Wear behavior of sintered hexagonal boron nitride under atmosphere and water vapor ambiences

Hexagonal boron nitride was pressed and sintered at 2000 °C with CaB₂O₄ as an additive to promote its crystallization, which was used as an abradable sealing coating for aircraft turbo engines. Microstructures, phase compositions and tribological properties of the sintered hBN were tested, and the results show that CaB₂O₄ can effectively promote crystal growth of hBN at 2000 °C for 5 h in N₂ ambience. The friction coefficients of the sintered hBN under atmosphere ambience increase as the temperature increasing from room temperature to 400 °C, and then decrease with further increasing of temperature up to 800 °C. Under water vapor ambience, friction coefficients of the sintered hBN are much lower than those under atmosphere ambience, which are attributed to a lamella-slip of hBN and the solid lubrication effect of H₃BO₃.     

Effect of triangle vacancy on thermal transport in boron nitride nanoribbons

Recently, triangle vacancy in hexagonal boron nitride is observed experimentally. Using nonequilibrium Green’s function method, we investigate thermal transport properties of boron nitride nanoribbons (BNNRs) with a triangle vacancy. The effect of triangle vacancy on the phonon transmission of zigzag-edged BNNRs (Z-BNNRs) is different from that of armchair-edged BNNRs (A-BNNRs). The triangle vacancy induces antiresonant dips in the spectrum of Z-BNNRs. Moreover, the boron-terminated triangle vacancy causes antiresonant zero-transmission dip and the number of the zero-transmission dip increases with the geometrical size of triangle vacancy. For the A-BNNRs with triangle vacancy, except some antiresonant dips, a resonant peak is found in the transmission. The antiresonant and resonant phenomena are explained by analyzing local density of states and local thermal currents. Although the antiresonant dip and the resonant peak are both originated from quasibound states, their distributions of local thermal currents are distinct, which leads to the transport discrepancy. In addition, the thermal conductance of BNNRs decreases linearly with increasing the vacancy size.     

Charge distribution of a potassium-doped combined system of graphene and hexagonal boron nitride

By using first-principles density functional theory, we investigate the charge distribution of a potassium-doped layered combined system of graphene and hexagonal boron nitride. Two configurations of potassium-doped hexagonal boron nitride layers on graphenes and the reverse geometry of graphenes on hexagonal boron nitride layers are considered. We find that the charge distribution exhibits different features in these two situations. In the former case, the outmost hexagonal boron nitride layer cannot screen the external charges offered by potassium atom completely and most of the transferred charges reside on the two bounding layers. In contrary, the outmost graphene layer near the potassium atom can accept almost all of the transferred charges and only a few of them stay at interior layers in the latter case. A more amazing result is that the characteristics of charge transfer are independent of the number of hexagonal boron nitride layers and graphenes.     

基于二维六方氮化硼材料的光子晶体非对称传输异质结构设计

二维六方氮化硼(hexagonal boron nitride,hBN)材料在产生光学稳定的超亮量子单光子光源领域有着潜在应用,有望用于量子计算和信息处理平台,已成为研究热点.而光学非对称传输设备是集成量子计算芯片中的关键器件之一.本文从理论上提出了一种基于hBN材料光子晶体异质结构的纳米光子学非对称光传输器件.运用平...     

First-principles study of transition metal linear monoatomic chains adsorption on boron nitride nanotube

Structural, electronic and magnetic properties of six 3d transition metals (TM=V, Cr, Mn, Fe, Co and Ni) linear monoatomic chains adsorbed on the (5,5) boron nitride nanotube (BNNT) at five different sites have been investigated by first-principle calculations. The results indicate all TM chains can be spontaneously adsorbed on the outer surface of the BNNT. The stable adsorption sites are different for different TM chains. All TM chains can be adsorbed on the N site, while the adsorption on the Z site is unstable. The dispersion character occurs in energy band curves of stable TM/BNNT systems and bring about the band gap disappearance in comparison with that of pure (5,5) BNNT. Interestingly, the TM/BNNT systems with nearly half-filled 3d metals V and Cr at H and N sites, as well as Mn at A site show a half-metal character and are usable in spintronics devices. The different electronic properties of BNNT can also be achieved through decorations of the same TM chain on different sites. The TM chain adsorbed BNNT systems exhibit high stability, promising electronic properties and high magnetic moments, which may be useful for a wide variety of next-generation nanoelectronic device components.     

Electromigration with enhanced green emission in the titanium dioxide nanotube/graphene composite

One of the most studied photoluminescence emission peaks of anatase titanium dioxide (TiO₂) is green, located at about 520 nm, which is assigned to the radiative recombination between a mobile electron in the conduction band and oxygen vacancy defect as a trapped hole in the bandgap. Composite materials of TiO₂ with graphene are normally shown by the gradual quenching of photoluminescence intensity as a result of carrier lifetime extension, which is important to enhance photocatalytic activity. Herein we report an observation of the intensity enhancement of the green PL emission in a composite TiO₂ nanotube (TNT) and graphene produced through facile hydrothermal synthesis. The heterojunction formation of graphene and TNT makes the excited photoelectrons easy to diffuse from TNT to graphene. Hence, the recombination rate of mobile electrons in graphene and trapped holes located on the nanotube surface is enhanced due to the high mobility of electrons in graphene.     

Ethylene glycol reflux synthesis of carbon nanotube/ceria core-shell nanowires

Carbon nanotube (CNT)/ceria core-shell nanowires were prepared facilely on a large scale under the boiling reflux of ethylene glycol. The composites are characterized by transmission electron microscopy, X-ray diffraction as well as Fourier transformed infrared spectra. It is found that the entire outer surface of CNTs is fully sheathed with a dense layer of uniform nanosized CeO₂, and that the thickness of the coating sheath can be readily manipulated by tuning the molar ratio of ceria to CNTs. Finally, a possible formation mechanism has been suggested as follows: with the high reaction temperature, ethylene glycol is partially converted to oxalic acid, and the surface hydroxyl groups of CeO₂ tiny particles react with oxalic acid to form the polymer-like inorganic-organic compounds. Subsequently, in view of the low-energy point, the polymer-like inorganic-organic compounds are coated on the surface of CNTs, and thus CNTs/ceria core-shell composites are obtained.     

Synthesis, characterization and electrochemical behavior of polypyrrole/carbon nanotube composites using organometallic-functionalized carbon nanotubes

Thorn-like, organometallic-functionalized carbon nanotubes were successfully developed via a novel microwave hydrothermal route. The organometallic complex with methyl orange and iron (III) chloride served as reactive seed template, resulting in the oriented polymerization of pyrrole on the modified carbon nanotubes without the assistance of other oxidants. Morphological and structural characterizations of the carbon nanotube/methyl orange-iron (III) chloride and polypyrrole/carbon nanotube composites were examined using transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), infrared spectroscopy and X-ray diffraction (XRD). The electrochemical property of the polypyrrole/carbon nanotube composite was elucidated by cyclic voltammetry and galvanostatic charge-discharge. A specific capacitance of 304 F g⁻¹ was obtained within the potential range of −0.5-0.5 V in 1 M KCl solution.     

Compressive characteristics of single walled carbon nanotube with water interactions investigated by using molecular dynamics simulation

The elastic properties of single walled carbon nanotube (SWCNT) with surrounding water interactions are studied using molecular dynamics simulation technique. The compressive loading characteristic of carbon nanotubes (CNTs) in a fluidic medium such as water is critical for its role in determining the lifetime and stability of CNT based nano-fluidic devices. In this paper, we conducted a comprehensive analysis on the effect of geometry, chirality and density of encapsulated water on the elastic properties of SWCNT. Our studies show that defect density and distribution can strongly impact the compressive resistance of SWCNTs in water. Further studies were conducted on capped SWCNTs with varying densities of encapsulated water, which is necessary to understand the strength of CNT as a potential drug carrier. The results obtained from this paper will help determining the potential applications of CNTs in the field of nano-electromechanical systems (NEMS) such as nano-biological and nano-fluidic devices.     

Study on selective adsorption of deuterium on boron nitride using photon-stimulated ion-desorption

Adsorption behavior of atomic deuterium on a hexagonal boron nitride (h-BN) thin film is studied by photon-stimulated ion desorption (PSID) of D⁺ and near edge X-ray absorption fine structure (NEXAFS) at the B and N K-edges. After the adsorption of atomic deuterium, D⁺ desorption yield η(hν) shows clear enhancement at the B K-edge and almost no enhancement at the N K-edge. NEXAFS spectra show a large change in the B K-edge and a small change in the N K-edge after the adsorption. We propose selective adsorption of atomic deuterium on the h-BN thin film based on the experimental results, and mention the effectiveness of applying the PSID method with X-ray to study hydrogen storage materials.     

六方氮化硼单层中一种(CN)3VB缺陷的第一性原理计算

二维六方氮化硼(hBN)的点缺陷最近被发现可以实现室温下的单光子发射,而成为近年的研究热点.尽管其具有重要的基础和应用研究意义,hBN中发光缺陷的原子结构起源仍然存在争议.本文采用基于密度泛函理论的第一性原理计算,研究hBN单层中一种B空位附近3个N原子被C替代的缺陷(CN)3VB.在hBN的B空位处,3个N原子各自带...     

Effects of electromigration on copper atoms in carbon nanotube channels

The effects of electromigration on copper in carbon nanotube (CNT) channels are investigated using molecular dynamics simulations. The study shows that the potential energy of copper and the resistive forces on copper are dependent on the shape of the CNT junction, and the increase in bias voltages magnifies these effects. Bias voltages affect the density of copper in the downstream CNT. The velocity of copper in the downstream CNT is relatively lower than that in the upstream CNT when the biased voltage is high.     

Amino functionalization of carbon nanotube surfaces with NH3 plasma treatment

NH₃ plasma treatment of carbon nanotube (CNT) surfaces was performed with the purpose of incorporating amino groups onto the surface. Amino groups incorporated onto the CNT surface were indentified and quantified using chemical derivatization with pentafluorobenzaldehyde and subsequent characterization with X-ray photoelectron spectroscopy (XPS). The amount of incorporated amino groups reached a maximum value with increasing plasma power. The incorporation of amino groups was seriously affected by the degradation of the CNT surface during the plasma treatment, which became very serious at high plasma power, as verified with optical emission spectroscopy (OES) and FT-IR analyses. The type of species present in the plasma discharge also seems to be important for amino group functionalization; partially decomposed ammonia species are considered to be more favorable than fully decomposed atomic species.     

First-principles study of two-dimensional van der Waals heterostructure based on ZnO and Mg(OH)2: A potential photocatalyst for water splitting

In this study, the structural, electronic and optical properties of the two-dimensional heterostructure based on ZnO and Mg(OH)₂ are investigated by first-principle calculations. The ZnO/Mg(OH)₂ heterostructure, formed by van der Waals (vdW) interaction, possesses a type-II band structure, which can separate the photogenerated electron–holes constantly. The heterostructure has decent band edge positions for the redox reaction to decompose the water at pH 0 and 7. As for the interfacial properties of the heterostructure, the trend of band bending of the ZnO and Mg(OH)₂ layers in the heterostructure is addressed, which will result a built-in electric field. Besides, the charge-density difference and potential drop across the interface of the ZnO/Mg(OH)₂ vdW heterostructure are also calculated. Finally, the heterostructure is demonstrated that it not only has excellent ability to capture the light near the visible spectrum region, but also can improve the optical performance for the monolayered ZnO and Mg(OH)₂.     

Distinct transport properties of O2 and CH4 across a carbon nanotube

It is of fundamental importance to investigate either O₂ or CH₄ molecules across nanochannels in many areas such as breathing or separation. Thus, many researches have focused on such a single type of molecules across nanochannels. However, O₂ and CH₄ can often appear together and crucially affect human life, say, in a mine. On the basis of molecular dynamics simulations, here we attempt to investigate the mixture of O₂ and CH₄, in order to identify their different transport properties in a nanochannel. We take a single-walled carbon nanotube (SWCNT) as a model nanochannel, and find that their transport properties are distinctly different. As the concentration of O₂ increases up to a high value of 0.8, it is always faster for CH₄ molecules to transport across the SWCNT, and the total number of gas molecules transporting across the SWCNT is decreased. Meanwhile, CH₄ molecules are always dominant in the SWCNT, and the total number of O₂ or CH₄ inside the SWCNT is a constant. By calculating the van der Waals interaction between the SWCNT and O₂ or CH₄, we find that the net interaction between CH₄ and the SWCNT is much stronger. Our findings may offer some hints on how to separate CH₄ from O₂, and/or store CH₄ efficiently.     

Composites of multiwall carbon nanotubes and conducting polyaniline: Bulk samples and films produced from a solution in chloroform

Multiwall carbon nanotubes and conducting polyaniline, doped with dodecylbenzenesulfonic acid, are blended by employing the solubility of both materials in chloroform. Pellets are made by pressing the dried powder of the obtained composite, and films by sedimentary deposition onto a plastic substrate. In these composites, the advantageous properties of carbon nanotubes can be utilized in fully conducting bulk and planar structures while the strong decrease of the conductivity of doped polyaniline at low temperatures is simultaneously suppressed. The nanotube content in pellets can be as high as 40% by weight, and this wide range leads to a control over the shape and magnitude of the conductivity versus temperature curves. As the nanotube content grows, the temperature dependence of the conductivity becomes less steep, which is similar to the effect of annealing temperature on the conductivity of certain polycrystalline graphene films. In our case, this change is most likely caused by the increase of the density of highly conducting channels and not by homogeneous delocalization effects.     

Bound states of solitons in a fiber laser mode locked with carbon nanotube saturable absorber

We report on the experimental observation of bound states of solitons in an erbium-doped fiber laser passively mode-locked by the carbon nanotube saturable absorber. Bound states of solitons with various pulse separations are obtained. While the tightly bound solitons always exhibit the same set of fixed discrete pulse separations with π or π/2 phase difference, the feature becomes less obvious for the loosely bound solitons. The result that various states of the bound solitons were obtained in the same fiber laser makes a systematic experimental study on them and a comparison of their properties possible. Our results once again show that the bound soliton emission is an intrinsic feature of the mode-locked soliton fiber lasers.     

Molecular dynamics simulation of the oscillatory behaviour and vibrational analysis of an adamantane molecule encapsulated in a single-walled carbon nanotube

In this study, we employed classical molecular dynamics to simulate the encapsulation and examine the dynamical behaviour of an adamantane molecule inside a single-walled carbon nanotube. As a result, we found that the critical and optimal diameters of the tube for molecular encapsulation were about 9.5 and 10.86 Å, respectively, and that the speed of encapsulation mainly depended on tube’s diameter. Furthermore, the encapsulated adamantane molecule exhibited irregular motion and frequent collisional motion along the tube’s longitudinal axis and on the tube’s cross-sectional plane, respectively. In addition, we examined the influence of the tube diameter and temperature on the mean free path and average collisional frequency of the molecule’s motion. Lastly, the influence of the host–guest interaction on the systematic vibrational optic mode was studied using density functional theory calculation.