Bio-inspired design of multiscale structures for function integration

Light-driven phenomena both in living systems and nonliving materials have enabled truly fascinating and incredible dynamic architectures with terrific forms and functions. Recently, liquid crystalline materials endowed with photoresponsive capability have emerged as enticing systems. In this Review, we focus on the developments of light-driven liquid crystalline materials containing photochromic components over the past decade. Design and synthesis of photochromic liquid crystals (LCs), photoinduced phase transitions in LC, and photoalignment and photoorientation of LCs have been covered. Photomodulation of pitch, polarization, lattice constant and handedness inversion of chiral LCs is discussed. Light-driven phenomena and properties of liquid crystalline polymers, elastomers, and networks have also been analyzed. The applications of photoinduced phase transitions, photoalignment, photomodulation of chiral LCs, and photomobile polymers have been highlighted wherever appropriate. The combination of photoc...

Light-Driven Liquid Crystalline Materials: From Photo-Induced Phase Transitions and Property Modulations to Applications.

Recent progress in antireflection and self-cleaning technology – From surface engineering to functional surfaces

Reducing the reflection and improving the transmission or absorption of light from wide angles of incidence in a broad wavelength range are crucial for enhancing the performance of the optical, optoelectronic, and electro-optical devices. Inspired by the structures of the insect compound eyes, nanostructure arrays (NSAs) have been developed as effective antireflective surfaces, which exhibit promising broadband and quasi-omnidirectional antireflective properties together with multifunctions. This review summarizes the recent advances in the fabrication and performance of antireflective surfaces based on NSAs of a wide variety of materials including silicon and non-silicon materials. The applications of the NSA-based antireflective surfaces in solar cells, light emitting diodes, detection, and imaging are highlighted. The remaining challenges along with future trends in NSA-based antireflective surfaces are also discussed.

Recent advances in antireflective surfaces based on nanostructure arrays

Among diverse wetting phenomena in surface science, superamphiphobicity is regarded as one of the most special super-antiwetting states. In this paper, a systematic summary has been generated to cover the characterization of surface wettability, the construction techniques, and selected functional applications. With respect to fabrication techniques, we will discuss the following three types of technology routes, viz., ‘pre-texturing + post-modifying’, ‘pre-modifying + post-texturing’, and in-situ one-step construction. Discussion has been made on the merits and demerits of each technology route. It is vital to rationally design or adopt appropriate construction strategies in diverse conditions. Appropriately constructed superamphiphobic multifunctional surfaces can be applied in many fields, however, most have not been scale-up and utilized for practical applications due to some specific difficulties required to be resolved in the future. These challenges and further outlook for super-antiwetting surfaces are discussed in this review.

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Bioinspired surfaces with superamphiphobic properties : concepts, synthesis, and applications

We propose and implement a technique for arbitrary pattern fabrication in liquid crystal (LC) alignments and local polarization control for light wavefront. A micro-lithography system with a digital micro-mirror device as dynamic mask forms arbitrary micro-images on photoalignment layers and further guides the LC molecule orientations. Besides normal phase gratings, more complex 2D patterns such as quasicrystal and checkerboard structures are demonstrated. To characterize the optical performances of the fabricated structures, the electro-optically tunable diffraction patterns and efficiencies are demonstrated in several 1D/2D phase gratings. Compared to other techniques, our method enables the arbitrary and instant manipulation of LC alignments and light polarization states, facilitating wide applications in display and photonic fields.

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Arbitrary Photo-Patterning in Liquid Crystal Alignments Using DMD Based Lithography System

Corrugated silicon nanocone (SiNC) arrays have been fabricated on a silicon wafer by two polystyrene-sphere- monolayer-masked etching steps in order to create high-performance antireflective coatings. The reflectance was reduced from above 35% to less than 0.7% in the range 400-1050 nm, and it remained below 0.5% at incidence angles up to 70° at 632.8 nm for both s- and p-polarized light. The fluorinated corrugated SiNC array surface exhibits superhydrophobic properties with a water contact angle of 164° .

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Biomimetic Corrugated Silicon Nanocone Arrays for Self-Cleaning Antireflection Coatings

We develop a fluorinated phenyl-tolane based nematic mixture NJU-LDn-4 and evaluate its frequency-dependent birefringence utilizing terahertz time domain spectroscopy (THz-TDS). A large mean birefringence of 0.306 is obtained in a broad range from 0.4 to 1.6 THz, with a maximum of 0.314 at 1.6 THz. Furthermore, relation between molecular structures and birefringence property is discussed. This work reveals new insights for tailing liquid crystal molecules with desirable large birefringence in THz range, which is extremely meaningful for the design and fabrication of fast, compact and tunable terahertz devices.

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Large birefringence liquid crystal material in terahertz range

Using sub-wavelength metallic gratings as both transparent electrodes and broadband high-efficiency polarizers, a highly-compact self-polarizing phase shifter is demonstrated by electrically tuning the effective birefringence of a nematic liquid crystal cell. The metal grating polarizers ensure a good polarizing efficiency in the range of 0.2 to 2 THz. Phase shift of more than π/3 is achieved in a 256 μm-thick cell with a saturation root mean square voltage of around 130 V in this integrated device.

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Self-polarizing terahertz liquid crystal phase shifter

A diffraction grating is proposed by periodically defining the liquid-crystal director distribution to form alternate parallel aligned and twist nematic regions in a cell placed between two crossed polarizers. Based on the combined phase and amplitude modulation, both 1D and 2D tunable gratings are demonstrated. Low voltage ON/OFF switching of 1st order diffracted light with extinction ratio over 80 is achieved within a small voltage interval of 0.15 Vrms. Unique four-state feature of the cell is obtained and their applications in optical logic devices are discussed.

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Xiao-wen Lin

Papers

Arbitrary Photo-Patterning in Liquid Crystal Alignments Using DMD Based Lithography System

Biomimetic Corrugated Silicon Nanocone Arrays for Self-Cleaning Antireflection Coatings

Large birefringence liquid crystal material in terahertz range

Self-polarizing terahertz liquid crystal phase shifter

Liquid crystal gratings based on alternate TN and PA photoalignment