Transmission Electron Microscopy (TEM)

The TEM group of the LMA develops research lines in the area of Electron Microscopy applied to Material Science in close connection to the main INMA research activities:

• One is closely related to the “Nanomaterials” “Nanobiomedicine” and “Nanomaterials” research lines of INMA and concerns the study of nanosystems for physical biological or biological physical applications. The aim of the studies of these nano-objects is to establish correlations between the structures at the atomicnanometer scale of these nano-objets with their functional properties. The systems we are studying are magnetic and non-magnetic nanoparticles (metallic or oxide), semiconducting nanostructures, carbon and related nanotubes, graphene and other 2D materials, mesoporous compounds, semiconducting nanostructures, and biological materials.
• Another line of research is dedicated to the study of structural biology and molecular mechanisms of membrane protein complexes. As well as the signal transduction mediated by these protein complexes.
• Another line is focused on the Glycosylation of proteins and its role in disease
• Another important research line concerns the study of interfaces in heterostructures. This activity is closely related to works carried out in the “Physics of Nanosystems” research line of INMA. Our studies concern the study of structural properties (defects, epitaxy, strain) studied by Q-HRTEM and the chemistry and electronic structure of the interfaces investigated by the analysis of the EELS core loss fine structure of interfaces in thin films or multilayers of 3d metals and oxides (perovskite or spinel type).

Main research lines in this area:

• Magnetic materials
• Nanoparticles and nanomaterials
• Interfaces in heterostructures
• Carbon-based materials
• Soft Matter and electron sensitive materials
• Plasmonic and opto-electronic properties of materials
• Structure biology and signal transduction studies of membrane protein complexes
• Glycosylation of proteins and its role in disease

The TEM techniques that we are developing for these research lines are:

• Quantitative High Resolution TEM (Q-HRTEM)
• Energy Electron Loss Spectroscopy (EELS) performed at high spatial and energy resolution
• HRSTEM – HAADF
• Electron Holography
• Tomography
• Cryo TEM

Note that the two Titans G2 60-300 allows the study of carbon-based and related materials (graphene/2D materials, carbon nanotubes, fullerenes, nanodiamonds, carbon dots…) at low voltage with high resolution unavailable on other TEMs in Europe (and even around the world). That should be a major advantage of the LMA for the study of such materials sensitive to electron irradiation.

The other research lines are not so closely related to the main INMA ones, even if they should find applications in the “Nanobiomedicine”, “Nanomaterials” and “Physics of nanosystems” INMA activities:

One concerns the development of Electron Holography for mapping electrostatic, magnetic and strain fields. Electron Holography allows recovering the phase of the electron beam that has interacted with a thin TEM sample. Measuring the phase shift of that electron beam gives information about the local electrostatic potential and magnetic induction within the sample and about the surrounding stray fields. Thus, it is possible to measure locally and quantitatively these internal fields with a resolution of few nanometers. Moreover, when measuring the phase of diffracted beams one gets information about the local strain within the sample. It is then possible to locally correlate the structure and composition of a given material or nanosystem to the fields (magnetic, electrostatic and strain) associated to a specific structure. For instance, this is of great interest in the study of the magnetic properties of magnetic nanoparticles or thin films used for magnetic or spintronic applications, or the effect of strain in electronic devices.

Within the TEM activities on magnetic and spintronic nanosystems, another important topic that we tackle concerns the “in-situ TEM” experiments. Most of the electron holography and Lorentz experiments on magnetic materials are performed in the remnant state, while it is of great interest to study the magnetic device in more realistic conditions, i.e. under the application of an external magnetic field or even when an electric current flows through it. The aim of such development is to study the influence of local defects, interfaces, constrictions, etc. on the nucleation and propagation processes of magnetic domain walls at the nanometer scale on nano-objects.

Another research line that we develop concerns plasmonics. The capabilities of the two Titans in terms of energy resolution combined to the spatial resolution permit the study of the optical response of nanomaterials in the spectral range between 0.5 to 5 eV. Our purpose is the study of the optical properties of metallic nanomaterials focusing our work on the dependence of the plasmonic excitations with the size and shape of the nano-objects. In a second step, we will work on the plasmon interactions between neighbouring objects. The development of such studies is carried out in spectroscopic experiments both in EELS and also in Energy Filtered imaging mode (EFTEM), especially in the probe corrected and monochromated Titan.