(7) Rotation angle of the symmetry vector = ψ = 2 π/ N (in radians) (5) Number of hexagons in the unit cell = N = (2 * ( n 2 + m 2 + n * m)/ dR) (3) Length of chiral vector = L = a √ ( n 2 + m 2 + n * m), where a is the lattice constant Many parameters and vectors can have an effect on nanotube structures such as the following : When n − m is a multiple of 3, then the nanotube is described as ‘metallic’ or highly conducting nanotubes, and if not, then the nanotube is a semimetallic or semiconductor.Īt all times, the armchair form is metallic, whereas other forms can make the nanotube a semiconductor. Where a = 1.42 × 3 Å corresponds to the lattice constant in the graphite sheet. In a bundle structure, SWCNTs are hexagonally organized to form a crystal-like construction. SWCNTs usually can come together and form bundles (ropes). On other hand, SWCNT diameters differ from 0.4 to 2 to 3 nm, and their length is typically of the micrometer range. The role of the half-fullerene molecules (pentagonal ring defect) is to help in closing of the tube at the two ends. Both tips of MWCNT usually have closed and the ends are capped by dome-shaped half-fullerene molecules (pentagonal defects), and axial size differs from 1 μm up to a few centimeter. ĭepending on the number of layers, the inner diameter of MWCNTs diverges from 0.4 nm up to a few nanometers and outer diameter varies characteristically from 2 nm up to 20 to 30 nm. The real-space analysis of multiwall nanotube images has shown a range of interlayer spacing (0.34 to 0.39 nm). A few to a few tens of concentric cylinders with the regular periodic interlayer spacing locate around ordinary central hollow and made MWCNTs. The sp 2 hybridization of carbon builds a layered construction with weak out-of-plane bonding of the van der Waals form and strong in-plane bounds. Nanotubes with single well are described as single-wall carbon nanotubes (SWCNTs) and were first reported in 1993, while the ones with more than one well are multiwall carbon nanotubes (MWCNTs) and were first discovered in 1991 by Iijima (Figure 1).Ĭarbon nanotubes: structure and propertiesĬarbon can bond in different ways to construct structures with completely different properties. It can divide into a single well or multiple wells. Carbon nanotube is theoretically distinct as a cylinder fabricated of rolled up grapheme sheet. In graphene, carbon atoms are densely organized in a regular sp 2-bonded atomic-scale honeycomb (hexagonal) pattern, and this pattern is a basic structure for other sp 2 carbon bonded materials (allotropes) such as fullerenes and carbon nanotubes. Most of the physical properties of carbon nanotubes derive from graphene. Discoveries of very constant nanometer size sp 2 carbon bonded materials such as graphene, fullerenes, and carbon nanotubes have encouraged to make inquiries in this field. It can hybridize in sp, sp 2, or sp 3 forms. Carbon is the chemical element with atomic number 6 and has six electrons which occupy 1 s 2, 2 s 2, and 2p 2 atomic orbital.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |