Carbon peapod is a hybrid nanomaterial consisting of spheroidal fullerenes encapsulated within a carbon nanotube. It is named due to their resemblance to the seedpod of the pea plant. Since the properties of carbon peapods differ from those of nanotubes and fullerenes, the carbon peapod can be recognized as a new type of a self-assembled graphitic structure. [4] Possible applications of nano-peapods include nanoscale lasers, single electron transistors, spin-qubit arrays for quantum computing, nanopipettes, and data storage devices thanks to the memory effects and superconductivity of nano-peapods. [5] [6]
Single-walled nanotubes (SWNTs) were first seen in 1993 as cylinders rolled from a single graphene sheet. In 1998, the first peapod was observed by Brian Smith, Marc Monthioux and David Luzzi. [7] The idea of peapods came from the structure that was produced inside a transmission electron microscope in 2000. [4] They were first recognized in fragments obtained by a pulsed-laser vaporization synthesis followed by treatment with an acid and annealing. [8] [9] [10]
Carbon peapods can be naturally produced during carbon nanotube synthesis by pulsed laser vaporization. C60 fullerene impurities are formed during the annealing treatment and acid purification, and enter the nanotubes through defects or vapor-phase diffusion. [11] Fullerenes within a nanotube are only stabilized at a diameter difference of 0.34 nm or less, and when the diameters are nearly identical, the interacting energy heightens to such a degree (comparable to 0.1 GPa) that the fullerenes become unable to be extracted from the SWNT even under high vacuum. [4] The encapsulated fullerenes have diameters close to that of C60 and form a chain inside the tube. Controlled production of carbon peapods allow for greater variety in both the nanotube structure and the fullerene composition. Varying elements can be incorporated into a carbon peapod through doping and will dramatically affect the resulting thermal and electrical conductivity properties.
The existence of carbon peapods demonstrates further properties of carbon nanotubes, such as potential to be a stringently controlled environment for reactions. C60 molecules normally form amorphous carbon when heated to 1000–1200 °C under ambient conditions; when heated to such a high temperature within a carbon nanotube, they instead merge in an ordered manner to form another SWNT, thus creating a double-wall carbon nanotube. [4] Owing to the ease with which fullerenes can encapsulate or be doped with other molecules and the transparency of nanotubes to electron beams, carbon peapods can also serve as nano-scale test tubes. After fullerenes containing reactants diffuse into an SWNT, a high-energy electron beam can be used to induce high reactivity, thus triggering formation of C60 dimers and merging of their contents. [12] [13] Additionally, due to the enclosed fullerenes being limited to only a one-dimensional degree of mobility, phenomena such as diffusion or phase transformations can easily be studied. [11]
The diameter of carbon peapods range from ca. 1 to 50 nanometers. Various combinations of fullerene C60 sizes and nanotube structures can lead to various electric conductivity property of carbon peapods due to orientation of rotations. For example, the C60 @ (10,10) is a good superconductor and the C60 @ (17,0) peapod is a semiconductor. The calculated band gap of C60 @ (17,0) equals 0.1 eV. [14] Research into their potential as semiconductors is still ongoing. Although both the doped fullerides and ropes of SWNTs are superconductors, unfortunately, the critical temperatures for the superconducting phase transition in these materials are low. There are hopes that carbon nano-peapods could be superconducting at room temperature. [15]
With chemical doping, the electronic characteristics of peapods can be further adjusted. When carbon peapod is doped with alkali metal atoms like potassium, the dopants will react with the C60 molecules inside the SWNT. It forms a negatively charged C606− covalently bound, one-dimensional polymer chain with metallic conductivity. Overall, the doping of SWNTs and peapods by alkali metal atoms actively enhances the conductivity of the molecule since the charge is relocated from the metal ions to the nanotubes. [16] Doping carbon nanotubes with oxidized metal is another way to adjust conductivity. It creates a very interesting high temperature superconducting state as the Fermi level is significantly reduced. A good application would be the introduction of silicon dioxide to carbon nanotubes. It constructs memory effect as some research group has invented ways to create memory devices based on carbon peapods grown on Si/SiO2 surfaces. [17] [18]
A carbon nanotube (CNT) is a tube made of carbon with a diameter in the nanometer range (nanoscale). They are one of the allotropes of carbon.
A fullerene is an allotrope of carbon whose molecules consist 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 molecules may be hollow spheres, ellipsoids, tubes, or other shapes.
Buckminsterfullerene is a type of fullerene with the formula C60. It has a cage-like fused-ring structure (truncated icosahedron) made of twenty hexagons and twelve pentagons, and resembles a football. Each of its 60 carbon atoms is bonded to its three neighbors.
Endohedral fullerenes, also called endofullerenes, are fullerenes that have additional atoms, ions, or clusters enclosed within their inner spheres. The first lanthanum C60 complex called La@C60 was synthesized in 1985. The @ (at sign) in the name reflects the notion of a small molecule trapped inside a shell. Two types of endohedral complexes exist: endohedral metallofullerenes and non-metal doped fullerenes.
Hybrid solar cells combine advantages of both organic and inorganic semiconductors. Hybrid photovoltaics have organic materials that consist of conjugated polymers that absorb light as the donor and transport holes. Inorganic materials in hybrid cells are used as the acceptor and electron transporter in the structure. The hybrid photovoltaic devices have a potential for not only low-cost by roll-to-roll processing but also for scalable solar power conversion.
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.
Fullerene chemistry is a field of organic chemistry devoted to the chemical properties of fullerenes. Research in this field is driven by the need to functionalize fullerenes and tune their properties. For example, fullerene is notoriously insoluble and adding a suitable group can enhance solubility. By adding a polymerizable group, a fullerene polymer can be obtained. Functionalized fullerenes are divided into two classes: exohedral fullerenes with substituents outside the cage and endohedral fullerenes with trapped molecules inside the cage.
Carbon nanotubes (CNTs) are cylinders of one or more layers of graphene (lattice). Diameters of single-walled carbon nanotubes (SWNTs) and multi-walled carbon nanotubes (MWNTs) are typically 0.8 to 2 nm and 5 to 20 nm, respectively, although MWNT diameters can exceed 100 nm. CNT lengths range from less than 100 nm to 0.5 m.
In nanotechnology, a carbon nanobud is a material that combines carbon nanotubes and spheroidal fullerenes, both allotropes of carbon, forming "buds" attached to the tubes. Carbon nanobuds were discovered and synthesized in 2006.
Alex K. Zettl is an American experimental physicist, educator, and inventor.
Selective chemistry of single-walled nanotubes is a field in Carbon nanotube chemistry devoted specifically to the study of functionalization of single-walled carbon nanotubes.
Organic photovoltaic devices (OPVs) are fabricated from thin films of organic semiconductors, such as polymers and small-molecule compounds, and are typically on the order of 100 nm thick. Because polymer based OPVs can be made using a coating process such as spin coating or inkjet printing, they are an attractive option for inexpensively covering large areas as well as flexible plastic surfaces. A promising low cost alternative to conventional solar cells made of crystalline silicon, there is a large amount of research being dedicated throughout industry and academia towards developing OPVs and increasing their power conversion efficiency.
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.
Carbon nanotubes (CNTs) are very prevalent in today's world of medical research and are being highly researched in the fields of efficient drug delivery and biosensing methods for disease treatment and health monitoring. Carbon nanotube technology has shown to have the potential to alter drug delivery and biosensing methods for the better, and thus, carbon nanotubes have recently garnered interest in the field of medicine.
C70 fullerene is the fullerene molecule consisting of 70 carbon atoms. It is a cage-like fused-ring structure which resembles a rugby ball, made of 25 hexagons and 12 pentagons, with a carbon atom at the vertices of each polygon and a bond along each polygon edge. A related fullerene molecule, named buckminsterfullerene (or C60 fullerene) consists of 60 carbon atoms.
Techniques have been developed to produce carbon nanotubes (CNTs) in sizable quantities, including arc discharge, laser ablation, high-pressure carbon monoxide disproportionation, and chemical vapor deposition (CVD). Most of these processes take place in a vacuum or with process gases. CVD growth of CNTs can occur in a vacuum or at atmospheric pressure. Large quantities of nanotubes can be synthesized by these methods; advances in catalysis and continuous growth are making CNTs more commercially viable.
A cycloparaphenylene is a molecule that consists of several benzene rings connected by covalent bonds in the para positions to form a hoop- or necklace-like structure. Its chemical formula is [C6H4]n or C
6nH
4n Such a molecule is usually denoted [n]CPP where n is the number of benzene rings.
Fullerides are chemical compounds containing fullerene anions. Common fullerides are derivatives of the most common fullerenes, i.e. C60 and C70. The scope of the area is large because multiple charges are possible, i.e., [C60]n− (n = 1, 2...6), and all fullerenes can be converted to fullerides. The suffix "-ide" implies their negatively charged nature.
Fullerene whiskers are thin rods composed of fullerene molecules, such as C60, C70, or their mixtures. Hollow fullerene whiskers are called fullerene tubes. Such structures typically have a diameter of a few micrometers. When the diameter becomes smaller than 1 micron, the corresponding structures are called fullerene nanowhiskers or fullerene nanotubes.