Nanocarbon. NANO54 Foothill College. Carbon Engineering. Current trends in fullerene chemistry and nanochemistry. Allotropy and Allotropes of Carbon (family). http://chemistry.tutorvista.com/inorganic-chemistry/allotropes-of-carbon.html. Allotropes of Carbon.
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Current trends in fullerene chemistry and nanochemistry
There are several allotropes of carbon of which the best known are graphite, diamond, and amorphous carbon. The physical properties of carbon vary widely with the allotropic form. For example, diamond is highly transparent, while graphite is opaque and black. Diamond is among the hardest materials known, while graphite is soft enough to form a streak on paper. Diamond has a very low electrical conductivity, while graphite is a very good conductor. Under normal conditions, diamond has the highest thermal conductivity of all known materials. More recent discoveries of carbon allotropes include fullerenes (buckyballs), carbon nanotubes (single and mutliwalled) and carbon nanospheres, also known as ‘nano-onion’ (graphitic) carbon.
The (n,m) nanotube naming scheme can be thought of as a vector (Ch) in an infinite graphene sheet that describes how to "roll up" the graphene sheet to make the nanotube. T denotes the tube axis, and a1 and a2 are the unit vectors of graphene in real space
A SWNT can be rolled by a sheet of graphite, for example the armchair type SWNT
Extended sp2 hybridized carbon and p-p* network
Lattice constants m and n
Delocalized pi e- bonding network
from a ‘structure’ to a ‘system’
From the network architecture, add interactions, observe emergent properties
Partial list of fabrication techniques for various types of carbon nanostructures
Onion-like carbon (OLC) was fabricated by annealing nanodiamond at 1000 °C for 2 hours in low vacuum (1 Pa). The OLC was characterized by X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy and differential scanning calorimetry (DSC). The experimental results show that the OLC exhibits similarity to the original nanodiamond particles in shape. The size of the OLC is found to be approximately 5 nm. The transformation mechanism of the OLC from nanodiamond was discussed also.
Nanocarbon structures include common allotropes of carbon from sp2 and sp3 bonding. Graphite, graphene, fullerenes, carbon nanotubes (single and multiwall) and more recently nanospheres. The novel structure described in this work comprises a mixture of sp3 and sp2 hybridized carbon, thought to be a nucleus (seed) of sp3 diamond wrapped with fullerene structures (corannulene) also described as ‘graphitic flakes’ thought to be the building blocks of nanospheres. There are multiple routes to nanocarbon synthesis, including carbon furnaces, Chemical Vapor Deposition (CVD), and thermal decomposition . In each of these processes, intermediate carbon structures interact, fuse, etc. to form more complex nanostructures.
Combustion synthesis of fullerenes and fullerenic nanostructures. Courtesy Vander Sande Lab. MIT Open Courseware - http://ocw.mit.edu/courses/materials-science-and-engineering/
Fullerenes were discovered by Kroto et al. in 1985 as products of the evaporation of carbon into an inert gas . They consist of closed spherical shells comprised only of carbon atoms. This special structure results in unusual physical and chemical properties with a large potential for applications such as superconductors, sensors, catalyst, optical and electronic devices, polymers, and biological and medical applications. Fullerenes can also be formed in low-pressure fuel-rich flames of certain hydrocarbons [2,3,4], the highest yields being obtained under conditions of substantial soot formation. Other interesting classes of fullerenic or curved-layer carbon that can also be found in fullerene producing systems are nanostructures having tubular, spheroidal, or other shapes and consisting of onion-like or nested closed shells [5,6,7,8] and soot particles having considerable curved-layer content [9,10,11]. More information on the formation of fullerenic carbon in flames under different conditions is needed to understand the formation mechanisms and kinetics and to enable the design of practical systems for large-scale production.
A simple, low cost and continuous growth method for the production of well graphitized multi-wall carbon nanotubes, combines the underwater growth with the use of an AC power supply and computer control. An AC electric arc is generated between two identical carbon rods of 6 mm in diameter, submerged in deionized water. Two computer controlled stepper motors are used to regulate the distance between the electrodes. At a voltage of 40 V the arc is stable in the range of 85–45 A. At lower current values a higher fraction of carbon nanotubes is obtained in the product. There is no product on the electrodes, the deposit peels off the actual cathode into the water in the next half cycle when the role of the electrodes is reversed. No vacuum is needed, a continuous flow of water makes easy the removal of the product from the system. This makes our method suitable for up-scaling. http://www.nanotechnology.hu/results/arc.html
Laser ablation of graphite doped with 1-2% metal ions such as nickel and cobalt produces loose nanotube material called single walled nanotubes (SWNTs) and single walled nanohorns (SWNHs). These short pulse duration lasers, however, produced only a few tens of watts and a rather low vaporization rate of about 0.2g/hour.
The plasma plume created above a graphite target irradiated by a KrF laser beam (248 nm) has been investigated using three experimental methods: ion detection, time and spatially resolved emission spectroscopy and double Langmuir probe. Measurements give information on the energetic distribution of ionic species, on the kinetic temperature of the gas and on the electronic density of the plasma plume. Carbon thin films have been deposited on silicon substrates: for high fluence values (above 1000 J cm−2) and low temperature (30°C), the films are harder than c-BN, their refractive index is 2.4, and XPS analysis gives spectra with a high sp3 configuration
Nanocrystalline diamond thin films have been prepared using hot filament CVD technique with a mixture of CH4/H2/Ar as the reactant gas. We demonstrated that the ratio of H2 to Ar in the reactant gas plays an important role in control of the grain size of diamonds and the growth of the nanocrystalline diamonds. In addition, we have investigated the growth of carbon nanotubes from catalytic CVD using a hydrocarbon as the reactant gas. Furthermore, focused ion beam technique has been developed to control the growth of carbon nanotubes individually. Fig. 1. Surface morphology of diamond thin films as a function of methane concentrations. (a) 3% of CH4, (b) 4% of CH4, and (c) 5% of CH4. The corresponding Raman spectra are shown on the right panel
L. Chow et al. / Thin Solid Films 368 (2000) 193-197
Chemical vapor deposition of diamond has received a great deal of attention in the materials sciences because it allows many new applications of diamond that had previously been considered too difficult to make economical. CVD diamond growth typically occurs under low pressure (1–27 kPa; 0.145–3.926 psi; 7.5-203 Torr) and involves feeding varying amounts of gases into a chamber, energizing them and providing conditions for diamond growth on the substrate. The gases always include a carbon source, and typically include hydrogen as well, though the amounts used vary greatly depending on the type of diamond being grown. Energy sources include hot filament, microwave power, and arc discharges, among others.
PAHs are one of the most widespread organic pollutants. In addition to their presence in fossil fuels they are also formed by incomplete combustion of carbon-containing fuels such as wood, coal, diesel, fat, tobacco, and incense. Different types of combustion yield different distributions of PAHs in both relative amounts of individual PAHs and in which isomers are produced. Crystal structure of a hexa-tert-butyl derivatized hexa-peri-hexabenzo(bc,ef,hi,kl,no,qr)coronene, reported by Klaus Müllen and co-workers. The tert-butyl groups make this compound soluble in common solvents such as hexane, in which the unsubstituted PAH is insoluble. Other PAH structures can include naphthalene, pyrene, and benzene additions to pyrene.
Nanocarbon forms in a series of steps with increasing time and temperature
Carbon nanostructures including nanotubes, fullerenes, and nanospheres are comprised of ‘graphitic motifs’ which combine at varied geometries to produce extended networks of sp2 carbon. PAH motifs are thought to form in combustion flames, and also during annealing of amorphous carbon (soot etc.). During high temperature annealing, PAH motifs are hypothesized to ‘fuse’ and additionally drive off hydrogen along basal planes. Conversion of amorphous carbon to PAH can be both an external and internal process.
Selected samples of heat-treated carbon black
Structure being analyzed
Carbon phase state
Diamond Like Carbon (DLC)
(C-C / C-H), C=C, branching
Atomic / lattice imaging
Characterization of Carbon Nanotubes by Raman spectroscopy
Characterization of Carbon Nanotubes by Raman spectroscopy
Typical Soot Soot Annealed at 2000 Celsius