ruthenium staining

In the backscattered electron imaging of high polymers using SEM, it is difficult to acquire a high contrast image because the atomic numbers of the constituent elements are close to each other. In such cases, a technique of Ruthenium (a heavy metal) staining of the specific components is used to obtain their high contrast images.
The staining is performed by immersing a specimen in a solution of ruthenium tetroxide or is placed in a vapor environment of the solution. Ruthenium has a high oxidizing ability and reacts with saturated hydrocarbon of polyolefin, etc. in high polymers. In particular, the amorphous region formed by the saturated hydrocarbon is stained. As a result, the number of backscattered electrons from the sites stained by ruthenium of heavy atomic number increases and thus, the specific sites (components) are clearly observed. Ruthenium tetroxide is highly volatile and it is very dangerous if an operator breathes the vapor of ruthenium tetroxide or contacts the solution on their skin. So when using ruthenium, it is requisite to wear gloves in a draft chamber under the guide of the Safety Data Sheet (SDS) issued by reagent manufacturers.

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