Insights into the Self-Assembly of Ferecrystalline Compounds from Designed Amorphous Precursors

Transition metal dichalcogenides, TSe2 with T = V, Ti, and Ta, were synthesized through self-assembly of designed amorphous precursors. All three compounds formed with the expected layered transition metal dichalcogenide structure with highly preferred orientation of the TSe2 layers aligned parallel with the substrate surface. VSe2 and TiSe2 self-assembled as the 1T polytype, which is the only known polytype found in the bulk form, while TaSe2 self-assembled into a new turbostratically disordered polytype. This turbostratic disorder is common among compounds made by self-assembly of designed amorphous precursors, also known as the modulated elemental reactant synthetic approach. The data obtained in this study on the formation of transition metal dichalcogenides suggest that templated nucleation at interfaces is the self-assembly growth mechanism that produces crystallographic alignment between structural units. If there is only one potential low energy orientation for the templated nucleation of the next layer, then a crystalline polytype is formed. If there is more than one low energy orientation for the templated nucleation of the next layer, a disordered polytype, referred to as a ferecrystal, is formed.