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Single-step Superlatticed Nanorod Synthesis


  TEM images of superlattices formed through partial cation exchange. (A) The original 4.8–by–64-nm CdS nanorods. (B and C) Transformed CdS-Ag2S superlattices.  


  • Biological labeling /quantum dots
  • Solar cells
  • Light emitting diodes (LEDs)
  • Thermoelectric devices
  • Transistors


  • Single step, solution-phase fabrication
  • Low cost
  • Compatible with disparate environments
  • Materials display tunable shifts in photoluminescence
  • Produces superlattices with up to 12 layers


Nanorod Superlattices – nanometer sized crystalline rods made up of alternating layers of material – are highly valued for their potential to serve in a variety of nanodevices, including transistors, biochemical sensors and light-emitting diodes (LEDs).  Until now the potential of superlatticed nanorods has been limited by the relatively expensive and exacting process required to make them.

Paul Alivisatos and colleagues at Berkeley Lab and UC Berkeley have found a way to make nanorod superlattices through a single-step, chemical transformation of a colloid.  This colloidal method has the advantages of low-cost synthesis and compatibility of the particles with disparate environments.  A colloidal approach opens up the possibility of using the superlatticed nanorods in biological labeling, and in solution-processed LEDs and solar cells.  Previously, nanorod superlattices were made through a complex, vapor deposition process in which the rods were attached to a solid support. In the vapor deposition process, each layer of the superlattice must be grown sequentially, whereas the colloidal method can produce nanorod superlattices with up to twelve  layers. 

The researchers have demonstrated the application of strain engineering in a colloidal quantum-dot system by introducing a method that spontaneously creates a regularly spaced arrangement of quantum dots within a colloidal quantum rod.  A linear array of quantum dots within a nanorod effectively creates a one-dimensional superlattice.  The researchers demonstrated colloidal synthesis principles by converting a CdS nanorod into an Ag2S-CdS nanorod superlattice.

Today’s electronics industry is built on two-dimensional semiconductor materials that feature carefully controlled doping and interfaces. Tomorrow’s industry will be built upon one-dimensional materials, in which controlled doping and interfaces are achieved through superlatticed structures.  Formed from alternating layers of semiconductor materials with wide and narrow band gaps, superlattice structures not only can display outstanding electronic properties, but photonic properties as well.

Even though the colloidal nanorod superlattices form spontaneously, it should be possible to control their periodic pattern – hence their properties ­­– by adjusting the length, width, composition, etc., of the original nanocrystals.  However, much more work remains to be done before the colloidal method of fabricating superlatticed nanorods can match some of the “spectacular results” that have been obtained from vacuum fabrication.



Robinson, R.D., et al., Spontaneous Superlattice Formation in Nanorods Through Partial Cation Exchange. Science 317, 355 (2007)




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