Reference-free X-ray Fluorescence 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.

Reference-free X-ray fluorescence analysis using well-known polychromatic synchrotron radiation

A reliable and reference-free X-ray fluorescence (XRF) analysis can be achieved by using accurate knowledge of the spectral distribution of the polychromatic excitation source.

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.

In-line characterization of ultrathin transition metal dichalcogenides using X-ray fluorescence and X-ray photoelectron spectroscopy

Industry-scalable fabrication methods of sulfur-based transition metal dichalcogenides are being developed, which puts strong requirements on the characterization of these mono- and few-layer materials in a cleanroom environment. In this paper, we show that the stoichiometry of ultrathin molydbenum disulfide layers can be determined by inline X-ray photoemission spectroscopy and wavelength-dispersive X-ray fluorescence, within the uncertainty provided by reference-free X-ray fluorescence in grazing incidence performed at the Physikalisch-Technische Bundesanstalt. In addition, we demonstrate that automated inline wavelength-dispersive X-ray fluorescence analysis can accurately determine the mass deposition of molybdenum and sulfur. Such information is crucial to support and accelerate the development of multi-parametric sulfur-based transition metal dichalcogenides processes, for instance by careful adjustment of the mass deposition per deposition cycle, both on samples and full wafers.

Towards a traceable enhancement factor in surface-enhanced Raman spectroscopy

Determination of the SERS enhancement factor through the challenging measurement of the molecular surface density by reference-free X-ray fluorescence.

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.

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.

Development and characterization of sub-monolayer coatings as novel calibration samples for X-ray spectroscopy

With the advent of both modern X-ray fluorescence (XRF) methods and improved analytical reliability requirements the demand for suitable reference samples has increased. Especially in nanotechnology with the very low areal mass depositions, quantification becomes considerably more difficult. However, the availability of suited reference samples is drastically lower than the demand. Physical vapor deposition techniques have been enhanced significantly in the last decade driven by the need for extremely precise film parameters in multilayer production. We have applied those techniques for the development of layer-like reference samples with mass depositions in the ng-range and well below for Ca, Cu, Pb, Mo, Pd, Pb, La, Fe and Ni. Numerous other elements would also be possible. Several types of reference samples were fabricated: multi-elemental layer and extremely low (sub-monolayer) samples for various applications in XRF and total-reflection XRF analysis. Those samples were characterized and compared at three different synchrotron radiation beamlines at the BESSY II electron storage ring employing the reference-free XRF approach based on physically calibrated instrumentation. In addition, the homogeneity of the multi-elemental coatings was checked at the P04 beamline at DESY. The measurements demonstrate the high precision achieved in the manufacturing process as well as the versatility of application fields for the presented reference samples.

A calibration procedure for a traceable contamination analysis on medical devices by combined X-ray spectrometry and ambient spectroscopic techniques

There is a strong need in the medical device industry to decrease failure rates of biomedical devices by reducing the incidence of defect structures and contaminants during the production process. The detection and identification of defect structures and contaminants is crucial for many industrial applications. The present study exploits reference-free X-ray fluorescence (XRF) analysis as an analytical tool for the traceable characterization of surface contaminants of medical devices, in particular N,N’-ethylene-bis (stearamide), an ubiquitous compound used in many industrial applications as a release agent or friction reduction additive.Reference-free XRF analysis as primary method has been proven to be capable of underpinning all other applied methods since it yields the absolute mass deposition of the selected N,N’-ethylene-bis (stearamide) contaminant whilst X-ray absorption fine structure analysis determines the chemical species. Ambient vibrational spectroscopy and mass spectroscopy methodologies such as Fourier transform infrared, Raman, and secondary ion mass spectroscopy have been used in this systematic procedure providing an extensive range of complementary analyses.The calibration procedure described in this paper was developed using specially designed and fabricated model systems varying in thickness and substrate material. Furthermore, typical real medical devices such as both a polyethylene hip liner and a silver-coated wound dressing have been contaminated and investigated by these diverse methods, enabling testing of this developed procedure. These well-characterized samples may be used as calibration standards for bench top instrumentation from the perspective of providing traceable analysis of biomaterials and surface treatments. These findings demonstrate the potential importance and usefulness of combining complementary methods for a better understanding of the relevant organic materials.

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.

Complementary Characterization of Buried Nanolayers by Quantitative X-ray Fluorescence Spectrometry under Conventional and Grazing Incidence Conditions

The determination of the thickness and elemental composition is an important part of the characterization of nanolayered structures. For buried nanolayers, X-ray fluorescence spectrometry is a qualified method for the thickness determination whereas conventional electron emission based methods may reach their limits due to rather restricted information depths. The aim of the presented investigation was the comparison of reference-free X-ray fluorescence spectrometry under conventional and grazing incidence conditions offering complementary information with respect to quantification reliability, elemental sensitivity, and layer sequences. For this purpose, buried boron-carbon layers with nominal thicknesses of 1, 3, and 5 nm have been studied using monochromatized undulator radiation in the laboratory of the Physikalisch-Technische Bundesanstalt (PTB) at the synchrotron radiation facility BESSY II. The results for the two beam geometries are compared and show particulate good agreements, thus encouraging the complementary use of both methodologies.

Elemental depth profiling of Cu(In,Ga)Se 2 thin films by reference-free grazing incidence X-ray fluorescence analysis

The semiconductor band gap of the Cu(In,Ga)Se 2 (CIGSe) compound can be varied by the In to Ga ratio. This composition variation determines the photovoltaic properties of CIGSe thin films. Their composition depth profile has to be optimized in order to obtain maximum efficiencies in solar cell applications. Synchrotron-radiation-based X-ray fluorescence (XRF) analysis under grazing incidence conditions provides non-destructive access to the compositional depth profile of the CIGSe thin films and, hence, represents a new non-destructive method, which does not require well-characterized standards for calibration purposes. Based on an analytical description of the physical processes, fluorescence line intensities of the specimen can be calculated by using fundamental atomic parameters. The general suitability of the method for determining depth gradients in CIGSe thin films is first shown by calculations. Reference-free XRF test measurements were carried out at the FCM beamline in the PTB laboratory at BESSY II. X-ray fluorescence was induced by photon excitation at energies of 4.0 keV and 10.5 keV, respectively, using various shallow incident angles. The calculations and the experimental measurements show that even small differences in the Ga/In profile may be distinguished, indicating that grazing incidence XRF is a promising tool for a non-destructive characterization of compositional depth profiles. Further refinement of the operational parameters may contribute to the sensitivity of the method.

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.

Advanced Metrologies for Wafer Contamination and Nanolayer Characterization Using XRF Methods

X-ray fluorescence (XRF) analytical methods based on synchrotron radiation can effectively contribute to the characterization of both semiconductor surface contamination and nanolayered systems. Total-reflection XRF allows for contamination analysis, reference-free XRF for the determination of nanolayer thicknesses and composition, and grazing-incidence XRF for elemental depth profiling of nanolayered systems. Due to the tunability of synchrotron radiation, each of these XRF methods can be easily combined with NEXAFS investigation to determine the species of contamination as well as nanolayer constituents.

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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