X-ray Photoelectron Spectrocopy Research Articles

Iron Selenide-Based Heterojunction Construction and Defect Engineering for Fast Potassium/Sodium-Ion Storage.

Suitable anode materials with high capacity and long cycling stability, especially capability at high current densities, are urgently needed to advance the development of potassium ion batteries (PIBs) and sodium ion batteries (SIBs). Herein, a porous Ni-doped FeSe2 /Fe3 Se4 heterojunction encapsulated in Se-doped carbon (NF11 S/C) is designed through selenization of MOFs precursor. The porous composite possesses enriched active sites and facilitates transport for both ion and electron. Ni-doping is adopted to enrich the lattice defects and active sites. The Se-C bond and carbon framework endow integrity of the composite and hamper aggregation of selenide nano-particles during potassiation/de-potassiation. The NF11 S/C exhibits exceptional rate performance and ultra-long cycling stability (177.3mA h g-1 after 3050 cycles at 2 A g-1 for PIBs and 208.8mA h g-1 after 2000 cycles at 8 A g-1 for SIBs). The potassiation/de-potassiation mechanism is investigated via ex-situ X-ray powder diffraction, high-resolution transmission electron microscopy, X-ray photoelectron spectrocopy and Raman analysis. PTCDA//NF11 S/C full cell stably cycles for 1200 cycles at 200mA g-1 with a capacity of 103.7mA h g-1 , indicating the high application potential of the electrode for highly stable rechargeable batteries.

Band Alignment of N- and P- Doped InP at Electrolyte and Ultra High Vacuum Junctions: Fundamental Correlation between the Open Circuit Potential Under Illumination and XPS Photopeak Energy

Electrochemistry measurements have provided in-situ studies of surface and interfaces at the semiconductor / electrolyte junction. It has required monitoring the current/voltage responses at the semiconductor/ electrolyte interface associated with impedance measurements. In this work, energy band diagram of InP has been given by determining Fermi level (work function), conduction band (electron affinity) and valence band positions. They have been referred by a theoretical absolute scale with vacuum level as a reference point. The electrochemical potential of electrons is given by Nernst equation according to an electrochemical reference electrode. The solid state scale at 0 eV and the electrochemical scale have been offset from one another by a defined voltage according to the reference electrode. For example 0 eV corresponded to -4.5 V vs. NHE (Normal Hydrogen Electrode) or -4.46 V SCE (Sulfate Calomel Electrode). The contact between InP and the electrolyte acted as a liquid schottky junction providing the equalization of both Fermi levels giving rise to the electrolyte work function. In the dark at open circuit potential conditions (Voc), the equilibrium junction of InP/aqueous electrolyte made InP Fermi level in depletion region. For this band bending, the Boltzmann relation described the distribution of electrons in the space charge region and the electric field was determined by Gauss’ law. Poisson’s equation could be solved within that region to give the Mott–Schottky equation. For both -n and –p doped InP, flat band potentials and the doping levels were deduced from the resulting linear straight lines of the C-2(V) curves. The energy band diagram using –n and –p types InP was accurately deduced. Another interesting interfacial features are the open circuit potentials in dark and under illumination. They reflect on -n and -p type the electronic transfer processes associated to the junction building. Under illumination the variation of Voc (ΔVoc) between both types vs illumination intensity is related to the equilibrium evolution due to hole / electron distribution through the junction under light perturbation. Figure 1 shows the Voc separation from the dark (ΔVoc~ 130mV) and for the highest illumination condition (ΔVoc~ 550mV). Highest separation should be obtained by still increasing the light power. Note that in this case the electrolyte is diluted with sulfuric acid (0.5M), which maintains a perfect oxide free interface. This gives rise to a perfect reversibility of Voc between the dark and illuminated situations contrary to observations which have been already studied in neutral pH [1]. Similar access to the absolute energy diagram of -n and -p InP samples can be observed in Ultra High vacuum condition (UHV). As for liquid junction an absolute energy position towards the Fermi level of an X-ray Photoelectron Spectrocopy spectrometer (XPS) can be observed. Figure 2 shows the binding energy position variation of core levels for -n and -p InP samples. Again the surfaces are oxide free. The variation between -n and -p is around 0.7eV corresponding again to samples submitted to strong illumination due in this case to X-rays flux. Even if the junction has been under high vacuum, persuasive analogies have been observed between the variation of Fermi level at open circuit potential under illumination and their respective relative position by XPS. Specific band bending at interfaces UHV/SC and Liquid/SC are compared and discussed through the data obtained by interfacial electrochemistry and XPS considerations. [1] J. C. Meldeje, A.-M.Gonçalves, N. Simon, L. Ouattara, A. Etcheberry. J. of Electrochem. Soc. 165 (4) H3138-H3142 (2018) Figure 1

Corrosion Resistance of Mild Steel Coated with Orgainc Material Containing Pyrazol Moiety

Pyridine (P1) and benzoic acid (P2) derivatives with pyrazole moieties were synthesized and evaluated as corrosion inhibitors for mild steel in acidic medium. The evaluation was performed by electrochemical impedance spectroscopy (EIS), potentiodynamic polarization, and weight loss measurement. The surface morphologies of the control and steel samples coated with the pyrazole derivatives P1 and P2 were examined by the scanning electron microscopy (SEM), UV-Vis, and X-ray photoelectron spectrocopy (XPS) spectroscopies. Results revealed minor changes on steel surfaces before and after immersion in a 1 M HCl solution. Both derivatives, P1 and P2, showed good inhibition efficiency that is dependent on inhibitor concentration. Both P1 and P2 act as mixed-type inhibitors. The benzoic acid derivative (P2) showed a higher efficiency than P1, which could be attributed to the carboxyl group that is located at the para position to the amino group. This induces a direct electronic resonance between the two groups, the amino and the carboxyl. As a result of this, a higher electron density on the carboxyl group and a stronger bonding to the metal surface occurred. Results also show that, the bonding of both pyrazoles on mild steel surface obey Langmuir adsorption isotherm. Quantum chemical calculations were performed to theoretically define the relationship between the molecular structures and inhibition efficiencies of P1 and P2.

In-situ preparation and properties of gold nanoparticles embedded polypyrrole composite

A composite was formed by polypyrrole (Ppy), gold nanoparticles (AuNPs) and multi-walled carbon nanotubes (MWCNT) using chloroauric acid (HAuCl4). MWCNT were carboxy functionalized by oxidation resulting into oxidized MWCNT (OMWCNT). The composite was characterized spectroscopically, structurally and morphologically by Fourier transform infrared (FT-IR) spectroscopy, Ultraviolet-visible (UV-Vis) spectroscopy, X-ray photoelectron spectrocopy (XPS), X-ray diffraction (XRD), Scanning electron microscopy (SEM) and High-resolution transmission electron microscopy (HRTEM) studies which revealed about its successful formation. UV-Vis spectroscopy suggested the in-situ formation of AuNPs, their dispersion into the composite and presence of OMWCNT. XPS analysis revealed the existence of Au, C, N and O elements, signifying the desired formation of the composite. Morphological studies depicted the wrapping of OMWCNT by Ppy along with the presence of dispersed AuNPs. Its electrochemical examination suggested good electron transfer ability of AuNPs and OMWCNT. The interaction of composite with Cd2+ ions was investigated both optically and electrochemically, making it a potential candidate for Cd2+ sensing. Furthermore, its catalytic activity was also shown, by reduction of methylene blue dye.

Behaviour of Nanostructured Si-Based Anode Materials Studied By Atom Probe Tomography and Hard X-Ray Photoelectron Spectrocopy

Lithium-ion batteries (LIB) are considered for electric vehicles (EV) as well as for home or off-grid energy storage for example in combination with photovoltaics. These specific applications drive the research on high energy density, cost-effective, safe and environmental friendly battery materials. To obtain deeper insight into the reaction mechanisms advanced characterization such as in-situ TEM or in-situ XRD1 are often used in combination with simplified model systems. For LIB anodes Si has the highest specific capacity among all anode materials. However, the mechanical fatigue (lack of microstructural integrity) associated with large volume expansion of pure Si during the lithiation process has hindered their wider use for commercial applications so far. Also, there are a series of side reactions which happen at the surface forming the solid electrolyte interface (SEI). In this work we investigate the role of mechanically confined nanocrystalline Si particles being embedded in a SiTiNi matrix2. Samples are produced by melt-spinning from a rapidly solidified SiTiNi alloy. The ribbon exhibits a nanocomposite microstructure with nano-Si particles (~50-200 nm) as potential sites for Li-storage embedded in an amorphous matrix of SiTiNi (STN). Such alloys have shown potential for anode materials in high capacity Li-ion batteries. Systematic lithiation and de-lithiation cycles were performed and selected samples after different cycles were investigated using Atom Probe Tomography (APT) to understand the Li diffusion mechanism in and out of the Si particles. We consider Atom Probe Tomography as a powerful tool to understand the phase changes at an atomic level3. Aided by Focus Ion Beam (FIB), we can address the nm-scale element distribution in any local structure. On the other hand, Hard X-Ray Photoelectron Spectroscopy (HAXPES) is adopted for a detailed SEI study. The employed high energy X-ray beams can probe deeper information of core level photoemission [1] Bach, P.; Valencia-Jaime, I.; Ruett, U.; Gutowski, O.; Romero, A.H.; Renner, F.U. Chemistry of Materials (2016), doi: 10.1021/acs.chemmater.5b04719; Renner, F.U.; Kageyama, H.; Siroma, Z.; Shikano, M.; Schröder, S.; Gründer, Y.; Sakata, O. Gold Model Anodes for Li-Ion Batteries: Single Crystalline Systems Studied by In Situ X-ray Diffraction, Electrochim. Acta 2008, 53, 6064-6069. [2] Son et al. “A Highly Reversible Nano Si Anode Enabled by Mechanical Confinement in an Electrochemically Activated LiXTi4Ni4Si7 Matrix.” Advanced Energy Materials 2 (2012), 1226. [3] Diercks et al., Microscopy of Chemical and Mechanical Heterogeneities in Lithium Cobalt Oxide, Microscopy and Microanalysis 21 (2015), 523.

Nanopore fabrication in silicon oxynitride membranes by heating Au-particles

We report the fabrication of nanopores in a silicon oxynitride (SiON) membrane by heating a silicon rich-silicon nitride (SiRN) membrane with a gold nanoparticle array deposited on its surface. The gold nanoparticle array was realized by photolithography and the membrane by wet-etching. The entire process is wafer scale. Nanopore through-holes of an average diameter of 150 nm were produced in a ~22 nm thick membrane. Membranes and nanopores were characterized by atomic force microscopy, scanning transmission electron microscopy, and x-ray photo-electron spectrocopy.

Temperature-Dependent Reactions of Phthalic Acid on Ag(100)

We have investigated the adsorption and temperature-dependent reactions of phthalic acid on Ag(100), in the temperature range 110–700 K, by synchrotron radiation X-ray photoelectron spectrocopy (SR-XPS), temperature-programmed desorption (TPD) and near-edge X-ray absorption fine structure (NEXAFS). Phthalic acid adsorbs intact at 110 K, but decomposes to phthalic anhydride and polyanhdride at 150 K. When heated further, phthalic anhydride desorbs at 250 K, leaving only polyanhydride on the surface, which at 350 K decomposes into a carboxylate, through desorption of phthalic anhydride and water. The carboxylate is stable until 500 K, after which it decomposes, through desorption of CO2 and benzene, into carbon; the latter diffuses into the bulk, leaving only a little carbon on the Ag(100) surface at 600 K.

Structures and electrical properties of Mn- and Co-doped lead-free ferroelectric K0.5Na0.5NbO3 films prepared by a chemical solution deposition method

The un-doped, 2mol% Mn- and 2mol% Co-doped K0.5Na0.5NbO3 (KNN) films were prepared by a chemical solution deposition method. The crystalline phase and surface morphologies of KNN films hardly changed after Mn- and Co-doping. X-ray photoelectron spectrocopy analysis indicates that the introduction of both Mn and Co promoted the formation of KNN perovskite structure, and the most Mn2+ and Co2+ ions were oxidized into high-valence ions during thermal process. As a result, the leakage current density of the KNN films was decreased and the electrical properties were enhanced after the doping.

Direct synthesis of H2O2 on model Pd surfaces

We experimental demonstrated that model catalysts in the form of ideal Pd surfaces, either single (100) and poly crystalline, are active for H2O2 direct synthesis at 15°C and pressure in excess of 20bars, in methanol. Activity scaled on the available surface is much larger than some of the best powder catalyst suggested so far (Pd–Au on sulphated zirconia). The surface with a long range order, i.e. single crystal Pd (100), was far more active that the corresponding polycristalline surface, suggesting an actual correlation between structure and reactivity, extremely relevant for performances. Prereduction treatments and corresponding X-ray photoelectron spectrocopy of the surfaces confirmed the presence of surface oxidized specie, whose structure appear to be related to the underlying Pd texture. These results, well validated, open new perspectives for an effective catalyst design, taking surface science speculations, based on either ultra high vacuum experiments in the gas phase and DFT calculations, closer to an experimental validation. This contribution goes well beyond the investigation of the H2O2 direct synthesis mechanism.

High-capacity cathodes for lithium-ion batteries from nanostructured LiFePO4 synthesized by highly-flexible and scalable flame spray pyrolysis

Olivine, LiFePO4 is a promising cathode material for lithium-ion batteries due to its low cost, environmental acceptability and high stability. Its low electric conductivity prevented it for a long time from being used in large-scale applications. Decreasing its particle size along with carbon coating significantly improves electronic conductivity and lithium diffusion. With respect to the controlled formation of very small particles with large specific surface, gas-phase synthesis opens an economic and flexible route towards high-quality battery materials. Amorphous FePO4 was synthesized as precursor material for LiFePO4 by flame spray pyrolysis of a solution of iron acetylacetonate and tributyl phosphate in toluene. The pristine FePO4 with a specific surface from 126–218 m2 g−1 was post-processed to LiFePO4/C composite material via a solid-state reaction using Li2CO3 and glucose. The final olivine LiFePO4/C particles still showed a large specific surface of 24 m2 g−1 and were characterized using X-ray diffraction (XRD), electron microscopy, X-ray photoelectron spectrocopy (XPS) and elemental analysis. Electrochemical investigations of the final LiFePO4/C composites show reversible capacities of more than 145 mAh g−1 (about 115 mAh g−1 with respect to the total coating mass). The material supports high drain rates at 16 C while delivering 40 mAh g−1 and causes excellent cycle stability.

Synthesis and Characterization of Carbon Nanostructures as Catalyst Support for PEMFCs

A detailed procedure for synthesis, characterization, and possibility of carbon nanostructures (CNS) as support for catalysts in polymer electrolyte membrane fuel cells (PEMFCs) is presented. The fabrication process is two-staged ballmilling of carbon graphite in the presence of hydrogen and transition metals (Fe, Co) followed by heating of the milled carbon initially in an argon atmosphere. The milling induces amorphous forms of carbon and metal, as well as C-H bonds. During the second stage, the production of methane by catalytic reaction of the bonded carbon and hydrogen is first observed, followed by the formation of metallic nanocrystals, and, finally, the formation of carbon structures on the metallic nanocrystals at a temperature of . Subsequently, metals and carbon nanoparticles are removed from the as-prepared sample. The purified samples are platinized after surface treatment by either air or chemical oxidation. Material characterization results obtained by X-ray diffraction, transmission electron microscopy, thermogravimetric analysis, X-ray photoelectron spectrocopy, and atomic adsorption spectroscopy are presented. In addition, we also report their measured electrical conductivity, specific surface, and porosity. The real electrochemical active surface area was evaluated by cyclic voltammetry on a thin porous coated electrode.

Growth of ZnO Submicron Single-Crystalline Platelets, Wires, and Rods by Ultrasonic Spray Pyrolysis

Submicron single crystals of ZnO were grown by spray pyrolysis: the mist of an aqueous solution was generated by ultrasonic agitation and then pyrolyzed on a heated glass substrate. Hexagonal platelets of ZnO 10–90 nm thick were obtained when ammonium acetate was incorporated into the precursor solution of zinc acetate. Single-crystalline wires and rods, which were 50–150 and 300–4000 nm thick respectively, were obtained when indium nitrate was co-incorporated into the solution as a metal catalyst. The crystallographic direction of wires and rods was parallel to one of the [0001], [1010], or [1120] axis of wurtzite. As substrate temperature increased, the aspect ratio of the crystal thus tended to decrease. Structural and compositional analyses of these crystals were performed by scanning electron microscopy, scanning ion microscopy, transmission electron microscopy and electron diffraction, X-ray diffraction, X-ray photoelectron spectrocopy, and energy dispersive X-ray spectroscopy.

Microstructural and Chemical Characterisation of Metal Particles Nanostructures

In order to achieve a full characterisation of metal particles nanostructures at the microstructural level, we show in this overview the use of different techniques: i) High resolution transmission electron microscopy (TEM) or energy filtered TEM (EFTEM) associated to energy dispersive X-Ray analysis (EDX) and electron energy loss spectroscopy (EELS). ii) A surface analysis technique like X-Ray photoelectron spectrocopy (XPS). iii) A technique sensitive to the local structure and chemical state like X-Ray absorption spectroscopy (XAS). Two systems will be described to illustrate this study: i) Nickel particles dispersed in an amorphous carbon matrix have been synthesized by a sonication method, and further heated at 773 K under Ar atmosphere. The as-prepared sample shows amorphous spherical particles (TEM) formed by Ni 2þ highly dispersed in carbon (XPS, XAS). The heated sample shows spherical grains formed by nanocrystalline Ni particles embedded in an amorphous carbon matrix (HRTEM). Heterogeneities at micro- and nanoscopic scale have been determined by TEM/EELS and EFTEM. Quantification of the oxidation level for the heated sample was also determined by XAS. ii) Gold nanoparticles modified with neoglycoconjugates molecules have been prepared by a wet chemical method. Aggregates, isolated nanoparticles or two-dimensional self-organised nanostructures have been obtained by controlling the interaction forces between biological significant oligosaccharides. The EFTEM analysis has been used to demonstrate the role of divalent cations in the formation of the nanostructures.

Surface modification of polymers with self-assembled molecular structures: multitechnique surface characterization.

A simple, one-step procedure for generating ordered, crystalline methylene chains on polymeric surfaces via urethane linkages was developed. The reaction of dodecyl isocyanate with surface hydroxyl functional groups, catalyzed by dibutyltin dilaurate, formed a predominantly all-trans, crystalline structure on a cross-linked poly(2-hydroxyethyl methacrylate) (pHEMA) substrate. Allophanate side-branching reactions were not observed. Both X-ray photoelectron spectrocopy and time-of-flight secondary ion mass spectrometry show that the surface reaction reached saturation after 30 min at 60 degrees C. Unpolarized Fourier transform infrared-attenuated total reflection showed that, after 30 min, the stretching frequencies, vCH2,asym and vCH2,sym, decreased and approached 2920 and 2850 cm-1, indicative of a crystalline phase. The distance between two hydroxyl groups is roughly 4 A. A tilt angle of 33.5 degrees +/- 2.4 degrees was estimated by dichoric ratios measured in polarized ATR according to the two-phase and Harrick thin film approximations. The findings reported here are significant in that the possibilities for using structures similar to self-assembled monolayers (SAMs) are expanded beyond the rigid gold and silicon surfaces used through most of the literature. Thus, SAMs, biomimetics for ordered lipid cell wall structures, can be applied to real-world biomedical polymers to modify biological interactions. The terminal groups of the SAM-like structure can be further functionalized with biomolecules or antibodies to develop surface-based diagnostics, biosensors, or biomaterials.

Performance and Characterization of Novel Re−Sb−O Catalysts Active for the Selective Oxidation of Isobutylene to Methacrolein

The catalytic behavior of three well-defined Re−Sb−O compounds, SbOReO4·2H2O, Sb4Re2O13, and SbRe2O6, was investigated in the selective oxidation of isobutylene to methacrolein at 673 K. We have directed our attention to the correlation between the catalytic performance of the compounds and their structural and superficial changes undergone under the reaction conditions. For the purpose, the effects of the pretreatment conditions for the catalysts and of the isobutylene/oxygen ratio in the reaction atmosphere on the performance of the catalysts were explored. Each Re−Sb−O compound was characterized before and after the pretreatments and the catalytic reactions by X-ray diffraction, X-ray photoelectron spectrocopy, scanning electron microscopy, and in situ laser Raman microscopy. Among the three Re−Sb−O compounds, a novel SbRe2O6 compound exhibited the highest catalytic performance for selective oxidation. The compound underwent a progressive decomposition to Sb4Re2O13 and Re2O7 when pretreated or reacted at 673 K in the presence of oxygen. The decomposition was favored under more oxidative conditions, and a close parallelism between the catalytic performance and the quantity of Re2O7 stabilized at the surface of the catalyst was observed. On the other hand, the activities of pure Re2O7 and a new Sb4Re2O13 compound were very low when each of them was used as a catalyst independently. The results indicate that the reactivity of SbRe2O6 is likely due to the presence of Re2O7 at the surface, benefitting from a cooperation with Sb4Re2O13. The model also accounts for the performance of SbOReO4·2H2O. SbOReO4·2H2O decomposed to Sb4Re2O13 and Re2O7 regardless of the reaction atmosphere, which explains a higher activity of SbOReO4·2H2O than Sb4Re2O13. However, the amount of Re2O7 stabilized at the surface was smaller than that for the case of SbRe2O6, which leads to lower performances of SbOReO4·2H2O than those of SbRe2O6.

Analysis of the Surface Chemical Structure of Copolymers of Poly(sebacic anhydride) with Ricinoleic Acid Maleate Using XPS and ToF−SIMS

X-ray photoelectron spectrocopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF−SIMS) have been used to characterize the surface chemistry of copolymers of poly(sebacic anhydride) with ricinoleic acid maleate. ToF−SIMS analysis yielded fragmentation patterns consisting of ions diagnostic of both monomers. Across the copolymer series, relative peak intensities of these diagnostic ions showed a good comparison between surface and bulk composition, in accordance with the XPS analysis. ToF−SIMS data also indicated that these copolymers consisted of either random or block sections.

Characterization of modified NG7 graphite as an improved anode for lithium-ion batteries

Mild oxidation (burnoff) has been found to improve the performance of NG7 (natural graphite) in Li/Li x C 6 cells. The reversible capacity of the graphite ( Q R) increased (up to 405 mAh/g for the 0–2 V range at 4–11% burnoff), its irreversible capacity ( Q IR) decreased with burnoff and the degradation rate of the Li x C 6 electrode was much lower. The increase in capacity at 4–11% burnoff of NG7 was found to be associated with the formation of less than 1% void volume. On further burning beyond 11% weight loss, the density decreases faster, down to 1.92 g/cm 3 at 34% burnoff. This is associated with some decrease in Q R. X-ray photoelectron spectrocopy studies showed that the surface oxygen content of NG7 has a broad minimum at 4–22% burnoff. The highest oxygen peak shifted monotonically with burnoff time, rising from 531.05 eV for pristine NG7 to 534.0 eV for 34% burnoff sample. The X-ray photoemission spectra may be assigned to hydroxyl surface groups in the case of the pristine sample and to surface acid groups in the case of burnt samples. From the powder X-ray diffraction and d q/d v results, it was found that a more ordered structure appears on cycling. Performance improvement was attributed to the formation of a solid electrolyte interface chemically bonded to the surface carboxylic groups at the zigzag and armchair faces, better wetting by the electrolyte and to accommodation of extra lithium at the zigzag, armchair and other edge sites and nanovoids.

Application of X-ray photoelectron spectroscopy and fourier transform IR-reflection absorption spectroscopy to studies of the composition of Langmuir-Blodgett films

The composition of icosanoic acid films deposited on substrates from an aqueous subphase containing metal such ions as cadmium, calcium, barium and lead at various pH values was investigated by X-ray photoelectron spectrocopy and Fourier transform IR-reflection absorption spectroscopy. It was found that the composition of the Langmuir-Blodgett films is changed by the pH of the subphase and that the pH range of formation of acid, salt and mixed films is characteristic for each metal ion. Also, the results obtained are in good agreement with the data of different methods of analysis.