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Recent Submissions

  • Hybrid distributed acoustic-temperature sensing using a few-mode fiber

    Ashry, Islam; Mao, Yuan; Ng, Tien Khee; Hveding, Frode; Arsalan, Muhammad; Ooi, Boon S. (SPIE, 2020-03-02) [Conference Paper]
    Optical fiber distributed acoustic sensor (DAS) and distributed temperature sensor (DTS) are considerably desirable for many important applications including oil and gas industry. Simultaneous measurements of vibration and temperature will exclude the need for two separate DAS and DTS systems, reduce overall cost, and ensure continuous real-time monitoring of these two important sensing parameters. We here devise a hybrid DAS-DTS system using a few-mode fiber (FMF). Although the system requirements for DAS and DTS are quite different, FMF is considered an ideal compromise to satisfy the requirements of the two systems.
  • Titanium Carbide MXene Nucleation Layer for Epitaxial Growth of High-Quality GaN Nanowires on Amorphous Substrates

    Prabaswara, Aditya; Kim, Hyunho; Min, Jung-Wook; Subedi, Ram Chandra; Anjum, Dalaver H.; Davaasuren, Bambar; Moore, Kalani; Conroy, Michele; Mitra, Somak; Roqan, Iman S.; Ng, Tien Khee; Alshareef, Husam N.; Ooi, Boon S. (ACS Nano, American Chemical Society (ACS), 2020-02-03) [Article]
    Growing III-nitride nanowires on 2D materials is advantageous, as it effectively decouples the underlying growthsubstrate from the properties of the nanowires. As a relatively new family of 2D materials, MXenes are promising candidates as III-nitride nanowire nucleation layers capable of providing simultaneous transparency and conductivity. In this work, we demonstrate the direct epitaxial growth of GaN nanowires on Ti3C2 MXene films. The MXene films consist of nanoflakes spray coated onto an amorphous silica substrate. We observed an epitaxial relationship between the GaN nanowires and the MXene nanoflakes due to the compatibility between the triangular lattice of Ti3C2 MXene and the hexagonal structure of wurtzite GaN. The GaN nanowires on MXene show good material quality and partial transparency at visible wavelengths. Nanoscale electrical characterization using conductive atomic force microscopy reveals a Schottky barrier height of ∼330 meV between the GaN nanowire and the Ti3C2 MXene film. Our work highlights the potential of using MXene as a transparent and conductive preorienting nucleation layer for high-quality GaN growth on amorphous substrates.
  • Time–Energy Quantum Uncertainty—Quantifying the Effectiveness of Surface Defect Passivation Protocols for Low-Dimensional Semiconductors

    Alfaraj, Nasir; Alghamdi, Wael; Alawein, Meshal; Ajia, Idris A.; Priante, Davide; Janjua, Bilal; Sun, Haiding; Ng, Tien Khee; Ooi, Boon S.; Roqan, Iman S.; Li, Xiaohang (ACS Applied Electronic Materials, American Chemical Society (ACS), 2020-01-22) [Article]
    The degree of enhancement in radiative recombination in ensembles of semiconductor nanowires after chemical treatment is quantified within a derived limit, by correlating the energy released during the photoemission processes of the light–matter reaction and the effective carrier recombination lifetimes. It is argued that the usage of surface recombination velocity or surface saturation current density as passivation metrics that assess the effectiveness of surface passivation does not provide strict and universal theoretical bounds within which the degree of passivation can be confined. In this context, the model developed in this study provides a broadly applicable surface passivation metric for direct energy bandgap semiconductor materials. This is because of its reliance on the dispersion in energy and lifetime of electron–hole recombination emission at room temperature, in lieu of the mere dependence on the ratio of peak emission spectral intensities or temperature- and power-dependent photoluminescence measurements performed prior and subsequent to surface treatment. We show that the proposed quantification method, on the basis of steady-state and transient photoluminescence measurements performed entirely at room temperature, provides information on the effectiveness of surface state passivation through a comparison of the dispersion in carrier lifetimes and photon energy emissions in the nanowire ensemble before and after surface passivation. Our measure of the effectiveness of a surface passivation protocol is in essence the supremum of lower bounds one can derive on the product of Δt and ΔE.
  • High-speed colour-converting photodetector with all-inorganic CsPbBr3 perovskite nanocrystals for ultraviolet light communication

    Kang, Chun Hong; Dursun, Ibrahim; Liu, Guangyu; Sinatra, Lutfan; Sun, Xiaobin; Kong, Meiwei; Pan, Jun; Maity, Partha; Ooi, Ee-Ning; Ng, Tien Khee; Mohammed, Omar F.; Bakr, Osman; Ooi, Boon S. (Light: Science & Applications, Springer Science and Business Media LLC, 2019-10-16) [Article]
    Optical wireless communication (OWC) using the ultra-broad spectrum of the visible-to-ultraviolet (UV) wavelength region remains a vital field of research for mitigating the saturated bandwidth of radio-frequency (RF) communication. However, the lack of an efficient UV photodetection methodology hinders the development of UV-based communication. The key technological impediment is related to the low UV-photon absorption in existing silicon photodetectors, which offer low-cost and mature platforms. To address this technology gap, we report a hybrid Si-based photodetection scheme by incorporating CsPbBr3 perovskite nanocrystals (NCs) with a high photoluminescence quantum yield (PLQY) and a fast photoluminescence (PL) decay time as a UV-to-visible colour-converting layer for high-speed solar-blind UV communication. The facile formation of drop-cast CsPbBr3 perovskite NCs leads to a high PLQY of up to ~73% and strong absorption in the UV region. With the addition of the NC layer, a nearly threefold improvement in the responsivity and an increase of ~25% in the external quantum efficiency (EQE) of the solar-blind region compared to a commercial silicon-based photodetector were observed. Moreover, time-resolved photoluminescence measurements demonstrated a decay time of 4.5 ns under a 372-nm UV excitation source, thus elucidating the potential of this layer as a fast colour-converting layer. A high data rate of up to 34 Mbps in solar-blind communication was achieved using the hybrid CsPbBr3–silicon photodetection scheme in conjunction with a 278-nm UVC light-emitting diode (LED). These findings demonstrate the feasibility of an integrated high-speed photoreceiver design of a composition-tuneable perovskite-based phosphor and a low-cost silicon-based photodetector for UV communication.
  • Ultraviolet-to-blue color-converting scintillating-fibers photoreceiver for 375-nm laser-based underwater wireless optical communication

    Kang, Chun Hong; Trichili, Abderrahmen; Alkhazragi, Omar; Zhang, Huafan; Subedi, Ram Chandra; Guo, Yujian; Mitra, Somak; Shen, Chao; Roqan, Iman S.; Ng, Tien Khee; Alouini, Mohamed-Slim; Ooi, Boon S. (Optics Express, The Optical Society, 2019-10-08) [Article]
    Underwater wireless optical communication (UWOC) can offer reliable and secure connectivity for enabling future internet-of-underwater-things (IoUT), owing to its unlicensed spectrum and high transmission speed. However, a critical bottleneck lies in the strict requirement of pointing, acquisition, and tracking (PAT), for effective recovery of modulated optical signals at the receiver end. A large-area, high bandwidth, and wide-angle-of-view photoreceiver is therefore crucial for establishing a high-speed yet reliable communication link under non-directional pointing in a turbulent underwater environment. In this work, we demonstrated a large-area, of up to a few tens of cm2, photoreceiver design based on ultraviolet(UV)-to-blue color-converting plastic scintillating fibers, and yet offering high 3-dB bandwidth of up to 86.13 MHz. Tapping on the large modulation bandwidth, we demonstrated a high data rate of 250 Mbps at bit-error ratio (BER) of 2.2 × 10−3 using non-return-to-zero on-off keying (NRZ-OOK) pseudorandom binary sequence (PRBS) 210-1 data stream, a 375-nm laser-based communication link over the 1.15-m water channel. This proof-of-concept demonstration opens the pathway for revolutionizing the photodetection scheme in UWOC, and for non-line-of-sight (NLOS) free-space optical communication.
  • Catalyst-Free Vertical ZnO-Nanotube Array Grown on p-GaN for UV-Light-Emitting Devices

    Alwadai, Norah M.; Ajia, Idris A.; Janjua, Bilal; Flemban, Tahani H.; Mitra, Somak; Wehbe, Nimer; Wei, Nini; Lopatin, Sergei; Ooi, Boon S.; Roqan, Iman S. (ACS Applied Materials & Interfaces, American Chemical Society (ACS), 2019-07-25) [Article]
    One-dimensional (1D) structures-based UV-light-emitting diode (LED) has immense potential for next-generation applications. However, several issues related to such devices must be resolved first, such as expensive material and growth methods, complicated fabrication process, efficiency droop, and unavoidable metal contamination due to metal catalyst that reduces device efficiency. To overcome these obstacles, we have developed a novel growth method for obtaining a high-quality hexagonal, well-defined, and vertical 1D Gd-doped n-ZnO nanotube (NT) array deposited on p-GaN films and other substrates by pulsed laser deposition. By adopting this approach, the desired high optical and structural quality is achieved without utilizing metal catalyst. Transmission electron microscopy measurements confirm that gadolinium dopants in the target form a transparent in situ interface layer to assist in vertical NT formation. Microphotoluminescence (PL) measurements of the NTs reveal an intense ZnO band edge emission without a defect band, indicating high quality. Carrier dynamic analysis via time-resolved PL confirms that the emission of n-ZnO NTs/p-GaN LED structure is dominated significantly by the radiative recombination process without efficiency droop when high carrier density is injected optically. We developed an electrically pumped UV Gd-doped ZnO NTs/GaN LED as a proof of concept, demonstrating its high internal quantum efficiency (>65%). The demonstrated performance of this cost-effective UV LED suggests its potential application in large-scale device production.
  • Wideband Self-Injection-Locked Green Tunable Laser Diode

    Shamim, Md. Hosne Mobarok; Ng, Tien Khee; Ooi, Boon S.; Khan, Mohammed Zahed Mustafa (Institute of Electrical and Electronics Engineers (IEEE), 2019-07-01) [Conference Paper]
    A wideband tunability of 6.53 nm with appreciable SMSR (> 10 dB) and linewidth (~0.1 nm) is demonstrated from a simple and low-cost tunable self-injection locked InGaN/GaN green laser based external-cavity system, for the first time.© 2019 The Author(s)
  • All-day radiative cooling using beam-controlled architectures

    Zhou, Lyu; Song, Haomin; Liang, Jian-Wei; Singer, Matthew; Zhou, Ming; Stegenburgs, Edgars; Zhang, Nan; Ng, Tien Khee; Yu, Zongfu; Ooi, Boon S.; Gan, Qiaoqiang (Institute of Electrical and Electronics Engineers (IEEE), 2019-07-01) [Conference Paper]
    We report an inexpensive planar polydimethylsiloxane (PDMS)/metal thermal emitter in a beam-controlled architecture for all-day radiative cooling and realized∽11°C reduction compared with the ambient temperature. © 2019 The Author(s)
  • Electrical Characterization of Solar-Blind Deep-Ultraviolet (Al0.28Ga0.72)2O3Schottky Photodetectors Grown on Silicon by Pulsed Laser Deposition

    Alfaraj, Nasir; Li, Kuang-Hui; Kang, Chun Hong; Priante, Davide; Braic, Laurentiu; Guo, Zaibing; Ng, Tien Khee; Li, Xiaohang; Ooi, Boon S. (Institute of Electrical and Electronics Engineers (IEEE), 2019-07-01) [Conference Paper]
    This study reports on (Al0.28Ga0.72)2O3-based ultraviolet-C Schottky metal-semiconductor-metal and metal-insulator-metal photodetectors with peak responsivities of 1.17 and 0.40 A/W, respectively, for an incident-light wavelength of 230 nm at 2.50 V reverse-bias. © 2019 The Author (s)
  • Producing OAM Information Carriers using Micro-structured Spiral Phase Plates

    Stegenburgs, Edgars; Bertoncini, Andrea; Trichili, Abderrahmen; Alias, Mohd Sharizal; Ng, Tien Khee; Alouini, Mohamed-Slim; Liberale, Carlo; Ooi, Boon S. (Institute of Electrical and Electronics Engineers (IEEE), 2019-07-01) [Conference Paper]
    We report on small foot-print spiral phase plates for orbital angular momentum (OAM) light beam generation used in free space communication. A modal decomposition process confirms high purity of the generated beams at 980-nm wavelength. © 2019 The Author(s)
  • Blue Superluminescent Diodes with GHz Bandwidth Exciting Perovskite Nanocrystals for High CRI White Lighting and High-Speed VLC

    Alatawi, Abdullah; Holguin Lerma, Jorge Alberto; Kang, Chun Hong; Shen, Chao; Dursun, Ibrahim; Sinatra, Lutfan; Albadri, Abdulrahman M.; Alyamani, Ahmed Y.; Ng, Tien Khee; Bakr, Osman; Ooi, Boon S. (Conference on Lasers and Electro-Optics, The Optical Society, 2019-05-08) [Conference Paper]
    A 442-nm GaN-based superluminescent diode (SLD) is demonstrated with a GHz modulation bandwidth and a linewidth of 7 nm. When use for exciting CsPbBr3-perovskite nanocrystal-phosphor, warm-white light with a high CRI of 91 was achieved.
  • Boosted CO2 reduction using ultra-thin TiO2 photocatalyst films on nanocavities

    Song, Haomin; Wu, Wei; Liang, Jian-Wei; Maity, Partha; Mohammed, Omar F.; Ooi, Boon S.; Liu, Dongxia; Gan, Qiaoqiang (The Optical Society, 2019-05-07) [Conference Paper]
    We created an ultra-thin film photocatalytic light absorber (UFPLA) with 2~22-nm-thick TiO2 films. The UFPLA structure conquered the intrinsic trade-off between optical absorption and charge carrier extraction efficiency and therefore boosted CO2 reduction efficiency.
  • Perovskite-Based Artificial Multiple Quantum Wells

    Lee, Kwangjae; Turedi, Bekir; Sinatra, Lutfan; Zhumekenov, Ayan A.; Maity, Partha; Dursun, Ibrahim; Naphade, Rounak; Merdad, Noor; Alsalloum, Abdullah; Oh, Semi; Wehbe, Nimer; Hedhili, Mohamed N.; Kang, Chun Hong; Subedi, Ram Chandra; Cho, Namchul; Kim, Jin Soo; Ooi, Boon S.; Mohammed, Omar F.; Bakr, Osman (Nano Letters, American Chemical Society (ACS), 2019-04-22) [Article]
    Semiconductor quantum well structures have been critical to the development of modern photonics and solid-state optoelectronics. Quantum level tunable structures have introduced new transformative device applications and afforded a myriad of groundbreaking studies of fundamental quantum phenomena. However, noncolloidal, III-V compound quantum well structures are limited to traditional semiconductor materials fabricated by stringent epitaxial growth processes. This report introduces artificial multiple quantum wells (MQWs) built from CsPbBr3 perovskite materials using commonly available thermal evaporator systems. These perovskite-based MQWs are spatially aligned on a large-area substrate with multiple stacking and systematic control over well/barrier thicknesses, resulting in tunable optical properties and a carrier confinement effect. The fabricated CsPbBr3 artificial MQWs can be designed to display a variety of photoluminescence (PL) characteristics, such as a PL peak shift commensurate with the well/barrier thickness, multiwavelength emissions from asymmetric quantum wells, the quantum tunneling effect, and long-lived hot-carrier states. These new artificial MQWs pave the way toward widely available semiconductor heterostructures for light-conversion applications that are not restricted by periodicity or a narrow set of dimensions.
  • Study on laser-based white light sources

    Shen, Chao; Ooi, Ee-Ning; Sun, Xiaobin; Ooi, Boon S.; Ng, Tien Khee (Light-Emitting Devices, Materials, and Applications, SPIE-Intl Soc Optical Eng, 2019-03-01) [Conference Paper]
    We reported on the design, demonstration, and analysis of white lighting systems based on GaN laser diodes. Compared to light-emitting-diodes (LEDs), lasers have been proposed for the development of high-power light sources for many potential advantages, including circumventing efficiency droop, reduced light emitting surface, directional beam characteristics. Laser-based white light sources are also attractive for visible light communication (VLC) applications that enabling lighting and communication dual functionalities. In this work, we detailed the color-rendering index (CRI), correlated color temperature (CCT), and luminous flux analysis of laser white light sources by using the GaN laser diode exciting color converters at various driving conditions. By using a blue-emitting laser exciting a yellow YAG phosphor crystal, a luminous flux greater than 600 lm has been achieved with a moderate CRI of 67.2. By constructing a white lighting system using phosphor crystal array based on a reflection configuration, an improved CRI of 74.4 and a luminous flux of ~400 lm with a CCT of 6425 K was obtained at 3A. Using a novel ceramic phosphor plate as color converter, the CRI for the white light source has been further improved to ~ 84.1 with a CCT of ~ 4981 K, which suggests that the laser-based white light source is capable of high-quality illumination applications. The CCT of the white laser sources can be engineered from 5000 K to 6500 K and a potential approach to use laser array for high power white lighting is discussed.
  • Large intermixing in the InGaP/InAlGaP laser structure using stress engineering at elevated temperature

    Majid, Mohammed Abdul; Al-Jabr, Ahmad; Elafandy, Rami T.; Oubei, Hassan M.; Anjum, Dalaver H.; Shehata, Mohamed; Ng, Tien Khee; Ooi, Boon S. (SPIE, 2019-03-01) [Conference Paper]
    In this paper, a thermally induced dielectric strain on quantum well intermixing (QWI) technique is employed on tensilestrained InGaP/InAlGaP laser structure, to promote inter-diffusion, in conjunction with cycle annealing at elevated temperature. A bandgap blueshift as large as large as ~250meV was observed for samples capped with a single and bilayer of the dielectric film (1μm-SiO2 and 0.1μm-Si3N4) and annealed at a high temperature (700-1000oC) for cycles of annealing steps. Samples subjected to this novel QWI technique for short duration and multiple cycle annealing steps shown a high degree of intermixing while maintaining strong photoluminescence (PL) intensity, narrow full wave at half maximum (FWHM) and good surface morphology. Laser devices fabricated using this technique, lased at a wavelength of 608nm with two facet power of ~46mW, indicating the high quality of the material. Our results show that thermal stress can be controlled by the engineering dielectric strain opening new perspectives for QWI of photonics devices.
  • Visible diode lasers for high bitrate underwater wireless optical communications

    Ooi, Boon S.; Sun, Xiaobin; Alkhazragi, Omar; Guo, Yujian; Ng, Tien Khee; Alouini, Mohamed-Slim (Optical Fiber Communication Conference (OFC) 2019, The Optical Society, 2019-02-25) [Conference Paper]
    This talk provides an overview of the latest underwater wireless optical communication (UWOC) research from the system to the device level. Besides, studies investigating underwater channel characterization are also described.
  • Towards Early Detection of Red Palm Weevil Using Optical Fiber Distributed Acoustic Sensor

    Mao, Yuan; Ashry, Islam; Ng, Tien Khee; Ooi, Boon S. (Optical Fiber Communication Conference (OFC) 2019, The Optical Society, 2019-02-25) [Conference Paper]
    Red palm weevil (RPW) is a severe danger to the dates farming. We use optical fiber distributed acoustic sensor (DAS) as a solution to the detection of RPW via sensing the RPW activities sound.
  • Tunable Twisting Motion of Organic Linkers via Concentration and Hydrogen-Bond Formation

    El-Zohry, Ahmed; Alturki, Abdullah; Yin, Jun; Mallick, Arijit; Shekhah, Osama; Eddaoudi, Mohamed; Ooi, Boon S.; Mohammed, Omar F. (The Journal of Physical Chemistry C, American Chemical Society (ACS), 2019-02-20) [Article]
    Benzothiadiazole dibenzoic acid (BTDB) derivative is a well-known organic linker in various metal–organic framework structures as well as a fluorescent probe in biological systems. Here, we demonstrate that the radiative and nonradiative decay channels of BTDB can be interplayed and precisely controlled through concentration and hydrogen-bond interactions as directly evidenced experimentally and theoretically. This leads to excited-state structural changes that significantly suppress the torsional motion around the benzothiadiazole moiety, leading to an enormous increase in the emission quantum yields from ∼1 to 70%. These changes are associated with the existence of two equilibria, where dimers and small oligomers form in dimethylformamide (DMF), with high formation constants of 18 000 M–1 and 1.2 × 1013 M–3, respectively. These evolving species, i.e., the dimers and oligomers, are formed via hydrogen bonds between carboxylic acid groups present at the far edge of the rodlike BTDB molecules. The estimated repeating number for this small-oligomer formation via bonded monomers is eight in DMF, as shown by emission spectra analysis. With deprotonation as a control experiment, these associated species can easily collapse with the initial monomer species, confirming the role of the hydrogen-bond formation in the observed phenomena. Theoretical studies and NMR experiments not only confirm the existence of the dimers, but also demonstrate the important role of the hydrogen bonds in the excited-state dynamics. These new findings provide a better understanding of the photophysical behaviors of organic linkers used in a wide range of chemical and biological applications.
  • On the Reciprocity of Underwater Turbulent Channels

    Guo, Yujian; Trichili, Abderrahmen; Alkhazragi, Omar; Ashry, Islam; Ng, Tien Khee; Alouini, Mohamed-Slim; Ooi, Boon S. (IEEE Photonics Journal, Institute of Electrical and Electronics Engineers (IEEE), 2019-02-12) [Article]
    Through a series of experiments incorporating two counter-propagating communication channels, we investigate the reciprocity nature of underwater turbulence. Bit error rate measurement and statistical data analysis reveal a high reciprocal nature of turbulence induced by the presence of bubbles, temperature, and salinity. We further demonstrate the effect of distortions at the beam level that could potentially be used for underwater communication system design considerations.
  • Extraordinary Carrier Diffusion on CdTe Surfaces Uncovered by 4D Electron Microscopy

    El-Zohry, Ahmed; Shaheen, Basamat S.; Burlakov, Victor M.; Yin, Jun; Hedhili, Mohamed N.; Shikin, Semen; Ooi, Boon S.; Bakr, Osman; Mohammed, Omar F. (Chem, Elsevier BV, 2019-02-01) [Article]
    The lack of understanding and control over losses of charge carriers at the surfaces/interfaces of solar cell materials is the major factor limiting overall device conversion efficiency. This work describes a breakthrough in real-space visualization of charge-carrier dynamics at the atomic surface level of CdTe, a leading direct bandgap semiconductor in commercial thin-film solar cells. We present a fundamentally new understanding of charge-carrier diffusion and carrier trapping of CdTe single crystals using a four-dimensional scanning ultrafast electron microscope (4D-SUEM)—the only instrument of its kind currently in operation. We found that the diffusion of charge carriers at surfaces vary within extreme ranges, from extraordinary to virtually trapped when surface orientation was changed from (110) to (211). The work presented here is a milestone in addressing the device performance bottlenecks stemming from surfaces and a new avenue to create CdTe-based optoelectronic devices.

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