Structure and electronic structure of S-doped graphitic C3N4 investigated by density functional theory

The structures of the heptazine-based graphitic C3N4 and the S-doped graphitic C3N4 are investigated by using the density functional theory with a semi-empirical dispersion correction for the weak long-range interaction between layers.The corrugated structure is found to be energetically favorable for both the pure and the S-doped graphitic C3N4.The S doptant is prone to substitute the N atom bonded with only two nearest C atoms.The band structure calculation reveals that this kind of S doping causes a favorable red shift of the light absorption threshold and can improve the electroconductibility and the photocatalytic activity of the graphitic C3N4.     

Influence of Nitrogen Supply and Temperature on Stable Carbon Isotope Ratios in Plants of Different Photosynthetic Pathways (C3, C4, CAM)

Abstract

One representative species of each of the three photosynthetic pathways (C₃, C₄, CAM) were cultivated in growth chambers with high and low nitrogen nutrition level respectively once at 20°C day/13°C night temperature, once at 30°C day/13°C night. Leaf conductances and δ¹³C values of the leaves of each plant were determined. At 20°C day temperature the C₃ species showed higher leaf conductance with low nitrogen nutrition level than with high nitrogen level, which is also reflected in a more negative δ¹³C value, whereas both C₄ and CAM plants did not respond in this manner to nitrogen supply. An increase of day temperature to 30°C diminished the significant response of the C₃ plant, while the response of C₄ and CAM representatives to nitrogen nutrition did not change markedly.     

Growth of gem-grade nitrogen-doped diamond crystals heavily doped with the addition of Ba（N3）2

Additive Ba(N 3) 2 as a source of nitrogen is heavily doped into the graphite-Fe-based alloy system to grow nitrogendoped diamond crystals under a relatively high pressure (about 6.0 GPa) by employing the temperature gradient method.Gem-grade diamond crystal with a size of around 5 mm and a nitrogen concentration of about 1173 ppm is successfully synthesised for the first time under high pressure and high temperature in a China-type cubic anvil highpressure apparatus.The growth habit of diamond crystal under the environment with high degree of nitrogen doping is investigated.It is found that the morphologies of heavily nitrogen-doped diamond crystals are all of octahedral shape dominated by {111} facets.The effects of temperature and duration on nitrogen concentration and form are explored by infrared absorption spectra.The results indicate that nitrogen impurity is present in diamond predominantly in the dispersed form accompanied by aggregated form,and the aggregated nitrogen concentration in diamond increases with temperature and duration.In addition,it is indicated that nitrogen donors are more easily incorporated into growing crystals at higher temperature.Strains in nitrogen-doped diamond crystal are characterized by micro-Raman spectroscopy.Measurement results demonstrate that the undoped diamond crystals exhibit the compressive stress,whereas diamond crystals heavily doped with the addition of Ba(N 3) 2 display the tensile stress.     

Evaluation of fracture toughness of ZrO2 and Si3N4 engineering ceramics following CO2 and fibre laser surface treatment

The fracture toughness property (K_1C) of Si₃N₄ and ZrO₂ engineering ceramics was investigated by means of CO₂ and a fibre laser surface treatment. Near surface modifications in the hardness were investigated by employing the Vickers indentation method. Crack lengths and the crack geometry were then measured by using the optical microscopy. A co-ordinate measuring machine was used to investigate the diamond indentations and to measure the lengths of the cracks. Thereafter, computational and analytical methods were employed to determine the K_1C. An increase in the K_1C of both ceramics was found by the CO₂ and the fibre laser surface treatment in comparison to the as-received surfaces. The K_1C of the CO₂ laser radiated surface of the Si₃N₄ was over 3% higher in comparison to that of the fibre laser treated surface. This was by softening of the near surface layer of the Si₃N₄ which comprised of lowering of hardness, which in turn increased the crack resistance. The effects were not similar in ZrO₂ ceramic to that of the Si₃N₄ as the fibre laser radiation in this case had produced an increase of 34% compared to that of the CO₂ laser radiation. This occurred due to propagation of lower crack resulting from the Vickers indentation test during the fibre laser surface treatment which inherently affected the end K_1C through an induced compressive stress layer. The K_1C modification of the two ceramics treated by the CO₂ and the fibre laser was also believed to be influenced by the different laser wavelength and its absorption co-efficient, the beam delivery system as well as the differences in the brightness of the two lasers used.     

内掺氮富勒烯N_2@C_(60)的几何结构和电子性质的密度泛函计算研究

采用密度泛函理论中的广义梯度近似对内掺氮富勒烯N2@C60的几何结构和电子性质进行计算研究.发现在N2@C60中,氮倾向以分子形式存在于C60中心处.键长分析、能级图、态密度图和电荷分析表明内掺氮分子对C60几何结构和电子结构带来的影响甚微.     

微波等离子体化学气相沉积法制备C3N4薄膜的结构研究

采用微波等离子体化学气相沉积法,用高纯氮气(99.999%)和甲烷(99.9%)作反应气体,在单晶Si(100)基片上沉积C₃N₄薄膜.利用扫描电子显微镜观察薄膜形貌,表明薄膜由密排的六棱晶棒组成.X射线衍射和透射电子显微镜结构分析说明该薄膜主要由β-C₃N₄和α-C₃N₄组成,并且这些结果与α-C₃N₄相符合较好.由虎克定律近似关 关键词： 3N₄')" href="#">C₃N₄ 微波等离子体化学气相沉积法 薄膜沉积     

C3 or C4 Macrophytes: A Specific Carbon Source for the Development of Semi-Aquatic and Terrestrial Arthropods in Central Amazonian River-Floodplains According to δ13C Values

Abstract

C₄ plant species were proposed to generally represent inferior food sources compared to C₃ plants thus are avoided by herbivores, particularly insects. This was tested in semi-aquatic and terrestrial arthropods from Amazonian river-floodplains by carbon isotope discrimination (δ¹³C). Two semi-aquatic grasshopper species (Stenacris f. fissicauda, Tucayaca gracilis—Acrididae) obtain their carbon during development from specific C₄ macrophytes and two semi-aquatic species (Cornops aquaticum—Acrididae, Paulinia acuminata—Pauliniidae) from specific C₃ macrophytes. The terrestrial millipede Mestosoma hylaeicum (Paradoxosomatidae) obtains about 45% of its carbon from roots of one C₄ macrophyte during the development of immatures whereas adults use other food sources, including C₃ trees. Results suggest, that (1) both C₄ and C₃ plants represent distinct hosts for terrestrial arthropods in Amazonia; (2) immatures may use plant species with a different photosynthetic pathway than adults.     

High pressure raman studies of GaAs/A1As superlattices: folded-acoustic phonons and resonant second-order scattering

Abstract

Materials containing light elements and characterized by a dense structure present specific physico-chemical properties.

The carbonitrides C_xN_y, and in particular C₃N₄, have attracted the attention of the scientific community during these last ten years.

The main chemical problem in the synthesis of such materials is to introduce nitrogen into the lattice, due to the strong stability of N₂.

In order to prevent nitrogen loss, the use of high pressures and the selection of nitriding media can be developed.

The present contribution describes the main results obtained through two routes:

(i) the thermal decomposition of precursors containing carbon and nitrogen under high pressure conditions (2-6GPa) (without or with nitrogen solvent)

(ii) the high pressure condensation of “organic” precursors containing carbon and nitrogen.     

Raman spectroscopy of melamine at high pressures up to 60 GPa

In this work, the Raman scattering of melamine was studied under high pressure up to 60 GPa. The behavior of the most intensive peaks of the Raman spectrum of melamine, 677 cm^?1 and 985 cm^?1 modes, and their line widths do not show any phase transition or indication of formation of sp ³ bonds. Comparing the behavior of the line width of the Raman peaks of graphite under pressure and that of melamine leads us to conclude that the s-triasine (C–N) ring is more rigid than the C–C graphite ring. High pressure results with melamine suggest that the direct phase transition g-C₃N₄ to dense C₃N₄ phase should occur above 60 GPa.     

石墨相氮化碳的制备条件优化用以提高其在可见光下的光催化活性

通过染料的光降解实验和敏感性数学分析探讨了石墨相氮化碳(g-C₃N₄)的制备条件与其稳定性和光催化活性之间的联系. 结果表明,相比于焙烧时间,焙烧温度的改变更为显著地影响了g-C₃N₄ 的光催化活性. 制备条件优化之后的g-C₃N₄在可见光照射下催化降解罗丹明B(RhB)的活性比未优化时提高了约100倍,归因于材料比表面积的增大和表面光生电子-空穴迁移速度的增强.     

Si-doped C3N monolayers as efficient single-atom catalysts for the reduction of N2O: a computational study

Density functional theory calculations are performed to probe reaction pathways of N₂O reduction by CO molecule catalysed over Si-doped C₃N (Si-C₃N) nanosheets. According to our results, a single Si atom can be stabilised above the C- or N-vacancy site of C₃N due to the formation of strong Si-N or Si-C covalent bonds. The reduction of N₂O over Si-C₃N is characterised as a two-step process. First, N₂O is dissociated to N₂ and an activated oxygen atom (O_ads) without an energy barrier. Then, the O_ads moiety is removed by CO molecule by overcoming negligible activation energy.     

Exohedral chemical functionalization of C48B6N6 with NH3: Binding energies and electronic structures of C48B6N6–(NH3)n=1−6

Theoretical study of exohedral chemical functionalization of C₄₈B₆N₆ with NH₃ molecules has been investigated using DFT. It was found that NH₃ molecule can be chemically adsorbed on boron sites of C₄₈B₆N₆, with a charge transfer from NH₃ to C₄₈B₆N₆. Adsorption energy and the quantity of electron charge transfer from latest adsorbed ammonia to C₄₈B₆N₆ decreased with increasing in the adsorbed NH₃ molecules. Despite the strong adsorption energies, electronic properties of C₄₈B₆N₆ is preserved after modification(s) with NH₃ molecule(s) and chemical modification of C₄₈B₆N₆ with NH₃ molecules can be viewed as some kind of safe modification.     

Feeding and Growth of Apple Snail Pomacea lineata in the Pantanal Wetland,Brazil—a Stable Isotope Approach

Abstract

Apple snails Pomacea lineata (SPIX 1827) are widespread in the tropical regions of Brazil as well as in the Pantanal wetland of Mato Grosso in the western part of the country. They have a key position in the Pantanal food web and serve as food for many animals e.g. fishes, birds, and caimans. However, little is known about their feeding preferences and growth rates. Stable isotopes have been used successfully on numerous studies as food source indicator. Therefore, the δ¹⁵N and δ¹³C values of snails from 0.45 to 3.03cm in length, which were collected in the rainy season from March through May, were analyzed. Snails signatures revealed ambiguous evidence for food preferences. δ¹⁵N and δ¹³C values ranged between ?2.8 and 12.4‰ and between ?24.2 and ?16.4‰, respectively. This range of values mirrors the highly variable isotope values of possible food sources comprising C₃ and C₄ macrophytes. To test whether all common food sources were similarly assimilated, feeding experiments with different diets were conducted. Snail eggs were reared in tanks and offered different but single plants. Snails fed different diets and δ¹³C values of the food were reflected in the animal tissue. Growth varied considerably in experiments with different diets indicating the preference for certain food sources. Also, the fractionation of nitrogen isotopes between food and animal varied from 0.1 to 17.0‰. The results are explained by different feeding habits, and it is supposed that animals fed either on the plant itself or on bacteria mats growing in the tanks. In an additional experiment juvenile snails were offered one single food with a distinctive C₄ grass signature. These snails did not grow detectably, but nevertheless isotope signatures approached to values of the diet.     

Structural stability and mechanical properties of Be3N2 under high pressure

Abstract

A theoretical investigations on the structural stability and mechanical properties of Be₃N₂ crystallising in α and β phases was performed using first-principles calculations based on density functional theory. The obtained ground state structure and mechanical properties are in excellent agreement with the available experimental and theoretical data. A full elastic tensor and crystal anisotropy of Be₃N₂ in two phases are determined in the wide pressure range. Results indicated that the two phases of Be₃N₂ are mechanically stable and strongly pressure dependent in the range of pressure from 0 to 80 GPa. The superior mechanical properties show that the two phases of Be₃N₂ are potential candidate structures to be the hard material. And the α-Be₃N₂ has better mechanical properties than β-Be₃N₂. By the calculated B/G ratio, it is predicted that both phases are intrinsically brittleness and strongly prone to ductility when the pressure is above 65.6 and 68.5 GPa, respectively. Additionally, the pressure-induced elastic anisotropy analysis indicates that the elastically anisotropic of Be₃N₂ in both phases is strengthening with increasing pressure, and strongly dependent on the propagation direction.     

掺杂质子化石墨相氮化碳增强碳基太阳能电池中钙钛矿的结晶

钙钛矿层的品质极大影响钙钛矿太阳能电池性能. 然而,在溶液法生成多晶钙钛矿膜过程中会不可避免地形成缺陷和陷阱位. 通过在钙钛矿层中嵌入添加物改善钙钛矿晶化,用于减少和钝化缺陷是非常重要的. 本文合成一种环境友好的二维纳米材料质子化石墨相氮化碳(p-g-C₃N₄),并掺杂于碳基钙太阳能电池的钙钛矿层中. 实验证明,在钙钛矿前驱体溶液中添加p-g-C₃N₄不仅能调解碘铅甲胺(MAPbI₃)结晶的成核和生长速率,获得大晶粒尺寸的平滑表面,还能减少钙钛矿层的本征缺陷. 质子化过程在氮化碳表面引入活性基团-NH₂/-NH₃,它们和钙钛矿晶体表面N-H键发生强化学作用,有效地钝化电子陷阱,提高钙钛矿结晶质量. 结果表明,与不掺杂的对照电池(效率为4.48%)和掺杂石墨相氮化碳(g-C₃N₄)电池(效率为5.93%)相比,掺杂质子化石墨相氮化碳(p-g-C₃N₄)的电池获得了6.61%的较高效率. 本工作展示了一种通过掺杂改性添加物改善钙钛矿膜的简单方法,为碳基钙钛矿太阳能电池的低成本制备提供了建议.     

Studying the effect of hydrogen on diamond growth by adding C10H10Fe under high pressures and high temperatures

In this paper, hydrogen-doped industrial diamonds and gem diamonds were synthesized in the Fe–Ni–C system with C₁₀H₁₀Fe additive, high pressures and high temperatures range of 5.2–6.2?GPa and 1250–1460°C. Experimental results indicate similar effect of hydrogen on these two types of diamonds: with the increasing content of C₁₀H₁₀Fe added in diamond growth environment, temperature is a crucial factor that sensitively affects the hydrogen-doped diamond crystallization. The temperature region for high-quality diamond growth becomes higher and the morphology of diamond crystal changes from cube-octahedral to octahedral. The defects on the {100} surfaces of diamond are more than those on the {111} surfaces. Fourier transform infrared spectroscopy (FTIR) results indicate that the hydrogen atoms enter into the diamond crystal lattice from {100} faces more easily. Most interestingly, under low temperature, nitrogen atoms can also easily enter into the diamond crystal lattice from {100} faces cooperated with hydrogen atoms.     

Si3N4的晶体化和ZrN/Si3N4纳米多层膜的超硬效应

研究了Si₃N₄层在ZrN/Si₃N₄纳米多层膜中的晶化现象及其对多层膜微结构与力学性能的影响. 一系列不同Si₃N₄层厚度的ZrN/Si₃N₄纳米多层膜通过反应磁控溅射法制备. 利用X射线衍射仪、高分辨透射电子显微镜和微力学探针表征了多层膜的微结构和力学性能. 结果表明，由于受到ZrN调制层晶体结构的模板作用，溅射条件下以非晶态存在的Si₃N₄层在其厚度小于0.9 nm时被强制晶化为NaCl结构的赝晶体，ZrN/Si₃N₄纳米多层膜形成共格外延生长的柱状晶，并相应地产生硬度升高的超硬效应. Si₃N₄随层厚的进一步增加又转变为非晶态，多层膜的共格生长结构因而受到破坏，其硬度也随之降低.     

AlN/Si3N4纳米多层膜的外延生长与力学性能

采用射频磁控溅射方法制备单层AlN, Si₃N₄薄膜和不同调制周期的AlN/Si₃N₄纳米多层膜.采用X射线衍射仪、高分辨透射电子显微镜和纳米压痕仪对薄膜进行表征.结果发现,多层膜中Si₃N₄层的晶体结构和多层膜的硬度依赖于Si₃N₄层的厚度.当AlN层厚度为4.0nm、 Si₃N₄层厚度 关键词： 3N₄纳米多层膜')" href="#">AlN/Si₃N₄纳米多层膜 外延生长 应力场 超硬效应     

Mechanical properties and electronic structure of TiC,Ti0.75W0.25C,Ti0.75W0.25C0.75N0.25, TiC0.75N0.25 and TiN

The first-principles calculations are performed to investigate the mechanical properties and electronic structure of TiC, Ti_0.75W_0.25C, Ti_0.75W_0.25C_0.75N_0.25, TiC_0.75N_0.25 and TiN. Density functional theory and ultrasoft pseudopotentials are used in this study. From the formation energy, it is found that nitrogen can increase the stability of TiC. The calculated elastic constants and elastic moduli of TiC compare favorably with other theoretical and experimental values. Tungsten and nitrogen are observed to significantly increase the bulk, shear and Young's modulus of TiC. Through the analysis of B/G and Cauchy pressure, tungsten can significantly improve the ductility of TiC. The electronic structure of TiC, TiN, Ti_0.75W_0.25C, Ti_0.75W_0.25C_0.75N_0.25, and TiC_0.75N_0.25 are used to describe nonmetal–metal and metal–metal bonds. Based on the Mulliken overlap population analysis, the hardness values of TiC, Ti_0.75W_0.25C, Ti_0.75W_0.25C_0.75N_0.25, TiC_0.75N_0.25 and TiN are estimated.     

Si3N4在h-AlN上的晶体化与AlN/Si3N4纳米多层膜的超硬效应

采用反应磁控溅射法制备了一系列具有不同Si₃N₄层厚度的AlN/Si₃N₄纳米多层膜,利用X射线衍射仪、高分辨透射电子显微镜和微力学探针表征了多层膜的微结构和力学性能.研究了Si₃N₄层在AlN/Si₃N₄纳米多层膜中的晶化现象及其对多层膜生长结构与力学性能的影响.结果表明,在六方纤锌矿结构的晶体AlN调制层的模板作用下,通常溅射条件下以非晶态存在的Si₃N₄层在其厚度小于约1nm时被强制晶化为结构与AlN相同的赝形晶体,AlN/Si₃N₄纳米多层膜形成共格外延生长的结构,相应地,多层膜产生硬度升高的超硬效应.Si₃N₄随层厚的进一步增加又转变为非晶态,多层膜的共格生长结构因而受到破坏,其硬度也随之降低.分析认为,AlN/Si₃N₄纳米多层膜超硬效应的产生与多层膜共格外延生长所形成的拉压交变应力场导致的两调制层模量差的增大有关. 关键词： 3N₄纳米多层膜')" href="#">AlN/Si₃N₄纳米多层膜 外延生长 赝晶体 超硬效应