Depth profiling at a steel-aluminum interface using slow-flow direct current glow discharge mass spectrometry

Direct current glow discharge mass spectrometry (dc-GDMS), which relies on sector field mass analyzers, is not commonly used for depth profiling applications because of its slow data acquisition. Nevertheless, dc-GDMS has good reproducibility and low limits of detection, which are analytical features that are encouraging for investigating the potential of dc-GDMS for depth profiling applications. In this work, the diffusion of traces of chromium and nickel was profiled at the interface of a steel-aluminum bilayer using a new sensitive dc-GDMS instrument. The depth profile of the non-treated sample was compared with that of a heat-treated specimen at 400°C for 30 min. Scanning electron micrographs, energy dispersive X-ray spectroscopy (EDS), and electron probe microanalysis (EPMA) were used to study the diffusion process. The results of the study show that both chromium and nickel are enriched at the steel-aluminum interface, with higher concentrations of both elements for the heat-treated specimen. Two peaks for both chromium and nickel were clearly present at the interface, with a high concentration of chromium in the aluminum layer. This observation is likely a consequence of elemental diffusion from the interface towards the aluminum layer. The presence of the third layer, steel beneath the aluminum layer, might also have contributed to this observation.acceptedVersio

Glycation of Plant Proteins under Environmental Stress — Methodological Approaches, Potential Mechanisms and Biological Role

Environmental stress is one of the major factors reducing crop productivity. Due to the oncoming climate changes, the effects of drought and high light on plants play an increasing role in modern agriculture. These changes are accompanied with a progressing contamination of soils with heavy metals. Independent of their nature, environmental alterations result in development of oxidative stress, i.e. increase of reactive oxygen species (ROS) contents, and metabolic adjustment, i.e. accumulation of soluble primary metabolites (amino acids and sugars). However, a simultaneous increase of ROS and sugar concentrations ultimately results in protein glycation, i.e. non-enzymatic interaction of reducing sugars or their degradation products (α-dicarbonyls) with proteins. The eventually resulting advanced glycation end-products (AGEs) are known to be toxic and pro-inflammatory in mammals. Recently, their presence was unambiguously demonstrated in vivo in stressed Arabidopsis thaliana plants. Currently, information on protein targets, modification sites therein, mediators and mechanisms of plant glycation are being intensively studied. In this chapter, we comprehensively review the methodological approaches for plant glycation research and discuss potential mechanisms of AGE formation under stress conditions. On the basis of these patterns and additional in vitro experiments, the pathways and mechanisms of plant glycation can be proposed

Exploring glow discharge mass spectrometry applications in materials characterization

Glow discharge mass spectrometry (GDMS) relying on continuous direct current discharge source coupled to sector field mass analyzer (SF-GDMS) is popular for its ability to detect impurities in sub-ppb level. Astrum GDMS is one of the recent instruments introduced of this category. Despite of its introduction in 2010, there are only a few articles available presenting Astrum’s application and theory. Moreover, no systematic approach for determining the mode of Astrum operation, no figures of merit, relative sensitivity factors (RSFs) determination, or depth profiling are available. Therefore, the PhD thesis is focused on these limitations. Hence, broadly two applications are investigated, i.e., bulk analysis and depth profiling. To achieve this, different materials were studied, such as tantalum, silicon powder, and steel-aluminum bi-layered material. Understanding the effect of glow discharge parameters is important as they affect quantification and, in turn, accuracy and reproducibility. Further, measurement of relative sensitivity factors (RSFs) is important to determine accurate results. Hence, firstly influence of glow discharge parameters on variation of elemental concentration was studied using a homogenous tantalum pin (˃99.5% Ta) sample using a range of current and voltage settings (0.5 – 5 mA at 1 kV and 0.6 – 1.5 kV at 3 mA). The variation in concentration change was related to unequal change of absolute intensity of elemental impurities as compared to that of tantalum. Hence, RSFs vary with glow discharge parameters. Interestingly, this work hinted that measurement of discharge gas and other gaseous elements can contribute to optimization of discharge parameters before determining RSFs. This followed analysis of silicon powder after pressing against high purity indium sheets. Various impurity elements were analyzed using glow discharge current and voltage settings of 1 – 3.5 mA and 1 – 1.4 kV, respectively. Further, argon was quantified using current and voltage settings of 1– 5 mA and 1.2 – 1.6 kV, respectively. Remarkably the concentration of most of the impurity elements and quantification of argon is found to vary less in range of 2 – 3 mA and 1.2 – 1.4 kV. This observation is consistent with argon and oxygen quantification using flat silicon and nitrogen quantification using aluminum flat samples. Further, gaseous elements such as carbon, oxygen, nitrogen and argon present in tantalum pin and nitrogen present in aluminum pin followed the same pattern. Hence, measurement of gaseous elements and discharge gas can contribute to RSFs determination in other matrices also. Finally, relative sensitivity factors of 16 impurity elements valuable for solar cell silicon application are determined using certified silicon standard. For depth profiling application, the glow discharge settings leading to optimum crater shapes are determined using tantalum flat samples. The results of the study indicate that current to voltage ratio in range of 0.2 – 0.35 kV/mA results into flat craters in tantalum. Hence, five different combinations of current and voltage are found namely, (i) 2 mA, 0.6 kV; (ii) 2.3 mA, 0.7 kV; (iii) 3 mA, 0.8 kV; (iv) 4 mA, 0.9 kV and (v) 5 mA, 1 kV. Further, the sputtering rates increase with increasing current and voltage settings. Sputtering of tantalum of small and large grains indicated that differential sputtering of grains of different crystal orientation leads to crater bottom roughness. This followed analysis of steel-aluminum bi-layered material where firstly crater shape optimization using base aluminum material was carried out using similar approach as with tantalum flat sample. The depth profiling of chromium and nickel is carried out in non-heated and heat treated (at 400 °C for 30 min) steel-aluminum bi-layered joints. The analysis was performed using glow discharge current and voltage of 5 mA and 0.75 kV, respectively. Using Astrum GDMS, the diffusion behavior of trace alloying elements such as chromium and nickel at the aluminum-steel interface was investigated. The results of the work indicate enrichment of both impurity elements for both sets of samples at the steel-aluminum interface. The heat-treated sample demonstrated higher content of chromium and nickel at the interface as well as formation of thin intermetallic layer formation. Further, chromium precipitates along with iron were found in the aluminum layer correlating with high chromium content in the aluminum layer

Influence of polycrystalline material on crater shape optimization and roughness using low power/low-pressure direct-current glow discharge mass spectrometry

Depth profiling is an attractive approach for analysis of non-homogeneous samples and layered materials. This application requires an optimum sputtered crater profile, which means a flat crater bottom with steep walls and a low roughness. It is known that discharge parameters are one of the most important factors influencing the crater shape. Hence, in the present work, different combinations of GDMS discharge current, voltage and argon flow, giving a flat crater bottom in tantalum are presented. A combination of mechanical profilometry, scanning electron microscopy and electron back scattered diffraction is used to show the contribution of grain orientation on various sputtering characteristics and crater bottom roughness. The results of the study indicate that differential sputtering is consistent at both higher and lower discharge conditions. The crater bottom roughness can be attributed to the differential sputtering of grains in polycrystalline materials

Depth profiling at a steel-aluminum interface using slow-flow direct current glow discharge mass spectrometry

Direct current glow discharge mass spectrometry (dc-GDMS), which relies on sector field mass analyzers, is not commonly used for depth profiling applications because of its slow data acquisition. Nevertheless, dc-GDMS has good reproducibility and low limits of detection, which are analytical features that are encouraging for investigating the potential of dc-GDMS for depth profiling applications. In this work, the diffusion of traces of chromium and nickel was profiled at the interface of a steel-aluminum bilayer using a new sensitive dc-GDMS instrument. The depth profile of the non-treated sample was compared with that of a heat-treated specimen at 400°C for 30 min. Scanning electron micrographs, energy dispersive X-ray spectroscopy (EDS), and electron probe microanalysis (EPMA) were used to study the diffusion process. The results of the study show that both chromium and nickel are enriched at the steel-aluminum interface, with higher concentrations of both elements for the heat-treated specimen. Two peaks for both chromium and nickel were clearly present at the interface, with a high concentration of chromium in the aluminum layer. This observation is likely a consequence of elemental diffusion from the interface towards the aluminum layer. The presence of the third layer, steel beneath the aluminum layer, might also have contributed to this observation