Nanoscale graphene and carbon nanotube lithography using an atomic force microscope

In this work, we demonstrate the use of a voltage-applied Atomic Force Microscopy (VAFM) local anodic oxidation nanolithography process to precisely fabricate small (<20 nm) structures from graphene and carbon nanotube material. These graphitic materials have exceptional electrical properties which give them a niche in emerging nanoelectronics applications requiring quantum structures. While several methods for nanoscale patterning of these materials exist, the VAFM nanolithography technique has lately been shown to address the fabrication issues of graphitic nanodevices on the order of tens of nanometers [1]. If the tip is raised sufficiently from the substrate, in high atmospheric humidity, a water meniscus forms between the two (Fig 1). Application of an appropriate electric field between the tip and substrate dissociates the H2O molecules into H+ and OH-. The H+ ions rush towards the negatively charged tip and the OH- ions gather near the positively substrate. The oxygen reacts with the carbon in the graphitic material to form volatile or nonvolatile carbon oxides depending on the voltage applied. This oxidation, coupled with the x-y scanning capability of the AFM allows for thin structure patterning ability. Depending on such process parameters as applied voltage, pulse width, tip dimensions, contact force, and humidity, the oxidation of the graphitic material into carbon oxides enables the formation of insulating trenches or bumps to make any structure or morphology conceivable [2]. This technique can also be performed in the ambient environment, eliminating several fabrication steps, such as the poly(methyl methacrylate) (PMMA) processing required in conventional electron-beam lithography process.