Nanofibrils play a pivotal role in spider silk and are responsible for many of the impressive properties of this unique natural material. However, little is known about the internal structure of these protein fibrils. We carry out polarized Raman and polarized Fourier-transform infrared spectroscopies on native spider silk nanofibrils and determine the concentrations of six distinct protein secondary structures, including β-sheets, and two types of helical structures, for which we also determine orientation distributions. Our advancements in peak assignments are in full agreement with the published silk vibrational spectroscopy literature. We further corroborate our findings with X-ray diffraction and magic-angle spinning nuclear magnetic resonance experiments. Based on the latter and on polypeptide Raman spectra, we assess the role of key amino acids in different secondary structures. For the recluse spider we develop a highly detailed structural model, featuring seven levels of structural hierarchy. The approaches we develop are directly applicable to other proteinaceous materials.
Nonuniform strain on multilayer transition-metal
dichalcogenide
(TMDC) nanosheets is an exciting path toward practical optoelectronic
devices, as it combines the advantages of localized control of optical
and electronic properties with ease of fabrication. However, the weaker
photoluminescence (PL) due to their indirect nature poses a challenge
to their application. Here, we demonstrate extraordinary enhancement
of PL from multilayer MoS2 nanosheets under nonuniform
strain generated by nanopillars. We observe charge and exciton funneling
to the pillar strain apex. The screening from the increased exciton
and charge density lowers the exciton binding energy and renormalizes
the band gap. Hence, we attribute the dramatic increase in PL to dissociation
of bound excitons to free electron–hole pairs, showing that
nonuniform strain on TMDC nanosheets can effectively manipulate the
nature of light–matter interaction in these atomically thin
materials for application in novel strain-engineered optoelectronics.
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