Exploration of M(100)-2×1 (M=Si, Ge) surface termination through hydrogen passivation using ethane and ammonia-borane derivatives: A theoretical approach.

ABSTRACT

Termination process of Si(100)-2 × 1 as well as Ge(100)-2 × 1 reconstructed surfaces have been explored comprehensively through the dehydrogenation of ethane and ammonia-borane and their several analogues by employing density functional theory (DFT). From our study, it is evident that the termination of Si-surface via the dehydrogenation of aforementioned ethane and NH3BH3 derivatives is more feasible compared to Ge-surface. For ethane, the investigation shows that the substitution of non-participating hydrogens with +I group (electron donating) causes an enhancement in the kinetic and thermodynamic feasibility of the termination process, whereas the implementation of -I substituent (electron withdrawing) makes an adverse effect. While exploring the termination of Si- as well as Ge-surfaces through the dehydrogenation of NH3BH3 and its derivatives, it is noticed that from both the kinetic as well as thermodynamic perspectives, the termination processes are more feasible than that of ethane and its derivatives. We have further examined the detailed mechanism of each termination process by analyzing the geometrical parameters and NPA charges. From bonding evaluation, it is evident that the hydrogen abstraction from ethane by both the surfaces is symmetric in nature, where both the hydrogens show slightly positive charge. But for NH3BH3 the hydrogen abstraction process becomes asymmetric, where the boron associated hydrogen is abstracted as hydride by the electrophilic surface Si (Ge) and the hydrogen bonded with the N-centre is abstracted as proton by the nucleophilic surface Si (Ge). Overall, the present theoretical work reveals one of the efficient chemical processes for terminating Si as well as Ge(100)-2 × 1 reconstructed surfaces through the formation of non-polar SiH bonds.