reverse engineering How we made the carbon nanotube transistor Developments in nanotechnology in the 1990s made building electronic devices from single molecules a possibility. Cees Dekker recounts how his team created a room-temperature transistor based on a single carbon nanotube. Cees Dekker hat if, instead of using low-temperature experiments by a Drain electrode conventional top-down silicon brilliant PhD student in my group, Source electrode electronics, transistors could Sander Tans (now a valued colleague W Nanotube be built from the bottom up using single and professor at Delft University of molecule organic molecules as the switching Technology with an active research lab at elements? This idea, which became the basis AMOLF in Amsterdam), we showed that of today’s field of molecular electronics, carbon nanotubes were genuine quantum Silicon oxide first emerged in the 1970s. It was only in the wires with very long (micrometres) 1990s though, when nanotechnology had electronic coherence lengths — confirming Silicon gate advanced to a level where single molecules theoretical predictions of metallic could be manipulated, that the first behaviour. Around the same time, experimental devices began to appear. the group of Paul McEuen, who was then In 1993, as a young and eager associate based at the University of California, professor at Delft University of Technology, Berkeley, showed similar results on ropes Fig. 1 | The first carbon nanotube transistor. I had initially focused the research efforts of bundled nanotubes. Depending on the Atomic force microscopy image of the device. of my group on measuring the electrical wrapping angle, nanotubes can come in The conductance of an individual semiconducting conductance of a single conducting- metallic or semiconducting variants, a carbon nanotube (red), connected to source polymer molecule. Within two years, we prediction that we and Charles Lieber’s and drain electrodes (yellow), can be modulated had created a device in which a single wire group at Harvard University independently by a voltage on the silicon back gate (light-blue of a phthalocyaninepolysiloxane polymer confirmed using scanning tunnelling bottom), creating a field-effect transistor. was connected between two closely spaced spectroscopy experiments. Figure adapted from P. L. McEuen, Nature 393, metal nanoelectrodes. There was one At this time, we also realized that 15–17 (1998), Springer Nature Ltd. problem though — we did not observe any it should be possible to use a single measurable electrical conduction from the semiconducting carbon nanotube to make single polymer molecules. We concluded a transistor — and we set out to make it. that at the single-molecule level, conducting We stretched individual semiconducting nanotube junctions that acted as rectifying polymers were actually not such great nanotubes across metallic electrodes and diodes, and coupled multiple transistors into conductors, which was rather disappointing. used the underlying silicon substrate as small proof-of-principle electronic circuits. We thus broadened our view to try to find a gate electrode, establishing the basic In the years following these discoveries, more promising molecules. three-terminal layout of a field-effect my research interests shifted to biophysics Back in 1991, Sumio Iijima of the NEC transistor (Fig. 1). The current–voltage and nanobiology, and I became less involved Corporation had reported the synthesis curves showed significant modulations with in the development of nanotube electronics. of carbon nanotubes. Band structure gate voltage, even at room temperature, The focus of many researchers in the field calculations suggested that these nanotubes which was consistent with band bending also shifted to graphene (where, funnily could exhibit metallic band conduction. in a ~0.6 eV bandgap semiconducting enough, the first graphene ribbons were This would be a significant advantage nanotube. These data also showed that described as ‘nanotubes that are cut open over the conducting polymers we had the conductance could be modulated by along their length’) after the discovery of explored, which were, in fact, disordered six orders of magnitude by changing the the two-dimensional material in 2004. But semiconductors offering merely variable- gate voltage. The results of this work — a carbon nanotubes have remained a research range hopping conductivity. Unfortunately, room-temperature transistor made from a topic of considerable interest to many. Indeed, for years after Iijima’s report, the production single carbon nanotube molecule — were the outlook on using carbon nanotubes to of clean nanotubes was cumbersome. In published in Nature in May 1998. build practical devices, in areas such as radio- 1996, however, the group of Richard Smalley Our work was quickly followed up by frequency electronics, digital electronics and at Rice University managed to produce others, most notably by Phaedon Avouris flexible electronics, remains bright. ❐ single-walled carbon nanotubes at high and colleagues at IBM, who in October yield. Shortly after, I contacted Smalley, and 1998 published their findings on transistors Cees Dekker we decided to join forces to measure the made from single- and multi-walled carbon Department of Bionanoscience, Delf University of transport through a single carbon nanotube. nanotubes in Applied Physics Letters. Many Technology, Delf, Te Netherlands. This yielded a breakthrough. Within related developments followed, where e-mail: [email protected] only a few months, we were able to our group established different transistor measure transport through an individual variants such as single-electron transistors Published online: 13 September 2018 single-walled carbon nanotube. Based on at room temperature and intramolecular https://doi.org/10.1038/s41928-018-0134-9 518 NATURE ELECTRONICS | VOL 1 | SEPTEMBER 2018 | 518 | www.nature.com/natureelectronics.