Determination of the local contact potential difference of PTCDA on NaCl: a comparison oftechniques

Abstract

There has been increasing focus on the use of Kelvin probe force microscopy (KPFM) forthe determination of local electronic structure in recent years, especially in systems whereother methods, such as scanning tunnelling microscopy/spectroscopy, may be intractable.We have examined three methods for determining the local apparent contactpotential difference (CPD): frequency modulation KPFM (FM-KPFM), amplitudemodulation KPFM (AM-KPFM), and frequency shift–bias spectroscopy, on a testsystem of 3,4,9,10-perylene tetracarboxylic dianhydride (PTCDA) on NaCl, anexample of an organic semiconductor on a bulk insulating substrate. We willdiscuss the influence of the bias modulation on the apparent CPD measurementby FM-KPFM compared to the DC-bias spectroscopy method, and provide acomparison of AM-KPFM, AM–slope detection KPFM and FM-KPFM imagingresolution and accuracy. We will also discuss the distance dependence of the CPD asmeasured by FM-KPFM for both the PTCDA organic deposit and the NaCl substrate.