Preprint Article Version 1 This version is not peer-reviewed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.

Journal reference: Appl. Sci. 2019, 9, 3991
DOI: 10.3390/app9193991

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.

Subject Areas

silk; anisotropy; absorbance; retardance

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