Growth of highly crystalline ultrathin two-dimensional selenene

Elemental two-dimensional (2D) crystals have recently emerged as promising materials for advanced electronics and optoelectronics applications. However, it remains challenging to achieve controllable growth of high-quality, ultra-thin flakes of elemental 2D materials. Here, we demonstrate, for the first time, a seed-assisted chemical vapor transport growth of ultra-thin triangular flakes of highly crystalline trigonal selenium (t-Se) oriented in (0001) direction, with lateral size >30 mu m. The polarization angle-resolved Raman spectra of bilayer selenene show in-plane isotropic properties, owing to the highly symmetric lattice resulting from its unique growth orientation. Density functional theory calculations support the experimental findings in establishing the structure and stability of the as-grown selenene. We studied the optical response of a photodetector fabricated using a bilayer selenene. Our growth strategy can be extended to other elemental 2D materials to realize their full potential in applications ranging from optoelectronics and electronics to energy conversion.