MSGID: 1:317/3 63eb0e7a   
   PID: hpt/lnx 1.9.0-cur 2019-01-08   
   TID: hpt/lnx 1.9.0-cur 2019-01-08   
    Atom-thin walls could smash size, memory barriers in next-gen devices   
    Nanomaterial feature could help electronic circuits adopt benefits of   
   human memory    
      
     Date:   
         February 13, 2023   
     Source:   
         University of Nebraska-Lincoln   
     Summary:   
         For all of the still-indistinguishable-from-magic wizardry packed   
         into the three pounds of the adult human brain, it obeys the same   
         rule as the other living tissue it controls: Oxygen is a must. So it   
         was with a touch of irony that a scientists offered his explanation   
         for a technological wonder -- movable, data-covered walls mere   
         atoms wide -- that may eventually help computers behave more like   
         a brain. 'There was unambiguous evidence that oxygen vacancies   
         are responsible for this,' Tsymbal said.   
      
      
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   FULL STORY   
   ==========================================================================   
   For all of the unparalleled, parallel-processing,   
   still-indistinguishable-from- magic wizardry packed into the three   
   pounds of the adult human brain, it obeys the same rule as the other   
   living tissue it controls: Oxygen is a must.   
      
      
   ==========================================================================   
   So it was with a touch of irony that Evgeny Tsymbal offered his   
   explanation for a technological wonder -- movable, data-covered walls mere   
   atoms wide -- that may eventually help computers behave more like a brain.   
      
   "There was unambiguous evidence that oxygen vacancies are responsible   
   for this," said Tsymbal, George Holmes University Professor of physics   
   and astronomy at the University of Nebraska-Lincoln.   
      
   In partnership with colleagues in China and Singapore, Tsymbal and a few   
   Husker alumni have demonstrated how to construct, control and explain   
   the oxygen- deprived walls of a nanoscopically thin material suited to   
   next-gen electronics.   
      
   Unlike most digital data-writing and -reading techniques, which speak   
   only the binary of 1s and 0s, these walls can talk in several electronic   
   dialects that could allow the devices housing them to store even more   
   data. Like synapses in the brain, the passage of electrical spikes sent   
   via the walls can depend on which signals have passed through before,   
   lending them an adaptability and energy-efficiency more akin to human   
   memory. And much as brains maintain memories even when their users sleep,   
   the walls can retain their data states even if their devices turn off   
   -- a precursor to electronics that power back on with the speed and   
   simplicity of a light.   
      
   The team investigated the barrier-smashing walls in a nanomaterial,   
   named bismuth ferrite, that can be sliced thousands of times thinner   
   than a human hair. Bismuth ferrite also boasts a rare quality known   
   as ferroelectricity: The polarization, or separation, of its positive   
   and negative electric charges can be flipped by applying just a pinch   
   of voltage, writing a 1 or 0 in the process. Contrary to conventional   
   DRAM, a dynamic random-access memory that needs to be refreshed every   
   few milliseconds, that 1 or 0 remains even when the voltage is removed,   
   granting it the equivalent of long-term memory that DRAM lacks.   
      
   Usually, that polarization is read as a 1 or 0, and flipped to rewrite   
   it as a 0 or 1, in a region of material called a domain. Two oppositely   
   polarized domains meet to form a wall, which occupies just a fraction of   
   the space dedicated to the domains themselves. The few-atom thickness   
   of those walls, and the unusual properties that sometimes emerge in or   
   around them, have cast them as prime suspects in the search for new ways   
   to squeeze ever-more functionality and storage into shrinking devices.   
      
   Still, walls that run parallel to the surface of a ferroelectric material   
   - - and net an electric charge usable in data processing and storage   
   -- have proven difficult to find, let alone regulate or create. But   
   about four years ago, Tsymbal began talking with Jingsheng Chen from   
   the National University of Singapore and He Tian from China's Zhejiang   
   University. At the time, Tian and some colleagues were pioneering a   
   technique that allowed them to apply voltage on an atomic scale, even   
   as they recorded atom-by-atom displacements and dynamics in real time.   
      
   Ultimately, the team found that applying just 1.5 volts to a bismuth   
   ferrite film yielded a domain wall parallel to the material's surface --   
   one with a specific resistance to electricity whose value could be read   
   as a data state.   
      
   When voltage was withdrawn, the wall, and its data state, remained.   
      
   When the team cranked up the voltage, the domain wall began migrating down   
   the material, a behavior seen in other ferroelectrics. Whereas the walls   
   in those other materials had then propagated perpendicular to the surface,   
   though, this one remained parallel. And unlike any of its predecessors,   
   the wall adopted a glacial pace, migrating just one atomic layer at a   
   time. Its position, in turn, corresponded with changes in its electrical   
   resistance, which dropped in three distinct steps -- three more readable   
   data states -- that emerged between the application of 8 and 10 volts.   
      
   The researchers had nailed down a few W's -- the what, the where, the   
   when - - critical to eventually employing the phenomenon in electronic   
   devices. But they were still missing one. Tsymbal, as it happened,   
   was among the few people qualified to address it.   
      
   "There was a puzzle," Tsymbal said. "Why does it happen? And this is where   
   theory helped."  Most domain walls are electrically neutral, possessing   
   neither a positive nor a negative charge. That's with good reason:   
   A neutral wall requires little energy to maintain its electric state,   
   effectively making it the default. The domain wall the team identified   
   in the ultra-thin bismuth ferrite, by contrast, possessed a substantial   
   charge. And that, Tsymbal knew, should have kept it from stabilizing   
   and persisting. Yet somehow, it was managing to do just that, seeming   
   to flout the rules of condensed-matter physics.   
      
   There had to be an explanation. In his prior research, Tsymbal and   
   colleagues had found that the departure of negatively charged oxygen   
   atoms, and the positively charged vacancies they left in their wake,   
   could impede a technologically useful outcome. This time, Tsymbal's   
   theory-backed calculations suggested the opposite -- that the positively   
   charged vacancies were compensating for other negative charges   
   accumulating at the wall, essentially fortifying it in the process.   
      
   Experimental measurements from the team would later show that the   
   distribution of charges in the material lined up almost exactly with the   
   location of the domain wall, exactly as the calculations had predicted. If   
   oxygen vacancies turn up in other ferroelectric playgrounds, Tsymbal   
   said, they could prove vital to better understanding and engineering   
   devices that incorporate the prized class of materials.   
      
   "From my perspective, that was the most exciting," said Tsymbal, who   
   undertook the research with support from the university's quantum-focused   
   EQUATE project.   
      
   "This links ferroelectricity with electrochemistry. We have some kind of   
   electrochemical processes -- namely, the motion of oxygen vacancies --   
   which basically control the motion of these domain walls.   
      
   "I think that this mechanism is very important, because what most people   
   are doing -- including us, theoretically -- is looking at pristine   
   materials, where polarization switches up and down, and studying what   
   happens with the resistance. All the experimental interpretations of this   
   behavior were based on this simple picture of polarization. But here,   
   it's not only the polarization.   
      
   It involves some chemical processes inside of it."  The team detailed   
   its findings in the journal Nature. Tsymbal, Tian and Chen authored the   
   study with Ze Zhang, Zhongran Liu, Han Wang, Hongyang Yu, Yuxuan Wang,   
   Siyuan Hong, Meng Zhang, Zhaohui Ren and Yanwu Xie, as well as Husker   
   alumni Ming Li, Lingling Tao and Tula Paudel.   
      
       * RELATED_TOPICS   
             o Matter_&_Energy   
                   # Construction # Materials_Science # Physics #   
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             o Computers_&_Math   
                   # Computers_and_Internet # Information_Technology #   
                   Hacking # Neural_Interfaces   
       * RELATED_TERMS   
             o Carbon_dioxide o Ozone o Carbohydrate o Oxygen o   
             Nitrogen_oxide o Quantum_computer o Oxidizing_agent o Statistics   
      
   ==========================================================================   
   Story Source: Materials provided by   
   University_of_Nebraska-Lincoln. Original written by Scott Schrage. Note:   
   Content may be edited for style and length.   
      
      
   ==========================================================================   
   Journal Reference:   
      1. Zhongran Liu, Han Wang, Ming Li, Lingling Tao, Tula R. Paudel,   
      Hongyang   
         Yu, Yuxuan Wang, Siyuan Hong, Meng Zhang, Zhaohui Ren, Yanwu Xie,   
         Evgeny Y. Tsymbal, Jingsheng Chen, Ze Zhang, He Tian. In-plane   
         charged domain walls with memristive behaviour in a ferroelectric   
         film. Nature, 2023; 613 (7945): 656 DOI: 10.1038/s41586-022-05503-5   
   ==========================================================================   
      
   Link to news story:   
   https://www.sciencedaily.com/releases/2023/02/230213201035.htm   
      
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