Collection mode and Reflection mode NSOM on ferroelectrics

Authors Camarillo and colleagues from Universidad of Autonoma de Madrid, Univ of Mexico, and Univ of Glasgow, study the behavior  of various periodic ferroelectric domains with NSOM to probe these periodically poled structures as optical superlattices.  They used a Multiview 2000 in both collective and reflection mode, finding a correlation in the NSOM signal intensity with ferroelectric domain structure.   Quasi-periodic ferroelectric domains structures act as optical super=lattices as a result of their refractive index modulation along the domain structure. The authors use the NSOM results to understand the refractive index modulation in their structures.

In the image below, AFM and NSOM in reflection mode were collected simultaneously using a CW laser beam from a Nd:YAG laser coupling into the NSOM probe, and detected by an avalanche photodiode (APD).  The domains that are topographically depressed (dark brown regions in (a)  ) showing a higher NSOM intensity than the domains that are topographically elevated.  Thus, they surmise that the topographically depressed domains are more effective as waveguides than the topographically elevated domains, suggesting that the refractive index value is higher in the topographically depressed regions.

In a ferroelectric structure fabricated in another way, the authors observe a different structure as seen in the AFM topography (a) and NSOM (b) image obtained here in collection mode.   Again, the areas of higher NSOM intensity are correlated to topographically depressed regions in the AFM image; though the topography in the AFM is not very strong, the authors surmise this is a result of polishing.  These observations are important to understanding the optical behavior of ferroelectric crystlas, which have potential application for nonlinear optics.

Published:  Ferroelectrics, 467 (p.6-12),  (2014)

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