Breakdown of Native Oxide Enables Multifunctional, Free-Form Carbon Nanotube-Metal Hierarchical Architectures

Ultra-thin light-weight laser-induced-graphene (LIG) diffractive optics

The realization of hybrid optics could be one of the best ways to fulfill the technological requirements of compact, light-weight, and multi-functional optical systems for modern industries. Planar diffractive lens (PDL) such as diffractive lenses, photonsieves, and metasurfaces can be patterned on ultra-thin flexible and stretchable substrates and be conformally attached on top of arbitrarily shaped surfaces. In this review, we introduce recent research works addressed to the design and manufacturing of ultra-thin graphene optics, which will open new markets in compact and light-weight optics for next-generation endoscopic brain imaging, space internet, real-time surface profilometry, and multi-functional mobile phones. To provide higher design flexibility, lower process complexity, and chemical-free process with reasonable investment cost, direct laser writing (DLW) of laser-induced-graphene (LIG) is actively being applied to the patterning of PDL. For realizing the best optical performances in DLW, photon-material interactions have been studied in detail with respect to different laser parameters; the resulting optical characteristics have been evaluated in terms of amplitude and phase. A series of exemplary laser-written 1D and 2D PDL structures have been actively demonstrated with different base materials, and then, the cases are being expanded to plasmonic and holographic structures. The combination of these ultra-thin and light-weight PDL with conventional bulk refractive or reflective optical elements could bring together the advantages of each optical element. By integrating these suggestions, we suggest a way to realize the hybrid PDL to be used in the future micro-electronics surface inspection, biomedical, outer space, and extended reality (XR) industries.

A photon-recycling incandescent lighting device

Energy-efficient, healthy lighting is vital for human beings. Incandescent lighting provides high-fidelity color rendering and ergonomic visual comfort yet is phased out owing to low luminous efficacy (15 lumens per watt) and poor lifetime (2000 hours). Here, we propose and experimentally realize a photon-recycling incandescent lighting device (PRILD) with a luminous efficacy of 173.6 lumens per watt (efficiency of 25.4%) at a power density of 277 watts per square centimeter, a color rendering index (CRI) of 96, and a LT70-rated lifetime of >60,000 hours. The PRILD uses a machine learning-designed 637-nm-thick visible-transparent infrared-reflective filter and a Janus carbon nanotube/hexagonal boron nitride filament to recycle 92% of the infrared radiation. The PRILD has higher luminous efficacy, CRI, and lifetime compared with solid-state lighting and thus is promising for high-power density lighting.

Host-Guest Chemistry in Boron Nitride Nanotubes: Interactions with Polyoxometalates and Mechanism of Encapsulation

Boron nitride nanotubes (BNNTs) are an emerging class of molecular container offering new functionalities and possibilities for studying molecules at the nanoscale. Herein, BNNTs are demonstrated as highly effective nanocontainers for polyoxometalate (POM) molecules. The encapsulation of POMs within BNNTs occurs spontaneously at room temperature from an aqueous solution, leading to the self-assembly of a POM@BNNT host-guest system. Analysis of the interactions between the host-nanotube and guest-molecule indicate that Lewis acid-base interactions between W═O groups of the POM (base) and B-atoms of the BNNT lattice (acid) likely play a major role in driving POM encapsulation, with photoactivated electron transfer from BNNTs to POMs in solution also contributing to the process. The transparent nature of the BNNT nanocontainer allows extensive investigation of the guest-molecules by photoluminescence, Raman, UV-vis absorption, and EPR spectroscopies. These studies revealed considerable energy and electron transfer processes between BNNTs and POMs, likely mediated via defect energy states of the BNNTs and resulting in the quenching of BNNT photoluminescence at room temperature, the emergence of new photoluminescence emissions at cryogenic temperatures (<100 K), a photochromic response, and paramagnetic signals from guest-POMs. These phenomena offer a fresh perspective on host-guest interactions at the nanoscale and open pathways for harvesting the functional properties of these hybrid systems.

Absorbing light using time-reversed lasers

Laser cavities can be reverse engineered to create an efficient light trap.

Dual-Active Au@PNIPAm Nanozymes for Glucose Detection and Intracellular H2O2 Modulation

As a nanozyme, gold nanoparticles have some advantages compared with natural enzymes, such as stable structure, adjustable catalytic activity, multifunctionality, and recyclability. Due to their special dimension, they are easy to aggregate rapidly and lose their catalytic performance when exposed to normal saline or special pH environment. To avoid such a situation, Au@PNIPAm nanozymes with core-shell structure are constructed and their mimic peroxidase and glucose oxidase enzymatic activities are investigated. Kinetic examinations manifest that Au@PNIPAm nanozymes exhibited a high affinity for 3,3,5,5-tetramethylbenzidine (TMB), hydrogen peroxide (H₂O₂), and glucose. These predominant peroxidase-like and glucose-like oxidase Au@PNIPAm catalytic activities are successfully used in the detection of H₂O₂ or glucose (LOD is 2.43 mM or 5.07 mM). Otherwise, the potential Au@PNIPAm nanozymes are provided with a clear ability for decomposing the intracellular H₂O₂ in living cells. And it could protect cells from oxidative stress damage with inducing by H₂O₂. Therefore, it is easy to consider that Au@PNIPAm nanozymes show a certain possibility to retard cell senescence and increase the production of the hydroxyl radical which could prevent carcinogenesis of the cell.

Nanostructured Broadband Solar Absorber for Effective Photothermal Conversion and Electricity Generation

Photothermal conversion is an environmentally friendly process that harvests energy from the sun and has been attracting growing research interest in recent years. However, nanostructured strategies to improve light capture performance deserve further development, and the application of solar heating effects for clean energy needs to be explored. Herein, a multiscale nanomaterial was prepared by in situ polymerizing the polyaniline (PANI) nanoparticles into porous anodic aluminum oxide (AAO) membrane. As a result, the as-prepared PANI-AAO shows broadband solar absorption and provides a platform for efficient photothermal conversion. What is more, we introduced a typical thermoelectricity generator (TEG) with excellent output performance and combined it with PANI-AAO to prepare a solar thermoelectric generator (s-TEG). The s-TEG harvests solar energy and converts it into electricity, showing an outstanding power generation capability in outdoor conditions. Thus, the nanostructured broadband solar absorber and the integrated solar thermoelectric generator offer a promising candidate for a sustainable and green energy source in the future.

Fabrication of Antireflection Micro/Nanostructures on the Surface of Aluminum Alloy by Femtosecond Laser

Designed micro-nano structures on the surface of aluminum alloy provide excellent light trapping properties that can be used extensively in thermal photovoltaics, sensors, etc. However, the fabrication of high-performance antireflective micro-nano structures on aluminum alloy is challenging because aluminum has shallow intrinsic losses and weak absorption. A two-step strategy is proposed for fabricating broadband antireflection structures by superimposing nanostructures onto microscale structures. By optimizing the processing parameters of femtosecond laser, the average reflectances of 2.6% within the visible spectral region (400–800 nm) and 5.14% within the Vis-NIR spectral region (400–2500 nm) are obtained.

Beyond Color: The New Carbon Ink

For thousands of years, carbon ink has been used as a black color pigment for writing and painting purposes. However, recent discoveries of nanocarbon materials, including fullerenes, carbon nanotubes, graphene, and their various derivative forms, together with the advances in large-scale synthesis, are enabling a whole new generation of carbon inks that can serve as an intrinsically programmable materials platform for developing advanced functionalities far beyond color. The marriage between these multifunctional nanocarbon inks with modern printing technologies is facilitating and even transforming many applications, including flexible electronics, wearable and implantable sensors, actuators, and autonomous robotics. This review examines recent progress in the reborn field of carbon inks, highlighting their programmability and multifunctionality for applications in flexible electronics and stimuli-responsive devices. Current challenges and opportunities will also be discussed from a materials science perspective towards the advancement of carbon ink for new applications beyond color.

Bioinspired Microstructured Polymer Surfaces with Antireflective Properties

Over the years, different approaches to obtaining antireflective surfaces have been explored, such as using index-matching, interference, or micro- and nanostructures. Structural super black colors are ubiquitous in nature, and biomimicry thus constitutes an interesting way to develop antireflective surfaces. Moth-eye nanostructures, for example, are well known and have been successfully replicated using micro- and nanofabrication. However, other animal species, such as birds of paradise and peacock spiders, have evolved to display larger structures with antireflective features. In peacock spiders, the antireflective properties of their super black patches arise from relatively simple microstructures with lens-like shapes organized in tightly packed hexagonal arrays, which makes them a good candidate for cheap mass replication techniques. In this paper, we present the fabrication and characterization of antireflective microarrays inspired by the peacock spider’s super black structures encountered in nature. Firstly, different microarrays 3D models are generated from a surface equation. Secondly, the arrays are fabricated in a polyacrylate resin by super-resolution 3D printing using two-photon polymerization. Thirdly, the resulting structures are inspected using a scanning electron microscope. Finally, the reflectance and transmittance of the printed structures are characterized at normal incidence with a dedicated optical setup. The bioinspired microlens arrays display excellent antireflective properties, with a measured reflectance as low as 0.042 ± 0.004% for normal incidence, a wavelength of 550 nm, and a collection angle of 14.5°. These values were obtained using a tightly-packed array of slightly pyramidal lenses with a radius of 5 µm and a height of 10 µm.

Structure development of carbon-based solar-driven water evaporation systems

Pressing need goes ahead for accessing freshwater in insufficient supply countries and regions, which will become a restrictive factor for human development and production. In recent years, solar-driven water evaporation (SDWE) systems have attracted increasing attention for their specialty in no consume conventional energy, pollution-free, and the high purity of fresh water. In particular, carbon-based photothermal conversion materials are preferred light-absorbing material for SDWE systems because of their wide range of spectrum absorption and high photothermal conversion efficiency based on super-conjugate effect. Until now, many carbon-based SDWE systems have been reported, and various structures emerged and were designed to enhance light absorption, optimize heat management, and improve the efficient water transport path. In this review, we attempt to give a comprehensive summary and discussions of structure progress of the carbon-based SDWE systems and their working mechanisms, including carbon nanoparticles systems, single-layer photothermal membrane systems, bi-layer structural photothermal systems, porous carbon-based materials systems, and three dimensional (3D) systems. In these systems, the latest 3D systems can expand the light path by allowing light to be reflected multiple times in the microcavity to increase the light absorption rate, and its large heat exchange area can prompt more water to evaporate, which makes them the promising application foreground. We hope our review can spark the probing of underlying principles and inspiring design strategies of these carbon-based SDWE systems, and further guide device optimizations, eventually promoting in extensive practical applications in the future.

Carbon Nanotube Films for Energy Applications

This perspective article describes the application opportunities of carbon nanotube (CNT) films for the energy sector. Up to date progress in this regard is illustrated with representative examples of a wide range of energy management and transformation studies employing CNT ensembles. Firstly, this paper features an overview of how such macroscopic networks from nanocarbon can be produced. Then, the capabilities for their application in specific energy-related scenarios are described. Among the highlighted cases are conductive coatings, charge storage devices, thermal interface materials, and actuators. The selected examples demonstrate how electrical, thermal, radiant, and mechanical energy can be converted from one form to another using such formulations based on CNTs. The article is concluded with a future outlook, which anticipates the next steps which the research community will take to bring these concepts closer to implementation.

Remarkable bactericidal traits of a metal-ceramic composite coating elated by hierarchically structured surface

A ceramic-based coating with a hierarchical surface structure was synthesized via solid-state reaction enabled by a double cathode glow discharge technique. This innovative coating comprises two distinct layers, specifically an outer layer with a well-aligned micro-pillar array and a dense inner layer. Both are composed of a face-centered cubic Cu(Co,Ni,Fe) solid solution phase together with a spinel-type Fe(Al,Cr)2O4 oxide. This coating exhibits superhydrophobicity and, yet, a very strong adhesion to water, i.e., the so-called "rose petal effect". This coating also exhibits highly efficient antibacterial ability against both Staphylococcus aureus and Escherichia coli bacteria under both dark and visible light conditions. The excellent antibacterial property originates from the synergistic effects through the release of Cu ions coupled with photothermal activity upon light activation.

Plasmonic wavy surface for ultrathin semiconductor black absorbers

In this work, we propose and demonstrate a near-unity light absorber in the ultra-violet to near-infrared range (300-1100 nm) with the average efficiency up to 97.7%, suggesting the achievement of black absorber. The absorber consists of a wavy surface geometry, which is formed by the triple-layer of ITO (indium tin oxide)-Ge (germanium)-Cu (copper) films. Moreover, the minimal absorption is even above 90% in the wide wavelength range from 300 nm to 1015 nm, suggesting an ultra-broadband near-perfect absorption window covering the main operation range for the conventional semiconductors. Strong plasmonic resonances and the near-field coupling effects located in the spatially geometrical structure are the key contributions for the broadband absorption. The absorption properties can be well maintained during the tuning of the polarization and incident angles, indicating the high tolerance in complex electromagnetic surroundings. These findings pave new ways for achieving high-performance optoelectronic devices based on the light absorption over the full-spectrum energy gap range.

Defect-Engineered Nanostructured Ni/MOF-Derived Carbons for an Efficient Aqueous Battery-Type Energy Storage Device

A Ni-based metal-organic framework (Ni-MOF) has been synthesized using a microwave-assisted strategy and converted to nanostructured Ni/MOF-derived mesoporous carbon (Ni/MOFDC) by carbonization and acid treatment (AT-Ni/MOFDC). The materials are well characterized with Raman, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), and Brunauer-Emmett-Teller (BET), revealing that chemical etching confers on the AT-Ni/MOFDC-reduced average nanoparticle size (high surface area) and structural defects including oxygen vacancies. AT-Ni/MOFDC displays low series resistances and a higher specific capacity (C _s) of 199 mAh g^-1 compared to Ni/MOFDC (92 mAh g^-1). This study shows that the storage mechanism of the Ni-based electrode as a battery-type energy storage (BTES) system can be controlled by both non-faradic and faradic processes and dependent on the sweep rate or current density. AT-Ni/MOFDC reveals mixed contributions at different rates: 75.2% faradic and 24.8% non-faradic contributions at 5 mV s^-1, and 34.1% faradic and 65.9% non-faradic at 50 mV s^-1. The full BTES device was assembled with AT-Ni/MOFDC as the cathode and acetylene black (AB) as the anode. Compared to recent literature, the AT-Ni/MOFDC//AB BTES device exhibits high energy (33 Wh kg^-1) and high power (983 W kg^-1) with excellent cycling performance (about 88% capacity retention over 2000 cycles). This new finding opens a window of opportunity for the rational designing of next-generation energy storage devices, supercapatteries, that combine the characteristics of batteries (high energy) and supercapacitors (high power).

Broadband absorption of nanostructured stainless steel surface fabricated by nanosecond laser irradiation

Highly efficient broadband absorbing surfaces covering the UV, visible and near-IR regions are of great importance for low-light imaging devices, optical devices and optoelectronic devices. In this work, we demonstrate the fabrication of remarkably efficient absorbing surfaces due to the formation of nanoflower-like cavity structures on a stainless steel (SS304) surface, along with micropatterning in a hierarchical fashion. The fabrication process is carried out using noncontact, programmable, single-step laser irradiation by an inexpensive and robust 532 nm nanosecond laser. The measured specular antireflection properties over a wide spectral region (250-1800 nm) are extremely low, less than 0.5%, over a large range of incident angles and for both orthogonal polarizations. These special hierarchical structures with nanorods, nanoparticles, and nanocavities, completely trap the photon incident on these surfaces due to multiple reflections. These surface structures evolve with time to give better nanostructured features with higher oxygen content on the surfaces, revealed by FESEM elemental analysis, which increases the ability to trap photons. We believe these antireflection surfaces, with high efficiencies and long-term stability, will play a vital role in many modern technological applications.

Structure and pigment make the eyed elater's eyespots black

Surface structures that trap light leading to near complete structural absorption creates an appearance of "super black." Well known in the natural world from bird feathers and butterfly scales, super black has evolved independently from various anatomical structures. Due to an exceptional ability to reduce specular reflection, these biological materials have garnered interest from optical industries. Here we describe the false eyes of the eyed elater click beetle, which, while not classified as super black, still attains near complete absorption of light partly due to an array of vertically-aligned microtubules. These cone-shaped microtubules are modified hairs (setae) that are localized to eyespots on the dorsum of the beetle, and absorb 96.1% of incident light (at a 24.8° collection angle) in the spectrum between 300-700 nm. Filled with melanin, the setae combine structure and pigment to generate multiple reflections and refractions causing light to travel a greater distance. This light-capturing architecture leaves little light available to receivers and the false eyes appear as deep black making them appear more conspicuous to predators.

Flexible Ultra-Wideband Terahertz Absorber Based on Vertically Aligned Carbon Nanotubes

Ultra-wideband absorbers have been extensively used in wireless communications, energy harvesting, and stealth applications. Herein, with the combination of experimental and theoretical analyses, we develop a flexible ultra-wideband terahertz absorber based on vertically aligned carbon nanotubes (VACNTs). Measured results show that the proposed absorber is able to work efficiently within the entire THz region (e.g., 0.1-3.0 THz), with an average power absorptance of >98% at normal incidence. The absorption performance remains at a similar level over a wide range of incident angle up to 60°. More importantly, our devices can function normally, even after being bent up to 90° or after 300 bending cycles. The total thickness of the device is about 360 μm, which is only 1/8 of the wavelength for the lowest evaluated frequency of 0.1 THz. The new insight into the VACNT materials paves the way for applications such as radar cross-section reduction, electromagnetic interference shielding, and flexible sensing because of the simplicity, flexibility, ultra-wideband operation, and large-scale fabrication of the device.