Simple Holographic Patterning for High‐Aspect‐Ratio Three‐Dimensional Nanostructures with Large Coverage Area

Using the vertical standing wave phenomena commonly regarded as a deterrent in holographic lithography, multifaceted three‐dimensional (3D) nanostructures are fabricated on polymeric photoresist materials using a simple two‐beam interferometer. Large‐area 3D nanostructures with high aspect ratios (greater than 10) are readily produced using this methodology, including grating, pillar and pore patterns. Furthermore, manipulation of the lithography process conditions results in unique sidewall profiles of the nanostructures. Such 3D holographic control even produces highly porous polymer membranes composed of 3D interconnected pore networks, which resembles the 3D photonic crystal compound nanostructures that were previously attainable only with limited pattern coverage area using complex multibeam holographic lithography processes. Such well‐tailored high‐aspect‐ratio 3D nanostructures with large pattern coverage area further enable the fabrication of novel nanostructures for functionalized materials via various additive and subtractive pattern transfer techniques such as etching, deposition, and molding. In particular, direct molding followed by thermal decomposition process leads to the synthesis of hierarchical titanium oxide nanostructures of tunable 3D geometry, which would be of great significance in applications of photonic crystals, photovoltaic solar cells, and photocatalyst in water decontamination.     

Electrochemical and Top‐Down 3D Ion‐Carving to Change Magnetic Properties

It is challenging to develop new top‐down approaches to tailor particles into subnanometer size structures on a large scale to further reveal their structure‐dependent physicochemical properties. Here, we demonstrate a non‐conventional, electrochemical, 3D ion‐carving process to tailor particles into subscale flower‐like nanostructures at room temperature. The technology is based on the electrochemical insertion/extraction of lithium ions as a carving “knife” to carve the single‐crystalline particle precursor into higher‐order, flower‐like nanostructures with hexagonal nanopetals as the building units. Our study demonstrates that the morphology of the as‐carved, flower‐like nanostructures can be controlled by the electrochemical parameters, such as the current density and the number of cycles. Particularly interesting is that dramatically different magnetic properties can be achieved depending on the morphology through careful tuning by the electrochemical ion‐carving process. The as‐carved, flower‐like particles may find many important applications, including magnetic nanodevices. Our approach, in principle, is applicable to prepare various kinds of 3D‐structured materials with different compositions.     

Three‐Dimensional Nanostructures for Photonics

Recent progress in direct laser writing of three‐dimensional (3D) polymer nanostructures for photonics is reviewed. This technology has reached a level of maturity at which it can be considered as the 3D analogue of planar electron‐beam lithography. Combined with atomic‐layer deposition and/or chemical‐vapor deposition of dielectrics—the 3D analogues of planar evaporation technologies, the 3D polymer templates can be converted or inverted into 3D high‐refractive‐index‐contrast nanostructures. Examples discussed in this review include positive and inverse 3D silicon‐based woodpile photonic crystals possessing complete photonic bandgaps, novel optical resonator designs within these structures, 3D chiral photonic crystals for polarization‐state manipulation, and 3D icosahedral photonic quasicrystals. The latter represent a particularly complex 3D nanostructure.     

MOF Nano‐Vesicles and Toroids: Self‐Assembled Porous Soft‐Hybrids for Light Harvesting

Metal‐organic vesicular and toroid nanostructures of Zn(OPE)·2H₂O are achieved by coordination‐directed self‐assembly of oligo‐phenyleneethynylenedicarboxylic acid (OPEA) as a linker with Zn(OAc)₂ by controlling the reaction parameters. Self‐assembled nanostructures are characterized by powder X‐ray diffraction, field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and adsorption study. The amphiphilic nature of the coordination‐polymer with long alkyl chains renders different soft vesicular and toroidal nanostructures. The permanent porosity of the framework is established by gas adsorption study. Highly luminescent 3D porous framework is exploited for Froster's resonance energy transfer (FRET) by encapsulation of a suitable cationic dye ( DSMP ) which shows efficient funneling of excitation energy. These results demonstrate the dynamic and soft nature of the MOF, resulting in unprecedented vesicular and toroidal nanostructures with efficient light harvesting applications.     

Recent Progress in Photonic Processing of Metal‐Oxide Transistors

Over the past few decades, significant progress has been made in the field of photonic processing of electronic materials using a variety of light sources. Several of these technologies have now been exploited in conjunction with emerging electronic materials as alternatives to conventional high‐temperature thermal annealing, offering rapid manufacturing times and compatibility with temperature‐sensitive substrate materials among other potential advantages. Herein, recent advances in photonic processing paradigms of metal‐oxide thin‐film transistors (TFTs) are presented with particular emphasis on the use of various light source technologies for the photochemical and thermochemical conversion of precursor materials or postdeposition treatment of metal oxides and their application in thin‐film electronics. The pros and cons of the different technologies are discussed in light of recent developments and prospective research in the field of modern large‐area electronics is highlighted.     

A Double‐Layer Mechanochromic Hydrogel with Multidirectional Force Sensing and Encryption Capability

Hydrogel‐based soft mechanochromic materials that display colorimetric changes upon mechanical stimuli have attracted wide interest in sensors and display device applications. A common strategy to produce mechanochromic hydrogels is through photonic structures, in which mechanochromism is obtained by strain‐dependent diffraction of light. Here, a distinct concept and simple fabrication strategy is presented to produce luminescent mechanochromic hydrogels based on a double‐layer design. The two layers contain different luminescent species—carbon dots and lanthanide ions—with overlapped excitation spectra and distinct emission spectra. The mechanochromism is rendered by strain‐dependent transmittance of the top‐layer, which regulates light emission from the bottom‐layer to control the overall hydrogel luminescence. An analytical model is developed to predict the initial luminescence color and color changes as a function of uniaxial strain. Finally, this study demonstrates proof‐of‐concept applications of the mechanochromic hydrogel for pressure and contact force sensors as well as for encryption devices.     

Asymmetric Tunable Photonic Bandgaps in Self‐Organized 3D Nanostructure of Polymer‐Stabilized Blue Phase I Modulated by Voltage Polarity

Electrically responsive photonic crystals represent one of the most promising intelligent materials for technological applications in optoelectronics. In this research, a polymer‐stabilized blue phase (PSBP) I film with the self‐organized 3D nanostructure is fabricated, and an electrically tunable photonic bandgap (PBG) is achieved. Interestingly, the large‐scale shift of the PBG covering the entire visible spectrum is found to be asymmetric and can be modulated by the polarity and magnitude of bias voltage. Moreover, to demonstrate the usability in optical devices, blue phase lasers are developed by doping the PSBP material with fluorescent dyes. And mirrorless lasing emission with electrically tunable wavelength is observed. This self‐assembled soft material is prospective to produce large‐scale electrically responsive photonic crystals in facile fabrication process and has enormous potential applications in intelligent optoelectronic devices, such as 3D tunable lasers, reflective full‐color displays, or photonic integrated circuits.     

A Hybrid Carrier System Based on Origami Nanostrucutures and Layer‐by‐Layer Microparticles

Recent progress in DNA nanotechnology allows the fabrication of 3D structures that can be loaded with a large variety of molecular cargos and even be responsive to external stimuli. This makes the use of DNA nanostructures a promising approach for applications in nanomedicine and drug delivery. However, their low stability in the extra‐ and intracellular environment as well as low cellular uptake rates and release rates from endosomes into the cytoplasm hamper the efficient and targeted use of DNA nanostructures in medical applications. Here, such major obstacles are overcome by integrating DNA origami nanostructures into superordinated layer‐by‐layer based microparticles made from biopolymers. The modular assembly of the polymer layer allows a high‐density incorporation of the DNA structures at different depth. This enables controllable protection of the DNA nanostructures over extended durations in a broad range of extra‐ and intracellular conditions without compromising the cell viability. Furthermore, by producing protein‐complexed DNA nanostructures it is demonstrated that molecular cargo can be conveniently integrated into the developed hybrid system. This work provides the basis for a new multistage carrier system allowing for an efficient and protected transport of active agents inside responsive DNA nanostructures.     

Unique Necklace‐Like Phenol Formaldehyde Resin Nanofibers: Scalable Templating Synthesis,Casting Films,and Their Superhydrophobic Property

1D necklace‐like nanostructures have exhibited different potential applications due to their unique geometry and property. However, their macroscopic and controllable synthesis has been a challenge. Herein, a facile and scalable template‐directed hydrothermal process is reported to synthesize a series of necklace‐like phenol‐formaldehyde resin (PFR) wrapped nanocables. The 1D templates involved in the synthesis can be various, such as tellurium nanowires (TeNWs), silver nanowires, and carbon nanotubes. After removal of the TeNWs template, pure PFR necklace‐like nanofibers with different morphologies can be prepared. Owning to their multiscale roughness and formed 3D network structures, such necklace‐like PFR nanofibers can be further used as building blocks for constructing robust superhydrophobic coatings with excellent mechanical properties on various substrates.     

Soft Nanostructured Films for Actuated Surface‐Based siRNA Delivery

Substrate‐mediated gene delivery is an emerging technology that enables spatial control of gene expression and localized delivery. This is of particular interest for siRNA where surface‐based release can greatly impact the fields of stem‐cell reprograming, wound healing, and medical device coatings in general. However, reports on the use of siRNA for substrate‐mediated delivery are scarce and have suffered from low efficiency. Here, an alternative strategy is reported by designing self‐assembled substrates that experience stimuli‐responsive topological transformations. Specifically, a methodology is established to promote the molecular organization of lipid films having 3D‐bicontinuous cubic, 2D‐inverted hexagonal, or 1D‐lamellar nanostructures encapsulating siRNA. In response to a compositional, temperature, or humidity stimulus, the nanostructures evolve from 1D‐lamellar or 2D‐hexagonal to 3D‐cubic resulting in efficient siRNA release to human cell cultures. Grazing incidence X‐ray diffraction reveals that film nanostructures are highly ordered and preferentially aligned. The results indicate that film structure substantially affects siRNA delivery, with the supported 3D‐bicontinuous cubic phase yielding the most effective reduction of gene expression. Subsequent studies suggest this enhanced performance arises due to the ability of this phase to cross cell membranes, particularly those of endocytic compartments. This work underpins that nanostructure tuning is decisive to the performance of therapeutic films.     

2D Tellurium Based High‐Performance All‐Optical Nonlinear Photonic Devices

Tellurium (Te), as one of the rarest stable solid elements far more common in the universe than on earth, is a p‐type semiconductor with excellent optical properties. Herein, a novel two‐dimensional (2D) Te nanosheets (Ns)‐based air‐stable nonlinear photonic devices: all‐optical switcher and photonic diode, owing to its strong light–matter interaction in the visible‐to‐infrared band are reported. The findings validate that the proposed photonic diode can be utilized for the function of nonreciprocal light propagation in optical telecommunications or integrated photonics. Moreover, 2D Te‐based light‐modulate‐light system is successfully designed to realize “ON” and “OFF” modes for all‐optical switching operation. This work highlights a good promise of 2D Te in the field of nonlinear photonics, leading to an important step toward 2D Te‐based advanced photonics devices. The versatile solution process allows a universal access of 2D Te as a new 2D material in a wider range of photonics device applications such as, detector, modulator, switcher, etc.     

Amphiphilic Poly(p‐phenylene)s for Self‐Organized Porous Blue‐Light‐Emitting Thin Films

Micro‐ and nanostructuring of conjugated polymers are of critical importance in the fabrication of molecular electronic devices as well as photonic and bandgap materials. The present report delineates the single‐step self‐organization of highly ordered structures of functionalized poly(p‐phenylene)s without the aid of either a controlled environment or expensive fabrication methodologies. Microporous films of these polymers, with a honeycomb pattern, were prepared by direct spreading of the dilute polymer solution on various substrates, such as glass, quartz, silicon wafer, indium tin oxide, gold‐coated mica, and water, under ambient conditions. The polymeric film obtained from C₁₂PPPOH comprises highly periodic, defect‐free structures with blue‐light‐emitting properties. It is expected that such microstructured, conjugated polymeric films will have interesting applications in photonic and optoelectronic devices. The ability of the polymer to template the facile micropatterning of nanomaterials gives rise to hybrid films with very good spatial dispersion of the carbon nanotubes.     

Low‐Dimensional Transition Metal Dichalcogenide Nanostructures Based Sensors

Two‐dimensional (2D) transition metal dichalcogenides (TMDs) nanostructures have been widely applied in environmental and biological analysis, biomedicine, electronic devices, and hydrogen evolution catalysis. Meanwhile, this excitement in 2D TMDs has spilled over to their counterparts of different dimensionalities like one‐dimensional (1D) and zero‐dimensional (0D) TMDs nanostructures. Eventual physical and chemical properties of TMDs nanostructures still remain to be highly dependent on their dimensionalities and size scale, and recently creatively exploring these physical and chemical properties is extremely impactful for the sensing field of TMD nanomaterials. Herein, we review a wide range of sensing applications based on not only graphene‐like 2D TMDs nanostructures but also the rapidly emerging subclasses of 1D, and 0D TMDs nanostructures. Their unique and interesting structures, excellent properties, and valid preparation methods are also included and the analytical objectives, ranging from heavy metal ions to small molecules, from DNA to proteins, from liquids to even vapors, can be met with extremely high selectivity and sensitivity. We have also analyzed our current understanding of 0D and 1D TMDs nanostructures and learning from graphene with the goal of contributing fresh ideas to the overall development of more advanced future TMDs based sensors.     

Cell‐Instructive Multiphasic Gel‐in‐Gel Materials

Developing tissue is typically soft, highly hydrated, dynamic, and increasingly heterogeneous matter. Recapitulating such characteristics in engineered cell‐instructive materials holds the promise of maximizing the options to direct tissue formation. Accordingly, progress in the design of multiphasic hydrogel materials is expected to expand the therapeutic capabilities of tissue engineering approaches and the relevance of human 3D in vitro tissue and disease models. Recently pioneered methodologies allow for the creation of multiphasic hydrogel systems suitable to template and guide the dynamic formation of tissue‐ and organ‐specific structures across scales, in vitro and in vivo. The related approaches include the assembly of distinct gel phases, the embedding of gels in other gel materials and the patterning of preformed gel materials. Herein, the capabilities and limitations of the respective methods are summarized and discussed and their potential is highlighted with some selected examples of the recent literature. As the modularity of the related methodologies facilitates combinatorial and individualized solutions, it is envisioned that multiphasic gel‐in‐gel materials will become a versatile morphogenetic toolbox expanding the scope and the power of bioengineering technologies.     

Two‐Dimensional Nanostructured Materials for Gas Sensing

Two‐dimensional (2D) nanostructures are highly attractive for fabricating nanodevices due to their high surface‐to‐volume ratio and good compatibility with device design. In recent years 2D nanostructures of various materials including metal oxides, graphene, metal dichalcogenides, phosphorene, BN and MXenes, have demonstrated significant potential for gas sensors. This review aims to provide the most recent advancements in utilization of various 2D nanomaterials for gas sensing. The common methods for the preparation of 2D nanostructures are briefly summarized first. The focus is then placed on the sensing performances provided by devices integrating 2D nanostructures. Strategies for optimizing the sensing features are also discussed. By combining both the experimental results and the theoretical studies available, structure‐properties correlations are discussed. The conclusion gives some perspectives on the open challenges and future prospects for engineering advanced 2D nanostructures for high‐performance gas sensors devices.     

Acrylate‐Based Photopolymer for Two‐Photon Microfabrication and Photonic Applications

This paper provides a photopolymerizing material suitable for stereolithography of complex submicrometer‐sized three‐dimensional (3D) structural elements to a broad scientific public. Here, we present the formulation of a polymer (LN1 resin) that allows further research in the field of nanofabrication and ‐technology as it surpasses current material limitations. The polymer consists of multifunctional acrylate oligomers as binder, polyfunctional monomers, and a photoinitiator (PI). The chemistry to form 3D structures is based on photopolymerization of the acrylate system initiated by free‐radical species that are triggered by two‐photon absorption of a PI. Important parameters of photocuring, such as the effects of PI concentration, temperature, and light intensity, were studied using photocalorimetry. The thermal stability of the material was tested using thermal gravimetric analysis, providing key information for electronic and photonic applications. Photonic‐crystal structures generated from this resin exhibiting photonic stop gaps in near‐infrared‐ and telecommunication‐wavelength regions are presented.     

Photoresponsive Soft‐Robotic Platform: Biomimetic Fabrication and Remote Actuation

Biomimetic microsystems, which can be driven by various stimuli, are an emerging field in micro/nano‐technology and nano‐medicine. In this study, a soft and fast‐response robotic platform, constituted by PDMS/graphene‐nanoplatelets composited layer (PDMS/GNPs) and pristine PDMS layer, is presented. Due to the differences in coefficient of thermal expansion and Young's modulus of the two layers, the bilayer platform can be driven to bend to the PDMS/GNPs side by light irradiation. The robotic platform (1 mm in width and 7 mm in length) can be deflected about 1500 μm by near infrared irradiation (nIR)(808 nm in wavelength) within 3.4 s, and excellent reversibility and repeatability in actuation are also revealed by sweeping and multicycle light irradiation. The experiments also show that, the presented bilayer platform in various shapes, that is, fish‐like shapes, can float and swim to perspective location in fluid (i.e., water), whose moving directions and velocities can be remotely adjusted by light, indicating an excellent light‐actuation ability and well controllability. The results may be not only hopeful in developing light‐driven drug‐delivery platform, but also the bio‐robotic microgrippers applying in vivo and in vitro.     

A Stimuli‐Responsive Nanocomposite for 3D Anisotropic Cell‐Guidance and Magnetic Soft Robotics

Stimuli‐responsive materials have the potential to enable the generation of new bioinspired devices with unique physicochemical properties and cell‐instructive ability. Enhancing biocompatibility while simplifying the production methodologies, as well as enabling the creation of complex constructs, i.e., via 3D (bio)printing technologies, remains key challenge in the field. Here, a novel method is presented to biofabricate cellularized anisotropic hybrid hydrogel through a mild and biocompatible process driven by multiple external stimuli: magnetic field, temperature, and light. A low‐intensity magnetic field is used to align mosaic iron oxide nanoparticles (IOPs) into filaments with tunable size within a gelatin methacryloyl matrix. Cells seeded on top or embedded within the hydrogel align to the same axes of the IOPs filaments. Furthermore, in 3D, C2C12 skeletal myoblasts differentiate toward myotubes even in the absence of differentiation media. 3D printing of the nanocomposite hydrogel is achieved and creation of complex heterogeneous structures that respond to magnetic field is demonstrated. By combining the advanced, stimuli‐responsive hydrogel with the architectural control provided by bioprinting technologies, 3D constructs can also be created that, although inspired by nature, express functionalities beyond those of native tissue, which have important application in soft robotics, bioactuators, and bionic devices.     

Bio‐Inspired Photonic Materials: Prototypes and Structural Effect Designs for Applications in Solar Energy Manipulation

Natural creatures have evolved elaborate photonic nanostructures on multiple scales and dimensions in a hierarchical, organized way to realize controllable absorption, reflection, or transmitting the desired wavelength of the solar spectrum. A bio‐inspired strategy is a powerful and promising way for solar energy manipulation. This feature article presents the state‐of‐the‐art progress on bio‐inspired photonic materials on this particular application. The article first briefly recalls the physical origins of natural photonic effects and catalogues the typical natural photonic prototypes including light harvesting, broadband reflection, selective reflection, and UV/IR response. Next, typical applications are categorized into two primary areas: solar energy utilization and reflection. Recent advances including solar‐to‐electricity, solar‐to‐fuels, solar‐thermal (e.g., photothermal converters, infrared detectors, thermoelectric materials, smart windows, and solar steam generation) are highlighted in the first part. Meanwhile, solar energy reflection involving infrared stealth, radiative cooling, and micromirrors are also addressed. In particular, this article focuses on bioinspired design principles, structural effects on functions, and future trends. Finally, the main challenges and prospects for the next generation of bioinspired photonic materials are discussed, including new design concepts, emerging ideas, and possible strategies.     

All‐Dielectric Programmable Huygens' Metasurfaces

Low‐loss nanostructured dielectric metasurfaces have emerged as a breakthrough platform for ultrathin optics and cutting‐edge photonic applications, including beam shaping, focusing, and holography. However, the static nature of their constituent materials has traditionally limited them to fixed functionalities. Tunable all‐dielectric infrared Huygens' metasurfaces consisting of multi‐layer Ge disk meta‐units with strategically incorporated non‐volatile phase change material Ge₃Sb₂Te₆ are introduced. Switching the phase‐change material between its amorphous and crystalline structural state enables nearly full dynamic light phase control with high transmittance in the mid‐IR spectrum. The metasurface is realized experimentally, showing post‐fabrication tuning of the light phase within a range of 81% of the full 2π phase shift. Additionally, the versatility of the tunable Huygen's metasurfaces is demonstrated by optically programming the spatial light phase distribution of the metasurface with single meta‐unit precision and retrieving high‐resolution phase‐encoded images using hyperspectral measurements. The programmable metasurface concept overcomes the static limitations of previous dielectric metasurfaces, paving the way for “universal” metasurfaces and highly efficient, ultracompact active optical elements like tunable lenses, dynamic holograms, and spatial light modulators.