Materials with large chiral optical activity at visible wavelengths are of great interest in photonics, particularly as a route to chiral optical metamaterials. Here, we demonstrate the plasmonic enhancement of the chiral optical activity of chiral poly(fluorene-alt-benzothiadiazole) (PFBT) doped with gold nanoparticles. The supramolecular helical organization of polymeric chains with simultaneous dipole-dipole interaction of the helically ordered nanoparticles with the polymer and one another results in unprecedented values of chirality parameter (κ ~0.02) at visible wavelengths in thin films.
Chiral photonics deals with enantioselective polarization control of linear and nonlinear optical functions and holds a great promise for a wide range of applications including optical signal processing, biosensing, and chiral bioimaging. Development of chiral materials with optical activity exceeding that of natural materials therefore becomes a prerequisite to realizing the full potential of this field. Herein, we report on a study of structure−property relations of two chiral polymers with ester functional groups in lateral branch. To enhance rotational strength, the macroscopic measure of chirality, we employ a fluorene−quinoxaline motif in the monomer unit. To the best of our knowledge, we find the optical activity of one of the studied polymers to be the highest reported so far. Theoretical calculations reveal a correlation between the topological conformations and the simulated CD spectra in agreement with the experimental measurements and help clarify the mechanism of optical activity enhancement that could create insight for further enhancement of chirality.
A polymeric composite material composed of colloidal gold nanoparticles (<10 nm) and SU8 has been utilized for the fabrication of large-area, high-definition photonic crystal. We have successfully fabricated near-infrared photonic crystal slabs from composite materials using a combination of multiple beam interference lithography and reactive ion etching processes. Doping of colloidal gold nanoparticles into the SU8 photopolymer results in a better definition of structural features and hence in the enhancement of the optical properties of the fabricated photonic crystals. A 2D air hole array of triangular symmetry with a hole-to-hole pitch of approximately 500 nm has been successfully fabricated in a large circular area of 1 cm diameter. Resonant features observed in reflectance spectra of our slabs are found to depend on the exposure time, and can be tuned over a range of near-infrared frequencies.
We report that pentacene can be used as a protection layer of graphene using synchrotron radiation-based photoemission spectroscopy. When pentacene was deposited on a single layer graphene, molecular states of pentacene were clearly observed, yet no change in the band structure of graphene could be identified. Unique electronic properties of graphene can be preserved in the presence of pentacene layers, and this finding can be exploited for fundamental research as well as application of graphene in electronic devices. After exposing the pentacene-covered graphene to air followed by a subsequent annealing under vacuum, band structure of graphene was completely maintained.
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