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REFERENCE LINKING PLATFORM OF KOREA S&T JOURNALS
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Applied Science and Convergence Technology
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Journal DOI :
The Korean Vacuum Society
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Volume & Issues
Volume 23, Issue 6 - Nov 2014
Volume 23, Issue 5 - Sep 2014
Volume 23, Issue 4 - Jul 2014
Volume 23, Issue 3 - May 2014
Volume 23, Issue 2 - Mar 2014
Volume 23, Issue 1 - Jan 2014
Selecting the target year
Electronic Structure of the SrTiO
(001) Surfaces: Effects of the Oxygen Vacancy and Hydrogen Adsorption
Takeyasua, K. ; Fukadaa, K. ; Oguraa, S. ; Matsumotob, M. ; Fukutania, K. ;
Applied Science and Convergence Technology, volume 23, issue 5, 2014, Pages 201~210
DOI : 10.5757/ASCT.2014.23.5.201
The influence of electron irradiation and hydrogen adsorption on the electronic structure of the
(001) surface was investigated by ultraviolet photoemission spectroscopy (UPS). Upon electron irradiation of the surface, UPS revealed an electronic state within the band gap (in-gap state: IGS) with the surface kept at
. This is considered to originate from oxygen vacancies at the topmost surface formed by electron-stimulated desorption of oxygen. Electron irradiation also caused a downward shift of the valence band maximum indicating downward band-bending and formation of a conductive layer on the surface. With oxygen dosage on the electron-irradiated surface, on the other hand, the IGS intensity was decreased along with upward band-bending, which points to disappearance of the conductive layer. The results indicate that electron irradiation and oxygen dosage allow us to control the surface electronic structure between semiconducting (nearly-vacancy free: NVF) and metallic (oxygen de cient: OD) regimes by changing the density of the oxygen vacancy. When the NVF surface was exposed to atomic hydrogen, in-gap states were induced along with downward band bending. The hydrogen saturation coverage was evaluated to be
with nuclear reaction analysis. From the IGS intensity and H coverage, we argue that H is positively charged as
on the NVF surface. On the OD surface, on the other hand, the IGS intensity due to oxygen vacancies was found to decrease to half the initial value with molecular hydrogen dosage. H is expected to be negatively charged as
on the OD surface by occupying the oxygen vacancy site.
Optical and Structural Properties of Emerging Dilute III-V Bismides
Santos, B.H. Bononi Dos ; Gobatoa, Y. Galvao ; Heninib, M. ;
Applied Science and Convergence Technology, volume 23, issue 5, 2014, Pages 211~220
DOI : 10.5757/ASCT.2014.23.5.211
In this paper, we present a review of optical and structural studies of
epilayers grown by Molecular Beam Epitaxy (MBE) on (311)B and (001) GaAs substrates with different As fluxes. The results indicate that under near-stoichiometric conditions the bismuth incorporation is higher for samples grown on (311)B GaAs substrates than for those grown on (001) GaAs. In addition, carrier localization effects in GaBiAs layers are clearly revealed for both samples by optical measurements. The (311)B samples showed evidence of higher density of defects. It has also been found that the nonradiative centers play a significant role in the recombination process in this material system. The influence of post-growth annealing on the microstructural, optical, and magneto-optical properties was also investigated. An important improvement of optical and spin properties after thermal annealing due to the reduction of defects in the GaBiAs layers was observed.
Near-IR Quantum Cutting Phosphors: A Step Towards Enhancing Solar Cell Efficiency
Jadhav, Abhijit P. ; Khan, Sovann ; Kim, Sun Jin ; Cho, So-Hye ;
Applied Science and Convergence Technology, volume 23, issue 5, 2014, Pages 221~239
DOI : 10.5757/ASCT.2014.23.5.289
The global demand for energy has been increasing since past decades. Various technologies have been working to find a suitable alternative for the generation of sustainable energy. Photovoltaic technologies for solar energy conversion represent one of the significant routes for the green and renewable energy production. Despite of remarkable improvement in solar cell technologies, the generation of power is still suffering with lower energy conversion efficiency, high production cost, etc. The major problem in improving the PV efficiency is spectral mismatch between the incident solar spectrum and bandgap of a semiconductor material used in solar cell. Luminescent materials such as rare-earth doped phosphor materials having the quantum efficiency higher than unity can be helpful for photovoltaic applications. Quantum cutting phosphors are the most suitable candidates for the generation of two or more low-energy photons for the absorption of every incident high-energy photons. The phosphors which are capable of converting UV photon to visible and near-IR (NIR) photon are studied primarily for photovoltaic applications. In this review, we will survey various near IR quantum cutting phosphors with respective to their synthesis method, energy transfer mechanism, nature of activator, sensitizer and dopant materials incorporation and energy conversion efficiency considering their applications in photovoltaics.
Modelling and Measurements of Normal and Lateral Stiffness for Atomic Force Microscopy
Choi, Jinnil ;
Applied Science and Convergence Technology, volume 23, issue 5, 2014, Pages 240~247
DOI : 10.5757/ASCT.2014.23.5.221
Modelling and measurements of normal and lateral stiffness for atomic force microscopy (AFM) are presented in this work. Important issues, such as element discretisation, stiffness calibration, and deflection angle are explored using the finite element (FE) model. Elements with various dimension ratios are investigated and comparisons with several mathematical models are reported to verify the accuracy of the model. Investigation of the deflection angle of a cantilever is also shown. Moreover, AFM force measurement experiments with conical and colloid probe tips are demonstrated. The relationships between force and displacement, required for stiffness measurement, in normal and lateral directions are acquired for the conical tip and the limitations of the colloid probe tip are highlighted.
Numerical Investigation of RF Pulsing Effect on Ion Energy Distributions at RF-biased Electrodes
Kwon, Deuk-Chul ; Song, Mi-Young ; Yoon, Jung-Sik ;
Applied Science and Convergence Technology, volume 23, issue 5, 2014, Pages 246~253
DOI : 10.5757/ASCT.2014.23.5.246
The ion energy distributions (IEDs) arriving at a substrate strongly affect the etching rates in plasma etching processes. In order to determine the IEDs accurately, it is important to obtain the characteristics of radio frequency (rf) sheath at pulsed rf substrates. However, very few studies have been conducted to investigate pulsing effect on IEDs at multiple rf driven electrodes. Therefore, in this work, we extended previous one-dimensional dynamics model for pulsed-bias electrodes. We obtained the IEDs using the developed rf sheath model and observed that numerically solved IEDs are in a good agreement with the experimental results.
Surface Treatment of Air Gap Membrane Distillation (AGMD) Condensation Plates: Techniques and Influences on Module Performance
Harianto, Rachel Ananda ; Aryapratama, Rio ; Lee, Seockheon ; Jo, Wonjin ; Lee, Heon Ju ;
Applied Science and Convergence Technology, volume 23, issue 5, 2014, Pages 248~253
DOI : 10.5757/ASCT.2014.23.5.229
Air Gap Membrane Distillation (AGMD) is one of several technologies that can be used to solve problems fresh water availability. AGMD exhibits several advantages, including low conductive heat loss and higher thermal efficiency, due to the presence of an air gap between the membrane and condensation wall. A previous study by Bhardwaj found that the condensation surface properties (materials and contact angle) affected the total collected fresh water in the solar distillation process. However, the process condition differences between solar distillation and AGMD might result in different condensation phenomena. In contrast, N. Miljkovic showed that a hydrophobic surface has higher condensation heat transfer. Moreover, to the best of our knowledge, there is no study that investigates the effect of condensation surface properties in AGMD to overall process performance (i.e. flux and thermal efficiency). Thus, in this study, we treated the AGMD condensation surface to make it hydrophobic or hydrophilic. The condensation surface could be made hydrophilic by immersing and boiling plate in deionized (DI) water, which caused the formation of hydrophilic aluminum hydroxide (AlOOH) nanostructures. Afterwards, the treated plate was coated using hexamethyldisiloxane (HMDSO) through plasma-enhanced chemical vapor deposition (PECVD). The result indicated that condensation surface properties do not affect the permeate flux or thermal efficiency significantly. In general, the permeate flux and thermal efficiency for the treated plates were lower than those of the non-treated plate (pristine). However, at a 1 mm and 3 mm air gap, the treated plate outperformed the non-treated plate (pristine) in terms of permeate flux. Therefore, although surface wettability effect was not significant, it still provided a little influence.
PEDOT:PSS Thin Films with Different Pattern Structures Prepared Using Colloidal Template
Yu, Jung-Hoon ; Lee, Jin-Su ; Nam, Sang-Hun ; Boo, Jin-Hyo ;
Applied Science and Convergence Technology, volume 23, issue 5, 2014, Pages 254~260
DOI : 10.5757/ASCT.2014.23.5.235
Organic solar cells have attracted extensive attention as a promising approach for cost-effective photovoltaic devices. However, organic solar cell has disadvantage of low power conversion efficiency in comparison with other type of solar cell, due to the recombination ratio of hole and electron is too large in the active layer. Thus we have change the surface structure of PEDOT:PSS layers to improve the current density by colloidal lithography method using various-size of polystyrene sphere. The two types of coating method were applied to fabricate the different pattern shape and height, such as spin coating and drop casting. Using the organic solvent, we easily eliminate the PS sphere and could make the varied pattern shapes by controlling the wet etching time. Also we have measured the electrical properties of patterned PEDOT:PSS film to check whether it is suitable for organic photovoltaics.
Room-Temperature Luminescence from Ion Beam or Atmospheric Pressure Plasma-Treated SrTiO
Song, J.H. ; Choi, J.M. ; Cho, M.H. ; Choi, E.J. ; Kim, J. ; Song, J.H. ;
Applied Science and Convergence Technology, volume 23, issue 5, 2014, Pages 261~264
DOI : 10.5757/ASCT.2014.23.5.242
(STO) single crystal irradiated with a 3-MeV proton beam exhibits blue and green mixed luminescence. However, the same proton beam when used to irradiate STO with a very thin layer of deposited Pt does not show any luminescence. This Pt layer prevents any damage which may otherwise be caused by arcing, which stems from the accumulated surface voltage of tens of kV due to the charge induced by secondary electrons on the surface of the insulator during the ion beam irradiation process. Hence, the luminescence of ion-irradiated STO originates from the modification of the STO surface layer caused by arcing rather than from any direct ion beam irradiation effect. STO treated with atmospheric-pressure plasma, a simple and cost-effective method, also exhibits the same type of blue and green mixed luminescence as STO treated with an ion beam, as the plasma also creates a layer of surface damage due to arcing.
Magnetic Properties of Strained L1
-ordered FePt and CoPt: An ab initio Study
Choi, Heechae ;
Applied Science and Convergence Technology, volume 23, issue 5, 2014, Pages 273~278
DOI : 10.5757/ASCT.2014.23.5.254
Using ab initio calculations, the effects of uniaxial, biaxial, and hydrostatic strains on the magnetocrystalline anisotropy of
-orderd FePt and CoPt alloys were systematically investigated. Interestingly, the rates and the signs of magnetocrystalline anisotropy changes of FePt and CoPt were determined by the directions and dimensions of strains. The calculation results are consistent with the previous experimental observations and are expected to provide directions to tailor magnetic properties of various types of
-ordered FePt and CoPt systems.
Characterization of Al Doped ZnO Thin Films Prepared by RF Magnetron Sputtering Under Various Substrate Temperatures
Kim, Deok Kyu ; Kim, Hong Bae ;
Applied Science and Convergence Technology, volume 23, issue 5, 2014, Pages 279~283
DOI : 10.5757/ASCT.2014.23.5.260
Al doped ZnO thin films have been deposited by a RF magnetron sputtering technique from a ZnO (2 wt.%
) target onto glass substrates heated at temperature ranging from RT to
. X-ray diffraction analysis shows that the deposits have a preferential growth along the c-axis of a hexagonal structure. The full with at half maximum decreases from 0.45 to
in the studied temperature range. The root main square surface roughness increases with substrate temperature from 1.89 to 2.67 nm. All films are transparent up to 80% in the visible wavelength range and the adsorption edge is red-shifted with substrate temperature from RT to
. The sheet resistance increases from 92 ohm/sq to 419 ohm/sq when the deposition temperature increases from RT to
. The increment of sheet resistance is caused by lowered carrier concentration resulting from an increase in surface roughness.
Fabrication of Gallium Phosphide Tapered Nanostructures on Selective Surfaces
Song, Young Min ; Park, Hyun Gi ;
Applied Science and Convergence Technology, volume 23, issue 5, 2014, Pages 284~288
DOI : 10.5757/ASCT.2014.23.5.265
We present tapered nanostructures fabricated on a selective area of gallium phosphide substrates for advanced optoelectronic device applications. A lithography-free fabrication process was accomplished by dry etching of metal nanoparticles. Thermal dewetting of micro-patterned metal thin films provides etch masks for tapered nanostructures. This simple process also allows the formation of plasmonic surfaces with corrugated shapes. Rigorous coupled-wave analysis calculations provide design guidelines for tapered nanostructures on gallium phosphide substrates.
Visible Emission Properties of V
Nanorods Prepared by Different Growth Methods
Kang, Manil ; Kim, Sok Won ; Ryu, Ji-Wook ;
Applied Science and Convergence Technology, volume 23, issue 5, 2014, Pages 289~295
DOI : 10.5757/ASCT.2014.23.5.270
nanorods were grown by means of electron beam irradiation and thermal oxidation methods and the visible emission properties of the nanorods grown by both methods were investigated. The growth and crystallinity of the nanorods were greatly enhanced by the insertion of a buffer layer. The emission spectra of the nanorods grown by thermal oxidation and electron beam irradiation showed a peak centered at 710~720 nm, which is believed to be due to oxygen vacancies introduced during the growth process. Also, the emission peak centered at 530 nm observed in the
nanorods grown by electron beam irradiation was considered to be due to the band edge transition as a result of the enhanced crystallinity.
White Light Generation from Single Gallium Oxide Nanoparticles co-doped with Rare-Earth Metals
Patil, Prashant ; Park, Jinsung ; Lee, Seung Yong ; Park, Jong-Ku ; Cho, So-Hye ;
Applied Science and Convergence Technology, volume 23, issue 5, 2014, Pages 296~300
DOI : 10.5757/ASCT.2014.23.5.277
The synthesis of pure and rare-earth doped gallium oxide (
) nanoparticles is reported. The synthesized nanoparticles are characterized with XRD, TEM, and PL analyses. Strong blue emission is observed from un-doped gallium oxide nanoparticles, while nanoparticles doped with
give strong red and green emissions, respectively. When doped with
together, gallium oxide nanoparticles emit white light. The CIE coordinate of the emitted light was found to be (0.33, 0.33), which is well within the white light region.
Fabrication of SnO
/Zn Core-shell Nanowires and Photoluminescence Properties
Kong, Myung Ho ; Kwon, Yong Jung ; Cho, Hong Yeon ; Kim, Hyoun Woo ;
Applied Science and Convergence Technology, volume 23, issue 5, 2014, Pages 301~307
DOI : 10.5757/ASCT.2014.23.5.282
We have fabricated
/Zn core-shell nanowires by employing a sputtering technique with a Zn target. Scanning electron microscopy indicated that the surface of the nanowires became rougher by the coating. X-ray diffraction of the coated nanowires exhibited the hexagonal Zn diffraction peaks. TEM image of coated structures showed that shell layer was mainly comprised of hexagonal Zn phase. EDX spectra suggested that the shell layer consisted of Zn elements. The photoluminescence spectrum of the coated nanowires in conjunction with Gaussian fitting analysis revealed that the emission was disconvoluted with three Gaussian functions, which are centered at 2.1 eV in the yellow region, 2.4 eV in the green region, and 3.3 eV in the ultraviolet region. We speculated the possible mechanisms of these emission peaks.