Effect of Trapped Charges on Local Potential Measurement of Carbon Nanotubes Using Frequency-Modulation Kelvin-Probe Force Microscopy

Abstract

The performance of field effect transistors based on single-walled carbon nanotubes (SWNTs) is determined by their chirality the potential barrier at the SWNT/electrode interface, and defects in the SWNTs. Kelvin-probe force microscopy (KFM) is a powerful technique that can measure local surface potential (SP) on SWNTs for investigating local electrical properties at the interface and defects. However, the electrical potential measurement of SWNTs is often hindered by the surrounding trapped charges on the silicon oxide surface. We performed KFM imaging on an SWNT aligned between the electrodes on a silicon oxide surface by KFM using the frequency modulation (FM) method. We investigated the effect of these surface charges on the electrical potential of the SWNT measured by FM-KFM, especially in terms of the tip-sample distance. We introduced a novel two-dimensional (2D) SP mapping method in which the tip is scanned in a plane normal to the sample surface while recording the SP. The 2D SP map showed that the SP measured on the SWNT was significantly affected by the surrounding trapped charges, even when the tip-sample distance was minimized, and the electrical potential of the SWNT could not be measured accurately. [DOI: 10.1380/ejssnt.2011.210]