Low Light Reflectivity Research Articles

Construction of Al/Ti₃C₂Tₓ composites via electrostatic self–assembly for visible–infrared camouflage applications

Attaining the equilibrium of subdued luminance, low visible light reflectance, and high infrared reflectance constitutes a formidable challenge in the realm of visible–infrared camouflage. Here, an electrostatic self–assembly method was proposed to fabricate the Al/Ti₃C₂Tₓ (AT) composite. The synergy between Ti3C2Tx’s favorable optical properties and significant conductivity of Al powder grants the AT composite excellent visible–infrared camouflage capabilities. At a mass ratio of 4:1 for Al powder to Ti3C2Tx (AT–4), the composite displays a gray coloration, achieving a 40 % reduction in visible light reflectance and an emissivity value of 0.28. Such properties enable the AT–4 composite to effectively blend into various thermal environments, showcasing its superior infrared camouflage capabilities. Additionally, incorporating Ti3C2Tx layers significantly boosts the local electric field in the composite, enhancing photon–material interactions and consequently reducing its visible light reflectance. This work offers valuable insights for the development of advanced materials with integrated visible–infrared camouflage capabilities.

Formation conditions of the tungsten porous thin film with pulsed laser deposition under various gas atmosphere

Abstract Pulsed laser deposition (PLD) under gas atmospheres has been used to fabricate thin films for various applications. In this study, PLD was performed under various gas atmospheres (helium, oxygen, and argon) using tungsten (W) to investigate the morphology of thin films. Various types of structures were formed, including uniform, nanoparticles, and columnar structures. In particular, the substrate fabricated at an argon pressure of 100 Pa had a high porosity and a low light reflectance in the 200–1400 nm wavelength range. In addition, it was shown that the growth of the thin film thickness was non-linear with respect to time, and the formation of a fuzz-like structure may be influenced by particle diffusion in the gas phase and on the substrate.

Enhancing photovoltaic cell efficiency: A comprehensive study on BN-Si3N4 blend antireflective coatings and their impact on power conversion

Antireflective surface coatings were one of the most important factors that contributed to the improvement of the functionality of photovoltaic cells. The coatings were performed by different methods such as RF sputtering, spin coating, dip coating, electro spraying etc. The coating materials such as BN, Si3N4 and BN-Si3N4 blends were applied to solar cells using the RF sputtering technique in this study. Several distinct characterization methods were adopted to assess the productivity of Si3N4 coated cells. The BN-Si3N4 blend coated cell has a low light reflection of 8 % and exhibits uniform layer deposition, which shows a significant improvement over conventional solar cell. The BN-Si3N4 solar cell was able to obtain the highest possible power conversion efficiency of 19.70 % when exposed to direct sunlight and 21.28 % when exposed to neodymium light. It possess the narrow scope of visible spectrum and acts as green/yellow filter in visible spectrum. This light is capable of delivering light similar to sunlight with consistent radiation. This was accomplished by increasing the transmission of photons that reached the depletion region. The four-probe experiment was employed to measure the electrical resistivity of BN-Si3N4 solar cell, which was found to be 0.00298 Ω-cm. This value was lower than the electrical resistivity of other solar cell samples. Based on the results, BN-Si3N4combination outperformed both coated and bare cells. It was found that BN-Si3N4blendwas a remarkable antireflective coating to maximize the performance.

Pressure-induced investigation of structural, electronic, optical, and mechanical properties of BaCeO3

The exploration of the hydrostatic pressure effect on the characteristics of materials is essential for various applications. Our study uses Density Functional Theory (DFT) to investigate the pressure-induced influence on the structural, electronic, optical, and mechanical properties of BaCeO3. According to formation enthalpy and Born stability criteria, BaCeO3 is mechanically and thermodynamically stable from 0 GPa to 80 GPa. The tunable band gap of BaCeO3 within the visible spectrum under applied pressure makes it a potential candidate for absorber layer fabrication of solar cells. The electronic state, mainly attributed to O-2p in the valence band (VB) and Ce-4f in the conduction band (CB), is observed through Partial Density of States (PDOS), although its intensity varies with pressure. The refractive index shows that pressurized BaCeO3 is appropriate for photonics. Its significant absorption at high energy under pressure makes it an excellent candidate for Ultraviolet (UV) detectors, and it also has low light reflection, with static values routinely less than 0.2. Additionally, as pressure increases, elastic constants, elastic moduli, ductility, machinability index, and anisotropy all increase, except for hardness, which decreases. BaCeO3 is approaching to minimal bond stretching with pressure according to Kleinman parameter. These pressure-induced changes in mechanical properties have potential applications in flexible electronics, structural uses, and more.

Surface engineering of Sio2-Zro2 films for augmenting power conversion efficiency performance of silicon solar cells

Improving solar cell performance hinges significantly on the application of anti-reflective surface coatings. A wide variety of coating techniques, including blade coating, spin coating, dip coating, and others were employed. The present research investigation employed various coating materials, namely SiO2 (Silicon dioxide), ZrO2 (Zirconium dioxide), and SiO2–ZrO2 blends, to apply a protective layer onto polycrystalline silicon solar cells using the sputter coating process. The efficiency of these solar cells with multilayer coating was assessed through diverse characterization methods. The uniform thin films were obtained using a 45-min coating process using an input voltage source of 17 kV, which was confirmed through analyses conducted using FESEM and AFM techniques. The UV–Vis spectroscopy and current-voltage source metre were employed to examine the light absorption and transmittance of bare and coated silicon solar cells. When compared to alternative solar cells, the solar cell coated with a combination of SiO2 and ZrO2 demonstrated uniform deposition and a low light reflectance of only 6 %. SiO2–ZrO2 gains a highest power conversion efficiency (PCE) of 17.6 % under controlled light source. This superior performance was due to the increase in photon transmittance in to the depletion region. Furthermore, the electrical resistivity of the SiO2–ZrO2 blend coated solar cell was measured using the four-probe method was found to be 2.89 × 10−3 Ω-cm, which was lower than that of other solar cells. From the experimental results, it was clear that SiO2 - ZrO2 blend-coated solar cells outperformed both other coated and uncoated solar cells. Consequently, SiO2–ZrO2 blends emerged as superior anti-reflective materials for achieving peak performance.

Effects of sound insulation and light reflection of desktop partitions on subjective impression during conversation

In recent years, transparent desktop partitions have often been placed in public spaces to prevent the spread of COVID-19. Moreover, to clarify the view during conversation, surface materials with low light-reflectivity are developed for the partitions. In this paper, we conducted sound insulation measurements for partitions with four different materials, and two psychological experiments in order to examine the audio-visual effects on the ease of conversation. First, in non-visual conversation between two persons, better subjective evaluation of speech transmission was confirmed for partitions with lower surface density which have less insertion loss. However, in normal audio-visual conversation, the low light-reflective partitions got higher evaluations of not only visual but also auditory impressions, regardless of sound insulation performance. In addition, subjective evaluations among different materials varied in the quiet condition more remarkably than in the noisy condition.

Role of O2 and N2 addition on low-reflectance Si surface formation using moderate-pressure (3.3 kPa) hydrogen plasma

We prepared ‘black Si’ with Si nanocone structures using a moderate-pressure H2 plasma at 3.3 kPa with a minor air addition. The roles of N2 and O2 as additives in Si-nanocone formation were investigated. Air additives in H2 gas are required to form Si oxynitride micromasks on the surface, and the O2 concentration in the additive modifies the chemical and physical characteristics of the micromasks. When the additive in the H2 gas was only O2, a relatively smooth sample surface or a low-aspect-ratio nanocone structure was formed. In contrast, the N2-only additive of H2 gas resulted in a fine nanopillar structure with a low height. An O2 concentration in the additives of approximately 20% is desirable for black Si fabrication. In addition, the etching rate of the SiO2 film using moderate-pressure H2 plasma was three times higher than that of the SiNx film. In addition, an adequate additive O2 concentration in the H2 gas increased the atomic H density in the plasma. As a result, a Si surface with a very low light reflectance of less than 0.5% in the wavelength range of 380–830 nm was obtained.

Array structure of monocrystalline silicon surface processed by femtosecond laser machining assisted with anisotropic chemical etching

Monocrystalline silicon (m-Si) with array structure has excellent optical and surface properties in the application of solar cells and optoelectronics. However, due to its hard and brittle properties, the efficient and high-quality micro-processing of complex array structured m-Si surface is difficult. In this work, micron array structure, such as inverted pyramid (IP) array structure, V-shaped groove array structure, and positive pyramid array structure, was generated on the m-Si surface by an efficient femtosecond laser machining assisted with anisotropic chemical etching. The morphology changes of microholes during the etching process, as well as the surface and optical properties of array structured m-Si, have also been studied. Experimental results showed that V-shaped groove array structure m-Si achieved superhydrophilic performance. The m-Si of IP array structure and V-shaped groove array structure exhibit high absorptivity (>95 %) and low light reflectivity (<5%) within a wide spectral range from 400 to 950 nm. This study reveals that femtosecond laser machining assisted with anisotropic chemical etching is a facile and feasible avenue to produce array structured m-Si with excellent optical performance.

Dynamic anticounterfeiting polymeric inks for multipurpose time-dependent encryption with a high level of security

Development of dynamic anticounterfeiting inks with time-dependent photochromism and photoluminescence characteristics has become highly interesting in advanced encryption systems. These inks are applicable in different fields, such as tracking UV rays and gas leakage and also quality monitoring. In this study, semi-continuous copolymerization of butyl acrylate and methyl methacrylate in the heterogeneous miniemulsion medium was used to synthesize colloidal nanoparticles with different flexibilities and polarities. Then, hydroxyl-functional spiropyran (SPOH) was physically incorporated into the nanoparticles to prepare photochromic and photoluminescent inks. The nanoparticles showed low light reflectance due to their small size, which makes them applicable in photoresponsive and sensing applications. In addition, the nanoparticles exhibited different glass transition temperature (Tg) that affects their photoresponsivity. Microscopic analysis revealed that all the latex samples have spherical nanoparticles with a mean size of about 70 nm and a low polydispersity index. UV–vis absorption and fluorescence emission spectra, isomerization kinetics, and photofatigue resistance of the photochromic latex nanoparticles were studied, which depend on chain polarity and flexibility of the latex nanoparticles. The optical properties of the photochromic materials are closely related to the structure and composition of the latex samples. Time-dependent features of the inks originate from their spiropyran molecules which gradually turns into the merocyanine form upon visible light induction. Photochromic inks with advanced encryption and dynamic characteristics were developed from the SPOH-doped colloidal latex nanoparticles. Different polarities and Tg of the inks result in their different dynamic chromism, which show their high level of information encryption technology. By virtue of these unique time-dependent properties, the encryption capabilities of these inks are significantly improved. These inks achieved unprecedented advances in the field of information security and encryption because of their innovative features.

DMPH-Net: a deep multi-scale pyramid hybrid network for low-light image enhancement with attention mechanism and noise reduction

Aiming at the problems of color bias and noise enhancement on the output image by the traditional low-light image enhancement algorithm, we propose a deep multi-scale pyramid hybrid network (DMPH-Net) algorithm that fuses attention mechanism and multi-scale pyramid is proposed in this paper. The algorithm uses DecomNet to decompose reflectance and light components, and uses multi-scale illumination attention module to fuse light and reflectance for the decomposed low-light reflectance to improve the realism and details of reflectance; by using five-layer feature pyramid and kernel selection in PRID-net module to achieve the fusion of contextual information between different scale feature layers, while effectively removing the enhanced of noise, and the added color loss effectively suppresses the color bias of the output image; using multi-scale cascading and channel attention mechanisms to adjust the illumination and fuse the illumination ratios, effectively enhancing the brightness, texture, and other feature information in the image. The DMPH-Net algorithm is experimentally validated on LOL and no-reference LIME, MEF, and NPE datasets, and the objective evaluation metrics PSNRuparrow , SSIMuparrow , LIPIPSdownarrow , and NIQEdownarrow are 23.3772, 0.8442, 0.1386, and 3.5966 on LOL dataset. The objective evaluation metrics NIQE on the reference-free datasets LIME, NPE, and MEF are 3.0735, 3.1711, and 2.9464, respectively. The experiments show that the DMPH-Net algorithm maintains high image details and textures in image enhancement and denoising, effectively enhances low-light images, and reduces noise and color bias of images. Compared with RUAS, UnRetinex-Net, and other enhancement algorithms, it improves in objective evaluation metrics PSNR, SSIM, LIPIPS, and NIQE.

New insight into ZnO@ZIFs composite: an efficient photocatalyst with boosted light response ability and stability for CO2 reduction.

One of the main causes of climate change and energy exhaustion is the excessive use of fossil fuels. Photocatalytic carbon dioxide (CO2) reduction technology uses inexhaustible sunlight to directly convert CO2 into value-added chemicals or fuels not only solving the problem of greenhouse effect but also alleviating the shortage of fossil energy. In this work, a well-integrated photocatalyst is synthesized through growing zeolitic imidazolate frameworks (ZIFs) with different metal nodes on ZnO nanofiber (NFs) for CO2 reduction. One-dimensional (1D) ZnO NFs have better CO2 conversion efficiency due to the high surface-to-volume ratio and low light reflectivity. 1D nanomaterials with superior aspect ratios can be assembled into free-standing flexible membranes. In addition, it has been found that ZIFs nanomaterials with bimetallic nodes not only have better CO2 reduction capabilities but also exhibit superior thermal and water stability. The photocatalytic CO2 conversion efficiency and selectivity of ZnO@ZCZIF are shown to be significantly enhanced which can be attribute to the strong CO2 adsorption/activation, efficient light capture, excellent electron-hole pair separation efficiency, and specific metal Lewis sites. This work provides insights into the rational construction of well-integrated composite materials to improve the photocatalytic carbon dioxide reduction performance.

Sustainable production of clean water: 1 T-MoS2/PDA composite enhanced the photothermal conversion

The scarcity of fresh water resources necessitates us to develop an efficient technique for sustainable production of clean water from seawater and wastewater. Here, we constructed the 1 T-MoS2/PDA (polyaniline) as a photothermal material for purification of seawater and wastewater to produce clean water through interfacial evaporation by virtue of sunlight. 1 T-MoS2 has a higher evaporation capacity of water than 2 H-MoS2, which was selected to prepare 1 T-MoS2/PDA composite for photothermal conversion. As expected, 1 T-MoS2/PDA composite offers a higher evaporation rate of water than both 1 T-MoS2 and PDA, which owes to an excellent light absorbance, low light reflectance and good wettability. Under irradiation of 1 sun, the evaporation rate of water over the 1 T-MoS2/PDA composite in pure water reached 1.51 kg m−2h−1, and the photothermal conversion efficiency reached 92%. Encouragingly, 1 T-MoS2/PDA composite can be well used to treat real seawater and various wastewater such as organic dye solution and heavy metal ion solution, in which the evaporation rate of water is close to pure water, and the quality of water is better than the standard of drinking water established by the World Health Organization (WHO). Besides, 1 T-MoS2/PDA composite still maintain an excellent evaporation performance after treatment of acidic solution and alkaline solution, indicating an excellent durability. This work provides a feasible solution for producing clean water by solar-driven interfacial evaporation from seawater and wastewater.

Preparation of cool composite pigment by the layer-by-layer assembling of phthalocyanine green on the surface of rutile TiO2

Purpose This study aims to fabricate a cool phthalocyanine green/TiO2 composite pigment (PGT) with high near-infrared (NIR) reflectance, good color performance and good heat-shielding performance under sunlight and infrared irradiation. Design/methodology/approach With the help of anionic and cationic polyelectrolytes, the PGT composite pigment was prepared using a layer-by-layer assembly method under wet ball milling. Based on the light reflectance properties and color performance tested by ultraviolet-visible-NIR spectrophotometer and colorimeter, the preparation conditions were optimized and the properties of PGT pigment with different assembly layers (PGT-1, PGT-3, PGT-5 and PGT-7) were compared. In addition, their heat-shielding performance was evaluated and compared by temperature rise value for their coating under sunlight and infrared irradiation. Findings The PGT pigment had a core/shell structure, and the PG thickness increased with the self-assembly layers, which made the PGT-3 and PGT-7 pigment show higher color purity and saturation than PGT-1 pigment. In addition, the PGT-3 and PGT-7 pigment showed 11%–16% lower light reflectance in the visible region. However, their light reflectance in the NIR region was similar. Under infrared irradiation the PGT-5 and PGT-7 pigment coating showed 1.1°C–3.4°C and 1.3°C–4.7°C lower temperature rise value than PGT-1 pigment coating and physical mixture pigment coating, respectively. And under sunlight the PGT-3 pigment coating showed 1.5–2.6°C lower temperature rise value than the physical mixture pigment coating. Originality/value The layer-by-layer assembling makes the core/shell PGT composite pigment possess low visible light reflectance, high NIR reflectance and good heat-shielding performance.

High-Performance Ultraviolet Photodetector Based on Single-Crystal Integrated Self-Supporting 4H-SiC Nanohole Arrays.

Currently, the photodetectors (PDs) assembled by vertically aligned nanostructured arrays have attracted intensive interest owing to their unique virtues of low light reflectivity and rapid charge transport. However, in terms of the inherent limitations caused by numerous interfaces often existed within the assembled arrays, the photogenerated carriers cannot be effectively separated, thus weakening the performance of target PDs. Aiming at resolving this critical point, a high-performance ultraviolet (UV) PD with a single-crystal integrated self-supporting 4H-SiC nanohole arrays is constructed, which are prepared via the anode oxidation approach. As a result, the PD delivers an excellent performance with a high switching ratio (∼250), remarkable detectivity (6 × 1010 Jones), fast response (0.5 s/0.88 s), and excellent stability under 375 nm light illumination with a bias voltage of 5 V. Moreover, it has a high responsivity (824 mA/W), superior to those of most reported ones based on 4H-SiC. The overall high performance of the PDs could be mainly attributed to the synergistic effect of the SiC nanohole arrays' geometry, a whole single-crystal integrated self-supporting film without interfaces, established reliable Schottky contact, and incorporated N dopants.

Electronic, Optical, and Magnetic Properties of Fe‐ or Co‐Doped 2D 2H‐CrSe2

AbstractThe effect of substitution of Cr in 2H‐CrSe2 by Fe and Co on its electronic, optical, and magnetic properties is studied by first‐principles density functional theory. Spin‐polarized semiconducting state is realized in CrSe2 by substitutional doping of Fe and Co, while a semimetallic state is obtained by Fe doping and the magnetic moment after Fe doping is 4.52 μB. On Co substitution, it is observed that the system presents metallic properties, with relatively low light absorption and reflectance, and good transparency. The magnetic moment after Co doping is 2.71 μB. The absorption coefficient of CrSe2 to visible light increases with the doping of Fe and Co, and the peak value is redshifted, which is conducive to the further application of CrSe2 in the field of optoelectronics.

Fluorobenzene and Water-Promoted Rapid Growth of Vertical Graphene Arrays by Electric-Field-Assisted PECVD.

Vertical graphene (VG) arrays show exposed sharp edges, ultra-low electrical resistance, large surface-to-volume ratio, and low light reflectivity, thus having great potential in emerging applications, including field emission, sensing, energy storage devices, and stray light shields. Although plasma enhanced chemical vapor deposition (PECVD) is regarded as an effective approach for the synthesis of VG, it is still challenging to increase the growth rate and height of VG arrays simultaneously. Herein, a fluorobenzene and water-assisted method to rapidly grow VG arrays in an electric field-assisted PECVD system is developed. Fluorobenzene-based carbon sources are used to produce highly electronegative fluorine radicals to accelerate the decomposition of methanol and promote the growth of VG. Water is applied to produce hydroxyl radicals in order to etch amorphous carbon and accelerate the VG growth. The fastest growth rate can be up to 15.9µm h-1 . Finally, VG arrays with a height of 144µm are successfully synthesized at an average rate of 14.4µm h-1 . As a kind of super black material, these VG arrays exhibit an ultra-low reflectance of 0.25%, showing great prospect in stray light shielding.

First-principles investigation on structural and photoelectric properties of (Nb, Ta) codoped anatase TiO2

The structural and photoelectric properties of (Nb, Ta) codoped anatase TiO2 were studied by first-principles calculations based on density functional theory and the Hubbard U correction. The results demonstrated that hybridized states composed of Ta 5d and Nb 4d orbitals at the bottom of the conduction band enabled the Fermi level to enter the conduction band and facilitated (Nb, Ta) codoped anatase TiO2 to exhibit n-type metallic characteristics, and the conductivity of Ti0·875Nb0·0625Ta0·0625O2(I) is approximately 3.2 times that of Ti0·9375Nb0·0625O2. Noted that both conductivity and mobility decreased with the increase of the distance between impurity Nb and Ta atoms and the Nb doping concentration. Moreover, the calculated results of optical properties presented the shifts of the absorption edges towards the ultraviolet region, and (Nb, Ta) codoped anatase TiO2 possessed the high transmittance thanks to its low absorption and reflection of visible light.

Multifunctional Ag-ZrB2 composite film with low infrared emissivity, low visible light reflectance and hydrophobicity

Zirconium Boride (ZrB2) thin film exhibits excellent low infrared emissivity property, but the infrared emissivity in the mid-infrared waveband is still higher than that of traditional metal film. In this work, we reported Ag -ZrB2 nanocomposite film with low emissivity in the mid-infrared waveband by magnetron co-sputtering method. The effect of Ag content on properties of Ag-ZrB2 nanocomposite film were discussed in details. As the increase of Ag content, the infrared emissivity ε3-5μm and ε8-14μm decrease to 0.11 and 0.04 respectively. In addition, the reflectivity(R = 65%) of visible light is still lower than that of conventional metals. Consequently, the Ag-ZrB2 nanocomposite film shows low detectability in the infrared and visible wavebands, which is beneficial for infrared–visible compatible stealth. Meanwhile, ZrB2 matrix changes from hydrophilic to hydrophobic due to Ag segregation to the surface.

P‐128: Student Poster: Optimizing OLED Pixel Structures for Consistently Low Ambient Light Reflection over Viewing Angles

Achieving low ambient light reflection is essential for OLED displays. However, inevitable surface undulation associated with pixel structures naturally induces scattering reflection over larger viewing angles, even with circular polarizers. This work reports optimized designs of OLED pixel structures for minimizing such scattering reflection and for achieving consistently low ambient light reflection over angles and enhanced viewing experiences.

Determination of Design Solutions to Overcome the Daylighting Design Failure Observed in Existing Educational Building

Malaysia is blessed with abundant natural light throughout the year. However, as buildings absorb heat from it, the amount of energy required for cooling purposes increases, which is one of the causes of electricity consumption. This research focused on investigating daylight level with a variety of case study classroom characteristics that contribute to daylighting design failure factors. Hence, indoor and outdoor daylight levels were measured for five (5) days in each of the classrooms through field measurement method. The observation wasconducted simultaneously with the field measurement to assess the obstacles to implementing efficient daylighting strategies in the classrooms. The results show that the daylight performance for all of the case study classrooms was not withinthe prescribed suitable range as specified in MS1525 (2019). The classroom design is insufficient to manage daylight in classrooms, which is the most likely reason for the poor illuminance level results. Furthermore, the amount and performanceof daylight in the classroom are influenced by the classroom's specificdesign. The main factors leadingto design failures, according to theobservation analysis are poor classrooms orientation, double-loaded buildings with single-loaded windows, small glazing areas, low window placement, inappropriate glazing properties, and low light reflectance value. Based on the failure criteria stated, the best practices of classroom daylighting design were found.Furthermore, this study makes a few recommendations to increase the daylight value in all classrooms. This researchidentified problems that impact low daylight performance in educational buildingsand should be used to raise awareness of the benefits of daylight for occupants.