Photoelectron Spectroscopy Methods Research Articles

Aliovalent Doping of CeO2 Improves the Stability of Atomically Dispersed Pt.

Atomically dispersed supported catalysts hold considerable promise as catalytic materials. The ability to employ and stabilize them against aggregation in complex process environments remains a key challenge to the elusive goal of 100% atom utilization in catalysis. Herein, using a Gd-doped ceria support for atomically dispersed surface Pt atoms, we establish how the combined effects of aliovalent doping and oxygen vacancy generation provide dynamic mechanisms that serve to enhance the stability of supported single-atom configurations. Using correlated, in situ X-ray absorption, photoelectron, and vibrational spectroscopy methods for the analysis of samples on the two types of support (with and without Gd doping), we establish that the Pt atoms are located proximal to Gd dopants, forming a speciation that serves to enhance the thermal stability of Pt atoms against aggregation.

Chitosan functionalized gold-nickel bimetallic magnetic nanomachines for motion-based deoxyribonucleic acid recognition

In this present study, the preparation of chitosan functionalized gold‑nickel wire nanomachines (nanomotors) (CS@Au-Ni NMs) for motion-based double-stranded deoxyribonucleic acid (dsDNA) recognition and detection was described. Synthesis of the nanomachines was accomplished by Ni layer formation using direct current (DC) magnetron sputtering over electrochemically deposited Au wires. Subsequently, biopolymer chitosan was dispersed onto this bimetallic layer by drop casting which could provide a novel and functional surface for leading bio-applications. CS@Au-Ni NMs were characterized via scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and zeta potential analysis methods for the elucidation of structural morphology, elemental composition and electrophoretic mobility. On account of presenting the application of these magnetic nanomachines, they were interacted with different concentrations of dsDNA and the changes in their velocities were investigated. The speed CS@Au-Ni NMs were measured as 19 μm/s under 22 mT magnetic field. These magnetically guided nanomachines demonstrated a practical and good sensing ability by recognizing dsDNA between 0.01 mg/L and 10 mg/L. Electrochemical characterization was also performed to identify the surface characteristics. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) experiments presented the interaction of the NMs with dsDNA by indicating the convenient recognition.

Synthesis of conical Co–Fe alloys structures obtained with crystal modifier in superimposed magnetic field

The addition of crystal modifier to electrolyte used during electrodeposition of metals and alloys allows obtaining conical structures without using any template. This method is fast and ensures covering large areas during one single electrodeposition process. In this work, Co–Fe cones were obtained by one-step method with ammonium chloride as a crystal modifier. The influence of electrodeposition parameters and electrolyte compositions were investigated. Electrodeposition conditions (duration, electrolyte temperature, and addition of NH4Cl), which allow obtaining the most uniform conical structures, were applied during sample fabrication in the magnetic field. The influence of its value and direction on the quality and compositions of obtained alloys was investigated using Scanning Electron Microscope (SEM) photos. To check if there is any change in the sample crystal system, the X-Ray Diffraction (XRD) analysis was performed. To confirm the synthesis of Co–Fe cones, they were analyzed using the X-ray photoelectron Spectroscopy (XPS) method.

STRUCTURAL FEATURES OF CHROMIUM CARBID COATINGS OBTAINED BY THE MOCVD METHOD FROM THE COL “BARKHOS”

Investigations of the structure and properties of gas-phase coatings obtained with the use of chromium organic liquid (COL) “Barkhos” have been carried out. The studies were carried out by the methods of nanoindentation, fractography, and X-ray photoelectron spectroscopy. It was found that such coatings have a two-level horizontallayered structure.

Corrosion evolution of Cu-Pb alloys from the Western Zhou Dynasty in simulated archaeological soil environment

• The corrosion behaviour of Cu-Pb alloy has been explained. • The Cu-13.28Pb alloy exhibited the best corrosion resistance. • The corrosion products are composed of metal oxides and metal-insoluble compounds. The corrosion behaviour study of Cu-Pb alloy in simulated archaeological soil environment were investigated using electrochemical accelerated corrosion, Field emission scanning electron microscopy/energy dispersive spectroscopy, laser scanning confocal microscope, X-ray photoelectron spectroscopy and electrochemical methods. It is crucial that the corrosion resistance of the Cu-Pb alloy was found to alter with the Pb content in the alloy. The results demonstrated that Cu-13.28Pb alloy exhibited the best corrosion resistance with the smallest corrosion current density and the lowest anodic dissolution rate. The corrosion products are mainly composed of matrix metal oxides and metal-insoluble inert compounds. The correlation between Pb content and corrosion behaviour and the corresponding corrosion mechanism were clarified.

Synthesis of a durable and efficient superhydrophobic copper mesh coated by organosilica nano/microstructures for separating oil from water

Superhydrophobic materials are widely utilized to separate oil from water. Proposing a facial method to synthesis a durable hydrophobic/superhydrophobic surface for efficient and easy oil/water separation is necessary due to the danger of oil spills for ecosystems. Herein, a robust superhydrophobic filter is introduced for oil/water separation. Organosilica nano/microstructures covered resorcinol-formaldehyde resin are loaded on the copper mesh surface to earn a roughened surface then modified by 1-dodecanethiol to get a low surface energy mesh. The prepared superhydrophobic copper mesh was shaped to a basket-like as an oil skimmer device that repels the water and collects the oil through its pores. The sample was analyzed by scanning electron microscopy, energy-dispersive X-ray spectroscopy, atomic force microscopy and X-ray photoelectron spectroscopy methods. The sample exhibits high water contact angle, θ=149±1° and the oil contact angle, showing its superhydrophobic nature. The prepared superhydrophobic mesh was used as an efficient and robust filter to separate oil from water. Its oil/water separation efficiency is more than 90% and this value approximately preserves after 50 cycles. The prepared sample also shows self-cleaning property. Thanks to the stable and rough structured created by resorcinol-formaldehyde resin covered by organosilica particles and also the low surface energy provided by 1-dodecanethiol, the prepared sample shows superhydrophobic property with high efficiency to separate oil from water.

Chemical degradation in Thermally Cycled Stainless Steel 316 with High-Temperature Phase Change Material

Analysis of stainless steel 316 as a containment material in the presence of a phase change material (PCM) cycled at high temperature was carried out through a combination of X-ray photoelectron spectroscopy and X-ray diffraction methods. In this work, stainless steel tokens were half-immersed in a chloride carbonate-based PCM, which were then thermally cycled in an air or a nitrogen environment up to 500 times, allowing the PCM to repeatedly transform between solid and liquid phases. Spectroscopy and diffraction methods were applied on the tokens, as well as the cycled PCM, to investigate the extent and nature of corrosion in such steel alloys. With varying sputtering conditions, the oxidation state at different depths of token surfaces was quantified. From the outermost corroded layer through to the bulk, this study shows a gradual change in distribution in both Cr and oxidation of Fe, while Cr was specifically found to have depleted and migrated into the PCM. The oxidation and depletion have been found to increase with increasing exposure time to PCM while sigma-phase structure embrittled in the corrosion layer. • Chemical degradation of thermal cycled SS 316 with PCM was analysed. • X-ray photoelectron spectroscopy methods were applied to analyse corrosion layers. • Chloride carbonate based PCM in air and nitrogen environment was studied. • With varying sputtering conditions, oxidation state of steel was quantified.

Preparation of WS2/C composite material and its electrocatalytic hydrogen evolution performance

With H2WO4 and EDA as precursors, WO3/C intermediate is obtained by mechanical stirring and in-situ solid-phase pyrolysis, then WS2/C composite material is obtained by high temperature vulcanization. The WS2/C composite is characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS) and other instrumental analysis methods. At the same time, the electrocatalytic performance of the catalyst was analyzed by the electrocatalytic steady-state polarization curve (LSV), Tafel slope (Tafel), cycle stability (CP), electrochemical impedance (PEIS) and Electrochemically Active Surface Area (ECSA) tests of the material. The results showed that when the current density of the WS2/C composite is 10 mA/cm2, overpotential is 179 mV, and Tafel slope is 98 mV/dec.

Laser-generated high entropy metallic glass nanoparticles as bifunctional electrocatalysts

High entropy metallic glass nanoparticles (HEMG NPs) are very promising materials for energy conversion due to the wide tuning possibilities of electrochemical potentials offered by their multimetallic character combined with an amorphous structure. Up until now, the generation of these HEMG NPs involved tedious synthesis procedures where the generated particles were only available on highly specialized supports, which limited their widespread use. Hence, more flexible synthetic approaches to obtain colloidal HEMG NPs for applications in energy conversion and storage are highly desirable. We utilized pulsed laser ablation of bulk high entropy alloy targets in acetonitrile to generate colloidal carbon-coated CrCoFeNiMn and CrCoFeNiMnMo HEMG NPs. An in-depth analysis of the structure and elemental distribution of the obtained nanoparticles down to single-particle levels using advanced transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) methods revealed amorphous quinary and senary alloy phases with slight manganese oxide/hydroxide surface segregation, which were stabilized within graphitic shells. Studies on the catalytic activity of the corresponding carbon-HEMG NPs during oxygen evolution and oxygen reduction reactions revealed an elevated activity upon the incorporation of moderate amounts of Mo into the amorphous alloy, probably due to the defect generation by atomic size mismatch. Furthermore, we demonstrate the superiority of these carbon-HEMG NPs over their crystalline analogies and highlight the suitability of these amorphous multi-elemental NPs in electrocatalytic energy conversion.

The Relationship between Cyclic Multi-Scale Self-Organized Processes and Wear-Induced Surface Phenomena under Severe Tribological Conditions Associated with Buildup Edge Formation

This paper presents experimental investigations of various interrelated multi-scale cyclic and temporal processes that occur on the frictional surface under severe tribological conditions during cutting with buildup edge formation. The results of the finite element modeling of the stress/temperature profiles on the friction surface are laid out. This study was performed on a multilayer coating with the top alumina ceramic layer deposited by CVD (chemical vapor deposition) on a WC/Co carbide substrate. A detailed analysis of the wear process was conducted by 3D wear evaluation, scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM/EDS) and electron backscattered diffraction (EBSD), as well as X-ray photoelectron spectroscopy (XPS) methods. The following cyclic phenomena were observed on the surface of the tribo-system during the experiments: a repetitive formation and breakage of buildups (a self-organized critical process) and a periodical increase and decrease in the amount of thermal barrier tribo-films with a sapphire structure (which is a self-organization process). These two processes are interrelated with the accompanying progression of cratering, eventually resulting in the catastrophic failure of the entire tribo-system.

Platinum Nanoparticles Decorated IrO2@MWCNT as an Improved Catalyst for Oxygen Evolution Reaction

AbstractIn this paper, IrO2 nanoparticles supported on multi‐walled carbon nanotubes (MWCNTs) are synthesized via a facile hydrothermal method and calcination process at different temperature. Platinum nanoparticles decorated IrO2@MWCNT‐400 °C are prepared by chemical reduction method. The influence of MWCNTs and Pt on physicochemical properties and oxygen evolution reaction (OER) activity of IrO2@MWCNT composites were studied via transmission electron microscope (TEM), X‐ray diffraction (XRD), Raman spectra, thermogravimetric analysis (TGA), X‐ray photoelectron spectroscopic (XPS) and electrochemical methods. Among the samples, Pt/IrO2@MWCNT‐400 °C exhibits better catalytic activity with an overpotential of 270 mV at the current density of 10 mA cm−2 with a low Tafel slope of 85.1 mV dec−1. The outstanding OER performance of Pt/IrO2@MWCNT‐400 °C is ascribed to the introduction of the MWCNTs, which can not only act as a support to prevent agglomeration of IrO2 nanoparticles that produces high surface area of catalytic sites, but also facilitates electron transfer between IrO2 nanoparticles and MWCNTs. On the other hand, the Pt optimizes electronic structure for excellent electrocatalytic performance. Therefore, the Pt/IrO2@MWCNT‐400 °C catalyst is a good choice for application in OER.

Electronic structure and stability of hexanuclear complex [Cu6(hfa)4(dpm)4(OH)4

Interatomic interactions and charge state of atoms in hexanuclear complex [Cu6(hfa)4(dpm)4(OH)4] have been studied by the methods of quantum chemistry and X-ray photoelectron spectroscopy (XPS). The shape and energy position of the Cu2p3/2-lines indicate that all copper atoms state could be interpreted as Cu2+. It was also analyzed the quantum chemical and XPS data on atomic charge distribution for monoligandic bis-β-diketonate Cu(hfa)2 and Cu(dpm)2 complexes. The comparison of calculated and experimental data for monoligandic and hexanuclear complexes revealed the electronic density redistribution on the oxygen and copper atoms in 1 due to the charge transfer interaction between Cu(hfa)2- and Cu(dpm)-fragments with participation of the bridging OH-groups, which was confirmed by NBO analysis.

Yolk-shell ZnO@C-CeO2 ternary heterostructures with conductive N-doped carbon mediated electron transfer for highly efficient water splitting

Herein, carbon-incorporated yolk-shell ZnO@C-CeO2 ternary heterostructures are employed as visible light responsive photocatalyst for highly efficient photoelectrochemical (PEC) water splitting. Compared to conventional ZnO/CeO2 semiconductors, introduction of a thin PDA shell layer assures the generation of a conductive N-doped graphitic carbon layer after a calcination post-treatment with mesoporous hollow morphologies. The evaluation of PEC water splitting performance of ZnO@C-CeO2 photoanodes reveals the maximum photocurrent density as 7.43 mA/cm2 at 1.18 V RHE under light whereas almost no response is recorded at dark. These superior PEC H2 evolution performance strongly implies efficient charge separation, facilitated charge transfer between photoanode and electrolyte interface as well as within the semiconductor bulk by means of rapid electron transfer ability of N-doped graphitic carbon layer and prolong life time of light inside yolk-shell structure. Furthermore, considerable depression in PL intensity of ZnO@C-CeO2 photoanodes compared to ZnO clearly reveals a higher photon absorption due to the reflection of light in hollow region and increase in electron hole separation efficiency. Moreover, plausible Z-scheme charge transfer mechanism using ZnO@C-CeO2 photoanodes under visible light illumination is verified using radical trapping experiments and X-ray photoelectron spectroscopy (XPS) methods, suggesting new generation of heterostructures for sufficient conversion of sunlight to H2 fuels.

X‐ray photoelectron spectroscopy characterization of band offsets of MgO/Mg2Si and SiO2/Mg2Si heterojunctions

MgO and SiO2 are the natural oxide layer on the surface of Mg2Si and the excellent gate dielectric layer materials. MgO/Mg2Si and SiO2/Mg2Si heterojunctions were successfully prepared by magnetron sputtering. The valence band offset (VBO) and conduction band offset (CBO) of the two heterojunctions were measured by X‐ray photoelectron spectroscopy (XPS) method, and the values were 2.64 and 3.90 eV for MgO/Mg2Si and 3.24 and 4.43 eV for SiO2/Mg2Si, respectively. Different degree of band bending occurs on the two interfaces. As a result, the band diagrams of the both interfaces are all Type‐I (Straddled) band alignment. Such high VBO and CBO can provide suitable barrier heights for both electrons and holes (>1 eV); therefore, both MgO and SiO2 can be suitable candidates for the preparation of Mg2Si‐based thin film transistors.

Pd-loaded “Two-in-one” Covalent Organic Framework Composite Material: Synthesis, Characterization and Detection of Bisphenol A

We report a novel type of Pd-BFBAPy-COF (Pd-COF) loaded with Pd-NPs was synthesized for the first time by using “two-in-one” imine covalent organic framework materials as carrier. By using BFBAPy-COF (Py-COF) as the carrier and H2PdCl4 as the palladium source, Py-COF and Pd-NPs were combined by a simple heating and reflux method to successfully prepare Pd-COF. Through X-ray photoelectron spectroscopy (XPS) and other methods, it is proved that the loading of Pd-NPs on Pd-COF is completed by coordination. Finally, the application of Pd-COF as electrode coating material in the detection of Bisphenol A (BPA) by differential pulse voltammetry (DPV) shows that Pd-COF has a good electrochemical induction to BPA. This work provides a cheap and facile synthesis route for the preparation of an electrochemical detection material with practical value.

Green synthesis of reduced graphene oxide (RGO) using the plant extract of Salvia spinosa and evaluation of photothermal effect on pancreatic cancer cells

Pancreatic cancer (PC, uncontrollable cell growth in pancreas) shows no symptoms until advancement and thus it become difficult to diagnose at early stages. The treatment strategies for PC include chemotherapy, surgery, and radiotherapy. However, the recovery rate is very low and thus an effective alternative treatment is required to fight against PC. Therefore, the present was attempted to evaluate the photothermal destruction of PC cells by biologically reduced graphene oxide (RGO). The plant extract of Salvia spinosa was found to facilitate the conversion of graphene oxide (GO) to RGO, due to presence of numerous bioactive molecules. The biomolecules act as a reducing agent and this process paves the way for green technology. The green synthesized RGO was analyzed through various characterization techniques (spectroscopic methods: ultra-violet visible (UV-Vis); fourier-transform infrared (FTIR); X-ray diffraction (XRD); Raman; X-ray photoelectron spectroscopy (XPS) and microscopic method: scanning electron microscope, SEM). The results indicate that green synthesis of RGO is simple, economical and eco-friendlier. An evaluation of photothermal conversion efficacy revealed that green-synthesized RGO has the ability to enhance the temperature to a greater extent in comparison to GO. Furthermore, cell viability assay performed through MTT dye revealed the non-toxic nature of RGO. Nevertheless, it significantly destructed the PC cells (Panc02-H7) after exposing the RGO loaded PC cells to laser radiation. The obtained results were further corroborated through live/dead cell assay.

The Physico-Chemical Properties and Exploratory Real-Time Cell Analysis of Hydroxyapatite Nanopowders Substituted with Ce, Mg, Sr, and Zn (0.5-5 at.%).

Cation-substituted hydroxyapatite (HA), standalone or as a composite (blended with polymers or metals), is currently regarded as a noteworthy candidate material for bone repair/regeneration either in the form of powders, porous scaffolds or coatings for endo-osseous dental and orthopaedic implants. As a response to the numerous contradictions reported in literature, this work presents, in one study, the physico-chemical properties and the cytocompatibility response of single cation-doped (Ce, Mg, Sr or Zn) HA nanopowders in a wide concentration range (0.5–5 at.%). The modification of composition, morphology, and structure was multiparametrically monitored via energy dispersive X-ray, X-ray photoelectron, Fourier-transform infrared and micro-Raman spectroscopy methods, as well as by transmission electron microscopy and X-ray diffraction. From a compositional point of view, Ce and Sr were well-incorporated in HA, while slight and pronounced deviations were observed for Mg and Zn, respectively. The change of the lattice parameters, crystallite size, and substituting cation occupation factors either in the Ca(I) or Ca(II) sites were further determined. Sr produced the most important HA structural changes. The in vitro biological performance was evaluated by the (i) determination of leached therapeutic cations (by inductively coupled plasma mass spectrometry) and (ii) assessment of cell behaviour by both conventional assays (e.g., proliferation—3-(4,5-dimethyl thiazol-2-yl) 5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium assay; cytotoxicity—lactate dehydrogenase release assay) and, for the first time, real-time cell analysis (RTCA). Three cell lines were employed: fibroblast, osteoblast, and endothelial. When monophasic, the substituted HA supported the cells’ viability and proliferation without signs of toxicity. The RTCA results indicate the excellent adherence of cells. The study strived to offer a perspective on the behaviour of Ce-, Mg-, Sr-, or Zn-substituted HAs and to deliver a well-encompassing viewpoint on their effects. This can be highly important for the future development of such bioceramics, paving the road toward the identification of candidates with highly promising therapeutic effects.

Deposition of TiN and TiAlN Thin Films on Stainless Steel Tubes by a Cylindrical Magnetron Sputtering Method

Abstract Titanium nitride (TiN) and titanium aluminum nitride (TiAlN) coatings are very hard materials that are mostly coated on cutting tools to increase the tool life. These coatings have also been successfully applied as a coating material for biomedical applications mainly due to their tribological properties, biocompatibility, and affordable price. In an attempt to develop transition metal nitride coatings on specimens of cylindrical geometry, TiN and TiAlN thin films were deposited successfully on stainless steel tubes using a direct-current cylindrical magnetron cosputtering method. Both types of coatings were uniform in nature and had good adherence to the substrate. TiN and TiAlN thin films were characterized systematically to determine their structure, surface morphology, chemical states, chemical structure, and electrochemical behavior using X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and potentiodynamic methods, respectively. The XRD patterns of the TiN and TiAlN coatings indicated (111) preferential orientation. Cross-sectional SEM images revealed a columnar growth of the coatings with an arrow-headed geometry. XPS characterization showed the presence of TiN, Titanium dioxide, titanium oxynitride, aluminum oxide, and aluminum nitride phases. Potentiodynamic polarization tests in 3.5 % sodium chloride solution revealed that the TiAlN coating exhibited superior corrosion resistance compared with the TiN coating. Furthermore, TiAlN coating showed 94 % of average absorption in ultraviolet-visible region using photospectrometry. The cylindrical magnetron sputter deposition technique enables development of uniform protective coatings on tubular geometries, which are frequently employed in solar thermal and nuclear applications.

Excellent interfacial structural integrity of pre-oxidized carbon fiber-reinforced carbon-carbon composites

ABSTRACT Carbon-carbon composites are widely used in thermal management, photocatalysis, aerospace, high-speed railway, and nuclear energy applications, owing to their low density, high temperature stability, corrosion resistance, and excellent self-lubrication performance. Improving the weak combination interface of carbon-carbon composites has always been challenging. Prior to the present study, there was no effective method for stimulating the interaction between the reinforcing phase and the carbon matrix. In this study, pre-oxidized carbon fibers with abundant active functional groups were introduced into ultrafine carbon powder, for significantly improving interfacial structural integrity in carbon-carbon composites. The effects of pre-oxidized carbon fiber on the composites were systematically studied using metallographic microscopy, scanning electron microscopy, Fourier-transform infrared spectroscopy, and X-ray photoelectron spectroscopy methods. The results show that chemical bonds are formed between pre-oxidized carbon fibers and the carbon matrix, increasing the interfacial bonding strength. The pre-oxidized carbon fibers expanded adaptively after sintering, with the diameter increasing by 19.47%. The fiber expansion process inhibited cracks, decreasing the composites’ porosity by 21.6%. Compared with carbon fibers, the pre-oxidized carbon fibers improved the flexural strength, impact resistance, electrical conductivity, and thermal conductivity by 31.8%, 53.3%, 18.58%, and 14.06%, respectively.

High-performance humidity sensor based on graphitic carbon nitride/polyethylene oxide and construction of sensor array for non-contact humidity detection

This paper presented a novel flexible humidity sensor and sensor array based on graphitic carbon nitride/polyethylene oxide (g-C3N4/PEO) hybrid film with excellent performances. The nanostructure, morphology and composition characteristics of the g-C3N4/PEO nanomaterial were characterized through scanning electron microscope (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS) method. The humidity sensing performances were tested under 11–97 % RH at 20 °C and the experimental results revealed that g-C3N4/PEO humidity sensor has ultrahigh response, fast response/recovery behavior, excellent repeatability and outstanding long-term stability. The humidity sensing mechanism of g-C3N4/PEO nanomaterial was further explained through complex impedance spectroscopy (CIS) and bode diagrams. This proposed high-performance humidity sensor could be applied in practical applications such as human breath monitor under different states, finger approaching and skin moisture detection. Meanwhile, a 4 × 4 sensor array was also fabricated to monitor the approaching of fingertips and identify wet objects with specific shape demonstrating great application potential of the g-C3N4/PEO humidity sensor in non-contact systems.