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3-D cadmium arsenide emulates graphene

Researchers say a II-V semiconductor could yield practical devices with the same electronic properties as 2-D graphene
Scientists have discovered a material that has the same extraordinary electronic properties as 2-D graphene, but in a sturdy 3-D form that should be much easier to shape into electronic devices such as very fast transistors, sensors and transparent electrodes.

Cadmium arsenide (Cd3As2) is an inorganic, crystalline compound semiconductor with a tetragonal structure in the II-V family.

Cd3As2 is being explored independently by three groups, one of which includes researchers at the University of Oxford, SLAC, Stanford and Lawrence Berkeley National Laboratory who described their results in a paper published May 25th in Nature Materials.

“Now more and more people realize the potential in the science and technology of this particular material. This growing interest will promote rapid progress in the field - including the exploration of its use in functional devices and the search for similar materials,” says Yulin Chen of the University of Oxford, who led the research.

Scientists at Oxford, SLAC, Stanford and Berkeley Lab have discovered that a sturdy 3-D material, cadmium arsenide, mimics the electronic behavior of 2-D graphene. This illustration depicts fast-moving, massless electrons inside the material. The discovery could lead to new and faster types of electronic devices (Image: Greg Stewart/SLAC)

The group’s work builds on its earlier studies of a sodium bismuth compound that also mimics graphene but turns to powder when exposed to air. Both compounds had been predicted by co-authors Zhong Fang and Xi Dai, theoretical physicists from the Chinese Academy of Sciences, who suggested that cadmium arsenide, which is used in detectors and sensors, would provide the same properties in a much more stable form.

Their prediction proved correct, says Zhongkai Liu, the paper’s first author and a graduate student at SIMES, the Stanford Institute for Materials and Energy Sciences at SLAC. “The environmental stability of cadmium arsenide allows us to explore it very systematically, and makes it easier to study,” he comments.

Graphene is a one-atom-thick sheet of carbon atoms peeled from a piece of graphite, which is familiar as the lead in pencils. One of its hallmarks is the weird behaviour of its electrons: When confined to this thin layer of regularly spaced atoms, these lightweight particles act as if they have no mass at all.

This allows them to zip through the material much faster than usual. The scientists who first isolated graphene in 2004 were awarded the Nobel Prize in Physics; and researchers have been racing to explore its properties and find practical uses for it ever since.

One such quest has been to find graphene-like materials that are three-dimensional, and thus much easier to craft into practical devices. Two other international collaborations based at Princeton University and in Dresden, Germany, have also been pursuing cadmium arsenide as a possibility. One published a paper on its results in the May 7th issue of Nature Communications, and the other has posted an unpublished paper on the preprint server arXiv.

Chen’s group made samples of cadmium arsenide at Oxford and tested them at the Diamond Light Source in the United Kingdom and at Berkeley Lab’s Advanced Light Source.

“We think this family of materials can be a good candidate for everyday use,” Chen says, “and we’re working with theorists to see if there are even better materials out there. In addition, we can use them as a platform to create and explore even more exotic states of matter; when you open a door, you find there are many

A state of matter known as a three-dimensional Dirac semimetal has latterly garnered significant theoretical and experimental attention. Using angle-resolved photoelectron spectroscopy, it is shown that Cd3As2 is an experimental realisation of a three-dimensional Dirac semimetal that is stable at ambient conditions.

This work is described in detail in the paper, " A stable three-dimensional topological Dirac semimetal Cd3As,"by Z. K. Liu et al, published online on 25th May 2014. doi:10.1038/nmat3990.

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