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Exotic topological domains in BiFeO3 nanoislands have attracted much attention regarding their potential applications in advanced electronic devices. Here, different from the earlier reported disordered distributed BiFeO3 nanoislands formed by a self-assembly method, we fabricated an ordered BiFeO3 nanoisland array by mask-assisted pulsed laser deposition on a SrTiO3 substrate, which exhibits a center-converged in-plane polarization component and a monodomain pattern along the vertical direction. Such center-type quad-domain structures exhibit high stability, maintaining their topological structures after heating to 250 °C and subsequently cooling to room temperature. Moreover, they can be switched by applying a scanning electric field and recovered by applying a heating and cooling process. Observing this topological structure in BiFeO3 nanoislands might provide a suitable platform for further exploration of its topological phase transition properties, new functions, and potential applications. [ABSTRACT FROM AUTHOR]

In this study, we present an electrically switchable window that can dynamically transmit both visible light and infrared (IR) light. The window is based on polymer stabilized cholesteric liquid crystals (PSCLCs), which are placed between a top plate electrode substrate and a bottom interdigitated electrode substrate. By applying a vertical alternating current electric field between the top and bottom substrates, the transmittance of the entire visible light can be adjusted. The cholesteric liquid crystals (CLC) texture will switch to a scattering focal conic state. The corresponding transmittance decreases from 90% to less than 15% in the whole visible region. The reflection bandwidth in the IR region can be tuned by applying an in-plane interdigital direct current (DC) electric field. The non-uniform distribution of the in-plane electric field will lead to helix pitch distortion of the CLC, resulting in a broadband reflection. The IR reflection bandwidth can be dynamically adjusted from 158 to 478 nm. The electric field strength can be varied to regulate both the transmittance in the visible range and the IR reflection bandwidth. After removing the electric field, both features can be restored to their initial states. This appealing feature of the window enables on-demand indoor light and heat management, making it a promising addition to the current smart windows available. This technology has considerable potential for practical applications in green buildings and automobiles. [ABSTRACT FROM AUTHOR]

Deterministically controllable multi‐state polarizations in ferroelectric materials are promising for the application of next‐generation non‐volatile multi‐state memory devices. However, the achievement of multi‐state polarizations has been inhibited by the challenge of selective control of switching pathways. Herein, an approach to selectively control 71° ferroelastic and 180° ferroelectric switching paths by combining the out‐of‐plane electric field and in‐plane trailing field in multiferroic BiFeO3 thin films with periodically ordered 71° domain wall is reported. Four‐state polarization states can be deterministically achieved and reversibly controlled through precisely selecting different switching paths. These studies reveal the ability to obtain multiple polarization states for the realization of multi‐state memories and magnetoelectric coupling‐based devices. [ABSTRACT FROM AUTHOR]

Colloidal assembly is a key strategy in nature and artificial device. Hereby, an electromicrofluidic assembly platform (eMAP) is proposed and validated to achieve 3D colloidal assembly and manipulation within water droplets. The water‐in‐oil emulsion droplets autoposition in the eMAP driven by dielectrophoresis, where the (di)electrowetting effect induces droplet deformation, facilitating quadratic growth of the electric field in water droplet to achieve "far‐field" dielectrophoretic colloidal assembly. Reconfigurable 3D colloidal configurations are observed and dynamically programmed via applied electric fields, colloidal properties, and droplet size. Binary and ternary colloidal assemblies in one droplet allow designable chemical and physical anisotropies for functional materials and devices. Integration of eMAP in high throughput enables mass production of functional microcapsules, and programmable optoelectronic units for display devices. This eMAP is a valuable reference for expanding fundamental and practical exploration of colloidal systems. [ABSTRACT FROM AUTHOR]

An electrically switchable multi-stable liquid crystal device is demonstrated based on a non-uniform cholesteric liquid crystal (CLC) structure in a single cell. The non-uniform CLC structure consists of a polymer stabilised CLC layer and a non-polymer stabilised CLC layer. By taking advantage of the difference in driving electric field strength of the two layers, the device can be switched electrically to four different states: the reflecting state, the reflecting and scattering co-existing state, the scattering-only state and the transparent state. The optical properties of the four states and the transition conditions between the states were elucidated. Moreover, all states with reflecting and/or scattering properties are stable for an extended period of time after switching off the electric field. Thanks to its multi-stability, this device can be used for energy-saving smart windows of automobiles, buildings and in architectural aesthetics. An electrically switchable multi-stable liquid crystal device is demonstrated based on a non-uniform cholesteric liquid crystal (CLC) structure in a single cell. The device can be switched electrically to four different states. All states with reflecting and/or scattering properties are stable for an extended period of time after switching off the electric field. Thanks to its multi-stability, this device can be used for energy-saving smart windows of automobiles, buildings and in architectural aesthetics. [ABSTRACT FROM AUTHOR]

Electrowetting is a highly recognized way to control droplet movement on a solid surface and induce motion in the oil/water interface. It is still challenging to manipulate liquid/liquid interface dynamics due to the electro‐capillary instability caused by the electric field in the electrowetting system. Here a dielectric bridge is induced near the oil/water interface by constructing a conductive micropillar (CMP) directly on the hydrophobic surface in an electrowetting system. The CMP height can be adjusted by regulating the wettability of the hydrophobic surface. The electric‐field gradient induced by CMP can precisely control the rupture position and guide the contraction direction of the oil film. For application, the CMPs are added in the full‐color electrowetting display panel, and the average transmittance can increase 25% at white state due to the consistent oil contract direction. The rupture voltage is reduced, and the response time of the electrowetting display is also improved. The COMSOL simulation results are consistent with experimental results indicating the oil rupture position is controlled by the electric field strength. Combing with program patterning, the authors demonstrate a new display function in an unpatterned indium‐tin oxide‐based electrowetting display. These findings will benefit most switchable electrofluidic applications and devices with two‐phase liquid. [ABSTRACT FROM AUTHOR]

Morphological properties of surfaces play a key role in natural and man‐made objects. The development of robust methods to fabricate micro/nano surface structures has been a long pursuit. Herein, an approach based on molecular self‐assembling of liquid crystal polymers (LCPs) is presented to directly translate 2D molecular director profiles obtained by a photoalignment procedure into 3D topographies, without involving further multi‐step lithographic processes. The principle of surface deformation from a flat morphology into complex topographies is based on the coupling between electrostatic interactions and the anisotropic flow in LCPs. When activated by an electric field, the LCP melts and is driven by electrohydrodynamic instabilities to connect the electrode plates of a capacitor, inducing topographies governed by the director profile of the LCP. Upon switching off the electric field, the formed structures vitrify as the temperature decreases below the glass transition. When heated, the process is reversible as the formed topographies disappear. By pre‐programming the molecular director a variety of structures could be made with increasing complexity. The height, pitch, and the aspect ratio of the textures are further regulated by the conditions of the applied electric field. The proposed approach will open new opportunities for optical and electrical applications. [ABSTRACT FROM AUTHOR]

Electroconvection (EC) in liquid crystals (LCs) is extensively studied for the formation of regular nonequilibrium structures, and the applications that require strong light scattering and high haze. Doping the LCs with ionic species has proven to be an effective method to obtain uniform and high‐quality textures. Herein, zwitterion is explored as a new class of ionic dopant that has little problem of ion accumulation as compared to typical organic electrolytes. A rich variety of EC patterns are observed and characterized for both positive and negative LCs doped with a zwitterion Reichardt's dye. The initial homogeneous or homeotropic alignment, as well as the voltage and frequency of the applied electric field, is shown to influence the formation of EC patterns, among which the dynamic scattering mode (DSM) is specially examined for the application as privacy‐protecting smart windows. Using an LC mixture doped with zwitterions, the smart window demonstrates outstanding performance, as well as much improved durability for a wide range of operating conditions. Such a method offers a simple strategy for the fabrication of polymer‐free smart windows. [ABSTRACT FROM AUTHOR]

Electrical manipulation of skyrmions attracts considerable attention for its rich physics and promising applications. To date, such a manipulation is realized mainly via spin-polarized current based on spin-transfer torque or spin–orbital torque effect. However, this scheme is energy consuming and may produce massive Joule heating. To reduce energy dissipation and risk of heightened temperatures of skyrmion-based devices, an effective solution is to use electric field instead of current as stimulus. Here, we realize an electric-field manipulation of skyrmions in a nanostructured ferromagnetic/ferroelectrical heterostructure at room temperature via an inverse magneto-mechanical effect. Intriguingly, such a manipulation is non-volatile and exhibits a multistate feature. Numerical simulations indicate that the electric-field manipulation of skyrmions originates from strain-mediated modification of effective magnetic anisotropy and Dzyaloshinskii–Moriya interaction. Our results open a direction for constructing low-energy-dissipation, non-volatile, and multistate skyrmion-based spintronic devices. Spin-polarized current manipulation of magnetic skyrmions is energy consuming. Here, the authors achieve an electric-field manipulation of individual skyrmions in a nanostructured ferromagnetic/ferroelectrical heterostructure at room temperature via an inverse magneto-mechanical effect. [ABSTRACT FROM AUTHOR]

Electrically tunable infrared (IR) reflectors based on polymer stabilised cholesteric liquid crystals (PSCLC) have been fabricated. The influence of polymerisation time on bandwidth broadening and response time of the IR reflector was investigated. Such IR reflector can reflect broad band of infrared light from 725 to 1435 nm upon application of a DC electric field, while remaining predominantly transparent in the visible region, with the transmittance in the region of 400-700 nm being above 90%. Bandwidth broadening was induced using low operational power with acceptable switching speeds. Model tests reveal that this IR reflector can effectively control the indoor temperature. The distinct properties of such IR reflector make it a good candidate for smart windows of automobiles and buildings to control interior temperature and save energy. [ABSTRACT FROM AUTHOR]

The three‐color electrophoretic displays (EPDs) technology has filled the gap in the color demand in the electrophoretic displays. However, there are problems of dim brightness and insufficient color saturation. In this paper, a driving waveform based on a damping oscillation is proposed to optimize the red saturation in three‐color EPDs. The optimized driving waveform is composed of an erasing stage, a particles activation stage, a red electrophoretic particles purification stage, and a red display stage. Correspondingly, the driving duration is set to 360 ms, 880 ms, 400 ms, and 2400 ms, respectively. And the red electrophoretic particles purification stage is a damping oscillation driving waveform. The red and black electrophoretic particles are separated by changing the magnitude and polarity of the applied electric field so that the red electrophoretic particles are purified. The experimental result shows that the maximum red saturation could reach 0.583, which is increased by 27.57% compared with the traditional driving waveform. [ABSTRACT FROM AUTHOR]

Alignment layer plays a critical role on liquid crystal (LC) conformation for most LC devices. Normally, polyimide (PI) or polyvinyl alcohol (PVA), characterized by their outstanding thermal and electrical properties, have been widely applied as the alignment layer to align LC molecules. Here, we used a semi-conductive material poly(N-vinylcarbazole) (PVK) as the alignment layer to fabricate the cholesteric liquid crystal (CLC) device and the polymer-stabilized cholesteric liquid crystals (PSCLC)-based infrared (IR) reflectors. In the presence of ultraviolet (UV) irradiation, there are hole–electron pairs generated in the PVK layer, which neutralizes the impurity electrons in the LC–PVK junction, resulting in the reduction in the built-in electric field in the LC device. Therefore, the operational voltage of the CLC device switching from cholesteric texture to focal conic texture decreases from 45 V to 30 V. For the PSCLC-based IR reflectors with the PVK alignment layer, at the same applied electric field, the reflection bandwidth is enhanced from 647 to 821 nm, ranging from 685 to 1506 nm in the IR region, which makes it attractive for saving energy as a smart window. [ABSTRACT FROM AUTHOR]

A pixel in an electrowetting display (EWD) can be viewed as a confined water/oil two-phase microfluidic system that can be manipulated by applying an electric field. The phenomenon of charge trapping in the protective dielectric and conductivity of the oil phase reduce the effective electric field that is required to keep the three-phase contact line (TCL) in place. This probably leads to an oil-backflow effect which deteriorates the electro-optical performance of EWD devices. In order to investigate charge trapping and conduction effects on the device electro-optical response, an EWD device was studied, which was fabricated with a black oil, aiming for a high-contrast ratio and color-filter display. For comparison, we also prepared a device containing a purple oil, which had a lower electrical conductivity. As anticipated, the black-oil device showed faster backflow than the purple-oil device. A simple model was proposed to explain the role of oil conductivity in the backflow effect. In addition, the rebound and reopening effects were also observed after the voltage was switched to zero. The above observations were strongly dependent on polarity. By combining observations of the polarity dependence of the oil conductivity and assuming that negative charges trap more strongly in the dielectric than positive charges, our experimental results on rebound and reopening can be explained. In the AC optical response, the pixel closing speed decreased in time for intermediate frequencies. This is likely related to the phenomenon of charge trapping. It was also found that the periodic driving method could not suppress the backflow effect when the driving frequency was above ~10 kHz. Our findings confirm the significance of the above charge-related effects of EWD devices, which need to be investigated further for better understanding in order to properly design/use materials and driving schemes to suppress them. [ABSTRACT FROM AUTHOR]

Bi24O31Br10 microcrystals composed of nanobelts and nanosheets with exposed (30-4) and (117) facets were synthesized by a simple hydrothermal method. The desired morphology and facets were obtained by adjusting the pH of the reaction system. Bi24O31Br10 nanobelts (BOB-NBs) with dominant (30-4) exposed facets were used for the photocatalytic degradation of tetracycline hydrochloride under visible light irradiation, with a degradation efficiency of up to 91% after 60 min of irradiation. The BOB-NBs possessed a higher charge separation and transfer efficiency, and showed less charge carrier recombination compared to the Bi24O31Br10 nanosheets (BOB-NSs), ascribed to a cooperative effect between the internal electric fields and surface active sites. A higher photocurrent response (2.6 times higher) was observed for BOB-NBs (12.8 μA cm−2) compared to that of BOB-NSs (4.9 μA cm−2). These findings are directional for a comprehensive understanding of the influence of the crystal facets of Bi24O31Br10 microcrystals on their photocatalytic activity and could help to guide the future design of high-performance photocatalytic materials. [ABSTRACT FROM AUTHOR]

Electrowetting display (EWD) is a reflective display technology in which fluidic pixels can response and switch quickly by electronic control, showing the capability for video-speed reflective display applications. In this paper, a new driver system is proposed and realized for video playing function of active matrix electrowetting display (AM-EWD). The hardware system is designed based on Field-Programmable-Gate-Array (FPGA) and the existing electrophoretic display (EPD) driving integrated chips (IC). A driving logic circuit and FPGA software is introduced for providing the EWD system with driving and timing control. And a set of specific driving waveforms, which is loaded to a lookup table of the FPGA in advance, is designed to display grayscale on EWDs. 4-level gray scale videos have been successfully performed by applying the driving waveforms. To our knowledge, such work has not been reported before. [ABSTRACT FROM AUTHOR]

We propose and validate a strategy for quick, cheap and reliable fabrication of high performance surface-enhanced Raman scattering (SERS) substrates via a surfactant-assisted galvanic reaction on silicon surface. The amphiphilic CTAB molecules play key roles for controllable preparation of high density Ag nano-assemblies (NAs), working as "hotspots" to contribute to the electromagnetic enhancement of SERS effect; and at the same time, for the chemical enrichment of probe molecules to enhance SERS signal. Such high sensitive SERS substrates show detection limit down to single-molecule level for R6G, and possibility for characterization of amino acids. • Ag nano-assemblies were prepared via one-step CTAB-assisted galvanic reaction. • SERS substrates with high density Ag nano-assemblies show high sensitivity to single-molecule detection. • Such high-sensitive SERS substrates enables determination of amino acids with low Raman cross-sections. In this work, we report a quick and controllable method for fabricating Ag nanoparticles (NPs) and nano-assemblies (NAs) on silicon (Si) surface via a galvanic reaction assisted by surfactant hexadecyltrimethylammonium bromide (CTAB). Obtained Si substrates with high density Ag NAs serve as surface-enhanced Raman scattering (SERS) substrates for unlabelled molecular sensing. The addition of CTAB enables not only the electromagnetic enhancement by controllable producing Ag NAs "hotspots", but also the signal enhancement by enriching probe molecules via hydrophobic interaction. Two concentration regimes of 1.0 × 10−8–1.0 × 10−11 M and 1.0 × 10−12–1.0 × 10−16 M have been obtained for quantitative and qualitative detection of Rhodamine 6G (R6G) in aqueous solution, respectively. As a result, for determination of R6G, the quantitative and qualitative detection limits of 1.0 × 10−11 and 1.0 × 10−16 M have been obtained, respectively, with high reproducibility showing the relative standard deviation (RSD) of ∼7.3%. Simulation has been carried out using finite-difference time-domain (FDTD) to evaluate the dependence of electric field on the size and inter-gap of Ag NPs, showing good agreement with experimental results. The high sensitivity also enables SERS characterization of non-resonant and low Raman cross-section biomolecules, for example, amino acids. Such a fabrication process is simple, fast, cheap and reproducible; and therefore, it would be helpful to produce high sensitive SERS substrates to broaden their applications in chemical and biological fields for molecular diagnostics to single-/multiple-molecule detection. [ABSTRACT FROM AUTHOR]