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Graphitic carbon nitride (g-CN) has emerged as a promising metal-free photocatalyst, while the catalytic mechanism for the photoinduced redox processes is still under investigation. Interestingly, this heptazine-based polymer optically behaves as a “quasi-monomer”. In this work, we explore upstream from melem (the heptazine monomer) to the triazine-based melamine and melam and present several lines of theoretical/experimental evidence where the catalytic activity of g-CN originates from the electronic structure evolution of the C–N heterocyclic cores. Periodic density functional theory calculations reveal the strikingly different electronic structures of melem from its triazine-based counterparts. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy also provide consistent results in the structural and chemical bonding variations of these three relevant compounds. Both melam and melem were found to show stable photocatalytic activities, while the photocatalytic activity of melem is about 5.4 times higher than that of melam during the degradation of dyes under UV–visible light irradiation. In contrast to melamine and melam, the frontier electronic orbitals of the heptazine unit in melem are uniformly distributed and well complementary to each other, which further determine the terminal amines as primary reduction sites. These appealing electronic features in both the heterocyclic skeleton and the terminated functional groups can be inherited by the polymeric but quasi-monomeric g-CN, leading to its pronounced photocatalytic activity.

Polymeric graphitic carbon nitride (g-CN) has emerged as a promising metal-free photocatalyst; however, the polymerization process is still poorly understood, and the synthesized g-CN shows a struc...

We report intrinsic surface magnetism in pristine α rhombohedral boron (α-boron) using first-principles calculations. Semiconducting α-boron has been cleaved along the (001), (102̅), and (101) planes to produce icosahedral-based non-van der Waals face-boron, t-face-boron, and edge-boron structures, respectively. Face-boron is found to be metallic, while t-face-boron and edge-boron show semiconducting features. In particular, edge-boron exhibits layer-dependent magnetism with a transition from an overall antiferromagnetic (AFM) state with AFM surfaces to either an AFM or a ferromagnetic (FM) state with FM surfaces as the number of layers increases. The magnetism in edge-boron arises from the spin polarization of boron atoms with unsaturated bonds at the edge sites in the upper and lower surfaces, and magnetic exchange coupling can be mediated via adjacent boron icosahedra by up to a maximum of 8.4 Å. These findings deepen our understanding of icosahedral-based boron and boron-rich materials, which may be useful in potential spintronics applications.

It is a highly relevant topic concerning how to improve the electrochemical performance of anode materials for the next generation lithium-ion batteries (LIBs). Herein, for the first time, we report a facile and controllable approach to modify MoS2 nanosheets, a typical 2D material, as an anode material for advanced LIBs via oxygen plasma engineering. An oxygen plasma treatment not only generates vacancies/defects but also incorporates heteroatom doping to form Mo–O–C bonds. This unique hybrid specialty enables the oxygen-plasma-treated MoS2 to achieve superior electrochemical performance with high reversible capacities, a long-term cycle life, and good rate capabilities. The plasma-assisted modification is believed to be applicable for other 2D materials as an efficient anode for energy storages.

To reduce the conservativeness of robust optimization-based unit commitment methods, an uncertainty set is usually prespecified with respect to the distributions of uncertain renewable resources, i.e., wind power. However, since the law of large numbers does not always work in practice, the obtained probability distribution may be unreliable. In this paper, a data-driven adaptive robust optimization method for the unit commitment of bulk power systems with high-level wind power integration is proposed. Different from the conventional robust unit commitment methods, the distributional uncertainty of wind power is well respected in the proposed approach. An imprecise-Dirichlet-model-based method is developed to construct the ambiguity set of wind power, which incorporates all possible probability distributions confirmed by historical data. The set can dynamically change with the data, i.e., the more valid data we have, the smaller the ambiguity set will become. With respect to the bounds of the ambiguity set, a polyhedron uncertainty set of wind power is constructed. By tuning the parameters of the uncertainty set, a balance between operational efficiency and risk can be achieved. An adaptive, robust unit commitment model is constructed based on the uncertainty set. By using the duality principle and big-M method, the formulations are converted into a mixed integer linear programming problem and solved using a column and constraint generation algorithm. Case studies on two benchmark systems illustrate the effectiveness and efficiency of the proposed method.

Semiconductor materials are favoured in the field of photocatalysis due to their unique optoelectronic properties. When a semiconductor is excited by external energy, electrons will transition through the band gap, providing electrons or holes for the reaction. This is similar to the chemical enhancement mode of a catalytic reaction initiated by the rough noble metal on the surface excited by plasmon resonance. In this study, different types of semiconductor silicon loaded with silver nanoparticles were used as SERS substrates. SERS detection of p-aminothiophenol (PATP) and p-nitrothiophenol (PNTP) probe molecules was performed using typical surface plasmon-driven coupling reactions, and the mechanism of optical drive charge transfer in semiconductor–metal–molecular systems was investigated. Scanning electron microscopy and plasmon luminescence spectroscopy were used to characterize the silver deposited on the substrate surface. Mapping technology and electrochemistry were used to characterize the photocatalytic reaction of the probe molecules. This study proposed a mechanism for the coupling reaction of “hot electrons” and “hot holes” on the surface of plasmon-driven molecules and provides a method for preparing a stable SERS substrate.

There is much evidence that surface plasmon photocatalytic reactions can occur on organic molecules on metal surfaces. In this paper, we focus on the photocatalytic reaction of 4-ethynylaniline (PEAN) on silver nanoparticles (Ag NPs) in a liquid environment by surface-enhanced Raman spectroscopy (SERS). Our experiments used SERS to characterize p,p′-diynylazobenzene produced from PEAN via a selective catalytic coupling reaction on Ag NPs. This discovery not only achieved the expected results but also broadens the known plasmon-driven surface catalytic reaction system. In our work, we also regulated the photocatalytic coupling reaction conditions of PEAN on Ag NPs by laser power-dependent and time-dependent SERS spectra.

In this study, we demonstrate that plasma treatment can be a facile and environmentally friendly approach to perform surface modification of graphitic carbon nitride (g-CN), leading to a remarkable modulation on its photocatalytic activity. The bulk properties of g-CN, including the particle size, structure, composition, and electronic band structures, have no changes after being treated by oxygen or nitrogen plasma; however, its surface composition and specific surface area exhibit remarkable differences corresponding to an oxygen functionalization induced by the plasma post-treatment. The introduced oxygen functional groups play a key role in reducing the recombination rate of the photoexcited charge carries. As a consequence, the oxygen-plasma-treated sample shows a much superior photocatalytic activity, which is about 4.2 times higher than that of the pristine g-CN for the degradation of rhodamine B (RhB) under visible light irradiation, while the activity of nitrogen-plasma-treated sample exhibits a slight decrease. Furthermore, both of the plasma-treated samples are found to possess impressive photocatalytic stabilities. Our results suggest that plasma treatment could be a conventional strategy to perform surface modification of g-CN in forms of both powders and thin films, which holds broad interest not only for developing g-CN-based high-performance photocatalysts but also for constructing photoelectrochemical cells and photoelectronic devices with improved energy conversion efficiencies.

The effect of plating temperatures between 60 and 90°C on structure and corrosion resistance for electroless NiWP coatings on AZ91D magnesium alloy substrate was investigated. Results show that temperature has a significant influence on the surface morphology and corrosion resistance of the NiWP alloy coating. An increase in temperature will lead to an increase in coating thickness and form a more uniform and dense NiWP coatings. Moreover, cracks were observed by SEM in coating surface and interface at the plating temperature of 90°C. Coating corrosion resistance is highly dependent on temperature according to polarization curves. The optimum temperature is found to be 80 ∘ C and the possible reasons of corrosion resistance for NiWP coating have been discussed.

The interlayer interactions in nonpolar graphite and other B C N layered materials involving polar covalent bonds (h-BN, g-C3N4, graphite-like BC3 and BC2N) have been investigated by dispersion-corrected density functional calculations. Lattice parameters, bulk moduli and interlayer binding energies of these layered materials have been calculated using different dispersion correction schemes for comparison. Charge density difference plots have also been presented to elucidate the charge transfer behaviors along the nonpolar/polar covalent bonds as well as in the interlayer region. At first, graphite and h-BN were examined as benchmarks; the former contains planar graphene layers regardless of the interlayer binding, while the monolayers in the latter exhibit an asymmetric charge distribution along the B N polar bonds, leading to a slightly puckered feature induced by the interlayer interaction. Similar geometric deviations have also been observed in other layered structures involving C N and/or B C polar bonds, but with distinct characteristics directly related to their specific interlayer stacking situations. By contrast, all of the isolated monolayers free from interlayer binding show a pristine planar feature in despite of the polar covalent bonds involved. Our theoretical findings further address the necessity of considering the electron-density variations induced by specific bonding environments in polar B C N layered materials, which can be properly described by the Tkatchenko-Scheffler correction.

Understanding the intermolecular interactions in the context of crystal packing is of fundamental significance in molecular materials science. Infrared (IR) spectroscopy can provide complementary structural information; however, it still remains a great challenge to accurately predict the molecular IR vibrations in the crystalline phase. Here we report a cluster-model approach to simulate the IR spectra of triazine-based molecular crystals via density functional theory (DFT) calculations. In the properly designed cluster models, the molecular IR vibrations are expressed by a representative unit, while the nearest-neighbouring molecules are treated as a “frozen shell” to mimic the surrounding crystallographic environments. Much smaller clusters can be built by considering the crystallographic equivalence in the unit cell, which are able to perform DFT calculations on more complicated crystal structures with endurable computational costs. The simulated spectra show excellent consistencies with the experimental ones, particularly providing an in-depth understanding of the vibrational modes closely related to hydrogen bonding. Most importantly, the selectively built clusters based on the crystallographically independent molecules in the unit cell allow us to perform specific IR-spectral simulations, by which their distinct hydrogen-bonding environments have been clearly revealed for the first time.

Possible bulk black phosphorus (BP) allotropes are constructed based on single-layer BP with various stacking sequences. Our stacking algorithm shows that there are eight possible allotropes with two stacking layers in their unit cells possessing relatively high symmetries, and six of them are retained after structural relaxation using a van der Waals correction of optB88-vdW. The AF, AG, and AH bulk structures are presented for the first time. The structural relationship of these configurations has been explained via an interlayer slipping process. The total energy of the AF allotrope is closest to the most stable bulk BP structure (AB stacking) among all explored 2-layer stacked bulk structures. The calculated band structure of the AF allotrope using HSE06 shows a direct band gap of 0.48 eV with anisotropic electronic structures. We also presented six possible BP allotropes with three stacking layers in their unit cells. The newly reported AAF and ABC stacked structures show semiconducting and metallic features, respectively. After the bulk structures were explored, we further built the corresponding few-layer phosphorene structures and investigated their electronic properties. The results show that all the few-layer phosphorenes show semiconducting features. The AE, AAE, and AEA phosphorenes have indirect band gaps while the other explored phosphorenes possess direct band gaps located at the Γ point.

A large number of literatures have investigated the selective photocatalytic reaction of 4-aminothiophenol (PATP) to p,p'-dimercaptoazobenzene (DMAB). Most of them mainly study the contribution of substrate, excitation wavelength, exposure time, pH and added cations to plasmon-assisted surface catalytic reactions. However, we mainly study focuses on the effects of solvents on the dimerization of PATP to DMAB under the action of Ag nanoparticles (NPs). In experiments, a variety of diols was selected as solvents for the probe molecule PATP, and power-dependent SERS spectra were obtained at an excitation wavelength of 532 nm. From the laser-dependent SERS spectrum, we found that the characteristic peak enhancement effect of the product DMAB in different solvents is significantly different. That is, different solvents could regulate the rate at which DMAB is produced from PATP. Based on the experimental results, we further explored how different diol solvents regulate the response of PATP to DMAB. Our conclusion is that the solvent in the system can quickly capture the hot electrons generated by the decay of the plasmon, so that the remaining holes can oxidize PATP to form DMAB. The ability to trap hot electrons is different due to the difference in the position of the functional groups in the solvent, so that the photocatalytic reaction rate of the hole-oxidized PATP is different. The ability to capture electrons varies depending on the position of the functional groups in the solvent, so the oxidation rate of the photocatalytic reaction is also different. This work not only deepens our understanding of the mechanism of hole-driven surface catalysis oxidation reaction, but also provides a convenient method for regulating the rate of catalytic oxidation.

Single-walled carbon nanotubes (SWNTs) grown by chemical vapor deposition (CVD) are widely used for fabrication of high-performance nanotube devices. However, the high-temperature growth is incompatible with the current complementary metal-oxide semiconductor (CMOS) technology. We demonstrate a low-temperature and direct deposition of the CVD-grown SWNTs. The nanotubes are synthesized by floating catalytic CVD technique and further carried by the flowing gas directly to the low- temperature area. Individual SWNTs have been successfully deposited on Si/ SiO2 substrates covered with a polymethylmethacrylate layer, which results in a suspended geometry of the nanotube in the fabricated devices. We subsequently investigate the electrical-transport properties of a representative small band gap nanotube, which exhibits an ambipolar feature with p-channel mobility up to 1410 cm 2 V −1 S −1 at room temperature. Furthermore, low- temperature measurements down to 4 K reveal different transport characteristics with the gate voltage biased near zero or at a large negative value, respectively.

Although polymeric graphitic carbon nitride (g-C3N4) has been widely studied as metal-free photocatalyst, the description of its structure still remains a great challenge. Fourier transform infrared (FTIR) spectroscopy can provide complementary structural information. In this paper, we reconsider the representative crystalline melamine and develop a strategic approach to theoretically calculate the IR vibrations of this triazine-based nitrogen-rich system. IR calculations were based on three different models: a single molecule, a 4-molecule unit cell, and a 32-molecule cluster, respectively. By this comparative study the contribution of the intermolecular weak interactions were elucidated in detail. An accurate and visualized description on the experimental FTIR spectrum has been further presented by a combinatorial vibration-mode assignment based on the calculated potential energy distribution of the 32-molecule cluster. The theoretical approach reported in this study opens the way to the facile and accurate assignment for IR vibrational modes of other complex triazine-based compounds, such as g-C3N4.

The resistance of single-walled carbon nanotube (SWNT) bundles has been investigated by two-terminal measurements. We find that the time dependence of resistance (dR/dt) exhibits different behaviors at different currents. At low currents, a positive dR/dt is observed. However, dR/dt shows a negative sign when the applied current exceeds a critical current (I-c). I-c coincides with the current when the sample begins to emit light. The variation of dR/dt can be interpreted as the thermal effects owing to Joule heating in the SWNTs. Our lighting SWNTs sample has a small change in resistance and exhibits high stability.

One-dimensional structures of nitrogen-rich carbon nitride are synthesized via a thermal evaporation process. The C-N atomic rings (s-triazine and/or tri-s-triazine) present in the precursor remain stable during the thermal evaporation and vapor transfer. They act as basic building blocks during the microstructure assembly; thus ensuring a high nitrogen content in the final product.

Individual zinc oxide tetrapods were designed as multiterminal sensors by the e-beam lithography method. Different from double-terminal sensors, these sensors can give multiple responses to a single signal at the same time. The designed tetrapod devices were employed to detect light with different wavelength. The results indicate that they are remarkable optoelectronic devices, sensitive to ultraviolet light, and have advantages on distinguishing noises and increasing sensitivity. This should be helpful for weak signal measurements of nanodevices.

The photocurrent generated in single-walled carbon nanotube bundles upon camera flash illumination has been studied under different ambient pressures and light intensities. The results show that the intensity of photocurrent depends closely on the ambient pressure and light intensity. With the ambient pressure reduced, the photocurrent exhibits a logarithmic growth behaviour. Meanwhile, the photocurrent increases with the increase in light intensity. In this work, a dynamic model is employed to unveil the origins of the observed photocurrent. A much smaller lifetime of photocarriers (~10?ms) is observed than that needed for gas molecular desorption or photodesorption (seconds or longer). Our results are consistent with the model of Schottky barriers being responsible for photocurrent generation.

In this paper, we present a new insight into nonequilibrium electrodeposition. Owing to the nanoscale confinement effect of the template channels, the large overpotential leads to a highly nonequilibrium process and generates segmented metal-metal hydroxide one-dimensional (1D) nanostructures. The synthesized Ni-Ni(OH)x≈2 nanotubes vividly reflect the evolution of the local electrochemical environments, by which both the morphology and the composition have been modulated. The electrochemical mechanisms responsible for this unexpected deposition have been identified and discussed. It was exploited to obtain bi-segmented Ni nanowire-Ni(OH)x≈2 nanotube. This work opens the way to a versatile synthesis of metal-metal hydroxide 1D nanostructures that could be applicable for the integration of well-aligned metal-hydroxide nanostructures into large-scale energy-storage devices.

Turbostratic carbon nitride was prepared by the pyrolysis of melamine and then treated with a pulse discharge for different times. It is found that after this high-temperature short-time treatment, the structures of the products have changed while the high nitrogen content has been effectively maintained. The obtained product was characterized by X-ray diffraction and infrared spectroscopy. The composition was measured by an element analyzer. An orthorhombic CN x phase has been obtained, identified by transmission electron microscopy coupled with selected area electron diffraction. High-resolution transmission electron microscopy revealed that the product has some nanocrystals having a fringe spacing of approximately 0.32 nm, which embedded in a turbostratic matrix.

In this paper, we report that the electrical conductance of single-walled carbon nanotubes networks decreases when the nanotubes are illuminated by camera flash in high vacuum up to 10(-6) Torr. The decreasing conductance shows step-like characteristics at each illumination. The magnitude of conductance change step reduces gradually after each illumination; finally, the conductance reaches saturation. Controlled experiments in air, oxygen and nitrogen gas indicate that mechanism for these observations is photodesorption of molecular oxygen from singled-walled carbon nanotubes.

Since the theoretical calculations predicted that the hardness of C3N4 covalent compound might be comparable to or even higher than that of diamond [1, 2], many attempts have been made to synthesis this novel substance. Due to the great thermodynamic stability of N2, however, the ideal structural transition from precursor to crystalline carbon nitride is difficult to realize. In most cases, only amorphous products with low nitrogen content were obtained [3]. To solve this problem, it is good to prepare carbon nitride in graphitic or turbostratic form firstly, and then using it as precursor to synthesize other carbon nitride crystalline phases. Therefore, graphitic C3N4 have recently attracted more attention. Through different routes, graphitic C3N4 has been synthesized [4–6]. For previous work, the claimed graphitic-like C3N4 with unique (002) diffraction peak has the turbostratic structure actually [7–10], for the lake of other peaks in their XRD patterns. Meanwhile, the (002) spacing of those obtained turbostratic carbon nitrides are in the range of 0.32–0.33 nm. The graphitic C3N4 predicted by Teter and Hemley [11] can be described as a perfect de-ammonation polycondensate of melamine, therefore, melamine was often chosen as the carbon nitride precursor to synthesize graphitic C3N4 by electrodeposition [6] and solvothermal method [7]. Pyrolysis of melamine was investigated [12] in 1988, however, the authors focused their attention only on its thermal behavior, and they didn’t consider the possibility as potential candidate for carbon nitrides after complete polycondensate. Recently, pyrolysis of melamine under high pressure was studied at the temperatures up to 700 ◦C [13]. Obvious nitrogen loss made the attempt unsuccessful. In this letter, we report an improved pyrolysis route to prepare turbostratic carbon nitride from melamine. The pyrolysis was performed in two steps: first, the temperature was maintained at 300 ◦C in order to realize the primary condensation (melamine → melam) as complete as possible; and then it was risen to 650 ◦C to perform the advanced condensation. In the experimental, melamine was pyrolyzed in a quartz tube with a diameter of 35 mm, and an outer-thimble-shape heater was used. Melamine was placed at the middle of the quartz tube. The pyrolysis was conducted at 300 ◦C for 1 hr, then at 600◦ for 2 hr in atmosphere; after milling, the obtained powder was maintained at 300 ◦C for 0.5 hr, then at 650 ◦C for 1 hr in vacuum. Finally, a kind of brown carbon nitride powder was obtained. The chemical composition was analyzed by using elemental analyzer (LECO, CHN-1000) and EDX (EDAX INC., Phoenix). The product was characterized by X-ray diffraction (XRD) with Cu-Kα radiation (JEOL, ROTEX JRX-12), fourier transfer infrared (FTIR) spectroscopy (Bruker, EQUINOX55), scanning electron microscopy (SEM) (TOPCON, SM520), and transmission electron microscopy (TEM) coupled with selected area diffraction (SAED) (JEOL, JEM-2010) and thermogravimetry (TG) (NETZSCH, STA449C/6/G). The composition of the product characterized by elemental analysis and EDX is listed in Table I. SEM observation found that the particles dimension ranged from 5 μm to 20 μm. Most of the particles show the flake-like morphology. Fig. 1 shows a typical XRD pattern of the product. There is a single main peak at the position of 27.62 ◦, which suggests that the product was turbostratic. Its corresponding d-spacing is 0.321 nm similar to the (002) plane of the turbostratic/graphitelike carbon nitrides obtained in previous work [9, 14]. The FTIR spectrum of the prepared turbostratic carbon nitride and melamine are shown in Fig. 2. The IR spectrum of melamine presents three absorption bonds: 3000–3650 cm−1, 1100–1700 cm−1, and the last one centered at about 810 cm−1. The 3000– 3650 cm−1 band is assigned to N H stretching vibration modes, the 1100–1650 cm−1 band corresponds to the stretching vibrations related to C N, C N, and is generally associated with the skeletal stretching vibrations of these aromatic rings. The absorption at 810 cm−1 is characteristic of out-of-plane bending modes of these rings. The 460–850 cm−1 band is linked to the C NH2 group and the ring breadth or bending vibration modes [15]. Comparing the FTIR spectrum of the turbostratic carbon nitride with that of melamine, it reveals that after pyrolysis, the previous strong absorption peaks in the range of 3000–3650 cm−1 have disappeared, only a board absorption bond is left, which suggest that most of the N H bonds have been destroyed during the de-ammonation condensation. While the increased number of absorption peaks ranging from 1100 to 1700 cm−1 implies the condensation of 1,3,5-s-triazine rings making the related chemi

International audience; This work presents a simple method to generate ordered chromophore/dispersant nanoarrays through a pore-filling process for a nanoporous polymer template to enhance chromophore luminescence. Fluorescence results combining with the morphological evolution examined by scanning probe microscopy reveal that the enhanced luminescence intensity reaches the maximum intensity as the nanopores of the template are completely filled by the chromophore/dispersant mixture. The variation is attributed to nanoscale spatial effect on the enhanced mixing efficiency of chromophore and dispersant, that is, the alleviation of self-quenching problem, as evidenced by the results of attenuated total reflection Fourier transform IR spectroscopy combining with grazing incident wide-angle X-ray diffraction. The enhanced luminescence of the chromophore/dispersant nanoarrays driven by the nanoscale spatial effect is highly promising for use in designing luminescent nanodevices.

International audience; We successfully address the challenge of aligning single-walled carbon nanotubes (SWNTs) and conjugated polymer chains in composite nanofibers for enhancing their opto-electrical properties. A pore-filling template strategy has been developed to prepare such nanocomposites from SWNTs and poly(para-phenylene vinylene) (PPV) chains, with both species well-oriented aligned along the pore axis. Addition of the SWNTs leads to a remarkable increase in photocurrent of four orders of magnitude as compared to equivalent pristine PPV nanofibers. Further analysis indicates that the strong photocurrent enhancement is not simply an effect of alignment, but additionally benefits from alignment-enhanced interaction of polymer chains with SWNTs, as supported by density functional theory (DFT) calculations.

International audience; This work presents a simple method to generate ordered conjugated polymer nanoarrays through a pore-filling process for nanoporous polymer templates so as to enhance the efficiency of photoluminescence (PL). PL results combined with the morphological evolution examined by scanning probe microscopy revealed that the enhanced PL reaches maximum intensity as the template pores are completely filled by conjugated polymers. Polarized PL spectroscopy and grazing incidence Fourier transform infrared spectroscopy were used to determine the chain orientation of templated conjugated polymer; the spectroscopic results indicate a parallel chain orientation along the cylindrical direction of nanopores. The induced alignment of the polymer chains is attributed to a nanoscale spatial effect that increases the PL intensity and the lifetime of the conjugated polymer. The enhanced luminescence of nanostructured conjugated polymers is highly promising for use in designing luminescent nanodevices.

International audience; The radial nanostructure of the binary liquid triethylamine/water confined in 60 nm diameter independent cylindrical pores of anodic aluminium oxide membranes is studied by small angle neutron scattering. It is shown that composition inhomogeneities are present in the confined mixtures well below the bulk critical point. An analysis of the neutron scattering form factor reveals the existence of an adsorbed water layer of a few nanometers at the liquid/alumina interface, coexisting with a TEA-rich phase in the core.

In this paper, a diameter-dependent Raman $G$ band splitting phenomenon in carbon nanotube ring structures is reported and analyzed. In Raman spectra of such structures, more modes became visible as the diameters of rings decrease, and the frequencies of these modes keep unchanged. We attribute this to the resonance condition changes caused by additional curvatures in rings. In this case, perpendicular polarized light would take more effect in rings than in straight tubes as the additional curvature increases, thus intensity enhancements for ${E}_{1}({E}_{1g})$ and ${E}_{2}({E}_{2g})$ modes are observed.

In this paper, we report the surface-enhanced Raman scattering and normal Raman scattering from different parts of one individual single-walled carbon nanotube. We found that the intensity of radial breathing mode can be remarkably enhanced for surface-enhanced Raman scattering. And no frequency shift of the radial breathing mode has been observed. For the tangential mode at approximately 1590 cm(-1), the peak becomes slightly narrower for surface-enhanced Raman scattering. Both semiconducting and metallic nanotubes can be identified based on the line shape of tangential mode. Meanwhile, the intensities of tangential mode depend on laser excitation energies sensitively, which can be explained by different resonant transitional conditions.

In this paper we report efficient growth of well-aligned multi-walled carbon nanotube (MWNT) forest by chemical vapor deposition (CVD). Under optimized parameters, the growth rate can be 15 microm/min and the average diameter is about 10 nm. Large photocurrent can be generated in a bundle of MWNT using camera flash. The photocurrent depends linearly on the light intensity. We propose that photon induced electron-hole pair generation in multi-walled carbon nanotubes and subsequent charge separation across the Schottky barrier is the main origin of the photocurrent.

Silicon nanocomposite with various structures was designed to improve the water-retention ability of the proton exchange membrane for elevated temperature performance. The results show that the amorphous SiO(2) nanoparticles and SiO(2) nanocrystals with size of several nanometers have little influence on the membrane preparation and possess good water-retention of 5.82 similar to 7.11 wt% at temperature of 100 degrees C. The mesoporous SiO(2)/Nafion membrane, however, have large gas crossover of 5.54 mA cm(-2) because of the grain size increase during the crystallinity procedure. The results also demonstrate that the crystallinity of the silica in the membrane significantly increases the water-retention membrane stability. The amorphous SiO(2)/Nafion membrane has obvious performance decay after a soaked period in water for 20 days with a considerable silicon loss about 25.3%. However, with the crystallinity of the silica, the nanocrystals SiO(2)/Nafion membrane and the mesoporous SiO(2)/Nafion membrane have little OCV and power output decrease after the soaking period. The nanocrystals SiO(2)/Nafion membrane is most favorable PEM because the superiorities of outstanding initial performance and excellent durability. After the soaking period, the maximum power output still can achieve 451 mW/cm(-2) at condition of 100 degrees C and 50 RH%.

A novel approach based on Coulomb explosion has been developed to separate single-walled carbon nanotubes (SWNTs) from their bundle. With this technique, we can readily separate a bundle of SWNTs into smaller bundles with uniform diameter as well as some individual SWNTs. The separated SWNTs have a typical length of several microns and form a nanotree at one end of the original bundle. More importantly, this separating procedure involves no surfactant and includes only one-step physical process. The separation method offers great conveniences for the subsequent individual SWNT or multiterminal SWNTs device fabrication and their physical properties studies.

We have developed a low-cost and effective method to align single-walled carbon nanotubes (SWNTs) using a series of diamond wire drawing dies. The obtained SWNTs are highly dense and perfectly aligned. X-ray diffraction (XRD) indicates that the highly dense and perfectly aligned SWNTs (HDPA-SWNTs) form a two-dimensional triangular lattice with a lattice constant of 19.62 angstrom. We observe a sharp (002) reflection in the XRD pattern, which should be ascribed to an intertube spacing 3.39 angstrom of adjacent SWNTs. Raman spectra reveal that the radical breath mode (RBM) of SWNTs with larger diameter in the HDPA-SWNTs is suppressed compared with that of as-grown SWNTs. The HDPA-SWNTs have a large density, similar to 1.09 g/cm(3), and a low resistivity, similar to 2 m Omega cm, at room temperature, as well as a large response to light illumination.

We report the direct synthesis of strong, highly conducting, and transparent single-walled carbon nanotube (SWNT) films. Systematically, tests reveal that the directly synthesized films have superior electrical and mechanical properties compared with the films made from a solution-based filtration process: the electrical conductivity is over 2000 S/cm and the strength can reach 360 MPa. These values are both enhanced by more than 1 order. We attribute these intriguing properties to the good and long interbundle connections. Moreover, by the help of an extrapolated Weibull theory, we verify the feasibility of reducing the interbundle slip by utilizing the long-range intertube friction and estimate the ultimate strength of macroscale SWNTs without binding agent.

In this letter, individual ZnO tetrapod was designed as a multiterminal sensor. The gas-sensing properties of water and oxygen of the device have been investigated. We found that if water was preadsorbed on the device, the sensitivity of oxygen can be effectively enhanced; meanwhile, the response time can also be remarkably shortened. The mechanism of these phenomena, we propose, is the adsorption competition of the two kinds of molecules. Our results show that the preadsorption of appropriate gas can enhance the performance of the sensors, which is helpful for sensor designing.

Small zinc oxide tripodlike arms were assembled at the end of nanowires through thermal evaporation of zinc powder in a horizontal tube furnace. These arms are hundreds of nanometers in length, and they are tens of nanometers in diameter, similar to that of the based nanowires. High-resolution transmission electron microscopy investigation exhibits that they are wurtzite structure and have clear twin planes at the junction of the arms and the based nanowires. The growth mechanism, Raman, and photoluminescence properties were discussed.

Zinc oxide tetrapods were synthesized on a large scale through thermal evaporation of zinc powder with a vapor transportation deposition method. Scanning electron microscope images gave clear evidences of twin planes at the junction of the tetrapods. Photoluminescence and waveguide behaviors of a single tetrapod were demonstrated with a near-field scanning optical microscope.