Binding Energy Shifts Research Articles

AC-Modulated XPS Enables to Externally Control the Electrical Field Distributions on Metal Electrode/Ionic Liquid Devices.

X-Ray Photoelectron Spectroscopy (XPS) has been utilized to extract local electrical potential profiles by recording core-level binding energy shifts upon application of the AC [square-wave (SQW)] bias with different frequencies. An electrochemical system consisting of a coplanar capacitor with a polyethylene membrane (PEM) coated with the Ionic Liquid (IL) N,N-diethyl-N-methyl-N-(2-methoxyethyl) ammonium bis(trifluoromethanesulfonyl)imide (DEME-TFSI) as the electrolyte is investigated. Analyses are carried out in operando, such that XPS measurements are recorded simultaneously with current measurements. ILs have complex charging/discharging processes, in addition to the formation of Electrical Double Layers (EDL) at the interfaces, and certain properties of these processes can be captured using AC modulation within appropriate time windows of observation. Herein, we select two frequencies, namely, 10 kHz and 0.1 Hz, to separate effects of the fast polarization and slow migratory motions, respectively. Moreover, the local potential developments after adding two equivalent series resistors at three different physical positions of the device have been carefully evaluated from the binding energy shifts in the F 1s peak representing the anion of the IL. This circuit modification allows us to quantify the AC currents passing through the device, as well as the system's impedance, in addition to revealing the potential variations due the IR drops. The complex AC-modulated local XPS data recorded can also be faithfully reproduced using the unmodulated F 1s spectrum and by convoluting it with electrical circuit output provided by the LT-Spice software. The outcome of these efforts is a more realistic equivalent circuit model, which can be related to chemical/physical makeup of the electrochemical system. An important finding of this methodology emerges as the possibility to induce additional local electrical field developments within the device, the directions of which can be reversed controllably.

A facile synthesis of 2D bimetallic solid solution nitrides for robust stability in lithium-ion battery

Nanostructured transition metal nitrides (TMNs) demonstrate immense promise for lithium-ion battery applications owing to their outstanding conductivity and high theoretical capacity. However, challenges such as the expansion of volume, aggregation concerns, and rapid capacity decay still need to be effectively addressed. Herein, a facile synthesis of 2D nitrides, including TiVN, NbVN and TiNbN, is achieved through nitriding their corresponding MXenes. The distinct 2D layered structure enables them fast lithium-ion transport and inhibits volume variation, thereby improving rate performance and stability. Moreover, the incorporation of bimetallic elements in solid solution induces lattice distortion, creating lattice vacancies and increasing lithium storage capacity. Atomic-level interactions within solid solutions, confirming by the shifts of binding energy, contribute to improved structural stability and accelerated charge transfer. The theoretical calculation further proves that the bimetallic solid solution structure elevates the d-band center and increases the Li+ adsorption energy. Consequently, the synthesized TiVN, NbVN and TiNbN demonstrate remarkable lithium storage performance. Especially, NbVN with a porous morphology stands out by achieving a specific capacity of 216.6 mAh/g after 1,400 cycles at 1 A/g, significantly outperforming Nb4N5 and VN. This work may provide valuable insights for the efficient synthesis and electrochemical applications of two-dimensional solid-solution nitrides.

Photocatalytic enhancement of n-p-n ternary heterostructure of BiVO4/rGO/BiOBr for RhB degradation under visible light irradiation

Herein, the ternary phase of n-type BiVO4/p-rGO/n- BiOBr (3%rGO/1V2Br) was synthesized by one-pot hydrothermal method and firstly evaluated for its potential application in photocatalysis. The 3 %rGO/1V2Br shows the highest photocatalytic efficiency of 100 % compared to that of the binary BiVO4/BiOBr (1V2Br), single BiVO4, and BiOBr phases of 87 %, 25 %, and 55 % respectively. Scanning electron microscope and X-ray diffraction results suggest successful preparation of the ternary BiVO4/rGO/BiOBr phase and close contacts among the three components. Chemical interactions at heterointerface, supported by new V-C bond formation and binding energy shift from X-ray photoelectron spectroscopy study, could facilitate charge transfer and promote charge separation as evidenced by photoluminescence and photoelectrochemical studies. Photocatalytic mechanism and energy band alignment are proposed based on Mott-Schottky, UV–vis diffuse reflectance, and scavenger trapping experiments.

Electrostatic shielding effects and binding energy shifts and topological phases of bilayer molybdenum chalcogenides

AbstractBy combining binding energy and bond‐charge (BBC) model and density functional theory (DFT) calculations, the electrostatic shielding effects and binding energy shifts of bilayer MoS2, MoSe2, and MoTe2 are studied. In this study, the bilayer MoS2, MoSe2, and MoTe2 had bandgaps of 1.38, 1.28, and 1.01 eV, respectively. It is found that electrostatic shielding by electron exchange is the main cause of density fluctuation and determine the bonding state. We found that the edge polarization exactly vanishes after the bulk phase transition, just as we saw the corner‐localized modes disappear in a system with full open boundaries of bilayer MoTe2. Finally, this study establishes a method for calculating the lattice density with Green's function with energy level shift and provides new methods and ideas for the further study of the electrostatic shielding, bond states and topological phases of nanomaterials.

NaCl-assisted synthesis of MoS2 films: Large area fabrication with evidence of phase shift

Two-dimensional (2D) nanomaterials have shown unique electrical and chemical characteristics essential for the enhancement of electronic and optoelectronic devices. Large-area fabrication of 2D materials like MoS2 is challenging due to poor nucleation and vertical multilayer growth. In this study, we employed wafer-scale CVD with gaseous precursors for MoS2 to facilitate large-area deposition and utilized NaCl to assist nucleation control. Precise control of the nucleation with NaCl has significantly increased the grain size of MoS2 from about 1–2 nm to 300 nm. However, a phase shift in MoS2 thin films from semiconductive 2H to metallic 1T phase was observed due to the Na intercalation. As a result, a shift in lower binding energy occurs in XPS analysis. Our findings contribute to the comprehension of phase transition phenomena in MoS2 thin films and further advancement in the synthesis techniques of MoS2 thin films within wafer-scale deposition environments.

Chemodynamic PtMn Nanocubes for Effective Photothermal ROS Storm a Key Anti-Tumor Therapy in-vivo.

Chemodynamic therapy (CDT) is a new treatment approach that is triggered by endogenous stimuli in specific intracellular conditions for generating hydroxyl radicals. However, the efficiency of CDT is severely limited by Fenton reaction agents and harsh reaction conditions. Bimetallic PtMn nanocubes were rationally designed and simply synthesized through a one-step high-temperature pyrolysis process by controlling both the nucleation process and the subsequent crystal growth stage. The polyethylene glycol was modified to enhance biocompatibility. Benefiting from the alloying of Pt nanocubes with Mn doping, the structure of the electron cloud has changed, resulting in different degrees of the shift in electron binding energy, resulting in the increasing of Fenton reaction activity. The PtMn nanocubes could catalyze endogenous hydrogen peroxide to toxic hydroxyl radicals in mild acid. Meanwhile, the intrinsic glutathione (GSH) depletion activity of PtMn nanocubes consumed GSH with the assistance of Mn3+/Mn2+. Upon 808 nm laser irradiation, mild temperature due to the surface plasmon resonance effect of Pt metal can also enhance the Fenton reaction. PtMn nanocubes can not only destroy the antioxidant system via efficient reactive oxygen species generation and continuous GSH consumption but also propose the photothermal effect of noble metal for enhanced Fenton reaction activity.

Effect of Lanthanum Loading on the Photocatalytic Degradation of Brilliant Yellow and Acid Blue Dyes in Visible Light and Sunlight over La2O3-TiO2 Nanocomposites

La-doped TiO2 nanocomposites were synthesized using the sol-gel process with different proportions of lanthanum doping (1-5 wt.%). The synthesized nanocomposites were analyzed thoroughly by X-ray diffraction (XRD), nitrogen adsorption, scanning electron microscopy (SEM) with extended X-ray diffraction (EDAX), transmission electron microscopy, ultraviolet-visible DRS spectra for optical properties, photoluminescence (PL) for emission behaviours, Fourier transform infrared (FTIR) spectroscopy (FTIR) for chemical bonding analysis and X-ray photoelectron spectroscopy (XPS) for surface chemical composition. The XRD analysis confirmed the anatase phase for all synthesized La-TiO2 nanocomposites. The UV-Vis spectra showed an increased absorption in the visible range and a slight red shift of binding energy as the % La doping increased from 1-5 wt.%. Similarly, the binding energy values varied from 3.02 to 2.75 eV with increased La doping. These nanocomposites exhibited the photocatalytic activity achieving 99% degradation of acid blue dye and 96% degradation of brilliant yellow dye in the presence of visible light irradiation. Scavenger studies indicated that the dye degradation was suppressed, suggesting the involvement of superoxide (O2–), hydroxyl radical (OH•) and holes (h+) in the reaction mechanism.

Tuning of excitons in phosphorene atomic chains

An universal scaling between the exciton binding energy and quasiparticle (QP) band gap was first discovered in two-dimensional (2D) semiconductors such as graphene derivatives, various transition materials dichalcogenides, and black phosphorus (Choi et al 2015 Phys. Rev. Lett. 115 066403; Jiang et al 2017 Phys. Rev. Lett. 118 266401), and later extended to quasi one-dimensional (1D) systems such as carbon nanotubes and graphene nanoribbons. In this work we study the excitonic states in phosphorene atomic chains by using the exact diagonalization method and show that the linear scaling between the exciton binding energy (Ex ) and QP shift () can be easily tuned by the dielectric environment. In the presence of weak screening, Ex is seen to increase with and exhibits a similar scaling as those 2D materials. As the screening becomes stronger, however, the dependence is found to be reversed, i.e. Ex now decreases when increases. More interestingly, we also reveal that Ex may even become nearly constant, independent on the system dimension and when the screening reaches a certain strength. These abnormal scaling relations are attributed to the complex nature of excitons in the strongly correlated 1D system.

Facilely prepared heterogeneous Fenton catalyst Fe(Fe0.69Al0.31)2O4@C for catalytic wet peroxide oxidation of ciprofloxacin in batch and continuous reactor: Reaction intermediates and toxicity evaluation

Herein, by using a simple co-precipitation method Al-doped magnetite spinel nanoparticle encapsulated in the carbon matrix Fe(Fe0.69Al0.31)2O4@C was synthesised and its catalytic activity was examined as a heterogeneous Fenton catalyst towards the catalytic wet peroxide oxidation (CWPO) of antibiotic pollutant 20 ppm ciprofloxacin (CIP) in batch and continuous reactors. Under the optimized conditions, 0.5 g·L-1 Fe(Fe0.69Al0.31)2O4@C in batch reactor mineralized 51 % of CIP was achieved within 180 min at 50 °C and pH 3 by utilizing 1.2 mM or 4S H2O2 (S = stoichiometry; 47 mol H2O2:1 mol CIP) which is significantly less concentration compared to other heterogeneous Fenton catalysts. Impressive long-lasting catalytic activity was demonstrated in the up-flow fixed bed reactor, for 110 h with 44 % TOC removal and less than 1 ppm Fe leaching in the effluent water. Kinetic studies on the rate of decomposition of H2O2 revealed that Fe(Fe0.69Al0.31)2O4@C effectively decomposed the H2O2 like the homogeneous Fenton catalyst. The XPS results confirmed the influence of Al on iron ions in the magnetite structure through a substantial shift in higher binding energy for Fe3+ and introduced a more electropositive character on the Fe3+(δ+) that successively expedites the kinetically slow Fe3+ reduction reaction with H2O2 to produce HOO•. The π electrons of the graphitic carbon facilitate the electron transfer between the carbon matrix and Fe(Fe0.69Al0.31)2O4 nanoparticles to enhance the CIP degradation. The acute toxicity assessment studies validated the non-toxic nature of the effluent water obtained from batch and continuous reactors. A degradation pathway was proposed based on the eleven intermediate products identified using LC-HRMS analysis.

Influence of the tetraneutron on the EoS under core-collapse supernova and heavy-ion collision conditions

Context. Recently, a resonant state of four neutrons (tetraneutron) with an energy of E4n = 2.37 ± 0.38(stat) ± 0.44(sys) MeV and a width of Γ = 1.75 ± 0.22(stat) ± 0.30(sys) MeV was reported. Aims. In this work, we analyze the effect of including such an exotic state on the yields of other light clusters; these clusters not only form in astrophysical sites, such as core-collapse supernovae and neutron star (NS) mergers, but also in heavy-ion collisions. Methods. To this aim, we used a relativistic mean-field (RMF) formalism, where we consider in-medium effects in a two-fold way – that is, via the couplings of the clusters to the mesons, and via a binding energy shift – to compute the low-density equation of state (EoS) for nuclear matter at finite temperature and fixed proton fraction. We consider five light clusters – namely deuterons, tritons, helions, α-particles, and 6He – immersed in a gas of protons and neutrons, and we calculate their abundances and chemical equilibrium constants with and without the tetraneutron. We also analyze how the associated energy of the tetraneutron would influence such results. Results. We find that the low-temperature, neutron-rich systems are the ones most affected by the presence of the tetraneutron, making NSs excellent environments for their formation. Moreover, its presence in strongly asymmetric matter may increase the proton and α-particle fractions considerably. This may have an influence on the dissolution of the accretion disk of the merger of two NSs.

New visible-light-driven Bi2MoO6/Cs3Sb2Br9 heterostructure for selective photocatalytic oxidation of toluene to benzaldehyde

Herein, new Bi2MoO6/Cs3Sb2Br9 heterostructure (BiMo/CSB) was investigated for the first time as a visible-light-driven photocatalyst for C(sp3)–H bond activation using molecular oxygen as a green oxidant and toluene as a model substrate. The optimized BiMo/CSB photocatalyst exhibited enhanced toluene oxidation activity (2,346 μmol g-1h−1), which was almost two- and five-fold that of pristine CSB (1,165 μmol g-1h−1) and BiMo (482 μmol g-1h−1), respectively. The improved photocatalytic performance was essentially attributed to the formation of staggered band energy lineup in the BiMo/CSB hybrid, which promoted S-scheme charge transfer across the BiMo/CSB heterointerface as supported by ultraviolet photoelectron spectroscopy (UPS), density functional theoretical (DFT), time-resolve photoluminescence (TRPL), and photoelectrochemical studies. Spin–trapping electron paramagnetic resonance (EPR) and radical scavenging studies revealed that photoinduced hole, molecular oxygen, and superoxide radical are key active species in this photocatalytic system. The developed BiMo/CSB catalyst provided good selectivity toward benzaldehyde product (94–98 %), presumably due to the inhibiting effect of benzyl alcohol on benzaldehyde oxidation. No significant change in structure and morphology was observed for the spent catalyst, however small negative shift of Sb 3d and Bi 4f binding energy was found suggesting partial reduction of Sb3+ and Bi3+. This work not only provides a new visible-light-driven photocatalyst for C(sp3)–H bond activation but also opens the doors for exploitation of the conversion and functionalization of this inert bond toward the production of high value-added organic chemicals.

Chemical significance of x-ray photoelectron spectroscopy binding energy shifts: A Perspective

The principal intent of this Perspective is to review the mechanisms that are responsible for the shifts of binding energies, ΔBE, observed in x-ray photoelectron spectroscopy (XPS) measurements and so to relate the shifts to the electronic structure and the chemical bonding in the systems studied. To achieve this goal, several theoretical considerations are necessary beyond just the calculation of XPS BEs. Though briefly discussed here, we are not primarily interested in absolute values of BE or quantitation using relative intensities. Within the molecular orbital (MO) theory framework, it is shown that the analysis of orbital properties is critical for the correct interpretation of XPS. In particular, rigorous definitions are given for the initial state and final state contributions to BEs and to BE shifts, ΔBE. It is first shown how the BEs of core levels are related to the electronic structure by consideration of the BEs for a model atomic system to establish the origins and magnitudes of BE shifts. The mechanisms established for the model system are then applied to a review of XPS measurements and MO theory on a set of real examples. An important focus of the paper is to demonstrate that, in many cases, initial state mechanisms allow for a definitive interpretation of the XPS BE shifts and that an important role of theory is to provide qualitative explanations rather than quantitative agreement with XPS measurements. The mechanisms established are a guide to the interpretation of XPS measurements and consideration of these mechanisms may suggest additional calculations that would be useful. It is concluded that there is still a bright future for the coupling of ab initio MO theory with XPS measurements.

Hydrogen-induced Sulfur Vacancies on the MoS2 Basal Plane Studied by Ambient Pressure XPS and DFT Calculations.

Sulfur vacancy on an MoS2 basal plane plays a crucial role in device performance and catalytic activity; thus, an understanding of the electronic states of sulfur vacancies is still an important issue. We investigate the electronic states on an MoS2 basal plane by ambient-pressure X-ray photoelectron spectroscopy (AP-XPS) and density functional theory calculations while heating the system in hydrogen. The AP-XPS results show a decrease in the intensity ratio of S 2p to Mo 3d, indicating that sulfur vacancies are formed. Furthermore, low-energy components are observed in Mo 3d and S 2p spectra. To understand the changes in the electronic states induced by sulfur vacancy formation at the atomic scale, we calculate the core-level binding energies for the model vacancy surfaces. The calculated shifts for Mo 3d and S 2p with the formation of sulfur vacancy are consistent with the experimentally observed binding energy shifts. Mulliken charge analysis indicates that this is caused by an increase in the electronic density associated with the Mo and S atoms around the sulfur vacancy as compared to the pristine surface. The present investigation provides a guideline for sulfur vacancy engineering.

Trace Ru-tuned NiO/CNT electrocatalysts outperform benchmark Pt for alkaline hydrogen evolution with superior mass activity

The exploitation of highly active and durable electrocatalysts that can replace high-cost Pt/C for hydrogen evolution reaction (HER) is urgently required. The challenge lies in diminishing the usage of noble metals without sacrificing HER activity. In this work, trace Ru-doped transition metal oxides (TMOs) nanoparticles (∼7 nm) with high dispersion loaded by the carbon nanotubes (CNTs) were developed. Specifically, Ru-NiO/CNTs with a low Ru content of 0.94 wt% exhibits excellent alkaline HER activity with the low overpotential of 19 mV and 98 mV to achieve the current density of 10 mA·cm−2 and 100 mA·cm−2, respectively, outperforming Ru/CNTs counterpart and most previously Ru-based nanocatalysts. Notably, the mass activity (1.83 A·mgRu-1) and price activity (301.51 A·dollar-1) of Ru-NiO/CNTs are separately more than 7 times and 18 times higher than that of the commercial 20% Pt/C benchmark. Moreover, the catalyst can operate without activity decay after 100 h long-term stability test. DFT calculation reveals that the synergy effects are originated from (i) the accelerated adsorption and dissociation of H2O by Ru, and (ii) the optimized electronic structure of Ni that tunes the H* adsorption/desorption. Furthermore, we discover that Ru-promoted HER activity shows a metal-dependent relationship (Ni ≈ Cu > Mn > Co > Fe), which can use binding energy shift (ΔE) as a highly correlated descriptor. This work may provide an insightful understanding of Ru dopant for enhanced HER activity.

Revealing charge migration in a Multi-Multi photocatalyst by in situ irradiated X-ray photoelectron spectroscopy

Constructing efficient photocatalysts to produce solar fuels has been regarded as a potential way to alleviate energy crisis and environmental pollution. So far, simply modified single- and dual- component photocatalysts still suffer low efficiency due to their inherent weaknesses, making researchers turn their attention to multiple modified multi-component photocatalysts (“multi-multi” photocatalysts). However, the complex structure and composition of “multi-multi” photocatalysts will make it difficult for in-depth investigations on their working mechanisms, principally due to the lack of a method for direct observation of the migration route of charge carriers under the light irradiation in these systems. Herein, we report an in situ irradiated X-ray photoelectron spectroscopy (ISI-XPS) method to show the transfer pathway of charge carriers through the shifts of binding energies using a triple-modified WS2/carbon nanofibers (CNFs)/ZnIn2S4 model system. With this method, we manage to reveal the role of each subcomponent and demonstrated that the synergy of multiple modifications significantly enhances the performance of the “multi-multi” photocatalyst. This novel method opens up a new avenue for studying the mechanisms of photocatalytic systems, facilitating the future development of highly efficient photocatalysts.

Cu2In alloy-embedded ZrO2 catalysts for efficient CO2 hydrogenation to methanol: promotion of plasma modification.

Cu1In2Zr4-O-C catalysts with Cu2In alloy structure were prepared by using the sol-gel method. Cu1In2Zr4-O-PC and Cu1In2Zr4-O-CP catalysts were obtained from plasma-modified Cu1In2Zr4-O-C before and after calcination, respectively. Under the conditions of reaction temperature 270°C, reaction pressure 2MPa, CO2/H2 = 1/3, and GHSV = 12,000mL/(g h), Cu1In2Zr4-O-PC catalyst has a high CO2 conversion of 13.3%, methanol selectivity of 74.3%, and CH3OH space-time yield of 3.26mmol/gcat/h. The characterization results of X-ray diffraction (XRD), scanning electron microscopy (SEM), and temperature-programmed reduction chemisorption (H2-TPR) showed that the plasma-modified catalyst had a low crystallinity, small particle size, good dispersion, and excellent reduction performance, leading to a better activity and selectivity. Through plasma modification, the strong interaction between Cu and In in Cu1In2Zr4-O-CP catalyst, the shift of Cu 2p orbital binding energy to a lower position, and the decrease in reduction temperature all indicate that the reduction ability of Cu1In2Zr4-O-CP catalyst is enhanced, and the CO2 hydrogenation activity is improved.

New insights into the enhancement of TiO2/ZnIn2S4 heterojunction via cerium doping

S-scheme heterojunction photocatalysts are promising for practical application as their high efficiency in the generation and separation of photogenerated charges. In this work, simple Ce doping was utilized to modify TiO2/ZnIn2S4, a TiO2-based S-scheme heterojunction. The Ce-TiO2/ZnIn2S4 sample with 10 wt% ZnIn2S4 supported and 5 at.% Ce doping possessed excellent photocatalytic activity and reusability. Compared with other heterojunction photocatalysts presented in previous studies, the optimal Ce-TiO2/ZnIn2S4 showed delightful photocatalytic reduction activity. Combining DFT calculation, the shift of binding energies, electrochemical tests and quantitative built-in electric field (IEF) intensity, it was confirmed that low-electronegativity Ce doping could improve the IEF intensity at TiO2/ZnIn2S4 interface, resulting in an outstanding separation efficiency of photogenerated charges. This work proposes an ordinary but effective technology to facilitate the interface transference of photogenerated charges.

Influence of Gas for Thermal Treatment on Hydrogen Permeation in V-Ni Alloy Membranes.

Hydrogen separation is an important step for the utilization of hydrogen energy. Metallic alloys, such as vanadium-nickel, are potential hydrogen separation materials. Due to the strong propensity of vanadium to form oxides and hydrides, vanadium alloy has a lower hydrogen permeability, and it is difficult to maintain the permeability over time. Therefore, special preparation processes such as Pd coating have been suggested for hydrogen separation vanadium-based membranes. However, aside from the prohibitive price of palladium, the interdiffusion of palladium and vanadium makes the coated membrane inviable to be used at a high temperature. Thermal treatment with inert gas was investigated in this study to assess the applicability of the vanadium alloy without palladium coating for hydrogen separation and clarify the mechanism behind the thermal treatment. Argon is inert with vanadium and displayed permeability recovery after 43 h thermal treatment, but the permeability declined under certain conditions. In contrast, nitrogen is known to interact with vanadium and the hydrogen permeability was maintained at a level lower than the test with argon. Given that nitrogen can compete with hydrogen for the active sites on vanadium, nitrogen might hinder hydrogen adsorption and hydride formation, whereas argon reduced the partial pressure of hydrogen during the thermal treatment, enhancing the driving force of hydrogen desorption. In the X-ray diffraction spectrum, vanadium hydrides and oxides were confirmed after hydrogen permeation and thermal treatment. In the X-ray photoelectron spectroscopy data, oxygen was a dominant element due to vanadium oxides and adsorbed nitrogen was also observed. According to binding energy shifts of nitrogen, nitrogen used for thermal treatment might substitute or compete for active sites with adsorbed nitrogen and hydrogen, existing in vanadium lattice. Although thermal treatment can be used to recover hydrogen permeability, the alloy cannot be recovered as hydrogen-free. However, results demonstrate the potential of thermal treatment to complement an uncoated vanadium alloy for a hydrogen separation membrane.

Ag-oxide signature in Ag 3d photoelectron spectra: A study on free nanoparticles

Over decades the Ag 3d-level binding energy has been puzzling researchers with its unusual sign and value in silver oxides. For the absolute majority of metals, the metal-to-oxide binding energy shifts are positive and depend significantly on the oxidation state, while in Ag-oxides the oxide shift was time after time reported negative, small, and close for the two very different Ag(I) and Ag(III) oxidation states. In the current work, a photoelectron spectroscopy (PES) investigation on the in-situ created free nanoparticles simultaneously containing both metallic silver and silver-oxide parts provided the grounds to reconsider the old consensus on the Ag-oxide shifts. The Ag 3d energies for the metallic and the oxide parts established in the current experimental work allowed estimating a ≈ 1.2 eV positive shift for the realized oxidation state. This estimate was made possible by using a beam of free nanoparticles with finely controlled composition. The PES experiments on such a beam allowed for a continuous and fast renewal of the poorly conducting sample and for a reliable and accurate calibration relative to vacuum. The constant oxide shift observed at several different oxidation conditions, as well as the relatively narrow and symmetric oxide peaks, point to one dominating oxidation state being present in the particles.

Transition Metal β-Diketonate Adhesion Promoters in Epoxy-Anhydride Resin.

Epoxy to copper adhesion supports the reliability of numerous structures in electronic packaging. Compared to substrate pre-treatment, processing and cost considerations are in favor of adhesion promoters loaded in epoxy formulations. In this work, first row transition metal β-diketonates present such a compelling case when added in epoxy/anhydride resins: over 30% (before moisture aging) and 50% (after moisture aging) enhancement in lap shear strength are found using Co(II) and Ni(II) hexafluoroacetylacetonate. From extensive X-ray photoelectron spectroscopy (XPS) analyses on the adhesively failed sample surfaces, increased population of oxygen-containing functional groups, especially esters, is linked to the adhesion improvement. Assisted by XPS depth profile on the fractured epoxy side and in situ Fourier-transform infrared spectroscopy (FTIR), the previously discovered latent cure characteristics endowed by the metal chelates interacting with phosphine catalysts are regarded pivotal for pacing the anhydride consumption and allowing interfacial esterification reactions to occur. Further examinations on the XPS binding energy shifts and dielectric properties of the doped epoxy also reveal metal-polymer coordination that contribute to the adhesion and moisture resistance properties. These findings should stimulate future research of functional additives targeting at cure kinetics control and polar group coordination ideas for more robust epoxy-Cu joints.