The fundamental properties of electrons in the prototypical n-type oxide nanocrystal, Al³⁺-doped ZnO, have been studied at both the ensemble and single-particle levels by spectroscopic and electron force microscopic techniques. We developed and implemented a new synthetic methodology that enables the tunable incorporation of Al³⁺ in the ZnO nanocrystal in an “etching–regrowth–doping” (ERD) strategy in a single-pot reaction. The ensemble-averaged properties and evolution of the Al³⁺ speciation in ZnO were studied using electronic absorption spectroscopy and powder X-ray diffraction and reveal the successful substitution of Al³⁺ only after implementation of the ERD strategy. Characterization of individual ZnO, surface Al³⁺-doped ZnO, and internal Al³⁺-doped ZnO nanocrystals using electrostatic force microscopy reveals strong responses in both the quantity of surface charges and electron polarizabilities, which are dependent on the amount of Al³⁺ in the ZnO lattice. These results appear to suggest that an upper limit to the electron polarizability exists for Al³⁺-doped ZnO nanocrystals.

中文翻译：

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n型Al掺杂ZnO中表面电荷的直接证据

已通过光谱和电子力显微镜技术研究了典型n型氧化物纳米晶体Al ³⁺掺杂的ZnO中电子的基本性质。我们开发并实施了一种新的合成方法，该方法可通过单罐反应中的“蚀刻—再生—掺杂”（ERD）策略以可调节的方式将Al ³⁺掺入ZnO纳米晶体中。使用电子吸收光谱和粉末X射线衍射研究了ZnO中Al ^3+的总体平均性质和演化，并揭示了仅在实施ERD策略后才能成功替代Al ³⁺。单个ZnO，表面Al ^3+的表征静电力显微镜观察掺杂的ZnO和内部掺杂有Al ^3+的ZnO纳米晶体在表面电荷量和电子极化率方面均显示出强响应，这取决于ZnO晶格中Al ³⁺的量。这些结果似乎表明，对于Al ³⁺掺杂的ZnO纳米晶体，存在电子极化率的上限。