Electron Microscopy Unit - Case Studies

Electron microscopy has become a key characterisation tool since it provides structural, chemical and morphological information of a wide range of nanomaterials and nanostructures. Recent developments in both scanning and transmission electron microscopes have dramatically improved their image and nanoanalysis capabilities, making feasible for instance the day-to-day study of crystallographic periodicity of structures at the atomic level and the study of high-vacuum incompatible specimens by SEM working in environmental mode, among others.

Since the installation of the equipment in 2012, a wide variety of studies have been performed in the Electron Microscopy unit. Here we show some representative examples:

CASE STUDY 1: IN-SITU GROWTH OF ICE IN THE ESEM

Controlling the freezing of water to form ice crystals has many with snow producing aim but also in ice formation prevention such as food industry, machinery protection, preservation of biological samples, among others.

We are able to in-situ grow ice in the FEI Quanta 650F by a careful control of temperature and humidity conditions using a Peltier cell.

in-situ grow ice in the FEI Quanta 650F
Sample courtesy: Albert Verdaguer (ICMAB-CSIC)

CASE STUDY 2: DETERMINATION OF THE ELEMENTAL DISTRIBUTION OF CORE-SHELL NANOPARTICLES BY STEM-EELS

Using STEM-EELS we have been able to determine the location of Fe2O3 and Mn2O3 in core-shell nanoparticles of less than 20 nm in size.

Elemental distribution of core-shell nanoparticles by STEM-EELS
Sample courtesy: Alejandro Gómez i Josep Nogués (Magnetic Nanostructures Group)

CASE STUDY 3: CHEMICAL STUDY OF FUNCTIONAL GRAPHENE

EELS proves useful to detect the chemical composition of functionalized graphene samples. As an example, the EELS spectrum of amine-functionalized dodecahydrocloso-dodecaborate (B12) anions grafted on graphene oxide is shown here, where energy loss peaks with onsets at 188 eV, 284 eV, 401 eV and 532 eV correspond respectively to B, C, N and O contained in the sample.

CHEMICAL STUDY OF FUNCTIONAL GRAPHENE

Besides, mapping the K-ionization edges of B and C by Energy Filtered TEM (EFTEM) we can observe that carbon is found both on the graphene flake and the carbon support film, whereas the boron map only shows bright intensity on the graphene flake, proving the successful functionalization of the flake and the homogeneous distribution of the functional moieties.

graphene flakes

CASE STUDY 4: INTERACTION OF CARBON NANOTUBES WITH CELLS

Investigation of the ability of amino-functionalized multi-walled carbon nanotubes (MWNTs-NH3+) to cross the Blood-Brain Barrier (BBB) has been carried out by low voltage STEM imaging. Solid evidence using electron microscopy for each step of the transcytosis process.

amino-functionalized multi-walled carbon nanotubes crossing the Blood-Brain Barrier
Translocation of individual MWNTs-NH3+ across porcine brain endothelial cells membrane.
Image acquired using the STEM detection system on the Magellan HRSEM at 20 kV

CASE STUDY 5: STUDY OF FLAKE SIZES IN 2D MATERIALS BY HRSEM

The Magellan XRSEM can be operated at low voltages with excellent resolution, which provides surface-sensitive images as those required for imaging graphene flakes. Graphene can be indeed be studied deposited not only on conducting substrates but also on non-conducting surfaces, such as silicon oxide. The beam deceleration mode together with the use of a backscattered electron detector is used to image non-conducting samples.

Graphene flakes
Graphene flakes deposited on a silicon wafer studied in the Magellan 400L