Strain-dependent photoluminescence behavior in three geometries of CdSe/CdS nanocrystals Page: 2 of 21
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In recent years, a new generation of quantum confined colloidal semiconductor
structures has emerged, with more complex shapes than simple quantum dots1' 2. These
include nanorods3 and tetrapods4. Beyond shape, it is also now possible to spatially vary
the electron and hole potentials within these nanoparticles by varying the composition.
Examples of these new structures include seeded dots, rods, and tetrapods, which
contain a CdSe core embedded within a CdS shell5'6. These structures may have many
uses beyond those envisioned for simple quantum dots, which are frequently employed
in luminescent applications7. This paper is concerned with changes in the optoelectronic
properties of tetrapods when the arms are bent. We demonstrate that seeded tetrapods
can serve as an optical strain gauge, capable of measuring forces on the order of
nanonewtons. We anticipate that a nanocrystal strain gauge with optical readout will be
useful for applications ranging from sensitive optomechanical devices to biological force
A tetrapod nanocrystal consists of a central core with four arms branching out at the tetrahedral
angle4. We have previously shown a few ways in which tetrapod arms can be bent. For
instance, when a CdTe tetrapod (4 nm wide and 100 nm long arms) is deposited on a substrate
through solvent evaporation, the fluid exerts a capillary force which pulls the tetrapod towards
the substrate, in some cases permanently deforming the arms8. Salmeron and coworkers used
an atomic force microscope to press on the outward-projecting arms of surface-immobilized
CdTe tetrapods, and have shown that for forces below 100 nN, the tetrapod flexes elastically9.
Motivated by these observations, Wang and coworkers calculated the electronic level structure
of a CdTe tetrapod with different degrees of arm bending, induced by nanonewton forces, and
predicted a red-shift of the energy gap with increasing strain.
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Choi, Charina L; Koski, Kristie J; Sivasankar, Sanjeevi & Alivisatos, A Paul. Strain-dependent photoluminescence behavior in three geometries of CdSe/CdS nanocrystals, article, May 26, 2009; Berkeley, California. (https://digital.library.unt.edu/ark:/67531/metadc1013869/m1/2/: accessed April 25, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.