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A carbon nanotube is a cylindrical carbon nanostructure with a graphitic bonding framework. Single-walled tubes can be described by the way a graphene-like sheet wraps around the cylinder; multiwalled tubes contain nested shells.

Diameter and wrapping geometry influence electronic and optical properties, including whether an idealized tube behaves as metallic or semiconducting. Thus carbon composition alone cannot predict the behavior of a particular nanotube.

A dense population of approximately aligned carbon nanotubes growing from a support. Collective crowding can favor alignment even when the support does not epitaxially select every tube orientation.

A missing carbon atom or group of atoms in a carbon nanotube wall. Local reconstruction can produce a 5–9 monovacancy or 5–8–5 divacancy ring inventory; larger vacancies can interrupt a shell.

Continuous withdrawal and consolidation of a connected carbon nanotube aerogel from a synthesis reactor. It differs from later spinning of a prepared liquid dispersion and from drawing a pre-grown substrate-supported forest.^[ref]

A chemical vapor deposition route in which catalyst particles form or travel in the gas stream rather than remaining on a macroscopic support. For carbon nanotubes, particle nucleation, tube growth and aggregation can occur in one flowing reactor. Product withdrawal becomes possible when the growing network is sufficiently connected.

A plot of optical transition energies against carbon nanotube diameter, usually organized by wrapping indices and electronic type. It relates optical and resonant Raman spectroscopy observations to nanotube structure.

Mildred Dresselhaus investigated the electronic band structure and optical response of carbon materials, from graphite to carbon nanotubes. Her group's Raman spectroscopy studies used resonant enhancement to distinguish nanotubes by their geometry and electronic transitions. Measurements on individual carbon nanotubes connected the vibrational spectrum with diameter and chirality, making light scattering a structural probe at the scale of a single tube.^[ref]

Her authored solid-state lecture notes also explain how impurity spectra test models of electrons and holes in semiconductors, including the limitations of treating every impurity as a simple hydrogen-like system.^[ref]

MIT memorial profile and portrait: physics.mit.edu/faculty/mildred-dresselhaus/

A carbon nanotube comprising several nested graphitic walls. Each shell can have its own wrapping indices; their difference alone is not a structural defect.

The conventional nineteenth-century answer is diamond, graphite and so-called amorphous carbon. These exhibit strikingly different physical properties while sharing the same chemical element, carbon.

Diamond is a crystalline, usually transparent form, very hard and ordinarily an electrical insulator. Its three-dimensional covalent bond network joins each carbon chemical atom to four neighbours. Graphite is a dark, soft, crystalline form with layered bonding; easy shear between layers makes it useful for marking and lubrication. Its electronic structure permits much greater electrical conductivity than that of ordinary diamond.

The historical “amorphous” class includes charcoal, coke, lampblack and soot, as well as carbon-rich materials such as gas-retort carbon. Such names describe preparation and texture as well as structure: restricted-air heating of wood gives charcoal, destructive distillation of coal gives coke, and incomplete combustion of a carbon-bearing fuel produces soot. Modern structural examination shows that these materials can contain small, imperfect graphitic regions. They are not necessarily one distinct pure allotrope. Coal itself is a chemically complex, impure carbon-rich material, rather than a pure form of the chemical element.

A common chemical connection is that pure samples of these carbon forms can yield carbon dioxide upon complete combustion in excess oxygen:Their different hardness, appearance and electrical conductivity arise from structure and impurities, rather than from being different chemical elements. This is the explanatory role of allotropy.

Modern lists also include fullerenes, carbon nanotubes and graphene. These are useful present-day extensions, not discoveries to credit to the 1867 candidate.^[ref]

Use substrate-supported chemical vapor deposition. Prepare a clean quartz support with a suitable supported transition-metal catalyst, often nanoscale Fe-containing particles. Catalyst loading, support chemistry and pretreatment control the active particle size and density. A heated carbon-containing gas supplies carbon to those particles, from which carbon nanotubes grow.

At sufficiently high nucleation density, neighboring tubes constrain one another's lateral motion, producing a roughly aligned carbon nanotube forest normal to the support. This is collective crowding, not a requirement that quartz epitaxially orient every tube. Gas delivery, catalyst lifetime and growth time set length and uniformity. Depending on catalyst–support adhesion, catalyst particles can remain near the support or move with growing tips.

The catalyst is supported and the carpet remains attached to a substrate. Check particle distribution and film uniformity separately from tube diameter and alignment; a dense black coating alone does not establish a nanotube forest. The original growth sketch contrasts this supported route with a floating-catalyst reactor.

The floating-catalyst direct-spinning route commonly requires a small sulfur promoter addition. sulfur changes catalyst-particle nucleation and surface chemistry, influencing the active Fe-particle population, carbon incorporation and whether sufficiently long, numerous tubes form a drawable aerogel.

A sulfur-rich catalyst surface or Fe–S-containing state can alter surface energy, wetting and particle coarsening; a low-melting interfacial state can also affect catalyst activity. These are process-dependent mechanisms, not a statement that sulfur is a structural constituent required in every carbon nanotube. Excess sulfur can suppress useful growth or worsen impurities. The useful dose therefore has a window and depends on catalyst and feed chemistry.

A controlled comparison changes sulfur supply while holding the carbon/catalyst feed and collection conditions fixed, then measures tube population, catalyst residue and spinnability rather than judging only the presence of soot. The primary direct-spinning study specifically treats sulfur-dependent processing and purity.^[ref]

Yes: carbon nanotubes can store lithium and form a porous, conducting anode network. Their external surfaces, defects and intertube spaces provide possible storage sites. Open ends and suitable defects may make internal surfaces accessible; a closed pristine tube should not be credited with its full internal area.

Axial conduction and an entangled mechanical scaffold can support either active storage or a composite electrode. Limitations include tube–tube contact resistance, low packing density, catalyst residues and large-area solid electrolyte interphase formation. Opening or functionalizing tubes may improve ion access while increasing defects and irreversible reactions. Compare reversible capacity, first-cycle efficiency, retention and full-cell lithium inventory under matched loading and voltage-window conditions. A high first-cycle capacity alone is insufficient evidence of a superior anode.

A 2013 experiment by Paul A. Williams and collaborators mounted a 25-mm dielectric mirror on a commercial force-restoration balance. Removing its pan-weight compensation spring allowed horizontal force sensing with a horizontal laser path. They measured mirror optical reflectance and varied incidence from about $7^{\circ }$ to $45^{\circ }$. A 1071-nm laser, capable of 530 W, was switched at 0.1 Hz. Digitized mass-equivalent readings were converted to force using $g$; quadrature demodulation isolated the switched signal from drift. ^[ref]

Measurement calibration used a 20-g mass, with checks down to 1 mg. The optical forces lay below that checked range, limiting the accuracy claim. An angle scan tested the predicted cosine dependence at fixed intercepted power. Replacing the mirror with a carbon nanotube coated absorber increased absorbed power while reducing the predicted optical force; no modulation peak was detected. This bounded gas-heating artifacts under those conditions, rather than proving their universal absence. The fitted slope was about 7% below $2/c$. Inferring laser power requires calibrated force, optical reflectance, radiometric absorptance and angle of incidence, with measurement uncertainty for each. ^[ref]

Sergei M. Bachilo coauthored research on single-walled carbon nanotube.^[ref]

A carbon nanotube comprising one rolled graphene wall. The wrapping indices determine its allowed circumferential electronic wave vectors and therefore its metallic or semiconducting band structure.

Shunsuke Sakurai is the first-listed author of A phenomenological model for selective growth of semiconducting single-walled carbon nanotubes based on catalyst deactivation by Shunsuke Sakurai and others. The work uses catalyst deactivation to model why growth conditions can select semiconducting carbon nanotubes. It connects a change in catalyst activity to the composition of the resulting nanotube population.^[ref]

A carbon nanotube comprising one rolled graphene wall. The wrapping indices determine its allowed circumferential electronic wave vectors and therefore its metallic or semiconducting band structure.

A researcher who studied direct production of carbon nanotube fibers by chemical vapor deposition. In this process, growing nanotubes collect into an aerogel that can be drawn continuously into a fiber. The study examined how trace sulfur and the timing of carbon availability affect nanotube structure and fiber properties, showing why chemical process control matters to a macroscopic material.^[ref]

A researcher who coauthored a direct-spinning process for carbon nanotube fibers. Chemical vapor deposition creates a floating assembly of nanotubes inside a furnace; drawing this material out converts nanoscale growth into a continuous macroscopic fiber. The approach links synthesis and assembly in one operation, addressing the challenge of turning exceptional individual nanotubes into a usable bulk material.^[ref]