IKZ SEM Measurements

[budschi]

Here we collect the tasks for IKZ_SEM schemas
@kernke

[budschi]

@kernke next steps:

• define EM Experiment in a data revision: sample preparation steps, measurements
• review data revisions for SEM and EDX by Sabine

After this we can start implementing the custom yaml schemas and I can check which sample preparation steps we can reuse from already defined other user schemas.