Oxygen Doping Levels Research Articles

Effect of oxygen doping on cutting performance of CVD diamond coated milling cutters in zirconia ceramics machining

Diamond thin films were deposited on WC-Co tools using the hot-filament chemical vapor deposition (HFCVD) technique at varying pressures and oxygen doping levels. As the oxygen doping content increased, the purity of the diamond phase improved, and the density of the <111> crystal plane on the film's surface increased. The growth rate of diamond films initially increased and then decreased under low pressure, with a corresponding decrease in residual compressive stress. Conversely, at high pressure, increased oxygen doping enhanced the diamond phase purity and growth rate while reducing residual compressive stress. Cutting experiments on pre-sintered zirconia ceramics for milling linear slots and engraving dentures demonstrated that diamond-coated milling cutters exhibited superior cutting performance under consistent oxygen and carbon source concentrations and stable air pressure conditions. The oxygen-doped diamond-coated milling cutter grown at a pressure of 1 KPa exhibited the longest service life, attributed to its reduced surface roughness, lower cutting force, and increased density of the <111> crystal plane orientation. This cutter could machine up to 1300 crowns, making it approximately 80% more durable than non‑oxygen-doped diamond-coated milling cutters and about 20 times more durable than uncoated ones.

The Impact of Oxygen Content in O-Doped MoS2 on the Kinetics of Polysulfide Conversion in Li-S Batteries.

Polysulfide shuttle and sluggish sulfur redox kinetics remain key challenges in lithium-sulfur batteries. Previous researches have shown that introducing oxygen into transition metal sulfides helps to capture polysulfides and enhance their conversion kinetics. Based on this, further investigations are conducted to explore the impact of oxygen doping levels on the physical-chemical properties and electrocatalytic performance of MoS2. The findings reveal that MoS2 doped with high-content oxygen exhibits enhanced conductivity and polysulfides conversion kinetics compared to MoS2 with low-content oxygen doping, which can be attributed to the alteration of crystal structure from 2H-phase to the 1T-phase, the introduction of increased Li-O interactions, and the effect of defects resulting from high-oxygen doping. Consequently, the lithium-sulfur batteries using high-oxygen doped MoS2 as a catalyst deliver a high discharge capacity of 1015 mAh g-1 at 0.25C and maintain 78.5% capacity after 300 more cycles. Specifically, lithium-sulfur batteries employing paper-based electrodedemonstrate an areal capacity of 3.91 mAh cm-2 at 0.15C, even with sulfur loading of 4.1mg cm-2 and electrolyte of 6.7µL mg-1. These results indicate that oxygen doping levels can modify the properties of MoS2, and high-oxygen doped MoS2 shows promise as an efficient catalyst for lithium-sulfur batteries.

Decoding intrinsic features of carbons from their capacitive performance

Carbon-based materials, prized for their diverse applications, are at the forefront of scientific exploration. Performance of these materials relies on their basic properties, yet traditional characterization methods are often laborious. In our study, we introduce a machine learning (ML) based approach that leverages electrochemical performance data to elucidate the intrinsic properties of carbon materials. We highlight a technique, Cap2SSA, that expeditiously and precisely determines the specific surface area (SSA) of carbon materials through capacitive responses gathered during electrochemical tests. The efficacy of Cap2SSA is substantiated using the commercial carbon material across diverse current densities in both aqueous and organic electrolytes. Our findings reveal that the SSA values derived from capacitance measurements align closely with actual measurements, with discrepancies under 14 %. Significantly, this evaluation method extends beyond the SSA estimation, offering a versatile tool for inferring additional carbon material features, such as nitrogen and oxygen doping levels. Overall, combining electrochemical measurements with ML enables rapid assessment of material composition and structure, driving forward material science analysis.

Topological surface states and phase transition in BaTh2Fe4As4(N1−xOx)2 superconductors

We perform density functional theory and density functional theory plus dynamical mean-field theory calculations to study the electronic structures and topological properties of iron-based superconductors ${\mathrm{BaTh}}_{2}{\mathrm{Fe}}_{4}{\mathrm{As}}_{4}{({\mathrm{N}}_{1\ensuremath{-}x}{\mathrm{O}}_{x})}_{2}$ ($x=0.1$, 0.2, and 0.3). Taking into account electronic correlation corrections, we find that at small oxygen dopings ($x=0.1$ and 0.2), the ${\mathrm{BaTh}}_{2}{\mathrm{Fe}}_{4}{\mathrm{As}}_{4}{({\mathrm{N}}_{1\ensuremath{-}x}{\mathrm{O}}_{x})}_{2}$ superconductors have nontrivial band topology and Dirac-cone type topological surface states around the Fermi level on the (001) surface, which indicates that they can harbor Majorana zero modes on the (001) surface. Increasing the oxygen doping level, the ${\mathrm{BaTh}}_{2}{\mathrm{Fe}}_{4}{\mathrm{As}}_{4}{({\mathrm{N}}_{1\ensuremath{-}x}{\mathrm{O}}_{x})}_{2}$ superconductor undergoes a topological phase transition between $x=0.2$ and 0.3, and has trivial band topology and no topological surface states on the (001) surface at $x=0.3$. The coexistence of high-temperature superconductivity, topological surface states, and topological phase transition in ${\mathrm{BaTh}}_{2}{\mathrm{Fe}}_{4}{\mathrm{As}}_{4}{({\mathrm{N}}_{1\ensuremath{-}x}{\mathrm{O}}_{x})}_{2}$ superconductors makes them potential platforms to study topological superconductivity, Majorana zero modes and effects induced by a topological phase transition.

Tailoring the transesterification activity of MgO/oxidized g-C3N4 nanocatalyst for conversion of waste cooking oil into biodiesel

As a prospective heterogeneous catalyst for transesterification, magnesium oxide (MgO) has long been regarded as a possible candidate. Pure MgO, on the other hand, has a narrow range of applications because of its small surface area and short catalytic lifetime. To overcome these problems, in this work, graphitic carbon nitride (g-C3N4) with higher oxygen doping levels was applied to construct a noteworthy, persistent, and carbon-modified MgO catalyst. The molar ratios of urea to melamine and the mass ratios of oxidized g-C3N4 to MgO in the preparation step are two effective parameters, which were optimized with the Response Surface Methodology (RSM). The significant increase in oil conversion was attained by incorporating O@g-C3N4 nanoparticles composed of urea to melamine at a molar ratio of 2:1 in MgO at a mass percentage of 16.7. O@g-C3N4 had an outstanding effect on the immobilization of oxygen-rich functional groups on the MgO-based catalyst and an increase in the surface area. Also, the effects of transesterification parameters and their interactions on oil conversion were explored using the RSM, and then reusability tests were carried out using the fine-tuned parameters. The prepared catalysts were characterized using a variety of methods, including Field-Emission Scanning Electron Microscopy with Energy Dispersive X-ray Spectroscopy (FESEM-EDS), Fourier Transform Infrared (FTIR) spectroscopy, Temperature Programmed Desorption of CO2 (CO2-TPD), Brunauer-Emmett-Teller (BET) analysis, and powder X-Ray diffraction, in order to determine their basicity, morphology, and composition. The optimum biodiesel yield of 98.80% was attained at 99.6 °C for 133 min with a catalyst quantity of 5.9 wt% and a methanol to oil molar ratio of 14.6. The stability and lifespan of the as-optimized catalyst (OCN2MgO(0.2)) were confirmed over four consecutive cycles. It can be concluded that this solid catalyst could be used to convert low-cost waste cooking oil into biodiesel in a single step.

Synergistic effect of nitrogen and oxygen dopants in 3D hierarchical porous carbon cathodes for ultra-fast zinc ion hybrid supercapacitors

Zinc-ion hybrid supercapacitor is one of the most promising electrochemical energy storage devices for the applications needing both high energy densities and power densities. Nitrogen doping is an effective way to enhance the capacitive performance of porous carbon cathodes in zinc-ion hybrid supercapacitor. However, accurate evidence is yet needed to demonstrate how nitrogen dopants influence the charge storage of Zn2+ and H+ cations. Herein, we prepared 3D interconnected hierarchical porous carbon nanosheets by a one-step explosion method. The effect of nitrogen dopants on pseudocapacitance was analyzed by the electrochemical behaviors of as-prepared porous carbon samples with similar morphology and pore structure but different nitrogen and oxygen doping levels. Ex–situ XPS and DFT calculation demonstrate that nitrogen dopants promote the pseudocapacitive reactions by lowering the energy barrier for the change of oxidation states of carbonyl moieties. Owing to the improved pseudocapacitance by nitrogen/oxygen dopants and fast diffusion of Zn2+ ions in 3D interconnected hierarchical porous carbon matrix, the as-constructed ZIHCs show both high gravimetric capacitance (301 F g−1 at 0.1 A g−1) and excellent rate capability (a capacitance retention of 30% at 200 A g−1).

Tailoring the oxygen concentration in Ge-Sb-O alloys to enable femtojoule-level phase-change memory operations

Chalcogenide phase-change materials (PCMs), in particular, the flagship Ge2Sb2Te5 (GST), are leading candidates for advanced memory applications. Yet, GST in conventional devices suffer from high power consumption, because the RESET operation requires melting of the crystalline GST phase. Recently, we have developed a conductive-bridge scheme for low-power phase-change application utilizing a self-decomposed Ge-Sb-O (GSO) alloy. In this work, we present thorough structural and electrical characterizations of GSO thin films by tailoring the concentration of oxygen in the phase-separating GSO system. We elucidate a two-step process in the as-deposited amorphous film upon the introduction of oxygen: with increasing oxygen doping level, germanium oxides form first, followed by antimony oxides. To enable the conductive-bridge switching mode for femtojoule-level RESET energy, the oxygen content should be sufficiently low to keep the antimony-rich domains easily crystallized under external electrical stimulus. Our work serves as a useful example to exploit alloy decomposition that develops heterogeneous PCMs, minimizing the active switching volume for low-power electronics.

Molten Salt Self-Template Synthesis Strategy of Oxygen-Rich Porous Carbon Cathodes for Zinc Ion Hybrid Capacitors.

Porous carbon materials are widely used in capacitive energy storage devices because of their chemical stability, low cost, and controllable textures. Molten salt self-template methods are powerful and sustainable synthesis strategies for preparing porous carbons with tunable pore textures and surface chemistries. Herein, we propose a self-template synthesis strategy for preparing oxygen-rich porous carbons (ORC) by directly carbonizing potassium chloroacetate (ClCH2COOK) as the single carbon source. The potassium chloride salts generated in the carbonization play the roles of the template and etchant agent in the pore formation process. The as-prepared ORC samples feature abundant mesopores (average pore sizes of 1.95-2.19 nm and mesopore ratio of 36.4%), high specific surface areas (1410-1886 m2 g-1), and high oxygen doping levels (4.3-8.2 atom %). The zinc ion hybrid capacitors with an ORC cathode exhibited an ultrahigh capacitance of 308 F g-1 at 0.5 A g-1 and a high energy density of 136.5 Wh kg-1 at a power density of 570 W kg-1. Density functional theory demonstrates that oxygen-containing functional groups are conducive to the adsorption of Zn ions. Our work proposes a general synthesis methodology for the synthesis of oxygen-rich porous carbons for a variety of electrochemical energy storage devices.

Manipulating high-temperature superconductivity by oxygen doping in Bi2Sr2CaCu2O8+δ thin flakes.

Harnessing the fascinating properties of correlated oxides requires precise control of their carrier density. Compared to other methods, oxygen doping provides an effective and more direct way to tune the electronic properties of correlated oxides. Although several approaches, such as thermal annealing and oxygen migration, have been introduced to change the oxygen content, a continuous and reversible solution that can be integrated with modern electronic technology is much in demand. Here, we report a novel ionic field-effect transistor using solid Gd-doped CeO2 as the gate dielectric, which shows a remarkable carrier-density-tuning ability via electric-field-controlled oxygen concentration at room temperature. In Bi2Sr2CaCu2O8+δ (Bi-2212) thin flakes, we achieve a reversible superconductor-insulator transition by driving oxygen ions in and out of the samples with electric fields, and map out the phase diagram all the way from the insulating regime to the over-doped superconducting regime by continuously changing the oxygen doping level. Scaling analysis indicates that the reversible superconductor-insulator transition for the Bi-2212 thin flakes follows the theoretical description of a two-dimensional quantum phase transition. Our work provides a route for realizing electric-field control of phase transition in correlated oxides. Moreover, the configuration of this type of transistor makes heterostructure/interface engineering possible, thus having the potential to serve as the next-generation all-solid-state field-effect transistor.

Tuning the morphology of 2D transition metal chalcogenides via oxidizing conditions

Two-dimensional transition metal chalcogenides (TMCs) are emerging as an intriguing platform to realize nascent properties in condensed matter physics, materials science and device engineering. Controllable growing of TMCs becomes increasingly important, especially for the layer number, doping, and morphology. Here, we successfully tune the morphology of MoS2, MoSe2, WS2 and WSe2, from homogenous films to individual single crystalline grains only via changing the oxidizing growth conditions. The oxidization degrees are determined by the oxygen that adsorbed on substrates and the oxygen concentrations in reaction gas together. We find the homogenous films are easily formed under the reductive conditions, triangular grains prefer the weak oxidizing conditions, and medium oxidizing conditions bring in dendritic grains with higher oxygen doping and inhomogenous photoluminescence intensities from edge to interior regions shown in the dendritic grains. These growth rules under different oxidizing conditions are easily generalized to other TMCs, which also show potential for growing specific TMCs with designed oxygen doping levels.

Cotrollable growth of monolayer MoS&lt;sub&gt;2&lt;/sub&gt; films and their applications in devices

Monolayer molybdenum disulfide (MoS&lt;sub&gt;2&lt;/sub&gt;) is an emerging two-dimensional (2D) semiconductor material.The MoS&lt;sub&gt;2&lt;/sub&gt; film has a natural atomic-level thickness, excellent optoelectronic and mechanical properties, and it also has the potential applications in very large-scale integration technology in the future. In this article we summarize the research progress made by our group in the studying of monolayer MoS&lt;sub&gt;2&lt;/sub&gt; films in the past few years. The controlled growth of large-size MoS&lt;sub&gt;2&lt;/sub&gt; single crystals is achieved by oxygen-assisted chemical vapor deposition method. By a unique facile multisource CVD growth method, the highly oriented and large domain size ML MoS&lt;sub&gt;2&lt;/sub&gt; films are epitaxially grown on a 4-inch wafer scale. Almost only 0° and 60° oriented domains are present in films, and the average size of MoS&lt;sub&gt;2&lt;/sub&gt; grains ranges from 100 μm to 180 μm . The samples exhibit their best optical and electrical quality ever obtained, as evidenced from their wafer-scale homogeneity, nearly perfect lattice structure, average room-temperature device mobility of ~70 cm&lt;sup&gt;2&lt;/sup&gt;·V&lt;sup&gt;–1&lt;/sup&gt;·s&lt;sup&gt;–1&lt;/sup&gt; and high on/off ratio of ~10&lt;sup&gt;9&lt;/sup&gt; on SiO&lt;sub&gt;2&lt;/sub&gt; substrates. By adjusting the oxygen doping concentration in the MoS&lt;sub&gt;2&lt;/sub&gt; film through using an effective CVD technique, electrical and optical properties can be well modified, thereby greatly improving the carrier mobilities and controllable n-type electronic doping effects resulting from optimized oxygen doping levels of MoS&lt;sub&gt;2–&lt;i&gt;x&lt;/i&gt;&lt;/sub&gt;O&lt;sub&gt;&lt;i&gt;x&lt;/i&gt;&lt;/sub&gt; . In terms of MoS&lt;sub&gt;2&lt;/sub&gt; thin film devices and applications, the 4-inch wafer-scale high-quality MoS&lt;sub&gt;2&lt;/sub&gt; monolayers are used to fabricate the transparent MoS&lt;sub&gt;2&lt;/sub&gt;-based transistors and logic circuits on flexible substrates. This large-area flexible FET device shows excellent electrical performance with a high device density (1,518 transistors per cm&lt;sup&gt;2&lt;/sup&gt;) and yield (97%), and exhibits a high on/off ratio (10&lt;sup&gt;10&lt;/sup&gt;), current density (~35 μA·μm&lt;sup&gt;–1&lt;/sup&gt;), mobility (~55 cm&lt;sup&gt;2&lt;/sup&gt;·V&lt;sup&gt;–1&lt;/sup&gt;·s&lt;sup&gt;–1&lt;/sup&gt;) and flexibility. Based on the vertically integrated multilayer device via a layer-by-layer stacking process, an individual layer of all-2D multifunctional FET is successfully achieved with nearly multiplied on-current density, equivalent device mobility, and persevered on/off ratio and subthreshold swing (SS) of the individual layer, the combined performance of the device is fully utilized, and the integration of “sensing-storing-computing” is realized. A two-terminal floating-gate memory (2TFGM) based artificial synapse built from all-2D van der Waals materials is prepared, the 2TFGM synaptic device exhibits excellent linear and symmetric weight update characteristics with high reliability and tunability. A large number of states of up to ≈3000, high switching speed of 40 ns and low energy consumption of 18 fJ for a single pulse are demonstrated experimentally. The introduction of structural domain boundaries in the basal plane of monolayer MoS&lt;sub&gt;2&lt;/sub&gt; can greatly enhance its hydrogen evolution reaction performance by serving as active sites. The progress we have made in the preparation of monolayer MoS&lt;sub&gt;2&lt;/sub&gt; films and the research on device characteristics is of guiding significance for the basic and application research of MoS&lt;sub&gt;2&lt;/sub&gt;, and also is universal and instructive for other 2D transition metal dichalcogenides.

(RE)Ba2Cu3O7-δ and the Roeser-Huber Formula.

We apply the Roeser–Huber formula to the (RE)BaCuO (REBCO with RE= rare earths) high- superconducting material class to calculate the superconducting transition temperature, , using the electronic configuration and the crystallographic data. In a former publication (H. P. Roeser et al., Acta Astronautica 2008, 62, 733–736), the basic idea was described and was successfully calculated for the YBaCuO compound with two oxygen doping levels 0.04 and 0.45, but several open questions remained. One of the problems remaining was the determination of for the 0.45 sample, which can be explained regarding the various oxygen arrangements being possible within the copper-oxide plane. Having established this proper relation and using the various crystallographic data on the REBCO system available in the literature, we show that the Roeser–Huber equation is capable to calculate the of the various REBCO compounds and the effects of strain and pressure on , when preparing thin film samples. Furthermore, the characteristic length, x, determined for the REBCO systems sheds light on the size of the -pinning sites being responsible for additional flux pinning and the peak effect.

Roles of oxygen-containing functional groups of O-doped g-C3N4 in catalytic ozonation: Quantitative relationship and first-principles investigation

Graphitic carbon nitride (g-C3N4) with varied oxygen doping levels was fabricated to investigate the quantitative relationship between oxygen-containing groups and activity of catalytic ozonation employing atrazine as a model pollutant. The regulation on both the types and the amounts of different oxygen-containing groups (CO/CO/COOH) were achieved by simply varying the dosage of the oxalate precursor. The regression analysis showed that the increase of CO/CO groups within appropriate range promoted the catalytic activity for ozonation, while the presence of carboxyl groups induced by excessive oxygen doping exhibited adverse effect. Moreover, the corresponding quantitative structure-activity relationships were established. The electron-rich O centers of oxygen doped g-C3N4 (CO/CO) were identified as the active sites for catalytic ozonation, and the enhanced adsorption of ozone on the active sites were substantiated by DFT calculations. This study is believed to shed light upon the roles of different oxygen-containing functional groups in catalytic ozonation by carbonaceous catalysts.

Tunable superconductivity of epitaxial TiN films through oxygen doping

Titanium nitride (TiN) film is a remarkable material for a variety of applications ranging from superhard coating to superconducting quantum devices, which can be easily oxidized when it works in the atmosphere. However, the study of its oxidation effect on the crystal and electronic structures of epitaxial TiN films is rare as yet. Here, we coherently synthesize TiN epitaxial films on MgO single crystal substrates via reactive magnetron sputtering and, then, dope oxygen into these films via a controllable oxidation process. The crystal and electronic structures are characterized by high-resolution x-ray diffraction, x-ray photoelectron spectra, and Raman spectra. It is revealed that the crystal structure remains to be of the rocksalt type in these films even with heavy oxygen doping. The data of temperature-dependent electrical transport measurements indicate that the superconducting critical temperature (kinetic inductance) decreases (increases) from 4.6 K (0.672 pH/□) in the pristine TiN film to 3.4 K (1.13 pH/□) in the film with a maximum oxygen doping level. Our work provides a controllable way to tune the superconductivity of TiN films, which enables the flexibility to engineer the resultant performance of TiN-based superconducting quantum devices.

Fabrication, Characterization and Implementation of Thermo Resistive TiCu(N,O) Thin Films in a Polymer Injection Mold

This paper presents the development of metallic thermoresistive thin film, providing an innovative solution to dynamically control the temperature during the injection molding process of polymeric parts. The general idea was to tailor the signal response of the nitrogen- and oxygen-doped titanium-copper thin film (TiCu(N,O))-based transducers, in order to optimize their use in temperature sensor devices. The results reveal that the nitrogen or oxygen doping level has an evident effect on the thermoresistive response of TiCu(N,O) films. The temperature coefficient of resistance values reached 2.29 × 10−2 °C−1, which was almost six times higher than the traditional platinum-based sensors. In order to demonstrate the sensing capabilities of thin films, a proof-of-concept experiment was carried out, integrating the developed TiCu(N,O) films with the best response in an injection steel mold, connected to a data acquisition system. These novel sensor inserts proved to be sensitive to the temperature evolution during the injection process, directly in contact with the polymer melt in the mold, demonstrating their possible use in real operation devices where temperature profiles are a major parameter, such as the injection molding process of polymeric parts.

Untwinned YBa2Cu3O7−δ thin films on MgO substrates: A platform to study strain effects on the local orders in cuprates

We have grown untwinned YBa$_2$Cu$_3$O$_{7-\delta}$ (YBCO) films on (110) MgO substrates that were pre-annealed at high temperature in oxygen atmosphere. The annealing results in surface reconstruction with shallow facets, which induce the suppression of the YBCO twinning domains, and the preferential alignment of the CuO chains along one of the in-plane directions of the substrate. Because of the large mismatch between the in-plane lattice parameters of film and substrate, the strain induced by the MgO into the YBCO layer is strong and very peculiar. The YBCO film is compressed, with respect to the bulk, and presents a unidirectional buckling of the atomic planes, along the chains' direction, due to a deformation of the copper-oxygen octahedra. The YBCO films, which can be grown with thicknesses down to few unit cells and oxygen doping levels spanning most of the superconducting dome, are patterned into nanowires with dimensions down to 50 nm. The anisotropies due to the untwinning state are preserved in these structures; moreover, additional anisotropies appear, in ultrathin structures where strain effects become more pronounced. Such untwinned and compressively strained films can therefore be used as a platform to study the interplay between strain and the various local orders in the normal state of YBCO.

Insights on the impact of doping levels in oxygen-doped gC3N4 and its effects on photocatalytic activity

In recent years, graphitic carbon nitride (gC3N4) has hit the limelight as a bright, metal-free and visible-light responsive photocatalyst. Pristine gC3N4, however, suffers from inadequate light absorption profile, limited surface area and significant recombination of photo-induced electron-hole pairs, thus requiring reformative strategies. Herein, this work has employed elemental doping of oxygen to gC3N4 (O-gC3N4) and uncovered the evolution of properties that arises in conjunction with increasing doping level. These intrusive changes in properties by increasing oxygen doping levels are then evaluated based on the trends observed from photocatalytic hydrogen (H₂) evolution. It is revealed that oxygen doping had a competing dual effect to the photocatalytic activity. On one hand, oxygen doping introduced more porosity and added sub-gap impurity states in its electronic band structure, which resulted in enhanced light harvesting capabilities. On the other hand, impurity levels from high density oxygen groups behave detrimentally as potent electron-holes recombination centers. This became the governing factor for higher doping levels O-gC3N4, which thereby resulted in a weakened photoactivity compared to pristine gC3N4. In overall, it is hoped that the findings of this study can provide a new understanding of the rational design and oxygen-doping strategy for gC3N4 for its photocatalytic enhancement.

White-light emission of blue-luminescent graphene quantum dots by europium (III) complex incorporation

Traditionally, graphene quantum dots are prepared by fragmentation of graphene sheets into the nanoscale particles of controlled sizes followed by band gap adjustment by doping with electron-donating elements. Our novel synthetic aqueous arc discharge process has been developed to produce the blue-luminescent graphene quantum dots (bGQDs). The resulting bGQDs are ∼15 nm in diameter and the amount of oxygen-including functional groups can be controlled to 27.4% and 30.8% at 1 and 4 A of a current level, respectively. The presence of a band gap is confirmed by using scanning tunneling microscopy/spectroscopy (STM/STS). Additionally, we investigated the effect of oxygen doping levels on the band gap by photoluminescence (PL) behaviors and a density functional theory (DFT). The PL emission is red-shifted from 397 to 425 nm corresponding to the amount of oxygen-including functional groups in bGQDs and the DFT calculation confirms the decrease in a band gap from ∼2.0 to ∼1.7 eV due to electron donation from oxygen. In addition, our quantum dots have promising applications for practical use in optoelectronics devices. For example, tris-dibenzoylmethane mono-1,10-phenanthroline-europium (III) (EuIIIDP) is incorporated with bGQDs for white-light emission and is shown to be successfully fabricated into light-emitting polymer films.

Examination of the Thermal Annealing Process in Producing YBa $_{2}$Cu$_{3}$O $_{\nabla x}$ Films and Characterization of Pressure Stabilized Oxygen Chain States

We examine the nature of thermal flow during the annealing process of a recently reported method to produce films of the high-T c superconducting compound YBa 2 Cu 3 O x wherein the oxygen content (x) spatially varies across the length of the sample. In this context, we discuss contrasting annealing results that can be expected under differing annealing configurations-including the formation of discrete regions of pressure stabilized oxygen content associated with known lattice superstructures. We also examine characteristic energy scales associated with the corresponding normal and superconducting states of these stabilized superstructures. A relationship between ratios of the superconducting gap energy, superconducting electronic kinetic energy, and the BCS-Eliashberg coupling constant associated with each lattice superstructure is found. The near integer ratios observed suggest that the superstructures can be viewed as “quantum structural” lattice states in the sense that oxygen doping levels in between are composed of a superposition of ordered structures.

Oxygen vacancy induced ferromagnetism in Cu-doped ZnO

Cu-doped ZnO was synthesized by hydrothermal method in a pulsed magnetic field. X-ray diffraction reveals the hexagonal wurtzite structure as with pure ZnO. The application of pulsed magnetic field increases the oxygen vacancy content and doping level of Cu2+ analyzed by Raman spectra and X-ray photoelectron spectroscopy. The origin of ferromagnetism is attributed to the oxygen vacancies induced Cu2+ ferromagnetic coupling.