The chances are that you own a microelectromechanical device?aprobably dozens of them. These devices fill the modern world. They make possible the accelerometers in smartphones,Security Management Software the microphones in laptops, and the micromirrors in digital projectors, to name just a few. They are typically a few micrometers in size, tiny by any standards. If possible, but engineers and scientists want them even smaller?aon the nanometer scale. At that size, these machines can work as simple switches in logic and memory devices, raising the prospect of more powerful and more efficient data-processing devices.
These micromachines are generally carved into silicon chips. But as they get smaller, silicon switches become less efficient because they leak current when they are off. A better option is a graphene switch, which is easy to carve on a nanometer scale and relatively straightforward to build into conventional silicon chips. Neither does it leak current when it is off.But there is a problem. When graphene touches silicon, it tends to stick fast. Imagine a switch consisting of a flexible graphene bar that forms a circuit when the bar touches a silicon electrode. If the bar sticks to the electrode, it cannot be switched off again.
This problem is known as stiction. And despite significant financial investment in graphene research by governments all over the world, nobody has found a good way to solve it.Enter Kulothungan Jothiramalingam at the Japan Advanced Institute of Science and Technology and colleagues, who have found a solution. Using it, they have created graphene-based nanoelectromechanical devices that can act as switches and even as logic gates. Their method is straightforward. They coat a silicon chip with nanocrystalline graphene, which sticks fast to the surface. Then they cover this with a layer of hydrogen silsesquioxane, which acts as a resist and can be carved into various shapes. On top of this they place another layer of graphene.
The trick is to carve the top layer of graphene into a bar shape that is anchored at both ends by electrodes. Then they remove the hydrogen silsesquioxane layer underneath part of the graphene bar to leave it suspended above the graphene layer. Bending this bar is simple. A potential difference between the layers creates a force that bends the bar to toward the chip. When it touches this lower surface, it forms a circuit, a process that can be exploited for logic and for data storage.That's the switch. And because the two surfaces that come into contact are both graphene, there is no stiction. Switching off the potential difference releases the bar, which springs back into its original position.