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Hui-Youn Shin,K. H. Park,K. T. Lee,M. J. Cho,S. K. Kwon,Y. I. Chang 한국물리학회 2007 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.50 No.4
The growth characteristics of a GaN layer deposited on a cone-shaped patterned sapphire substrate (PSS) by using metalorganic chemical vapor deposition (MOVCD) were observed by transmission electron microscope (TEM) to investigate the influence of cone-shaped PSS on the GaN layer. The GaN/sapphire interfaces were analyzed by using high-resolution TEM (HRTEM) and convergent beam electron diffraction (CBED), and the residual strain was evaluated by measuring the variation of the lattice parameters quantitatively. From the TEM images, a large number of threading dislocations were found above the flat region of the GaN/sapphire interface. In contrast, only a few threading dislocations were identified above the cone-shaped region. The HOLZ pattern analysis revealed that the lattice parameter of the GaN layer was lower above the flat region of the GaN/sapphire interface compared with the cone-shaped region, and the difference was estimated to be about 0.1 %. This may be attributed to the formation of a GaN layer by the lateral overgrowth above the cone-shaped region, resulting in less lattice mismatch and incoherency between the GaN layer and the sapphire substrate.
Evaluation of the Localized Residual Strain States of GaN Layer by TEM-CBED Method
Hui-Youn Shin,Y. I. Chang,Y. W. Jung,M. J. Cho,K. H. Park 한국물리학회 2006 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.48 No.II
The convergent beam electron diffraction (CBED) method of transmission electron microscopy (TEM) is well known to be a useful technique for evaluating the localized residual strain by measuring the quantitative variations of the lattice parameters. The multi quantum wells (MQWs) affect on the localized residual strain in a GaN layer, where the AlGaN layer is deposited in order to reduce the strain. We used TEM in order to determine the variations of the lattice parameters of the GaN layer both with and without the AlGaN layer. The lattice parameters of the GaN layer were measured every 100 nm along to the transverse direction below the MQWs. The lattice parameters of the lower part of the GaN layer were shown to have lower values than those of the higher part (below MQWs), which is caused by the compressive stress formed by the sapphire substrate. Also, due to the tensile stress formed by an InGaN in the MQWs, the lattice parameters of the higher part were shown to have higher values. The AlGaN layer deposited on the MQWs produced a compressive stress on the GaN layer so that the average lattice parameters of the GaN layer with the AlGaN layer were lower than those without the AlGaN layer. Therefore, we conclude that the AlGaN layer plays a role in reducing the localized residual strain on the GaN layer below the MQWs.
Comparison of the Microstructural Characterizations of GaN Layers Grown on Si (111) and on Sapphire
Hui-Youn Shin,Kisung Jeon,Youngil Jang,Mingu Gang,Myungshin Choi,박원화,박규호 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.63 No.8
Due to the large differences in the lattice constants and the thermal expansion coefficients betweenGaN and Si, GaN growth on a Si substrate usually leads initially to high defect densities andcracks. If high-quality GaN films on Si substrate are to be obtained, it is essential to understandthe different growth characteristics of GaN layers grown on Si and on sapphire. In this study, theGaN specimens were grown on sapphire and Si (111) substrates with AlGaN and AlN buffer layers,respectively, by metalorganic chemical vapor deposition (MOCVD). Using transmission electronmicroscopy (TEM) and micro-Raman spectroscope, we carried out a comparative investigation ofGaN growth by characterizing lattice coherency, defect density, and residual strain. These analysesrevealed that the GaN layers grown on Si have much residual tensile strain and that strain has aneffect on the formation of InGaN/GaN multiple quantum wells (MQWs) above the GaN layers.
Youn-Mook Lim,Hui-Jeong Gwon,Junwha Shin,Joon Pyo Jeun,Young Chang Nho 한국공업화학회 2008 Journal of Industrial and Engineering Chemistry Vol.14 No.4
Macroporous poly(e-caprolactone) (PCL) scaffolds were prepared by gas foaming/salt leaching method. Their degradation behaviors were investigated as a function of radiation dose (total dose; 50, 100, 200, and 300 kGy: dose rate; 10 kGy/h) in vitro and in vivo. The PCL scaffolds have porosity of 86–96.8%. The porosity and mechanical strength could be controlled by the adjustment of an acid–base gas evolving reaction between citric acid and ammonium bicarbonate. The irradiated scaffolds were degraded faster than unirradiated ones. And scaffolds were degraded more slowly in vitro than in vivo regardless of irradiated or unirradiated ones.
Shin, Young Min,Kim, Taek Gyoung,Park, Jong-Seok,Gwon, Hui-Jeong,Jeong, Sung In,Shin, Heungsoo,Kim, Kyung-Soo,Kim, Dongyoon,Yoon, Myung-Han,Lim, Youn-Mook The Royal Society of Chemistry 2015 Journal of Materials Chemistry B Vol.3 No.13
<P>The alginate hydrogel has been used as an attractive scaffold for tissue regeneration. In particular, its simple cross-linking, high water absorption, and biocompatibility have facilitated its utility in regulating the interaction with cells or organs. However, three-dimensional (3D) networks of the alginate hydrogel do not provide fibrous anchorage sites such as the collagen fibres in the natural extracellular matrix (ECM). This has partially limited the survival of anchorage-dependent cells in the 3D hydrogel environment. In this report, we established a hybrid hydrogel containing fibrous particles (FP) that closely mimics the ECM. The RGD peptide-coupled FP (R-FP) has a wide range of distribution and was homogeneously dispersed in the hydrogel. The encapsulated human mesenchymal stem cells in the hydrogel could bind to the R-FP presenting remarkable spreading morphology, augmented viability and differentiation. These findings may elicit the significance of a physical interaction in which the R-FP provides structural and biological cues to the cells. This strategy can be widely applicable to a variety of hydrogel systems.</P>
Shin, Young Min,Park, Jong-Seok,Jeong, Sung In,An, Sung-Jun,Gwon, Hui-Jeong,Lim, Youn-Mook,Nho, Young-Chang,Kim, Chong-Yeal 한국생물공학회 2014 Biotechnology and Bioprocess Engineering Vol.19 No.2
An artificial construct mimicking the intrinsic properties of the natural extracellular matrix in bones has been considered an ideal platform for bone tissue engineering, as it can present an appropriate microenvironment and regulate cell behaviours. In this report, we introduce biodegradable composite scaffolds consisting of polycaprolactone (PCL) and biphasic calcium phosphate (BCP). The scaffolds were fabricated by a salt-leaching process, and the ability of the scaffolds to facilitate osteogenic differentiation was investigated using human mesenchymal stem cells (hMSCs). The scaffolds had an inter-connected porous structure with quadrilateral pores of approximately $200{\sim}500{\mu}m$ in width. The mechanical properties of the scaffolds changed as the BCP content was increased in the starting mixture. In the hMSC experiment, although we found that hMSCs adhered to the surface, as well as the inside, of the scaffolds, the incorporated BCP did not increase the proliferation of the hMSCs over 7 days in culture. Interestingly, the alkaline phosphatase (ALP) activity was 4 times higher on the PCL/BCP composite scaffold ($0.12{\pm}0.03nmol/min/{\mu}g$ protein) thanon the PCL scaffold ($0.03{\pm}0.01nmol/min/{\mu}g$ protein), suggesting that BCP can aid in generating a local environment that promotes bone regeneration. Therefore, a strategy combining polymers and ceramics can be considered a useful platform for bone tissue engineering.