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Amorphous carbon is an Allotropes of carbon that does not have any
crystalline structure. As with all Amorphous solid materials, some short-range order can be observed, but there is no long-range pattern of atomic positions. Amorphous carbon is often abbreviated to
aC for general amorphous carbon,
aC:H for hydrogenated amorphous carbon, or to
ta-C for tetrahedral amorphous carbon (also called diamond-like carbon).
In mineralogy, amorphous carbon is the name used for coal, soot and other carbon compounds that are neither graphite nor diamond. In a crystallographic sense, however, these materials are not truly amorphous, but are polycrystalline or nanocrystalline materials of graphite or diamond within an amorphous carbon matrix.
In mineralogy
Historically, the term "amorphous carbon" was used to describe carbonaceous materials found in soot and coal that could not be categorized as either diamond or graphite. However, these materials are not truly amorphous, but consist of crystallites of graphite or
diamond with varying amounts of amorphous carbon holding them together, making them technically polycrystalline or nanocrystalline materials. Commercial carbon also usually contains significant quantities of other elements, which may form crystalline impurities.
Coal and
soot are both informally called amorphous carbon. However, both are products of pyrolysis, which does not produce true amorphous carbon under normal conditions. The coal industry divides coal up into various grades depending on the amount of carbon present in the sample compared to the amount of impurities. The highest grade,
Anthracite coal, is about 90 percent carbon and 10% other elements. Bituminous coal is about 75-90 percent carbon, and
lignite is the name for coal that is around 55 percent carbon.
All practical forms of hydrogenated carbon—including cigarette smoke, wood fire smoke, smoked sausages, chimney soot, mined coal such as bitumen and anthracite—contain large amounts of polycyclic aromatic hydrocarbon tars, and are therefore carcinogenic.
In modern science
With the development of modern thin film deposition and growth techniques in the latter half of the 20th century, such as chemical vapour deposition, sputter deposition, and ion beam deposition, it became possible to fabricate truly amorphous carbon materials.
In technical terms, true amorphous carbon has localized π electrons (as opposed to the Aromaticity
π bonds in graphite), and its bonds form with lengths and distances that are inconsistent with any other
allotropy allotropes of carbon. It also contains a high concentration of dangling bonds, which cause deviations in interatomic spacing (as measured using
diffraction) of more than 5%, and noticeable variation in bond angle.
The properties of amorphous carbon films vary depending on the parameters used during deposition. One of the most common ways to characterize amorphous carbon is through the ratio of
sp2 to
sp3 hybridized bonds present in the material. Graphite consists purely of
sp2 hybridized bonds, whereas diamond consists purely of
sp3 hybridized bonds. Materials that are high in
sp3 hybridized bonds are referred to as tetrahedral amorphous carbon (owing to the tetrahedral shape formed by
sp3 hybridized bonds) or as
diamond-like carbon (owing to the similarity of many physical properties to those of diamond).
Experimentally, sp2 to sp3 ratios can be determined by comparing the relative intensities of various spectroscopic peaks (including Electron energy loss spectroscopy, X-ray photoelectron spectroscopy, and Raman Spectroscopy) to those expected for graphite or diamond. In theoretical works, the sp2 to sp3 ratios are often obtained by counting the number of carbon atoms with three bonded neighbors versus those with four bonded neighbors. (Note that this relies heavily on deciding on a 'cutoff' distance that determines whether neighbouring atoms are bonded or not, and is therefore merely used as an indication of the relative sp2-sp3 ratio.)
Although the characterization of amorphous carbon materials by the sp2-sp3 ratio may seem to indicate a one-dimensional range of properties between graphite and diamond, this is most definitely not the case. Research is currently ongoing into ways to characterize and expand on the range of properties offered by amorphous carbon materials.
Amorphous carbon materials may also be stabilized by terminare dangling-π bonds with hydrogen. These materials are then called
hydrogenated amorphous carbon.
See also
References
Amorphous carbon is an
Allotropes of carbon that does not have any
crystalline structure. As with all Amorphous solid materials, some short-range order can be observed, but there is no long-range pattern of atomic positions. Amorphous carbon is often abbreviated to
aC for general amorphous carbon,
aC:H for hydrogenated amorphous carbon, or to
ta-C for
tetrahedral amorphous carbon (also called diamond-like carbon).
In mineralogy, amorphous carbon is the name used for coal, soot and other carbon compounds that are neither graphite nor diamond. In a crystallographic sense, however, these materials are not truly amorphous, but are polycrystalline or nanocrystalline materials of graphite or diamond within an amorphous carbon matrix.
In mineralogy
Historically, the term "amorphous carbon" was used to describe carbonaceous materials found in soot and coal that could not be categorized as either diamond or graphite. However, these materials are not truly amorphous, but consist of crystallites of graphite or diamond with varying amounts of amorphous carbon holding them together, making them technically polycrystalline or nanocrystalline materials. Commercial carbon also usually contains significant quantities of other elements, which may form crystalline impurities.
Coal and
soot are both informally called amorphous carbon. However, both are products of pyrolysis, which does not produce true amorphous carbon under normal conditions. The coal industry divides coal up into various grades depending on the amount of carbon present in the sample compared to the amount of impurities. The highest grade,
Anthracite coal, is about 90 percent carbon and 10% other elements. Bituminous coal is about 75-90 percent carbon, and lignite is the name for coal that is around 55 percent carbon.
All practical forms of hydrogenated carbon—including cigarette smoke, wood fire smoke, smoked sausages, chimney soot, mined coal such as bitumen and anthracite—contain large amounts of
polycyclic aromatic hydrocarbon tars, and are therefore carcinogenic.
In modern science
With the development of modern thin film deposition and growth techniques in the latter half of the 20th century, such as
chemical vapour deposition, sputter deposition, and ion beam deposition, it became possible to fabricate truly amorphous carbon materials.
In technical terms, true amorphous carbon has localized π electrons (as opposed to the
Aromaticity π bonds in graphite), and its bonds form with lengths and distances that are inconsistent with any other
allotropy allotropes of carbon. It also contains a high concentration of dangling bonds, which cause deviations in interatomic spacing (as measured using diffraction) of more than 5%, and noticeable variation in bond angle.
The properties of amorphous carbon films vary depending on the parameters used during deposition. One of the most common ways to characterize amorphous carbon is through the ratio of
sp2 to
sp3 hybridized bonds present in the material. Graphite consists purely of
sp2 hybridized bonds, whereas diamond consists purely of
sp3 hybridized bonds. Materials that are high in
sp3 hybridized bonds are referred to as tetrahedral amorphous carbon (owing to the tetrahedral shape formed by
sp3 hybridized bonds) or as diamond-like carbon (owing to the similarity of many physical properties to those of diamond).
Experimentally, sp2 to sp3 ratios can be determined by comparing the relative intensities of various spectroscopic peaks (including Electron energy loss spectroscopy, X-ray photoelectron spectroscopy, and Raman Spectroscopy) to those expected for graphite or diamond. In theoretical works, the sp2 to sp3 ratios are often obtained by counting the number of carbon atoms with three bonded neighbors versus those with four bonded neighbors. (Note that this relies heavily on deciding on a 'cutoff' distance that determines whether neighbouring atoms are bonded or not, and is therefore merely used as an indication of the relative sp2-sp3 ratio.)
Although the characterization of amorphous carbon materials by the sp2-sp3 ratio may seem to indicate a one-dimensional range of properties between graphite and diamond, this is most definitely not the case. Research is currently ongoing into ways to characterize and expand on the range of properties offered by amorphous carbon materials.
Amorphous carbon materials may also be stabilized by terminare dangling-π bonds with
hydrogen. These materials are then called hydrogenated amorphous carbon.
See also
References
Amorphous carbon - Wikipedia, the free encyclopedia
Amorphous carbon is an allotrope of carbon that does not have any crystalline structure. As with all glassy materials, some short-range order can be observed, but there is no long ...
Amorphous Carbon | Chemical Source
Amorphous Carbon ChemAce Chemical Supply Formula: C Please use this form for amorphous carbon technical and sales information:
Amorphous Carbon and Silicon
Amorphous Carbon and Silicon ... Stewart Clark Thu Oct 31 19:32:00 GMT 1996
IUPAC Compendium of Chemical Terminology
amorphous carbon A carbon material without long-range crystalline order. Short-range order exists, but with deviations of the interatomic distances and/or interbonding angles with ...
AMORPHOUS CARBON EMITTERS FOR FIELD EMISSION DISPLAYS
Principal Investigator: Professor WI Milne: Other Investigators: Professor J Robertson: Researcher Co-investigators: Project Partner: Philips Research Labs
e-Prints Soton - Microstructural studies of copper incorporated ...
The effects of the incorporation of copper on the microstructure of amorphous carbon nitride films has been studied. Copper incorporated amorphous carbon nitride films (a-C : N
e-Prints Soton - Microstructural properties of amorphous carbon ...
Amorphous carbon nitride (a-C:N) films have been prepared on silicon(1 0 0) substrates by direct current magnetron sputtering of graphite using a gaseous mixture of Ar and N2.
Amorphous Carbon Fluoride - What does ACF stand for? Acronyms and ...
Acronym Definition; ACF: Acceptance Check Flight: ACF: Access Control Facility: ACF: Access Control Factor: ACF: Access Control Field: ACF: Access Coordination Fee
Special issue: Amorphous carbon into the next millennium proceedings ...
Special issue: Amorphous carbon into the next millennium proceedings of the second international specialist meeting on amorphous carbon. Shi, X. and Silva, S.R.P. and Milne, W.I ...
Diamond-like Amorphous Carbon - CUED Publications Database
Diamond-like Amorphous Carbon. Robertson, J. (2002) Diamond-like Amorphous Carbon Materials Science and Engineering R: Reports, 37 (4-6). pp. 129-281.
