Carbon nanotubes (NTs) can be synthesized at medium temperature (T~700°C) by decomposing a carbonaceous gas on the surface of a metal nanocatalyst (Fe, Co or Ni). Despite significant progress over the past 25 years, precise control of their structure during synthesis remains a major challenge for nanoelectronics applications. In recent years, the use of bimetallic catalysts (CoW, Mo2C,…) seems to be the most promising way forward since quite spectacular selectivities towards the chirality of NTs have been observed without being fully understood. Among the assumptions, it has been proposed that the presence of an alloying element with a high melting point tends to keep the particle solid during synthesis. Under such conditions, the catalyst structure has facets that allow direct control of the tube structure by epitaxy. Although elegant, this interpretation is subject to many controversies since no precise experimental study can determine the state of the catalyst during synthesis.
The objective of this internship is therefore to focus on the synthesis of nanoparticles (NPs) in a perfectly defined and controlled structural state in order to achieve a real manufacturing engineering of controlled structure. For this, we will focus on the structural temperature study of AgPt NPs where Pt, with a high melting point, will be the key element to keep the particle in a solid state. The first step will be to optimize the conditions of physical synthesis (pulsed laser ablation) to manufacture AgPt NPs of controlled structures (size, morphology and composition). Then, the structural evolution at high temperature of NPs will be carried out. More precisely, the structural study of AgPt NPs (alloy formation, phase separation, order/disorder transition) at different temperatures will then be possible where different microscopy techniques will be coupled (high resolution, diffraction, X-ray energy dispersion, etc.). In collaboration with the MPQ laboratory for the experimental part, all the results will be compared with atomic-scale numerical simulations developed at LEM and CINaM in Marseille.
Job: Internship (4-6 months)
Academic level : Master degree
Location: LEM, Châtillon
Expertise: Good level of knowledge of condensed matter physics (thermodynamics, electron-matter interaction,…) with a strong interest in conducting advanced experiments in interaction with numerical simulations. Scientific exchanges, in particular within the framework of collaborative structures in which LEM participates (various GDRs, ANR projects,…), will be encouraged.
Contacts: Hakim Amara