The nanospheres of cadmium sulfide were prepared in the laboratories of Paul Alivisatos, Berkeley Lab's Deputy Director and Division Director of MSD, and a member of UC Berkeley's MSE and Chemistry Departments. The chemical methods used to create the hollow spheres allow their dimensions to be manipulated with great precision, including the outer diameter of the spheres and the thickness of the shells.
"Essentially we're investigating structural hierarchy, which is known to play an important role in determining the strength of many bulk materials bone, for example only here we're applying it on the nanoscale," says Minor. "In this case the hierarchy is the size of the crystal domains, from three or four nanometers up to 10 nanometers; the thickness of the shells, from 35 to 70 nanometers; and the diameter of the spheres, from about 200 to 450 nanometers. We experimented on dozens of nanospheres with variations in each of these dimensions."
What they observed as the diamond anvil slowly bore down on the hollow nanospheres was that the spheres gradually bulged at the sides as they were squashed. Cadmium sulfide is inherently brittle and might have been expected to break easily, but instead the spheres deformed by as much as 20 percent of their original diameter before they shattered.
To understand the distribution of stresses throughout the sphere, Daryl Chrzan of MSD and MSE and his research group performed theoretical calculations. The sphere was computationally divided into a fine grid and the deformation for each grid element was calculated, giving the reaction to the applied force for the overall geometry of the sphere
|Contact: Paul Preuss|
DOE/Lawrence Berkeley National Laboratory