Intitulé du poste : Thesis : Low-dose electron diffraction tomography (LD-EDT) for highly sensitive MOFs 
Ville : Grenoble
Laboratoire/Institut : Institut Néel
Description du poste : This doctoral work aims to exploit the new possibilities of electron diffraction in low-dose tomography (LD-EDT), an innovative and efficient method recently developed in our laboratory to study the atomic structure of metal-organic frameworks (MOF), which are highly radiation sensitive, and whose structure remains inaccessible to traditional methods.

Context: 
Metal-organic frameworks (MOF) are materials whose structure and properties can be controlled by assembling functional organic molecules with metal atoms. The wide range of different MOFs has enabled their use in many applications such as catalysis, fuel storage (hydrogen, methane), carbon dioxide capture, proton conductors for fuel cells, photovoltaics, sensors and electronic materials. Recent years have seen an almost exponential increase in MOF structures in the Cambridge Structural Database (CSD) so there is no doubt that MOF will be one of the most important material classes for innovation in the future. The development of these materials depends closely on structural characterizations, but for most MOFs, it is notoriously difficult to obtain crystals large enough and of sufficient quality to determine their structures by X-ray diffraction. Thus, there are a large number of potentially interesting compounds that are not exploited because of the difficulty of studying their structures.However, in recent decades, impressive advances in the technical performance of transmission electron microscopes have led to significant advances in physics, materials science and life sciences. Thanks to these fabulous technological advances, electron diffraction-based methods now compete with X-ray diffraction and neutron diffraction, because they exploit advantageously the specificity of electron diffraction, perfectly adapted to the study of single crystals of a few tens of nanometers in diameter, i.e. whose volume is 106 times smaller than that required for single crystal X-ray diffraction.In addition, MOFs often have low resistance to radiation. For this aspect too, the use of electron diffraction is more favourable than that of X-rays, because it is sufficient to apply a dose 103 to 104 times lower than in X-ray diffraction to obtain the same useful signal.We have therefore developed an innovative method of electron diffraction in tomography (LD-EDT) that requires only a very low irradiation dose (less than 1 e-/Ų). In addition, our method provides a better quality dataset than other methods for crystal structure resolution. In this thesis, the student will be trained in the use of the transmission electron microscope and the application of LD-EDT to different MOFs. The goal is to optimize the experimental parameters of the technique and to solve the structures of the relevant MOFs synthesized by our collaborators in Grenoble and Lyon.

Method: 
The thesis will consist of several steps:
  • Conducting electron diffraction experiments in a transmission electron microscope under low-dose conditions on MOFs.
  • Optimization of experimental conditions to obtain diffracted intensity sets of the highest quality.
  • Structural resolution of MOFs from LD-EDT data.
  • Refinement of structures from LD-EDT and/or X-ray powder diffraction data.
For his or her research work, the doctoral student will be integrated into the MRS team at the Institut Néel. He/she will perform 3D electron diffraction experiments on the "transmission electron microscopy" platform of the Institut Néel which includes a space dedicated to sample preparation and a transmission electron microscope (TEM) adapted to LD-EDT, equipped with a fast C-MOS camera with high sensitivity and a device for diffraction in precession mode. The software required for data processing is also available in the laboratory. The synthesis of MOF materials will be carried out by our collaborators in Grenoble and Lyon.

Bibliography:
  • Low-dose electron diffraction tomography (LD-EDT), S. Kodjikian and H. Klein, 2019, Ultramicroscopy, 200, 12-19, https://doi.org/10.1016/j.ultramic.2019.02.010
  • The structure of nano-twinned rhombohedric YCuO2.66 solved by electron crystallography, Holger Klein, V. Ovidiu Garlea, Céline Darie, Pierre Bordet, 2019, Acta Cryst. B, 75, 107-112, https://doi.org/10.1107/S205252061801627X
  • Structure solution of oxides from precession electron diffraction, H. Klein, 2013, Z. Kristallogr., 228, 35 – 42
Durée du contrat : 3 ans
Date de prise de fonction : as soon as possible
Personne à contacter : Stéphanie Kodjikian and Holger Klein
Téléphone : 04 76 88 74 24 / 04 76 88 79 41
Email : Cette adresse e-mail est protégée contre les robots spammeurs. Vous devez activer le JavaScript pour la visualiser. and Cette adresse e-mail est protégée contre les robots spammeurs. Vous devez activer le JavaScript pour la visualiser.