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.

Post-production

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.