Microstructural characterization of oxide layers in CaO added AZ31 Mg alloy

Lee, Taeg Woo,Park, Hyun Woong,Lim, Hyunkyu,Kim, Shae K.,Lim, Sung Hwan ELSEVIER SCIENCE 2017 JOURNAL OF ALLOYS AND COMPOUNDS Vol.714 No.-

<P><B>Abstract</B></P> <P>Using transmission electron microscopy (TEM) we studied the oxidation behaviors of CaO added Mg-3.5Al-1.4Zn (AZ31) alloys as a function of the CaO content and oxidation time, at 500 °C in air. It was shown that the AZ31 alloys with CaO exhibit substantially enhanced oxidation resistance. We identified the mechanism for this behavior: with added CaO the AZ31 alloys form protective oxide layers consisting of inner columnar and outer Ca/Mg rich structures. The thicknesses of the protective layers were observed and found to be correlated with the CaO content. The inner columnar layer grows along the [100]<SUB>MgO</SUB> due to the small energy barrier to the diffusion of interstitial oxygen ions in MgO. We observed three distinctive steps during the oxidation reaction: the formation of oxide islands, the dissipation of scale and the growth of a columnar oxide layer, and the formation of a double oxide layer due to Ca reduced from CaO. We clearly captured the microstructural evolution of the three different steps, leading to a detailed description of the formation of the protective oxide layers.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Addition of CaO in AZ31 facilitated the double oxide layer, suppressing a scales. </LI> <LI> The double oxide layer was composed of a columnar and outer (Ca, Mg) rich layer. </LI> <LI> The thickness of a columnar layer increased with amount of added CaO in AZ31. </LI> <LI> A columnar oxide layers grew along [100]<SUB>MgO</SUB> due to lowest activation energy. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

메모리소자를 위한 Ti_1-xAl_xN 방지막의 산화 거동

박상식,Park, Sang-Shik 한국재료학회 2002 한국재료학회지 Vol.12 No.9

$Ti_{1-x}$ $Al_{ x}$N thin films as barrier layer for memory devices application were deposited by reactive magnetron sputtering. The crystallinity, micro-structure, oxidation resistance and oxidation mechanism of films were investigated as a function of Al content. Lattice parameter and grain size of thin films were decreased with increasing the Al content Oxidation of the film with higher Al content is slow and then, total oxide thickness is thinner than that of lower Al content film. Oxide layer formed on the surface is AlTiNO layer. Oxidation of $Ti_{1-x}$ /$Al_{x}$ N barrier layer is diffusion limited process and thickness of oxide layer with oxidation time increased with a parabolic law. The activation energy of oxygen diffusion, Ea and diffusion coefficient, D of $Ti_{0.74}$ /X$0.74_{0.26}$N film is 2.1eV and $10^{-16}$ ~$10^{-15}$ $\textrm{cm}^2$/s, respectively. $_Ti{1-x}$ /$Al_{x}$ XN barrier layer showed good oxidation resistance.

산화그래핀 층수에 따른 폴리스타이렌 표면 코팅 특성

이지훈,박재범,박단비,허증수,임정옥,Lee, Jihoon,Park, Jaebum,Park, Danbi,Huh, Jeung Soo,Lim, Jeong Ok 한국재료학회 2021 한국재료학회지 Vol.31 No.7

Graphene, a new material with various advantageous properties, has been actively used in various fields in recent years. Applications of graphene oxide are increasing in combination with other materials due to the different properties of graphene oxide, depending on the number of single and multiple layers of graphene. In this study, single-layer graphene oxide and multi-layer graphene oxide are spray coated on polystyrene, and the physicochemical properties of the coated surfaces are characterized using SEM, Raman spectroscopy, AFM, UV-Vis spectrophotometry, and contact angle measurements. In single-layer graphene oxide, particles of 20 ㎛ are observed, whereas a 2D peak is less often observed, and the difference in surface height increases according to the amount of graphene oxide. Adhesion increases with an increase in graphene oxide up to 0.375 mg, but decreases at 0.75 mg. In multi-layer graphene oxide, particles of 5 ㎛ are observed, as well as a 2D peak. According to the amount of graphene oxide, the height difference of the surface increases and the adhesive strength decreases. Both materials are hydrophilic, but single-layer graphene oxide has a hydrophilicity higher than that of multi-layer graphene oxide. We believe that multi-layer graphene oxide and single-layer graphene oxide can be implemented based on the characteristics that make them suitable for application.

The Characteristics of Amorphous-Oxide-Semiconductor Thin-Film-Transistors According to the Active-Layer Structure

Ho-Nyeon Lee(이호년) 한국산학기술학회 2009 한국산학기술학회논문지 Vol.10 No.7

비정질 인듐-갈륨-아연 산화물 박막트랜지스터를 모델링 하여서, 능동층의 구조, 두께, 평형상태의 전자밀도 에 대응하는 박막트랜지스터의 특성을 연구하였다. 단일 능동층 박막트랜지스터의 경우, 능동층이 얇을 때 높은 전계 효과이동도를 보였다. 문턱전압의 절대값은 능동층의 두께가 20 nm일 때 최저치를 보였으며, 문턱전압이하 기울기는 두께에 대한 의존성을 보이지 않았다. 복층구조 능동층의 경우, 하부의 능동층이 높은 평형상태 전자밀도를 가질 때 보다 우수한 스위칭 특성을 보였다. 이 경우에도 능동층의 두께가 얇을 때에 높은 전계효과 이동도를 보였다. 높은 평형상태 전자밀도의 능동층의 두께를 증가시키면 문턱전압은 음의 방향으로 이동하였다. 문턱전압이하 기울기는 능 동층의 구조에 대하여 특별한 의존성을 보이지 않았다. 이상과 같은 데이터는 산화물반도체 박막트랜지스터 능동층의 구조, 두께, 도핑비율을 최적화함에 효과적으로 사용될 것으로 기대된다. Amorphous indium-gallium-zinc-oxide thin-film-transistors (TFTs) were modeled successfully. Dependence of TFT characteristics on structure, thickness, and equilibrium electron-density of the active layer was studied. For mono-active-layer TFTs, a thinner active layer had higher field-effect mobility. Threshold voltage showed the smallest absolute value for the 20 nm active-layer. Subthreshold swing showed almost no dependence on active-layer thickness. For the double-active-layer case, better switching performances were obtained for TFTs with bottom active layers with higher equilibrium electron density. TFTs with thinner active layers had higher mobility. Threshold voltage shifted in the minus direction as a function of the increase in the thickness of the layer with higher equilibrium electron-density. Subthreshold swing showed almost no dependence on active-layer structure. These data will be useful in optimizing the structure, the thickness, and the doping ratio of the active layers of oxide-semiconductor TFTs.

Impact of thin metal layer on the optical and electrical properties of indium-doped-tin oxide and aluminum-doped-zinc oxide layers

Kumar, M.D.,Park, Y.C.,Kim, J. Academic Press 2015 Superlattices and microstructures Vol.82 No.-

The distinguished transparent conductive oxide (TCO) layers like indium-doped-tin oxide (ITO) and aluminum-doped-zinc oxide (AZO) layers were prepared in different combinations with and without thin Ni metal layer. The optical and electrical properties of prepared samples were analyzed and compared with the objective to understand the role and influence of the Ni layer in each TCO combination. The highest transmittance value of 91.49% was exhibited by prepared AZO layers. Even though if the transmittance of Ni inserting TCO layers was marginally reduced than that of the ordinary TCO samples, they exhibited balanced optical properties with enhanced electrical properties. Carrier concentration of indium doped tin-oxide and aluminum doped zinc oxide (ITO/AZO) bilayer sample is increased more than double the times when the Ni layer was inserted between ITO and AZO. Thin layer of Ni in between TCO layers reduced sheet resistance and offered substantial transmittance, so that the figure of merit (FOM) value of Ni embedding TCOs was greater than that of TCOs without Ni layer. The ITO/Ni/AZO combination provided optimum results in all the electrical properties. As compared to other TCO/metal combinations, the overall performance of ITO/Ni/AZO tri-layer combination was appreciable. These results show that the optical and electrical properties of TCO layers could be enhanced by inserting a Ni layer with optimum thickness in between them.

Effect of Ca Addition on the Oxidation Resistance of AZ91 Magnesium Alloys at Elevated Temperatures

Choi, Byung-Ho,You, Bong-Sun,Park, Won-Wook,Huang, Yan-Bin,Park, Ik-Min 대한금속재료학회 2003 METALS AND MATERIALS International Vol.9 No.4

AZ91 magnesium alloys containing 0.27-5.22 wt.% Ca, were melted and cast to study the effects of Ca addition on oxidation resistance at elevated temperatures. An ignition temperature test showed that the ignition of AZ91 alloy occurred at about 350-450℃ below the melting point, whereas that of the Ca-containing AZ91 alloys did so at above 650 ℃. Weight gain measurements indicated that the oxidation resistance of the AZ91 alloys improved with Ca addition. The oxidation rate was dependent on the oxidation temperature. In the temperature range of 300-400 ℃, the oxidation rate increased linearly. By contrast, the weight of 5 wt.% Ca-containing AZ91 alloy increased slowly due to the formation of a protective oxide layer. The oxidized surfaces were analyzed with low-angle XRD, FE-SEM equipped with EDS and AES. Complex structures were found in the oxide layers of the Ca-containing alloys: the outer layer mainly consisted of CaO, which was of uniform thickness, and the inner layer was a mixture of CaO, MgO, and A1201. In contrast to the loose and porous MgO formed on the surface of AZ91, the compact and dense oxide layers acted as an effective barrier to the further oxidation of the Ca-containing AZ91 alloys.

<i>In Situ</i> Determination of the Pore Opening Point during Wet-Chemical Etching of the Barrier Layer of Porous Anodic Aluminum Oxide: Nonuniform Impurity Distribution in Anodic Oxide

Han, Hee,Park, Sang-Joon,Jang, Jong Shik,Ryu, Hyun,Kim, Kyung Joong,Baik, Sunggi,Lee, Woo American Chemical Society 2013 ACS APPLIED MATERIALS & INTERFACES Vol.5 No.8

<P>Wet-chemical etching of the barrier oxide layer of anodic aluminum oxide (AAO) was systematically investigated by using scanning electron microscopy (SEM), secondary ion mass spectrometry (SIMS), and a newly devised experimental setup that allows accurate <I>in situ</I> determination of the pore opening point during chemical etching of the barrier oxide layer. We found that opening of the barrier oxide layer by wet-chemical etching can be significantly influenced by anodization time (<I>t</I><SUB>anodi</SUB>). According to secondary ion mass spectrometry (SIMS) analysis, porous anodic aluminum oxide (AAO) samples formed by long-term anodization contained a lower level of anionic impurity in the barrier oxide layer compared to the short-term anodized one and consequently exhibited retarded opening of the barrier oxide layer during the wet-chemical etching. The observed compositional dependence on the anodization time (<I>t</I><SUB>anodi</SUB>) in the barrier oxide layer is attributed to the progressive decrease of the electrolyte concentration upon anodization. The etching rate of the outer pore wall at the bottom part is lower than that of the one at the top part due to the lower level of impurity content in that region. This indicates that a concentration gradient of anionic impurity in the outer pore wall oxide may be established along both the vertical and radial directions of cylindrical pores. Apart from the effect of electrolyte concentration on the chemical composition of the barrier oxide layer, significantly decreased current density arising from the lowered concentration of electrolyte during the long-term anodization (∼120 h) was found to cause disordering of pores. The results of the present work are expected to provide viable information not only for practical applications of nanoporous AAO in nanotechnology but also for thorough understanding of the self-organized formation of oxide nanopores during anodization.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/aamick/2013/aamick.2013.5.issue-8/am400520d/production/images/medium/am-2013-00520d_0010.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/am400520d'>ACS Electronic Supporting Info</A></P>

Enhanced device efficiency in organic light-emitting diodes by dual oxide buffer layer

Jesuraj, P. Justin,Hafeez, Hassan,Rhee, Sang Ho,Kim, Dong Hyun,Lee, Jong Chan,Lee, Won Ho,Choi, Dae Keun,Song, Aeran,Chung, Kwun-Bum,Song, Myungkwan,Kim, Chang Su,Ryu, Seung Yoon Elsevier 2018 ORGANIC ELECTRONICS Vol.56 No.-

<P><B>Abstract</B></P> <P>We have demonstrated an improvement in device performance of fluorescent organic light-emitting diodes (OLEDs) by inserting a dual anode buffer layer composed of tungsten oxide (WO<SUB>3</SUB>) and molybdenum oxide (MoO<SUB>3</SUB>). The advantage of adding dual anode buffer layers with different deposition sequences over individual and composite oxide buffer layers has been systematically analyzed based on their electronic and optical properties. The incorporation of single and composite buffer layers has been revealed to induce a very low injection barrier for holes in tri-layer fluorescent OLEDs which results in a charge imbalance in the emission layer. In contrast, a proper sequence of buffer layers (WO<SUB>3</SUB>/MoO<SUB>3</SUB>) exhibiting higher contact angle (lower surface energy) and higher surface roughness, together with a step-wise increment of potential barrier leads to a better overall charge balance in the active emission layer. Therefore, an enhanced current efficiency and power efficiency of ∼5.8 cd/A and ∼5.2 lm/W respectively were recorded for the WO<SUB>3</SUB>/MoO<SUB>3</SUB> buffer unit, which was better than the insertion of individual and composite layers.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The dual oxide buffer layers in fluorescent OLEDs have been explored. </LI> <LI> A dual buffer layer consists of tungsten oxide (WO<SUB>3</SUB>)/Molybdenum oxide (MoO<SUB>3</SUB>). </LI> <LI> The increment in hole interface barrier, higher contact angle and surface roughness of dual oxide layers is beneficial to achieve improved charge balance. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

플라즈마 산질화처리된 SCM435강의 표면경화층의 미세조직과 특성

전은갑,박익민,이인섭,Jeon Eun-Kab,Park Ik-Min,Lee Insup 한국재료학회 2004 한국재료학회지 Vol.14 No.4

Plasma nitrocarburising and post oxidation were performed on SCM435 steel by a pulsed plasma ion nitriding system. Plasma oxidation resulted in the formation of a very thin ferritic oxide layer 1-2 $\mu\textrm{m}$ thick on top of a 15~25 $\mu\textrm{m}$ $\varepsilon$-F $e_{2-3}$(N,C) nitrocarburized compound layer. The growth rate of oxide layer increased with the treatment temperature and time. However, the oxide layer was easily spalled from the compound layer either for both oxidation temperatures above $450^{\circ}C$, or for oxidation time more than 2 hrs at oxidation temperature $400^{\circ}C$. It was confirmed that the relative amount of $Fe_2$$O_3$, compared with $e_3$$O_4$, increased rapidly with the oxidation temperature. The amounts of ${\gamma}$'-$Fe_4$(N,C) and $\theta$-$Fe_3$C, generated from dissociation from $\varepsilon$-$Fe_{2-3}$ /(N,C) phase during $O_2$ plasma sputtering, were also increased with the oxidation temperature.e.

Self-organized honeycomb-like nanoporous oxide layer for corrosion protection of type 304 stainless steel in an artificial seawater medium

Saha, Sourav Kr.,Park, Yang Jeong,Kim, Jung Woo,Cho, Sung Oh Elsevier 2019 Journal of molecular liquids Vol.296 No.-

<P><B>Abstract</B></P> <P>A new passivation technology for growing a self-organized nanoporous oxide layer with a honeycomb morphology on Type 304 stainless steel is proposed. FESEM, cross-sectional EDX and XRD are employed to evaluate the morphology, composition and crystal structure of the developed anodic film. Cross-sectional EDX analysis reveals that the nanoporous oxide layer contains a significant amount of fluoride species, which becomes negligible after successive annealing in air at 773 K for 2 h. XRD indicates that the amorphous nanoporous oxide layer is converted to a crystalline magnetite phase (Fe<SUB>3</SUB>O<SUB>4</SUB>) after annealing. Electrochemical analysis such as potentiodynamic polarization and electrochemical impedance spectroscopy reveals stainless steel with a thermally treated nanoporous oxide layer has improved corrosion resistance in an artificial seawater medium. FESEM analyses are employed to evaluate the stability and microscopic changes in the morphologies of the nanoporous oxide layer after prolonged immersion in the artificial seawater medium. The key factors and corrosion inhibition mechanism by the nanoporous oxide layer are also discussed.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Self-organized nanoporous oxide layer has been developed by one step anodization. </LI> <LI> XRD reveals crystalline magnetite phase (Fe<SUB>3</SUB>O<SUB>4</SUB>) dominant after successive annealing. </LI> <LI> Stable and compact thermal oxide has formed beneath the nanoporous oxide layer. </LI> <LI> Thermally treated nanoporous oxide layer reduces corrosion rate of stainless steel. </LI> <LI> Oxide layer hindered the penetration of corrosive ions towards metal surface atoms. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>