• Korean Journal of Materials Research
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• v.34 no.3
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• pp.152-162
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• 2024

In this study, we introduce a novel TiN/Ag embedded TiO₂/FTO resistive random-access memory (RRAM) device. This distinctive device was fabricated using an environmentally sustainable, solution-based thin film manufacturing process. Utilizing the peroxo titanium complex (PTC) method, we successfully incorporated Ag precursors into the device architecture, markedly enhancing its performance. This innovative approach effectively mitigates the random filament formation typically observed in RRAM devices, and leverages the seed effect to guide filament growth. As a result, the device demonstrates switching behavior at substantially reduced voltage and current levels, heralding a new era of low-power RRAM operation. The changes occurring within the insulator depending on Ag contents were confirmed by X-ray photoelectron spectroscopy (XPS) analysis. Additionally, we confirmed the correlation between Ag and oxygen vacancies (V_o). The current-voltage (I-V) curves obtained suggest that as the Ag content increases there is a change in the operating mechanism, from the space charge limited conduction (SCLC) model to ionic conduction mechanism. We propose a new filament model based on changes in filament configuration and the change in conduction mechanisms. Further, we propose a novel filament model that encapsulates this shift in conduction behavior. This model illustrates how introducing Ag alters the filament configuration within the device, leading to a more efficient and controlled resistive switching process.

• Applied Chemistry for Engineering
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• v.35 no.4
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• pp.352-359
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• 2024

Environmental pollution from heavy metal ions (HMIs) is a global concern. Recently, biosorption methods using cellulose sorbents have gained popularity. The objective of this study was to assess the removal efficiency of Cu(II), Pb(II), and Hg(II) ions at low concentration levels (100-700 ppb) from aqueous solutions using three different cellulose fiber-based filter media. Sample A was pure cellulose fiber, Sample B was 10% activated carbon-cellulose fiber, and Sample C was cellulose fiber-glass fiber-30% activated carbon-20% amorphous titanium silicate (ATS). The samples were characterized by several physicochemical techniques. The porosity measurements using N₂ sorption isotherms revealed that Samples A and B are nonporous or macroporous materials, whereas the addition of 50% filler materials into the cellulose resulted in a microporous material. The Brunauer-Emmett-Teller (BET) surface area and pore volume of Sample C were found to be 320.34 m²/g and 0.162 cm³/g, respectively. The single ion batch adsorption experiments reveal that at 700 ppb initial metal ion concentration, Sample A had removal efficiencies of 7.5, 11.5, and 13.7% for Cu(II), Pb(II), and Hg(II) ions, respectively. Sample B effectively eliminated 99.6% of Cu(II) ions compared to Pb(II) (14.2%) and Hg(II) (31.9%) ions. Cu(II) (99.37%) and Pb(II) (96.3%) ions are more efficiently removed by Sample C than Hg(II) (68.2%) ions. The X-ray photoelectron spectroscopy (XPS) wild survey spectrum revealed the presence of Cu(II), Pb(II), and Hg(II) ions in HMI-adsorbed filter media. The high-resolution C1s spectra of Samples A and B reveal the presence of -C-OH and -COOH groups on their surface, which are essential for HMIs adsorption via complexation reactions. Additionally, the ATS in Sample C facilitates the adsorption of Pb(II) and Hg(II) ions through ion exchange.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.38 no.12
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• pp.8-13
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• 2001

Cerium oxide ($CeO_2$) thin film has been proposed as a buffer layer between the ferroelectric thin film and the Si substrate in Metal-Ferroelectric-Insulator-Silicon (MFIS) structures for ferroelectric random access memory (FRAM) applications. In this study, $CeO_2$ thin films were etched with $Cl_2$/Ar gas mixture in an inductively coupled plasma (ICP). Etch properties were measured for different gas mixing ratio of $Cl_2$($Cl_2$+Ar) while the other process conditions were fixed at RF power (600 W), dc bias voltage (-200 V), and chamber pressure (15 mTorr). The highest etch rate of $CeO_2$ thin film was 230 ${\AA}$/min and the selectivity of $CeO_2$ to $YMnO_3$ was 1.83 at $Cl_2$($Cl_2$+Ar gas mixing ratio of 0.2. The surface reaction of the etched $CeO_2$ thin films was investigated using x-ray photoelectron spectroscopy (XPS) analysis. There is a Ce-Cl bonding by chemical reaction between Ce and Cl. The results of secondary ion mass spectrometer (SIMS) analysis were compared with the results of XPS analysis and the Ce-Cl bonding was monitored at 176.15 (a.m.u). These results confirm that Ce atoms of $CeO_2$ thin films react with chlorine and a compound such as CeCl remains on the surface of etched $CeO_2$ thin films. These products can be removed by Ar ion bombardment.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.16 no.4
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• pp.157-161
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• 2006

InGaN layers on GaN templated sapphire (0001) substrates were grown by mixed-source hydride vapor phase epitaxy (HVPE) method. In order to get InGaN layers, Ga-mixed In metal and $NH_3$ gas were used as group III and group V source materials, respectively. The InGaN material was compounded from chemical reaction between $NH_3$ and indium-gallium chloride farmed by HCl flowed over metallic In mixed with Ga. The grown layers were confirmed to be InGaN ternary crystal alloys by X-ray photoelectron spectroscopy (XPS). In concentration of the InGaN layers grown by selective area growth (SAG) method was investigated by the photoluminescence (PL) and cathodoluminescence (CL) measurements. Indium concentration was estimated to be in the range 3 %. Moreover, as a new attempt in obtaining InAlGaN layers, the growth of the thick InAlGaN layers was performed by putting small amount of Ga and Al into the In source. We found the new results that the metallic In mixed with Ga (and Al) as a group III source material could be used in the growth process of the In(Al)GaN layers by the mixed-source HVPE method.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.25 no.2
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• pp.62-67
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• 2015

The carbon microspheres of a core-shell type were grown by the method of mixed-source hydride vapor phase epitaxy (HVPE). The surface and the cross section of the carbon microsphere grown by a new method were observed by scanning electron microscope (SEM). The characteristics of the carbon microsphere were investigated by X-ray photoelectron spectroscopy (XPS) and a high resolution-transmission electron microscope (HR-TEM). From these measurements, the diameters of carbon sphere were about few hundred micrometers. Furthermore, we show that the carbon microsphere of the core-shell type by mixed-source HVPE method can be grown successfully with the larger size than those of the existing one. This mixed-source HVPE method is proposed a new method for making of carbon microsphere.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.29 no.8
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• pp.489-493
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• 2016

In this study, the effect of vanadium oxide ($V_2O_5$) content and pre-sintering atmosphere on sealing property of glass frit that consisted of $V_2O_5-BaO-ZnO-P_2O_5-TeO_2-CuO-Fe_2O_3-SeO_2$ was investigated by XPS (X-ray photoelectron spectroscopy). The content of V2O5 was changed to 15, 30, and 45 mol%, and the pre-sintering was carried out in air and $N_2$ condition, respectively. XPS analysis conducted before and after laser irradiation with identical sample. Before laser treatment, glass frits that were pre-sintered at air condition showed both $V^{4+}$ and $V^{5+}$, but the valence state was changed to $V^{5+}$ after laser irradiation when the glass frits contained 30 and 45 mol% $V_2O_5$; this change led to non-adhesive property. On the other hand, glass frits that were pre-sintered at $N_2$ condition exhibited only $V^{4+}$ and it showed fine adhesion irrespective of the $V_2O_5$ content. As a result, the existence of $V^{4+}$ seems to be a major factor for controlling the adhesive property of glass frit for laser sealing.

• Applied Chemistry for Engineering
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• v.32 no.4
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• pp.478-482
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• 2021

The catalytic yields of partial oxidation of methane (POM) to hydrogen over Ln(1)-Ni(5)/SBA-15 (Ln = Dy, Eu, Pr, and Tb) were investigated in a fixed bed flow reactor under atmosphere. As 1 wt% of Eu was added to Ni(5)/SBA-15 catalyst, the O1s and Si2p core electron levels of Eu(1)-Ni(5)/SBA-15 showed the chemical shift by XPS. XPS analysis also demonstrated that the atomic ratio of O1s, Ni2p_3/2, and Si2p increased to 1.284, 1.298, and 1.058, respectively, and exhibited O^-, and O^2- oxygen and metal ions such as Eu³⁺, Ni⁰, Ni²⁺, and Si⁴⁺ on the catalyst surface. The yield of hydrogen on the Eu(1)-Ni(5)/SBA-15 was 57.2%, which was better than that of Ln(1)-Ni(5)/SBA-15 (Ln = Dy, Pr, and Tb), the catalytic activity was kept steady even 25 h. As 1 wt% of Eu was added to Ni(5)/SBA-15, the oxygen vacancies caused by strong metal-support interaction (SMSI) effect due to the strong interaction between metals and carrier are made. They are resulted in increasing the dispersion of Ni⁰, and Ni²⁺ nano particles on the surface of catalyst, and are kept catalytic activity.

• Journal of the Korean Vacuum Society
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• v.17 no.4
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• pp.311-316
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• 2008

Since the presence of the chemical impurities and defect at surfaces and interfaces greatly influence the properties of various semiconductor devices, an unambiguous chemical characterization of the metal and semiconductor surfaces become more important in the view of the miniaturization of the devices toward nano scale. Among the various conventional surface characterization tools, Electron-induced Auger Electron Spectroscopy (EAES), X-ray Photoelectron Spectroscopy (XPS) and Secondary Electron Ion Mass Spectroscopy (SIMS) are being used for the identification of the surface chemical impurities. Recently, a novel surface characterizaion technique, Positron-annihilation induced Auger Electron Spectroscopy (PAES) is introduced to provide a unique method for the analysis of the elemental composition of the top-most atomic layer. In PAES, monoenergetic positron of a few eV are implanted to the surface under study and these positrons become thermalized near the surface. A fraction of the thermalized positron trapped at the surface state annihilate with the neighboring core-level electrons, creating core-hole excitations, which initiate the Auger process with the emission of Auger electrons almost simultaneously with the emission of annihilating gamma-rays. The energy of electrons is generally determined by employing ExB energy selector, which shows a poor resolution of $6{\sim}10eV$. In this paper, time-of-flight system is employed to measure the electrons energy with an enhanced energy resolution. The experimental result is compared with simulation results in the case of both linear (with retarding tube) and reflected TOF systems.

• Journal of the Korean Electrochemical Society
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• v.23 no.3
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• pp.57-65
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• 2020

It is crucial to investigate the thermal degradation of lithium-ion batteries (LIBs) to understand the possible malfunction at high temperature. Herein, we investigated the effects of surface film formation on the thermal degradation of lithium cobalt oxide (LiCoO₂, LCO) cathode that is one of representative cathode materials. Cycling test at 60℃ exhibited poorer cycleability compared with the cycling at 25℃. Cathodes after the initial 5 cycles at 60℃ (60-LCO) exhibited higher impedance compared to the cathode after initial 5 cycles at 25℃ (25-LCO), resulting in the lower rate capability upon subsequent cycling at 25℃, although the capacity values were similar at the lowest C-rate of 0.1C. In order to understand degradation of the LCO cathode at the high temperature, we analyzed the cathodes surface using X-ray photoelectron spectroscopy (XPS). Among various peaks, intensity of lithium hydroxide (LiOH) increased substantially after the operation at 60℃, and the C-C signal that represents the conductive agent was distinctly lower on 60-LCO compared to 25-LCO. These results pointed to an excessive formation of cathode-electrolyte interphase including LiOH at 60℃, leading to the increase in the resistance and the resultant degradation in the electrochemical performances.

• Proceedings of the Korean Vacuum Society Conference
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• 1999.07a
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• pp.201-201
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• 1999

소수성의 특성을 가지는^g , pp (polypropylene)의 표면을 이온 보조 반응법(IAR)으로 처리하여 친수성으로 개질하였다. 이온빔 보조 반응법은 고에너지 이온빔을 이용한 기존의 표면처리 방식과는 달리 1keV 영역의 에너지를 가진 이온빔을 조사하면서 시료 주위에 반응성 가스를 불어넣어 줌으로써 표면의 성질을 변화시키는 방법이다. 여기서 조사된 수소이온의 에너지는 0.6에서 1.0keV까지 변화시키고 시료의 주변에 불어주는 산소의 양은 0에서 8ml/min으로 변화시켰으며 이온 조사량은 5x1014에서 1x1017ions/$\textrm{cm}^2$까지 변화시켰다. 그 결과 처리하지 않은 시료의 접촉각은 93$^{\circ}$이었으며 이온조사량이 1x1017ions/$\textrm{cm}^2$이고 가속에너지가 1.0keV인 조건에서 수소 이온빔만으로 처리한 시편의 경우 접촉각은 60$^{\circ}$정도 였으나 수소이온보조 반응법으로 처리한 시편의 경우는 $10^{\circ}$이하까지 접촉각이 감소하였음을 알 수 있었다. 이는 표면처리에 따른 표면의 친수성 작용기의 형성을 예상할 수 있으며 그 존잴르 확인하기 위하여 대기중과 물속에서 각각 보관한 시료의 접촉각과 표면에너지를 계산하여보았다. 그 결과 대기중에서 방치한 시편의 경우40$^{\circ}$ 정도로 감소하였으나 증류수에 보관한 시료의 경우는 15$^{\circ}$정도의 변화를 보였다. 물과 Formamide의 접촉각의 측정으로 표면에너지를 계산한 결과 산소분위기에서 수소이온빔으로 처리된 시료는 23dyne/cm에서 64dyne/cm이상까지 변화함을 관찰하였다. 위의 결과들이 표면거칠기에 미치는 영향을 고찰하기 위해 처리되지 않은^g , pp 의 근(root mean square)값은 8.30nm이었고 1kevdpsj지에서 불어준 산소4ml/min이고 이온 조사량이 1x1017ions/$\textrm{cm}^2$인 경우 접촉각은 $10^{\circ}$를 나타냈으며 rms값은 20.8nm를 나타내었다. XPS (X-ray photoelectron spectroscopy) 분석을 통하여 1x1017ions/$\textrm{cm}^2$에서 산소기체를 4ml/min 불어넣어준 후 C-O, C=O, (C=O)-O등의 친수성 작용기가 형성되었음을 확인하였다.^g , pp 의 접착력을 알아보기 위해 유성 페인트를 전도성 고분자위에 후막 처리하였다. 스카치 테이프를 테스트를 통하여 이온 보조 반응법으로 처리된^g , pp 표면이 처리하지 않은 시편에 비하여 접착력 향상되었음을 확인하였다.