Dr. Torsten Hegmann Profile

Dr. Torsten Hegmann

at Kent State Univ

SPIE Involvement:

Author

Publications (5)

Proceedings Article | 20 August 2020 Presentation + Paper

Optical properties of nematic microlenses doped with chiral nanoparticles

K. Perera, A. Nemati, E. Mann, T. Hegmann, A. Jákli

Proceedings Volume 11472, 114720O (2020) https://doi.org/10.1117/12.2568570

KEYWORDS: Nanoparticles, Liquid crystals, Microlens, Circular polarizers, Water, Molecules, Microscopes

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Proceedings Article | 25 August 2017 Paper

Effects of size and ligand density on the chirality transfer from chiral-ligand-capped nanoparticles to nematic liquid crystals

Taizo Mori, Anshul Sharma, Ahlam Nemati, Leah Bergquist, Torsten Hegmann

Proceedings Volume 10361, 103610M (2017) https://doi.org/10.1117/12.2275262

KEYWORDS: Gold, Liquid crystals, Nanoparticles, Anisotropy, Molecules, Nanomaterials, Nanostructures

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Proceedings Article | 11 February 2012 Paper

New developments in nanoparticle-liquid crystal composites: from magic-sized semiconductor nanoclusters to alignment pattern formation via nanoparticle stenciling

Javad Mirzaei, Ryan Sawatzky, Anshul Sharma, Martin Urbanski, Kui Yu, Heinz-S. Kitzerow, Torsten Hegmann

Proceedings Volume 8279, 827913 (2012) https://doi.org/10.1117/12.909022

KEYWORDS: Gold, Liquid crystals, Glasses, Optical alignment, Semiconductors, Nanoparticles, Electro optics, Transmission electron microscopy, Quantum dots, Photomicroscopy

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We here report on the alignment and electro-optic properties of nematic liquid crystals (LCs) either containing nanoscale particles as additives or featuring particles patterned on substrates. The investigated nematic LCs or LC dispersions are doped or in contact with magic-sized semiconductor CdSe nanocrystals (MSNCs) or silane- and alkylthiol monolayercapped gold nanoparticles. Three single-sized CdSe quantum dots capped with myristic acid exhibiting bright bandgap photoluminescence (PL) at λ_max ~ 463 nm were tested as additives. Two of the quantum dots only vary in the amount of defects as indicated by different bandgap and deep trap PL. The third MSNC sample is compositionally different, doped with Zn. These MSNCs with almost identical sizes were doped at different concentrations (1-5 wt%) into the nematic phase of the 2-phenylpyrimidine-based LC1. Only the Zn-doped MSNCs showed the formation of birefringent stripes surrounded by areas of homeotropic alignment between plain glass slides at all concentrations as observed for many other nanoparticle-doped nematic LCs reported earlier by our group. In polyimide-coated glass slides favoring planar orientation of the nematic director, planar alignment was observed. Similarly, siloxane-coated gold nanoparticle additives with narrow size distribution, but larger size, show homeotropic alignment between plain glass and planar alignment in rubbed polyimide-coated cells. Surprisingly then, we succeeded in creating alignment patterns using smaller, ~2 nm alkylthiol-capped gold nanoparticles using a process called stenciling that allowed us to generate patterns of homeotropic alignment in a continuum of planar alignment of the nematic LC. Finally, electro-optic investigations on some of these samples revealed that only the Zn-doped magic-sized MSNCs significantly lower the dielectric anisotropy as well as the splay elastic constant of the nematic host, despite identical size and surface functionality of the three used MSNCs, which highlights the tremendous effect of the nanocrystal core composition on the electro-optic properties of the nematic host.