posted on Aug, 10 2014 @ 08:48 PM
Synthesis of structurally pure carbon nanotubes using molecular seeds
For 20 years, carbon nanotubes (CNTs) have been the subject of intensive fundamental as well as applied research. With their extraordinary
mechanical, thermal and electronic properties, these tiny tubes with their graphitic honeycomb lattice have become the paragon of nanomaterials. They
could help to create next-generation electronic and electro-optical components that are smaller than ever before, and thus to achieve even faster
As uniform as possible
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.
For some time, the Empa team working under the direction of Roman Fasel, Head of the "nanotech@surfaces" Laboratory at Empa and Professor of
Chemistry and Biochemistry at the University of Berne, has been investigating the subject of "how molecules can be transformed or joined together to
form complex nanostructures on a surface." For instance, 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.
Now how does the process actually work? In the first step, in a manner reminiscent of origami, the flat starting molecule must be transformed into a
three-dimensional object, the germling. This takes place on a hot platinum surface (Pt(111)) by means of a catalytic reaction in which hydrogen atoms
are split off and new carbon-carbon bonds are formed at very specific locations. The "germ" -- a small, dome-like entity with an open edge that sits
on the platinum surface -- is "folded" out of the flat molecule. This "end cap" forms the "lid" of the growing SWCNT. In a second chemical
process, further carbon atoms are attached, which originate from the catalytic decomposition of ethylene (C2H4) on the platinum surface. They position
themselves on the open edge between the platinum surface and the end cap and raise the cap higher and higher; the nanotube grows slowly upwards.
Only the germ defines the latter's atomic structure, as the researchers were able to demonstrate through the analysis of the vibration modes of the
SWCNTs and scanning tunnel microscope (STM) measurements. Further investigations using the new scanning helium ion microscope (SHIM) at Empa show that
the resulting SWCNTs reach lengths in excess of 300 nanometers.
WOW!! Now I'm not going to pretend I'm an expert on this subject, I'm still learning a lot about the subject.
This is going to be a huge breakthrough for nanotubes & technology!! They still have some things to learn about it but I can't imagine it would take
too long to figure out the rest & get this rolled out.