Have we ever seen an atom? If not, how do we know they exists?

Question

Question is what exactly title says that have we ever seen an atom through any means (microscopes/equipments.etc)? If not, how do we know they exists?

Answer 1

Scanning tunneling microscopes can "see" atoms. Here is a 2008 issue of Nature magazine:

What you're really seeing here is an electrical equipotential surface, which is close enough to being a solid surface for most purposes. A scanning tunneling microscope (or the similar atomic force microscope) is like a very precise phonograph; it traces over a surface and senses the atomic-scale bumps in a surface. It's not too much inference to assume that the atomic-scale bumps are really atoms. The colors are added though; any atom is smaller than a wavelength of visible light.

How did we know atoms existed before that? Well, that's quite a story, and Wikipedia probably tells it better than I can.