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Recent Submissions

  • Plasmonic Nb2CTx MXene-MAPbI3 Heterostructure for Self-Powered Visible-NIR Photodiodes

    Liu, Zhixiong; El Demellawi, Jehad K.; Bakr, Osman; Ooi, Boon S.; Alshareef, Husam N. (ACS Nano, American Chemical Society (ACS), 2022-05-01) [Article]
    The ability of MXenes to efficiently absorb light is greatly enriched by the surface plasmons oscillating at their two-dimensional (2D) surfaces. Thus far, MXenes have shown impressive plasmonic absorptions spanning the visible and infrared (IR) regimes. However, their potential use in IR optoelectronic applications, including photodiodes, has been marginally investigated. Besides, their relatively low resistivity has limited their use as photosensing materials due to their intrinsic high dark current. Herein, heterostructures made of methylammonium lead triiodide (MAPbI3) perovskite and niobium carbide (Nb2CTx) MXene are prepared with a matching band structure and exploited for self-powered visible-near IR (NIR) photodiodes. Using MAPbI3 has expanded the operation range of the MAPbI3/Nb2CTx photodiode to the visible regime while suppressing the relatively large dark current of the NIR-absorbing Nb2CTx. In consequence, the fabricated MAPbI3/Nb2CTx photodiode has responded linearly to white light illumination with a responsivity of 0.25 A/W and a temporal photoresponse of <4.5 μs. Furthermore, when illuminated by NIR laser (1064 nm), our photodiode demonstrates a higher on/off ratio (∼103) and faster response times (<30 ms) compared to that of planar Nb2CTx-only detectors (<2 and 20 s, respectively). The performed space-charge-limited current (SCLC) and capacitance measurements reveal that such an efficient and enhanced charge transfer depends on the coordinate bonding between the surface groups of the MXene and the undercoordinated Pb2+ ions of the MAPbI3 at the passivated MAPbI3/Nb2CTx interface.
  • Maritime Communications: A Survey on Enabling Technologies, Opportunities, and Challenges

    Alqurashi, Fahad S.; Trichili, Abderrahmen; Saeed, Nasir; Ooi, Boon S.; Alouini, Mohamed-Slim (arXiv, 2022-04-27) [Preprint]
    Water covers 71% of the Earth's surface, where the steady increase in oceanic activities has promoted the need for reliable maritime communication technologies. The existing maritime communication systems involve terrestrial, aerial, and satellite networks. This paper presents a holistic overview of the different forms of maritime communications and provides the latest advances in various marine technologies. The paper first introduces the different techniques used for maritime communications over the RF and optical bands. Then, we present the channel models for RF and optical bands, modulation and coding schemes, coverage and capacity, and radio resource management in maritime communications. After that, the paper presents some emerging use cases of maritime networks, such as the Internet of Ships (IoS) and the ship-to-underwater Internet of things (IoT). Finally, we highlight a few exciting open challenges and identify a set of future research directions for maritime communication, including bringing broadband connectivity to the deep sea, using THz and visible light signals for on-board applications, and data-driven modeling for radio and optical marine propagation.
  • Wide-field-of-view Perovskite Quantum-dots Fibers Array for Easing Pointing, Acquisition and Tracking in Underwater Wireless Optical Communication

    Kang, Chun Hong; Alkhazragi, Omar; Sinatra, Lutfan; Alshaibani, Sultan; Wang, Yue; Li, Kuang-Hui; Kong, Meiwei; Lutfullin, Marat; Bakr, Osman; Ng, Tien Khee; Ooi, Boon S. (IEEE, 2022-04-13) [Conference Paper]
    We demonstrated, for the first time, perovskite quantum-dots optical fibers array successfully eases the pointing, acquisition and tracking requirement facing visible-laser-based underwater wireless optical communication.
  • Metal–Organic Frameworks in Mixed-Matrix Membranes for High-Speed Visible-Light Communication

    Wang, Jian-Xin; Wang, Yue; Nadinov, Issatay; Yin, Jun; Gutierrez Arzaluz, Luis; Healing, George; Alkhazragi, Omar; Cheng, Youdong; Jia, Jiangtao; Alsadun, Norah Sadun; Kale, Vinayak Swamirao; Kang, Chun Hong; Ng, Tien Khee; Shekhah, Osama; Alshareef, Husam N.; Bakr, Osman; Eddaoudi, Mohamed; Ooi, Boon S.; Mohammed, Omar F. (Journal of the American Chemical Society, American Chemical Society (ACS), 2022-04-12) [Article]
    Mixed-matrix membranes (MMMs) based on luminescent metal-organic frameworks (MOFs) and emissive polymers with the combination of their unique advantages have great potential in separation science, sensing, and light-harvesting applications. Here, we demonstrate MMMs for the field of high-speed visible-light communication (VLC) using a very efficient energy transfer strategy at the interface between a MOF and an emissive polymer. Our steady-state and ultrafast time-resolved experiments, supported by high-level density functional theory calculations, revealed that efficient and ultrafast energy transfer from the luminescent MOF to the luminescent polymer can be achieved. The resultant MMMs exhibited an excellent modulation bandwidth of around 80 MHz, which is higher than those of most well-established color-converting phosphors commonly used for optical wireless communication. Interestingly, we found that the efficient energy transfer further improved the light communication data rate from 132 Mb/s of the pure polymer to 215 Mb/s of MMMs. This finding not only showcases the promise of the MMMs for high-speed VLC but also highlights the importance of an efficient and ultrafast energy transfer strategy for the advancement of data rates of optical wireless communication.
  • Large-Scale and High-Quality III-Nitride Membranes Through Microcavity-Assisted Crack Propagation by Engineering Tensile-Stressed Ni Layers

    Min, Jung-Hong; Lee, Kwangjae; Chung, Tae-Hoon; Min, Jung-Wook; Li, Kuang-Hui; Kang, Chun Hong; Kwak, Hoe-Min; Kim, Tae-Hyeon; Yuan, Youyou; Kim, Kyoung-Kook; Lee, Dong-Seon; Ng, Tien Khee; Ooi, Boon S. (Elsevier BV, 2022-04-11) [Preprint]
    Epitaxially-grown III-nitride alloys are one of tightly-bonded materials with mixed covalent-ionic bonds. This tight bonding presents tremendous challenges in developing III-nitride membranes even though the semiconductor membranes can provide numerous advantages by removing the thick, inflexible, and costly substrates. Herein, cavities with various sizes were introduced by overgrowing target layers such as undoped GaN and green LED on nanoporous templates prepared by electrochemical etching of n-type GaN. The large primary interfacial toughness was effectively reduced according to the design of the cavity density, and the overgrown target layers were then conveniently exfoliated by engineering tensile-stressed Ni layers. The resulting III-nitride membranes maintained the high crystal quality even after the exfoliation due to the use of the GaN-based nanoporous templates having the same lattice constant. The microcavity-assisted crack propagation process developed for the current III-nitride membranes forms a universal process for developing various kinds of large-scale and high-quality semiconductor membranes.
  • Underwater turbulence on scintillating-fiber based omnidirectional underwater wireless optical communication system

    Guo, Yujian; Marie, Sohailh; Kong, Meiwei; Sait, Mohammed; Ng, Tien Khee; Ooi, Boon S. (SPIE, 2022-03-03) [Conference Paper]
    The underwater wireless optical communication (UWOC) technology is vastly developing due to its advantages of high bandwidth, large capacity, and low latency. However, the complex underwater channel characteristics and strict requirements on pointing, acquisition, and tracking (PAT) systems hinder the performance and augmentation of UWOC. A large-area scintillating-fiber-based UWOC system is proposed to solve the PAT issue while offering high-speed, omnidirectional data detection over turbulent underwater channels. In this work, we utilized 120-cm2 coverage area scintillating fibers as a photoreceiver. The large area scintillating fibers realize omnidirectional signal detection by absorbing an incident optical radiation, re-emitting it at a longer wavelength, and then guided to the end of the fibers connected with an avalanche photodetector. The UWOC system offers a 3-dB bandwidth of 66.62 MHz, and a 250 Mbit/s data rate is achieved using non-return-to-zero on-off keying (NRZ-OOK) modulation. The system was tested over a 1.5-m underwater channel under turbulences of air bubbles, temperature, salinity, and turbidity. We generated bubbles by blowing 0.20, 0.63, and 1.98 mL/s speeds of Nitrogen gas flow. A temperature gradient of 1.33 and 2.67 Celsius/m was introduced by circulating warm and cold water at the two tank ends, respectively. Salinity concentrations at 35 and 40 ppt were introduced to emulate the salinity in the Red Sea. Lastly, different volumes of MaaloxTM were added into pure water to emulate pure sea, coastal ocean, and turbid harbor water. The fiber-based UWOC system operates under those turbulence conditions with error-free communication and 0% outage probability.
  • Efficient channel modeling of structured light in turbulence using generative adversarial networks

    Briantcev, Dmitrii; Cox, Mitchell; Trichili, Abderrahmen; Drozdov, Alice V.; Ooi, Boon S.; Alouini, Mohamed-Slim (Optics Express, The Optical Society, 2022-02-17) [Article]
    We present a fast and efficient simulation method of structured light free space optics (FSO) channel effects from propagation through a turbulent atmosphere. In a system that makes use of multiple higher order modes (structured light), turbulence causes crosstalk between modes. This crosstalk can be described by a channel matrix, which usually requires a complete physical simulation or an experiment. Current simulation techniques based on the phase-screen approximation method are very computationally intensive and are limited by the accuracy of the underlying models. In this work, we propose to circumvent these limitations by using a data-driven approach for the decomposition matrix simulation with a conditional generative adversarial network (CGAN) synthetic simulator.
  • Ultrafast Transient Infrared For Probing Trapping States In Hybrid Perovskite Films

    El-Zohry, Ahmed M.; Türedir, Bekir; Alsalloum, Abdullah; Maity, Partha; Bakr, Osman; Ooi, Boon S.; Mohammed, Omar F. (Research Square Platform LLC, 2022-02-07) [Preprint]
    Studying the charge dynamics of perovskite materials is a crucial step to understand the outstanding performance of these materials in various fields. Herein, we utilize transient absorption in the mid-infrared region, where solely electron signatures in the conduction bands are monitored without external contributions from other dynamical species. Within the measured range of 4000 nm to 6000 nm (2500-1666 cm-1), the recombination and the trapping processes of the excited carriers could be easily monitored. Moreover, we reveal that within this spectral region the trapping process could be distinguished from recombination process, in which the iodide-based films show more tendencies to trap the excited electrons in comparison to the bromide-based derivatives. The trapping process was assigned due to the emission released in the mid-infrared region, while the traditional band-gap recombination process did not show such process. Various parameters have been tested such as film composition, excitation dependence and the probing wavelength. This study open new frontiers for the transient mid-infrared absorption to assign the trapping process in perovskite films both qualitatively and quantitatively.
  • (InxGa1-x)2O3 grown using oxygen-plasma-assisted molecular beam epitaxy

    Wagstaff, Jonathan; Li, Zhirun; Ng, Tien Khee; Wehbe, Nimer; Ogieglo, Wojciech; Apreutesei, Mihai; Wang, Yue; Zhang, Huafan; Davaasuren, Bambar; Al Ibrahim, Redha H.; Ooi, Boon S. (2022) [Conference Paper]
    In this work, oxygen-plasma-assisted molecular beam epitaxy grown Ga2O3 and (InxGa1-x)2O3 semiconductors were deposited on c-plane sapphire substrates using low temperature (450°C) epitaxial growth process. Indium (In) incorporation was confirmed by secondary ion mass spectrometry (SIMS), X-ray diffraction (XRD) peak shift, and bandgap tuning. The incorporation has changed the material surface roughness and bandgap (Eg) from 5.084 to 4.858 eV as measured using spectrophotometry. Additionally, a difference in refractive index ~ 0.02 to 0.04 was found via spectroscopic ellipsometry over the wavelength range of 400 nm to 1690 nm. The structural and optical properties of (InxGa1-x)2O3 suggest a potential for photonic applications.
  • Compact scintillating-fiber/450-nm-laser transceiver for full-duplex underwater wireless optical communication system under turbulence

    Guo, Yujian; Kong, Meiwei; Sait, Mohammed; Marie, Sohailh; Alkhazragi, Omar; Ng, Tien Khee; Ooi, Boon S. (Optics Express, The Optical Society, 2021-12-20) [Article]
    The growing need for ocean monitoring and exploration has boosted underwater wireless optical communication (UWOC) technology. To solve the challenges of pointing, acquisition, and tracking (PAT) in UWOC technology, herein, we propose a 450-nm-laser/scintillating-fiber-based full-duplex (FD)-UWOC system for omnidirectional signal detection in real scenarios. The FD-UWOC system has a −3 dB bandwidth of 67 MHz with a low self-interference level of −44.59 dB. It can achieve a 250-Mbit/s data rate with on–off keying modulation scheme. The system’s robustness was validated by operating over 1.5-m underwater channel with air-bubble-, temperature-, salinity-, turbidity-, and mobility-induced turbulence with a low outage probability. Under air-bubble-induced turbulence, the highest outage probability was 28%. With temperature-, salinity-, and turbidity-induced turbulence, the system performed adequately, showing a highest outage probability of 0%, 3%, and 4%, respectively. In mobile cases, the highest outage probability of the FD-UWOC system was 14%, compared to an outage probability of 100% without utilizing the fluorescent optical antenna. To further validate its robustness, a deployment test was conducted in an outdoor diving pool. The system achieved a 250-Mbit/s data rate over a 7.5-m working distance in the stationary case and a 1-m working range in the mobile case with a 0% outage probability. The scintillating-fiber-based detector can be employed in UWOC systems and would help relieve PAT issues.
  • Theory and Practice of Orbital Angular Momentum and Beyond

    Trichili, Abderrahmen; Cox, Mitchell A.; Perez-Garcia, Benjamin; Ooi, Boon S.; Alouini, Mohamed-Slim (Wiley, 2021-12-14) [other]
    Nearly three decades since its discovery, orbital angular momentum (OAM) has proven to be highly versatile for a wide range of applications. It is an indispensable tool in quantum optics, has made a significant impact in optical tweezing, enabled higher contrast and more detailed imaging, and offers a convenient way to harness the space degree of freedom in telecommunications. In this paper, we present a review of a wide range of applications of OAM as well as describing the creation and detection of OAM modes, with a focus on the use of OAM in communications. In addition, we detail various similar higher-order optical modes, such as vector vortex modes, and provide an introduction to the use of OAM in quantum optics, pitched for readers new to the field.
  • Visible-Light Laser Diodes and Superluminescent Diodes: Characteristics and Applications

    Alkhazragi, Omar; Holguin Lerma, Jorge Alberto; Ng, Tien Khee; Ooi, Boon S. (Wiley, 2021-12-14) [Article]
    Semiconductor light-emitting technology has seen tremendous strides in recent decades and a rapidly increasing interest in it. The unique advantages and characteristics of this form of light generation include compactness, high efficiency, and reliability. With these recent advancements, light-emitting diodes (LEDs), laser diodes, and superluminescent diodes (SLDs) have become an indispensable part of our homes, factories, and research facilities. In particular, the sensitivity of the human eye to the visible wavelengths of the electromagnetic spectrum extending from 400 to 700 nm, and the optical response of many materials to such spectrum, make visible light indispensable for a plethora of applications ranging from displays for entertainment, to imaging in the medical field, to light-based atomic clocks. While LEDs are the most commonly found type of semiconductor light sources, laser diodes and SLDs are of special interest due to their higher output optical power, spectral purity, and coherence. In this tutorial, we first go over the main unique characteristics of the different types and configurations of visible-light laser diodes and SLDs and their general structures with a focus on their advantages compared to LEDs. We then discuss the applications in which these characteristics are of great interest in the fields of displays, communication, instrumentation, and photonic integrated circuits.
  • Coupling Plasmonic Pt Nanoparticles with AlGaN Nanostructures for Enhanced Broadband Photoelectrochemical-Detection Applications

    Kang, Yang; Wang, Danhao; Fang, Shi; Liu, Xin; Yu, Huabin; Jia, Hongfeng; Zhang, Haochen; Luo, Yuanmin; Ooi, Boon S.; He, Jr-Hau; Sun, Haiding; Long, Shibing (ACS Applied Nano Materials, American Chemical Society (ACS), 2021-12-02) [Article]
    Coupling the plasmonic metals with semiconductors often induces strong charge and energy transfer across heterointerfaces, offering an unprecedented opportunity to break the fundamental limit of semiconductor optoelectronic devices. Herein, we demonstrate a broadened photodetection bandwidth with drastically enhanced photoresponsivity of photoelectrochemical cells by coupling the plasmonic–platinum nanoparticles with p-type AlGaN-semiconductor nanostructures. Benefiting from the localized surface plasmon resonance at the platinum-AlGaN nanostructure interface, our devices exhibit a striking 3 orders of magnitude boost of the photoresponsivity in the visible band, which is barely attainable in pristine wide band gap semiconductors. Simultaneously, a nearly sevenfold enhancement of the photoresponsivity can also be achieved under 254 nm light illumination, demonstrating high-responsive deep ultraviolet-sensitive broad-bandwidth photodetection. Most importantly, the proposed plasmon-induced metal/semiconductor hybrid nanoarchitectures, by embracing a diversity of plasmonic metals combined with the wide tunable band gap of the group III-nitride semiconductors via synergy of the plasmonic–photoelectric effect, show significant promise in designing specific wavelength-dominance broadband photosensing systems of the future.
  • Silicon-integrated monocrystalline oxide-nitride heterostructures for deep-ultraviolet optoelectronics

    Alfaraj, Nasir; Li, Kuang-Hui; Kang, Chun Hong; Braic, Laurentiu; Zoita, Nicolae Catalin; Kiss, Adrian Emil; Ng, Tien Khee; Ooi, Boon S. (OPTICAL MATERIALS EXPRESS, The Optical Society, 2021-12-01) [Article]
    New opportunities for high-performance CMOS-compatible optoelectronic devices have accelerated the interest in vertically configured device topologies that enable next-generation photonic technologies. Lately, TiN has been identified as a promising refractory metal–ceramic for the hybrid integration of emerging semiconductor materials on a variety of substrates, including Si, MgO, and sapphire. Among these, Si is the least expensive and most commonly used element and substrate material in the semiconductor device industry. Following these examples, a hybrid oxide–nitride–Si stack is proposed and thoroughly investigated herein for its potential use in DUV optoelectronic device applications. The stack comprises β-Ga2O3 thin films grown heteroepitaxially on TiN/Si platforms, wherein the TiN interlayers were heteroepitaxially grown on bulk (100)-oriented Si and act as lattice-mismatched templates and bottom device electrodes. Albeit the relatively large lattice mismatch between Si and TiN, a low in-plane rotation of 3∘ revealed that the TiN layers continued to grow as a bulk crystal, paving the way for heteroepitaxial β-Ga2O3 thin films being grown without exhibiting amorphous and metastable phases. DUV photodetectors based on this optoelectronic heterostructure exhibited average peak spectral responsivity and external quantum efficiency levels as high as 249 A/W and 1.23 × 105%, respectively, in the ultraviolet-C regime at an illuminating power density of around 12 µW/cm2.
  • Influences of ALD Al2O3 on the surface band-bending of c-plane, Ga-face GaN

    Gong, Jiarui; Lu, Kuangye; Kim, Jisoo; Ng, Tien Khee; Kim, Donghyeok; Zhou, Jie; Liu, Dong; Kim, Jeehwan; Ooi, Boon S.; Ma, Zhenqiang (Japanese Journal of Applied Physics, IOP Publishing, 2021-11-25) [Article]
    The recently demonstrated approach of grafting n-type GaN with p-type Si or GaAs, by employing ultrathin Al2O3 at the interface, has shown the feasibility to overcome the poor p-type doping challenge of GaN. However, the surface band-bending of GaN that could be influenced by the Al2O3 has been unknown. In this work, the band-bending of c-plane, Ga-face GaN with ultrathin Al2O3 deposition at the surface of GaN was studied using X-ray photoelectron spectroscopy (XPS). The study shows that the Al2O3 can help suppress the upward band-bending of the c-plane, Ga-face GaN with a monotonic reduction trend from 0.48 eV down to 0.12 eV as the number of Al2O3 deposition cycles increases from 0 to 20. The study further shows that the band-bending can be mostly recovered after removing the Al2O3 layer, concurring that the introduction of ultrathin Al2O3 is the main reason for the surface band-bending modulation.
  • All-inorganic halide-perovskite-polymer luminescent fibers for high-bitrate ultraviolet free-space optical communication

    Kang, Chun Hong; Alkhazragi, Omar; Sinatra, Lutfan; Alshaibani, Sultan; Li, Kuang-Hui; Kong, Meiwei; Lutfullin, Marat; Bakr, Osman; Ng, Tien Khee; Ooi, Boon S. (IEEE, 2021-11-13) [Conference Paper]
    We demonstrate, for the first time, halide-perovskite-polymer-based luminescent fibers as a high-bitrate and near-omnidirectional photodetection platform for 375-nm ultraviolet laser-based free-space optical communication. Our demonstrations could enable future ultraviolet-to-visible optical receivers based on all-inorganic halide-perovskite nanomaterial to cater various dynamic scenarios in optical wireless communication.
  • Orientation Heredity in The Transformation of Two-Dimensional Epitaxial Films

    Xu, Xiangming; Smajic, Jasmin; Li, Kuang-Hui; Min, Jung-Wook; Lei, Yongjiu; Davaasuren, Bambar; He, Xin; Zhang, Xixiang; Ooi, Boon S.; Da Costa, Pedro M. F. J.; Alshareef, Husam N. (Advanced Materials, Wiley, 2021-11-11) [Article]
    Controlling the lattice orientation is significant for both two-dimensional (2D) vdW layered and non-layered film growth process. Here we report a unique and universal phenomena termed lattice orientation heredity (LOH). The LOH enables product films (including 2D layered materials) to inherit the lattice orientation from reactant films in a chemical conversion process, excluding the requirement on the substrate lattice order. We demonstrate the process universality by investigating the lattice transformations in the carbonization, nitridation, and sulfurization of epitaxial MoO2, ZnO, and In2O3 thin films. Their resultant compounds all inherit mono-oriented feature from their precursor oxides, including 2D vdW layered semiconductors (e.g., MoS2), metallic films (e.g., MXene-like Mo2C and MoN), wide bandgap semiconductors (e.g., hexagonal ZnS), and ferroelectric semiconductors (e.g., In2S3). Using LOH-grown MoN as a seeding layer, we achieved mono-oriented GaN on an amorphous quartz substrate. The LOH process is a universal strategy capable of growing epitaxial thin films (including 2D vdW layered materials) not only on single-crystalline but also the non-crystalline.
  • Dual-wavelength luminescent fibers receiver for wide field-of-view, Gb/s underwater optical wireless communication

    Sait, Mohammed; Trichili, Abderrahmen; Alkhazragi, Omar; Alshaibaini, Sultan; Ng, Tien Khee; Alouini, Mohamed-Slim; Ooi, Boon S. (Optics Express, The Optical Society, 2021-10-29) [Article]
    Extending the field-of-view (FoV) of underwater wireless optical communication (UWOC) receivers can significantly ease the need for active positioning and tracking mechanisms. Two bundle of scintillating fibers emitting at 430- and 488-nm were used to detect two independent signals from ultraviolet and visible laser sources. A zero-forcing approach to minimize inter-channel crosstalk was further implemented. A net aggregated UWOC data rate of 1 Gb/s was achieved using two wavelengths and a non-return-to-zero on-off keying scheme.
  • Photovoltage-Competing Dynamics in Photoelectrochemical Devices: Achieving Self-Powered Spectrally Distinctive Photodetection

    Liu, Xin; Wang, Danhao; Kang, Yang; Fang, Shi; Yu, Huabin; Zhang, Haochen; Memon, Muhammad Hunain; He, Jr-Hau; Ooi, Boon S.; Sun, Haiding; Long, Shibing (Advanced Functional Materials, Wiley, 2021-10-22) [Article]
    Multiple-band and spectrally distinctive photodetection play critical roles in building next-generation colorful imaging, spectroscopy, artificial vision, and optically controlled logic circuits of the future. Unfortunately, it remains challenging for conventional semiconductor photodetectors to distinguish different spectrum bands with photon energy above the bandgap of the material. Herein, for the first time, a photocurrent polarity-switchable photoelectrochemical device composed of group III-nitride semiconductors, demonstrating a positive photocurrent density of 10.54 µA cm−2 upon 254 nm illumination and a negative photocurrent density of −0.08 µA cm−2 under 365 nm illumination without external power supply, is constructed. Such bidirectional photocurrent behavior arises from the photovoltage-competing dynamics across two photoelectrodes. Importantly, a significant boost of the photocurrent and corresponding responsivity under 365 nm illumination can be achieved after decorating the counter electrode of n-type AlGaN nanowires with platinum (Pt) nanoparticles, which promote a more efficient redox reaction in the device. It is envisioned that the photocurrent polarity-switch behavior offers new routes to build multiple-band photodetection devices for complex light-induced sensing systems, covering a wide spectrum band from deep ultraviolet to infrared, by simply engineering the bandgaps of semiconductors.
  • Sustainable and Inexpensive Polydimethylsiloxane Sponges for Daytime Radiative Cooling

    Zhou, Lyu; Rada, Jacob; Zhang, Huafan; Song, Haomin; Mirniaharikandi, Seyededriss; Ooi, Boon S.; Gan, Qiaoqiang (Advanced Science, Wiley, 2021-10-20) [Article]
    Radiative cooling is an emerging cooling technology that can passively release heat to the environment. To obtain a subambient cooling effect during the daytime, chemically engineered structural materials are widely explored to simultaneously reject sunlight and preserve strong thermal emission. However, many previously reported fabrication processes involve hazardous chemicals, which can hinder a material's ability to be mass produced. In order to eliminate the hazardous chemicals used in the fabrication of previous works, this article reports a white polydimethylsiloxane (PDMS) sponge fabricated by a sustainable process using microsugar templates. By substituting the chemicals for sugar, the manufacturing procedure produces zero toxic waste and can also be endlessly recycled via methods widely used in the sugar industry. The obtained porous PDMS exhibits strong visible scattering and thermal emission, resulting in an efficient temperature reduction of 4.6 °C and cooling power of 43 W m−2 under direct solar irradiation. In addition, due to the air-filled voids within the PDMS sponge, its thermal conductivity remains low at 0.06 W (m K)−1. This unique combination of radiative cooling and thermal insulation properties can efficiently suppress the heat exchange with the solar-heated rooftop or the environment, representing a promising future for new energy-efficient building envelope material.

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