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.

Thermal Conductivity of BAs under Pressure

Abstract: Boron arsenide (BAs) is an ultrahigh thermal conductivity material with special phonon-phonon scattering properties. At ambient pressure, the bunching of acoustic phonon branches in BAs leads to a small phase-space for three-phonon scattering. Density functional theory predicts that this acoustic phonon bunching effect is sensitive to pressure. To explore this physics, we measure the thermal conductivity of BAs from 0 to 25 GPa using time-domain thermoreflectance in a diamond anvil cell. We characterized two BAs samples with ambient thermal conductivities of 320 and 480 W m-1 K-1. Our experiments show that the thermal conductivity of both samples depends weakly on pressure from 0 to 25 GPa. We attribute the weak dependence of the thermal conductivity of BAs on pressure to the weak pressure dependence of phonon-phonon scattering rates. Our experimental results are consistent with DFT predictions that three-phonon scattering rates increase from 0 to 25 GPa, while four-phonon scattering rates decrease.

Thermoelectric properties of Bi-FeSb2 nanocomposites: Evidence for phonon-drag effect

Abstract: The thermoelectric properties of Bi-FeSb2 nanocomposites are reported. The electrical resistivity and the Seebeck coefficient measurements show a significant dependence on bismuth concentration. Our results reveal that the shifting of the Seebeck peak in FeSb2 nanocomposites is purely a grain size-effect. The thermal conductivity data indicates a presence of an electron-phonon interaction. Over all, our analysis of the the thermoelectric properties of Bi-FeSb2 nanocomposites provide additional evidence for phonon-drag in FeSb2.

Scratch resistant flexible transparent electrodes and methods for fabricating ultrathin metal films as electrodes

Abstract: Systems and methods of fabricating electrodes, including thin metallic films, include depositing a first metallic layer on a substrate and passivating the deposited layer. The processes of deposition and passivation may be done sequentially. In some embodiments, a plurality of substrates may be coated with a metallic layer and further processed at a later time, including passivation and disposal of additional layers as discussed herein.

Measurement Techniques of Aligned Carbon Nanotubes

Abstract: The microstructures of individual CNTs can be characterized by TEM, AFM, and STM etc. In this chapter, we introduce some powerful techniques to characterize the alignment of CNTs besides the structures of individual CNTs. These advanced techniques including electron microscopy, diffraction, and spectroscopy can determine the unique ordering properties of aligned CNTs, such as the degree of alignment.

Procédés pour un facteur de mérite élevé dans des matériaux thermoélectriques nanostructurés

Abstract: L'invention concerne des materiaux thermoelectriques avec des facteurs de merite eleves, des valeurs ZT elevees. Dans de nombreux exemples, de tels materiaux comprennent des domaines nanodimensionnes (par exemple, nanocristallins), qui sont hypothetiques pour aider a augmenter la valeur ZT du materiau (par exemple, par l'augmentation de la diffusion des phonons en raison d'interfaces au niveau de limites de grains ou de limites grains/inclusions). La valeur ZT de tels materiaux peut etre superieure a environ, 1, 1,2, 1,4, 1,5, 1,8, 2 et meme superieure. De tels materiaux peuvent etre fabriques a partir d'un materiau de depart thermoelectrique par la generation de nanoparticules a partir de celui-ci, ou de nanoparticules a alliage mecanique a partir d'elements qui peuvent etre ulterieurement consolides (par exemple, par l'intermediaire d'une presse a chaud induite par courant continu) en un nouveau materiau massif. Des exemples non limitatifs de materiaux de depart comprennent des materiaux a base de bismuth, de plomb et/ou de silicium, qui peuvent etre allies, elementaires et/ou dopes. L'invention concerne en outre diverses compositions et des procedes apparentes aux aspects de materiaux thermoelectriques nanostructures (par exemple, dopage par modulation).

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.