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Reference : UPR8011-SYLCHA-001
Workplace : TOULOUSE
Date of publication : Tuesday, June 30, 2020
Type of Contract : FTC Scientist
Contract Period : 12 months
Expected date of employment : 1 January 2021
Proportion of work : Full time
Remuneration : 2617€ to 3729€ gross/month as a function of experience
Desired level of education : PhD
Experience required : 1 to 4 years
We are looking for a resourceful postdoctoral research scientist to join the team at CEMES-CNRS working on transmission electron microscopy of functional oxides (MEM group, MEM, in collaboration with the I3EM group, I3EM) and within an international project between France and Germany.
Our aim is to develop a detailed understanding of the physics of oxide ferroelectrics when integrated at the nanoscale on a semiconductor platform examining their characteristics at the atomic scale with transmission electron microscopy-based methods. Ferroelectricity at the nanoscale has attracted considerable attention in the past years both from fundamental standpoint and for potential application in nanoelectronics, nanophotonics and photovoltaics as shown by recent review articles. A key functionality of ferroelectrics is the ability to switch their polarization between two stable orientations by application and reversal of an electrical field. As the size shrinks and depending on the electrical, mechanical and chemical boundaries conditions, polarization might become unstable, non-switchable or extremely low, which is intimately bounded to the ability of the system to redistribute the screening charges at the surfaces upon polarization switching. This is particularly true when the ferroelectric is on a semiconductor.
The ferroelectricity of nanoscale objects on semiconductors remains scarcely studied. In 2017, it has been shown that a ferroelectric polarization is stabilized and can be switched in epitaxial BaTiO3 films as thin as 1.6 nm (4 unit cells) on silicon. Following this work, we now aim at deciphering the nature of the polar phase in nanoscale structures with not only ultrathin thickness but also sub-micrometer lateral dimensions on planar silicon. We will study BaTiO3 cylindrical nanostructures on silicon with different aspect ratio, which can be considered as elemental bricks for future devices as memory, sensors or photonic component.
The key to the advanced transmission electron microscopy (TEM) work to be done is the quality of the specimen preparation, observations and data treatment/analysis. In particular, we will focus on atomic-scale advanced characterization, both structural and chemical, using scanning transmission electron microscopy (STEM) in HAADF/ABF/EELS modes and the detailed quantitative analysis of the results to establish the polarization mapping of the nanostructures as a function of boundary conditions and chemistry. Part of the work will involve optimising FIB preparation for atomic-resolution studies.
The initial contract of 12 months is extendable to 24 months (2 years). Starting date January 2021 or before.
The main activities will be
• specimen preparation,
• initial and advanced STEM characterisation,
• data treatments,
• analysis of the experimental results,
• understanding of the physical processes.
We are particularly looking for a candidate experienced in advanced TEM characterization and data analysis/simulation. STEM-HAADF and ABF will be of concern to determine the location of heavy cations and light O anions atomic columns with few tens picometers precision in the collected images. FIB specimen preparation techniques and experience in extracting EELS elemental maps and determination of the strain state in the nanostructures using the GPA software (pioneered at CEMES) are of course welcome. Knowledge of the physics of ferroelectrics and/or microelectronics devices is a definite plus.
The successful candidate should have good team spirit, dedicated work ethic and fluent in written and spoken English.
The post-doc will give support to the French-German ANR FEAT (Ferroelectricity at the nanoscale on Si), led by the MEM group at CEMES, which aims at addressing the ferroelectricity of nanostructures on a semiconductor, with not only ultrathin thickness but also sub-micrometer lateral dimensions.
The post-doc will be in close contact with members of the I3EM group at CEMES working on the development of strain measurements and in-situ electron holography experiments in ferroelectric oxides. The post-doc will interact with another post-doc in charge of the complementary work concerning the dynamic study of the switching mechanism using in situ and operando TEM.
Specimen preparation will be carried out on a dual-beam FIB-SEM (ThermoFisher Helios Nanolab 600i) equipped with Omniprobe micromanipulator and 5 gas injectors.
STEM work will be conducted either on the probe-corrected JEM-ARM200F Cold FEG at the Toulouse characterisation platform (UMS Castaing) near CEMES or on the probe corrected FEI Titan 60–300 microscope at the Aragon Nanoscience Institut in Zaragoza (INA, LMA). The ARM is equipped with a GATAN GIF QUANTUM ER, a GATAN camera ULTRASCAN 2kx2k and an EDX SDD CENTURIO-X and the Titan with a high-brightness field emission gun (X-FEG), a Tridiem GIF Image Filter/Spectrometer 866 ERS from Gatan, a Gatan 2k x 2k CCD camera and an an EDS (EDAX) detector.
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