Physicists at the University of Pennsylvania have demonstrated that the combined "on" time of a collection of semiconductor nanorods has increased significantly, thus providing information about its strange blinking characteristics. The exposure of semiconductor nanorods to light causes them to blink in a random manner.
Semiconductors impart light when provided with electricity, light or chemical energy.This electroluminescence property remains steady at the macro scale. LED bulbs consume only a fraction of energy when compared to compact-fluorescent bulbs and can provide illumination for years together. However, semiconductors reduced to nanometer dimensions do not shine in a consistent way, instead they turn "on" and "off" in a random manner..
Associate professor Marija Drndic with her research team combined several imaging methods to demonstrate that grouping these nanorods increases the total "on" time significantly in a "campfire effect." When a rod is added to the group, it has a compounding influence on the "on" period of the group.
Drndic's group showed this by allowing cadmium selenide nanorods to be deposited onto a substrate and subjecting them to a blue laser. They then captured videos with an optical microscope to detect the red light emitted by the nanorods. While that method provided information on the time taken by each cluster to stay "on," the team had to use transmission electron microscopy to spot each 5-nm rod and calculate the size of each group.
Researchers could mark and detect each nanorod group using a collection of gold gridlines. Graduate student Siying Wang then precisely overlaid a thousand TEM images with the luminescence information taken using the optical microscope. The researchers witnessed the "campfire effect" in groups containing two as well as 110 nanorods, when the group shows macroscale properties and stops blinking completely.
Drndic's team's claim that the interactions between electrons present in the group are responsible for the effect. Drndic stated that biologists make use of nanocrystals for fluorescent labels and the only vital limitation is their blinking feature. He added that if the emission time could be prolonged by several minutes it will make them more useful.
Researchers will understand the dynamics of particle interactions by using more uniform nanorod assemblies and controlled inter-particle divisions.
Source: http://www.upenn.edu/