Preprint Article Version 1 Preserved in Portico This version is not peer-reviewed

Near-Field IR Orientational Spectroscopy of Silk

Version 1 : Received: 31 August 2019 / Approved: 1 September 2019 / Online: 1 September 2019 (12:56:05 CEST)

A peer-reviewed article of this Preprint also exists.

Ryu, M.; Honda, R.; Reich, A.; Cernescu, A.; Li, J.-L.; Hu, J.; Juodkazis, S.; Morikawa, J. Near-Field IR Orientational Spectroscopy of Silk. Appl. Sci. 2019, 9, 3991. Ryu, M.; Honda, R.; Reich, A.; Cernescu, A.; Li, J.-L.; Hu, J.; Juodkazis, S.; Morikawa, J. Near-Field IR Orientational Spectroscopy of Silk. Appl. Sci. 2019, 9, 3991.

Abstract

Orientational dependence of the IR absorbing amide bands of silk is demonstrated from two orthogonal longitudinal and transverse microtome slices only $\sim 100$~nm thick. A scanning near-field optical microscopy (SNOM) which preferentially probes orientation perpendicular to the sample's surface was used. Spatial resolution of silk-epoxy boundary was defined with a $\sim 100$~nm resolution while the spectra were collected by a $\sim 10$~nm tip. Ratio of the absorbance of the amide-II C-N at 1512~cm$^{-1}$ and amide-I C=O $\beta$-sheets at 1628~cm$^{-1}$ showed sensitivity of SNOM to the molecular orientation. SNOM characterisation is complimentary to the far-field absorbance which is sensitive to the in-plane polarisation. Volumes with cross sections smaller than 100~nm can be characterised for molecular orientation. A method of absorbance measurements at four angles of slice cut orientation, which is equivalent to the four polarisation angles absorbance measurement is proposed.

Keywords

silk; anisotropy; absorbance; retardance

Subject

Chemistry and Materials Science, Nanotechnology

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