Conductivity in carbon nanotube polymer composites: A comparison between model and experiment

Carbon nanotubes (CNTs) demonstrate remarkable conductive behaviour, which suggests promising applications. Their outstanding properties have been used in the development of CNT–polymer composites as possible alternative materials for various applications, such as flexible electrodes, antistatic coatings and piezoresistive sensors. In our study we focused our attention on the evaluation and modelling of CNT-filled epoxy resin electrical conductivity. We discuss the results with regard to the influence of CNTs dimensions and content. Exploiting the Dijkstra algorithm, we implemented a simulation code which determines the shortest route between electrodes in the polymer. The longer the path inside the polymer, the more non-conductive the composite becomes, since polymer resistivity is orders of magnitude higher than that of CNTs. We compared these simulated results with experimental data obtained at several wt% and found a good correspondence between modelling and experimental results.     

Diamond based field-effect transistors with SiNx and ZrO2 double dielectric layers

A diamond-based field-effect transistor (FET) with SiN_x and ZrO₂ double dielectric layer has been demonstrated. The SiN_x and ZrO₂ gate dielectric are deposited by plasma-enhanced chemical vapor deposition (PECVD) and radio frequency (RF) sputter methods, respectively. SiN_x layer is found to have the ability to preserve the conduction channel at the surface of hydrogen-terminated diamond film. The leakage current density (J) of SiN_x/ZrO₂ diamond metal-insulator-semiconductor FET (MISFET) keeps lower than 3.88 × 10^− 5 A·cm^− 2 when the gate bias was changed from 2 V to − 8 V. The double dielectric layer FET operates in a p-type depletion mode, whose maximum drain-source current, threshold voltage, maximum transconductance, effective mobility and sheet hole density are determined to be − 28.5 mA·mm^− 1, 2.2 V, 4.53 mS·mm^− 1, 38.9 cm²·V^− 1·s^− 1, and 2.14 × 10¹³ cm^− 2, respectively.     

A universal programmable driving circuit for spatial light modulators

ea of only 65 × 65μm2.     

基于蓝宝石纳米图形衬底上氮化镓生长的研究

利用两步生长法在蓝宝石纳米图形衬底（NPSS）上生长得到高质量的氮化镓薄膜。通过XRD和SEM对薄膜质量的表征和研究发现,为得到高质量的氮化镓（GaN）薄膜,在NPSS上生长时得到的最优缓冲层厚度为15nm,而在微米级尺寸的图形衬底（MPSS）上得到的最优缓冲层厚度远大于15nm。同时,在NPSS上生长氮化镓薄膜的过程中观察到一个有趣的现象,即GaN在NPSS上生长的初始阶段,氮化镓晶粒主要在图形之间的平面区域生长,极少量的GaN在衬底图形的侧面上聚集生长。这一有趣的现象明显不同于GaN在MPSS上的生长过程。接着,又在NPSS上生长了GaN基LED结构,并对其光电性能进行了研究。     

Alcohol-assisted rapid growth of vertically aligned carbon nanotube arrays

Millimeter-to-centimeter scale vertically aligned carbon nanotube (VACNT) arrays are widely studied because of their immense potential in a range of applications. Catalyst control during chemical vapor deposition (CVD) is key to maintain the sustained growth of VACNT arrays. Herein, we achieved ultrafast growth of VACNT arrays using Fe/Al₂O₃ catalysts by ethanol-assisted two-zone CVD. One zone was set at temperatures above 850 °C to pyrolyze the carbon source and the other zone was set at 760 °C for VACNT deposition. By tuning synthesis parameters, up to 7 mm long VACNT arrays could be grown within 45 min, with a maximal growth rate of ∼280 μm/min. Our study indicates that the introduction of alcohol vapor and separation of growth zones from the carbon decomposition zone help reduce catalyst particle deactivation and accelerate the carbon source pyrolysis, leading to the promotion of VACNT array growth. We also observed that the catalyst film thickness did not significantly affect the CNT growth rate and microstructures under the conditions of our study. Additionally, the ultralong CNTs showed better processability with less structural deformation when exposed to solvent and polymer solutions. Our results demonstrate significant progress towards commercial production and application of VACNT arrays.     

Fabrication and functionalization of carbon nanotube films for high-performance flexible supercapacitors

1. Download : Download full-size image

Carbon nanotube (CNT) films have shown many promising advantages in the development of high-performance flexible supercapacitors in terms of electrode specific area, mechanical reliability under bending and stretching, electron and ionic mobility tailored for high-rate performance etc. In this review, the recent progress in the design, preparation and functionalization of CNT film based electrodes for the fabrication of high-performance flexible supercapacitors are introduced in details, including the synthesis of conductive CNT films for the electrodes of supercapacitors, and the functionalizations of CNT film with other high-capacitance materials by both mixing and in situ growth strategies for high-performance composite electrodes. Furthermore, we also discussed the assembly strategies, prototypes and electrochemical performance of flexible supercapacitors based on CNT film composite electrodes. At last, the challenges and trends of the CNT film based flexible supercapacitors are prospected as well.     

Mechanical and electrical properties of aligned carbon nanotube/carbon matrix composites

To synthesize carbon nanotube/carbon matrix (CNT/C) composites rivaling or exceeding the mechanical and electrical properties of current carbon fiber/carbon matrix composites, it is essential to align carbon nanotubes in the composite. In this work, we fabricated CNT/polyacrylonitrile (PAN) precursor composites with high degree of CNT alignment, and carbonized and graphitized them at high temperatures. Carbonizing the precursor composites significantly improved their elastic modulus, strength, and electrical conductivity. The matrix was uniformly carbonized and highly graphitized. The excellent mechanical and electrical properties make the CNT/C composites promising for many high temperature aerospace applications.     

High performance carbon nanotube spun yarns from a crosslinked network

We report a new method to create covalent crosslinks between carbon nanotubes (CNTs) with reduced intertube and interbundle spaces, for improving the mechanical properties of CNT spun yarns. This is achieved through the pretreatment of a CNT yarn with 4-carboxybenzenediazonium tetrafluoroborate to form reactive carboxyphenyl groups on the CNT sidewalls. These carboxyphenyl groups are then reacted with a multifunctional crosslinker hexa(methoxymethyl) melamine, leading to a highly crosslinked network within the yarn. The CNT yarns were characterized by X-ray photoelectron spectroscopy, focused ion beam scanning electron microscope, and also assessed for their mechanical properties. The results showed that the method developed effectively improved mechanical properties of CNT yarns: we are able to produce CNT yarns with a tensile strength up to 2.5 GPa and Young’s modulus 121 GPa.     

Chemical routes toward long-lasting lithium/sulfur cells

Lithium/sulfur (Li/S) cells have great potential to become mainstream secondary batteries due to their ultra-high theoretical specific energy. The major challenge for Li/S cells is the unstable cycling performance caused by the sulfur’s insulating nature and the high-solubility of the intermediate polysulfide products. Several years of efforts to develop various fancy carbon nanostructures, trying to physically encapsulate the polysulfides, did not yet push the cell’s cycle life long enough to compete with current Li ion cells. The focus of this review is on the recent progress in chemical bonding strategy for trapping polysulfides through employing functional groups and additives in carbon matrix. Research results on understanding the working mechanism of chemical interaction between polysulfides and functional groups (e.g. O–, B–, N–and S–) in carbon matrix, metal-based additives, or polymer additives during charge/discharge are discussed.

Open image in new window