Cross-linking multiwall carbon nanotubes using PFPA to build robust, flexible and highly aligned large-scale sheets and yarns.

Multi-walled carbon nanotube (CNT) structures, including unidirectionally aligned sheets and spun yarns, were fabricated by direct dry-spinning methods from spinnable CNT arrays. We improved the mechanical properties of the CNT structures. CNTs were tailored in sheets and yarns using perfluorophenyl azide (PFPA) as a binding agent. The azide group of PFPA bonds to graphene crystal surfaces under UV radiation exposed for 1 h. For the CNT sheet, Young's modulus increased from 1.6 to 32.9 GPa and tensile strength increased from 35.9 MPa to 144.5 MPa. For the CNT yarns Young's modulus increased from 29.5 to 78.0 GPa and tensile strength increased from 639.1 to 675.6 MPa. With this treatment, the CNT sheets became more robust and more flexible materials. Since cross-linking of CNTs by PFPA is a simple and rapid process, it is suitable for fabrication of enhanced CNT materials.

Interfacial oxygen stabilizes composite silicon anodes.

Silicon can store Li(+) at a capacity 10 times that of graphite anodes. However, to harness this remarkable potential for electrical energy storage, one has to address the multifaceted challenge of volume change inherent to high capacity electrode materials. Here, we show that, solely by chemical tailoring of Si-carbon interface with atomic oxygen, the cycle life of Si/carbon matrix-composite electrodes can be substantially improved, by 300%, even at high mass loadings. The interface tailored electrodes simultaneously attain high areal capacity (3.86 mAh/cm(2)), high specific capacity (922 mAh/g based on the mass of the entire electrode), and excellent cyclability (80% retention of capacity after 160 cycles), which are among the highest reported. Even at a high rate of 1C, the areal capacity approaches 1.61 mAh/cm(2) at the 500th cycle. This remarkable electrochemical performance is directly correlated with significantly improved structural and electrical interconnections throughout the entire electrode due to chemical tailoring of the Si-carbon interface with atomic oxygen. Our results demonstrate that interfacial bonding, a new dimension that has yet to be explored, can play an unexpectedly important role in addressing the multifaceted challenge of Si anodes.

Magnetic tunneling with CNT-based metamaterial.

Multiwall carbon nanotubes (MWCNTs) fabricated by chemical vapor deposition contain magnetic nanoparticles. While increasing frequency of electromagnetic field (EMF) exposure (up to <10 kHz) of MWCNTs resulted in slight induced magnetization decrease due to skin effect of the conducting carbon, we discovered that higher frequencies (>10 kHz) contained an exponential magnetization increase. We show that puzzling magnetization increase with decreasing magnetic field amplitude (less than 0.5 A/m for 512 kHz) is due to matching the field amplitudes of the magnetic nanoparticles inside nanotubes. This observation reveals a possibility of magnetic tunneling in MWCNTs (change of magnetic state of blocked magnetic moments). This interpretation is supported by observation of unblocking larger magnetic remanence (MR) portion from MWCNTs with progressively smaller amplitude of oscillating magnetic field.