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Retaining the ultrathin structure of two‐dimensional materials is very important for stabilizing their catalytic performances. However, aggregation and restacking are unavoidable, to some extent, due to the van der Waals interlayer interaction of two‐dimensional materials. Here, we address this challenge by preparing an origami accordion structure of ultrathin two‐dimensional graphitized carbon nitride (oa‐C3N4) with rich vacancies. This novel structured oa‐C3N4 shows exceptional photocatalytic activity for the CO2 reduction reaction, which is 8.1 times that of the pristine C3N4. The unique structure not only prevents restacking but also increases light harvesting and the density of vacancy defects, which leads to modification of the electronic structure, regulation of the CO2 adsorption energy, and a decrease in the energy barrier of the carbon dioxide to carboxylic acid intermediate reaction. This study provides a new avenue for the development of stable high‐performance two‐dimensional catalytic materials. [ABSTRACT FROM AUTHOR]

This paper reviews the recent development of nano-multilayers and nanocomposite coatings. The hardening mechanisms and design of hard coating are discussed in details. Recent research on Ti/TiN and nitride/nitride multilayer, Ti-Si-N and Ti-Al-Si-N nanocomposite coatings is described, and the perspectives of the related research are proposed. [ABSTRACT FROM AUTHOR]

Fe–N thin films were deposited on glass substrates by DC magnetron sputtering at different Ar/N2 discharges (N2 fraction of 30, 10, and 5%, respectively). The composition of the films was analyzed by using X-ray photoelectron spectroscopy (XPS). X-ray diffraction (XRD), grazing incidence X-ray scattering (GIXS), and atomic force microscopy (AFM) were used for analyzing the structure and the universality classes. Films deposited at different nitrogen pressures exhibited different structures with different nitrogen contents. The FeN, ϵ-Fe3N, FeN0.056 were detected in iron nitride films which deposited at N2 fractions of 30, 10, and 5%, respectively. The exponents for all of them are in agreement with KPZ universality classes. [Copyright &y& Elsevier]

Two-dimensional (2D) nanosheets materials have attracted extensive attention because of their promising practical application and theoretical values. In order to enhance the photocatalytic activity of bulk C 3 N 4 , we designed a 2D fabrication in which g-C 3 N 4 nanosheets was in the middle of MoS 2 /graphene layered structure. Here, we report an effective strategy to synthesize ternary g-C 3 N 4 /MoS 2 /graphene nanocomposite photocatalyst via an in-situ adsorption method, which exhibits superior photocatalytic activity owing to enhanced charge carrier separation via well-contacted interface and fast charge transfer pathway. This work indicates a new insight into the design of such 2D heterostructure and a promising cocatalyst strategy for designing a more efficient g-C 3 N 4 -based semiconductor photocatalyst toward degradation of organic pollutants. [ABSTRACT FROM AUTHOR]

Transition metal nitrides are being widely applied, as durable sensors, semiconductor and superconductor devices, their electrical conductivity and wear resistance having a significant influence on these applications. However, there are few reports about how to improve above properties. In this paper, tantalum was incorporated into hafnium nitride films through Hf 1- x Ta x N y [ x =Ta/(Hf+Ta), y =N/(Hf+Ta)] solid solution. The electrical conductivity and wear resistance of the films were significantly improved, due to the increase of the electron concentration (tantalum has one more valence electron than hafnium) and the increase in H/E and H 3 /E 2 ratios caused by the effect of solid solution hardening, respectively. The highest electrical conductivity of Hf 1- x Ta x N y films is 8.3×10 5 S m −1 , which is 1.7 times and 5.2 times of that of hafnium nitride and tantalum nitride films, respectively. In addition, the lowest wear rate of films is 1.2×10 −6 mm 3 /N m, which is only 10% and 48% of that of hafnium nitride and tantalum nitride films, respectively. These results indicate that alloying with another transition metal is an effective method to improve electrical conductivity and wear resistance of transition metal nitrides. [ABSTRACT FROM AUTHOR]

Although surface roughening of films holds an important role in determining the final surface morphologies and properties, how to control it is not yet well explored. Here, we report that the surface roughening of hafnium nitride films varies significantly as a stoichiometry-driven phase transformation takes place. Through a combination of surface morphological measurements and simulations, we demonstrate that the variation of roughening mechanisms arises from the changes in diffusion behavior during growth. This study shows that the phase transformation can induce surface roughening transition, thus providing a new handle in controlling the morphologies and physical properties of thin films. [ABSTRACT FROM AUTHOR]

[Display omitted] • Pyridine conjugated graphitic carbon nitride is successfully synthesized. • As-prepared catalyst exhibits superior photocatalytic hydrogen evolution. • Modulated localization of electron cloud density in as-prepared catalyst. • Narrowed bandgap and enhanced carriers' separation efficiency in as-prepared catalyst. High photogenerated carrier recombination and poor visible light response in symmetry graphitic carbon nitride are two classical problems for photocatalytic hydrogen evolution. In this work, we rationally design a novel carbon nitride (DPCN) with asymmetric embeddedness of pyridine ring. The embedded pyridine ring modulates the localization of electron cloud density, resulting in a narrowed bandgap and an enhanced carriers' separation efficiency. They are further confirmed by UV–vis spectra and femtosecond transient absorption (fs-TA) spectroscopy, whose results are consistent with DFT theoretical calculations. This DPCN catalyst shows enhanced photocatalytic hydrogen evolution rate of 180.5 μmol h−1 and the apparent quantum efficiency of 14.6 % at 420 nm, surpassing most reported g-C 3 N 4 -based photocatalysts. This work provides a new sight on designing two-dimensional photocatalysts by modulating the localization of electron cloud density through breaking topological symmetry. [ABSTRACT FROM AUTHOR]

Although the control of bond structure and optical properties in hydrogenated amorphous germanium carbonitride films (a-GeC 1− x N x :H) is important for technological applications, the composition dependence of chemical bonds, especially hydrogen-containing bonds, is not yet well explored. The evolution in refractive index ( n ) and Urbach tail width ( E 0 ) remains unclear. Here, we show that nitrogen content ( C N ) exerts a significant effect on bonding structure and optical properties of a-GeC 1− x N x :H films. As C N increases, the fraction of N H increases, whereas that of C H and Ge H bonds reduces, and Ge N bonds form at expense of Ge C bonds. The replacement of carbon by nitrogen induces a substantial decrease in n from 3.0 to 2.3 because of decrease in electronic polarizability. With increasing C N , a significant increase in E 0 from 198.8 to 327.9 meV takes place. This behavior arises from decrease in dielectric coefficient ( ε ), rather than the change in the degree of disorder previously believed. The change in E 0 is proportional to the variation in 1/ ε 2 , which agrees well with hydrogen-like atom model. This study discovers that a-GeC 1− x N x :H films have the apparent tunability of n and E 0 over a wide range, which is useful in controlling the optical transmission and absorption characteristics of these films. [ABSTRACT FROM AUTHOR]

Although vacancies exist commonly in nonstoichiometric transition metal nitrides, their roles on structure and properties are not yet well explored. We show that in rocksalt hafnium nitride films creation of nitrogen and hafnium vacancies leads to an asymmetrical lattice contraction and distortion from cubic to rhombohedral structure owing to the presence of strong texture and compressive stress, and also causes decrease in hardness because of reduction in bulk modulus and decrease in electrical conductivity due to reduction in electron relaxation time. This new insight into vacancy-induced “negative effect” is demonstrated through good matches between our experiments and theoretical calculations. [ABSTRACT FROM AUTHOR]

A stoichiometry-driven phase transition from rocksalt to “nitrogen-rich” structure exists in group-IVB transition metal nitride films. As this phase transition is critical in controlling the film properties it has attracted numerous studies. However, researchers are still divided with regard to the structural identity of this “nitrogen-rich” phase, not to mention detailed exploration of the phase transition mechanisms. In this study, we confirmed that the “nitrogen-rich” phase in hafnium nitride (HfN x ) films had a cubic Th 3 P 4 structure of space group symmetry of I- 43 d (220), namely c -Hf 3 N 4 . The confirmation was obtained by combining the first-principle calculations with a series of experiments: Selected Area Electron Diffraction, High Resolution Transmission Electron Microscopy, Raman, Gracing Incident X-ray Diffraction and X-ray Photoelectron Spectroscopy. The mechanisms of the phase transition were elucidated through calculations on enthalpy of formation ( EOF ). The experimental results agree well with the theoretical calculations. We conclude that with increasing nitrogen, phase transition takes place from rocksalt ( δ -HfN) to c -Hf 3 N 4 through three stages of structural evolution: δ -HfN (containing Hf vacancies) → mixture of ( δ -HfN + c -Hf 3 N 4 ) → c -Hf 3 N 4 . The driving force of the phase transition is energy minimization. The three stages of structural evolution are explained by comparing the EOF of the δ -HfN and c -Hf 3 N 4 phases. As the phase transition takes place, the hafnium nitride film morphs from a conductive and opaque metal into an insulating and transparent semiconductor. [ABSTRACT FROM AUTHOR]

Abstract: Novel iridium nitrides (IrN x ) have been synthesized from a double decomposition reaction between IrCl3 and Li3N powders under high pressure (5GPa) and high temperature (1273K) conditions. X-ray diffraction and Raman spectra analysis reveals that the as-synthesized IrN x have a cubic crystal structure. The lattice constants of IrN x are 4.06Å. The x-ray photoelectron spectrum indicates the N content (x) in IrN x is ∼0.3. The first-principles calculations further suggest that iridium nitride is face-centered cubic structure, which has not ever been reported experimentally. Such structure is mechanical stable even under 10GPa and 1273K conditions. [Copyright &y& Elsevier]

[Display omitted] • Intramolecular heterostructured carbon nitride is successfully synthesized. • The as-prepared sample exhibits superior photocatalytic hydrogen production. • Rapid separation and transfer of photogenerated carriers in as-prepared sample. • The addition of salt mixture regulates the localized electronic structure. Efficient separation and transfer of photogenerated carriers is vital for efficient photocatalytic hydrogen evolution. We report development of a new type of intramolecular heterostructure graphitic carbon nitride with heptazine-triazine (CN-HT) by use of a one-step thermal polymerization method. This intramolecular heterostructure changes the electronic structure to promote charge transfer and enhances the adsorption of H*. The as-prepared CN-HT exhibits superior photocatalytic hydrogen evolution of 88.29 μmol/h, which is 14.2 times that of pristine CN. The apparent quantum yield is 10.1% at 400 nm and 9.6% at 450 nm. The efficient separation and transfer of photogenerated carriers as well as the expanded visible light absorption in this intramolecular CN heterostructure contribute to the efficient utilization of photogenerated carriers, thus enhancing the photocatalytic hydrogen evolution. [ABSTRACT FROM AUTHOR]

Asymmetric Embedding Benzene Ring in graphite carbon nitride changes local charge distribution and electron transfer kinetics, and promote the photocatalytic water splitting to produce hydrogen at a higher rate. • The A-GCN is successfully prepared using dicyandiamide and terephthalonitrile. • Embedding benzene regulate the localized electronic structure. • Theoretical results predicts the localized asymmetry promotes the charge transfer. • For hydrogen production, the A-GCN-1.0 displays 10.8 times as good as pristine GCN. Preventing the high carrier recombination rate of graphitized C 3 N 4 (GCN) is an urgent problem to be solved for its application as a photocatalyst for hydrogen production. Here, we first rationally embed the benzene ring in GCN to modify the local symmetry without changing its long-order structure. Theoretical calculation predicts that this design can change the electronic structure and promote the effective charge transfer in GCN. The benzene ring embedded GCN is successfully prepared by copolymerization using dicyandiamide and terephthalonitrile as precursors. Photoluminescence (PL) and time-resolved transient PL (TRPL) spectra confirm that the electron transfer efficiency of the benzene ring embed GCN is greatly improved. This nanomaterial displays 10.8 times higher photocatalytic hydrogen production rate than that of pristine GCN with the apparent quantum yield of 11.3% at 400 nm and 9% at 420 nm. This work provides a novel strategy for designing high-efficiency two-dimensional (2D) photocatalytic materials for water splitting. [ABSTRACT FROM AUTHOR]