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Single-crystalline Ge nanowires covered with amorphous carbon were synthesized by using GeO2 as the Ge source and reacting it with a mixed gas of C2H4 and NH3 at 750 °C. Electron microscopy studies show that the nanowires have a diameter distribution ranging from 15 to 50 nm and a length up to tens of micrometres. The growth mechanism of the Ge nanowires could be attributed to the well known vapour–liquid–solid (VLS) catalytic growth process promoted by nanoparticles attached at the end of the nanowires. [ABSTRACT FROM AUTHOR]

Antibiotics can easily enter the water environment through direct or indirect approach, causing environmental pollution and endangering the health of organisms. Therefore, development of highly efficient adsorbent materials to adsorb and remove antibiotics is necessary. Here, cobalt oxide and nickel oxide are uniformly and tightly bonded on the surface of porous boron nitride fibers (PBNFs-NiCo), increasing the number of functional groups (B-O and N-H) and hydrogen bond receptors within PBNFs. The total pore volume and specific surface area of resulting PBNFs-NiCo can reach up to 0.48 cm 3 g -1 and 720.3 m 2 g -1 , respectively. Encouraged by the unique micromorphology and chemical composition mentioned above, PBNFs-NiCo exhibits excellent ceftriaxone sodium (CS) adsorption ability, showing the adsorption capacity and removal efficiency up to 410.9 mg g -1 and 96.5%, respectively. Chemical adsorption plays an important role in their adsorption behavior, abiding by Langmuir adsorption theory and pseudo-second-order kinetic equation. Importantly, PBNFs-NiCo exhibits fascinating adsorption effects in surroundings with pH ranging from 4 to 6, 25 °C and varying salt concentrations. This work would establish a practical and feasible foundation for the practical application of PBNFs-NiCo for CS adsorption in aqueous solution., (© 2024 IOP Publishing Ltd. All rights, including for text and data mining, AI training, and similar technologies, are reserved.)

Although enhanced performances of photovoltaic devices by embedding metal nanoparticals in charge transport layer, doping into active layer bulk, decorating the active layer surface, and inserting at the interface between semiconductor and the electrode were reported, the effect of incorporating metal NPs at the interface of single crystal semiconductor and perovskite is rarely tackled. Herein the effects of incorporating Ag nanoparticals (AgNPs) at p-Si/MAPbI3 perovskite interface on the photodiode performances were investigated. The results showed that compared with reference device (without AgNPs) the photoresponsivity of the device incorporating AgNPs is greatly improved with the exception for light with wavelengths fall in the spectral range where AgNPs have strong optical absorption. This effect is extremely significant for relatively shorter wavelengths in visible region, and a maximal improvement of around 10.6 times in photoresponsivity was achieved. The physical origin of the exception for spectral range that AgNPs have strong optical absorption is the cancelation of scatter resulted enhancement through AgNPs by band-to-band absorption resulted reduction of photocurrent, in which the generated electron has energy near the fermi level and the hole has large effective mass, which relax by nonradiative recombination, thus making not contribution to the photocurrent. More importantly, the AgNP decorated device showed much faster photo response speed than reference device, and a maximal improvement of around 7.9 times in rise and fall time was achieved. These findings provide a novel approach for high responsive and high speed detection for weak light., (NA.)

One-dimensional nanowire structures composed of perovskite are widely recognized for their exceptional optoelectronic performance and mechanical properties, making them a popular area of investigation in photodetection research. In this work, a perovskite nanowire/copper phthalocyanine heterojunction-based photodetector was fabricated, which exhibits high photoresponse in the visible-near-infrared region. The incorporation of a heterojunction significantly enhanced the photoelectric performance. Specifically, the photoresponsivity and external quantum efficiency of the nanowire-based device were elevated from 58.5 A W -1 and 1.35 × 10 4 % to 84.5 A W -1 and 1.97 × 10 4 % at 532 nm, respectively. The enhanced photoresponse of the heterojunction device can be attributed to the unique microstructure of nanowire arrays. The wrapping of the nanowires by copper phthalocyanine forms heterojunctions with a larger dissociation area, which facilitated exciton dissociation and enhanced device performance. This work provides a promising example for optimizing the performance of nanowire devices., (© 2023 IOP Publishing Ltd.)

Narrow-band photodetectors based on halide perovskite have recently attracted significant attention due to their exceptional narrow-band detection performance and tunable absorption peaks covering a wide optical range. In this work, we report mixed-halide CH 3 NH 3 PbCl x Br 3- x single crystal-based photodetectors have been fabricated, where the Cl/Br ratios were varied (3:0, 10:1, 5:1, 1:1, 1:7, 1:14 and 0:3). Vertical and parallel structures devices were fabricated which exhibited ultranarrow spectral responses under bottom illumination, with a full-width at half-maximum less than 16 nm. The observed performance can be ascribed to the unique carrier generation and extraction mechanisms within the single crystal under short and long wavelength of illumination. These findings offer valuable insights into the development of narrow-band photodetectors that do not necessitate the use of filters and hold tremendous potential for a diverse array of applications., (© 2023 IOP Publishing Ltd.)

Based on the first-principle, the friction anisotropy, structural super-lubricity and oxidation induced ultra-low friction of black phosphorus at atomic scale under different loads have been studied. The results show that the interface friction of black phosphorus is anisotropic, that is, the friction along the armchair direction is greater than that along the zigzag direction. Moreover, the friction between the black phosphorus interfaces shows a structural superlubricity property, and the incommensurate interface friction is approximately one thousandth of the commensurate interface friction, which is mainly due to the less electronic charge and the smaller amplitude of electronic charge change between the incommensurate interfaces during the friction process. In addition, the oxidation of black phosphorus is beneficial for lubrication between interfaces., (© 2023 IOP Publishing Ltd.)

Lithium-rich layered manganese-based cathodes (LRLMOs) with first-class energy density (∼1000 W h kg -1 ) have attracted wide attention. Nevertheless, the weak cycle stability and bad rate capability obstruct their large-scale commercial application. Here, single crystal Li 1.2- x Na x Ni 0.2 Mn 0.6 O 2 ( x  = 0, 0.05, 0.1, 0.15) nanoparticles are designed and successfully synthesized due to the single crystal structure with smaller internal stress and larger ionic radius of Na. The synergistic advantages of single crystal structure and Na doping are authenticated as cathodes for Li ion batteries (LIBs), which can consolidate the crystallographic structure and be benefit for migration of lithium ion. Among all the Na doping single crystals, Li 1.1 Na 0.1 Ni 0.2 Mn 0.6 O 2 cathode possesses supreme cycling life and discharge capacity at large current density. To be more specific, it exhibits a discharge capacity of 264.2 mAh g -1 after 50 charge and discharge cycles, higher than that of undoped material (214.9 mAh g -1 ). The discharge capacity of Li 1.1 Na 0.1 Ni 0.2 Mn 0.6 O 2 cathode at 10 C (1 C = 200 mA g -1 ) is enhanced to 160.4 mAh g -1 (106.7 mAh g -1 for x  = 0 sample). The creative strategy of Na doping single crystal LRLMOs might furnish an idea to create cathode materials with high energy and power density for next generation LIBs., (© 2021 IOP Publishing Ltd.)

By means of quotient-graph associated crystal prediction method, a new graphyne allotrope with unique Dirac nodal grid state is reported in this work. It is named as 191-E24Y24-1 according to its hexagonal lattice (with P6/mmm symmetry, No. 191) containing 24 sp 2 -hybridized carbon atoms and 24 sp-hybridized ones. The first-principles results show that the total energy of 191-E24Y24-1 is more favorable than that of recent synthesizedβ-graphdiyne and carbon ene-yne. It is also demonstrated to be dynamically, thermally, and mechanically stable. Interestingly, the 191-E24Y24-1 harbors intrinsic semimetal features showing intriguing hexagonal Dirac nodal grid state in the reciprocal space. Such unique electronic state is stable against small external tensile strains, and it is tunable under compression strains which will transform to new triangle Dirac nodal grid state. Moreover, a new metastable graphyne allotrope named 191-E12Y36-4 with Dirac nodal loop state is also observed in the process of stretching 191-E24Y24-1 with large tensile strains. The results presented in this work reveal two novel graphyne allotropes with exotic electronic properties. These discoveries are not only physical interesting, but also provide potential material candidates for carbon-based high performance electronic nanodevices., (© 2021 IOP Publishing Ltd.)

We numerically demonstrate an ultraviolet graphene ultranarrow absorption in a hybrid graphene-metal structure. The full-width at half maximum of the absorption band being 9 nm in ultraviolet range is achieved based on the coupling of lattice plasmon resonances of the metallic nanostructure to the optical dissipation of graphene. The position, absorbance and linewidth of the hybridized narrow resonant mode tuned by controlling geometrical parameters and materials are systematically investigated. The proposed structure possesses high refractive index sensitivity of 288 nm/RIU and figure of merit of 72, and can also be used to detect small molecules layer of sub-nanometer thickness and refractive index with small changes, providing promising applications in ultra-compact efficient biosensors., (© 2021 IOP Publishing Ltd.)

Graphite possessing extraordinary frictional properties has been widely used as solid lubricants. Interesting frictional characteristics have been observed for pristine graphene layers, for defective graphene, the frictional signal shows richer behaviors such as those found in topological defective graphene and graphene step edges. Recently discovered nanoporous graphene represents a new category of defect in graphene and its impact on graphene frictional properties has not yet been explored. In this work, we perform molecular dynamics simulations on the frictional responses of nanoporous graphene layers when slid using a silicon tip. We show that the buried nanopore raises maximum friction signal amplitude while preserving the stick-slip character, the size of the nanopore plays a key role in determining the maximum frictional force. Negative friction is observed when the silicon tip scanned towards the center of the nanopore, this phenomenon originates from the asymmetrical variation of the in-plane strain and the out-of-plane deformation when indented by the silicon tip. Moreover, the layer dependent frictional character is examined for the buried graphene nanopores, showing that increasing graphene layers weakens the effect of nanopore on the frictional signal., (© 2021 IOP Publishing Ltd.)

Penta-graphene is a new two-dimensional metastable carbon allotrope composed entirely of carbon pentagons with unique electronic and mechanical properties. In this work we evaluate the mechanical properties of new classes of defective penta-graphene (DPG) subjected to tensile and shear loading by using molecular dynamics simulations. The types of defects considered here are monovacancy at either 4-coordinated C1 site or 3-coordinated C2 site, and double vacancy (DV). We focus in particular on the effects of the different topologies of defects and their concentrations on the elastic constants and the nonlinear mechanics of this allotropic form of carbon. The results indicate that DPG has a plastic behavior similar to pristine penta-graphene, which is caused by the irreversible pentagon-to-polygon structural transformation occurring during tensile and shear loading. The tensile and shear moduli decrease linearly with the concentration of defects. Monotonic reductions of the tensile yield and shear stresses are also present but less pronounced, while the yield strains are unaffected. Penta-graphene with 4-coordinated and DVs feature a change of the Poisson's ratio from negative to positive when the defect concentration rises to about 3% and 6%. Temperature can trigger structural reconstruction for free-standing DPG. The critical transition temperature increases due to the vacancy defects and the defects can delay the structure transition. These findings are expected to provide important guidelines for the practical applications of penta-graphene based micro/nano electromechanical systems., (© 2021 IOP Publishing Ltd.)

Two-dimensional (2D) hexagonal boron nitride (h-BN) is becoming increasingly interesting for wider engineering applications. Thermal exfoliation is being suggested as a facile technology to produce large quantities of 2D h-BN. Further optimization of the process requires fundamental understanding of the exfoliation mechanism, which is hardly realized by ex situ techniques. In this study, in situ synchrotron x-ray powder diffraction experiments are conducted while heat treating bulk h-BN up to 1273 K. During the heating process, linear expansion of c-axis is observed and the contraction of a-axis up to around 750 K is consistent with previous research. However, a changing behavior from contraction to expansion in a-axis direction is newly observed when heating over 750 K. With the consideration of previous thermally oxidation studies, a hypothesis of thermal assisted exfoliation with oxygen interstitial and substitution of nitrogen at high temperature is proposed.

Blue phosphorus is an emerging 2D material that exhibits finite electronic band gap and may find promising applications in advanced semiconducting devices. Comparing to its allotrope, black phosphorus, mechanical properties of blue phosphorus have not been explored in detail. Here we report molecular dynamics simulations of mechanical responses of blue phosphorus under uniaxial tensile, biaxial tensile and shear loadings. It is found that blue phosphorus shows less anisotropic effect as compared to black phosphorus, the room temperature Young's modulus is about 122.3 GPa and 121.6 GPa along armchair and zigzag directions, respectively, shear modulus is about 27.1 GPa and 28.6 GPa, respectively, along armchair and zigzag directions. Temperature effect on mechanical responses is also systematically studied within a range of 5-400 K. It is found that temperature reduces both Young's modulus and fracture strain and fracture strength of blue phosphorus, owing to the interplay between thermal energy and strain energy applied to the models. Brittle fracture mode is found in blue phosphorus in all loading conditions, with varied crack nucleation and propagation modes. The role of strain rate on the mechanical properties is examined and found to systematically modify the ultimate stress and ultimate strain of BlueP. Structural details including bond length and bond angle variations to external strain are analyzed to gain deeper insights into the underlying mechanisms.

In this work, the nanoparticle agglomeration process has been studied via molecular dynamics simulations to uncover the agglomeration mechanism. When the nanoparticles were far from each other in an aqueous solution, they mainly diffused because of influence of water molecules. When nanoparticles were close to each other, hydrogen bonds between the nanoparticles actively contributed to their agglomeration. In addition, the agglomeration of nanoparticles was also related to their sizes and concentration. A higher nanoparticle concentration led to an increased probability of nanoparticle contact and easier agglomeration. Smaller nanoparticles could diffuse quickly and aggregate more easily, hence resulting in agglomeration. Additionally, to restrain the agglomeration of silicon dioxide nanoparticles, promote compatibility between the inorganic silicon dioxide nanoparticles and organic polymer meta-aramid fibers, and strengthen the interaction between the two molecules, 3-aminopropyltriethyloxy silane was used for chemical modification of the surface of the nanoparticles. By comparing the interaction energy and hydrogen bond energy between interfaces before and after modification, a grafting density of 502% (1/Å 2 ) was achieved, which was comparatively the best. The results of this work provide a valuable basis for further discussion and improvement of the performance of meta-aramid fiber insulation via doping hybridization with silicon dioxide nanoparticles.

Thermal anisotropy/isotropy is one of the fundamental characteristics of the thermal properties of a material, playing a significant role in the high-performance thermal management in micro-/nanoelectronics. It has been well documented in the literature that the symmetry of geometric structures governs the anisotropy/isotropy of thermal transport. However, the fundamental correlation and the underlying mechanism remain unclear. In this paper, using a new two-dimensional (2D) van der Waals (vdW) phosphorus nanotube array as a case study, we show that the lattice thermal conductivity can be abnormally almost isotropic although the geometric structure presents remarkable anisotropy, which contradicts the previous consensus. The key factor for the abnormal isotropic thermal conductivity is mainly the essentially analogous group velocities along the intratube and intertube directions. Compared with a carbon-nanotube array, a traditional vdW system, a microscopic picture is established to underpin the underlying mechanism. The quasi-bond (non-covalent bonding, but far stronger than the vdW interatomic interaction) between the phosphorus nanotubes is found to be responsible for such diverse isotropic transport phenomena. The findings in this paper are expected to deepen our understanding of the anisotropy/isotropy thermal transport of materials and are also helpful for future thermal management technology.

Flexible, heteroatoms-rich activated carbon nanofibers with fascinating cross-linked architectures are successfully gained in a facile and controllable way via electrospinning polyacrylonitrile (PAN) /dicyandiamide (DICY) composite nanofibers followed by carbonation and a CO 2 activation process. The unique inter-bonded structures and heteroatoms contents could be easily controlled by adjusting the preoxidation temperature applied in the calcining procedure and the addition of DICY. Significantly, the resultant samples display hierarchical pores with micro/meso/macropores, abundant N, O species doped and unique fiber-fiber interconnections, which considerably boost the electrochemical properties. As an electrode material, the activated N-doped cross-linked carbon nanofibers (ANCLCNFs) show a high capacitance of 323 F g -1 with a current density of 0.5 A g -1 , excellent rate capacity (230.1 F g -1 at 20 A g -1 ) and long-term duration (over 95% after 10000 cycles). Furthermore, the symmetrical supercapacitor delivers a maximum energy density of 14.3 Wh kg -1 at a power density of 162.5 W kg -1 .

In this study, molecular dynamics simulations were used to investigate the micro-scale effects of modification of nano-SiO 2 with commonly used silane coupling agents (KH550, KH560, KH570, and KH792) on the cellulose/nano-SiO 2 interface. The relative optimum silane coupling agent and grafting density for nano-SiO 2 modification to improve the cellulose/nano-SiO 2 interface were determined. The results showed that at the same grafting density, modification of nano-SiO 2 with KH792 yielded the highest interfacial binding energy and binding energy density, the largest number of hydrogen bonds at the cellulose/nano-SiO 2 interface, the strongest binding to the cellulose chains, and the largest overlapping area at the cellulose/nano-SiO 2 interface. We found that the non-bonding interaction energy played a decisive role in the energy of the model system and the interfacial interaction force mainly consisted of van der Waals forces and the hydrogen-bonding energy. When silane coupling agents with amino groups (KH550 and KH792) were used to modify nano-SiO 2 , the number of hydrogen bonds at the cellulose/nano-SiO 2 interface was larger than that for unmodified nano-SiO 2 . When silane coupling agents without amino groups (KH560 and KH570) were used to modify nano-SiO 2 , the number of hydrogen bonds at the cellulose/nano-SiO 2 interface was lower than the case for unmodified nano-SiO 2 . Nano-SiO 2 modification with various amounts of KH792 was investigated. The results showed that the interfacial bonding energy increased with grafting density. When the grafting density was 1.57 nm -2 , the interfacial bonding energy and number of hydrogen bonds formed at the cellulose/nano-SiO 2 interface was relatively stable, which indicates that the interface had reached a relatively stable state. Modification of nano-SiO 2 with KH792 achieved the greatest improvement of the cellulose/nano-SiO 2 interface; this interface reached a relatively stable state when the grafting density of KH792 was 1.57 nm -2 .

Gallium nitride (GaN) nanowires (NWs) hold technological significance as functional components in emergent nano-piezotronics. However, the examination of their mechanical responses, especially the mechanistic understanding of behavior beyond elasticity (at failure) remains limited due to the constraints of in situ experimentation. We therefore performed simulations of the molecular dynamics (MD) of the mechanical behavior of [Formula: see text]-oriented GaN NWs subjected to tension or compression loading until failure. The mechanical properties and critical deformation processes are characterized in relation to NW sizes and loading conditions. Detailed examinations revealed that the failure mechanisms are size-dependent and controlled by the dislocation mobility on shuffle-set pyramidal planes. The size dependence of the elastic behavior is also examined in terms of the surface structure determined modification of Young's modulus. In addition, a comparison with c-axis NWs is made to show how size-effect trends vary with the growth orientation of NWs.

Nitrogenated holey graphene (NHG), a new two-dimensional graphene variant with a large fundamental direct band gap, has recently been successfully synthesized via a simple wet-chemical reaction. Motivated by its unique geometry and novel properties, we investigated the phonon transport properties of the material by combining first-principle calculations and the phonon Boltzmann transport equation. The lattice thermal conductivity of NHG at room temperature is predicted to be about 82.22 W mK -1 , which is almost two orders of magnitude lower than that of graphene (about 3500 W mK -1 ). Deviating from the traditional understanding that thermal transport is usually largely contributed by the acoustic phonon modes for most suspended 2D materials, both out-of-plane flexural acoustic (ZA) and optical phonon modes make a more or less equal contribution, and their combination abnormally dominates the overall thermal transport in NHG. The major three-phonon process in NHG is further analyzed and the scattering between the acoustic and optical phonon modes like [Formula: see text] is the main phonon process channel. Meanwhile, the mean free path distribution of different phonon modes is calculated for the purpose of the thermal management of NHG-based devices. Our results elucidate the unusual thermal transport properties of NHG as compared with the representative case of graphene, and underpin its potential application for use by the thermal management community.

In this letter, we report on hydrothermal growth of nickel diselenide nanowall film on carbon cloth (NiSe2 NW/CC) through topotactic transformation from a Ni(OH)2 precursor based on anion exchange reactions. When tested as an integrated 3D hydrogen-evolving cathode in strongly acidic media, NiSe2 NW/CC exhibits outstanding catalytic activity superior to its powder counterpart and strong long-term durability. It displays 10 and 100 mA cm(-2) at overpotentials of 145 and 183 mV, respectively, with its catalytic activity being retained for 40 h.

Volatile organic compounds, especially formaldehyde (HCHO), are considered to be great sources of contaminants in indoor air. However, design and preparation of safe, cost-affordable, and reusable materials for HCHO removal at ambient conditions are still remarkably challenging. Here, we have developed a kind of novel NaOH-embedded three-dimensional porous boron nitride (NaOH-3D BN) with high and hierarchical porosities, which exhibit excellent removal performance for HCHO. The as-prepared 3D BN is used as an adsorbent and catalytic support, while the embedded NaOH is applied as a catalyst, giving rise to catalytic transformation from high-toxic HCHO to less-toxic formate and methoxy salts at room temperature. Furthermore, their effective reusability has been confirmed. Given the high removal and reusability performance as well as no use of precious materials, the NaOH-3D BN is envisaged to be valuable practically for indoor air purification.

Polymer composites with enhanced mechanical, thermal or optical performance usually suffer from poor ductility induced by confined mobility of polymer chains. Herein, highly ductile UV-shielding polymer composites are successfully fabricated. Boron nitride (BN) materials, with a wide band gap of around ∼6.0 eV, are used as fillers to achieve the remarkably improved UV-shielding performance of a polymer matrix. In addition, it is found that spherical morphology BN as a filler can keep the excellent ductility of the composites. For a comparison, it is demonstrated that traditional fillers, including conventional BN powders can achieve the similar UV-shielding performance but dramatically decrease the composite ductility. The mechanism behind this phenomenon is believed to be lubricant effects of BN nanospheres for sliding of polymer chains, which is in consistent with the thermal analyses. This study provides a new design to fabricate UV-shielding composite films with well-preserved ductility.

Ripple is a common deformation in two-dimensional materials due to localized strain, which is expected to greatly influence the physical properties. The effects of the ripple deformation in the MoS2 layer on their physics, however, are rarely addressed experimentally. We here grow atomically thin MoS2 nanostructures by employing a vapor phase deposition method without any catalyst and observed the ripples in MoS2 nanostructures. The MoS2 ripples exhibit quasi-periodical ripple structures in the MoS2 surface. The heights of the ripples vary from several angstroms to tens of nanometers and the wavelength is in the range of several hundred nanometers. The growth mechanism of rippled MoS2 nanostructures is elucidated. We have also simultaneously investigated the electrostatic properties of MoS2 ripples by using Kelvin probe force microscopy, which shows inhomogeneous surface potential and charge distributions for MoS2 ripple nanostructures with different local strains.

Molecular dynamics simulations of amorphous silica nanowires under tension were analyzed for size and surface stress effects on mechanical properties and for structural modifications via bond angle distributions. Their fracture behavior was also investigated beyond the elastic limit. The Young's moduli of silica nanowires were predicted to be about 75-100 GPa, depending on the nanowire size. The ultimate strength was calculated to be ∼10 GPa, depending on the diameter, which is in excellent agreement with the experiments. The dependence of the Young's modulus on nanowire diameter is explained in terms of surface compressive stress effects. The fracture behavior of nanowires was also found to be influenced by surface compressive stresses. Bond angle distribution analysis of various nanowires reveals significant compressive surface states, as evidenced by the appearance of a secondary peak in the Si-O-Si bond angle distribution at ∼97°, which is absent in bulk silica. The strain rate was found to have a negligible effect on the Young's modulus of the silica nanowires, but it has a critical role in determining their fracture mode.

We have demonstrated a novel method to enhance TiO₂ photocatalysis by adopting a new ultrathin tetrahedral-amorphous-carbon (ta-C) film coating on Ag nanoparticles to create strong plasmonic near-field enhancement. The result shows that the decomposition rate of methylene blue on the Ag/10 Å ta-C/TiO₂ composite photocatalyst is ten times faster than that on a TiO₂ photocatalyst and three times faster than that on a Ag/TiO₂ photocatalyst. This can be ascribed to the simultaneous realization of two competitive processes: one that excites the surface plasmons (SPs) of the ta-C-film/Ag-nanoparticle hybrid and provides a higher electric field near the ta-C/TiO₂ interface compared to Ag nanoparticles alone, while the other takes advantage of the dense diamond-like ta-C layer to help reduce the transfer of photogenerated electrons from the conduction band of TiO₂ to the metallic surface, since any electron transfer will suppress the excitation of SP modes in the metal nanoparticles.

We report on the controlled growth of novel BN-coated Ca(1-x)Sr(x)S:Eu nanowires via a solid-liquid-solid process. The Ca(1-x)Sr(x)S solid solution forms as one-dimensional nanowires and has been coated with homogeneous protective BN nanolayers. The structure and luminescence properties of this new nanocomposite have been systematically investigated. High-spatial-resolution cathodoluminescence investigations reveal that effective red color tuning has been achieved by tailoring the composition of the Ca(1-x)Sr(x)S nanowires. Moreover, codoping of Ce(3+) and Eu(2+) in the CaS nanowire can induce energy transfer in the matrix and make it possible to obtain enhanced orange color in the nanowires. The BN-coated Ca(1-x)Sr(x)S:Eu solid-solution nanowires are envisaged to be valuable red-emitting nanophosphors and useful in advanced nanodevices and white LEDs.

We report on the synthesis of high-quality microporous/mesoporous BN material via a facile two-step approach. An extremely high surface area of 1687 m(2) g(-1) and a large pore volume of 0.99 cm(3) g(-1) have been observed in the synthesized BN porous whiskers. The formation of the porous structure was attributed to the group elimination of organic species in a BN precursor, melamine diborate molecular crystal. This elimination method maintained the ordered pore structure and numerous structural defects. The features including high surface area, pore volume and structural defects make the BN whiskers highly suitable for hydrogen storage and wastewater treatment applications. We demonstrate excellent hydrogen uptake capacity of the BN whiskers with high weight adsorption up to 5.6% at room temperature and at the relatively low pressure of 3 MPa. Furthermore, the BN whiskers also exhibit excellent adsorption capacity of methyl orange and copper ions, with the maximum removal capacity of 298.3 and 373 mg g(-1) at 298 K, respectively.

As a structural analogue of the carbon nanotube (CNT), the boron nitride nanotube (BNNT) has become one of the most intriguing non-carbon nanostructures. However, up to now the pre-existing restrictions/limitations of BNNT syntheses have made the progress in their research rather modest. This work presents a new route toward the synthesis of highly pure ultrafine BNNTs based on a modified boron oxide (BO) CVD method. A new effective precursor--a mixture of Li₂O and B--has been proposed for the growth of thin, few-layer BNNTs in bulk amounts. The Li₂O utilized as the precursor plays the crucial role for the present nanotube growth. The prepared BNNTs have average external diameters of sub-10 nm and lengths of up to tens of µm. Electron energy loss spectrometry and Raman spectroscopy demonstrate the ultimate phase purity of the ultrafine BNNTs. Property studies indicate that the ultrafine nanotubes are perfect electrical insulators exhibiting superb resistance to oxidation and strong UV emission. Moreover, their reduced diameters lead to a dramatically decreased population of defects within the tube walls and result in the observation of near-band-edge (NBE) emission at room temperature.

Well-aligned single-crystalline ZnS nanowire arrays have been grown on highly conductive Cu substrates through controlling the morphology evolution of self-patterned ZnS nanoparticles. The ZnS nanowires have sharp tips with an average size of approximately 30 nm and a length of approximately 3 microm. Field emission measurements demonstrated that the aligned ZnS nanowires grown on Cu substrates are excellent field emitters having a turn-on field as low as 2.92 V microm(-1) and a field-enhancement factor as high as 3400. The use of highly conductive metal substrate may promote the commercial applications of ZnS-based emitters in flat panel displays and other optoelectronic devices.

Cubic spinel structured gallium oxynitride has been synthesized through the reaction of metallic gallium and water in the presence of organic ethylenediamine. The relative content of the mixed solvent of water and ethylenediamine controls the product morphology and structure. A novel well-defined nanoporous structure has finally been obtained, whose large surface area and peculiar surface chemistry will generate novel physical and chemical properties. As an example, lithium intercalation properties for prospective applications in lithium ion batteries are demonstrated in this work.

High-quality, crystalline AlN whiskers with large yield have been synthesized through the direct nitridation of Al vapor at high temperature. The AlN whiskers exhibited a strong and uniform ultraviolet emission at approximately 352 nm, which is notably shorter compared with the wavelength of previously reported one-dimensional AlN nanostructures. Energy filtered transmission electron microscope (TEM) analyses indicated that nitrogen deficiency and rather lower oxygen content in the AlN lattice might be responsible for the strong 352 nm ultraviolet emission.

We fabricated ellipsoid-shaped ZnGa(2)O(4) nanorods using a newly-designed chemical vapor deposition (CVD) process, different from the conventional methods. The optical properties of nanorods were studied using cathodoluminescence (CL) measurements. The nanorods displayed three distinct emissions centered at 360, 450 and 550 nm. The luminescence mechanism is thoroughly discussed and explained based on a detailed structural and compositional study with a transmission electron microscope (TEM) equipped with an electron energy loss spectrometer (EELS).

High-purity, crystalline [001]-oriented GaN nanotubes with outer diameters of 200 nm or more, rough surfaces and irregular internal channels were synthesized under epitaxial growth on [001]-oriented sapphire substrates. Elastic property measurements on free-standing individual GaN nanotubes, using the in situ transmission electron microscopy (TEM) electromechanical resonance technique, pointed at an average Young's modulus E of 37 GPa and minimum quality factor of 320. These numbers are notably lower than those for previously reported GaN nanowires. The crystallography and chemistry of the GaN nanotubes were analyzed using TEM and energy dispersion x-ray spectroscopy (EDS). It is suggested that the lowered Young's modulus and quality factor of the nanotubes are mainly due to the surface roughness and defectiveness.

Boron nitride (BN) microtubes were synthesized in a vertical induction furnace using Li(2)CO(3) and B reactants. Their structures and morphologies were investigated using x-ray diffraction, scanning and transmission electron microscopy, and energy-dispersive x-ray spectroscopy. The microtubes have diameters of 1-3 microm, lengths of up to hundreds of micrometers, and well-structured ultrathin walls only approximately 50 nm thick. A mechanism combining the vapor-liquid-solid (VLS) and template self-sacrificing processes is proposed to explain the formation of these novel one-dimensional microstructures, in which the Li(2)O-B(2)O(3) eutectic reaction plays an important role. Cathodoluminescence studies show that even at room temperature the thin-walled BN microtubes can possess an intense band-edge emission at approximately 216.5 nm, which is distinct compared with other BN nanostructures. The study suggests that the thin-walled BN microtubes should be promising for constructing compact deep UV devices and find potential applications in microreactors and microfluidic and drug delivery systems.

Electronic eigenstates of a square graphene quantum dot (GQD) terminated by both zigzag and armchair edges are derived in the theoretical framework of the Dirac equation. We find that the Dirac equation can determine the eigenenergy spectrum of a GQD with high accuracy even if its size is reduced to a few nanometers. More importantly, from the Dirac equation description we can readily work out the number and energy gap of the conjugate surface states, which are intimately associated with the magnetic properties of the GQD. By using the Hartree-Fock mean field approach, we study the size dependence of the magnetic ordering formation in this square GQD. We find that there exists a critical size of the width between the two zigzag edges to indicate the onset of the stable magnetic ordering. On the other hand, when such a width increases further, the magnetic ground state energy of a charge neutral GQD tends to a saturated value. These results coincide with the previous results obtained from the first-principles calculation. Then, based on the Dirac equation solution about the surface state, we establish a simple two-state model which can quantitatively explain the size dependence of the magnetic ordering in the square GQD.

We report a systematic investigation of the charging effect on hydrogen molecule chemisorption on (3, 3), (5, 5), (5, 0), and (8, 0) carbon nanotubes by first-principles calculations. The influence of injected charge on the chemisorption energy barriers is found to be sensitive to the nanotube diameter and chirality. The calculated results also indicate that electron injection is more effective in lowering the energy barrier for armchair carbon nanotubes while hole injection is more effective for zigzag nanotubes. The origin of these interesting trends and systematics can be understood by a close examination of the underlying electronic structure and the electron transfer between the hydrogen molecules and the nanotubes.

High-quality large-area beta-MnO(2) nanowires can be easily synthesized using KNO(3) as the mineralizing agent in a process of mineralization from Mn(NO(3))(2) aqueous solution. The morphological evolution of the beta-MnO(2) nanowires and the influences of mineralizing agents and their concentrations on the morphology of the final products were investigated in detail. KNO(3) was the best mineralizing agent among KNO(3), NaNO(3), KCl, and NaCl. More interestingly, when the concentration of the mineralizing agent KNO(3) was not saturated, only irregular short faceted nanorods, instead of nanowires, can be observed. Finally, the formation mechanism is discussed.