Last Month's Most Accessed Feature: Always forever: Ultraviolet diamond spintronics

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  • Published: Mar 1, 2018
  • Categories: UV/Vis Spectroscopy
thumbnail image: Last Month's Most Accessed Feature: Always forever: Ultraviolet diamond spintronics

Spintronic diamonds

Diamond plates undergoing surface termination treatment in a hydrogen plasma.  CREDIT: Daniel Creedon

Optoelectronic and spintronics devices that can work with ultraviolet light might be possible thanks to research into the electrical and magnetic properties of diamond.

Standard electronics devices use electrons as their currency, charge matters. However, in the quantum world electrons are not simply tiny spheres with a negative charge, they have the property of spin. Over the last few years, researchers have been looking for ways to exploit the spin of the electron to add another facet to electronics and create the realm of spintronics. The ultimate maturing of spintronics could lead to a whole new class of devices and computers that rely on charge and this quantum property.

Now, writing in the journal Applied Physics Letters, Golrokh Akhgar, a physicist at La Trobe University in Australia and his colleagues explain how they have measured how strongly the spin property of a charge carrier in the carbon allotrope, diamond, interacts with a magnetic field. This important property reveals that diamond could be a promising material for spintronic devices. Given that diamond is transparent to ultraviolet radiation and visible light, this adds another optical factor to the gamut.


Conventional semiconductors are generally opaque, moreover, they are quite difficult to fabricate and manipulate. In contrast, can readily be fabricated into thin films on complex surfaces and even made into hollow wires. As such, the fact that it can be processed quite readily could lead the way to easy to fabricate spintronic devices. Experimental quantum devices based on multiple thin layers of semiconductors are already revealing how complicated fabrication processes in an ultrahigh vacuum might be a limiting factor, diamond could very well circumvent that manufacturing obstacle.

However, before diamond might be used in spintronics devices, its chemistry will need a few tweaks. "Diamond is normally an extremely good insulator," Akhgar explains. "But, when exposed to hydrogen plasma, the diamond incorporates hydrogen atoms into its surface. When a hydrogenated diamond is introduced to moist air, it becomes electrically conductive because a thin layer of water forms on its surface, pulling electrons from the diamond. The missing electrons at the diamond surface behave like positively charged particles, holes, making the surface conductive."

Researchers have shown that these diamond holes have many of the requisite properties for spintronics devices. The most important property is the relativistic quantum effect of spin-orbit coupling. In this phenomenon we see the spin of a charge carrier interacting directly with its orbital motion and strong coupling between these two properties would mean that researchers could control the spin of the "particle" with an electric field. In earlier work, the team had measured how strongly the spin-orbit coupling of a hole might be engineered with an electric field and found that an external electric field could tune the strength of this coupling. Now, they have looked at the interaction of a hole's spin with a magnetic field.

More diamond devices

In the magnetic measurements, the scientists applied constant magnetic fields of different strengths parallel to the surface of a diamond held at a more than chilling 4 Kelvin. At the same time, they applied a steadily varying perpendicular field. By monitoring how the electrical resistance of the diamond changed, they could determine the g-factor, a parameter that will ultimately determine how well spin might be controlled by a magnetic field.

"The coupling strength of carrier spins to electric and magnetic fields lies at the heart of spintronics," Akhgar explains. "We now have the two crucial parameters for the manipulation of spins in the conductive surface layer of diamond by either electric or magnetic fields." The transparency of diamond to ultraviolet and visible light will also then allow such components to be interfaced with optical and optoelectronic devices. In addition, by exploiting nitrogen-vacancy diamonds - materials where some carbon atoms are missing and have nitrogen atoms in their place in the crystal structure - it might be possible to use diamond as a quantum bit, or qubit, too. Qubits are, of course, the basis for quantum information processing. Akhgar adds that this additional layer of interest widens the potential to yet more classes of device.

Related Links

Appl Phys Lett 2018, 112, 042102: "G-factor and well width variations for the two-dimensional hole gas in surface conducting diamond"

Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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