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This report describes a liquid crystalline material that can be cured and patterned with green light and photoaligned with blue light.

A newly developed LC command system can be used as a secret pattern indicator. Encrypted military operation is deciphered by adjusting the polarizer configuration.

Optically tunable and switchable reflection grating LC gels can be used in anti-counterfeiting materials for optical security and encryption. Reflection colors and patterns appear by applying an AC field and a DC field controls the holographic color of the samples.

Blue phase liquid crystals (BPLCs) composed of double-twisted cholesteric helices are promising materials for use in next-generation displays, optical components, and photonics applications. However, BPLCs are only observed in a narrow temperature range of 0.5–3 °C and must be stabilized with a polymer network. Here, we report on controlling the phase behavior of BPLCs by varying the concentration of an amorphous crosslinker (pentaerythritol triacrylate (PETA)). LC mixtures without amorphous crosslinker display narrow phase transition temperatures from isotropic to the blue phase-II (BP-II), blue phase-I (BP-I), and cholesteric phases, but the addition of PETA stabilizes the BP-I phase. A PETA content above 3 wt% prevents the formation of the simple cubic BP-II phase and induces a direct transition from the isotropic to the BP-I phase. PETA widens the temperature window of BP-I from ~6.8 °C for BPLC without PETA to ~15 °C for BPLC with 4 wt% PETA. The BPLCs with 3 and 4 wt% PETA are stabilized using polymer networks via in situ photopolymerization. Polymer-stabilized BPLC with 3 wt% PETA showed switching between reflective to transparent states with response times of 400–500 μs when an AC field was applied, whereas the application of a DC field induced a large color change from green to red.

Light manipulation strategies of nature have fascinated humans for centuries. In particular, structural colors are of considerable interest due to their ability to control the interaction between light and matter. Here, wrinkled photonic crystal papers (PCPs) are fabricated to demonstrate the consistent reflection of colors regardless of viewing angles. The nanoscale molecular self-assembly of a cholesteric liquid crystal (CLC) with a microscale corrugated surface is combined. Fully polymerizable CLC paints are uniaxially coated onto a wrinkled interpenetrating polymer network (IPN) substrate. Photopolymerization of the helicoidal nanostructures results in a flexible and free-standing PCP. The facile method of fabricating the wrinkled PCPs provides a scalable route for the development of novel chirophotonic materials with precisely controlled helical pitch and curvature dimensions. The reflection notch position of the flat PCP shifts to a lower wavelength when the viewing angle increased, while the selective reflection wavelength of wrinkled PCP is remained consistent regardless of viewing angles. The optical reflection of the 1D stripe-wrinkled PCP is dependent on the wrinkle direction. PCPs with different corrugated directions can be patterned to reduce the angular-dependent optical reflection of wrinkles. Furthermore, 2D wavy-wrinkled PCP is successfully developed that exhibit directionally independent reflection of color.

The adaptation of systems to external influences is of broad interest. We study the influence of microwave signals of different shapes on the magnetoacoustic wave system with a giant nonlinearity in canted antiferromagnet FeBO3 at room temperature, which is close to its phase transition to the paramagnetic state. The classical nonlinear system obeys external deterministic signals; the modulation response describes the shape of these signals. In response to a noisy spectrum, the system shows self-organization, and mode competition selects one excited mode while suppressing others. With an increase in the power of the external signal, another self-organization is observed in the form of a narrow peak at the frequency of the fundamental minimum. This represents the first observation of the macroscopic quantum statistical phenomenon, Bose-Einstein condensation of magnetoacoustic wave quanta in a wave system with a high level of thermal fluctuations. The resulting picture of adaptation can analogously be transferred to many other adaptive wave systems, including large scale adaptive wave systems in the natural environment.

The classical "chair-twist boat-boat" conformational dynamics (CD) of cyclohexane is thermally activated. Here we report on the photoinduced/azobenzene-assisted CD of bilaterally fused cyclohexane moieties contributing to large photomechanical response of cross-linked azobenzene-functionalized polyimides (X-azoPI), based on 1,2,4,5-cyclohexane-tetracarboxylic-dianhydride (CHDA), exhibiting a photobending angle and photogenerated stress, up to ∼90° and 370 kPa, respectively. In contrast, X-azoPI containing planar pyromellitimide (PMDI) or cage-like bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic-diimide (BCDI) show smaller photomechanical responses. The superior photomechanical performance of X-azoPI with constrained cyclohexane-diimide (CHDI) units is attributed to an increased mobility of segments comprising "hinged" p-phenylene rings, azobenzene, and CHDI units in the cross-link sites. Blue light irradiation initiates the motions driven by photoisomerization/reorientation of azobenzenes connected to CHDI units, whose CD is then amplified, leading to longer-range segmental mobility, more local free volume, and culminating in large photoinduced bending. The trapping of redistributed CHDI's stereoisomers in X-azoPI backbone at

Self-organized functional soft materials, enabled by specific chemical architectures, are currently attracting tremendous attention because of their stimuli-responsive attributes and applications in advanced technological devices. A novel axially chiral molecular switch containing two azo linkages and six terminal alkyl chains on two elongated rod-shaped wings, that exhibits superior solubility, high helical twisting power, and reversible photoisomerization in an achiral liquid crystal host, is synthesized and utilized in the development of a photoresponsive, self-organized helical superstructure, that is, cholesteric liquid crystal (CLC). The planar CLC adopts a standing helix (SH) configuration because of surface alignment layers on the substrates. This SH can be transitioned to a lying helix configuration, enabling tunable diffraction gratings under the application of electric field. Adjustment of the initial pitch of the planar CLC by photoirradiation yields the diffraction gratings with stripes either parallel or perpendicular to the rubbing direction upon the application of an appropriate electric field. Tunable beam steering along orthogonal directions has been demonstrated. Such tunable stimuli-responsive soft materials fabricated with artificial chiral switches show great potential in optics, photonics, and beyond.

Thin film holographic gratings have attracted significant attention due the tailorability of their photonic properties. The ability of holography to create materials with unique photonic properties...

Magnetically ordered materials belong to systems with broad spectra of collective magnetic oscillations, spin waves, and systems with the highest degree of nonlinearity. We consider the possibility of studying spin waves using high-frequency harmonics, the possibility of parametric excitation of high-frequency collective magnetic oscillations using alternating magnetic fields of the lower frequency. As a model system allowing us to show proof of the principle, we use a system of magnetoelastic waves (MEWs) of high-temperature antiferromagnet with easy-plane anisotropy. The modulation method is used when an additional RF magnetic field was applied to the sample, which yielded satellites at the multiple of the pump field frequency microwave signal that passed the sample in a helix resonator when the parametric pump threshold was exceeded. We observed the process of parametric excitation of MEWs up to 64 harmonics of the pump field at a pump power up to 30 dBm. Our research is of interest for magnetic materials of nano sizes.

A great challenge in power/RF electronics has been achieving integrated magnetic inductors with high quality factor ( $Q$ -factor) and high inductance density at gigahertz frequencies. In this article, integrated solenoid magnetoelectric inductors based on FeGaB/Al2O3 multilayer as the magnetic core are designed to operate at high gigahertz frequencies, high $Q$ -factor, and inductance tunability. A high self-resonant frequency of >3 GHz with a flat inductance of 1.4 nH and a peak $Q$ -factor of ~32.7 has been achieved within a wide operating frequency ranging from 0.3 to 3 GHz with magnetic annealing treatment to enhance the inductance density and $Q$ -factor. Two different inductance-tuning methods are tested. For magnetic field tuning, an external magnetic field from 0 to 500 Oe is applied to achieve an inductance tunability $\Delta {\mathbf {L}/\mathbf {L}} _{\mathbf {min}}$ of ~69.2%. Voltage tuning is also tested based on the magnetoelectric coupling between FeGaB/Al2O3 multilayer and ferroelectric slab achieving a maximum tunability of 191% with a flat inductance within the operating frequency. Such a high $Q$ -factor and high inductance density together with giant electrical tunability will greatly improve the integration level and performance of tunable radio frequency integrated circuits while reducing their power consumption and cost.

Visible-light-driven molecular switches endowing reversible modulation of the functionalities of self-organized soft materials are currently highly sought after for fundamental scientific studies and technological applications. Reported herein are the design and synthesis of two novel halogen bond donor based chiral molecular switches that exhibit reversible photoisomerization upon exposure to visible light of different wavelengths. These chiral molecular switches induce photoresponsive helical superstructures, that is, cholesteric liquid crystals, when doped into the commercially available room-temperature achiral liquid crystal host 5CB, which also acts as a halogen-bond acceptor. The induced helical superstructure containing the molecular switch with terminal iodo atoms exhibits visible-light-driven reversible unwinding, that is, a cholesteric-nematic phase transition. Interestingly, the molecular switch with terminal bromo atoms confers reversible handedness inversion to the helical superstructure upon irradiation with visible light of different wavelengths. This visible-light-driven, reversible handedness inversion, enabled by a halogen bond donor molecular switch, is unprecedented.

We have previously reported that the application of a DC field can adjust the position and/or bandwidth of the selective reflection notch in polymer-stabilized cholesteric liquid crystals (PSCLCs). The proposed mechanism of these electro-optic (EO) response is ion-facilitated electromechanical deformation of the polymer stabilizing network. Accordingly, the concentration of ions trapped within the polymer network should considerably influence the EO response of PSCLC. Our prior studies have indicated that photoinitiators can increase ion density in PSCLC by an order of magnitude. Here, we isolate the contribution of ionic impurities associated with liquid crystal monomers (LCMs) by utilizing initiator-less polymerization. PSCLCs prepared with LCM with low ion concentration show bandwidth broadening of the reflection band whereas PSCLCs prepared with LCM with high ion concentration exhibit a red shifting tuning of the reflection band. The extent of the tuning or bandwidth broadening of the CLC reflection band depends on the concentration of LCMs and the chirality of the LCM.

The dynamic electro‐optic (EO) response of polymer‐stabilized cholesteric liquid crystals prepared using unpolarized UV light (U–PSCLC), such as reflection bandwidth broadening and either red or blue tuning of the reflection peak, has been previously reported. Herein, recent efforts to use a polarized single argon‐ion laser beam to create PSCLCs (L–PSCLCs) with higher‐order reflections are described. The L–PSCLCs exhibit a primary reflection peak in the near‐infrared (NIR) regime and a second‐order reflection band with a narrow bandwidth in the visible regime that results from a deformed in‐plane CLC helical structure. The initial positions of the reflection bands are adjusted by the chiral dopant concentrations of the CLC mixture, and red, green, and blue reflection colors from the second‐order Bragg reflection are demonstrated. The primary and the second‐order reflection bands can be shifted to longer wavelengths by application of a DC electric field. The reflection efficiency of the higher‐order reflection notch increases with polymer concentration, which affects the degree of in‐plane deformation and fixation of the CLC helix. Modeling is used to further explain the formation of the higher‐order reflection bands of PSCLCs observed experimentally.

Thin-film geo-phase optics have the potential to dramatically reduce size, weight, and power for large-aperture optical components as well as provide nonmechanical functionality. Topics are presented in manner of increasing conceptual and system complexity to convey the different levels and aspects of system performance improvements. An 8 ′ ′ aperture, lightweight geo-phase lens is presented followed by discussions on both mechanical and nonmechanical beam steering embodiments. Laser damage thresholds for the thin-film geo-phase prisms are reported. Highly efficient and spectrally broadband nonmechanical line-of-sight steering is also demonstrated. Lastly, novel fabrication techniques, to the best of our knowledge, and the associated reduced fabrication cost implications are presented.

Thin film holographic liquid crystal gratings are of great interest due to their controllable photonic properties. Holographic polymer dispersed liquid crystal (H-PDLC) with a polymer concentration of 40-90% is an example of a system where nonuniform irradiation is used to template alternating polymer-rich and polymer-poor regions with a periodicity related to the illumination wavelength. Here, we present a tunable holographic polymer stabilized liquid crystal (H-PSLC) reflection grating using a relatively small amount of polymer (6-20 wt%). Switching behavior from transparent to reflective state will be discussed by heating or applying an AC field. Heating above the isotropic temperature of the polymer-poor regions leads to the refractive index mismatch between the ordered LC polymer-rich regions and the disordered isotropic polymer-poor. Alternatively, the application of an AC field can be used as an Ohmic heat source to induce the thermal color change.

It has been just over 20 years from the first disclosure of a thin and transparent film that would allow controlling propagation of light, an unpolarized and broadband light, with 100% efficiency. First it was an idea seemingly at odds with conventional optics. Then came demonstrations of the thinnest planar optics - “prisms”, lenses, beam shapers, arrays and vortices, switchable or not, - in sizes currently 8” and larger. Novel film architectures extended spectral and angular bandwidths of planar optics to unprecedented scales, changing the ways optics is made and opening avenues to long cherished dreams of adaptation, tunability, multifunctionality, and cost. History is in the making and will be presented first hand with an outline of the marvels in functionality and capabilities waiting for optics behind the horizon.

This presentation reveals the re-writability property of azobenzene liquid crystal photoalignment. Stable in thermal fluctuations, one can change existing photoalignment by exposing it to polarized light in the visible regime. One can use this unique property by patterning photoalignment through the liquid crystal bulk in that the sample’s front and back have differing director orientations. Photoalignment using linear polarized light as well as complex polarizations will be covered. No surface alignment on sample substrates is necessary because the azobenzene is mixed with the liquid crystal in-situ in sample preparation.

We aim to realize a novel nanotechnology-based biosensor specifically utilized to detect harmful bacteria in potable water. The nano-inspired device makes use of a chemically functionalized gold nanorods array (for the selective selection of specific pathogens) layered with a photo-responsive nematic liquid crystal (NLC) film for real-time and high sensitivity detection. The first experimental results are presented and discussed.

A systematic investigation of the soft magnetism, the change of modulus of elasticity with magnetization ( $\Delta \sf{E}$ effect), magnetostriction, and microwave properties has been carried out on iron-gallium-carbon thin films over a wide carbon content range. The phase transformation of the Fe-Ga-C films from bcc polycrystalline to amorphous leads to excellent magnetic softness with a low coercivity of less than 1 Oe, high saturation magnetization, narrow ferromagnetic resonance linewidth at 10 GHz of 20 to 30 Oe, and an ultra-low Gilbert damping constant of 0.0027. A record high piezomagnetic coefficient of 9.71 ppm/Oe, high saturation magnetostriction constant of 81.2 ppm, and large $\Delta \sf{E}$ effect of −120 GPa at 500 nm were achieved.

Low temperature synthesis of high quality two-dimensional (2D) materials directly on flexible substrates remains a fundamental limitation towards scalable realization of robust flexible electronics possessing the unique physical properties of atomically thin structures. Herein, we describe room temperature sputtering of uniform, stoichiometric amorphous MoS2 and subsequent large area (>6.25 cm2) photonic crystallization of 5 nm 2H-MoS2 films in air to enable direct, scalable fabrication of ultrathin 2D photodetectors on stretchable polydimethylsiloxane (PDMS) substrates. The lateral photodetector devices demonstrate an average responsivity of 2.52 μW A−1 and a minimum response time of 120 ms under 515.6 nm illumination. Additionally, the surface wrinkled, or buckled, PDMS substrate with conformal MoS2 retained the photoconductive behavior at tensile strains as high as 5.72% and over 1000 stretching cycles. The results indicate that the photonic crystallization method provides a significant advancement in incorporating high quality semiconducting 2D materials applied directly on polymer substrates for wearable and flexible electronic systems.

There has been considerable interest in nanomaterials for the development of anisotropic molecular alignment layers for electronic and biomedical applications. This review covers the recent progress in the design, synthesis, and characterization of automatic liquid crystal (LC) alignment layers. Amphiphilic hybrid nanomaterials consisting of organic parts and inorganic cores can interact favorably on LC media and substrates resulting in the uniaxial orientation of LC molecules in a specific direction. Among such systems, this review emphasizes giant surfactants showing automatically self-assembled 2D monolayers. Polymerizable giant surfactants allow us to build robust molecular alignment layers via a one-bottle approach. We believe that the automatic LC alignment layer constructed by doping giant surfactants can realize practical applications in smart materials.

Cholesteric liquid crystal (CLC) is a one-dimensional photonic crystal and is promising for various applications, including smart windows, optical components, and displays. Previous work has reported that polymer stabilized cholesteric liquid crystals (PSCLCs) have shown dynamic photonic properties with the application of direct current (DC) field, including bandwidth broadening, switchable scattering, red tuning and blue tuning. Recently, PSCLCs have been prepared upon exposure of a 363.8 nm Argon laser, and higher order diffraction peaks, such as the second and/or third order diffraction peaks, are observed. The higher order reflection bands are caused by the deformed helical structure of the polymer stabilizing network formed during the exposure of a single laser beam or under reflection grating conditions. The spectral position of the second-order reflection band, which is half the spectral position of the main CLC reflection band, is simply adjusted by chiral dopant concentrations in the CLC mixture. The selective main and higher order reflection notches can be red-tuned and broadened by the application of DC fields. A potential mechanism for higher order diffraction peaks in the PSCLCs will be discussed.

Surface photoalignment has been utilized to control the liquid crystalline (LC) orientation by exposing the photosensitive surface coatings to linearly polarized light. However, there are limitations in cell thickness and director orientation complexity if surface photoalignment was conducted. An alternative approach in controlling the director orientation is bulk photoalignment. Azobenzenes, which have been used for surface photoalignment due to fast reorientation during exposure, are homogeneously mixed into a nematic LC. We present results on how azobenzene doped LCs can be aligned in various standard orientations. In addition, rewriting alignment and patterning complex director orientations via bulk alignment will be discussed.

A self-crosslinkable side-chain liquid crystal polysiloxane containing cyanostilbene (Si-CSM) was newly synthesized for the development of a new generation of flexible optical paints. The photoisomerization of the cyanostilbene moiety at the molecular level was transferred and amplified to the phase transition of Si-CSM, resulting in changes in the macroscopic optical properties of the Si-CSM thin film. The self-crosslinking reaction between Si-H groups in the Si-CSM polymer backbone caused the self-crosslinked Si-CSM thin film to be very elastic and both thermally and chemically stable. Therefore, the self-crosslinked Si-CSM thin film endured stretching and bending deformations under relatively harsh conditions. In addition, the uniaxially oriented and self-crosslinked Si-CSM thin film generated linearly polarized light emission. Polarization-dependent and photopatternable secret coatings were fabricated via a spontaneous self-crosslinking reaction after coating the Si-CSM paint and irradiating ultraviolet (UV) light through a photomask. This newly developed flexible optical Si-CSM paint can be applied in next-generation optical coatings.

We report and discuss our first efforts devoted to realizing an innovative and miniaturized nanotechnology-based biosensor capable of real-time detect and quantify the presence of harmful pathogens dispersed in potable water. Gold nanorods, selected for their colorimetric sensitivity to the refractive index change, are functionalized, via the electrostatic linking method, with anti-Escherichia coli (E.coli) antibody. Selective recognition experiments are performed by utilizing a physiological solution containing different E.coli concentrations, thus exploiting the interaction between E.coli surface antigens and the anti-E.coli antibody. The system is characterized in terms of morphological, optical, and spectroscopic properties. Results reveal an excellent capability to discriminate small changes in the E.coli concentration in a range from 10 to 102 CFU/mL.

Previous work has reported that polymer stabilized cholesteric liquid crystals (PSCLCs) have shown dynamic photonic properties with the application of direct current (DC) field, including bandwidth broadening, switchable scattering, red tuning and blue tuning. Recently, we have prepared holographic polymer stabilized cholesteric liquid crystals reflection gratings (H-PSCLCs). High order diffraction peaks, such as the second or/and third order diffraction peaks, are observed from the H-PSCLC samples written with a 363.8 nm Argon laser. The higher order reflection bands are caused by the deformed helical structure of the polymer stabilizing network formed under reflection grating conditions. The spectral position of the second-order reflection band is simply adjusted by chiral dopant concentrations in the CLC mixture. The selective main and higher order reflection notches can be red-tuned and broadened by the application of DC fields.

Planar cholesteric liquid crystals (CLCs) are well known for having vibrant reflective coloration that is associated with the handedness and the pitch length of the helicoidal twist of the liquid crystalline molecules. If one observes these films at oblique angles, the reflected colors blue-shift with increasing angles from normal. On the other hand, uniform lying helix (ULH) CLCs, where the helicoidal axis lies in the plane of the substrate, are well-known but are not typically associated with vibrant colors. Here, we examine the unique optical properties of CLCs at oblique incidence angles, specifically the spectral and polarization changes associated with switching between planar and ULH CLCs for various incidence angles. At small angles of incidence (0° < ψ < 45°, where ψ is the angle of incidence relative to the surface normal at the substrate-CLC interface), the electrically driven helical reorientation from planar to ULH results in a blue-shifting of the color and circularly polarized to unpolarized switching behavior. At large angles (45° < ψ < 90°), the behavior is reversed, with a red-shifting color change occurring and the polarization switching from unpolarized to circularly polarized. Modeling of the light propagation through ULH CLCs is used to confirm the change in position and polarization characteristic of the reflection band with incidence angle observed experimentally. This study provides a new perspective on ULH CLCs and reveals a unique reconfigurable angular chromaticity.

It has previously been shown that for polymer-stabilized cholesteric liquid crystals (PSCLCs) with negative dielectric anisotropy, the position and bandwidth of the selective reflection notch can be controlled by a direct-current (DC) electric field. The field-induced deformation of the polymer network that stabilizes the devices is mediated by ionic charges trapped in or near the polymer. A unique and reversible electro-optic response is reported here for relatively thin films (&le, 5 &mu, m). Increasing the DC field strength redshifts the reflection notch to longer wavelength until the reflection disappears at high DC fields. The extent of the tuning range is dependent on the cell thickness. The transition from the reflective to the clear state is due to the electrically controlled, chirped pitch across the small cell gap and not to the field-induced reorientation of the liquid crystal molecules themselves. The transition is reversible. By adjusting the DC field strength, various reflection wavelengths can be addressed from either a different reflective (colored) state at 0 V or a transparent state at a high DC field. Relatively fast responses (~50 ms rise times and ~200 ms fall times) are observed for these thin PSCLCs.

Strong strain-mediated magnetoelectric (ME) coupling in magnetic/ferroelectric heterostructures has great potential for different high-frequency multiferroic devices. In this article, we present the most recent progress in integrated multiferroic devices. Integrated magnetic tunable inductors with a wide operation frequency range, integrated nonreciprocal bandpass filters with dual magnetic and electric-field tunability based on magnetostatics surface waves, and novel radio-frequency nanomechanical ME resonators with pico-Tesla sensitivity for direct current magnetic fields are presented. Finally, a new antenna miniaturization mechanism, acoustically actuated nanomechanical ME antennas, which can successfully miniaturize the size by 1–2 orders, is introduced. With the advantages of high magnetic field sensitivity, highest antenna gain among all nanoscale antennas at similar frequency, integrated capability with complementary metal oxide semiconductor technology, and ground-plane immunity from metallic surfaces and the human body, ME antennas have a bright future for biomedical applications, wearable antennas, and the Internet of Things due to their unique and particular properties.