Determination Of Depth Profiles Research Articles

Temperature Effects of Nuclear and Electronic Stopping Power on Si and C Radiation Damage in 3C-SiC.

Silicon carbide has been considered a material for use in the construction of advanced high-temperature nuclear reactors. However, one of the most important design issues for future reactors is the development of structural defects in SiC under a strong irradiation field at high temperatures. To understand how high temperatures affect radiation damage, SiC single crystals were irradiated at room temperature and after being heated to 800 °C with carbon and silicon ions of energies ranging between 0.5 and 21 MeV. The number of displaced atoms and the disorder parameters have been estimated by using the channeling Rutherford backscattering spectrometry. The experimentally determined depth profiles of induced defects at room temperature agree very well with theoretical calculations assuming its proportionality to the electronic and nuclear-stopping power values. On the other hand, a significant reduction in the number of crystal defects was observed for irradiations performed at high temperatures or for samples annealed after irradiation. Additionally, indications of saturation of the crystal defect concentration were observed for higher fluences and the irradiation of previously defected samples.

Ion Beam Analysis including ToF-ERDA of complex composition layers

When developing new materials for example, for high-temperature nuclear reactors with the potential of hydrogen production, that are characterized by radiation, high temperature and corrosion resistance, it is indispensable the knowledge of their detailed elemental composition and its possible variation with depth from surface. Several analytical methods based on different physical principles are used to determine the depth distribution of elements in the surface layers of materials. For the quantitative determination of elemental depth profile to a depth of several micrometres are applicable established Ion Beam Analysis (IBA) methods such as RBS, EBS, NRA and ERDA. Their advantage is that they are considered to be absolute and to a certain extent non-destructive. Each of these methods is advantageously used to analyse a certain range of elements, sometimes depending on the combination of other elements present. The recently commissioned Time of Flight Elastic Recoil Analysis (ToF-ERDA) measuring system at the Slovak University of Technology MTF in Trnava significantly enhanced the Ion Beam Laboratory capability of a comprehensive elemental analysis of thin films to the depth of hundreds of nanometres. Using the primary analysing 50 MeV Au beam, the depth profiles of all elements from W to H can be obtained within a single measurement. Analysis of complex samples using traditional IBA methods and high-energy ToF-ERDA is discussed and compared. The first measurements on the new ToF-ERDA installation are also presented.

Suitability of 210Pbex, 137Cs and 239+240Pu as soil erosion tracers in western Kenya

Land degradation resulting from soil erosion is a global concern, with the greatest risk in developing countries where food and land resources can be limited. The use of fallout radionuclides (FRNs) is a proven method for determining short and medium-term rates of soil erosion, to help improve our understanding of soil erosion processes. There has been limited use of these methods in tropical Africa due to the analytical challenges associated with 137Cs, where inventories are an order of magnitude lower than in the Europe. This research aimed to demonstrate the usability of 239+240Pu as a soil erosion tracer in western Kenya compared to conventional isotopes 210Pbex and 137Cs through the determination of FRN depth profiles at reference sites. Across six reference sites 239+240Pu showed the greatest potential, with the lowest coefficient of variation and the greatest peak-to-detection limit ratio of 640 compared to 5 and 1 for 210Pbex and 137Cs respectively. Additionally, 239+240Pu was the only radionuclide to meet the ‘allowable error’ threshold, demonstrating applicability to large scale studies in Western Kenya where the selection of suitable reference sites presents a significant challenge. The depth profile of 239+240Pu followed a polynomial function, with the maximum areal activities found between depths 3 and 12 cm, where thereafter areal activities decreased exponentially. As a result, 239+240Pu is presented as a robust tracer to evaluate soil erosion patterns and amounts in western Kenya, providing a powerful tool to inform and validate mitigation strategies with improved understanding of land degradation.

Experimental and numerical investigation of the deep rolling process focussing on 34CrNiMo6 railway axles

Deep rolling is a powerful tool to increase the service life or reduce the weight of railway axles. Three fatigue-resistant increasing effects are achieved in one treatment: lower surface roughness, strain hardening and compressive residual stresses near the surface. In this work, all measurable changes introduced by the deep rolling process are investigated. A partly deep-rolled railway axle made of high strength steel material 34CrNiMo6 is investigated experimentally. Microstructure analyses, hardness-, roughness-, FWHM- and residual stress measurements are performed. By the microstructure analyses a very local grain distortion, in the range < 5 µm, is proven in the deep rolled section. Stable hardness values, but increased strain hardening is detected by means of FWHM and the surface roughness is significantly reduced by the process application. Residual stresses were measured using the XRD and HD methods. Similar surface values are proven, but the determined depth profiles deviate. Residual stress measurements have generally limitations when measuring in depth, but especially their distribution is significant for increasing the durability of steel materials. Therefore, a numerical deep rolling simulation model is additionally built. Based on uniaxial tensile and cyclic test results, examined on specimen machined from the edge layer of the railway axle, an elastic–plastic Chaboche material model is parameterised. The material model is added to the simulation model and so the introduced residual stresses can be simulated. The comparison of the simulated residual stress in-depth profile, considering the electrochemical removal, shows good agreement to the measurement results. The so validated simulation model is able to determine the prevailing residual stress state near the surface after deep rolling the railway axle. Maximum compressive residual stresses up to about -1,000 MPa near the surface are achieved. The change from the induced compressive to the compensating tensile residual stress range occurs at a depth of 3.5 mm and maximum tensile residual stresses of + 100 MPa at a depth of 4 mm are introduced. In summary, the presented experimental and numerical results demonstrate the modifications induced by the deep rolling process application on a railway axle and lay the foundation for a further optimisation of the deep rolling process.

Fundamentals of thin film depth profiling by glow discharge optical emission spectroscopy

Glow discharge optical emission spectroscopy (GDOES) is a useful technique for qualitative plasma characterization. It also enables depth profiling of solid materials upon exposure of samples to energetic positively charged ions from gaseous plasma, providing specifics of both surface- and gas-phase collision phenomena that are considered. The early stages of developing GDOES useful for the determination of surface composition and depth profiling of solid materials are reviewed and analyzed, stressing the contribution of early authors. The advantages as well as drawbacks of the GDOES technique are presented and discussed. The recent applications of this technique for depth profiling of various materials are presented, and the directions for constructing a laboratory-scale device are provided.

Ångstrom-Depth Resolution with Chemical Specificity at the Liquid-Vapor Interface.

The determination of depth profiles across interfaces is of primary importance in many scientific and technological areas. Photoemission spectroscopy is in principle well suited for this purpose, yet a quantitative implementation for investigations of liquid-vapor interfaces is hindered by the lack of understanding of electron-scattering processes in liquids. Previous studies have shown, however, that core-level photoelectron angular distributions (PADs) are altered by depth-dependent elastic electron scattering and can, thus, reveal information on the depth distribution of species across the interface. Here, we explore this concept further and show that the experimental anisotropy parameter characterizing the PAD scales linearly with the average distance of atoms along the surface normal obtained by molecular dynamics simulations. This behavior can be accounted for in the low-collision-number regime. We also show that results for different atomic species can be compared on the same length scale. We demonstrate that atoms separated by about 1Å along the surface normal can be clearly distinguished with this method, achieving excellent depth resolution.

What is the actual exposure of organic compounds on Chironomus riparius? - A novel methodology enabling the depth-related analysis in sediment microcosms

A novel active sampling method enabled determination of sediment depth profiles revealing the spatial distribution of model compounds N,N-dimethylsulfamide, fluopyram and bixafen (low, medium, high adsorption affinity) in sediment microcosms according to OECD Test 218/219 (Sediment-Water Chironomid Toxicity Test Using Spiked Sediment/Spiked Water). After the overlying water was removed, plastic tubes were inserted into the sediment and the microcosms were frozen. For depth-related analysis, each “sediment core” was mounted in a cutting device and sawed into three 5-mm-slices, respectively (top, middle, bottom). Each slice was centrifuged for sediment and pore water separation. By various sampling dates within 28 days, we could follow the behavior of model compounds depending on sorption affinities and display specific distribution patterns within the sediment. N,N-dimethylsulfamide showing no sediment adsorption, migrated unhindered in (OECD 219) and out (OECD 218) of the sediment via pore water, resulting in homogenous distributions in both test designs. Fluopyram with moderate adsorption affinity revealed a concentration gradient with declining amounts from top to bottom layer (OECD 219) and higher amounts in the middle and bottom layer as compared to the top layer (OECD 218). Bixafen providing a strong adsorption affinity accumulated in the top layer in OECD 219, while no concentration gradients became visible in OECD 218. For establishing a Toxic Substances in Surface Waters (TOXSWA) model, we compared our measurements with simulated results revealing good agreements. The presented methodology is a useful tool to determine more realistic sediment and pore water concentrations, which the Chironomid larvae are exposed to.

Effect of nitrogen ion implantation on the life time of WC-Co tools used in particleboard milling

ABSTRACT This work explores an effect of nitrogen ion implantation on the life time of WC-Co tools used in particleboard milling. Nitrogen ions with different energy of 5, 50, and 500 keV and fluence of 1e17 and 5e17 cm−2 were implanted into the surface of commercially available WC-Co composite indexable knives, using the implanters with mass-separated ion beams. Both untreated and modified samples were subjected to microstructural and durability tests. Microstructural tests involved surface observation, determination of the nature of wear and cracks, determination of element depth profiles, and phase changes occurring in the modified area. Durability tests were conducted with the use of a computerized numerical control (CNC) machining center. The tests included determination of wear curves and calculation of quantities such as cutting length, relative tool life index, standard deviation, standard error, coefficient of variation and quality index and wear increases. Additionally, a histogram of the relative durability distribution of samples implanted with N+ was determined. In this study, an attempt was made to relate the durability results with the microstructure of the knives. Tools modified with a nitrogen ion beam of 50 keV showed the best durability results.

Concepts for nondestructive and depth-resolved X-ray residual stress analysis in the near-surface region of nearly single crystalline materials with mosaic structure.

Two evaluation concepts for nondestructive depth-resolved X-ray residual stress analysis in the near-surface region of materials with cubic symmetry and nearly single crystalline structure are introduced by simulated examples. Both concepts are based on the same data acquisition strategy, which consists in the determination of lattice-spacing depth profiles along the 〈hkl〉 poles by stepwise sample rotation around the scattering vector. Segmentation of these profiles parallel to the sample surface provides the lattice strain state as a function of depth. The first evaluation concept extends the crystallite group method developed for materials with pronounced crystallographic texture by the feature of depth resolution and can be applied to samples with arbitrary orientation. The second evaluation concept, which adapts the linear regression approach of the sin2ψ method for the case of single crystalline materials, is restricted to samples with (001) orientation. The influence of the strain-free lattice parameter a 0 on residual stress analysis using both evaluation concepts is discussed on the basis of explicitly derived relations.

In vivo non-invasive determination of the water concentration and water bonding properties in the human stratum corneum using confocal Raman microspectroscopy (mini-review)

Water plays an important role for normal functioning of the skin. The stratum corneum (SC) – the outermost layer of the epidermis – maintains the skin barrier function and regulates the water balance in the organism. Water is non-homogeneously distributed in the SC and its correct determination is important in dermatology and cosmetology. Confocal Raman microspectroscopy (CRM) is the most suitable non-invasive method to determine depth profiles of the water concentration, water with different mobility and hydrogen bonding states of water molecules in human skin in vivo, i.e. to study the SC hydration and moisturising. An in vivo application of CRM on normal human skin for investigation of the water concentration and water bonding properties in the SC is reviewed in this paper. Investigations performed on volunteers of two age groups reveal changes, which show that the SC of older skin binds water more efficiently compared to younger skin.

Influence of the Measurement Parameters on Depth-Resolved Residual Stress Measurements of Deep Rolled Construction Steel using Energy Dispersive X-ray Diffraction

Abstract In this study, the influence of different measurement parameters of energy dispersive residual stress measurements on the obtained residual stress depth profiles of deep rolled construction steel S355 G10+M was investigated. Especially the diffraction angle θ and afterwards the measuring time t per inclination angle ψ were varied. A diffraction angle of θ = 20° shows an acceptable compromise between achievable information depth and detected total intensity of diffracted X-ray quanta. Furthermore, a measuring time per inclination angle ψ of t = 2,400 s leads to an acceptable standard deviation regarding the determined residual stress states. With these parameters for the energy-dispersive measurement, a comparison between angle-dispersive and energy-dispersive determination of residual stress depth profiles was carried out. Quantitative similarities between these two methods were observed, whereby the energy-dispersive determined residual stress depth profiles are rather discontinuous. A possible explanation could be found in the model used for the calculation of the net-plane-dependent radiographic elastic constants (XEC). In general, the energy-dispersive residual stress measurement was qualified for the determination of residual stress depth profiles of deep rolled construction steel. Based on the findings, a time-efficient non-destructive residual stress measurement can be carried out in the future with the discussed measurement parameters at maximum possible information depth.

Surface analysis of corroded XV–XVI century copper coins by μ-XRF and μ-PIXE/μ-EBS self-consistent analysis

Particle Induced X-ray Emission (PIXE) and X-ray Fluorescence (XRF) are nowadays routinely used for analysing historical coins. However, its characterization, especially in the presence of a superficial chemically altered layer (corrosion), is difficult due to its layered structure which cannot be probed using these two techniques in the general case. Elastic backscattering (both Rutherford and non-Rutherford) spectrometry is commonly used to determine depth profiles but by its own it is insufficient to unveil these complex structures. Using a PIXE detector and a particle detector recording simultaneously it is possible to perform a self-consistent analysis to obtain results about concentration variation of different elements along depth. In the present work this method was tested for two Portuguese centenary copper-based coins, and XRF was used to complement PIXE information. It is shown that elemental depth profiles with the evaluation of the superficial altered layer can be clearly solved providing relevant results about corrosion extension and composition.

Novel method for determination of tritium depth profiles in metallic samples

Tritium accumulation in fusion reactor materials is considered a serious radiological issue, therefore a lot of effort has been concentrated on the development of radiometric techniques. A novel method, based on gradual dissolution, for the determination of the total tritium content and its depth profiles in metallic samples is demonstrated. This method allows for the measurement of tritium in metallic samples after their exposure to a hydrogen and tritium mixture, tritium containing plasma or after irradiation with neutrons resulting in tritium formation. In this method, successive layers of metal are removed using an appropriate etching agent in the controlled regime and the amount of evolved gases are measured by means of chromatography (gas composition and release rate) and a proportional gas flow detector (tritium). Results for the tritium profiles in neutron irradiated, plasma exposed and gas loaded beryllium are reported.

Historical records of mercury deposition in dated sediment cores reveal the impacts of the legacy and present-day human activities in Todos os Santos Bay, Northeast Brazil

We determined depth profiles of total mercury (T-Hg) in six 210Pb-dated sediment cores from Todos os Santos Bay to reconstruct the history of anthropogenic Hg accumulation. We also assessed superficial sediments samples from five estuaries. T-Hg concentrations (5–3500 μg kg−1) presented a large spatial and temporal variability. T-Hg concentrations in Ribeira Bay increased up to 200-fold along time, whereas the fluxes of T-Hg are substantially higher (up to 10,000 fold) than present-day wet deposition for industrialized areas. Sedimentary records indicate that a chlor-alkali plant has been the main source of Hg pollution until the present, although the T-Hg records suggest that harbor, shrimp farming, and oil refinery activities, besides Hg atmospheric depositions, are important across the bay. Sediments in the Ribeira Bay act as an important Hg sink. If sediments are eroded or disturbed, they may release Hg, thus posing a serious risk to wildlife and ecosystem health. CapsuleSedimentary cores provide data on preindustrial levels and also anthropogenic fluxes of Hg for the appraisal of the magnitude, processes and potential risks of the contamination.

In Situ Rutherford Backscattering Spectrometry for Electrochemical Studies

A new in situ ultra-high vacuum (UHV) electrochemical cell containing a liquid electrolyte solution and Ti working electrode was designed and constructed to perform Rutherford backscattering spectrometry (RBS), under controlled electrochemical potentials. The depth resolution of RBS allowed for the determination of depth profiles for Ti, O, and other key transported species, in the electrode and in near-surface regions. Upon biasing the Ti electrode, subsequent RBS spectra releveled the time evolution of elemental depth profiles, characteristic of anodization, with Ti, O and Cl being mobile species. The differences between in situ and ex situ RBS measurements are emphasized. This work demonstrates the potential for in situ RBS to become a powerful tool for the investigation of a wide range of electrochemical processes including oxidation, electromigration, and deposition in batteries and other devices.

Depth profiling of titanium nitride thin films deposited on stainless steel utilizing combined EBS and NRA techniques

Abstract Composition and depth profiling of titanium nitride thin films deposited on stainless steel using vacuum arc discharge device have been determined. A combination of two ion beam analysis techniques has been applied to allow accurate quantification of nitrogen in the prepared titanium nitride thin films. These include elastic backscattering (EBS) spectrometry together with nuclear reaction analysis (NRA) technique utilizing 14N(α,p0)17O nuclear reaction, both performed at resonance energy for incident alpha beam of 4500 keV. They were applied simultaneously, using two independent charged particle detectors, one is dedicated for combined EBS/NRA measurements and the other for pure NRA one. Experimental conditions have been carefully optimized to avoid overlapping of peaks of the two spectra correspond to each reaction. Novel Multi-SIMNRA software has been utilized to enable simultaneous elemental depth profile determination of both data sets. Experimental setup of the in-vacuum system has been carefully characterized. Independent complement measurements utilizing scanning electron microscopy (SEM) equipped with energy dispersive X-ray analysis (EDX) were also applied to verify the experimental findings obtained by combined EBS and NRA techniques. The results have revealed N/Ti ratio of around 1 for the prepared films, with low levels of contamination elements. Finally, X-ray diffraction (XRD) measurements have demonstrated TiN structure with low oxygen contamination.

SIMS study of oxygen diffusion in monoclinic HfO2

The diffusion of oxygen in dense ceramics of monoclinic HfO2 was studied by means of (18O/16O) isotope exchange annealing and subsequent determination of isotope depth profiles by Secondary Ion Mass Spectrometry. Anneals were performed in the temperature range of 573 ≤T/K≤ 973 at an oxygen partial pressure of pO2=200 mbar. All measured isotope profiles exhibited two features: the first feature, closer to the surface, was attributed mainly to slow oxygen diffusion in an impurity silicate phase; the second feature, deeper in the sample, was attributed to oxygen diffusion in bulk monoclinic HfO2. The activation enthalpy of oxygen tracer diffusion in bulk HfO2 was found to be ΔHD∗≈0.5 eV.

Be ITER-like wall at the JET tokamak under plasma

The JET tokamak is operated with beryllium and tungsten plasma-facing components to prepare for the exploitation of ITER. To determine beryllium erosion and migration in JET a set of markers were installed. Specimens from different beryllium marker tiles of the main wall of the ITER-like wall (ILW) JET tokamak from the first and the second D–D campaign were analyzed with nuclear reaction analysis, x-ray fluorescence spectroscopy, scanning electron microscopy and x-ray diffraction (XRD). Emphasis was on the determination of carbon plasma impurities deposited on beryllium surfaces. The 12C(d, p0)13C reaction was used to quantify carbon deposition and to determine depth profiles. Carbon quantities on the surface of the Be tiles are low, varying from (0.35 ± 0.07) × 1017 to (11.8 ± 0.6) × 1017 at cm−2 in the deposition depth from 0.4 to 6.7 μm, respectively. In the 0.4–0.5 mm wide grooves of castellation sides the carbon content is found up to (14.3 ± 2.5) × 1017 at cm−2 while it is higher (up to (38 ± 4) × 1017 at cm−2) in wider gaps (0.8 mm) separating tile segments. Oxygen (O), titanium (Ti), chromium (Cr), manganese (Mn), iron (Fe), nickel (Ni) and tungsten (W) were detected in all samples exposed to plasma and the reference one but at lower quantities at the latter. In the central part of the Inner Wall Guard Limiter from the first ILW campaign and in the Outer Poloidal Limiter from the second ILW campaign the Ni interlayer has been completely eroded. XRD shows the formation of BeNi in most specimens.

Counter-diffusion biofilms have lower N2O emissions than co-diffusion biofilms during simultaneous nitrification and denitrification: Insights from depth-profile analysis

The goal of this study was to investigate the effectiveness of a membrane-aerated biofilm reactor (MABR), a representative of counter-current substrate diffusion geometry, in mitigating nitrous oxide (N2O) emission. Two laboratory-scale reactors with the same dimensions but distinct biofilm geometries, i.e., a MABR and a conventional biofilm reactor (CBR) employing co-current substrate diffusion geometry, were operated to determine depth profiles of dissolved oxygen (DO), nitrous oxide (N2O), functional gene abundance and microbial community structure. Surficial nitrogen removal rate was slightly higher in the MABR (11.0 ± 0.80 g-N/(m2 day) than in the CBR (9.71 ± 0.94 g-N/(m2 day), while total organic carbon removal efficiencies were comparable (96.9 ± 1.0% for MABR and 98.0 ± 0.8% for CBR). In stark contrast, the dissolved N2O concentration in the MABR was two orders of magnitude lower (0.011 ± 0.001 mg N2O-N/L) than that in the CBR (1.38 ± 0.25 mg N2O-N/L), resulting in distinct N2O emission factors (0.0058 ± 0.0005% in the MABR vs. 0.72 ± 0.13% in the CBR). Analysis on local net N2O production and consumption rates unveiled that zones for N2O production and consumption were adjacent in the MABR biofilm. Real-time quantitative PCR indicated higher abundance of denitrifying genes, especially nitrous oxide reductase (nosZ) genes, in the MABR versus the CBR. Analyses of the microbial community composition via 16S rRNA gene amplicon sequencing revealed the abundant presence of the genera Thauera (31.2 ± 11%), Rhizobium (10.9 ± 6.6%), Stenotrophomonas (6.8 ± 2.7%), Sphingobacteria (3.2 ± 1.1%) and Brevundimonas (2.5 ± 1.0%) as potential N2O-reducing bacteria in the MABR.

Non-Destructive Determination of Residual Stress Depth Profiles of Hybrid Components by Energy Dispersive Residual Stress Measurement

Through the combination of two or more materials to one compound, for example high-strength steel and aluminum, hybrid massive components can be manufactured, whose properties are specially adapted to the respective application. One of the challenges is the joining zone which is influenced by machining induced residual stresses. In order to examine the residual stress modifications by the machining process and in addition to analyze the influence of these residual stress gradients on the lifespan of hybrid components a non-destructive method of measuring depth-resolved residual stress is necessary. Therefore, an innovative energy dispersive X-ray measurement technique is used in the collaborative research center 1153 (CRC 1153). In this study the suitability of the method is examined by comparing the results with the angle dispersive method both in machined front surface of mono materials and hybrid shafts. A parametrical study shows the possibility to get greater depth information by variation of the measuring parameters Bragg angle, tilting angle, collimator and current. In addition, the results of the energy dispersive method combined with electrolytic removal is shown. Based on these results the evaluation of the reliability and reproducibility of energy dispersive residual stress measurements is completed.