Synchrotron Radiation Total Reflection X-ray Fluorescence Research Articles

Comparison of techniques for detecting metal contamination in silicon wafers

In this work we present the results of experiments aimed at comparing the performances of various techniques for the detection of metal contamination in the silicon technology. Techniques for the measurement of surface contamination such as Total Reflection X-Ray Fluorescence (TXRF) and Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) are compared with techniques for the measurement of contamination in the silicon volume, specifically the Deep Level Transient Spectroscopy and techniques for the measurement of carrier lifetime. Carrier lifetime measurements were obtained by photocurrent measurements and by Surface Photovoltage measurements.In a first experiment, Synchrotron-Radiation TXRF (SR-TXRF) was used as the reference technique to assess the sensitivity of a commercial TXRF instrument and of carrier lifetime measurements to detect iron contamination in wafers cleaned by ordinary cleaning processes.Samples intentionally contaminated by spinning with various elements were used for another experiment comparing TXRF and ToF-SIMS measurements of surface contamination.Then, a few case studies are discussed, specifically tungsten contamination by sputtering in ion-implanted samples and palladium contamination due to contact with a contaminated chuck.In all these experiments, advantages and disadvantages of the different techniques are discussed. The results of this study clearly show that it is not possible to define a unique recipe that can be applied in all cases. The maximum tolerated contaminant concentration per unit area depends on the contaminant diffusivity, and is much lower for slow diffusers. The contaminant diffusivity and solid solubility in silicon determine the in-depth distribution of the contaminant, and hence the most effective approach.

Synchrotron radiation total reflection X-ray fluorescence (SR-TXRF) and X-ray absorption near edge structure (XANES) of fractionated air particulates collected from Jeddah, Saudi Arabia

Fractionated atmospheric aerosols with sizes ranged from 0.25μm to >16μm have been collected on silicon wafers using a 7-stage cascade impactor from the centre location of Jeddah city, Saudi Arabia during May 2015. Two fractionated sizes were selected in the present work, namely 0.5–0.25μm (PM0.5–0.25) and 2–1μm (PM2.0–1.0), because their mass concentrations were the most dominant. Fractionated atmospheric aerosols were examined under ultra-high vacuum environment with synchrotron radiation total reflection X-ray fluorescence (SR-TXRF) and X-ray absorption near edge structure (XANES) spectroscopy techniques at the International Atomic Energy Agency (IAEA) experimental end station operating at Elettra Sincrotrone Trieste, Italy. The mass concentrations in PM2.0–1.0 were found greater than those within PM0.5–0.25 material and the mass concentration ratio of PM2.0–1.0/PM0.5–0.25 was reached to 2. The homogeneity in the spatial deposition of different elements in both PM0.5–0.25 and PM2.0–1.0 fractions was evaluated by the means of X-ray fluorescence (XRF) scanning. XANES showed us that Cr species exist mainly in the trivalent oxidation state, while for Mn the co-existence of both the divalent and trivalent oxidation states was determined. The results of the present study provide an improved understanding on the origin of Cr and Mn species in these two fractionated particulates and give an insight to their contribution to atmospheric and physicochemical processes.

Rainwater analysis by synchrotron radiation-total reflection X-ray fluorescence

Total reflection X-ray fluorescence analysis excited with synchrotron radiation was used to quantify the elemental concentration of rainwater in Córdoba, Argentina. Standard solutions with gallium as internal standard were prepared for the calibration curves. Rainwater samples of 5μl were added to an acrylic reflector, allowed to dry, and analyzed for 200s measuring time. The elemental concentrations of As, Ca, Co, Cr, Cu, Fe, K, Mn, Ni, Pb, S, Sr, V, and Zn were determined. The electrical conductivity, pH, and elemental concentrations were compared to data previously reported for the soluble fraction of rainwater at different sites. A factor analysis was performed in order to determine the sources that contributed to the elemental concentration in rainwater. Anthropogenic sources were identified as traffic pollution, vehicular emissions, and metallurgical factories. The quality of rainwater was analyzed by comparing the concentrations of all the elements in rainwater samples with the WHO guideline values for drinking water. The results show the need to control the atmospheric emissions in order to preserve the quality of rainwater. SR-TXRF analysis of chemical composition of rainwater in Córdoba represents the very first contribution in the region to the knowledge of the concentration of trace metals in the soluble fraction of rainwater. These data are scarce, especially in the Southern Hemisphere.

Study of dinuclear Rh(II) complexes of phenylalanine derivatives as potential anticancer agents by using X-ray fluorescence and X-ray absorption

In vitro antitumor efficacy of several dinuclear bridgings and one chelate structure dirhodium(II) complex of N-protected phenylalanine derivatives were tested on HT-29 cells. The following synthesized and previously characterized complexes were applied in the present work: Rh2(OAc)4−n(O-Phe-Z)n (n=1–4, −O-Phe-Z=N-benzyloxycarbonyl-l-phenylalaninate), Rh2(OAc)4−n(O-Phe-Ac)n (n=1–4, −O-Phe-Ac=N-acetyl-l-phenylalaninate), Rh2(OAc)2(N-Me-D-Phe-O)2 corresponding to N-methyl-d-phenylalaninate as well as Rh2(OAc)4 (−OAc=acetate). Depending on the complex ligand type and its coordination number, the intracellular rhodium (Rh) content determined by total reflection X-ray fluorescence (TXRF) spectrometry in the HT-29 cells varied between 25 and 2500ng/106 cells. In vitro cytotoxicity and cytostatic evaluations of the compounds on HT-29 human cell culture were performed using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium assay. Compared to Rh2(OAc)4, the Rh compounds containing one or two -O-Phe-Z moieties proved to be the most effective on the HT-29 cells. Moreover, synchrotron radiation TXRF–X-ray absorption near edge structure measurements suggested a change of the molecular symmetry of the dirhodium(II) center for the moderately in vitro cytotoxic, lipophilic l-phenylalanine derivative complexes, characterized also by low ligand exchange rate when they were studied on HT-29 cells.

Observation of X-ray shadings in synchrotron radiation-total reflection X-ray fluorescence using a color X-ray camera

Absorption effects and the impact of specimen shape on TXRF analysis has been discussed intensively. Model calculations indicated that ring shaped specimens should give better results in terms of higher counts per mass signals than filled rectangle or circle shaped specimens. One major reason for the difference in signal is shading effects. Full field micro-XRF with a color X-ray camera (CXC) was used to investigate shading, which occurs when working with small angles of excitation as in TXRF. The device allows monitoring the illuminated parts of the sample and the shaded parts at the same time. It is expected that sample material hit first by the primary beam shade material behind it. Using the CXC shading could be directly visualized for the high concentration specimens.In order to compare the experimental results with calculation of the shading effect the generation of controlled specimens is crucial. This was achieved by “drop on demand” technology. It allows generating uniform, microscopic deposits of elements. The experimentally measured shadings match well with those expected from calculation.

Analyses of heavy metals in sewage and sludge from treatment plants in the cities of Campinas and Jaguariúna, using synchrotron radiation total reflection X-rayfluorescence

A major consequence of accelerated urban and industrial development in the last decades is water pollution. In particular, metal contamination is a significant problem, causing serious changes to the environment and adversely affecting human health. The cities of Campinas and Jaguariúna are inserted in the Campinas Metropolitan Region (CMR), one of the most dynamic regions in the Brazilian economy, accounting for 2.7% of Gross National Product (GNP) and 7.83% of São Paulo State Product—or approximately $ 70.7 billion per year. Besides having a strong economy, the region also presents an infrastructure that provides the development of the entire metropolitan area. Therefore, to study the anthropogenic influences of the cities, the evaluation of the quality of raw and treated effluent and, the sludge generated in sewage treatment plants (STP), especially with regard to heavy metals was performed by Total Reflection X-Ray Fluorescence with Synchrotron Radiation technique. The results were compared with the allowed values established by Brazilian Legislation. For raw and treated effluents collected in Jaguariúna and Campinas city in the Stations of Treatment of Sewage (Camanducaia and Anhumas), Cr presented higher concentrations than the maximum allowed values established by CONAMA 357. However, it is necessary to do other studies to define the fraction of Cr+3 and Cr+6 to compare to the new legislation. The other elements were in agreement with established regulations. For sludge sampled in the same locations, the concentrations of Cr, Cu, Pb, Ni and Zn were compared with the CONAMA 375 and showed values smaller than the maximum allowed values, indicating the possibility to re-use the sludge.

Elements concentration analysis in groundwater from the North Serra Geral aquifer in Santa Helena-Brazil using SR-TXRF spectrometer

In this work the analysis of elements concentration in groundwater was performed using the synchrotron radiation total-reflection X-ray fluorescence (SR-TXRF) technique. A set of nine tube-wells with serious risk of contamination was chosen to monitor the mean concentration of elements in groundwater from the North Serra Geral aquifer in Santa Helena, Brazil, during 1 year. Element concentrations were determined applying a SR-TXRF methodology. The accuracy of SR-TXRF technique was validated by analysis of a certified reference material. As the groundwater composition in the North Serra Geral aquifer showed heterogeneity in the spatial distribution of eight major elements, a hierarchical clustering to the data was performed. By a similarity in their compositions, two of the nine wells were grouped in a first cluster, while the other seven were grouped in a second cluster. Calcium was the major element in all wells, with higher Ca concentration in the second cluster than in the first cluster. However, concentrations of Ti, V, Cr in the first cluster are slightly higher than those in the second cluster. The findings of this study within a monitoring program of tube-wells could provide a useful assessment of controls over groundwater composition and support management at regional level.

Determination of cobalt marker in cow ruminal fluid by EDXRF and SRTXRF

AbstractThis article describes a comparison of conventional energy‐dispersive X‐ray fluorescence (EDXRF) and synchrotron radiation total‐reflection X‐ray fluorescence (SRTXRF) for Co determination in ruminal fluid from Holstein cow. This element is used as marker for animal nutrition studies. For EDXRF, 200 µl of the sample were dried on 6.35 µm Mylar film at 60 °C. The excitation was carried out using an X‐ray tube with Mo target and Zr filter operated at 30 kV/20 mA. For SRTXRF, 10 µl of the sample were pipetted on a Lucite carrier and dried at 60 °C. In both the techniques, Ga was used as internal standard and the acquisition time was 200 s. The trueness of both techniques was evaluated through the standard addition method, the recoveries obtained by SRTXRF and EDXRF were 76 and 99%, and the limits of detection, 13 and 240 µg l−1, respectively. Copyright © 2011 John Wiley & Sons, Ltd.

Speciation of copper and zinc in size-fractionated atmospheric particulate matter using total reflection mode X-ray absorption near-edge structure spectrometry

The health effects of aerosol depend on the size distribution and the chemical composition of the particles. Heavy metals of anthropogenic origin are bound to the fine aerosol fraction (PM 2.5). The composition and speciation of aerosol particles can be variable in time, due to the time-dependence of anthropogenic sources as well as meteorological conditions. Synchrotron-radiation total reflection X-ray fluorescence (SR-TXRF) provides very high sensitivity for characterization of atmospheric particulate matter. X-ray absorption near-edge structure (XANES) spectrometry in conjunction with TXRF detection can deliver speciation information on heavy metals in aerosol particles collected directly on the reflector surface. The suitability of TXRF-XANES for copper and zinc speciation in size-fractionated atmospheric particulate matter from a short sampling period is presented. For high size resolution analysis, atmospheric aerosol particles were collected at different urban and rural locations using a 7-stage May cascade impactor having adapted for sampling on Si wafers. The thin stripe geometry formed by the particulate matter deposited on the May-impactor plates is ideally suited to SR-TXRF. Capabilities of the combination of the May-impactor sampling and TXRF-XANES measurements at HASYLAB Beamline L to Cu and Zn speciation in size-fractionated atmospheric particulate matter are demonstrated. Information on Cu and Zn speciation could be performed for elemental concentrations as low as 140 pg/m 3. The Cu and Zn speciation in the different size fraction was found to be very distinctive for samples of different origin. Zn and Cu chemical state typical for soils was detected only in the largest particles studied (2–4 μm fraction). The fine particles, however, contained the metals of interest in the sulfate and nitrate forms.

Evaluation of water and sediment of the Graminha and Águas da Serra streams in the city of Limeira (Sp-Brazil) by Synchrotron Radiation Total Reflection X-ray Fluorescence

The city of Limeira is located in the state of São Paulo, Brazil and has the second largest economy and demographic growth of the state. It comprises an expressive economy with industries in several productive sectors. The source of the Graminha and Águas da Serra streams is located within the Limeira urban zone. The streams cross part of the rural zone and unite by draining into the Piracicaba River. It is possible that these basins suffer or have already suffered the impacts of environmental pollution caused by anthropogenic factors. Since the city has galvanization industries for the production of precious and semi-precious jewels as well as imitation jewelry, the concentration descriptions and interpretations of heavy metals in waters and sediments indicate anthropogenic influence and the dumping of these compounds into the Piracicaba River. The Synchrotron Radiation Total Reflection X-Ray Fluorescence (SR-TXRF) was used for determining the metals. All measurements were performed using a white beam of synchrotron radiation for excitation and a Ge hyperpure detector. Detection limits for water samples were 0.04 μg L − 1 and in sediment samples 0.03 μg g − 1 for Cu and Zn elements. In the water samples, concentrations higher than permissible as established by the Brazilian legislation (CONAMA) for Al, Fe, Zn, Cr, Ni, Cu and Pb, were observed. For sediment samples, values higher than quality reference values defined by the Brazilian legislation (CETESB) were verified for Cr, Zn, Cu, Ni and Pb.

Multi-elemental analysis of produced water by synchrotron radiation total reflection X-ray fluorescence

The synchrotron radiation total reflection X-ray fluorescence (SRTXRF) technique was used for the analysis of heavy metals in produced water samples from oil field in Rio Grande do Norte, in order to determine potential sources of pollution. Since the inorganic components in produced water generally resembling sea water, pre-concentration procedures have been applied to increase the concentration of the analyte of interest and to minimize the salt matrix effects. This technique allows us to determine the contents of V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Hg and Pb in 20 produced water samples. The great majority of the sampling points presented low elemental concentration value. However, in some sample, the Fe, Ni, Cu, Zn and Hg concentration were higher than the established limits by the Brazilian legislation.

Evaluation of the availability of heavy metals in lake sediments using SR-TXRF

The analytical technique Synchrotron Radiation Total Reflection X-ray Fluorescence (SR-TXRF) was used to evaluate the contamination and bioavailability of heavy metals in samples of sediment collected at different depths. The samples were collected in one of the lakes located next to ceramic industries in Santa Gertrudes, São Paulo state in the southwest region of Brazil during the rainy season. In order to determine the concentration of bioavailable metals (mobile fraction) and metals that are representative of the geological matrix (residual fraction) in sediment samples, procedures of acid extraction were implemented. All measurements were carried out in the Synchrotron Light Source Laboratory (LNLS), located in Campinas, São Paulo state. For sample excitation, a polychromatic beam of approximately 2 mm (width) and 0.3 mm (height) was used, and for the detection of the characteristic X-rays produced, a Si(Li) detector was employed. The net areas of the X-ray peaks were obtained from the program (Quantitative X-ray Analysis System; QXAS). The elements V, Cr, Co, Cu, Zn and Pb, which are considered to cause higher environmental damage, showed high availability. The concentrations of these elements are above the reference values which correspond to soil protection and underground water quality of São Paulo state. The concentrations obtained indicate that the area in study is contaminated.

Synchrotron radiation total reflection X-ray fluorescence (SR-TXRF) for evaluation of food contamination

The objective of this study was to use synchrotron radiation total reflection X-ray fluorescence analysis (SR-TXRF) for the determination of metals and other elements in food available to the population in commercial establishments, in order to evaluate the risks of contamination by these products. The analyzed species were vegetables, leafy vegetables, fruits, cereal and grain. The results indicated that some species were contaminated by Cr, Cu, Zn and Pb with concentrations much higher than the reference values.

Determination of Trace Elements in Alternanthera brasiliana and Pfaffia glabrata by SRTXRF: Application in Environmental Pollution Control

Aiming at environmental control, we report the use of synchrotron radiation total reflection x‐ray fluorescence (SRTXRF) analysis as a technique for trace elements determination in plants. The analyses were performed in two species (total plant) of Amaranthaceae family: Alternanthera brasiliana from four sites and Pfaffia glabrata from a single site. Some elements, such as P, S, K, Ca, Mn, Fe, Cu, Zn, Sr, and Pb were detected in all samples, and the elements Cl, Ti, Cr, Co, Ni, Br, Rb, Sr, Cd, Sn, Sb, and Ba were detected in some samples. The limit of detection (LOD) varied from 0.315 (Cu) to 121.4 (P) µg g−1.

Metal-binding proteins scanning and determination by combining gel electrophoresis, synchrotron radiation X-ray fluorescence and atomic spectrometry

In the present work, protein bands from in vitro embriogenic callus ( Citrus sinensis L. Osbeck) were investigated using micro-synchrotron radiation X-ray fluorescence (μSR-XRF) after sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) separation. Metal-binding protein quantification was done after microwave oven decomposition of gel by synchrotron radiation total reflection X-ray fluorescence (SR-TXRF), flame atomic absorption spectrometry (FAAS) and flame atomic emission spectrometry (FAES). According to the analysis of the protein bands, it is possible to observe that both 81 and ca. 14 kDa proteins present different Fe signal intensity at different positions. The analysis of 53 kDa protein, showed even more interesting results. Besides Fe, the μSR-XRF experiments indicate the presence of Ca, Cu, K and Zn. Chemical elements such as Cu, K, Fe and Zn were determined by SR-TXRF, Mg by FAAS and Na by FAES. Ca was determined by SR-TXRF and FAAS only for accuracy check. In the mineralised protein bands of 81 and around 14 kDa band, only Fe was determined (105 and 21.8 μg g −1). For those protein bands (86—ca. 14 kDa) were determined, Ca, K, Cu and Zn in a wide concentration range (42.4–283, 2.47–96.8, 0.91–15.9 and 3.39–29.7 μg g −1, respectively).

Analysis of Medicinal Plants and Crude Extracts by Synchrotron Radiation Total Reflection X-Ray Fluorescence

Abstract Plants and aqueous extracts of Alternanthera maritima (aerial parts and roots), Alternanthera brasiliana and Alternanthera tenella colla (total plant) were selected for analysis of metals bioaccumulation. The synchrotron radiation total reflection X-ray fluorescence (SRTXRF) was used for excitation of the samples and a Si(Li) detector for the detection of the characteristic X-rays emitted by the sample elements. The elements P, S, K, Ca, Ti, Mn, Fe, Cu, Zn, Rb, and Sr were detected in all samples. Further-more Al, Si, Cl, Ni, Br, Rb, Cd, Sn, Sb, Hg, and Pb in Alternanthera maritima samples; Si, Co, Cd, Sn, Sb, and Ce in Alternanthera brasiliana and Al, Si, Co, Ni, Br, Cd, Sn, Sb, and Ce in Alternanthera tenella colla were found. The concentration obtained in the samples for K-shell lines varied from 1.63 µg g−1 for Ni to 3.34 × 105 µg g−1for K, and for L-shell the values ranged from 1.64 x 101 µg g−1 for Cd to 6.71 × 102 µg g−1 for Sn.

Laboratory and synchrotron radiation total-reflection X-ray fluorescence: new perspectives in detection limits and data analysis

Having established detection limits for transition elements exceeding current requirements of the semiconductor industry, our recent efforts at the Stanford Synchrotron Radiation Laboratory (SSRL) have focused on the improvement of the detection sensitivity for light elements such as Al. Data analysis is particularly challenging for Al, due to the presence of the neighboring Si signal from the substrate. Detection limits can be significantly improved by tuning the excitation energy below the Si–K absorption edge. For conventional TXRF systems this can be done by using a W–Mα fluorescence line (1.78 keV) for excitation. At a synchrotron radiation facility energy tunability is available. However, in both cases this results in a substantial increase in background due to resonant X-ray Raman scattering. This scattering dominates the background under the Al Kα fluorescence line, and consequently limits the achievable sensitivity for the detection of Al surface contaminants. In particular, we find that for a precise determination of the achievable sensitivity, the specific shape of the continuous Raman background must be taken into account in the data analysis. The data deconvolution presented here opens a new perspective for conventional TXRF systems to mitigate this background limitation. This results in a minimum detection limit of 2.4×10 9 atoms/cm 2 for Al. Based on these results it will also be demonstrated that by improving the detector resolution, the minimum detection limit can be improved significantly. For a detector resolution of 15 eV as predicted for novel superconducting tunnel junction detectors, an improvement in minimum detection limit of approximately a factor of 3 can be estimated.

Beijing synchrotron radiation total-reflection X-ray fluorescence analysis facility and its applications on trace element study of cells

The feasibility of total-reflection X-ray fluorescence (TXRF) analysis excited by synchrotron radiation applied to trace element analysis of biological cells is investigated. The Beijing synchrotron radiation TXRF facility and the related experimental method are also described. The elemental minimum detection limits of some standard reference materials are determined. The elemental compositions of a cluster of small intestine cells of a small white mouse are given, and hence the average trace element contents of the single small intestine cell are also obtained. With this technique, the changes of some trace elements in the cells of lung and cervix cancer before and after apoptosis are also preliminarily studied.

Recent advances and perspectives in synchrotron radiation TXRF

Total reflection X-ray fluorescence (TXRF) using Synchrotron Radiation is likely to be the most powerful non-destructive technique for the analysis of trace metal impurities on silicon wafer surfaces. Of fundamental importance in TXRF is the achievable sensitivity as characterized by the minimum detection limit. This work describes the progress we achieved recently at the Stanford Synchrotron Radiation Laboratory (SSRL) in minimum detection limits for transition metals and will give an estimate of what can be achieved using a third generation synchrotron radiation source such as SPEAR3.

Trace element analysis on Si wafer surfaces by TXRF at the ID32 ESRF undulator beamline.

Synchrotron radiation total-reflection X-ray fluorescence (SR-TXRF) has been applied to the impurity analysis of Si wafers using a third-generation synchrotron radiation undulator source. A lower limit of detectability (LLD) for Ni atoms of 17 fg (1.7 x 10(8) atoms cm(-2)) has been achieved with an optical set-up based on an Si(111) double-crystal monochromator and a horizontal sample geometry. These first results are very promising for synchrotron radiation trace element analysis since we estimate that it is possible to lower the LLD by a factor of about 25 by employing appropriate optics and detectors. The use of a crystal monochromator opens new possibilities to perform absorption and scattering experiments (NEXAFS and X-ray standing-wave methods) for chemical and structural analysis of ultratrace elements.