Reflectance Spectra Research Articles

High-efficiency fabrication of uniform photonic crystals by a vertical deposition method from multiple glass slides of simple moulds and their application in isomer recognitions

Vertical deposition method is a simple, cheap and common method for fabricating photonic crystals (PCs). However, a majority of PCs are obtained based on the traditional vertical deposition method from one glass slide, the method is low efficiency. Herein, it is proposed to efficiently fabricate uniform PCs by an optimized vertical deposition method from double or multiple glass slides of simple moulds. Amounts of SiO2 spheres, distances of two glass slides of moulds, preparation temperatures and different diameters of SiO2 spheres are investigated for obtaining uniform PCs. And different types of PCs (the bottom-middle-top 3D PCs, bilayer 2D PCs and amorphous PCs) are also fabricated based on the optimized vertical deposition method. The above method is a simple, cheap and high-efficiency way for mass production of uniform PCs. Meanwhile, the chemicals with similar refractive indices (isomers and cis-trans isomers) can be easily distinguished under high humidity based on dynamic reflection spectra of the PCs. For example, the difference in the refractive indices of m-xylene and p-xylene is only 0.002, the difference of desorption balance time of PCs is 263 s. The PCs have potential applications in visual detections, isomer recognitions and monitoring of volatilization rates of trace liquids.

A novel iron metal organic framework-based nanocomposite for the synergistic degradation and adsorption of organic pollutants and Cr (Ⅵ) under visible light

In this work, a novel nitrogenous Fe-TPPE metal-organic-framework (MOF) with excellent visible light catalytic activity was successfully prepared, and a magnetic composite (Fe3O4@Fe-TPPE) with Z-type heterojunction structure was designed to synergistically treat organic pollutants and Cr(Ⅵ). The materials were carefully characterized by powder X-ray diffractometry, scanning electron microscope, Fourier transform infrared analysis, UV–visible diffuse reflectance spectra, X-ray photoelectron spectroscopy, thermogravimetric analysis, etc. The characterizations of photoelectric properties showed that the novel Fe-TPPE MOF exhibited strong response to visible light and Fe3O4@Fe-TPPE had even stronger response. Furthermore, the adsorption and photocatalytic degradation capabilities of Fe-TPPE and Fe3O4@Fe-TPPE, and the versatility as photocatalysts for aqueous pollutants were assessed through removal studies of the model pollutants tetracycline, rhodamine, methyl blue and Cr (VI). Additionally, the removal mechanism of the Fe3O4@Fe-TPPE for the above pollutants was explored. The high removal efficiency, fast magnetic separation, great recycling stability and minimal leak during application all demonstrate the good potential of Fe3O4@Fe-TPPE for practical and sustainable treatment of aqueous pollutants.

Analysis of four heavy metal concentrations in sediments from the Jiaozhou Bay, China by visible and near infrared spectroscopy (225–975 nm)

As an important component ofbiogeochemical cyclein coastal ecosystems, sediments are the sink of heavy metals. Therefore, distribution and dynamics of heavy metals in sediments could assess ecological quality and predict ecological risks. In the new era, rapid and green technology are highly needed, especially that could determine multi-parameters simultaneously. Here, we explored a new method to rapidly determine concentrations of heavy metals in sediments by visible and near infrared reflectance spectroscopy (VIRS).We sampled sediments in the Jiaozhou Bay, China, collected their reflectance spectra, and measured concentrations of four heavy metals (As, Cr, Cu, and Zn). Heavy metal models were established and evaluated using substances highly correlated with heavy metals. This study provides an effective reference for rapid analysis of As, Cr, Cu, and Zn simultaneously in sediments, at least in the Jiaozhou Bay, and for ecological environment protection and resource development of the Jiaozhou Bay.

First-principles calculations on electronic, mechanical and optical properties of ScMC2 (M = Ti, V, Cr, and Mn) ternary carbides

First-principles calculations have been employed to investigate the physical properties of scandium-based ternary carbides, denoted as ScMC2 (M = Ti, V, Cr, Mn). All the studied carbides demonstrate both structural and mechanical stability. Mechanical anisotropy and optical properties are reported for the first time to enhance their importance on an industrial scale. The calculated mechanical parameters are correlated with the previously reported results to check the reliability of the current work. Poisson's and Pugh ratios indicate that ScMC2 (M = Ti, V, Cr) compounds are brittle whereas ScMnC2 is ductile. Thermal shock resistance is also investigated which suggests that ScMC2 carbides could be used as TBC's materials. DOS and optical characteristics reflect the metallic behavior of studied carbides. Optical properties indicate the existence of anisotropy in ScMC2 carbides up to 10 eV photon energy. The reflectance spectra suggest that ScMnC2 could be used to reduce solar heating.

Modeling order–disorder boundaries of colloidal dispersions in organic solvents using interaction force measurements

HypothesisThe formation of soft colloidal crystals, which are nonclose-packed ordered arrays of colloidal particles suspended in a solvent, is dictated by a single physical factor that yields a fixed threshold at order–disorder boundaries for different experimental conditions such as ion concentration, solvent type, and particle size. Identifying the determinant factor and its threshold value should enable the prediction of the critical concentrations of colloidal particles to form soft colloidal crystals. ExperimentsSoft colloidal crystals were fabricated using a series of monohydric alcohols as dispersion media and reflectance spectra were measured to locate order–disorder boundaries. The interaction forces acting between particles were also measured by employing atomic force microscopy. FindingsThe interparticle forces at the order–disorder boundaries exhibited a universal threshold that was independent of the solvent types including alcohols and water. Therefore, the determinant factor for the formation of soft colloidal crystals was determined to be the force acting between the particles. Furthermore, a priori calculation of this critical force and consequently the critical particle concentration in colloidal systems was demonstrated by referring to the pressure at the liquid-to-solid transition in a hard sphere system (Alder transition).

All-optical high-contrast femtosecond switching using nonlinearity from an epsilon-near-zero effect in plasmonic metamaterials.

Metamaterials opened a new realm to control light-matter interactions at sub-wavelength scale by engineering meta-atoms. Recently, the integration of several emerging nonlinear materials with metamaterial structures enables ultra-fast all-optical switching at the nanoscale and thus brings enormous possibilities to realize next-generation optical communication systems. This Letter presents a novel, to the best of our knowledge, design of plasmonic metamaterials for high-contrast femtosecond all-optical switching. We leverage magnetic plasmon (MP) resonance combined with the nonlinear effects of an epsilon-near-zero (ENZ)-material. The proposed design comprises a periodic array of two closely spaced Au-nanogratings deposited on an optically thick Au-substrate to excite MP-resonance. To enable a dynamically tunable resonance, the nanogrooves in meta-atoms are filled with an ENZ-material, cadmium-oxide (CdO). The intraband transition-induced optical nonlinearities in the ENZ-medium are studied using a two-temperature model. The MP-resonance ensures strong light-matter interactions enabling enhancement of the nonlinearities of the proposed structure. We observe that the pump-induced refractive index change in the CdO layer causes a redshift of the MP-resonance dip wavelength in the reflectance spectrum, leading to a high modulation depth of 0.83 at 1.55 µm. With an ultra-fast response time of 776 fs while maintaining a low pump-fluence of 75 µJ/cm2, the proposed metamaterial could help in realizing switches for next-generation optical computation systems.

Test for Echo: X-Ray Reflection Variability in the Seyfert-2 Active Galactic Nucleus NGC 4388

We report on a study of the narrow Fe Kα line and reflection spectrum in the well-known Seyfert-2 active galactic nucleus (AGN), NGC 4388. X-ray spectra summed from two extensive NICER monitoring campaigns, separated by years, show strong evidence of variation in the direct continuum and reflected emission, but only small variations in the obscuring gas. Fits to the spectra from individual NICER observations find a strong, positive correlation between the power-law photon index, Γ, and direct flux that is commonly observed in unobscured AGN. A search for a reverberation lag between the direct and reflected spectra—dominated by the narrow Fe Kα emission line—measures a timescale of t=16.37−0.38+0.46 days, or a characteristic radius of r=1.374−0.032+0.039×10−2 pc =3.4−0.1+0.1×104GM/c2 . Only one cycle of this tentative lag is observed, but it is driven by a particularly sharp drop in the direct continuum that leads to the subsequent disappearance of the otherwise prominent Fe Kα line. Physically motivated fits to high-resolution Chandra spectra of NGC 4388 measure a line production radius of r=2.9−0.7+1.2×104GM/c2 , formally consistent with the tentative lag. The line profile also prefers a Compton-thick reflector, indicating an origin in the disk and/or thick clumps within a wind. We discuss the strengths and weaknesses of our analysis and methods for testing our results in future observations, and we note the potential for X-ray reverberation lags to constrain black hole masses in obscured Seyferts wherein the optical broad line region is not visible.

Computational neural network for processing light-reflective spectra of plants and remote phytosanitary monitoring of potatoes

The article is devoted to studying the possibility of using the WaveLetNN artificial neural network to analyze the results of remote phytosanitary monitoring of early detection of plants in potato plantings affected by late blight. Various methods for analyzing the spectral characteristics of plant reflection are considered, including the classification method. To detect plants infected with late blight, the WaveLetNN neural network analyzes the light reflective characteristics of potato plants obtained as a result of research (in the range of 300–1100 nm) and calculates the cognitive significance index (CSI = 0...10), which characterizes the intensity of biochemical processes inside plants aimed at countering phytopathogenic microflora. It was found that a significant increase in the CSI index signals infection of plants by phytopathogenic microflora and activation of protective biochemical processes on the part of plants. To reliably indicate infected plants, the WaveLetNN neural network underwent test training on a large number of light reflectance spectra of uninfected plants and plants artificially infected with late blight. The spectral reflectance characteristics of infected and uninfected plants were measured during 3, 4, 7 and 8 days after infection. Processing the obtained spectra using the WaveLetNN neural network made it possible to identify significant differences between the second- and third-order spectral characteristics of uninfected and late blight infected plants on the third day after infection. Moreover, for infected plants the CSI index values were 6.1...6.7, and CSI for healthy plants – 1.9...2.5. The Wave-LetNN neural network eliminates the influence on the light reflectance spectra of the spatial arrangement of plant leaves, unevenness of the soil surface and shading of individual sections of the field, normalizing the spectra to the total intensity of light reflected from the leaves. Thus, the WaveLetNN neural network can be used as the software core of online systems for remote phytosanitary monitoring of potato plants.

Investigation of the physico-chemical properties of In2S3 powder synthesized via solid-state reaction and In2S3 thin films prepared through thermal evaporation

In this study, we examined the physico-chemical properties of In2S3 powder produced using the solid-state reaction and of the In2S3 thin film obtained using the thermal evaporation technique. Thermally evaporated In2S3 thin films were subjected to vacuum annealing to study the impact of heating on the structural, morphological and optical properties of the samples. According to the X-ray diffraction analysis, the microstructure of as-grown thin films were an amorphous in nature which transformed into polycrystalline structure after annealing at T≥250 °C. This polycrystalline structure suggests the formation of the β-In2S3 phase with a tetragonal and/or cubic crystal structure. In addition, the energy dispersive spectroscopy analysis revealed that all samples show a slight excess of indium and a deficit of sulfur, compared to the stoichiometric ratios. Moreover, surface micrographs recorded by atomic force microscopy showed an increase in surface roughness after annealing. Optically, the transmittance spectra, T(λ), illustrated a high transmittance average value,∼70 %, while the reflectance spectra, R(λ), showed an average value of 25 % in the visible and NIR region. It appeared that heat treatment had no significant impact on the T and R spectra. The optical dispersion parameters of the treated samples were also studied. The direct and indirect allowed bandgap transitions values of all samples were found to ranging from 1.75 to 2.48 eV and from 1.80 to 2.38 eV, respectively. Such observation shows that the bandgap increased with annealing temperature. Electrically, n-type conductivity for In2S3 films annealed at 250 °C was recorded.

Angle-Resolved Fluorescence of a Dye Coupled to a Plasmonic Nanohole Array

Gold nanohole arrays are periodic metasurfaces that are gathering huge interest in biosensing applications. The bi-dimensional grating-like structure defines their plasmonic response, together with the corresponding mode of angular dispersion. These properties can be used to investigate the interaction processes with the fluorescence features of a properly chosen emitting molecule. By employing a custom gold nanohole array alongside a commercial organic dye, we conducted an accurate angle-resolved optical characterization resorting to fluorescence, reflectance, and transmittance spectra. The coupling between the plasmonic modes and the fluorescence features was then identified as a modification of the dye fluorescence signal in terms of both spectral redistribution and enhancement. By carefully analyzing the results, different measurement efficiencies can be identified, depending on the set-up configuration, to be properly engineered for sensitivity maximization in plasmon-enhanced fluorescence-based applications.

Blaze-angle led dark-blue iridescence and superhydrophobicity features of non-morpho Euploea midamus butterfly wing scale

We report on backlit iridescent blue structural coloration as well as superhydrophobicity in a non-morpho butterfly of Euploea midamus (blue-spotted crow) belonging to the Lepidoptera order. Select forewing and hindwing parts were characterized by employing optical microscopy, field emission electron microscopy, UV–vis-NIR spectrophotometry, and an advanced contact angle meter. As substantiated from variable incident angle reflectance spectra and chromaticity plots, the apparent visual effect is most pronounced in the forewing case and at an incident angle of 30–40°, with reflectance peak maxima positioned at ~ 412 nm and 478 nm. Additionally, the forewing scale of this butterfly acts as an anti-reflection filter (< 460 nm) for p-polarized light, showing greater polarization anisotropy in the lower wavelength region. Numerical simulationand microstructure-based analytical calculations with blaze angle grating effects have been considered to elucidate the observed dark-blue iridescence at large. Moreover, both the forewing and hindwing of the butterfly exhibit the ‘lotus effect’, with a contact angle as high as of ~ 150°, low contact angle hysteresis (16° and 13°) as well as low roll-off angles (10° and 7°) to favor self-cleaning action. Theoretical calculations attributing to dual roughnesses would encompass micro-textured and nanoscale asperities within the wing scale interface. The scope of the bifunctional features including optical and dewetting responses in natural systems would provide valuable insights and clues for biomimetics, particularly in nanophotonic and nanocoating applications.

Rapid estimates of leaf litter chemistry using reflectance spectroscopy

Measuring the chemical traits of leaf litter is important for understanding plants’ roles in nutrient cycles, including through nutrient resorption and litter decomposition, but conventional leaf trait measurements are often destructive and labor-intensive. Here, we develop and evaluate the performance of partial least-squares regression (PLSR) models that use reflectance spectra of intact or ground leaves to estimate leaf litter traits, including carbon and nitrogen concentration, carbon fractions, and leaf mass per area (LMA). Our analyses included more than 300 samples of senesced foliage from 11 species of temperate trees, including needleleaf and broadleaf species. Across all samples, we could predict each trait with moderate-to-high accuracy from both intact-leaf litter spectra (validation R2 = 0.543-0.941; %RMSE = 7.49-18.5) and ground-leaf litter spectra (validation R2 = 0.491-0.946; %RMSE = 7.00-19.5). Notably, intact-leaf spectra yielded better predictions of LMA. Our results support the feasibility of building models to estimate multiple chemical traits from leaf litter of a range of species. In particular, the success of intact-leaf spectral models allows non-destructive trait estimation in a matter of seconds, which could enable researchers to measure the same leaves over time in studies of nutrient resorption.

DFT insights into i-MAB phase, Mo4Y2Al3B6: a potential thermal barrier coating and solar heat reducing material

We have investigated the physical properties of the i-MAB: Mo4Y2Al3B6 phase via the density functional theory (DFT) approach. The optical properties, thermal properties, and Vickers hardness of the compound Mo4Y2Al3B6 have been studied theoretically for the first time. The correctness of the fine-tuned structural parameters is confirmed by their close match with experimental results. The compound’s metallic nature is established by an analysis of its electronic band structure, which is demonstrated by the overlap of the valence and conduction bands at the Fermi level. The mechanical and dynamic stability of the compound is supported by the single crystal elastic constants and computed phonon dispersion curve. The brittleness and machinability index has been studied to predict its usefulness in any form/shape. The compound’s ability to be exfoliated into 2D nanosheets has been proven by the f-index value. The obtained Vickers hardness value indicate the materials’ softness and ease of machining, aligning with the experimental findings. The thermodynamic properties are evaluated through phonon dispersion curves, including Debye temperature, free energy, enthalpy, entropy, and specific heat capacity. The potential of Mo4Y2Al3B6 as a thermal barrier coating (TBC) material is demonstrated by its low minimum thermal conductivity (K min), low volume expansion coefficient and high melting temperature (T m ). Key optical parameters, including dielectric functions, refractive index, photoconductivity, reflectivity, absorption coefficient, and loss function, have been computed and analyzed. The reflectivity spectrum suggests that the titled compound acts as a promising coating material for mitigating solar heating.

Construction of Zn0.5Cd0.5S/Bi4O5Br2 Heterojunction for Enhanced Photocatalytic Degradation of Tetracycline Hydrochloride

The development of efficient catalysts with visible light response for the removal of pollutants in an aqueous environment has been a hotspot in the field of photocatalysis research. A Zn0.5Cd0.5S (ZCS) nanoparticle/Bi4O5Br2 ultra-thin nanosheet heterojunction was constructed by ultrasound-assisted solvothermal method. The morphology, structure, and optoelectronic properties of the composite were characterized by scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and UV–vis diffuse reflectance spectra. Under simulated visible light illumination, the photocatalytic performance was evaluated through degradation of tetracycline hydrochloride. Results show that the degradation effect by the optimum ZCS/Bi4O5Br2 catalyst is superior to pure materials with the kinetic constant that is 1.7 and 9.6 times higher than those of Bi4O5Br2 and ZCS, and also has better stability and reusability. Trapping experiments and electron paramagnetic resonance tests find that free radicals in the photocatalytic system are superoxide radicals and holes. This work provides a referable idea for the development of more efficient and recyclable photocatalysts.

2D Cadmium(II) Coordination Polymer Based on 2,5-Furandicarboxylate and 1,4-Bis(1H-imidazol-1-yl)butane Linkers: Synthesis, Characterization and DFT Studies

AbstractAs a result of hydrothermal synthesis of 2,5-furandicarboxylate (fdc2−), Cd(II) ion and bis(imidazole) derivative 1,4-bis(1H-imidazole-1-yl)butane (bib) ligand, a novel two-dimensional Cd(II) coordination polymer {[Cd(µ-fdc)(H2O)(µ-bib)]·H2O}n (1) was synthesized. According to the results of single crystal X-ray diffraction analysis, the complex was crystallized in the monoclinic system and in the P21/n space group. In addition, the thermal, luminescence and optical properties of the complex were investigated. The complex emits a maximum at 509 nm and also shows semi-conductor properties according to the solid-state UV–Vis diffuse reflection spectra results. To determine chemical structure, vibrational properties and some chemical properties of complex, theoretical calculations were carried out. All theoretical computations were performed using the DFT method at the B3LYP/LanL2DZ level of theory. The obtained experimental results were in good agreement with theoretical results. To calculate HOMO–LUMO energy values, which provided insights into the material's electronic properties, DFT calculations were used. Detailed information about the local and global chemical activity, as well as the electrophilic and nucleophilic nature of the complex, were also obtained.

Electron Structure of α‐, β‐Te2MoO7 and Photocatalytic Decomposition of Antibiotics

Two modifications of Te2MoO7 oxide have been prepared by different synthetic methods. The crystal structure and composition have been studied by X‐ray diffraction analysis and X‐ray microanalysis. The phase of α‐Te2MoO7 has been synthesized by solid‐state reaction from ammonium salts and characterized by monoclinic structure with P21/c. The β‐Te2MoO7 compound has been formed in hydrothermal conditions and has amorphous nature. The thermal behavior of β‐Te2MoO7 modification is characterized by the phase transition into α‐form, however after melting the amorphous state has restored. The electron structure has been investigated experimentally by X‐ray photoelectron spectroscopy and UV‐vis diffusion reflectance spectra and theoretically by approximation using atomic electronegativity. Despite the same composition, the band gap of β‐Te2MoO7 corresponds to visible light, whereas α‐Te2MoO7 adsorbs light in UV region. The both modifications are able to generate superoxide radicals in vacuum or air and hydroxyl radicals in water under irradiation. The HPLC‐MS analysis has shown the quite deep decomposition of dye and antibiotics by α‐Te2MoO7, whereas amorphous phase almost does not lead to any oxidation.

In-Line Chemical Composition Monitoring for the Injection Molding Process of Biodegradable Polymer Blends Using Simultaneous Measurement of Near-Infrared Diffuse Reflectance and Transmission Spectra.

In the processing of polymer blends and composites, in-line near-infrared (NIR) spectroscopy enables monitoring of the composition and its composite uniformity and contributes to rapid process development and quality control. However, in the injection molding process, the study of the composition of polymer materials has been delayed due to high-pressure conditions. Our research group developed NIR probes for transmission and diffuse reflectance measurements that can withstand high-pressure and temperature conditions up to 130 MPa and 200 °C. In this research, transmission and diffuse reflectance spectra were measured inline during the injection molding process of polymer blends of poly(lactic acid) and polybutylene succinate adipate. The intensity of each polymer band in the second-derivative spectra exhibited a monotonic increase or decrease in response to changes in the blend ratio. Using transmission and diffuse reflectance spectra as explanatory variables of the partial least squares regression model simultaneously, the model showed high estimation accuracy for the entire region of the blend ratio. Finally, this model was applied to monitor the polymer changeover operation, and the change in the blend ratio in the molded product was successfully estimated in line.

Na3K6(CO3)3(NO3)2X·6H2O (X = NO3, Cl, Br): Exploring High-Performance UV Birefringent Crystals Induced by Coplanar π-Conjugated CO3 and NO3 Groups.

Planar π-conjugated groups, like CO3, NO3, and BO3 triangles, are ideal functional units for designing birefringent materials due to their large optical anisotropy and wide band gap. The key point for designing birefringent crystals is to select appropriate functional building blocks (FBBs) and the proper arrangement mode. It is well known that the substitution strategy has proven to be a promising and accessible approach. In this work, alkali metals were chosen to regulate and control two different π-conjugated groups, CO3 and NO3, to build new compounds with large birefringence. Subsequently, three new compounds, Na3K6(CO3)3(NO3)2X·6H2O (X = NO3, Cl, Br), were successfully synthesized using the hydrothermal method. The aliovalent substitution between the [NO3]- anionic group and halogen anions [Cl]-/[Br]- has been achieved in these compounds. Na3K6(CO3)3(NO3)2X·6H2O feature the well-coplanar CO3 and NO3 groups in their crystal structure. This coplanar arrangement mode may effectively enhance the anisotropic polarizability of Na3K6(CO3)3(NO3)2X·6H2O. And their experimental birefringence can reach 0.094-0.131 at 546 nm. Diffuse reflectance spectra demonstrate that these compounds exhibit short ultraviolet (UV) absorption edges of ∼235 nm. Meanwhile, Na3K6(CO3)3(NO3)2X·6H2O also have an easily grown capacity under facile conditions. This work not only reports three new potential UV birefringent crystals but also provides a strategy to make the π-conjugated MO3 group coplanar.

Construction of flexible BiOBr/W18O49/polyacrylonitrile discrete heterojunction nanofibers as a dual-functional photocatalyst for simultaneous hydrogen evolution and organic pollutant degradation

Dual-functional photocatalysis has attracted increasing attention due to its ability to achieve efficient synergistic hydrogen (H2) evolution and pollutant removal. Energy band structure engineering and surface morphology modification of photocatalysts is a useful strategy to improve the activity of photocatalysis. This paper uses a combination of electrospinning technology and hydrothermal method to prepare flexible BiOBr/W18O49/PAN discrete heterojunction flexible nanofibers (NFs) with staggered energy bands and spatially separated redox surfaces. The BiOBr/W18O49 heterojunction can improve carrier separation and migration, as evidenced by the photoluminescence and photoelectrochemical experiments. The localized surface plasmon resonance (LSPR) effect of W18O49 can achieve injection of “hot electrons” and lead to expanding the light absorption range according to the UV–visible-near infrared diffuse reflection spectra results. The discrete structure of BiOBr/W18O49/PAN NFs can provide spatially separated active sites for simultaneous photocatalytic redox reaction. As expected, the BiOBr/W18O49/PAN discrete heterojunction NFs greatly enhance the photocatalytic activity in simultaneous dual-functional reaction for H2 evolution and RhB degradation. The highest simultaneous H2 evolution rate and RhB degradation rate of BiOBr/W18O49/PAN NFs are 31.7 times and 34.1 times of BiOBr/PAN, respectively. The design and construction of this flexible discrete heterojunction NFs structures can provide novel ideas and directions for simultaneous dual-functional photocatalysts.

The subtle usage of NH4BF4: Facile and economical fabrication of Ti black surface for enhanced optical absorption performance

The Ti black surface has been widely used in aerospace and photocatalysis for many years. However, the preparation technique for the Ti black surface has several disadvantages, such as a complex process, high cost and safety concerns. In this study, a new chemical immersion method using the mixed aqueous solution of 0.715 mol/L NH4BF4 and 0.004 mol/L HF was proposed to prepare a uniform Ti black surface, which is very facile, economical and efficient. Due to the etching of HF, the light-trapping nanostructure was formed on Ti surface. Grazing incidence X-ray diffraction (GIXRD) and X-ray photoelectron spectroscopy (XPS) observations indicated that the black surface was covered by the film mainly composed of TiOx, Ti(OH)x, and TiH2. The diffuse reflectance spectra demonstrated that the black surface exhibited great optical absorption performance with the maximum reflectance of 7.6 % to the UV–visible light and 35.3 % to the near-infrared light. The as-fabricated TiOx film with narrower bandgap could be contributed to the doping of Ti3+ and F− ions. The presence of F− ions in the film prevented the Ti3+ ions in the bulk of TiOx from being oxidized. The combined contribution of light-trapping nanostructure and TiOx film enhanced the optical absorption performance of Ti surface.