Toward efficient light diffraction and intensity variations by using wide bandwidth surface acoustic wave

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>

Propagation characteristics of shock waves from a plane carbon-nanotube-coated optoacoustic transducer in water

Fan, Xiaofeng,Baek, Yonggeun,Ha, Kanglyeol,Kim, Moojoon,Kim, Jungsoon,Kim, Duckjong,Kang, Hyun Wook,Oh, Junghwan Institute of Pure and Applied Physics 2017 Japanese Journal of Applied Physics Vol. No.

<P>An optoacoustic transducer made of light-absorbing and elastomeric materials can generate high-pressure wide-band ultrasound waves in water when it is illuminated by a pulse laser. To generate such waves with high efficiency, carbon nanotubes (CNTs) and poly(dimethylsiloxane) (PDMS) are widely used as the light-absorbing and elastomeric materials, respectively. It was previously reported that an optoacoustic concave transducer made of these materials can produce strong shock waves, namely, blast waves, within its focal zone. In this study, we have shown that these waves can also be generated by a plane optoacoustic transducer fabricated by coating CNTs-PDMS on a poly(methyl methacrylate) (PMMA) plate. Some propagation characteristics of the blast wave generated were measured and compared with the calculated results. It was found that the propagation speed and attenuation of the wave are different from those of usual sounds. From the comparison of the measured and the calculated acoustic fields, it is assumed that every point on the transducer surface produces almost the same blast wave. (C) 2017 The Japan Society of Applied Physics.</P>

Two-stage unified stretched-exponential model for time-dependence of threshold voltage shift under positive-bias-stresses in amorphous indium-gallium-zinc oxide thin-film transistors

Jeong, Chan-Yong,Kim, Hee-Joong,Hong, Sae-Young,Song, Sang-Hun,Kwon, Hyuck-In Institute of Pure and Applied Physics 2017 Japanese Journal of Applied Physics Vol. No.

<P>In this study, we show that the two-stage unified stretched-exponential model can more exactly describe the time-dependence of threshold voltage shift (Delta V-TH) under long-term positive-bias-stresses compared to the traditional stretched-exponential model in amorphous indium-gallium-zinc oxide (a-IGZO) thin-film transistors (TFTs). Delta V-TH is mainly dominated by electron trapping at short stress times, and the contribution of trap state generation becomes significant with an increase in the stress time. The two-stage unified stretched-exponential model can provide useful information not only for evaluating the long-term electrical stability and lifetime of the a-IGZO TFT but also for understanding the stress-induced degradation mechanism in a-IGZO TFTs. (C) 2017 The Japan Society of Applied Physics.</P>

Comparison null imaging ellipsometry using polarization rotator

Park, Sungmo,Kim, Eunsung,Kim, Jiwon,An, Ilsin Institute of Pure and Applied Physics 2018 Japanese Journal of Applied Physics Vol. No.

<P>In this study, two-reflection imaging ellipsometry is carried out to compare the changes in polarization states between two samples. By using a polarization rotator, the parallel and perpendicular components of polarization are easily switched between the two samples being compared. This leads to an intensity image consisting of null and off-null points depending on the difference in optical characteristics between the two samples. This technique does not require any movement of optical elements for nulling and can be used to detect defects or surface contamination for quality control of samples. (C) 2018 The Japan Society of Applied Physics</P>

Numerical simulation of p-type diamond Schottky barrier diodes for high breakdown voltage

Kang, Dong-Won,Chang, Hae Nyung,Ha, Min-Woo Institute of Pure and Applied Physics 2017 Japanese Journal of Applied Physics Vol. No.

<P>P-type diamond devices have high potential for power semiconductors due to their high critical field, hole mobility, and thermal conductivity. The electrical characteristics of p-type pseudovertical diamond Schottky barrier diodes (SBDs) were investigated by numerical simulation. The impact ionization coefficients were required to obtain the breakdown voltage. They were revised to satisfy a parallel-plane breakdown field of 10MV/cm. The doping concentration and thickness of a low-doped drift layer were key parameters in determining the parallel-plane breakdown voltage. The p-type pseudovertical diamond SBDs exhibited lower breakdown voltage than the parallel-plane breakdown voltage because field crowding occurred at the edge of the cathode. When the doping concentration and thickness of the p- drift layer were 10(16)cm(-3) and 4 mu m, respectively, the breakdown voltage of the p-type pseudovertical diamond SBD was 961V, which was considerably less than the parallel-plane breakdown voltage of 3646V. (C) 2017 The Japan Society of Applied Physics</P>

Current-driven magnetic domain wall motion and its real-time detection

Kim, Kab-Jin,Yoshimura, Yoko,Ono, Teruo Institute of Pure and Applied Physics 2017 Japanese Journal of Applied Physics Vol. No.

<P>Current-controlled magnetic domain wall motion has opened the possibility of a novel type of shift register memory device, which has been optimistically predicted to replace existing magnetic memories. Owing to this promising prospect, intensive work has been carried out during the last few decades. In this article, we first review the progress in the study of current-induced magnetic domain wall motion. Underlying mechanisms behind the domain wall motion, which have been discovered during last few decades, as well as technological achievements are presented. We then present our recent experimental results on the real-time detection of current-driven multiple magnetic domain wall motion, which directly demonstrates the operation of a magnetic domain wall shift register. (C) 2017 The Japan Society of Applied Physics</P>

Acoustic band gaps due to diffraction modes in two-dimensional phononic crystals

Kang, Hwi Suk,Lee, Kang Il,Yoon, Suk Wang Institute of Pure and Applied Physics 2017 Japanese Journal of Applied Physics Vol. No.

<P>In this study, we experimentally and theoretically investigated acoustic band gap control with diffraction modes in two-dimensional (2D) phononic crystals (PCs) consisting of periodic arrays of stainless steel (SS) rods immersed in water. We could classify the acoustic band gaps into two types with diffraction modes in the reflection region, and control the center frequencies of the band gaps by varying the vertical lattice constants. Pressure transmission coefficients and acoustic pressure fields were calculated using the finite element method (FEM), to classify and control the acoustic band gaps. As the vertical lattice constants were varied, the center frequencies of the band gaps, where only normal reflection occurred, were almost constant while those of the band gaps, where additional reflected waves with different propagation directions occurred, decreased with increasing the vertical lattice constants. This work can be used to manipulate acoustic band gap adding, splitting, and shifting. (C) 2017 The Japan Society of Applied Physics</P>

Controlled growth of large-area and high-quality molybdenum disulfide

Kim, Ja-Yeon,Kim, Doo-Hyung,Kwon, Min-Ki Institute of Pure and Applied Physics 2017 Japanese Journal of Applied Physics Vol. No.

<P>We describe a method of synthesizing large-area and uniform molybdenum disulfide (MoS2) films with control over the size and layer number at predetermined locations, using a step-edge mediated growth technique with simple lithography. Controlling various growth parameters such as temperature and pressure enables the synthesis of high quality, crystalline, monolayer MoS2, with electrical and optical properties that are comparable to those of exfoliated MoS2. This approach to the precise control of the size and orientation of MoS2 atomic layers can open a path toward the scalable production of high-quality devices based on MoS2 for applications in flexible displays. (C) 2017 The Japan Society of Applied Physics</P>

Chipless wireless neural probes based on one-port surface acoustic wave delay line and neural-firing-dependent capacitors

Jung, In Ki,Chen, Fu,Lee, Kee Keun Institute of Pure and Applied Physics 2014 Japanese Journal of Applied Physics Vol. No.

<P>A wireless, battery-free neural probe system was developed for reading neural signals in the brain using a one-port surface acoustic wave (SAW) reflective delay line, neural-firing-dependent capacitive electrodes, two antennas, and a network analyzer as a measurement unit. The one-port SAW reflective delay line supersedes the existing complex wireless transceiver system composed of a few hundreds of transistors and a heavy rechargeable battery and makes battery-free, wireless measurements possible. The multicapacitive electrodes placed on a sharp shank were electrically connected to the corresponding interdigital transducer (IDT)-type reflectors on a one-port SAW reflective delay line. Each electrode on the sharp shank was made using a copolymer poly(vinylidene-fluoride-trifluoroethylene) (PVDF-TrFE) ferroelectric material sandwiched between two metals. As electrical pulses were applied to the capacitive electrode, overall impedance perturbations between the IDT and the external capacitive electrode system were observed, resulting in amplitude changes in the reflection peaks in the time domain depending on the magnitude of the electrical pulses. Good linearity and sensitivity were observed at the amplitude variations in terms of applied electrical pulses. Coupling-of-modes (COM) modeling and impedance matching simulations were also performed to predict device performances and compare experimental results. (C) 2014 The Japan Society of Applied Physics</P>

Sn-doped β-Ga₂O₃nanowires deposited by radio frequency powder sputtering

Lee, Su Yong,Kang, Hyon Chol Institute of Pure and Applied Physics 2018 Japanese Journal of Applied Physics Vol. No.

<P>We report the synthesis and characterization of Sn-doped beta-Ga2O3 nanowires (NWs) deposited using radio frequency powder sputtering. The growth sequence of Sn-doped beta-Ga2O3 NWs is similar to that of the undoped beta-Ga2O3 NWs. Self-assembled Ga clusters act as seeds for initiating the growth of Sn-doped beta-Ga2O3 NWs through a vapor-liquid-solid process, while Sn atoms are incorporated into the trunk of NWs uniformly. Different from the straight shape of undoped NWs, the conical shape of NWs is observed, which is attributed to the change in supersaturation conditions and the diffusion of the catalyst tip and reaction species. (c) 2018 The Japan Society of Applied Physics</P>