糖心视频

(糖心视频Org.com) -- 鈥淧eople want a faster computer chip,鈥� Philip Kim tells 糖心视频Org.com. 鈥淎nd it needs to be smaller. But in order to increase the speed of the chip, or to get it smaller, we are approaching a point where you need materials other than silicon.鈥�

Kim, professor at Columbia University, believes that graphene may be just that material. Along with his colleagues, Bolotin, Sikes, Hone and Stormer, Kim thinks that suspended graphene may provide the transport capability needed to reach greater speeds in computer ships. The work of the group from Columbia University can be found in 糖心视频ical Review Letters: 鈥淭emperature-Dependent Transport in Suspended Graphene.鈥�

When one looks at the structure of graphite, stacked layers of pure carbon are apparent. However, it wasn鈥檛 until 2004 that a process sophisticated enough to 鈥渟lice鈥� off one of the layers was discovered. This single layer is called graphene. Graphene is basically a sheet of bonded carbon atoms, with the thickness of only one atom. If one could look down at graphene from the top, one would observe that the sheet bears a strong resemblance to honeycomb, with its hexagons fitted snugly together.

鈥淕raphene behaves almost like semiconductor but without a energy gap,鈥� Kim explains. This is why it would do well as a material for computer chips. 鈥淲hen you apply an electric field perpendicular to graphene, the number of electrons 鈥� the carrier density 鈥� can be tuned.鈥�

鈥淥ne of the main themes is how fast the charge can move in graphene,鈥� Kim continues. 鈥淗igher mobility means electron conducts faster in the system. It has always been speculated that the mobility of graphene can be quite high. But it has not been shown as high as some of the highest semiconductors in the past.鈥�

The group at Columbia University, however, has shown that graphene can exceed the transport speed of even the semiconductors with the highest mobility. They have done this by suspending the graphene at room temperature. 鈥淲e have found that this transport ability is higher in the graphene than in any known semiconductor at room temperature.鈥�

鈥淟ower mobility in graphene comes from external impurities, rather than intrinsic limitations,鈥� Kim explains. 鈥淪o the question becomes how to remove these impurities. Many of the impurities actually come from the substrate; this is the substance the graphene is sitting on. Suspending the graphene and subsequently annealing it would help 鈥榗lean鈥� the graphene, and increase the mobility.鈥�

The current work also shows that temperature plays a role in the transport ability of graphene. 鈥淲e found that the graphene has the highest mobility at room temperature,鈥� Kim says. 鈥淭his is great, since various applications would get more use out of something that can work in the real world.鈥�

And the future? Kim believes that there are still impurities in the graphene. 鈥淭here are still limits right now,鈥� he says. 鈥淚 think we can bring the mobility even higher.鈥�

Kim maintains that this discovery of temperature-dependent transport in graphene goes beyond practical application. 鈥淓very time you discover something like this 鈥� where mobility is really enhanced 鈥� it results in a discovery of new physics. I think the same thing will happen with graphene. Improving mobility will allow us to look at new physics in a very exotic system.鈥�

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