Hi,
Microscopic investigations revealed good disperse of the nanofibers in the preform.
My suggestion was: Microscope inspection showed a good distribution of nanofibers in the preform.
Do you see a difference between "microscopic investigations" and "microscopic inspection"? Or do you reject the former term entirely?
'Microscopic' sounded a bit to me like it suggested 'tiny' (He has a microscopic brain. His chances of marrying me are microscopic. ), so I favoured 'Microscope'. ' . . . by microscope' also seems reasonable.
'Investigation' sounded like an elaborate search for an answer. I thought they probably just took a look at it, so I suggested 'inspection'. However, perhaps the required technology is more elaborate,. I don't really understand it.
Best wishes, Clive