Bistable Devices Research Articles

A bistable ion-doped cholesteric liquid crystal smart window with a small amount of polymer

Bistable liquid crystal devices, which require electricity only at the switching processes of the two states, have advantages in energy saving and safety compared with monostable liquid crystal devices. Due to electrohydrodynamic and dielectric effects, the ion-doped cholesteric liquid crystal can switch between a focal conic state and a planar state with different frequencies of the driving voltage. However, the cholesteric liquid crystal that self-assembles from the dynamic scattering state always has a poor focal conic state, resulting in a low contrast ratio. This paper presents a bistable polymer-stabilized ion-doped cholesteric liquid crystal device. The introduction of a small amount of polymer network can greatly enhance the light scattering capabilities of the focal conic state, endowing the device with excellent electro-optic performance. The electro-optical properties of the device are investigated with the various content of monomer and chiral dopant, and rotational viscosity of liquid crystal. Liquid crystal with a low rotational viscosity coefficient is beneficial to the formation of a good polymer network. The pitch induced by chiral dopant impacts the formation process of the polymer network, which subsequently affects the electro-optical properties. The bistable device has a low driving voltage and a high contrast ratio, making it ideal for use in smart windows.

High-contrast optical bistability using a subwavelength epsilon-near-zero material.

Optical bistability opens up a promising avenue toward various optical nonlinear functions analogous to their electrical counterparts, such as switches, logic gates, and memory. Free-space bistable devices have unique advantages in large-scale integration. However, most proposed free-space schemes for optical bistability have limitations in one or more aspects of low contrast ratio, compromised compatibility, slow switching speed, and bulk size. Epsilon-near-zero (ENZ) materials have recently shown an ultrafast and giant optical nonlinearity within a subwavelength scale, potentially overcoming these obstacles. Using large-mobility indium-doped cadmium oxide (CdO) as the ENZ material, we numerically demonstrate two efficient schemes for high-contrast optical bistability within a deep subwavelength size based on the ENZ mode and the Berreman mode. The ENZ wavelength can be optically tuned with a typical time scale of sub-picoseconds, giving rise to a switchable bistability between the near-zero state and the high-reflection state. Our work contributes to the advances on compact and ultrafast all-optical signal processing.

An all-solid-state bistable electrochromic device based on an amorphous WO3−x nanostructured film

A new all-solid-state bistable electrochromic device based on an amorphous WO3−x nanostructured film was constructed. This device had a promising performance and showed potential applications in energy-saving smart windows and reflective displays.

Vibration Characteristics and Experimental Research of an Improved Bistable Piezoelectric Energy Harvester

Bistable piezoelectric energy harvester (BPEH) can remove mechanical energy waste, which is expected to realize the self-power supply of wireless sensors. To further improve the energy harvesting efficiency, we designed an improved bistable piezoelectric energy harvester (IBPEH). The restoring force model of the composing beam is acquired based on fitting experimental data, and the nonlinear magnetic model is obtained by using the magnetic dipole method. The electromechanical coupling dynamics model of the system is established based on Newton’s second law and Kirchhoff’s law. Based on the control variable method, the influences of excitation frequency and excitation amplitude on the vibration characteristics of IBPEH and BPEH are compared in simulation analysis. Moreover, the correctness of the theoretical analyses is verified by experiments. The results show that variations in the number of magnets and appropriate adjustments in their positions can broaden the operating frequency bandwidth of the bistable piezoelectric energy harvester, and realize large-amplitude periodic motion at lower excitation amplitudes. IBPEH can yield a higher voltage than BPEH under the same excitation conditions. This paper provides a theoretical basis for optimizing the potential well and further improving the electric energy harvest efficiency of the bistable piezoelectric energy harvester device.

A bistable electrochromic device based on poly(viologen)s

A bistable electrochromic device based on poly(viologen)s is demonstrated with good overall performance, including bistability (4981 s), switch-on voltage (−1.0 V) and reversibility (≥1000 cycles). Overall, these results imply that the control of the diffusivity of viologens is an effective methodology for achieving excellent bistability and low energy consumption.

Dirac semimetals Tamm plasmons-induced low-threshold optical bistability at terahertz frequencies

In this paper, we theoretically study the optical bistability (OB) of reflected beams in a composite multilayer structure with three-dimensional Dirac semimetals (3D DSMs) and one-dimensional photonic crystal (1D PC) on both sides of the spacer layer. The optical Tamm states (OTSs) excited by the 3D DSMs-1D PC multilayer structure significantly enhances the local electric field near the nonlinear 3D DSMs, which provides a positive condition for the realization of low threshold OB. Through parameter optimization, we obtain a threshold electric field with an incident electric field of 106 V/m levels. Furthermore, the influences of the Fermi energy of 3D DSMs, the angle of the incident light and dispersion characteristics of the spacer layer on the hysteretic behavior and the threshold of OB are clarified. We believe above results will provide possible options for nonlinear optical bistable devices.

Spatial Nonreciprocal Transmission and Optical Bistability Based on Millimeter‐Scale Suspended Metasurface

AbstractWhen light interacts with microscopic objects at the micro‐ and nano‐scale, the momentum exchange between photons and objects can be very significant. While the optical radiation pressure at the same level is usually too weak to change the mechanical state of macro‐scale objects at millimeter scale or beyond. Suspended metasurfaces with excellent mechanical and optical properties are ideal candidates for light‐matter interactions. Here, without sound insulation conditions, the spatial optical nonreciprocity based on an optomechanical system with a 2 mm × 2 mm × 110 nm Si3N4 suspended metasurface at the telecom wavelength is demonstrated, with peak wavelength shift up to 1.1 pm, which is about 4.0 times of the full width at half maximum, together with optical bistability at only about 10 W cm−2 input intensities, which is more than 4 orders of magnitude lower than traditional nonlinear optical mechanism. This work may pave new avenues for spatially nonreciprocal devices and bistable devices, and benefit the applications such as precision sensing, cavity quantum optomechanics, and all‐optical switching.

A novel bistable device to study mechanosensitive cell responses to instantaneous stretch

The behavior of cells and tissues in vivo is determined by the integration of multiple biochemical and mechanical signals. Of the mechanical signals, stretch has been studied for decades and shown to contribute to pathophysiological processes. Several different stretch devices have been developed for in vitro investigations of cell stretch.In this work, we describe a new 3D-printed uniaxial stretching device for studying cell response to rapid deformation. The device is a bistable compliant mechanism holding two equilibrium states—an unstretched and stretched configuration—without the need of an external actuator. Furthermore, it allows multiple simultaneous measurements of different levels of stretch on a single substrate and is compatible with standard immunofluorescence imaging of fixed cells as well as live-cell imaging.To demonstrate the effectiveness of the device to stretch cells, a test case using aligned myotubes is presented. Leveraging material area changes associated with deformation of the substrate, changes in nuclei density provided evidence of affine deformation between cells and substrate. Furthermore, intranuclear deformations were also assessed and shown to deform non-affinely.As a proof-of-principle of the use of the device for mechanobiological studies, we uniaxially stretched aligned healthy and dystrophic myotubes that displayed different passive mechanical responses, consistent with previous literature in the field. We also identified a new feature in the mechanoresponse of dystrophic myotubes, which is of potential interest for identifying the diseased cells based on a quick mechanical readout. While some applications of the device for elucidating passive mechanical responses are demonstrated, the simplicity of the device allows it to be potentially used for other modes of deformation with little modifications.

Low-voltage, solution-processed, two-terminal organic bistable memory device

An low-voltage, solution-based spin cast-processed two-terminal bi-stable memory device was fabricated by using organic-inorganic-organic tri-layer structure (MEHPPV/ZnO/MEHPPV) onto indium tin oxide coated glass. Tri-layer device structure displayed the significant switching characteristics. The absence of degradation after 1 h retention test at 120 °C was noticed. The consistent memory behavior was noticed even after 50 cycles. Electron tunneling mechanism was utilized for describing switching mechanism of the device. The result emphasizes that the class of memory devices have been fabricated with organic-inorganic-organic nanocomposites, which has led to considerable research and development efforts to the scene of latent applications.

Defect Dynamics in Anomalous Latching of a Grating Aligned Bistable Nematic Liquid Crystal Device

Deliberate manipulation of topological defects is of particular interest for liquid crystal applications. For example, surface bistability occurs in the grating aligned Zenithal Bistable Device due to the stabilisation of ±½ defects at the points of high surface curvature. Conventional latching between continuous and defect states has previously been simulated satisfactorily using Q-tensor models that include the effect of weak-anchoring and flexoelectricity. However, experimental studies show that some arrangements lead to anomalous latching regimes. The Q-tensor model is used to show that such effects occur when the defects become detached from the surface and have more complex paths in the bulk of the sample.

Bistable electrochromic dual-output array display based on intramolecular proton coupled electron transfer

Bistable electrochromic systems are widely considered as a promising information and energy storage devices, attributed to the capability of maintaining their optical states without consuming energy. However, long response time and shorter steady-state duration hinder its development. Here, we report a series of R-amide-fluorane dyes with quick switching and bistability based on intramolecular proton-coupled electron transfer (PCET) electrochromic mechanism and dynamic hydrogen bonding effects. PCET channel building and stable-state reaction energy barrier are proved using DFT simulation. Optimized bistable electronic device based on R-amide-fluorane dyes shows excellent performance including good bistability (>86 h), fast switching (<1.8 s), bright color, dual output (color and fluorescence), high discoloration contrast, coloration efficiency (>1338 cm2·C−1), and reversibility (>1000 cycles). The successful exploration and design concept provide a new viable path and potential applications in energy saving materials.

Optical Bistability in a Tunable Gourd-Shaped Silicon Ring Resonator.

In this study, a tunable gourd-shaped ring resonator is demonstrated to generate optical bistability. The system consists of two sub-rings for a gourd shape configuration with a U-shaped wave guiding pathway. The transfer matrix method and FDTD simulation are used to acquire the spectral characteristics of the system. For the fabricated device, the spectra profile and extinction ratio can be effectively tuned by the microheater above the U-shaped waveguide, which matches with the theoretical results. Due to the gourd structure of the resonator, the light waves in two rings can be cross-coupled with each other, and the optical bistability could come out effectively with the change in the input optical power around 6 mW. The presented optical bistability devices have great application potential in optical information processing such as optical storage, switch and logic operation.

Tunable optical bistability in graphene Tamm plasmon/Bragg reflector hybrid structure at terahertz frequencies

Tunable optical bistability (OB) plays an active role in the manipulation of optical switches. Here, by combining graphene with one-dimensional photonic crystal (1D PC) with a defect layer, we theoretically design a simple multilayer structure to manipulate OB. Through the coupling of Tamm plasmon (TP) and defect mode (DM), an induced narrow peak can be generated in the original wide reflection angle, so it presents a richer situation of OB. The theoretical results show that the OB can be adjusted by optimizing the Fermi energy, the number of graphene layers. In addition, the effects of incident angle, the thickness of defect layer, and other structural parameters on OB are also clarified. We believe the above results can provide a new paradigm for the construction of controllable bistable devices.

Tunable optical bistability based on Bloch surface waves in one-dimensional photonic crystal with graphene

Graphene possesses large nonlinear conductivity in terahertz region, which makes it a very promising material for nonlinear bistable devices. In this paper, we theoretically study the optical bistability (OB) of reflected beam in a multilayer structure with graphene embedded between the truncated layer and the substrate. The Bloch surface wave excited by the one-dimensional photonic crystal (1D PC) coupling structure significantly enhances the local electric field near the nonlinear graphene, which provides a positive condition for the realization of low-threshold OB. Through parameter optimization, we obtain a threshold electric field with an incident electric field of 105 V/m levels. Furthermore, the influences of graphene’s Fermi energy and relaxation time, as well as those of the incidence angle, on the hysteretic behavior and the threshold of OB are clarified. This approach may provide a feasible scheme for the nonlinear optical bistable devices.

MoS2 nanosheets functionalized with ferrocene-containing polymer via SI-ATRP for memristive devices with multilevel resistive switching

Designing and preparing memristive materials with multilevel memristive switching characteristics is an effective strategy for improving the data storage capacity of devices. Herein, by grafting a ferrocene-containing polymer (PFMMA) from molybdenum disulfide nanosheets (MoS2 NSs) via polydopamine (PDA)-mediated surface-initiated atom transfer radical polymerization (SI-ATRP), we synthesized a novel two-dimensional nanomaterial, MoS2-PDA-PFMMA. The fabricated Al/MoS2-PDA-PFMMA/ITO sandwich-structured electronic device exhibited asymmetric multilevel resistive switching characteristics, which should give it a larger data storage capacity compared with traditional electrical bistable memristive devices. This work realized multilevel resistive switching in the device by material structure design, which opens up a new perspective for developing memristive devices with ultra-large data storage capacities.

Novel Bistable Electrochromic Devices Inspired by “Hydroxyl‐Acids”

AbstractThe development of bistable electrochromic materials is a promising way to reduce the energy consumption of displays. However, bistable devices with ideal implementation schemes and electrochromic performance still remain challenging due to the inherent limitations of existing electrochromic materials. Herein, a theory of “hydroxyl‐acids” assisted improvement of electrochromic rate and bistability of fluorane dyes is proposed and applied to solid‐state electrochromic devices. 80% hydroxypropyl acrylate‐20% methyl methacrylate copolymer‐based electrochromic film prepared by the theory of “hydroxyl‐acids” has a higher electrochromic rate (4.1 times) and bistability (5.4 times) than traditional PMMA‐based electrochromic films in the device. In addition, the optimum device is obtained by optimizing each layer component content of the device. The novel electrochromic device has good overall performance, including coloring time (7.5 s), transmittance change (&gt;70%), coloration efficiency (872 cm2 C‐1), bistability (50 h), and reversibility (1,000 cycles). The theory of “hydroxyl‐acids” is suitable for a variety of fluorane dyes, and polychromatic bistable electrochromic windows are developed.

Electrical Properties of Eggshell-Derived CaO Composited with Polyvinylpyrrolidone for Bistable Device

In this work, bistable devices were fabricated from eggshell-derived calcium oxide (CaO). CaO powders can be obtained from the calcination of chicken eggshells at temperatures from 700-1000 °C. The properties of derived CaO were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, and field-emission scanning electron microscopy. CaO was composited with polyvinylpyrrolidone (PVP) polymer to fabricate a bistable device with the device structure of ITO/PVP:CaO/Al. The maximum ON/OFF current ratio for the device was approximately 104. In addition, the retention time operations reached higher than 104 s, which revealed the stability of the bistable device. The theoretical model and conduction mechanisms were presented to explain the behavior of the bistable device.

Low-Threshold Optical Bistability in the Graphene-Oxide Integrated Asymmetric Nanocavity at Visible Light Frequencies.

Here, we propose an optical bistable device structure with a few layers of graphene oxide integrated in the metal-dielectric-metal based asymmetric nanocavity. Through the light confinement in the nanocavity, the third order nonlinear absorption of graphene oxide can be significantly enhanced, which experimentally delivers low-threshold optical bistability at the visible wavelength of 532 nm with only 267 KW/cm2 intensity. In addition, the switching threshold can be further reduced via increasing the graphene oxide thickness, hence paving a new way for achieving tunable optical bistable devices at visible light frequencies.

A Wirelessly Controlled Shape‐Memory Alloy‐Based Bistable Metal Swimming Device

Shape memory Nitinol has long been used for actuation. However, utilizing Nitinol to fabricate novel devices for various applications is a challenge, but has shown incredible promise and impacts. Bistable metal strips are widely adopted for shape morphing purposes (primarily in kid's toys, e.g., snap bracelets) due to their easy and robust transformation between two states. Herein, Nitinol shape memory alloy and bistable metal strip are combined to fabricate a swimming actuator with both slow moving and fast snapping capability, akin to an octopus swimming slowly in water, but quickly moving upon encountering a threat. The actuator developed here can also swim in multiple directions, all controlled by a wireless module. Furthermore, it is demonstrated that an onboard sensor can be incorporated for potential environmental monitoring applications. The fact that the device developed here has no mechanical parts, makes this an interesting potential alternative to more expensive, and energy consuming boats. A preprint version of the article can be found at: https://www.authorea.com/doi/full/10.22541/au.164199106.60208565.

Controllable optical bistability with perfect photon absorption

We propose a scheme for controlling nonlinear coherent perfect absorption (CPA) in a three-level Λ-type atom-cavity system. Generally, the normally nonlinear CPA and the bistable CPA can be attained at different frequencies of an input probe field. With a coherent control field coupling one of the ground states and the excited state of the atoms, two types of CPA can be attained at the same frequency. Besides, for the bistable CPA, the highest output-input ratio of the high stable state and the low stable state is approximately 1, and the threshold and the hysteresis cycle of the bistability are controllable by the control field. The results of our study may potentially be applied in optical bistable switching and optical logic devices.