Infrared Research Articles

Multispectral metal-based electro-optical metadevices with infrared reversible tunability and microwave scattering reduction

Abstract The demand for advanced camouflage technology is increasing in modern military warfare. Multispectral compatibility and adaptive capabilities are increasingly desired features in camouflage materials. However, due to the strong wavelength dependence and limited tunability of electromagnetic wave responses, achieving simultaneous multispectral compatibility and adaptive capability in a single structure or device remains a challenge. By integrating coding metamaterials with infrared (IR) electrochromic devices, we demonstrate a highly integrated multispectral metal-based electro-optical metadevice. The fabricated metadevices enable the reversible tunability of IR emissivity (0.58 at 3–5 µm, 0.50 at 7.5–13 µm) and wideband microwave scattering reduction (>10 dB at 10–20 GHz). The excellent integration performance is attributed to the remarkable electromagnetic control capabilities of the coding metamaterials in a chessboard-like configuration and the IR electrochromic devices based on metal reversible electrodeposition. Furthermore, the monolithic integrated design with shared barium fluoride substrate and electrodes allows the metadevices to have a simple architecture, and the careful design avoids coupling between functions. Our approach is general enough for the design of various electrochromic devices and metamaterials for multispectral camouflage, offering valuable insights for the development of advanced adaptive multispectral camouflage systems.

Infrared Photodissociation Spectroscopy of Water-Tagged Ions with a Widely Tunable Quantum Cascade Laser for Planetary Science Applications.

This work presents a benchtop method for collecting the room temperature gas phase infrared (IR) action spectra of protonated amino acids and their isomers. The adopted setup uses a minimally modified commercial electrospray ionization linear ion trap mass spectrometer (ESI-LIT-MS) coupled to a broadband continuous wave (cw) quantum cascade laser (QCL) source. This approach leverages messenger assisted action spectroscopic techniques using water-tagged molecular ions with complex formation, irradiation, and subsequent analysis, all taking place within a single linear ion trap stage. This configuration thus circumvents the use of multiple mass selection and analysis stages, cryogenic buffer cells, and complex high-power laser systems typically called upon to execute these techniques. The benchtop action spectrometer is used to collect the 935-1600 cm-1 (6.2-10.7 μm) IR action spectrum of a collection of amino acids and a dipeptide with results cross referenced against literature examples obtained with a free electron laser source. Recorded IR spectra are used for the analysis of binary mixture samples composed of constitutional isomers α-alanine and β-alanine with ratios determined to ∼4% measurement uncertainty without the aid of a front-end separation stage. This turn-key QCL-based approach is a major step in showing the viability of tag-based action spectroscopic techniques for use in future in situ planetary science sensors and general analytical applications.

Thermally emitting isolated neutron star candidates from the SRG/eROSITA All-Sky Survey

The SRG/eROSITA All-Sky Survey (eRASS) allows for the creation of a complete sample of X-ray dim isolated neutron stars (XDINSs), which will significantly facilitate the study of their population properties, evolution, and connection to other families of isolated neutron stars (INSs). In this work, we conduct a systematic search for XDINSs on the eROSITA western Galactic hemisphere down to an X-ray flux limit of 10$^ and discuss the resulting candidate sample. Consistently with the properties of the known XDINSs, we selected all eRASS sources possessing a soft X-ray spectral distribution and that are unlikely to be associated with optical or infrared sources. Our selection criteria allowed us to recover all known XDINSs and previously proposed candidates. In addition, we put forward 33 new candidate members for dedicated follow-up identification campaigns. We found the resulting candidate sample to be about 30 -- 50<!PCT!> complete, mainly due to source confusion and the stringent cross-matching criteria adopted to select the most promising candidates for immediate follow-up investigation. The candidates of the sample presented here can be broadly divided into two groups: 13 rather soft and 20 hot and somewhat hard X-ray emitters. Interestingly, the remarkably thermal nature of the candidates in the first group as well as their spatial distribution, lack of known counterparts, and absence of significant flux variability agree well with the properties of other confirmed thermally emitting INSs. For the candidates in the second group, the current observational data do not allow one to discern between rotation-powered or recycled pulsars, cataclysmic variables, or quiescent neutron stars in binary systems or even to rule out an extragalactic nature. On the basis of population synthesis and the estimated source completeness of the search, we expect that between one and three new XDINSs are among the already singled-out list of XDINS candidates -- a long-sought increase in the proposed number of members of this elusive class of X-ray emitters.

Nano-Plasticity of an Electrified Ionic Liquid/Electrode Interface: Uncovering Hard-Soft Structuring via Controlled Metal Fill Factor.

Ionic liquids (ILs) nanostructuring at electrified interfaces is of both fundamental and practical interest as these materials are increasingly gaining prominence in energy storage and conversion processes. However, much remains unresolved about IL potential-controlled (re)organization under highly polarized interfaces, mostly due to the difficulty of selectively probing both the distal and proximal surface layers of adsorbed ions. In this work, the structural dynamics of the innermost layer (<10 nm from the surface) were independently interrogated from that of the ionic layers in the sub-surface region (>100 nm from the surface), using an infrared (IR) spectroscopy approach. By tuning the metal fill factor of gold films deposited on conductive metal oxide-modified IR internal reflection elements, the charge-driven (re)structuring of the inner and distal layers of 1-butyl-1-methylpyrrolidinium trifluoromethanesulfonate is unveiled. Within a relatively wide potential region (∼±1 V) bounding the potential of zero charges, the ionic liquid is shown to undergo a reversible (i.e., soft) reorganization whereby the innermost layer of anions (cations) is exchanged by a layer of cations (anions). Kinetically unhindered changes in the number density of constituent cations and anions largely follow electrostatic expectations in the subsurface region, whereas the innermost layer exhibits a pronounced hysteresis and very slow relaxation. Under larger negative potential bias, IL restructuring is characterized by a highly irreversible (i.e., hard) and intense interfacial densification of the BMPy+ cations, consistent with the formation of nanoscale segregated liquids. The outcomes of this work reveal a plastic IL nanostructuring under a strong electric field.

Terahertz and Infrared Plasmon Polaritons in PtTe2 Type-II Dirac Topological Semimetal.

Surface plasmon polaritons (SPPs) are electromagnetic excitations existing at the interface between a metal and a dielectric. SPPs provide a promising path in nanophotonic devicesforlight manipulation at the micro and nanoscale with applications in optoelectronics, biomedicine, and energy harvesting. Recently, SPPs are extended to unconventional materials like graphene, transparent oxides, superconductors, and topological systems characterized by linearly dispersive electronic bands. In this respect, 3D Dirac and Weyl semimetals offer a promising frontier for infrared (IR) and terahertz (THz) radiation tuning by topologically-protected SPPs.In this work, the THz-IR optical response of platinum ditelluride (PtTe2) type-II Dirac topological semimetal films grown on Si substrates is investigated. SPPs generated on microscale ribbon arrays of PtTe2are detected in the far-field limit,finding an excellent agreement among measurements, theoretical models, and electromagnetic simulation data.The far-field measurements are further supported by near-field IR data which indicate a strong electric field enhancement due to the SPP excitation near the ribbon edges. The present findings indicate that the PtTe2ribbon array appears an idealactive layout for geometrically tunable SPPs thus inspiring a new fashion of optically tunable materials in the technologically demanding THz and IR spectrum.

A Study on the Effect Mechanism of Pectin Modification on the Carrot Cell Wall’s Texture Formation under Ultrasonic and Infrared Drying

The carrot has a high water content, and dehydration is an important means to extend its edible period and reduce storage and transportation costs. In the case of infrared (IR) drying, the porosity of the product is low and the structure is compact; the textural properties of the product are improved by using combined ultrasound and infrared (US-IR) drying; however, there is a lack of reports on the mechanism of this. Pectin has an important influence on the formation of the textural properties of fruit and vegetable tissues. In order to investigate the mechanism of the change in endogenous pectin properties in the carrot cell wall under US-IR drying on the improvement of the textural properties of the product, different fractions of pectins (water-soluble pectin, chelating pectin, alkali-soluble pectin) of the carrot were extracted, separated, and analysed. The thermal stability, component and content changes, Fourier infrared (FTIR), X-ray diffraction (XRD), esterification degree, molecular weight, monosaccharide composition, Ca ion content, and atomic force microscopy (AFM) of the pectins were determined. The results showed that the changes in the contents and properties of the carrot pectins under US-IR conditions had a positive effect on the improvement of the textural properties of the carrot tissues.

A Spectroscopic Method for Distinguishing Two Novel Sandwich-Type Tungsten Oxide Cluster Compounds.

This study introduces two novel sandwich-type tungsten-oxygen cluster compounds synthesized by hydrothermal methods, H4(C6H12N2H2)3{Na(H2O)2[Mn2(H2O)(GeW9O34)]}2 (Compound 1) and H2(C6H12N2H2)3.5{Na3(H2O)4[Co2(H2O)(GeW9O34)]2}·17H2O (Compound 2). The two compounds comprise cluster anions [GeW9O34]10- coordinated with transition metal atoms, either Mn or Co, and are stabilized by organic ligands. These compounds are crystallized in the hexagonal crystal system and P63/m space group. The two compounds were characterized through various techniques. Fourier transform infrared (IR) spectroscopy showed absorption peaks of anionic backbone vibrations of the Keggin cluster at 500-1000 cm-1, IR spectral peaks of δ(N-H) and νas(C-N) of the ligand triethylenediamine at 1000-2000 cm-1, and IR spectral peaks of the ligand νas(N-H) and νas(O-H) of water at 3000-3500 cm-1. Despite similar one-dimensional (1D) IR spectra due to the same cluster anions and similar molecular structures, the two compounds exhibited distinct responses in two-dimensional correlation spectroscopy with IR under magnetic and thermal perturbations. Under magnetic perturbation, Compound 1 showed a strong response peak for νas(W-Ob-W), while Compound 2 exhibited a strong response peak for νas(W=Od), possibly linked to differing magnetic particles. Similarly, Compound 1 displayed a strong response peak under thermal perturbation for νas(W-Oc-W). In contrast, Compound 2 showed a strong response peak for νas(W=Od); these results may be attributed to the different hydrogen bonding connections between the two compounds, which affect the groups in distinct ways through vibration and transmit these vibrations to the W-O bonds. The research presented in this paper expands the theoretical and experimental data of 2D correlation IR spectroscopy.

Cu-doped NiO thin film's structural, optical, and electrical properties and its negative absorption behaviour in the Infra-Red region

NiO undoped and Cu-doped thin films on FTO-coated glass (fluorine-doped tin oxide) are prepared by employing the sol-gel spin coating method. The Cu-doping effect was observed in all the characterized reports such as absorption, transmittance, field emission scanning electron microscope (FESEM), Grazing Incidence X-ray Diffraction (GIXRD), photoluminescence (PL), Raman spectra, current-voltage measurement (IV), and X-ray photoelectron spectroscopy (XPS). Enhancement in electrical conductivity due to Cu doping and IR illumination has been found. Band gap can also be tuned by varying doping concentrations. One new phenomenon called negative absorption (NA) has been found while investigating the optical properties in the infrared (IR) region for both undoped and Cu-doped NiO on the FTO substrate, which opens a new door for advanced research. The multifarious properties of NiO thin films offer various applications in many different fields.

Physics-Informed Approximation of Internal Thermal History for Surface Deformation Predictions in Wire Arc Directed Energy Deposition

Abstract This work presents a physics-informed fusion methodology for deformation detection using multi-sensor thermal data. A challenge with additive manufacturing (AM) is that abnormalities commonly occur due to rapid changes in the thermal gradient. Different non-destructive in-situ thermal sensors capture parts of the thermal history but are limited by the visible temperature spectrum and sensor field of view of the fabrication process. Various sensors mitigate problems with the loss of thermal history information; however, it brings forth challenges with integrating different data streams and the need to interpolate the internal thermal history. This study develops a thermal data-informed heat flux methodology that fills the gap in fusing numerical temperature approximation with data-driven knowledge of the surface of additive manufactured components. First, this study fuses infrared (IR) thermal data complexities during the AM process with the Goldak double ellipsoidal heat flux to model the energy input into the component. Second, a thermal physics-informed model input (PIMI) is created with thermal data-informed heat flux to capture internal thermal history. Lastly, a regression convolutional neural network (CNN) captures the relationship between the three-dimensional thermal gradient and the resulting surface deformation. The rapid thermal gradient formation and identification of deformation is a key step toward using thermal history data and machine learning to improve quality control in AM. The proposed surface deformation detection model achieved an mean squared error of 1.14 mm and an R2 of 0.89 in the case study when fabricating thin-walled structures.

Biological and equilibrium studies of Co(II), Cu(II), Zn(II), and Cd(II) complexes of 1‐formyl‐3‐semicarbazide: Docking studies

1‐Formyl‐3‐semicarbazide (FSC, HL) and its metal complexes with Co(II), Cu(II), Zn(II), and Cd(II) ions have been synthesized and characterized by elemental analysis, liquid chromatography‐mass spectrometry (LC–MS), infrared (IR), electronic, nuclear magnetic resonance (NMR) and electron spin resonance (ESR) spectroscopy, thermogravimetric analysis (TGA), magnetic susceptibility, and conductivity measurements. The chelates are non‐electrolytic in nature with distorted octahedral geometry. The kinetic and thermodynamic properties were calculated using the Coats–Redfern relation results in positive enthalpy change values and negative entropy change values. The equilibrium studies of FSC with Co(II), Zn(II), and Cd(II) ion have been carried out by potentiometric pH titrations in 70% v/v DMF‐water medium at 303 K and 0.1 M (KNO3) ionic strength. The study revealed that FSC is monobasic acid with pKa value of 8.84. The stability constants suggested the formation of 1:1 Co(II)‐FSC complex, and Zn(II)‐FSC and Cd(II)‐FSC systems revealed the formation of both 1:1 and 1:2 complexes in the solution. DNA binding studies for the metal chelates have been carried out using electronic absorption spectra, fluorescence emission spectra, and viscosity measurements revealing groove binding for Co(II), and Zn(II) complexes, and intercalation mode of binding for Cu(II)‐FSC complex with CT‐DNA. The Kb values from absorption studies are Co(II)‐FSC = 0.9990 × 102, Cu(II)‐FSC = 2.433 × 104, and Zn(II)‐FSC = 8.277 × 102 M−1, and the KSV values from the competitive fluorescence emission studies are Co(II)‐FSC = 0.19212 and Cu(II)‐FSC = 0.11482 M−1. Molecular docking carried out for both ligand and its Co(II) and Zn(II) complexes also revealed groove mode of binding, and Cu(II) complex showed intercalative mode of binding. The inhibition constants for HL, Co(II), Cu(II), and Zn(II) are 1460, 0.478, 0.122, and 0.194 μM, respectively. The antimicrobial activity has been studied using agar disk diffusion method against Escherichia coli and Bacillus subtilis. FSC has been found to be more active against gram +ve and gram –ve bacteria than its metal chelates.

A theoretical study on the solvent effects on adsorption behavior of naproxen with PLGA nanoparticles

The objective of this research is to study the influence of naproxen (NPX) adsorption on structural, electronic, and optical features of poly (lactic-co-glycolic acid) (PLGA) in the dichloromethane (CH2Cl2), chloroform (CHCl3), and water (H2O) phases through density functional dispersion correction (DFT-D) calculations. The analyses conducted in the chloroform phase, considering binding energy and chemical reactivity parameters, indicate that NPX forms stronger hydrogen bonds with PLGA in state B (−0.60 eV) compared to states A (−0.37 eV) and C (−0.47 eV), primarily through its carboxyl (–COOH) group by using B3LYP-D/6–311 + G** level of theory. The formation of hydrogen bonds between naproxen and PLGA in the chloroform phase is most stable compared to the dichloromethane and water phases. According to time-dependent density functional theory (TDDFT) calculations, the B3LYP method predicts the maximum optical absorption in the UV region for complex B, with an optical energy of 5.41 eV and an oscillator strength of 0.781, resulting in a maximum absorption peak at 229 nm. Based on the infrared (IR) spectra analysis, we find alterations in pristine PLGA and NPX due to their interaction. The interaction between NPX and PLGA results in more negative Gibbs free energy (ΔG) values, which in turn lead to an elevation in dipole moment, enhanced solubility, and a decrease in the energy gap (Eg). As a result of NPX adsorption, the decreased energy gaps enhance the electronic and optical sensitivity of PLGA to the NPX molecule.

Synthesis, characterisation and voltammetric study of dimethylammonium lead iodide perovskite

In the last decade, the most investigated perovskite materials are the hybrid organic-inorganic perovskites (HOIPs) due to their optoelectronic properties and possible application in the production of photovoltaics. This interest has led to an ongoing search for new HOIP variants, alongside thorough investigations of the properties of existing HOIPs. That is why our research in the field of organic-inorganic perovskites is aimed at the synthesis, characterization, and investigation of the electrochemical properties of dimethylammonium lead iodide (DMAPbI3) using voltammetric studies. A modified synthesis of DMAPbI3, differing slightly from the one described in the literature, was performed by combining stoichiometric amounts of lead iodide (PbI2) and dimethylammonium iodide (DMAI) dissolved in acetonitrile. After conducting controlled evaporation, a yellow crystalline powder of DMAPbI3 was obtained. The identity and purity of the obtained compound were confirmed by powder X-ray diffraction (PXRD), infrared (IR) and Raman spectroscopy, and scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDX). Investigations on the electrochemical properties of DMAPbI3 by cyclic voltammetry were performed with dichloromethane (DCM) and tetrabutylammonium chloride (TBAC) as the electrolyte. A paraffin-impregnated graphite electrode (PIGE) was used as a working electrode, on which the perovskite microparticles were immobilized. The electrochemical activity of DMAPbI3 is recognized through an intense, broad, and irreversible anodic peak attributed to the oxidation of the constituents to different possible products and the decomposition of the perovskite structure.

Isolation and Identification of Flavonoid Compound from the Rambutan Stem Bark (Nephelium lappaceum L.)

Flavonoids derived from the stem barks of Rambutan (Nephelium Lappaceum L.) have been extracted. The extraction of Rambutan stem bark was performed by maceration using a methanol solvent. The concentrated methanol extract was diluted in ethyl acetate until the solution became devoid of all positive and flavonoid compounds. The highly concentrated ethyl acetate extract was subsequently dissolved using methanol and separated into different parts using an n-hexane. The methanol content was determined using thin-layer chromatography and separated using column chromatography using eluent chloroform: methanol in various ratios (90:10, 80:20, 70:30) v/v. The chemicals were purified using preparative thin-layer chromatography (TLC) and yielded 7.9 mg of amorphous solids with an Rf value of 0.25. The eluent was a chloroform and ethyl acetate mixture in a 50:50 volume-to-volume ratio. The substance was analyzed using Spectrophotometer Ultraviolet Visible (UV-Vis), Fourier Transform Infra Red Spectrophotometer (FT-IR), and Proton Nuclear Magnetic Resonancy Spectrophotometer (1H-NMR). The analysis identified the chemical as a flavonoid of the flavonol.

Preparation and Characterization of Ferrihydrite: Application in Arsenic Removal from Aqueous Solutions

Arsenic pollution is a public health hazard in Burkina Faso due to its impact on human health and water resources. To mitigate this pollution, ferrihydrite material has been synthesized and characterized to be used as adsorbent for arsenic removal in aqueous solutions. This study aimed to contribute to improve of access to clean drinking water by removing arsenic from water using ferrihydrite. Arsenic species such as As(III) and As(V) were removed through batch adsorption. Experiments were carried out in batch mode using arsenic aqueous solutions. The characterization of ferrihydrite using Scanning Electron Microscopy (SEM) coupled with Energy Dispersive Spectroscopy (EDX), X-ray Diffraction (XRD), Infrared (IR), and Brunauer Emmett Teller (BET) showed that an amorphous and microporous 2-line ferrihydrite. The total specific surface area and pH at point of zero charge (pHpzc) were 184.518 m²/g and 9.41, respectively. The optimal adsorbent doses were 4 g/L for As (V) and 8 g/L for As (III). The optimum pH range for the adsorption of As (V) and As (III) was between 2 and 10, The maximum adsorption capacity was 15.07 mg/g for As(V) and 13.01 mg/g for As(III) with increasing concentration between 2 and 16 mg/L. Equilibrium time for As (V) and As (III) on ferrihydrite was found to be 720 min and 960 min, respectively. The adsorption of As(V) and As(III) was consistent with the Langmuir monolayer model on ferrihydrite. Arsenic adsorption was occurred according to spontaneous chemical reaction. Arsenic removal was occurred on a monolayer following the pseudo-second order kinetic.

Expedient Bayesian prediction of subfossil bone protein content using portable ATR-FTIR data

Rapid and minimally destructive methods for estimating the endogenous organic content of subfossil bone save time, lab consumables, and valuable ancient materials. Fourier transform infrared (FTIR) spectroscopy is an established method to estimate bone protein content, and portable spectroscopes enable field applications. We review the ability of benchtop and portable FTIR indices to predict %N and %collagen from 137 bone specimens drawn from eight taxa. We also explore associations of these indices with the endogenous DNA content estimated for 105 specimens. Bulk bone elemental abundance and crystallinity index data reflect diagenetic alteration of these specimens, which come from a variety of depositional environments in four countries (Madagascar, Greece, Monaco, and Germany). Infrared (IR) indices from benchtop and portable units perform similarly well in predicting observed sample N content and collagen yields. Samples that include little collagen (0–5 wt%) tend to have similar IR index values, and we present a Bayesian approach for the prediction of collagen yields. Bone type best explains variation in target species DNA content (endogenous DNA being particularly abundant in petrosals), but low IR index values were consistently associated with minimal DNA content. We conclude that, although portable FTIR fails to distinguish collagen preservation among poorly preserved samples, a simple approach with minimal sample preparation can effectively screen bone from a variety of taxa, elements, and environments for the extraction of organics.

Exploring the scaling factors for infrared modes of PANHs - A case study on cationic 3-Azafluoranthene.+ and protonated 3-Azafluoranthene.

Infrared (IR) emission bands by interstellar Polycyclic Aromatic Hydrocarbons (PAHs) and Polycyclic Aromatic Nitrogen Heterocycles (PANHs) are observed towards a large variety of interstellar objects and offer detailed insights into the chemistry and physics of the interstellar medium. The analysis of the emission bands, and thus the interpretation of the molecular characteristics of the carriers, heavily relies on the use of density functional theory (DFT) calculated IR spectra. However, there are significant challenges in accurately predicting the experimental IR band positions, particularly for PANH emission vibrational modes around 6 mm. In this work, we present gas-phase mid-infrared (mid-IR) spectra of cationic 3-azafluoranthene (3AF.+) and protonated 3-azafluoranthene (3AFH+) to investigate their experimental IR band positions in relation to DFT calculated bands. The experimental spectra are compared to DFT simulated spectra, where different approaches were followed to correct for anharmonicities. The best agreement is achieved by scaling frequencies of modes with large nitrogen displacements with a different factor. Even though our findings might be limited to a small number of PANH structures, they indicate, that nitrogen atom incorporation needs to be accounted for by carefully adjusting the corresponding scaling factors while computing IR spectra of PANHs on DFT level.

Visible-infrared compatible and independent camouflage with multicolor patterns and tunable emissivity

Abstract With the rapid development and wide application of visible (VIS) and infrared (IR) detections, it is necessary to explore visible-infrared (VIS-IR) compatible camouflage. Here, we report a VIS-IR compatible and independent camouflage device which is composed of the upper IR-transparent VIS-color-patterned layer and the lower electrochromic IR layer. The upper layer has amorphous photonic structure of polystyrene nanospheres (PSNSs). By customizing the PSNS size, various colors can be realized for VIS camouflage. The lower electrochromic IR layer takes advantage of multiwall carbon nanotubes (MWCNTs) as the electrode as well as the IR active material. Experimental results reveal that different colors (including blue, green, and purple) have been obtained, and the IR emissivity can be electrically regulated from 0.43 to 0.9. Moreover, the prototype also exhibits good electrical stability as well as hydrophobic characteristic (the water contact angle of the outmost surface exceeds 120°). These output performances demonstrate the success of our design strategy for promoting the finding applied in camouflage fields as well as energy conservation fields.

Reductive Dynamic and Static Excited State Quenching of a Homoleptic Ruthenium Complex Bearing Aldehyde Groups.

A new homoleptic Ru polypyridyl complex bearing two aldehyde groups on each bipyridine ligand, [Ru(dab)3](PF6)2, where dab is 4,4'-dicarbaldehyde-2,2'-bipyridine, was synthesized, characterized, and utilized for iodide photo-oxidation studies. In acetonitrile (CH3CN) solution, the complex displayed an intense metal-to-ligand charge transfer (MLCT) absorbance maximum at 475 nm (ε = 22,000 M-1 cm-1) and an infrared (IR) band at 1712 cm-1 assigned to the pendent aldehyde groups. Visible light excitation in air-saturated solution resulted in room temperature photoluminescence (PL) with a maximum at 675 nm, a quantum yield, ϕPL = 0.048, and an excited state lifetime, το = 440 ns, from which radiative and nonradiative relaxation rate constants were extracted, kr = 9.1 × 104 s-1 and knr = 1.8 × 106 s-1. Pulsed visible light excitation yielded transient UV-vis and IR absorption spectra consistent with an MLCT excited state; relaxation occurred with the maintenance of two isosbestic points in the visible region, and a lifetime that agreed with that measured by time-resolved PL. Cyclic voltammetry studies in a CH3CN solution with 0.1 M TBAPF6 electrolyte revealed a quasi-reversible oxidation, E°(RuIII/II) = +1.25 V vs. Fc+/0, and three sequential one-electron reductions at -1.10, -1.25, and -1.54 V vs. Fc+/0. An excited state reduction potential of E°(Ru*2+/+) = +0.89 V vs. Fc+/0 was estimated with the Rehm-Weller expression. Titration of tetrabutylammonium iodide, TBAI, into a CD3CN solution of [Ru(dab)3](PF6)2 resulted in significant shifts in the aldehyde H atom and 3,3'-biypridyl resonances that were analyzed with a 1:1 equilibrium model, from which Keq = 460 M-1 was extracted, increasing to 5800 M-1 when the solvent was changed to acetone-d6. Iodide titrations resulted in a significant quenching of the [Ru(dab)3]*2+ lifetime and quantum yield in both CH3CN and acetone solvents. In CH3CN, the quenching was mainly dynamic and well described by the Stern-Volmer model, from which a quenching rate constant, kq, of 4.5 × 1010 M-1 s-1 and an equilibrium constant, Keq, of 8.3 × 103 M-1 were obtained. In acetone, the static quenching pathway by iodide was greatly enhanced, with a Keq of 1.2 × 104 M-1 and a higher kq of 9.2 × 1010 M-1 s-1.

ZnIn2S4-based multi-interface coupled photocatalyst for efficient photothermal synergistic catalytic hydrogen evolution

Photothermal synergistic catalysis is a novel technology that converts energy. In this study, ZnIn2S4 with S-vacancy (ZIS-Vs) is combined with Nickel, Nickle Oxide and Carbon Nanofiber aggregates (Ni-NiO@CNFs) to create a multi-interface coupled photocatalyst with double Schottky barrier, double channel and mixed photothermal conversion effect. Theoretical calculation confirms that the Gibbs free energy (ΔG*H) of the S-scheme heterojunction in the composite material is −0.07 eV, which is close to 0. This promotes the adsorption of H* and accelerates the formation of H2. Internal photothermal catalysis is achieved by visible-near infrared (Vis-NIR, RT) irradiation. The internal photothermal catalytic hydrogen production rate of the best sample (0.9Ni-NiO@CNFs/ZIS-Vs) is as high as 17.24 mmol·g−1·h−1, and its photothermal conversion efficiency (η) is as high as 61.42 %. Its hydrogen production efficiency is 20.52 times that of ZIS-Vs (0.84 mmol·g−1·h−1) under visible light (Vis, RT) conditions. When the Vis-NIR light source is combined with external heating (75 ℃), the hydrogen production efficiency is further improved, and the hydrogen production efficiency (29.16 mmol·g−1·h−1) is 26.75 times that of ZIS-Vs (1.09 mmol·g−1·h−1, Vis-NIR, RT). Further analysis shows that the increase in hydrogen production resulted from the apparent activation energy (Ea) of the catalyst decreasing from 16.7 kJ·mol−1 to 9.28 kJ·mol−1. This study provides a valuable prototype for the design of an efficient photothermal synergistic catalytic system.

Plasmonic metamaterial absorber for MWIR and LWIR bispectral microbolometers

Plasmonic metamaterial absorbers (PMAs) designed for multispectral imaging in the infrared (IR) with uncooled microbolometers are investigated. The study presents Fourier transform infrared spectroscopy (FTIR) measurements of PMAs consisting of metal-insulator-metal-stacks (MIM) with square-shaped micropatches as top metal layers. The measurements reveal high absorptances of 82% to 99% for distinct wavelengths within a range from 2 μm to 9.2 μm. The spectra are evaluated with respect to the lateral dimensions of the patches and to the refractive indices of the used dielectrics SiO2, Al2O3 and Ta2O5. Numerical simulations and analytical calculations of the TM010-mode using the transmission line model (TLM) for microstrip antennas show good qualitative agreement with the measurement results. Additionally, bispectral PMAs were fabricated consisting of fields of PMAs with two different patch sizes arranged in a chessboard pattern. The individual fields of this pattern correspond to microbolometers with 12 μm pitch in shape and size. Two distinct absorption maxima can be seen in the spectra measured by FTIR. The choice of materials, deposition methods and patterning processes is suitable for the integration into the existing Fraunhofer IMS's nanotube microbolometer technology to realize multispectral infrared imaging. The fabrication process is CMOS-compatible and carried out on 8-in. wafers.