  When Mg metal burns in air the resulting rock-salt MgO smoke consists of
perfect [100] cubes of about 100 nm. On contrast, we found that intensification
of self-burning of Mg micropowder either by injecting it into oxy-hydrogen
diffusion flame or under an infrared laser beam switches the growth mechanism
producing mostly single-crystalline spheres and terraced nanoparticles. MgO
molecule condensation onto primary spherical nanoparticles can account for
generation of terraced nanoparticles with regular steps proportional to the
nanoparticle size.
