Effect Of Oxygen Doping Research Articles

Composition-dependent effects of oxygen on atomic structure and mechanical properties of metallic glasses

Although minor alloying in metallic glasses (MGs) has been extensively investigated, the effect of O doping is still a debatable topic. In the present study, the atomic-level structures and mechanical properties of Zr-based MGs doped with different O contents have been analyzed using ab initio molecular dynamics simulations. It is revealed that O atoms prefer to bond to Zr atoms due to their low mixing enthalpy, and that O atoms degrade the properties of Zr-lean MGs but hardly affect the properties of Zr-rich MGs, with results suggesting a compositional dependence of O doping. For Zr-lean MGs, the fraction of full icosahedra, size of the medium-range-order clusters, Young's modulus and shear modulus decrease sharply with O content, while accompanied by a sharp increase of the non-Frank-Kasper polyhedra, and the ratio of bulk modulus to shear modulus and Poisson's ratio, indicating decreased strength and improved plasticity. For Zr-rich MGs, however, the above-mentioned structural and mechanical features experience little change or only change slightly after O doping, showing low oxygen sensitivity. It is shown that the high Zr content weakens the effect of Zr-O bonding to some extent. The present study not only sheds light on the atomic-level structures of O-doped MGs, which may provide guidelines for designing MGs with low-grade materials, but also helps to explain the previous conflicting results based on the composition-dependence effect.

Oxygen doping through oxidation causes the main active substance in g-C3N4 photocatalysis to change from holes to singlet oxygen

Improving the photocatalytic activity of graphitic carbon nitride (g-C3N4) for organic pollutant removal from water and in-depth study of the effect of oxygen doping on its photocatalytic mechanism are deserving of research attention. Oxygen-doped g-C3N4 with a suitable degree of oxidation was prepared by oxidation using concentrated acid–ultrasound double oxidation. Oxygen doping by oxidation changed the physical and chemical properties of g-C3N4, and improved its rhodamine B photocatalytic degradation efficiency. The physical and chemical properties of g-C3N4 were characterized by scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, and zeta potential analysis, among other methods. The photocatalytic mechanism was also studied in depth using photoluminescence, electrochemical impedance spectroscopy, transient photocurrent measurements, diffuse reflectance spectroscopy, and Mott–Schottky plots. An appropriate degree of oxidation introduced pit-like defects rich in oxygen-containing functional groups onto the g-C3N4 surface, which improves its photocatalytic performance. Furthermore, in the photocatalytic process of oxidized g-C3N4, oxygen doping was confirmed to change the main active substance of g-C3N4 photocatalysis from holes to singlet oxygen. This study provides an in-depth explanation of the photocatalytic mechanism of g-C3N4 doped with oxygen, which provides guidance and reference for the design of photocatalysts for organic pollutant removal from water and the analysis of photocatalytic mechanisms for water treatment.

Oxygen doped MoS2 quantum dots for efficient electrocatalytic hydrogen generation.

In this study, we report an oxygen-doped MoS2 quantum dot (O-MoS2 QD) hybrid electrocatalyst for the hydrogen evolution reaction (HER). The O-MoS2 QDs were prepared with a one-pot microwave method by hydrazine-mediated oxygen-doping. The synthetic method is straightforward, time-saving, and can be applied in large scale preparation. Ultra-small O-MoS2 QDs with the average size of 5.83 nm and 1-4 layers can be uniformly distributed on the surface of reduced graphene oxide (RGO). Benefited from the unique structure and the doping effect of oxygen in the MoS2 QDs and the great number of active sites, the O-MoS2 QD hybrid displayed outstanding electrocatalytic performance toward HER. A low overpotential of 76 mV at 10 mA/cm2 and a Tafel slope of 58 mV/dec were obtained in an acidic solution toward HER. Additionally, the resultant O-MoS2 QD hybrid also exhibited excellent stability and durability toward HER, displaying negligible current density loss after 1000 cycles of cyclic voltammetry. The design and synthesis of the electrocatalyst in this work open up a prospective route to prepare active and stable electrocatalysts toward substituting precious metals for hydrogen generation.

Development of Li10GeP2S12-Type Solid Electrolytes with Electrochemical Stability to Li Metal Anode

Solid-state Li-ion battery promises potentially high-power characteristics, although increase in energy density remains as an issue to be solved.1,2 Therefore solid electrolytes that possess electrochemical stability to Li metal electrode as well as high ionic conductivity are urgently demanded. This study synthesized solid electrolytes using Li10GeP2S12(LGPS),3 a supersonic conductor showing Li ion conductivity over 10−2 S cm−1, as a structural template; we performed material search for LGPS-derivatives in the Li–M–P–S–O–X (M = Ge, Si, Sn; X = F, Cl, Br, I) system in order to elucidate effects of doped- anion/cation towards the stability to Li metal electrode. We discovered various LGPS-type electrolytes through optimization of synthesis condition for each chemical composition. For the Li–M–P–S–X system, heating at 400–550°C is required, for Li–P–S–O–X at 200–280°C, and for Li–Si–P–S–O at 950–1000°C, respectively. The synthesized solid electrolytes were characterized by structure analysis based on diffraction data and AC impedance method. Electrochemical stability for electrolytes was evaluated by charge–discharge cycling tests of solid-state cell, in which the synthesized electrolyte, Li metal, and the mixture of LiNbO3-coated-LiCoO2 and LGPS was used as a separator, anode, and cathode, respectively. The retention rate of discharge capacity was used as an indicator for evaluating stability towards Li metal. The effects of oxygen doping were clarified in the Li–M–P–S–O and Li–P–S–O systems. The cell using Li9.42Si1.02P2.1S9.96O2.04 or Li3.2PS3.7O0.3 respectively showed retention rate of more than 98% whereas Li–M–P–S cells showed less than 20% after 5th cycle.4 However, these oxygen-doped electrolytes suffer from lower conductivity on the order of 10−4 S cm−1. These results indicate oxygen doping improves electrochemical stability but at the cost of decrease in conductivity. On the other hand, the Li–P–S–X system showed 99% capacity retention after 5th cycle as well as a high conductivity of 4×10−3 S cm, suggesting doping halogen elements is a promising technique for achieving a better balance between stability and conductivity for LGPS-type electrolytes. References Kato, Y.; Hori, S.; Saito, T.; Suzuki, K.; Hirayama, M.; Mitsui, A.; Yonemura, M.; Iba, H.; Kanno, R., High-power all-solid-stae batteries using sulfide superionic conductors. Nature Energy 2016, 1, (16030).Janek, J.; Zeier, W. G., A solid future for battery development. Nature Energy 2016, 1 (9).Kamaya, N.; Homma, K.; Yamakawa, Y.; Hirayama, M.; Kanno, R.; Yonemura, M.; Kamiyama, T.; Kato, Y.; Hama, S.; Kawamoto, K.; Mitsui, A., A lithium superionic conductor. Nat. Mater. 2011, 10, 682-686.Hori, S.; Suzuki, K.; Hirayama, M.; Kato, Y.; Kanno, R., Lithium Superionic Conductor Li9.42Si1.02P2.1S9.96O2.04 with Li10GeP2S12-Type Structure in the Li2S–P2S5–SiO2 Pseudoternary System: Synthesis, Electrochemical Properties, and Structure–Composition Relationships. Frontiers in Energy Research 2016, 4 (38).

Effect of oxygen doping on the stability and band structure of borophene nanoribbons

By using first-principles calculations, the effect of oxygen dopants on the stability and electronic properties of borophene nanoribbons (BNRs) is studied. The doping by oxygen atoms is found as an effective way to increase the stability of BNRs and switched them from a metallic material to semimetal or semiconductor. Our results suggest that the line-edge BNRs exhibit a high stability, while the zigzag-edge BNRs are unstable. In addition, it is predicted that oxygen dopants can stabilize the structure of zigzag-edge BNRs and increase the stability of the line-edge BNRs.

Oxygen impurity effects on the mechanical properties of SiC studied by first principles calculations

First principle calculations are performed to study the oxygen doping effects on the mechanical properties of SiC. Both interstitial and substitutional oxygen atoms decrease the shear and tensile modulus and strength of SiC. The substitutional oxygen atoms decrease the shear and tensile modulus and strength more than the interstitial oxygen atoms do. Local distortions around the oxygen doping atoms are found in both of tensile and shear stress strain curve calculations in the elastic region. The shear strength of SiC decreases linearly with the increase of the oxygen concentration. The tensile strength of SiC also decreases with the oxygen concentration and it drops dramatically at low concentration region.

Study of Superconducting, Structural, and Thermal Properties of SnO2 Added MgB2 Bulks.

A series of SnO2 added MgB2 bulk superconductors were prepared by in situ route to study the effect of oxygen doping on superconducting and structural properties of MgB2. Several (MgB2)1-x (SnO2) x samples were fabricated with x ranging from 0, 3 wt%, 4 wt%, and 6 wt%. Upper critical field (B C2) and irreversible field (B irr) were measured by physical property measurement system. Thermal analysis was performed on the as-received SnO2 powder. Critical current densities (J cm ) were obtained at 4.2 K using magnetic measurement. X-ray diffraction results showed evidence of full SnO2 decomposition in all the doped bulk samples and a shift of a-axis in MgB2 lattice was seen. Oxygen was successfully released during heat treatment, yet no enhancement of B C2 or B irr was seen, indicating that oxygen atoms did not end up in the host lattice. Further exploration of different processing procedures is still needed in order to get oxygen substitution on the host lattice sites.

First principles study of structural, electric, and magnetic properties of fluoride perovskite NaFeF<sub>3</sub>

<sec>On the basis of first-principles calculations, the systematic researches of the structural, electronic and magnetic properties of NaFeF<sub>3</sub> are carried out in the present work. The influences of anion substitution and strain effect are taken into consideration in the reaearch. </sec><sec>First, the basic properties of the NaFeF<sub>3</sub> bulk are determined. The fully relaxed structure exhibits a distinct GdFeO<sub>3</sub>-type distortion and a relatively weak Jahn-Teller distortion. The band gap is estimated at 3 eV from our DFT calculations with Hubbard U correction. Moreover, the magnetic structure is of G-type antiferromagnetism (G-AFM). This intrinsic G-AFM magnetic state is robust, and cannot be easily destroyed by small perturbations, includinganion doping and epitaxial strain.</sec><sec>Secondly, we study the oxygen doping effect on the properties of material with considering the fact that the radius of oxygen anion is very close to that of fluoride anion, and the oxygen substitution can be accommodated by the further oxidation of iron cation from divalent to trivalent state. According to our energy comparison calculations, when one of the twelve F sites in the NaFeF<sub>3</sub> unit cell is taken up by an oxygen anion, whose corresponding doping concentration is approximately 8.3%, the O ion is more likely to occupy the in-plane site of the FeF<sub>6</sub> octahedron. This low concentration doping may induce unequal Fe—O bonds, which lead to diverse valence states of surrounding Fe cations, and therefore result in local polarization and non-zero net magnetic moment. The local dipole and magnetic moment are inherently correlated with each other due to the common origin, i.e., the incoordinate Fe—O bonds. Therefore, the net magnetic moment together with the local polarization may be reversed simultaneously by an external electric field. However, when the doping concentration is further increased to 33%, the overall iron valence will rise to a higher state where the local charge order and the net moment disappear.</sec><sec>In addition, the electronic properties of NaFeF<sub>3</sub> also show obvious change due to the influence of biaxial strain. Specifically, the energy gap decreases monotonically as the in-plane stress gradually changes from compression to extension. However, the band structure does not change significantly. The top of the valence band and the bottom of the conduction band are both located at the Gamma point, thus making it a direct bandgap semiconductor material with an adjustable energy gap.</sec><sec>These findings may promote further theoretical and experimental research on fluoride family and introduce a new candidate to the multiferroic field.</sec>

Adjustment of the microstructure and selected mechanical properties of biomedical Ti-15Zr-Mo alloys through oxygen doping

This study investigated the effect of oxygen doping on the crystalline structure, microstructure, and selected mechanical properties (Vickers microhardness, Young's modulus and internal friction) of Ti-15Zr-xMo (x = 5, 7.5, 10, 15 and 20 wt%) alloys for use as biomaterials. The monitoring of oxygen pressure along with the doping treatment indicated that the interstitial element was successfully absorbed into the samples. Results showed that oxygen content slightly altered the α”/β phase proportion and β phase crystalline parameter without abruptly changing their microstructure. Moreover, the selected mechanical properties suffered variations in a non-linear manner. Oxygen content was found to be suitable to produce small variations in the microstructure and in the selected properties of biomedical Ti alloys, keeping the main composition unchanged.

Analysis of Influencing Factors on Air-Stable Organic Field-Effect Transistors (OFETs)

The primary emphasis in this paper is on the major developments in the field of air-stable organic field-effect transistors (OFETs) over the past 20 years. The studies about the factors influencing the stability of OFETs, including air, humidity, oxygen and temperature, are reviewed and analyzed. The possible mechanisms that result in the degradation of OFETs, such as the penetrating of H2O molecules, the doping effect of oxygen or the crystalline structure difference caused by temperature, are summarized. At same time, the reason why the field-effect mobility and the on/off current ratio of the transistor might change greatly with different ambient is concluded. The overall lives of OFET-based sensor in the detection of hazardous gases including nitrogen dioxide and ammonia are discussed, several breakthrough findings and technologies about how to solve the problem of instability of OFETs are also presented. DOI: http://dx.doi.org/10.5755/j01.ms.24.2.18197

Effect of oxygen doping on the hydrogen evolution reaction in MoS2 monolayer

Molybdenum disulphide (MoS2) monolayer is regarded as one of the most promising non-noble metal electro-catalysts for hydrogen evolution reaction (HER). Increasing the catalytic active sites in MoS2 monolayer is critical for further improvement of catalytic behaviour. In this paper, the effects of oxygen (O) doping on the HER of MoS2 monolayer were investigated by using the density functional theory. The results showed that the O-doping assists in the formation of S and Mo vacancies. The hydrogen adsorption free energy is greatly reduced from 2.18 eV on pristine MoS2 monolayer to −0.01 eV on MoS1.96O0.04 and MoS1.88O0.12 monolayers with S vacancies. The Gibbs free energies for hydrogen adsorption on MoS1.92O0.08 and MoS1.84O0.16 monolayers with Mo vacancies are 0.02 and −0.02 eV, respectively. These results provide a general design methodology to increase hydrogen production in the electrochemical reaction of MoS2 monolayer by defect engineering.

Influence of dopants, particularly carbon, on β-rhombohedral boron

Due to the high affinity of carbon to boron, the preparation of carbon-free boron is problematic. Even high-purity (6 N) β-rhombohedral boron contains 30–60 ppm of C. Hence, carbon affects the boron physical properties published so far more or less significantly. We studied well-defined carbon-doped boron samples based on pure starting material carefully annealed with up to about 1% C, thus assuring homogeneity. We present and discuss their electrical conductivity, optical absorption, luminescence and phonon spectra. Earlier attempts of other authors to determine the conductivity of C-doped boron are revised. Our results allow estimating the effects of oxygen and iron doping on the electrical conductivity using results taken from literature. Discontinuities at low T impair the electronic properties.

Oxygen doping effect on the wettability of diamond-like carbon thin films

Diamond like carbon (DLC) thin films as a great coating to protect biomedical tools and optical devices are being developed. Modifying the surface properties, such as wettability, is necessary in some application. In this research, oxygen doping effect on the DLC films wettability was investigated. Oxygen doped diamond-like carbon (DLC) thin films were deposited by the RF-PECVD method with different oxygen concentrations in feeding gas (0.0, 1.9, 3.8, 5.6, 7.4 and 9.1vol%). The film's structure was studied by Raman spectroscopy (RS) and attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR). The chemical composition was determined by a combination of elastic recoil detection analysis (ERDA) and Rutherford backscattering spectroscopy (RBS). Surface roughness and morphology of the films were analyzed by an atomic force microscopy (AFM). Wettability of the films was characterized by measuring the contact angles of the films with water. The results showed that by increasing the incorporation of oxygen into the films' structure, the contact angles of water with films were reduced. The increase in the oxygen content of the films, from zero to 11at%, caused to reduce water contact angles from 78.4° to 66.0°. By adding the oxygen into the film's structure, CO and CC bonds content increased in the films. Due to the more polarizability of CO and CC bonds in comparing with CC and CH bonds, a polar component of films' surface energy was increased by adding the oxygen to the films' structure. The surface roughness of the un-doped and doped DLC films were so low (less than 1nm) that they had no roles in the films' surface energy. Doping the DLC films with oxygen caused to increase wettability, without no significant change in the morphology and surface roughness.

Sputtered Gum metal thin films showing bacterial inactivation and biocompatibility

Super-elastic Titanium based thin films Ti-23Nb-0.7Ta-2Zr-(O) (TNTZ-O) and Ti-24Nb-(N) (TN-N) (at.%) were deposited by direct current magnetron sputtering (DCMS) in different reactive atmospheres. The effects of oxygen doping (TNTZ-O) and/or nitrogen doping (TN-N) on the microstructure, mechanical properties and biocompatibility of the as-deposited coatings were investigated. Nano-indentation measurements show that, in both cases, 1sccm of reactive gas in the mixture is necessary to reach acceptable values of hardness and Young⿿s modulus. Mechanical properties are considered in relation to the films compactness, the compressive stress and the changes in the grain size. Data on Bacterial inactivation and biocompatibility are reported in this study. The biocompatibility tests showed that O-containing samples led to higher cells proliferation. Bacterial inactivation was concomitant with the observed pH and surface potential changes under light and in the dark. The increased cell fluidity leading to bacterial lysis was followed during the bacterial inactivation time. The increasing cell wall fluidity was attributed to the damage of the bacterial outer cell which losing its capacity to regulate the ions exchange in and out of the bacteria.

Controllable Growth of Ultrathin P-doped ZnO Nanosheets.

Ultrathin phosphor (P)-doped ZnO nanosheets with branched nanowires were controllably synthesized, and the effects of oxygen and phosphor doping on the structural and optical properties were systematically studied. The grown ZnO nanosheet exhibits an ultrathin nanoribbon backbone with one-side-aligned nanoteeth. For the growth of ultrathin ZnO nanosheets, both oxygen flow rate and P doping are essential, by which the morphologies and microstructures can be finely tuned. P doping induces strain relaxation to change the growth direction of ZnO nanoribbons, and oxygen flow rate promotes the high supersaturation degree to facilitate the growth of nanoteeth and widens the nanoribbons. The growth of P-doped ZnO in this work provides a new progress towards the rational control of the morphologies for ZnO nanostructures.

Preparation and physicochemical characterisation of functionalised multi-walled carbon nanotubes

A series of new functionalised carbonaceous materials were prepared by means of oxidation and ammoxidation of commercially available multi-walled carbon nanotubes. The effect of oxygen and nitrogen doping on the textural, surface as well as thermal properties of the prepared adsorbents was tested. The materials were characterized by elemental analysis, low-temperature nitrogen sorption, determination of the surface oxygen groups content as well as by coupled thermogravimetric and spectroscopic methods (TG/DSC/MS). Depending of the variant of raw nanotubes modification, the final products were oxygen- and nitrogen-doped materials of medium-developed surface area and mesoporous structure, showing highly diverse acidic-basic character of the surface, from the weakly acidic to slightly alkaline.

Effect of edge chemistry doping on the transport and optical properties for asymmetric armchair-edge graphene nanoribbons under a uniaxial strain

The effect of edge n-type nitrogen (N) and p-type oxygen (O) doping on the transport and optical properties for asymmetric 6- and 8-armchair-edge graphene nanoribbons (AGNRs) under a uniaxial strain has been demonstrated in the method of the first-principles density functional theory combined with nonequilibrium Green’s function. The transmission spectra and current–voltage (I–V) curves of the semiconducting 6- and metallic 8-AGNRs have been found to be qualitatively unchanged as the uniaxial strain along the armchair edge (Ac-strain), while the quantitative variations come from the mutual actions of the strain and edge doping. However, the observed semiconductor–metal transition and metal–semiconductor transition in the transport properties for 6- and 8-AGNRs should be mainly from the resonance scattering of the doping edges when the external strain is applied along the zigzag edge (Zz-strain). The distinct variation trends of the system transport properties are well confirmed from the optical absorption spectra. It is believed that the obtained results are of importance in exploiting chemistry at the reactive edges of the asymmetric AGNRs and strain engineering of the nanoelectronic/optoelectronic devices based on AGNRs.

First principle modeling of oxygen-doped monolayer graphitic carbon nitride

The effect of oxygen doping on the electronic and geometric structures of monolayer graphitic carbon nitride was calculated by first principle. It reveals the favorable O doping configurations over all the Fermi levels utilizing the Ab initio thermodynamics approach. The valence charge density difference contour map presents a weaker covalent nature on O–C bonds for ON2-doped structure and a complex ionic-covalent character associated with O–N2 bonds for Oi-doped structure. Based on the analysis of the electronic structures of the doped and un-doped systems, it is found that O doping facilitates the visible-light absorption of monolayer g-C3N4. Especially, Oi doping shows an intrinsic semiconductor behavior and the occupied doping band can be avoided to be the recombination center. In addition, O doping causes slightly stronger delocalization of the HOMO and LUMO which facilitates the enhancement of the carrier mobility. Moreover, Oi doping can induce more activity sites, and, thus, is beneficial for the separation of photogenerated e−/h+ pairs to some extent.

Effects of intentional oxygen and carbon doping in MOVPE‐grown GaN layers on photoelectric properties

In order to qualitatively and quantitatively analyze the effects of N source impurity species and concentrations on the properties of epitaxial GaN layers, we intentionally introduced the oxygen‐containing species CO and CO2 into GaN layers during growth. Subsequently, we determined the impurities or elements that had a strong effect on the photoelectric properties of the GaN layers and investigated the doping mechanism. The results of this study show that changes in the carrier density are more sensitive to CO2 than to CO. Oxygen as the main donor was found to affect the carrier density and photoluminescence (PL) emission intensities of CO and CO2‐doped GaN, and the carbon incorporation efficiency of these molecules was found to be lower than the oxygen incorporation efficiency. In order to obtain ideal epitaxial GaN layers with a reduced carrier density of 1013 cm−3, the CO and CO2 concentrations in the ammonia source should be less than 100 ppb (CO) and 10−1 ppb (CO2).

Effect of Oxygen Doping on the Structure of TiN Surface Coatings

Abstract In the present work the influence of the level of oxygen doping on the structure of TiN films was investigated by dedicated experiments. The films were deposited at 400°C in an all metal UHV device by unbalanced magnetron sputtering at the same Ar and nitrogen flow rates, but the oxygen flow rate was changed in the experiments, incorporating oxygen in the range of 4 and 20 at.%. The structure of the films was investigated by XRD, Auger electron (AES) and X-ray photon electron (XPS) spectroscopy and transmission electron microscopy (TEM). The results discovered the crystal face anisotropy in the incorporation-segregation of oxygen leading to the change of the <111> texture to <002>. The structure analysis revealed that the <002> texture is developing also by competitive growth of crystals, which is the result of the limitation of the growth of the <111> oriented crystals by the TiO2 layer developing on their growth surface by the segregated oxygen species. The oxygen incorporating in the crystal lattice on the 002 crystal faces of the <002> oriented crystals is segregated by surface spinodal decomposition, developing nm sized 3D TiO-2 inclusion both in the bulk of the columns and the column boundaries.