Fig. 1: Schematic diagram of the nanotube transistors and their light-controlled operation.
NPG Asia Materials featured highlight | doi:
Published online 11 May 2009
Carbon nanotubes: See the light
Inclusion of azafullerenes makes carbon nanotube transistors light-sensitive.
There are high expectations that carbon nanotubes will be key building blocks in future electronic nanodevices. Whilst field-effect transistors made from carbon nanotubes have already been demonstrated, finding ways to control the electronic properties of nanotubes is vital for the creation of complex devices. Yongfeng Li of Tohoku University and colleagues1 demonstrate that the inclusion of azafullerenes—fullerenes with a single carbon replaced with nitrogen—inside single-walled carbon nanotubes leads to a photoswitching effect in nanotube transistors. The conductance of the so-called nanopeapods is very sensitive to the wavelength of incident light, suggesting optical applications such as photodetectors.
In their experiments, Li and colleagues operated their transistors in the dark at a fixed voltage, and then irradiated them with a one second pulse of 400 nm light (Fig.1). This pulse caused the current to drop to around a quarter of its dark-value, and even though there was no further irradiation, the current recovered very slowly to its original level. Further experiments showed pulses of lower energy light to have a less pronounced effect on the current—the lower the energy, the less the current drops when exposed to a light pulse. This effect had a threshold at 480 nm, below which energy had no effect on the current.
The researchers say that the azafullerenes partially bond to the nanotubes via their nitrogen atom, lending the nanotube additional electrons to aid conduction. When the nanotube is irradiated with light, this bond is broken either directly by the photons or by heat generated when the photons are absorbed by the nanotube. The broken bond means that the electrons are no longer donated to the nanotube by the azafullerene, reducing conductivity. The system returns to the higher conductance state as the bond slowly reforms during normal transistor operation.
“After encapsulating azafullerenes the conductivity of nanotubes can be controlled by light,” says Li. “The nanotube devices also show repeatable switching behaviour.” He hopes that the azafullerene peapods can be used to make “optoelectronic devices such as photosensors or photodetectors”, and says that the researchers plan to explore temperature and concentration effects in the future.
Reference
- Li, Y., Kaneko, T., Kong, J. & Hatakeyama, R. Photoswitching in azafullerene encapsulated single-walled carbon nanotube FET devices. J. Am. Chem. Soc. 131, 3412 (2009). | article
Author affiliation
Yongfeng Li,*,† Toshiro Kaneko,† Jing Kong,‡ and Rikizo Hatakeyama†
Department of Electronic Engineering, Tohoku UniVersity, Sendai 980-8579, Japan, and Department of Electrical
Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139
† Tohoku University.
‡ Massachusetts Institute of Technology.
This research highlight has been approved by the author of the original article and all empirical data contained within has been provided by said author.
Top Home
