Two-dimensional materials grown on cones given tailored properties
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Researchers at Rice University, Texas, USA, have developed a method for manipulating defects in 2D materials in order to control a range of the materials’ properties.
Previously, the team, based in the laboratory of theoretical physicist Professor Boris Yakobson, had found that they were able to add defects to 2D materials (one atom thick materials). They transformed perfectly electrically conducting graphene into a semiconductor and turned a grain boundary – a tiny “seam” where mismatched edges of material meet – into a conductive wire and gave it magnetic properties.
Now, the researchers have combined theory and practical experimentation to determine how to design specific defects into these materials, particularly grain boundaries. These grain boundaries can be used to enhance the electronic, magnetic, mechanical, catalytic and optical properties of the material.
They achieved these new and improved properties by curving the landscape of the sheets around textured substrates, such as a cone. By adjusting the size and tilt angle of the cone, the researchers were able to control what kind of defects appear and whereabouts.
In their ACS Nano paper, the authors describe growing tungsten disulphide over atom-scale cones in a real-world version of their previous computer models. The grain boundaries that appeared in the material perfectly matched those that they predicted.
“The nonplanar shape of the substrate forces the 2D crystal to grow in a curved “non-Euclidian” space,” said Profressor Yakobson. “This strains the crystal, which occasionally yields by giving way to the seams or grain boundaries.”
“It’s no different from the way a tailor would add a seam to a suit or a dress to fit a curvy customer.”
In their experimentation, the Rice University team also found that by tilting the cone by 38.9° (a “magic cone”), they could grow a material completely free of boundaries.