Steiner Dov, Dorfs Dirk, Banin Uri, Della Sala Fabio, Manna Liberato, Millo Oded
Racah Institute of Physics, the Center for Nanoscience and Nanotechnology, The Hebrew University of Jerusalem, Jerusalem 91904, Israel.
Nano Lett. 2008 Sep;8(9):2954-8. doi: 10.1021/nl801848x. Epub 2008 Aug 9.
The ability to tailor the properties of semiconductor nanocrystals through creating core/shell heterostructures is the cornerstone for their diverse application in nanotechnology. The band-offsets between the heterostructure components are determining parameters for their optoelectronic properties, dictating for example the degree of charge-carrier separation and localization. So far, however, no method was reported for direct measurement of these factors in colloidal nanocrystals and only indirect information could be derived from optical measurements. Here we demonstrate that scanning tunneling spectroscopy along with theoretical modeling can be used to determine band-offsets in such nanostructures. Applying this approach to CdSe/CdS quantum-dot/nanorod core/shell nanocrystals portrays its type I band structure where both the hole and electron ground state are localized in the CdSe core, in contrast to previous reports which predicted electron delocalization. The generality of the approach is further demonstrated in ZnSe/CdS nanocrystals where their type II band alignment, leading to electron-hole separation, is manifested.
通过创建核/壳异质结构来定制半导体纳米晶体性质的能力是其在纳米技术中实现多种应用的基石。异质结构组件之间的带隙是决定其光电性质的参数，例如决定着电荷载流子的分离和定位程度。然而，到目前为止，尚未有关于直接测量胶体纳米晶体中这些因素的方法的报道，只能从光学测量中获得间接信息。在此，我们证明扫描隧道光谱法结合理论建模可用于确定此类纳米结构中的带隙。将该方法应用于CdSe/CdS量子点/纳米棒核/壳纳米晶体，描绘出其I型能带结构，其中空穴和电子基态都定域在CdSe核中，这与之前预测电子离域的报道相反。该方法的通用性在ZnSe/CdS纳米晶体中得到了进一步证明，其中表现出导致电子-空穴分离的II型能带排列。
