AFM for Graphene and 2D Materials

The 2004 report by Novoselov and Geim on transistors made from single-layer graphitic films created overnight the field of graphene AFM research. This single, free-standing plane of carbon atoms has proven to exhibit many unique and desirable properties: it provides a high surface area, excellent electrical and thermal conductivity, and superior mechanical strength. Graphene is an ideal two-sided surface without a bulk in between, has the highest known room-temperature carrier mobility, 25 times the thermal conductivity of silicon, a reported Young's modulus of ~1 TPa and breaking strength approaching the theoretical limit. Potentials for breakthrough technologies thus abound, including: next generation electronics (quantum computing, spintronics); energy collection and storage (photovoltaics, fuel cells, supercapacitors); nanoelectromechanical (NEMS) devices and resonators; and electrochemical sensors and lab-on-chip biosensors. This has also spurred attendant interest in other 2D materials such as MoS₂ and boron nitride films.
 
Atomic force microscopy is a critical enabling technology in graphene research. Its high (sub-angstrom) resolution distinguishes with ease single atomic layers on a substrate, and is suitable for characterizing film quality, such as morphology, roughness, and uniformity. Moreover, AFM imaging requires a probe to be in physical contact with the surface, which makes it possible to determine electrical and mechanical properties simultaneously with topography. Material properties such as conductivity and permittivity, stiffness and dissipation, viscoelastic and friction responses can thus be mapped-out with nanoscale lateral precision. Long-range electrical properties such as electrostatic charge, surface potential, and magnetic fields can be probed as well by bringing the tip in close proximity of the surface during measurement.