Chae Byeong Gyu, Lee Jun Ho, Park Seongyong, Lee Eunha, Kwak Chang Min, Jafari Majid, Jeong Young Kyu, Park Chan Gyung, Seol Jae Bok
Department of Materials Science and Engineering , POSTECH , Pohang 37673 , South Korea.
Analytical Engineering Group , Samsung Advanced Institute of Technology , Suwon 16678 , South Korea.
ACS Nano. 2018 Dec 26;12(12):12109-12117. doi: 10.1021/acsnano.8b05379. Epub 2018 Nov 28.
Synthesizing semiconductor nanoparticles through core/shell structuring is an effective strategy to promote the functional, physical, and kinetic performance of optoelectronic materials. However, elucidating the internal structure and related atomic distribution of core/shell structured quantum dots (QDs) in three dimensions, particularly at heterostructure interfaces, has been an overarching challenge. Herein, by applying complementary analytical techniques of electron microscopy and atom probe tomography, the dimensional, structural, topological, and compositional information on commercially available 11.8 nm-sized CdSSe/ZnS QDs were obtained. Systematic experiments at high resolution reveal the presence of a 1.8 nm-thick Cd Zn S inner shell with a composition gradient between the CdSe core and the ZnS outermost shell. More strikingly, the inner shell shows compositional variation because of competitive atomic configuration between Cd and ZnS, but it structurally retains a zinc-blende crystal structure with the core. The inner shell may grow through the decreased reactivity of S with Cd, followed by atomic diffusion-related processes. The composition-competitive gradient inner shell alleviates lattice misfit strain at heterostructure interfaces, thereby enhancing the quantum yield and photostabilty to a greater extent than those of other single-shell structures. Thus, this precise measurement approach could offer a potential pathway to develop a wide variety of three-dimensional core/shell-structured materials.
通过核/壳结构合成半导体纳米颗粒是提高光电子材料功能、物理和动力学性能的有效策略。然而，阐明核/壳结构量子点（QD）在三维空间中的内部结构和相关原子分布，特别是在异质结构界面处，一直是一个首要挑战。在此，通过应用电子显微镜和原子探针断层扫描的互补分析技术，获得了市售11.8nm尺寸的CdSSe/ZnS量子点的尺寸、结构、拓扑和成分信息。高分辨率的系统实验揭示了存在一个1.8nm厚的Cd Zn S内壳，其在CdSe核和ZnS最外壳之间具有成分梯度。更引人注目的是，由于Cd和ZnS之间的竞争性原子构型，内壳显示出成分变化，但在结构上它与核保持闪锌矿晶体结构。内壳可能通过S与Cd反应性的降低，随后是与原子扩散相关的过程而生长。成分竞争梯度内壳减轻了异质结构界面处的晶格失配应变，从而比其他单壳结构更大程度地提高了量子产率和光稳定性。因此，这种精确的测量方法可以为开发各种三维核/壳结构材料提供一条潜在途径。
