Broadband Absorption Research Articles

Lightweight composite from graphene-coated hollow glass microspheres for microwave absorption

In developing the effective and lightweight materials for microwave absorption, graphene holds a bright promise because of its excellent electrical properties and low density, but it suffers from poor impedance matching; while the hollow glass microspheres on the other hand have extremely low density and are dielectric. Their synergistic combination could achieve a perfect impedance matching and thus create a novel lightweight absorption composite. The metamaterial structure absorber can efficiently absorb electromagnetic waves over a wide frequency range. This study employs a hydrothermal method to deposit graphene onto the surfaces of hollow glass microspheres, followed by the design of a metamaterial absorber. Upon coating with graphene flakes, the composite material effectively dissipates electromagnetic wave energy through mechanisms such as interfacial polarization, dielectric loss, and the multiple scattering effects of hollow glass microspheres and graphene flakes. The composite exhibits an effective absorption bandwidth up to 4.02 GHz under a graphene flakes mass fraction of 30 %. More importantly, the incorporation of the metamaterial absorber design further significantly enhances the absorption bandwidth to 7.7 GHz. This material demonstrates significant advantages in terms of lightweight and broadband absorption performance, providing new insights for the research of high-performance lightweight and wideband absorbing materials in the future. However, further investigation is required to examine its long-term stability and performance in complex environments.

One-step fabrication of a novel fiber-based absorber for flexible, tunable and boosted microwave absorption

The increasingly intricate electromagnetic environment necessitates higher anti-electromagnetic interference capabilities for electronic devices, thereby demanding a flexible absorbing material that can adapt to multiple forms, is lightweight, and exhibits excellent electromagnetic wave (EMW) absorption properties. In this study, we have developed a novel flexible absorbing material (FAM) based on glass-coated amorphous magnetic fibers (SFs) and Dallenbach-like absorbing structures through wet forming technology. By combining high-performance absorbing fiber with textile structures, the FAM demonstrates EMW absorption performance along with lightweight flexibility and shape adaptability. This paper explores the influence of process parameters in wet forming technology on FAM formation; as well as examines the construction of broadband absorbers through structural optimization. A single-layer FAM with a thickness of 1.7 mm (SFs length 8 mm, content 3 g/m2) achieves an impressive reflection loss (RL) value of −60.1 dB at 11.6 GHz. Furthermore, optimized multi-layer FAM attains effective absorption bandwidth (EAB: RL ≤ −5 dB) across a wide range from 3–14 GHz. This work presents a new approach for developing ’lightweight, thin, wide, and strong’ absorbing materials based on fiber and textile structures which holds significant implications for civilian electromagnetic interference protection as well as military electromagnetic stealth technology.

NIR-ViS-UV broadband absorption in ultrathin electrochemically-grown, graded index nanoporous platinum films.

Nanoporous platinum broadband absorber has attracted interest in thermosensorics and IR photodetection due to its unique properties. In this work we report the physical mechanism underlying broadband absorption in electrochemically-grown, nanoporous Pt films by analyzing NIR-ViS-UV spectral ellipsometry data of nanoporous Pt films in dependence on the Pt film thickness (27, 35, 38, 48nm). For the two thinner films a single layer model with a graded optical index Pt surface layer was used. For the two thicker films a two-layer optical model with a constant optical index Pt substrate layer and a graded optical index Pt surface layer was used. The graded optical index of the Pt surface layer reduces surface reflectivity and the constant optical index Pt substrate layer supports multiple reflections in the Pt film. Finally, we relate the thickness dependent optical index with the nanostructure of the nanoporous Pt film, which can be controlled in the electrochemical growth process. We observed that while in the transverse plane the multilayer exhibits graded refractive index, in the top horizontal planes the multilayer assembly exhibits discontinuous refractive index values due to the distribution of platinum crystal islands in air, which allows a metamaterial behavior of the whole system.

A Broadband Light‐Trapping Nanostructure for InGaP/GaAs Dual‐Junction Solar Cells Using Nanosphere Lithography‐Assisted Chemical Etching

III–V‐based multijunction solar cells have become the leading power generation technology for space applications due to their high power conversion efficiency and reliable performance in extraterrestrial environments. Thinning down the absorber layers of multijunction solar cells can considerably reduce the production cost and improve their radiation hardness. Recent advances in ultrathin GaAs single‐junction solar cells suggest the development of light‐trapping nanostructures to increase light absorption in optically thin layers within III–V‐based multijunction solar cells. Herein, a novel and highly scalable nanosphere lithography‐assisted chemical etching method to fabricate light‐trapping nanostructures in InGaP/GaAs dual‐junction solar cells is studied. Numerical models show that integrating the nanostructured Al2O3/Ag rear mirror significantly enhances the broadband absorption within the GaAs bottom cell. Results demonstrate that the light‐trapping nanostructures effectively increase the short‐circuit current density in GaAs bottom cells from 14.04 to 15.06 mA cm−2. The simulated nanostructured InGaP/GaAs dual‐junction structure shows improved current matching between the GaAs bottom cell and the InGaP top cell, resulting in 1.12x higher power conversion efficiency. These findings highlight the potential of light‐trapping nanostructures to improve the performance of III‐V‐based multijunction photovoltaic systems, particularly for high‐efficiency applications in space.

High responsivity zero-biased Mid-IR graphene photodetector based on chalcogenide glass waveguide

Graphene’s unique properties have made it a promising material for high-performance photodetectors due to its interesting features including broadband absorption, fast speed, and strong photothermoelectric effect. Here, an optimized waveguide photodetector incorporating double graphene layers with two cores is presented to boost the responsivity (∼twice), at Mid-IR range. The proposed structure operates in the zero-bias regime to eliminate the dark current issue associated with the zero bandgap nature of graphene and leads to lower noise equivalent power. The presented photodetector operating based on split gates to electrostatically induce the p-n junction in graphene channels, operates based on the photothermoelectric effect and provides responsivity, NEP, and 3 dB bandwidth of 6.3 V/W, 0.34 nW/Hz1/2, and 1.54 GHz, respectively for the detection at λ = 5.2 μm. The feasibility of the proposed structure is proved according to recent experimentally demonstrated photodetectors. Hence, the obtained results are reliable, in practice. The study has been accomplished by numerical simulation of mode profiles and solving the heat equation to extract the characteristics of the proposed photodetector. The zero-power consumption and tunability of the proposed structure make it a promising candidate for sensing, industrial, defense, and environmental monitoring applications with high accuracy.

Flexible Terahertz Broadband Absorber Based on a Copper Composite Film.

Terahertz absorbers play a crucial role in terahertz detectors, radar stealth, electromagnetic shielding, and other fields. However, the design and fabrication of flexible terahertz broadband absorbers remain a challenge at present. Here, we demonstrated a terahertz broadband absorber based on a copper composite film (CCF) consisting of a copper foam and an organic silica gel doped with Fe3O4 powder. The CCF can be fabricated by the infiltration method. The influence of the thickness and the pore size of the copper foam and the mass fraction of doped Fe3O4 powder on the absorption bandwidth were investigated. When the thickness of the CCF is 1.5 mm, the pore size of the copper foam is 95 pores per inch (ppi), and the mass fraction of Fe3O4 is 1%; a broadband absorption is achieved in the range of 0.11-3.5 THz. It is noted that the mass fraction of Fe3O4 has a significant impact on the absorption bandwidth. In addition, the thickness of the CCF and the pore size of the copper foam also have an impact on the absorption. The impedance matching theory is introduced to understand the mechanism of broadband absorption. This flexible broadband absorber has potential application in terahertz stealth, shielding, and the sixth-generation (6G) broadband wireless communication in the future.

A tunable function broadband absorber based on graphene fractal metasurface in the very long-wave infrared region

The combination of fractal structures with metasurfaces has proven to be an extremely effective method for achieving broadband absorption. A broadband absorber tunable in a very long wavelength infrared (VLWIR) region based on graphene of the Hilbert fractal pattern is proposed. The unique space-filling pattern of this structure enables the generation of gap plasmon resonance mode, thereby extending the absorber's bandwidth. The absorption spectrum can be dynamically adjusted by changing external parameters such as the azimuth angle, the graphene's Fermi level, and the relaxation time. Numerical simulations indicate that under optimal parameters, the proposed absorber achieves ultra-broadband absorption within the long-wave infrared target range (14‐32 μm). The fractal absorber achieves consistently exceeded 90 % absorption in 15.2–30.6 μm with an average absorption of 95.73 %. Furthermore, the proposed absorber exhibits an excellent wide angle of incident stability. Our findings provide a novel strategy for designing fractal absorbers with broadband absorption capabilities in VLWIR. Our design has potential applications in VLWIR imaging and modulators, also can be applied to sensors, thermal emitters and photoelectric switches.

Synergistically magnetic and dielectric properties of two dimensional Fe3Al@PPy lamellae exhibiting broadband and strong electromagnetic wave absorption

Addressing the issue of low impedance characteristics is essential to improve the electromagnetic wave absorption performance of magnetic materials. Herein, two dimensional Fe3Al@polypyrrole (PPy) lamellae with synergistic magnetic and dielectric properties are fabricated by a mechanical alloying, ordering transformation and polymerization process, which exhibits excellent electromagnetic wave absorption performance. By carefully controlling the thickness of the PPy shell, the optimized Fe3Al@PPy lamellae show a minimum reflection loss of −45.6 dB and an effective absorption bandwidth of 9.1 GHz at a thickness of only 1.5 mm. The conformal growth of Fe3Al@PPy lamellae can induce strong interfacial polarization, dipole polarization, multiple scattering effect and magnetic loss behaviors for the attenuation of electromagnetic waves. This study demonstrates a facile strategy for the development of efficient Fe3Al@PPy composite absorbents showing great potential for practical applications.

Three-Dimensionally Printed K-Band Radar Stealth Lightweight Material with Lotus Leaf Structure.

K-band radar waves have high penetration and low attenuation coefficients. However, the wavelength of this radar wave is relatively short; thus, designing and preparing both broadband and wide-angle radar wave absorbers in this band presents considerable challenges. In this study, a resin-based K-band radar wave absorber with a biomimetic lotus leaf structure was designed and formed by UV curing. Here, microscale lotus leaf papillae and antireflection structures were prepared using a DLP 3D printer, and the contact angle between the material and water droplets was increased from 56° to 130°. In addition, the influence of the geometric parameters of the lotus leaf antireflection structure on the electromagnetic absorption performance and mechanical strength was investigated. After simulation optimization, the maximum electromagnetic loss of the lotus leaf structure 3D-printed sample was -32.3 dB, and the electromagnetic loss was below -10 dB in the 20.8-26.5 GHz frequency range. When the radar incidence angle was 60°, the maximum electromagnetic loss was still less than -10 dB. The designed lotus leaf structure has a higher mechanical energy absorption per unit volume (337.22 KJ/m3) and per unit mass (0.55 KJ/Kg) than commonly used honeycomb lightweight structures during the elastic deformation stage, and we expect that the designed structure can be used as an effective lightweight material for K-band radar stealth.

Dual-type heterogeneous interface design enables customized tuning of dielectric parameters of multifunctional, lightweight, flexible absorbers for broadband electromagnetic wave absorption

With the boom in 5 G technology comes widespread concern about electromagnetic (EM) interference and the safe use of electronics. Conventional electromagnetic wave (EMW) absorbing materials in the form of coatings are often inflexible and poorly adapted to different EM environments. Diversified application scenarios require EMW absorbing materials with a wide absorption band and multifunctional properties. Herein, the frequency dispersion (FD) requirements of the EM parameters of the broadband absorber in different frequency bands are determined by EM simulation. Based on the dominant role of interface polarization on FD, we designed different types of heterogeneous interfaces to meet the needs of strong FD in the low-frequency band and weak FD in the high-frequency band. Through the optimized design of heterogeneous interfaces, CC@ZnO/ZnS composites exhibit excellent EMW absorption performance, achieving flexible, ultrathin (2.1 mm), ultralight (10 wt%), and broadband (7.02 GHz), which is superior to EMW absorbing materials of similar compositions. In addition, the composites have good piezoelectric/inverse piezoelectric properties, which can convert EM energy into mechanical energy while absorbing EMW, thus realizing applications in multifunctional fields such as sensors, controllers and energy converters. More noteworthy is the sample's highly efficient thermal insulation, flame retardant and anti-frosting properties, demonstrating important advantages for service in harsh environments. Therefore, CC@ZnO/ZnS composites not only have good practical application characteristics while realizing broadband absorption, but also are expected to achieve multifunctional applications in different fields.

Broadband Solar Absorber and Thermal Emitter Based on Single-Layer Molybdenum Disulfide.

In recent years, solar energy has become popular because of its clean and renewable properties. Meanwhile, two-dimensional materials have become a new favorite in scientific research due to their unique physicochemical properties. Among them, monolayer molybdenum disulfide (MoS2), as an outstanding representative of transition metal sulfides, is a hot research topic after graphene. Therefore, we have conducted an in-depth theoretical study and design simulation using the finite-difference method in time domain (FDTD) for a solar absorber based on the two-dimensional material MoS2. In this paper, a broadband solar absorber and thermal emitter based on a single layer of molybdenum disulfide is designed. It is shown that the broadband absorption of the absorber is mainly due to the propagating plasma resonance on the metal surface of the patterned layer and the localized surface plasma resonance excited in the adjacent patterned air cavity. The research results show that the designed structure boasts an exceptional broadband performance, achieving an ultra-wide spectral range spanning 2040 nm, with an overall absorption efficiency exceeding 90%. Notably, it maintains an average absorption rate of 94.61% across its spectrum, and in a narrow bandwidth centered at 303 nm, it demonstrates a near-unity absorption rate, surpassing 99%, underscoring its remarkable absorptive capabilities. The weighted average absorption rate of the whole wavelength range (280 nm-2500 nm) at AM1.5 is above 95.03%, and even at the extreme temperature of up to 1500 K, its heat radiation efficiency is high. Furthermore, the solar absorber in question exhibits polarization insensitivity, ensuring its performance is not influenced by the orientation of incident light. These advantages can enable our absorber to be widely used in solar thermal photovoltaics and other fields and provide new ideas for broadband absorbers based on two-dimensional materials.

Ultra-wideband solar absorber via vertically structured GDPT metamaterials

We explore a new solar absorber via vertically structured metamaterials integrating 2D graphene, dielectric layers of silica (SiO2), aluminum oxide (Al2O3), and phase-transition vanadium dioxide (VO2) graphene, dielectric, phase transition (GDPT), achieving broadband absorption and polarization independence. Applying the finite-difference time-domain (FDTD) method, the optical performance of the absorber is analyzed under the normal incidence of a plane wave spanning wavelengths from 250 to 4000 nm. Particularly, our investigation reveals a broad bandwidth exceeding 90 % absorption, spanning 3559 nm from 250 to 3809 nm, with an impressive average absorption efficiency of over 95.9 %. Significantly, the absorber demonstrates polarization independence and insensitivity to large angles of incidence, enhancing its practical capability. We illuminate the important role of Fabry-Perot resonance in absorption by precisely tuning layer thicknesses to induce interference effects. The integration of graphene, dielectric layers, and VO2, augmented by Fabry-Perot resonance, provides a vital foundation for high-performance solar energy conversion technology. This technology has important applications in efficient and broadband solar absorbers, and these absorbers can maintain high performance under different conditions. Our goal is to solve current technological challenges and contribute to the development of next-generation solar energy conversion for various photon technologies, such as energy harvesting, electromagnetic wave capture, and photovoltaic devices.

Heterogeneous interface engineering of spindle shaped Fe/C through optimizing impedance response for enhanced microwave absorption and thermal conductivity

Heterogeneous interface design is pivotal in creating lightweight, broadband, and high-efficiency electromagnetic wave (EMW) absorption materials. These materials enhance wave absorption by adaptively matching impedance. In this study, spindle-shaped Fe/C nanocomposites with heterogeneous interfaces and diverse surface microtopographies were synthesized by calcining iron-supported metal-organic frameworks (MOFs). During controlled pyrolysis, Fe3+ was reduced by carbon and conversely induced the graphitization of carbon, which is essential for the distribution and appearance of Fe and graphitized carbon as well as for modulating impedance matching. The porous structure of the Fe/C composites and the polarization loss and ferromagnetic resonance from the defective carbon and Fe magnetic particles synergistically enhance the wave absorption performance. The Fe/C-700 nanocomposite achieves a reflection loss (RL) of −55.9 dB at 12.48 GHz with an effective absorption bandwidth (EAB, RL ≤ −10 dB) of 3.9 GHz at 1.8 mm. The Fe/C-900 nanocomposite demonstrates a significant RL of −63.5 dB at 15.8 GHz with an EAB of 4.4 GHz between 13.6 GHz and 18 GHz at 1.5 mm, and an EAB of 5.5 GHz at 1.63 mm. These improvements are attributed to the impedance matching facilitated by the introduction of Fe magnetic particles and graphitized carbon. Additionally, the thermal conduction pathway formed among the Fe/C nanocomposites significantly enhances the thermal conductivity to 0.502 W m−1 K−1. Thus, this work offers a novel approach to the design of advanced wave-absorbing and thermal conductive materials by optimizing impedance through heterogeneous interfaces.

Highly efficiency up and down -conversion photoluminescence in Er/Tm/Yb co-doped lutecia-stabilized zirconia single crystals

High-quality transparent cubic lutecia-stabilized zirconia and LSZ:Yb1Er0.05Tm0.5 single crystals were grown by the optical floating zone method for the first time. For comparison, YSZ and YSZ:Yb1Er0.05Tm0.5 single crystals were also grown. No absorption peaks were observed in the 200 ∼1100 nm range in the transmission and absorption spectra of LSZ and YSZ, indicating that both crystals are excellent matrix crystals. The absorption spectra of LSZ:Yb1Er0.05Tm0.5 and YSZ:Yb1Er0.05Tm0.5 crystals exhibit several absorption peaks at 377, 408, 462, 488, 516, 679, 785 nm and a strong broad absorption band in the 836 ∼ 1050 nm range. The up-conversion photoluminescence of the LSZ:Yb1Er0.05Tm0.5 crystal excited by a 980 nm laser exhibited several distinct emission peaks at 300, 372, 476, 531, 548, 642 and 798 nm; similar emission peaks were observed in the up-conversion photoluminescence spectrum of the YSZ:Yb1Er0.05Tm0.5 crystal, except for the absence of the 300 nm peak. The intensity of the emission peaks of the former was higher than that of the corresponding peaks of the latter. Power curves indicated that the 300 nm emission is a four-photon up-conversion process, the 372 nm and 476 nm emissions are three-photon processes, and the 548 nm and 642 nm emissions are two-photon processes. Under excitation at 379 nm, the down-conversion photoluminescence spectra of the LSZ:Yb1Er0.05Tm0.5 and YSZ:Yb1Er0.05Tm0.5 crystals showed emission peaks at 450, 457, 511, 531 and 637 nm, the peak intensities of the former are higher than those of the latter, which is due to the former with higher density and lower phonon energy as compare to the latter. These results indicate that LSZ:Yb1Er0.05Tm0.5 single crystal has advantages over YSZ:Yb1Er0.05Tm0.5 single crystal for luminescence in photonic devices.

Enhancing broadband absorption and photocurrent generation in carbon dots via P3HT integration

The growing interest in carbon dots (CDs) arises from their diverse applications and unique properties. This study addresses challenges in CDs for photodetector (PD) applications, specifically surface defects and trap states hindering efficient charge transport. CDs/P3HT composites were prepared to overcome these issues by incorporating CDs in a poly(3-hexylthiophene) (P3HT) matrix. Broad absorption in spectroscopic characterization revealed its utility in fabricating a broadband PD. The CDs/P3HT PD displays a remarkable broadband photoresponse, spanning both UV and visible regions. The CDs and P3HT are effectively combined via non-covalent π-π interactions constituted by their conjugated systems. The π-π interaction increases electron delocalization and facilitates efficient charge transfer due to band alignment at the junction interface. Hence, fabricated CDs/P3HT PD demonstrated enhanced photocurrent compared to pure CDs, exhibiting high responsivity of 6.12 × 10−3 AW−1 and detectivity of 0.69 × 109 Jones. This study highlights the potential of CD/P3HT composites for broadband photodetector applications with enhanced photoelectric conversion.

Advancing environmental remediation through tailored TiO2 nanomaterials in water and air purification

This study investigates the green synthesis of TiO2 nanoparticles at varying concentrations (0 %, 0.1 %, 2.5 %, 5 %, and 10 %) using Viola betonicifolia plant extract, focusing on their application in environmental purification, specifically in water and air decontamination. X-ray diffraction (XRD) analysis confirmed the anatase crystal structure of TiO2 nanoparticles, with an average crystallite size of approximately 22 nm. Transmission electron microscopy (TEM) revealed a median diameter of around 22 nm, corroborating the findings from XRD. The effectiveness of these TiO2 nanomaterials was evaluated through bench-scale models simulating real-world conditions, targeting a broad range of pollutants, including heavy metals, organic dyes, volatile organic compounds (VOCs), and microbial pathogens. Advanced analytical techniques such as High-performance liquid chromatography (HPLC), Inductively coupled plasma mass spectrometry (ICP-MS), and microbial plate count methods quantified the pollutant removal efficiency, demonstrating the significant potential of the synthesized TiO2 nanoparticles. Dynamic light scattering (DLS) analysis showed a mean hydrodynamic diameter of 22 nm and a polydispersity index (PDI) below 0.1, indicating a uniform size distribution. The FTIR spectrum revealed a broad absorption band at 3400 cm−1, corresponding to O–H stretching vibrations, indicative of hydroxyl groups crucial for the photocatalytic activity of TiO2. The UV–visible spectroscopy indicated a maximum absorption at 642 nm, associated with the п-п* transition. Photocatalytic degradation of methylene blue under UV irradiation achieved a degradation efficiency of 94 % after 120 min, underscoring the superior efficiency of the green synthesis method.

Study on multi-degree-of-freedom septum liners for broadband noise reduction

Silent aeroengine nacelle highlights the demand for advanced acoustic liners providing broadband absorption. This paper studies the multi-degree-of-freedom (MDOF) septum liner that is a promising candidate. The steady-flow resistance of the septum as the necessary input parameter is measured on a steady-flow resistance tube herein, and an impedance prediction model is introduced and validated through the experimental measurement and the numerical simulation. Then, three liners with embedded septa of varied types, numbers and depths are designed, and the acoustic characteristics are analyzed in a wide frequency range under different incident sound pressure levels (SPL). It indicates that such liners can perform well in an ultra-broadband range up to 10000 Hz, and the impedance is relatively insensitive to the incident SPL. It is worth noting that, achieving broadband absorption for such liners is influenced by the coupling effect between zeros of the reflection coefficient, which correspond to the resonance frequencies of the liner. Moreover, the simulated results illustrate that the significant absorption for MDOF septum liners stems mainly from the sound energy dissipation at specific spatial positions depending on the frequency.

Graphene-Wrapped Magnetic Multichamber Ti3C2Tx Spheres for Stable Broadband Microwave Absorption.

Two-dimensional transition metal carbides/nitrides (MXenes) have aroused widespread interest in the field of microwave absorption because of their unique layered structures. However, the inherent aggregation, poor impedance matching, and low chemical stability of MXenes inevitably obstruct their practical applications. Herein, a multichamber Fe3O4/Ti3C2Tx@reduced graphene oxide (FT@RGO) hierarchical structure was constructed through self-assembly and sacrificial template strategies where the Ti3C2Tx nanosheets were assembled into hollow microspheres that were decorated with Fe3O4 nanospheres and wrapped by RGO nanosheets. The massive heterointerfaces and interior cavities favor enhanced microwave absorption performance via interfacial polarization, multiple scattering/reflections, and dielectric-magnetic synergistic effects. Consequently, the synthesized ultralight FT@RGO foam (0.009 g/cm3) presents superior microwave absorption ability with the minimum reflection loss of -50.5 dB at the matching thickness of 2.5 mm and effective absorption bandwidth of 8.0 GHz covering the frequency range of 10.0-18.0 GHz at the thickness of 2 mm. Furthermore, the encapsulation of hollow Ti3C2Tx spheres by RGO nanosheets avoids direct contact with external air, which considerably improves the stability of Ti3C2Tx and ensures the long-term application of FT@RGO foam in a conventional environment. This work provides a reference for the structural design of MXene-based materials as broadband and durable microwave absorbers.

Angular- and polarization-insensitive free-standing graphene oxide films for broadband light absorbing applications

Free-standing graphene oxide (FSGO)-based films with angular and polarization insensitivities are demonstrated for broadband absorption applications. The modified Hummers’ method was used to prepare the GO powder. An easily scalable process (evaporation-induced self-assembly) was used to synthesize the FSGO films. The FSGO broadband absorbers with omni-direction and polarization-independent nature was achieved by varying the GO concentrations. The FSGO films were prepared at different GO concentrations to achieve different thicknesses (2–15 μm). The FSGO film with the highest GO concentration (∼10 mg/ml) exhibited high absorptance (α = 0.91) in the broadband region (i.e., 250–2500 nm). The transition from narrow band absorber to a broadband absorber is achieved by varying the GO concentration. The optimized FSGO film (8 mg/ml) shows α of 0.91 with angular and polarization-insensitivity in the visible region. At concentrations <8 mg/ml, the FSGO films are translucent and do not exhibit broadband absorption behavior. Spectroscopic ellipsometry measurements indicate the low refractive index nature of the FSGO films (n = 1.7–1.2 at 400–800 nm). The low refractive index combined with the unique surface morphology of the FSGO films resulted in broadband absorption. Optical simulations were performed to validate the absorption mechanism of the FSGO films.

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 %.