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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>
Current transport in Pt Schottky contacts to <i>a</i>-plane n-type GaN
Phark, Soo-Hyon,Kim, Hogyoung,Song, Keun Man,Kang, Phil Geun,Shin, Heung Soo,Kim, Dong-Wook Institute of Physics [etc.] 2010 Journal of physics. D, applied physics Vol.43 No.16
<P>The temperature-dependent electrical properties of Pt Schottky contacts to nonpolar <I>a</I>-plane n-type GaN were investigated. Barrier height and ideality factor, estimated from the conventional thermionic emission model, were highly temperature dependent. A notable deviation from the theoretical Richardson constant value was also observed in the conventional Richardson plot. Analyses using the thermionic field emission model showed that consideration of defect-assisted tunnelling was necessary to explain the observed electrical behaviours.</P>
A controllable viewing angle LCD with an optically isotropic liquid crystal
Kim, Min Su,Lim, Young Jin,Yoon, Sukin,Kang, Shin-Woong,Lee, Seung Hee,Kim, Miyoung,Wu, Shin-Tson Institute of Physics [etc.] 2010 Journal of physics. D, applied physics Vol.43 No.14
<P>An optically isotropic liquid crystal (LC) such as a blue phase LC or an optically isotropic nano-structured LC exhibits a very wide viewing angle because the induced birefringence is along the in-plane electric field. Utilizing such a material, we propose a liquid crystal display (LCD) whose viewing angle can be switched from wide view to narrow view using only one panel. In the device, each pixel is divided into two parts: a major pixel and a sub-pixel. The main pixels display the images while the sub-pixels control the viewing angle. In the main pixels, birefringence is induced by horizontal electric fields through inter-digital electrodes leading to a wide viewing angle, while in the sub-pixels, birefringence is induced by the vertical electric field so that phase retardation occurs only at oblique angles. As a result, the dark state (or contrast ratio) of the entire pixel can be controlled by the voltage of the sub-pixels. Such a switchable viewing angle LCD is attractive for protecting personal privacy.</P>
Hwang, Chanoh,Hyung, Jung-Hwan,Lee, Seung-Yong,Jang, Chan-Oh,Kim, Tae-Hong,Choi, Pyung,Lee, Sang-Kwon Institute of Physics [etc.] 2008 Journal of physics. D, applied physics Vol.41 No.10
<P>We report on the fabrication and characterization of Ti/Au Ohmic contacts to unintentionally doped gallium nitride (n-GaN) nanowires. The specific contact resistance and resistivity were determined to be ∼1.1 × 10<SUP>−5</SUP> ± 5 × 10<SUP>−6</SUP> Ω cm<SUP>2</SUP> and ∼6.9 × 10<SUP>−3</SUP> ± 3 × 10<SUP>−4</SUP> Ω cm, respectively, with a diameter of ∼140 nm using a transmission line model (TLM). We also present the electrical characterizations of metal/GaN nano-Schottky diodes with four Schottky metals (Al, Ti, Cr and Au) on unintentionally doped GaN nanowires using current–voltage (<I>I</I>–<I>V</I>) characteristics at room temperature. We observed the abnormal electrical characteristics of GaN nano-Schottky diodes for each Schottky metal.</P>
Micromagnetic computer simulations of spin waves in nanometre-scale patterned magnetic elements
Institute of Physics [etc.] 2010 Journal of physics. D, applied physics Vol.43 No.26
<P>Current needs for further advances in the nanotechnologies of information-storage and -processing devices have attracted a great deal of interest in spin (magnetization) dynamics in nanometre-scale patterned magnetic elements. For instance, the unique dynamic characteristics of non-uniform magnetic microstructures such as various types of domain walls, magnetic vortices and antivortices, as well as spin wave dynamics in laterally restricted thin-film geometries, have been at the centre of extensive and intensive researches. Understanding the fundamentals of their unique spin structure as well as their robust and novel dynamic properties allows us to implement new functionalities into existing or future devices. Although experimental tools and theoretical approaches are effective means of understanding the fundamentals of spin dynamics and of gaining new insights into them, the limitations of those same tools and approaches have left gaps of unresolved questions in the pertinent physics. As an alternative, however, micromagnetic modelling and numerical simulation has recently emerged as a powerful tool for the study of a variety of phenomena related to spin dynamics of nanometre-scale magnetic elements.</P><P>In this review paper, I summarize the recent results of simulations of the excitation and propagation and other novel wave characteristics of spin waves, highlighting how the micromagnetic computer simulation approach contributes to an understanding of spin dynamics of nanomagnetism and considering some of the merits of numerical simulation studies. Many examples of micromagnetic modelling for numerical calculations, employing various dimensions and shapes of patterned magnetic elements, are given. The current limitations of continuum micromagnetic modelling and of simulations based on the Landau–Lifshitz–Gilbert equation of motion of magnetization are also discussed, along with further research directions for spin-wave studies.</P>
Morphology transformation of patterned, uniform and faceted GaN microcrystals
Kim, Tae Woong,Hong, Young Joon,Yi, Gyu-Chul,Kwon, Ji-Hwan,Kim, Miyoung,Han, Heung Nam,Kim, Do Hyun,Oh, Kyu Hwan,Kong, Ki-jeong,Kwon, Young-Kyun Institute of Physics [etc.] 2008 Journal of physics. D, applied physics Vol.41 No.1
<P>We report on the growth and characterization of patterned and uniformly distributed GaN microcrystals with well-defined facets and epitaxy. The microcrystals were grown on a mask patterned by lithography. The GaN microcrystals were formed by selective-area epitaxy using metal-organic chemical-vapour deposition. The GaN microcrystals have similar sizes and shapes. Each microcrystal consists of an upper and a lower part, which are rotated by 30?. Transmission electron microscopy shows that there is a rather clear interface between the two parts of the crystal, suggesting a sudden change in the growth direction. We performed <I>ab initio</I> calculations for the surface energies of hexagonal GaN, and the growth morphology is explained based on surface energy considerations.</P>
Gaillard, M,Britun, N,Kim, Yong M,Han, Jeon G Institute of Physics [etc.] 2007 Journal of physics. D, applied physics Vol.40 No.3
<P>This paper presents an optical diagnostic examination of dc planar magnetron discharge used for titanium deposition at 30 mTorr in argon bulk gas. The results were obtained by optical absorption (OAS) and emission (OES) spectroscopy for two distances from the target without substrate. The absolute density of titanium in the ground and metastable states at 4 cm from the target ranged, respectively, between 8 × 10<SUP>10</SUP> cm<SUP>−3</SUP> and 10<SUP>12</SUP> cm<SUP>−3</SUP> and between 6 × 10<SUP>10</SUP> cm<SUP>−3</SUP> and 3 × 10<SUP>11</SUP> cm<SUP>−3</SUP>, in the range 0.2–1.0 A. OES results were used to prepare an assumed interpretation in terms of differences in loss mechanisms, mainly by either diffusion towards the walls for all particles at 8 cm from the target or collision losses for non-radiative species at 4 cm from the target, except for the titanium ground state. This was confirmed by our results of the argon metastable density measurement at 4 cm which was constant at around 7 × 10<SUP>10</SUP> cm<SUP>−3</SUP> with discharge current.</P>
Lee, Soon-Gun,Chung, Yong-Chae Institute of Physics [etc.] 2009 Journal of physics. D, applied physics Vol.42 No.13
<P>The deposition behaviour for a Fe–Cu magnetic multilayer system in an early stage of the deposition process was investigated by molecular dynamics (MD) simulation. Specifically, the steering effect was quantitatively investigated through extensive measurements of the trajectory, deposition flux and force of atoms near the artificially structured Fe or Cu step positioned on the Cu(0 0 1) or Fe(0 0 1) surface. Near the step edges of the planar structure at a low incident energy of 0.1 eV, the steering effect for the case of Fe/Cu(0 0 1) was observed more significantly than for Cu/Fe(0 0 1). Additionally, the mechanism of down-diffusion from the step was discussed and the corresponding energetic was calculated using the molecular statics method.</P>
Lee, D,Park, Y-A,Yang, S M,Song, T K,Jo, Y,Hur, N,Jung, J H,Noh, T W Institute of Physics [etc.] 2010 Journal of physics. D, applied physics Vol.43 No.45
<P>We report on the epitaxial growth of single-phase [Pb(Zr<SUB>0.57</SUB>Ti<SUB>0.43</SUB>)O<SUB>3</SUB>]<SUB>0.8</SUB>[Pb(Fe<SUB>2/3</SUB>W<SUB>1/3</SUB>)O<SUB>3</SUB>]<SUB>0.2</SUB> (PZT–PFW) solid-solution thin films using pulsed laser deposition. X-ray diffraction measurements reveal that the films have a tetragonal structure. The films exhibit ferroelectric properties and weak ferromagnetic responses at room temperature. The magnetoelectric effects were investigated; the nonlinear magnetocapacitance coefficient, β<SUB>33</SUB>, was measured and found to be comparable to those of multiferroic hexagonal manganites, but at least two orders of magnitude smaller than that for polycrystalline PZT–PFW films.</P>
Nie, Z G,Lim, K S,Jang, W Y,Lee, H Y,Lee, M K,Kabayashi, T Institute of Physics [etc.] 2010 Journal of physics. D, applied physics Vol.43 No.48
<P>We report on multilayer optical data storage using Sm(DBM)<SUB>3</SUB>Phen-doped poly(methyl methacrylate) and a tightly focused 800 nm, 1 kHz, 100 fs pulsed laser. After pulsed femtosecond laser irradiation, refractive-index change and a visible fluorescent bit were formed at the irradiated position inside the bulk sample. The photoluminescence should result from the ligands peeled from the central Sm<SUP>3+</SUP> ions via bond scission induced by laser irradiation. Multilayer patterns recorded by tightly focusing the pulsed laser beam were read out by a reflection-type fluorescence confocal microscope, which can detect the scattered signal and also the fluorescent signal of the stored bits. The dependence of fluorescence and scattering signals on recording pulse energy was examined. The signal-to-noise ratios via two retrieval modes were compared as a function of recording depth. The detection of the fluorescence signal enables retrieval of the stored bits with a higher S/N ratio.</P>