CNT

CNT
Name	Carbon nanotube
Classification	Nanomaterial
Discovered	1991
Discoverer	Sumio Iijima
Composition	Carbon
Structure	Cylindrical graphene
Common uses	Electronics, composites, energy storage, sensors

CNT

Carbon nanotubes are cylindrical allotropes of carbon composed of one or more concentric layers of graphene rolled into seamless tubes. First described in transmission micrographs by Sumio Iijima and later modeled using concepts from Pauling and Wallace, carbon nanotubes attracted rapid interest from researchers at IBM, Rice University, and University of Tokyo for their exceptional mechanical strength, electronic behavior, and thermal conductivity. Investigations have linked carbon nanotube performance to earlier studies of graphite, fullerene chemistry, and theoretical work by Saito, R. and Dresselhaus.

Introduction

Carbon nanotubes occur as single-walled and multi-walled variants and are often studied in the context of nanoscale materials alongside graphene, buckminsterfullerene, and nanoribbon structures. Research groups at California Institute of Technology, MIT, and Stanford University pursued early electronic device demonstrations, while teams at IMEC and Hitachi explored integration into fabrication flows. Funding and coordination by agencies such as the National Science Foundation and European Commission programs accelerated translation toward applications pursued by companies such as Nanocyl and OCSiAl.

Types and Structure

Single-walled carbon nanotubes (SWCNTs) consist of a single graphene cylinder, classified by a chiral vector (n,m) derived from graphene lattice vectors studied in Saito, R.'s work. Multi-walled carbon nanotubes (MWCNTs) are concentric shells resembling nested Russian doll geometry and were observed in early electron microscopy by Sumio Iijima. Chiral, armchair, and zigzag designations correspond to electronic classification connected to band structure calculations by Wallace and later refined in publications by Dresselhaus and Saito. Structural defects such as Stone–Wales transformations were analyzed in computational studies at Argonne National Laboratory and by groups led by Tomanek, D..

Properties and Characterization

Carbon nanotube properties vary strongly with chirality and diameter; armchair nanotubes often behave as metallic conductors, while certain chiral and zigzag types are semiconducting—a behavior predicted by band theory used by Saito, R. and confirmed in experiments at Bell Labs and IBM Research. Mechanical properties, including Young's modulus and tensile strength, were quantified using atomic force microscopy in labs at Rice University and Northwestern University, with theoretical limits connected to bond energies studied by Pauling. Thermal conductivity measurements performed by groups at MIT and NIST showed exceptional ballistic phonon transport at low temperatures, while Raman spectroscopy by teams at Raman Research Institute and Columbia University remains a routine probe for diameter and defect density. Electron microscopy at Lawrence Berkeley National Laboratory provides high-resolution imaging; scanning tunneling spectroscopy in experiments at University of Cambridge and EPFL elucidates local electronic density of states.

Synthesis and Manufacturing

Synthesis methods include arc discharge pioneered in early experiments at NEC Corporation and Scripps Research, laser ablation developed by teams at Rice University and Sumio Iijima's collaborators, and chemical vapor deposition (CVD) optimized by researchers at Stanford University and ETH Zurich. Catalysts based on transition metals such as iron, cobalt, and nickel were studied at Max Planck Institute for Solid State Research and Oak Ridge National Laboratory. Scalable growth on substrates for aligned arrays was advanced by groups at LG Electronics and Samsung Advanced Institute of Technology, while post-growth purification and dispersion strategies were refined by teams at Dow Chemical Company and 3M. Techniques for chirality-selective sorting were developed at Tsinghua University and in spin-off ventures like Raymor Industries.

Applications

Applications span nanoelectronics, composites, energy, and sensing. Field-effect transistors incorporating single-walled nanotubes were demonstrated by researchers at Stanford University and commercialized in prototypes by Intel collaborators. Reinforcement of polymer matrices using multi-walled nanotubes has been pursued by BASF and DuPont for lightweight structural components in aerospace projects with partners such as Boeing and Airbus. Supercapacitor and battery electrodes using nanotube networks were developed by teams at Samsung and Panasonic, while transparent conductive films based on aligned nanotubes competed with indium tin oxide in projects at Corning Incorporated. Chemical and biological sensors leveraging high surface area and functionalization chemistry were validated by researchers at Imperial College London and Johns Hopkins University; biomedical delivery concepts were explored at Harvard Medical School and MIT Koch Institute.

Safety and Environmental Impact

Toxicology studies in laboratories at NIH, EPA, and World Health Organization-funded consortia examined inhalation, dermal, and environmental pathways, comparing responses to asbestos-like fibers considered by studies at International Agency for Research on Cancer. Life-cycle assessments by groups at University of Cambridge and Stockholm Environment Institute evaluated energy inputs and end-of-life scenarios. Occupational exposure limits and handling guidelines were proposed by OSHA and adapted by industrial partners such as DuPont and BASF. Remediation and recycling efforts were investigated at Lawrence Livermore National Laboratory and Fraunhofer Society to mitigate persistence in waste streams. Emerging consensus emphasizes controlled manufacturing, exposure monitoring, and targeted ecotoxicological research supported by agencies like European Chemicals Agency.

Category:Nanomaterials