It’s strong, lightweight, and flexible. Borophene, an atomically thin (two-dimensional, 2-D) form of boron, has attracted much attention in the scientific community as a candidate material platform for high-speed, transparent, and flexible electronics. However, precisely determining the material’s structural and physical properties is difficult. Why? It’s hard to grow a large enough crystal to define the structural properties and physics of this material. Now, researchers have grown single-crystal domains of a new borophene phase as big as 100 square micrometers by growing it on copper substrate instead of silver. With this larger size, which is also device quality, researchers can measure more of the material’s properties.
The large crystals of this previously unknown borophene phase are expected to allow electrons to move through the structure quickly. This property is crucial for developing flexible electronic devices. Add in borophene’s resilience to bending and tensile stress. The result? This discovery could accelerate borophene use for wearable electronic devices and quantum computers.
Scientists at Yale University and Brookhaven National Laboratory discovered a new borophene phase with potentially highly advantageous properties for electronic devices. The researchers found the new phase while working to test a prediction that borophene would be more stable if grown on copper. So far, the quest for ultrathin electronic devices has been focused on graphene, which is promising but with a structure that’s difficult to modify and control. Attention is being increasingly focused on potential substitutes including the more flexible borophene. Before this study, borophene had only been grown on silver substrates. However, only nanoscale phase domains had been produced, which prevented more detailed analyses and any device fabrication. In this research, scientists used advanced electron microscopy techniques to directly visualize and verify that growing borophene on copper substrate allows formation of much larger single-crystal domains. Unlike silver, copper interacts with boron, which is essential in creating the large borophene domains. Copper’s ability to interact without alloying (combining the two metals) and sustain heating to the high temperature required for crystal formation made it ideal for growing larger crystal domains. Copper contributes extra electrons, allowing stable crystal growth without forming covalent bonds that permanently attach the borophene. These large-area domains open the door to exploration of next-generation electronic devices. Importantly, these larger crystals allow the mechanical and electrical properties of borophene to be measured and studied, something that was not previously possible. Also, the large crystals of borophene may allow electron transport unhindered by defects that tend to decrease the electrical and thermal conductivity of a material. This is a sought-after attribute for developing flexible yet resilient electronic devices.
Department of Energy (DOE), Office of Science, Basic Energy Sciences including research at the Center for Functional Nanomaterials, a DOE Office of Science user facility; Gordon and Betty Moore Foundation’s Emergent Phenomena in Quantum Systems Initiative (R.W. and A.G); Brookhaven National Laboratory Gertrude and Maurice Goldhaber Distinguished Fellowship (I.K.D.); and the National Science Foundation Graduate Research Fellowship (S.E.). Researchers used computing resources at the Yale University Faculty of Arts and Sciences High Performance Computing Center as well as National Science Foundation’s Extreme Science and Engineering Discovery Environment.
R. Wu, I.K. Drozdov, S. Eltinge, P. Zahl, S. Ismail-Beigi, I. Božović, and A. Gozar, “Large-area single-crystal sheets of borophene on Cu(111) surfaces.” Nature Nanotechnology 14, 44 (2018). [DOI: 10.1038/s41565-018-0317-6]