Photoelectron Spectroscopy Energy Research Articles

Preparation and properties of silver-carrying nano-titanium dioxide antimicrobial agents and silicone composite

The characteristics of dopamine self-polymerization were used to cover the nano-titanium dioxide (TiO2) surface and produce nano-titanium dioxide-polydopamine (TiO2-PDA). The reducing nature of dopamine was then used to reduce silver nitrate to silver elemental particles on the modified nano-titanium dioxide: The resulting TiO2-PDA-Ag nanoparticles were used as antimicrobial agents. Finally, the antibacterial agent was mixed with silicone to obtain an antibacterial silicone composite material. The composition and structure of antibacterial agents were analyzed by scanning electron microscopy, transmission electron microscopy, X-ray photoelectron energy spectroscopy, and X-ray diffraction. Microscopy and the antibacterial properties of the silicone antibacterial composites were studied as well. The TiO2-PDA-Ag antimicrobial agent had good dispersion versus nano-TiO2. The three were strongly combined with obvious characteristic peaks. The antibacterial agents were evenly dispersed in silicone, and the silicone composite has excellent antibacterial properties. Bacillus subtilis (B. subtilis) adhesion was reduced from 246 × 104 cfu/cm2 to 2 × 104 cfu/cm2, and colibacillus (E. coli) reduced from 228 × 104 cfu/cm2 leading to bacteria-free adhesion.

Ta3N5 Nanobelt-Loaded Ru Nanoparticle Hybrids' Electrocatalysis for Hydrogen Evolution in Alkaline Media.

Electrochemical hydrogen evolution is a highly efficient way to produce hydrogen, but since it is limited by high-cost electrocatalysts, the preparation of high-efficiency electrocatalysts with fewer or free noble metals is important. Here, Ta3N5 nanobelt (NB)-loaded Ru nanoparticle (NP) hybrids with various ratios, including 1~10 wt% Ru/Ta3N5, are constructed to electrocatalyze water splitting for a hydrogen evolution reaction (HER) in alkaline media. The results show that 5 wt% Ru/Ta3N5 NBs have good HER properties with an overpotential of 64.6 mV, a Tafel slope of 84.92 mV/dec at 10 mA/cm2 in 1 M of KOH solution, and good stability. The overpotential of the HER is lower than that of Pt/C (20 wt%) at current densities of 26.3 mA/cm2 or more. The morphologies and structures of the materials are characterized by scanning electron microscopy and high-resolution transmission electron microscopy, respectively. X-ray photoelectron energy spectroscopy (XPS) demonstrates that a good HER performance is generated by the synergistic effect and electronic transfer of Ru to Ta3N5. Our electrochemical analyses and theoretical calculations indicate that Ru/Ta3N5 interfaces play an important role as real active sites.

Molecular traps and exposed Mo sites induced by oxygen knockout enhanced H2S sensing of MoO3 nanoflowers

Limited by the dense arrangement of oxygen atoms in the outer layer, the active Mo sites of MoO3 ultrathin nanoflowers are shielded by oxygen, making it difficult for efficient gas adsorption. Here, oxygen atoms on the surface of MoO3 nanoflowers (MoO3 NFs) were knocked out based on a simple hydrogenation strategy to obtain MoO3 defective nanoflowers (MoO3 DNFs) with abundant molecular traps and exposed Mo sites. Notably, the response of MoO3 DNFs-10 to 2 ppm H2S is 3 times that of MoO3 NFs. Oxygen atom knockout was verified based on Laser Raman Spectroscopy, Photoluminescence (PL), UV–Visible Spectroscopy (UV–Vis), and X-ray photoelectron energy Spectroscopy (XPS), while calculations based on density functional theory (DFT) were used to reveal the sensing enhancement of molecular traps and exposed Mo sites. On the one hand, molecular traps can effectively trap H2S molecules to facilitate further adsorption. On the other hand, exposed Mo sites have higher charge activity and exhibit higher adsorption capacity for H2S gas. This work breaks through the limitations of the traditional oxygen vacancy model and innovatively discusses the synergistic effect of molecular traps and exposed Mo sites on enhanced sensing, which can provide a reference for the gas sensing by metal oxide semiconductors.

Application on oxidation behavior of metallic copper in fire investigation

Abstract In fire investigations, the most important aspect is determining the presence of a liquid accelerant at the fire scene. The presence or absence of accelerants is critical evidence during trials for fire cases. Upon exposure to high temperatures, metallic substances undergo oxidation, which can be imparted by accelerants in the fire. Oxides and substrates found on metal surfaces offer valuable information on the characteristics of fire, including exposure temperature, duration, and involvement of a liquid accelerant. In this study, we investigated the oxidation behavior of copper at high temperatures in a simulated flame environment using ethanol combustion. After oxidation, the morphological, oxide phase composition, and microstructural features of specimens were characterized by observation, X-ray diffraction, X-ray photoelectron energy spectroscopy, transmission electron microscopy, and scanning electron microscopy with energy-dispersive spectroscopic analysis. The elemental carbon with a hexagonal structure deposited on the sample’s surface was found, which may be incomplete combustion and the chemical composition of ethanol. Copper has a preferred orientation of oxide on the (111) crystal plane, which differs from oxidation in ordinary hot air that is related to the large Coulomb force of the (111) crystal plane. Hot air convection due to combustion may cause large areas of oxide layer on the copper surface to crack and peel. Oxide properties and surface state of metals strongly depended on oxidation duration, temperature, and atmosphere. These data shall offer reference information for determining the presence of combustion accelerants at fire scenes.

A new benchmark of soft X-ray transition energies of mathrm {Ne}, mathrm {CO}_2, and mathrm {SF}_6: paving a pathway towards ppm accuracy

A key requirement for the correct interpretation of high-resolution X-ray spectra is that transition energies are known with high accuracy and precision. We investigate the K-shell features of mathrm {Ne}, mathrm {CO}_2, and mathrm {SF}_6 gases, by measuring their photo ion-yield spectra at the BESSY II synchrotron facility simultaneously with the 1s–np fluorescence emission of He-like ions produced in the Polar-X EBIT. Accurate ab initio calculations of transitions in these ions provide the basis of the calibration. While the mathrm {CO}_2 result agrees well with previous measurements, the mathrm {SF}_6 spectrum appears shifted by sim 0.5 eV, about twice the uncertainty of the earlier results. Our result for mathrm {Ne} shows a large departure from earlier results, but may suffer from larger systematic effects than our other measurements. The molecular spectra agree well with our results of time-dependent density functional theory. We find that the statistical uncertainty allows calibrations in the desired range of 1–10 meV, however, systematic contributions still limit the uncertainty to {sim }40–100 meV, mainly due to the temporal stability of the monochromator energy scale. Combining our absolute calibration technique with a relative energy calibration technique such as photoelectron energy spectroscopy will be necessary to realize its full potential of achieving uncertainties as low as 1–10 meV.Graphical abstract

Enhanced photocatalytic performance and stability of multi-layer core-shell nanocomposite C@Pt/MoS2@CdS with full-spectrum response

The nanocomposite material C@Pt/MoS 2 @CdS was prepared by a simple microwave-assisted hydrothermal method combined with photoreduction method. The crystal structure, microstructure, and surface physical chemistry properties of the material were analyzed by X-ray diffraction (XRD), ultraviolet–visible diffuse reflectance absorption spectroscopy (UV–vis/DRS), X-ray photoelectron energy spectroscopy (XPS), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HR-TEM), nitrogen adsorption–desorption measurement, photoluminescence spectroscopy (PL), and electrochemical tests. As a result, this material has full-spectrum light absorption property and the composited CdS presents a good hexagonal phase. Moreover, the composite material presents a nanorod-like multi-layer core-shell structure, wherein the rod-like MoS 2 @CdS surface is covered with Pt and C. The formation of the multi-layer core-shell structure increases the specific surface area of as-composite material and strengthens its light absorption performance. The electrochemical impedance and transient photocurrent test results show that C@Pt/MoS 2 @CdS has the highest charge separation efficiency and enhanced photocurrent density compared with other systems. Photogenerated charge carriers have higher separation efficiency, and photogenerated electrons and holes exhibit longer life. During the photocatalysis experiments, the nanocomposite C@Pt/MoS 2 @CdS shows enhanced photodegradation activity under multi-modal photocatalytic experiments and excellent stability under visible light irradiation. In addition, C@Pt/MoS 2 @CdS has a strong photocatalytic water splitting ability. Under the same experimental conditions, its hydrogen production is 60 times that of commercially available P25. Through capture experiments, the reactive species in the photocatalytic reaction process were determined, and the possible photocatalytic reaction mechanism of this multi-layer core-shell C@Pt/MoS 2 @CdS nanocomposite was inferred. • Constructed a multi-layer core-shell structure photocatalytic composite material. • Improved the photocatalytic activity and stability of CdS-based photocatalyst. • The hydrogen production of C@Pt/MoS 2 @CdS was approximately 60 times that of commercially available P25. • Recombination rate of photogenerated charge carriers was effectively restrained.

Fabrication and Study of the Electronic Structure of МоO3/Мо Nanofilms

The composition, the surface morphology, and the crystalline and electronic structure of МоО3 nanofilms are studied using a set of methods, namely, scanning electron spectroscopy and high energy electron diffraction, photoelectron spectroscopy, and secondary electron emission. These nanofilms are obtained by implanting $${\text{O}}_{{\text{2}}}^{{\text{ + }}}$$ ions into a Mo single crystal heated to Т = 850 K. Films with different thicknesses (~30, 60, and 90 A) are obtained at an ion energy of 1–5 keV and a dose of D = (4–8) × 1017 cm–2. It is shown that a continuous and homogeneous polycrystalline МоО3 film with a surface roughness of at most 1.5 nm is formed. The band gaps of these films are ~3.4 eV, and the widths of the conduction bands are 4.5 eV. It is discovered that there are four maxima of the density of electronic states in the valence band; probably, they are due to hybridization of the N5, N45, N4 energy levels of Mo with the L2, L23, and L3 energy levels of oxygen.

Surface Organic Modification of CaCO3-TiO2 Composite Pigment

To improve the properties and dispersibility of CaCO3-TiO2 composite pigments (CaCO3-TiO2) in organic matrices, the surface modification of CaCO3-TiO2 was performed with sodium stearate (SS) as an organic modifier by wet ultra-fine grinding in a stirred mill. The pigment properties of modified CaCO3-TiO2 and its dispersibility in organic media were tested and characterized. The binding mechanism between CaCO3-TiO2 and SS was explored by infrared spectrometry (IR) and X-ray photoelectron energy spectroscopy (XPS). The results showed that the mechanical grinding strength and SS dosage had a significant effect on the activation index and sedimentation rate of CaCO3-TiO2. After surface modification, the surface of CaCO3-TiO2 turned from a hydrophilic surface to a hydrophobic surface and the surface free energy was reduced. In addition, the hiding property and dispersibility of CaCO3-TiO2 in the organic medium were significantly improved. IR and XPS results indicated that the modifier SS was adsorbed on the surface of CaCO3-TiO2 by chemical combination.

Effect of Zn addition on the direct synthesis of hydrogen peroxide over supported palladium catalysts

Alumina-supported Pd-Zn bimetallic catalysts were prepared and evaluated for direct synthesis of hydrogen peroxide. The effect of Zn on the catalytic performance was studied via characterizations by transmission electron microscopy (TEM), temperature-programmed reduction (TPR), X-ray photoelectron energy spectroscopy (XPS), temperature-programmed desorption of H2/O2 (H2-/O2-TPD), CO chemisorption and diffuse reflectance infrared Fourier transform spectroscopy of CO adsorption (CO-DRIFTS). H2O2 productivity of up to 25431molkgPd−1h−1 was observed with the optimal bimetallic catalyst 1Pd5Zn, much higher than that over the monometallic catalyst 1Pd (8533molkgPd−1h−1). This increase may be attributed to the geometric change caused by the Zn additive and the electronic interactions between Pd and Zn. The addition of Zn increases the isolated Pd sites (the primary active sites for H2O2 formation), which can promote H2O2 selectivity. PdZn catalysts show a higher Pd dispersion and incremental Pd0 content than monometallic Pd owing to electronic interactions between Pd and Zn, which result in increased H2O2 productivity. However, a high Pd dispersion and incremental Pd0 content can increase the H2O2 hydrogenation rate, negatively affecting the H2O2 selectivity.

Co-electrodeposition of MnO2/graphene oxide coating on carbon paper from phosphate buffer and the capacitive properties

MnO2/graphene oxide sheet composite (MnO2/GOS) has been co-electrodeposited on the thermally treated carbon paper (TTCP) in phosphate buffer solution containing GOS and KMnO4. The resulted samples have been characterized by scanning and transmission electron microscopy, Raman, X-ray diffraction, and X-ray photoelectron energy spectroscopy. The results show that the synthesized MnO2 may be δ-MnO2 and the morphology of MnO2/GOS is very different from that of MnO2, indicating that the introduction of GOS in electrolyte can influence the morphology during the deposition. The capacitive properties of the samples are investigated by using cyclic voltammetry, galvanostatic charge/discharge, and electrochemical impedance spectroscopy. The specific capacitance of MnO2 for MnO2/GOS can reach about 829 F g−1 at discharged current density of 1.0 A g−1 in 1 M Na2SO4 aqueous solution, which is larger than that of MnO2 deposited on TTCP. The composite of MnO2/GOS also exhibits excellent cyclic stability with a decrease of 18.5 % specific capacitance after 1,500 cycles.

Monolithic coal-based carbon counter electrodes for highly efficient dye-sensitized solar cells

A novel method for the preparation of monolithic coal-based porous carbon counter electrodes (CEs) for high performance dye-sensitized solar cells has been reported. Rigid monolithic coal-based carbon CE has been synthesized by preferential densification of one side of porous carbon plate formulated by caking bituminous coal powder. The phase, surface composition, and surface micro&nanotexture of the monolithic porous carbon plates have been characterized by X-ray diffraction, X-ray photoelectron energy spectroscopy, nitrogen sorption, scanning electron microscopy, and transmission electron microscopy. The coal-based carbon monolithic CEs exhibit a low internal resistance and high energy conversion efficiency (up to 6.38%). When the surface of the porous substrate was modified with mesoporous carbon as catalytic layer, the energy conversion efficiency can be further enhanced up to 8.73%, which is comparable to that of the platinized fluorine-doped tin oxide glass based device.

A mobile UHV-system designed for femtosecond time, energy and spin resolved photoelectron spectroscopy

We report on the design and tests of a completely mobile photoemission end station for femtosecond time, energy and spin resolved magnetodynamics experiments. The setup is designed for the use at free-electron laser (FEL) x-ray beamlines as well as at synchrotron facilities. In situ sample preparation in an adjacent UHV chamber is performed. The assembly can be altered to obtain energy resolved measurements with the help of a hemispherical electron energy analyzer or to obtain energy integrated measurements by inserting an electron transfer lens system. The magnetic information is obtained by spin analysis with a 50 kV Mott detector. The setup is tested in house with an electron gun, at the Swiss Light Source (SLS) and has been used at the FEL at FLASH in Hamburg. Results show the practicability of the system and exemplarily the kinetic energy dependent polarization of the low energy secondary electrons emitted from a 15 ML iron film on W(110) is presented.

Solvothermal synthesis of boron-doped graphene and nitrogen-doped graphene and their electrical properties

In this work, pristine graphene, nitrogen-doped graphene and boron-doped graphene were synthesized by a facile solvothermal process using potassium or lithium nitride as catalyst. The formation mechanism of graphene and doped graphene was discussed, and the chlorine gas generated during the reaction performed a significant role. High yield of graphene and doped graphene can be produced via the solvothermal route with relatively mild conditions, and X-ray photoelectron energy spectroscopy analysis confirmed the doping status and concentration of nitrogen or boron within graphene sheets. Especially, electrical properties of graphene-based field effect transistors revealed that the introduction of nitrogen or boron atoms into graphene sheets can effectively tailor electrical property of graphene from conducting characteristics to semiconducting behaviors.

The capacitive properties of amorphous manganese dioxide electrodeposited on different thermally-treated carbon papers

The surface structure of the commercial carbon paper (CP) has been modified through thermal treatment, and then MnO2 was electrodeposited on the thermally-treated carbon paper (TTCP) by cyclic voltammetry (CV) method in the phosphate buffer solution (PBS, pH 9.18) containing KMnO4. The obtained samples were characterized by X-ray diffraction (XRD), X-ray photoelectron energy spectroscopy (XPS) and scanning electron microscopy (SEM). The results showed that the phase of the obtained MnO2 was amorphous, and that the morphology of the MnO2 deposited on the substrates was influenced strongly by the substrates. The capacitive properties of MnO2 deposited on the carbon substrates were investigated by CV, galvanostatic charge/discharge, electrochemical impedance spectroscopy technique. It was found that the specific capacitance of MnO2 deposited on the optimum TTCP can reach to 749Fg−1 based on the charge/discharge measurement, which was far larger than that on the CP (345Fg−1).

Solvothermal synthesis of solid and hollow CoO nanospheres and their electrochemical properties in lithium-ion battery

Solid and hollow CoO nanospheres were synthesized by solvothermal method with oleic acid as reactant and SiO2 as template. Each sample of high-purity CoO was characterized by X-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy and X-ray photoelectron energy spectroscopy, respectively. Both solid and hollow CoO nanospheres as anode for lithium-ion battery were tested by galvanostatic discharge–charge experiments. The first discharge capacity of 1598 and 1640 mAh g−1 was obtained at 0.1C for solid and hollow CoO nanospheres, respectively. Hollow CoO nanospheres showed better cycle performance.

Photoelectron Spectroscopy of LiV2O4with Photons from 8.4 to 8100 eV: Bulk Sensitivity, Hybridization, and Recoil Effects

Hard- and soft-X-ray photoelectron spectroscopies (HAXPES and SXPES) are very powerful for studying the bulk electronic structures of strongly correlated electron systems. The presence of an intrinsic surface layer on clean fractured surfaces is demonstrated for LiV 2 O 4 . In this material, single-nucleus recoil effects are very prominent not only for all core levels but also for valence states at 20 K. However, such recoil effects are negligible in VO 2 even at 350 K in spite of the fact that VO 2 has a similar V–O 6 octahedron structure. The marked intensity increase in the high-binding-energy part of the so-called O 2p band relative to the V 3d band in HAXPES is interpreted to be due to the V 4s state contribution. Very high resolution extremely low energy photoelectron spectroscopy (ELEPES) is performed with Kr and Xe lamps at 10.1 and 8.4 eV, respectively, demonstrating its bulk sensitivity for this material with heavy-Fermion-like behavior.

Investigation of epitaxial Nd1.85Ce0.15CuO4 − y film surface by low energy electron diffractometry

The surface of epitaxial Nd1.85Ce0.15CuO4 − y (001) (NCCO) film has been studied by low energy electron diffractometry (LEED) and photoelectron spectroscopy. Ar+ ion etching of a surface with subsequent annealing in oxygen at atmosphere pressure has been found to lead to the ordered structure restoration of surface layers with the symmetry type and lattice parameters corresponding to the NCCO phase. Annealing in vacuum at temperatures close to the boundary of thermodynamic phase stability results in the formation of epitaxial Ce0.5Nd0.5O1.75 phase on a surface that is indicated in the LEED pattern as additional spots corresponding to the surface lattice (√2 × √2)R45°.

X-ray photoelectron spectroscopy energy band alignment of spin-on CoTiO3 high-k dielectric prepared by sol-gel spin coating method

The characteristics of CoTiO3 high-k dielectric prepared by sol-gel spin coating method had been demonstrated. High electrical permittivity (k∼40.2) of CoTiO3 dielectric was extracted via the transmission electron microscopy image and capacitance-voltage curves. In addition, the valence band offset between thermal SiO2 and spin-on CoTiO3 was about 4.0 eV, which was detected by x-ray photoelectron spectroscopy. The band gaps of thermal SiO2 and spin-on CoTiO3 were 9.0 and 2.2 eV, respectively. Energy band alignment of spin-on CoTiO3 directly with SiO2 and indirectly with Si was determined in this work.

Potential and restriction of high resolution, high energy photoemission in 400–8,000 eV for studying strongly correlated electron systems

High energy photoelectron spectroscopy (PES) is an essential tool to overcome the high surface sensitivity of the conventional photoelectron spectroscopy for the study of bulk electronic structures of strongly correlated electron systems, which often have many different electronic structures in the surface and the bulk. The potential of the soft X-ray ARPES (SX-ARPES) in the several hundred eV region for bulk Fermiology of such systems is first demonstrated. Higher bulk sensitivity is achieved by hard X-ray PES (HAXPES) beyond several keV. Deconvolution of the surface, subsurface and bulk is feasible by combining SX-PES and HAXPES spectra measured at several very different h ν. Recoil effects of photoelectrons are observed in HAXPES not only in core spectra but also in valence band spectra of some materials with light elements. The present status and future possibility of high energy PES are discussed.

Ultrahigh-Resolution Vacuum Ultraviolet Light Source System for Extremely Low Energy Photoelectron Spectroscopy

We propose an efficient monochromatization method for the new ultrahigh-resolution Ar, Kr, and Xe light sources to be used for extremely low energy photoelectron spectroscopy (ELEPES). By fully utilizing the short-wavelength transmittance limits known as the Urbach tail of LiF, CaF2, and sapphire, we can extract only the longest wavelength lines of the resonance lamp with Ar, Kr, and Xe gases by using LiF heated up to ∼50 °C as well as CaF2 and sapphire at room temperature. The full width at half maximum of the longest wavelength Xe I resonance line is found to be narrower than 500 µeV. Using these light sources, we can perform ELEPES in laboratories at three photon energies with ultrahigh energy resolution and high efficiency.