With the rapid growth in global energy consumption, the recovery of waste heat is becoming an important issue. Nevertheless, the recovery of near-room-temperature waste heat remains challenging ...because the slight temperature difference with the surroundings leads to extremely low thermoelectric power generation. In this study, we combined a daytime radiative cooling (DRC) technology with a thermoelectric generator (TEG) to efficiently recover near-room-temperature waste heat. We investigated the effects of the thermal radiation and thermal conduction properties of DRC materials on near-room-temperature waste heat recovery (WHR). We designed a hierarchical micro-nano h-BN/ZnO composite (MNHZC) that possessed an outstanding daytime radiative cooling ability and moderate thermal conductivity. With this hierarchical h-BN/ZnO composite, we achieved record-high levels of thermoelectric power generation of 225.3 and 412.3 mW m
−2
during the daytime and nighttime, respectively, with enhancements in thermoelectric power of 1030 and 190%, respectively. The attractive power generation ability of the MNHZC/TEG system suggests its great potential in low-grade waste heat recovery and environmental energy harvesting by consistently generating power in both the daytime and nighttime.
A newly designed daytime radiative cooling (DRC) strategy significantly enhances near-room-temperature waste heat recovery, generating power in both the daytime and nighttime.
This study displays the emissivities and optical properties of thin‐film metallic glasses in the thermal infrared (IR) region. It is found that the amorphous structure of the metallic glass hinders ...the movement of electrons, leading to unique optical properties in the thermal IR region. Measurements of the optical constants of NiNb thin‐film metallic glasses reveal that a high processing pressure and sputtering power yield high optical conductivity and a low damping constant. Adjusting the parameters of the sputtering processes allows the fabrication of thin‐film metallic glasses with a range of damping constants and also the change in the reflectance and emissivity. Applying optical thin film theory, the emissivity of thin‐film metallic glass in the thermal IR region can be modulated. The measured emissivity of the thin‐film metallic glass (45.35%) is significantly enhanced when compared with that of a Si substrate or metal film. Furthermore, the cooling ability of the optimal metallic glass is much higher than that of Si and metal films. These findings reveal that metallic glass films can display thermal radiative properties superior to those of metals and semiconductors, making them promising materials for use in electronic devices with excellent mechanical characteristics and heat dissipation properties.
Besides excellent mechanical properties, metallic glasses also have distinct optical properties and thermal radiation properties due to the amorphous structure. The optical properties of metallic glass films can be greatly modulated with different deposition processes. Moreover, metallic glass films with high emissivity can be obtained by applying optical thin film theory. The result shows that metallic glass films have great potential for improving the performance of electronic and optoelectronic devices and systems.
Optical inspection is a rapid and non‐destructive method for characterizing the properties of two‐dimensional (2D) materials. With the aid of optical inspection, in situ and scalable monitoring of ...the properties of 2D materials can be implemented industrially to advance the development and progress of 2D material‐based devices toward mass production. This review discusses the optical inspection techniques that are available to characterize various 2D materials, including graphene, transition metal dichalcogenides (TMDCs), hexagonal boron nitride (h‐BN), group‐III monochalcogenides, black phosphorus (BP), and group‐IV monochalcogenides. First, the authors provide an introduction to these 2D materials and the processes commonly used for their fabrication. Then they review several of the important structural properties of 2D materials, and discuss how to characterize them using appropriate optical inspection tools. The authors also describe the challenges and opportunities faced when applying optical inspection to recently developed 2D materials, from mechanically exfoliated to wafer‐scale‐grown 2D materials. Most importantly, the authors summarize the techniques available for largely and precisely enhancing the optical signals from 2D materials. This comprehensive review of the current status and perspective of future trends for optical inspection of the structural properties of 2D materials will facilitate the development of next‐generation 2D material‐based devices.
This review discusses the optical inspection techniques that are available to characterize various 2D materials. The current status and perspective of future trends for optical inspection of the structural properties of 2D materials are comprehensively reviewed, which will facilitate the development of next‐generation 2D material‐based devices.
Large-area surface-enhanced Raman spectroscopy (SERS) sensing platforms displaying ultrahigh sensitivity and signal uniformity have potentially enormous sensing applicability, but they are still ...challenging to prepare in a scalable manner. In this study, silver nanopaste (AgNPA) was employed to prepare a wafer-scale, ultrasensitive SERS substrate. The self-generated, high-density Ag nanocracks (NCKs) with small gaps could be created on Si wafers via a spin-coating process, and provided extremely abundant hotspots for SERS analyses with ultrahigh sensitivity—down to the level of single molecules (enhancement factor: ca. 1010; detection limit: ca. 10–18 M)—and great signal reproducibility (variation: ca. 3.6%). Moreover, the Ag NCK arrays demonstrated broad applicability and practicability for on-site detection when combined with a portable 785 Raman spectrometer. This method allowed the highly sensitive detection of a diverse range of analytes (benzoapyrene, di-2-ethylhexyl phthalate, aflatoxins B1, zearalenone, ractopamine, salbutamol, sildenafil, thiram, dimethoate, and methamidophos). In particular, pesticides are used extensively in agricultural production. Unfortunately, they can affect the environment and human health as a result of acute toxicity. Therefore, the simultaneous label-free detection of three different pesticides was demonstrated. Finally, the SERS substrates are fabricated through a simple, efficient, and scalable process that offers new opportunities for mass production.
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•Wafer-scale SERS substrates manufactured by silver nanopaste via a simple process.•Silver nanocracks with abundant gaps can form through disconnection of nanopaste.•Enhancement factor: 1010; detection limit: attomolar; signal reproducibility: 3.6%.•Trace amount of dimethoate (0.66 ppb) was detected with portable Raman spectrometer.•Simultaneous label-free detection of various pesticides can be achieved.
The localized surface plasmon resonance of plasmonic nanoparticles (NPs) can be coupled with a noble metal substrate (S) to induce a localized augmented electric field (E-field) concentrated at the ...NP–S gap. Herein, we analyzed the fundamental near-field properties of metal NPs on diverse substrates numerically (using the 3D finite-difference time-domain method) and experimentally using surface-enhanced Raman scattering (SERS). We systematically examined the effects of plasmonic NPs on noble metals (Ag and Au), non-noble metals (Al, Ti, Cu, Fe, and Ni), semiconductors (Si and Ge), and dielectrics (TiO2, ZnO, and SiO2) as substrates. For the AgNPs, the Al (11,664 times) and Si (3969 times) substrates produced considerable E-field enhancements, with Al in particular generating a tremendous E-field enhancement comparable in intensity to that induced by a Ag (28,224 times) substrate. Notably, we found that a superior metallic character of the substrate gave rise to easier induction of image charges within the metal substrate, resulting in a greater E-field at the NP–S gap; on the other hand, the larger the permittivity of the nonmetal substrate, the greater the ability of the substrate to store an image charge distribution, resulting in stronger coupling to the charges of localized surface plasmon resonance oscillation on the metal NP. Furthermore, we measured the SERS spectra of rhodamine 6G (a commonly used Raman spectral probe), histamine (a biogenic amine used as a food freshness indicator), creatinine (a kidney health indicator), and tert-butylbenzene an extreme ultraviolet (EUV) lithography contaminant on AgNP-immobilized Al and Si substrates to demonstrate the wide range of potential applications. Finally, the NP–S gap hotspots appear to be widely applicable as an ultrasensitive SERS platform (∼single-molecule level), especially when used as a powerful analytical tool for the detection of residual contaminants on versatile substrates.
Although gallium arsenide (GaAs) is one of the most commonly used semiconductor substrate materials, its intrinsic bandgap of 1.42 eV hinders the use of GaAs photodetectors for optical communication. ...In this study, hot‐electron‐based GaAs active antenna devices are demonstrated, displaying photoresponses well below the bandgap at the telecommunication wavelengths. Using a deep‐trench/thin metal (DTTM) active antenna, a metallic plasmonic structure, high photoresponsivities are achieved under zero bias at wavelengths of 1310 and 1550 nm. Even though the resistance of the semi‐insulating GaAs substrate is approximately 106 times larger than that of the n‐type silicon (Si) substrate, the photoresponsivities are commensurate with most previously reported hot‐electron n‐Si‐based photodetectors operating at communication wavelengths. Furthermore, the devices can be operated under a reverse‐biased voltage with significant enhancements in the photoresponsivities; the highest photoresponsivity (19.96 mA W−1 at 1310 nm) is greater than those reported in all previous studies. Moreover, these GaAs‐based devices are sufficiently robust to be operated over a wide range of operating temperatures (from −193 to +200 °C) while displaying a relatively large bandgap, low dark leakage currents, and high electron mobilities at low temperature. Because these devices can operate at high and low temperatures and at large voltage biases, they are suitable for use under harsh environmental conditions.
This paper demonstrates the first examples of hot‐electron‐based GaAs active antenna devices with photoresponse well below its bandgap at wavelengths of 1310 and 1550 nm. With the advantages of a relatively large bandgap, low leakage currents, and high electron mobilities, GaAs‐based devices are robust to be operated at extreme temperatures and large voltage biases for use under harsh environmental conditions.
Abstract
Particulate matter emitted through human activities not only pollutes the air, but also cools the Earth by scattering shortwave solar radiation. However, coarser dust particles have been ...found to exert a warming effect that could, to some extent compensate for the cooling effect of fine dust. Here we investigate the radiative effects of sulfate containing aerosols of various sizes and core/shell structures using Mie scattering and three-dimensional finite difference time domain simulations of the electromagnetic fields inside and around particulate matter particles. We find that not only coarse dust, but also fine non-light-absorbing inorganic aerosols such as sulfate can have a warming effect. Specifically, although the opacity of fine particles decreases at longer wavelengths, they can strongly absorb and re-emit thermal radiation under resonance conditions at long wavelength. We suggest that these effects need to be taken into account when assessing the contribution of aerosols to climate change.
This study reports the first attempt to characterize the quality, defects, and strain of as‐grown monolayer transition metal dichalcogenide (TMDC)‐based 2D materials through exciton anisotropy. A ...standard ellipsometric parameter (Ψ) to observe anisotropic exciton behavior in monolayer 2D materials is used. According to the strong exciton effect from phonon–electron coupling processes, the change in the exciton in the Van Hove singularity is sensitive to lattice distortions such as defects and strain. In comparison with Raman spectroscopy, the variations in exciton anisotropy in Ψ are more sensitive for detecting slight changes in the quality and strain of monolayer TMDC films. Moreover, the optical power requirement for TMDC characterization through exciton anisotropy in Ψ is ≈10−5 mW cm−2, which is significantly less than that of Raman spectroscopy (≈106 mW cm−2). The standard deviation of the signals varies with strain (defects) in Raman spectra and exciton anisotropies in Ψ are 0.700 (0.795) and 0.033 (0.073), indicating that exciton anisotropy is more sensitive to slight changes in the quality of monolayer TMDC films.
This study reports the first attempt to characterize the as‐grown quality, defects, and strain of transition metal dichalcogenide (TMDC)‐based 2D materials through exciton anisotropy. A simple ellipsometric parameter‐based method for observing the anisotropic excitonic behavior in 2D monolayer materials is demonstrated. The change in the exciton of TMDCs in the Van Hove singularity is superior to the detection indicator.
Passive daytime radiative cooling (PDRC), as a strategy to dissipate heat through an atmospheric transparency window (ATW) to outer space without any extra energy consumption, has been recently ...considered as a novel approach for global net-zero emissions. However, limited to expensive manufacturing, poor thermal/chemical stability, or insufficient weather-resistance, the development of a PDRC building material for long-term outdoor usages still remains a challenge. Here, a scalable superhydrophobic silica metafibers (sh-SMF) was fabricated via an electrospinning process combined with the fluorosilane-modification on fiber surface. The optically engineered sh-SMF could attain an extremely high average reflectivity (∼97 %) with near-zero absorption in the solar spectral region, due to the multiple backscattering at the fiber/air interfaces. In addition, the sh-SMF possessed a high average emissivity (∼90 %) in ATW, originated from the strong phonon resonances of the abundant Si-O bonds. Thus, the optimal sh-SMF realized a sub-ambient cooling performance of 6 °C (4 °C in nighttime) and the maximum cooling power of 112 W/m2 (87 W/m2 in nighttime) under a solar irradiance of ∼790 W/m2. Besides, the temperature decline for the sh-SMF-covered building and vehicle models could also achieve 12.7 °C and 17 °C under sunlight, respectively. Noteworthily, the ceramic sh-SMF could withstand high temperatures over 1200 °C, which might effectively prolong the time for resident to evacuate from buildings in fireground situation. Moreover, the superhydrophobic surface (contact angle=155°) of sh-SMF demonstrated attractive self-cleaning and anti-mildew properties. Furthermore, the excellent weather resistance against acid rain and ultraviolet exposure endowed the sh-SMF with long-term cooling performance. Finally, the sh-SMF with above mentioned properties opens a path for future energy-efficient and sustainable architectural applications.
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•Superhydrophobic silica metafibers (sh-SMFs), fabricated through electrospinning, serving as a scalable, flexible, and flame- and weather-resistant ceramic PDRC emitter.•The optimal sh-SMFs operated with a near-zero value of Psun (<3 W/m2), and a high value of Pcooling (112 W/m2) during the daytime, resulting from high solar reflectivity (97 %) and thermal emissivity (90 %).•Maximum temperature decreases of sh-SMF–covered building and vehicle models of 12.7 and 17 °C, respectively, under sunlight.•The sh-SMFs could withstand high temperatures (>1200 °C), making them especially suitable as a building material that could effectively prolong the time available for residents to evacuate buildings in the event of fire.•The sh-SMFs display excellent self-cleaning, anti-mildew, and anti-acid abilities, combined with great UV-resistance, resulting in great weather-resistance for long-term outdoor applications.
Fluorescent nanodiamonds (FNDs) having nitrogen-vacancy (NV) centers have drawn much attention for their biocompatibility and stable optical properties. Nevertheless, the NV centers are located in ...the interior of the FNDs, and it has not been possible to increase the fluorescence intensity of FNDs efficiently using previously developed enhancement methods. In this paper, we present a simple nanocavity structure that enhances the fluorescence intensity of FNDs. The designed Al/SiO2 nanocavities are stable and inexpensive, and provide a large region for efficient enhancement of fluorescence that can cover most 100 nm FNDs. By tuning the thickness of the capping SiO2 layer of the Al/SiO2 nanocavities, the distributions of both the spatial and spectral electric field intensities of the FNDs could be controlled and manipulated. In general, the FNDs were excited using a green-yellow laser; the broadband fluorescence of the FNDs comprised the emissions from neutral (NV0) and negatively charged (NV-) NV centers. To enhance the fluorescence intensity from the NV- centers of the FNDs, we designed an Al/70 nm SiO2 nanocavity to function at excitation and emission wavelengths of 633 and 710 nm, respectively, allowing the NV- centers to be excited efficiently; as a result, we achieved an enhancement in fluorescence intensity of 11.2-fold. Moreover, even when we covered 100 nm FNDs with polyglycerol (forming p-FND), the fluorescence intensities of the p-FND particles placed on the nanocavities remained greatly enhanced.
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