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>

Modification of pinch instability theory for analysis of spray mode in GMAW

Park, Ah-Young,Kim, Sun-Rak,Hammad, Muhammad A,Yoo, Choong D Institute of Physics [etc.] 2009 Journal of Physics. D, Applied Physics Vol.42 No.22

<P>While the pinch instability theory (PIT) has been widely used to analyse the spray mode in gas metal arc welding (GMAW), it assumes an infinite cylinder and no current leakage on the cylinder surface. The PIT is modified in this work to predict the spray mode more accurately by considering reduction of the molten tip radius, the finite cylinder geometry and current leakage. The effective cylinder radius is formulated as a function of current to consider the tapered cone shape of the molten tip, and the critical wavelength of the modified PIT is derived considering a finite cylinder with a hemispherical end and current leakage. The effective radius is found to have most significant effects on drop transfer followed by the finite cylinder geometry and current leakage, and the predicted results of the modified PIT are in reasonable agreement with the experimental data of the spray mode.</P>

All-solution-processed bottom-gate organic thin-film transistor with improved subthreshold behaviour using functionalized pentacene active layer

Kim, Jinwoo,Jeong, Jaewook,Cho, Hyun Duk,Lee, Changhee,Kim, Seul Ong,Kwon, Soon-Ki,Hong, Yongtaek Institute of Physics [etc.] 2009 Journal of Physics. D, Applied Physics Vol.42 No.11

<P>We report organic thin-film transistors (OTFTs) made by simple solution processes in an ambient air environment. Inkjet-printed silver electrodes were used for bottom-gate and bottom-contacted source/drain electrodes. A spin-coated cross-linked poly(4-vinylphenol) (PVP) and a spin-coated 6,13-<I>bis</I>(triisopropylsilylethynyl) pentacene (TIPS-pentacene) were used as a gate dielectric layer and an active layer, respectively. A high-boiling-point solvent was used for TIPS-pentacene and the resulting film showed stem-like morphology. X-ray diffraction (XRD) measurement showed the spin-coated active layer was well crystallized, showing the (0 0 1) plane. The reasonable mobility, on/off ratio and threshold voltage of the fabricated device, which are comparable to those of the previously reported TIPS-pentacene OTFT with gold electrodes, show that the printed silver electrodes worked successfully as gate and source/drain electrodes. Furthermore, the device showed a subthreshold slope of 0.61 V/dec in the linear region (<I>V</I><SUB>DS</SUB> = −5 V), which is the lowest value for spin-coated TIPS-pentacene TFT ever reported, and much lower than that of the thermally evaporated pentacene OTFTs. It is thought that the surface energy of the PVP dielectric layer is well matched with that of a well-ordered TIPS-pentacene (0 0 1) surface when a high-boiling-point solvent and a low-temperature drying process are used, thereby making good interface properties, and showing higher performances than those for pentacene TFT with the same structure.</P>

Optical characterization of thermally oxidized Ni films

Seo, Y K,Lee, D J,Koh, Y-D,Chung, J-S,Lee, Y S,Jo, Y Institute of Physics [etc.] 2009 Journal of Physics. D, Applied Physics Vol.42 No.11

<P>We investigated the electronic properties of thermally oxidized Ni films using the optical spectroscopic technique and found that the optical properties of the NiO films exhibit systematic changes with oxidation degree in accord with structural and magnetic analysis results. We discuss our findings in relation to the doping to a Mott insulator and the inhomogeneous phase of a Ni(metal)–NiO(insulator) nano-composite.</P>

Synthesis and growth mechanism of catalyst free ZnO nanorods with enhanced aspect ratio by high flow additional carrier gas at low temperature

Kim, Dong Chan,Kong, Bo Hyun,Cho, Hyung Koun Institute of Physics [etc.] 2009 Journal of Physics. D, Applied Physics Vol.42 No.6

<P>This paper reports an effective catalyst free metal–organic chemical vapour deposition method for obtaining vertically well-aligned ZnO nanorods with enhanced aspect ratio at relatively low temperature (300 °C) by supplying additional Ar carrier gas at high flow rates. An increase in the flow rate of Ar gas through a by-pass line caused remarkable changes in the surface morphology from film-like to nanorods at the same growth temperature. These nanorods exhibited superior optical properties due to the elimination of grain boundaries and increase in emissive area. The enhanced aspect ratio of the nanorods was attributed to the increase in adsorption efficiency and the high directionality of the deposited atoms through the enhanced transfer velocity of the reactive gas. A schematic growth model for the formation of nanorods is also proposed.</P>

Smooth, transparent, conducting and flexible SWCNT films by filtration–wet transfer processes

Shin, Jun-Ho,Shin, D W,Patole, S P,Lee, J H,Park, S M,Yoo, J B Institute of Physics [etc.] 2009 Journal of Physics. D, Applied Physics Vol.42 No.4

<P>Single-walled carbon nanotube (SWCNT) films were prepared using a novel filtration–wet transfer process. The sheet resistance, optical transmittance, optical conductivity, dc conductivity and flexibility of the fabricated films were measured and compared with those of commercialized flexible indium tin oxide films. The shorter fabrication time, use of only water as the transferring medium, surface roughness of <3 nm, film thickness of <12 nm and maintenance of its electrical properties after film deformation make it an attractive material for flexible plastic electronics.</P>

Recent progress in thin film processing by magnetron sputtering with plasma diagnostics

Institute of Physics [etc.] 2009 Journal of Physics. D, Applied Physics Vol.42 No.4

<P>The precise control of the structure and related properties becomes crucial for sophisticated applications of thin films deposited by magnetron sputtering in emerging industries including the flat panel display, digital electronics and nano- and bio-industries. The film structure is closely related to the total energy delivered to the substrate surface for nucleation and growth during all kinds of thin film processes, including magnetron sputtering. Therefore, the energy delivered to the surface for nucleation and growth during magnetron sputtering should be measured and analysed by integrated diagnostics of the plasma parameters which are closely associated with the process parameters and other external process conditions. This paper reviews the background of thin film nucleation and growth, the status of magnetron sputtering technology and the progress of plasma diagnostics for plasma processing. The evolution of the microstructure during magnetron sputtering is then discussed with respect to the change in the process variables in terms of the plasma parameters along with empirical data of the integrated plasma diagnostics for various magnetron sputtering conditions with conventional dc, pulsed dc and high power pulsed dc sputtering modes. Among the major energy terms to be discussed are the temperature change in the top surface region and the energies of ions and neutral species.</P>

Surface morphology and domain structure during the evolution of ZnO nanorods into films

Park, Dong Jun,Lee, Jeong Yong,Kim, Dong Chan,Cho, Hyung Koun Institute of Physics [etc.] 2009 Journal of Physics. D, Applied Physics Vol.42 No.3

<P>We investigated the effects of growth temperature on the surface morphology and domain structure of ZnO nanorods and films grown on Al<SUB>2</SUB>O<SUB>3</SUB> (0 0 0 1) substrates in a temperature range of <I>T</I><SUB>g</SUB> = 180–330 °C by metal–organic chemical vapour deposition. As the growth temperature decreased, ZnO nanorods having a sharp tip changed into ZnO films with a faceted surface morphology. The ZnO films grown at a lower growth temperature (e.g. <I>T</I><SUB>g</SUB> ⩽ 240 °C) consisted of two domains with different in-plane orientations, while 30°-twist ZnO domains became dominant for higher growth temperature (e.g. <I>T</I><SUB>g</SUB> ⩾ 280 °C) to reduce the lattice mismatch. It was found that the inclination angle of the side facet observed in the surface of the ZnO layers was determined by the surface area of several facets such as <img SRC='http://ej.iop.org/images/0022-3727/42/3/035413/jphysd294991in001.gif' ALIGN='MIDDLE' ALT='(0\,1\,\bar{1}\,3)_{\rm ZnO} '/>, <img SRC='http://ej.iop.org/images/0022-3727/42/3/035413/jphysd294991in002.gif' ALIGN='MIDDLE' ALT='(0\,1\,\bar{1}\,2)_{\rm ZnO} '/> and <img SRC='http://ej.iop.org/images/0022-3727/42/3/035413/jphysd294991in003.gif' ALIGN='MIDDLE' ALT='(0\,1\,\bar{1}\,0)_{\rm ZnO} '/> planes. A detailed discussion regarding the effects of growth temperature on the growth behaviour and evolution of ZnO layers is presented in this work.</P>

Vapor phase synthesis of TaS₂ nanocrystals with iodine as transport agent

Jin, Gangtae,Kim, Chaeeun,Jo, Hyunjin,Kwon, Se-Hun,Jeong, Seong-Jun,Lee, Han-Bo-Ram,Ahn, Ji-Hoon Institute of Pure and Applied Physics 2017 Japanese Journal of Applied Physics Vol. No.

<P>TaS2 is a transition metal dichalcogenide material with a layered two-dimensional crystal structure and physically interesting behavior. 1T-TaS2 in particular exhibits a complex interaction between electron-electron and electron-lattice, as well as unique two-dimensional charge density wave characteristics with varying phase transitions depending on the temperature range. However, few reports exist on the synthesis of TaS2 crystals, and a relatively long time is required for the synthesis of TaS2 nanostructures. Here, we present an efficient method for 1T-TaS2 synthesis by chemical vapor deposition using iodine as a transport agent. We successfully synthesized 1T-TaS2 nanocrystals or thin films in a short processing time of a few hours, and their structural and chemical properties were characterized. (C) 2017 The Japan Society of Applied Physics</P>

Novel source follower transistor structure without lightly doped drain for high performance CMOS image sensor

Song, Hyeong-Sub,Kwon, Sung-Kyu,Jeon, So-Ra,Oh, Dong-Jun,Lee, Ga-Won,Lee, Hi-Deok Institute of Pure and Applied Physics 2016 Japanese Journal of Applied Physics Vol. No.

<P>To realize high-resolution pixels in the CMOS image sensor, it is necessary to reduce low-frequency noise, particularly random telegraph signal (RTS) noise of the source-follower transistor (SFT). To achieve less relative variation of drain noise current, Delta I-D/Delta I-D, a metal-oxide-semiconductor field-effect transistor structure without the lightly doped drain (LDD) for the SFT transistor is proposed. Then, a comparison of RTS noise characteristics between the proposed SFT structure without LDD and the conventional SFT structure with LDD was conducted. Although the RTS noise occurrence probability of the proposed SFT structure without LDD is somewhat greater than that of the conventional SFTstructure with LDD, the amplitude of relative variation of drain noise current of the proposed SFTstructure is significantly less than that of the conventional SFT. Despite changes in several factors in the proposed SFT, such as effective channel length, trap depth profile in gate oxide, and random dopant fluctuation (RDF), it is believed that the change of trap depth profile is a primary factor for the improved RTS characteristic. Therefore, the proposed SFT is highly desirable for the high-resolution CMOS image sensor. (C) 2016 The Japan Society of Applied Physics</P>