The growth and surface structures of ultrathin chromia (Cr2O3) films on Cu(111), Co(0001), and on thin graphene/graphitic carbon films on Co(0001) have been investigated, and compared to epitaxial chromia films grown on Al2O3(0001). On metallic substrates, chromia grows with strong texture along the (0001) direction with little mosaic spread. On cobalt, a thin interfacial oxide is observed, which is stable upon exposure to ambient or annealing in ultrahigh vacuum. In the case of chromia growth on graphite, chromia-catalyzed oxidation and etching of the carbon layers is observed above 800 K in ultra high vacuum. The results show that highly ordered and continuous, ultrathin films of chromia (Cr2O3) can be grown on a variety of substrates and that magnetic tunnel junction structures, based on the magnetoelectric chromium oxide, may be built from the "bottom up".