Diamonds: doped & quantum

Tuesday 19th November 2013
Diamond doping; Courtesy:http://scitation.aip.org/content/aip/journal/apl/103/20/10.1063/1.4832455

The Nano-Electronic Diamond Devices and Systems Group at Glasgow University School of Engineering have emerged with an answer to an age old doping and stability problem issue in diamond electronics. Over at Basel University, with tiny diamond crystals, physicists discover new quantum information possibilities for the material.

"Diamond electronics has been held up for the past few decades because it is very difficult to dope diamond to introduce the mobile charge that is required for electronic devices (this is because diamond has such a small atomic number and small lattice constant, it’s difficult to squeeze anything else into the diamond lattice to dope it)," says NEDDS expert diamond researcher, Dr David Moran.

"The best electronic devices such as transistors that have been made in diamond have used a process called surface transfer doping. Unfortunately this relies on atmospheric components clinging to the surface of the diamond to work, which makes the devices extremely unstable and limits their robustness. As one of the main pitches for diamond electronics is robustness, such device instability is of course unacceptable.

"What we have done, is to substitute the atmospheric elements on the surface with a solid material in the form of a transition metal oxide.

"A lot of people have tried to encapsulate the diamond surface before with various materials, but this has almost always reduced the amount of doping in the diamond and degraded performance.
"With our material however, we have more than doubled the amount of charge carriers in the diamond, thus potentially fixing the stability issues and simultaneously improving the device's high power operation, which again is the main drive for diamond devices like transistors.
"Needless to say," he adds, with great research charm, "we are quite excited about the results."

Caption: Below: Scanning tunneling microscopy image showing the surface structure of nanodiamonds. Courtesy: Department of Physics at the University of Basel

With the help of tiny diamond crystals, physicists at the University of Basel have discovered new  quantum information possibilities:  at specific circumstances electric currents made it possible to identify defects in the carbon lattice of single diamonds measuring only a few nanometers.

The team from the University of Basel and the French German Research ISL (Institute St. Louis) have investigated five nanometer sized diamond crystals  using STM and AFM (scanning tunnelling  and atomic force microscopy). The physicists then identified the atomic structure of the surface and observed crystalline, hexagonal carbon facets as well as graphitic reconstructions.

Doing so, they discovered extra currents at specific voltages when the crystals were illuminated by green light.

These extra currents are related to the presence of NV-centre (Nitrogen-vacancy centre) defects in the diamond carbon lattices that are optically active. These centres are promising candidates for future applications in quantum information processing systems, spin-magnetometry sensors or single photon sources.

"With this study, we are able to show that it is possible to prove, with high resolution, the presence of optical centres in single nanodiamond", says Prof. Ernst Meyer of  Department of Physics at the University of Basel. In future, NV-centers could allow quantum computers to work  more efficiently than today's devices.

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