Effect Of Nitrogen Doping Research Articles

Rapid Access to Ordered Mesoporous Carbons for Chemical Hydrogen Storage.

Ordered mesoporous carbon materials offer robust network of organized pores for energy storage and catalysis applications, but suffer from time-consuming and intricate preparations hindering their widespread use. Here we report a new and rapid synthetic route for a N-doped ordered mesoporous carbon structure through a preferential heating of iron oxide nanoparticles by microwaves. A nanoporous covalent organic polymer is first formed in situ covering the hard templates of assembled nanoparticles, paving the way for a long-range order in a carbonaceous nanocomposite precursor. Upon removal of the template, a well-defined cubic mesoporous carbon structure was revealed. The ordered mesoporous carbon was used in solid state hydrogen storage as a host scaffold for NaAlH4 , where remarkable improvement in hydrogen desorption kinetics was observed. The state-of-the-art lowest activation energy of dehydrogenation as a single step was attributed to their ordered pore structure and N-doping effect.

Boron- and nitrogen-doped graphene quantum dots with enhanced supercapacitance

Graphene quantum dots (GQDs) with their very large specific surface area and numerous edges can offer promising novel features as metal-free and inexpensive electrodes of supercapacitors. Here, we investigated the effect of boron and nitrogen doping in GQDs on their electrochemical energy storage properties. The GQDs as well as B-GQDs and N-GQDs were synthesized by a facile hydrothermal method and characterized by X-ray diffractometry, UV-Vis absorption spectrophotometry, transmission electron microscopy, and energy-dispersive X-ray mapping techniques. Electrochemical properties of the nanoparticles were investigated in a three-electrode setup using cyclic voltammetry and galvanostatic charge/discharge techniques in KOH electrolyte. The N-GQDs electrode showed the highest specific capacitance of 283 F/g at 1 A/g as compared to the GQDs and B-GQDs electrodes. The N-GQDs electrode exhibited the specific energy and specific power of 6.2 Wh/Kg and 108 W/Kg, respectively. The N-GQDs electrode showed also better cycling stability (80% capacity retention) than the GQDs and B-GQDs electrodes.

Synergistic improvement of device performance and bias stress stability of IGZO TFT via back-channel graded nitrogen doping

The electrical instability of a-IGZO TFTs limits its application in future display. Here, we investigate the effects of nitrogen doping on the electrical properties and bias stability of a-IGZO TFTs, and the IGZO films were obtained by magnetron sputtering using ceramic targets (In:Ga:Zn = 4:2:2). The performance and bias stability of a-IGZO TFTs are improved synergistically. The optimized device has a high mobility of 38.36 cm2/vs, threshold voltage of 1.11 V, subthreshold swing of 101.2 mV/dec, and the performance and stability are effectively improved, which may be mainly due to the back channel gradient nitrogen doping avoiding the formation of heterojunction interface and reducing the defect of bulk channel layer.

Effect of Nitrogen and Aluminum Doping on 3C-SiC Heteroepitaxial Layers Grown on 4° Off-Axis Si (100).

This work provides a comprehensive investigation of nitrogen and aluminum doping and its consequences for the physical properties of 3C-SiC. Free-standing 3C-SiC heteroepitaxial layers, intentionally doped with nitrogen or aluminum, were grown on Si (100) substrate with different 4° off-axis in a horizontal hot-wall chemical vapor deposition (CVD) reactor. The Si substrate was melted inside the CVD chamber, followed by the growth process. Micro-Raman, photoluminescence (PL) and stacking fault evaluation through molten KOH etching were performed on different doped samples. Then, the role of the doping and of the cut angle on the quality, density and length distribution of the stacking faults was studied, in order to estimate the influence of N and Al incorporation on the morphological and optical properties of the material. In particular, for both types of doping, it was observed that as the dopant concentration increased, the average length of the stacking faults (SFs) increased and their density decreased.

Columnar nitrogen-doped ZnO nanostructured thin films obtained through atomic layer deposition

The present study was aimed to develop nitrogen-doped nanostructured ZnO thin films. These films were produced in a sequential procedure involving the atomic layer deposition technique, and a hydrothermal process supported by microwave heating. Employing the atomic layer deposition technique, through self-limited reactions of diethylzinc (DEZn) and H2O, carried out at 3.29 × 10−4 atm and 190 °C, a high-quality ZnO seed was grown on a Si (100) substrate, producing a textured film. In a second stage, columnar ZnO nanostructures were grown perpendicularly oriented to the silicon substrate on those films, using a solvothermal process in a microwave heating facility, employing Zn(NO3)2 as zinc precursor, while hexamethylenetetramine (HMTA) was used to produce the bridging of Zn2+ ions. The consequence of N-doping concentration on the physicochemical properties of ZnO thin films was studied. The manufactured films were structurally analyzed by scanning electron microscopy and x-ray diffraction. Also, x-ray photoelectron spectroscopy, Raman, and UV–vis spectroscopies were used to provide further insight on the effect of nitrogen doping. The N-doped films displayed textured wurtzite-like structures that changes their preferential growth from the (002) to the (100) crystallographic plane, apparently promoted by the increase of nitrogen precursor. It is also shown that nitrogen-doped films undergo a reduction in their bandgap, compared to ZnO. The methodology presented here provides a viable way to perform high-quality N-ZnO nanostructured thin films.

Nitrogen and bismuth-doped rice husk-derived carbon quantum dots for dye degradation and heavy metal removal

In this study, heteroatoms doped carbon quantum dots were synthesized using rice husk as a biowaste precursor. The effects of nitrogen and bismuth doping are investigated by adjusting the amount of ethylenediamine (EDA) as the nitrogen source, and bismuth nitrate pentahydrate as the bismuth source. HRTEM analysis depicted the formation of spherical carbon quantum dots, with a size of less than 10 nm. FTIR and XPS analysis confirmed the presence of essential functional groups and chemical composition in both of the doped carbon quantum dots. UV–Vis spectra showed peaks which are associated to the electronic transition of the C = C bonding. The addition of EDA and bismuth nitrate pentahydrate tuned the fluorescence intensity and shifted the emission wavelength from the blue region to green one. The performance of the doped rice husk derived carbon quantum dots (RHCQDs) was evaluated via photodegradation of the methylene blue (MB), under a 300 W Xenon lamp. as well as via copper (II) removal. N-RHCQDs (10 vol%) and Bi-RHCQDs (5 wt%) demonstrated the highest MB degradation performance, at 72.16% and 68.91%, respectively. The degradation of MB of the two doped RHCQDs fitted with the pseudo-second kinetic model. The doped RHCQDs were then tested for copper (II) removal, obtaining removal performance of 56.23% and 33.13%, respectively. The results suggest that the Cu (II) adsorption onto the N-RHCQDs and Bi-RHCQDs agrees with the pseudo-second kinetic model and the Langmuir isotherm, with maximum adsorption capacity of 5.73 and 4.08 mg/g, respectively.

Effect of nitrogen doping on the microstructure and thermal stability of diamond-like carbon coatings containing silicon and oxygen

Using hexamethyldisiloxane, acetylene, and N2 as the precursors, binary Si/O and ternary Si/O/N co-doped diamond-like carbon (DLC) coatings were deposited on 316 L stainless steel and single-crystal Si wafer substrates via high-bias voltage plasma-enhanced chemical deposition. The coated specimen was annealed in the temperature range 200–650 °C in a chamber maintained at 5 Pa vacuum. The microstructure and chemical bonds were characterized using X-ray diffraction, Fourier-transform infrared spectroscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy. The mechanical properties were investigated using a residual stress tester and a nano-indenter. It was found that approximately 50% of the Si in the binary Si/O co-doped coating were present as SiO bonds. Notably, N doping reduced the sp3 CC fraction, hindered the formation of O-containing bonds, and enhanced the SiC bonds in the as-deposited ternary Si/O/N co-doped coatings; however, the dominant chemical state of the N atom remained in the form of CN bonds. Furthermore, N doping was beneficial toward the stabilization of the SiC and SiO bonds and hindered graphitization during annealing. The thermal stability of the microstructure and mechanical performance of the ternary co-doped DLC coatings were superior to those of the binary Si/O-co-doped DLC coatings. After annealing at 500 °C, the ternary coatings retained a hardness of 16.5 GPa.

Effect of Nitrogen Doping on the Crystallization Kinetics of Ge2Sb2Te5.

Among the phase change materials, Ge2Sb2Te5 (GST-225) is the most studied and is already integrated into many devices. N doping is known to significantly improve some key characteristics such as the thermal stability of materials and the resistance drift of devices. However, the origin, at the atomic scale, of these alterations is rather elusive. The most important issue is to understand how N doping affects the crystallization characteristics, mechanisms and kinetics, of GST-225. Here, we report the results of a combination of in situ and ex situ transmission electron microscopy (TEM) investigations carried out on specifically designed samples to evidence the influence of N concentration on the crystallization kinetics and resulting morphology of the alloy. Beyond the known shift of the crystallization temperature and the observation of smaller grains, we show that N renders the crystallization process more “nucleation dominated” and ascribe this characteristic to the increased viscosity of the amorphous state. This increased viscosity is linked to the mechanical rigidity and the reduced diffusivity resulting from the formation of Ge–N bonds in the amorphous phase. During thermal annealing, N hampers the coalescence of the crystalline grains and the cubic to hexagonal transition. Making use of AbStrain, a recently invented TEM-based technique, we evidence that the nanocrystals formed from the crystallization of N-doped amorphous GST-225 are under tension, which suggests that N is inserted in the lattice and explains why it is not found at grain boundaries. Globally, all these results demonstrate that the origin of the effect of N on the crystallization of GST-225 is not attributed to the formation of a secondary phase such as a nitride, but to the ability of N to bind to Ge in the amorphous and crystalline phases and to unbind and rebind with Ge along the diffusion path of this atomic species during annealing.

Nitrogen doping and oxygen vacancy effects on the fundamental properties of BeO monolayer: a DFT study

In practice, modifying the fundamental properties of low-dimensional materials should be realized before incorporating them into nanoscale devices. In this paper, we systematically investigate the nitrogen (N) doping and oxygen vacancy (OV) effects on the electronic and magnetic properties of the beryllium oxide (BeO) monolayer using first-principles calculations. Pristine BeO single layer is a non-magnetic insulator with an indirect K–Γ gap of 5.300 eV. N doping induces a magnetic semiconductor nature, where the spin-up and spin-down band gaps depend on the dopant concentration and N–N separation. Creating one OV leads to the energy gap reduction of 31.06% with no spin-polarization, which is due to the abundant 2p electrons of the Be atoms nearest the OV site. The further increase to two OVs and varying the OV–OV distance affect the band gap values, however the spin independence is retained. The magnetic semiconducting behavior is also obtained by the simultaneous N doping and OV presence. Calculations reveal significant magnetization of the BeO@1N, BeO@2N-n, BeO@NOV-n systems, which is produced mainly by the spin-up N–2p state. Except for the BeO@NOV-1 and BeO@NOV-2, whose magnetic properties are created by the spin-up 2p state of the Be atoms closest to the OV site. The variation of the N–N and N–OV distances keeps the ferromagnetic ordering in the BeO@2N and BeO@NOV layers. Results presented herein may propose efficient methods to artificially modify the physical properties of BeO monolayer, leading to the formation of novel two-dimensional (2D) materials for optoelectronic and spintronic applications.

Nitrogen and Fluorine Dual Doping of Soft Carbon Nanofibers as Advanced Anode for Potassium Ion Batteries.

Potassium-ion batteries (PIBs) are recognized as promising alternatives for lithium-ion batteries as the next-generation energy storage systems. However, the larger radius of K+ hinders the K+ insertion into the conventional carbon electrode and results in sluggish potassiation kinetics and poor cycling stability. Here, nitrogen and fluorine dual doping of soft carbon nanotubes (NFSC) anode are synthesized in one pot, achieving extraordinary electrochemical performance for PIBs. It is demonstrated that NFSC with a doping dose of 5.6 at% nitrogen and 1.3 at% fluorine together exhibits the highest reversible capacity of 238 mAh g-1 at 0.2 A g-1 and cycling stability of 186 mAh g-1 after 1000 cycles at 1 A g-1 . The extraordinary electrochemical performance can be attributed to the hollow structure, expanded interlayer distance, nitrogen and fluorine dual doping, and the binding ability of abundant defect sites. Moreover, density functional theory shows that the extra fluorine modification can dramatically enhance the conventional nitrogen doping effect and reduces the formation energy which makes a great contribution to the improvement of electrical conduction and K-ions insert. This work may promote the development of low-cost and sustainable carbon-based materials for PIBs and other advanced energy storage devices.

Effect of nitrogen doping on the structure of metastable β-W on SiO2

Metastable β-W phase exhibits a large spin Hall effect which has attracted a great interest for spin-orbit torque-based memory applications. Here we study the growth and structure of W films prepared by magnetron sputtering under different argon and nitrogen gas mixture conditions. X-ray diffraction and sheet resistivity show that low argon with low nitrogen gas flow stabilizes the β-W phase in thick films. High argon gas flow promotes the growth of porous β-W films which increases the oxygen content and the resistivity of the films. It is observed that the N2 doping of the W films reduce the perpendicular magnetic anisotropy of an adjacent CoFeB layer.

Nitrogen-Doped Graphdiyne as a Robust Electrochemical Biosensing Platform for Ultrasensitive Detection of Environmental Pollutants.

Owing to its unique chemical structure, natural pores, high structure defects, good surface hydrophilicity and biocompatibility, and favorable electrical conductivity, nitrogen-doped graphdiyne (NGDY) has been attracting attention in the application of electrochemical sensing. Taking advantage of these fascinating electrochemical properties, for the first time, two types of electrochemical enzymatic biosensors were fabricated for the respective detection of organophosphorus pesticides (OPs) and phenols based on the immobilization of acetylcholinesterase or tyrosinase with NGDY. Results revealed that the sensitivities of the NGDY-based enzymatic biosensors were almost twice higher than that of the matching biosensor in the absence of NGDY, proving that NGDY plays a vital role in immobilizing the enzymes and improving the performance of the fabricated biosensors. The effects of nitrogen doping on improving the biosensing performance were studied in depth. Graphitic N atoms can enhance the electrical conductivity, while imine N and pyridinic N can help to adsorb and accumulate the substance molecules to the electrode surface, all of which contribute to the significantly improved performance. Furthermore, these two types of biosensors also demonstrated excellent reproducibility, high stability, and good recovery rate in real environmental samples, which showed a valuable way for the rapid detection of OPs and phenols in the environment. With these excellent performances, it is strongly anticipated that NGDY has tremendous potential to be applied to many other biomedical and environmental fields.

Effect of Nitrogen Doping on Structural, Electrical, and Optical Properties of CuO Thin Films Synthesized by Radio Frequency Magnetron Sputtering for Photovoltaic Application

Effects of N-doping in CuO thin films synthesized in an ambient of Ar, O2 and N2 using a pure Cu target by radio frequency (RF) magnetron sputtering are investigated systematically with the detailed analyses on the structural, electrical, and optical properties of the thin films. A strong N-doping effect was observed on the composition, morphology, and functional properties of the resulting CuO films with the change of N2 gas flow rate (). X-ray diffraction (XRD) and Raman spectroscopy confirmed the formation of the single phase of N-doped CuO at the studied from 0 to 4 sccm. The atomic force microscopy (AFM) showed sub-rounded shape of the CuO grains. N concentrations in the N-doped CuO thin films were increased almost linearly from 1.3 × 1020 to 3.3 × 1020 cm−3 which was investigated and confirmed by SIMS. Optical absorption results of both undoped and N-doped CuO films demonstrated a direct transition at E g = 1.52 ∼ 1.56 eV with high absorption coefficient. All the undoped and N-doped CuO thin films showed p-type conductivity, and the resistivity of N-doped CuO decreases from 810 to 18 Ωcm with the increase of from 0 to 4 sccm. These results demonstrate the p-type conductivity control by N-doping, leading to the potential of N-doped CuO as an absorber material for solar cells.

Effect of amino acid-derived nitrogen and/or sulfur doping on the visible-light-driven antimicrobial activity of carbon quantum dots: A comparative study

• Un-doped CQD (C-CQD), N doped CQD (N-CQD), and NS doped CQD were synthesized with malic acid, alanine, and cysteine. • N and/or S doping lowered the band gap energy, making CQD have the visible-light-driven (VLD) antimicrobial activity. • VLD antimicrobial activity increases as the ratio of S decreases during N and S doping. • N-CQD had greater specific surface area, the fluorescence quantum yield and photoluminescence lifetime values than NS-CQD. The purpose of this study was to investigate the effects of nitrogen and sulfur derived from amino acids on the visible-light-driven (VLD) antimicrobial activity of carbon quantum dots (CQDs) and to establish an optimal doping form. Various CQDs were synthesized by combining malic acid as a carbon source, alanine containing N, and cysteine containing N and S through microwave heating. The results showed that the VLD antimicrobial activity of the CQD against Gram-positive ( Staphylococcus aureus and Listeria monocytogenes ) and Gram-negative pathogens ( Escherichia coli O157:H7 and Salmonella Typhimurium) was improved by N and/or S doping, which increased as the ratio of S decreased. The doping of N and/or S made CQDs have a lower band gap energy, and CQD doped with only N (N-CQDs) exhibited greater specific surface area and fluorescence quantum yields (FLQYs), and longer photoluminescence (PL) lifetimes than CQD doped with N and S (NS-CQDs) even though NS-CQD and N-CQD had similar hand gap energies. Based on these results, the mechanism by which the VLD antimicrobial activity of CQD changes by doping was discussed. Furthermore, this study suggests that for CQD synthesis using food by-products, the more amino acids that can induce the doping of N and/or S, wherein the smaller ratio of S containing amino acids, the better VLD antimicrobial activity the synthesized CQD will have.

How Nitrogen Doping Affects Hydrogen Spillover on Carbon-Supported Pd Nanoparticles: New Insights from DFT

The process of hydrogen spillover on metal nanoparticle decorated carbon surfaces has been discussed for many years due to its importance for heterogeneous catalysis and hydrogen storage. The present density functional theory (DFT) study supports recent experimental observations of the hydrogen spillover process. By use of model systems of carbon-supported palladium nanoparticles, the details of hydrogen spillover are investigated and the effects of nitrogen doping on such processes are elucidated. It is found that graphitic nitrogen atoms and water molecules significantly facilitate the hydrogen spillover reaction and serve as anchoring sites for the spillover hydrogen atoms.

Plasma enhanced atomic layer deposition of a (nitrogen doped) Ti phosphate coating for improved energy storage in Li-ion batteries

The use of Ti phosphate as a functional coating for Li ion battery electrodes has been investigated, as well as the effect of nitrogen doping on its electrochemical properties. First, previous knowledge on PE-ALD of Ti phosphate (using an exposure sequence of trimethylphosphate plasma–oxygen plasma–titaniumisopropoxide) was used to study an altered process using a nitrogen plasma, i.e. TMP* - N2* - TTIP. This enabled the deposition of a nitrogen doped (6 at.%) Ti phosphate with a growth per cycle of 0.4 nm/cycle. Next, a dual-source precursor (diethylphosphoramidate plasma, or DEPA*) was introduced instead of TMP*, allowing for a higher growth rate (0.6 nm/cycle) and a higher nitrogen level (8.6 at.%). The ionic transparency of the phosphate slightly decreased due to nitrogen incorporation, but the effective transversal electronic conductivity showed to be three times higher after nitrogen doping. A 2 nm coating of (un)doped Ti phosphate significantly improved the rate capability of a lithium nickel manganese cobalt oxide (NMC) electrode, increasing the amount of energy that can be stored at high (dis)charging speeds with a factor 10 (at 5C). In addition, the undoped titanium phosphate coating offered increased stability, retaining 84% of the capacity after 100 cycles at 1C with respect to 79% for the uncoated electrode.

Investigation of the metal-to-insulator transition of N-doped VO2(M1) thin films

This work reports the effect of nitrogen doping on the electrical and optical properties of VO2 thin films. An innovative method based on a VN target and an O2 ambient gas was used to synthesize N:VO2 films on quartz substrates using reactive pulsed laser deposition (RPLD). The doping percentage was determined by elastic recoil distribution (ERD) measurements, while temperature-dependent Raman spectroscopy as well as electrical resistivity and infrared reflectance measurements were performed to investigate the effect of N-doping on the insulator monoclinic-to-metallic tetragonal phase transition (IMT) of VO2. A small doping percentage around 0.7 at.% was achieved, inducing a decrease of the transition temperature TIMT from 68 °C to 50 °C, with slightly reduced electrical contrast ΔR and optical contrast ΔA. By comparing the volume fraction of monoclinic phase, obtained from Raman data to the volume fraction of metallic phase deduced concurrently from both electrical and optical measurements, the IMT in our nitrogen-doped VO2 films occurs through a percolation process.

Investigation into surface composition of nitrogen-doped niobium for superconducting RF cavities

Systematic analysis of the surface morphology, crystalline phase, chemical composition and elemental distribution along depth for nitrogen-doped niobium was carried out using different methods of characterization, including Scanning Electron Microscopy (SEM), Atomic-Force Microscopy (AFM), Grazing Incidence X-ray Diffraction (GIXRD), Rutherford Backscattering Spectrometry (RBS) and layer-by-layer X-ray Photoelectron Spectroscopy (XPS) analysis. The results showed that, after nitrogen doping, the surface was covered by densely distributed trigonal precipitates with an average crystallite size of 32 ± 8 nm, in line with the calculation result (29.9 nm) of nitrogen-enriched β-Nb2N from GIXRD, demonstrating the phase composition of trigonal precipitates. The depth analysis through RBS and XPS indicated that β-Nb2N was dominant in the topmost 9.7 nm and extended to a depth of 575 nm, with gradually decreased content. In addition, the successive change along depth in the naturally oxidized states of niobium after nitrogen doping, was revealed. It was interesting to find that the oxygen diffusion depth could be moderately enhanced by the nitridation process. These results established the near-surface phase composition of nitrided niobium, which is of great significance in evaluating the effect of nitrogen doping and further understanding the Q improvement of the superconducting radio frequency cavities.

Effect of facile nitrogen doping on catalytic performance of NaW/Mn/SiO2 for oxidative coupling of methane

The oxidative coupling of methane (OCM) has great potential as a cost-effective pathway to directly convert methane to C2 species such as ethane and ethylene. Although NaW/Mn/SiO2 is one of the most promising catalysts for OCM, an improvement in its catalytic performance is required to achieve high C2 yield. Herein, we show that a relatively simple pyridine treatment of NaW/Mn/SiO2 leads to nitrogen-doping of the active sites, resulting in significantly high CH4 conversion rate while maintaining high C2 selectivity. Various characterisation techniques such as X-ray diffraction analysis, X-ray photoelectron spectroscopy, temperature-programmed reduction analysis, transmission electron microscopy, and density functional theory calculations are employed to understand the effect of N doping on the performance of NaW/Mn/SiO2 for OCM.

Cu-Co bimetal oxide hierarchical nanostructures as high-performance electrocatalyst for oxygen evolution reaction

Electrochemical water splitting requires efficient and low-cost catalysts to accelerate the sluggish kinetics of the oxygen evolution reaction (OER). Nanostructural engineering is an effective way to achieve improved catalytic performance. Herein, hierarchical nanostructures consisting of porous nanofiber arrays on vertically aligned and interconnected copper-cobalt bimetal oxide nanoflakes are fabricated. The effect of annealing temperature and microstructure on the OER performance has been systematically investigated. The optimized sample exhibits a low overpotential of 293 mV at 10 mA/cm2, with a Tafel slope of 62 mV/dec for OER in an alkaline solution. Effect of nitrogen doping has also been investigated, which results in a further lowered overpotential of 265 mV at a current density of 10 mA/cm2 and a 60 mV/dec Tafel slope. This work demonstrates the effectiveness of nanocrystalline catalysts with rationally tuned hierarchical structures in enhancing the OER performance.