• Korean Journal of Materials Research
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• v.22 no.10
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• pp.545-551
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• 2012

In semiconductor manufacturing, the circuit integrity of packaged BGA devices is tested by measuring electrical resistance using test sockets. Test sockets have been reported to often fail earlier than the expected life-time due to high contact resistance. This has been attributed to the formation of Sn oxide films on the Au coating layer of the probe pins loaded on the socket. Similar to contact failure, and known as "fretting", this process widely occurs between two conductive surfaces due to the continual rupture and accumulation of oxide films. However, the failure mechanism at the probe pin differs from fretting. In this study, the microstructural processes and formation mechanisms of Sn oxide films developed on the probe pin surface were investigated. Failure analysis was conducted mainly by FIB-FESEM observations, along with EDX, AES, and XRD analyses. Soft and fresh Sn was found to be transferred repeatedly from the solder bump to the Au surface of the probe pins; it was then instantly oxidized to SnO. The $SnO_2$ phase is a more stable natural oxide, but SnO has been proved to grow on Sn thin film at low temperature (< $150^{\circ}C$). Further oxidation to $SnO_2$ is thought to be limited to 30%. The SnO film grew layer by layer up to 571 nm after testing of 50,500 cycles (1 nm/100 cycle). This resulted in the increase of contact resistance and thus of signal delay between the probe pin and the solder bump.

• Restorative Dentistry and Endodontics
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• v.39 no.4
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• pp.282-287
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• 2014

Objectives: The aim of the present study was to investigate the bond strength of RelyX Unicem (3M) to root canal dentin when used as an endodontic sealer. Materials and Methods: Samples of 24 single-rooted teeth were prepared with Gates Glidden drills and K3 files. After that, the roots were randomly assigned to three experimental groups (n = 8) according to the filling material, (1) AH Plus (Dentsply De Trey GmbH)/Gutta-Percha cone; (2) Epiphany SE (Pentron)/Resilon cone; (3) RelyX Unicem/Gutta-Percha cone. All roots were filled using a single cone technique associated to vertical condensation. After the filling procedures, each tooth was prepared for a push-out bond strenght test by cutting 1 mm-thick root slices. Loading was performed on a universal testing machine at a speed of 0.5 mm/min. One-way analysis of variance and Tukey test for multiple comparisons were used to compare the results among the experimental groups. Results: Epiphany SE/Resilon showed significantly lower push-out bond strength than both AH Plus/Gutta-Percha and RelyX Unicem/Gutta-Percha (p < 0.05). There was no significant difference in bond strength between AH Plus/Gutta-Percha and RelyX Unicem/Gutta-Percha (p > 0.05). Conclusions: Under the present in vitro conditions, bond strength to root dentin promoted by RelyX Unicem was similar to AH Plus. Epiphany SE/Resilon resulted in lower bond strength values when compared to both materials.

• Korean Journal of Metals and Materials
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• v.48 no.12
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• pp.1097-1102
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• 2010

Silver coated copper powders were prepared by a chemical reduction method with controlling the deposition process variables such as the feeding rate of the silver ionic solution and concentration of the reductants at room temperature. The characteristics of the products were evaluated by scanning electron microscope (SEM), X-ray diffractometer (XRD), atomic absorption spectrophotometer (AA) and a 4 probe resistivity measurement system. The optimum condition of the preparation of Ag coated Cu powders was at 0.05 M of potassium sodium tartrate and 2 ml/min of the feeding rate of the silver ionic solution. Our method successfully produced dense, uniform, and well-dispersed Ag coated Cu powder of $2{\sim}2.5{\mu}m$ witha silver layer of 100~200 nm. Additionally, we found that thespecific resistivity of the 30 wt.% Ag coated Cu powder was similar to that of pure silver, so that the composite powder could be used as an alternative electromagnetic shielding material for silver.

• Journal of Powder Materials
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• v.26 no.5
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• pp.432-436
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• 2019

This study demonstrates the effect of addition of Fe particles of different sizes on the critical properties of the superconductor $MgB_2$. Bulk $MgB_2$ is synthesized by ball milling Mg and B powders with Fe particles at $900^{\circ}C$. When Fe particles with size less than $10{\mu}m$ are added in $MgB_2$, they easily react with B and form the FeB phase, resulting in a reduction in the amount of the $MgB_2$ phase and deterioration of the crystallinity. Accordingly, both the critical temperature and the critical current density are significantly reduced. On the other hand, when larger Fe particles are added, the $Fe_2B$ phase forms instead of FeB due to the lower reactivity of Fe toward B. Accordingly, negligible loss of B occurs, and the critical properties are found to be similar to those of the intact $MgB_2$.

• Corrosion Science and Technology
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• v.20 no.5
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• pp.289-294
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• 2021

In this study, after measuring polarization characteristics of 97.3 wt% Ag, Au-Coated 97.3 wt% Ag (ACA) and 100 wt% Au wires in 1 wt% H₂SO₄ and 1 wt% HCl electrolytes at 25 ℃, corrosion rate and corrosion characteristics were comparatively analyzed. Comparing corrosion potential (E_CORR) values in sulfuric acid solution, ACA wire had more than six times higher E_CORR value than Au wire. Thus, it seems possible to use a broad applied voltage range of bonding wire for semiconductor packaging which ACA wire could be substituted for the Au wire. However, since the E_CORR value of ACA wire was three times lower than that of the Au wire in a hydrochloric acid solution, it was judged that the use range of the applied voltage and current of the bonding wire should be considered. In hydrochloric acid solution, 97.3 wt% Ag wire showed the highest corrosion rate, while ACA and Au showed similar corrosion rates. Additionally, in the case of sulfuric acid solution, all three types showed lower corrosion rates than those under the hydrochloric acid solution environment. The corrosion rate was higher in the order of 97.3 wt% Ag > ACA > 100 wt% Au wires.

• Smart Structures and Systems
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• v.24 no.1
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• pp.83-94
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• 2019

Passive negative stiffness dampers (NSDs) that possess superior energy dissipation abilities, have been proved to be more efficient than commonly adopted passive viscous dampers in controlling stay cable vibrations. Recently, inertial mass dampers (IMDs) have attracted extensive attentions since their properties are similar to NSDs. It has been theoretically predicted that superior supplemental damping can be generated for a taut cable with an IMD. This paper aims to theoretically investigate the impact of the cable sag on the efficiency of an IMD in controlling stay cable vibrations, and experimentally validate superior vibration mitigation performance of the IMD. Both the numerical and asymptotic solutions were obtained for an inclined sag cable with an IMD installed close to the cable end. Based on the asymptotic solution, the cable attainable maximum modal damping ratio and the corresponding optimal damping coefficient of the IMD were derived for a given inertial mass. An electromagnetic IMD (EIMD) with adjustable inertial mass was developed to investigate the effects of inertial mass and cable sag on the vibration mitigation performance of two model cables with different sags through series of first modal free vibration tests. The results show that the sag generally reduces the attainable first modal damping ratio of the cable with a passive viscous damper, while tends to increase the cable maximum attainable modal damping ratio provided by the IMD. The cable sag also decreases the optimum damping coefficient of the IMD when the inertial mass is less than its optimal value. The theoretically predicted first modal damping ratio of the cable with an IMD, taking into account the sag generally, agrees well with that identified from experimental results, while it will be significantly overestimated with a taut-cable model, especially for the cable with large sag.

• Korean Journal of Materials Research
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• v.28 no.11
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• pp.680-684
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• 2018

We investigate the effect of light intensity and wavelength of a solar cell device using photoconductive atomic force microscopy(PC-AFM). A $POCl_3$ diffusion doping process is used to produce a p-n junction solar cell device based on a polySi wafer, and the electrical properties of prepared solar cells are measured using a solar cell simulator system. The measured open circuit voltage($V_{oc}$) is 0.59 V and the short circuit current($I_{sc}$) is 48.5 mA. Moreover, the values of the fill factors and efficiencies of the devices are 0.7 and approximately 13.6 %, respectively. In addition, PC-AFM, a recent notable method for nano-scale characterization of photovoltaic elements, is used for direct measurements of photoelectric characteristics in limited areas instead of large areas. The effects of changes in the intensity and wavelength of light shining on the element on the photoelectric characteristics are observed. Results obtained through PC-AFM are compared with the electric/optical characteristics data obtained through a solar simulator. The voltage($V_{PC-AFM}$) at which the current is 0 A in the I-V characteristic curves increases sharply up to $18W/m^2$, peaking and slowly falling as light intensity increases. Here, $V_{PC-AFM}$ at $18W/m^2$ is 0.29 V, which corresponds to 59 % of the average $V_{oc}$ value, as measured with the solar simulator. Furthermore, while the light wavelength increases from 300 nm to 1,100 nm, the external quantum efficiency(EQE) and results from PC-AFM show similar trends at the macro scale but reveal different results in several sections, indicating the need for detailed analysis and improvement in the future.

• Journal of Korean Library and Information Science Society
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• v.50 no.2
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• pp.285-310
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• 2019

The integrated management of community archives, which is conducted by incorporating them into the category of library data through the system of library materials management is more necessary for residents to use community archives by arranging and preserving them collected by public libraries, than management implemented through a separate system. This study therefore draw25 descriptive factors by comparatively analyzing descriptive factors of the descriptive standards for community archives such as ISAD(G) and DC, etc. and integrating common or similar ones. Such 25 drawn descriptive factors were empirically tested three times by professionals through the Delphi technique, and 3 descriptive sectors and 21 descriptive factors were finally drawn. The drawn descriptive factors were divided into mandatory, mandatory if applicable and optional through KORMARC-integrated format for bibliographic data and mapping and applied to the system of library materials management, by adjusting the descriptive factors for the systems.

• Journal of Korean Neurosurgical Society
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• v.62 no.6
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• pp.635-642
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• 2019

Objective : The aim of this study was to investigate the biomechanical differences between human dura mater and dura mater substitutes to optimize biomimetic materials. Methods : Four groups were investigated. Group I used cranial dura mater (n=10), group II used $Gore-Tex^{(R)}$ Expanded Cardiovascular Patch (W.L. Gore & Associates Inc., Flagstaff, AZ, USA) (n=6), group III used $Durepair^{(R)}$ (Medtronic Inc., Goleta, CA, USA) (n=6), and group IV used $Tutopatch^{(R)}$ (Tutogen Medical GmbH, Neunkirchen am Brand, Germany) (n=6). We used an axial compression machine to measure maximum tensile strength. Results : The mean tensile strengths were $7.01{\pm}0.77MPa$ for group I, $22.03{\pm}0.60MPa$ for group II, $19.59{\pm}0.65MPa$ for group III, and $3.51{\pm}0.63MPa$ for group IV. The materials in groups II and III were stronger than those in group I. However, the materials in group IV were weaker than those in group I. Conclusion : An important dura mater graft property is biomechanical similarity to cranial human dura mater. This biomechanical study contributed to the future development of artificial dura mater substitutes with biomechanical properties similar to those of human dura mater.

• Journal of Ceramic Processing Research
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• v.19 no.5
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• pp.378-382
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• 2018

It is a known fact that the cement production is responsible for almost 5% of total worldwide $CO_2$ emission, the primary factor affecting global warming. Geopolymers are valuable as ordinary Portland cement (OPC) substitutes because geopolymers release 80% less $CO_2$ than OPC and have mechanical properties sufficiently similar to those of OPC. Therefore, geopolymers have proven attractive to eco-friendly construction industries. Geopolymers can be fabricated from aluminum silicate materials with alkali activators such as fly ash, blast furnace slag, and so on. Integrated gasification combined cycle (IGCC) slag has been used for fabricating geopolymers. In general, IGCC slag geopolymers are fabricated with finely ground and sieved (<128 mesh) IGCC slag. The grinding process of as-received IGCC slag is one of the main costs in geopolymer production. Therefore, the idea of using as-received IGCC slag (before grinding the IGCC slag) as aggregates in the geopolymer matrix was introduced to reduce production cost as well as to enhance compressive strength. As-received IGCC slag (0, 10, 20, 30, 40 wt%) was added in the geopolymer mixing process and the mixtures were compared. The compressive strength of geopolymers with an addition of 10 wt% as-received IGCC slag increased by 19.84% compared to that with no additional as-received IGCC slag and reached up to 41.20 MPa. The enhancement of compressive strength is caused by as-received IGCC slag acting as aggregates in the geopolymer matrix like aggregates in concrete. The density of geopolymers slightly increased to $2.1-2.2g/cm^3$ with increasing slag addition. Therefore, it is concluded that a small addition of as-received IGCC slag into the geopolymer can increase compressive strength and decrease the total cost of the product. Moreover, the direct use of as-received IGCC slag may contribute to environment protection by reducing process time and $CO_2$ emission.