• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.321-321
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• 2014

GaN는 LED, 태양전지, 그리고 전자소자 등에 쓰이는 물질로, 관련 연구가 활발히 진행되고 있으며, 이와 더불어 top-down방식을 활용한 소자제작 방법 또한 발달되고 있다. 하지만, top-down공정 시 발생 되는 건식 식각에 의한 소자의 손상이 발생되고, 이로 인하여 누설전류가 발생하는 등 여러 가지 문제점이 발생하고 있다. 특히, top-down에서 널리 사용하는 건식식각을 통한 GaN 식각의 경우, nonpolar 면이 아닌, semipolar 면이 드러나게 되며, 이 면은 건식 식각시 발생하는 손상을 포함하고 있다. 본 연구에서는 이러한 문제를 해결하기 위해서, 약 $2{\mu}m$ 크기의 diameter를 갖는 micro-sized column LED를 제작하고, 건식 식각 이후, KOH surface treatment를 통해 손상된 면을 제거함과 동시에 nonpolar면을 드러내는 실험을 실시하였으며, 더불어 column의 diameter를 줄이는 방법을 논하고자 한다.

• Bulletin of the Korean Chemical Society
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• v.13 no.6
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• pp.613-620
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• 1992

The solvent-dependent photophysical properties of 2-biphenylcarboxylic acid (2BPCA) and 4-biphenylcarboxylic acid(4BPCA), which have a pre-twisted conformation in the ground state, have been investigated. The fluorescence spectra of 4BPCA show vibrational structure with a non-mirror image to the absorption spectra in nonpolar solvent while those of 2BPCA show no structure even in nonpolar solvents. As the solvent polarity increases, the fluorescence spectra become diffuse and broad with a strong red shift resulting in the large Stokes shift. The large fluorescence Stokes shift of BPCA's in polar solvent is also partially due to an intramolecular charge transfer (ICT) interaction in the excited state, as demonstrated by the large dipole moment in the excited state (7.6-10.6 D). The fluorescence decay behaviors of BPCA's (decay-times and their pre-exponential factors) also depend on solvent polarity in agreement with the solvent-dependent properties of the steady-state fluorecence. The data have been discussed in terms of change in the excited-state potential energy surface with respect to change of the dihedral angle of biphenyl moiety.

• Archives of Pharmacal Research
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• v.11 no.2
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• pp.155-158
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• 1988

To study the behavior of nucleic acid base in a nonpolar organic solvent, chloreform, we synthesized a derivative of guanosine. This erivative, guanosine-2', 3', 5'- trisobutyrate was obtained by reaction of guanosine with isobutyric anhydride, and identified by TLC, EA, IR and NMR. Hydrogen bonding specificity of this compound was revealed by IR and NMR. The molecules of guanosine 2',3',5'-trisobutyrate are self-associated in nonpolar solvent, and hydrogen bonds by imino protent become important as the concentration increases. In the presence of a cytosine derivative, the self-association of theguanosine drivative is destroyed, resulting from interaction with cytosine derivative.

• Archives of Pharmacal Research
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• v.8 no.3
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• pp.109-117
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• 1985

The interaction of salicylic acid (S. A.), salicylamide (S,M) with nucleic acid base derivatives such as 9-ethyl adenine (A), 1-cyclohexyl uracil (U), 2', 3'-benzylidine-5' trityl-cytidine (C), gaunosine-2', 3', 5'-isobutylate (G) has been spectroscopically investigated to determine the binding mechanism. NMR and IR spectra were measured in nonpolar solvents. The association constant K of the formation of complex was calculated from the IR spectra. Compounds S. A. and A form a 1:1 or 1:2 cyclic hydrogen-bonded complex depending on the sample concentration. Compounds S. A. and U form a 1:1 or 1:2 hydrogen-bonded complex on the sample concentration. Compounds S. A. and C form a 2:1 hydrogen-bonded complex at low concentration (0.0016M). Compound S. A. binds compound G, but its binding does not completely break the self-association of compound G, Compound S. M. binds compounds A. U. C. G. very weakly.

• Journal of the Semiconductor & Display Technology
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• v.20 no.3
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• pp.167-171
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• 2021

The core-shell InGaN/GaN Multi Quantum Well-Nanowires (MQW-NWs) that were selectively grown on oxide templates with perfectly circular hole patterns were highly crystalline and were shaped as high-aspect-ratio pyramids with semi-polar facets, indicating hexagonal symmetry. The formation of the InGaN active layer was characterized at its various locations for two types of the substrates, one containing defect-free MQW-NWs with GQDs and the other containing MQW-NWs with defects by using HRTEM. The TEM of the defect-free NW showed a typical diode behavior, much larger than that of the NW with defects, resulting in stronger EL from the former device, which holds promise for the realization of high-performance nonpolar core-shell InGaN/GaN MQW-NW substrates. These results suggest that well-defined nonpolar InGaN/GaN MQW-NWs can be utilized for the realization of high-performance LEDs.

• Macromolecular Research
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• v.17 no.1
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• pp.5-7
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• 2009

• Journal of Photoscience
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• v.9 no.2
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• pp.66-69
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• 2002

Zinc chlorin 1 possessing tertiary 3$^1$_hydroxy and 13$^1$-oxo groups was synthesized as a model for the antenna chlorophylls of photosynthetic green bacteria. Self-aggregation of 1 in nonpolar organic solvents was examined and compared to 2 and 3 possessing a secondary and primary 3$^1$_hydroxy group, respectively. Zinc chlorin 1 self-aggregated in I％(v/v) CH$_2$Cl$_2$-hexane to form oligomers and showed a red-shifted Qy maximum at 704 nm compared to the monomer (648 nm in CH$_2$CI2$_2$). This red-shift is larger than that of 3$^1$S-2 (648 to 697 nm) and comparable to that of3$^1$R-2 (648 to 705 nm), but smaller than that of 1 (648 to 740 nm), indicating that while a single 3$^1$-methyl group (primary to secondary OH) suppressed tight and/or extended aggregation, the additional 3$^1$-methyl group (secondary to tertiary OH) did not further suppress aggregation. The relative stability of the aggregates was in the order 3> 3$^1$R-2∼ 1 > 3$^1$S-2 as determined by visible spectral analyses. Molecular modeling calculations on oligomers of zinc chlorins 1, 3$^1$ R-2 and 3 gave similar well-ordered energy-minimized structures, while 3 stacked more tightly than 3$^1$ R- 2 and 1. In contrast, 3$^1$S-2 gave a relatively disordered (twisted) structure. The calculated oligomeric structures could explain the visible spectral data of 1-3 in nonpolar organic solvents. Moreover, self- aggregation of synthetic zinc 13$^1$_oxo-hlorins 4-6 possessing a 2-hydroxyethyl, 3-hydroxypropyl and 3- hydroxy-I-propenyl group at the 3-position in nonpolar organic solvents was discussed.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.31 no.2A
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• pp.137-143
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• 2011

This study evaluated the effects of maleic anhydride grafted polypropylene powder (mPP) contents on the bond properties of cement mortar and nonpolar macro synthetic fibers (macro synthetic fiber). Dog-bone bond tests were performed to evaluate the bond performance of macro synthetic fiber in cement mortar with varying amounts of mPP (0%, 5%, 10%, 15%, 20%, 25%, 30% of cement weight). The bond properties (pullout behavior, pullout load and interface toughness) of macro synthetic fiber in cement mortar increased as the mPP contents was increased. The bond properties increased with the mPP contents. The microstructure of macro synthetic fiber surface was examined after the pullout test to analyze the frictional resistant force according to mPP contents during the pullout process of macro synthetic fiber in cement mortar. The scratched of macro synthetic fiber increased with the mPP contents.

• Journal of the Microelectronics and Packaging Society
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• v.18 no.3
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• pp.25-32
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• 2011

We have studied on the slicing and polishing processes of R-plane sapphire wafers for the substrates of UHB nonpolar a-plane GaN LED. The fabrication conditions of the R-plane and c-plane wafers were influenced by the large anisotropic properties (mechanical properties) of the sapphire. The slicing process was more affected by the anisotropic properties of R-plane than the polishing process. When the slicing direction was $45^{\circ}$ to the a-flat, the slicing time was shorter and the quality of as-slicing wafers was better than the slicing direction of normal to the a-flat. The MRR(Material removal rate) of mechanical polishing processes such as lapping and DMP(Diamond mechanical polishing) did not show significant differences between the R-plane and c-plane. The MRR of the c-plane was about two times higher than that of R-planes at the CMP(Chemical mechanical polishing) process due to the formation of hydrolysis reaction layers on the surface of the c-plane.

• Proceedings of the Korean Vacuum Society Conference
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• 2009.08a
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• pp.166-166
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• 2009