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.

Synthesis and characterization of heavily overdoped Tl2Ba2CuO6+δ thin films

Abstract: Heavily overdoped epitaxial superconducting Tl 2 Ba 2 CuO 6+ δ (Tl-2201) thin films with single superconducting transition temperatures as low as 1.5 K (zero resistance) have been successfully synthesized. The films were made by “off-axis” radiofrequency magnetron sputtering and post-deposition annealing with slow cooling. Our investigations showed that the achievement of a single transition can be attributed to an off-axis configuration during sputter deposition, whereas the reduced T c results from a slow-cooling process immediately after annealing at high temperature. Transmission electron microscopy reveals that the films are pure 2201 phase with good crystallinity and modulated structure. Such samples are very much desired for detailed investigations of upper critical magnetic fields using conventional laboratory superconducting magnets, or the dc facilities at National Laboratories.

Thermoelectric Figure-of-merit in Bulk p-type PbTe

Abstract: Submitted for the MAR09 Meeting of The American Physical Society Thermoelectric Figure-of-merit in Bulk p-type PbTe BO YU, HUI WANG, Boston College, BED POUDEL, GMZ Energy Inc., KENNETH MCENANEY, GANG CHEN, Mass. Institute of Technology, ZHIFENG REN, Boston College, BOSTON COLLEGE, DEPT. OF PHYSICS TEAM, MASS. INSTITUTE OF TECHNOLOGY, DEPT. OF MECHANICAL ENGINEERING COLLABORATION — Lead telluride and its related chalcogenide alloys have been well studied for decades. With various achievements in not only bulk by also in thin films, quantum dots, superlattices, nanowires, etc., they always come up as one of the best thermoelectric materials for middle-range temperature applications. Recently, thallium was reported as a good candidate for band structure engineering in p-type lead telluride ingot system to largely enhance the thermoelectric power factor and hence the dimensionless figure-of-merit (ZT). Here we used mechanical alloying as the approach for large-scale production and achieved ZT value of 1.05 at 300 ̊C. The details will be presented in this talk. Bo Yu Boston College Date submitted: 11 Dec 2008 Electronic form version 1.4

Enhanced Thermoelectric Performance of p‐Type Mg3Sb2 for Reliable and Low‐Cost all‐Mg3Sb2‐Based Thermoelectric Low‐Grade Heat Recovery

Abstract: Bi2Te3‐based devices have long dominated the commercial market for thermoelectric cooling applications, but their narrow operating temperature range and high cost have limited their possible applications for conversion of low‐grade heat into electric power. The recently developed n‐type Mg3Sb2‐based compounds exhibit excellent transport properties across a wide temperature range, have low material costs, and are nontoxic, so it would be possible to substitute the conventional Bi2Te3 module with a reliable and low‐cost all‐Mg3Sb2‐based thermoelectric device if a good p‐type Mg3Sb2 material can be obtained to match its n‐type counterpart. In this study, by comprehensively regulating the carrier concentration, carrier mobility, and lattice thermal conductivity, the thermoelectric performance of p‐type Mg3Sb2 is significantly improved through Na and Yb doping in Mg1.8Zn1.2Sb2. Moreover, p‐ and n‐type Mg3Sb2 are similar in terms of their coefficients of thermal expansion and their good performance stability, thus allowing the construction of a reliable all‐Mg3Sb2‐based unicouple. The decent conversion efficiency (≈5.5% at the hot‐side temperature of 573 K), good performance stability, and low cost of this unicouple effectively promote the practical application of Mg3Sb2‐based thermoelectric generators for low‐grade heat recovery.

High Performance Bulk Thermoelectric Materials

Abstract: Over 13 plus years, we have carried out research on electron pairing symmetry of superconductors, growth and their field emission property studies on carbon nanotubes and semiconducting nanowires, high performance thermoelectric materials and other interesting materials. As a result of the research, we have published 104 papers, have educated six undergraduate students, twenty graduate students, nine postdocs, nine visitors, and one technician.

Enhancement of thermoelectric performance in n-type PbTe[subscript 1−y]Se[subscript y] by doping Cr and tuning Te:Se ratio

Abstract: Lead telluride and its alloys have been extensively studied for medium temperature thermoelectric applications due to decent figure-of-merit (ZT) at temperature close to 900 K. However, little emphasis has been given to improve the ZT near room temperature. In this investigation, we report a systematic study of Cr doping in PbTe1-ySey with y = 0, 0.25, 0.5, 0.75, 0.85, and 1. We found the peak ZT temperature increased with increasing concentration of Se. The highest ZT of ~0.6 at room temperature in Te-rich Cr0.015Pb0.985Te0.75Se0.25 was obtained due to a lowered thermal conductivity and enhanced power factor resulted from high Seebeck coefficient of about -220 μV K -1 and high Hall mobility ~1120 cm 2 V -1 s -1 at room temperature. A room temperature ZT of ~0.5 and peak ZT of ~1 at about 573 K to 673 K is shown by Se-rich sample Cr0.01Pb0.99Te0.25Se0.75. This improvement of the room temperature ZT improved the average ZT over a wide temperature range and could potentially lead to a single leg efficiency of thermoelectric conversion for Terich Cr0.015Pb0.985Te0.75Se0.25 up to ~11 % and Se-rich Cr0.01Pb0.99Te0.25Se0.75 up to ~13 % with cold side and hot side temperature at 300 K and 873 K, respectively, if matched with appropriate p-type legs.

I and i

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 …

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

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。

Carbon Nanotubes--the Route Toward Applications

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.