2p X-ray Photoelectron Spectra Research Articles

Mechanistic Insights into the Appel Reaction Mediated by a Poly-Phosphamide Material as a Heterogeneous Catalyst.

Due to notable thermochemical stability, polyphosphamides are often regarded as flame retardants, while molecular phosphamides can serve as versatile Lewis base to catalyze diverse organic transformations. Being chemically analogous to phosphine oxide, phosphamide can also be considered as a mediator for the phosphine-mediated reaction. Herein, an amorphous polymeric material consisting of phosphamide (-NH-P(O)) in the repeating unit (POP) has been prepared via condensation of tris(2-aminoethyl)amine (TREN) and phenyl phosphinic dichloride (PPDC). The POP is isolated as a metal-free and pure organic material which is made of a strong covalent bond and the phosphamide unit is deployed in the organic framework. The presence of phosphamide in the repeating unit of the isolated amorphous POP material can be confirmed by 31P CPMAS NMR, FTIR, and Raman studies. The core-level N 2p and P 2p X-ray photoelectron spectra are in accordance with the presence of tertiary amine nitrogen attached to carbon and secondary amine nitrogen attached to phosphorus. Elemental analyses have depicted approximately 19.7% of phosphorus content in the material, which is being utilized to study the catalytic Appel reaction with 76% conversion of alcohol to a corresponding halide and TON of 462. Quasi in situ Raman study has identified that amino phosphine formed via in situ reduction of the phosphamide unit of the POP catalyzes the halogenation of primary and secondary alcohols with wide substrate scope and functional group tolerance. Kinetic studies have established a first-order dependence with respect to alcohol, while deuterium labeling experiments emphasize that the deprotonation of alcohol is the rate-limiting step. High thermal stability of the material, scope of easy catalyst recyclability, and a cumulative TON of 1386 have led the POP as an emerging pure organic material to be explored further for other phosphine-mediated organocatalysis.

Regeneration of Activated Sludge into SiO2-Decorated Heteroatom-Doped Porous Carbon as Advanced Electrodes for Li-S Batteries.

The regeneration of harmful activated sludge into an energy source is an important strategy for municipal sludge treatment and recycling. Herein, SiO2-modified N,S auto-doped porous carbon (NSC@SiO2) with high conductivity (70 S m-1) is successfully obtained through a simple calcination method of the activated sludge from wastewater treatment. Further, P-doped NSC@SiO2 (NSPC@SiO2) is designed to achieve a higher surface area (891 m2 g-1 vs 624 m2 g-1), a larger pore volume (0.87 cm3 g-1 vs 0.08 cm3 g-1), and more carbon defects. Due to its special structure, NSPC@SiO2 is used as a sulfur host of lithium-sulfur batteries. The results of polysulfide adsorption experiments, S 2p X-ray photoelectron spectra (XPS), Li2S nucleation experiments, polysulfide symmetric cells, measurement of the galvanostatic intermittent titration (GITT), polarization voltage difference, lithium-ion diffusion rate, and Tafel slope verified that NSPC@SiO2 greatly improved the adsorption capacity of polysulfides, lowered the barrier to Li2S formation and the internal resistances of cells, and accelerated Li+ ion diffusion and the reaction kinetics of polysulfide conversion, resulting in the excellent performance of polysulfide capture and superior rate performance and cyclic stability. By comparing NSPC@SiO2 with NSC@SiO2, a higher initial capacity (1377 mAh g-1 vs 1150 mAh g-1 at 0.1C), better rate capacity (912 mAh g-1 vs 719 mAh g-1 at 2C), and low capacity decay (0.094% per cycle within 200 cycles) are obtained. Our work provides direction for the treatment, disposal, and resource utilization of activated sludge.

Interpretation of Shakeup Mechanisms in Copper L-Shell Photoelectron Spectra.

We report on an original full ab initio quantum molecular approach designed to simulate Cu 2p X-ray photoelectron spectra. The description includes electronic relaxation/correlation and spin-orbit coupling effects and is implemented within nonorthogonal sets of molecular orbitals for the initial and final states. The underlying mechanism structuring the Cu 2p photoelectron spectra is clarified thanks to a correlation diagram applied to the CuO4C6H6 paradigm. This diagram illustrates how the energy drop of the Cu 3d levels following the creation of the Cu 2p core hole switches the nature of the highest singly occupied molecular orbital (H-SOMO) from dominant metal to dominant ligand character. It also reveals how the repositioning of the Cu 3d levels induces the formation of new bonding and antibonding orbitals from which shakeup mechanisms toward the relaxed H-SOMO operate. The specific nature, ligand → ligand and metal → ligand, of these excitations building the satellite lines is exposed. Our approach finally applied to the real Cu(acac)2 system clearly demonstrates how a definite interpretation of the XPS spectra can be obtained when a correct evaluation of binding energies, intensities, and relative widths of the spectral lines is achieved.

Adsorption characteristics of silver atoms and silver ions on silica surface in silver nanoparticle hydrosol system

Previous studies have demonstrated that silver ions (Ag+) can be released from silver nanoparticles (AgNPs) to produce a system of silver atoms (Ag0) and Ag+ in equilibrium, which may affect the environment through adsorption on sediment. Here, the adsorption behaviour of Ag0 and Ag+ in a AgNP hydrosol system on a silica surface was systematically investigated using experimental evaluation and first-principles calculations based on density functional theory. The adsorption environment and performance were first analysed by batch and fixed-bed experiments, which indicated that less adsorption occurred between silica and silver. Subsequent energy calculations and structural optimisation revealed that both Ag0 and Ag+ were more likely to be chemisorbed on the silica surface through covalent (AgO) bonds. The average adsorption energies of SiO2/Ag+ and SiO2/Ag0 were −5.445 and −3.61 eV, respectively. In addition, Ag0 lost an average of 0.86 electrons to the O4–silica bond. By contrast, only a few electrons, which bonded with O1, were transferred from silica to Ag+. Analyses of the density of states and crystal orbital Hamilton population revealed that O and Ag were hybridised with the 2p–4d orbitals after adsorption. In addition, the peak shifts in the high-resolution Ag 3d, O 1s and Si 2p X-ray photoelectron spectra after adsorption revealed changes in the chemical state. The presence of AgO bonds was confirmed by the surface-enhanced Raman scattering spectrum. Silica was selected as the main component of sediment in this study, and it is hoped that this work will motivate a simulation of the migration and transformation of silver by sediment in the water environment.

Phase-Controlled 1T Transition-Metal Dichalcogenide-Based Multidimensional Hybrid Nanostructures

Phase-Controlled 1T Transition-Metal Dichalcogenide-Based Multidimensional Hybrid Nanostructures

Analysis of the Fe 2p XPS for hematite α Fe2O3: Consequences of covalent bonding and orbital splittings on multiplet splittings.

The origins of the complex Fe 2p X-Ray Photoelectron Spectra (XPS) of hematite (α-Fe2O3) are analyzed and related to the character of the bonding in this compound. This analysis provides a new and novel view of the reasons for XPS binding energies (BEs) and BE shifts, which deepens the current understanding and interpretation of the physical and chemical significance of the XPS. In particular, many-body effects are considered for the initial and the final, 2p-hole configuration wavefunctions. It is shown that a one-body or one-configuration analysis is not sufficient and that the many-body, many-determinantal, and many-configurational character of the wavefunctions must be taken into account to describe and understand why the XPS intensity is spread over an extremely large number of final 2p-hole multiplets. The focus is on the consequences of angular momentum coupling of the core and valence open shell electrons, the ligand field splittings of the valence shell orbitals, and the degree of covalent mixing of the Fe(3d) electrons with the O(2p) electrons. Novel theoretical methods are used to estimate the importance of these various terms. An important consequence of covalency is a reduction in the energy separation of the multiplets. Although shake satellites are not considered explicitly, the total losses of intensity from the angular momentum multiplets to shake satellites is determined and related to the covalent character of the Fe-O interaction. The losses are found to be the same for Fe 2p1/2 and 2p3/2 ionization.

The ability of GexGa4S96-x chalcogenide glasses dissolving rare earth probed by x-ray photoelectron spectra analysis

We have synthesized the ternary chalcogenide glasses GexGa4S96-x (x = 22.5, 27, 30, 33, 36), and studied the structural evolution of the glasses by the high-resolution x-ray photoelectron spectra (XPS) technique. We decomposed S 2p, Ge 3d and Ga 3d core XPS spectra into different structural units and found that, with increasing Ge content, part of S-Ge(Ga)-S structure changes into (Ge,Ga)-Ge(Ga)-S, and finally Ge(Ga) clusters appear in the chemically stoichiometric and S-poor glasses. The formation of Ge(Ga) clusters in the chemically stoichiometric and S-poor glasses indicates that, only S-rich Ge–Ga–S glasses can be effectively used as hosts for the doping of rare earth ions, in which no Ga clusters exist and the rare earth ions can be uniformly distributed in the glasses to avoid any possible photoluminescence quenching.

Synthesis and structural properties of xLi2MnO3⋅(1-x)LiNi0.5Mn0.5O2 single crystals towards enhancing reversibility for lithium-ion battery/pouch cells

A series of xLi2MnO3·(1-x)LiNi0.5Mn0.5O2 (x = 0.3, 0.4, 0.5 and 0.6) single crystals is successfully synthesized via wet mechanical ball milling. Considering the components of Li2MnO3 and LiNi0.5Mn0.5O2 in xLi2MnO3·(1-x)LiNi0.5Mn0.5O2, the Mn 2p X-ray photoelectron spectra are successfully refined to Mn3+ and Mn4+ states in each component. Through GITT evaluation of the dynamic DLi+, the minimum DLi+ value is observed for the initial charging, which is attributed to the irreversible process of Li2O being removed from the layered Li2MnO3 structure. The DLi+ values in the 1st charge process are lower than those in the 3rd charge process. The 0.4Li2MnO3·0.6LiNi0.5Mn0.5O2 sample exhibits the best electrochemical properties compared to the other samples. At a 0.1 C current rate, it delivers 212 mAh g−1 without capacity loss for 100 cycles. At current rates of 1 and 2 C, it delivers 158.5 and 102.1 mAh g−1, respectively. In the full cell state (pouch cell), the 0.4Li2MnO3·0.6LiNi0.5Mn0.5O2 sample presents practical electrochemical properties that deliver 180 mAh g−1 for 100 cycles at a 0.1 C rate.

Preparation and characterization of high infrared emissivity Mn-doped NCO spinel composites

NiCr2O4 (NCO) spinel composites with different Mn/Ni atomic ratios (Mn/Ni = 0.05, 0.10, 0.15, and 0.20) were synthesized via solid state reaction method. Phase compositions and microstructure of samples were characterized by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The TG-DSC curves showed that the appropriate baking temperature for Mn-doped NCO spinel preparation was approximately 1 320 °C. X-ray diffraction patterns exhibited the formation of NCO spinel with Fd-3m space group. Valence state of the Mn ions was determined from 2p and 3s X-ray photoelectron spectra. Manganese ions were mostly in divalent and trivalent states, and the ratio of Mn2+/Mn3+ was 0.78-0.98. Fourier transform infrared spectroscopy (FTIR) was used to analyze the spectral emissivity of Mn doped NCO spinel. It was revealed that the infrared emissivity of Mn-doped NCO spinel in 1.8-5 μm could be significantly enhanced with increasing content of Mn2+, reaching as high as 0.9398. Mn-doped NCO spinel showed excellent radiation performance and good prospect in high emissivity applications in the temperature range of 800-1 200 °C.

Direct Synthesis of Vanadium Phthalocyanine and Its Electronic and Magnetic States in Monolayers and Multilayers on Ag(111)

Vanadium phthalocyanine (VPc) monolayers and multilayers were synthesized on Ag(111), and the electronic and magnetic states of an unachieved VPc with a divalent state of V were investigated. The VPc monolayer was fabricated by directly depositing the V atoms on a metal-free phthalocyanine (H2Pc) monolayer under ultra-high-vacuum conditions. The VPc multilayer was synthesized by repeated VPc monolayer deposition and subsequent sample annealing at approximately 450 K. The N 1s X-ray photoelectron spectra (XPS) of these samples showed a remarkable reduction in the peak assigned to H-bonded N atoms, concomitant with the appearance of a new peak attributed to V-bonded N atoms close to the peak of iminic N. Additionally, the oxidation state of V estimated from the V 2p XPS peak position corresponded to 1.6 and 2.4 in the monolayer and multilayer samples, respectively. These results clearly imply that VPc monolayers and multilayers were successfully obtained. The main ground-state electronic configuration of th...

Valence state of transition metal ions in Co1−xFexCr2O4 (x = 0.1, 0.2, 0.5) ceramics from X-ray photoelectron and Mössbauer spectroscopy data

Ceramics with nominal composition Co1−xFexCr2O4 (x=0.1, 0.2, 0.5) are synthesized via a solid state reaction method. Crystal structure of samples is studied with X-ray diffraction. Actual elemental composition is determined using X-ray microanalysis and X-ray photoelectron spectroscopy (XPS). Samples’ morphology is studied with scanning electron microscopy. Valence state of the Co, Fe and Cr ions is determined from 2p X-ray photoelectron spectra and Mössbauer spectra. XPS are assigned based on calculations with allowance for the multiplet splitting, crystal field, and the charge-transfer effects. Cobalt ions are found to be bivalent in tetrahedral coordination; chromium ions are trivalent in octahedral coordination. Fe ions are mostly in trivalent states, although Fe2+ ions are also present in significant amounts. Fe2+ ions are in tetrahedral coordination while Fe3+ ions occupy both tetrahedral and octahedral sites. Bulk and near-surface elemental compositions of the ceramic grains are noticeably different. Relative Fe3+/Fe2+ contents are the same in the volume and at the surface of the samples; relative number of Fe3+ ions increases upon the increase of x. A model of partly inverse spinel structure is suggested where the atoms of iron substitute both Co and Cr atoms.

Hydrogen reduction of vanadium in vanadium-doped LiMnPO4

The samples of vanadium-doped LiMnPO4 have been synthesized by the solid-state reaction technique. To reduce the oxidation state of vanadium from V5+ to V4+, the samples have been additionally annealed under hydrogen atmosphere. The tetravalent state of vanadium was proved by analysis of V 2p X-ray photoelectron spectra. Raman spectroscopy, first-principle studies and magnetic measurements were used to determine the effect of V4+ on the Li–Mn phosphate properties.

Temperature effect on X-ray photoelectron spectra of 3d transition metal ions

Temperature effect on 2p- 3s- and 3p X-ray photoelectron spectra (XPS) of various ions of Ti, V, Cr, Mn and Fe is studied theoretically within an isolated ion approximation. It is shown that the 2p XPS of those ions are temperature dependent even at room temperature due to a very slight energy splitting between the ground-state-term total-momentum J-components which can be thermally populated. Most significant temperature effect is expected in the 2p-spectra of Ti2+(3d2), V2+(3d3), Cr2+(3d4), Mn3+(3d4), and Mn3+(3d4) ions. The temperature effect on 3p XPS is slight. No temperature effect on 3s XPS is expected.

Valence state of the manganese ions in mixed-valence La1−αBiβMn1+δO3±γ ceramics by Mn 2p and Mn 3s X-ray photoelectron spectra

Valence state of Mn in La1−αBiβMn1+δO3±γ (LBMO) ceramic samples and in orthorhombic manganates RMn2O5 (R=Y, Bi, Eu, Gd), is studied using Mn 2p- and Mn 3s-spectra. Both Mn3+ and Mn4+ ions are shown to be present in those compounds. Relative Mn3+/Mn4+ ions contents are determined by fitting experimental Mn 2p-spectra with weighted superpositions of theoretical spectra of Mn3+ and Mn4+ ions calculated in one-configuration Pauli–Fock approximation considering thermal excitations in initial state. Content of the Mn4+ ions correlates with the deviation δ in La1−αBiβMn1+δO3±γ from stoichiometry, La1−xBixMnO3. Separation of low-spin and high-spin components of Mn 3s-spectrum can be sensible to the relative content of Mn3+ and Mn4+ ions. Mn3+/Mn4+ ratios derived from Mn 2p- and from Mn 3s-spectra compare well in the case of the RMn2O5 manganates, while in the case of the LBMO ceramics the results obtained from the Mn 3s spectra are physically meaningless. Due to a complex interplay between 3d-electrons delocalization and strong many-electron effects the 3s spectra of 3d-elements may be misleading.

Resonant photoemission at the L3 absorption edge of Mn and Ti and the electronic structure of 1T-Mn0.2TiSe2

Resonant valence band x-ray photoelectron spectra (ResPES) excited near the 2p3/2 core level energies, 2p x-ray photoelectron spectra (XPS) and L3,2 x-ray absorption spectra (XAS) of Ti and Mn in single crystals of 1T-Mn0.2TiSe2 were studied for the first time. The ionic–covalent character of the bonds formed by the Mn atoms with the neighboring Se atoms in the octahedral coordination is established. From the XPS and XAS measurements compared with the results of atomic multiplet calculations of Ti and Mn L3,2 XAS, it is found that the Ti atoms are in the ionic state of 4 + and the Mn atoms are in the state of 2 + . In ResPES of Mn0.2TiSe2 excited near the Ti 2p3/2 and Mn 2p3/2 absorption edges the Ti 3d and Mn 3d bands at binding energies just below the Fermi level are observed. According to theoretical calculations of E(k) the Ti 3d states are localized in the vicinity of the Γ point and the Mn 3d states are localized along the direction K–Γ–M in the Brillouin zone of the crystal.

X-ray photoelectron study of the valence state of iron in iron-containing single-crystal (BiFeO3, PbFe1/2Nb1/2O3), and ceramic (BaFe1/2Nb1/2O3) multiferroics

Fe2p, Fe3p, and Fe3s X-ray photoelectron spectra (XPS) are measured with high resolution in single-crystal multiferroics BiFeO3 and PbFe1/2Nb1/2O3, as well as in reference samples Fe2O3, FeSO4·7H2O, FeC2O4·2H2O. The spectra are assigned based on an isolated-ion approximation calculation. Single-crystal multiferroics and Fe2O3 are shown to have the Fe ions only in the Fe3+ valence state. Ceramic samples of BaFe1/2Nb1/2O3 with various relative Fe2+/Fe3+ abundances are synthesized in various conditions. An approximate method to determine the Fe2+/Fe3+ ratio in a sample is suggested. The method is based on the fitting of the sample's 2p XPS with a superposition of Fe2+ and Fe3+ 2p spectra. An effect of temperature regimes of sintering and annealing on the Fe2+/Fe3+ ratio is demonstrated.

Wet Chemical Functionalization of III−V Semiconductor Surfaces: Alkylation of Gallium Phosphide Using a Grignard Reaction Sequence

Single-crystalline gallium phosphide (GaP) surfaces have been functionalized with alkyl groups via a sequential Cl-activation, Grignard reaction process. X-ray photoelectron (XP) spectra of freshly etched GaP(111)A surfaces demonstrated reproducible signals for surficial Cl after treatment with PCl(5) in chlorobenzene. The measured Cl content consistently corresponded to approximately a monolayer of coverage on GaP(111)A. In contrast, GaP(111)B surfaces treated with the same PCl(5) solution under the same conditions exhibited macroscale roughening and yielded XP spectra that showed irreproducible Cl surface content often below the limit of detection of the spectrometer. The Cl-activated GaP(111)A surfaces were reactive toward alkyl Grignard reagents. Sessile contact angle measurements between water and GaP(111)A after various levels of treatment showed that GaP(111)A surfaces became significantly more hydrophobic following reaction with either CH(3)MgCl or C(18)H(37)MgCl. GaP(111)A surfaces reacted with C(18)H(37)MgCl demonstrated wetting properties consistent with surfaces modified with a dense layer of long alkyl chains. High-resolution C 1s XP spectra indicated that the carbonaceous species at GaP(111)A surfaces treated with Grignard reagents could not be ascribed solely to adventitious carbon. A shoulder in the C 1s XP spectra occurred at slightly lower binding energies for these samples, commensurate with the formation of Ga-C bonds. High-resolution P 2p XP spectra taken at various times during prolonged direct exposure to ambient laboratory air indicated that the resistance of GaP(111)A to surface oxidation was greatly enhanced after surface modification with alkyl groups. GaP(111)A samples that had been functionalized with C(18)H(37)- groups exhibited less than 0.1 nm of surface oxide after 7 weeks of continuous exposure to ambient air. GaP(111)A surfaces terminated with C(18)H(37)- groups were also used as platforms in Schottky heterojunctions with Hg. In comparison to freshly etched GaP(111)A, the alkyl-terminated GaP(111)A samples yielded current-voltage responses that were in accord with metal-insulator-semiconductor devices and indicated that this reaction strategy could be used to alter rates of heterogeneous charge transfer controllably. The wet chemical surface functionalization strategy described herein does not involve thiol/sulfide chemistry or gas-phase pretreatments and represents a new synthetic methodology for controlling the interfacial properties of GaP and related Ga-based III-V semiconductors.

Photocatalytic activity of TiO 2 thin films doped with nitrogen using a cathodic magnetron plasma treatment

TiO 2 films are treated using a magnetron nitrogen-plasma apparatus that can generate high density plasma to realize nitrogen-doping. The films are treated for 5 min with nitrogen plasma at a discharge power from 30 to 100 W by a radio frequency generator operating at 13.56 MHz. The plasma treated films show visible light absorption in the range of around 400–500 nm. Light absorption above approximately 500 nm is also observed in the film plasma treated at a high discharge power. It is confirmed from N 1s and Ti 2p X-ray photoelectron spectra of the films that Ti–N bonds and oxygen vacancies are formed. Visible light activity of photocatalysis in the film increases with increasing discharge power and then decreases. Such an increase and decrease in the visible light activity are due to the formation of Ti–N bonds and oxygen vacancies, respectively. The visible light activity is improved with the optimum plasma treatment.

Ni 2p X-ray photoelectron spectroscopy study of nanostructured nickel oxide

Herein the detailed analysis of the Ni 2p X-ray photoelectron spectra of nanostructured nickel oxide samples with three different average crystallite sizes is reported. The observed main line broadening and the increase in the relative intensity of the ∼1.5 eV satellite structure are discussed taking into account the large surface to volume ratio, high concentration of Ni 2+ vacancies and enhancement in the Ni 3d–O 2p hybridization. The influence of these factors on the possible local and non-local screening mechanisms accompanying the photoemission of Ni 2p core level electron is analyzed on the basis of the Ni 7O 36 cluster calculations.

Chemical States in Oxide Films on Stainless Steel Treated in Supercritical Water: Factor Analysis of X-Ray Photoelectron Spectra

A preliminary study of the corrosion films of stainless steel SUS304 was carried out by X-ray photoemission spectroscopy for supercritical water having no oxidant or reactant. The corrosion films produced by the supercritical water at and were compared with those by anodic polarization in aqueous solution. The chemical states in the films were determined by factor analysis of Fe, Cr, and Ni 2p X-ray photoelectron spectra. Factor analysis of the passivated SUS304 surface was successfully carried out using four reference spectra, Fe metal, , , and FeOOH, with careful treatment excluding wüstite phase from the standpoint of thermochemistry. In the surface treated by supercritical water, the ratio of iron and nickel increased even when compared to the bulk composition of SUS304 and the major component of nickel was attributed to . In contrast, the content of chromium decreased remarkably. This was explained by effective removal of and its protonated form, , which are predicted in the Pourbaix diagram prepared for chromium in supercritical water ( and ).