Sep 8, 2011
Nanolithography prepares graphene devices
The nano-characterization group at Sejong University in South Korea has reported a graphite patterning method based on scanning probe lithography (SPL) that benefits from a controlled gas environment and could offer a route to preparing graphene-based electronic devices.
Patterning of graphite or graphene by SPL has typically been performed in air because water molecules form a meniscus between tip and sample, which mediates the etching reaction. This water meniscus, however, may prohibit uniform patterning due to its strong surface tension or large contact angle on sample surfaces.
Controlled gas environment
To combat this side effect, the team patterns its samples in a chamber where the gas environment can be controlled. The researchers found that methyl alcohol (MA) facilitates graphite etching and gives a line width as narrow as 3 nm. Due to its low surface tension and highly adsorptive behavior, MA provides advantages for narrow line width and high speed etching operation.
The bias voltage and tunneling current were in the same range as water-assisted etching, but the line width of the etched features were much narrower in a MA environment. The line drawing speed was about 100 nm/s, which is 20 times faster than other STM-based etching. This improvement in patterning speed is attributed to the lower viscosity of MA and the reduction in enthalpy change compared with the reactions occurring with water.
By applying a top layer transfer technique to the graphite sample, controlled gas environment SPL could be used to generate graphene-based nano devices.
More details are given in the journal Nanotechnology.
About the author
The nano-characterization group at Sejong University, South Korea, has expertise in using SPM techniques for the patterning and analysis of graphene-based devices. The group leader, Prof. Yongho Seo, received his PhD at Seoul National University in 2000, and started as a faculty member in the Nano-engineering department at Sejong University in 2006. He has focused on the fabrication of nano-devices using SPM techniques for more than a decade. The experimental researcher Joonkyu Park is a graduate student at Sejong University and plans to study abroad in this field after completing his MSc. He conducted the experiments, which included the experimental set-up, programming and data analysis.