Templated Self-assembly of Sub-10-nm Quantum Dots
Patterned templates can guide the self-assembly of nanoparticles into ordered arrays [1]. Our motivation in pursuing templated self-assembly is to develop a robust method for the creation of ordered structures at length scales below ten nanometers. The basic process entails creating surface-relief templates via electron-beam lithography and spin-coating a suspension of colloidal nanoparticles onto the template. These templates were created either via metal evaporation and lift-off, or direct fabrication through the negative resist hydrogen silsesquioxane (HSQ). As the solvent evaporates, the quantum dots self-assemble primarily through the capillary forces created by the dewetting of the template [2].
We demonstrated this technique at sub-10–nm-length scales by spin-coating a solution of organically-capped CdZnS semiconducting quantum dots [3] onto nanopatterned grating structures on silicon substrates. We observed the geometric confinement of the quantum dots via physical templating and capillary forces into well-ordered monolayer aggregates with defined lattice orientations. While recent research has demonstrated the ability to self-assemble sub-10 nm metallic nanoparticles via capillary forces into physical templates of similar size [2], this work is unique in demonstrating lattice orientation control via physical templating at sub-10-nm-length scales.
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- Figure 1: Scanning electron micrograph of a self-assembled quantum dot monolayer on a silicon substrate with lines formed by hydrogen silsesquioxane, on which 8-nm CdZnS quantum dots have self-assembled.
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- Figure 2: Image analysis of the template-imposed ordering. Superimposed on the image are the positional networks of selected areas. The templated areas (blue) clearly show positional ordering, while the untemplated regions (red) exhibit little ordering.
References
- Y. Yin, Y. Lu, B. Gates, and Y. Xia, “Template-Assisted Self-Assembly: A Practical Route to Complex Aggregates of Monodispersed Colloids with Well-Defined Sizes, Shapes, and Structures,” J. Am. Chem. Soc., vol. 123, pp. 8718-8729, 2001. [↩]
- J.A. Liddle, Y. Cui, and P. Alivisatos, “Lithographically directed self-assembly of nanostructures,” J. Vac. Sci. Technol. B., vol. 22, no. 6, pp. 3409-3414, Nov/Dec 2004. [↩] [↩]
- B. Fisher, J. M. Caruge, D. Zehnder, and M. Bawendi, “Room-Temperature Ordered Photon Emission from Multiexciton States in Single CdSe Core-Shell Nanocrystals,” Phys. Rev. Lett., vol. 94, p. 087403, 2005. [↩]
Filed under: Nanotechnology |
Tags: joshua leu, karl berggren, vladimir bulovic
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