Browsing by Author "Guo, Zhanhu"

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    Flexible polydimethylsiloxane/multi-walled carbon nanotubes membranous metacomposites with negative permittivity
    (Elsevier, 2017-09) Sun, Kai; Xie, Peitao; Wang, Zhongyang; Su, Tongming; Shao, Qian; Ryu, JongEun; Zhang, Xihua; Guo, Jiang; Shankar, Akash; Li, Jianfeng; Fan, Runhua; Cao, Dapeng; Guo, Zhanhu; Department of Mechanical Engineering, School of Engineering and Technology
    Metacomposites with negative electromagnetic parameters can be promising substitute for periodic metamaterials. In this paper, we devoted to fabricating flexible metacomposite films, which have great potential applications in the field of wearable cloaks, sensing, perfect absorption and stretchable electronic devices. The conductivity and the complex permittivity were investigated in flexible polydimethylsiloxane (PDMS)/multi-walled carbon nanotubes (MWCNTs) membranous nanocomposites, which were fabricated via in-situ polymerization process. With the increase of conductive one-dimension carbon nanotubes concentration, there was a percolation transition observed in conduction due to the formation of continuous networks. The dielectric dispersion behavior was also analyzed in the spectra of complex permittivity. It is indicated that the conduction and polarization make a combined effect on the dielectric loss in flexible PDMS/MWCNTs composites. The negative permittivity with a dielectric resonance was obtained, and was attributed to the induced electric dipoles.
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    Ionic liquid-assisted synthesis of Yb3+-Tm3+ codoped Y7O6F9 petal shaped microcrystals with enhanced upconversion emission
    (Elsevier, 2018-07) Zhao, Jinbo; Wu, Lili; Zhang, Chuanjiang; Li, Tingxi; Jiang, Qinglong; Wang, Feng; Zhao, Ping; Ryu, Jong Eun; Guo, Zhanhu; Mechanical Engineering, School of Engineering and Technology
    Petal-like Yb3+-Tm3+ codoped Y7O6F9 microparticles were achieved via ionic liquid-assisted (IL) hydrothermal process. The emission efficiency of Y7O6F9:Yb3+/Tm3+ powders is much stronger than that of Y2O3:Yb3+/Tm3+ sample. Under excitation at 980 nm with an unfocused laser beam under weak pump density of ∼0.1 W/cm2 (pump power 10 mW), the UC emission of the sample can been seen clearly. Four emission bands at 477, 540, 647 and 692 nm are observed and correspond to the 1G4 state to 3H6 state, 1D2 state to 3H5 state, 1G4 sate to 3F4 state, and 3F3 state to 3H6 state transition of Tm3+ ions. The enhanced UC emission is related to high crystallinity and lower effective phonon energy of oxyfluorides. The ionic liquid (IL) of [BMIM][BF4] is used both as the reaction medium and the source of F−.
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    Poly(sulfur-random-(1,3-diisopropenylbenzene)) Based Mid-Wavelength Infrared Polarizer: Optical Property Experimental and Theoretical Analysis
    (Elsevier, 2019-08) Berndt, Aaron J.; Hwang, Jehwan; Islam, Md Didarul; Sihn, Amy; Urbas, Augustine M.; Ku, Zahyun; Lee, Sang J.; Czaplewski, David A.; Dong, Mengyao; Shao, Qian; Wu, Shide; Guo, Zhanhu; Ryu, Jong E.; Mechanical and Energy Engineering, School of Engineering and Technology
    Development of polymer based mid-wavelength infrared (MWIR) optics has been limited mainly due to high optical loss of organic polymers used in general optical components. In this study, a MWIR polarization grating based on a sulfuric polymer poly(sulfur-random-(1,3-diisopropenylbenzene)) with a low loss in the MWIR range was fabricated using a simple two-step process: imprint and metal deposition. Fourier-transform infrared (FTIR) spectroscopy measurement showed that this polymeric MWIR polarizer selectively transmitted the polarized IR in transverse magnetic (TM) mode over the transverse electric (TE) mode at normal incidence. The measured extinction ratios (  = The ratio of transmissions in TM and TE) were 208, 176, and 212 at the wavelength of 3, 4, and 5 μm, respectively. The computational simulation and analytical model confirmed that the enhanced TM transmission efficiency and followed a Fabry-Pérot (FP) resonance mode within the created sulfuric polymer film. This polymeric MWIR polarizer demonstrated a great potential for broader applications in IR photonics to realize low-cost and durable optical components.
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    Reinforcement of Cu Nanoink Film with Extended Carbon Nanofibers for Large Deformation of Printed Electronics
    (Office of the Vice Chancellor for Research, 2016-04-08) Kim, Jeonghwan; Shankar, Akash; Zhu, Jiahua; Choi, Daniel S.; Guo, Zhanhu; Ryu, Jong Eun
    Metallic nanoparticle inks (nanoinks) have attracted great interest in the manufacturing of printed flexible electronics. However, micro-cracks and pores generated during the sintering process deteriorate mechanical and electrical characteristics of the sintered nanoink film. To alleviate these problems, we demonstrated the use of very long carbon nanofiber (CNF, average length 200 μm) to reinforce the sintered nanoink films. In this study, different weight fractions of CNFs are dispersed into the Cu nanoink to improve the mechanical bending characteristics. Scanning electron micrographs (SEM) shows improved dispersion of oxidized CNF in the nanoink compared to the as-received CNF. The composite nanoinks are stencil printed on polyethylene terephthalate (PET) film and sintered by intense pulsed light system using Xe-flash. The electrical measurements show 90 %, 65 %, and 66 % improved electrical conductivity in the composite nanoink film (0.7 % of oxidized CNF) compared to the pure Cu nanoink under the 75 mm, 50 mm, and 25 mm of bending radii, respectively.