• Applied Science and Convergence Technology
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• 제23권1호
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• pp.14-26
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• 2014

Copper is an important component from coin metal to electronic wire, integrated circuit, and to lithium battery. Copper oxides, mainly including $Cu_2O$ and CuO, are important semiconductors for the wide applications in solar cell, catalysis, lithium-ion battery, and sensor. Due to their low cost, low toxicity, and easy synthesis, copper oxides have received much research interest in recent year. Herein, we review the crystallization of copper oxides by designing various chemical reaction routes, for example, the synthesis of $Cu_2O$ by reduction route, the oxidation of copper to $Cu_2O$ or CuO, the chemical transformation of $Cu_2O$ to CuO, the chemical precipitation of CuO. In the designed reaction system, ligands, pH, inorganic ions, temperature were used to control both chemical reactions and the crystallization processes, which finally determined the phases, morphologies and sizes of copper oxides. Furthermore, copper oxides with different structures as electrode materials for lithium-ion batteries were also reviewed. This review presents a simple route to study the reaction-crystallization-performance relationship of Cu-based materials, which can be extended to other inorganic oxides.

• Applied Science and Convergence Technology
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• 제23권5호
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• pp.221-239
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• 2014

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.

• Applied Science and Convergence Technology
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• 제23권5호
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• pp.261-264
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• 2014

$SrTiO_3$ (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.

• Applied Science and Convergence Technology
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• 제23권5호
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• pp.279-283
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• 2014

Al doped ZnO thin films have been deposited by a RF magnetron sputtering technique from a ZnO (2 wt.% $Al_2O_3$) target onto glass substrates heated at temperature ranging from RT to $400^{\circ}C$. 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 $0.43^{\circ}$ 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 $400^{\circ}C$. The sheet resistance increases from 92 ohm/sq to 419 ohm/sq when the deposition temperature increases from RT to $400^{\circ}C$. The increment of sheet resistance is caused by lowered carrier concentration resulting from an increase in surface roughness.

• Applied Science and Convergence Technology
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• 제23권3호
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• pp.151-159
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• 2014

We investigated the effects of the chemical composition and the relative density on the plastic deformation behavior of sintered Fe-based alloys by means of compressive tests. Overall compressive stresses increased as the amount of alloying elements and the relative density were respectively increased. Addition of alloying elements except for Mo increased the yield stress regardless of the relative density. The relationship between the effects of the chemical composition and the relative density and the mean rate of the stress increase was analyzed. A constitutive equation based on the Ludwik equation with the regressed parameters was proposed to predict the compressive true stress-true strain curves of the sintered Fe-based alloys. The K and n values used in the proposed equation were regressed as a function of the alloying elements and the relative density based on the individual K and n values. The plastic deformation behavior predicted using the proposed constitutive equation showed reliable accuracy compared with experimental data.

• Applied Science and Convergence Technology
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• 제23권3호
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• pp.134-138
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• 2014

One-dimensional nanostructures such as nanowires have been extensively investigated as a promising type of material for applications of nanoscale technology. The fabrication of single-nanowire devices are consequently important and interesting. This study introduced a feasible method for growing CuO nanowires on Cu foils. The nanowires had diameters of 10~150 nm and lengths of more than $7{\mu}m$ and were grown by means of thermal oxidation in a vacuum. They were entirely and uniformly grown over the Cu foil surfaces and could be extracted and dispersed in an ethanol solution for further purposes. In addition, a simple fabrication method for realizing device functionality from a single CuO nanowire was reported. Fabricated devices were carefully checked by field-emission scanning electron microscopy (SEM). The probability of the realization of a single-CuO-nanowire device relative to that of all other types was estimated to be around 25%. Finally, the I-V characteristics of the devices were analyzed.

• Applied Science and Convergence Technology
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• 제23권2호
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• pp.72-82
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• 2014

Lithium-ion batteries (LIBs) have become popular electrochemical devices. Due to the unique advantages of LIBs in terms of high operating voltage, high energy density, low self-discharge, and absence of memory effects, their application range, which was primarily restricted to portable electronic devices, is now being extended to high-power applications, such as electric vehicles (EVs) and hybrid electrical vehicles (HEVs). Among various anode materials, $Li_4Ti_5O_{12}$ (LTO) is believed to be a promising anode material for high-power LIBs due to its advantages of high working potential and outstanding cyclic stability. However, the rate performance of LTO is limited by its intrinsically low electronic conductivity and poor $Li^+$ ion diffusion coefficient. This review highlights the recent progress in improving the rate performance of LTO through doping, compositing, and nanostructuring strategies.

• Applied Science and Convergence Technology
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• 제26권2호
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• pp.21-25
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• 2017

The shape of the reflection spectrum is complex and appears to overlap with several signals, because the surface state is uneven due to the natural oxide film, so that the spectrum becomes a complicated signal shape divided into regions 1 and 2 due to diffuse reflection. On the other hand, it is seen that the reflection spectrum after PEO surface treatment is overlapped with several signals. In addition, the reflectance of the energy band varies from 1.32 to 1.46 eV. Usually, the MgO-type oxide film was observed at an energy band of ~4.2 eV. The thickness of the oxide film was increased as the DC voltage was increased by the thin film thickness meter (QuaNix; 7500M) after Plasma Electrolytic Oxidation (; PEO) surface treatment. This is because the higher the DC voltage, the easier the binding of the $OH^-$ ions in the solution solution and the $Mg^+$ ions of the magnesium alloy. An important part of the bonding of ordinary ions is the energy source (plasma) which can promote bonding. However, when a certain threshold voltage or more is applied, the material is adversely affected. The oxide film of the surface may be destroyed without increasing the thickness of the oxide film, that is, whitening of the material may occur.

• Applied Science and Convergence Technology
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• 제26권2호
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• pp.26-29
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• 2017

Thin films of europium-doped yttrium oxide ($Y_2O_3$:Eu) were prepared on Si (100) substrates by using a radio frequency (RF) magnetron sputtering. After the deposition, the films were annealed at $1000^{\circ}C$ in an air ambient for 1 hour. X-ray diffraction analysis revealed that the $Y_2O_3$:Eu films had a polycrystalline cubic ${\alpha}-Y_2O_3$ structure. The as-deposited films showed no photoluminescence (PL), which was due to poor crystalline quality of the films. The crystallinity of the $Y_2O_3$:Eu films was significantly improved by annealing. The strong red PL emission was observed from the annealed $Y_2O_3$:Eu films and the highest intensity peak was centered at around 613 nm. This emission peak originated from the $^5D_0{\rightarrow}^7F_2$ transition of the trivalent Eu ions occupying the $C_2$ sites in the cubic ${\alpha}-Y_2O_3$ lattice. The broad PL excitation band was observed at wavelengths below 280 nm, which was attributed to the charge transfer transition of the trivalent Eu ion.

• Applied Science and Convergence Technology
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• 제25권3호
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• pp.51-55
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• 2016

The surface treatment of a titanium implant is investigated with a non-thermal atmospheric pressure plasma jet. The plasma jet is generated by the injection of He and $O_2$ gas mixture with a sinusoidal driving voltage of 3 kV or more and with a driving frequency of 20 kHz. The generated plasma plume has a length up to 35 mm from the jet outlet. The wettability of 4 different titanium surfaces with plasma treatments was measured by the contact angle analysis. The water contact angles were significantly reduced especially for $O_2/He$ mixture plasma, which was explained with the optical emission spectroscopy. Consequently, plasma treatment enhances wettability of the titanium surface significantly within the operation time of tens of seconds, which is practically helpful for tooth implantation.