• 한국표면공학회지
• /
• 제33권5호
• /
• pp.356-364
• /
• 2000

Factors that affect the hardness of the zinc electrodeposits in the sulfate electrolyte were investigated. The hardness of zinc deposit was enhanced by increasing the concentration of impurities such as iron and nickel in the bath that changed the crystallographic orientation of the zinc deposit from the strong basal plane to the random orientation. The increase of the concentration of sodium sulfate and current density in iron contained bath improved the hardness of zinc deposit because those were easily codeposited in zinc layer. However the increase of the concentration of sodium sulfate up to 80g/$\ell$ in the bath darkened the surface of zinc electrodeposits due to change of morphology by the codeposition of iron.

• Bulletin of the Korean Chemical Society
• /
• 제21권10호
• /
• pp.1049-1051
• /
• 2000

A chromia-pillared clay has been prepared by ion exchange type intercalation reaction between the sodium ion in montmorillonite and the trimeric chromium oxyformate (TCF) ion, and by subsequent heat-treatment. The structural and thermal properties have been systematically studied by thermal analysis, powder XRD, IR spec-troscopy, and XAS. The gallery height of~6.8 $\AA$ upon intercalation of the TCF ion suggests that the $Cr_3O$ plane is parallel to the aluminosilicate layers. Even though the basal spacing of TCF intercalated clay decreases slightly upon heating, the layer structure was retained up to $550^{\circ}C$ as confirmed by XRD and TG/DTA. Ac-cording to the EXAFS spectroscopic analysis, it is identified that the (Cr-Cr) distance of 3.28 $\AA$ between vertex-linked CrO6 octahedra in TCF splits into 2.64 $\AA$, 2.98 $\AA$, and 3.77 $\AA$ due to the face-, edge-, and corner-shared CrO6 octahedra after heating at $400^{\circ}C$, implying that a nano-sized chromium oxide phase was stabilized within the interlayer space of clay.

• 한국전기전자재료학회:학술대회논문집
• /
• 한국전기전자재료학회 2010년도 하계학술대회 논문집
• /
• pp.31-31
• /
• 2010

The growth of the high-quality GaN epilayers is of significant technological importance because of their commercializedoptoelectronic applications as high-brightness light-emitting diodes (LEDs) and laser diodes (LDs) in the visible and ultraviolet spectral range. The GaN-based heterostructural epilayers have the polar c-axis of the hexagonal structure perpendicular to the interfaces of the active layers. The Ga and N atoms in the c-GaN are alternatively stacked along the polar [0001] crystallographic direction, which leads to spontaneous polarization. In addition, in the InGaN/GaN MQWs, the stress applied along the same axis contributes topiezoelectric polarization, and thus the total polarization is determined as the sum of spontaneous and piezoelectric polarizations. The total polarization in the c-GaN heterolayers, which can generate internal fields and spatial separation of the electron and hole wave functions and consequently a decrease of efficiency and peak shift. One of the possible solutions to eliminate these undesirable effects is to grow GaN-based epilayers in nonpolar orientations. The polarization effects in the GaN are eliminated by growing the films along the nonpolar [$11\bar{2}0$] ($\alpha$-GaN) or [$1\bar{1}00$] (m-GaN) orientation. Although the use of the nonpolar epilayers in wurtzite structure clearly removes the polarization matters, however, it induces another problem related to the formation of a high density of planar defects. The large lattice mismatch between sapphiresubstrates and GaN layers leads to a high density of defects (dislocations and stacking faults). The dominant defects observed in the GaN epilayers with wurtzite structure are one-dimensional (1D) dislocations and two-dimensional (2D) stacking faults. In particular, the 1D threading dislocations in the c-GaN are generated from the film/substrate interface due to their large lattice and thermal coefficient mismatch. However, because the c-GaN epilayers were grown along the normal direction to the basal slip planes, the generation of basal stacking faults (BSFs) is localized on the c-plane and the generated BSFs did not propagate into the surface during the growth. Thus, the primary defects in the c-GaN epilayers are 1D threading dislocations. Occasionally, the particular planar defects such as prismatic stacking faults (PSFs) and inversion domain boundaries are observed. However, since the basal slip planes in the $\alpha$-GaN are parallel to the growth direction unlike c-GaN, the BSFs with lower formation energy can be easily formed along the growth direction, where the BSFs propagate straightly into the surface. Consequently, the lattice mismatch between film and substrate in $\alpha$-GaN epilayers is mainly relaxed through the formation of BSFs. These 2D planar defects are placed along only one direction in the cross-sectional view. Thus, the nonpolar $\alpha$-GaN films have different atomic arrangements along the two orthogonal directions ($[0001]_{GaN}$ and $[\bar{1}100]_{GaN}$ axes) on the $\alpha$-plane, which are expected to induce anisotropic biaxial strain. In this study, the anisotropic strain relaxation behaviors in the nonpolar $\alpha$-GaN epilayers grown on ($1\bar{1}02$) r-plane sapphire substrates by metalorganic chemical vapor deposition (MOCVO) were investigated, and the formation mechanism of the abnormal zigzag shape PSFs was discussed using high-resolution transmission electron microscope (HRTEM).

• 한국재료학회지
• /
• 제1권1호
• /
• pp.54-61
• /
• 1991

$YBa_2Cu_3O_{7-\delta}$ 단일 타게트를 사용하여 R. F. 마그네트론 스퍼터링법으로 MgO(100), Si(100)기판 위에 박막을 증착한 후, $880^{\circ}C$의 산소 분위기에서 1시간 동안 열처리를 하였다. 열처리 전 박막의 미세한 조성변화에 의해서도 열처리 후 박막의 미세구조 및 전기적 특성은 크게 변화했다. MgO(100)기판의 표면에 성장되는 입자들은 선택 배향적으로 성장하려는 경향을 가지므로 가늘고 길쭉한 입자 형상을 띠는 반면에 이들 입자위에 성장되는 다른 입자들은 결정 성장 방향의 선호도가 없으므로 둥근 모양의 입자형상을 가진다. 열처리 전 박학의 조성이 1-2-3을 벗어나면 증착 후 열처리할 때 액상이 형성되며, 액상의 양이 많을수록 선택 배향적 성장이 용이해져 texture를 쉽게 이룬다. 그러나 이러한 액상은 냉각 시에 초전도입자의 입계에 이차상으로 형성되기 때문에 초전도 박막의 전기적 특성, 특히 임계온도를 저하시킨다. 또한 $T_{c,\;zero}$는 $T_{c,\;on}$에 비해서 입계에 형성되는 이차상의 영향을 더 크게 받는다.

• 한국결정성장학회지
• /
• 제28권4호
• /
• pp.152-158
• /
• 2018

PVT(Physical vapor transport)법은 고품질의 대면적 웨이퍼를 생산하기에 이점을 가져 질화물계 반도체의 상용화를 위해 많은 연구가 진행되고 있는 단결정 성장 방법이다. 하지만 복잡한 공정 변수들로 인하여 비평형적인 성장 조건을 갖게 될 경우 수많은 결함들이 발생하게 된다. 결정성장 후 어닐링 공정은 결정성 개선을 위해 널리 사용된다. 효과적인 결정성 개선을 위해서는 적절한 온도, 압력과 시간을 설정하는 게 중요하다. 본 연구에서는 PVT법으로 성장된 AlN 단결정 및 어닐링 조건에 따른 단결정의 결정 미세구조 변화를 X-ray topography, Electron Backscattered Diffraction(EBSD), Rietveld refinement를 통해 분석하였다. Synchrotron Whitebeam X-ray topography 분석 결과 어닐링을 진행하지 않은 단결정에 2차상 및 sub grain, impurity가 존재하였으며 이로 인해 결정성이 저하되는 것을 확인 할 수 있었다. EBSD 결과 어닐링을 진행한 시편의 경우 결정립수가 증가함과 동시에 basal plane의 뒤틀림이 일어나는 것을 관찰할 수 있었다. Rietveld refinement 결과 일부 격자들이 a, b, c축 방향으로 응력을 받아 변형된 것으로 분석되었다. 이는 어닐링 과정 중 hot zone 내의 상하 온도구배에 의해 발생한 응력으로 결정립 방향의 뒤틀림이 일어날 뿐만 아니라 격자 상수가 달라진 것으로 분석된다.

• 한국전기전자재료학회:학술대회논문집
• /
• 한국전기전자재료학회 2009년도 하계학술대회 논문집
• /
• pp.23-23
• /
• 2009

GaN-based nitride semiconductors have attracted considerable attention in high-brightness light-emitting-diodes (LEDs) and laser diodes (LDs) covering from green to ultraviolet spectral range. LED and LD heterostructures are usually grown on (0001)-$Al_2O_3$. The large lattice mismatch between $Al_2O_3$ substrates and the GaN layers leads to a high density of defects(dislocations and stacking faults). Moreover, Ga and N atoms are arranged along the polar [0001] crystallographic direction, which leads to spontaneous polarization. In addition, in the InGaN/GaN MQWs heterostructures, stress applied along the same axis can also give rise to piezoelectric polarization. The total polarization, which is the sum of spontaneous and piezoelectric polarizations, is aligned along the [0001] direction of the wurtzite heterostructures. The change in the total polarization across the heterolayers results in high interface charge densities and spatial separation of the electron and hole wave functions, redshifting the photoluminescence peak and decreasing the peak intensity. The effect of polarization charges in the GaN-based heterostructures can be eliminated by growing along the non-polar [$11\bar{2}0$] (a-axis) or [$1\bar{1}00$] (m-axis) orientation instead of thecommonly used polar [0001] (c-axis). For non-polar GaN growth on non-polar substrates, the GaN films have high density of planar defects (basal stacking fault BSFs, prismatic stacking fault PSFs), because the SFs are formed on the basal plane (c-plane) due to their low formation energy. A significant reduction in defect density was recently achieved by applying blocking layer such as SiN, AlN, and AlGaN in non-polar GaN. In this work, we were performed systematic studies of the defects in the nonpolar GaN by conventional and high-resolution transmission electron microscopy.

• Bulletin of the Korean Chemical Society
• /
• 제21권10호
• /
• pp.1041-1043
• /
• 2000

We present the effects of temperature (between 10 K and 298 K) and of hole concentration on the frequency and intensity of characteristic phonons in polycrystalline $La_2CuO_4-related$ compounds using FT-IR spectros-copy. The influences of the concentration of carrier doped on the phonon modes are prominent in the IR spectra of $La_2CuO_4-related$ compounds. For $La_2-xSrxCuO_4({\chi}=$ 0.00, 0.03, 0.07, 0.10, and 0.15) and electrochemically (or chemically) oxidized $La_2CuO_4$, the intensities of the transverse oxygen mode around 680cm $-^1$ which cor-responds mainly to Cu-O(1) stretching vibration in the basal plane of CuO6 octahedron, are decreased and dis-appeared depending on the Sr-substitution rate and the amount of excess oxygen, while the longitudinal oxygen mode around 510 cm $-^1$ corresponding to the Cu-O(2) stretching in the basal plane of CuO6 octahedron are near-ly invariable. In particular, after two cycles of cooling-heating between 10 K and 298 K for these sample, the phonons around 680 cm $-^1$ are blue shif 13-15 cm $-^1$, while the phonons around 510 cm $-^1$ are nearly constant. The introduction of the charge carrier by doping would give rise to the small contraction of CuO6 oc-tahedron as Cu $^3+$ requires a smaller site than Cu $^2+$, which results in the shortening of the Cu-O(1) bond length and Cu-O(2) bond length with the increased La-O(2) bond length. These results in the frequency shift of the characteristic phonons. The IR spectra of $La_2Li0.5Cu0.5O_4$ which exhibits an insulator behavior despite the $Cu^3+$ of nearly 100%, corroborate our IR interpretations. The mode around 710 cm $-^1$ corresponding to Cu-O(1) stretching vibration is still strongly remained even at low temperature (10 K). Thus, we conclude that the con-duction electrons formed within $CuO_2$ planes of $La_2CuO_4-related$ superconductors screen more effectively the transverse oxygen breathing mode around 680 $cm-^1$ depending on the concentration of the doped charge carrier in $La_2CuO_4-related$ compounds, which might use as a superconductivity probe.

• 청정기술
• /
• 제28권3호
• /
• pp.249-257
• /
• 2022

Grand canonical Monte Carlo 전산모사 방법에 의하여 77.16 K에서 국부분자배향 모델을 가지는 나노 기공 탄소 흡착제에 대한 질소의 평형 흡착량을 계산하였다. 국부분자배향 모델은 일정한 공간을 가지는 규칙적인 격자에 동일한 크기를 배열하였다. 국부분자배향 영역의 연속적인 평면의 직교(out-of-plane)의 제거에 의해 미세기공을 도입하였고, 기본구조단위의 기울임을 통해 기울어진 기공을 도입하였다. 이런 기공 구조는 틈새형 기공 구조보다 나노기공을 가지는 탄소계 흡착제의 흡착 연구에 보다 현실적인 모델이 된다. 또한 이들 기공 구조에 대해 기공도, 표면적 그리고 제한된 비선형 최적화 기법을 활용하여 기공크기분포에 구하였다. 또한 참고 자료로써 틈새형 기공에서의 등온 평형흡착량도 계산하였다. 틈새형 기공에서는 질소분자의 5배 이상의 기공에서 hysteresis 루프가 관찰되었고, 모세관 응축과 응축의 역과정인 증발이 한 압력에서 한 번에 일어났다. 국부분자배향 기공모델에서는 질소분자의 크기의 6배 큰 기공에서 기저 슬립면, armchair 슬립면 그리고 상호연결된 채널에서 각각 세 가지 연속적인 응축이 관찰되었다. 탈착 과정의 hysteresis 루프에서는 단일 또는 두 압력에서 응축의 반대인 증발이 관찰되었다.

• 한국결정성장학회지
• /
• 제9권2호
• /
• pp.162-167
• /
• 1999

3가지 방향성을 가진 사파이어 기판 위에 GaN 박막을 OMVPE방식으로 증착시켜 증착된 GaN epilayer를 투과전자현미경으로 분석하여 각 미세구조의 차이를 비교분석하였다. 3 가지 방향 모두에서 GaN 증착층이 관찰되어졌으며 그중 가장 좋은 경계면의 상태와 단일결정성을 보여준 것은 사파이어{0001} 방향의 기판을 사용한 경우였다. 결함들도 {0001} 방향의 기판을 사용한 경우에서 가장 적게 나타났다. 모든 경우에서 buffer layer는 발견되어지지 않았고 그럼에도 불구하고 경계면에서의 격자 뒤틀림이 일어나는 지역이 수 나노미터(nanometer) 정도밖에 안되는 우수한 경계면들이 관찰되었다. 따라서 일반적으로 GaN 박막 증착시에 가장 많이 사용되는 사파이어 basal plane 외에도 결함이 많기는 하지만, {1120}와 {1102} plane 위에도 GaN 증착층이 buffer layer 없이 증착 될 수 있다는 사실을 TEM 관찰을 통하여 알 수 있었으며 사파이어 {0001}면를 기판으로 사용한 경우에 미세구조 측면에서 볼 때 hetero-epitaxial한 GaN 박막층을 얻을 수 있는 것을 확인하였다.

• Bulletin of the Korean Chemical Society
• /
• 제34권12호
• /
• pp.3615-3620
• /
• 2013

Two novel copper(II) bromide complexes with pyridine containing Schiff base ligands, $Cu(pmed)Br_2$ and $Cu(pmed)Br_2$ where pmed = N'-((pyridin-2-yl)methylene)ethane-1,2-diamine (pmed) and dpmed = N,N-diethyl-N'-((pyridin-2-yl)methylene)ethane-1,2-diamine (dpmed) were synthesized and characterized using X-ray single crystal structure analysis, optical and magnetic susceptibility measurements. Crystal structural analysis of $Cu(pmed)Br_2$ showed that the copper(II) ion has a distorted square-pyramidal geometry with the trigonality index of ${\tau}=0.35$ and two intermolecular hydrogen bonds, which result in the formation of two dimensional networks in the ab plane. On the other hand, $Cu(pmed)Br_2$ displayed a near square-pyramidal geometry with the value of ${\tau}=0.06$. In both compounds, the NNN Schiff base and one Br atom occupy the basal plane, whereas the fifth apical position is occupied by the other Br atom at a greater Cu-Br apical distance. The reported complexes show $g_{\mid}$ > $g_{\perp}$ > 2.0023 with a $d_{x2-y2}$ ground state and a penta-coordinated square pyramidal geometry. Variable temperature magnetic susceptibility measurements showed that the developed copper(II) complexes follow the Curie-Weiss law, that is there are no magnetic interactions between the copper(II) ions since the Cu--Cu distance is too far for magnetic contact.