Quasi-1D zirconium telluride nanoribbons boast an exceptionally high current density – of around 100 MA/cm2 – according to new experiments by researchers at the University of California, Riverside and the University of Georgia. This value exceeds that of any conventional interconnect metal, such as copper, by almost two orders of magnitude, and comes thanks to the single-crystal nature of the van der Waals material. The nanoribbons could be used to make extremely downscaled interconnects and transistor channels.
Just as 2D layered materials, such as graphene, consist of covalently-bonded layers separated by so-called van der Waals (vdW) gaps, 1D materials are also made up of covalently-bonded one-dimensional wires with vdW gaps between them. The term vdW gap refers to the weak binding force that separates atomic planes in 2D- and atomic chains in 1D materials.
Metallic or semiconducting
“Thanks to their lower dimensionality, 1D vdW materials have even more fascinating quantum properties than their 2D counterparts,” explains team leader Alexander Balandin. “Examples of 1D vdW materials include transition metal trichalcogenides, which have strong covalent bonds in one direction and weaker bonds in the cross-plane. They can be prepared as crystalline nanowires consisting of 1D “atomic threads” (atomic chains).
The UC Riverside researchers used a shadow mask technique to prepare devices from 1D zirconium telluride (ZrTe3) nanoribbons (obtained by physically exfoliating or shaving off slivers from bulk ZrTe3). They then interfaced the nanoribbons with conventional metal contacts to electronically characterize them. Depending on the specific polymorph, shape and the cross-sectional dimension of the nanoribbons, the nanoribbons are either metallic or semiconducting, which means that they might be used in a wide variety of device applications, says Balandin.
High current density
“Conventional metals are polycrystalline and they have grain boundaries and surface roughness, which scatter electrons,” he explains. “In contrast, quasi-one-dimensional materials such as TaSe3 or ZrTe3 consist of single-crystal atomic chains in one direction. They do not have grain boundaries and often have atomically smooth surfaces. We attributed the exceptionally high current density we measured in ZrTe3 to its single-crystal nature.”
The result means that ZrTe3 is a promising material for making downscaled interconnects or device channels, he tells nanotechweb.org. In principle, such quasi-1D materials could be made smaller by exfoliation or grown directly into nanowires with a cross-section of around 1 nm x 1 nm, which corresponds to the ultimately small cross-section of an individual atomic thread. “In our present study, the level of the current sustained by the ZrTe3 quantum wires is 100 MA/cm2. This value is higher than that reported for any metal or indeed other 1D material and reaches that of extremely conductive materials such as carbon nanotubes or even graphene.”
The team reports its work in IEEE Electron Device Letters 10.1109/LED.2018.2820140 and acknowledges funding from the Semiconductor Research Corporation and the National Science Foundation. Adane Geremew, the first author of the paper, is a doctoral student in Balandin’s group. He fabricated devices at UC Riverside’s Nanofabrication facilities using material provided by Tina Salguero’s team at the University of Georgia.
