Influence of the Ion Coordination Number on Cation Exchange Reactions with Copper Telluride Nanocrystals

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• 作者：Renyong Tu ; Yi Xie ; Giovanni Bertoni ; Aidin Lak ; Roberto Gaspari ; Arnaldo Rapallo ; Andrea Cavalli ; Luca De Trizio ; Liberato Manna
• 刊名：Journal of the American Chemical Society
• 出版年：2016
• 出版时间：June 8, 2016
• 年：2016
• 卷：138
• 期：22
• 页码：7082-7090
• 全文大小：646K
• 年卷期：0
• ISSN：1520-5126

文摘

Cub>2–xb>Te nanocubes were used as starting seeds to access metal telluride nanocrystals by cation exchanges at room temperature. The coordination number of the entering cations was found to play an important role in dictating the reaction pathways. The exchanges with tetrahedrally coordinated cations (i.e., with coordination number 4), such as Cd²⁺ or Hg²⁺, yielded monocrystalline CdTe or HgTe nanocrystals with Cub>2–xb>Te/CdTe or Cub>2–xb>Te/HgTe Janus-like heterostructures as intermediates. The formation of Janus-like architectures was attributed to the high diffusion rate of the relatively small tetrahedrally coordinated cations, which could rapidly diffuse in the Cub>2–xb>Te NCs and nucleate the CdTe (or HgTe) phase in a preferred region of the host structure. Also, with both Cd²⁺ and Hg²⁺ ions the exchange led to wurtzite CdTe and HgTe phases rather than the more stable zinc-blende ones, indicating that the anion framework of the starting Cub>2–xb>Te particles could be more easily deformed to match the anion framework of the metastable wurtzite structures. As hexagonal HgTe had never been reported to date, this represents another case of metastable new phases that can only be accessed by cation exchange. On the other hand, the exchanges involving octahedrally coordinated ions (i.e., with coordination number 6), such as Pb²⁺ or Sn²⁺, yielded rock-salt polycrystalline PbTe or SnTe nanocrystals with Cub>2–xb>Te@PbTe or Cub>2–xb>Te@SnTe core@shell architectures at the early stages of the exchange process. In this case, the octahedrally coordinated ions are probably too large to diffuse easily through the Cub>2–xb>Te structure: their limited diffusion rate restricts their initial reaction to the surface of the nanocrystals, where cation exchange is initiated unselectively, leading to core@shell architectures. Interestingly, these heterostructures were found to be metastable as they evolved to stable Janus-like architectures if annealed at 200 °C under vacuum.