Carbon nanocone

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SEM images of a carbon disk (top left image) and free-standing hollow carbon nanocones produced by pyrolysis of heavy oil in the Kvaerner Carbon Black & Hydrogen Process. Maximum diameter is about 1 micrometer. Carbon-nanocones.JPG
SEM images of a carbon disk (top left image) and free-standing hollow carbon nanocones produced by pyrolysis of heavy oil in the Kvaerner Carbon Black & Hydrogen Process. Maximum diameter is about 1 micrometer.

Carbon nanocones are conical structures which are made predominantly from carbon and which have at least one dimension of the order one micrometer or smaller. Nanocones have height and base diameter of the same order of magnitude; this distinguishes them from tipped nanowires which are much longer than their diameter. Nanocones occur on the surface of natural graphite. Hollow carbon nanocones can also be produced by decomposing hydrocarbons with a plasma torch. Electron microscopy reveals that the opening angle (apex) of the cones is not arbitrary, but has preferred values of approximately 20°, 40°, and 60°. This observation was explained by a model of the cone wall composed of wrapped graphene sheets, where the geometrical requirement for seamless connection naturally accounted for the semi-discrete character and the absolute values of the cone angle. A related carbon nanoform is the single-walled carbon nanohorn which typically form aggregates 80–100 nm in size.

Contents

Free-standing hollow cones

History and synthesis

Carbon nanocones are produced in an industrial process that decomposes hydrocarbons into carbon and hydrogen with a plasma torch having a plasma temperature above 2000 °C. This method is often referred to as Kvaerner Carbon Black & Hydrogen Process (CBH) and it is relatively "emission-free", i.e., produces rather small amount of air pollutants. At certain, well optimized and patented conditions, [2] the solid carbon output consists of approximately 20% carbon nanocones, 70% flat carbon discs and 10% carbon black. [1]

Plasma-assisted decomposition of hydrocarbons has long been known and applied, for example, for production of carbon fullerenes. Even if not optimized, it yields small amounts of carbon nanocones, which had been directly observed with an electron microscope already in 1994, [3] and their atomic structure was theoretically modeled the same year. [4] [5]

Atomic model of a cone with the 38.9deg apex angle. Carbon cone tip.JPG
Atomic model of a cone with the 38.9° apex angle.

Modeling

Statistical distribution of the apex values measured over 1700 hollow nanocones. Carbon cone angle.PNG
Statistical distribution of the apex values measured over 1700 hollow nanocones.

The open carbon cone can be modeled as a wrapped graphene sheet. In order to have strain-free, seamless wrapping, a sector has to be cut out of the sheet. That sector should have an angle of n × 60°, where n = 1, ..., 5. Therefore, the resulting cone angle should have only certain, discrete values α = 2 arcsin(1 − n/6) = 112.9°, 83.6°, 60.0°, 38.9°, and 19.2° for n = 1, ..., 5, respectively. The graphene sheet is composed solely of carbon hexagons which can not form a continuous cone cap. As in the fullerenes, pentagons have to be added to form a curved cone tip, and their number is correspondingly n = 1, ..., 5. [1]

Observation

Electron microscopy observations do confirm the model prediction of discrete cone angles. Two experimental artifacts must be considered though: (i) charging of the poorly conducting carbon samples under electron beam, which blurs the images and (ii) that electron microscopy observations at a fixed sample tilt only yield a two-dimensional projection whereas a 3D shape is required. The first obstacle is overcome by coating the cones with a metal layer of a few nanometers thickness. The second problem is solved through a geometrical shape analysis. Combined with significant statistics on the number of cones, it yields semi-discrete apex angles. Their values deviate from prediction by about 10% due to the limited measurement accuracy and slight variation of the cone thickness along its length. [1]

Image of a coffee filter illustrating one of the anomalous structures in the carbon nanocone growth. Koffiefilter RA.jpg
Image of a coffee filter illustrating one of the anomalous structures in the carbon nanocone growth.

The absolute value of the cone wall thickness varies between 10 and 30 nm, but can be as large as 80 nm for some nanocones. To elucidate the structure of the cone walls, electron diffraction patterns were recorded at different cone orientations. Their analysis suggests that the walls contain 10–30% of ordered material covered with amorphous carbon. High-resolution electron microscopy reveals that the ordered phase consists of nearly parallel layers of graphene. [6] The amorphous fraction can be converted into well-ordered graphite by annealing the cones at temperatures about 2700 °C. [1]

The remarkable feature of the open carbon nanocones produced by the CBH process is their almost ideal shape, with straight walls and circular bases. Non-ideal cones are also observed, but these are exceptions. One such deviation was a "double" cone, which appeared as if a cone started to grow from its tip with a certain apex angle (e.g. 84°), but then abruptly changed the apex angle (e.g. to 39°) in a single point on its surface, thus producing a break in the observed cross-section of the cone. Another anomaly was a cone with the apex extended from a point to a line segment, as in the expanded coffee filter (flat form is shown in the picture). [1]

Statistical distribution of the apex values measured over 554 cones grown on natural graphite. Carbon cone angle2.PNG
Statistical distribution of the apex values measured over 554 cones grown on natural graphite.

Other cones

Carbon cones have also been observed, since 1968 or even earlier, [8] on the surface of naturally occurring graphite. Their bases are attached to the graphite and their height varies between less than 1 and 40 micrometers. Their walls are often curved and are less regular than those of the laboratory made nanocones. The distribution of their apex angle also shows a strong feature at 60°, but other expected peaks, at 20° and 40°, are much weaker and the distribution is somewhat broader for large angles. This difference is attributed to the different wall structure of the natural cones. Those walls are relatively irregular and contain numerous line defects (positive-wedge disclinations). This breaks down the angular requirement for a seamless cone and therefore broadens the angular distribution. [7]

Potential applications

Sequential electron micrographs showing the process of capping a gold needle with a CBH carbon nanocone (top left) Capping Au tip with C nanocone.jpg
Sequential electron micrographs showing the process of capping a gold needle with a CBH carbon nanocone (top left)

Carbon nanocones have been used to cap ultrafine gold needles. Such needles are widely used in scanning probe microscopy owing to their high chemical stability and electrical conductivity, but their tips are prone to mechanical wear due to the high plasticity of gold. Adding a thin carbon cap mechanically stabilizes the tip without sacrificing its other properties. [9]

Related Research Articles

Carbon Chemical element, symbol C and atomic number 6

Carbon is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Carbon makes up only about 0.025 percent of Earth's crust. Three isotopes occur naturally, 12C and 13C being stable, while 14C is a radionuclide, decaying with a half-life of about 5,730 years. Carbon is one of the few elements known since antiquity.

Carbon nanotube Allotropes of carbon with a cylindrical nanostructure

Carbon nanotubes (CNTs) are tubes made of carbon with diameters typically measured in nanometers.

Fullerene Allotrope of carbon

A fullerene is an allotrope of carbon whose molecule consists of carbon atoms connected by single and double bonds so as to form a closed or partially closed mesh, with fused rings of five to seven atoms. The molecule may be a hollow sphere, ellipsoid, tube, or many other shapes and sizes. Graphene, which is a flat mesh of regular hexagonal rings, can be seen as an extreme member of the family.

Allotropes of carbon Materials made only out of carbon

Carbon is capable of forming many allotropes due to its valency. Well-known forms of carbon include diamond and graphite. In recent decades, many more allotropes have been discovered and researched, including ball shapes such as buckminsterfullerene and sheets such as graphene. Larger-scale structures of carbon include nanotubes, nanobuds and nanoribbons. Other unusual forms of carbon exist at very high temperatures or extreme pressures. Around 500 hypothetical 3‑periodic allotropes of carbon are known at the present time, according to the Samara Carbon Allotrope Database (SACADA).

Graphene Hexagonal lattice made of carbon atoms

Graphene is an allotrope of carbon consisting of a single layer of atoms arranged in a two-dimensional honeycomb lattice nanostructure. The name is derived from "graphite" and the suffix -ene, reflecting the fact that the graphite allotrope of carbon contains numerous double bonds.

Transmission Electron Aberration-Corrected Microscope

Transmission Electron Aberration-Corrected Microscope (TEAM) is a collaborative research project between four US laboratories and two companies. The project's main activity is design and application of a transmission electron microscope (TEM) with a spatial resolution below 0.05 nanometers, which is roughly half the size of an atom of hydrogen.

Boudouard reaction

The Boudouard reaction, named after Octave Leopold Boudouard, is the redox reaction of a chemical equilibrium mixture of carbon monoxide and carbon dioxide at a given temperature. It is the disproportionation of carbon monoxide into carbon dioxide and graphite or its reverse:

Carbon nanofiber

Carbon nanofibers (CNFs), vapor grown carbon fibers (VGCFs), or vapor grown carbon nanofibers (VGCNFs) are cylindrical nanostructures with graphene layers arranged as stacked cones, cups or plates. Carbon nanofibers with graphene layers wrapped into perfect cylinders are called carbon nanotubes.

Stone–Wales defect Bond transition dependent defect in the structure of molecular materials

A Stone–Wales defect is a crystallographic defect that involves the change of connectivity of two π-bonded carbon atoms, leading to their rotation by 90° with respect to the midpoint of their bond. The reaction commonly involves conversion between a naphthalene-like structure into a fulvalene-like structure, that is, two rings that share an edge vs two separate rings that have vertices bonded to each other.

Carbon nanobud Synthetic allotrope of carbon combining carbon nanotube and a fullerene

In nanotechnology, a carbon nanobud is a material that combines carbon nanotubes and spheroidal fullerenes, both allotropes of carbon, in the same structure, forming "buds" attached to the tubes. Carbon nanobuds were discovered and synthesized in 2006.

A carbon–nitrogen bond is a covalent bond between carbon and nitrogen and is one of the most abundant bonds in organic chemistry and biochemistry.

The Kværner process or the Kværner carbon black and hydrogen process (CB&H) is a method of producing carbon black and hydrogen gas from hydrocarbons such as methane, natural gas and biogas with no greenhouse gas pollution. The process was developed in the 1980s by the Norwegian engineering firm Kværner, and was first commercially exploited in 1999. Further refinement enabled the methane pyrolysis process for implementation at high-volume and low-cost.

Optical properties of carbon nanotubes Optical properties of the material

The optical properties of carbon nanotubes are highly relevant for materials science. The way those materials interact with electromagnetic radiation is unique in many respects, as evidenced by their peculiar absorption, photoluminescence (fluorescence), and Raman spectra.

Graphite oxide

Graphite oxide (GO), formerly called graphitic oxide or graphitic acid, is a compound of carbon, oxygen, and hydrogen in variable ratios, obtained by treating graphite with strong oxidizers and acids for resolving of extra metals. The maximally oxidized bulk product is a yellow solid with C:O ratio between 2.1 and 2.9, that retains the layer structure of graphite but with a much larger and irregular spacing.

Rodney S. Ruoff

Rodney S. "Rod" Ruoff is an American physical chemist and nanoscience researcher. He is one of the world experts on carbon materials including carbon nanostructures such as fullerenes, nanotubes, graphene, diamond, and has had pioneering discoveries on such materials and others. Ruoff received his B.S. in Chemistry from the University of Texas at Austin (1981) and his Ph.D. in Chemical Physics at the University of Illinois-Urbana (1988). After a Fulbright Fellowship at the MPI fuer Stroemungsforschung in Goettingen, Germany (1989) and postdoctoral work at the IBM T. J. Watson Research Center (1990–91), Ruoff became a staff scientist in the Molecular Physics Laboratory at SRI International (1991-1996). He is currently UNIST Distinguished Professor at the Ulsan National Institute of Science and Technology (UNIST), and the director of the Center for Multidimensional Carbon Materials, an Institute for Basic Science Center located at UNIST.

Graphyne

Graphyne is an allotrope of carbon. Its structure is one-atom-thick planar sheets of sp and sp2-bonded carbon atoms arranged in crystal lattice. It can be seen as a lattice of benzene rings connected by acetylene bonds. Depending on the content of acetylene groups, graphyne can be considered a mixed hybridization, spn, where 1 < n < 2, and thus differs from the hybridization of graphene and diamond.

A rapidly increasing list of graphene production techniques have been developed to enable graphene's use in commercial applications.

Discovery of graphene

Single-layer graphene was explored theoretically by P. R. Wallace in 1947. It was first unambiguously produced and identified in 2004, by the group of Andre Geim and Konstantin Novoselov, though they credit Hanns-Peter Boehm and his co-workers for the experimental discovery of graphene in 1962. Boehm et al. introduced the term graphene in 1986.

Epitaxial graphene growth on silicon carbide (SiC) by thermal decomposition is a method to produce large-scale few-layer graphene (FLG). Graphene is one of the most promising nanomaterials for the future because of its various characteristics, like strong stiffness and high electric and thermal conductivity. Still, reproducible production of Graphene is difficult, thus many different techniques have been developed. The main advantage of epitaxial graphene growth on silicon carbide over other techniques is to obtain graphene layers directly on a semiconducting or semi-insulating substrate which is commercially available.

References

  1. 1 2 3 4 5 6 7 Naess, Stine Nalum; Elgsaeter, Arnljot; Helgesen, Geir; Knudsen, Kenneth D (2009). "Carbon nanocones: wall structure and morphology". Science and Technology of Advanced Materials. 10 (6): 065002. Bibcode:2009STAdM..10f5002N. doi:10.1088/1468-6996/10/6/065002. PMC   5074450 . PMID   27877312.
  2. ↑ EP 1017622,Lynum S, Hugdahl J, Hox K, Hildrum R and Nordvik M,"Production of micro domain particles by use of a plasma process",issued 2000-07-12
  3. ↑ Ge, Maohui; Sattler, Klaus (1994). "Observation of fullerene cones". Chemical Physics Letters. 220 (3–5): 192. Bibcode:1994CPL...220..192G. doi:10.1016/0009-2614(94)00167-7.
  4. ↑ Terrones, Humberto (1994). "Curved graphite and its mathematical transformations". Journal of Mathematical Chemistry. 15: 143. doi:10.1007/BF01277556.
  5. ↑ Balaban, A; Klein, D; Liu, X (1994). "Graphitic cones". Carbon. 32 (2): 357. doi:10.1016/0008-6223(94)90203-8.
  6. 1 2 Krishnan, A.; Dujardin, E.; Treacy, M. M. J.; Hugdahl, J.; Lynum, S.; Ebbesen, T. W. (1997). "Graphitic cones and the nucleation of curved carbon surfaces". Nature. 388 (6641): 451. Bibcode:1997Natur.388..451K. doi: 10.1038/41284 .
  7. 1 2 Jaszczak, J (2003). "Naturally occurring graphite cones" (PDF). Carbon. 41 (11): 2085. doi:10.1016/S0008-6223(03)00214-8.
  8. ↑ Gillot, J; Bollmann, W; Lux, B (1968). "181. Cigar-shaped conical crystals of graphite". Carbon. 6 (2): 237. doi:10.1016/0008-6223(68)90485-5.
  9. 1 2 Cano-Marquez, Abraham G.; Schmidt, Wesller G.; Ribeiro-Soares, Jenaina; Gustavo Cançado, Luiz; Rodrigues, Wagner N.; Santos, Adelina P.; Furtado, Clascidia A.; Autreto, Pedro A.S.; Paupitz, Ricardo; Galvão, Douglas S.; Jorio, Ado (2015). "Enhanced Mechanical Stability of Gold Nanotips through Carbon Nanocone Encapsulation". Scientific Reports. 5: 10408. Bibcode:2015NatSR...510408C. doi:10.1038/srep10408. PMC   4470435 . PMID   26083864.
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