Ntegra system

The AFM topography maps and KPFM contact potential
difference (CPD) maps were recorded using an NTEGRA system from NT-MDT
Spectrum Instruments. High-quality topography maps were recorded in
semicontact mode using cantilever A on a HA_NC tip from NT-MDT with
a nominal force constant of 12 N/m. The CPD was recorded with 2-pass
KPFM in ambient conditions using an ElectriTap300-G tip from BudgetSensors
having a nominal force constant of 40 N/m. For the thin films on FTO,
conductive HQ:NSC18/Pt probes from μmasch with a nominal force
constant of 2.8 N/m were used. The freshly sputtered Pt and Au samples
were used as potential references and examined before and after every
measurement. During the second pass, the cantilever was lifted 100
nm above the sample surface, and the amplitude of the applied AC voltage
was 3 V. The sample substrate was connected to the ground during the
entire measurement.

The nanoscale near-field Talbot measurement (Fig. 1c) was performed on a near-field scanning optical microscope (NSOM, NTMDT Ntegra system) equipped with two laser sources with wavelengths of 532 and 660 nm. An amplitude measurement was done with the NSOM in transmission mode as depicted in Fig. 5a. A cantilever with clear aperture of (70 ± 20 nm) was positioned proximate to the MIM grating structure surface. Local electric field transmits through the cantilever clear tip, and couples into a fiber through a 100x objective and its amplitude is recorded using a PMT. The cantilever, mounted on a piezo stage, scanned the local light intensity in a volume of 4 × 4 × 4 µm³⁵ , with lateral (Δx, Δy) resolutions of 22 nm and vertical resolution (Δz) of 250 nm.
The x-locations of peak intensities in the Talbot image were detected in each y-slice to align the data before subsequent averaging over all y, reducing measurement noise and introducing tolerance to sample rotational misalignment. The image is interpolated in the z-direction to match the x–y resolution. Bending of the Talbot image in the 532-nm measurement is attributed to drift in the piezoelectric elements, as a volume acquisition took 45 minutes to complete.