Raman spectroscopy of carbon nanotubes

Materials with good flexibility and high conductivity that can provide electromagnetic interference (EMI) shielding with minimal thickness are highly desirable, especially if they can be easily processed into films. Two-dimensional metal carbides and nitrides, known as MXenes, combine metallic conductivity and hydrophilic surfaces. Here, we demonstrate the potential of several MXenes and their polymer composites for EMI shielding. A 45-micrometer-thick Ti3C2Tx film exhibited EMI shielding effectiveness of 92 decibels (>50 decibels for a 2.5-micrometer film), which is the highest among synthetic materials of comparable thickness produced to date. This performance originates from the excellent electrical conductivity of Ti3C2Tx films (4600 Siemens per centimeter) and multiple internal reflections from Ti3C2Tx flakes in free-standing films. The mechanical flexibility and easy coating capability offered by MXenes and their composites enable them to shield surfaces of any shape while providing high EMI shielding efficiency.

Electromagnetic interference shielding with 2D transition metal carbides (MXenes)

Carbon materials have attracted intense interests as electrode materials for electrochemical capacitors, because of their high surface area, electrical conductivity, chemical stability and low cost. Activated carbons produced by different activation processes from various precursors are the most widely used electrodes. Recently, with the rapid growth of nanotechnology, nanostructured electrode materials, such as carbon nanotubes and template-synthesized porous carbons have been developed. Their unique electrical properties and well controlled pore sizes and structures facilitate fast ion and electron transportation. In order to further improve the power and energy densities of the capacitors, carbon-based composites combining electrical double layer capacitors (EDLC)-capacitance and pseudo-capacitance have been explored. They show not only enhanced capacitance, but as well good cyclability. In this review, recent progresses on carbon-based electrode materials are summarized, including activated carbons, carbon nanotubes, and template-synthesized porous carbons, in particular mesoporous carbons. Their advantages and disadvantages as electrochemical capacitors are discussed. At the end of this review, the future trends of electrochemical capacitors with high energy and power are proposed.

Carbon Materials for Chemical Capacitive Energy Storage

Hexagonal ferrites: A review of the synthesis, properties and applications of hexaferrite ceramics

Carbon nanotubes are unique tubular structures of nanometer diameter and large length/diameter ratio. The nanotubes may consist of one up to tens and hundreds of concentric shells of carbons with adjacent shells separation of ∼0.34 nm. The carbon network of the shells is closely related to the honeycomb arrangement of the carbon atoms in the graphite sheets. The amazing mechanical and electronic properties of the nanotubes stem in their quasi-one-dimensional (1D) structure and the graphite-like arrangement of the carbon atoms in the shells. Thus, the nanotubes have high Young’s modulus and tensile strength, which makes them preferable for composite materials with improved mechanical properties. The nanotubes can be metallic or semiconducting depending on their structural parameters. This opens the ways for application of the nanotubes as central elements in electronic devices including field-effect transistors (FET), single-electron transistors and rectifying diodes. Possibilities for using of the nanotubes as high-capacity hydrogen storage media were also considered. This report is intended to summarize some of the major achievements in the field of the carbon nanotube research both experimental and theoretical in connection with the possible industrial applications of the nanotubes.

Carbon nanotubes: properties and application

We report here the discovery of the smallest possible carbon nanotube. This has a diameter of 4 A, which is the narrowest attainable that can still remain energetically stable, as predicted by theory. These nanotubes are confined inside multiwalled carbon nanotubes and their diameter corresponds to that of a C20 dodecahedron with a single carbon atom at each of its twenty apices. Unlike larger carbon nanotubes, which, depending on their diameter and helicity, can be either metallic or semiconducting, these smallest nanotubes are always metallic.

/pdf/the-smallest-carbon-nanotube-5dj5ifnd65.pdf

The smallest carbon nanotube.

A new type of one-dimensional (1D) carbon structure, carbon nanowires (CNWs), was discovered in the cathode deposits prepared by hydrogen arc discharge evaporation of carbon rods. Observation of high-resolution transmission electron microscopy (HRTEM) indicates that a CNW consists of a multiwalled carbon nanotube (MWNT) with a long 1D linear carbon chain (C chain) inserted into its innermost tube of 0.7 nm in diameter. The characteristic Raman peaks of CNWs appeared at around 1850 cm(-1). Raman scattering and HRTEM studies show the formation of a long linear C chain involving more than 100 carbon atoms inside a MWNT. This novel 1D carbon allotrope has potential applications in nanoelectronics, nanomechanics, and nanomaterials.

Carbon nanowire made of a long linear carbon chain inserted inside a multiwalled carbon nanotube.

Previous energetic considerations have led to the belief that carbon nanotubes (CNTs) of 4 A in diameter are the smallest stable CNTs. Using high-resolution transmission electron microscopy, we find that a stable 3 A CNT can be grown inside a multiwalled carbon nanotube. Density functional calculations indicate that the 3 A CNT is the armchair CNT(2,2) with a radial breathing mode at 787 cm(-1). Each end can be capped by half of a C12 cage (hexagonal prism) containing tetragons.

/pdf/smallest-carbon-nanotube-is-3-a-in-diameter-17gxpzul72.pdf

Xinluo Zhao

Papers

The smallest carbon nanotube.

Carbon nanowire made of a long linear carbon chain inserted inside a multiwalled carbon nanotube.

Smallest carbon nanotube is 3 a in diameter.

Physical properties of multiwalled carbon nanotubes

Growing carbon nanotubes