In addition to the more elaborate sample-preparation methods, the following are also available:
Staining / contrast enhancement
Biological specimens and soft matter such as polymers or macromolecules consist mainly of light elements and therefore generate only weak amplitude contrast in the TEM. Staining with heavy-metal compounds, for example uranyl acetate, osmium tetroxide, ruthenium tetroxide or phosphotungstic acid, selectively attaches heavy atoms to particular structural features and locally increases electron scattering. Both negative staining (embedding the object in a heavy-metal film) and positive staining (selective binding to the structure) are used to reveal morphology and internal organisation that would otherwise remain invisible.
Epitaxy
For beam-sensitive organic materials, epitaxial crystallisation is used to prepare thin, well-oriented specimens. By crystallising the compound on a suitable oriented substrate, the nanocrystals adopt a common preferential orientation and form films thin enough for high-resolution imaging and electron diffraction.This oriented growth improves the quality and interpretability of the diffraction data and is particularly valuable for organic pigments and other molecular crystals.
Ultrasonic sprayer
Suspended nanoparticles and fine powders tend to re-agglomerate during conventional drop-casting, which leads to thick, overlapping deposits on the TEM grid. To avoid this, the sample is dispersed in ethanol and sprayed onto a carbon-coated copper grid using a modified ultrasonic sonifier (Hielscher UIS250v) equipped with a caved tip that holds the specimen dispersion. The ultrasonic vibration atomises the suspension into a fine mist; the droplets dry almost instantly on contact, which prevents re-agglomeration and yields grids with homogeneously distributed, well-separated particles which is an ideal starting point for electron microscopy and electron diffraction. The method was described for the structure solution of BaSO4 nanocrystals in: E. Mugnaioli, T. Gorelik and U. Kolb, Ultramicroscopy 109, 58–765 (2009).