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Atom-thick carbon transistor could succeed silicon

作者:蔡椐蜃    发布时间:2019-03-01 13:13:06    

By Tom Simonite (Image: Jannik C. Meyer, U.C. Berkeley) Transistors less than one-quarter the size of the tiniest silicon ones – and potentially more efficient – can be made using sheets of carbon just one-tenth of a nanometre thick, research shows. Unlike other experimental nanoscopic transistors, the new components require neither complex manufacturing nor cryogenic cooling. The transistors are made of graphene, a sheet of carbon atoms in a flat honeycomb arrangement. Graphene makes graphite when stacked in layers, and carbon nanotubes when rolled into a tube. Graphene also conducts electricity faster than most materials since electrons can travel through in straight lines between atoms without being scattered. This could ultimately mean faster, more efficient electronic components that also require less power. The first graphene transistor was demonstrated in 2004. But this leaked current and could never switch it off, because electrons hopped too easily between the carbon atoms (see Pencils sketch out next electronics revolution). Andre Geim and colleagues at the University of Manchester, UK, have now made a graphene transistor that does not leak current that can control the flow of just a single electron efficiently. The leak-free transistor is made from a “nano-ribbon” of graphene less than 10 nanometres wide and just a single carbon atom thick (0.1 nm). This thin strip of graphene constrains the quantum energy levels available to flowing electrons, preventing them from hopping around so easily. An electric field is used to control this flow, tweaking the energy levels to switch the current on and off. The device not only works at room temperature but, unlike other transistors of a similar size, it is relatively simple to make (see Buckled nanotubes make tiny transistors). The ribbon at the heart of the device, as well as the surrounding connections, can be cut from a graphene sheet using electron beam lithography – the same method used to make silicon devices. “We are beginning to see the potential of graphene as the successor to silicon,” says Geim, who was also a member of the team that discovered graphene in 2004. Edward McCann at Lancaster University, UK, expects to see increasing computer-company investment in research into potential uses of graphene. “This new material has properties that suggest it could have a range of powerful applications,” he says. McCann notes that nanoribbon transistors lack the tuneable qualities of earlier graphene devices, but using two layers of graphene could solve this issue. “It should then be possible to control the density of electrons as well,” he adds. In a related paper published in the same issue of Nature this week, Geim and colleagues at Manchester University, the Max Planck Institute for Solid State Research in Stuttgart, Germany, and Radboud University of Nijmegen in the Netherlands, also show how graphene is able to exist in such a thin form at all. “Theory and experiment tells us flat, two-dimensional crystals can’t exist,” Geim explains, “Buffeting from surrounding particles should make them unstable and melt.” They placed a piece of graphene on top of silicon and positioned this over a metallic grate. Acid was used to dissolve the silicon, leaving graphene suspended across 500 nm gaps. A transmission electron microscope then revealed it is covered in tiny ripples, which keep the material stable. The ripples extend about 1 nm up and down and are around 25 nm across. “To our surprise it’s not flat at all,” Geim says. Journal references: Nature Materials (DOI: 10.1038/nmat1849), Nature (DOI:

 

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