Kelvin probe force microscopy (KPFM) on graphene

Graphene belongs to the category of 2D materials and is of interest in the research and development of new devices and materials. Besides atomic resolution imaging of graphene to learn more about crystal orientation, edges and defects, the functional properties of graphene are also of great interest.

In this application note, multilayer graphene was imaged with Kelvin probe force microscopy (KPFM) using a CoreAFM to study the contact potential difference variation on a single flake.

 

Multilayer graphene flakes were generated by mechanical exfoliation of graphite and subsequent transfer to a silicon-silicondioxide substrate. The KPFM measurement was carried out in single-run mode, recording the contact potential during the scanning of the topography.

Thin flakes were localized on the substrate with an upright microscope. Using markers on the substrate, the same flakes were placed under the cantilever using the topview camera of the CoreAFM, after which AFM images of graphene and KPFM data were recorded.

 

 

 

Sample courtesy: Hiske Overweg, Klaus Ensslin, ETH Zürich, Switzerland

All measurements were performed using a CoreAFM system equipped with a PPP-EFMR cantilever from Nanosensors. AFM images of graphene were processed using the MountainsMap SPM.

Out of plane piezoresponse force microscopy (PFM) on Lithium Niobate

Lithium Niobite (LiNbO₃) is an optically transparent, piezo responsive material used, for example, in piezo sensors or in mobile phones. We tested a LiNbO₃ sample (PFM03, obtained from TipsNano, Estonia) with CoreAFM. The sample has a regular domain structure with 10-µm period. The spontaneous polarization has the opposite direction in the neighboring domains.

To measure the piezoresponse during imaging, a 7.5 V AC voltage was applied to the cantilever while raster scanning the tip over the sample. In response to the applied voltage, the sample periodically expands and shrinks, either in phase with or in counter phase to the excitation frequency. Despite a small measured RMS roughness of 0.3 nm, the domains could not be recognized in the topography. The domains could however be readily identified in the out of plane piezoresponse.

Lithium Niobite (LiNbO₃) is an optically transparent, piezo responsive material used, for example, in piezo sensors or in mobile phones. We tested a LiNbO₃ sample (PFM03, obtained from TipsNano, Estonia) with CoreAFM. The sample has a regular domain structure with 10-µm period. The spontaneous polarization has the opposite direction in the neighboring domains.

 

 

 

To measure the piezoresponse during imaging, a 7.5 V AC voltage was applied to the cantilever while raster scanning the tip over the sample. In response to the applied voltage, the sample periodically expands and shrinks, either in phase with or in counter phase to the excitation frequency. Despite a small measured RMS roughness of 0.3 nm, the domains could not be recognized in the topography. The domains could however be readily identified in the out of plane piezoresponse.

 

 

 

 

 

 

 

 

 

Electrostatic force microscopy (EFM)
Phase contrast imaging on aluminum-gold microstructure

FM measurement of Aluminum-gold microstructure, scansize: 8 µm, structure height: 90 nm, phase range: 6 °. Image processing: Nanosurf Report software

 

 

 

 

 

 

 

 

Phase imaging of a SBS-PS polymer blend

Topography (top row) and phase images (bottom row) at scan ranges of 2 µm (left column) and 1 µm (right column) of a spin-cast SBS-PS blend film on mica. The topography images clearly show two different height levels. The lower level phase exhibits a wrinkled topography that is more evident in the 1 µm-sized scan. The phase images show that the different height levels correspond to different material, i.e. polymers in this case. The image recorded at 1 µm scan size shows the area in the center of the 2 µm scan size image. The height range of the images corresponds to 30 nm and the phase range to 20°

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