Near-ultraviolet Incoherent Broadband Cavity Enhanced Absorption Spectroscopy for OCIO and CH20 in Cl-initiated Photooxidation Experiment

Chlorine dioxide （OC10） is an important indicator for Cl-activation. The monitoring of OC10 appears to be crucial for understanding the chemistry of Cl-initialed oxidation and its impact on air quality in polluted coastal regions and industrialized areas. We report the development of a Xe arc lamp based near-ultraviolet （335-375 nm） incoherent broad- band cavity enhanced absorption spectroscopy （IBBCEAS） spectrometer for quantitative assessment of OC10 in an atmospheric simulation chamber. The important intermediate compound CH20, and other key atmospheric trace species （NO2） were also simultaneously measured. The instrumental performance shows a strong potential of this kind of IBBCEAS instrument for field and laboratory studies of atmospheric halogen chemistry.

Deposition of hexagonal boron nitride thin films on silver nanoparticle substrates and surface enhanced infrared absorption

Silver nanoparticle thin films with different average particle diameters are grown on silicon substrates. Boron nitride thin films are then deposited on the silver nanoparticle interlayers by radio frequency （RF） magnetron sputtering. The boron nitride thin films are characterized by Fourier transform infrared spectra. The average particle diameters of silver nanoparticle thin films are 126.6, 78.4, and 178.8 nm. The results show that the sizes of the silver nanoparticles have effects on the intensities of infrared spectra of boron nitride thin films. An enhanced infrared absorption is detected for boron nitride thin film grown on silver nanoparticle thin film. This result is helpful to study the growth mechanism of boron nitride thin film.

Experimental Study on Enhancement of Bubble Absorption of Gaseous CO2 with Nanofluids in Ammonia

In order to study the effects of nanoparticles on the CO_2 absorption in ammonia,nanofluids with different ammonia concentration and different nanoparticle solid loading were prepared by a two-step method.The nanofluids-enhanced gas absorption test devices were also established. The CO_2 absorption in TiO_2,CuO,SiO_2 nanofluids,which nanoparticles solid loading were 1. 0-8. 0 g/L,was tested respectively. In comparison with the blank absorption experiment,the effects of nanoparticle solid loading,nanoparticle types,ammonia concentration on the removal efficiency and removal rate were obtained. Experimental results show that adding nanoparticles can enhance the removal efficiency and removal rate,which increase first and then decrease with the increase of nanoparticle solid loading,and there exists an optimum solid loading of TiO_2 nanoparticles. The effect of SiO_2 nanofluid is inhibitory on the reaction. The enhancement factor of CuO nanofluid is always hovering around 1,which does not show the obvious enhancement or inhibition on the reaction. The optimum solid loading decreases gradually with the increase of ammonia concentration. In addition,according to the experimental results,the mechanism of enhanced absorption was analyzed theoretically.

Optical Frequency Comb-Based Cavity-Enhanced Fourier-Transform Spectroscopy:Application to Collisional Line-Shape Study

Direct-comb spectroscopy techniques uses optical frequency combs(OFCs)as spectroscopic light source.They deliver high sensitivity,high frequency resolution and precision in a broad spectral range.Due to these features,the field has burgeoned in recent years.In this work we constructed an OFC-based cavity-enhanced Fourier-transform spectrometer in the nearinfrared region and used it for a line-shape study of rovibrational transitions of CO perturbed by Ar.The highly sensitive measurements spanned the wavenumber range from 6270 cm^-1 to 6410 cm^-1,which covered both P and R branch of the second overtone band of CO.The spectrometer delivers high-resolution surpassing the Fourier-transform resolution limit determined by interferogram length,successfully removing ringing and broadening effects caused by instrumental line shape function.The instrumental-line-shape-free method and high signal-to-noise ratio in the measurement allowed us to observe collisional effects beyond those described by the Voigt profile.We retrieved collisional line-shape parameters by fitting the speed-dependent Voigt profile and found good agreement with the values given by precise cavity ring-down spectroscopy measurements that used a continuous-wave laser referenced to a stabilized OFC.The results demonstrate that OFC-based cavity-enhanced Fouriertransform spectroscopy is a strong tool for accurate line-shape studies that will be crucial for future spectral databases.

Experimental and Theoretical Studies of CO2 Absorption Enhancement by Nano-Al203 and Carbon Nanotube Particles

The influence of nano-particles on CO2 absorption was studied experimentally in a stirred thermostatic reactor. Nano-A1203 and carbon nanotube （CNT） particles which showed different hydrophobic properties were chosen for the investigation. The experimental results were compared with that of micron-size activated carbon （AC） and Al2O3 particles. From the results, no enhancement by micron-size A1203 was found, and with the increase of A1203 concentration, the enhancement factor decreased. However, nano-Al203 showed a weak enlaancement tor me COz absorption. AC and CNT particles all intensified the gas-liquid mass transfer effectively, yet the trend of the enhancement factor with stirring speed for the two particles was different. With increasing stirring speed, the enhancement factor of AC particles was decreased, wl＇iereas in CNT suspensions it was increased. The experimental phenomena demonstrated a difference in enhancement mechanism for different size particles. For nano-particles, besides the influence of adsorbability and hydrophobicity, the micro-convection caused by Brownian motion should be also taken into account. Considering the micro-convection effect, a theoretical model was developed to shed light on the absorption enhancement bv nano-oarticles.

The Effect of Hydrophobic Modification of Zeolites on CO2 Absorption Enhancement

Two methods of the modification of zeolite were employed： framework element modification and surface coating, and the influence of the zeolites before and after modification on the CO2 absorption was investigated. It was found that although hydrophobicity of zeolite could be obtained by means of the surficial organic coating in the method of surface coating _mod!fication, partial channel of zeolite would be plugged, as a result, leading to the surface area reducing greatly. Distinctively, the framework element modification method could maintain not only complete lattice structure and adsorption capability of zeolite, but would also obtain a good hydrophobic property. Consequently, significant enhancement on gas absorption by this modified zeolite was achieved and up to a maximum enhancement factor of 2.62. This shows that the solid particles with good enhancement role to gas absorption need not only good adsorptive capability but also certain hydrophobicity. An unsteady heterogeneous model was employed to predict enhancement factor and the calculated results agree well with the experimental data.

Design of periodic metal-insulator-metal waveguide back structures for the enhancement of light absorption in thin-film solar cells

To increase the absorption in a thin layer of absorbing material （amorphous silicon, a-Si）, a light trapping design is presented. The designed structure incorporates periodic metal-insulator-metal waveguides to enhance the optical path length of light within the solar cells. The new design can result in broadband optical absorption enhancement not only for transverse magnetic （TM）-polarized light, but also for transverse electric （TE）-polarized light. No plasmonic modes can be excited in TE-polarization, but because of the coupling into the a-Si planar waveguide guiding modes and the diffraction of light by the bottom periodic structures into higher diffraction orders, the total absorption in the active region is also increased. The results from rigorous coupled wave analysis show that the overall optical absorption in the active layer can be greatly enhanced by up to 40%. The designed structures presented in this paper can be integrated with back contact technology to potentially produce high-efficiency thin-film solar cell devices.

Sound Absorption Enhancement by Thin Multi-Slit Hybrid Structures

We report an extraordinary sound absorption enhancement in low and intermediate frequencies achieved by a thin multi-slit hybrid structure formed by incorporating micrometer scale micro-slits into a sub-millimeter scale meso-slit matrix. Theoretical and numerical results reveal that this exotic phenomenon is attributed to the noticeable velocity and temperature gradients induced at the junctures of the micro- and meso-slits, which cause significant loss of sound energy as a result of viscous and thermal effects. It is demonstrated that the proposed thin multi-slit hybrid structure with micro-scale configuration is capable of controling low frequency noise with large wavelength, which is attractive for applications where the size and weight of a sound absorber are restricted.

Optical Absorption Enhancement Effects of Silver Nanodisk Arrays in the Application of Silicon Solar Cell

Surface plasmon resonance of noble metal nanoparticles leads to the optical absorption enhancement effects,which have great potential applications in solar cell.By using the general numerical method of discrete dipole approximation （DDA）,we study the absorption and scattering properties of two-dimensional square silver nanodisks （2D SSN） arrays on the single crystal silicon solar cell.Based on the effective reflective index model of the single crystal silicon solar cell,we investigate the optical enhancement absorption of light energy by varying the light incident direction,particle size,aspect ratio,and interparticle spacing of the silver nanodisks.The peak values and position of the optical extinction spectra of the 2D square arrays of noble metal nanodisks are obtained with the different array structures.

Soybean Lecithin Acts as both Absorption Enhancer and Oily Phase in an Insulin-loaded Emulsion System for Transmucosal Delivery

An insulin-loaded emulsion system （IES） was developed as a hypoglycaemic drug for transmucosal delivery. The selected formulation was a stable oil/water emulsion system. The particles in the emulsion system were distributed evenly, and the particle size ranged from 20 to 260 nm（ average size ： 67.5 nm ）. Soybean lecithin played an important role in the emulsion system due to its abilities of acting as both absorption enhancer for insulin uptake through sublingual mucosa and oily phase for the emulsion system. The laser confocal scanning microscopic（LCSM） study showed that FITC-labelled insulin could penetrate the sublingual mucosa of rabbits, and the phase diagrams of the emulsion system suggested that soybean lecithin could take the place of oily phase to construct a stable emulsion system even if the traditional oil was absent. The applications of soybean lecithin as pharmaceutical biomaterial were extended for the further usage by present studies.

Broadband absorption enhancement with ultrathin MoS2 film in the visible regime

The broadband absorption enhancement effect in ultrathin molybdenum disulfide(Mo S2)films is investigated.It is achieved by inserting the Mo S2 film between a dielectric film and a one-dimensional silver grating backed with a silver mirror.The broadband absorption enhancement in the visible region is achieved,which exhibits large integrated absorption and short-circuit current density for solar energy under normal incidence.The optical properties of the proposed absorber are found to be superior to those of a reference planar structure,which makes the proposed structure advantageous for practical photovoltaic application.Moreover,the integrated absorption and short-circuit current density can be maintained high for a wide range of incident angles.A qualitative understanding of such broadband absorption enhancement effect is examined by illustrating the electromagnetic field distribution at some selected wavelengths.The results pave the way for developing high-performance optoelectronic devices,such as solar cells,photodetectors,and modulators.

Simulation of Intermediate State Absorption Enhancement in Rare-Earth Ions by Polarization Modulated Femtosecond Laser Field

We extend the third perturbation theory to study the polarization control behavior of the intermediate state absorption in Nd^（3＋）ions. The results show that coherent interference can occur between the single-photon and three-photon excitation pathways, and depends on the central frequency of the femtosecond laser field. Moreover,single-photon and three-photon absorptions have different polarization control efficiencies, and the relative weight of three-photon absorption in the whole excitation processes can increase with increasing the laser intensity.Therefore, the enhancement or suppression of the intermediate state absorption can be realized and manipulated by properly designing the intensity and central frequency of the polarization modulated femtosecond laser field.This research can not only enrich theoretical research methods for the up-conversion luminescence manipulation of rare-earth ions, but also can provide a clear physical picture for understanding and controlling multi-photon absorption in a multiple energy level system.

Coherent Features of Resonance-Mediated Two-Photon Absorption Enhancement by Varying the Energy Level Structure,Laser Spectrum Bandwidth and Central Frequency

The femtosecond pulse shaping technique has been shown to be an effective method to control the multi-photon absorption by the light–matter interaction. Previous studies mainly focused on the quantum coherent control of the multi-photon absorption by the phase, amplitude and polarization modulation, but the coherent features of the multi-photon absorption depending on the energy level structure, the laser spectrum bandwidth and laser central frequency still lack in-depth systematic research. In this work, we further explore the coherent features of the resonance-mediated two-photon absorption in a rubidium atom by varying the energy level structure, spectrum bandwidth and central frequency of the femtosecond laser field. The theoretical results show that the change of the intermediate state detuning can effectively influence the enhancement of the near-resonant part, which further affects the transform-limited （TL）-normalized final state population maximum. Moreover, as the laser spectrum bandwidth increases, the TL-normalized final state population maximum can be effectively enhanced due to the increase of the enhancement in the near-resonant part, but the TL-normalized final state population maximum is constant by varying the laser central frequency. These studies can provide a clear physical picture for understanding the coherent features of the resonance-mediated two-photon absorption, and can also provide a theoretical guidance for the future applications.

Advanced modeling of the absorption enhancement of black carbon particles in chamber experiments by considering the morphology and coating thickness

Measurements studies have shown that the absorption of radiation by black carbon(BC)increases as the particles age.However,there are significant discrepancies between the measured and modeled absorption enhancement(E_(abs)),largely due to the simplifications used in modeling the mixing states and shape diversities.We took advantage of chamber experiments on BC aging and developed an efficient method to resolve the particle shape based on the relationship between the coating fraction(ΔD_(ve)/D_(ve),0)and fractal dimension(D_(f)),which can also reflect the variations of D_(f)during the whole BC aging process.BC with externally and partly mixed states(0≤ΔD_(ve)/D_(ve),0≤0.5)can be considered to be uniformly distributed with the D_(f)values of 1.8–2.1,whereas the Df values are constrained in the range 2.2–2.8 for fully mixed states(ΔD_(ve)/D_(ve),0>0.5).The morphological parameters(i.e.,the effective density and the dynamic shape factor)were compared with the measured values to verify the simulated morphology.The simulated mean deviations of morphological parameters were smaller than 8%for the method resolving the particle shape.By applying a realistic shape and refractive index,the mass absorption cross for fully mixed states can be improved by 11%compared with a simplified core–shell model.Based on our understanding of the influence of D_(f)andΔD_(ve)/D_(ve),0 on E_(abs),we propose a two-stage calibration equation to correct the E_(abs)values estimated by the core–shell model,which reduces the simulation error in the Mie calculation by 6%–14%.

Composition Optimization and Microstructure Design in MOFs-Derived Magnetic Carbon-Based Microwave Absorbers:A Review

Magnetic carbon-based composites are the most attractive candidates for electromagnetic(EM)absorption because they can terminate the propagation of surplus EM waves in space by interacting with both electric and magnetic branches.Metal-organic frameworks(MOFs)have demonstrated their great potential as sacrificing precursors of magnetic metals/carbon composites,because they provide a good platform to achieve high dispersion of magnetic nanoparticles in carbon matrix.Nevertheless,the chemical composition and microstructure of these composites are always highly dependent on their precursors and cannot promise an optimal EM state favorable for EM absorption,which more or less discount the superiority of MOFs-derived strategy.It is hence of great importance to develop some accompanied methods that can regulate EM properties of MOFs-derived magnetic carbon-based composites e ectively.This review comprehensively introduces recent advancements on EM absorption enhancement in MOFs-derived magnetic carbon-based composites and some available strategies therein.In addition,some challenges and prospects are also proposed to indicate the pending issues on performance breakthrough and mechanism exploration in the related field.

Seasonal variations of mass absorption efficiency of elemental carbon in PM_(2.5) in urban Guangzhou of South China

This study investigates seasonal variations of mass absorption efficiency of elemental carbon(MAE_(EC))and possible influencing factors in urban Guangzhou of South China.Mass concentrations of elemental carbon(EC)and organic carbon(OC)in PM_(2.5) and aerosol absorption coefficient(b_(ap))at multi-wavelengths were simultaneously measured in four seasons of 2018-2019 at hourly resolution by a semi-continuous carbon analyzer and an aethalometer.Seasonal average mass concentrations of EC were in the range of 1.36-1.70μgC/m^(3) with a lower value in summer than in the other seasons,while those of OC were in the range of 4.70–6.49μgC/m^(3) with the lowest value in summer and the highest in autumn.Vehicle exhaust from local traffic was identified to be the predominant source of carbonaceous aerosols.The average aerosol absorption Angstrom exponents(AAE)were lower than 1.2 in four seasons,indicating EC and b_(ap) were closely related with vehicle exhaust.Seasonal MAE EC at 550 nm was 11.0,8.5,10.4 and 11.3 m^(2)/g in spring,summer,autumn,and winter,respectively.High MAE EC was related with the high mass ratio of non-carbonaceous aerosols to EC and high ambient relative humidity.

Enhanced optical absorption in semiconductor nano- particles enabled by nearfield dielectric scattering

The optical absorption of semiconducting AgBr nanocubes is significantly increased by up to 5 times in the measured spectral range when they are bonded to the surface of dielectric SiO2 nanospheres through electrostatic interaction. The absorption enhancement factor depends on the wavelength and the size of the SiO2 nanoparticles （NPs）. Finite-difference time-domain calculations provide the nearfield intensity mapping of a heterostructure that is composed of a AgBr nanocube in close contact with a SiO2 nanosphere. The electric-field distributions indicate the field enhancement near the SiO2/AgBr interface due to light scattering and absorption enhancement in the AgBr nanocube, implying that the enhanced scattering nearfield increases the absorption cross section of the AgBr nanocube. The absorption cross-section spectra calculated using Mie theory agree with the experimental observations. This discovery sheds light on the utilization of dielectric spherical particles to increase the absorption in semiconductor NPs, thus improving the light-harvesting efficiency for solar-energy conversion.

A new strategy of enhancing absorptivity and safety for evodiamine: polyamidoamine derivatives modified by polyethylene glycol chain

Background:Traditional Chinese medicine involves complex ingredients and mixtures of ingredients that often exhibit low bioavailability,and excipients are often lacking to increase the absorption-enhancing effects.This study modified the generation 4 polyamidoamine dendrimer with polyethylene glycol of different molecular weights(5000,2000,1000)to form a series of polyamidoamine-co-polyethylene glycol(PAMAM-co-PEG)as a novel class of oral absorption enhancers.Evodiamine,the major alkaloid found in the traditional Chinese medicine Wu Zhu Yu(Fructus Evodiae),was used as a model drug to verify the absorption-enhancing effects and the safety of this alkaloid.Methods:This study utilized the solubility determination method documented in the Pharmacopoeia of the People’s Republic of China(2015 edition)and the D0 values recommended in the US FDA guidelines to comprehensively evaluate the solubility of evodiamine.The permeability of evodiamine was assessed using the apparent permeability coefficient in experiments based on in vitro cell models.Multiple aspects of the biological safety of PAMAM-co-PEG were explored using the MTT assay,LDH assay,and total protein release of the rat intestinal tract.Moreover,the absorption-enhancing effects of PAMAM-co-PEG at different molecular weights on evodiamine were verified via the use of in vitro cell models and in vivo intestinal loop circulation experiments with rats.Results:Evodiamine exhibited low solubility and permeability and was classified into class IV compounds using the biopharmaceutical classification system.PAMAM-co-PEG 2000 demonstrated improvement in the biosafety and absorption-enhancement effect of evodiamine at a specific concentration.This study showed that 0.05%(w/v)of PAMAM-co-PEG 2000 increased the cumulative penetration of evodiamine via cell transport by 1.32 times,and 0.10%(w/v)of PAMAM-co-PEG 2000 increased the area under curve value of evodiamine by 1.31 times.Conclusion:Evodiamine possesses low solubility and permeability and leads to poor oral bioavailability and a certain degree of cytotoxicity.PAMAM-co-PEG 2000 was found to be a potentially safe and efficient oral absorption enhancer.The results of this study might create a foundation for the development of novel excipients suitable for the complex active ingredients of traditional Chinese medicine.

Advances in porous volumetric solar receivers and enhancement of volumetric absorption

Porous volumetric solar receivers are one type of solar receivers that can volumetrically absorb solar radiation and achieve efficient solar-to-thermal energy conversion.Porous volumetric solar receivers have been developed since 1980s.In this review,we focus on the development progress of the atmospheric and pressurized porous volumetric solar receivers,in which the structural designs,the material selections,the experimental research methods,the comparison of thermal performance,and the transient response characteristic of the receivers were reviewed.On the other hand,the theoretical research methods including the direct pore-scale and volume averaging simulations were introduced.The pore-scale reconstruction method and the procedure to investigate the fluid flow and heat transfer processes at the pore-scale were presented.For the volume averaging method,detailed descriptions for the selection of empirical parameters in the governing equations to be solved were summarized.Typical research results based on these methods were presented and research limitations were also pointed out.Furthermore,the methods for the enhancement of volumetric absorption and the improvement of thermal efficiency of the receivers have been comprehensively reviewed.Two methods including geometrical parameters optimization and spectrally selective absorption were presented in detail.This review will provide a better understanding of the development and research methods for porous volumetric solar receivers,and inspire future studies for the performance improvement of the receivers.

Broadband light absorption and photoresponse enhancement in monolayer WSe_(2) crystal coupled to Sb_(2)O_(3) microresonators

Monolayer(1L)transition metal dichalcogenides(TMDCs)have been attracting tremendous interest in recent years as promising candidate materials in atomic-scale optoelectronic devices due to their direct band gaps(1.5-2.2 eV)and strong light-matter interactions.Unfortunately,their practical applications are limited by low visible light absorption stemming from atomic thickness and negligible infrared response.Here,we report the triangular Sb_(2)O_(3) microresonators in wide thickness and lateral size distributions grown on 1L TMDCs and their created significant broadband enhancement of light adsorption and photoresponse in 1L WSe_(2) crystal via coexisting Fabry-Perot and whispering gallery type resonances.As an example of demonstration,1L WSe_(2) crystal coupled to Sb_(2)O_(3) microresonators with widely distributed sizes exhibits the enhanced visible light absorption by up to 5 folds and the simultaneously extended near infrared(NIR)one of more than 50%.For application of 1L WSe_(2) in photodetection,incorporation of Sb2O3 microresonators leads to significantly enhanced visible light responsivity by~10^(4) order and expanded NIR one of more than 400 mA·W^(-1).Similar results have been observed in the other 1L W(Mo)dichalcogenides coupled to Sb2O3 microresonators.This work provides a new route for development of the high-performance monolayer TMDCs-based optoelectronic devices.