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Lee, Young Ok,Chen, Fu,Lee, Kee Keun Institute of Pure and Applied Physics 2016 Japanese Journal of Applied Physics Vol.55 No.6
<P>We have developed acoustic-optic (AO) based display units for implementing a handheld hologram display by modulating light deflection through wide bandwidth surface acoustic wave (SAW). The developed AO device consists of a metal layer, a ZnS waveguide layer, SAW inter digital transducers (IDTs), and a screen for display. When RF power with a particular resonant frequency was applied to IDTs, SAW was radiated and interfered with confined beam propagating along ZnS waveguide layer. The AO interacted beam was deflected laterally toward a certain direction depending on Bragg diffraction condition, exited out of the waveguide layer and then directed to the viewing screen placed at a certain distance from the device to form a single pixel. The deflected angles was adjusted by modulating the center frequency of the SAW IDT (SAW grating), the RF power of SAW, and the angles between propagating light beam path along waveguide and radiating SAW. The diffraction efficiency was also characterized in terms of waveguide thickness, SAW RF input power, and aperture length. Coupling of mode (COM) modeling was fulfilled to find optimal device parameters prior to fabrication. All the parameters affecting the deflection angle and efficiency to form a pixel for a three-dimensional (3D) hologram image were characterized and then discussed. (C) 2016 The Japan Society of Applied Physics</P>
Moon, Jeongmin,Lee, Sungrae,Lee, Sejin,Jung, Woohyun,Oh, Kyunghwan Institute of Pure and Applied Physics 2014 Japanese Journal of Applied Physics Vol. No.
<P>We propose and demonstrate a new polarized backlight unit (BLU) configuration to enhance light transmission in a twisted nematic (TN) mode liquid crystal (LC) panel. By adding an optimized phase retardation film (PRF) to the BLU, we efficiently controlled the polarization state of the light from the light guide plate (LGP), enabling it to be aligned along the transmission axis of the bottom polarizer of the LC panel. We designed and fabricated a 7 in. edge-lit BLU with a PRF. To obtain a uniform positional distribution in both light intensity and degree of polarization (DOP), the LGP was optimized with linear groove patterns. To maximize BLU light transmission through the bottom, polarizer in a TN-mode LC panel, the slow axis of the PRF was aligned at 22.5 degrees with respect to the LED array axis. We improved the transmittance from 45 to 72%. (C) 2014 The Japan Society of Applied Physics</P>
Hossain, Mohammad Faruk,Yin, Junli,Park, Jae-Yeong Institute of Pure and Applied Physics 2014 Japanese Journal of Applied Physics Vol. No.
<P>Electro-chemically synthesized nickel hydroxide Ni(OH)(2) on reduced graphene oxide (RGO) made from graphene oxide (GO) has been investigated as electrode materials for electrical energy storage applications. The electrochemical deposition of Ni(OH)(2) on highly hybridized RGO was more effective to improve the catalytic activity of electrode and to increase the capacity performance of the overall system. By virtue of the unique two-dimensional nanostructure of RGO, the as-obtained Ni(OH)(2) was closely protected by RGO, effectively suppressing their microstructural degradation during the charge and discharge processes, and enabling an enhancement in cycling capability. Electrochemical measurements demonstrated that the specific capacitance of the as-obtained supercapacitor is high as 729mF/cm(2) and power density of 1.5 mW/cm(2). The electrical conductivity of RGO was determined to be 104 S/cm. In addition, there was no marked decrease in capacitance at a constant current density after 200 cycles, suggesting excellent long-term cycling stability. (C) 2014 The Japan Society of Applied Physics</P>
Effect of dynamic stress on off leakage of small-dimension pMOSFETs at high temperature
Kim, Gang-Jun,Seo, Ji-Hoon,Son, Donghee,Lee, Nam-Hyun,Kang, YoungHa,Hwang, YuChul,Kang, Bongkoo Institute of Pure and Applied Physics 2014 Japanese Journal of Applied Physics Vol. No.
<P>The degradation of the off leakage current I-off in small-dimension pMOSFETs is investigated experimentally while applying a dynamic stress to the pMOSFETs. During the OFF-state stress, the dynamic stress induced an increase of I-off due to generation of negative oxide charges N-ox in the gate dielectric, and in the shallow trench isolation (STI) near the gate edge. When channel width W decreased, negative N-ox in STI increase I-off significantly, and the degradation of I-off is more critical than degradation of V-th. These observations indicate that the effect of the dynamic stress in pMOSFETs on I-off should be seriously considered when evaluating small-dimension pMOSFETs. (C) 2014 The Japan Society of Applied Physics</P>
Electron collision ionized plasma waves in the positive column of a fine discharge tube
Kim, Junghyun,Jeong, Jongmun,Hwang, Hachung,Jin, Dongjun,Koo, Jehuan,Kwon, Gichung,Choi, Eunha,Cho, Guangsup,Uhm, Han Sup Institute of Physics [etc.] 2009 Journal of physics. D, applied physics Vol.42 No.20
<P>In fluorescent lamp tubes, a few millimetres in radius, operating at several tens of kilohertz, the initiation of light radiation is characterized by the propagation of an electron plasma wave, accompanied by ionization caused by electron collision. Due to the effects of the ionization collision of electrons on the dispersion behaviour of the plasma waves, the electron plasma waves generated by the pulses of operation voltage, propagate along the positive column plasma without experiencing damping. The propagation velocity of radiated light, which represents the propagation of the electron plasma wave, can be higher than the electron thermal velocity.</P>
Kim, Hyungchul,Woo, Sanghyun,Lee, Jaesang,Lee, Hyerin,Jeon, Hyeongtag Institute of Physics [etc.] 2010 Journal of Physics. D, Applied Physics Vol.43 No.50
<P>The interface stability and memory properties of an Al<SUB>2</SUB>O<SUB>3</SUB> blocking oxide deposited using remote plasma atomic layer deposition (RPALD) at various RF powers were investigated. The plasma density increased with an increase in radio frequency (RF) power from 50 to 300 W due to increased neutral impact excitation rate. Based on x-ray photoelectron spectroscopy and auger electron spectroscopy, an oxygen-deficient interfacial layer was formed for Al<SUB>2</SUB>O<SUB>3</SUB> film deposition at 50 W. In addition, increased migrations of Si and N atoms were observed at low power due to the formation of fewer oxygen radicals. While reduced migrations of Si and N atoms from Si<SUB>3</SUB>N<SUB>4</SUB> to Al<SUB>2</SUB>O<SUB>3</SUB> were observed when the RF power was sufficient due to the sufficient oxygen radicals. Therefore, the interfacial reaction between Al<SUB>2</SUB>O<SUB>3</SUB> and Si<SUB>3</SUB>N<SUB>4</SUB> is dependent on the RF power. After applying 18 V, the program speed of Al<SUB>2</SUB>O<SUB>3</SUB> with 100 W, 200 W and 300 W were 10<SUP>−2</SUP> s, 10<SUP>−5</SUP> s and 10<SUP>−6</SUP> s, respectively.</P>
Oh, Yongsuk,Zahaf, Riyan,Zachariah, Michael R.,Lee, Donggeun Institute of Pure and Applied Physics 2014 Japanese Journal of Applied Physics Vol. No.
<P>Here we study the interaction of a nanosecond laser pulse with a nanoparticle to explore the mechanism of energetic ion formation and in particular the particle size dependence. Multiphoton ionization and the subsequent electron impact ionization accompanied by inverse Bremsstrahlung process are determined appropriate for generation of multiple charged ions. The Coulomb expansion of a positive ion cloud is then calculated with molecular dynamics simulations, resulting in temporal evolution of ions, a radial distribution of kinetic energy of ions, and size-dependency of the ion kinetic energy. A mass spectrum peak of ion simulated by the present model is found comparable to the experimental data. Alternatively, a direct measurement of kinetic energy is also explained by the model. (C) 2014 The Japan Society of Applied Physics</P>
Numerical simulations of supersonic gas atomization of liquid metal droplets
Firmansyah, Dudi Adi,Kaiser, Rashed,Zahaf, Riyan,Coker, Zach,Choi, Tae-Youl,Lee, Donggeun Institute of Pure and Applied Physics 2014 Japanese Journal of Applied Physics Vol. No.
<P>Computational fluid dynamics simulations incorporating supersonic turbulent gas flow models and a droplet breakup model are performed to study supersonic gas atomization for producing micron-sized metal powder particles. Generally such atomization occurs in two stages: a primary breakup and a secondary breakup. Since the final droplet size is primarily determined by the secondary breakup, parent droplets of certain sizes (1 to 5 mm) typically resulting from the primary breakup are released at the corner of the nozzle and undergo the secondary breakup. A comparison of flow patterns with and without the introduction of a liquid melt clearly indicates that the mass loading effect is quite significant as a result of the gas-droplet interactions. The flow pattern change reasonably explains why the final droplets have a bimodal mass size distribution. The transient size changes of the droplets are well described by the behavior of the Weber number. The present results based on the 1 mm parent droplets best fit previous experimental results. Moreover, the effects of inlet gas pressure and temperature are investigated in an attempt to further reduce droplet size. (C) 2014 The Japan Society of Applied Physics</P>
Lee, D H,Son, K,Park, W I Institute of Physics [etc.] 2010 Journal of Physics. D, Applied Physics Vol.43 No.24
<P>Selective and lateral growth of ultrafine ZnO nanowires using metalorganic chemical vapour deposition (MOCVD) is studied. For selective growth of ZnO nanowires, oxidized substrates were patterned with Au layers, which serve as nucleation sites for the initial stage of ZnO nanowire growth. Electron microscopy confirmed that ultrafine ZnO nanowires with a mean diameter in the range ∼8–20 nm were rooted selectively in Au patterns and laterally extended to several micrometres on the substrate surfaces. Interestingly, nanowire bridges crosslinking the Au patterns or nanowire link-ups were frequently observed, indicating that self-organizing electrical interconnects and optical networks can be developed. Photoresponse measurements showed that exposure of the ultrafine ZnO nanowires to ultraviolet light rapidly increased the channel current from ∼150 to ∼400 nA at an applied bias voltage of 1 V.</P>
Kim, Youngjun,Yang, Heesun,Park, Byoungnam Institute of Physics Publishing Ltd. 2017 Journal of Physics. D, Applied Physics Vol.50 No.27
<P>We report electrical properties of Zn<SUB>1−<I>x</I> </SUB>Mg<SUB> <I>x</I> </SUB>O nanocrystal solid solution (NCSS) depending on the composition of Mg using a bottom-contact field-effect transistor. In the Zn<SUB>1−<I>x</I> </SUB>Mg<SUB> <I>x</I> </SUB>O NCSS, as the composition of Mg increases, the field-effect mobility decreases with the threshold voltage shifting to a more positive value. The decrease in the field-effect mobility is attributed to the decrease in the size of the Zn<SUB>1−<I>x</I> </SUB>Mg<SUB> <I>x</I> </SUB>O NCSS. The increase in the electron trap density in the Zn<SUB>1−<I>x</I> </SUB>Mg<SUB> <I>x</I> </SUB>O NCSS with the addition of Mg caused a more positive threshold voltage shift. Change in the trap density as a function of Mg composition was demonstrated through comparison of the photoluminescence intensity.</P>