Strong Broadband Absorption Research Articles

Enhanced Microwave Absorption in Organogels:The Synergy of Polar Molecules and Magnetic Particles

Herein, wideband microwave absorbing materials with high flexibility are developed by creating a novel layered organogel composite consisting of carbonyl iron particles (CIP) and polyacrylamide (PAM), employing ethylene glycol (EG) as the solvent. The microwave absorbing properties of layered absorbers with different CIP contents are investigated over the 1–18GHz range. An integrated stratified architecture was obtained using polar EG molecules and magnetic CIP particles, which were the main contributors to magnetic and dielectric losses in the PAM matrix. The results indicated that the minimum reflection loss reaches a value of −48.0dB at a thickness of 2mm and a frequency of 15.5GHz; meanwhile, an effective absorption bandwidth of 3.2GHz in the C-band can also be obtained. An analysis of the absorption mechanism shows that the combination of an impedance-matching layer composed of CIP magnetic particles and an absorption layer composed of EG polar molecules in the PAM matrix provides strong broadband absorption in the C-band. Overall, the CIP/EG@PAM organogel composites have simple preparation, high flexibility, and it has adhesion. This study provides a new strategy for designing wideband microwave absorbing materials.

Multilayer thin film mid-infrared broadband absorber with high visible light transmittance

Few reports on absorbers achieve both high transmittance of visible light and strong absorption of mid-infrared light. Here a multilayered absorber with high visible light transmittance and strong broadband absorption in the mid-infrared band is proposed. The absorber is four-layer films of ITO/SiO2/ITO/SiO2 successively deposited on single-sided conductive glass by electron beam evaporation technology. The experiment shows that the integral transmittance in the 400–800 nm range is 82.8 %, and the integral absorption in the 3–5 μm band is 88.2 %.

Ultrablack surface with omnidirectional high absorption.

Black surface plays an important role in solar-thermal conversion systems and space optical systems. Despite the significant efforts in developing a black surface with strong broadband absorption, realizing scalable omnidirectional high absorption ultrablack surfaces remains challenging. Here, we report an ultrablack surface based on a structural black paint (SBP), realized by femtosecond (fs) laser fabrication of high aspect ratio microstructure mold followed by mold transferring on black paint coating. The SBP exhibits extremely low hemispheric reflectance (R < 1.2%) in the solar spectrum at a normal incident angle; even at an 80° incident angle, the SBP also has good anti-reflection performance (R < 9%). Based on such properties, we further show the enhanced solar-thermal performance over commercial black paints. Our approach holds promises for scalable and cost-effective manufacturing of ultrablack surface, with potential applications in solar-thermal conversion efficiency improvement and space optical system stray light suppression.

Enhancing Defect-Induced Dipole Polarization Strategy of SiC@MoO3 Nanocomposite Towards Electromagnetic Wave Absorption

HighlightsOxygen-vacancy-rich SiC@MoO3 nanocomposite with strong reflection loss (− 50.49 dB at 1.27 mm thickness) and broadband absorption band (8.72 GHz at 2.68 mm thickness) were constructed via in situ etching strategy.The presence of oxygen vacancy leads to an increased conductive loss and defect-induced dipole polarization, which plays significant role in attenuating the incident electromagnetic wave.

Facile and scalable preparation of Ni/NiO/SiO2@porous carbon network with strong and wide bandwidth microwave absorption

Researchers are exploring high-performance electromagnetic wave absorbing materials to mitigate electromagnetic interference, focusing on minimizing surface reflection and enhancing attenuation capability. However, one single component and structure struggle to meet the aforementioned requirements. Here, a Ni/NiO/SiO2@porous carbon network (Ni/NiO/SiO2@PCN) with porous structures is synthesized via a pyrolysis process. The magnetic Ni/NiO and dielectric SiO2 nanoparticles are uniformly dispersed within the PCN matrix. The absorption capability of the material can be controlled by adjusting the SiO2 content in Ni/NiO/SiO2@PCN. Particularly, when the SiO2 loading is 0.5 wt%, the resulting Ni/NiO/SiO2@PCN-0.05 demonstrates outstanding EMW absorption properties, exhibiting strong broadband absorption attributed to its 3D porous architectures, the hybrid composition of Ni/C, NiO/C, and SiO2/C, and good impedance matching. At a filler loading of 20 wt%, the Ni/NiO/SiO2@PCN-0.05 achieves remarkable EMW absorption performance, with a minimal reflection loss reaching −71.42 dB at 2.6 mm and 11.18 GHz, and an effective absorption band extending over 6.24 GHz within the frequency range of 11.52 to 18.0 GHz at a thickness of 2.25 mm, effectively covering the entire Ku band. This study introduces a cost-effective and efficient fabrication approach for producing high-performance microwave absorbers, thereby offering promising prospects for applications in the field of microwave telecommunications.

Kapok derived microtubular FeCo/CMT with high specific surface area for broadband microwave absorption

Since biomass-derived carbon materials possess the advantages of peculiar morphology and low density. They have received significant attention on microwave absorption materials. We synthesize a one-dimensional hollow FeCo/carbon microtubule (FeCo/CMT) derived from homogeneous kapok fiber using a feasible solvothermal method and calcination process. The graphitization degree and magnetic properties of FeCo/CMT could be controlled by manipulating the calcination temperature. The FeCo/CMT composite with the calcination temperature of 600 °C demonstrated exceptional microwave absorption performance, characterized by strong absorption (−50.6 dB), broadband absorption (12.4–18.0 GHz), thin thickness (2.5 mm), and low loading (10 wt%). The hollow structure, interfacial polarization, and the synergistic effect between FeCo and CMT collectively account for the microwave absorption mechanisms. Considering its outstanding comprehensive characteristics and performance, the biomass-derived hollow FeCo/CMT shows great potential for widespread application as a high-performance microwave absorption material.

Photothermal catalytic oxidation of toluene by perovskite oxide/biochar nanocomposite: Effect of biomass incorporation

The utilization of waste biomass for the development of full-spectrum response photothermal catalysts shows significant potential in catalytic oxidation of volatile organic compounds (VOCs). Herein, perovskite oxide LaCoO3/biomass-derived biochar nanocomposite was synthesized by the sol–gel method using wasted pomegranate peel as complex agent. The introduction of biomass resulted in improved dispersion of LaCoO3 particles and enhanced the adsorption of toluene attributed to the large specific surface area and rich functional groups of biochar. Furthermore, the biochar exhibited strong broadband absorption and efficient photo-thermal conversion under light illumination, which not only activated the lattice oxygen on the surface to react with toluene, but also increased the transmission rate of photogenerated charge carriers. The defects of LaCoO3 caused by carbon doping facilitated the circulation of oxygen species, leading to the generation of more reactive oxygen species. When the mass ratio of LaCoO3 to biomass was 1:0.6, the LaCoO3/biochar composite exhibited excellent photothermal catalytic performance with a T90 value of 270 °C (temperature at 90 % degradation) and displaying high stability. Moreover, In-situ DRIFTS analysis revealed that both adsorbed oxygen and lattice oxygen participated in the reaction with toluene, promoting the ring-opening reaction of toluene and subsequent conversion of intermediates.

Multiresonant Grating to Replace Transparent Conductive Oxide Electrode for Bias Selected Filtering of Infrared Photoresponse.

Optoelectronic devices rely on conductive layers as electrodes, but they usually introduce optical losses that are detrimental to the device performances. While the use of transparent conductive oxides is established in the visible region, these materials show high losses at longer wavelengths. Here, we demonstrate a photodiode based on a metallic grating acting as an electrode. The grating generates a multiresonant photonic structure over the diode stack and allows strong broadband absorption. The obtained device achieves the highest performances reported so far for a midwave infrared nanocrystal-based detector, with external quantum efficiency above 90%, detectivity of 7 × 1011 Jones at 80 K at 5 μm, and a sub-100 ns time response. Furthermore, we demonstrate that combining different gratings with a single diode stack can generate a bias reconfigurable response and develop new functionalities such as band rejection.

Bio-inspired selective filtration of sphagnum for efficient solar driven purification of high salinity seawater

Solar-driven interfacial evaporation has emerged as an efficient and sustainable way to generate freshwater from seawater to address the crisis of drinkable water. Though rational designs of photothermal materials and structures are essential to the interfacial solar evaporation process, the salt accumulation remains a challenge to the long-term operation of seawater desalination. Here, we report a high-yield and low-cost natural sphagnum as solar steam generator with ultra-fast water transportation, unique microstructure to prevent salting out, and high evaporation rates. The carbonized sphagnum based photothermal evaporator exhibits a strong broad-band light absorption (>97.0 %). During the solar steam generation, a high evaporation rate of 3.53 kg m−2 h−1 was achieved under 1.0 sun illumination. More significantly, the 3D sphagnum evaporator shows excellent selective filtration of salt ions and cycling stability in actual sea water even high salinity solution (10 wt.% NaCl) for 7 days. This work provides an environmentally friendly and cost-effective photothermal material for large-scale seawater desalination, and treatment of waste water with high ions concentration.

Structure Control of Large‐Sized Graphene Foams for Outstanding Microwave Absorption, Thermal Insulation, and Mechanical Stability

AbstractWith the rapid development of microwave technologies, electromagnetic pollution and stealth have become important problems to be solved. Although great efforts have been made in recent years, it is still a great challenge to achieve strong and broadband absorption combined with thermal and mechanical functionalities. Herein, a multi‐functional design toward three‐dimensional graphene foams (GFs) is provided. These foams are prepared to have large sizes by simple freezing and air‐drying of a structure‐integrated graphene oxide (GO) hydrogel, and polydimethylsiloxane (PDMS) is introduced to reinforce the GO framework. The remarkable finding is that the GF/PDMS composite possesses strong broad band absorption (reflection loss &lt; ‐10 dB) over the entire frequency range of radar microwaves (2–18 GHz). This is attributed to the synergistic effects of dielectric loss of the GO material itself and the multi‐layer attenuation brought by the porous foam structure. Experimental results also show that the light foams have very low thermal conductivity of 0.03–0.13 W m−1 k−1 and mechanical flexibility for compression, extension, and torsion. Therefore, this study provides a new strategy for large‐scale production of multifunctional microwave absorbing foam materials for applications in both civil and military fields.

Carbonized waste polyphenylene sulfide non-woven decorated wood evaporator for clean water production from solar photothermal desalination

Solar-driven water desalination is regarded as a promising and sustainable approach for clean water generation to mitigate the issue of freshwater shortage. However, most solar evaporators suffer poor water evaporation rates or depend on high-cost light absorbers and complex processes. Here, we present a bilayer wood-based solar evaporator decorated with carbonized waste polyphenylene sulfide non-woven for desalination to produce clean water. The sulfur-doped carbon was obtained from the waste polyphenylene sulfide non-woven after carbonization with more electrons and enhanced hydrophilic compared with pure carbon structure which is combined with natural wood with porous structure, exhibiting excellent photothermal water evaporation performance. The photothermal wood-based solar evaporator shows a strong broad-band light absorption of an average of 94 %. The sulfur-doped carbon decorated high 3 cm natural wood (CP wood) indicates a high evaporation rate of 2.32 kg m−2 h−1 and photothermal conversion efficiency of 132.49 % under 1 sun radiation. Furthermore, the reusability, salt rejection, and outdoor experiment were performed to prove the potential of the evaporator in practical desalination. This work indicates the great potential of sulfur-doped carbon for efficient solar-driven clean water production to address the issue of global freshwater shortage.

Hierarchical porous metallic glass with strong broadband absorption and photothermal conversion performance for solar steam generation

The development of a strong light absorption absorber with a facile preparation process are crucial for some photothermal conversion applications, such as solar steam generation, photothermal catalysis and detectors. Here, a hierarchical structure based on microporous surface equipped with nanoporous layer is ingeniously designed and fabricated benefiting from the unique thermoplastic forming ability of metallic glasses by using the soluble clusters as template in less than 30 s. The presence of hierarchical porous structures induces multiple reflection of light and excites the plasmonic behavior of surface, achieving over 90% light absorption in the 380–20 µm wavelength range and the broad light incident angle from 0° to 70°, resulting in a remarkable photothermal conversion performance. Compared to conventional and existing absorber, the innovatively designed and fabricated metallic surface offers outstanding advantages in terms of light absorption range, heating rate and maximum temperature rise. Afterwards, the hierarchical porous structures for solar steam generation shows an evaporation efficiency of up to 94.2% and evaporation rate of 1.72 kg m−2 h−1 at 1 kW m−2. The design of unprecedented structure on metallic glass opens up a new strategy for solar energy harvesting, water treatment and other related fields.

Incorporating Ytterbium (III) and Bismuth (III) ions into NaInS2 nanocrystals toward enhanced visible absorption and near-infrared emission

Constructing lanthanide doped semiconductor nanocrystals (Ln-SNCs) is a promising strategy for combining of bright, long-lived, and spectrally narrow Ln3+ emission, along with strong broadband absorption and low-phonon-energy crystalline environment of semiconductor to make new spectral-conversion nanophosphors. NaInS2 SNC is one of the most important host series for its high stability and non-toxicity as compared to those widely explored Ln doped perovskite SNCs. Such a family SNCs provide high cation coordination numbers (CN) of 6, which fulfills the cation the fundamental prerequisite for Ln3+ doping. However, the photoluminescence quantum yields (PL QYs) of Yb3+ doped NaInS2 are still below 8% in most SNCs thus far, restricting their further application in near-infrared (NIR) bio-probe. Here, we demonstrate a strategy for accessing Yb3+/Bi3+-codoped NaInS2 SNCs for strong NIR emission. In order to improve the NIR emission, we introduce Bi3+ ions to create new excitation channels, aiming at enhancing the ultra-violet (UV) and visible light absorption. Furthermore, an ZnS outer-layer growth on Ln-doped NaInS2:Bi passivates the surface of SNCs and suppresses the surface defect related non-radiative recombination losses. Our NaInS2:Yb/Bi@ZnS SNCs exhibit efficient NIR emission around 1000 nm with a notable PL QY of 9.5%, suggesting their potential applications in NIR bio-imaging.

Evaluation of the influence of thermal annealing on the performance of vertical topological insulator p-n heterojunction broadband photodetector

The rapid progress and continuum search for new broadband photodetectors generation with ultrafast response synchronizes with the conductive surface electronic structure and the strong broadband absorption properties of 3D topological insulators. Here, we introduce the fabrication of a vertical p-n heterojunction based on thermally evaporated thin films of Sb2Te3/Bi2Te3 on Si substrate for broadband photodetection. The realization of these characteristics dictated us to study the structural, optical absorption, and morphological properties of each layer in the fabricated device as a function of annealing temperature using XRD, spectrophotometric measurements, and FE-SEM techniques, respectively. The annealing process up to T = 423 K enhanced the film’s crystallinity, and grain growth process besides improving the film quality and surface roughness. Furthermore, the optoelectronic characterizations showed that all fabricated photodetectors exhibit a good response to halogen light illumination in the wavelength range (310–1100) nm with different intensities (10–50) mW/cm2. Whilst the 423 K annealed photodetector showed the highest photosensitivity with a conspicuous stable and fast response. The main device parameters, including spectral responsivity, specific detectivity, and response times were determined in addition to explaining the forward and reverse bias conduction mechanisms. The estimated spectral responsivity of the fabricated devices was about 0.247, 0.397, and 0.148 A/W for the as fabricated and 423 K and 573 K, respectively. This significant improvement of the device’s performance rather than other topological insulator devices may be due to the strong built-in field at the topological insulators’ interfaces. Moreover, the fabricated photodetectors showed improved and repeatable ON/OFF transient switching behavior with 85.23 ms and 84.66 ms as a rise and fall time, respectively. According to the prominent results in addition to the simple architecture of the fabricated photodetectors, this topological insulator photosensor can be considered a potential candidate in prospective high-performance optoelectronics.

Novel broadband electromagnetic-wave absorption metasurfaces composed of C-doped FeCoNiSiAl high-entropy-alloy ribbons with hierarchical nanostructures

Although various absorbers have been developed for electromagnetic-wave absorption materials (EAMs), the uniform composition and microstructure limit the design freedom of the soft magnetic properties, thus resulting in a ceiling of the absorption properties. Herein, we propose a revolutionary concept of C-doped FeCoNiSiAl high-entropy-alloy (HEA) ribbons with hierarchical nanostructures composed of ultrafine grains (400 nm), B2 nanoprecipitates (80 nm), and C@FeNi core–shell nanoparticles (15 nm) to induce superior soft magnetization and absorption. The hierarchical nanostructures resulted in a low coercivity (HC, 589.04 A/m) and a low conductivity (294.1 S/cm) to support the loss effect and impedance matching, and 87% of the saturation magnetization (MS, 135.13 emu/g) was maintained, even at the high temperature of 973 K, corresponding to ultra-stable magnetization. Furthermore, the Curie-temperature was greater than 1000 K. The B2 nanoprecipitates and corresponding interfaces created strong stray magnetic flux lines and magnetic domain vortices, and thus, the metasurfaces innovatively fabricated with HEA ribbons induced a strong absorption peak (−50.88 dB) and effective broadband absorption (reflection loss (RL) ≤ −10 dB within 5.86–18 GHz) due to the strong magnetic coupling. The hierarchical nanostructure is a promising strategy to tailor magnetic HEAs with a new degree of freedom for advanced EAMs.

Luminescence properties of Cr3+-doped Al6Ge2O13 broadband near-infrared phosphor

Near-infrared (NIR) phosphor-converted light-emitting diodes (pc-LEDs) are gaining attention as new solid-state light sources for food safety and health monitoring. Herein, a series of Cr3+-doped Al6Ge2O13 (AGO) NIR phosphors were obtained by the high-temperature solid state reaction. The photoluminescence (PL) excitation spectrum of AGO:Cr3+ shows a strong broadband absorption in the 400–500 nm region, which corresponds well to the blue light chip. The phosphor's PL emission spectrum exhibits a broadband spanning 600–1000 nm. The integrated emission intensity of AGO:3%Cr3+ at 420 K can keep 81% of that at 300 K, demonstrating good luminous thermal stability. The near-infrared output power of pc-LED device integrating AGO:Cr3+ phosphor with a 430 nm blue light chip reaches 81.7 mW at 300 mA. The device's electroluminescence spectrum displays a broadband centered at 780 nm, with a full width at half maximum (FWHM) of 160 nm. These findings could drive the development of NIR pc-LED light sources for miniaturized near-infrared spectrometers.

Nonlinear optical properties of two-dimensional palladium ditelluride (PdTe2) and its application as aerosol jet printed saturable absorbers for broadband ultrafast photonics

Two-dimensional (2D) transition metal dichalcogenides (TMDs) have recently gathered substantial interest in the advanced photonic field due to their strong broadband absorption, tunable bandgap, and excellent nonlinear optical (NLO) properties. Palladium ditelluride (PdTe2) is a novel TMD material with high carrier mobility, great stability, and narrow bandgap, allowing it to be used in a wide range of applications such as superconductors, phototransistors, and millimeter-wave receivers. Here, the NLO properties of PdTe2 are investigated by Z-scan technology. The highest nonlinear absorption coefficient of PdTe2 has been determined as -9.25 × 103 cm/GW (1 µm) and -0.55 × 103 cm/GW (1.5 µm), implying its admirable NLO characteristics. Subsequently, for the first time, broadband PdTe2-based saturable absorbers (SAs) are prepared by utilizing the aerosol jet printing (AJP) method. By employing this PdTe2 based SA, the generation of broadband ultrafast laser pulses from the near-to-mid-infrared regime with pulse durations in the ps to fs range (170 ps, 570 fs, and 1.59 ps in 1 μm, 1.5 μm, and 2 μm laser sources, respectively) further signify the capability of PdTe2 as an ideal NLO material for ultrafast photonics devices. Moreover, Q-switched and high-repetition-rate (0.7 GHz) based 58th harmonic mode-locked pulses in the telecommunication band are also obtained with this SA. These findings indicate that 2D-PdTe2 is a promising material for nonlinear optics and broadband ultrafast photonics applications.

A self-floating electrospun nanofiber mat for continuously high-efficiency solar desalination

Solar desalination is an environment-friendly and sustainable technology to address the shortage of freshwater resources. However, it still faces huge challenges to develop a salt-rejection solar desalination system with continuous high efficiency. Herein, an electrospun nanofiber mat was fabricated for continuously high-efficiency solar desalination with carbon nanotube as a photothermal material, polyvinylidene fluoride as a floating support material and polyvinylpyrrolidone as a pore-forming agent. The porous structure and superhydrophilic surface provide significant water transport channels and thus avoid salt deposition, even in the high-salinity brine (20 wt% NaCl). The integration of strong broadband absorption property, excellent photothermal performance, floatability, durability and stability endows the solar desalination system with continuously high evaporation efficiency. The evaporation rate and solar conversion efficiency reached up to 1.372 kg m−2 h−1 and 86.1%, respectively, in simulated seawater under one sun irradiation and lasted for 11 h with little fluctuation. This work opens a new avenue for the rational design and fabrication of solar desalination systems to promote practical application.

Polypyrrole/γ-Fe2O3/g-C3N4 nanocomposites for high-performance electromagnetic wave absorption

Magnetic/dielectric composites offer good impedance matching for electromagnetic wave absorption, though achieving both strong absorption and broadband absorption in such composites is challenging. Herein polypyrrole-Maghemite-graphitic carbon nitride (PPy/γ-Fe2O3/g-C3N4) composites were successfully fabricated via the one-step chemical synthesis of PPy/γ-Fe2O3 nanospheres in the presence g-C3N4 nanosheets. The PPy/γ-Fe2O3/g-C3N4 composites demonstrated outstanding electromagnetic wave (EMW) absorption properties at microwave frequencies. A compositionally optimized PPy/γ-Fe2O3/g-C3N4 composite delivered a minimum reflection loss (RLmin) value of −53.66 dB at 11.92 GHz and the effective absorption bandwidth (EAB, RL < −10 dB) of 5.13 GHz (10.46–15.59 GHz) at a thickness of 2.5 mm. The excellent EMW absorption properties of the composite could be attributed to the introduction of g-C3N4 nanosheets with a lamella structure, which enhanced interfacial polarization losses, multi-reflections, scattering, and impedance matching within the composite. This work offers a simply and effective strategy for the preparation of high-performance EMW absorbers.

Tuning the impedance matching of microsphere Co for strong broadband absorption

Efficient absorption bandwidth and attenuation capability are two crucial indicators for evaluating the high-performance microwave absorbers. Proper impedance matching is the precondition for obtaining broadband absorption, while it still remains a challenge to fabricate the absorbers with better impedance matching and strong attenuation over a wide frequency range. Here, we successfully prepared Co powders by a simple ethylene glycol reduction process and researched the corresponding structures, morphologies and electromagnetic (EM) parameters. The normalized input impedance |Z| (|Zin/Z0|) values of Co at various reaction times were calculated to investigate the effect of morphology on the impedance matching. It was demonstrated that Co powders were composed of fcc-Co and hcp-Co. Compared with the compact structures, the loose ones can cause the EM wave multiple scattering and reflections and increase the EM energy dissipation, however, the balance between the attenuation and impedance matching is suboptimal. The compact microspheres Co exhibited the optimal microwave absorption performance when the reaction time was 8 h. The distribution area of |Z|~1.0 is relatively broad. When the thickness varies from 1.15 to 5.00 mm, the effective absorption bandwidth (EABW, RL ≤ −10 dB) covers the bands of 3.45–18 GHz. The EABW as large as 8.16 GHz and the minimum reflection loss of −64.67 dB have been reached at a sample thickness of only 1.83 mm. We believe that this research may serve as an effective guideline for the synthesis of other optimal broadband absorbers.