A promising approach to the fabrication of materials with nanoscale features is the transfer of liquid-crystalline structure to polymers. However, this has not been achieved in systems with full three-dimensional periodicity. Here we demonstrate the fabrication of self-assembled three-dimensional nanostructures by polymer templating blue phase I, a chiral liquid crystal with cubic symmetry. Blue phase I was photopolymerized and the remaining liquid crystal removed to create a porous free-standing cast, which retains the chiral three-dimensional structure of the blue phase, yet contains no chiral additive molecules. The cast may in turn be used as a hard template for the fabrication of new materials. By refilling the cast with an achiral nematic liquid crystal, we created templated blue phases that have unprecedented thermal stability in the range -125 to 125 °C, and that act as both mirrorless lasers and switchable electro-optic devices. Blue-phase templated materials will facilitate advances in device architectures for photonics applications in particular.

We demonstrate a room temperature processed ferroelectric (FE) nonvolatile memory based on a ZnO nanowire (NW) FET where the NW channel is coated with FE nanoparticles. A single device exhibits excellent memory characteristics with the large modulation in channel conductance between ON and OFF states exceeding 10(4), a long retention time of over 4 × 10(4) s, and multibit memory storage ability. Our findings provide a viable way to create new functional high-density nonvolatile memory devices compatible with simple processing techniques at low temperature for flexible devices made on plastic substrates.

Photonic band structures [1][2][3][4] have revolutionized our understanding of how light propagates in periodic dielectric media when the periodicity is on a length scale that matches the wavelength of light. Through the creation of photonic bandgaps (PBGs), which prohibit the propagation of light within a range of 'forbidden' frequencies, the flow of light can be controlled through careful tailoring of the periodic dielectric structure. However, in order to enable new applications in photonic information technology, ultralow threshold tunable lasers, [5] and lab-on-a-chip devices, [6] direct, electrical, and in-situ control of the PBG is of crucial importance. Here, we report the demonstration of broadband wavelength tuning of a PBG that is electrically driven in a chiral nematic liquid crystal. Remarkably, this tuning is not only broadband but is found to occur without altering the reflection quality of the optical structure. In addition, under certain conditions, the helical structure can be made to exhibit multiple bandgaps across the visible spectrum. Despite being known for over 100 years chiral nematic liquid crystals (N*LCs) recently have attracted substantial interest [7] as they spontaneously self-organize to form a photonic band structure with no complex fabrication procedure required. For an N*LC, a gap in the photonic bands opens up as a result of the periodic dielectric tensor and the optical anisotropy: this is adequately described by the relation Dl ¼ Dn Á p, where 'Dl' is the width of the gap, 'Dn' is the birefringence of LC material and 'p' represents the pitch of the helical structure in the N*LC. [8][9][10] Similarly, the position of either edge of the gap is governed by l L ¼ n jj p and l S ¼ n ? p for the long (L) and short (S) wavelength photonic band edges, respectively, and n jj and n ? are the refractive indices parallel and perpendicular to the LC director. Tuning of the PBG is achieved through control of the pitch, which is sensitive to external stimuli such as temperature, [11,12] mechanical stress, [13][14][15] and magnetic fields. [16] For practical and simple to construct devices an electrically addressable PBG is required that is both reversible and allows access to a wide range of wavelengths in the visible spectrum whilst maintaining good optical finesse. Hitherto, however, the electrical control of the PBG of an N*LC has been restricted due to the disruption of the helical structure and hence destruction or deterioration of the PBG under an applied electric field. [17][18][19][20][21][22][23][24] Recently, we reported electrical PBG tuning using an indirect method of switching via ferroelectric liquid crystal (FLC) command surfaces. [25,26] The blue-shift of the PBG was fully reversible and finely controlled with good transmission/reflection qualities. However, the tuning range was restricted to a few tens of nanometers due to the limitations in the rotation angle of the FLC at the surfaces. A very broad tuning range has been successfully demonstrated using the cis-trans confor...

Recently, metal halide perovskites (MHPs) have attracted increasing attention as promising emitting materials for use in light-emitting diodes (LEDs), because of their high color purities and facile color tunabilities. [1][2][3][4][5][6][7] However, the low exciton binding energy of MHPs results in the thermal dissociation of the excitons at room temperature, [8][9][10] leading to poor geminate radiative recombination. The generated free charges are trapped in defect states rather than undergoing radiative decay, resulting in trap-mediated nonradiative charge recombination. To overcome the poor radiative recombination yield, several strategies, including reduction in perovskite grain size [7,11,12] and use of quasi-2D perovskites, [5,6,13,14] have been employed to promote bimolecular radiative recombination. Defect passivation in MHPs is a potential solution for enhancing the luminescent properties by employing various passivating materials containing amine (NH 2 ), [4,15,16] hydroxyl (OH), [17,18] phosphine oxide (PO), [6,19,20] carbonyl (CO), carboxyl (COOH), [21,22] and ammonium bromide Metal halide perovskites (MHPs) have attracted significant attention as light-emitting materials owing to their high color purities and tunabilities.A key issue in perovskite light-emitting diodes (PeLEDs) is the fabrication of an optimal charge transport layer (CTL), which has desirable energy levels for efficient charge injection while blocking opposite charges and enabling perovskite layer growth with reduced interfacial defects. Herein, two poly(fluorene-phenylene)-based anionic conjugated polyelectrolytes (CPEs) with different counterions (K + and tetramethylammonium (TMA + )) are presented as multifunctional passivating and hole-transporting layers (HTLs). The crystal growth of MHPs grown on different HTLs is investigated through X-ray photoelectron spectroscopy, X-ray diffraction, and density functional theory calculation. The CPE bearing the TMA + counterions remarkably improves the growth of perovskites with suppressed interfacial defects, leading to significantly enhanced emission properties and device performance. The luminescent properties are further enhanced via aging and electrical stress application with effective rearrangement of the counterions on the interfacial defects in the perovskites. Finally, efficient formamidinium lead tribromide-based quasi-2D PeLEDs with an external quantum efficiency of 10.2% are fabricated. Using CPEs with varying counterions as a CTL can serve as an effective method for controlling the interfacial defects and improving perovskite-based optoelectronic device properties. Perovskite Light-Emitting DiodesThe ORCID identification number(s) for the author(s) of this article can be found under https://doi.

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