Navigation Links
Penn physicists observe 'campfire effect' in blinking nanorod semiconductors
Date:6/23/2011

PHILADELPHIA When semiconductor nanorods are exposed to light, they blink in a seemingly random pattern. By clustering nanorods together, physicists at the University of Pennsylvania have shown that their combined "on" time is increased dramatically providing new insight into this mysterious blinking behavior.

The research was conducted by associate professor Marija Drndic's group, including graduate student Siying Wang and postdoctorial fellows Claudia Querner and Tali Dadosh, all of the Department of Physics and Astronomy in Penn's School of Arts and Sciences. They collaborated with Catherine Crouch of Swarthmore College and Dmitry Novikov of New York University's School of Medicine.

Their research was published in the journal Nature Communications.

When provided with energy, whether in the form of light, electricity or certain chemicals, many semiconductors emit light. This principle is at work in light-emitting diodes, or LEDs, which are found in any number of consumer electronics.

At the macro scale, this electroluminescence is consistent; LED light bulbs, for example, can shine for years with a fraction of the energy used by even compact-fluorescent bulbs. But when semiconductors are shrunk down to nanometer size, instead of shining steadily, they turn "on" and "off" in an unpredictable fashion, switching between emitting light and being dark for variable lengths of time. For the decade since this was observed, many research groups around the world have sought to uncover the mechanism of this phenomenon, which is still not completely understood.

"Blinking has been studied in many different nanoscale materials for over a decade, as it is surprising and intriguing, but it's the statistics of the blinking that are so unusual," Drndic said. "These nanorods can be 'on' and 'off' for all scales of time, from a microsecond to hours. That's why we worked with Dmitry Novikov, who studies stochastic phenomena in physical and biological systems. These unusual Levi statistics arise when many factors compete with each other at different time scales, resulting in a rather complex behavior, with examples ranging from earthquakes to biological processes to stock market fluctuations."

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 interactions between electrons in the cluster are at the root of the effect.

"By moving from one end of a nanorod to the other, or otherwise changing position, we hypothesize that electrons in one rod can influence those in neighboring rods in ways that enhance the other rods' ability to give off light," Crouch said. "We hope our findings will give insight into these nanoscale interactions, as well as helping guide future work to understand blinking in single nanoparticles."

As nanorods can be an order of magnitude smaller than a cell, but can emit a signal that can be relatively easily seen under a microscope, they have been long considered as potential biomarkers. Their inconsistent pattern of illumination, however, has limited their usefulness.

"Biologists use semiconductor nanocrystals as fluorescent labels. One significant disadvantage is that they blink," Drndic said. "If the emission time could be extended to many minutes it makes them much more usable. With further development of the synthesis, perhaps clusters could be designed as improved labels."

Future research will use more ordered nanorod assemblies and controlled inter-particle separations to further study the details of particle interactions.


'/>"/>

Contact: Evan Lerner
elerner@upenn.edu
215-573-6604
University of Pennsylvania
Source:Eurekalert

Related biology technology :

1. McGill physicists find a new state of matter in a transistor
2. U of T physicists squeeze light to quantum limit
3. Physicists discover important step for making light crystals
4. Nanophysicists find unexpected magnetic effect
5. NYU physicists find way to explore microscopic systems through holographic video
6. Physicists at UC Santa Barbara make discovery in quantum mechanics
7. U-M physicists create first atomic-scale map of quantum dots
8. Physicists capture first images of atomic spin
9. UBC, Max Planck formalize partnership among worlds top quantum physicists
10. UC Riverside physicists pave the way for graphene-based spin computer
11. Rice physicists discover ultrasensitive microwave detector
Post Your Comments:
*Name:
*Comment:
*Email:
(Date:5/23/2017)... Diego, CA (PRWEB) , ... May 23, 2017 , ... ... matrix of polymeric molecules, can cause diverse pathologies ranging from food poisoning and catheter ... impact of biofilms is in the tens of billions of dollars per year, there ...
(Date:5/22/2017)... ... May 22, 2017 , ... Stratevi, a boutique firm that partners with healthcare ... has opened an office in downtown Boston at 745 Atlantic Ave. , “We ... to generate evidence on the value they provide, not just to patients, but also ...
(Date:5/21/2017)... ... May 19, 2017 , ... ... educational conference of the American Association of Bioanalysts (AAB) and the College of ... Houston. The conference reinforces AAB’s commitment to excellence in clinical laboratory services and ...
(Date:5/19/2017)... ... May 19, 2017 , ... ... Academic researchers with technologies ripe for commercialization, and who are affiliated with ... are encouraged to submit proposals. QED, now in its tenth round, is the ...
Breaking Biology Technology:
(Date:3/30/2017)... , March 30, 2017 Trends, opportunities and ... and behavioral), by technology (fingerprint, AFIS, iris recognition, facial ... and others), by end use industry (government and law ... financial and banking, and others), and by region ( ... , Asia Pacific , and the ...
(Date:3/28/2017)... India , March 28, 2017 ... IP, Biometrics), Hardware (Camera, Monitors, Servers, Storage Devices), Software ... Vertical, and Region - Global Forecast to 2022", published ... Billion in 2016 and is projected to reach USD ... between 2017 and 2022. The base year considered for ...
(Date:3/24/2017)... , March 24, 2017 The Controller General ... Controller Mr. Abdulla Algeen have received the prestigious international IAIR ... Continue Reading ... ... picture) and Deputy Controller Abdulla Algeen (small picture on the right) have ...
Breaking Biology News(10 mins):