Chemical States Of Oxygen Research Articles

Cobalt-doped ZnO nanoparticles and PLD-deposited thin film forms: structure, optical properties and nature of magnetic anisotropy.

Cobalt-doped zinc oxide nanoparticles (NPs) were synthesized using a modified sol-gel method. Thereafter, the obtained powder was deposited on a Suprasil glass substrate by employing a pulsed laser deposition (PLD) technique. X-ray diffraction analysis with Rietveld refinement confirmed a hexagonal wurtzite ZnO phase belonging to the P63 mc space group for both samples in the NP and thin film forms. In particular, the thin film exhibited an intensive (002) XRD peak, indicating that it had a preferred c-axis orientation owing to the self-texturing mechanism. No segregated secondary phases were detected. The crystallite structure, morphology, and size were investigated using high-resolution transmission electron microscopy (HRTEM). To study the crystalline quality, structural disorder, and defects in the host lattice, we employed Raman spectroscopy. UV-vis-NIR spectroscopy was performed to confirm the nature of the Co-doped ZnO NP powder and the film. The chemical states of oxygen and zinc in the thin film sample were also investigated via X-ray photoelectron spectroscopy (XPS). The M-T curve could be successfully fitted using both the three-dimensional (3D) spin-wave model and Curie-Weiss law, confirming the mixed state existence of weak ferromagnetic (FM) and paramagnetic (PM) phases. Magnetic interaction was quantitatively studied and explained by polaronic percolation of bound magnetic polarons (BMPs). Analysis of magnetic symmetry of the topological antiferromagnetic as-deposited thin film using torque measurements was performed. Based on a phenomenological model, it was revealed that the structure gives rise to uniaxial magneto-crystalline anisotropy (UMA) with the magnetic easy axis parallel to the c-axis.

Intrinsic Carbon Defects for the Electrosynthesis of H2O2.

Carbon materials have manifested promising potential in electrochemical reduction of O2 to H2O2. The oxygen functional groups have been identified as the catalytic sites. However, the intrinsic carbon defects abundant in carbon materials have often been neglected. Herein, a three-dimensional carbon framework with abundant intrinsic defects and oxygen functional groups (the oxygen content and chemical states of oxygen are comparable to those of commercial carbon black) was introduced and exhibited outstanding catalytic activity and selectivity toward H2O2 electrosynthesis. Through a combination of in situ Raman spectroscopy and density functional theory calculations, the intrinsic carbon defects, such as zigzag edge and zigzag pentagon sites with optimal binding energy for OOH, were also determined to be active sites. It was further revealed that intrinsic carbon defects with large negative charge density and asymmetric spin density may have high activity toward H2O2 production.

Structure, microstructure and surface of Nd3+-doped mesoporous anatase-phase TiO2

We prepared nanocrystalline mesoporous anatase-phase TiO2 doped in the range from 0.0 to 1.0 at.% of Nd3+ by the reverse microemulsion method (RMM). The analysis of electron microscopy of the nanocrystal revealed a truncated-tetragonal bipyramidal shape and agglomerates of spheroidal nanoparticles with inter-particle porosity. The inductively coupled plasma (ICP) technique corroborated the doping concentrations. The analysis of structural parameters by the Rietveld refinement technique indicated the variation of Ti–O(1) and Ti–O(2) bond lengths, suggesting the Nd3+ insertion in the lattice. The microstructural analysis by the Williamson–Hall plot (WH) and whole powder pattern fitting (WPPF) revealed that the doping addition has a slight inhibition effect on the crystal size (6–8 nm) with a minor strain increment. The surface analysis from N2 adsorption/desorption isotherms showed that the incorporation of the dopant in low amounts improved the mesoporous structure stability, increased the diameter of opening pores, and changed the pore structure network. The XPS analysis of the chemical states on the surface suggests that the Nd3+ presence changed the Ti 2p region and the presence of the two chemical states of oxygen (OI and OII).

Influence of Argon/oxygen Ratio on Linear and Nonlinear Optical Properties of Copper Doped ZnO Films

Copper (Cu)-doped ZnO (CZO) films were grown by simultaneous direct current and radio frequency magnetron sputtering technique under the situation of different gas flow rates of Ar: O2 (1:1, 2:1 and 1:0). The X-ray diffraction patterns revealed the naturally polycrystalline ZnO films with the predominant reflection (002) peak, which referred to the hexagonal wurtzite structure toward c-axis. The elemental composition of thin films was analyzed by energy dispersive spectroscopy (EDS). The Cu concentrations in thin films increased with Ar ratio of up to 1:0. The EDS spectra of three kinds of elements indicate that Cu-doping has obvious and sophisticated effect on the chemical state of oxygen, but less effect on those of copper and zinc. Furthermore, the nonlinear absorption of CZO films was investigated by the way of Z-scan technique. These films demonstrated good nonlinear absorption behavior for the different gas flow rates of Ar: O2.

Quantum Effects for a Proton in a Low-Barrier, Double-Well Potential: Core Level Photoemission Spectroscopy of Acetylacetone.

We have performed core level photoemission spectroscopy of gaseous acetylacetone, its fully deuterated form, and two derivatives, benzoylacetone and dibenzoylmethane. These molecules show intramolecular hydrogen bonds, with a proton located in a double-well potential, whose barrier height is different for the three compounds. This has allowed us to examine the effect of the double-well potential on photoemission spectra. Two distinct O 1s core hole peaks are observed, previously assigned to two chemical states of oxygen. We provide an alternative assignment of the double-peak structure of O 1s spectra by taking full account of the extended nature of the wave function associated with the nuclear motion of the proton, the shape of the ground and final state potentials in which the proton is located, and the nonzero temperature of the samples. The peaks are explained in terms of an unusual Franck-Condon factor distribution.

Molecular Orbital Principles of Oxygen-Redox Battery Electrodes.

Lithium-ion batteries are key energy-storage devices for a sustainable society. The most widely used positive electrode materials are LiMO2 (M: transition metal), in which a redox reaction of M occurs in association with Li+ (de)intercalation. Recent developments of Li-excess transition-metal oxides, which deliver a large capacity of more than 200 mAh/g using an extra redox reaction of oxygen, introduce new possibilities for designing higher energy density lithium-ion batteries. For better engineering using this fascinating new chemistry, it is necessary to achieve a full understanding of the reaction mechanism by gaining knowledge on the chemical state of oxygen. In this review, a summary of the recent advances in oxygen-redox battery electrodes is provided, followed by a systematic demonstration of the overall electronic structures based on molecular orbitals with a focus on the local coordination environment around oxygen. We show that a π-type molecular orbital plays an important role in stabilizing the oxidized oxygen that emerges upon the charging process. Molecular orbital principles are convenient for an atomic-level understanding of how reversible oxygen-redox reactions occur in bulk, providing a solid foundation toward improved oxygen-redox positive electrode materials for high energy-density batteries.

Characterization of novel BaZnSnO thin films by solution process and applications in thin film transistors

A novel BaZnSnO semiconductor is fabricated using solution process and the influence of Ba addition on the structure, the chemical state of oxygen and electrical performance of BaZnSnO thin films are investigated. A high performance BaZnSnO-based thin film transistor with 15mol% Ba is obtained, showing a saturation mobility of 1.94cm2/Vs, a threshold voltage of 3.6V, an on/off current ratio of 6.2×106, a subthreshold swing of 0.94V/decade, and a good bias stability. Transistors with solution processed BaZnSnO films are promising candidates for the development of future large-area, low-cost and high-performance electronic devices.

Engineering of electronic and optical properties of ZnO thin films via Cu doping

ZnO thin films doped with different Cu concentrations are fabricated by reactive magnetron sputtering technique. XRD analysis indicates that the crystal quality of the ZnO:Cu film can be enhanced by a moderate level of Cu-doping in the sputtering process. The results of XPS spectra of zinc, oxygen, and copper elements show that Cu-doping has an evident and complicated effect on the chemical state of oxygen, but little effect on those of zinc and copper. Interestingly, further investigation of the optical properties of ZnO:Cu samples shows that the transmittance spectra exhibit both red shift and blue shift with the increase of Cu doping, in contrast to the simple monotonic behavior of the Burstein-Moss effect. Analysis reveals that this is due to the competition between oxygen vacancies and intrinsic and surface states of oxygen in the sample. Our result may suggest an effective way of tuning the bandgap of ZnO samples.

Physicochemical Origin for Free Radical Generation of Iron Oxide Nanoparticles in Biomicroenvironment: Catalytic Activities Mediated by Surface Chemical States

A wide range of nanoparticles (NPs) have been found to generate free radicals in biological systems. Hence, it is hypothesized that free radical generation may play a key role in the mechanism of nanomaterial toxicity in vivo. However, the main physicochemical basis for the free radical generation particularly in the biomicroenvironment has not yet been fully established. In this study, we performed comprehensive spectroscopic techniques to probe the physicochemical origin of free radical generation induced by iron oxide nanoparticles in biomicroenvironment. We demonstrated that α-Fe2O3 and γ-Fe2O3 NPs induced hydroxyl radical (•OH) via homogeneous and heterogeneous Fenton process, depending on the biological microenvironment of pH and reducing agent presence. The physicochemical structures such as chemical states of oxygen and iron on nanosurface are the key factors in the homogeneous and heterogeneous catalytic reactions. A noteworthy finding was that in situ surface reduction of Fe2O3 NPs occurred in t...

Properties of Cu-doped ZnO films by RF sputtering method: Thickness dependence

We present results concerning the thickness dependence of structural, morphological and optical properties of the Zn0.98Cu0.02O films deposited on glass substrates using radio frequency (RF) sputtering method. The microstructure and the chemical state of oxygen, copper and zinc in ZnO and Zn0.98Cu0.02O films were investigated by X-ray diffraction spectroscopy (XRD) and X-ray photoelectron spectroscopy (XPS), respectively. The results indicate that Zn0.98Cu0.02O films are the wurtzite structure with strong c-axis orientation. Crystallinity of the films is closely related to the film thickness. With increasing film thickness, there are more surface (mainly nanopores) defects existing in the Zn0.98Cu0.02O films and surface roughness increases. XRD and XPS data show that the valence state of copper in the Zn0.98Cu0.02O films is Cu2+. The transparency of all films is more than 85% in the visible region.

A comparative study of the microstructures and optical properties of Cu- and Ag-doped ZnO thin films

Abstract Cu- and Ag-doped ZnO films were deposited by direct current co-reactive magnetron sputtering technique. The microstructure, the chemical states of the oxygen, zinc, copper and silver and the optical properties in doped ZnO films were investigated by X-ray diffraction spectroscopy (XRD), X-ray photoelectron spectroscopy (XPS) and UV–Visible spectroscopy. XRD analysis revealed that both of Cu- and Ag-doped ZnO films consist of single phase ZnO with zincite structure while the doping elements had an evident effect on the (0 0 2) preferential orientation. The XPS spectra showed that the chemical states of oxygen were different in Cu- and Ag-doped ZnO thin films, which may lead to the shift of the band gap as can be observed in the transmittance and absorption spectra. Meanwhile, the widths of band tails of ZnO films became larger after Cu and Ag doping.

X-ray diffraction spectroscopy and X-ray photoelectron spectroscopy studies of Cu-doped ZnO films

Cu-doped ZnO films have been prepared using direct current co-reactive magnetron sputtering technique at different oxygen partial pressures. The microstructure and the chemical state of oxygen, copper and zinc in ZnO films was investigated by X-ray diffraction spectroscopy (XRD) and X-ray photoelectron spectroscopy (XPS), respectively. The results indicate that ZnO films with moderate Cu doping can obtain wurtzite structure with strong c-axis orientation. The crystal quality of the ZnO:Cu films can also be enhanced with moderate enrichment of oxygen in the sputtering process. The XPS spectra of zinc, oxygen and copper results also show that moderate enrichment of oxygen is helpful for the stoichiometry of the ZnO:Cu films, which is consistent with the analysis results of XRD.

Optimization of growth conditions of ZnO nano thin films by chemical double dip technique

Zinc oxide (ZnO) nano thin films have been deposited by the chemical double-dip technique using aqueous ZnSO4 and NaOH solutions. The ZnO films were characterized in terms of surface morphology by x-ray diffraction, energy-dispersive x-ray analysis (EDX), the use of a scanning electron microscope (SEM) and atomic force microscope (AFM) for surface morphology. The films exhibited a smooth morphology. The chemical states of oxygen and zinc in the ZnO nano thin films were also investigated by x-ray photoelectron spectroscopy (XPS). In the present investigations, highly textured ZnO thin films with a preferential (002)-orientation were prepared on glass substrates. The deposition conditions were optimized to obtain device-quality films for practical applications.

Effect of Al-plasma based ion implantation on the composition and phase structure of AgMgNi alloy surface

Al-plasma based ion implantation (Al-PBII) into AgMgNi alloy is carried out using metal plasma generated from the unbalanced magnetron sputtering (UBMS) and RF stimulating. The depth profile and the chemical states of Al and O are analyzed using XPS. The phase structures of the samples before and after the implantation are determined by XRD analysis. The results show that an Al implantation layer appears on the surface of AgMgNi alloy substrates and the concentration of Al decreases gradually as the depth increases. There are three chemical states of Al in the implantation layer: pure Al, Al in solid solution and as Al 2O 3 and two chemical states of oxygen, i.e. solid solved oxygen and oxygen in Al 2O 3. The effect of the distance from magnetron target to substrates ( D s− t ) on the surface structure has also been studied. Comparing the surface structures before and after implantation shows that: with a shorter D s− t of 200 mm, the lattice constant α of the Ag phase in the implantation layer of AgMgNi alloy substrate decreases, while the intensity of the peak defined as the (311) plane increases; when D s− t is increased to 300 mm, the lattice constant α increases with no significant change of the intensity of the peak of any plane. At a moderate D s− t of 250 mm, no significant change of α can be detected, but the intensity of the peak defined as (311) increases. The reason for the changes of the surface structure of AgMgNi alloy is the formation of an Ag–Al implantation layer and the collision cascades of Ar + in the surface of the substrate.

X-ray photoelectron spectroscopy investigation on chemical states of oxygen on surfaces of mixed electronic–ionic conducting La 0.6Sr 0.4Co 1− yFe yO 3 ceramics

The chemical state of oxygen on the surfaces of mixed electronic–ionic conducting La 0.6Sr 0.4Co 1− y Fe y O 3 ceramics was characterized by X-ray photoelectron spectroscopy (XPS). It was ascertained that there are five different kinds of oxygen on the ceramic surfaces, including lattice oxygen (O L), chemisorbed oxygen (O C) in the forms of O 2−, O −, and O 2 −, and oxygen in hydroxyl environment (O H). The concentration of O C+O H relative to total detected oxygen enhanced with the increase of Co/Fe ratio. In order to examine the relation between the chemical states of oxygen on the surfaces and the electrical nature of the ceramics, the mixed electronic–ionic conducting properties were investigated. At an identical measuring temperature, the electronic conductivity and ionic conductivity of La 0.6Sr 0.4Co 1− y Fe y O 3 ceramics tended to rise with the increase of Co/Fe ratio. It was considered that the mixed electronic–ionic conducting properties are responsible for the complex chemical states of oxygen on the ceramic surfaces.

X-ray photoelectron spectroscopy and auger electron spectroscopy studies of Al-doped ZnO films

The chemical state of oxygen, aluminum and zinc in Al-doped ZnO (ZAO) films was investigated by X-ray photoelectron spectroscopy (XPS), as well as the transition zone of the film-to-substrate, by auger electron spectroscopy (AES). The results show that zinc remains mostly in the formal valence states of Zn 2+. A distinct asymmetry in Al 2p 3/2 photoelectron peaks has been resolved into two components, one is metallic Al and the other is oxidized Al. The depth profile of the two components revealed that metallic Al mainly exists in the thin surface layer. The close inspection of O1s shows that O1s is composed of three components, centered at 530.15±0.15, 531.25±0.20 and 532.40±0.15 eV, respectively. AES reveals an abrupt transition zone between the ZAO and quartz substrate.

Chemical states of oxygen implanted in SUS 304 stainless steel and pure metals studied by in situ XPS using synchrotron radiation

The chemical states of oxygen implanted in SUS304 stainless steel and pure metals (Fe,Ni,Cr) by O2+ ion bombardment have been investigated by means of X-ray photoelectron spectroscopy (XPS) using synchrotron soft X-ray. For SUS304, all of implanted oxygen is chemically combined with the constituent metals, forming metallic oxides. For pure metals, on the other hand, only a part of implanted oxygen react with the target metals. The other part of the implanted oxygen in pure metals does not react with the target, and they are inserted into the crystal lattice (we call them as “dissolved oxygen”). The ratio of “dissolved oxygen” to the reacted oxygen depends on the chemical reactivity of target metals.

Chemical state of oxygen in Ag+/Na+ ion-exchanged sodium silicate glass

Chemical state of oxygen in Ag+/Na+ ion-exchanged sodium silicate glass

Chemical state of oxygen in Ag +/Na + ion-exchanged sodium silicate glass

The chemical state of oxygen in Ag +/Na + ion-exchanged sodium silicate glass was investigated using X-ray photoelectron spectroscopy and 29Si nuclear magnetic resonance spectroscopy. Ion-exchange treatment was performed on 34Na 2O66SiO 2 glass at temperatures well below T g of the mother glass, giving glass samples with various Ag +/Na + ratios. The glass transition temperature decreased about 150 K with increase in Ag + concentration, accompanied by the simultaneous decrease of the thermal expansion coefficient by about 50%. Large changes in O1s XPS spectra were observed; the bridging and non-bridging oxygen peaks shifted toward larger binding energies, and the ratio of non-bridging oxygen (NBO) to bridging oxygen decreased with increasing Ag + concentration. This trend revealed that the increased covalency of Ag +O nb bonds decreased T g and the thermal expansion coefficients. 29Si-NMR results showed that Q 3 units decreased while Q 2 units increased without accompanying Q 4 units. These results suggested that two coordinated Ag + ions with non-bridging and bridging oxygen would be formed in the sample glasses.

Room-temperature water adsorption on the Si(100) surface examined by UPS, XPS, and static SIMS

The adsorption of water on the reconstructed Si(100)-(2 x 1) surface at room temperature is studied using an integrated multi-technique approach. UPS, XPS, and static SIMS surface examination in a variable temperature mode of experimentation indicates dissociative adsorption of water to hydroxyl (OH) and hydride (H) groups saturating the single dangling bonds on adjacent dimer-pair Si atoms of the reconstructed surface. No evidence of molecular water is found. Upon heating the surface the hydroxyl decomposes to bridge-bonded oxygen (Si-O-Si) and additional silicon hydride groups. This is complete at ≈400°C. Above 400°C the surface loses hydrogen, presumably as H 2, and above 600°C the substoichiometric silicon oxide sublimes as SiO to return to the clean, reconstructed surface. The chemical state of oxygen on the surface is monitored as a function of temperature through the use of a Δ parameter (Δ = binding energy O(1s) - binding energy Si(2p)). These results are consistent with experimental evidence and surface chemistry first proposed by others. Assignment of the observed DOS features is made by comparison of the experimental DOS spectra to calculations for the system and for system analogs (SiOH radical, oxygen-saturated Si surface, hydrogen-saturated Si surface), and to another hydroxyl system (NaOH). Four major features of the saturated hydroxyl/hydride surface are found : 5 eV Si-H bond, Sisp 3 + H1s character; 6.4 eV O 2p lone pair, π symmetry nonbonding orbital; 7.6 eV O-H bond, O 2p + H1s character, σ symmetry; 11.9 eV Si-OH bond, sp 3 + O 2p character (binding energies relative to the Fermi level).