Tunable Absorption Properties Research Articles

Absorption Band Tunable La-Sr Co-Doped BaCo2-W Type Hexaferrites.

La-Sr co-doped Ba1-x(La0.5Sr0.5)xCo2Fe16O27 (x = 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0, respectively) hexaferrites were prepared by the solid-state method. W-type hexaferrite single phase structure with space group P63/mmc was obtained when the doping amount was x < 0.4 and an M-type hexaferrite and a spinel phase with smaller grains gradually replaced the W phase as the primary phases when x ≥ 0.6. The maximum Ms is 76.2 emu/g and the minimum Hc is 60 Oe at x = 0.4, as obtained by VSM analysis. The magnetoelectric properties of the samples were tested at 1-18 GHz with a vector network analyzer and the reflection loss was calculated based on transmission line theory. It was found that the introduction of an appropriate amount of La-Sr provides a large number of porosity defects while increasing the grain size, which can effectively improve the reflection of electromagnetic waves inside the material and dissipate more energy. At the same time, co-doping also makes the resonance frequency of the samples shift to lower frequency, resulting in tunable absorption properties in the C, X and Ku bands. When x = 0.2, the minimum reflection loss is -40.61 dB at 1.5 mm thickness, with the effective absorption bandwidth of 5.76 GHz in the X band; when x = 0.4, the minimum reflection loss is -37.45 dB at 2.5 mm, with the bandwidth of 4.97 GHz in the C band; when x = 0.6, the material has good absorption in both the X and Ku bands with the thickness less than 2 mm. The simple preparation method and good performance make La-Sr co-doped Co2W ferrite a promising microwave absorbing material.

Absorption Properties of a One‐Dimensional Photonic Crystal with a Defect Layer Composed of a Left‐Handed Metamaterial and Two Monolayer Graphene

To construct photodetector and photovoltaic devices, light absorption is crucial. Herein, the absorption properties of a photonic crystal (PhC) consisting of high‐ and low‐index dielectric materials and a metamaterial defect layer are investigated. Two graphene sheets are assumed to surround the metamaterial layer. The study is theoretically investigated and numerically simulated in the gigahertz region. The metamaterial negative permittivity and permeability are assumed to follow the Drude model. The number of unit cells, graphene chemical potential (GCP), graphene phenomenological scattering rate (GPSR), and the metamaterial layer thickness are varied to examine the PhC tunable absorption properties. The following points are demonstrated: 1) the number of absorbance peaks increases as the number of unit cells increases; 2) when the GCP increases, the absorbance peaks dramatically decay; 3) the number of absorbance peaks in the absorption spectrum is independent of the GCP and GPSR; and 4) the absorbance peaks exhibit a significant enhancement with increasing GPSR. The proposed PhC can be used to design optical devices based on graphene and metamaterials, such as sensors, filters, and absorbers in the GHz range.

Yolk-shell structure synergistic defect engineering for boosting electromagnetic wave absorption in Co9S8@Humins-derived carbon

Exploring new strategies to incorporate the concepts of green chemistry and defect engineering into new architectures to address the problem of severe electromagnetic wave (EMW) pollution is challenging. In this work, by using a by-product of catalytic conversion of biomass as a carbon source, we prepare two-dimensional (2D) Co9S8-coated humins-derived carbon nanomaterials with a yolk-shell structure. The EMW attenuation ability is finally optimized by controlling the morphology and defects of the composite material through the pyrolysis temperature. As expected, with the synergy of conductive loss/interfacial polarization and defects regulating, the composite material achieves a reflection loss (RL) value of −51.4 dB in Ku-band and the effective absorption bandwidth (EAB) can be as high as 5.92 GHz (12.08–18.00 GHz) at 1.8 mm ultra-thin coating thickness. A strong absorption capacity in the low-frequency C-band (6.4 GHz) reaches RL value of −49.9 dB and a thickness of 3.50 mm, which grants it the characteristic of convertible microwave absorption from high frequency to low frequency. Taking account of the facile synthesis and tunable absorption properties, the encouraging findings shed light on exploring waste-turned-microwave absorbents with promising practical applications.

Optimal particle distribution induced interfacial polarization in hollow double-shell composites for electromagnetic waves absorption performance

Tunable designs of polymorphic structured transition metal dichalcogenide (TMDC) demonstrate promising applications in the field of electromagnetic wave absorption (EMW). However, it remains a technical challenge for achieving a balanced relationship between well-matched impedance characteristics and dielectric losses. Therefore, the co-modification strategies of polydopamine coating and wet impregnation are chosen to construct CoS2 magnetic double-shell microspheres with phase component modulation to achieve the optimized performance. Dopamine hydrochloride forms a coating on the surface of CoS2 microspheres by self-polymerization and forms a double-shell structure during the pyrolysis process. Then the different metal is doped to generate heterogeneous components in the process of heat treatment. The results show that the cobalt doped double-shell microspheres have an ultra-high electromagnetic wave absorption absorption capacity with an effective absorption bandwidth of 5.04 GHz (1.98 mm) and a minimum reflection loss value of −48.90 dB. The double-shell layer structure and metal ion hybridization can improve the interfacial polarization and magnetic loss behavior, which provides an explicit inspiration for the development of transition metal dichalcogenide and even transition metal compounds with tunable absorption properties.

High time and energy resolution semi-transparent scintillation detectors for application in [formula omitted] optics and Mössbauer spectroscopy

Recently, phenomena as a quantum entanglement, Raabi oscillations, a stimulated emission etc. have been expanded into short wavelengths, namely X-rays and the γ radiation. However, this brings new requirements for detection systems, especially for their time resolution and energy selectivity. In this article, two partially transparent scintillation detectors for the characterization of a gamma-photon beam are presented. The first detector is a partially transparent scintillation detector with the time resolution less than 10ns. The second detector is a partially transparent scintillation detector utilizing Mössbauer effect with the energy selectivity up to 20.2neV. The unique design of these detectors is possible due to the use of the YAP:Ce powder, which allows the preparation of the custom-shaped scintillators with tunable absorption properties. Using these detectors together in synergy makes them a comprehensive tool for the characterization of gamma photons both in the energy and time domain.

A tunable magnetorheological electromagnetic absorber based on multiscale design and topology optimization

Electromagnetic (EM) absorbers consisting of micro and macroscopic structures have attracted significant interest because of their high-performance absorption characteristics. However, difficult structural design and complex tunable methods limit the application of EM absorbers. Due to multiscale controlled property under magnetic field, magnetorheological (MR) materials can be an appropriate solution. Therefore, this paper demonstrates a tunable MR electromagnetic absorber based on multiscale design and topological optimization. Microscopically, by incorporating multi-walled carbon nanotubes (MWCNTs) into MR absorbers, the dielectric loss is reinforced while ensuring magnetic loss. Meanwhile, advanced microcomputed tomography (μ-CT) illustrates that applied ball milling and magnetic field can effectively design the particles and microstructures, enhancing the absorption and attenuation characteristics. Macroscopically, based on EM parameters, the thickness and mass can be reduced while improving the absorption property through topology optimization. The results show that the peak value of reflection loss (RLmin) can reach −19.04 dB and effective absorption bandwidth (EAB, RL below −10 dB) reach 6.72 GHz with a thickness of 2.6 mm and magnetic flux density up to 563 mT. In addition, based on the thermoplastic characteristics of MR absorbers, the multiscale structures can be reconfigured under the combined effect of thermal and magnetic field, achieving tunable absorption properties. The results demonstrate that RLmin still achieved −9.33 dB after three reconfigurations. This work not only provides a strategy for multiscale structural design of EM absorbers, but also offers an efficient and convenient method for preparation with high-performance and tunable MR absorbers.

Controllable Synthesis of Mo3C2 Encapsulated by N-Doped Carbon Microspheres to Achieve Highly Efficient Microwave Absorption at Full Wavebands: From Lemon-like to Fig-like Morphologies.

Mo3C2@N-doped carbon microspheres (Mo3C2@NC) have been discovered to be a family of superior microwave absorbing materials. Herein, Mo3C2@NC was synthesized through a simple high-temperature carbonization process by evaporating a graphite anode and Mo wire in Ar and N2 atmospheres with an N-doping content of 6.4 at. %. Attributing to the self-assembly mechanism, the number of Mo wires inserted into the graphite anode determined the morphologies of Mo3C2@NC, which were the unique lemon-like (1- and 2-Mo3C2@NC) and fig-like (3-, 4-, and 5-Mo3C2@NC) microstructures. 1- and 2-Mo3C2@NC exhibited powerful reflection losses (RLs) of -45.60, -45.59, and -47.11 dB at the S, C and X bands, respectively, which corresponded to thinner thicknesses. 3-, 4-, and 5-Mo3C2@NC showed outstanding absorption performance at the C, X, and Ku bands, respectively, with each value of a minimum RL less than -43.00 dB. In particular, the strongest RL (-43.56 dB) for 5-Mo3C2@NC corresponded to an ultrathin thickness of 1.3 mm. In addition, the maximum effective absorption bandwidth was 6.3 GHz for 4-Mo3C2@NC. After analysis, all Mo3C2@NC samples showed well-matched impedance due to the enhanced dielectric loss caused by the unique carbon structure and moderate magnetic loss derived from the weak magnetic property of Mo3C2. More importantly, the unique lemon-like and fig-like microstructures created sufficient interfaces and differentiated multiple reflection paths, which greatly contributed to the strong microwave absorptions at full wavebands. In full consideration of the simple preparation method and tunable absorption properties, Mo3C2@NC composites can be regarded as excellent electromagnetic wave absorption materials.

Miniaturized and Actively Tunable Triple-Band Terahertz Metamaterial Absorber Using an Analogy I-Typed Resonator

Triple-band terahertz metamaterial absorber with design of miniaturization and compactness is presented in this work. The unit cell of the terahertz absorber is formed by an analogy I-typed resonator (a rectangular patch with two small notches) deposited on top of dielectric sheet and metallic mirror. The miniaturized structure design exhibits three discrete frequency points with near-perfect absorption at terahertz regime. The three absorption peaks could be ascribed to localized resonances of analogy I-typed resonator, while the response positions of these absorption peaks at the analogy I-typed resonator are different by analyzing the near-field patterns of these resonance peaks. Changes in structure parameters of the analogy I-typed resonator are also investigated. Simulation results revealed that the notch sizes of the rectangular patch are the key factor to form the triple-band near-perfect absorption. Further structure optimization is given to demonstrate triple-band polarization insensitive performance. Moreover, actively tunable absorption properties are realized by inserting or introducing vanadium dioxide with adjustable conductivity into the metamaterial structure. It is revealed that the insulator–metal phase transition of vanadium dioxide is the main reason for the modulation of absorption performance. Compared with previous multiple-band absorbers, the device given here has excellent features of high degrees of simplification, miniaturization, and active modulation, these are important in practical applications.

Perovskite-Type 2D Materials for High-Performance Photodetectors.

Photodetectors are light sensors in widespread use in image sensing, optical communication, and consumer electronics. In current smart optoelectronic technology, conventional semiconductors have encountered a bottleneck caused by inflexibility and opacity. With the ever-increasing demands for versatile optoelectronic applications, perovskite-type 2D materials demonstrate great potential for advanced photodetectors inspired by molecularly thin 2D materials. Through the reduction of thickness to thin or molecularly thin levels, single-crystalline 2D perovskites can exhibit superior optoelectronic performance characteristics, such as tunable absorption property by chemical design, enhanced carrier separation by remarkable photosensing capability, and improved carrier extraction by versatile band engineering. More importantly, perovskite-type 2D materials exhibit great potential for large-scale monolithic integration to achieve all-in-one sensing-memory-computing optoelectronic devices. In this Perspective, recent progress in 2D perovskite-based photodetectors is presented in detail. The focus is on growth strategies for reducing thickness, thickness-dependent optical and electrical properties, device engineering, heterojunction fabrication, and device performance. Finally, the current challenges and future prospects in this field are presented.

Photochemical synthesis of bimetallic gold/silver nanoparticles in polymer matrix with tunable absorption properties: Superior photocatalytic activity for degradation of methylene blue

Bimetallic nanoparticles are widely used in chemical catalysis. Their practical performance can be better exploited through morphological control by adjusting the synthetic strategy. Herein, a photochemical synthesis route was used to achieve the controlled preparation of bimetallic Au/Ag BNps. Size and shape control is achieved depending on the type of initiating radical therefore synthesized new one-component Type II photoinitiator, namely 2-thioxanthone thioacetic acid-dioxide was employed for the synthesis of Au/Ag BNp both in solution and polymer matrix. The effect of the gold/silver ratio on the nanoparticle size, shape and distribution was investigated, and the characterization of the obtained nanoparticles was performed by UV–Vis spectrophotometry, DLS and SEM techniques. Additionally, photocatalytic oxidative degradation of methylene blue was achieved with the prepared Au/Ag bimetallic nanocomposite films. By evaluating the photocatalytic oxidation degradation of methylene blue under UV–Vis light irradiation, 2:1 ratio of Au/Ag nanoparticles containing nanocomposite film exhibit the best activity compared with other composition of Au/Ag. The size and high SPR absorption band are thought to be responsible for superior photocatalytic activity.

Dyes with tunable absorption properties from the visible to the near infrared range: 2,4,5,7-Tetranitrofluorene (TNF) as a unique electron acceptor

Fourteen dyes based on 2,4,5,7-tetranitrofluorene (TNF) as the electron acceptor have been designed and prepared in a one-step synthesis. By modifying the electron donor, optical properties of the dyes could be efficiently tuned and an absorption ranging between 450 nm and 700 nm could be determined by UV–visible absorption spectroscopy. To get a deeper insight into the optical properties, solvatochromism of the fourteen dyes has also been examined. For all dyes, a positive solvatochromism was determined using different solvent polarity scales such as the Kamlet-Taft and the Catalan empirical scales. Finally, electrochemical properties were also examined, and a comparison of the electrochemical and optical bandgaps could be established. Theoretical calculations were also performed to characterize the different dyes.

An Application of Multivariate Data Analysis to Photoacoustic Imaging for the Spectral Unmixing of Gold Nanorods in Biological Tissues.

Gold nanorods (GNRs) showed to be a suitable contrast agent in photoacoustics (PA), and are able to provide a tunable absorption contrast against background tissue, while a detectable PA signal can be generated from highly localized and targeted areas. A crucial issue for these imaging techniques is represented by the discrimination between exogenous and endogenous contrast and the assessment of the real PA signal magnitude. The application of image resolution/unmixing methods was implemented and optimized to recover the relative magnitude spectra and distribution maps of image constituents of the biological sample based on multivariate analysis (multivariate curve resolution—alternating least squares, MCR-ALS) in the presence of GNRs with tunable absorption properties. The proposed data analysis methodology is demonstrated on real PA images from experimental animal models and ex-vivo preparations.

Structurally and Compositionally Tunable Absorption Properties of AgCl@AgAu Nanocatalysts for Plasmonic Photocatalytic Degradation of Environmental Pollutants

Composite nanomaterials having Ag nanoparticles (NPs) that decorate nanostructured AgCl (Ag/AgCl) are promising as plasmonic photocatalysts because of the visible-light absorption of Ag NPs. However, the narrow absorption bands of Ag NPs near 400 nm cause inefficient absorption in the visible range and, consequently, unsatisfactory photocatalytic activity of Ag/AgCl nanomaterials. In this study, we introduce a new class of AgCl-based photocatalysts that are decorated with bimetallic Ag and Au NPs (AgCl@AgAu NPs) for visible-light-driven photocatalytic degradation of organic pollutants. Polyvinylpyrrolidone induces selective reduction of noble metal precursors on AgCl while leaving AgCl intact. The extended composition of the decorating NPs red-shifts the absorption band to 550–650 nm, which allows the catalysts to take advantage of more energy in the visible range for improved efficiency. Furthermore, we control the structures of the AgCl@AgAu NPs, and investigate their correlation with photocatalytic properties. The versatility, chemical stability, and practical application of the AgCl@AgAu NPs are demonstrated using various organic pollutants, recycling experiments, and natural aqueous media, respectively. Our fundamental investigation on the synthesis and applications of AgCl-based nano-photocatalysts is highly valuable for designing plasmonic photocatalysts and expanding their utilization.

Conjugated polymer nano-systems for hyperthermia, imaging and drug delivery.

Hyperthermia has shown tremendous therapeutic efficiency in the treatment of cancer due to its controllability, minimal invasiveness and limited side effects compared to the conventional treatment techniques like surgery, radiotherapy and chemotherapy. To improve the precision of hyperthermia specifically to a tumor location, near infra-red (NIR) light activatable inorganic metal nanoparticles have served as effective photothermal therapy materials, but toxicity and non-biodegradability have limited their clinical applications. Conjugated polymer nanoparticles have overcome these limitations and are emerging as superior photothermal materials owing to their excellent light harvesting nature, biocompatibility and tunable absorption properties. In this review we focus on the development of organic conjugated polymers (polyaniline, polypyrrole, polydopamine etc.) and their nanoparticles, which have broad NIR absorption. Such materials elicit photothermal effects upon NIR stimulation and may also serve as carriers for delivery of therapeutic and contrast agents for combined therapy. Subsequently, the emergence of donor-acceptor based semiconducting polymer nanoparticles with strong absorbance that is tunable across the NIR have been shown to eradicate tumors by either hyperthermia alone or combined with other therapies. The design of multifunctional polymer nanoparticles that absorb near- or mid- infrared light for heat generation, as well as their diagnostic abilities for precise biomedical applications are highlighted.

Design and synthesis of TiO2/Co/carbon nanofibers with tunable and efficient electromagnetic absorption

Carbon materials are widely used for electromagnetic wave absorption. However, to find out a more rational approach to improve the electromagnetic (EM) wave absorption performance is still worthy of attention. In this work, the carbon nanofibers (CNFs) decorated by titanium oxide and metallic cobalt (TiO2/Co/CNFs) were synthesized by electrospinning and carbonizing process, and the microtopography, structure, composition and magnetic properties of which were characterized in detail. The TiO2/Co/CNFs nanocomposites acquired optimal electromagnetism parameters and exhibited superb electromagnetic wave absorption property. The results showed that the minimum reflection loss (RL) values of TiO2/Co/CNFs samples with different filling ratios are less than −50 dB with the matching thickness less than 3.5 mm. The maximum effective absorption bandwidths (RL ≤ −10 dB) exceed 5.2 GHz. Besides, the strong absorption frequency range can be regulated by adjusting filling ratios to broaden the application. This work provides a unique approach to design carbon nanofibers loaded with oxides or metals, and the TiO2/Co/CNFs nanocomposites could be an ideal candidate as light-weight and high-efficiency electromagnetic wave absorption materials and the tunable absorption property portend the potential application in various environmental conditions.

Tuning the Optical Absorption Property of GeSe Thin Films by Annealing Treatment

As an emerging promising photovoltaic absorber material, GeSe has attracted significant interest recently due to its simple binary composition, attractive optical and electrical properties as well as earth‐abundant and low‐toxic constituents. However, no systematic study on the absorption property tuning of GeSe has been reported. Here, first it is shown that the crystallization temperature of amorphous GeSe is about 330 °C through differential thermal analysis and temperature‐dependent X‐ray diffraction. Next, GeSe films with tunable absorption property in the range of 1.79–1.14 eV are fabricated by annealing amorphous GeSe films at different temperatures. Finally, through the combined analysis of bandgaps measured by transmission spectroscopy and nanosheet thickness characterized by cross‐sectional high‐resolution transmission electron microscopy, the blue shift of bandgap with decreasing thickness of nanosheets has been attributed to the quantum confinement effect. Such continuously tunable absorption property of GeSe films makes it more useful for further optoelectronics.

Enhanced Microwave Absorption Properties by Tuning Cation Deficiency of Perovskite Oxides of Two-Dimensional LaFeO3/C Composite in X-Band.

Development of microwave absorption materials with tunable thickness and bandwidth is particularly urgent for practical applications but remains a great challenge. Here, two-dimensional nanocomposites consisting of perovskite oxides (LaFeO3) and amorphous carbon were successfully obtained through a one pot with heating treatment using sodium chloride as a hard template. The tunable absorption properties were realized by introducing A-site cation deficiency in LaFeO3 perovskite. Among the A-site cation-deficient perovskites, La0.62FeO3/C (L0.62FOC) has the best microwave absorption properties in which the maximum absorption is -26.6 dB at 9.8 GHz with a thickness of 2.94 mm and the bandwidth range almost covers all X-band. The main reason affecting the microwave absorption performance was derived from the A-site cation deficiency which induced more dipoles polarization loss. This work proposes a promising method to tune the microwave absorption performance via introducing deficiency in a crystal lattice.

Tailoring Colors by O Annulation of Polycyclic Aromatic Hydrocarbons.

The synthesis of O‐doped polyaromatic hydro‐ carbons in which two polycyclic aromatic hydrocarbon sub units are bridged through one or two O atoms has been achieved. This includes high‐yield ring‐closure key steps that, depending on the reaction conditions, result in the formation of furanyl or pyranopyranyl linkages through intramolecular C−O bond formation. Comprehensive photophysical measurements in solution showed that these compounds have exceptionally high emission yields and tunable absorption properties throughout the UV/Vis spectral region. Electrochemical investigations showed that in all cases O annulation increases the electron‐donor capabilities by raising the HOMO energy level, whereas the LUMO energy level is less affected. Moreover, third‐order nonlinear optical (NLO) measurements on solutions or thin films containing the dyes showed very good values of the second hyperpolarizability. Importantly, poly(methyl methacrylate) films containing the pyranopyranyl derivatives exhibited weak linear absorption and NLO absorption compared to the nonlinearity and NLO refraction, respectively, and thus revealed them to be exceptional organic materials for photonic devices.

Origin of Near-Infrared Absorption for Azulene-Containing Conjugated Polymers upon Protonation or Oxidation.

A series of azulene-containing conjugated polymers were studied to elucidate their tunable absorption properties in near-infrared (NIR) regions (i.e., 1.2-2.5 μm) upon protonation/oxidation. Density function theory (DFT) revealed that protonation-induced intramolecular charge transfer (ICT) in the polymer backbone lead to strong NIR absorption. Distinct spectral change was observed when tiny amount of peroxide was added to the protonated polymer in trifluoroacetic acid/chloroform solution. Electron paramagnetic resonance (EPR) study confirmed the presence of radical cation, which results in the occurrence of newly formed absorption band after the addition of peroxide. The spectro-electrochemical results and DFT study indicate that polarons and polaron pairs were formed during p-doping process, and both the chemical oxidation and electrochemical oxidation could be facilitated by TFA protonation. This represents the first reported mechanisms of NIR absorption under various protonation/oxidation conditions in a single polymer system.

Biodirected synthesis and nanostructural characterization of anisotropic gold nanoparticles.

Gold nanoparticles with anisotropic structures have tunable absorption properties and diverse bioapplications as image contrast agents, plasmonics, and therapeutic-diagnostic materials. Amino acids with electrostatically charged side chains possess inner affinity for metal ions. Lysine (Lys) efficiently controlled the growing into star-shape nanoparticles with controlled narrow sizes (30-100 nm) and produced in high yields (85-95%). Anisotropic nanostructures showed tunable absorbance from UV to NIR range, with extraordinary colloidal stability (-26 to -42 mV) and surface-enhanced Raman scattering properties. Advanced electron microscopy characterization through ultra-high-resolution SEM, STEM, and HR-TEM confirmed the size, nanostructure, crystalline structure, and chemical composition. Molecular dynamics simulations revealed that Lys interacted preferentially with Au(I) through the -COOH group instead of their positive side chains with a binding free energy (BFE) of 3.4 kcal mol(-1). These highly monodisperse and colloidal stable anisotropic particles prepared with biocompatible compounds may be employed in biomedical applications.