9401 x 6595 px | 79,6 x 55,8 cm | 31,3 x 22 inches | 300dpi
Aufnahmedatum:
2007
Weitere Informationen:
Helicoidal Graphite Hollow Graphitic Nanotubes The synthesis characterisation and properties of the all carbon fullerene molecules has been at the research forefront since their discovery by Kroto et al in 1985 and the subsequent large scale synthesis by Kratschmer et al in 1990 Iijima et al then reported Transmission Electron Microscopy TEM observations of hollow graphitic tubes nanotubes and the large scale nanotube synthesis by Ebbesen and Ajayan has seen an explosive research effort into these unusual graphitic forms TEM observations of graphitic tubes synthesised using pyrolytic methods e g pyrolysis of acetylene over cobalt and their derivatives have revealed fullerene geometries with closed cage arrangements and also other oddly shaped fullerene structures such as bucky onions It is generally recognised that C60 which consists of pentagons and hexagons formed with carbon atoms the pentagons play an essential role in creating the convex plane By wrapping a cylinder in a sheet of graphite we get nanotubes and in a study of the growth of nanotubes Iijima found that heptagons of carbon atoms appear in the negatively curved surface The positive curvature is achieved by inserting pentagons into the graphite sheet This can be visualised below where the pentagonal carbons are shown in red and the heptagonal carbons are shown in yellow Structures incorporating pentagons hexagons and heptagons include torroidal and helical forms Theoretical studies have shown that many of the new graphitic arrangements are very stable in some cases more that C60 itself and related structures appear naturally in certain graphitic materials One derivative helical in structure is analagous to that seen in crystal growth affected by screw disslocations It is felt that nanotubes may act as precursors to closed shell fullerene formation and the recent advances in the fundamental understanding of carbon structures heralds a new age in nanoscale materia
