Depth Profile Analysis Research Articles

Effect of Bias Potential on the Interface of a Solid Electrolyte and Electrode during XPS Depth Profiling Analysis.

Depth profiling is an essential method to investigate the physical and chemical properties of a solid electrolyte and electrolyte/electrode interface. In conventional depth profiling, various spectroscopic tools such as X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectroscopy (SIMS) are utilized to monitor the chemical states along with ion bombardment to etch a sample. Nevertheless, the ion bombardment during depth profiling results in an inevitable systematic error, i.e., the accumulation of mobile ions at the electrolyte/electrode interface, known as the ion pile-up phenomenon. Here, we propose a novel method using bias potential, the substrate-bias method, to prevent the ion pile-up phenomena during depth profiling of a solid electrolyte. When the positive bias potential is applied on the substrate (electrode), the number of accumulating ions at the electrolyte/electrode interface is significantly reduced. The in-depth XPS analysis with the biased electrode reveals not only the suppression of the ion pile-up phenomena but also the altered chemical states at the interfacial region between the electrolyte and electrode depending on the bias. The proposed substrate-bias method can be a good alternative scheme for an efficient yet precise depth profiling technique for a solid electrolyte.

Depth profile analysis and high-resolution surface mapping of lithium isotopes in solids using laser-induced breakdown spectroscopy (LIBS)

Lithium isotopic analysis is of interest in various fields from biology to energy. In addition to analytical methods commonly used for that purpose, a new complementary method for determining the spatial resolution of isotopic ratio in solid samples was previously developed: laser induced self-reversal isotopic spectrometry (LIBRIS), derived from laser-induced breakdown spectroscopy (LIBS). In this paper, we present a proof of concept of fast spatially-resolved quantitative isotopic analysis of lithium by LIBS both in depth (z resolution) and in configuration of high-resolution surface mapping (x and y resolution). First, a depth profile measurement where a 9% relative uncertainty on the 6Li isotopic ratio and 0.74 μm depth resolution is obtained. Then, we introduce the first high-resolution lithium isotopic mapping obtained by LIBS with a 3.3 μm lateral resolution and a typical 40% relative uncertainty on the 6Li isotopic ratio is obtained. Those results could be applied in the future to a large number of solid samples where fast information on the lithium isotopic distribution are needed, for instance in solid-state batteries development.

External Voltage-Induced Restructuring of the Solid-State Electrode/Electrolyte Interface Revealed by X-ray Photoelectron Spectroscopy Depth Profiling Analysis.

Solid/solid interfaces between electrodes and electrolytes play an important role in all-solid-state energy devices, while microscopic investigations of the buried interfaces remain challenging. Here, we construct metal|yttria-stabilized zirconia (YSZ)|Au model cells consisting of a metal film cathode (metal (M) = Au, Ni, and Ag), a single crystalline YSZ electrolyte, and a Au film anode, and use quasi in situ X-ray photoelectron spectroscopy depth profiling analysis to investigate the restructuring of buried interfaces between metal cathodes and YSZ. After applying 2.9 V at 500 °C, interfacial Zr4+ ions in the electrolyte are reduced and then interdiffuse with metal cathode overlayers, forming a miscible ZrM alloy interlayer. The interface restructuring degree follows the sequence of Au|YSZ|Au > Ni|YSZ|Au > Ag|YSZ|Au. Meanwhile, surface segregation of Zr on the cathode surface is also observed, whose degree follows the sequence of Ag|YSZ|Au > Ni|YSZ|Au > Au|YSZ|Au. Notably, the strong ZrM alloy formation enhances the interface restructuring but suppresses the Zr surface segregation. This work provides a fundamental understanding of the interfacial reaction at the buried electrode/electrolyte interface.

LIBS depth-profile analysis of W/Cu functionally graded material

A feature of Laser-Induced Breakdown Spectroscopy (LIBS), the ability to perform depth profiling, has been exploited to analyze a tungsten‑copper functionally graded material (FGM), considered a relevant candidate for components in a nuclear fusion reactor. The proposed method relies on establishing correlations between the depth of ablation craters and the number of laser pulses, along with the accompanying LIBS spectra acquired by varying a number of laser pulses. LIBS measurements were performed using a Q-switched Nd:YAG laser at 532 nm with 100 mJ/pulse energy under reduced Ar pressure. The ablation craters were analyzed using optical profilometry. The copper concentration at each specific depth was assessed using a univariate calibration curve constructed with intensity ratios of Cu I 521.82 nm and W I 522.47 nm spectral lines. The calibration samples were pure W and homogenous W/Cu composite samples with different Cu content (10.9% - 35.3%) whose composition was determined by X-ray fluorescence. The proposed method exhibits potential applicability for quantitative analysis of multilayered materials.

Migration of plasticizers from flexible PVC: Monitoring the concentration profiles by confocal Raman microspectroscopy

This study introduces and validates an effective approach for monitoring the plasticizer amount and its concentration profile in polyvinyl chloride (PVC) formulations. The method combines gravimetric measurements with confocal Raman depth profiling analysis. Several flexible PVC (pPVC) formulations were compared in this study, including: pPVC@DEHP, using the monomeric plasticizer di(2-ethylhexyl) phthalate (DEHP); pPVC@PBA, using the polymeric plasticizer poly(butylene adipate) (PBA); and crosslinked pPVC (cPVC@DEHP), where isophorone diamine (IPDA) served as the crosslinker. Migration tests were performed according to UNI EN ISO 177 standard. Spectroscopic findings were correlated with gravimetric data, highlighting strong differences in the migration behavior among the formulations. The results demonstrate the effectiveness of the proposed method in quantifying plasticizer leaching and obtaining detailed concentration profiles at fine scale.

Analysis of hydrogen in a hydrogenated, 3D-printed Ti–6Al–4V alloy by glow discharge optical emission spectroscopy: sample heating effects

In the analysis of hydrogen in a hydrogenated, 3D-printed Ti–6Al–4V alloy by GDOES, hydrogen diffuses from the depth due to sample heating, enters the plasma and affects the signal response. A model of heat conduction within the sample is presented.

A zircon LA-ICPMS reverse depth profiling analysis method and its geological application

A new LA-ICPMS analysis method for zircon U–Pb age and trace element composition and its geological application.

Threshold Switching of ALD-NbOx Films for Neuromorphic Applications

Neuromorphic architecture has been suggested as an alternative to the existing von Neumann counterpart. The neuromorphic approach allows massively parallel processing and asynchronous timing schemes with low power consumption. This work presents ALD- NbOx thin films as a potential material for neuromorphic computation. NbO2 shows metal-insulator transition which is the desired property for threshold switching (TS). However, direct forming of NbO2 is rather difficult and deposited NbOx tends predominantly to result in Nb2O5. To obtain NbO2 we used an oxygen scavenger layer of Ti to alter Nb2O5 to NbO2. After a proper electroforming process, the device with a Ti insert showed metal-insulator transition above a specific voltage, i.e., a threshold voltage, and a stable threshold switching characteristics with wide operation range, characteristics not observed in the absence of a Ti insert. The well-defined TS characteristics clearly indicated the Ti role in controlling the oxidation state of NbOx.To verify the oxidation state of NbOx, XPS depth profile analyses were used. The presence of a Ti insertion layer resulted in an increase of 10~30% in Nb4+ states, depending on the total thickness of the NbOx films, while Nb5+ states decreased. Bearing in mind practical applications, we used only CMOS-compatible materials and processes to fabricate TS devices. Our approach suggests a reliable method to fabricate NbO2 neurons.Acknowledgment: This work was supported by Electronics and Telecommunications Research Institute (ETRI) grant funded by the Korean government under grant " Non-CMOS Neuromorphic Device Basic Technology." (22BB1110).

Strong Catalyst-Support Interaction in WOx Nanowires Supported Iridium Nanocatalysts: A Pathway to Efficient Water Electrolysis

This paper investigates the use of sub-stoichiometric tungsten oxide nanowires (WOxNW) as a support material for Ir nanocatalysts in the oxygen evolution reaction (OER) for proton exchange membrane water electrolysis (PEMWE). The results demonstrate that Ir@WOxNW has exceptional activity and durability, which paves the way for large-scale PEMWE deployment. The catalyst-support interaction plays a crucial role in explaining this performance boost.The preparation and characterization of Ir@WOxNW involved loading ultra-fine Ir nanoparticles onto WOxNW through hydrothermal treatment. High-resolution transmission electron microscopy (HR-TEM) and energy-dispersive X-ray spectroscopy (EDS) mapping analysis revealed that the iridium nanoparticles were uniformly loaded on the WOxNW support material, indicating efficient loading and dispersion. X-ray photoelectron spectroscopy (XPS) analysis showed that the supported Ir catalysts had a mixed valence state of Ir0 and Ir4+. Ir@WOxNW was compared with three other Ir-based OER catalysts, outperforming them in terms of activity and durability.The Ir@WOxNW catalyst demonstrated superior OER activity compared to the other three catalysts, with a mass activity of 812 A/gIr at 1.55 V vs reversible hydrogen electrode (RHE). The Tafel slopes of the OER catalysts were grouped into two categories: Ir Black and Ir@WOxNW showed smaller values (about 40 mV/dec), and larger values for Ir@ATO and Ir Oxide (about 120 mV/dec), respectively. Electrochemical impedance spectroscopy (EIS) measurements indicated that the high mass activity of Ir@WOxNW was due to a high population of catalytic sites with fast intrinsic kinetics from the dispersed ultra-fine Ir catalyst on WOxNW. The durability of all catalysts was investigated using an accelerated durability test (ADT), and the Ir@WOxNW catalyst demonstrated unexpectedly high durability compared to the other catalysts.The postmortem XPS analysis showed that the Ir@WOxNW catalyst exhibited a subtle change in Ir0/Ir4+ ratio after the ADT, indicating suppressed Ir oxidation and greater stability compared to the other catalysts. Additionally, non-destructive depth profile analysis by synchrotron based XPS was conducted on the supported ultrafine Ir catalysts before and after the ADT test. The difference in oxidation state increased as the supported Ir catalysts were probed deeper into the core. The results showed that after oxidation potential cycles ADT, the WOxNW-supported Iridium exhibited strong resistance to oxidation. The core location remained a high percentage of metal peak, in contrast to the other three control catalysts.Density functional theory calculations suggested that the oxygen-deficient WOxNW support helps to maintain the OER-active metal@metal oxide core@shell-like form of the Ir catalyst particles by enhancing electron transfer from the WOxNW to the Ir surface, thereby weakening the binding of oxygen to the Ir surface and enhancing the oxidation resistance of the Ir metal to oxides.In conclusion, ultrafine Ir nanoparticles supported on WOxNW have significant potential for practical applications in electrochemical water splitting. The high activity and durability of Ir@WOxNW make it a promising candidate for large-scale PEMWE deployment.

Surface chemistry induced robust SEI on graphite surface via soft carbon coating enables fast lithium storage

The realization of fast-charging lithium-ion batteries with long cycle life using graphite anode is typically hindered by the uncontrollable lithium plating on graphite surface. Herein we have systematically investigated the effects of soft carbon coating on SEI properties and Li+ storage capability. A variety of analytical studies combined with three-electrode impedance measurement and interface analysis demonstrate that the carbon coating effectively mitigates the formation of resistive films on the graphite surface, leading to facilitated charge transfer and low energy barrier. The depth-profiling XPS analysis clearly shows that the formation of a uniform, robust and LiF-rich SEI plays a dominant role in enhancing the interfacial kinetics, whereas the Li+ diffusion in bulk electrode is merely affected. As a result, the graphite anode with carbon coating exhibits enhanced fast-charging performance and cycle life, including a capacity retention ratio of 98.3 % after 100 cycles at 2C-CV. In general, this work reveals the critical role of coating layer chemistry in regulating the SEI properties and Li+ storage performance, which provides a valuable guidance for the rational design of practical graphite anode for fast-charging.

Toward Comprehensive Analysis of the 3D Chemistry of Pseudomonas aeruginosa Biofilms.

Bacterial biofilms are structured communities consisting of cells enmeshed in a self-generated extracellular matrix usually attached to a surface. They contain diverse classes of molecules including polysaccharides, lipids, proteins, nucleic acids, and diverse small organic molecules (primary and secondary metabolites) which are organized to optimize survival and facilitate dispersal to new colonization sites. In situ characterization of the chemical composition and structure of bacterial biofilms is necessary to fully understand their development on surfaces relevant to biofouling in health, industry, and the environment. Biofilm development has been extensively studied using confocal microscopy using targeted fluorescent labels providing important insights into the architecture of biofilms. Recently, cryopreparation has been used to undertake targeted in situ chemical characterization using Orbitrap secondary ion mass spectrometry (OrbiSIMS), providing a label-free method for imaging biofilms in their native state. Although the high mass resolution of OrbiSIMS enables more confident peak assignments, it is still very challenging to assign most of the peaks in the spectra due to complexity of SIMS spectra and lack of automatic peak assignment methods. Here, we analyze the same OrbiSIMS depth profile data generated from the frozen-hydrated biofilm, but employ a new untargeted chemical filtering process utilizing mass spectral databases to assign secondary ions to decipher the large number of fragments present in the SIMS spectra. To move towards comprehensive analysis of different chemistries in the sample, we apply a molecular formula prediction approach which putatively assigns 81% of peaks in the 3D OrbiSIMS depth profile analysis. This enables us to catalog over 1000 lipids and their fragments, 3500 protein fragments, 71 quorum sensing-related molecules (2-alkyl-4-quinolones and N-acylhomoserine lactones), 150 polysaccharide fragments, and glycolipids simultaneously from one data set and map these separated molecular classes spatially through a Pseudomonas aeruginosa biofilm. Assignment of different chemistries in this sample facilitates identification of differences between biofilms grown on biofilm-promoting and biofilm-resistant polymers.

Anomalous efficiency elevation of quantum-dot light-emitting diodes induced by operational degradation

Quantum-dot light-emitting diodes promise a new generation of high-performance and solution-processed electroluminescent light sources. Understanding the operational degradation mechanisms of quantum-dot light-emitting diodes is crucial for their practical applications. Here, we show that quantum-dot light-emitting diodes may exhibit an anomalous degradation pattern characterized by a continuous increase in electroluminescent efficiency upon electrical stressing, which deviates from the typical decrease in electroluminescent efficiency observed in other light-emitting diodes. Various in-situ/operando characterizations were performed to investigate the evolutions of charge dynamics during the efficiency elevation, and the alterations in electric potential landscapes in the active devices. Furthermore, we carried out selective peel-off-and-rebuild experiments and depth-profiling analyses to pinpoint the critical degradation site and reveal the underlying microscopic mechanism. The results indicate that the operation-induced efficiency increase results from the degradation of electron-injection capability at the electron-transport layer/cathode interface, which in turn leads to gradually improved charge balance. Our work provides new insights into the degradation of red quantum-dot light-emitting diodes and has far-reaching implications for the design of charge-injection interfaces in solution-processed light-emitting diodes.

Resonant Laser Induced Breakdown Spectroscopy for quantitative elemental depth profile analysis of WTa coating

This work reports on the procedure of Resonant-LIBS, in which ablation and subsequent excitation is achieved by fine-tuning an Optical Parametric Oscillator (OPO) laser to the resonant transition of tungsten (W I) at 255.14 nm and analyzing the optical emission spectroscopy results. Compared to conventional LIBS, the ablation rate is significantly reduced in the resonant regime, resulting in finer resolution of depth profiles. This reduction in ablation rate can be attributed to a process called Resonance Laser Ablation (RLA) where a part of the laser energy is employed for ablation, while the rest is dedicated to resonant excitation. The sample under consideration is a WTa-coated (7μm) Mo substrate prepared by a dual magnetron sputtering system. These efforts are motivated by the need for improvement in quantitative depth analysis of W-based Plasma-Facing Components (PFC). Particularly to target the undesirable surface modifications due to the interaction with H isotopes in fusion plasma, such as fuel retention or erosion/deposition.

Cobalt distribution and enrichment in skarn iron deposits: A case study of the Zhuchong skarn iron deposit, Eastern China

Global Cobalt (Co) is mainly mined from sediment-hosted, magmatic sulfide, or laterite deposits, but rarely in skarns. The Middle-Lower Yangtze River Valley Metallogenic Belt (MLYB), eastern China, is an important skarn iron ore producer, where skarn iron deposits are often associated with Co. The Zhuchong iron deposit is a typical high-grade skarn iron deposit with Co enrichment in this belt. This deposit contains 50 Mt Fe ore @50.1 %, 4.3 Mt Cu ore @1.15 %, and ∼ 10000 t Co metal with an average grade of 0.019 %. In this study, the distribution and enrichment of Co at Zhuchong were investigated by detailed petrographic observations, mineral geochemistry, and whole-rock major and trace element data. Our results indicate that Co contents in the ore and gangue minerals at Zhuchong follow these trend: pyrite (median = 2138 ppm) > pyrrhotite (705 ppm) > sphalerite (352 ppm) > magnetite (72.1 ppm) > diopside (42.5 ppm) > chalcopyrite (3.11 ppm) > garnet (1.23 ppm). The negative correlation between Co + Ni and Fe in pyrite suggests that the incorporation of Co into pyrite can be achieved by the substitution mechanism of 2Fe2+ ↔ Co2+ + Ni2+. Depth profile analysis reveals that the Co-enriched pyrite is mainly developed in the contact zone between the diorite pluton and the skarn iron ore body. Pyrite far from the pluton has lowered Co contents ranging from several to hundreds ppm. This study highlights that the enrichment of Co in pyrite at Zhuchong is probably temperature-dependent. Co/Ni ratios of pyrite range from 0.01 to 10000, and where pyrrhotite occurs the ratios increase. Additionally, Our results establish pyrite as the primary carrier of Co at the Zhuchong deposit, contributing approximately 5000 tons of Co. Pyrrhotite and magnetite account for about a quarter proportion of total Co reserves, respectively. Our study emphasizes that finding out the Co-rich location and its occurrence nature of the deposit is of great significance for the recovery and utilization of Co in skarn iron deposits.

Inhibition efficiency and mechanism of nitrilo-tris(methylenephosphonato)zinc on mild steel corrosion in neutral fluoride-containing aqueous media

Abstract Corrosion-electrochemical behaviour of steel E 235 in borate buffer solution (pH = 7.4) containing F− ions with and with no added ZnNTP as an inhibitor, where NTP = N(CH2PO3)3, was studied by the potentiodynamic polarization and depth-profiling XPS analysis of specimens polarized at different potentials applied. Depending on the potential applied, F− ion was shown to influence differently on the formation, composition and structure of passive film. At E < 0.1–0.2 V/SSCE, F− ion promotes the passivation via forming sparingly soluble FeF2, and the resulting film is comprised of mainly iron(II) oxides and hydroxides, as well as sparingly soluble FeF2 and FeZnNTP. At E > 0.1–0.2 V/SSCE, F− ion works for the destruction of the passive film by forming soluble compounds with Fe3+ ions, which leads to its thinning. ZnNTP inhibitor forms FeZnNTP heterometallic complex with iron ions, which is the most stable constituent of the passive film. When F− ion concentration does not exceed 1.4 mmol/L, ZnNTP inhibitor is optimal to be added in amount of 0.5–1.0 g/L, whereas concentrations of 5.6 mmol/L F− ion and higher require 5 g/L ZnNTP or even more to be added.

Application of laser-induced breakdown spectroscopy for the analysis of pig bones

An application of the laser-induced breakdown spectroscopy technique (LIBS) for the elemental analysis of pig shoulder bone samples is reported. Measurements were performed using a compact laboratory-made LIBS system based on the TEA CO2 laser and time-integrated signal detection. The recorded spectra consisted of well-defined atomic and single-charged ionic lines of bone matrix elements (Ca and P) and other constituent elements (e.g. Mg, Zn, Na, K, and C) with a good signal-to-noise ratio suitable for chemical analysis. Based on the elemental composition of bone samples measured by inductively coupled plasma emission spectroscopy, limits of detection (LOD) of LIBS analysis were estimated for several elements. LOD ranged from 2.2 ppm (K) to 16 ppm (Zn). Carbon and Hα spectral lines were used for plasma diagnostics by measuring Stark widths. Optical profilometry was used to assess the capability of LIBS for depth profile analysis. For laser fluence between 13.0 and 18.2 J cm−2, the ablation rate per pulse ranged from 6 to 10 μm.

Hydrogen diffusion in proton-exchanged congruent Lithium Niobate during post-annealing

We investigated the diffusion of hydrogen during post annealing of proton-exchanged congruent LiNbO3 single crystals in the temperature range between 200 and 400 °C. Proton exchange was done in benzoic acid with 3.6 mol% lithium benzoate added. This process results in a 180 nm thin surface layer with a sharp interface where Li is substituted by H for about 45%. Depth profile analysis was carried out by secondary ion mass spectrometry. From the experimental results, diffusivities were extracted which follow the Arrhenius law with an activation enthalpy of diffusion of (1.39 ± 0.17) eV. The diffusivities are about two orders of magnitude lower than hydrogen tracer diffusivities in pure and in proton-exchanged LiNbO3 but are in good agreement to effective interdiffusion coefficients, governing the proton exchange. Also the activation energy for the latter case of (1.24 ± 0.04) eV is identical within error limits. The results indicate that the diffusional redistribution of high amounts of hydrogen in LiNbO3 is an interdiffusion process between H and Li that is governed by the migration of Li.

Depth profile CF LIBS analysis of the wall deposited layer in the COMPASS tokamak after LiSn testing campaign

Plasma-facing materials in tokamak nuclear reactors are subject to intense heat and radiation. The design of liquid metal (LM) divertor walls has several advantages over the solid counterparts. It is important to understand the migration and re-deposition of LMs such as lithium (Li), lead (Pb) or even tin (Sn). This work presents CF LIBS depth profile analysis of the deposited layer on Ni–Cr based screws situated at different places in the COMPASS tokamak vessel during the Capillary Porous System (CPS) LM (LiSn) divertor testing campaign. The experiment was carried out at low Ar pressure (100 mbar) using ns Nd:YAG laser operating at 532 nm. The spectra were recorded using echelle spectrometer (M5000, Andor Tech.) equipped with an iCCD camera (iStar DH743, Andor Tech.). The quantification was based on observed C I, B I, Li I and (weak) Sn I lines, in addition to trace elements (Ca, Na, K) and main matrix elements (Cr, Ni, Fe). The evaluation of electron temperature and density was based on Cr I-II, Ni-II and Fe I-II lines. The LM based content is estimated to be Li (0.3-0.81 at.%) and Sn (0.1-0.23 at.%) with Li/Sn at.% ratio ranging from 3 to 3.5 (wt.% ratio of 0.17-0.20). In practise, the limit of detection of Sn by CF LIBS for this type of Cr-Ni-Fe based matrix is observed to be ∼0.1 at.%.

LIBS depth profiling of Be-containing samples with different gaseous impurity concentrations

Understanding the interaction between the fusion plasma and the plasma-facing materials (PFMs) is crucial for achieving the optimal performance, safety, and lifetime of the fusion devices. Relevant materials have been intensely studied to determine fuel retention and the composition of the co-deposited layers on the PFMs by depth profile analysis using Laser-Induced Breakdown Spectroscopy (LIBS) and Calibration-Free (CF)-LIBS. However, the comparison between the layers containing a mixture of different (seeding) gases using LIBS, has not been studied systematically. Consequently, the aim of this work is the LIBS depth profile analysis of Be-based samples containing the fuel (D) and one of the seeding gases (N, Ne, He) with variable concentrations to study the potential impact on fuel retention in the PFMs. The LIBS measurements were performed using Nd:YAG laser (1064 nm) under Ar atmosphere (at 2 and 100 mbar). In LIBS the ablation rate was evaluated, spectral lines of all relevant elements except N and Ne were detected and compared with the SIMS depth profiles. The reasons for the non-detectability of Ne are discussed in detail.

Characterization of corona discharge treatment on PTFE surface for TENG applications

As for practical application of triboelectric nanogenerators (TENGs), corona discharge treatment (CDT) is often utilized further to enhance its power outputs by injecting charges. We report compositional analysis and corresponding triboelectric outputs of Poly(1,1,2,2-tetrafluoroethylene) (PTFE) based TENGs. PTFE and Al based TENGs with various PTFE film thickness are fabricated and their performances are measured with different CDT applied bias. XPS depth profile analysis reveals the relation of triboelectric outputs and depth of oxygen ions. Our discovery may give insight in the future development of high performance TENGs using CDT.