Hot Injection Synthesis of Ultrathin Bi₂Se₃ Nanosheets With Controllable Dimensions

In this work, a synthesis method for colloidal nanoplatelets (NPLs) of the topological insulator ${\mathrm{Bi}}_2{\mathrm{Se}}_3$ is presented. This method is based on the hot injection of a bismuth precursor into a selenium solution to achieve precise control over both the thickness and lateral dimensions of the NPLs. Through time-resolved aliquot studies, three growth stages are identified: (i) an initial nucleation stage where "baby platelets" are formed, already having the final platelet thickness, (ii) a rapid, reaction-limited lateral growth phase, and (iii) a second lateral growth phase slowed down by precursor depletion. By adapting the reactivity of the bismuth precursor in the nucleation stage, the NPL thickness can be tuned from 7 to 1 quintuple layers, largely independent of lateral size. The NPL lateral dimensions can be altered by adjusting the growth time in stage (ii) or (iii), by adapting the injection temperature, or by injecting additional precursor once the slow growth stage has been reached. This synthesis method, combined with mechanistic insights, can be used to synthesize tailored platelets for future studies on topological insulators.