• Applied Microscopy
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• v.25 no.3
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• pp.82-89
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• 1995

High resolution transmission electron microscopic observations on quaternary $Zn_{1-x}Mg_{x}S_y$ $S_{1-y}$(x=0.13, y=0.16) on (001) GaAs substrate grown up to $1.2{\mu}m$ with 20nm ZnSe buffer layer at $300^{\circ}C$ by RIBER MBE system which has a single growth chamber were investigated by HRTEM working at 300kV with point resolution of 0.18nm. The ZnSe buffer layer maintains the coherency with the GaAs substrate. The stacking faults had begun at ZnSe buffer/$Zn_{1-x}Mg_{x}S_{y}S_{1-y}$ interface, whose length and spacing became larger than 60nm and wider than 40nm, respectively. The inverse triangular stacking fault was bounded by stacking faults which were formed on {111} planes with different variants. There exists rare stacking faults inside the triangular defect. The epilayer surrounded by the straight stacking faults, which had formed in the same direction, became the columnar structure.

• Journal of the Korean Ceramic Society
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• v.43 no.6 s.289
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• pp.358-361
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• 2006

A two-step plasma-assisted boronizing process was carried out on the AISI 1045 steel substrate to reduce the pore density introduced by a conventional single plasma boronizing process. The specimens were plasma boronized for 1 h at $650^{\circ}C$ and subsequently far 7 h at $800^{\circ}C$ in an atmosphere of $BCl_3-H_2-Ar$. The boride layer thickness was parabolic in boronizing time, a high HV reading of 1540 was found up to the boride layer thickness of $25{\mu}m$. It was found that the morphology of the boride layer prepared by the two-step boronizing process was changed from a columnar to a tooth-like structure and the pores in the borided steel were eliminated completely in comparison to those synthesized by the conventional single boronizing process, implying that it is highly applicable for enhancing the dense and compact coating properties of the low-alloy steel.

• Journal of Korea Foundry Society
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• v.12 no.3
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• pp.220-229
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• 1992

The degree of purification and the macrostructure of high purity aluminium were studied through the alternate stirring method in order to improve the nonuniformity of solute concentration in the unidirectional stirring method. The $2^3$ factorial design was done to examine the effects of experimental factors more qualitatively. In the relatively low stirring speed of 1500 rpm with alternate stirring mode, the uniform solute profile and refined grain structure were obtained due to strong washing effect and turbulent fluid flow. It was induced by the transition of the momentum boundary layer by alternation of the stirrer. It was concluded from this study that the alternate stirring mode was more effective to obtain the uniformity of solute even in the stirring speed of 1500 rpm. But the degree of purification decreased below the critical alternating period. When 2N(99.8wt.%) aluminium was used as the starting material the morphology of solid-liquid showed the cellular shape and the columnar grains were inclined to the direction of rotation. This inclined grain growth resulted from the difference of relative velocities of solid and liquid. The inclined angle was increased as the stirring speed increased and solidification proceeded. In the case of 4N aluminium, there was no inclined grain growth and it was confirmed from the macrostructure and SEM work that the morphology of solid-liquid interface was planar. From the factorial design, it was found that the alternate stirring mode showed poorer purification effect than that of unidirectional stirring mode at low speed(500 rpm). In addition, the factor that had the most significant effect on the degree of purification was the stirring speed.

• Korean Journal of Materials Research
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• v.23 no.6
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• pp.304-308
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• 2013

The effect of a sputter deposition sequence of Cu, Zn, and Sn metal layers on the properties of $Cu_2ZnSnS_4$ (CZTS) was systematically studied for solar cell applications. The set of Cu/Sn/Zn/Cu multi metal films was deposited on a Mo/$SiO_2$/Si wafer using dc sputtering. CZTS films were prepared through a sulfurization process of the Cu/Sn/Zn/Cu metal layers at $500^{\circ}C$ in a $H_2S$ gas environment. $H_2S$ (0.1%) gas of 200 standard cubic centimeters per minute was supplied in the cold-wall sulfurization reactor. The metal film prepared by one-cycle deposition of Cu(360 nm)/Sn(400 nm)/Zn(400 nm)/Cu(440 nm) had a relatively rough surface due to a well-developed columnar structure growth. A dense and smooth metal surface was achieved for two- or three-cycle deposition of Cu/Sn/Zn/Cu, in which each metal layer thickness was decreased to 200 nm. Moreover, the three-cycle deposition sample showed the best CZTS kesterite structures after 5 hr sulfurization treatment. The two- and three-cycle Cu/Sn/Zn/Cu samples showed high-efficient photoluminescence (PL) spectra after a 3 hr sulfurization treatment, wheres the one-cycle sample yielded poor PL efficiency. The PL spectra of the three-cycle sample showed a broad peak in the range of 700-1000 nm, peaked at 870 nm (1.425 eV). This result is in good agreement with the reported bandgap energy of CZTS.

• Journal of the Korean Vacuum Society
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• v.12 no.2
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• pp.123-129
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• 2003

Thin transparent Cu films in the thickness range of 10 ~ 40 nm are deposited by rf-magnetron sputtering on porous silicon (PS) anodized on p-type silicon in dark. Microstructural features of the Cu films are investigated using SEM, AFM and XRD techniques. The RMS roughness of the Cu films is found to be around 1.47 nm and the grain growth is columnar with a (111) preferred orientation and follows the Volmer-Weber mode. The photoluminescence studies showed that a broad luminiscence peak of PS near the blue-green region gets blue shifted (~0.05 eV) with a small reduction in intensity and therefore, Cu-related PL quenching is absent. The FTIR absorption spectra on the PS/Cu structure revealed no major change of the native PS peaks but only a reduction in the relative intensity. The I-V characteristic curves further establish the Schottky nature of the diode with an ideality factor of 2.77 and a barrier height of 0.678 eV. An electroluminiscence (EL) signal of small intensity could be detected for the above diode.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.1
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• pp.162-171
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• 1993

This paper deals with the anisotropy of the mushy region during solidification process of a binary mixture. A theoretical model which specifies a permeability tensor in terms of pricipal values is proposed. Also, the governing equations are modified into convenient forms for the numerical analysis with the existing algorithm. Some test computations are performed for soeidification of aqueous ammonium chloride solution contained in a square cavity. Results show that not only the present model is capable of resolving fundamental characteristics of the tranport phenomena, but also the anisotropy significantly affects the interdendritic flow structure, i.e., double-diffusive convection and macrosegregation patterns.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.45-45
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• 2011

알루미늄과 그 합금은 내부식성(corrosion resistance)이 좋고, 밀도가 낮아 높은 연료소비 효율을 필요로 하는 항공기와 자동차 같은 운송수단의 내-외장 소재로 사용되고 있다. 또한 알루미늄의 높은 내부식성을 이용하여 철강소재의 부식을 방지하는 보호막으로도 폭 넓게 사용된다. 물리기상증착(physical vapor deposition)으로 알루미늄을 코팅하면 박막 성장 초기단계에서 핵(nucleus)을 형성하고, 형성된 핵을 중심으로 주상 구조(columnar structure)로 박막이 성장하는 것이 일반적으로 알려진 방식이다. 주상 구조의 알루미늄 박막은 주상정과 주상정 사이에 필연적으로 공극(pore)이 존재하게 되어 부식을 일으키는 물질이 박막으로 침투하게 되고, 부식 물질과 모재가 반응하여 공식(pitting corrosion)이 발생한다. 본 연구에서는 스퍼터링(magnetron sputtering)을 이용하여 치밀한 조직을 갖는 알루미늄 박막을 코팅할 수 있는 공정을 개발하고, 치밀한 알루미늄 조직이 내부식성에 어떠한 영향을 미치는지 평가하였다. 기판은 냉연강판(cold rolled steel sheet)이 사용되었으며, 알루미늄 타겟의 순도는 99.999%, 크기는 직경 4"이었다. 냉연강판은 진공용기(vacuum chamber)에 장착하기 전에 계면활성제를 이용하여 표면에 존재하는 기름성분을 제거하였으며, 진공용기에 장착한 후에는 아르곤 가스를 이용하여 발생시킨 글로우 방전으로 표면에 존재하는 산화물을 제거하였다. 알루미늄 박막의 조직에 영향을 미치는 공정변수를 확인하기 위해서 스퍼터링 파워, 공정 온도, 공정 압력, 외부 자기장 세기 등의 공정 조건을 변화시켜 코팅을 실시하였다. 실험을 통해서 얻어진 최적 조건으로 알루미늄을 코팅할 경우, 알루미늄 bulk의 밀도와 비교하여 약 94.7%의 밀도를 갖는 알루미늄 박막을 코팅할 수 있었다. 알루미늄 박막이 약 3 ${\mu}$m의 두께로 코팅된 냉연강판의 내부식성 평가(salt spray test, 5% NaCl) 결과, 평가를 시작한 후 72시간 후에도 적청이 발생하지 않았다.

• Journal of the Mineralogical Society of Korea
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• v.2 no.1
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• pp.26-36
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• 1989

Clinopyroxene in the Geodo mine belongs to diopside-hedenbergite series. It is widely distributed throughout the mine area together with garnet and is also closely related with Fe-mineralization. Clinopyroxenes in the Geodo mine including two samples from the sangdong and Ulchin Mines are studied using polarized microscope, EPMA, XRD, and IR spectroscopy for occurrence, chemistry, structure, and crystal chemistry. Especially, variations in unit-cell parameters are examined in relation with the substitution scheme between Fe and Mg cations. Clinopyroxenes in the Geodo mine occur in both endoskarn and exoskarn zone. It is mostly anhedral to subhedral with fine- to medium-grained in texture, but some have bigger crystals of short prismatic or columnar habits. Clinopyroxene occurs as monomineralic or is associated with mostly garnet and sometimes with actinolite, magnetite, epidote, and chlorite. Chemical analysis reveals that the Geodo clinopyroxene is diopsidic in composition (Di: 65-96%). This fact is in good contrast with garnet chemistry showing mostly andraditic (An: 41-82%). Especially, clinopyroxene coexisting with magnetite belongs to nearly end member diopside (Di: 97-99%). Thus, diopside-andradite pair indicates that Geodo skarns were formed under the reduced environment. X-ray diffraction analysis shows unit-cell parameters vary with increase of Fe contents: a = 9.765-9.838$\AA$, b = 8.943-9.020$\AA$, c= 5.240-5.253$\AA$.$\beta$ = 105.70-104.83$^{\circ}$, and V =440.64-448.19$\AA$3. It is noted from the least square regression that a, b and V increase linearly with increase of Fe content, while $\beta$ slightly decreases and c remains nearly unchanged as change in Fe content. These trends are to difference between synthetic and natural clinopyroxenes. This fact is also recognized in IR spectra which show a slight shift of several absorption bands toward lower wavenumber region with increasing Fe content.

• Journal of Powder Materials
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• v.20 no.6
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• pp.460-466
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• 2013

4 mol% Yttria-stabilized zirconia (4YSZ) coatings with $200{\mu}m$ thick are fabricated by Electron Beam Physical Vapor Deposition (EB-PVD) for thermal barrier coating (TBC). $150{\mu}m$ of NiCrAlY based bond coat is prepared by conventional APS (Air Plasma Spray) method on the NiCrCoAl alloy substrate before deposition of top coating. 4 mol% YSZ top coating shows typical tetragonal phase and columnar structure due to vapor phase deposition process. The adhesion strength of coating is measured about 40 MPa. There is no delamination or cracking of coatings after thermal cyclic fatigue and shock test at $850^{\circ}C$.

• Journal of the Korean GEO-environmental Society
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• v.2 no.2
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• pp.41-50
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• 2001

In this study, for the stability analysis of marine embankment, the slope stability analysis and possibility of lateral movement with the marine embankment in ${\bigcirc}{\bigcirc}$harbor were carried out. In order to simulate the practical site condition, the expected maximum sea water level and maximum embankment height were assumed for these analyses. For the evaluation of soil properties, field test, laboratory test, and especially chemical composition analysis were performed for the this analysis. Based on these test results, the soil parameters were determined by applying ground improvement concept under columnar stabilized ground condition and also the effect of staged backfilling was considered under the dredged ground condition. For the optimal design, the stability analyses of embankment with changed height and unchanged height were performed under unimproved soil condition. The result showed that both cases were unstable not only with slope stability but also with lateral movement. Therefore, Deep Mortar Piling was applied for stability analysis and this result was safe. As the conclusion, the deep mortar piling method was suggested as reinforced foundation design for this site.