Dissociative Adsorption of Hydrogen Molecules on Silicene Sheet and the Modification of Its Electronic properties

Silicene is a zero band gap semiconductor. However, it is essential to open its bandgap for the application in electronic devices. Hydrogenation of silicene was reported tobe an efficient way to open its band gap and manipulate its electronic properties.However, the reaction energy barrier of silicene hydrogenation is quite high, whichprevents the hydrogenation of silicene at room temperature. In this work, by usingdensity functional theory calculations, we propose alternative approaches to reduce theenergy barrier, thus facilitating hydrogenation of silicene. It is found that a positiveperpendicular electric field F can act as a catalyst to reduce the energy barrier of H2dissociative adsorption on silicene, which facility the hydrogenation of silicene. Inaddition, it is found that the barrier decreases as F increases, and when F is above 0.04au (1 au = 5.14 × 1011 V/m ), the barrier is quite low and hydrogenation of silicene cango through efficiently at room temperature. Applying tensile strain is another way toreduce the energy barrier of the hydrogenation of silicene. Our results demonstrate thatboth biaxial and uniaxial tensile strains can reduce the energy barrier of H2 dissociativeadsorption on silicene. When the strain is larger than 3%, the barrier drops a little moreunder the biaxial tensile strain. In addition, the barrier decreases as the both strainsincrease, and when strain reaches the critical strain of 14%, above which the structure ofsilicene would be destroyed, the barrier reduces from 1.75 to 0.83 eV andhydrogenation of silicene can accelerate significantly. The similar reduction of theenergy barrier is also found in the hydrogenation of defective silicene. When thehydrogenation happens at the single vacancy defect the energy barrier can be reduced to1.30 eV. While at divacancy defect, this can be further reduced to 0.95 eV. Themechanism of the effects of electric field, tensile strains and defects on hydrogenationof silicene will be understood through analysing the density of states of the system,pathways of dissociative adsorption of a H2 molecule on silicene and correspondingelectronic properties. This work provides a new insight into fundamental science toengineer the band gap structure of silicene for applications of electronic devices