Chemical Sharpening,Shortening, and Unzipping of Boron Nitride Nanotubes

Boron nitride nanotubes (BNNTs), the one‐dimensional member of the boron nitride nanostructure family, are generally accepted to be highly inert to oxidative treatments and can only be covalently modified by highly reactive species. Conversely, it is discovered that the BNNTs can be chemically dispersed and their morphology modified by a relatively mild method: simply sonicating the nanotubes in aqueous ammonia solution. The dispersed nanotubes are significantly corroded, with end‐caps removed, tips sharpened, and walls thinned. The sonication treatment in aqueous ammonia solution also removes amorphous BN impurities and shortened BNNTs, resembling various oxidative treatments of carbon nanotubes. Importantly, the majority of BNNTs are at least partially longitudinally cut, or “unzipped”. Entangled and freestanding BN nanoribbons (BNNRs), resulting from the unzipping, are found to be ～5–20 nm in width and up to a few hundred nanometers in length. This is the first chemical method to obtain BNNRs from BNNT unzipping. This method is not derived from known carbon nanotube unzipping strategies, but is unique to BNNTs because the use of aqueous ammonia solutions specifically targets the B‐N bond network. This study may pave the way for convenient processing of BNNTs, previously thought to be highly inert, toward controlling their dispersion, purity, lengths, and electronic properties.     

Towards Thermoconductive,Electrically Insulating Polymeric Composites with Boron Nitride Nanotubes as Fillers

Ultilizing boron nitride nanotubes (BNNTs) as fillers, composites are fabricated with poly(methyl methacrylate), polystyrene, poly(vinyl butyral), or poly(ethylene vinyl alcohol) as the matrix and their thermal, electrical, and mechanical properties are evaluated. More than 20‐fold thermal conductivity improvement in BNNT‐containing polymers is obtained, and such composites maintain good electrical insulation. The coefficient of thermal expansion (CTE) of the BNNT‐loaded polymers is dramatically reduced because of interactions between the polymer chains and the nanotubes. Moreover, the composites possess good mechanical properties, as revealed by Vickers microhardness tests. This detailed study indicates that BNNTs are very promising nanofillers for polymeric composites, allowing the simultaneous achievement of high thermal conductivity, low CTE, and high electrical resistance, as required for novel and efficient heat‐releasing materials.     

Surface Growth of Boron Nitride Nanotubes through Boron Source Design

Boron nitride nanotubes (BNNTs) are promising materials due to their unique physical and chemical properties. Fabrication technologies based on gas-phase reactions reduce the control and collection efficiency of BNNTs due to reactant and product dispersion within the reaction vessel. A surface growth method that allows for controllable growth of BNNTs in certain regions using a preburied boron source is introduced. This work leverages the high solubility of boron in metals to create a boronized layer on the surface which serves as the boron source to confine the growth of BNNTs. Dense and uniform BNNTs are obtained after loading catalysts onto the boronized substrate and annealing under ammonia. Confirmatory experiments demonstrate that the boride layer provides boron for BNNTs growth. Furthermore, the patterned growth of BNNTs is realized by patterning the boronizing region, demonstrating the controllability of this method. In addition, the Ni substrate with BNNTs growth exhibits better performance in corrosion resistance and thermal conductivity than pure Ni. This study introduces an alternative strategy for the surface growth of BNNTs based on boron source design, which offers new possibilities for the controllable preparation of BNNTs for various applications.     

Unveiling the Atomic Structure of Single‐Wall Boron Nanotubes

Despite recent successes in the synthesis of boron nanotubes (BNTs), the atomic arrangement of their walls has not yet been determined and many questions about their basic properties remain. Here, the dynamic stability of BNTs is unveiled by means of first‐principles molecular dynamics simulations. Free‐standing, single‐wall BNTs with diameters larger than 0.6 nm are found to be thermally stable at the experimentally reported synthesis temperature of 870 °C and higher. The walls of thermally stable BNTs are found to have a variety of different mixed triangular–hexagonal morphologies. These results substantiate the importance of mixed triangular–hexagonal morphologies as a structural paradigm for atomically thin boron.     

Facile Fabrication and Superparamagnetism of Silica‐Shielded Magnetite Nanoparticles on Carbon Nitride Nanotubes

Using conventional methods to synthesize magnetic nanoparticles (NPs) with uniform size is a challenging task. Moreover, the degradation of magnetic NPs is an obstacle to practical applications. The fabrication of silica‐shielded magnetite NPs on carbon nitride nanotubes (CNNTs) provides a possible route to overcome these problems. While the nitrogen atoms of CNNTs provide selective nucleation sites for NPs of a particular size, the silica layer protects the NPs from oxidation. The morphology and crystal structure of NP–CNNT hybrid material is investigated by transmission electron microscopy (TEM) and X‐ray diffraction. In addition, the atomic nature of the N atoms in the NP–CNNT system is studied by near‐edge X‐ray absorption fine structure spectroscopy (nitrogen K‐edge) and calculations of the partial density of states based on first principles. The structure of the silica‐shielded NP–CNNT system is analyzed by TEM and energy dispersive X‐ray spectroscopy mapping, and their magnetism is measured by vibrating sample and superconducting quantum interference device magnetometers. The silica shielding helps maintain the superparamagnetism of the NPs; without the silica layer, the magnetic properties of NP–CNNT materials significantly degrade over time.     

Flexible,Stretchable, Transparent Conducting Films Made from Superaligned Carbon Nanotubes

A straightforward roll‐to‐roll process for fabricating flexible and stretchable superaligned carbon nanotube films as transparent conducting films is demonstrated. Practical touch panels assembled by using these carbon nanotube conducting films are superior in flexibility and wearability—and comparable in linearity—to touch panels based on indium tin oxide (ITO) films. After suitable laser trimming and deposition of Ni and Au metal, the carbon nanotube film possesses excellent performance with two typical values of sheet resistances and transmittances (208 Ω □^?1, 90% and 24 Ω □^?1, 83.4%), which are comparable to ITO films and better than the present carbon nanotube conducting films in literature. The results provide a route to produce transparent conducting films more easily, effectively, and cheaply, an important step for realizing industrial‐scale applications of carbon nanotubes for transparent conducting films.     

Polyhedral Oligosilsesquioxane‐Modified Boron Nitride Nanotube Based Epoxy Nanocomposites: An Ideal Dielectric Material with High Thermal Conductivity

Dielectric polymer composites with high thermal conductivity are very promising for microelectronic packaging and thermal management application in new energy systems such as solar cells and light emitting diodes (LEDs). However, a well‐known paradox is that conventional composites with high thermal conductivity usually suffer from the high dielectric constant and high dielectric loss, while on the other hand, composite materials with excellent dielectric properties usually possess low thermal conductivity. In this work, an ideal dielectric thermally conductive epoxy nanocomposite is successfully fabricated using polyhedral oligosilsesquioxane (POSS) functionalized boron nitride nanotubes (BNNTs) as fillers. The nanocomposites with 30 wt% fraction of POSS modified BNNTs exhibit much lower dielectric constant, dielectric loss tangent, and coefficient of thermal expansion in comparison with the pure epoxy resin. As an example, below 100 Hz, the dielectric loss of the nanocomposites with 20 and 30 wt% BNNTs is reduced by one order of magnitude in comparison with the pure epoxy resin. Moreover, the nanocomposites show a dramatic thermal conductivity enhancement of 1360% in comparison with the pristine epoxy resin at a BNNT loading fraction of 30 wt%. The merits of the designed composites are suggested to originate from the excellent intrinsic properties of embedded BNNTs, effective surface modification by POSS molecules, and carefully developed composite preparation methods.     

碳纳米管的制备、修饰及其应用

简要介绍了碳纳米管的制备及其纯化技术，以及近年来碳纳米管修饰、管内填充方面的研究，并概述了碳纳米管在复合材料、发光材料、纳米器件方面的应用及其在固体基片上的定向组装。     

Amorphous Boron Nitride: A Universal,Ultrathin Dielectric For 2D Nanoelectronics

Next‐generation nanoelectronics based on 2D materials ideally will require reliable, flexible, transparent, and versatile dielectrics for transistor gate barriers, environmental passivation layers, capacitor spacers, and other device elements. Ultrathin amorphous boron nitride of thicknesses from 2 to 17 nm, described in this work, may offer these attributes, as the material is demonstrated to be universal in structure and stoichiometric chemistry on numerous substrates including flexible polydimethylsiloxane, amorphous silicon dioxide, crystalline Al₂O₃, other 2D materials including graphene, 2D MoS₂, and conducting metals and metal foils. The versatile, large area pulsed laser deposition growth technique is performed at temperatures less than 200 °C and without modifying processing conditions, allowing for seamless integration into 2D device architectures. A device‐scale dielectric constant of 5.9 ± 0.65 at 1 kHz, breakdown voltage of 9.8 ± 1.0 MV cm^?1, and bandgap of 4.5 eV were measured for various thicknesses of the ultrathin a‐BN material, representing values higher than previously reported chemical vapor deposited h‐BN and nearing single crystal h‐BN.     

Localized Surface Plasmon Resonance Enhanced Photocatalytic Hydrogen Evolution via Pt@Au NRs/C3N4 Nanotubes under Visible‐Light Irradiation

Au nanorods (NRs) decorated carbon nitride nanotubes (Au NRs/CNNTs) photocatalysts have been designed and prepared by impregnation–annealing approach. Localized surface plasmon resonance (LSPR) peaks of Au NRs can be adjusted by changing the aspect ratios, and the light absorption range of Au NRs/CNNTs is extended to longer wavelength even near‐infrared light. Optimal composition of Pt@Au NR₇₆₉/CNNT₆₅₀ has been achieved by adjusting the LSPR peaks of Au NRs and further depositing Pt nanoparticles (NPs), and the photocatalytic H₂ evolution rate is 207.0 µmol h^?1 (20 mg catalyst). Preliminary LSPR enhancement photocatalytic mechanism is suggested. On one hand, LSPR of Au NRs is beneficial for visible‐light utilization. On the other hand, Pt NPs and Au NRs have a synergetic enhancement effect on photocatalytic H₂ evolution of CNNTs, in which the local electromagnetic field can improve the photogenerated carrier separation and direct electron transfer increases the hot electron concentration while Au NRs as the electron channel can well restrain charge recombination, finally Pt as co‐catalyst can boost H⁺ reduction rate. This work provides a new way to develop efficient photocatalysts for splitting water, which can simultaneously extend light absorption range and facilitate carrier generation, transportation and reduce carrier recombination.     

纳米碳管的STM研究

本文应用扫描隧道显微镜对孤光放电方法得到的纳米碳管进行了观察。孤光放电法所产物的纳米碳管以直线型为主，并且多以束状存在。碳管束直径约２０ｎｍ，而单要碳管的直径大多在２ｎｍ到５ｎｍ之间。观察到单层碳秋的原子像，其表明为石墨网络的六角结构。纳米碳管的原子像及单极碳管表面均未发现明显缺陷存在，这可能是它具有很高强度质量比的主要原理之一。     

Selective Growth of Carbon Nanotubes for Nanoscale Transistors

The selective growth of vertically aligned carbon nanotubes (CNTs) and their application as field‐effect transistors (FETs) are demonstrated. Vertically aligned carbon nanotubes were selectively grown in nanoholes formed in an anodized aluminum oxide (AAO) template. Each device element is formed on a vertical carbon nanotube attached to bottom (source) and upper (drain) electrodes and a gate electrode, which can be integrated in large arrays with the potential for tera‐level density (10¹² cm^–2). Simulation of the potential distribution shows that the direction of potential formation would depend on the polarity of the gate bias, which is consistent with an experimental result of CNT‐FET operation.     

用碳纳米管膜测量转动速度

对多壁碳纳米管(MWCNTs)膜在高速转动下的压阻效应进行了研究，并讨论了利用这种效应来测量转动速度和制造这类传感器的可能性。实验所用的多壁碳纳米管是用热灯丝化学气相沉积法(CVD)合成。研究发现：在室温下，多壁碳纳米管膜的电阻随转子转速的增加而增加，在转子转速从1000r／min～3000r／min的变化过程中，多壁碳纳米管膜的电阻近似呈线性变化。并且碳纳米管膜在拉伸和压缩两种情况下电阻变化与转速之间的关系曲线近似对称．