- 标题
- 摘要
- 关键词
- 实验方案
- 产品
-
Surface-induced transition of nematic liquid crystals on graphene/SiC substrate
摘要： A nematic liquid-crystal director aligns along the armchair direction of graphene grown on a SiC substrate. The temperature-dependent textural change in the nematic phase is di?erent from the usual texture on the alignment layer. The isotropic-nematic phase transition temperature decreases over time after cell fabrication. Tiny domains occur with the phase transition and appear to be merged from a critical temperature with decreasing temperature in the nematic phase. This is thought to be due to the transition occurring at the interface. On the other hand, the nematic liquid crystal in graphene grown on a Cu foil does not show textural changes, and the phase transition temperature does not decrease even after a long time has elapsed. X-ray ?uorescence measurements indicate that silicon atoms exist in the liquid crystal possibly extracted from the SiC substrate. A model of ?rst-order phase transition on the graphene surface has been proposed. This transition is accompanied by an inhomogeneous distribution of scalar order parameters and the transformation from a small multi-grained structure to a large domain distribution in the director ?eld. This structural transformation takes place at a temperature di?erent from that corresponding to the bulk transition. Such behavior may be explained by the adsorption process of silicon atoms in contact with the SiC-graphene interface.
关键词： surface-induced transition,phase transition,SiC substrate,nematic liquid crystals,graphene
更新于2025-09-04 15:30:14
-
Liquid‐Crystal High‐Frequency Microwave Technology: Materials and Characterization
摘要： Ever since the advent of microwave technology, tunable devices, such as phase shifters, resonators, and antennas, have been indispensable in applications requiring radiofrequency signal filtering, beam shaping, or steering. This necessity becomes even more relevant in view of a new era in high-bandwidth wireless communications in 5G networks, satellite links, and advanced radars for sensing and safety. As the operating frequency is pushed toward the millimeter-wave range or beyond, the performance of traditional microwave tunable elements, such as PIN diodes, micro-electromechanical system switches, ferrites, or ferroelectric films, degrades, while their fabrication complexity and cost increases. In this respect, liquid crystals present a promising solution, as they provide continuous tuning, low dielectric constants, moderate losses, low dispersion, and potentially low cost. Here, a comprehensive overview of the available microwave liquid crystal materials is provided, including their key application-relevant properties, and the techniques employed for their characterization, focusing on the spectrum above 1 GHz. Their performance metrics in terms of dielectric constant tunability, response speed, insertion losses are discussed and guidelines for their selection in different microwave applications are provided. Moreover, the differences observed in the experimental data regarding their characterization are highlighted and possible sources of the observed discrepancies are discussed.
关键词： microwave technology,liquid crystals,microwave characterization techniques
更新于2025-09-04 15:30:14
-
Elusive torque sensed by liquid crystals
摘要： Almost half a century ago, it was predicted that the confinement of quantum fluctuations could induce mechanical rotation — the Casimir torque. This prediction has now been confirmed using liquid crystals. See Letter p.386
关键词： quantum fluctuations,liquid crystals,Casimir torque,mechanical rotation
更新于2025-09-04 15:30:14
-
Geometric stabilisation of topological defects on micro-helices and grooved rods in nematic liquid crystals
摘要： We demonstrate how the geometric shape of a rod in a nematic liquid crystal can stabilise a large number of oppositely charged topological defects. A rod is of the same shape as a sphere, both having genus g = 0, which means that the sum of all topological charges of defects on a rod has to be (cid:2)1 it usually shows only one hyperbolic hedgehog or a Saturn ring defect with negative unit charge. Multiple unit charges can be stabilised either by friction or large length, which screens the pair-interaction of unit charges. Here we show that the curved shape of helical colloids or the grooved surface of a straight rod create energy barriers between neighbouring defects and prevent their annihilation. The experiments also clearly support the Gauss–Bonnet theorem and show that topological defects on helices or grooved rods always appear in an odd number of unit topological charges with a total topological charge of (cid:2)1.
关键词： topological defects,geometric stabilisation,micro-helices,nematic liquid crystals,grooved rods
更新于2025-09-04 15:30:14