Reference : UMR6502-PHIMOR-008
Workplace : NANTES
Date of publication : Tuesday, October 18, 2022
Type of Contract : FTC Scientist
Contract Period : 18 months
Expected date of employment : 1 February 2023
Proportion of work : Full time
Remuneration : between 2690 and 3820 euros gross, depending on experience
Desired level of education : PhD
Experience required : Indifferent
The recent development of our modern societies largely relies on the research and development of high-tech devices. However, the properties on which many of these devices are based most often involve mechanisms that operate on a very small scale, well below a micrometer. In addition, most of these devices operate through the application of electrical current or voltage. Until very recently, the characterization at the nanometric scale and in operation ("operando") of these devices was not possible, thus limiting their development. This situation is changing rapidly thanks to recent advances in transmission electron microscopy, which now allow characterization of devices subjected to electrical stimuli with subnanometric resolution. It is in this context that the Institut des Matériaux de Nantes Jean Rouxel has just acquired such exceptional equipment.
The objective of this post-doc will be to prepare samples of different compounds, mainly chalcogenide and oxide Mott insulators, using the Focused Ion Beam technique (ZEISS Crossbeam 550L) before integrating them into one of the holders for electrical probing from the Nant'Themis (S)TEM microscope (Themis Z G3 from Thermo Fisher Scientific). Electrical pulses will then be applied in situ to the prepared samples in order to study the conductive filaments that are created when the pulses are applied. Local structural characterizations will be developed mainly through advanced techniques of electron nano-diffraction (4D-STEM), GPA (Geometric Phase Analysis) as well as through monochromated spectroscopic studies in Electron Energy Loss Spectroscopy (EELS).
The person recruited will therefore have to develop the experiments necessary to highlight the phenomena studied, in particular using two dedicated object holders (NanoEx 3D STM Electrical Probing and NanoEx i/v heating and biasing). Significant data processing work will be required to visualize the changes caused by the electrical stimuli.
The targeted study stems from research on a rapidly emerging theme, Mottronics. The enormous energy expenditure due to the development of microelectronics could be considerably reduced by “beyond CMOS” approaches. Among them, the insulator-to-metal transitions (IMT) existing in the class of Mott insulators are currently arousing great interest and the term 'Mottronics' has been coined to represent the concept of electronic technology exploiting such Mott transitions. The PMN team at IMN has demonstrated that the electric field, a control parameter suitable for microelectronics applications, offers a simple way to control IMT in Mott insulators. However, the success of Mottronics applications will closely depend on the understanding of the mechanisms at work in the electrical Mott transition. This team recently showed that this transition is linked to the creation of hot electrons [P. Diener et al., PRL 121, 016601 (2018).] in a conductive filament, which then leads to a compressive response of the network [D. Babich et al., ArXiv:2105.05093 (2021)]. However, important open questions remain, concerning both fundamental and applied aspects. Thus, the compressive response of the network involving a volume variation DeltaV/V of less than -1% was discovered in a small-gap oxide Mott insulator (EG =0.15 eV) but has never yet been characterized in transmission electron microscopy. Furthermore, the impact of the microstructure (100% dense monocrystal vs low density granular thin layer allowing local deformation or not) on the stabilization of the compressed conductive filament remains to be clarified.
In a second step, thin-layer materials (carbon-metal nanocomposites) developed in another team (PCM) of the IMN will also be studied with a view to sensor-type applications under high temperature conditions. The lamellae prepared with the FIB must here be placed on the heating and electric sample holder to mimic the operando conditions for these devices. The link between the structural observations and the piezoresistive and resistive properties will be sought.
You have (or are about to receive) a thesis with a background in materials science, physical sciences, transmission electron microscopy, or similar experience. During your work, you have acquired solid experience in the Focused Ion Beam technique, in particular for the preparation of TEM lamellae. You are enthusiastic and strongly interested in carrying out precise experimental work using advanced equipment and data processing methods. You want to invest in an interdisciplinary project with potential benefits for the industry. You are concerned about quality, conscientious, creative and cooperative, with a strong taste for scientific rigor. You are able to communicate with different audiences and have a high level of English. Some laboratory experience is required due to expected experimental methodological developments. Experience in digital data processing would be an advantage. Experience in the fields of transmission electron microscopy, spectroscopy (EELS, EDX), electrochemistry would also be appreciated.
This post-doc is funded by a contract with the I-SITE “NExT” (Nantes Excellence Trajectory) and is part of a larger project also including a thesis started in 2021. This project aims to develop the operando or in situ experiments in the IMN laboratory, in order to be able to establish new partnerships, particularly with industrialists. The project is part of the recent arrival in the IMN characterization platform of a probe-corrected (S)TEM microscope, monochromated and equipped with cameras and options allowing rapid measurements at a sub-nanometric scale evolution of compounds subjected to different stimuli.
The host laboratory is the Institut des Matériaux de Nantes Jean Rouxel (IMN), a joint research unit between the CNRS and the Nantes University (UMR6502). IMN brings together more than 200 people, including more than 75 permanent researchers and teacher-researchers and around 70 doctoral and post-doctoral students. The recruited person will benefit from the interaction with many colleagues working in several fields of materials science through experiments using a multitude of advanced characterization techniques and simulations. She/he will interact strongly with the doctoral student recruited in 2021 who is interested, in addition to Mott insulators, in operando studies in battery materials and in piezoelectric sensors. A large part of the activity will take place within the framework of the PMN team of the IMN given the expertise on the material mainly studied. In a second step, strong links with the PCM team will be developed.
Constraints and risks
No constraints or specific risks
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