Binding Energy Shifts Research Articles

Modeling the Interface between Lithium Metal and Its Native Oxide.

Owing to their high theoretical capacities, batteries that employ lithium (Li) metal as the negative electrode are attractive technologies for next-generation energy storage. However, the successful implementation of lithium metal batteries is limited by several factors, many of which can be traced to an incomplete understanding of surface phenomena involving the Li anode. Here, first-principles calculations are used to characterize the native oxide layer on Li, including several properties associated with the Li/lithium oxide (Li2O) interface. Multiple interface models are examined; the models account for differing interface (chemical) terminations and degrees of atomic ordering (i.e., crystalline vs amorphous). The interfacial energy, formation energy, and strain energies are predicted for these models. The amorphous interface yields the lowest interfacial formation energy, suggesting that it is the most probable model under equilibrium conditions. The work of adhesion is evaluated for the crystalline interfaces, and it is found that the O-terminated interface exhibits a work of adhesion more than 30 times larger than that of the Li-terminated model, implying that Li will strongly wet an oxygen-rich Li2O surface. The electronic structure of the interfaces is characterized using Voronoi charge analysis and shifts in the Li 1s binding energies. The width of the Li/Li2O interface, as determined by deviations from bulklike charges and binding energies, extends beyond the region exhibiting interfacial structural distortions. Finally, the transport of Li ions through the amorphous oxide is quantified using ab initio molecular dynamics. Facile transport of Li+ through the native oxide is observed. Thus, increasing the percentage of amorphous Li2O in the solid electrolyte interphase may be beneficial for battery performance. In total, the phenomena quantified here will aid in the optimization of batteries that employ high-capacity Li metal anodes.

Physical genetics: Cross-breeding density functional theory and X-ray photoelectron spectroscopy to rationalize chemical shifts of binding energies in solid compounds

Like other spectroscopic methods XPS and AES show characteristic chemical shifts depending on the elemental matrix of a compound, however, a satisfactory rationalization of the variance of such values is often difficult. By an extension of a previous approach we present a theory in a unifying equation which combines several parameters - some of them resulting from DFT calculations - which influence the energy of the outgoing electrons and thereby seemingly the binding energy. By calculating Bader charges, atomic volumes and site potentials we have produced a data basis for a set of chalcogenides and halides of Ba, Zn, Pb and Cu to rationalize the spread of measured binding energies and Auger energies. It has thereby become possible to quantify different factors separately which bias the measurement of the kinetic energies of the outgoing core electrons, both the photo-emitted and the Auger electrons. Such an analysis can also trace special features of an open-shell configuration and even show up effects of a semiconductor-type.

Stark shift of binding energy for on and off-center donor impurities in quantum rings under the influence of charged rods electric fields

In the present work, we study the stark shift of binding energy for a Hydrogenic donor impurity confined within a circular quantum ring composed from three different semiconducting heterostructures AlxGa1-xN/GaN, InxGa1-xN/GaN, Ga1−xAlxAs/GaAs under the electric fields along different directions. We supplied a position-dependent electric field by using a charged rod of radius ‘a' and charge density λ. By placing the charged rod and donor impurity in different positions, we have studied the changes in the on and off-center donor binding energies, system energy levels, probability densities, average position of the electron, and the probability finding electron inside the quantum ring. We describe the redshift and blueshift of the donor impurity binding energy when different parameters change.

New Interpretation of X-ray Photoelectron Spectroscopy of Imidazolium Ionic Liquid Electrolytes Based on Ionic Transport Analyses.

We reported a new perspective on the correlation between the electronic structure of an ionic liquid (IL)-based electrolyte probed by X-ray photoelectron spectroscopy and the transport properties analyzed by impedance spectroscopy. We highlighted the core level chemical shifts of 1-hexyl-3-methylimidazolium (bis(trifluoromethanesulfonyl)imide) (C1C6ImTFSI), 1-hexyl-3-methylimidazolium bis(fluorosulfonyl)imide (C1C6ImFSI), and 1-hexyl-2,3-dimethylimidazolium bis(trifluoromethylsulfonyl)imide (C1C1C6ImTFSI) laden with LiTFSI salt and vinylene carbonate (VC) or fluoroethylene carbonate (FEC) with regard to the transport properties of cations and anions. We pointed out based on detailed binding energy shift analyses a clear effect of the anion on the local organization of Li+ ions. The significant peak shift in the case of C1C6ImTFSI laden with LiTFSI corroborates the formation of [Li(TFSI)2]- complexes. On the contrary, the lower amplitude of the binding energy shift of C1C6ImFSI for both anion- and cation-related peaks indicates that the electronic distribution around the cation and the anion is not affected when the LiTFSI salt is added, which plays a strong role in the ion dynamics (lower viscosity) of the electrolyte. The X-ray photoelectron spectroscopy (XPS) result supports the preponderant role of imidazolium ionic liquid based on FSI anion to form an electrolyte less prone to form ionic complexes. The methylation of the imidazolium cation contributes to the reduction of the interaction between the C1C1C6Im cation and TFSI anion, while additives VC and FEC contribute to the change of the alkyl configuration in C1C6Im cation, leading to the modification of the macroscopic properties of the ILs.

Revealing unique energy level alignment at graphene/MoS2 2-dimensional layered junction using in situ ambient pressure x-ray photoelectron spectroscopy

The chemical/electronic structures of a 2-dimensional (2D) molybdenum disulfide (MoS2) monolayer were characterized using ambient pressure x-ray photoelectron spectroscopy (APXPS) under various gas environments. APXPS results captured the binding energy shifts for the MoS2 chemical states that represent the electronic-structure of the 2D MoS2 monolayer in a real gas environment. The effect of the presence of a 2D graphene (Gr) layer on the properties of the 2D MoS2 layer was simultaneously characterized. When coating a Gr layer on the MoS2 layer, electron injection from MoS2 to Gr occurs due to the Schottky barrier at the interface. As a result, the Gr layer and MoS2 layer attain relatively more n-type and p-type characteristics, respectively, compared to when they exist separately. The hole-injection barrier, formed between the MoS2 layer and the SiO2 substrate, is lower by about 0.3 eV in the Gr/MoS2/SiO2 structure compared to that in the MoS2/SiO2 structure. This gap in the energy level alignments is stable so that there is no change in Ar, N2, O2, and CO2 environments. Taken together, our results not only present an appropriate methodology for fabricating 2D material-based device components, but also suggest the need for consideration of the charge transfer at the MoS2/Gr junction when applied to a practical device.

Enhancement of catalytic toluene combustion over Pt–Co3O4 catalyst through in-situ metal-organic template conversion

A Pt–Co3O4 catalyst named Pt–Co(OH)2–O was prepared by metal-organic templates (MOTs) conversion and used for catalytic oxidation of toluene. Through the conversion, the morphology of catalysts transformed from rhombic dodecahedron to nanosheet and the coated Pt nanoparticles (NPs) were more exposed. The Binding energy shift in XPS test indicates that the strong metal-support strong interaction (SMSI) has enhanced, and the physicochemical changes caused by it are characterized by other techniques. At the same time, Pt–Co(OH)2–O showed the best catalytic performance (T50 = 157 °C, T90 = 167 °C, Ea = 40.85 kJ mol−1, TOFPt = 2.68 × 10−3 s−1) and good stability. In addition, the in situ Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) studies have shown that because SMSI weakened the Co–O bond, the introduction of Pt NPs can make the migration of oxygen in the catalyst easier. The change of binding energy change and the content of various species in the quasi in situ XPS experiment further confirmed that the Pt–Co(OH)2–O catalyst has stronger SMSI, resulting in its stronger electron transfer ability and oxygen migration ability, which is conducive to catalytic reactions. This work provides new ideas for the development of supported catalysts and provides a theoretical reference for the relevant verification of SMSI.

Important roles of native-oxides on the electronic band offsets at Ge-oxide/Ge(0 0 1) heterojunction in ambient environment

Metal/semiconductor-oxide interface is a major focus in condensed matter physics due to its rich fundamental properties and potential novel electronic applications. Our understanding of the impact of native oxide on metal/semiconductor-oxide interface (e.g. Ge) remains nonetheless elusive. Herein, we address this by purposefully exposing a clean Ge(001) surface to ambient environment (up to 600 days). The extend of Ge oxidation and binding energy (BE) shifts in the core-levels of Ge X-ray photoelectron peaks (Ge3d and Ge2p3/2) are found to correlate directly with the GeOx/Ge (x ≤ 2) atomic composition. A universal scaling in the band offsets at the GeOx/Ge heterojunction with increasing Ge-oxide content is established independent of oxidation time. A maximum upward band bending of ~0.6 eV is observed in the electronic band structure, which can be attributed to the presence of Ge valence states (Ge1+, Ge2+, Ge3+, Ge4+) at the GeOx/Ge junction formed during oxidation. Our results exemplify the importance of native oxide on semiconductor in determining the fundamental properties of semiconductor-oxide interfaces.

Lab-based operando x-ray photoelectron spectroscopy for probing low-volatile liquids and their interfaces across a variety of electrosystems

The understanding of fundamental processes in liquids and at the liquid/electrode interfaces of electrochemical systems is crucial for the development of new devices and technologies with higher efficiency and improved performance. However, it is generally difficult to isolate and study the component of interest in such complex systems. Additionally, ex situ analyses do not always reflect the same properties under operating conditions. Hence, operando characterization tools are required for observing related electrical and chemical processes directly at the places where and while they occur. Operando x-ray photoelectron spectroscopy (o-XPS) has been used, while the sample is imposed to DC/AC voltage stress, to record the binding energy shifts in and on liquids and their interfaces to extract local potentials, as well as many related properties specific to the application in a noncontact and chemically resolved fashion. The applications of o-XPS to low-volatile liquids shown in this review span well-defined studies of (1) electrochemical cells, (2) double-layer capacitors, and (3) electrowetting on dielectrics. The methodology and several applications selected from the authors’ recent publications are presented.

Tunable Plasmon-Induced Charge Transport and Photon Absorption of Bimetallic Au–Ag Nanoparticles on ZnO Photoanode for Photoelectrochemical Enhancement under Visible Light

Noble metal nanostructures have been widely explored as an effective method to increase photon absorption and charge separation in plasmonic photocatalysis. In this study, we integrated two different noble metals, gold (Au) and silver (Ag), into Au/Ag bimetallic nanoparticles (BNPs) via solid-state thermal dewetting to investigate the room-temperature electrical conductivity, visible light absorption, and its effect on photoelectrochemical (PEC) activity. The Au/Ag BNPs give rise to extended visible light absorption range, exhibiting localized surface plasmon resonance (LSPR) effect that lead to strong surface-enhanced Raman spectroscopy. X-ray photoelectron spectroscopy shows binding energy shift in Au/Ag BNPs, suggesting electron transfer from Ag to Au where charge transport behavior can be tailored. Kelvin probe force microscopy and conductive atomic force microscopy displayed a significantly enhanced electrical conduction in Au/Ag BNPs due to the lowered Schottky barrier height. When the Au/Ag BNPs are incorporated onto ZnO semiconductor photoanode, the photoactivity was improved with lower charge transport resistance compared to monometallic and pristine ZnO. This work delivers a general approach to understand the plasmon-induced charge interaction, hence the photochemistry of noble metal BNP/semiconductor photoanode by incorporating a controllable composition ratio, which is capable of exploiting the enhanced electrical conduction and LSPR effect for PEC water splitting.

Tuning of Schottky barrier height using oxygen-inserted (OI) layers and fluorine implantation

The effects of oxygen-insertion technology and low-energy fluorine (F) implantation on the Schottky barrier height (ΦBp) of a Pt/Ti/p-type Si metal–semiconductor contact are studied via electrical characterizations of Schottky diodes, physical analyses by secondary ion mass spectrometry , and chemical analyses by x-ray photoelectron spectroscopy. It is found that both oxygen-inserted (OI) layers and F can reduce ΦBp due to Ti 2p and Si 2p binding energy shifts before forming gas anneal (FGA) and due to retarded Pt diffusion into Si (facilitating low-ΦBp Pt mono-silicide formation) during FGA. The experimental findings also suggest that OI layers are more effective than F for reducing ΦBp.

Synergy between a Silver-Copper Surface Alloy Composition and Carbon Dioxide Adsorption and Activation.

Bimetallic electrocatalysts provide a promising strategy for improving performance, especially in the enhancement of selectivity of CO2 reduction reactions. However, the first step of CO2 activation on bimetallic materials remains obscure. Considering bimetallic silver-copper (AgCu) as an example, we coupled ambient pressure X-ray photoelectron spectroscopy (APXPS) and quantum mechanics (QM) to examine CO2 adsorption and activation on AgCu exposed to CO2 with and without H2O at 298 K. The interplay between adsorbed species and the surface alloy composition of Cu and Ag is studied in atomic details. The APXPS experiment and density functional theory (DFT) calculations indicate that the clean sample has a Ag-rich surface layer. Upon adsorption of CO2 and surface O, we found that it is thermodynamically more favorable to induce subsurface Cu atomssubstitution for some surface Ag atoms, modifying the stability and activation of CO2-related chemisorbed species. We further characterized this substitution effect by correlating the new adsorption species with the observed binding energy (BE)shift and intensity change in APXPS.

Elastic strain control of electronic structure, and magnetic properties of [Pr1−xCaxMnO3/SrTiO3]15 superlattices

We report the growth, electronic structure, and in-plane magnetic properties of pulsed laser deposition grown 2D superlattice structures [Pr0.7Ca0.3MnO3/SrTiO3]15 and [Pr0.5Ca0.5MnO3/SrTiO3]15 on (001) oriented SrTiO3 and LaAlO3 single crystal substrates. The x-ray reflectivity measurements reveal well-defined interfaces between the manganite and titanate layers along with the existence of Kiessig fringes, providing the evidence for the smooth periodic superlattice structure. The reciprocal space mapping provides signature of tetragonal distortion in all the superlattices. The electronic structure determined from the x-ray photoelectron spectroscopy reveals divalent Sr and Ca, tetravalent Ti, and mixed valent Mn with a pronounce shift of binding energy peaks toward the higher energy side in the superlattices grown on (001) oriented LaAlO3 as compared to those grown on SrTiO3. These superlattices exhibit highly anisotropic ferromagnetic character. We used the law of approach to saturation to determine the anisotropy field (HK) and cubic anisotropy constant (K1) for all the investigated superlattices. This analysis yields the highest HK∼9 kOe and K1∼8×105 erg/cc for the [Pr0.7Ca0.3MnO3/SrTiO3]15 superlattice system. Furthermore, significant enhancement of the overall magnetic moment and a decrease in TC (<100 K) was observed in the case of LaAlO3 grown superlattice, which indicates a substantial role of residual elastic strain on the magnetic ordering. Our results indicate that the strain induced elongation of MnO6 octahedra leads to finite possibility of non-orthogonal overlapping of orbitals in the presence of large crystal field splitting of eg levels, which, in turn, causes suppression of the ferromagnetic double exchange interaction.

Reaction mechanism and kinetics for CO2 reduction on nickel single atom catalysts from quantum mechanics

Experiments have shown that graphene-supported Ni-single atom catalysts (Ni-SACs) provide a promising strategy for the electrochemical reduction of CO2 to CO, but the nature of the Ni sites (Ni-N2C2, Ni-N3C1, Ni-N4) in Ni-SACs has not been determined experimentally. Here, we apply the recently developed grand canonical potential kinetics (GCP-K) formulation of quantum mechanics to predict the kinetics as a function of applied potential (U) to determine faradic efficiency, turn over frequency, and Tafel slope for CO and H2 production for all three sites. We predict an onset potential (at 10 mA cm−2) Uonset = −0.84 V (vs. RHE) for Ni-N2C2 site and Uonset = −0.92 V for Ni-N3C1 site in agreement with experiments, and Uonset = −1.03 V for Ni-N4. We predict that the highest current is for Ni-N4, leading to 700 mA cm−2 at U = −1.12 V. To help determine the actual sites in the experiments, we predict the XPS binding energy shift and CO vibrational frequency for each site.

Surface Engineering Cerium Oxide Nanoparticles for Biosensor Performance: Influence of Redox-Active, Oxo-Anion Ligand Modification on Sensitivity

Nanoscale cerium oxide surface chemistry has been studied intensively due to its pronounced activity in various catalytic applications. The material’s surface reactivity is generally attributed to oxygen vacancy density and the facile inter-conversion between Ce3+ and Ce4+ redox states. However, experimental and theoretical investigations suggest a more intricate surface chemistry. In this study, cerium oxide nanoparticles (CNPs) were modified with high-valence oxo-anions to modulate surface electronic structure and chemical interactions with medically-relevant analytes. Changes to the surface chemical environment were assessed via x-ray photoelectron spectroscopy (XPS) (e.g. binding energy shifts; peak number and character), while charge transfer properties were characterized through electrochemical impedance spectroscopy and circuit fitting (following ligand@particle electrophoretic deposition in dH2O onto glassy carbon electrodes, GCE). Further, the influence of vacancy density and ligand interaction was characterized via doping Sm3+ into CNPs in varying dopant fractions (0-15 mol%; oxygen vacancy concentration increases linearly with Sm3+ concentration). From here, ligand@CNP-modified GCEs were assessed for amperometric (via chronoamperometry) and voltametric (via square-wave voltammetry) sensitivity towards catechols, ascorbic acid, and glucose in phosphate buffered saline. Time of response and selectivity (in presence of structural chemical analogues) were also assessed in similar conditions. Relative sensitivities/performances were analyzed and compared in relation to XPS and electroanalysis trends/characters for future design of optimized biosensor platforms.

Lithiophilicity Chemistry of Heteroatom-Doped Carbon to Guide Uniform Lithium Nucleation in Lithium Metal Anodes

With the ever-increasing energy demands from the current world, batteries with high energy densities are highly required. Lithium (Li) metal anodes, with an ultrahigh theoretical specific capacity (3810 mAh g−1) and the lowest negative electrochemical potential (−3.040 V versus the standard hydrogen electrode), are strongly considered as the ultimate anode choice for Li batteries. However, the practical application of Li metal anodes faces huge challenges, such as the growth of Li dendrites, the low Coulombic efficiency, and the infinite relative volume change during cycling. In particular, the uncontrollable growth of Li dendrites, which is considered the most fundamental issue facing Li metal anodes and has attracted much more attention, not only induces the “dead Li” with severe capacity loss but also can penetrate through the separator, inducing an internal short circuit and other potential safety hazards.To address the challenging issue of Li dendrites, a dedicated design of lithiophilic conductive framework is strongly considered as one effective method. Up to now, various lithiophilic conductive frameworks, especially carbon hosts, are used to guide uniform Li nucleation and thus deliver a dendrite-free composite anode. Although a variety of lithiophilic hosts has been proposed and indicate superior performance in suppressing dendritic Li growth, the exact working mechanism between Li and the lithiophilic hosts is tightly sealed and the lithiophilic nature of these carbon hosts is far from clear. If a fundamental understanding of the lithiophilicity chemistry is built, then the rational design of lithiophilic frameworks for dendrite-free Li metal anodes can be achieved.In this contribution, the lithiophilicity chemistry of heteroatom-doped carbon to guide uniform heterogeneous Li nucleation is proved through both first principles calculations and experimental verifications to guide uniform Li nucleation. Three key factors (electronegativity, local dipole, and charge transfer) are proposed to reveal the lithiophilicity origin of heteroatom doping sites in carbon materials. O doping exhibits the best performance among all single-doping strategies, which was further validated by Li nucleation overpotential tests and transmission electron microscopy (TEM) characterizations. In addition, O/B co-doping is predicted to achieve better lithiophilicity than any single doping due to its large local dipole. Inspired from the Li bond theory, 7Li nuclearmagnetic resonance (NMR) spectroscopy can determine the lithiophilicity of hostmaterials as the linear relationship between Li binding energy and 7Li chemical shift. This work uncovers the lithiophilicity chemistry of heteroatom-doped carbons and affords a mechanistic guidance to Li metal anode frameworks for safe rechargeable batteries. This understanding is also applicable to sodium and potassium metal batteries.

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.

Au–Ag–Al Nano‐Alloy Thin Films as an Advanced Material for Photonic Applications: XPS Analysis, Linear and Nonlinear Optical Properties Under CW Regime

AbstractThe compositional and optical properties of an aluminum‐based transition‐metal alloy system (Au–Ag–Al) as an advanced material for photonic applications are investigated. The system is fabricated by sequentially evaporating thin layers of gold, silver, and aluminum. The thickness of Al is varied to reflect different percentages in the alloyed films. Alloying of the metals is confirmed from the shifts in the electronic binding energy of the pure elements through X‐ray photoelectron spectroscopy. The current–voltage measurements demonstrate good ohmic conductivity in the films and the optical properties are obtained by standard absorption and z‐scan techniques. Plasmonic peaks are observed in the alloyed system related to the participating metals. The thermal nonlinear optical response is conducted in the continuous wave (CW) regime. The films show large values for the thermo‐optical coefficient ( which results in high values (≈10−3 cm2 W−1) for the third‐order nonlinear coefficient (). A discussion of these values and their impact on the application of thin alloyed metals is presented.

Investigation of metal oxide additives onto Na2WO4-Ti/SiO2 catalysts for oxidative coupling of methane to value-added chemicals

The oxidative coupling of methane (OCM) is a closely related reaction process involving the transformation of methane (CH4) and O2 mixtures into value-added chemicals such as ethylene and ethane (i.e. C2+). This work presents the effects of metal oxide additives into the Na2WO4-Ti/SiO2 catalyst on the performance of the OCM reaction. Several metal oxide additives—including oxides of Co, Mn, Cu, Fe, Ce, Zn, La, Ni, Zr, Cr, and V—were investigated with the Na2WO4-Ti/SiO2 catalyst. All of the catalysts were prepared using co-impregnation and the catalyst activity test was performed in a plug flow reactor at a reactor temperature range of 600–800 °C and atmospheric pressure. The physicochemical properties of the prepared catalysts relating to their catalytic activity were discussed by using the information of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM) measurements. Na2WO4-Ti/SiO2 added Mn was found to be the most active catalyst, involving shifts of binding energies of W 4f and Ti 2p toward lower binding energies. Moreover, a variety of operating conditions—including reactant- to-nitrogen gas ratio, catalyst mass, reactor temperature, and total feed flow rate—were intensively examined for the OCM reaction using the Na2WO4-Ti-Mn/SiO2 catalyst. The maximum C2+ yield was subsequently discovered at 22.09% with 62.3% C2+ selectivity and 35.43% CH4 conversion. Additionally, the stability of the Na2WO4-Ti-Mn/SiO2 catalyst was also monitored with time on stream for 24 h.

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.

Ambient pressure x-ray photoelectron spectroscopy study of water formation and adsorption under two-dimensional silica and aluminosilicate layers on Pd(111).

Ambient pressure x-ray photoelectron spectroscopy (AP-XPS) supported by density functional theory (DFT) calculations was used to characterize the interaction of water with two-dimensional (2D) silica and aluminosilicate bilayers on Pd(111). Starting with oxygen adsorbed at the SiO2/Pd interface, exposure to water caused the SiO2-derived XPS peaks to shift to higher binding energy and the removal of an O 1s feature associated with interfacial adsorbed oxygen. These observations were attributed to the formation of a mixed water-hydroxyl interface, which eliminates the interfacial dipolar layer, and its associated electrostatic potential, created by adsorbed oxygen. Interfacial oxygen also reacted with H2 to produce adsorbed water which also caused an upward binding energy shift of the SiO2 peaks. Spectra recorded under 0.5 Torr water revealed additional water adsorption and a further shift of the overlayer peaks to higher binding energy. Incorporating Al into the 2D material caused the bilayer peaks to shift to lower binding energy which could be explained by electron donation from the metal to the bilayer. Although the stronger interaction between the bilayer and Pd substrate should restrict interfacial adsorption and reaction, similar trends were observed for water and hydrogen exposure to interfacial adsorbed oxygen. Less water adsorption was observed at the aluminosilicate interface which is a consequence of Al strengthening the bond to the metal substrate. The results reveal how the sensitivity of XPS to interfacial dipoles can be exploited to distinguish reactions taking place in confined spaces under 2D layers and how tuning the composition of the 2D layer can impact such reactions.