Photoelectron Spectroscopy Experiments Research Articles

In Situ Study of Hydrogen Permeable Electrodes for Electrolytic Ammonia Synthesis Using Near Ambient Pressure XPS.

Hydrogen permeable electrodes can be utilized for electrolytic ammonia synthesis from dinitrogen, water, and renewable electricity under ambient conditions, providing a promising route toward sustainable ammonia. The understanding of the interactions of adsorbing N and permeating H at the catalytic interface is a critical step toward the optimization of this NH3 synthesis process. In this study, we conducted a unique in situ near ambient pressure X-ray photoelectron spectroscopy experiment to investigate the solid-gas interface of a Ni hydrogen permeable electrode under conditions relevant for ammonia synthesis. Here, we show that the formation of a Ni oxide surface layer blocks the chemisorption of gaseous dinitrogen. However, the Ni 2p and O 1s XPS spectra reveal that electrochemically driven permeating atomic hydrogen effectively reduces the Ni surface at ambient temperature, while H2 does not. Nitrogen gas chemisorbs on the generated metallic sites, followed by hydrogenation via permeating H, as adsorbed N and NH3 are found on the Ni surface. Our findings suggest that the first hydrogenation step to NH and the NH3 desorption might be limiting under the operating conditions. The study was then extended to Fe and Ru surfaces. The formation of surface oxide and nitride species on iron blocks the H permeation and prevents the reaction to advance; while on ruthenium, the stronger Ru-N bond might favor the recombination of permeating hydrogen to H2 over the hydrogenation of adsorbed nitrogen. This work provides insightful results to aid the rational design of efficient electrolytic NH3 synthesis processes based on but not limited to hydrogen permeable electrodes.

Insights into the origin of the enhanced electrical conductivity of Pd-Sb2O3 nanoparticles: A combined experimental and theoretical study

Supported metal nanocrystallites play a paramount role in catalysis, electrocatalysis, and gas sensing, among other fields. Although the majority of studies are focused on the modification of the composition, size and morphology of the active metallic phase to meet specific needs, the influence of the properties of the support on the overall behavior of such materials is often neglected. In a previous publication, we described for the first time the use of antimony trioxide (Sb2O3) as a new support material for Pd nanoparticles for the electrochemical oxidation of ethanol in alkaline media. Despite its high catalytic activity, information for the intrinsic fundamental properties of Pd-Sb2O3, such as the electrical conductivity and presence of defects, is still lacking. In this work, we combined both experimental techniques and theoretical simulations to gain further knowledge into some relevant physicochemical properties of the Pd-Sb2O3 system. An increase in electrical conductivity of 1000x is found in the Sb2O3 phase after the deposition of a small amount (4.9% weight) of Pd, which cannot be explained by the metallic phase; rather, oxygen vacancies in the Sb2O3 (as indicated by photoluminescence experiments) are likely the origin of such behavior. Theoretical calculations performed by density functional theory show that oxygen vacancies not only lead to distortion in chemical bonds but also change the overall reactivity of the system, corroborating X-ray photoelectron spectroscopy and electrochemical experiments.

Novel, Simple, and Green Citrate-Based Copper Electronic Electroplating Bath in Microvia Void-Free Filling for Printed Circuit Board Application

In this work, a novel, simple, and green citrate-based copper electronic electroplating bath with the characteristics of weak corrosion, low copper ion concentration, and simple composition is developed in microvia void-free filling for printed circuit board application. Succinimide (SM), regarded as a leveler, is the core component of the bath. The action mechanisms of SM on microvia void-free copper filling are carefully expounded. UV–vis spectroscopy and theoretical calculations demonstrate that only the [Cu2(Cit)2]2– coordination ion exists in the bath containing SM at pH 9.0. Linear sweep voltammetry and in situ Fourier transform infrared spectroscopy combined with X-ray photoelectron spectroscopy experiments illustrate that SM can inhibit the electroreduction of the [Cu2(Cit)2]2– coordination ion and promote the electroreduction of intermediate Cu(I) to Cu(0), resulting in the improvement of coating quality. Galvanostatic measurements reveal that the reduction of the [Cu2(Cit)2]2– coordination ion is electrochemically controlled, and SM is diffusion-controlled. The leveler properties of SM (diffusion control and inhibition of [Cu2(Cit)2]2– coordination ion electroreduction) promote copper in bottom-up growing and void-free filling of microvias.

Quantum watch and its intrinsic proof of accuracy

We have investigated the rich dynamics of complex wave packets composed of multiple high-lying Rydberg states in He. A quantitative agreement is found between theory and time-resolved photoelectron spectroscopy experiments. We show that the intricate time dependence of such wave packets can be used for investigating quantum defects and performing artifact-free timekeeping. The latter relies on the unique fingerprint that is created by the time-dependent photoionization of these complex wave packets. These fingerprints determine how much time has passed since the wave packet was formed and provide an assurance that the measured time is correct. Unlike any other clock, this quantum watch does not utilize a counter and is fully quantum mechanical in its nature. The quantum watch has the potential to become an invaluable tool in pump-probe spectroscopy due to its simplicity, assurance of accuracy, and ability to provide an absolute timestamp, i.e., there is no need to find time zero.

Graphdiyne (g‐CnH2n−2)‐Supported Organic–Inorganic Composites with Zinc Cadmium Sulfide for Photocatalytic Hydrogen Evolution

As a new 2D carbon hybrid material, graphdiyne (GD) has attracted much attention due to its good conductivity, adjustable electronic structure, and special electron transfer enhancement properties. Due to its special properties, it has great potential in the field of photocatalytic hydrogen evolution. Considering the modification of GD from the perspective of nano size and bandgap matching, CuS@GDY hybrids to modify ZnCdS are introduced, and the sheet hybrid improved ZnCdS nanoparticles' dispersion. From another point of view, GD not only enhances the optical absorption of the composite but also acts as the main reduction site. Meanwhile, when GD appears in ZnCdS/CuS heterojunction in the form of an electronic bridge, the separation efficiency of photoinduced carriers in ternary system is greatly improved. Finally, the charge transfer mode of the composite system assisted by GD through radical trapping and in situ X‐ray photoelectron spectroscopy experiments are analyzed and verified. The ternary hybrid ZnCdS/CuS@GD prepared in this experiment has excellent photoelectrochemical properties and stability. The design idea and characterization analysis of this article can provide reference and reference value for further research of graphite acetylene in the field of photocatalysis.

Insights into the structure and growth of Lu-doped germanium clusters: comparing density functional theory calculations with photoelectron spectroscopy experiments

ABSTRACT The structure and growth of a series of Lu-doped germanium clusters, LuGe n q (n = 2–14, q = 0, −1) have been investigated by previous photoelectron spectroscopy (PES) and density functional theory (DFT) calculations. The ground states of the anionic LuGe n – clusters obtained from DFT calculations are verified by comparing simulated PES with experimental results. The simulated PES for smaller clusters LuGe n – (n ≤ 6) display relatively simple spectral patterns, suggesting high symmetry structures. It is observed that the pentagonal bipyramid shape is the basic framework for the nascent growth process of LuGe n – (n = 2–8). The structures of LuGe n – (n = 2–13) clusters are all exohedral structures with the Lu atom adsorbed at the surface of the bare Ge n – clusters, while LuGe14 – is the smallest endohedral Lu-doped germanium cluster with the Lu atom completely fallen into the germanium frame. It is found that the LuGe n – clusters with even n are more stable than those with odd n and in the LuGe n clusters there is an opposite trend. Especially, the LuGe n q (n = 9, 12, q = 0, −1) clusters are extremely stable compared to other size clusters. HOMO–LUMO gap shows that the chemical stability of bare Ge n – (n = 2–14) clusters are stronger than that of LuGe n q (n = 2–14, q = 0, −1) clusters owing to the doping of a Lu atom.

An Open-Shell Superatom Cluster Ta10- with Enhanced Stability by United d-d π Bonds and d-Orbital Superatomic States.

We carried out a comprehensive study on the gas-phase reactions of Tan- (n = 5-27) with nitrogen using a customized reflection time-of-flight mass spectrometer coupled with a velocity map imaging apparatus (Re-TOFMS-VMI). Among the studied tantalum clusters, Ta10- exhibits prominent mass abundance indicative of its unique inertness. DFT calculation results revealed a D4d bipyramidal prolate structure of the most stable Ta10-, which was verified by photoelectron spectroscopy experiments. The calculations also unveiled that Ta10- has the largest HOMO-LUMO gap and second-order difference of binding energy among the studied clusters. This is associated with its well-organized superatomic orbitals, which consist of both 6s and 5d orbitals of tantalum atoms, allowing for splitting of superatomic 1D and 2P orbitals and an enlarged gap between the singly occupied molecular orbital (SOMO) and unoccupied β counterpart, which brings forth stabilization energy pertaining to Jahn-Teller distortion. Also, the SOMO exhibits a united d-d π orbital pattern that embraces the central Ta8- moiety.

Bimetallic synergy boost TCPP(Ni)-Co MOF as the high-performance electrochemical sensor for enhanced detection of trace theophylline

A bimetallic porphyrin MOF TCPP(Ni)-Co has been synthesized by the combination of reflux method and hydrothermal method. Due to the inherent conjugated ligand TCPP and the synergistic effect between metal center Co2+ and Ni2+, the TCPP(Ni)-Co MOF could work as the high-performance electrochemical sensor by the modification on the GCE. TCPP(Ni)-Co@GCE could realize the detection of trace theophylline with high sensitivity, fast response time (less than 3 s), detection range of 10–100 nM, and the extreme detection limit as low as about 3.3 nM. The good stability, repeatability and anti-interference performance further support TCPP(Ni)-Co MOF function as an excellent electrochemical sensor for theophylline. The enhanced detection mechanisms have been carefully discussed with X-ray photoelectron spectroscopy (XPS) and cyclic voltammograms (CVs) experiments. The coordination of Ni2+ in higher electron affinity could construct more electron-deficient environment in the well conjugate TCPP ligand, which could reduce the electron compensation to Co2+ in the formation of Co-COO coordination bond and set “Co-COO” in a higher oxidation state, thus enables TCPP(Ni)-Co MOF as the high-performance sensor for trace theophylline.

Enhanced coalbed methane recovery by the modification of coal reservoir under the supercritical CO2 extraction and anaerobic digestion

Coal reservoir is considered as the ideal site for coalbed methane (CBM) occurrence, biomethanation and CO2 sequestration. Four coal samples with different ranks were selected to conduct supercritical CO2 (Sc-CO2) extraction and anaerobic digestion (AD). X-ray photoelectron spectroscopy, mercury intrusion, and isothermal adsorption experiments were performed on the raw coal samples and the remaining coal samples after Sc-CO2 and Sc–CO2–AD to analyze the mechanism of enhanced CBM recovery by reservoir modification. The results showed that coal pore volume and porosity are greatly increased after Sc-CO2 extraction. Meanwhile, the reduction of the oxygen-containing functional groups and the micropore specific surface area determined the weakening of the adsorption capacity of coal. After Sc–CO2–AD, the macropore volume and porosity of coal continued to increase, and the permeability of coal was effectively improved. And the oxygen-containing functional groups and micropore specific surface area continued to decrease, which determined that the adsorption capacity of coal for methane continued to decrease. Sc-CO2 and AD can mutually promote the modification of coal reservoirs. These effects are quite favorable for gas desorption, migration and production during CBM exploitation, which provide powerful supports for CO2 emission reduction, CO2 geological sequestration and CBM production enhancement.

Influence of support textural property on CO2 to methane activity of Ni/SiO2 catalysts

In this work, we elucidated the role of physicochemical textural properties of inert support on the catalyst activity by impregnating Ni on ordered mesoporous silica (SBA-15 and MCM-41) and non-mesoporous silica (nMPS). The catalyst Ni/SBA-15 exhibited the best CO2 conversion (83%) and product selectivity (99.9 %) followed by Ni/MCM-41 and the least by Ni/nMPS. The difference in the nature of the catalyst, degree of nanoparticle distribution and nanoparticle encapsulation by different silica support were studied by N2 adsorption-desorption and X-ray photoelectron spectroscopy (XPS) experiments. The Operando Diffused Reflectance Infrared Fourier Transform Spectroscopy were used to understand the variance in reaction pathway which is accredited to the textural properties of the support. The SBA-15 supported Ni catalyst followed dissociative CO pathway while MCM-41 and nMPS reacted through associative formate mechanism as major pathway. These findings provide a novel perspective on CO2 hydrogenation over Ni-silica, allowing us to tune both activity and selectivity.

High dielectric permittivity and ultralow dielectric loss in Nb-doped SrTiO3 ceramics

In this study, we prepared a series of Nb-doped SrTiO3 ceramics sintered in both air and N2 atmospheres. The X-ray diffraction (XRD) analysis indicated that all samples had a pure cubic phase perovskite structure with no secondary phase. The dielectric test showed that the Nb-doped SrTiO3 ceramics had a high dielectric permittivity (>3 × 104) and low dielectric loss (<0.004) over a broad temperature range from −100 to 300 °C with a breakdown strength over 20 kV/cm. The dielectric performance is attributed to the designated TiTi′−VO··−TiTi′ deep-lattice-defect states localising weak-hopping electrons to generate high defect-dipole concentrations, as verified by systematic X-ray photoelectron spectroscopy (XPS) experiments. This study offers a route for designing other types of high dielectric permittivity ceramics.

Hg0 Removal by a Palygorskite and Fly Ash Supported MnO2-CeO2 Catalyst at Low Temperature

MnO2-CeO2/PG-FA catalysts were prepared by supporting MnO2-CeO2 to PG-FA and used to remove Hg0 in simulated flue gas. The results show that MnO2-CeO2/PG-FA catalyst had excellent and stable Hg0 removal activity, which was mainly due to the combination effect of the catalytic oxidation activity by MnO2-CeO2 and the adsorption ability by PG-FA. Mn8-Ce0.5/PG-FA (with 8.0% MnO2 and 0.5% CeO2 loading) catalyst showed the highest Hg0 removal efficiency at 140 °C and Hg0 removal efficiency could be maintained above 95% with the space velocity of 6000 h−1 and Hg0 concentration of 160 μg/m3. O2 promoted Hg0 removal by MnO2-CeO2/PG-FA catalyst, while SO2 and H2O had inhibitory effects. In the presence of O2, the inhibitory effect of SO2 and H2O can be obviously weakened. MnO2-CeO2/PG-FA catalysts were characterized with scanning electron microscope (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and temperature-programmed desorption experiments (TPD). The results of SEM and XRD showed that the active components MnO2-CeO2 dispersed well on the surface of PG-FA support. The results of XPS and TPD show that the Hg0 removal process over MnO2-CeO2/PG-FA catalyst included adsorption and oxidation, HgO and HgSO4 were generated and adsorbed on the catalyst. MnO2-CeO2/PG-FA catalyst also showed excellent regeneration performance after Hg0 removal.

Experimental and Computational Studies on Octyl Hydroxamic Acid as an Environmentally Friendly Inhibitor of Cobalt Chemical Mechanical Polishing.

Octyl hydroxamic acid (OHA) was investigated as an inhibitor in H2O2-based alkaline silica dispersions for the polishing of cobalt (Co) films for interconnect applications. A combination of experiments and density functional theory (DFT) was used to investigate the inhibition effect and the mechanism of OHA on the Co surface. On the basis of the experiments, it can be proven that OHA has an inhibition effect on Co, which came from the inhibition of the cathodic reaction. The X-ray photoelectron spectroscopy (XPS) experiments show that the adsorption of OHA weakened the oxidation of the Co surface and protected the Co surface from corrosion. On the basis of the calculations, it can be proven that the OHAketone (ion) is most likely to react with the Co surface, and it can adsorb on the Co surface by Co-O bonds. This study provides important microscopic insights for understanding the corrosion protection of Co interconnect metals and helps to explain the corrosion inhibition mechanism of the organic-metal interface during the CMP process.

Lithium-induced intralayer rearrangement of molybdenum disulfide: Effect of graphene coating

Nanoscale composites consisting of molybdenum disulfide and graphene (MoS2/graphene) are promising anode materials for lithium-ion batteries. In this work, to gain insight into the role of graphene coating in the interaction of lithium with MoS2, we used in situ X-ray photoelectron spectroscopy (XPS) experiments. The deposition of lithium was carried out in a high vacuum simultaneously on the surface of polycrystalline MoS2 and MoS2 coated with a few-layer graphene. The XPS Mo 3d and S 2p spectra of lithiated samples exhibited the appearance of low-energy components assigned to MoMo bonds and weakened S–Mo bonds according to the density functional theory calculations. Such an atomic rearrangement in the MoS2 layer was much more significant for MoS2/graphene due to excess lithium in the interface. Annealing of the samples at 500 °C revealed that the lithium-induced intralayer MoS2 rearrangement is irreversible despite the removal of lithium. Moreover, at 800 °C, the rearranged MoS2 regions containing the residual lithium decomposed to form metallic molybdenum and Li2S2. This finding can help to understand the processes occurring in MoS2/graphene electrodes and to develop advanced materials for efficient lithium-ion batteries.

Signature of Au as a Halogen.

Gold, although chemically inert in its bulk state, is reactive at the nanoscale and, in small clusters, even behaves like a hydrogen atom. Using a photoelectron spectroscopy experiment and first-principles theory, we show that Au also behaves like a halogen in small clusters. This is evident not only in strong resemblance between the photoelectron spectra of Au2F- and AuF2- but also in Au exhibiting one of the signature properties of halogens, its ability to form superhalogens with electron affinities higher than that of any halogen atom. For example, the electron affinity (EA) of Au2F- is 4.17 eV, while AuF2-, a known superhalogen, has an EA of 4.47 eV. Of particular interest is Au2F2, which, in spite of being a closed-shell system, is a pseudohalogen with an EA of 3.3 ± 0.1 eV. Here, one of the Au atoms behaves like a halogen, making Au2F2 mimic the property of AuF3.

Nitrogenous gas formation mechanisms of chemically modified superfine pulverized coal during pyrolysis

ABSTRACT The pyrolysis products are affected by the O-containing groups in coal. The influences of the introduced O-containing groups on nitrogenous gas formation are rarely explored. To investigate this issue, superfine pulverized coal samples were modified by several kinds of selected chemical reagents. 13C nuclear magnetic resonance spectroscopy (NMR) experiments demonstrate that a considerable amount of carboxyl, hydroxyl structures is introduced into the carbon skeleton after peracetic acid modifications. X-ray photoelectron spectroscopy (XPS) experiments reveal that the content of quaternary nitrogen N-Q on the surface of the samples modified by peracetic acid remain unchanged in general. And oxidized nitrogen N-X structures are formed by the oxidation of pyridinic nitrogen N-6 and pyrrolic nitrogen N-5, which induces the proportion of N-X to increase more than 40%. Because of the introduction of O-containing functional groups, the discrepancy of nitrogenous gas composition has been found between the raw and modified samples during pyrolysis. The production of N2O soars between 200°C and 300°C. After H2O2 modifications, the formation paths of nitrogenous gas do not change significantly due to the absence of O-containing group introduction. This research uncovers that the introduced O-containing groups alter the formation paths of nitrogenous gas in coal during pyrolysis and elucidates the mechanism.

XPS, UV–Vis, XRD, and PL spectroscopies for studying nickel nanoparticle positioning effect on nanocomposite film properties

AbstractThis work studies the impact of positioning nickel nanoparticles (Ni‐NPs) on the surface of doped (P84‐PEO) nanocomposite films by using an ultra‐uniform magnetic field as a model for positioning magnetic NPs inside a polymeric matrix. This process is used to achieve desired and adjustable optoelectronic properties and to obtain new optical and electrical characteristics. P84‐PEO copolymer doped with Ni‐NPs exposed to a 450 mT magnetic field during the preparation give rise to a momentous increase in surface roughness, surface reactivity, and modified optical parameters, besides forming Ni oxides on the surface. Based on X‐ray photoelectron spectroscopy experiments, substantial extra shifts occurred in the binding energies of photo‐excited electrons from the O1s and C1s core levels. Additionally, the deconvoluted O1s spectra displays an additional photoelectron peak at 530.0 eV, most likely attributed to oxidized Ni‐NPs at the surface. Moreover, optical and structural properties were studied using UV–Vis and PL spectroscopy and X‐ray diffraction.

Metal-Free Chemoselective Reduction of Nitroarenes Catalyzed by Covalent Triazine Frameworks: The Role of Embedded Heteroatoms.

Chemoselective reduction of nitroarenes to arylamines is a core technology for the synthesis of numerous chemicals. The technology, however, relies on applying precious noble metal catalysts. We present our findings on the development of robust nanoporous covalent triazine frameworks (CTFs) as metal-free catalysts for the green chemoselective reduction of nitroarenes. The turnover frequency is found to be 43.03 h-1, exceeding activities of the heteroatom-doped carbon nanomaterials by a factor of 30. The X-ray photoelectron spectroscopy and control experiments provide further insights into the nature of active species for prompt catalysis. This report confirms the importance of quaternary 'N' and 'F' atom functionalities to create active hydrogen species via charge delocalization as a critical step in improving the catalytic activity.

A comparative study of activation of peroxymonosulfate and peroxydisulfate by greigite (Fe3S4) for the degradation of sulfamethazine in water

In this study, greigite (Fe3S4) was used to activate peroxymonosulfate (PMS) and peroxydisulfate (PDS) for sulfamethoazine (SMT) degradation in water. The possible influencing factors such as oxidant concentration, sulfur sources, iron sources and initial pH were investigated.Experimental results showed that SMT could be completely removed at 0.1 mM PMS in 15 min in Fe3S4/PMS system. 96.7% of SMT was removed at 1.0 mM PDS in 60 min in Fe3S4/PDS system.Both systems had good performance over a wide pH range of 3–9. In addition, different sulfur sources could affect the crystal structure, morphology and composition of the synthesized catalysts, while different iron sources had little influence. Quenching experiments and electron paramagnetic resonance (EPR) test evidenced that the activation of PMS and PDS by Fe3S4 was a multi-reactive oxygen species process with the coexistence of •OH, SO4•−, O2•− and 1O2. SO4•− was the main active species in the Fe3S4/PMS system, while SO4•− and •OH were the main free radicals in the Fe3S4/PDS system. X-ray photoelectron spectroscopy (XPS) experiments showed that Fe(II) on Fe3S4 surface effectively activated PMS and PDS, and S2− species were key factors controlling Fe(II) regeneration and subsequent activation of PMS and PDS.However, the consumption of Fe(II) and S2− in Fe3S4/PDS system was higher than that in Fe3S4/PMS system. In addition, in the two systems, the degradation intermediates of SMT and their practical application were also evaluated.This study provided a systematic evaluation of the performance of Fe3S4/PMS and Fe3S4/PDS systems for treatment of antibiotic contaminated water.

Sintering behavior, structure, and microwave properties of novel Li2xCu1-xMoO4 ceramics

In this study, we prepared a novel series of Li2xCu1-xMoO4 (x = 0.02, 0.04, 0.06, 0.08, and 0.10) microwave ceramics. The dynamic sintering behavior, crystal phases, micro-morphologies, and dielectric properties of the samples were studied. The substitution of Li+ contributed to refining the crystal grain size, promoting the densification of microstructure, and enhancing the quality factor. Due to different valence substitutions, Cu+ ions were created, which were verified by X-ray photoelectron spectroscopy (XPS) and Raman experiments. In addition, the Raman shift, full width at half maximum (FWHM) value of the A1g peak, and crystal microstrains were analyzed to gain a mechanistic understanding of the influence of structure on the dielectric properties. When x = 0.08, the Li2xCu1-xMoO4 ceramic sintered at 675 °C exhibited optimal comprehensive properties with εr = 8.17, Qf = 68 476 GHz, and τf = −25 ppm/°C, and good chemical stability between the ceramic and Al electrode was also achieved. These promising properties make Li2xCu1-xMoO4 (x = 0.08) more suitable for ultra-low temperature co-fired ceramic (ULTCC) applications.