The development of colloidal quantum dots has led to practical applications of quantum confinement, such as in solution-processed solar cells1, lasers2 and as biological labels3. Further scientific and technological advances should be achievable if these colloidal quantum systems could be electronically coupled in a general way. For example, this was the case when it became possible to couple solid-state embedded quantum dots into quantum dot molecules4,5. Similarly, the preparation of nanowires with linear alternating compositions—another form of coupled quantum dots—has led to the rapid development of single-nanowire light-emitting diodes6 and single-electron transistors7. Current strategies to connect colloidal quantum dots use organic coupling agents8,9, which suffer from limited control over coupling parameters and over the geometry and complexity of assemblies. Here we demonstrate a general approach for fabricating inorganically coupled colloidal quantum dots and rods, connected epitaxially at branched and linear junctions within single nanocrystals. We achieve control over branching and composition throughout the growth of nanocrystal heterostructures to independently tune the properties of each component and the nature of their interactions. Distinct dots and rods are coupled through potential barriers of tuneable height and width, and arranged in three-dimensional space at well-defined angles and distances. Such control allows investigation of potential applications ranging from quantum information processing to artificial photosynthesis.
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This work was supported by the US Department of Energy. Some high-resolution and analytical electron microscopy was performed at the National Center for Electron Microscopy (NCEM) with the help of E. C. Nelson and some low-resolution electron microscopy was performed at the Electron Microscope Laboratory at UCB with the help of M. Casula. For the theoretical calculations we used the National Energy Research Scientific Computing Center.
The authors declare that they have no competing financial interests.
TEM images of core/shell tetrapod shaped nanocrystals. (PDF 1330 kb)
Local EDS spectra of CdS/CdSe heterostructure. (PDF 25 kb)
XRD patterns of CdSe/CdTe heterostructures. (PDF 36 kb)
Length and diameter distributions of heterostructures. (PDF 27 kb)
Optical absorption spectra of heterostructures. (PDF 18 kb)
Additional high resolution TEM images of heterojunctions. (PDF 2618 kb)
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Milliron, D., Hughes, S., Cui, Y. et al. Colloidal nanocrystal heterostructures with linear and branched topology. Nature 430, 190–195 (2004). https://doi.org/10.1038/nature02695
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