Electron Binding Energy Shifts Research Articles

Ab initio-guided X-ray photoelectron spectroscopy quantification of Ti vacancies in [formula omitted] thin films

Ab initio calculations were employed to investigate the effect of oxygen concentration dependent Ti vacancies formation on the core electron binding energy shifts in cubic titanium oxynitride (Ti1−δOxN1−x). It was shown, that the presence of a Ti vacancy reduces the 1s core electron binding energy of the first N neighbors by ∼0.6 eV and that this effect is additive with respect to the number of vacancies. Hence it is predicted that the Ti vacancy concentration can be revealed from the intensity of the shifted components in the N 1s core spectra region. This notion was critically appraised by fitting the N 1s region obtained via X-ray photoelectron spectroscopy (XPS) measurements of Ti1−δOxN1−x thin films deposited by high power pulsed magnetron sputtering. A model to quantify the Ti vacancy concentration based on the intensity ratio between the N 1s signal components, corresponding to N atoms with locally different Ti vacancy concentration, was developed. Herein a random vacancy distribution was assumed and the influence of surface oxidation from atmospheric exposure after deposition was considered. The so estimated vacancy concentrations are consistent with a model calculating the vacancy concentration based on the O concentrations determined by elastic recoil detection analysis and text book oxidation states and hence electroneutrality. Thus, we have unequivocally established that the formation and population of Ti vacancies in cubic Ti1−δOxN1−x thin films can be quantified by XPS measurements from N 1s core electron binding energy shifts.

Photoelectron Spectroscopy of Benzene in the Liquid Phase and Dissolved in Liquid Ammonia.

We report valence band photoelectron spectroscopy measurements of gas-phase and liquid-phase benzene as well as those of benzene dissolved in liquid ammonia, complemented by electronic structure calculations. The origins of the sizable gas-to-liquid-phase shifts in electron binding energies deduced from the benzene valence band spectral features are quantitatively characterized in terms of the Born-Haber solvation model. This model also allows to rationalize the observation of almost identical shifts in liquid ammonia and benzene despite the fact that the former solvent is polar while the latter is not. For neutral solutes like benzene, it is the electronic polarization response determined by the high frequency dielectric constant of the solvent, which is practically the same in the two liquids, that primarily determines the observed gas-to-liquid shifts.

The Relationship between the Structure and Thermal Properties of Bi2O3-ZnO-B2O3 Glass System

The influence of Bi2O3 and melting temperature on the thermal and structural properties of xBi2O3-(60-x) ZnO-40B2O3 glasses has been investigated in this study. It is expected that these factors can be used to control the degree of reduction of Bi2O3, and the relationship between these factors and the color change of the process for bismuth glass is discussed. Due to high-temperature melting, the bismuth-doped borate glasses have changed into dark/black from original transparent yellow and the light transmittance will decrease, so it is not used in optical applications. The thermal properties of glass are measured by a thermomechanical analyzer (TMA), and the glass structure is analyzed by FTIR and XPS. The results show that the glass is mainly composed of [BiO6] octahedron, [BiO3] triangle, [BO4] tetrahedron, and triangle [BO3] units, and the network of the glass system is mainly bonded by B-O-B, B-O-Zn, B-O-Bi, and Bi-O-Bi. The glass thermal expansion coefficient (CTE) of this glass system increases with the increase of Bi2O3 content, and the O1s nuclear electron binding energy shifts to the lower energy direction with the increase of Bi2O3 addition. In terms of FTIR, as the melting temperature rises, the B-O-B bonding vibration concentration of [BO4] inside the borate glass decreases, and the density of B-O-B bonding vibration of [BO3] increases, Moreover, the increase in melting temperature increases the probability of reducing Bi ions to Bi0, reduces the bonding of Bi-O-B, and increases the bonding of B-O-B, and the CTE also slightly decreases.

CrV Bimetallic Phillips Catalyst Prepared by Citric Acid‐Assisted Impregnation on Ethylene Polymerization

AbstractThree CrV bimetallic Phillips catalysts are developed by a citric acid‐assisted impregnation method and studied in ethylene homopolymerization and ethylene/1‐hexene copolymerization. The method benefits to the dispersion of bimetallic active sites, especially for the V ones. The electron binding energy shift of V 2p3/2 in CrV‐1/2‐CA suggests the increased electron deficiency of V active center. The CrV‐1/2‐CA, CrV‐1/3‐CA catalysts present higher activity, broader molecular weight distribution, than the counterparts without CA‐assisted impregnation, suggesting more active sites involved in the reaction. The 1‐hexene is higher inserted in the polyethylene by CrV‐1/2 than the CrV‐1/2‐CA. But the results of temperature rising elution fractionation‐successive self‐nucleation and annealing (TREF‐SSA) show the thinner platelet thickness at the high molecular weight parts of high‐density polyethylene by CrV‐1/2‐CA, suggesting the higher insertion of 1‐hexene and higher tensile properties. The CrV‐1/2‐CA also shows the more hydrogen‐regulated response in the polymerization. The deconvolution of the gel permeation chromatography curves presents the higher fractions of high molecular weight polymer component.

Enhanced Emission of Deep Ultraviolet Light-Emitting Diodes through Using Work Function Tunable Cu Nanowires as the Top Transparent Electrode.

Deep ultraviolet light-emitting diodes (DUV LEDs) (<280 nm) have been important light sources for broad applications in, e.g., sterilization, purification, and high-density storage. However, the lack of excellent transparent electrodes in the DUV region remains a challenging issue. Here, we demonstrate an architectural engineering scheme to flexibly tune the work function of Cu@shell nanowires (NWs) as top transparent electrodes in DUV LEDs. By fast encapsulation of shell metals on Cu NWs and a shift of electron binding energy, the electronic work function could be widely tailored down to 4.37 eV and up to 5.73 eV. It is revealed that the high work function of Cu@Ni and Cu@Pt NWs could overcome the interfacial barrier to p-AlGaN and achieve direct ohmic contact with high transparency (91%) in 200-400 nm. Completely transparent DUV LED chips are fabricated and successfully lighted with sharp top emission (wall-plug efficiency reaches 3%) under a turn-on voltage of 6.4 V. This architectural strategy is of importance in providing highly transparent ohmic electrodes for optoelectronic devices in broad wavelength regions.

Core level photoelectron spectroscopy probed heterogeneous xenon/neon clusters

Binary rare gas clusters; xenon and neon which have a significant contrariety between sizes, produced by a co-expansion set up and have been studied using synchrotron radiation based x-ray photoelectron spectroscopy. Concentration ratios of the heterogeneous clusters; 1%, 3%, 5% and 10% were controlled. The core level spectra were used to determine structure of the mixed cluster and analyzed by considering screening mechanisms. Furthermore, electron binding energy shift calculations demonstrated cluster aggregation models which may occur in such process. The results showed that in the case of low mixing ratios of 3% and 5% of xenon in neon, the geometric structures exhibit xenon in the center and xenon/neon interfaced in the outer shells. However, neon cluster vanished when the concentration of xenon was increased to 10%.

Coordination-resolved local bond relaxation, electron binding-energy shift, and Debye temperature of Ir solid skins

Numerical reproduction of the measured 4f7/2 energy shift of Ir(100), (111), and (210) solid skins turns out the following: (i) the 4f7/2 level of an isolated Ir atom shifts from 56.367eV to 60.332eV by 3.965eV upon bulk formation; (ii) the local energy density increases by up to 130% and the atomic cohesive energy decreases by 70% in the skin region compared with the bulk values. Numerical match to observation of the temperature dependent energy shift derives the Debye temperature that varies from 285.2K (Surface) to 315.2K (Bulk). We clarified that the shorter and stronger bonds between under-coordinated atoms cause local densification and quantum entrapment of electron binding energy, which perturbs the Hamiltonian and the core shifts in the skin region.

Positive XPS binding energy shift of supported CuN-clusters governed by initial state effects

An initial state effect is established as origin for the positive 2p core electron binding energy shift found for CuN-clusters supported by a thin silica layer of a p-doped Si(100) wafer. Using the concept of the Auger parameter and taking into account the usually neglected Coulomb correlation shift in the Auger final state (M4,5M4,5) it is shown that the initial state shift is comparable to the measured XPS shift while the final state relaxation shift contributes only marginally to the binding energy shift. The cluster results differ from the negative surface core-level shift of crystalline copper which has been explained in terms of a final state relaxation effect.

Coverage-Dependent Adsorption at a Low Symmetry Surface: DFT and Statistical Analysis of Oxygen Chemistry on Kinked Pt(321)

We explore the influence of adsorbate interactions on the thermodynamic and spectroscopic properties of oxygen on the stepped, kinked Pt(321) surface. The ground state arrangements of atomic oxygen are identified with the aid of a cluster expansion and analyzed for coverages up to one oxygen per surface Pt (1 ML). We find that oxygen prefers to bind in bridge sites at the step edge at coverages up to 0.2 ML, but at higher coverages oxygen atoms actually experience mild, localized attractions such that both bridge and threefold hollow sites are occupied to form square planar, fourfold-coordinated PtO4-like structures. These structures progressively dominate the surface with increasing coverage up to 0.8 ML, at which point every kink Pt is saturated with four oxygens. We compute stability regions for these ground states with respect to gas-phase O2 and to NO/NO2 mixtures. The ground state structures at 0.2, 0.6, and 0.8 ML dominate over a wide range of conditions, with the 0.6 ML structure being most prominent. We also explore site preferences for molecular O2 adsorbed on key O ground state structures. Calculations of vibrational modes and core electron binding energy shifts allow us to relate both ground state and non-equilibrium structures to experimental HREELS and XPS results. We show that adsorption sites are primarily characterized by their surface coordination, such that O in atop, bridge, and threefold hollow sites possess distinct and identifiable vibrational modes and core level shifts. However, within these broad categories, we find variability due to interactions with proximal adsorbates. Adsorption energies and vibrational modes of O2 are found to be particularly sensitive to the local adsorption environment. Lastly, we develop a one-dimensional adsorption model to understand and rationalize experimentally observed non-equilibrium behavior at low coverages.

Evaluating the Structure of Catalysts Using Core-Level Binding Energies Calculated from First Principles

X-ray photoelectron spectroscopy (XPS) is a powerful and popular surface characterization technique, and the measured shifts in the core electron binding energies are sensitive to the chemical structure and local environment of the surface species. C 1s binding energies were calculated with density functional theory (DFT) for 17 structures including eight well-characterized structures on a Co(0001) surface and nine on a Pt(111) surface, while B 1s binding energies were calculated for six well-characterized structures and compared with experimental values. DFT calculations describe the 2.8 eV variation in the C 1s binding energies on Co surfaces, the 4.2 eV variation in the C 1s binding energies on Pt surfaces, and the 5.5 eV variation in the B 1s binding energies in the test sets with average deviations of 85, 73, and 53 meV, respectively. The shift in the C 1s and the B 1s binding energies can be correlated with the calculated charges, though only within homologous series. To illustrate how binding energ...

Substituent effects in chain and ring π-systems studied by core-electron binding energies calculated by density functional theory

The substituent effects of X- in 1-X-hexatrienes, which are chain π-systems with conjugated double bonds, was compared with those in Ph X, which are ring π-systems, using core electron binding energy shifts (ΔCEBE) of the carbon atoms in the molecules. The ΔCEBE of C 1 C 4 in 1-X-hexatrienes are generally close to ΔCEBE of C 1 C 4 in Ph X. The ΔCEBE of carbon atoms in the 1-X-hexatrienes are not only highly correlated to the Hammett σ substituent constants, but their numerical values are also close to each other. The core electron binding energies (CEBE) of the six carbons in 1-X-hexatriynes, which are the chain π-systems with conjugated triple bonds, were calculated by density functional theory (DFT) and the substituent effect was investigated. Average ΔCEBE of the five carbon atoms between C 2 and C 6 in 1-X-hexatriyne were calculated. The magnitude and sign of the average ΔCEBE provides quantitative strength and direction, electron withdrawing or donating, of a substituent X.

Coulomb Repulsion at the Nanometer-Sized Contact: A Force Driving Superhydrophobicity, Superfluidity, Superlubricity, and Supersolidity

Superhydrophobicity, superfluidity, superlubricity, and supersolidity (4S) at the nanometer-sized liquid−solid or solid−solid contacting interfaces have long been issues of puzzling with the common characteristics of nonsticky and frictionless motion. Although the 4S occurrences have been extensively investigated, the mechanism behind the common characteristics remains unclear. From the perspectives of broken-bond-induced local strain and the skin-depth charge and energy quantum trapping and the associated nonbonding electron polarization, we proposed herewith that the Coulomb repulsion between the “electric monopoles or dipoles locked in the elastic solid skins or the solidlike covering sheets of liquid droplets” forms the key to the 4S. The localized energy densification makes the skin stiffer and the densely and tightly trapped bonding charges polarize nonbonding electrons, if exist, to form locked skin monopoles. In addition, the sp-orbit hybridization of F, O, N, or C upon reacting with solid atoms generates nonbonding lone pairs or unpaired edge electrons that induce dipoles directing into the open end of a surface. The monopoles and dipoles can be, however, demolished by UV radiation, thermal excitation, or excessively applied compression due to ionization or sp orbit dehybridization. Such a Coulomb repulsion between the negatively charged skins of the contacting objects not only lowers the effective contacting force and hence the friction but also prevents charge from being exchanged between the counterparts of the contact. Being similar to magnetic levitation, such Coulomb repulsion should be the force driving the 4S. Density function theory calculations, X-ray photoelectron spectroscopy, scanning tunneling microscopy/spectroscopy, and very low energy electron diffraction measurements have been conducted to verify the proposal. In particular, agreement between theory predictions and the measured size dependence of the elastic modulus, lattice strain, core−electron binding energy shift, and band gap expansion of nanostructures evidence the validity of the proposal of interface Coulomb repulsion.

Accurate calculation of N1s and C1s core electron binding energies of substituted pyridines. Correlation with basicity and with Hammett substituent constants

Substituent shifts of the energetics of four related ionization processes of pyridines and benzoic acids (Fig. 1) were investigated. The first process is core-electron ionization of gas-phase pyridines (Fig. 1A), while the second concerns gas-phase acid-base reaction between a substituted pyridine and a conjugated acid (Fig. 1B), and the third and fourth processes are the acid dissociation of substituted benzoic acids in aqueous solution (Fig. 1C) and in vacuum (Fig. 1D), respectively. Core-electron binding energies for the first process were calculated using density-functional theory with the scheme Δ E KS (PW86x-PW91c/TZP+ C rel)//HF/6-31G∗. Average absolute deviation of calculated core electron binding energy shifts at N atom in substituted pyridines from experiment was 0.08 eV. The shift at N coincides highly with that at a ring carbon atom. The four shifts corresponding to the four processes shown in Figs. 1A–D correlate strongly with one another, with numerical values fairly close to each other when expressed in unit of electron volts.

Preferential site occupancy of krypton atoms on free argon-cluster surfaces

Argon clusters have been doped with krypton atoms in a pick-up setup and investigated by means of ultraviolet and x-ray photoelectron spectroscopy (UPS and XPS). The width of the krypton surface feature in the XPS spectra from mixed krypton/argon clusters has been studied and found to be narrower than in the case of homogeneous krypton clusters. By considering known spectral broadening mechanisms of the cluster features and the electron binding energy shift of the cluster surface feature relative to the atomic signal, we conclude that krypton ad-atoms preferentially occupy high-coordination surface sites on the argon host-cluster.

Core electron binding energy (CEBE) shifts as descriptors in structure activity relationship (SAR) analysis of cytotoxicities of a series of simple phenols

Core electron binding energy shifts (ΔCEBE's) of carbon atoms calculated with the semi empirical HAM/3 method were shown to serve as a useful descriptor for SAR analysis of cytotoxicities of a series of simple phenols. Using three selected ΔCEBE's of carbon atoms in the phenyl ring of the compounds, the compounds were well separated by a pattern recognition method such as principal component analysis.

Core electron binding energy (CEBE) shifts as descriptors in structure activity relationship (SAR) analysis of neolignans tested against Leishmania donovani

Core electron binding energy shifts (ΔCEBEs) of carbon atoms calculated with the semi-empirical Hydrogenic Atoms in Molecules, version 3, method were shown to serve as a useful descriptor for structure activity relationship analysis of 12 neolignans studied. Using five selected ΔCEBEs of carbon atoms in the two phenyl rings of the compounds, the compounds were well separated by pattern recognition methods such as principal component analysis and SIMCA.

The protection of MgO film against hydration by using Al 2O 3 capping layer deposited by magnetron sputtering method

Al 2O 3 capping layer was deposited by DC reactive sputtering method on MgO protective layer deposited by RF magnetron sputtering method. Thickness of capping layer, Al 2O 3, was varied from 1 to 15 nm. Deposited MgO thin films were hydrated in the ambience of 80% humidity and at room temperature. Surface morphology and rms roughness were observed by SEM and AMF, respectively. Chemical shift of electron binding energy was observed by XPS. And the composition and concentration of hydrogen were observed by RBS and ERD. From these analyses, it was found that Mg atoms diffused into Al 2O 3 layer and reacted with moisture at surface, forming Mg(OH) 2 phase during hydration reaction. At the thin capping layer region (1–5 nm thickness), as thickness of Al 2O 3 increased, total amount of hydration decreased. But, beyond 5 nm thickness, the tendency became reverse. Although Al 2O 3-capped MgO thin film was hydrated to some extent, total amount of hydration is much less than uncapped MgO single layer. Therefore, it can be concluded that Al 2O 3 might be suitable for protecting MgO layer against hydration.

Core electron binding energy (CEBE) shifts applied to structure activity relationship (SAR) analysis of neolignans

Core electron binding energy shifts (DCEBE's) and CEBE of carbon atoms calculated with the semi empirical HAM/3 method were shown to serve as a useful descriptor for SAR analysis of six neolignans studied. Using five selected DCEBE's of carbon atoms in the two phenyl rings of the compounds, the compounds were well separated by HCA, PCA, KNN and SIMCA methods.

X-ray photoelectron spectroscopy study of irradiation-induced amorphizaton of Gd2Ti2O7

The radiation-induced evolution of the microstructure of Gd2Ti2O7, an important pyrochlore phase in radioactive waste disposal ceramics and a potential solid electrolyte and oxygen gas sensor, has been characterized using transmission electron microscopy and x-ray photoelectron spectroscopy. Following the irradiation of a Gd2Ti2O7 single crystal with 1.5 MeV Xe+ ions at a fluence of 1.7×1014 Xe+/cm2, cross-sectional transmission electron microscopy revealed a 300-nm-thick amorphous layer at the specimen surface. X-ray photoelectron spectroscopy analysis of the Ti 2p and O 1s electron binding energy shifts of Gd2Ti2O7 before and after amorphization showed that the main results of ion-irradiation-induced disorder are a decrease in the coordination number of titanium and a transformation of the Gd–O bond. These features resemble those occurring in titanate glass formation, and they have implications for the chemical stability and electronic properties of pyrochlores subjected to displacive radiation damage.

Shifts of Core-level Electron Binding Energies for SrBi2Ta2O9 Nano-particles

Abstract The electron binding energies of Ta 4d5/2 and Sr 3p3/2 levels of SrBi2Ta2O9 nano-particles were larger by 1.2 eV than these of bulk SrBi2Ta2O9, while the Bi 4d5/2 electron binding energy was smaller by 1.4 eV than the bulk. Charge distribution in the unit cell of the nano-particles differs from that of the bulk.