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 nanometres.
Thus the researchers have proved that, by using made-to-measure molecular "germs", it is possible to clearly predefine the growth (and thus the structure) of long SWCNTs. The SWCNTs synthesised in this study are mirror
|Contact: Martina Peter|
Swiss Federal Laboratories for Materials Science and Technology (EMPA)