Diamonds are an effective electrical insulator, but that may not always be the case, according to a new study by the Massachusetts Institute of Technology and Singapore’s Nanyang Technological University (NTU). The team calculated that deforming the diamond nano-needle would change its conductivity from an insulator to a semiconductor, then to a highly conductive metal — and then change it back at will.
The strain of a material seems to be something that all walks of life usually want to avoid, but in some cases it can make the material better. For example, strained silicon makes it easier for electrons to pass through it, increasing the switching speed of transistors by 35%, but the key to all this is to apply enough strain to affect the arrangement of atoms in the crystal lattice, but not so much that the lattice itself is destroyed.
The degree to which electrons move in a material is measured by the “bandgap” of the material, the greater the band gap, the harder it is for electrons to pass through. At 5.6 electronic Ford (eV), diamonds usually have extra wide band gaps, making them an insulator. But in the new study, researchers have found a way to make diamond strain to change its band gaps.
Using computer simulations of quantum mechanics and mechanical deformation, the team found that diamond nano needles could be bent with diamond probes to varying degrees of strain. The greater the strain applied, the narrower the band gap until it disappears completely the moment before the needle breaks. At this point, the diamond is “metalized” and transformed into an excellent conductor.
Top left: Image of an electron microscope in which the nanochip is bent Right: An image of the nano-needle bent under an electron microscope.
“We found that band gaps could be reduced from 5.6 electron volts to 0, ” said Ju Li, the study’s counterpart. “If you can change from 5.6 electron volts to 0 electron volts in a row, you can cover all band gaps. Strain engineering allows diamonds to have silicon band gaps, which are the most widely used semiconductors, or band gaps for nitride, which in turn are commonly used on LEDs. It can even be used as an infrared detector, or to detect light from infrared to the entire range of ultraviolet parts of the spectrum. “
The team says the new technology could lead to a range of interesting applications. Solar cells, for example, can capture a wider range of light frequencies on a single device — a task that currently requires stacking of different materials. The technology could also make new quantum detectors and sensors.
Despite the appeal of the study, it is still in the early stages of concept validation, so it is too early to design any practical equipment.
The study was published in the Proceedings of the National Academy of Sciences.