Turning Diamond Into Metal – For Improved Solar Cells, LEDs, and Power Electronics

Electronic Properties of Nanoscale Needles of Diamond

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Researchers have actually found a method to change the electronic homes of nanoscale needles of diamond. Credit: MIT News

Normally an insulator, diamond ends up being a metal conductor when subjected to big stress in a brand-new theoretical design.

Long called the hardest of 100% natural products, diamonds are likewise extraordinary thermal conductors and electrical insulators. Now, scientists have actually found a method to fine-tune small needles of diamond in a regulated method to change their electronic homes, calling them from insulating, through semiconducting, all the method to extremely conductive, or metal. This can be caused dynamically and reversed at will, without any destruction of the diamond product.

The research study, though still at an early proof-of-concept phase, might open a broad variety of possible applications, consisting of brand-new type of broadband solar batteries, extremely effective LEDs and power electronic devices, and brand-new optical gadgets or quantum sensing units, the scientists state.

Their findings, which are based upon simulations, estimations, and previous speculative outcomes, were released on October 5, 2020, in the Proceedings of the National Academy of Sciences. The paper is by MIT Professor Ju Li and college student Zhe Shi; Principal Research Scientist Ming Dao; Professor Subra Suresh, who is president of Nanyang Technological University in Singapore along with previous dean of engineering and Vannevar Bush Professor Emeritus at MIT; and Evgenii Tsymbalov and Alexander Shapeev at the Skolkovo Institute of Science and Technology in Moscow.

The group utilized a mix of quantum mechanical estimations, analyses of mechanical contortion, and artificial intelligence to show that the phenomenon, long thought as a possibility, truly can take place in nanosized diamond.

The principle of straining a semiconductor product such as silicon to enhance its efficiency discovered applications in the microelectronics market more than 20 years back. However, that approach involved little stress on the order of about 1 percent. Li and his partners have actually invested years establishing the principle of flexible stress engineering. This is based upon the capability to trigger considerable modifications in the electrical, optical, thermal, and other homes of products merely by warping them — putting them under moderate to big mechanical stress, enough to change the geometric plan of atoms in the product’s crystal lattice, however without interrupting that lattice.

In a significant advance in 2018, a group led by Suresh, Dao, and Yang Lu from the City University of Hong Kong revealed that small needles of diamond, simply a couple of hundred nanometers throughout, might be bent without fracture at space temperature level to big stress. They had the ability to consistently flex these nanoneedles to tensile stress as much as 10 percent; the needles can then return undamaged to their initial shape.

Key to this work is a home called bandgap, which basically identifies how easily electrons can move through a product. This residential or commercial property is therefore crucial to the product’s electrical conductivity. Diamond typically has a really large bandgap of 5.6 electron volts, suggesting that it is a strong electrical insulator that electrons do stagnate through easily. In their newest simulations, the scientists reveal that diamond’s bandgap can be slowly, constantly, and reversibly altered, supplying a vast array of electrical homes, from insulator through semiconductor to metal.

“We found that it’s possible to reduce the bandgap from 5.6 electron volts all the way to zero,” Li states. “The point of this is that if you can change continuously from 5.6 to 0 electron volts, then you cover all the range of bandgaps. Through strain engineering, you can make diamond have the bandgap of silicon, which is most widely used as a semiconductor, or gallium nitride, which is used for LEDs. You can even have it become an infrared detector or detect a whole range of light all the way from the infrared to the ultraviolet part of the spectrum.”

“The ability to engineer and design electrical conductivity in diamond without changing its chemical composition and stability offers unprecedented flexibility to custom-design its functions,” states Suresh. “The methods demonstrated in this work could be applied to a broad range of other semiconductor materials of technological interest in mechanical, microelectronics, biomedical, energy and photonics applications, through strain engineering.”

So, for instance, a single small piece of diamond, bent so that it has a gradient of stress throughout it, might end up being a solar battery efficient in recording all frequencies of light on a single gadget — something that presently can just be accomplished through tandem gadgets that combine various type of solar battery products together in layers to integrate their various absorption bands. These may at some point be utilized as broad-spectrum photodetectors for commercial or clinical applications.

One restriction, which needed not just the correct amount of stress however likewise the best orientation of the diamond’s crystalline lattice, was to avoid the stress from triggering the atomic setup to cross a tipping point and becoming graphite, the soft product utilized in pencils.

The procedure can likewise make diamond into 2 kinds of semiconductors, either “direct” or “indirect” bandgap semiconductors, depending upon the designated application. For solar batteries, for instance, direct bandgaps offer a a lot more effective collection of energy from light, permitting them to be much thinner than products such as silicon, whose indirect bandgap needs a a lot longer path to gather a photon’s energy.

The procedure might be pertinent for a wide array of possible applications, Li recommends, such as for extremely delicate quantum-based detectors that utilize flaws and dopant atoms in a diamond. “Using strain, we can control the emission and absorption levels of these point defects,” he states, permitting unique methods of managing their electronic and nuclear quantum states.

But offered the excellent range of conditions enabled by the various measurements of stress variations, Li states, “if we have a particular application in mind, then we could optimize toward that application target. And what is nice about the elastic straining approach is that it is dynamic,” so that it can be constantly differed in genuine time as required.

This early-stage proof-of-concept work is not yet at the point where they can start to develop useful gadgets, the scientists state, however with the continuous research study they anticipate that useful applications might be possible, partially since of appealing work being done all over the world on the development of uniform diamond products.

Reference: “Metallization of diamond” by Zhe Shi, Ming Dao, Evgenii Tsymbalov, Alexander Shapeev, Ju Li and Subra Suresh, 5 October 2020, Proceedings of the National Academy of Sciences.
DOI: 10.1073/pnas.2013565117

The work was supported by the U.S. Office of Naval Research.

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