Mentions: To further characterize the domains at the nanoscale and investigate in situ whether they are susceptible to electrical bias, we used the PTIR technique (36, 37). PTIR is a novel method that combines the lateral resolution of AFM with the specificity of absorption spectroscopy. PTIR was initially developed in the mid-infrared (IR) (36) and has attracted much interest for enabling label-free composition mapping (38–41), material identification (42), and conformational analysis (43, 44) at the nanoscale. For example, PTIR data yielded direct evidence of MA+ electromigration in OIP lateral structure solar cells (39). Very recently, we extended PTIR to the visible and near-IR spectral ranges (45), an advance that has enabled the determination of the local bandgap in CH3NH3PbI3−xClx films and estimating the local Cl− content as a function of the annealing process (46). In our PTIR setup, a pulsed wavelength-tunable laser (spot size ≈30 μm) is used to illuminate the sample via total internal reflection (Fig. 5A). An AFM tip contacting the sample locally transduces the thermal expansion of the sample due to light absorption into cantilever oscillations that are monitored by the AFM four-quadrant detector. The amplitude of the cantilever oscillation (PTIR signal) is proportional to the absorbed energy (47, 48) and yields nanoscale absorption spectra (vibrational or electronic) when sweeping the laser wavelength while holding the tip at a given location. Alternatively, PTIR absorption maps are obtained by illuminating the sample at a given wavelength at a time and by plotting the PTIR signal as a function of the tip position. To enable PTIR characterization at both mid-IR and visible ranges, we fabricated a polycrystalline OIP lateral device on the surface of a zinc sulfide prism by spin-coating (sample A2; see Materials and Methods for details). Here, we show that the PTIR transduction scheme enables the visualization of ferroelastic domains, thanks to their orientation-dependent anisotropic thermal expansion coefficient.
Evidence and control of ferroelastic (but not ferroelectric) domains in CH3NH3PbI3 perovskite are provided.
No MeSH data available.