Know your full potential: Kelvin probe force microscopy on nanoscale electrical devices and at solid-liquid interfaces
Amelie Axt a, Ilka Hermes a, Stefan A.L. Weber a
a Max-Planck-Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany
nanoGe Fall Meeting
Proceedings of nanoGe Fall Meeting19 (NGFM19)
#MapNan19. Mapping Nanoscale Functionality with Scanning Probe Microscopy
Berlin, Germany, 2019 November 3rd - 8th
Organizer: Stefan Weber
Poster, Amelie Axt, 340
Publication date: 16th July 2019

KPFM is widely used to map the nanoscale potential distribution in operating devices, e.g. in thin film transistors, battery materials, solar cells or even in liquids on e.g. membranes and coatings.

Surface potential measurements are crucial for understanding the operation principles of functional nanostructures in electronic devices. Knowing the local surface potential can also contribute to understanding effects like corrosion and membrane aging.

Nevertheless, KPFM is prone to certain imaging artifacts, such as crosstalk from topography or stray electric fields.

We compare different amplitude modulation (AM) and frequency modulation (FM) KPFM methods on a reference structure consisting of a glass-platinum interdigitated electrode array. This structure allows to modify the surface potential externally and minimizes corrosion, while mimicking the sample geometry in device measurements, e.g. on thin film transistors or battery materials.

We found that when operated with a feedback, FM KPFM methods provide more quantitative results that are less affected by the presence of stray electric fields compared to AM KPFM methods[1]. Since a feedback limits the scanning speed, voltage range, is prone to artifacts and is not applicable in liquids, we also tested open loop methods. In open loop operation, FM KPFM methods provide more contrast compared to AM KPFM methods.

 

Figure 1: CPD line profiles of two closed loop KPFM experiments on the same cross section of a mesoscopic perovskite solar cell under short circuit conditions with and without illumination, visualized by the red and blue line, respectively. The cell consisted of a fluorine-doped tin oxide (FTO) electrode, a compact TiO2 electron extraction layer and a mesoscopic TiO2 layer (meso) filled with the perovskite light-absorber methylammonium lead iodide (MAPI). The mesoscopic layer was followed by a compact MAPI capping layer, the hole transport material spiro-OMETAD and a gold electrode. Prior to the measurement, the cross section of the solar cell was polished with a focused ion beam (FIB) to minimize topographic crosstalk. The CPD line profiles on the left were extracted from double side band frequency modulation KPFM (FM sideband) scans in single pass with VAC of 3V [2]. The CPD line profiles on the right were extracted from amplitude modulation KPFM (AM lift mode) scans in lift mode with a tip-sample distance of 10 nm, an oscillation amplitude of ~80 nm and a tip voltage UAC of 1 V. Each line profile is an average of three adjacent scan lines. [1]

© Fundació Scito
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