Adsorption and Reaction of C2N2 on Si(100)-2 × 1: A Computational Study with Single- and Double-Dimer Cluster Models

Atomistic Insight into Nitrogen-Terminated Diamond(001) Surfaces by the Adsorption of N, NH, and NH2: A Density Functional Theory Study

Layer-by-layer construction of diamond devices for spin-sensing calls for the atomistic understanding of the nitrogen species on diamond surfaces. Motivated by recent experiments, we used density functional theory simulations to examine the adsorption of nitrogen species (N, NH, and NH₂) on bare and hydrogenated diamond(001) surfaces. On the bare substrate, we find that nitrogen species favor to attack the C═C dimers at low coverages, forming N(ad) and NH(ad) in a bridge configuration and NH₂(ad) in a terminal configuration. At increasing coverages up to one full monolayer, the computed adsorption geometries and energetics suggest that the adsorbate-adsorbate interactions are attractive for N(ad), but repulsive for NH(ad) and NH₂(ad). On the hydrogenated substrate, the adsorbed nitrogen species are subject to structural modification, as resulted from the weakened adsorbate-substrate interactions. Further, we calculated the vibration of nitrogen species and the 1s core-level shift of surface carbons, providing atomistic insights into the nature of surface bonding. Lastly, we simulated images of representative nitrogen species adsorbed on diamond(001), guiding future work using scanning tunneling microscopy.

Theoretical Study on Reactions of Nitroethylene with the Si(100)-2 × 1 Surface

Possible reaction pathways of nitroethylene with the Si(100)-2 x 1 surface have been investigated by unrestricted density functional theory. The facile occurrence of the studied reactions was demonstrated by the low activation energies of the rate-determining steps (1.07-5.23 kcal/mol). It was found that the [4 + 2] cycloaddition reaction of nitroethylene is most kinetically favorable. The isomerization reactions of the addition products were also investigated. The [3 + 2] cycloaddition product may further undergo a rearrangement by overcoming a 12.37 kcal/mol activation energy barrier into an isomer, with an oxygen atom of the nitryl group inserted between two silicon atoms of the Si(100) surface.

[2+2] Cycloaddition Reactions of Ethylene Derivatives with the Si(100)-2 × 1 Surface: A Theoretical Study

Possible mechanisms of the [2+2] cycloaddition reactions of ethylene (1), propylene (2), vinyl chloride (3), and styrene (4) with the Si(100)-2 x 1 surface have been investigated by theoretical calculations with the unrestricted density functional theory (DFT) and the second-order Møller-Plesset perturbation theory (MP2). Facile occurrence of the studied reactions is supported by the low activation energies (2.45-5.76 kcal/mol) in the rate-determining steps. The buckled Si(100) surface facilitates the reactions via the low-symmetric pathways. The reactions follow the diradical mechanism of thermal [2+2] cycloaddition reactions between pi-electron donors (the ethylene derivatives) and acceptors (the Si surface) through a pi-complex precursor and a singlet diradical intermediate. The influence of substituents on the relative reactivity takes a qualitative sequence of 1 < 2 < 3 < 4. The natural bond orbital (NBO) analysis and the released heat of some model reactions suggest that the relative reactivity might be partially understood by the pi-electron-donating abilities of the substituent to stabilize the radical centers at the transition states of the rate-determining steps.