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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.

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.

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 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.

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.

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.