[Phd] 研究透射电镜新的使用方法
首发： 欧洲科研学术职位 公号
Introduction
This doctoral work aims to exploit the new possibilities of electron diffraction in low dose tomography (LDEDT), 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  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   to  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-Å2). In addition, our method provides a better quality dataset than other methods for crystal structure resolution (Figure 1).

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.



Figure1: a) Electron diffraction tomography: a non-oriented crystal is tilted around the goniometer axis in small steps. A small angle of beam precession is applied. b) Non-oriented crystal and selected area aperture. c) LD-EDT structural model obtained for Mn Formiate.

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

Thesis supervisors:
Stéphanie Kodjikian  

stephanie.kodjikian@neel.cnrs.fr,  

04 76 88 74 24

Holger Klein

holger.klein@neel.cnrs.fr,  

04 76 88 79 41

Thesis localisation: Institut Néel, CNRS et Université Grenoble Alpes

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