Researchers at Empa [Switzerland] and the Max Planck Institute for Solid State Research have succeeded in "growing" single-wall carbon nanotubes (CNT) with a single predefined structure - and hence with identical electronic properties. And here is how they pulled it off: the CNTs "assembled themselves", as it were, out of tailor-made organic precursor molecules on a platinum surface, as reported by the researchers in the latest issue of the journal "Nature". In future, CNTs of this kind may be used in ultra-sensitive light detectors and ultra-small transistors.
With a diameter of roughly one nanometre, single-wall CNTs (or SWCNTs) need to be considered as quantum structures; the slightest structural changes, such as differences in diameter or in the alignment of the atomic lattice, may result in dramatic changes to the electronic properties: one SWCNT may be metallic, whilst another one with a slightly different structure is a semiconductor. Hence, there is a great deal of interest in reliable methods of making SWCNTs as structurally uniform as possible. In fact, corresponding synthesis concepts were formulated about 15 years ago. However, it is only now that surface physicists at Empa and chemists at the Max Planck Institute have successfully implemented one of these ideas in the laboratory. In the latest issue of "Nature", they describe how, for the first time, it has been possible to “grow" structurally homogenous SWCNTs and, hence, managed to clearly define their electronic properties.
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Scanning tunneling microscopy images the precursor, the «folded» end cap, and the resulting carbon nanotube, together with the corresponding structural models. (Source: Empa / Juan Ramon Sanchez Valencia)
By means of "bottom-up" synthesis, the Empa researchers managed to produce specific nanostructures such as defined chains of "buckyballs" (essentially, CNTs shrunk into ball form) or flat nanoribbons on gold substrates. "The great challenge was to find the suitable starting molecule that would also actually 'germinate' on a flat surface to form the correct seed," says Fasel, whose team has gained broad expertise in the field of molecular self-organisation over the years. Finally, their colleagues at the Max Planck Institute in Stuttgart successfully synthesised the suitable starting molecule, a hydrocarbon with no fewer than 150 atoms.
Nature cover story - Controlled synthesis of single-chirality carbon nanotubes
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With a diameter of roughly one nanometre, single-wall CNTs (or SWCNTs) need to be considered as quantum structures; the slightest structural changes, such as differences in diameter or in the alignment of the atomic lattice, may result in dramatic changes to the electronic properties: one SWCNT may be metallic, whilst another one with a slightly different structure is a semiconductor. Hence, there is a great deal of interest in reliable methods of making SWCNTs as structurally uniform as possible. In fact, corresponding synthesis concepts were formulated about 15 years ago. However, it is only now that surface physicists at Empa and chemists at the Max Planck Institute have successfully implemented one of these ideas in the laboratory. In the latest issue of "Nature", they describe how, for the first time, it has been possible to “grow" structurally homogenous SWCNTs and, hence, managed to clearly define their electronic properties.
By means of "bottom-up" synthesis, the Empa researchers managed to produce specific nanostructures such as defined chains of "buckyballs" (essentially, CNTs shrunk into ball form) or flat nanoribbons on gold substrates. "The great challenge was to find the suitable starting molecule that would also actually 'germinate' on a flat surface to form the correct seed," says Fasel, whose team has gained broad expertise in the field of molecular self-organisation over the years. Finally, their colleagues at the Max Planck Institute in Stuttgart successfully synthesised the suitable starting molecule, a hydrocarbon with no fewer than 150 atoms.
Nature cover story - Controlled synthesis of single-chirality carbon nanotubes
Read more »
