C49 AFM imaging on XE7 (Wanhao Cai, Bizan N. Balzer)

Sample cleaning
All the samples were rinsed extensively with pure H2O (Purelab Chorus 1, Elga LabWater, Celle, Germany, 18.2 MΩ cm) and dried with N2, then used immediately for the AFM imaging.

AFM imaging
The imaging of the cleaned samples was performed on a XE7 (Park Systems, Korea) in the intermittent-contact mode (tapping mode) at 25 ℃ in air. Scout 70 RAI (NuNano, Bristol, UK) cantilevers with a resonance frequency of approx. 70 kHz and a tip radius of 5 nm were used for imaging. The imaging process was carried out with the fast scan direction perpendicular to the cantilever axis (i.e., scan angle of 90° for XE7), using of 1024×1024 pixels, a scan rate of 1 Hz, and scan sizes of 30×30, 10×10, 5×5, 1×1 μm2, respectively.

Data processing
The height data of both trace and retrace images were analyzed with Gwyddion Free SPM analysis software [1]. The images were evaluated using the following tools: align rows via the polynomial method (degree: 5) and fix zero. Then, the root mean square (RMS) roughness of the images was calculated via the statistical quantities tool.

If the images show dust particles, the following additional steps were performed:
after using mask of outliers (masking all data values exceeding the confidence interval of 3 sigma), align rows via the polynomial method (degree: 5) and fix zero were applied. Finally, the root mean square (RMS) roughness of the images was calculated via the statistical quantities tool excluding the masked areas.