Antireflection Mechanism Research Articles

Enhancing light trapping efficiency: Germanium-coated porous silicon structures for optimal antireflection performance

Porous silicon structures are effective in trapping light due to the abundance of pores on their surface, finding widespread use in optical applications like photoelectric conversion, photon collection, and detection. We have successfully created micro-porous silicon with exceptionally high antireflection performance through electrochemical etching using different concentrations of silver catalysts. Results show that this germanium coated porous silicon structure has a smaller range of pore sizes, leading to a reduced reflectivity of 2.6 % under light radiation with wavelengths. To understand the antireflective mechanism further, we explored the surface reflectivity of porous silicon structures by coating the germanium metal on the porous structure. Importantly, germanium coated porous silicon structures with high surface quality and well-preserved pore integrity are identified as beneficial for achieving lower reflectivity in the incident light wavelength range of 300–1200 nm. These findings are significant for the design of porous silicon antireflective materials.

Anti-reflective properties of butterfly-wing-micro-nano structures in the infrared band

The delicate and intricate micro-nano structure on the surface of butterfly wings is genuinely remarkable. Despite its potential for anti-reflection purposes, this surface structure's theoretical analysis, optimal design, and anti-reflection performance regulation remain a mystery. The anti-reflection characteristics of butterfly Papilio epiphorbas, butterfly Parthenos syvia, and butterfly Sasakia charonda butterfly wings in the infrared band were carefully examined using finite difference time domain simulation and equivalent medium theoretical calculation. The anti-reflection mechanism of the surface micro-nano structure parameters and infrared wavelength of the butterfly wings of butterfly Papilio epiphorbas, butterfly Parthenos syvia, and butterfly Sasakia charonda were revealed. By Fourier infrared reflectance test and simulation of the three butterfly wings, the results show that the structural color scales of the three butterfly wings can achieve a better anti-reflection effect in the infrared band. The anti-reflection performance of the extracted bionic butterfly wings is improved by 0.34%, 2.44%, and 5.46%, respectively, compared with the original butterfly wings. These findings provide valuable theoretical and data support for the continued development of the design and manufacture of bionic anti-reflective surface optics.

3D surface microstructure of silicon modified by QDs to improve solar cell performance through down-conversion and anti-reflection mechanism

Improving the photoelectric conversion efficiency (PCE) of solar cells is an important subject for a wide range of photovoltaic research. One of the main reasons for low PCE is the mismatch between solar spectrum and solar cells. The use of down-conversion and anti-reflection mechanisms is a reasonable method to increase PCE. Down-conversion can convert low-absorbance photons in silicon solar cells into high-absorbance photons while the special 3D surface structure formed by the down-conversion material produces an anti-reflection effect to increase the PCE of the solar cell. In this study, cadmium selenide (CdSe) quantum dots (QDs) coating hybrid structure of monocrystalline silicon solar cells was proposed to increase the utilization. Here, the CdSe QDs were synthesized with a high absorption strength in the 300–500 nm and a photoluminescence (PL) peak at 628 nm. Benefiting from the larger absorption cross-section and weaker electron-phonon coupling characteristics of CdSe QDs, the down-conversion was achieved successfully, and the reflectance test of the CdSe QDs covered silicon solar cells also shows an anti-reflection effect. Therefore, by using the dual mechanism of down-conversion and anti-reflection, the PCE of solar cells was improved by the proposed system. The results show that the PCE of the CdSe QDs coating hybrid structure based monocrystalline silicon solar cells is increased by 1.42% from 14.45% to 15.87%. Besides, by using finite element method, the reflection reduction mechanism for lower transition layer was also simulated to further explain the experiment results. Due to the low synthesis cost of QDs, this work can be well integrated into the photovoltaic industry, which provides a new technical route and guidance for improving the PCE of silicon cells.

Broadband Antireflective Hybrid Micro/Nanostructure on Zinc Sulfide Fabricated by Optimal Bessel Femtosecond Laser.

Enhancing the infrared window transmittance of zinc sulfide (ZnS) is important to improve the performance of infrared detector systems. In this work, a new hybrid micro/nanostructure was fabricated by an optimal Bessel femtosecond laser on ZnS substrate. The surface morphologies and profiles of ASS ablated by a 20× microscope objective Bessel beam are described, indicating that the nanoripples on the micropore were formed by the SPP interference and the SPP scattering in a particular direction. Further, the maximum average transmittance of ASS increased by 9.7% and 12.3% in the wavelength ranges of 5~12 μm and 8~12 μm, respectively. Finally, the antireflective mechanism of the hybrid micro/nanostructure is explored using the novel electromagnetic field model based on the FDTD method, and we attribute the stable antireflective performance of ASS in broadband to the interface effective dielectric effect and LLFE.

Analysis of anti-reflection mechanisms of the black aluminum alloy made by femtosecond laser processing

Mitigating the optical reflection of aluminum alloy over a broad spectral range from 0.45 μm to 15 μm is vital for many applications. This can be realized by introducing efficient light-absorbing textured surfaces via femtosecond laser surface processing. However, a clear analysis of antireflection performance has not been reported yet. This paper proposes a numerical model of anti-reflective structures is proposed based on SEM and EDS characterization. Multiple anti-reflective mechanisms were revealed intuitively through FDTD simulation.

Blasting Law of Liquid CO2 Phase Change in Coal Mine Based on Numerical Simulation.

In order to obtain the best CO2 blasting drilling efficiency and improve the gas permeability coefficient of the coal seam in the mining area, a research method of liquid CO2 phase change blasting in the coal seam based on electrochemical numerical simulation is proposed. In this paper, the electrochemical numerical simulation of coalbed methane caused by liquid CO2 phase change blasting is studied through theoretical analysis, the antireflection mechanism of liquid carbon dioxide gas explosion on broken coal seam is obtained, and the initial fracture length of coal body caused by gas explosion stress wave is deduced by the mathematical model. A method for improving CBM desorption with nonmechanical coal was proposed, namely, a method for electrochemically strengthening CBM desorption. A comprehensive theory and application system of liquid carbon dioxide phase change gas explosion and anti-reflection technology are established by combining theoretical analysis, experimental research, and numerical simulation with field industrial comparative experiment. According to the gas tracing method, the precise measurement of the working face shows that the impact radius of the collision caused by the explosion of the liquid carbon dioxide phase change gas is 2 m. Gas emissions increased the emissions of coal seam drilling in the affected areas by 4 to 8 times, and the gas emission attenuation coefficient decreased from 0.76 times to 0.93 times. The carbon dioxide phase change gas cracking theory and antireflection theory and their application technology system are systematically studied. The research shows that the liquid carbon dioxide phase transfer gas blasting and infiltration technology is not limited by the geological conditions of the coal seam and has the characteristics of high efficiency and inherent climate. In view of the wide area of coal mines and the harsh geological conditions of coal seams, carbon dioxide phase change gas-induced cracking antireflection technology has application prospects and expandability.

Anti-reflection metallic anode-enhanced performance of organic solar cells via cross coupling between Fabry-Perot cavity modes and microcavity modes.

An effective anti-reflection metallic anode with the structure of glass/dielectric2 /Ag (D1D2M) is demonstrated both in small-molecule (SM) and conjugated polymer (CP) organic solar cells (OSCs). The anti-reflection mechanism is investigated by the finite-difference time-domain numerical calculation method and the experimental method. By tuning the refractive index and the thickness of the D2 layer, the reflection light is confined in the Fabry-Perot (F-P) cavity modes, which effectively enhances the transmittance of the D1D2M anode in the wavelength range of 420 nm-800 nm. Compared with the conventional glass/Ag (D1M) anode, the experimental transmittance of the D1D2M anode is enhanced by 33.24% at a wavelength of 550 nm. By replacing the D1M anode with the D1D2M anode in the OSCs, the F-P cavity modes cross couple with the microcavity modes in the active layers. As a result, the absorption intensity is obviously increasing in a wide angle range (0≤θ≤85∘) in the wavelength ranges of 475 nm-650 nm and 540 nm-720 nm for the SM and CP OSCs, respectively. The short circuit current density and power conversion efficiency of the SM OSC is increased by 25.07% and 27.23%, respectively.

Characterization of anti-reflection structures fabricated via laser micro/nano-processing

The optical reflection properties of material surfaces are crucial for the performance of many optical and optoelectronic devices. In this study, different single-scale surface structures, e.g., gratings, holes, and cones were fabricated via laser micro/nano-processing and their optical properties were determined. The anti-reflection mechanism for these surface structures was revealed visually by using a ray-tracing algorithm and wave optics calculations. To fully exploit the advantages of single-scale nanostructures or microstructures, a novel preparation method for multi/scale structures was proposed. It not only improves absorption efficiency, but also broadens the absorption spectrum. Moreover, a substantial improvement of the infrared anti-reflection performance was realized. In addition, the relationship between the characteristic of surface structure and the spectral region in response to incident light, was established.

Research and Application of Hydraulic Punching Pressure Relief Antireflection Mechanism in Deep “Three‐Soft” Outburst Coal Seam

To solve the problems of gas predrainage in deep seams with “three softs” and low‐air permeability, hydraulic punching pressure relief antireflection technology is proposed on the basis of the research background of gas predrainage technology in Lugou Mine to alleviate technical problems, such as low gas drainage efficiency, in this mine. Through the analysis of the mechanism of hydraulic punching and coal breaking, combined with FLAC3D software, a hydraulic punching pressure relief antireflection model is established. Then, the fracture radii of coal rock are simulated and calculated. The results show that, under hydraulic punching with a water pressure of 10 MPa and coal outputs of 3 m3, 6 m3, 9 m3, and 12 m3, the fracture radii of coal and rock are 3.4 m, 4.8 m, 5.5 m, and 5.9 m, respectively. Using the software to fit the relationship between coal output V and hydraulic punching fracture radius R under the same water pressure, R = 2.32479 V0.3839 is obtained. The field test is carried out in the bottom drainage roadway of 32141 in Lugou Mine. The application effect is as follows: the gas concentration of hydraulic punching with a coal output of 3 m3 is twice that of ordinary drilling, and the coal output of hydraulic punching with a coal output of 6 m3 is four times that of ordinary drilling. The extraction concentration is four times that of ordinary drilling, and the extraction concentration of hydraulic punching with a coal output of 9 m3 is 6.4 times that of ordinary drilling. Combining the results of the numerical simulation and taking into account the actual construction situation on site, the coal output of water jetting from the borehole is 9 m3, and the fracture radius is 5.5 m. This outcome means that the effective half radius is 5.5 m, and the borehole spacing is 7.7 m. These values are the construction parameters for large‐scale applications. This proposal provides effective technology and equipment for gas drainage in the deep three‐soft coal seam. Consequently, it has promotion and reference significance for gas drainage in coal seam of the same geological type.

Mining‐Induced Pressure‐Relief Mechanism of Coal‐Rock Mass for Different Protective Layer Mining Modes

The protective layer mining method of the traditional deep coal seam in has been confronted with great challenges, and it is difficult for coal and gas to be extracted together. Taking the occurrence conditions of III1 mining area of Luling Coal Mine located at Huaibei, China, as engineering background, the influence law of the lithology on stress environment in front of the stope was analyzed by theoretical analysis and numerical simulations. The mining‐induced mechanical effect of coal‐rock mass was studied under different protective layer mining modes. The results showed that the peak value of the advanced abutment pressure decreased with the decrease of lithologic strength under the same mining conditions. For simulated geological conditions, the stress concentration coefficient of soft rock and coal seam protective layer mining modes was 1.9 and 1.7, respectively. Under the mining stress path of different protective layers, the ratio of axial stress increase and confining pressure unloading in secondary unloading phase were 2 : 1 and 1.5 : 1, respectively. The axial stress‐strain curves of different protective layer mining modes had similar trends, and they had a volume expansion at the end of unloading (failure stage). In addition, it revealed the pressure‐relief antireflection mechanism of the protective layer mining. Under the same confining pressure condition, the peak stress and peak strain increased with the increase of loading and unloading velocity ratio. The reduced value of the confining pressure increased, while the volume expansion decreased at failure. The results were applied to III1 mining area in soft rock protective layer mining, which created the mining way of traditional coal seam protective layer. Furthermore, the gas control technology of soft rock protective layer working face was put forward for deep coal seam with low permeability and high gas, enriching the pressure‐relief mining theory of protective layer.

Anti-reflection silicon with self-cleaning processed by femtosecond laser

The creation of functional surfaces has been studied extensively in the past due to their potential applications in corrosion resistance, anti-fouling, drag-reduction, and self-cleaning. In this paper, we present a simple method to fabricate an anti-reflection silicon surface with good self-cleaning effect by combined femtosecond laser processing with chemical modification. The reflectance of the prepared silicon is lower than 5%, and the surface exhibits a contact angle of 166° and a sliding angle of 3° for water. The water droplets can easily carry the contamination particles away from the prepared surface. More importantly, by changing the defocusing amount, we find that there are two different anti-reflection mechanisms. In the first mechanism, the light enters the object mainly through small surface nanostructures with dimensions greater than the wavelength of the incident light. In the second mechanism, the incident light is mostly reflected back and forth in the micro-hole and then absorbed by the silicon. In both mechanisms, the micro-hole structures are more suitable as an anti-reflection structure. Finally, photo-thermal conversion experiments are conducted on the prepared anti-reflection silicon surface.

Antireflection in Green Lacewing Wings with Random Height Surface Protrusions

Wings of insects exhibit many functions apart from flying. In particular, their antireflection function is important for insects to avoid detection by their enemies. This function can be applied to antireflection biomimetic films in engineering fields. For such applications, confirming the antireflection mechanisms of insect wings is important. Herein, we used electron microscopy to compare the surfaces of green lacewing wings with and without a surface wax structure and recorded the transmittance spectra to clarify the surface structural and optical properties of insect wings. The spectral transmittance was higher for wings with a surface wax structure than for wings without a wax layer in the light wavelength regime from 500 to 750 nm. We constructed a concise model of the green lacewing wing with flake-like surface structure with a graded effective refractive index corresponding to the wing samples with a surface wax layer; we also constructed a simple thin-film model corresponding to the wing samples without a wax layer. The graded refractive indices were calculated using the effective medium theory, and the transmittance spectra of such models were then calculated using the transfer-matrix method. It was observed that the calculated spectra are in good agreement with the experimental results. In addition, wing samples without a surface structure induce thin-film interference. These results suggest that a wax structure can reduce the reflectance and increase the transmittance enabling the green lacewings to avoid detection by their enemies. These findings may lead to further advances in both the biomimetic field and fundamental research fields.

Design and Fabrication of Dual-Scale Broadband Antireflective Structures on Metal Surfaces by Using Nanosecond and Femtosecond Lasers.

Antireflective surfaces, with their great potential applications, have attracted tremendous attention and have been the subject of extensive research in recent years. However, due to the significant optical impedance mismatch between a metal surface and free space, it is still a challenging issue to realize ultralow reflectance on a metal surface. To address this issue, we propose a two-step strategy for constructing antireflective structures on a Ti-6Al-4V (TC4) surface using nanosecond and femtosecond pulsed lasers in combination. By controlling the parameters of the nanosecond laser, microgrooves are first scratched on the TC4 surface to reduce the interface reflection. Then, the femtosecond laser is focused onto the sample surface with orthogonal scanning to induce deep air holes and nanoscale structures, which effectively enhances the broadband absorption. The antireflection mechanism of the dual-scale structures is discussed regarding morphological characterization and hemispherical reflectance measurements. Finally, the modified sample surface covered with micro-nano hybrid structures is characterized by an average reflectance of 3.1% over the wavelengths ranging from 250 nm to 2250 nm.

Enhanced Tunable Light Absorption in Nanostructured Si Arrays Based on Double‐Quarter‐Wavelength Resonance

AbstractSimultaneously tuning light absorption wavelength and absorbance is a critical challenge in photoelectric detection, mimic of photosynthesis, and simulation of photoreceptors in some animals' retinas. Here, highly ordered hexagonal nanostructured Si arrays are fabricated using monolayer colloid crystal templates. A quantitative relationship between geometric size and light absorption is unveiled in the Si arrays, namely double‐quarter‐wavelength resonance (DQWR). Based on the DQWR model, the absorption wavelength can be readily tuned from 200 to 2400 nm, and the absorbance can be enhanced from ≈80% to above 99% in the full spectrum. Due to the hemisphere‐shell structural feature of the Si arrays, excellent omnidirectional antireflective performance can also be realized. Most importantly, the outstanding antireflection performance of the nanostructures is independent of the substrate. The results not only have important implications for understanding the antireflective mechanism of the nanostructured arrays, but also endow the approach promising in diverse applications, including biomimicry, antireflective film, infrared imagery, and other optoelectronic devices.

Magnetron sputtered Dy2O3 with chromium and copper contents for antireflective thin films with enhanced absorption

Dy2O3 is a rare earth oxide having a number of advanced applications in various fields including protective or antireflective coatings. Main objective of this novel research work is to check the effect of Cr and Cu addition on different properties of Dy2O3 and achievement of antireflective thin films with enhanced absorption. Thin films of these materials were deposited using DC magnetron with reactive co-sputtering. XRD studies reveals the crystalline nature of thin films having Dy2O3 (222) reflection in all samples with Cr2O3 (116) and CuO (111) reflections in Cr and Cu containing compositions. Field emission scanning electron microscopy demonstrates the homogeneous deposition of thin films with uniform shape, size and distribution of grains. Refractive index, extinction coefficient and absorption coefficient significantly increase while optical reflectance decreases with Cr and Cu mediation corroborating an improved antireflective mechanism. The imaginary part of dielectric constant is found to increase slightly with low tangent loss for Cr containing composition considered favorable for energy storage applications.

ANALYSIS OF LONG-CIRCUIT TYPE CAISSONS FOR ATTENUATION OF LONG-PERIOD WAVES

Breakwaters provide convenient shelter for short-period waves, thus limiting the amount of energy entering the harbor. This wave energy in the port basins may be amplified, due to the wave reflection, disturbing port operations. Anti-reflective Jarlan-type (ARJ) structures (see Jarlan, 1961) have been proposed in the literature, along with other structures, to alleviate wave disturbance within port basins. ARJ anti-reflective mechanism is based on the destructive interference of waves. An anti-reflective zone width, B, must be almost a quarter of the wavelength for maximum efficiency. Longer waves easily enter the port-sheltered area where resonance phenomena could magnify its energy under certain conditions. This low-frequency energy is much more difficult to dissipate. Port resonance is the phenomenon of energy amplification that takes place in a harbor or port basin if the incident waves have frequencies close to those of the natural oscillation of the mass of water in the port basin. These infragravity long waves are frequently reported as causing trouble in cargo handling areas of many ports (see Rabinovich, 2009), even causing breakages of mooring lines and other relevant damage (see Thotagamuwage and Pattiaratchi, 2014).

Realization of omnidirectional ultra-broadband antireflection properties via subwavelength composite structures

An advanced subwavelength composite structure (SCS) consisting of the hexagonally arranged silicon nanopillars and the misaligned TiO2/SiO2 double-layer films was proposed on the surface of crystalline silicon (c-Si). After optimization through the finite difference time domain (FDTD) method, the SCS possesses omnidirectional ultra-broadband antireflection properties (average reflectance < 1.8% within 300–2500 nm) which are suitable for a photovoltaic-thermoelectric (PV-TE) hybrid system to enhance the full-spectrum solar energy utilization. Furthermore, the antireflection mechanism was studied in detail. The composition of nanopillars and double-layer films has combined the effect of interference, interpillar scattering and waveguide resonance to realize outstanding antireflection proprieties. The SCS was prepared on a 3 cm × 3 cm silicon wafer by ICP etching and magnetron sputtering, and the measured results matched well with the simulation results. Further, such antireflection concept can be applied to other materials for particular ultra-broadband spectrum regulation.

Improved Light Management in Silicon Heterojunction Solar Cells by Application of a ZnO Nanorod Antireflective Layer

This study reports successful application of ZnO nanorod arrays for efficient reduction of reflection losses in heterojunction solar cells on flat non-textured silicon wafers. In addition, aluminium doped zinc oxide (AZO) is proposed as a cheap, abundant and environment-friendly substitution for indium doped tin oxide (ITO), commonly used in transparent front electrodes. The results show a significant reduction of the average weighted cell reflectivity and hence an enhancement in the external quantum efficiency and in the short circuit current density. The main antireflective mechanism was found to be a grading of the refractive index at the AZO/air interface, which has been shown by optical simulations describing the nanorod layer as an effective medium.The ZnO nanorod layers were grown by electrochemical deposition, which is a low-cost and industrially applicable method, since no vacuum conditions and high temperatures are required. Therefore, this concept could be a promising process step in the photovoltaic industry to improve light management in silicon heterojunction solar cells with AZO front contacts, especially attractive for the production utilizing very thin wafers, where wafer texturing for antireflection purposes shows important drawbacks.

Intense thermal terahertz-to-infrared emission from random metallic nanostructures under femtosecond laser irradiation.

We report intense (~10 mW), ultra-broadband (~150 THz wide), terahertz-to-infrared, Gaussian-wavefront emission from nanopore-structured metallic thin films under femtosecond laser pulse irradiation. The proposed underlying mechanism is thermal radiation. The nanostructures of the metal film are produced by random holes in the substrate. Under pulse-train femtosecond laser irradiation, we found dramatically enhanced optical absorption, with an absorptivity that was equal to as much as 95% of the metallic surface nanostructure, due to both an antireflection mechanism and dissipation of excited surface plasmon polaritons into the metal surface.

Study and Application of Hydraulic Fracturing Technology to Increase Permeability in Soft and Low Permeability Coal Seam

In order to improve gas drainage of soft and outstanding coal seam in Huainan mine area, for eliminating outburst hazard, hydraulic fracturing is applied at west one (13-1) rock cross-cut coal uncovering face. By analysising antireflection mechanism of hydraulic fracturing, hydraulic fracturing is designed and construct at rock cross-cut coal uncovering face, and then investigate the effect of hydraulic fracturing, at last it get a hydraulic fracturing complete set of technical system.