Bistability Effect Research Articles

808 nm-excited multiband NIR emission with looping mechanism and intrinsic bistability in Er3+ singly-doped BiOCl layered semiconductor

In this work, under excitation at 808 nm, not only an unusual dominant emission of 2I11/2 → 4I15/2 transition (1.0 μm) but also the relatively weaker 1.55 μm luminesce (2I13/2 → 4I15/2) of Er3+ ions are observed with multi-phonon process and optical bistability behavior simultaneously for the first time. The bistability loops exhibit uniformly clockwise cycle characterized by a relatively lower trace of emission intensity at decreasing pump power. The result show that the looping behavior of NIR emissions has been found to be related to the 808 nm excited multi-photon band transition of BiOCl. Temperature sensing behavior of Er3+ indicate that such bistability effect is associated with thermally enhanced nonradiative decay and reduced luminescence quantum yield due to the strong pump-induced local thermal loading. This work may offer a novel insight into the transition behavior of lanthanides in layered semiconductors and promote the potential applications in optical switchers and temperature sensing.

Enhanced Small-Signal Responsivity in Silicon Microring Photodetector Based on Two-Photon Absorption

We experimentally investigated methods of enhancing the small-signal responsivity of a silicon pin microring photodetector based on two-photon absorption for detecting small optical signals in the telecommunication wavelength range. Two approaches are demonstrated, the first exploiting the bistability effect in the nonlinear microring resonator while the second employing an optical bias at a different wavelength to increase the differential responsivity. We achieved a small-signal responsivity of 180 mA/W with the first approach and 141 mA/W with the second approach, both of which represent almost 10-fold enhancement over direct detection of small optical signals by the same silicon pin microring detector. Our techniques have potential applications in amplitude demodulation, heterodyne detection, and optical power monitoring in WDM communication channels.

Electron bistability and switching effects in Mo/p-CdTe/Mo structure

It has been experimentally shown that in a simple metal–semiconductor-metal structure with ohmic contacts, a reversible transition from a high-resistance state to a state with high electrical conductivity is possible under the influence of short current pulses of 80-ns duration with a peak voltage of more than 20 V. It was established that after the breakdown under static voltage, the structure irreversibly goes into a state with high electrical conductivity. At the same time, sections with negative differential resistance and negative differential conductivity appear on its low-frequency current–voltage characteristics at voltages less than 1 V. The most probable physical mechanisms that can provide such current–voltage characteristics are considered.

The Effect of Quartz Window on Bistability of the Silicon Wafer in Lamp-Based Reactor

The effect of a quartz plate (window) on the silicon wafer temperature is studied in the conditions of the combined thermal transfer in a lamp-based chamber for the rapid thermal treatment (RTP) set up. The chamber for RTP is simulated by a radiative-closed thermal system including the influence of quartz window as a spectral filter of lamp emission and a source of emitted thermal radiation. Energy equations for thermal fluxes involved in the heat input and output from the working wafer and quartz window are solved in spectral approximation. The transfer characteristics that are defined by the temperature dependencies of the silicon wafer and the quartz window on the temperature of the heater are accounted. It is shown that temperature bistability in the silicon wafer initiates an induced bistability into the quartz window that does not reveal bistable behavior because of the linear temperature dependence of its total optical characteristics. A possibility for simulation of the quartz window by spectral restriction of the heater radiation is confirmed. The availability of the weak bistable effect in the mode of zero effective heat exchange coefficient of a non-radiative component of the thermal flux removed from the working wafer has been obtained.

Influence of top electrode on resistive switching effect of chitosan thin films

Abstract

Finite‐Dimensional Bistable Topological Insulators: From Small to Large

AbstractPhotonic topological insulators supporting unidirectional topologically protected edge states represent an attractive platform for the realization of disorder‐ and backscattering‐immune transport of edge excitations in both linear and nonlinear regimes. While the properties of the edge states at unclosed interfaces of two bulk media with different topologies are known, the existence of edge states in practical finite‐dimensional topological insulators fully immersed in a nontopological environment remains largely unexplored. In this work, using realistic polariton topological insulators built from small‐size honeycomb arrays of microcavity pillars as an example, it is shown how topological properties of the system build up upon gradual increase of its dimensionality. To account for the dissipative nature of the polariton condensate forming in the array of microcavity pillars, the impact of losses and resonant pump leading to rich bistability effects in this system is considered. The mechanism is described in accordance with which trivial‐phase pump “selects” and excites specific nonlinear topological edge states circulating along the periphery of the structure in the azimuthal direction, dictated by the direction of the external applied magnetic field. The possibility of utilization of vortex pump with different topological charges for selective excitation of different edge currents is also shown.

Critical phenomena and nonlinear dynamics in a spin ensemble strongly coupled to a cavity. I. Semiclassical approach

We present a theoretical study on the nonlinear dynamics and stationary states of an inhomogeneously broadened spin ensemble coupled to a single-mode cavity driven by an external drive with constant amplitude. Assuming a sizeable number of constituents within the ensemble allows us to use a semiclassical approach and to formally reduce the theoretical description to the Maxwell-Bloch equations for the cavity and spin amplitudes. We explore the critical slowing-down effect, quench dynamics, and asymptotic behavior of the system near a steady-state dissipative phase transition accompanied by a bistability effect. Some of our theoretical findings have recently been successfully verified in a specific experimental realization based on a spin ensemble of negatively charged nitrogen-vacancy centers in diamond strongly coupled to a single-mode microwave cavity (see Science Adv. 3, e1701626 (2017)).

Low Velocity Impact of Bistable Laminated CFRP Composites

Laminated carbon fiber reinforced polymer (CFRP) composites have gained popularity in engineering applications due to their lightweight and strong in-plane mechanical properties. This material, however, performs poorly with respect to out-of-plane impact resistance. The objective of this research was to investigate the effect of bistability on the low velocity impact resistance of laminated CFRP composites. Bistable composites have the ability to alternate between two different geometric equilibria through external loading, and when unloaded, do not require external forces to maintain either geometry. Laminated CFRP composite specimens of bistable, flat symmetric, and curved symmetric configurations were subjected to low velocity impacts of 20 J. The acceleration and force of each impact was recorded using an accelerometer and a load cell mounted on the impactor. The sensor data was used to analyze the dynamic response and calculate the energy absorption of each impact. Post-impact crack length measurements and damage characterization were used to conduct a damage resistance analysis. The effects of geometry, stacking sequence, and bistability of the impacted specimens were determined. The results showed that bistability improves the low velocity impact damage resistance of laminated CFRP composites through increased energy absorption and specimen kinetic energy.

A Semianalytical Model for the Determination of Bistability and Curvature of Metallic Cylindrical Shells

Bistable metal shells with a fully closed unfolded geometry are of great interest as lightweight construction parts which could be transported without housing and unfolded at the construction place. In order to achieve the effect of bistability in metallic shells, residual stresses with a specific distribution along the shell thickness are necessary. These residual stresses can be introduced in bending processes. The tools with specific bending radii are used to influence the curvature of the shell in the different stable states and thus determine whether a completely closed profile can be achieved. In addition to the forming process, the shell thickness and the shell material have an effect on the achievable geometries and stability. In order to manufacture bistable metallic cylindrical shells from different materials and shell thicknesses, it is necessary to be able to determine a promising process sequence and corresponding bending radii in advance. For this reason, this article presents a semianalytical model for the calculation of bistability and final curvatures. This model is applied to an incremental die-bending process using two bending operations with bending radii of 6 to 12 mm and a 0.2 mm thick steel shell of grade 1.1274 (AISI 1095). The calculation results show that bistability cannot be reached for all combinations of the two bending radii. Moreover, the model indicates that a bistable and fully closed shell is only achieved for a bending radii combination of R1 = 6 mm and R2 = 6 mm. With the aim of model verification, experiments with a closed-die incremental bending tool were performed. Calculated and experimental results show good correlation regarding bistability and curvature. In addition, X-ray diffraction measurement of the residual stresses shows a good qualitative agreement regarding the calculated and experimental results.

Production of bistable fully closed metallic shells by introducing residual stresses during bending processes

Bistable fully closed metallic shells are of great interest as lightweight construction components, which could be transported without enclosure and unfolded at the construction place. The effect of bistability in metallic shell structures is achieved by a specific distribution of residual stresses over the shell thickness, which can be introduced by bending processes. So far no fully closed structures have been achieved in metallic shells. Hence, the aim of this paper is the identification of suitable bending radii combinations in order to produce a bistable shell with a fully closed tube shape in the deployed state. Therefore, a Finite Element (FE) model was established to determine whether bistability occurs in dependence on the bending radii. The numerical model indicates, that bistability can be achieved for 0.2 mm thick spring steel 1.1274 (AISI 1095) by applying two die-bending operations with small bending radii of 6–8 mm. Accompanying experiments with a closed-die incremental bending tool were performed. A good transferability of the numerical results regarding the occurrence of bistability and the calculated residual stresses is shown. For the second aspect, X-ray diffraction measurements of residual stresses were used for comparison. Finally, the present work presents a process route to generate a bistable shell with a fully closed tube shape structure in the deployed state, having a radius of 40.95 mm.

Thermally induced dispersive optical bistability in silver nanosuspensions produced by pulsed laser ablation method

The thermally induced optical bistability in prepared silver (Ag) nanosuspensions have been studied experimentally, using Fabry–Perot and Mach–Zehnder interferometry methods. Two Ag nanosuspensions of different sizes were produced by different fluences of pulsed laser ablation method in distilled water. The pulsed Nd:YAG laser of 7 ns pulse width, 1064 nm wavelength and different fluences was employed to produce Ag nanosuspensions. Experimental observations were performed by an ultraviolet–visible–near infrared spectrophotometry. Structure and size of prepared Ag nanoparticles were diagnosed using transmission electron microscope images. Fabry–Perot and Mach–Zehnder interferometry methods were used to carry out the optical bistability process in prepared Ag nanosuspensions. In two considered interferometers, the obtained phase shifts of the hysteresis loops based on the optical bistability are inversely proportional to the nonlinear refractive index of samples and thickness of Ag nanosuspensions cells. Results indicate that the induced thermal effect of the optical bistability can be tuned by modifying parameters such as the nonlinear refractive index and applied interferometry methods. Hence, a desirable situation for the thermo-optical effects of the optical bistability can be easily realized in Ag nanosuspensions.

A sensitive biosensor based on optical bistability in a semiconductor quantum dot-DNA nanohybrid

We propose a scheme of a sensitive biosensor based on optical bistability (OB) in a biological semiconductor quantum dot (SQD)-DNA coupled nanohybrid. By plotting bistability phase diagrams within the system’s parameter space, we show that the bistable effect can be switched on or off by only tuning the pumping intensity or the detuning of the pump field from the exciton resonance. Simultaneously, we reveal that the bistability only exists in the strong SQD-DNA coupling regime. Specifically, we derive the matching relation between the excitation conditions and the coupling strength when the bistability just appears. Moreover, we demonstrate that the OB is highly sensitive to the SQD-DNA coupling strength which is strongly correlated to the length of DNA molecules and DNA concentration. This investigation may be useful for opening a new way to build optical switches and providing a novel and convenient platform to detect DNA molecules.

Progression of heavy plates from stable falling to tumbling flight

This study examines the transition of stable falling to tumbling flight for freely falling heavy plates in a two-dimensional viscous fluid, solved via direct numerical simulation with the immersed boundary method. The simulations are performed at a range of Reynolds number ($Re$) of up to 500 and a dimensionless moment of inertia ($I^{\ast }$) up to 10. It is found that a plate may settle to stable falling or develop into tumbling descent depending on the initial angle of release $\unicode[STIX]{x1D703}_{0}$. The characteristics and performance that distinguish two flight states are investigated. This bistability is analysed with phase portraits and the region mapped across the regime of $I^{\ast }$ and $Re$ at a specific thickness ratio. In determining the flight state, the respective critical $\unicode[STIX]{x1D703}_{0}$ is found to follow a power law through $I^{\ast }$ and $Re$. It is suggested that the changing slope of the lift curve that the plate undergoes sets the two flight states apart. Flow fields also reveal that the recirculation behind the plate is confined by the vortex structures and provides an additional rotation to the plate. An experiment is performed suggesting that bistability also occurs at Re ${\sim}O(10^{4})$. Other shapes are also simulated and the different bistable effects are discussed.

Nonelectric Sustaining Bistable Polymer Framework Liquid Crystal Films with a Novel Semirigid Polymer Matrix.

In this work, a bistable polymer framework liquid crystal (PFLC) thin film by thermal curing of epoxy monomers with two different thiols, a traditional flexible-structure thiol and a novel original rigid-structure thiol, has been successfully fabricated, combining a novel mixed morphology of polymer matrix and cholesteric liquid crystals with negative dielectric anisotropy. The polymer framework morphology has been formed by curing two types of epoxy monomers with two types of thiols, and the liquid crystals tend to be focal conic textures with large size domains at the initial state in the PFLC film so that it has a moderate light transmissivity at this state between the transparent state and the opaque state. Thus, the devices based on PFLC films can be switched reversibly between the transparent state and the opaque state by alternative electric field. In addition, the states can be sustained after the electric field is removed. The bistable memory effect comes from the anchoring effects of the polymer frameworks with a novel morphology in the microdomains of the PFLCs. Therefore, the optimized bistable PFLC film keeps its initial state without external electric field and any other energy consumption for a long time after altering the state by applying an instant electric field. The special polymer frameworks in the bistable PFLC films endow the films with excellent electro-optical properties and mechanical properties. The devices are energy-efficient and cost-saving and have great potential applications in energy-efficient reflective displays, electronic papers, writing tablets, and smart windows.

Bistable Topological Insulator with Exciton-Polaritons.

The functionality of many nonlinear and quantum optical devices relies on the effect of optical bistability. Using microcavity exciton-polaritons in a honeycomb arrangement of microcavity pillars, we report the resonance response and bistability of topological edge states. A balance between the pump, loss, and nonlinearity ensures a broad range of dynamical stability and controls the distribution of power between counterpropagating states on the opposite edges of the honeycomb lattice stripe. Tuning energy and polarization of the pump photons, while keeping their momentum constant, we demonstrate control of the propagation direction of the dominant edge state. Our results facilitate the development of practical applications of topological photonics.

Mixed Bromine–Chlorine Induced Great Dielectric and Second-Order Nonlinear Optical Properties Changes in Phase Transitions Compounds [H2mdap][BiBr5(1-x)Cl5x] (x = 0.00–1.00)

Doping/mixing method plays an important role in modulating the structures and physical properties of functional materials. Herein, we report that the mixed crystals [H2mdap][BiBr5(1-x)Cl5x] (H2mdap = protonated N-methyl-1,3-diaminopropane, x = 0.00–1.00) undergo phase transitions with the trend that the larger x, the higher phase transition temperature. Variable-temperature structure analysis shows that anionic and cationic moieties in the crystal lattice contribute to the phase transition. Room-temperature structure comparisons reveal that phase transition point moving to a higher temperature is mainly due to the decrease of the Bi–Cl/Br–Bi angles in the anionic chains and slightly alter the intermolecular interactions with mixed different components of halogen atoms Cl and Br. Dielectric and second harmonic generation experiments demonstrate their similar phase transition behaviors and coexistence of switchable dielectric behaviors and bistable nonlinear optical effects. Mixed Br–Cl induced great dielec...

Optical bistability effect in SPP-based metallic grating containing Kerr nonlinear medium

We theoretically investigate the characteristics of the resonant modes and the optical bistability (OB) effect in the proposed metal–insulator–metal plasmonic structure containing Kerr nonlinear medium. By using finite difference time domain (FDTD) method, it is found that the plasmon resonance modes can be modulated with the change of the height of metallic grating, the thickness of Kerr material layer and refractive index. We also study the characteristic of OB with the correspondingly detuning parameters. The designed plasmonic structure can be potentially applied to projecting SPP-based nonlinear optical devices in integrated optical circuits.

Effects of boundary conditions on bistable behaviour in axisymmetrical shallow shells.

Multistable shells are thin-walled structures that have more than one stable state of self-stress. We consider isotropic axisymmetrical shallow shells of arbitrary polynomial shapes using a Föppl-von Kármán analytical model. By employing a Rayleigh-Ritz approach, we identify stable shapes from local minima in the strain energy formulation, and we formally characterize the level of influence of the boundary conditions on the critical geometry for achieving bistable inversion-an effect not directly answered in the literature. Systematic insight is afforded by connecting the boundary to ground through sets of extensional and rotational linear springs. For typical cap-like shells, it is shown that bistability is generally enhanced when the extensional spring stiffness increases and when the rotational spring stiffness decreases, i.e. when boundary movements in-plane are resisted but when their rotations are not; however, for certain other shapes and large in-plane stiffness values, bistability can be enhanced by resisting but not entirely preventing edge rotations. Our predictions are furnished as detailed regime maps of the critical geometry, which are accurately correlated against finite-element analysis. Furthermore, the suitabilities of single degree-of-freedom models, for which solutions are achieved in closed form, are evaluated and compared to our more accurate predictions.

Hydrogen-Bonded Switchable Dielectric Material Showing the Bistability of Second-Order Nonlinear Optical Properties

Physical properties of phase transition materials are directly linked to the transformation of structural moieties. Here, we report a new hydrogen-bonded binary crystal of cyclohexylaminium chlorodifluoroacetate (1), consisting of two distinct types of the anion–cationic structural moieties, which shows an order–disorder phase transition around 153 K (phase transition point, Tc). Thermal analyses, dielectric, and second-order nonlinear optical (NLO) measurements solidly confirm the symmetry transformation from the point group mmm to mm2. It is noteworthy that 1 exhibits a coexistence of switchable dielectric behaviors and bistable NLO effects. In detail, it is NLO-active below Tc, while its quadratic NLO effects completely disappear above Tc. Such a change reveals the bistable feature of its quadratic NLO properties. Further, variable-temperature structure analyses reveal that the emergence of NLO effects below Tc is ascribed to partial ordering of anions and small-angle reorientation of cations. This mec...

Nonperturbative quasiclassical theory of the nonlinear electrodynamic response of graphene

An electromagnetic response of a single graphene layer to a uniform, arbitrarily strong electric field $\mathbit{E}(t)$ is calculated by solving the kinetic Boltzmann equation within the relaxation-time approximation. The theory is valid at low (microwave, terahertz, infrared) frequencies satisfying the condition $\ensuremath{\hbar}\ensuremath{\omega}\ensuremath{\lesssim}2{E}_{F}$, where ${E}_{F}$ is the Fermi energy. We investigate the saturable absorption and higher harmonics generation effects, as well as the transmission, reflection, and absorption of radiation incident on the graphene layer, as a function of the frequency and power of the incident radiation and of the ratio of the radiative to scattering damping rates. We show that the optical bistability effect, predicted in Phys. Rev. B 90, 125425 (2014) on the basis of a perturbative approach, disappears when the problem is solved exactly. We show that under the action of a high-power radiation $(\ensuremath{\gtrsim}100\phantom{\rule{4pt}{0ex}}\mathrm{kW}/{\mathrm{cm}}^{2})$ both the reflection and absorption coefficients strongly decrease and the layer becomes transparent.