Given an arithmetic variety $f: X \rightarrow Spec(\mathbb{Z})$.

Is there a notion of boundedness for families of sheaves on $X$?

I only found the notion for families on the fibers of $f$. But i am interested in sheaves defined on $X$.

All definitions / theorems i found only work when $X$ is defined over some field $k$, where one has the Hilbert polynomial, slope etc, which we don't have in this case. Is there some substitute for these terms?

Or are there even results about moduli spaces of sheaves on arithmetic varieties?