The usefulness of graphene for electronics has been limited because it does not have an energy bandgap. Although graphene nanoribbons have non-zero bandgaps, lithographic fabrication methods ...introduce defects that decouple the bandgap from electronic properties, compromising performance. Here we report direct measurements of a large intrinsic energy bandgap of approximately 50 meV in nanoribbons (width, approximately 100 nm) fabricated by high-temperature hydrogen-annealing of unzipped carbon nanotubes. The thermal energy required to promote a charge to the conduction band (the activation energy) is measured to be seven times greater than in lithographically defined nanoribbons, and is close to the width of the voltage range over which differential conductance is zero (the transport gap). This similarity suggests that the activation energy is in fact the intrinsic energy bandgap. High-resolution transmission electron and Raman microscopy, in combination with an absence of hopping conductance and stochastic charging effects, suggest a low defect density.
Atomic resolution at a low accelerating voltage with aberration correction is required to reduce the electron irradiation damage in scanning transmission electron microscopy imaging. However, the ...reduction in resolution caused by the diffraction limit becomes severe with increasing electron wavelength at low accelerating voltages. The developed aberration corrector can compensate for higher-order aberration in scanning transmission electron microscopy to expand the uniform phase angle. The resolution for imaging graphene at 30 kV is evaluated by changing the convergence angle for a probe-forming system with a higher-order aberration corrector. A single-carbon atom on graphene is successfully imaged at atomic resolution with a cold-field emission gun by dark-field imaging at an accelerating voltage of 30 kV.
Infrared response on a carbon nanotube is weak because this homonuclear allotrope of carbon does not bear permanent dipoles. Here, we report the discovery of an exaltation of the infrared absorption ...response in single-walled carbon nanotubes from dye molecule interactions. A study performed on dimethylquaterthiophene confined into the hollow core of single-walled carbon nanotubes or π-stacked at the outer surface of the latter leads to a symmetry breaking, allowing us to probe interactions between both subsystems. The nature of these interactions is discussed taking into account the tube diameter. This new phenomenon opens a new route to detect weak vibrations thanks to a confinement effect.
We combine first-principles molecular-dynamics simulations with high-resolution transmission electron microscopy experiments to draw a detailed microscopic picture of irradiation effects in hexagonal ...boron nitride (h-BN) monolayers. We determine the displacement threshold energies for boron and nitrogen atoms in h-BN, which differ significantly from the tight-binding estimates found in the literature and remove ambiguity from the interpretation of the experimental results. We further develop a kinetic Monte Carlo model which allows to extend the simulations to macroscopic time scales and make a direct comparison between theory and experiments. Our results provide a comprehensive picture of the response of h-BN nanostructures to electron irradiation.
In this work we report on modification of electrical and optical properties of extended thin films of single-wall carbon nanotubes induced by iodination from gaseous phase. High resolution ...transmission electron microscopy and Raman data have revealed formation of different types of polyiodide species or one-dimensional iodine crystals (depending on pristine nanotube geometry) inside nanotubes. UV–vis–NIR optical absorption spectra of iodinated nanotubes demonstrated a clear suppression of the optical absorption band corresponding to the first electron transition for semiconducting nanotubes (with the factor determined by the nanotube geometry). It was interpreted as a result of charge transfer from nanotubes to polyiodide species formed inside them. Because of this effect the Fermi level shifted down into the valence band, and the nanotube conductivity type was changed. For filled nanotube films the metallic type of temperature-dependent electrical resistance behavior was observed at elevated temperatures. A reduction of the electrical resistance of pristine films by an order of magnitude (from 1550Ohm/sq to 270Ohm/sq; from 865Ohm/sq to 150Ohm/sq; from 700Ohm/sq to 70Ohm/sq at 300K) has been observed. The obtained sheet resistances are comparable with those for the most popular today material for transparent conductive electrodes – indium tin oxide.
Development of materials and structures leading to lithium ion batteries with high energy and power density is a major requirement for catering to the power needs of present day electronic industry. ...Here, we report an in situ formation of a sandwiched structure involving single-walled carbon nanotube film, copper oxide, and copper during the direct synthesis of nanotube macrofilms over copper foils and their electrochemical performance in lithium ion batteries. The sandwiched structure showed a remarkably high reversible capacity of 220 mAh/g at a high cycling current of 18.6 A/g (50 C), leading to a significantly improved electrochemical performance which is extremely high compared to pure carbon nanotube and any other carbon based materials.
Nitrification, a microbial process, is a key component and integral part of the nitrogen (N) cycle. Soil N is in a constant state of flux, moving and changing chemical forms. During nitrification, a ...relatively immobile N-form (NH
4
+
) is converted into highly mobile nitrate-N (NO
3
−
). The nitrate formed is susceptible to losses via leaching and conversion to gaseous forms via denitrification. Often less than 30% of the applied N fertilizer is recovered in intensive agricultural systems, largely due to losses associated with and following nitrification. Nitrogen-use efficiency (NUE) is defined as the biomass produced per unit of assimilated N and is a conservative function in most biological systems. A better alternative is to define NUE as the dry matter produced per unit N applied and strive for improvements in agronomic yields through N recovery. Suppressing nitrification along with its associated N losses is potentially a key part in any strategy to improve N recovery and agronomic NUE. In many mature N-limited ecosystems, nitrification is reduced to a relatively minor flux. In such systems there is a high degree of internal N cycling with minimal loss of N. In contrast, in most high-production agricultural systems nitrification is a major process in N cycling with the resulting N losses and inefficiencies. This review presents the current state of knowledge on nitrification and associated N losses, and discusses strategies for controlling nitrification in agricultural systems. Limitations of the currently available nitrification inhibitors are highlighted. The concept of biological nitrification inhibition (BNI) is proposed for controlling nitrification in agricultural systems utilizing traits found in natural ecosystems. It is emphasized that suppression of nitrification in agricultural systems is a critical step required for improving agronomic NUE and maintaining environmental quality.
We have found a new type of carbon particle produced by the CO
2 laser ablation of carbon at room temperature without a metal catalyst. The product has a powder form of graphitic particles with a ...uniform size of about 80 nm. An individual particle is composed of an aggregate of many horn-shaped sheaths of single-walled graphene sheets, which we named carbon nano-horns. The nano-horns can be produced at about 10 g/h.
•Kiwifruit leaf extracts inhibited the test plant growth in a dose dependent manner.•The kiwifruit roots were more sensitive to the leaf extracts than the hypocotyls.•(-)-Epicatechin was identified ...as a phytotoxic substance in kiwifruit leaves.•(-)-Epicatechin inhibited seedling growth of kiwifruit in a dose dependent manner.
When aged kiwifruit (Actinidia deliciosa (A. Chev.) C.F. Liang et A.R. Ferguson) plants are replaced with young ones, the growth and productivity of the young plants were occasionally lower than expected. This symptom is typical of the replant problems reported in several fruit trees. Phytotoxic substances released from the plant are assumed to be involved in the replant problems. Although some substances contained in kiwifruit leaves have been reported to have phytotoxic activity, little is known about phytotoxicity and phytotoxic substances in kiwifruit leaves on the growth of the kiwifruit itself. Therefore, this study determined the phytotoxic activity of kiwifruit leaf extracts and soil extracts and identified a phytotoxic substance in kiwifruit leaves. Extracts of kiwifruit leaves inhibited the growth of Lepidium sativum, Lactuca sativa, Medicago sativa, Phleum pratense, Lolium multiflorum, Echinochloa crus-galli, and kiwifruit seedlings. The soil extracts also inhibited the growth of L. sativum. These results suggest that kiwifruit leaf extracts and soil extracts may possess phytotoxic substances. (-)-Epicatechin was isolated from the extracts with bioassay-guided separations using chromatography. The concentrations of (-)-epicatechin required for 50% growth inhibition of the hypocotyls and radicles of L. sativum were 27.9 and 10.7 mM, respectively, and those for the hypocotyls and radicles of kiwifruit were 13.9 and 7.6 mM, respectively. This substance may contribute to the phytotoxic activity of kiwifruit leaf extracts and may be involved in the kiwifruit replant problem.
Eleocharis atropurpurea is an annual weed and distributed widely in pantropical and subtropical regions. Yet, there have been no studies on the allelopathy of E. atropurpurea. Therefore, we ...investigated the allelopathic potential of E. atropurpurea to identify allelopathic substances from it. The aqueous methanolic extracts of E. atropurpurea showed an inhibitory effect on the seedling growth of lettuce, rapeseed, barnyard grass and foxtail fescue. Inhibition was species- and concentration-dependent. Two substances, syringaldehyde and acetosyringone, were isolated by using chromatography and using spectroscopy their structures were determined. Syringaldehyde and acetosyringone inhibited the shoot and root growth of cress and barnyard grass at concentrations greater than 3.0 mM except shoot growth of barnyard grass by acetosyringone. Concentration and seedling growth of cress and barnyard grass displayed a negative correlation. The I
50
values of syringaldehyde and acetosyringone for the shoot and root growth of cress were 1.67 and 1.61 mM, and 1.49, and 1.29 mM, respectively, whereas for the shoot and root growth of barnyard grass the values were 4.09 and 2.41 mM, and 4.54 and 1.92 mM, respectively. Therefore, it is suggested that these compounds may contribute to the inhibitory effects of E. atropurpurea.
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