X-ray Photoelectric Spectroscopy Research Articles

Hydrothermal synthesis of Hydrangea macrophylla-like Ce-doped SnO2 microspheres and their enhanced sensing properties

The hydrangea macrophylla-like SnO2 microspheres doped with different Ce contents (0, 2, 6 and 10 mol%) were synthesized by a facile hydrothermal method. The crystal phase, micro morphology and element composites were investigated by x-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) with energy-dispersive spectroscopy (EDS) and x-ray photoelectric spectroscopy (XPS). The results demonstrated the hydrangea macrophylla-like microstructure of the prepared samples and the existence of Ce3+/Ce4+ when doped with Ce element. Furthermore, the synthesized Ce-doped SnO2 samples’ sensing properties were investigated. The SnO2 microspheres doped with 6 mol% showed the largest response to acetone during 0.2–20 ppm at 320 °C as well as good selectivity and reproducibility. As discussed, the Ce doping that generates n-n type heterojunction and the Ce3+/Ce4+ conversion increases the resistance change of Ce-doped SnO2 in reducing atmosphere and enhances the response.

CoO-Co2P composite nanosheets as highly active catalysts for sodium borohydride hydrolysis to generate hydrogen

In this paper, CoO[Formula: see text]Co2P composite nanocatalysts as highly active catalysts were successfully prepared for catalytic hydrolysis of sodium borohydride (NaBH[Formula: see text] to generate hydrogen. For catalyst preparation, pre-synthesized Co(OH)2 nanosheets were uniformly mixed with sodium hypophosphite (NaH2PO[Formula: see text] and then treated through vapor-phase phosphorization process. For characterization, field-emission scanning electron microscopy (FE-SEM), energy dispersive spectrometry (EDS), X-ray diffraction (XRD), N2 adsorption–desorption measurement and X-ray photoelectric spectroscopy (XPS) were carried out, and traditional water-displacement method was performed to measure the hydrogen generation rate (HGR). It was found that component and catalytic activity of the composites were greatly affected by the ratio of Co(OH)2 to NaH2PO2. When the ratio was 2:1, the obtained catalyst composed of CoO and Co2P presented the highest HGR up to 3.94[Formula: see text]L min[Formula: see text] g[Formula: see text] using a 2[Formula: see text]wt.% NaBH[Formula: see text][Formula: see text]wt.% NaOH solution at [Formula: see text]C, and the apparent activation energy was detected as low as 27.4[Formula: see text]kJ mol[Formula: see text]. Additionally, the optimum CoO[Formula: see text]Co2P catalyst still retains 60% of the initial activity after recycling four times.

Optical properties of ultrathin ZnO films fabricated by atomic layer deposition

Ultrathin zinc oxide (ZnO) films with thickness down to several nanometers have been fabricated by atomic layer deposition. The chemical composition, surface morphology, crystalline structure, optical properties and photoluminescence characteristics of the ZnO films with various thicknesses were investigated. The X-ray photoelectric spectroscopy illustrates that the deposited films are uniformly distributed with zinc and oxygen atoms. Spectroscopic ellipsometric measurements reveal that both the refractive index and extinction coefficient decrease monotonically as the thickness of the film decreases. The thickness of the ZnO films obtained via ellipsometry is consistent with X-ray reflectivity measurements. The excitonic emission peak of the photoluminescence spectrum shifts to higher energies when the film thickness decreases to a few nanometers. This blueshift phenomenon is consistent with the expansion of the fundamental optical bandgap determined from ellipsometry, which could be well described by the effective mass model using physically meaningful parameters. The results obtained in this study could provide guidance to the design and optimization of optoelectronic devices based on ultrathin ZnO films.

Sodium tungstate-promoted CaMnO3 as an effective, phase-transition redox catalyst for redox oxidative cracking of cyclohexane

Oxidative cracking, which combines catalytic oxidation and cracking reactions, represents a promising approach to reduce the energy and carbon intensities for light olefin production from naphtha. The need to co-feed gaseous oxygen with hydrocarbons, however, leads to significant COx formation and safety concerns. The cost and energy consumption associated with air separation also affects its economic attractiveness. In this study, we investigated a redox oxidative cracking (ROC) scheme and evaluated perovskites (La0.8Sr0.2FeO3 and CaMnO3) and Na2WO4-promoted perovskite (La0.8Sr0.2FeO3@Na2WO4 and CaMnO3@Na2WO4) as the redox catalysts for ROC. CaMnO3@Na2WO4 redox catalyst shows high activity, selectivity, and stability for light olefin production from cyclohexane. Operated under a redox oxidative cracking (ROC) scheme, CaMnO3@Na2WO4 enhances the catalytic cracking of cyclohexane, while showing high selectivity towards hydrogen combustion with its built-in, active lattice oxygen. Over three-fold increase in olefin yield compared to thermal cracking and 35% yield increase compared to conventional O2-cofeed oxidative cracking were achieved. Low energy ion scattering (LEIS), X-ray photoelectric spectroscopy (XPS), and differential scanning calorimetry (DSC) indicated a core-shell structure, where a molten Na2WO4 layer covers the CaMnO3 core. Na2WO4 modifies the oxygen donation behavior of CaMnO3 and provides a catalytically active surface for cyclohexane activation. In-situ XRD revealed that CaMnO3@Na2WO4 exhibited excellent structural stability and regenerability. The transformation of Mn4+ ↔ Mn3+ ↔ Mn2+ in CaMnO3, facilitated by reversible phase transition to (Ca/Mn)O solid solution, is responsible for the lattice oxygen donation and uptake during redox cycles. Electrochemical impedance spectroscopy (EIS) measurements further confirmed that the oxygen species were transported through the molten Na2WO4 layer to participate in ROC. These findings offer mechanistic insights to design effective redox catalysts for hydrocarbon valorization using the chemical looping strategy.

Co−O−P composite nanocatalysts for hydrogen generation from the hydrolysis of alkaline sodium borohydride solution

In recent years, catalytic hydrolysis of sodium borohydride is considered to be a promising approach for hydrogen generation towards fuel cell devices, and highly efficient and noble-metal-free catalysts have attracted increasing attention. In our present work, Co3O4 nanocubes are synthesized by solvothermal method, and then vapor-phase phosphorization treatment is carried out for the preparation of novel Co−O−P composite nanocatalysts composed of multiple active centers including Co, CoO, and Co2P. For catalyst characterization, field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), energy dispersive spectrometry (EDS), X-ray diffraction (XRD) and X-ray photoelectric spectroscopy (XPS) are conducted. Optimal conditions for catalyst preparation and application were investigated in detail. At room temperature (25 °C), maximum hydrogen generation rate (HGR) is measured to be 4.85 L min−1 g−1 using a 4 wt% NaBH4 − 8 wt% NaOH solution, which is much higher than that of conventional catalysts with single component reported in literature. It is found that HGR remarkably increases with the increasing of reaction temperature, and apparent activation energy for catalytic hydrolysis of NaBH4 is calculated to be 63 kJ mol−1. After reusing for five times, the Co−O−P composite nanocatalysts still retains 78% of the initial activity.

Highly selective NO2 chemiresistive gas sensor based on hierarchical In2O3 microflowers grown on clinoptilolite substrates

Hierarchical In2O3 microflowers (HIMF) were prepared via a simple one-step hydrothermal method on the surface of the clinoptilolite substrate (CS). Structural characterizations were investigated by various techniques including X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectric spectroscopy (XPS), and Fourier transform infrared spectroscopy (FTIR). The results demonstrated that the HIMF were comprised of abundant ultrathin two-dimensional nanosheets with a width of about 500 nm and the thickness of approximately 20 nm. The high-yield HIMF with a hexagonal phase were loose and uniformly distributed on the surface of the CS. The CS accompanied with the HIMF was made into a gas sensor to test NO2 sensing properties. It indicated that the gas sensor exhibited excellent NO2 sensing performance of low operating temperature, fast response, high selectivity and good reversibility. The outstanding NO2 sensing properties of the HIMF could be ascribed to its unique hierarchical structure and the synergistic effect of the CS. The possible formation process and sensing mechanism of the HIMF were proposed. The results show a potential prospect for using the natural porous mineral as the substrate to synthesize high-performance sensing material.

Physical and in-vitro evaluation of ϵ-Fe3N@Fe3O4 nanoparticles for bioapplications

Recently the core-shell nanostructures are employed for various applications. In this trend, ϵ-Fe3N@Fe3O4 (INIO) magnetic nanoparticles (core/shell structured) were synthesized by a solvothermal process followed by calcination. The X-ray diffraction (XRD), selected area diffraction pattern (SAEDP), X-ray photoelectric spectroscopy (XPS) and Mössbauer spectroscopy validates the formation of the spherical core-shell structure of the ϵ-Fe3N@Fe3O4 nanoparticles having size range (5–32 nm). The saturation magnetization values for the sample at ±2 T field were around 128 and 99 Am2/kg at 5 and 300 K respectively. The values were higher than the known values for iron oxide nanoparticles. The pluronic acid (F-127) based ferrofluid of these nanoparticles, displayed excellent stability (Zeta potential values) and good heating ability (external AC magnetic fields). The best specific loss power was found to be around 90 W/g at 23 mT field. The cell viability with human lung adenocarcinoma A549 cells was observed to be 88 and 85% at 1 mg/mL for these nanoparticles after the treatment for 24 and 48 h respectively.

Syngas production in DRM by use Ni,Pd,Pt/CaO catalyst with ZrO2 as promoter

Through adopting the co-precipitation method using K2CO3Nickel, palladium and platinum catalysts (every 1 wt.%) On CaO and ZrO2 to develop Pt,Pd and Ni /Ca1-xZrxO (where x = 0, 0.03, 0, 07 and 0.15) were manufactured. As a precipitate, X-ray diffraction (XRD), X-ray photoelectric spectroscopy (XPS), Brunauer-Emmett-Teller (BET), Transmission Electron Microscope (TEM), Programmed H2 (H2-TPR) and thermo-thermal analysis (TGA). Pt,Pd,Ni/Ca0.85Zr0.15O reported best methane dry reform (DRM) activity at 98.02% and 85.94% for Carbon dioxide and methane conversions and 1.14 for H2/CO- ratio at 900°C and 1:1 of CH4:CO2 ratio. Various effects were observed when ZrO2 was used as a catalyst promoter. First, the cubic CaO stage has stabilized. Second, there was an increase thermal stability and basic support. In the end, carbon deposits and Ni2+, Pd2+ and Pt2+ ions have shrunk

The Methods to Unlock Molybdenum Disulfide

Author(s): Rodriguez, Anthony | Abstract: In today’s world, we’ve invented many new technologies that have allowed us to map out the earth’s surface but just as we can map out surfaces in a large scale, we can also map out surfaces in a very small scale such as in nanometers. Thus, giving us opportunities to study a discover various materials such as molybdenum disulfide (MoS2) crystalline flakes. MoS2 being a material that has a similar yet different structure to graphene, low friction when compared to SiO2 (a low friction material as is), and provides many potential applications that can be implemented into aerospace as a solid lubricant. But like any fellow researcher studying a material, each has their own methods/techniques that they use to obtain results. In our proposal, we will cover the research that has taken place to provide a consensus of MoS2’s potential application as a solid lubricant in aerospace to its low frictional properties in the nanometer scale. And the technologies we’ll be looking into to access for our methods/techniques for researching will be Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM), X-Ray Photoelectric Spectroscopy (XPS), X-Ray Diffraction (XRD), and Tribometers at the University of California, Merced (UC Merced).

A Study on the Thermal Conductivity of Poly(lactic acid)/Alumina Composites: The Effect of the Filler Treatment.

The excessive utilization of petroleum-based products has given rise to environmental concerns that have led to the shift in the research interest toward recyclable and biodegradable products. Polylactic acid (PLA), an aliphatic polyester that can be obtained from renewable sources, is used in a wide range of applications in different industrial sectors. This study demonstrates the change in the thermal conductivity of 30% alumina filled PLA after a hydrophobic surface modification was applied to the filler. Fourier transmission infrared and X-ray photoelectric spectroscopy results confirmed the successful modification of the alumina particles surfaces. The improvement in the interaction between the modified alumina and PLA matrix was revealed by examining the morphology micrograph obtained by field emission scanning electron microscopy. Since alumina is a highly thermally conductive material, the enhancement in the interfacial adhesion between the filler and matrix leads to an increase of 120% in the thermal conductivity of the PLA/Alumina composite compared to that of the neat PLA. In addition, the PLA/Alumina composite showed an increase in the storage modulus due to the high stiffness of alumina.

Performances of In-doped CuO-based heterojunction gas sensor

In this work, the pure and In-doped CuO nanostructure was successfully synthesized by a simple one-step hydrothermal method. X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy and X-ray photoelectric spectroscopy were employed for characterization of the structure and morphology of the as-prepared nanostructure materials. Then, the gas sensing properties of the pure and In-doped CuO nanostructure were investigated. Compared with pure CuO, the sensors based on 2 mol% In-doped CuO exhibited enhanced gas sensing and low working temperature obviously. The response to 300 ppm ethanol gas reached to 67.1 at 116 °C, which was almost 9.5 times higher than that of pure CuO. The flow and recombination of carriers at the n–p junction are the main reason for the decrease in the carrier concentration of In2O3/CuO gas sensors in reducing gas. Therefore, we believe that the change of carrier concentration and material surface caused by In doping could be responsible for the enhancement of the gas sensing properties.

Co0.59Fe0.41P nanocubes derived from nanoscale metal–organic frameworks for removal of diethyl phthalate by activation of peroxymonosulfate

In this study, Co0.59Fe0.41P nanocubes were derived from nanoscale metal-organic frameworks to activate peroxymonosulfate (PMS) for the diethyl phthalate (DEP) removal in water. The structure, morphology, and physicochemical properties of the fresh and used materials were comprehensively studied using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and X-ray photoelectric spectroscopy. Degradation tests were performed and an excellent degradation performance was observed. The achieved DEP removal rate within a 60 min period was approximately 95%. Electron paramagnetic resonance (EPR) analysis and quenching tests showed that both sulfate and hydroxyl radicals contributed to the removal of the pollutant. The degradation products were detected by GC–MS and UHPLC-Q-TOF-MS, and the proposed degradation pathways were concluded. The study showed that the cobalt elements in the materials were the primary contributors for the activation of PMS for the removal of DEP. The reduction ability of PMS could assist in the recycling of Co3+/Co2+.

The Unoccupied Electronic States of the Ultrathin Diphenylphthalide Films on the Surface of the Highly Oriented Pyrolytic Graphite

The results of diagnostics of the atomic composition of a diphenylphthalide (DPP) film thermally precipitated in vacuum by the of X-ray photoelectric spectroscopy (XPS) method are presented. The results of examination of the unoccupied electronic states of the ultrathin DPP films with the thickness up to 10 nm on the surface of the highly oriented pyrolytic graphite (HOPG) by the total current spectroscopy (TCS) method in the energy range from 5 to 20 eV above EF are presented. In this range, the main maxima in the total current spectra are identified. The analysis of the TCS results with consideration of the theoretical calculation results has shown that the low-energy maxima observed at the energies from 6 to 7.5 eV are induced predominately by π* electron orbitals of DPP films. The values of the energy Evac in relation to EF, i.e., of the electron work function in the DPP films at the film thickness of 5–10 nm, are found experimentally at a level of 4.3 ± 0.1 eV. The negative charge transfer from an organic film to the substrate corresponds to the formation of the HOPG/DPP boundary potential barrier during the thermal deposition of the DPP film.

Degradation characteristics of membrane electrode assembly under drive cycle test protocol

ABSTRACTOne of the key factors determining the lifetime of proton exchange membrane fuel cell (PEMFC) is the degradation and eventually the failure of membrane electrode assembly (MEA). To assess the long-term durability of MEA in fuel cells for vehicular applicatoin, this study adopted the accelerating technique using drive cycle test protocol developed by Chinese NERC Fuel Cell & Hydrogen Technology. The protocol includes starts/stops, idling, and acceleration, simulating major degradation processes in real automobile application. After 900 h of accelerated test, MEA’s performance declined from the initial 0.65 V to 0.58 V@500 mA cm−2, dropping by more than 10% and giving an average voltage decay rate of 70 μV h−1. To examine the underlying mechanisms for the degradation, post-mortem analyses such as X-ray photoelectric spectroscopy (XPS), scanning electron microscopy (SEM) and energy dispersive X-Ray spectroscopy (EDX) were carried out for the MEA before and after 900 h drive cycle test. The post-mortem analyses indicate that the thinning of the electrolyte membrane at H2 outlet region is the decisive factor leading to the end-of-life of PEMFC, and the Pt catalysts loss and microstructural damage of MEA are the decisive factors for the performance degradation and stability deterioration of PEMFC.

Novel thiolated-PEG linker molecule for biosensor development on gold surfaces

The surface modifying linker molecules can directly influence the performance and longevity of biosensors. They must allow the attachment of biological recognition layer on the sensor surface, as well as the protection of the surface from fouling effects. Recent advances in this field identified several key factors that can increase the efficiency, stability and the anti-fouling effect of a layer formed by surface modifying linker molecules. Herein, this work presents a simple synthetic procedure, characterization, and application of a novel thiolated-PEG surface modifying molecule (DSPEG2) that could act as a multi-purpose linker for gold surfaces. The analyses of the molecular spatial distribution of DSPEG2 on gold surfaces were performed using time-of-flight secondary ion mass spectrometry (TOF-SIMS) imaging and X-ray photoelectric spectroscopy (XPS). The immobilization of DSPEG2 on gold surfaces was examined using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and surface plasmon resonance (SPR). Our preliminary results demonstrated that DSPEG2 is a promising novel linker molecule that can be applied in a wide range of biosensors based on gold surfaces.

Gold nanoparticles immobilized on single-layer α-zirconium phosphate nanosheets as a highly effective heterogeneous catalyst

Gold nanoparticles (Au NPs) were immobilized on single-layered α-zirconium phosphate (ZrP) nanosheets as a highly efficient heterogeneous catalyst. The nanoparticles were characterized by thermogravimetric analysis (TGA), X-ray diffraction (XRD), X-ray photoelectric spectroscopy (XPS), UV–Vis spectroscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM) techniques. The characterizations showed that the Au NPs with a size distribution of 2.0 ± 1.0 nm were uniformly dispersed and immobilized on single-layer ZrP nanosheets. The supported AuNPs could serve as an effective catalyst for the reduction of 4-nitrophenol by sodium borohydride (NaBH4).

Property Improvement of GaAs Surface by 1-Octadecanethiol Passivation

In this study the effects of 1-Octadecanethiol (ODT, 1-CH3 [CH2]17SH) passivation on GaAs (100) surface and GaAs/Al2O3 MOS capacitors are investigated. The results measured by X-ray photoelectric spectroscopy (XPS), Raman spectroscopy and scan electron microscopy (SEM) show that the ODT passivation can obviously suppress the formation of As-O bonds and Ga-O bonds on the GaAs surface and produce good surface morphology at the same time, and especially provide better protection against environmental degradation for at least 24 h. The passivation time is optimized by photoluminescence (PL), and the maximum enhancement of PL intensity was 116%. Finally, electrical property of a lower leakage current was measured using the metal-oxide-semiconductor capacitor (MOSCAP) method. The results confirm the effectiveness of ODT passivation on GaAs (100) surface.

Effects of lithium excess and SnO2 surface coating on the electrochemical performance of LiNi0.8Co0.15Al0.05O2 cathode material for Li-ion batteries

Four LiNi0.8Co0.15Al0.05-based Li-ion-battery cathode materials, i.e., the pristine LiNi0.8Co0.15Al0.05, Li-excess Li1+xNi0.8Co0.15Al0.05, SnO2-coated LiNi0.8Co0.15Al0.05 and SnO2-coated Li-excess Li1+xNi0.8Co0.15Al0.05 are prepared via a facile oxalate coprecipitation route, and are studied with respect to the effects of Li excess and SnO2 coating on the structure and electrochemical properties. X-ray diffraction and X-ray photoelectric spectroscopy demonstrate that a small amount of Li+ and/or Sn2+ ions are incorporated into the transition-metal slabs of the modified materials, and hence reduce the cationic disorder of Li+/Ni2+. High-resolution transmission electron microscopy and scanning electron microscopy confirm the formation of a SnO2 surface layer that prevents the growth and aggregation of the primary particles during high-temperature solid reaction, and therefore results in formation of the SnO2-coated materials with nano/submicron sphere-like morphology. Lithium excess and SnO2 coating enhance the electrochemical performance. The SnO2-coated Li-excess Li1+xNi0.8Co0.15Al0.05 exhibits not only higher specific capacity and better rate capability but also excellent cycling stability. After 400 cycles at 1C rate, the capacity is decreased from 123.7 to 86.7 mAh g−1, giving capacity retention of 70.1%. Li excess is believed to decrease the cationic mixing and SnO2 modification is deemed to restrict the undesirable side reaction between the active material and electrolyte.

Effectiveness of pre-silanization in improving bond performance of universal adhesives or self-adhesive resin cements to silica-based ceramics: Chemical and in vitro evidences

ObjectivesTo examine effectiveness of pre-silanization in improving bond performance of multipurpose products such as universal adhesives or self-adhesive resin cements to silica-based ceramics. MethodsThe present study investigated reactions between silanol groups of γ-methacryloxypropyltrimethoxysilane (γ-MPS) and silica, dehydration self-condensation of γ-MPS, and condensation polymerization between γ-MPS and 10-methacryloyloxydecyl dihydrogen phosphate (10-MDP) by using thermodynamic calculations. Shear bond strength (SBS) tests were used to evaluate the influence of pre-silanization on resin bonding when a silane-containing universal adhesive, a silane-unknown universal adhesive, or two self-adhesive resin cements were applied for bonding lithium disilicate to resin. In addition, reactions between silane and lithium disilicate were analyzed using X-ray photoelectric spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). ResultsAcquired thermodynamic data indicated formation of siloxane between γ-MPS and silica. However, self-condensation of γ-MPS and reaction between γ-MPS and 10-MDP consumed the silanol. Pre-silanization enhanced SBS for self-adhesive resin cements or universal adhesives when applied for bonding silica-based ceramics. Thermocycling and aging decreased SBS in most groups. XPS and FTIR supported formation of siloxane between the employed silane coupling agent and two universal adhesives and lithium disilicate. SignificancePre-silanization is beneficial in further enhancing bond performance of universal adhesives or self-adhesive resin cements to silica-based ceramics.

Незаполненные электронные состояния ультратонких пленок дифенилфталида на поверхности высокоупорядоченного пиролитического графита

AbstractThe results of diagnostics of the atomic composition of a diphenylphthalide (DPP) film thermally precipitated in vacuum by the of X-ray photoelectric spectroscopy (XPS) method are presented. The results of examination of the unoccupied electronic states of the ultrathin DPP films with the thickness up to 10 nm on the surface of the highly oriented pyrolytic graphite (HOPG) by the total current spectroscopy (TCS) method in the energy range from 5 to 20 eV above E _F are presented. In this range, the main maxima in the total current spectra are identified. The analysis of the TCS results with consideration of the theoretical calculation results has shown that the low-energy maxima observed at the energies from 6 to 7.5 eV are induced predominately by π* electron orbitals of DPP films. The values of the energy E _vac in relation to E _F, i.e., of the electron work function in the DPP films at the film thickness of 5–10 nm, are found experimentally at a level of 4.3 ± 0.1 eV. The negative charge transfer from an organic film to the substrate corresponds to the formation of the HOPG/DPP boundary potential barrier during the thermal deposition of the DPP film.