Built on columns

The self-assembly of organic molecules into columns leads to the formation of a photoresponsive field-effect transistor

Credit: © 2009 NAS, USA

The size and conducting properties of single-wall carbon nanotubes (SWNTs) make them attractive building blocks for nanoelectronic devices. SWNTs have successfully been exploited in various molecular electronic systems — instead of metal electrodes — circumventing problems associated with gold–thiol junctions.

Now Colin Nuckolls and co-workers from Columbia University, working in collaboration with researchers from China, have constructed a field-effect transistor using molecules that are able to self-assemble within a nanogap created in a SWNT¹. The molecules are polycyclic aromatic hydrocarbons with two separate π systems: a conductive inner core and an insulating shell. On heating, they self-assemble into liquid-crystalline columns that are parallel to the nanogaps and have a diameter similar to that of SWNTs. Owing to the one-dimensional nature of the charge transport through the SWNT electrodes, the device shows improved electronic properties over those that use metallic electrodes.

Moreover, the organic molecules can also be excited by visible light. Intracolumnar transport through the core of the molecules lead to the generation of a reversible photocurrent, suggesting potential applications for solar-energy harvesting. Other high-performance photosensitive nanoscale field-effect transistors could be formed by changing the organic species.