PUBLICATIONS

Journals

  • 24

    Synthesis and luminescence properties of reddish-orange-emitting Ca2GdNbO6 :Sm3+ phosphors with good thermal stability for high CRI white applications

    Abstract


    Novel reddish-orange-emitting Ca2GdNbO6:Sm³⁺ phosphors based on the emission of ⁴G5/2 → ⁶H9/2 transition at 651 nm with the chromatic coordinate of (0.633, 0.366) were synthesized. The crystal structure and chemical purity were identified in detail. Under the 407 nm excitation, the optimum concentration of Sm³⁺ ion was found to be 5 mol% dominated by the dipole-dipole interaction in the Ca2GdNbO6 host material. The color purity of the sample with optimum doping was estimated to be about 78.38%. Besides, the thermal stability was also studied, and it was further found that the emission intensity remained 65.32% at 423 K. The packaged white LED device exhibited excellent CRI and CCT values of 92.43 and 4896 K. Finally, the polydimethylsiloxane film with a stable structure and flexible property was prepared. These above results reveal that novel reddish-orange-emitting Ca2GdNbO6:Sm³⁺ phosphors can be applied in high CRI white communication and flexible display applications.
  • 23

    Suppression of self-heating in nanoscale interfaces using h-BN based anisotropic heat diffuser

    Abstract

    Thermal management of integrated circuits (ICs) is becoming increasingly important as the feature-size of transistors is now comparable to the phonon mean free path, and the power density is reaching a critical level. The thermal effect is especially pronounced in 3D ICs with limited heat dissipation paths due to stacked transistors with insulators interposed between them. Hexagonal boron nitride (h-BN) is an insulating 2D material with a strong anisotropy in its heat-conducting property; the heat transfer coefficient is very high in the lateral direction, rivaling that of copper, but relatively low in the vertical direction. In this work, we studied the heat dissipation efficiency of integrated h-BN gate dielectrics with varying thicknesses in an environment similar to that of a stacked IC. High-power GaN transistors were interposed between thick insulators to emulate the hotspot propagation in a confined environment with minimized convective and radiative heat transfer. Devices were compared via in situ thermographic imaging, and at least a 20 K decrease in hotspot temperature was observed at the power density of 10 to 12.5 Wmm−1. Importantly, the drain current which was suppressed due to the self-heating effect was restored to its normal level after the heat conduction rate increased.

  • 22

    Y-ZnO Microflowers Embedded Polymeric Composite Films to Enhance the Electrical Performance of Piezo/Tribo Hybrid Nanogenerators for Biomechanical Energy Harvesting and Sensing Applications

    Abstract

    Nowadays, hybrid nanogenerators (HNGs) have attracted much interest in mechanical energy-harvesting technology because of their assertable advantages in self-powered portable electronic devices. However, the HNG output performance is highly dependent on the active material, the structure of the device, the applied mechanical pressure, and so forth. In this regard, to develop a high-performance HNG, yttrium (Y)-doped zinc oxide (ZnO) microflowers (Y-ZnO MFs) were synthesized and embedded into polydimethylsiloxane (PDMS) for developing rationally designed composite films. Unlike the previously reported ZnO HNGs, the synthesized Y-ZnO MFs/PDMS-based HNG exhibits an improved electrical output because of the enhanced ferroelectricity of Y-ZnO MFs and the resultant increase of the charge density in the composite films. In addition, the effects of Y concentration on ZnO MFs and Y-ZnO MFs loaded into PDMS on the output performance of Y-ZnO MFs/PDMS HNG were studied systematically, and the optimized Y dopant concentration in ZnO MFs was found. Thus, the 0.5 mol % of Y-ZnO MFs and the 2.5 wt % of Y-ZnO MFs embedded in PDMS achieved a stable and enhanced performance. The obtained voltage (VOC), current (ISC), and instantaneous power density of the composite film-based HNG (Y-ZnO MFs/PDMS) were 247 V, 7 μA, and ∼6 W/m2, respectively. Furthermore, the practical and commercial applications of the proposed HNG were demonstrated by sensing and harvesting biomechanical motions available in everyday human activities and powering various portable electronics.

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  • 21

    One-Pot Synthesis of SiO2@Ag Mesoporous Nanoparticle Coating for Inhibition of Escherichia coli Bacteria on Various Surfaces

    Abstract

    Silver nanoparticles (Ag NPs) as antibacterial agents are of considerable interest owing to their simplicity, high surface area to volume ratio, and efficient oligodynamic properties. Hence, we investigated the synthesis of silica-supported Ag NPs (SiO2@Ag) as an effective antibacterial agent by using a wet-impregnation method. The formation of SiO2@Ag with Ag NP (5–15 nm diameter) on the silica particle (100–130 nm diameter) was confirmed with transmission electron microscopy (TEM). The study on antibacterial activity was performed in a liquid culture to determine the minimum inhibitory concentration (MIC) against Escherichia coli (E. coli) and Bacillus subtilis (B. subtilis) bacteria. Both bacteria are chosen to understand difference in the effect of Ag NPs against Gram-negative (E. coli) and Gram-positive (B. subtilis) bacteria. SiO2@Ag mesoporous nanoparticles had excellent antibacterial activity against E. coli bacteria and fully restricted the bacterial growth when the material concentration was increased up to 1.00 mg/mL. In addition, the obtained material had good adhesion to both steel and polyethylene substrates and exhibited a high inhibition effect against E. coli bacteria.

    Keywords: silver nanoparticles, Gram-negative vs. Gram-positive, antibacterial agents, impregnation method, coating
  • 20

    Harsh environment-tolerant and robust triboelectric nanogenerators for mechanical-energy harvesting, sensing, and energy storage in a smart home

    Abstract

    Ever-increasing demand for energy is driving efforts to develop environmentally sustainable technologies that can harvest and store energy. Energy-harvesting technologies that use renewable energy sources are preferable when designing sustainable and self-charging electronic devices. Large quantities of mechanical energy are available in typical homes. Fabricating a triboelectric nanogenerator (TENG) to harvest such energy could provide a renewable source of power for a variety of devices. However, practical TENGs have proven elusive due to a scarcity of triboelectric materials. Here, we describe the utilization of plastic and electronic waste commonly available in homes to fabricate a smart-home-applicable TENG (SHA-TENG). Because electrical performance depends on the triboelectric series, device structure is examined comprehensively. Voltage, current, charge density, and power density values of ~300 V, ~15 µA, ~70 µC/m2, and ~54 W/m2 are achievable, respectively. The resulting lightweight SHA-TENG is a smart-home fabricable device that can withstand in a harsh environment. Furthermore, the TENG can not only be employed to harvest mechanical energy and directly applied to power portable electronics, but it can also be used in self-charging energy-storage systems and motion/anti-thief sensors, as demonstrated by combing it with a power management circuit to create a self-charging lithium-ion battery. A circuit that detects spikes in voltage from the SHA-TENG in various parts of the home can serve as a smart-home motion sensor. When placed in different regions of the home, the SHA-TENG can sense motion, harvest mechanical energy involved in everyday human activities, and power various portable electronic devices.

  • 19

    Multi-wall carbon nanotubes decorated MnCo2O4.(5) hexagonal nanoplates with enhanced electrochemical behavior for high-performance electrochemical capacitors

    Abstract

    The MnCo2O4.5 hexagonal nanoplates and multi-wall carbon nanotube (MWCNT)@MnCo2O4.5 composite were prepared via a rapid and low-cost co-precipitation method. The prepared materials were characterized by various characterization techniques and used as an electrode for supercapacitors. The specific capacitance values of 451 and 1292 F g−1 were obtained from MnCo2O4.5 and MWCNT@MnCo2O4.5, respectively at 1 A g−1. Furthermore, MWCNT@MnCo2O4.5//AC-based device indicated the higher energy density value of 33 Wh kg−1 at the power density of 362.5 W kg−1 under the current density of 0.5 A g−1. The practical electronic application of the device was tested by powering twelve light-emitting diodes, a digital watch and a motor fan. From the results of the MnCo2O4.5 with MWCNTs, the MnCo2O4.5 is expected to be a potential viable material for high-performance electrochemical capacitors.

  • 18

    Excellent photoluminescence and cathodoluminescence properties in Eu3+-activated Sr2LaNbO6 materials for multifunctional applications

    Abstract


    Single Eu³⁺-activated Sr2LaNbO6 (SLN) phosphors with double-perovskite structure were successfully synthesized and their photo/cathodoluminescence properties were investigated in detail. The optimal doping concentration was confirmed to be about 0.3 mol while the concentration quenching was dominated by the dipole–dipole interaction. The optimum SLN:0.3Eu³⁺ phosphor exhibited good photoluminescence emission intensity, color purity, thermal stability, and quantum yield. With the help of the Judd-Oflet theory, Eu³⁺ ions would possess the stronger symmetry sites in SLN host lattice. Besides, the packaged red and white lighting-emitting diodes (LEDs) based on optimum sample were fabricated. Particularly, the packaged white LED device displayed good color rendering index value of 86.89 and correlated color temperature value of 4835 K. Moreover, the novel LED structure based on the SLN:0.3Eu³⁺-polydimethylsiloxane film having stable physicochemical structure was prepared and emitted a strong red light. Eventually, the strong cathodoluminescence intensity with large electron penetration depth was provided. These above results imply that SLN:Eu³⁺ phosphors with excellent photo/cathodoluminescence properties could be promised for multifunctional applications.
  • 17

    Three-dimensional porous SnO2/carbon cloth electrodes for high-performance lithium- and sodium-ion batteries

    Abstract

    The tin oxide nanoparticles (SnO2-NPs) were successfully synthesized on the conductive carbon cloth (CC) using a simple one-step solvothermal method to form three-dimensional (3D) porous SnO2/CC composite. The SnO2-NPs were uniformly deposited on CC and fine pores existed between the SnO2-NPs. The synthesized 3D porous SnO2/CC composite was investigated as an anode material for lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs). When tested as an anode for LIBs, the as-prepared 3D porous SnO2@CC composite electrode delivered a discharge capacity of 1038 mA h g−1 over 200 cycles at a current density of 0.5 A g−1. For SIBs, a discharge capacity of 498 mA h g−1 was delivered at 0.2 A g−1 over 100 cycles. Even at 0.5 A g−1, the electrode exhibited a discharge capacity of 205 mA h g−1 over 100 cycles. The excellent electrochemical properties of 3D porous SnO2/CC composite electrode for both lithium and sodium storage can be attributed to the good porous structure between the SnO2-NPs on the surface of CC and improved electrical conductivity due to CC, which not only releases the strain during the Li+/Na+ insertion/extraction process but also can improve the ionic and electronic transportation.

  • 16

    A microwave method to remotely assess the abdominal fat thickness

    We introduce a method to measure the fat thickness by harnessing the physics of destructive interference. At certain frequencies, when the fat thickness equals a quarter wavelength, the amplitude of the reflected wave is minimized due to the destructive interference. Therefore, by observing the frequency where the reflection is minimized, we are able to deduce the fat thickness. This work demonstrates that this simple method can operate not only on a planar tissue model but also on a cylindrical model as well as the Zubal human phantom model. Finally, we experimentally demonstrate the estimation of the fat thickness for the planar tissue model with a broadband antenna. This method for assessing one’s abdominal fatness can allow continuous self-monitoring due to its low cost and simple measurement procedure. 

  • 15

    Contact Engineering of Vertically Grown ReS2 with Schottky Barrier Modulation

    Abstract

    Forming metal contact with low contact resistance is essential for the development of electronics based on layered van der Waals materials. ReS2 is a semiconducting transition metal dichalcogenide (TMD) with an MX2 structure similar to that of MoS2. While most TMDs grow parallel to the substrate when synthesized using chemical vapor deposition (CVD), ReS2 tends to orient itself vertically during growth. Such a feature drastically increases the surface area and exposes chemically active edges, making ReS2 an attractive layered material for energy and sensor applications. However, the contact resistances of vertically grown materials are known to be relatively high, compared to those of common 2H-phase TMDs, such as MoS2. Most reported methods for lowering the contact resistance have been focused on exfoliated 2H-phase materials with only a few devices tested, and few works on distorted T-phase materials exist. Moreover, nearly all reported studies have been conducted on only a few devices with mechanically exfoliated fl Most reported methods for lowering the contact resistance have been 2 contacts was modulated by conformally coating a thin tunneling interlayer between the metal and the dendritic ReS2 film. Over a hundred devices were tested, and contact resistances were extracted for large-scale statistical analysis. Importantly, we compared various known materials and techniques for lowering contact resistance and found an optimized method. Finally, the reductions in barrier height were directly correlated with exponential reductions in contact resistance and increases in drive-current by almost 2 orders of magnitude.

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