Subject: What is the smallest possible average particle size for a powdered solid?

Is is possible to produce a separable solid powder in which the individual
particles are as small as a single atom or molecule?  If so, how, and please
give some examples, preferably at room temperature & pressure.  If not, what is
the lower limit for separable solid particle size and have any rules been
developed for estimating the minimum solid particle size for various materials
under various conditions. By "separable solid," I mean the particles can be
compressed together (even if only slightly) without bonding together chemically,
and are NOT gaseous, liquid or in a plasma.

Re: What is the smallest possible average particle size for a powdered solid?