• Title/Summary/Keyword: Amorphous matrix

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Rapid Surface Heating Promotes Laser Desorption Ionization of Thermally Labile Molecules from Surfaces

  • Han, Sang Yun
    • Mass Spectrometry Letters
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    • v.7 no.4
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    • pp.91-95
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    • 2016
  • In recent years, matrix-free laser desorption ionization (LDI) for mass spectrometry of thermally labile molecules has been an important research subject in the pursuit of new ionization methods to serve as alternatives to the conventional matrix-assisted laser desorption ionization (MALDI) method. While many recent studies have reported successful LDI of thermally labile molecules from various surfaces, mostly from surfaces with nanostructures, understanding of what drives the LDI process still requires further study. This article briefly reviews the thermal aspects involved in the LDI mechanism, which can be characterized as rapid surface heating. The thermal mechanism was supported by observed LDI and postsource decay (PSD) of peptide ions produced from flat surfaces with special thermal properties including amorphous Si (a-Si) and tungsten silicide ($WSi_x$). In addition, the concept of rapid surface heating further suggests a practical strategy for the preparation of LDI sample plates, which allows us to choose various surface materials including crystalline Si (c-Si) and Au tailorable to specific applications.

Effect of Annealing Temperature on the Permeability and Magneto-Impedance Behaviors of Fe68.5Mn5Si13.5B9Nb3Cu1 Amorphous Alloy

  • Le Anh-Than;Ha, Nguyen Duy;Kim, Chong-Oh;Rhee, Jang-Roh;Chau Nguyen;Hoa Nguyen Quang;Tho Nguyen Due;Lee, Hee-Bok
    • Journal of Magnetics
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    • v.11 no.1
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    • pp.55-59
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    • 2006
  • The effect of annealing temperature on the permeability and giant magneto-impedance (GMI) behaviors of $Fe_{68.5}Mn_{5}Si_{13.5}B_9Nb_3Cu_1$ amorphous alloy has been systematically investigated. The nanocrystalline $Fe_{68.5}Mn_{5}Si_{13.5}B_9Nb_3Cu_1$ alloys consisting of ultra-fine $(Fe,Mn)_3Si$ grains embedded in an amorphous matrix were obtained by annealing their precursor alloy at the temperature range from $500^{\circ}C\;to\;600^{\circ}C$ for 1 hour in vacuum. The permeability and GMI profiles were measured as a function of external magnetic field. It was found that the increase of both the permeability and the GMI effect with increasing annealing temperature up to $535^{\circ}C$ was observed and ascribed to the ultrasoft magnetic properties in the sample, whereas an opposite tendency was found when annealed at $600^{\circ}C$ which is due to the microstructural changes caused by high-temperature annealing. The study of temperature dependence on the permeability and GMI effect showed some insights into the nature of the magnetic exchange coupling between nanocrystallized grains through the amorphous boundaries in nanocrystalline magnetic materials.

Comparsions for Flexural Performance of Amorphous Steel Fiber Reinforced Concrete (비정질강섬유보강콘크리트의 휨성능 비교분석)

  • Kim, Byoung-Il;Lee, Sea-Hyun
    • Resources Recycling
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    • v.24 no.3
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    • pp.66-75
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    • 2015
  • The flexural performance of amorphous steel fibers having environmental and economy benefits due to relatively short manufacturing process were evaluated as well as that of hooked steel fibers by varing fiber length and volume fraction. Fiber lengths were 10 mm, 20 mm, 30 mm and fiber volume fractions were varied from 0.3% to 1.2%. Test results with flexural performance showed that mixing design needs to be careful because of relatively high volume of amorphous steel fiber compared to hooked steel fibers. High flexural strength was obtained from both longer fiber length and higher volume fraction. Residual strength and toughness of amorphous steel fiber were similar to that of hooked steel fiber, even though rapid dropping of applied load right after concrete matrix breaking. It can be judged that relatively high ability of energy dissipation around first cracking area relatively overcome rapid dropping of loading.

Amorphous Vanadium Titanates as a Negative Electrode for Lithium-ion Batteries

  • Lee, Jeong Beom;Chae, Oh. B.;Chae, Seulki;Ryu, Ji Heon;Oh, Seung M.
    • Journal of Electrochemical Science and Technology
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    • v.7 no.4
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    • pp.306-315
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    • 2016
  • Amorphous vanadium titanates (aVTOs) are examined for use as a negative electrode in lithium-ion batteries. These amorphous mixed oxides are synthesized in nanosized particles (<100 nm) and flocculated to form secondary particles. The $V^{5+}$ ions in aVTO are found to occupy tetrahedral sites, whereas the $Ti^{4+}$ ions show fivefold coordination. Both are uniformly dispersed at the atomic scale in the amorphous oxide matrix, which has abundant structural defects. The first reversible capacity of an aVTO electrode ($295mAhg^{-1}$) is larger than that observed for a physically mixed electrode (1:2 $aV_2O_5$ | $aTiO_2$, $245mAhg^{-1}$). The discrepancy seems to be due to the unique four-coordinated $V^{5+}$ ions in aVTO, which either are more electron-accepting or generate more structural defects that serve as $Li^+$ storage sites. Coin-type Li/aVTO cells show a large irreversible capacity in the first cycle. When they are prepared under nitrogen (aVTO-N), the population of surface hydroxyl groups is greatly reduced. These groups irreversibly produce highly resistive inorganic compounds (LiOH and $Li_2O$), leading to increased irreversible capacity and electrode resistance. As a result, the material prepared under nitrogen shows higher Coulombic efficiency and rate capability.

Ballistic Properties of Zr-based Amorphous Alloy Surface Composites Fabricated by High-Energy Electron-Beam Irradiation (고에너지 전자빔 투사방법으로 제조된 Zr계 비정질 합금 표면복합재료의 탄도충격 성능)

  • Do, Jeonghyeon;Jeon, Changwoo;Nam, Duk-Hyun;Kim, Choongnyun Paul;Song, Young Buem;Lee, Sunghak
    • Korean Journal of Metals and Materials
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    • v.48 no.12
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    • pp.1047-1055
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    • 2010
  • The objective of this study is to investigate the ballistic properties of Zr-based amorphous alloy surface composites fabricated by high-energy electron-beam irradiation. The mixture of Zr-based amorphous powders and $LiF+MgF_2$ flux powders was deposited on a pure Ti substrate, and then an electron beam irradiated this powder mixture to fabricate a one-layer surface composite. A four-layer surface composite, in which the composite layer thickness was larger than 3 mm, was also fabricated by irradiating the deposited powder mixture by an electron beam three times on the one-layer surface composite. The microstructural analysis results indicated that a small amount of fine crystalline particles were homogeneously distributed in the amorphous matrix of the surface composite layer. According to the ballistic impact test results, the surface composite layers effectively blocked a fast traveling projectile, while many cracks were formed at the composite layers, and thus the surface composite plates were not perforated. The surface composite layer containing ductile ${\beta}$ dendritic phases showed a better ballistic performance than the one without dendrites because dendritic phases hindered the propagation of shear bands or cracks.

A Parametric Study on the Glass Transition and Mechanical Properties of CNT Based Nanocomposites Using Molecular Dynamics Simulation (분자동역학 전산모사를 이용한 나노튜브 강화 복합재료의 유리전이와 기계적 물성에 관한 파라메트릭 연구)

  • Yang, Seung-Hwa;Cho, Maeng-Hyo
    • Proceedings of the Computational Structural Engineering Institute Conference
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    • 2007.04a
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    • pp.421-426
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    • 2007
  • A parametric study to investigate the effects of composition variables on the glass transition and mechanical properties of CNT-based nanocomposites was performed using molecular dynamics simulations. In this study, matrix chain length and CNT length were chosen as the candidate characteristic parameters. In order to understand the effect of both parameters in detail, three sample sets having different chain lengths with the same CNT configuration and two sample sets having different CNT lengths with same chain length were prepared. Other parameters such as volume fraction and density were fixed to enable rigorous comparisons. Amorphous polyethylene is used as matrix polymer and (10,0) zigzag CNT is embedded into the matrix to reinforce polymer matrix. As a result, longer polymer chain length of matrix solely increased glass transition temperature but no reinforcing enhancement was observed. CNT length showed similar increase with little enhancement of elastic modulus. In addition to this, nanocomposites showed temperature-dependent elastic modulus jump passing thorough the glass transition region agrees well with experimental results.

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Nano-Structure Control of SiC Hollow Fiber Prepared from Polycarbosilane (폴리카보실란으로부터 제조된 탄화규소 중공사의 미세구조제어)

  • Shin, Dong-Geun;Kong, Eun-Bae;Cho, Kwang-Youn;Kwon, Woo-Tek;Kim, Younghee;Kim, Soo-Ryong;Hong, Jun-Sung;Riu, Doh-Hyung
    • Journal of the Korean Ceramic Society
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    • v.50 no.4
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    • pp.301-307
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    • 2013
  • SiC hollow fiber was fabricated by curing, dissolution and sintering of Al-PCS fiber, which was melt spun the polyaluminocarbosilane. Al-PCS fiber was thermally oxidized and dissolved in toluene to remove the unoxidized area, the core of the cured fiber. The wall thickness ($t_{wall}$) of Al-PCS fiber was monotonically increased with an increasing oxidation curing time. The Al-PCS hollow fiber was heat-treated at the temperature between 1200 and $2000^{\circ}C$ to make a SiC hollow fibers having porous structure on the fiber wall. The pore size of the fiber wall was increased with the sintering temperature due to the decomposition of the amorphous $SiC_xO_y$ matrix and the growth of ${\beta}$-SiC in the matrix. At $1400^{\circ}C$, a nano porous wall with a high specific surface area was obtained. However, nano pores grew with the grain growth after the thermal decomposition of the amorphous matrix. This type of SiC hollow fibers are expected to be used as a substrate for a gas separation membrane.

The effect of thermal anneal on luminescence and photovoltaic characteristics of B doped silicon-rich silicon-nitride thin films on n-type Si substrate

  • Seo, Se-Young;Kim, In-Yong;Hong, Seung-Hui;Kim, Kyung-Joong
    • Proceedings of the Korean Vacuum Society Conference
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    • 2010.02a
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    • pp.141-141
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    • 2010
  • The effect of thermal anneal on the characteristics of structural properties and the enhancement of luminescence and photovoltaic (PV) characteristics of silicon-rich silicon-nitride films were investigated. By using an ultra high vacuum ion beam sputtering deposition, B-doped silicon-rich silicon-nitride (SRSN) thin films, with excess silicon content of 15 at. %, on P-doped (n-type) Si substrate was fabricated, sputtering a highly B doped Si wafer with a BN chip by N plasma. In order to examine the influence of thermal anneal, films were then annealed at different temperature up to $1100^{\circ}C$ under $N_2$ environment. Raman, X-ray diffraction, and X-ray photoemission spectroscopy did not show any reliable evidence of amorphous or crystalline Si clusters allowing us concluding that nearly no Si nano-cluster could be formed through the precipitation of excess Si from SRSN matrix during thermal anneal. Instead, results of Fourier transform infrared and X-ray photoemission spectroscopy clearly indicated that defective, amorphous Si-N matrix of films was changed to be well-ordered thanks to high temperature anneal. The measurement of spectral ellipsometry in UV-visible range was carried out and we found that the optical absorption edge of film was shifted to higher energy as the anneal temperature increased as the results of thermal anneal induced formation of $Si_3N_4$-like matrix. These are consistent with the observation that higher visible photoluminescence, which is likely due to the presence of Si-N bonds, from anneals at higher temperature. Based on these films, PV cells were fabricated by the formation of front/back metal electrodes. For all cells, typical I-V characteristic of p-n diode junction was observed. We also tried to measure PV properties using a solar-simulator and confirmed successful operation of PV devices. Carrier transport mechanism depending on anneal temperature and the implication of PV cells based on SRSN films were also discussed.

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Microstructural Characteristics of the Fuel Cladding Tubes Irradiated in Kori Unit 1

Synthesis and Mechanical Properties of nc-TiN/a-Si$_3$N$_4$ Nanocomposite Coating Layer (나노복합체 nc-TiN/a-Si$_3$N$_4$ 코팅막의 합성 및 기계적 성질)

  • 김광호;윤석영;김수현;이건환
    • Journal of Surface Science and Engineering
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    • v.35 no.3
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    • pp.133-140
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    • 2002
  • The Ti-Si-N coating layers were synthesized on SKD 11 steel substrate by a DC reactive magnetron co-sputtering technique with separate Ti and Si targets. The high resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectroscopy (XPS) analyses for the coating layers revealed that microstructure of Ti-Si-N layer was nanocomposite, consisting of nano-sized TiN crystallites surrounded by amorphous $Si_3$$N_4$ phase. The highest hardness value of about 39 GPa was obtained at the Si content of ~11at.%, where the microstructure had fine TiN crystallites (about 5nm in size) dispersed uniformly in amorphous matrix. As the Si content in Ti-Si-N films increased, the TiN crystallites became from aligned to randomly oriented microstructure, finer, and fully penetrated by amorphous phase. Free Si appeared in the layers due to the deficit of nitrogen source at higher Si content. Friction coefficient and wear rate of the Ti-Si-N coating layer significantly decreased with increase of relative humidity. The self-lubricating tribe-layers such as $SiO_2$ or (OH)$Si_2$ seemed to play an important role in the wear behavior of Ti-Si-N film against steel.