doi:10.1038/nindia.2011.93 Published online 24 June 2011
Researchers have carved charge-storing islands surrounded by nano-sized trenches on a graphite surface. The islands and trenches, formed using atomic force microscopy (AFM), could be useful for developing new memory devices.
Carbon nanomaterials such as fullerenes, carbon nanotubes and graphene find use as active components in a wide variety of nanoscale devices, thanks to their extraordinary physical and electrical properties. Of all the carbon nanomaterials currently available, devices fabricated from few-layer graphene stand out for their extremely small size and exciting electrical properties.
The researchers used AFM to electrochemically etch the surface of a highly oriented pyrolytic graphite substrate. They applied negative potentials to the hydrophilic AFM tip, which moved across the hydrophobic graphite surface in contact or tapping mode. The electric field generated by the potentials caused the electrolysis of polarized water molecules collected between the tip and the substrate. This formed oxygen-containing anions, which in turn oxidized or etched the graphite surface to form islands — regions surrounded by either raised graphitic oxide or trenches.
A negative tip potential of −8 V in contact mode was capable of etching a trench 40 nm wide and 1.5 nm deep, which is around four or five carbon layers. The AFM tip also formed charge-storing islands on the top layer of the graphite substrate. Electric current can flow through the islands, which suggests that the persistence of the interior charge distribution is likely to result from a permanent charge polarization that sets up in the top few layers of highly oriented pyrolytic graphite during the electrochemical oxidation.
"The study offers a way of creating spatially confined graphene-like structures, which could form the foundation of functional devices," says lead researcher G. U. Kulkarni.
The authors of this work are from: Chemistry and Physics of Materials Unit and DST Unit on Nanoscience, Jawaharlal Nehru Centre for Advanced Scientific Research, Bangalore, India and Birck Nanotechnology Center, Purdue University, USA.
- Kurra, N. et al. Charge storage in mesoscopic graphitic islands fabricated using AFM bias lithography. Nanotechnology 22, 245302 (2011)