stability - Is a single carbon atom stable?

It is well known that single atom of oxygen is not stable, and it forms $\ce{O2}$ molecule. But elements like carbon form a network of repeated bonds. As answered in another question, last atoms in such network are unstable and need to create some bonds.

Is it possible to have a (free-standing) single atom of carbon? Stable in the form of a stable powder like graphite or diamond.

If not, what is the minimum size of a carbon particle (diamond or graphite network)?

Further Clarification: I meant normal chemical stability to have a powder material at room temperature. I do not mean highly reactive carbon, quickly turning into a compound.