Bookmark and Share


Graphene has dazzled scientists, ever since its discovery more than a decade ago, with its unequalled electronic properties, its strength and its light weight. But one long-sought goal has proved elusive: how to engineer into graphene a property called a band gap, which would be necessary to use the material to make transistors and other electronic devices.

Now, new findings by researchers at MIT are a major step toward making graphene with this coveted property. The work could also lead to revisions in some theoretical predictions in graphene physics. The new technique involves placing a sheet of graphene – a carbon-based material whose structure is just one atom thick – on top of hexagonal boron nitride, another one-atom-thick material with similar properties. The resulting material shares graphene’s amazing ability to conduct electrons, while adding the band gap necessary to form transistors and other semiconductor devices.

“By combining two materials we created a hybrid material that has different properties than either of the two. Graphene is an extremely good conductor of electrons, while boron nitride is a good insulator, blocking the passage of electrons. We made a high-quality semiconductor by putting them together,” said Pablo Jarillo-Herrero, the assistant professor of physics at MIT.

To make the hybrid material work, the researchers had to align, with near perfection, the atomic lattices of the two materials, which both consist of a series of hexagons. The size of the hexagons (known as the lattice constant) in the two materials is almost the same, but not quite: Those in boron nitride are 1.8% larger. So while it is possible to line the hexagons up almost perfectly in one place, over a larger area the pattern goes in and out of register.

The MIT graphene-hexagonal boron nitride research team. From left: professor Ray Ashoori, postdocs Andrea Young and Ben Hunt, graduate student Javier Sanchez-Yamagishi, and professor Pablo Jarillo-Herrero.

At this point, the researchers say they must rely on chance to get the angular alignment for the desired electronic properties in the resulting stack. However, the alignment turns out to be correct about one time out of 15, they say.

“The qualities of the boron nitride bleed over into the graphene. But what’s most spectacular is that the properties of the resulting semiconductor can be tuned by just slightly rotating one sheet relative to the other, allowing for a spectrum of materials with varied electronic characteristics,” said Ray Ashoori, a professor of physics at MIT.

Others have made graphene into a semiconductor by etching the sheets into narrow ribbons, but such an approach substantially degrades graphene’s electrical properties. By contrast, the new method appears to produce no such degradation.

The band gap created so far in the material is smaller than that needed for practical electronic devices; finding ways of increasing it will require further work, the researchers say.

“If a large band gap could be engineered, it could have applications in all of digital electronics. But even at its present level this approach could be applied to some optoelectronic applications, such as photodetectors,” said Mr. Jarillo-Herrero.

The results surprised the researchers pleasantly and will require some explanation by theorists. Because of the difference in lattice constants of the two materials, the researchers had predicted that the hybrid’s properties would vary from place to place. Instead, they found a constant, and unexpectedly large, band gap across the whole surface.

In addition, Mr. Jarillo-Herrero said that the magnitude of the change in electrical properties produced by putting the two materials together is much larger than theory predicts.

The MIT team also observed an interesting new physical phenomenon. When exposed to a magnetic field, the material exhibits fractal properties – known as a Hofstadter butterfly energy spectrum – that were described decades ago by theorists, but thought impossible in the real world.

Tags: Semiconductor, MIT


Comments currently: 2
Discussion started: 05/23/13 03:27:28 AM
Latest comment: 05/23/13 07:55:52 AM


This is a potential step in the correct direction but the major hurdle is being able to find a solution for the mismatch of hexagon sizes - which is a significant challenge. Otherwise this is just another dead end.
1 0 [Posted by: beenthere  | Date: 05/23/13 07:55:51 AM]


Add your Comment

Latest News

Monday, April 14, 2014

8:23 am | Microsoft Vows to Release Xbox 360 Emulator for Xbox One. Microsoft Xbox One May Gain Compatibility with Xbox 360 Games

Tuesday, April 1, 2014

10:39 am | Microsoft Reveals Kinect for Windows v2 Hardware. Launch of New Kinect for Windows Approaches

Tuesday, March 25, 2014

1:57 pm | Facebook to Acquire Virtual Reality Pioneer, Oculus VR. Facebook Considers Virtual Reality as Next-Gen Social Platform

1:35 pm | Intel Acquires Maker of Wearable Computing Devices. Basis Science Becomes Fully-Owned Subsidiary of Intel

Monday, March 24, 2014

10:53 pm | Global UHD TV Shipments Total 1.6 Million Units in 2013 – Analysts. China Ahead of the Whole World with 4K TV Adoption

10:40 pm | Crytek to Adopt AMD Mantle Mantle API for CryEngine. Leading Game Developer Adopts AMD Mantle

9:08 pm | Microsoft Unleashes DirectX 12: One API for PCs, Mobile Gadgets and Xbox One. Microsoft Promises Increased Performance, New Features with DirectX 12

3:33 pm | PowerVR Wizard: Imagination Reveals World’s First Ray-Tracing GPU IP for Mobile Devices. Imagination Technologies Brings Ray-Tracing, Hybrid Rendering Modes to Smartphones and Tablets

2:00 pm | Nokia Now Expects to Close Deal with Microsoft in Q2. Sale of Nokia’s Division to Close Next Month