Quantum Confinement Effect of Thermoelectric Properties

제구철,Chang-Ho Cho 한국물리학회 2009 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.54 No.1

Using the quantum confinement effect based on the conduction band model, we theoretically determine the optimal concentration for the best figure-of-merit in n-type Bi2Te3 quantum well structures. The Bi2Te3 system has polycrystalline structures that can be prepared by using powders of hot-pressed alloys. The enhanced figure-of-merit due to the quantum confinement is almost caused by the enhanced Seebeck coefficient and by improved resistivity. It results from competition between the strong intrinsic characteristic and the enhancement of the volume ratio of the concentration in the quantum-confined system. The optimum concentration for the best figure-of-merit in the system amounts to 2.1 × 10^11 cm^-2 at room temperature. Control of the carrier concentration, as well as the quantum confinement effect, is also a very important effect to optimize the figure-of-merit in low-dimensional systems. Using the quantum confinement effect based on the conduction band model, we theoretically determine the optimal concentration for the best figure-of-merit in n-type Bi2Te3 quantum well structures. The Bi2Te3 system has polycrystalline structures that can be prepared by using powders of hot-pressed alloys. The enhanced figure-of-merit due to the quantum confinement is almost caused by the enhanced Seebeck coefficient and by improved resistivity. It results from competition between the strong intrinsic characteristic and the enhancement of the volume ratio of the concentration in the quantum-confined system. The optimum concentration for the best figure-of-merit in the system amounts to 2.1 × 10^11 cm^-2 at room temperature. Control of the carrier concentration, as well as the quantum confinement effect, is also a very important effect to optimize the figure-of-merit in low-dimensional systems.

0.5 vol% TiO₂ 나노분말을 분산시킨 n형 Bi₂(Te_0.9Se_0.1)₃ 가압소결체의 열전특성

박동현,오태성,Park, D.H.,Oh, T.S. 한국마이크로전자및패키징학회 2013 마이크로전자 및 패키징학회지 Vol.20 No.1

용해/분쇄법으로 제조한 n형 $Bi_2(Te_{0.9}Se_{0.1})_3$ 분말에 0.5 vol% $TiO_2$ 나노분말을 분산시켜 가압소결 후, $TiO_2$ 나노분말의 분산이 $Bi_2(Te_{0.9}Se_{0.1})_3$ 가압소결체의 열전특성에 미치는 영향을 분석하였다. $Bi_2(Te_{0.9}Se_{0.1})_3$ 가압소결체는 $2.93{\times}10^{-3}/K$의 최대 성능지수 및 1.02의 최대 무차원 성능지수의 우수한 열전특성을 나타내었다. 0.5 vol% $TiO_2$ 나노분말의 첨가에 의해 $Bi_2(Te_{0.9}Se_{0.1})_3$ 가압소결체의 최대 성능지수가 $2.09{\times}10^{-3}/K$로 감소하였으며, 최대 무차원 성능지수는 0.68로 저하하였다. The n-type $Bi_2(Te_{0.9}Se_{0.1})_3$ powders, which were fabricated by melting/grinding method and dispersed with 0.5 vol% $TiO_2$ nanopowders, were hot-pressed in order to investigate the effects of $TiO_2$ dispersion on the thermoelectric properties of the hot-pressed $Bi_2(Te_{0.9}Se_{0.1})_3$. Excellent thermoelectric properties such as a maximum figure-of-merit of $2.93{\times}10^{-3}/K$ and a maximum dimensionless figure-of-merit of 1.02 were obtained for the hot-pressed $Bi_2(Te_{0.9}Se_{0.1})_3$. With dispersion of 0.5 vol% $TiO_2$ nanopowders, the maximum figure-of-merit and the maximum dimensionless figure-of-merit decreased to $2.09{\times}10^{-3}/K$ and 0.68, respectively.

토지 이용 변화 예측 모형의 정확도 검정을 위한 통계량 연구

김오석 ( Oh Seok Kim ) 한국경제지리학회 2013 한국경제지리학회지 Vol.16 No.3

본 논문은 토지 이용 변화를 예측하는 계량 모형의 정확도 평가에 필수적인 통계량인 성능 지수를 심도 있게 이해사는 것을 목적으로 한다. 이 통계량은 기존의 토지 이용 변화 연구에서 소개된 예측 모형으 ㅣ정확도를 평가하는 다른 통계량들 (예: 카파 통계량)의 단점을 보완하여 만들어진 것이나, 이 또한 계량 모형으 예측력을 명학하게 평가하고 해석하기에는 제한적이다. 본 논문에서는 성능 지수의 보다 명확한 해석을 위해서 결과물으 ㅣ공간해상도를 고정해야 함을 밝히고, 그 특정 공간해상도를 "성능 해상도"라 정의한다. 성능 해상도는 예측오류가 현격하게 줄어들면서 계량모형으 ㅣ예측력이 증가하는 시점의 공간해상도를 일컫는다. 따라서 토지 이용 변화 예측 모형의 예측력을 정확하게 평가하기 위해 두 통계량, 즉 성능 지수와 성능 해상도를 함께 이용할 것을 제안한다. This paper addresses the limitation of a map comparison metric entitled Figure of Merit through employing a simple land change model. The metric was originally designed to overcome limitations of other existing statistics, such as Kappa, when assessing predictive accuracy of land change models. A series of comparisons between null and predicted outcomes at multiple resolutions as well as a multi-resolution Figure of Merit analysis techniques of validation are compared for spatially segregated calibration and validation datasets. The Figure of Merit at the null resolution in this paper was 57%, although future research must be done to determine if this was simply a coincidence. A Figure of Merit greater than 50% would seem to represent a “Resolution of Merit” in that the Figure of Merit at that resolution becomes greater than the error. Thus, these two metrics should be used in tandem to assess predictive accuracy of a land change model.

Analysis of Pull-in-Voltage and Figure-of-Merit of Capacitive MEMS Switch

Santanu Maity,Rajesh Saha,Ngasepam Monica Devi,Chandan Tilak Bhunia 한국전기전자재료학회 2016 Transactions on Electrical and Electronic Material Vol.17 No.3

Theoretical and graphical analysis of pull-in-voltage and figure of merit for a fixed-fixed capacitive MicroElectromechanical Systems (MEMS) switch is presented in this paper. MEMS switch consists of a thin electrodecalled bridge suspended over a central line and both ends of the bridge are fixed at the ground planes of a coplanarwaveguide (CPW) structure. A thin layer of dielectric material is deposited between the bridge and centre conductorto avoid stiction and provide low impedance path between the electrodes. When an actuation voltage is appliedbetween the electrodes, the metal bridge acquires pull in effect as it crosses one third of distance between them. Inthis study, we describe behavior of pull-in voltage and figure of merit (or capacitance ratio) of capacitive MEMS switchfor five different dielectric materials. The effects of dielectric thicknesses are also considered to calculate the valuesof pull-in-voltage and capacitance ratio. This work shows that a reduced pull-in-voltage with increase in capacitanceratio can be achieved by using dielectric material of high dielectric constant above the central line of CPW.

다양한 매개변수에 따른 관내 나노유체의 성능지수

손민재,최종욱 한국전산유체공학회 2022 한국전산유체공학회지 Vol.27 No.2

The figure of merit for nanofluids represents the heat transfer performance of nanofluids against basic fluid. In previous studies, only the material properties of nanofluids have been considered for the figure of merit. In this study, the computational thermal flow analyses are performed including not only the material properties but also the geometric shapes and the external effects. The figures of merit are obtained with the four parameters, which are the inlet pressure, the number of return bends, the radius of curvature, and the volume fraction of nanoparticles in the pipes with the return bends. The results show that the three remaining parameters other than the number of return bends act on the figures of merit in a complicated manner. Therefore, a correlation equation with Euler number, Dean number, and Prandtl number associated with the three parameters is derived through the nonlinear regression. These results are expected to be helpful in designing and manufacturing heat exchangers using nanofluids.

Analysis of Pull-in-Voltage and Figure-of-Merit of Capacitive MEMS Switch

Saha, Rajesh,Maity, Santanu,Devi, Ngasepam Monica,Bhunia, Chandan Tilak The Korean Institute of Electrical and Electronic 2016 Transactions on Electrical and Electronic Material Vol.17 No.3

Theoretical and graphical analysis of pull-in-voltage and figure of merit for a fixed-fixed capacitive Micro Electromechanical Systems (MEMS) switch is presented in this paper. MEMS switch consists of a thin electrode called bridge suspended over a central line and both ends of the bridge are fixed at the ground planes of a coplanar waveguide (CPW) structure. A thin layer of dielectric material is deposited between the bridge and centre conductor to avoid stiction and provide low impedance path between the electrodes. When an actuation voltage is applied between the electrodes, the metal bridge acquires pull in effect as it crosses one third of distance between them. In this study, we describe behavior of pull-in voltage and figure of merit (or capacitance ratio) of capacitive MEMS switch for five different dielectric materials. The effects of dielectric thicknesses are also considered to calculate the values of pull-in-voltage and capacitance ratio. This work shows that a reduced pull-in-voltage with increase in capacitance ratio can be achieved by using dielectric material of high dielectric constant above the central line of CPW.

Recent Advances in Thermoelectric Power Generation Technology

Sharma, Ashutosh,Lee, Jun Hyeong,Kim, Kyung Heum,Jung, Jae Pil The Korean Microelectronics and Packaging Society 2017 마이크로전자 및 패키징학회지 Vol.24 No.1

Thermoelectric power generation (TEG) technology with high figure of merit (ZT) has become the need of the modern world. TEG is a potent technology which can tackle most of the environmental issues such as global warming, change in climatic conditions over the globe, and for burning out of various resources of non-renewable energy like as petroleum deposits and gasolines. Although thermoelectric materials generally convert the heat energy from wastes to electricity according to the theories Seebeck and Peltier effects yet they have not been fully exploited to realize their potential. Researchers are focusing mainly on how to improve the current ZT value from 1 to 2 or even 3 by various approaches. However, a higher ZT value is found to be difficult due to complex thermoelectric properties of materials. Hence, there is a need for developing materials with high figure of merit. Recently, various nanotechnological approaches have been incorporated to improve the thermoelectric properties of materials. In this review paper, the authors have performed a thorough literature survey of various kinds of TEG technology.

중성자 에너지 측정을 위한 NE213-PSD 장치의 감응 분석

이경주,Lee, Kyung-Ju 한국분석과학회 1992 분석과학 Vol.5 No.4

방사선 중성자 선원의 에너지 스펙트럼을 측정하기 위하여 액체 섬광 검출기(NE213)와 펄스모형 분리장치를 감마선 선원과 중성자 선원을 이용하여 그 감응 특성을 분석하였다. Am-Be 선원을 이용하여 이 장치에 대한 "Figure of Merit"을 측정한 결과 1.13 이었다. 이 값은 단색 에너지 중성자 선원인 $^{12}C(d,\;n)^{13}N$에서의 1.3 과 상당히 유사한 값을 보여 준다. NE213-PSD 장치의 성능 시험을 위한 이 실험결과는 중성자-감마 혼합 방사선장에서 스펙트럼의 측정과 중성자 에너지 스펙트럼과 속밀도 측정표준을 확립하는 데 기술적으로 유용하게 쓰일 것이다. In order to measure the energy spectrum of a radioactive neutron source, the pulse shape discrimination (PSD) system with organic scintillator, NE-213, was characterized by using some of the gamma ray sources and neutron source, Am-Be. The figure of merit of the rise time spectrum of AmBe source measured by this system was about 1.13. This value agrees well with the value of 1.3 which is measured for monoenergetic source, $^{12}C(d,\;n)^{13}N$. The results of present experiment for performance test of NE213-PSD system will provide the useful technique to measure the spectrum of neutron-gamma mixed field and to establish the neutron energy spectrum and flux density standards.

N-형 전하밀도를 갖는 저차원의 Bi₂Te₃의 열전특성

제구출 한국물리학회 2008 새물리 Vol.57 No.2

We investigate the quantum-confined thermoelectric properties of Bi$_2$Te$_3$ quantum well structures as a function of temperature. The Seebeck coefficient is strongly improved by quantum confinement effects, and the thermal conductivity is improved by grain effects due to the well size. As a result, the figure of merit is enhanced. In contrast to the single-crystal system, the figure of merit for quantum-well structures increases with increasing temperature, and quantum confinement effects allow for more degrees of freedom for optimizing the figure of merit. \end{abstract} 본 연구에서는 Bi$_2$Te$_3$ 양자우물구조에서 열전성능을 결정하는 Seebeck 계수와 전기전도도들에 대한 양자감금효과와 grain 효과로 작용하는 우물폭 크기에 대한 열전도도를 온도변화에 따라 살펴본다. 고정된 밀도에서 양자감금효과로 인하여 Seebeck 계수는 커지나 전기 전도도는 양자감금 효과에 크게 영향을 받지 않는다. 따라서 저차원 구조의 성능지수 증가는 양자감금효과로 인한 Seebeck 계수와 grain 효과로 인한 열전도도의 개선으로 이루어지며, 단결정과는 다르게 온도가 증가할수록 커지는 현상을 보여 준다.

$n/{\gamma}$ 복합 방사선장에서의 중성자 스펙트럼 분리 측정연구(1)

이광필,김원식,Lee, Kwang-Pill,Kim, Wuon-Shik 한국분석과학회 1993 분석과학 Vol.6 No.5

$^{241}Am-Be$(${\alpha}$, n) 중성자 선원의 중성자/감마선(n/${\gamma}$) 복합 방사선장에서 $^6Li$(n, ${\alpha}$)T 핵반응을 이용하고 두 섬광체, BC 501($C_8H_{10}$)과 Cerium의 섬광 감쇠 시간차와 동일 섬광체 내에서의 n/${\gamma}$에 대한 서로 다른 섬광감쇠 시간차를 병용하여 PSD(Pulse Shape Disciminator) 및 CFD(Constant Fraction Discriminator) 방법으로 n와 ${\gamma}$성분을 분리 측정하였으며 $^6Li$ 속중성자 분광계의 figure of merit는 1.36으로 평가되었다. In n/${\gamma}$ mixed field of $^{241}Am-Be$(${\alpha}$, n) neutron source, we seperated the neutron component from gamma ray component. At the center of the detector, $^6Li$ was doped on the cerium activated glass plate for $^6Li$(${\alpha}$, n)T nuclear reaction. The time differences of the light following excitations by different scintillators, BC501($C_8H_{10}$) and cerium, and by the same scintillator for different radiations as neutrons and gamma-rays are used to apply the methods of PSD(Pulse Shape Discriminator) and CFD(Constant Fraction Discriminator). The figure of merit of $^6Li$ fast neutron spectrometer is estimated as 1.36.