An official website of the United States government
Disclination lines play a key role in many physical processes, from the fracture of materials to the formation of the early universe. Achieving versatile control over disclinations is key to developing novel electro-optical devices, programmable origami, directed colloidal assembly, and controlling active matter. Here, we introduce a theoretical framework to tailor three-dimensional disclination architecture in nematic liquid crystals experimentally. We produce quantitative predictions for the connectivity and shape of disclination lines found in nematics confined between two thinly spaced glass substrates with strong patterned planar anchoring. By drawing an analogy between nematic liquid crystals and magnetostatics, we find that i) disclination lines connect defects with the same topological charge on opposite surfaces and ii) disclination lines are attracted to regions of the highest twist. Using polarized light to pattern the in-plane alignment of liquid crystal molecules, we test these predictions experimentally and identify critical parameters that tune the disclination lines’ curvature. We verify our predictions with computer simulations and find nondimensional parameters enabling us to match experiments and simulations at different length scales. Our work provides a powerful method to understand and practically control defect lines in nematic liquid crystals.
more »
« less
Spatial Photo‐Patterning of Nematic Liquid Crystal Pretilt and its Application in Fabricating Flat Gradient‐Index Lenses
Abstract Liquid crystals offer a dynamic platform for developing advanced photonics and soft actuation systems due to their unique and facile tunability and reconfigurability. Achieving precise spatial patterning of the liquid crystal alignment is critical to developing electro‐optical devices, programmable origami, directed colloidal assembly, and controlling active matter. Here, a simple method is demonstrated to achieve continuous 3D control of the directions of liquid crystal mesogens using a two‐step photo‐exposure process. In the first step, polarized light sets the orientation in the plane of confining substrates; the second step uses unpolarized light of a prescribed dose to set the out‐of‐plane orientation. The method enables smoothly varying orientational patterns with sub‐micrometer precision. As a demonstration, the setup is used to create gradient‐index lenses with parabolic refractive index profiles that remain stable without external electric fields. The lenses' focal length and sensitivity to light polarization are characterized through experimental and numerical methods. The findings pave the way for developing next‐generation photonic devices and actuated materials, with potential applications in molecular self‐assembly, re‐configurable optics, and responsive matter.
more »
« less
- Award ID(s):
- 2104747
- PAR ID:
- 10525561
- Publisher / Repository:
- Wiley
- Date Published:
- Journal Name:
- Advanced Materials
- Volume:
- 36
- Issue:
- 23
- ISSN:
- 0935-9648
- Page Range / eLocation ID:
- 23100083
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Here, we demonstrated directed self-assembly of quasi-2D cesium lead bromide perovskite nanoplates by liquid–air interfacial assembly. Due to their ionic crystal nature, perovskite nanocrystals are susceptible to degradation by most polar immiscible sublayer solvents (acetonitrile, diethylene glycol). We used glyceryl triacetate as a liquid substrate for nanoplate self-assembly. By tuning the interfacial energy and volume fraction of nanoplates, we achieved monolayer ensembles of nanoplates with face-down and edge-up ordering >100 μm2 in area. Controlled ordering of these confined structures allowed us to access aligned electronic transition vectors in perovskite nanocrystal thin films. The dipole orientation factor, or proportion of horizontal dipoles, was modulated from Θ = 0.78 for face-down assemblies to Θ = 0.48 for edge-up assemblies, which corresponds to the majority in-plane and out-of-plane emissive modes, respectively. Control over nanoparticle ordering and dipole orientation in perovskite nanocrystals could lead to enhanced waveguides, light outcoupling, and photon coherence in photonic devices.more » « less
-
Abstract Tunable optical lenses are in great demand in modern technologies ranging from augmented and virtual reality to sensing and detection. In this work, electrically tunable microlenses based on a polymer‐stabilized chiral ferroelectric nematic liquid crystal are described. The power of the lens can be quickly (within 5 ms) varied by ≈500 diopters by ramping an in‐plane electric field from 0 to 2.5 V µm−1. Importantly, within this relatively low‐amplitude field range, the lens is optically isotropic; thus, its focal length is independent of the polarization of incoming light. This remarkable performance combines the advantages of electrically tuned isotropic lenses and the field‐controlled shape of the lens, which are unique properties of chiral ferroelectric nematic liquid crystals and have no counterpart in other liquid crystals. The achieved lens performance represents a significant step forward as compared to liquid lenses controlled by electrowetting and opens new possibilities in various applications such as biomimetic optics, security printing, and solar energy concentration.more » « less
-
Abstract Patchy particles, i.e., colloidal particles whose surface properties have been modified in predetermined patterns, can serve as building blocks for efficient self‐assembly of well‐defined, ordered structures. This paper introduces MicroSphere AutoLithography (µSAL), a scalable lithographic method for production of patchy particles with arbitrary patch motifs. This technique leverages dielectric microspheres as both a lithographic substrate and the illuminating optic, using the fact that when a plane wave of light is refracted through a sphere, it produces a circular patch of high‐intensity illumination on the back hemisphere. Exposing a collection of microspheres to multiple plane waves, every sphere simultaneously projects identical patterns of illuminated patches onto its own surface. Here, µSAL is demonstrated in barium titanate glass (BTG) microspheres that are coated with a thin (≈40 nm) conformal film of poly(dopamine) acting as the photoresist, fixating the optical pattern into a permanent metal structure through light‐induced reduction of silver ions from the liquid suspension. Varying the index of refraction of the BTG spheres and the suspension produces a range of patch sizes and geometries in good agreement with theoretical modeling.more » « less
-
Abstract Heterogeneously integrated hybrid photonic crystal cavities enable strong light–matter interactions with solid state, optically addressable quantum memories. A key challenge to realizing high quality factor (Q) hybrid photonic crystals is the reduced index contrast on the substrate compared to suspended devices in air. This challenge is particularly acute for color centers in diamond because of diamond’s high refractive index, which leads to increased scattering loss into the substrate. Here, we develop a design methodology for hybrid photonic crystals utilizing a detailed understanding of substrate-mediated loss, which incorporates sensitivity to fabrication errors as a critical parameter. Using this methodology, we design robust, high-Q, GaAs-on-diamond photonic crystal cavities, and by optimizing our fabrication procedure, we experimentally realize cavities withQapproaching 30,000 at a resonance wavelength of 955 nm.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript
- Journal Article:
- https://doi.org/10.1002/adma.202310083
