Thin Nitride Research Articles

Superhydrophilic 2D Carbon Nitrides Prepared by Direct Chemical Vapor Deposition

Surface wetting greatly impacts the performances of many photocatalysts in a water/humid‐involved medium. Carbon nitrides and its isotopes, as emerging metal‐free low‐cost photocatalysts for water splitting, usually require strong chemical or irradiation treatments to obtain highly hydrophilic surfaces, which can undermine their photocatalytic performances. Herein, an alternative method for the direct synthesis of superhydrophilic carbon nitride thin films (CN x , x ≈ 0.86–1.04) and graphitic carbon nitride powder (g‐C3N4) by using chemical vapor deposition is proposed. Less than 5° contact angle with water is accessible on both the surface of the as‐grown CN x thin films and the membranes made from the g‐C3N4 powder. It is found that the remarkable wetting property can be attributed to the spontaneous hydrophilic functionalization group (e.g., –OH, –NO x , = O) supplied by a constant multielemental air flow. The abundant CN triple bonds also promote needle‐shaped nanostructures on the 2D surfaces, which enhances their chemical wettability. Finally, the tremendous potential of this novel technique for direct synthesis of superhydrophilic carbon nitride in photocatalysis applications is demonstrated.

Mass-Mediated Phase Modulation of Thin Molybdenum Nitride Crystals on a Liquid Cu-Mo Alloy

The high-quality and controllable preparation of molybdenum nitrides (MoxNy) will significantly advance the fields of heterogeneous catalysis, energy storage, and superconductivity. However, the complex structure of MoxNy, which contains multiple phases, makes exploring the structure-property relationship challenging. The selective preparation of MoxNy with distinct phases is undoubtedly an effective method for addressing this issue, but it is lacking experimental cases and theoretical reports. Here we demonstrate a feasible chemical vapor deposition (CVD) strategy for selectively producing γ-Mo2N or δ-MoN through modulating the mass quantity of N precursors. A liquid Cu-Mo alloy was used as a Mo precursor and catalyst in this system. The resulting γ-Mo2N was systematically characterized and found to be of high quality. Furthermore, the morphology evolutions of γ-Mo2N and δ-MoN with growth time were summarized in detail, as a result of growth and etching dynamics. This work promotes the phase modulation of MoxNy and provides a framework for future research on the structure-property relationship.

Interfacial thermal conductance between atomically thin boron nitride and graphene.

Atomically thin hexagonal boron nitride (BN) is a promising dielectric substrate for graphene and other two-dimensional (2D) materials for performance enhancement and heat dissipation. However, the interfacial heat conductance between atomically thin BN and graphene has not been experimentally studied yet. Here, we report that the interfacial thermal conductance between high-quality graphene and trilayer BN is 9.64 ± 2.12 MW m-2 K-1 in the temperature range of 293-393 K, indicating that the interfacial thermal conductance is depressed when the heterostructure thickness is smaller than the wavelength of the low-frequency phonons, e.g. ZA in BN.

Aluminum nitride on insulator: Material and processing optimization for integrated photonic applications

Thin film aluminum nitride on insulator (AlNOI) has gained attention as a promising material platform for integrated photonic circuits (PICs) due to its ability to operate over a wide spectral range covering the ultra-violet to mid-infrared regions, while enabling a broad range of passive photonic functionalities. This study aims to optimize sputtered AlNOI films for PICs, with an emphasis on the spectroscopic ellipsometry study over a range from 0.19 µm to 25 µm. Furthermore, we discuss our approach for fabricating AlNOI PICs components, with a particular focus on optimizing the etching process to attain smooth sidewall waveguides.

Higher-than-common temperature short-time processed polymeric carbon nitride nanosheets as an efficient photocatalyst for H2 production

Two-dimensional polymeric carbon nitride nanosheets exhibiting unique optical properties are considered promising materials for visible light active photocatalysts. Here, we synthesized thin polymeric carbon nitride nanosheets via the higher-than-common temperature (710 °C) pyrolysis of a polymeric carbon nitride intermediate for 20 min. The exfoliation efficiency of the nanosheets was dramatically improved by the higher-than-common temperature treatment. Notably, compared with the pristine polymeric carbon nitride nanosheets, the synthesized thin polymeric carbon nitride nanosheets exhibited a reduced optical bandgap and more negative conduction band (ECB) positions, which ensured enhanced visible-light absorption and reductive ability. When applied to photocatalytic water-splitting reaction for H2 evolution, the thin polymeric carbon nitride nanosheets exhibited enhanced activity under visible light irradiation, accounting for an optimal H2-evolution rate of 8187 µmol·g−1·h−1 with a Pt loading of 1 wt%, which was approximately six-fold higher than that obtained with the urea-derived pristine polymeric carbon nitride nanosheets. This work provides a rapid, affordable and facile method for synthesizing polymeric carbon nitride nanosheets with high photocatalytic performances.

Thermal stability of thin hexagonal boron nitride grown by MOVPE on epigraphene

Passivating graphene with a layer of hexagonal boron nitride (hBN) is known to protect it from environment effects that degrade its mobility. However, growth of high-quality BN on graphene is challenging because of the lack of surface dangling bonds. Here, we report the growth of thin BN films (down to 10 nm) on monolayer epigraphene grown on silicon carbide single-crystal substrates using metal–organic vapor phase epitaxy (MOVPE). The BN film has continuous coverage on the epigraphene surface, with smooth morphology. Particles consisting of layered BN are also observed on the surface with a higher density at the step edges. High-Resolution Scanning Transmission Electron Microscopy (HRSTEM) reveals high structural quality BN layers, with a clean and abrupt interface with graphene. The BN/epigraphene/SiC heterostructure is stable up to high temperature (1550 °C), and annealing improves its crystallinity. These results show that MOVPE growth technique has a potential for large-scale production of BN fully coated graphene and high-temperature applications.

2D/3D- C3N4/CeO2 S-scheme heterojunctions with enhanced photocatalytic performance

• Successfully developed a novel method to obtain g-C 3 N 4 /CeO 2 composite photo-catalysts via simple, ball milled thermal spreading technique. • Facile control of surface morphology of carbon nitride on ceria. The optical absorption is tuned by morphology control. • The optimum loading was found to be 7.5 wt. %. • Morphology with an intermediate thickness between very thin and bulk carbon nitride on ceria surface is important to achieve maximum efficiency. • High efficiency of methylene blue degradation and good recycling performance. A facile, green and easily scalable method has been developed to facilitate the construction of 2D-C 3 N 4 /3D-CeO 2 heterojunction materials. It uses only cheap urea and ceria in a thermal spreading technique that allows the controlled growth of carbon nitride layers on cerium oxide surface. The exfoliation of bulk carbon nitride and subsequent stabilization of layers on ceria takes place during thermal spreading technique in a single step. Simple variation of carbon nitride allowed to control the morphology of carbon nitride from highly dispersed thin layer up to bulk-like structures over ceria surface. The optical absorption was enhanced with 2D-C 3 N 4 /3D-CeO 2 materials. The variation of structure and consequent differences in the solar powered decomposition of methylene blue has been analyzed. Results reveal that, the optimum loading of 7.5 wt.% carbon nitride can lead to the formation of intermediate structure in between very thin layers and bulk-like structure, that achieves best contact between the two phases making effective heterojuctions. This best catalyst exhibits 98% conversion at a timing of 100 minutes. The radical scavenging studies showed that •O 2− and h+ performed an imperative role. In addition, a plausible mechanism of photo catalytic decomposition is also proposed for 2D-C 3 N 4 /3D-CeO 2 materials.

Preparation of C3N4 Thin Films for Photo-/Electrocatalytic CO2 Reduction to Produce Liquid Hydrocarbons

Thermal vapor condensation of melamine at various temperatures was used to fabricate thin graphitic carbon nitride (g-C3N4) films on fluorine-doped tin oxide (FTO) coated glass substrates. Photoanodic (n-type) and photocathodic (p-type) responses were observed simultaneously in the g-C3N4 films. The g-C3N4 film formed at 520 °C with the longest average lifetime of the photo-excited electrons shows the best cathodic photocurrent performance, which was then chosen for electrochemical and photoelectrochemical reduction of CO2. When the basic electrolyte (CO2-saturated 0.5 M KHCO3, pH = 7.6) was adopted, CO2 was electrochemically converted into formaldehyde ((54.6 μM/h)) in the liquid product. When the acidic electrolyte (CO2-saturated 0.5 M KCl, pH = 4.1) was adopted, formaldehyde (39.5 μM/h) and ethanol (15.7 μM/h) were generated through photoelectrochemical reduction, stimulated by the presence of sufficient protons from the electrolyte in the reduction process. Therefore, the pure g-C3N4 film has a great potential for CO2 reduction to value-added liquid hydrocarbons products via electrochemical or photoelectrochemical ways.

Boosted solar water photoreduction by conjugated polymer-mediated tandem charge transfer

Semiconductor materials anchored with transition metal cluster are promising photocatalysts for photocatalytic hydrogen evolution. In this paper, Co, N-co-doped graphene modified thin mesoporous carbon nitride (Co-NG/TMCN) was be synthesized through electrostatic adsorption treatment. Extensive characterization was used to explore the morphology, structures and optical properties of the as-prepared photocatalysts. The 10 wt% Co-NG/TMCN exhibited the high photocatalytic hydrogen evolution rate (2949 μmol g−1) within 4 h visible light irradiation, which was about 113 times than that of the pure TMCN (26 μmol g−1). Co-NG material with excellent electrical conductivity played a major role in accelerating charge transfer from TMCN material to cobalt atomic clusters. The photocatalytic hydrogen evolution performance of Co-NG/TMCN material was effectively improved. Consequently, a feasible approach for doping transition metal clusters to enhance photocatalytic activity was provided.

Chemical potential imbalance mediated CVD growth of atomically thin hexagonal boron nitride fractal patterns

• The fractal controllable growth of monolayer hexagonal boron nitride by CVD. • Fractal patterns are generated in a severe N/B chemical potential imbalance. • Chemical potential influences the kinetic growth dynamics of edges. • Fractal dimension analysis reveals rough boundaries and self-similarity. Fractal patterns produced in non-equilibrium processes are ubiquitous in nature, but the mechanisms behind them are not fully understood. Here, we successfully fabricated nitrogen-rich edge monolayer hexagonal boron nitride (h-BN) fractal flakes using the relatively high N precursor flux through chemical vapor deposition. Fractal dimension analysis was introduced to characterize the boundary roughness of fractal flake, the fractal dimension calculated by the box-counting method is 1.92, suggesting that the h-BN fractal flake possesses a rough boundary. Moreover, a possible morphogenesis mechanism was proposed based on the crystal growth principle, elucidating the role of severe chemical potential imbalance in the formation of fractal flakes.

Integration Aspects of Plasmonic TiN-based Nano-Hole-Arrays on Ge Photodetectorsin a 200mm Wafer CMOS Compatible Silicon Technology

In this work we present the progress in regard to the integration of a surface plasmon resonance refractive index sensor into a CMOS compatible 200 mm wafer silicon-based technology. Our approach pursues the combination of germanium photodetectors with metallic nanohole arrays. The paper is focused on the technology development to fabricate large area photodetectors based on a modern design concept. In a first iteration we achieved a leakage current density of 82 mA/cm2 at reverse bias of 0.5 V and a maximum optical responsivity of 0.103 A/W measured with TE polarized light at λ = 1310 nm and a reversed bias of 1 V. For the realization of nanohole arrays we used thin Titanium nitride (TiN) layers deposited by a sputtering process. We were able to produce very homogenous TiN layers with a thickness deviation of around 10 % and RMS of 1.413 nm for 150 nm thick TiN layers.

NiCoP/g-C3N4 Schottky heterojunctions towards efficient photocatalytic NO oxidation

NiCoP/g-C3N4 Schottky heterojunctions were created by a two-step synthesis for enhanced NO oxidation. NiCo-layered double hydroxides (LDH) were grown on superior thin graphic carbon nitride (g-C3N4) nanosheets by a controlling chemical co-precipitation method. A phosphating process at 300 °C resulted in the transformation in situ of NiCo-LDH into NiCoP composite nanoparticles to create Schottky heterojunctions. Using optimized conditions, heterojunction sample 15-NiCoP/CN revealed excellent photocatalytic NO oxidation with a removal rate of 78%. Photogenerated electrons were efficiently separated and transferred because of Schottky barrier, interfacial charge transport channel, and enhanced light absorption efficiency. Photogenerated electrons reacted with adsorbed O2 to generate superoxide radicals (·O2¯) as crucial active species of NO oxidation. The test indicated that the concentration of·O2¯ for sample 15-NiCoP/CN reached 7.1 × 10−5 M which was 6.5 times higher than that of g-C3N4 after light irradiation. In addition, low NO2 generation and mineralization rate (92%) suggested that NO was converted into NO3- or NO2- rather than NO2 to mitigate secondary pollution. This result supplied a novel approach to explore the application of transition metal phosphides and g-C3N4 in photocatalytic NO oxidation.

Improvement of the Interface between the Lithium Anode and a Garnet-Type Solid Electrolyte of Lithium Batteries Using an Aluminum-Nitride Layer.

The next generation of all-solid-state batteries can feature battery safety that is unparalleled among conventional liquid batteries. The garnet-type solid-state electrolyte Li7La3Zr2O12 (LLZO), in particular, is widely studied because of its high Li-ion conductivity and stability in air. However, the poor interface-contact between Li and the electrolyte (garnet) severely limits the development of solid electrolytes. In this study, we synthesize cubic phase Li6.4La3Zr1.4Ta0.6O12 (LLZTO) using a secondary sintering method. In addition, a thin aluminum nitride (AlN) layer is introduced between the metal (Li) and the solid electrolyte. Theoretical calculations show that AlN has a high affinity for Li. Furthermore, it is shown that the AlN coating can effectively reduce the interface impedance between Li and the solid electrolyte and improve the lithium-ion transport. The assembled symmetric Li cells can operate stably for more than 3600 h, unlike the symmetric cells without AlN coating, which short-circuited after only a few cycles. The hybrid solid-state battery with a modified layer, which is assembled using LiFePO4 (LFP), still has a capacity of 120 mAh g−1 after 200 cycles, with a capacity retention rate of 98%. This shows that the introduction of an AlN interlayer is very helpful to obtain a stable Li/solid-electrolyte interface, which improves the cycling stability of the battery.

Iron Nitride Thin Films: Growth, Structure, and Properties.

The current state-of-the-art in the growth, structure, and physicochemical properties of iron nitride thin films is presented. First, different iron nitride phases are introduced based on their crystallographic structure and the Fe–N phase diagram. Second, preparation methods for thin iron nitride films are described. Next, the structure, electronic, and magnetic properties of the films are discussed. Finally, potential applications of iron nitride films, as well as the challenges to be faced in the field, are highlighted. This Review constitutes a starting point for anyone who would like to conduct research on these fascinating materials, the scientific and technological potential of which has not been fully explored to date.

Deposition of carbonitride titanium coatings by magnetron sputtering and its effect on tribo-mechanical properties

Metal parts in machinery often fail as a result of damage caused by wear and tear, resulting in the loss of functionality of the products. Thin film solid nitride coatings are used to improve the wear resistance and service life of parts and are considered to be effective. The article presents a brief overview of modern literature in the field of obtaining wear resistant coatings of titanium carbonitride by using magnetron sputtering. The review presents a detailed assessment of the scientific results obtained depending on the deposition parameters and the conditions for obtaining coatings. The results of the coefficient of friction, wear rate of the coating and counterbody, nanohardness and adhesion force of coatings obtained by magnetron sputtering and its modifications are shown. The influence of alloying elements on the mechanical and tribological properties of titanium carbonitride coatings is considered. Recent advances in the production of titanium carbonitride coatings with improved wear characteristics are discussed.

In situ measurements of electrical resistivity of metals in a cubic multi-anvil apparatus by van der Pauw method.

On the basis of the van der Pauw method, we developed a new technique for measuring the electrical resistivity of metals in a cubic multi-anvil high-pressure apparatus. Four electrode wires were introduced into the sample chamber and in contact with the pre-pressed metal disk on the periphery. The sample temperature was measured with a NiCr-NiSi (K-type) thermocouple, which was separated from the sample by a thin hexagonal boron nitride layer. The electrodes and thermocouple were electrically insulated from each other and from the heater by an alumina tube as well. Their leads were in connection with cables through the gap between the tungsten carbide anvils. We performed experiments to determine the temperature dependence of electrical resistivity of pure iron at 3 and 5 GPa. The experiments produce reproducible measurements and the results provide an independent check on electrical resistivity data produced by other methods. The new technique provides reliable electrical resistivity measurements of metallic alloys and compounds at high pressure and temperature.

Molten Salt Assisted Synthesis of Boron Carbon Nitride Nanosheets for Enhanced Photocatalytic Activity of Silver Phosphate

Thin 2D boron carbon nitride nanosheets (BCNNS) possess high thermal and chemical stability as well as tunable electronic properties, but the lack of effective synthesis methods hinders their practical application. Herein, a facile and efficient approach for the synthesis of large-area boron carbon nitride nanosheets in molten KCl–NaCl salt media has been proposed. A Single precursor compound, ethylenediamine bisborane, was first heated to 1000 °C in KCl–NaCl salt melts and then held for only two minutes to produce BCNNS. Benefiting from the effective solvation of precursors and reduced surface energy in liquid salt melt, the lateral size of resultant BCNNS can reach up to 12 microns. The as-prepared products are subsequently used as a co-catalyst with silver phosphate (Ag3PO4) for degradation methyl orange under simulated sunlight. Due to the improved electronic property and interfacial effect of BCNNS, the photocatalytic performance of Ag3PO4 was significantly improved. The photodegradation rate increased from 0.369 min−1 of Ag3PO4 to 1.006 min−1 of BCN/Ag3PO4 composite with only 0.6 wt% BCNNS loading, a 2.73-fold higher value than that of pure Ag3PO4.

Increased solar absorption and promoted photocarrier separation in atomically thin 2D carbon nitride sheets for enhanced visible-light photocatalysis

The preparation of sulfur-doped and nitrogen-vacant CN (S-CN V ) by annealing CN in S vapor is reported. The results show that the formation of C-S-C bonds and the introduction of nitrogen vacancies in S-CN V matrix could contribute to increased solar absorption and promoted photocarrier separation as well as greatly enhanced photocatalytic activity. • The preparation of sulfur-doped and nitrogen-vacant CN (S-CN V ) by annealing CN in S vapor is reported. • This strategy can dramatically increase solar absorption and promote photocarrier separation in atomically thin CN. • The visible-light photocatalytic activity of S-CN V photocatalyst significantly exceeds CN photocatalyst. Atomically thin two-dimensional (2D) carbon nitride (CN) has been widely used in solar energy conversion as a metal-free photocatalyst. However, because of the wide band gap (3.06 eV) and rapid recombination of photogenerated electron-hole pairs, the visible-light photocatalytic efficiency of CN is still low. In this study, successful preparation of sulphur-doped and nitrogen-vacant CN (S-CN V ) by annealing CN in S vapour is reported. The photocatalytic hydrogen production rate of S-CN V under visible-light irradiation (>420 nm) reached 5192.2 μmol h −1 g −1 , which is much higher than that of previously reported CN. The structural characterisations combined with theoretical calculations show that (i) the formation of C-S-C bonds and introduction of nitrogen vacancies in the edges can narrow the band gap of CN from 3.06 to 2.79 eV, which expands the visible-light absorption band; and (ii) the S-CN V charge distribution has local characteristics, which promotes the separation and transmission of photogenerated carriers. This study provides a new approach to narrow the band gap and promote the photoexcited carrier separation in 2D carbon-nitride-based materials.

Precursor-modified strategy to synthesize thin porous amino-rich graphitic carbon nitride with enhanced photocatalytic degradation of RhB and hydrogen evolution performances

The photocatalytic activity of carbon nitride (CN) materials is mainly limited to small specific surface areas, limited solar absorption, and low separation and mobility of photoinduced carriers. In this study, we developed a precursor-modified strategy for the synthesis of graphitic CN with highly efficient photocatalytic performance. The precursor dicyandiamide reformed by different acids undergoes a basic structural change and transforms into diverse new precursors. The thin porous amino-rich HNO3-CN (5H-CN) was calcined by dicyandiamidine nitrate, formed by concentrated nitric acid modified dicyandiamide, and presented the best photocatalytic degradation rate of RhB, more than 34 times that of bulk graphitic CN. Moreover, the photocatalytic hydrogen evolution rate of 5H-CN significantly improved. The TG-DSC-FTIR analyses indicated that the distinguishing thermal polymerization process of 5H-CN led to its thin porous amino-rich structure, and the theoretical calculations revealed that the negative conduction band potential of 5H-CN was attributed to its amino-rich structure. It is anticipated that the thin porous structure and the negative conduction band position of 5H-CN play important roles in the improvement of the photocatalytic performance. This study demonstrates that precursor modification is a promising project to induce a new thermal polycondensation process for the synthesis of CN with enhanced photocatalytic performance.

3D Fe-MOF embedded into 2D thin layer carbon nitride to construct 3D/2D S-scheme heterojunction for enhanced photoreduction of CO2

Regulating charge transfer to achieve specific transfer path can improve electron utilization and complete efficient photoreduction of CO2. Here, we fabricated a S-scheme heterojunction of CN/Fe-MOF by an in-situ assembly strategy. The S-scheme charge transfer mechanism was confirmed by band structure, electron spin resonance (ESR) and work function (Φ) analysis. On the one hand, the response of Fe-MOF in the visible region improved the utilization of light energy, thus increasing the ability of CN/Fe-MOF to generate charge carriers. On the other hand, CN, as the active site, not only had strong adsorption capacity for CO2, but also retained photogenerated electrons with high reduction capacity because of S-scheme charge transfer mechanism. Hence, in the absence of any sacrificial agent and cocatalyst, the optimized 50CN/Fe-MOF obtained the highest CO yield (19.17 μmol g−1) under UV-Vis irradiation, which was almost 10 times higher than that of CN. In situ Fourier transform infrared spectra not only revealed that the photoreduction of CO2 occurred at the CN, but also demonstrated that the S-scheme charge transfer mechanism enabled 50CN/Fe-MOF to have a stronger ability to generate HCOO− than CN.