Synthesis of InP Branched Nanostructures by Controlling the Intermediate Nanoclusters
Magic sized clusters (MSCs) are thermodynamically stable intermediate nanoclusters often captured during growth of semiconductor nanoparticles (NPs). To investigate the role of MSCs in the nucleation and growth to InP NPs and to find new ways to control the InP NP growth pathways, a kind of InP MSCs (386-MSCs) was used as a precursor to InP NPs. A series of heat-up syntheses using InP 386-MSCs were performed as varying the reaction conditions and extra additives. Upon heating, 386-MSCs underwent fragmentations before further evolutions. The fragmentations were significantly impeded by extra indium myristate complex and accelerated by extra fatty acids such as myristic acid. Co-use of the both resulted in InP branched nanostructures (BNSs) which include nanorods, pods, hyper-branched NSs and dendrimer-like NSs. Before reaching such BNSs, 2 nm sized spherical NPs and 4 nm tetrahedral seeds appeared as intermediates. Fragmentaions of 386-MSCs which have polytwistane crystal structure resulted in the 2 nm sized spherical NPs which are amorphous. In turn, the 2 nm NPs participated in the growth of BNSs of which final crystal structure is zinc-blende. The amorphous 2 nm NPs should be an intermediate in the crystal structure transformation or evolution to a phase more stable in bulk. In syntheses of anisotropic NSs, structure-directing agents are commonly used which typically bind selectively to particular crystal facets and promote anisotropic growths. Highly anisotropic InP structures such as various BNSs were obtained without using any structure-directing agent. This demonstrates that sophisticated controls over the growth pathways using MSCs offer novel NSs that cannot be attained by conventional synthetic protocols.