Theoretical prediction of stable cluster-assembled CdSe bilayer and its functionalization with Co and Cr adatoms

In this article, we present our results on bilayers assembled upon strategic placement of Cd₆Se₆ clusters. These bilayers are studied for their stability and electronic structure with the help of density functional theory and are further analyzed using Bardeen, Tersoff and Hamann formalism for their tunneling properties. Our calculations show that the hexagonal arrangement of these clusters prevails as the most stable geometry showing all real phonon modes. First-principles molecular dynamics studies on this 2D structure show that it remains intact even at room temperature. This bilayer shows an indirect semiconducting band gap of 1.28 eV with the current-voltage (I-V) characteristics similar to a tunnel diode. Furthermore, we functionalized this bilayer using transition metal atoms, Co and Cr. The aim was to see whether the bilayer sustains magnetism and how the concentration affects its electronic and magnetic properties. Co functionalization brings ferromagnetic ordering in the bilayer which turns near half-metallic upon increasing the concentration. On the other hand, Cr functionalization shows a transition from antiferro- to ferromagnetic ordering upon increasing the concentration. The I-V characteristics of all these functionalized bilayers show negative differential conductance similar to a tunnel diode.