Shape-Controlled and Well-Arrayed Heterogeneous Nanostructures via Melting Point Modulation at the Nanoscale

Micro-/Nanohierarchical Structures Physically Engineered on Surfaces: Analysis and Perspective

The high demand for micro-/nanohierarchical structures as components of functional substrates, bioinspired devices, energy-related electronics, and chemical/physical transducers has inspired their in-depth studies and active development of the related fabrication techniques. In particular, significant progress has been achieved in hierarchical structures physically engineered on surfaces, which offer the advantages of wide-range material compatibility, design diversity, and mechanical stability, and numerous unique structures with important niche applications have been developed. This review categorizes the basic components of hierarchical structures physically engineered on surfaces according to function/shape and comprehensively summarizes the related advances, focusing on the fabrication strategies, ways of combining basic components, potential applications, and future research directions. Moreover, the physicochemical properties of hierarchical structures physically engineered on surfaces are compared based on the function of their basic components, which may help to avoid the bottlenecks of conventional single-scale functional substrates. Thus, the present work is expected to provide a useful reference for scientists working on multicomponent functional substrates and inspire further research in this field.

Illuminating Recent Progress in Nanotransfer Printing: Core Principles, Emerging Applications, and Future Perspectives

As the demand for diverse nanostructures in physical/chemical devices continues to rise, the development of nanotransfer printing (nTP) technology is receiving significant attention due to its exceptional throughput and ease of use. Over the past decade, researchers have attempted to enhance the diversity of materials and substrates used in transfer processes as well as to improve the resolution, reliability, and scalability of nTP. Recent research on nTP has made continuous progress, particularly using the control of the interfacial adhesion force between the donor mold, target material, and receiver substrate, and numerous practical nTP methods with niche applications have been demonstrated. This review article offers a comprehensive analysis of the chronological advancements in nTP technology and categorizes recent strategies targeted for high-yield and versatile printing based on controlling the relative adhesion force depending on interfacial layers. In detail, the advantages and challenges of various nTP approaches are discussed based on their working mechanisms, and several promising solutions to improve morphological/material diversity are presented. Furthermore, this review provides a summary of potential applications of nanostructured devices, along with perspectives on the outlook and remaining challenges, which are expected to facilitate the continued progress of nTP technology and to inspire future innovations.

Current advances in anisotropic structures for enhanced osteogenesis

Bone defects are a challenge to healthcare systems, as the aging population experiences an increase in bone defects. Despite the development of biomaterials for bone fillers and scaffolds, there is still an unmet need for a bone-mimetic material. Cortical bone is highly anisotropic and displays a biological liquid crystalline (LC) arrangement, giving it exceptional mechanical properties and a distinctive microenvironment. However, the biofunctions, cell-tissue interactions, and molecular mechanisms of cortical bone anisotropic structure are not well understood. Incorporating anisotropic structures in bone-facilitated scaffolds has been recognised as essential for better outcomes. Various approaches have been used to create anisotropic micro/nanostructures, but biomimetic bone anisotropic structures are still in the early stages of development. Most scaffolds lack features at the nanoscale, and there is no comprehensive evaluation of molecular mechanisms or characterisation of calcium secretion. This manuscript provides a review of the latest development of anisotropic designs for osteogenesis and discusses current findings on cell-anisotropic structure interactions. It also emphasises the need for further research. Filling knowledge gaps will enable the fabrication of scaffolds for improved and more controllable bone regeneration.

Nanotransfer-on-Things: From Rigid to Stretchable Nanophotonic Devices

The growing demand for nanophotonic devices has driven the advancement of nanotransfer printing (nTP) technology. Currently, the scope of nTP is limited to certain materials and substrates owing to the temperature, pressure, and chemical bonding requirements. In this study, we developed a universal nTP technique utilizing covalent bonding-based adhesives to improve the adhesion between the target material and substrate. Additionally, the technique employed plasma-based selective etching to weaken the adhesion between the mold and target material, thereby enabling the reliable modulation of the relative adhesion forces, regardless of the material or substrate. The technique was evaluated by printing four optical materials on nine substrates, including rigid, flexible, and stretchable substrates. Finally, its applicability was demonstrated by fabricating a ring hologram, a flexible plasmonic color filter, and extraordinary optical transmission-based strain sensors. The high accuracy and reliability of the proposed nTP method were verified by the performance of nanophotonic devices that closely matched numerical simulation results.

Nanoscale three-dimensional fabrication based on mechanically guided assembly

The growing demand for complex three-dimensional (3D) micro-/nanostructures has inspired the development of the corresponding manufacturing techniques. Among these techniques, 3D fabrication based on mechanically guided assembly offers the advantages of broad material compatibility, high designability, and structural reversibility under strain but is not applicable for nanoscale device printing because of the bottleneck at nanofabrication and design technique. Herein, a configuration-designable nanoscale 3D fabrication is suggested through a robust nanotransfer methodology and design of substrate's mechanical characteristics. Covalent bonding-based two-dimensional nanotransfer allowing for nanostructure printing on elastomer substrates is used to address fabrication problems, while the feasibility of configuration design through the modulation of substrate's mechanical characteristics is examined using analytical calculations and numerical simulations, allowing printing of various 3D nanostructures. The printed nanostructures exhibit strain-independent electrical properties and are therefore used to fabricate stretchable H₂ and NO₂ sensors with high performances stable under external strains of 30%.

Designed Growth of AgNP Arrays for Anti-counterfeiting Based on Surface-Enhanced Raman Spectroscopy Signals

Based on etched PS sphere arrays, the different growths of Ag nanoparticles with tunable LSPR are designed when SiO2-25 nm/Ag-30 nm/SiO2-100 nm sandwich nanocavity structures are annealed at 500 °C, including the hexagonal silver nanoparticle rings, circular silver nanoparticle rings, and aggregated silver nanoparticles. The uniformity of particle size and regularity of position generate enhanced electromagnetic field and good surface-enhanced Raman spectroscopy signals as confirmed by UV-vis observation and finite difference time domain method simulation. The developed nanostructures are effectively used as stable, nonreproducible, and markable anti-counterfeiting signs.

Spherical Micro/Nano Hierarchical Structures for Energy and Water Harvesting Devices

Three-dimensional (3D) hierarchical structures have been explored for various applications owing to the synergistic effects of micro- and nanostructures. However, the development of spherical micro/nano hierarchical structures (S-HSs), which can be used as energy/water harvesting systems and sensing devices, remains challenging owing to the trade-off between structural complexity and fabrication difficulty. This paper presents a new strategy for facile, scalable S-HS fabrication using a thermal expansion of microspheres and nanopatterned structures. When a specific temperature is applied to a composite film of microspheres and elastomers with nanopatterned surfaces, microspheres are expanded and 3D spherical microstructures are generated. Various nanopatterns and densities of spherical microstructures can thereby be quantitatively controlled. The fabricated S-HSs have been used in renewable electrical energy harvesting and sustainable water management applications. Compared to a triboelectric nanogenerator (TENG) with bare film, the S-HS-based TENG exhibited 4.48 times higher triboelectric performance with high mechanical durability. Furthermore, an S-HS is used as a water harvesting device to capture water in a fog environment. The water collection rate is dramatically enhanced by the increased surface area and locally concentrated vapor diffusion flux due to the spherical microstructures.

One material, many possibilities via enrichment of luminescence in La2Zr2O7:Tb3+ nanophosphors for forensic stimuli aided applications

Engineering a single material with multidirectional applications is crucial for improving productivity, low cost, flexibility, least power consumption, etc. To achieve these requirements, novel design structures and high-performance materials are in urgent need. Lanthanide-doped nanophosphors have the greatest strengths and ability in order to tune their applications in various dimensions. However, applications of nanophosphor in latent fingerprints visualization, anti-counterfeiting, and luminescent gels/films are still in their infancy. This study demonstrated a simple strategy to enhance the luminescence of Tb³⁺ (1-11 mol %) doped La₂Zr₂O₇ nanophosphors by conjugating various fluxes via a simple solution combustion route. The photoluminescence emission spectra reveal intense peaks at ~ 491, 546, 587, and 622 nm, which arises from ⁵D₄ → ⁷F_J (J = 6, 5, 4, 3) transitions of Tb³⁺ ions, respectively. The highest emission intensity was achieved in the NH₄Cl flux assisted nanophosphor as compared to NaBr and NH₄F assisted samples. The colorimetric images of fingerprints visualized using the optimized nanophosphor on forensic related surfaces exhibit level -III ridge details, including sweat pores, the width of the ridges, bifurcation angle, and the successive distance between sweat pores, etc. These results are decisive parameters that clearly support the statement "no two persons have ever been found to have the same fingerprints". The anti-counterfeiting security ink was formulated using optimized nanophosphor and various patterns were designed by simple screen printing and dip pen technologies. The encoded information was decrypted only under ultraviolet 254 nm light. All the designed patterns are exhibit not just what it looks/feel like and how better it works. As a synergetic contribution of enhanced luminescence of the prepared nanophosphor, the green-emissive films were fabricated, which display excellent flexibility, uniformity, and transparency in the normal and ultraviolet 254 nm light illumination. The aforementioned results revealed that the prepared NH₄Cl flux-assisted La₂Zr₂O₇: Tb³⁺(7 mol %) NPs are considered to be the best candidate for multi-dimensional applications.

Wafer-scale, highly uniform, and well-arrayed suspended nanostructures for enhancing the performance of electronic devices

Suspended nanostructures play an important role in enhancing the performance of a diverse group of nanodevices. However, realizing a good arrangement and suspension for nanostructures of various shapes remains a significant challenge. Herein, a rapid and simple method for fabricating wafer-scale, highly uniform, well-arrayed suspended nanostructures via nanowelding lithography is reported. Suspended nanostructures with various shapes (nanowires, nanoholes, nanomesh, and nanofilms) and materials (gold, silver, and palladium metals) were employed to demonstrate the applicability of our method. Moreover, gas sensors and thermoacoustic speakers with suspended nanowires outperformed those with unsuspended nanostructures. The proposed method is expected to help advance the development of future nanodevices based on suspended nanostructures.