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High-Resolution Nanochemical Mapping


is mandatory for soſt or fragile samples. Hence, nanooptical, nanomechanical, nanoelectrical, and nanopotential experi- ments are now accessible, and, in the case of polymer science, this technology could be employed to correlate functionality and phase distributions in organic photovoltaics, fuel cells, conducting polymers, organic electronics, or liquid crystal fi lms.


Conclusion


Functional polymer blends with smaller and smaller domain sizes require novel techniques such as s-SNOM to image their material distribution. S-SNOM as implemented in the Inspire tool can directly acquire the sample’s nanoscale absorption and refl ection, thus providing easily interpretable, modeling-free IR data that can be compared to standard FTIR spectra. In combination with other AFM techniques, s-SNOM can be employed to simultaneously measure nanooptical, nanomechanical, and nanoelectrical properties, enabling correlated experiments to enhance our understanding and allow optimization of materials in various fi elds of polymer science.


Acknowledgments T e authors thank Bede Pittenger and Natalia Erina for sample preparation, and Greg Andreev for providing the data presented in Figure 5 .


Figure 6 : Analysis of a contaminated PS-PMMA fi lm. Simultaneously acquired (a) topography, (b) modulus, (c) IR refl ection, and (d) absorption. IR refl ection and absorption were measured for a laser frequency of 1728cm -1 , tuned to the C=O vibrational mode characteristic of PMMA and absent in PS. While topography, modulus, and refl ection cannot unambiguously identify the nature of the tallest feature in topography (close to the image center), the combination with IR absorption establishes it to be neither PS, nor PMMA, but some sort of contamination.


but not in PS allowed to unambiguously identify the PMMA domains. Off resonance, the contrast between PS matrix and PMMA domains vanished. Both absorption and reflection properties extracted via s-SNOM exhibited the expected line profi le of a Lorentz oscillator [ 30 ], highlighting the chemical specifi city, but also the modeling-free data interpretation that renders s-SNOM so valuable for applications. As another example we imaged PHBV ( Figure 4 ). Here, s-SNOM could map the PHBV domains in the PS matrix and additionally resolved structures within single PHBV domains that possibly result from incomplete phase separation or varying degrees of crystallinity. T ese features were hard or impossible to resolve in AFM topography alone. Mapping of the non-resonant refl ection properties of a PS-LDPE blend (Figure 5) demonstrated that imaging in an absorption-free region can be employed to identify materials on the nanoscale as well. S-SNOM as an AFM-based technique can be further enhanced by combining it with other versatile AFM modes. Two examples of correlative nanooptical and nanomechanical mapping were given ( Figure 5 and 6 ); this combination of s-SNOM with PeakForce Tapping is expected to have many interesting applications. Not only can the nanomechanical properties be mapped, but PeakForce Tapping enables either amplitude modulation or frequency modulation kelvin-probe force microscopy without the need to turn to tapping mode for feedback. In addition it enables high-resolution conduc- tivity mapping in tunneling or conducting AFM without requiring contact mode for conductivity measurements, which


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