Chemical vapor deposition of two-dimensional boron sheets by thermal decomposition of diborane

Two-dimensional (2D) boron sheets (borophenes) are promising materials for the next generation of electronic devices because of their metallic conductivity. Molecular beam epitaxy has remained the main approach for the growth of borophene, which considerably restricts large-scale production of 2D boron sheets. The high melting point of boron and the growth of borophenes at moderate temperatures posed a significant challenge for the synthesis of borophenes. Employing diborane (B₂H₆) pyrolysis as a pure boron source, we report, for the first time, the growth of atomic-thickness borophene sheets by chemical vapor deposition (CVD). A methodical study on the effect of temperature, deposition rate, and pressure on the growth of 2D boron sheets is provided and detailed analyses about the morphology and crystalline phase of borophene sheets are presented. The CVD-borophene layers display an average thickness of 4.2 Å, χ₃ crystalline structure, and metallic conductivity. We also present experimental evidence supporting the formation of stacked bilayer and trilayer borophene sheets. Our method paves the way for empirical investigations on borophenes.