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

Abstract

Silicene is a zero band gap semiconductor. However, it is essential to open its band gap for the application in electronic devices. Hydrogenation of silicene was reported to be an efficient way to open its band gap and manipulate its electronic properties. However, the reaction energy barrier of silicene hydrogenation is quite high, which prevents the hydrogenation of silicene at room temperature. In this work, by using density functional theory calculations, we propose alternative approaches to reduce the energy barrier, thus facilitating hydrogenation of silicene. It is found that a positive perpendicular electric field F can act as a catalyst to reduce the energy barrier of H2 dissociative adsorption on silicene, which facility the hydrogenation of silicene. In addition, it is found that the barrier decreases as F increases, and when F is above 0.04 au (1 au = 5.14 × 1011 V/m ), the barrier is quite low and hydrogenation of silicene can go through efficiently at room temperature. Applying tensile strain is another way to reduce the energy barrier of the hydrogenation of silicene. Our results demonstrate that both biaxial and uniaxial tensile strains can reduce the energy barrier of H2 dissociative adsorption on silicene. When the strain is larger than 3%, the barrier drops a little more under the biaxial tensile strain. In addition, the barrier decreases as the both strains increase, and when strain reaches the critical strain of 14%, above which the structure of silicene would be destroyed, the barrier reduces from 1.75 to 0.83 eV and hydrogenation of silicene can accelerate significantly. The similar reduction of the energy barrier is also found in the hydrogenation of defective silicene. When the hydrogenation happens at the single vacancy defect the energy barrier can be reduced to 1.30 eV. While at divacancy defect, this can be further reduced to 0.95 eV. The mechanism of the effects of electric field, tensile strains and defects on hydrogenation of silicene will be understood through analysing the density of states of the system, pathways of dissociative adsorption of a H2 molecule on silicene and corresponding electronic properties. This work provides a new insight into fundamental science to engineer the band gap structure of silicene for applications of electronic devices.