• Light-infused particles go the distance

    From ScienceDaily@1:317/3 to All on Fri Apr 29 22:30:48 2022
    Light-infused particles go the distance in organic semiconductors

    Date:
    April 29, 2022
    Source:
    Cornell University
    Summary:
    Polaritons offer the best of two very different worlds. These
    hybrid particles combine light and molecules of organic material,
    making them ideal vessels for energy transfer in organic
    semiconductors. They are both compatible with modern electronics
    but also move speedily, thanks to their photonic origins.



    FULL STORY ========================================================================== Polaritons offer the best of two very different worlds. These hybrid
    particles combine light and molecules of organic material, making them
    ideal vessels for energy transfer in organic semiconductors. They are
    both compatible with modern electronics but also move speedily, thanks
    to their photonic origins.


    ========================================================================== However, they are difficult to control, and much of their behavior is
    a mystery.

    A project led by Andrew Musser, assistant professor of chemistry and
    chemical biology in the College of Arts and Sciences, has found a way to
    tune the speed of this energy flow. This "throttle" can move polaritons
    from a near standstill to something approaching the speed of light and
    increase their range -- an approach that could eventually lead to more efficient solar cells, sensors and LEDs.

    The team's paper, "Tuning the Coherent Propagation of Organic Exciton- Polaritons through Dark State Delocalization," published April 27 in
    Advanced Science. The lead author is Raj Pandya of the University of
    Cambridge.

    Over the last several years, Musser and colleagues at the University of Sheffield have explored a method of creating polaritons via tiny sandwich structures of mirrors, called microcavities, that trap light and force
    it to interact with excitons -- mobile bundles of energy that consist
    of a bound electron-hole pair.

    They previously showed how microcavities can rescue organic semiconductors
    from "dark states" in which they don't emit light, with implications
    for improved organic LEDs.



    ==========================================================================
    For the new project, the team used a series of laser pulses, which
    functioned like an ultrafast video camera, to measure in real time how
    the energy moved within the microcavity structures. But the team hit a speedbump of their own.

    Polaritons are so complex that even interpreting such measurements can
    be an arduous process.

    "What we found was completely unexpected. We sat on the data for a good
    two years thinking about what it all meant," said Musser, the paper's
    senior author.

    Eventually the researchers realized that by incorporating more mirrors
    and increasing the reflectivity in the microcavity resonator, they were
    able to, in effect, turbocharge the polaritons.

    "The way that we were changing the speed of the motion of these particles
    is still basically unprecedented in the literature," he said. "But now,
    not only have we confirmed that putting materials into these structures
    can make states move much faster and much further, but we have a lever to actually control how fast they go. This gives us a very clear roadmap now
    for how to try to improve them." In typical organic materials, elementary excitations move on the order of 10 nanometers per nanosecond, which is
    roughly equivalent to the speed of world- champion sprinter Usain Bolt, according to Musser.



    ==========================================================================
    That may be fast for humans, he noted, but it is actually quite a slow
    process on the nanoscale.

    The microcavity approach, by contrast, launches polaritons a
    hundred-thousand times faster -- a velocity on the order of 1% of the
    speed of light. While the transport is short lived -- instead of taking
    less than a nanosecond, it's less than picosecond, or about 1,000 times
    briefer -- the polaritons move 50 times further.

    "The absolute speed isn't necessarily important," Musser said. "What is
    more useful is the distance. So if they can travel hundreds of nanometers,
    when you miniaturize the device -- say, with terminals that are 10's of nanometers apart -- that means that they will go from A to B with zero
    losses. And that's really what it's about." This brings physicists,
    chemists and material scientists ever closer to their goal of creating
    new, efficient device structures and next-generation electronics that
    aren't stymied by overheating.

    "A lot of technologies that use excitons rather than electrons only
    operate at cryogenic temperatures," Musser said. "But with organic semiconductors, you can start to achieve a lot of interesting, exciting functionality at room temperature. So these same phenomena can feed into
    new kinds of lasers, quantum simulators, or computers, even. There are a
    lot of applications for these polariton particles if we can understand
    them better." Co-authors include Scott Renken, MS '21 of the Musser
    Group; and researchers from the University of Cambridge, the University
    of Sheffield and Nanjing University.

    The research was supported by the Engineering and Physical Sciences
    Research Council in the United Kingdom, the University of Cambridge and
    the U.S.

    Department of Energy.


    ========================================================================== Story Source: Materials provided by Cornell_University. Original written
    by David Nutt. Note: Content may be edited for style and length.


    ========================================================================== Journal Reference:
    1. Raj Pandya, Arjun Ashoka, Kyriacos Georgiou, Jooyoung Sung, Rahul
    Jayaprakash, Scott Renken, Lizhi Gai, Zhen Shen, Akshay Rao,
    Andrew J.

    Musser. Tuning the Coherent Propagation of Organic
    Exciton‐Polaritons through Dark State Delocalization. Advanced
    Science, 2022; 2105569 DOI: 10.1002/advs.202105569 ==========================================================================

    Link to news story: https://www.sciencedaily.com/releases/2022/04/220429144921.htm

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