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Secondary Crystal Growth on a Cracked Hydrotalcite-Based Film Synthesized by the Sol–Gel Method
Lee, Wooyoung,Lee, Chan Hyun,Lee, Ki Bong American Chemical Society 2016 Inorganic Chemistry Vol.55 No.9
<P>The sol-gel synthesis method is an attractive technology for the fabrication of ceramic films due to its preparation simplicity and ease of varying the metal composition. However, this technique presents some limitations in relation to the film thickness. Notably, when the film thickness exceeds the critical limit, large tensile stresses occur, resulting in a cracked morphology. In this study, a secondary crystal growth method was introduced as a post-treatment process for Mg/Al hydrotalcite-based films synthesized by the sol-gel method, which typically present a cracked morphology. The cracked hydrotalcite-based film was hydrothermally treated for the secondary growth of hydrotalcite crystals. In the resulting film, hydrotalcite grew with a vertical orientation, and the gaps formed during the sol-gel synthesis were filled with hydrotalcite after the crystal growth. The secondary crystal growth method provides a new solution for cracked ceramic films synthesized by the sol-gel method.</P>
Lee, Hwijong,Kim, Gwansik,Lee, Byunghun,Kim, Jeongmin,Choi, Soon-Mok,Lee, Kyu Hyoung,Lee, Wooyoung Elsevier 2017 Scripta materialia Vol.135 No.-
<P><B>Abstract</B></P> <P>Polycrystalline bulks of Si-content tuned Ge-doped higher manganese silicides (HMSs) were fabricated to elucidate the effects of Si content on the phase formation behavior and thermoelectric properties. The phase formation and electronic transport characteristics of HMSs were significantly dependent on Si content. Improved power factor was obtained at higher Si contents because of an enhanced Seebeck coefficient due to the increase in density of states effective mass, maintaining electrical conductivity. Furthermore, the lattice thermal conductivity was reduced through Si-content tuning, which suppressed the formation of secondary phases. Thus, a maximum <I>ZT</I> of 0.61 at 823K was obtained in MnSi<SUB>1.77</SUB>Ge<SUB>0.027</SUB>.</P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Lee, Eunsongyi,Lee, Jun Min,Koo, Ja Hoon,Lee, Wooyoung,Lee, Taeyoon Elsevier 2010 International journal of hydrogen energy Vol.35 No.13
<P><B>Abstract</B></P><P>We report the fabrication of a novel hydrogen sensor that utilizes the electrical resistance changes in the palladium thin films with nanometer thicknesses. The sensing mechanism is based on transitory absorption of hydrogen atoms into the palladium layer, which leads to the reversible alteration of the electrical resistance. In concentrated hydrogen ambient, the excess hydrogen absorption process leads to mechanical deformation on the surface of the palladium films, corresponding to the phase transition from α-phase to β-phase. The reversible sensing process results in a hysteresis curve for resistive properties, of which the height (sensitivity) could be controlled by manipulating the thickness of the palladium layers. The peel-off phenomena on the surface of the palladium film were suppressed by decreasing the thickness of the film. At the thickness of 20nm, a hysteresis curve of resistance was obtained without any structural change in the palladium thin film. These results provide a significant insight to the fundamental understanding of the relationship between the electrical sensitivity of pure Pd thin films and related structural deformation, which is essential to develop robust H-sensors with high sensibility.</P>
Lee Eunsil,Pee Jae-Hwan,Lee Sung-Min,Kim Jong-Young,Shim Wooyoung 한국물리학회 2020 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.77 No.8
An enhanced high- temperature electrical resistivity of AlN at high voltage was obtained by using MgO doping to modulate the Schottky barrier. Doped MgO was precipitated in an ~100-nm-thick layer near grain boundaries, which reduced not only anionic carriers, but also the carrier mobility, due to the formation of defects (Mg´Al, O·N). According to an impedance analysis, the activation energy and the resistivity due to grain boundaries were increased by MgO doping, suggesting an elevated Schottky barrier. As a result, a remarkable high-voltage electrical resistivity, which is greater than 1010 Ω·cm at 550 °C/100 V, can be achieved, which is valuable for electrostatic chucking devices.