Photoelectron Spectroscopy Peak Research Articles

Effect of 60Co Irradiation on Boehmite Dissolution in Caustic Solutions.

Here, we examine how radiation impacts the dissolution behavior of boehmite by subjecting dry nanoparticles of different sizes to 60Co γ radiation and subsequently analyzing their dissolution behavior in caustic solutions as a function of temperature. The measured kinetics show that irradiation with an amount 228.24 Mrad significantly slows the dissolution rate, particularly for smaller sizes at lower temperatures. Specifically, the temperature-dependent dissolution rates of irradiated 20 nm boehmite versus pristine material in 3 M NaOH solutions were several times lower (e.g., rate constant of 0.026 vs 0.075 h-1 at 60 °C), with an apparent activation energy 40 kJ mol-1 higher. Although various imaging techniques and X-ray diffraction measurements consistently revealed no obvious differences between pristine and irradiated samples, after irradiation significant binding energy shifts were detected in the X-ray photoelectron Spectroscopy peaks of Al 2p and O 1s, and a change in their relative intensities indicated a lower O/Al ratio. This suggests that γ-irradiation may stabilize boehmite particle surfaces by driving their chemistry and structure toward more stable aluminum oxide forms. This finding may help explain slower dissolution rates of boehmite in nuclear waste and may be useful for the development of more robust predictive models and effective strategies for waste processing.

Following the propagation of erroneous x-ray photoelectron spectroscopy peak fitting through the literature. A genealogical approach

This study considers how poor x-ray photoelectron spectroscopy (XPS) peak fitting in the scientific literature is both affected by previous precedent and affects future published work. It focuses on a highly cited paper (the “Subject” paper) from a respected journal that contains incorrect S 2p peak fits. This paper was studied in a genealogical fashion vis-à-vis the XPS peak fitting in its “child,” “parent,” “grandparent,” and “great-grandparent” papers. Interestingly, precedents were not followed to a high degree between parent and child papers. However, in many cases, even when the authors of a study did not follow the incorrect precedent that they cited, they still incorrectly fit their data. Thus, not necessarily for good reasons, the effects of poor XPS peak fits on future generations of papers may be less than some experts had expected or feared. In many cases, older papers appear to contain better XPS peak fitting than newer ones.

Effect of ozone gas exposure on drain current of solution-processed IGZO-TFT

The drain current (ID) of indium gallium zinc oxide thin-film transistors (IGZO-TFTs), fabricated by spin coating, decreases even when they are exposed to ozone gas at a concentration equal to or lower than 5 ppm. The ID reduction rate increases when the film thickness and the firing temperature in the spin-coating process of IGZO layer decreases. In these samples, the peak intensity ratio of the O 1s X-ray photoelectron spectroscopy (XPS) peak due to the OH group and the intensity of the infrared (IR) absorption band at 3000 cm−1–3500 cm−1 due to the OH stretching vibration increase. This indicates that OH groups within the IGZO film contribute to the ozone reaction mechanism. These findings are significant for developing high-sensitivity ozone sensors using a simpler process.

Optimization of Electrode Materials Using Nanocarboxylic Polystyrene Promotes Accumulation for Chromium in Zea mays from Water and Soil Contamination.

Chromium is a multivalent metal with great development in the energy storage field because it can effectively improve the electrochemical performance of the material. However, chromium(VI) is soluble in water and toxic, which causes serious metal pollution in the environment. In addition, nanoplastics are difficult to degrade and easy to accumulate, which is an urgent environmental problem to be solved. Therefore, we choose Zea mays to absorb chromium ions, nanopolystyrene, nanocarboxylic polystyrene, and their complexes, which can coordinate and decompose with various polymers in Z. mays, and produce coordination, conjugation, mixed valence, and adjacent group effects. Due to the above effects, the UV-vis spectrum of the material is blueshifted; the X-ray photoelectron spectroscopy peaks of Cr 2p have a chemical shift; the pore structure is optimized; the graphitization degree is improved; the content of N, O, and Cr in the material increases; and the elements are evenly distributed. The series of optimization processes makes the electrodes exhibit excellent electrochemical performance in both supercapacitors and lithium-ion batteries. At 0.5 A·g-1, the specific capacitance of the electrode reaches 490 F·g-1. After 10,000 cycles, its specific capacitance remains at 429.3 F·g-1, and the Coulombic efficiency is 89.9%. In lithium-ion batteries, the initial discharging capacity of the electrode is 1071.7 mAh·g-1 at 0.05 A·g-1. After 5000 cycles, its specific capacity can still reach 242 mAh·g-1 at 0.2 A·g-1, and the Coulombic efficiency is above 95%.

Insight note: X‐ray photoelectron spectroscopy (XPS) peak fitting of the Al 2p peak from electrically isolated aluminum foil with an oxide layer

X‐ray photoelectron spectroscopy (XPS) is the most widely used and important method for chemically analyzing and speciating surfaces. XPS has surface sensitivity (5–10 nm), is quantitative, and is able to probe the oxidation states of the elements at surfaces. However, during the past few years, a great deal of incorrect XPS data analysis has entered the scientific literature. Accordingly, efforts, including this Insight Note, are being made to provide tutorial information to the scientific community. Aluminum is a scientifically and technologically important element. Here we discuss approaches for fitting the Al 2p peak envelope from a sample of aluminum foil with a thin layer of oxide on it. Signals from the metal and oxide are present. We discuss methods for electrically isolating (or not isolating) the sample during data acquisition, the choice of the baseline, fitting the oxide peak with one or two synthetic peaks, and fitting the metal signal with two symmetric or two asymmetric peaks. The thickness of the oxide is calculated based on the areas of the oxide and metal signals.

Layered Metal Oxide Nanosheets with Enhanced Interlayer Space for Electrochemical Deionization.

Electrochemical deionization is regarded as one of the promising water treatment technologies. Here, CoAl-layered metal oxide nanosheets intercalated by sodium dodecyl sulfate (SDS) with an enhanced interlayer spacing from 0.76 to 1.33nm are synthesized and used as an anode. The enlarged interlayer spacing provides an enhanced ion-diffusion channel and improves the utilization of the interlayer electroactive sites, while heat treatment, transferring layered double hydroxides to layered metal oxides (LMOs), offers additional active oxidation reaction sites to facilitate the electro-sorption rate, contributing to the high salt adsorption capacity (31.78mgg-1 ) and average salt adsorption rate (3.75mgg-1 min-1 ) at 1.2V in 500mgL-1 NaCl solution. In addition, the excellent long-term cycling stability (92.9%) after 40 cycles proves the strong electronic interaction between SDS and the host layer, which is validated by density functional theory calculations later on. Moreover, the electro-sorption mechanism of LMOs that originated from the reconstruction of the layered structure based on the "memory effect" is revealed according to the X-ray photoelectron spectroscopy peak shifts of Co element. This strategy of expanding the interlayer spacing combined with heat treatment makes LMOs a competitive candidate for electrochemical water deionization.

Facilitated physisorption of ibuprofen on waste coffee residue biochars through simultaneous magnetization and activation in groundwater and lake water: Adsorption mechanisms and reusability

The adsorption of ibuprofen (IBU) onto the pristine (CB), magnetic (MCB), and simultaneously magnetic activated waste coffee residue biochars (MACB) in groundwater and lake water was rigorously investigated in order to offer profound insights into the differences in their adsorption mechanisms and performances (i.e., adsorption capacity and separability). The higher adsorption capacity of IBU for MACB compared CB and MCB in groundwater and lake water was mainly attributed to the well-developed micropore structures of MACB via the simultaneous magnetization and activation. These phenomena were pronounced for groundwater than lake water due to its lower dissolved organic carbon concentrations. The calculated kinetic, intra-particle diffusion, isotherm, and thermodynamic parameters indicate that the adsorption of IBU onto CB, MCB, and MACB proceeded spontaneously and endothermically and their adsorption processes in groundwater and lake water were mainly governed by the physisorption (i.e., pore-filling effects, hydrogen bonding, and π-π electron donor-acceptor interactions), liquid film diffusion, and intra-particle diffusion. The noticeable increase of the X-ray photoelectron spectroscopy peak intensity related to the CO bond of the carbonyls in IBU-loaded MACB suggests that the accelerated pore-filling effects via the simultaneous magnetization and activation lead to the adsorption capacity improvement of IBU in groundwater and lake water. From the superior reusability of MACB in 3–4 adsorption-desorption cycles even under real water matrices (reuse efficiency > 60%), it can be postulated that the simultaneous magnetization and activation might provide a practicable way for enhancing the adsorption capacity of IBU toward waste coffee residue biochars and their separability in groundwater and lake water.

A detailed view of the Gaussian–Lorentzian sum and product functions and their comparison with the Voigt function

The Gaussian–Lorentzian sum (GLS) and product (GLP) functions remain important in X‐ray photoelectron spectroscopy (XPS) peak fitting. Here, we present a detailed view of these functions, comparing them with each other and with the Voigt function (the “LA(m)” function). First, we show the GLS, GLP, and LA(m) functions as a function of their mixing parameters, m, which reveals differences between them. We then illustrate the use of these functions to fit a series of spectra acquired at different pass energies (resolutions). Next, we show the underlying Gaussian and Lorentzian components of a series of GLS and GLP functions as a function of m, which confirms that the GLS is a simple linear combination of Gaussian and Lorentzian functions. However, one of the two functions used to make the GLP can be very wide, that is, at its extremes, one of these functions has infinite width. We then discuss a plot of the areas of the GLS, GLP, and LA(m) functions as a function of m, which reveals the expected, linear increase in area of the GLS, but nonlinear changes in the areas of the other two functions. Finally, to better understand them, we fit these functions to each other. These results indicate that the GLS and GLP better match the LA(m) function at lower and higher values of the mixing parameter, respectively.

Determination of common peak structure from multiple X-ray photo-electron spectroscopy data sets

X-ray photo-electron spectroscopy (XPS) peak structure (i.e. peak parameters and the number of peaks) offers critical insights in chemical analysis of materials. Reference XPS spectral data are ava...

Impact of interfacial chemical state on spin pumping and inverse spin Hall effect in YIG/Pt hybrids

The interface between ferromagnetic (FM) and nonmagnetic (NM) metal plays a fundamental role in the generation, transmission, detection of spin current, and spin-based devices. The impact of physical properties on the interface such as roughness, crystallization conditions, and even impedance matching has been widely investigated. In this work, the effects of interfacial chemical state at the interface of ${\mathrm{Y}}_{3}{\mathrm{Fe}}_{5}{\mathrm{O}}_{12}$ and Pt (YIG/Pt) are systematically investigated through spin injection. Prior to Pt deposition, the spin mixing conductance and inverse spin Hall voltage of YIG/Pt hybrids increased up to 300%, using surface chemical processing on YIG. The interfacial chemical state is identified from x-ray photoelectron spectroscopy spectra and peak decomposition. Both ${\mathrm{Fe}}^{2+}$ and ${\mathrm{Fe}}^{3+}$ cations appear at the interface and higher content of ${\mathrm{Fe}}^{3+}$ enhances the interface magnetic moment which consequently plays a crucial role in spin injection efficiency and inverse spin Hall voltage. In order to prevent the influence of magnetic proximity effect of Pt layers close to the FM/NM interface, a Cu spacer is inserted. It is found that the improved spin injection efficiency due to iron cations still exists in the YIG/Cu/Pt structure, which confirms the universal influence of the interfacial chemical state on spin pumping efficiency. This discovery has potential implications for spin generation, detection, and even optimization of spintronic devices.

Nanostructured of SnO2/NiO composite as a highly selective formaldehyde gas sensor

Abstract

Analysis of Carbon and Carbon-Containing Materials by X-Ray Photoelectron Spectroscopy

The results of the analysis of carbon-containing materials are presented based on an analysis of the peaks of X-ray photoelectron spectroscopy (XPS) formed by the electrons leaving the analyzed sample in a vacuum without energy loss (peak shape analysis, PSA) and based on the interpretation of the widest possible area of energy loss adjacent to the photoelectron spectroscopy (PES) peak. It is shown that the PES analysis of diamond-like materials containing alloying additives, the concentration of which is comparable with the concentration of carbon, is not effective. The PES analysis of graphene oxide samples that were heat-treated to remove oxygen gave detailed information about the laws of the energy loss of photoelectrons emitted from the 1s level, which determines the allotropic variety of carbon.

Understanding the excitation wavelength dependent spectral shift and large exciton binding energy of tungsten disulfide quantum dots and its interaction with single-walled carbon nanotubes

Herein, we investigate the origin of excitation wavelength dependent spectral features and high fluorescence quantum yield in fluorescent 2D tungsten disulfide (WS2) quantum dots (QDs) of average size 2.4 nm. The as-prepared WS2 QDs possess high optical bandgap and reasonably high fluorescence quantum yield ~15.4% in the green region without any functionalization. The broad photoluminescence (PL) spectrum consists of multiple peaks owing to emissions from excitonic transitions and surface defect-related transitions. The excitation wavelength-dependent spectral redshift and narrowing of line shape in the PL peak are analyzed carefully, and it is attributed to the selective excitation/recombination of carriers from different energy levels. The temperature-dependent PL analysis yields an exciton binding energy of ~301 meV in the QDs. Furthermore, we study the interaction between fluorescent WS2 QDs and single-walled carbon nanotubes (SWCNTs) and explore the mechanism of systematic quenching of PL of QDs by SWCNTs. The nature of the Stern–Volmer plot is found to be linear, and the time-resolved fluorescence measurements reveal that the quenching follows primarily the static behavior. Our study further reveals that defect sites in SWCNTs primarily act as the binding sites for WS2 QDs and form non-fluorescent complexes for effective quenching of the PL. The strong interaction between the WS2 QDs and the SWCNTs is evidenced from the spectral shift in the X-ray photoelectron spectroscopy and Raman peaks. Our study reveals the origin of excitation wavelength dependent PL emission from WS2 QDs and the nature of the interaction between WS2 QDs and SWCNTs, which are important for their applications in biomedical imaging and sensing, such as surface-enhanced Raman scattering, etc.

Generation of oxygen interstitials with excess in situ Ga doping in chemical bath deposition process for the growth of p-type ZnO nanowires

The current work focuses on the incorporation of excess amount of gallium (Ga) in zinc oxide (ZnO) nanowires to generate oxygen interstitials for developing p-type conductivity. Ga has been used as an n-type dopant in ZnO lattice by reducing its inherent vacancies up to 3% molar ratio of Ga and Zn employing chemical bath deposition technique. However, the addition of more than 4% of gallium nitrate in the bath solution creates oxygen interstitials which are confirmed from the presence of X-ray photoelectron spectroscopy (XPS) peak at 532.6 eV and the relevant cathodoluminescence (CL) peak at 626 nm of the grown Ga-doped ZnO nanowires. The p-type conductivity of such ZnO nanowires has been confirmed from current–voltage, capacitance–voltage and Hall voltage measurements. The reproducibility of the results indicates the incorporation of excess Ga to be a promising technique for growing p-type ZnO nanowires.

Modulated transition metal-oxygen covalency in the octahedral sites of CoFe layered double hydroxides with vanadium doping leading to highly efficient electrocatalysts.

The development of efficient and stable non-noble-metal electrocatalytic materials for the oxygen evolution reaction (OER) is a huge and important challenge at present. Herein, we report the prominent enhancement of OER activity via doping vanadium into CoFe-based layered double hydroxide (LDH) electrocatalysts. Electrochemical characterization shows that the Co2Fe0.5V0.5 LDH grown on carbon papers (CPs) has an enormous electrochemical surface area (ECSA) and exhibits the smallest overpotential of 242 mV at 10 mA cm-2, which only requires a small Tafel slope of 41.4 mV dec-1 in 1 M KOH solution. The X-ray photoelectron spectroscopy (XPS) peak position of Co, Fe and O moves slightly to higher binding energy, elucidating the improved covalency of the metal-oxygen bond after V doping. DFT+U simulation indicates that the outstanding electrocatalytic activity of Co2Fe0.5V0.5 could be ascribed to the increased metal-oxygen covalency in LDH after V element doping, and facilitates the charge-transfer from oxygen to the metal. This finely tuned strategy by V doping into the CoFe-based LDH matrix can adjust the covalency of metal-oxygen bridges and enhance its electrocatalytic activity for the OER. In this work, we also present a general method to study various highly efficient metal hydroxide catalysts for the OER.

Pt Supported on Nb-Doped-TiO2 As a Highly Selective and Durable Electrocatalyst for PEFC Applications

Insufficient durability of commercial catalysts is a persistent issue for PEFC applications.1 Herein, Pt on Nb-doped-TiO2 is reported as a highly durable electrocatalyst on which the direct 4-electron reduction of oxygen to water is more facile compared to Pt/C. All performance metrics are reported comparing Pt/Nb-TiO2 with a 15% Pt loading, against a commercial Pt/C catalyst (46.5% Pt loading, Tanaka, K. K.). Nb-doped-TiO2 with high surface area and high electronic conductivity was synthesized using the supercritical fluid method. Initially, the durability of the catalyst was characterized using accelerated stability tests (ASTs) involving 10,000 high potential cycles (DOE/FCCJ protocol) and the Pt/Nb-TiO2 was found to retain 78% of its initial electrochemically active surface area (ECSA) compared to the 57.6 % retained by Pt/C. These observations were in excellent agreement with previous reports that the Pt particle size of Pt/C grew from 2nm to 8nm during the AST protocol along with severe corrosion and amorphization of the carbon surface.2, 3 TEM and XPS studies of the Pt-Nb-doped-TiO2 catalyst showed that the Pt particle size grew from 3nm to 6nm and the Nb(IV) and Ti(III) in the support were oxidized to Nb(V) and Ti(IV) after the durability test. Thus, the improvement in Pt/Nb-TiO2 ECSA retention was attributed to the lower extent of particle growth and lack of oxidative support loss upon oxidation as compared to Pt/C. The oxygen reduction reaction (ORR) performance was characterized by linear polarization using a rotating disk electrode (RDE). The electrochemical surface areas of Pt/Nb-TiO2 and Pt/C were found to be 48m2·g-1 and 83m2·g-1 respectively, and the mass activity for the ORR at 0.9V vs. RHE were found to be 150 mA·mg-1 Pt and 124 mA·mg-1 Pt respectively. The improved mass activity on Pt/Nb-TiO2 was attributed to strong metal support interaction (SMSI) between the Nb-TiO2 support and the Pt catalyst based on the 625 meV decrease in the binding energy of the Pt4f x-ray photo-electron spectroscopy (XPS) peaks of Pt/Nb-TiO2 compared to Pt/C. To quantify the impact of the SMSI, a kinetic model was applied to calculate the elementary reaction rate constants for the various steps of the ORR on both catalysts. The reaction rate constant (k1) for the direct 4-electron transfer pathway to produce H2O was significantly larger in Pt/Nb-TiO2 as compared to Pt/C. Thus, the reduction in the electron binding energy as observed in the XPS was found to aid the facile filling of the higher energy 2p orbitals of O2 thereby leading to improved 4-electron transfer kinetics and improved overall activity.

The Effect of New Modified Fatty Acid (CY-23) Collector on Chlorite/Hematite Separation

The flotation separation on chlorite and hematite with the new modified fatty acid collector CY-23 was studied. The investigation included both flotation and reagent adsorption tests. And all the characteristics of chlorite surface before and after the adsorption of new collector CY-23 have been studied with X-ray photoelectron spectroscopy (XPS). The flotation results showed that caustic starch (CS) could depress the flotation of hematite and chlorite and CaCl2 could activate chlorite flotation but failed on hematite when using CY-23 as collector. The adsorption rate of CY-23 on the surface of chlorite after being inhibited by CS was relatively smaller, but the amount of CY-23 adsorbed on the inhibited chlorite was greatly increased after adding activator CaCl2. The results of XPS analysis showed that the photoelectron spectroscopy peaks of Mg2p and Al2p moved towards low energy after collector CY-23 was absorbed on chlorite surface, which indicated that chemical bonding through electron cloud transfer occurred between collector CY-23 and Mg, Al ions of chlorite surface. The chemical reaction promoted the adsorption of CY-23 on chlorite surface and eventually improved the ability of CY-23 to float and collect chlorite.

Thiophene Derivatives on Gold and Molecular Dissociation Processes

We report a systematic study of thiophene derivatives on gold surfaces. These molecules are of interest in molecular electronics, and the characracteristics of the thiophene–electrode interface in devices needs to be understood as it affects electron transport characteristics. Some experiments indicated S–C bond scission in contact with metals resulting in disruption of the π-electron system that affects charge transport, which would also be affected by presence of split-off chemisorbed sulfur. We explored this dissociation aspect by photoemission for the case of monocrystalline Au(111) surfaces and Au films grown on mica for a series of polythiophenes molecules (nT, n = 1–4, 6) as well as for α,ω-diquaterthiophene (DH4T) and dihexylsexithiophene (DH6T). The S 2p X-ray photoelectron spectroscopy peaks are found to have complex line shapes corresponding to S atoms with different core level binding energies (CLBE). Density functional theory calculations of adsorption energies and CLBEs were performed for va...

High performance PtxEu alloys as effective electrocatalysts for ammonia electro-oxidation

Pt-rare-earth alloys are rarely studied as electrocatalysts for direct ammonia fuel cells. Thus, their electrocatalytic performance of ammonia electro-oxidation is worth studying, especially for PtxEu alloys. Herein, a series of PtxEu/C (x = 1, 3 and 5) electrocatalysts has been prepared using polyol reduction method. Among them, PtEu/C is found to be a promising candidate for ammonia electro-oxidation. Physical characterizations show that PtEu/C has a small lattice parameter and narrow size distribution. X-ray photoelectron spectroscopy peak shifts of PtEu/C indicate the electron transfer from Eu to Pt. Electrochemical measurement results indicate that PtEu/C is highly active. Particularly, it has a higher current density, lower activity loss and apparent activation energy toward ammonia electro-oxidation compared to Pt/C catalyst.

Carbonization of Silicon Nanoparticles via Ablation Induced by Femtosecond Laser Pulses in Hexane

Silicon carbide (SiC) has been widely used in various technological applications, including power devices, light-receiving devices, and light-emitting devices. Several methods for fabricating SiC particles with nanometer dimensions have been reported, including carbo-thermal reduction of silica, chemical vapor deposition, laser pyrolysis, and microwave irradiation. To develop a new and simple method for fabricating SiC nanoparticles, we investigated the possibility of using femtosecond-laser ablation. In this paper, we report the formation of SiC nanoparticles by femtosecond-laser ablation on silicon immersed in hexane. By using a high-peak-power laser that can achieve extremely high temperatures and pressures on the silicon surface, SiC nanoparticles were successfully fabricated via ablation in hexane. In our experiments, femtosecond pulses from a Yb-fiber laser were used to irradiate to silicon single crystal. The laser was focused onto a spot on the silicon surface. After ablation, we evaluated the particles on the target substrate and particles in the irradiated hexane. Scanning electron microscopy revealed that the particles range in size from 100 to 400 nm. X-ray diffraction analysis indicated that the nanoparticles might be SiC. The characteristic X-ray photoelectron spectroscopy peaks of nanoparticles were Si-2p (100.1 eV) and C-1s (282.9 eV), which are identical to the characteristic peaks of SiC (John et al. in Handbook of X-ray photoelectron spectroscopy, Physical Electronics, Eden Prairie, 1995; Hijikata et al. in Appl Surf Sci 184:161–166, 2001; Shen et al. in Chem Phys Lett 375:177–184, 2003). We also used transmission electron microscopy and electron energy-loss spectroscopy to evaluate particles from the irradiated hexane. Such a simple method of fabricating SiC nanoparticles by femtosecond-laser ablation may open new possibilities in the development of growth techniques for SiC.