Understanding the surface of semiconductor nanocrystals (NCs) prepared using colloidal methods is a long-standing goal of paramount importance for all their potential optoelectronic applications, which remains unsolved largely because of the lack of site-specific physical techniques. Here, we show that multidimensional ¹¹³Cd dynamic nuclear polarization (DNP) enhanced NMR spectroscopy allows the resolution of signals originating from different atomic and magnetic surroundings in the NC cores and at the surfaces. This enables the determination of the structural perfection, and differentiation between the surface and core atoms in all major forms of size- and shape-engineered CdSe NCs: irregularly faceted quantum dots (QDs) and atomically flat nanoplatelets, including both dominant polymorphs (zinc-blende and wurtzite) and their epitaxial nanoheterostructures (CdSe/CdS core/shell quantum dots and CdSe/CdS core/crown nanoplatelets), as well as magic-sized CdSe clusters. Assignments of the NMR signals to specific crystal facets of oleate-terminated ZB structured CdSe NCs are proposed. Significantly, we discover far greater atomistic complexity of the surface structure and the species distribution in wurtzite as compared to zinc-blende CdSe QDs, despite an apparently identical optical quality of both QD polymorphs.

中文翻译：

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使用动态核极化增强 PASS-PIETA NMR 光谱解析 CdSe 量子点和纳米片的核心和表面

了解使用胶体方法制备的半导体纳米晶体 (NC) 的表面是对其所有潜在光电应用至关重要的长期目标，这主要是由于缺乏特定位置的物理技术而仍未解决。在这里，我们展示了多维¹¹³Cd 动态核极化 (DNP) 增强核磁共振波谱允许解析源自 NC 核心和表面的不同原子和磁性环境的信号。这可以确定结构完美，以及在所有主要形式的尺寸和形状工程 CdSe NCs 中区分表面和核心原子：不规则面量子点 (QDs) 和原子平面纳米片，包括两种主要的多晶型物（锌- blende 和纤锌矿）及其外延纳米异质结构（CdSe/CdS 核/壳量子点和 CdSe/CdS 核/冠纳米片），以及神奇大小的 CdSe 簇。提出了将 NMR 信号分配给油酸封端 ZB 结构的 CdSe NCs 的特定晶面。显着地，