Depth Profiling Studies Research Articles

In-Situ Neutron Depth Profiling Studies (Measurements and Simulations) to Characterize the Surface of Silicon Anodes and Complementary Neutron Techniques for in-Situ and Operando Characterization

In-situ methods for characterizing electrochemical systems are becoming increasingly important to understand the mechanism of lithiation and delithiation processes. The characterization of surfaces that have been under electrochemical influence is of great interest because many electrochemical processes originate here and are therefore crucial for cell performance. Pure silicon anodes with their large volume expansion, which leads to a short service life, can be modified at WACKER company by partial lithiation of microscale silicon particles [1]. Such anode types promise higher specific capacity. Neutron depth profiling (NDP) is a very well suitable technique to study the Li quantity with depth dependence on the first micrometers. The NDP method uses the capture reaction of Li atoms and neutrons with subsequent decay into ions of well-defined energies. The depth at which ions are created in the material is defined from their energy loss through the material to the detector with an accuracy of tens of nanometers [2, 3]. After formation different lithiation stages of SiG anodes are presented and compared with simulations. The lithiation process involving SEI formation, electrode swelling and phase transformation from crystalline to amorphous is presented. In the second part, a brief overview of other neutron techniques for in-situ and operando characterization of individual battery components or entire cells is given [4].

XPS Depth-Profiling Studies of Chlorophyll Binding to Poly(cysteine methacrylate) Scaffolds in Pigment-Polymer Antenna Complexes Using a Gas Cluster Ion Source.

X-ray photoelectron spectroscopy (XPS) depth-profiling with an argon gas cluster ion source (GCIS) was used to characterize the spatial distribution of chlorophyll a (Chl) within a poly(cysteine methacrylate) (PCysMA) brush grown by surface-initiated atom-transfer radical polymerization (ATRP) from a planar surface. The organization of Chl is controlled by adjusting the brush grafting density and polymerization time. For dense brushes, the C, N, S elemental composition remains constant throughout the 36 nm brush layer until the underlying gold substrate is approached. However, for either reduced density brushes (mean thickness ∼20 nm) or mushrooms grown with reduced grafting densities (mean thickness 6-9 nm), elemental intensities decrease continuously throughout the brush layer, because photoelectrons are less strongly attenuated for such systems. For all brushes, the fraction of positively charged nitrogen atoms (N+/N0) decreases with increasing depth. Chl binding causes a marked reduction in N+/N0 within the brushes and produces a new feature at 398.1 eV in the N1s core-line spectrum assigned to tetrapyrrole ring nitrogen atoms coordinated to Zn2+. For all grafting densities, the N/S atomic ratio remains approximately constant as a function of brush depth, which indicates a uniform distribution of Chl throughout the brush layer. However, a larger fraction of repeat units bound to Chl is observed at lower grafting densities, reflecting a progressive reduction in steric congestion that enables more uniform distribution of the bulky Chl units throughout the brush layer. In summary, XPS depth-profiling using a GCIS is a powerful tool for characterization of these complex materials.

Origin of near-failure in Au contacts to polycrystalline β-Ga2O3 at high temperatures using interfacial studies

Suitable contacts to gallium oxide are a controversial topic with contact behavior depending heavily on the pre- and post-processing conditions. Especially for the extreme environment applications such as those involving high temperatures, contact chemistry is varied and severely lacks understanding. Herein, we report on conventional pure Au contacts to polycrystalline β-Ga2O3, used as Schottky contacts, and explore the origin of their near-failure at high temperature up to 850 °C. For this purpose, β-Ga2O3 with Au interdigitated electrodes is subjected to high temperature annealing and their interface chemistry is studied and correlated with device performance for solar-blind photodetection. Around the optimized temperature of 450 °C, the performance of the PDs is found to be maximum, whereas it reduces drastically at 850 °C. Physical damage to the electrodes along with the formation of intermetallic gold-gallium alloy is observed via XPS depth profile studies and found to be the reason for the near-failure of device at extreme conditions. Although the alloy formation begins to slightly appear at 650 °C and reduces the performance, still it does not lead to device breakdown. This study proves that unlike its counterparts GaN and GaAs, which have reported alloy formation at lower temperatures, β-Ga2O3 shows a higher resilience to the formation of Au–Ga alloy and can withstand higher temperatures before the actual device failure is reached. The proposed study shows the stability of standard metal contacts to Ga2O3 based devices, which have far-reaching implications for the future commercialization of wideband gap semiconductor based (opto)electronics.

Morphology, crystal structure and XPS depth profiling study of Ni-Zr co-doped M-type Sr-ferrite and adjustment of their magnetic properties

Morphology, crystal structure and XPS depth profiling study of Ni-Zr co-doped M-type Sr-ferrite and adjustment of their magnetic properties

Experimental and model study of LIBS depth profile for multilayer deposition materials

The patterns of erosion and deposition occurred in the plasma-facing materials (PFMs) of a magnetic confinement fusion device are crucial for the investigation of plasma-wall interaction (PWI). The deposition behavior can be identified by the elemental depth profile of the deposition layer. As an effective remote monitoring method for the wall in nuclear fusion devices, laser-induced breakdown spectroscopy (LIBS) shows excellent potential for the depth profiling of the deposition layer on the PFMs. However, some potentially influencing factors lead to the difficulty of distinguishing and identifying the interfaces between the deposition layers and substrate. The measuring accuracy of the deposition layer thickness plays an essential role in PWI research. In this paper, depth profiling of multilayer samples with Ni layers on Cu were performed using LIBS with an ns-pulse laser. The experiment was carried out under 5 × 10−5 mbar to simulate the operation of a nuclear fusion device. Meanwhile, a two-dimensional model for multi-pulse LIBS depth analysis based on the laser beam profile factor and interface roughness factor was established to reconstruct and predict the elemental depth profile distribution of NiCu multilayer materials. The correlation coefficients between the experimental and modeling data were all >0.99. We introduced a locating approach for the interface based on model prediction, and the relative errors of all Ni layer thicknesses were < 5.1%, demonstrating the feasibility and accuracy of the model. All the results show that the two-dimensional numerical model can improve the accuracy of LIBS depth profile on layer thickness analysis and further promote the application of in situ LIBS diagnosis in PWI research.

Negative muons for the characterization of thin layers in Cultural Heritage artefacts

Muonic atom X-ray Emission Spectroscopy (µ-XES) is a novel technique based on the detection of high-energy X-rays emitted after the interaction of a negative muon beam with matter. Thanks to the multi-elemental range, negligible self-absorption of the x-rays and the possibility of performing depth profile studies, the technique is a very powerful probe for the analysis of cultural heritage artefacts. By tuning the energy of the incident muon beam, indeed, it is possible to investigate the different layers that constitute a sample. In this work, we report preliminary results of the analysis on two fire-gilded surfaces, in which the data analysis is coupled with Monte Carlo-based simulation software. Here, to perform a depth profile characterization, the samples were analysed at different beam energies (or momentum). Each of the resulting x-ray spectra was then analysed and compared with the output of the simulations software and a remarkably good agreement was reached. The results of the work are promising and with this approach, it will be possible to enhance the capability offered by the technique, both in terms of data analysis and data interpretation.

Practical guide on chemometrics/informatics in x-ray photoelectron spectroscopy (XPS). I. Introduction to methods useful for large or complex datasets

Chemometrics/informatics and data analysis, in general, are increasingly important topics in x-ray photoelectron spectroscopy (XPS) because of the large amount of information (data/spectra) that are often collected in degradation, depth profiling, operando, and imaging studies. In this guide, we discuss vital, theoretical aspects and considerations for chemometrics/informatics analyses of XPS data with a focus on exploratory data analysis tools that can be used to probe XPS datasets. These tools include a summary statistic [pattern recognition entropy (PRE)], principal component analysis (PCA), multivariate curve resolution (MCR), and cluster analysis. The use of these tools is explained through the following steps: (A) Gather/use all the available information about one's samples, (B) examine (plot) the raw data, (C) developing a general strategy for the chemometrics/informatics analysis, (D) preprocess the data, (E) where to start a chemometrics/informatics analysis, including identifying outliers or unexpected features in datasets, (F) determine the number of abstract factors to keep in a model, (G) return to the original data after a chemometrics/informatics analysis to confirm findings, (H) perform MCR, (I) peak fit the MCR factors, (J) identify intermediates in MCR analyses, (K) perform cluster analysis, and (L) how to start doing chemometrics/informatics in one's work. This guide has Paper II [Avval et al., J. Vac. Sci. Technol. A 40, 063205 (2022)] that illustrates these steps/principles by applying them to two fairly large XPS datasets. In these papers, special emphasis is placed on MCR. Indeed, in this paper and Paper II, we believe that, for the first time, it is suggested and shown that (1) MCR components/factors can be peak fit as though they were XPS narrow scans and (2) MCR can reveal intermediates in the degradation of a material. The other chemometrics/informatics methods are also useful in demonstrating the presence of outliers, a break (irregularity) in one of the datasets, and the general trajectory/evolution of the datasets. Cluster analysis generated a series of average spectra that describe the evolution of one of the datasets.

Practical guide on chemometrics/informatics in x-ray photoelectron spectroscopy (XPS). II. Example applications of multiple methods to the degradation of cellulose and tartaric acid

Chemometrics/informatics, and data analysis in general, are increasingly important in x-ray photoelectron spectroscopy (XPS) because of the large amount of information (spectra/data) that is often collected in degradation, depth profiling, operando, and imaging studies. In this guide, we present chemometrics/informatics analyses of XPS data using a summary statistic (pattern recognition entropy), principal component analysis, multivariate curve resolution (MCR), and cluster analysis. These analyses were performed on C 1s, O 1s, and concatenated (combined) C 1s and O 1s narrow scans obtained by repeatedly analyzing samples of cellulose and tartaric acid, which led to their degradation. We discuss the following steps, principles, and methods in these analyses: gathering/using all of the information about samples, performing an initial evaluation of the raw data, including plotting it, knowing which chemometrics/informatics analyses to choose, data preprocessing, knowing where to start the chemometrics/informatics analysis, including the initial identification of outliers and unexpected features in data sets, returning to the original data after an informatics analysis to confirm findings, determining the number of abstract factors to keep in a model, MCR, including peak fitting MCR factors, more complicated MCR factors, and the presence of intermediates revealed through MCR, and cluster analysis. Some of the findings of this work are as follows. The various chemometrics/informatics methods showed a break/abrupt change in the cellulose data set (and in some cases an outlier). For the first time, MCR components were peak fit. Peak fitting of MCR components revealed the presence of intermediates in the decomposition of tartaric acid. Cluster analysis grouped the data in the order in which they were collected, leading to a series of average spectra that represent the changes in the spectra. This paper is a companion to a guide that focuses on the more theoretical aspects of the themes touched on here.

A Novel Non-Destructive Technique for Cultural Heritage: Depth Profiling and Elemental Analysis Underneath the Surface with Negative Muons

Scientists, curators, historians and archaeologists are always looking for new techniques for the study of archaeological artefacts, especially if they are non-destructive. With most non-destructive investigations, it is challenging to measure beneath the surface. Among the vast board of techniques used for cultural heritage studies, it is difficult to find one able to give information about the bulk and the compositional variations, along with the depth. In addition, most other techniques have self-absorption issues (i.e., only surface sensitive) and limited sensitivity to low Z atoms. In recent years, more and more interest has been growing around large-scale facility-based techniques, thanks to the possibility of adding new and different insights to the study of material in a non-destructive way. Among them, muonic X-ray spectroscopy is a very powerful technique for material characterization. By using negative muons, scientists are able to perform elemental characterization and depth profile studies. In this work, we give an overview of the technique and review the latest applications in the field of cultural heritage.

The Potential of 233U/236U as a Water Mass Tracer in the Arctic Ocean

AbstractThis study explores for the first time the possibilities that the 233U/236U atom ratio offers to distinguish waters of Atlantic or Pacific origin in the Arctic Ocean. Atlantic waters entering the Arctic Ocean often carry an isotopic signature dominantly originating from European reprocessing facilities with some smaller contribution from global fallout nuclides, whereas northern Pacific waters are labeled with nuclides released during the atmospheric nuclear testing period only. In the Arctic Ocean, 233U originates from global fallout while 236U carries both, a global fallout and a prominent nuclear reprocessing signal. Thus, the 233U/236U ratio provides a tool to identify water masses with distinct U sources. In this work, 233U and 236U were analyzed in samples from the GN01 GEOTRACES expedition to the western Arctic Ocean in 2015. The study of depth profiles and surface seawater samples shows that: (a) Pacific and Atlantic waters show enhanced signals of both radionuclides, which can be unraveled based on their 233U/236U signature; and (b) Deep and Bottom Waters show extremely low 233U and 236U concentrations close to or below analytical detection limits with isotopic ratios distinct from known anthropogenic U sources. The comparably high 233U/236U ratios are interpreted as a relative increase of naturally occurring 233U and 236U and thus for gradually reaching natural 233U/236U levels in the deep Arctic Ocean. Our results set the basis for future studies using the 233U/236U ratio to distinguish anthropogenic and pre‐anthropogenic U in the Arctic Ocean and beyond.

Agriculture Drought Management in Ramanathapuram District of Tamil Nadu, India

Drought is one of the recurring features of Indian agriculture, especially in the rain fed areas. It affects not only the national food security but also causes miseries to human life and live stock. The study area, i.e., Ramanathapuram district of Tamilnadu, India (Latitude 9°40′and Longitude 78°70′) has been affected consecutively for the last three years from 2015 to 2018 by drought, due to the failure of rainfall of northeast and southwest monsoons. So, the economic status of the area has declined due to the drought and the people from this district have migrated to other districts to improve their socio-economic status. This district has seven taluks, eleven blocks and four hundred villages. Major physiography units of the district are vast coastal plain, adjacent alluvial plain and a small area of buried pediments. The predominant geological formations are recent alluvium, and laterite followed by mio-pliocene Cuddalore Sandstone, upper cretaceous calcareous sandstone and proterozoic basement rocks. The total thickness of sedimentary rocks may be upto 3000 metre. The shallow aquifer in the district is severely affected by sea water intrusion and the inland salinity of marine sedimentary formations. Since the shallow aquifer is saline, paddy cultivation practices are generally being done through rain fed lake irrigation. According to the Central Ground Water Board report, the deeper groundwater aquifer in this district would give a continuous supply of freshwater. In order to develop agriculture activities and avoid drought management, the following steps are to be undertaken immediately. 1. River linking scheme of westerly debouching, i.e., Western Ghat Rivers in the Arabian Sea with the ephemeral rivers of the study area such as Vaigai, Gundar and Kottakkarai Rivers to improve the recharge of groundwater and prevent sea water intrusion. 2. Delineation of the depth of deeper fresh water in Tertiary and Cretaceous aquifer by sub-surface mapping study through 2D resistivity imaging depth profile study and borehole data. 3. Augmentation of engineering structures in the coastal area will prevent sea water intrusion in the shallow aquifer. 4. To improve the socio-economic status of the farmer and for drought management, a crop insurance scheme should be implemented for farmers. 5. Providing long term loans with subsidy facilities should be implemented for the construction of bore holes to improve crop production by getting fresh water from a deeper aquifer. 6. The study area is located nearer to the sea, so the large scale desalination plant system should be implemented by government organisation to get fresh water for improving agriculture practices.

Depth profiling of energetic Au ions inside P-type Si 〈1 0 0〉 substrate

Gold implanted silicon substrates are widely used for the fabrication of microelectronic devices, such as detectors for infrared imaging applications, optoelectronic devices as well as for synthesis of implanted nano-particles. The continuous down scaling of physical size of these devices motivated us to develop methodologies for the reliable depth profile studies of various implanted ion species using sensitive and non-destructive methods. In this article, we present depth profile studies for gold ions implanted in silicon substrates using simultaneous X-ray reflectivity and grazing incidence X-ray fluorescence measurements. Results obtained using the XRR-GIXRF studies were found to be fairly consistent with the experimental measurements of secondary ion mass spectrometry. Furthermore, it was noticed that energetic gold ions cause substantial amorphization of crystalline Si material in the vicinity of implanted region, which was confirmed using the GIXRD measurements. Ion implantation also induces large surface modifications and roughness effects on the top of the silicon substrate, as revealed from atomic force microscope measurements.

The Baltic Sea methane pockmark microbiome: The new insights into the patterns of relative abundance and ANME niche separation

Pockmarks are important “pumps”, which are believed to play a significant role in the global methane cycling and harboring a unique assemblage of very diverse prokaryotes. This study reports the results of massive sequencing of the 16S rRNA gene V4 hypervariable regions for the samples from thirteen pockmark horizons (the Baltic Sea) collected at depths from 0 to 280 cm below seafloor (cmbsf) and the rates of microbially mediated anaerobic oxidation of methane (AOM) and sulfate reduction (SR). Altogether, 76 bacterial and 12 archaeal phyla were identified, 23 of which were candidate divisions. Of the total obtained in the pockmark sequences, 84.3% of them were classified as Bacteria and 12.4% as Archaea; 3.3% of the sequences were assigned to unknown operational taxonomic units (OTUs). Members of the phyla Planctomycetota, Chloroflexota, Desulfobacterota, Caldatribacteriota, Acidobacteriota and Proteobacteria predominated across all horizons, comprising 58.5% of the total prokaryotic community. These phyla showed different types of patterns of relative abundance. Analysis of AOM-SR-mediated prokaryotes abundance and biogeochemical measurements revealed that ANME-2a-2b subcluster was predominant in sulfate-rich upper horizons (including sulfate-methane transition zone (SMTZ)) and together with sulfate-reducing bacterial group SEEP-SRB1 had a primary role in AOM coupled to SR. At deeper sulfate-depleted horizons ANME-2a-2b shifted to ANME-1a and ANME-1b which alone mediated AOM or switch to methanogenic metabolism. Shifting of the ANME subclusters depending on depth reflect a tendency for niche separation in these groups. It was shown that the abundance of Caldatribacteriota and organohalide-respiring Dehalococcoidia (Chloroflexota) exhibited a strong correlation with AOM rates. This is the first detailed study of depth profiles of prokaryotic diversity, patterns of relative abundance, and ANME niche separation in the Baltic Sea pockmark microbiomes sheds light on assembly of prokaryotes in a pockmark.

Synthesis and Electrochemical Properties of Aluminum Hexafluorophosphate.

We report the first synthesis of aluminum hexafluorophosphate (Al(PF6)3) and its electrochemical properties in dimethyl sulfoxide (DMSO). The single crystal structure of the synthesized Al(PF6)3 is revealed as [Al(DMSO)6](PF6)3, and 0.25 M Al(PF6)3 in DMSO with high ionic conductivity is obtained. The purity of this electrolyte was further confirmed with nuclear magnetic resonance spectroscopy and electrospray ionization mass spectrometry. We then demonstrated the reversibility of Al deposition-stripping in this electrolyte using scanning electron microscopy and an X-ray photoelectron spectroscopy depth profiling study. The parasitic reaction involving DMSO decomposition during Al deposition is also identified via gas chromatography/electron ionization mass spectrometry.

X-Ray Photoelectron Spectroscopy Depth Profiling of As-Grown and Annealed Titanium Nitride Thin Films

Titanium nitride thin films were grown on Si(001) and fused silica substrates by radio frequency reactive magnetron sputtering. Post-growth annealing of the films was performed at different temperatures from 300 °C to 700 °C in nitrogen ambient. Films annealed at temperatures above 300 °C exhibit higher surface roughness, smaller grain size and better crystallinity compared to the as-grown film. Bandgap of the films decreased with the increase in the annealing temperature. Hall effect measurements revealed that all the films exhibit n-type conductivity and had high carrier concentration, which also increased slightly with the increase in the annealing temperature. A detailed depth profile study of the chemical composition of the film was performed by x-ray photoelectron spectroscopy confirming the formation of Ti-N bond and revealing the presence of chemisorbed oxygen in the films. Annealing in nitrogen ambient results in increased nitrogen vacancies and non-stoichiometric TiN films.

Depth profile study on Ti/Al bilayer Ohmic contacts to AlGaN/GaN

The electrical performance of double layered Ohmic contacts not only depends on layer thicknesses, annealing temperatures and annealing time etc. but also Ohmic contact metals and reactions with substrates and each other. Furthermore, oxidation tendency of Ohmic contact metals is highly important for contact quality and stability. In this study, we have investigated Ti/Al Ohmic contact formation on undoped AlGaN substrates by X-ray photoelectron spectroscopy (XPS) depth profile analysis. We aimed to reveal the oxide compounds and reaction products of metals and dependencies to the contact depth. In survey mode and depth profile mode five atoms core level (Ga 3d, Al 2p, N 1 s, Ti 2p and O 1 s) was observed and the XPS core level peaks were convoluted with Gaussian profiles to identify the origin of the peaks. Our results show that Ohmic contact metals strongly incorporated with oxygen, leading to high specific contact resistivity (ρs) confirmed by the TLM measurement. Also it is found that thermal treatments cause a TiAl3 metallic alloy in the Ti/Al interface and the presence of excess Ga and TiN indicates that out diffusion of N atoms at the metal semiconductor (MS) interface.

A critical discussion on the analysis of buried interfaces in Li solid-state batteries. Ex situ and in situ/operando studies

Rigorous approaches to study electro-chemo-mechanical processes at the analytically challenging buried interfaces in solid-state batteries are discussed. Furthermore, new experiments evidence potential misinterpretations in depth-profiling studies.

Metabolite Detection and Profiling Using Analytical Methods

To develop effective and safe drugs and to take them to the market in short period of time is the mission of pharmaceutical research companies. A selection of few of the lead compounds are done for the evaluation of safety and their ADMET (absorption, distribution, metabolism, excretion and toxicology) properties are tested in in-vitro (test systems), in-vivo (living organisms) and in-silico (computational methods). From initial stages to final stages of modern drug discovery processes, the vital tool for detecting and characterizing metabolites is MS (Mass spectrometry) hyphenated with other techniques. The methods used for generation of metabolites are in vitro techniques and cell lines (containing expressing drug metabolizing enzymes and heterologous genes). The use of HPLC-MS/UPLC-MS and high resolution MS, enables the in depth metabolite detection and profiling studies and it may also be likely to identify and characterize the site and types of biotransformation.

Determination of the microscopic mineralogy of inclusion in an amygdaloidal pillow basalt by fs-LIMS

Depth profiling and atomic intensity correlation studies on mineralogical inclusion embedded in calcium carbonate phase using a miniature laser mass spectrometer are presented. The method allows the determination of complex mineralogical phases.

Applications of Raman spectroscopy in art and archaeology

Applications of Raman spectroscopy in art and archaeology