Chang-Hoon Kim

Correlation between internal stress and ferroelectric fatigue in Bi4−xLaxTi3O12 thin films

La-substituted bismuth titanate [Bi4−xLaxTi3O12(BLT)] films were synthesized using pulsed-laser deposition and ferroelectric fatigue phenomenon was investigated. The internal strain present in the films, which was analyzed through the evaluation of the x-ray diffraction peak, was partially responsible for the fatigue in BLT films. When x⩾0.75, the change in the internal strain was saturated and there was no significant degradation of switching charge, at least up to 1010 cycles. It revealed that the internal strain, as well as chemical stability of oxygen ions, contributed to the ferroelectric fatigue of the BLT films. The origin of the internal strain is discussed in terms of the lattice mismatch between bulk materials and thin films.

Substrate Temperature Dependence of Phase and Orientation of Pulsed Laser Deposited Bi-La-Ti-O Thin Films

Bi3.25La0.75Ti3O12 (BLT) thin films were grown by pulsed laser deposition at substrate temperatures ranging from 400 to 800°C. The phase, orientation, and surface morphology of the deposited films were investigated in order to understand the deposition behavior of the BLT films. As the substrate temperature was increased to 800°C, the films showed a tendency to grow with c-axis preferred orientation and a rough surface. At lower substrate temperatures, however, polycrystalline BLT films were formed. In addition, at the lowest substrate temperature of 400°C, the film consisted mostly of a nonferroelectric fluorite-like phase. This was attributed to the difficulty in forming a perfectly layered structure. The fluorite-like phase was transformed to a ferroelectric polycrystalline BLT phase through annealing in flowing oxygen at 600°C.

Structural properties of ZnSe layers grown on (001) GaAs substrates tilted toward [110] and [010]

We have investigated the structural properties of ZnSe epilayers that were molecular beam epitaxially grown on (001) GaAs substrates with different tilt angles and tilt directions. We measured the properties of the epilayers by x-ray diffraction, transmission electron microscopy, and etch pit density analysis. Tilting the (001) GaAs substrate toward [010] was very effective in reducing the surface defect density of the ZnSe layers, while tilting toward the [110] direction was of no use. We could observe the increasingly two-dimensional nature of the initial growth mode in the (001) GaAs substrate tilted toward [010]. Growth of a 1.8-μm-thick ZnSe layer on (001) GaAs tilted 4° toward [010] resulted in a very low surface defect density of 1×104u2009cm−2. Such a low defect density has seldom been obtained in ZnSe, without growing a GaAs buffer layer below the ZnSe layer.

α-Substituted 2-(3-fluoro-4-methylsulfonamidophenyl)acetamides as potent TRPV1 antagonists

A series of α-substituted acetamide derivatives of previously reported 2-(3-fluoro-4-methylsulfonamidophenyl)propanamide leads (1, 2) were investigated for antagonism of hTRPV1 activation by capsaicin. Compound 34, which possesses an α-m-tolyl substituent, showed highly potent and selective antagonism of capsaicin with Ki(CAP)=0.1 nM. It thus reflected a 3-fold improvement in potency over parent 1. Docking analysis using our homology model indicated that the high potency of 34 might be attributed to a specific hydrophobic interaction of the m-tolyl group with the receptor.

Discovery of N-(3-fluoro-4-methylsulfonamidomethylphenyl)urea as a potent TRPV1 antagonistic template.

A series of homologous analogues of prototype antagonist 1 and its urea surrogate were investigated as hTRPV1 ligands. Through one-carbon elongation in the respective pharmacophoric regions, N-(3-fluoro-4-methylsulfonamidomethylphenyl)urea was identified as a novel and potent TRPV1 antagonistic template. Its representative compound 27 showed a potency comparable to that of lead compound 1. Docking analysis of compound 27 in our hTRPV1 homology model indicated that its binding mode was similar with that of 1S.

2-Sulfonamidopyridine C-region analogs of 2-(3-fluoro-4-methylsulfonamidophenyl)propanamides as potent TRPV1 antagonists.

A series of 2-sulfonamidopyridine C-region derivatives of 2-(3-fluoro-4-methylsulfonamidophenyl)propanamide were investigated as hTRPV1 ligands. Systematic modification on the 2-sulfonamido group provided highly potent TRPV1 antagonists. The N-benzyl phenylsulfonamide derivatives 12 and 23 in particular showed higher affinities than that of lead compound 1. Compound 12 exhibited strong analgesic activity in the formalin pain model. Docking analysis of its chiral S-form 12S in our hTRPV1 homology model indicated that its high affinity might arise from additional hydrophobic interactions not present in lead compound 1S.

Comparison of microstructures of pulsed laser deposited YBa2Cu3O7−δ thin films using solid-state sintered and modified melt-textured grown targets

Abstract YBa 2 Cu 3 O 7−δ (YBCO) thin films were deposited by pulsed laser deposition (PLD) using differently prepared targets. The targets were fabricated using both solid-state sintering (SSS) and modified melt-textured growth (MTG) methods. The films deposited from MTG targets had better superconducting properties, such as T c , Δ T and J c , than the films deposited from SSS targets. In order to understand the enhanced superconducting properties, the film microstructures were investigated using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). As the laser energy density was increased, the films showed an increase of a -axis outgrowth. However, the observed a -axis outgrowth formation indicated that the deposition using MTG targets would result in a more homogeneous and stable film growth as compared to SSS targets. Also, TEM analysis implied that the film deposited from MTG targets had an enhanced grain connectivity that would reduce weak-link effects in the film. Thus, these microstructural differences of films deposited from MTG targets were considered to result in higher J c than the films deposited from SSS targets.

t -Butyl Pyridine and Phenyl C-region Analogues of 2-(3-Fluoro-4-methylsulfonylaminophenyl)propanamides as Potent TRPV1 Antagonists

A series of 2-substituted 6-t-butylpyridine and 4-t-butylphenyl C-region analogues of 2-(3-fluoro-4-methylsulfonamidophenyl)propanamides were investigated for hTRPV1 antagonism. The analysis of structure activity relationships indicated that the pyridine derivatives generally exhibited a little better antagonism than did the corresponding phenyl surrogates for most of the series. Among the compounds, compound 7 showed excellent antagonism toward capsaicin activation with Ki=0.1nM and compound 60S demonstrated a strong antiallodynic effect with 83% MPE at 10mg/kg in the neuropathic pain model. The docking study of 7S in our hTRPV1 homology model indicated that the interactions between the A/B-regions of 7S with Tyr511 and the interactions between the t-butyl and ethyl groups in the C-region of 7S with the two hydrophobic binding pockets of hTRPV1 contributed to the high potency.

Discovery of (S)-4-isobutyloxazolidin-2-one as a novel leucyl-tRNA synthetase (LRS)-targeted mTORC1 inhibitor

A series of leucinol analogs were investigated as leucyl-tRNA synthetase-targeted mTORC1 inhibitors. Among them, compound 5, (S)-4-isobutyloxazolidin-2-one, showed the most potent inhibition on the mTORC1 pathway in a concentration-dependent manner. Compound 5 inhibited downstream phosphorylation of mTORC1 by blocking leucine-sensing ability of LRS, without affecting the catalytic activity of LRS. In addition, compound 5 exhibited cytotoxicity against rapamycin-resistant colon cancer cells, suggesting that LRS has the potential to serve as a novel therapeutic target.

Scanning Rapid Thermal Annealing Process for Poly Silicon Thin Film Transistor

Polycrystalline silicon (poly-Si) thin-film transistors (TFTs) were fabricated on transparent glass substrates using lamp-scan rapid thermal annealing. Scan-radiation-annealed silicon islands were crystallized by metal-induced lateral crystallization (MILC). The activation energy of Ni-MILC was calculated to be 1.56 eV. In order to enhance the MILC rate, we deposited a capping SiO2 layer over the self-aligned TFT, which was found to increase the MILC rate several times. Thus fabricated TFTs exhibited different electrical characteristics depending on the annealing conditions.