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Scaling Relations of Plasmon Resonance Peak in Au@Fe3O4 Core-Shell Nanohybrids Structure
摘要： In this paper, we study the absorption efficiency spectra of Au nanoparticles enveloped with Fe3O4 nanoshell by applying the discrete dipole approximation method. Three kinds of Au@Fe3O4 core-shell nanohybrids (NHs) structure, including the same core with different shell thickness, the same outer shell with different core radius, and the same size of total radius, have been discussed in detail. The simulation results show that the square of localized surface plasmon resonance (LSPR) peak wavelength of NHs is linearly proportional with the volume fraction of the shell, regardless of the outer shell material properties. Compared to the plasmon resonance peak of the Au nanoparticles, the LSPR shift of the NHs is dependent on both the total particles size and the outer Fe3O4 shell thickness. Our calculation results would provide some key guidances to design the structure variables of NHs for a broad range of plasmon applications.
关键词： Nanohybrids,Discrete dipole approximation,Absorption efficiency
更新于2025-09-23 15:23:52
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Artifacts in Transient Absorption Measurements of Perovskite Films Induced by Transient Reflection from Morphological Microstructures
摘要： Organolead halide perovskites MAPbX3 (MA = CH3NH3+; X = Cl?, Br?, I?) have attracted broad tremendous interest in the past 10 years for applications in solar cells and light-emitting devices. In evaluating the quality of the perovskite materials, spectroscopic characterizations such as static and time-resolved absorption and photoluminescence measurements are essential to examine their photophysical properties. A recent report found that the correct measurement of static absorption spectra of MAPbX3 films is indeed difficult due to the strong light scattering caused by their poor surface coverage or complex microstructures. These morphological complexities seem to be inevitable in thin-film fabrication and should not only affect the steady-state spectroscopic measurements but also can significantly impact the time-resolved spectroscopic characterizations, whose results are crucial for understanding photoinduced carrier dynamics in the examined materials. Photoexcited states in semiconductor materials induce changes in the real and imaginary parts of the dielectric function. This leads to changes in absorption (imaginary part) and reflectivity (real part), which can be substantial for materials with significant values of refractive index such as lead halide perovskites. Transient absorption (TA) spectroscopy is a typical technique that has been broadly used to probe photoexcited state dynamics in perovskites and other semiconductor materials. In TA measurements, a pump laser pulse is used to excite the perovskite films, and the induced absorption changes (ΔA) are recorded as a function of both wavelength and time. With the transmitted light as the probe (Figure 1a), the TA signal (ΔA) is mainly decided by the ratio of the intensity of transmitted probe light with and without pump excitation (see eq S1 in the SI), assuming that the loss of transmitted probe light completely results from the sample absorption. On the basis of the same experimental setup, transient reflection (TR) measurements can also be carried out by using the reflected probe light as detection signal (Figure 1b). The TR signal (ΔR/R) can also be determined by the ratio of the intensity of reflected probe light with and without pump excitation (see eq S4 in the SI). Unlike the TA measurements that mainly probe the bulk property of samples, the TR signal mainly detects the photoinduced reflection variations due to the refractive index change at the sample surface. Therefore, the TR spectrum and kinetics can be significantly different from those of TA even in the same sample. For example, previous TA and TR measurements have found dramatically faster carrier recombination kinetics on the surface than in the bulk of MAPbX3 perovskite films or single crystals because of the presence of more surface defects. There is an abnormal case in the regular TA measurements particularly when performed on the films with large and heterogeneous microstructures (e.g., films with poor coverage, large grains, and pinholes) because the loss of transmitted probe light in their TA measurements likely results not only from the sample absorption but also from the reflection of the film surface or the boundary of microstructures in samples. In this case, the measured transient spectrum, though collected in the transmittance mode as in TA, can contain contributions from both TA and TR signals (see Figure 1c and eq S6 in the SI). This could lead to distorted TA spectra and thus inaccurate analysis of photoinduced kinetics. A solution-processed organic or inorganic halide perovskite thin film is a typical material whose morphological microstructures were found to have significant impact on device performance. Although the photoinduced carrier dynamics in perovskite films has been extensively studied using TA spectroscopy, the possible artifacts in TA results induced by TR signal originating from the photoinduced reflectivity variation of film surfaces and microstructures have been overlooked. Herein, in order to clarify the influence of TR signal in the regular TA measurements, we performed a careful transient spectroscopic analysis on a series of MAPbBr3 perovskite films with different microstructure morphology. Meanwhile, TR measurements on MAPbBr3 single crystals (SCs) were carried out for comparison. We confirmed that the TA spectra measured in MAPbBr3 perovskite films with large and heterogeneous microstructures do comprise non-negligible TR signals from the photoinduced reflection of microstructures, with the weight of contribution increased from ～20 to ～100% as the size of the microstructure increased from <200 nm to 1?2 μm. The presence of TR signal leads to an “artifact” feature in the TA spectra and faster observed kinetics owing to the faster surface carrier recombination, which will thus mislead the analysis of bulk carrier dynamics. We also provided a method to reduce the TR signal in actual TA measurements by adding solvent with its refractive index close to the samples, by which the TR distortion can be suppressed to some extent.
关键词： artifacts,transient reflection,transient absorption,carrier dynamics,perovskite films,microstructures
更新于2025-09-23 15:23:52
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Theoretical model of absorption coefficient of an inhomogeneous MPP absorber with multi-cavity depths
摘要： Micro-perforated panel (MPP) absorber has been known as an alternative absorber to classical porous material given its facile installation, long durability, environmental friendliness and attractive appearance. Extensive studies of MPP absorber proposing the improvement of its absorption frequency bandwidth have been published. This study presents a MPP absorber introduced with inhomogeneous perforations and with multi-cavity depths. The MPP is divided into two sub-area, where each area has different hole diameter, perforation ratio and a separated backed cavity depth. The acoustic impedance is modelled using electrical equivalent circuit and the absorption coefficient is calculated under normal-incidence of sound. It is found that the inhomogeneous MPP can have good bandwidth of absorption by designing the sub-MPP of smaller perforation ratio with large hole diameter and the one having the larger perforation ratio with smaller hole diameter. The absorption bandwidth can be conveniently controlled by adjusting the cavity depth of each sub-MPP. The results from the experimental work show good agreement with the theoretical model.
关键词： Micro-perforated panel,Inhomogeneous MPP,Absorption coefficient,Acoustics
更新于2025-09-23 15:23:52
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Non-destructive inspection of food and technical oils by terahertz spectroscopy
摘要： Quality control and non-destructive monitoring are of notable interest of food and pharmaceutical industries. It relies on the ability of non-invasive inspection which can be employed for manufacturing process control. We hereby apply terahertz (THz) time-domain spectroscopy as non-destructive technique to monitor pure and degraded oils as well as hydrocarbon chemicals. Significant differences in the spectra of refractive index (RI) and absorption coefficient arising from the presence of ester linkages in the edible and technical oils were obtained. Explicit increase from 1.38 to 1.5 of the RI in all THz spectrum range was observed in hydrocarbons and mono-functional esters with the increase of molar mass. This fact is in contrast of RI dependence on molar mass in multi-functional esters, such as Adipate or vegetable oils, where it is around 1.54. Degradation products, Oleic Acid (OA) and water in particular, lead only to some changes in absorption coefficient and RI spectra of vegetable oils. We demonstrate that complex colloidal and supramolecular processes, such as dynamics of inverse micelles and oil hydrolysis, take part during oil degradation and are responsible for non-uniform dependence of optical properties on extent of degradation.
关键词： absorption coefficient,terahertz spectroscopy,oils,degradation,non-destructive inspection,refractive index
更新于2025-09-23 15:23:52
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Interpretation of linear dichroism at S L2,3 x-ray absorption edges of small organic molecules at surfaces
摘要： Resonant soft x-ray absorption was applied at the S L2,3 (2p) edges of thin films of 1,4-benzenedimethanethiol (BDMT) on gold and of sexithiophene (6 T) on flat and patterned CaF2 surfaces. Linear dichroism effects were clearly observed depending on the orientation of the electric field vector of the incoming radiation. They were related to the organization of the molecules. For the interpretation of the angular dependencies of the spectral features, density functional theory (DFT) simulations of the absorption cross sections were calculated. It was possible to confirm the generally accepted chemisorption geometry of BDMT on Au(111), composed of molecules nearly vertical at the surface with one of the S atoms participating in the bonding with Au and the other left pending at the outermost surface and contributing mostly to the measured x-ray absorption. For 6 T on CaF2 a new chemisorption phase was identified on ridge-patterned CaF2(110), coexisting with a previously known phase given by 6 T crystallites highly oriented along the ridges. The new phase being composed of molecules oriented perpendicular to the ridges and lying on their edges.
关键词： Organic thin films,X-ray absorption,Sulphur
更新于2025-09-23 15:23:52
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Cobalt doping-induced strong electromagnetic wave absorption in SiC nanowires
摘要： Understanding the electronic structure-property relationship in doped systems is a prerequisite to designing functional materials. We fabricated Co-doped SiC nanowires with different Co contents by a facile carbothermal reduction approach. The nanowires were characterized in terms of microstructure, electronic structure, and electromagnetic (EM) parameters to uncover the effect of Co dopants on enhancing the EM wave absorption ability. Microstructure analysis and density functional theory calculations verified that the doped Co species inhibited the formation of stacking faults and point defects and increased the conductivity of Co-doped SiC nanowires, which indicated the dominant role of conductivity in enhancing dielectric loss. The Co dopants also imparted the Co-doped SiC nanowires with distinct room-temperature ferromagnetic property, which led to enhanced magnetic loss and impedance matching. The induced synergism among SiC nanowires and Co dopants endowed Co-doped SiC nanowires with strong EM wave absorption ability. The minimum reflection loss of Co-doped SiC nanowires reaches (cid:1)50 dB, and the effective absorption bandwidth is 4.0 GHz with only 1.5 mm sample thickness. Thus, Co-doped SiC nanowires can be used as effective EM wave absorption materials. This study also provided a guideline for designing high-performance EM wave absorbers.
关键词： Dielectric loss,Doping,Density functional theory calculations,Electromagnetic wave absorption,Magnetic property
更新于2025-09-23 15:23:52
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Facile strategy for controllable synthesis of hierarchical hollow MoS2 microspheres with enhanced photocatalytic properties
摘要： Tailored design of photocatalysts with complicated hollow structures is of great importance for promoting environmental remediation. In this paper, monodispersed hierarchical hollow MoS2 microspheres have been prepared via a facile and economical hydrothermal method with the assistance of surfactant (polyethylene-polypropylene glycol (F68)). The unusual design displays three important features: large specific surface area, strong light absorption, and rich catalytic active sites. The specific surface area of the hierarchical hollow MoS2 microspheres is 21.75 m2g-1, which is higher than that of MoS2 particles (4.05 m2g-1) and commercial MoS2 (2.84 m2g-1). Meanwhile, the hierarchical hollow MoS2 microspheres possess strong light absorption around a broadband wavelength from 200 nm to 800 nm. Furthermore, the ordered MoS2 nanosheets which assemble to the outer surface of the hierarchical hollow MoS2 microspheres display rich catalytic active sites, which are beneficial in promoting the fast transport of charge carriers during the process of photocatalytic reaction. As a result, the photodegradation activity test demonstrates that the hierarchical hollow MoS2 microspheres exhibit excellent photocatalytic activity and recycling stability. The reaction rate constant of the hierarchical hollow MoS2 microspheres for the photodegradation of RhB is 25.32 and 18.18 times faster than that of MoS2 particles and commercial MoS2, respectively.
关键词： Unusual design,Photocatalysts,MoS2,Rich catalytic sites,Large surface area,Broadband absorption
更新于2025-09-23 15:23:52
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Band structure and optical constants of SnS <sub/>2</sub> single crystals
摘要： Absorption (K), reflection (R) and wavelength modulated transmission (ΔT/Δλ) spectra in SnS2 crystals of hexagonal phase (space group P63/mmc) were investigated in temperature interval from 300 to 10 K. It was established that indirect band gap (Eg ind - 2.403 eV) is due to unpolarized indirect transitions between Γ and M points of Brillouin zone. A minimal direct band gap (Eg dir - 2.623 eV) in E||b polarization is formed by direct allowed transitions and in E⊥b polarization (2.698 eV) by forbidden transitions in Γ point of Brillouin zone. A magnitude of refractive index (n) changes from 3 to 4 and has a maximum at 2.6 eV. Optical functions (n, k, ε1 and ε2) in energy region E > Eg (3 - 6.5 eV) were calculated from measured reflection spectra by Kramers-Kronig analysis. Features observed in reflection and optical function spectra were assigned to electron transitions. This electron transitions were localized in framework of theoretically calculated band structure.
关键词： optical functions,electronic band structure,layered SnS2 crystals,absorption, reflection and transmission spectra
更新于2025-09-23 15:23:52
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Incoherent Gain-Assisted Ring Enhanced Gas Absorption Spectroscopy
摘要： A novel incoherent gain-assisted ring enhanced spectroscopy technique is presented overcoming the need for precise optical alignment and high reflectivity dielectric mirrors. A gain medium pumped below the lasing threshold is used to improve the ring finesse and, thus, the interaction length. Two configurations are considered and compared. The first configuration is dual coupler ring with the source outside the ring and the gain medium inside the ring, while the second configuration is single coupler resonator with the gain medium acting as the source. The configurations are studied analytically and experimentally for different system parameters. The experimental results are obtained for a coupling ratio of 90/10. The broadband source is the amplified spontaneous emission of a semiconductor optical amplifier (SOA), while another SOA is used as the gain medium. Acetylene (C2H2) gas absorption is measured around 1540 nm wavelength. The output spectrum of the ring is measured using a 70 pm resolution. The interaction length is found to be enhanced by a factor of 9.35 and 44 in case of the dual coupler and single coupler resonator, respectively, compared to the direct absorption of the gas cell.
关键词： Gas spectroscopy,effective length enhancement,fiber sensors,finesse enhancement,incoherent broadband cavity enhanced absorption spectroscopy (IBBCEAS),active fiber cavities
更新于2025-09-23 15:23:52
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Tunable white-light emission from Pr3+/Dy3+ co-doped B2O3 - TeO2 PbO - ZnO Li2O - Na2O glasses
摘要： In this paper, structural and optical analysis of boro-tellurite based glasses co-doped with Dy3+ and Pr3+ ions has been carried out. The glasses were fabricated by traditional melt quenching technique. XRD results confirm the amorphous-like nature of the glasses. FTIR spectroscopy was applied to explore the functional groups and interactions for the samples. The transition temperatures of glasses were identified by TGA/DSC analysis. Optical absorption and emission spectra of all the glasses have been recorded in the UVe Vis- NIR spectral range. Tauc's method was applied to determine the direct and indirect optical band gaps. Luminescence spectra show intense emission bands at ～482 nm and ～574 nm wavelengths under λexc = 388 nm corresponding to Dy3+: 4F9/2 → 6H15/2 and 4F9/2 → 6H13/2 transitions. Decay time data revealed the occurrence of a non-radiative energy transfer from Dy3+ to Pr3+ ions. Intense emission bands are identified at ～602 nm (orange), ～487 nm (blue) and ～574 nm (yellow) observed upon λexc = 437 nm, corresponding to Pr3+:1D2→3H4, Pr3+:3P0,1,2 → 3H4/Dy3+: 4F9/2 → 6H13/2 and Dy3+: 4F9/2 → 6H13/2 transitions, respectively, where the Dy3+ emissions are due to energy transfer from Pr3+ to Dy3+ ions. The CIE chromaticity results confirm that different colors can be generated by tuning the exciting wavelength, where all the glasses are capable to emit white light under λexc = 388 nm, while at λexc = 437 nm the samples (S2eS4) emit reddish orange light. Accordingly, it is plausible to suggest these glasses for white LED and SSL applications.
关键词： Optical absorption,Photoluminescence,W-LEDs,Raman spectroscopy,Borotellurite glass,Energy transfer
更新于2025-09-23 15:23:52