Question

what is a electron microscope? who invented this? why it is invented?

Answer 1

An electron microscope consists of an electron gun which fires high speed electrons to the target specimen, which is to be viewed. The electron beam is accelerated using a positive potential and can be focussed using magnetic lenses. They can provide surprisingly high magnifications on screen and even topographical details.
The electron microscope was invented by the German scientists, Max Knoll and Ernst Ruska in 1931.
Dual behaviour of matter proposed by de Broglie led to the discovery of electron microscope often used for the highly magnified images of biological molecules and other type of material.