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Transmission Electron Microscopy (TEM)

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Transmission electron microscope FEI Tecnaï 20F

Responsable

Mohamed Sennour

General context

The École des Mines de Paris / ARMINES, the Génopole and INSERM have created a common microscopy and site imaging center in Évry. In this context, the partners, strongly supported by the Region, have acquired a new transmission electron microscope: a Tecnai F 20 ST from FEI, operating at 200 KV.

This microscope has been installed in the Centre des Matériaux of the École des Mines de Paris, which is in charge of the management and routine maintenance, and which is also in charge of user training. The activity "Biology" and the activity "Physics of materials" share the time of use of the microscope at the rate of 50% each.

The microscope

The concept of Tecnai microscopes focuses on the complete digital integration of all the signals collected by the column detectors. The images or analyzes of the same sample can thus be acquired simultaneously by the detectors STEM (Scanning Transmission) in darkfield and brightfield, EDX (X analysis), ELS / GIF (energy loss spectrometry / energy filtering). ), HAADF (atomic number contrast), video camera or CCD, and be viewed on the same screen.

The spatial resolution of the Tecnai F 20 ST in "High Resolution" mode (HRTEM) is 0.24nm, while it is 0.16nm in "High Resolution Sweep" mode (HRSTEM / HAADF). This microscope thus makes it possible to directly visualize, in many cases, the atomic columns of the materials.

      
Self-assembled nanoporous "cérine-silice" catalyst (col.J.Y.Chane-Ching, RHODIA)

 

This device, equipped with a field emission gun (FEG), is particularly well suited to EDX elementary chemical analysis, including light elements thanks to a very fine and very bright electronic probe, which allows to probe materials. at the nanometer scale.

Thanks to an excellent energy resolution (0.65eV), the Electron Energy Loss Spectrometry (ELS), in addition to the basic chemical dosing, gives access to the chemical bond and, in some cases, to the measurement of local properties (dielectric function, optical indices). Coupled with a system of filtering energy (GIF), as is the case on our microscope, it allows to acquire chemical maps in real time.

Expertise

The Tecnai F 20 ST is a versatile device that perfectly meets the current demands of biologists and material physicists, but whose main characteristics are focused on elemental chemical analysis at the nanoscale. Regarding applications in Materials Science, it was chosen to meet the current demands of the Materials Center while allowing to address the materials of tomorrow. In liaison with the researchers of the laboratory and our external partners, this microscope plays and will play a determining role in the following lines of research :

  • Development of new alloys
  • Structure and properties of the interfaces
  • Corrosion and protection of materials
  • Assemblies and multimaterials
  • Nanomaterials
  • Biomaterials
Fielfd of activity
  • Energy
  • Automobile
  • Aeronautics
  • Space
  • Chemistry
  • Microelectronic
  • Environment
  • Iron and steel industry, etc.

Particles of TiO2 on a carbon nanotube ; photocatalytic application
(col. S Bonnamy CNRS Orleans

Image of silicon, filtered in energy on a transistor gate
(col. ST Microelectronics)

Chemical image of Cr in a thermal barrier system
(col. SNECMA, groupe SAFRAN)

 

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Transmission electron microscope FEI Tecnaï G2 30T

Responsable

Loïc Nazé

General context

"Conventional" transmission electron microscopy, which allows diffraction analysis of crystallographic structures and imaging and analysis of dislocation microstructures in crystalline materials, has been used at the Materials Center since its inception. Several transmission electron microscopes particularly adapted to mechanical metallurgy activities have thus succeeded the CdM before the recent acquisition of Tecnai 30T operating at 300 kV.

The microscope

The configuration of the microscope has been chosen to allow observation and analysis of microstructures ― in particular deformation microstructures ― of metal alloys (Nickel-based superalloys, steels, titanium-based alloys, aluminum alloys or Copper, etc.) for which the configuration of Tecnai F20ST is not optimized.

Thus, the characteristics of the LaB6 cathode thermoelectronic emission gun and the "Twin" objective lens, which leaves space for the use of a goniometric plate with large inclination angles, are particularly suitable for analysis. exhaustive of crystalline defects (dislocations, stacking faults) and the description of the dislocation microstructures in the samples taken from the specimens experimentally deformed in creep, stress relaxation, traction, fatigue (...) at the Centre des Matériaux. The configuration of this microscope lends itself particularly well to dark diffraction contrast imaging in weak beam ("weak beam") dislocations.

figure 1 : strain deformation microstructure
at 700 °C under 650MPa
(dislocations et fautes d'empilement) dans le superalliage AD5 (champ clair)

figure 2 : dislocations in Ti-6242 alloy deformed at stress
relaxation at 400 °C ("weak beam")

The wide inclination amplitudes of the sample allowed by the goniometric stage, equipped with a "double tilt-rotation" object-holder, make it possible to reconstruct stereographic projections of the crystallographic structures of the precipitated phases that are sought. to identify.

figure 3 : cliché de diffraction d'axe de zone <100> de la matrice
et des précipités γ' et γ" dans le superalliage In718

In addition, the 300 kV acceleration voltage of the electron gun makes it possible to work comfortably on relatively thick areas of thin nickel-base alloys or elements of this atomic mass range (Iron, Copper, Cobalt, etc.)..

The Tecnai 30T is devoid of chemical analysis equipment but the total compatibility between its goniometric stage and that of Tecnai F20ST allows, when the chemical analysis of a phase observed ― and possibly analyzed in diffraction ― on the Tecnai 30T it is necessary to transfer the sample from one microscope to another without having to change the microscope and, as a result, risk losing the position of the observed zone. It is then possible to quickly carry out the desired chemical analyzes on Tecnai F20ST before eventually returning to complete his exams on Tecnai 30T.

Expertise

The Tecnai 30T is particularly suitable for studies of deformation microstructures and precipitation microstructures in metal alloys based on relatively heavy elements. The observations and analyzes carried out on this microscope are essential in the research activities related to the following themes :

  • Development of new metal alloys (Superalloys, Intermetallic Alloys)
  • Metallurgical optimization of superalloys by selection of heat treatment ranges
  • High temperature mechanical behavior of metal alloys

figure 4 : precipitated γ' in an experimental microstructure
N19 superalloy (dark field)

figure 5 : microstructure in alloy Ti2AlNb - S12
(bright field)
Field of activity
  • Aeronautics - Space
  • Automobile
  • Energy

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Transmission Electron Microscopy (TEM) - MINES ParisTech
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