NH3 Annealing Research Articles

Nitrogen Doping Engineering of V2CTx based Zinc Ion Hybrid Microcapacitors with Quadruple High Energy Density

To accommodate the long-term and stable energy supply requirements for wearable electronics, the reported flexible zinc ion hybrid microcapacitor (ZIHMC) needs to further increase the energy density. So, a nitrogen doped V2CTx (N-V2CTx) based ZIHMC was proposed to achieve high electrochemical performance. The introduction of N heteroatoms by NH3 annealing can dramatically increase the electrical conductivity of V2CTx and simultaneously widen the voltage window to 1.9 V. In detail, the doped nitrogen atoms in V2CTx based device has a maximum capacity of 293.0 mF cm–2, four times higher than that of pure V2CTx based ZIHMC. The mechanism of the enhanced electrochemical performance by nitrogen doped V2CTx was revealed by the experimental analysis and theoretical simulation. And the N-V2CTx based ZIHMC demonstrated high energy density with 150.0 μWh cm–2 at a power density of 380.0 μW cm–2 and excellent stability with 94.80% capacitance retention after 3000 charge-discharge cycles. The N-V2CTx based ZIHMC also presents excellent flexibility without virtually capacity loss after 3000 bending cycles. The good electrochemical performance and flexibility of N-V2CTx ZIHMC make it has potential applications in flexible wearable electronics.

Influencing the surface quality of free-standing wurtzite gallium nitride in ultra-high vacuum: Stoichiometry control by ammonia and bromine adsorption

Gallium nitride (GaN), a wide bandgap semiconductor with absorption and emission in the ultraviolet/visible range, is proposed as an alternative to metallic surfaces for assembling organic molecular structures aiming at optoelectronic applications. However, the formation of a persistent surface oxide layer in air considerably limits the use of GaN for well-defined interfaces. In this work, we have investigated, characterized and processed n-type free-standing c-plane hexagonal wurtzite GaN crystals grown by hydride vapor phase epitaxy and ammonothermal growth methods. Surface cleaning and full removal of the oxide layer on GaN surfaces could be reproducibly achieved via sputtering and annealing cycles, as evidenced by X-ray photoelectron spectroscopy and low-energy electron diffraction. Scanning tunneling microscopy, however, indicated substantial roughening of the GaN surface and the formation of unwanted Ga-rich islands and clusters. Although ammonia (NH3) and bromine (Br) treatments compensated the N/Ga atoms ratio reduced by sputtering, the surface morphology remained rough, exhibiting randomly shaped and distributed hillocks. In addition, we studied the effect of electron bombardment on the surface quality of GaN during NH3 annealing, on-surface debromination and polymerization of 1,3,5-tris(4-bromophenyl) benzene on GaN, and the removal of Ga atoms by Br atoms during the desorption.

Nanostructured N-doped Ti3C2/TiO2 composite for high-performance supercapacitor

Herein, the N-doped Ti3C2/TiO2 nanostructure has been synthesized via hydrothermal treatment and following annealing in NH3. TiO2 nanoparticles in-situ grow on the surface of Ti3C2 spontaneously, resulting in the stable electron transport between TiO2 and Ti3C2. Besides, Ti3C2 nanosheets as conductive substrates make up for the poor conductivity of TiO2. The doping of N in Ti3C2/TiO2 composite further improves the electrical conduction. The ultimate N-doped Ti3C2/TiO2 composite achieves a higher specific capacitance of 737.4 F g−1 than Ti3C2 (324.4 F g−1) at 0.5 A g−1. More importantly, the composite displays a high specific capacitance retention of 81 % over 12,000 cycles. Besides, the assembled symmetrical supercapacitor (SSC) manifests an excellent specific capacitance of 236.4 F g−1 at 1 A g−1 and a comparable energy density of 32.8 Wh kg−1 at the power density of 500 W kg−1. This work provides promising guidance for the fabrication of durable electrodes for energy storage application.

Research on Evolution of Relevant Defects in Heavily Mg-Doped GaN by H Ion Implantation Followed by Thermal Annealing.

This study focuses on the heavily Mg-doped GaN in which the passivation effect of hydrogen and the compensation effect of nitrogen vacancies (VN) impede its further development. To investigate those two factors, H ion implantation followed by thermal annealing was performed on the material. The evolution of relevant defects (H and VN) was revealed, and their distinct behaviors during thermal annealing were compared between different atmospheres (N2/NH3). The concentration of H and its associated yellow luminescence (YL) band intensity decrease as the thermal annealing temperature rises, regardless of the atmosphere being N2 or NH3. However, during thermal annealing in NH3, the decrease in H concentration is notably faster compared to N2. Furthermore, a distinct trend is observed in the behavior of the blue luminescence (BL) band under N2 and NH3. Through a comprehensive analysis of surface properties, we deduce that the decomposition of NH3 during thermal annealing not only promotes the out-diffusion of H ions from the material, but also facilitates the repair of VN on the surface of heavily Mg-doped GaN. This research could provide crucial insights into the post-growth process of heavily Mg-doped GaN.

Preparation of nitrogen-doped activated carbon used for catalytic oxidation removal of H2S

In this study, nitrogen-doped modified activated carbons were synthesized for H2S removal from Zhuxi activated carbon and 4,4′-bipyridine as raw material and nitrogen source, respectively. The synthesis strategy was hydrothermal treatment and subsequent NH3 annealing, and the formation and conversion patterns of the different N configurations were investigated. When the annealing temperatures were 500 °C and 600 °C, N-5 account for the majority. As the annealing temperature increased, the proportion of N-6 gradually increased. After the temperature increased to 1000 °C, N-5 and N-6 were converted to N-Q to a certain degree, while the amount of nitrogen doping decreased significantly. The sample H160-0.2-800 exhibited excellent H2S removal with a high sulfur capacity of up to 206.89 mg/g, significantly higher than that of the original activated carbon ZX1200 (67.56 mg/g). The reason for this is that the micropores (Vmic = 0.5155 cm3/g) and specific surface area (SBET = 1369.5 m2/g) of the modified activated carbon are more developed than those of the original activated carbon. A high nitrogen content (3.14 wt%) and N-6 configuration proportion (73.56 %) are significant reasons for the excellent adsorption properties. The mechanism of the catalytic oxidation was investigated. The introduction of surface nitrogen-containing functional groups alkalizes the activated carbon surface, enhancing the adsorption and dissociation of H2S and O2 and facilitating the formation of sulfur radicals and elemental sulfur.

Effect of post-treatment on photocatalytic activity of anodic titania photonic crystals

One of the possible ways to enhance photocatalytic activity is the use of photonic band gap (PBG) materials. Anodic titania photonic crystals (PhCs) are promising PBG structures, whose structure can be tuned easily by anodizing conditions. However, the effect of various doping approaches on the photocatalytic activity of anodic titania PhCs has never been studied before. Here anodic titania PhCs were synthesized by cycling anodizing of titanium with voltage versus charge density modulation followed by annealing at 450 °C in air. The PhCs were post-treated by electrochemical reduction in 0.1 M Na2SO4, annealing in H2/Ar mixture or NH3. The phase composition and structure of titania PhCs were studied by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, and electron paramagnetic resonance spectroscopy. Photocatalytic activity of PhCs in the degradation of the methylene blue dye decreases after electrochemical reduction and annealing in NH3, whereas the annealing in H2/Ar at 600 °C for 2 h leads to an increase in the degradation rate constant by 60%.

High-performance 2D WS2 photodetector enhanced by charge-transfer doping through NH3 annealing

Transition metal dichalcogenides (TMDs) are potential candidates towards the next-generation photodetector, owing to their tunable energy bandgap and strong light–matter interaction. However, the low charge-carrier mobility and insufficient quantum efficiency of TMDs-based devices restrain their optoelectronic performances. Therefore, an effective and facile doping method needs to be developed for overcoming their poor optoelectronics properties. Here, we demonstrate a controllable nondegenerate n-doping technique for 2D TMDs materials by annealing under NH3 flow. The on/off current ratio and field-effect mobility of the device after annealing treatment increases about 2 orders of magnitude and 23 times, respectively. We attribute this remarkable doping effect to the physical adsorption and chemical adsorption of NH3 as well as the associated formation of isolated sulfur vacancies, which is dynamically activated during the annealing treatment, and further verified by the atomic-scale characterization and density functional theory calculations. The annealing temperature and time present a controllable modulation on the electron doping levels of the WS2 channel. The fabricated WS2 photodetector can operate in a broad range of visible light at room temperature. At 532 nm wavelength, the responsivity of 2.97 A/W, external quantum efficiency of 699% and specific detectivity of over 1010 Jones indicate its great potential in sensitive and power-efficient photodetectors. Our results provide an effective method to realize controllable n-doping of 2D materials, aiming for fabricating high-performance 2D photodetectors.

Impact of operation voltage and NH3 annealing on the fatigue characteristics of ferroelectric AlScN thin films grown by sputtering.

This work investigates the impact of the magnitude of cycling voltage on the fatigue characteristics of 40 nm-thick AlScN ferroelectric thin film. The fatigue rate and the rejuvenation of remanent polarization vary with the cycling voltage. The primary fatigue mechanism is identified to be the interfacial layer formation and domain wall pinning at high and low cycling voltages, respectively. Additionally, annealing the film under the NH3 atmosphere decreases the fatigue rate and improves endurance by eliminating impurities in the film. The amount of trapped charges at the interface also decreases after NH3 annealing, leading to a reduction in leakage current. Furthermore, the ferroelectric performance of the AlScN film is not degraded after the thermal annealing at 900 °C under the NH3 environment, suggesting its robustness against the severe thermal budget. It is concluded that NH3 annealing is a promising method to address the reliability issue of the AlScN film.

Toward a Mechanistic Understanding of the Formation of 2D-GaNx in Epitaxial Graphene

Ultrathin 2D-GaNx can be formed by Ga intercalation into epitaxial graphene (EG) on SiC followed by nitridation in ammonia. Defects in the graphene provide routes for intercalation, but the nature and role of the defects have remained elusive. Here we examine the influence of graphene layer thickness and chemical functionalization on Ga intercalation and 2D-GaNx formation using a combination of experimental and theoretical studies. Thin buffer layer regions of graphene near steps on SiC readily undergo oxygen functionalization when exposed to air or a He/O2 plasma in contrast to thicker regions which are not chemically modified. Oxygen functionalization is found to inhibit Ga intercalation leading to accumulation of Ga droplets on the surface. In contrast, Ga readily intercalates between EG and SiC in the thicker graphene regions that do not contain oxygen. When NH3 annealing is carried out immediately after Ga exposure, 2D-GaNx formation is observed only in the oxygen-functionalized regions, and Ga intercalated under thicker nonfunctionalized graphene does not convert to GaNx. Density functional theory calculations demonstrate that oxygen functionalization of graphene alters the binding energy of Ga and NH3 species to the graphene surface. The presence of hydroxyl groups on graphene inhibits binding of Ga to the surface; however, it enhances the chemical reactivity of the graphene surface to NH3 which, in turn, enhances Ga binding and facilitates the formation of 2D-GaNx. By modifying the EG process to produce oxygen-functionalized buffer layer graphene, uniformly intercalated 2D-GaNx is obtained across the entire substrate surface.

Origin of trap assisted tunnelling in ammonia annealed SiC trench MOSFETs

The interface between silicon carbide (SiC) and silicon dioxide (SiO2) is of considerable importance for the performance and reliability of 4H-SiC (trench) metal oxide semiconductor field effect transistors (MOSFETs) and various different post oxidation anneals (POAs) have been used to optimize its quality. Whereas nitric oxide (NO) POA leads to very reliable and well performing MOSFETs, ammonia (NH3) can further improve the device performance, however, at the cost of the gate oxide (GOX) reliability, e.g. leading to trap assisted tunneling (TAT). We investigate the origin of TAT and GOX leakage in differently annealed gate oxides experimentally, using 4H-SiC trench MOSFETs, and theoretically, using Density Functional Theory (DFT) simulations. Our findings reinforce the view that the NO anneal for SiC devices results in the best overall quality as devices annealed in NH3 and nitrogen N2 show higher oxide charge density and leakage currents. DFT simulations demonstrate that, contrary to what has often been assumed so far, NH3 annealing leads to the formation of additional hydrogen related defects, which open leakage paths in the oxide otherwise not present in NO treated oxides.

A Flexible NO2 Gas Sensor Based on Single-Wall Carbon Nanotube Films Doped with a High Level of Nitrogen.

Carbon nanotubes (CNTs) are considered a promising candidate for the detection of toxic gases because of their high specific surface area and excellent electrical and mechanical properties. However, the detecting performance of CNT-based detectors needs to be improved because covalently bonded CNTs are usually chemically inert. We prepared a nitrogen-doped single-wall CNT (SWCNT) film by means of gas-phase fluorination followed by thermal annealing in NH3. The doped nitrogen content could be changed in the range of 2.9–9.9 at%. The N-doped SWCNT films were directly used to construct flexible and transparent gas sensors, which can work at a low voltage of 0.01 V. It was found that their NO2 detection performance was closely related to their nitrogen content. With an optimum nitrogen content of 9.8 at%, a flexible sensor had a detection limit of 500 ppb at room temperature with good cycling ability and stability during bending.

Platinum-Nickel alloy supported on Nitrogen-Doped carbon modified titanium nitride nanotubes derived from metalorganic frameworks as an efficient catalyst for methanol electrooxidation

Synthesis of high-performance MOR electrocatalysts is of vital importance for the development of DMFCs as a viable technology for portable applications. Herein, we present a systematic study of a nanostructured Pt99Ni1/TiN NTs@NC catalyst for MOR, synthesized by a process concluding solvothermal, chelation, post-nitriding, and ethylene glycol reduction. The simultaneous production of TiN NTs@NC and Ni nanoclusters was obtained from the Ni/TiO2 NTs@PDA complexes derived from Ni-MOF and its pyrolysis under NH3 annealing process. The Ni/TiN NTs@NC substrate is in possession of a mesoporous nanotubes structure with unique sharp nanothorns on surface owing to the usage of Ni-MOF as precursor, resulting in the homogeneous distribution and intimate contact of Ni nanoclusters on the TiN NTs@NC substrate. The unique nanostructure, formation of open active diffusion channels and a large number of accessible active sites on supports provided an opportunity for nucleation and growth of PtNi alloys, leading to the improved metal-support interaction. The formation of PtNi alloys with small size and well-dispersion view not only improves the synergistic effect of electronics and strain but also weakens interaction between Pt and intermediate. Benefiting from above advantages, the Pt99Ni1/TiN NTs@NC exhibits superior MOR performance with enhanced catalytic activity, remarkable CO-resilient capacity, and excellent stability.

Mechanism and enhancement of anti-parasitic-reaction catalytic activity of tungsten-carbide-coated graphite components for the growth of bulk GaN crystals

The working mechanism of the anti-parasitic-reaction (APR) catalyst of tungsten carbide (WC) coating on graphite in hydride vapor phase epitaxy GaN growth were examined. During NH3 annealing, the surface of WC is reduced as well as nitrided. The W2N topmost layer was found to work as an APR-active catalyst to suppress the formation of GaN polycrystals during high-rate HVPE-GaN growth, while the regions covered with thick pyrolytic graphite residues were catalytically inert. The formation of an additional W2C top layer on the WC underlayer was demonstrated to exhibit superior APR activity, i.e. complete suppression of GaN polycrystal formation.

Constructing Structurally Ordered High-Entropy Alloy Nanoparticles on Nitrogen-Rich Mesoporous Carbon Nanosheets for High-Performance Oxygen Reduction.

Recent efforts have observed nanoscaled chemical short-range order in bulk high-entropy alloys (HEAs). Simultaneously inspired with the nanostructuring technology, HEA nanoparticles (NPs) with complete chemical order may be achieved. Herein, structurally ordered HEA (OHEA) NPs are constructed on a novel 2D nitrogen-rich mesoporous carbon sandwich framework (OHEA-mNC) by combining a ligand-assisted interfacial assembly with NH3 annealing. Characterization results show that the resultant materials possess an ultrathin 2D nanosheet structure with large mesopores (≈10nm), where structurally ordered HEA NPs with an L12 phase are homogeneously dispersed. The atom-resolved chemical analyses explicitly determine the location of each atomic site. When being evaluated for the oxygen reduction reaction, the OHEA-mNC NPs afford a greatly enhanced catalytic performance, including a large half-wave potential (0.90eV) and a high durability (0.01V decay after 10 000 cycles) compared with the disordered HEA and commercial Pt/C catalysts. The excellent performance is attributed to the enhanced mass transfer rate, improved electron conductivity, and the presence of the stable chemically ordered HEA phase, as revealed by both the experimental results and theoretical calculation. This study suggests a highly feasible process to achieve structurally ordered HEA NPs with advanced mesoporous function in the electrochemical field.

Rational design of a polysulfide catholyte electrocatalyst by interfacial engineering based on novel MoS2/MoN heterostructures for superior room-temperature Na–S batteries

A suitable electrocatalyst plays an essential role in room-temperature Na–S (RT/Na–S) batteries owing to the more severe dissolution of polysulfides and sluggish kinetics of the conversion of polysulfides during charging and discharging processes. In this study, a novel MoS2/MoN heterostructure synthesized via NH3 annealing was introduced as an electrocatalyst into RT/Na–S batteries to promote the evolution of polysulfides in the catholyte with an initial specific capacity of 703 mA h g−1 and retains 392 mA h g−1 after 300 cycles. The density-functional theory (DFT) calculations, ex-situ XPS and Raman spectra were utilized to reveal moderate anchoring and the fast redox kinetics of polysulfides, significantly enhancing the cycling performance and electrochemical performance of the RT-Na/S batteries when compared with those of the RT-Na/S batteries containing pure MoS2 or MoN as the catalyst. The work provides a new strategy for guiding the design of high‐performance catalysts with manipulated chemical components and optimized adsorption ability.

Nitrogen‐Doped Porous Carbon Nanosheets with Ultrahigh Capacity and Quasicapacitive Energy Storage Performance for Lithium and Sodium Storage Applications

One of the great challenges in the development of rechargeable batteries is developing electrode materials with high capacities and good rate performance. Herein, thin carbon nanosheets with hierarchical porous structure and high nitrogen content (10.6 at%) are elaborately designed and fabricated from phenolic resin through a two‐step method including N2 carbonization and NH3 annealing. The as‐obtained nitrogen‐doped porous carbon nanosheets (NPCNs) exhibit abundant electroactive sites from large surface area and nitrogen species for lithium/sodium storage, and short diffusion channels from unique porous 2D structure for rapid charge transfer. As a result, the optimal NPCNs show outstanding lithium storage capacities of 2065 and 300 mAh g−1 at current densities of 0.05 and 200 A g−1, respectively, as well as good cycle stability. Moreover, the NPCNs also carry out an excellent sodium storage performance of 222 and 134 mAh g−1 at 1 and 10 A g−1, respectively. Further electrochemical analysis demonstrates that the superior rate capability of NPCNs might attribute to the surface‐dominated energy storage process. A new route for the preparation and development of high‐performance electrode materials for new‐generation energy storage devices is provided.

Possibility of ferroelectric bismuth and nitrogen co-doped barium titanate

The possibility of bismuth (Bi) and nitrogen (N) co-doped barium titanate (BaTiO3) as a ferroelectric material was investigated by calculation and experiment. From first principles calculations, it was found that Bi and N co-doped BaTiO3 has a higher spontaneous polarization than undoped BaTiO3 since dopant Bi and N ions contribute to the enhancement of covalent interactions between cations and anions. Because it was revealed that the ferroelectricity of BaTiO3 can be improved by co-doping of Bi and N, we demonstrated the synthesis of (Ba,Bi)Ti(O,N)3. Single phase oxynitride (Ba,Bi)Ti(O,N)3 powder was fabricated by annealing (Ba,Bi)TiO3 in NH3 gas. The tetragonal distortion of (Ba,Bi)Ti(O,N)3 was smaller than that of BaTiO3, which may be due to A-site and O-site vacancies in the perovskite lattice introduced during NH3 annealing.

Co5.47N loaded N-doped carbon as an efficient bifunctional oxygen electrocatalyst for a Zn-air battery.

Highly active bifunctional electrocatalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) play a pivotal role in Zn-air batteries. The high cost, scarcity and instability of precious-metal-based electrocatalysts for the ORR and OER dramatically hamper their practical application in such clean-energy set-ups. Here, we report highly active Co5.47N-loaded N-doped carbon (CoNMC), prepared via the direct NH3 annealing of a millet-CoCl2 mixture, which is a cheap and mass-producible form of biomass. The optimized product shows superior ORR activity (a half-wave potential of 0.81 V vs. RHE) and electrochemical stability (a 16.5 mV negative shift of the half-wave potential after 2000 cycles) in alkaline media. Also, it shows appealing OER activity (an operating potential at 10 mA cm-2 of 1.62 V vs. RHE). This excellent electrochemical performance can be attributed to the formation of active Co5.47N nanoparticles, the large specific surface area, the abundance of nitrogen active sites, and the high graphitization degree. When assembled into a Zn-air battery, the CoNMC-based cell shows comparable performance to a Pt/C-RuO2 one.

Preparation of Nb-doped TiO2 nanopowder by liquid-feed spray pyrolysis followed by ammonia annealing for tunable visible-light absorption and inhibition of photocatalytic activity

Visible-light absorbing TiO2 with color tunability and negligible photocatalytic activity was developed by synthesizing Nb-doped TiO2 using liquid-feed flame spray pyrolysis (LF-FSP) followed by NH3 annealing. Nb-doped TiO2 nanopowders with selected Nb contents were synthesized by changing ratios of metalloorganic precursors. By using Ti and Nb precursors whose thermal decomposition behavior is very similar, the maximum Nb doping concentration was improved compared to Nb-doped TiO2 prepared by flame spray pyrolysis (FSP) in previous reports. As-synthesized Nb-doped TiO2 nanopowders were white regardless of the Nb content, while all became colored after NH3 annealing. In addition, the color of Nb-doped TiO2 after NH3 annealing varied from yellow to dark green depending on the Nb content. Light absorption characterization indicates that the color variation is attributable to the localized levels formed by interstitial N-doping and Nb-doping-induced Ti3+ formation resulting from reduction by H2, formed as a result of NH3 decomposition.

Preparation and electrochemical performance of titanium nitride-graphene nanocomposite with high Ti contents and tailored morphology

Titanium nitride (TiN) - graphene (G) nanocomposites are promising for electrochemical charge storage where a high content of Ti species is desired. Herein, we propose an effective method for the preparation of TiN-G nanocomposites with a high concentration of Ti species. These nanocomposites can be successfully achieved through a further deposition of Ti on Ti-graphene oxide (GO) or a thermally exfoliated Ti-GO. Depending on the annealing condition employed (NH3 and N2), two types of TiN-G nanocomposites (NH3 annealing for TiN/G and TiN/G-TE, TE: thermal exfoliation) and a TiO2-G nanocomposite (N2 annealing for TiO2/G-TE) were prepared. These nanocomposites were then investigated for potential application as an electrochemical supercapacitor. Compare with TiO2/G-TE, the TiN-G nanocomposites both exhibited a higher specific capacitance, although one of these nanocomposites had a lower surface area than TiO2/G-TE. Among the nanocomposites prepared, TiN/G-TE delivered the best electrochemical performance. The relationship between the physical properties and the capacitive performance of the nanocomposites were systematically evaluated.