Core Level Analysis Research Articles

Physical characteristics of a PWR core loaded with micro-cell UO2 pellet fuels

In this work, the physical characteristics of PWR cores are evaluated for several micro-cell UO2 pellets with Cr-coated Zircaloy-4 cladding through consistent fuel assembly (FA) and core-level analyses. The micro-cell UO2 pellets that are currently researched as accident tolerant fuel (ATF) candidates in the Korea Atomic Energy Research Institute (KAERI) are UO2-Cr, UO2-Mo, and UO2-SiO2-TiO2. In particular, a calculational matrix is used to consider not only the micro-cell UO2 pellets and the cladding coating, but also to estimate the achievable cycles within the usual 5.0 wt% uranium enrichment limit and the uranium enrichment required to achieve a reference cycle length of 480 effective full power days (EFPDs). The core analyses using the 3D nodal diffusion code MASTER showed that the cores loaded with micro-cell UO2 pellets (i.e., UO2-Cr and UO2-Mo) with Cr-alloy coating on Zircaloy-4 cladding have considerably shorter cycle lengths, lower discharge burnups, and more negative fuel temperature coefficients than the conventional UO2 fuel. The more negative fuel temperature coefficients lead to a more rapid stabilization under rod ejection accident with a substantially lower fuel temperature. In particular, the Mo-based micro-cell UO2 fueled cores have a much shorter cycle length and more negative moderator temperature coefficient than Cr-based one due to the large thermal and resonance capture cross sections of Mo isotopes and due to its lower critical boron concentration (CBC). However, the effect of Cr-alloy coating on core performance is not significant in comparison with the effects of the micro-cell UO2 pellets.

Growth, morphology and stability of Au in contact with the Bi2Se3(0 0 0 1) surface

We report a combined microscopy and spectroscopy study of Au deposited on the Bi2Se3(0001) single crystal surface. At room temperature Au forms islands, according to the Volmer–Weber growth mode. Upon annealing to 100 °C the Au deposits are not stable and assemble into larger and thicker islands. The topological surface state of Bi2Se3 is weakly affected by the presence of Au. Contrary to other metals, such as Ag or Cr, a strong chemical instability at the Au/Bi2Se3 interface is ruled out. Core level analysis highlights Bi diffusion toward the surface of Au islands, in agreement with previous findings, while chemical interaction between Au and atomic Se is limited at the interfacial region. For the investigated range of Au coverages, the Au/Bi2Se3 heterostructure is inert towards CO and CO2 exposure at low pressure (10−8 mbar) regime.

Quantitative determination of elemental diffusion from deeply buried layers by photoelectron spectroscopy

The recent advances in the inelastic background analysis of XPS spectra recorded with hard X-rays (HAXPES) make this method a powerful, non-destructive solution to retrieve the depth distribution of deeply buried elements. In this work, we apply this technique to study diffusion phenomena, upon annealing, in power transistor devices. We present a complete analysis of a sample under different stages of the fabrication process. We investigate the accuracy of the determination of the elemental depth distributions and concentrations with the inelastic background analysis. This is done by cross-checking with destructive techniques such as TEM/EDX and XPS depth profiling, and we shed light on the complementarities with HAXPES core-level analysis. We obtain consistent results which show the formation of an inhomogeneous structure, consisting of a blend of Al, Ga, and Ta, created during annealing. The inelastic background analysis permits us to successfully retrieve the depth distributions of Al, Ga, and Ta as well as the concentration of these elements in each layer, over 70 nm below the surface. This is a reliable solution to investigate diffusion phenomena and improve the fabrication processes of devices with critical and deeply buried interfaces.

New insight on early oxidation stages of austenitic stainless steel from in situ XPS analysis on single-crystalline Fe–18Cr–13Ni

In situ X-ray photoelectron spectroscopy real-time measurements and angular-dependent high resolution core level analysis were used for the first time to investigate the Cr enrichment and oxide growth mechanisms on a model 304 austenitic stainless steel surface in the very initial stages of oxidation leading to pre-passivation. The oxidation kinetics was followed for increasing oxygen exposure and temperature, revealing an early nucleation regime (for exposure <10 L) leading to the formation of a strongly Cr-enriched Cr3+/Fe3+ mixed layer followed by an oxide growth regime where preferential iron oxidation takes over and mitigate the initial chromium enrichment.

Structure-Electrochemical Property Relationships of Lipons Thin-Films Electrolytes for All Solid-State Microbatteries

All-solid-state microbatteries have interested many researchers and companies for the last decade, in order to supply in electrical energy small sensors and connected object. In these systems, Lithium Phosphorus Oxy-Nitride (LiPON) is generally used as solid-state electrolyte since its discovery in the early 1990s by Bates et al. [1]. However, LiPON presents a quite low ionic conductivity around 10-6 S/cm at room temperature. To increase this value, Sulfur can be added to the LiPON structure [2,3]. The present work focuses on the deposition of LiPONS thin-film electrolytes, and their chemical, structural, and electrochemical properties. LiPONS glassy films were deposited by reactive radio-frequency magnetron sputtering from a pure Li3PO4 target at room temperature in a mixed N2:H2S plasma, with H2S gas flow varying from 0 to 5% to fine tune the S concentration in the LiPONS thin films. LiPOS materials were also obtained by sputtering the same target under a Ar:H2S plasma. Constant power, pressure and deposition time were used. Potentiostatic Electrochemical Impedance Spectroscopy (PEIS), Scanning Electron Microscopy (SEM) and X-Ray Photoelectron Spectroscopy (XPS) measurements were performed to probe the changes in morphology and composition, and understand the structure-electrochemical property relationships. Whereas an improvement of the electrochemical properties of LiPON with the addition of Sulfur was expected, the opposite occurred (Fig. 1). In order to correlate the chemical structure to the ionic conductivity and identify the causes for the performance degradation, the electronic structure of LiPONS and LiPOS materials will be discussed based on XPS core level and valence band structure analyses, and compared with the classical LiPON electronic structure. The observed decrease in ionic conductivity when the S content in the LiPONS thin-films increases from 0 to 15 at% (Fig. 1) can be related with the appearance of two groups of species in the High-resolution S2p XPS spectra (Fig 2). For low S concentrations, doublets from 160 to 164 eV assigned to S-P structures are dominant whereas signals from 165 to 168 eV, corresponding to more oxidized S species that can originate from reactions between Sulfur and Nitrogen, become non-negligible at higher S-contents and may be the cause of the electrochemical properties degradation. [1] J. B. Bates, N. J. Dudney, G. R. Gruzalski et al, Solid State Ionics, vol. 53–56, pp. 647–654, 1992. [2] J. B. Bates, “Thin film battery and electrolyte therefor,” US 6,818,356 B1, 2004. [3] N. Mascaraque, H. Takebe, G. Tricot et al, J. Non. Cryst. Solids, vol. 405, pp. 159–162, Dec. 2014. Figure 1

Enhanced visible light photocatalytic activity of LaMnO3 nanostructures for water purification

Lanthanum manganite (LaMnO3), a perovskite-like oxide material, is one of the most promising and efficient photocatalysts for the degradation of organic pollutants. In this work, we report a high rate of photodegradation of aqueous methyl orange (MO) dye under visible light illumination on LaMnO3 nanoparticles prepared by the hydrothermal route. The phase formations of the obtained nanoparticles were investigated by powder X-ray diffraction analysis. The structure and nature of the chemical bonds were identified by FT-IR and Raman analysis. The morphology and core level analysis has been carried out by HRSEM, HRTEM, AFM and XPS. The optical behavior of LaMnO3 nanoparticles was analyzed by UV–Vis absorption spectroscopy, and the result suggests that LaMnO3 nanoparticles can be used as efficient photocatalysts to remove MO dye from water.

Large area planar stanene epitaxially grown on Ag(1 1 1)

Artificial post-graphene elemental 2D materials have received much attention recently. Especially, stanene, the tin analogue of graphene, is expected to be a robust 2D topological insulator, even above room temperature. We have grown epitaxial 2D stanene on a Ag(1 1 1) single crystal template and determined its crystalline structure synergetically by scanning tunneling microscopy, high-resolution synchrotron radiation photoemission spectroscopy, and advanced first principles calculations. From the STM images, we show that stanene forms a nearly planar structure in large domains. A detailed core-level spectroscopy analysis as well as DFT calculations reveal that the stanene sheet lays over an ordered 2D Ag2Sn surface alloy, but not directly on a bulk-terminated Ag(1 1 1) surface. The electronic structure exhibits a characteristic 2D band with parabolic dispersion due to the non-negligible interaction with the underlying surface alloy.

Effects of Co for Mn substitution on the electronic properties of Mn2-xCoxVAl as probed by XPS

Detailed theoretical and experimental investigations on the electronic and magnetic properties of the Heusler compounds Mn2-xCoxVAl with L21 structure are presented. The samples have been examined by X-ray diffraction, magnetization measurements and X-ray photoemission. The magnetic measurements show that the Curie temperatures decrease with Co content, ranging between 771 K (x = 0) and 289 K (x = 1), while the magnetization of the samples follows the Slater-Pauling rule.Additionally, electronic band structure calculations using the Korringa-Kohn-Rostoker (KKR) Greens function method have been performed. The evolution of the half-metallic character with the Co content x in the Mn2-xCoxVAl alloys is discussed based on the density of states (DOS) calculations. The influence of the Co doping on the individual magnetic moments of the Mn and V has been evidenced. Also, the small individual spin moments of Mn and V determined by theoretical calculations in MnCoVAl (x = 1) are confirmed by the Mn 3s and V 3s core level analysis of the X-ray photoemission spectroscopy investigations.

Low-Dimensional Carbon Allotropes: Ground- and Excited-State Charge Transfer with NIR-Absorbing Heptamethine Cyanine

Summary At the focal point of our studies are mutual interactions between an anionic heptamethine cyanine and individualized single-walled carbon nanotubes (SWCNTs) or exfoliated nanographene (NG). Here, we report the distinct near-infrared absorption of the heptamethine cyanine, which assists in visualizing the electronic interactions in the ground state with ease and precision. In statistical Raman assays, we conclude from downshifted 2D- and G-modes for SWCNTs, as well as upshifted 2D- and downshifted G-modes for NG, that these electronic interactions result in stable n-doping of SWCNTs and NG. Key to this shift of charge density is the electron-donating character of the heptamethine cyanine. In the excited state, a complete but metastable transfer of charges is accompanied by a radical-ion-pair state that lives for several nanoseconds. Such a time domain has not yet been realized, for example, in NG to date.

Adsorptive Removal of Carbamazepine and Diatrizoate in Iron Oxide Nanoparticles Amended Sand Column Mimicing Managed Aquifer Recharge

The sorption–desorption of recalcitrant pharmaceuticals in sand/soil columns can be used to infer performance of managed aquifer recharge. Removal of carbamazepine (CBZ) and diatrizoate (DTZ) from synthetic wastewater, containing 100 µg·L−1 of each pharmaceuticals, was studied in recirculating sand columns amended with uncoated or methacrylic acid (MAA) coated magnetite nanoparticles. Removal of CBZ and DTZ in MAA-magnetite column (68.34% and 61.91%, respectively) was much higher than that with uncoated magnetite (53.47% and 50.26%, respectively). Rapid decrease of dissolved organic carbon concentrations across nanoparticle amended columns (between 42.28% and 50.08% on Day 1), followed by slow recuperation suggests adsorption–desorption dynamics and competition of dissolved organic matter for sorption sites. Core-level binding energy and charge analysis for Fe(2s) and O(1s) in X-ray photoelectron spectroscopy suggests involvement of physisorption process on the NP surfaces.

Thermally activated ionic conduction and local structure in solid LiPON thin films

Compact lithium phosphorous oxynitride (LiPON) thin films, as a solid-state electrolyte for all solid-state Li batteries and electrochromic (EC) devices, with the high ratio of the triply coordinated –N< (Nt) over the doubly coordinated –N= (Nd) structural units was deposited by a conventional reactive RF magnetron sputtering of a Li3PO4 target at a low pure N2 pressure. The effect of heat treatment from 200 to 500 °C on the ionic conductivity and local structure of LiPON thin films were investigated by scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS) core level analysis. A dramatical improvement of ionic conductivity from 1.1 to 3.28 μS/cm and microstructure changes were happened on the LiPON thin films while annealed for 1 h at 300 °C, which was linked to structural differences with a highest ratio of –N< over –N= structural units. The work proves that a proper heat treatment on LiPON thin film can effectively improve its ionic conductivity and change its microstructure.

Effective inelastic scattering cross-sections for background analysis in HAXPES of deeply buried layers

Inelastic background analysis of HAXPES spectra was recently introduced as a powerful method to get access to the elemental distribution in deeply buried layers or interfaces, at depth up to 60nm below the surface. However the accuracy of the analysis highly relies on suitable scattering cross-sections able to describe effectively the transport of photoelectrons through overlayer structures consisting of individual layers with potentially very different scattering properties. Here, we show that within Tougaard’s practical framework as implemented in the Quases-Analyze software, the photoelectron transport through thick (25–40nm) multi-layer structures with widely different cross-sections can be reliably described with an effective cross-section in the form of a weighted sum of the individual cross-section of each layer. The high-resolution core-level analysis partly provides a guide for determining the nature of the individual cross-sections to be used. We illustrate this novel approach with the practical case of a top Al/Ti bilayer structure in an AlGaN/GaN power transistor device stack before and after sucessive annealing treatments. The analysis provides reliable insights on the Ti and Ga depth distributions up to nearly 50nm below the surface.

Multi-walled carbon nanotube supported CdS-DETA nanocomposite for efficient visible light photocatalysis

Designing high performance functional nanomaterials by tuning their dimension at nanoscale and constructing novel interface has been a hot topic in recent years. In this work, multi-walled carbon nanotube (MWCNT)/CdS-diethylenetriamine (DETA) composite photocatalyst was synthesized via hydrothermal method. The structure, morphology, optical property and core level analysis of MWCNT/CdS-DETA nanocomposite were characterized by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), energy-dispersive X-ray spectroscopy spectra (EDS), UV–Vis diffuse reflectance spectroscopy (DRS) and X-ray photoelectron spectrum (XPS). CdS-DETA can be uniformly dispersed on the surface of MWCNT. Photocatalytic properties of as-prepared photocatalysts were investigated under 410 nm LED light irradiation for photodegradation of methylene bule (MB). The kapp of MWCNT/CdS-DETA is 0.034 min−1, which is about 6 times more than pure CdS-DETA. Photostability test indicated that MWCNT/CdS-DETA hybrid can be reused for degradation of organic pollution, suggesting the possible application of MWCNT/CdS-DETA hybrid is the most promising strategy for advanced photocatalyst material design.

Effects of oxygen plasma treatments on the work function of indium tin oxide studied by in-situ photoelectron spectroscopy

Using UV and X-ray photoelectron spectroscopy (UPS & XPS), we have studied the work function (WF) evolution and chemical changes of an indium-tin-oxide (ITO) surface after a series of in-situ oxygen plasma treatments (OPTs). We took special care not to damage the sample’s surface with OPT by employing the weakest possible plasma conditions. Even after such gentle OPT the WF of ITO dramatically increased up to 6.6 eV after about 300 s of OPT. The carbon contamination at the surface was completely removed after only 40 s of the gentle OPT. However, in contrast to similar studies, the compositions and the chemical states of In, Sn, and O at the ITO surface showed only minimal changes as confirmed by XPS core-level peak analyses.

Effects of crystallite structure and interface band alignment on the photocatalytic property of bismuth ferrite/ (N-doped) graphene composites

Bismuth ferrite/graphene (N-doped graphene) photocatalysts are successfully prepared by a facile and effective two-step hydrothermal method. Bismuth ferrite/graphene shows superior photocatalytic activity compared with bismuth ferrite/N-doped graphene and pure BiFeO3. X-ray diffraction, scanning electron microscopy and energy-dispersive spectroscopy analyses indicate that Bi25FeO40 crystalline phase is obtained with the addition of graphene, while BiFeO3 is formed under the same hydrothermal conditions in the presence of N-doped graphene. Core-level and valence-band X-ray photoelectron spectroscopy analyses reveal a downward band bending of bismuth ferrite (∼0.5 eV) at the interface of the bismuth ferrite/(N-doped) graphene composites, which facilitates the electron transfer from bismuth ferrite to (N-doped) graphene and suppresses the recombination of photo-generated electron–hole pairs. This downward bending band alignment at the interface supposes to be the main mechanism underlying the enhanced photocatalytic activity of the bismuth ferrite/graphene composites that are currently of great interest in the photocatalysis field.

Fabrication and characteristics of silicon-rich oxide thin films with controllable compositions

Silicon-rich oxide films with controllable optical constants and properties are deposited by the reactive magnetron sputtering method on a Si target. The O/Si atomic ratio x of SiOx is tuned from 0.12 to 1.84 by adjusting the oxygen flow rate, which is found to be a more effective way to obtain SiOx films compared with changing the oxygen content [O2/(Ar+O2) ratio]. The optical properties of SiOx films can be tuned from semiconductor to dielectric as a function of ratio x. The structures and components are also investigated by an x ray photoelectron spectroscopy analysis of the Si 2p core levels, the results of which exhibit that the structures of SiOx can be thoroughly described by the random bonding model.

Effects of Precursor Ratios and Annealing on Electronic Structure and Surface Composition of CH3NH3PbI3 Perovskite Films

The electronic structure and surface composition of CH3NH3PbI3 (MAPbI3) films fabricated by one-step method with different precursor ratios of PbI2 to CH3NH3I (PbI2/MAI) have been investigated with ultraviolet photoelectron spectroscopy (UPS) and X-ray photoelectron spectroscopy (XPS). It is found that the core levels of all components in the MAPbI3 film shift toward lower binding energy with decreasing the precursor ratio of PbI2/MAI, indicating that the electronic structures of the MAPbI3 film can be adjusted by the precursor ratio of PbI2/MAI. The elemental compositions of the MAPbI3 film also depend on the precursor ratio and annealing process, and the compositions are strongly correlated to the electronic properties of the films. The electronic properties remain unchanged with an annealing at 110 °C. However, a core level shift of 0.5 eV toward higher binding energy is observed with an annealing at 150 °C, together with noticeable composition change from the XPS core level analysis. The distribution ...

Vacancy assisted SrO formation on La0.8Sr0.2Co0.2Fe0.8O3 − δ surfaces—A synchrotron photoemission study

We present a systematic synchrotron radiation photoemission spectroscopy study of the interaction of O2 with defective La0.8Sr0.2Co0.2Fe0.8O3−δ(100) surfaces at low temperatures. First, the surface chemical evolution during low energy Ar+ ion sputtering is investigated and is found to create oxygen vacancies. Subsequently, the interaction of the O2 molecules with La0.8Sr0.2Co0.2Fe0.8O3−δ(100) surface is observed to create an insulating phase. We performed a detailed core-level peak-fitting analysis to identify the chemical nature of this phase and to probe the role of vacancies in the formation of this phase.

Interfacial Effects of Electrochemical Lithiation of Epsilon-VOPO4 and Evolution of the Electronic Structure

The epsilon polymorph of vanadyl phosphate ε-VOPO4 is a promising cathode material for high-capacity Li ion batteries, owing to its demonstrated ability to reversibly incorporate more than one lithium per redox center, with a total theoretical capacity of 331 mAh/g. As in the case of the olivines, the problem of the inherently low electronic conductivity of ε-VOPO4 is overcome by the use of nano-sized particles within the cathode. At these dimensions the electrochemical reaction can be largely affected by the interfacial chemistry at the nanoparticle surface. An investigation of these surface reactions is critical for obtaining a complete understanding of the mechanism by which lithium intercalates and how it relates to the electrochemical performance. We performed x-ray photoelectron spectroscopy using both soft (XPS) and hard (HAXPES) x-rays to chemically distinguish and depth-resolve the interfacial phase transitions as a function of electrochemical discharge. Core level analysis supports a straightforward two-phase reaction as the first lithium is intercalated. In contrast, the insertion of the second lithium is more complicated with evidence of a significant radial lithium gradient, due to a possible to a disruption of the kinetics. From inspection of the valence band region, we were able to monitor the reversible evolution of ε-VOPO4 to Li2VOPO4 at the surface of our nanoparticles. These assignments were supported by hybrid density functional theory of the three phases. The origin of the radial gradient is likely associated with the presence of stable intermediate phases during the second reaction and warrants further attention. This work was supported as part of NECCES, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Number DE-SC0001294. Figure 1

Photocatalytic degradation of RhB and TNT and photocatalytic water splitting with CZTS microparticles

Cu2ZnSnS4 (CZTS) is a main candidate material for solar energy conversion through both photovoltaics and photocatalysis based on environmentally friendly elements and with a direct band gap of 1.5 eV. We report the synthesis of quasi Cu2ZnSnS4 microparticles with unprecedented narrow size distributions. The structural, morphological and core level analysis has been carried out by XRD, SEM and XPS techniques. These microparticles have shown excellent photocatalytic activity toward degradation of Rhodamine B dye (RhB) and TNT under visible light. The extent of mineralization has been analyzed by COD and TOC values. Photocatalytic water splitting for H2 generation has also been reported.