Electrical Characteristics of a Carbon Nanotube-Functionalized Probe for Kelvin Probe Force Microscopy

Carbon nanotubes (CNTs) have been demonstrated as a functional probe for scanning probe microscopy because of their good mechanical properties, small diameter, and high aspect ratio. However, their application and performance in Kelvin probe force microscopy (KPFM) are largely unexplored. Here, the electrical properties of CNTs used as the KPFM probe in terms of surface potential measurement and mapping are investigated. The local contact potential difference measured by the CNT probe on the Ag(111) surface shows a dependence on tip- sample distance, indicative of the existence of a permanent dipole moment at the end of CNT tips. A model is established to quantify the dipole moment of the CNT using in situ measured geometric parameters, thereby deriving the precise work function difference between the CNT tip and the metal substrate. The enhanced spatial resolution in surface potential mapping using the CNT-functionalized probe as compared to conventional metal probes is attributed to the small radius of the CNT tip and the presence of a spontaneous dipole moment at the tip apex.