MSGID: 1:317/3 63f05471   
   PID: hpt/lnx 1.9.0-cur 2019-01-08   
   TID: hpt/lnx 1.9.0-cur 2019-01-08   
    Smooth sailing for electrons in graphene    
    Physicists directly measured, at nanometer resolution, the fluid-like   
   flow of electrons in graphene    
      
     Date:   
         February 17, 2023   
     Source:   
         University of Wisconsin-Madison   
     Summary:   
         Physicists have directly measured, for the first time at nanometer   
         resolution, the fluid-like flow of electrons in graphene. The   
         results have applications in developing new, low-resistance   
         materials, where electrical transport would be more efficient.   
      
      
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   FULL STORY   
   ==========================================================================   
   Physicists at the University of Wisconsin-Madison directly measured, for   
   the first time at nanometer resolution, the fluid-like flow of electrons   
   in graphene. The results, which will appear in the journal Science on   
   Feb. 17, have applications in developing new, low-resistance materials,   
   where electrical transport would be more efficient.   
      
      
   ==========================================================================   
   Graphene, an atom-thick sheet of carbon arranged in a honeycomb pattern,   
   is an especially pure electrical conductor, making it an ideal material   
   to study electron flow with very low resistance. Here, researchers   
   intentionally added impurities at known distances and found that electron   
   flow changes from gas- like to fluid-like as temperatures rise.   
      
   "All conductive materials contain impurities and imperfections that block   
   electron flow, which causes resistance. Historically, people have taken   
   a low- resolution approach to identifying where resistance comes from,"   
   says Zach Krebs, a physics graduate student at UW-Madison and co-lead   
   author of the study. "In this study, we image how charge flows around   
   an impurity and actually see how that impurity blocks current and causes   
   resistance, which is something that hasn't been done before to distinguish   
   gas-like and fluid-like electron flow.   
      
   The researchers intentionally introduced obstacles in the graphene,   
   spaced at controlled distances and then applied a current across the   
   sheet. Using a technique called scanning tunneling potentiomentry (STP),   
   they measured the voltage with nanometer resolution at all points on   
   the graphene, producing a 2D map of the electron flow pattern.   
      
   No matter the obstacle spacing, the drop in voltage through the channel   
   was much lower at higher temp (77 kelvins) vs lower temp (4 K), indicating   
   lower resistance with more electrons passing through.   
      
   At temperatures near absolute zero, electrons in graphene behave like a   
   gas: they diffuse in all directions and are more likely to hit obstacles   
   than they are to interact with each other. Resistance is higher, and   
   electron flow is relatively inefficient. At higher temperatures -- 77 K,   
   or minus 196 C -- the fluid-like behavior of electron flow means they   
   are interacting with each other more than they are hitting obstacles,   
   flowing like water between two rocks in the middle of a stream. It is   
   as if the electrons are communicating information about the obstacle to   
   each other and diverting around the rocks.   
      
   "We did a quantitative analysis [of the voltage map] and found that at   
   the higher temperature, the resistance is much lower in the channel. The   
   electrons were flowing more freely and fluid-like," Krebs says. "Graphene   
   is so clean that we're forcing the electrons to interact with each other   
   before they interact with anything else, and that is crucial in getting   
   them to behave like a fluid."  Former UW-Madison graduate student Wyatt   
   Behn is a co-first author on this study conducted in physics professor   
   Victor Brar's group. Funding was provided by the U.S. Department of   
   Energy (DE-SC00020313), the Office of Naval Research (N00014-20-1-2356)   
   and the National Science Foundation (DMR-1653661).   
      
       * RELATED_TOPICS   
             o Matter_&_Energy   
                   # Graphene # Nature_of_Water # Spintronics #   
                   Inorganic_Chemistry # Materials_Science # Chemistry #   
                   Physics # Engineering_and_Construction   
       * RELATED_TERMS   
             o Viscosity o Turbulence o Materials_science o Flow_measurement   
             o Aerodynamics o Carbon_nanotube o Pyroelectricity o   
             Drag_(physics)   
      
   ==========================================================================   
   Story Source: Materials provided by   
   University_of_Wisconsin-Madison. Original written by Sarah Perdue. Note:   
   Content may be edited for style and length.   
      
      
   ==========================================================================   
   Journal Reference:   
      1. Zachary J. Krebs, Wyatt A. Behn, Songci Li, Keenan J. Smith, Kenji   
         Watanabe, Takashi Taniguchi, Alex Levchenko, Victor W. Brar. Imaging   
         the breaking of electrostatic dams in graphene for ballistic   
         and viscous fluids. Science, 2023; 379 (6633): 671 DOI:   
         10.1126/science.abm6073   
   ==========================================================================   
      
   Link to news story:   
   https://www.sciencedaily.com/releases/2023/02/230217081442.htm   
      
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