Drndic and her research team, through a combination of imaging techniques, have shown that clustering these nanorod semiconductors greatly increases their total "on" time in a kind of "campfire effect." Adding a rod to the cluster has a multiplying effect on the "on" period of the group.
"If you put nanorods together, if each one blinks in rare short bursts, you would think the maximum 'on' time for the group will not be much bigger than that for one nanorod, since their bursts mostly don't overlap," Novikov said. "What we see are greatly prolonged 'on' bursts when nanorods are very close together, as if they help each other to keep shining, or 'burning.'"
Drndic's group demonstrated this by depositing cadmium selenide nanorods onto a substrate, shining a blue laser on them, then taking video under an optical microscope to observe the red light the nanorods then emitted. While that technique provided data on how long each cluster was "on," the team needed to use transmission electron microscopy, or TEM, to distinguish each individual, 5-nanometer rod and measure the size of each cluster.
A set of gold gridlines allowed the researchers to label and locate individual nanorod clusters. Wang then accurately overlaid about a thousand stitched-together TEM images with the luminescence data that she took with the optical microscope. The researchers observed the "campfire effect" in clusters as small as two and as large as 110, when the cluster effectively took on macroscale properties and stopped blinking entirely.
While the exact mechanism that causes this prolonged luminescence can't yet be pinpointed, Drndic's team's findings support the idea that interacti
|Contact: Evan Lerner|
University of Pennsylvania