Full Information Acquisition
technique, band excitation polarization switching (BEPS) that uses a slow (0.25–2 Hz) polarization switching waveform, the ultrafast excitation waveform of G-VS (10–60 kHz) results in a 3,500-fold improvement in measurement speed over BEPS. T e sheer speed of the polarization switching waveform enables G-VS to enjoy high spatial resolution, minimal driſt , and short measurement durations typical of imaging modes such as S-PFM, while having the polarization switching capability of spectroscopy techniques. Once the data are fi ltered, relevant material-specifi c properties may be extracted from the shape of the strain loops. Alternatively, statistical methods may be applied to analyze the data. Figure 5b
compares the spatial resolutions of S-PFM, BEPS, and G-VS for measurements on a Pb(Zr 0.2 Ti 0.8 )O 3 (PZT) thin fi lm sandwiched between gold nanocapacitor discs and a SrRuO 3 bottom electrode on a SrTiO 3 substrate. T e S-PFM and G-VS measurements resulted in high-resolution 256 × 256 pixel images acquired in 8.5 and 17 minutes, respectively, while the BEPS measurement resulted in a 40 × 40 pixel image acquired in 77 minutes. New SPM modes enabled by full data acquisition . Besides adaptations to traditional imaging techniques, G-Mode also can give rise to fundamentally new modes of SPM operation [ 88 ]. For example, in order to completely characterize any system,
Figure 6 : General dynamic mode (GDM) applies G-Mode to frequency sweeps. (a) In GDM, the complete response from the AFM is recorded for a sequence of excitation waveforms of increasing frequency to generate a 2D spectrogram with the excitation frequency on one axis and the response frequency on the other for each spatial location. (b-c) Results of PCA applied to a GDM imaging dataset on a silicon substrate with gold and aluminum electrodes. The fi rst four PCA loading maps (b) and eigenvectors (c), which are GDM spectrograms. Reprinted from S Somnath et al., Nanotechnology 27 (2016) 414003 with permission of IOP Publishing.
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