• Korean Journal of Materials Research
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• v.15 no.4
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• pp.217-223
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• 2005

Thermal, electrical and mechanical properties of high purity niobium and tantalum refractory rare metals were investigated tn evaluate the physical purity. Higher purity niobium and tantalum metals showed lower hardness due to smaller solution hardening effect. Temperature dependence of electrical resistivity showed a typical metallic behavior. Remarkable decrease in electrical resistivity was observed for a high purity specimen at low temperature. However, thermal conductivity increased for a high purity specimen, and abrupt increase in thermal conductivity was observed at very low temperature, indicating typical temperature dependence of thermal conductivity for high purity metals. It can be known that reduction of electron-phonon scattering leads to increase in thermal conductivity of high purity niobium and tantalum metals at low temperature.

• Journal of Adhesion and Interface
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• v.11 no.4
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• pp.174-180
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• 2010

The effect of carbon nanotube surface treatment on the interface and thermal conductivity of carbon nanotube-based poly(methylmethacrylate) (PMMA) composites was investigated. Coagulation and atomic-transfer radical polymerization (ATRP) was applied to modify the surface of multi-wall carbon nano-tube. The composite of ATRP method used carbon nanotube showed the higher transparency and thermal conductivities than that of the coagulation method used. In comparison to the thermal conductivity of pure PMMA, 0.21 W/mK, the ATRP carbon nanotube used PMMA/MWNT composite showed a thermal conductivity of 0.38 W/mK. The interface between carbon nanotube and PMMA was observed by scanning electron microscope and uniform dispersion of carbon nanotube was observed without any void in the PMMA matrix. It may be beneficial to transport the phonon without any scattering and it may result in a higher thermal conductivity.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.4 no.3
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• pp.697-703
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• 2000

As device dimensions are lastly scaled down, impact ionization(I.I.) events are very important to analyze hot carrier transport in high energy region, and the exact model of impact ionization is demanded on device simulation. We calculate full band model by empirical pseudopotential method and the impact ionization rate is derived from modified Keldysh formula. We calculate impact ionization coefficients by full band Monte Carlo simulator to investigate temperature dependent characteristics of impact ionization for GaAs as a function of field. Resultly impact ionization coefficients are in good agreement with experimental values at look. We how energy is increasing along increasing the field, while energy is decreasing along increasing the temperature since the phonon scattering rates for emission mode are very high at high temperature. The logarithmic fitting function of impact ionization coefficients is described as a second orders function of temperature and field. The residuals of the logarithmic fitting function are mostly within 5%. We Dow, therefore, the logarithm of impact ionization coefficients has quadratic dependence on temperature, and we can save time of calculating the temperature dependent impact ionization coefncients as a function of field.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.33A no.10
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• pp.123-129
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• 1996

LDD structure is widely accepted in fabricating short channel MOSFETs due to reduced short channel effect originated form lower drain edge electric field. However, modeling of the LDD device is troublesome because the analysis methods of LDD region known are either too complicated or inaccurate. To solve the problem, this paper presents a nonlinear resistance model for the LDD region based on teh fact that the electron mobility changes with positive gate bias because accumulation layer of electrons is formed at the surface of the LDD region. To prove the usefulness of the model, single source/drain and LDD nMOSFETs were fabricated with 0.35$\mu$m CMOS technolgoy. For the fabricated devices we have measured I$_{ds}$-V$_{gs}$ characteristics and compare them to the modeling resutls. First of all, we calculated channel and LDD region mobility from I$_{ds}$-V$_{gs}$ characteristics of 1050$\AA$ sidewall, 5$\mu$m channel length LDD NMOSFET. Then we MOSFET and found good agreement with experiments. Next, we use calculated channel and LDD region mobility to model I$_{ds}$-V$_{gs}$ characteristics of LDD mMOSFET with 1400 and 1750$\AA$ sidewall and 5$\mu$m channel length and obtained good agreement with experiment. The single source/drain device characteristic modeling results indicates that the cahnnel mobility obtained form our model in LDD device is accurate. In the meantime, we found that the LDD region mobility is governed by phonon and surface roughness scattering from electric field dependence of the mobility. The proposed model is useful in device and circuit simulation because it can model LDD device successfully even though it is mathematically simple.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2000.05a
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• pp.451-454
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• 2000

The impact ionization(I.I.) is necessary to analyze carrier transport properties under the influence of high electric field. The full band I-k relation and Fermi's golden rule are used for the calculation of impact ionization rate. We have investigated the temperature- and field-dependent impact ionization coefficient for silicon using full band Monte Carlo simulation. The impact ionization coefficients calculated by our impact ionization model are agreed with experimental data at look. We know that impact ionization coefficients and electron energies are decreasing along increasing temperature due to increase of phonon scattering, especially by emission. The logarithm of impact ionization coefficients are fitted to linear function for temperature and field. The residuals of linear function are within the error bound of 5%. We know logarithmic impact ionization coefficients are linearly dependent on temperature and field.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2000.05a
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• pp.460-464
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• 2000

As device dimensions are lastly scaled down, impact ionization(I.I.) events are very important to analyze hot carrier transport in high energy region, and the exact model of impact ionization is demanded on device simulation. We calculate full band model by empirical pseudopotential method and the impact ionization rate is derived from modified Keldysh formula. We calculate impact ionization coefficients by full band Monte Carlo simulator to investigate temperature-and field-dependent characteristics of impact ionization for GaAs. Resultly impact ionization coefficients are In good agreement with experimental values at 300k. We know energy is increasing along increasing the field. while energy is decreasing along increasing the temperature since the phonon scattering rates for omission mode are very high at high temperature. The logarithmic fitting function of impact ionization coefficients is described as a second orders function for temperature and field. The residuals of the logarithmic fitting function are mostly within 5%. We know, therefore, logarithm of impact ionization coefficients has quadratic dependence on temperature and field, and we can save time of calculating the temperature- and field-dependent impact ionization coefficients.

• Journal of the Korean Ceramic Society
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• v.45 no.12
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• pp.827-831
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• 2008

Spark plasma sintering (SPS) of AlN ceramics were carried out with ${Y_2}{O_3}$ as sintering additive at a sintering temperature $1,550{\sim}1,700^{\circ}C$. The effect of ${Y_2}{O_3}$ addition on sintering behavior and thermal conductivity of AlN ceramics was studied. ${Y_2}{O_3}$ added AlN showed higher densification rate than pure AlN noticeably, but the formation of yttrium aluminates phases by the solid-state reaction of ${Y_2}{O_3}$ and ${Al_2}{O_3}$ existed on AlN surface could delay the densification during the sintering process. The thermal conductivity of AlN specimens was promoted by the addition of ${Y_2}{O_3}$ up to 3 wt% in spite of the formation of YAG secondary phase in AlN grain boundaries because ${Y_2}{O_3}$ addition could reduced the oxygen contents in AlN lattice which is primary factor of thermal conductivity. However, the thermal conductivity rather decreased over 3 wt% addition because an immoderate formation of YAG phases in grain boundary could decrease thermal conductivity by a phonon scattering surpassing the contribution of ${Y_2}{O_3}$ addition.

• Journal of Powder Materials
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• v.23 no.4
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• pp.263-269
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• 2016

Graphene oxide (GO) powder processed by Hummer's method is mixed with p-type $Bi_2Te_3$ based thermoelectric materials by a high-energy ball milling process. The synthesized GO-dispersed p-type $Bi_2Te_3$ composite powder has a composition of $Bi_{0.5}Sb_{1.5}Te_3$ (BSbT), and the powder is consolidated into composites with different contents of GO powder by using the spark plasma sintering (SPS) process. It is found that the addition of GO powder significantly decreases the thermal conductivity of the pure BSbT material through active phonon scattering at the newly formed interfaces. In addition, the electrical properties of the GO/BSbT composites are degraded by the addition of GO powder except in the case of the 0.1 wt% GO/BSbT composite. It is found that defects on the surface of GO powder hinder the electrical transport properties. As a result, the maximum thermoelectric performance (ZT value of 0.91) is achieved from the 0.1% GO/BSbT composite at 398 K. These results indicate that introducing GO powder into thermoelectric materials is a promising method to achieve enhanced thermoelectric performance due to the reduction in thermal conductivity.

• Polymer(Korea)
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• v.37 no.5
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• pp.638-641
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• 2013

GNS/PVDF composites were prepared using graphite nanosheets (GNS) and poly(vinylidene fluoride) (PVDF) for flexible thermoelectric application. We measured the electrical conductivity, thermal conductivity and Seebeck coefficient of GNS/PVDF composites with different contents of GNS and then evaluated the thermoelectric properties of GNS/PVDF composites. The electrical conductivity of GNS/PVDF composites increased from 389 to 1512 S/m with increasing the content of GNS from 10 to 70 wt%. While the electrical conductivity dramatically increased, Seebeck coefficient and thermal conductivity did not show any big difference as the content of GNS increases. In this study, we demonstrated that GNS/PVDF composites improved the thermoelectric properties by decreasing the thermal conductivity due to the phonon scattering at the interfaces between polymer and GNS nanoplatelets.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.11a
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• pp.126-127
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• 2007

Sn-filled and Fe-doped $CoSb_3$ skutterudites were synthesized by encapsulated induction melting. Single ${\delta}$-phase was successfully obtained by subsequent annealing and confirmed by X-ray diffraction analysis. Temperature dependences of Seebeck coefficient, electrical resistivity and thermal conductivity were examined from 300 K to 700 K. The positive Seebeck coefficient confirmed the p-type conduction. Electrical resistivity increased with increasing temperature, which shows that the $Sn_zCo_3FeSb_{12}$ skutterudite is highly degenerate. Thermal conductivity was reduced by Sn-filling because the filler atoms acted as phonon scattering centers in the skutterudite lattice. Thermoelectric figure of merit was enhanced by Sn filling and its optimum filling content was considered to be z=0.3 in the $Sn_zCo_3FeSb_{12}$ system.