Electron Microscope Sample Preparation
Proper specimen preparation is an essential factor in achieving quality electron microscopy results. As such, specimen preparation is an important consideration for LVEM5 and LVEM25 imaging as well.
Sample Preparation for Transmission Electron Microscopy (TEM)
TEM sample thin-sectioning of bulk materials (Polymers, biological thin sections)
Some materials will need to be thinned down (sectioned with an ultramicrotome) before they can be imaged in TEM mode. The LVEM25 can work with thin sectioned material prepared as it would be for conventional TEM, at around 100nm. The LVEM5 performs best with thin sections in the range of 50 nm or thinner.
In our experience most materials can be prepared in this manner. If you question the ability to cut your sections at this level, please contact us so we can share our experiences with your sample types. If there is any remaining doubt we would be happy to receive a block from you so that we may test the sectioning and imaging of your samples.
TEM Sample Staining
Many samples lack the inherent density differences necessary to provide adequate contrast using traditional TEM. Stains (heavy metals compounds such as uranyl acetate or lead citrate) are added to the samples in order to enhance the contrast. The benefit of staining is increased density gradients to the extent that traditional TEM can provide contrasted images. The drawbacks, aside from the additional preparation step and the fact that many stains are toxic, are staining artifacts (features that are not inherent to the sample but caused by stains), sample distortion (when staining leads to undesired changes in the sample) and may ruin the sample entirely.
The LVEM25 and LVEM5 require no staining of samples to achieve highly contrasted images. The reduced accelerating voltage leads to a greater degree of electron scattering so that even tiny density differences are resolved in the TEM image. The LVEM25 still does allow for staining as an option since there are instances where staining is desirable for diagnostic purposes.
TEM Grids for Bulk Materials (Polymers, Biological Thin Sections)
A variety of standard size (3mm diameter) TEM grids made of Cu, Ni, Mo or others, can be used on LVEM25 and LVEM5. Specialty grids (Si-based membranes, functionalized substrates etc) can also be used.
In order to keep the overall penetration volume to a minimum, we encourage the use of unsupported grids. The sample should be laid on a bare, 3mm standard TEM grid. Lacey or thin carbon support films are also acceptable.
TEM Grids for Particulate Materials (Nanoparticles, Nanotubes, Viruses, DNA)
This type of material can easily be deposited at the appropriate concentration onto a TEM grid with a carbon support.
Grids with a thin carbon support should be used where support is essential. Formvar support film is not recommended since it increases overall sample density and affects ultimate resolution.
Grids with active surfaces are available that can control how your sample interacts with the substrate. By matching the grid type to your sample, you can dramatically improve sample uniformity and coverage while eliminating sample preparation artifacts such as aggregation and drying effects.
Sample Preparation for Scanning Electron Microscopy (SEM)
SEM Sample Coating
The LVEM5 uses lower voltages, so it is well suited to image non-conductive samples. However, similar to conventional SEM, best results are obtained from conductive samples or samples that have been coated with a very thin conductive layer.
SEM Sample Size
Samples for SEM analysis must fit into the standard TEM grid holder and should be less than 1 mm in height. Samples are supported either by a TEM grid or LVEM5 SEM stubs.