고순도 나이오븀과 탄탈륨 희유금속의 물리적 특성평가

김일호,박종범,유신욱,조경원,최국선,서창열,김병규,김준수,Kim Il-Ho,Park Jong-Bum,You Sin-Wook,Cho Kyung-Won,Choi Good-Sun,Suh Chang-Youl,Kim Byoung-Gyu,Kim Joon-Soo 한국재료학회 2005 한국재료학회지 Vol.15 No.4

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.

기계적합금화로 제조된 Ni-20Cr-20Fe-5Nb 합금에서 PCA로서 H₂O의 역할과 시효석출거동

김일호,권숙인,이원식,채수원,황선근,김명호,Kim Il-Ho,Kwun S.I.,Lee Won-Sik,Chae S.W.,Hwang S.K.,Kim M.H. 한국분말야금학회 2006 한국분말재료학회지 (KPMI) Vol.13 No.3

The effect of use of $H_2O$ as PCA(process control agent) to prevent the carbon contamination during mechanical alloying process and the precipitation behavior in Ni-20Cr-20Fe-5Nb bulk alloy after aging were investigated. NbC and $Cr_2O_3$ were formed during mechanical alloying and consolidation processes in the Ni-20Cr-20Fe-5Nb alloy in which methanol($CH_3OH$) was added as PCA. Formation of NbC in this alloy decreased the amount of Nb dissolved in the Ni matrix. The use of $H_2O$ as PCA in Ni-20Cr-20Fe-5Nb alloy prevented the formation of NbC and increased the hardness. The increase of hardness in this alloy was attributed to the increased amount of Nb dissolved in the Ni matrix. After aging treatment for 20 hours at $600^{\circ}C\;and\;720^{\circ}C$ of Ni-20Cr-20Fe-5Nb bulk alloy in which $H_2O$ added as PCA, ${\gamma}"$$(Ni_3Nb,\;tetragonal)\;and\;{\delta}\;(Ni_3Nb,\;orthorhombic)$ precipitates were formed, respectively. The precipitation temperatures of ${\gamma}"$ and ${\delta}$ in this bulk alloy were lower than those in commercial IN 718 alloy. It seemed that the lower precipitation temperatures for ${\gamma}"$ and ${\delta}$ in this bulk alloy than in commercial IN 718 alloy were due to severe plastic deformation during mechanical alloying.

'직업을 통한 사회봉사만이 정화의 지름길'

김일호,Kim, Il-Ho 대한건축사협회 1984 建築士 Vol.1984 No.3

AlGaAs/GaAs HBT 에미터 전극용 Pd/Ge계 오믹 접촉

김일호,Kim, Il-Ho 한국재료학회 2003 한국재료학회지 Vol.13 No.7

Pd/Ge/Ti/Pt and Pd/Ge/Pd/Ti/Au ohmic contacts to n-type InGaAs were investigated for applications to AlGaAs/GaAs HBT emitter ohmic contacts. In the Pd/Ge/Ti/Pt ohmic contact minimum specific contact resistivity of $3.7${\times}$10^{-6}$ $\Omega$$\textrm{cm}^2$ was achieved by rapid thermal annealing at $^400{\circ}C$/10 sec. In the Pd/Ge/Ti/Au ohmic contact, minimum specific contact resistivity of $1.1${\times}$10^{-6}$ $\Omega$$\textrm{cm}^2$ was achieved by annealing at 40$0^{\circ}C$/10 sec but the ohmic performance was degraded with increasing annealing temperature due to the reaction between the ohmic contact materials and the InGaAs substrate. However, non-spiking planar interface and relatively good ohmic contact (high-$10^{-6}$ /$\Omega$$\textrm{cm}^2$) were maintained after annealing at $450^{\circ}C$/10 sec. Therefore, these thermally stable ohmic contact systems are promising candidates for compound semiconductor devices. RF performance of the AlGaAs/GaAs HBT was also examined by employing the Pd/Ge/Ti/Pt and Pd/Ge/Pd/Ti/Au systems as emitter ohmic contacts. Cutoff frequencies were 63.5 ㎓ and 65.0 ㎓, respectively, and maximum oscillation frequencies were 50.5 ㎓ and 51.3 ㎓, respectively, indicating very successful high frequency operations.

기혼 여성의 직업이 신체적, 정신적 건강에 미치는 영향

김일호,천희란,Kim, Il-Ho,Chun, Hee-Ran 대한예방의학회 2009 예방의학회지 Vol.42 No.5

Objectives : The aim of this study was to investigate whether working married women in different occupational classes affected diverse health outcomes. Methods : We used data for married women aged 25-59 (N=2,273) from the 2005 National Health and Nutritional Examination Survey. Outcome measures included physical/mental and subjective/objective indicators (selfrated poor health, chronic diseases, depression, and suicidal ideation from reported results; metabolic syndrome dyslipidemia from health examination results). Agestandardized prevalence and logistic regression were employed to assess health status according to three types working groups (housewives, married women in manual jobs, married women in non-manual jobs). Sociodemographic factors (age, numbers of children under 7, education, household income) and health behaviors (health examination, sleep, rest, exercise, smoking, drinking) and a psychological factor (stress) were considered as covariates. Results : Non-manual married female workers in Korea showed better health status in all five health outcomes than housewives. The positive health effect for the non-manual group persisted in absolute (age-adjusted prevalence) and relative (odds ratio) measures, but multivariate analyses showed an insignificant association of the non-manual group with dyslipidemia. Manual female workers showed significantly higher age-adjusted prevalence of almost all health outcomes than housewives except chronic disease, but the associations disappeared after further adjustment for covariates regarding sleep, rest, and stress. Conclusions : Our results suggest that examining the health impact of work on married women requires the consideration of occupational class.

Chalcogenide계 열전재료

김일호,Kim, Il-Ho 한국전기전자재료학회 2011 전기전자재료 Vol.24 No.7

현재 개발 중인 Chalcogenide계 열전재료 중에서, 이방성 재료인 Thallium chalcogenide, Alkalimetal bismuth chalcogenide, Bismuth telluride와 등방성 재료인 Lead telluride, Silver antimony telluride, TAGS, LAST 및 SALT를 소개하였고, 이 재료들에 대한 연구 동향을 살펴보았다. Chalcogenide는 S, Se, Te 및 다른 원소와의 다양한 조합에 의해, 넓은 온도범위에서 열전재료로 응용하기 위한 밴드갭 에너지의 조절이 가능하다. 또한 합성공정에 따른 상변태, 석출 등 구조변화에 따른 열전특성의 변화를 기대할 수 있어 열전재료 개발 초기부터 활발한 연구가 진행되어 왔다. 과거의 전통적인 Chalcogenide계 열전재료뿐만 아니라, Chalcogenide계 열전 신소재에 대해서도 살펴보았다. Chalcogenide는 전자적, 광학적, 열적 성질 등 특성이 독특하고 변화가 무궁무진하여 아주 매력적이기 때문에, 앞으로도 계속 열전재료로서 각광받는 물질군으로 판단된다. 그림 11에 현재까지 ZT의 최댓값이 1이 넘는다고 보고된 열전재료의 성능지수를 요약하였다.

열전 박막 $Bi_{0.5}Sb_{1.5}Te_3/Bi_2Te_{2.4}Se_{0.6} p/n$ 접합에서의 확산 장벽에 관한 연구

김일호,이동희,Kim, Il-Ho,Lee, Dong-Hui 한국재료학회 1996 한국재료학회지 Vol.6 No.7

In the fabrication processes of thin film thermoelectrics, a subsequent annealing treatment is inevitable to reduce the defects and residual stresses introduced during the film growth, and to make the uniform carrier concentration of the film. However, the diffusion-induced atomic redistribution and the broadening of p/n junction region are expected to affect the thermoelectric properties of thin film modules. The present study intends to investigate the diffusion at the p/n junctions of thermoelectric thin films and to relate it to the property changes. The film junctions of p-type(Bi0.5Sb1.5Te3)and n-type(Bi2Te2.4Se0.6)were prepared by the flash evaporation method. Aluminum thin layer was employed as a diffusion barrier between p-and n-type films of the junction. This was found to be an effective barrier by showing a negligible diffusion into both type films. After annealing treatment, the thermoelectric properties of p/n couples with aluminum barrier layer were accordingly retained their properties without any deterioration.

P형 Bi_0.5Sb_1.5Te₃ 박막의 열전 특성에 미치는 두께 및 어닐링 효과

김일호,장경욱,Kim Il-Ho,Jang Kyug-Wook 한국재료학회 2004 한국재료학회지 Vol.14 No.1

P-type $Bi_{0.5}$$Sb_{1.5}$ $Te_3$ thin films were deposited by the flash evaporation technique, and their thermoelectric properties and electronic transport parameters were investigated. The effective mean free path model was adopted to examine the thickness effect on the thermoelectric properties. Annealing effects on the carrier concentration and mobility were also studied, and their variations were analyzed in conjunction with the antisite defects. Seebeck coefficient and electrical resistivity versus inverse thickness showed a linear relationship, and the effective mean free path was found to be 3150$\AA$. No phase transformation and composition change were observed after annealing treatment, but carrier mobility increased due to grain growth. Carrier concentration decreased considerably due to reduction of the antisite defects, so that electrical conductivity decreased and Seebeck coefficient increased. When annealed at 473 K for 1 hr, Seebeck coefficient and electrical conductivity were $160\mu$V/K and 610 $W^{-1}$ $cm^{ -1}$, respectively. Therefore, the thermoelectric quality factor were also enhanced to be $16\mu$W/cm $K^2$.>.

차세대 열전소재-Skutterudite

김일호,어순철,Kim, Il-Ho,Eo, Sun-Cheol 한국전기전자재료학회 2007 전기전자재료 Vol.20 No.1

N형 $Bi_2Te_{2.4}Se_{0.6}$ 박막의 열전 특성에 미치는 두께 및 열처리 효과

김일호,장경욱,Kim Il-Ho,Jang Kyung-Wook 한국진공학회 2005 Applied Science and Convergence Technology Vol.14 No.3

순간 증착법으로 제조한 n형 $Bi_2Te_{2.4}Se_{0.6}$ 박막에 대하여 유효 평균 자유 행로 모델을 적용하여 박막의 두께가 열전 특성에 영향을 미치지 않는 임계 두께를 구하였다. 또한 열처리 전후 전자 농도 및 이동도의 변화를 조사하여 열처리에 의한 열전 특성의 변화를 역구조 결함과 관련하여 설명하였다. Seebeck 계수와 전기 비저항 모두 두레의 역수와 직선적인 관계를 보였으며, 이로부터 구한 평균 자유 행로는 $5120\AA$이었다. 열처리에 의해 전자의 이동도가 증가하였지만, 역구조 결함의 감소로 인해 운반자의 전자 농도가 현저히 감소하여, 결국 전기전도도가 감소하고 Seebeck 계수가 증가하였다 473k에서 1시간 동안 열처리한 Seebeck 계수와 전기전도도는 각각 $-200\;\mu V/k$와 $510\omega^{-1}cm^{-1}$이었다 또한, 열처리에 의해 열전 성능 인자가 상당히 향상되어 $20\times10^{-4}\;W/(mK^2)$를 나타내었다. The effective mean free path model was adopted to examine the thickness effect on the thermoelectric properties of flash-evaporated n-type $Bi_2Te_{2.4}Se_{0.6}$ thin films. Annealing effects on the electron concentration and mobility were also studied, and their variations were analyzed in conjunction with antisite defects. Seebeck coefficient and electrical resistivity versus inverse thickness showed a linear relationship, and the mean free path was found to be $5120\AA$ Electron mobility was increased by annealing treatment and electron concentration was decreased considerably due to reduction of antisite defects, so that electrical conductivity was decreased and Seebeck coefficient was increased. When annealed at 473k for 1 hour, Seebeck coefficient and electrical conductivity were $-200\;\mu V/k\;and\;510\omega^{-1}cm^{-1}$, respectively. Therefore, the thermoelectric power factor was improved to be $20\times10^{-4}\;W/(mK^2)$.