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Past and future events

December 9, 2016

thesis defense of Hicham ZAID

thesis defense of Hicham ZAID
We are pleased to invite you to attend the PhD defense of Hicham ZAID untitled :
Two-dimensional gas oxide heterostructure for microelectronic in extreme environments
The work was conducted in the Centre des Matériaux in Evry, France (Mines ParisTech, PSL Research University - MAT)
Friday 9th Dec. 2016
at 14:30 at the Ecole des Mines de Paris
Room Vendôme V334

Adress : 60, Boulevard Saint Michel, Paris (RER B Station Luxembourg)

Abstract : Novel behavior at the interface between two insulating polar/non polar perovskites has been recently discovered. The polarization discontinuity at LaAlO3/SrTiO3 drives the formation of quasi two dimensional electron gas. Both the local mechanism and quantification of such behavior remain unclear due to interplay of structural, chemical and electronic factors. Several mechanisms have been proposed, such as the polar catastrophe, structural distortions, oxygen vacancies, cationic intermixing at the interface and film non-stoichiometry. In the frame of an international project conductive and insulating heterostructures have been synthetized by Pulsed-Laser Deposition. In this thesis, we have developed a comprehensive approach to investigate the origin of the charge carriers. The interfaces have been systematically analyzed by combining high resolution imaging (STEM-HAADF) to atomic resolved electron (EELS) and ion (MEIS) spectroscopies. The observed and quantified parameters have been related to the electrical properties of the interfaces measured in the consortium. Buckling of the atomic layers, intermixing and electron transfer reduce the polar divergence. This rules out the polar catastrophe scenario. The formation of donor defects at the film surface is favored above a critical film thickness. Electrons are transferred to interface in the STO conduction band. A competing compensation mechanism of the positive interfacial charge by negatively charged strontium vacancies has been demonstrated that generates an in-plane compression of the STO, unfavorable for a strict 2D confinement of the charges. Varying the process parameters such as growth duration, oxygen partial pressure, temperature, and plume stoichiometry, shifts the equilibrium of the different mechanisms highlighted. This thesis emphasizes the complex relations between the process and the properties through the defects distribution around these singular interfaces.

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