Transition Metal (Fe and Cr) Adsorptions on Buckled and Planar Silicene Monolayers: A Density Functional Theory Investigation

Abstract

The adsorption of metals on the silicene monolayer may potentially offer advantageous applications in electronic and spintronic devices. In this study, by employing first-principles calculations, we investigate the attachment of two 3d transition metals (Fe and Cr) on buckled and planar silicene surfaces. Besides examining structural stability, we also explore interesting ferromagnetic as well as half-metallic features of the material. All Fe adsorption cases are found to be more stable (with the lowest binding energy being 3.39 eV) than Cr adsorption cases. When the metal adsorption rate is high, Fe tends to penetrate into both buckled and planar silicene layers. This insertion behavior allows the 3d shells of Fe to enhance bonding interactions with all 3px, 3py, and 3pz orbitals of Si, thus producing more stable structures. The adsorptions of Cr with high distribution ratio are found to be more stable than the low-Cr-distribution structures. It is observed that Cr does not penetrate into the silicene layer like Fe. Overall, ferromagnetism is dominant with five nanostructures. Two Cr adsorption cases on planar silicene preferentially behave as antiferromagnets, and one Fe adsorption case is nonmagnetic. From our observation, there is an inversed interplay between structural stability and magnetic moments; i.e., FeSix nanostructures (more stable) tend to exhibit lower ferromagnetic moments. The half-metallic characteristic is found in four nanostructures, which can be potentially applied in spin-electronic devices. The gaps derived from spin-down states for those half-metallic nanostructures vary from 0.28 to 0.57 eV.