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Wave packet dynamics in slowly modulated photonic graphene
摘要： Mathematical analysis on electromagnetic waves in photonic graphene, a photonic topological material which has a honeycomb structure, is one of the most important current research topics. By modulating the honeycomb structure, numerous topological phenomena have been observed recently. The electromagnetic waves in such media are generally described by the 2-dimensional wave equation. It has been shown that the corresponding elliptic operator with a honeycomb material weight has Dirac points in its dispersion surfaces. In this paper, we study the time evolution of the wave packets spectrally concentrated at such Dirac points in a modulated honeycomb material weight. We prove that such wave packet dynamics is governed by the Dirac equation with a varying mass in a large but ?nite time. Our analysis provides mathematical insights to those topological phenomena in photonic graphene.
关键词： Photonic graphene,Dirac points,Bloch decomposition,Honeycomb structure
更新于2025-09-19 17:13:59
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Diffractive dipolar coupling in non-Bravais plasmonic lattices
摘要： Honeycomb plasmonic lattices are paradigmatic examples of non-Bravais lattices. We experimentally measure surface lattice resonances in effectively free-standing honeycomb lattices composed of silver nanospheres. By combining numerical simulations with analytical methods, we analyze the dispersion relation and the near-field properties of these modes along high symmetry trajectories. We find that our results can be interpreted in terms of dipole-only interactions between the two non-equivalent triangular sublattices, which naturally lead to an asymmetric near-field distribution around the nanospheres. We generalize the interaction between the two sublattices to the case of variable adjacent interparticle distance within the unit cell, highlighting symmetry changes and diffraction degeneracy lifting associated to the transition between Bravais and non-Bravais lattices.
关键词： honeycomb plasmonic lattices,surface lattice resonances,non-Bravais lattices,diffraction degeneracy lifting,silver nanospheres,near-field properties,dipole-only interactions
更新于2025-09-19 17:13:59
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Heating Rate-Controlled Thermal Exfoliation for Foldable Graphene Sponge
摘要： Foldable supercapacitors are desired for the next generation of wearable electronics. In this study, highly foldable graphene sponges with a honeycomb structure are prepared at 300 °C using the convenient thermal exfoliation process. A slow heating rate (5?10 °C·min?1) around 200 °C and an external con?nement force are critical to a favorable exfoliation degree and uniform thickness of the graphene sponges. After being annealed at 1050 °C for 1 h, the conductivity of the graphene sponge has been improved from 2700 to 6900 S·m?1 without degrading its ?exibility. The capacitance of the annealed graphene sponge has been measured in an aqueous electrolyte solution of 1 M Na2SO4. Its best capacitance is 138.74 F·g?1, and it reduces by 3.6% at a half-fold state and by 8.9% at a quarter-fold state.
关键词： wearable electronics,Foldable supercapacitors,honeycomb structure,thermal exfoliation,graphene sponges
更新于2025-09-19 17:13:59
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Honeycomb-shaped charge collecting electrodes for dipole-assisted back-contact perovskite solar cells
摘要： Dipole-field-assisted charge-transporting-material-free lead halide perovskite solar cells (PSCs) using a back-contact configuration feature intrinsic advantages, such as no parasitic light absorption and high architectural defect tolerance. Herein, a newly designed, highly defect tolerant honeycomb-shaped back-contact (HBC) electrode was incorporated into dipole-field-assisted-back-contact PSCs, aiming to optimize the charge transport distance before being collected by the electrodes. HBC-PSCs with three feature sizes were fabricated in order to understand the effect of charge transport distance on device performance. The photovoltaic performance of HBC-PSCs correlates inversely proportional to the feature sizes. The mechanism behind the performance difference is elucidated via a detailed analysis through device current voltage characterization, transient photovoltage decay measurement and photocurrent mapping. A comprehensive comparison between honeycomb-shaped and interdigitated finger back-contact electrodes for PSCs is also conducted.
关键词： surface modification,charge transport distance,perovskite solar cells,honeycomb-shaped back-contact electrodes
更新于2025-09-19 17:13:59
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Switching Quasi-Flat Modes at the Interface between Detuned Anomalous Floquet Topological Insulators
摘要： Anomalous Floquet Topological Insulators (A-FTIs) [1–3] are time-dependent arrangements with topologically non-trivial phases. These recently discovered systems are characterized by an integer Winding number W [4]. We theoretically investigate photonic A-FTI comprised of honeycomb lattices of waveguides (see Fig. 1(a)). Crucially, the couplings between adjacent lattice sites are periodically modulated in time so that, at any point in time, a site is coupled to only one of its three next neighbors. This system exhibits a number of non-degenerate bands separated by a gap centered on the quasi-energy (cid:2) = 0. Since time-periodicity translates to periodicity in quasi-frequency, another band gap appears around (cid:2) = ±π. By varying the coupling angle θc, we obtain di?erent values (W0, Wπ) for the Winding numbers of the two gaps, as well as for the band’s Chern numbers (C). We ?nd that C = 0 if topological modes appear across both gaps. In contrast, the Winding numbers ful?ll (W0 ∨Wπ) = 1 and correctly count the number of protected modes across each gap, as predicted in [4] (see Fig. 1(b)). Based on these considerations, we explore the interface between two mutually detuned realizations of the aforementioned A-FTI, placed next to one another. The detuning is implemented by a constant on site potential and results in a relative shift of the respective band structures. If, as a result, the π-gap of the second system becomes matched with the 0-gap of the non detuned system, the boundary between these two domains identi?es a transition between di?erent, albeit topologically equivalent, media that share the same band gap. While the bulk-edge correspondence principle doesn’t allow topological modes to exist on such interfaces, we can nevertheless observe a number of seemingly trivial, quasi-?at, defect modes (see Fig. 1(c) inset). Their existence is enabled by the interplay between counter-propagating modes on the inside edges of each sub-system. Both interface modes are phase-matched with the edge modes for exactly one value of the wave vector k. This behaviour is con?rmed by tight-binding simulations of the dynamics of a broad beam (i.e. a narrow wave packet in k-space), which show no coupling between the topological mode and the trivial interface state except for the phase-matching points between the two (see Fig. 1(c)). This mechanism can be harnessed to selectively extract a fraction of light that is propagating in a topologically protected edge channel by depositing it into quasi-static defect modes.
关键词： honeycomb lattices,Anomalous Floquet Topological Insulators,quasi-?at defect modes,topological modes,Chern numbers,Winding number,photonic A-FTI
更新于2025-09-16 10:30:52
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Optical Properties of Buckled Bismuthene
摘要： In this paper, the optical properties of buckled bismuthene (a new 2D material) are studied in different strains. Different transitions in bismuthene’s band structure are mentioned and the optical advantages of buckled bismuthene are discussed. It is found that buckled bismuthene is strain independent infrared (IR) reducer and could be used in bio photonics.
关键词： 2D material,optical properties,reflection,group V monolayers,honeycomb lattice,absorption spectra,density functional theory,dielectric function,buckled bismuthene
更新于2025-09-11 14:15:04
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Electron Depleted ZnO Nanowalls based Broadband Photodetector
摘要： Pristine ZnO has been extensively reported for high responsivity UV photodetectors based applications. However, in general, its photo-response in visible and NIR region is very poor. In this article, a simple and cost-effective technique of synthesizing pristine ZnO honeycomb nanostructure based high responsivity broadband (200 nm - 950 nm) photodetector is demonstrated. The dark current of the device was found to be as low as 5.6 pA at 10 V applied bias. The maximum photo-current to dark current ratio was ~3.2 x 107 at 300 nm wavelength (measured at -10 V applied bias). The calculated linear dynamic range of the device is as high as 128.9 dB. The maximum specific photodetectivity, photoresponsivity and external quantum efficiency (@ 300 nm) calculated at -10 V bias was 2.07x1015 cm·Hz1/2·W-1, 115 A·W-1 and 47,583% respectively, which is comparable to some of the existing commercial broadband photodetectors.
关键词： Honeycomb,ZnO,Photodetector,Hydrothermal
更新于2025-09-11 14:15:04
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Chern and Z2 topological insulating phases in perovskite-derived 4d and 5d oxide buckled honeycomb lattices
摘要： Based on density functional theory calculations including a coulomb repulsion parameter U, we explore the topological properties of (LaXo3)2/(LaAlo3)4 (111) with X = 4d and 5d cations. the metastable ferromagnetic phases of Latco3 and Lapto3 with preserved P321 symmetry emerge as Chern insulators (CI) with C = 2 and 1 and band gaps of 41 and 38 meV at the lateral lattice constant of LaAlo3, respectively. Berry curvatures, spin textures as well as edge states provide additional insight into the nature of the ci states. While for X = Tc the CI phase is further stabilized under tensile strain, for X = Pd and Pt a site disproportionation takes place when increasing the lateral lattice constant from aLAo to aLno. the ci phase of X = Pt shows a strong dependence on the Hubbard U parameter with sign reversal for higher values associated with the change of band gap opening mechanism. Parallels to the previously studied (X2o3)1/(Al2o3)5 (0001) honeycomb corundum layers are discussed. Additionally, non-magnetic systems with X = Mo and W are identified as potential candidates for Z2 topological insulators at aLAo with band gaps of 26 and 60 meV, respectively. The computed edge states and Z2 invariants underpin the non-trivial topological properties.
关键词： density functional theory,perovskite-derived oxides,Chern insulators,Z2 topological insulators,honeycomb lattices
更新于2025-09-11 14:15:04
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Nanocomposites based on 3D honeycomb-like carbon nitride with Cd0·5Zn0·5S quantum dots for efficient photocatalytic hydrogen evolution
摘要： Honeycomb-like graphitic carbon nitride (HeC3N4) with unique morphology has been studied as a promising polymer photocatalyst. Herein, a novel binary metal sulfide constructed with HeC3N4 (Cd0·5Zn0·5S/HeC3N4) was prepared though the facile in situ precipitation method. The characterization data suggest that Cd0·5Zn0·5S quantum dots (QDs) are well dispersed on the macroporous structure of HeC3N4 (156 m2 g?1), which can provide higher surface area, more catalytic active sites and larger interface contact area with accelerating the migration and separation of charge carriers. By taking advantage of 0D/3D heterojunction structure, the Cd0·5Zn0·5S/HeC3N4 dramatically boosts the photocatalytic H2 evolution rate with the visible-light illumination. The Cd0·5Zn0·5S/HeC3N4-3 yields the highest photocatalytic activity of 5145 mmol h?1 g?1, which is 4.3 times as high as that of pure Cd0·5Zn0.5S. Furthermore, Cd0·5Zn0·5S/HeC3N4 composite presents high stability after four recycles. The enhanced visible-light-driven photocatalytic H2 production is attributed to the construction of n-n type heterojunction as well as the large surface area, which can inhibit the agglomeration of Cd0·5Zn0·5S nanoparticles, and efficiently transfer the photo-excited electron-hole pairs in Cd0·5Zn0.5S. Therefore, this work provides a potential way for designing advanced 0D/3D heterojunction.
关键词： Heterojunction,Honeycomb-like graphitic carbon nitride,Cd0·5Zn0·5S,Photocatalytic hydrogen generation
更新于2025-09-11 14:15:04
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Microstructure-Stabilized Blue Phase Liquid Crystals
摘要： We show that micron-scale two-dimensional (2D) honeycomb microwells can significantly improve the stability of blue phase liquid crystals (BPLCs). Polymeric microwells made by direct laser writing improve various features of the blue phase (BP) including a dramatic extension of stable temperature range and a large increase both in reflectivity and thermal stability of the reflective peak wavelength. These results are mainly attributed to the omnidirectional anchoring of the isotropically oriented BP molecules at the polymer walls of the top and bottom substrates. This leads to an omnidirectional stabilization of the entire BPLC system. This study not only provides a novel insight into the mechanism for the BP formation in the 2D microwell but also points to an improved route to stabilize BP using 2D microwell arrays.
关键词： honeycomb microwells,temperature range,stability,thermal stability,reflectivity,blue phase liquid crystals
更新于2025-09-11 14:15:04