Dr. Jer-Lai Kuo of Academia Sinica to give a talk on synthesis of semiconductor alloys and on graduate programs in Taiwan

Dr. Jer-Lai Kuo of Academia Sinica shall give a talk on November 29, 2011 entitled, “Synthesizing semiconductor alloys on the CLOUD–A 1st principles based multi-scale approach to map out the phase diagrams of semiconductor alloys.  The talk will be from 10:30 a.m. to 12:00 noon at the Department of Chemistry, Room C-109.   After the talk, Dr. Kuo shall give an introduction to the Taiwan International Graduate Program.

Synthesizing Semiconductor Alloys on the CLOUD – A 1st-Principles Based Multi-scale approach to Map out the Phase Diagrams of Semiconductor Alloys

Jer-Lai Kuo
Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei, Taiwan

Binary semiconductor alloys have been commonly proposed/synthesized to provide a much wider range of material properties than their parent compounds. However, theoretical studies are hindered by the intrinsic complexity. We have developed a CLOUD-ready multi-scale algorithm to effectively explore the configurational space (~2N) and applied it to study the newly synthesized BexZn1-xO. Examining the formation enthalpy we found the possible existence of three meta-stable order states. The calculated band-gap of the BexZn1-xO is also compared with the experimental measurements and surprisingly we found that some alloy configurations with the same concentration can have band-gaps differed by ~ 1.5 eV1,2. We have also considered the composition-temperature phase diagram of BexZn1-xO alloys3. The predicted phase diagram is consistent with the experimental observation that alloying Mg with BexZn1-xO suppresses phase separation. Furthermore, we have also looked into anionic replacements – ZnOxS1-x4 and other BN and C alloys5-7.

We are working toward to port our methods to CLOUD facility not only to speed up this process but also to make it more accessible to experimentalists. Thus, we believe that our work reported here is not only related to material simulations but also should be of interests to experimentalists who are working on synthesizing the binary semiconductor alloys.
[1] Fan X.F., Zhu Z, Ong YS, Shen Z.X, and Kuo J-L, Lu Y.M., Appl. Phys. Lett. 91, 121121 (2007).
[2] Fan X.F., Sun H.D., Lu Y.M. , Shen Z.X, and Kuo J-L, J. Phys. Cond. Matt. 20, 235221 (2008)
[3] Gan C.K, Fan X.F., and Kuo J-L, Comp. Mater. Sci. 49, S29 (2010)
[4] Xiao-feng Fan, Y.M. Lu, Zexiang Shen, and Jer-Lai Kuo, New J. Phys. 11, 093008 (2009)
[5] Fan X.F., Zhu ZX. , Shen Z.X, and Kuo J-L, J. Phys. Chem. C 112, 15691 (2008)
[6] Fan X.F., Wu H, Shen Z.X. and Kuo J-L, Diamond and Related Materials, 18, 1278 (2009)
[7] Wu H, Fan X.F. and Kuo J-L, Diamond and Related Materials, 19, 100 (2010)

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Christian G’Sell of CNRS: Dependence of fracture toughness of a compatibilized polypropylene/polyamide blend to the local mechanisms of plastic deformation

DEPENDENCE OF FRACTURE TOUGHNESS OF A COMPATIBILIZED POLYPROPYLENE / POLYAMIDE BLEND TO THE LOCAL MECHANISMS OF PLASTIC DEFORMATION

Christian G’SELL
Professor Emeritus
Institut Jean Lamour (CNRS)
Ecole des Mines de Nancy (France)

Date / Time: February 23 (Wednesday) / 2:00 – 3:30pm
Place: C-205, Schmitt Hall

Abstract

Although polypropylene (PP) is a very versatile plastic with lots of practical applications, it suffers somehow from its critical brittleness under tensile loading, due to the relatively high value of the glass-transition temperature. This is the reason why
it is often filled with rubbery particles that provide it with an improved toughness. Despite this positive result, such “high impact PP” blends present an insufficient Young’s modulus. In this work, we developed a new family of PP-based materials that: i) keeps the modulus and the yield stress as close as possible to their original values for neat PP and, ii) increases the impact strength as much as possible. The key of this improvement was to blend the PP with polyamide 6 (PA6) that is known for its excellent behavior under uniaxial tension. Since PP and PA6 show some reciprocal allergy, some quantity of a thermoplastic elastomer (polyethylene-octene, POE) was added to form a ternary system. Mechanical tests, including Izod impact tests and tensile tests at constant true strain rate (with the VidéoTraction ? system invented by the author) proved that the aimed properties were correctly attained. These properties are discussed in terms of the local mechanisms of plastic deformation in the system on the basis of transmission electron micrographs. It is thus shown that, in blends, each of the three components plays its role with the others in a synergistic way