in addition to optional X-ray reflectometry measurements or polarization-dependent X-ray absorption fine structure analyses. With this instrument samples having a size of up to 100 mm × 100 mm can be analyzed with respect to their mass deposition, elemental or spatial composition, or the species in order to probe surface contamination, layer composition and thickness, the depth profile of matrix elements or implants, the species of nanolayers, nanoparticles or buried interfaces as well as the molecular orientation of bonds. Selected applications of this advanced ultra-high vacuum instrument demonstrate both its flexibility and capability.

Characterisation of High-k Containing Nanolayers by Reference-Free X-Ray Fluorescence Analysis with Synchrotron Radiation

Using reference-free X-ray fluorescence analysis (XRF) in different geometries carried out in the laboratory of the Physikalisch-Technische Bundesanstalt at the electron storage ring BESSY II in Berlin various nanolayered systems have been investigated. As an example the investigation of Hf containing thin oxide layers is shown. For comparison reasons these samples have been also measured by X-ray reflectometry (XRR) in the PTB laboratory and by other partners within the ANNA project, which confirmed the thickness of the Hf containing top layers determined by XRF within their respective uncertainties. The XRF spectra were deconvolved employing the detector response functions to deduce the intensity of the corresponding Hf L3 fluorescence lines. The investigation of nanolayered systems especially in the lower energy range shows advantages, like different absorption conditions which allow for better dynamics and the suppression of the silicon fluorescence signal from the substrate, but needs more effort in determining the respective fundamental parameters.

Nanolayer Characterisation by Reference-free X-ray Fluorescence Analysis with Synchrotron Radiation

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Wafer Contamination Analysis, Speciation and Reference-free Nanolayer Characterization using Synchrotron Radiation based X-ray Spectrometry

Total-reflection, grazing-incidence and reference-free X-ray fluorescence analysis employing synchrotron radiation can substantially contribute to the contamination analysis and speciation on semiconductor surfaces as well as to the non-destructive characterization of nanolayered systems allowing for high information depths.

F15 Thickness Determination of Copper and Nickel Nanolayers: Comparison of Completely Reference-Free X-ray Fluorescence Analysis and X-ray Reflectometry

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Thickness determination for Cu and Ni nanolayers: Comparison of completely reference-free fundamental parameter-based X-ray fluorescence analysis and X-ray reflectometry

Monochromatized synchrotron radiation of the electron storage ring BESSY II has been used for the non-destructive thickness determination of nanolayered materials by two different methods. The aim of these investigations was the comparison of completely reference-free fundamental parameter-based X-ray fluorescence analysis with X-ray reflectometry to validate the quantification of X-ray fluorescence analysis as an absolute method. For this purpose, Cu and Ni layers with a thickness varying between 5 nm and 50 nm as well as double layers of both metals deposited on Si have been studied. In X-ray reflectometry characterization experiments, the tunability of the photon energy allows the determination of not only the total layer thickness but also the individual layer thicknesses of the Cu/Ni double-layer systems. Reference-free X-ray fluorescence analysis involves both the fundamental parameter approach and the knowledge of all relevant experimental parameters obtained by instrumentation calibrated absolutely. The layer thickness determined by both methods agreed within their combined uncertainties. In view of the limits of X-ray reflectometry for very thin layers, laterally inhomogeneous samples, and multi-elemental layer compositions, reference-free X-ray fluorescence analysis offers the potential for the thickness determination of such samples.

Comparison of reference-free X-ray fluorescence analysis and X-ray reflectometry for thickness determination in the nanometer range

X-ray reflectometry is the method of choice to determine the thickness of nanolayered systems with small uncertainties. In view of known limitations of this method for extremely thin or laterally inhomogeneous layers we compared X-ray reflectometry with fundamental parameter based X-ray fluorescence analysis using synchrotron radiation in the radiometry laboratory of the PTB. The results of both methods for a set of sample systems with transition metal layers of various thicknesses deposited on silicon wafers were compared and showed a good agreement within their respective uncertainties. For the investigation of layered systems both methods are very appropriate and, in addition, can give complementary information about the layers. Thus, the density is determined by X-ray reflectometry, and X-ray fluorescence analysis gives information about trace elements within the layers and the layer homogeneity.