Black phosphorus (BP) is a stack of monoatomic layers of phosphorus, bound together by Van der Waals forces. This 2d material is today attracting a great interest due to its widely tunable band gap, depending on the thickness of the material, the very high mobility of its carriers, for its application in field effect transistors (FETs), and the possible emergence of topologically protected states. It has been shown that electrostatic action or evaporation of alkali metals, as electron donors, can be successfully used for doping the PB from a semiconductor phase to a semi-metallic phase with Dirac cone transport channels (with linear dispersion).
Experimentalists and theoreticians at the Laboratory for Irradiated Solids (LSI) have thus studied the excited electronic states of black phosphorus after deposition of an increasing dose of alkaline atoms. The FemtoARPES (angle-resolved photoemission) experimental device at the LSI was used to monitor the band gap closure with unprecedented accuracy. This engineering of the electronic band structure would enable the design of devices with improved and optimized electronic and optoelectronic functionality.