  We have investigated the formation of dust in the ejecta of Type II
supernovae (SNe), mostly of primordial composition, to answer the question of
where are the first solid particles formed in the universe. However, we have
also considered non-zero progenitor's metallicity values up to Z=Zsun. The
calculations are based on standard nucleation theory and the scheme has been
first tested on the well studied case of SN1987A, yielding results that are in
agreement with the available data. We find that: i) the first dust grains are
predominantly made of silicates, amorphous carbon (AC), magnetite, and
corundum; ii) the largest grains are the AC ones, with sizes around 300 A,
whereas other grain types have smaller radii, around 10-20 A. The grain size
distribution depends somewhat on the thermodynamics of the ejecta expansion and
variations in the results by a factor ~ 2 might occur within reasonable
estimates of the relevant parameters. Also, and for the same reason, the grain
size distribution, is essentially unaffected by metallicity changes. The
predictions on the amount of dust formed are very robust: for Z=0, we find that
SNe with masses in the range (12-35) Msun produce about 0.08 Msun < M_dust <
0.3 Msun of dust/SN. The above range increases by roughly 3 times as the
metallicity is increased to solar values. We discuss the implications and the
cosmological consequences of the results.
