Stanene May Be Better Than Graphene

PORTLAND, Ore. — A team of researchers led by Stanford University professor Shoucheng Zhang now have high hopes that a new material they call stanene will conduct electricity on next-generation microchips with “100 percent efficiency” at room temperature and above.


The team, including researchers at Stanford University and the US Department of Energy’s (DoE’s) SLAC National Accelerator Laboratory, both in Menlo Park, Calif., named their new tin-based material stanene to liken it to graphene (plus the prefix of the Latin term for tin, stannum). However, instead of being based on atomically thin two-dimensional (2D) monolayers of carbon as is graphene, stanene is based on monolayers of tin. And while they are careful not to call it a room-temperature superconductor, it nevertheless has striking similarities.

Adding fluorine atoms (yellow) to a 2-D monolayer of tin atoms (grey) should allow a predicted new material, stanene, to offer zero resistance along its edges (blue and red arrows) at temperatures up to 100 degrees Celsius (212 Fahrenheit). (Yong Xu/Tsinghua University; Greg Stewart/SLAC) (Source: SLAC)

Adding fluorine atoms (yellow) to a 2-D monolayer of tin atoms (grey) should allow a predicted new material, stanene, to offer zero resistance along its edges (blue and red arrows) at temperatures up to 100 degrees Celsius (212 Fahrenheit). (Yong Xu/Tsinghua University; Greg Stewart/SLAC) (Source: SLAC)

“This is not a superconductor, with the following distinction — it only conducts with 100 percent efficiency on the edges — the interior of this two-dimensional material is an insulator,” Zhang told us.


In practice, stanene interconnection lines will behave like dual side-by-side superconducting wires, since each ribbon of stanene will support two lanes of zero resistance data traffic — one on each edge. The only resistance offered by a stanene interconnection line would be at the end points where a contact must be made with the traditional on-chip circuitry.


“The key difference is that with a normal conductor, the total resistance scales linearly with the length — the longer the wire the larger the resistance,” said Zhang. “But for stanene the only resistance is the contact, so the total resistance of a line is constant regardless of the wire’s length.”


Experimental confirmation

Experiments to confirm Zhang’s group’s simulations are currently underway in Germany and China, and if they succeed in fabricating stanene and confirm its properties, that could be good news for chip makers, since switching to thin ribbons of stanene for high-speed interconnects could cut chip power and reduce heat buildup.


Zhang has high hopes that their simulation results will be confirmed, since he and his colleagues already have a history of predicting the properties of topological insulators — materials that conduct electricity on their surface but not in their interior. Zhang’s team already predicted that mercury telluride and several other compounds should be topological insulators that were subsequently confirmed experimentally. These compounds were predicted to conduct electricity with 100 percent efficiency along their edges, when fabricated in monolayers, albeit only at low temperatures like a superconductor.


“The effect is not exactly the same, but somewhat similar to superconductors — the key difference is that in the field of superconductors, no material was ever predicted and then confirmed — they were all found experimentally. But in topological insulators everything was predicted and then confirmed — so you can appreciate the tremendous power of being able to predict a material theoretically much more quickly that trying to discover it experimentally in a chemistry lab,” said Zhang.


Indeed, Zhang and visiting scientist Yong Xu — now at Tsinghua University — have used the same kind of detailed simulations to predict that monolayers of tin should be able to achieve zero resistance on their edges at room temperature and at even higher temperatures — as high at 100 degrees Celsius (212 Fahrenheit) — when terminated with flourine atoms on the top and bottom of the monolayer to make the material’s bandgap larger.


“A lot of materials research today is still experimental, but now we are actually using the power of the computer and the power of theoretical thinking to push ahead in materials research, so we can design materials with the desired functionality — which is a kind of a revolution going on in semiconductor material’s discovery,” said Zhang.


Zhang is also working on adding a gate to his stanene ribbons, in order to make three-terminal devices that replace the silicon in transistor channels with stanene. If successful, Zhang muses that someday the Silicon Valley may be renamed Tim Valley.


Contributors to the work included researchers at Tsinghua University and the Max Planck Institute for Chemical Physics of Solids in Dresden, Germany.


Funding was provided by the Defense Advanced Research Projects Agency (DARPA).

— R. Colin Johnson, Advanced Technology Editor, EE Times Circle me on Google+

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