Ballistic- and quantum-conductor carbon nanotubes: The limits of the liquid-metal contact method

The liquid-metal contact method (LMC method), which consists of immersing a carbon nanotube (CNT) placed on the apex of a metallic tip into a drop of liquid mercury (Hg), has been previously employed to show ballistic and quantum conductance properties of different kinds of CNTs. Using numerical simulations based on an analytical model of the mechanical interaction between the CNTs and the Hg surface, we show that the LMC method is unsuited for the analysis of ballistic conductance because most CNTs under realistic experimental conditions will not create a mobile contact this way. Furthermore, we show that the apparent electronic mean free path value deduced from these experiments will be exclusively due to elasticity induced CNT bending, geometry induced CNT sliding, and contact angle induced Hg meniscus related effects, and not to the electronic properties of the CNTs. These findings have strong consequences for the interpretation of previously reported works.