• 한국진공학회:학술대회논문집
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• 한국진공학회 2010년도 제39회 하계학술대회 초록집
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• pp.185-185
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• 2010

Programmable Metallization Cell (PMC) Random Access Memory is based on the electrochemical growth and removal of electrical nanoscale pathways in thin films of solid electrolytes. In this study, we investigated the nature of thin films formed by the photo doping of copper ions into chalcogenide materials for use in programmable metallization cell devices. These devices rely on metal ions transport in the film so produced to create electrically programmable resistance states. The results imply that a Cu-rich phase separates owing to the reaction of Cu with free atoms from chalcogenide materials.

• Applied Microscopy
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• 제50권
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• pp.28.1-28.6
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• 2020

Contamination on two-dimensional (2D) crystal surfaces poses serious limitations on fundamental studies and applications of 2D crystals. Surface residues induce uncontrolled doping and charge carrier scattering in 2D crystals, and trapped residues in mechanically assembled 2D vertical heterostructures often hinder coupling between stacked layers. Developing a process that can reduce the surface residues on 2D crystals is important. In this study, we explored the use of atomic force microscopy (AFM) to remove surface residues from 2D crystals. Using various transmission electron microscopy (TEM) investigations, we confirmed that surface residues on graphene samples can be effectively removed via contact-mode AFM scanning. The mechanical cleaning process dramatically increases the residue-free areas, where high-resolution imaging of graphene layers can be obtained. We believe that our mechanical cleaning process can be utilized to prepare high-quality 2D crystal samples with minimum surface residues.

• Current Photovoltaic Research
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• 제1권2호
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• pp.115-121
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• 2013

ZnO film has been used for CIGS solar cells as a buffer layer as itself or by doping Mg and Sn; ZnO film also has been used as a transparent conducting layer by doping Al or B for solar cells. Since ZnO itself is a host material for many applications it is necessary to understand the electrical and optical properties of ZnO film itself with various preparation conditions. We prepared ZnO films by converting ZnS precursor into ZnO film by thermal annealing. ZnO film was formed at low temperature as low as $500^{\circ}C$ by annealing a ZnS precursor layer in air. In the air annealing, the electrical resistivity decreased monotonically with increasing annealing temperature; the intensity of the green photoluminescence at 505 nm increased up to $750^{\circ}C$ annealing. The electrical resistivity further decreased and the intensity of green emission also increased in reducing atmospheres. The results suggest that deep-level defects originated by oxygen vacancy enhanced green emission, which reduce light transmittance and enhance the recombination of electrons in conduction band and holes in valence. More oxidizing environment is necessary to obtain defect-free ZnO film for higher transparency.

• 한국재료학회지
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• 제8권6호
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• pp.526-531
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• 1998

HVPE(hydride vapor phase epitaxy)법으로 (111) $MgAl_2O_4$기판 위에 $10~240\mu{m}$두께의 GaN를 성장하고, GaN의 두께에 따 광학적 성질을 조사하였다. $MgAl_2O_4$기판 위에 성장된 GaN의 PL 특성은 결정성장온도에서 기판으로부터 Mg이 out-diffusion하여 auto-doping 됨으로써 불순물이 첨가된 GaN의 PL 특성을 나타내었다. 10K의 온도데서 측정된 PL 스펙트럼은 자유여기자와 속박여기자의 재결합천이에 의한 피크들과 불순물과 관련된 도너-억셉터 쌍 사이의 재결합 및 이의 포논 복제에 의한 발광으로 구성되었으며, 깊은 준위로부터의 발광은 나타나지 않았다. 중성 도너에 속박된 여기자 발광 에너지와 라만 $E_2$모드 주파수는 GaN의 두께가 증가함에 따라 지수 함수적으로 감소하였으며, GaN 내의 잔류 응력에 대하여 라만 E2 모드 주파수는$\Delta$$\omega$=3.93$\sigma$($cm^{-1}$/GPa)의 관계로 변화하였다.

• Nuclear Engineering and Technology
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• 제54권6호
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• pp.2253-2261
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• 2022

In this study, nano-scaled shielding materials were assembled and fabricated by doping different weight percentages of Nano-mercuric oxide (N-HgO) into Nano-Bentonite (N-Bent) based on using (100-x% N-Bent + x% N-HgO, x = 10, 20, 30, and 40 wt %). The fabricated N-HgO/N-Bent nanocomposites were characterized by FT-IR, XRD, and SEM and evaluated to evaluate their shielding properties toward gamma radiation by using four different γ-ray energies form three point sources; 356 keV from ¹³³Ba, 662 keV from ¹³⁷Cs as well as 1173, and 1332 keV from ⁶⁰Co. The γ-rays mass attenuation coefficients were plotted as a function of the doped N-HgO concentrations into N-HgO/N-Bent nanocomposites. The computed values of mass attenuation coefficients (µ_m), effective atomic number (Z_eff) and electron density (N_el) by the as-prepared samples were found to increase, while the half value layer (HVL) and mean free path (MFP) were identified to decrease upon increasing the N-HgO contents. It was concluded also that the increase in N-HgO concentration led to a direct increase in the mass attenuation coefficient from 0.10 to 0.17 cm²/g at 356 keV and from 0.08 to 0.09 cm²/g at 662 keV. However, a slight increase was observed in the identified mass attenuation coefficients at (1172 and 1332 keV).

• 한국진공학회:학술대회논문집
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• 한국진공학회 2014년도 제46회 동계 정기학술대회 초록집
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• pp.168.1-168.1
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• 2014

We developed poly (3,4-ethylene dioxylene thiophene):poly (styrene sulfonic acid) (PEDOT:PSS)-free organic solar cells (OSCs) using buffer and anode combined Ta doped $In_2O_3$ (ITaO) electrodes. To optimize the ITaO electrodes, we investigated the effect of $Ta_2O_5$ doping power on the electrical, optical, and structural properties of the co-sputtered ITaO films. The optimized ITaO film doped with 20 W $Ta_2O_5$ radio frequency power showed sheet resistance of 17.11 Ohm/square, a transmittance of 93.45%, and a work function of 4.9 eV, all of which are comparable to the value of conventional ITO electrodes. The conventional bulk heterojunction OSC with ITaO anode showed a power conversion efficiency (PCE) of 3.348% similar to the OSCs (3.541%) with an ITO anode. In addition, OSCs fabricated on an ITaO electrode successfully operated without an acidic PEDOT:PSS buffer layer and showed a PCE of 2.634%, which was much higher than the comparable no buffer OSC with an ITO anode. Therefore, co-sputtered ITaO electrodes simultaneously acting as a buffer and an anode layer can be considered promising transparent electrodes for cost-efficient and reliable OSCs because they can eliminate the use of an acidic PEDOT:PSS buffer layer.

• Transactions on Electrical and Electronic Materials
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• 제13권6호
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• pp.283-286
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• 2012

(1-X)$(Na_{0.5}K_{0.5})NbO_3-XK_{5.4}Cu_{1.3}Ta_{10}O_{29}$ (NKN-KCT) lead-free piezoelectric ceramics have been synthesized by the conventional solid state sintering method, and their sinterability and piezoelectric properties were investigated. Typically, this material is sintered between 1,025 and $1,100^{\circ}C$ for 2 hours to achieve the required densification. Crystalline structures and Microstructures were analyzed by X-ray diffraction and scanning electron microscope. The density, dielectric constant (${\varepsilon}_r$), piezoelectric constant $d_{33}$, electromechanical coupling factor $k_p$ and mechanical quality factor $Q_m$ value of the NKN ceramics depended upon the KCT content and the sintering temperature. In particular, the KCT addition to NKN greatly improved the mechanical quality factor $Q_m$ value. The ceramic with X = 1.0 mol% sintered at $1,050^{\circ}C$ exhibited optimum properties (${\varepsilon}_r$=246, $d_{33}$=95, $k_p$=0.38 and $Q_m$=1,826). These results indicate that the ceramic is a promising candidate material for applications in lead free piezoelectric transformer and filter materials.

• 한국재료학회지
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• 제15권12호
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• pp.756-759
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• 2005

A lead free piezoelectric material, bismuth sodium barium titanate $(Bi_{0.5}Na_{0.5})_{0.94}Ba_{0.06}TiO_3$ (BNBT), was considered as an environment-friendly alternatives for the current PZT system. A perovskite BNBT was synthesized by conventional bulk ceramic processing technique. In order to improve piezoelectric properties, $La_2O_3$ as a dopant was incorporated into the BNBT system up to 0.025 moi, ana the effects on subsequent the piezoelectric ana dielectric properties were systematically investigated. With increasing $La_2O_3$ contents, the equilibrium grain shape was remarkably evidenced and sintered density was increased. Piezoelectric and dielectric properties were s]town to have maximum values at the $La_2O_3$ contents of 0.02 mol. $La^{3+}$ ions seemed to act as a softener in the BNBT system and to enhance dielectric and piezoelectric properties in this study.

• Transactions on Electrical and Electronic Materials
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• 제11권3호
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• pp.126-129
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• 2010

(1-X) $(Na_{0.5}K_{0.5})NbO_3-X$ $K_4CuNb_8O_{23}$ (NKN-X KCN) ceramics were produced using the conventional solid state sintering method, and their sinterability and electric properties were investigated. The density, dielectric constant (${\varepsilon}_r$), piezoelectric constant $d_{33}$, electromechanical coupling factor $k_p$ and mechanical quality factor $Q_m$ value of the NKN ceramics depended upon the KCN content and the sintering temperature. In particular, the KCN addition to the NKN greatly improved the mechanical quality factor $Q_m$ value. The ceramic with X = 2.0 mol% sintered at $1,150^{\circ}C$ possesses the optimum properties (${\varepsilon}_r=241$, $d_{33}=78$, $k_p=0.34$ and $Q_m=1,121$). These results indicate that the ceramic is a promising candidate material for applications in lead free piezoelectric transformer and filter materials.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2012년도 제42회 동계 정기 학술대회 초록집
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• pp.196-196
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• 2012

Graphene, two-dimensional one-atom-thick planar sheet of carbon atoms densely packed in a honeycomb crystal lattice, has grabbled appreciable attention due to its extraordinary mechanical, thermal, electrical, and optical properties. Based on the graphene's high carrier mobility, high frequency graphene field effect transistors have been developed. Graphene is useful for photonic components as well as for the applications in electronic devices. Graphene's unique optical properties allowed us to develop ultra wide-bandwidth optical modulator, photo-detector, and broadband polarizer. Graphene can support SPP-like surface wave because it is considered as a two-dimensional metal-like systems. The SPPs are associated with the coupling between collective oscillation of free electrons in the metal and electromagnetic waves. The charged free carriers in the graphene contribute to support the surface waves at the graphene-dielectric interface by coupling to the electromagnetic wave. In addition, graphene can control the surface waves because its charge carrier density is tunable by means of a chemical doping method, varying the Fermi level by applying gate bias voltage, and/or applying magnetic field. As an extended application of graphene in photonics, we investigated the characteristics of the graphene-based plasmonic waveguide for optical signal transmission. The graphene strips embedded in a dielectric are served as a high-frequency optical signal guiding medium. The TM polarization wave is transmitted 6 mm-long graphene waveguide with the averaged extinction ratio of 19 dB at the telecom wavelength of $1.31{\mu}m$. 2.5 Gbps data transmission was successfully accomplished with the graphene waveguide. Based on these experimental results, we concluded that the graphene-based plasmonic waveguide can be exploited further for development of next-generation integrated photonic circuits on a chip.