Phase stabilities of ternary rare earth metal disilicides

Chen et al. recently carried out self-assembled growth of epitaxial sub-10 nm erbium disilicide (C32, hP3) nanowires on Si(001). They pointed out that the success of this self-assembly process is due to asymmetric lattice mismatches in the two orthogonal crystallographic directions of the two materials, i.e. [0001]ErSi2/[110]Si,+6.5% and [1120]RESi2/[110]Si,-1.3%. In this paper, we have established experimentally that (Er1-xGdx)Si2 and (Er1-xSmx)Si2 exist with values of x from 0 to 1 and that their lattice parameters follow Vegard’s law. Since the binary GdSi2 and SmSi2 end members in each of these ternary systems have a and c unit cell parameters greater than those of the ErSi2 end member, we have determined that an optimal lattice mismatch can be achieved with the Si substrate at a composition of (Er0.45Gd0.55)Si2 and (Er0.62Sm0.38)Si2. It is reasonable to expect a higher quality of self-assembled nanowire growth on Si by employing these ternary silicides. A review of the atomic sizes of the rare earth metal elements of the lanthanide series indicates that many of the binary disilicides, when exhibiting the C32 structure, should have a tendency to form ternary and higher-order disilicides. These materials would offer many possibilities for the growth of silicide nanowires with interesting electronic, magnetic and optical properties.