Synthesis and characterization of Borophene

Synthesis and characterization of Borophene

Fig.1 (topview) two dimensional (2D) boron on Ag (111)  

Borophene, a cousin of graphene, had been predicted more than 10 years, but not successfully synthesized so far. Even there are several samples, such as thin films or small planar clusters; however, their structures are extremely difficult to be characterized due to the structural complexity, and consequently be one of distinguished open questions in condensed matter physics and material physics. An international team led by Profs. Xiang-Feng Zhou, Hui-Tian Wang at Nankai University, and Prof. Artem R. Oganov at Stony Brook University, predicted a novel 2D-boron with thickness can exhibit massless Dirac fermions with anisotropic Dirac cones i.e. that transport properties of these Dirac fermions will depend on direction, which gives an additional degree of freedom for electronic applications [Phys. Rev. Lett. 112, 085502 (2014)]. This work further stimulates experimentalists to challenge the realization of borophene or boron sheets. Fortunately, scientists from Argonne National Lab, Northwestern University, Stony Brook University, Nankai University and so on, collaborated closely to achieve a major breakthrough by growing atomic borophene on Ag (111) surface under ultrahigh-vacuum (UHV) conditions. The experiment combined with theory show that this stable, atomic borophene displays remarkable properties. For example, calculations reveal that it has an anisotropic conductivity, and possesses a rarely “negative Poisson’s ratio” (tensile strain results in an unusual expansion along its perpendicular direction). Meanwhile, its in-plane Young’s modulus (a measure of stiffness) is equal to 398 GPa·nm along the a axis, which potentially rivals graphene (the hardest 2D material), at 340 GPa·nm.

This work was published in Science on 12/18/2015 [Science 350, 1513 (2015)]

with the perspective viewpoint at