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Zhifeng Ren

Bio: Zhifeng Ren is an academic researcher from Texas Center for Superconductivity. The author has contributed to research in topics: Thermoelectric effect & Thermoelectric materials. The author has an hindex of 122, co-authored 695 publications receiving 71212 citations. Previous affiliations of Zhifeng Ren include Massachusetts Institute of Technology & University of Cincinnati.


Papers
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TL;DR: In this paper, the authors investigated the thermoelectric performance of p-type SmMg2Bi2, a new member of this 1-2-2 Zintl family.
Abstract: Thermoelectric Zintl phases have attracted increasing attention in the past few decades, with good thermoelectric performance observed in many different families. Due to their intrinsic low lattice thermal conductivity, p-type CaAl2Si2 (1-2-2)-type Zintl phases, which also exhibit relatively higher electrical transport performance, have been demonstrated to be promising thermoelectric materials for mid- to high-temperature applications. Here we investigate the thermoelectric performance of p-type SmMg2Bi2, a new member of this 1-2-2 Zintl family. Band structure calculations reveal that the calculated band gap of SmMg2Bi2 is smaller in comparison to that of other Bi-based Zintl phases, which inevitably contributes to the bipolar effect clearly observed at higher temperature. Further successful substitution of Eu and Yb is effective in suppressing the bipolar effect and ensures achievement of superior electronic performance, resulting in a peak figure of merit (ZT) of ∼0.9 at 773 K. The current work has successfully expanded the family of Bi-based p-type 1-2-2 Zintls, and could play an essential role in stimulating further investigation of other Zintl compounds.

19 citations

Journal ArticleDOI
TL;DR: In this article, the phase transition of cubic and hexagonal diamond polytypes with the structural features was predicted to be stable even up to very high pressures for carbon and boron nitride, and some of these polytypes have impressively high thermal conductivities at ambient conditions.
Abstract: Zinc-blende (zb) boron arsenide (BAs) has been confirmed to have impressively high thermal conductivity. However, studies on its phase transitions under pressure have been few. Here, through a recently developed structure search method, we predicted that many polytypes with the structural features of cubic and hexagonal diamond, which are known to be unstable even up to very high pressures for carbon and boron nitride, can become stable at low pressures and might be retained to ambient conditions. Moreover, some of these BAs polytypes are calculated to have impressively high thermal conductivities at ambient conditions and the thermal conductivities for zb- and $2H$-BAs will decrease with increasing pressure, which are mainly attributed to the stronger third anharmonic interaction. The current study will open up a route to the search for high thermal conductors.

19 citations

Journal ArticleDOI
TL;DR: The experimental results indicate that a high concentration of NaOH is essential to the formation of carbon nanotubes, which opens a new route for the synthesis of CNTs and other carbon nanostructured materials.
Abstract: We report the synthesis of highly crystallized multiwalled carbon nanotubes through a modified Wolff−Kishner reduction process at a low temperature of 180 °C without adding the conventional catalysts of Fe/Co/Ni into the reaction vessel The as-synthesized carbon nanotubes are about 10−40 nm in diameter and several tens of micrometers in length The experimental results indicate that a high concentration of NaOH is essential to the formation of carbon nanotubes This technique opens a new route for the synthesis of CNTs and other carbon nanostructured materials

19 citations

Journal ArticleDOI
TL;DR: Parker et al. as discussed by the authors showed that n-type PbSe has large thermopowers characteristic of a high performance material, with values as high in magnitude as 250μV/K at 1000
Abstract: It was recently predicted [D. Parker D. J. Singh, Phys. Rev. B 82, 035204 (2010)], contrary to then-prevalent opinion, that p-type PbSe would be a good thermoelectric material. This prediction was confirmed in Wang et al. [Adv. Mater. 23, 1367 (2011)], and recent experimental work (Zhang et al. Energy Env. Sci. 5, 5246 (2012)] now indicates that n-type PbSe may show good thermoelectric performance. In light of this work, we now re-examine the thermoelectric performance of n-type PbSe with a revised approximation (not available at the time of the original work) which improves band gap accuracy. We now find that n-type PbSe has large thermopowers characteristic of a high performance material, with values as high in magnitude as 250 μV/K at 1000 K and 300 μV/K at 800 K. We further find that optimal 1000 K n-type doping ranges are between 2 × 1019 cm−3 and 7 × 1019 cm−3, while at 800 K, the corresponding range is from 7 × 1018 to 4 × 1019 cm−3.

19 citations

Patent
24 Aug 2006
TL;DR: In this paper, an apparatus and methods for nanolithography using nanoscale optics are disclosed, where submicron-scale structures may be obtained using standard photolithography systems (710) with a de-magnifying lens (600).
Abstract: An apparatus and methods for nanolithography using nanoscale optics are disclosed herein. Submicron-scale structures may be obtained using standard photolithography systems (710) with a de-magnifying lens (600). A de-magnifying lens (600) for use in a standard photolithography system (710) includes a film (670) having a top surface (610), a bottom surface (620) and a plurality of cylindrical channels (160) containing a dielectric material (280); and an array of carbon nanotubes (640) penetrating the film (670) through the plurality of cylindrical channels (160), wherein an image on the top surface (610) of the film (670) is converted into a de-magnified image on the bottom surface (620) of the film (670) by the carbon nanotubes (640).

19 citations


Cited by
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[...]

08 Dec 2001-BMJ
TL;DR: There is, I think, something ethereal about i —the square root of minus one, which seems an odd beast at that time—an intruder hovering on the edge of reality.
Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

33,785 citations

28 Jul 2005
TL;DR: PfPMP1)与感染红细胞、树突状组胞以及胎盘的单个或多个受体作用,在黏附及免疫逃避中起关键的作�ly.
Abstract: 抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1(PfPMP1)与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用,在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员,通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

18,940 citations

Journal ArticleDOI
02 Aug 2002-Science
TL;DR: Many potential applications have been proposed for carbon nanotubes, including conductive and high-strength composites; energy storage and energy conversion devices; sensors; field emission displays and radiation sources; hydrogen storage media; and nanometer-sized semiconductor devices, probes, and interconnects.
Abstract: Many potential applications have been proposed for carbon nanotubes, including conductive and high-strength composites; energy storage and energy conversion devices; sensors; field emission displays and radiation sources; hydrogen storage media; and nanometer-sized semiconductor devices, probes, and interconnects. Some of these applications are now realized in products. Others are demonstrated in early to advanced devices, and one, hydrogen storage, is clouded by controversy. Nanotube cost, polydispersity in nanotube type, and limitations in processing and assembly methods are important barriers for some applications of single-walled nanotubes.

9,693 citations