Quantitative Measurement of the Local Surface Potential of π‐Conjugated Nanostructures: A Kelvin Probe Force Microscopy Study

Abstract

We describe a systematic study on the influence of different experimental conditions on the Kelvin probe force microscopy (KPFM) quantitative determination of the local surface potential (SP) of organic semiconducting nanostructures of perylene‐bis‐dicarboximide (PDI) self‐assembled at surfaces. We focus on the effect of the amplitude, frequency, and phase of the oscillating voltage on the absolute surface potential value of a given PDI nanostructure at a surface. Moreover, we investigate the role played by the KPFM measuring mode employed and the tip–sample distance in the surface potential mapping by lift‐mode KPFM. We define the ideal general conditions to obtain a reproducible quantitative estimation of the SP and we find that by decreasing the tip–sample distance, the area of substrate contributing to the recorded SP in a given location of the surface becomes smaller. This leads to an improvement of the lateral resolution, although a more predominant effect of polarization is observed. Thus, quantitative SP measurements of these nanostructures become less reliable and the SP signal is more unstable. We have also devised a semi‐quantitative theoretical model to simulate the KPFM image by taking into account the interplay of the different work functions of tip and nanostructure as well as the nanostructure polarizability. The good agreement between the model and experimental results demonstrates that it is possible to simulate both the change in local SP at increasing tip–sample distances and the 2D potential images obtained on PDI/highly oriented pyrolytic graphite samples. These results are important as they make it possible to gain a quantitative determination of the local surface potential of π‐conjugated nanostructures; thus, they pave the way towards the optimization of the electronic properties of electroactive nanometer‐scale architectures for organic (nano)electronic applications.

Self‐Organization and Nanoscale Electronic Properties of Azatriphenylene‐Based Architectures: A Scanning Probe Microscopy Study

“…[35] From profiles in the KPFM image, we measured DSP = SP HOPG -SP HAT to be (83.1 ± 10.3) meV. The measured surface potential of HOPG corresponds to its work function [36] and, given its value reported in the literature, the layers of 1 on HOPG exhibited a surface potential of (4.53 ± 0.02) eV. This estimation is of fundamental importance in molecular electronics because it enables the elucidation and correct tuning of differences in energy levels between molecular nanostructures and electrodes, thereby allowing optimization of charge injection.…”

Unconventional nanotubes self-assembled in alumina channels: morphology and surface potential of isolated nanostructures at surfaces

“…This effect is also reflected in the simulated KPFM image (figure 4d ). Such an image type is calculated using a two-dimensional convolution procedure (Liscio et al 2006) between the effective area and the KPFM image, which is reconstructed with infinitesimal lateral resolution by assigning to each point of the topographic image the asymptotical SP value of either mica or nanotube. The effective area is well described by a two-dimensional Voigt curve calculated as proportional to the perpendicular electric field of the tip along the sample surface, in which the analytical expression was calculated by Lyuksyutov et al (2004).…”

“…In the case of macroscopic graphite sample, the measured SP corresponds to the WF. For nanostructures, it is important to define the asymptotic SP as the potential value measured on an ideal infinite and uniform layer of the material under study (Liscio et al 2006). The angles between neighbouring nanotubes amount to multiples of approximately 308, therefore reflecting the threefold symmetry of the mica substrate (Samorì et al 1998).…”

“…We deposited these different nanotubes on an atomically flat substrate from solution and studied their morphology using scanning force microscopy (SFM; Samorì 2005). To explore the effect of chemical structure and order on the electronic properties of the nanotubes, two-dimensional surface potential (SP) maps were obtained by Kelvin probe force microscopy (KPFM; Nonnenmacher et al 1991;Liscio et al 2006).…”

Advantages of a Programmed Surface Designed by Organic Monolayers

“…Depth distribution profiles acquired from those KPFM images show potential difference between the SAM-modified and -unmodified surfaces of about 6 mV (for TESUD/SiO 2 ), 18 mV (for ODS/SiO 2 ) and 37 mV (for AHAPS/SiO 2 ), respectively. A surface potential distribution between the SAM-covered and -uncovered regions is given by following equation [8][9][10]:…”