Coverage-Dependent Behavior on Organic Functionalization of the Semiconductor X(100)-2 × 1 Surface (X = C, Si, and Ge) by Carbene, Silylene, Germylene, and Nitrene:A Periodic DFT Study

摘要

Coverage-dependent behavior for chemical functionalization of the semiconductor X(100) (X = C, Si, and Ge) surface by cycloadditions of organic molecules, including carbene (CH2), silylene (SiH2), germylene (GeH2), and nitrene (NH), has been investigated using density functional theory (DFT) coupled with periodic slab models. In particular, we have performed calculations on models with 1, 2, 4, and 8 of these organic molecules, corresponding to coverages of 0 = 0.125, 0.25, 0.5, and 1, respectively. The results demonstrate that the adsorption energies decrease when coverage is increased, being attributed to the intermolecular repulsion at high coverage. For the NH molecule, due to its smaller molecular size than CH2, SiH2, and GeH2, the adsorption energy is relatively insensitive to the variation of coverage. Interestingly, at the saturated coverage, the structure of as-formed monolayer organic film among C(100), Si(100), and Ge(100) is different. The large adsorption energies at the saturated coverage clearly suggest the feasibility of forming organic layer films of carbenes and nitrenes onto the semiconductor X(100) surface, thus leading to new hybrid multifunctional materials. In addition, it has also been found that the band gaps can be finely tuned by addition of organic layers onto the X(100) surface; for example, the band gap is significantly widened for the CH2/ C(100) and NH/C(100) systems at the saturated coverage in comparison to that of bare C(100). These suggest that there is a promising flexibility for engineering the semiconductor C( 100), Si(100), and Ge(100) surfaces by tuning the coverage and type of organic molecules, given the well-known abundance of carbene and nitrene chemistry.